摘要:

Electroactive polymer films of silver complexes with intertwined and interlocked ligands: the AgI–Ag0 redox couple as a topological probe† Martial Billon,a Bernadette Divisia-Blohorn,a Jean-Marc Kernb and Jean-Pierre Sauvageb aCEA, De�partement de Recherche Fondamentale sur la Matie`re Condense�e, S.I.3M., L aboratoire d’ElectrochimieMole�culaire, 17 rue desMartyrs, F-38054 Grenoble, France bL aboratoire de Chimie Organo-Mine�rale, UA 422 au CNRS, Institut L e Bel, Universite� L ouis Pasteur, 4 rue Blaise Pascal, 67000 Strasbourg, France The electrochemical properties of bis(2,9-diaryl-1,10-phenanthroline)silver complexes are reported.The redox potentials of the coordinated metal centre are strongly dependent on the topology of the organic backbone surrounding the metal centre and its set of ligands.This particular property can be used for the evaluation of the topological characteristics of dierent polypyrrole matrices built around entwined 2,9-diaryl-1,10-phenanthroline moieties. Although the functionalization of electronic conducting poly- that the metal is zerovalent. It simply means that the monomers (ECP) with a view to obtaining predetermined chemical valent complex has been reduced in a one-electron process to or physical properties has been extensively studied,1 there are aord a neutral species (overall charge=0) with no indication very few results on the topological properties of these materials, of whether this process is metal- or ligand-localized. More probably owing to the diversity of possible connections, and recently, electrochemical hysteresis properties have been consequently, the diculties in characterising the relation observed for catenates where one of the macrocyclic subunit between the particular properties of the material and their contains both di- and ter-dentate ligands12 Our previous topological features. To our knowledge, the only studies work13 has demonstrated the electropolymerisation of dierent reported concern the thermodynamic properties of specific metallic complexes with acyclic chelating fragments (end-functypes of polymers such as polyrotaxanes and polycatenanes.2 tionalized dpp) covalently linked to either the nitrogen13a atom Elaborations of conducting polymetallorotaxanes using supra- or the 3-carbon13b of the pyrrole unit, through a polymethylene molecular approaches, with the aid of transition metals as spacer.Removal of the gathering metal centre allows the templating agents, have been recently described.3 anchoring of preformed sites in a rigid polymeric conducting At present, there is a growing interest in topology in network [Scheme 1(B)]. These coordinating sites are able to molecular chemistry due to the challengeto build supramolecu- complex other transition-metal species.An increase in the lar edifices displaying new topological properties.4 Over the topological complexity of the precursor for electropolymeris- last few years, interesting topology related properties have ation, by the substitution of one acyclic ligand by the coordinat- been observed for certain molecular structures such as inter- ing macrocycle m-30 (a 30-membered 2,9-dpp-containing ring) locked macrocycles, especially the enhancement of basicity,5 [Scheme 1(C)], leads to the ECP films deposited on the kinetic eects,6 NMR properties7 and photochemical and electrodes exhibiting an enhancement of the electronic accessi- photophysical properties.4f,8 Recently, interesting electro- bility of the redox metal centres.3a These electropolymerisations chemical properties have been reported for purely organic produce random connections, which can be inter- or intra- catenanes or rotaxanes formed by a self-assembly process.9 molecular, between pyrrole units. Processes B and C allow the They display cathodic or anodic shifts of the half-wave poten- elaboration of ECP-modified electrodes with varying topologi- tials of the redox subunits included in the host complexing cal properties.Thus, electropolymerisation according to pro- macrocycle, reflecting either the intensity of the interaction cess B produces a multi-entangled criss-cross of molecular between aromatic units or the steric hindrance imposed by the wires with possible ring formation leading to ECP films rotaxane structure.Dierent behaviour has been observed10 containing local catenane- and rotaxane-like structures, whilst for catenands synthesized by the template eect of a transition electropolymerisation of preformed rotaxanes produces, after metal coordinated to 2,9-diphenyl-1,10-phenanthroline (dpp) demetallation, a polyrotaxane [Scheme 1(C)].Consequently, units [Scheme 1(A)].They exhibit stabilization of the low it appears to be interesting to investigate and to compare the oxidation states of the metal ion concerned, this being due to topological properties of these dierent materials. the pseudo-tetrahedral geometry imposed by the phenanthro- Here, we report the electrochemical properties of the three line units around the metal centre.As a matter of fact, silver complexes 1, 2 and 3; with the same topographical transition-metal complexes of entwined phenanthroline-con- features but dierent topologies, by increasing the number taining ligands show very similar electrochemical properties. of macrocyclic ligands around the metal centre (Scheme 2). Particular electrochemical characteristics arising from the The entwined system 1, the threaded complex 2 and the silver topological properties of interlocked macrocyclic complexes catenate 3 exhibit dierent electrochemical behaviour for the have been reported11 and include the emergence of reversibility reduction process of the metal.Hence the formal AgI–Ag0 of the one-electron reduction of the formal CuI–Cu0 redox redox centre can be used as an electrochemical probe to couple and a cathodic shift of the reduction potential between evaluate the topological properties of the dierently func- a AgI–Ag0 catenate and its analogous entwined complex.It tionalized ECP films elaborated by utilizing dierent starting should be noted that the index 0 in Cu0 or Ag0 does not imply materials. The electrochemical response of the cobalt centre in cobalt-containing films (poly-5) prepared with cobalt(II) as a templating centre is not sensitive to the topological properties † Dedicated to Professor H.J. Scha�fer on the occasion of his 60th birthday. of the polymeric network. However, this resulting polyrotaxane J. Mater. Chem., 1997, 7(7), 1169–1173 1169Scheme 1 Synthetic strategy used for constructing: (A) a [2]catenate, by means of a strategy based on the three-dimensional template eect induced by a transition metal on the molecular fragment represented by fMf; f and g represent functional groups which are able to react to form a covalent bond; (B) multi-entangled criss-cross molecular wires produced by electropolymerisation of preformed entwined complexes; (C) polyrotaxanes, by means of electropolymerisation of suitable rotaxane monomers, where E represents the electropolymerisable unit like system is able to undergo a reversible complexing–decom- voltammetry.The modified electrodes were washed in pure solvent before further analytical experiments. plexing process.3a Cobalt–silver exchange has therefore been monitored by voltammetric measurements in order to observe As the electrochemical study of the silver complexes turned out to be especially dicult due to non-reproducible adsorp- the sensitive electrochemical response of silver and to use it as a probe of the topological properties of the network matrix.tion poisoning phenomena on the platinum electrode, electropolymerisation experiments were performed on carbon felt electrodes.The results reported herein concern the first Experimental cathodic CV made after electrodeposition of the film. Chemicals The synthetic procedures for the synthesis of the macrocycle Results and Discussion m-30,14 the dierent ligands13 and the catenate11 3 have been Electrochemical properties of free Ag+ and complexes previously reported.The complexes 1, 2, 4 and 5 were formed 1, 2 and 3 in solution immediately prior to the electrochements by addition of slightly less than the stoichiometric The voltammograms of the free Ag+ ion and complexes 1, 2 amount of Ag+ (AgBF4) or Co2+ [Co(BF4 )2 ] to the linear and 3 exhibit the same shape and are characteristic of thinand macrocyclic ligands. layer electrochemical behaviour due to the nature of the working electrode (carbon felt) and the low scan rate used.Reagents, electrochemical apparatus and procedure They exhibit an irreversible one electron reduction attributed to the AgI–Ag0 redox centre leading to formal Ag0 complexes. Electrochemical studies were performed in a dry-box under an In addition, the complexes 1 and 2 show irreversible oxidation argon atmosphere.Acetonitrile (MeCN) (BDH, HiPer Solv) of the pyrrole units at 0.80 V. The relative intensities of the was distilled over P4O10. Tetraethylammonium tetrafluorobo- peaks associatedwith the silver redox process and the oxidation rate (Et4NBF4 ) (Fluka purum) was dried at 100 °C under of the pyrrole units are consistent with the stoichiometry of vacuum for 1 day prior to use.The concentration of the each complex (number of pyrrole nuclei per metal) and the pyrrole units was 4×10-1 mol l-1 for complexes 1, 2, 4 and 5. number of electrons transferred for each electrochemical pro- The electrochemical apparatus consisted of PAR 273A from cess. The half-potential values E1/2, defined as (Epc+Epa)/2 EG&G Princeton Applied Research, monitored by a Hewlett (Epc and Epa are the cathodic and anodic peak potentials Packard 9836C computer ensuring data acquisition and con- respectively), and the dierence between the cathodic and the nected to a Kipp & Zonen recorder. All potentials are relative anodic peak potential values DEp for the three complexes 1, 2 to a 10-2 mol l-1 Ag+–Ag reference electrode.The working and 3 and for the free silver ion are reported in Table 1.electrodes were made of carbon felt (s=3 cm2). The redox potential of free Ag+ at carbon felt determined in CH3CN is in good agreement with previous published data Elaboration of the films at a dropping mercury electrode.15 Only a slight irreversibility of the electron transfer process is observed due to silver Anodic electropolymerisation of the functionalized ECP films was performed in MeCN either by repeated potential linear desorption during the anodic scan.As the three complexes 1, 2 and 3 exhibit the same voltammo- scanning or by electrolysis at a controlled potential of 0.850 V vs. the Ag+–Ag reference electrode, [Ag+]=10-2 mol l-1 in gram shape as the free Ag+ ion, it is not possible to determine if their reoxidation occurs with or without partial silver MeCN.The film growth was monitored by anodic cyclic 1170 J. Mater. Chem., 1997, 7(7), 1169–1173Fig. 1 Cyclic voltammetric response of the silver redox centre of 2. 2×10-3 mol l-1 in MeCN–Et4NBF4 (0.1 mol l-1), sweep rate v= 5mV s-1 on a carbon felt electrode, Ag+ (10-2 mol l-1)/Ag as reference. desorption, free silverpossibly being formedfrom the complexes by demetallation during the reductive scan.The E1/2 and DEp values for the silver redox centre of complex 1 are in agreement with those reported by El Hajbi et al.16 for several phenanthroline complexes of silver which undergo an irreversible one-electron reduction at -0.17 V vs. SCE with low DEp. Surprisingly, concerning the metal redox response, a relatively strong cathodic shift (0.21 V) of the Epc values is observed between 1 and 2, together with a remarkable cathodic shift (0.70 V) between 1 and 3 (Table 1).In addition, DEp increases slightly (0.13 V) between 1 and 2 but increases drastically (0.30 V) between 1 and 3. This observation shows that each successive substitution of an acyclic phenanthroline ligand by a macrocyclic one induces a strong stabilization of the corresponding silver complex.This remarkable topological eect on the redox properties of the complexed AgI–Ag0 centre led us to use it as an electrochemical probe for evaluating the topology of complexes linked to dierent polypyrrole matrices, i.e. their degree of interlocking and entanglement. Electrochemical properties of silver (I ) complexes covalently linked to polypyrrole matrices The polypyrrole films modified by 1 and 2 display very similar cyclic voltammograms composed of both the characteristic anodic and cathodic response of the N-substituted polypyrrole matrix centred at 0.30 V and, in the cathodic potential range, an irreversible one-electron transfer attributed to the reduction of the metal centre (Fig. 2). Further scans produce main changes in the metal centre response, indicating silver electrodeposition. As the formal zerovalent silver complexes are very unstable, all reported results concern the first scan. The Scheme 2 Structural formulae of the catenate 3 and of the precursors of the polymers Table 1 Cyclic voltammetry data for AgBF4 and complexes 1, 2 and 3.All potentials refer to Ag+ (10-2 mol l-1)/Ag reference in MeCN–Et4NBF4 (0.1 mol l-1), v=5 mV s-1; potentials were determined by CV on a carbon felt electrode complex c/mol l-1 Epc/V Epa/V E1/2/V DEp/V Fig. 2 Cyclic voltammetry of poly-2 on a carbon felt electrode (s= AgBF4 10-2 -0.07 0.00 -0.04 0.07 3 cm2) in MeCN–Et4NBF4 (0.1 mol l-1 ), v=5 mVs-1, Ag+(10-2 mol 1 10-3 -0.24 -0.05 -0.15 0.20 l-1)/Ag as reference.Synthesis of the film performed at 0.85 V in 2 2×10-3 -0.40 -0.12 -0.26 0.33 MeCN–Et4NBF4 (0.1 mol l-1), at a monomer concentration of 3 10-3 -0.94 -0.44 -0.69 0.50 2×10-3 mol l-1, by passing 14 mC cm-2. J. Mater. Chem., 1997, 7(7), 1169–1173 1171Table 2 Cyclic voltammetry data of the substituted polypyrroles deter- 3-substituted polypyrrole which occurs near -0.20 V, loss of mined by CV on a carbon felt electrode vs.Ag+ (10-2 mol l-1)/Ag electrochemical activity as a result of the removal of cobalt reference in MeCN–Et4NBF4 (0.1 mol l-1), v=5 mVs-1 and the appearance of a reduction process located, here again, at -1.10 V and assigned to the complexed AgI–Ag0 electro- metal centre phore. This identical reduction potential value for the com- ppy matrix polymer Epc/V Epa/V E1/2 plexed silver ion in three films issued from three dierent precursors, the entwined complex 1, the thread and ring poly-1a -1.10 -0.35 +0.30 complex 2 and the thread and ring 5, after silver–cobalt poly-2b -1.10 -0.20 +0.30 exchange, suggests that these films have very similar polyrotax- poly-5 after -1.10 -0.10 -0.20 ane network structures.Consequently, in the specific case of Co2+–Ag+ exchangec the poly-1, inter- or intra-molecular ring formation must occur free-ligand film <-2.0 -0.20 during electropolymerisation. The linkage position of the silver complex through the alkyl chain on the pyrrole ring, i.e. 3- a,bSynthesis of the film performed at 0.85 V in MeCN+Et4NBF4 0.1 mol l-1+4×10-3 mol l-1 pyrrole units by passing 14 mC cm-2, substituted or N-substituted pyrrole, has no influence on the as=4 cm2, bs=3 cm2.cSynthesis of the film by ion exchange within an topological properties of the films. analogous film polymer with cobalt as the complexing transition metal (see text). Conclusion cathodic peak is situated at -1.1 V for the two films while, We had previously noticed that the redox potential of the on the anodic scan, the associated reoxidation peak is observed AgI–Ag0 couple was strongly dependent on the topology of in the potential range where the polymer matrix is conductive its 2,9-diphenyl-1,10-phenanthroline based ligands, being more (Table 2).These reduction peaks are not due to the reduction negative in the case of the catenate structure than in the case of protons which are formed during electropolymerisation and of the entwined one by 700 mV.In this study we took which could be trapped by the polymer matrix and/or initiate advantage of this particular property to characterise the partial decomplexation of silver, despite the relative stabilities topology of bis(2,9-diaryl-1,10-phenanthroline)silver(I) based of silver catenates and proton [2]catenates.Indeed, dipping complexes covalently linked to polypyrrole matrices. In the of the modified electrodes into a basic 10-3 mol l-1 solution case of coordinating polymers built around other metallic of 2,4,6-trimethylpyridine in MeCN before the first voltam- templates, the topology could be evidenced by exchanging metric measurement led to no significant modification of the the metallic centre for AgI and determining the redox voltammogram. For each film, the ratio of the metal centre potential of the corresponding electroactive polymer.This reduction peak area to the area of the polypyrrole matrix observation is of course valid for the present family of redox peak is in agreement with its own stoichiometry, the coordinating polymers only. number of electrons transferred for the electrochemical process concerned and the doping level values (ca. 0.2).13a As the reoxidation of the zerovalent complex occurs in the References conducting matrix potential range, DEp has no significance 1 G. Bidan in Polymer films in sensor applications, ed G. Harsanyi, and it is not possible to determine E1/2.So the discussion will Technomic Publishing Co., Lancaster, Basel, 1995, p. 206 and ref- concern only the Epc values of the one-electron transfer of the erences therein. AgI–Ag0 centre. Both polymers exhibit the same one-electron 2 (a) H. L. Frisch,New. J. Chem., 1993, 17, 697; (b) S. J. Clarson, New. J. Chem., 1993, 17, 319; (c) Y. Lipatov and Y. Nizel’sky, New. reduction potential value of the silver centre, -1.1 V, corre- J.Chem., 1993, 17, 715. sponding respectively to a cathodic potential shift of 0.86 and 3 (a) J. M. Kern, J. P. Sauvage, G. Bidan, M. Billon and B. Divisia- 0.70 V between the precursors 1 and 2 and their polymers. Blohorn, Adv. Mater., 1996, 8, 580; (b) S. S. Zhu, P. J. Caroll and This potential is measured for a solid-phase species, in a T.M. Swager, J. Am. Chem. Soc., 1996, 118, 8713. potential range in which the polymer matrix is electrically 4 (a) D. B. Amabilino and J. F. Stoddart, Chem. Rev., 1995, 95, 2725; insulating, which is expected to create an overpotential as (b) J. P. Sauvage, Acc. Chem. Res., 1990, 23, 319; (c) H. W. Gibson and H. Marand, Adv. Mater., 1993, 5, 11; (d) C. Dietrich-Buchecker compared to the same redox species in solution.Nevertheless, and J. P. Sauvage, New J. Chem., 1992, 16, 277; (e) P. L. Anelli, this strongly negative value of the silver(I) complex reduction P. R. Ashton, R. Ballardini, V. Balzani, M. Delgado, M. T. potential Epc for the polymers is remarkable. It reflects the Gandolfi, T. T. Goodnow, A. E. Kaifer, D. Philp, pronounced stabilization of the complex as compared to the M.Pietraszkiewicz, L. Prodi, M. V. Reddington, A. M. Z. Slawin, monomer in solution and is likely to originate from the highly N. Spencer, J. F. Stoddart, C. Vicent and D. J. Williams, J. Am. entangled nature of the matrix. The fact that this reduction Chem. Soc., 1992, 114, 193; ( f ) A. C. Benniston, A. Harriman and V. M. Lynch, J.Am. Chem. Soc., 1995, 117, 5275. occurs in all the polymers at the same potential values suggests 5 M. Cesario, C. O. Dietrich, A. Edel, J. Guilhem, J. P. Kintzinger, that the two films poly-1 and poly-2 have very similar multi- C. Pascard and J. P. Sauvage, J. Am. Chem. Soc., 1986, 106, 6250. catenate-like network structures. 6 A. M. Albrecht-Gary, C. Dietrich-Buchecker, Z. Saad and To take advantage of these observations and of the special J.P. Sauvage, J. Am. Chem. Soc., 1988, 110, 1467. relationship between the topological properties of the matrix 7 C. O. Dietrich-Buchecker, P. A. Marnot, J. P. Sauvage, backbone and the reduction potential of the silver(I) complex J. P. Kintzinger and P. Malte`se, New. J. Chem., 1984, 8, 573. 8 N. Armaroli, L. De Cola, V.Balzani, J. P. Sauvage, C. O. Dietrich- used as a probe, it can be useful to substitute any metal of a Buchecker, J. M. Kern and A. Bailal, J. Chem. Soc., Dalton T rans., polymer to be tested by silver(I). To demonstrate the usefulness 1993, 3241. of the technique, ion-exchange experiments have been per- 9 (a) D. B. Amabilino, P. R. Ashton, C. L. Brown, E. Cordova, L. A.formed on analogous 3-substituted polypyrroles covalently Godinez, T. T. Goodnow, A. E. Kaifer, S. P. Newton, M. linked to Co(dpp,m-30)2+. The successive cobalt exclusion– Pietraszkiewicz, D. Philp, F. M. Raymo, A. S. Reder, J. F. Stoddart silver inclusion reactions have been performed on a poly-5 and D. J. Williams, J. Am. Chem. Soc., 1995, 117, 1271; (b) E. Cordova, R. A. Bissell and A.E. Kaifer, J. Org. Chem., 1995, modified electrode. The poly-5 is demetallated by action of 60, 1033. thiocyanate ions by dipping the polymer film into an 10 C. O. Dietrich-Buchecker, J. P. Sauvage and J. M. Kern, J. Am. MeCN–H2O/KSCN (0.1 mol l-1) solution and subsequently Chem. Soc., 1984, 106, 3043. metallated by silver ion by dipping in an MeCN–AgBF4 11 C. Dietrich-Buchecker, J. P. Sauvage and J. M. Kern, J. Am. Chem. (0.1 mol l-1) solution. Cobalt demetallation and silver metall- Soc., 1989, 111, 7791. ation were monitored by cyclic voltammetry. After treatment, 12 A. Livoreil, C. O. Dietrich-Buchecker and J. P. Sauvage, J. Am. Chem. Soc., 1994, 116, 9399. the film always displays the characteristic electroactivity of 1172 J. Mater. Chem., 1997, 7(7), 1169–117313 (a) G. Bidan, B. Divisia-Blohorn, M. Lapkowski, J. M. Kern and 15 I. M. Koltho and J. F. Coetzee, J. Am. Chem. Soc., 1957, 79, 1852. 16 A. El Hajbi, N. Alonso Vante, P. Chartier, G. Goetz-Grandmont, J. P. Sauvage, J. Am. Chem. Soc., 1992, 114, 5986; (b) G. Bidan, R. Heimburger and M. J. F. Leroy, J. Electroanal. Chem., 1986, B. Divisia-Blohorn, M. Billon, J. M. Kern and J. P. Sauvage, 206, 127. J. Electroanal. Chem., 1993, 360, 189. 14 C. Dietrich-Buchecker and J. P. Sauvage, T etrahedron, 1990, 46, 503. Paper 7/00014F; Received 2nd January, 1997 J. Mater. Chem., 1997, 7(7), 1169–1173 1173

ISSN:0959-9428    

DOI:10.1039/a700014f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Tetrathiafulvalenophanes and their catenanes† Mogens Brøndsted Nielsen, Zhan-Ting Li and Jan Becher* Department of Chemistry, Odense University, DK-5230 OdenseM, Denmark Monomacrocycles of the two electron donors tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene have been prepared, together with three symmetric TTF-containing bismacrocycles, two of which have been prepared by a two-step deprotection–cyclization approach.By utilizing the donor–acceptor interactions of these donors with the dipyridinium dication of 1,1¾-[1,4-phenylenebis( methylene)]bis-4,4¾-bipyridinium bis(hexafluorophosphate), [2]catenanes were synthesized. In the case of one of the bismacrocycles it was possible to isolate a minor amount of a bis[2]catenane. The catenanes were characterized by 1H NMR spectroscopy, electrospray mass spectroscopy (ESMS) and their fragmentation in the gas phase was also analysed by collisional activation (ESMS/MS).Also, one tetramacrocyclic compound, the first TTF-based ribbon compound, has been synthesized. This compound shows complex electrochemical properties. In recent years, there has been increasing interest in incorporating the tetrathiafulvalene unit into macrocyclic and supramolecular compounds due to its reversible redox characteristics.1,2 By using the self-assembly strategy developed by Stoddart et al.3 several TTF-containing catenanes and rotaxanes have been prepared from macrocyclic and linear compounds, respectively.4 The key starting materials in our synthesis are 2,7(6)-bis- Traditionally, TTF-based macrocyclic molecules have been syn- (2-cyanoethylthio)-3,6(7)-bis(methylthio)tetrathiafulvalene 1 thesized mainly by coupling of the corresponding 1,3-dithiole (cis/trans), 2,3-bis(2-cyanoethylthio)-6,7-bis(methylthio)- derivatives, 1,3-dithiole-2-thionesor 1,3-dithiolium salts, forming tetrathiafulvalene 2, and 2,3,6,7-tetrakis(2-cyanoethyl- the central fulvene double bond in the last step.5 This route thio)tetrathiafulvalene 3, which are readily prepared from 4,5- involves multistep reactions for preparations of the starting bis(2-cyanoethylthio)-1,3-dithiole-2-thione.8 Compounds 1 and materials and a number of substituents cannot withstand the 2 are used to prepare TTF-incorporating linear diiodides in coupling reaction conditions usually required.We have pre- one-step deprotection–alkylation reactions.viously reported that dicyanoethylated TTFs can be used to synthesize a variety of TTF derivatives via conversion to the Results and Discussion corresponding mono- or di-caesium salts with caesium hydrox- Preparation of monomacrocycles ide and the subsequent reaction of the di-caesium salts with Monocyclic compounds 6 and 7 consisting of TTF and 1,5- a,v-ditosylates to produce monomacrocyclic compounds.2a,b dihydroxynaphthalene units connected through diethylene glycol This route has provided a novel and ecient approach to TTF ether chains were prepared from tetrathiafulvalene 2 and bis- containing macrocycles.Recently, we have also utilized the alkylating reagents 4 and 5, respectively (Scheme 1).Under high similar deprotection–cyclization reaction of tetracyanoethylated dilution conditions using a perfusor pump, 4 (5) was reacted with TTF to construct TTF containing bismacrocycles incorporating the di-caesium salt produced in situ from 2 by treating with 2 two phenylene, anthrylene or naphthylene units, which were equiv. of caesium hydroxide monohydrate in dimethylformamide used to build a novel type of catenanes.6 A subsequent objective (DMF) to generate 6 (7) in a yield of 42% (51%).was to explore the construction of more topologically complex Treatment of 1 with 2 equiv. of caesium hydroxide mono- macrocyclic systems containing multiple TTF units. In this paper, we report the synthesis of four monomacrocyclic compoundsand three bismacrocyclic compounds, in orderto investigate their abilities to form catenanes. Also, one tetramacrocyclic compound, the first TTF-based ribbon compound,7 has been synthesized.The electrochemical redox properties of these compounds are also discussed. † Note added in proof: TTF macrocycles similar to 13 and 22 have recently been published: S.-I. Yunoki, K. Takimiya, Y. Aso and Scheme 1 Reagents and conditions: i, CsOH·H2O (2 equiv.), MeOH, T.Otsubo, T etrahedron L ett., 1997, 17, 3017. DMF, room temp., 16 h, 42% (for n=2) and 51% (for n=3) J. Mater. Chem., 1997, 7(7), 1175–1187 1175hydrate and excess of 1,2-bis(2-iodoethoxy)ethane in DMF and 1 the monocycle 11 was prepared as a mixture of cis/trans isomers in 68% yield. generated compound 8 in 79% yield (Scheme 2).No cyclization products were detected in this reaction.The reaction of 8 with 1 in the presence of 2 equiv. of caesium hydroxide under high Preparation of bismacrocycles dilution conditions resulted in the formation of monomacro- Bismacrocycles 13 and 15 were prepared by a two-step depro- cycle 9 as an inseparable mixture of cis/trans configurational tection–cyclization approach (Scheme 4 and 5).Reaction of 8 isomers in 80% yield. Treatment of 2 with 2 equiv. of caesium hydroxide monohydrate and excess of 1,2-bis(2-iodoethoxy)ethane in DMF generated compound 10 in 60% yield (Scheme 3). From 10 Scheme 2 Reagents and conditions: i, CsOH·H2O (2 equiv.), MeOH, I(CH2CH2O)2CH2CH2I (8 equiv.), DMF, room temp., 12 h, 79%; ii, Scheme 4 Reagents and conditions: i, 3, CsOH·H2O (2 equiv.), MeOH, 1, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 20 h, 80% DMF, room temp., 20 h, 53%; ii, 8, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 20 h, 50% Scheme 3 Reagents and conditions: i, CsOH·H2O (2 equiv.), MeOH, Scheme 5 Reagents and conditions: i, 3, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 20 h, 63%; ii, 10, CsOH·H2O (2 equiv.), MeOH, I(CH2CH2O)2CH2CH2I (8 equiv.), DMF, room temp., 14 h, 60%; ii, 1, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 20 h, 68% DMF, room temp., 20 h, 55% 1176 J.Mater. Chem., 1997, 7(7), 1175–1187Scheme 6 Reagents and conditions: i, 8, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 11 h, 40%; ii, 1, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 15 h, 31%; iii, Hg(OAc)2, CHCl3–CH3CO2H, room temp., 2 h, 95%; iv, 8, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 11 h, 16%; v, CsOH·H2O (2 equiv.), MeOH, I(CH2CH2O)2CH2CH2I (8 equiv.), DMF, room temp., 1 d, 16%; vi, 1, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 15 h, 44% vii, P(OEt)3, PhMe, 120°C, 4.5 h, 57% (10) and 3 in the presence of 2 equiv.of caesium hydroxide the repeated deprotection–cyclization protocol, the first TTFbased ribbon compound 28, having four rings, was prepared generated monomacrocyclic compound 12 (14) in 53% (63%) yield.No 2,3-deprotection–cyclization products were generated (Scheme 8). 2,7-Bis(2-cyanoethylthio)-3,6-[9,10-bis{2-[2-(2- thioethoxy)ethoxy]ethoxy}anthrylene]-1,4,5,8-tetrathiaful- since thin-layer chromatography (TLC) indicated that no other important products were formed except for a small amount of valene 25 was chosen as the starting material because a TTFbased bismacrocyclic compound incorporating two 9,10-dioxy- insoluble linear oligomers.The reaction of 12 (14) with 8 (10) resulted in the formation of bismacrocycle 13 (15) in 50% anthracene units was used successfully for preparation of TTFcatenanes. 6 Thus, the reaction of 25 with excess of 1,2-bis(2- (55%) yield.Since it is not possible to selectively deprotect only the 2 iodoethoxy)ethane in DMF at room temperature aorded compound 26, the key intermediate, in 75% yield. Under high and 3 positions of 3, bismacrocycle 22 had to be prepared from a coupling of the 1,3-dithiole-2-one macrocycle 21 by dilution conditions, 26 reacted with 3 aording bismacrocycle 27 in 59% yield.Similarly, the reaction of 27 and 26 resulted triethyl phosphite in toluene (Scheme 6). Macrocycle 21 could be prepared by transchalcogenation of the thione 18 using in the formation of tetracyclic compound 28 in 38% yield. mercury(II) acetate. The instability of the dithiolate of 19 probably causes the low yield in the reaction between 19 and Preparation of catenanes 8.Dibromide 17 was prepared according to Scheme 7 from Catenanes were prepared by treating the macrocycle with 1,1¾- the dihydroxy compound 24 by the action of Ph3P–CBr4 in [1,4-phenylenebis(methylene)]bis-4,4¾-bipyridinium bis(hexa- 74% yield. fluorophosphate) 29–2PF6 and 1,4-bis(bromomethyl)benzene 30 in DMF and subjecting the mixture to 10 kbar for 4 d.9 The Preparation of a TTF-based ribbon system catenation ofmacrocycles 6 and 7 is shown in Scheme 9,aording [2]catenanes 31-4PF6 and 32-4PF6, respectively. The small Because of its tetravalency, the TTF unit represents an attractive building block for preparation of ribbon type systems.By cavity catenane 31-4PF6 is less flexible than 32-4PF6 as evidenced J. Mater. Chem., 1997, 7(7), 1175–1187 1177Table 1 Product yields Yield (%) 31-4PF6 50 32-4PF6 45 33-4PF6 16 34-4PF6 7 35-4PF6 9 36–8PF6 <3 37-4PF6 9 yields are given in Table 1. The positions of the tetracationic cyclophane cyclobis(paraquat-p-phenylene) (blue box) in the catenanes produced from the bismacrocycles have been concluded from the 1H NMR spectra.Any selection of a cis/trans isomer in the complexation process is not observed for any of these macrocycles.The bis[2]catenane 36–8PF6 was only isolated as an impure minor product and assigned by its ES mass spectrum. Bismacrocycle 15 exclusively gives a cis- Scheme 7 Reagents and conditions: i,I(CH2CH2O)2CH2CH2OH (6 equiv.), catenane in 20% yield under ultra-high pressure.4c Thus, two MeCN, reflux, 1.5h, 56%; ii,CBr4, PPh3, CH2Cl2, room temp., 1 d, 74% peripheral TTFs and not only one as in the monomacrocycle 11 are necessary for the selection of a single isomer.As has by 1H NMR and UV spectroscopy. The products of catenation previously been shown, the yields of catenation are strongly of macrocycles 9, 11, 13 and 22 are shown below and the aected by electronic and structural features,4d and the formation of the precatenane problably occurs with dierent yields depending on the conformation of the isomers.Electrospray mass spectrometry (ESMS) The catenanes were characterized by ESMS, and the data are listed in Table 2. It can be seen that the compounds give peaks for [M-4PF6]4+, [M-3PF6]3+ and [M-2PF6]2+. Small peaks due to fragmentation of the catenane structure can also be seen in the spectra. These peaks are more evident in the daughter ion spectra (ESMS/MS) of selected parent ions (Table 3).Collisional activation of [M-nPF6]n+ by argon results in fragmentation of the supramolecular structure. For 34-4PF6 the ESMS and ESMS/MS spectra are shown in Fig. 1. The peaks can be explained by the mechanisms in Scheme 10. The breakdown of the tetracationic cyclophane is accompanied by one or two electron transfers from the macrocycle to the cyclophane.A similar fragmentation pattern is observed for all the catenanes. Thus, ESMS/MS presents a very powerful tool for analysing catenanes of this type. 1H NMR Spectroscopy The chemical shifts of the a- and b-protons of the tetracationic cyclophanes are listed in Table 4. Catenanes 31-4PF6 and 32- 4PF6 both show dierent inner and outer a- and b-protons, but the inner protons of the small cavity catenane 31-4PF6 are also dierent due to decreased flexibility.The b-protons show large upfield shifts, but the most dramatic shifts are seen for the 4-H naphthalene protons, which move upfield to ca. 2.4 ppm. This large shift is in accordance with published results.10 When the tetracationic cyclophane is locked around the TTF unit the SCH3 groups move ca. 0.2 ppm downfield. For both catenanes 35-4PF6 and 37-4PF6 it is therefore possible to conclude that the tetracationic macrocycle is interlocked around one of the peripheral TTF units and not around the central TTF unit. When recorded in CD3CN the SCH3 protons of the uncomplexed TTF unit in 37-4PF6 are hidden 1178 J.Mater. Chem., 1997, 7(7), 1175–1187Scheme 8 Reagents and conditions: i, CsOH·H2O (2 equiv.), MeOH, I(CH2CH2O)2CH2CH2I (8 equiv.), DMF, room temp., 1 h, 75%; ii, 3, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 20 h, 59%; iii, 26, CsOH·H2O (2 equiv.), MeOH, DMF, room temp., 25 h, 38% under solvent peaks or are very broad peaks. However, in there may be aromatic p–p interactions between the peripheral dimethyl sulfoxide (DMSO) the SCH3 protons of 37-4PF6 are and central TTF units of compound 13 when they adopt trans seen as singlets at ca. 2.44 ppm. All the catenanes 33-, 34-, 35-, configurations, 13 also reveals two reversible redox couples at 37-4PF6 and 36–8PF6 are mixtures of cis/trans isomers.11 In ED=0.55 and 0.91 V, respectively. However, a change of solvent comparison, catenation of 15 results selectively in the formation to CH2Cl2–MeCN (10% v/v) causes a splitting of the first of a cis-catenane.4c wave.Compound 22 and the monocycles all exhibit two reversible couples. In contrast, compound 28 exhibits more Cyclic voltammetry complex electrochemical properties as seen from its cyclic voltammogram shown in Fig. 3.The first two oxidative waves The redox behaviour of the compounds is shown in Table 5. are consistent with the loss of an electron from the peripheral Compound 15 exhibits two reversible redox couples (ED=0.57 and central TTFs. The third and fourth oxidative waves arise and 0.92 V in CH2Cl2), which are typical of the TTF system. from their second oxidations, whereas the last oxidative wave This result indicates that there is no interaction between the peripheral and central TTF units of 15.Although in principle corresponds to the anthracene giving o one electron. The fact J. Mater. Chem., 1997, 7(7), 1175–1187 1179tetracationic cyclophane. For the other catenanes the first oxidation potential is more or less increased, but the peaks from complexed and uncomplexed TTFs are unresolved.Charge-transfer absorption UV–VIS spectra reveal charge-transfer (CT) absorption bands for the catenanes (Table 6). For 31-4PF6 and 32-4PF6 CT bands are seen in the naphthalene donor region ata wavelength lmax of ca. 460–500 nm. For 32-4PF6 a shoulder at ca. 670 nm is seen, which can be ascribed to an interaction between TTF and blue box. For 31-4PF6 only a tail is seen in this region.A reasonable explanation is that 32-4PF6 has a higher degree of flexibility for such an interaction to be established. For catenanes 33-, 34-, 35- and 37-4PF6 the absorptions are much stronger. This can be ascribed to the better donating abilities of TTF compared to naphthalene. Conclusions We have demonstrated that a variety of tetrathiafulvalenophanes will form mono[2]catenanes with the cyclic acceptor blue box.In most cases the catenanes are obtained as inseparable mixtures of cis/trans isomers. This problem may be solved by the use of an alternative TTF-type donor without geometrical isomers, or alternatively by using sterically constrained TTF-donors. Experimental Scheme 9 Reagents and conditions: i, 6, DMF, room temp., 10 kbar; General methods ii, 7, DMF, room temp., 10 kbar All reactions were carried out under an atmosphere of dry N2.MeOH was distilled from Mg. DMF was allowed to stand that compound 28 shows two reductive waves seems to indicate that the first and second electron reception processes of the over molecular sieves (4 A° ) for at least 3 days before use. All reagents were standard grade and used as received.Analytical peripheral and central TTFs take place simultaneously. The first oxidation peaks for the TTFs in the catenanes 31- TLC was performed on Merck DC-Alufolien Kieselgel 60 F254 0.2 mm thickness. Column chromatography was carried out 4PF6 and 32-4PF6 are increased relative to the free macrocycles. This may be explained by an interaction (electro- using silica gel 60F (Merck, 9385, 230–400 mesh).Melting points were determined on a Bu� chi melting point apparatus statically or by folding) between the TTF moiety and the Table 2 ESMS data of catenanes [M-nPF6]n+ (n: 8, 6, 5) [M-4PF6]4+ [M-3PF6 ]3+ [M-2PF6 ]2+ [M-PF6 ]+ 31-4PF6 317 471 779 1703 32-4PF6 339 500 823 33-4PF6 367 538 879 34-4PF6 367 538 879 35-4PF6 507 724 1159 36–8PF6 31973 597 782 1091 37-4PF6 507 724 1159 Table 3 ESMS/MS data of catenanes daughter ions blue box fragment ions [(C18H16N2 )n]2n+ parent ion [C8H8 ]?+ (n: 1, 2) [C28H24N4]2+ [C18H16N2].+ [macrocycle]2+ [macrocycle]?+ 31-4PF6 317 104 130 208 260 374 748 471 104 208, 561a 748 32-4PF6 339 104 130 208 260 418 836 33-4PF6 367 104 130 208 260 474 948 34-4PF6 367 104 130 208 260 474 948 538 104 130 208, 561a 260 948 35-4PF6 507 104 130 208 260 754 1508 37-4PF6 507 208 754 a[C28H24N4, PF6]+. 1180 J. Mater. Chem., 1997, 7(7), 1175–1187Fig. 1 (a) ESMS and (b) ESMS/MS selected spectra for 34-4PF6 (parent ion m/z 367) and are uncorrected. 1H NMR spectra were recorded on a UV-160 instrument. Elemental analyses were performed at the Microanalytical Laboratory, University of Copenhagen.Bruker AC250, a Varian 300 or a Varian 500 spectrometer; all chemical shifts are referenced to Me4Si; J values are in Hz. Electron impact (EI) and fast atom bombardment (FAB) mass 1,5-Bis( 2-{2-[2-(2-iodoethoxy)ethoxy] ethoxy}ethoxy)- spectra were obtained on a Varian MAT 311A instrument and naphthalene 5 a Kratos MS 60 TC, respectively. Plasma desorption (PD) mass spectra were carried out on a BioIon 10 K time of flight A mixture of 1,5-dihydroxynaphthalene (2.04 g, 13 mmol), bis- [2-(2-iodoethoxy)ethyl] ether (47.5 g, 115 mmol), and K2CO3 mass spectrometer (Biosystems, Uppsala, Sweden) over 5×105 fissions (252Cf ). Electrospray (ES) mass spectra were recorded (1.76 g, 13 mmol) in anhydrous acetone (150 ml) was refluxed with stirring for 16 h.The solvent was then removed in vacuo. using a Finnigan MAT TSQ 700 triple quadrupole mass spectrometer. The catenanes were electrosprayed from aceto- The residue was extracted with CH2Cl2 (200 ml), and the organic phase washed with water and saturated aqueous NaCl nitrile solution. The typical conditions were: flow rate: 10 ml min-1, capillary potential: 5.1 kV, heated capillary: solution.The solvent was dried over anhydrous MgSO4 and removed in vacuo. The residue was subjected to column 50–100°C, sheath gas pressure: 30 psi. ESMS/MS experiments were performed using argon at a typically pressure of chromatography (silica gel) with CH2Cl2–EtOAc (1051) as the eluent. 5 (3.40 g, 36%) was obtained as a pale-yellow solid. 0.7 mTorr. The ion of interest was selected by the first quadrupole, collisionally activated in the second (actually an octapole), Mp 36–38 °C; dH (CDCl3) 3.22 (t, 4 H, J 6.9; ICH2), 3.61–3.82 (m, 20 H; OCH2), 3.99 (t, 4 H, J 4.9; OCH2), 4.30 (t, 4 H, J and the products analysed by the third quadrupole.CV measurements were carried out with Bu4NPF6 as supporting 4.9; OCH2), 6.84 [d, 2 H, J 7.6; 2-H (naph)], 7.34 [t, 2 H, J 8.0; 3-H (naph)], 7.86 [d, 2 H, J 8.5; 4-H (naph)]; dC (CDCl3) electrolyte, with a sweep rate of 100 mV-1.Counter and working electrodes were made of Pt and the reference electrode 67.92, 69.81, 70.19, 70.63, 70.75, 70.99, 71.94, 105.66, 114.60, 125.03, 126.76, 154.32; MS (EI): m/z (%): 732 (M+, 26), 199 was Ag/AgCl. UV–VIS spectra were recorded on a Shimadzu J.Mater. Chem., 1997, 7(7), 1175–1187 1181Scheme 10 (26), 155 (100), 45 (10); Found: C, 42.87; H, 5.22; C26H38I2O8 in methanol (10 ml) with stirring over 10 min. The solution was stirred for 1 h. Then this solution and a solution of requires C, 42.64; H, 5.23%. 1,5-bis{2-[2-(2-iodoethoxy)ethoxy]ethoxy}naphthalene 44d 2,3-Bis(methylthio)-6,7-[naphthalene-1,5-diyldioxybis(ethane- (0.55 g, 0.9 mmol) in DMF (50 ml) were added simultaneously, 1,2-diyl )dioxybis(ethane-1,2-diyl ) dioxybis(ethane-1,2-diyl )- during 16 h at room temp., to DMF (100 ml) under highbisthio] tetrathiafulvalene 6 dilution conditions by means of a perfusor pump.Stirring was continued for an additional 3 h, and the reaction mixture was To a solution of 2 (0.40 g, 0.9 mmol) in DMF (40 ml) was dropwise added a solution of CsOH·H2O (0.32 g, 1.9 mmol) then concentrated in vacuo.CH2Cl2 (100 ml) was added, and 1182 J. Mater. Chem., 1997, 7(7), 1175–1187Table 4 Selected 1H NMR resonances (d) of the tetracationic cyclophanes in the catenanes compared to the free tetracationic cyclophane a-H b-H free 8.93 8.23 31-4PF6 8.55 (d, 2H) 8.71 (d, 4H) 8.95 (d, 2H) 7.23 (d, 4H) 7.44 (d, 2H) 7.66 (d, 2H) 32-4PF6 8.64 (d, 4H) 9.08 (d, 4H) 7.24 (d, 4H) 7.37 (d, 4H) 33-4PF6 9.07–9.16 (8H) 8.08 (m, 8H)a 34-4PF6 9.08 (d, 4H) 9.16 (d, 4H) 7.96–8.28 (8H)a 35-4PF6 9.07–9.14 (8H) 8.07 (m, 8H) 37-4PF6 9.07 (d, 4H) 9.17 (d, 4H) 7.96–8.28 (8H) aSee Fig. 2 Table 5 Half-wave potentials for the oxidation by cyclic voltammetry ED1a ED2a ED1b ED2b 6 0.52 0.86 0.48 0.74 7 0.53 0.86 0.48 0.75 9 0.55 0.92 0.50c 0.86 11 0.55 0.91 0.51 0.85 13 0.55 0.91 0.49 0.58 0.85 15 0.57 0.92 0.53 0.85 22 0.54 0.88 0.51 0.85 31-4PF6 0.56 0.79 32-4PF6 0.57 0.81 33-4PF6 0.57 0.85 34-4PF6 0.54 0.81 35-4PF6 0.54 0.81 36–8PF6 0.55 (br) 0.84 (br) 37-4PF6 0.52 0.84 Fig. 3 Cyclic voltammogram of compound 28 aSolvent: CH2Cl2. bSolvent: CH2Cl2–MeCN (10% v/v) for macrocycles and MeCN for catenanes.cA minor shoulder was seen at ED 0.69 V. br=broad. Reference electrode: Ag/AgCl; working and counter Table 6 Charge-transfer absorptions recorded in MeCN at room electrodes: Pt; sweep rate 100 mV s-1; supporting electrolyte: Bu4NPF6 temperature 0.1 M; conc. of compound: 3×10-4 M. e/dm3 mol-1 e/dm3 mol-1 lmax/nm cm-1 lmax/nm cm-1 31-4PF6 460 (sh)a 1500 >650 (t )b 32-4PF6 495 1100 670 (sh) 620 33-4PF6 799 3500 34-4PF6 786 3300 35-4PF6 801 3700 37-4PF6 786 3400 ash=shoulder, bt=tail.the organic solution washed with water, saturated aqueous NaCl, and dried (MgSO4 ). The solvent was then removed and the residue purified by column chromatography (silica gel, CH2Cl2–EtOAc 1051), aording 6 (0.27 g, 42%) as an orange solid. Mp 93.5–95°C (from ethanol); dH (CDCl3) 2.41 (s, 6 H; SCH3), 2.63 (t, 4 H, J 6.8; SCH2), 3.43 (t, 4 H, J 6.8; OCH2 ), 3.55 (m, 4 H; OCH2), 3.72 (m, 4 H; OCH2), 3.96 (m, 4 H; OCH2), 4.39 (m, 4 H; OCH2), 6.92 [d, 2 H, J 7.6; 2-H (naph)], 7.36 [t, 2 H, J 8.0; 3-H (naph)], 7.89 [d, 2 H, J 8.4; 4-H (naph)]; MS (FAB): m/z: 748 (M+); Found: C, 47.89; H 4.65; C30H36O6S8 requires C, 48.10; H, 4.84%. 2,3-Bis(methylthio)-6,7-[naphthalene-1,5-diyldioxybis(ethane- 1,2-diyl) dioxybis(ethane-1,2-diyl )dioxybis(ethane-1,2- diyl )dioxybis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 7 Compound 7 was prepared from 2 and 5 in 51% yield as an orange oil.dH (CDCl3) 2.41 (s, 6 H; SCH3), 2.81 (t, 4 H, J 6.8; SCH2), 3.43–3.52 (m, 8 H; OCH2), 3.56–3.60 (m, 4 H; OCH2 ), 3.64–3.69 (m, 4 H; OCH2 ), 3.76–3.80 (m, 4 H; OCH2), 3.99 (t, 4 H, J 4.5; OCH2), 4.35 (t, 4 H, J 4.5; OCH2), 6.89 [d, 2 H, J 7.6; 2-H (naph)], 7.35 [t, 2 H, J 8.1; 3-H (naph)], 7.88 [d, 2 H, J 8.4; 4-H (naph)]; dC (CDCl3) 18.84, 35.03, 67.90, 69.50, 69.60, 70.15, 70.30, 70.49, 70.86, 105.77, 110.43, 110.75, 114.44, 124.93, Fig. 2 Selected proton NMR spectra for (a) 33-4PF6 and (b) 34-4PF6 126.69, 127.23, 127.43, 154.22; MS (FAB): m/z: 836 (M+); J. Mater.Chem., 1997, 7(7), 1175–1187 1183Found: C, 48.67; H, 5.08; C34H44O8S8 requires C, 48.78; H, 2,3-Bis(methylthio)-6,7-[2,7(6)-bis(methylthio)-tetrathia- 5.30%. fulvalene-3,6(7)-diylbisthiobis(ethane-1,2-diyl )dioxybis(ethane- 1,2-diyl) dioxybis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 11, cis/trans 2,7(6)-Bis(methylthio)-3,6(7)-bis{2-[2-(2-iodoethoxy)ethoxy]- Compound 11 was prepared from 1 and 10 in 68% yield as ethylthio}tetrathiafulvalene 8, cis/trans an orange oil.dH (CDCl3) 2.43 (s, 6 H; SCH3), 2.45 (m, 6 H; A solution of CsOH·H2O (1.48 g, 8.8 mmol) in methanol SCH3), 2.97–3.06 (m, 8 H; SCH2 ), 3.63–3.74 (m, 16 H; OCH2 ); (10 ml) was added to a solution of 1 (1.86 g, 4.0 mmol) in dC (CDCl3) 19.07, 19.11, 35.04, 35.51, 35.55, 35.66, 69.94, 69.99, DMF (100 ml) with stirring at room temp.in 10 min. After 70.16, 70.34, 70.38, 70.48, 70.60, 70.62, 110.57, 111.20, 111.30, 1 h, 1,2-bis(2-iodoethoxy)ethane (29.6 g, 80 mmol) was added 124.12, 124.81, 127.48, 127.89, 128.15, 130.46, 131.87; MS and the mixture was stirred for 12 h. The reaction mixture was (FAB): m/z: 948 (M+); Found: C, 35.65; H, 3.82; C28H36O4S16 concentrated in vacuo.CH2Cl2 (200 ml) was added, and the requires C, 35.42; H, 3.82%. organic phase was washed with water, saturated aqueous NaCl, and dried (MgSO4 ). Concentration in vacuo gave an oil which was chromatographed on silica gel using CH2Cl2–AcOEt 2,7(6)-Bis( 2-cyanoethylthio)-3,6(7)-[ 2,7(6)-bis(methylthio)- (4051) as an eluent. Isolation of the main fraction gave tetrathiafulvalene-3,6(7)-diylbisthiobis(ethane-1,2-diyl )dioxy- compound 5 (2.66 g, 79%) as an orange oil.dH (CDCl3) 2.44 bis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl ) bisthio]tetrathia- (s, 6 H; SCH3), 3.01 (t, 4 H, J 6.7; SCH2), 3.27 (t, 4 H, J 6.8; fulvalene 12, cis/trans ICH2), 3.66 (m, 8 H; OCH2), 3.70 (t, 4 H, J 6.7; OCH2), 3.77 (t, 4 H, J 6.8; OCH2); dC (CDCl3 ) 2.72, 2.82, 19.00, 29.51, 33.94, Compound 12 was prepared from 3 and 8 in 53% yield as an 35.36, 68.57, 69.48, 70.06, 70.38, 71.88, 110.48, 110.51, 124.28, orange oil.dH (CDCl3) 2.45 (m, 6 H; SCH3), 2.69–2.76 (m, 4 124.43, 130.59, 130.74; MS (EI): m/z (%): 844 (M+, 83), 474 H; CH2CN), 2.97–3.10 (m, 12 H; SCH2), 3.65 (m, 8 H; OCH2 ), (18), 199 (26), 155 (100), 142 (80), 127 (26); Found: C, 28.76; 3.69–3.76 (m, 8 H; OCH2); dC (CDCl3 ) 14.12, 18.48, 18.72, H, 3.69; C20H30I2O4S8 requires C, 28.44; H, 3.59%. 19.08, 19.14, 19.17, 20.94, 25.89, 29.59, 31.28, 31.36, 35.19, 35.29, 35.49, 35.61, 35.70, 51.10, 60.26, 70.06, 70.10, 70.48, 70.57, 70.62, 110.43, 110.59, 117.50, 117.59, 122.90, 123.01, 123.35, 124.29, 2,3-Bis(methylthio)-6,7-bis{2-[2-(2-iodoethoxy)ethoxy]ethyl- 124.60, 124.68, 130.77, 131.22, 132.78, 133.10; MS (FAB): m/z: thio}tetrathiafulvalene 10 1026 (M+); Found: C, 37.25; H, 3.72; N, 2.88; C32H38N2O4S16 requires C, 37.40; H, 3.73; N, 2.73%.Compound 10 was prepared in a similar way from 2 and 1,2- bis(2-iodoethoxy)ethane in 60% yield as an orange oil. dH (CDCl3) 2.42 (s, 6 H; SCH3), 3.04 (t, 4 H, J 6.7; SCH2), 3.25 (t, 4 H, J 6.8; ICH2), 3.64 (m, 12 H; OCH2), 3.68 (t, 4 H, J 2,7(6)53,6(7)-Bis[2,7(6)-bis(methylthio) tetrathiafulvalene- 5.1; OCH2); dC (CDCl3) 2.96, 19.16, 35.41, 70.04, 70.11, 70.43, 3,6(7)-diylbisthiobis(ethane-1,2-diyl )dioxybis(ethane-1,2- 71.92, 110.38, 110.90, 127.36, 127.81; MS (EI): m/z (%): 844 diyl )dioxybis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 13, (M+, 55), 570 (19), 474 (70), 386 (33), 155 (100), 142 (75); cis/trans Found: C, 28.60; H, 3.55; C20H30I2O4S8 requires C, 28.43; Compound 13 was prepared from 8 and 12 in 50% yield as a H, 3.59%.semicrystalline orange oil. dH (CDCl3) 2.44 (m, 12 H; SCH3 ), 2.97–3.02 (m, 16 H; SCH2), 3.60–3.74 (m, 32 H; OCH2); MS 2,7(6)-Bis{2-[2-(2-iodoethoxy)ethoxy] ethylthio}-3,6(7)- (PD): m/z: 1509.2 (M+); Found: C, 36.74; H, 4.12; C46H60O8S24 [anthracene-9,10-diyldioxybis(ethane-1,2-diyl ) dioxybis(ethane- requires C, 36.57; H, 4.01%. 1,2-diyl )dioxybis(ethane-1,2-diyl ) bisthio]tetrathiafulvalene 26, cis/trans 2,7(6)-Bis( 2-cyanoethylthio)-3,6(7)-[ 2,3-bis(methylthio) tetra- Compound 26 was prepared in a similar way from 256 and thiafulvalene-6,7-diylbisthiobis(ethane-1,2-diyl )dioxybis(ethane- 1,2-bis(2-iodoethoxy)ethane in 75% yield as a semicrystalline 1,2-diyl) dioxybis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 14, orange solid.dH (CDCl3) 2.82–3.20 (m, 12 H; ICH2, SCH2), cis/trans 3.23–3.50 (m, 4 H; OCH2), 3.52–4.00 (m, 28 H; OCH2), 4.32–4.40 (m, 4 H; OCH2 ), 7.39–7.53 [m, 4 H; 1-H (anth)], Compound 14 was prepared from 3 and 10 in 63% yield as 8.40–8.47 [m, 4 H; 2-H (anth)]; dC (CDCl3) 2.93, 2.98, 35.38, an orange oil.dH (CDCl3) 2.43 (s, 6 H; SCH3), 2.74 (m, 4 H; 35.42, 35.56, 35.65, 69.69, 69.81, 70.01, 70.06, 70.17, 70.31, 70.42, CH2CN), 3.07 (m, 12 H; SCH2), 3.64 (m, 12 H; OCH2), 3.71 70.60, 70.69, 70.83, 71.39, 71.58, 71.76, 71.88, 74.86, 74.99, (m, 4 H; OCH2); dC(CDCl3) 14.11, 18.71, 18.85, 19.09, 20.91, 109.71, 109.89, 122.71, 122.78, 125.03, 125.07, 125.27, 125.31, 29.57, 31.31, 31.42, 35.40, 35.47, 35.68, 60.23, 69.95, 70.12, 70.40, 127.19, 127.29, 128.27, 128.69, 146.96, 146.99; MS (FAB): m/z: 70.57, 70.60, 70.66, 110.96, 111.29, 117.47, 117.64, 123.17, 124.11, 1254 (M+); Found: C, 42.25; H; 4.59; C44H56I2O10S8 requires 127.39, 127.74, 127.99, 128.71, 130.77, 132.53, 132.59; MS (PD): C, 42.10; H, 4.51%.m/z: 1027.5 (M+); Found: C, 37.48; H, 3.71; N, 3.01; C32H38N2O4S16 requires C, 37.40; H, 3.73; N, 2.73%. 2,7(6)-Bis(methylthio)-3,6(7)-[2,7(6)-bis(methylthio)-tetrathiafulvalene- 3,6(7)-diylbisthiobis(ethane-1,2-diyl )dioxybis- 2,7(6)53,6(7)-Bis[2,3-bis(methylthio)tetrathiafulvalene-6,7- (ethane-1,2-diyl ) dioxybis(ethane-1,2-diyl )bisthio]tetrathiadiylbisthiobis( ethane-1,2-diyl )dioxybis(ethane-1,2-diyl ) dioxy- fulvalene 9, cis/trans bis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 15, cis/trans Compound 9 was prepared from 1 and 8 in 80% yield as an Compound 15 was prepared from 10 and 14 in 55% yield as orange oil.dH (CDCl3) 2.44 (m, 12 H; SCH3), 2.96–3.03 (m, 8 a semicrystalline orange oil. dH (CDCl3) 2.43 (s, 12 H; SCH3 ), H; SCH2), 3.65–3.73 (m, 16 H; OCH2); dC (CDCl3 ) 19.04, 3.02 (m, 16 H; SCH2), 3.63–3.73 (m, 32 H; OCH2); dC (CDCl3) 19.08, 19.12, 35.09, 35.16, 35.30, 35.39, 68.64, 69.53, 70.09, 70.20, 19.09, 26.79, 29.55, 30.07, 35.20, 35.41, 35.64, 69.97, 70.10, 70.37, 70.46, 70.53, 70.58, 110.77, 110.80, 111.11, 124.22, 124.48, 124.95, 70.55, 70.66, 110.40, 110.78, 111.40, 127.36, 127.58, 127.77, 124.99, 130.20, 131.13, 131.55; MS (FAB): m/z: 948 (M+); 127.00, 128.62; MS (PD): m/z: 1509.2 (M+); Found: C, 36.33; Found: C, 35.73, H; 3.83; C28H36O4S16 requires C, 35.42; H, 3.82%.H, 3.74; C46H60O8S24 requires C, 36.57; H, 4.01. 1184 J. Mater. Chem., 1997, 7(7), 1175–11874,5-Bis{2-[2-(2-hydroxyethoxy)ethoxy]ethylthio}-1,3-dithiole- Method 3: Hg(OAc)2 (0.31 g, 1.0 mmol) was added to a solution of 18 (0.31 g, 0.4 mmol) in chloroform (50 ml) and glacial 2-thione 24 acetic acid (20 ml).The solution was stirred for 2 h, whereupon To a solution of bis(tetraethylammonium) bis(2-thioxo-1,3- it was filtered on Celite. The filtrate was washed with NaHCO3 dithiole-4,5-dithiolato)zincate 23 (2.76 g, 3.8 mmol) in MeCN (aq), water, and dried (MgSO4 ). The solvent was then removed (100 ml) was added 2-[2-(2-iodoethoxy)ethoxy]ethanol (6.0 g, to aord 21 (0.29 g, 95%). 23 mmol) and the mixture was refluxedfor 90 min. The resulting solution was cooled to room temp. and concentrated in vacuo. 2,356,7-Bis[2,7(6)-bis(methylthio)tetrathiafulvalene-3,6 (7)- The product was redissolved in CH2Cl2 (500 ml), washed with diylbisthiobis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl ) dioxy- water, and dried (MgSO4).The solvent was then removed and bis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 22, cis/trans the residue purified by column chromatography (silica gel, CH2Cl2–MeOH 951), aording 24 (2.00 g, 56%) as an orange A solution of 21 (0.32 g, 0.4 mmol) in toluene (4 ml) and oil. dH (CDCl3) 2.63 (t, 2 H, J 5.7; OH), 3.09 (t, 4 H, J 6.3; freshly distilled P(OEt)3 (7 ml) was heated to 120 °C.The SCH2), 3.59–3.76 (m, 20 H; OCH2); dC (CDCl3) 36.08, 61.71, mixture was stirred for 4.5 h and then allowed to cool to room 69.82, 70.32, 70.58, 72.57, 136.61, 211.01; MS (EI): m/z (%): 462 temp., whereupon it was concentrated in vacuo. The oily (M+, 100), 429 (81), 198 (38), 121 (36), 89 (75); Found: C, residue was subjected to column chromatography (silica gel, 38.69; H, 5.25; C15H26O6S5 requires C, 38.94; H, 5.66%. CH2Cl2–EtOAc 1051), aording 22 (0.18 g, 57%) as an orange oil.dH (CDCl3) 2.45 (m, 12 H; SCH3), 2.95–3.06 (m, 16 H; 4,5-Bis{2-[2-(2-bromoethoxy)ethoxy]ethylthio}-1,3-dithiole-2- SCH2), 3.62–3.74 (m, 32 H; OCH2); dC(CDCl3 ) 19.10, 19.14, thione 17 34.76, 34.90, 35.08, 35.58, 35.62, 69.83, 69.96, 70.00, 70.19, 70.38, 70.42, 70.51, 70.65, 111.20, 111.27, 124.18, 124.85, 127.92, 128.17, To a solution of 24 (1.94 g, 4.2 mmol) in CH2Cl2 (100 ml) was 130.48, 131.88; MS (PD): m/z: 1510.3 (M+); MS (FAB): m/z: added CBr4 (2.92 g, 8.8 mmol).Then PPh3 (2.85 g, 10.9 mmol) 1508 (M+); Found: C, 37.03; H, 4.06; C46H60O8S24 requires C, was added during 2 h. The reaction mixture was left overnight 36.58; H, 4.00%.with stirring, whereupon it was concentrated in vacuo and the residue subjected to column chromatography (silica gel, CH2Cl2–MeOH 951), aording 17 (1.82 g, 74%) as an orange 2,7(6)-[Anthracene-9,10-diyldioxybis(ethane-1,2-diyl ) dioxy- oil. dH (CDCl3 ) 3.09 (t, 4 H, J 6.3; SCH2), 3.48 (t, 4 H, J 6.2; bis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl ) bisthio]-3,6(7)- BrCH2), 3.64–3.84 (m, 16 H; OCH2); MS (EI): m/z (%): 588 [2,7(6)-bis(2-cyanoethylthio)tetrathiafulvalene-3,6 (7)- (M+, 25), 393 (65), 223 (23), 147 (29), 121 (32), 107 (100), 88 diylbisthiobis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl )- (24); Found: C, 30.64; H 3.97; C15H24Br2O4S5 requires C, 30.62; dioxybis(ethane-1,2-diyl ) bisthio]tetrathiafulvalene 27, cis/trans H, 4.11%.Compound 27 was prepared from 3 and 26 in 59% yield as a dark-orange oil. dH (CDCl3) 2.65–2.72 (m, 4 H; CH2CN), 4,5-Bis{2-[2-(2-iodoethoxy)ethoxy] ethylthio}-1,3-dithiole-2- 2.98–3.04 (m, 16 H; SCH2), 3.43–3.87 (m, 28 H; OCH2 ), one 20 3.93–3.99 (m, 4 H;OCH2), 4.33–4.39 (m, 4 H;OCH2), 7.41–7.53 To a solution of 4,5-bis(2¾-cyanoethylthio)-1,3-dithiole-2-one [m, 4 H; 1-H (anth)], 8.38–8.47 [m, 4 H; 2-H (anth)]; MS 19 (1.24 g, 4.3 mmol) in DMF (50 ml) was dropwise added a (FAB): m/z: 1436 (M+); Found: C, 46.80; H, 4.32; N, 1.99; solution of CsOH·H2O (1.52 g, 9.1 mmol) in methanol (10 ml) C56H64N2O10S16 requires C, 46.76; H, 4.49; N, 1.95%. under stirring in 30 min.After stirring for 30 min 1,2-bis(2- iodoethoxy)ethane (15.9 g, 43 mmol) was added.The reaction 2,7(6)53,6(7)-Bis{3,6(7)-[anthracene-9,10-diyldioxybis(ethane- mixture was left overnight with stirring, whereupon it was 1,2-diyl) dioxybis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl )- concentrated in vacuo. CH2Cl2 (200 ml) was added, and the bisthio]tetrathiafulvalene-2,7 (6)-diylbisthiobis(ethane-1,2- organic solution washed with water, saturated aqueous NaCl, diyl )dioxybis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl )- and dried (MgSO4).The solvent was then removed and the bisthio}tetrathiafulvalene 28, cis/trans residue purified by column chromatography (silica gel, CH2Cl2–EtOAc 1051), aording 20 (0.46 g, 16%) as an orange Compound 28 was prepared in 38% yield from 26 and 27 as oil. dH (CDCl3) 3.07 (t, 4 H, J 6.5; SCH2), 3.27 (t, 4 H, J 6.8; a dark-orange semicrystalline oil.dH (CDCl3) 2.83–3.12 (m, 24 ICH2), 3.65–3.79 (m, 16 H; OCH2 ); MS (FAB): m/z: 666 (M+); H; SCH2), 3.43–3.86 (m, 72 H; OCH2), 3.96 (m, 8 H; OCH2 ), Found: C, 27.12; H, 3.11; C15H24I2O5S4 requires C, 27.04; 4.37 (m, 8 H; OCH2), 7.26–7.53 [m, 8 H; 1-H (anth)], 8.39 [m, H 3.63%. 8 H; 2-H (anth)]; MS (FAB): m/z: 2328 (M+); Found: C, 48.66; H, 5.33; C94H112O20S24 requires C, 48.42; H, 4.85%. 2,7(6)-Bis(methylthio)-3,6(7)-[2-thioxo-1,3-dithiole-4,5-diylbisthiobis (ethane-1,2-diyl )dioxybis(ethane-1,2-diyl ) dioxy- {2,3-Bis(methylthio)-6,7-[naphthalene-1,5-diyldioxybis(ethane- bis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 18, cis/trans 1,2-diyl) dioxybis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl )- Method 1: 18 was prepared from 8 and 16 in 40% yield as an bisthio]tetrathiafulvalene}–{5,12,19,26-tetraazoniaheptacyclo- orange oil.dH (CDCl3) 2.44 (m, 6 H; SCH3) 2.95–3.11 (m, 8 H, [24.2.2.22,5.27,10.212,15.216,19.221,24]tetraconta-2,4,7,9,12,14,16, J 7.0; SCH2), 3.62–3.76 (m, 16 H; OCH2); MS (FAB): m/z: 786 18,21,23,26,28,29,31,33,35,37,39-octadecaene tetrakis- (M+); Found: C, 34.83; H, 3.57; C23H30O4S13 requires C, 35.09; (hexafluorophosphate)} (31-4PF6) H, 3.84%.A solution of 6 (0.120 g, 0.16 mmol), 29–2PF6 (0.340 g, Method 2: 18 was prepared from 1 and 17 in 31% yield. 0.48 mmol), and 30 (0.148 g, 0.56 mmol) in DMF (12 ml) was transferred to a high-pressure-reaction Teflon tube, which was 2,7(6)-Bis(methylthio)-3,6(7)-[2-oxo-1,3-dithiole-4,5-diyl- then compressed (10 kbar) at room temp.for 4 d. The solvent bisthiobis (ethane-1,2-diyl )dioxybis(ethane-1,2-diyl ) dioxy- was then removed in vacuo to give a residue, which was bis(ethane-1,2-diyl )bisthio]tetrathiafulvalene 21, cis/trans subjected to column chromatography on silica gel with MeOH–aqueous NH4Cl (2 M)–MeNO2 (75251) as the eluent. Method 1: 21 was prepared from 8 and 19 in 16% yield as an orange oil.dH (CDCl3) 2.45 (m, 6 H; SCH3) 2.94–3.10 (m, 8 H; Collection of the violet fraction aorded a violet solid after evaporation of the solvent in vacuo. The solid was partially SCH2), 3.61–3.76 (m, 16 H; OCH2); MS (FAB): m/z: 770 (M+); Found:C,35.93;H,3.65; C23H30O5S12 requiresC,35.82; H,3.92%. dissolved in methanol and filtered, and the solvent evaporated in vacuo. The solid residue was then redissolved in a minimum Method 2: 21 was prepared from 1 and 20 in 44% yield. J.Mater. Chem., 1997, 7(7), 1175–1187 1185amount of methanol, and saturated aqueous NH4PF6 was of the green fraction aorded a green solid after evaporation of the solvent in vacuo. The solid was dissolved in a minimum added until precipitation was complete. The solid product was removed by filtration (Celite), washed with water, pumped dry, amount of MeOH, and saturated aqueous NH4PF6 was added until precipitation was complete.The green solid product was and then extracted with acetonitrile. After the solvent was removed in vacuo, 31-4PF6 (0.148 g, 50%) was obtained as a removed by filtration, washed with water and pumped dry. Yield: 0.067 g (16%). Mp>250°C; dH (CD3CN) 2.38 (m, 6 H; dark violet solid.Mp 213–215 °C (decomp.); dH (CD3CN) 2.34 (s, 6 H; SCH3), 2.37 [d, 2 H, J 8.5; 4-H (naph)], 2.42–2.63 (m, SCH3), 2.57 (m, 6 H; SCH3), 2.88–3.00(m,4 H; SCH2), 3.07–3.11 (m, 4 H; SCH2), 3.68–3.87 (m, 16 H; OCH2), 5.70–5.76 (m, 8 H; 4 H; SCH2 ) , 3.48–3.65 (m, 4 H; OCH2), 3.74–4.03 (m, 10 H; OCH2), 4.18–4.26 (m, 2 H; OCH2 ), 4.38–4.44 (m, 2 H; OCH2), NCH2), 7.72–7.77 (m, 8 H; C6H4), 8.08 (m, 8 H; b-H), 9.07–9.16 (m, 8 H; a-H); MS (ES): m/z: 104, 130, 208, 260, 561, 367 4.61–4.69 (m, 2 H; OCH2), 5.60–5.80 (m, 8 H; NCH2), 5.96 [t, 2 H, J 8.1; 3-H (naph)], 6.40 [d, 2 H, J 7.8; 2-H (naph)], 7.23 [M-4PF6]4+, 538 [M-3PF6]3+, 879 [M-2PF6]2+, 948 [macrocycle] ?+; MS/MS (ES): parent ion: m/z: 367, daughter [d, 4 H, J 6.4; b-H), 7.44 [d, 2 H, J 7.0; b-H), 7.66 [d, 2 H, J 6.6; b-H), 7.95–8.04 (m, 8 H; C6H4), 8.55 [d, 2 H, J 6.5; a-H), ions: m/z: 104, 130, 208, 260, 474, 948; Found: C, 37.11; H, 3.37; N, 2.70; C64H68F24N4O4P4S16 requires C, 37.50; H, 3.34; N, 8.71 [d, 4 H, J 6.2; a-H), 8.95 [d, 2 H, J 6.0; a-H); MS (ES): m/z: 130, 317 [M-4PF6]4+, 471 [M-3PF6]3+, 748 2.73%. [macrocycle]?+, 779 [M-2PF6]2+, 1703 [M-PF6 ]+; MS/MS (ES): parent ion: m/z: 317, daughter ions: m/z: 104, {2,3-Bis(methylthio)-6,7-[2,7(6)-bis(methylthio)tetrathia- 130, 208, 260, 374, 748; parent ion: m/z: 471, daughter ions: fulvalene-3,6(7)-diylbisthiobis(ethane-1,2-diyl )dioxybis(ethanem/ z: 104, 208, 561, 748; Found: C, 41.94; H, 3.66; N, 2.95; 1,2-diyl) dioxybis(ethane-1,2-diyl )bisthio]tetrathiafulvalene C66H68F24N4O6P4S8,2H2O requires C, 42.04; H, 3.85; N, (cis/trans)}-{5,12,19,26-tetraazoniaheptacyclo- 2.97%.[24.2.2.22,5.27,10.212,15.216,19.221,24]tetraconta-2,4,7,9,12,14,16, 18,21,23,26,28,29,31,33,35,37,39-octadecaene {2,3-Bis(methylthio)-6,7-[naphthalene-1,5-diyldioxybis(ethane- tetrakis(hexafluorophosphate)} (34-4PF6) 1,2-diyl )dioxybis(ethane-1,2-diyl ) dioxybis(ethane-1,2-diyl )- A solution of 11 (0.120 g, 0.13 mmol), 29–2PF6 (0.268 g, dioxybis(ethane-1,2-diyl ) bisthio]tetrathiafulvalene}{5,12,19,26- 0.38 mmol), and 30 (0.117 g, 0.44 mmol) in DMF (12 ml) was tetraazoniaheptacyclo[24.2.2.22,5.27,10.212,15.216,19.221,24]tetraconta- subjected to 10 kbar at room temp.for 4 d. The solvent was 2,4,7,9,12,14,16,18,21,23,26,28,29,31,33,35,37,39-octadecaene then removed in vacuo to give a green residue, which was tetrakis(hexafluorophosphate)} (32-4PF6 ) subjected to column chromatography on silica gel with MeOH–aqueous NH4Cl (2 M)–MeNO2 (75251) as the eluent.A solution of 7 (0.120 g, 0.14 mmol), 29–2PF6 (0.304 g, Collection of the green fraction aorded a green solid after 0.43 mmol) and 30 (0.132 g, 0.50 mmol) in DMF (12 ml) was evaporation of the solvent in vacuo.The solid was partially subjected to 10 kbar at room temp. for 4 d. The solvent was dissolved in methanol and the green solid filtered o. This was then removed in vacuo to give a residue, which was subjected then dissolved in a minimum amount of MeOH–H2O (151), to column chromatography on silica gel with MeOH–aqueous and saturated aqueous NH4PF6 was added until precipitation NH4Cl (2 M)–MeNO2 (75251) as the eluent. Collection of the was complete.The solid product was removed by filtration brown fraction aorded a brown solid after evaporation of the (Celite), washed with water, pumped dry, and then extracted solvent in vacuo. The solid was washed with water, whereupon with acetonitrile. After the solvent was removed in vacuo, 34- it was dissolved in MeNO2 (20 ml).Then it was washed with 4PF6 (0.017 g, 7%) was obtained as a green solid. Mp>250°C; saturated aqueous NH4PF6 and finally with water. dH (CD3CN) 2.38 (s, 6 H; SCH3), 2.58 (m, 6 H; SCH3 ), Evaporation of the solvent aorded 32-4PF6 (0.126 g, 45%) as 2.69–2.82 (m, 2 H; SCH2), 2.87 (t, 4 H, J 5.5; SCH2), 3.06 (t, a brown solid; Mp>250 °C; dH (CD3CN) 2.42 [m, 10 H; SCH3, 2 H, J 6.1; SCH2), 3.53–3.88 (m, 16 H; OCH2), 5.72–5.77 (m, 4-H (naph), SCH2], 2.77 (s, 1 H; SCH2), 2.89 (s, 1 H; SCH2), 8 H; NCH2), 7.71–7.75 (m, 8 H; C6H4), 7.96 (d; b-H), 8.06 [d, 3.16 (m, 4 H; OCH2), 3.47 (m, 4 H; OCH2), ), 3.70 (m, 4 H; J 7.2; b-H), 8.09 [d, J 7.9; b-H), 8.17 (d; b-H), 8.28 (d; b-H), OCH2), 3.89 (m, 4 H; OCH2), 4.03 (m, 4 H; OCH2), 4.21 (m, 7.96–8.28 (8 H), 9.08 [d, 4 H, J 6.9; a-H), 9.16 [d, 4 H, J 6.9; 4 H; OCH2), 4.32 (m, 4 H; OCH2), 5.68–5.76 (m, 8 H; NCH2), a-H); MS (ES): m/z: 104, 130, 208, 260, 561, 367 [M-4PF6]4+, 5.99 [t, 2 H, J 7.9; 3-H (naph)], 6.27 [d, 2 H, J 7.8; 2-H 474 [macrocycle]2+; 538 [M-3PF6]3+, 879 [M-2PF6]2+, (naph)], 7.24 [d, 4 H, J 5.2; b-H), 7.37 [d, 4 H, J 5.2; b-H), 948 [macrocycle]?+; MS/MS (ES): parent ion: m/z: 367, 7.95 (s, 4 H; C6H4), 8.04 (s, 4 H; C6H4), 8.64 [d, 4 H, J 6.3; adaughter ions: m/z: 104, 130, 208, 260, 474, 948; parent ion: H), 9.08 [d, 4 H, J 5.0; a-H); MS (FAB): m/z: 665 [blue box, m/z: 538, daughter ions: m/z: 104, 130, 208, 260, 561, 948; PF6]+, 836 [macrocycle]+, 1501 [M-3PF6]+, 1646 Found: C, 37.12; H, 3.22; N, 2.94; C64H68F24N4O4P4S16 requires [M-2PF6]+, 1791 [M-PF6]+; MS (ES): m/z: 561, 339 C, 37.50; H, 3.34; N, 2.73%.[M-4PF6]4+, 418 [macrocycle]2+, 500 [M-3PF6]3+, 823 [M-2PF6]2+, 836 [macrocycle] ?+; MS/MS (ES): parent ion: m/z: 339, daughter ions: m/z: 104, 130, 208, 260, 418, 836; {2,7(6)53,6(7)-Bis[2,7 (6)-bis(methylthio)-tetrathiafulvalene- Found: C, 42.29; H, 3.89; N, 3.00; C70H76F24N4O8P4S8,2.5H2O 3,6(7)-diylbisthiobis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl )- requires C, 42.40; H, 4.12; N, 2.83%. dioxybis(ethane-1,2-diyl ) bisthio]tetrathiafulvalene (cis/trans)}-{5,12,19,26-tetraazoniaheptacyclo- {2,7(6)-Bis(methylthio)-3,6(7)-[2,7(6)-bis(methylthio)tetra- [24.2.2.22,5.27,10.212,15.216,19.221,24]tetraconta-2,4,7,9,12,14, thiafulvalene-3,6(7)diylbisthiobis(ethane-1,2- 16,18,21,23,26,28,29,31,33,35,37,39-octadecaene (circum diyl ) dioxybis(ethane-1,2-diyl )dioxybis(ethane-1,2- peripheral TTF) tetrakis(hexafluorophosphate)} (35-4PF6), diyl ) bisthio]tetrathiafulvalene (cis/trans)}-{5,12,19,26- and {2,7(6)53,6(7)-Bis[2,7(6)-bis(methylthio)-tetrathiatetraazoniaheptacyclo[ 24.2.2.22,5.27,10.212,15.216,19.221,24]tetraconta- fulvalene-3,6(7)-diylbisthiobis(ethane-1,2-diyl )dioxy- 2,4,7,9,12,14,16,18,21,23,26,28,29,31,33,35,37,39-octadecaene bis(ethane-1,2-diyl )dioxybis(ethane-1,2-diyl ) bisthio]- tetrakis(hexafluorophosphate)} (33-4PF6 ) tetrathiafulvalene (cis/trans)}-bis{5,12,19,26-tetraazoniaheptacyclo-[ 24.2.2.22,5.27,10.212,15.216,19.221,24]tetraconta- A solution of 9 (0.200 g, 0.21 mmol), 29–2PF6 (0.446 g, 2,4,7,9,12,14,16,18,21,23,26,28,29,31,33,35,37,39-octadecaene 0.63 mmol), and 30 (0.195 g, 0.74 mmol) in DMF (12 ml) was (circum peripheral TTFs) tetrakis(hexafluorophosphate)} subjected to 10 kbar at room temp.for 4 d. The solvent was (36–8PF6) then removed in vacuo to give a green residue, which was subjected to column chromatography on silica gel with MeOH– A solution of 13 (0.200 g, 0.13 mmol), 29–2PF6 (0.374 g, 0.53 mmol), and 30 (0.154 g, 0.58 mmol) in DMF (12 ml) was aqueous NH4Cl (2 M)–MeNO2 (75251) as the eluent. Collection 1186 J.Mater. Chem., 1997, 7(7), 1175–1187subjected to 10 kbar at room temp. for 4 d. The solvent was cycle]?+; MS/MS (ES): parent ion: m/z: 507, daughter ions: m/z: 208, 754. then removed in vacuo to give a green residue, which was subjected to column chromatography on silica gel with MeOH–aqueous NH4Cl (2 M)–MeNO2 (75251) as the eluent.We would like to thank Steen B. Nielsen for carrying out the Collection of the green fraction aorded a green solid after electrospray mass spectra. We also thank Odense University evaporation of the solvent in vacuo. Changing the eluent to for a PhD scholarship to M.B.N.Forskerakademiet of MeOH–aqueous NH4Cl (2 M)–DMF (45552) aorded a Denmark is thanked for a Danvis fellowship to Z.-T. L. second green fraction which was evaporated in vacuo. The first fraction was worked up as 34-4PF6, aording 35- References 4PF6 (0.030 g, 9%) as a green solid. Mp>250°C; dH (CD3CN) 2.40 (m, 6 H; SCH3), 2.58 (m, 6 H; SCH3), 2.90–3.10 (m, 16 H; 1 For reviews on TTF macrocyclic chemistry, see (a) T.Jørgensen, T. K. Hansen and J. Becher, Chem. Soc. Rev.,1994, 41; (b)M. Adam SCH2), 3.51–3.86 (m, 32 H; OCH2 ), 5.71–5.76 (m, 8 H; NCH2), and K. Mu�llen, Adv. Mater., 1994, 6, 439. 7.71–7.77 (m, 8 H; C6H4 ), 8.07 (m, 8 H; b-H), 9.07–9.14 (m, 8 2 For recent examples, see (a) J. Becher, J. Lau, P. Leriche, P. Mørk H; a-H); MS (ES): m/z: 208, 260, 507 [M-4PF6]4+, 724 and N.Svenstrup, J. Chem. Soc., Chem. Commun., 1994, 2715; (b) [M-3PF6]3+, 1159 [M-2PF6]2+; MS/MS (ES): parent ion: J. Lau, O. Simonsen and J. Becher, Synthesis, 1995, 521; (c) m/z: 507, daughter ions: m/z: 104, 130, 208, 260, 754, 1508; K. Takimiya, Y. Shibata, K. Imamura, A. Kashihara, Y. Aso, Found: C, 37.78; H, 3.55; N, 2.25; C82H92F24N4O8P4S24 requires T.Otsubo and F. Ogura, T etrahedron L ett., 1995, 36, 5045; (d) P. Hascoat, D. Lorcy, A. Robert, K. Boubekeur, P. Batail, R. C, 37.72; H, 3.55; N, 2.15%. Carlier and A.Tallec, J. Chem. Soc., Chem. Commun., 1995, 1229; (e) Second fraction: The solid was partially dissolved in meth- K. Matsuo, K. Takimiya, Y. Aso, T. Otsubo and F. Ogura, Chem. anol and filtered.The filtrate was concentrated in vacuo. This L ett., 1995, 523; ( f ) M. R. Bryce, W. Devonport and A. J. Moore, was then dissolved in a minimum amount water, and saturated Angew. Chem., Int. Ed. Engl., 1994, 33, 1761; (g) F. Bertho- aqueous NH4PF6 was added until precipitation was complete. Thoroval, A. Talle, A. Souizi, K. Boubekeur and P. Batail, J. Chem. The solid product was removed by filtration (Celite), washed Soc., Chem. Commun., 1991, 843; (h) K.Boubekeur, C. Lenoir, P. Batail, R. Carlier, A. Robert, M. P. Le Paillard and D. Lorcy, with water, pumped dry, and then extracted with acetonitrile. Angew. Chem., Int. Ed. Engl., 1994, 33, 1379. After the solvent was removed in vacuo, 36–8PF6 (0.010 g, 3%) 3 (a) D. Philp and J. F. Stoddart, Angew. Chem., Int.Ed. Engl., 1996, was obtained as an impure green solid. Mp>250 °C; MS 35, 1154; (b) D. B. Amabilino and J. F. Stoddart, Chem. Rev., 1995, (ES): m/z: 319 [M-8PF6]8+, 473 [M-6PF6]6+, 597 95, 2725. [M-5PF6]5+, 782 [M-4PF6]4+, 1091 [M-3PF6]3+. 4 (a) P. R. Ashton, R. A. Bissell, N. S. Spencer, J. F. Stoddart and M. S. Tolley, Synlett, 1992, 915; (b) D. Philp, A. M. Z. Slawin, N.Spencer, J. F. Stoddart and D. J. Williams, J. Chem. Soc., Chem. {2,356,7-Bis[2,7(6)-bis(methylthio)tetrathiafulvalene-3,6 (7)- Commun., 1991, 1584; (c) Z.-T. Li and J. Becher, Chem. Commun., diylbisthiobis(ethane-1,2-diyl )dioxybis(ethane-1,2- 1996, 639; (d) Z.-T. Li, PC. Stein, J. Becher, D. Jensen, P. Mørk diyl ) dioxybis(ethane-1,2-diyl )bisthio]tetrathiafulvalene and N.Svenstrup, Chem. Eur. J., 1996, 2, 624. (cis/trans)}-{5,12,19,26-tetraazoniaheptacyclo- 5 (a) G. Schukat, A. M. Richter and E. Fangha�nel, Sulfur Rep., 1987, [24.2.2.22,5.27,10.212,15.216,19.221,24] tetraconta- 7, 155; (b) G. Schukat and E. Fangha�nel, Sulfur Rep., 1993, 14, 155. 2,4,7,9,12,14,16,18,21,23,26,28,29,31,33,35,37,39-octadecaene 6 Z.-T. Li, P. C. Stein, N. Svenstrup, K.H. Lund and J. Becher, Angew. Chem., Int. Ed. Engl., 1995, 34, 2524. (circum peripheral TTF) tetrakis(hexafluorophosphate)} 7 For recent examples of ribbons, see (a) S. Breidenbach, S. Ohren, (37-4PF6) M. Nieger and F. Vo� gtle, J. Chem. Soc., Chem. Commun., 1995, 1237; (b) W. Josten, D. Karbach, M. Nieger, F. Vo� gtle, K. Ha�gele, A solution of 22 (0.168 g, 0.11 mmol), 29–2PF6 (0.393 g, M. Svobofa and M. Przybylski, Chem. Ber., 1994, 127, 767; (c) 0.56 mmol), and 30 (0.161 g, 0.61 mmol) in DMF (12 ml) was A. Schro�der, H.-B. Mekelburger and F. Vo� gtle, T op. Curr. Chem., subjected to 10 kbar at room temp. for 4 d. The solvent was 1994, 172, 179; (d) T. Freund, U. Scherf and K. Mu�llen, Angew. then removed in vacuo to give a green residue. Column Chem., Int. Ed. Engl., 1994, 33, 2424; (e)M. Pollman and K. Mu�llen, chromatography on silica gel followed by preparative chroma- J. Am. Chem. Soc., 1994, 116, 2318; (f ) J. Benkho, R. Boese, F.- tography with MeOH–aqueous NH4Cl (2 M)–DMF (45552) G. Kla�rner and A. E. Wigger, T etrahedron L ett., 1994, 35, 73; (g) P. R. Ashton, U. Girreser, D. Giura, F. H. Kohnke, J. P. Mathias, as the eluent aorded a green solid after evaporation of the F. M. Raymo, A. M. Z. Slawin, J. F. Stoddart and D. J. Williams, solvent in vacuo. The compound was worked up as described J. Am. Chem. Soc., 1993, 115, 5422 and references therein. for 36–8PF6, aording 37-4PF6 (0.025 g, 9%) as a green solid. 8 (a) N. Svenstrup and J. Becher, Synthesis, 1995, 215; (b) Mp>250 °C; dH (CD3CN) 2.58 (m, 6 H; SCH3), 2.76–3.08 (m, N. Svenstrup, K. M. Rasmussen, T. K. Hansen and J. Becher, 16 H; SCH2), 3.52–3.85 (m, 32 H; OCH2), 5.72–5.77 (m, 8 H; Synthesis, 1995, 215. NCH2), 7.71–7.78 (m, 8 H; C6H4 ), 7.96 (m; b-H), 8.07 (m; b- 9 Ultra-high pressure has been used to promote the formation of catenanes; see D. B. Amabilino, P. R. Ashton, M. S. Tolley, J. F. H), 8.17 (m; b-H), 8.28 (m; b-H), 7.96–8.28 (8 H), 9.07 [d, 4 Stoddart and D. J. Williams, Angew. Chem., Int. Ed. Engl., 1993, H, J 6.8; a-H), 9.17 [d, 4 H, J 6.7; a-H); dH [(CD3 )2SO] 2.44 32, 1297. (m, 6 H; SCH3 ), 2.61 (m, 6 H; SCH3), 2.69–3.23 (m, 16 H; 10 P. R. Ashton, D. Philp, N. Spencer, J. F. Stoddart and D. SCH2), 3.38–3.83 (m, 32 H; OCH2), 5.82 (m, 8 H; NCH2), J. Williams, J. Chem. Soc., Chem. Commun., 1994, 181. 7.74–7.85 (m, 8 H; C6H4), 8.26 (m; b-H), 8.47 (m; b-H), 8.66 11 The mixture of cis/trans isomers makes it almost impossible to (m; b-H), 8.26–8.66 (8 H), 9.48 (m, 4 H; a-H), 9.62 (m, 4 H; a- produce single crystals for X-ray diraction. H);MS (ES): m/z: 130, 507 [M-4PF6]4+, 724 [M-3PF6]3+, 754 [macrocycle]2+, 1159 [M-2PF6]2+, 1508 [macro- Paper 7/00129K; Received 6th January, 1997 J. Mater. Chem., 1997, 7(7),

ISSN:0959-9428    

DOI:10.1039/a700129k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Synthesis and electrochemistry of new tetrathiafulvalene (TTF) dendrimers: X-ray crystal structure of a tetrafunctionalised TTF core unit ChangshengWang, Martin R. Bryce,* Andrei S. Batsanov, Leonid M. Goldenberg and Judith A. K. Howard Department of Chemistry, University of Durham, Durham DH1 3L E, UK A new synthetic approach to tetrathiafulvalene (TTF) dendrimers is reported. Tetrakis(4-chloromethylbenzylthio)tetrathiafulvalene 7 is a functionalised core unit which reacts with four equivalents of the thiolate ion generated from compound 16 to aord the trisdeca-TTF derivative 3.Compound 3 is a shelf-stable solid which has been characterised by elemental analysis, MALDI-TOF mass spectrometry, 1HNMR spectroscopy and solution electrochemistry. Thin layer cyclic voltammetry studies on pentakis-TTF and trisdeca-TTF derivatives 11 and 3 in dichloromethane solution in the presence of 2,3-dichloronaphthoquinone as an internal reference, show that all the TTF units undergo two single-electron oxidations. The single crystal X-ray structure of compound 7 is reported: the molecules have crystallographic Ci symmetry and form chair-like stacks parallel to the crystallographic y axis.A bourgeoning topic within the arena of nanochemistry1 is the tors,13 because of their propensity to form highly-ordered stacks along which there is high electron mobility. The stacks study of dendritic and hyperbranched macromolecules.2 Of are stabilised by intermolecular p–p interactions and non- particular interest is the fact that these materials possess a bonded sulfur,sulfur interactions.Most multi-TTF deriva- high degree of structural order, and their size and architecture tives reported to date14 are dimers,15 although some trimers,16 can be precisely controlled in their synthesis, providing unique pentamers,17 higher oligomers18 and main-chain and side-chain molecular scaolds for the emplacement of functional groups polymeric TTFs19 are now known.A key feature of these in predetermined spatial arrangements.2d,3 A range of substitu- multi-TTFsystems is that they generally yield multiply-charged ents (e.g. crown ethers,4 chiral units,5 polynuclear metal com- species upon electrochemical oxidation in solution. plexes6 and liquid crystal groups7) have recently been appended In our initial work on TTF dendrimers, a convergent strategy to, or embedded within, dendrimer frameworks to impart based on a repetitive coupling/deprotection sequence, using 4- special properties to these macromolecules.8,9 A variety of (hydroxymethyl)-TTF as the starting monomer, furnished den- redox-active organic and organometallic groups have been drimer 1 comprising a benzene-1,3,5-triester core, and surface- incorporated into dendritic and hyperbranched systems10 with functionalised with twelve TTF units.12 A conceptually similar several long-term aims in mind.These include: (i) new electron- synthesis using a 4,4¾-biphenyl ether diester core gave the transfer catalysts; (ii) studies on the dynamics of electron octakis-TTF system 2 possessing a more open structure than transport at surfaces and within restricted reaction spaces; analogue 1.20 The solution electrochemical redox behaviour of (iii) new materials for energy conversion; (iii) organic semi- systems 1 and 2 was studied by classical cyclic voltammetry conductors; (iv) organic magnets; and (v) mimics of biological (CV), cyclic voltammetry with ultramicroelectrodes (UME redox processes.CV) and chronoamperometry.12,20,21 For compound 1, the CV Some dendrimer systems contain a single redox-active unit waves were quasi-reversible, with slight broadening, which (e.g. a metalloporphyrin)11 at the core, for which the key issue became more noticable with repeated scans, when the second is generally to observe how the redox behaviour of this central TTF oxidation peak became irreversible and deposition of ‘encapsulated’ group is modulated by the shielding eect of material on the electrode surface was observed: each wave the rest of the dendrimer structure, which should provide a represented a multi-electron transfer with essentially no inter- more compact insulating layer than would an analogous linear action between the charged TTF units.We were unable to polymer.The majority of studies, however, concern multiple establish unambiguously the number of electrons involved in redox units (e.g. polynuclear metal complexes)6 emplaced each redox wave for compounds 1 and 2: the dierent diusion within the branches and/or at peripheral sites, where the redox rates of the internal standard (2,3-dichloronaphthoquinone) groups may act independently in multi-electron processes (n and the dendrimer could readily account for the apparent identical electroactive centres which undergo electron transfer incomplete oxidation of all the TTF units.(Scanning to higher in a single n-electron wave) or they may interact intra- or potentials showed no further oxidation waves, precluding the inter-molecularly (overlapping or closely-spaced redox waves presence of any TTF groups buried within the dendrimer at dierent potentials).structure.) We first recognised12 that tetrathiafulvalene (TTF) units Herein we report an entirely dierent approach to TTF oered considerable potential as components of novel redox- dendrimers which has culminated in the synthesis of macro- active dendrimers.The incorporation of TTF into dendrimers molecule 3 comprising thirteen TTF units. There are several presents a fascinating prospect for the following reasons: novel features of this work: (i) TTF units are emplaced at all (i) oxidation of the TTF ring system to the cation radical and layers of the structural hierarchy (unlike compounds 1 and 2); dication species occurs sequentially and reversibly at very (ii) compound 7 is presented as a new, versatile building accessible potentials in a range of organic solvents (for unsub- block for macromolecular TTF assemblies, and its single stituted TTF, E11/2=+0.34 and E21/2=+0.78 V, vs.Ag/AgCl crystal structure is described; (iii) thin layer cyclic in acetonitrile); (ii) the oxidation potentials can be finely tuned voltammetry (TLCV) has been applied to redox-active denby the attachment of appropriate substituents; (iii) the TTF drimer systems for the first time, and it is clear that all the cation radical is thermodynamically very stable; and (iv) oxi- TTF groups of 3 are involved in the solution electrochemical redox processes.dised TTF units are key components of molecular conduc- J.Mater. Chem., 1997, 7(7), 1189–1197 1189S S S MeS S S S S S S S S Me Me S S MeS S S S S Me Me S S MeS S S S S S S S MeS S S S S S S S S Me Me S S MeS S S S S Me Me S S MeS S S S S S S S SMe S S S S S S S S Me Me S S SMe S S S S Me Me S S SMe S S S S S S S SMe S S S S S S S S Me Me S S SMe S S S S Me Me S S SMe S S S S 3 1190 J. Mater. Chem., 1997, 7(7), 1189–1197by a combination of elemental analysis, MALDI TOF mass Results and Discussion spectrometry and 1H NMR spectroscopy.In particular, the Synthesis MALDI TOF spectrum of 3, showed a parent ion peak at m/z 7377 (M+, calc. for C314H276S104, 7372) with several other Zincate salt 422 reacted with a-chloro-p-xylene 5a or with peaks observed in the spectrum due to fragmentation of the a,a¾-dichloro-p-xylene 5b to yield 4,5-disubstituted 1,3-dithi- parent molecule.ole-2-thione derivatives 6a (90% yield) and 6b (60% yield), respectively. The latter was converted to the ketone 6c (84% yield) using the standard mercuric acetate procedure Solution electrochemistry (Scheme 1). Compound 7 was synthesised in 78% yield by The solution redox properties of compounds 3,7,9–11,15 and self-coupling of 6c in the presence of triethyl phosphite under 16 in benzonitrile are collated in Table 1, together with data standard conditions,23 and isolated as orange crystals suitable for TTF for comparison. All these new compounds exhibited for X-ray analysis (see below).Compound 7 is our key core two redox couples typical of the TTF system25 and for the unit and displacement of the benzylic chlorines by thiolate multi-TTF derivatives there was no apparent interaction anions proved to be a facile process. We identified 10 as a between the dierent TTF units.The redox waves were revers- promising building block from which a reactive thiolate anion ible, at least up to scan rates of 500 mV s-1: the criterion could be generated, following the protocol developed by applied for reversibility was a ratio of 1.0±0.5 for the intensities Becher and coworkers for related cyanoethyl-protected TTFof the cathodic and anodic currents Ic/Ia, and no shift of the thiolate systems.24 Accordingly, compound 6a was crosshalf wave potentials with varying scan rates.The attachment coupled with ketone 8 to furnish TTF derivative 9 in 67% of thioalkyl substituents to the TTF ring is known to raise the yield (Scheme 2).Sequential deprotection of 9 allowed unsymoxidation potential25,26 (an additive eect has been noted for metrical substitution reactions. Initial treatment of 9 with one, two and four thioalkyl substituents)26 and the new com- caesium hydroxide (1.05 equiv.), followed by methylation of pounds in Table 1 follow this trend.It is notable that the the resulting monothiolate anion, aorded 10 (96% yield) values of both the first and second redox potentials appear to which was deprotected using a second equivalent of caesium be further raised slightly by the presence of the cyanoethyl hydroxide to yield the caesium salt of the thiolate anion of groups (viz. compounds 9, 10 and 15), although for compound 10, four equivalents of which reacted with 7 to yield the 16 inequivalence of the TTF groups (only one of which carries pentakis-TTF derivative 11 in almost quantitative yield.a cyanoethyl group) was not observed. Compound 11 was purified by column chromatography and More significant are the results of thin layer cyclic voltam- isolated as a yellow–brown solid.The parent molecular ion metric (TLCV) studies on compounds 11 and 3, which contain of 11 was observed in the matrix-assisted laser desorption five and thirteen TTF units, respectively. In contrast to conven- time-of-flight (MALDI TOF) mass spectrum at m/z 2964 tional cyclic voltammetry, in TLCV27 the current is not limited (M+, calc. for C130H116S40; 2956). by the kinetics of mass transfer to the electrode. TLCV has An analogous synthetic protocol enabled assembly of the been applied recently to the detection of mixed valence states trisdeca-TTF derivative 3, which can be viewed as a second in TTF and its derivatives.28 However, we are not aware of generation dendrimer.For this synthesis we needed the monoany reports of this technique being applied to multi-TTF thiolate derivative of 16 as the reactive ‘wedge’ to undergo systems or to redox-active dendrimers. As mentioned above, four-fold reaction with core reagent 7.The synthesis of 3 is classical CV, UME CV and chronoamperometry had pre- shown in Scheme 3. Compound 13 was prepared in high yield viously given inconclusive results concerning the number of by the literature route from 12,24b and converted into ketone electrons involved in the redox waves of compounds 112,21 and 14 (98% yield) using mercuric acetate.Cross-coupling of 2.20,21 For other multi-TTF systems (e.g. pentamers) oxidation equimolar amounts of thione 6b and ketone 14, in the presence of all the TTF units had been assumed, based on the shapes of triethyl phosphite, gave compound 15 in an optimised yield of the CV waves, but not rigorously established.17 For other of 45%.By direct analogy with the preparation of 11, comdendrimers and branched systems containing multiples of pound 15 was converted into 16 in 74% yield. The caesium structurally very similar (or identical) redox groups (e.g. ferro- thiolate salt of 16 (4 equiv.) reacted cleanly with compound 7 cene29 and related iron sandwiches30) the extent of oxidation to furnish compound 3 in 66% yield as an air-stable yellow– brown solid.Compound 3 was characterised unambiguously of the system can be calculated using formulae which take into S S S S S S S S S S Cl Y S S X S S S S S S S S S S Cl Cl Cl Cl Y Y i iii Zn 4 (NEt4 +)2 a X = S Y = H b X = S Y = Cl c X = O Y = Cl 5a Y = H b Y = Cl 7 6 + 2- ii Scheme 1 Reagents and conditions: i, acetone, reflux; ii, Hg(OAc)2 , CHCl3–MeCO2H, 20 °C; iii, P(OEt)3, 120°C J.Mater. Chem., 1997, 7(7), 1189–1197 1191S S O S S CN CN S S S S Me Me S S S S CN CN S S S S Me Me S S S SMe CN S S S MeS S S S S S S Me S S S MeS S S S S Me Me S S S S S SMe S S S S Me S S S S S SMe S S S S Me S S Me Me Me 11 6a + 9 8 10 i ii iii Scheme 2 Reagents and conditions: i, P(OEt)3 , 120 °C; ii, CsOH.H2O (1.05 equiv.) DMF–MeOH, 20 °C, followed by MeI; iii, CsOH·H2O, DMF–MeOH, then compound 7, 20–50°C account the dierent diusion coecients of a model com- the voltammetric waves, the number of electrons exchanged per oxidation wave was calculated to be five for compound 11 pound and the dendrimer.31 A very elegant alternative method is provided by certain macromolecules which contain within (which contains five TTF units) and 12–14 (E1) and 11–12 (E2) for compound 3 (which contains 13 TTF units).These their structure two (or more) dierent redox units in a known ratio, which are oxidised or reduced at dierent potentials, data clearly suggest that complete oxidation occurs for all the TTF units in compounds 11 and 3.For compound 3, the small thereby providing a covalently-bound internal reference.6,32 However, this is not the case with the compounds herein where variation in the number of electrons calculated for dierent experiments is within reasonable experimental limits, given the all the TTF units are tetrathio-substituted. TLCV studies were conducted on known concentrations of very small quantities of the compound used and the large number of TTF groups present.We note that for both com- compounds 11, 3 and 2,3-dichloronaphthoquinone (DCNQ) in dichloromethane solution. The one-electron reduction peak pounds 11 and 3 the second TTF oxidation wave was slightly narrower than the first wave, which was probably due to of DCNQ provided the internal reference, and by integrating 1192 J.Mater. Chem., 1997, 7(7), 1189–1197S S S SMe S S S S S S S S Me Me S S SMe S S S S S Me Me S S SMe S S S S S S CN CN CN S S X S SMe CN S S S SMe S S S S CN Cl Cl 16 15 12 13 X = S 14 X = O i ii iii iv v 3 Scheme 3 Reagents and conditions: i, CsOH.H2O (1 equiv.), DMF–MeOH, 20°C, followed by MeI; ii, Hg(OAc)2, CHCl3–MeCO2H, 20 °C; iii, compound 6b, P(OEt)3, 125 °C; iv, compound 10, CsOH H2O (1 equiv.), DMF–MeOH, then compound 15, 20°C; v, CsOH.H2O, DMF–MeOH, then compound 7, 20–80°C Table 1 Solution redox properties of compounds 3,7,9–11,15 and 16a compound E11/2/V E21/2/V TTF 0.34 0.78 3 0.57 0.90 7 0.58 0.92 9 0.67 1.01 10 0.63 0.97 11 0.56 0.89 15 0.64 0.98 16 0.57 0.90 aPlatinum electrodes, supporting electrolyte Bu4NPF6 (0.1 M) in Fig. 1 TLCV of dendrimer 3 (0.5×10-4 M) and 2,3-dichloronaphtho- benzonitrile, scan rate 100 mV s-1 versus Ag/AgCl. quinone (6.4×10-4 M) as internal reference, in Bu4NClO4 (1 M)–CH2Cl2 solution, reference vs. Ag/Ag+, scan rate 5 mV s-1 adsorption phenomena. Fig. 1 shows the TLCV of compound 3 in the presence of DCNQ. mation of all the substituents in 7 is profoundly out-of-(the TTF)plane.Thus the overall molecular conformation is similar X-Ray crystal structure of compound 7 to those in other TTF derivatives with long linear-chain substituents,33 and so is the crystal packing. The molecules Compound 7 is a functionalised, four-directional core unit which oers considerable potential for future studies. It was of form a stair-like stack in the direction parallel to the crystallographic y axis, in which the TTF planes are parallel with interest, therefore, to establish the structure of 7 in the solid state.The single crystal X-ray structure reveals that the mol- interplanar separations of ca. 3.6 A° . The adjacent TTF moieties in the stack overlap through only one dithiole ring each. ecule has a crystallographic Ci symmetry (Fig. 2). The TTF moiety displays a chair-like distortion, the dithiole rings folding Apparently, the more eective (and more common) ring-overbond (i.e. the central CNC bond) overlap is prevented by the by 6.4° along the S,S vectors. One of the two independent 4- (chloromethyl)benzyl substituents is ordered, while the other steric bulk of the substituents. It is noteworthy that in the crystal the disordered side-chain one is disordered over two positions (A and B) with approximately equal occupancies, diering in the torsion angles around of 7 is surrounded by such chains of other molecules on three sides (the ordered chain of the same molecule being on the the S(3)–C(2), S(3)–C(4), C(4)–C(5) and C(8)–C(11) bonds (by 30, 27, 81 and 27°, respectively) and consequently in the fourth side) viz.two parallel chains of the neighbours within the stack and one antiparallel chain of the inversion-equivalent orientation of the benzene ring plane (by 44°), but basically occupying the same area of space (the positions of the terminal molecule of another stack. Thus the structure contains a vast area of disorder, in the form of a wide (ca. 10×10 A° ) infinite chlorine atom dier by only 0.67 A° ). In any case, the confor- J. Mater. Chem., 1997, 7(7), 1189–1197 1193Fig. 2 Molecular structure of 7. Position A of the disordered chain is shown solid, position B dashed. Primed atoms are symmetry-related via the inversion centre. Selected bond distances (A° ): C(1)–S(1) 1.752(7), C(1)–S(2) 1.754(8), S(1)–C(2) 1.759(7), S(2)–C(3) 1.761(7), C(1)–C(1¾) 1.345(13), C(2)–C(3) 1.342(9), C(2)–S(3) 1.755(7), C(3)–S(4) 1.738(7).channel parallel to the y axis. It is not clear whether the choice irradiation from a nitrogen laser at 337 nm. The matrix was 2,5-dihydroxybenzoic acid and spectra were averaged over 100 between the A and B positions of a chain is aected by that of the adjacent chains or can be independent from them.The pulses whilst scanning across the sample: peak half-widths were between 6–10 amus. Melting points were obtained on a shortest intermolecular contacts between these positions, interstack C(4A),C(6A) 3.43 and C(6A),C(6A) 3.36 A° and Reichert hot-stage microscope apparatus and are uncorrected. Electrochemical data were obtained on a BAS CV-50W intrastack C(7B),C(10B) 3.36 A° , are not prohibitively short.Voltammetric Analyser. The counter, working and reference electrodes were Pt wire, Pt disc (1.6 mm diameter from BAS) Conclusions and Ag/AgCl, respectively. Cyclic voltammetry was performed under argon using IR compensation. The thin layer cyclic We have developed new expedient methodology for the synthesis of TTF-based dendrimers which possess well-defined voltammetry cell used in this work was constructed as described previously.27b redox activity, notably the trisdeca-TTF derivative 3.The methodology should be applicable to higher generation TTF systems. Thin layer cyclic voltammetry has demonstrated that 4,5-Bis( 4-methylbenzylthio)-1,3-dithiole-2-thione 6a† the electrochemical oxidation of these macromolecules involves A mixture of zincate salt 422 (7.2 g, 10 mmol) and a-chloro-p- all of the TTF units, and in these experiments there was no xylene 5a (11.25 g, 80 mmol) in acetone (60 ml) was refluxed observable interaction between the redox sites.These data for 1 h. The red solid which precipitated during the reaction support our earlier suggestion10 that the TLCV technique was removed by filtration, then the filtrate was concentrated should be well-suited to electrochemical studies on dendritic in vacuo aording a bright yellow solid, recrystallisation of macromolecules containing multiple redox centres.Several new which from ethanol yielded yellow needles of 6a (7.50 g, 90%), functionalised TTF and multi-TTF reagents, e.g. compounds mp 85–86°C (Found: C, 55.85; H, 4.42.C19H18S5 requires C, 7 and 16, synthesised during the course of this work are now 56.11; H, 4.46%); dH(CDCl3) 2.33(s, 6H), 3.89 (s, 4H), 7.12 readily-available in synthetically useful quantities, and they (s, 8H). oer great potential as reactive building blocks in the assembly of supramolecular34 and polymeric TTF systems. In particular, 4,5-Bis( 4-chloromethylbenzylthio)-1,3-dithiole-2-thione 6b by virtue of the four reactive benzylic halide groups at the periphery of 7 this molecule is a very attractive core unit for By analogy with 6a, compound 4 (3.6 g, 5 mmol) and a,a¾- future studies, and the facile deprotection of 16, to generate a dichloro-p-xylene 5b (10.5 g, 60 mmol) in acetone (150 ml) reactive thiolate anion, makes this system eminently suited to gave yellow needles of 6b (2.86 g, 60%) after purification by a range of further synthetic transformations.column chromatography [silica, eluent: dichloromethane–light petroleum (bp 40–60°C), 151 (v/v)], mp 123.5–124.5°C (Found: C, 48.03; H, 3.39; C19H16Cl2S5 requires C, 48.00; H, Experimental 3.39 dH(CDCl3 ) 3.91 (s, 4H), 4.57 (s, 4H), 7.23 (d, 4H, J 8.2), General 7.35 (d, 4H, J 8.2). All reagents and solvents were of commercial quality and were dried where necessary using standard procedures. 1H NMR † Compound 6a has recently been prepared independently in 75% Spectra were obtained on a VXR 200 spectrometer operating yield by a similar route in Professor Becher’s laboratory (R. P. at 200.14 MHz. MALDI TOF Mass spectra were obtained on Clausen and J.Becher, T etrahedron, 1996, 52, 3171). We thank Professor Becher for bringing this reference to our attention. a Kratos IV instrument in the reflection mode, operating with 1194 J. Mater. Chem., 1997, 7(7), 1189–11974,5-Bis(4-chloromethylbenzylthio)-1,3-dithiol-2-one 6c was stirred at 20°C overnight to obtain a brown–red solution. Compound 7 (130 mg, 0.146 mol) was then added in one To a solution of compound 6b (3.5 g, 7.36 mmol) in a mix- portion and the mixture was aggitated with ultrasound for ture of chloroform and acetic acid (80 ml; 351, v/v), mercuric 10 min, followed by stirring at 20°C for 1 h and then at 50°C acetate (7.0 g, 22 mmol) was added and the mixture was stirred for 4 h, to aord a precipitate.The reaction mixture was at 20°C overnight.Filtration of the product through Celite evaporated in vacuo and water (20 ml) was added to the and evaporation of the filtrate yielded a yellow oil, which was residue. A brown–yellow solid was collected by filtration and washed with 5% aqueous NaHCO3 (100 ml) and filtered to washed with a large amount of methanol. Column chromatog- give a pale yellow solid, which was chromatographed on a raphy of the solid [silica, eluent: dichloromethane–light pet- silica column [eluent: light petroleum (bp 40–60°C)–di- roleum (bp 40–60°C), 251 (v/v)] gave compound 11 (430 mg, chloromethane, 151 (v/v)] aording 6c as o-white crystals 99.5%) as an amorphous yellow–brown solid, mp ca. 150 °C (2.85 g, 84%), mp 67–68.5 °C (Found: C, 49.59; H, 3.46; (Found: C, 52.45; H, 3.93.C130H116S40 requires C, 52.73; H, C19H16Cl2OS4 requires C, 49.66; H, 3.51%); dH(CDCl3) 3.87 3.95%); m/z (MALDI-TOF) 2964 (M+ calc. 2956); dH(CDCl3) (s, 4H), 4.56 (s, 4H), 7.22 (d, 4H, J 8.2), 7.34 (d, 4H, J 8.2). 2.22 (s, 12H), 2.31 (s, 24H), 3.81 (s, 8H), 3.83 (s, 8H), 3.85 (s, 8H), 3.97 (s, 8H), 7.1–7.3 (m, 48H). Tetrakis(4-chloromethylbenzylthio)tetrathiafulvalene 7 Compound 6c (2.8 g, 6.09 mmol) in triethyl phosphite (25 ml) 4-(2-Cyanoethylthio)-5-methylthio-1,3-dithiole-2-thione 13 was stirred under argon and heated at 120 °C for 1 h.The Following the reported method,24b reaction of compound 1222b mixture was cooled to 20°C and methanol (70 ml) was added. (1.5 g, 4.93 mmol) in DMF (30 ml) with CsOH·H2O (0.83 g, The precipitate was collected by filtration and washed with a 4.94 mmol) in methanol (30 ml) at 20°C followed by addition large volume of methanol, followed by purification by column of methyl iodide (1.5 ml) gave a product which was purified chromatography (silica, eluent: dichloromethane), aording by column chromatography (silica, eluent: dichloromethane) compound 7 as orange crystals (2.1 g, 78%), mp 181–183 °C, to yield 13 as yellow crystals (1.2 g, 92%), mp 88–89°C (Found: which after recrystallisation from carbon disulfide gave red C, 31.56; H, 2.62; N, 4.91.C7H7NS5 requires C, 31.67; H, 2.66; needles which were suitable for X-ray analysis (Found: C, N, 5.28%); dH(CDCl3) 2.56 (s, 3H), 2.76 (t, 2H, J 7.0), 3.09 (t, 51.40; H, 3.63. C38H32Cl4S8 requires C, 51.46; H, 3.64%); 2H, J 7.0).dH(CDCl3 ) 3.84 (s, 8H), 4.56 (s, 8H), 7.24 (d, 8H, J 8.2), 7.34 (d, 8H, J 8.2). 4-(2-Cyanoethylthio)-5-methylthio-1,3-dithiol-2-one 14 4,5-Bis(2-cyanoethylthio)-4¾,5¾-bis (4-methylbenzylthio)tetrathia- To the solution of 13 (1.2 g, 4.52 mmol) in a mixture of fulvalene 9 chloroform and acetic acid [351 (v/v), 40 ml], mercuric acetate (4.0 g, 12.6 mmol) was added and the mixture was stirred at A mixture of compound 822b (2.88 g, 10 mmol), compound 6a 20°C overnight.Filtration of the product mixture through (6.10 g, 15 mmol) and triethyl phosphite (50 ml) was heated Celite and evaporation of the filtrate yielded a yellow residue, with stirring at 120 °C for 75 min under argon. Ethanol (50 ml) which was dissolved in dichloromethane and washed with was added to the reaction mixture which was then cooled to saturated NaHCO3 solution.The organic phase was separated, 20°C. The orange solid which precipitated was collected by dried over MgSO4, concentrated and chromatographed (silica filtration, washed with a large volume of ethanol and then column, eluent: dichloromethane), aording white needles of chromatographed (silica column, eluent: dichloromethane) to 14 (1.1 g, 98%), mp 57.5–58.5°C (Found: C, 33.42; H, 2.78; N, aord compound 9 (4.36 g, 67%) as orange needles, mp 5.24.C7H7NOS4 requires C, 33.71; H, 2.83; N, 5.62%); dH 142–143.5 °C (from ethanol–dichloromethane) (Found: C, (CDCl3 ) 2.52 (s, 3H), 2.75 (t, 2H, J 7.0), 3.08 (t, 2H, J 7.0). 52.05; H, 3.99; N, 4.37. C28H26N2S8 requires C, 51.98; H, 4.05; N, 4.33%); dH(CDCl3 ) 2.32 (s, 6H), 2.75 (t, 4H, J 7.0), 3.09 (t, 4-(2-Cyanoethylthio)-5-methylthio-4¾,5¾-bis( 4-chloromethyl- 4H, J 7.0), 3.85 (s, 4H), 7.13 (s, 8H).benzylthio)tetrathiafulvalene 15 4-(2-Cyanoethylthio)-5-methylthio-4¾,5¾-bis (4-methylbenzyl- A mixture of 14 (125 mg, 0.5 mmol) and 6b (238 mg, 0.5 mmol) thio)tetrathiafulvalene 10 in triethyl phosphite (5 ml) was heated to 125 °C and stirred under argon for 1.5 h.The mixture was evaporated in vacuo To a stirred solution of compound 9 (3.0 g, 4.64 mmol) in and the orange oily residue was chromatographed on a silica dimethylformamide (30 ml) under argon at 20°C, a solution column (eluent: dichloromethane), aording 15 as an orange of CsOH·H2O (0.82 g, 4.88 mmol) in methanol (25 ml) was solid (153 mg, 45%), mp 146.5–148.5 °C (Found: C, 46.15; H, added dropwise over 2 h.Stirring was continued for 1 h at 3.38; N, 1.64. C26H23Cl2NS8 requires C, 46.13; H, 3.42; N, 20°C, then methyl iodide (4.5 ml) was added and the mixture 2.07%); dH(CDCl3) 2.48 (s, 3H), 2.72 (t, 2H, J 7.0), 3.04 (t, 2H, was stirred for a further 1 h. Evaporation of the reaction J 7.0 ), 3.85 (s, 4H), 4.57 (s, 4H), 7.25 (d, 4H, J 8.2), 7.34 (d, mixture in vacuo gave an orange residue, which was dissolved 4H, J 8.2).in dichloromethane (50 ml) and washed with water, then the organic layer was separated and dried over MgSO4. Column chromatography of the concentrated solution (silica, eluent: 4,5-Bis( 4-{[4¾,5¾-bis (4-methylbenzylthio)-5-methylthiotetrathia- dichloromethane) yielded an orange solid which crystallised fulvalen-4-yl]thiomethyl}benzylthio)-4¾-( 2-cyanoethylthio)-5’- from ethanol–chloroform as orange needles (2.24 g, 92%) mp methylthiotetrathiafulvalene 16 135–136.5 °C (Found: C, 51.15; H, 4.07; N, 2.08.C26H25NS8 By analogy with the preparation of compound 11, compound requires C, 51.36; H, 4.14; N, 2.03%); dH(CDCl3) 2.32 (s, 6H), 16 was synthesized from 10 (277 mg, 0.456 mmol) in DMF 2.48 (s, 3H), 2.71 (t, 2H, J 7.2), 3.03 (t, 2H, J 7.2), 3.84 (s, 4H), (20 ml), CsOH H2O (76.5 mg, 0.456 mmol) in methanol (4 ml) 7.13 (s, 8H).and compound 15 (154 mg, 0.227 mmol) at 20°C with stirring for 6 h. Purification was achieved by vacuum evaporation, 4,4¾,5,5¾-Tetrakis(4-{[4¾,5¾-bis(4-methylbenzylthio)-5-methylthio- washing with water and chromatography on a silica column tetrathiafulvalen-4-yl]thiomethyl}benzylthio)tetrathiafulvalene 11 (eluent: chloroform) to yield 16 (298 mg, 74%) as an orange solid, mp 55°C (Found: C, 49.77; H, 3.77; N, 0.72.C72H65NS24 To the stirred solution of 10 (358 mg, 0.589 mmol) in degassed DMF (20 ml) under argon, CsOH H2O (99.4 mg, 0.59 mmol) requires C, 50.46; H, 3.83; N, 0.82%); m/z 1710.84200 (M+ calc. 1710.84142); dH(CDCl3) 2.22 (s, 6H), 2.30 (s, 12H), 2.44 in methanol (2 ml) was added in one portion. The mixture J. Mater. Chem., 1997, 7(7), 1189–1197 11953 P. Hodge, Nature, 1993, 362, 18. (s, 3H), 2.56 (t, 2H, J 6.7), 2.97 (t, 2H, J 6.7), 3.81 (s, 4H), 3.83 4 T. Nagasaki, O. Kimura, M. Ukon, S. Arimori, I. Hamachi and (s, 4H), 3.85 (s, 4H), 3.96 (s, 4H), 7.1–7.3 (m, 24H).S. Shinkai, J. Chem. Soc., Perkin T rans 1, 1994, 75. 5 (a) G. R. Newkome, X. Liu and C. D. Weis, T etrahedron: 4,4¾,5,5¾-Tetrakis(4-{[4¾,5¾-bis(4-{[4¾,5¾-bis(4-methylbenzylthio)- Asymmetry, 1991, 2, 957; (b) J. F. G. A. Jansen, H. W. I. Peerlings, 5-methylthiotetrathiafulvalen-4-yl]thiomethyl}benzylthio)-5- E. M. M. de Brabander-Van den Berg and E. W.Meijer, Angew. methylthiotetrathiafulvalen-4-yl]thiomethyl}benzylthio)tetra- Chem., Int. Ed. Engl., 1995, 34, 1206. 6 S. Campagne, G. Denti, S. Serroni, A. Juris, M. Venturi, thiafulvalene 3 V. Ricevuto and V. Balzani, Chem. Eur. J., 1995, 1, 211. By analogy with the synthesis of compound 11, compound 3 7 (a) V. Percec, P. Chu and M. Kawasumi,Macromolecules, 1994, 27, was synthesized from compound 16 (178 mg, 0.104 mmol) in 4441; (b) K.Lorenz, D. Ho�lter, B. Stu�hn, R.Mu�lhaupt and H. Frey, Adv. Mater., 1996, 8, 414. DMF (10 ml), CsOH H2O (20 mg, 119 mmol) in methanol 8 For reviews which emphasise the functional properties of dendri- (1.5 ml) and compound 7 (23 mg, 0.0259 mmol) with stirring mers see: (a) J. Issberner, R. Moors and F. Vo� gtle, Angew.Chem., for 3 h, both at 20°C and at 80°C. After work-up, the dark Int. Ed. Engl., 1994, 33, 2413; (b) R. Moors and F. Vo� gtle, in yellow filtrate was filtered through alumina 90 using a short Advances in Dendritic Macromolecules, ed. G. R. Newkome, JAI column (eluent: chloroform). The resultant solid was then Press, London, 1996, vol. 2, p.41. triturated with DMF (2×10 ml) to give compound 3 as a light 9 For an article summarising recent publications on functional den- brown tar, which solidified into an amorphous solid (126 mg, drimers, see R.Dagani, Chem. Eng. News, June 3, 1996, 30. 10 For a review of redox-active dendrimers, see M. R. Bryce and 66%), mp ca. 75°C, upon trituration with a large amount of W. Devonport, in Advances in Dendritic Macromolecules, ed.methanol (Found: C, 50.81; H, 3.79. C314H276S104 requires C, G. R. Newkome, JAI Press, London, 1996, vol. 3, p.115. 51.07; H, 3.77%); m/z (MALDI-TOF) 7377 (M+ calc. 7372); 11 (a) P. J. Dandliker, F. Diederich, M. Gross, C. B. Knobler, dH(CDCl3 ) 2.21 (s, 36H), 2.30 (s, 48H), 3.82 (s, 56H), 3.95 (s, A. Louati and E. M. Sanford, Angew. Chem., Int. Ed. Engl., 1993, 24H), 7.11(s) and 7.21 (m, 112H). 33, 1739; (b) P. J. Dandliker, F. Diederich, J-P. Gisselbrecht, A Louati and M. Gross, Angew. Chem., Int. Ed. Engl., 1994, 34, 2725. Crystal structure determination of compound 7 12 M. R. Bryce, W. Devonport and A. J. Moore, Angew. Chem., Int. Edn. Engl., 1994, 33, 1761. The X-ray diraction experiment was performed on a Siemens 13 (a) J. R. Ferraro and J. M.Williams, Introduction to Synthetic 3-circle diractometer with a CCD area detector, using graph- Electrical Conductors, Academic Press, London, 1987; ite-monochromated Mo-Ka radiation, l=0.71073 A° . Crystal (b) M. Chem. Soc. Rev., 1991, 20, 355; (c) A. E. Underhill, J. Mater. Chem., 1992, 2, 1; (d) J. Mater. Chem., Special Issue on data: C38H32Cl4S8, M=886.9, monoclinic, space group P21/c Molecular Conductors, 1995, 5, 1469.(No.14), a=12.706(2), b=5.789(1), c=28.159(3) A° , b= 14 Review: M. Adam and K. Mu�llen, Adv. Mater., 1994, 6, 439. 99.69(1)°, V=2041.7(5) A° 3, Z=2, Dc=1.44 g cm-3, F(000)= 15 (a)M. Jørgensen, K. A. Lerstrup and K. Bechgaard, J. Org. Chem., 912, m=7.3 cm-1, crystal size 0.32×0.18×0.08 mm, v scan 1991, 56, 5684; (b) M. R.Bryce, G. J. Marshallsay and A. J. Moore, mode, 2h 52°, 10429 total, 3515 unique, 1978 observed J. Org. Chem., 1992, 57, 4859; (c) I. V. Sudmale, G. V. Tormos, [|F|>4s(F)] data, Rint(F2)=0.060. The structure was solved V. Yu. Khodorkovsky, A. S. Edzina, O. J. Neilands and by direct methods and refined by full-matrix least squares M. P. Cava, J. Org. Chem., 1993, 58, 1355; (d) L.M. Goldenberg, V. Yu. Khodorkovsky, J. Y. Becker, M. R. Bryce and M. C. Petty, against F2 of all data, using SHELXTL software.35 The C(4) J. Mater. Chem., 1995, 5, 191; (e) J. Y. Becher, J. Bernstein, to C(11) and Cl(1) atoms were refined as disordered over two A. Ellern, H. Gershenman and V. Khodorkovsky, J. Mater. Chem., positions (A and B) with equal occupancies and their geo- 1995, 5, 1557; ( f ) Review: T.Otsubo,Y. Aso and K. Takimiya, Adv. metries restrained to similarity. The refinement (ordered non- Mater., 1996, 8, 203. H atoms anisotropic, disordered ones isotropic, H atoms 16 (a) F. Gerson, A. Lamprecht and M. Fourmigue�, J. Chem. Soc., ‘riding’, 217 variables, 145 restraints) converged at wR(F2, all Perkin T rans. 2, 1996, 1409; (b)M.Adam, E.Fangha�nel, K. Mu�llen, data)=0.247, R(F, obs. data)=0.079, goodness-of-fit 1.07. Y-J. Shen and R. Wegner, Synth.Met., 1994, 66, 275; (c) R. P. Parg, J. D. Kilburn, M. C. Petty, C. Pearson and T. G. Ryan, J. Mater. Residual electron density features: Drmax=0.64, Drmin= Chem., 1995, 5, 1609; (d) Z-T. Li and J. Becher, Chem. Commun, -0.74 eA° -3. 1996, 639. Atomic coordinates, thermal parameters, and bond lengths 17 (a) G.J. Marshallsay, T. K. Hansen, A. J. Moore, M. R. Bryce and and angles have been deposited at the Cambridge J. Becher, Synthesis, 1994, 926; (b) J. Lau, O. Simonsen and Crystallographic Data Centre (CCDC). See Information for J. Becher, Synthesis, 1995, 521. Authors, J. Mater. Chem., 1997, Issue 1. Any request to the 18 M. A. Blower, M. R.Bryce and W. Devonport, Adv. Mater., 1996, CCDC for this material should quote the full literature citation 8, 63. and the reference number 1145/30. 19 S. Frenzel, S. Arndt, R. Ma. Gregoroius and K. Mu�llen, J. Mater. Chem., 1995, 5, 1529. 20 M. R. Bryce and W. Devonport, Synth. Met., 1996, 76, 305. We thank the EPSRC for funding (to C. S .W.). L. M. G. 21 W. Devonport, Ph.D. Thesis, University of Durham, 1995.thanks the University of Durham and the Royal Society for 22 (a) G. Steimecke, H-J. Sieler, R. Kirmse and E. Hoyer, Phosphorus financial support. A. S. B. thanks the EPSRC. M. R. B. thanks Sulfur, 1979, 7, 49; (b) Review: N. Svenstrup and J. Becher, the University of Durham for the award of the Sir Derman Synthesis, 1995, 215. Christopherson Research Fellowship. 23 A. Krief, T etrahedron, 1986, 42, 1209. 24 (a) N. Svenstrup, K. M. Rasmussen, T. K. Hansen and J. Becher, Synthesis, 1994, 809; (b) J. Becher, J. Lau, P. Leriche, P. Mørk and References N. Svenstrup, J. Chem. Soc., Chem. Commun., 1994, 2715. 25 (a) D. L. Lichtenberger, R. L. Johnston, K. Hinkelmann, T. Suzuki 1 G. M. Whitesides, J. P. Mathias and C. T. Seto, Science, 1991, and F.Wudl, J. Am. Chem. Soc., 1990, 112, 3302 and references 254, 1312. cited therein. 2 Reviews: (a) G. R. Newkome, C. N. Moorefield and G. R. Baker, 26 A. J. Moore and M. R. Bryce, J. Chem. Soc., Chem. Commun., Aldrichim. Acta, 1992, 25, 31; (b) D. A. Tomalia and H. D. Durst, in 1991, 1638. Supramolecular Chemistry I—Directed Synthesis and Molecular 27 (a) A. T. Hubbard and F.C. Anson, in Electroanalytical Chemistry, Recognition, ed. E. Weber, Springer-Verlag, Berlin, 1993, 193; ed. A. J. Bard, Marcel Dekker, New York, 1970, vol. 4, pp.129–210; (c) C. N. Moorefield and G. R. Newkome, in Advances in Dendritic (b) R. Carlier and J. Simonet, Bull. Soc. Chim. Fr., 1988, 831. Macromolecules, ed. G. R. Newkome, JAI Press, London, 1994, 28 (a) R. Carlier, P. Frere, M. Salle�, J. Roncali, M. Jubault, A. Tallec vol. 1, p.1; (d) J. M. J. Fre� chet, Science, 1994, 263, 1710; and A. Gorgues, Adv. Mater., 1993, 5, 445; (b) P. Frere, R. Carlier, (e) D. A. Tomalia, Adv. Mater., 1994, 6, 529; ( f ) G. R. Newkome K. Boubekeur, A. Gorgues, J. Roncali, A. Tallec, M. Jubault and and C. N. Moorefield, in Mesomolecules: From Molecules to P. Batail, J. Chem. Soc., Chem. Commun., 1994, 2071. Materials, ed. G. D. Mendenhall, A. Greenberg and J. F. Liebman, 29 C. M. Casaco, I. Cuadrado, M. Mora�n and J. Losada, J. Chem. Chapman and Hall, New York, 1995, p.27; (e) N. Ardoin and D. Astruc, Bull. Soc. Chim. Fr., 1995, 132, 875. Soc., Chem. Commun., 1994, 2575. 1196 J. Mater. Chem., 1997, 7(7), 1189–119730 F. Moulines, L. Djakovitch, R. Boese, B. Gloaguen, W. Thiel, J- (b) A. S. Batsanov, N. Svenstrup, J. Lau, J. Becher, M. R. Bryce and J. A. K. Howard, J. Chem. Soc., Chem. Commun., 1995, 1201. L. Fillaut, M-H. Delville and D. Astruc, Angew. Chem., Int. Ed. Engl., 1993, 32, 1075. 34 For a review of TTF derivatives in supramolecular chemistry, see T. Jørgensen, T. K. Hansen and J. Becher, Chem. Soc. Rev., 1994, 31 D. Astruc, Electron T ransfer and Radical Processes in T ransition Metal Chemistry, VCH, New York, 1995, ch. 2. 23, 41. 35 G. M. Sheldrick, SHELXTL, ver. 5/VMS, Siemens Analytical X- 32 (a) J-L. Fillaut, J. Linars and D. Astruc, Angew. Chem., Int. Ed. Engl., 1994, 33, 2460; (b) P. Jutzi, C. Batz, B. Neumann and H- Ray Instruments Inc., Wisconsin, USA, 1995. G. Stammler, Angew. Chem., Int. Ed. Engl., 1996, 35, 2118. 33 (a) C. Nakano, K. Imaeda, T. Mori, Y. Maruyama, H. Inokuchi, N. Iwasawa and G. Saito, J. Mater. Chem., 1991, 1, 37; Paper 6/07597E; Received 7th November, 1996 J. Mater. Chem., 1997, 7(7), 1189

ISSN:0959-9428    

DOI:10.1039/a607597e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Hydrophobically modified poly(amidoamine) (PAMAM) dendrimers: their properties at the air–water interface and use as nanoscopic container molecules Yasmin Sayed-Sweet, David M. Hedstrand, Ralph Spinder* and Donald A. Tomalia* MichiganMolecular Institute, 1910 W. St. Andrews Road,Midland,MI 48640, USA Tri- and tetra-dendron poly(amidoamine) (PAMAM) dendrimers were converted into hydrocarbon-soluble polymers and used as hydrophobic nanoscopic scaolding by reacting their primary amino chain ends with various epoxyalkanes.These hydrophobically modified modules performed well as nanoscopic transport molecules. They mimicked classical inverse micelle behaviour by transporting copper(II) sulfate from an aqueous solution into an organic phase to form homogeneous, transparent, intensely blue toluene solutions.The modified dendrimers were examined at the air–water interface both with and without copper guest molecules. A number of critical macromolecular design parameters (CMDPs) such as generation (size), core (shape, topology) and surface groups were varied to determine their influence on Langmuir film properties. Nanostructures are macromolecular assemblies containing which is associated with most classical covalent polymerization methodology.The major shortcoming of these approaches is from 103 to 109 atoms with molecular masses of 103 to 1010 Da. Their dimensions vary from 1 to 102 nm. These nano- the inability to readily isolate precise macromolecular structures or control critical macromolecular design parameters dimensions and masses have very broad implications in such traditional disciplines as polymer science,1a–b catalysis,2 interfa- (CMDPs) such as: (a) size, (b) shape, (c) surface chemistry and (d) topology.On the other hand, nature solved this problem cial/colloid science,3 supramolecular chemistry,4 electronic microfabrication5a –b and molecular biology.6 It is quite apparent some 4.5 billion years ago during a critical phase in our natural molecular evolution from atoms to very complex molecular that the development of viable synthetic and characterization methodology which will allow systematicexamination of ‘struc- structure.The reproducible synthesis of proteins, DNA, RNA and bio-assemblies possessing precise CMDP controlled fea- ture-controlled nanostructures’ would be of significance to these evolving areas.7–9 For that reason, considerable inter- tures are prime examples of this success.Using strictly abiotic synthetic methods, it has been widely national interest has focused on these objectives. Synthetic polymer chemists routinely produce nano-struc- demonstrated over the past decade that dendrons, dendrimers10 –13 and more recently dendrigrafts3,14 can be routinely tures as part of a statisticalmacromolecular product continuum Plate 1 Scaled comparison of tri-dendron (NH3 core) poly(amidoamine) dendrimers; generation=4–7, sizes and shapes with various proteins, DNA and bio-assemblies J. Mater.Chem., 1997, 7(7), 1199–1205 1199constructed with CMDP control that rivals the structural dendrimers: a G2(NH3) dendrimer (0.25 g, 2.5 mmol) was dissolved in 10 ml of methanol and 0.35 g (4.0 mmol) of 1,2- regulation found in biological systems.Acomparison of various nanoscopic biostructures with tri-dendron poly(amidoamine) epoxyhexane was added. The reaction solution was heated for five days at 40°C. Additional methanol was added to the (PAMAM) dendrimers clearly illustrates the close scaling of size and shape that is possible (see Plate 1).reaction solution to give a final dendrimer concentration of 5 mass%, followed by filtering through a 0.2 micron Teflon filter. The ability to prepare well-defined dendrons and dendrimers15 leads to the concept of using these materials as funda- This solution was ultrafiltered using a flatstock Amicon unit employing a YM3 membrane with a MWCO of 1000.Fourteen mental nanoscopic building blocks, suitable for the construction of nanoscopic compounds16a,b and other complex recirculations were required to completely remove the excess epoxide. Methanol was removed by rotoevaporation and the assemblies. More recently, these dendritic materials have been identified as nanoscopic scaolding for catalysis,17,18 gene dendrimer was dried at room temperature under vacuum to give 0.37 g (80% yield) of modified product.dc (CDCl3 ): vectors,19–21 magnetic resonance imaging agents,22 electron conduction,23 photon transduction,24a–b as well as nanoscopic 172.6–172.9 (m), 69.8, 68.1, 67.8, 67.7, 64.3, 61.9, 56.6, 55.2, 54.9, 52.3, 50.0, 49.1, 38.5, 37.5, 37.2, 34.6, 34.3, 33.7, 33.2, 27.8, host compartments or ‘unimolecular regular micelle mimics’ suitable for the containment of pharmaceuticals,agrochemicals, 27.7, 22.6, and 13.9. ESI–MS: theoretical MW=4817; observed MW=4818.5 (MH+).dyes and other guest molecules.25a–c,32,48 In this paper, we describe the facile conversion of amine terminated hydrophobic poly(amidoamine) dendrimers into Copper(II ) transport studies—‘blue toluene-chloroform ‘unimolecular inverse micelle’ modules by surface modification experiments’ with hydrophobic epoxy reagents.We use the term ‘unimolecu- A 3.9 mass% solution of epoxydecane-functionalized G4- lar inverse micelle’ to dierentiate these covalently fixed macro- (EDA) C10 PAMAM dendrimer in toluene was carefully lay- molecular structures from the dynamic equilibrium structure ered on top of a 0.1 M CuSO4 solution.After standing for of a ‘classic’ inverse micelle. The resulting hydrocarbon-soluble several hours at room temperature, a dark-blue colour emerged assemblies functioned as nanoscopically sized container mol- above the aqueous–organic interface. The experiment was ecules as evidenced by the transport of copper(II) salts into continued for several days over which time the toluene solution various hydrocarbon solvents.In this fashion, transparent, assumed a very intense, transparent blue colour. intensely blue toluene and chloroform solutions were formed. Copper(II)-containing hydrophobically modified dendrimers In order to understand better the phase transfer properties of for Langmuir film studies were prepared by the following these non-classical micelles, both tri- and tetra-dendron dendri- procedure: an 1,2-epoxyoctane-modified G5(NH3) C8 mers were examined with and without copper(II) guest mol- PAMAM dendrimer (0.30 g) was dissolved in 2 ml of chloro- ecules as Langmuir films at the air–water interface.form, and aqueous copper sulfate (30 mg in 2 ml water) was placed on top of the chloroform solution.The mixture was Experimental agitated on an orbital shaker for 24 h. After that time, no blue copper colour remained in the aqueous phase. The aqueous General procedures phase was decanted and the blue chloroform solution was The 13C (75.4 or 90.5 MHz) NMR spectra were recorded on dried with anhydrous sodium sulfate. Filtration and removal either a Varian Unity 300 or a Bruker WM360 SF spec- of the solvent by distillation in vacuo gave 0.24 g of a blue oil: trometer.The 13C NMR spectra were recorded in CDCl3 using dc (CDCl3): 173, 69, 51, 35, 32.0, 29.7, 25.8, 22.8, 14.2. the solvent line as the standard (77 ppm) or in D2O using 1,4- Over the time frame of these experiments (ca. one month), dioxane as an internal standard (66.3 ppm).Electrospray ioniz- there was no indication that the incorporation of copper ions ation mass spectroscopy was obtained using a Finnigan TSQ- into these dendrimers resulted in degradation of the dendrimer 700 spectrometer. The spectra were deconvoluted using the structure. BIOMASS software. Visible spectra were recorded on a Varian Cary 1 spectrometer using matched cells with pure solvent in Monolayer studies the reference beam.The PAMAM dendrimers were prepared ALauda FW-2 film balance was used to examine the properties as previously described.26a–c The conditions used to prepare of the dendrimer monolayers. Distilled water from a Millipore the PAMAM dendrimers employed reaction stoichiometries system (18 MV) was used as the subphase and maintained at and rigorous purification procedures which minimize both 23°C.Millimolar solutions of the dendrimers were prepared intramolecular (missing repeat units, intramolecular loops) and in CHCl3. In a typical experiment, dilute dendrimer solutions intermolecular (dimers, lower generation dendrimers) defects were added dropwise to the top of the subphase, while the that have been described and characterized previously.27 The solvent was allowed to evaporate before another drop was intramolecular defects contained in these samples can be added.This procedure was repeated until all the solution was thought of as ‘quantized’ coproducts, since they are exact delivered. In order to ensure that residual solvent was not multiples of the molecular mass of the desired structure.This present, dendrimer was equilibrated for 10–20 min before the is in contrast to defects found in conventional polymers which experiment was initiated. Surface pressure vs. area isotherms cover a broad Gaussian distribution, even in the case of were measured at a compression rate of 25–30 cm2 min-1. polymers prepared by living polymerization techniques. The The limiting areas reported in this paper are an average of at epoxyalkanes [1,2-epoxyhexane (99%), 1,2-epoxyoctane least three measurements.(99.9%), 1,2-epoxydecane (99.9%) and 1,2-epoxydodecane (99.9%)] were purchased from either Lancaster or Aldrich. Methyl acrylate (99.9%), 1,4-diaminobutane (99.9%), 1,8- Results and Discussion diaminooctane (99.9%), and 1,12-diaminododecane (99.9%) Hydrophobic modification of dendrimers were all purchased from Aldrich. Ethylenediamine was received from Fisher and distilled before use.Perhaps one of the unique features of dendrimeric architecture, compared to classical random coil polymers, is the large Surface modification of PAMAM dendrimers number of well-defined chain ends. Several studies have shown that changing the chemical nature of the surface groups can Modification of generation 2, PAMAM dendrimers, ammonia core, G2(NH3), with 1,2-epoxyhexane is representative of the dramatically aect the physical properties of these polymers.For example, Fre� chet and co-workers have shown that poly- general method used to prepare hydrophobically modified 1200 J. Mater. Chem., 1997, 7(7), 1199–1205(ether) dendrimers can be transformed from organic solventsoluble polymers to water-soluble materials by a simple surface group transformation.28a–b It is important to note that other physical properties such as glass transitions are also influenced by the nature of the surface groups.29a–b Critical architectural components of the dendrimers such as the nature of the surface groups/chemistry, repeat unit composition and degree of branching all undoubtedly influence their physical properties and hence many of their eventual applications.At this point, the interplay between these parameters is not totally understood. In this study, we focused on the surface modification of water-soluble, amine-terminated PAMAM dendrimers to form ‘unimolecular inverse micelle’ prototypes which would be soluble in organic solvents such as toluene or chloroform.This transformation was easily accomplished by reacting the Plate 2 PAMAM dendrimer’s terminal primary amino groups with a variety of hydrophobic epoxyalkanes. These reactions were typically run in methanol, although modifications employing solved in toluene to form a clear solution.This solution was long chain epoxyalkanes, such as 1,2-epoxydodecane, required layered on a 0.1 M aqueous CuSO4 solution. During this the addition of a cosolvent (toluene) to maintain homogeneous quiescent experiment, a gradient of a dark-blue colour slowly reaction conditions. We found the reaction could be run either diused up from the organic–aqueous interface into the toluene with an excess of epoxide, which was then removed through layer.After a period of several days, the entire organic layer ultrafiltration of the product, or by simply utilizing stoichio- took on a dark-blue colour (see Plate 2). As expected, control metric amounts of the epoxide. By either method, we saw no experiments showed that copper ions were not transported indication that an ‘all or nothing’ distribution of modified and into the organic phase in the absence of dendrimer.Fig. 1 unmodified dendrimers formed, as has recently been reported compares the UV–VIS spectrum of the blue toluene layer with by Meijer and co-workers for the reaction of alkyl acid that of the starting aqueous CuSO4 solution. The blue-shift of chlorides with POPAM dendrimers.30 Even in experimental the absorption maximum in the visible region is characteristic runs where sub-stoichiometric quantities of epoxyalkane were of copper coordinated by amine ligands,40 which in this case used, only a modified product with a statistical distribution of could only come from the interior of the dendrimer.The ability surface alkyl groups centred around the stoichiometric value of the interior of a dendrimer to coordinate copper ions has calculated for the reaction was observed.31 The products were been extensively probed recently by EPR spectroscopy.41 This characterized by 13C NMR spectroscopy, and for the low example clearly shows that the dendrimer acts as a covalently molecular mass products, electrospray ionization mass spec- fixed phase transfer agent, with sucient interaction at the troscopy was also used.27b–c interface between the organic and aqueous solution to allow the interior of the dendrimer to coordinate copper ions.Further studies will be needed to determine the potentially complex Transport of copper(II ) salts into an organic solvent to form solution structure of these dendrimer unimolecular inverse ‘blue toluene’ micelles.The ability to use dendrimers as container molecules has continued to excite wide scientific interest. Encapsulation of Characterization of dendrimer monolayers at the air–water guest molecules into the interior of dendrimer hosts was first interface demonstrated by the incorporation of acetylsalicylic acid or Properties of synthetic polymers at the air–water interface 2,4-dichlorophenoxyacetic acid into ester-terminated PAMAM have been studied for many years.42a–b Generally, polymers dendrimers as early as 1989.32 We have referred to this have the ability to act as amphiphiles either through the phenomenon as ‘unimolecular encapsulation.’33 As an elegant interaction of polar groups on the chain of the polymer,43 continuation and expansion of this theme, Meijer and co- through the special construction of block/star polymers con- workers have described a so-called ‘dendrimer box’ phenom- sisting of both hydrophilic and hydrophobic chains,44a–b or by enon.25 It involves the trapping of certain guest molecules in preparing polymer surfactants with hydrophilic chain ends.45 the interior void spaces by post reaction with bulky surface group reagents.Dendritic micellar behaviour has been demonstrated on numerous occasions by the dissolution of organic molecules in dendrimers34a–e or by the polymerization of water-insoluble monomers in the interiors of carboxy-terminated dendrimers to form novel linear-dendritic composites.35 On the other hand, some dendrimers have been employed as micellar structures in electrokinetic capillary chromatography.34f,h Considerable experimental and characterization work by Turro et al.36–39 has unequivocally demonstrated the ‘unimolecular micelle’ features of dendrimers.In all of these cases, dendrimers are regarded as regular unimolecular micelles, which consist of a non-polar core and a polar outer shell. Evidence that modified PAMAM dendrimers behaved as unimolecular inverse micelles, and that the interior space of the dendrimer remains functionally active was clearly demonstrated by the following experiment: a G4(EDA) PAMAM Fig. 1 Visible spectrum of (a) an aqueous 0.1 M CuSO4 solution and dendrimer which was obtained from the exhaustive reaction (b) the complex formed betweean epoxydecane-modified G4 (EDA) PAMAM dendrimer and CuSO4 in toluene of amine-terminated dendrimer with 1,2-epoxyoctane was dis- J.Mater. Chem., 1997, 7(7), 1199–1205 1201Polymers that have no amphiphilic character at all can still form films at the air–water interface.46 Recently, first reports of the properties and structure of poly(ether) dendrimers at the air–water interface were published.47a–b Only dendrons of generation 4 and below, with hydroxy groups at the focal point, were found to act as surfactant-like molecules, while the higher generation dendrons and all the poly(ether) tri-dendron dendrimers above generation 1 did not act as surfactant-like polymers or show the ability to form multilayer structures.For these experiments, PAMAM dendrimers, prepared from both ammonia and various alkylenediamine core molecules, were exhaustively modified with several epoxyalkanes.These cores are illustrated in Scheme 1. The modified dendrimer samples were carefully placed on the water surface of a Langmuir trough as dilute chloroform solutions. In order to ensure total removal of the solvent, the dendrimer was equilibrated at the interface for 10–20 min.A typical isotherm Fig. 2 Langmuir isotherm of a G3(EDA) C8 PAMAM dendrimer obtained for all of the hydrophobically modified dendrimers modified with epoxyoctane we investigated is shown in Fig. 2. As the area available to the molecules decreases, the surface pressure increases until a plateau is reached. Decreasing the area available to the dendrimers beyond this point presumably causes the monolayer film to collapse and form multilayer structures, while the surface pressure remains constant upon further compression. This response is quite dierent from that observed by Fre� chet for poly(ether) dendrimers,47a–b where a nucleation phenomenon was observed for the low generation dendrons.The general shape of the isotherms was shown not to be dependent on the compression rate.The isotherms were found to be reversible, with only slight changes in the collapse pressure, as long as the surface pressure applied to the film remained below the collapse point. Addition of sulfuric acid to the subphase (pH= 2) did not strongly aect the shape of the isotherms, although the collapse pressure increased 10–15%. One of our goals was to examine the eect of certain critical macromolecular design parameters, such as the core type (multiplicity of branching sites and size of the core), the nature of the surface groups (length of the alkyl chain) and the dendrimer generation (size), in influencing the Langmuir film data.For these experiments, the area occupied per dendrimer molecule was calculated by extrapolating to the x-axis from the point where the collapse curve and the linear region of the increasing pressure part of the isotherm meet.The dendrimers were assumed to be spherical molecules for these calculations. Table 1 summarizes the isotherm data for three surface modifications and five cores over a range of dendrimer generations. In Fig. 3 the surface radii obtained from the Langmuir data for the epoxyoctane-substituted PAMAM dendrimers are compared to the hydrodynamic radii of unsubstituted ammonia core dendrimers as determined by size exclusion chromatography (SEC).15b In general, the agreement is very good.The experimental areas determined from the isotherms increased as a function of generation. It is only at the highest generations that diameters determined from the isotherms diers significantly from the SEC data.Changing the hydrocarbon length on the dendrimer surface does not appear to have a significant eect on the surface area occupied by the dendrimer at the collapse point (Fig. 4). Even at the highest generation studied (generation 5), the limiting surface areas were all the same within the experimental errors associated with the measurements.We also examined the eect of the core length and multiplicity on the isotherm. Fig. 5 shows the surface area plotted vs. dendrimer generation for ammonia and ethylenediamine (EDA) core dendrimers. Both EDA and alkylenediamine core dendrimers build molecular mass 25% faster than dendrimers based on ammonia, since tetravalent cores produce tetra- Scheme 1 Tetra-dendron poly(amidoamine) (PAMAM) dendrimers amplified from various alkylenediamine cores dendron dendrimers, while ammonia core leads to tri-dendron 1202 J.Mater. Chem., 1997, 7(7), 1199–1205Table 1 Dendrimer isotherm dataa surface area/ surface area/ sample A° 2 per molecule sample A° 2 per molecule G0(NH3) C8 154 G2(EDA) C6 727 G1NH3) C8 284 G2(EDA) C8 877 G2(NH3) C8 756 G2(EDA) C12 798 G2(NH3) C12 702 G3(EDA) C6 1249 G3(NH3) C8 1211 G3(EDA) C8 1344 G3(NH3) C12 1147 G3(EDA) C12 1233 G4(NH3) C8 2804 G4(EDA) C6 2363 G4(NH3) C12 2848 G4(EDA) C8 2620 G5(NH3) C8 4369 G4(EDA) C12 3243 G5(NH3) C12 4742 G5(EDA) C6 5779 G2(Butane) C12 944 G5(EDA) C8 6449 G2(Octane) C12 889 G5(EDA) C12 5733 G2(Dodecane) C12 871 aNomenclature: the following nomenclature is used to describe the dendrimers prepared for this study.A fifth generation PAMAM dendrimer grown from an ethylenediamine core and modified with 1,2-epoxyhexane is noted as G5(EDA) C6. Fig. 5 A surface area vs. generation number plot for epoxydecane Fig. 3 Comparison of the radii of various generations of PAMAM dendrimers prepared from ammonia cores determined by size exclusion modified dendrimers grown from ammonia (#) and EDA ($) cores chromatography for the unmodified dendrimers ($) and by the limiting area measurements obtained from the Langmuir film studies for the epoxyoctane-modified dendrimers (#) Fig. 6 A plot of surface area vs. the number of carbons contained in the epoxyalkane chains for fifth generation dendrimers based on EDA ($) and ammonia (#) cores Fig. 4 Plot of surface area vs. generation number for PAMAM dendrimers grown from EDA cores and substituted with epoxyhexane (#), epoxyoctane ($) and epoxydecane (() Previous theoretical studies have suggested that the shape of PAMAM dendrimer becomes more highly spherical as a function of increasing generation number.32 Experimental con- dendrimers. There was no significant dierence in the limiting surface areas obtained by comparing the two types of cores firmation of the importance of this shape change has shown that a number of physical properties also exhibit dramatic for generations 2–4.At generation 5, Fig. 6 shows that dendrimers based on EDA cores have a surface area at collapse changes coincidental with the shape change.33 It may be possiblethat the increasing dierence seen in this study between 20–47% larger than that obtained for the ammonia core dendrimers depending on the length of the surface alkyl chain.the surface areas of the higher generation dendrimers may be J. Mater. Chem., 1997, 7(7), 1199–1205 1203influenced by this shape change. To further investigate the Model of hydrophobically modified PAMAM dendrimers at the eect of core length, a number of dendrimers with longer tetra- air–water interface dendron cores (1,4-diaminobutane, 1,8-diaminooctane and With these limited data, one can only speculate as to how 1,12-diaminododecane) were also examined.These data, pre- these hydrophobically modified dendrimers are organized at sented in Fig. 7, indicate that for the lower generation dendri- the air–water interface.Since the surface pressure vs. area mers there is no significant dierence as a function of the core curves do not show significant shape changes as a function of length. As was seen for the comparison between the ammonia the dendrimer size, the terminal hydrophobe length or the and EDA cores in Fig. 6, it is possible that a greater eect length/hydrophobicity of the core, it appears that the isotherms would be seen at higher generations for these dendrimers.are either not sensitive to these structural parameters, or that all of the dendrimers examined are interacting with the sub- Copper(II ) salt-containing dendrimers at the air–water interface phase in a very similar manner. One model which may be A key question was whether these copper-loaded dendrimers appropriate for the wer generation PAMAM dendrimers is could still be organized at the air–water interface.This issue that the accessible hydrophilic dendrimer interior interacts was examined by using dendrimer copper(II) complexes pre- with the aqueous subphase while the hydrophobically modified pared in chloroform solutions, which were introduced at the terminal groups reorganize to extend outward away from the air–water interface as described previously.Fig. 8 shows an air–water interface. Since the length of the hydrophobic chain isotherm obtained for a G5(NH3) C8 sample loaded with does not seem to impact the surface area occupied by the copper. In general, all the copper-loaded samples exhibit dendrimer, either the chains from adjacent dendrimers are able isotherms that are similar in shape to those containing no to interdigitate or they extend upward away from each other.copper. The collapse pressure increased slightly upon incorpor- For the low pH experiments (i.e. pH=2), the subphase was ating copper, which may indicate a slight stiening of the acidic enough to protonate the interior tertiary amines (pKa dendrimer interior due to copper complexation.Over the range ca. 4.5), which should help to increase the interaction between of dendrimers investigated [i.e. G2(NH3) C8 to G7(NH3) C8], the dendrimer interior and the subphase, thereby causing the no dierences were observed in the isotherms except for the observed larger collapse pressure. At higher generations, it higher collapse pressure noted above.This work clearly demon- would seem that a dendrimer reorganization of this type would strates that metal-loaded dendrimers can be readily organized become increasingly more dicult. A second model one must into two-dimensional layers. consider is that the dendrimers are simply acting like hydrophobic spheroids floating at the air–water interface.At this point, it is dicult to tell which of these models is the most probable. Perhaps there is a transition from the first model which may be operable for the lower generations to the floating hydrophobic spheroid model for the more congested higher generations. Conclusions Hydrophilic PAMAM dendrimer scaolds were readily converted to hydrophobic modules by facile reactions of amine groups with epoxyalkanes.The modified dendrimers perform as nanoscopic container molecules, reminiscent of ‘unimolecular inverse micelles’ as demonstrated by the transport of copper(II) ions from an aqueous solution into toluene or chloroform. These experiments, as well as other work,25,27,35 clearly show that the interior void spaces of dendrimers are Fig. 7 A plot showing the surface area versus the number of methylene available for the incorporation of guest molecules. The proper- units contained in the core for generation two PAMAM dendrimers ties of the modified PAMAM dendrimers at the air–water modified with epoxydodecane interface were most strongly influenced by the dendrimer generation. Even changing the length of the dendrimer surface hydrophobefrom hexyl to dodecyl did not cause any significant dierences in the limiting area of the dendrimer at the collapse point. Only for the highest generation dendrimers (generation 5) did the size of the core seem to influence the area taken up by the dendrimer at the collapse point. Further examination of these dendrimers structures at the air–water interfaces will be required to gain a complete understanding of these unique nanoscopic organizations.The authors wish to thank Drs June W. Klimash and Douglas R. Swanson for providing several of the dendrimers used in these studies. The Air Force Oce of Scientific Research (Contract No. AFOSR-91-0366) is gratefully acknowledged for their support of this work. D.M.H., R.S. and D.A.T. also acknowledge the support of Dendritech, Inc, the Army Research Laboratory as a sponsor of the MMI/ARL Dendritic Fig. 8 Langmuir isotherm of a G4 (NH3) C8 PAMAM dendrimer Polymer Center of Excellence, and the Army Research Oce surface modified with epoxyoctane and its interior void space loaded with copper ions (Grant No. DAAH04-95-1-0652). 1204 J. Mater. Chem., 1997, 7(7), 1199–120527 (a) P.B. Smith, S. J. Martin, M. J. Hall and D. A. Tomalia, in References Applied Polymer Analysis and Characterization, ed. J. Mitchell, 1 (a) P. R. 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ISSN:0959-9428    

DOI:10.1039/a700860k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Nanosized polyphenylene dendrimers based upon pentaphenylbenzene units Frank Morgenroth, Christian Ku� bel and Klaus Mu�llen* Max-Planck-Institut fu� r Polymerforschung, Ackermannweg 10, D-55128 Mainz, Germany A facile divergent synthesis of monodisperse polyphenylene dendrimers having diameters of 21–55 A° is presented. These nanoparticles have been prepared via a [2+4]cycloaddition–deprotection sequence using an excess of tetraphenylcyclopentadienone 1a as monomer and the tetraethynylbiphenyl 2 as core.Due to the dense packing of 22, 62 or 142 benzene rings in generations G1, G2 and G3 , respectively, the conformational freedom of the higher generations G2 and G3 is limited. Molecular mechanics calculations as well as molecular dynamics simulations are included in a discussion of the structure and the shape-persistence of G2.The calculations revealed that selected inner distances of the molecule varied only 5–10% during the molecular dynamics simulations, thus indicating that the overall shape of the molecule essentially did not change throughout the simulation time. Within the past decade, chemists have established new methods Results and Discussion to synthesize complex molecules and also to control their Synthesis macromolecular and supramolecular architecture.These eorts are connected tightly to a transition in molecular scale from We have recently introduced 3,4-bis(4-triisopropylsilylethynyl- the picometre to the nanometre range.1 Supramolecular chem- phenyl)-2,5-diphenylcyclopenta-2,4-dienone (1a) as a building istry and nanostructure engineering assemble organic and block for the synthesis of monodisperse polyphenylene dendri- inorganic molecules using covalent as well as non-covalent mers such as 3a and 4a (Scheme 1).8 A key step of our interactions to obtain complex systems such as liquid crystals approach was the [2+4] cycloaddition of 1a to a core such or nanotubes.2 By focusing on all-hydrocarbon, covalent bond- as 3,3¾,5,5¾-tetraethynylbiphenyl (2).Compound 1a contained based dendritic nanostructures,3–6 Moore and his co-workers a diene function and two dienophile functions and could thus built nanosized phenylacetylene dendrimers.3 Hart et al. have be considered an AB2 building block. Since the two dienophile reported the construction of polyaromatic iptycenes.4 A functions in 1a were blocked by triisopropylsilyl groups, four remarkable feature of these nanostructures is their essentially equivalents of the tetraphenylcyclopentadienone 1a could be invariant shape (shape-persistence).7 Shape-persistence is a reacted selectively in a four-fold [2+4] cycloaddition with the requirement for the design of nanoparticles with tailor-made four dienophile functions of 2.Under the applied reaction topographic features and well-defined functional group dispo- conditions (180 to 200 °C, diphenyl ether–a-methylnaphthalene sitions. In the case of Moore’s phenylacetylene-based macro- 151) the Diels–Alder reaction proceeded with the loss of molecules, shape-persistence was accomplished using rigid carbon monoxide to yield the first generation 3a of the phenylacetylene subunits.The cascades of Hart are highly rigid dendrimer. Compound 3a was used for an eight-fold addition due to the connection of bicyclo[2.2.2]octane moieties with of 1a after an easy deprotection with tetrabutylammonium benzenes. In this paper, we present an alternative route to fluoride (Bu4NF) in THF resulting in the second generation generation G3 , of a new type of nanosized all-hydrocarbon 4a (Scheme 1).As discussed below in detail, characterization dendrimers. Our idea for obtaining shape-persistence was to was accomplished by mass spectrometry and 1H and 13C NMR create an extremely dense packing of benzene rings, thereby spectroscopy. limiting the conformational freedom of the dendrimer.This paper outlines the synthetic aspects of our dendrimer Considering these structural aspects, we present molecular construction and its extension to the fabrication of G3. The mechanics calculations of G2, which provide insight into the procedure employed worked for generation growth as well as three dimensional structure of this molecule. Additionally, in activation both in high yields and with no significant side this report we will discuss molecular dynamics simulations reactions.The yields of white amorphous polyphenylene den- investigating the shape-persistence of G2. drimers, from the Diels–Alder growth reaction, were higher than 80% and the deprotection reaction was nearly quantitative. However, the growth steps had to be optimized to avoid an incomplete reaction of the terminal ethynyl groups since this severely aected the growth scheme.Simply heating a solution of 5 equiv. of 1a and 2 in diphenyl ether–a-methylnaphthalene to 200 °C for 1 h led to a mixture of two-, three- and the desired four-fold Diels–Alder reaction product. As expected, this mixture could not be separated chromatographically. In contrast, a quantitative formation of G1 was obtained by adding 2 in a-methylnaphthalene slowly to a hot solution of 5 equiv.of 1a in diphenyl ether–amethylnaphthalene. By focusing on the growth step from G1 to G2, a longer reaction time was essential to avoid growth imperfections. This was expected since our divergent approach required the cycloaddition to be carried out at an increasing number of ethynyl groups.In addition, the use of pentaphenyl substituted benzene rings as repetitive units resulted in a very J. Mater. Chem., 1997, 7(7), 1207–1211 1207Scheme 1 Chemical structure and procedure for the preparation of the polyphenylene dendrimer generations G1 to G3. The dotted lines mark ‘half-G1’ and ‘half-G2’, respectively (see text). Overlapping phenyl rings in the 2D projection of 5 are plotted in bold.Reagents and conditions: i, 1a, heat; ii, Bu4NF. compact structure. Furthermore, steric crowding in the vicinity methylnaphthalene to a solution of 1a in diphenyl ether–amethylnaphthalene at 180 to 200 °C over a period of 25 h. The of the ethynyl groups had presumably lowered the reaction rate (see Fig. 1). Accordingly, the addition of 3b to 5 equiv. 1a mixture was stirred for an additional 15 h at 180 °C. In the case of G3 , the addition of fresh 1a was required in order to at 180 to 200 °C over 2 h and an additional reaction time of the same time, yielded a mixture of seven- and eight-fold sustain a sucient excess of the cyclopentadienone during reaction, otherwise traces of 10- to 15-fold cycloaddition [2+4] cycloaddition product.However, the addition of 3b over 5 h and an additional reaction time of 4 h selectively led products were observed. The latter could be converted into 5a by a second treatment with an excess of 1a. We obtained 5a to the desired eight-fold Diels–Alder product. By extending this concept, the synthesis of G3 was achieved as a white amorphous powder in 81% yield. A comparison of our divergent approach with the convergent synthesis of an by adding a mixture of 4b and 1a in diphenyl ether–a- 1208 J.Mater. Chem., 1997, 7(7), 1207–1211caused a mass dierence of ca. 717 g mol-1 (1a less CO) relative to the completely reacted product. The perfect agreement between calculated and experimentally determined m/z ratios for G1 to G3 confirmed the monodispersity of the dendrimers (see Experimental).Computer simulations Molecular mechanics calculations12 performed for G1 and G2 (without acetylene units) provided a first insight into the 3D structure of the dendrimers (Fig. 1). In the first step, one half of the molecule (see Scheme 1) was optimised by energy minimisation using 144 and 1024 dierent conformers (obtained by torsion about the marked bonds in Scheme 1) of G1 and G2, respectively.Thereby we obtained one conformer for ‘half-G1’ (see Scheme 1) with an energy 3 kcal mol-1 (1 cal=4.184 J) lower than any other and another 20 conformers diering by less than 10 kcal mol-1. This observation was even more pronounced in the case of ‘half-G2’ (see Scheme 1 and Fig. 1), where wd more than 100 conformers diering by less than 15 kcal mol-1.In both cases we used the conformer with the lowest energy to generate the complete dendrimer. This was finally optimised by varying the Fig. 1 The 3D structure of G2 (without acetylene units) according to torsional angle of the central phenyl–phenyl unit (bond a, see molecular mechanics calculations12 Fig. 2). The latter was generated by connecting two ‘half-G2’ to obtain G2 itself.oligophenylene-dendrimer with 46 benzene rings carried out Therefore, we obtained a 3D structure of G2, which could by Miller and Neenan9 revealed that in our experiments a be regarded as consisting of a twisted central biphenyl unit faster dendrimer growth, in terms of the number of benzene carrying four branches which were nearly orthogonal to the rings, was achieved in fewer steps and without the use of central biphenyl unit.The two pentaphenylbenzene units in catalysts. Our synthetic approach has also enabled products each branch were twisted. They were nearly parallel to each to be purified simply by precipitation from acetone with other, but the protons of the central phenyl rings pointed in ethanol.dierent directions (Fig. 1). The dimensions of the dendrimer The larger dendrimer generations G2 and G3, accessible by G2, in the three main directions, were 36, 27and 14 A° according our process, had 62 and 142 benzene rings, respectively. We to the molecular mechanics calculations. used computer models to estimate the dimensions of these The existence of several local energy minima of similar nanoparticles.As an indication of the impressive size of our energy is a requirement for a flexible molecule, but the dynamic dendrimers, the diameters of G2 and G3 were found to be behaviour is controlled by the activation energy for trans- approximately 38 and 55 A° (Table 1). forming the conformers into one another. A first insight into The success of our dendrimer synthesis was complemented the dynamic behaviour of the dendrimer was gained by molecu- by the full characterization of the new structures.lar dynamics (MD) simulations13 of G2. We analysed the trajectory of the MD simulations by inspecting specific intra- Characterization molecular distances and torsional angles (specified in Fig. 2 and summarized in Table 2) to obtain information about the Mass spectrometry is an excellent tool for determining the motions within the dendrimer.purity and structural composition of dendrimers.10 The triisopropylsilyl- protected as well as the oligoethynyl substituted dendrimers exhibited an unexpectedly good solubility in common solvents such as dichloromethane, acetone or tetrahydrofuran (THF). Therefore, characterization was performed using matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) as well as 1H and 13C NMR spectroscopy.By 1H NMR spectroscopy it was only possible to check the correct intensity ratio of aromatic and aliphatic (or acetylenic) protons.11 Employing MALDI-TOFMS allowed potential growth imperfections during the [2+4] cycloaddition to be detected without any ambiguity, even at the higher generations, since each unreacted ethynyl group Table 1 Summary of the molecular mass and the approximate diameter of the dendrimers.These diameters were estimated from molecular models generated using the CERIUS2 program number formula of mass/ benzene generation formula gmol-1 rings diameter/A° G0, 2 C20H10 250 2 7 G1, 3b C148H90 1868 22 21 Fig. 2 2D projection of G2 (without acetylene units). The distances G2, 4b C404H250 5104 62 38 and torsional angles used to determine intramolecular rotations and G3, 5b C916H570 11577 142 55 the overall shape of the dendrimer G2 are labelled. J. Mater. Chem., 1997, 7(7), 1207–1211 1209Table 2 Intramolecular distances and torsional angles (values obtained of the dendrimer during the whole simulation time.Therefore, by MD simulations,13 compare Fig. 2) used to determine intramolecu- the functional groups were exposed for further reaction and lar rotations and the overall shape of the dendrimer G2 had a well-defined chemical environment due to the shapepersistence of the dendrimer. distance/A° The next generation, G3, had an even higher packing density number (%) torsion angle/° of phenylene units.We expected the dierent branches of this 1 2.8±0.16 a 20–60 dendrimer to be even more correlated (details have yet to be (±5.3) revealed by further MD simulations) resulting in an even more 2 4.7±0.15 b1 115–140 shape-persistent 3D structure with a diameter of ca. 55 A° . (±3.2) 3 6.7±0.25 b2 -25–(-50) (±3.7) Summary and Outlook 4 17.1±1.3 (±7.3) Our innovative approach can be summarized as follows: 5 11.3±1.0 $ A simple synthetic process led quickly to nanosized mol- (±8.8) 6 7.4±0.6 ecules with well-defined size and shape.(±8.0) $ A new type of polyphenylene dendrimer based on penta- 7 8.0±1.0 phenylbenzene units was obtained. (±12.5) $ The synthesized materials were soluble in common organic 8 13.8±1.0 solvents and, therefore, were readily processable.(±7.2) $ It was possible to control the chemical functionalization 9 27.5±2.5 (±9.1) of the nanoparticles. 10 31.0±1.5 With respect to the last point, it should be mentioned that (±4.8) we are working on the functionalization of our dendrimers. A 11 34.2±1.7 straightforward approach would be afinal Diels–Alder reaction (±5.0) with tetraphenylcyclopentadienones carrying functional groups 12 35.8±2.2 such as MNR3+ (1b), MCN (1c), MOH (1d), MCOOH (1e) (±6.1) or M(CH2)nCH3 (1f ).Such groups are relevant for chemical, physical and potentially catalytic properties.14 Our approach uses charged as well as neutral lipophilic or hydrophilic and The observed distribution of distances had several reasons.hydrogen-bonding substituents. In addition, units which facili- There were three (approximately) independent motions: tate the covalent coupling of electronically active components vibration, rotation and bending of the oligophenylenes. In such as redox-systems (in particular viologen), dyes, NLO- order to distinguish between these motions we compared two phores or active metal complexes are attractive.The synthesis distance distributions: a distance sensitive to the rotations of of such species is the subject of our current investigations. interest and one with similar connectivity, but being insensitive to any rotation (for example, distances 2 and 3 or 6 and 7, Fig. 2). The dierence between both distributions was assumed Experimental to be due to independent rotations.Furthermore, the corre- Melting points are uncorrected. 1H NMR spectra were sponding torsional angles revealed that the rotations were recorded at 500 MHz on a Bruker DRX 500 spectrometer. (nearly) frozen or that they were correlated strongly. 13C NMR spectra were recorded on the same instrument at The calculations indicated the following qualitative picture 125 MHz. Chemical shifts are given in parts per million (ppm) for the internal rotations of the dendrimer: using the solvent signal as reference;15 J values are in Hz. Mass $ We observed a rotation of the central phenyl–phenyl unit spectral analyses were carried out on ZAB2-SE-FPD (VG (bond a) with the torsional angle varying by ±20° and Analytical) and Bruker Reflex-TOF.MALDI-TOF-MS spec- an average torsional angle of ca. 40°. The average torsional tra were measured using 1,8,9-trihydroxyanthracene as matrix. angle was not the one found during the energy minimiz- Compounds 1a and 2 were prepared from commercially avail- ation, instead a continuous change of the torsional angle able starting materials by methods to those already in of bond a was observed throughout the equilibration time literature.16–18 (distance 1, torsional angle of bond a).$ A rotation about bond b was observed (torsional angle Generation G1, 3a, 3b of bond b1 and b2 ), but this rotation was accompanied only by a small change in distance 3, thus indicating a To a degassed solution of 1a (3.27 g, 0.00440 mol) in a mixture of diphenyl ether–a-methylnaphthalene (3 ml/3 ml), 2 (55.0 mg, strongly correlated rotation of both branches of the dendrimer.The same results were obtained by comparing 0.220 mmol) in a-methylnaphthalene (2 ml) was added over 30 min at 180–200 °C under a stream of argon. After stirring distances 4 and 5. $ There was an (partially) independent rotation of the for 30 min at this temperature the mixture was allowed to cool.The cold reaction mixture was diluted with methanol pentaphenylbenzene units about the bonds c4 or d4 (comparison of the distances 6 and 7). (40 ml) and stirred overnight at 25°C. A crude red product was filtered. Contaminating 1a was removed either by reprecip- In spite of the aforementioned rotations, the overall shape of the molecule changed only slightly. The distances 8 to 12 itating from acetone with ethanol or by passage of the crude product through a short column of silica gel using light generated a network measuring the diameter of the dendrimer in several directions. All these distances changed by only ±5 petroleum–dichloromethane (351) as eluent.Yield: 0.611 g (0.196 mmol, 89%) white amorphous solid, mp 169–170°C. to 10% throughout the whole simulation time, thereby indicating that the dendrimer was a shape-persistent molecule.We MS m/z (FD): 3118 (M+, 100%), calc. for C220 H250 Si8 3119. Deprotection was achieved by adding tetrabutylammonium suppose that this behaviour was due to the high packing density of phenylene rings, which caused the strongly correlated fluoride (0.820 g, 3.14 mmol) to a stirred solution of 3a (0.611 g, 0.196 mmol) in THF (50 ml).After stirring for 5 h at 25°C, rotations within the molecule. Thus the shape-persistent dendrimer retained some flexibility which enhanced solubility in the THF was evaporated under reduced pressure to give a yellow solid, which was taken up in acetone. The resulting common solvents. In addition, the phenylene groups carrying the functional groups (acetylene units) in G2 were pointing out solution was added dropwise to ethanol (100 ml).The desired 1210 J. Mater. Chem., 1997, 7(7), 1207–1211product precipitated as white solid and was filtered. Foundation of the Chemical Industries (Fonds der Chemischen Industrie) for scholarships. Deprotection was nearly quantitative, mp>300°C, dH (500 MHz, CD2Cl2, 303 K): 7.25–7.21 (br, 12 H), 7.14–6.97 (br, 28 H), 6.88–6.68 (br, 38 H), 6.45–6.38 (br, 4 H), 3.03–3.00 References (br, 8 H).dC (125 MHz, CD2Cl2 , 303 K): 141.54, 141.49, 141.27, 1 J.-M. Lehn, Supramolecular Chemistry, Concepts and Perspectives, 141.11, 141.00, 140.67, 140.04, 139.31, 138.66, 132.11, 131.87, VCH, Weinheim, 1995. 131.84, 131.79, 131.18, 130.88, 130.31, 128.12, 127.64, 127.01, 2 F.Vo� gtle, Supramolekulare Chemie, Eine Einfu� hrung, 126.93, 126.50, 119.80, 119.50, 83.78, 77.43, 77.33. MS m/z B. G. Teubner, Stuttgart, 1992. (MALDI-TOF): 1907 in the presence of K, calc. for 3 Z. Xu and J. S. Moore, Angew. Chem., 1993, 105, 1394; Angew. C148H90K+, 1907. Chem., Int. Ed. Engl., 1993, 32, 1354; Z. Xu and J. S. Moore, Acta Polym., 1994, 45, 83. 4 S. B. Singh and H.Hart, J. Org. Chem., 1990, 55, 3412; K. Shahlai, Generation G2, 4a, 4b H. Hart and A. Bashir-Hashemi, J. Org. Chem., 1991, 56, 6812. Preparation of 4a and 4b was analogous to 3a and 3b except 5 A. Rajca, J. Org. Chem., 1991, 56, 2557; A. Rajca and for the reaction time of the [4+2] cycloaddition. Compound S. Utamapanya, J. Am. Chem. Soc., 1993, 115, 10688. 6 G. R. Newkome, C.N. Moorefield and F. Vo� gtle, Dendritic 3b was added over 5 h to the hot reaction mixture and the Molecules, VCH, Weinheim, 1996; J. M. J. Fre� chet and solution was allowed to stir for an additional 4 h. Yield: 87%, C. J. Hawker, in Comprehensive Polymer Science, 2nd. Suppl., ed. white amorphous solid, 4a, mp>300°C. MS m/z (MALDI- G. Allen, S. L. Aggarwal and S. Russo, Elsevier, Oxford, 1996, TOF): 7645 in the presence of K, calc.for C548H570Si16K+, pp. 70–129. 7645. 7 J. K. Young and J. S. Moore in Modern Acetylene Chemistry, ed. 4b, mp>300 °C, dH (500 MHz, CD2Cl2, 303 K): 7.46–6.45 P. J. Stang and F. Diederich, VCH,Weinheim, 1995, p. 415. 8 F. Morgenroth, E. Reuther and K. Mu�llen, Angew. Chem., 1997, (br, 388 H), 3.03–2.99 (br, 404 H). dC (125 MHz, CD2Cl2, 109, 647. 303 K): 142.22, 141.71, 141.66, 141.29, 141.22, 141.12, 140.41, 9 T. M. Miller and T. X. Neenan, Chem. Mater., 1990, 2, 346; 139.90, 139.48, 139.39, 138.95, 138.56, 131.90, 131.84, 131.43, T. M. Miller, T. X. Neenan, R. Zayas and H. E. Bair, J. Am. Chem. 131.30, 131.15, 130.86, 130.46, 130.22, 128.92, 128.60, 128.08, Soc., 1992, 114, 1018. 127.98, 127.37, 126.89, 126.27, 126.19, 121.31, 119.77, 119.46, 10 K.L. Walker, M. S. Kahr, C. L. Wilkins, Z. Xu and J. S. Moore, 102.69, 83.80, 77.39, 77.33. Am. Soc.Mass Spectrom., 1994, 5, 730. 11 Due to the limited accuracy of the integration, traces of side products due to incomplete [2+4] cycloaddition could not be detected Generation G3, 5a by 1H NMR spectroscopy, but appeared in the MALDI-TOF-MS as distinguished peaks. Compound 1a (1,87 g, 2.51 mmol) was taken up in a mixture 12 The molecular mechanics calculations were carried out using the of diphenylether–a-methylnaphthalene (8 ml/8 ml).The stirred MM2 (85) forcefield with the CERIUS2 program package and solution was degassed and heated to 180–200°C under argon. applying the Conjugate Gradient 200 algorithm. G1 and G2 were Then a degassed solution of 4b (80.0 mg, 0.0157 mmol) and 1a minimized by considering only one half of the molecule.In the case (1.17 g, 1.57 mmol) in a mixture of diphenyl ether–a-methyl- of G1, two torsional angles b1 and b2 (as shown in Fig. 2) were naphthalene (5 ml/5 ml) was added dropwise over 25 h under varied stepwise by 30°, whereas four torsional angles were varied in the case of G2 (as shown in Fig. 2) in 45° steps.In a second step, a stream of argon. After the addition was complete, the reaction two of those ‘half-molecules’ were connected and the torsional mixture was allowed to stir for an additional 15 h at 180 °C. angle of this newly created, central phenyl–phenyl bond was The cold reaction mixture was diluted with methanol (40 ml) optimised.and stirred overnight at 25°C. The crude red product was 13 NVT-molecular dynamics simulations were carried out at 300 K filtered and reprecipitated from acetone with ethanol. Yield: (temperature dumping, 0.1 ps relaxation time) with a time step of 210.9 mg (0.0127 mmol, 81%), white amorphous solid, 0.001 ps. For the evaluation of the molecular shape a simulation time of 35 ps was used after an initial equilibration time of 5 ps.mp>300 °C, dH (500 MHz, CD2Cl2, 303 K): 7.43–6.41 (br, Intramolecular distances were calculated by averaging the dis- 538 H), 1.21–0.99 (br, 672 H). dC (125 MHz, CD2Cl2, 303 K): tances measured for every tenth conformer, torsional angles were 142.21, 141.89, 141.50, 141.24, 141.12, 140.77, 140.40, 140.33, measured every ps. 140.04, 139.54, 139.46, 138.92, 138.65, 138.51, 138.21, 131.81, 14 R. Dagani, Chem. Eng. News, 1996, June 3, p. 30. 131.40, 131.20, 131.05, 130.78, 130.45, 130.22, 128.90, 128.59, 15 H. O. Kalinowski, S. Berger and S. Braun, 13C-NMR- 128.10, 127.96, 127.40, 127.23, 126.85, 126.24, 121.18, 120.88, Spektroskopie, Thieme, Stuttgart 1984, p. 74. 16 S. Takahashi, Y. Kuroyama, K. Sonogashira and N. Hagihara, 119.22, 107.30, 90.95, 90.86, 18.80, 18.45, 11.93, 11.71, 11.48. Synthesis, 1980, 627. MS m/z (MALDI-TOF): 16619 in the presence of K, calc. for 17 M. A. Ogliaruso, M. G. Romanelli and E. I. Becker, Chem. Rev., C1204H1210Si32K+, 16619. 1965, 65(3 ), 261; W. Broser, J. Reusch, H. Kurreck and P. Siegle, Chem. Ber., 1969, 102, 1715. Financial support by the Volkswagenstiftung and the 18 F. L. W. van Roosmalen, Recl. T rav. Chim. Pays-Bas, 1934, 53, 359. Bundesministerium fu�r Bildung und Forschung is gratefully acknowledged. C. K. and F. M. would also like to thank the 2D; Received 2nd January, 1997 J. Mater. Chem., 1997, 7(7), 1207–1211 1211

ISSN:0959-9428    

DOI:10.1039/a700032d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Self-assembly of hyperbranched spheres Wilhelm T. S. Huck, Frank C. J. M. van Veggel* and David N. Reinhoudt* L aboratory of Supramolecular Chemistry and T echnology, T wente University, P.O. Box 217, 7500 AE Enschede, T he Netherlands A new type of building block with two coordinatively unsaturated palladium centres has been described that self-assembles in nitromethane solution and disassembles when acetonitrile is added.The resulting hyperbranched, organopalladium spheres have a remarkably narrow size distribution as was evidenced by light-scattering, AFM and TEM measurements. Variation of the structure of the building blocks showed the possibility to vary the size of the self-assembled spheres between 100 and 400 nm. There is an ongoing demand for the development of nanosize tures have been synthesized and the resulting assemblies have been studied by quasi-elastic light scattering (QELS), atomic materials.Especially, the electronics industry is searching for force microscopy (AFM) and transmission electron microscopy nanosize architectures permitting increased processing speeds, (TEM). In this paper we present a general methodology to and higher levels of integration.Current nanophysical ‘enginsynthesize spherical particles in the range 100–400 nm. eering down’ approaches can routinely fabricate structures in the range of 0.1–0.2 mm. Alternatively, chemists exploit a ‘bottom up’ approach to synthesize nanosize devices with Experimental molecular precision. In this respect, synthetic organic chemistry Melting points were determined with a Reichert melting point oers a powerful and versatile tool for the synthesis of large apparatus and are uncorrected. 1H NMR and 13C NMR and complex molecules with a variety of functions and shapes. spectra were recorded in CDCl3 (unless indicated otherwise) However, the synthesis of very large molecules using only with Me4Si as internal standard on a Bruker AC 250 spec- covalent bonds is less practical.Non-covalent interactions can trometer. Mass spectra were recorded with a Finnigan MAT be exploited to connect building blocks in the construction of 90 spectrometer using m-nitrobenzyl alcohol as a matrix. THF much larger architectures. The rational use of non-covalent was freshly distilled from Na/benzophenone, hexane (referring interactions requires the understanding of the principles of to light petroleum with bp 60–80 °C) and CH2Cl2 fromK2CO3.self-assembly.1 Our current research aims at the development Nitromethane was washed with 1 M HCl and water and of new methods of self-assembly that will lead to large struc- distilled from CaCl2. NaH was a 50% dispersion in mineral tures.2 Dendrimers represent a class of polymers that combine oil and was used after washing with hexane.Other chemicals a high molecular mass with a well defined spherical shape of were of reagent grade and were used as received. Column nanometre dimensions. Sequential synthesis, either divergent3 chromatography was performed with silica gel 60H or convergent,4 can be used to grow dendrimers stepwise, (0.005–0.040 mm) from Merck.[Pd(MeCN)4 ][BF4]2,8 5- generation after generation. Alternatively, instead of using this hydroxyisophthalic acid dimethyl ester,9 and a,a¾,a-tribromo- laborious method a one-pot polymerization of suitable building mesitylene10 were prepared according to literature procedures. blocks yields less regular hyperbranched organic polymers. QELS was performed with a Malvern PCS 100 goniometer Recently, Fre� chet et al.used branched monomers that contain (Malvern Instruments, Malvern, England) at an angle of 90°, polymerizable groups at both ends, so-called AB2-type mon- with an Adlas Model DPY 305 II, 50 mW, continuous wave omers, that yield hyperbranched polymers with a relatively narrow size distribution and high molecular masses.5 Recently, several groups have used transition metals to build small metallodendrimers.6 Our approach is to design AB2-type building blocks for the self-assembly of hyperbranched coordination polymers.7 These building blocks should contain all information necessary to form well defined three-dimensional hyperbranched structures.In each building block 1, two kinetically inert Pd centres and one kinetically labile CH2CN ligand, are present.In a coordinating solvent, like MeCN, a solvent molecule is weakly coordinating to the fourth coordination site and hence the building blocks remain monomeric. Removal of this solvent and introduction of a non-coordinating solvent, such as MeNO2, initiates intermolecular coordination of the labile ligands. This means that a new building block is added to the starting nucleus generating two new sites for further growth.Schematically the self-assembly process is shown in Fig. 1. In a dendritic model, the centre of the self-assembled spheres will be less dense than the surface. Therefore, the size of the 1 building blocks should be related to the size of the assemblies Fig. 1 Schematic representation of the self-assembly of hyperbranched polymers formed.For this reason, building blocks with dierent struc- J. Mater. Chem., 1997, 7(7), 1213–1219 1213diode pumped YAG laser, wavelength 532 nm (Adlas, Lu�beck, layer was concentrated under reduced pressure. The TBDMS groups were then removed by dissolving the thioether in THF Germany), and an ALV 5000 multiple tau digital correlator (ALV, Langen, Germany).The correlation function was trans- (100 ml) and adding 1 equiv. of CsF (2.0 g, 0.013 mol). After stirring overnight at 50°C, THF was evaporated and the formed into a diameter distribution with the CONTIN program. The instrument used for atomic force microscopy (AFM) residue dissolved in dichloromethane followed by washing with brine, drying over MgSO4 and concentration in vacuo.Column was a Nanoscope III operating in constant force (ca. 50 nN) mode with cantilever force constants of 0.58 N m-1 and a chromatography (silica gel, eluent CH2Cl2) gave pincer ligand 6a as a colourless oil. Yield 3.38 g (77%); 1H NMR d, 7.29–7.16 home-made supertip. Samples for transmission electron microscopy (TEM) were prepared by slow evaporation of a (m, 10H, SPh), 6.79 (s, 1H, ArH), 6.64 (s, 2H, ArH), 4.89 (br s, 1H, OH), 4.00 (s, 4H, CH2S); 13C NMR d, 155.7, 139.5, nitromethane solution on a carbon-coated copper grid. 131.2, 129.9, 128.9, 128.6, 126.4, 121.8, 114.6, 38.7; EIMS m/z, 5-tert-Butyldimethylsilyloxyisophthalic acid dimethyl ester 3 338.078 (M+, calc. for C20H18OS2: 338.080). TBDMSiCl (16.0 g, 0.106 mol) was dissolved inCH2Cl2 (50 ml) 3,5-Bis(-1-naphthylthiamethyl)phenol 6b.White solid. Yield and was slowly added to a solution of 5-hydroxyisophthalic 76%, mp 75–77°C; 1H NMR d, 7.88–7.68 (m, 8H, Snaphthyl), acid dimethyl ester 2 (11.18 g, 0.053 mol), Et3N (6.99 g, 7.48–7.30 (m, 6H, Snaphthyl), 6.90 (s, 2H, ArH), 6.72 (s, 1H, 0.069 mol), and DMAP (catalytic amount) in CH2Cl2 (150 ml) ArH), 4.09 (s, 4H, CH2S) 13C NMR d, 155.8, 139.4, 133.7, at 0°C.After stirring overnight at room temperature, the 131.9, 128.4–125.8, 122.0, 114.8, 38.5; EIMS m/z, 438.402 (M+, mixture was washed with 1 M HCl, a saturated aqueous calc. for C28H22OS2 : 438.601). solution of NaHCO3, and brine. After drying (MgSO4), the solvent was evaporated and 3 was obtained as a white solid 3,5-Bis(tert-butylthiamethyl)phenol 6c.Colourless oil, solidi- upon drying under high vacuum. Yield 15.3 g (89%), mp fied slowly upon standing. Yield 47%, mp 80–82 °C; 1H NMR 68–70°C; 1H NMR d, 8.29 (s, 1H, ArH), 7.68 (s, 2H, ArH), d, 6.89 (s, 1H, ArH), 6.70 (s, 2H, ArH), 4.68 (bs, 1H, OH), 3.67 3.93 (s, 6H, OCH3), 1.00 (s, 9H, But), 0.23 (s, 6H, SiCH3); 13C (s, 4H, CH2S), 1.30 (s, 18H, CH3); 13C NMR d, 155.0, 140.5, NMR d, 166.1, 156.0, 131.8, 125.4, 123.7, 52.6, 25.6, 18.2, -4.5; 122.0, 114.5, 33.2, 30.9, 23.6; EIMS m/z, 298.142 (M+, calc.for FAB MS m/z, 324.1 (M+, calc. 324.1); Anal. Calc. for C16H26OS2 : 298.143). C16H24O5Si: C, 59.23; H, 7.46. Found: C, 59.55; H, 7.60%. 3,5-Bis(ethylthiamethyl)phenol 6d. Pale yellow oil. Yield 3,5-Bis(hydroxymethyl )phenol tert-butyldimethylsilther 4 23%; 1H NMR d, 6.83 (s, 1H, ArH), 6.69 (s, 2H, ArH), 5.21 LiAlH4 (4.8 g, 0.12 mol) was suspended in dry THF (200 ml) (br s, 1H, OH), 3.62 (s, 4H, CH2S), 2.44 (q, 4H, J 8.4 Hz, and a solution of diester 3 (20.0 g, 0.062 mol) in THF (100 ml) SCH2CH3), 1.23 (t, 6H, J 8.4 Hz, CH3); 13C NMR d, 155.8, was slowly added.The mixture was stirred overnight at room 140.5, 121.8, 114.4, 35.6, 25.6, 14.4; EIMS m/z, 242.080 (M+, temperature after which THF was evaporated.The resulting calc. for C12H18OS2 : 242.080). paste was dissolved in dichloromethane (200 ml) and cooled to 0°C and 2 M HCl (100 ml) was added, after which the layers a,a¾-Dibromo-a-cyanomesitylene 7. To a solution of a,a¾,a- were separated. Extraction of the aqueous layer with dichloro- tribromomesitylene (5.0 g, 0.014 mol) in MeCN (200 ml) were methane (3×100 ml) and drying of the combined organic added powdered KCN (0.91 g, 0.014 mol), 18-crown-6 (0.25 g, layers gave, after removal of the solvent, pure 4 as a white 0.95 mmol), and water (0.5 ml).The mixture was refluxed for solid. Yield 15.3 g (93%), mp 99–100 °C; 1H NMR d, 6.94 (s, 48 h after which the solvent was evaporated and the residue 1H, ArH), 6.77 (s, 2H, ArH), 4.62 (s, 4H, CH2O), 0.99 (s, 9H, was taken up in CH2Cl2 (100 ml). After washing with brine But), 0.20 (s, 6H, SiCH3); 13C NMR d, 156.0, 142.8, 118.1, 64.9, and drying over MgSO4 the crude reaction mixture was 25.7, 18.2, -4.4; FAB MS m/z, 268.0 (M+, calc. 268.1); Anal. concentrated in vacuo and purified by column chromatography Calc.for C14H24O3Si: C, 62.64; H, 9.01. Found: C, 62.59; (SiO2, eluent CH2Cl2). This yielded pure 7 as a colourless oil H, 9.19%. which solidified upon standing. Yield 0.85 g (20%), mp 67–69°C; 1H NMR d, 7.40 (s, 1H, ArH), 7.32 (s, 2H, ArH), 3,5-Bis(chloromethyl ) phenol tert-butyldimethylsilyl ether 5 4.47 (s, 4H, CH2Br), 3.72 (s, 2H, CH2CN); 13C NMR d, 139.6, 131.3, 129.3, 128.5, 117.3, 32.0, 23.4; EIMS m/z, 302.9 (M+, Diol 4 (4.0 g, 0.015 mol) and Et3N (6.2 g, 0.045 mol) were calc. 303.0); IR (KBr) 2252 cm-1 (CON); Anal. Calc. for dissolved in dry CHCl3 and cooled to 0°C. Mesityl chloride C10H9NBr2: C, 39.64; H, 2.99; N, 4.62. Found: C, 39.69; H, (MsCl) (3.44 g, 0.045 mol) was slowly added at 0°C after 2.94; N, 4.50%. which the reaction mixture was slowly heated to 50°C.Stirring overnight and subsequent washing with 1 M NaOH and 1 M General procedure for the synthesis of thioether ligands 8a–d HCl, drying over MgSO4 and evaporation of the solvent gave 5 as a colourless oil. Yield 4.2 g (92%); 1H NMR d, 6.80 (s, a,a¾-Bis[3,5-bis(phenylthiamethyl)phenyloxy]-a-cyano- 1H, ArH), 6.62 (s, 2H, ArH), 4.32 (s, 4H, CH2Cl), 0.78 (s, 9H, mesitylene 8a.Compound 6a (0.3 g, 0.75 mmol) was stirred But), 0.00 (s, 6H, SiCH3); 13C NMR d, 156.1, 139.2, 121.4, with K2CO3 (0.13 g, 0.94 mmol) in MeCN (50 ml) for 1 h at 118.9, 45.7, 26.6, 24.7, -3.5; EIMS m/z, 304.081 (M+, calc. for room temperature (r.t.). Spacer 7 (0.13 g, 0.38 mmol) was added C14H22SiCl2O: 304.081). and the reaction mixture was stirred for 4 days at r.t. The reaction was concentrated under reduced pressure and General procedure for the synthesis of thioethers 6a–d dichloromethane (50 ml) was added to the residue.The organic layer was washed with brine, dried over MgSO4 and concen- 3,5-Bis(phenylthiamethyl)phenol 6a. Thiophenol (5.77 g, 0.052 mol) was added to a stirred suspension of NaH (2.52 g, trated. Column chromatography (silica gel, CH2Cl2–hexanes 80520) gave pure 8a as a colourless oil.Yield 0.26 g (72%); 0.104 mol) in THF (200 ml) and the mixture was stirred for 1 h to allow formation of the sodium thiophenolate salt. To 1H NMR d, 7.31 (s, 1H, ArCNH), 7.29–7.16 (m, 22H, SPh+ArCNH), 6.85 (s, 2H, ArOH), 6.79 (s, 4H, ArOH), 4.94 (s, the resulting milky solution dichloride 5 (4.0 g, 0.013 mol) was added and the reaction mixture was stirred overnight at 50°C. 4H, CH2O), 4.03 (s, 8H, CH2S), 3.73 (s, 2H, CH2CN); 13C NMR d, 158.6, 139.3, 138.4, 136.1, 130.7, 129.9, 128.9, 126.4, After removal of the solvent the crude reaction mixture was dissolved in dichloromethane (200 ml) and washed with brine 126.0, 122.2, 117.6, 114.0, 69.2, 38.9, 23.5; EIMS m/z, 817.216 (M+, calc. for C50H43NO2S4 : 817.218); IR (KBr) 2251 cm-1 (100 ml).To remove excess of thiol the organic layer was washed with 2 M NaOH (100 ml). After drying, the organic (CON). 1214 J. Mater. Chem., 1997, 7(7), 1213–1219a,a¾-Bis[3,5-bis(1-naphthylthiamethyl)phenyloxy]-a-cyano- 0.14 g (20%), mp 131–132 °C; 1H NMR d, 7.38 (s, 1H, ArCNH), 7.32 (s, 2H, ArCNH), 6.68 (s, 4H, ArPdH), 4.97 (s, 4H, CH2O), mesitylene 8b.Colourless oil. Yield 70%; 1H NMR d, 7.80–7.59 (m, 16H, Snaphthyl), 7.47–7.32 (m, 12H, Snaphthyl), 7.30 (s, 4.10 (br s, 8H, CH2S), 3.81 (s, 2H, CH2CN), 1.69 (s, 36H, But); 13C NMR d, 156.2, 150.6, 138.5, 130.8, 126.5, 117.6, 108.4, 69.5, 1H, ArCNH), 7.21 (s, 2H, ArCNH), 6.95 (s, 2H, ArOH), 6.75 (s, 4H, ArOH), 4.74 (s, 4H, CH2O), 4.12 (s, 8H, CH2S), 3.62 (s, 52.0, 42.7, 30.6, 23.6; FAB MS m/z 984.3 [(M-Cl)+, calc. 983.6]; Anal. Calc. for C50H41NO2S4Pd2Cl2·H2O: C, 46.97; H, 2H, CH2CN); 13C NMR d, 158.7, 139.2, 138.3, 133.6, 131.9, 130.5, 128.8, 128.0, 127.8, 127.7, 126.5, 126.3, 125.9, 125.8, 122.3, 5.36; N, 1.38. Found: C, 47.58; H, 5.36; N, 1.38%. 114.2, 69.2, 38.8; EIMS m/z, 1017.280 (M+, calc. for C66H51NO2S4: 1017.280). Bis (PdMCl) complex 9d.Brownish solid. Yield 16%, mp 106–107 °C; 1H NMR d, 7.39 (s, 1H, ArCNH), 7.36 (s, 2H, a,a¾-Bis[3,5-bis(tert-butylthiamethyl)phenyloxy]-a-cyano- ArCNH), 6.68 (s, 4H, ArPdH), 4.98 (s, 4H, CH2O), 4.2 (br s, 8H, mesitylene 8c. Slightly yellow oil. Yield 25%. 1H NMR d, 7.46 CH2S), 3.81 (s, 2H, CH2CN), 3.19 (q, 8H, J 8.4 Hz, SCH2CH3 ), (s, 1H, ArCNH), 7.37 (s, 2H, ArCNH), 6.96 (s, 2H, ArOH), 6.85 1.67 (t, 12H, J 8.4 Hz, CH3); FAB MS m/z 871.8 [(M-Cl)+, (s, 4H, ArOH), 5.08 (s, 4H, CH2O), 3.80 (s, 2H, CH2CN), 3.71 calc. 871.3]. Anal. Calc. for C34H41NO2S4Pd2Cl2·0.5C6H14: C, (s, 4H, CH2S), 1.33 (s, 36H, CH3); 13C NMR d, 158.7, 140.4, 46.74; H, 5.09; N, 1.47. Found: C, 46.33; H, 4.96; N, 1.66%. 138.6, 130.6, 126.4, 122.5, 113.9, 69.3, 42.9, 33.4, 30.9, 23.6; EIMS m/z, 737.339 (M+, calc.for C42H59NO2S4: 737.343). Results and Discussion a,a¾-Bis[3,5-bis(ethylthiamethyl)phenyloxy]-a-cyano- Synthesis of building blocks mesitylene 8d. Colourless oil. Yield 48%; 1H NMR d, 7.47 (s, A convergent synthesis route has been exploited to connect 1H, ArCNH), 7.37 (s, 2H, ArCNH), 6.88 (s, 2H, ArOH), 6.85 (s, two pincer ligands to a spacer containing the kinetically labile 4H, ArOH), 5.06 (s, 4H, CH2O), 3.77 (s, 2H, CH2CN), 3.67 (s, (cyano) ligand.Key intermediates 6 were synthesized in six 8H, CH2S), 2.44 (q, 8H, J 8.4 Hz, SCH2CH3 ), 1.22 (t, 12H, J steps from 5-hydroxyisophthalic acid as shown in Scheme 1. 8.4 Hz, CH3); 13C NMR d, 158.7, 141.3, 138.5, 130.7, 127.8, The first step is the esterification of 5-hydroxyisophthalic acid 126.1, 122.2, 120.7, 117.6, 113.7, 69.2, 53.5, 37.5, 25.4, 23.5, 14.4; according to literature procedures.8 The phenolic group was FAB MS m/z, 625.620 (M+, calc.for C34H43NO2S4: 625.959). protected with TBDMSiCl in 95% yield and subsequently the esters were reduced with LiAlH4 to the diol 4 in 70% yield. General procedure for the cyclopalladation of the pincer ligands The diol was stirred overnight with MsCl–Et3N at 50°C which 8a–d and conversion into the chloride complexes 9a,b and d gave complete conversion into the dichloride 5.The thioether Bis(PdMCl ) complex 9a. Ligand 8a (0.50 g, 0.62 mmol) was functions were introduced by stirring the appropriate thiol dissolved in acetonitrile (150 ml) and placed under an Ar with NaH in THF to generate the sodium thiolate, and atmosphere.Solid [Pd(MeCN)4 ][BF4 ]27 (0.54 g, 1.22 mmol) subsequent addition of the dichloride 5. This reaction yielded was added in one portion. The orange solution was warmed the SCS pincer ligands with the p-hydroxy functions protected. to 40°C and stirred until the colour changed to pale yellow. The TBDMSi ether was deprotected with CsF to give the SCS After cooling to r.t.and evaporation of the solvent the yellow pincer type ligand 6 in 10% overall yield from 5-hydroxyisoph- cyclopalladated product was obtained in quantitative yield. thalic acid. The thioethers 6 were coupled to spacer 7 which This product was dissolved in CH2Cl2–MeCN (351, 100 ml) introduces the weakly coordinating cyano group. The spacer and the reaction mixture was stirred vigorously for 30 min 7 was prepared from a,a¾,a-tribromomesitylene by refluxing with brine (100 ml).The layers were separated and the organic in acetonitrile for two days with powdered KCN. From the layer was washed with water (100 ml) and evaporated to resulting mixture 7 could be isolated in 20% yield. The dryness. Purification by column chromatography (silica gel, formation of the benzylic ethers proceeded in rather poor CH2Cl2–MeOH, 9555) gave 9a as a yellow solid (1.18 g, 50%), yields because 7 slowly decomposed.Ligands 8a–d were cyclo- mp 132–133 °C; 1H NMR d, 7.81–7.74 (m, 8H, SPh), 7.39 (s, palladated with [Pd(MeCN)4][BF4]2 in acetonitrile in high 1H, ArCNH), 7.35–7.29 (m, 14H, SPh+ArCNH), 6.64 (s, 4H, yields. Prior to self-assembly studies, the cationic solvento ArPdH), 4.95 (s, 4H, CH2O), 4.5 (bs, 8H, CH2S), 3.76 (s, 2H, complexes were converted into chloropalladium complexes by CH2CN); 13C NMR d, 156.4, 152.3, 150.2, 138.4, 132.3, 131.4, stirring a solution in CH2Cl2 and MeCN with brine.This 130.9, 129.8, 129.7, 126.6, 126.0, 117.7, 109.2, 69.5, 51.7, 23.6; made purification easier and allowed the simple introduction FAB MS m/z, 1064.3 [(M-Cl)+, calc. 1064.3]; IR (KBr), of various non-coordinating anions (vide infra). The tert-butyl 2252 cm-1 (CON). Anal. Calc. for C50H41NO2S4Pd2Cl2·H2O: derivative 9c was prepared by stirring the cationic palladium C, 53.72; H, 3.88; N, 1.25. Found: C, 53.65; H, 3.73; N, 1.64%. complex from 8c with NMe4Cl, as reaction with brine only gave intractable polymeric products.Bis(PdMCl ) complex 9b. Orange solid. Yield 56%, mp The 1H NMR spectra of 9a–d in CD3CN show a broad 160–162 °C; 1H NMR d, 8.30 (s, 4H, Snaphthyl), 7.94–7.76 (m, singlet for the CH2SR protons at d 4.6 because of the slow 16H, Snaphthyl), 7.52–7.49 (m, 8H, Snaphthyl), 7.40 (s, 1H, conformational interconversion of the palladium(II)-containing ArCNH), 7.34 (s, 2H, ArCNH), 6.67 (s, 4H, ArPdH), 4.99 (s, 4H, five-membered rings.11 The signal for the protons ortho to CH2O), 4.63 (br s, 8H, CH2S), 3.76 (s, 2H, CH2CN); 13C both donor atoms in 9a–d at d 6.85 is absent, indicating NMR d, 157.2, 150.3, 138.4, 133.4, 133.2, 131.2, 129.7, 129.3, complete cyclopalladation.The 1H NMR spectrum clearly 128.2, 127.8, 127.6, 127.1, 109.2, 69.5, 52.4, 23.1; FAB MS showed that no cyclopalladation had occurred at other m/z 1264.3 ([M-Cl]+, calc. 1264.6). Anal. Calc. for aromatic positions. C66H49NO2S4Pd2Cl2 ·2H2O: C, 59.33; H, 3.99; N, 1.05; S, 9.60. Self-assembly takes place when the CH2CN group of one Found: C, 58.93; H, 3.73; N, 1.18; S, 9.46%. building block coordinates intermolecularly to the Pd centre of another. Therefore the Pd centres were first activated by Bis(PdMCl ) complex 9c.The cyclopalladation of ligand 8c the replacement of the chloride by dierent non-coordinating (0.50 g, 0.68 mmol) was performed as described for 9a. The anions. Addition of one equivalent of the appropriate silver crude palladium complex was dissolved in CH2Cl2–MeCN salt activates the Pd centre by precipitation of AgCl in a fast (151, 50 ml) and excess NMe4Cl (0.50 g, 4.57 mmol) was added and quantitative reaction.† In acetonitrile solution a bis- in one portion.The reaction mixture was stirred overnight. After removal of the salts, the filtrate was evaporated to dryness. Purification by column chromatography (silica gel, † This has been demonstrated using 31P NMR spectroscopy in an analogous PCP pincer complex; unpublished results.CH2Cl2–MeOH, 9555) gave 9c as a brownish solid. Yield J. Mater. Chem., 1997, 7(7), 1213–1219 1215Scheme 1 Scheme 2 X-=BF4-, ClO4-, PF6-, triflate, tosylate, BPh4- acetonitrile complex·2X- (X-=BF4-, ClO4-, PF6-, triflate, indicating large structures. When small amounts of acetonitrile were added to these solutions all signals became sharp. This tosylate or BPh4-) is formed (Scheme 2).proves that the self-assembly of 1a–d and disassembly of the hyperbranched polymer is a reversible process. In order to Self-assembly and characterization obtain information on the size and shape the resulting assembl- The self-assembly process of 1a–d was initiated by elimination ies were further characterized by QELS, TEM and AFM.‡ of the acetonitrile ligands.After removal of the acetonitrile QELS measurements of nitromethane solutions of assemblies (the 1H NMR spectrum in CD3NO2 showed no acetonitrile), of 1a (X-=BF4-) showed particles with an average hydrody- the CH2CN groups of the bis-palladium complexes occupy the namic diameter of 180 nm using the CONTIN curve-fitting fourth coordination site. In the IR spectrum the coordination of the cyano group was confirmed by the characteristic shift of the CON stretch vibration from 2250 cm-1 for the mon- ‡ Gel permeation chromatography (GPC) was not successful.Probably omeric building blocks to 2290 cm-1 upon coordination.12 the highly charged assemblies have a strong interaction with the column material and are therefore dicult to characterize using GPC.The 1HNMRspectra of 1a–d showed broad peaks in CD3NO2, 1216 J. Mater. Chem., 1997, 7(7), 1213–1219aggregates than expected, but this might be explained by solvent or water coordination to the anion even inside the spheres, making the apparent size of this anion larger. Increasing the thioether bulk from ethyl to phenyl groups (X-=tosylate) gave smaller aggregates.The naphthyl thioether building blocks showed a similar trend as the phenyl thioethers. The larger naphthyl groups gave smaller spheres in all cases. The combination of naphthyl thioethers with triflate anions formed rather small aggregates. The general conclusion from these data is that larger anions and/or thioether groups give smaller assemblies. The size of the aggregates was also measured by contact 400 300 200 100 0 25 125 225 320 – – – anion volume/Å3 diameter/nm Fig. 2 Relationship between the sphere size and monomer or anion mode AFM. Samples were prepared by evaporation of a volume as measured by light-scattering (+, Et; *, Ph; l, But; nitromethane solution of self-assembled spheres 1a–d on a $, naphthyl) clean gold surface. A representative part of these surfaces is shown in Fig. 3(a)–( f ). In all cases, large, spherical objects Fig. 3 AFM pictures of self-assembled spheres of (a) 9a (X-=BF4-); (b) 9b (X-=BF4-); (c) 9b (X-=OTf-); (d) 9d (X-=BF4-); (e) 9a (X-=Tos); ( f ) 9a (X-=PF6-) program. This size is independent of the sample concentration were observed that correspond quite well with the dimensions determined by light-scattering.The average diameter for indicating that these are single particles and no clusters. From the peak width a standard deviation of approximately 30 nm assemblies of 1a (X-=BF4-), as found by the grain size analysis routine of the instrument software of these aggregates was estimated. By changing the anion from ClO4- to BPh4- the size of the spheres as measured by QELS decreased from is 205 nm, with a standard deviation of 30 nm.The aggregates seem to have a disc-like shape when studied with AFM. The 400 to 180 nm in diameter (Fig. 2). The sizes of the anions were calculated using the Connoly flattening might be caused by spreading of the spheres on the surface or by interaction of the sample with the AFM tip. Surfaces option implemented in the Cerius2 program package. 13 This gave arbitrary volumes which should be used only Repetitive scans of one spot ‘wiped’ the surface clean, which indicates that the organic material has a soft constitution. in a relative sense. The BF4- anion gave much smaller J. Mater. Chem., 1997, 7(7), 1213–1219 1217When a glass substrate was used instead of gold, the same A linear, non-branched palladium(II) complex containing one pincer complex and one cyanomethyl group was treated spheres were observed of roughly the same size.This indicates that the possible interaction of sulfur atoms in the building according to the same self-assembly procedures but AFM and TEM measurements did not show globular structures. This blocks and the gold surface did not significantly alter the morphology of the spheres.Grazing-angle FTIR spectroscopy supports our concept in which branching is essential. Indications for a dendritic structure, which results in a dense on a gold surface covered with the spheres showed the characteristic CON signal of coordinated cyano groups at 2289 cm-1 outer sphere, came from additional disassembly experiments. Light-scattering experiments show that when ca. 20 equiv. of in agreement with the bulk spectra. From AFM data sizes of 160 (±20) nm for 1b (X-=BF4-) and 110(±20) nm for 1b acetonitrile per building block are added to a nitromethane solution of the spheres, they slowly disassemble in the course (X-=OTf-) were measured respectively [Fig. 3(b) and (c)]. This is in good agreement with the QELS data (140 and of 10–15 min.The slow rate of disassembly indicates that acetonitrile cannot easily penetrate the outer shell of building 104 nm, respectively). In the case of 1a (X-=Tos) and 1a (X-=PF6-) extensive clustering made size determination blocks. When a larger nitrile like benzonitrile is used, disassembly is hardly observed, even after heating to 70°C unreliable [Fig. 3(e)–( f )]. The samples for TEM were used without additional shading for 15 min.Dendrimers with a similar dense shell with a solid-phase character have been reported by Meijer and or staining and the contrast results from the Pd centres that are distributed throughout the spherical assembly. In all pic- co-workers.15 The explanation for the formation of rather well defined tures, the only structures that could be observed had spherical shapes in the expected size range.Fig. 4(a) and (b) clearly show spheres and the relationship between the size of the spheres and the structure of the monomers and the non-coordinating globular aggregates in the range 150–200 nm for 1a and 1c (both with BF4- counter anions). This is in good agreement anions, remains speculative. In our dendritic model the anions will occupy the voids created by the branching of the mon- with the diameter measured with QELS.Fig. 4(a) shows globular structures with a light shell and a little darker nucleus. omers. When these cavities become too small the anions are forced out of the sphere and will occupy the surface, thereby This indicates that the structures are a little thicker in the middle than at the edges, as expected for spherical assemblies.blocking the assembly process. The size at which this occurs, is apparently dependent on both the bulk of the bis-palladium Energy dispersive X-ray spectrometry (EDX) revealed the presence of the elements Pd and S in these aggregates. The complexes as well as the size of the anion. TEM image for 1a (X-=Tos) shows assemblies of ca. 225 nm [Fig. 4(c)], which is also in good agreement with QELS data Conclusions (220 nm). As shown in Fig. 4(d), strong clustering is observed for 1d (X-=BF4-). By dividing the radius of the spheres by Building blocks that contain all information necessary for self- the size of the building blocks we estimate a number of roughly assembly give regular assemblies with a (relatively) small 50 ‘generations’.The outer layer of Pd complexes is not polydispersity. The self-assembled structures are held together occupied by MeCN ligands, as these are not observed in the via coordinative bonds. Introduction of bulky groups in the 1H NMR spectrum. Probably, water present in nitromethane building blocks and/or dierent sizes of non-coordinating is coordinating to these Pd centres.14 counter anions influences the outcome of the self-assembly process.In this way spherical assemblies are obtained ranging from 100 to 400 nm in diameter. We are grateful to Dr. E. G. Keim (Center for Materials Research, University of Twente) for TEM measurements and Dr. J. W. Th. Lichtenbelt (Akzo Nobel Central Research) for assistance with QELS measurements.We thank the Dutch Foundation for Chemical Research (SON) for financial support. References 1 D. Philp and J. F. Stoddart, Angew. Chem., Int. Ed. Engl., 1996, 35, 1155. 2 R. H. Vreekamp, J. P. M. van Duynhoven, M. Hubert, W. Verboom and D. N. Reinhoudt, Angew. Chem., Int. Ed. Engl., 1996, 35, 1215; W. T. S. Huck, F. C. J. M. van Veggel and D. N. Reinhoudt, Angew. Chem., Int. Ed.Engl., 1996, 35, 1213. 3 D. A. Tomalia, A. Naylor and W. A. Goddard III, Angew. Chem., Int. Ed. Engl., 1990, 29, 138. 4 C. J. Hawker and J. M. J. Fre� chet, J. Am. Chem. Soc., 1990, 112, 7638. 5 J.M.J.Fre�chet, M. Henmi, I. Gitsov, S. Aoshima, M. R. Leduc and R. B. Grubbs, Science, 1995, 269, 1080. 6 S. Campagna, G. Denti, S. Serroni, A. Juris, M. Venturi, V. Ricevuto and V. Balzani, Chem. Eur. J., 1995, 1, 211; S. Achar and R. J. Puddephatt, Angew. Chem., Int. Ed. Engl., 1994, 33, 847. 7 W. T. S. Huck, F. C. J. M. van Veggel, B. L. Kropman, D. H. A. Blank, E. G. Keim, M. M. A. Smithers and D. N. Reinhoudt, J. Am. Chem. Soc., 1995, 117, 8293; W. T. S. Huck, B. H. M. Snellink-Rue�l, J. W. Th. Lichtenbelt, F. C. J. M. van Veggel and D. N. Reinhoudt, Chem. Commun., 1997, 9. 8 A. Sen and L. Ta-Wang, J. Am. Chem. Soc., 1981, 103, 4627. 9 A. H. van Oijen, N. P. M. Huck, J. A. W. Kruijtzer, C. Erkelens, Fig. 4 TEM pictures of (a) 9a (X-=BF4-); (b) 9c (X-=BF4-); J. H. van Boom and R. J. M. Liskamp, J. Org. Chem., 1994, 59, 2399. (c) 9a (X-=Tos); (d) 9d (X-=BF4-) (bar represents 100 nm) 1218 J. Mater. Chem., 1997, 7(7), 1213–121910 F. Vo� gtle, M. Zuber and R. Lichtenhaler, Chem. Ber., 1973, 106, and H. J. C. Ubbels, J. Am. Chem. Soc., 1982, 104, 6609. 15 J. F. G. A. Jansen, E. M. M. de Brabander-van den Berg and 717. 11 A. J. Canty and N. J. Minchin, J. Chem. Soc., Dalton T rans., 1987, E. W. Meijer, Science, 1994, 266, 1226. 1477. 12 B. N. Storho and H. C. Lewis, Coord. Chem. Rev., 1977, 23, 1. Paper 6/08577F; Received 23rd December, 1996 13 Cerius2, Molecular Simulations Inc,Waltham, MA. 14 D. M. Grove, G. van Koten, J. N. Louwen, J. G. Noltes, A. L. Spek J. Mater. Chem., 1997, 7(7), 1213–1

ISSN:0959-9428    

DOI:10.1039/a608577f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

SANS investigation of self-assembling dendrimers in organic solvents Pappannan Thiyagarajan,a* Fanwen Zeng,b C. Y. Kua and Steven C. Zimmermanb* aIPNS, Argonne National L aboratory, Argonne, IL 60439, USA bDepartment of Chemistry, University of Illinois, Urbana, IL 61801, USA The self-assembly behaviour of tetraacids 1a–c and tetraester 4 in CDCl3 and [2H8]tetrahydrofuran {[2H8 ]THF} has been investigated by the small-angle neutron scattering (SANS) technique.The experimental SANS data were compared with simulated scattering data derived from structural models proposed previously for the aggregates. These studies suggest that dendritic monomers 1b,c self-assemble into cyclic hexameric aggregates, whereas 1a forms a large tubular aggregate in CDCl3. Further study on 1c in CDCl3 as a function of concentration suggests that the cyclic hexameric aggregates strongly interact with each other at higher concentrations.The control compound 4 was shown to be monomeric in both solvents. There is significant current interest in organic compounds that information on supramolecular assemblies in their native state in aqueous solution7 and their interparticle interactions.8b form stable, discrete aggregates in solution.1 These aggregates may have a particular function or they may serve as synthetic intermediates for the construction of larger, covalently linked nano- or meso-structures.In this regard, hydrogen-bond Materials and Methods mediated self-assembly is a powerful approach because the Materials directionality of hydrogen bonding allows control over the aggregate structure, while its strength in apolar solvents pro- The synthesis and characterization of compounds 1a–c and 4 vides a considerable enthalpic driving force to overcome the were described previously3 and material was available from disfavourable entropy of aggregation.One successful approach the prior studies. [2H1 ]Chloroform and [2H8]tetrahydrofuran, to forming discrete aggregates is to target closed assemblies, purchased from Cambridge Isotope Laboratory, were used such as those formed in cyclic arrays of monomers. An added directly.benefit of the cyclic aggregation approach is the cooperativity which often manifests itself in highly stable and discrete selfassembled structures. SANS measurements One of the continuing unsolved challenges in this area is to SANS experiments of compounds 1a–c and 4 were performed characterize the aggregate structure in solution.Because there in CDCl3. The self-assembly behaviour of compounds 1c and is no single method for unambiguously determining the number 4 was also investigated in [2H8]THF to study the eect of density and structure of aggregates present, the characteriz- this solvent, which is more competitive toward hydrogen- ation is often based on a combination of several indirect bonding interactions.The corresponding solution was injected methods.2 The commonly used techniques are size-exclusion into a Suprasil cylindrical cell with a 2 mm pathlength chromatography (SEC), 1H NMR spectroscopy, vapour press- (volume=0.7 ml).SANS data were collected at the Intense ure osmometry (VPO), UV–VIS and IR spectroscopy, and Pulsed Neutron Source of Argonne National Laboratory, sometimes mass spectrometry. We recently reported that using the time-of-flight SANS instrument, Small Angle Neutron dendritic tetraacids 1b,c self-assemble into cyclic hexamer 2, Diractometer (SAND).9a This instrument uses pulsed neu- whereas 1a forms a series of linear aggregates such as 3 trons derived from spallation with wavelengths in the range (Fig. 1).3 Hexamer 2, whose structure was supported by SEC, 0.5–14 A° and a fixed sample-to-detector distance of 2 m.The VPO, and comparison with a covalently linked model, is the scattered neutrons are measured using a 128×128 array of largest known discrete abiotic aggregate formed by weak position sensitive, gas filled, 40×40 cm2, proportional counters interactions.4 Herein, we report the use of small-angle neutron with the wavelengths measured by time-of-flight through scattering (SANS) technique to characterize the self-assembly binning the pulse to 68 constant Dt/t=0.05 time channels.The behaviour of 1a–c and test the previously proposed models.size range in a SANS experiment depends on the range of SANS and small-angle X-ray scattering (SAXS) are direct momentum transfer Q [see eqn. (2)] which is determined by techniques which can yield unique information about the the geometry of the instrument and the range of wavelengths structure and interactions of macromolecules with sizes in the of the neutrons.Given the characteristics of the SAND at the range of 10 to 1000 A° . A distinguishing feature of neutron Intense Pulsed Neutron Source (IPNS), useful SANS data in scattering compared to X-ray scattering is that neutrons inter- the Q range 0.0035–0.8 A° -1 can be obtained in a single act with atomic nuclei, while X-rays interact with the electron measurement. The data for each sample is corrected for the clouds of the atoms.This property renders neutron scattering backgrounds from the instrument, the Suprasil cell, and the very sensitive to dierent isotopes, such as proton and deu- solvent as well as for detector non-linearity.9b Data are terium whose coherent lengths are quite dierent.5 SANS is presented on absolute scale by using the known scattering one of the highly applied neutron scattering techniques for the cross-section of a silica gel sample.characterization of macromolecules and several reviews dealing with the application of this technique for biological systems have been published.6 This technique allows extraction of form Small-angle neutron scattering factors, which are descriptions of macromolecular size and shape, and particle–particle structure factors in solutions.The dierential scattering cross-section I (Q) measured as a function of momentum transfer Q by SANS is a convolution SANS has also been demonstrated to provide structural J. Mater. Chem., 1997, 7(7), 1221–1226 1221Fig. 1 (a) Dendritic tetraacids 1a–c and the proposed cyclic hexameric aggregate 2 and linear aggregate 3, (b) tetraester 4 1222 J.Mater. Chem., 1997, 7(7), 1221–1226of two terms, namely, intraparticle correlations P(Q) and concentration dependent eects, such as aggregation, it is possible to obtain the true Rg of the particle by the linear interparticle correlations S(Q). extrapolation of measured Rg values at several concentrations. I(Q)=nP(Q)S(Q) (1)The magnitude of the slope of the curve (second virial coecient) in the apparent Rg vs.concentration plot yields In eqn. (1), n is the number of particles per unit volume and qualitative information on the interparticle interactions. Q=4pl-1 sin h (2) In the case of polydisperse systems, the Rg and I (0) values are respectively the Z-averaged and mass-averaged quantities. where l is the wavelength of neutrons and 2h is the scat- For example, the Z-averaged Rg value is defined as tering angle.The intraparticle structure factor P(Q) is defined as Rg2 =. NiMi2(Rg2)i . NiMi2 (7) P(Q)=T.i,j bibj exp[iQ(ri-rj )]U (3) where Ni and Mi and (Rg)i are the number density, molecular mass, and radius of gyration of the aggregates of type i, and the interparticle structure factor respectively.The shape of the scattering particles can be analysed by S(Q)=1 NT.N i=1 .N j=1 exp[iQ(Ri-Rj)]U (4) fitting the scattering pattern in the whole Q range by either using the analytical functions for the form factors of dierent In eqn. (3), ri and rj are the position vectors of the atoms in a geometrical objects,11 or by calculating the scattering pattern particle and bi and bj are the scattering lengths5 of atoms i using a suitable molecular model, as was done for proteins and j and the braces indicate that averaging for all orientations using eqn.(3).10 The molecular models of compounds 1a–c of the particles is taken. In general, the scattering power of an and 4 and their possible aggregate structures were constructed atom depends on the isotope.5 Eqn.(3) can be used to calculate with the Macromodel program12 on a Silicon Graphics workthe scattering from the particle, if atomic coordinates are station. Because of the limitations on the number of atoms available. In eqn. (4), Ri and Rj are the position vectors of the used, the dendrimer substituents and the tetraacid core unit particle centres and N is the total number of particles.were minimized separately and then covalently linked. Each In the case of dilute solutions the particles are far apart and structure was first minimized using molecular mechanics:MM2 S(Q) in the low Q region will oscillate around unity and hence force field with the Polak–Ribier conjugate gradient method I(Q) is predominantly due to P(Q). The I (Q) data can be of optimization.These minimized structures were then further readily analysed to obtain the correct size, shape and molecular minimized by molecular dynamics with automatic set-up parmass of the particle. At higher concentrations where the ameters of 300 K, initial temperature, 10 ps run with a 15 fs excluded volume eects become significant the size and molecu- timestep using SHAKE and zero momentum.lar mass parameters derived from the low-Q region become The atomic coordinates of the structures derived from the lower in values. This is due to the increased eect of S(Q) on modelling studies were used to calculate the scattering patterns. I(Q) and one has to decompose I(Q) to obtain the P(Q) and It is important to state that we used only the atomic coordi- S(Q) terms prior to analysis.This step, however, requires nates of the molecular models for calculating the scattering information on the size and morphology of the particles as curves, but did not use the neutron scattering cross-sections well as the interaction potentials. Under these conditions it of individual atoms. What this means is that the shape of the is possible to obtain the surface potentials of the colloidal scattering curve for a given system is appropriate, but the objects.8 scaling is not.We arbitrarily scaled the calculated scattering data and compared the shapes with the experimental data to test the validity of the proposed models. In the case of 10.6 mM Analysis of SANS data CDCl3 solution of 1a none of the aggregate models generated At the low-Q region, the experimental scattering intensity I(Q) by the Macromodel program could explain the measured vs.Q data can be used to obtain size information by using scattering data (discussed later) and hence modelling using the eqn. (5)11 which is an approximation of eqn. (1) in the low- form factor for a hollow cylinder was used. The form factor of Q region. a cylindrical shape particle with or without a hollow inner portion (tube vs.rod) can be written as I (Q)=I(0) exp(-Q2Rg2/3) (5) where A(Q)=2 sin(QaL /2) QaL /2 GAJ1(QcRo) QcRo B-ARi RoB2AJ1(QcRi) QcRi BH I(0)=n(rp-rs)2 V 2 (6) (8) In eqn. (6), rp and rs are the scattering length densities (r= where L is the length of the cylinder, Ro is the outer radius of S bi/V ) of the particles and the solvents, V is the volume of the cylinder, Ri is the inner radius of the cylinder, Qa is the the particle, and bi is the scattering length of individual atoms.component of Q in the axial direction, Qc is the component of The radius of gyration, Rg is the root-mean-squared distances Q in the cross-section plane, and J1 is the first-order Bessel of all of the atoms to the centroid of the scattering volume of function of the first kind.The orientationally averaged particle the particle. This parameter is shape independent and one structure factor used to fit is needs to know the shape of the particle in order to derive sizes in terms of the familiar physical dimensions. For example, for P(Q)=V 2 4p P1 -1 dm P2p 0 dw|A(Q)|2 (9) a sphere with a radius of R, Rg2=0.6R2 and for an ellipsoid, Rg2=(a2+d2+c2)/5 where a, d, c are the semiaxes of an where V=pRo2L .ellipsoid. The value of Rg is obtained from the absolute value of the slope (k) of a line in the natural log of I (Q) vs. Q2 plot (Guinier plot)11 in the Q region where QRg#1.0, as Rg2=3k. Results and Discussion In dilute solutions where the interparticle interactions are either nonexistent or minimal, this value will represent the true Fig. 2 shows the measured SANS data for 1c in CDCl3 at three concentrations. Each curve is superimposed by the size of the particle. However, in the presence of interparticle interactions the value of Rg will be smaller and this value has calculated SANS data from the coordinates generated for the cyclic hexamer 2 (see Fig. 1) proposed for this system.It is to be denoted as apparent value. In the absence of any other J. Mater. Chem., 1997, 7(7), 1221–1226 1223Fig. 2 Experimental SANS data for 1c in CDCl3 at three concentrations: (a) 12mgml-1, (b) 24mgml-1 and (c) 50mgml-1. The Fig. 3 Corresponding Guinier plots for the data in Fig. 2. The Guinier calculated scattering pattern (—) from the coordinates generated for plots for the calculated curves (+) are shown in each case.The value the cyclic hexamer model proposed for this system is superimposed of the slopes in the experimental data (—) decreases with increasing on the experimental data. concentration; all of them are smaller than that for the calculated data. clearly demonstrated that the calculated and measured data agree reasonably well for a solution with a concentration of 3.8 mM (12 mg ml-1) [Fig. 2(a)] and the agreement becomes poorer with increasing concentration. The actual disagreement is in the low-Q region of the high concentration sample which suggests the presence of interparticle interactions between these hexamer aggregates in CDCl3. The interparticle eects can be seen better in the corresponding Guinier plots (Fig. 3) which exhibit decreasing slopes (decrease of apparent Rg values) with increasing concentration, when compared to the calculated data for the cyclic hexamer. The calculated SANS data for the cyclic hexamer yields an Rg of 33.6 A° , while the apparent Rg values for the measured samples with a monomer concentration of 3.8 mM (12 mg ml-1), 7.6 mM (24 mg ml-1) and 15.7 mM (50 mg ml-1) are 30.4, 28.9 and 23.7 A° , respectively. Fig. 4 shows the linear dependence of apparent Rg as a function of concentration. The Rg value at infinite dilution from Fig. 4 is 33.1 A° which agrees quite well with the expected value of 33.6 A° on the basis of the proposed model. Thus the cyclic hexamer model (see Fig. 1) proposed for 1c in CDCl3 is consistent with the SANS results.However, it is noteworthy Fig. 4 Apparent Rg values as a function of concentration for 1c in to mention that SANS also suggests the presence of concen- CDCl3. The linearity implies that the particles are intact but interact tration-dependent interactions between these aggregates at the strongly. The extrapolated Rg value at infinite dilution agrees well with the Rg value calculated for the cyclic hexamer.high concentration range investigated here. 1224 J. Mater. Chem., 1997, 7(7), 1221–1226Fig. 6 Experimental SANS data for 16 mg ml-1 4 in [2H8 ]THF ($) and in CDCl3 (#). The lines are the calculated scattering patterns for the monomer. The dierent scaling between these data sets is due to the dierence in contrast provided by the solvent for the scattering from the monomer.[2H8]THF is due to dierent contrasts [see eqn. (6)] provided by the dierent scattering length densities of the solvents CDCl3 (3.16×1010 cm-2) and [2H8]THF (6.36×1010 cm-2). It is evident that the contrast for neutron scattering from these particles is higher in [2H8]THF when compared to that in CDCl3 as seen from the low signal intensity and large error bars for the latter, even though both samples used similar beam times. Tetraacids 1 with second- and first-generation dendritic substituents were also investigated.Experimental SANS data for an 8.5 mM solution of 1b in CDCl3 along with the calculated data derived from a cyclic hexameric aggregate are shown in Fig. 5 (a) Experimental SANS data of a 6.3 mM solution of 1c in Fig. 7. The experimental Rg of 27.1±1 A° agrees quite well with [2H8]THF ($) along with the calculated data for a monomer (%). that from the calculated data (Rg=28.6 A° ). The shapes of the (b) Guinier plots for the data in (a). scattering patterns also agree well in the whole Q region thus validating the correctness of the proposed model for this system. When 1c is dissolved in [2H8]THF the aggregation proper- Previous SEC dilution study in methylene chloride showed ties change.The I(Q) data and the corresponding Guinier that the aggregation of tetraacid 1a is concentration dependent. curves for a solution of 1c in [2H8 ]THF at a concentration of This behaviour, as well as the broadness of the SEC peak, 8.2 mM are shown in Fig. 5. Compound 1c was proposed to suggested that 1a forms a series of linear aggregates.Molecular exist as a monomer in this media as THF competes with the modelling studies suggested that this preference resulted from hydrogen-bonding contacts thus preventing aggregate forma- the small size of the first-generation dendritic substituent which tion. The measured I (Q) data for this is compared with the could be accommodated in the linear aggregate structure calculated SANS data for a monomer.The Rg value of 13.5 A° (Fig. 1). Non-specific aggregation was also observed in the for the calculated SANS curve agrees reasonably well with the SANS studies which suggest the formation of large and polydis- experimental Rg value of 14.6±1 A° obtained from the middle- perse aggregates in a 10.6 mM CDCl3 solution of 1a (Fig. 8). Q region of the data. Also the data in the high-Q region for This Fig. shows the measured SANS data and calculated form both the experimental and the calculated data for a monomer factors for linear aggregates with 8 and 20 monomers. The agree quite well. However, in the low-Q region, the two data Guinier plot for the measured data has at least two dierent sets do not agree.Interestingly, the low-Q region of the experimental data exhibits a power law [I(Q)#Q-1.8 ] which points to extremely large structures resembling mass fractals.13 Nevertheless this unusual SANS curvature in the low-Q region is not reproducible. For example, in a dierent run, the experimental SANS data fit to the calculated value for a dimeric structure.The dierences between runs may originate from a slow disassembly process of the hexameric aggregate.14 To demonstrate the appropriateness of the SANS technique for examining this class of macromolecules, as well as to probe the eect of solvent on conformation, tetraester 4 was investigated in both CDCl3 and [2H8]THF. Tetraester 4, a close analogue of 1c, was shown previously to exist as a monomer in both solvents due to the absence of hydrogen-bonding sites.3 The SANS data collected for 4 in CDCl3 and [2H8]THF at a concentration of 8.0 mM are shown in Fig. 6. These results validate the monomer model proposed for this system (see Fig. 1). Thus, these data show that the experimental scattering Fig. 7 SANS data for 1b in CDCl3 (#) along with the calculated data patterns are identical to the calculated ones for the monomer.for a cyclic hexamer. The data agree quite well, validating the proposed model. The large dierence in the scaling of data for 4 in CDCl3 and J. Mater. Chem., 1997, 7(7), 1221–1226 1225models and compared with the measured scattering data. This oers a direct way to compare the validity of the models and thus increase our understanding of these systems.The SANS studies provide strong support for the cyclic hexamer model previously proposed for 1b,c in CDCl3. SANS further suggests a concentration dependent interaction between these hexameric aggregates. The ester analogue 4 was studied in both THF and CDCl3 and found to exist as a monomer, as expected. Compound 1a seems to form large and non-discrete aggregates.However, the previously proposed linear aggregate model could not explain the experimental data rather the aggregate may have a thin, hollow, cylindrical structure. This work was supported by the US Department of Energy, Oce of Basic Energy Sciences, Division of Material Sciences, under Contract W-31-109-Eng-38 to IPNS. S.C.Z. gratefully acknowledges support from the National Institutes of Health (GM39782).F. Z. thanks the University of Illinois Department of Chemistry for a fellowship. We gratefully acknowledge the technical support provided by D. G. Wozniak at IPNS. References 1 (a) J-M. Lehn, Angew. Chem., Int. Ed. Engl., 1990, 29, 1304; (b) J. S. Lindsey, New J. Chem., 1991, 15, 153; (c) D. S. Lawrence, T. Jiang and M. Levett, Chem. Rev., 1995, 95, 2229; (d) J.F. Stoddart and D. Philp, Angew Chem., Int. Ed. Engl., 1996, 35, 1154. 2 (a) J. P. Mathias, E. E. Simanek and G. M. Whitesides, J. Am. Chem. Soc., 1994, 116, 4326; (b) G. M. Whitesides, E. E. Simanek, J. P. Mathias, C. T. Seto, D. N. Chin, M. Mammen and D. M. Gordon, Acc. Chem. Res., 1995, 28, 37; (c) N. Branda, Fig. 8 (a) SANS data for 1a in CDCl3 (#) along with the calculated R.Wyler and J. Rebek Jr., Science, 1994, 263, 1267; (d) M. R. scattering patterns for a linear aggregate with 8 monomers (,) and Ghadiri, J. R. Granja, R. A. Milligan, D. E. McRee and with 20 monomers (—). The scattering pattern has a secondary peak N. Khazanovich, Nature (L ondon), 1993, 366, 324; (e) E. E. Schrier, which indicates a more ordered structure.The linear aggregate model J. Chem. Educ., 1968, 45, 176. does not explain the data well. (b) Guinier plots for the data in (a). 3 S. C. Zimmerman, F. Zeng, D. E. C. Reichert and S. V. Kolotuchin, Experimental data (#), Rg=137±35 A° (—), Rg=36±5 A° (,); calcu- Science, 1996, 271, 1095. lated data for linear aggregates with 8 monomers ($) and with 20 4 S. C. Zimmerman, Curr.Opin. Colloid Interfac. Sci., in press. monomers (+). The experimental data indicate the presence of 5 G. E. Bacon, Neutron Diraction, Oxford University Press, polydispersity as at least two dierent linear regions are seen. Melbourne, 3rd edn., 1975. 6 (a) B. Jacrot, Rep. Prog. Phys., 1976, 39, 911; (b) H. B. Stuhrmann linear regions corresponding to Rg values of 36±5 and and A.Miller, J. Appl. Crystallogr., 1978, 11, 325; (c) L. A. Feigin and D. I. Svergun, Structure Analysis by Small Angle X-Ray and 137±35 A° . On the other hand, the Rg values for the calculated Neutron Scattering, Plenum, New York, 1987. data for the linear aggregates of 8 and 20 monomers, respect- 7 (a) B. Jacrot, Comp. V irol., 1981, 17, 129; (b) P. Thiyagarajan and ively, are 24.6 and 50.6 A° .The scattering patterns for linear D. M. Tiede, J. Phys. Chem., 1994, 98, 10 343; (c) R. P. Hjelm Jr., aggregates with dierent polymer indices were calculated, but P. Thiyagarajan and H. A. Alkan, J. Phys. Chem., 1992, 96, 8653. none of them could fit the secondary peak at Q=0.12 A° -1 in 8 (a) S. H. Chen, Annu. Rev. Phys. Chem., 1986, 37, 351; the experimental data.The best fit of the scattering data was (b) D. S. Jayasuriya, N. Tcheurekdjian, C. F. Wu, S. H. Chen and P. Thiyagarajan, J. Appl. Crystallogr., 1988, 21, 843. however accomplished by using eqn. (9) for a hollow cylindrical 9 (a) R. K. Crawford, P. Thiyagarajan, J. E. Epperson, F. Trouw, aggregate with an outer radius of 31 A° , inner radius of 26–28 A° R. Kleb, D. Wozniak and D.Leach, Proc. 13th International and a length of 49 A° . It is not obvious how 1a can form such Collaboration on Advanced Neutron Sources, Switzerland, Oct a structure, except perhaps an open helical assembly formed 11–14, 1995, PSI-Proc, 1996, 95–02, 99–117; (b) P. Thiyagarajan, from an extremely flat and extended monomer. Further SANS J. E. Epperson, R. K. Crawford, J. M. Carpenter, T. E. Klippert and molecular modelling studies are needed to elucidate the and D. G. Wozniak, J. Appl. Crystallogr., 1997, 30, in press. 10 P. Thiyagarajan, S. J. Henderson and A. Joachimiak, Structure, exact aggregate structure for compound 1a. 1996, 4, 79. 11 A. Guinier andG. Fournet, Small Angle Scattering of X-Rays, John Wiley & Sons, New York, 1955. Conclusions 12 W. C. Still, Macromodel 3.5a, Columbia University, New York, Hydrogen-bond mediated self-assembling dendrimers have 1992. been studied by a variety of techniques and structural models 13 (a) J. Feder, Fractals, Plenum, New York, 1988; (b) T. Freltoft, J. K. Kjems and S. K. Sinha, Phys. Rev. B, 1986, 33, 269; have been proposed based on the results of SEC, NMR and (c) P. McMahon and I. Snook, J. Chem. Phys., 1996, 105, 2223. VPO studies. Small-angle neutron scattering (SANS) was 14 F. Zeng and S. C. Zimmerman, unpublished work. shown to be a direct and powerful technique for studying these systems in dierent solvents. Scattering data were calculated Paper 7/00581D; Received 24th January, 1997 from the atomic coordinates generated from the proposed 1226 J. Mater. Chem., 1997, 7(7), 1221–1226

ISSN:0959-9428    

DOI:10.1039/a700581d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Polynuclear metal complexes of nanometre size. A versatile synthetic strategy leading to luminescent and redox-active dendrimers made of an osmium(II )-based core and ruthenium(II )-based units in the branches Scolastica Serroni,*a Alberto Juris,*b Margherita Venturi,*b Sebastiano Campagna,a Immaculada Resino Resino,b† Gianfranco Denti,c Alberto Credib and Vincenzo Balzanib aDipartimento di Chimica Inorganica, Chimica Analitica e Chimica Fisica, Universita` diMessina—98166 V illaggio S.Agata,Messina, Italy bDipartimento di Chimica ‘G. Ciamician’, Universita` di Bologna—40126 Bologna, Italy cIstituto di Chimica Agraria, Universita` di Pisa—56124 Pisa, Italy A docosanuclear metal complex of nanometric size and dendritic shape made of an osmium(II)-based core and containing 21 ruthenium(II)-based units in the branches has been prepared.The key building blocks are the [Os(2,3-dpp)3]2+ ‘complex ligand’, and the [Ru(2,3-Medpp)2Cl2 ]2+ and [{Ru(bpy)2(m-2,3-dpp)}2RuCl2]4+ ‘complex metals’ {2,3-dpp=2,3-bis(2-pyridyl)pyrazine; 2,3-Medpp+=2-[2-(1-methylpyridiniumyl)]-3-(2-pyridyl)pyrazine; bpy=2,2¾-bipyridine}. The first step of the synthesis is the formation of the tetranuclear [Os{(m-2,3-dpp)Ru(2,3-Medpp)2 }3]14+ species in which the peripheral ligands 2,3-Medpp+ are 2,3- dpp ligands with the second chelating site inactivated (protected) by methylation.This species is obtained from the reaction of the [Os(2,3-dpp)3]2+ ‘complex ligand’ core, which contains three open chelating positions, with three equivalents of the [Ru(2,3- Medpp)2Cl2]2+ ‘complex metal’, where the labile Cl- ligands can be replaced by the chelating units of the core.Successive demethylation (deprotection) of the tetranuclear compound opens the six peripheral chelating sites. At this stage, the divergent synthesis can be iterated {reaction with six equivalents of the [Ru(2,3-Medpp)2Cl2]2+ ‘complex metal’} with formation of the protected decanuclear compound [Os{(m-2,3-dpp)Ru[(m-2,3-dpp)Ru(2,3-Medpp)2]2}3]32+.Alternatively, in a convergent approach, the reaction of the deprotected tetranuclear species with six equivalents of the trinuclear [{Ru(bpy)2(m-2,3- dpp)}2RuCl2 ]4+ ‘complex metal’ leads to the docosanuclear [Os{(m-2,3-dpp)Ru[(m-2,3-dpp)Ru{(m-2,3-dpp)Ru(bpy)2}2]2}3 ]44+ species. The absorption spectra, luminescence properties, and electrochemical behaviour of [Os(2,3-dpp)3]2+, [Os(m-2,3- dpp)3{Ru(2,3-Medpp)2}3]14+, [Os{(m-2,3-dpp)Ru[(m-2,3-dpp)Ru(2,3-Medpp)2]2}3 ]32+, and [Os{(m-2,3-dpp)Ru[(m-2,3- dpp)Ru{(m-2,3-dpp)Ru(bpy)2}2]2}3]44+ have been investigated.complexes as ligand’ syntheticstrategy is that one can introduce Miniaturization of components for the construction of useful devices is currently pursued by a ‘large-downward’ approach.the desired building block at each stage of the synthesis. We have taken advantage of this flexibility to build up a new This approach, however, which leads physicists to deal with progressively smaller molecular aggregates, becomes dicult docosanuclear dendrimer which contains an osmium(II) core and three branches, each one containing 7 ruthenium(II) units. or even impossible when the size of the miniaturized component has to be in the dimension of nanometres.The metals and ligands used to build up our compounds are shown in Fig. 1 together with their graphic symbols and Chemists can construct nanometre-size species by a ‘smallupward’ approach starting with molecular components. This abbreviations.Fig. 2 shows the schematic representations of relevant compounds dealt with in this paper. The abbreviations approach is very appealing since it allows the assembly of functionally integrated molecular building blocks to obtain indicate the type and number of metal atoms contained in the compound, and the nature of the peripheral ligands (d= molecular-level devices.1 Assembly of molecular components into large and functional deprotected 2,3-dpp ligands; p=protected 2,3-dpp ligands; t=terminal monochelating ligands).arrays (supramolecular species) can be based on a variety of intermolecular forces such as hydrogen bonds, donor–acceptor interactions, stacking interactions, or on coordination and covalent bonds.2 When the molecular building blocks contain Results and Discussion transition metals, a strategy called ‘complexes as metal/com- Synthetic strategies plexes as ligand’ can allow the construction of large polynuclear metal complexes via metal–ligand coordination bonds.3,4 In Dendrimers can be constructed by two dierent approaches.7 the last few years we have synthesized a variety of polynuclear One approach, called divergent or ‘inside out’, starts with an transition-metal complexes having dendrimer type structure initial core containing n reactive sites.To this core (zero- and exhibiting interesting photophysical and electrochemical generation of the dendrimer), n units (building blocks) can be properties.5 The largest metal-based dendrimer reported by connected. This process aords the first generation of the our group contains 22 RuII centres.6 The interest in these dendrimer.If the peripheral units of the dendrimer so obtained species is not only related to their size, but also to the presence still contain reactive sites, the process can be iterated, yielding of chemically dierent units since each unit introduces into the a second-generation dendrimer, and so on.For example, if the supramolecular structure its own ‘pieces of information’ (in chosen core and each building block both contain three the form of specific properties such as excited states, redox chelating reactive sites (as is the case of our compounds, see levels, etc.). One of the advantages of the ‘complexes as metal/ later), the peripheral reactive sites will progress as follows: 3 (zero generation); 6 (first generation); 12 (second generation); 24 (third generation), etc.† Present address: Departamento de Quimica Inorganica, Facultad de Quimicas—08028 Barcelona, Spain. An alternative strategy is the convergent (or ‘outside in’) J. Mater. Chem., 1997, 7(7), 1227–1236 1227The divergent iterative approach requires the availability of a bifunctional species.In dealing with coordination compounds, such species have to be complexes capable of behaving both as a ligand and as a metal. A simple example is the compound Ru(2,3-dpp)2Cl2, shown in Fig. 4. Unfortunately, a species like this is unavoidably self-reactive because the free chelating sites of one molecule would substitute the labile ligands of another molecule, leading to a mixture of dispersed and uncontrolled nuclearities.Thus, in order to carry on a Fig. 1 Metals, ligands, and abbreviations used divergent synthesis, potentially bifunctional species, where one of the two functions is temporarily blocked, have to be used. construction of the dendrimer, whereby preformed branched This is the case of the preparation of the complex metal arms are attached to a more or less large core.[Ru(2,3-Medpp)2Cl2]2+,6b obtained by using the ‘protected’ The ‘complexes as metal/complexes as ligand’ synthetic ligand 2,3-Medpp+,4b where one of the two chelating sites is strategy3,4 can be exploited both for the divergent and the methylated. The protection is stable in the reaction conditions convergent approaches. Such a strategy is based on the use, used when [Ru(2,3-Medpp)2Cl2]2+ acts as a complex metal.as building blocks, of metal complexes that possess free chelat- Subsequent demethylation of the product restores the presence ing sites and metal complexes containing labile ligands (Fig. 3). of free chelating sites, i.e. its complex ligand ability. An itera- The complexes with free chelating sites play the role of ligands tive, divergent synthesis is therefore possible, as shown in (‘complex ligands’), and those with labile ligands play the role Fig. 5. of metals (‘complex metals’). The reaction of complex ligands It should also be emphasized that each deprotected comwith complex metals in the appropriate stoichiometric ratio pound of the divergent approach can be used as a ligand core in a convergent process with complex metals to yield dendri- then leads to complexes of higher nuclearity (Fig. 3). Fig. 2 Schematic representation of the compounds used for and/or obtained by our synthetic strategy. The graphic symbols used to represent metals and ligands are explained in Fig. 1. In the label used to designate each compound, the number indicates the nuclearity (number of metal ions), the letter indicates the type of the peripheral ligands (d, deprotected bridging ligand; p, protected bridging ligand; t, terminal monochelating ligand). 1228 J. Mater. Chem., 1997, 7(7), 1227–1236Fig. 3 Schematic representation of the reaction between the mononuclear Os-d complex metal and the mononuclear Cl2Ru-t complex ligand to give the tetranuclear OsRu3-t complex.Arrows indicate free chelating sites of Os-d and labile ligands of Cl2Ru-t. mers of higher generation (Fig. 5).8 Such a strategy has been previously used to obtain homonuclear ruthenium(II) dendrimers containing up to 22 metal centres.6 As mentioned in the introductory section, the interest in highly branched polynuclear metal complexes, and more generally in dendritic species, is related to the ‘small upward’ construction of nanometre-size species.In this field, an important goal is the design and construction of dendrimers containing units of dierent chemical nature. An ordered array of dierent components can in fact generate valuable properties, such as the presence of cavities having dierent sizes, surfaces with specific functions, gradients for photoinduced directional energy and electron transfer, and sites for multi-electron transfer catalysis (Fig. 6). The divergent and convergent synthetic strategies shown in Fig. 5 allow a step-by-step control of the growing process, so that building blocks containing dierent metals and/or ligands can be introduced at each step. In this work, we have used an [Os(2,3-dpp)3]2+ core and [Ru(2,3-Medpp)2Cl2]2+ units in a divergent approach to prepare [Os{(m-2,3-dpp)Ru(2,3- Medpp)2}3]14+ and [Os{(m-2,3-dpp)Ru(2,3-dpp)2 }3]8+ (tetranuclear dendrimers of the first generation) and then [Os{(m- 2,3-dpp)Ru[(m-2,3-dpp)Ru(2,3-Medpp)2]2}3 ]32+ and [Os{(m- 2,3-dpp)Ru[(m-2,3-dpp)Ru(2,3-dpp)2]2}3]20+ (decanuclear dendrimers of the second generation).Moreover the tetranuclear [Os{(m-2,3-dpp)Ru(2,3-dpp)2}3]8+ core and the trinuclear [{Ru(bpy)2(m-2,3-dpp)}2RuCl2]4+ units have been used in a convergent approach to obtain the docosanuclear [Os{(m-2,3- dpp)Ru[(m-2,3-dpp)Ru{(m-2,3-dpp)Ru(bpy)2}2]2}3]44+ (third generation) dendrimer.To our knowledge, the docosanuclear compound is the first mixed-metal third-generation dendrimer Fig. 4 Bifunctional self-reactive Ru(2,3-dpp)2Cl2 complex and its prepared so far.protected [Ru(2,3-Medpp)2Cl2]2+ form A further extension of this strategy towards the synthesis of J. Mater. Chem., 1997, 7(7), 1227–1236 1229Fig. 5 Divergent and convergent synthetic approaches for the preparation of dendrimers based on transition metal complexes. The symbols used are explained in Fig. 1. dendrimers containing units of dierent chemical nature can can exist as dierent isomers, depending on the fac or mer arrangement of the ligands around each metal centre.be based on the use, in the convergent approach, of branches Furthermore, since each metal centre is a stereogenic centre, containing metals and/or ligands dierent from those present the preparation of polymetallic complexes necessarily leads to in the core.Besides [{Ru(bpy)2(m-2,3-dpp)}2RuCl2]4+,4 intermixtures of several diastereoisomeric species. For these reasons esting examples of trinuclear complex metal branches structural investigations on these systems are dicult. are [{Ru(biq)2(m-2,3-dpp)}2RuCl2]4+,8c,f [{Ru(bpy)2(m- Dierences in the electrochemical and spectroscopic properties 2,5-dpp)}2RuCl2]4+,4 [{Os(bpy)2(m-2,3-dpp)}2RuCl2]4+,4b,8f arising from the presence of isomeric species are not expected [{Os(bpy)2(m-2,3-dpp)}2OsCl2 ]4+,9 [{Ru(bpy)2 (m-2,3-dpp)}2 to be large.10 OsCl2]4+.9 The species with high nuclearity exhibit a three-dimensional branching structure.Therefore, endo- and exo-receptor proper- General properties ties7,11 can be expected (Fig. 6). The largest of our dendrimers The compounds reported in this paper are soluble in common contains 22 metal atoms, 21 bridging ligands, 24 peripheral solvents (e.g., water, acetone and acetonitrile) and are stable ligands, and has an approximate size of 5 nm.We would like to stress that our dendrimers dier from most of those prepared both in the dark and under light excitation. In principle, they 1230 J.Mater. Chem., 1997, 7(7), 1227–1236two metal centres, as evidenced by its reduction potential that becomes more positive by about 0.4 V.6 Since the methylation of 2,3-dpp mainly concerns one of the pyridine rings, the electron donor and acceptor properties of the chelating site are only slightly aected; on the other hand a new easily reducible centre (the methylated pyridine ring) becomes present, 22 that is likely to contain the LUMO orbital of the complex.In the dendritic species each metal-based unit will bring its own excited state and redox properties. It should be pointed out, however, that these properties are aected by intercomponent interaction (vide infra). From the above considerations, it follows that the energy order of the lowest excited states for the metal-based units relevant for our discussion (see later) is: [Os(m-2,3-dpp)3]2+<[(m-2,3-dpp)Ru(bpy)2]2+<[Ru(m-2,3- dpp)3]2+<[(m-2,3-dpp)Ru(2,3-Medpp)2]4+. Absorption and emission properties Fig. 7 shows the absorption spectra of OsRu21-t and of the lower nuclearity OsRu9-t and OsRu3-t analogues. The spectra of the corresponding homonuclear Ru22-t, Ru10-t, and Ru4-t complexes6b are shown in Fig. 8. In Fig. 9 the spectra of the protected OsRu3-p and OsRu9-p dendrimers are displayed. Absorption and emission data are collected in Table 1. As one can see, all the compounds exhibit intense ligand-centred (LC) bands in the UV region and moderately intense metal-to- Fig. 6 Schematic representation of a docosanuclear dendrimer.Some ligand charge transfer (MLCT) bands in the visible. To a first properties are indicated. approximation, each metal-based unit carries its own absorption properties in the polynuclear species, so that the molar so far for two fundamental reasons: (i) each metal-containing absorption coecients are proportional to the nuclearity unit exhibits valuable intrinsic properties such as absorption of visible (solar) light, luminescence, and oxidation and reduction levels at accessible potentials;12 (ii) by a suitable choice of the building blocks, they can incorporate many ‘pieces of information’ and therefore they can be used to perform valuable functions such as light harvesting, directional energy transfer, and exchange of a controlled number of electrons at a certain potential.13,‡ Previous investigations carried out on mono- and polynuclear compounds of the ruthenium(II) and osmium(II) polypyridine family6,8,15,16 have shown that: (i) oxidation is metal centred; (ii) OsII is oxidized at potentials considerably less positive than RuII; (iii) the electron donor power decreases in the ligand series bpy>2,3-dpp>2,3-Medpp+m-2,3-dpp; (iv) the interaction between equivalent metal centres is noticeable for metals coordinated to the same bridging ligand, whereas it is negligible for metals that are further apart; (v) the interaction between equivalent ligands is noticeable for ligands Fig. 7 Absorption spectra of (a) OsRu3-t, (b) OsRu9-t, and (c) coordinated to the same metal, whereas it is negligible for OsRu21-t in acetonitrile solution at room temperature.Inset shows ligands that are further apart. their emission spectra under the same experimental conditions. In the ruthenium(II) and osmium(II) polypyridine complexes luminescence originates from the lowest MLCT excited state which is formally spin forbidden.12,17 Deactivation of the upper excited states to the lowest one is a very fast (picosecond timescale)18 and highly ecient (100%)19 process.In the ‘localized molecular orbital’ approach,20 the excited electron and the corresponding hole are considered to be centred on the ligand and on the metal, respectively. The ligands involved in our dendrimers exhibit dierent electron donor and electron acceptor properties. The electrochemical6,8b, 21 and luminescent6,8b behaviour of the complexes of the [Ru(bpy)n(2,3-dpp)3-n]2+ family indicates that bpy is a better electron donor ligand than 2,3-dpp, and that monochelated 2,3-dpp is easier to reduce than coordinated bpy.When 2,3-dpp plays the role of a bis-chelating bridging ligand, its electron donor power toward a single metal decreases because the pyrazine ring is involved in the coordination of Fig. 8 Absorption spectra of (a) Ru4-t, (b) Ru10-t, and (c) Ru22-t in acetonitrile solution at room temperature.Inset shows their emission ‡ Dendrimers made of dierent organic chromophores have been recently reported by Moore and coworkers.14 spectra under the same experimental conditions. J. Mater. Chem., 1997, 7(7), 1227–1236 1231other (at higher energy) due to the peripheral [(m-2,3- dpp)Ru(bpy)2]2+ units.8f This can be rationalized on the basis of the energy level diagram of Fig. 10(a). The lowest energy excited state is localized on the [Os(m-2,3-dpp)3]2+ core, and the energy of the peripheral [(m-2,3-dpp)Ru(bpy)2]2+ units is lower than that of the intermediate [Ru(m-2,3-dpp)3]2+ units. Therefore energy transfer from the peripheral units to the central one is at least in part prevented.For OsRu21-t, a stronger contribution from ruthenium-based units is apparent (Fig. 7, inset). This is consistent with (i) a larger number of ruthenium-based units and (ii) the presence of intermediate ruthenium-based units having higher energy than the peripheral ones as in OsRu9-t. In the homonuclear ruthenium-based t-type dendrimers, luminescence occurs almost at the same wavelength (Fig. 8, inset) and exhibits comparable lifetimes and quantum yields Fig. 9 Absorption spectra of (a) OsRu3-p and (b) OsRu9-p in regardless of nuclearity. This is an expected result because in acetonitrile solution at room temperature. Inset shows their emission all cases the lowest energy excited states are localized on the spectra under the same experimental conditions.peripheral [(m-2,3-dpp)Ru(bpy)2]2+ units and there is a gradient for energy transfer from the centre to the periphery Table 1 Spectroscopic and photophysical dataa [Fig. 10(b)].6,8f The emission properties of the p-type family can be inter- absorptionb luminescence preted on the basis of the discussion above. lmax/nm (e/dm3 mol-1 cm-1 ) lmaxc/nm td/ns Wemd/103 Electrochemical properties Os-de 476 (18 000), 300 (27 800) 765 82 — The electrochemical behaviour has been studied in argon- OsRu3-pf 526(sh) (34 500), 454 (45 000) 832 445g 6.5 purged MeCN solution at room temperature.The polynuclear OsRu3-th 551 (40 000), 283 (144 000) 875 18 1.0 complexes contain a large number of redox-active units, and Ru4-ti 545 (46 000), 285 (149 000) 811 60 1.0 OsRu9-p 459 (118 000), 298 (460 000) 700 380 4.1 it is known from previous investigations on analogous com- OsRu9-tj 550 (117 000), 283 (358 000) 808 65 ca.0.5 plexes6,8,12,21 that each metal centre can undergo a one-electron Ru10-tj 541 (125 000), 282 (329 000) 809 55 1.0 oxidation and each ligand can undergo at least one reduction OsRu21-t 547 (213 000), 284 (801 000) 805 200 0.85 process.The half-wave potential values are gathered in Table 2. Ru22-tk 542 (202 000), 284 (682 000) 786 45 0.30 Oxidation. The polynuclear complexes examined here con- aAcetonitrile solution, 298 K. bLowest energy band in the visible and prominent absorption maximum in theUV region. cCorrected emission tain one osmium-based core and several ruthenium-based maxima.dDeaerated solution, unless otherwise noted. eSee also units. In all cases, the observed oxidation processes are revers- ref. 8(a), 15 and K. Kalyanasundaram and Md. K. Nazeeruddin, Chem. ible and, as expected,6,8,12 oxidation of the osmium-based unit Phys. L ett., 1989, 158, 45. fFor preliminary data, see V. Balzani, preceeds oxidation of the ruthenium-based ones. In the polynu- S.Campagna, G. Denti, A. Juris, S. Serroni and M. Venturi, Coord. clear compounds oxidation of the osmium-based core occurs Chem. Rev., 1994, 132, 1. gAir-equilibrated solution. hSee also ref. 8(a). at more positive potentials than in the mononuclear Os-d iSee also ref. 8(b) and W. R. Murphy Jr., K. J. Brewer, G. Gettlie and J. D. Petersen, Inorg. Chem., 1989, 28, 81. jRef. 8( f ).kRef. 6. compound, according to the weaker electron donor power of m-2,3-dpp compared with 2,3-dpp (see General properties). The overall positive charge of the dendrimer increases strongly (Fig. 8 and 9). Therefore the light harvesting capability (i) with increasing nuclearity and (ii) on replacing the peri- increases with increasing nuclearity. It is well known that the pheral bpy ligands with protected 2,3-Medpp+.The increase transition from the singlet ground state to the lowest triplet of positive charge has only little eect on the oxidation MLCT level is more allowed in the osmium(II) than in the potential of the osmium-based core because (i) the increase in ruthenium(II) complexes. This results in a more intense tail in nuclearity is accompanied by an increase in the dendrimer size the red region of the spectra of the osmium-based complexes.and (ii) the charges of the protected ligands are localized in This dierence can be easily noted comparing the spectra of the periphery of the structure. OsRu3-t (Fig. 7) and Ru4-t (Fig. 8). In the p-type compounds the MLCT bands are displaced to higher energy compared to the analogous t-type compounds because the protected bridging ligand is a worse electron donor than bpy (Fig. 9). All the dendrimers reported in this paper display luminescence in fluid solution at room temperature. The emission spectra of OsRu21-t, OsRu9-t and OsRu3-t (Fig. 7, inset), Ru22-t, Ru10-t and Ru4-t (Fig. 8, inset) and OsRu3-p (Fig. 9, inset) are shown. The most important photophysical parameters are gathered in Table 1.In the heteronuclear t-type dendrimers, the emission band moves to higher energy and broadens with increasing nuclearity (Fig. 7, inset). The emission of OsRu3-t is characteristic of the osmium-based core, showing that energy transfer takes place from the three peripheral ruthenium-based moieties to the core. The corrected excitation spectrum shows that energy transfer occurs with unitary eciency.8a In OsRu9-t, the emis- Fig. 10 Simplified schematic diagram showing the energy of the lowest sion band clearly results from two dierent contributions excited state for the metal-based units along a branch of the OsRu9-t (a) and Ru10-t (b) dendrimers (Fig. 7, inset), one due to the [Os(m-2,3-dpp)3]2+ core, and the 1232 J. Mater. Chem., 1997, 7(7), 1227–1236Table 2 Electrochemical results in argon-purged acetonitrile solution at room temperaturea compound E1/2ox [n]b (site)c E1/2red[n]b (site)c Os-dd +1.21[1](Os) -0.83[1](2,3-dpp), -1.04[1](2,3-dpp), -1.39[1](2,3-dpp) OsRu3-td +1.36[1](Os), +1.61[3](Rup) -0.44[1](2,3-dpp), -0.62[1](2,3-dpp), -1.08[1](2,3-dpp), -1.20[ca.1](2,3-dpp)e OsRu3-p +1.36[ca.1](Os) -0.45[1](2,3-dpp), -0.78irr[6](2,3-Medpp+), -0.99[1](2,3-dpp), -1.18[1] (2,3-dpp), -1.31[1](2,3-dpp)e OsRu9-t +1.35[1](Os), +1.55[6](Rup)f -0.43[1](2,3-dpp), -0.58[2](2,3-dpp), -0.68[6](2,3-dpp), -0.91[1]e OsRu9-p +1.45[1](Os), +1.82[3](Rui) -0.78irr[12](2,3-Medpp+), -1.00[ca.6](2,3-dpp)e OsRu21-t +1.42[1](Os), +1.54[12](Rup) -0.63[ca.12](2,3-dpp)e aPotentials in volts vs.SCE; unless otherwise noted, the waves are reversible; for irreversible reductions (irr), the potential is evaluated from the DPV peaks; for the symbols used to indicate the compounds, see caption to Fig. 2. bNumber of exchanged electrons. cSite(s) involved in the redox processes; the subscripts p and i on the metal stand for peripheral and intermediate positions. dRevised data; for previously reported data, see G.Denti, S. Campagna, L. Sabatino, S. Serroni, M. Ciano and V. Balzani, in Photochemical conversion and storage of solar energy, ed. E. Pelizzetti and M. Schiavello, Kluwer, Dordrecht, 1991, p. 27. eOther broad waves follow at more negative potential. fRevised data; for previously reported data, see ref. 8( f ). Oxidation of the osmium-based core can be followed by (for the mononuclear Ru-d compound, as many as 12 reduction processes have been evidenced21 in the range -0.94 to oxidation processes involving ruthenium-based units which occupy internal or peripheral sites (Fig. 2). In the deca- and -2.83 V). We will only discuss briefly the behaviour of the compounds of lower nuclearity, excluding the d-type com- docosa-nuclear compounds, all the internal ruthenium-based units are equivalent from the viewpoint of the first coordination pounds because of their electrode adsorption.The mononuclear Os-d compound shows three one-electron sphere since each metal is surrounded by three bridging ligands, [Ru(m-2,3-dpp)3]2+. The dendrimers, however, have an onion- processes. They correspond to the successive reduction of the three 2,3-dpp ligands which interact because they are linked shaped structure (Fig. 2) and therefore only the units that belong to the same shell are topologically equivalent and to the same metal. In OsRu3-t the osmium-based core is linked to three exhibit the same properties. Slightly dierent properties can be expected for units belonging to dierent inner shells. [Ru(bpy)2]2+ units. It is well known that the bpy ligands are more dicult to reduce than the 2,3-dpp ligands.21 Therefore The peripheral sites in our dendrimers can be of type t, or p, or d (Fig. 2). Since the d-type dendrimers give rise to even in this compound the first reduction processes should involve 2,3-dpp. Furthermore, it is expected that bridging 2,3- electrode adsorption, we discuss only the t- or p-type compounds.Previous studies showed that the units belonging to dpp is easier to reduce that monocoordinated 2,3-dpp. In agreement with such expectations, OsRu3-t shows three one- the same shell (inner or peripheral) interact only weakly and are therefore oxidized simultaneously in multielectron electron reduction waves at less negative potentials than Osd, assigned to the first reduction of the three bridging ligands.processes. For OsRu3-p no oxidation process is observed after the This series of waves is followed by a single wave, presumably due to the second reduction of a bridging ligand, and other oxidation of the osmium-based core. In OsRu9-p, oxidation of the core is followed by a three-electron oxidation process at high and broad waves assigned to overlapping second reduction of the other two bridging ligands and first reduction +1.82 V (Table 2).The number of electrons involved and the potential value (which is that found for the [Ru(m-2,3-dpp)3]2+ of the six bpy ligands. In OsRu3-p the osmium-based core is linked to three inner units of Ru4-p and Ru10-p)6b suggest that this process is due to the simultaneous oxidation of the three equivalent [Ru(2,3-Medpp)2]4+ units.The methylated site of the 2,3- Medpp+ ligand undergoes an irreversible reduction at ruthenium-based units occupying the intermediate positions in the dendrimer structure. The results obtained for OsRu3-p and -0.76 V.22 Such a reduction process is practically unaected by coordination of a metal on the other site of the ligand.In OsRu9-p indicate that the peripheral p-type units cannot be oxidized in the potential window examined, as previously fact, it occurs practically at the same potential as in the free ligand.22 Therefore in OsRu3-p it is expected that the reduction observed for the protected homonuclear ruthenium dendrimers. 6b In the analogous OsRu3-t and OsRu9-t compounds, pattern of the three inner bridging ligands, observed for OsRu3- t, is perturbed by the reduction processes of the six peripheral oxidation of the osmium core is always followed by the simultaneous oxidation of the peripheral t-type ruthenium- protected ligands.The experimental results show that a small wave at -0.45 V is followed by an approximately six times based units. Accordingly, for OsRu3-t a three-electron process at +1.61 V, and for OsRu9-t a six-electron process at +1.55 V larger wave at -0.78 V, followed by three small waves at -0.99, -1.18, and -1.31 V, and other large waves.are observed. The slightly more positive potential observed for the first complex is probably due to the closeness of the Tentatively, we assign (i) the first wave to the one-electron reduction of an inner bridging ligand, as observed for OsRu3- ruthenium units with the already oxidized osmium core.Even in the case of OsRu21-t, oxidation of the osmium core is t, (ii) the big wave at -0.78 V to the simultaneous reduction of the six peripheral methylated sites, (iii) the two successive followed by the oxidation of the peripheral t-type units, as shown by the twelve-electron process observed at +1.54 V small waves to the first reduction of the two other inner bridging ligands, (iv) the small wave at -1.31 V to the second (Table 2).Previous studies6 have shown that the oxidation of the peripheral t-type ruthenium-based units in the homonuclear reduction of a bridging ligand, and (v) the following broad and large waves to overlapping second reduction of the other ruthenium dendrimers occurs at a potential very similar to that found for the t-type heteronuclear compounds.These two bridging ligands and of the peripheral ligands. For the decanuclear OsRu9-t and OsRu9-p, the reduction results show that the potential at which the oxidation of peripheral units takes place does not substantially depend on patterns are similar to those of the corresponding tetranuclear compounds, albeit much more complicated because of the the nature of the internal part of the dendrimer.presence of an intermediate shell containing six bridging ligands not exactly equivalent to the three inner ones. In Reduction. Because of the presence of a large number of polypyridine ligands, each capable of undergoing several addition, for OsRu9-p, the irreversible reduction of the twelve protected peripheral ligands prevents the observation of one- reduction processes,6b,21 the electrochemical reduction of polynuclear compounds of this type shows very complex patterns electron process(es) that could be present at less negative J.Mater. Chem., 1997, 7(7), 1227–1236 1233potential. For OsRu21-t, the first, broad, strongly asymmetric cyclic voltammetric peaks.For irreversible processes the wave with a maximum at -0.63 V, corresponding to approxi- reported values are those evaluated from the peak potentials mately 12 electrons, can be assigned to the reduction of in the DPV experiments. Both CV and DPV techniques have bridging ligands, and the following huge waves with maxima been used to measure the number of the exchanged electrons at-1.43 and-1.76 V (not reported in Table 2), corresponding in each redox process,25 utilizing [Ru(bpy)3]2+ as a reference to large numbers of electrons, should be due to overlapping compound, for which the oxidation and reduction processes second reduction of the bridging ligands and first and second are reversible and monoelectronic.26 To establish the reversireduction of the peripheral bpy ligands.bility of a process, we used the criteria of (i) separation of 60 mV between cathodic and anodic peaks, (ii) close to unity ratio of the intensities of the cathodic and anodic currents, Conclusions and (iii) constancy of the peak potential on changing sweep rate in the cyclic voltammograms. The divergent and convergent synthetic strategies to the dendri- Experimental errors in the reported data are as follows: mers described in this paper are characterized by a step-by- absorption maxima, 2 nm; emission maxima, 5 nm; emission step control of the growing process.Therefore, building blocks lifetimes, 10%; emission quantum yields, 20%; redox potentials, containing dierent metals and/or ligands can be introduced 20 mV.As far as molar absorption coecients are concerned, at each step. We have used the [Os(2,3-dpp)3]2+ core and the uncertainty in their absolute values is ca. 10% because of [Ru(2,3-Medpp)2Cl2]2+ units in a divergent approach to the highly diluted solutions used (10-5–10-4 M). prepare tetra- and deca-nuclear mixed-metal dendrimers. Moreover, we have used the tetranuclear [Os{(m-2,3- dpp)Ru(2,3-dpp)2}3]8+ core and trinuclear [{Ru(bpy)2(m-2,3- Characterization of the dendrimers dpp)}2RuCl2 ]4+ units in a convergent approach in order to obtain the [Os{(m-2,3-dpp)Ru[(m-2,3-dpp)Ru{(m-2,3- Characterization of large molecules like dendrimers is a dicult dpp)Ru(bpy)2}2]2}3]44+ docosanuclear compound.To our task.7 For neutral compounds, techniques based on colligative knowledge, this compound is the first mixed-metal third- properties can be used to determine the molecular mass.Our generation dendrimer prepared so far. compounds, however, are highly charged ions, and the use of To a first approximation, in the dendrimers each metal- the above techniques is not advisable because of the large based unit carries its own absorption properties.Therefore the number of counter ions. Mass spectrometry has not yet been light harvesting capability increases with increasing nuclearity. developed for compounds carrying such a high electric charge, All the dendrimers reported in this paper display luminescence and light scattering can hardly be used because of the strong in fluid solution at room temperature.Exoergonic inter- absorption in all the UV and visible spectral region. component energy-transfer processes are very ecient. In spite of the above diculties, a reliable characterization The dendrimers contain a large number of redox-active of our dendrimers has been achieved by using a variety of units. On oxidation, a reversible one-electron process of the techniques.osmium-based core occurs first, and is then followed by (1) Each compound (including precursors) was purified until oxidation processes involving ruthenium-based units which TLC showed the presence of only one spot. occupy internal or peripheral sites. On reduction, complex (2) Each building block was checked to be stable under the patterns are observed because of the presence of a large number experimental conditions.It is already known that in such of polypyridine ligands (as many as 45 in the docosanuclear compounds no ligand or metal scrambling occurs, as shown dendrimer), each capable of undergoing several reduction by the synthesis of a number of tetra-,8c hexa-4a and deca- processes. nuclear8d,f species containing dierent metals and/or ligands in predetermined sites of the structure.(3) Each one of the reaction steps (Fig. 5) was accurately Experimental monitored as follows. (i) The reaction of the ‘complex ligand’ Equipment and methods compounds (Os-d and OsRu3-d) with the ‘complex metal’ Cl2Ru-p was carried out under stoichiometric conditions. TLC Absorption spectra were obtained in acetonitrile solution at analysis [Al2O3, CH2Cl2–MeOH (951)] showed that in each room temperature using a Perkin-Elmer l-6 spectrophoto- case at least 90% of Cl2Ru-p had reacted.(ii) For the product meter. Luminescence spectra were obtained with a Perkin- of the p-type compounds obtained in each growing step the Elmer LS-50 spectrofluorimeter. Emission lifetimes were meas- ratio between aromatic and aliphatic protons in the 1H NMR ured with an Edinburgh 199 single-photon counting equip- spectrum (where the strong signals of the methyl protons lie ment.Emission quantum yields were measured at room in a clean spectral window around d 4) was consistent with temperature (20°C) with the optically dilute method23 calibrat- the expected formulations. (iii) IR analysis on the p-type ing the spectrofluorimeter with a standard lamp.[Ru(bpy)3]2+ compounds showed the absence of the 990 cm-1 band of in aerated aqueous solution was used as a quantum yield unbridged 2,3-dpp. standard, assuming a value of 0.028.24 The deprotection steps were carried out with a large excess Electrochemical measurements were carried out in argon- of demethylating agent. The purified products did not show purged acetonitrile solution at room temperature with a PAR any 1H NMR signal due to the presence of methyl groups, so 273 multipurpose equipment interfaced to a PC.The working we can exclude the presence of residual methylated sites (<1%). electrode was a Pt microelectrode or a glassy carbon (8 mm2, The reaction of OsRu3-d with the ‘complex metal’ Cl2Ru3-t Amel) electrode.The counter electrode was a Pt wire, and the (which was fully characterized by several techniques including reference electrode was a SCE separated with a fine glass frit. FAB MS)8f,27 was carried out under stoichiometric conditions The concentration of the complexes was 3×10-4 M and tetrauntil complete (90%) disappearance of Cl2Ru3-t (TLC ethylammonium hexafluorophosphate 0.05 M was used as supanalysis).porting electrolyte. Cyclic voltammograms were obtained at (4) Consistent elemental analyses were obtained. It should sweep rates of 20, 50, 200, 500 and 1000 mV s-1; dierential be noted, however, that the C, H, and N values do not change pulse voltammetry (DPV) experiments were performed with a significantly on increasing the dendrimer size.For this reason, scan rate of 20 mV s-1, a pulse height of 75 mV, and a duration we measured the ruthenium and osmium content of the of 40 ms. For reversible processes the half-wave potential OsRu21-t species with atomic absorption spectrometry using a values are reported; the same values are obtained from the DPV peaks and from an average of the cathodic and anodic method described elsewhere.28 1234 J.Mater. Chem., 1997, 7(7), 1227–1236(5) The luminescence and electrochemical properties are acetonitrile (15 ml) was refluxed for 6 d. After cooling of the solution to room temperature and addition of EtOH, the fully consistent with the reported formulations. reaction mixture was concentrated to induce the precipitation of the crude product which was separated by filtration.This Synthesis was then dissolved in a small amount of MeCN and purified The preparations of the complexes [Os(2,3-dpp)3][PF6]2 (Os- by chromatography on Sephadex G-25 (acetonitrile eluent). d),15 [Ru(2,3-Medpp)2Cl2][PF6]2 (Cl2Ru-p),6b and [Ru{(m- On adding Et2O to the partially evaporated eluate the product 2,3-dpp)Ru(bpy)2}2Cl2][PF6]4 (Cl2Ru3-t)4a have been pre- precipitated as brown powder, which was filtered o, washed viously reported.All the compounds dealt with in this paper with Et2O and dried in vacuo (yield: 90%). Anal. calc. for have been characterized using the same methods previously C294H210F120N84P20OsRu9: C, 39.5; H, 2.4; N, 13.2. Found: C, described.6b 39.4; H, 2.5; N, 13.1%. [Os{(m-2,3-dpp)Ru(2,3-Medpp)2}3][PF6]14 (OsRu3-p).Solid [Os{(m-2,3-dpp)Ru[(m-2,3-dpp)[Ru(m-2,3-dpp)Ru- AgNO3 (0.009 g, 0.053 mmol) was added to a suspension of (bpy)2]2]2}3 ][PF6 ]44 (OsRu21-t). [Ru{(m-2,3- [Ru(2,3-Medpp)2Cl2][PF6]2 (0.026 g, 0.027 mmol) in dpp)Ru(bpy)2}2Cl2][PF6]4 (0.106 g, 0.052 mmol) in 5 ml of H2O–EtOH (152, v/v) (10 ml). After 2 h stirring at room water–ethanol (151, v/v) was treated with silver nitrate (0.014 g, temperature, [Os(2,3-dpp)3][PF6]2 (0.011 g, 0.009 mmol) was 0.082 mmol).After the mixture had been stirred at room added, and the reaction mixture refluxed for 72 h. After cooling temperature for 2 h, a solution of [Os{(m-2,3-dpp)Ru(2,3- to room temperature the AgCl formed was removed by dpp)2}3][PF6]8 (OsRu3-d) (0.032 g, 0.009 mmol) in ethylene repeated centrifugations, then the reaction mixture was rotary- glycol (3 ml) was added.The reaction mixture was refluxed evaporated to a small volume (about 3 ml) and a saturated for 7 d, then cooled to room temperature. AgCl was separated methanolic solution of NH4PF6 (ca. 4 ml) was added. The by repeated centrifugations, the mother-liquor concentrated solid so obtained was separated by filtration, dissolved in a by evaporation in vacuo, and an excess of solid NH4PF6, small volume of MeCN and purified by flash chromatography methanol (2 ml) and diethyl ether (10 ml) were added.The on Sephadex G-10. From the eluate a wine-red solid was crude product was filtered o, dissolved in a small amount of recovered by addition of CH2Cl2 , partial evaporation in vacuo MeCN and purified by chromatography on Sephadex G-75 and filtration. A further recrystallization from MeCN–CH2Cl2 (acetonitrile eluent). The eluate was rotary evaporated in vacuo of the solid provided the product which was washed with small to 2 ml, and the OsRu21-t product was recovered as a purple portions of CH2Cl2, then with Et2O, and dried in vacuo (yield: powder by addition of about 20 ml of diethyl ether (yield: 67%).Anal. calc. for C132H108F84N36P14OsRu3·2H2O: C, 33.3; 76%). Anal. calc. for OsRu21-t: Os, 1.1; Ru, 12.2. Found: Os, H, 2.4; N, 10.6. Found: C, 33.3; H, 2.5; N, 10.5%. 0.9; Ru, 10.5%. [Os{(m-2,3-dpp)Ru(2,3-dpp)2}3][PF6]8 (OsRu3-d). A solu- We thank Mr. Fausto Puntoriero for his valuable help in the tion containing [Os{(m-2,3-dpp)Ru(2,3-Medpp)2}3][PF6 ]14 synthesis of some trinuclear compounds.This work was sup- (0.080 g, 0.17 mmol) and a very large excess of 1,4-diazabicy- ported by Consiglio Nazionale delle Ricerche (Progetto clo[2.2.2]octane (DABCO, 0.370 g, 3.3 mmol) in dry aceto- Strategico Tecnologie Chimiche Innovative), Ministero nitrile (15 ml) was refluxed for 6 d. After cooling of the solution dell’Universita` e della Ricerca Scientifica e Tecnologica, and to room temperature and addition of EtOH, the reaction Universita` di Bologna (Funds for selected research topics).mixture was concentrated to induce the precipitation of the crude product that was separated by filtration. This was then References dissolved in a small amount of MeCN and purified by flash 1 (a)Molecular Electronics Devices, ed.F. L. Carter, R. E. Siatkowski chromatography on Sephadex G-10. On adding Et2O to and H. Wohltjen, North-Holland, Amsterdam, 1988; the partially evaporated eluate the product precipitated as (b) Nanostructure based on MolecularMaterials, ed. W. Go�pel and a brown powder, which was filtered o, washed with Ch. Ziegler, VCH, Weinheim, 1992; (c) A. J. Bard, Integrated Et2O, and dried in vacuo (yield: 75%).Anal. calc. for Chemical Systems, Wiley, New York, 1994; (d) J.-M. Lehn, C126H90F48N36P8OsRu3·3H2O: C, 39.6; H, 2.5; N, 13.2. Found: Supramolecular Chemistry, VCH, Weinheim, 1995; (e) G. Denti, C, 39.4; H, 2.4; N, 13.0%. S. Campagna and V. Balzani, in Mesomolecules: fromMolecules to Materials, ed. D. Mendenhall, A. Greenberg and J. Liebman, Chapman and Hall, New York, 1995, p. 69. [Os{(m-2,3-dpp)Ru[(m-2,3-dpp)Ru(2,3-Medpp)2 ]2}3[PF6]32 2 (a) Supramolecular Chemistry, ed. V. Balzani and L. De Cola, (OsRu9-p). Solid AgNO3 (0.035 g, 0.208 mmol) is added to Kluwer, Dordrecht, 1992; (b) F.Vo� gtle, Supramolecular Chemistry, a suspension of [Ru(2,3-Medpp)2Cl2][PF6]2 (0.100 g, Wiley, Chichester, 1993. 0.104 mmol) in H2O–EtOH (152, v/v) (10 ml).After 2 h stirring 3 G. Denti, S. Serroni, S. Campagna, A. Juris, M. Ciano and V. Balzani, in Perspectives in Coordination Chemistry, ed. at room temperature, [Os{(m-2,3-dpp)Ru(2,3-dpp)2 }3][PF6]8 A. F. Williams, C. Floriani and A. E. Merbach, VCH, Basel, 1992, (0.065 g, 0.017 mmol) was added, and the reaction mixture was p. 153. refluxed for 7 d. After cooling to room temperature the AgCl 4 (a) S.Campagna, G. Denti, S. Serroni, M. Ciano and V. Balzani, formed was removed by repeated centrifugations, then the Inorg. Chem., 1991, 30, 3728; (b) S. Serroni and G. Denti, Inorg. reaction mixture was rotary-evaporated to a small volume (ca. Chem., 1992, 31, 4251 and references therein. 3 ml) and an excess of solid NH4PF6 was added. The solid so 5 S.Serroni, S. Campagna, G. Denti, A. Juris, M. Venturi and V. Balzani, in Advances in Dendritic Macromolecules, ed. obtained was separated by filtration, dissolved in a small G. R. Newkome, JAI Press Inc., Greenwich, CT, 1996, vol. 3, p. 61. volume of MeCN and purified by flash chromatography 6 (a) S. Serroni, G. Denti, S. Campagna, A. Juris, M. Ciano and on Sephadex G-25. From the eluate the brown–red product V.Balzani, Angew. Chem., Int. Ed. Engl., 1992, 31, 1493; was recovered by addition of EtOH, partial evaporation (b) S. Campagna, G. Denti, S. Serroni, A. Juris, M. Venturi, in vacuo and filtration (yield: 25%). Anal. calc. for V. Ricevuto and V. Balzani, Chem. Eur. J., 1995, 1, 211. C306H246F192N84P32OsRu9: C, 33.8; H, 2.3; N, 10.8. Found: C, 7 (a) D.A. Tomalia and H. D. Durst, T op. Curr. Chem., 1993, 165, 193; (b) J.M. J. Fre� chet, Science, 1994, 263, 1710; (c) N. Ardoin and 33.7; H, 2.4; N, 10.6%. D. Astruc, Bull. Soc. Chim. Fr., 1995, 132, 875; (d) G. R. Newkome, C. N. Moorefield and F. Vo� gtle, Dendritic Molecules, VCH, [Os{(m-2,3-dpp)Ru[(m-2,3-dpp)Ru( 2,3-dpp)2]2}3 ][PF6 ]20 Weinheim, 1996. (OsRu9-d ). A solution containing [Os{(m-2,3-dpp)Ru[(2,3- 8 (a) S.Campagna, G. Denti, L. Sabatino, S. Serroni, M. Ciano and dpp)Ru(2,3-Medpp)2]2}3][PF6 ]32 (0.030 g, 0.003 mmol) and V. Balzani, J. Chem. Soc., Chem. Commun., 1989, 1500; (b) G. Denti, S. Campagna, L. Sabatino, S. Serroni, M. Ciano and V. Balzani, a very large excess of DABCO (0.185 g, 1.65 mmol) in dry J. Mater. Chem., 1997, 7(7), 1227–1236 1235Inorg.Chem., 1990, 29, 4750; (c) G. Denti, S. Serroni, S. Campagna, 16 A. Juris, V. Balzani, S. Campagna, G. Denti, S. Serroni, G. Frei and H. U. Gu�del, Inorg. Chem., 1994, 33, 1491. V. Ricevuto and V. Balzani, Coord. Chem. Rev., 1991, 111, 227; (d) S. Serroni, G. Denti, S. Campagna, M. Ciano and V. Balzani, 17 (a) G. A. Crosby, R. J. Watts and D. H. W. Carstens, Science, 1970, 170, 1195; (b) V.Balzani, A. Juris, M. Venturi, S. Campagna and J. Chem. Soc., Chem. Commun., 1991, 944; (e) S. Campagna, G. Denti, S. Serroni, M. Ciano, A. Juris and V. Balzani, Inorg. S. Serroni, Chem. Rev., 1996, 96, 759. 18 (a) P. C. Bradley, N. Kress, B. A. Hornberger, R. F. Dallinger and Chem., 1992, 31, 2982; ( f ) G. Denti, S. Campagna, S. Serroni, M. Ciano and V.Balzani, J. Am. Chem. Soc., 1992, 114, 2944; W. H. Woodru, J. Am. Chem. Soc., 1989, 103, 7441; (b) P. J. Carrol and L. E. Brus, J. Am. Chem. Soc., 1987, 109, 7613; (c) T. Yabe, (g) S. Serroni, A. Juris, S. Campagna, M. Venturi, G. Denti and V. Balzani, J. Am. Chem. Soc., 1994, 116, 9086. D. R. Anderson, L. K. Orman, Y. J. Chang and J. B. Hopkins, J. Phys. Chem., 1989, 93, 2302; (d) L.F. Cooley, P. Bergquist and 9 S. Serroni, A. Juris, M. Venturi, S. Campagna, A. Credi and V. Balzani, unpublished work. D. F. Kelley, J. Am. Chem. Soc., 1990, 112, 2612. 19 (a) J. N. Demas and G. A. Crosby, J. Am. Chem. Soc., 1971, 93, 10 See, for example: R. Hage, A. H. J. Dijkhnis, J. G. Haasnoot, R. Prins, J. Reedijk, B. E. Buchanan and J. G. Vos, Inorg. Chem., 2841; (b) J. N. Demas and D. G. Taylor, Inorg. Chem., 1979, 18, 3177; (c) F. Bolletta, A. Juris, M. Maestri and D. Sandrini, Inorg. 1988, 27, 2185. 11 (a) D. A. Tomalia, A. M. Naylor and W. A. Goddard III, Angew. Chim. Acta, 1980, 44, L175. 20 V. Balzani and V. Carassiti, Photochemistry of Coordination Chem., Int. Ed. Engl., 1990, 29, 138; (b) G. R. Newkome, C. N. Moorefield and G. R. Baker, Aldrichim. Acta, 1992, 25, 31; Compounds, Academic, London, 1970. 21 S. Roa, M. Marcaccio, C. Paradisi, F. Paolucci, V. Balzani, (c) E.M. M. de Brabander-van den Berg and E. W. Meijer, Angew. Chem., Int. Ed. Engl., 1993, 32, 1308; (d) R. Dagani, Chem. Eng. G. Denti, S. Serroni and S. Campagna, Inorg. Chem., 1993, 32, 3003. News, 1996, June 3rd, p. 30. 22 A. Juris, M. Venturi, L. Pontoni, I. R. Resino, V. Balzani, 12 (a) A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser and S. Serroni, S. Campagna and G. Denti, Can. J. Chem., 1995, 73, A. von Zelewsky, Coord. Chem. Rev., 1988, 84, 85; (b) T. J. Meyer, 1875. Acc. Chem. Res., 1989, 22, 163; (c) F. Scandola, M. T. Indelli, 23 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991. C. Chiorboli and C. A. Bignozzi, T op. Curr. Chem., 1990, 158, 73; 24 K. Nakamaru, Bull. Chem. Soc. Jpn., 1982, 55, 2697. (d) K. Kalyanasundaram, Photochemistry of Polypyridine and 25 J. B. Flanagan, S. Margel, A. J. Bard and F. C. Anson, J. Am. Porphyrin Complexes, Academic Press, London, 1991. Chem. Soc., 1978, 100, 4248. 13 V. Balzani, S. Campagna, G. Denti, A. Juris, S. Serroni and 26 M. K. DeArmond and C. M. Carlin, Coord. Chem. Rev.,Venturi, Sol. Energy Mater. Sol. Cells, 1995, 38, 159; G. Denti, 36, 325. S. Campagna, S. Serroni, V. Balzani, A. Juris and M. Venturi, in 27 G. Denti, S. Serroni, G. Sindona and N. Uccella, J. Am. Soc.Mass Polymeric Materials Encyclopedia, ed. J. C. Salamone, CRC Press, Spectrom., 1993, 4, 306. Boca Raton, FL, 1996, vol. 3, p. 1799. 28 M. Taddia, C. Lucano and A. Juris, Euroanalysis IX, September 14 C. Devadoss, P. Bharathi and J. S. Moore, J. Am. Chem. Soc., 1996, 1–7, 1996, Bologna, Italy, Abstracts p.We P166. 118, 9635. 15 G. Denti, S. Serroni, L. Sabatino, M. Ciano, V. Ricevuto and S. Campagna, Gazz. Chim. Ital., 1991, 121, 37. Paper 7/00426E; Received 17th January, 1997 1236 J. Mater. Chem., 1997, 7(7), 1227–1236

ISSN:0959-9428    

DOI:10.1039/a700426e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Nanometric dendritic macromolecules: stepwise assembly by double (2,2¾56¾,2-terpyridine)ruthenium(I ) connectivity George R. Newkome* and Enfei He Center forMolecular Design and Recognition, University of South Florida, T ampa, Florida 33620, USA The construction of nanometric, dendritic macromolecules by bis(2,2¾56¾,2-terpyridine)ruthenium(II) connectivity is investigated. The assembly methodology, which incorporates both the control of metal complexation sites and degree of flexibility within the linkages, has been demonstrated.Interest in specifically assembled, dendritic nanostructures has saturated aqueous NaHCO3 solution was carefully added, then the solvent was removed in vacuo to aord a white solid, which continued to escalate over the past decade1 and will continue to do so due to the anticipation of their novel properties.was extracted with absolute EtOH (3×100 cm3). The extract was concentrated in vacuo to give tetraol 4, as a colourless oil. Dendritic systems which incorporate metal centres are either of a random nature by simple molecular inclusion within the (8.26 g, 95%) (Found: C, 55.69; H, 9.61. C17H36O8 requires C, 55.42; H, 9.85%); 1H NMR (MeOD), d 1.78 (m, 2H, macrostructure,2 or at a specific predetermined binding locus3 either within the assembly or on its surface.Such metallo- CH2CH2OH), 3.38 (s, 2H, CH2O), 3.55 (t, J 5.0 Hz, 2H, OCH2), 3.69 (t, J 5.1 Hz, 2H, CH2OH); 13C NMR (MeOD), macroassemblies aord entrance to materials capable of novel magnetic, electronic, photooptical or catalytic properties.As a d 31.8 (CH2CH2OH), 44.9 (Cquat), 60.5 (CH2OH), 69.7 (OCH2 ), 70.7 (CH2O); IR (neat), 3364, 2948, 2879, 1493, 1424, 1363, prelude to the construction process, we previously reported4–6 the use of bis(2,2¾56¾,2-terpyridine)ruthenium(II) (herein 1109 cm-1. denoted by [—<Ru>—]), as the mode of connectivity, in order to combine preconstructed, pseudo-spherical dendritic Tetrakis{5-[4¾-oxa-(2,2¾56¾,2-terpyridinyl )]-2- fragments in a predetermined way.Such connectivity permitted oxapentyl}methane 5 the analysis of the final product by the easy quantification of To a suspension of powdered KOH (1.10 g) in dry Me2SO the metal centre(s) by simple electrochemical procedures. This (15 cm3), was added tetraol 4 (600 mg, 1.63 mmol) in Me2SO type of connectivity (i.e., incorporation of multiple centres) (5 cm3).The suspension was heated to 60°C for 30 min, then gave rise to the dodecaruthenium complex4 1 and the single 4¾-chloro-2,2¾56¾,2-terpyridine9 (4¾-Cl-tpy; 1.92 g, 4.4 equiv.) metal centre aorded the bisdendrimer5 2 (Fig. 1); these rep- was added. After 24 h at 60°C, the mixture was cooled and resent our initial approaches to the specific assembly of discrete poured into cold water (300 cm3).The resultant white solid dendritic networks by the connection of established constructs. was filtered, washed with water, and dried in vacuo to give a We herein describe the use of two metal centres per appendage o-white solid, which was column chromatographed eluting [—<Ru>—(×)—<Ru>—] for attachment to a four-direc- with 15% EtOAc in CH2Cl2 to aord 5, as a white solid tional core; this assembly methodology incorporates (i) pos- (1.65 g, 78%), mp 161–164 °C (Found: C, 71.70; H, 5.57; N, itional control over the metal complexation sites and (ii) a 12.78; C77H72N12O8 requires C, 71.50; H, 5.61; N, 12.99%); 1H variable flexibility within the linkages (×) between those con- NMR, d 1.98 (m, 8H, J 5.6 Hz, OCH2CH2 ), 3.42 (s, 8H,CH2O), nectivity sites. 3.52 (t, 8H, J 5.6 Hz, OCH2), 4.18 (t, 8H, J 5.6 Hz, OCH2CH2CH2 ), 7.24 (t, 8H, J 5.2 Hz, H5,5), 7.74 (t, 8H, Experimental J 7.6 Hz, H4,4), 7.94 (s, 8H, H3¾,5¾), 8.54 (d, 8H, J 7.9 Hz, H3,3), 8.62 (d, 8H, J 4.7 Hz, H6,6); 13C NMR, d 29.4 Equipment and materials (OCH2CH2), 45.6 (Cquat), 65.2 (OCH2CH2CH2), 67.6 (OCH2 ), 69.9 (CH2O), 107.5 (C5,5), 121.3 (C4,4), 123.8 (C3,3), 136.7 Melting points are uncorrected and were measured on a Mel- (C3¾,5¾), 149.1 (C6,6), 156.2 (C2,2), 157.0 (C2¾,6¾), 167.2 (C4¾); IR Temp apparatus.All reactions were conducted under a nitrogen (KBr), 3063, 2933, 2876, 1609, 1593, 1570, 1493, 1440, 1416, atmosphere. 1H and 13C NMR spectra were recorded on a 1362, 1209, 1093, 801 cm-1.Bruker AC250 MHz spectrometer using CDCl3 as solvent, unless otherwise indicated, with Me4Si as the internal standard (d=0). IR spectra were recorded on a Perkin-Elmer 621 grating 4-[4¾-Oxa-(2,2¾56¾,2-terpyridinyl )]butanoic acid 6 IR spectrometer. UV–VIS spectra were recorded on a To a solution of 4-hydroxybutanoic acid (942 mg, 7.47 mmol) HP8452A diode array spectrophotometer.Elemental analyses and KOH (3 g) in dry Me2SO (30 cm3) at 60°C, was added were performed by M-H-W Laboratories, Phoenix, AZ. 4¾-Cl-tpy (2.00 g, 7.47 mmol). The mixture was maintained for All reagents were purchased from Aldrich. Column chroma- 36 h, then cooled to 25°C and poured into water (600 cm3) tography was performed using activated basic aluminium oxide aording a yellow transparent solution.The pH was adjusted (150 mesh, Brockmann I; Aldrich). to neutral by the addition of 10% aqueous HCl resulting in the formation of a white precipitate, which after standing for Tetrakis(5-hydroxy-2-oxapentyl )methane 4 at least 2 h, was filtered, washed with water, dried in vacuo to give the acid 6, as a white solid (2.15 g, 86%); mp 173–175 °C To a solution of 6,6-bis(carboxy-2-oxabutyl)-4,8-dioxaundecane- 1,11-dicarboxylic acid7 3 (10 g, 23.6 mmol) in dry THF (Found: C, 68.29; H, 5.29; N, 12.30.C19H17N3O3 requires C, 68.05; H, 5.11; N, 12.53%); 1H NMR, d 2.21 (m, 2H, J 6.0 Hz, (50 cm3) at 0°C, was added dropwise a BH3·THF8 solution (104 cm3, 4.4 equiv.) over 30min. The solution was stirred for OCH2CH2CH2 ), 2.57 (t, 2H, J 7.1 Hz, CH2CO2H), 4.31 (t, 2H, J 6.0 Hz, OCH2), 7.38 (td, 2H, J 4.9, 1.0 Hz, H5,5), 7.88 (td, 1 h, then warmed to 25°C and stirred for 3 h.Excess of a J. Mater. Chem., 1997, 7(7), 1237–1244 1237Fig. 1 Dendritic architectures incorporating (—<Ru>—) units 2H, J 7.8, 1.8 Hz, H4,4), 7.92 (s, 2H, H3¾,5¾), 8.61 (d, 2H, tert-butyl 4-[(2-tert-butoxycarbonyl)ethyl]-4-aminoheptanedicarboxylate 710 (2.48 g, 5.97 mmol) was added.The reaction J 7.9 Hz, H3,3), 8.67 (d, 2H, J 4.3 Hz, H6,6); 13C NMR, d 24.6 mixture was stirred for 36 h, after which the white precipitate (OCH2CH2CH2), 30.7 (CH2CO2H), 67.4 (OCH2), 107.6 (C5,5), was filtered o. The filtrate was concentrated in vacuo aording 121.9 (C4,4), 124.1 (C3,3), 137.3 (C3¾,5¾), 148.9 (C6,6), 156.1 a crude oil, which was dissolved in Et2O (200 cm3), washed (C2,2), 157.0 (C2¾,6¾), 167.2 (C4¾), 175.7 (CO2H); IR (KBr), 3063, with 10% aqueous Na2CO3 (2×100 cm3), brine (2×100 cm3), 2956, 2918, 2879, 1709, 1593, 1570, 1478, 1450, 1416, 1370, dried (MgSO4), and concentrated in vacuo to aord a solid, 1262, 1209, 1040, 801, 747 cm-1.which was recrystallized from cyclohexane (3.15 g, 72%); mp 146–149 °C (Found: C, 67.36; H, 7.51; N, 7.85.C41H56N4O8 N-{Tris[(2-tert-butoxycarbony)ethyl]methyl}[4¾-oxa- requires C, 67.19; H, 7.70; N, 7.64%); 1H NMR, d 1.42 (s, 27H, ( 2,2¾56¾,2-terpyridinyl )]butamide 8 CH3), 2.01 (t, 6H, J 8.2 Hz, CH2CO2), 2.23 (m, 8H, To a solution of acid 6 (2.0 g, 5.97 mmol) in dry DMF (30 cm3), CH2CH2CONH, CH2CH2CO2), 2.36 (t, 2H, J 7.1 Hz, were added dicyclohexylcarbodiimide (DCC; 1.23 g, CH2CONH), 4.28 (t, 2H, J 5.9 Hz, OCH2 ), 6.03 (s, 1H, NH), 5.97 mmol) and 1-hydroxybenzotriazole (1-HOBT; 806 mg, 7.32 (td, 2H, J 4.8, 1.8 Hz, H5,5), 7.84 (td, 2H, J 7.8, 1.7 Hz, H4,4), 8.01 (s, 2H, H3¾,5¾), 8.60 (d, 2H, J 8.0 Hz, H3,3), 8.68 (d, 5.97 mmol) at 25°C.This mixture was stirred for 1 h, then di- 1238 J.Mater. Chem., 1997, 7(7), 1237–1244Scheme 1 Reagents and conditions: i, BH3 ·THF, 1 h, 0°C, then 3 h, 25 °C; ii, 4¾-Cl-tpy, KOH, Me2SO, 24 h, 60 °C Scheme 2 Reagents and conditions: i, 4¾-Cl-tpy, KOH, Me2SO, 36 h, 60 °C; ii, DCC, 1-HOBT, DMF, 36 h, 25 °C; iii, RuCl3 3H2O, MeOH, 3 h,reflux J. Mater. Chem., 1997, 7(7), 1237–1244 1239Scheme 3 Reagents and conditions: i, 4¾-Cl-tpy, KOH, Me2SO, 36 h, 60°C; ii, 4-ethylmorpholine, MeOH, 2 h, reflux Scheme 4 Reagents and conditions: i, DCC, 1-HOBT, DMF, 48 h, 25 °C; ii, RuCl3 ·3H2O, MeOH, 6 h, reflux 1240 J.Mater. Chem., 1997, 7(7), 1237–1244Scheme 5 Reagents and conditions: i, 4-ethylmorpholine, MeOH–CHCl3, 4 h, reflux 2H, J 4.3 Hz, H6,6); 13C NMR, d 25.2 (CH2CH2CON), 28.2 (2×10 cm3) then dried in vacuo, yielding 9, as a yellow–brown solid (1.94 g, 76%); mp>202°C (decomp.); (Found C, 52.17; (CH3 ), 29.9 (CH2CO2), 30.2 (CH2CH2CO2), 33.6 (CH2CON), 57.6 (NHC), 67.4 (OCH2), 80.8 [C(CH3)3], 107.5 (C5,5), 121.4 H, 5.95; N, 6.06.C41H56Cl3N4O8Ru requires C, 52.37; H, 6.00; N, 5.96%); IR (KBr), 3340, 3071, 2987, 2940, 1732, 1670, 1609, (C4,4), 123.9 (C3,3), 136.9 (C3¾,5¾), 149.1 (C6,6), 156.2 (C2,2), 157.2 (C2¾,6¾), 167.2 (C4¾), 171.6 (CONH), 173.0 (CO2); IR 1555, 1471, 1370, 1224, 1160, 1047, 801 cm-1; UV–VIS, lmax= 232 (e=3.27×104), 278 (2.91×104), 312 (1.63×104), 402 (KBr), 3341, 3063, 3010, 2987, 2933, 1732, 1671, 1586, 1563, 1478, 1452, 1362, 1155, 793 cm-1.(9.32×103), 466 nm (3.73×103 dm3 mol-1 cm-1). 5-Aminopentyl 4¾-(2,2¾56¾,2-terpyridinyl ) ether 10 Ruthenium(III ) complex of N-{tris[(2-tertbutoxycarbony) ethyl]methyl}[4¾-oxa-(2,2¾56¾,2- To a suspension of powdered KOH (2.0 g) in dry Me2SO terpyridinyl )]butamide 9 (30 cm3), was added 5-aminopentan-1-ol (770 mg, 7.47 mmol).The suspension was stirred at 60°C for 30 min, then 4¾-Cl-tpy A solution of RuCl3·3H2O (709 mg, 2.71 mmol) and 8 (2.0 g, 2.71 mmol) in MeOH (50 cm3) was refluxed for 3 h.After (2.00g, 7.47 mmol) was added. The whole mixture was stirred at 60°C for an additional 36 h. After cooling to 25°C, the cooling, the yellow–brown precipitate was filtered, washed sequentially with MeOH (5 cm3), water (2×20 cm3) and Et2O mixture was poured into water (600 cm3), stirred, then allowed J. Mater. Chem., 1997, 7(7), 1237–1244 1241to set for 3 h.The precipitate was filtered, washed with water, (CONHCH2), 57.4 (CONHC), 67.4 (free tpy-OCH2,), 69.3 (OCH2), 71.0 (CH2O), 107.2 (free tpy C5,5), 111.1 (C5,5), 121.2 and dried in vacuo to give a crude product, which was column chromatographed eluting with 10% MeOH in CH2Cl2 to yield (free tpy C4,4), 123.9 (free tpy C3,3), 124.5 (C4,4), 127.8 (C3,3 ), 136.9 (free tpy C3¾,5¾), 137.7 (C3¾,5¾), 148.9 (free tpy C6,6), 10, as a light yellow solid (1.78 g, 71%); mp 104–106 °C (Found: C, 72.04; H, 6.46; N, 16.60.C20H22N4O requires C, 152.0 (C6,6), 153.7 (C2,2), 156.7, 156.8 (C2¾,6¾, free tpy C2,2), 158.0 (free tpy C2¾,6¾), 162.5 (CONHCH2), 165.9, 166.2, 166.8 71.83; H, 6.63; N, 16.75%); 1H NMR, d 1.49–1.55 (m, 6H, NH2, NCH2CH2CH2), 1.82 (m, 2H, CH2CH2O), 2.67 (t, 2H, (C4¾, free tpy C4¾), 172.1 (CONHC), 172.9 (CO2); IR (KBr), 3418, 3333, 3071, 2980, 2940, 2851, 1724, 1678, 1616, 1563, J 6.1 Hz, NCH2), 4.17 (t, 2H, J 6.2 Hz, CH2O), 7.29 (td, 2H, J 4.9, 1.6 Hz, H5,5), 7.78 (td, 2H, J 7.2, 1.4 Hz, H4,4), 8.01 (s, 1470, 1393, 1370, 1216, 1162, 847, 790, 754 cm-1; UV–VIS, lmax=244 (e=6.86×104), 270 (7.13×104), 304 (7.19×104), 2H, H3¾,5¾), 8.59 (d, 2H, J 7.9Hz, H3,3), 8.65 (d, 2H, J 4.4 Hz, H6,6); 13C NMR, d 23.2 (NCH2CH2CH2 ), 28.8 (CH2CH2O), 488 nm (1.99×104 dm3 mol-1 cm-1). 33.3 (NCH2CH2), 42.0 (NCH2), 67.9 (CH2O), 107.3 (C5,5), 121.2 (C4,4), 123.7 (C3,3), 136.6 (C3¾,5¾), 148.9 (C6,6), 156.0 Ruthenium(II ) ruthenium(III ) complex 13 (C2,2), 156.9 (C2¾,6¾), 167.1 (C4¾); IR (KBr), 3359, 3299, 3059, A solution of RuCl3·3H2O (80 mg, 306 mmol) and 12 (542 mg, 3014, 2947, 2865, 1598, 1583, 1576, 1470, 1448, 1410, 1358, 306 mmol) in MeOH (20 cm3) was refluxed for 6 h.After 1208, 1043, 803 cm-1. cooling to 25°C, the red precipitate was filtered, washed with cold MeOH (2 cm3), water (2×10 cm3), and dried in vacuo to Amino-ruthenium(II ) complex 11 yield crude product 13, as a dark-red solid (206 mg, 34% crude To a suspension of complex 9 (300 mg, 318 mmol) in MeOH yield); mp>152°C (decomp.); IR (KBr), 3425, 3071, 2980, (20 cm3) were added amine 10 (106 mg, 318 mmol) and 4- 2940, 1724, 1655, 1617, 1547, 1470, 1371, 1163, 847, 793 cm-1; ethylmorpholine (73 mg).The mixture was refluxed for 2 h UV–VIS, lmax=232 (e=7.25×104 ), 270 (7.53×104), 304 until it turned into a clear red solution.After cooling to 25°C, (7.49×104), 488 nm (2.06×104 dm3 mol-1 cm-1). This prod- saturated NH4PF6 in MeOH (10 cm3) was added, then the uct was not purified but carried on to the next reaction. methanol was removed in vacuo, the resulting red solid was dissolved in CHCl3 (4 cm3), which was then slowly added to Dendritic complex 14 Et2O (100 cm3) with stirring, to yield a red precipitate, which was filtered, and dried in vacuo to give complex 11, as a red To a suspension of complex 13 (429 mg, 216 mmol, 4.4 equiv.) solid (336 mg, 72%); mp>152 °C (decomp.); (Found: C, 49.92; in MeOH (30 cm3) were added tetrakisterpyridine core 5 H, 5.29; N, 7.28.C61H78F12N8O9P2Ru requires C, 50.24; H, (63.5 mg, 49 mmol) and 4-ethylmorpholine (45 mg) in MeOH– 5.39; N, 7.68%); 1H NMR (CD3CN), d 1.11–1.45 (m, 31H, CHCl3 (251, v/v, 5 cm3). The mixture was refluxed for 4 h NCH2CH2CH2, CH3 ) , 1.8–2.0 (m, 10H, CH2CH2O, until it turned into a clear red solution.After cooling to 25°C, OCH2CH2, CH2CH2CO2), 2.22 (m, 6H, CH2CO2), 2.45 (t, 2H, an excess of NH4PF6 was directly added to the solution to J 7.0 Hz, CH2CON), 3.00 (br s, 2H, H2NCH2), 4.52 (m, 4H, form a red precipitate, which was filtered, washed sequentially CH2O, OCH2), 6.67 (s, CONH), 7.16 (m, 4H, H5,5), 7.42 (m, with cold MeOH (2×5 cm3), water (2×15 cm3), Et2O 4H, H6,6), 7.88 (m, 4H, H4,4), 8.35–8.60 (m, 8H, H3,3, H3¾,5¾); (2×5 cm3), and dried in vacuo to yield 14, as a red solid 13C NMR (CD3CN), d 23.8 (NCH2CH2CH2), 25.0 (416 mg, 85%); mp 219–221 °C (Found: C, 47.66; H, 4.32; N, (CH2CH2CON), 28.4 (d, CH3, CH2CH2O), 29.7 (d, 7.95.C397H444F96N56O52P16Ru8 requires C, 47.87; H, 4.49; N, CH2CH2CO2 ), 32.7 (d, CH2CON, H2NCH2CH2), 7.88%); 1H NMR (CD3CN), d 1.30–3.90 (br m, 236H, CH2, 41.7(H2NCH2 ), 58.6 (NHC), 70.3 (OCH2), 71.1 (CH2O), 112.2 CH3), 4.53 (m, 40H, OCH2, CH2O), 6.47 (s, 4H, CONH), 7.15 (C5,5), 125.4 (C4,4), 128.5 (C3,3), 138.7 (C3¾,5¾), 153.5 (C6,6), (m, 32H, H5,5), 7.40 (m, 32H, H6,6), 7.86 (m, 32H, H4,4), 157.5 (C2,2), 159.4 (C2¾,6¾), 167.0 (d, C4¾), 172.9 (CONH), 173.7 8.35–8.60 (m, 64H, H3,3, H3¾,5¾); 13C NMR (CD3CN), d 23.1, (CO2 ); IR (KBr), 3417, 3295, 3086, 2980, 2940, 1719, 1614, 25.0, 25.9, 28.4 (CH3), 29.8, 29.9, 30.5, 30.6, 32.7, 32.8, 40.0 1470, 1394, 1370, 1213, 1162, 1040, 840, 788, 754 cm-1; (CONHCH2), 58.0 (CONHC), 68.0–70.0 (m, all CH2O, UV–VIS, lmax=244 (e=4.76×104 ), 270 (5.17×104), 304 OCH2), 81.3 (CO2C), 112.1 (d, C5,5), 125.5 (d, C4,4), 128.5 (6.08×104), 488 nm (1.81×104 dm3 mol-1 cm-1).(C3,3), 138.8 (C3¾,5¾), 153.5 (C6,6), 157.4 (C2,2), 159.4 (C2¾,6¾), 167.1 (d, C4¾), 172.4 (CONHC), 174.0 (CO2); IR (KBr), 3425, Complex 12 3118, 3079, 2979, 2941, 1724, 1671, 1617, 1547, 1470, 1425, 1217, 848, 786 cm-1; UV–VIS, lmax=244 (e=3.68×105 ), 270 To a solution of 4-[4¾-oxa-(2,2¾56¾,2-terpyridinyl)]butanoic (3.99×105), 304 (4.77×105), 488 nm (1.41×105 dm3 acid 6 (207 mg, 618 mmol) in dry DMF (15 cm3) were added mol-1 cm-1).DCC (128 mg, 618 mmol) and 1-HOBT (83.5 mg, 618 mmol) at 25°C. The mixture was stirred for 1 h, then amine 11 (901 mg, 618 mmol) was added. The whole mixture was stirred for 48 h, Results and Discussion after which the white precipitate was filtered.The red filtrate was concentrated in vacuo to aord a crude residue, which Synthesis of the tetrakisterpyridine core 5 was dissolved in CHCl3 (200 cm3), washed with saturated aqueous NaHCO3 (2×50 cm3), then brine (2×100 cm3), dried The synthesis of tetrakisterpyridine core 5 was initiated from the readily available tetracarboxylic acid 3, which has been (MgSO4), and concentrated in vacuo.The crude residue was column chromatographed eluting with 10% MeOH in CH2Cl2 demonstrated to be an ideal core for the construction of a four-directional dendritic materials.7 Acid 3, prepared10 in high to yield 12, as a red solid (465 mg, 42%); mp 90–94°C (Found: C, 53.95; H, 5.50; N, 9.47.C80H93F12N11O11P2Ru requires C, yield and purity from pentaerythritol and acrylonitrile, followed by hydrolysis, was reacted8 with BH3 in THF at 0°C 54.11; H, 5.28; N, 8.68%); 1H NMR, d 1.11–1.45 (m, 31H, NCH2CH2CH2, CH3 ) , 1.8–2.0 (m, 12H, OCH2CH2, to aord tetraol 4, which was then treated with at least 4 equivalents of 4¾-chloro-2,2¾56¾,2-terpyridine9 (4¾-Cl-tpy) in the CH2CH2O, OCH2CH2, CH2CH2CO2), 2.22 (m, 6H, CH2CO2), 2.40–2.46 (m, 4H, CH2CONH, CH2CONH), 3.10 (m, 2H, presence of powered KOH in anhydrous Me2SO at 60°C to give the desired tetrakisterpyridine core 5 in 74% yield after CONHCH2), 4.52 (m, 6H, OCH2, CH2O, OCH2), 6.56 (s, CONHC), 7.16–8.70 (m, tpy H); 13C NMR, d 23.1 purification, Scheme 1.The structure of core 5 was confirmed (1H NMR) by the definitive upfield shift (Dd=-0.52 ppm) for (NCH2CH2CH2 ), 25.0 (d, CH2CH2CONH, CH2CH2CONH), 28.0 (d, CH3, CH2CH2O), 29.8 (d, CH2CH2CO2), 31.7, 32.3, the singlet for the 3¾,5¾-terpy H upon the 4¾-terpy Cl to 4¾-terpy OR conversion. In 13C NMR, the peak shifts for the C5,5 from 32.7 (CH2CONH, H2NCH2CH2, CH2CONH), 39.2 1242 J.Mater. Chem., 1997, 7(7), 1237–1244d 121.1 to 107.3 and for C4¾ from d 146.5 to 167.1 further complex heteroaryl H region supports the presence of structurally dissimilar terpyridine environments. Whereas in its 13C support the transformation. NMR spectrum, the two pairs of dierent terpyridines aorded Synthesis of ruthenium(II ) complex connectors complex patterns with peaks for each carbon atom due to the small dierence caused by the two layers of ruthenium(II) 4-[4¾-Oxa-(2,2¾56¾,2-terpyridinyl)]butanoic acid 6, was pre- terpyridines centres connected by the slightly dierent organic pared by the reaction of 4¾-Cl-tpy with 4-hydroxybutanoic acid linkages.All signals (13C NMR) were, however, resolved to in the presence of solid KOH in anhydrous Me2SO at 60°C show each moiety of the dendritic complex, with the exception in 86% yield.The structure of 6 can be supported (NMR) by of the quaternary core carbon, which should have appeared at the shift of H3¾,5¾ at d8.46 to 7.92 denoting the formation of d 45.6; the absence of this signal is reasonable since it is the the 4¾-ethereal bond.By taking advantage of the peptide only unique atom in the dendritic assembly. coupling method11 (Scheme 2) using dicyclohexylcarbodiimide Hydrolytic or thermal deprotection, followed by subsequent (DCC) and 1-hydroxybenzotriazole (1-HOBT) in DMF, acid formation of a larger ‘dendritic’ surface can be accomplished 6 was reacted with ‘Behera’s amine’ 710 to aord terpyridine at either the appendage stage (8 or 12) or the four-directional amide 8 in 72% yield.The new peak (1H NMR) at d 6.03 dendrimer (14). The former oers solubility advantages as well denotes the formation of the amide bond. In 13C NMR, the as the ability to conveniently attach these metallo-modules to formation of the ethereal bond can be concluded based on the other macromolecular materials; applications of these metallo- significant shifts of C5,5 and C4¾; the successful amidation is macromolecules are in progress and will be reported elsewhere.supported by the shift of the signal assigned to newly introduced quaternary carbon moiety (CONHC) from d 52.8 to 57.6. The yellow–brown microcrystalline, paramagnetic Conclusion ruthenium(III ) complex 9 was prepared by refluxing 1 equival- The construction of this new type of double tiered metallodend- ent of 8 with RuCl3 3H2O in methanol to give 76% yield, rimer shows the importance of the stepwise construction by which was used without further purification.means of controlled metal complexation. This modular Preferential O- vs. N-arylation was realized when 5-amino- approach also provides a much more versatile methodology pentan-1-ol was reacted with 4¾-Cl-tpy in the presence of for the synthesis of specifically assembled metallodendrimers powered KOH in dry Me2SO to aord the free 5-aminopentyl and related polymers by using a combination of divergent and 4¾-(2,2¾56¾,2-terpyridinyl) ether 10 in 71% conversion, convergent approaches.Scheme 3.The structure of 10 was readily confirmed by the lack of change for the signals of H2NMCH2 in both 1H and This work was supported, in part, by the National Science 13C NMR spectra. The significant chemical shifts (1H NMR) Foundation (DMR-96–22609) and the Army Research Oce for H3¾,5¾ and C5,5, as well as for C4¾ (13C NMR) confirmed (DAAH04–93-G-0448). the free amino group and the preferential formation of the 4¾- ethereal bond.The aminoterpyridine 10 was then reacted with 1 equivalent of the ruthenium(III ) complex 9 in boiling meth- References anol and N-ethylmorpholine, as the reducing agent, followed by addition of an excess of NH4PF6, to aord the amino 1 For recent reviews see: (a) G. R. Newkome, C. N. Moorefield and F. Voegtle, Dendritic Molecules: Concepts, Syntheses, Perspectives, complex 11, as a red hexafluorophosphate salt in 72% yield.VCH,Weinheim, 1996;(b) N. Ardoinand D. Astruc,Bull. Soc. Chim. Confirmation of the structure of this ruthenium(II) complex Fr., 1996, 132, 875; (c) B. I. Voit, Acta Polym., 1995, 46, 87; (d) was demonstrated by the upfield shift (Dd=-1.23 ppm) for J. Issberner, R. Moors and F. Voegtle, Angew.Chem., Int. Ed. Engl., H6,6 in 1H NMR, and all downfield shifts of C5,5 from d 1994, 106, 2507; (e) J. M. J. Fre� chet, C. J. Hawker and K. L.Wooley, 107.3 to 112.2, C4,4 from d 121.2 to 125.4, C3,3 from d 123.7 J.Macromol. Sci. Part A, 1994, 31, 1627; (f ) J. M. J. Fre� chet, Science, to 128.5, C3¾,5¾ from d 136.6 to 138.7, C6,6 from d 148.9 to 1994, 263, 1710; (g) D.A. Tomalia, A. M. Naylor and W. A. Goddard, III, Angew Chem., Int. Ed. Engl., 1990, 29, 138. 153.5, C2,2 from d 156.0 to 157.5, C2¾,6¾ from d 156.9 to 159.4; 2 M. F. Ottaviana, S. Bossmann, N. J. Turro and D. A. Tomalia, notably the signal for C4¾ remained nearly constant. J. Am. Chem. Soc., 1994, 116, 661. Reaction of acid 6 with amine 11 was accomplished by using 3 For metallo-related dendrimer reviews: Advances in Dendritic the DCC coupling method, as described above, to give (42%) Macromolecules, ed.G. R. Newkome, JAI Press, Greenwich, CT, the complex 12, as a red solid. Any unreacted acid 6, which 1996, vol. 3, ch 3: S. Serroni, S. Campagna, G. Denti, A. Juris, contains the uncomplexed terpyridine moiety, was eliminated M. Venturi and V. Balzani, pp. 61–113; ch. 4: M. R. Bryce and W. Devonport, pp. 115–149; ch. 5: I. Cuadrado, M. More�n, by column chromatography so that no unexpected metal J. Losada, C. M. Casado, C. Pascual, B. Alonso and F. Lobete, complexation sites would be carried to the subsequent reaction. pp. 151–195. Other references not included in ref. 1: (a) R. L. C. Lau, An equimolar solution of ligand 12 with RuCl3·3H2O in T-W.D. Chan, I. Y.-K. Chan and H.-F. Chow, Eur.Mass Spectrom., methanol was refluxed to give the red paramagnetic complex 1995, 1, 371; (b) M.Haga, M. M. Ali and R. Arakawa, Angew. Chem., 13, which was filtered from the miin 34% crude yield, Int. Ed. Engl., 1996, 35, 76; (c)W. T. S. Huck, F. C. J. M. van Veggel Scheme 4. and D. N. Reinhoudt, Angew. Chem., Int. Ed.Engl., 1996, 35, 121; (d) U. Stebani, G. Lattermann, M. Wittenberg and J. H. Wendor, Angew. Chem., Int. Ed. Engl., 1996, 35, 1858; (e) E. Alessio, Synthesis of the dendritic complex 14 M. Macchi, S. Heath and L. G. Marzilli, Chem. Commun., 1996, 1411; (f ) D.-L. Jiang and T. Aida, Chem. Commun., 1996, 1523; (g) The synthesis of the final product, the dendritic macromolecule E. C.Constable, P. Harverson and M. Oberholzer, Chem. Commun., with two layers of ruthenium(II) terpyridine complexes, is 1996, 1821; (h) D. Armspach, M. Cattalini, E. C. Constable, C. E. shown in Scheme 5. The tetrakisterpyridine core 5 was treated Housecroft and D. Phillips, Chem. Commun., 1996, 1823; (i ) with 4.4 equivalents of complex 13 in the presence of 4- P. Bhyrappa, J. K. Young, J.S. Moore and K. S. Suslick, J. Am. ethylmorpholine in methanol–chloroform, followedby addition Chem. Soc. 1996, 118, 5708; (j) Y. Tomoyose, D.-L. Jiang, R.-H. Jin, of a slight excess NH4PF6 to aord the red, microcrystalline, T. Aida, T. Yamashita, K. Horie, E. Yashima and Y. Okamoto, Macromolecules, 1996, 29, 5236; (k) K. R. Seddon, Platinum Met. dendritic complex 14 in 85% yield. At this point, the traces of Rev., 1996, 40, 128; (l ) O.Mongin and A. Gossauer, T etrahedron impurities, which were present in the reaction mixture due to L ett., 1996, 37, 3825; (m) M. Bardaji, M. Kustos, A.-M. Caminade, the lack of purification of complex 13, conveniently remained J.-P. Majoral and B. Chaudret, Organometallics, 1997, 16, 403. in solution. The structure of the dendritic complex 14 was 4 G. R. Newkome, F. Cardullo, E. C. Constable, C. N. Moorefield confirmed by elemental analysis and NMR spectroscopy. The and A. M. W. C. Thompson, J. Chem. Soc., Chem. Commun., 1993, 1H NMR spectrum of 14 demonstrated the absence of para- 925. 5 G. R. Newkome, R. Guether, C. N. Moorefield, F. Cardullo, magnetic species as well as terminal terpyridines and the J. Mater. Chem., 1997, 7(7), 1237–1244 1243L. Echegoyen, E. Perez-Cordero and H. Luftmann, Angew. Chem., 8 G. R. Newkome, C. N. Moorefield and K. J. Theriot, J. Org. Chem., Int. Ed. Engl., 1995, 34, 2023. 1988, 53, 5552. 6 G. R. Newkome and C. N. Moorefield, Macromol. Symp., 1994, 77, 9 E. C. Constable and M. D. Ward, J. Chem. Soc., Dalton T rans., 63; G. R. Newkome, C. N. Moorefield, R. Guether and G. R. Baker, 1990, 1405. Polym. Preprints, 1995, 36, 609; G. R. Newkome, V. V. Narayanan, 10 G. R. Newkome and C. D. Weis, Org. Prep. Proc. Int., 1996, 28, 485. A. K. Patri, J. Groß, C. N. Moorefield and G. R. Baker, Polym. 11 J. Klausner and B. Bodansky, Synthesis, 1972, 453. Mater. Sci. Eng., 1995, 73, 222. 7 G. R. Newkome and X. Lin, Macromolecules, 1991, 24, 1443; G. R. Newkome and C. D.Weis, Org. Prep. Proc. Int., 1996, 28, 242. Paper 7/00127D; Received 6th January, 1997 1244 J. Mater. Chem., 1997, 7(7), 1237–1244

ISSN:0959-9428    

DOI:10.1039/a700127d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Eects of central metal ion (Mg, Zn) and solvent on singlet excited-state energy flow in porphyrin-based nanostructures Feirong Li,a Steve Gentemann,b William A. Kalsbeck,c Jyoti Seth,c Jonathan S. Lindsey,*a Dewey Holten*b and David F. Bocian*c aDepartment of Chemistry, North Carolina State University, Raleigh, NC 27695–8204, USA bDepartment of Chemistry, Washington University, St. L ouis, MO 63130–4899, USA cDepartment of Chemistry, University of California, Riverside, CA 92521–0403, USA Zinc porphyrins have been widely used as surrogates for chlorophyll (which contains magnesium) in photosynthetic model systems and molecular photonic devices.In order to compare the photodynamic behaviour of Mg- and Zn-porphyrins, dimeric and starshaped pentameric arrays comprised of free-base (Fb) and Mg- or Zn-porphyrins with intervening diarylethyne linkers have been prepared.A modular building block approach is used to couple ethynyl- or iodo-substituted porphyrins in defined metallation states (Fb, Mg or Zn) via a Pd-catalysed reaction in 2–6 h. The resulting arrays are purified in 45–80% overall yields by combinations of size exclusion chromatography and adsorption chromatography (95% purity).High solubility of the arrays in organic solvents facilitates chemical and spectroscopic characterization. The star-shaped Mg4Fb- and Zn4Fb-pentamers, where the Fb-porphyrin is at the core of the array, have pairwise interactions similar to those of dimeric MgFb- and ZnFb-arrays. The arrays have been investigated by static and time-resolved absorption and fluorescence spectroscopy, as well as resonance Raman spectroscopy.The major findings include the following. (1) The rate of singlet excited-state energy transfer from the Mg-porphyrin to the Fb-porphyrin [(31 ps)-1] is comparable to that from the Zn-porphyrin to the Fb-porphyrin [(26 ps)-1] in the dimeric arrays. Qualitatively similar results are obtained for the star-shaped pentamers. The similar rates of energy transfer for the Mgand Zn-containing arrays are attributed to the fact that the electronic coupling between the metalloporphyrin and Fb-porphyrin is approximately the same for Mg- vs.Zn-containing arrays. (2) The quantum yield of energy transfer is slightly higher in the Mgarrays (99.7%) than in the Zn-arrays (99.0%) due to the longer inherent lifetime of Mg-porphyrins (10 ns) compared with Znporphyrins (2.5 ns).(3) The rate of energy transfer and the magnitude of the electronic coupling are essentially independent of the solvent polarity and the coordination geometry of the metalloporphyrin (four- or five-coordinate for Zn-porphyrins, five- or sixcoordinate for Mg-porphyrins). (4) Polar solvents diminish the fluorescence yield and lifetime of the excited Fb-porphyrin in arrays containing either Mg- or Zn-porphyrins. These eects are attributed to charge-transfer quenching of the Fb-porphyrin by the adjacent metalloporphyrin rather than to changes in electronic coupling. The magnitude of the diminution is greater for the Mg-containing arrays, which is due to the greater driving force for charge separation.(5) The Zn-containing arrays are quite robust while the Mg-containing arrays are slightly labile toward demetallation and photooxidation. Taken together, these results indicate that porphyrin-based nanostructures having high energy-transfer eciencies can be constructed from either Mg- or Znporphyrins. However, Mg-containing arrays may be superior in situations where a succession of energy-transfer steps occurs (due to a slightly higher yield per step) or where charge transfer is a desirable feature.On the other hand, Zn-porphyrins are better suited when it is desirable to avoid charge transfer quenching reactions. Accordingly, the merits of constructing a device from Mgvs. Zn-containing porphyrins will be determined by the interplay of all of the above factors.The ability to construct molecular systems with well defined The natural antenna complexes absorb light and funnel the resultant energy to the reaction centres via excited-state energy three-dimensional architectures on the nanometre scale holds revolutionary potential for many disciplines, especially mate- migration processes.1 The energy migration process is extremely rapid (hopping time of ca. 0.1–1 ps per bacterio- rials chemistry where macroscopic objects can be designed and constructed with molecular-level precision. Nanostructures chlorophyll)2 and has a quantum eciency of nearly unity. Creating synthetic mimics of the natural antenna complexes designed for manipulation of optical phenomena are of particular interest for a variety of applications that are not possible has been a major objective of the field of artificial photosynthesis.More recently, such synthetic mimics have been tailored with bulk materials. Some examples include the following. (1) Light-harvesting nanostructures can be used as energy funnels to serve as molecular photonic devices in materials chemistry. The versatile optical (absorption and emission), redox, and with applications in solar energy or as energy sources to power molecular devices.(2) Molecular photonic wires and gates can photochemical properties of the porphyrins makes them ideally suited as components of nanostructures with optical features be used to transmit and manipulate signals in nanoscale information processing systems. (3) Structured composites of in the visible or near-IR spectral regions.Towards this goal, we have developed a modular building block synthesis of absorbers and emitters can serve as nanoscale optical sources or nanoscale imaging elements. All of these structures represent soluble multiporphyrin arrays comprised of metalloporphyrins or a composite of both metallo- and free-base porphyrins.3–11 a broad class of photonic devices whose performance can be controlled in the nanoscale regime.This building block approach has been used to construct a variety of molecular architectures containing from two to nine A major source of inspiration for the design and synthesis of optical nanostructures derives from the light-harvesting porphyrin constituents. The ability to construct successively more complicated, soluble molecular structures in a systematic antenna complexes of natural photosynthetic systems.The antenna complexes are comprised of a large number of pig- fashion has permitted us to investigate the mechanisms and factors controlling electronic communication in the synthetic ments that are arranged in a rigid three-dimensional matrix.J. Mater. Chem., 1997, 7(7), 1245–1262 1245multiporphyrin arrays, starting with the fundamental pairwise are structurally analogous to a series of previously studied Znporphyrin systems.4,6,12 The dimers and star-shaped pentamers interactions characteristic of the dimeric systems. Our previous work on dimeric, trimeric, and star-shaped pentameric arrays have dimensions along the porphyrin–diphenylethyne framework of ca. 4 and 6 nm, respectively. The availability of both has provided significant insights into the nature of these basic interactions.12–15 The information garnered from our studies sets of arrays enables a direct comparison of the synthesis, purification, chemical characterization, and spectroscopic has been used as a guide for constructing prototypical molecular photonic wires5 and optoelectronic gates10 that utilize the properties of multiporphyrin arrays comprised of Mg- vs.Znporphyrins. Inasmuch as Zn-porphyrins are four- or five- multiporphyrin motif. Other workers have also developed routes to large covalently linked porphyrin arrays. coordinate depending on the solvent, while Mg-porphyrins are five- or six-coordinate, the new arrays provide the opportunity Architectures prepared include star-shaped pentamers,16–18 linear pentamers,19 larger linear arrays up to nonamers,20 to investigate the eects of solvent and metal coordination state on the photodynamics of energy transfer. three-dimensional nonamers,18 polymeric arrays,21 and selfassembled pentamers.22 However, only a few of these routes enable precise specification of the metallation state of the Experimental various porphyrins in the array.Synthetic procedures A key structural element common to all of our multiporphyrin arrays is a diarylethyne linker that joins the constituent General. 1H NMR spectra (300 MHz, IBM FT-300, GN porphyrins at the meso-carbon atom of the porphyrin macro- 300), absorption spectra (HP 8451A, Cary 3), fluorescence cycles. The diarylethyne linkers are non-polar, establish a spectra (Spex Fluoromax) and electrochemical data12 were relatively fixed inter-porphyrin distance (ca. 20A° centre-to- collected routinely.Mass spectra were obtained by laser- centre) albeit with free rotation about the ethyne in fluid desorption mass spectrometry.11 Toluene (Fisher, certified solution,15 and enable weak electronic interactions among the ACS) and THF (Fisher, certified) were distilled from LiAlH4. porphyrins.12–14 These features of the molecular architecture CH2Cl2 (Fisher, certified ACS) was distilled from K2CO3.promote extremely ecient (ca. 99%) energy transfer which Triethylamine (Fluka, puriss) was distilled from CaH2. All predominantly involves a through-bond process mediated by reagents were obtained from Aldrich.TLC plates were pur- the diarylethyne linker.13 Our previous studies of dimeric chased from Baker (Baker-flex, aluminium oxide IB-F). arrays indicate that the rate of energy migration can be Column chromatography was performed using silica (Baker explicitly controlled by structural modification of the linker, flash silica), alumina (Fisher A540, 80–200 mesh) or various specifically, via alteration of the substituent groups on the aryl grades of deactivated alumina.Chromatography of porphyrins rings. We anticipate that the rates of energy transfer would was performed with shielding from ambient light. The isolated also be aected by other properties of the linker such as its yields of Mg- or Zn-porphyrins do not take into account any eective length and geometry.Another important design ligands on the metal ion. The Fb-porphyrin building blocks element for controlling the physico-chemical properties of the FbU, FbU¾, FbU-I, FbU-I4, and FbU-core have been prepared multiporphyrin arrays is the selection of the metal ion in the previously,3 as have the Zn-porphyrin building blocks ZnU metalloporphyrin.The metal ion modulates the redox poten- and ZnU¾ (Fig. 1).6 tial,23 conformation,24 and excited-state lifetime25 of the metalloporphyrin constituent and hence, could aect the electronic Preparation of alumina with various activities. Deactivated communication in the arrays. alumina of various grades was prepared for use in column Studies in the field of artificial photosynthesis ultimately chromatography.To a sample of alumina (Fisher, A540, require a molecular species which plays the role of (bacterio)- 80–200 mesh, grade I) in an open beaker was added deionized chlorophyll. Although (bacterio)chlorophyll contains a central water dropwise via a pipette under vigorous mechanical stir- magnesium ion, most studies in artificial photosynthesis have ring, after which stirring was continued for 1 h to ensure employedZn- rather thanMg-complexes.26 Relativelyfewmodel homogeneity. In this manner alumina with 9% w/w water, systems containing Mg-porphyrins have been prepared, and 12% w/w water, 15% w/w water (grade V), or 20% w/w water these have involved porphyrin monomers,27 dimers,28 trimers,29 was prepared.35 and larger aggregates of non-covalently linked porphyrins.30 The dearth of artificial photosynthetic systems containing Mg- Analytical size exclusion chromatography (SEC).The complexes originates mainly in historic synthetic diculties in methods employed for analytical SEC have been described in preparing Mg-porphyrins. Although Mg- and Zn-porphyrins detail.6,9 Briefly, analytical SEC columns (styrene–divinylben- have grossly similar features, Mg-porphyrins have four- to five- zene copolymer) were purchased from Hewlett Packard and fold larger fluorescence yields (Wf=0.15),31 four- to five-fold Phenomonex.Analytical SEC was performed with a Hewlett- longer fluorescence lifetimes (t=8–10 ns),31 and 100–300 mV Packard 1090 HPLC using 500 A° (300×7.8 mm), 500 A° lower oxidation potentials.10,23,32 The photochemical conse- (300×7.5 mm) and 100 A° (300×7.5 mm) columns (5 mm) in quences of these distinctions between Mg- and Zn-porphyrins, series eluting with THF (flow rate=0.8 ml min-1; void volume particularly with regards to energy- and/or electron-transfer ca. 14.4 ml). Reaction monitoring was performed by removing reactions, remain largely unexplored. Probing these distinctions ca. 5 ml aliquots from the reaction mixture, diluting with 500 ml is essential not only for understanding artificial photosynthetic toluene (Fisher, certified ACS) and injecting 50 ml to the models but also for the rational design of molecular devices HPLC. Sample detection was achieved by absorption spec- that transcend photosynthesis, such as molecular optoelectronic troscopy using a diode array detector with quantitation at gates where a Zn-porphyrin provides for energy transfer and a 420 nm (±10 nm bandwidth, reference wavelength 475 nm), Mg-porphyrin functions as a redox switch.10 which best captures the Soret bands of the porphyrins.Recently, we developed two simple methods for the preparation of Mg-porphyrins.33,34 The removal of this synthetic Magnesium 5,10,15-trimesityl-20-{4-[2- obstacle aords an opportunity for systematically exploring (trimethylsilyl) ethynyl]phenyl}porphyrin (MgU) the physico-chemical properties of these systems.In this paper, we combine the new synthesis of Mg-porphyrins with the Magnesium insertion was accomplished using the heterogeneous method.33 To a solution of FbU (220 mg, 0.263 mmol) building block synthesis of multiporphyrin arrays.These methods are used to prepare a series of dimeric and star- in 25 ml CH2Cl2 was added N,N-diisopropylethylamine (DIEA) (1.1 ml, 5.26 mmol) and MgI2 (731 mg, 2.63 mmol). shaped pentameric arrays containing Mg-porphyrins, and an identical set comprised of Zn-porphyrins (Fig. 1). These arrays The reaction mixture was stirred at room temperature. After 1246 J. Mater. Chem., 1997, 7(7), 1245–1262Fig. 1 Monomers, dimers and pentamers for spectroscopic study. Each compound has an unhindered, diphenylethyne linker, which is designated U for consistency with our previous nomenclature for related arrays.13 The Zn-porphyrins are four- or five-coordinate, while the Mg-porphyrins are five- or six-coordinate (ligands are not shown) depending on the solvent.Although this diagram portrays the porphyrins in the arrays in coplanar geometries, in fluid solution at room temperature the porphyrins rotate freely about the ethyne, and the diphenylethyne linker bends slightly.15 Replacement of the TMS-group with H in FbU, MgU, and ZnU aords FbU¾, MgU¾, and ZnU¾. 30 min the reaction was judged to be complete by fluorescence to proceed for 60 min at room temperature. The reaction mixture was diluted with 30 ml ethyl acetate, extracted with excitation spectroscopy. The reaction mixture was diluted with 30 ml CH2Cl2, washed with 10% NaHCO3 (2×50 ml), dried 5% NaHCO3 (2×50 ml) and water (2×50 ml) and then the organic layer was dried (Na2SO4 ).Column chromatography (Na2SO4 ), filtered, concentrated and chromatographed [Fisher A540 alumina, toluene–acetone (1051), 3.8×5 cm] aording [Fisher A540 alumina, toluene–acetone (1051), 3.8×5 cm] aorded 175 mg (95%). 1H NMR (CDCl3) d 1.82 (s, 12 H, 223 mg (99% yield). 1H NMR (CDCl3) d 0.36 (s, 9 H, SiCH3), 1.81 (s, 18 H, ArCH3 ), 2.61 (s, 9 H, ArCH3 ), 7.82 (AA¾BB¾, 2 ArCH3), 1.87 (s, 6 H, ArCH3), 2.60 (s, 9 H, ArCH3), 3.32 (s, 1 H, CCH), 7.82 (AA¾BB¾, 2 H, ArH), 8.16 (AA¾BB¾, 2 H, ArH), H, ArH), 8.14 (AA¾BB¾, 2 H, ArH), 8.59–8.70 (m, 8 H, bpyrrole); C58H54MgN4Si calc.av. mass 859.5u, obs. m/z 859.4; 8.59–8.72 (m, 8 H, b-pyrrole); C55H46MgN4 calc. av. mass 787.3u, obs. m/z 787.0; labs (toluene) 406(sh), 426, 566, 606 nm. labs (toluene) 406(sh), 426, 566, 606 nm.Magnesium 5,10,15-trimesityl-20-(4-ethynylphenyl )porphyrin 4-(Magnesium 5,10,15-trimesityl-20-porphinyl )-4¾-(5,10,15- trimesityl-20-porphinyl )-diphenylacetylene (MgFbU) (MgU¾) A solution of MgU (200 mg, 0.233 mmol) in 30 ml THF was The Pd-mediated coupling reaction follows the general procedure established previously.6,9 Samples of ethynyl porphyrin treated with tetrabutylammonium fluoride (TBAF) on silica (373 mg, 1.0–1.5 mmol F g-1) and the reaction was allowed MgU¾ (32.2 mg, 41 mmol) and free-base iodoporphyrin FbUJ. Mater.Chem., 1997, 7(7), 1245–1262 1247I (29.5 mg, 34 mmol) were dissolved in 15 ml toluene–triethyl- 4-(Magnesium 5,10,15-trimesityl-20-porphinyl )-4¾-(magnesium 5,10,15-trimesityl-20-porphinyl) diphenylacetylene (Mg2U) amine (TEA) (551) in a 25 ml one-neck round-bottomed flask.The flask was heated to 35°C and was fitted with a 15 cm To a solution of Fb2U (13.7 mg, 0.0091 mmol) in 1 ml CH2Cl2 reflux condenser through which a drawn glass pipette was was addedN,N-diisopropylethylamine (32 ml, 0.182 mmol) and mounted for deaeration with argon. The reaction vessel was MgI2 (25.5 mg, 0.091 mmol).33 The reaction mixturewas stirred deaerated with a high flow rate of argon for 15 min.The tip at room temperature. After 30 min the reaction was judged to of the pipette was then immersed in the solution. The argon be complete by fluorescence excitation spectroscopy. The reac- flow rate was turned down and bubbling was continued for tion mixture was diluted with 10 ml CH2Cl2, washed with another 15 min.The condenser was then elevated, leaving the 10% NaHCO3 (2×10 ml), dried (Na2SO4), filtered, concen- pipette tip in the solution, and Pd2dba3 (4.7 mg, 5.1 mmol) and trated and passed over a column [Fisher alumina, toluene– AsPh3 (12.5 mg, 41 mmol) were added to the mixture as solids acetone (1051), 3.8×5 cm] aording 14 mg (99% yield). simultaneously.The pipette was removed from the reaction 1H NMR (CDCl3) d 1.85 (s, 24 H, ArCH3), 2.38 (s, 18 H, mixture and positioned about 2 cm above the solution. The ArCH3), 2.62 (s, 12 H, ArCH3), 7.24 (s, 12 H, ArH), 8.00 argon flow rate was turned up slightly and the reaction was (AA¾BB¾, 4 H, ArH), 8.26 (AA¾BB¾, 4 H, ArH), 8.61–8.84 (m, allowed to proceed. After 2 h the reaction mixture was analysed 16 H, b-pyrrole); C108H90Mg2N8 calc.av. mass 1548.6u, obs. by analytical SEC prior to concentration under reduced press- m/z 1547.0; labs (toluene) 406(sh), 426, 526, 566, 606 nm. ure. Analytical SEC showed a trace of material eluting at the leading edge of the product (tR<24.4 min), the product (tR Mg4FbU 25.4 min), and small amounts of monomeric porphyrin materials (tR 27.5 and 28.2 min).TLC analysis [Baker alumina, In a 50 ml reaction vessel was added tetraiodoporphyrin FbUI 4 (19.9 mg, 17.8 mmol) and 20 ml toluene–triethylamine (551). toluene–acetone(1551)] showed starting material FbU-I (Rf 0.9), a non-fluorescent component (Rf 0.6), MgFbU (Rf 0.5), Sonication (Fisher sonicating bath, FS14) aorded complete dissolution of FbU-I4, after which MgU¾ (70 mg, 89.2 mmol) MgU¾ (Rf 0.3), and some baseline materials.The reaction mixture was dissolved in toluene and passed over an alumina was added. The flask was immersed in an oil-bath at 35 °C and was equipped with a reflux condenser through which a (deactivated with 15% w/w water) column (3.8×5 cm) and eluted with toluene. AsPh3 elutes rapidly, followed by a mixture drawn glass pipette was positioned for deaeration with argon. The reaction apparatus was deaerated with a high flow rate of of mobile porphyrins, and dark material including the Pdreagents remains at the top of the column.The band consisting argon for 15 min. The solution was then deaerated with the tip of the pipette immersed in the solution with gentle bubbling of MgFbU and trace amounts of high molecular mass materials and porphyrin monomers was collected.The mixture of por- of argon for 15 min. Then the condenser was elevated and Pd2dba3 (9.8 mg, 10.7 mmol) and AsPh3 (26.2 mg, 85.6 mmol) phyrins was concentrated, dissolved in toluene and loaded onto a preparative SEC column (BioRad Bio-Beads SX-1 in were added as solids simultaneously. The condenser was repositioned and argon bubbling was continued for 5 min.The THF, 4.8×60 cm, gravity-flow, 4 ml min-1). The high molecular mass material eluted first followed by the dimer MgFbU. pipette tip was then replaced about 2 cm above the solution and the argon flow rate was turned up slightly. The reaction Analytical SEC indicated that the dimer band contained trace amounts of high molecular mass material and monomeric course was monitored by analytical SEC.Aliquots (ca. 5 ml) were taken by a drawn glass capillary tube through the porphyrin. The impure dimer was then chromatographed again on alumina as described for the first column. A faint yellowish condenser in order to minimize admission of air into the reaction flask. After 2 h the reaction mixture consisted of a band eluted quickly.The second band was collected and aorded MgFbU (38 mg) in 74% yield. 1H NMR (CDCl3) d small amount of high molecular mass materials, a large amount of pentamer, small amounts of porphyrinic intermediates and -2.53 (br s, 2 H, NH), 1.87 (s, 24 H, ArCH3), 2.44 (s, 18 H, ArCH3), 2.64 (s, 12 H, ArCH3), 7.28 (s, 8 H, ArH), 7.29 (s, 4 unreacted MgU¾.Additional Pd2dba3 (9.8 mg, 10.7 mmol) and AsPh3 (26.2 mg, 85.6 mmol) were added. At 6.5 h, the reaction H, ArH), 8.02–8.08 (m, 4 H, ArH), 8.26–8.30 (m, 4H, ArH), 8.62–8.87 (m, 16 H, b-pyrrole); C108H92MgN8, calc. av. mass was judged to be complete. TLC analysis [Baker alumina, toluene–acetone (1051)] showed the starting material MgU¾ 1526.3u, obs. m/z 1526.6; labs (toluene) 430, 516, 564, 604, 650 nm.followed by a streak of fluorescent porphyrinic materials and some baseline materials. The crude mixture was concentrated 4-(Zinc 5,10,15-trimesityl-20-porphinyl )-4¾-(5,10,15-trimesityl- to dryness, dissolved in toluene–CHCl3 (352) and passed over 20-porphinyl )-diphenylacetylene (ZnFbU) a short column (3.8×5 cm) of alumina (deactivated with 15% w/w water) and eluted with toluene–CHCl3 (352). The chroma- Prepared previously.6 tography column was shielded with a black cloth.AsPh3 eluted first followed by an intense band consisting of porphyrins. 4-(5,10,15-Trimesityl-20-porphinyl )-4¾-(5,10,15-trimesityl-20- Some dark-coloured materials remained at the top of the porphinyl )-diphenylacetylene (Fb2U) column. The mixture of porphyrins was concentrated, dissolved in toluene and loaded onto a preparative SEC column (BioRad Samples of ethynyl porphyrin FbU¾ (19.9 mg, 26 mmol) and iodoporphyrin FbU-I (20.4 mg, 23.5 mmol) were coupled under Bio-Beads SX-1 in THF, 4.8×60 cm, gravity-flow, 4 ml min-1).The pentamer band was collected with small amounts of high similar conditions as described for MgFbU. Analytical SEC of the crude reaction mixture showed a trace amount of high molecular mass materials, tetrameric and trimeric porphyrin intermediates. The impure pentamer was rechromatographed molecular mass materials (tR ca. 24.0 min), the product (tR 25.5 min) and a small amount of monomeric porphyrin mate- by SEC in the same manner aording a mixture of the pentamer and trace amounts of higher molecular mass porphy- rials (tR 28.3 min).TLC [silica, toluene–hexanes (352)] showed starting material FbU-I (Rf 0.74), Fb2U (Rf 0.53) and some rinic materials, and tetrameric and trimeric porphyrins. This mixture was then chromatographed on alumina (deactivated slow-moving materials (Rf <0.18). No butadiyne-linked dimer9 (Rf 0.59) was observed. Flash chromatography [silica, toluene– with 15% w/w water; column=3.8×10 cm) with elution using toluene–CHCl3(552).The third band was collected, aording hexanes (352), 3.8×10 cm] aorded the product (28 mg, 79%). 1H NMR (CDCl3) d -2.56 (s, 4 H, NH), 1.85 (s, 36 H, o- 30 mg (45%) of pentamer Mg4FbU. A final passage over the same preparative SEC column, with removal of the leading ArCH3), 2.61 (s, 18 H, p-ArCH3), 7.26 (s, 12 H, ArH), 8.04 (AA¾BB¾, 4 H, ArH), 8.26 (AA¾BB¾, 4 H, ArH), 8.65,8.78 (m, 16 edge of the band (<5% of total material) resulted in sharpening of the analytical SEC peak from FWHM=0.71 to 0.65 min.H, b-pyrrole); C108H94N8 calc. av. mass 1503.9u, obs. m/z 1502.4; labs (toluene) 424, 516, 550, 594, 650 nm. 1H NMR 500 MHz (CDCl3 ) d -2.61 (s, 1 H, NH), 1.88 (s, 24 1248 J.Mater. Chem., 1997, 7(7), 1245–1262H, o-ArCH3), 1.89 (s, 48 H, o-ArCH3), 2.65 (s, 12 H, p-ArCH3), UV chip) was used as the detector. All RR experiments were conducted at ambient temperature on samples dissolved in 2.67 (s, 24 H, p- ArCH3), 7.28 (s, 8 H, ArH), 7.31 (s, 16 H, ArH), 8.10 (AA¾BB¾, 8 H, ArH), 8.17 (AA¾BB¾, 8 H, ArH), rigorously degassed HPLC grade or spectroscopic grade solvents (toluene, 2-nitrotoluene, CH2Cl2, DMF, or THF).The 8.35–8.40 (m, 16 H, ArH), 8.65 (m, 16 H, b-pyrrole peripheral porphyrins), 8.76 (d, 8H, J=4.4 Hz, b-pyrrole peripheral por- sample concentration was typically 0.05 mM. The sample solutions were contained in spinning 5 mm quartz NMR tubes. phyrins), 8.89 (d, 8H, J=4.4 Hz, b-pyrrole peripheral porphyrins), 9.07 (s, 8 H, b-pyrrole core porphyrin); C264H206Mg4N20 Spinning was found to be essential in order to prevent photodecomposition of the Mg-porphyrins.The excitation wavelengths calc. av. mass 3755.9u, obs. m/z 3759.4; labs (toluene) 430, 522, 564, 606, 648 nm. were provided by the output of an Ar ion (Coherent Innova 400–15UV) laser. The Raman shifts were calibrated by using Zn4FbU the known values of indene, fenchone and acetonitrile.The Raman shifts are accurate to ±1 cm-1 for strong and/or Samples of FbU-I4 (19.9 mg, 17.8 mmol) and ZnU¾ (73.9 mg, isolated bands. The laser power at the sample was typically 89.2 mmol) were coupled exactly as described for Mg4FbU, 5–7 mW and the spectral resolution was ca. 2 cm-1 at a and the product distribution observed by analytical SEC was Raman shift of 1600 cm-1.identical with that of Mg4FbU. The crude mixture was concentrated to dryness, dissolved in CH2Cl2 and passed over a short Time-resolved absorption and fluorescence spectroscopy. column of silica (CH2Cl2, 3.8×5 cm) shielded with a black Fluorescence lifetimes were acquired on an apparatus having cloth. AsPh3 eluted first, followed by an intense band of a time response of ca. 0.5 ns. Samples (ca. 50 mM) in 1cm porphyrins, with dark-coloured materials left at the top of the cuvettes were degassed on a vacuum line. Excitation flashes at column. The mixture of porphyrinswas concentrated, dissolved 532 nm having a duration of 30 ps were obtained by frequency in toluene and loaded onto a preparative SEC column (BioRad doubling the output of an actively/passively mode-locked Bio-Beads SX-1 in THF, 4.8×60 cm, gravity-flow, 4 ml min-1). Nd5YAG laser operating at 7 Hz.The flashes had an energy The pentamer band was collected with small amounts of high of 0.5 mJ and were focused to 3 mm at the sample. Emission molecular mass materials, tetrameric and trimeric porphyrin at 90° from the excitation path was collected by a lens, intermediates. The impure pentamer was rechromatographed transmitted through a long-pass filter (Schott OG570 for via SEC in the same manner aording a mixture of the metalloporphyrin emission or OG630 for Fb-porphyrin emis- pentamer and trace amounts of higher molecular mass porphy- sion) and focused on a pin photodiode (Newport Research rinic materials, and tetrameric and trimeric porphyrins.This 818-BB-21 PIN). The output of the photodiode was connected mixture was then chromatographed on silica (3.8×10 cm) directly to the input of a Tektronix 7912AD transient digitizer using CH2Cl2–hexanes(352). The first band aorded 38 mg that was controlled by a personal computer. Typically 64 (55%) of pentamer Zn4FbU. A final passage over the same traces were averaged to obtain a fluorescence decay profile.preparative SEC column, with removal of the leading edge of Transient absorption data were acquired as described else- the band (<5% of total material) resulted in sharpening of where.39 Samples in 2 mm pathlength cuvettes had a concen- the analytical SEC peak from FWHM=0.68 to 0.64 min. tration of ca. 10mM for measurements in the 410–560 nm 1H NMR 500 MHz (CDCl3) d -2.60 (s, 2 H, NH), 1.90 (s, 72 region and a concentration of ca. 100 mM for measurements in H, o-ArCH3), 2.62 (s, 12 H, p-ArCH3), 2.65 (s, 24 H, p-ArCH3), the 600–750 nm region. The samples were excited with flashes 7.31 (s, 8 H, ArH), 7.33 (s, 16 H, ArH), 8.13 (AA¾BB¾, 8 H, at 582 nm having a duration of 0.2 ps. The flashes had an ArH), 8.18 (AA¾BB¾, 8 H, ArH), 8.36 (AA¾BB¾, 8 H, ArH), 8.40 energy of 100 mJ and were focused to 1.5 mm at the sample.(AA¾BB¾, 8 H, ArH), 8.75 (m, 16 H, b-pyrrole peripheral The absorption changes were probed with weak white-light porphyrins), 8.85 (d, 8 H, J=4.5 Hz, b-pyrrole peripheral (400–1000 nm) pulses also having a duration of ca. 0.2 ps. porphyrins), 8.98 (d, 8 H, J=4.5 Hz, b-pyrrole peripheral Absorption changes over a 150 nm wavelength span were porphyrins), 9.08 (s, 8 H, b-pyrrole core porphyrin); acquired using a two-dimensional detection system.For each C264H206N20Zn4 calc. av. mass 3920.2u, obs. m/z 3918.5; labs(to- spectrum, data acquired with 300 flashes were averaged, giving luene) 424, 429, 519, 551, 590, 651 nm. a resolution in DA of ±0.005.Absorption changes were obtained as a function of time by sending the probe pulse Spectroscopic methods down an optical delay line, which permitted pump–probe time Absorption and fluorescence spectroscopy. Absorption spectra delays of -300 ps to 3 ns. were collected using a Varian Cary 3 with 1 nm bandwidths and 0.25 nm data intervals. Fluorescence spectra were collected Results using a Spex Fluoromax with 1 mm slit widths (4.25 nm) and 1 nm data intervals.Emission spectra were obtained with Synthesis of the building blocks and the arrays Alexc <0.1. Quantum yields were determined by ratioing inte- Porphyrin building blocks. Monofunctionalized porphyrin grated corrected emission spectra to MgTPP (0.15),31 ZnTPP building blocks were prepared via mixed aldehyde conden- (0.030)36 or TPP (0.11)36 in toluene.Fluorescence quantum sations. Lindsey and co-workers previously prepared the free- yield measurements in other solvents were corrected for refracbase trimesityl-monoethynylporphyrin (FbU) by condensing tive index dierences relative to toluene.37 Excitation spectra 4-[2-(trimethylsilyl)ethynyl]benzaldehyde and benzaldehyde were not corrected.Measurements were made at room temwith pyrrole,3 but the separation of FbU from the mixture of perature without deaeration of samples. The solvent relative six porphyrins was dicult. A more ecient separation method permittivities (e) at room temperature for various solvents are (Scheme 1) involves separation of the Zn- rather than the Fb- as follows: toluene (2.38), ethyl acetate (6.02), tetrahydrofuran porphyrins.6 In this method, the crude reaction mixture con- (THF, 7.58), acetone (20.7), 2-nitrotoluene (27.4), acetonitrile taining six porphyrins was chromatographed to remove non- (37.5), dimethyl sulfoxide (DMSO, 46.7).38 porphyrinic materials.The mixture of six porphyrins was subjected to zinc-insertion conditions and column chromatog- Resonance Raman spectroscopy.Resonance Raman (RR) spectra were recorded with a triple spectrograph (Spex 1877) raphy of the mixture of Zn-porphyrins readily aorded ZnU. After isolation, ZnU was demetallated with trifluoroacetic acid equipped with either a 1200 or 2400 groove mm-1 holographically etched grating in the third stage. A liquid-nitrogen- (TFA) in CH2Cl2 to aord the corresponding FbU.The magnesium chelate was prepared by treating FbU with MgI2 cooled, UV-enhanced 1152X298 pixel charge coupled device (Princeton Instruments, LN/CCD equipped with an EEV1152- and N,N-diisopropylethylamine in CH2Cl2 at room tempera- J. Mater. Chem., 1997, 7(7), 1245–1262 1249procedure. The attempted separation of MgU was carried out on alumina of various activities and with eluents of various polarities.Separation of the mixture of six Mg-porphyrins was achieved on alumina TLC [Baker alumina, toluene–CHCl3 (2051)]. However, column chromatography on alumina grade I or deactivated alumina containing 9, 15 or 20% water was ineective in separating the porphyrins. Accordingly, the preferable route for forming MgU involves isolation of ZnU followed by demetallation and magnesium insertion.By this sequence, each of the metalloporphyrin building blocks (ZnU, MgU) was prepared in 200 mg quantities in ca. 2 days. Trimesitylmonoiodoporphyrin (FbU-I) was prepared via condensation of 4-iodobenzaldehyde and mesitaldehyde with pyrrole as described previously.3 In contrast to FbU, FbU-I was easily separated by column chromatography on silica.3,6 The tetraiodoporphyrin FbU-I4 was synthesized by condensation of 4-iodobenzaldehyde and pyrrole and was purified by column chromatography.3 Dimeric arrays.The key reaction for the synthesis of the arrays involves the Pd-catalysed coupling of an ethynylphenyl porphyrin and an iodophenyl porphyrin.We previously optimized this coupling reaction for the synthesis of multiporphyrin arrays containing Fb-porphyrins and Zn-porphyrins,9 and used this method to prepare ZnFbU.6 The optimization was performed in order to achieve good yields of the diarylethyne- Scheme 1 Separation of FbU from the mixed condensation reaction linked porphyrin array under mild conditions in the absence mixture of any copper cocatalysts, and to minimize formation of higher molecular mass byproducts as well as diarylbutadiyne-linked ture with stirring for 30 min.33 Column chromatography of the dimers.The optimized conditions enable the coupling to be crude reaction mixture aorded MgU in 99% yield. performed with 1.5–5 mM of each porphyrin in toluene–tri- The trimethylsilyl group of MgU or ZnU was removed by ethylamine (551) in the presence of tris(dibenzylideneacetone) treatment with TBAF on silica in THF at room temperature dipalladium(0) (Pd2dba3 ) and triphenylarsine (AsPh3) under for 60 min (Scheme 2).No demetallation of either metallopor- argon at 35°C for 2 h. The molar ratio of the components is phyrin was observed during this reaction. ZnU¾ was isolated as follows: ethyne (1.25), iodide (1), Pd2dba3 (0.15), AsPh3 by chromatography on silica.3 However, due to the slightly (1.2).To establish the compatibility of Mg-porphyrins with acidic nature of silica, chromatography of MgU¾ was performed these coupling conditions, magnesium tetraphenylporphyrin on alumina in order to avoid demetallation. Both ZnU¾ and (MgTPP) was subjected to the same coupling reaction con- MgU¾ were isolated in 95% yield.In general, we have found ditions. After 2 h, TLC and analytical SEC showed no that chromatography of the Zn-porphyrins could be performed decomposition, demetallation, or transmetallation of MgTPP. on either silica or alumina, while Mg-porphyrins generally For the synthesis of porphyrin arrays, the reaction course is require chromatography on alumina rather than silica to avoid easily monitored by analytical size exclusion chromatography demetallation. (SEC) coupled with a UV–VIS diode array detector.In pursuit of a direct route to MgU mirroring that used to Chromatograms collected periodically provide a clear indi- isolate ZnU, we converted the mixture of Fb-porphyrins into cation of product distribution over time. Mg-porphyrins using the heterogeneous magnesium insertion The reaction of ethynylporphyrin MgU¾ (2.73 mM) and iodoporphyrin FbU-I (2.27 mM) under the Pd-mediated coupling conditions (30 mol% Pd atom–iodide and 120 mol% AsPh3–iodide) was performed under argon at 35°C (Scheme 3).After 2 h, SEC analysis of the reaction mixture showed a trace amount of high molecular mass materials, dimer MgFbU, and a small amount of porphyrin monomers.TLC analysis [Baker alumina, toluene–acetone (1551)] showed FbU-I (Rf 0.9), a non-fluorescent component (Rf 0.6), MgFbU (Rf 0.5), MgU¾ (Rf 0.3), and some baseline materials. The reaction mixture was concentrated and chromatographed [toluene–acetone (1551)] on a short column of deactivated alumina (15% water), which removed the Pd-reagents and AsPh3 from the porphyrin components. Preparative size exclusion chromatography of the mixture of porphyrins aorded MgFbU and a trace amount of monomeric porphyrins.Subsequent chromatography on deactivated alumina (15% water) aorded MgFbU in 74% overall yield. Characterization of MgFbU was performed by TLC, analytical SEC, 1H NMR spectroscopy, absorption and fluorescence spectroscopy, and laser desorption mass spectrometry. In an early attempt to synthesize MgFbU, we sought to insert magnesium selectively into the core of one porphyrin unit in the all-free-base dimer, Fb2U. Fb2U was prepared via Scheme 2 Synthesis of porphyrin building blocks ZnU¾ and MgU¾ the Pd-catalysed coupling reaction of ethynyl porphyrin FbU¾ 1250 J. Mater.Chem., 1997, 7(7), 1245–1262Scheme 3 Formation of dimeric arrays MgFbU and Fb2U and iodo porphyrin FbU-I, and was isolated in 79% yield revealed that the reaction mixture consisted of pentamer, small amounts of high molecular mass material, intermediates (tetra- after one flash silica chromatography column.Upon treatment of Fb2U with MgI2 (2–8 equiv.) and DIEA (4–16 equiv.) in mer, trimer and dimer) and starting material ZnU¾.Tetraiodoporphyrin FbU-I4 was completely consumed. CH2Cl2, no metallation was observed, while exposure to 10 equiv. MgI2 and 20 equiv. DIEA aorded the completely Another portion of catalyst and ligand was added, and after an additional 3 h, the formation of Zn4FbU levelled o. The metallated Mg2U. These experiments aimed at selective metal insertion in a preformed array comprised of Fb-porphyrins product distribution during the course of reaction is shown in Fig. 2. The peaks of the dimeric, trimeric and tetrameric proved ineective in yielding the monomagnesiated dimer. In contrast, the desired MgFbU dimer is easily prepared by the materials are well separated (tR dierences>1 min). The peaks of the tetrameric, pentameric and high molecular mass mate- rational coupling of Fb-porphyrin and Mg-porphyrin building blocks.rials are clearly present but are not well resolved. By visual inspection, the pentamer-forming reaction remained homogeneous at all times. The crude reaction mixture was chromato- Star-shaped pentameric arrays. Previously we prepared two star-shaped Zn4Fb-pentamers bearing 2,6-dimethoxyphenyl graphed first on silica to remove Pd-reagents and AsPh3, then on two SEC columns which aorded the pentamer with trace units or mesityl groups at the non-linked meso-positions.This synthetic work was done prior to the investigation of optimized amounts of tetrameric and trimeric porphyrins, and finally on silica which aorded the purified Zn4FbU (55% overall yield). Pd-coupling methods and before we had refined the chromatographic separation methods for these compounds.The di- We found that the FWHM of the peak obtained by analytical SEC aorded one measure of purity. A subsequent passage of phenylethyne-linked pentamer bearing 2,6-dimethoxyphenyl groups was prepared by a coupling reaction at 100°C for 12 h Zn4FbU over the preparative SEC column led to removal of only a trace amount of the leading edge of the band, but (45.6 mg, 45% isolated yield),4,6 while a diphenylethyne-linked pentamer bearing mesityl groups was prepared by a coupling caused the peak in the analytical SEC to sharpen from 0.68 to 0.64 min.This material was used for spectroscopic studies. at 50°C for two weeks (8.8 mg, 5.5% isolated yield).40 For solubility reasons we have since focused on the mesityl- In the preparation of Mg4FbU, the coupling reaction of MgU¾ and FbU-I4 and the product distribution as determined substituted arrays.6 We now report a refined synthesis of a diphenylethyne-linked pentamer (Zn4FbU), extend this route by analytical SEC were indistinguishable from that in the synthesis of Zn4FbU.However, the purification procedure to the synthesis of aMg4FbU pentamer, and develop improved separation methods for isolating the pentamers.involved successive chromatography columns of deactivated alumina, SEC, SEC, deactivated alumina, and SEC. The devel- The precursorto the core of the pentameric arrays, tetraiodoporphyrin FbU-I4 ,has limited solubility in the couplingsolvent opment of this chromatography sequence involved examination of alumina having various degrees of deactivation, and toluene–triethylamine(551). To facilitate formation of the pentamer, we sought to keep the porphyrin concentrations as high alumina containing 12% water was found to give the best separation.The chromatography of Mg4FbU on deactivated as possible while maintaining homogeneous solutions.We found that the concentration of FbU-I4 can be raised to 0.9 mM alumina was often complicated by streaking during the prolonged elution. Nonetheless, deactivated alumina was more by dissolution with the aid of sonication. Thus, the metalloethynylporphyrin (ZnU¾ or MgU¾) and tetraiodoporphyrin eective for these arrays than sugar and other mild chromatographic media, which have traditionally been employed for FbU-I4 concentrations were kept at 4.5 mM (5 equiv.) and 0.9 mM, respectively.The Pd-mediated coupling reaction was separation of chlorophylls.41 The pentamer can be purified to a considerable extent solely by chromatography on alumina performed similarly as for the dimer syntheses (Scheme 4). In the synthesis of pentamer Zn4FbU, SEC analysis at 3 h columns, but the use of successive columns with dierent J.Mater. Chem., 1997, 7(7), 1245–1262 1251the putative hexamer peak intensity was 5% of that of the molecule ion peak. These higher mass peaks were observed in both laser desorption mass spectrometry (neat samples) and in matrix-assisted laser desorption mass spectrometry.11 We believe these peaks to be synthesis byproducts, not mass spectrometric artifacts, although such impurities were not detected by analytical SEC.Based on these mass spectral peak intensities, and the amount of residual fluorescence emanating from the metalloporphyrins in the arrays, we estimate the purity of each pentameric array to be 95%. The dimers are estimated to be 97% pure. NMR features. The porphyrin building blocks and arrays were readily characterized by 1H NMR spectroscopy at 300 or 500 MHz at room temperature in CDCl3 at ca. 5mM (monomers and dimers) or ca. 1mM (pentamers) concentration. Upon formation of the arrays, the resonances from the bpyrrole protons and from the protons flanking the ethynylunit exhibit characteristic features. For example, upon coupling of MgU¾ and FbU-I to form MgFbU, the observed splitting pattern of the b-pyrrole protons is the sum of the splitting pattern of each of the component parts.The signals from the aryl protons flanking the ethyne linkage in the dimers shift downfield by ca. 0.2 ppm compared with the monomers. The changes in splitting pattern and chemical shift are similar to those previously reported for ZnFbU.6 The pentameric arrays (Mg4FbU and Zn4FbU) exhibited similar spectral features in comparison with their respective monomeric precursors.A key diagnostic in the star-shaped pentamers is the singlet at d ca. 9 originating from the b-pyrrole protons of the core Fbporphyrin, which has four-fold symmetry (assuming rapid NMH tautomerism). The chemical shifts of the respective protons in Mg4FbU and Zn4FbU dier by <0.2 ppm.However, the peaks of Mg4FbU, particularly in the aromatic region, are slightly broader than those of Zn4FbU. The line broadening observed with Mg4FbU may be caused by the Fig. 2 Size exclusion chromatograms of the reaction forming Zn4FbU various accessible coordination states and ligands of the mag- pentamer. Top, starting materials (ZnU¾ and FbU-I4) before the nesium in the peripheral porphyrins.At higher concentration catalyst was added. Middle, crude reaction mixture after 6 h. Bottom, purified Zn4FbU pentamer. Identical chromatograms were observed (ca. 5mM), samples of Mg4FbU and Zn4FbU exhibit severe for Mg4FbU. line broadening in the spectra, a sign of aggregation. Solubility. For easy purification and characterization, high separation modalities provides the most eective purification solubility of the arrays in various solvents is essential.The procedure. The purified pentamer Mg4FbU was isolated in operational solubilities we have observed during the course of 45% overall yield. In analogy with the Zn4FbU pentamer, a handling these compounds are listed in Table 1. These are not subsequent passage of Mg4FbU over the preparative SEC necessarily upper solubility limits.In addition, the dimers and column led to removal of only a trace amount of the leading pentamers are soluble in dilute solution in a wide range of edge of the band, but caused the peak in the analytical SEC solvents. For example, analytical SEC is performed in THF to sharpen from 0.71 to 0.65 min. This material was used for (10-5–10-4 M), and absorption and fluorescence spectroscopy spectroscopic studies. has been performed at 20 mM in solvents such as ethyl acetate, acetone, acetonitrile and DMSO.Chemical characterization and physical properties of the arrays Purity. Each array (MgFbU, ZnFbU, Mg4FbU, Zn4FbU) Chemical stability. In our routine handling of Mg-porphyrinbased arrays, we did not observe any decomposition or demet- was characterized by analytical SEC, 1H NMR spectroscopy, laser desorption mass spectrometry, and absorption and fluo- allation of solid samples stored at room temperature in the dark over a period of 1–2 weeks. The Mg-porphyrin containing rescence spectroscopy.Mass spectrometry indicates that there is no demetallation or transmetallation during the conversion arrays remain intact at -5 °C for ca. 3 months. The Mgporphyrin monomers could be stored at -5 °C for longer of the porphyrin building blocks into the arrays. Discerning the presence of any impurities having lower molecular mass periods, indicating their greater stability compared with the corresponding arrays. TLC analysis provided an eective assay than the molecule ion is dicult due to fragmentation of the molecule ion.However, higher molecular mass impurities are for small amounts of decomposition of the Mg-porphyrin arrays. In particular, a fast-moving greyish-blue decomposition readily observed. In the mass spectrum of Mg4FbU a strong molecule ion was observed at m/z 3759.4, and in addition a component was observed on alumina TLC.The solution absorption spectra of such samples also exhibited slight much weaker peak was observed at m/z 4549.6. The latter is consistent with a hexamer comprised of five magnesium por- changes in the relative intensities of the Q bands. Samples of Mg-porphyrin arrays that exhibited any signs of deterioration phyrins and one free-base porphyrin. Similarly in the spectrum of the Zn4FbU pentamer, a strong molecule ion was observed were passed over a short column of deactivated alumina, which readily removed the mobile greyish-blue decomposition at m/z 3918.5 and a much weaker peak was observed at m/z 4750.0.The latter is consistent with a hexamer comprised of product(s). During synthesis and characterization, all Mgporphyrins were protected against unnecessary exposure to five zinc porphyrins and one free-base porphyrin.In each case 1252 J. Mater. Chem., 1997, 7(7), 1245–1262Scheme 4 Building block approach in the synthesis of pentamers Mg4FbU and Zn4FbU air and light. In contrast to the Mg-porphyrin arrays, the Zn- (MgTMP),33 and magnesium tetrakis(pentafluorophenyl)- porphyrin (MgPFPP)34 in CH2Cl2 with acetic acid (0.3 M) at porphyrin arrays appear to be stable indefinitely when stored in solid form at -5 °C.room temperature. After 1 h, MgTPP and MgTMP were demetallated quantitatively, while MgPFPP exhibited no Although the Mg-porphyrins and Mg-porphyrin-based arrays were suciently stable for routine handling and spectro- demetallation after 24 h. This experiment illustrates the design principle that incorporation of electron-withdrawing groups scopic characterization, thoughts about future, more robust, arrays containing Mg-porphyrins prompted us to follow up provides enhanced stability of Mg-porphyrins toward demetallation.an earlier observation concerning electronic eects on stability of Mg-porphyrinic compounds. We observed that Mgphthalocyanines are more stable toward demetallation than Mg-porphyrins,34 which can be attributed to electron with- Electrochemical properties.The redox potentials of the Znand Fb-porphyrins have been previously reported.12,14 For drawal by the four meso-nitrogens in the former compounds. To investigate whether this phenomenon carried over to Mg- these arrays the redox potentials of the constituent porphyrins are identical to those of the monomers.This is also the case porphyrins bearing electron-withdrawing groups, we treated 2 mM solutions of MgTPP, magnesium tetramesitylporphyrin for the components of MgFbU and Mg4FbU. It is noteworthy Table 1 Operational solubilities (mM) of arrays array toluene–TEA (551)a chromatography solventb toluenec CDCl3d Fb2Ue 5.8 5–8f 8 MgFbU 2.3 5–7g 10 8 Mg4FbU 1 2.5h 2.5 3 Zn4FbU 1 2.5i 2.5 5 aSolvent for Pd-mediated coupling reactions. bSolvent for adsorption chromatography (silica or deactivated alumina).cSEC loading solvent. dNMR solvent. eThe solvent for magnesium insertion is CH2Cl2 in which the solubility is 9.1 mM. fToluene–hexanes (352). gToluene-acetone (1551).hToluene–CHCl3 (351). iCH2Cl2–hexanes (352). J. Mater.Chem., 1997, 7(7), 1245–1262 1253Table 2 Absorption maxima in various solvents (298 K) ethyl toluene (FWHM) acetate THF (FWHM) acetone acetonitrile DMSO monomers TPP 419 (12.0) 415 417 (15.0) 414 413 419 548 545 546 546 547 550 MgTPP 426 (12.5) 422 429 (11.0) 422 425 426 563 562 570 562 565 564 ZnTPP 423 (11.2) 421 423 (11.2) 422 422 427 550 552 555 554 555 560 FbU 420 (12.7) 420 418 (13.5) 415 414 419 548 548 547 545 546 548 MgU 428 (12.5) 425 433 (12.7) 425 425 428 565 564 573 565 565 565 ZnU 423 (12.9) 424 425 (10.0) 424 424 430 550 554 556 555 558 562 FbU-core 424 (15.0) 420 (14.0) 555 550 dimers MgFbU 430 (19.5) 428 427 427 431 565 564 564 564 565 ZnFbU 426 (18.9) 426 426 (16.7) 426 426 431 550 553 556 554 556 562 pentamers Mg4FbU 431 (16.0) 433 (12.7) 522, 565, 604, 650 518, 574, 615, 648 Zn4FbU 424, 429 (20.0) 429 (15.0) 519, 551, 590, 651 516, 558, 597, 648 that the Mg-porphyrin is ca. 300 mV easier to oxidize than shifts observed for the Zn-porphyrins are attributed to solvent ligation which converts the zinc ion from a four- to a five- the Zn-porphyrin.10 coordinate geometry. Regardless of the solvent, the spectrum in the Q-band region of a given array closely resembles the Spectroscopic and photochemical properties of the arrays sum of the spectra of the component parts in the same solvent.Absorption spectra. The absorption spectra of various porphyrins and the arrays were measured in toluene at room temperature (Table 2). A slight bathochromic shift in the Soret Fluorescence spectra and quantum yields.The fluorescence emission spectra of the dimers were measured in toluene. band (2 nm) and Q bands (2 nm) is observed with building block MgU compared to MgTPP. In MgFbU, the Soret band Illumination of MgFbU at 648 nm, where the Fb-porphyrin absorbs about 20 times more strongly than the Mg-porphyrin, shows no splitting but the absorption band is slightly red shifted (lmax 430 nm, shoulder at 420 nm at ca. 75% height) results in typical Fb-porphyrin emission with quantum yield (Wf=0.13) nearly identical with the monomeric Fb-porphyrins, and broadened (FWHM=19.5 nm) compared with MgU (428 nm) and FbU (420 nm). However, the visible absorption FbU or TPP. Illumination of MgFbU at 565 nm, where the Mg-porphyrin absorbs about 11 times as intensely as the Fb- bands are nearly the sum of the spectra of the Fb- and Mgporphyrin components.Similarly for Mg4FbU, a broadened porphyrin, results in emission predominantly from the Fbporphyrin. The Mg-porphyrin emission yield (Wf=0.009) is and red-shifted Soret band (431 nm, FWHM=16 nm) is observed compared with the model porphyrins MgU (428 nm) diminished 17-fold compared with MgU. The fluorescence yield measurements of MgFbU are summarized in Table 3.and FbU-core (424 nm), while the visible bands of Mg4FbU (522, 565, 604 and 650 nm) are nearly a superposition of those ZnFbU, which we have characterized previously,13 has nearly identical features to MgFbU, including 20-fold quenching of the building blocks. The spectra of ZnFbU in various solvents have been described previously.6,13 The pentamer of the Zn-porphyrin compared with ZnU and dominant emission from the Fb-porphyrin upon illumination at 550 nm, Zn4FbU exhibits nearly identical absorption spectral features as Mg4FbU, though the former exhibits a very slightly split where the Zn-porphyrin absorbs 80% of the light.Measurement of the small amounts of residual metalloporphy- Soret band (424, 429 nm).The absorption spectra of selected compounds were also rin fluorescence is not a reliable means of placing a bound on the energy-transfer eciency, due to diculties in quantitation collected in several more polar solvents. For MgTPP, MgU and MgFbU, only a slight shift (1–3 nm) in the Soret band arising from spectral overlap, and the presence of fluorescent impurities at the few percent level that become significant in and the Q bands is observed in ethyl acetate, acetone, acetonitrile or DMSO compared with toluene (Table 2).In THF, comparison to the strongly quenched metalloporphyrin in the arrays.13 In particular, the small but quantifiable metallopor- however, Mg-porphyrins exhibit bathochromic shifts of ca. 8 nm and a two-fold increase in intensity of the Q(1,0) band, phyrin emission in MgFbU (in contrast to the negligible metalloporphyrin emission in ZnFbU) is likely due to impurit- giving green solutions.The absorption spectral changes of Mgporphyrins in THF are attributed to the binding of two axial ies at the 3% level. Fluorescence excitation spectra provide a better overall view of the yield of energy transfer in donor– THF molecules, yielding a six-coordinate geometry, consistent with the Raman data reported below.Mg-porphyrins are five- acceptor systems.42,43 Close matching of the fluorescence excitation spectrum and absorption spectrum through the Q bands coordinate in non-coordinating solvents, where water presumably serves as the fifth ligand. In all solvents examined here (lem=720 nm) was observed for each array (MgFbU, ZnFbU, Mg4FbU, Zn4FbU) in toluene.These results indicate a high with the exception of THF, the Mg-porphyrins are predominantly if not exclusively five-coordinate. The small spectral yield of energy transfer, as absorption by the metalloporphyrin contributes fully to the observed emission of the Fb-porphyrin. shift of the Mg-porphyrins in acetone, acetonitrile or DMSO is in contrast to their zinc counterparts, which exhibit batho- The fluorescence properties of MgFbU were examined in several more polar solvents. Again, close matching of absorp- chromic shifts of up to 10 nm in these polar solvents.The 1254 J. Mater. Chem., 1997, 7(7), 1245–1262Table 3 Fluorescence yields in various solvents (298 K) obtained with ZnFbU, as noted earlier.13 However, the magnitude of the decline in Fb-porphyrin fluorescence with increased ethyl solvent polarity was less than that with MgFbU (Fig. 3). Thus, toluene acetate acetone acetonitrile DMSO MgFbU and ZnFbU exhibit high yields of energy transfer in all solvents but the emission from the Fb-porphyrin is monomers FbU 0.12 0.13 0.13 0.13 0.15 quenched as the solvent polarity increases. The quenching of MgU 0.16 0.20 0.20 0.19 —a the excited-state Fb-porphyrin is attributed to charge transfer ZnU 0.034 0.041 0.041 0.063 0.051 with the neighbouring ground-state metalloporphyrin follow- FbU-core 0.15 ing energy transfer. arrays Matched solutions of Mg4FbU and of Zn4FbU in toluene MgFbU were illuminated at 565 nm, a wavelength where the two Fb(em)b 0.13 0.13 0.069 0.050 0.017 Mg(em)c 0.009 0.013 0.009 0.009 samples exhibit equal absorbance.The fluorescence emission ZnFbU spectrum of each sample was comprised predominantly of Fb- Fb(em)b 0.13 0.11 0.14 0.072 0.065 porphyrin emission. However, the Fb-porphyrin emission Zn(em)c 0.002 0.002 0.004 0.004 0.003 (measured in the range 625–800 nm) from Mg4FbU was 13% Mg4FbU less than that from Zn4FbU.In addition, illumination of the Fb(em)b 0.11 Fb-porphyrin at 648 nm in Mg4FbU and Zn4FbU yielded Mg(em)c 0.010 Zn4FbU Wf=0.11 and 0.14, respectively (Table 3). These results indicate Fb(em)b 0.14 a slight amount of quenching of the Fb-porphyrin emission in Zn(em)c 0.004 Mg4FbU compared with that of Zn4FbU in toluene. aAggregation prevented measurement.bThe emission from the Fb- Resonance Raman spectra. The high-frequency regions of porphyrin (lexc=648 nm) was measured in the range 660–800 nm. The the B-state excitation (lexc=457.9 nm) RR spectra of ZnU, total emission from the Fb-porphyrin (620–800 nm) was then inferred assuming the Fb-porphyrin in the array has the same emission spectral MgU, ZnFbU, and MgFbU in toluene are shown in Fig. 4 profile as the Fb-porphyrin monomer, and these values are reported (left panel). The spectra obtained in 2-nitrotoluene are also in this Table.6 cThe emission from the metalloporphyrin (lexc= shown in Fig. 4 (right panel). The key spectral features shown 550–555 nm for Zn-porphyrins and lexc=562–565 nm for Mg- in the figure are the ethyne stretching mode, nCOC,12 which is porphyrins) was measured in the range 570–800 nm.The total emission observed for the monomers at ca. 2156 cm-1 and for the from the metalloporphyrin was inferred by measurement of the dimers at ca. 2213 cm-1, and the porphyrin skeletal mode, n2, emission intensity in the 570–620 nm region and assuming the metalloporphyrin in the array has the same emission spectral profile which is observed in the region 1543–1551 cm-1 for all the as the metalloporphyrin monomer.6 compounds.Inspection of the RR data reveals that the frequencies of the tion and excitation spectra was observed in all solvents, consistent with a high yield of energy transfer. However, illumination at 648 nm gave typical Fb-porphyrin emission in all solventsbut the quantum yield of the Fb-porphyrin emission decreased steadily with increasing solvent polarity (Fig. 3). In contrast, the fluorescence yields of the Fb-porphyrin monomers (or the Mg-containing monomers) changed only slightly as a function of solvent polarity. Illumination of the Mg-porphyrin (563–565 nm) in MgFbU yields a constant high degree of quenching of the Mg-porphyrin emission in all solvents, though the relative amount of Fb-porphyrin emission declined as the solvent polarity increased.Qualitatively similar results were Fig. 4 The high-frequency regions of the B-state excitation (lexc= Fig. 3 Fluorescence quantum yield of TPP (&), and the Fb-porphyrins in MgFbU ($) and ZnFbU (+) measured by illumination at 648 nm 457.9 nm) RR spectra of ZnU, MgU, ZnFbU and MgFbU in toluene (A) and 2-nitrotoluene (B) obtained at 295 K.The bands marked by as a function of solvent relative permittivity (corrected for solvent refractive index) at 298 K asterisks are due to solvent. J. Mater. Chem., 1997, 7(7), 1245–1262 1255nCOC modes of MgU and ZnU are essentially identical. This is Time-resolved absorption spectra. The energy-transfer also the case for MgFbU and ZnFbU.On the other hand, the dynamics from the excited metalloporphyrin to the groundfrequencies of the nCOC modes of the dimers are somewhat state Fb-porphyrin in the ZnFbU and MgFbU dimers was higher than those of the monomers. These dierences are not probed using femtosecond transient absorption spectroscopy. due, however, to eects of linking the porphyrins in the array, Representative data for MgFbU and ZnFbU are shown in but rather to the fact that the ethyne substituent of the Fig. 5. The use of 582 nm pump flashes results in absorption monomers (FbU, ZnU, MgU) contains a terminal trimethylsi- by both the metalloporphyrin and Fb-porphyrin. Therefore, lyl group rather than an appended aryl ring. In monomeric the transient absorption dierence spectra immediately after metalloporphyrins containing a diarylethyne substituent excitation contain mixtures in which either the metalloporphy- (MgU, ZnU), nCOC is at ca. 2217 cm-1,12 nearly the same rin of the dimer is excited or the Fb-porphyrin is excited. This frequency observed for MgFbU and ZnFbU. The frequencies fact is revealed by the 1ps spectrum for MgFbU in toluene of the nCOC modes of the various Mg- and Zn-porphyrins are shown in Fig. 5A. Although there are dierences in peak also identical in toluene and 2-nitrotoluene [and CH2Cl2, positions and intensities, the singlet excited states of both the DMF, and THF (not shown)]. Together, these results indicate Mg- and Fb-porphyrins exhibit strong absorption between that the ground-electronic-state structure of the linkers is 430 and 500 nm corresponding to the Soret band of the excited essentially identical in the Mg- and Zn-porphyrins and is not state.44 The dip near 515 nm in the 1ps spectrum is due to influenced by the properties of the solvent.bleaching of the shortest wavelength of the four ground-state The RR spectra show that the frequencies of the n2 modes Q bands of the Fb-porphyrin, namely the Qy(1,0) band.The of both MgU and MgFbU are lower than those of the Zn- dip near 560 nm is mostly due to bleaching of the Q(0,0) containing analogues. These frequency dierences are attri- ground-state absorption band of the Mg-porphyrin, along with buted to the fact that Mg- and Zn-porphyrins have slightly some Fb-porphyrin bleaching. The trough at 610 nm is com- dierent structures and core geometries.24 On the other hand, prised of Q(0,0) bleaching and stimulated emission from the the frequencies of the n2 modes of MgFbU and ZnFbU are Mg-porphyrin along with some bleaching of the Qx (1,0) band approximately the same as those of MgU and ZnU, respect- of the Fb-porphyrin.The dip near 650 nm also has overlapping ively, indicative of the fact that array formation does not aect contributions, namely Qx(0,0) bleaching and stimulated emis- the structure of the porphyrin ring(s).12 The general appearance sion from the Fb-porphyrin and Q(0,1) stimulated emission of the n2 spectral features of MgFbU are, however, dierent from the Mg-porphyrin.Finally, the dip near 720 nm is due from those of ZnFbU, whereas those of MgU and ZnU are quite similar.In particular, the n2 feature of ZnFbU is relatively narrow and comparable in width to that of ZnU and MgU. On the other hand, the n2 feature of MgFbU is somewhat broader and exhibits a shoulder on the high-frequency side. The narrowness of the n2 feature of ZnFbU arises because the frequencies of the n2 modes of the Zn- and Fb-components of the dimer are nearly coincident at ca. 1550 cm-1. This was confirmed by RR data obtained for the free-base monomer (not shown). The slightly downshifted frequency of the n2 mode of the Mg-component of MgFbU reveals the n2 band of the Fb-component which remains at ca. 1550 cm-1. The frequencies of the n2 modes of ZnU and ZnFbU are nearly the same in toluene and 2-nitrotoluene [and CH2Cl2 , THF and DMF (not shown)].This is also the case for MgU and MgFbU in all solvents with the exception of THF. Accordingly, the ground-electronic-state structures of the porphyrin ring(s) are relatively insensitive to the dielectric properties of the solvent. In the case of the Mg-porphyrins in THF, the n2 modes are downshifted to ca. 1536 cm-1 (not shown). This frequency shift is attributed to the fact that the Mg-porphyrin is hexacoordinate in THF, commensurate with the dierent absorption spectra observed in this solvent (vide supra).Further inspection of the RR data reveals that the relative intensities of the nCOC vs. n2 modes are approximately the same for the Mg- and Zn-porphyrins. In addition, these relative intensities remain the same in all of the solvents investigated (toluene, 2-nitrotoluene, CH2Cl2, THF and DMF). The increased relative intensities of the nCOC vs.n2 modes of the dimers vs. monomers again arises because of the presence of terminal aryl vs. trimethylsilyl groups in the two systems Fig. 5 Room-temperature transient dierence spectra acquired follow- (rather than being an eect of covalent linkage in the array).12 ing excitation of the dimers in toluene with a 0.2 ps flash at 582 nm.The apparent increased relative intensity of the nCOC vs. n2 The spectra for MgFbU in (A) were acquired at time delays of 1 ps mode of MgFbU vs. ZnFbU is solely due to the fact that the (solid) and 100 ps (dashed). The spectra for ZnFbU in (B) were n2 feature of the former dimer is broader than that of the latter.acquired at time delays of 1 ps (solid) and 100 ps (dashed). Note that Integration of the RR band contours for MgFbU and ZnFbU the data in the red region were acquired with a sample of concentration reveals that the relative intensities of the nCOC vs. n2 modes of ca. ten times that used for the blue region so that quantitative comparison of the absorption changes in the two regions should not the two dierent arrays are in fact identical.Collectively, these be made. The insets show representative kinetic traces at 510–515 nm. results indicate that the excited-state electronic coupling Only the first 200 ps are shown, because from 200 ps to 3 ns there is between the ethyne group and the p system of the porphyrin no further change due to the long lifetime (12–13 ns) of the excited ring (which dictates the relative intensities of the nCOC vs.n2 Fb-porphyrin under these conditions. The curves through the kinetic modes12,14 ) is similar in the Mg- and Zn-porphyrins and is data are fits to a single exponential function with time constants of not strongly influenced by the coordination of the metal ion 31±3 ps (A) and 26±3 ps (B) that represent the lifetime of the excited metalloporphyrin component of the dimer.or the dielectric properties of the solvent. 1256 J. Mater. Chem., 1997, 7(7), 1245–1262to Qx (0,1) stimulated emission from the Fb-porphyrin. The in toluene. In 2-nitrotoluene, MgFbU and ZnFbU each exhibited lifetimes of ca. 8 ps; however, in this solvent, MgU and stimulated (by the white-light probe pulse) emission features are characteristic of the excited singlet states of the porphyrins ZnU also exhibited dramatically shortened lifetimes (14 and 52 ps, respectively). The shortened lifetime of each metallopor- and occur near the wavelengths of the features observed in the spontaneous emission (fluorescence) spectrum, as is observed phyrin (MgU, ZnU) indicates that the results observed in the dimers are attributable to solvent–porphyrin interactions for the dimers under investigation here.Fig. 5A shows that at 100 ps the Qy(1,0) bleaching near rather than to enhanced energy-transfer rates or competitive electron-transfer pathways inherent in the dimers. 515 nm due to the Fb-porphyrin in MgFbU has grown in magnitude while bleaching of the Q(0,0) band near 560 nm of the Mg-porphyrin has decreased.Changes are also observed Time-resolved fluorescence. The lifetimes of the Fbporphyrins in the arrays, and the metalloporphyrins in the in the other regions of the spectrum. The dierences between the spectra at 1 and 100 ps clearly reflect disappearance of the MgU and ZnU monomers, were measured by time-resolved fluorescence spectroscopy.The results are summarized in Mg-porphyrin excited state (Mg*) and the formation of the Fb-porphyrin excited state (Fb*) in that fraction of the dimers Table 4. Also included in Table 4 are lifetimes obtained previously in toluene and DMSO for the ZnFbU dimer and the in which the Mg-porphyrin had been excited by the pump flash. Note, however, that the fraction in which the Fb* excited ZnU and FbU control complexes.13 These values and those obtained here for these systems are in excellent agreement. For state was initially produced does not change over the ca. 3 ns timescale of the measurements because the Fb* lifetime in example, the fluorescence lifetime of 13.1±0.6 ns obtained here for the Fb-porphyrin emission in the ZnFbU dimer in toluene toluene is 12–13 ns, as determined by fluorescence methods (vide inf ra).is the same within experimental error as the value of 12.5±0.2 ns obtained previously from time-correlated single A representative kinetic trace is shown in the inset to Fig. 5A along with a fit to a single exponential function with a time photon counting measurements. The same lifetime is found for FbU in toluene (13.3 vs. 12.5 ns). The lifetime of the Fb- constant of 31 ps. The same value (31±4 ps) is found from analysis of the data at all wavelengths where suciently large porphyrin in MgFbU in toluene is the same again (13.1 ns). The finding of the same lifetime (12–13 ns) of the excited absorption changes are observed. We assign this time constant as the Mg* lifetime for MgFbU in toluene. singlet state of the Fb-porphyrin in the monomer and dimers is in full accord with the observation that the fluorescence The ZnFbU dimerintoluene showssimilar results as observed for MgFbU.The transient absorption spectra and kinetic data yield (Wf#0.12) is basically the same in these molecules (Table 3 and ref. 13). Collectively, these results demonstrate in Fig. 5B are in excellent agreement with the data presented for ZnFbU previously.13 The observed lifetime of the Zn- that neither the Zn- nor Mg-porphyrin in these dimeric arrays in non-polar media introduces any new decay channels that porphyrinexcitedstate of 26±3 ps isthe same within experimental error as the value of 22±2 ps obtained previously.In compete eectively with the inherent decay routes (fluorescence, internal conversion, intersystem crossing) of the Fb- analogy with the above results on MgFbU, this time constant reflects the energy-transfer process Zn*Fb�ZnFb*.The life- porphyrin. The lifetime observed for the Fb-porphyrin in each of the pentamers (Mg4FbU and Zn4FbU) is shorter than that times of the pentameric arrays and representative monomers were also collected in toluene (Table 4).Each pentamer of the FbU-core porphyrin and of the Fb-porphyrin in the dimers (Table 3). The shortened values could be due to a (Mg4FbU, Zn4FbU) shows a metalloporphyrin lifetime that is slightly shorter than that observed in the respective dimer. quenching process or an altered structure of the core Fbporphyrin due to the presence of the four appended metal- The excited-state lifetimes of the metalloporphyrin (M*) in the MgFbU and ZnFbU dimers were examined in polar loporphyrins.As the polarity of the solvent increases, the lifetime of the solvents (Table 4). In acetone and DMSO, MgFbU and ZnFbU each exhibit essentially the same lifetime as observed Fb-porphyrin in the dimers becomes shorter. For example, the Table 4 Excited-state lifetimes of metallo- (M) and free-base (Fb) porphyrins (296 K)a toluene EAb THF acetone 2-nitrotoluene acetonitrile DMSO compound M Fb Fb M Fb M Fb M Fb M Fb M Fb MgFbU 31 ps 13.1 ns 13.8 ns 34 ps 12.8 ns 37 psc 6.5 ns 9 ps 2.2 ns 3.8 ns 31 ps 1.3 ns 2.0 nsd 1.8 nsd ZnFbU 26 ps 13.1 ns 13.5 ns 13.3 ns 30 psc 11.7 ns 8 ps 4.4 ns 7.3 ns 4.3 ns 22 pse 12.5 nse 4.5 nsd 23 pse 4.8 nse Mg4FbU 23 ps 10.7 ns Zn4FbU 17 ps 10.6 ns MgU 10.0 ns 9.7 ns 9.8 ns 14 ps 9.6 ns 8.4 ns ZnU 2.5 ns 2.6 ns 2.7 ns 52 ps 2.4 ns 2.4 ns 2.4 nse 2.3 nse FbU 13.3 ns 13.8 ns 13.7 ns 13.6 ns 12.3 ns 13.5 ns 13.0 ns 12.6 nse FbU-core 12.5 ns MgTPP 8.3 ns ZnTPP 2.2 ns 2.1 ns 2.1 ns aThe lifetimes of the excited metalloporphyrin in the dimers and pentamers were determined using transient absorption spectroscopy. The lifetimes for the excited Fb-porphyrin monomers, metalloporphyrin monomers, and the Fb-porphyrins in the dimers were obtained by timeresolved fluorescence spectroscopy.The error limits for the lifetimes obtained by time-resolved fluorescence spectroscopy are ±5% and those from time-resolved absorption spectroscopy are ±10%. bData reported only for the Fb-porphyrin in ethyl acetate. cA slightly longer value (ca. 60 ps) is measured in the range 450–500 nm, whereas the reported value was obtained at 515 nm. In all other solvents, the same lifetime was observed at alwavelengths between 450 and 550 nm. Because the same ca. 30 ps value is measured in the 515 nm region in all the solvents, we believe that this value reflects the excited metalloporphyrin lifetime in all of the media, and the slower kinetics measured in acetone in the blue region involve some other processes that do not aect the excited metalloporphyrin lifetime. dThese values, also obtained from transient absorption spectroscopy, are only rough estimates because the kinetic data did not span a sucient time span for an accurate determination.eThese values are reproduced from a previous study13 and are in good agreement with the values obtained here.J. Mater. Chem., 1997, 7(7), 1245–1262 1257lifetime of the Fb-porphyrin in MgFbU in acetonitrile is 3.8 ns, depopulating the excited metalloporphyin in the arrays other than the intrinsic processes (intersystem crossing, internal which is a factor of 3.4 shorter than the value in toluene.This result parallels the behaviour observed for the fluorescence conversion, radiative decay) also present in the benchmark monomer. The close matching of the excitation spectra and yields (Table 3, Fig. 3). Qualitatively similar results are obtained with ZnFbU, though the extent of quenching is less absorption spectra for the arrays in diverse solvents indicates a high yield of energy transfer and supports this assumption.than with MgFbU. We attribute the yield and lifetime reductions in polar media to charge-transfer quenching of the However, within experimental uncertainty we cannot exclude the possibility of a small amount (10%) of electron transfer Fb-porphyrin excited state. from the M* excited state. The lifetimes observed for the metalloporphyrins in the Discussion arrays (Table 4) were used to compute the rates and yields of energy transfer in toluene (Table 5).For MgFbU, the lifetime Zinc has been widely employed as a surrogate for magnesium of the Mg* (tMg*=31 ps) gives kEnT ca. (31 ps)-1 due to the in the preparation of porphyrin-based synthetic models of inherent lifetime (t0Mg*) of 10.0 ns observed for Mg* in the chlorophylls.26 Our new synthetic methods for preparing Mg- MgU control compound.Similarly for ZnFbU, the lifetime of porphyrins and Mg-containing porphyrin arrays obviate the the Zn* (tZn*=26 ps) gives kEnT ca. (26 ps)-1 due to the reliance on Zn-porphyrins and shift the focus in light-har- inherent lifetime (t0Zn*) of 2.5 ns observed for Zn* in the ZnU vesting or molecular photonics applications from the question control compound. Thus, the rate of energy migration is nearly of ‘What is synthetically feasible?’ to the design issue of ‘Which identical in MgFbU and ZnFbU.metal exhibits more desirable photochemical and materials Although the rates of energy transfer are nearly identical for properties?’ We have explored the latter issue by examining the Mg- and Zn-containing arrays, the yields dier slightly as the pairwise interactions between metalloporphyrins (Mg, Zn) these reflect the inherent lifetime of the metalloporphyrin and Fb-porphyrins in dimers and star-shaped pentamers.These excited state [eqn. (2)]. For MgFbU, WEnT is ca. 99.7% (31 ps studies serve as a prelude to the design and preparation of lifetime in MgFbU vs. 10 ns lifetime in MgU) while for ZnFbU, larger multiporphyrin arrays. The major photochemical results WEnT is ca. 99.0% (26 ps lifetime in ZnFbU vs. 2.5 ns lifetime from this comparative study are as follows. (1) The choice of in ZnU). Thus the yield of energy transfer is greater for the metal ion (MgII vs. ZnII ) does not appreciably aect the rate Mg-containing array in spite of the marginally slower rate.of energy transfer in the arrays. The similarity in rates of Similar results are observed for the pentamers Zn4FbU and energy transfer for the Mg- and Zn-containing arrays is Mg4FbU, where a marginally faster rate [(17 ps)-1 vs. (23 attributed to the fact that the electronic coupling between the ps)-1, respectively] is observed for the former but the latter metalloporphyrin and Fb-porphyrin is approximately the same gives the higher yield (99.3 vs. 99.8%, respectively). Thus, the for Mg- vs. Zn-containing arrays. (2) The quantum yields of general features observed for Mg- and Zn-containing arrays energy transfer are 99% for arrays containing either metal are quite similar. ion. However, the yield of energy transfer is slightly higher in The similarity in rates of energy transfer observed for the the Mg- vs.Zn-containing arrays owing to the longer intrinsic Mg- and Zn-containing arrays can be attributed to the fact lifetime of the former metalloporphyrin. (3) Solvent polarity that the electronic coupling between the metalloporphyrin and and changes in coordination geometry of the Mg- or Zn- Fb-porphyrin is approximately the same for the Mg- vs.Zn- porphyrin have very little eect on the rates and yields of containing arrays. In this connection, our prior studies of a energy transfer. (4) Polar solvents diminish the fluorescence variety of ZnFb-dimers have shown that the predominant yield and lifetime of the excited Fb-porphyrin in arrays contain- pathway for energy transfer involves a through-bond rather ing either Mg- or Zn-porphyrins.The magnitude of the dimin- than a through-space mechanism.13 The through-space energy- ution is greater for the Mg-containing arrays. These eects are transfer rate was calculated to be (720 ps)-1 for the ZnFb- attributed to charge-transfer quenching of the excited Fb- dimeric arrangement (which is substantially slower than the porphyrin by the adjacent metalloporphyrin.The enhanced observed rates), and the MgFb-dimeric structure is expected quenching in the Mg-containing arrays is a result of the greater to have the same through-space rate. The through-bond driving force for charge separation. In the following section, energy-transfer process is explicitly mediated by the nature of we discuss each of these points in more detail. Next, we the conformational energy surface of the diarylethyne linker, compare the energy-transfer characteristics of our MgFb- or which dictates the extent of electronic communication between ZnFb-containing arrays with qualitatively similar phenomena the p systems of linker and porphyrin ring(s).The Raman exhibited by selected arrays made by other workers.Finally, intensity of the nCOC mode of the arylethyne linker (relative to we comment on the merits of Mg- vs. Zn-porphyrins for the n2 mode of the porphyrin) was shown to be a convenient materials applications in the context of their photochemical static spectroscopic signature of the extent of this electronic properties and their diering stabilities. interaction.14 In particular, the intensity of the nCOC mode was shown to parallel the rate of energy transfer in a series of Photochemical characteristics of Mg- vs.Zn-containing arrays ZnFb dimers containing diering degrees of torsional con- Energy transfer rates and yields. The static fluorescence yield straint.13,14 In the case of MgFbU vs. ZnFbU, the similarity and fluorescence excitation spectral measurements indicate in the relative intensities of the nCOC modes again parallels the that the yield of energy transfer is essentially quantitative in similarity in the rates of energy transfer.Collectively, these both the Mg- and Zn-containing arrays. In this regime of high eciency, a precise determination of the yield is best obtained Table 5 Calculated energy transfer rate constants and yields in via time-resolved measurements. From the measured lifetime toluene (298 K)a of the metalloporphyrin in an array (tM*) and the lifetime of a benchmark monomeric porphyrin (t0M*), the rate constant kEnT WEnT (%) for energy transfer (kEnT) from M* to Fb and the yield of energy transfer (WEnT) can be calculated as shown in eqn.(1) MgFbU (31 ps)-1 99.7 ZnFbU (26 ps)-1 99.0 and (2).Mg4FbU (23 ps)-1 99.8 kEnT=(tM*)-1-(t0M*)-1 (1) Zn4FbU (17 ps)-1 99.3 WEnT=kEnTtM*=1-tM*/t0M* (2) aCalculated from the excited-state lifetimes in Table 4 using eqn. (1)–(4). These equations assume there are no other pathways for 1258 J. Mater. Chem., 1997, 7(7), 1245–1262Table 6 Calculated charge-transfer (MFb*�MV+FbV-) rate constants and yields (298 K)a compound process toluene ethyl acetate THF acetone 2-nitrotoluene acetonitrile DMSO MgFbU kFb*CT NAb NA (195 ns)-1 (12.5 ns)-1 (2.7 ns)-1 (5.3 ns)-1 (1.4 ns)-1 WFb*CT (%) NA NA 7 52 82 72 90 ZnFbU kFb*CT NA NA (456 ns)-1 (84 ns)-1 (6.9 ns)-1 (15.3 ns)-1 (6.4 ns)-1 WFb*CT (%) NA NA 3 14 64 46 67 aCalculated from the excited-state lifetimes in Table 4 using eqn.(1)–(4).bNot applicable. The lifetime is the same as in the FbU control compound, indicating no charge transfer occurs in this solvent. trends lead to the assessment that the extent of electronic the data obtained for MgFbU allow a more in-depth analysis of the charge-transfer process. coupling is similar in the Mg- and Zn-containing arrays. The lifetime of the Fb-porphyrin emission in the dimeric arrays (tFb*) and the fluorescence lifetime of the FbU control Eects of solvent on photodynamics of energy transfer.The solubility of the arrays provides the opportunity for examining complex (t0Fb*) can be used to determine the rate constant for charge-transfer quenching (kFb*CT ) and the yield for the the eects of dierent media on the excited state photodynamics.Our previous study of ZnFbU showed that the energy- quenching process (WFb*CT) via eqn. (3) and (4) (Table 6). transfer rate changed by a factor of 2.5-fold upon changes kFb*CT=(tFb*)-1-(t0Fb*)-1 (3) in viscosity (fluid medium to rigid glass), temperature (298–150 K), or polarity (solvent static relative permittivity WFb*CT=kFb*CT tFb*=1-tFb*/t0Fb* (4) e=2.38–46.7).13 In MgFbU, the fluorescence yield and lifetime of the Mg-porphyrin are basically unchanged in going from For example, MgFbU in acetonitrile has kFb*CT ca.(5.3 ns)-1 toluene to acetone to DMSO, indicating that the rate of energy and WFb*CT ca. 72% under these conditions (the competing transfer is unaected by this dramatic change in solvent processes being fluorescence, internal conversion, and inter- polarity.Similar results were observed for ZnFbU. system crossing), while ZnFbU in acetonitrile has kFb*CT ca. Although the rates of energy transfer do not change with (15.3 ns)-1 and WFb*CT ca. 46%. The most polar solvent increased solvent polarity, the reasonably polar solvent 2- examined, DMSO, gives substantial quenching, with WFb*CT nitrotoluene is exceptional compared with the rest of the ca. 90 and 67% for the MgFb- and ZnFb-dimers, respectively. solvents in giving shortened lifetimes. In this solvent, the Note that for both types of arrays, the values of kFb*CT and lifetimes of the MgU and ZnU control complexes are dramati- WFb*CT generally increase as the solvent polarity increases, cally reduced (to 14 ps and 52 ps, respectively) from the though the trend is not exactly linear as 2-nitrotoluene lifetimes in toluene (10.0 and 2.5 ns, respectively).Thus, the quenches slightly more than expected given its polarity. There similar shortening in the lifetimes in the arrays does not reflect is no reason to expect this trend to follow the solvent polarity enhanced energy transfer (or competitive electron transfer) but precisely, because other factors such as porphyrin electrochemi- is a consequence of a direct quenching interaction with the 2- cal potentials are of critical importance in determining the nitrotoluene which provides a very fast decay route for M*.extent of charge-transfer quenching, and these also are aected The invariance in rates of energy transfer upon changes in by the nature of the solvent.23b solvent is supported by the RR data. These data show that Collectively, the analysis of the fluorescence yield (Fig. 3) the magnitude of the electronic coupling in both the Mg- and and lifetime (Table 4) data of the MgFbU vs.ZnFbU array as Zn-containing arrays is not strongly aected by the nature of a function of solvent polarity indicate that the charge-transfer the solvent (polar vs.non-polar) or the coordination number process is more pronounced for the former arrays. The more of the metal ion (and hence the conformation of the porphyrin facile charge-transfer quenching observed for MgFbU vs. ring). The constancy of the electronic coupling under a variety ZnFbU is attributed to the larger driving force of conditions has important implications for the interpretation for the MgFb*�MgV+FbV- process relative to the of the eects of solvent on the photochemical properties of ZnFb*�ZnV+FbV- reaction.This dierence derives from the the arrays. ca. 300 mV greater ease of oxidation of the Mg-porphyrin relative to the Zn-porphyrin.10,23,32 Hence, Mg-containing Eects of solvent on fluorescence of the Fb-porphyrin. arrays oer some advantage over Zn-containing arrays in Although the rate of energy transfer and the magnitude of situations wherein charge transfer is a desired property of the electronic coupling remain constant upon changes in solvent, assembly.both the fluorescence yield and excited-state lifetime of the Fbporphyrin are diminished in polar solvents. Together these Energy-transfer properties of other dimers observations lead to the assessment that the quenching phenomenon is best attributed to a charge-transfer process A large number of dimers have been prepared for studies of (MFb*�MV+FbV-) that occurs following energy transfer energy transfer, with most containing Zn- and Fb- from the metallo(M)- to Fb-porphyrin (or following direct porphyrins.6,26 Among these, the most relevant to this dis- excitation of the Fb-porphyrin).The quenching of the Fb- cussion are those where charge-transfer quenching of the porphyrin excited state must occur within its nominal 12–13 ns Fb-porphyrin has been observed. Also relevant are those arrays lifetime. A model that accounts for this quenching is shown in where energy transfer has been studied between Mg- and Fb- Scheme 5.We previously reported quenching of the Fb- porphyrins, though these are far fewer in number.28k,29a porphyrin in ZnFbU in the polar solvent DMSO.13 The more Gust et al. prepared a ZnFb-dimer joined by a phenyl– comprehensive data base reported here for ZnFbU along with amide–phenyl linker and observed fast energy transfer [kEnT= (43 ps)-1] with WEnT=0.97 in CH2Cl2 .45 A dimer with the same linker but electron-deficient substituents on the Fbporphyrin exhibited slightly slower energy transfer [kEnT=(106 ps)-1] which was competitive with electron transfer (WET= 0.77, WET=0.18).In addition, the excited-state lifetime of the Fb-porphyrin was shortened from 8.5 to 2.7 ns which was Scheme 5 Charge-transfer quenching of the excited Fb-porphyrin (Fb*) by the ground-state metalloporphyrin (M) attributed to charge-transfer quenching (WFb*CT=0.68). J.Mater. Chem., 1997, 7(7), 1245–1262 1259Although both dimers were examined in the non-polar solvent Mg-containing arrays is due to the fact that magnesium is less electronegative than zinc (x=1.31 vs. 1.65); consequently, Mg- CH2Cl2, the electron-deficientgroups provide increaseddriving force for the charge-transfer process and thus play a role porphyrins are more easily oxidized than Zn-porphyrins.(3) MgII is a harder (less malleable) ion and strongly prefers similar to that of a polar solvent in enhancing this process. Two related ZnFb-dimers, each with an electron-rich Zn- oxygenic rather than nitrogenous ligands, while ZnII is softer and has similar anity for both.49 This preference for ligand porphyrin and an electron-deficient Fb-porphyrin, were examined in a wide variety of solvents.46 The charge-transfer quench- type and geometry leads to much easier acid-induced demetallation of Mg-porphyrins than Zn-porphyrins, a property with ing process of the Fb-porphyrin was not detected in toluene, became apparent in solvents such as ethyl acetate, and considerable practical implications (in chromatographic puri- fication of the arrays, silica is suciently acidic to demetallate increased dramatically in rate upon going to polar solvents such as DMSO.Mg- but not Zn-porphyrins; thus, the former generally cannot be chromatographed on silica).33 Several dimers28 and trimers29 containing Mg-porphyrins have been prepared, but in almost all cases electron transfer The viemerges from the above considerations is that the construction of molecular photonic devices based on Mg- rather than energy transfer has been the dominant photochemical process.Osuka et al. prepared a series of MgFb dimers or Zn-porphyrins will be based on a host of factors in addition to the photochemical properties of the two types of arrays.joined by hydrocarbon spacers of various lengths wherein energy transfer was studied.28k In one bis-spiroindane linked Clearly, either metal ion could be used if the rate of energy transfer is the only factor to be considered. However, Mg- MgFb dimer examined in DMF, fast energy transfer [kEnT= (62 ps)-1] and faster electron transfer [kET=(42 ps)-1] were containing arrays may oer certain advantages in cases where a succession of energy-transfer steps occur.For example, observed with quantum yields of 0.4 and 0.6, respectively. In other MgFb dimers with assorted linkers, energy transfer assuming the yields observed for MgFbU (99.7%) and ZnFbU (99.0%) carry over to extended arrays of metalloporphyrins, occurred with no observable competing electron-transfer processes.In the series of MgFb dimers, the rates of energy then upon 100 transfer steps, the all-Mg-containing arrays would give 74% eciency while the all-Zn-containing arrays transfer changed little (less than two-fold) in going from toluene to THF. In the same series in DMF, however, quench- would give 37% eciency. Such a large number of transfer steps would be required in realistic models of the natural light- ing of the Fb-porphyrin fluorescence was observed with a rate increasing with shorter linkers and this also was attributed to harvesting arrays.These considerations must be balanced with the fact that Mg-porphyrins are more prone to oxidation, and charge separation (MgFb*�MgV+FbV-) as proposed here.this must be suppressed in a light-harvesting array. Conversely, the propensity toward oxidation of Mg-porphyrins might be Merits of Mg- vs. Zn-containing arrays for materials attractive in other types of devices such as switching elements. applications Indeed, we have applied the basic elements of this concept in the construction of a prototypical molecular optoelectronic Synthetic multiporphyrin nanostructures constitute a relatively new class of optical and photonic materials.The modularity gate.10 Finally, from a processing or device packaging standpoint, Zn-porphyrins are more robust toward demetallation. of the building block approach enables relatively easy preparation of diverse composite arrays containing dierent meta- However, Mg-chelates of electron-deficient porphyrins are less susceptible to demetallation than are those with electron-rich llo- or Fb-porphyrins.The studies reported herein indicate that the energy-transfer characteristics of the Mg-containing substituents. Thus, the incorporation of appropriate electronwithdrawing groups with the Mg-porphyrin may provide arrays are generally similar to those of their Zn-containing counterparts. The overall similarity in this property of the two protectiontoward demetallation, charge transfer, and photooxidation while maintaining the desired long lifetime of the types of arrays is on the surface surprising given the fact that magnesium (atomic number 12) is an alkaline earth metal singlet excited state.All of these factors need to be considered in the design of metalloporphyrin-based light-harvesting arrays while zinc (atomic number 30) is a transition metal with a filled 3d shell of electrons.For example, the MgII ion prefers and nanostructures for materials applications. an octahedral coordination sphere but also can accommodate a square-pyramidal geometry, while the presence of the mal- Conclusions leable 3d shell of electrons in ZnII leads to tolerance of a variety of coordination spheres.Nonetheless, MgII and ZnII Multiporphyrin arrays comprised of Fb- and Mg- or Znporphyrins can be constructed using a modular building block have nearly the same ionic radius (0.72 A° and 0.74 A° , respectively), 47 which is slightly larger than optimal for a comfortable approach. No significant dierences exist in the synthesis of Mg- or Zn-containing porphyrins or related arrays.Arrays fit in the porphyrin core.48 Regardless, these basic dierences in electronic structure and coordination-sphere geometry have containing Mg-porphyrins provide new models for biomimetic investigations of natural light-harvesting phenomena. In many very little influence on the linker-mediated electronic coupling between the metallo- and Fb-porphyrin which dictates the regards, magnesium and zinc can be used almost interchangeably in many light-harvesting arrays.The choice of energy-transfer rates. Certain dierences do exist in the photochemical and mate- metal can be based on subtle factors such as the slightly faster rate of energy transfer provided by Zn-porphyrins, the slightly rials properties of the Mg- vs.Zn-containing arrays. However, all of the dierences can be directly traced to dierences which higher yield of Mg-porphyrins emanating from the inherently longer lifetime of Mg-porphyrins, or the desire to favour are intrinsic to monomeric Mg- vs. Zn-porphyrins rather than being a consequence of array formation. These dierences are charge-transfer processes to which Mg-porphyrins are more inclined.Regardless, the choice of metal is now a design issue as follows. (1) Although both MgII and ZnII are diamagnetic and support metalloporphyrin singlet excited states with nano- rather than a synthetic consideration. The ability to tune the photodynamic properties of the arrays through choice of metal second lifetimes, Zn-porphyrins have a shorter lifetime (and commensurably diminished fluorescence yield) than Mg- is an important handle for controlling the flow of energy in porphyrin-based nanostructures.Finally, metalloporphyrins porphyrins (2–2.5 ns vs. 8–10 ns, respectively). The shorter lifetime of Zn-porphyrins is due to the increased rate of containing metals with far larger dierences than magnesium and zinc should also be accessible via this modular synthetic intersystem crossing, which stems from the heavy-atom eect, not dierences in radiative decay [MgTPP and ZnTPP have approach, in turn broadening the scope of photonic and electronic properties that can be elicited in these porphyrin- identical fluorescent radiative decay rates, kf ca.(60 ns)-1].36 (2) The somewhat increased charge-transfer propensity of the based materials. 1260 J. Mater. Chem., 1997, 7(7), 1245–126225 M. Gouterman, in T he Porphyrins, ed. D. Dolphin, Academic This work was supported by a grant from Division of Chemical Press, New York, 1978, vol. 3, pp. 1–166. Sciences, Oce of Basic Energy Sciences, Oce of Energy 26 For reviews, see: (a) S. G. Boxer, Biochim.Biophys. Acta, 1983, 726, Research, Department of Energy (J.S.L.), the LACOR Program 265; (b) D. Gust and T. A. 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ISSN:0959-9428    

DOI:10.1039/a700146k

出版商:RSC    

年代:1997

数据来源: RSC