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FEATURE ARTICLE Design and synthesis of TCNQ and DCNQI type electron acceptor molecules as precursors for ‘organic metals’ Nazario Martý�n,* Jose� L. Segura and Carlos Seoane* Departamento Quý�mica Orga�nica I, Facultad Ciencias Quý�micas, Universidad Complutense, E-28040 Madrid, Spain The main types of cyano-containing electron acceptor molecules, particularly those derived from TCNQ and DCNQI acceptors, have been reviewed.Ring substitution, the presence of heteroatoms and extended p-conjugation have been used as the principal structural modifications on the acceptor framework. Recent examples of C60 based electron acceptors bearing an acceptor organic addend and other single-component donor–acceptor systems exhibiting semiconducting behaviour are also discussed.The synthesis of the highly conducting charge transfer (CT) Other remarkable and structurally dierent acceptor molcomplex formed by tetracyano-p-quinodimethane (TCNQ) and ecules containing sulfur or selenium atoms on the periphery tetrathiafulvalene (TTF), as electron acceptor and electron are represented by the [M(dmit)2] complexes (dmit2-=2- donor components respectively, has opened up the field of thioxo-1,3-dithiole-4,5-dithiolate, Fig. 1) with ten peripheral molecular organic conductors.1 A large number of dierent sulfur atoms, thus increasing the intra- and inter-stack inter- CT complexes have been prepared in the search for electrical actions. Such compounds derived from transition metal comproperties. The synthesis of the so called ‘organic metals’ or plexes are, together with the more recent fullerides, the only ‘synthetic metals’ has mainly focused on the modification of materials in which an organic acceptor molecule (dmit and the donor fragment and, as has been often stated, much less C60) is responsible for superconductivity.synthetic eort has been devoted to the preparation of novel Formation of sulfur-containing donor molecules from the acceptors.2 In this review we discuss some highlights in the dmit ligand has been recently reviewed by Svenstrup and design and synthesis of electron acceptors as precursors of Becher13 and the state of the art on the M(dmit)2 systems such electrically conducting materials.as crystal growth, stacking, oxidation state and conducting Taking into account the fact that the requirements needed and superconducting properties have been excellently reviewed to obtain a conducting molecular arrangement have been by Cassoux and Valade.14 reviewed in detail by dierent authors3–11 and given that the Despite the lack of superconducting properties in salts and possibility of designing organic conducting materials has been complexes formed from TCNQ and DCNQI derivatives, these recently reviewed by Khodorkovsky and Becker,12 we will two molecules and other structurally related analogues have focus our attention on the main types of acceptors according been the subject of striking synthetic eorts and a wide variety to their dierent molecular nature.In particular, we will focus of electrically conducting salts and charge transfer complexes on derivatives of the parent molecules TCNQ, dicyano-p- have been obtained from these unique molecules. quinone diimine (DCNQI), other polycyano derivatives, and A few years ago, a review article dealing with DCNQIs as some interesting cases in the emerging chemistry of modified a new type of electron acceptor was published by Hu�nig and fullerenes, as shown in Fig. 1.Erk.15 We are herein concerned with recent advances on the chemistry and properties of the most significant electron acceptor molecules (TCNQ and DCNQI) and other cyano containing related molecules. We will highlight some of the novel acceptors prepared as precursors of materials with relevant conducting, magnetic and optical properties. Electron Acceptors: Design and Structural Modifications After the discovery of TTF–TCNQ,1 chemical research focused on synthesizing a remarkable number of new derivatives of TTF and TCNQ.Three general synthetic approaches have been used for the modification of the acceptor structure, which have been used for both TCNQ and DCNQI derivatives: (i) ring substitution with the aim of tuning the redox behaviour through careful choice of substituents, (ii) introduction of heteroatoms or heterocyclic rings into the TCNQ skeleton in order to increase inter- and intra-stack interactions which enhance the dimensionality of the corresponding charge transfer complexes, and (iii ) extension of the p-system which leads to a lowering of the intramolecular Coulomb repulsion in the Fig. 1 Selected representative electron acceptor molecules charged species.J. Mater. Chem., 1997, 7(9), 1661–1676 1661Ring substitution on TCNQ and DCNQI rings lengthening of the double bonds and the shortening of the single bonds. The introduction of the second electron completes TCNQ derivatives. In an important early paper, Wheland the aromatization process of the TCNQ, leading to the dianion. and Martin from the Dupont company characterized 21 TCNQ In agreement with the excellent EPR and ENDOR study derivatives,16 and their complexes with TTF and some other previously reported for the radical anions of p-extended donors were obtained.17,18 These syntheses most frequently TCNQs,28 the attached electrons are accommodated in the started with the corresponding p-xylylene dihalide 2 prepared dicyanomethylene units, the extra negative charges taken by by direct bis(chloromethyl)ation from the appropriate substieach C(CN)2 unit being 0.38e- for the radical anion and tuted benzene 1 as shown in Scheme 1.Although this procedure 0.83e- for the dianion. The stability of the radical anion of is not general and involves the use of the highly toxic cyanogen TCNQ explains the two one-electron reduction waves observed chloride to form intermediate 4, it allowed the preparation of for the parent TCNQ in the cyclic voltammetric studies.a wide variety of substituted TCNQs. In general, it has been found that substitution on the basic TCNQ skeleton results in CT complexes that are less con- DCNQI derivatives. Taking into account the chemical analogy between CNO and CNC(CN)2 and between CNC(CN)2 ducting than those of TCNQ itself.2 This behaviour could be explained in some cases by lower acceptor properties or may and CNNMCN, Hu� nig reported the N,N¾-dicyanoquinone diimines 8 (DCNQIs) as a new class of ecient electron be due to the complete charge transfer of stronger electron acceptors in other cases.However, interest in TCNQ deriva- acceptor molecules29 in the preparation of CT complexes and especially in highly conducting CT salts.These acceptors are tives for the preparation of novel organic conductors and, more recently, their potential application as organic rectifiers,19 readily available from the corresponding quinones in a onestep procedure by reaction with bis(trimethylsilyl )carbodiim- non-linear optical materials20 or organic ferromagnets21 led to the search for other, simpler, synthetic routes.ide 7 (BTC) in the presence of titanium tetrachloride. Considering the synthetic availability of the starting quinones, One of the alternative routes for preparing TCNQ derivatives is the reaction of 1,4-diiodobenzenes with malononitrile a great variety of DCNQI derivatives have been prepared by following the general synthetic route shown in Scheme 3(a).30 anion in the presence of a palladium catalyst to yield phenylenedimalononitrile derivatives, which after oxidation form the Theoretical calculations (AM1)31 carried out on the DCNQI molecule reveal that the LUMO energy of TCNQ is 0.4 eV TCNQ system.22 Nevertheless, the most widely used synthetic procedure for the preparation of TCNQ derivatives, first lower than the LUMO of DCNQI.Although the symmetries and atom coecients of the LUMO orbital of TCNQ and reported by Hu� nig,23 takes place by direct condensation of the appropriate quinone 6 with Lehnert’s reagent (malononitrile, DCNQI are almost identical (Fig. 2), the electron density on the nitrogen atom of the cyano group is larger in DCNQI, TiCl4 and pyridine)though this method has been said to be capricious,25 the reaction seems to be of general thus increasing the solvation energy. This has been used to explain the similar values found for the reduction potentials applicability at least for the preparation of tri- or tetrasubstituted TCNQ derivatives 5.26 of both TCNQ and DCNQI molecules.15 In contrast to the above TCNQ derivatives and in addition Theoretical calculations have been carried out to understand the reduction process of TCNQ.27 The evolution of the to the easy synthetic route from the readily available quinones, DCNQI derivatives have the flexible and less sterically geometry and electron structure of the molecule upon reduction have been calculated for TCNQ and also for its anion and demanding CNNMCN group, resulting in planar molecules even for the tetrasubstituted derivatives.32 dianion.As is shown in Scheme 2, the introduction of one electron into the TCNQ molecule to form the radical anion The acceptor ability of the DCNQI molecule is similar to that of TCNQ and the reduction potential can easily be tuned induces an aromatization of the planar TCNQ ring with a reduction of the quinoid character, as can be seen in the within a wide potential range by means of the substituents.Scheme 1 1662 J. Mater. Chem., 1997, 7(9), 1661–1676Scheme 2 dicyanoquinomethanes 9 which, on reaction with BTC, aorded the hybrid tricyano derivatives 11. The acceptor strength of the parent compound (R1=R2=R3=R4=H) proved to be very close to those of TCNQ and DCNQI and the single crystal X-ray analysis of the trimethyl substituted derivative showed a geometry which was essentially planar, although it was highly distorted for the tetramethyl derivative.40 Another synthetic strategy for functionalizing quinodimethanes leading to new dicyanoquinodimethane electron acceptors 12 and 13 has been reported.41 The multi-step synthesis takes place by substitution of a,a¾-dicyano-p-xylene anions with electrophiles, followed by oxidative dehydrogen- Fig. 2 LUMO energies of DCNQI and TCNQ (coecients are given ation. Unlike most of the other examples, the quinodimethanes as 10-3) are a substituted rather than ring substituted. These compounds, which are obtained as mixtures of syn and anti isomers, exhibit lower reduction potentials than the parent TCNQ and Thus, Hu� nig reported an interesting electrochemical study by no CT complexes have been reported so far.cyclic voltammetry of a series of substituted DCNQIs in dierent solvents and electrodes, finding a Hammett correlation for the substituent eect on the redox potentials.33 The unique properties exhibited by the DCNQI molecule are responsible for its excellent behaviour as electron acceptor component in the preparation of CT complexes and CT salts.Considering that the preparation of these electrically conducting materials has been the focus of several review articles, 15,34 we will mention only that in the last years and following the discovery of a metal–insulator–metal transition (re-entrant behaviour) in (Me2DCNQI)2Cu at low pressure, the search for re-entrant phenomena at ambient pressure has attracted much interest.Selective deuteration of Me2DCNQI [9, R1=R3=Me; R2=R4=H, Scheme 3(a)] has been performed. 35,36 By controlling the position and number of deuterium atoms, the low pressure region (500 bar) in the pressure–temperature phase diagram of (Me2DCNQI)2Cu was reproduced at ambient temperature.The equivalency of the deuteration and pressure eects is explained by steric eects: ‘contraction’ caused by the slightly shorter CMD bond (steric isotope eect) and ‘constriction’ by pressure.37–39 Other polycyano derivatives. During the last years a variety of novel acceptors, based on the TCNQ and DCNQI molecules have been reported.We will present some of the most significant modifications carried out on the quinoid skeleton. N,7,7- A very promising and totally dierent approach to the synthesis of novel acceptors was reported by Hu�nig in 1991.42 Tricyanoquinomethane imines 11 [Scheme 3(b)], which can be considered as hybrids of the TCNQ and DCNQI systems, The most important acceptor molecules, TCNQ and DCNQI, display two-stage reversible redox systems belonging to the were reported by Bryce and co-workers in 1989.40 These new electron acceptors were prepared from the corresponding Wurster type acceptors, in which the oxidized stage has quinone character.43 Hu� nig’s approach is based on the preparation of quinones 6 by treatment with Lehnert’s reagent to form the J.Mater. Chem., 1997, 7(9), 1661–1676 1663Scheme 4 Scheme 5 The redox potentials of these novel acceptors are similar to those of the TCNQ or DCNQI, and thus they form black CT complexes with donors such as TTF exhibiting a room temperature conductivity s=120 S cm-1 and semiconducting behaviour.42 Scheme 3 In addition to the benzenebis(diazocyanides), 1,4-bis(tricyanovinyl) benzene 20 has been previously reported by Wudl as a redox system of the inverse Wurster type.44 This new type of two-stage redox systems of inverse Wurster type, that is, the aromatic oxidized stage.42 Scheme 4 displays benzene-1,4- acceptor can be considered a derivative from tetracyanoethylene 21 (TCNE) which is an excellent acceptor and the simplest bis(diazocyanide)s (DCNAB), showing the dierent oxidation states (17–19), which were prepared as the first acceptors of of the symmetrical percyanoalkenes (cyanocarbons).45 Following the discovery of TCNE, a series of neutral cyanocar- the Wurster type.42 These aromatic diazocyanides 19 can be obtained by nitro- bons, such as hexacyanobutadiene 22 (HCBD)46 and a series of cyanocarbon acids such as pentacyanopropenide 23 sation of N-arylamides 14 and thermal rearrangement of intermediate 15 in the presence of trimethylsilyl cyanide 16 in (PCP-),47 heptacyanopentadienide 24 (HCP-),48 hexacyanotrimethylenemethanediide 25 (HCTMM2-)49 and tris(dicyano- an organic solvent to yield the diazocyanides 19 in good yields (Scheme 5).methylene)cyclopropandiide 26 (HCP2-)50 were prepared. 1664 J. Mater. Chem., 1997, 7(9), 1661–1676the insoluble silver salt by treatment with silver nitrate followed by bromine oxidation to yield cyanil as a yellow crystalline material.Cyanil forms CT salts with a variety of donors. However, isolation of the radical anion in the solid state has not been achieved.51 Other cyanoquinones like the already mentioned DDQ 2852 and 2,3-dicyano-1,4-naphthoquinone 29 (DCNQ)53 have also been used in order to synthesize conducting CT complexes.The work by Miller describing the new procedure for the synthesis and characterization of cyanil (tetracyano-p-benzoquinone, 27) as the strongest isolated electron acceptor (Ered= Finally, another type of cyano-containing electron acceptors with a completely dierent chemical structure is also worth 0.90 V vs.SCE in MeCN) and its reduced forms deserves attention.51 The synthesis was carried out in a three-step mentioning. Thus, electron acceptors of the fluorene series54 like 9-dicyanomethylene-2,4,7-trinitrofluorene 30 (DTF)55 form procedure from commercially available 2,3-dichloro-5,6-dicyano- p-benzoquinone 28 (DDQ) and NaCN in methanol to solid charge transfer complexes with a number of aromatic hydrocarbons.Also, acceptor molecules with structural simi- form the tetracyanohydroquinone, which was transformed into J. Mater. Chem., 1997, 7(9), 1661–1676 1665larity to the strong donor system TTF have been recently structure of 2,5-bis(dicyanomethylene)-2,5-dihydrothiophene and tris (4-oxocyclohexa-2,5-dienylidene)cyclopropane have reported to form charge transfer complexes.Thus, semicondrecently been reported as strong novel electron acceptors with ucting charge transfer complexes of TTF with 4,4¾,5,5¾-tetracyinteresting electrochemical properties. They form conducting ano-1,1¾,3,3¾-tetraazafulvalene 31 (TCTAF)56 have been 151 molecular complexes with TTF and other known electron synthesized. donors.63,64 Heteroquinoid electron acceptors p-Extended acceptor systems Most of the novel acceptors prepared have a modquinoid One of the most interesting aspects in the synthesis of tetracy- backbone, with terminal dicyanomethylene or cyanoimine ano-p-quinodimethanes other than TCNQ was to increase the groups.A very successful variation leading to good conducting p-extension of the electron acceptors.From theoretical calcu- CT complexes was performed with the thieno[3,2-b]thiophene lations, Garito and Heeger concluded, twenty years ago, that system. Thus, the novel sulfur-containing heteroquinoid an extension of the p-system in such compounds would lead electron acceptors 2,5-bis(dicyanomethylene)-2,5-dihydrothito a lowering of the intramolecular Coulomb repulsion in the eno[3,2-b]thiophene 3257 and, more recently, 2,5-bis(cyananions of the acceptors, resulting in more stable radical anions oimino)-2,5-dihydrothieno[3,2-b]thiophene 33 (DCNTT) were and hence in highly conducting CT complexes.3 Thus, in the synthesised from the respective quinones and BTC.58 last two decades novel acceptor structures such as 9,9,10,10- In this case, the standard conditions used for the preparation tetracyano-2,6-naphthoquinodimethane 44 (TNAP),65,66 of DCNQIs were not satisfactory and the reaction had to be 7,7,7¾,7¾-tetracyano-4,4¾-diphenoquinodimethane 45 (TCN- carried out in o-dichlorobenzene at 60 °C.These compounds DQ),67,68 11,11,12,12-tetracyano-4,5,9,10-tetrahydro-2,7-pyr- showed good acceptor abilities which could be tuned within a enoquinodimethane 46 (TCNTHPQ)68,69 and 11,11,12,12- wide range depending upon the substituents R1 and R2.tetracyano-2,7-pyrenoquinodimethane 47 (TCNPQ)70 were The search for increased dimensionality via interstack sulfur– prepared. However, some of these novel acceptors were not sulfur contacts led to the synthesis of other acceptor molecules stable and, although some CT complexes have been with the thiophene moiety. Thus, 2,5-bis(dicyanomethydescribed, 68,69,71,72 few solid state data have been reported due lene)2,5-dihydrothiophene 3457 and its vinilogue 3559 were to their inability to form stable crystalline complexes.Thus, prepared and, more recently, 1,3-bis(dicyanomethylene)-1,3- this approach was not as successful as was initially expected.dihydrobenzo[c]thiophene 36 and its vinylogue 37, as the first electron acceptor derived from isothianaphthene, were synthesized. 60 The half-wave redox potentials possess a weaker acceptor character in comparison with that of TCNQ. However, electron withdrawing substituents on the thienoquinoid ring increase the acceptor strength. Tricyanovinylthiophenes 41 have been recently examined as electron acceptors for organic metals.61 This molecule had been previously used as the acceptor moiety in D–p–A systems exhibiting non-linear optical properties.62 The synthesis was carried out by condensation of thiophenecarbaldehyde 38 with malononitrile in the presence of acetic acid–ammonium acetate and azeotropic distillation of water to form the dicyanovinylthiophene 39.Further treatment of 39 with potassium cyanide and then acidic conditions led to the tricyanoethane derivative 40 which was finally oxidized with N-chlorosuccinimide (Scheme 6). Although the X-ray data reveal an almost planar molecule, the reduction potentials lie far away from those of the parent TCNQ or TCNE molecules. Radialene derivatives have also been used as promising acceptor components in the preparation of conducting materials.[3]Radialene derivatives 42 and 43 having a hybrid Scheme 6 1666 J. Mater. Chem., 1997, 7(9), 1661–1676Extended p-systems based on TCNQ and DCNQI analogues. 11,11,12,12-tetracyano-1,4-anthraquinodimethane (1,4-TCAQ) had been previously reported from 1,4-bis(bromomethyl)- Much less was known, however, on TCNQ analogues laterally fused with aromatic rings. 11,11,12,12-Tetracyano-9,10-anthra- anthracene using a multistep procedure in a very low yield.73 Although the use of Lehnert’s reagent seemed to be only quinodimethane 48 (TCAQ) was prepared by four dierent partially applicable to the synthesis of TCNQ derivatives, we groups during the period 1983–1985.23,73–75 More p-extended have proved the validity of this reagent for preparation of tri- linear systems have been described more recently by reaction and tetrasubstituted derivatives.26 These molecules show of the corresponding quinones and malononitrile in the presdi ering electrochemical behaviour depending upon the substi- ence of Lehnert’s reagent76 (Table 1).tution pattern. Although the reduction potentials are shifted By following Hu� nig’s methodology,23 several synthetic routes to negative values, related to TCNQ, substitution with chlorine have been used to prepare TCAQ, the most expeditious atoms results in reduction potential values similar to that of procedure being that reported for anthraquinone as starting the parent TCNQ.The geometries and electronic structures of material.23,74 Cyclic voltammetry measurements of some of the TCAQs have also been studied, and follow a similar trend to p-extended acceptors are summarized in Table 1.that predicted for the above p-extended systems.81 As is shown in Table 1, an increase in benzannulation results Taking advantage of the more flexible and less sterically in a shift of the reduction potentials towards more negative demanding CNNMCN bond in comparison with the values, due to the major influence of the molecular distortion CNC(CN)2 moiety, a series of fused aromatic DCNQI deriva- of the fused benzene rings rather than to the electronic eect tives 51–54 have been synthesised by reaction of the corre- of increasing p-delocalization.76 sponding quinones with BTC, in which the p-system has been In contrast to TCAQ and TBAQ, which show a two-electron systematically extended in order to correlate the degree of reduction to the dianion,77 the other p-extended molecules conjugation with the acceptor ability of these molecules.82 showed two single-wave reductions to the corresponding radical anion and dianion.The single-wave reduction involving two electrons was confirmed by coulometric analysis of TCAQ in DMF.75 Therefore, the first reversible redox wave in the CV of TCAQ is an overall process leading to the dianion (TCAQ2-).The formation of radical trianions in which the third electron is located in the aromatic skeleton is in agreement with the EPR observation of related systems.28,78 The facile access to these radical trianions is related to that of the analogous dialkylsubstituted aromatic hydrocarbons.75,79 The electrochemical data clearly show that benzannulated TCNQs are poorer acceptors than TCNQ and the charge transfer complexes formed proved to be poorer conductors.80 To rationalize how the extension of the p-system aects the molecular geometry and the electronic properties, the molecular and electronic structures of 6,13-TCPQ 49 have recently been reported as a largely extended TCNQ derivative by using quantum-chemical methods.81 The geometry found is highly distorted from planarity due to the strong steric interactions between the cyano groups and the hydrogens in the peri positions. To avoid this interactions, the TCNQ ring adopts a boat conformation with the dicyanomethylene units and the naphthalene rings folded in opposite directions. The 6,13- TCPQ molecule 49 adopts a butterfly-type structure, similar to that observed for TCAQ from X-ray data in which the lateral aromatic moieties preserve their planarity (Fig. 3). The electronic structure of 6,13-TCPQ was calculated using its PM3-optimized geometry. Fig. 4 displays the Valence Eective Hamiltonian atomic orbital composition of the HOMO and the LUMO calculated for TCAQ and 6,13-TCPQ.The HOMO and the LUMO of TCAQ preserve the topology of the HOMO (3b1u, -8.53 eV) and LUMO (3b3g, -6.23 eV) of TCNQ showing, respectively, non-bonding and weak antibonding interactions with the outer carbon atoms. The LUMO of TCAQ is therefore destabilized by 1.01 eV with respect to the LUMO of TCNQ. An additional destabilization of 0.18 eV The CV measurements reveal that the increase in benzannulis calculated for the LUMO of 6,13-TCPQ which shows the ation results in ahift of the reduction potentials towards same topology.Since the reduction process implies the introduc- more negative values, following the same trend observed tion of an electron into the LUMO, the continuous destabiliz- for the TCNQ analogues mentioned above.More planar ation of this orbital when passing from TCNQ to TCAQ and p-extended DCNQI derivatives 56 have been prepared from to 6,13-TCPQ explains the more negative reduction potential substituted 1,4-anthracenediones 55 by reaction with BTC and values observed in the CV measurements. Thus, the lowering TiCl4 in dichloromethane83 (Scheme 7).of the acceptor ability with benzannulation is due to the loss Molecular mechanics calculations indicate that these of planarity, which reduces the bonding interactions in the DCNQI derivatives are nearly planar. Even the presence of LUMO of the TCNQ moiety, and also to the annulation itself, two bromine atoms does not seem to disturb the planarity of which gives rise to new destabilizing antibonding interactions.the molecule, all of the dihedral angles being smaller than 2°. In order to obtain more planar p-extended acceptors, the synthesis and characterization of 11,11,12,12-tetracyano-1,4- Heterocyclic fused TCNQ and DCNQI analogues acceptors. anthraquinodimethanes 50 (1,4-TCAQs) was reported.26 From A dierent approach, intended to increase the p-extension of the electron acceptor, involves the use of heterocyclic systems a synthetic point of view only the parent unsubstituted J.Mater. Chem., 1997, 7(9), 1661–1676 1667Table 1 CV data for TCNQ and fused aromatic ring derivatives potential/V vs. SCE compound formula solvent E11/2 E21/2 |E21/2-E11/2| E31/2 ref. CH3CN 0.08 -0.48 0.56 23 TCNQ BuCN -0.09 -0.75 0.66 75 — DMF -0.12 -0.72 0.59 75 CH3CN -0.04 -0.41 0.37 73 benzo-TCNQ BuCN -0.26 -0.74 0.48 — 75 DMF -0.30 -0.73 0.43 75 naphtho-TCNQ CH3CN -0.18 -0.48 0.30 — 73 CH3CN -0.285 75 TCAQ BuCN -0.71 — -2.06 75 DMF -0.705 75 TCTQ CH3CN -0.44 -0.93 0.49 -1.85 76(a),(b) (MeO)2-TCTQ CH3CN -0.44 -0.89 0.45 -1.59 76(a),(b) 5,14-TCPQ CH3CN -0.50 -0.92 0.42 -1.54 76(a),(b) 6,13-TCPQ CH3CN -0.57 -0.91 0.34 -1.61 76(a),(b) BDCNBA CH3CN -0.44 — — — 76(c) TBAQ DMF -0.70 — — 76(d) 1668 J.Mater. Chem., 1997, 7(9), 1661–1676Scheme 7 which, despite the steric crowding introduced by ring fusing, has proven experimentally that planar molecules are formed when pentagonal heterocyclic systems, bearing no peri hydrogen atoms, are fused to the TCNQ ring. Fig. 3 (a) PM3-optimized bond lengths (in A ° ) and bond angles (in Although the synthesis of thiophene-fused TCNQs was degrees) of TCPQ.The PM3 parameters calculated for the naphthalene firstly reported in 1986 by Kobayashi and Gajurel,84 a few molecule are included on the right within parentheses. (b) View showing years later, in 1992, the preparation and physicochemical the distortions from planarity of the molecule.Fig. 4 VEH atomic orbital calculations of the HOMO and the LUMO for TCNQ, TCAQ and 6,13-TCPQ J. Mater. Chem., 1997, 7(9), 1661–1676 1669properties of an isomeric series of thiophene-fused TCNQs thanes 6694 has also been reported. In them, the TCNQ moiety is simultaneously fused to both benzene and thiophene rings were reported.85 Their crystal and molecular structures,86 the crystal structure of CT complexes with the strong donor TTF87 as a hybrid acceptor between the TCAQ molecule and the dithiophene-fused TCNQ acceptors (Scheme 8).Compounds and also the crystal structure of a 253 CT salt with the tetraethylammonium cation88 were described. The conductivit- 66 are better acceptors than TCAQ, providing a more planar structure due to the presence of the thiophene ring.ies of the complexes are strikingly high for 57–TTF (s= 4.78 S cm-1) and 58–TTF (s=0.89 S cm-1) and very low DCNQI analogues have also been synthesized by reaction of quinones 65 (Scheme 8) with BTC following Hu� nig’s for 59–TTF (s<10-6 S cm-1). On the other hand, the radical anion salt of 57 with tetraethylammonium as counter procedure.94,95 Their high resolution 1H NMR spectra suggest a favoured configuration with the cyano groups pointing to cation exhibits a high conductivity at room temperature (s=0.46 S cm-1).the thiophene ring, in agreement with the X-ray data obtained for compound 67a. The CV measurements showed two one-electron reduction waves to the corresponding radical anion and dianion. Replacing the benzene ring with a thiophene ring leads to a better acceptor due to the lowering of steric hindrance.The presence of four fluorine atoms on the benzene ring (67c) significantly decreases the reduction potential values. Unlike compounds 67a,b, fluorine-substituted 67c showed evidence of The synthesis was carried out from the corresponding heterocyclic quinones by treatment with Lehnert’s reagent following the Hu� nig’s procedure reported for the carbocyclic TCAQ.23 The molecular structures of molecules 57, 58 and 59 were determined by X-ray analysis,88 and showed a butterfly shape, although much less distorted than the benzene-fused TCAQ molecule and closer to that of benzo-TCNQ.89 Thus, acceptors 57, 58 and 59 formed 151 CT complexes with TTF, whereas 60 did not form complexes due to its poor acceptor ability and highly deformed structure.86,87 Another interesting type of heterocyclic-fused TCNQ acceptors are the thiadiazole-fused TCNQ derivatives 61 and 62 reported by Yamashita, who described TCNQ acceptors bearing one90 or two91 thiadiazole units fused to the TCNQ ring.These compounds display good acceptor properties and their planar geometry, in addition to the presence of S,N contacts, allowed the preparation of charge transfer complexes exhibiting high electrical conductivities.92 Owing to the large size of the chalcogen atoms, the interstack as well as the intrastack interactions are increased, and as a consequence, the conductivity and stabilization of the metallic state are enhanced.93 The synthesis, electrochemistry and crystallographic study Scheme 8 of 9,9,10,10-tetracyanothieno[2,3-b][1,4]naphthoquinodime- 1670 J.Mater. Chem., 1997, 7(9), 1661–1676complexation in solution with the strong donor N,N,N¾,N¾- Recently, CT complexes from [60]fullerene–tetrathiafulvalene (C60–TTF) systems 70 have been reported to show sem- tetramethyl-p-phenylenediamine (TMPD) and forms a copper iconducting behaviour by reaction with the very strong salt by reaction with copper(I) iodide.95 electron acceptor tetrafluorotetracyano-p-quinodimethane Isomeric thiophene-fused dicyanoquinone diimines 68 and (TCNQF4).109 In contrast, no intramolecular electronic inter- 69 have been prepared and reacted with copper(I ) iodide to actions were observed in solution for C60–TTF,110 although a aord a novel class of highly conducting complexes of CuI specific solid state interaction cannot be ruled out.111 which exhibited metallic behaviour down to ca. 170 K with A dumbbell type [60]fullerene dimer in which both C60 room temperature conductivities of 45 and 100 S cm-1, units are covalently attached to a double donor spacer has respectively.96 X-Ray powder diraction studies suggested a also recently been prepared by a double cycloaddition of highly layered structure and thermoelectric powder and X-ray azomethine ylide to C60.112 photoelectron spectroscopy suggested that the electrical trans- The C60 molecule can be derivatized with organic groups to port properties occur via hole conduction along the CuI chains.yield organofullerenes exhibiting redox properties dierent In order to evaluate the eect of the presence of heteroatoms than those of C60.113–116 Wudl and co-workers have reported on the electronic properties of the acceptors without aecting the synthesis and redox behaviour of spiroannulated methano- the geometry of the molecule, we synthesized the aza-TCAQ fullerenes exhibiting better reduction ability than the parent analogue 11,11,12,12-tetracyano-2-azaanthraquinodimethane C60 molecule.117–120 In these molecules the aromatic rings are (TCAAQ) as a new nitrogentaining acceptor in a fused held rigidly perpendicular to the surface of the ball, and a pyridine ring.97 The presence of the electronegative heteroatom ‘periconjugative eect’ takes place between the pz orbitals of led to a slightly less negative reduction potential in comparison the addends and the pz orbitals of the fullerene carbon atoms with TCAQ, resulting in a better acceptor molecule.These adjacent to the bridge atom. results can be generalized in the sense that they allow a TCNQ and DCNQI type spiromethanofullerenes 72 and 73 correlation of the acceptor ability of fused TCNQ derivatives were obtained from the quinone-type 71 by reaction with with the p-deficient or p-excessive character of the heteromalononitrile and bis(trimethylsilyl )carbodiimide respectively cyclic rings.in the presence of TiCl4 and pyridine (Scheme 9). The cyclic voltammetry measurements of the novel acceptors show that the methanofullerene derivatives are slightly better acceptors than the parent C60.[60]Fullerene Based Acceptors In comparison with the quinone-type precursor spirome- Since the preparation of fullerene C60 on a large scale in 199098 thanofullerene 71, the reduction potentials of compounds 72 a great deal of eort has been devoted to the exploration of and 73 are shifted toward less negative values (70–80 mV) due the chemical and physical properties of this new allotrope to the stronger electron-withdrawing eect of the dicyanomeof carbon.99 thylene and cyanoimino groups.The electron acceptor ability of the C60 molecule in solution A dierent approach towards the search for novel organofullhas been measured by charge transfer absorption energy and erenes showing better acceptor abilities than the parent C60 also by redox potentials, and it has been concluded that C60 have been recently carried out in our group.121 Thus, the C60 is a weak acceptor molecule, comparable to p-benzoquinone cage is covalently linked to strong electron-acceptor moieties or 2,3-dichloro-1,4-naphthoquinone, the adiabatic electron anity of the C60 molecule being estimated as 2.10±0.1 eV.100 The finding of superconducting properties of salts prepared for C60 and alkali and alkaline-earth metals with relatively high transition temperatures (Tc33 K) led to the observation that the temperature Tc of the superconductivity of these fullerides was related to the size of the metallic atoms and the lattice constant.101 Consequently, the preparation of complexes with bigger organic donor molecules was thought to increase the Tc values and a number of charge transfer complexes with a variety of donor molecules have been prepared.100 Complexation with strong electron donors such as cobaltocene102 or tetrakis(dimethylamino)ethylene (TDAE)103 formed fully ionic CT complexes which proved to be electrically insulating, although with interesting magnetic properties.104 Complexation with other donor organic molecules such as ferrocene,105 hexamethylenetetratellurafulvalene,106 bis(ethylenedithio) tetrathiafulvalene (BEDT-TTF)107 or the dimer of BEDT-TTF108 gave insulating neutral CT complexes in which C60 cocrystallizes with the donor unit.Scheme 9 J. Mater. Chem., 1997, 7(9), 1661–1676 1671derived from DCNQI 74 and TCNQ 75 as precursors for novel C60 based organic metals. Each of the cyclic voltammograms of compounds 74 and 75 shows a reduction wave for each of the organic addends, in addition to the first three one-electron quasi-reversible reduction waves corresponding to the reduction steps of the fullerene moiety.The first reduction potential for these fulleropyrrolidines is shifted to more positive values related to the parent C60, TCAQ and DCAQI, these novel [60]fullerene based electron acceptors being suitable precursors for the preparation of intermolecular CT complexes by reaction with strong electron donor molecules.TCNQ and DCNQI Based Intramolecular Acceptor–Donor Systems The design of novel organic molecules containing electron donor (D) and electron acceptor (A) moieties constitutes a promising field of study due to the interesting optical and electronic properties they can display.D–s–A structures are the basis for the development of molecular electronic devices,122–124 and for the design of artificial photosynthetic systems constituted by electron donor–spacer–electron acceptor compounds125 using long spacers such as proteins and peptides.126 Other biomimetic novel compounds resem- Fig. 5 Representative donor–spacer–acceptor compounds bling the pigments of nature have also been constructed from porphyrins and quinones127 (Fig. 5). Donor–acceptor (D–A) conjugated systems have been used this modification of the chain length has no influence on the stacking motif in comparison with compound 76, the two for the preparation of molecular chromophores exhibiting nonlinear optical response.128 On the other hand, organic com- phenyl rings being nearly orthogonal to the TCNQ moiety, thus preventing the formation of segregated stacks of donor pounds exhibiting semiconducting properties based on a single component have only recently been described.129–131 and acceptor moieties, which is one of the structural requirements to obtain an electrically conducting arrangement.TCNQ derivative 2,5-dibenzyl-7,7,8,8-tetracyano-p-quinodimethane 76 (DBTCNQ) reported by Becker in 1983 was In order to avoid the orthogonality of the phenyl rings, we have prepared a new type of single-component donor–acceptor designed as a novel and interesting prototypical donor– acceptor–donor (D–A–D) system.132 compounds in which the donor and acceptor moieties are linked by two heteroatoms (sulfur, oxygen or nitrogen)27,135–137 Other DBTCNQ derivatives with electron-withdrawing substituents on the phenyl ring or naphthalene units as donor This type of molecules presents, in principle, the following advantages: (i) as the above D–A–D system, the molecule fragments were latter published, and a significant dierence in the colour of these compounds depending upon the donating contains a prefixed D5A stoichiometric ratio, and consequently, it would be possible to tune the electron transfer by strength was observed in the solid state.133 The characteristic architectural finding in the structure of using dierent substituents; (ii) the presence of two heteroatom bridges overcomes the orthogonal relative geometry between compound 76 was a packing motif of isolated triplets D,A,D formed by the central TCNQ ring of a molecule and two donor and acceptor moieties found when only one bridge is present;132,134 (iii ) the crystal packing in the solid state can be phenyl rings of two other neighbouring molecules.The donor phenyl ring moieties are orthogonal to the acceptor TCNQ modified by changing the intermolecular connectivity; and (iv) the presence of heteroatoms, and particularly the presence moiety as a consequence of the steric hindrance of the phenyl rings and the olefinic hydrogens on the TCNQ, thus preventing of sulfur atoms, may reinforce the intermolecular interactions, thus increasing the dimensionality in the solid state.donors from properly stacking.132,133 In order to mitigate this steric hindrance, we carried out the synthesis and electrochemi- The target molecules 80 and 81 were prepared by reaction of the corresponding quinones 79 with malononitrile and cal and crystallographical studies of the novel molecules 7,7,8,8- tetracyano-2,5-bis(3-phenylpropyl)-p-quinodimethane 77 and Lehnert’s reagent and with BTC in the presence of TiCl4, respectively (Scheme 10).N,N¾-dicyano-2,5-bis(3-phenylpropyl)-p-quinone diimine 78 in which an extension of the linking chains units between the Interestingly, previous attempts to prepare TCNQ derivatives 84 from the corresponding quinone 82 were unsuccessful, donor and acceptor moieties has been performed.134 However, 1672 J. Mater. Chem., 1997, 7(9), 1661–1676Scheme 10 The cyclic voltammetry measurements performed on comleading to the tricyano derivative 83 instead of the expected pounds 79, 80 and 81 show, together with the reduction waves TCNQ derivative.138 corresponding to the quinoid moiety, an oxidation wave at Substitution of sulfur or nitrogen atoms by one or two positive potential value due to the oxidation of oxathiine, oxygen atoms in the dioxine 6,11-quinone results in a favoured dithiine and oxazine fragments which give rise to stable cation 1,2-addition of malononitrile to both carbonyl groups.The radicals. This behaviour has also been observed in sulfurreaction of quinones with nucleophilic agents has recently been containing twin-DCNQI-type acceptors.140 reviewed considering modern mechanistic aspects.139 Semiempirical PM3 molecular orbital calculations predict The electronic spectra of the starting quinones and TCNQ that TCNQ and DCNQI derivatives 80 and 81 show a and DCNQI derivatives show, in addition to the expected non-planar conformation in which the acceptor and the bands in the UV region, the presence of a charge-transfer band donor moieties are bent.Distortions from planarity are as a low energy absorption in the visible region which is shifted found to be larger for the TCNQ derivative owing to the bathochromically when the donor fragment bears electron- presence of the more voluminous and rigid dicyanomethyreleasing methyl groups.This feature suggests an intramolecu- lene units. lar electron transfer from the donor to the acceptor part of the molecule.The intramolecular character of this electronic transition was confirmed by UV–VIS dilution experiments. J. Mater. Chem., 1997, 7(9), 1661–1676 1673larly the copper salts of 2,5-disubstituted DCNQIs reported by Hu� nig, which exhibit metallic conductivity and are among the better studied acceptors. We have also pointed out the first examples from the emerging chemistry of C60 based electron acceptors, which pave the way for the preparation of novel CT complexes in which the conducting properties of CT complexes are combined with the unique properties of fullerenes, thus resulting in novel multiproperty materials.TCNQ and DCNQI based intramolecular acceptor–donor The electronic properties of these compounds have been stud- (A–D) systems constitute a promising field of application for ied using the non-empirical VEH method.27,135,137 The the known acceptor molecules due to the interesting optoelec- HOMO–LUMO transition corresponds to an electronic transtronic properties they can exhibit.In particular, conjugated fer from the donor to the acceptor moieties, thus supporting D–A molecules bearing TCNQ or DCNQI derivatives as the the charge-transfer nature of the lowest energy absorption acceptor moiety constitutes an unexplored area within the field observed experimentally.of non-linear optical (NLO) materials. The X-ray structural analysis performed for the DCNQI derivative 81 [X=Y=S; R1=R2=R3=H; R4, R5= M(CHNCH)2M, Scheme 10] shows that these molecules The authors are indebted to all those who collaborated in this adopt a non-planar conformation and are packed in vertical research and whose names appear in the references given.We stacks where donor and acceptor moieties alternate their also acknowledge financial support from CICYT (Grants PBposition. In agreement with this aggregation in mixed stacks 89-0495, PB-92-0237 and PB-95-0428-C02) and Complutense [,(A–D) (D–A) (A–D),], the electrical conductivity of this University for research grants and fellowships.compound is less than 10-6 S cm-1.137 A dierent approach for the preparation of intramolecular References CT complexes consists of the synthesis of donor–s–acceptor systems bearing the strong donor TTF. Until now, only the 1 (a) J. Ferraris, D. O. Cowan, V. V.Walatka and J. H. 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ISSN:0959-9428    

DOI:10.1039/a702314f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

FEATURE ARTICLE Chemistry and physical properties of sulfamide and its derivatives: proton conducting materials Vero�nica de Zea Bermudez,*† Christiane Poinsignon and Michel B. Armand‡ L aboratoire d’Electrochimie et de Physicochimie des Mate�riaux et des Interfaces, ENSEEG/INPG, Domaine Universitaire BP 75, 38402 St.Martin d’He` res, France The state of the art in proton conducting polymers is described and the interest in the use of sulfonamide groups to prepare a series of such polymers is stressed.The most relevant aspects of the chemical and physical characteristics of sulfamide are reviewed. Its history is briefly presented. A detailed description of the structure and molecular environment of crystalline sulfamide is given. Our contribution to the interpretation of the Raman and IR spectra of sulfamide in the 4000–50 cm-1 range at melt temperature, 300 and 77 K is reported.The magnitude of the intra- and inter-molecular couplings existent in the NH stretching bands in sulfamide at room temperature and the geometry of the NH2 groups in this compound are discussed. The existence of a phase transition is proposed and the participation of hydrogen bonds examined.The protonation and hydrolysis of sulfamide and related compounds are referred to. Reactions with amines, amine exchange and rearrangements of several sulfamide type compounds are analysed. Some data associated with the sublimation of sulfamide are indicated. The eect of ionizing radiation on sulfamide is mentioned. The interpretation of the thermochemistry and pyrolysis of sulfamide suggested in the literature is analysed.Several possible applications of sulfamide in polymer synthesis are pointed out. The results we present indicate that pristine sulfamide may be classified as the fourth known molecule to work as a solvent for acidic protons, in a way similar to water, phosphoric acid or imidazole. Our studies reveal that the electrochemical stability of crystalline sulfamide spans ca. 1 V. Future directions in the field of proton conducting materials based on sulfamide are suggested. During the past two decades most of the activity in the field of proton conductivity has been undertaken by the materials science community whose major motivation has been to develop suitable proton conducting materials for application in all solid-state electrochemical devices, such as fuel cells, batteries, smart windows and sensors. Organic/inorganic systems exhibiting moderate proton conductivity were first proposed by Takahashi et al.1 as early as 1976.It was found that acids like sulfuric acid, H2SO4, or phosphoric acid, H3PO4, form compounds, in narrow composition ranges, with organic molecules containing basic groups.Compounds based on H2SO4 and triethylenediamine, From the standpoint of structure, these ionomers are formed C6H12N2, or hexamethylenetetramine, C6H12N4, have been by a hydrophobic matrix containing interconnected hydro- reported. philic ionic aggregates. In the presence of water, Nafion An important contribution to the present state of the art is becomes a conductor.The morphology of the aggregates has attributed to the American company E. I. Du Pont de Nemours a remarkable influence on the transport properties of the which introduced, during the mid-1960s, a novel series of membranes. The more the polymer absorbs water, the higher conducting perfluorosulfonate polymers. The discovery of these are the average size of the aggregates, the number of accessible materials was seminal to the development of all future memexchange sites per aggregate and the number of water molecules branes.The polymers, named subsequently Nafion, were origper exchange site. Small aggregates favour high cationic selec- inally conceived as elastomers but it was quickly recognized tivity. By adding a minimum amount of water, conductivities they had potential technological applications as ion exchange of ca. 10-3–10-2 V-1 cm-1 are achieved at room temperature.3 membranes in cells for the production of chlorine and caustic The use of Nafion as a protonic electrolyte in all solid-state soda.2 Chemically, these materials are copolymers based on a electrolytes is however limited because: (1) it does not conduct Teflon backbone to which particularly stable perfluorosulfonwhen dry and (2) its performance strongly depends on the ate anions are grafted. The SO3- groups bond to acid protons electroactivity domain of the solvent (water or other) added.(or alkaline cations). Therefore the material closely resembles a conducting polyelectrolyte in liquid medium. The strong demand aroused in the 1980s for thin proton conducting films led to the obvious concept of anhydrous † Present address: Secc�a� o de Quý�mica, Universidade de Tra� s-os- proton conduction in polymer systems.It consists of mixing Montes e Alto Douro, Quinta de Prados, Apartado 202, 5001 Vila strong acids with polymers bearing oxygen or nitrogen donor Real Codex, Portugal. centres, a strategy quite similar to the one successfully adopted ‡ Present address: De� partement de Chimie, Universite� de Montre�al, CP 6128, Succursale A, Montre�al, Quebec H3C 357, Canada.in the area of polymer electrolytes through the complexation J. Mater. Chem., 1997, 7(9), 1677–1692 1677of inorganic salts by polyethers.4 The acids used have been conduction regimes (regions I, II and III) can be distinguished (Fig. 3). At low protonation degrees (x<0.15, region I), the essentially H2SO4 and H3PO4. Due to extensive self-ionization and self-dehydration, these acids are themselves good proton compounds are amorphous elastomers. Spectroscopic results support the hypothesis of conduction assured by proton conductors when pure.5–8 At 25 °C, the conductivities observed for supercooled H3PO4 and for liquid H2SO4 reach 10-2 and exchange between protonated and non-protonated nitrogen sites.At higher acid contents, BPEI- and LPEI-based materials 5×10-2 V-1 cm-1, respectively. A polymer is expected to induce the dissociation of the acids either by means of hydrogen become glassy and crystalline, respectively. Above x=ca. 0.35 (region II), the observed increase of conductivity is ascribed bonds or by protonation of the basic sites.One of the main concerns is to prepare chemically stable blends. It is known to proton migration along the mixed HSO4-/SO42- or H2PO4-/HPO42- anionic chains by successive proton transfer that the CMO bond of ethers and alcohols is readily broken by strong acids. This degradation is especially fast in the and anion reorientation steps.Above x=ca. 0.7 (region III), conductivity reaches a plateau of the same order of magnitude presence of traces of water. Moreover, some polymers are easily hydrolysed in acidic solutions [poly(acrylamide), Paam], as the conductivity of the pure acids. A completely dierent new class of highly basic polymers whereas others [poly(2-vinylpyridine), P2VP, or poly(4-vinylpyridine), P4VP] are oxidized by H2SO4.Fortunately, in spite was presented by Charbouillot19,20 and later by Rousseau.21–23 The structure of these ormolytes (organically modified silicate of the fact that most of the polymers are water-soluble, it is possible to obtain blends by carrying out the synthesis by electrolytes), so-called aminosils, appears to be that of a noncrosslinked ladder polymer based on a silicate network sup- suppressing water or by eliminating it at the end.Blends of oxoacids with a great variety of polymers have recently been porting amino functions (e.g. aminopropyl, Fig. 4). The continuous solid solutions formed with strong mono- reviewed by Lasse`gues.9 The nature of the basic polymers is illustrated in Table 1. Acid–polymer blends are generally classi- acids (perchloric acid, HClO4, trifluoromethanesulfonic acid, HCF3SO3, hydrochloric acid, HCl, and nitric acid, HNO3) fied according to the kind of interaction established between the acid, HX, and the polymer whose pK decreases when the exhibit remarkable conductivities which may reach ca. 3×10-5 V-1 cm-1 at room temperature (Fig. 3). Proton trans- degree of ionization, aribed in eqn.(1).10 port is believed to occur by hopping between protonated and pK=pK0+a1a+a2a2+… (1) non-protonated amine sites, probably induced by the movements of the neighbouring alkylamine chains. When the doping Weakly basic polymers, polymers with intermediate basicity and strongly basic polymers may thus be considered. agent is H3PO4, the incorporation of a phosphate group in the silicate network is thought to occur.The network modifier The prototype of a weak polybase is poly(oxyethylene), POE, which exhibits a pK0 of -3. Well-defined complexes of alkylamine chain plays an important role in the transport properties, since as a base, it interacts with the acid, yielding POE–H3PO4 blends have been referred to.11,12 Fig. 1 shows the phase diagram established for this system and the conduc- transparent monolithic films. In addition, the dried products are non-porous, hard and thermally stable up to 180 °C. An tivity isotherms. A crystalline stoichiometric compound, POE0.75H3PO4, associated with minimum conductivity, and electrochemical stability domain of 1.3 V has been reported for the aminosils doped with HCF3SO3.For all the reasons two eutectics, one of them represented by the formula POE0.48H3PO4, exist. The maximum conductivity at room just mentioned and also because of the simplicity and versatility of the sol–gel chemistry, aminosils are considered excellent temperature (ca. 4×10-5 V-1 cm-1) is attained with the latter composition. This result has been explained in terms of the candidates for electrochemical devices such as smart windows.Mention must also be made of the protonic conductors diusional segmental movements of the POE chains. Polyamides, such as Paam and poly(vinylpyrrolidone), PVP, investigated by Polak et al.24 The materials, prepared with poly(vinyl alcohol), PVA, and H3PO4, contain water, since and polyamines, such as P2VP and P4VP, are polymers of intermediate basicity with pK0 of 3–6.The corresponding acid the presence of anhydrous acids is known to catalyse the dehydration of the polymer into polyacetylene. Though solid mixtures have been extensively analysed by Lasse`gues’ group at Bordeaux.13–17 The specific conductivity of the complexes solutions are obtained apparently without protonation of the weakly basic oxygens of PVA, the exact nature of the inter- obtained with strong inorganic acids is extremely low at small acid concentration, but increases suddenly at x=ca. 1 up to action has not yet been established. The interest in proton conducting polymers has not declined values as high as 6×10-3 V-1 cm-1 for Paam,1.5H2SO4, 10-4 for PVP,2H2SO4 and 4×10-3 for P2VP2,2H2SO4 at room in the last decade.More recently, other protonic ormolytes which bear suitable characteristics for high requirement ap- temperature (Fig. 2). Polyamides possess a basicity comparable to that of water plications have been introduced.25,26 The remarkable room temperature conductivity (10-2 V-1 cm-1) and good pro- or ethers and can be protonated at either oxygen or nitrogen. Due to their highly polar nature, they have strong interchain cessability of these poly(benzylsulfonic acid)siloxane based materials makes it possible to foresee their use as membranes coupling.PVP is thus a glass, but the addition of the acid progressively plasticizes the macromolecule to an elastomer. in direct methanol fuel cells. A series of benzylimidazole–H3PO4 complexes, characterized The participation of hydrogen bonding between the amide group of Paam and H3PO4 has been demonstrated.In mixtures by an extraordinary mechanical strength and toughness, is currently being studied for application in fuel cell involving H2SO4, several techniques support the claim that the polymer is protonated by the first dissociation of the acid, technology.27–29 In the hope of finding polymer electrolytes exhibiting good while the second proton belongs to the anion HSO4-.However, the possibility of intrachain protonic exchange has compatibility with electrode materials, whose stability lies in the 4–12 pH range (e.g. Ni, Ti, Mn or Ir oxides and hydroxides), not been excluded in order to account for the remarkable conductivity observed at room temperature (10-2 V-1 cm-1).we decided for the first time in 1990 to focus our eorts on the preparation of systems containing the sulfonamide function, A prototype of a smart window based on Paam,1.5H3PO4 and using tungsten and iridium oxides as electrochromic electrodes RSO2NH2, since it is known that this group has a pKa of ca. 11,30 corresponding to the acid–base equilibrium shown in has been described.17 Alkyleneimine polymers, such as linear poly(ethyleneimine), eqn.(2). LPEI,18 and branched poly(ethyleneimine), BPEI,13–16 have RSO2NH2=H++RSO2NH- (2) been thoroughly investigated. Due to their high basicity, these polymers are easily protonated. It has been concluded that These preliminary studies induced us to introduce a novel family of basic to neutral protonic polymeric electrolytes based conductivity depends strongly on acid concentration and three 1678 J.Mater. Chem., 1997, 7(9), 1677–1692Table 1 Polymers used in blends of strong acids (adapted from ref. 9) concentration polymer and abbreviation chemical formula acid range ref. poly(oxyethylene) (POE) H3PO4 0<x<2 11, 12 poly(vinyl alcohol) (PVA) H3PO4/H2O 24 H3PO4 0.6<x<2 poly(acrylamide) (Paam) 14, 16, 17 H2SO4 0.6<x<2 H3PO4 0.5<x<8 poly(vinylpyrrolidone) (PVP) 11, 16 H2SO4 1<x<3 H3PO4 0.5<x<3 poly(2-vinylpiridine) (P2VP) 16 H2SO4 0.5<x<3 poly(4-vinylpiridine) (P4VP) H3PO4 0.5<x<3 16 linear poly(ethyleneimine) (LPEI) H3PO4 0<x<1 18 H2SO4 0<x<1 H3PO4 0<x<3 branched poly(ethyleneimine) (BPEI) H2SO4 0<x<3 13–16 HCl 0<x<0.8 aminosils HClO4 0<x<0.3 19–23 poly(benzylsulfonic acid)silsesquioxane CF3SO3H 25, 26 (PBSS) on sulfamide, NH2SO2NH2.Unlike the systems described of high molecular mass POE represents a serious disadvantage, though, since it is responsible for the low conductivity above, whose conductivity lies in an excess of protons, these materials are obtained by extracting protons from a sulfonam- exhibited by the corresponding POE–salt complexes. It is accepted that conduction in semi-crystalline electrolytes ide function (RSO2NH) present in the polymer, leading to the creation of defects or proton-vacancies in the latter.This occurs exclusively in the amorphous phase. Nevertheless, these materials have been widely investigated and therefore process, which we have designated proton-vacancy doping, requires the addition of a minimum amount of an appropriate are considerably better understood than proposed systems based on other host polymers.This is the reason why we base (doping or deprotonating agent). The remarkable solvating properties of POE versus cations initially introduced a family of basic proton conducting polymers synthesized by adding sulfamide to POE.31 explains the enormous amount of eort which has been devoted in the last few years to the study and development In order to carry on these studies, a closer view of pristine sulfamide was demanded.Its complex and versatile chemistry of polymer electrolytes based on this host polymer.4 In terms of application at room temperature, the intrinsic crystallinity will be analysed in this work.Some of the countless J. Mater. Chem., 1997, 7(9), 1677–1692 1679Fig. 4 possibilities of applications of this very simple molecule will be indicated. The thermal and electrochemical behaviour will be extensively examined and discussed as well. We have presented elsewhere32 a detailed study dealing with the IR and Raman spectra of protonated and deuteriated sulfamide.The main conclusions of this spectroscopic study will be given in this article too. Some Historical Facts Sulfamides (or more precisely, sulfonamides) involve a family of products widely known mainly because of their pharmaceutical applications, in particular in several areas of antimicrobial chemotherapy.Sulfanilamide was discovered in 1908. Though sulfonamides first found application in the dye industry, they were used 25 years later as therapeutic drugs for the treatment Fig. 1 (a) Conductivity isotherms and (b) phase diagram for the system of infectious diseases. Typically, these products are p-amino- POE–H3PO4 (ref. 11) phenylsulfonamides. Because it is possible to introduce dierent substituents in the sulfonamide function, an unlimited number of substances may be obtained without any loss of activity.33 The structure and the applications of some of the best known substituted derivatives are described in Table 2.It should be noted that nearly 5000 sulfanilamide substitutes have been mentioned by Northey.35 Apart from being innocuous to human beings, sulfonamides are very ecient against pathogenic germs.They have also been used as oral antidiabetic agents. Their diuretic properties have limited use though. The production of sulfonamide increased rapidly immediately after their introduction and especially during World War II. However, in 1944, with antibiotic commercialisation it suered an abrupt decrease.The production level, at low price, has been practically stable ever since. Crystal Structure Fig. 2 Concentration dependence of the conductivity of several H2SO4 The only reported studies on the crystal structure of sulfamide blends at room temperature; (&) H2SO4–PVP (refs. 11, 16), (%) date back to the 1950s and are attributed to Trueblood et al.36 H2SO4–Paam (refs. 14, 16, 17) and (+) H2SO4–P2VP (ref. 16) According to these authors, sulfamide forms orthorhombic crystals whose density was determined to be 1.807 g cm-3.Its structure is represented by the space group Fdd2 (C2v19). The crystallographic parameters are a=9.14, b=16.85 and c= 4.58 A ° . The unit cell contains eight molecules and the primitive cell contains two molecules related by a glide plane.Molecule The sulfamide molecule is represented in Fig. 5. Its bond lengths and bond angles are shown in Table 3. Excluding hydrogen atoms, the molecule of sulfamide has mm2 symmetry implying that both the OMN and OMN¾ distances are the same within experimental error and that the OMSMN and OMSMN¾ angles are likewise not significantly dierent. The SMO lengths in sulfamide are unusually short.Comparable dimensions of related molecules are listed in Table 4. It is apparent that the SMO and SMN lengths are Fig. 3 Concentration dependence of the conductivity of several acid appreciably shorter than the single-bond distances deduced on blends at room temperature; (&) BPEI–H2SO4 (refs. 13–16), ($) the basis of the Pauling radii (equal to 1.69 and 1.73 A ° , BPEI–H3PO4 (refs. 13–16), (+) LPEI–H2SO4 (ref. 18) and (%) Aminosil–HClO4 (refs. 19–23) respectively). In the great majority of these molecules the SMO 1680 J. Mater. Chem., 1997, 7(9), 1677–1692Table 2 General structure and applications of some sulfamides34 common designation chemical formula applications sulfamide (general formula) sulfanilamide antibacterial sulfamidochrysoidine hydrochloride as antibacterial sulfadiazine antibacterial sulfamethoxazole antibacterial carbutamide hypoglycaemic tolbutamide antidiabetic carbonic anhydrase inhibitor, diuretic; acetazolamide treatment of glaucoma methazolamide carbonic anhydrase inhibitor sulfaguanidine antibacterial Table 4 Bond lengths and bong angles in sulfamide and analogous molecules36 distance/A° angle (°) SMO SMN OMSMO OMSMN NH2SO2NH2 1.39 1.60 119 106, 107 KO3SNH2 1.44 1.57 110, 114 106, 107 K2(O3S)2NH 1.44–1.45 1.66 112–114 103–107 KO3SN2O2 1.43 1.63 108, 116 106, 108 O3SNH3 1.47–1.49 1.73 114–119 92–102 (CH3SO2)2CCNCH3 1.43 118 KOSO2OC2H5 1.44–1.49a 110–116a 1.60b 101–109b Fig. 5 Sulfamide molecule (ref. 53) SO2 1.432 119 1.43 119 1.43 120 Table 3 Bond lengths and bond angles in the molecule of sulfamide36 SO3 1.43 120 SOF2 1.412 — atoms distance/A° atoms angle (°) SO2F2 1.37 129.6 1.43 130 SMO 1.391 OMSMO¾ 119.4 SOCl2 1.45 — SMN 1.600 NMSMN¾ 112.1 SO2Cl2 1.43 120 OMO¾ 2.402 OMSMN 106.6 C5H8SO2 1.44 114 NMN¾ 2.654 OMSMN¾ 106.2 S4N4 1.62 106 OMN 2.401 1.60 102 OMN¾ 2.394 aNot including esterified oxygen.bIncluding esterified oxygen. J. Mater. Chem., 1997, 7(9), 1677–1692 1681distance is comparable or even shorter than that predicted for a conventional covalent double bond, while the distance to the second atom corresponds to a bond order of 1.5 or greater.According to Cruickshank,37 the contraction of the XMO bond in XO4n- tetrahedral ions (where X=Si, P, S or Cl ) is due to the formation of two strong p-bonding molecular orbitals between the 3dx2-y2 and 3dz2 orbitals of X and the appropriate 2pp and 2pp¾ orbitals of each oxygen atom.In these XO4n- ions, each of the two 3d orbitals of the central atom is p-bonded to four oxygen atoms, meaning that, in terms of valence bond theory, each XMO bond has a bond order of 1/2=1/4+1/4. In sulfamide the situation is slightly dierent since two nitrogen atoms replace two oxygen atoms leading to a N2XO2 tetrahedron.Since each nitrogen atom only possesses one available p orbital for the participation in the p-system, the problem is to know whether one of the molecular orbitals embraces the two oxygen atoms and both nitrogens and the other just the oxygens or whether both molecular orbitals embrace the nitrogen atoms separately. The relative orientation of the SNH2 allows the conclusion to be drawn that the p orbitals of both nitrogen atoms hybridise with the same d orbital.Therefore, the SMN bonds are of order 1/4 and the SMO bonds are of the order 3/4=1/4+1/2. The knowledge of the HMNMH angle in sulfamide is of great importance. A nitrogen atom forming three bonds can be found in two extreme configurations: either trigonal pyramidal (a=109.5°) or trigonal planar (a=120°).The NH2 group is generally assumed to be pyramidal in amines and planar in amides.37 However, Pedersen38 concluded that the amine groups of sulfamide may be regarded as pyramidal. Assuming Fig. 6 Molecular environment of sulfamide in the layer (ref. 32). an NMH distance equal to 1.03 A ° , he found a HNH angle of Reprinted from J. Mol.Struct., 297, V. de Zea Bermudez, G. Lucazeau, 110° and a corresponding HMH bond length of 1.693 A ° . L. Abello and C. Poinsignon, ‘Vibrational spectra, structure and phase transition in crystalline sulfamide’, 185–206, 1993 with kind permission of Elsevier Science, NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands. Molecular environment In the crystal, sulfamide molecules are packed in an approximately hexagonal array (Fig. 6) in layers parallel to (010) (Fig. 7).36 Four equivalent NMH,O hydrogen bonds bond each sulfamide molecule to four other close neighbours in the layer, ensuring the molecular cohesion (dashed lines in Fig. 6). The intermolecular lengths shorter than 3.6 A ° are listed in Table 5. These values clearly indicate that several contacts of dierent nature are present in the structure of sulfamide.32 In-layer contacts.Each oxygen atom makes one short contact (A, 3.02 A ° ) and four longer contacts (B, C, D and D, of ca. 3.5 A ° ) in the xz plane. The distance 3.02 A ° is appreciably shorter than that of any other contact and may be properly described as a weak NMH,O bond. The fact that the SMN,O angle is 111° (practically tetrahedral) supports this interpretation.However, an associated N,OMS angle equal to 156° suggests that the localized unshared pairs of electrons in the oxygen atom are Fig. 7 Molecular environment of sulfamide in the primitive cell (g= very unfavourably placed for interaction with the proton, thus glide plane) (ref. 32). Reprinted from J. Mol.Struct., 297, V. de Zea explaining the weakness of the bond. Bermudez, G. Lucazeau, L. Abello and C. Poinsignon, ‘Vibrational Contrary to what could be expected, the oxygen atoms are spectra, structure and phase transition in crystalline sulfamide’, not located in the xz plane (otherwise the site symmetry would 185–206, 1993 with kind permission of Elsevier Science, NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands. be C2v instead of C2), but deviate from it by approximately 0.55 A ° .Consistent with this, the nitrogen atoms are also tilted out of yz plane of about 0.63 A °. Spectroscopy While Homan et al.39 were the first to obtain in 1956 the Raman spectrum of sulfamide in aqueous solutions, it was not Out-of-layer contacts. Although the shortest out-of-layer contact corresponds to a distance of 3.14 A ° , the presence of a until 1965 that Herrick et al.40 recorded the IR spectra of thin sublimed films of sulfamide and deuteriosulfamide in the range strong hydrogen bond is highly improbable.However, the other short distance equal to 3.18 A ° might be associated with 5000–300 cm-1 at room temperature and 197 K (-76 °C) and 83 K (-190 °C).The observed spectra were satisfactorily a very weak NMH,N hydrogen bond taking place between adjacent layers. interpreted on the basis of the structure of NH2SO2NH2 with 1682 J. Mater. Chem., 1997, 7(9), 1677–1692Table 5 Intermolecular distances in crystalline sulfamide36 a each amine group, the NH stretching modes were thus designated nNHb (where b stands for bonded) and nNHf, respectively.primarily parallel to (010) The frequencies observed in the Raman spectrum of the deuteriated sulfamide and the frequency components found in atoms contact distance/A° the polarized spectra of the fully protio compound were used 0 to N202 A 3.02 to derive the intra- and inter-molecular couplings existent in 0 to N004 B 3.48 the NH stretching bands in sulfamide at room temperature. 0 to N0¾04 C 3.48 Intramolecular coupling will take place between NHf and NHb 0 to O2� 02 D 3.55 groups within the same molecule. Two sorts of intramolecular primarily out of the plane parallel to (010) coupling were considered: one between dierent NH groups 0 to N1� 13 E 3.14 in the same amine group (N1Hf–N1Hb) and the other between N to N111 F 3.18 identical NH groups belonging to dierent amine groups in 0 to N1� 11� G 3.74 the same molecule (N1Hf–N2Hf¾) and (N1Hb–N2Hb¾).The aSubscripts refer to the position of the sulfur atom of the molecule in intermolecular coupling will involve identical amine groups quarter-translations; thus 0111 is attached to the sulfur atom at (1/4, belonging to two dierent neighbouring molecules or layers 1/4, 1/4) and N004� is attached to the sulfur atom at (0, 0, 1�).Atoms (N1Hf–N1¾Hf) and (N1Hb–N1¾Hb). The frequencies of the without subscript are attached to the sulfur at the origin. uncoupled amine groups are 3310 and 3256 cm-1 [Fig. 8(a)]. They belong to the NH vibrators of NHD groups dispersed site symmetry C2, almost C2v. The assignments seemed to be in ND2 groups, the corresponding ND frequencies being consistent with the normal coordinate treatment based on a 2452 cm-1 and probably the shoulder at 2391 cm-1 [Fig. 8(c)]. single valence force potential function. Partial double bonding The dierence in the chemical bonding of the Hf and Hb of the SMN bonds was indicated, but no indications protons leads to a Dn� of 54 (=3310–3256) cm-1. The interof the ionic, NH3+(NHN)SO2-, or isodiamidic, action between Hf and Hb protons within the same amine NH2(NHN)S(O)OH, forms were observed.Participation of group generates a shift of approximately 22 (3332–3310) cm-1 all the hydrogen atoms in a moderate hydrogen bond was for Hf and 21 (=3256–3235) cm-1 for Hb. Values of 1 and suggested. 28 cm-1 were found for the intramolecular coupling resulting A year later, Uno et al.41 recorded the IR spectra of sulfamide from the interaction between identical amine groups in the and [2H4]sulfamide under ordinary and polarized radiations.same molecule, respectively, for the Hf and for the Hb protons. Their vibrational assignment was made by referring to the IR The polarized components of the crystal vibrations derived dichroism as well as the isotopic eect.Normal coordinate from the nNHf mode present extremely close frequencies, analysis of sulfamide was carried out by assuming C2v molecuindicating that the coupling in the crystal at room temperature lar symmetry and is essentially consistent with that of Herrick is very weak. In the case of the nNHb modes, a much more et al.40 except for dierences in the assignment of the skeletal important coupling is present: while the dierence between the frequencies in the deuteriated compound.highest and lowest frequency component is 3 cm-1 for the Preliminary results obtained with the sulfamide-based elecnNHf vibration, the value obtained for nNHb is 38 cm-1. trolytes indicated the need for a full understanding of the The strong polarization eects observed in the IR spectra spectral signals of the NH groups in crystalline sulfamide.of sulfamide in the form of powder and orientated film Mainly because many contradictory questions arose when we (deposited on a silicon plate) allowed us to deduce the geometry compared our results with those reported by the authors of the NH2 groups of sulfamide.Taking into account the mentioned above, we were led to the conclusion that some minimization of energy of the strong intralayer hydrogen details needed further reexamination. Especially, the lack of bonds and symmetry considerations, both planar and pyrami- Raman data for crystalline sulfamide, in particular the lowdal geometries were acceptable. A trigonal planar bonding frequency region, stimulated our work.It was also clear from situation would result in the presence of a relatively linear, the available literature that the important NH stretching region parallel to the xz plane, short NMH,O contact. According was far from being fully interpreted, thus deserving a closer to this model, the NMH,O angle should be close to 160° look. Moreover, the studies of Trueblood et al.,36 on crystalline and the hydrogen bond would form an angle of 45° with the sulfamide are incomplete as the position of the protons in the x direction, instead of being primarily directed along the x structure was not determined.We have therefore undertaken direction, as proposed by Trueblood et al.36 Nevertheless, in a deeper IR and Raman analysis on both protio- and deuteriothis model none of the NH bonds of each amine group is sulfamide, especially by recording polarized Raman spectra.32 strictly parallel to the xy plane or perpendicular to it and We have studied the Raman spectra of powdered sulfamide cannot account for the IR results. Thus, a model of trigonal and deuteriosulfamide at 300 and 77 K in the 4000–50 cm-1 pyramidal NH2 groups, in which the NHf bond is strictly range.Polarised Raman spectra of orientated microcrystals parallel to the xy plane, seems to be more acceptable. In such and orientated films have also been obtained. New bands have a model the NMH,O angle is approximately 150°, a value been detected and some framework modes have been reaswhich is still admissible for hydrogen bonding.Since the NHf signed. Special attention has been given to the low-frequency band appears in both spectra, whereas the NHb band is region for which no data existed in the literature. The main polarized, it was concluded that the hydrogen atoms Hb, results of this study are collected in Table 6. involved in the moderately strong intralayer hydrogen bonds, The presence of non-equivalent protons within the same lie approximately in the xz plane, whereas the Hf atoms are amine group of the sulfamide molecule was confirmed by the directed perpendicularly to the same plane, so being more presence of two bands in the high frequency Raman spectrum suited for the weak, long interlayer hydrogen bonding situation.recorded for the 95% deuteriated compound [Fig. 8(a)]. The We have also analysed the melting transition of sulfamide high frequency narrow band at 3310 cm-1 corresponds to a by Raman spectroscopy. Fig. 9 shows the spectral evolution of practically free proton Hf (where f stands for free) having a sulfamide with the increase of temperature in the NH stretching negipation in an interlayer hydrogen bond and region. Between 80 and 90-e °C, the bands associated with completely decoupled from other protons (in the same NH2 the tNH2 and nNH modes become broader.In reaching the group, in the same molecule or in the cell). In contrast, the low liquid state, at temperatures higher than 90+e °C, the torsion frequency broad band at 3256 cm-1 has been associated with a modes are no longer present, whereas the NH stretching bands NH vibrator involved in a moderately strong intralayer hydrogen bond.Considering the dierent nature of the protons in are dramatically modified. An increase of the frequency of the J. Mater. Chem., 1997, 7(9), 1677–1692 1683Table 6 Room temperature spectra of crystalline sulfamide32 a NH2SO2NH2 ND2SO2ND2 IR 300 K Raman 300 K Raman 300 K orientated orientated isotopic powder powder film (pol) powder microcrystals ratio assignments xx xx, yy zz xz yz (A1) (B1) [A1+A2+B2(?)] 3332 3330 1.33 nNHf ip A1 2499 3333 A2 3334 S 3330 (s) 3332 nNHf op B1 B2 2452 vw 3256 ep 3241 nNHb op B1 B2 3238 S 3238 (p) 3222 3226 1.36 A2 2373 3216 nNHb ip A1 3099 2dNH2 2313 1559 dNH2 op A2 1560 op B2 1560 m 1560 w(s,p) 1557 w 1556 1.34 ip A1 1167 1553 ip B1 1375 sh 1367 0.99 naSO2 B2 1358 1356 S 1356 (s) 1358 w 1356 B1 1339 1181 sh 1179 nsSO2 A2 1165 (p) 1150 S 1150 1.02 A1 1140 S 1128 S 1130 sh 1127 1.12 vNH2 op B1 1000 vw 1122 sh B2 980 vNH2 ip A2 A1 1078 2*528 A1 933 931 (s,p) 932 1.02 naSN2 B1 910 vw B2 870 909 nsSN2 A2 831 vw 906 904 (p) 908 S 901 1.09 A1 811 729 sh 729 S (s) rNH2 op B1 B2 722 S (p) 724 m 724 724 1.15 rNH2 ip A1 629 A2 570 w 568 (s) 571 569 1.01 rSO2 B1 564 B2 535 m (p) 527 1.02 dOSO A1 516 528 m 526 A2 544 (s) 542 sh 538 1.17 rSN2 B1 469 504 w 505 (s) B2 435 sh 420 420 1.00 tO2SN2 A2 438 417 m 420 (p) 420 1.00 A1 423 356 360 S 360 1.10 dNSN A1 325 360 A2 326 w 1.21 tNH2 op B1 259 331 B2 320 w 320 1.27 tNH2 ip A1 251 320 A2 140 138 1.03 T¾x B2 136 121 m 121 123 1.06 B1 116 R¾x B2 116 1.07 and B1 108 R¾y B2 88 88 1.06 R¾z A1 83 A2 72 1.01 T¾z A2 71 A1 49 m 48 49 1.00 T¾y B1 48 B2 aip and op=in-phase and out-of-phase vibration relatively to the C2 axis of the molecule, respectively; A1, A2, B1, B2=crystalline components (in-phase and out-of-phase A and B type vibrators relatively to the glide plane).S=strong, m=medium, w=weak, vw=very weak, sh=shoulder. NHb band is observed as the temperature is increased, reflecting the external modes disappear at this stage and are replaced by an important Rayleigh scattering.weaker intermolecular interactions. Moreover, this frequency appears to approach that of the NHf band. The frequency of As sulfamide is a non-centrosymmetric crystal at room temperature, a phase transition may be expected, probably leading this latter band is approximately constant, confirming the proton’s free character.In the liquid state, the two protons to a more symmetric structure including a centre of inversion. Due to the dynamic disorder which accompanies the rise in become equivalent and couple. Modes belonging to the framework spectral region undergo similar changes. As expected, temperature, sulfamide may suer an evolution from a non- 1684 J.Mater. Chem., 1997, 7(9), 1677–1692Fig. 9 Spectral evolution of the N–H stretching region of sulfamide when temperature is raised from 35 °C to melting (ref. 32); (a) 35, (b) 70, (c) 80, (d) 90-e, (e) 90+e, ( f) 100 and (g) 110 °C. Reprinted from J. Mol. Struct., 297, V. de Zea Bermudez, G. Lucazeau, L. Abello and C.Poinsignon, ‘Vibrational spectra, structure and phase transition in crystalline sulfamide’, 185–206, 1993 with kind permission of Fig. 8 High frequency Raman spectra of the fully protonated and Elsevier Science, NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, 95% deuteriated sulfamide at (a) 300 and (b) 77 K [(i) corresponds to The Netherlands. NH2SO2NH2 and (ii ) corresponds to 5% of H among 95% of D)]; (c) high frequency Raman spectra at (i) 300 and (ii) 77 K for ND2SO2ND2 (ref. 32). Reprinted from J. Mol. Struct., 297, V. de Zea Bermudez, G. Lucazeau, L. Abello and C. Poinsignon, ‘Vibrational spectra, structure and phase transition in crystalline sulfamide’, 185–206, 1993 with kind permission of Elsevier Science—NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.centrosymmetric (and possibly ferroelectric) phase to a centrosymmetric (and possibly paraelectric) phase. The DSC thermogram of crystalline sulfamide, represented in Fig. 10, suggests that a phase transition could take place some degrees before melting. In the hope of finding spectroscopic evidence for this phenomenon, we analysed the Raman spectra for this compound at increasing temperatures, from room temperature up to the melting temperature (Fig. 9). A systematic anomaly in terms of a positive (+Dn� ) or negative (-Dn� ) wavenumber deviation with respect to the general trend (for instance, DnaSO2=-5 cm-1, DrNH2=+3 cm-1 and DnNHf ca. +4 cm-1) is present in the 80 to 90-e °C temperature range. Naturally, this very subtle anomaly would not be recognised without support from the DSC result.Reactions Fig. 10 DSC thermogram of crystalline sulfamide (Tp=phase trans- Protonation ition temperature; Tm=melting temperature) (ref. 32). Reprinted from J. Mol. Struct., 297, V. de Zea Bermudez, G. Lucazeau, L. Abello and The NMR studies of Birchall et al.,42 provide conclusive C. Poinsignon, ‘Vibrational spectra, structure and phase transition in evidence that the protonation of sulfamide occurs preferentially crystalline sulfamide’, 185–206, 1993 with kind permission of Elsevier on the nitrogen atom.In a previous paper, the same authors Science, NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands. established unambiguously that in the case of amides, which J. Mater. Chem., 1997, 7(9), 1677–1692 1685are analogous weak bases, protonation occurs on the carbonyl Hydrolysis oxygen atom and not on the nitrogen.43 At the end of the last century, Traube45 demonstrated that The protonation and deprotonation mechanisms in sulfamwhen sulfamide is heated to boiling under reflux in a sodium ide were also studied by Garrett et al.44 A dependence of the hydroxide solution, ammonia rapidly evolves.Aminosulfonic width of the NMR signal of water in aqueous solutions of acid (NH2SO3H, also called sulfamic acid), which is very sulfamide with pH was observed. The evolution of linewidth resistant to alkaline hydrolysis, is produced simultaneously at half height of the water signal Dn1/2 with pH exhibits two [eqn. (6)]. maxima (at pH 4.1 and 5.7) and one minimum (at pH 5.1), which are interpreted in terms of the following two reactions NH2SO2NH2+H2O CA NaOH NH2SO3H+NH4OH (6) involving proton exchange between water and sulfamide [eqn.(3) and (4)], If diluted hydrochloric acid is used instead, aminosulfonic acid is rapidly formed too, but the reaction continues with NH2SO2NH2+H+ CA k1 NH2SO2NH3+ (3) slow hydrolysis of the sulfamic acid, yielding ammonia and sulfuric acid [eqn. (7)].NH2SO2NH2+OH- CA k2 NH2SO2NH-+H2O (4) where k1 and k2 are sulfamide protonation and deprotonation rate constants, respectively. The sum of the rates of the acid- and the base-catalysed exchange reactions is represented by eqn. (5). The studies of Yamaguchi et al.46 focused on the hydrolysis of N-monosubstituted and N,N- and N,N¾-disubstituted sulfa- R=k1(H+) (NH2SO2NH2)+k2(OH-) (NH2SO2NH2) (5) mides in water and in alkaline solution, and show that the Relying on experimental data, k1=3×107 and k2= major products formed are the corresponding ammonium 2×1011 dm3 mol-1 s-1 have been proposed.The magnitude sulfamates. of sulfamide protonation rate constant k1 is similar to that of An example is the hydrolysis of a N-monosubstituted sulfamweak bases, such as hydrogen peroxide, H2O2 (2×107 dm3 ide [eqn.(8)]. mol-1 s-1) and methanol, CH3OH (108 dm3 mol-1 s-1). RNHSO2NH2+H2O�(RNHSO3-)(NH4+) (8) However, the protonation rate constant of N-methylacetamide (NMA), CH3CONH(CH3), which might be expected to be In contrast, eous sodium hydroxide, a hydrolytic comparable to that of sulfamide, is considerably lower (400 dm3 cleavage reaction is responsible for the formation of sodium mol-1 s-1).This result, attributable to the presence of partial sulfamate and ammonia [eqn. (9)]. double bonding of the type O--(CH3)=N+H(CH3), indicates either the absence of a partial double bond SNN in sulfamide RNHSO2NH2+H2O CA NaOH RNHSO3Na+NH3 (9) or a considerably less important contribution than in NMA.The rate constant k2 is in good agreement with the rate The hydrolysis kinetics of a series of N,N¾-diarylsulfamides constants for the deprotonation of acids stronger than water (K ca. 1010 to 1011 dm3 mol-1 s-1). The deprotonation equilibrium of sulfamide is indicated by a pKa constant of ca. 11,30 whereas the corresponding aquoacid (water molecule having a proton replaced by a group R), sulfamic acid, NH2SO2OH, has a pKa=1.Other sulfamides [phenylsulfonamide, C6H5SO2NH2, and sulfanilamide, were analysed by Spillane et al.47 who claimed that several mechanisms may be envisaged for the hydrolysis reaction. The (NH2)C6H4SO2NH2] exhibit pKa close to 10.30 Scheme 1 Hydrolysis catalysed by N,N¾-diphenylsulfamide (ref. 47) 1686 J. Mater.Chem., 1997, 7(9), 1677–1692hydrolysis of the N,N¾-diphenylsulfamide is exemplified in Schemes 1 and 2. Irrespective of whether the first step is an acid-catalysed displacement at the sulfur atom (path A, Scheme 1), an acid-catalysed heterolysis yielding substituted sulfamoylium ions (path B, Scheme 1) or a spontaneous bimolecular hydrolysis of unprotonated sulfamide (Scheme 2), phenylsulfamic acid is a likely intermediate.It was proved that: (1) the rate determining step is the formation of phenylsulfamic acid; (2) the participation of the sulfamoylium ions is not consistent with the results revealed by the substitution eect. It was also concluded that the major hydrolytic pathway involves bimolecular water attack on the unprotonated diarylsulfamide.Reactions with amines Reaction with primary and secondary amines. The reactions of sulfamide or monosubstituted sulfamides (i.e. sulfamylamines) and primary or secondary amines to displace ammonia are well known48,49 [eqn. (10)]. RNHSO2NH2+R¾NH2�RNHSO2NHR¾+NH3 (10) Though ordinarily N,N-disubstituted sulfamylamines are unreactive, an unexpected reaction which provides a facile method for preparing new sulfamylguanidines was reported by Lombardino.50 He observed that treating substituted guani- Scheme 2 Non-catalysed hydrolysis of the N,N¾-diphenylsulfamide dines with N,N-disubstituted sulfamylamines, at temperatures (ref. 47) close to 100 °C, did not result in the displacement of ammonia; instead sulfamylguanidine I was detected. Moreover evidence ines are best represented by a zwitterionic structure.The indicated that this reaction appeared to be of general appliincrease of the thermal stability of the zwitterionic form over cation when guanidines, monosubstituted guanidines or N,Nthe neutral one arises from the resonance energy of guanidin- disubstituted guanidines were reacted with N,N-disubstituted ium and the proximity of the opposite charges arranged in a sulfamylamines. five-membered ring.Rearrangements Amine exchange. The amine exchange reactions undergone by sulfonamides, leading to the cleavage of the sulfur–nitrogen bond, are essentially aminolyses [eqn. (12)]. Such reactions are generally carried out by heating a sulfonamide with a primary or secondary amine, in the presence of the hydrochloride of the latter.51 If an aliphatic amine is used, acid catalysis is not required.ArSO2NRR¾+RR+NH=ArSO2NRR++RR¾NH (12) The susceptibility of sulfonamides in amine exchange depends largely on their basicity, alkyl substituents increasing it and aryl ones decreasing it. On a kinetic basis, the ease of breaking of the sulfur–nitrogen bond in sulfonamides increases in the following series: N-phenylsulfonanilide<NThe reaction in eqn.(11) could be initiated by the proton ethylsulfonanilide<sulfamide<N-ethylsulfonamide<N,Ntransfer from the slightly acidic sulfamylamine to the very diethylsulfonamide. basic guanidine. In its anionic form, sulfamylamine, unable to The reaction of amine exchange occurs by a dissociative lose ammonia, forms a cyclic ion pair II with the guanidin- mechanism involving the conjugated acid of the sulfonamide.ium cation. In the absence of catalyst, a displacement reaction takes place [eqn. (13)]. The five-centred cyclic intermediate facilitates bond formation between the guanidine nitrogen and the sulfamylamine sulfur, with concomitant elimination of R2NH and formation of I. The abnormal reactivity of N,N-disubstituted sulfamylam- Amine exchange of sulfonamides has been widely utilized for synthetic purposes.The synthesis of sulfanilylguanidine ines is encouraged both by the high basicity of guanidines and the ability to form a cyclic intermediate II. from sulfanilamide and guanidine,52 which has been patented, is an example. The inertness of sulfamylguanidines towards a variety of amines under various experimental conditions, even at tem- We have recently reported the preparation of low mass polymers exhibiting a conductivity of 3×10-6 V-1 cm-1 peratures up to 150 °C, supports the claim that sulfamylguanid- J.Mater. Chem., 1997, 7(9), 1677–1692 1687at room temperature by reacting a Jeamine difunctional amine, a,v-diaminepoly(oxyethylene-co-oxypropylene), with NH2SO2NH2.53 Trans-sulfamoylation.At the beginning of the 1960s, Scott et al.54,55 reported a new aromatic rearrangement, mechanistically very interesting, based on an intermolecular transfer of a sulfamoyl function (RNHSO2) from N,N-diarylsulfamides. This rearrangement, designated trans-sulfamoylation, is best interpreted in terms of direct nucleophilic attack on sulfur in the protonated sulfamide, most probably by the p-aryl carbon site in the aromatic nucleophilic substrate.56 Hence, the presence or absence of trans-sulfamoylation and amine exchange results from the competition of the reactive N and C centres Pyridyl substituted rearrangement products could not be of the nucleophile, the attack occurs via carbon atom in the isolated, presumably because the cleavage reaction to give a first case and via nitrogen atom in the second. 2-pyridylsulfamoylonium ion is not competitive with the facile Trans-sulfamoylation and amine exchange are probably the amide exchange. most characteristic reactions of sulfamides. In excess of N,N-dimethylaniline, the N-(2-pyridyl)-4- dimethylaminobenzenesulfonamide VIII forms56 [eqn. (19)]. Sulfamide, NH2SO2NH2.By reacting sulfamide and aniline at 150 °C, Scott et al.55 observed the production of sulfanilanilide III [eqn. (14)]. At the same temperature and using an excess of aniline, 1,3- diphenylsulfamide IV is the major product, though small amounts of III are also obtained [eqn. (15)]. However, by refluxing IV in N-methylaniline, 4-Nmethylaminobenzenesulfonanilide VII results.55 The possible exchange product does not rearrange [eqn.(20)]. By further heating IV with aniline in the presence of catalysts such as ammonium, anilinium or triethylammonium hydrochlorides, it can be converted to III [eqn. (16)]. Both reactions demonstrate the fundamental role played by steric factors, apparently favouring transfer reactions, before exchange reactions.Trisubstituted sulfamides, NRR¾SO2NHR. Scott et al.54 reported that a trans-sulfamoylation reaction occurs when trisubstituted sulfamides IX react with excess N,N-dimethyl- Moreover, when IV is heated to 150 °C, with an excess of aniline to yield 4-dimethylaminobenzenesulfonanilides X N,N-dimethylaniline, 4-dimethylaminobenzenesulfonanilide V [eqn. (21)]. is formed. The reaction mechanism implies the transfer of a phenylsulfamoyl group of IV to the amine and suggests that the rearrangements undergone by the 1,3-diphenylsulfamide IV are intermolecular [eqn.(17)]. The most probable mechanism involves a displacement process at the sulfonyl sulfur [eqn. (22)]. This reaction sequence explains why rearrangements may be catalysed by acid (ptonation facilitates bond scission in XII) and why the greatest yields of XI are obtained with Ar groups containing Disubstituted sulfamides, NHRSO2NHR or NRR¾SO2NH2.Scott et al.55–57 showed that N,N¾-di(-2-pyridyl )sulfamide VI electron attracting groups that increase the acidity of the sulfur atom, facilitating the formation of XII. The lack of reaction of readily undergoes an amide exchange with aniline to give IV, which further rearranges to III [eqn.(18)]. tetrasubstituted sulfamides is consistent with the proposed 1688 J. Mater. Chem., 1997, 7(9), 1677–1692Table 7 Vapour pressures of crystalline sulfamide58 mechanism since these sulfamides oer steric hindrance to the approach of the base in the process forming XII. T /K p/10-5 mmHg 347.8 6.370 348.7 7.017 349.7 7.960 350.7 8.671 352.7 10.430 354.7 12.810 357.7 17.040 Eect of Ionizing Radiation Mishra et al.59 have shown that exposure of sulfamide to 60Co c rays at 77 K gave results summarized in eqn. (25)–(27).NH2SO2NH2�H2+N� SO2NH2+e- (25) H2+N� SO2NH2+NH2SO2NH2�HN� SO2NH2 +H3+NSO2NH2 (26) NH2SO2NH2+e-�NH2-+NH2S�O2 (27) Thermochemistry and Pyrolysis It is stated in Traube’s work60 that the thermal decomposition of sulfamide starts at 100 °C and that at ca. 200 °C sulfimide XIV forms. Owing to the instability of monomeric sulfimide, Tetrasubstituted sulfamides, NRR¾SO2NRR+. In general only the trimeric form has been isolated [eqn. (28)]. tetrasubstituted sulfamides, RR¾NSO2NRR+, are extremely unreactive and do not undergo hydrolysis, amide exchange or NH2SO2NH2 CA heat SO2=NH+NH3F (28) trans-sulfamoylation reactions. The great stability of the tetrasubstituted sulfamides contrasts strongly with the behaviour XIV of mono- and di-substituted sulfamides for which these pro- Heinze et al.61 prepared the ammonium salt of cesses take place easily. trisulfimide XV by heating sulfamide to 200 °C [eqn.(29)]. In contrast Scott et al.56 have found that N,N¾- Decomposition of XV occurred above 210 °C.sulfuryldiimidazole XIII undergoes hydrolysis and on refluxing with aniline gives sulfanilanilidine III, possibly via amide exchange, followed by rearrangement [eqn. (23)]. The thermal decomposition of sulfamide between its melting temperature (ca. 92°C) and 200 °C was later examined by Ito.62 This author proposed that below 170 °C the ammonium salt of imidodisulfamide XVI is obtained [eqn. (30)].Above this temperature sulfamide would be transformed first into the ammonium salt of sulfuryldisulfamide XVII and then into the ammonium salt of trisulfimide XV [eqn. (31) and (32)]. Sublimation According to Tagaki et al.58 the experimental values of the vapour pressures of crystalline sulfamide, listed in Table 7, are well reproduced by eqn.(24). log10P=11.047-5300.4/T (24) The heat, entropy and free energy of sublimation of sulfamide were found to be 101.46±1.00 kJ mol-1, 155.89±2.84 J K-1 mol-1 and 54.85 kJ mol-1, respectively. A value of 19.7 kJ mol-1 was obtained for the intralayer NMH,O hydrogen bond of sulfamide by subtracting from the observed heat of sublimation the contribution of both the dispersion energy and the electrostatic interaction energy. J.Mater. Chem., 1997, 7(9), 1677–1692 1689sition occurs in the range 220–270 °C) limits the usefulness of these materials for high temperature applications. Based on the relative thermal stability of the acid- and base-catalysed compounds, of both the ternary polymers and those from condensations of sulfamide and HCHO, Florentine et al.67 have concluded that acid catalysis favours asymmetric polymerization about the sulfamide fragment and proposed that the thermal decomposition of the product at 225 °C may The study carried out by Cuilleron et al.63 at 92–300 °C provide a novel polymerization route to CMNMC type polysuggests that sulfamide undergoes appreciable changes as it mer chains, where N* was originally part of the sulfamide.decomposes (Scheme 3) in a way far more complex than proposed by the authors mentioned above. Cuilleron et al. demonstrated that sulfamide is thermally stable up to 140 °C. Above this temperature, isomerisation and polymerisation of sulfamide are found to occur simultaneously. Isomerisation, favoured by slow heating, results in the formation of the Basic catalysis favours symmetric polymerization around ammonium salt of trisulfimide XV whose decomposition starts SO2 but can produce di- and tetra-functional fragments of at ca. 220 °C. Polymerization takes place below 180 °C. It is sulfamide in the polymerization. facilitated by rapid heating and gives rise above 150 °C to The reaction of sulfamide–formaldehyde compounds (molar the ammonium salts of imidodisulfamide XVI and ratio 154) with melamine suggests that basic catalysis can lead sulfuryldisulfamide XVII, together with linear amides of forto the inclusion of reactive hydroxymethyl groups (CH2OH) mula H(HNMSO2)nNH2 (with n>3).At temperatures higher as side groups in the polymer. Thermal copolymerization of than 180 °C, sulfamide and imidodisulfamide XVI are no longer melamine with these CH2OH groups appears to occur at detected, but sulfuryldiamide, monosulfonic sulfamide and 225 °C.Linear sulfamide–formaldehyde–melamine polymers more condensed amides, stable up to 250 °C, remain. Above containing tetrasubstituted sulfamide fragments are proposed 280 °C, the only stable product which has been isolated is as those SMNMC polymers likely to possess maximal thermal ammonium sulfate, (NH4)2SO4.Monteil64 obtained mass specstability, suitable solubility and desirable plastic properties. trometric evidence for the ion SO2NH2+ and proposed that this cation may be responsible for the polymerization of sulfamide. Conductivity and Electrochemical Stability It was stated in the introduction that the anomalous proton Use in Polymer Synthesis conductance observed in several non-aqueous media, such as Scott et al.65,66 have pointed out the ecient cross-linking anhydrous H3PO4 and anhydrous H2SO4, is the result of properties of sulfamide by preparing a series of copolymers of extensive self-ionisation and self-dehydration.Sulfamide might sulfamide–formaldehyde and sulfamide–formaldehyde–mela- be expected to exhibit proton conductivity as well considering mine.The products are hard resins, insoluble in water and its amphoteric nature which allows us to foresee the selfmost organic solvents, and form cohesive plaques by applying protonation equilibrium in eqn. (33). heat and pressure. The presence of melamine allows a workable 2NH2SO2NH2 =NH2SO2NH3++NH2SO2NH- (33) material to be obtained. In spite of being extremely resistant to chemical attack, their lack of thermal stability (decompo- Surprisingly, only one reference, the work of Monteil,64 has dealt with its conducting properties.In his conductimetric study, aimed at finding the intermediate responsible for the thermal transformations of sulfamide, he reported a maximum conductivity of 10-2 V-1 cm-1 at approximately 166 °C.This temperature would correspond to the maximum rate of transformation of sulfamide into more condensed products. Above it, conductivity dropped reaching 6×10-3 V cm-1 at 200 °C. Mass spectrometry has provided conclusive evidence of the presence of the ion SO2NH2+.64 Solid sulfamide and solutions of sulfamide in water and dioxane had been closely examined by Devoto in the early 1930s. Magnetic susceptibility measurements supported the claim that in the solid state sulfamide must be described by an amidic form XVIII.68 The fact that solutions of sulfamide in dioxane exhibited a dipole moment of 3.9 D indicated that sulfamide is best represented by an isoamidic or semi-polar form XIX in solvents of low relative permittivity.69 In solvents of high relative permittivity, such as water, sulfamide is present in its polar form XX.70 Sulfamide is certainly an interesting compound.Kreuer et al.71 recently stated that only three compounds may act as Scheme 3 Thermal decomposition of sulfamide (ref.ed solvents for acidic protons in polymers and liquids: water, by permission from Bull.Soc. Chim. Fr., J. Cuilleron and Y. Monteil, phosphoric acid and imidazole (pyrazole). All these systems ‘Pre�paration et de�composition thermique du sulfamide-nø 143-III’, 892, 1966. allow for the formation of protonic defects and provide strongly 1690 J. Mater. Chem., 1997, 7(9), 1677–1692fluctuating proton donor and acceptor functions in an other- should be avoided as it is presumably responsible for an oxidation reaction which limits the electrochemical stability wise unpolar environment.Our results suggest that sulfamide might be the fourth system.53 Fig. 11 represents the behaviour region anodically.72 The Raman and IR spectra of POE and POE-based complexes of sulfamide with compositions of of solid state sulfamide in the undoped and doped states.While at room temperature sulfamide exhibits a conductivity of n=2, 2.5, 4, 5, 20 and 30 have been recorded at 300 K in the 4000–100 cm-1 range.74 The evolution of sulfamide–polymer 10-6 V-1 cm-1, at 60°C proton doping, achieved by the addition of sulfamic acid, enhances that value tenfold. We have interactions with sulfamide concentration was studied on the basis of the changes in the spectral feature of the NH stretching also concluded that the electrochemical stability region of crystalline sulfamide spans ca. 1 V (Fig. 12).53 region. For the more concentrated samples a situation similar to that found in crystalline sulfamide is observed (non-equival- The interest in the use of sulfamide for providing new basic proton conducting polymers was intensified after the recog- ence of the protons).For the more dilute samples, the spectroscopic behaviour of sulfamide supports the absence of specific nition that the materials we had initially introduced, based on POE, did exhibit good electrochemical performance.31 interactions and the complete orientational disorder accounts for the weak character of the hydrogen bonds, a situation also It was found that the POEnNH2SO2NH2 system (where n= O/S indicates the ratio of monomer units per sulfamide mol- encountered in molten sulfamide.The Raman spectra of compositions 2, 4 and 5 show that doping induces disorder in the ecule) presents a phase diagram with three eutectics at compositions n=2, 4 and 30 and three stoichiometric compounds at materials.The degree of crystallinity of the compounds was observed to depend on the nature of the substrate, as well as compositions n=2.5, 5 and 20.53 The electroactivity domain of the electrolytes is approximately 1.7 V.72 By doping the on the thickness of the films. We concluded that in situ micro Raman techniques provide a good tool to assess the level of eutectics with the guanidinium cation acting as a protonvacancy inducer, introduced as guanidine carbonate, heterogeneity of the samples.This series of new materials has been enlarged by the use of [H2NC(=NH)NH2]2·H2CO3, a remarkable enhancement of the conductivity results. For all the compositions analysed the other polyethers, such as tetraethylene glycol dimethyl ether, TEGDME,75 and polymethoxy[poly(ethylene glycol monome- optimum doping level is N/H=5% (where N/H indicates the ratio of guanidine molecules added per proton extracted) and thacrylate)], PMPEGMM.76 The polymer electrolytes based on the latter host polyether are particularly interesting.They the best room temperature conductivity (6×10-5 V-1 cm-1) is observed for the most concentrated sample considered (n= comprise a comb polymer with a poly(methyl methacrylate) backbone and side oligo(oxyethylene) chains of variable length, 2).Complementary investigations have been recently performed by 1H PFG NMR spectroscopy.73 Cyclic voltammetry sulfamide and a doping agent (guanidinium cation). Sulfamide compositions with n ratios of 2, 4 and 30 and N/H doping studies indicate however that the use of the guanidinium cation levels of 0, 1, 5, 10 and 20% have been studied.Copolymers with shorter side chains lead to entirely amorphous systems, regardless of sulfamide concentration or doping level. Best conductivities at 25 °C (3×10-5 V-1 cm-1) have been reported for the copolymer based on short side chains, high concentration in sulfamide (n=2) and a doping level of 5%. Considering their mechanical, thermal and transport properties, these materials constitute a good alternative to sulfamide complexes of POE.Two families of very attractive proton-vacancy conducting polymers have also been synthesized via the sol–gel method by copolymerization of trialkoxysilanes which, through the hydrolysis-condensation process, leads to a silica-based backbone: the sulfonamidosils, which include a methanesulfonamide group (CH3SO2NH) or a benzenesulfonamide group (C6H5SO2NH) grafted to the inorganic network, and the free sulfamoyl ormolytes, in which the sulfamoyl group (NH2SO2) belongs to free sulfamide.77 The products are entirely amorphous, non-porous, hard and obtained as transparent monolithic Fig. 11 Arrhenius conductivity plot of (%) doped (10% sulfamic acid) films.Methanesulfonamidosils are thermally stable up to and (&) undoped crystalline sulfamide (ref. 53) 220 °C and benzenesulfonamidosils up to 350 °C. The electrochemical stability range of the most conducting methanesulfonamidosil is close to 2 V. Free sulfamoyl ormolytes constitute a viable alternative to sulfonamidosils, as they lead to higher conductivities (2×10-7 V-1 cm-1 at room temperature).The authors wish to thank the Commission of the European Communities for having supported this work through a BRITE-EURAM PhD grant. The financial assistance of the JNICT (Junta Nacional de Investigac�a� o Cientý�fica e Tecnolo� gica)/French Embassy Cooperation is also gratefully acknowledged. l/mAcm–2 References Fig. 12 Cyclic voltammogram of crystalline sulfamide (working electrode= vitreous carbon, counter electrode=stainless steel, reference 1 T.Takahashi, S. Tanase, O. Yamamoto and S. J. Yamauchi, J. Solid State Chem., 1976, 17, 353. electrode=ring-shaped palladium laden with hydrogen on the ab plateau, scanning rate=500 mV min-1, number of cycles=50, T= 2 P. J. Smith, in Electrochemical Science and T echnology of Polymers 1, ed. R.G. Linford, Elsevier, 1987, p. 293. 90 °C) (ref. 53) J. Mater. Chem., 1997, 7(9), 1677–1692 16913 P. Aldebert, F. Novel-Cattin, M. Pineri, P. Millet, C. Doumain 38 B. Pedersen, Acta Chem. Scand., 1968, 22, 1813. 39 H. J. Homan and K. Andress, Z. Anorg. Allg. Chem., 1956, 284, and R. Durand, Solid State Ionics, 1989, 35, 3. 234. 4 M. Armand, J. M. Chabagno and M.T. Duclot, in Fast Ion 40 I. W. Herrick and E. L. Wagner, Spectrochim. Acta, 1965, 21, 1569. T ransport in Solids, ed. Vashishta, J. N. Mundy and G. K. Sheryo, 41 T. Uno, K. Machida and K. Hanai, Spectrochim. Acta, 1966, 22, North Holland, NY, 1979, p. 131. 2065. 5 R. J. Gillespie and E. A. Robinson, in Non-Aqueous Solvent 42 T. Birchall and R. J. Gillespie, Can. J. Chem., 1963, 41, 2642.Systems, ed. T. C. Waddington, Academic Press, London, 1965, 43 T. Birchall and R. J. Gillespie, Can. J. Chem., 1963, 41, 148. vol. 4, p. 117. 44 M. Garrett, T. Tao and W. L. Jolly, J. Phys. Chem., 1964, 68(4), 6 N. N. Greenwood and A. Thompson, J. Chem. Soc., 1959, 3485. 824. 7 R. A. Munson, J. Phys. Chem., 1964, 68, 3374. 45 W. Traube, Ber., 1893, 26, 607. 8 Chemistry of the Elements, ed. N. N. Greenwood and A. Earnshaw, 46 H. Yamaguchi and K. Nakano, Chem. Abstr., 1973, 79, 65420. Pergamon, Oxford, 1984. 47 W. J. Spillane, J. A. Barry and F. L. Scott, J. Chem. Soc., Perkin. 9 J. C. Lasse`gues, in Proton conductors: Solids, membranes and gels— T rans. 2, 1973, 481. materials and devices, ed. P. Colomban, Cambridge University 48 E. Muller, Methoden der Organischen Chemie, vol. 11, part 2, Press, Cambridge, 1992, p. 311. Thieme, Stuttgart, 1958, p. 720. 10 M. Mandel, Encyclopedia of Polymer Science and T echnology, John 49 A. Paquin, Angew Chem., 1948, A60 (11/12), 316. Wiley, NY, 1988, vol. 11, p. 739. 50 J. G. Lombardino, J. Org. Chem., 1963, 28, 861. 11 F. Defendini, PhD Thesis, U Grenoble, France, 1987. 51 S.Searles and S. Nukina, Chem. Rev., 1959, 59, 1077. 12 P. Donoso, W. Gorecki, C. Berthier, F. 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Litt, 69 G. Devoto, Gazz. Chim. Ital., 1933, 63, 495. J. Electrochem. Soc., 1995, 142, L121. 70 G. Devoto, Atti. Accad. Nazl. L incei, 1931, 14, 432; Chem. Abstr., 28 J.-T. Wang, S. Wasmus and R. F. Savinell, J. Electrochem. Soc., 1932, 26, 4737. 1995, 142, 4218. 71 K. D. Kreuer, A. Fuchs, M. Ise, M. Spaeth and J. Mayer, 29 D. Weng, J. S. Wrainwright, U. Landau and R. F. Savinell, Electrochim. Acta, 1996, in the press. J. Electrochem. Soc., 1996, 143, 1260. 72 V. de Zea Bermudez, M. Armand, J.-Y. Sanchez, C. Poinsignon 30 W. L. Jolly, J. Phys. Chem., 1956, 60, 507. and D. Deroo, An. Quý�m., 1993, 89, 526. 31 V. De Zea Bermudez, M. Armand, C. Poinsignon, L. Abello and 73 V. de Zea Bermudez, C. Poinsignon, W. Gorecki and M. B. J.-Y. Sanchez, Electrochim. Acta, 1992, 27, 1603. Armand, unpublished results. 32 V. De Zea Bermudez, G. Lucazeau, L. Abello and C. Poinsignon, 74 V. de Zea Bermudez, G. Lucazeau, L. Abello, C. Poinsignon, J.- J.Mol. Struct., 1993, 297, 185. Y. Sanchez and M. Armand, Solid State Ionics, 1993, 61, 219. 33 E. F. Gale, E. Cundlie, P. E. Reynolds, M. H. Richmond and 75 V. de Zea Bermudez, G. Lucazeau, L. Abello and C. Poinsignon, M. J.Waring, T he Molecular Basis of Antibiotic Action. J.Mol. Struct., 1993, 301, 7. 34 T he Merck Index, Merck Inc., Rahway, New Jersey, 10th edn., 76 V. de Zea Bermudez and J.-Y. Sanchez, Solid State Ionics, 1993, 1983. 61, 203. 77 V. de Zea Bermudez, D. Baril, J.-Y. Sanchez, M. Armand and 35 E. H. Northey, T he Sulfonamides and Allied Compounds, Reinhold C. Poinsignon, SPIE, 1992, 1728, 180. Publishing Corp., New York, 1948. 36 K. N. Trueblood and S. W. Mayer, Acta Crystallogr., 1956, 9, 628. 37 D. W. J. Cruikshank, J. Chem. Soc., 1961, 4, 5486. Paper 7/01836C; Received 10thMarch, 1997 1692 J. Mater. Chem., 1997, 7(9), 1677–16

ISSN:0959-9428    

DOI:10.1039/a701836c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Selective betainisation of tertiary amine methacrylate block copolymers Vural Bu�tu�n, Claire E. Bennett, Maria Vamvakaki, Andrew B. Lowe, Norman C. Billingham and Steven P. Armes* School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer, Brighton, UK BN1 9QJ 2-(Dimethylamino)ethyl methacrylate (DMAEMA) was block copolymerised in turn with three other tertiary amine methacrylate comonomers using group transfer polymerisation; the DMAEMA residues of each of these diblock copolymers were selectively betainised using propane-1,3-sultone under mild conditions to yield a series of novel water-soluble sulfobetaine block copolymers which exhibit reversible pH- and temperature-induced micellisation.Recently, several groups have described the polymerisation of are summarised in Table 1.Copolymer compositions were determined by 1H NMR spectroscopy and corresponded closely 2-(dimethylamino)ethyl methacrylate (DMAEMA) via anionic1,2 or group transfer polymerisation (GTP).3,4 (within experimental error) to those expected from the comonomer feeds. For example, Fig. 1(a) shows the NMR spectrum of DMAEMA homopolymer is a weak polybase which is water soluble at neutral pH or in acidic media due to protonation a 61539 DMAEMA–DPAEMA block copolymer dissolved in DCl–D2O.The signal at d 3.0 is due to the six dimethylamino of the tertiary amine groups. In 1996 we reported that nearmonodisperse DMAEMA homopolymers and DMAEMA– protons in the DMAEMA residues5 and the signal at d 1.4–1.5 corresponds to the twelve equivalent methyl protons of the alkyl methacrylate block copolymers can be quantitatively betainised under remarkably mild conditions using propane- two isopropyl groups in the DPAEMA residues.Ratioing the peak integrals of these signals gives the block copolymer 1,3-sultone.5 In the present work DMAEMA was block copolymerised composition. Experimental conditions for the betainisation reaction have with three related tertiary amine methacrylate monomers, 2- (diethylamino)ethyl methacrylate (DMAEMA), 2-(diisopro- been described previously.5 A 10 mol% excess of propane-1,3- sultone based on DMAEMA residues was used.Preliminary pylamino)ethyl methacrylate (DPAEMA) and 2-(N-morpholino) ethyl methacrylate (MEMA) (see Scheme 1). Homopolymers betainisation experiments on the DMAEMA, DEAEMA, DPAEMA and MEMA homopolymers confirmed that only the of each of these four tertiary amine methacrylates were also synthesised.All (co)polymers were prepared via GTP DMAEMA homopolymer was quantitatively betainised at room temperature in THF within 16–24 h. The DEAEMA and techniques using a 1-methoxy-1-trimethylsilyloxy-2-methyl prop-1-ene (MTS) initiator and tetrabutylammonium biben- MEMA homopolymers both required significantly longer reaction times (48–96 h) and/or refluxing THF for any significant zoate (TBABB) [Bu4N+(PhCO2-)2H+] catalyst at 25 °C in dry THF as previously described.3–5 Narrow molecular weight degree of betainisation to be observed, as judged by the onset of gelation.The DPAEMA homopolymer remained completely distributions (Mw/Mns1.15) were obtained in all cases as judged by gel permeation chromatography [THF eluent, unbetainised even after four days in refluxing THF.Presumably this much reduced reactivity is due to steric crowding of poly(methyl methacrylate) standards, RI detector]. The molecular weights of the four homopolymers ranged from 4 800 the tertiary amine residues.These observations suggested that the DMAEMA residues in the DMAEMA–DEAEMA, to 12 400. The DMAEMA and MEMA homopolymers were water soluble at room temperature and neutral pH but precipi- DMAEMA–MEMA and DMAEMA–DPAEMA block copolymers could be selectively betainised at room temperature by tated from aqueous solution at 32–47 °C, depending on their molecular weight.6 In contrast, the DMAEMA and DPAEMA restricting the reaction time to 24 h (see Scheme 1).This proved to be the case. The degrees of betainisation of the DMAEMA homopolymers were both completely insoluble in aqueous media at neutral pH. However, these latter homopolymers block sequences were determined by elemental microanalyses (see Table 1) and confirmed by 1H NMRspectroscopy. Fig. 1(b) both dissolved readily in acidic aqueous solution (ca.pH 3–4) due to protonation of the tertiary amine residues. In the block shows the NMR spectrum of a betainised 61539 DMAEMA– DPAEMA block copolymer dissolved in DCl–D2O, which is copolymer syntheses the DMAEMA monomer was always polymerised first and quantitative yields were obtained in all a good solvent for both block sequences. The signal at d 3.2–3.3 is due to the six dimethylamino protons of the cases; molecular weights and polydispersities of the copolymers Table 1 A summary of the molecular weights, polydispersities, copolymer compositions and degrees of betainisation of the four tertiary amine methacrylate diblock copolymers block copolymer Man/g mol-1 Mw/Man DMAEMA degree of calc.Mn for contentb betainisationc betainised (mol%) copolymersd DMAEMA–DEAEMA 9500 1.15 49 88±5 12 400 DMAEMA–DEAEMA 12 100 1.10 78 89±5 18 500 DMAEMA–DPAEMA 15 700 1.11 61 80±5 21 100 DMAEMA–DPAEMA 11 500 1.10 80 93±5 17 900 DMAEMA–MEMA 5200 1.11 36 92±5 7400 aAs determined by GPC using PMMA standards for the precursor blocks prior to betainisation.bAs determined for the precursor blocks using 1H NMR spectroscopy. cCalculated from the S/N ratio taking into account the DMAEMA content of the precursor block obtained from 1H NMR spectroscopy.dCalculated using a combination of GPC, 1H NMR and microanalytical data. J. Mater. Chem., 1997, 7(9), 1693–1695 1693CH3 C C O CH2 CH2 R O CH2 m CH3 C C O CH2 CH2 N O CH2 n H3C CH3 S O O O THF, 25 °C CH3 C C O CH2 CH2 R O CH2 m CH3 C C O CH2 CH2 N O CH2 n H3C CH3 CH2CH2CH2SO3 – Selectively betainised tertiary amine methacrylate block copolymer N CH3 CH3 N CH3 CH3 CH3 CH3 N O R = , , + Scheme 1 Selective betainisation of 2-(dimethylamino)ethyl methacrylate residues in tertiary amine methacrylate block copolymers using propane-1,3-sultone under mild conditions betainised DMAEMA residues,5 whereas the signal at d 1.4–1.5 corresponds to the twelve protons of the four equivalent methyl groups in each of the non-betainised DPAEMA residues.Ratioing the peak integrals of these two signals gives the same 61539 copolymer composition as that determined for the original DMAEMA–DPAEMA precursor block prior to betainisation. Thus betainisation of the DMAEMA residues is both selective and near-quantitative.Similar results were obtained with DMAEMA–MEMA and DMAEMA– DEAEMA block copolymers. In an earlier communication4 we reported that DMAEMA– Fig. 1 1H NMR spectra of (a) a 61539 DMAEMA–DPAEMA precursor block synthesised by GTP; (b) the same 61539 DMAEMA– DEAEMA block copolymers exhibited highly pH-dependent DPAEMA block dissolved in DCl–D2O after selective betainisation surface activity and micellisation.It was suggested that the of the DMAEMA residues using propane-1,3-sultone; (c) a micellar more hydrophobic DEAEMA block adsorbed at the air–water solution of the same betaine block copolymer achieved by adjusting interface and also formed the interior of the copolymer micelles. the solution pH with excess NaOD (the disappearance of the signal Our NMR studies of the betainised 61539 DMAEMA– at d 1.4–1.5 due to the DPAEMA residues indicates that this non- DPAEMA block copolymer now support this hypothesis.solvated block forms the interior of the micelle) Initially, this copolymer was molecularly dissolved in DCl–D2O [see Fig. 1(b)]. On addition of excess NaOD, the strong signal at d 1.4–1.5 observed in Fig. 1(b) due to the In contrast, since the betainised DMAEMAresidues are soluble in alkaline media the betainised blocks remain in solution as twelve equivalent methyl protons of the DPAEMA residues completely disappears [see Fig. 1(c)], indicating that this micelles up to pH 12.However, betainisation sigcantly reduces the surface activities of the copolymers.7 For example, deprotonated block sequence is no longer solvated.This is strong evidence for the DPAEMA block forming a hydro- the limiting surface tension for a selectively betainised 78522 DMAEMA–DEAEMA block is only ca. 51 mN m-1, whereas phobic micellar core, as expected. Similar, though less striking, spectral changes are observed in the NMR spectrum of the the precursor block is much more surface active, exhibiting a limiting surface tension as low as 34 mN m-1.betainised DMAEMA–DEAEMA block under similar conditions. It is noteworthy that the surface activity and micellis- Dynamic light scattering studies of pH- and temperatureinduced micellisation were carried out on dilute aqueous ation behaviour previously reported4 for the DMAEMA– DEAEMA precursor blocks only occur over a rather narrow solutions of the betainised block copolymers.The betainised DMAEMA–DEAEMA and DMAEMA–DPAEMA blocks pH range, since precipitation occurs above pH 8–9 due to deprotonation of the more hydrophilic DMAEMA residues. each formed micelles of ca. 20 nm with reasonably narrow size 1694 J. Mater. Chem., 1997, 7(9), 1693–1695distributions. A betainised 36564 DMAEMA–MEMA block (GR/K86855) was used to purchase the argon ion laser used for the light scattering studies.exhibited temperature-induced micellisation behaviour at around 70 °C, forming micelles of around 100 nm diameter with a narrow size distribution. Micellisation was completely References reversible in both cases. Addition of acid caused complete dissolution of the betainised DMAEMA–DEAEMA micelles. 1 N.G. Hoogeveen, M. A. Cohen-Stuart, G. J. Fleer, W. Frank and M. Arnold,Macromol. Chem. Phys., 1996, 197, 2553. Similarly, micellar solutions of the betainised DMAEMA– 2 S. Creutz, P. Teyssie and R. Jerome, Macromolecules, 1997, 30, 6. MEMA dissociated on cooling to form the original unimers. 3 F. L. Baines, S. P. Armes and N. C. Billingham, Macromolecules, In summary, the unexpectedly selective betainisation of 1996, 29, 3416. DMAEMA residues in DMAEMA-based block copolymers 4 V.Bu� tu� n, N. C. Billingham and S. P. Armes, Chem. Commun., 1997, provides a facile route to new hydrophilic–hydrophilic betaine 671. 5 A. B. Lowe, S. P. Armes and N. C. Billingham, Chem. Commun., block copolymers. Preliminary studies confirm that these mate- 1996, 1555. rials exhibit interesting aqueous solution properties. 6 V.Bu� tu� n, N. C. Billingham and S. P. Armes, unpublished results. 7 A. B. Lowe, N. C. Billingham and S. P. Armes, ACS Polym. Prepr., 1997, 38(1), 465. The Turkish government is thanked for funding a DPhil studentship for V.B. ICI Paints and EPSRC are acknowledged Paper 7/03566G; Received 22nd May, 1997 for a CASE studentship for A.B.L. An EPSRC ROPA grant J. Mater. Chem., 1997, 7(9), 1693–1

ISSN:0959-9428    

DOI:10.1039/a703566g

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Synthesis and properties of novel components for organic metals dihydrotellurophene derivatives Eva H. Mørkved,*a Gerardo Faccin,b Davide Manfrotto,b Helge Kjøsen,a James Y. Becker,c Lev Shapiro,c Arkady Ellern,c Joel Bernsteinc and Vladimir Khodorkovsky*c aDepartment of Organic Chemistry Norwegian University of Science and T echnology 7034 T rondheim Norway bDepartment of Chemistry University of Padova 35131 Padova Italy cDepartment of Chemistry Ben-Gurion University of the Negev Beer-Sheva 84120 Israel Two series of dihydrotellurophenes have been synthesized derivatives of 4,6-dihydro-1H,3,H-telluropheno[3,4-c]tellurophene (1) and derivatives of 1,3,6,8-tetrahydrobenzo[1,2-c;3,4-c¾]ditellurophene (2). X-Ray structure determinations confirm the tetraiodo structures of 1a and 2a. The tetraiodo derivatives are reduced by sodium borohydride to the corresponding dihydrotellurophenes 1b and 2b which undergo the characteristic divalent tellurium reaction with iodomethane to form telluronium methiodides.Both dihydrotellurophenes 1b and 2b are moderate electron donors and react with 7,7,8,8-tetracyanoqiunodimethane TCNQ aording blue semiconductive solids. The present study was initiated with the purpose of exploring a vicinal bis(bromomethyl) compound reacts with tellurium and a large excess of sodium iodide in 2-methoxyethanol to various aspects of dihydrotellurophene chemistry and in particular the potential of dihydrotellurophenes to form give a derivative of 2,2-diiodo-1,3-dihydrotellurophene. Compounds 1a and 2a were separated from unreacted tellurium conducting charge-transfer (CT) complexes with electron acceptors.A comprehensive survey of tellurium heterocycles with cold dimethyl sulfoxide (DMSO). Undissolved tellurium was filtered o and water was added to the DMSO filtrates has appeared recently,1 and some derivatives of dihydrotellurophene have been reported to form CT complexes with electron to precipitate pure 1a and 2a which were obtained as stable yellow or orange amorphous solids in fair to good yields acceptors.2,3 Methyl benzo and quinoxalino derivatives of 2,5- dihydrotellurophene form low conducting CT complexes with (60–80%). The identity of compound 1a was verified by 1H and 13C NMR mass and IR spectroscopy and microanalysis. 7,7,8,8-tetracyanoquinodimethane (TCNQ) or chloranil but the electronic structures of these complexes are not well Compound 2a was identified by spectroscopic means only.A reported synthesis5 of an [1,2-c;4,5-c¾] isomer of 2a understood. where the isomer was obtained as a yellow solid in comparable yields to 2a has been reinvestigated recently.6 The crude Results and Discussion [1,2-c;4,5-c¾] isomer precipitated as a yellow–orange solid and recrystallization from dimethylformamide (DMF) aorded The procedure reported by Ziolo and Gu� nther4 was used to prepare 4,6-dihydro-1H,3,H-telluropheno[3,4-c]tellurophene pure isomer as orange–red crystals in low yield (10–14%). However most of the crude product (80–90%) was recovered 1a and 2,2,7,7-tetraiodo-1,3,6,8-tetrahydrobenzo[1,2-c; 3,4- c’]ditellurophene 2a as outlined in Scheme 1. By this method as a yellow amorphous precipitate which was not further identified.Having this contradiction in mind we attempted to grow single crystals for X-ray crystal structure determinations of both 1a and 2a. Both compounds form shiny orange crystals from DMSO. Compound 2a forms a powdery precipitate at first but after several days the powder is replaced with crystals. The crystals of 1a are hygroscopic and convert into an amporphous solid in a few weeks. The X-ray diraction study of 2a shows that all three rings are almost planar within 0.0119 A ° (Fig. 1). The iodine atoms Scheme 1 Reagents i NaI MeOCH2CH2OH; ii NaBH4 EtOH; iii Fig. 1 Molecular structure of 2a showing 50% probability ellipsoids MeI MeNO2 J. Mater. Chem. 1997 7(9) 1697–1700 1697 are found on either side of and in a plane almost perpendicular the dark but somewhat unstable to light in good agreement with observations on dihydrobenzo[c]tellurophene.7 The to this ring system.The IMTeMI angles are 174–1760 and the TeMI bond lengths are in the range of 2.889(1)–2.940(1) A ° . structure of 2b was verified by 1H and 13C NMR spectroscopy and microanalysis. Compound 1b decomposes visibly in air In the five-membered rings the lengths of the saturated TeMC bonds are 2.120(4)–2.149(4) A ° and the CMTeMC angles are and light in less than 1 h. A high resolution mass spectrum was not obtained for this compound. However the 1H and 85.7(2)0. The most interesting feature of the 2a structure is the molecular packing. Firstly there is a distinct intermolecular 13C NMR spectra are in good agreement with the spectra reported for other dihydrotellurophene derivatives.8 interaction between an iodine atom of one molecule and the Reactions of dihydrotellurophenes with methyl iodide are Te atom of the next molecule.The Te,I intermolecular generally found to give the corresponding methyltelluronium contacts are 3.79–3.93 A ° which is significantly shorter than iodides.1 The precipitate from a reaction of 1b with methyl the sum of the van der Waals radii of the corresponding atoms iodide is slightly soluble in DMSO but the solution deposited (Te=2.06 I=2.06 A ° ). Secondly there is an interaction between some dark-grey solid apparently due to decomposition of the the Te atoms and the solvent the polar molecules of DMSO product. The 1H NMR spectrum of this product also supports are orientated in a crystal to form a Te,O contact of this observation since the strong singlet at d 2.15 (CH3) is 2.82–2.91 A ° (the van der Waals radius of oxygen is equal to mixed with several others of low intensity.In addition several 1.52 A ° ). Both kinds of intermolecular interaction complete the doublets at d 3.2–3.3 (CH2) are partly covered by the signal coordination of the Te atom to form a distorted octahedral from the residual H2O in the DMSO. Microanalysis shows a coordination (Fig. 2). somewhat higher content of tellurium and a correspondingly The geometrical parameters of 1a are very similar to those lower content of iodine than would be in good agreement with of 2a (Fig. 3). The iodine atoms are situated on either side of structure 1c. The analysis is consistent with loss of hydrogen the planar (within 0.009 A ° ) bicyclic ring system the IMTeMI iodide from one quarter of the tellurium moieties of 1c; in angle is 176.92(5)0 the TeMI bond lengths are other words one quarter of the methyldihydrotelluronium 2.735(2)–2.786(2) A ° and the CMTeMC angle is 86.2(4)0.The iodide rings have apparently been oxidized to T e–methyl- packing diagram of 1a exhibits the same type of intermolecular hydrotellurophene rings. interactions as for 2a i.e. the coordination number of Te is 6 The cyclic voltammetry measurements of 1b and 2b showed in a distorted octahedron. However the arrangement of molonly poorly resolved irreversible oxidation peaks at ca. ecules in the crystal is quite dierent. Whereas the ‘herringbone’ 1.3–1.5 V (vs. standard calomel electrode SCE on a glassy type structure is observed for 2a the layers of molecules in 1a carbon electrode).Reactions of 1b and 2b with TCNQ aorded are separated by layers of solvent molecues and the Te,I dark-blue microcrystalline powders. Conductivity of the shortened contacts (3.54 A ° ) are intralayer ones (Fig. 4). 1b–TCNQ complex is 1.3–2.5×10-5 and the conductivity of Diiododihydrotellurophenes 1a and 2a were reduced with 2b–TCNQ is ca. 5×10-7 S cm-1 (measured on pressed pellets sodium borohydride in ethanol to give the dihydrotellurofour probe measurements). Microanalysis of 2b–TCNQ indi- phenes 1b and 2b. Compound 2b is fairly stable when kept in cates a 151 adduct. The IR spectra of the present TCNQ complexes confirm the presence of TCNQ radical anions. Li–TCNQ a known radical anion salt of TCNQ has CN absorptions at 2202 and 2186 cm-1; the corresponding absorptions of the complexes a at 2218 2186 2211 and 2186 cm-1 (neutral TCNQ absorbs at 2224 cm-1).Other characteristic absorptions of Li–TCNQ at 1575 1508 1361 1349 and 1182 cm-1 are found at approximately the same wavenumbers for the 2b–TCNQ complex also. Conclusions The facile formation of the stable tetraiodo tellurophenotellurophene derivative 1a is demonstrated and its structure proved by X-ray diraction measurements. A reductive elimination of the four iodines on 1a gives compound 1b which is unstable to air and light and was therefore characterised by spectroscopic means only. Microanalysis of the adduct from 1b and methyl iodide indicates a 151 mixture of 1c and (1c–HI). Compound 2a was prepared in good yields and its structure has been proved by X-ray structure determination.Compound 2a was reduced to Fig. 2 Projection of the crystal structure of 2a in the bc plane the dihydrobenzotellurophene derivative 2b characterised by 1H and 13C NMR spectroscopy and C H microanalysis. Cyclic voltammetry indicates that both 1b and 2b are electron donors of moderate strength and they undergo irreversible oxidation. Both compounds react with TCNQ with the formation of semiconducting complexes. The IR spectra of both confirm the presence of TCNQ anion radicals. Compounds 1 and 2 merit further investigation and the continuation of our studies will be reported in due course. Experimental General Mass spectra were obtained on an AEI MS-902 spectrometer Fig. 3 Molecular structure of 1a showing 50% probability ellipsoids at 70 eV electron energy.IR spectra were obtained on a Nicolet 1698 J. Mater. Chem. 1997 7(9) 1697–1700 Fig. 4 Projection of the crystal structure of 1a in the bc plane 20-SXC FTIR spectrometer. 1H and 13C NMR spectra were 2a) was added tellurium (6 mmol) and sodium iodide (36 mmol). The suspension was stirred vigorously under reflux recorded on a JEOL EX400 NMR spectrometer at 399.65 and 100.40 MHz respectively and with tetramethylsilane (TMS) for 1 h. The bright orange precipitate was filtered o together with unreacted tellurium and washed with acetone to remove as internal standard. UV–VIS spectra were obtained on a Perkin-Elmer 500 UV–VIS spectrophotometer. Melting points iodine and sodium iodide. Water was added to the methoxyethanol filtrate and some additional orange precipitate was were obtained on a Bu� chi 530 apparatus and are uncorrected.Merck Kieselgel 60F 254 was used for TLC and Merck silica filtered o. The combined precipitate was dissolved in a minimal amount of DMSO at ambient temperature tellurium 63–200 mm was used for column chromatography. Microanalyses were performed by the Analytische was removed by filtration and water was added to the filtrate Laboratorien Lindlar Germany. whereupon compound 1a or 2a precipitated and was filtered The X-ray diraction measurements of 2a were carried out o and dried at ambient temperature at 1 Torr for 15 h. using a Syntex P-1 diractometer (Mo-Ka radiation graphite Compound 1a 1.51 g (59%) was a yellow amorphous solid monochromator h/2h scan 2h52 °). Crystal data monoclinic mp 200–210 °C (charring I2 evolved); MS [m/z (% rel.int.)] C10H10I4Te2·2DMSO 20 °C a=12.786(3) b=14.116(3) c= 384 (2.1) 382 (1.5) 338 (5.4) 336 (6.9) 332 (6) 128 (59.5) 15.266(3) A ° ; b=112.72(3) ° V=2601.0(9) A ° 3 Z=4 space 127 (32.2) 79 (100); u/cm-1 (KBr) 1618 (CNC) 1376 1133 group P21/c 5661 independent reflections. The structure was 1039 817 706 590; dH[(CD3)2SO] 3.95 (CH2 s); dc[(CD3)2SO] interpreted by direct methods and refined anisotropically using 45.85 126.29 (Found C 9.03; H 1.17; I 56.95; Te 32.30. Calc. SHELX93 to WR2=0.0689 GOF=1.05. The H-atoms were for C6H8I4Te2 C 8.55; H 0.96; I 60.22; Te 30.27%). placed in calculated positions and included in the calculations Compound 2a 1.3 g (51%) was a yellow–orange powder with fixed positional and isotropic thermal parameters. mp 240 °C (charring iodine evolved); MS [m/z (% rel.int.)] The X-ray diraction measurements of 1a were carried out 389 (2.3) 388 (1.6) 386 (2.1) 384 (7.2) 260 (13) 258 (26.4) using a Syntex P-1 diractometer (Mo-K a radiation graphite 256 (21.6) 254 (67.8) 128 (70) 127 (57.4) 45 (100); dH monochromator h/2h scan 2h60 °). Because of the very weak [(CD3)2SO] 4.68 (4H s) 4.82 (4H s) 7.28 (2H s); u/cm-1 diracting capacity of 1a the crystals were tested for the (KBr) 2923 2874 1688 1453 1354 1092 832. possibility of low temperature measurements. However all Preparation of a crystalline sample of 1a. Compound 1a attempts to reach low temperature resulted in the destruction (100 mg) was mixed with DMSO (1 ml) and the mixture was of the samples due to transformation into a microcrystalline state. Measurements were therefore carried out at ambient filtered through glass wool.The yellow solution was left in a temperature. Crystal data monoclinic C6H8I4Te2·2DMSO stoppered vial for ca. four weeks. Crystals separated slowly 20 °C a=12.336(3) b=11.008(3) c=8.660(2) A ° ; b= from the solution. 102.22(2) ° V=1149.3(5) A ° 3 Z=4 space group P21/c; 3493 Crop 1. Some of the crystals were collected with a spatula and independent reflections. The semiempirical y-scan absorption washed with diethyl ether. These crystals had decomposed in correction was used. The structure was interpreted by direct air after ca. two weeks. methods and refined anisotropically using SHELX93 toWR2= Crop 2. This was used for X-ray analysis. 0.1973 [(R1=0.087 for 1838 reflections with F>4s(F)] 100 Preparation of a crystalline sample of 2a.Compound 2a refined parameters; GOF=1.05. The H-atoms were placed in (60 mg) was mixed with DMSO (1 ml) and the lemon coloured calculated positions and included in the calculations with fixed suspension was filtered (gravity) through glass wool. The positional and isotropic thermal parameters. The poorly yellow–orange filtrate became cloudy and after 12 h a pale diracting sample and the disorder of the solvent moecules yellow fluy precipitate appeared. After one week some orange lead to a comparatively high R-factor. crystals had formed but some of the yellow powdery precipitate 1,4-Dibromo-2,3-bis(bromomethyl)but-2-ene mp 159– was present as well. After 10 d all of the yellow precipitate had 160 °C (recrystallized twice from ethyl acetate) was prepared9 been replaced with shiny orange crystals.Some of the crystals from 2,3-dimethylbutane; lit.9 mp 158–159 °C. 1,2,3,4-Tetrakis were collected with a spatula washed with diethyl ether and (bromomethyl)benzene mp 116–118 °C (ethanol) was presubjected to X-ray analysis. pared10 from 1,2,3,4-tetramethylbenzene; lit.10 mp 124–126 °C. Preparation of 4,6-dihydro-1H,3H-telluro- Preparation of 2,2,5,5-tetraiodo-4,6-dihydro-1H,3Hpheno[ 3,4-c]tellurophene 1b and 1,3,6,8-tetrahydro- telluropheno[3,4-c]tellurophene 1a and 2,2,7,7-tetraiodo- 1,3,6,8-tetrahydrobenzo[1,2-c;3,4-c¾]ditellurophene 2a benzo[1,2-c;3,4-c¾]ditellurophene 2b. General procedure. A suspension of sodium borohydride General procedure. To a solution of the bromomethyl compound (3 mmol) in 2-methoxyethanol (8 ml for 1a 25 ml for (0.64 g 16 mmol) in ethanol (35 ml ) was added dropwise J.Mater. Chem. 1997 7(9) 1697–1700 1699 during 10 min to a stirred suspension of 1a or 2a (2 mmol) in Compound 1b+TCNQ; dark-blue powder/microcrystals. u/cm-1 (KBr) 2218 (w) 2186 1657 1592(s) 1377 (s) 1262 (s) ethanol (25 ml ) kept at 0 °C. A grey precipitate formed upon 1106 1014 637. addition of the reducing agent. The reaction mixture was Compound 2b+TCNQ; dark blue powder/microcrystals. protected from light and stirred at 0 °C for 1 h after complete u/cm-1 (KBr) 2950 (w) 2211 (sh) 2185 (s) 2120 (sh) 1658 addition. Water (60 ml ) was added and the suspension was (sh) 1595 1566 (sh) 1502 1475 1443 1366 1344 1244 1189 extracted with benzene (3×40 ml) and dichloromethane (Found C 47.08; H 3.44; N 7.67. Calc. for C22H14N4Te2 C (3×40 ml) for 1b or chloroform (3×15 ml) for 2b.The organic 44.82; H 2.39; N 9.50; Te 43.28%). extracts were filtered and evaporated to dryness atmbient Li–TCNQ (reference). u/cm-1 (KBr) 2202 2186 1575 1508 temperature. 1361 1349 1182. Compound 1b 0.36 g (54%) mp 155–160 °C (black sintering) 180 °C (gas evol.) MS [m/z (% rel. int.)] 340 (26 M Preparation of 2,5-diiodo-2,5-dimethyl-4,6-dihydro-1H,3H- 130Te,130Te) 338 (50.5,M 130Te,128Te) 336 (50.7,M,128Te,128Te) telluropheno[3,4-c]tellurophene 1c 335 (13.6) 334 (35.6 M 128Te,126Te) 332 (20 M 126Te,126Te) 254 (22.3) 130 (12.0) 128 (10.5) 126 (6.6) 79 (100); u/cm-1 Iodomethane (0.34 g 2.4 mmol) was added to a solution of 1b (KBr) 1437 1270 1120 1070 (s) 777 (s) 629 (s) 587; (0.034g 0.1 mmol) in benzene (10 ml ) at ambient temperature. dH[(CD3)2SO] 3.74 (CH2 s); dc[(CD3)2SO] 3.33 125.99.The precipitate was filtered o washed with diethyl ether and Compound 2b 1.79 g was a yellow–grey powder air dried; 1c 0.06 g (70%) grey amorphous solid mp 160 °C mp>300 °C (discoloured 170 °C). The work-up procedure for (sintering black). u/cm-1 (KBr) 3411 2902 1391(v.s) 1130 this compound was modified since a substantial part of 2b 1069 871 631; dH[(CD3)2SO] 2.15 (CH3 s) 3.2–3.3 (CH2 was undissolved after the first chloroform extraction and H2O m) [Found C 16.65; H 2.18; I 33.35; Te 47.10. Calc. for settled as a yellow powder at the bottom of the separation 0.5 (C8H14I2Te2+C8H13ITe2) C 17.54; H 2.48; I 33.41; Te funnel. This solid was taken out through the bottom of the 46.58%]. funnel and dried and was found to be spectroscopically identical to the rest of 2b obtained from the chloroform E.H.M.thanks the Norwegian University of Science and extracts; MS [m/z (% rel. int.)] 390 (9.0 M 130Te,130Te) 388 Technology Trondheim Norway for support and a sabbatical (16.8 M 128Te,130Te) 386 (19.4 M 128Te,128Te) 384 (11.9 M leave of absence. G.F. and D.M. thank the ERASMUS 128Te,126Te) 382 (6.7 M 126Te,126Te) 258 (4.9) 256 (2.5) 130 Interuniversity Cooperation Programme for the award of (100) 129 (17.1) 128 (14.7) 115 (17.3); u/cm-1 (KBr) 2919 student exchange grants. 2873 1468 1353 1090 1028 838; dH[(CD3)2SO] 4.47 (8H s) 6.98 (2H s); dH(CDCl3) 4.53 (4H s) 4.59 (4H s) 6.95 (2H s); References dc [(CD3)2SO] 8.10 125.94 (Found C 28.02; H 2.37. Calc. for 1 Chemistry of Heterocyclic Compounds ed. E. C. Taylor Vol. 53 C10H10Te2 C 31.17; H 2.62; Te 66.21%).M. R. Detty and M. B. O’Regan T ellurium Containing Heterocycles Wiley New York 1994. 2 K. Y. Abid and W. R. McWhinnie J. Organomet. Chem. 1987 Reactions of 1b and 2b with TCNQ 330 337. 3 H. B. Singh W. R. McWhinnie R. F. Ziolo and C. H. W. Jones General procedure. The dihydrotellurophenes 1b or 2b J. Chem. Soc. Dalton T rans. 1984 1267. (0.05 mmol) and TCNQ (0.05 mmol) were dissolved separately 4 R. F. Ziolo and W. H. H. Gu� nther J. Organomet. Chem. 1978 in minimum amounts of warm acetonitrile. The two solutions 146 245. were mixed heated under reflux for 1 h and then filtered to 5 H. B. Singh P. K. Khanna and S. K. Kumar J. Organomet. Chem. remove small amounts of undissolved material. The reaction 1988 338 1. mixture from 1b darkened almost immediately whereas the 6 H.A. Al-Shirayda Heteroatom Chem. 1993 4 537. 7 E. Cuthbertson and D. D. MacNicol T etrahedron L ett. 1975 one from 2b became gradually darker over several hours. The 1893. solutions were transferred to open beakers and were left for 8 J. Bergman and L. Engman J. Am. Chem. Soc. 1981 103 2715. slow evaporation at ambient temperature and finally at ca. 9 H. Stetter and E. Tresper Chem. Ber. 1971 104 71. 50 °C. Some red–brown material settled on the upper part of 10 J. T. Stapler and J. Bornstein J. Heterocycl. Chem. 1973 983. the walls of the beakers whereas dark-blue–black crystals that eventually formed at the bottom of the beakers were collected. Paper 7/00975E; Received 11th February 1997 1700 J. Mater. Chem. 1997 7(9) 1697–17

ISSN:0959-9428    

DOI:10.1039/a700975e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Evaluation of halomethylated poly(methylphenylsilane)s as electron-beam resists Simon J. Holder, Richard G. Jones* and Julian J. Murphy Centre for Materials Research, Department of Chemistry, University of Kent at Canterbury, Kent, UK CT 2 7NH Polysilane analogues of halomethylated poly(styrene)s, chloromethylated and bromomethylated poly(methylphenylsilane), have been prepared from the parent polymer by reaction with the appropriate halomethyl methyl ether.The polymers undergo a singlestage crosslinking reaction when irradiated with 20 kV electrons. As electron beam resists they operate in negative-working mode but their performance is poor in comparison to the corresponding poly(styrene) derivatives. The low lithographic sensitivities and attainable contrasts are shown to arise as a consequence of a competitive chain scission reaction which in the case of the bromomethylated system increases with increasing bromomethyl content.The radiation chemistries of the systems are rationalised in terms of modifications of the crosslinking and scission mechanisms that are thought to operate in the corresponding resists based on poly(chloromethylstyrene-stat-styrene). Since the discovery of tractable poly(diorganosilanes) in the of so-called CMS negative-working resists.10–18 Halogenated 1970s,1,2 a number of potential applications have been pro- resists derived from the homopolymer, PMPS, can be conposed.Interest in these unique polymers stems not only from sidered no less appropriate for comparison with the CMS the catenated silicon backbone which has led to one of their structures.Accordingly, in the present study, chloromethylated most important commercial applications, namely as ceramic and bromomethylated poly(methylphenylsilanes) over a range precursors,3 but also from the unusual conjugation of the s- of compositions were synthesised with the intention that their bonds of the backbone which gives rise to electron delocalis- application within e-beam lithography might be assessed, and ation. This has resulted in the polymers being assessed for a an understanding gained of the underlying radiation chemical number of electrical and optical applications.4,5 processes that occur within electron beam resists that might Arising from the direct photosensitivity of the silicon back- be based on PMPS and its derivatives.bone of polysilanes, one of their most promising potential uses is as positive-working resists in microlithography. An important advantage that they possess over carbon-based polymers for such applications is a high silicon content, imparting the O2 plasma and reactive-ion etch resistance required in multilayer microlithographic processing.Accordingly, a large number of organopolysilanes have been tested as photoresists although none have found wide application.6 However, future generations of very large scale integrated (VLSI) circuitry will require microlithographic resolutions that are beyond those Experimental that can be attained using conventional resists and photoprocessing. Typically, resolutions of less than 0.25 mm will have Apparatus and procedures to be routinely achieved.To this end electron-beam (e-beam) The polymer structures were characterised by 1H, 13C and 29Si lithography finds increasing application in the production of NMR, FTIR and UV spectroscopy. FTIR and NMR spectra application specific integrated circuitry (ASIC) and photomwere obtained using ATI Mattson Genesis Series FTIR and asks with target resolutions down to 0.1 mm.7 Thus, it is as JEOL JNM-GX270 NMR spectrometers, respectively. NMR electron beam resists that polysilanes might find a useful role samples were prepared as solutions in CDCl3 and chemical if they can be tailored to suit the requirements of this imaging shifts are quoted in relation to SiMe4.Cr(acac)3 was used as technique, which must be performed with structures which an internal relaxation agent to record the 29Si NMR spectra.would not release silicon-containing fragments to the gas UV spectra were obtained from ca. 10-4 mol dm-3 CH2Cl2 phase, that might contaminate the writing tool, during the solutions using a PU 8740 UV–VIS scanning spectrophoto- lithographic process. meter. Thermal analyses of the polymer samples were per- Poly(methylphenylsilane) (PMPS) is the cheapest tractable formed under a nitrogen atmosphere on a Perkin-Elmer DSC7 homopolysilane available in relatively high yields from the dierential scanning calorimeter operating at scan rates of Wurtz-type condensation polymerisation of dichloroorganosil- 10 K min-1.anes. However, positive-working behaviour (i.e.polymer chain Molecular weights of the polymers were obtained relative degradation) with only a very low sensitivity has been preto polystyrene standards using HPLC equipment (Polymer viously observed for this polymer upon e-beam exposure, Laboratories) with a 30 cm×10 mm PLgel mixed-D column. disqualifying its use as a possible resist in an unmodified form.8 The eluent was THF and determinations were carried out at The introduction of chloromethyl groups onto the pendant a flow rate of 2 ml min-1 at ambient temperature using a UV phenyl of poly(methylphenylsilane)-co-(dimethylsilane) has detector. It has been reported4 that the molecular weights of been shown to result in a marked increase in the sensitivity of polysilanes as determined by size exclusion chromatography this polymer towards negative-working behaviour.9 Arising relative to polystyrene standards are likely to be too low by a from its structural similarity to polystyrene, the trivial name factor of ca. 2.3. However, recent studies19 have indicated that poly(silastyrene) has been coined for poly(methylphenylsilane)- the dierence in the hydrodynamic volumes of polystyrene and co-(dimethylsilane).It follows that its chloromethylated deriv- PMPS is very small. It is also unlikely that relatively low atives might reasonably be compared to chloromethylated polystyrenes which are examples of the well-characterised class loadings of halomethyl groups would substantially aect the J. Mater. Chem., 1997, 7(9), 1701–1707 1701hydrodynamic volume of the PMPS. Accordingly, it is assumed dierent from the remaining halomethylated polymers. Both series of copolymers were isolated from samples of halomethyl- that the molecular weights as determined by size exclusion chromatography are suciently accurate for the purposes of ation reaction mixtures taken at various times during extended reactions.The polymer structural and thermal parameters are the present study.Resist solutions were formulated by dissolving the copoly- given in Table 1. mers in chlorobenzene to produce 20% w/v solutions. The BPMPS solutions were filtered through 0.5 mm Millipore filters and spun directly onto 3 inch silicon wafers using a Headway ECdH( CDCl3) -1.1 to 0.6 (vbr m, CH3Si), 3.0 (br m, CH3O), 4.3 101 spinner and prebaked at 120 °C for 30 min to produce (br s, ClCH2), 6.0–7.7 (vbr m, aromatic).dC(CDCl3) -8.0, good quality uniform films with a thickness of approximately -7.5, -6.9, -6.0 (br m, CH3Si), 33.5 (s, CH2Br), 50.5 (s, 1 mm. Exposure was performed using a Cambridge Instruments CH3O), 126.8, 126.5, 134.2, 135.7 (m, aromatic). dSi(CDCl3) EBMF-10.5 electron beam lithography tool operating at 20 kV -41.1, -39.9, -39.2 (br t, SiCH3Ph), 8.7 (s, SiOCH3), 14.6 accelerating potential.Development was accomplished by (d, SiCl). nmax(thin film)/cm-1 3065, 3046, 3014 (C–H stretch, immersing a wafer fragment in methyl isobutyl ketone (MIBK) aromatic), 2958, 2893, 2868 (C–H stretch, aliphatic), 1426 (C–C for 60 s, followed by a 30 s rinse in isopropyl alcohol (IPA). ring stretch, Si–phenyl), 1394 (CH2Cl bend), 1245 (C–H bend, This development procedure was not optimised but was chosen CH3Si), 1095 (C–C ring stretch+Si–C stretch, Si-phenyl), 782, to follow established practice for the corresponding halomethy- 754, 730, 697, 664 (various C–C ring stretch+Si–C stretch), lated poly(styrene) resists.15,16 Developed wafers were dried in 605, 619 (Si–Br stretch), 465 (Si–Si stretch).lmax/nm (e) 239 a filtered stream of nitrogen. Film thickness measurements (5700), 279 (3800), 341 (7900). before and after exposure were taken using a Nanospec/AFT 210 film thickness system. Sensitivities were estimated as the CPMPS dose corresponding to 50% thickness remaining after development (Dn0.5). All resist thicknesses were normalised to the dH(CDCl3) -1.2 to 0.6 (vbr m, CH3Si), 3.0 (br m, CH3O), 4.4 original spun thickness.Lithographic contrasts (c) were calcu- (br s, ClCH2), 6.0–7.6 (br m, aromatic). dC(CDCl3) -8.0, lated from Dn0.5 and the gel dose (Dn0) using eqn. (1). -7.3, -6.8, -5.9 (br m, CH3Si), 46.0 (s, CH2Cl), 50.6 (s, CH3O), 126.7, 134.3, 135.8 (m, aromatic). dSi(CDCl3) -41.0, c=1/[2 log (Dn0.5/Dn0)] (1) -39.9, -39.1 (br t, SiCH3Ph), 8.7 (s, SiOCH3).nmax(thin film)/cm-1 3047, 3012, 2991 (C–H stretch, aromatic), 2958, 2893, 2868 (C–H stretch, aliphatic), 1427 (C–C ring stretch, Materials Si–phenyl), 1394 (CH2Cl bend), 1259, 1246 (C–H bend, CH3Si), 1097 (C–C ring stretch+Si–C stretch, Si–phenyl), 781, 754, Polymer syntheses and characterisation. The PMPS samples 730, 698, 664 (various C–C ring stretch+Si–C stretch), 465 used for halomethylation were prepared from the Wurtz-type (Si–Si stretch).lmax/nm (e) 239 (6300), 279 (4100), 341 (8600). reaction of distilled dichloromethylphenylsilane (Lancaster) using freshly prepared sodium sand in refluxing diethyl ether Results in the presence of 15-crown-5.20 Fractionation of PMPS was accomplished by washing the broad distribution polymer that Polymer structure and thermal characterisation is initially prepared with n-hexane.Halomethylations of unfractionated PMPS samples were carried out in accordance with We have previously reported that the halomethylation of PMPS by halomethyl ether prepared in situ leads to a substan- published procedures.21 Based on the composition range identified as being optimal for the lithographic performance of tial degradation of the polysilane backbone as evidenced by size exclusion chromatography.21,22 This probably occurs via corresponding copolymers of the CMS series of resists such as poly(styrene-stat-chloromethylstyrene), the extents of halome- the mechanisms outlined in Scheme 1, as both the SnCl4 and the halomethyl ethers have been observed to degrade polymers, thylation were targeted within the range 15 to 40%.The homopolymer PMPS 1 was prepared by the direct reaction of although it must be emphasised that no conclusive evidence for the formation of terminal SiCH2X groups (X=Br or Cl) dichloromethylphenylsilane with molten sodium in the absence of a solvent. Fractionation of this sample by repeated Soxhlet has yet been obtained.However, when bromomethyl octyl ether is used in the bromomethylation reaction in place of extractions of the sample with hexane gave the fractionated homopolymer PMPS 2. bromomethyl ether, after several purifications of the product by precipitation, washing and drying under vacuum, a number Representative spectroscopic data are given below for both bromomethylated PMPS and chloromethylated PMPS of alkyl peaks in the region d 2.0 to 0.5 can be observed in the 1H NMR spectrum.These are presumed to arise from end- samples, BPMPS and CPMPS respectively. BPMPS 1 and CPMPS 1 were prepared from PMPS samples that were capping of the polysilane chains by octyloxy groups, so provid- Table 1 Characterisation and lithographic parameters of the homo- and co-polysilanes studied DSC polymer Mw [PD] CH2X (%) T peak/°C Qpeak/J g-1 D0.5/mC cm-2 c Gx Gs Gs/Gx PMPS1 51500 7.5 0 a a >300 — — — — PMPS2 3300 1.4 0 a a %300 — — — — BPMPS1 15400 2.1 16 — — >300 — 0.32±0.03 0.66±0.09 2.4 BPMPS2 14500 2.3 24 284 -240 135 1.2 0.45±0.03 0.64±0.06 1.4 BPMPS3 12600 2.2 33 295 -290 110 0.9 0.71±0.02 0.93±0.03 1.3 BPMPS4 9900 1.8 38 299 -350 86 0.8 1.36±0.04 0.98±0.05 0.72 CPMPS1 8000 2.4 23 269 - 86 137 1.5 0.85±0.02 0.55±0.04 0.65 CPMPS2 14300 2.1 32 303 -260 60 1.7 0.62±0.02 0.38±0.04 0.61 CPMPS3 13900 2.1 33 299 -305 55 1.9 0.64±0.02 0.30±0.03 0.47 CPMPS4 14000 1.9 39 310 -367 46 1.8 0.83±0.03 0.45±0.04 0.54 a No distinct peak attributable to melting or decomposition observed 1702 J.Mater. Chem., 1997, 7(9), 1701–1707cessing.To this end, they should have glass transition temperatures in excess of 80 °C. Weak glass transition temperatures were observed at 113 °C for PMPS 1 and at 96 °C for PMPS 2. The diculty of observing a glass transition temperature for PMPS has previously been noted, however our observations are in accordance with previous observations.24,25 Even weaker thermal events were observed in the region 90–100 °C for some of the halomethylated polymers.It is therefore on this basis that the copolymers are considered to have thermal properties that are acceptable for application as resists. However, it must be stated that for the solutions in the casting solvent of the BPMPS series of polymers in particular, significant alterations to their molecular weight distributions were observed to occur over a period of days.This would be a most unattractive feature in the lithographic context. Lithographic assessments Lithographic contrast curves for PMPS are shown in Fig. 1, and a representative pair of contrast curves for the copolymer systems are shown in Fig. 2. The lithographic parameters are listed in Table 1. Unfractionated PMPS 1 displays positive-working behaviour with a very low sensitivity when exposed to the electron beam.Over the same dose range, the fractionated PMPS 2, which is of comparable molecular weight to the BPMPS and CPMPS samples, shows considerably less sensitivity to radiation- induced processes. In a recent study of the radiation chemistry of poly(cyclohexylmethylsilane) it was shown that two values for the radiation chemical yield for chain scission, Gs, could be determined.26 For high and low molecular weight polymers the values were 17.4 and 1.8 respectively.This Scheme 1 Polymer degradation accompanying the halomethylation of PMPS ing indirect evidence for the degradation mechanism given in Scheme 1(a). Peaks are always observed in the 1H, 13C and 29Si NMR spectra corresponding to terminal methoxy groups and also, occasionally, for terminal SiCl groups, the latter most probably remaining from their incomplete conversion to methoxy groups during the isolation and purification of the precursor PMPS.Contrary to an earlier explanation that these scission reactions occurred at randomly placed siloxy linkages in the polymer chain, it is now believed that they occur at points of conformational disorder that separate the otherwise extended s-conjugated sequences23 in PMPS which are known to be on average approximately 40 repeat units long.19 The extent of halomethylation was calculated from the Fig. 1 Representative contrast curves for PMPS: (&) PMPS 1, 1H NMR spectra. For both the bromomethylated and chloro- unfractionated; ($) PMPS 2, fractionated methylated samples, a general increase in halomethyl content from XPMPS 1–4 (X=Br or Cl) is indicated by NMR spectroscopy.Two structural features that must be emphasised as being of relevance to the subsequent assessment of the copolymers for lithographic applications are as follows: (i) the NMR, FTIR and UV analyses confirm the copolymers to have the expected statistical structures; (ii) the main position of substitution by the halomethyl groups is the para position but previous studies21 indicate that a small percentage are in the meta position.Data from the thermal analysis of the copolymers are also given in Table 1. A broad exotherm was observed for all of the samples at temperatures in excess of 250 °C.The peak temperatures and the energies of these transitions increase with increasing extent of halomethylation and they are accordingly attributed to thermally induced crosslinking processes. No similar exotherms were observed for the homopolymer samples PMPS 1 and PMPS 2. Polymers for application as resists Fig. 2 Representative contrast curves for halomethylated PMPS: ($) BPMPS 3; (&) CPMPS 3 should be robust under the conditions of lithographic pro- J.Mater. Chem., 1997, 7(9), 1701–1707 1703observation accords with the observations of the present study of PMPS and the phenomenon is perhaps more general amongst polysilanes than has previously been recognised. The structures of the high and low molecular weight polysilanes, and in the present context the two PMPS samples, probably dier in one crucial respect.It is likely that the fractionated sample of low molecular weight consists of polymer molecules in which the silicon atoms tend to catenate in all-trans sequences, whilst the unfractionated polymer, which has a higher average molecular weight and a bimodal distribution, contains molecules in which the all-trans sequences are separated by some linkages that are gauche.27 Such linkages continuously translate themselves along the high molecular weight polymer chain when they are in solution and they are considered to be points of weakness in the chain.It is proposed that in the solid state in which these gauche linkages are immobilised, they are then the positions that are most vulnerable to scission following electron transfer to the polymer chain such as might occur during irradiation.In clear contrast to the positive-working PMPS samples, all the resists of the two copolymer series are negative-working. Although the lithographic sensitivities within each series increase with increasing halomethyl content, the contrasts are low, and are particularly poor for the BPMPS series.The sensitivity variations are to be expected given that the crosslinking sites in these systems are presumed to arise from the halomethyl groups (see Scheme 2) and that scission is expected to remain at a constant level irrespective of halomethyl content, therefore the greater the number of active sites the greater the extent of crosslinking for the same radiation doses.However, it is notable that the BPMPS systems respond more sluggishly than the CPMPS systems and that for both systems the curves tend to normalised thicknesses remaining of only 0.7 to 0.8. This is indicative of a radiation-induced chain scission competing with crosslinking. Furthermore, the contrast curves of Fig. 2 are for bromomethylated and chloromethylated PMPS systems of comparable loadings so it is clear that the replacement of the chloromethyl by bromomethyl groups results in a significantly decreased sensitivity.This is surprising, since the lower bond dissociation energy and the higher reactivity of the C–Br bond when compared with the C–Cl bond (average bond enthalpies at 25 °C of 285 and 339 kJ mol-1, respectively) would be expected to lead to higher lithographic sensitivities for the BPMPS systems.This observation would seem to indicate that the radiation chemistries of the two systems are not directly comparable. A measure of the relative extents of crosslinking and chain scission can be obtained by plotting the lithographic data for the halomethylated, negative-working systems in accordance with the Charlesby–Pinner equation [eqn.(2)] for radiationinduced crosslinking of polymers with a most-probable (normal) molecular weight distribution.28 From the polydispersities shown in Table 1, the application of the equation is Scheme 2 Simple crosslinking mechanism for a halomethylated PMPS appropriate to the present systems (X=Br or Cl) s+Ós=Gs/2Gx+9.65×105/MwGxr (2) where s (=1-g) is the sol fraction in the exposed region, g values in Table 1 even approach this figure but neither are being the gel fraction and taken to be equal to the normalised they suciently low as to characterise a satisfactory negativethickness remaining after development, r is the absorbed working performance.Taken with the very low sensitivities radiation dose in Mrad and Gs and Gx are the radiation and poor contrast values, this signifies that on a number of chemical yields for chain scission and crosslinking, respectively.accounts these systems fail as potentially useful electron beam In Fig. 3 the data points of the representative contrast curves resists. It is nonetheless worthwhile to rationalise the variations of Fig. 2 are plotted in accordance with eqn.(2). A dose of Gs and Gx values with possible radiation chemical mechanconversion factor of 2 Mrad cm2 mC-1 has been applied.29 The isms in order to establish the reasons for the failure of the values of Gs and Gx, estimated from the slopes and intercepts halomethylated systems in the lithographic context, and to of these and similar plots for the remaining halomethylated serve that end the variations of the G values with composition polymers, are listed in Table 1 together with values of the ratio are depicted in Figs. 4 and 5. A value of Gx=0 is represented Gs/Gx. Values of Gs/Gx that are at least 4 are usually taken to for PMPS as it is appears from Fig. 1 that it does not undergo radiation-induced crosslinking. characterise a potential positive-working resist.30 None of the 1704 J.Mater. Chem., 1997, 7(9), 1701–1707further shown to correlate with a concerted crosslinking reaction of either chain-centred or substituent-centred benzylic radicals which originated from a radiation-induced excited state charge transfer interaction, and evidence for the requisite intermediates was provided from pulse radiolysis studies. This mechanism was assumed to operate over and above the crosslinking mechanism that results from the combination of benzylic radicals formed directly through the radiation-induced scission of carbon–chlorine bonds.Whether or not the details of such processes are accepted, in all the systems studied the optimal values of Gx were found to correlate with copolymer compositions in which there are about 33% halogenated (electron accepting) substituents, the remaining substituents being non-halogenated and therefore electron-donating.The Gx values of the CPMPS systems display similar variations with composition to those described above but they never attain values that compare favourably with those of the CMS systems. Although only a narrow band of composition has been investigated, it is considered that the composition at Fig. 3 Charlesby–Pinner plots of the data taken from the contrast maximum Gx, in the region of a 30 mol% chloromethyl curves for BPMPS 3 ($) and CPMPS 3 (&) shown in Fig. 2 loading, is suciently close to that found for the CMS systems as to allow the comparison. Within the composition range investigated, the variation of the Gs values with composition appears to follow the Gx values, a feature which might be taken as an indication that scission and crosslinking arise from similar intermediates.This is also the case for those CMS systems in which the two processes, when they occur, can be identified as stemming from chain centred benzylic radicals. It is not possible to identify analogous structures in the CPMPS systems and in the absence of data that are representative of a wider range of compositions it would be unwise to take either these comparisons or the analysis any further, other than to observe that chain scission in the chloromethylated systems is significantly more ecient than in the CMS systems.There are three reasons why the radiation chemistry of the bromomethylated polymers would dier from that of the chloromethylated polymers: (i) the lesser electronegativity of Fig. 4 Variation of the radiation chemical yields for ($) scission (Gs) bromine would not be as favourable as chlorine for excited and (&) crosslinking (Gx) with composition for CPMPS state charge transfer interactions, (ii) with bromine being a heavier atom than chlorine and the C–Br bond being weaker than the C–Cl bond, there is an increased likelihood of direct scission of the carbon–halogen bond, and (iii ) bromine atoms are significantly less reactive than chlorine atoms towards hydrogen atom abstraction.† The variation of G values with composition for the BPMPS system are indeed quite dierent from those of the CPMPS system, though the changes that occur within the narrow composition range investigated are again notable. Whereas both parameters apparently increase linearly up to about 30% bromomethyl content, thereafter Gx undergoes an extremely sharp increase.A log10Gx versus log10[CH2Br] plot is shown in Fig. 6 from which it is evident that, whereas Gx varies linearly with bromomethyl content at low values of the latter, at greater values the variation is of a higher order and appears, at the very least, to be in accordance with the square of the bromomethyl content.Any mechanism Fig. 5 Variation of the radiation chemical yields for ($) scission (Gs) of radiation-induced crosslinking that is consistent with these and (&) crosslinking (Gx) with composition for BPMPS observations requires a concerted reaction of increasing probability as the bromomethyl loading is increased.It would be in addition to the crosslinking reaction that follows from the Discussion direct formation of benzylic radicals through the radiationinduced scission of carbon–bromine bonds, and it would have It has previously been shown for the CMS series of resists prepared by statistical copolymerisation of chlorostyrene or to become the dominant crosslinking reaction at high bromomethyl loadings. A possible mechanism is shown in Scheme 3 chloromethylstyrene with either styrene or methylstyrene, that it is not uncommon for the variation of Gx with composition in which PBr represents a bromomethyl group in the polymer, D represents some kind of proximate association of bromo- to display both maximum and minimum values.31 The maximum values of Gx in the lithographically useful systems methyl groups such as a dimer, P is any repeat unit of the (copolymers of vinyl benzyl chloride and a methylstyrene) are least 2 and they occur in copolymers with chlorine-containing † For the reaction XV+CH3–H�HX+CH3V, the values of DH° are monomer loadings of about 30–40 mol%, at which Gs is estimated to be -4 and -69 kJ mol-1 for bromine and chlorine respectively (ref. 28). eectively zero. Such variations of Gx with composition were J. Mater. Chem., 1997, 7(9), 1701–1707 1705intercept of Fig. 5 the Gs value for PMPS can be estimated to be about 0.3. Some of the reactions depicted in Scheme 3 are as likely to apply to the CPMPS series as to the BPMPS series of copolymers.The most notable of these is the halogen atom induced chain scission reaction. The apparent greater eciency with which chain scissions occur in the BPMPS series can be attributed to the bromine atoms being ineectual at abstracting hydrogen atoms from the methyl substituents of the polymer chain. Without this alternative reaction pathway the bromine atoms are bound to induce chain scissions, i.e.k1>k2. As indicated above, hydrogen abstraction by chlorine atoms is significantly more exothermic so if chlorine atoms are formed within the CPMPS resists, they have the choice of two reaction pathways. It is reasonable to assume that in this case k1<k2. Fig. 6 A log–log plot for the Gx data of Fig. 5 Conclusion It is evident that the halomethylated PMPS series of resists are more susceptible to chain scission than their polystyrene counterparts and this can be attributed to halogen atom attack on the polymer backbone in a reaction that is particular to the polysilanes.Chain scission in the CMS series of resists arises from a b-scission reaction following the abstraction of a main chain hydrogen atom from the substituted carbon atom.The polysilanes do not have main chain hydrogen atoms, but the Si–Si bond is weaker than the C–H bond‡ and is readily susceptible to radical attack. Furthermore, the halomethylated PMPS resists do not undergo crosslinking with comparable eciency to the chloromethylated polystyrenes or poly(methylstyrene) s. For the CPMPS series, in which the eects of chain scission appear to be confined, Gx values of 0.8 would at best make them comparable to the chlorostyrene–methylstyrene copolymer resists.Though greater values of Gx may well be Scheme 3 A representation of a possible mechanism for the radiation chemistry of BPMPS accessible for the BPMPS series of resists at higher bromomethyl contents, not only would the enhanced chain scission reactions preclude their application in e-beam lithography, polymer chain, RV is a substituent-centred benzylic radical or but so also would their shelf life.Notwithstanding the high a radical formed by abstraction of a hydrogen atom from a silicon content which lends them a high resistance under the substituent methyl group of the polymer chain, and RE is a conditions of oxygen reactive-ion etching, simple derivatives chain end-centred radical resulting from chain scissions.The of PMPS are most unlikely to ever make useful negativenatures of the other species represented are self evident, and working electron beam resists. G1, G2 and G3 are radiation chemical yields for the primary processes represented. We thank the EPSRC for the award of a Research Studentship Assuming stationary state conditions for all radical species, (J.J.M.) and of a Postdoctoral Research Fellowship (S.J.H.).it follows that: We also gratefully acknowledge the assistance of Professor Ron Lawes and the sta of the Central Microstructure Facility [BrV]= G1PBr k1+k2 (3) of the Rutherford Appleton Laboratory, and in particular Mr Ejaz Huq, for facilitating the microlithographic evaluations.so References Gx=k3[RV]+G2D=G1PBr+k2 [BrV] P+G2D (4) 1 K. S. Mazdyasni, R. West and L. D. David, J. Am. Chem. Soc., =G1{1+k1/(k1+k2)}PBr+G2KPBr2 (5) 1978, 61, 504. and 2 R. E. Trujillo, J. Organomet. Chem., 1980, 198, C27. 3 S. Yajima, J. Hayashi and M. Omori, Chem. L ett., 1975, 931. 4 R. D. Miller and J. Michl, Chem. Rev., 1989, 89, 1359. GsP=G3P+k1 [BrV] P=G3P+ k1G1PBrP k1+k2 (6) 5 Inorganic Polymers, ed.J. E. Mark, H. R. Allcock and R. West, Prentice-Hall, New Jersey, 1992, ch. 5, p. 186. so 6 R. D. Miller and G. M. Wallraf, Adv. Mater. Opt. Electron., 1994, 4, 95. 7 D. R. Brambley, B. Martin and P. D. Prewett, Adv. Mater. Opt. Gs=G3+ k1G1PBr k1+k2 (7) Electron., 1994, 4, 55. 8 S. J.Webb, Ph.D. T hesis, University of Kent, 1994.The requisite variations of Gx and Gs are represented in eqns. 9 T. Tada and T. Ushirogouchi, Solid State T echnol., 1989, 91. 5 and 7. At low bromomethyl loadings when the first term of 10 S. Imamura, T. Tamamura, K. Harada and S. Sugawara, J. Appl. Polym. Sci., 1982, 27, 937. eqn. 5 dominates, Gx is directly proportional to [PBr], but as 11 S. Imamura, T. Tamamura, K. Sukegawa, O.Kogura and the loading increases and the probability of bromomethyl S. Sugawara, J. Electrochem. Soc., 1984, 131, 1122. groups being in close proximity increases, in accordance with observation the second term assumes a greater importance until it eventually dominates. Also in accordance with obser- ‡ The Si–Si bond dissociation energy in Me3Si–SiMe3 is 337 kJ mol-1 (ref. 32) whilst that of the C–H bond in Et–H is 410 kJ mol-1 (ref. 33). vation, eqn. 7 shows Gs varying linearly with PBr and from the 1706 J. Mater. Chem., 1997, 7(9), 1701–170712 R. G. Tarascon, M. A. Hartney and M. J. Bowden, inMaterials for 23 K. A. Klingensmith, J. W. Downing, R. D. Miller and J. Michl, J. Am. Chem. Soc., 1986, 108, 1046. Microlithography, ed. L. F. Thompson, C. G. Wilson and J.M. J. Frechet, ACS Symp. Ser. No. 266, American Chemical 24 S. Demoustier-Champagne, S. Cordier and J. Devaux, Polymer, 1995, 36, 1003. Society, Washington DC, 1984, p. 361. 13 A. Ledwith, M. Mills, P. Hendy, A. Brown, S. Clements and 25 J. M. Ziegler,Mol. Cryst. L iq. Cryst., 1990, 190, 265. 26 J. Kumagain, K. Oyama, H. Yoshida and T. Ishikawa, Radiat. R. Moody, J. Vac.Sci. T echnol. B., 1985, 3, 339. 14 Ll. G. Griths, R. G. Jones, D. R. Brambley and P. C. Miller Tate, Phys. Chem., 1996, 47, 631. 27 R. G. Jones, U. Budnik, S. J. Holder and W. K. C. Wong, Makromol. Chem., Macromol. Symp., 1989, 24, 201. 15 D. R. Brambley, R. G. Jones, Y. Matsubayashi and P. C. Miller Macromolecules, 1996, 25, 8036. 28 A. Charlesby and S. H. Pinner, Proc. R. Soc. L ond., Ser. A., 1959, Tate, J. Vac. Sci. T echl, B., 1990, 8, 1412. 249, 367. 16 R. G. Jones, Y. Matsubayashi, P. C. Miller Tate and D. R. 29 A. Novembre and T. N. Bowmer, in Materials for Brambley, J. Electrochem. Soc., 1990, 137, 2820. Microlithography, ed. L. F. Thompson, C. G. Wilson and 17 M. A. Hartney, J. Appl. Polym. Sci., 1989, 37, 695. J. M. J. Frechet, ACS Symp. Ser. No. 266, American Chemical 18 R. G. Jones, P. C. Miller Tate and D. R. Brambley, J.Mater. Chem., Society, Washington DC, 1984, p. 241. 1991, 1, 401. 30 Introduction to Microlithography, ed. L. F. Thompson, 19 C. Strazielle, A.-F. de Mahieu, D. Daoust and J. Devaux, Polymer, M. J. Bowden and C. G. Wilson, ACS Symp. Ser. No. 219, 1992, 33, 4174. American Chemical Society, Washington DC, 1983. 20 R. H. Cragg, R. G. Jones, A. C. Swain and S. J. Webb, J. Chem. 31 R. G. Jones, P. C. Miller Tate and D. R. Brambley, Polymer, 1993, Soc., Chem. Commun., 1990, 1147. 34, 1768. 21 A. C. Swain, S. J. Holder, R. G. Jones, A. J. Wiseman, M. J. Went 32 R. Walsh, Acc. Chem. Res., 1981, 14, 246. and R. E. Benfield, in Metal-containing Polymers, ed. 33 S. W. Benson, T he Foundations of Chemical Kinetics, McGraw- C. U. Pittman, Jr., C. E. Carraher, Jr., M. Zeldin, J. E. Sheats and Hill, New York, 1960. B. M. Culbertson, Plenum, New York, 1996, p. 161. 22 R. G. Jones, R. E. Benfield, A. C. Swain, S. J.Webb and M. J.Went, Polymer, 1995, 36, 393. Paper 7/00413C; Received 17th January, 1997 J. Mater. Chem., 1997, 7(9), 1701–1707 1707

ISSN:0959-9428    

DOI:10.1039/a700413c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Properties of chiral liquid crystals with inner hydrogen bonds Damian Pociecha,a Adam Kro�wczyn�ski,a Jadwiga Szyd�owska,a Ewa Go�recka,a Milada Glogarovab and Jan Przedmojskic aWarsaw University, Department of Chemistry, L aboratory of Dielectrics andMagnetics, Al. Zwirki i Wigury 101, 02-089 Warsaw, Poland bAcademy of Sciences of the Czech Republic, Institute of Physics, Na Slovance 2, 180 40 Prague 8, Czech Republic cWarsaw University of T echnology, Department of Physics, 00-662 Warsaw, Poland A sequence of tilted smectic phases, SmC-SmF-SmG-SmH, has been observed in a series of enamino ketone derivatives with a 2-methylbutoxy chiral terminal group.In spite of the rather weak chiral centre, these compounds are characterized by high spontaneous polarization (ca. 0.5 mC cm-2), which seems to be induced by the large molecular tilt (ca. 40°) observed in all mesophases. A memory eect in the switching process has been observed due to the formation of ion layers at electrodes. The high hydrogen ion concentration is a result of the dissociation of hydrogen bonded material under an applied electric field. Compounds with inner hydrogen bonds forming thermotropic o and recrystallized.Yield 87%, mp 142.5 °C, clearing point 168 °C. The molecular structure was confirmed for the LAC1 liquid crystalline phases have been studied because of their unique properties such as their chelating ability. Among them compound by 1H NMR spectroscopy: dH 0.88–2.00 [m, 9H, OCH2CH(CH3)CH2CH3]; 3.70–3.92 (m, 5H, OCH2, OCH3); enamino ketone structures are the most extensively examined because simple synthetic procedures lead to a variety of 5.93 (d, J 7.8, 1H, H2); 6.80–7.10 (m, 7H, aromatic); 7.38 (dd, J1 7.8, J2 12.8, 1H, H1); 7.90 (d, J 8.95, 1H, H2); 12.10 (d, molecular structures.1–3 Recently, several series of enamino ketone mesogens have J 12.8, 1H, NH).Liquid crystalline properties were examined using polarizing been reported and it has been argued that their phase sequence can be controlled by molecular factors such as the electric microscopy (Nikon Optiphot2-Pol equipped with P101 photometer and Mettler FP82HT hot stage) and by dierential dipole moment of the molecular structure or the electron donating and accepting properties of terminal groups, which scanning calorimetry (Perkin-Elmer DSC7).Thermograms were taken at several scanning rates, and temperatures and aect the electron distribution within the mesogenic core.4 In this paper, we present properties of a new chiral enamino thermal eects were recalculated at 5 °C min-1 if necessary. Layer spacing data were obtained from X-ray scattering in ketone derivatives series denoted by (-)-LACn reflection mode for homotropically aligned samples placed in a double oven.The measurements were taken with a modified DRON spectrometer. The wave vector was determined to within 10-3 A ° -1. Dielectric properties were studied using a Wayne Kerr Precision Component Analyzer 6425. which was designed to give a sequence of tilted smectic phases: Measurements of spontaneous polarization, Ps, and apparent liquid-like SmC, hexatic SmF and crystalline SmG, SmH.In tilt, h, were recorded. The spontaneous polarization was order to obtain this phase sequence, strongly electron donating obtained from the Ps(E) hysteresis loop detected during the n-alkoxy and 2-methylbutoxy groups were attached to the Ps switching. The apparent tilt was determined from an angle three-ring phenyl–enamino ketone–phenyl core.For compari- dierence between minimum transmission positions of a planar son the racemic counterparts (±)-LACn were examined. Some sample placed between crossed polarizers under opposite DC other chiral three-ring enamino ketone derivatives have also fields. Molecular dimensions were estimated by molecular been synthesized to establish the eect of molecular structure modelling (HYPERCHEM 3.0).on liquid crystalline properties. Experimental Results and Discussion The phase diagram for the (-)-LACn series is presented in The enamino ketone compounds were synthesized by reacting hydroxymethylene derivatives of 4-(2-methylbutoxy)phenyl- Fig. 1. Phase transition temperatures and thermal eects are collected in Table 1. In materials studied there is no pro- acetophenone with 4-alkoxyanilines and purifying by crystallization from toluene.A typical synthetic procedure is described nounced chiral discrimination eect;5,6 the phase transition temperatures and enthalpies are almost equal for the chiral for 1-(4-methoxyphenylamino)-3-[4-(2-methylbutoxy)phenyl]- prop-1-en-3-one: the sodium salt of 3-(4-methoxyphenyl)-3- and racemic materials.In the compounds studied exclusively tilted smectic phases oxopropanal was obtained by the Claisen formylation reaction by adding 4-(2-methylbutoxy)phenylacetophenone (15 mmol) were detected. This is in agreement with our predictions, since the strongly electron donating alkoxy groups (Hammett con- and ethyl formate (5 ml) to sodium powder (0.4 g) dispersed in diethyl ether (25 ml ) and stirring the mixture for 12 h.After stant s ca. -0.3) used as the terminal chains promote tilted phases for three-ring enamino ketone molecules.4 The nematic the diethyl ether and excess ethyl formate had evaporated, the crude sodium salt (yield ca. 70%) was dissolved in methanol phase was observed only for short homologues. The compounds studied have distinctly lower clearing and (20 ml ).To this solution (ca. 10 mmol) anisidine (10 mmol) in methanol (20 ml ) was added, then neutralized with acetic acid melting temperatures compared to materials with nonbranched n-butoxy terminal chains.7 The dierence is of the and left for 12 h. Yellow crystals of the product were filtered J. Mater. Chem., 1997, 7(9), 1709–1712 1709alkoxy terminal group.For short homologues the hexatic– crystalline phase transition is accompanied by freezing of the schlieren texture leading to the paramorphic mosaic texture retaining schlieren characteristics;10 for higher homologues the texture changes are small and dicult to detect. The SmG–SmH phase transition is detectable using calorimetric and microscopic methods.For all chiral substances textures with dechiralization lines could be observed in the SmC and SmF phases which indicates the existence of a helical structure of the director.11,12 The helical pitch calculated from dechiralization line spacing is of the order of 1 mm, which points to a rather weak twisting power of the molecular chiral centre. X-Ray All compounds studied show interlayer distances (d) markedly smaller than the fully extended molecular length (L ) calculated from molecular modelling.The d/L ratio is 0.75–0.82. This indicates a strong molecular tilt within the smectic layers— the tilt angle calculated from the d/L ratio is ca. 40–45°. This value is in agreement with data obtained from electrooptic switching measurements in the SmC and SmF phase.In the higher ordered phases the electrooptic measurements with a DC electric field could not be carried out because of the high Fig. 1 Phase diagram for the (-)-LACn homologues series threshold switching field and conductivity of the material. The tilt angle is nearly constant in the temperature range of the SmC and SmF phases. However, the layer spacing was found order of 30 °C.This behaviour is typical since non-linear to exhibit a critical anomaly at the SmC–SmF phase transition terminal groups do not allow close molecular packing. (Fig. 2). For short homologues the layer spacing decreases As with previously reported series,2,7 one can observe that with decreasing temperature while for long homologues the the liquid-like SmC to hexatic SmF phase transition temperalayer spacing changes are inverted—increase of layer thickness tures and enthalpy changes depend slightly on terminal chain with decreasing temperature is observed, the magnitude of length.The SmC–SmF phase transition, which theoretically changes being smaller for long homologues. For materials with should be of the first order,8 is always accompanied by strong intermediate terminal chain length ges are less pro- both-side heat capacity anomalies seen as very broad peaks nounced. The layer spacing changes at the SmC–SmF phase on DSC thermograms.9 In contrast, enthalpy changes at the transition seem to be caused by two opposing factors—small strongly first order, as detected by X-ray measurements, hexatilt angle changes (ca. 1–2°) and the chain melting phenomenon.tic–crystalline smectic (SmF–SmG) phase transition are small For compounds with short terminal groups the chain melting and rapidly decrease with increasing terminal chain length. In eect is weak so one can correlate the decreasing d/L ratio at the LACn series the SmF–SmG phase transition enthalpy the SmC–SmF phase transition with the small increase in the changes become undetectable (DH<0.01 J g-1) for homoltilt angle.For the long homologues the chain melting aects ogues n>12 [series (-)-LACn] or n>11 [series (±)-LACn]. the layer spacing more strongly than the tilt angle changes, so Moreover, while the stability of the hexatic phase is almost a lower interlayer distance in the SmC phase than in the SmF independent in the homologous series, the crystalline SmG phase is strongly destabilized with increasing length of the phase is observed.Table 1 Temperatures and, in parentheses, enthalpies of the phase transitions for the compounds of the LACn series T /°C T /°C T /°C T /°C T /°C T /°C n Cry (DH/J g-1) SmH (DH/J g-1) SmG (DH/J g-1) SmF (DH/J g-1) SmC (DH/J g-1) N (DH/J g-1) Iso 1 $ 142.6 (97.4) $ 168.1 (2.2) $ 2 $ 162.4 (92.4) 144.6 (4.9) $ 183.4 (3.9) $ 3 $ 145.4 (46.4) 147.0 (5.8) $ 166.7 (3.4) $ 4 $ 144.7 (37.4) $ 136.4 (8.6) 161.6 (6.5) $ 174.2 (4.4) $ 5 $ 115.7 (26.4) $ 136.9 (0.5) $a 138.0 (7.1) 161.3 (9.8) $ 167.1 (4.6) $ 6 $ 94.2 (20.8) $ 139.5 (10.3) 167.5 (10.0) $ 170.6 (5.2) $ 7 $ 93.6 (27.5) $ 135.8 (3.1) $ 139.7 (6.8) $ 167.0 (18.6) $ 8 $ 92.6 (29.1) $ 110.1 (0.3) $ 131.7 (1.6) $ 138.7 (7.8) $ 167.9 (19.0) $ 9 $ 91.9 (32.0) $ 124.2 (0.8) $ 136.2 (7.8) $ 166.1 (18.2) $ 10 $ 87.8 (32.0) $ 118.2 (0.4) $ 135.1 (5.0) $ 165.5 (17.7) $ 11 $ 88.2 (77.0) $ 108.4 (0.4) $ 133.2 (7.1) $ 163.2 (16.9) $ 12 $ 99.9 (75.0) $ 103.0 (0.1) $ 132.9 (5.6) $ 162.9 (16.4) $ 13 $ 99.6 (70.4) $ 131.8 (2.4) $ 161.0 (16.1) $ 14 $ 94.4 (62.6) $ 131.2 (3.3) $ 159.9 (16.0) $ 15 $ 86.1 (75.4) $ 130.2 (4.0) $ 157.5 (15.7) $ 16 $ 89.8 (72.4) $ 129.8 (5.1) $ 156.2 (15.7) $ 17 $ 84.5 (71.0) $ 128.8 (3.9) $ 154.0 (15.6) $ 18 $ 86.4 (84.0) $ 127.7 (3.9) $ 152.2 (15.0) $ aSmG¾. 1710 J. Mater. Chem., 1997, 7(9), 1709–1712compounds studied are characterized by long switching times. Unfortunately, the enamino ketone derivatives studied are not stable under high electric fields.Under the fields, dissociation of hydrogen atoms takes place, which breaks the hydrogen bond and destroys the molecular core. The high hydrogen ion concentration then leads to the relatively high conductivity of the material, which precludes detection of the Goldstone mode in the dielectric measurements. A non-typical optical switching with memory eect was found when applying a DC electric field in the studied materials near the SmC–SmF phase transition, in both phases (Fig. 4). A planar sample was placed between crossed polarizers in a position which gives the minimum transmission in one of the uniform states. After full switching to the other uniform state minimum transmission was also observed because the tilt angle value is close to 45°. The uniform states are separated by the Fig. 2 Temperature dependence of the ratio of smectic layer thickness twisted state, in which the director has opposite orientations (d) to molecular length (L ) for (-)-LAC7 (#, left axis) and (-)-LAC18 on sample surfaces so that the director projection onto the ($, right axis) compounds. The arrow indicates the SmF–SmG phase surface has to twist along the surface normal.14 This director transition temperature for (-)-LAC7.configuration within the sample gives maximum transmission. An observed hysteresis of switching through the twisted state Electric Properties is probably caused by screening of one electrode by a layer of heavy non-mobile ions,15 which makes absolute values of the Although having a weak electric dipole moment at the chiral electric field dierent at cathode and anode.The screening centre, the materials of the (-)-LACn series are characterized eect results in switching of spontaneous polarization direction by spontaneous polarization as high as 600 nC cm-2 for first at one electrode when the applied field is increased and (-)-LAC8 in the SmC phase. It seems that the result of the thus forces the twisted state to be formed.strong molecular tilt observed in the smectic phases is pronounced hindrance of molecular rotation around the long molecular axis.13 Measurements of spontaneous polarization Modifications in Molecular Structure wererather dicult for (-)-LACn compounds due to high In order to establish the eect of the molecular structure on electric conductivity of enamino ketone substances that appears the liquid crystalline properties some other chiral three-ring as strong ionic currents in the sample.While the tilt angle is enamino ketone derivatives have also been synthesized; their almost temperature independent, the spontaneous polarization structures as well as phase transition temperatures and thermal depends strongly on temperature (Fig. 3). However, decrease eects are collected in Table 2. It was found that exchanging in the spontaneous polarization with decreasing temperature of the terminal group positions in (-)-LAC6 resulting in may result from non-complete polarization reversal because of compound I had no influence on the phase sequence and only insucient applied electric field intensity since rather high weakly suppressed the temperature range of the mesophases.coercive fields were found in ordered smectics. The switching In compound II the 2-methylbutoxy chiral group was replaced current peaks are relatively broad, which indicates that the with the 2-methylbutoxycarbonyl group. The change resulted in an increase in the melting and clearing temperatures by more than 60 and 10 °C, respectively, in comparison with (-)-LAC6.This seems to be an eect of lengthening the rigid part of the molecule as the carbonyl group is sti enough to be considered as a part of the molecular mesogenic core. In this case the phase sequence was also aected; the orthogonal SmA phase was formed above the SmC phase. The occurrence of the orthogonal phase is most probably due to the electron Fig. 3 Temperature dependence of spontaneous polarization for Fig. 4 Light transmission through a planar sample of (-)-LAC6 compound in the SmC phase vs. applied DC electric field (-)-LAC7 (%), (-)-LAC8 (#) and (-)-LAC18 ($) compounds J. Mater. Chem., 1997, 7(9), 1709–1712 1711Table 2 Temperatures and, in parentheses, enthalpies of the phase transitions for the compounds I–III T /°C T /°C T /°C T /°C T /°C Cry (DH/J g-1) SmH (DH/J g-1) SmC (DH/J g-1) SmA (DH/J g-1) N (DH/J g-1) Iso I $ 116.4 (20.7) $ 138.6 (7.9) $ 164.7 (15.2) $ 168.6 (3.9) $ II $ 156.0 (65.3) 159.5 (0.9) $ 179.0 (9.4) $ III $ 128.0 (48.1) $ 166.2 (19.7) $ accepting (Hammet constant s ca. 0.5) properties of the 2- References methylbutoxycarbonyl terminal group. The same eect was 1 W.Pyzÿuk, E. Go� recka, A. Kro�wczyn� ski and J. Przedmojski, L iq. observed for compound III with fluorine (Hammet constant Cryst., 1993, 14, 773. s=0.06) attached to the mesogenic core instead of the n- 2 W. Pyzÿuk, J. Szyd�owska, E. Go� recka, A. Kro�wczyn� ski, alkoxy chain. This material was found to exclusively form the D. Pociecha and J. Przedmojski, Mol. Cryst.L iq. Cryst., 1995, 260, 449. SmA phase. The tendency towards formation of the orthogonal 3 J. Szyd�owska, W. Pyzÿuk, A. Kro�wczyn� ski and I. Bikchantaev, phase is enhanced by another molecular factor—the more J.Mater. Chem., 1996, 6, 733. linear shape of III compared to II. 4 W. Pyzÿuk, E. Go� recka, A. Kro�wczyn� ski, D. Pociecha, J. Szyd�owska, L iq.Cryst., 1996, 21, 885. Conclusion 5 D. P. Craig and D. P. Mellor, in T opics in Current Chemistry, vol. 63, Springer-Verlag, Berlin, 1976. A novel series of chiral enamino ketone derivatives, designed 6 Ch. Bahr and G. Hepke, Phys. Rev. L ett., 1990, 65, 3297. to obtain the sequence of tilted smectic phases, was synthesized 7 E.Go� recka, W. Pyzÿuk, A. Kro�wczyn� ski and J. Przedmojski, L iq.and examined for liquid crystalline and electric properties. Cryst. 1993, 14, 1837. According to our predictions all compounds studied exclusively 8 C.W. Garland, J. D. Lister and K. J. Stines,Mol. Cryst. L iq. Cryst. form strongly tilted phases. The high tilt angle values might 1989, 170, 71. 9 H. Yao, T. Chan and C. W. Garland, Phys. Rev. E, 1995, 51, 4585. be responsible for the rather high spontaneous polarization 10 G.W. Gray and J. W. Goodby, Smectic L iquid Crystals, ed. (ca. 0.5 mC cm-2) observed in the liquid-like and hexatic smec- Leonard Hill, Glasgow, 1984. tic phases. The memory eect was found during electrooptic 11 M. Brunet and C. Williams, Ann. Phys., 1978, 3, 137. switching, which is most probably caused by hydrogen ion 12 M. Glogarova, L. Lejcek, J. Pavel, U. Janovec and F. Fousek,Mol. layers at the electrodes. The relatively high concentration of Cryst. L iq. Cryst., 1983, 91, 309. hydrogen ions results from dissociation under an applied 13 N. A. Clark and S. T. Lagerwall, ‘Introduction to Ferroelectric Liquid Crystals’ in Ferroelectric L iquid Crystals—Principles, electric field. The liquid crystalline properties of other enamino Properties and Applications, Gordon and Breach Science ketone derivatives confirm the eect of molecular factors such Publishers, Amsterdam, 1991. as electron distribution within the mesogenic core or molecular 14 M. Glogarova and J. Pavel, Mol. Cryst. L iq. Cryst., 1984, 114, 249. shape on phase sequence as well as on mesophase stability. 15 A. K. Jonscher, Dielectric relaxation in solids, Chelsea Dielectrics Press, London 1983. The authors wish to thank K. Kosiel for his help in calorimetric measurements. This work is a contribution to the KBN 3 T09A 147 10 project and to the grant 202/96/1687 of GACR. Paper 7/01129F; Received 18th February, 1997 1712 J. Mater. Chem., 1997, 7(9), 1709&ndas

ISSN:0959-9428    

DOI:10.1039/a701129f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Axial chiral allenylacetates as novel ferroelectric liquid crystals Ralph Lunkwitz,a Carsten Tschierske,*a Arne Langhoff,b Frank Gießelmannb and Peter Zugenmaierb aInstitute of Organic Chemistry,Martin-L uther-University Halle, D-06120 Halle, Kurt-Mothes-Str. 2, Germany E-mail: coqfx@mlucom.urz.uni-halle.de bInstitute of Physical Chemistry, TU Clausthal, Arnold Sommerfeld-Str. 4, D-38678 Clausthal-Zellerfeld, Germany Liquid crystalline alkane-3,4-dienoates (allenylacetates) have been synthesized.Most compounds incorporate a heterocyclic 1,3,4- thiadiazole ring or a pyrimidine ring as a constituent of the rigid core. These axial chiral allene derivatives were at first obtained as racemic mixtures. Some of them were also synthesized in enantiomerically enriched form by enantioselective synthesis.The compounds were investigated by polarizing microscopy and by dierential scanning calorimetry. The three-ring compounds exhibit broad regions of smectic C-phases. The optically active three-ring compounds show broad Sc*-phases with moderate values of spontaneous polarization. Due to their special physical properties and potential technical teric phase.5c Only cholesteric and non-tilted smectic phases have been described for some low molecular mass alkylidene- applications,1 chiral mesophases have grown to be a central topic in liquid crystal research.Materials exhibiting a chiral cyclohexanes,4a,b,e but by appending alkylidenecyclohexanes to a polymeric backbone Sc*-phases can be obtained.4c,d smectic C-phase are of particular interest because of their ferroelectric properties and their use for displays and light shutter In a project aimed at the synthesis of novel mesogenic compounds with ferroelectric properties, the first liquid crystal- devices.2,3 Until now most liquid crystals with chiral mesophases have incorporated a centre of chirality. Only a few examples of line allene derivatives displaying broad Sc*-phases have recently been synthesized10,11 (e.g.compounds 1 and 2). mesogenic compounds and dopants that possess an axis4–7 or a plane8,9 of chirality have been reported (Fig. 1). A major drawback of these compounds is the fact that the rigid rod-like molecular shape is significantly disturbed by the structural units necessary to realize an axis or a plane of chirality.Thus, none of the binaphthyl derivatives exhibits liquid crystalline properties6 and only one axial chiral biphenyl derivative has been reported to form an enantiotropic choles- These are the first axial chiral low molecular mass liquid crystals with broad Sc-phase ranges. It was found that enantiomerically enriched allene derivatives can exhibit ferroelectric switchable Sc*-phases with surprisingly large values of spontaneous polarization.To make ferroelectric materials, it is also important to tailor other properties, such as tilt angle, optical anisotropy, smectic Crange and response time. This can be done by mixing the ferroelectric liquid crystals with other liquid crystals. Therefore it is useful to have materials with high values of the spontaneous polarization which can tolerate the presence of rather large amounts of non-chiral additives.In order to further increase the magnitude of the spontaneous polarization, we set out to synthesize liquid crystalline allene derivatives with increased dipole moments2 within the substituents attached to the axis of chirality. Herein we report on the synthesis and on preliminary investigations of chiral alka-3,4-dienoates incorporating phenylpyrimidine and phenyl-1,3,4-thiadiazole mesogens.In order to find suitable systems exhibiting broad Sc-phases and in order to investigate the influence of changes in the substitution pattern of the allene moiety on the mesogenic behaviour we first synthesized several types of chiral allene derivatives as racemates.After checking the liquid crystalline properties of the racemic derivatives, selected compounds were synthesized in their enantiomerically enriched form. Results and Discussion Synthesis According to Scheme 1, the alka-3,4-dienoic acids have been Fig. 1 Structural units of axial chiral and planar chiral mesogens and dopants synthesized starting from substituted prop-2-ynylic alcohols.J. Mater. Chem., 1997, 7(9), 1713–1721 1713Scheme 1 Synthesis of the racemic and the enantiomerically enriched alka-3,4-dienoates 7a, 8a, 11a (n=1), 8b–10b, 12b, 13–16 (n=5) and 8c–10c, 12c (n=7) For the synthesis of the heptyl substituted derivatives 8c–10c The racemic allenylacetates were synthesized according to Scheme 1 starting with the racemic prop-2-ynylic alcohols.26 and 12c, n-octanal (n=7) was treated with ethynylmagnesium bromide to yield racemic dec-1-yn-3-ol (rac-3c).12 Oxidation Compound 20, in which one of the hydrogen atoms of the allene moiety is replaced by a bromine atom, was synthesized with CrO3 (Jones’ reagent13) provided the prochiral dec-1-yn- 3-one 4c, which was treated with (R)-Alpine borane14 to give in its racemic form according to Scheme 2.27 the optically active prop-2-ynylic alcohol 3c in 87% ee after oxidative work-up.15–17 By comparison with models for the Liquid-crystalline properties of the racemic compounds diastereomeric transition states of (R)-Alpine borane reduction Phase transition temperatures were determined by microscopy of dec-1-yn-3-one, the absolute configuration (R) was assigned between crossed polarizers and were checked by dierential to the major enantiomer.15 The enantiomeric purity of this scanning calorimetry.The results of these investigations are compound was determined by derivation with (S)-a-methoxysummarized in Tables 1 and 3. a-trifluoromethylphenylacetyl chloride [(S)-MTPACl] and All racemic three-ring pyrimidine and thiadiazole derivatives analysing the resulting (R)-MTPA-esters by 19F NMR specdisplay broad smectic C-phases with the dierence that the troscopy (Mosher’s method).18 To obtain the allenic moiety (R)-dec-1-yn-3-ol [(R)-3c] was transformed to the appropriate propynyl vinyl ether by heating with triethyl orthoacetate.This immediately undergoes the stereospecific Claisen-type [3,3] sigmatropic rearrangement.19 Thereby chirality from the asymmetric centre is transferred to the stereogenic axis of the allene moiety formed.The ester (R)- 5c was easily purified by distillation and transformed into the appropriate (R)-dodeca-3,4-dienoic acid (R)-6c by acid-catalysed aqueous hydrolysis.† In the final step the enantiomerically enriched (R)-dodeca-3,4-dienoic acid (R)-6c was appended to the appropriate phenols20–23 by carbodiimide esterification.24 Although we were not able to directly determine the enantiomeric purity of the allenylacetic acid or its esters by chromatographic methods or by NMR investigations in the presence of chiral shift reagents, the success of chirality transfer was revealed by comparison of the molar optical rotation of the ethyl ester (R)-5c ([a]22D=-90.4) with the molar optical rotation of the homologous compound ethyl 3,4-tridecadienoate ([a]22D=-112; ee=90%).25 Therefrom we calculated that the enantiomeric purity should be ca. 73% ee. Scheme 2 Synthesis of the racemic 3-bromododeca-3,4-dienoate rac-20 † Alkaline hydrolysis gave the dodeca-3,5-dienoic acid, see ref. 26. 1714 J. Mater. Chem., 1997, 7(9), 1713–1721Table 1 Transition temperatures and corresponding enthalpy values (italicised) of the racemic allenylacetates rac-7–rac-13 phase transitions T /°C R n comp.enthalpy values DH/kJ mol-1 1 rac-7a C 68 Iso 1 rac-8a C 102 SC 161 N 224 Iso 20.1 1.9 0.7 5 rac-8b C 61 SC 147 N 167 Iso 27.6 1.8 0.5 7 rac-8c C 76 SC 149 N 164 Iso 25.9 2.1 1.2 5 rac-9b C 82 SC 166 Iso 27.6 7.8 7 rac-9c C 83 SC 158 Iso 26.7 6.6 5 rac-10b C 58 SC 149 Iso 7 rac-10c C 65 SC 137 Iso 42.6 8.3 1 rac-11a C 78 (SA 75) Iso 5 rac-12b C 144 SC 176 Iso 7 rac-12c C 143 SC 174 Iso 23.8 7.1 5 rac-13 C 106 SC 153 N 155 Iso Table 2 Comparison of transition temperatures of the thiadiazole melting points of the thiadiazole derivatives are mostly shifted derivatives rac-9b, 2120 and rac-2220 with dierent side chains R to lower temperatures in comparison to the pyrimidine derivatives.Thus, the Sc-ranges of the thiadiazole derivatives are increased. The Sc-phases of the butoxy derivatives rac-8 are accompanied by a nematic phase in contrast to the long chain derivatives rac-9 and rac-10, which show only Sc-phases. As evident in comparing compounds rac-8a, rac-8b and rac-8c, comp.R phase transitions T /°C the nematic and also the Sc-phases are stabilized by cutting 21 MC9H19 C 90 SC 194 Iso the alkyl chain attached to the allene moiety. Stabilization of rac-22 MCH(CH3)MC8H17 C 65 (SX 64) SC 135 Iso a smectic phase by decreasing the length of a terminal chain rac-9b MCH2MCHNCNCHMC5H11 C 82 SC 166 Iso is a remarkable observation. In Table 2 the mesomorphic properties of structurally related thiadiazole derivatives having the same number of carbon atoms, but diering in the structure of one side chain are compared.By replacing the n-nonyl chain of compound 21 by the nona-3,4-dienyl group (rac-9b) a mesophase destabilization of ca. 30°C is observed. However, the mesophase destabilizing influence of the branching of the alkyl chain in compound rac-22 is even more pronounced (DT=ca. 60°C). This means, that the disturbance necessary to obtain a centre of chirality by branching an alkyl chain is more severe than that one caused by the bent structure (Fig. 2) of the 1,3-disubstituted allene unit necessary to obtain an axis of chirality. It was also possible to get smectic C compounds incorporating two axes of chirality at each end of a rigid 2,5-diphenyl- 1,3,4-thiadiazole mesogen (compound 14)‡.However, the pterphenyl derivative 15‡ is only a nematic compound. In order to further investigate the potential of the allene moiety a laterally substituted terphenyl derivative (compound rac-16) has also been synthesized. ‡ Compounds rac-14 and rac-15 are mixtures of two diastereomers. J. Mater. Chem., 1997, 7(9), 1713–1721 1715transition temperatures to lower values was observed for compound (R)-8c and, even more pronounced, for the bromo derivative 20.This can be explained by thermal decomposition (Claisen rearrangement) at temperatures close to the clearing point of these compounds. In conclusion, we have prepared the first axial chiral allenylacetates with broad Sc*-phases. These compounds exhibit ferroelectric properties, but the values obtained for their spon- Fig. 2 Molecular model of the allene derivative 8c taneous polarization are smaller than those of the corresponding allenyl ethers. Experimental General considerations 1H NMR, 13C NMR and 19F NMR spectra were recorded on a Varian Gemini (200 MHz) or a Varian Unity (500 MHz) spectrometer, respectively. IR spectra were recorded on Perkin- Elmer FT-IR 1000 spectrometers. Phase transition temperatures were measured using a Mettler FP 82 HT hot stage and control unit in conjunction with a Nikon Optiphot-2 polarizing To increase the polarity of the substituents at the allene microscope, and were confirmed by dierential scanning calormoiety, compound rac-20 having a bromine atom directly imetry on a Perkin-Elmer DSC-7.Mass spectra were recorded attached to the allene unit was synthesized. Because decompoon an AMD 402 mass spectrometer (70 eV). Microanalyses sition occurs at temperatures as low as 100 °C, the synthesis were performed using an Carlo-Erba 1104 and Leco CHNSof an optically active compound 20 was not attractive. 932 elemental analyser.Refractive indices were measured using a Carl Zeiss Forsina refractometer. Thin layer chromatography was performed on Merck TLC aluminium sheets (silica gel 60 F254) and visualized under UV light by treatment with iodine vapour, or by using a spray-solution of bromothymol blue and developing with gaseous ammonia. Column chromatography was performed with silica gel from Merck [0.040–0.063 mm (flash chromatography) or 0.063–0.20 mm].Solvents were purified and dried according to standard procedures. 29 But-1-yn-3-ol (Aldrich), oct-1-yn-3-ol (Aldrich), (R)- Alpine borane (Aldrich) and N-cyclohexyl-N¾-(2-morpholinoethyl) carbodiimide methotoluene-p-sulfonate (Aldrich) were The thermal stability of the allene derivatives depends largely used as obtained. 4-(5-Undecyl-1,3,4-thiadiazol-2-yl )phenol,20 on the substitution pattern at the allene moiety and also on 4-[5-(4-alkoxyphenyl)-1,3,4-thiadiazol-2-yl]phenols,20 4-[5- the type of rigid core. With the exception of the compounds (4-decylphenyl)-1,3,4-thiadiazol-2-yl]phenol,20 4-(5-octyloxy- rac-13 and rac-20 all other allene derivatives synthesized were pyrimidin-2-yl)phenol,21 4-[5-(4-butoxyphenyl)pyrimidin-2- thermally stable at least up to 100 °C.This was confirmed by yl]phenol,21 4-(4¾-undecyloxybiphenyl-4-yloxycarbonyl)phen- annealing samples at this temperature for 1 h. The transition ol,22 4-[5-(4-hydroxyphenyl)-1,3,4-thiadiazol-2-yl]phenol,23 temperatures and the 1H NMR spectra remain unchanged 1,4-bis(4-hydroxyphenyl)-2-methylbenzene23 and 2-decyloxy- after this time.However at the clearing temperatures (>150 °C) 5-[4-(4-decyloxyphenyl)phenyl]benzyl alcohol30 were synthe- slow decomposition occurs which can be seen by the slight sized according to the references given. decrease in the clearing temperature. Synthesis of the allenylacetic acids 6a–6c Properties of the optically active allene derivatives Dec-1-yn-3-ol, rac-3c.Compound rac-3c was obtained as After investigating the liquid crystalline properties of the described for the synthesis of rac-undec-1-yn-3-ol12 from ethynracemic derivatives, some thiadiazole derivatives were syntheylmagnesium bromide (0.2 mol) and octanal (17.9 g, 0.14 mol). sized in their enantiomerically enriched forms. The phase Yield 11.9 g (55%); bp 50–53 °C at 0.05 mbar; nD20: 1.449; dH transitions of these compounds are summarized and compared (500 MHz; CDCl3; J/Hz): 0.87 (t, 3H, J 6.5, CH3), 1.2–1.52 to a related allenyl ether [cf.(R)-111] in Table 3. (m, 10H, CH2), 1.73 (m, 2H, CH2), 1.93 (s, 1H, br s, OH), 2.44 Compound (R)-8c not only exhibits a broad chiral smectic (d, 1H, J 2.1, COCMH), 4.35 (m, 1H, CH2CH), dC(126 MHz; C, but also a chiral nematic phase as well as a blue phase CDCl3): 96.56 (COCMH), 72.81 (COCMH), 62.35 (tert-CH), (Fig. 3) in a small temperature range. 37.64, 31.85, 31.73, 29.16, 24.98, 22.61, 14.05 (CH3); nmax The spontaneous polarization of this compound was investi- (neat)/cm-1 3600–3200 (OH), 3580 (OH), 3300 (COCMH), gated by means of the triangular field method28 after aligning 2920, 2850, 2100 (COC), 1460, 1380, 1300.the sample in a homogeneous bookshelf configuration, using a 4 mm liquid crystal cell (EHC, Tokyo). A plot of the spon- Dec-1-yn-3-one, 4c. A solution of chromium trioxide (6 g, taneous polarization Ps versus the temperature T is given in 0.06 mol) and conc. sulfuric acid (5 ml) in water (20 ml ) was Fig. 4. The steep, steplike decrease of Ps at ca. 140 °C reflects added during 2 h to a stirred solution of rac-3c (7.7 g, 0.05 mol) the first-order Sc*–N* phase transition.The spontaneous polarin acetone (20 ml ) at 5–10 °C. After stirring for an additional ization of allenylacetate (R)-8c is significantly lower than for 2 h at room temp., the mixture was diluted with water (200 ml). the analogous allenyl ether (R)-1.§ A gradual shift of phase The reaction mixture was extracted with diethyl ether (3×100 ml).After drying the organic solutions (Na2SO4), the § It has to be considered that the enantiomeric purity of both comsolvent was removed under reduced pressure and the residue pounds is dierent. Linear extrapolation of the Ps value of (R)-8c to was purified by distillation in vacuo to yield a colourless liquid. an ee of 95% [which is the enantiomeric purity of (R)-1] would give an Ps of ca. 15–16 nC cm-2. Yield 5.6 g (73%); bp 72–75 °C at 18–20 mbar; dH(200 MHz; 1716 J. Mater. Chem., 1997, 7(9), 1713–1721Table 3 Transition temperatures and corresponding enthalpy values (italicised) of the enantiomerically enriched allenylacetates (R)-7c, (R)-8c, (R)-9c and (R)-23 and the allenyl ethyl (R)-1 phase transitions T /°C R X comp.enthalpy values DH/kJ mol-1 % ee Ps/nC cm-2 OOC (R)-7c C1 62 C2 68 Iso 73 10.5 34.9 O (R)-1 C 47 SC* 115 N* 130 BP 131 Iso 95 38 OOC (R)-8c C 76 SC* 152 N* 163 BP 164 Iso 73 12 37.3 2.2 0.8 OOC (R)-9c C1 60 C2 81 SC* 157 Iso 73 5.7 23.2 5.4 OOC (R)-23 C 38 Iso 73 26.5 (R)-Dec-1-yn-3-ol, (R)-3c. (R)-Alpine borane in tetrahydrofuran (108 ml of a 0.5 M solution, 54 mmol) was placed in a 500 ml three-necked flask, equipped with thermometer, magnetic stirrer, argon inlet and outlet.Tetrahydrofuran was removed under reduced pressure (12 mbar, 30 °C) and the vacuum was replaced by argon. The resulting oil was cooled to a temperature between 0 and -5 °C and 4c (5.5 g, 36 mmol) was added dropwise. During the addition the temperature was kept below 0 °C.After the addition was complete, the cold bath was removed and the mixture was allowed to warm to room temp. The orange mixture was stirred at this temperature until TLC indicated complete consumption of 4c. To destroy excess Alpine borane, acetaldehyde (3 ml) was added dropwise, whilst the temperature was maintained below 30 °C. The resulting mixture was stirred at room temp.for 1 h. Tetrahydrofuran (50 ml ) was added, followed by sodium Fig. 3 Optical texture (crossed polarizers) of the blue phase of compound (R)-8c at 163.5 °C hydroxide (50 ml of a 3 M aqueous solution). After this, hydrogen peroxide (50 ml of a 30% aqueous solution) was added dropwise (CAUTION! exothermic reaction). During the addition, the temperature was kept below 40 °C.After the addition was complete, the mixture was stirred for 2 h at 40 °C. After the mixture had cooled to room temp., it was poured into diethyl ether (200 ml) and the phases were separated. The aqueous layer was extracted with diethyl ether (3×100 ml) and the combined organic layers were washed with brine (100 ml) and dried over Na2SO4. After filtration, the solvent was removed under reduced pressure (18 mbar, 25 °C) and the resulting oil was fractionated by chromatography on silica gel ( light petroleum–ethyl acetate 1052, 40 cm×8 cm, Rf 0.3) to aord (R)-3c (3.8 g, 24.7 mmol, 69%) as a colourless oil.[a]D24 3.48 (c 1.61 CHCl3), 87% ee (Mosher’s method). The analytical data of (R)-3c correspond to those given for rac-3c. Ethyl dodeca-3,4-dienoate, rac-5c.A mixture of rac-3c (10.9 g, 0.07 mol), propanoic acid (0.4 g, 5 mmol) and triethyl orthoacetate (81 g, 0.5 mol) was heated for 8–10 h at 130 °C Fig. 4 Spontaneous polarization Ps of compound (R)-8c vs. under an argon atmosphere. After cooling, the mixture was temperature concentrated in vacuo, diluted with diethyl ether (100 ml), washed with aq. NaHCO3 (2×40 ml) and brine (2×40 ml), and was dried over Na2SO4.Distillation under reduced press- CDCl3; J/Hz): 0.87 (t, 3H, J 6.6, CH3); 1.2–1.38 (m, 8H, CH2), 1.56–1.75 (m, 2H, CH2), 2.58 (t, 2H, J 7.6, COCH2), 3.2 (s, ure gave pure rac-5c. Yield 13.3 g (85%); bp 70–74 °C at 0.04 mbar; nD20 1.4596; dH(500 MHz; CDCl3; J/Hz): 0.84 (t, 1H, COCMH); dc(126 MHz, CDCl3): 187.63 (CNO), 81.4 (COCMH), 78.27 (COCMH), 45.38, 33.85, 31.52, 28.87, 23.69, 3H, J 6.6, CH3), 1.42–1.44 (m, 13H, CH2, COOCH2CH3), 1.9–2.01 (m, 2H, CH2), 2.99 (dd, 2H, 3J 2.9, 5J 6.8, 22.49, 13.96 (CH3).J. Mater. Chem., 1997, 7(9), 1713–1721 1717CHNCNCHCH2), 4.12 (q, 2H, J 2.96, COOCH2CH3), reaction mixture was quenched by adding water (100 ml). The aqueous phase was twice extracted with diethyl ether 5.09–5.24 (m, 2H, HCNCNCH); dc(126 MHz, CDCl3): 205 (CNCNC), 171.6 (CNO), 92.2 (CNCNC), 84.1 (CNCNC), (2×100 ml).The combined organic phases were washed twice with saturated NaHCO3 (50 ml ), brine (50 ml ) and finally with 60.6 (CH2COOEt), 35.1, 31.8, 29.1, 29.02, 29.03, 28.5, 22.6, 14.21 (CH3), 14.05 (CH3); nmax/cm-1 (neat) 2960, 2925, 2845, water (50 ml ). After drying over Na2SO4 the solvent was removed under reduced pressure and the residue was purified 1960 (CNCNC), 1730 (CNO), 1470, 1400, 1370, 1320.by distillation in vacuo to give a colourless liquid. Yield 10.1 g (68%); nD20 1.4876; bp 53–55 °C at 0.04 mbar; dH(200 MHz; Ethyl (R)-dodeca-3,4-dienoate, (R)-5c. Prepared as described CDCl3; J/Hz): 0.9 (t, 3H, J 6.6, CH3), 1.22–1.5 (m, 6H, CH2), for rac-5c from (R)-3c (3.4 g, 22 mmol).Yield 3.8 g (77%); 1,82 (s, 1H, OH), 1.86–1.95 (m, 2H, CH2), 4.39 (dt, J 5.4, [a]D24-40.35 (c 4.5 in CHCl3); the other analytical data of 1H, CHOH). (R)-5c correspond to those given for rac-5c. Ethyl 3-bromodeca-3,4-dienoate, rac-18. Synthesized accord- Ethyl hexa-3,4-dienoate, rac-5a. Prepared as described for ing to the procedure given for rac-5c from rac-17 (10.1 g, rac-5c from rac-3a (8.6 g, 0.12 mol).Yield 12 g (70%); bp 49 mmol). Yield 6.2 g (46%); nD20 1.4902; bp 105–110 °C at 63–65 °C at 12 mbar; nD20 1.4548; dH(500 MHz; CDCl3; J/Hz): 0.15 mbar; dH(200 MHz; CDCl3; J/Hz): 0.88 (t, 3H, J 6.8, 1.24 (t, 3H, J 6.6, COOCH2CH3), 1.64 (dd, 3H, 3J=6.9, 5J= CH3), 1.2–1.8 (m, 9H, COOCH2CH3, CH2), 2.04–2.18 (m, 2H, 3.3, CH3CHNCNCH), 2.98 (dd, 2H, 3J 6.9, 5J 2.9, CH2), 3.41 (d, 2H, 5J 2.3, HCNCNCBrCH2), 4.18 (q, 2H, J CHNCNCHCH2), 4.13 (q, 2H, J 2.9, COOCH2CH3), 7.2, COOCH2CH3), 5.35–5.45 (m, 1H, HCNCNCBr). 5.09–5.15 (m, 1H, HCNCNCH), 5.15–5.20 (m, 1H, HCNCNCH). 3-Bromodeca-3,4-dienoic acid, rac-19. Synthesized from rac- Ethyl deca-3,4-dienoate, rac-5b. Prepared as described for 18 (1.11 g, 4 mmol) according the procedure given for rac-6c.rac-5c from rac-3b (22.7 g, 0.18 mol). Yield 23.6 g (67%); bp Purification by column chromatography (CHCl3 MeOH; v/v 63–65 °C at 0.15 mbar; nD20 1.4563; dH(500 MHz; CDCl3; 1051) gave rac-19 as a colourless oil. Yield 350 mg (35%); dH J/Hz): 0.85 (t, 3H, J 6.5, CH3), 1.24–1.44 (m, 9H, CH2, (200 MHz; CDCl3; J/Hz): 0.90 (t, 3H, CH3), 1.8–1.2 (m, 6H, COOCH2CH3), 1.92–2.05 (m, 2H, CH2), 2.97 (dd, 2H, 3J 6.9, CH2), 2.08–2.18 (m, 2H, CH2), 3.59 (d, 2H, 5J 1.6, 5J 3.1, CHNCNCHCH2), 4.12 (q, 2H, J 2.9, COOCH2CH3), HCNCNCBrCH2), 5.40 (m, 1H, HCNCNCBr). 5.10–5.23 (m, 2H, HCNCNCH). General procedure for the esterification of the alka-3,4-dienoic Dodeca-3,4-dienoic acid, rac-6c. A mixture consisting of acid hydrochloric acid (20 ml, 20%), dioxane (15 ml ), tetrahydro- The appropriate phenolic compound (0.8 mmol), N-cyclofuran (THF) (6 ml ) and rac-5c (1.12 g, 5 mmol) was vigorously hexyl-N¾-(2-morpholinoethyl)carbodiimide methotoluene-pstirred for 24 h at room temp.The reaction mixture was poured sulfonate (1.1 mmol 465 mg) and 4-dimethylaminopyridine into diethyl ether (100 ml), the organic layer was separated, (DMAP; 30 mg) were dissolved in dry chloroform (30 ml ).The washed with saturated NaHCO3 (2×40 ml) and brine solution was stirred magnetically for 5 min at room temp. The (2×40 ml), and was dried with Na2SO4. After filtration, the appropriate alka-3,4-dienoic acid (1 mmol), dissolved in dry solvent was removed under reduced pressure. The residue was chloroform (5 ml), was added with a syringe.The mixture was purified by column chromatography using CHCl3–MeOH (v/v stirred at 20 °C until no starting material could be detected by 1051) as eluent to obtain rac-6c as a pale-yellow oil. Yield TLC (ca. 20 h). Afterwards, it was poured into water (30 ml ) 0.4 g (40%); nD20 1.4702; dH(500 MHz; CDCl3; J/Hz): 0.87 (t, and the phases were separated. The aqueous layer was 3H, J 6.45, CH3), 1.24–1.48 (m, 10H, CH2), 1.95–2.05 (m, 2H, extracted with chloroform (2×50 ml) and the combined CH2), 3.07 (dd, 2H, CHNCNCHCH2), 5.10–5.25 (m, 2H, organic layer was washed with saturated NaHCO3 (50 ml ) HCNCNCH), 8.3 (s, br, 1H, COOH).and brine (50 ml ) and dried (Na2SO4). After filtration the solvent was removed under reduced pressure and the resulting (R)-Dodeca-3,4-dienoic acid, (R)-6c.Prepared as described crude product was purified by chromatography on silica gel for rac-6c from (R)-5c (0.9 g, 4 mmol). Yield 0.32 g (40%); (chloroform–methanol, v/v 2051) and crystallized several times [a]D24 -30.68 (c 0.88 CHCl3); the NMR data correspond to from ethanol. those given for rac-6c. 4-(5-Undecyl-1,3,4-thiadiazol-2-yl)phenyl hexa-3,4-dienoate, Hexa-3,4-dienoic acid, rac-6a.Prepared as described for rac- rac-7a. Synthesized from 4-(5-undecyl-1,3,4-thiadiazol-2- 6c from rac-5a (1.4 g, 10 mmol). Purification by column chromyl )phenol and rac-6a. Yield 105 mg (46%); mp 68 °C (Found: atography (CHCl3–MeOH; v/v 1051) gave rac-6a as a colour- C, 69.63; H, 8.11; N, 6.67; S, 7.64%; C25H34O2N2S requires C, less oil. Yield 0.4 g (35%); dH(200 MHz; CDCl3; J/Hz): 1.65 70.39; H, 8.03; N, 6.57; S, 7.51%); dH(200 MHz; CDCl3; J/Hz): (m, 3H, CH3CHNCNCH), 3.05 (m, 2H, CHNCNCHCH2), 0.85–0.89 (m, 3H, CH3), 1.2–1.48 (m, 16H, CH2), 1.68 (dd, 3H, 5.13–5.19 (m, 2H, HCNCNCH), 9.5 (s, br, 1H, COOH). 3J 6.8, 5J 2.7, CH3), 1.78–1.88 (m, 2H, CH2), 3.1 (t, 2H, J 7.6, ArCH2), 3.27 (dd, 2H, 3J 6.9, 5J 2.8, HCNCNCHCH2O), Deca-3,4-dienoic acid, rac-6b.Prepared as described for rac- 5.20–5.30 (m, 2H, HCNCNCH), 7.20 (d, 2H, J 8.8, ArH), 7.94 6c from rac-5b (1.3 g, 6.6 mmol). Yield 0.5 g (45%); nD20 1.4741; (d, 2H, J 8.8, ArH); m/z 426 (M+, 71%), 398 (4), 383 (5), 355 dH(200 MHz; CDCl3; J/Hz): 0.87 (t, 3H, J 7.1, CH3), 1.24–1.44 (4), 333 (100), 299 (11), 286 (25), 274 (22), 261 (10), 245 (24), (m, 6H, CH2), 1.98 (m, 2H, CH2), 3.06 (m, 2H, 219 (4), 205 (37), 192 (83), 137 (17), 95 (24), 67 (44).CHNCNCHCH2), 5.16–5.23 (m, 2H, HCNCNCH), 9.5 (s, br, 1H COOH). (R)-4-(5-Undecyl-1,3,4-thiadiazol-2-yl )phenyl dodeca-3,4- dienoate (R)-7c. Synthesized from 4-(5-undecyl-1,3,4-thiadia- Synthesis of 3-bromodeca-3,4-dienoic acid, rac-19 zol-2-yl )phenol and (R)-6c. Yield 60 mg (45%); transitions (°C): C1 62 C2 68 Iso; [a]D24 -30.95 (c 0.84 CHCl3) (Found: 1-Bromooct-1-yn-3-ol, rac-17.Bromine (7 ml, 21.7 g, 0.135 mol) was added slowly to aqueous KOH (4 M, 200 ml) C, 73.06; H, 9.23; N, 5.21; S, 5.18%; C31H46O2N2S requires C, 72.90; H, 9.08; N, 5.48; S, 6.28%); dH(500 MHz; CDCl3; J/Hz): while the temperature was kept below 5 °C. This freshly prepared solution was added within 10 min to rac-3b (7.25 g, 0.85–0.88 (m, 6H, CH3), 1.2–1.44 (m, 26H, CH2), 1.79–1.85 (m, 2H, CH2), 2.0–2.05 (m, 2H, CH2), 3.11 (t, 3H, J 7.6, ArCH2), 57 mmol) at 20 °C.After vigorously stirring for 30 min the 1718 J. Mater. Chem., 1997, 7(9), 1713–17213.27 (dd, 2H, 3J 7.2, 5J 3.0, HCNCNCHCH2O), 5.23–5.33 (m, 5.26; S, 6.02%); dH(500 MHz; CDCl3; J/Hz): 0.89–0.86 (m, 6H, CH3), 1.2–1.48 (m, 16H, CH2), 1.77–1.83 (m, 2H, CH2), 2H, HCNCNCH), 7.20 (d, 2H, J 8.5, ArH), 7.94 (d, 2H, J 8.5, ArH); m/z 510 (M+, 56%), 482 (10), 467 (3), 439 (3), 411 (2), 2.0–2.05 (m, 2H, CH2), 3.28 (dd, 2H, 3J 7.1, 5J 2.7, HCNCNCHCH2O), 4.01 (t, 3H, J 6.5, OCH2), 5.23–5.33 (m, 391 (4), 383 (8), 370 (13), 358 (11), 342 (3), 333 (100), 205 (18), 192 (33), 179 (20), 137 (8). 2H, HCNCNCH), 6.97 (d, 2H, J 8.7, ArH), 7.23 (d, 2H, J 8.9, ArH), 7.91 (d, 2H, J 8.9, ArH), 7.99 (d, 2H, J 8.8, ArH); m/z 532 (M+, 27%), 504 (1), 382 (100), 270 (40), 249 (3), 151 (17), 4-[5-(4-Butoxyphenyl)-1,3,4-thiadiazol-2-yl]phenyl hexa- 3,4-dienoate, rac-8a. Synthesized from 4-[5-(4-butoxyphenyl)- 137 (8). 1,3,4-thiadiazol-2-yl]phenol and rac-6a. Yield 110 mg (62%); transitions (°C): C 102 SC 161 N 224 Iso (Found: C, 68.69; H, 4-[5-(4-Octyloxyphenyl)-1,3,4-thiadiazol-2-yl]phenyl dodeca-3,4-dienoate, rac-9c.Synthesized from 4-[5-(4-octyloxy- 5.66; N, 6.37; S, 7.42%; C24H24O3N2S requires C, 68.55; H, 5.75; N, 6.66; S, 7,62%; dH(500 MHz; CDCl3; J/Hz): 0.98 (t, phenyl)-1,3,4-thiadiazol-2-yl]phenol and rac-6c. Yield 100 mg (61%); transitions (°C): C 83 SC 158 Iso (Found: C, 72.96; H, 3H, J 7.3, CH3), 1.5 (m, 2H, CH2), 1.69 (dd, 3H, 3J 6.9, 5J 3.4, CH3), 1.80 (m, 2H, CH2), 3.28 (dd, 2H, 3J 6.8, 5J 3, 7.67; N, 4.87; S, 5.49%; C34H44O3N2S requires C, 72.82; H, 7.91; N, 5.00; S, 5.72%); dH(200 MHz; CDCl3; J/Hz): 0.87 (m, HCNCNCHCH2O), 4.02 (t, 3H, J 6.4, OCH2), 5.19–5.31 (m, 2H, HCNCNCH), 6.97 (d, 2H, J 8.8, ArH), 7.23 (d, 2H, J 8.8, 6H, CH3), 1.18–1.48 (m, 20H, CH2), 1.76–1.84 (m, 2H, CH2), 2.0 (m, 2H, CH2), 3.28 (dd, 2H, HCNCNCHCH2O), 4.00 (t, ArH), 7.91 (d, 2H, J 8.9, ArH), 8.00 (d, 2H, J 8.8, ArH). 3H, J 6.3, OCH2), 5.26–5.31 (m, 2H, HCNCNCH), 6.97 (d, 2H, J 8.8, ArH), 7.22 (d, 2H, J 8.8, ArH), 7.92 (d, 2H, J 8.8, 4-[5-(4-Butoxyphenyl)-1,3,4-thiadiazol-2-yl]phenyl deca- 3,4-dienoate, rac-8b. Synthesized from 4-[5-(4-butoxyphenyl)- ArH), 7.99 (d, 2H, J 8.8, ArH); m/z 560 (M+, 54%), 532 (2), 382 (100), 270 (65), 249 (5), 242 (3), 199 (4), 179 (10), 151 1,3,4-thiadiazol-2-yl]phenol and rac-6b.Yield 180 mg (67%); transitions (°C): C 61 SC 147 N 167 Iso (Found: C, 70.42; H, (13), 137 (17). 6.98; N, 5.67; S, 6.56%; C28H32O3N2S requires C, 70.56; H, 6.77; N, 5.88; S, 6.73%); dH(500 MHz; CDCl3; J/Hz): 0.88 (t, (R)-4-[5-(4-Octyloxyphenyl )-1,3,4-thiadiazol-2-yl]phenyl dodeca-3,4-dienoate, (R)-9c.Synthesized from 4-[5-(4- 3H, J 7.1, CH3), 0.98 (t, 3H, J 7.3, CH3), 1.24–1.49 (m, 8H, CH2), 1.79 (m, 2H, CH2) 2.03 (m, 2H, CH2), 3.28 (dd, 2H, 3J octyloxyphenyl)-1,3,4-thiadiazol-2-yl]phenol and (R)-6c. Yield 110 mg (65%); transitions (°C): C1 60 C2 81 Sc* 157 Iso; [a]D24 6.8, 5J 2.8, HCNCNCHCH2O), 4.02 (t, 3H, J 6.6, OCH2), 5.25–5.33 (m, 2H, HCNCNCH), 6.97 (d, 2H, J 8.8, ArH), 7.23 -20 (c 1.1 CHCl3) (Found: C, 72.96; H, 7.63; N, 4.87; S, 5.49%; C34H44O3N2S requires C, 72.82; H, 7.91; N, 5.00; S, 5.72%); (d, 2H, J 8.6, ArH,), 7.92 (d, 2H, J 8.6, ArH), 8.00 (d, 2H, J 8.5, ArH); m/z 476 (M+, 28%), 448 (1), 424 (1), 326 (100), 270 dH(500 MHz; CDCl3; J/Hz): 0.87 (m, 6H, 2CH3), 1.24–1.49 (m, 20H, CH2), 1.79 (m, 2H, CH2), 2.03 (m, 2H, CH2), 3.28 (dd, (37), 193 (2), 151 (19), 137 (10), 81 (3), 67 (8); lmax/nm (CHCl3) 324.7 (0.76). 2H, 3J 7.1, 5J 2.9, HCNCNCHCH2O), 4.02 (t, 3H, J 6.6, OCH2), 5.25–5.33 (m, 2H, HCNCNCH), 6.97 (d, 2H, J 8.8, ArH), 7.23 (d, 2H, J 8.6, ArH), 7.92 (d, 2H, J 8.6, ArH), 8.00 4-[5-(4-Butoxyphenyl)-1,3,4-thiadiazol-2-yl]phenyl dodeca- 3,4-dienoate, rac-8c.Synthesized from 4-[5-(4-butoxyphenyl)- (d, 2H, J 8.5, ArH); m/z 560 (M+, 38%), 532 (1), 382 (100), 270 (52), 249 (5), 179 (14), 151 (12), 137 (15). 1,3,4-thiadiazol-2-yl]phenol and rac-6c. Yield 50 mg (24%); transitions (°C): C 76 SC 149 N 164 Iso (Found: C, 71.11; H, 7.15; N, 5.52; S, 6.39%; C30H36O3N2S requires C, 71.40; H, 4-[5-(4-Decylphenyl)-1,3,4-thiadiazol-2-yl]phenyl deca-3,4- dienoate, rac-10b.Synthesized from 4-[5-(4-decylphenyl)-1,3,4- 7.19; N, 5.55; S, 6.35%); dH(200 MHz; CDCl3; J/Hz): 0.87–0.82 (m, 3H, CH3), 0.97 (t, 3H, J 7.3, CH3), 1.2–1.48 (m, 12H, CH2), thiadiazol-2-yl]phenol and rac-6b. Yield 35 mg (22%); transitions (°C): C 58 SC 149 Iso (Found: C, 75.05; H, 8.05; N, 5.3; 1.74–1.82 (m, 2H, CH2), 2.0 (m, 2H, CH2), 3.28 (m, 2H, HCNCNCHCH2O), 4.01 (t, 3H, J 6.4, OCH2), 5.23–5.31 (m, S, 5.1%; C34H44O3N2S requires C, 75.0; H, 8.1; N, 5.1; S, 5.9%); dH(500 MHz; CDCl3; J/Hz): 0.8–0.97 (m, 6H, CH3), 2H, HCNCNCH), 6.97 (d, 2H, J 9.1, ArH), 7.22 (d, 2H, J 8.8, ArH), 7.91 (d, 2H, J 9.1, ArH), 8.00 (d, 2H, J 8.4, ArH); 1.2–1.72 (m, 22H, CH2), 1.97–2.08 (m, 2H, CH2), 2.65 (t, 2H, J 7.7, ArCH2), 3.27 (dd, 2H, 3J 6.9, 5J 2.7, HCNCNCHH2O), dC(126 MHz, CDCl3): 13.82, 14.08, 19.21, 22.64, 28.47, 28.99, 29.05, 29.11, 31.18, 31.84, 35.15, 67.97, 83.36, 92.88, 115.07, 5.23–5.28 (m, 1H, HCNCNCH), 5.28–5.31 (m, 1H, HCNCNCH), 7.23 (d, 2H, J 8.0, ArH), 7.28 (d, 2H, J 8.0, 122.35, 128.05, 129.01, 129.49, 152.68, 155.95, 161.63, 165.6, 168.2, 169.7, 205.35; m/z 504 (M+, 17%), 326 (100), 270 (34), ArH), 7.89 (d, 2H, J 8.9, ArH), 8.01 (d, 2H, J 8.8, ArH). 242 (2), 199 (3), 179 (10), 151 (10), 137 (12), 119 (2). 4-[5-(4-Decylphenyl)-1,3,4-thiadiazol-2-yl]phenyl dodeca- 3,4-dienoate, rac-10c. Synthesized from 4-[5-(4-decylphenyl)- (R)-4-[5-(4-Butoxyphenyl )-1,3,4-thiadiazol-2-yl]phenyl dodeca-3,4-dienoate, (R)-8c. Synthesized from 4-[5-(4-butoxy- 1,3,4-thiadiazol-2-yl]phenol and rac-6c. Yield 155 mg (42%); transitions (°C): C 65 SC 137 Iso (Found: C, 75.45; H, 8.42; N, phenyl)-1,3,4-thiadiazol-2-yl]phenol and (R)-6c.Yield 150 mg (55%); transitions (°C): C 76 Sc* 152 N* 163 BP 164 Iso; 4.48; S, 5.5%; C36H48O2N2S requires C, 75.48; H, 8.45; N, 4.89; S, 5.6%); dH(200 MHz; CDCl3; J/Hz): 0.8–0.97 (m, 6H, CH3), [a]D24 -26.96 (c 2.3 CHCl3) (Found: C, 71.29; H, 7.33; N, 5.55; S, 6.41%; C30H36O3N2S requires C, 71.4; H, 7.19; N, 5.55; 1.2–1.72 (m, 26H, CH2), 1.97–2.08 (m, 2H, CH2), 2.65 (t, 2H, J 7.5, ArCH2), 3.28 (m, 2H, HCNCNCHCH2O), 5.23–5.31 S, 6.35%); dH(200 MHz; CDCl3; J/Hz): 0.86 (t, 3H, J 6.5, CH3), 0.97 (t, 3H, J 7.3, CH3), 1.2–1.48 (m, 12H, CH2), (m, 2H, HCNCNCH), 7.21–7.34 (m, 4H, ArH), 7.89 (d, 2H, J 8.9, ArH), 8.01 (d, 2H, J 8.8, ArH); m/z 572 (M+, 10%), 394 1.72–1.84 (m, 2H, CH2), 1.95–2.08 (m, 2H, CH2), 3.28 (dd, 2H, 3J 6.9, 5J 3.0, HCNCNCHCH2O), 4.02 (t, 3H, J 6.4, OCH2), (27), 363 (100), 331 (4), 281 (6), 265 (47), 239 (7), 207 (14), 199 (17), 187 (7), 139 (4). 5.23–5.31 (m, 2H, HCNCNCH), 6.97 (d, 2H, J 8.8, ArH), 7.22 (d, 2H, J 8.7 ArH), 7.91 (d, 2H, J 8.9, ArH), 8.00 (d, 2H, J 8.7, ArH); m/z 504 (M+, 22%), 326 (100), 270 (35), 193 (4), 179 4-(5-Octyloxypyrimidin-2-yl)phenyl hexa-3,4-dienoate, rac- 11a.Synthesized from 4-(5-octyloxypyrimidin-2-yl)phenol and (12), 151 (11), 137 (11), 119 (3). rac-6a. Yield 45 mg (34%); transitions (°C): C 78 (SA 75) Iso (Found: C, 72.68; H, 7.64; N, 6.63%; C24H30O3N2 requires C, 4-[5-(4-Octyloxyphenyl)-1,3,4-thiadiazol-2-yl]phenyl deca- 3,4-dienoate, rac-9b. Synthesized from 4-[5-(4-octyloxyphenyl)- 73.07; H, 7.66; N, 7.10%); dH(200 MHz; CDCl3; J/Hz): 0.85–0.89 (t, 3H, J 6.6, CH3), 1.18–1.88 (m, 15H, CH2, 1,3,4-thiadiazol-2-yl]phenol and rac-6b.Yield 120 mg (57%); transitions (°C): C 82 SC 166 Iso (Found: C, 71.96; H, 7.54; N, H3CHNCNC), 3.27 (dd, 2H, 3J 6.9, 5J 3.3, HCNCNCHMCH2O), 4.08 (t, 3H, J 6.5, OCH2), 5.18–5.32 5.23; S, 6.11%; C32H40O3N2S requires C, 72.15; H, 7.57; N, J.Mater. Chem., 1997, 7(9), 1713–1721 1719(m, 2H, HCNCNCH), 7.18 (d, 2H, J 8.8, ArH), 8.36 (d, 2H, C, 81.22; H, 7.69%); dH(200 MHz; CDCl3; J/Hz): 0.84–0.91 (m, 6H, CH3), 1.2–1.48 (m, 12H, CH2), 1.94–2.06 (m, 4H, CH2), J 8.8, ArH), 8.43 (s, 2H, ArH). 2.32 (s, 3H, ArCH3), 3.27 (dd, 4H, 3J 6.7, 5J 2.5, CHNCHCH2O), 5.22–5.35 (m, 4H, HCNCNCH), 7.14 (d, (R)-4-(5-Octylpyrimidin-2-yl )phenyl dodeca-3,4-dienoate, (R)-23.Synthesized from 4-(5-octylpyrimidin-2-yl)phenol and 2H, J 8.8, ArH), 7.16 (d, 2H, J 9.0, ArH), 7.24–7.44 (m, 7H, ArH), 7.60 (d, 2H, J 8.6, ArH); m/z 576 (M+, 18%), 426 (37), (R)-6c. Yield 50 mg (35%); mp 38 °C; dH(200 MHz; CDCl3; J/Hz): 0.82–0.95 (m, 6H, CH3), 1.2–1.86 (m, 22H, CH2), 276 (100), 151 (8). 1.95–2.05 (m, 2H, CH2), 2.6 (t, 2H, J 7.2, ArCH2), 3.27 (dd, 2H, 3J 6.8, 5J 2.9, HCNCNCHCH2O), 5.21–5.34 (m, 2H, 2-Decyloxy-5-[4-(4-decyloxyphenyl)phenyl]benzyl deca-3,4- HCNCNCH), 7.20 (d, 2H, J 9.0, ArH), 8.43 (d, 2H, J 8.9, dienoate, rac-16.Synthesized from 2-decyloxy-5-[4-(4-decyl- ArH), 8.59 (s, 1H, ArH). oxyphenyl)phenyl]benzyl alcohol and rac-6b. Yield 25 mg (34%); transitions (°C): C 60 SC 66 N 71 Iso; dH(500 MHz; 4-[5-(4-Butoxyphenyl)pyrimidin-2-yl]phenyl deca-3,4-dieno- CDCl3; J/Hz): 0.82–0.92 (m, 9H, CH3), 1.11–1.48 (m, 32H, ate, rac-12b.Synthesized from 4-[5-(4-butoxyphenyl )pyrimid- CH2), 1.77–1.83 (m, 4H, CH2), 1.92–1.98 (m, 2H, CH2), 3.08 in-2-yl]phenol and rac-6b. Yield 45 mg (22%); transitions (°C): (dd, 2H, HCNCNCHCH2O), 3.98–4.03 (m, 4H, OCH2), C 144 SC 176 Iso; dH(500 MHz; CDCl3; J/Hz): 0.85–0.90 (m, 5.14–5.26 (m, 2H, HCNCNCH), 5.25 (s, 2H, ArCH2OOC), 3H, CH3), 0.98 (t, 3H, J 7.3, CH3), 1.25–1.6 (m, 8H, CH2), 6.92–6.95 (m, 4H, ArH), 7.20–7.38 (m, 1H, ArH), 7.54–7.58 (m, 1.75–1.86 (m, 2H, CH2), 2.01–2.04 (m, 2H, CH2), 3.29 (dd, 2H, 6H, ArH); m/z found 722.5290 (M+; 100%), C49H70O4 3J 7.1, 5J 2.7, HCNCNCHCH2O,), 4.04 (t, 2H, J 6.5, OCH2), requires 722.5274. 5.24–5.28 (m, 1H, HCNCNCH), 5.30–5.34 (m, 1H, HCNCNCH), 6.99 (d, 2H, J 8.8, ArH), 7.25 (d, 2H, J 8.7, 4-[5-(4-Butoxyphenyl )-1,3,4-thiadiazol-2-yl]phenyl 3-bromo- ArH), 7.60 (d, 2H, J 8.5, ArH), 8.41 (d, 2H, J 9.0, ArH), 8.93 deca-3,4-dienoate, rac-20.Synthesized from 4-[5-(4-butoxy- (s, 1H, ArH); m/z found: 470.2545 (M+, 15%); C30H34N2O3 phenyl)-1,3,4-thiadiazol-2-yl]phenol and rac-19b. Yield 25 mg requires 470.2569.(10%); transitions (°C): C 51 SC 107 N 135 Iso; dH(200 MHz; CDCl3; J/Hz): 0.87 (t, 3H, CH3), 0.98 (t, 3H, J 7.6, CH3), 4-[5-(4-Butoxyphenyl)pyrimidin-2-yl]phenyl dodeca-3,4- 1.20–1.46 (m, 6H, CH2), 1.56 (m, 2H, CH2), 1.82 (m, 2H, CH2), dienoate, rac-12c. Synthesized from 4-[5-(4-butoxyphenyl)pyri- 2.08 (m, 2H, CH2), 3.7 (m, 2H, HCNCNCHCH2O), 4.02 (t, midin-2-yl]phenol and rac-6c.Yield 95 mg (48%); transitions 3H, J 6.4, OCH2), 5.46 (m, 1H, HCNCNCBr), 6.97 (d, 2H, J (°C): C 143 SC 174 Iso (Found: C, 76.52; H, 7.66; N, 5.49%; 8.8, ArH), 7.26 (d, 2H, J 8.6, ArH,), 7.92 (d, 2H, J 8.6, ArH), C32H38O3N2 requires C, 77.08; H, 7.68; N, 5.62%); dH 8.01 (d, 2H, J 9.0, ArH); m/z found 554.1321 (M+ -1; 0.33%), (200 MHz; CDCl3; J/Hz): 0.85–0.9 (m, 3H, CH3), 1.0 (t, 3H, J C28H31O3N2SBr requires 554.1238. 7.3, CH3), 1.25–1.6 (m, 12H, CH2), 1.75–1.86 (m, 2H, CH2), 2.0–2.1 (m, 2H, CH2), 3.32 (m, 2H, HCNCNCHCH2O), 4.05 This work was supported by the Deutsche For- (t, 2H, J 6.7, OCH2), 5.23–5.39 (m, 2H, HCNCNCH), 7.01 schungsgemeinschaft and the Fonds der Chemischen (d, 2H, J 9.0, ArH), 7.26 (d, 2H, J 8.7, ArH), 7.62 (d, 2H, J Industrie. 8.6, ArH), 8.42 (d, 2H, J 8.9, ArH), 8.95 (s, 1H, ArH); dC(126 MHz, CDCl3): 13.83, 14.06, 19.22, 22.64, 28.48, 28.97, 29.03, 29.09, 31.28, 31.82, 35.13, 67.81, 83.44, 92.82, 114.53, References 122.55, 127.76, 129.61, 129.76, 130.07, 132.48, 151.14, 155.02, 161.63, 163.55, 169.98, 205; m/z 490 (M+, 42%), 320 (100), 264 1 N.A. Clark and S.T. Lagerwall, Appl. Phys. L ett., 1980, 36, 899. 2 J.W. Goodby, J. Mater. Chem., 1991, 1, 307. (42), 235 (1), 179 (3), 118 (5); lmax/nm (CHCl3) 308.2, 306.2. 3 J. W. Goodby, A. J. Slaney, C. J. Booth, I. Nishiyama, J. D. Vuijk, P. Styring and K. J. Toyne, Mol. Cryst. L iq. Cryst., 1994, 243, 231. 4-(4¾-Undecyloxybiphenyl-4-yloxycarbonyl)phenyl deca-3,4- 4 Methylenecyclohexanes: (a) G.Solladie and R. Zimmermann, dienoate, rac-13. Synthesized from 4-(4¾-undecyloxybiphenyl- Angew. Chem., 1985, 97, 70; Angew. Chem., Int. Ed. Engl., 1985, 24, 4-yloxycarbonyl)phenol and rac-6b. Yield 125 mg (45%); trans- 64; (b) G. Solladie and R. Zimmermann, J. Org. Chem., 1985, 50, 4062; (c) H. Poths, R. Zentel, S. U. Vallerien and F. Kremer, Mol. itions (°C): C 107 SC 153 N 155 Iso; dH(CDCl3, 200 MHz): Cryst.L iq. Cryst., 1991, 203, 101; (d) H. Poths, R. Zentel, F. Kremer 0.88 (m, 6H, CH3), 1.50–1.20 (m, 20H, CH2), 1.75–1.85 (m, 2H, and K. Siemensmeyer, Adv. Mater., 1992, 4, 351; (e) Y. Zhang and CH2), 2.00–2.05 (m, 2H, CH2), 3.27 (dd, 2H, G. B. Schuster, J. Org. Chem., 1994, 59, 1855. HCNCNCHCH2O), 4.0 (t, 2H, J 6.45, ArOCH2), 5.23–5.23 5 Atropisomeric biphenyl derivatives: (a) K.Yang and (m, 2H, HCNCNCH), 6.91 (d, 2H, J 8.8, ArH), 6.95 (d, 2H, R. F. Lemieux, Mol. Cryst. L iq. Cryst., 1995, 260, 247; J 9, ArH), 7.23 (d, 2H, J 8.6, ArH), 7.48 (d, 2H, J 8.9, ArH), (b) G. Solladie�, P. Hugele�, R. Bartsch and A. Skoulios, Angew. Chem., 1996, 108, 1640; Angew. Chem., Int. Ed. Engl., 1996, 35, 7.56 (d, 2H, J 8.6, ArH), 8.12 (d, 2H, J 8.8, ArH); m/z found: 1533; (c) K.Yang, B. Campbell, G. Birch, V. E. Williams and 610.3655 (M+, 2%); C40H50O5 requires 610.3658. R. P. Lemieux, J. Am. Chem. Soc., 1996, 118, 9557. 6 Atropisomeric binaphthyl derivatives as dopants: (a) G. Gottarelli 4-{5-[4-(Nona-2,3-dienylcarbonyloxy)phenyl]-1,3,4-thiadi- and G. P. Spada, Mol. Cryst. L iq. Cryst., 1985, 123, 377; azol-2-yl}phenyl deca-3,4-dienoate, 14.Synthesized from 4-[5- (b) G. Heppke, D. Lo� tzsch and F. Oestereicher, Z. Naturforsch. (4-hydroxyphenyl)-1,3,4-thiadiazol-2-yl]phenol and rac-6b. T eil A, 1986, 1, 1214; (c) J. C. Bhatt, S. S. Keast, M. E. Neubert and R. C. Petschek, L iq. Cryst., 1995, 18, 367H.-J. Deußen, P. V. Yield 95 mg (40%); transitions (°C): C1 80 C2 92 SC 149 Iso Shibaev, R. Vinokur, T.Bjornholm, K. Schaumburg, K. Bechgaard (Found: C, 72.11; H, 7.26; N, 4.53; S, 5.34%; C34H38O4N2S and V. P. Shibaev, L iq. Cryst., 1996, 21, 327. requires C, 71.55; H, 6.71; N, 4.91; S, 5.62%); dH(500 MHz; 7 Biphenanthryl derivatives with an unknown mesophase: CDCl3; J/Hz): 0.84–0.91 (m, 6H, CH3), 1.2–1.48 (m, 12H, K. Yamamura, Y. Okada, S. Ono, M. Watanabe and I.Tabushi, CH2), 1.96–2.08 (m, 4H, CH2), 3.28 (dd, 4H, J. Chem. Soc., Chem. Commun., 1988, 443; K. Yamamura, S. Ono HCNCNCHCH2O), 5.20–5.37 (m, 4H, HCNCNCH), 7.24 and I. Tabushi, T etrahedron L ett., 1988, 29, 1797. 8 Racemic 1,3-disubstituted ferrocenes: R. Deschenaux and (d, 4H, J 8.8, ArH), 8.02 (d, 4H, J 8.8, ArH); m/z 570 (M+, J. Santiago, T etrahedron L ett., 1994, 35, 2169. 8%), 421 (23), 270 (100), 151 (66), 137 (44). 9 Butadiene iron-tricarbonyl complexes: (a) L. Ziminski and J. Malthete, J. Chem. Soc., Chem. Commun. 1990, 1495; (b) P. Jacq 1,4-Bis-[4-(nona-2,3-dienylcarbonyloxy)phenyl]-2-methyl- and J. Malthete, L iq. Cryst., 1996, 21, 291. benzene, 15. Synthesized from 1,4-bis(4-hydroxyphenyl)-2- 10 K. Zab, H. Kruth and C. Tschierske, Chem. Commun., 1996, 977. methylbenzene and rac-6b. Yield 95 mg (55%); transitions (°C): 11 J. Stichler-Bonaparte, H. Kruth, R. Lunkwitz and C. Tschierske, L iebigs Ann., 1996, 1375. C 59 N 64 Iso (Found: C, 81.11; H, 7.69%; C39H44O4 requires 1720 J. Mater. Chem., 1997, 7(9), 1713–172112 E. R. H. Jones, L. Skattebo� l and M. C. Whiting, J. Chem. Soc., 23 B. Neumann, D. Joachimi and C. Tschierske, Adv. Mater., 1997, 9, 241. 1956, 4765. 13 K. Bowden, J. M. Heilbron, E. R. C. Jones and B. C. L. Weedon, 24 C. Tschierske and H. Zaschke, J. Prakt. Chem., 1989, 331, 365. 25 C. J. Elsevier, in Houben-Weyl—Methods of Organic Chemistry, 4th J. Chem. Soc., 1946, 39. 14 M. M. Midland, A. Tramontano and S. A. Zderic, J. Am. Chem. edn., ed. G. Helmchen, R. W. Homann, J. Mulzer and E. Schaumann, Georg Thieme Verlag, 1995, vol. E 21a, p. 537. Soc., 1977, 99, 5211. 15 M. M. Midland, A. Tramontano, A. Kazubski, R. S. Graham, 26 S. Tsuboi, T. Masuda, S. Mimura and A. Takeda, Org. Synth., 1988, 66, 22. D. J. S. Tsai and D. B. Cardin, T etrahedron, 1984, 40, 1371. 16 H. C. Brown and G. G. Pai, J. Org. Chem., 1982, 47, 1606. 27 R. W. Saalfrank, A. Welch and M. Haubner, Angew. Chem., 1995, 107, 2937; Angew. Chem., Int. Ed. Engl., 1995, 34, 2937. 17 M. M. Midland and A. Kazubski, J. Org. Chem., 1982, 47, 2814; M. M. Midland, D. C. McDowell, R. L. Hatch and A. Tramontano, 28 K. Miyasato, S. Abe, H. Takazoe and Fukuda, Jpn. J. Appl. Phys. L ett., 1983, 22, L-661. J. Am. Chem. Soc., 1980, 102, 867. 18 J. A. Dale and H. S. Mosher, J. Am. Chem. Soc., 1973, 95, 512. 29 Organikum, ed. Autorenkollektiv, Deutscher Verlag der Wissenschaften, Berlin, 1984. 19 K. Mori, T. Nukada and T. Ebata, T etrahedron, 1981, 37, 1343. 20 C. Tschierske, H. Zaschke, H. Kresse, A. Ma�dicke and D. Demus, 30 J. Andersch and C. Tschierske, L iq. Cryst., 1996, 21, 51. Mol. Cryst. L iq. Cryst., 1990, 191, 223. 21 H. Zaschke and R. Stolle, Z. Chem., 1975, 15, 441. Paper 7/01032J; Received 13th February, 1997 22 R. Lunkwitz and C. Tschierske, unpublished results. J. Mater. Chem., 1997, 7(9), 1713–1721

ISSN:0959-9428    

DOI:10.1039/a701032j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Magnetostructural study of substituted a-nitronyl aminoxyl radicals with chlorine and hydroxy groups as crystalline design elements Oriol Ju�rgens, Joan Cirujeda, Montse Mas, Ignasi Mata, Araceli Cabrero, Jose� Vidal-Gancedo, Concepcio� Rovira, Elies Molins and Jaume Veciana* Institut de Cie`ncia deMaterials de Barcelona (CSIC), Campus de la UAB, 08193-Bellaterra, Barcelona, Spain We present a new family of phenyl substituted a-nitronyl aminoxyl radicals which contain hydroxy- and chlorine-substituents as crystal engineering tools.The magnetic behaviour of these radicals strongly diers in dimensionality and strength, showing in all cases antiferromagnetic interactions. We have determined the X-ray crystal structure and analysed the crystal packings of these radicals. From this analysis all the observed magnetic properties can be conveniently rationalized by only considering the close contacts of NO groups of neighbouring molecules according to the generally accepted mechanisms for intermolecular magnetic interactions.Beside the strong OMH,O(MN) hydrogen bonds and the weaker CMH,O(MN) hydrogen bonds, weak Cl,H bonds also seem to play a significant role in determining the molecular arrangement in the solid state and, therefore, the magnetic properties.In only one case are close Cl,Cl contacts observed, pointing to attractive interactions between chlorine atoms. Magnetic properties of molecular solids depend both on the molecular electronic properties and on the intermolecular electronic interactions present in the solid state.Since the discovery of the b-phase of 4-nitrophenyl a-nitronyl aminoxyl,† the first example of a purely organic free radical with a bulk ferromagnetic transition,1 much work has been devoted to the design of new substituted a-nitronyl aminoxyl radicals as building blocks for new molecular magnetic materials and bonding through OH substituents has been demonstrated to be a powerful crystal engineering element of a-nitronyl aminoxyl radicals providing new supramolecular architectures with relevant magnetic properties.2 One of these new molecular solids was obtained with 4-hydroxyphenyl a-nitronyl aminoxyl radical.3 This radical in the solid state forms a two-dimensional network built up by OMH,O(MN) and CMH,O(MN) hydrogen bonds that explains its quasi-two-dimensional ferromagnetic behaviour.On the other hand the 2-hydroxyphenyl and 2,5-dihydroxyphenyl a-nitronyl aminoxyl radicals4,5 undergo bulk ferromagnetic transitions at 0.45 and 0.5 K, respectively, being two of the rare examples of purely organic Cl N N+ O• O– N N+ O• O– Cl N N+ O• O– N N+ O• O– OH OH HO N N+ O• O– 1 2 3 4 5 Cl Cl Cl ferromagnets. Beside their crystal packing, which is controlled by a complex network of weak CMH,O(MN) hydrogen Radicals with only one Cl atom at the ortho and meta bonds, the twist angles between the phenyl rings and the mean positions, radicals 1 and 2, have also been studied here as planes defined by the ONCNO groups seem to play a signifi- reference compounds in order to evaluate the role played by cant role in determining this unusual magnetic property. this bulky and electroactive atom in crystal packing.Therefore such results clearly show that the control of the Interestingly, the radical with one Cl atom at the ortho position molecular conformation and the crystal packing are key points also provides an opportunity to evaluate the eect of a large torsion between the two rings of the radical without introduc- in molecular magnetism. ing any strong OMH,O(MN) hydrogen bonds.Chlorine atoms have long been known for their steering ability in crystal engineering of molecular solids. Attractive Cl,Cl interactions and CMH,Cl hydrogen bonds have been described as responsible for this ability.6,7 Herein we report a Experimental detailed magnetostructural study of a new family of phenyl anitronyl aminoxyl radicals 3–5 that combine OH groups and General procedures Cl atoms, attached to dierent positions of the phenyl rings, Radicals 1–5 were prepared using the procedure described by as crystalline design elements.The combination of these two Ullman and co-workers.10 The 2,3-(dihydroxylamino)-2,3- crystalline design elements has provided an eective way to dimethylbutane used as a precursor was obtained by following modulate the crystal packing of several chlorine substituted the reported procedure.11 Melting points were determined by phenols,8,9 leading to interesting applications to magnetic dierential scanning calorimetry (Perkin-Elmer, DSC-7 calormolecular solids.imeter) and are given as the maxima of the observed peaks.All radicals containing OH groups, radicals 3–5, melt with decomposition. IR (Nicolet 710 FT-IR spectrometer) and UV–VIS spectra (Cary 5 UV–VIS-NIR spectrometer) of the † a-Nitronyl aminoxyl is used throughout to indicate 4,5-dihydro- 4,4,5,5-tetramethyl-3-oxido-1H-imidazol-3-ium-1-oxyl. synthesized radicals were also recorded. J. Mater. Chem., 1997, 7(9), 1723–1730 1723Synthesis of free radicals Superconducting SQUID susceptometer and using microcrystalline samples (80–115 mg) of the radicals 1–5.The diamag- 2-(2-Chlorophenyl)-4,5-dihydro-4,4,5,5-tetramethyl-3-oxidonetic contributions of the sample holder and the radicals were 1H-imidazol-3-ium-1-oxyl 1. 2,3-(Dihydroxylamino)-2,3- determined by extrapolation from the xT vs. T plots in the dimethylbutane (2.11 g; 14.2 mmol) was added to a stirred high-temperature range and were used later to correct the solution of 2-chlorobenzaldehyde (2 g; 14.2 mmol) in 30 ml of SQUID outputs.methanol. Stirring at room temp. was continued for 20 h and the resulting white precipitate was filtered o and dried in X-Ray measurements vacuo. This solid was oxidized with a solution of NaIO4 (1.5 g; 7.1 mmol) in 50 ml of water at 5 °C and extracted with X-Ray data for single crystals of 1, 2, 4 and 5 were collected at 293 K on an Enraf-Nonius CAD 4 FR-590 diractometer dichloromethane.The solution was evaporated and the crude product was purified by column chromatography (SiO2) with working at 1 kW with monochromatic Mo-Ka (l=0.71069 A ° ) radiation. Data were collected by using an v/2h scan method.ethyl acetate dichloromethane (151) as eluent (2.55 g; yield, 67% from the aldehyde). Single crystals of 1 were grown by The structures were all refined by a full-matrix least squares method which minimized Sw(DF)2.‡ The presence of dierent evaporation at room temp. from a toluene solution. Mp 168.3 °C (Found: C, 58.27; H, 6.02; N, 10.42.Calc. for polymorphs in each crystalline material used for magnetic measurements was ruled out by means of powder X-ray C13H16N2O2Cl: C, 58.32; H, 6.02; N, 10.46%); nmax/cm-1 (KBr) 1595w, 1449m, 1404s, 1367s, 1211w, 1171m, 1133m, 1055m, diraction spectra by comparing the experimental spectra with the simulated ones based on the single crystal X-ray diraction 766m; UV–VIS (CH2Cl2) lmax/nm (e): 354 (18 000), 554 (780); MS (EI) m/z: 267 (M+), 179, 138, 114, 84, 69, 56.structure. These spectra were simulated by using the CERIUS2 2.0 program (Molecular Simulations Inc.). Powder diraction 2-(3-Chlorophenyl)-4,5-dihydro-4,4,5,5-tetramethyl-3-oxido- spectra were collected on a Rigaku Dimax RC-200 1H-imidazol-3-ium-1-oxyl 2. Radical 2 was synthesized by the diractometer with a 12 kW rotating anode generator and a same procedure as 1.Crystals were grown by slow evaporation monochromator of single crystalline graphite for Cu-Ka of a heptane–dichloromethane (1051) solution at room temp. radiation. Mp 123.5 °C (Found: C, 58.30; H, 6.01; N, 10.40. Calc. for C13H16N2O2Cl: C, 58.32; H, 6.02; N, 10.46%); yield, 92% from EPR spectroscopic measurements the aldehyde; nmax/cm-1 (KBr) 1580m, 1418m, 1395m, 1364s, The EPR spectra of radicals 1–5 in toluene solutions under 1134m, 795m; UV–VIS (CH2Cl2) lmax/nm (e): 271 (16 000), 367 free tumbling conditions were recorded on a Bruker ESP-300E (18 000), 584 (480); MS (EI) m/z: 267 (M+), 179, 138, 114, spectrometer operating in the X-band (9.3 GHz) with a rec- 84, 69.tangular TE1ity and equipped with a field-frequency (F/F) lock accessory and a built-in NMR gaussmeter.Signal- 2-(2-Chloro-4-hydroxyphenyl)-4,5-dihydro-4,4,5,5- to-noise ratio was increased by accumulation of scans using tetramethyl-3-oxido-1H-imidazol-3-ium-1-oxyl 3. Radical 3 was the F/F lock accessory to guarantee a high-field reproducibility. obtained in a similar way to 1, but instead of stirring the Precautions to avoid undesirable spectral line broadening such reactants, they were refluxed in benzene for 19 h.All attempts as that arising from microwave power saturation and magnetic to grow large single crystals of radical 3 failed, and so its X- field overmodulation were taken. In order to avoid dipolar ray structure could not be determined. Mp 166.2 °C (decomp.) broadening, the radical solutions were carefully degassed by (Found: C, 55.21; H, 5.75; N, 9.70.Calc. for C13H16N2O3Cl: C, bubbling with pure argon. 55.03; H, 5.68; N, 9.87%); yield, 22% from the aldehyde; nmax/cm-1 (KBr): 1604s, 1456m, 1364m, 1106m, 858w; UV–VIS (CH2Cl2) lmax/nm (e): 269 (13 000), 328 (12 000), 561 (1040); Results and Discussion MS (EI) m/z: 283 (M+), 195, 153, 114, 84, 69.Spin density distribution of the radicals 2-(3-Chloro-4-hydroxyphenyl)-4,5-dihydro-4,4,5,5- The most widely accepted mechanism for rationalizing the tetramethyl-3-oxido-1H-imidazol-3-ium-1-oxyl 4. Radical 4 was intermolecular magnetic interactions in organic molecular synthesized by the same procedure as for 3. Crystals were solids is the so-called McConnell I mechanism based on the grown by a slow diusion of pentane into a concentrated overlap of the orbitals on atoms with large spin densities of toluene solution at room temp.Mp 158.4 °C (decomp.) (Found: neighbouring molecules.12,13 According to this mechanism, C, 55.31; H, 5.75; N, 9.81. Calc. for C13H16N2O3Cl: C, 55.03; dominant contacts of atoms with spin densities having the H, 5.68; N 9.87%); yield, 93% from the aldehyde; nmax/cm-1 same sign produce an antiferromagnetic interaction between (KBr): 1605m, 1490m, 1387m, 1340s, 1300m, 1273m, 1214m, the two neighbouring molecular units.In contrast, ferromag- 1169m, 1133m, 831m, 702w, 541w; UV–VIS (CH2Cl2) lmax/nm netic interactions are favoured if opposite signs in these (e): 282 (16 000), 369 (12 000), 618 (720); MS (EI) m/z: 283 contacts are predominant.For this reason it is important in (M+), 195, 153, 114, 84, 69. magnetic molecular materials to know how the spin density of the unpaired electron is distributed within the building block 2-(5-Chloro-2-hydroxyphenyl)-4,5-dihydro-4,4,5,5- molecules. tetramethyl-3-oxido-1H-imidazol-3-ium-1-oxyl 5. Radical 5 was Free tumbling solution EPR spectra provide the necessary obtained similarly to 3.Crystals were grown by slow evapor- information about such spin density distributions in organic ation of a heptane–dichloromethane (1051) solution at room free radicals, through the determination of the coupling contemp. Mp 118.7 °C (decomp.) (Found: C, 55.78; H, 5.94; N, stants with the magnetically active nuclei of the molecules. 9.05. Calc. for C13H16N2O3Cl: C, 55.03; H, 5.68; N, 9.87%); The EPR spectra of radicals 1–5 show basically five main yield, 25% from the aldehyde; nmax/cm-1 (KBr): 1573w, 1471s, groups of lines with relative intensities of 152535251, resulting 1375m, 1341m, 1278m, 1135m, 825m, 646w; UV–VIS (CH2Cl2) from the coupling of the unpaired electron with two equivalent lmax/nm (e): 349 (4400), 581 (440); MS (EI) m/z: 283 (M+), nitrogen nuclei (I=1), as shown in Fig. 1(a) for radical 4. The 195, 153, 114, 84, 69. ‡ Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Magnetic measurements Centre (CCDC). See Information for Authors, J. Mater. Chem., 1997, DC magnetic susceptibility data from 2 to 300 K, in a magnetic Issue 1.Any request to the CCDC for this material should quote the full literature citation and the reference number 1145/40. field of 1 T, were collected using a ‘Quantum Design’ MPMS 1724 J. Mater. Chem., 1997, 7(9), 1723–1730agreement with those previously reported by other authors,16 who have determined by NMR measurements that the N and O atoms carry a large and positive spin density while the acarbon atom has a significant negative spin density.The methyl groups and the aromatic ring also carry a spin density, as inferred from the observed EPR hyperfine couplings with all these hydrogen atoms. The coupling constants for the aromatic hydrogen atoms are smaller in radicals 1, 3 and 5 than in radicals 2 and 4. The loss of planarity between the five- and the six-membered rings, due to the presence of a substituent at the ortho position in compounds 1, 3 and 5, yields a satisfactory explanation for this fact.Assignments of the coupling constants of aromatic hydrogen atoms for radicals 1–5 have been performed by comparison with a whole series of radicals with non-magnetically active substituents located at dierent positions of the phenyl rings.17 Molecular and crystal structures of radicals General crystallographic information for radicals 1, 2, 4 and 5 is summarized in Table 2.Atomic numbering schemes used for these radicals are shown in Fig. 2 together with their molecular conformations. Structure of radical 1. Radical 1 crystallizes in the orthorhombic system with an asymmetric unit which contains one radical molecule.The most relevant feature of the solid state molecular conformation of radical 1 is the large angle (62°) formed by the phenyl ring and the mean plane of the OMNMCMNMO unit. This twist angle is larger than that reported for the unsubstituted phenyl a-nitronyl aminoxyl radical (29°)18 as well as for the p-chloro- (24°),19 the o-hydroxy- (40°)4 and the p-hydroxyphenyl- (30°)3a substituted examples. Therefore, this result suggests that the large angle in 1 is merely due to steric hindrance of the bulky Cl atom at the ortho position.The intramolecular Cl,O distance in radical 1 (3.24 A ° ) is quite similar to intermolecular distances found between halogen and nucleophile atoms by Murray-Rust and co-workers.20 Fig. 1 (a) Complete EPR spectrum of radical 4 in toluene at 293 K. This fact suggests that, in spite of the strong steric hindrance (b) Experimental (upper) and simulated (lower) central groups of EPR between the Cl and the O atom, a slightly attractive interaction lines. The computer simulation was carried out using a Lorentzian between both atoms cannot be excluded. The measured dis- line shape with DH1/2 of 0.13 G and the hfcc valves given in Table 1. tance would be the resulting equilibrium position between the steric repulsion and such halogen–nucleophile attracting forces.values of the isotropic hyperfine coupling constants in all In our case, the CMCl,O angle is obviously much smaller cases are between 7.2 and 7.8 G; i.e. aN=7.5(3) G; which is typical for freely tumbling substituted a-nitronyl aminoxyl radicals.1,14,15 A more detailed analysis of these five main Table 2 Crystallographic data for radicals 1, 2, 4 and 5 groups of signals reveals a complex pattern of lines arising compound 1 2 4 5 from supplementary couplings with the twelve equivalent hydrogen atoms (I=1/2) of the four methyl groups and all the a/A° 10.483(3) 9.946(2) 13.735(1) 9.741(6) hydrogen atoms of the phenyl ring.b/A° 10.921(3) 11.522(1) 11.819(2) 11.663(5) Computer simulations of the experimental EPR spectra of c/A° 11.671(3) 12.700(2) 17.153(3) 13.324(14) 1–5 yield the hyperfine coupling constants summarized in b/° — 109.91(1) — 111.23(7) Table 1. All values are in agreement with those previously data/parameters 3887/165 4130/213 2441/176 2037/223 V /A° 3 1336.2(6) 1368.4(4) 2785.5(7) 1411(2) reported for other a-phenyl nitronyl aminoxyl radicals,15 indi- Dc/g cm-3 1.331 1.300 1.354 1.336 cating, therefore, that the chloro- and hydroxy-substituents do space group P212121 P21/c Pbca P21/n not alter the electron distribution in the radicals significantly. Z 4 4 8 4 Consequently, the unpaired electron is mainly distributed on R 0.0394 0.0478 0.0514 0.0488 both NO groups and the a-carbon atom.This result is in Table 1 Summary of hyperfine coupling constants (a/G; 1 G=10-4 T) obtained for radicals 1–5 by computer simulation of the EPR spectra of toluene solutions compound aN aH(methyl) aH(ortho) aH(meta) aH(para) 1 7.26 (2N) 0.20 (12H) 0.24 0.15, 0.12 a 2 7.40 (2N) 0.19 (12H) 0.52 (2H) 0.21 0.43 3 7.65 (2N) 0.18 (12H) 0.23 0.16 (2H) — 4 7.50 (2N) 0.21 (12H) 0.54, 0.50 0.17 — 5 7.81, 7.40 0.20 (12H) 0.33 0.25 0.30 aNot observed.J. Mater. Chem., 1997, 7(9), 1723–1730 1725Fig. 2 Molecular conformations of radicals 1, 2, 4 and 5 with the atomic numbering schemes used in the text and tables (75°) than in the examples described by Murray-Rust and co- perpendicular to the crystallographic [1 0 -1] direction.Between adjacent planes no H,O contacts with workers20 because of the intramolecular nature of that contact. As shown in Fig. 3, the molecules of radical 1 are packed in d(H,O)<3 A° are observed. Molecules of adjacent planes are just connected by weak CmethylMH11B,C11iii interactions such a way that one of the two NO groups of each molecule forms a hydrogen bond with a methyl group of a neighbouring [iii=-x, 1/2+y, 3/2-z; d(H11B,C11iii)=3.01 A ° ; h(C111MH11B,C11iii)=172°], and these interactions are molecule [d(H11D,O14i, i=-x, 1/2+y, 5/2-z)=2.64 A ° ; h(C112MH11D,O14i)=154°] giving rise to twisted chains propagated along the b axis.As a result of this complex crystal packing, the shortest along the b axis.Each of these chains is connected to two neighbouring chains by means of CaromMH7,O14iiMN13ii distance between the NO groups of dierent molecules [d(O14,N9iv)=4.94 A ° ; iv=-x, -1/2+y, -5/2-z; hydrogen bonds [ii=1/2+x, 1/2-y, 2-z; d(H7,O14ii)= 2.66 A ° ; h(C7MH7,O14ii)=130°] forming molecular sheets d(O14,O10iv)=5.39 A ° ] occurs between neighbouring molecules in the chains along the b axis.These kinds of contacts are responsible for the magnetic behaviour as will be discussed below. Structure of radical 2. This compound crystallizes in the monoclinic P21/c space group with an asymmetric unit containing one radical molecule. Fig. 2 shows its solid state molecular conformation. The torsion angle between the two rings of radical 2 is 26°, being very similar to those of other radicals with similar steric requirements at the ortho position. 18,19,3a The crystal structure of 2 clearly shows alternating planes perpendicular to the crystallographic [1 0 -1] direction. Within these planes, the molecules are connected to each other forming chains along the b axis [see Fig. 4(a)] by means of CaromMH14,O2iMN2i hydrogen bonds [i=1-x, -1/2+y, 1/2-z; d(H14,O2i)=2.47 A ° ; h(C14MH14,O2i)= 129°].These chains are linked to each other by weak CmethylMH44,O5iiMN5ii hydrogen bonds [ii=-x, 1/2+y, -1/2-z; d(H44,O5ii)=2.55 A ° ; h(C42MH44,O5ii)=148°]. As happens with radical 1, between adjacent planes containing the stronger CMH,O hydrogen bonds, no other H,O contacts with d(H,O)<3 A° are observed. In a similar way as Fig. 3 Crystal packing of radical 1. Crystallographic (1 0-1) plane occurs with radical 1 there are CaromMH15,C113iii interformed by chains of molecules connected through actions [iii=x, 1/2-y, 1/2-z; d(H15,C113iii)=3.12 A ° ; Cmethyl–H11D,O14i–N13i (i=-x, 1/2+y, 5/2-z) hydrogen bonds h(C15MH15,C113iii)=154°] between the planes. Also, (dashed lines) along the b axis. The dotted line connects the nearest between chains of neighbouring (1 0 -1) planes, we have NO groups of dierent molecules, N13–O14,N9iv (iv=-x, -1/2+y, -5/2-z).found short C113,C113iv contacts [iv=1-x, -y, -z; 1726 J. Mater. Chem., 1997, 7(9), 1723–1730strong intermolecular O8MH8,O15iMN14i bond [i=1-x, -1/2+y, 1/2-z; d(H8,O15i)=1.72 A ° ; h(O8MH8,O15i)= 168°] which connects each molecule to two neighbours giving rise to zigzag chains along the b axis.This arrangement is reinforced by a second hydrogen bond [d(H6,O15i)=2.65 A ° ; h(C6MH6,O15i)=128°] between the same NO group and an aromatic H atom in the meta position which is adjacent to the OH group which forms the strong hydrogen bond. Further, these chains are arranged into planes perpendicular to the crystallographic [1 0 0] direction by means of weak CmethylMH134,O11iiMN10ii hydrogen bonds [ii=1-x, -y, -z; d(H134,O11ii)=2.71 A ° ; h(C132MH134,O11ii)=160°], as shown in Fig. 5(a). This pattern resembles very much the crystal packing reported for the 4-hydroxyphenyl a-nitronyl aminoxyl radical3 but there are two basic dierences caused by the presence of the Cl atom at the meta position. The first is that the rings of radical 4 are not coplanar to the (1 0 0) plane; i.e.the molecules are alternately canted within the chains. The second dierence refers to the stacking of the planes along the crystallographic a direction, which in radical 4 takes place through CmethylMH125,Cl1iii interactions [iii=-1/2+x, 1/2-y, -z; d(H125,Cl1iii)=3.07 A ° ; h(C122MH125,Cl1iii)=167°], CmethylMH121,Cl1iv interactions [iv=-1/2+x, y, 1/2-z; d(H121,Cl1iv)=3.08 A ° ; h(C121MH121,Cl1iv)=134°] [shown in Fig. 5(b)] and CmethylMH131,O11vMN10v hydrogen bonds [v=1/2-x, 1/2+y, z; d(H131,O11v)=2.75 A ° ; h(C131MH131,O11v)=151°], while in the para-hydroxy substituted radical the stacking of planes occurs through van der Waals interactions. The lack of planarity of the molecules of radical 4, within the twisted chains in the (1 0 0) plane, means that the shortest intermolecular distance between NO groups occurs pairwise Fig. 4 Crystal packing of radical 2. (a) Crystallographic (1 0-1) plane formed by chains of molecules connected through Carom–H14,O2i–N2i (i=1-x, -1/2+y, 1/2-z) hydrogen bonds (dashed lines) along b axis. (b) Molecules of two neighbouring (1 0-1) planes showing as dashed lines C113,C113iv close contacts (iv= 1-x, -y, -z).The dotted lines connect the nearest NO groups of dierent molecules, N2,O5v–N5v (v=-x, 1-y,-z). d(C113,C113iv)=3.72 A ° ], which are depicted in Fig. 4(b). The distances of such contacts are in accordance with those described by Desiraju7 for several other compounds which clearly show non-covalent attractive Cl,Cl interactions.Therefore this result suggests that the Cl,Cl interactions are driving forces for the packing of molecules in (1 0 -1) planes. As will be discussed below, from the magnetic point of view, the most important aspect of the crystal packing of radical 2 is the presence of short intermolecular distances between the NO groups of two molecules in neighbouring (1 0 -1) planes.This kind of contact permits us to consider the molecular system as being composed of dimeric magnetic entities which are clearly shown in Fig. 4(b). Structure of radical 4. Radical 4 crystallizes in the orthorhom- Fig. 5 Crystal packing of 4. (a) Crystallographic (100) plane formed by zigzag chains of molecules connected through strong bic Pbca group and also contains one molecule in the asymmet- O8–H8,O15i–N14i (i=1-x, -1/2+y, 1/2-z) hydrogen bonds ric unit.In this case the phenyl ring is twisted with respect to along b axis depicted as dashed lines. The dotted lines connect the the mean OMNMCMNMO plane by 28.5°. This result is nearest NO groups of dierent molecules, N10,O11vi–N10vi (vi= again in accordance with the twist angles observed for other 1-x, -y, -z).(b) Molecules of neighbouring (100) planes showing radicals with similar steric requirements, that is, those without Cmethyl–H125,C11iii (iii=-1/2+x, 1/2-y, -z) and substituents at the ortho positions. Cmethyl–H121,C11iv (iv=-1/2+x, y, 1/2-z) interactions which are depicted as dashed lines. The main feature of the crystal packing of radical 4 is the J. Mater. Chem., 1997, 7(9), 1723–1730 1727between molecules of neighbouring chains as shown in Fig. 5(a) leading to a dimeric magnetic pattern, as will be discussed below. Structure of radical 5. This compound does not crystallize in the orthorhombic system, as occurs for radicals 1 and 4, but in the monoclinic one, similarly to radical 2 which also has one chlorine atom in the meta position. The presence of the OH group at the ortho position results in the formation of a strong intramolecular O51MH51,O15MN14 hydrogen bond [d(H51,O15)=1.66 A ° ; h(O51MH51,O15)=170°].Consequently, there is a twist angle of 35° between the two rings of the molecule, as was also observed for the radical with one OH group in the ortho position.4 Fig. 2 shows the molecular structure of 5, where the lack of planarity is clear.Due to the establishment of these strong intramolecular OMH,OMN hydrogen bonds, the molecules are packed in the crystal through other types of weak hydrogen bonds. Thus, the molecules are arranged into zigzag chains parallel to the [1 0 1] direction by means of rather weak CaromMH7,O11iMN10i hydrogen bonds [i=-1/2+x, 1/2-y, -1/2+z; d(H7,O11i)=2.22 A ° ; h(C7MH7,O11i)=157°].The chains are layered into planes perpendicular to the [1 0 -1] direction by CmethylMH13B,O15iiMN14ii hydrogen bonds [ii=1/2+x, 3/2-y, 1/2+z; d(H13B,O15ii)=2.82 A ° ; h(C131M H13B,O15ii)=155°] as shown in Fig. 6(a). Furthermore, the planes are connected pairwise through other CmethylMH12A,O11iiiMN10iii hydrogen bonds [iii= 1-x, 1-y, 1-z; d(H12A,O11iii)=2.68 A ° ; h(C121M H12A,O11iii)=174°] giving rise to an alternating pattern in which the radical molecules of two neighbouring planes form dimers, related by an inversion centre shown in Fig. 6(b). As will be seen below, these dimers are responsible for the magnetic behaviour of the compound. As can be inferred from geometric considerations, all CMH,Cl distances present in this radical are longer than 3.3 A ° .{The shortest ones are [d(H6,Cl1i)=3.33 A ° ; h(C6MH6,Cl1i)=156°] and [d(H123,Cl1iv)=3.36 A ° ; h(C122MH123,Cl1iv)=110.6°; iv=x, 1+y, z]}. The crystal packing of radical 5 is therefore very similar to the molecular arrangement of radical 2. This result can be Fig. 6 Crystal packing of 5. (a) Crystallographic (1 0-1) plane formed rationalized by noting that both compounds have similar by chains of molecules connected through Carom–H7,O11i–N10i (i= crystalline design elements: in fact both radicals have one Cl -1/2+x, 1/2-y, -1/2+z) hydrogen bonds parallel to the a+c atom at the meta position and the additional OH substituent direction.(b) Molecules of two neighbouring (1 0-1) planes forming at the ortho position of radical 5 seems to aect only the dimers by intermolecular Cmethyl–H12A,O11iii–N10iii (iii=1-x, intramolecular conformation and not the intermolecular inter- 1-y, 1-z) hydrogen bonds.The strong intramolecular O51–H51,O15–N14 hydrogen bonds are also depicted. actions. The fact that no Cl,Cl contacts are observed in radical 5 may be explained as a consequence of the lower planarity7 of this molecule due to the OH substituent at the ortho position.Magnetic properties of radicals Summarizing the above structural analysis, the arrangement of molecules of the radicals 1, 2, 4 and 5 in the solid state is Static magnetic susceptibility measurements of radicals 1–5 mainly governed by strong OMH,OMN (only possible in are shown in Fig. 7. Such measurements indicate that the radicals 4 and 5) and weak CMH,OMN hydrogen bonds molecular solids studied present in all cases intermolecular giving rise to molecular solids with one- or two-dimensional antiferromagnetic (AFM) interactions with dierent strengths.structural character.6,21 The CMH,Cl hydrogen bonds only As we will discuss later, the magnetic dimensionalities vary seem to play an important role in the crystal packing of the from one compound to another in close relationship with their radicals without OH substituents on the phenyl ring, as shown crystal packings.by the shorter H,Cl distances in radicals 1 and 2 compared The magnetic susceptibility data of 1 were nicely fitted to a with radicals 4 and 5. Cl,Cl interactions have only been 1D Heisenberg model of S=1/2 molecular units having weak found for radical 2.According to Desiraju et al.,7 the lack of AFM interactions with a magnetic exchange interaction of planarity, especially in radicals 1 and 5, and the presence of J/kB=-0.95 K. In the crystal structure of radical 1, all the other stronger intermolecular interactions, as occurs for 4, may intermolecular distances between atoms carrying the larger be responsible for the absence of Cl,Cl interactions in radicals spin densities are quite large.As described previously, the 1, 4 and 5. As a consequence of such considerations, it shortest one [d(O14,N9iv)=4.94 A ° ; iv=-x, -1/2+y, has been observed that the placement of an additional Cl -5/2-z] occurs among atoms having a positive sign of spin atom modulates considerably the crystal packing of phenyl density and that belong to molecules forming the previously described chains along the crystallographic b direction.In a-nitronyl aminoxyl radicals. 1728 J. Mater. Chem., 1997, 7(9), 1723–1730maximum at 9 K in the x vs. T plot strongly suggests a low magnetic dimensionality for this molecular solid. Actually, the data can be fitted to a dimer chain model23 of S=1/2 molecular units with an intradimer exchange interaction of J1/kB=-14.9 K and an interdimer exchange interaction of J2/kB=-10.5 K.For radical 4, the shortest distance between NO groups of dierent molecules [d(N10,O11ii)=3.69 A ° , d(O11,O11ii)=3.81 A ° , ii=1-x, -y, -z] occurs within the (1 0 0) layers among molecules belonging to neighbouring chains. The shortest distance between the spin-carrying units of dierent dimers [d(O15,O15vi)=4.61 A ° ; vi=1-x, 1-y, -z] takes place along the b axis within the (1 0 0) plane.Moreover, the remaining distances between dimers are much longer, the lowest one being 5.65 A ° . Therefore, all these facts explain the goodness of the experimental data to a dimer chain model for radical 4. This magnetostructural correlation has short intra- and inter-dimer distances between NO units that Fig. 7 Temperature dependence of the paramagnetic susceptibility x are responsible for the strong antiferromagnetic couplings of radicals (%) 1, (+) 2, (&) 3, (') 4 and ($) 5. The inset shows an enlargement of the temperature dependence for radicals 4 and 5. The within and between the magnetic dimers.Both distances are solid lines represent the fits of experimental data to the magnetic clearly shorter than those observed for radicals 1 and 2 in models explained in the text. agreement with the stronger antiferromagnetic couplings observed for 4. The x vs. T plot of radical 5 shows a broader maximum at consequence, this molecular arrangement is in agreement with ca. 50 K indicating again a low dimensionality with a very the observed weak 1D antiferromagnetic behaviour.strong antiferromagnetic interaction. The experimental data The magnetic behaviour of 2 is properly explained by a can be fitted to a simple dimer model with strong AFM (J/kB= dimer model with antiferromagnetic interactions. However, the -42.3 K) interactions.24 An additional Curie tail (C=0.0043 fitting of experimental data is considerably improved if an emu K mol-1) is necessary to fit the low temperature values, additional interdimer antiferromagnetic term is included in the which takes into account possible crystal surface eects or the Bleaney–Bowers equation for S=1/2 molecular units with an presence of dislocations in the crystals.The strength of the antiferromagnetic interaction of J/kB=-1.82 K, by means of intradimer interaction is remarkable, since it is one of the a temperature correction with a Weiss constant of h= largest reported to date for a purely organic compound.-1.39 K.22 This result means that the dominant magnetic As mentioned previously in the description of the molecular interactions take place within the dimers but such dimers also packing of radical 5, there are molecules linked by interact weakly with each other in a quite isotropic antiferro- CMH,OMN hydrogen bonds that clearly form dimeric enti- magnetic fashion.Analysing the crystal structure of 2, we have ties. The shortest distance between the spin-carrying units for found that the shortest distance between NO groups of dierent radical 5 occurs inside these dimers [d(O11,O11iii)=3.37 A ° ; molecules is slightly shorter [d(N2,O5v)=4.89 A ° ; iii=1-x, 1-y, 1-z].This short intermolecular distance is d(O2,O5v)=5.03 A ° ; v=-x, 1-y, -z] than in radical 1, the shortest one observed in this family of radicals and explains occurring in a dimer geometry instead of in chains. This the strong intermolecular magnetic interaction observed for structural pattern therefore explains the observed magnetic radical 5.characteristics of this molecular solid. The distances between From the magnetostructural study it has been possible to NO groups of dierent dimers are larger than 5.24 A ° and can establish a complete correlation between the solid state mag- be associated with the weaker interdimer antiferromagnetic netic properties and the molecular arrangement in the crystals interactions.for all the radicals studied. Table 3 summarizes the main The experimental data for radical 3 can be fitted either by features of the structure and magnetic behaviour for radicals a 1D AFM model with J/kB=-0.62 K or by the Curie–Weiss 1, 2, 4 and 5 showing in addition that the structural dimension- law with h=-0.89 K.Thus, such data clearly show the alities, based on packing motifs linked by hydrogen bonds, are antiferromagnetic nature of the intermolecular interactions dierent from the magnetic dimensionalities. even though they do not have any singularity that permits us It also seems clear that the magnitude of exchange inter- to distinguish the magnetic dimensionality of this molecular actions between radical molecules in these molecular solids system.In contrast, in the case of radical 4, the presence of a broad strongly decreases as the mean intermolecular distances Table 3 Summary of structural and magnetic dimensionalities of radicals 1, 2, 3 and 5 together with the most relevant intermolecular contacts from the structural and magnetic points of view.See text for symmetry operations compound structural dimensionalitya structurally relevant contacts magnetic dimensionalityb magnetically relevant contacts 1 2D d(H11D,O14i)=2.64 A ° 1D, regular chains d(H7,O14ii)=2.66 A ° (J/kB=-0.95 K) d(O14,O10iv)=5.39 A ° c 2 2D d(H14,O2i)=2.47 A ° 0D AFM, dimers d(H44,O5ii)=2.55 A ° (J/kB=-1.82 K) d(O2,O5v)=5.03 A ° d 4 2D d(H8,O15i)=1.72 A ° 1D, dimer chains d(H134,)15ii)=2.71 A ° (J/kB=-14.9 K) d(O15,O15vi)=4.61 A ° (J2/kB=-10.5 K) d(O11,O11ii)=3.81 A ° e 5 1D d(H7,O11i)=2.22 A ° 0D, dimers (J/kB=-42.3 K) d(O11,O11iii)=3.37 A ° aBased on the observed packing motifs linked by H,O hydrogen bonds with distances shorter than 2.8 A ° .bBased on the fits of experimental magnetic data to magnetic models.Figures in parentheses are the strengths of dominant magnetic exchange interactions which are in all cases antiferromagnetic. cThe corresponding O,N contact is shorter at d(O14,N9iv)=4.94 A ° . dThe corresponding O,N contact is shorter at d(N2,O5v)=4.89 A ° . eThe corresponding O,N contact is shorter at d(N10,O119ii)=3.69 A ° . J. Mater. Chem., 1997, 7(9), 1723–1730 172910 J.H. Osiecki and E. F. Ullman, J. Am. Chem. Soc., 1968, 90, 1078; between ONCNO units increases, being insignificant for O,O E. F. Ullman, J. H. Osiecki, D. G. B. Boocock and R. J. Darcy, distances larger than 6.0 A ° . Moreover, the AFM nature of J. Am. Chem. Soc., 1972, 94, 7049. such interactions can be rationalized by the McConnell I 11 M. Lamchen and T. W. Mittag, J.Chem. Soc. C, 1966, 2300. mechanism, through the contacts of atoms with the same sign 12 (a) H. M. McConnell, J. Phys. Chem., 1963, 39, 1910; of spin density, that belong to the NO units carrying the large (b) J. B. Goodenough, Magnetism and the Chemical Bond, Interscience, New York, 1963, p. 163; (c) H. M. McConnell, Proc. spin density. An alternative but coincident rationalization of R.A. Welch Found, Conf. Chem. Res., 1967, 11, 144. such magnetic interactions can be provided by the overlap of 13 In some aspects the McConnell I mechanism is a restatement of the SOMOs of neighbouring molecules.13 concepts introduced many years before by Heitler and London. Thus, dominant contact of atoms of two neighbouring molecules This research was financially supported by the C.I.C.y T. with spin densities having the same sign is equivalent to a non- (Grant,MAT 94-0797), Spain and the Generalitat de Catalunya zero overlap integral between their singly occupied molecular orbitals (SOMO) because such SOMOs are located on those (Grant, SGR 95/00507). O. J. and J. C. thank also the atoms. Generalitat de Catalunya for the award of doctoral fellowships. 14 M. S. Davis, K. Morokuma and R. W. Kreilick, J. Am. Chem. Soc., 1974, 96, 652. 15 J. A. D’Anna and J. H. Wharton, J. Chem. Phys., 1970, 53, 4047. References 16 (a) M. S. Davis, K. Morokuma and R. W. Kreilick, J. Am. Chem. Soc., 1972, 94, 5588; (b) J. W. Neely, G. F. Hatch and 1 M. Tamaura, Y. Nakazawa, D. Shiomi, K. Nozawa, Y. Hosokoshi, M. Ishikawa, M. Takahashi and M. Kinoshita, Chem.Phys. L ett., R. W. Kreilick, J. Am. Chem. Soc., 1974, 96, 652. 17 (a) J. Veciana, J. Cirujeda and O. Ju� rgens, Manuscript in prep- 1991, 186, 401. 2 (a) J. Veciana, J. Cirujeda, C. Rovira and J. Vidal-Gancedo, Adv. aration; (b) J. Cirujeda, Ph D Thesis, 1997, Universitat Ramon Llull. Mater., 1995, 7, 221; (b) J. Cirujeda, C. Rovira and J. Veciana, Synth. Met., 1995, 71, 1799; (c) J.Cirujeda, E. Herna�ndez-Gasio� , 18 C. W. Wang and S. F. Watkins, J. Chem. Soc., Chem. Commun., 1973, 888. F. Lanfranc de Panthou, J. Laugier, M. Mas, E. Molins, C. Rovira, J. J. Novoa, P. Rey and J. Veciana, Mol. Cryst. L iq. Cryst., 1995, 19 (a) J.-L. Stagner, Doctoral Thesis, 1995, Universite� Louis Pasteur de Strasbourg; (b) Y. Hosokoshi, Doctoral Thesis, 1995, University 271, 1. 3 (a) H. Herna�ndez-Gasio� , M. Mas, E. Molins, C. Rovira and of Tokyo. 20 N. Ramasubbu, R. Parthasarathy and P. Murray-Rust, J. Am. J. Veciana, Angew. Chem., Int. Ed. Engl., 1993, 32, 882; (b) J. Cirujeda, E. Herna�ndez-Gasio� , C. Rovira, J. L. Stanger, Chem. Soc., 1986, 108, 4308. 21 G. R. Desiraju, Acc. Chem. Res., 1991, 24, 290. P. Turek and J. Veciana, J.Mater. Chem., 1995, 5, 243. 22 The equation used to fit the data corresponds to a modified 4 J. Cirujeda, M. Mas, E. Molins, F. Lanfranc de Panthou, Bleaney–Bowers equation which includes a multiplying term to J. Laugier, J. G. Park, C. Paulsen, P. Rey, C. Rovira and J. Veciana, take account of intradimer interactions: x= J. Chem. Soc., Chem. Commun., 1995, 709. [Ng2mB2/3k(T-h)][1+(1/3) exp(-2J/kT )]-1. See R. L. Carlin in 5 T. Sugawara, M. M. Matsuskita, A. Izuoka, N. Wada, N. Takeda Magnetochemistry, Springer Verlag, Berlin, 1986, p. 88. and M. Ishikawa, J. Chem. Soc., Chem. Commun., 1994, 1723. 23 T. Barnes and J. Riera, Phys. Rev. B, 1994, 50, 6817. 6 R. Taylor and O. Kennard, J. Am. Chem. Soc., 1982, 104, 5063. 24 However, the fitting of the experimental data for 5 is slightly 7 (a) J. A. R. P. Sarma and G. R. Desiraju, Acc. Chem. Res., 1986, 19, improved if the same model as for radical 2 is employed, with an 222; (b) G. R. Desiraju, in Organic Solid State Chemistry, ed., intradimer interaction of J/kB=-50.1 K and an additional inter- G. R. Desiraju, Elsevier, 1987, p. 519; (c) J. A. R. P. Sarma and dimer term of h=+10.4 K, corresponding to the magnetic inter- G. R. Desiraju, Chem. Phys. L ett., 1985, 117, 160. actions among the dimers. 8 G. R. Desiraju, in Organic Solid State Chemistry, ed., G. R. Desiraju, Elsevier, 1987, p. 539. 9 N.W. Thomas and G. R. Desiraju, Chem. Phys. L ett., 1984, 110, 99. Paper 7/00589J; Received 27th January, 1997 1730 J. Mater. Chem., 1997, 7(9),

ISSN:0959-9428    

DOI:10.1039/a700589j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

New chlorin-e 6 trimethyl ester compounds as holographic data storage media at liquid helium temperature Dieter Franzke,a Hansruedi Gygax,b Alois Renn,c Urs P. Wild,c Heinz Wollebd and Heinz Spahnid aGeneral Energy Research, Paul Scherrer Institute, CH-5232 V illigen, Switzerland bGivaudan-Roure Research LT D, CH-8600 Du�bendorf, Switzerland cPhysical Chemistry L aboratory, Swiss Federal Institute of T echnology, ETH Zentrum, CH-8092, Zu�rich, Switzerland dCorporate Research Units, Ciba-Geigy L imited, Marly Research Center, CH-1723 Marly, Switzerland The chlorin–polyvinylbutyral (PVB) guest–host system has been the workhorse for most of the previously reported holographic hole burning experiments. In order to extend the spectral range and to improve on some of its properties we synthesized chlorin-e6 trimethyl ester 1 and brominated chlorin-e6 trimethyl ester 2, which require a much shorter synthesis pathway than chlorin.We studied the hole burning behaviour of these new dyes with dierent matrix materials and film preparation methods at liquid helium temperature and measured important properties like hole width and burning kinetics.One result was that we found the methyl ester compounds embedded into a photopolymer to have a five times faster burning rate than the chlorin–photopolymer system.In recent years, persistent spectral hole burning (SHB) has synthesis the two compounds have the advantage that the introduction of the methyl ester groups improves the solubility revealed an unshared potential for high density information storage.1–6 In combination with holography up to 12 000 of the dye in polymer matrices. The bromine atom was brought in because we expected the photochemical reaction to be holograms have been stored in a single chlorin-polyvinylbutyral (PVB) film.7 Though the memory properties of this dye- accelerated by the ‘heavy-atom eect’.11 The photochemistry of our molecules is assumed to occur during relaxation via the in-polymer system are already impressive and many eorts have been made to optimize the storage device, the perfect triplet state.Therefore an increase of the intersystem crossing (ISC) rate, which can be induced by ‘heavy atoms’, enhances system has not yet been found. The dye should have a broad inhomogeneous absorption band but a small homogeneous the probability of photoproduct formation.line width because the maximum number of dierent holograms which can be stored in one sample is limited by the Chlorin-e 6 trimethyl ester 1. To 400 ml of degassed MeOH in a 1 l round-bottomed flask, equipped with magnetic stirrer, ratio of the homogeneous line width and the inhomogeneous broadening. To obtain permanent spectral holes the dye has reflux condenser and thermometer, were added 2 g (3.36 mmol) of chlorin e6.The resulting black suspension was degassed to undergo a photoreaction to a product with an absorption band in a dierent spectral region which is, at least at liquid with argon for 10 min and then 20 ml of conc. H2SO4 in 200 ml of degassed MeOH were added within 15 min. The resulting helium temperature, stable against thermal back-reaction.A Debye–Waller factor close to 1 is required as well as a high green solution was refluxed for 1 h. The reaction mixture was cooled to room temp., poured on 1 l of iced water and quantum eciency of the burning process and a good contrast of the spectral hole. It is also desirable that the dye is neutralized to pH 7 with solid NaHCO3.The aqueous phase was extracted with ethyl acetate (2×700 ml). The combined commercially available or easy to synthesize. Though being the passive part of the system, the choice of organic phases were washed twice with 100 ml of brine, dried with MgSO4, filtered and evaporated. Flash chromatography the matrix is also of great importance. The dye solubility should be suciently high to yield films with an optical density (ethyl acetate then MeOH) aorded 1.80 g (84%) of 1 as a violet powder.TLC (propanol–ethyl acetate–H2O–25% aq. of 1–2, even for samples with a thickness of only a few microns. The films have to display good optical quality, i.e. flat surface and no tarnish. Further it is known that the matrix can aect the homogeneous line width and the temporal stability of the holes.8,9 Our most promising results were previously obtained with chlorin in a PVB matrix.The ‘figure of merit’ of this system is shown in Fig. 1. It was the goal of a recent research project to find new systems which extend the spectral range of the chlorin–PVB system without losing its exceptional qualities and which require a less sophisticated synthesis.In this paper, we report the synthesis and hole burning properties of two chlorin analogues which can be derivatized from commercially available materials. Experimental Synthesis of chlorin-e 6 trimethyl ester 1 and brominated chlorine 6 trimethyl ester 2 In contrast to the complex synthesis of chlorin10 we used the Fig. 1 Figure of merit of chlorin: points on the outer circles indicate good properties, and points on the inner circles poor properties method described below to get to 1 and 2.Apart from ease of J. Mater. Chem., 1997, 7(9), 1731–1735 1731to make use of the Stark eect, very thin samples are required (<50 mm) to achieve a homogeneous and strong electric field on the sample. We used three methods to prepare our samples. Casting.On a glass plate with a freshly cleaned, flat surface a glass cylinder of ca. 3–5 cm diameter is mounted by gluing. This cylinder is filled with a solution of polymer, dye and an appropriate solvent. The amount of polymer is calculated in such a way that after evaporation of the solvent the desired film thickness is reached. The concentration of the dye is determined by the desired optical density.The glass cylinder is then covered partially by a glass plate and the solvent is allowed to evaporate in a place with no air turbulence. By this method, films of thicknesses 40–200 mm can be produced. If a polymer with a low glass transition or melting point is used, the quality can be improved by a subsequent step: the film on the glass plate is covered with a second glass plate and pressed while it is heated to a temperature a few degrees below its melting point.After a few hours the homogeneity of the film has improved, bubbles are removed and the thickness has decreased. This method is limited to thermoplastic polymers which have a melting point which is suciently below the decomposition point of the embedded dye.Spin coating. The dye–polymer solution is placed on to the centre of a freshly cleaned glass substrate which is mounted on a fast rotating stage. By centrifugal force a film of homogeneous thickness is formed. The properties of the resulting films are determined by various process parameters, such as rotation speed, acceleration, time, sample volume, concentration and viscosity.This coating method, which can be automated easily, is especially suited for films with a thickness below 10 mm. If the viscosity of the solution used is too high the surface of the resulting films is mostly very rough. Fig. 2 Chemical structures of chlorin, chlorin-e6 trimethyl ester 1 and brominated chlorin-e6 trimethyl ester 2 Photopolymerization. For this approach, we dissolved the dyes in an epoxy oligomer solution of Ebecryl 600 (straight epoxyacrylate based oligomer from UCB) and Darocur 1173 NH3, 70510520510): Rf=0.67; UV (N-methylpyrrolidine): (photoinitiator for UV curing from Ciba-Geigy), which was lmax/nm 662.dH [300 MHz, (CD3)2SO] 9.79 (s, 1H, b-H); 9.68 kindly supplied as a stock solution by Dr M. Ko�hler of the (s, 1H, a-H); 9.11 (s, 1H, d-H); 8.35 (dd, 1H, J 12, J 18, 2a- Additive Division Ciba-Geigy.A few ml of the stock solution Hx); 6.44 (dd, 1H, J 1, J 18, 2b-HB); 6.15 (dd, 1H, J 1, J 12, were introduced carefully between two glass plates which were 2b-HA); 5.95 (d, 1H, J 18, 10-CH); 5.41 (d, 1H, J 18, 10-CH); kept apart by thin spacers. After 2 s of irradiation with a xenon 4.60 (m, 1H, 8-H); 4.31 (m, 1H, 7-H); 3.81 (m, 2H, 4a-CH2); arc lamp we obtaimogeneous polymer films of approxi- 3.62; 3.58; 3.55; 3.51; 3.35; 3.33 (6s, 18H, 9a-CH3, 10b-CH3, mately 200 mm thickness.The optical quality was very good. 7d-CH3, 5a-CH3, 1a-CH3, 3a-CH3); 2.7–1.4 (m, 4H, 7a,7b- This method is restricted to dyes which are soluble in the CH2); 1.69 (t, 3H, J 7, 8a-CH3); 1.61 (d, 3H, J 7, 4b-CH3). photopolymer and also to dyes which do not undergo an irreversible photoreaction upon UV irradiation.In the case of Brominated chlorin-e 6 trimethyl ester 2. In a 50 ml roundchlorin and its derivatives this method worked well. bottomed flask, equipped with magnetic stirrer and thermometer were placed 0.836 g (1.31 mmol) of chlorin-e6 trimethyl ester 1 in 200 ml of CHCl3. A solution of 0.21 g Investigation of photochemical and photophysical properties (1.31 mmol) of bromine in 5 ml of CHCl3 was added within For a first examination of our samples we utilized the optical 5 min at -10 °C under an argon atmosphere. The reaction setup shown in Fig. 3. A dye laser (Lambda Physik FLD 3002) mixture was warmed to room temp. within 20 min and then is pumped by an excimer laser (Lambda Physik LPX 130).evaporated. Flash chromatography (ethyl acetate then MeOH) The beam is expanded to 0.5 cm diameter and is then directed aorded 0.649 g (72%) of 2 as a violet powder. dH [300 MHz, to the sample which was placed into a flow cryostat (Oxford (CD3)2SO] showed that the product was a mixture of isomers, Instruments) in a UV photospectrometer (Perkin-Elmer with bromination at the C2aMC2b double bond and the meso Lambda 9).After irradiation, the sample is rotated by 90° for positions, mainly at the b-position. TLC (propanol–ethyl measurements. Although the spectral resolution of this instruacetate –H2O–25% aq. NH3, 70510520510): Rf=0.57. UV ment (0.2 nm) is much broader than the expected spectral hole (NMP): lmax/nm 656 (Found: C, 60.39; H, 6.15; N, 7.24; Br, width, we used this setup because it allowed us a relatively 7.80.Calc. for C37H39BrN4O6: C, 62.09; H, 5.49; N, 7.83; fast test of some material properties. This method allowed us, Br, 11.16%). for example, to see whether a certain sample shows hole burning at all and to detect the spectral position of the Sample preparation photoproduct as well. For a quantitative comparison between chlorin and its two For our holographic data storage experiments we need homogeneous films of high optical quality, i.e.flat surfaces, a perfect derivatives 1 and 2 with respect to the kinetics, line width and hole stability, we used a setup12 as in Fig. 4. The beam of a transparency and a high optical density (OD 1–2) at the absorption maximum of the dye.If experiments are performed Coherent autoscan dye laser is divided into two parts which 1732 J. Mater. Chem., 1997, 7(9), 1731–1735and built samples of 1 and 2 by the spin coating technique described above. On glass substrates with ca. 2 mm thickness we prepared PMMA–dye films with a thickness of 5–10 mm with optical densities between 1 and 3.We tried several solvents and found that the best results were obtained with isobutyl methyl ketone.In this case the optical quality of the films was obviously very good. The naked eye could detect no inhomogeneities. The samples were brought to the setup described in the Experimental section (Fig. 3) and cooled to ca. 5 K. Comparing the absorption spectra of the samples at room temperature and at 5 K we found that on cooling the absorption band gets narrower, the peak is shifted a few nm to the blue and the optical density at this point increases.This eect is already known.14 The following experiments were performed with Rhodamine 101 as laser dye. In the case of 2–PMMA we first tried to burn a hole at 657.5 nm which was at the maximum of the absorption. The area of irradiation was ca. 1 cm2 and the pulse energy was estimated to be 0.5 mJ pulse-1 at the sample. After 100 000 pulses only a small hole could be Fig. 3 Setup for testing the hole burning properties; the sample was observed and the OD dropped from ca. 1.2 to 1.125. With a brought into a cryostat which was built in a UV spectrometer. After burning wavelength of 650 nm we did not manage to burn a irradiation (a) the sample holder could be turned from outside by 90° detectable hole though the energy per pulse at this wavelength for measurements of the absorption spectra (b).was twice as much as in the case before. Slightly better results were obtained with 1–PMMA. Subsequently, spectral holes are combined on the sample again to write a holographic could be burnt at 662.5, 656.5 and 659.5 nm.But when we grating. The setup allows us to measure the transmitted light burnt at 659.5 nm we observed that the hole at 662.5 nm was of one of the beams as a function of time. If one of the writing partially refilled while the hole at 659.5 nm remained beams is blocked and the other one attenuated, the hologram unchanged. In summary, the 1–PMMA and 2–PMMA systems written can be detected and by spectral scanning with the are not very appropriate devices for data storage.read-out laser beam, the line width of the hologram (diraction Next we embedded 1 and 2 in the photopolymer as described mode) can be obtained as well as the line width in trans- in the ‘Photopolymerisation’ section above. After cooling to mission mode. 5 K we burnt several holes at 646.5–660.5 nm.The pulse For measurements of the fluorescence lifetime at room temp. energies at the sample were 0.2–1 mJ cm-2. Also, we observed we used the setup described in ref. 13. The method of time- a refilling of existing holes if new ones were burnt at shorter correlated single-photon-counting (TCSPC) was used. The wavelengths. A typical experiment is shown in Fig. 5. In trace light source consists of a Coherent Antares mode-locked (a) the result of an experiment is shown where a spectral hole Nd5YAG laser and a home built synchronously pumped dye was burnt at 652 nm in a sample of 1 embedded in photopolaser. This system supplies at 76 MHz repetition rate pulses of lymer. The laser was operated at 20 Hz for 500 s (10 000 ca. 10 ps duration. The emission is detected with a Spex 1400 pulses).Trace (b) was recorded after providing 5000 pulses at double monochromator equipped with a photomultiplier tube. 648 nm to the same sample. Another 5000 pulses at 648 nm [trace (c)] results in a significantly deeper hole at this position while the hole at 652 nm meanwhile clearly shows refilling. Results and Discussion Traces (d)–( f ) show subsequent hole burning experiments at We started with poly(methyl methacrylate) (PMMA) as matrix, 646 and 656 nm, respectively, which also cause a decrease in since it is a standard polymer with good optical properties, the holes previously burnt.After having burnt these holes we recorded the UV spectra over a larger range, as shown in Fig. 6 and we could observe the formation of a new absorption maximum centred at ca. 600 nm which is due to the photoproduct. For technical reasons this experiment could not be performed at the same resolution as the measurements shown in Fig. 5 and therefore the single holes in the main absorption Fig. 4 Setup for quantitative measurements of hole burning properties. It allowed measurement in absorption and in holographic mode, Fig. 5 Holes formed in the absorption band of 1 in the photopolymer respectively. The setup has been described in detail in a previous publication (ref. 12). also showing hole refilling. For details see text. J. Mater. Chem., 1997, 7(9), 1731–1735 1733with compound 1 we observed a photoproduct with an absorption maximum at 600 nm. In this case we tried to burn spectral holes in the photoproduct.At 595, 600 and 605 nm stable holes could successfully be detected. After these experiments which showed that hole burning was in principle possible with our new samples we made a comparison with the well known chlorin and embedded this substance in a photopolymer also. Now we used the setup described in the Experimental section (Fig. 4) to measure the kinetics of the hole burning processes, the hole widths and the time stability of the holes. With the setup shown in Fig. 4, a holographic grating was written. During the writing procedure the transmission of the sample was recorded. After the burning process the hole was detected in two ways. First we made a scan around the burning frequency using a laser power much lower than that used during the burning process.In addition the hole width was determined holographically which is a more accurate method Fig. 6 Larger range UV–VIS spectrum of 1 (a) before and (b) after because it is background free. The measured values were fitted irradiation, also showing photoproduct formation indicated by a new absorption band at ca. 600 nm. In this spectrum several holes which with an exponential decay curve and as shown in Fig. 7 the were burnt around the absorption maximum are not resolved. burning rate of 1 and 2 is about five times faster than for chlorin itself. The hole widths of the new compounds, however, are up to 50% larger. This is a drawback in terms of the maximum theoretical storage density which can be achieved. Furthermore, we investigated the hole stability of chlorin in the photopolymer for comparison with the well known chlorin–PVB system. For this purpose we burnt a hole at 636.09 nm, then held the sample at liquid helium temperature without further bleaching and measured the hole depth as well as line width as a function of time (Fig. 8). These measurements showed that the photopolymer is worse than PVB. Another quantity we determined was the Debye–Waller factor of chlorin in the photopolymer.The higher this number the more of the absorption band can be used for SHB. It was found to be 0.55, which is in the same range as for chlorin–PVB (0.65). As one of the quantities of interest in a photochemical reaction is the fluorescence lifetime we did some room temperature measurements with the setup described in ref. 13. For the same matrix, i.e. photopolymer, Table 1 shows that the lifetimes Fig. 7 Burning kinetics. The modified chlorins burn at similar burning of 1 and chlorin have almost the same value, while the lifetime eciencies five times faster; (%) chlorin (26 mJ cm-2), (') 1 (5.5 of the brominated species 2 is significantly shorter. In addition, mJ cm-2) and (1) 2 (7.2 mJ cm-2).we observe a strong matrix eect; the lifetimes of the new compounds embedded in PMMA are much shorter than in the photopolymer (Table 1). Conclusions From the results described in this paper, we can conclude that 1 and 2 are good alternatives to chlorin for use as data storage materials at liquid helium temperature. Their synthesis is much easier than that of chlorin and they show five-fold faster burning kinetics. The spectra of both compounds are shifted ca. 20 nm to the red compared to chlorin. Almost over the whole inhomogeneous bandwidth, spectral holes can be burnt which are stable for reasonable times. The absorption spectra of these compounds as well as the spectra of their photoproducts show no overlap with the spectra of chlorin in the region useful for SHB.Therefore it is possible to build up films consisting of a matrix, chlorin and one of these new com- Fig. 8 Temporal hologram stability of chlorin in photopolymer: (a) 0 min, 2.05 GHz; (b) 5 min, 2.19 GHz; (c) 30 min, 2.46 GHz; pounds. This leads to an extension of the spectral range which (d) 45 min, 2.52 GHz can be used for data storage. The hole burning properties of 1 and 2 are almost identical though we assumed the brominated compound to be faster by enhancing the ISC rate due to the band after irradiation are not resolved.Only an overall decrease of the absorption is observed. When the temperature presence of the ‘heavy atom’. The fluorescence lifetime measurements at room temperature show that the decay of the excited then was raised to 293 K the absorption band of the photoproduct had disappeared again and the original spectrum of 1 state of 2 is faster than that of 1 and decay of both is faster than that of chlorin.was obtained with no changes from its appearance prior to cooling and burning. With 2 in the photopolymer we obtained The photopolymer which we used showed very good optical properties and the preparation of the samples could be per- similar results.The range where holes could be burnt was 646–666 nm, somewhat broader than in the case of 1. As seen formed very quickly. Disadvantages, however, are the broader 1734 J. Mater. Chem., 1997, 7(9), 1731–1735Table 1 Comparison of selected properties of chlorin and compounds 1 and 2 in dierent matricesa abs. max. fluorescence material abs.max./nm photoprod./nm burning rate hole stability lifetime/ns chlorin–PVB 634 580 + ++ 8 chlorin–photopol. + + 7.5 1–PMMA 662 - - 0.96 1–photopol. 652 598 ++ + 6.14 2–PMMA 657 - - 0.61 2–photopol. 654 598 ++ + 3.02 a++: very good, + good, - poor. Frequency selective optical data storage system, US Pat. 4 101 976, line width and the faster decay times of holes burnt into July 18, 1978.chlorin–photopolymer compared to chlorin–PVB. This behav- 3 P. Saari, R. Kaarli and A. Rebane, Opt. Soc. Am. B, 1986, 3, 527. iour might be improved if the photopolymer mixture is modi- 4 T.W. Mossberg, Opt. L ett., 1982, 7, 77. fied such that the network built during photopolymerization 5 Persistent Spectral Hole-Burning: Science and Applications, in is less flexible.T opics in Current Physics 44, ed. W. E. Moerner, Springer Verlag, Berlin, New York, 1988, ch. 2, p. 33. 6 U. P. Wild and A. Renn, J.Mol. Electronics, 1991, 7, 1. We thank the Kommission zur Fo� rderung der 7 (a) E. S. Manilo, S. B. Altner, S. Bernet, F. R. Graf, A. Renn and U. P. Wild, Appl. Optics, 1995, 34(20), 4140; (b) Holographic stor- Wissenschaftlichen Forschung for funding the Project-Nr. age of 12 000 images by spectral holeburning, B. Plagemann et al., 2296.1, Dr N. Bogdanova-Arn for major work in sample to be published. preparations as well as for many stimulating discussions and 8 S.Vo� lker, in Relaxation processes in molecular excited states, ed. Dr M. Ko�hler for contributing the photopolymer system. J. Fu� nfschilling, Kluwer, Dordrecht, 1989, p. 113. D. Reiss and M. Tschanz did the fluorescence lifetime measure- 9 T. Tani, Y. Sakakibara and K. Yamamoto, Jpn. J. Appl. Phys. Suppt., 1989, 28/3, 239. ments. We also thank S. Altner, S. Bernet and W. Ferri for 10 U. Eisner and R. P. Linstead, J. Chem. Soc., 1955, 4, 3742. help with some of the hole burning experiments. 11 (a) D. S. McClure, N. W. Blake and P. L. Hanst, J. Chem. Phys., 1954, 22, 255; (b) M. Kasha, J. Chem. Phys., 1952, 20, 71. 12 S. Bernet, ETH Thesis No. 10 292, 1993. 13 H. Gygax, ETH Thesis No. 10 374, 1993. References 14 Th. Sesselmann, D. Haarer and W. Richter, Phys. Rev. B, 1987, 36/14, 7601. 1 A. Szabo, Frequency selective optical memory, US Pat. 3 896 420, July 22, 1975. 2 G. Castro, D. Haarer, R. M. Macfarlane and H. P. Trommsdor, Paper 7/01465A; Received 3rd March, 1997 J. Mater. Chem., 1997, 7(9), 1731–1

ISSN:0959-9428    

DOI:10.1039/a701465a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

Alkyl phenylglyoxylates as radical photoinitiators creating negative photoimages1 Shengkui Hu and Douglas C. Neckers* Center for Photochemical Sciences, Bowling Green State University, Bowling Green, OH 43403, USA Alkyl phenylglyoxylates are shown to be ecient photoinitiators for acrylate polymerization. Benzoyl and phenyl radicals derived from intermolecular hydrogen abstraction are the initiating species.A negative photoimage system was developed based on this observation. The imaging material consists of a polymeric phenylglyoxylate initiator and to-be-crosslinked diacrylate monomers. The contrast and sensitivity of this system have been measured. In the last two decades, photopolymerization has found an a Varian Unity Plus 400 NMR spectrometer using CDCl3 as solvent. Chemical shifts are in ppm with SiMe4 as the internal increasing number of applications, most notably in the printing standard; J values in Hz.GC measurements were carried out and electronics industries.2 It is a versatile and widely used on a Hewlett-Packard(HP) 5890 Gas Chromatograph with a route to dierent UV curable coatings, adhesives and inks. 30 m×0.253 mm ID×0.25 mm film thickness DB-1 column Photopolymerization processes have many advantages over (J & B Scientific) and a flame ionization detector.GC–MS thermal polymerization reactions. The production rates of were taken on Hewlett-Packard 5988 mass spectrometer photopolymers are higher and the processes can be carried coupled to a HP 5880A GC with a 30 m×0.25 mm out under less demanding conditions.3 ID×0.25 mm film thickness DB-5 ms column (J & B Scientific), Almost all commercial photoinitiators are compounds which interfaced to a HP 2623A data processor. Thin layer chroma- produce either free radicals and/or acids upon irradiation at tography was performed with Whatman silica gel coating TLC appropriate wavelength.4 The most common are benzoin and plates.Silica gel (60 A ° , 60–200 mesh) used in column chroma- its derivatives, acetophenone and its derivatives, aromatic tography was from J. T. Baker Chemical Company. High ketone–amine combinations and various onium salts. resolution mass spectra were obtained from the University of Methyl phenylglyoxylate was sold commercially as a photo- Illinois at Urbana-Champaign. initiator many years ago, and we have been interested in understanding the processes by which it initiates polymer- Photochemical polymerization forming processes.The photochemical reactions of alkyl phenylglyoxylates have been studied extensively.5 Considering Polymeric thin films were made by exposing 15mm films of the radical species generated in the intermolecular hydrogen target monomer and alkyl phenylglyoxylate to UV light in a abstraction induced radical chain processes (Scheme 1),5a we Colight M218 light bath (two 400W medium-pressure Hg have elucidated the mechanism for phenylglyoxylate initiation lamps).Fluorescent probe was added when necessary. of photopolymerization processes. Monomeric films were made by squeezing a drop of the mixture In our earlier study,5a alkyl phenylglyoxylates were found between two Pyrex glass plates divided by a 15 mm Teflon spacer.to undergo both intramolecular (Norrish Type II) and inter- Photochemical reactions in benzene were carried out in Pyrex molecular hydrogen abstraction leading to radical chain reac- test tubes. Samples were dissolved in solvent and sealed with a tions in aprotic solvents.The overall process as exemplified by rubber septum bound by sticky parafilm. Degassing was achieved ethyl phenylglyoxylate is shown in Scheme 1. by bubbling dry argon gas through the solution for 10–15 min. The intermediate hydroxyphenyl ketene can be trapped by Irradiation was carried out in a Rayonet RPR-100 photoreactor alcohols5b and imines6 or decarbonylate to form benzaldehyde equipped with sixteen 350 nm GE F8T5·BLB UV lamps. 2 when ecient ketene trapping reagents are absent. Benzoyl Resist films were prepared by spin coating a 25% (w/w) radicals are produced by intermolecular hydrogen abstractions benzene solution of 9 and 10 (154, w/w) at 6000 rpm for 20 s by one excited alkyl phenylglyoxylate molecule on the ground with a Headway Research, Inc.spin-coater onto silicon wafers state of another like itself. Products resulting from benzoyl (Si-tech, Inc.) of appropriate sizes. Irradiations of resist films radical addition to ground state alkyl phenylglyoxylates, 4, and were performed by defocused UV irradiation from a 200 W subsequent coupling with other radicals, 5, were also isolated. high-pressure mercury arc lamp filtered through a 365 nm Biphenyl 6 results from solvent involvement in the hydrogen filter (bandwidth ca. 40 nm). The distance from the film to the abstraction process. However, phenyl radicals may also result lamp was fixed at 11 cm. The photon flux from the irradiation from a loss of carbon monoxide from benzoyl radical. One or source was measured by a Scientech 365 power and energy more of these radicals can initiate radical polymerization meter positioned at the same position as the resist films.processes. Time resolved laser flash photolysis Nanosecond laser flash photolysis was carried out on a setup Experimental described by Ford and Rodgers7 using the third harmonic of a Materials Q-switched Nd5YAG laser (Continuum, YG660) as excitation source. The sample solution in a quartz cuvette was purged by Benzene (Aldrich) was dried over sodium benzophenone ketyl Argon for 5 min before and during the experiment.The samples under argon. Acrylate monomers and styrene were also were excited with 355 nm pulses (pulse width ca. 7 ns). obtained from Aldrich. All monomers contain radical inhibitors, typically 10–100 ppm hydroquinone, and were used with- Ethyl [2H5]phenyl glyoxylate [2H5]-1 out further purification.Other chemicals were obtained from commercial sources and used as received. NMR spectra were [2H6] benzene 0.8 g (10 mmol), 1.4 g (10 mmol) ethyl oxalyl chloride and 25 ml of anhydrous methylene chloride were taken with either a Varian Gemini 200 NMR spectrometer or J. Mater. Chem., 1997, 7(9), 1737–1740 1737Scheme 1 placed in a 50 ml flask equipped with a magnetic stirrer and of the initiation, 0.1% (vs.monomer) of N,N-di-n-butyl-5- (dimethylamino)naphthalene-1-sulfonamide (DASD) was suspended in an ice–salt bath. After stirring for 10 min, 1.7 g (12 mmol) of aluminium chloride was added in small portions incorporated as a fluorescent probe,9 and the progress of polymerization followed with a cure monitor.10 A typical result over 10 min.When the solution turned red-brown and became homogeneous, the ice–salt bath was removed and the mixture for the polymerization of di(ethylene glycol) dimethacrylate is shown in Fig. 1. The ratio of probe fluorescence intensities at was poured over 50 g of crushed ice and 30 ml of concentrated hydrochloric acid. The organic layer was washed with 30 ml 456 and 558 nm indicates the extent of polymerization.of 0.1 M sodium hydroxide (×3) and water (×3). After separating the organic layer and evaporating the solvent, the crude Initiator species product was purified by column chromatography using Equal amounts of 1 and methyl acrylate were dissolved in dry hexanes–ethyl acetate (1051) as the eluting solvent. 1.5 g (83%) benzene and degassed by purging with argon. After irradiation, of pure product was obtained. dH (400 MHz, CDCl3), 1.33 (t, the major product observed was diethyl 2,3-dihydroxy-2,3- J 6.8, 3H), 4.36 (q, J 6.8, 2H). dC (50 MHz, CDCl3), 14.04, diphenyl succinate 3. The putative benzoyl and phenyl radical 62.26, 128.30 (t), 129.54 (t), 132.21, 134.32 (t), 163.75, 186.33. MS: 54 (11), 82 (31), 110 (100), 155 (2.0), 183 (0.1).HRMS m/z 183.0941; calc. 183.0944. Results Photopolymerization of dimethacrylates For practical purposes, photocurable resins consist of a combination of multifunctional acrylates that form complex polymeric networks upon polymerization. For instance, a mixture of di-, tri-, and penta-acrylates is used as standard resin in our group for stereolithography studies.8 We used pure dimethacrylate monomers in this study to simplify the structures of resulted polymers.Ethyl phenylglyoxylate (1) was tested as the photoinitiator to polymerize various monomers. Generally, 0.5% (by mass vs. monomer) of ethyl phenylglyoxylate was dissolved in a benzene solution of the monomer contained in a Pyrex testtube and the solution was degassed by purging with dry argon for 15 minutes.Irradiation with a medium-pressure mercury Fig. 1 Ethyl phenylglyoxylate initiated polymerization of di(ethylene lamp (maximum emission 365 nm) converted the monomeric glycol ) dimethacrylate. The progress of the reaction was monitored by a cure monitor with an added fluorescence probe. solution to a non-mobile polymer gel.To reveal the eciency 1738 J. Mater. Chem., 1997, 7(9), 1737–1740Scheme 2 Scheme 4 Fig. 2 AFM micrograph of image produced poly(methacryloylethyl phenylglyoxylate) 10.12 We describe its initiation ability herein. (Scheme 4) Irradiation of a benzene solution of 9 and 10 (154, w/w) resulted in a precipitate due to the polymerization of 9 initiated by radicals derived from the photolysis of 10.To exclude the possibility that the precipitate is the result of photoreaction solely of 10,12 a neat mixture of 9 and 10 (154, w/w) was irradiated. Solidification of the whole mixture was observed due to the polymerization of 9. An imageable material was Scheme 3 derived from a mixture of a multimethylacrylate monomer (9) and a polymeric phenylglyoxylate (10), that serves as the polymeric free radical photoinitiator.Tri(ethylene glycol ) derived products 2, 4, 5 and 6 were not found, but the presence dimethylacrylate (9) was chosen as the working monomer of ethyl 3-benzoylpropionate 7 and methyl 3-phenylpropionate since a benzene solution of the mixture of 9 and 10 forms a 8 (Scheme 2) was confirmed from comparison of the mass good film on a silicon surface upon spin coating.A typical spectral cracking patterns obtained from GC–MS analyses, as negative photoimage produced upon irradiation at a dose well as by comparing their retention times on two dierent larger than the Di (the insolubilization dose, vide infra) is GC columns with authentic samples. The relative quantities of shown in Fig. 2. The image was produced by irradiating a spin 7 and 8 were assessed by GC analysis with the instrument calibrated using undecane as the added internal standard.The presence of 7 and 8 suggests that both benzoyl radical and phenyl radical initiates the polymerization process. In order to clarify the origin of the phenyl radical, ethyl pentadeuterophenylglyoxylate ([2H5]-1) was synthesized and photolysed in benzene, Scheme 3.Normal isotopic patterns were observed for compounds [2H5]-2, [2H10]-3, [2H10]-4. The presence of pentadeuterobenzene and biphenyl with dierent isotopic patterns (6 and [2H5]-6) indicates that phenyl radicals are derived from both [2H5]-1 and the solvent, benzene. As indicated in Scheme 1, a benzoyl radical decarbonylates forming the phenyl radical, which can abstract a hydrogen from the solvent molecule and produce the solventderived phenyl radical.Negative photoimaging system Polymeric photoinitiators oer advantages in that they generally have greater reactivity over their monomeric Fig. 3 Sensitivity plot of the negative photoimage counterparts.11 We have studied the photochemistry of J. Mater. Chem., 1997, 7(9), 1737–1740 1739coated film through a TEM T2000-Cu grid with holes of 7.5×7.5 mm and bars of 5 mm separating the holes as a soft contact mask.After irradiation, the surface was rinsed with dry benzene for 30 s. The non-irradiated part of the film was totally removed by this development procedure. It is clear that resolution up to 5 mm can be achieved and better resolution could be anticipated with masks having finer structures.The sensitivity of the photoimage forming process was measured by atomic force microscopy (AFM).12 The sensitivity curve of this photoimaging system is shown in Fig. 3. The gel dose, Dg (the dose at which the gel makes its first appearance), is about 1.5 J cm-2. The insolubilization dose, Di, is 6 J cm-2. The sensitivity of the resist, Ds, is defined as the dose required to retain 50% of the original film, and is 3.1 J cm-2.13 The contrast c=1/log(Di/Dg), is calculated as 1.7.The sensitivity of this photoimage system is higher than the sensitivities of currently employed photoresists (25–200 mJ cm-2), however, the system is of high contrast.14 Since insolubilization is Fig. 4 Decay rate constants of methyl phenylglyoxylate triplet at achieved by the crosslinks of the multiacrylate monomer dierent styrene concentration initiated by photochemically produced radicals, it is expected that the sensitivity of this system could be improved by using were purchased with funds from NSF (CHE9302619), the Ohio monomers with multiacrylic functionalities.Board of Reagents, and Bowling Green State University.We acknowledge their support. Conversations with Dr G. S. Discussion Hammond are gratefully acknowledged. Alkyl phenylglyoxylates as photoinitiators for styrene polymer- References ization have also been studied. Although some degree of polymerization was observed, the rate of polymerization is 1 Contribution No. 311 from the Center for Photochemical Sciences. low.The expected adducts of the initiating radicals to styrene, 2 W. S. Deforest, Photoresist: Materials and Process, McGraw-Hill, b-phenylpropiophenone (from the benzoyl radical) and New York, 1975. 3 G. Moad, D. H. Soloman, T he Chemistry of Free Radical bibenzyl (from the phenyl radical) were not observed. The Polymerization, Elsevier Science Ltd, Amsterdam, 1995. Paterno`–Bu� chi reaction between alkyl phenylglyoxylate and 4 (a) S.P. Pappas, UV Curing: Science and T echnology, Vol. 2, styrene is not expected since the double bond in styrene is not Technology Marketing Corp., CO, 1985; (b) N. W. Allen, suciently electron rich.15 On the other hand, related alkenes Photopolymerization and Photoimaging Science and T echnology, have been shown able to quench excited phenylglyoxylate Elsevier Science Ltd., Amsterdam, 1989.triplets by electron transfer.16 The oxidation potential of 5 (a) S. Hu and D. C. Neckers, J. Org. Chem., 1996, 61, 6407; (b) E. S. Huyser and D. C. Neckers, J. Org. Chem., 1964, 29, 276; styrene is 2.22 eV (vs. standard calomel electrode, SCE).17 (c) A. Scho� nberg; N. Latif; R. Moubasher and A. Sina, J. Chem. Taking the reduction potential (-1.227 eV, vs.SCE) and triplet Soc., 1951, 1364; (d) M. W. Encinas; E. A. Lissi; A. Zanocco; energy (66 kcal mol-1; 1 cal=4.184 J)16 of methyl phenylglyox- L. C. Stewart and J. C. Scaiano, Can J. Chem., 1984, 62, 386; ylate, from the Weller equation,18 eqn. (1), (e) P. A. Leermakers, P. C. Warren and G. F. Vesley, J. Am. Chem. Soc., 1964, 86, 1768; ( f ) R. J.Tepper, M. C. Pirrung, J. Org. Chem., DGET=23.06 (EDox-EAred)-ET-C (1) 1995, 60, 2461. 6 H. Aoyama, M. Sakamoto, K. Yoshida and Y. Omote, DGET, the free energy change for electron transfer is positive J. Heterocycl. Chem., 1983, 20, 1099. and the electron transfer process is endothermic. However, the 7 W. E. Ford and M. A. J. Rodgers, J. Phys. Chem., 1994, 98, 3822. triplet energy of styrene is 61.7 kcal mol-1,19 lower than that 8 A.Torres-Filho and D. C. Neckers, J. Appl. Polym. Sci., 1994, of a typical alkyl phenylglyoxylate. Energy transfer from the 51, 931. excited triplet state of the alkyl phenylglyoxylate to monomeric 9 W. F. Jager, A. A. Volkers and D. C. Neckers, Macromolecules, styrene is thereby expected. The eciency of this process is 1995, 28, 8153. 10 R. Popielarz and D. C. Neckers, RadT ech ’96 North America indicated by the rate constant of styrene quenching methyl UV/EB Conference Proc., Nashville, TN, 1996. pp. 271–277. phenylglyoxylate triplet, 8.0×108 dm3 mol-1 s-1, which was 11 R. S. Davidson, J. Photochem. Photobiol. A: Chem., 1993, 69, 263. obtained by measuring the glyoxylate triplet lifetime in the S. N.Gupta; L. Thijs and D. C. Neckers, J. Polym. Sci., Polym. presence of various concentrations of styrene (Fig. 4). Chem. Ed., 1981, 19, 855. I. Gupta, S. N. Gupta D. C. Neckers, If triplet reactivity is not hindered by the monomer, alkyl J. Polym. Sci., Polym. Chem. Ed., 1982, 20, 147. phenylglyoxylates are ecient photoinitiators. The quantum 12 S. Hu, A. Mejiritski and D. C.Neckers, Chem. Mater., submitted. 13 Other definitions for Ds have been reported, see L. F. Thompson; yields of the hydrogen abstraction processes are high,5a and C. G. Willson and M. J. Bowden, Introduction toMicrolithography, these a-keto esters dissolve well in various monomers. 2nd edn., ACS Professional Reference Book, American Chemical Functionalization of both the alkyl12 and the phenyl5a functions Society, Washington DC, 1994. of the ester is readily achievable such that initiators designed 14 S. A. McDonald, C. G. Willson and J. M. J. Fre�chet, Acc. Chem. to fit varying requirements may be constructed. Res., 1994, 27, 151. In conclusion, we have discovered the initiation mechanism 15 S. Hu and D. C. Neckers, J. Org. Chem., 1997, 62, 564. 16 S. Hu and D. C. Neckers, J. Am. Chem. Soc., submitted. for alkyl phenylglyoxylates as photoinitiators for acrylate 17 M. Kojima, H. Sakuragi and K. Tokumaru, Bull. Chem. Soc. Jpn., photopolymerization and successfully employed this chemistry 1985, 58, 521. in a negative photoimage system. 18 D. Rehm and A. Weller, Isr. J. Chem., 1970, 8, 259. 19 S. L. Murov, Handbook of Photochemistry, Marcel Dekker, New We thank the National Science Foundation (DMR-90113109) York, 1973. and the Oce of Naval Research (Navy N00014-91-J-1921) for financial support of this work. The NMR spectrometers Paper 7/01797I; Received 14thMarch, 1997 1740 J. Mater. Chem., 1997, 7(9), 1737–17

ISSN:0959-9428    

DOI:10.1039/a701797i

出版商:RSC    

年代:1997

数据来源: RSC