摘要:

J O U R N A L O F C H E M I S T R Y Materials Poly(5-tert-butyl )benzothiophene: a soluble form of polyisothianaphthene with a large nonlinear optical response Anna Drury, Simon Burbridge, Andrew P. Davey and Werner J. Blau* Physics Department, Trinity College, Dublin 2, Ireland Received (in Cambridge) 4th June 1998, Accepted 6th August 1998 A soluble form of polybenzothiophene has been produced and chemically characterised.NMR spectroscopy indicates that there is a large quinoidal character contribution to the ground state of the polymer. The third order nonlinear optical properties of the polymer have been probed and it is found that the response is relatively large in the near-infrared region. The third order nonlinear optical properties of conjugated method of Hanack6 and the product isolated by careful low pressure distillation.The dihydro precursor 2 was synthesised organic semiconducting polymers have been the subject of much investigation for the past 15 years. It is expected that using the method previously reported for the unsubstituted derivative.7 The polymerisation is catalysed by 1 equiv. of such materials will find use in optical switching devices based on planar waveguides.1 FeCl38.NMR analysis of 3 is in good agreement with values Many diVerent classes of such polymers have been investigated2 in the search for a material which exhibits a reported for PITN9 and suggests that there is a large degree of quinoidal character in the ground state. The 1H NMR suYciently large third order nonlinear optical response for use in all optical switching devices.To date, a material which analysis serves to confirm this observation, the broad signal at d 8.2–8.6 being assigned to the deshielded environment of meets all device requirements has still not been identified. For certain applications within telecommunications, materials the proton attached to carbon 6 (see Scheme 1). The broadness of the signals may also be explained by this observation since which exhibit a large and fast third order nonlinearity in the region of 1.3–1.5 mm are required.a large contribution of quinoidal structure serves to ‘rigidise’ the polymer backbone, decreasing freedom of rotation about More recently, conjugated molecules with absorption in the near-infrared region have attracted attention since it is hoped the bonds connecting repeat units.The product polymer is soluble in polar organic solvents that the nonlinear optical response will be relatively large. Polyisothianaphthene (PITN) (or polybenzothiophene) is just such as chloroform, THF or toluene. Fig. 1 shows the visible/ near-infrared absorption spectrum of a 1 g l-l solution of the such a material.It was first produced some years ago in an insoluble form3 and has been shown to possess a small polymer in chloroform. The broad absorption shows several vaguely defined bandgap4 (ca. 1 eV ). The absence of soluble forms of this polymer has however shoulders probably indicating a large degree of coupling between electronic transitions and vibrational levels. precluded any study of its nonlinear optical properties in solution or high quality thin film forms.Recently, Pomerantz Temperature dependent absorption studies currently in progress will yield further information regarding this point. An et al. reported the synthesis of a soluble form of a similar polymer in a preliminary communication.5 estimate of the optical gap from this spectrum gives Eg=ca. 1.1 eV. This value is in close agreement with that reported by We report here on the synthesis and optical (both linear and nonlinear) characterisation of another soluble form of Pomerantz et al.5 and is marginally greater than the value originally reported for the insoluble form.3 this polymer, namely, poly(5-tert-butyl )benzothiophene. The route employed to synthesise this polymer is depicted The experimental method used to determine the microscopic third order nonlinear optical coeYcient (c) of a compound at in Scheme 1.The key intermediate 1 was produced by the 1064 nm in solution is described in detail elsewhere.10 It is based on self-diVraction from transient laser-induced diVraction gratings. Under thin grating conditions,11 an expression relating the diVraction eYciency, g into the first order, to the H3C CH3 BrH2C CH2 Br S S n 3 iii 2 1 ii i But But But But 1 3 3a 7a 7 4 5 6 Scheme 1 Reagents and conditions: i, NBS, CCl4, reflux, 1 h, then room temp., 18 h; ii, Na2S, EtOH, reflux, 1 h; iii, FeCl3, CHCl3, 50°C, Fig. 1 Electronic absorption spectrum of 3. dry air, 72 h. J. Mater. Chem., 1998, 8(11), 2353–2355 2353been synthesised and characterised.The optical properties of the polymer show that the material possesses a small gap, slightly larger than that of the insoluble form. It is also likely from these spectra that there is a strong degree of coupling between electronic transitions and vibrational states. This last point is the subject of further investigations. The microscopic nonlinear optical response is larger than that of comparable molecules and polymers.This is most likely due to the closer position of the absorption band to the measurement wavelength. Experimental Fig. 2 Concentration dependence of the laser induced grating All solvents were dried prior to use using standard methods. diVraction eYciency for 3. All reactions were carried out in an argon atmosphere unless otherwise stated.NMR spectra were recorded on a Bruker third order material nonlinearity x(3) is valid [eqn. (1)], MSL 300 spectrometer and TMS was used as an internal reference. IR spectra were recorded on a Nicolet 510-P FTIR |x(3)|=4 eoc n2 l Óg/(3 p d Io) (1) spectrometer. GPC analysis was performed using a Waters where c is the speed of light, eo is the permittivity of free 600t system.space, n is the refractive index of the sample, d is the sample thickness and Io is the input pulse intensity. In the experiments 4-tert-Butyl-1,2-dimethylbenzene reported here, d=1 mm and n is taken to be the refractive index of the solvent, because of the low fractional volume 106.2 g (1 mol ) o-Xylene and 92.1 g (1 mol ) tert-butyl chloride of solute. were well mixed (magnetic stirrer). 1.l g Anhydrous ferric The third order nonlinearity x(3) for a solvent/solute mixture chloride was added slowly (30 min) at room temperature. may be expressed as shown in eqn. (2), When the evolution of hydrogen chloride had ceased, excess tert-butyl chloride (20.5 g) was added and the mixture stirred |x(3)|=[(x(3)solv+Re x(3)sol)2+(Im x(3)sol)2]1/2 (2) for a further 1 h. It was then heated in a water bath for 15 min where Re x(3)sol and Im x(3)sol are the real and imaginary (turning brown at approx. 65 °C) and filtered through charcoal components of the material nonlinearity. By determining the (125 g). The resulting yellow solution was distilled and various concentration dependence of |x(3)|, the contribution from x(3)solv fractions of colourless liquid were collected (bp 155–175, may be extracted and the magnitude of Re x(3)sol and Im x(3)sol 185–200 and 205–210 °C).The highest boiling fraction was may be determined. Furthermore, the sign of Re x(3)sol may found to be 4-tert-butyl-1,2-dimethylbenzene. Yield: 90.6 g be determined from the concentration dependence of the real (55.8%); dH(300 MHz, CDC13) 1.3 (s, 9H), 2.2 (s, 3H), 2.25 part of |x(3)|.(s, 3H), 7.1 (m, 3H). The c values of a solute may then be derived [eqn. (3)], 1,2-Bis(bromomethyl )-4-tert-butylbenzene 1 c=|x(3)|/(NA C LL4) (3) 8.125 g 4-tert-Butyl-o-xylene (0.05 mol), 17.8 g N-bromosuc- where C is the molecular concentration (for polymer samples, cinimide (0.1 mol), 0.2 g benzoyl peroxide and 50 ml dry the repeat unit concentration), NA is Avogadro’s constant and carbon tetrachloride were placed in a 250 ml round-bottomed LL is the Lorentz local field factor, which is taken to be that flask and refluxed with magnetic stirring in the dark under of a linear molecule (i.e.LL=1).12. argon for 3 h. The mixture was left overnight at room tempera- Fig. 2 shows the concentration dependence of the diVraction ture (under argon), then it was filtered (to remove succinimide eYciency.As already described, theory predicts a parabolic salts) and concentrated in vacuo. The product was collected dependence. It is clear however that there is a deviation from by vacuum distillation (bp 116–118 °C at 0.12 mmHg). Yield: such a dependence in this case. At low concentration, the 4.66 g (29%); dH(300 MHz, CDCl3 1.31 (s, 9H), 4.79 (s, 2H), dependence on diVraction eYciency is parabolic.At a certain 4.81 (s, 2H), 7.40 (m, 2H), 7.55 (d, 1H); dC(CDCl3) 30.53 limit, however, this dependence begins to deviate before and 30.56 (CH2Br), 31.03 (CH3), 34.86 (Me3C), 126.83 (CH), returning at higher concentrations to a second parabolic 128.66 (CH), 131.53 (CH), 134.39 (quaternary C), 136.88 dependence.Such behaviour is not well understood but is (quaternary C), 152.95 (quaternary C). clearly due to some form of electronic interaction between polymer chains. The values of c measured for 3 from fitting data in the low 1,3-Dihydro-5-tert-butylisothianaphthene 2 concentration region are given in Table 1. The c values l.05 g (0.013 mol) Anhydrous sodium sulfide was dissolved in obtained for 3 are remarkably high in comparison to other 75 ml dry ethanol in a 250 ml round-bottomed two-necked polymers. In comparison to a polythiophene (a structural flask fitted with a magnetic stirrer and condenser. 3.98 g relative), for example, the values are one order of magnitude (0.012 mol) 1,2-Bis(bromomethyl )-4-tert-butylbenzene was greater. This is thought to be due to relatively closer posadded dropwise during 30 min.The solution went from pale itioning of the electronic absorption band to the wavelength blue to bright yellow. It was refluxed for 1 h and the ethanol of measurement. removed in vacuo. The remaining brown–black oil was dis- In summary, a soluble form of polyisothianaphthene has solved in CH2Cl2 and filtered to remove sodium bromide.The CH2Cl2 was removed in vacuo and the final product obtained Table 1 Values of c for 3 compared to those of a polythiophene by vacuum distillation (bp 88 °C at 6×10-2 mmHg). Yield: (ref. 13). 1.53 g (64%); dH(300 MHz, CDCl3) 1.33 (s, 9H), 4.25 (s, 2H), Compound cRe (esu) |c|Im (esu) |c| (esu) 4.28 (s, 2H), 7.18 (dd, 1H), 7.26 (dd, 1H), 7.29 (s, 1H); dC(CDCl3) 31.30 (CH3), 34.49 (Me3C), 37.67 (CH2), 38.16 3 -7.2×10-32 21.5×10-32 22.7×10-32 (CH2), 121.41 (CH), 123.97 (CH), 129.32 (CH), 137.38 (quat- Poly(3-butyl )thiophene -4.3×10-33 7.2×10-33 8.4×10-33 ernary C), 140.28 (quaternary C), 150.02 (quaternary C) (Calc. 2354 J. Mater. Chem., 1998, 8(11), 2353–2355for C12H16S: Theory: C, 74.94; H, 8.39; S, 16.28. Found: C, This work has been carried out as part of the E.C.’s RACE 2015 ARTEMIS & ACTS 053 MIDAS projects.We would 74.71; H, 8.52; S, 16.46%). also like to thank Professor M. Hanack for helpful discussions. Poly (5-tert-butyl-1,3-dihydroisothianaphthene) 3 References 0.7 g (3.6 mmol) 5-tert-Butyl-1,3-dihydroisothianaphthene 1 G. I. Stegeman and R. H. Stolen, J. Opt. Soc. Am. B, 1989, 6, 652. 2 H. S. Nalwa, Adv.Mater., 1993, 5, 341. was placed into a three-necked flask equipped with condenser 3 F. Wudl, M. Kobayashi and A. J. Heeger, J. Org. Chem., 1984, and drying tube, dropping funnel and inlet for dry air. 0.5 g 49, 3382. Anhydrous ferric chloride dissolved in 50 ml chloroform was 4 M. Kobayashi, N. Colaneri, M. Boysel, F.Wudl and A. J. Heeger, added (20 min). The solution was warmed to 50 °C and stirred J.Chem. Phys., 1985, 82, 5717. 5 M. Pomerantz, B. Chaloner-Gill, L. O. Harding, J. J. Tseng and for 24 h, with air bubbling through. The resulting black W. J. Pomerantz, J. Chem. Soc., Chem. Commun., 1992, 1672. solution was then washed with water to remove FeCl3. 6 M. Hanack, personal communication. Concentrated ammonia (20 ml ) was added and the solution 7 M.P. Cava, M. J. Mitchell and A. A. Deana, J. Org. Chem., 1960, stirred for 30 min at room temperature. It was washed several 25, 1481. times with water and dried over magnesium sulfate. The 8 M. Pomerantz, J. J. Tseng, H. Zhu, S. J. Sproull, J. R. Reynolds, R. Uitz, H., J. Arnott and M. I. Haider, Synth. Met., 1991, solvent was removed in vacuo and the low molecular weight 41–43, 825.fractions removed by Soxhlet extraction with methanol. Yield: 9 I. Hoogmartens, P. Adriaensens, R. Carleer, D. Vanderzande, 0.25g (36.5%). The experiment was repeated using monomer H. Martens and J. Gelan, Synth. Met., 1992, 51, 219. recovered from the methanol wash giving a total yield of 10 H. J. Byrne, W. Blau and K. Y. Jen, Synth. Met., 1989, 32, 229. 53.1%. GPC measurement indicated a high molecular weight 11 H. J. Eichler, P. Gu� nter and D. W. Pohl, in Laser Induced Gratings, Springer Series in Optical Sciences, Springer Verlag, for the product: Mw=49 362; Mn=10 842; dH(CDCl3) 0.9–1.7 Berlin, 1986, vol. 50. (9H), 7.1–7.6 (2H), 8.2–8.6 (1H); dC(CDCl3) 30–33, 36–38, 12 Y. R. Shen, The Principles of Nonlinear Optics,Wiley Interscience, 120–127, 137–143; nmax(KBr)/cm-1 1686, 1595, 1545, 1480, New York, 1984. 1458, 1410, 1362, 1254, 1140, 1003, 943 and 843 (Calc. for 13 H. J. Byrne, Ph.D. thesis, University of Dublin, 1989. C12H12S: C, 76.57; H, 6.42; S, 17.01. Found: C, 76.06; H, 6.66; S, 17.11%). Paper 8/04209H J. Mater. Chem., 1998, 8(11), 2353–2355 23

ISSN:0959-9428    

DOI:10.1039/a804209h

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Quaterrylenebis(dicarboximide)s: near infrared absorbing and emitting dyes Yves Geerts,a† Heribert Quante,a Harald Platz,a Rainer Mahrt,b M. Hopmeier,b Arno Bo�hmc and Klaus Mu�llen*a‡ aMax-Planck-Institut fu�r Polymerforschung, Ackermannweg 10, D-55128 Mainz, Germany bFachbereich Physikalische Chemie und Zentrum fu�r MaterialwissenschaVen, Philipps Universita�t, Renthof 5, D35032 Marburg, Germany cBASF AG, ZDP/0-M311, 67056 Ludwigshafen, Germany Received 8th June 1998, Accepted 2nd September 1998 New ladder-type chromophores, the quaterrylenebis(dicarboxdiimide)s 2, 18 and 23, have been synthesised which, despite their extended p-system, exhibit good solubility in organic solvents and film forming properties when adequately substituted.These unprecedented dyes, which absorb and even emit light in the NIR window, are also characterized by oustanding chemical, thermal and photochemical stability with regard to their absorption range. The potential formation of J-aggregates in strongly acidic media has been investigated and has been ruled out by combined 1H NMR and UV–VIS–NIR spectroscopy experiments.In addition, their photophysical and electrochemical characteristics have been explored and are discussed. Introduction The search for novel, near infrared (NIR) absorbing and emitting dyes is a challenge in dyestuV chemistry, mainly because of the potential high-technology applications in optical recording, thermally written displays, laser printers, laser filters, infrared photography and medicine.1 Despite the high demand, only a few NIR dyes, such as cyanine dyes, are eVectively used in practice.A prerequisite in the design of chromophores is the consideration of their chemical, thermal and photochemical stability.2 Perylene derivatives and, in particular, perylenebis(dicarboximide)s 1, are well-known for their outstanding chemical, thermal and photochemical inertness. 3,4 Their uses range from paints and varnishes to hightechnology applications such as tracers in fluorescence analytical assays,5 charge-transport in Langmuir–Blodgett films,6 photovoltaic cells,7 xerography,8 optical switches,9 laser-dyes10 and fluorescent collectors.11 Clearly, new chromophores such as quaterrylenebis(dicarboximide)s 2, which combine the outstanding properties of perylenebis(dicarboximide)s 1 with NIR absorption, are highly desirable.N N O O O O N N O O O O O O O O Ar Ar Ar Ar 1a 1b 12 7 11 8 a b c d 2 5 1 6 The first attempts at extending the p-system of perylene 3 to higher rylenes, namely terrylene 4 and quaterrylene 5, were the perylenebisamidine 9.16 These NIR dyes are characterized carried out by Clar.12 However, due to the lack of adequate by high photochemical and thermal stability.Moreover terry- alkyl substitution, resulting in extreme insolubility, the purifi- leneimides 7 and 8 exhibit oustanding quantum fluorescence cation and characterization of terrylene 4 and quaterrylene 5 yields of 0.9±0.1 and 0.6±0.1, respectively. were not possible.13 In this paper, we report the detailed synthesis and the More recently, we synthesized the first soluble oligorylene characterization of quaterrylenebis(dicarboximide)s 2, 18 and series 6.14 The introduction of tert-butyl groups at the periph- 23, which are higher homologues of perylenebis(dicarboxim- ery of the rigid aromatic structure drastically improved their ide)s 117 and of terrylenebis(dicarboximide)s 7.15 In addition, solubility in common organic solvents. Remarkably enough, the photophysical, thermal and electrochemical properties of terrylene, quaterrylene and even pentarylene were fully characquaterrylenebis( dicarboximide)s 2, 18 and 23 are compared to terized and their photophysical behavior correlated with their those of perylenebis(dicarboximide)s 1 and to terrylenebis- structure.14b (dicarboximide)s 7 and discussed in the light of their structures.We have also reported some new fluorescent dyes emitting at long wavelengths (600<l<750 nm) and even in the NIR range (l>750 nm), which are structurally related to quaterry- Results and discussion lenebis(dicarboximide)s, namely the terryleneimides 7,815 and Synthesis The synthetic pathway to quaterrylenebis(dicarboximide)s 2a,b †Chercheur Qualifie� au Fonds National de le Recherche Scientifique, is illustrated in Scheme 1.The key building block for the synthesis Universite� libre de Bruxelles, Chimie Macromole�culaire, CP 206/1, of quaterrylenebis(dicarboximide)s is the N-substituted pery- Boulevard du Triomphe, 1050 Bruxelles, Belgium. ‡E-mail: muellen@mpip-mainz.mpg.de lene-3,4-dicarboximides 11a,b which are obtained via the partial J.Mater. Chem., 1998, 8(11), 2357–2369 2357N O O R N O O R 16 11 15 12 18 9 17 10 2 5 1 6 2a R = C12H25 20 7 19 8 b R = C6H3-2,6-Pri 2 c R = Bu 3 4 5 N O O N N O N O N N O O R' O O O O Ar Ar Ar Ar N N O N N O O O O O Ar Ar Ar Ar N O O O R R R R Br Br Br Br Br Br Br Br 7a,b a R = H, b R = OAr R' = C8H17, C6H3-2,6-Pri 2 8a,b 9- syn 9- anti However, we recently reported some developments in the field of organometallic aryl–aryl coupling which allows the synthesis of 14a,b in higher yields.15,17 Specifically, two organometallic synthetic pathways from the monobromo Nsubstituted perylene-3,4-dicarboximide 12a,b to the biperylene 14a,b have been attempted.The first synthetic route, a one step Yamamoto homocoupling20 with the zero-valent nickel catalyst bis(cycloocta-1,5-diene)nickel(0) [Ni(cod)2] has successfully been applied and aVorded the biperylenes 14a,b in excellent yields (83–89%).The second synthetic route to the biperylene 14b is based on the Stille heterocoupling of 6 a b c d n n 0 1 2 3 monobromo N-substituted perylene-3,4-dicarboximide 12b with its stannylated analogue 13b in the presence of the zero-valent tetrakis(triphenylphosphine)palladium catalyst decarboxylation of perylenedicarboxylic anhydrides 10a,b.18,19 The bromination of the N-substituted perylene-3,4-dicarboxim- [Pd(PPh3)4].15,21 This route requires an additional step, but presents the advantage of replacing the relatively toxic, air- ides 11a,b at position 9 leads to the monobromo N-substituted perylene-3,4-dicarboximides 12a,b in 94–98% yield.Misono sensitive and expensive Ni(cod)2 by the more conventional Pd(PPh3)4. Moreover, the coupling of two diVerently substi- and Nagao have synthesized the biperylene 14c via an Ullmann coupling of the 9-bromo-N-butylperylene-3,4-dicarboximide tuted perylene derivatives, resulting in non-symmetrically Nsubstituted quaterrylenebis(dicarboximide)s, is therefore pos- 12c in low yield.18,19 The low yield has been attributed to the large amount of side products rendering the purification diY- sible.This significantly widens the scope of applications of the quaterrylenebis(dicarboximide)s which could be introduced as cult and to the inadequate alkyl substitution at the imide position resulting in low solubility of the biperylene 14c.side chain functions in polymers to combine the processability 2358 J. Mater. Chem., 1998, 8(11), 2357–2369N O O R N O O O O O R N O O R N O O R N O O R Br N O O R SnBu3 N O O R N O O R 2a,b 14a–c 10a–c 11a–c 12a –c 13b a R = C12H25 b R = C6H3-2,6-Pri 2 c R = Bu Scheme 1 Synthetic pathway to quaterrylenebis(dicarboximide) 2a.and good film-forming properties of polymers with the intrinsic which consists of introducing phenoxy substituents into the bay-regions of the aromatic core, is well-known in the case of properties of quaterrylenebis(dicarboximide)s. One could also selectively introduce another functional group, e.g. an electron the perylenebis(dicarboximide) 1b.15,16,25 The introduction of substituents in the bay-region of the perylenebis(dicarboxim- donor for photoinduced electron transfer or a biologically active molecule for NIR fluorescence analytical assays.5 ide) 1b presents the additional advantage of further extending the absorption maxima to longer wavelength. In analogy to The last synthetic step of Scheme 1 involves the cyclization of the biperylenes 14a,b into quaterrylenebis perylenebis(dicarboximide) 1b, we have attempted the synthesis of tetraphenoxy substituted quaterrylenebis(dicarboxim- 2a,b in the presence of a base and an oxidizing agent.23,24 Specifically, the cyclization reaction has been carried out in a ide) 18. The synthetic pathway to the tetraphenoxy substituted quaterrylenebis(dicarboximide) 18 is given in Scheme 2 and KOH/ethanol melt containing glucose as oxidizing agent at 120 °C.24 The resulting quaterrylenebis(dicarboximide) 2b was shares many similarities with that of the unsubstituted quaterrylenebis( dicarboximide)s 2a,b.readily purified by recrystallization, aVording the desired product 2b in 83% yield, whereas the less soluble quaterrylenebis- The three-fold bromination of 11 under drastic conditions gives the perylene tribromide 15 in excellent yield (91%).The (dicarboximide) 2a was obtained in lower yield (37%) and was purified by extraction of the by-products with chloroform. In selective nucleophilic substitution under basic conditions of the two bromine atoms in the bay-regions with phenol deriva- the case of quaterrylenebis(dicarboximide) 2b, further purifi- cation by column chromatography was only performed for tives aVords 16 in a yield of 33%.The moderate yield is due to side reactions, namely the substitution of all three bromine the preparation of analytical samples. The quaterrylenebis(dicarboximide) 2a is only slightly atoms by phenoxy groups and dehalogenation. Comparable to the synthesis of the biperylenes 14a,b, the soluble in organic solvents (typically <10-5 M) at room temperature and is better viewed as a pigment than a dye.Yamamoto coupling aVords the biperylene 17 in a yield of 88%. The cyclization of 17 to the tetraphenoxy substituted However for numerous applications, good processability, i.e. high solubility in organic media and good film-forming proper- quaterrylenebis(dicarboximide) 18, in a yield of 85%, has been carried out as described for the unsubstituted perylene 14.As ties, is required. As previously mentioned, one way to achieve processability is to introduce quaterrylenebis(dicarboximide) expected, the solubility of quaterrylenebis(dicarboximide) 18 is much higher than that of 2 and reaches ~10-2 M in 2a as a pendant group on a polymer chain. Another method, J.Mater. Chem., 1998, 8(11), 2357–2369 2359N O O R N O O R N O O R N O O R N O O R Br N O O R N O O R Br R' R' R' R' R' R' R' R' R' R' Br Br 18 17 R = C6H3-2,6-Pri 2 R' = OC6H4-4-Bu t 15 11 16 Scheme 2 Synthetic pathway to quaterrylenebis(dicarboximide) 18. chlorinated solvents. These encouraging results suggest that and Oda28 where the catalyst, tetrakis(triphenylphosphine)- nickel(0), is generated in situ.29 The biperylene 22 was then an additional increase of solubility should result from an eightfold substitution by phenoxy groups of the quaterrylenebis- obtained in 79% yield.The reaction conditions used for the cyclization of biperyl- (dicarboximide) core. Therefore, we have embarked on the synthesis of octaphenoxy substituted quaterrylenebis(dicar- enes 14 and 17 resulted, in the case of 22, also in the partial cleavage of the phenoxy groups of the resulting octasubstituted boximide) 23 (Scheme 3).The entry point to the synthetic scheme is the perylenedicar- quaterrylenebis(dicarboximide) 23. Consequently, milder reaction conditions have been applied to aVord the octaphenoxy boximide 20 carrying four phenoxy substituents, which has been synthesized by hydrolysis of one imide function of substituted quaterrylenebis(dicarboximide) 24 in very low yield (0.3%).The separation of octaphenoxy substituted quaterry- perylenebis(dicarboximide) 19 under basic conditions, followed by decarboxylation with copper(I) oxide under vacuum. lenebis(dicarboximide) 24 from numerous side products was conducted by gel permeation chromatography (GPC) on Purification by chromatography and recrystallisation aVords tetraphenoxyperylenedicarboximide 20 in 53% yield.The polystyrene as stationary phase with chloroform as eluent. monobromination of 20 under the mild conditions described by Mitchell26 with N-bromosuccinimide in dimethylformamide Structure elucidation leads selectively to bromoperylenedicarboximide 21 in high yield (98%).Surprisingly enough, the Yamamoto coupling of The structures of quaterrylenebis(dicarboximide)s were proven by 1H and 13C NMR spectroscopy, field desorption mass spec- the bromoperylenedicarboximide 21 under the conditions previously described for the bromoperylenedicarboximides 13 and troscopy (FD-MS), FT-IR spectroscopy and UV–VIS spectroscopy.Due to a plane of symmetry, the 1H NMR spectra of 16 resulted mainly in the cleavage of the phenoxy substituents. The reason for this unexpected side reaction remains enigmatic quaterrylenebis(dicarboximide)s 2b, 18 and 23 have a simpler appearance than those of their synthetic precursors, the bipery- and could not be explained by simple mechanistic considerations.However, this forced us to use another coupling lene diimides 14, 17 and 22. The aromatic region of the 1H NMR spectrum of quaterrylenebis(dicarboximide) 2b exhibits reaction reported by Sontheimer27 and modified by Iyoda 2360 J. Mater. Chem., 1998, 8(11), 2357–2369N O O R N O O R N O O R N O O R N O O R Br N O O R N O O R R' R' R' R' R' R' R' R' R' R' R' R' R' R' R' R' N O O R' R' R' R' R R' R' R' R' R' R' R' R' 23 22 R = Pr R' = OC6H4-4-OC6H13 20 19 21 Scheme 3 Synthetic pathway to quaterrylenebis(dicarboximide) 23.six resonances, as expected from the structure. The assignment, appropriate reference compounds. The parent ions of the quaterbased on 1H,1H correlated NMR analysis, of the resonnances rylenebis(dicarboximide)s 2a,b, 18 and 23 are in good agreement of 2b is given in Table 1.The chemical shifts for H-7,10,17,20 with the calculated masses and isotopic distributions corroboratare almost identical to those of H-8,9,18,19 and no unambigu- ing, therefore, the proposed chemical structures. The FT-IR ous assignment of these protons has been achieved. spectra of the quaterrylenebis(dicarboximide)s 2a,b, 18 and 23 The 13C NMR spectrum of the tetraphenoxy substituted quat- confirm the presence of the characteristic carbonyl bands, which errylenebis(dicarboximide) 18 exhibits thirteen quaternary and appear between 1700 and 1670 cm-1, depending on the substiseven tertiary aromatic C-atoms, in accordancewith the proposed tution at the nitrogen atoms.structure. However, a comprehensive assignment of the reson- The comparison of the UV–VIS–NIR spectra of perylenebisances to the carbon atoms has been hindered by the lack of (dicarboximide) 1a and terrylenebis(dicarboximide) 7a with the spectrum of quaterrylenebis(dicarboximide) 2b, given in Fig. 1, is very instructive. Specifically, a bathochromic shift of Table 1 1H NMR Chemical shifts of quaterrylene 2b (C2D2Cl4, the absorption maxima from 526 nm for 1a, to 650 nm for 7a 500 MHz, 135 °C) and extending to 764 nm for 2b is clearly observed.The d (ppm) Type H Integration extinction coeYcient increases from e=80 000 M-1 cm-1 for the perylenebis(dicarboximide) 1a to e=120 000 M-1 cm-1 for 8.68 d 2, 5, 12, 15 4 H terrylenebis(dicarboximide) 7a and up to e=162 000 M-1 cm-1 8.68, 8.63 d, d 7, 10, 17, 20, for the quaterrylenebis(dicarboximide) 2b. 8, 9, 18, 19 8 H A comparison with the absorption maximum of the previously 8.56 d 1, 6, 11, 16 4 H 7.42 dd a 2 H reported tetra-tert-butylquaterrylene 6c,14 shows that the two 7.29 d b 4 H dicarboximide functions at the peri-position of the quaterrylene- 2.80 q c 4 H bis(dicarboximide) 2b are responsible for a bathochromic shift of 1.19 d d 24 H more than 100 nm, as expected from the comparison of the J.Mater. Chem., 1998, 8(11), 2357–2369 2361tion maxima of the quaterrylenebis(dicarboximide) 2b with that of the tetraphenoxy substituted quaterrylenebis(dicarboximide) 18 and tetraphenoxy substituted perylenebis(dicarboximide) s 23 indicates a bathochromic shift of 19 (lmax=762 nm) and 28 nm (lmax=790 nm), respectively.The observed bathochromic shifts are due to the electron donating eVect of the phenoxy groups, and the eVect has already been observed in the case of tetraphenoxy substituted perylenebis(dicarboximide) s.16,17 Also of practical relevance, films of good optical quality are easily cast from a solution of the tetraphenoxy substituted quaterrylenebis(dicarboximide) 18.The VIS–NIR spectra of 18, both in solution and as a film, show diVerent aspects. Instead of the sharp absorption maximum at 781 nm accompanied by a shoulder at 709 nm observed in solution, as a film 18 displays two absorption maxima of nearly equal intensity at 724 and 795 nm. The high extinction coeYcients of quaterrylenebis(dicarboximide)s 2a,b, 18 and 23, which are Fig. 1 UV–VIS–NIR spectra of perylenebis(dicarboximide) 1a (solid only equalled in the NIR range by a few squarylium dyes,1 line) terrylenebis(dicarboximide) 7a (dotted line) and quaterrylenebis- suggest their use in optical data storage, where an excellent (dicarboximide) 2b (solid bold line) in CH2Cl2. signal to noise ratio could be reached.31 UV–VIS spectrum of perylene 3with the one of perylenebis(dicar- J-Aggregates and absorption behavior in strongly acidic boximide) 1a.The UV–VIS–NIR spectrum of quaterrylenebis- media. A totally new situation arises when the quaterrylenebis- (dicarboximide) 2b appears less structured than those of the (dicarboximide) 2b is dissolved in strongly acidic media. reference chromophores: the quaterrylene 6c, the perylenebis- Characteristically enough, a bathochromic shift of 112 nm is (dicarboximide) 1b, and the terylenebis(dicarboximide) 7a.We obtained when 2b is dissolved in a mixture of sulfuric acid attribute this feature to the enlarged p-system of quaterrylenebisand oleum (57%) (451) instead of chlorinated solvents. (dicarboximide) 2b in regards to 1b and 7a. Specifically, two peaks are observed, one at l=813 nm with an e of 111 000 M-1 cm-1, while the l of the second reaches a Properties value as high as 912 nm with an e of 581 000 M-1 cm-1.The value of lmax is slightly higher than those reported earlier.17 Solubility. The solubility of the quaterrylenebis(dicarboximide) s 2a,b, 18 and 23, which is the key to their processability, This is due, we believe, to traces of water in the sulfuric acid/oleum mixture, inducing diVerences in the oleum/ has been investigated in chlorinated solvents at room and elevated temperatures. The results are collected in Table 2.sulfuric ratio (see below). After dilution with water, the quaterrylenebis(dicarboximide) 2b can be recovered, which The low solubility of quaterrylenebis(dicarboximide) 2a compared to the much higher solubility of 2b is striking.indicates that the chromophore is chemically stable even in the presence of strong acids and oxidizing agents. The fact Despite the presence of two long dodecyl chains, quaterrylenebis( dicarboximide) 2a remains poorly soluble. The improved that 2b remains chemically unaltered also indicates that the large bathochromic shift and the sharp increase of e are solubility of quaterrylenebis(dicarboximide) 2b is due to facially encumbering substituents,31 i.e.the two 2,6-diisopro- presumably due to the protonation of the carboximide functions. The role of the protonation of this group on the NIR pylphenyl groups at the imide position, which decrease the tendency of the quaterrylenebis(dicarboximide) core to form spectrum of quaterrylenebis(dicarboximide) 2b was further confirmed by slightly changing the nature of the acidic medium.p-stacks. The solubility of the quaterrylenebis(dicarboximide) core is further increased by the introduction of four substitu- A dramatic change of the spectrum of 2b in concentrated sulfuric acid, in comparison to chlorinated solvents, is also ents in the bay-region, as shown by the good solubility of 18 at room temperature.Note as well that either the introduction observed. However, the NIR spectrum of quaterrylenebis- (dicarboximide) 2b in concentrated sulfuric acid and in a of eight substituents in the bay-regions or four substituents in the bay-region and the additional eVect of 2,6-diisopropylphe- sulfuric acid/oleum mixture are not superimposable (Fig. 2). Specifically, in concentrated sulfuric acid, three absorption nyl groups give rise to similar solubilities. maxima are present at 868, 907 and 992 nm, with e of 137 000, 493 000 and 143 000 M-1 cm-1, respectively, whereas only two Absorption behavior. From a practical aspect, it is worth mentioning the almost colorless solutions, which are only absorption maxima are observed in the sulfuric acid/oleum mixture.slightly blue, of quaterrylenebis(dicarboximide) 2b. This weak absorption in the visible window strictly contrasts with the Similarly, a large bathochromic shift and a dramatic increase of e, by a factor 5.4, have also been observed for terrylenebis- deeply orange–red and blue colored solutions of perylene 1a and terrylene 7a, respectively, observed for comparable concen- (dicarboximide) 7a in sulfuric acid as compared to a chloroform solution.15 Together, the large bathochromic shift and trations.As hitherto mentioned, the substitution of the quaterrylenebis( dicarboximide) in the bay-regions oVers not only a the dramatic increase of e could suggest for both the quaterrylenebis( dicarboximide) 2b and terrylenebis(dicarboximide) 7a way to increase the solubility, but also to finely tune the absorption maximum.For instance, comparison of the absorp- the formation of a J-aggregate.32 J-Aggregates are supramol- Table 2 Solubility and colors in solution of quaterrylenebis(dicarboximide)s Solubility in Solubility in Color in Compound CH2Cl2 at r.t./mg ml-1 C2H2Cl4 at 135 °C/mg ml-1 chlorinated solvents 2a — — purple–green 2b <0.2 ~2 green 15 ~30 >80 green 20 ~40 >80 green 2362 J.Mater. Chem., 1998, 8(11), 2357–2369strongly acidic solutions, i.e. tightly packed aggregates or individual molecules, 1H NMR experiments in D2SO4 were conducted on the oligomeric series: perylenebis(dicarboximide) 1a, terrylenebis(dicarboximide) 7a and quaterrylenebis(dicarboximide) 2b.Since the three members of this oligomeric series behave similarly, and for the sake of clarity, only the 1H NMR spectra of the perylenebis(dicarboximide) 1a and the quaterrylenebis( dicarboximide) 2b are presented in Fig. 4. Fig. 2 UV–VIS–NIR spectra of quaterrylenebis(dicarboximide) 2b in a mixture of sulfuric acid and oleum (57%) (451) (solid line) and in concentrated sulfuric acid (96%) (dotted line).N N N N SO3Na SO3 – Cl Cl Cl Cl 24 Three observations are made: Firstly, the 1H NMR spectra of 1a, 7a and 2b are suYciently resolved in a viscous solvent such as D2SO4. Secondly, the 1H NMR spectra of 1a, 7a, and 2b are independent of concentration in the range 10-2–10-3 M. Thirdly, the chemical shifts of the protons of 1a, 7a, and 2b, located on the N-substituent and on the aromatic core, are comparable within the oligomeric series.It also follows from the 1H NMR spectra of 1a, 7a and 2b that the protons adjacent to the isopropyl groups on the phenyl substituents at the imide positions undergo rapid exchange with deuterium in D2SO4. This has also been confirmed by FD-MS analysis. Clearly, the well-resolved and concentration independent spectra of 1a, 7a and 2b are inconsistent with the Fig. 3 UV–VIS spectra of perylenebis(dicarboximide) 1a in CH2Cl2 formation of any aggregates in solution.Moreover, 1H NMR (dotted line) and in concentrated sulfuric acid (96%) (solid line). spectra of a commercially available dye forming J-aggregates in D2O, namely the benzimidocyanine 24, have been recorded ecular assemblies of chromophores in which head-to-tail at 30 and 80 °C.Beside the characteristic peak of the solvent, arrangement of transition dipole moments results in a sharp, the expected peaks of the dye were so broad that they could intense and bathochromically shifted absorption band com- not be detected, indicating the formation of tightly packed pared to the isolated chromophore.32 aggregates.This last finding corroborates the view that no JAfter discussing the absorption spectra of terrylenebis(dicar- aggregates are formed in the case of the oligomeric series 1a, boximide) 7a and quaterrylenebis(dicarboximide) 2b in 7a and 2b in concentrated sulfuric acid. strongly acidic media, it is important to consider also that of Therefore, the exact nature of the species present in perylenebis(dicarboximide) 1a.Three observations are easily strongly acidic solutions of perylenebis(dicarboximide) 1a, made from the comparison between Fig. 2 and 3. Firstly, a terrylenebis(dicarboximide) 7a and quaterrylenebis(dicarboxilarge bathochromic shift of all the visible spectrum occurs also mide) 2b remains unknown. One can only conclude that the for perylenebis(dicarboximide) 1a in concentrated sulfuric acid diVerent behavior of 1a, 7a and 2b in chlorinated solvents in comparison to chloroform solution.Secondly, the absorp- and strongly acidic media must be related to the protonation tion peaks of 1a in concentrated sulfuric acid are not sharper and are only slightly more intense than their corresponding peaks in chloroform solution.The increase in intensity for the absorption maxima of 1a in concentrated sulfuric acid in comparison to chloroform solution, i.e. by a factor 1.4, is significantly less pronounced than for terrylenebis(dicarboximide) 7a and quaterrylenebis(dicarboximide) 2b, i.e. by a factor 5.4 and 3.0, respectively. Thirdly, the shape of the absorption curve of 1a in concentrated sulfuric acid remains somewhat similar to the one in chloroform solution (Fig. 3). This observation contrasts with the very diVerent shapes of the absorption curves of the quaterrylenebis(dicarboximide) 2b in concentrated sulfuric acid and in chloroform solution. It should be concluded for the perylenebis(dicarboximide) 1a that, despite the large bathochromic shift observed, the absence of a sharp and intense absorption in concentrated sulfuric acid seems not to indicate the formation of J-aggregates.32 It is well documented that temperature and concentration dependent 1H NMR experiments are particularly suited to the investigation of the presence of aggregates in solution.33 Fig. 4 1H NMR Spectra of (a) perylenebis(dicarboximide) 1a and (b) quaterrylenebis(dicarboximide) 2b [D2SO4 (96%), 500 MHz, 30 °C].Therefore, to elucidate the nature of the species present in J. Mater. Chem., 1998, 8(11), 2357–2369 2363of the carboximide functions, and do not result from chemical In a semiquantitative analysis, the radiative lifetime tFM, defined as the reciprocal of the radiative transition probability, modification or from aggregation of the chromophores.can be estimated from the Strickler–Berg35 equation, which for dilute solutions becomes eqn. (1), Photophysical behavior. Based on the remakably large quantum yield of fluorescence (wf) of perylene 1a and terrylene 7a approaching unity in solution,15,34 one would have expected 1 tFM =2.88×10-9 n2 v� -3-1 Pe(v� ) v� dv� (1) that quaterrylenebis(dicarboximide) 2b will, to some degree, emit light in the NIR window. However, no luminescence where n is the refractive index and v� -3-1 is the reciprocal could be detected for quaterrylenebis(dicarboximide) 2b in of an appropriate average over the fluorescence spectrum dilute solutions.Similarly, a dramatic decrease of wf has been defined in eqn. (2). observed for quaterrylenebis(dicarboximide) 6c (wf=0.05) in comparison with perylene 6a and terrylene 6b.14 Remarkably enough, it was recently discovered that the lack of emission v� -3-1 = PF(v)dv PF(v)dv v3 (2) of 2b is related to traces of unknown impurities. Normally, samples of quaterrylenebis(dicarboximide) 2b purified by column chromatography on silica gel with methylene chloride as eluent and precipitation in methanol, do not emit in The essential values needed eqn.(1) and (2) can be inferred chloroform solution, even though no impurities were observed from the absorption spectrum as well as from the steady state by 1H NMR and UV–VIS–NIR spectroscopy, FD-MS, and PL spectrum. Insertion of these parameters then leads to a thin layer chromatography. Nevertheless if quaterrylenebis- radiative lifetime of about tFM=65 ns.(dicarboximide) 2b is further purified by several extractions in Further information about the photophysical properties of ethyl acetate, an emission centered at 797 nm in chloroform quaterrylenebis(dicarboximide) 2b are given by time resolved solution is observed (Fig. 5). Characteristically, the emission photoluminescence measurements. In Fig. 6(a) a transient of maxima [lmax (em)] of quaterrylenebis(dicarboximide) 2b the PL detected at the PL maximum at 800 nm is displayed.extends to even longer wavelength in the NIR window than The measurement shows a monoexponential decay with a those of terrylenebis(dicarboximide) 7a [lmax (em)=673 nm], surprisingly short fluorescence decay time of about 320 ps. All benzoylterryleneimide 8a [lmax (em)=701 nm] and perylenebis- transients taken at diVerent wavelength of the PL spectrum amidine 9 [lmax (em)=768 nm].15,16 exhibit exactly the same time dependence, as can be seen from In Fig. 5 the absorption as well as the steady state photoluminescence (PL) are shown for the sake of comparison. The ground state absorption spectrum shows a strong inhomogeneously broadened S0–S1 (0–0) transition centered at 763 nm followed by inhomogeneously broadened vibronic satellites centered at 695 and 626 nm, respectively.Deconvolution of the ground state absorption spectrum with Gaussian profiles allows the estimation of the absorption coeYcient e as well as the oscillator strength f of the observed transitions. The molar extinction coeYcients for the optical transitions are e= 90000 cm2 mol-1, corresponding to an oscillator strength of about f=0.9, and e=51700 cm2 mol-1, relating to f=0.67, for the pure electronic (0–0) and the dominant vibronic (0–1) transitions, respectively.The dominant vibrational mode is energetically oVset by about 1300 cm-1, indicating a ring breathing mode. Comparing the transition intensities of the pure electronic transition with the ones of the vibronic transitions, it becomes evident that the quaterrylenebis(dicarboximide) 2b is a very rigid material showing a slight distortion in the excited state only.Furthermore, the slight deviations from mirror symmetry indicate only minor diVerences in the nuclear configurations of the ground and the excited state. Therefore, we conclude that the large Stokes shift (about 35 nm) observed in emission is mainly due to solvation eVects.Fig. 6 (a) Time dependence behaviour of the emission detected at Fig. 5 Absorption and emission spectra of quaterrylenebis(dicarboxi- 800 nm after excitation with 100 fs pulses. (b) Semilogarithmic plot of PL decays monitored at diVerent detection energies. mide) 2b in CHCl3. The photoluminescence excitation is at 740 nm. 2364 J. Mater. Chem., 1998, 8(11), 2357–2369Fig. 6(b), in which the transients are displayed on a semi- the perylenebis(dicarboximide) 1b, the terrylenebis(dicarboximide) 7b, and the quaterrylenebis(dicarboximide) 18 do not logarithmic scale. diVer significantly. This proves that no time and energy dependent rate, e.g. filling process, is involved in the radiative transition.However, Photochemical stability. The photostability of quaterrylene- the decay time seems to be surprisingly short compared to bis(dicarboximide) 2b has been estimated by exposing under other members of this molecular family. Following the work air a polystyrene film of roughly 10 mm containing 0.5 wt% of on radiationless transitions in molecules one can roughly dyes to UV light (l=366 nm) for a prolonged period of time.15 estimate that the probability of nonradiative transitions After 10 days of irradiation, no significant alteration of the increases exponentially with decreasing energy gap DE between absorption spectrum could be observed, demonstrating the the potential minima for the state involved [eqn.(3)],36 photochemical inertness of quaterrylenebis(dicarboximide) 2b in a polymer matrix.knr3exp A- cDE 2phvB (3) where v is the vibrational frequency and c is a quantity expressible in terms of molecular parameters. By comparing The synthesis of three quaterrylenebis(dicarboximide)s 2a,b, quaterrylenebis(dicarboximide) with perylene on the basis of 18 and 23 diVering by their substitution pattern has been this expression and taking into account that the main excess achieved.The extension of the p-system of the quaterrylenebisenergy is dissipated through C–H vibrational modes (ca. (dicarboximide)s 2a,b, 18 and 23, in comparison to the 300 cm-1) an increase of the nonradiative transition prob- perylenebis(dicarboximide)s 1, has several intriguing conseability of roughly a factor 25 can be estimated, which concurs quences for their photophysical and electrochemical properties.fairly well with the PL decay time of tFM=320 ps measured. Firstly, the quaterrylenebis(dicarboximide)s 2a,b, 18 and 23 Moreover, by insertion of the values obtained throughout the are characterized by an intense absorption in the NIR, between analysis above the quantum eYciency expressed as Q=t/tFM 750 and 800 nm in chlorinated solvents, whereas the absorption can be estimated to approximatively 5%.of perylenebis(dicarboximide)s 1 ranges between 520 and 590 nm. Secondly, the quaterrylenebis(dicarboximide) 2b pre- Electrochemical behavior. The reduction potentials of substi- sents an emission centered at 797 nm with a quantum eYciency tuted perylenebis(dicarboximide) 1b and quaterrylenebis- estimated at 5%, which is significantly lower than those of (dicarboximide) 18 are collected in Table 3.The cyclic voltam- perylenebis(dicarboximide)s 1 which approach one. Thirdly, mogram (CV) shows a four-fold reduction of the quaterrylene- a definite stabilization of the tri- and tetra-anion of the bis(dicarboximide)s 18. The first two electrons are localized quaterrylenebis(dicarboximide) 18 occurs, whereas little on the carbonyl groups because only a small diVerence is diVerence is observed between the two first reduction potentials observed for the first (-0.74 V) and second reduction poten- of 18 and 1b.Fourthly, the quaterrylenebis(dicarboximide) tials (-1.10 V) of quaterrylenebis(dicarboximide) 18 as com- 2b exhibits, in strongly acidic solvents, an extremly intense pared to the smaller homologue, perylenebis(dicarboximide) absorption around 900 nm.However, this intense absorption 1b, at -0.85 and -1.11 V, respectively. This suggests that the cannot be explained by the formation of J-aggregates in two first reduction potentials are independent of the size of solution, and is more likely caused by the protonation of the the conjugated p-system, indicating that the electrons go in to carboximide functions.the quaterrylenebis(dicarboximide) 18 and the perylenebis- In addition to these new photophysical and electrochemical (dicarboximide) 1b in two diVerent locations, presumably at properties the quaterrylenebis(dicarboximide)s 2a,b, 18 and the two imide functions, without appreciable interaction.37 23 also display good chemical, photochemical and thermal In contrast, a definite charge stabilization, due to the stability. Clearly, this unusual ensemble of properties qualifies extension of the p-system of the quaterrylenebis(dicarboxim- the quaterrylenebis(dicarboximide)s 2a,b and 18 as functional ide) 18 in comparison to the perylene 1b, is observed for the NIR materials and suggests the synthesis of even larger reduction to the tri- and tetra-anion.The third reduction rylenebis(dicarboximides) dyes. potential of the quaterrylenebis(dicarboximide) 18 (-1.97 V) We gratefully acknowledge the financial support of BASF AG has a much lower absolute value than the one of the and the Bundesministerium fu� r Forschung und Technologie.corresponding perylenebis(dicarboximide) 1b (-2.64 V). Remarkably enough, a fourth reduction is observed for the quaterrylenebis(dicarboximide) 18. Moreover, this fourth Experimental reduction potential lies at -2.26 V, i.e. 0.38 V lower than the Spectral data were obtained on Nicolet FT-IR 320 (IR), third reduction potential of perylenebis(dicarboximide) 1b.Perkin-Elmer Lambda 9 and 15 (UV–VIS), Varian Gemini 200, Bruker AC 300 or AMX 500 (NMR), Potentiostat/ Thermal stability. Thermogravimetric analyses (TGA) con- Galvanostat PAR Model 173 (CV), Finnigan MAT 312 (FD- ducted under nitrogen atmosphere show that quaterrylenebis- MS) and Mettler TG 50 (TGA) instruments. For the cyclovol- (dicarboximide) 18 possesses a high thermal stability.The first tammetric experiments with 18 (in THF, with Bu4NPF6 added) weight loss is observed between 485 and 500 °C and correa Potentiostat/Galvanostat PAR Model 173 was used. The sponds to the cleavage of the isopropyl groups. In this respect, setup for photoluminescence consisted of an XeCl excimer pumped dye laser system (15 Hz rep. rate and 10 ns pulse Table 3 Reduction potentials versus saturated calomel electrode of width) running at 740 nm.The emission from the sample was perylenebis(dicarboximide) 1b and quaterrylenebis(dicarboximide) 18 collected and focussed into the entrance slit of a 270 cm grating in tetrahydrofuran at 0 °C monochromator fitted with a charge coupled device (CCD) array for detection. Fluorescence lifetime measurements were E/V vs.SCE performed with an Kerr-lens mode-locked Ti5sapphire laser operating at 740 nm and producing 100 fs pulses at a repetition Charge Perylene 1b Quaterrylene 18 rate of 80 MHz. Here, as in the time integrated experiments, -1 -0.85 -0.74 the emission was dispersed in a monochromator and monitored -2 -1.11 -1.10 by a streak camera to follow the potoluminescence decay with -3 -2.64 -1.97 a time resolution of about 6 ps.All measurements were -4 — -2.26 performed at room temperature. The photostability tests were J. Mater. Chem., 1998, 8(11), 2357–2369 2365conducted with a UV lamp (Camag, 0.25 A, 220 V), placing N-Dodecyl-9-bromoperylene-3,4-dicarboximide 12a the polystyrene films 12 cm away from the lamp. The 2.5 g (5.1 mmol) N-Dodecylperylene-3,4-dicarboximide 11a melting points (mp) are reported uncorrected. All solvents were dissolved in 750 ml methylene chloride and a catalytic for reactions were distilled before use.Ni(cod)2 was puramount of iron powder was added. After 15 min, 8 g chased from Strem Chemicals, all other chemicals were (50 mmol) of bromine in 50 ml methylene chloride were added purchased from Aldrich and used as received. 3,4,9,10- to the reaction mixture. The temperature was slowly increased Perylenetetracarboxylic dianhydride and N-(2,6-diisopro- and the reaction mixture was refluxed for 3 h. After cooling pylphenyl )perylene-3,4-dicarboximide (11b) were obtained to room temperature, the excess bromine and most of the from BASF AG. The N-propyl-1,657,12-tetra(4-hexyloxy- methylene chloride were evaporated under vacuum.The phenoxy)perylene-3,459,10-bis(dicarboximide) (19) has been resulting concentrated solution was poured into a large volume previously described in the literature.17,25 of methanol and this solution was stored at -20 °C for 1 h. The resulting precipitate was filtered and washed with plenty N-Dodecylperylene-3,4,9,10-tetracarboxylic acid 3,4-anhydride of methanol.Drying under vacuum aVorded 2.73 g of the title 9,10-dicarboximide§ compound 12a as a red powder (94% yield). dH (500 MHz, C2D2Cl4, 135 °C) 8.6–8.5 (m, 2H, H-2,5), 15.0 g (38 mmol) 3,4,9,10-Perylenetetracarboxylic dianhydride 8.5–8.3 (m, 4H, H-12,7,1,6), 8.15 (d, 1H, H-10), 7.90 (d, 1H, and 84.0 g (0.45 mmol) dodecylamine were added to a mixture H-8), 7.71 (dd, 1H, H-11), 4.23 (t, 2H, a-CH2), 1.84 (m, 2H, of 1 L propan-1-ol and 0.5 L water. The reaction mixture was b-CH2), 1.48 (m, 2H, c-CH2), 1.35 [br, 16H, (CH2)8], 0.94 (t, stirred at 65 °C for 7 h.After cooling to room temperature, 3H, CH3); nmax/cm-1 2954, 2921, 2870, 2851, 1694 (CNO), 150 mL of concentrated HCl were added to the reaction 1651 (CNO), 1616, 1594, 1562, 1497, 1467, 1455, 1383, 1359, mixture and 1 L of water was added.The precipitate was 1333, 1296, 1244, 812, 805, 751; lmax(CH2Cl2)/nm (e) (absorp- separated from the liquid phase by centrifugation and dri tion) 255 (18930), 263 (34690), 480 (31240), 504 (32090); m/z under vacuum, aVording 20 g of the title compound as an (FD) 569.4 (M+, 100%) [C34H34NO2Br (568.55 g mol-1) orange powder (94% yield).N-Dodecylperylene-3,4,9,10- calc.: C, 71.83; H, 6.03; N, 2.46; Br, 14.05. Found: C, 70.59; tetracarboxylic acid 3,4-anhydride 9,10-dicarboximide 10a was H, 5.71; N, 2.40; Br, 14.21%]; mp 231 °C. used directly for the next reaction without further purification. For characterization purposes, a small amount was purified N-(2,6-Diisopropylphenyl )-9-bromoperylene-3,4-dicarboximide by chromatography on silica gel with chloroform as eluent. 12b dH (300 MHz, C2D2Cl4, 135 °C) 8.68 (d, 2H, H-8,11), 8.66 (d, 2H, H-2,5), 8.60 (d, 2H, H-7,12), 8.59 (d, 2H, H-1,6), 4.20 10 g (21 mmol) N-(2,6-diisopropylphenyl )perylene-3,4-dicar- (t, 2H, a-CH2), 1.79 (m, 2H, b-CH2), 1.41 (m, 2H, c-CH2), boximide 11b were dissolved under slight heating in 1 L 1.28 [br, 16H, (CH2)8], 0.87 (t, 3H, CH3); nmax/cm-1 2954, chlorobenzene.Bromine (15 g, 95 mmol) was added and the 2924, 2850, 1765 (CNO), 1743, 1724 (CNO), 1697 (CNO), reaction mixture was stirred for 4.5 h at 50 °C. Chlorobenzene 1656 (CNO), 1616, 1595, 1580, 1508, 1434, 1407, 1350, 1340, and unreacted bromine were removed under vacuum. The 1324, 1297, 1274, 1253, 1241, 1153, 1127, 1033, 1018, 866, resulting solid was recrystallised from methylene chloride– 810, 739; lmax(H2SO4)/nm (e) (absorption) 390 (8170), 544 methanol, yielding 11.4 g (98%) of the title compound 12b.(42800), 581 (60440); m/z (EI ) 559.3 (M+, 86%), 405.2 dH (300 MHz, CDCl3, 30°C) 8.64 (d, 1H, H-2), 8.62 (d, (M+-C11H22, 24%), 392.2 (M+-C12H24, 100%), 248.2 1H, H-5), 8.45 (d, 1H, H-1), 8.42 (d, 1H, H-6), 8.37 (d, 1H, (perylene+, 60%) (calc.M+, 558.7); mp >300 °C. H-12), 8.27 (d, 1H, H-7), 8.20 (d, 1H, H-10), 7.87 (d, 1H, H- 8), 7.69 (t, 1H, H-11), 7.47 (dd, 1H, H-16), 7.33 (d, 2H, HN- Dodecylperylene-3,4-dicarboximide 11a 15), 2.77 [m, 2H, CH(CH3)2], 1.18 [d, 12H, CH(CH3)2]; dC (125.5 MHz, CDCl3, 30°C) 163.85, 145.69, 136.90, 136.77, 5.0 g (8.9 mmol) 10a and 200 mL of a 12 wt% KOH solution 133.02, 132.09, 132.02, 131.31, 130.94, 130.43, 130.08, 129.66, were introduced into a 250 mL autoclave.The temperature 129.44, 129.21, 129.11, 128.21, 126.69, 126.20, 124.47, 123.98, was raised to 230 °C for 18 h. After cooling to room tempera- 123. 81, 121.43, 120.75, 120.48, 29.13, 23.96; nmax/cm-1 1701 ture, the resulting precipitate was filtered oV, washed with (CNO), 1660 (CNO); lmax(CH2Cl2)/nm (e) (absorption) 263 plenty of water and dried under vacuum.The resulting solid (34056), 355 (3065), 484 (34762), 509 (35319); (fluorescence) was extracted with diethyl ether and precipitated in a large 540; m/z (FD) 561.1 (M+, 100%) [C34H26NOBr volume of methanol. Then the red powder was dried under (560.49 g mol-1) calc.: C, 72.86; H, 4.68; N, 2.50; Br, 14.26.vacuum to aVord 3.25 g of the title compound (75% yield). Found: C, 71.93; H, 4.71; N, 2.50; Br, 13.77%]; mp >300 °C. N-Dodecylperylene-3,4-dicarboximide 11a was used directly Rf (silica gel ) 0.45 (CH2Cl2), 0.09 (toluene). for the next reaction without further purification. For characterization purposes a small amount (500 mg) was purified by N-(2,6-Diisopropylphenyl )-9-(tributylstannyl )perylene-3,4- column chromatography on silica gel with toluene as eluent.dicarboximide 13b dH (300 MHz, CDCl3, 30°C) 8.49 (d, 2H, H-2,5), 8.32 (d, 2H, H-7,12), 8.29 (d, 2H, H-1,6), 7.83 (d, 2H, H-9,10), 7.55 13.5 g (24 mmol) of the monobromoperylene 12b, 26.3 g (dd, 2H, H-8,11), 4.16 (t, 2H, a-CH2), 1.77 (m, 2H, b-CH2), (45 mmol) hexabutylditin and 0.1 g (0.1 mmol, 0.3 mol%) 1.42 (m, 2H, c-CH2), 1.28 [br, 16H, (CH2)8], 0.87 (t, 3H, Pd(PPh3)4 were refluxed in 700 ml toluene for 4 days.The CH3); dC (75.5 MHz, CDCl3, 30°C) 163.89 (C=O), 137.25, solvent was removed under vacuum. Purification was carried 134.74, 131.45, 130.85, 129.68, 128.37, 127.21, 123.72, 121.71, out by column chromatography on silica gel with CH2Cl2 as 120.36, 40.74, 32.00, 29.73, 29.70, 29.52, 29.36, 28.45, 27.43, eluent, aVording 16 g of the title compound as a red solid 22.67, 13.96; nmax/cm-1 2956, 2916, 2850, 1691 (CNO), 1652 (88% yield).(CNO), 1595, 1571, 1469, 1381, 1354, 1295, 1262, 1249, 1105, dH (500 MHz, CDCl3, 30°C) 8.66 (d, 1H), 8.65 (d, 1H), 1079, 1032, 1022, 813, 762, 753; lmax(CH2Cl2)/nm (e) (absorp- 8.50 (d, 1H), 8.47 (d, 1H), 8.46 (d, 1H), 8.40 (d, 1H), 7.88 tion) 263 (33100), 480 (28810), 502 (28330); m/z (FD) 489.3 (d, 1H), 7.84 (d, 1H), 7.69 (t, 1H), 7.49 (t, 1H), 7.35 (d, 2H), 2.79 (h, 2H), 1.69–1.56 (m, 6H), 1.44–1.33 (m, 6H), 1.31–1.27 (M+, 100%), 978.3 (M2+, 77%) [C34H35NO2 (489.66 g mol-1) (m, 6H), 1.20 (d, 12H), 0.92 (t, 9H); dC (125.5 MHz, C2D2Cl4, calc.: C, 83.40; H, 7.21; N, 2.86.Found: C, 82.87; H, 7.04; N, 30 °C) 164.0, 149.7, 145.7, 140.1, 138.0, 137.7, 136.3, 133.4, 2.71%]; mp 179 °C. 132.0, 131.1, 130.5, 129.8, 129.4, 129.2, 127.0, 126.8, 124.0, 123.7, 122.7, 120.8, 120.0, 119.9, 29.3, 29.2, 27.3, 24.0, §IUPAC name: N-dodecyl-13,15-dioxo-9,10-(methanoepiminomethano) perylene-3,4-dicarboxylic anhydride 13.6, 10.8; nmax(KBr)/cm-1 1699 (CNO), 1663 (CNO); 2366 J.Mater. Chem., 1998, 8(11), 2357–2369lmax(CHCl3)/nm (e) (absorption) 267 (4.45), 496 (4.56), 521 added in a 250 ml Schlenk flask under argon. The reaction (4.54); m/z (FD) 772.5 (M+, 100%) calc. M+, 772.5); mp mixture was vigorously stirred at 120 °C for 2.5 h. After 158–159 °C. cooling to room temperature, the solidified solution was dissolved in water and poured into 500 mL water–hydrochloric N,N¾-Bis(dodecyl )-9,9¾-biperylene-3,453¾,4¾-bis(dicarboximide) acid (551). The resulting precipitate was filtered and dried 14a under vacuum.Purification was carried out by extraction using CHCl3 as solvent until no colored side product could be Ni(cod)2 (180 mg, 0.67 mmol), cyclooctadiene (600 mg, extracted. Drying the resulting dark blue powder aVorded 5.6 mmol) and 2,2¾-bipyridyl (105 mg, 0.67 mmol) were added 369 mg of the title compound (83% yield ).to 80 ml DMF in a 100 ml Schlenk flask under argon. The dC(CP MAS TOSS, 4.5 kHz) 161.54 (CNO), 140–115 (C, mixture was stirred at room temperature for 1 h and bromoaromatic), 40.60, 30.75, 23.43, 14.42; lmax/cm-1 2921, 2851, perylenedicarboximide 12a (382 mg, 0.67 mmol) was added to 1690 (CNO), 1650 (CNO), 1594, 1575, 1548, 1502, 1455, the purple solution.After 36 h at 65 °C, the reaction mixture 1430, 1404, 1382, 1354, 1288, 1244, 1126, 1115, 810; was cooled to room temperature and poured into 120 mL lmax(H2SO4)/nm (e) 208 (0.375), 374 (0.055), 622 (0.170), water–hydrochloric acid–methanol (15152). The resulting pre- 858 (0.219), 896 (0.419), 989 (0.469), 1134 (0.021); lmax cipitate was filtered oV, washed with water and dried under [H2SO4–oleum (57%) (451)]/nm (e) 281 (524300), 323 (57700), vacuum, yielding 293 mg (89%) of the title compound 14a as 784 (34400), 876 (337000); m/z (FD) 974.2 (M+, 100%) (calc.a deep red powder. M+, 975.3); mp >300 °C. dH (500 MHz, C2D2Cl4, 135 °C) 8.53 (2d, 4H, H-5,2), 8.38 (d, 2H, H-7), 8.32 (d, 2H, H-6), 8.28 (2d, 4H, H-1,12), 8.12 N,N¾-(2,6-Diisopropylphenyl )quaterrylene-3,4513,14-bis- (d, 2H, H-8), 7.88 (d, 2H, H-10), 7.69 (t, 4H, H-11), 4.22 (t, (dicarboximide) 2b 4H, a-CH2), 1.81 (m, 4H, b-CH2), 1.48 (m, 4H, c-CH2), 1.34 [br, 32H, (CH2)8], 0.94 (t, 6H, CH3); dC(125.5 MHz, C2D2Cl4, N,N¾ -Bis(2,6-diisopropylphenyl )- 9,9¾-biperylene-3,453¾,4¾-bis- 135 °C) 164.85, 164.84, 137.58, 137.45, 134.40, 132.59, 132.56, (dicarboximide) (750 mg, 0.78 mmol), 80 g KOH and 6 g 132.53, 131.10, 131.08, 130.94, 130.52, 130.50, 129.41, 127.71, glucose, were added in a 250 ml Schlenk flask under argon. 127.23, 125.44, 124.75, 123.12, 123.10, 121.94, 121.66, 41.91, The reaction mixture was vigorously stirred at 120 °C for 2.5 h. 33.14, 30.87, 30.84, 30.82, 30.65, 30.50, 29.55, 28.55, 23.83, After cooling to room temperature, the solidified solution was 15.16; nmax/cm-1 2955, 2923, 2852, 1696, 1651, 1594, 1563, dissolved in water and poured into 500 mL water–hydrochloric 1497, 1384, 1359, 1245, 805, 750; lmax(CH2Cl2)/nm (e) (absorp- acid (551).The resulting precipitate was filtered and dried tion) 263 (56150), 481 (51030), 504 (53160); m/z (FD) 977.3 under vacuum.Purification was carried out by column chroma- (M+, 100%) [C68H68N2O4 (977.30 g mol-1) calc.: C, 83.57; tography on silica gel using CH2Cl2 as eluent. Precipitation H, 7.01; N, 2.87. Found: C, 83.09; H, 7.11; N, 2.92%]; from CH2Cl2 in methanol aVorded 620 mg of the title commp 204 °C. pound as a green powder (83% yield). dH(300 MHz, C2D2Cl4, 135 °C) 8.68 (d, 4H, H-2, 5, 12, 15), N,N¾-Bis(2,6-diisopropylphenyl )-9,9¾-biperylene-3,453¾,4¾- 8.68, 8.63 (d, 4H, H-7, 10, 17, 20, 8, 9, 18, 19), 8.56 (d, 4H, bis(dicarboximide) 14b H-1, 6, 11, 16), 7.42 (dd, 2H, Ph-H-24), 7.29 (d, 4H, Ph-H- 23), 2.80 [m, 4H, CH(CH3)2], 1.19 [d, 24H, CH(CH3)2]; Ni(cod)2 (496 mg, 1.78 mmol), cod (161 mg, 1.48 mmol) and nmax/cm-1 1702 (CNO), 1659 (CNO); lmax(CH2Cl2)/nm 2,2¾-bipyridyl (278 mg, 178 mmol) were added to 80 ml DMF (e)264 (97377), 274 (100124), 317 (9195), 375 (14689), 764 in a 100 ml Schlenk flask under argon.The mixture was stirred (162024); lmax [H2SO4–oleum (59%) (451)]/nm (e)281 at room temperature for 1 h and bromoperylenedicarboximide (698994), 326 (58801), 783 (83173), 876 (654705); m/z (FD) (1 g, 1.78 mmol) was added to the purple solution.After two 479.2 (M2+, 37%), 958.5 (M+, 100%), (calc. M+, 959.1); mp days at 70 °C, the reaction mixture was cooled to room >300 °C; Rf (silica gel ) 0.02 (CH2Cl2), 0.81 (THF). temperature and poured into 1 L water–hydrochloric acid (551). The precipitate was filtered oV, washed with water, N-(2,6-Diisopropylphenyl )-1,6,9-tribromoperylene-3,4- dried under vacuum and purified by silica gel column chromadicarboximide 15 tography using CH2Cl2 as eluent.Solvent was evaporated under vacuum, then the resulting solid was redissolved in a To a solution of N-(2,6-diisopropylphenyl )perylene-3,4-dicarminimum of CH2Cl2 and a large excess of methanol was boximide 11 (12 g, 25 mmol) in 1.5 L chloroform, 70 mL of added. The green precipitate was filtered, washed with meth- bromine were added and the reaction mixture was refluxed for anol and dried under vacuum, yielding 710 mg (83%) of the 6 h.After cooling to room temperature, the reaction mixture title compound 14b. was washed with a solution of 15 g KOH and 10 g sodium dH (300 MHz, CDCl3, 30°C) 8.72 (d, 2H, H-5), 8.70 (d, sulfite in 2 L water. The organic layer was separated and dried 2H, H-2), 8.65 (d 2H, H-7), 8.58 (d, 2H, H-6), 8.50–8.55 (m, on magnesium sulfate. Removing the solvent under vacuum 4H, H-12,1), 7.74 (d, 2H, H-8), 7.62 (d, 2H, H-10), 7.55 (d, aVorded 19.5 g of the title compound as an orange solid.The 2H, H-11), 7.48 (dd, 2H, Ph-H-16), 7.34 (d, 4H, Ph-H-15), purity was found to be suYcient for the next reaction.For 2.78 [m, 4H, CH(CH3)2], 1.18 [d, 24H, CH(CH3)2]; dC analytical purposes, 2 g of the orange solid were purified by (125.5 MHz, CDCl3, 30°C) 163.95, 145.74, 145.71, 140.53, column chromatography on silica gel using CH2Cl2 as eluent. 137.44, 137.23, 135.30, 133.71, 132.13, 130.99, 130.57, 129.65, Precipitation from CH2Cl2 in methanol aVorded 1.67 g of the 129.59, 129.48, 129.37, 129.27, 128.32, 127.47, 127.01, 124.08, title compound (91% yield). 124.04, 123.40, 121.34, 121.29, 120.61, 120.47, 29.17, 24.03; dH(500 MHz, CDCl3, 30°C) 9.33 (d, 1H, H-12), 9.11 (d, nmax/cm-1 1702 (CNO), 1662 (CNO); lmax(CH2Cl2)/nm (e) 1H, H-7), 8.94 (s, 1H, H-2), 8.93 (s, 1H, H-5), 8.45 (d, 1H, (absorption) 264 (57790), 355 (6503), 499 (66477), 528 H-10), 7.99 (d, 1H, H-8), 7.80 (t, 1H, H-11), 7.51 (t, 1H, Ph- (83055); (fluorescence) 597; m/z (FD) 480.8 (M2+, 29%), H-16), 7.36 (d, 2H, Ph-H-15), 2.73 [heptet, 2H, CH(CH3)2], 960.8 (M+, 100%) [C68H52N2O4 (961.17 g mol-1) calc.: C, 1.20 [d, 12H, CH(CH3)2]; dc(125.5 MHz, CDCl3, 30° C) 84.97; H, 5.45; N, 2.91.Found: C, 84.02; H, 5.39; N, 2.70%]; 162.54, 145.63, 135.37, 135.15, 134.56, 131.62, 130.92, 130.69, mp >300 °C; Rf (silica gel ) 0.12 (CH2Cl2), 0.84 (THF). 130.33, 130.28, 129.82, 129.78, 129.58, 128.86, 128.75, 127.53, 126.94, 126.91, 126.74, 126.50, 124.14, 120.94, 120.89, 119.24, N,N¾-Bis(dodecyl )quaterrylene-3,4513,14-bis(dicarboximide) 119.02, 29.25, 23.98; nmax(KBr)/cm-1 1711 (CNO), 1672 2a (CNO); lmax(CH2Cl2)/nm (e) 228 (78697), 281 (28194), 379 (3116), 401 (3398), 513 (33013); m/z (FD) 719.0 (M+, 100%) N,N¾-Bis(dodecyl )-9,9¾-biperylene-3,453¾,4¾-bis(dicarboximide) (977 mg, 1 mmol), 100 g KOH, 4 g glucose and 100 mL were [C34H24NO2Br3 (718.27 g mol-1) calc.: C, 56.86; H, 3.37; N, J.Mater. Chem., 1998, 8(11), 2357–2369 23671.95; Br, 33.37. Found: C, 56.49; H, 3.42; N, 1.72; Br, 32.01%]; methanol aVorded 421 mg of quaterrylenebis(dicarboximides) 18 as a green powder (85% yield).mp >300 °C; Rf (silica gel ) 0.77 (CH2Cl2), 0.48 (toluene). dH(500 MHz, CDCl3, 30°C) 9.09 (d, 4H, H-7, 10, 17, 20), 8.32 (s, 4H, H-2, 5, 12, 15), 7.76 (d, 4H, H-8, 9, 18, 19), 7.41 N-(2,6-Diisopropylphenyl )-1,6-bis(4-tert-butylphenoxy)-9- (t, 2H, Ph-H-24), 7.34 (d, 8H, Ph-H-24), 7.28 (d, 4H, Ph-H- bromoperylene-3,4-dicarboximide 16 23), 7.00 (d, 8H, Ph-H-2), 2.76 [m, 4H, CH(CH3)2], 1.26 (s, 36H, tert-butyl ), 1.13 [d, 24H, CH(CH3)2]; dC(125.5 MHz, N-(2,6-Diisopropylphenyl )-1,6,9-tribromoperylene-3,4-dicarboximide 15 (16 g, 22 mmol), 4-tert-butylphenol (6.6 g, CDCl3, 30°C) 162.99, 153.55, 152.93, 147.00, 145.75, 131.24, 130.85, 130.80, 129.40, 129.19, 128.87, 127.73, 127.47, 127.17, 0.044 mol) and potassium carbonate (6.9 g, 0.05 mol ) were stirred in 500 ml NMP at 120 °C for 6 h.After cooling to 126.42, 125.24, 124.32, 123.94, 122.53, 121.63, 117.39, 34.37, 31.44, 29.23, 24.10; nmax(KBr)/cm-1 1707 (CNO), 1669 room temperature, the reaction mixture was poured into 2 l water–HCl (551). The resulting precipitate was filtered, (CNO); lmax(CH2Cl2)/nm (e) (absorption) 262 (95819), 271 (97645), 382 (12895), 709 (71931), 781 (166571); (fluores- washed with water and dried under vacuum. The desired product was purified by column chromatography on silica gel cence) 806; m/z (FD) 775.2 (M2+, 38%), 1551.3 (M+, 100%) (calc.M+, 1552.0); mp >300 °C; Rf 0.43 (CH2Cl2), 0.03 using CH2Cl2 as eluent. Precipitation from CH2Cl2 into methanol aVorded 6.28 g of the title compound as a red powder (toluene). (33% yield).dH(300 MHz, CDCl3, 30°C) 9.40 (d, 1H, H-12), 9.16 (d, N-Propyl-1,6,7,12-tetra(4-hexyloxyphenoxy)perylene-3,4- 1H, H-7), 8.35 (d, 1H, H-10), 8.34 (s, 1H, H-2), 8.32 (s, 1H, dicarboximide 20 H-5), 7.88 (d, 1H, H-8), 7.69 (t, 1H, H-11), 7.4–7.5 (m, 5H, N-Propyl-1,6,7,12-tetra(4-hexyloxyphenoxy)perylene-3,459,10- Ph-H-16,3,3¾), 7.30 (d, 2H, Ph-H-15), 7.08 (m, 4H, Ph-Hbis( dicarboximide) 19 (15 g, 12 mmol) and 150 g KOH were 2,2¾), 2.72 [m, 2H, CH(CH3)2], 1.35 (s, 18H, tert-butyl ), 1.15 added to 1 L of propan-2-ol.The reaction mixture was refluxed [d, 12H, CH(CH3)2]; dC(125.5 MHz, CDCl3, 30°C) 163.14, for 105 min. After cooling to room temperature, 2.5 L water 153.80, 153.69, 153.17, 153.10, 147.35, 147.33, 145.64, 132.00, and 250 ml of concentrated hydrochloric acid were added.The 131.54, 131.01, 130.87, 130.67, 129.42, 129.32, 129.29, 128.68, resulting precipitate was filtered, washed with water and dried 128.05, 127.83, 127.55, 127.18, 126.63, 126.54, 125.35, 124.36, under vacuum. The crude product was then dissolved in a 124.30, 123.91, 123.02, 121.89, 121.87, 118.43, 118.36, 34.43, suspension of 25 g Cu2O in 800 ml quinoline.The temperature 31.45, 29.09, 23.99; nmax(KBr)/cm-1 1706 (CNO), 1670 was raised to 240 °C under vacuum and 500 ml quinoline were (CNO); lmax(CH2Cl2)/nm (e) 274 (40081), 420 (9949), 513 distilled over a period of 6 h. The reaction mixture was cooled (41553); m/z (FD) 855.2 (M+, 100%) [C54H50NO4Br to room temperature, and 2.5 L water and 150 mL concen- (856.90 g mol-1): calc.: C, 75.69; H, 5.88; N, 1.63; Br, 9.32.trated hydrochloric acid were added. The resulting precipitate Found: C, 75.27; H, 5.92; N, 1.41; Br, 8.69%]; mp 297 °C; Rf was filtered, washed with water and dried under vacuum. 0.86 (CH2Cl2), 0.56 (toluene). Purification was carried out by chromatography on silica gel with toluene as eluent. The second fraction was identified as N,N¾-Bis(2,6-diisopropylphenyl )-1,1¾,6,6¾-tetra(4-tert- the title compound.Precipitation in methanol aVorded 5.70 g butylphenoxy)-9,9¾-biperylene-3,453¾,4¾-bis(dicarboximide) 17 of the title compound as a red–orange powder (42% yield). dH(300 MHz, CDCl3, 30°C) 8.10 (s, 2H, H-2, 5), 7.72 (d, 770 mg (2.8 mmol) Ni(cod)2, 252 mg (2.34 mmol) cod, 2H, H-9, 10), 7.09 (d, 2H, H-8, 11), 6.7–7.0 (m, 16H, Ph-H), 440 mg (2.8 mmol) 2,2’-bipyridyl and 2 g (2.33 mmol) N-(2,6- 4.08 (t, 2H, -CH2), 3.93 [t, 8H, -CH2 (hexyl )], 2.75 [m, 8H, diisopropylphenyl )-1,6-bis(4-tert-butylphenoxy)-9-bromopery- -CH2 (hexyl )], 1.1–1.6 [m, 26H, (CH2)3 (hexyl ), -CH2 lene-3,4-dicarboximide 13 were reacted as described for the (propyl )], 0.96 [m, 15H, CH3 (hexyl ), CH3 (propyl )]; preparation of 14.Purification was carried out by column lmax(CH2Cl2)/nm (e) (absorption) 277 (1.23), 414 (0.27), 538 chromatography on silica gel with CH2Cl2–toluene as eluent. (0.55); m/z (FD) 1132.8 (M+, 100%) (calc. M+, 1132.5). Recrystallisation from CH2Cl2–methanol aVorded 1.55 g of the title compound as a red powder (86% yield). N-Propyl-1,6,7,12-tetra(4-hexyloxyphenoxy)-9-bromoperylene- dH(500 MHz, CDCl3, 30°C) 9.46 (d, 2H, H-7,7¾), 9.36 (d, 3,4-dicarboximide 21 2H, H-12,12¾), 8.36 (s, 2H, H-5,5¾), 8.34 (s, 2H, H-2,2¾), 7.64 (d, 2H, H-8,8¾), 7.60 (d, 2H, H-10,10¾), 7.4–7.5 (m, 12H, H- 5 g (4.4 mmol) N-Propyl-1,6,7,12-tetra(4-hexyloxyphenoxy)- 11,11¾, Ph-H-3,3¾,16,16¾), 7.29 (d, 4H, Ph-H-15,15¾), 7.09, 7.13 perylene-3,4-dicarboximide 20 and 2 g (11 mmol) NBS were (d, 4H, Ph-H-2,2¾), 2.73 [m, 4H, CH(CH3)2], 1.34 (s, 36H, dissolved in 600 mL of DMF.The reaction mixture was tert-butyl ) 1.15 [d, 24H, CH(CH3)2]; dC(125.5 MHz, CDCl3, reacted for 12 h at 60 °C. After cooling to room temperature, 30 °C) 163.2, 153.8, 153.7, 153.3, 147.3, 147.2, 145.7, 145.7, the reaction mixture was poured into 3 L water–HCl (551). 140.1, 132.8, 131.9, 130.7, 129.7, 129.4, 128.9, 128.3, 127.9, The resulting precipitate was filtered, washed with water and 127.9, 127.2, 127.2, 127.0, 126.9, 124.3, 124.2, 123.9, 123.1, dried under vacuum.Precipitation from CH2Cl2 into methanol 121.6, 118.6, 118.5, 34.4, 31.5, 29.1, 24.0; nmax(KBr)/cm-1 aVorded 4.68 g of the title compound 21 as a red powder 1709 (CNO), 1672 (CNO); lmax(CH2Cl2)/nm (e) 275 (66307), 93% yield). 417 (15681), 534 (91474); m/z (FD) 777.1 (M2+, 6%), 1554.1 dH(500 MHz, CDCl3, 30°C) 8.12 (s, 1H, H-2), 8.10 (s, 1H, (M+, 100%) [C108H100N2O8 (1553.99 g mol-1) calc.: C, 83.47; h-5), 8.09 (d, 1H, H-10), 7.38 (s, 1H, H-8), 7.18 (d, 1H, HH, 6.49; N, 1.80. Found: C, 83.31; H, 6.33; N, 1.62%]; mp 11), 6.7–7.0 (m, 16H, Ph-H), 4.05 (t, 2H, -CH2); 3.92 [t, 8H, 259 °C; Rf 0.84 (CH2Cl2), 0.26 (toluene).-CH2 (hexyl )]; 1.77 [m, 10H, -CH2/-CH2 (hexyl )], 1.2–1.6 [m, 24H, (CH2)3], 0.94 [m, 15H, CH3/CH3 (hexyl )]; m/z (FD) 1211.6 (M+, 100%) (calc. M+, 1211.4). N,N¾-Bis(2,6-diisopropylphenyl )-1,6,11,16-tetra(4-tertbutylphenoxy) quaterrylene-3,4513,14-bis(dicarboximide) 18 N,N¾-Dipropyl-1,1¾,6,6¾,7,7¾,12,12¾-octa(4- The synthesis was performed as described for 2.Modifications: hexyloxyphenoxy)-9,9¾-biperylene-3,453¾,4¾-bis(dicarboximide) 500 mg (0.32 mmol) N,N¾-bis(2,6-diisopropylphenyl )-1,1¾,6,6¾- 22 tetra(4-tert-butylphenoxy)-9,9¾-biperylene-3,453¾,4¾-bis(dicarboximide) 17, 80 g KOH and 6 g glucose. The desired product 654 mg (1 mmol) Bis(triphenylphoshine)nickel(II) chloride, 450 mg activated zinc and 131 mg (1 mmol) tetraethylam- was purified by column chromatography on silica gel with CH2Cl2–toluene as eluent.Precipitation from CH2Cl2 into monium iodide were poured into a 100 mL Schlenk flask under 2368 J. Mater. Chem., 1998, 8(11), 2357–23696 M. Burghard, C. Fischer, M. Schmelzer, S. Roth, M. Hanack and argon containing 80 mL of THF. After stirring for 4 h at room W. Go� pel, Chem.Mater., 1995, 7, 2104. temperature, 1.2 g (1.06 mmol) N-propyl-1,6,7,12-tetra(4-hex- 7 D.Schlettwein, D. Wo� hrle, E. Karmann and U. Melville, Chem. yloxyphenoxy)-9-bromoperylene-3,4-dicarboximide 21 were Mater., 1994, 6, 3. added. Then, the reaction mixture was stirred for 12 h at room 8 H. O. Loutfy, A. M. Hor, P. Kazmaier and M. Tam, J. Imaging temperature. The reaction mixture was filtered through Al2O3 Sci., 1989, 33, 151. 9 M.P. O’Neil, M. P. Niemczyk, W. A. Svec, D. Gosztola, G. L. and washed with CH2Cl2. Precipitation from CH2Cl2 into Gaines III and M. R. Wasielewski, Science, 1992, 257, 63. methanol aVorded 3.45 g of the title compound as a red 10 R. Gvishi, R. Reisfeld and Z. Bursheim, Chem. Phys. Lett., 1993, powder (75% yield). The purity was suYcient for the next 213, 338.reactions. For analytical purposes, 100 mg were purified by 11 G. Seybold and G. Wagenblast, Dyes Pigm., 1989, 11, 303. column chromatography on silica gel with toluene as eluent. 12 E. Clar, W. Kelly and R. M. Laird, Monatsh. Chem., 1956, 87, 391. 13 E. Clar and J. C. Speakman, J. Chem. Soc., 1958, 2492. dH(300 MHz, CDCl3, 30°C) 8.11 (s, 2H, H-2,2¾), 8.09 (s, 14 (a) K.-H.Koch and K. Mu� llen, Chem. Ber., 1991, 124, 2091; 2H, H-5,5¾), 7.42 (d, 2H, H-10,10¾), 7.1–7.2 (m, 20H, Ph-HA. Bonhen, K.-H. Koch, W. Lu� ttke and K. Mu� llen, Angew. 3,3¾,3,3, H-8,8¾,11,11¾), 6.7–6.9 (m, 16H, Ph-H-2,2¾,2,2¾), Chem., Int. Ed. Engl., 1990, 29, 525; (b) S. De Backer, M. R. 4.05 (t, 4H, N-CH2-), 1.68 (t, 4H, -CH2-CH2-CH3), 1.26 (3s, Negri, S.De Feyter, G. B. Dutt, M. Ameloot, F. C. De Schryver, 72H, tert-butyl ), 0.93 (t, 24H, CH3); m/z (FD) 1909.2 (M+, K. Mu� llen and F. Holtrup, Chem. Phys. Lett., 1995, 233, 538; A. Schmidt, N. R. Armstrong, C. Goeltner and K. Mu� llen, 100%), 955 (M2+, 92%) (calc. M+, 1910.4). J. Phys. Chem., 1994, 98, 11780; S. De Backer, G. B. Dutt, M. dH(300 MHz, CDCl3, 30°C) 8.12 (s, 2H, H-2,2¾), 8.11 (s, Ameloot, F.C. De Schryver, K. Mu� llen and F. Holtrup, J. Phys. 2H, H-5,5¾), 7.42 (d, 2H, H-10,10¾), 7.08 (s, 2H, H-8,8¾), Chem., 1996, 100, 512; Y. H. Meyer, P. Plaza and K. Mu� llen, 6.7–7.0 (m, 34H, H-11,11¾,Ph-H-2,2¾,2,2¾,Ph-H-3,3¾,3,3¾), Chem. Phys. Lett., 1997, 264, 643. 4.06 (t, 4H, -CH2), 3.93 [t, 16H, -CH2 (hexyl )], 1.76 [m, 15 F. Holtrup, G.R. Mu� ller, H. Quante, S. De Feyter, F. C. De 20H, -CH2/-CH2 (hexyl )], 1.3–1.7 [m, 48H, (CH2)3], 0.93 [m, Schryver and K. Mu� llen, Chem. Eur. J., 1997, 3, 219. 16 H. Quante, Y. Geerts and K. Mu� llen, Chem. Mater., 1997, 9, 495. 30H, CH3/CH3 (hexyl )]; m/z (FD) 1131.6 (M2+, 100%), 17 H. Quante and K. Mu� llen, Angew. Chem., Int. Ed. Engl., 1995, 34, 2263.1 (M+, 62%) (calc. M+, 2262.9). 1323; H. Quante, Ph.D. Dissertation, Mainz, 1995. 18 Y. Nagao and T. Misono, Bull. Chem. Soc. Jpn., 1981, 54, 1191. 19 Y. Nagao, Y. Abe and T. Misono, Dyes Pigm., 1991, 16, 19. N,N¾-Dipropyl-1,6,7,10,11,16,17,20-octa(4- 20 T. Yamamoto, A. Morita, Y. Miyazaki, Y. Maruyama, hexyloxyphenoxy)quaterrylenebis(dicarboximide) 23 H. Wakayama, Z. Zhou, Y. Nakamura and T. Kanbara, Macromolecules, 1992, 25, 1214. 500 mg (0.22 mmol) N,N¾-dipropyl-1,1¾,6,6¾,7,7¾,12,12¾-octa(4- 21 H. Azizian, C. Eaborn and A. Pidcock, J. Organomet. Chem., hexyloxyphenoxy)-9,9¾-biperylene-3,453¾,4¾-bis(dicarboximide) 1981, 215, 49. 22, 30 g KOH and 4 g glucose, dissolved in 30 mL of ethanol, 22 (a) J. K. Stille, Angew. Chem., 1986, 98, 504; Angew. Chem., Int. Ed. Engl., 1986, 25, 508; (b) I.P. Beletskaya, J. Organomet. Chem., were reacted as descrf 2. Purification 1983, 250, 551. was carried out by column chromatography on silica gel with 23 Ullmanns Enzyclopa�die der technischen Chemie, 4th edn., Verlag CH2Cl2 as eluent. Recrystallisation from CH2Cl2–methanol Chemie, Weinheim, 1974, vol. 18, p. 686. aVorded 119 mg of a green powder containing the title com- 24 W. Bradly and F. W. Pexton, J. Chem. Soc., 1954, 4432. pound and some degradation products, i.e. loss of hexyloxy- 25 D. Dotcheva, M. Klapper and K. Mu� llen, Macromol. Chem. Phys., 1994, 195, 1905; H. Quante, P. Schlichting, U. Rohr, Y. phenoxy side groups. The title compound was finally purified Geerts and K. Mu� llen, Macromol. Chem. Phys., 1996, 197, 4029. by gel permeation chromatography in chloroform on poly- 26 R. H. Mitchell, Y.-H. Lai and R. V. Williams, J. Org. Chem., styrene as stationary phase, aVording 15 mg (0.3% yield). 1979, 44, 4733. dH(500 MHz, CDCl3, 30°C) 8.08 (s, 4H, H-2,5,12,15), 8.06 27 I. T. Storie and F. Sontheimer, Tetrahedron Lett., 1978, 19, 4567. (s, 4H, H-8, 9, 18, 19), 6.93 (d, 4H, Ph-H-3,3¾), 6.92 (d, 4H, 28 (a) M. Iyoda, M. Sakaitami, H. Otsuka and M. Oda, Chem. Lett., 1985, 127; (b) M. Iyoda, M. Sakaitami, A. Kojima and M. Oda, Ph-H-3,3¾), 6.84 (d, 4H, Ph-H-2,2¾), 6.82 (d, 4H, Ph-HTetrahedron Lett., 1985, 26, 3719. 2,2¾), 4.04 [t, 4H, -CH2 (propyl )], 3.94 [m, 8H, -CH2 (Ph)], 29 A. S. Kende, L. S. Liebeskind and D. Braitsch, Tetrahedron Lett., 1.77 [m, 8H, -CH2 (Ph)], 1.68 [m, 4H, -CH2 (propyl )], 1.47 1975, 16, 3375. [m, 8H, -CH2 (Ph)], 1.37 [m, 16H, (CH2)2 (Ph)], 0.93 [m, 18H, 30 S. Prathapan, T. E. Johnson and J. Lindsey, J. Am. Chem. Soc., CH2 (Ph), CH2 (propyl )]; lmax(CH2Cl2)/nm (e) 258 (1.27), 1993, 115, 7519. 271 (1.28), 790 (1.45); m/z (FD) 2260.7 (M+, 100%), 2066.8 31 M. Emmelius, G. Pawlowski and H. W. Vollmann, Angew. Chem., 1989, 101, 1475. ([M-Ph]+, 54%), 1874.8 ([M-2Ph]+, 66%), 1681.6 32 (a) G. Scheibe, Angew. Chem., 1937, 50, 51; (b) G. Scheibe, Kolloid (M-3Ph]+, 49%), (calc. M+, 2261.1). Zeitsch., 1938, 82, 1; (c) E. E. Jelley, Nature, 1936, 138, 1009; (d) E. E. Jelley, Nature, 1937, 139, 631; (e) S. F. Mason, Proc. Chem. Soc., 1964, 119; ( f) D.Mo� bius, Adv. Mater., 1995, 7, 437. 33 K. A. Connors, Binding Constants, Wiley, New York, 1987. References 34 Y. Geerts and K. Mu� llen, Novel Light Emitting Dyes, Oligomers, Polymers, and Organic-Inorganic Hybrid Materials, in Applied 1 J. Fabian and R. Zahradnik, Angew. Chem., 1989, 101, 693; Fluorescence in Chemistry, Biology, and Medicine, ed. W. Rettig, Angew. Chem., Int. Ed. Engl., 1989, 28, 677; J. Fabian, B. Strehmel and S. Schrader, Springer Verlag, in the press. M. Nakazumi and T. J. Matsuoka, Chem. Rev., 1992, 92, 1197. 35 S. J. Strickler and R. A. Berg, J. Chem. Phys., 1962, 37, 814. 2 Y. Suzuki, in Infrared Absorbing Dyes Plenum Press, New York, 36 Electronic processes in organic crystals, ed. M. Pope and C. E. 1990. Swenberg, Clarendon Press, Oxford, New York, 1982. 3 Y. Nagao and T. Misono, Dyes Pigm., 1984, 5, 171. 37 A. J. Bard, personnal communication. 4 A. Rademacher, S. Ma�rkle and H. Langhals, Chem. Ber., 1982, 115, 2927. 5 H. Langhals, Heterocycles, 1995, 40, 477. Paper 8/04337J J. Mater. Chem., 1998, 8(11), 2357&nda

ISSN:0959-9428    

DOI:10.1039/a804337j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Molecular assemblies of novel amphiphilic phthalocyanines: an investigation into the self-ordering properties of complex functional materials Ziad Ali-Adib,a Guy J. Clarkson,a Neil B. McKeown,*a† Kevin E. Treacher,a Helen F. Gleesonb and Alexander S. Stennettb aDepartment of Chemistry, University of Manchester, UK M13 9PL bDepartment of Physics and Astronomy, University of Manchester, UK M13 9PL Received 17th July 1998, Accepted 18th August 1998 The synthesis and liquid crystalline properties of unsymmetrically substituted Pcs which contain both alkyl and hydroxy terminated tetra(ethyleneoxy) side-chains are described.Despite poor Langmuir–Blodgett film forming properties, the amphiphilic Pcs are of interest as they display a variety of columnar mesophases and the ability to form self-ordered lamellar films by simple solvent casting.Lamellar order can be obtained in spin-coated films of these derivatives by annealment at a temperature at which the Pc is liquid crystalline. These self-ordering spincoated films are an alternative to the laborious Langmuir–Blodgett technique for the fabrication of highly ordered and uniform films of functional molecular materials.In order to exploit the electronic or optical properties of between their liquid crystalline behaviour and the formation of ordered films. The liquid crystalline properties of the trityl- functional compounds it is necessary to understand, predict and control the structure of their condensed states. Since their protected precursors are also described.discovery seventy years ago, phthalocyanines (Pcs) have become one of the most studied of all organic functional materials. In addition to their use as blue and green colorants, Experimental Pcs are of increasing interest for applications in non-linear Liquid crystal characterisation optics, xerography, molecular electronics, photodynamic cancer therapy, solar energy conversion, catalysis and as the DiVerential scanning calorimetry measurements were made on active component of gas sensors.1 Much is now known about a Seiko DSC 220C machine and calibrated using an indium the structures of the various crystalline polymorphs of Pc and standard.Optical microscopy observations were made on a its metal ion containing derivatives.1a However, in order to Nikon Optiphot-2 microscope with a Mettler FP80 HT Hot optimise their potential utility in electronic and optoelectronic Stage.Photographs of the optical textures [Fig. 1(a)–(e)] were devices, it is necessary to fabricate Pcs as thin films in which taken using the same arrangement equipped with a Nikon the nano-scale architecture and ordering can be reproducibly FX-35 W camera.Low resolution X-ray diVraction (XRD) controlled. Vacuum sublimation1a,2 or the spin-coating of Pc from powder samples was recorded using Cu-Ka radiation particles dispersed in a soluble polymer matrix1a,3 remain the (l=1.54 A° ) from a Philips PW1130/00 generator with a nickel most important techniques for the fabrication of films derived filter.The samples were contained in glass capillaries from these insoluble compounds. However, research into the (Hilgenberg 0.01 mm thick glass, 1.0 mm outside diameter Xsynthesis of substituted Pcs has provided materials which are ray capillaries) and placed in the beam in an aluminium soluble and therefore suitable for film fabrication by the heating block. The temperature was regulated by a Control Langmuir–Blodgett (LB) technique1a,4 or by the spin-coating Techniques Process Instruments 453 Plus Thermal Controller. of pure material.1a,5 In addition, suitable substitution of the The diVracted X-rays were detected with a flat-plate photo- Pc macrocycle by flexible side-chains, either alkyl or oligo(ethy- graphic camera using Agfa-Gevaert Osray M3 X-ray film.The leneoxy), gives materials which self-order to form columnar system was calibrated using sodium chloride.High resolution mesophases.1,6 The external control over molecular orientation XRD analysis was carried out using the synchrotron radiation aVorded by liquid crystallinity may enable the fabrication of source (SRS) at Daresbury (Station 8.2, l=1.54 A° ) using monodomainal, ordered solid films.previously described methods for data collection and manipu- This paper describes the synthesis and self-ordering lation.8 The X-ray camera at the SRS was calibrated with properties of unsymmetrically substituted Pcs which contain collagen and both small and wide angle scattering data were both alkyl (hexadecyl ) and hydroxy terminated tetra(ethy- collected. The high X-ray flux available at the SRS allowed leneoxy) side-chains.These Pcs were originally designed as XRD patterns to be obtained rapidly, typically in just a few amphiphilic materials for deposition as LB multilayer films, minutes, enabling data to be collected at diVerent temperatures and their monolayer forming properties and failed attempts without any danger of sample degradation. to prepare LB films are described.Interestingly, it was discovered that they display a variety of thermotropic columnar mesophases and the ability to form self-ordered multilayer Langmuir film characterisation ( lamellar) films by simple solvent casting.7 Therefore, it was Isotherm behaviour was measured for monolayers, spread of interest to determine whether highly-ordered spin-coated from chloroform (Aldrich, HPLC grade) solution, on pure films, of uniform thickness, could be obtained from these water at pH 5.5 with no added ions using the apparatus and materials and to re-examine in more detail the relationship procedures described previously.9 Multilayer film formation was attempted on clean glass slides appropriately treated to provide either hydrophilic or hydrophobic surfaces.†E-mail: neil.mckeown@man.ac.uk J. Mater. Chem., 1998, 8(11), 2371–2378 2371Film fabrication and characterisation H; 10.54; N, 4.88%); lmax(toluene)/nm 706, 670, 644, 606, 350; dH(500 MHz, C6D6, 60°C) -0.6 (br s, 2H), 1.01 (t, 18H), Solvent cast films and spin-coated films were prepared from 1.22–1.7 (m, 144H), 1.78 (m, 12H), 2.14 (m, 12H), 3.33 (m, the same chloroform solutions (~0.02 g ml-1).The substrates 12H), 3.42 (t, 2H), 3.68 (t, 2H), 3.72 (m, 2H), 3.76 (m, 2H), were clean silicon or glass microscope slides pre-treated with 3.81–3.86 (m, 4H), 3.97 (br t, 2H), 4.35 (br t, 2H), 7.19 (tt, hexamethyldisilazane vapour. Spin-coating was achieved, at 3H), 7.70 (dd, 6H), 7.79 (d, 1H), 9.15 (br s, 1H), 9.45–9.77 5000 rpm, using a Headway Research Inc.PM80 wafer spin (br m, 7H); m/z (FAB) 2298, 13C2C153H240N8O5 (M+H+) cleaner. Glancing angle X-ray diVraction from the films was requires 2298. recorded using Cu-Ka radiation in a Philips PW1050 X-ray The third fraction was collected and applied to a fresh silica DiVractometer using a rotating intensity detector. column (eluent: toluene, 20 °C, Rf=0.30) and recrystallised from heptane to aVord 2,3,16,17-tetrakis(hexadecyl)-16,23(24)- Pc synthesis and structural characterisation bis(14,14,14-triphenyl-1,4,7,10,13-pentaoxatetradecyl)phthalocyanine 4 as a mixture of two isomers (108 mg, 3%) (Found C, Routine 1H NMR spectra were measured at 300 MHz using 79.15; H, 9.37; N, 4.86%.C150H206N8O10 requires C, 78.97; an Inova 300 spectrometer.High resolution (500 MHz) 1H H, 9.10; N, 4.91%); lmax(toluene)/nm 706, 670, 638, 608, 380, NMR spectra were recorded using a Varian Unity 500 spec- 292; dH (500 MHz, C6D6, 60°C) -1.10 (br s, 2H), 1.00 (br trometer. UV–Visible spectra were recorded on a Shimadzu t, 12H), 1.3–1.89 (br m, 104H), 2.10–2.25 (br m, 8H), UV-260 spectrophotometer using cells of pathlength 10 mm. 3.20–3.43 (br m, 8H), 3.44 (m, 4H), 3.69 (m, 4H), 3.73 (m, IR spectra were recorded on an ATI Mattson Genesis Series 4H), 3.77 (m, 4H), 3.82–3.85 (m, 8H), 4.04 (br s, 4H), 4.38 FTIR (KBr/Germanium beam splitter). Elemental analyses (br s, 4H), 7.19 (tt, 6H), 7.70 (dd, 12H), 7.83 (br s, 2H), were obtained using a Carlo Erba Instruments CHNS-O EA 8.95–9.45 (br m, 8H); m/z (FAB) 2282, 13C2C148H206N8O10 108 Elemental Analyser.Routine low resolution chemical (M++H+) requires 2281. ionisation (CI) and electron ionisation (EI ) were obtained The fourth fraction was collected and applied to a fresh using a Fisons Instruments Trio 2000. Fast atom bombardment silica column (eluent: toluene, 20 °C, Rf=0.2) and recrystal- (FAB) spectra were recorded on a Kratos Concept speclised from heptane to aVord 2,3,9,10-tetrakis(hexadecyl)- trometer.All solvents were dried and purified as described in 16(17),23(24)-bis(14,14,14-triphenyl-1,4,7,10,13-pentaoxatetra- Perrin and Armarego.10 Silica gel (60 Merck 9385) was used decyl)phthalocyanine 5 as a mixture of three isomers (268 mg, in the separation and purification of compounds by column 7.0%). (Found C, 79.06; H, 9.12; N, 4.80%.C150H206N8O10 chromatography. All Pcs were heated at 120–150 °C under requires C, 78.97; H, 9.10; N 4.80%); lmax(CH2Cl2)/nm 706, vacuum for 18 h as the final step of purification. 670, 638, 608, 380, 344, 292; dH(500 MHz, C6D6, 60°C)-1.10 4-(14,14,14-Triphenyl-1,4,7,10,13- (2H, br s), 1.00 (t, 12H), 1.34–1.89 (br m, 104H), 2.10–2.25 pentaoxatetradecyl)phthalonitrile 1 (br m, 8H), 3.26–3.40 (br m, 8H), 3.44 (m, 4H), 3.69 (m, 4H), 3.73 (m, 4H), 3.77 (m, 4H), 3.82–3.85 (m, 8H), 3.95–4.06 To a solution of 4-nitrophthalonitrile (1.4 g, 8.0 mmol, (br m, 4H), 4.34–4.50 (br m, 4H), 7.18 (tt, 6H), 7.70 (dd, Aldrich) and tetraethylene glycol monotrityl ether11 (3.4 g, 12H), 7.76 (br s, 2H), 8.95–9.65 (br m, 8H); m/z (FAB) 2283, 8.0 mmol) in anhydrous DMF (30 ml ) was added anhydrous 13C2C148H206N8O10 (M++H+) requires 2281.potassium carbonate (2 g, 14.5 mmol) and the mixture stirred The fifth fraction was collected and applied to a fresh silica under nitrogen for 6 days at 50 °C. Water was added (100 ml ) column (eluent: toluene–THF, 2051, 20 °C, Rf=0.2) and and the mixture extracted with Et2O (3×60 ml ), washed with recrystallised from heptane to aVord 2,3-bis(hexadecyl)- water (2×50 ml ) and dried over anhydrous magnesium sulf- 9(10),16(17),23(24)-tris(14,14,14-triphenyl-1,4,7,10,13-pentaate. The solvent was removed and the product recrystallised oxatetradecyl)phthalocyanine 6 as a mixture of four isomers from hexane–toluene (251) to give 1 as colourless plates (2.1 g, (298 mg, 8%).(Found C, 76.44; H, 7.38; N, 4.86%. 47%), mp 92–94 °C; n (KBr)/cm-1 2230 (CON) (Found C, C145H172N8O15 requires C, 76.82; H, 7.65; N, 4.94%); 74.55; H, 6.41; N, 5.02%. C35H34N2O5 requires C, 74.71; H, lmax(toluene)/nm 707, 671, 638, 610, 380, 344; dH(500 MHz, 6.09; N, 4.98%); dH(200 MHz, CDCl3) 3.21 (t, 2H), 3.64–3.70 C6D6, 60°C) -1.45 (br s, 2H), 1.00 (t, 6H), 1.34–1.89 (br (m, 10H), 3.84 (t, 2H), 4.04 (t, 2H), 7.05 (dd, 1H), 7.10 (d, m, 52H), 2.15–2.23 (br m, 4H), 3.22–3.40 (br m, 4H), 3.44 1H), 7.19 (t, 3H), 7.26 (t, 6H), 7.45 (d, 6H), 7.57 (d, 1H); (m, 6H), 3.68 (m, 6H), 3.74 (m, 6H), 3.77 (m, 6H), 3.82–3.85 m/z (CI) 580 (M++NH4+). (m, 12H), 3.90–4.08 (br m, 6H), 4.34–4.50 (br m, 6H), 7.18 (tt, 9H), 7.70 (dd, 18H), 7.76 (br m, 3H), 8.95–9.65 (br m, Phthalocyanines 2–7 8H); m/z (FAB) 2269, 13C2C143H172N8O15 (M++H+) requires 2267.To a rapidly stirred mixture of compound 1 (2.0 g, 3.55 mmol) and 4,5-bis(hexadecyl )phthalonitrile6c (1.9 g, 3.39 mmol) in The sixth fraction was collected and applied to a fresh silica column (eluent: toluene–THF, 1051, 20 °C, Rf=0.2) and refluxing pentanol (10 ml ), under a nitrogen atmosphere, was added excess lithium metal (0.2 g). Heating and stirring were recrystallised from heptane to aVord 2,9(10),16(17), 23(24)- tetrakis ( 14,14,14-triphenyl-1,4,7,10,13-pentaoxatetradecyl)- continued for 6 h.On cooling, water (30 ml ) was added and the reaction mixture heated to ensure complete removal of phthalocyanine 7 as a mixture of four isomers (105 mg, 3%) (Found C, 74.33; H, 6.12; N, 5.01%.C140H138N8O20 requires lithium ions from the central cavity of the Pcs. Evaporation of the water, under reduced pressure, left a green product C, 74.65; H, 6.18; N, 4.97%); lmax(toluene)/nm 704, 668, 646, 608, 384, 344; dH(500 MHz, C6D6, 60°C) -2.5 (br s, 2H), mixture. The resultant solid was dissolved in toluene and passed through a silica column, at 50 °C, using an eluent 3.45 (m, 8H), 3.70 (m, 8H), 3.76 (m, 8H), 3.81 (m, 8H), 3.89 (m, 16H), 4.00–4.15 (8H, br m), 4.32–4.51 (br m, 8H), 7.20 composed of an increasing amount of THF relative to toluene.The first fraction (85 mg, 2%) (Rf=0.9, 50 °C, toluene) (tt, 12H), 7.71 (dd, 24H), 7.76 (br m, 4H), 8.82–9.51 (m, 8H); m/z (FAB) 2254, 13CC138H138N8 O20 (M++H+) proved to be identical to a previously prepared sample of 2,3,9,10,16,17,23,24-octakis(hexadecyl)phthalocyanine 2.1g requires 2254.The second fraction was collected and applied to a fresh silica column (eluent: toluene–heptane, 151, 50 °C, Rf=0.5) 2,3,9,10,16,17-Hexakis(hexadecyl )-23-(12-hydroxy-1,4,7,10- and recrystallised from heptane to aVord 2,3,9,10,16,17-hexakis- tetraoxadodecyl)phthalocyanine 8 (hexadecyl)-23-(14,14,14-triphenyl-1,4,7,10,13-pentaoxatetradecyl) phthalocyanine 3 as a blue solid (316 mg, 8%).(Found A solution of compound 3 (200 mg, 95 mmol), THF (30 ml ) and hydrochloric acid (1 ml, 10 mol l-1) was heated at reflux C, 81.30; H, 10.70; N, 4.89%. C155H240N8O5 requires C, 81.10; 2372 J. Mater. Chem., 1998, 8(11), 2371–2378for 1 h. On cooling, the solvent was removed under reduced Results and discussion pressure and the resulting solid redissolved and eluted through Pc synthesis a silica column (eluent5toluene–THF). Recrystallisation from heptane gave 8 as a blue solid (160 mg, 82%) (Found C, 79.81; Pcs 2–12 are prepared by the route shown in Scheme 1.An H, 10.82; N, 5.40%. C136H226N8O5 requires C, 79.94; H; 10.66; aromatic nucleophilic substitution reaction6f,12 between tetra- N, 5.49%); llmax(toluene)/nm 706, 670, 644, 606, 350; ethylene glycol monotrityl ether and commercially available dH(500 MHz, C6D6, 60°C) -0.8 (br s, 2H), 1.00 (t, 18H), 4-nitrophthalonitrile provides the important precursor 1.22–1.7 (m, 144H), 1.78 (m, 12H), 2.14 (m, 12H), 3.33 (m, 4-(14,14,14-triphenyl-1,4,7,10,13-pentaoxatetradecyl )phthalo- 12H), 3.51 (t, 2H), 3.61 (t, 2H), 3.66 (m, 2H), 3.73 (m, 2H), nitrile 1.The mixed cyclotetramerisation of 4,5-bis- 3.82 (m, 2H), 3.98 (br t, 4H), 4.40 (br t, 2H), 7.82 (d, 1H), (hexadecyl )phthalonitrile and 1 gives a complex product 9.08 (br s, 1H), 9.45–9.77 (br m, 7H), signal of hydroxy mixture from which Pcs 2–7 are readily separated by simple proton hidden by alkyl resonances.column chromatography.6g The trityl protecting groups are removed from 2–7 under acid catalysed hydrolytic conditions 2,3,16,17-Tetrakis(hexadecyl )-9,23-(12-hydroxy-1,4,7,10- to give the amphiphilic Pcs 8–12, respectively. The structure tetraoxadodecyl)phthalocyanine 9 and purities of Pcs 2–12 were confirmed by fast atom bombardment mass spectrometry (FABMS), high resolution 1H NMR Pc 9 was prepared from 4 by a similar procedure to that for (500 MHz) and UV–VIS absorption spectroscopy, elemental 8 and recrystallised from toluene (39 mg, 62%) (Found C, analysis and HPLC (purity >99%).NMR analysis is consist- 74.58; H, 9.71; N,6.42%. C112H178N8O10 requires C, 74.87; H, ent with Pcs 4 and 9 being composed of a statistical mixture 9.99; N, 6.24%); lmax(toluene)/nm 708, 672, 642, 610, 384, of two inseparable regioisomers and Pcs 5 and 10 being 344; dH(500 MHz, C6D6, 60°C) -1.8 (br s, 2H), 1.00 (t, composed of three inseparable regioisomers.The separation 12H), 1.30–1.89 (br m, 104H), 2.10–2.25 (br m, 8H), of opposite (4 and 9) and adjacent (5 and 10) isomers contain- 3.10–3.43 (br m, 8H), 3.50 (m, 4H), 3.67 (m, 4H), 3.71 (m, ing both oligo(ethyleneoxy) and alkyl side chains has been 4H), 3.78 (m, 4H), 3.82–3.86 (m, 8H), 4.06 (br s, 4H), 4.45 demonstrated previously.6g Pc 8 is insuYciently soluble in cold (br s, 4H), 7.85 (br s, 2H), 8.85–9.45 (br m, 8H), signal of solvents to allow investigations into the fabrication of LB and hydroxy proton hidden by alkyl resonances; m/z (FAB) 1796, spin-coated films derived from this compound. 13C2C110H178N8O10 (M++H+) requires 1797. Mesophase properties 2,3,9,10-Tetrakis(hexadecyl )-16,23-bis(12-hydroxy-1,4,7,10- tetraoxadodecyl)phthalocyanine 10 All of the Pcs 2–12 display at least one thermotropic mesophase. The transition temperatures and enthalpies, as measured Pc 10 was prepared from 5 by a similar procedure to that for by diVerential scanning calorimeter (DSC), are given in 8 and recrystallised from toluene (94 mg, 80%) (Found C, Table 1.Polarising optical microscopy of these materials gave 74.59; H, 9.69; N, 6.04%. C112H178N8O10 requires C, 74.87; in total four distinct optical textures, only one of which is H, 9.99; N 6.24%); lmax (CH2Cl2)/nm 706, 670, 638, 608, 384, easily assigned as that of a columnar hexagonal mesophase 344, 292; dH(500 MHz, C6D6, 60°C) -1.40 (2H, br s), 1.00 [Qh;13 Fig. 1(a) and 2(a)]. Low resolution powder X-ray (t, 12H), 1.34–1.89 (br m, 104H), 2.10–2.30 (br m, 8H), diVraction (XRD) studies of each Pc were carried out, however 3.26–3.40 (br m, 8H), 3.55 (m, 4H), 3.65 (m, 4H), 3.69 (m, these failed to give adequate information for structural eluci- 4H), 3.77 (m, 8H), 3.85 (m, 4H), 3.86 (br m, 4H), 4.00–4.50 dation of the other mesophases.Therefore, high resolution (br m, 4H), 7.60–7.75 (br s, 2H), 8.75–9.65 (br m, 8H), measurements were made using a synchrotron X-ray source signal of hydroxy proton hidden by alkyl resonances; m/z for Pcs 2 and 8–11. These results and the low resolution data (FAB) 1797, 13C2C110H178N8O10 (M++H+) requires 1797. for Pcs 3–7 and 12 are collected in Table 2.High resolution XRD measurements confirm that the 2,3-Bis(hexadecyl )-9,16,23-tris(12-hydroxy-1,4,7,10- symmetrical Pc 2 has two distinct mesophases. Previously tetraoxadodecyl)phthalocyanine 11 there was some doubt as to whether the lower temperature Pc 11 was prepared from 6 by a similar procedure to that for mesophase of 2 was simply a textural variation of Qh,6g in 8 and recrystallised from toluene (79 mg, 68%) (Found C, analogy with behaviour displayed by 1,4,8,11,15,18,22,25- 68.64; H, 8.34; N, 7.14%.C88H130N8O15 requires C, 68.63; H, octaalkyl-Pcs.15 However, the two distinct small angle diVrac- 8.51; N, 7.28%); lmax(toluene)/nm 706, 670, 638, 608, 384, tion rings, observed by high resolution XRD, are assignable 346, 292; dH(500 MHz, C6D6, 60°C) -3.3 (br s, 2H), 1.00 to diVraction from the 200 and 110 planes of a rectangular (t, 6H), 1.34–2.3 (br m, 52H), 2.80–3.31 (br m, 4H), 3.65 lattice.These reflections would be coincident for a hexagonal (m, 6H), 3.74 (m, 6H), 3.78 (m, 6H), 3.86 (m, 6H), 3.95 (m, mesophase. The ‘striated focal conic’ optical texture [Fig. 1(b)] 12H), 3.99–4.21 (br m, 6H), 4.30–4.58 (br m, 6H), 7.46–7.82 has been associated with a columnar rectangular mesophase (br m, 3H), 8.00–9.65 (br m, 8H), signal of hydroxy with a P21/a plane group symmetry [Qr(P21/a , Fig. 2(b)].14 proton hidden by alkyl resonances; m/z (FAB) 1541, However, we did not observe a reflection from 210 for this or 13C2C86H130N8O15 (M++H+) requires 1541. the lower temperature mesophase of amphiphilic Pcs 9 which also displays the striated focal conic texture.The lack of a 2,9,16,23-Tetrakis(12-hydroxy-1,4,7-tetraoxadodecyl )- reflection from the 210 plane suggests C2/m plane group phthalocyanine 12 symmetry [Qr(C2/m), Fig. 2(c)], although it has been noted in previous studies of the Qr(P21/a) mesophase that diVraction Pc 12 was prepared from 7 by a similar procedure to that for from the 210 plane can be very weak and may not be 8 and recrystallised from THF–toluene (45 mg, 65%) (Found C, 59.53; H, 6.59; N, 8.47%.C64H82N8O20 requires C, 59.90; H, 6.44; N, 8.73%); lmax(CH2Cl2)/nm 704, 670, 646, 608, 384, 344; dH(500 MHz, d6-DMSO, 80 °C) -3.1 (br s, 2H), 3.50–3.60 (m, 8H), 3.70 (m, 8H), 3.75 (m, 8H), 3.85 (m, 8H), 3.94 (m, 8H), 4.20 (b m, 8H), 4.33 (b m, 8H), 4.66 (br m, CN CN O2N CN CN Tr(OCH2CH2)3O ii, iii 2 + 3–7 iv 8–12 i 8H,), 7.50–7.69 (b m, 4H), 8.10–8.29 (b m, 4H), 8.50–8.70 Scheme 1 Reagents and conditions: i, Tr(OCH2CH2)3OH, anhydrous (br m, 4H), signal of hydroxy proton hidden by alkyl reson- K2CO3, DMF, 50–70 °C; ii, 4,5-Bis(hexadecyl )phthalonitrile, lithium, ances; m/z (FAB) 1283, 13CC63H82N8O20 (M++H+) pentanol, 135 °C; iii, acetic acid, separation by chromatography; iv, HCl (aq), THF, reflux.requires 1284. J. Mater. Chem., 1998, 8(11), 2371–2378 2373N N N N N N N N H H R R R R R R R R N N N N N N N N H H R R R R R R N N N N N N N N H H O(CH2CH2O)3X R R R R X(OCH2CH2)3O N N N N N N N N H H O(CH2CH2O)3X R R R R O(CH2CH2O)3X N N N N N N N N H H R R X(OCH2CH2)3O O(CH2CH2O)3X N N N N N N N N H H O(CH2CH2O)3X X(OCH2CH2)3O O(CH2CH2O)3X O(CH2CH2O)3X 2 R = C16H33 3 X = -Trityl, R = C16H33 8 X = -H, R = C16H33 4 X = Trityl, R = C16H33 9 X = H, R = C16H33 5 X = Trityl, R = C16H33 10 X = H, R = C16H33 6 X = Trityl, R = C16H33 11 X = H, R = C16H33 7 X = Trityl 12 X = H O(CH2CH2O)3X O(CH2CH2O)3X discernible from the background ‘noise’.16 Therefore, we whereas 10 displays a monotropic Qh which is stable over only a few degrees.The stable higher temperature mesophase of 10 has denote this mesophase simply as Qr1. For the lower temperature mesophase of Pc 11, which displays the striated focal conic a ‘mosaic’ texture with large domain size [Fig. 1(c)]. High resolution XRD analysis allows assignment of some diVraction texture of Qr1, there is a weak diVraction assignable to the 210 plane suggesting P21/a symmetry.In addition, there is a strong peaks to a rectangular lattice but additional small angle diVractions (d-spacings=52.2 and 47.7 A° ) may be due to a bilayer diVraction (d-spacing=54.0 A° ) which appears to originate from the 100 plane of the rectangular lattice. Reflection from lamellar superstructure. This mesophase is denoted as Qr2. The lower temperature mesophase of 10 is characterised by a granular this plane is not consistent with the extinction rules17 for a rectangular lattice of P21/a or C2/m plane symmetry group texture [Fig. 1(d)] superimposed on the mosaic texture of the Qr2 mesophase on cooling.We initially described this as a bilayer and suggests additional bilayer lamellar ordering.A much weaker reflection from the 100 plane is also observed in the lamellar mesophase (QL) on the basis of low resolution XRD analysis and the pronounced lamellar self-ordering properties of Qh mesophase of 11 perhaps resulting from the asymmetry of the molecule and indicating segregation of the two types of this compound.7 However, high resolution XRD shows diVractions originating from further ordering (d-spacings=47.2 and side-chain even at high temperature.Pc 10 possesses exceptional mesophase behaviour. Most Pc 23.7 A° ) in addition to the stronger lamellar diVractions (dspacings= 57.2, 28.6 and 19.2 A° ). mesogens have a Qh mesophase over a broad temperature range 2374 J. Mater. Chem., 1998, 8(11), 2371–2378Table 1 Mesophase transition temperatures (°C) with enthalpy changes (DH/J g-1) in parentheses.K=crystal, QL=columnar lamellar mesophase, Qr1=columnar rectangular mesophase which displays striated focal conic texture [Fig. 1(b)], Qr2=columnar rectangular mesophase which displays mosaic texture [Fig. 1(c)]; Qh=columnar hexagonal mesophase. Transition temperature and enthalpies for the heating cycle. Pc Glass–Qh K–QL K–Qh K–Qr1 Qr1–Qh QL–Qr2 Qr2–I Qh–I 2 — — — 108 (96) 170a — — 196 (6) 3 — — — 86 (120) 89a — — 167 (3) 4 — — — 41 (81) 191 (1) — — 196 (3) 5 — — — 77 (88) — — — 152 (3) 6 — — — 32 (23) 76 (1) — — 177 (1) 7 30b — — — — — — 225(1) 8 — — — 81 (120) 107 (2) — — 189 (3) 9 — — — 71 (30) 109 (3) — — 234 (5) 10c — 79 (88) — — — 132 (1) 194 (4) — 11 — — — 80 (16) 252 (1) — — 273 (1) 12 — — 75(14) — — — — >320 aTransition not observed by DSC.bGlass transition temperature. cPc 10 also displays a monotropic Qh mesophase on cooling from the isotropic liquid. All of the Pc mesophases display broad wide-angle cofacial ordering of the Pc molecules within the molecular stacks. Previous studies have suggested that alkoxy substituted diVraction rings correlating to d-spacings of 4–5 A° .The mesophases of Pcs 6, 7, 11 and 12 display an additional sharp wide Pc mesogens are able to form relatively ordered columnar structures due to the smaller steric demand of the oxygen angle diVraction ring corresponding to 3.5 A° which indicates an untilted columnar structure in which there is significant linking group as compared to the methylene group of alkyl Table 2 Powder X-ray diVraction data for Pcs 2–12.Each diVraction is given in A° ngstrom units. For each mesophase the assignments are based on a rectangular lattice, but for the mesophase and solid phase assignments of Pcs 9–11 a lamellar structure is also considered. Pc Phase T / °C Observed d-spacings/A° (assignments) 2-D lattice dimensions/A° 2a Qh 30.0 17.3 15.0 4–5 b=34.6 (190) (110/200) (310/020) (400/220) a=Ó3b Qr1 31.3 28.9 18.3 16.3 4–5 a=62.6 (140) (200) (110) (310) (020) b=32.5 3b,c Qh 29.2 16.8 14.3 4–5 b=33.7 (120) (110/200) (310/020) (400/220) a=Ó3b 5b Qh 29.5 17.0 14.6 4–5 b=34.1 (120) (110/200) (310/020) (400/220) a=Ó3b 6b Qh 29.6 16.8 14.3 4–5 3.5 b=34.2 (130) (110/200) (310/020) (400/220) a=Ó3b Qr1 28.5 23.1 15.1 4–5 3.5 a=57.0 (60) (200) (110) (310) b=25.3 7b Qh 28.5 16.9 14.3 4–5 3.5 b=32.9 (120) (110/200) (310/020) (400/220) a=Ó3b glass 8.5 16.9 14.3 4–5 3.5 b=32.9 (25) (110/200) (310/020) (400/220) a=Ó3b 8b Qh 28.5 16.6 14.3 4–5 b=32.9 (150) (110/200) (310/020) (400/220) a=Ó3b Qr1 30.8 28.5 18.0 16.0 4–5 a=61.6 (100) (200) (110) (310) (020) b=32.1 9a Qh 29.7 17.1 15.1 4–5 b=34.3 (200) (110/200) (310/020) (400/220) a=Ó3b Qr1 27.9 23.1 15.0 4–5 a=55.8 (90) (200) (110) (310) b=25.4 Solid 29.8 15.1 4–5 L=29.8 (25) (n=1) (n=2) 10a Qr2 52.2 47.7 28.5 21.0 16.8 4–5 a=52.2 (180) (100, n=1) (?) (110) (210) (020) b=34.0 (L=52.2) QL 57.2 47.2 28.6 23.7 19.2 4–5 L=57.2 (120) (n=1) (?) (n=2) (?) (n=3) Solid 50.2 46.5 25.4 16.8 4–5 L=50.2 (25) (n=1) (?) (n=2) (n=3) 11a Qh 53.0 26.5 15.3 4–5 3.5 b=30.6 (265) (100, n=1) (110/200) (310/020) a=Ó3b (L=53) Qr1 54.0 27.2 25.5 19.5 17.6 3–5 a=54.0 (230) (100, n=1) (200, n=2) (110) (210) (300, n=3) b=28.8 (L=54.0) Solid 51.8 26.0 17.3 4–5 3.5 (L=51.8) (30) (n=1) (n=2) (n=3) 12b Qh 23.0 4–5 3.5 b=26.6 (200) (110/200) a=Ó3b aHigh resolution XRD using SRS.bLow resolution XRD. cLower temperature mesophase is stable over too small a range for XRD analysis on low resolution equipment.J. Mater. Chem., 1998, 8(11), 2371–2378 2375Fig. 1 The optical texture of (a) the Qh mesophase (Pc 2, 187 °C), (b) the Qr1 mesophase (Pc 2, 160 °C), (c) the Qr2 mesophase (Pc 10, 150 °C), (d) the QL mesophase (Pc 10, 120 °C) and (e) the lyotropic Nc mesophase of Pc 12 which appears between the isotropic dilute ethanolic solution and the pure material (right of micrograph).All textures observed through crossed polarisers at a magnification of ×100. substituted Pcs.16 The wide-angle XRD results of Pcs 6 and 11 Similar anisotropic glass formation has been described recently for Pcs containing large dendritic substituents.19 suggest that two alkyl substituents are insuYcient to reduce the intermolecular ordering within the columnar mesophase.Pc 12 is soluble in protic polar solvents such as ethanol. The analysis of concentrated ethanolic solutions of Pc 12 by Pc 7 forms an anisotropic glass, on cooling from the mesophase, in which the ordered structure of the Qh mesophase polarising optical microscopy shows a ‘marbled’ texture [Fig. 1(e)] which is one of the characteristic textures of the is frozen.DSC shows clearly the reversible glass transition and XRD indicates the hexagonal columnar structure of the columnar nematic lyotropic mesophase [Nc; Fig. 2(d)].1f UV–VIS analysis of dilute ethanolic solutions of Pc 12 resulting brittle solid.18 The bulky nature of the four large trityl end-groups appears responsible for this behaviour. (lmax=620 nm) indicates the presence of the columnar aggre- 2376 J.Mater. Chem., 1998, 8(11), 2371–2378area per molecule can be estimated as 93 A° from the intercolumnar distance (26.5 A° ) and the cofacial intermolecular distance (3.5 A° ) of the hexagonal mesophase of Pc 12 (Table 2). These estimated areas per molecule (Aest) are in reasonable agreement with the observed values of A0 and A30 for Pcs 10 and 11 (Table 3).The observed values of A0 and A30 for Pc 9 (Table 3) also imply a perpendicular orientation of the Pc molecules in its monolayer (estimated area=155 A° 2) rather than a parallel orientation (estimated minimum area=225 A° 2) that would allow both tetra(ethyleneoxy) side-chains to be immersed simultaneously. For Pcs 9, 10 and 11 the Langmuir isotherms are characterised by a lack of hysteresis and good monolayer stability for prolonged periods of time at a surface pressure of 30 mN m-1. Despite these encouraging monolayer properties, multilayer films of Pcs 9, 10 and 11 could not be deposited onto either hydrophilic or hydrophobic substrates. In each case, successful deposition on the up stroke was followed by the loss of the material on the down stroke.This was the case even after allowing the initially deposited monolayer to dry for over 1 h. It should be noted that conventional oligo(ethyleneoxy)-based non-ionic surfactants are also poor LB film forming materials.20 Order in solvent cast and spin-coated films The simple process of forming films cast from chloroform Fig. 2 (a) Columnar hexagonal mesophase (Qh, a=Ó3b), (b) columnar rectangular mesophase with P21/a plane group symmetry, (c) rectangu- solutions (20 mg ml-1) of Pcs 9, 10 and 11 onto clean, lar disordered with C2/m plane group symmetry and (d) columnar hydrophobic substrates gives films with a high degree of nematic mesophase (Nc).lamellar ordering—as indicated by glancing angle XRD. Films cast onto hydrophilic substrates show no evidence of a lamellar structure, suggesting that in the ordered films the non-polar gates which are a prerequisite for the formation of the Nc hexadecyl side-chains of the first monolayer are in contact mesophase.with the surface of the substrate. For the cast films of Pcs 10 and 11, the large d-spacings are consistent with a bilayer Langmuir–Blodgett film forming properties structure in which the Pc molecules are oriented perpendicular The LB technique, which involves film fabrication by the to the surface of the substrate. Pc 9 gives a cast film for which sequential deposition of a monolayer formed at an air–water the d-spacing is consistent with a monolayer structure interface, has been thoroughly investigated as a method of (Table 4).The formation of a bilayer from Pc 9 is disfavoured preparing multilayer films derived from soluble Pc deriva- by its substitution pattern which places side-chains of similar tives.1a,4 It is apparent that an amphiphilic character is highly polarity on opposite sides of the molecule. The apparent advantageous for obtaining a truly ordered multilayer film.4d–f degree of ordering within these films can be increased by Thus, the LB film forming properties of soluble amphiphilic annealing for a short time at a temperature at which the Pcs 9, 10 and 11 were studied. material is mesogenic (Fig. 3, Table 4).7 However, these sol- Table 3 summarises the important Langmuir isotherm vent cast films are of non-uniform thickness. A number of parameters of area per molecule extrapolated to a surface recent studies have indicated that spin coating is a useful pressure of 0 mN m-1 (A0), the area per molecule at a surface technique for the preparation of films of uniform thickness pressure of 30 mN m-1 (A30) and the collapse pressure (pc) derived from soluble Pcs.5 These films proved to be amorphous for the monolayer.For each Pc these figures are consistent or microcrystalline in structure. with the formation of a stable molecular monolayer at the Spin-coated films of Pcs 9–11 on hydrophobic substrates do air–water interface in which the Pc molecules are oriented not show any evidence of long-range order by glancing angle approximately perpendicular to the water surface.For Pc 10, XRD and the films appear non-birefringent by polarising assuming that both hydrophilic tetra(ethyleneoxy) chains are optical microscopy.Annealing the films for a short period of immersed in the water, the eVective area per molecule would time at a temperature at which the Pc is liquid crystalline be determined by the four hydrophobic hexadecyl chains. This value can be estimated as 155 A° 2 from the intercolumnar Table 4 Glancing angle XRD data for solvent cast and spin coated distance (35.5 A° ) and the cofacial intermolecular distance films of Pcs 9–11 after annealment in their mesophase (4.5 A° ) of the hexagonal mesophase of symmetrical Pc 2 (Table 2).Similarly for Pc 11, assuming that all three tetra- Film Lamellar Orders of Intensitya (ethyleneoxy) chains are immersed in the water, the eVective Pc fabrication d-spacing/A° diVraction (arbitrary units) 9 cast 29.5 2 838 Table 3 The monolayer (Langmuir isotherm) properties of the 9 spin coated 30.2 2 120b amphiphilic Pcs 9–11 at the air-water interface. The estimated values 10 cast 49.7 4 458 for the molecular area (Aest) are derived from the appropriate XRD 10 spin coated 48.6 3 85b data (see text). 11 cast 51.3 5 813c 11 spin coated 50.0 5 155b,c Pc A0/A° 2 A30/A° 2 Aest/A°2 pc/mN m-1 aIntensity of the first order diVraction peak.bThe spin coated films are significantly thinner than the solvent cast films, which may 9 154 140 155 43 10 143 122 155 49 account for the lower intensity of the diVraction peaks from these film. cSecond order diVraction peak is more intense by ~20%. 11 99 85 93 53 J.Mater. Chem., 1998, 8(11), 2371–2378 2377M. Hanack, Struc. Bonding, 1991, 74, 41; (d) C. Van Nostrum and R. J. M. Nolte, Chem. Commum., 1996, 2385. 2 S. Dogo, J. P. Germain, C. Maleysson and A. Pauly, Thin Solid Films, 1992, 219, 244. 3 N. Minami. K. Sasaki and K. Tsuda, J. Appl. Phys., 1983, 54, 6764. 4 (a) R. H. Tredgold, Order in Thin Organic Films, Cambridge University Press, Cambridge, 1994; (b) A.Ulman, Introduction to Ultrathin Organic Films, Academic Press, San Diego, 1991; (c) S. Baker, M. C. Petty, G. G. Roberts, M. V. Twigg, Thin Solid Films, 1983, 99, 53; (d) M. J. Cook, M. F. Daniel, K. J. Harrison, N. B. McKeown and A. J. Thompson, J. Chem. Soc., Chem. Commun., 1987, 1148; (e) J. D. Shutt, D. A. Batzel, R. V. Sudiwala, S. E. Rickert and M.E. Kenney, Langmuir, 1988, 4, 1240; ( f ) N. B. McKeown, M. J. Cook, A. J. Thomson, K. Fig. 3 Glancing angle X-ray diVractograms from the solvent cast films J. Harrison, M. F. Daniel, R. M. Richardson and S. J. Roser, Thin of Pcs (a) 9, (b) 10 and (c) 11 after heating at a temperature at which Solid Films, 1988, 159, 469; (g) P. A. Albouy, J. Phys. Chem., the Pc displays a columnar mesophase. 1994, 98, 8543; (h)M.Burghard,M. Schmelzer, S. Roth, P. Haisch and M. Hanack, Langmuir, 1994, 10, 4265. 5 S. M. Critchley, M. R. Willis, M. J. Cook, J. McMurdo and Y. Maruyama, J. Mater. Chem., 1992, 2, 157; S. M. Critchley, results in the formation of highly ordered films which possess M. R. Willis, Y. Maruyama, S. Bandow, M. J. Cook and both the lamellar structure of the solvent cast films (Table 4) J.McMurdo, Mol. Cryst. Liq. Cryst., 1993, 230, 287; M. J. Cook, and the uniform thickness of the unannealed spin-coated films. J. Mater. Chem., 1996, 6, 677. As such, these films are reminiscent of LB multilayers but are 6 (a) J. Simon and C. Piechocki, J. Am. Chem. Soc., 1982, 104, 5245; much easier to fabricate. There is reasonable agreement (b) M.J. Cook, M. F. Daniel, K. J. Harrison, N. B. McKeown and A. J. Thompson, J. Chem. Soc., Chem. Commun., 1987, 1086; between the lamellar spacings in the annealed films, solid and (c) K. Ohta, L. Jacquemin, C. Sirlin, L. Bosio and J. Simon, New lower temperature mesophases for Pcs 9–11 (Table 2 and 4). J. Chem., 1988, 12, 751; (d) J. F. Van der Pol, E. Neeleman, Clearly, the attainment of high lamellar order during J.W. Zwikker, R. J. M. Nolte, W. Drenth, J. Aerts, R. Visser and annealment is due to the self-ordering within the lower tem- S. J. Picken, Liq.Cryst., 1989, 6, 577; (e) A. N. Cammidge, perature mesophase of the Pc resulting in segregation of the M. J. Cook, K. J. Harrison and N. B. McKeown, J. Chem. Soc., non-polar hexadecyl side-chains from the polar hydroxy ter- Perkin Trans. 1, 1991, 3053; ( f ) N. B. McKeown and J. Painter, J. Mater. Chem., 1994, 4, 209; ( g) G. J. Clarkson, N. B. McKeown minated tetra(ethyleneoxy) side-chains. Similar eVects have and K. E. Treacher, J. Chem. Soc., Perkin Trans. 1, 1995, 1817; been observed in solvent cast films composed of other types (h) G. J. Clarkson, B. M. Hassan, D. R. Maloney and of amphiphilic molecules such as phospholipids.21 UV–VIS N.B. McKeown, Macromolecules, 1996, 29, 1854. spectra of the annealed films derived from Pcs 9–11 show that 7 K. E. Treacher, G. J. Clarkson, Z. Ali-Adib and N. B.McKeown, the major absorption (Q-band) is at 620 nm, shifted by exciton Chem. Commun., 1996, 73. interactions to a lower wavelength compared to the main 8 W.Bras, G. E. Derbyshire, A. J. Ryan, G. R. Mant, P. Manning, R. E. Cameron and W. Mormann, J. Phys., 1993, 3, 447; absorption band of their solution spectra (lmax=704 nm), A. S. Stennett, PhD thesis, University of Manchester (UK), 1998. indicating that the Pc molecules are in a columnar arrangement 9 F. Davies, P. Hodge, C. R. Towns and Z. Ali-Adib, within the solid lamellar structure.7 Macromolecules, 1991, 24, 5695. 10 D. D. Perrin and W. L. F. Armarego, Purification of Laboratory Chemicals, 3rd edn., Pergammon, Oxford, 1988. Conclusions 11 N. Jayasuriya, S. Bosak and S. L. Regen, J. Am. Chem. Soc., 1990, 112, 5844. The combination of spin-coating technology with meso- 12 W. O. Siegl, J. Heterocycl. Chem., 1981, 18, 1613; A. W. Snow and morphic ordering can produce highly ordered and uniform N.L. Jarvis, J. Am. Chem. Soc., 1984, 106, 4706; M. D. Pace, films of non-uniformly substituted Pcs 9–11. The antipathy W. R. Barger and A. W. Snow, Langmuir, 1989, 5, 973; of two types of side-chains which have diVerent polarity S. M. Marcuccio, P. I. Svirskaya, S. Greenberg, A. B. P. Lever induces lamellar ordering both within the columnar liquid and K.B. Tomer, Can. J. Chem., 1985, 63, 3057; C. C. LeznoV, crystal and the solid phase of these derivatives. This phenom- S. Greenberg, S. M. Marcuccio, P. C. Minor, P. Seymour and A. B. P. Lever, Inorg. Chim. Acta, 1984, 89, L35. enon can be used to form self-ordering spin-coated films which 13 The symbol Q has recently become the accepted abbreviated display the structure and uniformity of idealised LB films.notation for a columnar mesophase and has replaced the pre- Despite the structural control oVered by the LB technique and viously used D (discotic) nomenclature proposed in ref. 14. the intense research activity related to the possible applications 14 C. Destrade, P. Foucher, H. Gasparoux, N. H. Tinh A. M. Levelut of LB films over the past 15 years, the commercial exploitation and J. Malthete, Mol. Cryst. Liq. Cryst., 1984, 106, 121. of functional LB films composed of Pcs is unlikely. This is 15 A. S. Cherodian, A. N. Davies, R. M. Richardson, M. J. Cook, N. B. McKeown, A. J. Thomson, J. Feinjoo, G. Ungar and due to the prohibitively slow speed of deposition and the small K. J. Harrison, Mol. Cryst. Liq. Cryst., 1991, 196, 103. area of substrate that can be covered. Self-ordering spin- 16 P. Weber, D. Guillon and A. Skoulios, Liq. Cryst., 1991, 9, 369; coated films, such as described above, oVer a rapidly fabricated A. N. Cammidge, M. J. Cook, S. D. Haslam, R. M. Richardson alternative. and K. J. Harrison, Liq. Cryst., 1993, 14, 1847; N. Spielberg, M. Sarkar, Z. Lutz, R. Poupko, J. Billard and H. Zimmerson, Liq. We thank the EPSRC for financial support (G.J.C.), provision Cryst., 1993, 15, 311. 17 T. Komatsu, K. Ohta, T.Watanabe, H. Ikemoto, T. Fujimoto and of studentships (K.E.T., A.S.S.T.) and for allocation of beam I. Yamamoto, J. Mater. Chem., 1994, 4, 537. time at Daresbury (S.R.S.). 18 K. E. Treacher, G. J. Clarkson and N. B. McKeown, Liq. Cryst., 1995, 19, 887. 19 M. Brewis, G. J. Clarkson, A. M. Holder and N. B. McKeown, References Chem. Commun, 1998, 969. 1 (a) N. B. McKeown, Phthalocyanine Materials: Synthesis, 20 M. J. Schtick, Nonionic Surfactants: Physical Chemistry, Marcel Structure and Function, Cambridge University Press, Cambridge, Dekker, New York, 1987. 1998; (b) C. C. LeznoV and A. B. P. Lever, Phthalocyanines: 21 T. Kunitake, Angew. Chem., Int. Ed. Engl., 1992, 31, 709. Properties and Applications, vols. 1–4, VCH, New York, 1989, 1993, 1993, 1997; (c) H. Schultz, H. Lehmann, M. Rein and Paper 8/05557B 2378 J. Mater. Chem., 1998, 8(11), 2371–2378

ISSN:0959-9428    

DOI:10.1039/a805557b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Formation of columnar arrangements in copper(II ) complexes of 2-phenylazomethinopyridine derivatives Chung K. Lai,* Kuo-Wen Wang and Raymond Lin Department of Chemistry, National Central University, Chung-Li, Taiwan, ROC Received 7th August 1998, Accepted 20th August 1998 The synthesis and mesomorphic properties of a homologous series of 2-(3¾,4¾,5¾-trialkoxyphenyl )- azomethinopyridines and their copper(II) complexes are reported.Liquid crystalline properties of the copper(II) complexes were studied by DSC analysis and polarized optical microscopy. The results indicated that copper complexes with six sidechains (3) exhibited columnar phases, whereas copper(II ) complexes with two or four sidechains (1 and 2) formed only crystalline phases.The structures of the mesophases for copper(II ) complexes 3 were characterized and confirmed as disordered hexagonal columnar phases (Colhd) by powder X-ray diVraction. Relatively high clearing points and the short range of mesophase temperature for the copper complexes were attributed to a relatively strong interaction of pyridyl core–core groups within the columns. The EPR spectra measured at various temperatures were also examined.prepared 3,4,5-trialkoxybenzoic acid chlorides in dried pyri- Introduction dine. These pyridine-based ligands obtained were white and Generation of various geometries and molecular shapes by obtained in a yield of 86–90%, and are highly soluble in incorporation of metal centers into organic moieties has been organic solvents. The ligands were characterized by 1H and widely applied to produce metallomesogenic structures.1,2 13C NMR spectroscopy.Three characteristic peaks at d 5.64, Transition metal coordination compounds are the largest 6.75 and 10.19 were assigned to olefinic methine-H (–CHLC–), category among this type of metallomesogenic materials owing aldehyde-H (–CHLN–) and imine-H (–CLN–H), and correct to their well known chemistry and rich structural diversity.structures were also supported by characteristic 13C NMR Columnar arrangements3–5 can be generated by use of comp- peaks at ca. 189.63 and 153.73 assigned to keto C–O and C–N lementary shapes of various molecules; disc-like,3,4 half disc- groups. Copper(II) complexes were obtained by the reaction like5 or tapered molecules, and of those, disc-like molecular of 2-phenylazomethinopyridines with copper(II) perchlorate structures are often formed by symmetric bonds with coordi- hexahydrate in refluxing THF–methanol.Reactions with copnation metal centers. Ligands used in this group were mostly per(II) acetate or copper(II) chloride with or without a base of various derivatives;1a such as b-diketones, salicylaldehydes, (for example KOH) resulted in recovery of intact ligands.salicylaldimines, enaminoketones, aroylhydrazine and pyr- Recrystallization twice from THF–methanol gave pure yellow– roles. Metal complexes thus prepared often produced disc-like greenish solids. Copper (d9) compounds which are paramagshaped molecules, and usually exhibited hexagonal or/and netic display only broad alkoxy signals in 1H and 13C NMR rectangular columnar phases.These so-called metal-containing spectra. Elemental analysis data in Table 1 also confirmed the liquid crystals are highly promising potential candidates in purity and identity of the complexes. electro-magnetic applications. In addition, the metal centers incorporated are also found to play an important role in the Mesomorphic properties resulting mesomorphic properties and physical properties.Liquid crystalline behavior for these copper(II ) complexes was Selective incorporation of diVerent metal centers with a specific studied and characterized by DSC analysis and polarized ligand often results in completely opposite mesomorphic optical microscopy.The formation of mesophases was found properties. While a detailed explanation based on the structural to be sensitive to the numbers of sidechains and the carbon and electronic configuration of metal centers on the mesolength of the sidechains, as often observed in columnar phases. morphic properties has been extensively discussed, a precise Copper complexes with six sidechains (3) exhibited columnar prediction of phase behavior has not yet been feasible.Here, phases, whereas copper(II) complexes with two (1) or four we report the preparation, characterization and mesomorphic sidechains (2) formed only crystalline phases. The phase- properties of a new series of copper complexes derived transition temperatures and enthalpies of all copper complexes from 2-(3,4,5-trialkoxyphenyl )azomethinopyridine structures, 1–3 are given in Table 2.For complexes 3, only when the which exhibit disordered hexagonal columnar phases. carbon chain lengths (n) were 16, (i.e. n=16 and n=18) was liquid crystallinity observed. The DSC analysis of copper Results and discussion complexes 3 showed typical columnar phase transitions of crystal-to-columnar-to-isotropic (K�Col�I ).Additional Synthesis crystal-to-crystal (K1�K2) transitions were also observed for complexes with lower carbon chain lengths (i.e. n=10, 12, 14). The synthetic route used to prepare substituted 2-phenylazomethinopyridine derivatives and their copper(II ) complexes is Upon heating, copper complexes melt into liquid crystalline phases with an optical texture of columnar superstructures as shown in Scheme 1.Methyl 3,4,5-trialkoxybenzoates and 3,4,5- trialkoxybenzoic acids were synthesized by literature pro- is often observed for disc-shaped molecules, and the textures observed showed highly characteristic birefrigence.4 A typical cedures,4 and 3,4,5-trialkoxybenzoic acid chlorides were obtained from the reaction of 3,4,5-trialkoxybenzoic acids and larger enthalpy (10.6–20.7 kJ mol-1) for the crystal-to-liquid crystal transition at lower temperatures (161–177 °C) and thionyl chloride in dried tetrahydrofuran. The 2-(3,4,5-trialkoxyphenyl )azomethinopyridine derivatives were synthesized a relatively lower enthalpy (0.84–1.60 kJ mol-1) for the liquid crystal-to-isotropic transition at higher temperatures by a condensation reaction of 2-aminopyridine with freshly J.Mater. Chem., 1998, 8(11), 2379–2383 2379Scheme 1Reagents and conditions: i, KOH (2.0 equiv.), refluxing in THF–H2O (1051), 12–24 h, 92–96%; ii, SOCl2 (2.0 equiv.), refluxing in dried THF, 4 h; iii, 1-aminopyridine (1.0 equiv.), refluxing in dried pyridine at 0 °C, then warming up and stirring at room temp., 16 h, 86–90%; iv, Cu(ClO4)2·H2O, refluxing in THF–EtOH, 2 h, 76–82%.Table 1 Elemental analysis data (%) of copper(II) complexes 1–3a liquid-like correlations between the rigid cores occurred at wider angle regions of 5.21 A° . Two other weaker characteristic Compound C H N diVractions4 corresponding to Miller indices (110) and (200), respectively, with a d-spacing ratio of (1/3)1/2 and (1/4)1/2 3 n=12 74.01 (73.73) 10.53 (10.44) 3.54 (3.58) were however not observed.The absence of distinct peaks at 14 75.02 (74.89) 10.93 (10.82) 3.24 (3.23) 16 75.99 (75.84) 11.36 (11.14) 3.02 (2.95) higher angle was consistent with DSC analysis of a relatively 18 76.71 (76.63) 11.45 (11.40) 2.75 (2.71) lower enthalpy for the columnar-to-isotropic transition, indica- 2 18 75.55 (75.27) 10.68 (10.66) 3.72 (3.66) tive of a highly disordered mesophase; i.e.there is no long- 1 18 72.64 (72.43) 9.22 (9.12) 5.67 (5.63) range order along the columns. aRequired values in parentheses. In most metallomesogens reported, the formation of liquid crystals is found to be controlled or determined by the magnitude of the intermolecular interaction forces1a which (179–180 °C) were observed.This relatively low value of the hold the metallomesogenic structures together. When they are transition enthalpy indicated that the mesophases were highly either too weak or too strong, a liquid crystalline phase is not disordered. The temperature range of columnar mesophases observed. Compared with other similar cII ) complexes for the copper complexes is slightly sensitive to the carbon with six sidechains, one feature noted for copper complexes 3 number of sidechains.At the crystal-to-columnar transition is that only derivatives with longer chains (n=16 and 18) the flexible side chains undergo disordering but the central exhibited columnar phases and derivatives with shorter chains core remains stacked in columns, however, the core unstacked (n=10, 12, 14) formed crystalline phases.Meanwhile they at the columnar-to-isotropic transition. have a relatively short range (4.0–18 °C) of mesophase tem- When cooled from their isotropic phases, the liquid crystal- peratures. An increased electron density due to the presence line complexes displayed optical textures, shown in Fig. 1, of lone pair electrons on the nitrogen atoms appears to increase which were a mixture of pseudo focal-conics and mosaic the intermolecular interaction between the stacking molecules, regions with linear birefrigent defects, suggesting hexagonal and this increasing force causes an increase in molecular columnar structures.The possibility of rectangular phases was packing or regularity within the columns. Therefore, longer also easily excluded owing to the absence of mosaic textures chains or/and more chains were critically needed to induce the with prominent wedge-shaped defect patterns.To further mesophase, and only a short temperature range of the confirm the structure of the mesophases, we performed a mesophase was observed. powder XRD diVraction experiment. The copper complex 3 (n=18) displayed a diVraction pattern of a two-dimensional EPR studies hexagonal lattice with an intense peak at 2h=43.61° at 175 °C.This diVraction corresponded to an intercolumnar distance (a X-Band EPR spectra of the copper complex 3 (n=16) measured at diVerent temperatures are shown in Fig. 2. The parameter of the hexagonal lattice) of 50.34 A° . However, 2380 J. Mater. Chem., 1998, 8(11), 2379–2383Table 2 Phase behaviora of copper(II) complexes 1–3 78.7 (17.4) 196.7 (19.4) 3 n=12 K1 K2 I ,bbb) ,bbb) 71.5 (16.5) 176.2 (15.8) 88.3 (25.8) 185.0 (22.3) 14 K1 K2 I ,bbb) ,bbb) 82.4 (30.1) 172.7 (19.4) 87.7 (29.1) 176.8 (19.4) 179.1 (1.22) 16 K1 K2 Colhd I ,bbb) ,bbb) ,bbb) 83.3 (26.8) 159.8 (20.7) 173.4 (1.60) 94.3 (21.6) 161.2 (10.6) 179.6 (0.90) 18 K1 K2 Colhd I ,bbb) ,bbb) ,bbb) 88.3 (27.2) 137.9 (12.0) 172.4 (0.84) 84.3 (30.8) 240.2 2 18 K1 K2 Id ,bbb) ,bbb) 77.7 (33.0) 216.2 94.3 (21.6) 294.5 1 18 K1 K2 Id ,bbb) ,bbb) 88.3 (27.2) 269.2 an is the number of carbons in the alkoxy chain.K1,K2=crystal phases; Colhd=columnar hexagonal disordered phase; I=isotropic; Id= isotropic with decomposition. The transition temperatures (°C) and enthalpies (in parentheses, kJ mol) were determined by DSC at a scan rate of 5.0 °Cmin-1.Fig. 2 EPR spectra of copper complex 3 (n=16) measured at: (a) room temperature of as-prepared sample, (b) 459 K; isotropic phase, (c) 438 K; columnar phase, (d) 370 K; crystalline phase, (e) cooling back to room temperature. Fig. 1 Optica l textures (100×) exhibited by complex 3 (n=16).Colhd cooling to 165 °C [Fig. 2(c)] corresponding to the mesophase, phase at 170 °C (top: thick sample) and at 165 °C (bottom: showed signals with clear hyperfine lines in the low-field region, thin sample). with three signals being observable and resolved. As the temperature was further reduced to 97 °C [Fig. 2(d)] and 25 °C [Fig. 2(e)], similar signals were observed. The slight change of top spectrum in Fig. 2(a) was for the as-prepared sample measured at room temperature, and consisted of two features, these signals with temperature was probably due to a preferred molecular orientation or arrangement at diVerent tempera- one barely observable shoulder at low field and a high-field signal. When the sample was heated to the clearing point at tures. Mesogenic copper complexes of bidentate SchiV bases have been extensively6 studied by EPR spectroscopy.In most 186 °C the signal width [Fig. 2(b)] became broader and unsymmetric with increased intensity. However, the spectrum on derivatives broad and unsymmetric signals at diVerent tem- J. Mater. Chem., 1998, 8(11), 2379–2383 2381peratures were observed, and the absence of the hyperfine 31.74, 51.43, 67.95, 113.83(C2,6), 122.16(C1), 131.32(C3,5), 162.77(C4), 166.53(CLO).structures was generally attributed to the strong exchange interaction among the paramagnetic copper centers. 3,4,5-Tridodecyloxybenzoic acid (general procedure for 3,4,5- trialkoxylbenzoic acids) Conclusion A mixture of methyl 3,4,5-tridodecyloxy benzoate (5.0 g, Systematic studies on a homologous series of compounds have 0.07 mol) and KOH (0.56 g, 0.10 mol) was refluxed in 100 ml allowed for a better understanding of the relationship between of THF–H2O (654, v/v) for 24 h and the solution extracted the molecular structures and mesomorphic properties.twice with dichloromethane (100 ml ). The CH2Cl2 layer was Mesomorphic data obtained in this work suggested that the collected and dried over MgSO4.The solution was concenmesophases might be thermodynamically destabilized due to trated to give a white solid, which was recrystallized from the presence of nitrogen electron lone pairs. Strong molecular THF–MeOH or acetone. Yield 92%. 1H NMR (CDCl3): d interactions in the mesophase could be partially overcome 0.86(t, CH3, 9H), 1.14–1.83(m, CH2, 60H), 4.00(t, OCH2, with surrounding by more or/and longer flexible chains. 6H), 7.26(s, C6H2, 2H). 13C NMR (CDCl3): d 14.00, 22.70, 26.22, 29.43, 29.77, 30.04, 31.95, 68.88, 73.36, 107.97, 126.00, 141.96, 152.57, 172.02. Experimental All chemicals were reagent grade from Aldrich and used 3,4-Ditetradecyloxybenzoic acid without further purification. THF was dried over sodium Yield 94%. 1H NMR (CDCl3): d 0.92 (t, CH3, 6H), 1.31(m, benzophenone ketyl, and pyridine was predried over KOH CH2, 44H), 1.83(m, CH2, 2H), 4.07(t, 4H, OCH2, 4H), pellets for prolonged periods and followed by fresh distillation 6.89(d, C6H3, 1H), 7.53(s, C6H3, 1H), 7.58(d, C6H3, 1H).from BaO before use. 1H and 13C NMR spectra were measured 13C NMR (CDCl3): d 13.91, 22.53, 25.90, 25.73, 29.14, 29.21, on a Bruker DRS-200 spectrometer in CDCl3 using TMS as 29.25, 29.41, 29.44, 29.49, 29.52, 29.58, 30.19, 31.77, 31.79, an internal standard.IR spectra were recorded on a Bio-Rad 69.00, 73.35, 116.4, 121.2, 148.0, 152.7, 172.0. FTS-155 instrument using polystyrene as a standard. DSC thermograms were obtained on a Perkin-Elmer DSC-7 instru- 4-Octadecanoxybenzoic acid ment and calibrated with a pure indium sample.All phase behaviors were determined at a scan rate of 10.0 °C min-1 White solid, yield 85%. 1H NMR (CDCl3): d 0.86(t, 3H, unless otherwise noted. Optical polarized microscopy was CH3), 1.23–1.83(m, CH2, 32H), 3.93(t, 2H, OCH2), 6.98(d, carried out on Nikkon MICROPHOT-FXA instrument with 2H, C6H4), 8.02(d, 2H, C6H4). 13C NMR (CDCl3): d 14.03, a Mettler FP90/FP82HT hot stage system.X-Ray powder 22.61, 25.91, 29.04, 29.29, 29.61, 31.85, 68.71, 114.09, 126.03, diVraction (XRD) studies were conducted on an INEL MPD- 129.69, 162.33, 171.82. diVractometer with a 2.0 kW Cu-Ka X-ray source equipped with an INEL CPS-120 position sensitive detector and a 3,4,5-Tridecyloxybenzoic acid chloride (general procedure for variable temperature capillary furnace with an accuracy of the synthesis of 3,4,5-trialkoxybenzoic acid chlorides) ±0.10 °C in the vicinity of the capillary tube (80 mm 3,4,5-Tridecyloxybenzoic acid (5.0 g, 0.0085 mol) dissolved in long×0.01 mm thick from Charles Supper Co).The detector dried THF (100 ml ) was added dropwise to a THF solution was calibrated using mica and silicon standards. EPR measureof fresh SOCl2 (1.24 ml, 0.017 mol ) at ice-bath temperature ments were taken with a EMX Bruker spectrometer in X-band under N2 atmosphere.The mixture was stirred, and gently and powder samples were placed into quartz tubes of 2.0 mm warmed to room temperature. The mixture was allowed to diameter. Methyl 3,4,5-trialkoxybenzoate esters, methyl 4- reflux for 4 h. The solution was concentrated to remove THF alkoxybenzoate esters and ethyl 3,4-dialkoxybenzoate esters and excess SOCl2. The milky paste was redissolved in 100 ml were prepared by literature procedures. of dried THF, and then the solution concentrated.This process was repeated several times to remove any residual SOCl2 Methyl 3,4,5-tridodecyloxybenzoate which would aVect the following reactions.The white solid thus obtained was directly used for the next reaction without White solid, yield 90%. 1H NMR (CDCl3): d 0.86(t, CH3, any further purification or recrystallization. 9H), 1.26–1.84(m, CH2, 60H), 3.88(s, OCH3, 3H), 4.03(t, OCH2, 6H), 7.25(s, C6H2, 2H). 13C NMR (CDCl3): d 14.18, 22.75, 26.14, 29.36, 29.45, 29.62, 29.71, 29.75, 29.39, 30.39, 3,4,5-Trioctadecanoxy-N-pyridin-2-ylbenzamide (general 32.00, 52.13, 69.22, 75.53, 105.02(C2,6), 124.69(C1), procedure for the synthesis of N-pyridin-2-ylbenzamide 142.01(C3,5), 152.83(C4), 166.89(CLO).derivatives) Freshly prepared 3,4,5-trioctadecanoxybenzoic acid chloride Ethyl 3,4-ditetradecyloxybenzoate (5.0 g, 5.29 mmol) was dissolved in dried pyridine (50 ml ) under nitrogen atmosphere, and to this solution 2-aminopyrid- White solid, yield 87%. 1H NMR (CDCl3): d 0.87(t, CH3, ine (0.50 g, 5.29 mmol) in pyridine (20 ml ) was added slowly 6H), 1.24–1.83(m, CH2, 51H), 3.97(t, J=8.19 Hz, OCH2, at room temperature.The mixture was stirred for 8 h, and 4H), 4.28(q, OCH2, 2H), 6.80(d, J=8.44 Hz, C6H3, 1H), then gently refluxed for 3 h. The solution was concentrated to 7.47(s, C6H3, 1H), 7.57(d, J=6.42 Hz, C6H3, 1H). 13C NMR half its volume, and left in a freezer overnight. The resulting (CDCl3): d 13.91, 14.21, 22.51, 25.84, 28.93, 29.21, 31.74, white solid was filtered oV, and recrystallized from THF– 60.48, 68.84, 69.13, 111.7(C6), 114.2(C2), 122.6(C5), methanol. Yield 65%. 1H NMR (CDCl3): d 0.85(t, CH3, 9H), 123.2(C1), 148.3(C4), 152.9(C3), 166.3(CLO). 1.14–1.83(m, CH2, 96H), 4.01(t, OCH2, 6H), 7.06(dd, C5H4N, 1H), 7.12(s, C6H2, 2H), 7.75(dd, C5H4N, 1H), Methyl 4-octadecanoxybenzoate 8.26(d, C5H4N, 1H), 8.38(d, C5H4N, 1H), 8.81(s, NH, 1H). 13C NMR (CDCl3): d 14.10, 22.06, 22.68, 29.36, 29.71, 30.32, White solid, yield 95%. 1H NMR (CDCl3): d 0.82(t, J=6.73 Hz, CH3, 3H), 1.24–1.84 (m, CH2, 32H), 3.82(s, 31.92, 69.35, 73.54, 105.77, 114.13, 119.83, 128.89, 138.53, 141.77, 147.77, 151.65, 153.23, 165.48. IR (thin film): 3488, OCH3, 3H), 3.93(t, J=7.31 Hz, OCH2, 2H), 6.84(d, J= 8.82 Hz, C6H4, 2H), 7.97(d, J=8.82 Hz, C6H4, 2H). 3413, 2929, 2842, 1655, 1636, 1619, 1578, 1566, 1538, 1504, 1470, 1431, 1383, 1343, 1309, 1219, 1125, 987, 776 cm-1. 13C NMR(CDCl3): d 14.04, 22.57, 25.93, 29.00, 29.14, 2382 J. Mater. Chem., 1998, 8(11), 2379–23833,4-Dioctadecanoxy-N-pyridin-2-yl-benzamide Anal.Calc. for C60H90N4O4Cu: C, 72.43; H, 9.12; N, 5.63. Found: C, 72.64; H, 9.22; N, 5.67%. White solid, yield 65.5%. 1H NMR (CDCl3): d 0.85(t, CH3, 6H), 1.23–1.81(m, CH2, 64H), 4.01(t, OCH2, 4H), 6.87(d, C6H3, 1H), 7.08(dd, C5H4N, 1H), 7.43(s, C6H3, 1H), 7.47(d, Acknowledgments C6H3, 1H), 7.74(dd, C5H4N, 1H), 8.27(d, C5H4N, 1H), We thank the National Science Council of Taiwan, ROC for 8.39(d, C5H4N, 1H), 8.81 (s, NH, 1H). 13C NMR (CDCl3): funding (NSC-88-2113-M-008-009) in generous support of d 13.93, 22.52, 25.84, 29.03, 29.23, 29.55, 31.76, 69.14, 102.02, this work. 112.54, 114.09, 119.04, 120.15, 126.25, 138.30, 147.43, 148.91, 151.75, 152.47, 165.28. References 4-Octadecanoxy-N-pyridin-2-ylbenzamide 1 (a) J.L. Serrano, in Metallomesogens; Synthesis, Properties, and White solid, yield 62%. 1H NMR (CDCl3): d 0.80(t, CH3, Applications, VCH, New York, 1996; (b) D. W. Bruce and 3H), 0.94–1.79(m, CH2, 32H), 3.91(t, OCH2, 2H), 6.91(d, D. O’Hare, Inorganic Materials, John Wiley & Sons, 1992, C6H4, 2H), 7.07(dd, C5H4N, 1H), 7.75(dd, C5H4N, 1H), pp. 407–490. 7.74(d, C6H4, 2H), 8.28(d, C5H4N, 1H), 8.39(d, C5H4N, 1H), 2 S.A. Hudson and P. M. Maitlis, Chem. Rev., 1993, 93, 861; 8.81(s, NH, 1H). 13C NMR (CDCl3): d 14.03, 22.61, 25.91, P. Espinet, M. A. Esteruelas, L. A. Oro, J. L. Serrano and E. Sola, Coord. Chem. Rev., 1992, 117, 215; P. Maitlis and A. M. Giroud- 29.04, 29.29, 29.61, 31.85, 68.17, 114.32, 112.08, 119.44, 126.03, Godquin, Angew. Chem., Int. Ed.Engl., 1991, 30, 375. 129.21, 138.44, 147.36, 151.87, 162.34, 165.35. 3 (a) C. Destrade, P. Foucher, H. Gasparoux, H. T. Nguyen, A. M. Levelut and J. Malthete, Mol. Cryst. Liq. Cryst., 1984, 106, Bis[3,4,5-trioctadecanoxy-N-pyridin-2-ylbenzamide]copper(II ) 121; (b) S. Chandrasekhar and G. S. Ranganath, Rep. Prog. Phys., (general procedure for the synthesis of copper complexes of N- 1990, 53, 57.pyridin-2-ylbenzamide derivatives) 4 (a) C. K. Lai, C. H. Tsai and Y. S. Pang, J. Mater. Chem., 1998, 8, 1355; (b) C. K. Lai, C. H. Chang and C. H. Tsai, J. Mater. Chem., 3,4,5-Trioctadecanoxy-N-pyridin-2-ylbenzamide (0.20 g, 1998, 8, 599; (c) C. K. Lai, F. G. Chen, Y. J. Ku, C. H. Tsai and 0.023 mmol) dissolved in THF (5.0 ml ) was added to a R. Lin, J. Chem.Soc., Dalton Trans., 1997, 4683; (d) C. K. Lai and solution of copper(II) perchlorate hexahydrate (0.042 g, F. J. Lin, J. Chem. Soc., Dalton Trans., 1997, 17; (e) C. K. Lai, M. Y. Lu and F. J. Lin, Liq. Cryst., 1997, 23, 313; ( f ) H. Zheng, 0.0115 mmol) in methanol (10 ml ). Upon addition a light C. K. Lai and T. M. Swager, Chem. Mater., 1995, 7, 2067; green solid started to suspend in solution, and the solution (g) C.K. Lai, A. G. Serrete and T. M. Swager, J. Am. Chem. Soc., was gently refluxed for 2 h. The green solid was filtered oV, 1992, 114, 7948. collected and recrystallized from CH2Cl2–MeOH. Yield 82%. 5 (a) S. T. Trzaska and T. M. Swager, Chem. Mater., 1998, 10, 438; IR (thin film): 2929, 2848, 1624, 1577, 1529, 1503, 1469, 1429, (b) H. Zheng, C.K. Lai and T. M. Swager, Chem. Mater., 1994, 6, 1341, 1240, 1119, 1051, 783, 729, 628 cm-1. Anal. Calc. for 101; (c) J. Barbera�, C. Cativiela, J. L. Serrano and M. M. Zurbano, C132H234N4O8Cu: C, 76.63; H, 11.40; N, 2.71. Found: C, Adv. Mater., 1991, 3, 602; (d) H. Zheng, C. K. Lai and T. M. Swager, Chem. Mater., 1994, 6, 101; (e) A. G. Serrette, C. K. Lai 76.71; H, 11.45; N, 2.75%. and T. M. Swager, Chem.Mater., 1994, 6, 2252. 6 (a) P. J. Alonso, M. Marcos, J. I. Martý�nez, V. M. Orera, Bis[3,4-dioctadecanoxy-N-pyridin-2-ylbenzamide]copper(II ) M. L. Sanjua�n and J. L. Serrano, Liq. Cryst., 1993, 13, 585; (b) M. P. Eastman, M. Horng, B. Freiha and K. W. Shew, Liq. Green solid, yield 87%. IR (thin film): 2929, 2862, 1664, 1637, Cryst., 1987, 2, 223; (c) M. Ghedini, S. Morrone, D. Gatteschi and 1570, 1516, 1483, 1119, 1055, 781, 728, 631 cm-1. Anal. Calc. C. Zanchini, Chem. Mater., 1991, 3, 752; (d) N. Hoshino, for C96H162N4O6Cu: C, 75.27; H, 10.66; N, 3.66. Found: C, A. Kodama, T. Shibuya, Y. Matsunaga and S. Miyajima, Inorg. 75.55; H, 10.68; N, 3.72%. Chem., 1991, 30, 3091; (e) E. Campillos, M. Marcos, J. L. Serrano, J. Barbera�, P. L. Alonso and J. I. Martý�nez, Chem. Mater., 1993, Bis[4-octadecanoxy-N-pyridin-2-ylbenzamide]copper(II ) 5, 1518. Green solid, yield 78%. IR (thin film): 2922, 2862, 1617, 1604, 1516, 1475, 1355, 1268, 1240, 1180, 1093, 1066, 783, 622 cm-1. Paper 8/06268D J. Mater. Chem., 1998, 8(11), 2379&ndash

ISSN:0959-9428    

DOI:10.1039/a806268d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials X-ray and optical studies of the tilted phases of materials exhibiting antiferroelectric, ferrielectric and ferroelectric mesophases Joanne T. Mills,a Helen F. Gleeson,*a John W. Goodby,b Michael Hird,b Alexander Seedb and Peter Styringb aThe Department of Physics and Astronomy, The University of Manchester, Manchester, UK M13 9PL bThe School of Chemistry, The University of Hull, Hull, UK HU6 7RJ Received 20th July 1998, Accepted 2nd September 1998 X-Ray and optical techniques have been employed to probe the physical properties of six materials that exhibit various frustrated chiral smectic phases.The temperature dependent evolution of the layer spacing, measured by small angle X-ray diVraction, is discussed with respect to the molecular structures of the materials.The layer spacings are used to deduce the steric tilt angle of the systems across the ferro-, ferri- and antiferro-electric phase ranges. Measurements of the steric and saturated optical tilt of the phases are compared. In general, for most materials and at most temperatures, the steric tilt is lower than the X-ray tilt as would be expected.However, in three of the materials the X-ray tilt is higher than the optical tilt over part of the high temperature tilted phase regime, providing evidence of conformation driven inversion phenomena. Further, the ratio of the steric to optical tilt angle is strongly temperature dependent in all but two of the materials. Introduction The occurrence of antiferroelectric and ferrielectric phases in liquid crystals is well documented,1 though details of the structures of these phases are still the subject of some debate.The currently accepted structures of the ferroelectric, ferrielectric and antiferroelectric phases have been described in detail elsewhere.1 Briefly, all the phases include layers in which the director is tilted with respect to the layer normal at a temperature dependent angle.In the ferroelectric phase, all the layers tilt in the same direction, the antiferroelectric structure has alternating layers tilted in opposite directions, while the ferrielectric phases exhibit some proportion of layers tilted in either direction. The existence of antiferroelectricty and ferrielectricity in liquid crystals provides a challenge to both experimentalists and theoreticians who continue to carry out elegant work both deducing the structures and providing theories for their stabilisation.Many of the studies of antiferroand ferri-electric systems are on the well known material MHPOBC2 and a variety of experimental techniques have Fig. 1 The structures of the materials studied. been employed in the task of deducing the structures of the phases exhibited.It is clear that the most useful information is provided when several complementary techniques are used AS661, AS656, AS620 and AS657 all have the same high to probe the physical properties of the complex phases and temperature phase sequence with the SmC* phase occurring subphases that can occur in antiferroelectric liquid crystals.directly below the SmA phase. In AS618 there is a SmC*a This paper reports the phase behaviour of six new antiferroelec- phase intervening between the SmA phase and the SmC* tric materials and describes the behaviour of their tilt as a phase. AS666 lacks a SmC* phase exhibiting a direct phase function of temperature. Two diVerent techniques are transition from the SmA to a SmC*c phase.AS620 also employed to deduce the tilt of the systems. Both the optical exhibits a monotropic phase transition to a SmI*A phase at tilt and the tilt deduced from X-ray layer spacings are reported 42 °C which is not shown in the Table as it is well below the and compared. The results are interpreted in terms of the temperature range of the measurements reported. conformational structures of the molecules.The phase behaviour of materials that exhibit ferro-, ferriand antiferro-electricity is complex and there is still much debate about the subphases that appear in them. The diYculty Materials of identifying various of the mesophases that occur is reviewed by Itoh et al.4 who describe how misidentification occurs as a The molecular structures and phase transitions of the materials studied are presented in Fig. 1 and Table 1, respectively.The result of supercooling, phase sequences and surface interactions. For example, the phase sequences reported for AS573 materials were synthesised at Hull University and their synthesis is reported elsewhere.3 Fig. 1 shows that the materials (the opposite enantiomer of AS661)5–7 are reported to be diVerent according to the techniques employed to study the studied are structurally similar, including identical terminal chains and chiral centres.The diVerences between the materials temperature dependent material properties, though it seems likely that at least two ferrielectric phases and possibly two involve substitution on the ring systems. Table 1 shows that J.Mater. Chem., 1998, 8(11), 2385–2390 2385Table 1 Phase transition temperaturesa Transition temperature/ °C Material K-SmC*A SmC*A–SmC*c SmC*c–SmC* SmC*–SmC*a SmC*a–SmA SmC*–SmA SmA–I AS618 72.9 99.9 103.5 117.0 122.2 129.3 AS661 53.3 78.3 82.0 — — 90.7 105.7 AS666 39.6 108.4 — — — 118.6 126.7 (c–A) AS656 52.8 94.0 95.2 – – 99.5 110.8 AS620b 67.7 97.8 99.0 — — 109.4 116.6 AS657 46.3 79.7 83.3 — — 84.3 93.7 aNo distinction is made between the SmC*b and SmC* phases.The SmC*c phase encompasses possible subdivisions into other ferrielectric phases. bAS620 also exhibits SmI*A and SmI* phase transitions at 42.2 and 33.3 °C (not shown). antiferroelectric phases exist in the system. The complex phase thin Mylar windows to allow the passage of incident and scattered X-rays with minimal attenuation.The thickness of behaviour of AS661 and AS573 is the subject of a further publication.8 In this paper, no distinction is made between the the liquid crystal sample was approximately 1 mm. The layer spacing in the smectic mesophases was deduced from the SmC* phase and the SmC*b phase, nor is any subdivision made of the SmC*c phase into other ferrielectric subphases position of the first order Bragg scattering peak with an accuracy of 0.5%, which for a layer spacing of 35 A° equates since the techniques employed for the work reported here do not allow these subphases to be distinguished.to an uncertainty of ±0.2 A° . The steric tilt angle d was deduced from the layer spacing measurements using the equation cos d=d/l where d is the smectic layer spacing and l is Experimental the molecular length.The way in which the molecular length was determined is discussed later. The transition temperatures of the materials were determined by optical microscopy and diVerential scanning calorimetry to within ±0.2 °C. In the optical experiments the sample was Results and discussion held on a Linkam THMS 600 hot stage and the temperature was maintained with a relative accuracy of ±0.1 °C using a Layer spacing measurements Linkam TMS 91 control unit.In the X-ray measurements a The layer spacings of the materials are shown across their specially modified Linkam hot stage DSC system was used to mesophase ranges as a function of reduced temperature in control the sample temperature9 again with a relative accuracy Fig. 2. The phase transition from the orthogonal to tilted of ±0.1 °C. smectic phases is clear on the figures, occurring at the point The liquid crystal samples were held in commercially produced10 devices of nominal thickness 5 mm for the optical tilt angle measurements. The inner surfaces of the devices had been treated with rubbed polyimide to promote antiparallel alignment and the devices included transparent indium tin oxide electrodes to allow the application of electric fields.Alternating fields of up to 40 V mm-1 were produced across the device from a signal generator connected to a wide band amplifier constructed in-house. The optical tilt angles of the materials were determined with an accuracy of ±0.5° across the mesophase range by observation of the extinction angles of the samples when viewed between crossed polarisers.These experiments were performed using white light on an Olympus polarising microscope. The optical tilt angle of the materials are field dependent due to both the chiral and antiferro- or ferri-electric nature of the materials. Thus, suYciently large fields (±10 V mm-1) were applied during the measurements to the samples to ensure that the tilt angle value was saturated.Observation of the samples via polarising microscopy during the optical tilt angle measurements ensured that the high fields necessary to ensure saturation did not have the adverse eVect of distorting the alignment of the sample, a well known phenomenon that would result in erroneous tilt angle measurements.X-Ray diVraction was employed to probe the temperature dependent layer spacing of the materials. The small angle Xray scattering (SAXS) experiments were carried out on station 8.2 of the Synchrotron Radiation Source (SRS), Daresbury, UK. The apparatus has been described in detail elsewhere11 and includes facilities to perform concurrent DSC and SAXS, allowing the smectic to isotropic phase transition temperatures of the materials to be determined in situ with an accuracy of ±0.5 °C.The X-ray camera was 1.0 m in length, was equipped with an area detector and X-rays of wavelength of 1.54 A° Fig. 2 The layer spacings of the six materials studied as a function of were incident on the sample. The measurements were made reduced temperature (the temperature below the tilted to orthogonal SmA phase transition).on unaligned samples which were held in DSC pans fitted with 2386 J. Mater. Chem., 1998, 8(11), 2385–2390Table 2 The molecular lengths of the six materials studied, deduced where the layer spacing reduces dramatically. The temperatures from the layer spacing in the SmA phase at which this marked change in layer spacing occurs is consistent with the SmA to SmC* (or SmC*a) phase transition Material Molecular length/A° temperatures given in Table 1.In all six of the materials studied, the layer spacing in the AS 618 38.6±0.1 AS661 39.3±0.1 SmA phase increases slightly as the temperature is reduced. AS666 37.4±0.1 This observation implies that contraction of the layers does AS656 38.4±0.1 not occur as the temperature decreases, a phenomenon that is AS620 37.9±0.1 common in other SmA systems.12–14 Several eVects could result AS657 37.5±0.1 in a slightly increasing layer spacing with reducing temperature, including changes in the conformation of the alkyl chain or a changing population of the conformers occurring as function making no assumptions about packing or thermal eVects of temperature, a suggestion that is supported by further within a mesophase, but can give erroneous results as molecuevidence discussed in later sections of this paper.lar conformations other than those that actually occur in the Comparing the temperature range of the SmC*A phase in mesophase may be modelled. Molecular modelling was underthe six materials studied materials to the smectic layer spacings taken using Cerius2 on a silicon graphics workstation for one in the antiferroelectric phase leads to the conclusion that a of the materials reported here, AS661.The modelling yielded wider SmC*A range correlates with a smaller layer spacing. a molecular length of 39.3 A° (measured from tip to tip of the This phenomenon has also been observed by Ikeda et al.15 molecule). This value is only 0.1 A° diVerent from that deterand supports the theory that the molecular pairing believed to mined from the layer spacing, implying that the layers are well occur between adjacent layers in the SmC*A phase1 plays an defined and that there is little or no interpenetration of layers important role in its stabilisation.A greater degree of pairing in the SmA phase of AS661.Further, it seems that the implies a stronger antiferroelectric attraction between adjacent molecules are in an almost completely extended configuration layers, the stronger attraction resulting in a shorter the layer in the SmA phase. Given the structural similarities of the spacing. Thus a more stable SmC*A phase would be expected materials studied and their molecular lengths (Table 2), it is to have a shorter layer spacing.likely that the remainder of the materials behave in a similar Below the orthogonal to tilted phase transition, the layer manner. spacings initially decrease rapidly, then change little with The molecular lengths given in Table 2 are approximately temperature as the tilt angles saturate.It can also be seen that the same for all of the systems studied. This is not surprising at low temperatures, within the SmC*A phases, the spacings as all the materials have a C12 alkyl chain on one end and a of all the materials increase as the temperature is reduced, an C6 alkyl chain on the other with the same number of atoms eVect that is very marked in AS666. The general trend of layer across the length of the core.The two materials containing Se spacing as a function of temperature is similar to that reported atoms, AS620 and AS657, have shorter lengths than all of the by Rao et al. for an antiferroelectric compound with quite others apart from AS666. The selenophene group has been diVerent terminal groups.16 They attributed the increase of shown previously17 to promote a bend in the molecule (18° in layer spacing at lower temperatures in the SmC*A phase to an the core of AS620 relative to a structure containing biphenyl underlying SmI*A phase.The only compound for which that rings) so the shorter molecular lengths AS620 and AS657 are is possible here is AS620 as none of the other materials studied not unexpected. have been observed to exhibit underlying hexagonal phases.All of the compounds have an ester linkage between the Further, the increase in layer spacing in the SmC*A phase aromatic rings which will induce some bend into the core. The occurs well above the temperature associated with the mono- shortest molecular length is observed for AS666, possibly tropic phase transitions to the hexagonal smectic phases in because of an increased molecular bend caused by repulsion AS620. The observed increase in the layer spacing is not between the fluorine atom and the end ester group near the reflected in the optical tilt angles, as is shown in a later section, chiral centre.In AS661, the longest molecule, the fluorine and so cannot be attributed to changes in the director tilt atom is on the opposite side of the molecule to the ethyl group angle.The low temperature increase in layer spacing continues so this phenomenon does not occur. Rather, the inward the trend observed in the SmA phase and is likely to be due pointing F atom may repel the ester dipole, straightening the to increasingly restricted conformational structures and core to some extent and resulting in the longest molecular hindered rotation of the molecules as the temperature reduces. length.Tilt angle measurements The molecular length The steric tilt angle d can be deduced from the layer spacing Fig. 3(a) to (f ) show the optical and steric tilt angles of the materials AS618, AS661, AS666, AS656, AS620 and AS657, data using the equation cosd=d/l, where d is the layer spacing and l is the molecular length.In order to employ this technique respectively. It should be noted that the uncertainty in temperature associated with the two diVerent measurement techniques of deducing the steric tilt angle, it is clearly necessary to have a measure of the molecular length l for the materials studied. could translate into oVsets of the order of a degree between the data sets plotted on each graph.For all the materials the The simplest method of deducing a value for this parameter is to assume that the layer spacing in the SmA phase is optical tilt angle h was greater than the steric tilt angle d over the majority of the phase range, implying that the molecular identical to the molecular length, though the validity of such an assumption clearly depends on whether or not the layers cores are more tilted than the terminal alkyl chains.This observation is in keeping with the Wulf model.18 There is are intercalated. It also neglects the temperature dependence of the layer spacing reported in the previous section and evidence in three of the materials that d is larger than h over part of the high temperature tilted phase region, a phenomenon assumes that the molecules are in their most extended form in the SmA phase, an assumption which is rarely valid.Table 2 that is discussed in more detail later. The maximum values of the steric and optical tilt angles shows the molecular length for each of the materials studied, considered to be the layer spacing at the point at which the attained in the materials are compared in Table 3.The optical tilt angles are all relatively large (around 30°). The two orthogonal to tilted phase transition takes place. An alternative method of deducing the molecular length materials containing Se (AS620 and AS657) have significantly lower steric tilt angles than the other compounds. These relies on molecular modelling, which has the advantage of J.Mater. Chem., 1998, 8(11), 2385–2390 2387Fig. 3 The steric and optical tilt angles of (a) AS618, (b) AS661, (c) AS666, (d) AS656, (e) AS620 and (f ) AS657 as a function of reduced temperature. materials also had amongst the shortest molecular lengths, though the small steric tilt angles cannot be attributed to that factor as it is taken account of in the calculation of d.Although Table 3 A summary of the saturated values of the optical tilt angle h and the steric tilt angle d AS661 is a shorter molecule than AS620 and AS657, it has a larger steric tilt than either, and while d is still lower than that Saturated steric Saturated optical of the other three materials, the optical tilt of AS661 is also Material tilt angle d (°) tilt angle h (°) low.It is possible that the small steric tilts of AS620 and AS657 are because the electron dense selenium atom in these AS618 21.4 33.0 AS661 20.0 27.7 systems biases the X-ray tilt to lower values, which could AS666 21.1 36.1 happen if, on average, it remained on the inside of the cone. AS656 22.3 31.4 Such an eVect may be the result of hindered rotation about AS620 18.3 30.6 the molecular long axis.Alternatively, packing constraints in AS657 16.8 31.1 the mesophases, imposed due to the molecular bend that is 2388 J. Mater. Chem., 1998, 8(11), 2385–2390ratio d/h that as both d and h change rapidly directly below the SmA phase transition, the uncertainty in the ratio is greatest in this region. As mentioned previously, the uncertainty occurs primarily because of the diYculty in registering the absolute temperature measurements in the two diVerent Fig. 4 A schematic diagram of conformational changes in zig-zag experiments. Consequently, the ratios calculated within 2 °C molecules that result in inversion phenomena. of the phase transition are discarded and not shown in Fig. 5. In spite of this precaution, it is recognised that the data of known to occur these molecules, could equivalently cause the Fig. 5 are least reliable in the vicinity of the tilted to orthogonal axis of electron density to appear tilted at a lower angle than phase transition.would occur for unbent molecules. Rieker et al. report that the ratio of d/h for a ferroelectric The data for AS661 [Fig. 3(b)] clearly show a change from material (not containing antiferroelectric subphases) is almost d>h to h>d in the middle of the temperature regime identified temperature independent and that d/h~0.85, in common with as a SmC* phase.There is also some evidence of a similar many ferroelectric materials.22 The factor of 0.85 is of course eVect in the data for AS618, close to the tilted to orthogonal material dependent and is determined by the relative orienphase transition.Such an eVect is consistent with a confor- tations of axes of the electron density and polarisability in the mational change (inversion) occurring in the zig-zag shaped system. For the materials described here, it is clear that the molecules of the sort depicted in Fig. 4.19–21 Optical obser- ratio can fall within a number of diVerent values, as may be vations made of the pitch of this system show inversion expected from the diVerent degrees of molecular bend in the phenomena and are reported elsewhere.8 various systems, together with the inclusion of electron dense It is apparent from Fig. 3(a) to (f ) that the temperature selenium atoms in two of the compounds. The ratio d/h is dependence of h and d appears to be diVerent for some of the almost temperature independent for two of the materials, materials.In order to investigate the eVect further for all of AS666 and AS620, and takes values of 0.64 and 0.6, respectthe materials the data were replotted to show the variation of ively. These materials are therefore considered to behave as the ratio d/h with respect to reduced temperature, as is shown would be expected for ferroelectric systems.The ratio exhibits a strong temperature dependence for the three of the materials in Fig. 5. It is worth noting when examining the data for the Fig. 5 The ratio of the steric (d) to optical (h) tilt angle for the six materials studied. Note that the scales on the graphs corresponding to the value d/h is identical for all the materials apart from AS661, where it is significantly diVerent.The temperature scales are identical for all of the graphs, with zero reduced temperature at the orthogonal to tilted phase transition. J. Mater. Chem., 1998, 8(11), 2385–2390 2389studied, AS618, AS661 and AS656, passing through 1 for the The authors gratefully acknowledge the support of the EPSRC (through grant number GR/L/76648) and the DERA Displays latter two.Most of the temperature dependence occurs close Group, Malvern. Thanks are also due to Dr B. Komanschek to the tilted to orthogonal transition, and is most likely to be of Station 8.2 at Daresbury Laboratories, UK, for his help attributed primarily to the conformational change depicted in during the XRD work.Fig. 4. However, the ratio continues to be temperature dependent well below this transition, in common with the behaviour of the ratio for AS657. We attribute such behaviour to factors References other than the zig-zag conformational change, including 1 See for example: A. Fukuda, Y. Takanishi, T. Isozaki, K. Ishikawa increasingly restricted conformational structures and hindered and H.Takezoe, J. Mater Chem., 1994, 4, 997; A. D. L. Chandani, rotation of the molecules, as was discussed earlier. E. Gorecka, Y. Ouchi, H. Takezoe and A. Fukuda, Jpn. J. Appl. Phys., 1989, 28 L1265; A. Ikeda, Y. Takanishi, H. Takezoe and A. Fukuda, Jpn J. Appl Phys., 1993, 32 L97. 2 A. D. L. Chandani, Y. Ouchi, H. Takezoe and A. Fukuda, Jpn. Conclusions J. Appl. Phys., 1989, 28, L1261. 3 M. Hird, P. Styring, A. Seed, H. F. Gleeson and J. T. Mills, This paper presents layer spacing and tilt angle measurements unpublished work. for six diVerent materials that exhibit ferroelectric and anti- 4 K. Itoh, M. Kabe, K. Miyachi, Y. Takanishi, K. Ishikawa, ferroelectric phases and subphases. The tilt angles were meas- H. Takezoe and A. Fukuda, J Mater. Chem., 1997, 7, 407.ured both optically and deduced from X-ray layer spacing 5 J. W. Goodby and I. Nishiyama, unpublished DSC data. measurements. Several features are common to all the systems 6 W. K. Robinson, PhD Thesis, Manchester University, studied. Firstly, the layer spacing measurements in the ortho- Manchester, UK, 1995. 7 Y. Panarin, W. Kalinovskaya, J. K. Vij and J. W. Goodby, Phys gonal phases imply that the molecules are considerably bent, Rev.E, 1997, 55, 4345. in common with other systems that exhibit antiferroelectricity. 8 L. Baylis, unpublished work. There is evidence that the molecules are almost completely 9 W. Bras, G. E. Derbyshire, A. J. Ryan, J. Cooke, A. Devine, extended in the SmA phase. The layer spacing changes rapidly B. E. Komanschek and S.M. Clark J. Appl. Crystallogr., 1995, with temperature at the transition to the tilted phases, as 28, 26. 10 Lucid EEV, 106, Waterhouse Lane, Chelmsord, Essex, UK CM1 would be expected. The layer spacing reaches a minimum 2QU. value, then rises again as the temperature is reduced into the 11 W. Bras, G. E. Derbyshire, A. J. Ryan, G. R. Mant, A. Felton, antiferroelectric phase.Previous work has attributed such R. Lewis, C. Hall and N. Greaves, NIM, 1993, 587, A326. behaviour to underlying SmI*A and SmI* phases, though this 12 J. StamatoV, P. E. Cladis, D. Guillion, M. C. Cross, T. Bilash and cannot be the case here, since only one of the materials studied P. Finn, Phys. Rev. Lett., 1980, 44, 1509. exhibits such a sequence and none of the materials shows any 13 Y.Ouchi, Y. Takanishi, H. Takezoe and A. Fukuda, Jpn. J. Appl. Phys., 1989, 28, 2547. reduction in the optical tilt angle of the system in the range 14 A. S. Morse and H. F. Gleeson, Liq. Cryst., 1997, 23, 531. in question. The result must therefore be interpreted as being 15 A. Ikeda, Y. Takanishi, H. Takezoe and A. Fukuda, Jpn. J. Appl. due to increasingly restricted conformational structures and Phys., 1993, 32, L97.hindered rotation of the molecules as the temperature reduces. 16 D. S. S. Rao, S. K. Prasad, S. Chandrasekhar, S. Mery and Comparison of the optical and steric tilt angles shows R. Shashidhar, Mol. Cryst. Liq. Cryst., 1997, 292, 301. 17 J. T. Mills, R. J. Miller, H. F. Gleeson, A. J. Seed, M. Hird and convincing evidence of inversion behaviour occurring in the P. Styring, Mol. Cryst. Liq. Cryst., 1997, 303 145. regions corresponding to the SmC* phase in three of the 18 A. Wulf, Phys. Rev. A, 1975, 11, 365. materials. Such behaviour has been confirmed by independent 19 J. S. Patel and J. W. Goodby, Philos. Magazine Lett., 1987, 55, measurements of the pitch for AS661. It should be noted that 283. the phase behaviour of these materials, in particular AS661, 20 J. S. Patel and J. W. Goodby, J. Phys. Chem., 1987, 91, 5838. is the subject of considerable debate. Certainly inversion 21 J.-H. Kim, S.-D. Lee, J. S. Patel and J. W. Goodby, Mol. Cryst. Liq. Cryst., 1994, 247, 293. behaviour, in addition to the other factors mentioned pre- 22 T. P. Rieker, N. A. Clark, G. S. Smith, D. S. Parmar, E. B. Sirota viously, further complicates the phase identification process. and C. R. Safinya, Phys. Rev. Lett., 1987, 59, 2658. In particular, inversion behaviour will be important in many 23 T. Sako, Y. Kimura, R. Hayakawa, N. Okabe and Y. Suzuki, Jpn. of the measurements currently employed to distinguish the J. Appl. Phys., 1996, 35, L114. SmC*b phase from the SmC* phase as it will aVect 24 H. F. Gleeson, unpublished work. electroclinic23 and dielectric relaxation phenomena.7 This phenomenon will be the subject of a future publication.24 Paper 8/05611K 2390 J. Mater. Chem., 1998, 8(11), 2385–2390

ISSN:0959-9428    

DOI:10.1039/a805611k

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials An assessment of carborane-containing liquid crystals for potential device application Andrew G. Douglass, Krzysztof Czuprynski,†Michelle Mierzwa and Piotr Kaszynski* Organic Materials Research Group, Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA Received 8th June 1998, Accepted 30th July, 1998 Two 4-alkoxyphenyl 12-pentylcarborane-1-carboxylate nematic liquid crystals have been synthesized. The materials are found to exhibit ideal mixing of nematic phases in their binary mixtures with analogous bicyclo[2.2.2]octane derivatives and with the polar nematogen 4-(4-isothiocyanatophenyl )-1-(trans-hexyl )cyclohexane.The smectic phases for the bicyclo[2.2.2]octanes are destabilized by addition of the carborane derivative.For carborane compound 5BC5 the extrapolated dielectric anisotropy and measured optical anisotropy are-1.3 and 0.057 respectively at 20 °C. The refractive indices have been correlated with the calculated electronic polarizabilities and the low birefringence measured for 5BC5 can, at least in part, be attributed to the carborane cylindrical symmetry. Introduction Current liquid crystal display applications rely on nematic, smectic A or C materials.1,2 Molecules forming such liquid crystalline phases typically comprise a rigid core with flexible substituents attached in such a way as to produce an extended rod-like shape.3,4 While the chains reduce the melting point of a compound, the mesogenic rigid cores provide the anisotropic interactions necessary for the occurrence of the liquid crystal phase and, to a large extent, dictate the properties of the bulk materials.Our studies have focused on inorganic boron closo-clusters5 as rigid core structural elements and their role in modifying thermal, dielectric and optical properties of liquid crystalline materials.6–11 p-Carborane (1) shown in Fig. 1 appears to be an excellent candidate for use in the mesogenic core of a calamitic liquid crystal.It is a three-dimensional, s-aromatic ring system12 which readily undergoes C-substitution with a variety of organic groups13,14 and hence can easily be incorporated into typical organic molecules. Previously, we demonstrated that mesogens containing 1 are good nematogens and have a tendency to destabilize smectic phases.6,9,11 This desirable property prompted us to study in detail two-ring esters containing 1 since analogous hydrocarbons possess low negative dielectric anisotropies and are used as additives to improve the performance of nematic devices.1 Here we provide synthesis and miscibility studies and describe mesogenic, dielectric and optical properties of two H H CnH2n+1 O OCmH2m+1 O CnH2n+1 O OCmH2m+1 O C6H13 NCS n = 5, m = 5 6CHBT n = 5, m = 5 n = 5, m = 10 5BC10 1 n = 5, m = 10 5BO5 5BO10 n = 6, m = 10 6BO10 5BC5 carborane esters, 5BC5 and 5BC10, and compare them with Fig. 1 p-Carborane (1), liquid crystal compounds and designations. the analogous bicyclo[2.2.2]octane esters 5BO515 and 5BO10 For carborane each vertex represents a B–H fragment and each filled (Fig. 1). The esters have been studied in pure states and as circle a carbon atom. binary mixtures with their analogs and also with the polar nematogen 4-(isothiocyanatophenyl )-1-(trans-4-hexyl )cyclohexane (6CHBT).16 This provides an extensive assessment of alkoxyphenol (Scheme 1). The preferred reagent for the prepthe potential for these carborane-containing liquid crystalline aration of chloride 2 is PCl5,17 while the 4-pentylbicyclo[2.2.2]- esters for use in display devices.octane-1-carbonyl chloride (3) was prepared using SOCl2.18 Formation of esters with 3 required 48 h reflux for complete reaction15 whereas the apparently more reactive carborane Results carbonyl chloride (2) was reacted at room temperature Synthesis overnight. The carborane esters 5BC5 and 5BC10 were synthesized from Thermal analysis and miscibility studies carbonyl chloride 2 and the bicyclo[2.2.2]octane esters 5BO5 and 5BO10 from carbonyl chloride 3 using the appropiate 4- The transitional data for the five compounds 5BC5, 5BC10, 5BO5, 5BO10 and 6BO1019 are presented in Table 1.Both carborane-containing materials, 5BC5 and 5BC10, exhibit low †The 1997 COBASE fellow on leave from Military University of Technology, Warsaw, Poland.clearing temperatures and their supercooled nematic phases J. Mater. Chem., 1998, 8(11), 2391–2398 2391extent, and the smectic behavior is only extinguished above 55 mol% 5BO5 [Fig. 2(b)]. Fig. 3 presents the binary phase diagrams for 5BC10-6BO10 (a) and 5BO10-6BO10 (b). In common with data presented in Fig. 2 nematic phases are shown to exhibit perfect miscibility. Increasing the proportion of 5BC10 to 6BO10 depresses the smectic transition temperatures and SB and SA phases are not formed above 20 mol% and 60 mol% 5BC10, respectively [Fig. 3(a)]. The phase diagram for 5BO10-6BO10 exhibits normal behavior [Fig. 3(b)] and as the concentration of 6BO10 is increased then the smectic B phase is stabilized in preference OCmH2m+1 HO X H11C5 O O X H11C5 O Cl OCmH2m+1 3, X = 2, X = Benzene, Et3N to the smectic C. Scheme 1 The phase diagrams for corresponding carborane and bicyclo[2.2.2]octane homologues 5BC5-5BO5 and 5BC10- are stable at room temperature on the order of weeks. 5BO10 are presented in Fig. 4(a) and (b), respectively. For Increasing the terminal chain length from five to ten methylene both diagrams nematic phases exhibit ideal mixing and for units increases the nematic phase range for these materials mixtures of 5BC10-5BO10 the smectic behavior is extinguished from 2 °C for 5BC5 to 14 °C for 5BC10.The nematic–isotropic above 40 mol% of 5BC10. transition temperatures for the bicyclo[2.2.2]octyl compounds, Binary mixtures 5BC5-6CHBT and 5BO5-6CHBT (Fig. 5) 5BO5 and 5BO10, are significantly higher than those for the exhibit ideal mixing of the nematic phases. For mixtures of analogous carboranes. The enthalpies for the nematic– 5BO5-6CHBT an induced smectic A phase is observed in isotropic transitions for the carborane derivatives are equal addition to the nematic. This smectic induction is such that whereas that for 5BO10 is larger than that for 5BO5.Of the the nematic range is reduced to 25 °C for mixtures containing five compounds only 5BO10 and 6BO10 are smectogenic 50–80 mol% 5BO5. forming enantiotropic smectic A and either monotropic smectic C or hexatic B20 phases. The binary phase diagrams for 5BC5-6BO10 and 5BO5- Dielectric anisotropy 6BO10 (Fig. 2) demonstrate ideal mixing behavior for the The dielectric anisotropies of solutions of 5BC5 in 6CHBT nematic phases.The smectic phases for 6BO10 are, however, were measured for four diVerent concentrations and the results strongly destabilized upon addition of the carborane derivative are plotted in Fig. 6. Extrapolation of the values obtained for [Fig. 2(a)]. Indeed, at 30 mol% of 5BC5 no smectic behavior the four solutions to pure 5BC5 gave a value of De= could be observed to -20 °C.Similarly, the addition of 5BO5 destabilizes the smectic phases for 6BO10 although to a lesser -1.3±0.1. Table 1 Phase transition temperatures and transitional enthalpies for the BC and BO materialsa. Compound C1 C2 SB SC SA N I 5BC5 T/ °C · 34.1 · 36.1 · DH/kcal mol-1 · 4.27 · 0.18 · 5BC10 T/ °C · 29.2 · 42.9 · DH/kcal mol-1 · 5.90 · 0.18 · 5BO5b T/ °C · 49.5 · 93.5 · DH/kcal mol-1 · 5.20 · 0.10 · 5BO10 T/ °C · 55.5 · 58.4 (· 30.5)c · 71.0 · 92.5 0 DH/kcal mol-1 · 0.94 · 5.30 · 0.03 · 0.33 0 6BO10d T/ °C · 55 (· 35) · 77.8 · 89.5 0 aObserved phases are denoted by bullets and monotropic transitions in parentheses. bLit.C·50.5 N·93.5·I, G. W. Gray and S. M. Kelly, Mol. Cryst. Liq.Cryst., 1981, 75, 95. cTemperature recorded by optical microscopy. dR. Dabrowski, J. Szulc and B. Sosnowska, Mol. Cryst. Liq. Cryst., 1992, 215, 13. Fig. 2 Binary phase diagrams for (a) 5BC5-6BO10 and (b) 5BO5-6BO10. The lines are guides to the eye. 2392 J. Mater. Chem., 1998, 8(11), 2391–2398Fig. 3 Binary phase diagrams for (a) 5BC10-6BO10 and (b) 5BO10-6BO10. The lines are guides to the eye.Fig. 4 Binary phase diagrams for (a) 5BC5-5BO5 and (b) 5BC10-5BO10. The lines are guides to the eye. Fig. 5 Binary phase diagrams for (a) 5BC5-6CHBT and (b) 5BO5-6CHBT. The lines are guides to the eye. Optical anisotropy to its high clearing point. The ne and no values (ne>no) obtained for the carborane derivative 5BC5 are higher than those measured for the bicyclo[2.2.2]octane analog 5BO5 The refractive indices for 5BC5 and 5BO5 have been measured for a range of temperatures (Table 2) and the data are plotted while the resulting birefringence is slightly lower for the former.Table 3 compares the refractive indices for four analogous in Fig. 7 as a function of the shifted temperature T-TNI. The isotropic refractive indices for 5BO5 were not measured due phenyl esters at the same shifted temperature, T-TNI= J.Mater. Chem., 1998, 8(11), 2391–2398 2393Table 3 Experimental refractive indices measured at T-TNI= -12.5 °C T/ °C ne no n navg a 5BC5 22.8 1.571 1.514 0.057 1.533 5BO5 80.5 1.533 1.471 0.062 1.492 5CH5b 63.6 1.527 1.466 0.061 1.486 4PH6c 36.0 1.608 1.497 0.111 1.534 anavg=(ne+2no)/ 3. bS. Takahashi, S.Mita and S. Kondo, Mol. Cryst. Liq. Cryst., 1986, 132, 53. cI. H. Ibrahim and W. Haase, J. Phys. (Paris), 1979, 40, 191. model24 [eqn. (1)] which assumes that the internal field is isotropic even in an anisotropic medium. 3 Vm 4 p NA · n2e,o,avg-1 n2 avg+2 =ae,o,avg where n2 avg=(n2 e+2n2 o)/3 (1) Fig. 6 Plots of e, ed and e) vs. concentration for mixtures of 5BC5- The parameters ae and ao represent the electric vectors 6CHBT.Line fit for e is R=0.999. parallel and perpendicular to the optical axis. The molar volumes (Vm) have been obtained from the experimental Table 2 Measured refractive indices for 5BC5 and 5BO5 as a function specific densities for 5CH523 and 4PH6.22 These molar volumes of temperature and those for 5BC525 and 5BO526 have been estimated using 5BC5 5BO5 group additivity to molar volume27 and are provided in Table 4 for comparison.For self-consistency of the data the estimated T/ °C ne no T/ °C ne no molar volumes have been used in eqn. (1) to derive the experimental polarizability data collected in Table 4. 39.4 1.526 83.5 1.530 1.471 37.7 1.527 82.5 1.531 1.471 Calculations 36.7 1.527 81.3 1.532 1.471 35.7 1.556 1.514 80.5 1.533 1.471 The average molecular polarizability (aavg), polarizability 34.7 1.559 1.514 79.5 1.534 1.472 anisotropy (a) and dipole moments for each of the four 33.8 1.562 1.513 78.5 1.535 1.472 30.9 1.564 1.513 74.5 1.538 1.472 analogues 5BC5, 5BO5, 5CH5 and 5PH5 have been calculated 28.7 1.566 1.513 70.6 1.542 1.473 using the MNDO method (Table 4).A plot of experimental 27.7 1.568 1.514 66.6 1.545 1.474 versus calculated average polarizabilities (aavg) is given in 26.2 1.570 1.514 63.3 1.547 1.475 Fig. 8. The molecular coordinates used in the calculations have 22.8 1.571 1.514 58.5 1.550 1.476 been chosen in such a way that the X-axis is defined by a line connecting the two terminal carbon atoms of the core and the phenyl ring lies in the XY plane.The molecular geometry of each compound was optimized with conformational constraints consistent with those found by X-ray analysis of analogous compounds. Thus the alkoxy group was constrained to be coplanar with the benzene ring in all cases.28 The carbonyl group was set to be coplanar with the benzene ring of the benzoate,28 perpendicular to the cyclohexyl ring of 5CH529 and staggered for 5BO5.The alkyl chains were constrained to be staggered in all cases. 28,29 Electronic absorption spectra The UV absorption spectrum for 5BC5 in ethanol exhibits similar intensities in its absorption maxima to those for 5BO5 which are about half those reported for p-methoxyphenyl benzoate30 (Fig. 9). The carborane derivative 5BC5 shows a small hypsochromic shift compared to the bicyclo[2.2.2]octane analog and exhibits a shoulder absorption at about 240 nm.Absorption spectra for both 5BC5 and 5BO5 are blue-shifted Fig. 7 Dependence of refractive indices (ne, no and niso) on temperature for 5BC5 (%) and 5BO5 ($). Table 4 Comparison of experimental (T-T NI=-12.5 °C) and calculated (MNDO) molecular polarizabilities (A° 3) -12.5°.21 The refractive indices and birefringence for 4- hexyloxyphenyl 4-butylbenzoate (4PH6)22 are greatest whilst VM a aavg aavg (calc.) ae-ao Da (calc.) S the values for 4-pentylcyclohexane-1-carboxylic acid 4-pentyl- 5BC5 396 —b 48.7 54.5 6.3 22.0 0.29 oxyphenyl ester (5CH5)23 are comparable with those for 5BO5 382 —b 43.9 48.6 6.7 18.6 0.36 5BO5.Carborane 5BC5 has the lowest birefringence despite 5CH5 360 (382) 41.0 45.5 6.2 17.9 0.34 having an average refractive index [navg=(ne+2no)/3] equal to 5PH5 325 (346)c 40.1c 46.0 10.2c 26.0 0.39 that of 4PH6.aEstimated based on group additivity, see ref. 25–27; experimental The molecular electronic polarizabilities ax have been data are in parentheses. bNot available. cValues are for analog 4PH6. calculated from the observed refractive indices nx using Vuks 2394 J.Mater. Chem., 1998, 8(11), 2391–2398from this comparison that in order to have stabilization of smectic phases in mixtures comparable with that for bicyclo[2.- 2.2]octanes the carborane derivatives require a significant increase in terminal chain length. Further studies are necessary to test this hypothesis. The excellent miscibility demonstrated for the carboranyl compounds in the low polarity bicyclo[2.2.- 2]octyl hosts is also observed for mixtures in the polar nematogen 6CHBT.It is interesting that 5BO5 actually induced smectic behavior in its mixtures with 6CHBT as bicyclo[2.2.2]octane derivatives are generally regarded as being nematogenic rather than smectogenic compounds.15 Obviously, the formation of smectic phases within the operating temperature range of a nematic device is undesirable although we note that certain devices have improved performance if there is a neighbouring smectic transition.1 The small, negative value of De for 5BC5 (-1.3) is consistent with a value of -1.1 reported for cyclohexane close analog 4CH6.31 It also consistent with expectation as the major contributors to the dielectric anisotropy are the outboard dipoles due to lone electron pairs on oxygen.Indeed, the Fig. 8 Plot of calculated (MNDO) vs. experimental average molecular MNDO calculations show that the transverse vector consti- polarizabilities. Open circles represent data obtained using estimated molar volumes and filled circles experimentally determined molar tutes the major component of the molecular dipole moment volumes.The slope and line fit (open circles only) are 0.93 and 0.986, which is about 1.8 D for 5BC5 and 5BO5, 1.7 D for 5CH5 respectively. and 2.1 D for 5PH5 (D=Debye, 1 D#3.33564×10-30 Cm). The refractive indices for 5BC5 are greater than those for 5BO5 and 5CH5 as a result of the highly polarizable electrons in the carborane cage.32 However, because of the threedimensional spherocylindrical symmetry of the carborane cage, cf.two-dimensional planar symmetry of a benzene ring, the resultant birefringence is expected to be lower in carboranecontaining mesogens than in aromatic analogs. Indeed, calculations on biphenyl, 1,1¾-bicarborane and 1-phenylcarborane clearly demonstrate that the carborane imparts a high average polarizability but low anisotropy of polarizability (Table 5).The same trend is observed in the data collected in Table 4; 5BC5 is predicted to have the highest average polarizability and a polarizability anisotropy intermediate between the phenyl and alicyclic analogues. Comparing the calculated and experimental values for aavg it can be seen that the experimental values tend to be 10–15% lower than the theoretical predictions (Table 4).Part of this overestimation by theory can be attributed to the use of estimated rather than experimental molar volumes which tend to be underestimated by about 5%. In view of the fact that we are comparing results from calculations Fig. 9 Plot of molar absorptivity against wavelength for 5BC5 (solid on a single conformer in the gas phase to those obtained for line) and 5BO5 (dashed line).The literature lmax values (228 nm, log e=4.27; 274 nm, log e=3.67) for p-methoxyphenyl benzoate are conformationally mobile molecules in an anisotropic, conmarked for comparison. densed phase the correlation is reasonable (R=0.986 in Fig. 8). The polarizability anisotropy values obtained for an idealized, gas phase molecule diVer from those measured in the relative to that of p-methoxyphenyl benzoate30 (vertical lines in Fig. 9). nematic phase due to intermolecular (orientational ordering) and intramolecular dynamics (conformational mobility) in the latter. The orientational ordering is generally approximated Discussion and conclusions by the second rank orientational order parameter S where b is the angle between the long molecular axis and the director The carborane-containing compounds 5BC5 and 5BC10 both form nematic phases with lower clearing temperatures than [eqn.(2)].33 For an axially symmetric molecule the order those for the analogous bicyclo[2.2.2]octyl compounds. This is in accord with our general observation that clearing points Table 5 Calculated (MNDO) polarizabilities (A° 3) for benzene and are lowered when p-carborane is substituted into a mesogenic carborane compounds core.6,9–11 Previous studies have also noted a tendency for carborane-containing compounds to destabilize smectic aavg Da phases6,9,11 which has been rationalized on the basis of the greater breadth of the carborane cage cf.bicyclo[2.2.2]octane or benzene.11 The results from this study are consistent with this observation as 5BO10 is smectogenic whilst 5BC10 is not.Further, the binary phase diagrams with 6BO10 demonstrate that for equal homologues smaller percentages of the carboranes are required to suppress smectic behavior than for analogous bicyclo[2.2.2]octanes. In fact, the binary phase aExperimental value obtained from molar refraction and density at diagram for 5BC10-6BO10 [Fig. 3(a)] is similar to that for the 77 °C is 20.8 A° 3, A. L. von Steiger, Chem. Ber., 1922, 55, 1968. 5BO5-6BO10 binary mixture [Fig. 2(b)]. It could be inferred J. Mater. Chem., 1998, 8(11), 2391–2398 2395parameter can be expressed as a ratio of experimental and microscope with a HCS250 Instec hot stage. Thermal analysis was obtained using a Mettler DSC 30 instrument.Transition theoretical birefringences or anisotropies of molecular polarizabilities [eqn. (3)].22 temperatures for pure materials were measured using small samples (1–2 mg) and a heating rate of 1 °Cmin-1, while for S=(3<cos2b>-1)/2 (2) the transition enthalpies large samples (10–15 mg) and fast S=(ae-ao)/Da (3) heating (10 °Cmin-1) was used.The uncertainties in the transition temperatures and transitional enthalpies are esti- Thus, if the assumptions made in determining (ae-ao) are mated as ±0.1 °C and ±5% respectively. Mixtures were reasonable then the results suggest that 5BC5 has a lower prepared by evaporation of dichloromethane solutions. For degree of orientational ordering than its analogs (Table 4) at mixtures the transition temperature was taken as the upper the same shifted temperature and that the lowered orientational limit of the biphasic region as observed by optical microscopy. ordering is contributing to lowering the observed birefringence.The phase diagrams were determined by the single concen- Unfortunately the assumptions made in obtaining order partration method.NMR spectra were obtained on a Bruker ameters (in particular estimation of the molar volume for 300 MHz instrument in CDCl3 and referenced to the solvent 5BC5) prevent these data from being considered fully reliable. (1H and 13C NMR). 11B NMR spectra were obtained at Our intention was rather to assess whether semiempirical 64.2 MHz using a Bruker 200 MHz spectrometer and refer- methods can reproduce the experimental data and conseenced to B(OMe)3.IR spectra were recorded using an ATI quently can be used for making predictions. Certainly the Mattson Genesis FTIR by deposition of a thin film from average polarizabilities are overestimated but reproduced solution onto sodium chloride disks. Mass spectrometry reasonably consistently by calculations (Fig. 8). Calculations was performed using a Hewlett-Packard 5890 instrument also suggest that the anisotropy of polarizability should be (GC–MS). Elemental analysis was provided by Atlantic lower for mesogens containing carborane instead of phenyl. Microlab, Norcross, Georgia. Dielectric anisotropies were This is supported by experiment as the birefringence is low measured using an APT III Automated Polarization Testbed for 5BC5 cf. 4PH6. At present it is not possible to assess the at room temperature and version 4.12b software (Displaytech, relative contributions of the orientational ordering and the Inc). The error in measurement of the dielectric constant is molecular polarizability to this low birefringence for 5BC5. estimated to be ±0.1. Refractive indices for 589 nm radiation Answering this question is important because low birefringence were determined using a Leitz Abbe Mark II refractometer has been recognized as a desirable property for twisted nematic connected to a thermostated circulating-water bath.Samples device applications.34 In order to resolve this debate and to were aligned by pretreatment of the prism surfaces with lecithin further investigate these carboranyl mesogens we hope to and rubbing unidirectionally.The errors in readings are measure the temperature dependence of the density and the ±0.001 and ±0.002 for the extraordinary and ordinary rays temperature dependent order parameters via deuterium NMR respectively. The temperatures recorded by the refractometer spectroscopy. were scaled to those of the DSC by comparison of TNI.The contribution of the s-aromatic carborane to the UV–VIS spectra of solutions in absolute ethanol were recorded electronic absorption spectrum for 5BC5 is more comparable using a Hitachi U-3000 spectrophotometer. Benzene and with that of an aliphatic ring than with that of a p chromodichloromethane was dried by distillation from calcium phore. Molar absorptivities for the carborane and bicyclohydride and triethylamine by standing over potassium hydrox- [2.2.2]octane derivatives are very similar and they are essenide.Quantum mechanical calculations were performed tially half of those for the compound with two phenyl rings using AMPAC 6.0 package. Polarizabilities were obtained (Fig. 9). As evident from Fig. 9, both 5BC5 and 5BO5 show in the user-defined molecular coordinates by using the benzene E band at about 220 nm and the B band double BRUTEKPOLAR Keyword.absorption at about 280 nm. The E band for 5BC5 is blueshifted by 3 nm with respect to that for 5BO5 and 6 nm with respect to p-methoxyphenyl benzoate.30 The spectrum of 5BC5 Syntheses exhibits a broad shoulder absorption at about 240 nm which 12-Pentyl-1,12-dicarbadodecaborane(10)-1-carboxylic acid.is absent in the spectrum of the bicyclo[2.2.2]octane analog. p-Carborane (2.0 g, 13.8 mmol) was placed in a dry 100 ml Since UV spectra for the corresponding carboxylic acids are three-neck flask equipped with a condenser, stopper and suba- similar to each other the origin of this shoulder absorption is seal. After flushing with nitrogen, dry THF (50 ml ) was added not clear.and the solution cooled to -78 °C. n-Butyllithium (1.92 M in In summary, the carborane-containing compounds are mis- THF, 7.18 ml, 13.8 mmol) was added via syringe in a dropwise cible with all-organic mesogens, have clearing points about manner causing a white precipitate to form. The mixture was 50 °C lower than analogous bicyclo[2.2.2]octane derivatives allowed to warm (redissolution occurs) and stir at room and appear to be strong suppressants of smectic phases.temperature for 20 min after which n-pentyl iodide (1.79 ml, Substitution of carborane for bicyclo[2.2.2]octane into the 13.8 mmol) was added. After stirring a further 3 h the reaction mesogen does not appreciably increase the UV absorption or was recooled to -78 °C and n-butyllithium (1.92 M in THF, birefringence whilst refractive indices are increased markedly. 7.18 ml, 13.8 mmol) was added dropwise via syringe. The This unique eVect of the carborane cage on bulk properties reaction was allowed to stir at room temperature for 20 min can be rationalized on the basis of symmetry arguments and and then CO2 was bubbled through it for a further 1 h.The is supported by quantum mechanical calculations. The expersolvent was removed on a rotavapor and KOH added (2 M, imental birefringence for 5BC5 is excessively low compared to 30 ml ). The mixture was extracted with hexanes (3×30 ml ) calculations suggesting a low order parameter. Dielectric which were discarded. The aqueous phase was acidified with properties are not significantly aVected by substitution with conc.HCl (pH 1) causing a white precipitate to form. Diethyl carborane. The data collected thus far suggest that the carborether (30 ml ) was added eVecting dissolution and the organic ane-containing compounds satisfy the criteria for nematic phase was separated. The aqueous phase was again extracted devices and that more detailed studies of this class of with ether (3×30 ml ) and the combined organics dried over compounds are warranted.sodium sulfate. The ether was removed and the white solid stirred in refluxing hexanes to extract the 12-pentyl-1,12- Experimental dicarbadodecaborane-1-carboxylic acid which was purified by sublimation (120–124 °C, 1 Torr) yielding a white solid (1.57 g, The phase transition points of the compounds and their mixtures were determined using a PZO ‘Biolar’ polarized 44% yield): mp. 139–143 °C; 1H NMR ([2H6 ]acetone), d 0.81 2396 J. Mater. Chem., 1998, 8(11), 2391–2398(t, J=7.1 Hz, 3H), 1.02–1.28 (m, 6H), 1.67 (t, J=7.8 Hz, 4-Pentylbicyclo[2.2.2]octane-1-carboxylic acid 4-decyloxyphenyl ester (5BO10). 4-Pentylbicyclo[2.2.2]octane-1-carbonyl 2H), 10.06 (br s, 1H), 1.2–3.4 (br m); 13C NMR, d 14.12, 22.80, 29.80, 31.74, 38.83, 76.31, 84.57, 163.40; 11B NMR, d chloride (3, 220 mg, 0.91 mmol, formed from the carboxylic acid and thionyl chloride (bp 150 °C/ 1 Torr, 76% yield) and -13.5 (d, JBH=165 Hz); IR 2952, 2929, 2606, 1716, 1415, 1282 cm-1.Anal. Calc. for C8H22B10O2: C, 37.19; H, 8.58. 4-decyloxyphenol (210 mg, 0.91 mmol) were dissolved in dry benzene (5 ml ) and dry pyridine (2.5 ml ) was added dropwise.Found: C, 37.43; H, 8.47%. The reaction was stirred and refluxed for 48 h and the volatiles removed by rotary evaporation. The crude product was then 12-Pentyl-1,12-dicarbadodecaborane(10)-1-carboxylic acid 4- passed through a 3 cm layer of silica eluted with 100 ml of pentyloxyphenyl ester (5BC5). 12-Pentyl-1,12-dicarbadodeca- dichloromethane–hexanes (1/4 v/v). Chromatographic separaborane( 10)-1-carboxylic acid (1.0 g, 3.87 mmol) and phos- tion (same eluant) and recrystallization from ethanol yielded phorus pentachloride (841 mg, 4.04 mmol) were placed in a 322 mg (70%): mp 58.4 °C; 1H NMR (400 MHz), d 0.86 (t, dry 25 ml flask and dry benzene (10 ml ) added. The reaction J=7.1 Hz, 6H), 1.08–1.50 (m, 28H), 1.72–1.77 (m, 2H), 1.88 was stirred under nitrogen for 20 min at 40 °C forming a clear (t, J=7.9 Hz, 6H), 3.90 (t, J=6.5 Hz, 2H), 6.82 and 6.89 solution.The solvent was removed yielding a colorless oil and (AB d, J= 9.0 Hz, 4H); 13C NMR, d 14.07, 14.09, 22.66, after flushing with nitrogen dry benzene (10 ml ) was added to 23.34, 26.00, 28.57, 29.24, 29.30, 29.37, 29.54, 30.36, 30.44, dissolve acid chloride 2.This solution was added dropwise to 31.88, 32.78, 39.19, 41.31, 68.31, 114.87, 122.14, 144.31, 156.56, a stirred solution of 4-pentyloxyphenol (729 mg, 4.04 mmol) 177.05; EIMS, m/z 456 (10), 180 (14), 179 (100%); IR 2957, and triethylamine (0.56 ml, 4.04 mmol) in dry benzene (10 ml ) 2921, 2854, 1747, 1506, 1457, 1227, 1197 cm-1.Anal. Calc. and the reaction stirred overnight at room temperature under for C30H48O3: C, 78.90; H, 10.59. Found: C, 79.19; H, 10.79%. nitrogen. The solution was then filtered through a silica gel plug eluted with benzene and the solvent removed. The product was purified by chromatography (dichloromethane–hexanes, Acknowledgments 154) giving 1.3 g (80% yield) followed by repeated recrystalliz- This project has been funded in part by the National Research ation from pentane, decolorization with charcoal in diethyl Council under the Collaboration in Basic Science and ether and finally distillation (194–196 °C, 0.3 Torr) to yield Engineering Program(COBASE).Support for this project has 847 mg colorless, opaque liquid (52% yield): mp 34.1 °C; 1H also been provided by the NSF CAREER grant (DMR- NMR, d 1.0–3.4 (br m), 0.84 (t, J=7.1 Hz, 3H), 0.92 (t, J= 9703002).We are grateful to the Organic Chemistry 7.0 Hz, 3H), 1.05–1.50 (m, 10H), 1.59–1.65 (m, 2H), 1.70–1.79 Laboratory of the Military University of Technology, Warsaw (m, 2H), 3.88 (t, J=6.5 Hz, 2H), 6.80 and 6.84 (AB d, J= for the gift of 4-pentylbicyclo[2.2.2]octane-1-carboxylic acid, 9.3 Hz, 4H); 13C NMR, d 13.83, 14.00, 22.18, 22.41, 28.11, 6CHBT and 6BO10.We would also like to thank Mr. J. E. 28.86, 28.98, 31.12, 38.36, 68.31, 74.19, 84.37, 114.89, 121.46, Harvey for the diectric anisotropy measurements and Professor 143.73, 157.16, 161.56; 11B NMR, d -14.1 (d, JBH=162 Hz); D. Demus for bringing to our attention ref. 27. EIMS, m/z 423–417 (max.at 420, 58%, M), 244–237 (max. at 241, 100%); IR 2956, 2932, 2865, 2614, 1762, 1505, 1298, 1241 cm-1; UV, lmax/nm ( log emax) 222 (3.95), 277 (3.36), References 283 (3.24). Anal. Calc. for C19H36B10O3: C, 54.26; H, 8.63. 1 I. Sage, in Thermotropic Liquid Crystals, ed. G. W. Gray, John Found: C, 54.31; H, 8.71%. Wiley and Sons, 1987, pp. 64–98. 2 D. Coates, in Thermotropic Liquid Crystals, ed.G. W. Gray, John Wiley & Sons, New York, 1987, pp. 99–119. 12-Pentyl-1,12-dicarbadodecaborane(10)-1-carboxylic acid 4- 3 D. Demus, Mol. Cryst. Liq. Cryst., 1988, 165, 45. decyloxyphenyl ester (5BC10). Prepared by the method used 4 K. J. Toyne, in Thermotropic Liquid Crystals, ed. G. W. Gray, for 5BC5 and purified by distillation (220 °C, 0.1 Torr, 93 mg, John Wiley and Sons, New York, 1987, pp. 28–63. 52% yield) followed by recrystallization from ethanol: mp 5 Boron Hydride Chemistry, ed. E. L. Muetterties, Academic Press, New York, 1975. 29.2 °C; 1H NMR, d 1.0–3.5 (br m), 0.82 (t, J=7.2 Hz, 3H), 6 A. G. Douglass, M. Mierzwa and P. Kaszynski, SPIE, 1998, 0.86 (3H, J=6.6 Hz, 3H), 1.05–1.40 (m, 20H), 1.57–1.68 (m, 3319, 59. 2H), 1.70–1.77 (m, 2H), 3.88 (t, J=6.6 Hz, 2H), 6.79 and 7 P.Kaszynski and D. Lipiak, in Materials for Optical Limiting, ed. 6.85 (AB d, J=9.1 Hz, 4H); 13C NMR, d 13.83, 14.10, 22.18, R. Crane, K. Lewis, E. V. Stryland and M. Khoshnevisan, MRS, 22.66, 25.97, 28.98, 29.17, 29.30, 29.34, 29.53 (2C), 31.13, 1995, 374, 341. 31.87, 38.36, 68.37, 74.21, 84.36, 114.91, 121.48, 143.73, 157.16, 8 P.Kaszynski, J. Huang, G. S. Jenkins, K. A. Bairamov and D. Lipiak, Mol. Cryst. Liq. Cryst., 1995, 260, 315. 161.62; 11B NMR, d -14.2 (d, JBH=166 Hz); EIMS, m/z 9 K. Czuprynski, A. G. Douglass, P. Kaszynski and W. Drzewinski, 493–487 (max. at 490, 33, M), 244–237 (max. at 241, 100%); Liq. Cryst., submitted. IR 2954, 2926, 2855, 2614, 1761, 1504, 1242, 1188 cm-1. Anal. 10 P. Kaszynski and K.Czuprynski, Chem. Commun., submitted. Calc. for C24H46B10O3: C, 58.74; H, 9.45. Found: C, 58.85; 11 A. G. Douglass, K. Czuprynski, M. Mierzwa and P. Kaszynski, H, 9.44%. Chem. Mater., in press. 12 R. B. King, Russ. Chem. Bull., 1993, 42, 1283. 13 V. I. Bregadze, Chem. Rev., 1992, 92, 209 and references therein. 4-Pentylbicyclo[2.2.2]octane-1-carboxylic acid 4-pentyloxy- 14 R.N. Grimes, Carboranes, Academic Press, New York, 1970, 15 G. W. Gray and S. M. Kelly, Mol. Cryst. Liq. Cryst., 1981, 75, 95. phenyl ester (5BO5).15 Prepared and purified by the method 16 R. Dabrowski, J. Dziaduszek, T. Szczucinski and Z. Raszewski, used for 5BO10 giving 472 mg (66% yield): mp 49.5 °C; Mol. Cryst. Liq. Cryst., 1984, 107, 411. 1H NMR, d 0.87 (t, J=7.2 Hz, 3H), 0.91 (t, J=7.1 Hz, 3H), 17 V.V. Korshak, N. I. Bekasova, A. I. Solomatina, T. M. Frunze, 1.09-1.44 (m, 18H), 1.70-1.77 (m, 2H), 1.86-1.91 (m, J= A. A. Sakharova and O. A. Mel’nik, Izv. Akad. Nauk. SSSR, Ser. 7.8 Hz, 6H), 3.90 (t, J=6.4 Hz, 2H), 6.83 (d, J=9.1 Hz, 2H), Khim., 1982, 31, 1904. 6.89 (d, J=9.1 Hz, 2H); 13C NMR, d 14.00, 14.07, 22.43, 18 P. Adomenas, A. Nenishkis and D.Girdzhyunaite, J. Org. Chem. USSR, 1982, 18, 1100. 22.66, 23.33, 28.15, 28.59, 28.93, 30.36, 30.46, 32.78, 39.21, 19 R. Dabrowski, J. Szulc and B. Sosnowska, Mol. Cryst. Liq. Cryst., 41.31, 68.32, 114.90, 122.15, 144.31, 156.57, 177.11; EIMS, 1992, 215, 13. m/z 386 (13), 180 (18), 179 (100), 123 (20), 109 (29%); IR 20 J. Przedmojski, personal communication. 2954, 2922, 2870, 2856, 1746, 1504, 1458, 1227, 1198 cm-1; 21 The more commonly used reduced temperature scale (T/TNI in K) UV, lmax/nm ( log emax) 225 (4.01), 278 (3.30), 285 (3.21).gives similar results. Anal. Calc. for C25H38O3: C, 77.68; H, 9.91. Found: C, 77.76; 22 I. H. Ibrahim and W. Haase, J. Phys. (Paris), 1979, 40, 191. Data not available for 5PH5. H, 9.84%. J. Mater. Chem., 1998, 8(11), 2391–2398 239723 M. Takahashi, S. Mita and S. Kondo, Mol. Cryst. Liq. Cryst., 30 R. Martin, Monatsh. Chem., 1981, 112, 1155. 1986, 132, 53. 31 V. Vill, Liq. Cryst. 3.0, Hamburg, 1997, compound #22714. 24 M. F. Vuks, Opt. Spectrosc. (Engl. Transl.), 1966, 20, 361. 32 Experimental value for B12H122- has been measured as 22.0 A° 3; 25 The molar volume contribution for the carborane cage was esti- A. Kaczmarczyk and G. B. Kolski, Inorg. Chem., 1965, 4, 665; mated to be 126±9 cm3 mol-1 by statistical analysis of eight calculated (MNDO) value is 18.8 A° 3. Similarly for p-carborane disubstituted o- and m-carborane compounds. To our knowledge the calculated value is 18.7 A° 3 and for benzene 10.2 A° 3 (exptl. no density data have been reported for disubstituted p-carboranes. 10.4 A° 3). 26 The temperature dependence of the calculated molar volume for 33 A. Saupe and W. Maier, Z. Naturforsch., Teil A, 1961, 16, 816. 5BO5 was assumed to be equal to that measured experimentally 34 K. Toriyama, K. Suzuki, T. Nakagomi, T. Ishibashi and for 5CH5. K. Odawara, in The Physics and Chemistry of Liquid Crystal 27 R. F. Fedors, Polym. Eng. Sci., 1974, 14, 147. Devices, ed. G. Sprokel, Plenum, New York, 1976, pp. 153–171. 28 P. Kromm, H. Allouchi, J.-P. Bideau, M. Cotrait and H. T. Nguyen, Acta. Crystallogr., Sect. C, 1995, 51, 1229. 29 U. Baumeister, W. Brandt, H. Hartung, W. Wedler, H.-J. Deutscher, R. Frach and M. Jaskolski, Mol. Cryst. Liq. Cryst., Paper 8/04322A 1985, 130, 321. 2398 J. Mater. Chem., 1998, 8(11), 2391–2398

ISSN:0959-9428    

DOI:10.1039/a804322a

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Synthesis and electrochemical characteristics of spinel phase LiMn2O4-based cathode materials for lithium polymer batteries Yang-Kook Sun* and Sung-Ho Jin Polymer Materials Laboratory, Chemical Sector, Samsung Advanced Institute of Technology, 103-12, Moonji-Dong, Yusong-Gu, Daejon, Korea, 305-380. E-mail: yksun@saitgw.sait.samsung.co.kr Received 15th June 1998, Accepted 11th August 1998 Spinel LiMn2O4 and LiMn1.95Ni0.05O4 powders have been synthesized by a sol–gel method using an aqueous solution of metal acetates containing glycine.The dependence of the physicochemical properties of the spinel LiMn2O4 powders on the calcination temperature and glycine quantity have been extensively investigated. The porous LiMn2O4 and LiMn1.95N0.05O4 electrodes were electrochemically characterized by using charge/discharge experiments along with ac impedance spectroscopy.The LiMn1.95Ni0.05O4 electrode exhibited improved cycling performance in comparison with the stoichiometric LiMn2O4 one in spite of a small reduction in the initial capacity. The good capacity retention of the LiMn1.95Ni0.05O4 electrode is attributed to stabilization of the spinel structure by Ni doping for Mn ion sites and higher chemical diVusivity of lithium ions with cycling.In this work, LiMn2O4 and LiMn1.95Ni0.05O4 powders with Introduction uniform submicron-sized particles were synthesized by a The spinel LiMn2O4 has been extensively studied as the most sol–gel method using glycine as a chelating agent at considerpromising cathode material for lithium secondary batteries ably lower temperatures and shorter times compared with with high energy density.This material oVers several distinct solid-state reaction. Also, the origin of capacity fading on advantages; it is easier to prepare, less expensive and less toxic cycling was investigated in terms of interfacial characteristics than layered oxides such as LiCoO2 and LiNiO2.1,2 However, by using charge/discharge experiments complementary with ac LiMn2O4 has problems related to capacity fading and limited impedance measurements for Li/polymer electrolyte/LiMn2O4 cyclability in the 4 VLi/Li+ region in comparison with the and LiMn1.95Ni0.05O4 cells.layered oxides. The reason for capacity fading has not been clearly resolved, but some possible factors have been proposed. 3–5 In order to improve capacity fading and cyclability Experimental of the LiMn2O4 powders in the 4 VLi/Li+ region, the eVects of A stoichiometric amount of Li, Mn, and Ni acetates (Acros adding excess lithium to the LiMn2O4 spinel,3,6–8 and manga- Co., high purity) with the cationic ratio Li5Mn=152 or nese-substituted spinels LiMxMn2-xO4 (M=Mg, Zn, Co, Cr, Li5Mn5Ni=151.9550.05 were dissolved in doubly distilled Ni, Al, Ti, Fe, Ga)3,9–13 have been studied.water, mixed well with each other and an aqueous solution of The electrochemical properties of LiMn2O4 strongly depend glycine was added (Aldrich, high purity). Glycine was used as on its synthetic method. The LiMn2O4 powders have been a chelating agent to produce gel precursors.Ammonium usually prepared by solid-state reaction which consists of hydroxide was added slowly to this solution with constant extensive mechanical mixing and extended grinding, which is stirring until a pH of 5.0–7.5 was achieved. The resultant detrimental to the quality of the final products. These synthetic solution (0.1 mol aqueous solution of total metal ions) was conditions can result in inhomogeneity, irregular morphology, evaporated at 70–80 °C for 5 h until a transparent sol larger particle size with broad particle size distribution, and was obtained. To remove water from the sol the transparent poor control of stoichiometry. In order to achieve good sol was heated at 70–80 °C while being mechanically stirred eYciency of Li utilization at high current rates and reliability with a magnetic stirrer.As the evaporation of water proceeded, of lithium secondary batteries, a sol–gel method has been the sol turned into a viscous transparent gel. For the prep- introduced, which is a desirable method to obtain cathode aration of the gel precursors with diVerent molar ratios of materials with good homogeneity, uniform morphology and glycine to total metal ions the same procedure was repeated narrow size distribution.14,15 Recently, one of us has reported with the molar ratio of glycine to total metal ions being varied that the spinel LiMn2O4 powders being phase pure and having to 1, 1.5, 2, and 2.551.The gel precursors obtained were excellent rechargeability could be synthesized by the sol–gel decomposed at 250–800 °C for 10 h in air to obtain phase- method using glycolic acid and poly(acrylic acid) (PAA) as pure polycrystalline LiMn2O4 powders.chelating agents.8,16 Powder X-ray diVraction (Rint-2000, Rigaku) using Cu-Ka Lithium polymer batteries are now being studied extensively radiation was used to identify the crystalline phase of the as promising candidates for electric vehicles and portable materials calcined at various temperatures. Rietveld refinement electric equipment.The use of a polymer electrolyte would was then performed on the X-ray diVraction data to obtain make the batteries highly safe, flexible, light, and thin. One of lattice constants. The change in the particle morphology was the problems with the lithium polymer batteries is a progressive observed using a field emission scanning electron microscope capacity fading on repeated cycling.When a polymer electro- (TOPCON, ABT-150F). lyte is used, the establishment of a proper interfacial contact The electrochemical properties of LiMn2-xNixO4 powders between polymer electrolyte and electrode can be an issue of were determined in the Li/polymer electrolyte/LiMn2-xNixO4 major concern and essential to guarantee acceptable performcells. The polymer electrolyte was made from polyacrylonitrile ance and cycle life.A few studies have been carried out in (PAN), plasticized by a solution of LiClO4 in a 151 mixture order to investigate interfacial characteristics between polymer electrolyte and electrode.17–21 of ethylene carbonate (EC) and propylene carbonate (PC).J. Mater. Chem., 1998, 8(11), 2399–2404 2399A typical polymer electrolyte composition was PAN 12 wt.%–EC40 wt.%–PC 40 wt.%–LiClO4 8 wt.%. The ionic conductivity of the polymer electrolyte was 2×10-3 V-1 cm-1 at room temperature. The composite cathode was made from the as-synthesized LiMn2-xNixO4 spinel powders (89.5 wt.%.), acetylene black (Super-P, conducting agent; 5.5 wt.%), and PAN binder (5 wt.%).The LiMn2-xNixO4 spinel powders and acetylene black were added to PAN solution in dimethyl sulfoxide (DMSO) as a solvent. The slurry was spread onto an aluminum foil current collector, and dried at 110 °C in air. Dried composite cathode was then compressed with a roll presser and further dried under vacuum for 10 h at 110 °C.A three-electrode cell was used for the electrochemical measurements. The reference and counter electrodes consisted of 50 mm thick Li foil (Cyprus Foote Mineral Co.) pressed onto a Cu current collector. A rechargeable lithium polymer cell was assembled by sandwiching the polymer electrolyte between the lithium anode and the composite cathode. A lithium electrode contacting polymer electrolytes in proximity to the working electrode served as the reference electrode.The cell was then Fig. 2 EVect of the calcination temperature on the lattice constant of enclosed in a metallized plastic bag and vacuum sealed. All the LiMn2O4 powders ($: LiMn1.95Ni0.05O4 powders calcined at assemblies of the cell were carried out in a dry box filled with 800 °C) when the molar ratio of glycine to total metal ions was 1.051.argon gas. The cells were usually cycled between cut-oV voltages of 3.4 and 4.3 VLi/Li+ at a constant current density of 0.15 mA cm-2, unless otherwise noted. The cells were activated peaks are much sharper, the widths of the peaks are much narrower, and the positions of the diVraction lines shift to the during the first cycle at a constant current density of 0.1 mA cm-2.ac impedance measurements were performed low angle side in the XRD pattern with the increase of the calcination temperature, which indicates an increase in crystal- using a Zahner Elektrik IM6 impedance analyzer over the frequency range of 1 mHz–100 kHz with an amplitude of linity and a gradual growth of average size particles.Similar results had already been reported whereby the LiMn2O4 5 mV. Each sample was allowed to equilibrate for 30 min at each cycle before measurement at the fully charged state. powders were synthesized by the sol–gel method using glycolic acid and poly(acrylic acid) as chelating agents.8,16 Fig. 2 shows the eVect of the calcination temperature on the Results and discussion lattice constant a of the same powders as shown in Fig. 1, obtained from the Rietveld refinement on the XRD data in Fig. 1 shows the X-ray diVraction (XRD) patterns of the LiMn2O4 powders calcined at various temperatures and the cubic unit cell of the LiMn2O4 powders. It is seen from the figure that the lattice constant increases almost linearly LiMn1.95Ni0.05O4 powders calcined at 800 °C for 10 h in air, where the molar ratio of glycine to total metal ions was 1.051.from 8.1992 to 8.2260 A° with increasing calcination temperature from 250 to 800 °C. It is speculated that the value of the The X-ray diVraction patterns for the powders calcined at 250 °C represent the slow appearance of low crystalline average oxidation state of manganese in the spinel phase is closely related to the lattice constant of the cubic unit cell.A LiMn2O4 spinel. Impurity peaks corresponding to Li2CO3 and MnCO3 are not observed, but are often found in other low lower calcination temperature results in a more oxidized manganese cation because manganese ions are stable preferen- temperature techniques. It was confirmed from the XRD patterns that the well-defined spinel LiMn2O4 phase was tially as Mn4+ at lower temperatures.22 For example, MnO2 with all Mn4+ transforms progressively into Mn2O3 with all formed over the whole calcination temperature range.For all powders, there is no (220) diVraction line (2h=30.4°) which Mn3+ for the binary manganese oxide system as the temperature increases. The atomic radius of Mn4+ (0.67 A° ) is smaller is generated by Li ions at 8a sites in the LiMn2O4 host, because the scattering factor of Li ions is very small.The diVraction than that of Mn3+ (0.72 A° ) and thus the lattice constant of the cubic unit cell of the spinel LiMn2O4 calcined at higher temperatures is larger than that of the spinel LiMn2O4 calcined at lower temperatures. The lattice constant of LiMn1.95Ni0.05O4 powders calcined at 800 °C is 8.2236 A° which is in agreement with the literature value of 8.228 A° for LiNi0.04Mn1.96O4.15 The substitution of manganese with divalent nickel increases the average oxidation state of manganese above 3.5 to keep electrical neutrality in the spinel structure and thus there are many Mn4+ cations, which decrease the lattice constant of the LiMn1.95Ni0.05O4 host structure.Fig. 3 shows scanning electron micrographs (SEM) of the powders prepared from the gel precursors having the molar ratio of glycine to metal ions of 1.051 as a function of temperature. The presence of loosely agglomerated spherical particles with average grain size 70 nm was observed from the powders calcined at 220 °C. For the powders calcined at 650 °C, the particle size increased to 100 nm.As calcination temperature was increased, growth kinetics were favored and thus agglomerated spherical particles changed to larger par- Fig. 1 X-Ray diVraction patterns of the LiMn2O4 powders calcined ticulates. When the gel precursors were heated at 800 °C, the at various temperatures and LiMn1.95Ni0.05O4 powders calcined at particle size increased to about 600 nm with a fairly narrow 800 °C for 10 h in air when the molar ratio of glycine to total metal ions was 1.051.particle-size distribution. 2400 J. Mater. Chem., 1998, 8(11), 2399–2404Fig. 5 X-Ray diVraction patterns of the LiMn2O4 powders prepared from the gel precursors having various molar ratios of glycine to total metal ions and calcined at 700 °C; (a) 1.0, (b) 1.5, (c) 2.0, and (d) 2.551.could be formed regardless of the molar ratio of glycine to Fig. 3 Scanning electron micrographs of the LiMn2O4 powders total metal ions tested. A close look at Fig. 5 reveals that the calcined at (a) 220 °C, (b) 500 °C, (c) 650 °C, and (d) 800 °C. diVraction peaks are sharper and that their intensity is increased with increasing glycine quantity, which indicates an Fig. 4 shows the X-ray diVraction patterns for the LiMn2O4 increase in the crystallinity of the spinel phase. In order to powders prepared from gel precursors having the molar ratio investigate the structural diVerences in the spinel phase at the of glycine to metal ions of 0.5 and 1.551. Both the LiMn2O4 various molar ratios of glycine to total metal ions, the Rietveld powders were calcined at 250 and 400 °C for 10 h in air.refinement was performed on the XRD data to obtain lattice Whereas the X-ray diVraction pattern for the powders preconstants. Fig. 6 shows the eVect of the molar ratio of glycine pared by the molar ratio of glycine to metal ions of 1.551 and to total metal ions on the lattice constant of the same powders calcined at 250 °C presents no diVraction peaks indicating an as shown in Fig. 5. With increasing glycine quantity the lattice amorphous phase, the powders prepared by the molar ratio constant and thus the crystallinity of the LiMn2O4 powders of glycine to metal ions of 0.551 and calcined at 250 °C shows increases linearly, although the extent of increase is not as impurity phases such as b-MnO2, Mn2O3, and Li2CO3 apart much as the case of increasing calcination temperature as from the LiMn2O4 spinel phase.For the powders prepared by shown in Fig. 1. the molar ratio of glycine to metal ions of 0.551 and calcined In order to investigate the morphological features of the at 400 °C, Mn2O3 peaks were still observed, though the pro- LiMn2O4 powders having diVerent molar ratio of glycine to portion of the LiMn2O4 spinel phase is increased.On the total metal ions, scanning electron microscopy (SEM) was contrary, the gel precursors prepared by the molar ratio of used for the powders prepared from the gel precursors having glycine to metal ions of 1.551 and calcined at 400 °C crysmolar ratios of glycine to metal ions of 0.5 and 2.051, and tallized into a phase-pure LiMn2O4 spinel phase without any calcined at 700 °C for 10 h in air as shown in Fig. 7. The development of impurity phases. surface of the powders with a molar ratio of glycine to total Fig. 5 demonstrates the X-ray diVraction patterns for the metal ions of 0.551 contained monodispersed spherical fine powders prepared by the molar ratio of glycine to metal ions particulates with an average particle size of about 200 nm.For of 1.0, 1.5, 2.0, and 2.551 calcined at 700 °C for 10 h in air. It the powders with a molar ratio of glycine to total metal ions was confirmed from the XRD patterns that the spinel phase Fig. 4 X-Ray diVraction patterns of the LiMn2O4 powders prepared from the gel precursors having the molar ratio of glycine to metal Fig. 6 EVect of the molar ratio of glycine to total metal ions on the ions of (a) 0.551 and calcined at 250 °C, (b) 1.551 and calcined at 250 °C, (c) 1.551 and calcined at 400 °C, and (d) 1.551 and calcined lattice constant of the LiMn2O4 powders calcined at 700 °C for 10 h in air.at 400 °C for 10 h in air. J. Mater. Chem., 1998, 8(11), 2399–2404 2401Li/polymer electrolyte/LiMn1.95Ni0.05O4 cell at the current densities of 0.15–2.0 mA cm-2.In this cell, the composite cathode was prepared from the LiMn1.95Ni0.05O4 powders calcined at 800 °C. The discharge capacity of the cell decreased very slowly with an increase in current density. For example, the cell delivered a capacity of 126, 122, and 116 mA h g-1 at current densities of 0.15, 0.5, and 1 mA cm-2 respectively. The cell showed an attractive capacity of 105 mA h g-1 at 1.5 mA cm-2 or 1.7 C rate.However, the discharge capacity of the cell abruptly decreased to 57 mA h g-1 at a current density of 2 mA cm-2 or 2.2 C rate. This may be due to the low conductivity of the polymer electrolyte compared to the Fig. 7 Scanning electron micrographs of the LiMn2O4 powders liquid electrolyte. When the current densities were lowered calcined at 700 °C when the molar ratio of glycine to metal ions was to 0.15, 0.5, and 1.0 mA cm-2 at the 61, 71, 81st cycle, (a) 0.5 and (b) 2.051. respectively, the discharge capacities increased to the original value.The observed cycling stability of the spinel of 2.051, it was observed that the particle size of the powders LiMn1.95Ni0.05O4 could be due to a small structural transition was 100 nm.The particle size of the former was two times in the powders, and good contacts among the composite smaller than that of the latter at the same calcination cathode constituents. temperature. Fig. 9(a) and (b) show the charge/discharge curves with the Increase of the crystallinity and decrease of the particle size number of cycles for the Li/polymer electrolyte/LiMn2O4 of the LiMn2O4 powders with the quantity of glycine used in and LiMn1.95Ni0.05O4 cells using the LiMn2O4 and preparing gel precursors can be explained as follows; the less LiMn1.95Ni0.05O4 powders calcined at 800 °C.The Li/polymer glycine used in preparing gel precursors, the shorter is the electrolyte/LiMn2O4 cell showed two-stage reduction and oxidistance between the Li and Mn cations, and thus the higher dation processes which are characteristic of the manganese is the probability of crystallization between the cations.oxide spinel structure.23,24 For the Li/polymer electrolyte/ However, the amount of heterogeneously distributed cations LiMn1.95Ni0.05O4 cell, the two-stage reduction and oxidation in the calcined powders increased as shown in Fig. 4. Therefore, processes became less distinct. This behavior suggests that the bigger particles with a low crystallinity are produced at lower glycine quantity. On the contrary, when the quantity of glycine is increased, the highly cross-linked gel precursors suppress the cation mobility and eVectively prevent the cations from contacting each other. Thus, the degree of segregation of the cations occurring during calcination is decreased, and the homogeneously distributed cations crystallize into the spinel phase.It has been reported that the combustion heat from the chelating agents increases the crystallinity of the particles, yielding fluVy LiMn2O4 powders which result from large void volumes generated by CO and CO2 during the combustion of the chelating agent.8,16 This can be supported by the observation that the materials become more ‘puVed up’ after calcination in the presence of larger amounts of glycine at the same calcination temperature, which results in a decrease in the particle size of the LiMn2O4 powders. Therefore, it can be concluded that the amount of glycine determines the crystallinity and particle size of the LiMn2O4 powders.Fig. 8 represents the specific discharge capacity of the Fig. 9 Cycling charge/discharge curves with the number of cycles Fig. 8 Variation of specific discharge capacity with number of cycles at various discharge current densities of the Li/polymer electrolyte/ of (a) the Li/polymer electrolyte/LiMn2O4 and (b) the LiMn1.95Ni0.05O4 cells. LiMn1.95Ni0.05O4 cell. 2402 J. Mater. Chem., 1998, 8(11), 2399–2404local distortion of the host structure resulting from the substitution of nickel ions may eliminate the small Li–Li repulsion energy diVerence between the half-filled 8a sites in Li0.5Mn2O4 and the completely filled sites in LiMn2O4. Fig. 10 demonstrates the variation of discharge capacity with the number of cycles for the Li/polymer electrolyte/ LiMn2O4 and LiMn1.95Ni0.05O4 cells.The initial capacity of the LiMn2O4 electrode delivered 145 mA h g-1. To our best knowledge, this is the highest value that has ever been reported in practice. The capacity slowly decreases with cycling and remained at 129 mA h g-1 at the 50th cycle. The discharge capacity of the LiMn1.95Ni0.05O4 electrode decreased more slowly with cycling and remained at 120 mA h g-1 at the 50th cycle.This suggests that the theoretical capacity fading of the Ni-doped spinel phases is attributed to a decrease in the amount of Mn3+, because the deintercalation of Li+ from the spinel structure must be electrically compensated for by the oxidation of Mn3+ to Mn4+ and thus, the capacity of the LiMn1.95Ni0.05O4 electrode was lower than that of the LiMn2O4 one.The cycling stability of the Ni-doped spinel Fig. 11 Ac impedance spectra of the Li/polymer electrolyte/ compared to the stoichiometric LiMn2O4 was due to the LiMn1.95Ni0.05O4 cell in fully charged state as a function of number suppression of the Jahn–Teller distortion in the spinel electrode of cycles. at the end of discharge since the M–O bonds for M=Ni, Co, or Cr are stronger than the Mn–O bond.9 Therefore, the Ni is associated with lithium ion diVusion through the dopant could enhance the stability of the octahedral sites in LiMn1.95Ni0.05O4 particle.24 The high-frequency semicircle is the spinel host structure.It should also be noted from Fig. 2 progressively increased with the increase in number of cycles that the lattice constant of the Ni-doped spinel is smaller than which indicates an increased interfacial resistance between that of the standard LiMn2O4.Another factor of the cycling polymer electrolyte and electrode (Li and oxide electrode). stability of the Ni-doped spinel is attributed to the volume The apparent chemical diVusivity of lithium ions in the porous changes during the intercalation and deintercalation reaction LiMn2O4 and LiMn1.95Ni0.05O4 electrodes with respect to the of lithium ions, which will be less than those of the stoichionumber of cycles was calculated using the relation (1)25 metric LiMn2O4.In order to investigate the capacity fading of Li/polymer electrolyte/LiMn1.95Ni0.05O4 cell with cycling, ac impedence D� Li+= pfTr2 1.94 (1) spectra with respect to the number of cycles were measured.Fig. 11 illustrates typical Nyquist plots obtained from the where fT is the frequency at which the impedance spectrum Li/polymer electrolyte/LiMn1.95Ni0.05O4 cell in a fully charged shows a transition from semi-infinite diVusion behavior to state with respect to the number of cycles. The impedance finite-length diVusion behavior.The average radius r of the spectra consist of one semicircle in the high and intermediate oxide was determined from scanning electron microscopic frequency range, a line inclined at a constant angle to the real observation. axis in the low frequency range of 5 Hz to 10 mHz, and a The calculated chemical diVusivities of lithium ions in the capacitive line due to the accumulation of lithium ions at the LiMn2O4 and LiMn1.95Ni0.05O4 electrodes are plotted against center of the oxide particle in the frequency range below 10 number of cycles in Fig. 12. The chemical diVusivities were mHz. The semicircle in the higher frequency range is related determined to be of orders of 10-10 to 10-11 cm2 s-1. The to the reactions at the interface of the polymer electrolyte/ chemical diVusivity within both electrodes decreases with electrode (Li and oxide electrode) and the inclined line in the increasing number of cycles.However, it should be noted that lower frequency range is due to Warburg impedance which Fig. 12 Variation of chemical diVusivity of the porous (a) LiMn2O4 Fig. 10 Variation of discharge capacity with the number of cycles of and (b) LiMn2.95Ni0.05O4 electrodes as a function of the number of cycles.(a) Li/polymer electrolyte/LiMn2O4 and (b) LiMn1.95Ni0.05O4 cells. J. Mater. Chem., 1998, 8(11), 2399–2404 2403the chemical diVusivity of lithium ions markedly decreases References with cycling for the LiMn2O4 electrode. It is speculated that 1 T. Ohuzuka, M. Kitagawa and T. Hirai, J. Electrochem. Soc., the decrease in chemical diVusivity could be attributed to the 1990, 137, 760.decreased number of vacant sites ailable for the diVusion of 2 D. Guyomard and J. M. Tarascon, Solid State Ionics, 1994, 69, lithium ions which resulted from volume change and 222. Jahn–Teller distortion of the spinel host structure. Liu et al. 3 R. J. Gummow, A. de Kock and M. M. Thackeray, Solid State Ionics, 1994, 69, 59.reported that the LiMn2O4 powders after 80 cycles had a 4 D. H. Jang, Y. J. Shin and S. M. Oh, J. Electrochem. Soc., 1996, tetragonal phase, which suggests the onset of the Jahn–Teller 143, 2204. eVect causes a severe structural distortion, leading to a decrease 5 Y. Xia, Y. Zhou and M. Yoshio, J. Electrochem. Soc., 1997, 144, in vacant sites.12 The capacity fading of the LiMn2O4 and 2593.LiMn1.95Ni0.05O4 electrodes appears to be related to the 6 D. Guyomard and J. M. Tarascon, Solid State Ionics, 1994, 69, 222. decrease in chemical diVusivity as well as the increase in 7 X. Qiu, X. Sun, W. Shen and N. Chen, Solid State Ionics, 1997, interfacial resistance between polymer electrolyte and electrode 93, 335. (Li and oxide electrode). The good capacity retention for the 8 Y.-K.Sun, Solid State Ionics, 1997, 100, 115. LiMn1.95Ni0.05O4 electrode compared to the stoichiometric 9 Li Guohua, H. Ikuta, T. Uchida and M. Wakihara, LiMn2O4 is attributed to the suppression of the Jahn–Teller J. Electrochem. Soc., 1996, 143, 178. distortion, smaller volume change of the unit-cell (smaller 10 R. Bittihn, R. Herr and D.Hoge, J. Power Sources, 1993, 43–44, 223. lattice constant) and higher chemical diVusivity in the 11 G. Pistoia and G. Wang, Solid State Ionics, 1993, 66, 135. LiMn1.95Ni0.05O4 electrode as mentioned above. 12 W. Liu, K. Kowal and G. C. Farrington, J. Electrochem. Soc., 1997, 143, 3590. 13 A. D. Robertson, S. H. Lu, W. F. Averill and W. F. Howard, Jr., J. Electrochem. Soc., 1997, 144, 3500. 14 T.Tsumura, A. Shimizu and M. Inagaki, J. Mater. Chem., 1993, Conclusions 3, 995. The spinel LiMn2O4 powders with submicron, monodispersed, 15 W. Liu, G. C. Farrington, F. Chaput and B. Dunn, J. Electrochem. Soc., 1996, 143, 87. and highly homogeneous particles were synthesized by a 16 Y.-K. Sun, I.-H. Oh and K. W. Kim, Ind. Eng. Chem. Res., 1997, sol–gel method using an aqueous solution of metal acetate 36, 4839.containing glycine as a chelating agent. While the crystallinity 17 A. Hooper and B. C. Tofield, J. Power Sources, 1984, 11, 33. and lattice constant of the LiMn2O4 powders were increased, 18 B. C. H. Steele, G. E. Lagos, P. C. Spurdens, C. Forsyth and A. D. the particle size of the LiMn2O4 powders was decreased with Foord, Solid State Ionics, 1983, 9 and 10, 391. 19 P. G. Bruce and F. Krok, Solid State Ionics, 1989, 36, 171. an increase in glycine quantity. Polycrystalline LiMn2O4 pow- 20 B. V. Ratnakumar, S. DiStefano and C. P. Bankston, J. Appl. ders calcined at 250–800 °C were found to be composed of Electrochem., 1989, 19, 813. very uniformly sized particulates with an average particle size 21 R. Koksbang, I. I. Olsen, P. E. Tonder, N. Knudsen and of 70–600 nm depending on the processing conditions. The D. Fauteux, J. Appl. Electrochem., 1991, 21, 301. initial capacity of the cell with the LiMn1.95Ni0.05O4 was lower 22 C. Masquelier, M. Tabuchi, K. Ado, R. Kanno, Y. Kobayashi, Y. Maki, O. Nakamura and J. B. Goodenough, J. Solid State than the cell with the stoichiometric LiMn2O4, but the cycle Chem., 1996, 123, 255. performance was improved at the expense of capacity. The 23 M. M. Thackery, W. I. F. David, P. G. Bruce and good capacity retention of the LiMn1.95Ni0.05O4 electrode J. B. Goodenough, Mater. Res. Bull., 1983, 18, 461. compared to the stoichiometric LiMn2O4 is attributed to the 24 Y.-M. Choi and S.-I. Pyun, Solid State Ionics, 1997, 99, 173. suppression of the Jahn–Teller distortion, smaller volume 25 B. E. Conway, J. Electrochem. Soc., 1991, 138, 1569. change of the unit-cell and higher chemical diVusivity of lithium ions. Paper 8/04483J 2404 J. Mater. Chem., 1998, 8(11), 2399–2404

ISSN:0959-9428    

DOI:10.1039/a804483j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Electrochemical sodium insertion/extraction in Na2(MoOPO4)2(HPO4)·yH2O (y=2, 0)† L. Mesonero Herrero,a,b M. E. Arroyo y de Dompablo,b M. J. Ruiz Arago�nb and E. Mora�n*b aLaboratorio Complutense de Altas Presiones (LCAP), Facultad de Ciencias Quý�micas, Universidad Complutense, 28040 Madrid, Spain bDepartamento de Quý�mica Inorga�nica, Facultad de Ciencias Quý�micas, Universidad Complutense, 28040 Madrid, Spain.E-mail: emoran@eucmax.sim.ucm.es Received 17th August 1998, Accepted 17th August 1998 The electrochemical sodium insertion and extraction of the phosphomolybdates Na2(MoOPO4)2(HPO4)·yH2O ( y=2, 0) is reported. Both compounds show a similar behaviour upon electrochemical sodium extraction, while the insertion reaction is notably diVerent for each host compound.During the charge/discharge of electrochemical cells the existence of new phases Na2+x(MoOPO4)2(HPO4)·2H2O with compositions -0.7<x<-0.4, and 0.75<x<0.9, as well as Na2+x(MoOPO4)2(HPO4) with -1<x<-0.75 and 2.6<x<3.2 has been detected. A member of each solid solution has been synthesised and preliminarily structurally characterised by powder X-ray diVraction.Although all of these new phosphomolybdates present a similar monoclinic structure, the unit cell volume increases progressively with the introduction of sodium and water in the tunnels. Magnetic susceptibility measurements have also been performed in order to follow the electrochemical process. Peascoe and Clearfield,9 shows a structure made up of layers Introduction of MoOPO4.The tetragonal MoOPO4 structure contains equal Since many phosphomolybdates have layer structures or open numbers of corner-sharing octahedra and tetrahedra; on the crystalline lattices they can undergo redox reactions and other hand, the O atom of the MoNO molybdenyl group also therefore are potential candidates to be used in electrochemical forms the long, nearly nonbonded interaction, with the Mo in devices such as batteries, displays and sensors.Such structures the next octahedron, and therefore, chains of MMoMOM are unlikely to be thermally stable under traditional high- with alternating long and short MoMO distances are genertemperature solid state conditions, so that new low-tempera- ated. The [(MoOPO4)2(HPO4)]- structure type is related to ture approaches need to be found.One of these is mild the MoOPO4 structure by replacing the MOM in the chain by hydrothermal synthesis,1,2 defined as a reaction occurring in HPO4. The 3-D structure consists of the MoOPO4-like layers an aqueous medium between 100 °C and the critical tempera- bonded together by hydrogenphosphate groups.The ture of water (Tc=374.12 °C) under autogenous pressure. By [(MoOPO4)2(HPO4)]- anionic framework can accommodate these means, quite often, laminar, tunnel or cage structures both organic and inorganic cations of varying size and shape, are produced. the cation variability being accommodated by suitable On the other hand, molybdenum phosphates involving orientation of the interlamellar phosphate groups.pentavalent molybdenum represent an interesting family When the cations are H3O+ and Na+,9 the compound has because of their catalytic properties. Until 1983, MoV could a body-centered tetragonal lattice with at#6.4 and ct#16 A° . be considered an unusual valence for molybdenum in oxides, The small a dimension results from the four-fold disorder of especially in phosphates since only two molybdenum(V) phos- the interlamellar phosphate groups with the 16 A° spacing phates were known:3,4 MoOPO4 and Mo2P4O15.However, in corresponding to a two layer sequence. When the cations are recent years numerous MoV phosphates have been disco- Cs+ and H3O+11 the structure is monoclinic with am#bm#9.1 vered,5–7 some of them only being accessible by hydrothermal and cm#16 A° , a diagonal cell am#atÓ2 and cm#ct being synthesis.8–13 needed to describe the structure.The phosphate matrix shows a great ability to stabilise Taking into account all these features, it seemed us quite pentavalent molybdenum in octahedral coordination forming possible that related phosphomolybdates Na2±x(MoOPO4)2 molybdenyl cations, linked by tetrahedral phosphate groups, (HPO4)·yH2O (y=2, 0) could be synthesised by sodium contrary to pure octahedral structures for which such isolated insertion/extraction electrochemical routes.In the present con- MoV species are very rarely observed. In addition, for phospho- tribution, we report such a synthesis as well as the preliminary molybdates the Mo–O bond is oV-centred, so that the corre- structural and magnetic characterisation of these new phossponding oxygen apex is systematically free.As a result, the phomolybdates. ‘MoPO’ framework becomes more flexible, allowing tunnel and cage structures to be synthesised. Because of its open structure, and the pentavalent oxidation state of Mo cations, Experimental these materials seem to be good candidates to undergo insertion–extraction reactions.Synthesis of starting compound We have been applying hydrothermal techniques for the Na2(MoOPO4)2(HPO4)·2H2O was synthesised by hydrother- synthesis of materials similar to the title phosphomolybdates. mal treatment of Na2CO3, MoO3 , Mo, H3PO4 (85%) and The compound Na2(MoOPO4)2(HPO4)·2H2O, discovered by H2O in a mole ratio of 25150.055205200 at 250 °C in a similar manner, although not exactly the same, as used by Peascoe and Clearfield.9 The reaction was carried out in Teflon lined †Basis of the poster presentation given at Materials Chemistry stainless steel containers at autogenous pressure for 96 h Discussion No. 1, 24–26 September 1998, ICMCB, University of Bordeaux, France. followed by slow cooling to 150 °C at ca. 1°C h-1.The J. Mater. Chem., 1998, 8(11), 2405–2410 2405resulting yellow powder was washed several times with water, rinsed with acetone, and dried in a desiccator at ambient temperature. The anhydrous compound, Na2(MoOPO4)2(HPO4) was obtained by thermal treatment of Na2(MoOPO4)2 (HPO4)·2H2O at 250 °C during 24 h under vacuum. The resulting green sample was held under an argon atmosphere to avoid the reabsorption of water.In order to evaluate the amount of water lost, the same synthesis procedure was performed in a SEICO 320U thermobalance. Electrochemical synthesis of Na2±x(MoOPO4)2(HPO4)·yH2O (y=2, 0) Electrochemical sodium insertion and extraction reactions from the starting materials were carried out using a Swageloktype cell bearing metallic sodium as the anode.For the positive electrode a mixture of the corresponding phosphate, carbon black and ethylene–propylene–diene terpolymer (EDPTP) in a 79.552050.5 ratio was compresed in a 5 mm diameter pellet Fig. 1 X-Ray diVraction patterns of (a) Na2(MoOPO4)2 of approximately 25 mg. For the electrolyte a 1 mol dm-3 (HPO4)·2H2O and (b) Na2(MoOPO4)2(HPO4). solution of NaClO4 in propylene carbonate (PC) was used. After assembling the cells in an argon filled glove box, they Electrochemical sodium extraction/insertion were connected to a multichannel galvanostatic–potentiostatic system of the ‘MacPile’ type.Na2-x(MoOPO4)2(HPO4)·2H2O and Na2-x(MoOPO4)2- The electrochemical measurements were performed in a (HPO4). In order to explore the formation of new stepwise potentiostatic mode with a scan rate of ±10 mV h-1.Na2-x(MoOPO4)2(HPO4)·2H2O phases a cell of configur- The chronoamperometry at each potential level was recorded ation sodium|electrolyte|Na2(MoOPO4)2(HPO4)·2H2O was with a resolution of 0.001 mA h-1. charged up to 4 V vs. Na+/Na, as limited by the stability of the electrolyte. The variation of the cell voltage during the Preliminary structural characterization charge process vs.the amount of extracted sodium is shown in Fig. 2(a). At the final voltage, 4 V, the composition of the X-Ray powder diVraction patterns of the synthesised active material Na2-x(MoOPO4)2(HPO4)&middosponds compounds were collected using a D-501 power diVraction to the extraction of 0.68 sodium ions from the starting material.system, operating at 40 kV and 30 mA with monochromatic Preliminary information about the mechanism of the extraction Cu-Ka radiation (1.5406 A° ). The scan range was 10<2h<37° process is obtained from the incremental capacity curve, dx/dV with step size of 0.04 and counting time of 14 s. also plotted in Fig. 2(a). This curve exhibits a broad minimum For dehydrated and electrochemically synthesised comat ca. 3.6 V vs. Na+, indicating that a phase transition occurs pounds, the patterns were collected under an argon atmosphere at this voltage during the extraction process. using a hermetic closed sample holder containing a beryllium The nature of this phase transition can be clarified from the window. By using this technique the 2h scan was limited variation of the cell current intensity vs.time.14 In this way, below 37°. the corresponding chronoamperogram, shown in Fig. 2(b), The AFFMA program was used in order to index the with a quite diVerent current decay in both sides of the diVraction patterns and to calculate lattice parameters. minimum, is characteristic of a first order phase transition.15 From this experiment we can now infer that for the composi- Magnetic measurements tion 0<x<0.4 the system is in a two-phase region where the initial compound and a new solid solution coexist.Therefore, The magnetic moments of the samples were measured by a Na2 -x(MoOPO4)2(HPO4)·2H2O solid solution exists at SQUID magnetometry. The signal was registered using a field least in the compositional range 0.4<x<0.68.With the of 0.5 T. After zero field cooling, a magnetic field was applied aim of studying this new solid solution phase, the pellet at 4.2 K, and the measurements were performed up to 200 K. of the final product Na1.32(MoOPO4)2(HPO4)·2H2O was removed from the cell and used for preliminary structural Results characterisation. In order to study the reversibility of the extraction process, Starting materials another cell of the same configuration was charged and consecutively discharged down to the initial open circuit Fig. 1 shows the powder X-ray diVraction patterns of Na2(MoOPO4)2(HPO4)·2H2O.All the Bragg maxima can be voltage value and results are presented in Fig. 2(c) as voltage– composition and intensity–voltage representations (insert), indexed based on a tetragonal cell with parameters a=b= 6.43(1) A° and c=15.93(2) A° [V=660.5(3) A° 3] in the space respectively.From both plots, it is clear that the material Na2(MoOPO4)2(HPO4)·2H2O can reversibly undergo sodium group I4/mmm as previously reported by Peascoe and Clearfield.9. extraction reaction in the studied voltage window. Additionally, the reversibility of the reaction gives us an Concerning the water-free compound, thermogravimetric analysis results allow us to ensure that two water molecules idea of the close structural relationships between the two phosphomolybdates Na2(MoOPO4)2(HPO4)·2H2O and are lost upon heating Na2(MoOPO4)2(HPO4)·2H2O at 250 °C under vacuum.As shown in Fig. 1, the powder X-ray diVrac- Na1.32(MoOPO4)2(HPO4)·2H2O which is confirmed by XRD.This experiment was repeated but using the anhydrous tion pattern of Na2(MoOPO4)2(HPO4) can be indexed based on a monoclinic cell with parameters a=9.20(1), b=8.98(2), compound Na2(MoOPO4)2(HPO4) as the active material. Fig. 3(a) and (b) show the results of charging a cell of c=15.71(3) A° and b=90.7(2)° [V=1298.9(7) A° 3] and was refined to Rw=0.0027.This cell was confirmed using selected configuration sodium|electrolyte|Na2(MoOPO4)2(HPO4) up to 4 V vs. Na+/Na. As for Na2-x(MoOPO4)2(HPO4) the area electron diVraction experiments. 2406 J. Mater. Chem., 1998, 8(11), 2405–2410Fig. 2 Electrochemical extraction study of Na2(MoOPO4)2 (HPO4)·2H2O. (a) Representation of voltage and incremental capacity Fig. 3 Result of the first charge of a cell sodium| curves vs.the degree of extracted sodium. (b) Time dependence of the NaClO4+PC|Na2(MoOPO4)2(HPO4). (a) Representation of voltage current. (c) Consecutive charge and discharge cicles. and incremental capacity curve vs. the degree of deinsertion. (b) Variation of the intensity current with time during the first charge of extraction reaction proceeded through a first order transition the cell.(c) Charge and discharge plots. which in this case leads to the formation of a solid solution Na2-x(MoOPO4)2(HPO4) with 0.75<x<1. The upper limit of this new solid solution, Na(MoOPO4)2(HPO4) was used compound. Therefore, it seems that in the studied voltage range the molecules of water are not disturbing the removal for structural characterisation.To study the reversibility of the extraction reaction leading of sodium atoms from the structure. Moreover, the general features of the extraction reaction in both compounds are to the solid solution Na2-x(MoOPO4)2(HPO4) with 0.75<x<1 another cell of the same configuration was equivalent, independently of the water content. charged and discharged in the voltage range 3.3–4.0 V.As can be seen in Fig. 3(c) the voltage–composition curves for the Na2+x(MoOPO4)2(HPO4)·2H2O and Na2+x(MoOPO4)2- (HPO4). In the opposite direction new, sodium richer phases, charge and discharge processes have similar paths and shapes, which means that the extraction reaction is reversible. This Na2+x(MoOPO4)2(HPO4)·yH2O (y=2, 0) can also be obtained through the electrochemical route.With this aim is also noticeable in the voltage–intensity representation [Fig. 3(c), insert]. sodium cells using the phosphomolybdates as active material were discharged down to 1 V vs. Na+/Na. If now we compare the behaviour of Na2(MoOPO4)2 (HPO4)·2H2O and Na2(MoOPO4)2(HPO4), the amount of Fig. 4(a) shows the voltage–composition curve obtained from the discharge of a cell sodium|electrolyte| extracted sodium is only slightly higher in the water free J.Mater. Chem., 1998, 8(11), 2405–2410 2407Fig. 4 Result of the first discharge of a sodium| NaClO4+PC|Na2(MoOPO4)2(HPO4)·2H2O cell. (a) Plot of voltage Fig. 5 Electrochemical sodium insertion in Na2(MoOPO4)2(HPO4). and incremental capacity curve vs. composition. (b) Time dependence (a) Representation of voltage and incremental capacity curve vs.the of the current with 10 mV voltage steps. amount of inserted sodium and (b) variation of the intensity current with time during the first discharge of the cell. Na2(MoOPO4)2(HPO4)·2H2O and for a better visualization posing processes. Nevertheless, a Na2+x(MoOPO4)2(HPO4) of the involved processes the derivative curve, dx/dV, is also solid solution exists in the composition range 2.6<x<3.2, and plotted.In the derivative curve five minima consecutively a representative example, Na4.7(MoOPO4)2(HPO4), has been labelled as I–V appear, indicating that the insertion reaction synthesised and used for structural characterisation. involves five phase transitions, which in nature could, in principle, be investigated through the respective chronoamper- Preliminary structural characterization of the new ograms.However, as can be seen in Fig. 4(b), for processes Na2±x(MoOPO4)2(HPO4)·yH2O (y=2, 0) phases I–III the data are not suYciently well resolved so as to ensure the order of the phase transitions.16 For the phase transitions The X-ray diVraction patterns of the new sodium inserted and IV and V, the variation of the intensity current vs.time is extracted compounds obtained from water containing material characteristic of a first order transition.14 This means that the are plotted in Fig. 6, while the patterns corresponding to the region in between both first order transitions is a single phase water free phosphomolybdate are shown in Fig. 7.All patterns Na2+x(MoOPO4)2(HPO4)·2H2O, for which approximate can be indexed based on a monoclinic cell (am#bm#atÓ2 and composition limits, as estimated from Fig. 4(a), are b<90°), which is diagonal with regard to the former tetragonal 0.75<x<0.9. To study the structure of this solid solution a cell; corresponding to the starting, water-containing phosphocell of the same configuration was discharged limiting the molybdate.This modification of the symmetry is due to a degree of insertion up to x=0.9, and the pellet of the phase reorientation of the interlayer phosphate groups which occurs, Na2.9(MoOPO4)2(HPO4)·2H2O was studied by XRD. either by changing the sodium content or by elimination The result of the experiment carried out using of water.Na2(MoOPO4)2(HPO4) as active material is shown in Fig. 5. Since no large diVerences were observed in either the position During the first discharge of this cell, the material can accept or intensity of the reflections with sodium content, it seems 3.2 sodium ions in its structure, which is more than twice that all the Na2±x(MoOPO4)2(HPO4)·yH2O (y=0, 2) phases the amount inserted in the compound Na2(MoOPO4)2 are isostructural. However the unit cell parameters (Table 1) (HPO4)·2H2O.In this case, and contrary to what is seen in indicate that the introduction of a higher amount of sodium the extraction process, the behaviour of both compounds is cations produces an expansion of the unit cell. Clearly all the quite diVerent. Obviously, water removal from the tunnel phases have the same framework structure.Further investiresults in new available positions for inserting sodium: the gation will be needed in order to fully determine the structure lower the water content, the higher the capacity becomes. of these new phosphomolybdates. Concerning the processes involved during the insertion reaction in Na2(MoOPO4)2(HPO4), only one phase transition has Magnetic properties been detected in the incremental capacity curve.However, the minima in the related chronoamperogram [Fig. 5(b)] display The process of insertion and extraction in the hydrated material can be followed by magnetic susceptibility measurements. The associated shoulders that could be produced from superim- 2408 J. Mater. Chem., 1998, 8(11), 2405–2410Fig. 8 1/x vs. temperature for the Na2+x(MoOPO4)2(HPO4)·2H2O compounds with (a) x=0.9, (b) x=0 and (c) x=-0.68. Fig. 6 X-Ray diVraction patterns of the Na2+x(MoOPO4)2 (HPO4)·2H2O compounds with (a) x=-0.68, (b) x=0 and (c) x=0.9. 1.65 mB per Mo atom and the agreement with the theoretical value taking into account the individual contributions of MoV and MoVI is almost perfect. Fig. 8 also shows the 1/x vs.T plot for a sodium inserted material corresponding to a reduced phase the stoichiometry of which, as deduced from the voltage–composition measurements, is 2.9 sodium ions per formula unit, which would correspond to 0.9 MoIV and 1.1 MoV per formula unit. The eVective spin only magnetic moment calculated from this plot is higher than found before the insertion, meff=2.31 mB per Mo atom and the agreement with the theoretical value taking into account the individual contributions of MoIV and MoV is also very good. Concluding remarks This contribution is an example of how a sodium phosphomolybdate obtained by hydrothermal synthesis can be used as a matrix for both intercalation/extraction electrochemical reactions.As we have shown, the combination of these two soft Fig. 7 X-Ray diVraction patterns of the compounds Na2+x(MoOPO4)2(HPO4) with (a) x=-1, (b) x=0 and (c) x=2.7. chemistry techniques opens exciting avenues to obtain new metastable compounds, the properties of which can be quite diVerent from the original. Table 1 Cell parameters for Na2+x(MoOPO4)2(HPO4)·2H2O phases x ya/A° b/A° c/A° b/ ° V/A° 3 Rw This work has been possible thanks to a Complutense grant awarded to M.E.A.and financial support from the Spanish -0.68 2 9.09(2) 8.92(2) 16.02(5) 90.4(2) 1299.0(9) 0.0042 0 2 9.09(1) 9.09(1) 15.93(2) 90 1320.8(3) 0.0022 Ministery of Education (CICYT, Project MAT95-0809). 0.9 2 9.09(4) 9.01(3) 16.14(6) 90.5(3) 1322(2) 0.0050 -1 0 9.15(1) 8.89(1) 15.67(2) 91.1(1) 1274.9(5) 0.0019 0 0 9.20(1) 8.98(2) 15.71(3) 90.7(2) 1298.9(7) 0.0031 References 2.7 0 9.31(3) 8.82(4) 15.90(5) 90.8(3) 1304(1) 0.0057 1 A.Rabenau, Angew. Chem., Int. Ed. Engl., 1985, 24, 1026. 2 M. S. Whittingham, Curr. Opin. Solid State Mater. Sci., 1996, starting material, where MoV, a d1 paramagnetic cation is 1, 227. 3 P. Kierkegaard and J. M. Longo, Acta Chem. Scand., 1970, 24, present, shows a typical Curie–Weiss behaviour down to 4.2 K, 427.as can be seen in Fig. 8 where 1/x vs. T has been plotted. The 4 L. K. H. Minacheva, A. S. Antsyshkina, A. V. Lavrov, eVective spin only magnetic moment calculated from this plot V. G. Sakharova, V. P. Nikolaev and M. A. Porai-koshits, Russ. is 1.84 mB per Mo atom, which is close to the theoretical value J. Inorg. Chem., 1979, 24, 51. (1.73 mB).For sodium extracted materials, the oxidation to 5 R. C. Haushalter and L. A. Mundi, Chem. Mater., 1992, 4, 31. MoVI, a d0 diamagnetic cation, can also be followed by these 6 A. Leclaire, T. Hoareau, M. M. Borel, A. Grandin and B. Raveau, J. Solid State Chem., 1995, 114, 543. means. Curie–Weiss behaviour is also observed in the 1/x vs. 7 S. Ledain, A. Leclaire, M. M. Borel and B. Raveau, J. Solid State T plot corresponding to these materials. As an example, Fig. 8 Chem., 1997, 132, 249. shows the plot of an oxidized phase whose stoichiometry, as 8 L. A. Mundi and R. C. Haushalter, Inorg. Chem., 1990, 29, 2879. deduced from the voltage–composition measurements, is 1.32 9 R. Peascoe and A. Clearfield, J. Solid State Chem., 1991, 95, 289. sodium per formula unit, corresponding to 0.68 MoVI and 10 R. Peascoe and A. Clearfield, J. Solid State Chem., 1991, 95, 83. 1.32 MoV. The eVective spin only magnetic moment calculated 11 L. A. Mundi, l. Yacullo and R. C. Haushalter, J. Solid State Chem., 1991, 95, 283. from this plot is lower than that before the extraction, meff= J. Mater. Chem., 1998, 8(11), 2405–2410 240912 H. E. King, L. A. Mundi, K. G. Strohmaier and R. C. Haushalter, 15 G. B. M. Vaughan, M. Barral, T. Pagnier and Y. Chabre, Synth. Met., 1996, 77, 7. J. Solid State Chem., 1991, 92, 1. 13 A. Leclaire, C. Biot, H. Rebbah, M. M. Borel and B. Raveau, 16 A. H. Thompson, J. Electrochem. Soc., 1979, 126, 608. J. Mater. Chem., 1998, 8, 439. 14 Y. Chabre, NATO ASI Ser., 1993, 305, 181. Paper 8/06498I 2410 J. Mater. Chem., 1998, 8(11), 2405–2410

ISSN:0959-9428    

DOI:10.1039/a806498i

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Ferromagnetism and magnetoresistance in monolayered manganites Ca2-xLnxMnO4 A. Maignan,a C. Martin,a G. Van Tendeloo,b M. Hervieua and B. Raveaua aLaboratoire CRISMAT, UMR 6508 associe�e au CNRS, ISMRA et Universite� de Caen, 6 Boulevard du Mare�chal Juin, 14050 Caen Cedex, France bEMAT, University of Antwerp (RUCA), Groenenborgerlaan 171, B-2020 Antwerpen, Belgium Received 10th July 1998, Accepted 26th August 1998 Ferromagnetism (Tc) and negative magnetoresistive properties (maximum at 30 K) are observed in the monolayered manganites Ca2-xLnxMnO4 (Ln=Pr, Sm, Gd, Ho and 0<x0.20) despite their pure bidimensional character.A detailed structural study was carried out using X-ray diVraction, electron diVraction, and high resolution electron microscopy.This shows that they exhibit an orthorhombic cell, with a#b#apÓ2, c#12 A° and Aba2 or Abma as possible space groups. In all these oxides, (001)-type twinning is observed, on a unit cell scale, creating in this way a local periodicity of 24 A° . In the x=0.08 doped samples, it is observed that the microstructural state is strongly dependant on the synthesis process but it does not aVect the magnetotransport properties.Introduction Experimental The manganites Ca2-xLnxMnO4 were investigated for Ln= Numerous investigations performed recently on the Pr, Sm, Gd, Ho and for 0x0.20, such that the electron manganites Ln1-xAxMnO3 with the perovskite structure have concentration is not too high. The compounds were prepared shown their great ability to develop ferromagnetic metallic from stoichiometric mixtures of CaO, Ln2O3 or Pr6O11 and properties, allowing colossal magnetoresistance (CMR) to be MnO2 first heated at 1000 °C for 12 h, pressed into bars, generated.Such properties originate from double exchange sintered at 1200 °C, then at 1500 °C for 12 h and finally cooled (DE) interactions between Mn3+ and Mn4+ species.1–5 down to room temperature at a rate of 1 °Cmin-1.A second An important challenge is to modify the magnetoresistive process was used for one of the compounds, Ca1.92Pr0.08MnO4, properties of the manganites by introducing rock salt type in order to check the influence of the thermal treatment on layers between the octahedral layers, leading to layered mangathe microstructural state and the magnetic properties.It partly nites (Ln,A)n+1MnnO3n+1. In this respect, the study of the diVers from the above one only by the cooling rate: from 1500 n=1 member of this series, which exhibits the well known to 800 °C at 5 °Cmin-1 and then quench to room temperature. K2NiF4 structure is of great interest since it exhibits isolated The purity and homogeneity of the sample were checked by [MnO2]2 layers.Consequently, its bidimensionality should X-ray diVraction (XRD) and electron diVraction (ED), reduce the 3d-bandwidth with respect to the 3D manganites, coupled with energy dispersive spectroscopy (EDS). The XRD so that the hole mobility is decreased. From these considerpattern was collected by means of a Philips diVractometer ations, a weakening of the DE interactions leading to the using Cu-Ka radiation, in the angular range 102h/°110, disappearance of CMR properties can be expected.The study by steps of 0.02°. of La1-xSr1+xMnO4 performed by Rao et al.6,7 is of great The electron diVraction study was carried out with JEOL interest. It shows that this compound is insulating and does 200CX and 2010 electron microscopes, working at 200 kV.not exhibit any ferromagnetic ordering but shows a spin glass The high resolution electron microscopy study was carried out transition around 20 K. Recently Moritomo et al.8,9 confirmed with a TOPCON electron microscope, having a point reso- the existence of a spin glass phase for this compound and lution of 1.8 A°. The samples were prepared by crushing the showed the absence of magnetoresistance properties, in crystals in alcohol and the small flakes were deposited on a agreement with its bidimensional character.holey carbon film, deposited on a Cu grid. The three Although the above results strongly support the absence of microscopes are equipped with EDS analysers. CMR eVect in K2NiF4 type structure, owing to its bidimen- Magnetization was measured with a vibrating sample sionality, the possibility of inducing ferromagnetism in such magnetometer.The samples were first zero field cooled down oxides, by decreasing the thickness of the rock salt layer is to 5 K and then a magnetic field of 1.45 T was applied. The worthwhile investigating. For this reason we have explored data were collected upon warming up to 300 K.AC susceptibil- the manganites Ca2-xLnxMnO4, synthesised for the first time ity was registered with an AC-DC Quantum Design SQUID by Daoudi and Le Flem;10 the small size of Ca2+ and Ln3+ magnetometer. The resistance measurements were performed cations (Ln=Pr, Nd, Sm, Gd) should indeed allow DE by a four-probe technique. Four contacts of indium were interactions to be enhanced.This investigation was also motiv- deposited on bars by using ultrasonic waves. The data were ated by the fact that the electron doped tridimensional perov- registered during cooling from 300 to 5 K in 0 and 7 T. skites Ca1-xLnxMnO3 exhibit CMR properties.11–13 In the present paper we show the existence of ferromagnetism and of negative magnetoresistive properties in the monolayered Results and discussion manganites Ca2-xLnxMnO4 in spite of their bidimensional Evidence for ferromagnetism and magnetoresistance eVect character. A detailed structural study shows an orthorhombic symmetry and indicates that the existence of extended defects The evolution of the resistivity of the manganites Ca2-xLnxMnO4 vs.temperature in absence of magnetic field does not aVect their magnetotransport properties.J. Mater. Chem., 1998, 8(11), 2411–2416 2411Fig. 1 T-dependent resistivity (r) ofCa2-xPrxMnO4 samples registered in earth magnetic field; x values are labelled on the graph. is very similar whatever the nature of the lanthanide Ln=Pr, Sm, Gd or Ho. They all exhibit a semiconducting behaviour as illustrated for the praseodymium phases Ca2-xPrxMnO4 (Fig. 1). In the 200–250 K temperature domain, no inflection, which would correspond to a signature of charge ordering is observed on the r(T) curves, in contrast to La0.5Sr1.5MnO4.14 The most important point is related to the shape of the r(T ) curves for low electron concentrations (x=0.05 to 0.08), at low temperature. For these low x values a kind of plateau is observed between 50 and 20 K, followed by an upturn at the lower temperature, suggesting a re-entrant transition from an insulating to a semimetallic state.The magnetization, registered under 1.45 T, vs. temperature [Fig. 2(a)] shows that the doping of Ca2MnO4 with electrons Fig. 2 (a) T-dependent magnetization (M) for the series Ca2-xPrxMnO4 (1.45 T); (b) ac-x curves registered with hac=10 Oe; induces significant ferromagnetic interactions.Starting from frequencies are labelled on the graph. the antiferromagnetic Ca2MnO4, the magnetic moment at 4.2 K increases as x increases, reaches 0.46 mB per mol of Mn for x=0.06, remains practically constant in the range for x=0.20 [Fig. 3(d)]. The magnetoresistivity of these samples has also been confirmed from the r(H)T curves.An example 0.06x0.10, and finally decreases rapidly for x>0.10, so that the ferromagnetic interactions for x=0.20 have disap- is given for Ca1.92Pr0.08MnO4 [inset of Fig. 3(b)]. These curves exhibit the reversibility of the magnetoresistance eVect. peared. Note, that the shape of the M(T) curve for x= 0.06–0.10, is diVerent from that observed for a classical Very similar results are observed for all diVerent lanthanides of the series Ln=Pr, Sm, Gd, Ho.For each, the highest ferromagnetic transition, i.e. it is very smooth, in agreement with the fact that the magnetic moment at low temperature is ferromagnetic interactions are observed in the range x= 0.08-0.10. They all exhibit a smoothM(T) curve as illustrated far below the theoretical value (3.1 mB for x=0.10) characteristic of a perfect ferromagnetic However, in a small ac- in Fig. 4 for the oxides Ca1.92Ln0.08MnO4. However, the most interesting result deals with the fact that the magnetic moment field of 10 Oe, the ferromagnetic transition is sharp and this x¾(T) curve allows one to determine the Curie temperature at 4.2 K increases linearly as the size of the lanthanide decreases, starting from 0.46 mB for Ln=Pr going through TC=110 K [Fig. 2(b)]. Moreover, the strong frequency dependence of the data below 105 K, together with the existence of 0.56 mB and 0.64 mB for Ln=Sm and Gd, respectively, and reaching finally 0.70 mB for Ln=Ho. This size eVect strongly a peak at 105 K seems to indicate that the sample must be considered as a cluster glass rather than a ferromagnet, as supports our hypothesis that the thickness of the rock salt layer significantly influences the ferromagnetism in this one- already reported for the Ca1-xSmxMnO3 perovskite for x0.12.15 layered structure.Doping with thorium (Th4+) also indicates that the electron concentration plays a prominent role for the The above results, existence of a ferromagnetic component and evidence for a re-entrant transition on the r(T) curves, appearance of ferromagnetism.One indeed observes that the maximum magnetic moment of 0.44 mB, is obtained for suggest the possibility of finding magnetoresistive properties for 0.06x0.12. The r(T) curves (Fig. 3) registered under the oxide Ca1.96Th0.04MnO4 (Fig. 4), corresponding to the same electron concentration as the lanthanide based manga- 7 T support this viewpoint.The largest negative magnetoresistance is observed for x=0.06 and 0.08 samples [Fig. 3(a), (b)] nites Ca1.92Ln0.08MnO4, assuming the tetravalence of thorium. For Ca1.92Th0.08MnO4, the magnetic moment has already which exhibit practically identical r(T ) curves with a maximum resistivity ratio (RR=r0/r7T), RR=2.7 at 40 K i.e.a mag- decreased down to 0.05 mB. The increase of ferromagnetic interactions is not suYcient netoresistance MR=-64%, with MR=(RH-R0)/R0. For x= 0.12 [Fig. 3(c)] the negative magnetoresistance at 40 K is still to increase significantly the magnetoresistance as the size of the lanthanide decreases. This is illustrated by comparing the similar, MR=-50% at 40 K.This maximum magnetoresistive eVect for 0.06x0.12 is in agreement with the ferromagnet- r(T) curves of the manganites Ca1.92Ln0.08MnO4, registered under 0 and 7 T (with Ln=Sm and Ho in Fig. 5). One ism which is maximum for this composition range. Then, the magnetoresistance decreases rapidly as x increases, as shown observes similar shapes of the r(T) curves, characterised by a 2412 J.Mater. Chem., 1998, 8(11), 2411–2416Fig. 4 M(T ) curves for the oxides Ca1.92Ln0.08MnO4 with Ln=Pr, Sm, Gd and Ho and for Ca1.96Th0.04MnO4 (Th curve). Fig. 5 r(T ) curves for two Ca1.92Ln0.08MnO4 samples; (a) Ln=Sm and (b) Ln=Ho. Structure and defects—relations with magnetoresistance properties The main issue concerning the monolayered manganites Ca2-xLnxMnO4, is the origin of their magnetoresistance properties.Such properties may be intrinsic, or due to extended Fig. 3 r(T ) curves registered during cooling from 300 K down to 5 K defects or inhomogeneities.16 In order to answer this question in 0 and 7 T. The resistivity ratio r(T)H=0/r(T)H=7T is also shown a transmission electron microscopy (TEM) study is necessary. (right y-axis); (a) Ca1.94Pr0.06MnO4, (b) Ca1.92Pr0.08MnO4, (c) For comparison, the pure Ca2MnO4 has been studied first. Ca1.88Pr0.12MnO4 and (d) Ca1.80Pr0.20MnO4.Inset of (b): isothermal magnetoresistance [r(H) curves] registered for T=10 K, and T=50 K. Remarkably enough, we could not confirm the tetragonal structure previously described.17,18 We had to lower the symmetry to orthorhombic in order to index all diVraction patterns in a unit cell with lattice parameters a#5.2 A° , b#5.2 A° and re-entrant transition around 40 K, and an upturn at 20 K.The resistivity ratio r0/r7T at 40 K is very similar, i.e. is ca. 3 for c#12.1 A° . DiVraction evidence is presented in Fig. 6. Along the [001] zone [Fig. 6(a)], it is clear that the intensity of the Sm [Fig. 5(a)] and Ho [Fig. 5(b)]. Note however that the maximum around 40 K is more clearly observed for Sm reflections marked by two white triangles is not equal, violating the tetragonal symmetry; the very weak one belongs to a 90° [Fig. 5(a)] than for Ho [Fig. 5(b)] or for Pr [Fig. 3(b)]. J. Mater. Chem., 1998, 8(11), 2411–2416 2413along complex [hk0] zones [such as the zone in Fig. 7(a)] where additional weak reflections are clearly present in one row out of two.The pattern of Fig. 7(a) is again not compatible with a tetragonal symmetry. It can be interpreted on the basis of the superposition of the [1290] and [2190] zones, suggesting that twinning domains are systematically present in the crystallites. The 420 and 240 reflections are superposed due to the pseudotetragonal character of the cell (a#b); the weaker reflections [see the rows of dots indicated by arrows in Fig. 7(a)] are generated by the perovskite cell distortion (a#b#apÓ2). The A-type lattice implies the existence of the 120 and 122 reflections in the [2190] zone, the 121 being forbidden but the 211 is observed in the [1290] zone. In the bright (BF) and dark (DF) field images, given in Fig. 7(b) and (c), respectively, the basic (002) lattice fringes, separated by 6 A° are clearly resolved. Dark field imaging using several of these reflections produces images, with the 6 A° spaced fringes but where superimposed darker and lighter bands are visible. The width of these bands is hardly a few unit cells wide; they are the signature of the two orthorhombic variants, rotated 90° around the c-axis.Sometimes however, as in the area indicated A in Fig. 7(c), the twinning is locally periodic every 12 A° , creating in this way a local unit cell of 24 A° . The fact that this twinning, every 12 A° , is often on a unit cell scale, generating a doubling of the c parameter (24 A° ) is to compare with the similar supercell ‘apÓ2×apÓ2×2c’ observed by Leonowicz et al.17 on single crystals.Despite that the electron diVraction allows one to reject the hypothesis of the formation of such a double cell in our sample, the DF observations show a close relationship Fig. 6 Ca2MnO4: (a) [001], (b) [110] and (c) [100] ED patterns. between the two structures. In fact, by applying the above periodic twinning mechanism to the orthorhombic Aba2 cell (present work) with a#b#apÓ2, c#12 A° , we can create a P- oriented domain.The weak reflections h00 and 0k0 (h, k= type orthorhombic double cell with a#b#apÓ2, 2c#24 A° 2n+1) are present in this section due to double diVraction; and space group Pba2. If we consider the atomic positions of this is clear from the [100] section in Fig. 6(c). The [110] zone the as-built structure, it appears that simply by constraining is shown in Fig. 6(b). All these diVraction data show that the the y coordinate to the particular value y=1/2-x, we will conditions limiting the reflection are hkl5k+l=2n, 0kl5k=2n generate a tetragonal cell with the space group I41/acd, which and h0l h=2n and are compatible with space group Aba2 is identical with that previously proposed.17,18 Structure (no. 41) or Abma (no. 64). calculations were therefore carried out in the Aba2 and Further convincing evidence for the orthorhombic symmetry comes from tilting about the c* axis and dark field imaging I41/acd space groups from the powder XRD data for Fig. 7 Ca2MnO4: (a) enlarged ED pattern showing that the [1290] and [2190] zones are systematically superimposed, as the result of twinning phenomena; (b) bright and (c) dark field corresponding images. 2414 J. Mater. Chem., 1998, 8(11), 2411–2416Fig. 8 Ca1.92Pr0.08MnO4 sample: [110] ED pattern and HREM image, showing the characteristic contrast of the n=1 member of the (Ca,Ln)n+1MnnO3n+1 series. Most of the crystallites of the slowly cooled sample are defect free. Fig. 9 Dark field images of the ‘800 °C-quenched’ Ca1.92Pr0.08MnO4 sample: (a) showing that the existence of twinning phenomena is not Ca1.92Sm0.08MnO4 [a=5.2206(11), b=5.2195(11) and c= dependant on the thermal process (by selecting the weak extra 12.0055(4)A° for Aba2].Both lead to reasonable R values, reflections); (b) showing the existence of numerous defects and of the which attest to the validity of the model, but none allows an strain field associated with the pancake-like defects.accurate refinement of the positions of the oxygen atoms located in the [MnO2] plane. Considering the complexity of the twinning system [Fig. 7(c)], it appears indeed impossible to get significant results from powder XRD data. Clearly, it prepared following the same steps of the process as the other compounds, but was ‘quenched’ from 800 °C to room tempera- seems that Leonowicz et al.,17 obtained a diVerent distortion of the Ca2MnO4 structure due to the fact that they worked at ture. The EDS analyses showed that the actual composition is also very close to the nominal one.This ‘800 °C-quenched’ much lower temperature (900 °C instead of 1500 °C)and used a flux (CaCl2). Ca1.92Pr0.08MnO4 sample exhibits exactly the same magnetotransport properties as the ‘slowly cooled sample’, whose Doping Ca2MnO4 with praseodymium or with gadolinium (x=0.08) and slowly decreasing the temperature (see microstructure is very regular, if one excepts the twinning phenomena.The dark field images show that the formation Experimental section), produces the same remarkable microstructure. The overall bright field images show an even contrast of (001)-type twins is not dependant on the cooling rate [Fig. 9(a)]. However their microstructure shows a diVerent with a very few extended defects, and the [110] HREM images exhibit the characteristic centring of the n=1 members of the behaviour [Fig. 9(b)], involving the formation of ‘pancakelike’ defects along the [110] direction. The term ‘pancake-like’ (Ln,A)n+1MnnO3n+1 series, as the undoped Ca2MnO4 (Fig. 8). Only some occasional intergrowth defects corresponding to refers to the dimensions of the defect, which is large along two directions (in the present case, a few nanometers) and n=3 or n=4 members are detected. The dark field image, recorded according to the same conditions confirms the pres- small along the perpendicular direction. Along [110], it is clear that the internal structure of the defective area is perovskite ence of numerous (001)-type twins, similar to the undoped material [Fig. 7(c)]. Apparently the orthorhombic symmetry like. The width of the defects is variable but never larger than two or three perovskite units [white triangle in Fig. 10(b)], is maintained. EDS analyses over relatively large areas (ca. 100 nm) confirm, in the limit of accuracy of the technique, corresponding to the local formation of n=2 and n=3 members of the (Ln,A)n+1MnnO3n+1 series. In a number of cases that the cation ratio (Ca/Ln#24 and Mn/Ca#0.52) is in agreement with the nominal Ca1.92Ln0.08MnO4 composition. there is even no change in the periodicity of the basic Ca2MnO4 stacking, only a diVerence in intensity [see arrows in Fig. 10(a)]. The absence of 3D perovskite and the very small number of intergrowth defects clearly show that the ferromagnetism The dark field images, taken with a smaller objective aperture [Fig. 9(b)] clearly indicate however that there is a strain field and especially the magnetoresistance are intrinsic properties of the monolayered manganites Ca2-xLnxMnO4.associated with most of the precipitates. These results clearly show that the presence of pancake-like The possible influence of the presence of extended defects such as intergrowth members upon the properties of such defects, correlated to the local formation of n=2 members of the series, and the associated strain fields do not aVect the samples has also been studied. For this study, we considered a second type of preparation.A Ca1.92Pr0.08MnO4 sample was magnetotransport properties of these oxides. J. Mater. Chem., 1998, 8(11), 2411–2416 2415The authors gratefully acknowledge the University of Caen, for supporting this work through a position of Associate Professor. References 1 C. Zener, Phys. Rev., 1951, 82, 403. 2 P. W. Anderson and H.Hasegawa, Phys. Rev., 1955, 100, 675. 3 G. H. Jonker and J. H. Santen, Physica, 1950, 16, 337. 4 P. G. de Gennes, Phys. Rev., 1960, 118, 141. 5 J. B. Goodenough, Magnetism and the chemical bond, John Wiley and Sons, New York–London, 1963. 6 C. N. R. Rao, P. Ganguly, K. K. Singh and R. A. M. Mohan Ram, J. Solid State Chem., 1988, 72, 14. 7 R. A. Mohan Ram, P. Ganguly and C. N. R.Rao, J. Solid State Chem., 1987, 70, 82. 8 Y. Moritomo, Y. Tomioka, A. Asamitsu and Y. Tokura, Phys. Rev. B, 1995, 51, 3297. 9 Y.Moritomo, A. Asamitsu, H. Kuwahara and Y. Tokura, Nature, 1996, 340, 141. 10 A. Daoudi and G. Le Flem, J. Solid State Chem., 1972, 5, 57. 11 I. O. Troyanchuk, N. V. Samsonesko, H. Szymczak and A. Nabialek, J. Solid State Chem., 1997, 131, 144. 12 C. Martin, A. Maignan, F. Damay and B. Raveau, J. Solid State Chem., 1997, 134, 198 13 A. Maignan, C. Martin, F. Damay and B. Raveau, Chem.Mater., 1998, 10, 950. 14 B. J. Sternlieb, J. P. Hill, U. C. Wildgruber, G. M. Luke, B. Nachumi, Y. Moritomo and Y. Tokura, Phys. Rev. Lett., 1996, 76, 2169. Fig. 10 Enlarged [110] HREM images of ‘pancake-like’ defects in 15 A. Maignan, C. Martin, F. Damay, B. Raveau and J. Hejtmanek, Ca1.92Pr0.08MnO4; (a) example of defects (see white triangles) which Phys. Rev. B, 1998, 58, 2758. do not change the periodicity of the layer stacking, and only involve 16 P. LaVez, G. Van Tendeloo, R. Seshadri, M. Hervieu, C. Martin, a local diVerence in intensity; (b) example of defect corresponding to A. Maignan and B. Raveau, J. Appl. Phys., 1996, 80, 5850. the local formation of an n=3 member of the (Ln,A)n+1MnnO3n+1 17 M. E. Leonowicz, K. R. Poeppelmeier and J. M. Longo, J. Solid series (white triangles). State Chem., 1985, 59, 71. 18 J. Takahashi and N. Kamegashira, Mater. Res. Bull., 1993, 28, 565. Paper 8/05393F 2416 J. Mater. Chem., 1998, 8(11), 2411–2416

ISSN:0959-9428    

DOI:10.1039/a805393f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Curing and morphology of epoxy resin–silica hybrids Leno Mascia* and Tao Tang Institute of Polymer Technology and Materials Engineering, Loughborough University, Loughborough, UK LE11 3TU Received 3rd July 1998, Accepted 25th August, 1998 Hybrids of epoxy resin and silica cured respectively with methyl nadic anhydride (MNA) and 4,4¾-diaminodiphenyl sulfone (DDS) were prepared.Control of the morphology was achieved through functionalisation of a diglycidyl ether resin respectively with monofunctional and difunctional secondary amine trialkoxysilanes prior to being mixed with a solution of tetraethoxysilane (TEOS) and hardener. Scanning and transmission electron microscopy examinations (SEM and TEM) were carried out to study the morphology of the samples.The results have shown that the preparation conditions and nature of solvent play a vital role in the compatibilisation of the final hybrid. The addition of a hydrolysed TEOS solution into the epoxy resin to produce the corresponding hybrid was found to interfere with the cross-linking reactions with the hardener, inevitably resulting in a reduction in the Tg of the epoxy resin component.This was attributed to side reactions of MNA with the ethanol released from hydrolysis and condensation of the TEOS, producing monofunctional and difunctional esters which act as plasticisers and to decreased functionality of the epoxy resin from the reaction with the HCl used for the hydrolysis of TEOS. Recently, Nishijima et al.10,11 have reported the preparation Introduction of a hybrid material based on an epoxy resin/silica system, Prevention of phase separation and morphology control are using tetraglycidyl-meta-xylenediamine (TGMXDA) as the crucial factors in the preparation of organic–inorganic hybrid resin and 1,2-cyclohexanedicarboxylic anhydride (HHPA) as materials (also known as ceramers or nanocomposites) pro- curing agent. In this case, the hybrid was prepared by producing duced by the in situ polymerisation of a hydrolysed metal first a silica filler by the sol–gel method, containing N-balkoxide within the bulk of an organic component.aminoethyl-c-aminopropylmethyldimethoxysilane as a coupling It has been shown that highly transparent hybrid materials, agent which was subsequently incorporated in the epoxy resin with phase domains <100 nm, can be produced by a variety mixture. of compatibilisation techniques.e.g. (1) Through functionalis- Several workers have used the intercalation process to ation of the polymer or polymerisable oligomer with a trialkox- produce an epoxy resin–clay hybrid12–15 utilising the well ysilane.1–4 (2) By adding a functional trialkoxysilane, as a defined dimensions of the structure layers of the chosen clay coupling agent, to the precursor mixture to chemically link or (i.e.montmorillonite). Other workers have shown that the provide strong physical interactions between the organic and important factor in controlling the dimensions of the inorganic inorganic domains.5 (3) By using another polymer as compati- phase is the nature of the intercalating agent.16 biliser, which is miscible with the primary polymer component In this work the possibility of producing hybrids of a cured and is capable of producing strong interactions with the epoxy resin with silica is being investigated with the scope of siloxane component.6 determining the influence of curing agents and reaction con- Homogeneous hybrids have been prepared also without the ditions.Although the occurrence of some adverse reactions use of coupling agents from solutions of polymers containing between the components of the alkoxysilane precursor for the pendant carbonyl groups along the chains, such as polyvinyl inorganic phase and either the hardener or the epoxy resin acetate (PVAc) and poly(methyl methacrylate) (PMMA).7,8 can be anticipated, the extent to which they will aVect both David and Scherer9 have shown that hybrids of poly(ethy- the compatibilisation mechanism and the final properties loxazoline) and silica form a molecular semi-interpenetrating cannot be predicted. This work seeks to identify the major network, as a result of extensive hydrogen bonding being diYculties that are likely to be encountered in attempting to formed between the silanol groups of the siloxane network produce epoxy–silica hybrids.and the carbonyl groups in the polymer. Very little has been reported on the preparation of epoxy resin/silica hybrid. Landry et al.4 have prepared a hybrid Experimental material from a very high molecular weight epoxy resin (Mw= Materials 47000), functionalised with c-aminopropyltriethoxysilane and (a) Resin components.The resins used were all bisphenol-A silica. A dioxane solution of the reactants catalysed by 0.15 M types, namely Epikote 828, Epikote 1001 and Epikote 1009 HCl was cast in open air and subsequently allowed to gel and (manufactured by Shell Chemicals). These have a number the solvent to evaporate over a period of two days.This was average molecular weight of ca. 370, 880 and 5000, correspond- followed by further drying at 60 °C for 2 h and a curing step ing to an average degree of polymerisation of 0.1, 2 and 16, at 150 °C for 15 h. No specific mention was made, however, expressed in terms of central CH2CHOHCH2 units per mol- of any likely crosslinking reaction taking place within the organic polymer phase.ecule. Their general structure is as shown below: J. Mater. Chem., 1998, 8(11), 2417–2421 2417Two hardeners were used, respectively methyl nadic It is important to note that only partial functionalisation of the epoxy resin is being considered in these studies so that the anhydride (MNA), corresponding to methyl 4-endo-methylenetetrahydrophthalic anhydride, in conjunction with N-benzyldi- composition of the organic phase will remain essentially similar to that of a cured epoxy resin.This confers to the resulting methylamine (BDMA) as catalyst, and 4,4¾-diaminodiphenyl sulfone (DDS). hybrids features that are substantially diVerent from earlier systems in which the difunctional organic oligomer was part of the siloxane network, forming a separate phase from the (b) Alkoxysilanes.Tetraethoxysilane (TEOS) (purity> pure silica network. 95%), obtained from Fluka, was used as the precursor The expected advantages of using the epoxy functionality for the formation of the silica phase. The compatibilising to produce a network with conventional hardeners for epoxy agents were trialkoxysilanes types, N-phenylaminopropylresins are twofold: (a) it makes it possible to produce hybrid trimethoxysilane (Y-9669) (purity>98.5) and bis(cmaterials in which the organic component predominates so trimethoxysilylpropyl )amine (A-1170) (purity>95%), both that the inorganic phase acts primarily as a reinforcing obtained from OSI Specialities.component. (b) The formation of a purely organic network would make it possible to produce larger organic domains, (c) Auxiliaries.A 32 wt.% solution of HCl in water was thereby reducing the level of brittleness normally experienced used as catalyst for the hydrolysis of the TEOS component. with conventional oligomer based organic inorganic Dimethylformamide (DMF) and tetrahydrofuran (THF) were hybrids.1,2 used as solvents.Preparation of epoxy resin ceramers Functionalisation of the epoxy resin The trimethoxysilane functionalised epoxy resin was dissolved Preliminary attempts to functionalise the epoxy resin with in an anhydrous solvent, either DMF or THF, at ca. 25 wt.% either a primary amine silane (i.e. c-aminopropyltriconcentration and measured amounts of water and TEOS at ethoxysilane) or with an isocyanate silane (i.e. cmolar ratio of 3–451 were added.This was followed by the isocyanatopropyltriethoxysilane), from reactions in bulk at addition of the HCl solution to bring the pH in the range of 90 °C produced rapid gelation and, therefore, were not 2–3. The reactants were stirred until the mixture became clear studied further. (ca. 12 h) and finally the resin and the MNA hardener were Aliphatic primary amines are known to react very rapidly added.The ceramer solutions were cast in PTFE moulds and with epoxy groups and, despite their bifunctionality, they can the solvent allowed to evaporate slowly at room temperature promote the formation of highly branched species by catalysing for ca. 24 h to induce gelation and then cured at 80 °C for 48 h.the internal condensation reactions via the newly formed Further curing was carried out in several steps, i.e. 24 h at hydroxyl groups. 120 °C, 5 h at 150 °C and 3 h at 180°C. The gelation resulting from the reaction with the isocyanate The above reactions involve the formation of two primary silane is due to the very rapid reaction of –CNO with the networks, an epoxide–ester network and a high density silox- pendant hydroxyl groups in the –CH2CH(OH)CH2O segment ane network (silica), each forming two separate phases.The in the epoxy oligomer, and the subsequent reaction of the two main phases are linked by species consisting of a network urethane groups so formed with the epoxy groups, and containing the two components. with itself, to produce the corresponding allophonate A schematic example of this type of network is shown below: groups.Subsequent preliminary experiments have identified secondary amines to be suitable for the functionalisation of the chosen epoxy resin. The chemical structure of the silanes used is described in the materials section above. In a round bottom flask was added the epoxy resin and the secondary amine coupling agent at diVerent molar ratios.The mixture was stirred for 2 h at 90 °C and the progress of the reaction was followed by FTIR analysis and by observing qualitatively any increase in viscosity. 1H NMR measurements were used to determine the reaction yield using a 300 MHz equipment. The reaction scheme for the functionalisation of the epoxy Characterisation of the hybrids resin is as shown below: (a) The compatibility of hybrids was first assessed from a (a) Reaction with N-phenylaminopropyltrimethoxysilane visual inspection of the state of cast films in order to obtain a qualitative assessment of the dimensions of the phases.Cloudiness and opacity was taken to indicate the presence of heterogeneous structures of the order of ca. 0.5 mm or larger. (b) The morphology of the cured resins was characterised by examining fractured surfaces using a Cambridge stereoscan electron microscope (360 Model). Some samples were etched with a 10 wt.% aqueous HF solution to enhance the contrast between the two phases. Examinations were also made by (b) Reaction with bis(trimethoxysilylpropyl )amine 2418 J. Mater. Chem., 1998, 8(11), 2417–2421A molar ratio of epoxy resin to silane A1170 of 1051 was found to be suYcient to achieve compatibility as compared to a molar ratio of 451 for the monofunctional aminosilane Y9669.It is not known, however, to what extent, the higher degree of conversion in the functionalisation reaction is responsible for the above behaviour relative to the bifunctionality resulting from the use of silane A1170.The enormous eVect that an increase in the molecular weight of the epoxy resin has on the compatibility of the hybrid is very clearly demonstrated from the data in Table 1, which shows that the amount of Y-9669 is reduced by a factor of seven when the molecular weight of the epoxy resin is increased from 370 to 5000. This is expected to result from the increased number of pendant hydroxyl groups along the chains of the epoxide oligomer which provide stronger H-bonding interactions with the silanol groups of the silica phase, thereby reducing the rate of phase Fig. 1 Conversion of NH groups in the secondary amine silane (Y- separation and subsequent growth during the drying stage of 9669) in the reaction with Epikote 828 at a molar ratio of 251.the preparation of the ceramer films. For ceramers based on Epikote 1001 (M=880) using THF as solvent an appreciable eVect was observed for the stirring transmission electron microscopy (TEM-100CX apparatus time after adding the hardener, i.e., the longer the stirring time manufactured by JEOL Ltd) on thin slices microtomed from the higher is the compatibility of the hybrids.This eVect is cast films cast in epoxy resin. shown in the SEM micrographs in Fig. 2 and TEM micro- (c) The curing reactions of the functionalised epoxy resin graphs in Fig. 3. with hardener were followed by FTIR analysis (Mattson 3000 No eVect was observed on the compatibility of the cast films FTIR spectrometer) and the glass transition temperature (Tg) when THF was used to replace DMF as the solvent for the of the epoxide network in the ceramers was measured using a ceramer solution. However, the stirring time needed to compa- Dupont DSC 9000 apparatus.tibilise the ceramer increased considerably. Replacing DMF (d) Various model experiments were carried out to elucidate with methyl ethyl ketone (MEK) produced opaque systems the mechanism of the reactions involved in the curing process. even after prolonged stirring, e.g. 6 h at room temperature. (These are outlined in the next section.) This solvent related kinetic eVect for the compatibilisation of the ceramer is related to the solubility of the products of Results and discussion the reaction in the precursor ceramer solution. In other words, a more advanced stage of reaction between the functionalised Functionalisation of epoxy resins epoxy resin and the hydrolysed TEOS is required when the The reaction of the low molecular weight resin, Epikote 828, H-bonding power of the solvent is reduced.with the secondary aromatic amine silane (Y-9669) was monitored by FTIR analysis, measuring the intensity ratio of the Curing reactions of the epoxy resin in the corresponding silica NH peak at 3396 cm-1 for the silane component to the OH ceramers peak at ca. 3500 cm-1 formed in the epoxide network. EVects on glass transition temperature. It was observed that Plots of the NH/OH absorbance peak ratio against reaction ceramers based on the epoxy resin functionalised with the time at 80 and 90 °C are shown in Fig. 1. From these it is aromatic amine silane (Y-9669) containing 25 wt.% of silica, evident that the reaction is not complete, and that it reaches and cured with MNA under standard conditions, i.e. 24 hours about 50% conversion after 1–2 h. Since the reaction yield, at 120 °C, 5 hours at 150 °C and 3 hours at 180 °C, displayed even at 90 °C, did not increase appreciably after 2 h, this a glass transition (Tg) of ca. 75°C, as compared with the value condition was chosen for the final preparation of the telechelic of 106 °C for the pure epoxy resin system. functionalised epoxy resin. For the same system, i.e. Epikote Table 2 lists Tg values for the two modified epoxy resins, 828/Y-9669 at molar ratio of 251, 1H NMR measurements one with silane A-1170 and the other with dibutylamine (DBA) revealed a 44% conversion of the Y-9669.When the epoxy at various molar ratios. These show that systems containing resin was reacted with bis(c-trimethoxysilylpropyl )amine (ADBA displayed an increase in Tg from 96 to 125 °C and 1170) at molar ratio of 351, FTIR measurements showed that remained constant even after increasing the level of modifi- the conversion of A-1170 was much higher than with Y-9669 cation from 1051 to 1052 molar ratio of epoxy to amine and NMR data confirmed that the conversion was 85% after groups.The equivalent ceramer system also displayed a small only 1 h at 90 °C. In both cases the unreacted aminosilane was increase in Tg at 1051 molar ratio functionalisation, but the not removed from the functionalised oligomer as this would Tg dropped to 62 °C when the molar ratio of the epoxy to participate in the subsequent reactions with the hydrolysed amine groups was increased to 1052.TEOS in the sol mixture and in the post curing reactions of FTIR analysis showed, however, that when a TEOS solution the epoxy resin. in THF was mixed and heated for 2 h at 80 °C with MNA, there was no change in the anhydride absorption band at EVect of preparation conditions on the compatibility† of epoxy- 1780 cm-1. When, however, this was carried out with a TEOS silica hybrids The results have shown that for the low molecular weight Table 1 EVect of molecular weight of bisphenol-A epoxy resins on the resin (i.e., Epikote 828), the amount of secondary difunctional amount of Y-9669 (50% conversion) for compatibilization of epoxy resin/silica hybrids at room temperature aliphatic aminosilane A-1170 required in functionalised epoxy resin in order to obtain a compatible hybrid was much lower Molecular weight of than for the monofunctional aromatic aminosilane (Y-9669).epoxy resin 370 880 5000 †The term compatible is used to indicate that the morphological Molar ratio of Y-9669 structure consists of domains considerably less than the wavelength to epoxy resin 0.50 0.17 0.07 of visible light.J. Mater. Chem., 1998, 8(11), 2417–2421 2419Fig. 3 TEM micrographs of morphology of ceramers with diVerent stirring time after adding hardner. (a) 0 h (opaque), (b) 5 h (transparent). Table 2 EVect of functionalization of epoxy resin on the Tg (°C) of the resulting networka Epoxy resin: modifiers (molar ratio) 1050 1051 105 2 DBA 96 125 125 A-1170 96 100 62 aSystem: MNA hardener and BDMA catalyst.Curing conditions: 120 °C, 5 h; 150 °C, 3 h; 180 °C, 1 h. Side eVects of HCl used as catalyst for the precursor siloxane solution. It is worth noting also that DSC measurements showed that the presence of water did not aVect the Tg of Fig. 2 SEM micrographs showing the changes in morphology brought about by increasing stirring time.(a) 0 h (opaque), (b) 3 h epoxy resin cured by MNA. When C2H5OH was deliberately (translucent), (c) 5 h (transparent). added, on the other hand, to the epoxy resin mixture, the Tg of the cured epoxy resin decreased from 119 to 55 °C. When HCl was also added to the epoxy resin mixture containing C2H5OH, the Tg of the cured epoxy resin, however, decreased solution hydrolysed in the presence of HCl and then mixed from 119 °C to only 90 °C.This indicates that the reaction under the same conditions, a part of the anhydride groups between the anhydride and hydroxyl groups proceeds to a was converted to ethyl carboxylate groups (absorption band lower degree of conversion when HCl is present.It is known, at 1737 cm-1) as a result of the reaction with the ethanol in fact, that esterification reactions occur more readily under formed from the hydrolysis of TEOS (Fig. 4). basic conditions.17 It is noted in Fig. 4 that spectra (a) and (b) are similar, FTIR analysis of the products extracted from films after whereas spectrum (c) displayed a large reduction in the immersion in THF for 24 h at 60 °C has indicated the presence intensity of the peak at 1780 cm-1 and the formation of a of ester groups due to formation of monoesters and possibly large peak at 1737 cm-1.This means that, under the curing some biesters from the reaction of MNA with ethanol. The conditions used in this work, only ethanol formed from the evidence is provided by the appearance of a strong absorption hydrolysis of TEOS can react with MNA and not the SiOH peak at 3500 cm-1, which is attributed to hydroxyl groups in the carboxylic acid produced from the anhydride.groups. 2420 J. Mater. Chem., 1998, 8(11), 2417–2421experiment carried out under acidic condition revealed a large increase in the intensity of the hydroxyl groups in the mixture.From this it is deduced that the large reduction in the Tg of the epoxy phase in the ceramer has to be attributed primarily to the reduction in concentration of epoxy groups as a result of the reaction with HCl used for the hydrolysis of TEOS, irrespective of the type of hardener used. Conclusions The following conclusions can be drawn: (1) it is possible to produce organic–inorganic hybrid materials based on epoxy resins through the sol–gel method, provided that the epoxy resin is functionalised with an organo trialkoxysilane. (2) Secondary aliphatic aminosilanes are more eVective than aromatic/aliphatic aminosilanes for the compatibilisation of epoxy resin–silica hybrids.(3) The level of compatibilisation achievable for epoxy resin–silica hybrids can be enhanced by increasing the magni- Fig. 4 FTIR spectra for mixtures of MNA and TEOS solution in tude of the following parameters: (a) molecular weight of the THF. (a) mixture of MNA and TEOS solution dried at room resin, (b) degree of functionalisation of the epoxy resin, temperature, (b) mixture of MNA and TEOS in the presence of HCl, dried at room temperature and heated at 80 °C for 2 h, (c) mixture of (c) polarity of the solvent and (d) processing temperature.MNA and TEOS, heated at 80 °C for 2 h, then cast film at room (4) The glass transition temperature of the epoxy network temperature and dried at room temperature under vacuum. in a ceramer is lower than the value achievable in the absence of the inorganic phase. This is attributed primarily to the Table 3 EVect of nature of hardner on the Tg of the epoxy network following reasons: (a) side reactions between the hardener and in the ceramera by-products of the hydrolysis of TEOS, and (b) the reduction in eVective concentration of epoxy groups as a result of their SiO2 content (wt.%) MNA DDS reaction with the acid catalyst used for the hydrolysis of TEOS. 0 103 124 2 80 93References 10 63 89 1 H. H.Huang, B. Orler and G. L. Wilkes, Macromolecules, 1987, aCuring conditions: 120 °C, 24 h; 150 °C, 5 h; 180 °C, 3 h. 20, 1322. 2 D. E. Rodrigues, A. B. Brennan, C. Betrabet, B. Wang and G. L. Wilkes, Chem. Mater., 1992, 4, 1437. It was noted that under the same curing conditions, the Tg 3 B. K. Coltrain, C. J. T. Landry, J. M. O’Reilly, A. M. of the epoxy resin crosslinked with DDS was higher than Chamberlain, G.A. Rakes, J. S. Sedita, L. W. Kelts, M. R. when MNA was used as hardener (Table 3). The resulting Landry and V. K. Long, Chem. Mater., 1993, 5, 1445. ceramer, however, exhibited a similar reduction in Tg as for 4 M. R. Landry, B. K. Coltrain, C. J. T. Landry and J. M. O’Reilly, the MNA cured system, despite the lack of any possibilities J.Polym. Sci., Polym. Phys. Ed., 1995, 33, 637. 5 A. Kioul and L. Mascia, J. Non-Crystal. Solids, 1994, 175, 169. for the formation of network diluents as side products. To 6 C. J. T. Landry, B. K. Coltrain, D. M. Teegarden, T. E. Long and verify further that the main cause for the reduction in the Tg V. K. Long, Macromolecules, 1996, 29, 4712. of the organic phase is the reaction of the epoxy groups with 7 J.J. Fitzgerald, C. J. T. Landry and J. M. Pochan, HCl, an epoxy resin/DDS mixture was prepared with the Macromolecules, 1992, 25, 3715. addition of volumetric amounts of HCl and DMF correspond- 8 C. J. T. Landry, B. K. Coltrain and B. K. Brady, Polymer, 1992, ing to the levels used in the production of the corresponding 33, 1486. 9 I. A. David and G.W. Scherer, Chem. Mater., 1995, 7, 1957. ceramers and cured under the same conditions. 10 S. Nishijima, M. Hussain, A. Nakahira, T. Okada and K. Niihara, Thin films were prepared to ensure that there was no residual Mater. Res. Soc. Symp. Proc., 1996, 435, 243. solvent left in the material after curing. DSC analysis was 11 M. Hussain, S. Nishijima, A. Nakahira, T. Okada and K. Niihara, used to obtain confirmation of the total absence of residual Mater. Res. Soc. Symp. Proc., 1996, 435, 369. solvent in the film by showing that the Tg of the resin was the 12 M. S. Wang and T. J. Pinnavaia, Chem. Mater., 1994, 6, 468. same irrespective of the amount of DMF used in the resin 13 P. B. Messersmith and E. P. Giannelis, Chem. Mater., 1994, 6, 1719. mixture, i.e. 193 °C. 14 P. Kelly, A. Akelah, S. Qutubuddin and A. Moet, J. Mater. Sci., When both HCl and water were also added to the resin 1994, 29, 2274. mixture, Tg decreased to 160 °C, irrespective of the water 15 T. Lan and T. J. Pinnavaia, Mater. Res. Soc. Symp. Proc., 1996, content. The possibility of water reacting with the epoxy 435, 79. groups was also discounted by model experiments in which 16 A. Akelah and A. Moet, J. Appl. Polym. Sci., Appl. Polym. Symp., small amounts were mixed with the epoxy resin in a THF 1994, 55, 153. 17 T. Tang, H. Y. Li and B. T. Huang, Eur. Polym. J., 1994, 30, 479. solution and kept at 80 °C for 18 h. FTIR measurements showed that hydroxyl group intensity did not increase in Paper 8/05144E comparison to the pure epoxy resin. Conversely a similar J. Mater. Chem., 1998, 8(11), 2417–2421 2421

ISSN:0959-9428    

DOI:10.1039/a805144e

出版商:RSC    

年代:1998

数据来源: RSC