摘要:

J O U R N A L O F C H E M I S T R Y Materials Feature Article Phthalocyanines and related compounds: organic targets for nonlinear optical applications G. de la Torre,a P. Va� zquez,a F. Agullo�-Lo�pez*b and T. Torres*a aDepartamento de Quý�mica Orga�nica (C-I), Facultad de Ciencias, Universidad Auto�noma de Madrid, E-28049-Madrid, Spain bDepartamento de Fý�sica de Materiales (C-IV), Facultad de Ciencias, Universidad Auto�noma de Madrid, E-28049-Madrid, Spain Phthalocyanines (Pcs) and related compounds with their extended two-dimensional p-electronic delocalization are important targets to study nonlinear optical responses. The tailorability of these macrocycles allows the fine-tuning of the chemical structure and nonlinear optical response.In this article, the design and main properties of phthalocyanines for second- and third-order nonlinear optical (NLO) and optical limiting applications are discussed, both at the microscopic and macroscopic level.The points of view of synthetic organic chemists and physicists are accorded, the main aim of the review being to highlight the key problems of the field and place them within the general context of NLO materials.Phthalocyanines1,2 (Pcs) 1 are a family of aromatic macrocycles optical communications. In the early stages, research work was focused on inorganic materials but, in the last 20 years, based on an extensive delocalized two-dimensional 18p-electron system which exhibit a large number of unique properties. interest in organic materials for nonlinear optical applications has markedly increased.13,14,17–19 They oVer several advantages They are highly stable and versatile compounds, capable of including more than 70 diVerent metallic and non-metallic over inorganic materials, such as large nonlinearities, ultrafast response times and easy and economic processability, for the ions in the ring cavity.Moreover, it is possible to incorporate a variety of peripheral substituents around the phthalocyanine preparation of films and miniature integrated optics devices.Moreover, it is possible to optimize their NLO properties by core, as well as replace some of the four isoindole units by other heterocyclic moieties, giving rise to diVerent phthalocyan- rational modification of their structure. Nonlinear processes can be broadly classified in two main ine analogues.Phthalocyanines also show remarkable optical properties. The linear optical spectra of these compounds are categories, parametric and non-parametric. Macroscopic parametric processes are described through the following expansion dominated by two intense bands, the Q band (centered at around 670 nm) and the B band in the near UV region (at of the light-induced polarization in powers of the wave electric field [eqn.(1)], around 340 nm), both correlated to p–p* transitions (Fig. 1). Another peculiar and useful feature of these compounds is P=x(1)E+x(2)EE+x(3)EEE+... (1) their ability to form diVerent kinds of condensed phases, such as discotic liquid crystals,3,4 when they are adequately func- where x(1), x(2) and x(3) are, respectively, the linear, first-order and second-order susceptibilities.At the microscopic level a tionalized with long lipophilic chains. Furthermore, it is possible to build thin films by several techniques, such as spin- similar expansion can be written for the molecular polarization [eqn. (2)], coating,5 molecular beam epitaxy (MBE)6 and Langmuir– Blodgett (LB) technology,5 that allow the fabrication of devices.p=aE+bEE+cEEE+... (2) Notably, phthalocyanine-based thin films have been applied to a wide range of technological areas: gas sensors,7,8 electro- a, b and c being the linear polarizability and the quadratic and cubic hyperpolarizabilities, respectively. The higher-order chromic devices,9 field eVect transistors10 and photovoltaic cells.11 terms in eqn.(1) and (2) are not relevant in most experiments. Away from resonances, parametric processes may become N N N N N N N N M 1 Following the discovery of the laser by Maiman12 in 1960, Fig. 1 UV–VIS spectra of (a) tetra(tert-butyl)phthalocyanine considerable research attention has been paid to the field of (5×10-6 M), (b) trinitrosubphthalocyanine 10c (1.9×10-5 M, (c) trinonlinear optics13,14 in order to develop opto-electronic tech- azolephthalocyanine 9 (R1=R2=H, R3=But, M=Ni) (2.1×10-5 M) and (d) nickel tetra(tert-butyl)naphthalocyanine (8.5×10-5 M) nologies,15,16 such as high-speed information processing and J.Mater. Chem., 1998, 8(8), 1671–1683 1671extremely fast (i.e. subpicosecond response times), and obey carried out using the traditional EFISH23,24 (electric field induced second harmonic generation) measurements in solu- very selective phase-matching conditions.tion. In these experiments, a strong electric field applied to the On the other hand, non-parametric processes are always sample gives rise to the loss of inversion symmetry and allows resonant and rely on light-induced changes in the population second-harmonic generation to occur.Recently, a new tech- of the energy levels of the system (optical pumping nonlinearitnique based on hyper-Rayleigh light scattering (HRS)25–27 has ies). Susceptibilities ( hyperpolarizabilities) cannot be properly been developed. It uses an intense laser beam that is focused defined and phase-matching conditions are not applicable. on an isotropic solution of the nonlinear chromophores.The They are generally much slower and the response time depends scattered frequency-doubled light intensity arises from fluctu- on the lifetimes of the involved transitions. This article mostly ations of the induced molecular dipoles and is proportional to focuses on parametric processes, both second- and third-order, the square of the incident fundamental intensity.One advan- whereas the non-parametric processes will be considered in a tage of this technique over EFISH is that it can be applied to final section dealing with the subject of optical limiting. both polar and nonpolar molecules. Organic materials for nonlinear optics are typically based Due to their extensive delocalized two-dimensional p-system on a highly polarizable p-conjugated system.Phthalocyanines and their centrosymmetric structure, non-substituted or sym- and related compounds, with their extended two-dimensional metrically substituted phthalocyanines have been commonly p-electron delocalization, are key targets to study nonlinear studied as third-order NLO materials. However, an intriguing optical processes14,20 and are very promising candidates for topic is the observation of appreciable SHG from thin films of optical switching and optical limiting devices.The tailorability centrosymmetric phthalocyanines,28–33 such as unsubstituted of phthalocyanines allows the fine tuning of the chemical CoII, CuII, ZnII and metal-free derivatives. Several explanations structure and nonlinear optical response.In this way, the have been advanced such as excited-state noncentrosymmetric introduction of adequate peripheral substituents can alter the relaxation of Cu ions, surface eVects and magnetic dipole and electronic structure of the molecule and originate eVective electrical quadrupole contributions. These latter nonlocal intramolecular charge transfer processes. Additionally, the eVects are ignored in the usual local description of NLO possibility of introducing diVerent central metal atoms provides responses in terms of polarizabilities and susceptibilities.architectural flexibility to optimize the NLO and other physical Recently, the quadrupole origin of the second-order nonlin- properties. It is also possible to modulate the nonlinear earity appears to be supported by careful measurements on response by conventional organic synthesis, varying the exten- MBE films.32 SHG of electric quadrupole origin has been also sion of p-electron delocalization (i.e.the naphthalocyanine observed34 in isotropic and discotic phases of a thiooctadecyl- system) or modifying the electronic structure through formal substituted phthalocyanine.Resonant states due to inter- and substitution of one or mors by other heterointra- molecular transitions have been suggested. cyclic moieties. On the other hand, phthalocyanines present The SHG response has also been observed from nickel(II ) high self-organizing abilities, mainly due to the strong p–p tetrakis(cumylphenoxy)phthalocyanine.35 In this case, random interactions between their aromatic rings.The possibility of placement of the peripheral groups makes this material non- self-assembling two or more phthalocyanine units in one- or centrosymmetric, despite having the same kind of substitution even two-dimensional architectures can promote NLO properin all four isoindole moieties. On the other hand, SHG has ties at the supramolecular level by electron delocalization.been observed in films of unsusbstituted vanadyl phthalocyan- In this article we will discuss second- and third-order ine.36,37 This molecule is non-centrosymmetric and polar, since parametric NLO properties of phthalocyanine-related comthe VNO moiety lies perpendicular to the macrocycle plane. pounds and materials, both at the microscopic (molecular) and As expected, the second harmonic intensity increased quad- macroscopic level.The connection between the two views will ratically with film thickness. be emphasized. Finally, due to the present relevance of optical It has been suggested38 that unsymmetrically substituted limiting devices we will also discuss this (mostly non-paraphthalocyanines with suitable donor and acceptor groups metric) type of NLO response, involving changes in the popucapable of displaying eYcient intramolecular charge transfer lations of the energy levels of the system.Since some useful should exhibit second-order NLO responses. For this reason, and detailed reviews on the subject have been published in some research work has been carried out in order to develop recent years, we will focus our discussion on the latest results.non-centrosymmetric peripherally substituted phthalocyanines. Moreover, we will put the accent on the basic problems and On the other hand, some molecular engineering approaches general trends of the field rather than on an exhaustive to break the inversion symmetry of the macrocycle itself have description of data.The main aim should be to highlight the been also elaborated. These two strategies will be considered key problems and place them within the general context of successively in the next sections. NLO materials. Unsymmetrically substituted phthalocyanines Second-order NLO properties of phthalocyanines The synthesis of phthalocyanines1,2 involves a cyclotetrameriz- and analogues ation reaction of a phthalonitrile or 1,3-diiminoisoindoline.There has been continuous interest in the search for materials When the condensation is carried out between identically exhibiting large macroscopic second-order nonlinearities21 substituted precursors, centrosymmetrical compounds or mixbecause of their applicability in frequency doubling, parametric tures of regioisomers are obtained.The preparation of phthalooscillation and high-speed light modulation.16 Most experi- cyanines with diVerent substituents on the isoindole units ments yield x(2) (2v: v, v) through second-harmonic generation requires the synthetic strategies described below. (SHG) techniques and x(2) (v: v, 0) by using electrooptic (i) Attachment of a substituted diiminoisoindoline to an methods.It has been assessed that the second-order optical insoluble polymer39 and subsequent reaction with an excess of nonlinearity in many organic compounds arises from a highly another diVerently substituted diiminoisoindoline, followed by polarizable p-conjugated system capped with groups of diVer- the liberation of the phthalocyanine from the polymer. ent electron aYnities.To date, the research eVort has mostly (ii) Cross-condensation of a diiminoisoindoline derivative focused on one-dimensional molecules, i.e. donor–acceptor with a 1,3,3-trichloroisoindolenine or with another sterically disubstituted polyenes,22 which present one dominant hyperpo- crowded iminoisoindoline.40 In this way, identically face-tolarizability component lying in the direction of the intramolecu- face substituted phthalocyanines are obtained.lar charge transfer (ICT) axis. For these organic molecules, the (iii) Ring-expansion of a three-unit macrocycle (subphthalocyanine, see below) with a substituted diiminoisoindoline.41 experimental determination of the hyperpolarizability is usually 1672 J. Mater. Chem., 1998, 8(8), 1671–1683(iv) The most usual method is the statistical condensation for compound 2d).However, a significant influence of intramolecular charge transfer on the cubic nonlinear response (c) has of two diVerently substituted dinitriles or diiminoisoindolines followed by chromatographic separation of the statistical mix- been evidenced and correlated to the relative strengths of donor and acceptor substituents.48 This correlation appears to ture of compounds.42 Commonly, 351 to 951 ratios are employed, which favor the formation of the unsymmetrically be related to a strong two-photon resonance enhancement of the ICT contribution to c.This enhancement eVect of the cTHG substituted phthalocyanine with three identically substituted isoindole subunits. values due to the high dipolar moment associated to strong donor and acceptor substituents follows the trend previously Probably due to the diYculty in the preparation of pure unsymmetrically substituted phthalocyanines, few reports on observed in some porphyrin and phthalocyanine systems.49,50 A synthetic strategy that has been pursued in order to the second-order NLO properties of this kind of compound have been published.Wada, Sasabe and Liu and co-workers enhance the quadratic hyperpolarizabilities is the extension of the conjugation length between the donor and acceptor groups, reported SHG experiments on both Z-type deposition and in alternating deposition LB films of metal-free43,44 and copper45 by introducing p-delocalized electron-acceptor substituents.51 This approach seems quite reasonable, considering theoreti- nitrotri(tert-butyl )phthalocyanine (2a and 2b, respectively).The second-order NLO response of the film was found to be cal38,52 predictions and experimental53,54 results on the relationship between the magnitude of the first hyperpolariz- fairly intense (x(2)=2×10-8 esu for 2a and x(2)=2×10-5 esu for 2b), especially in the case of the copper compound. In the ability and the extent of the p-electron conjugation previously found for other systems.The influence of the position and case of alternated films, the dependence of the second harmonic intensity on the number of bilayers is nearly quadratic. Some electronic character of the substituents and the role of the central metal on the second and third NLO responses of this experiments have also been carried out on LB films of metalfree aminotri(tert-butyl)phthalocyanine 2c,46 showing a similar kind of systems, such as 4a–e, has been studied.55 EFISH experiments at 1900 nm do not show evidence of significant SHG response to that of the related metal-free phthalocyanine 2a.first-order hyperpolarizability and the main contribution to the EFISH signal derives from the third order electronic contribution to c (2v: v, v, 0).But in this case, cEFISH and cTHG are one order of magnitude larger than those of unsymmetrically substituted phthalocyanines 2a, 2d, 3a and 3b, thus demonstrating the eYcacy of the p-electronic extension in enhancing the nonlinear response (see next section). But N N N N N N N N M R But But 2a R = NO2; M = 2H 2b R = NO2; M = Cu 2c R = NH2; M = 2H 2d R = SO2C6H4CH3; M = 2H R1 R1 R1 N N N N N N N N M R2 R2 R2 R2 R2 R2 NO2 4a R1 = But, R2 = H,M = Cu 4b R1 = But, R2 = H, M = Co 4c R1 = But, R2 = H, M = Ni 4d R1 = H, R2 = C8H17, M = Ni 4e R1 = H, R2 = OC8H17, M = Ni N N N N NH N N HN R R 3a R = But 3b R = OC8H17 The first studies of the microscopic nonlinear responses of unsymmetrically substituted metal-free phthalocyanines, such as 2a, 2d, 3a and 3b, have been recently accomplished by thirdharmonic generation (THG) and EFISH generation techniques, at 1340 and 1064 nm, respectively.47,48 These experiments do not reveal evidence of important first-order hyperpolarizability.This fact suggests that the vector part of b is not important, the main contribution to the EFISH signal arising from the electronic contribution to the overall cubic hyperpolarizability (cEFISH=-12×10-34; cTHG=-19×10-34 O N N N N N N N N OCH2CF3 F3CH2CO F3CH2CO F3CH2CO F3CH2CO OCH2CF3 F3CH2CO OCH2CF3 F3CH2CO OCH2CF3 R1 V NO2 F3CH2CO F3CH2CO 5a R1 = NO2 5b R1 = J. Mater.Chem., 1998, 8(8), 1671–1683 1673Other diVerent ‘push-pull’ phthalocyanines (5a, b), some of groups have been established for porphyrin systems.49,59–61 them with exocyclic extended conjugation (5b), have been also Appropiate tuning of the p-delocalized cyclic porphyrin strucprepared. 56–58 These compounds bear donor groups that sup- tures may also result in large second harmonic responses. press molecular agreggation, even in the solid state. SHG EFISH measurements of unsymmetrically substituted aminoniexperiments were carried out on spin-coated poly(methyl trotetraphenyl porphyrins reported by Suslick et al.49 showed methacrylate) (PMMA) films doped with unsymmetrical vana- first hyperpolarizability values that were moderately high dyl phthalocyanines 5a and 5b.57,58 The authors reported that [(10–30)×10-30 esu].Similar values have been found in films of 5b showed larger second-harmonic signals than those related compounds.59 HRS experiments carried out on porphyof 5a, thus pointing out the eVect of the extended p-conjugation.rins with extended p-conjugation (6), achieved by the introduc- Similar relationships between the nonlinear response and tion of arylethynyl groups, showed larger b values than those the p conjugation length between the donor and acceptor end of their less-conjugated counterparts.60 More recently, SHG coeYcients of a number of ‘push-pull’ porphyrins with extended p-conjugation have been analyzed using semiempirical methods.61 The results obtained in some arylethynyl-substituted porphyrins, mentioned above, suggest that related phthalocyanine structures such as 7 are promising candidates for displaying large first order hyperpolarizabilities.62 Moreover, theoretical calculations on porphyrins60 suggest that it should be possible to obtain larger b values in structures based on two diVerently substituted phthalocyanine units linked by an ethynyl bridge, such as 8.63 Unsymmetric phthalocyanine-related systems Triazolephthalocyanines (TPcs)64 9 are core-modified phthalo- Me2N NO2 N N N N M 6 cyanines resulting from a formal substitution of one isoindole unit by a 1,2,4-triazole moiety.These compounds represent a novel class of intrinsically unsymmetric 18p-electron aromatic metallomacrocycles. Triazolephthalocyanines have a peculiar optical spectrum, which is shown in Fig. 1, showing absorption maxima shifted to lower wavelengths in comparison to those of phthalocyanines.Synthesis of triazolephthalocyanines involves either a one-step metal(II) template-assisted condensation of 3,5-diamino-1,2,4-triazole and the corresponding 1,3- diiminoisoindoline64 or a stepwise approach.65 The latter allows the introduction of both electron-donor and -acceptor substituents, able to promote charge-transfer processes.Actually, the acceptor character of the triazole subunit gives rise to a strong dipolar moment, which could be increased by the introduction of donor groups in the isoindole moiety opposite to the triazole one. Another remarkable feature of these compounds is their ability to self-organize in thin films via the Langmuir–Blodgett technique.66 The amphiphilic structure and the possibility of introducing long-chain substituents on the isoindole units make them suitable for preparing in-plane oriented LB films.Studies on the second- and third-order NLO properties in solution of these novel and promising class of compounds are currently being performed.67 N N N N N N N N M NMe2 Me2N Me2N Me2N O2N NO2 NO2 NO2 7 N N N N N N N N M R1 R1 R1 R1 R1 R1 N N N N N N N N M' R2 R2 R2 R2 R2 R2 8 1674 J. Mater.Chem., 1998, 8(8), 1671–1683and trinitro-substituted (10c) SubPcs evidenced high average b2 values,72 especially in the case of compound 10c. On the other hand, the electric field-induced second-harmonic generation yield from the same molecules was found to be very low. This result suggested that the measured b should be mostly associated to the octupolar component, arising from the coneshaped trigonal geometry.More recently, these results have been revised and completed.73 A systematic study of the microscopic NLO response of diVerently tri- and hexa-substituted subphthalocyanines, such as 10b–i, has been accomplished in order to elucidate the role of donor and acceptor substituents. EFISH experiments revealed that acceptor groups induce a much larger b than donor groups, N N N N N N N N N N M R1 R1 R1 R1 R2 R3 9 which may be associated with a correspondingly larger dipole moment for the excited state.The bHRS values are also strongly dependent on the donor/acceptor character of the substituents and show the same trend as the previously mentioned b values. Subphthalocyanines present a moderate permanent dipole moment which is presumably aligned along the BMCl axis for symmetry reasons.The existence of a dipole moment oVers the additional advantage of molecular ordering in spin-coated films via corona-poling. In fact, the second-order susceptibilities of both evaporated (x31(2)=2.36×10-9 esu) and spin-coated films (x31(2)=9.62×1010 to 1.14×10-9 esu) of trinitro-substituted subphthalocyanine 10c have been determined via SHG experiments.74 The high SHG yield also obtained for evaporated samples suggests that a strong ordering is achieved during the deposition process.Detailed studies of the SHG in trinitro- (10c), triiodo- (10d) and trioctylsulfonyl-subphthalocyanine (10e)75 thin films have more recently been carried out. They have allowed the determination of the three non-zero elements of the x(2)ij tensor in the film reference frame.The x(2)31 component is the highest, at variance with the case of linear (one-dimensional) molecules for which the relation x(2)33= N N N N N N B Cl R1 R2 R2 R1 R2 R1 C C C6H4NO2 10a R1 = R2 = H 10b R1 = H, R2 = But 10c R1 = H, R2 = NO2 10d R1 = H, R2 = I 10e R1 = H, R2 = SO2C8H17 10f R1 = H, R2 = SC8H17 10g R1 = R2 = SO2C8H17 10h R1 = R2 = SC8H17 10i R1 = H, R2 = 3×x(2)31 is expected.Assuming thermal equilibrium under the poling field, the components of the b tensor referred to the molecular axes have been also evaluated. The value for the On the other hand, formal structural modifications of the phthalocyanine ring allow the reduction of its symmetry, axial component b33 is very close to zero.yielding intrinsically non-centrosymmetric compounds like subphthalocyanines (SubPcs).68,69 They are cone-shaped 14pelectron aromatic compounds, having three coupled isoindole Third-order NLO response of phthalocyanines and units which contain a boron atom in the center with an axial related compounds halogen atom. The molecular symmetry can be C1, C3 or C3v, depending on the number and position of the substituents.There is a larger variety of third-order parametric eVects in comparison to those related to second-order. They are Preparation of SubPcs is carried out by a condensation reaction of phthalonitrile in the presence of BCl3 or BBr3. The described by x(3) (v5v1, v2, v3) susceptibilities having diVerent frequency dependencies or dispersion factors.76 Also some optical spectrum of a subphthalocyanine displays the same two bands as Pcs but slightly shifted to the blue (Fig. 1).diVerent physical mechanisms may contribute to the various processes. For example, third-harmonic generation (THG) only In the early nineties, Ledoux and Zyss brought into consideration octupolar molecules for second-order nonlinear optics.70 involves electronic mechanisms, whereas nonlinear refraction may result from electronic as well as thermal and optical These molecules lacking a permanent dipole moment can exhibit non-zero b due to the octupolar contribution. Both pumping mechanisms.At the molecular level, design criteria for optimized response are not as well-established as for dipolar and octupolar contributions to the hyperpolarizability have to be considered in accordance with the decomposition second-order eVects, although extensive electron conjugation appears indispensable.A similar situation applies to the macro- b=bj=1Cbj=3, valid whenever Kleinman’s symmetry applies. The adequate linear combination of the cartesian components scopic level and the role of molecular organization and packing has not been clearly ascertained yet.bijk of the b tensor generates irreducible representation bj=1 (with dimension 3) and bj=3 (with dimension 7) of the rotation A number of experimental techniques are available to learn about third-order NLO processes and measure the correspond- group. Up to now, most of the attention has focused on the dipolar part, bj=1, of b.Nevertheless, much research work has ing susceptibilities. Most works use one of these methods: THG,77 degenerate four-way wave mixing (DFWM)78 and Z- been centered recently on octupolar systems,71 mainly due to some advantages they may present over dipolar ones, including scan.79 Since they measure diVerent susceptibilities, the comparison of the results is not always easy and depends on the non-centrosymmetric crystallization and improved eYciencytransparency trade-oV.The development of the HRS technique experimental parameters (excitation wavelengths, pulse lengths). THG measures x(3) (3v5v, v, v) and exclusively enabled experimental determination of the hyperpolarizability of these octupolar molecules. involves electronic processes.On the other hand, DFWM measures x(3) (v5v, -v, v) and may include other contri- Thus, some recent experiments with subphthalocyanines have pointed out the possibility that these compounds may butions (thermal, non-parametric, etc.) whose relative importance depends on experimental conditions. A similar situation behave as predominantly octupolar. Preliminary HRS experiments on unsubstituted (10a) as well as tri-tert-butyl- (10b) applies to Z-scan, which measures nonlinear refraction and J.Mater. Chem., 1998, 8(8), 1671–1683 1675absorption and may also respond to several mechanisms. In excitation wavelength, suggesting the importance of frequency dispersion eVects. In fact, large resonance enhancements have these latter two techniques, ultrafast pulse experiments are necessary for a meaningful comparison with the THG results.been observed for (electronic) EFISH at 1064 nm and have been associated with one-photon resonance with a d–d trans- The third-order NLO response at microscopic and macroscopic level found in phthalocyanine derivatives will be dis- ition occurring at about 1000 nm. Similar or even larger eVects have been also observed in DFWM experiments where reson- cussed in the next sections.ance at the same wavelength is occurring.83,84 On the other hand, THG experiments at 1346 nm do not show significant Molecular hyperpolarizabilities enhancement, possibly due to the dominance of a strong The optimization of the second-order molecular hyperpolarizaresonance at 3v with the B band.80 bilities is an essential requirement for the design of useful The eVect of transition and rare-earth metals (M=Sc, Lu, materials for third-order NLO applications. Hence, it is interes- Yb, Y, Gd, Eu, Nd) on c has also been investigated in ting to clarify the factors aVecting microscopic third-order bis(phthalocyanines) 12.86 The c values were large, as expected optical nonlinearity in phthalocyanines, such as peripheral for such highly delocalized systems.The diVerences found in substitution, role of the central ion, aggregation of the metallothis series of compounds seem to be exclusively due to resonmacrocycles, and so on. ance eVects. Molecular hyperpolarizabilities c (v5v, -v, v) and c (3v5v, v, v) for a large number of metallophthalocyanines in solution have been determined by means of DFWM and THG experiments, respectively, and the results summarized in previous reviews.14,20 Experimental determination of both the amplitude and phase of the hyperpolarizability of compounds 11a–d, has been recently achieved by THG and EFISH experiments.80,81 The data on the phase are essential for a reliable analysis of the experiments.The real and imaginary parts of c have been obtained from the concentration dependence of the harmonic intensity. Data for the free phthalocyanines have been satisfactorily explained in terms of a four-level model including two one-photon allowed levels (corresponding to the Q and B bands) and a two-photon allowed level placed at around 500 nm from the ground state. Independent evidence for the two-photon level has also been gathered from nonlinear absorption experiments on films.82 N N N N N N N N N M N N N N N N N 12 M = Sc, Lu, Yb, Y, Gd, Eu, Nd It is well-known that the introduction of peripheral substituents can modify the third-order NLO response by altering the electronic structure of phthalocyanines.The NLO characterization of a family of unsymmetrically donor- and acceptorsubstituted metallophthalocyanines (MPcs), such as 2a, 2d, 3a and 3b, has been made by EFISH and THG at 1064 and 1340 nm, as mentioned above.A clear correlation of the c hyperpolarizability with the Hammett parameter for the compounds has been obtained,48 so that c becomes maximal for high absolute values of the parameter, i.e. for molecules having either strong donor or acceptor groups.A simple analysis based in a two-level model for the Q-band transition provides a rationale to account for the observed trends. The influence of molecular stacking on the microscopic NLO response has not yet been suYciently investigated. However, some theoretical analyses have identified two mechanisms which lead to enhancements in the value of c (-v5v, -v, v) for cofacial covalently linked phthalocyanine dimers and trimers over that of the monomers.87 This analysis is in agreement with recent DFWM experiments which showed a strong enhancement of c (-v5v, -v, v) for PcSiO oligomers as a function of the number of macrocycles.88 In this case p–p overlapping between the phthalocyanine macrocycles takes O O O O O O N O O N N N N N N N N O O N O O N N O O O O N N N N M 11a M = 2H 11b M = Cu 11c M = Ni 11d M = Co place.Thus, a 24-fold increase on going from monomers to dimers and 4-fold from dimers to trimers has been measured. However, THG experiments at 1064 nm of spin-cast films of The role of the central metal ion on the NLO response is a problem of physical relevance and it has been addressed in a [But4PcRu(dib)]n oligomers 13 (dib=1,4-diisocyanobenzene) revealed that the NLO response is mainly determined by the number of studies using both solutions as well as thin films80,83–85 (see also below).Although the situation is not yet individual phthalocyanine units. In this case, compared with the previous PcSiO oligomers, longer interplanar distances completely clear, marked progress has recently been achieved.A clear enhancement of the cubic hyperpolarizability has, between two adjacent macrocycles, originated by the diisocyanobenzene bridging ligands, prevent the p–p overlaping and, indeed, been observed for metallophthalocyanines containing uncomplete d-shell transition ions, particularly cobalt.80 therefore, the achievement of one-dimensional supramolecular optical behaviour.89 However, the enhancement is critically dependent on the 1676 J.Mater. Chem., 1998, 8(8), 1671–1683NC N N N N N N N N Ru CN NC CN N N N N N N N N Ru CN NC N N N N N N N N Ru CN NC n 13 Third-order experiments at the molecular level have also Films produced by sublimation and laser ablation. Due to the high thermal stability of Pcs, films of these compounds have been performed on Pc-related compounds, such as porphyrins and metallotriazolehemiporphyrazines. The non-resonant been prepared by sublimation and their NLO properties have been investigated by a number of researchers.14,20 More recent cubic hyperpolarizabilities of several tetraphenylporphyrinsubstituted derivatives have been measured by Z-scan at work has focused on the spectral dependence of the susceptibilities.The dispersive behavior of the magnitude and phase of 748 nm.90 Data are discussed in terms of the interaction between the porphyrin core and the external substituents. x(3) (3v5v, v, v) for evaporated metal-free and copper Pc films have been studied95 via third-harmonic generation spec- Moreover, the third-order nonlinear susceptibility of porphyrin oligomers has been also investigated by Z-scan with 30 ps laser troscopy in the range from 950 to 2000 nm.A two-photon state lying at about 500 nm has been identified in both Pcs, pulses at 640 and 1064 nm.91 The real part has been found to be proportional to the number of monomer units. The case of confirming the model proposed80 to account for c (3v5v, v, v) data in solution.Moreover, for the Cu-Pc an additional metallotriazolehemiporphyrazines 14 is also interesting since a low-lying two-photon allowed level, in addition to two one- two-photon state located at about 1000 nm has been inferred from the spectra, also in accordance with the solution results. photon allowed ones, are required to account for both the real and imaginary components of the hyperpolarizability.92 An Anyhow, the microscopic structure of the films should be very relevant in determining the NLO response.In fact, it has been influence of unfilled d-shell metal substitution has also been measured in this kind of compound and attributed to d–d shown that the microcrystal size and orientation in vacuumdeposited SnPcs on a rubbed polymide surface strongly aVect forbidden transitions, as in phthalocyanines.93 the THG susceptibility.96 NLO susceptibilities of vacuum-deposited Pc-related compounds, such as naphthalocyanines,97 have also been investigated.In particular, THG experiments have been performed in films of subphthalocyanine derivatives lacking inversion symmetry.98 The spectral dependence for the amplitude and phase of x(3) have been investigated in the range 959 to 2000 nm.x(3) values are about three times higher than those of phthalocyanines. A four-level model including the ground state and three one-photon excited states (B, Q and a shoulder at 540 nm) satisfactorily fits the data. Finally, one should mention that laser ablation methods have also been used recently as an alternative to thermal sublimation.99 Spin-coated films. Spin-coating is a simple technique that 14 M = 2H M = Mn M = Cu M = Co M = Fe M = Pb M = Zn C12H25 O O O O O O O O O N N N N N N N N N N N N M C12H25 O produces locally-homogeneous, good quality films.Therefore, it has often been used to measure NLO eVects in phthalocyan- One should also mention that eVorts have been made to ines and naphthalocyanines.14,20 Recently, some detailed NLO theoretically understand the third-order NLO behavior of spectroscopy experiments have been performed that throw porphyrins and phthalocyanines, as derived from their elecadditional light on the responsible physical mechanisms.In tronic structure.94 particular, the eVects of metal (Zn, Cu, Pd, Co and Ni) and peripheral substitution on the THG yield of octabutoxy- and Thin films octa(decyloxy)-phthalocyanines have been investigated in preliminary experiments at the 1907 nm fundamental wave- The processability of phthalocyanines in diVerent types of thin films allows the study of the macroscopic NLO responses.A length.100 Similarly, the THG responses for Si, Ge, Sn, Al, Mn and VO naphthalocyanine derivatives have been measured in variety of methods for deposition of Pc films have been used.Since the structure is diVerent depending on the particular the spectral range from 1050 to 2100 nm.101 Clear diVerences in the values of x(3) depending on the central metal have been method and it is not often well-characterized, detailed quantitative comparison is not easy, although some general trends observed.As for Pcs, the rise in the susceptibility observed at around 1500 nm has been explained in terms of resonance have been clearly identified. In many cases the behaviour measured in films is consistent with that found at the molecular enhancement with a two-photon level below the Q-level transition. level. As a general rule, NLO studies in films should be combined and correlated with other structural characterization A novel application of spin-coated films is the fabrication of NLO optical waveguides.Recent work on the subject includes methods in order to achieve meaningful conclusions. J. Mater. Chem., 1998, 8(8), 1671–1683 1677picosecond optical bistability in metallophthalocyanine-doped On the other hand, the potential of multilayers of CuPc and naphthalenetetracarboxylic dianhydride (NTCDA) on KCl for polystyrene waveguides102 and Z-scan and mode spectroscopy of Pc-doped PMMA waveguides.103 NLO applications has been explored,112 opening a promising approach for devices having tailored perfomances.Langmuir–Blodgett films. LB films provide unique systems to ascertain the influence of molecular stacking on the third- Sol-gel films.Pcs have been incorporated into sol-gel film glasses via the sol-gel technique.113 Because of the relatively order NLO response. In pioneering experiments, x(3) values of LB films of soluble silicon phthalocyanine were obtained at low preparation temperature, the method appears quite suitable to host organic molecules in inorganic materials.Few 602 nm by DFWM.104 The phase-conjugated signal, which has a resonant character, can be observed even for one-monolayer studies of the NLO reponse of these sol-gel systems have so far been performed. The THG susceptibilities of sol-gel hosts films. Time-resolved experiments gave information on the dynamics of the DFWM response, which is governed by the containing copper phthalocyanine at molecular concentrations in the range 10-4 to 10-5 have been measured at 1064 and presence of bimolecular exciton exciton interactions.More recently, x(3) (3v5v, v, v) values have been obtained 1904 nm in as prepared samples as well as after an annealing treatment at 200 °C.114 On the other hand, the nonlinear self- for LB films of several metallophthalocyanines.105 Values are not as high as expected from the molecular hyperpolarizabili- refraction of gaussian laser beams have been carried out at 532 nm.High values of the third-order susceptibility have been ties,80,81 possibly due to the particular arrangement of the molecules in the films. It has been shown that the molecules measured.115 are not lying flat on the substrate, but are tilted and stacked as in a pile of cards, thus reducing the p–p overlapping between Nonlinear absorption and refraction: optical limiting adjacent macrocycles.This may account for the reduced suscepbehavior tibility when the molecules are probed with light propagating perpendicular to the film faces. On the other hand, the data Nonlinear absorption and refraction are closely related NLO on the eVect of metal complexation are very consistent with eVects.In a general case several mechanisms, both parametric the discussion presented above on the experiments performed and non-parametric, may contribute to these nonlinearities at the molecular level. No significant diVerences with the and a reliable assessment of the responsible mechanisms central metal are measured at 1064 nm where the resonance requires experiments involving diVerent pulse lengths.The at 3v with the B band is dominant, whereas a large enhance- parametric contributions to the nonlinear response are very ment is found at 1904 nm for the cobalt-containing compound, small except for very short and intense light pulses and as for the experiments in solution. In this case the resonance therefore unsuitable for many practical devices.Therefore, the with the d–d two-photon allowed transition at around 1000 nm search for nonlinear absorbing materials mostly relies on nonis causing the enhancement. Therefore, the consistency between parametric (optical pumping) processes that take advantage of the results for solutions and LB films shows that the enhance- the particular level structure of the system.Due to its practical ment in the NLO response is an intrinsic molecular property relevance we will discuss these processes in relation to optical determined by the molecular energy scheme and not related limiting. to the stacking in the films. Optical limiting (OL) is a nonlinear eVect consisting of a THG experiments at 1064 and 1904 nm were performed106 decrease in the transmittance of a sample under high intensity on LB films of octakis(octylaminocarbonylmethoxy) metal- or fluence illumination. Ideally, the transmitted intensity should lophthalocyanines (related to 11), which present a high ability remain constant (or even decrease to a small value) above a to form aggregates by intermolecular hydrogen bonding.certain illumination threshold. Consequently, the initial constant Measured x(3) values do not show significant diVerences with transmittance should linearly decrease to zero above the respect to the values obtained for compounds 11, thus pointing threshold. This ideal behavior is illustrated in Fig. 2. out to a small influence of hydrogen bonding on the NLO The optical limiting eVect finds useful applications for sensor response.(e.g. CCD) protection including the human eye. In a way, optical limiting is the reverse of saturable absorption (RSA) MBE films. The fabrication of ordered (crystalline) films of where an increase in transmittance is observed at high illumi- Pc is now possible by molecular beam epitaxy (MBE) tech- nation levels. The two nonlinear eVects mentioned at the start niques.107 This is a very promising route for the preparation of the section may contribute to optical limiting, either directly of ordered organic structures, not yet suYciently exploited.An (nonlinear absorption) or through the use of an aperture that up-to-date review of the state of art of the technique has been recently published.6 Some of the epitaxial films consist of novel structures that open interesting routes for the preparation of NLO materials. The substrate plays a key role in determining the structure and physical properties of the film.In particular, the eVect of the lattice parameter of the substrate on the crystal orientation of vanadyl phthalocyanine (VOPc) films epitaxially grown on KCl–KBr mixed crystals has been clearly assessed.108 As a consequence, the NLO responses of the films are accordingly modified.One may quote that x(3) (3v5v, v, v) values of VOPc films epitaxially grown on KBr show almost an order of magnitude enhancement over polycrystalline films deposited on fused silica.109 Moreover, the epitaxial film presents a clear in-plane anisotropy for the THG yield that is absent in the polycrystalline film.110 This result highlights the influence of molecular orientation and stacking on third-order NLO behavior.85 More recently, the THG susceptibilities of both crystalline and amorphous films of VOPc, vanadyl dibenzophthalocyanine (VODBPc) and vanadyl naphthalocyanine Fig. 2 Ideal behavior of an optical limiter: (a) transmitted intensity (VONc) have been measured.111 For both types of films, the Iout versus incident intensity Iin (or fluence Fin); (b) transmittance T versus incident intensity (or fluence).x(3) values were in the order VOPc>VODBPc>VONc. 1678 J. Mater. Chem., 1998, 8(8), 1671–1683limits the cross-section of the illuminating beam (nonlinear where Ni is the population of level i and N the total concentration of molecules, I is the intensity of the light pulse, si the refraction).absorption cross-section from level i and ti the corresponding Phthalocyanines have been shown to be promising metallifetimes (t13-1 is the singlet-triplet crossover rate). The optical loorganic materials for optical limiting in the visible and NIR absorption is given in terms of the populations Ni by eqn.(9). spectral range, because of their appropriate photophysical properties. Moreover, the spectral bandwidth or window over a=s0N0+s1N1+s3N3 (9) which the limiter operates can be engineered by altering both the main ring and the peripheral substituents, permiting fine- When s3>s1>s0 a most favourable situation for optical tuning of the perfomance parameters. limiting is obtained.In phthalocyanines and naphthalocyan- Some useful reviews on the subject, including work on ines, values s1/s0>10 and s3/s0>30 have been achieved.117 phthalocyanines, have been recently published,14,20,116–118 so In particular, for pulses shorter than t3 but long enough to we will focus on the most recent developments. assure that most molecules are in the strongly absorbing triplet state (N$N3) one obtains a$s3NI/hn.This absorption is higher than the linear (low fluence) absorption coeYcient aL= Dynamics of RSA s0NI/hn by the factor s3/s0&1. Eqns. (3)–(8) are local in time and space. Therefore, for Most OL experiments on phthalocyanines and naphthalocyancomparison to experiment they have to be numerically inte- ines are discussed with reference to the five-level scheme shown grated for the duration of the pulse, transversal size of the in Fig. 3. S and T are singlet and triplet states, respectively. light beam and sample thickness. The calculations can be made Under illumination an initial photon of around 550 nm is for several wavelengths in order to determine the performance absorbed at the ground state level S0 and takes the molecule range of the limiter.Recently, powerful beam-propagation to a high vibrational level S1¾ of a singlet electronic excited methods have been applied to the propagation of light beams state S1 (corresponding to the Q band). This state rapidly in nonlinear absorbing materials.119 decays into a lower energy triplet T1 that may absorb another For enhanced optical limiting performance the photophysphoton, so that the system is excited to a higher triplet level ical parameters (cross-sections and lifetimes) should be optim- T2.Moreover, one-photon transitions from S1 to a higher ized for the particular working conditions of the limiting device. lying singlet S2 are also possible. In accordance with this scheme short-pulse processes are dominated by singlet–singlet absorption before a significant population of the triplet T1 Relevant experiments state has developed.In this case if the cross-section of the Experiments are usually carried out by focusing a good-quality S1–S2 transition is larger than that for S0–S1, reverse saturation laser beam onto the liquid or solid sample in order to reach a behavior occurs.Under these conditions the simplest threehigh intensity. They often use a frequency-doubled Nd5YAG level model (S0, S1 and S2) can be used to discuss the results. laser at 532 nm, but other wavelengths and a variable wave- On the other hand, the processes occurring under long pulse length optical parametric oscillator (OPO) have been used to illumination are dominated by triplet–triplet T1–T2 transitions.determine the spectral bandwidth. If the corresponding cross-section is larger than that of the S0–S1 transition, then optical limiting also takes place. This physical model leads to the following set of rate Molecular level. Phthalocyanine derivatives have received a equations [eqns. (3)–(8)] for the populations of the levels S0, great deal of attention as reverse saturable absorbers.Optical S1 and T1, limiting with phthalocyanines was first reported for chloroaluminium phthalocyanine 15 (CAP).120 dN0/dt=-s0N0I/hn+N1/t1+N3/t3 (3) dN1/dt=s0N0I/hn-s1N1I/hn+N2/t2-N1/t1-N1/t13 (4) dN2/dt=s1N1I/hn-N2/t2 (5) dN3/dt=-s3N3I/hn+N1/t13+N4/t4-N3/t3 (6) dN4/dt=s3N3I/hn-N4/t4 (7) N0+N1+N2+N3+N4=N (8) Cl Al N N N N N N N N 15 Experiments have been performed on many phthalocyanines in solution, particularly CAP, where much information is available.Much eVort is still being devoted to determining the main physical parameters and understanding the relevant mechanisms.121–123 The role of metal substitution and molecular stacking is being actively investigated,124 and modified twodimensional Z-scan methods125 are being used to improve the experimental information.The heavy-atom eVect has been exploited to obtain remarkable enhancements in the reverse saturable absorption of phthalocyanines. Several Pc series containing Al, Ga, In and Si, Ge, Sn, Pb as central atoms have been studied.126 Thus, for example, lead tetrakis(cumylphenoxy)phthalocyanine [PbPc(CP)4] 16 has shown eYcient optical limiting Fig. 3 Schematic diagram showing the levels and relevant transitions for optical limiting action (see text) performance.127 J. Mater. Chem., 1998, 8(8), 1671–1683 1679N N N N N N N N O O O O Me Me Me Me Me Me Me Me Pb 16 The reason for such behavior is that the intercrossing rate from S1 to T1 is enhanced for this heavy central metal ion due to the large value of the spin–orbit coupling parameter that couples singlet to triplet states.It has been shown that indium leads to a faster intercrossing rate than lead in spite of its lower atomic number and so improves the limiting threshold.128 Experiments have also been performed129 with paramagnetic phthalocyanines such as VOBut4Pc and Cu(SO3-)4Pc sodium salt. It appears that the magnetic moments contribute to the spin–orbit coupling and enhance the intercrossing rate.A number of naphthalocyanines have been shown to present reverse saturation behavior. Due to the shift of the Q-band to the IR (Fig. 1), the wavelength range is accordingly shifted with regard to that measured for phthalocyanines. For the two kinds of compounds the same general trends with central metal substitution have been observed.In particular, heavy metal ions130,131 enhance the response due to the higher intercrossing R1 In N N N N N N N N R3 R2 R3 R2 R2 R3 F F F F F F CF CF , , , R1 = R1 = Cl , R2 = But, n -C5H11 R3 R2 18 3 3 R3 = H, n -C5H11 rate. Very promising results have been obtained for lead octa(apentoxy) naphthalocyanine 17.130 The optical absorption spectrum of a related naphthalocyanine system is shown in Fig. 1, present a higher damage threshold due to self-healing, but in comparison to that of the related phthalocyanine comsolid- state materials are more robust and should be preferable pounds. Molecular engineering approaches have been used to for devices. Pc films with a glassy morphology have been tune the spectral range of the limiter by donor substitution of obtained by chemically functionalizing the ring periphery via naphthalocyanines. It is well-known that the introduction of amine-epoxy substitution,139 but the damage threshold is too alkoxy substituents into the a-position of the phthalocyanines low.A number of sol-gel host materials containing Pcs have and naphthalocyanines drastically shifts the position of the Qbeen also investigated.140–143 Polymer (PMMA), guest–host band to higher wavelength.132–134 Thus, for example, indium systems containing either CAP144 or a silicon phthalocyanine and tin octabutoxynaphthalocyanines with red-shifted optical [PcSi(OC7H15)2] have also been tried.145 A broadband limiting limiting response have been also studied.135 action has been achieved.One additional advantage of polymer matrixes over liquid hosts is the possibility of achieving a concentration gradient that leads to better overall performances, as mentioned below.A novel approach uses an elastic polymer and viscoelastic gels for guest–host optical limiting matrixes.146 Additional experiments have shown that an epoxy elastomer has a much higher laser damage threshold than an epoxy glassy thermoset and a PMMA thermoplastic.Silicon naphthalocyanine optical limiting performances have been improved by incorporating the dye into the elastomer host.147 From the device point of view, the use of several successive N N N N N N N N Pb H11C5O OC5H11 OC5H11 H11C5O H11C5O OC5H11 H11C5O OC5H11 17 limiters (tandem strategy) seems useful to optimize both the overall limiting and damage thresholds in Pcs. Two NcSi Very recently,136 Hanack and Heckmann have described the preparation of new highly-soluble axially-substituted indium solutions have been tested leading to a nonlinear transmission TNL=0.0017 and a damage threshold of 8.7 mJ.148 Signal phthalocyanines 18 especially designed for optical limiting.The optical limiting properties of these compounds are being suppression ratios near 600 have been achieved.Another strategy to optimize the limiter performance makes use of a presently studied.137 concentration gradient profile. As an example, it has been shown that a non-homogeneous distribution of indium tetra- Materials and devices. Once the most promising molecules for OL behavior have been identified, suitable macroscopic (tert-butyl )phthalocyanine chloride along the beam path enhances the excited-state absorption and leads to an eYcient systems should be prepared.Liquids and gels as well as solid host media have been essayed. In principle, liquid solutions138 optical limiter.149 In order to optimize the performance of the 1680 J. Mater. Chem., 1998, 8(8), 1671–168323 B. F. Levine and C.G. Bethea, J. Chem. Phys., 1975, 63, 2666. limiter diVerent non-homogeneous profiles have been pro- 24 A. Willets, J. E. Rice, D. M. Burland and D. P. Shelton, J. Chem. posed116 and tested.150 Phys., 1992, 97, 7590. 25 K. Clays and A. Persoons, Phys. Rev. L ett., 1991, 66, 2980. 26 K. Clays and A. Persoons, Rev. Sci. Instrum., 1992, 63, 3285. Future prospects 27 M. J. French, in Hyper Rayleigh and Hyper Raman Spectroscopy Phthalocyanines and related compounds are consolidating in Chemical Applications of Raman Spectroscopy, Academic Press.New York, 1981. their relevant position as optical limiters and third-order NLO 28 K. Kumagai, G. Mizutani, H. Tsukioka, T. Yamauchi and materials. Considerable basic photophysical and spectroscopic S. Ushioda, Phys.Rev. B: Condens.Matter, 1993, 48, 14488. information has recently been gathered that permits a better 29 H. Hoshi, T. Yamada, K. Kajikawa, K. Ishikawa, H. Takezoe and understanding of NLO behavior and the role of the central A. Fukuda, Mol. Cryst. L iq. Cryst. Sci. T echnol., Sect. A, 1995, metal ion. Much eVort still needs to be devoted to predict the 267, 1. eVect of molecular aggregation and supramolecular organiz- 30 T.Yamada, T. Manaka, H. Hoshi, K. Ishikawa, H. Takezoe and ation. New materials and strategies to optimize the optical A. Fukuda, Nonlinear Opt., 1996, 15, 193. 31 T. Yamada, H. Hoshi, K. Ishikawa, H. Takezoe and A. Fukuda, limiting and third-order NLO performance are (and should Nonlinear Opt., 1996, 15, 131. be) actively pursued. In particular, molecular beam epitaxy, 32 H.Hoshi, T. Yamada, K. Ishikawa, H. Takezoe and A. Fukuda, together with the LB technique, should oVer enormous perspec- Phys. Rev. B: Condens.Matter, 1996, 53, 12663. tives for materials design and fine control of the physical 33 T. Yamada, T. Manaka, H. Hoshi, K. Ishikawa, H. Takezoe and response. A. Fukuda, Phys. Rev. B: Condens.Matter, 1996, 53, R13314. On the other hand, new routes for the synthesis of second- 34 M.Sato, A. Takeuchi, T. Yamada, H. Hoshi, K. Ishikawa, T. Mori and H. Takezoe, Phys. Rev. E, 1997, 56, R6264. order NLO (i.e. non-centrosymmetric) compounds are being 35 R. D. Neuman, P. Shah and U. Akki, Opt. L ett., 1992, 17, 798. implemented. As an example, subphthalocyanines, which are 36 H. Hoshi, K.Hamamoto, T. Yamada, K. Ishikawa, H. Takezoe, intrinsically unsymmetric compounds, have shown high quad- A. Fukuda, S. Fang, K. Kohama and Y. Maruyama, Jpn. J. Appl. ratic hyperpolarizabilities that can be further enhanced by Phys., 1994, 33, L1555. suitable acceptor substitution. This and related approaches 37 H. Hoshi, T. Yamada, K. Ishikawa, H. Takezoe and A. Fukuda, could shift the focus of NLO studies from planar (two- J.Chem. Phys., 1997, 107, 1687. 38 D. A. Li, M. A. Ratner and T. J. Marks, J. Am. Chem. Soc., 1988, dimensional) molecules to more complex three-dimensional 110, 1707. systems, where oV-diagonal components of the b tensor become 39 C. C. LeznoV and T. W. Hall, T etrahedron L ett., 1982, 23, 3023. very relevant. 40 J. G. Young and W.Onyebuagu, J. Org. Chem., 1990, 55, 2155. 41 N. Kobayashi, R. Kondo, S. Nakajima and T. Osa, J. Am. Chem. The financial support of the CICYT, Spain (grants MAT- Soc., 1990, 112, 9640. 96/0654 and TIC-96/0668) and the Comunidad de Madrid 42 A. Sastre, B. del Rey and T. Torres, J. Org. Chem., 1996, 61, 8591. (grant 06T/017/96) is gratefully acknowledged. 43 Y. Liu, Y. Xu, D. Zhu, T.Wada, H. Sasabe, L. Liu and W. Wang, T hin Solid Films, 1994, 244, 943. 44 Y. Liu, Y. Xu, D. Zhu, T. Wada, H. Sasabe, X. Zhao and X. Xie, References J. Phys. Chem., 1995, 99, 6957. 45 Y. Liu, Y. Xu, D. Zhu and X. Zhao, T hin Solid Films, 1996, 1 Phthalocyanines. Properties and Applications, ed. C. C. LeznoV 289, 282. and A. B. P. Lever, VCH, Cambridge, 1989, 1993, 1996, vol. 1–4. 46 S. G. Liu, Y.-Q. Liu, Y. Xu, D.-B. Zhu, A.-C. Yu and X.-S. Zhao, 2 M. Hanack, H. Heckmann and R. Polley, in Methods of Organic L angmuir, 1998, 14, 690. Chemistry (Houben-Weyl), ed. E. Schaumann, Georg Thieme 47 M. A. Dý�az-Garcý�a, F. Agullo�-Lo� pez, A. Sastre, B. del Rey, Verlag, Stuttgart, 1998, vol. E 9d, p. 717. T. Torres, C. Dhenaut, I. Ledoux and J. Zyss, Nonlinear Opt., 3 Metallomesogens.Synthesis, Properties and Applications, ed. J. L. 1996, 15, 251. Serrano, VCH,Weinheim, 1996. 48 A. Sastre, M. A. Dý�az-Garcý�a, B. del Rey, C. Dhenaut, J. Zyss, 4 J. Simon and P. Bassoul, in Phthalocyanines. Properties and I. Ledoux, F. Agullo�-Lo�pez and T. Torres, J. Phys. Chem., 1997, Applications, ed. C. C. LeznoV and A. B. P. Lever, VCH, 101, 9773. Cambridge, 1993, vol. 2, p. 223. 49 K. S. Suslick, C. T. Chen, G. R. Meredith and L.-T. Cheng, J. Am. 5 M. J. Cook, J.Mater. Chem., 1996, 6, 677. Chem. Soc., 1992, 114, 6928. 6 A. Yamashita and T. Hayashi, Adv.Mater., 1996, 8, 791. 50 H. S. Nalwa and A. Kakuta, T hin Solid Films, 1995, 254, 218. 7 W. Snow and W. R. Barger, in Phthalocyanines. Properties and 51 G. de la Torre and T. Torres, J. Porphyrins Phthalocyanines, 1997, Applications, ed.C. C. LeznoV and A. B. P. Lever, VCH, 1, 221. Cambridge, 1989, vol. 1, p. 341. 52 D. Li, T. J Marks and M. A. Ratner, Chem. Phys. L ett., 1986, 8 J. Souto, M. L. Rodrý�guez-Me�ndez, J. A. de Saja and R. Aroca, 131, 370. Int. J. Electron., 1994, 76, 763. 53 R. A. Huijts and G. L. J. Hesselink, Chem. Phys. L ett., 1989, 9 M. L. Rodrý�guez-Me�ndez, J.Souto, J. A. de Saja and R. Aroca, 156, 209. J.Mater. Chem., 1995, 5, 639. 54 L-T. Cheng, W. Tam, S. R. Marder, A. E. Stiegman, G. Rikken 10 T. Thami, J. Simon, N. JaVrezic, A. Maillard and S. Spirkovitch, and C. W. Spangler, J. Phys. Chem., 1991, 95, 10643. Bull. Soc. Chim. Fr., 1996, 133, 759. 55 G. de la Torre, G. Rojo, J. Garcý�a-Ruiz, I. Ledoux, J. Zyss, 11 C.W. Tang, Appl. Phys. L ett., 1986, 48, 183. F. Agullo�-Lo�pez and T. Torres, in preparation. 12 T. H. Maiman, Nature, 1960, 187, 493. 56 M. Tian, T. Wada and H. Sasabe, J. Heterocyclic Chem., 1997, 13 Molecular Nonlinear Optics, ed. J. Zyss, Academic Press, New 34, 171. York, 1993. 57 M. Tian, T. Wada, H. Kimura-Suda and H. Sasabe, Mol. Cryst. 14 Nonlinear Optics of Organic Molecules and Polymers, ed.H. S. L iq. Cryst., 1997, 294, 271. Nalwa and S. Miyata, CRC Press, Boca Rato� n, FL 1997. 58 M. Tian, T. Wada, H. Kimura-Suda and H. Sasabe, J. Mater. 15 Nonlinear Optics: Materials, Physics and Devices, ed. J. Zyss, Chem., 1997, 7, 861. Academic Press, Boston, 1993. 59 A. Sen, P. C. Ray, P. K. Das and V. Krishnan, J. Phys. Chem., 16 R. Dagani, Chem. Eng., 1996, March 4, 22. 1996, 100, 19611. 17 H. S. Nalwa, Appl. Organomet. Chem., 1991, 5, 349. 60 S. M. LeCours, H-W. Guan, S. G. DiMagno, C. H. Wang and M. 18 D. F. Eaton, G. R. Meredith and J. S. Miller, Adv. Mater., 1991, J. Therien, J. Am. Chem. Soc., 1996, 118, 1497. S. Priyadarshy, 3, 564. T. M. J. Therien and D. N. Beratan, J. Am. Chem. Soc., 1996, 19 H. S. Nalwa, Adv. Mater., 1993, 5, 341. 118, 1504. 20 H. S. Nalwa and J. S. Shirk, in Phthalocyanines. Properties and 61 I. D. L. Albert, T. J. Marks and M. A. Ratner, Chem.Mater., 1998, Applications, ed. C. C. LeznoV and A. B. P. Lever, VCH, 10, 753. Cambridge, 1996, vol. 4, p. 79. 62 G. de la Torre, T. Torres and F. Agullo�-Lo� pez, Adv. Mater., 1997, 21 T. Verbiest, S. Houbrechts, M. Kauranen, K. Clays and 9, 265. A. Persoons, J.Mater.Chem., 1997, 7, 2175. 63 E. M. Maya, P. Va� zquez and T. Torres, Chem. Commun., 1997, 22 G. S. Craig, R. E. Cohen, R. R. Silbey, G. Pucceti, I. Ledoux and J. Zyss, J. Am. Chem. Soc., 1993, 115, 860. 1175. J. Mater. Chem., 1998, 8(8), 1671–1683 168164 F. Ferna�ndez-La�zaro, A. Sastre and T. Torres, J. Chem. Soc., 105 M. A. Dý�az-Garcý�a, J. M. Cabrera, F. Agullo�-Lo� pez, J.A. Duro, G. de la Torre, T. Torres, F. Ferna�ndez-La�zaro, P. Delhaes and Chem. Commun., 1994, 1525. 65 B. Cabezo� n, S. Rodrý�guez-Morgade and T. Torres, J. Org. Chem., C. Mingotaud, Appl. Phys. L ett., 1996, 69, 293. 106 M. A. Dý�az-Garcý�a, F. Ferna�ndez-La�zaro, G. de la Torre, E. M. 1995, 60, 1872. 66 F. Armand, B. Cabezo� n, M.V. Martý�nez-Dý�az, A. Ruaduel-Texier Maya, P. Va� zquez, F.Agullo�-Lo�pez and T. Torres, Synth. Met., 1997, 84, 923. and T. Torres, J.Mater. Chem., 1997, 7, 1741. 67 B. Cabezo� n, G. Rojo, I. Ledoux, J. Zyss, F. Agullo�-Lo�pez and 107 T. Maruno, A. Yamashita, T. Hayashi, H. Kanbara and K. Kubodera, Nonlinear Opt., 1995, 14, 151. T. Torres, in preparation. 68 M. Geyer, F. Plenzig, J. Rauschnabel, M. Hanack, B.del Rey, A. 108 K. Hammamoto, S. Nakao, M. Gomyou, H. Hoshi, K. Ishikawa, H. Takezoe and A. Fukuda, Jpn. J. Appl. Phys., Part 2, 1996, Sastre and T. Torres, Synthesis, 1996, 1139. 69 B. del Rey and T. Torres, T etrahedron L ett., 1997, 38, 5351. 35, L1120. 109 S. Fang, H. Tada and S. Mashiko, Appl. Phys. L ett., 1996, 69, 767. 70 I. Ledoux and J. Zyss, Chem. Rev., 1994, 94, 77. 71 I. Ledoux and J. Zyss, Pure Appl. Opt., 1996, 5, 603. 110 S. Fang, H. Hoshi, K. Kohama and Y. Mayurama, J. Phys. Chem., 1996, 100, 4104. 72 A. Sastre, T. Torres, M. A. Dý�az-Garcý�a, F. Agullo�-Lo� pez, C. Dhenaut, S. Brasselet, I. Ledoux and J. Zyss, J. Am. Chem. 111 A. Yamashita, S. Matsumoto, S. Sakata, T. Hayashi and H. Kanbara, Opt. Commun., 1998, 145, 141. Soc., 1996, 118, 2746. 73 B. del Rey, G. Rojo, U. Keller, S. Brasselet, S. Nonell, C. Marti, 112 Y. Imanishi, S. Hattori, T. Hamada, S. Ishihara, H. S. Nalwa and A. Kakuta, Nonlinear Opt., 1995, 13, 63. I. Ledoux, J. Zyss, F. Agullo�-Lo�pez and T. Torres, submitted. 74 G. Rojo, A. Hierro, M. A. Dý�az-Garcý�a, F. Agullo�-Lo� pez, B. del 113 R. Litra�n, E. Blanco, M. Ramý�rez-del-Solar and L. Esquivias, J. Sol-Gel Sci.T echnol., 1997, 8, 985. Rey, A. Sastre and T. Torres, Appl. Phys. L ett., 1997, 70, 1802. 75 G. Rojo, F. Agullo�-Lo� pez, B. del Rey and T. Torres, submitted. 114 R. Litra�n, E. Blanco, M. Ramý�rez-del-Solar, A. Hierro, M. A. Dý�az-Garcý�a, A. Garcý�a-Caban�es and F. Agullo�-Lo� pez, Synth. 76 Nonlinear Optics, ed. R. Boyd, Academic Press, San Diego, 1992. 77 F. Kajzar, J.Messier and C. Rosilio, J. Appl. Phys., 1986, 60, 3040. Met., 1996, 83, 273. 115 R. Ramos, P. M. Petersen, P. M. Johansen, L. Lindvold, 78 R. C. Lind, D. G. Steel and G. J. Dunning, Opt. Eng., 1982, 21, 190. 79 M. Sheik-bahae, A. A. Said, T. H. Wei, D. J. Hagan and E. W. M. Ramý�rez and E. Blanco, J. Appl. Phys., 1997, 81, 7728. 116 L. W. Tutt and T. F. Boggess, Prog. Quantum Electron., 1993, Van Stryland, IEEE J.Quantum Electron., 1990, 26, 760. 80 M. A. Dý�az-Garcý�a, I. Ledoux, J. A. Duro, T. Torres, F. Agullo� - 17, 299. 117 J. W. Perry, in Nonlinear Optics of Organic Molecules and Lo�pez and J. Zyss, J. Phys. Chem., 1994, 98, 8761. 81 M. A. Dý�az-Garcý�a, F. Agullo�-Lo� pez, M. G. Hutchings, P. G. Polymers, ed. H. S. Nalwa and S. Miyata, CRC Press, Boca Rato� n, FL 1997, p. 813. Gordon and F. Kajzar, Nonlinear Opt., 1995, 14, 169. 82 M. A. Dý�az-Garcý�a, A. Dogariu, D. J. Hagan and E. W. Van 118 E. W. Van Stryland, D. J. Hagan, T. Xia and A. A. Said, in Nonlinear Optics of Organic Molecules and Polymers, ed. H. S. Stryland, Chem. Phys. L ett., 1997, 266, 86. 83 J. S. Shirk, J. R. Lindle, F. J. Bartoli, C. A. HoVman, Z. H. Kafafi Nalwa and S.Miyata, CRC Press, Boca Rato� n, FL 1997, p. 841. 119 S. Hughes, J. M. Burzler aSnow 1997, 14, 2925. 120 D. R. Coulter, V. M. Miskowski, J. W. Perry, T. H. Wei, E. W. and M. E. Boyle, Int. J. Nonlinear Opt. Phys., 1992, 1, 699. 85 H. Kambara, T. Maruno, A. Yamashita, S. Matsumoto, Van Stryland and D. J. Hagan, Proc. SPIE, 1989, 1105, 42. 121 K. R. Welford, S. N. R. Swatton, S. Hughes, S. J. Till, G. Spruce, T. Hayashi, H. Konami and N. Tanaka, J. Appl. Phys. 1996, 80, 3674. R. C. Hollins and B. S. Wherret, Mater. Res. Soc. Symp. Proc., 1995, 374, 239. 86 J. S. Shirk, J. R. Lindle, F. J. Bartoli and M.E. Boyle, J. Phys. Chem., 1992, 96, 5847. 122 S. Hughes, G. Spruce, J. M. Burzler, R. Rangel-Rojo and B. S. Wherret, J. Opt. Soc. Am. B, 1997, 14, 400. 87 E. S. Manas, F. C. Spano and L. X. Chen, J. Chem. Phys., 1997, 107, 707. 123 S. Hughes, G. Spruce, B. S. Wherret and T. Kobayashi, J. Appl. Phys., 1997, 81, 5905. 88 L. X. Chen, B. K. Mandal, B. Bihari, A. K. Sinha and M. Kamath, Proc.SPIE-Int. Soc. Opt. Eng., 1995, 2527, 61. 124 T. C.Wen and I. D. Lian, Synth.Met., 1996, 83, 111. 125 P. Chen, I. V. Tomov and P. M. Rentzepis, Proc. SPIE-Int. Soc. 89 A. Grund, A. Kaltbeitzel, A. Mathy, R. Scharwz, C. Bubeck, P. Vermehren and M. Hanack, J. Phys. Chem., 1992, 96, 7450. Opt. Eng., 1997, 3146, 160. 126 J. W. Perry, K. Mansour, S. R. Marder, K. J. Perry, D.Alvarez 90 K. Kandasamy, S. J. Shetty, P. N. Puntambekar, T. S. Srivastava, T. S. Kundu and P. B. Singh, Chem. Commun., 1997, 1159. and I. Choong, Opt. L ett., 1994, 19, 625. 127 J. S. Shirk, R. G. S.Pong, S. R. Flom, F. J. Bartoli, M. E. Boyle 91 M. Terazima, H. Shimizu and A. Osuka, J. Appl. Phys., 1997, 81, 2946. and A. W. Snow, Pure Appl. Opt., 1996, 5, 701. 128 J. W. Perry, K.Mansour, S. R. Marder, C. T. Chen, P. Miles, M. 92 M. A. Dý�az-Garcý�a, I. Ledoux, F. Ferna�ndez-La�zaro, A. Sastre, T. Torres, F. Agullo�-Lo�pez and J.Zyss, Nonlinear Opt., 1995, 10, E. Kenney and G. Kwag, Mater. Res. Soc. Symp. Proc., 1995, 374, 257. 101. 93 M. A. Dý�az-Garcý�a, I. Ledoux, F. Ferna�ndez-La�zaro, A. Sastre, 129 J. W. Perry, L. R. Khundkar, D. R. Coulter, D. Alvarez, S.R. Marder, T.-H. Wei, M. J. Sence, E. W. Van Stryland and T. Torres, F. Agullo�-Lo�pez and J. Zyss, J. Phys. Chem., 1994, 98, 4495. D. J. Hagan, in Organic Molecules for Nonlinear Optics and Photonics, ed. J. Messier, F. Kajzar and P. Prasad, NATO ASI 94 B. H. Cardelino and C. E.Moore, Proc. SPIE-Int. Soc. Opt. Eng., 1996, 2852, 153. Series E: Applied Sciences, vol. 194, Kluwer Academic Publishers, Dordrecht, 1991, p. 369. 95 M. A. Dý�az-Garcý�a, F. Agullo�-Lo� pez, W. E. Torruellas and G. I. Stegeman, Chem. Phys. L ett., 1995, 235, 535. 130 J. S. Shirk, S. R. Flom, J. R. Lindle, F. J. Bartoli, A. W. Snow and M. E. Boyle,Mater. Res. Soc. Symp. Proc., 1994, 328, 661. 96 M. Yamashita, A. Wajiki, T. Tako, A. Morinaga, A. Mito, M. Sakamoto and T. Isobe, Mol.Cryst. L iq. Cryst. Sci. T echnol., 131 V. Dentan, P. Feneyrou, F. Soyer, M. Vergnolle, P. Le Barny and P. Robin,Mater. Res. Soc. Symp. Proc., 1997, 479, 261. Sect. A, 1996, 280, 33. 97 H. S. Nalwa, in Nonlinear Optics of Organic Molecules and 132 B. D. Rihter, M. E. Kenney, W. E. Ford and M. A. J. Rodgers, J. Am. Chem. Soc., 1990, 112, 8064. Polymers, ed. H. S. Nalwa and S. Miyata, CRC Press, Boca Rato� n, FL 1997, p. 611. 133 B. D. Rihter, M. E. Kenney, W. E. Ford and M. A. J. Rodgers, J. Am. Chem. Soc., 1993, 115, 8146. 98 M. A. Dý�az-Garcý�a, F. Agullo�-Lo� pez, A. Sastre, T. Torres, W. E. Torruellas and G. I. Stegeman, J. Phys. Chem., 1995, 99, 134 A. N. Cammidge, I. Chambrier, M. J. Cook, A. D. Garland, M. J. Heeney and K. Welford, J. Phorphyrins Phthalocyanines, 1997, 14988. 99 T. Fujii, H. Shima, N. Matsumoto and F. Kannari, Appl. Surf. 1, 77. 135 J. W. Perry, K. Mansour, S. R. Marder, C. T. Chen, P. Miles, M. Sci., 1996, 96–98, 625. 100 M. Sanghadasa, B. Wu, R. D. Clark, H. Guo and B. G. Penn, E. Kenney and G. Kwag, Mater. Res. Soc. Symp. Proc., 1995, 374, 257. Proc. SPIE-Int. Soc. Opt. Eng., 1997, 3147, 185. 101 H. S. Nalwa and S. Kobayashi, J. Porphyrins Phthalocyanines, 136 M. Hanack and H. Heckmann, Eur. J. Inorg. Chem., 1998, 367. 137 J. S. Shirk, M. Hanack and H. Heckmann, personal 1998, 2, 21. 102 J. Si, Y.Wang, J. Zhao, B. Zou, P. Ye, L. Qiu, Y. Shen, Z. Cai and communication. 138 S. R. Flom, R. G. S. Pong, J. S. Shirk, F. J. Bartoli, R. F. Cozzens, J. Zhou, Opt. L ett., 1996, 21, 357. 103 S. S. Sarkisov, A. Wilkosz and P. Venkateswarlu, Proc. SPIE-Int. M. E. Boyle and A. W. Snow, Mater. Res. Soc. Symp. Proc., 1997, 479, 23. Soc. Opt. Eng., 1996, 2693, 523. 104 M. K. Casstevens, M. Samoc, J. Pfleger and P. N. Prasad, 139 R. D. George, A. W. Snow, J. S. Shirk, S. R. Floom and R. G. S. Pong, Mater. Res. Soc. Symp. Proc., 1995, 374, 275. J. Chem. Phys., 1990, 92, 2019. 1682 J. Mater. Chem., 1998, 8(8), 1671–1683140 M. Burnel, M. Canva, A. Brun, F. Chaput, L. Malier and J. P. Sutherland and A. L. Campbell, Proc. SPIE-Int. Soc. Opt. Eng., Boilot, Mater. Res. Soc. Symp. Proc., 1995, 374, 281. 1997, 2966, 88. 141 A. Acosta, S. S. Sarkisov, A. Wilkosz, A. Leyderman and P. 147 M. E. De Rosa, W. Su, D. Krein, M. C. Brant and D. G.McLean, Venkateswarlu, Proc. SPIE-Int. Soc. Opt. Eng., 1997, 3136, 246. Proc. SPIE-Int. Soc. Opt. Eng., 1997, 3146, 134. 142 M. Burnel, F. Chaput, S.A. Vinogradov, B. Campagne, M. Canva, 148 D. J. Hagan, T. Xia, A. A. Said, T. H.Wei and E. W. Van Stryland, J.-P. Boilot and A. Brun, Mater. Res. Soc. Symp. Proc., 1997, Int. J. Nonlinear Opt. Phys., 1994, 2, 483. 479, 97. 149 J. W. Perry, K. Mansour, I.-Y.S. Lee, X.-L. Wu, P. V. Bedworth, 143 H. Jiang, W. Su, M. Brant, D. Tomlin and T.J. Bunning, Mater. C.-T. Chen, D. Ng, S. R. Marder, P. Miles, T.Wada,M. Tian and Res. Soc. Symp. Proc., 1997, 479, 129. H. Sasabe, Science, 1996, 273, 1533. 144 P. V. Kolinski, R. S. Hall, M. R. Venner, D. F. Croxall, K.Welford 150 B. H. Cumpston, K. Mansour, A. A. Heikal and J. W. Perry, and S. Swatton, Mater. Res. Soc. Symp. Proc., 1995, 374, 195. Mater. Res. Soc. Symp. Proc., 1997, 479, 89. 145 P. Le Barny, V. Dentan, P. Robin, F. Soyer and M. Vergnolle, Proc. SPIE-Int. Soc. Opt. Eng., 1996, 2852, 201. 146 M. C. Brant, M. E. De Rosa, H. Jiang, D. G. McLean, R. L. Paper 8/03533D; Received 12th May, 1998 J. Mate

ISSN:0959-9428    

DOI:10.1039/a803533d

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 Communication Synthesis of FER titanosilicates from a non-aqueous alkali-free seeded system Ranjeet Kaur Ahedi and A. N. Kotasthane* Catalysis Division, National Chemical L aboratory, Pune 411 008, India Various samples of TS-FER system were prepared with diVerent Si and Ti contents. Table 1 lists the chemical composi- We have demonstrated the preparation of a new family of TSFER products using organothermal synthesis. tion of the initial mixture and the corresponding products.For all the samples Ti5Si ratios were higher in the product than in the initial mixture, indicating that not all the silica was involved in the crystallization process. TS-FER was expected to crystallize more readily along with titanium butoxide to The discovery of TS-MFI by the Enichem group1 gave a major form SiMOMTi oligomers, however, the reaction mixture in boost to heterogeneous catalysis including epoxidation and which both SiO2 and titanium butoxide were co-hydrolyzed hydroxylation of olefins with H2O2.2,3 As the trend continues did not form any FER crystals even after 15–30 days heating, with more emphasis on new titanosilicates, diVerent structural but instead transformed to the ZSM-39 phase in contrast to analogs have been reported.4–7 Generally, the hydrothermal the pure Si derivative synthesis in which highest crystallinity synthesis of Ti-bearing molecular sieves is diYcult since for the FER phase was attained in 5–6 days under identical titanium often tends to form a white insoluble phase in alkaline conditions.These findings indicate that the presence of Ti4+ aqueous medium.8,9 Therefore, we have focused our research ions tend to impede and lower the nucleation rates in the eVorts on a non-aqueous alkali-free synthesis system.We report organothermal TS-FER system. It was, however, found that a first example showing the eYcient synthesis of the ferrierite adding seed crystals of the Si-FER derivative in small quantities (IUPAC code FER) topology in terms of TiIV framework (0.8–1.0 wt.% of gel mixture) accelerates both nucleation and insertion utilizing a non-aqueous alkali-free seeded system.crystallization. It can be seen in Table 1 that in no case was Synthetic ferrierite (FER) is a high silica, medium pore framework titanium in excess of 1.8% found.These results zeolite containing linked [54] polyhedral units having inter- indicate that there exists an upper limit of framework titanium secting channels outlined by 10 membered ring (MR) (TiIV) incorporation (maximum 2.0 wt.%), and extraframework (4.3×5.5 A ° ) and 8 MR (3.4×4.8 A ° ) pores. Although a pure TiIV appears in the form of TiO2 when the Ti concentration is silica derivative of FER topology is known,10,11 there are no increased to 50 mol% relative to the number of moles of Si reports on the Ti analog of the FER system.used (sample no. 4). The synthesis method for the pure silica derivative of FER Incorporation of Ti4+ ions into the framework would generdescribed by Kuperman et al.,11 using HF/pyridine as the ally cause a unit cell volume variation.Based on this, the unit mineralizing agent has been successfully applied to the syn- cell volumes of a series of samples as calculated from XRD thesis of TS-FER. The purpose of this work was to examine data are presented in Table 1. The unit cell volume of sample the potential of the organothermal system to mobilize titanium no. 1 showed a marked increase (1977.78 A ° 3) in comparison species in alkali-free media.Depending upon the synthesis with that of the pure silica FER derivative (1947.96 A ° 3). procedure, it can be prepared within a large composition Thermoanalytical studies on TS-FER samples revealed that range.12 the decomposition of occluded organic is complete at 750 °C A typical synthesis of TS-FER was as follows.Initially 75.5 g and structural integrity is maintained until about 1000 °C. (0.955 mol) pyridine (SQ, Qualigens) plus 31.5 g (0.533 mol) DiVuse reflectance UV–VIS spectroscopy is an eYcient propylamine (E. Merck) plus 3.6 g (0.018 mol) HF/pyridine technique for qualitative evaluation of the presence of frame- (Aldrich) were mixed in a polypropylene jar under stirring. work Ti in all types of Ti molecular sieves.As shown in Fig. 1A The resulting clear solution was divided into two equal parts (ca. 62 ml each); into one portion 0.5 g (1.47×10-3 mol) of tetrabutylorthotitanate (TBOT, Aldrich) dispersed in 5 ml of isopropanol (S. D. Fine Chemicals Ltd.) was mixed and into the other portion 6.0 g (0.1 mol) Cab-o-Sil (Fluka AG) were allowed to dissolve. The samples were then mixed together forming a silicotitanate clear solution under stirring.Finally, 0.5 g of silica-FER seed precursors synthesized according to a procedure described elsewhere11 were added to the entire mixture under continuous stirring to yield a uniform dispersion. The resulting solution had a pH of 11.0±0.2. This liquid was transferred to a PTFE lined autoclave for crystallizing at 170 °C for 5 to 7 days under static condition.The crystalline TS-FER was filtered, washed with acetone and dried at 110 °C. The X-ray (Rigaku D Max III VC) powder diVraction pattern confirmed the phase purity of the TS-FER product. The TSFER product was subsequently calcined at 550 °C (12 h) and then continued till 700 °C for another 4 h to decompose organic compounds occluded during the synthesis step.Fig. 1 (A) DiVuse reflectance spectra of sample nos. (a) 5, (b) 1, (c) 2, (d) 3 and (e) 4. (B) Framework region FTIR spectra of sample nos. (a) 5, (b) 3, (c) 2 and (d) 1 (sample numbers from Table 1). †E-mail: ank·@dalton.ncl.res.in J. Mater. Chem., 1998, 8(8), 1685–1686 1685Table 1 Physico-chemical properties of TS-FER gel unit cell parameters/A ° sample product no.Si/mol Ti/mol Ti/Si a0 b0 c0 U/A ° 3 Ti/wt.% 1 0.1 1.2×10-3 1.6×10-2 18.945 14.062 7.424 1977.78 1.8 2 0.1 8.3×10-4 9.0×10-3 18.900 14.061 7.422 1972.41 1.5 3 0.1 5.5×10-4 6.0×10-3 18.829 14.061 7.419 1964.20 1.2 4 0.1 0.05 FER+major ND ND ND ND ND anatase 5 0.1 no Al/Ti — 18.687 14.062 7.413 1947.96 no Al/Ti ND=not determined. system (sample 5).This band at 960 cm-1 is a good indicator (fingerprint) of the existence of framework metallic ions in a series of Ti analogs, e.g. TS-1,15 Ti-MCM-4113 and TS-NU-1.7 Scanning electron micrographs [Fig. 2(a) and 2(b)] revealed that the seed (Si-FER) precursor [Fig. 2(a)] aggregates are made up of very thin plates of 8×5 mm size and this morphology changes during the growth of TS-FER producing [Fig. 2(b)] regular hexagonal plates of a 28×28 mm (corner to corner) large crystal. This suggest that the presence of Ti in the non-aqueous alkali free seeded system influences the distribution of silicon species during the growth of TS-FER. TS-FER has been synthesized from an organic hydrothermal system in the presence of seeds. TS-FER was found to be thermally stable up to 1000 °C.Ti incorporation was confirmed by unit cell expansion data and further supported by IR and UV–VIS spectroscopies. Scanning electron micrographs also revealed changes in crystal morphology on incorporation of titanium. The authors thank Dr. P. A. Joy (Physical Chem. Division) and Mr. S. S. Shevade for their help and support. R. K. A. also thanks CSIR for a Senior Research fellowship.References 1 M. Taramasso, G. Perego and B. Notari, U.S. Pat. 4110501, 1983, assigned to Snamprogetti SPA. 2 G. Perego, G. Bellusi, C. Corno, M. Taramasso, F. Buonomo and A. Esposito, Stud. Surf. Sci. Catal., 1986, 28, 129. 3 M. G. Clerci and P. Ingallina, J. Catal., 1993, 71, 140. Fig. 2 Scanning electron micrographs of (a) silica FER (sample no. 5), 4 P. T. Taner, M.Chibwe and J. Pinnavaia, Nature, 1994, 368, 321. and (b) TS-FER (sample no. 1). 5 M. A. Camblor, A. Corma and J. Perez Pariente, J. Chem. Soc., Chem. Commun., 1992, 589. 6 T. Tatsumi, Chem. Commun., 1996, 156. 7 R. K. Ahedi, S. S. Shevade and A. N. Kotasthane, Zeolites, 1997, 18, 361. [(b)–(e), sample nos. 1, 2 and 3] showed a single UV absorption 8 G. K. Perego, G. Bellusi, C.Corma, M. Taramasso, F. Buonomo band at around 212 nm, corresponding to isolated framework and A. Esposita, Stud. Surf. Sci. Catal., 1987, 7, 442. Ti in tetrahedral coordination.13 The presence of this band 9 B. Notari, Stud. Surf. Sci. Catal., 1987, 37, 413. could be considered as further proof of Ti incorporation into 10 H. Gies and R. Gunawardane, Zeolites, 1987, 7, 442. the FER framework; however, sample no. 4 (Fig. 1A), which 11 A. Kuperman, S. Nadimi, S. Oliver, G. A. Ozin, J. M. Graces and has a high Ti content, showed in addition to the 212 nm band M. M. Olken, Nature, 1993, 365, 239. 12 A. N. Kotasthane, R. K. Ahedi, S. S. Shevade and A. V. another broad band between 300 and 350 nm that was not Ramaswamy, Indian Pat. appl. NF 203, 1997. detected in samples 1, 2 and 3. The broad band has been 13 M. R. Boccuti, K. M. Rao, A. Zecchina, G. Leofanti and G. assigned to the anatase phase.14 This clearly suggests that any Pertrini, Stud. Surf. Sci. Catal., 1989, 48, 133. excess of Ti in the non-aqueous reaction mixture would yield 14 A. Tuel and Y. Ben Taarit, J. Chem. Soc., Chem. Commun., 1994, a Ti-bearing extraframework phase. 1667. Fig. 1B [( b)–(d); samples 1, 2 and 3] shows the IR spectra 15 A. Zecchina, G. Spoto, S. Bordiga and M. Padovan, Stud. Surf. Sci. Catal., 1991, 69, 251. of the TS-FER products. The products showed a relatively well resolved IR band at 960 cm-1 which otherwise is not Communication 8/03170C; Received 28th April, 1998 detected in the presence of the organothermal pure Si-FER 1686 J. Mater. Chem., 1998, 8(8), 1685–1686

ISSN:0959-9428    

DOI:10.1039/a803170c

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 Processible poly[(p-phenyleneethynylene)-alt-(2,5- thienyleneethynylene)]s of high luminescence: their synthesis and physical properties Yi Pang,a*† Juan Lia and Thomas J. Bartonb aDepartment of Chemistry & Center for High Performance Polymers and Composites, Clark Atlanta University, Atlanta, GA 30314, USA bAmes L aboratory, Iowa State University, Ames, IA 50011, USA Several alternating copolymers, poly[(p-phenyleneethynylene)-alt-(2,5-thienyleneethynylene)]s (PPETEs), have been synthesized by using a Heck-type coupling reaction under mild conditions.The polymers are characterized by using 1H and 13C NMR, UV–VIS absorption and fluorescence spectroscopy. PPETEs produced under the mild conditions exhibit longer conjugation length (ca. 10 nm in UV–VIS absorption lmax) than the same polymers synthesized at high temperature. The chain rigidity of the copolymers is moderate with Mark–Houwink constant a=0.82–0.94, which is moderately higher than PTE 2 (a=0.68) but significantly lower than PPE 3 (a=1.92). The PL quantum eYciencies of PPETE copolymers are found to be wfl=0.37–0.48, which is comparable to PPE homopolymers and much higher than for PTE (wfl=0.18).Synthesis of copolymer PPETE thus successfully combines both the high luminescence of PPE and good solubility of PTE into a single polymer chain. Since the a constant is one of the important parameters in Introduction describing undisturbed polymer conformations in solution, Recent research indicates a considerable interest in the photolu- correlation between the a values and solution quantum yields minescent and electroluminescent properties of conjugated of p-conjugated polymers could be a very useful probe to polymers, following the first demonstration of the light-emitting study the eVect of the molecular rigidity of a polymer in properties from poly( p-phenylenevinylene) (PPV).1 Among the solution on its PL eYciency. reported luminescent polymers, which have been used as active Another example of a poly(aryleneethynylene) is poly(thienlayers in light-emitting diodes,2 are poly(p-phenylenevinylene) yleneethynylene) (PTE) 2 which exhibits green photolumin- (PPV),3 poly( p-phenylene) (PPP),4 poly(thiophene) (PT)5 and escence10,11 with moderate solution quantum eYciency poly( p-phenyleneethynylene) (PPE).6 Current research inter- (wfl#0.2).12 The a value of PTE 2 measured in THF solvent, ests in luminescent materials include tailoring of the spectral however, is about 0.68, which is typical for a random-coil characteristics and improving their processibility and long- molecular conformation.Clearly the presence of the a-linked term stability. One of the most challenging problems in the thiophene bridges has a large impact on the long-range molecu- field is to optimize the radiative decay of the materials in order lar rigidity and the corresponding physical properties.to achieve high quantum eYciencies in both photoluminescence It is obviously desirable to develop poly(aryleneethynylene) and electroluminescence. This obviously requires an under- materials which exhibit both the high luminescence of PPE 1 standing of the various structural eVects on the luminescence and processibility of PTE 2.A standard approach is to place eYciency of the materials. both p-phenylene–ethynylene and a-linked thiophene–ethyn- Poly(aryleneethynylene) is a special class of p-conjugated ylene units into a single polymer chain as shown in 3.The polymers in which aromatic rings alternate with carbon–car- short-range chain rigidity is increased by extending the linear bon triple bonds. The linear rod-like bonding geometry of the rod-like chain segment from thiophene–ethynylene–thiophene triple bond has the advantage of extending the molecular in 2 to thiophene–ethynylene–phenylene–ethynylene–thiorigidity in both short and long ranges.For example poly( p- phene in 3, and the PL eYciency of 3 is expected to be phenyleneethynylene)s (PPEs) 1 have a linear rod molecular significantly higher than 2. Inclusion of a-linked thiophenes in 3 will modify the rigid-rod backbone of PPE so as to improve the solubility and processibility relative to PPE 1. Although a few examples of copolymer 3 have been synthesized by this group13 and others,7,11,14 no systematic study has been carried out to evaluate their PL eYciencies and their dependence on chain rigidity.Here we report our results on the synthesis of three variously substituted examples of 3 under mild conditions, and characterization of their photoluminescent properties and molecular chain rigidities. Results and Discussion S S 1 2 3 n n n Polymer synthesis and characterization structure which has a characteristically large Mark–Houwink constant (a=1.92)7 in comparison with a=0.96 for polythio- Poly[(p-phenyleneethynylene)-alt-(thienyleneethynylene)]s (PPETEs 4–6) were prepared by Heck-type coupling.15 phene.8 The increased molecular rigidity in PPEs could be responsible for their high solution PL quantum eYciencies.9 Typically a substituted 2,5-diiodothiophene reacted with a diethynylbenzene in toluene in the presence of a catalytic system PdCl2(PPh3)2–CuI–Et3N to lead to a polymer back- †Email: ypang@cau.edu J.Mater. Chem., 1998, 8(8), 1687–1690 1687Fig. 2 UV–VIS absorption spectra of 4–6 measured in THF be discussed in a forthcoming paper to deal with the synthesis and characterization of regioregular 6.Fig. 2 shows the UV–VIS absorption spectra of PPETEs. The absorption lmax values of the polymers are listed in Table 1. It is noted that the absorption lmax values of PPETE 4 and 6 are at 444 and 413 nm, which are about 11 nm longer S OC8H17 H17C8O S OC8H17 H17C8O S C6H13 C6H13 n n n I Ar I Ar¢ PPETE + 'Pd' cat 4 5 6 than the same polymers7,11 prepared at elevated temperature.Scheme 1 Synthesis of co-polymer PPETEs Clearly the mild polymerization conditions are important in synthesizing poly(aryleneethynylene)s since phenylacetylenes16 bone where a-thiophene and benzene rings alternately occur are susceptible to thermal reactions. This is also in agreement along the polymer chain. Using diiodothiophene (as opposed with the sharper alkyl 1H NMR signals observed from 4 than to dibromothiophene) allows the polymerization to be carried that from the PPETE14e synthesized at 60 °C.out at room temperature, thus minimizing the unwanted side reactions. Molecular weight and chain stiVness PPETEs were yellow–orange in color in the solid state. The The molecular weights of the polymers were measured in THF polymers showed good solubility in common organic solvents eluent by using size exclusion chromatography with on-line such as toluene, THF and chloroform. Uniform films could be refractive index, viscosity and light-scattering detectors cast from their solutions.IR and 1H NMR spectra of the (referred to as SEC3). By using the SEC3 setting, the true polymers indicated that the polymerization was completed molecular weights were obtained versus the elution volume. A under the mild conditions used as evidenced from the disaptypical SEC3 chromatogram is shown in Fig. 3, indicating a pearance of the acetylenic groups. Sharp resonance signals in monomodel distribution in molecular weight. The comparable the 1H and 13C NMR spectra (Fig. 1) imply high linear peak molecular weights from refractive index (RI), viscosity regularity along the polymer chains. Originating from the (DP) and light-scattering (LS) detectors suggest a linear struc- unsymmetrical characteristics of the 3-hexyl-2,5-thienylene ture without branching.The polydispersity indices of the unit, PPETE 5 and 6 are expected to have a random distripolymers (listed in Table 1) are about 2, which is typical17 for bution of head-to-head and head-to-tail sequences along the condensation polymerization and in agreement with the pro- polymer chain.Both 1H and 13C NMR spectra failed to detect posed linear polymer structure. the structural regioregularity since the alkyl substituents on For p-conjugated polymers, a fundamental issue is how the thiophenes are well seperated from each other. Details of much molecular rigidity is imparted by the extended p- the eVect of the structural regioregularity on physical properconjugation.Until today little attention has been paid to the ties, including photoluminescence and molecular rigidity, will solution properties8,18 of these p-conjugated polymers. Information about the unperturbed molecular conformations or dimensions in dilute solutions could be a very useful probe to gain an insight into the extended chain stiVness of poly- (aryleneethynylene)s.A typical Mark–Houwink plot for PPETE is shown in Fig. 3, which exhibits a good linear relationship between intrinsic viscosity and molecular weight. The a values in the Mark–Houwink equation [g]=K Ma were determined to be about 0.82–0.94 for PPETEs which is only moderately higher than poly(3-hexylthienyleneethynylene) (P3HTE)12 (a=0.68) but significantly lower than PPE7 (a= 1.92).The low a value implies that the polymer chains of PPETEs are far less stiV than the rigid-rod polymer PPE as a result of the main chain modification. In other words, replacing alternate phenyl groups in PPE by thiophene rings has a large impact in reducing the long-range chain stiVness of PPE.This is in agreement with the observed good solubility for PPETE 6 in which there is no substituent on the phenyl ring. Photoluminescence PPETEs exhibited strong green luminescence in solution in organic solvents. The fluorescence spectra were obtained from diluted and deoxygenated THF solutions (Fig. 4). All spectral Fig. 1 1H NMR (top) and 13C NMR (bottom) spectra of PPETE 4 in data are summarized in Table 1. Similar to the fluorescence of CDCl3. The starred signal at 7.25 ppm (top spectrum) is attributed to PPE9 and PTE,12 two well-resolved bands (high and low CHCl3. The alkyl region in the 13C NMR spectrum is not shown for clarity. energy emissions) were observed in PPETEs, suggesting the 1688 J.Mater. Chem., 1998, 8(8), 1687–1690Table 1 UV–VIS, fluorescence and molecular weight data for PPETEs polymer absorptiona lmax/nm fluorescencea lmax/nm excitation lmax/nmb wfl c MW (PDI) Mark–Houwink constant a PPETE 4 444 (THF) 482, 514 (THF) 450 (THF) 0.37 (THF) 43 900 (2.12) 0.88 444(CHCl3) 485, 518 (CHCl3) 450 (CHCl3) 0.37 (CHCl3) PPETE 5 460 (THF) 489, 520 (THF) 468 (THF) 0.48 (THF) 61 600 (2.15) 0.82 457 (CHCl3) 492, 524 (CHCl3) 468 (CHCl3) 0.47 (CHCl3) PPETE 6 414 (THF) 451, 478 (THF) 398 (THF) 0.46 (THF) 78 500 (2.27) 0.94 413 (CHCl3) 455, 480 (CHCl3) 398 (CHCl3) 0.47 (CHCl3) P3HTEd 438 (THF) 525, 535 (THF) 420 (THF) 0.18 (THF) 20 100 (1.9) 0.68 aSolvent is shown in parentheses.bFluorescence excitation lmax observed while monitoring at fluorescence lmax.cQuantum yields are measuured in CHCl3 and THF solvent while excited at excitation lmax. dPoly(3-hexylthienyleneethynylene).12 structural analogue, poly[(m-phenyleneethynylene)-alt-(thienyleneethynylene)], 14d whose wfl value in CHCl3 is reported to be only 0.18. The greater enhancement observed from the pphenylene- containing PPETE is presumably due to the longer conjugation length permitted by p-phenylene than by mphenylene in the PPETE polymers.It is also interesting to make a comparison between the photophysical properties of PPETE (3) and P3HTE (2).12 Only slight changes in the absorption lmax are observed between P3HTE and PPETEs (Table 1), indicating similar conjugation lengths between the two polymer systems.The PL quantum eYciencies of PPETEs, however, are about 2.5 times as high as P3HTE (wfl=0.18). Clearly alternate replacement of the thiophene rings along the P3HTE chain with phenyl rings has a large impact on the nonradiative decay process. The enhancement is even more pronounced in the solid state, as the PPETE film emits about 15 times more strongly than P3HTE film with a head-to-tail chain sequence12 (Fig. 4) under the identical conditions. Conclusion Alternating copolymer PPETEs synthesized under mild reac- Fig. 3 SEC3 chromatogram (top) and Mark–Houwink plot (bottom tion conditions exhibit longer conjugation length (ca. 10 nm in of PPETE 5. The intrinsic viscosity in the plot is expressed in dl l-1. UV–VIS absorption lmax) than the same polymers synthesized at high temperature. The copolymers have moderate chain rigidity with Mark–Houwink constant a=0.82–0.94, which is higher than PTE 2 (a=0.68) but drastically lower than PPE 3 (a=1.92) homopolymers.The PL quantum eYciencies of PPETE copolymers are found to be much higher than PTE 2, attributed partially to the increased local (or short-range) chain rigidity in the copolymers.More interestingly, the quantum eYciencies of PPETEs are found to be comparable with, or even slightly higher than, homopolymer PPE 3. Thus synthesis of copolymer PPETE successfully combines both good solubility of PTE and high luminescence of PPE into a single polymer chain, making the material attractive for device applications. The PL enhancement in the solid state is even more pronounced as the PPETE film emits about 15 times as strongly as P3HTE film.Experimental Materials and instrumentation 2,5-Diiodo-3-hexylthiophene,20 1,4-diethynyl-2,5-bis(octyloxy)- Fig. 4 Fluorescence spectra of PPETEs in THF solvent (top, normalized) and film state (bottom) benzene9 and 1,4-diethynylbenzene21 were synthesized according to literature procedures. 2,5-Diiodothiophene and solvents were purchased from Aldrich Chemical Company.Solvents were existence of similar pathways for the radiative decay of the excited states. The PL quantum yields were determined relative dried, distilled and stored under argon. IR spectra were recorded on a Nicolet Impact 400 FT-IR spectrometer. UV–VIS spectra to quinine sulfate. The PPETEs were found to be highly luminescent in solutions with quantum eYciencies ranging were recorded in THF or CHCl3 solvents on a Beckman DU640 spectrophotometer at 23 °C.NMR spectra were acquired on a from 0.37 to 0.48, which are quite comparable to those of PPE homopolymers19 (wfl=0.35–0.40). The quantum yields (wfl) of Bruker ARX400 spectrometer at 400MHz for 1H and 100MHz for 13C. Fluorescence spectra were recorded on a PTI steady PPETEs were measured in both THF and CHCl3, giving very similar values (Table 1).It should be noted that the wfl values state fluorometer at 23±1 °C. UV–VIS and fluorescence spectra of polymer films were recorded on glass substrates in air. Size of PPETE are significantly larger than those of an isomeric J. Mater. Chem., 1998, 8(8), 1687–1690 1689exclusion chromatography (SEC) was carried out on a Viscotek solutions at the excitation wavelength; Fs and Fr are the corresponding emission integration areas; and ws and wr are SEC assembly consisting of a Model P1000 pump, a Model T60 dual detectors and a Model LR40 laser refractometer.quantum eYciencies of the sample and reference compound; ns and nr are refractive indices of the sample and standard solutions.Polymer concentrations for SEC experiments were prepared in a concentration of 2–3 mg ml-1. Solid state fluorescence spectra were acquired from spin-cast films whose photoabsorbance was between 0.7–1.0 at absorption lmax. Emission was detected at 90° from the incident beam by Preparation of poly[(3-hexyl-2,5-thienyleneethynylene)-altthe front face fluorescence method with the film placed at an (1,4-phenylene ethynylene)] 6, a general procedure for PPETEs angle of about 45° to both the incident beam and the detector. 3-Hexyl-2,5-diiodothiophene (2.776 g, 2.2 mmol), 1,4-diethyn- The relative emission intensity was estimated by using ylbenzene (0.277 g, 2.2 mmol) and triethylamine (2.6 g, 26 mmol) were dissolved in 40 ml of dry toluene in a 100 ml ws/wr=(Ar/As) (Fs/Fr) (ns2 /nr2)#(Ar/As) (Fs/Fr) oven-dried, one-necked, round-bottomed flask which was similarly defined in the solution measurement. Here the refracequipped with a magnetic stirrer and capped with a rubber tive indices are assumed to be similar for both PPETEs septum.The solution was deoxygenated by twice repeating a and P3HTE. cycle of freezing and thawing under vacuum, followed by filling with an argon atmosphere.Catalysts PdCl2(PPh3)2 (14.0 mg, Support of this work has been provided by U.S. Air Force 0.02 mmol) and CuI (3.8 mg, 0.02 mmol) were added at room (Grant No. F49620–96–1-0012) and NASA through the High temperature in a glove bag under a dry argon atmosphere. Performance Polymers and Composites Center. After stirring the solution at room temp.for 4 h ( lots of salts formed during this period), the reaction mixture was heated References to 42 °C overnight. The resulting orange–brown solution was twice precipitated from methanol to give a yellow resin (92% 1 J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks, yield). 1H NMR (CDCl3) d 0.89 ( br, 3H, CH3), 1.25–1.40 [br, K.MacKay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature, 1990, 347, 539. 6H, (CH2)3], 1.67 ( br, 2H, CH2), 2.73 ( br, 2H, CH2), 7.07 (s, 2 For a recent review see: A. Kraft, A. C. Grimsdale and 1H, thiophene H), 7.48 (s, 4H, phenyl H). Quantitative 13C A. B. Holmes, Angew. Chem., Int. Ed. Engl., 1998, 37, 402. NMR (CDCl3) d 13.6 (1C), 22.1 (1C), 28.4 (1C), 29.1 (1C), 3 N. C. Greenham, S.C. Moratti, D. D. C. Bradley, R. H. Friend and 29.6 (1C), 31.1 (1C), 83.8 (1C), 84.4 (1C), 93.3 (1C), 95.7 (1C), A. B. Holmes, Nature, 1993, 365, 628. 119.6 (1C), 122.3 (1C), 122.5 (1C), 122.7 (1C), 130.9 (4C), 132.7 4 G. Grem, G. Leditzky, B. Ulrich and G. Leising, Adv.Mater., 1992, (1C), 147.6 (1C). Anal. calc. for (C20H18S)n: C, 82.71; H, 6.25. 4, 36. 5 M. R. Andersson, M.Berggren, O. Ingana�s, G. Gustafsson, Found: C, 82.05; H, 6.19%. J. C. Gustafsson-Carlberg, D. Selse, T. Hjertberg and O. Wennerstro�m, Macromolecules, 1995, 28, 7525. Poly[(2,5-thienyleneethynylene)-alt-(2,5-dioctyloxy-1,4- 6 (a) L. S. Swanson, J. Shinar, Y. Ding and T. J. Barton, Synth. Met., phenyleneethynylene)] 4. PPETE 4 (yellow–orange resin) was 1993, 55–57, 1; (b) C.Weder, M. J. Wagner and M. S. Wrighton, synthesized in 89% yield using the same conditions as described Mater. Res. Soc. Symp. Proc., 1996, 413, 77. for 6. 1H NMR (CDCl3) d 0.87 ( br, 6H, CH3), 1.28 [br, 16H, 7 M. Moroni, J. L. Moigne and S. Luzzati, Macromolecules, 1994, (CH2)4], 1.52 (br, 4H, CH2), 1.83 ( br, 4H, CH2), 4.01 (br, 4H, 27, 562. 8 S. Holdcroft, J. Polym. Sci., Part B: Polym.Phys., 1991, 29, 1582. -CH2O-), 6.97 (s, 2H), 7.14 (s, 2H). 13C NMR (CDCl3) d 153.2 9 C. Weder and M. S. Wrighton, Macromolecules, 1996, 29, 5157. (2C), 131.5 (2C), 124.6 (2C), 116.1 (2C), 113.4 (2C), 90.6 (2C), 10 L. S. Swanson, P. A. Lane, J. Shinar, Y. Pang and T. J. Barton, 87.5 (2C), 69.5 (2C), 31.7 (2C), 29.1 (6C), 25.9 (2C), 22.5 (2C), Synth.Met., 1993, 55–57, 293. 13.9 (2C). Anal. calc. for (C30H38O2S)n: C, 77.88; H, 8.28. 11 T. Yamamoto, W. Yamada, M. Takagi, K. Kizu, T. Maruyama, N. Found: C, 77.01; H, 8.15%. Ooba, S. Tomaru, T. Kurihara, T. Kaino and K. Kubota, Macromolecules, 1994, 27, 6622. 12 J. Li and Y. Pang,Macromolecules, 1997, 30, 7487. Poly[(3-hexyl-2,5-thienyleneethynylene)-alt-(2,5-dioctyloxy- 13 Y. Pang, Z. Wang and T. J. Barton, Polym.Prepr., (Am. Chem. Soc. 1,4-phenyleneethynylene)] 5. PPETE 5 (yellow–orange resin) Div. Polym. Chem.), 1996, 37(2), 333. was synthesized in 95% yield using the same conditions as 14 (a) K. Sanechika, T. Yamamoto and A. Yamamoto, Bull. Chem. described for 6. 1H NMR (CDCl3) d 7.05 (s, 1H), 6.95 (s, 2H), Soc. Jpn., 1984, 57, 752; (b) T. Yamamoto, M. Takagi, K. Kizu, 4.00 ( br, 4H, -CH2O-), 2.75 (br, 2H, -CH2-thiophene), 1.82 ( br, T.Maruyama, K. Kubota, H. Kanbara, T. Kurihara and T. Kaino, 4H), 1.65 ( br, 2H), 1.51 ( br, 4H), 1.10–1.42 ( br, 22H), 0.87 ( br, J. Chem. Soc., Chem. Commun., 1993, 797; (c) M. Takagi, K. Kizu, Y. Miyazaki, T. Maruyama, K. Kubota and T. Yamamoto, Chem. 12H, CH3). Anal. calc. for (C36H50O2S)n: C, 79.07; H, 9.21, L ett., 1993, 913; (d) B.S. Kang, D. Y. Kim, S. M. Lim, J. Kim, M.- Found: C, 78.51, 9.08%. L. Seo, K.-M. Bark, S. C. Shin and K. Nahm, Macromolecules, 1997, 30, 7196; (e) T. Yamamoto, K. Honda, N. Ooba and Photoluminescence quantum yield measurements S. Tomaru, Macromolecules, 1998, 31, 7; J. Tsuji, Palladium Reagents and Catalysts: Innovations in Organic Synthesis, Wiley, All slits were kept at 2 nm for excitation and emission.New York, 1995, pp. 168–178. Photoluminescence spectra were corrected for the spectral 16 S. Amdur, T. Y. Cheng, C. J. Wong, P. Ehrlich and dispersion of the Xe lamp. All sample solutions were freshly R. D. Allendoefer, J. Polym. Sci., Polym. Chem. Ed., 1978, 16, 427. prepared in dry THF, purged with high purity argon and used 17 G. Odian, Principles of Polymerization,Wiley, New York, 1991, 3rd within four hours.Absorbances of all sample solutions were edn., ch. 2. 18 (a) X. Bi, Q. Ying and R. Qian, Makromol. Chem., 1992, 193, 2905; kept between 0.05–0.08. Quantum yields of fluorescence were (b) T. Yamamoto, D. Oguro and K. Kubota,Macromolecules, 1996, determined relative to quinine sulfate22,23 in 0.5 M H2SO4 at 29, 1833. 23±1 °C, assuming a quantum yield of 0.546 when excited 19 (a) T. M. Swager, C. J. Gil and M. S. Wrighton, J. Phys. Chem., at 365 nm. Refractive indices24 of pure 0.5 M H2SO4 and THF 1995, 99, 4886; (b) A. P. Davey, S. Elliott, O. O’Connor and were used for the standard and sample solutions during the W. Blau, J. Chem. Soc., Chem. Commun., 1995, 1433. calculation of quantum yield. The quantum yields reported 20 H. Mao, B. Xu and S. Holdcroft,Macromolecules, 1993, 26, 1163. 21 B. N. Ghose, Synth. React. Inorg.Met.-Org. Chem., 1994, 24(1), 29. here are averaged over at least three measurements, with a 22 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991. standard deviation below 0.02. The quantum eYciency of a 23 W. H. Melhuish, J. Phys. Chem., 1961, 65, 229. sample was calculated by using the following equation: 24 CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, FL, 62nd edn., 1982–1983. ws=wr (Ar/As) (Fs/Fr) (ns2/nr2) Here Ar and As are the absorbances of the sample and reference Paper 8/02032I; Received 13thMarch, 1998 1690 J. Mater. Chem., 1998, 8(8), 1687–

ISSN:0959-9428    

DOI:10.1039/a802032i

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 EVect of molar mass of an epoxy oligomer on the phase separation in epoxy based polymer dispersed liquid crystals Humaira Masood Siddiqi, Michel Dumon*† and Jean Pierre Pascault Institut National des Sciences Applique�es, L aboratoire des Mate�riaux Macromole�culaires UMR 5627 CNRS, ba�timent 403, 20 avenue Albert Einstein, F- 69 621 V illeurbanne cedex, France Polymer dispersed liquid crystals based on epoxy–amine crosslinked matrices and a nematic liquid crystal, E7, have been studied over the course of polymerisation, i.e.as a function of the polymerisation conversion. The influence of epoxy oligomer molar mass on the initial temperature–concentration and the temperature–conversion phase diagrams has been investigated. An increase of the epoxy oligomer molar mass greatly reduces the initial liquid crystal solubility and brings the cloud points to earlier polymerisation conversions, which have been quantified.Thus the phase separation is markedly enhanced. The temperature–conversion phase diagrams have been characterised at two isothermal polymerisation temperatures for one liquid crystal composition (50 wt.%).These diagrams (isotropic–nematic and nematic–isotropic transition temperatures) are shown to obey master curves when the epoxy molar mass is varied. Finally, the size of the liquid crystal droplets is shown to decrease when the epoxy molar mass increases. This eVect is mainly due to the viscosity increase resulting from the oligomer mass increase. Viscosity measurements were made at intervals during polymerisation.Microcomposites obtained from the phase separation of low by Kim4 and Ono.5 Both the authors reported a decrease in size of the dispersed particles upon increasing the average molar mass liquid crystal molecules in a polymer matrix combine the fluidity and anisotropy of mesophases and the molar mass of PMMA. According to Kim this is a consequence of an increased solution viscosity, which hinders the growth of characteristics of polymers (mechanical properties, film formation etc.).Polymer dispersed liquid crystals (PDLCs) are one the particles. A theoretical and experimental approach has also been reported by Kyu et al.,6 who concluded that the type exhibiting a closed cell structure where the liquid crystal is dispersed as fluid droplets.The properties of these hetero- critical temperature Tc moves to pure LC limits with an increase in the molar mass of PMMA. The increase in tempera- geneous materials are dependent on their morphologies. Therefore the control of morphology during the formation ture is of the order of 2–3 °C. In addition, the pure nematic region becomes narrower.process of PDLCs is of the utmost importance. Three main formation processes1 are currently found in the literature In previous papers7–8 we investigated the eVect of the polymerisation temperature, cure cycles and gelation on the [solvent induced phase separation (SIPS), thermal induced phase separation (TIPS) and polymerisation induced phase morphology. It was shown that an epoxy (low molar mass DGEBA)–amine/LC system remained homogeneous through- separation (PIPS)].This paper deals with the latter process, where a nematic liquid crystal (LC) is separated during the out the reaction at 100 °C, a temperature higher than the TN–I of the pure LC. However it could separate into two phases polycondensation of the diepoxy and diamine oligomers. The diamine is an a,v-amino poly(propylene-oxide) (JeVamine only when cooling the reaction mixture from the reaction temperature to room temperature (TIPS).At a temperature D400), while the diepoxy species, the diglycidyl ether of bisphenol A (DGEBA), has two diVerent molar masses. lower than the TN–I of the pure LC (e.g. 30 °C), an isotropic+nematic phase separation was obtained at the reac- The eVects of an increase in molar mass of one component on the isotropic polymer–polymer phase diagrams are well tion temperature (PIPS).Furthermore, when the TIPS is operative, TN–I is shown to be independent of the gelation, known.2 However, in the case of PDLC, few authors have studied this. In fact, one of the first reported phase diagrams, while in the case of PIPS we observe an increase of TN–I beyond gel point.This jump of TN–I was suggested to be due to the concerning PDLC, prepared by PIPS by Hirai and Niyama,3 dealt with monomer–oligomer/LC phase diagrams where appearance of elastic properties and thus a contribution of the matrix elastic term to the overall free energy of mixing. either the oligomer/monomer ratio or the monomer molar mass was varied.The monomers were monoacrylates of diVer- The morphologies were found to be strongly dependent on the thermal cycles selected. ent molar masses, while the oligomer was a urethane–acrylate oligomer of number average molar mass 2000 g mol-1. These Now we present the dependence of phase separation and morphology on the molar masses of the initial epoxy oligomer, authors showed that, as either the molar mass of the monomer or the oligomer concentration increases, the phase separation i.e.we will compare two DGEBA species with average constitutional repeating units equal to n:=0.03 or 0.49. The area extends and the binodal line in particular moves into higher temperature regions. On the other hand, the molar same diamine will be used in a stoichiometric amount.The polymerisation temperatures and the LC concentration will mass dependence of the oligomer does not contribute much to phase separation. The authors explained that the monomer also be kept the same. contributes to both terms of the free energy, i.e. enthalpic and entropic, while the oligomer contributes only to the enthalpic term. Other PDLC composites based on poly(methyl metha- Experimental crylate) and prepared by the SIPS process have been studied A detailed description of the reactants, the LC (E7 nematic mixture from Merck) and the preparation of samples is given in refs. 7 and 8. The abbreviations DGEBA0.03 and †E-mail: mdumon@insa.insa-lyon.fr J. Mater. Chem., 1998, 8(8), 1691–1695 1691isothermal temperature of 60 °C. The reactive mixture was confined between parallel plates in order to apply an angular periodic deformation.9,10 The plate diameter was 40 mm and the sample thickness close to 2 mm. In the measurements, the shear rates varied from 1 to 100 rad s-1 with an angular deformation of 10%.The dynamic mechanical measurements give access to the complex dynamic shear modulus (G¾, G) and also to the complex dynamic viscosity.9 The real part of the complex dynamic viscosity is currently named g¾ (g¾=G/v, where G is the loss shear modulus at an angular frequency v).In fact, in the frequency sweep mode, measurements were recorded at diVerent times of reaction, and at each frequency the reaction was maintained during the measurement time. However, the reaction rate is suYciently slow as to consider that the change in modulus during testing is negligible.Therefore the frequency sweeps were made on the same sample over the course of reaction, at several stages of reaction. Fig. 1 Size exclusion chromatograms of the epoxy oligomers as a Results and Discussion stoichiometric mixture with D400: (a) DGEBA0.03 and (b) DGEBA0.49 EVect of increase in molar mass of prepolymer DGEBA on the pure epoxy systems (without LC) DGEBA0.49 will be used for the two diepoxy monomers (0.03 The non-reacted mixtures of the DGEBA oligomers with the and 0.49 refer to the average constitutional repeating unit n:).7 diamino poly(propylene oxide) showed the initial glass trans- Their number average molar masses are respectively 348.5 and ition tempratures Tg00.03=-51 and Tg00.49=-29 °C, respect- 479 g mol-1.The diamine D400 has a number average molar ively. After a 3 h cure at 100 °C the polymers were checked for mass of 400 g mol-1. Fig. 1 shows size exclusion chromatoany residual heat of reaction by DSC. The final values are grams of the epoxy–amine stoichiometric mixtures. On both Tg2 0.03=39 and Tg2 0.49;C. chromatograms, the diamine D400 is neither detected by UV The gel point was determined experimentally as described spectroscopy nor by refractometry. The DGEBA0.49 oligomer previously;7 an average value of xgel=0.565±0.015 was contains epoxy i-mers with three main diVerent degrees of obtained, which agrees fairly well with the theoretical value polymerisation.It is therefore a polydisperse oligomer, while of 0.577.11 DGEBA0.03 is nearly monodisperse and contains mainly the oligomer n:=0.EVect of increase in molar mass of prepolymer DGEBA on the Temperature–concentration phase diagrams, before polyphase diagrams in oligomer/LC mixtures before merisation, were constructed in the following way: mixtures polycondensation with diVerent LC concentrations were prepared (LC percentages are given in wt.% of the total PDLC mixture), then a The initial temperature–composition phase diagrams before drop of the initial mixture was confined between two glass any reaction (considered as pseudo-binary diagrams between plates and mounted on a hot plate under a polarized optical the diepoxy–diamine monomers and the LC) are shown in microscope (POM) (Leica laborlux 12POLS equipped with a Fig. 2 and 3. Two kinds of curves are plotted: (i) the Mettler FP82 hot plate). The sample was heated rapidly to isotropic–nematic transition temperatures (TI–N) of DGEBA– 100 °C (homogeneous state) and then cooled at 1 K min-1 D400/LC mixtures corresponding to the appearance of until tiny nematic droplets are observed. This temperature was separated nematic droplets on cooling from a homogeneous taken as the TI–N=Tcp temperature (CP=cloud point).isotropic phase and (ii) the glass transition temperatures of Temperature–conversion phase diagrams, in the course of the DGEBA–D400/LC mixtures. polymerisation, were drawn for only one epoxy–amine/LC The TI–N values were obtained by two techniques, namely mixture (50/50 wt.%), which was cured isothermally at either POM and DSC, with 1 and 5 K min-1 cooling rates, 30 or 100 °C.The mixture was reacted in both DSC pans and between glass plates (POM). In the calorimetric measurements (DSC Mettler 3000), a series of samples was cured to diVerent stages of reaction and each system was analysed (TI–N, TN–I , Tg). Cooling scans were performed at 5 K min-1 and the TI–N was read at the onset of the exothermic peak.Heating scans were performed at 10 K min-1 and the TN–I was read at the maximum of the endothermic peak. For the isothermal cure at 30 °C, phase separation was characterized (POM) by the appearance of nematic droplets at a conversion xcp.7–8 The same sample was observed using POM at 30 °C during the rest of the polymerisation. For the cure at 100 °C, several samples were prepared and reacted, under POM, to diVerent extents of reaction (x100).Then each sample was cooled at 1 K min-1 to induce phase separation and to measure the I–N transition temperatures as Fig. 2 Initial phase diagrams for DGEBA0.03–D400/E7 system: a function of the conversion reached at 100 °C.7,8 (×) TI–N values, measured by DSC, on cooling at 5 K min-1, (1) TI–N The changes in the viscosity of the two reactive diepoxy– values, measured by POM, on cooling at 1 K min-1, (+) Tg onset, diamine systems (DGEBA0.03–D400 and DGEBA0.49–D400), measured by DSC, on cooling at 5 K min1, ($) Tg mid-point, measured in stoichiometric ratios, were followed upon curing by a by DSC, on cooling at 5 K min-1, and (&) Tg end, measured by DSC, on cooling at 5 K min-1 mechanical dynamic analyser (Rheometrics RDAII) at an 1692 J.Mater. Chem., 1998, 8(8), 1691–1695Fig. 4 Transition temperatures as a function of reaction conversion Fig. 3 Initial phase diagrams for DGEBA0.49–D400/E7 system: (measured by DSC on a heating ramp, 10 K min-1, after cooling to (×) TI–N values, measured by DSC, on cooling at 5 K min-1, (1) TI–N -100 °C) for the DGEBA0.49–D400/E7 (50 wt.%) system, cured at values, measured by POM, on cooling at 1 K min-1, (+) Tg onset, 30 °C: (1) Tg(b), ($) Tg(a) and (2, %, 6) TN–I measured by DSC, on cooling at 5 K min1, ($) Tg mid-point, measured by DSC, on cooling at 5 K min-1, and (&) Tg end, measured by DSC, on cooling at 5 K min-1 DGEBA0.03-based PDLC and xcp=0.28 for DGEBA0.49- based PDLC.This diVerence is a direct consequence of the respectively. Cooling scans were preferred over heating scans, decrease in miscibility as a result of the increase in Mn of thus TI–N curves are considered as cloud point curves. The TI–N DGEBA0.49. values increase with LC content because the temperature at In parallel with optical microscopic observations, the TN–I which the order parameter reaches a critical value of 0.44, and Tg temperatures were followed by DSC by increasing the according to the Maier–Saupe theory, increases with the LC reaction conversion for the DGEBA0.49-based PDLC cured content.12 The temperature at which the nematic interactions at 30 °C (Fig. 4). It is clear that two Tg and one TN–I are present appear (giving a nematic phase) increases with LC content.as early as a reaction conversion of 0.05, in contrast to the However, the minimum amount of LC required to demix the DGEBA0.03 PDLC,8 which required a conversion of 0.3. But system is quite diVerent for the two epoxy monomers: 65 wt.% in exactly the same way as for DGEBA0.03, there is a jump of LC for DGEBA0.03 and only 35 wt.% of LC for of TN–I values close to conversions of x=0.45 (DGEBA0.49) DGEBA0.49 (DSC measured values).This means that and x=0.55 (DGEBA0.03). In the DGEBA0.03 system, the oligomer/LC mixtures whose LC contents are less than 65 or TN–I jump was attributed to the role of elasticity in the mixing 35 wt.%, respectively, will not exhibit any LC phase and no energy;8 however, in the DGEBA0.49 system the increase in demixing will take place on cooling until the vitrification of a TN–I occurs before gelation is attained.So, in this case, the single homogeneous isotropic phase occurs. In other words, in eVect of gelation is overruled and this phenomenon is only an these LC concentration ranges, the DSC cooling scans of the eVect of cooling in the DSC. Indeed, the DSC measurements corresponding mixtures exhibit a single Tg and no isotropic– are carried out on a heating ramp after cooling to -100 °C, nematic transition.Therefore, 65 and 35 wt.% represent so the cooling will certainly have contributed to phase separathe solubility limits of the LC molecules in the initial tion. To prove this we measured the TN–I values of the glass DGEBA0.03–D400 and DGEBA0.49–D400 monomers.So an slide samples on the hot plate under POM (Fig. 5). It can be increase in epoxy oligomer molar mass decreases the LC initial seen that, without any previous cooling, a smooth increase of miscibility by a considerable amount. TN–I as a function of conversion is observed. Fig. 2 and 3 also show the decrease in Tg with the LC Subsequently, the DGEBA0.49–amine monomers were content.The Tg of the pure LC is -63 °C. According to the reacted at 100 °C in the presence of 50 wt.% LC. At this Fox equation,13 the introduction of LCs in epoxy–amine temperature, the system remains homogeneous throughout the monomers lowers the Tg of the mixture, and the calculated Tg reaction (DSC, POM) and its behaviour is quite similar to of a 65 wt.% LC mixture in DGEBA0.03–D400 is -59 °C PDLCs based on DGEBA0.03.Phase separation is only whereas that of a 35 wt.% LC mixture in DGEBA0.49–D400 is -42 °C. Both values agree well with the measured ones of -62 and -36 °C (mid points). This is consistent with the presence of a single homogeneous phase at these concentrations. EVect of increase in molar mass of prepolymer DGEBA on the phase separation during an isothermal cure at 30 or 100 °C of a 50 wt.% LC blend As described in the introduction and experimental sections, phase separation is obtained isothermally at 30 °C (PIPS) or on cooling partially reacted samples from the reaction temperature, 100 °C (TIPS).The conversion which is used in the following section is that attained at the reaction temperature. Firstly, we consider that the epoxy–amine monomers reacted isothermally at 30 °C in the presence of 50 wt.% LC. With both epoxy oligomers, phase separation takes place during Fig. 5 N–I transition temperatures (measured by POM) as a function cure at 30 °C in the form of birefringent points which of conversion for two DGEBA–D400/E7 (50 wt.%) PDLC are detected under POM. The cloud point conversions systems, cured at 30 °C: (%) DGEBA0.03–D400/E7 and (1) DGEBA0.49–D400/E7 where the nematic particles are detected are xcp=0.45 for J.Mater. Chem., 1998, 8(8), 1691–1695 1693Fig. 6 Transition temperatures as a function of reaction conversion Fig. 7 Master curves of the systems cured at 30 °C; shift factor equal to (measured by DSC on a heating ramp, 10 K min-1, after cooling to 0.09; reference curve is DGEBA0.49. (#) TN–I (POM measured) -100 °C) for the DGEBA0.49–D400/E7 (50 wt.%) system, cured at DGEBA0.49–D400/E7, (6) TN–I (POM measured) DGEBA0.03– 100 °C: (1) Tg(b), ($) Tg(a) and (2) TN–I D400/E7, ($) TI–N (POM measured) DGEBA0.49–D400/E7, (+) TI–N (POM measured) DGEBA0.03–D400/E7.obtained on cooling the reacting system at diVerent conversions. Fig. 6 presents the evolution of diVerent transition temperatures (DSC measurements on a heating ramp after cooling to -100 °C).Comparing Fig. 4 and 6 one can see that the 30 °C cure provides higher transition temperatures (Tg, TN–I) than the 100 °C cure, which reflects a better phase separation at lower temperatures. This is again mainly the result of the lower miscibility of DGEBA0.49 in terms of entropic contribution.In order to check this hypothesis, the number average molar mass of the epoxy–amine i-mers can be calculated using Makosco–Miller theory,14 without deriving the molar mass distribution function [eqn. (1)], Mn= 2MD400+4MDGEBA 2+4(1-2x) (1) Fig. 8 Master curves of the systems cured at 100 °C; shift factor equal to 0.23; reference curve is DGEBA0.49.A line is drawn to guide the where MD400=400 g mol-1, MDGEBA0.03=348.5 g mol-1, eye. (%) TN–I (DSC measured) DGEBA0.49–D400/E7 and (&) TN–I MDGEBA0.49=479 g mol-1 and x is the epoxy conversion. (DSC measured) DGEBA0.03–D400/E7 At x=0.05, we calculate Mn=485 g mol-1 for DGEBA0.49–D400, and at x=0.208 Mn2=498 g mol-1 for DGEBA0.03–D400. These conversions are those where phase Therefore it has been shown that master curves can be constructed on which the conversion evolution of the nematic– separation is first detected by DSC.One can note that the number average molar masses of the epoxy–amine i-mers are isotropic or isotropic–nematic temperatures of PDLCs based on diVerent molar masses can be superimposed. The shift comparable, showing only the eVects of entropy.factors can be determined experimentally both from DSC or POM measurements. Correlation and ‘master curves’ of TN–I–conversion curves We measured TN–I and/or TI–N of two 50 wt.% LC systems EVect of increase in molar mass of prepolymer DGEBA on the diVering by the DGEBA molar mass and the reaction temperamorphology of a 50 wt.% LC composite cured at 30 °C ture. These measurements provided us with several TN–I and TI–N conversion evolutions, namely TN–I=f (x) for Fig. 9 shows the evolution of the LC droplet diameter as a function of the reduced conversion x-xcp. It appears that the DGEBA0.03–D400/LC (50 wt.%), or DGEBA0.49–D400/LC (50 wt.%) at Ti=30 or Ti=100 °C for either DSC or POM diameters obtained with the higher epoxy oligomer are smaller than those obtained with the lower epoxy oligomer.This measurements. We attempted a correlation of these curves by plotting master curves. Can the TI–N, N-I curves, obtained with diameter evolution results from the influence of both miscibility and viscosity.8,16,17 We performed measurements of viscosity diVerent molar masses, be superimposed by applying a conversion- shift factor, a(T ) for a given temperature? Such a corre- over the course of polymerisation of the two neat systems at 60 °C.Experiments at 30 °C would be very slow, while at 100 °C lation would help predict the conversion dependence of the transition temperatures when one uses diVerent oligomer molar the systems are too fluid, but assuming a single activation energy, viscosity can be compared at 60 °C.At this temperature, masses. The final purpose is to plot transition temperature –conversion dependences on a unique curve. The approach we found that before the gel point (where only viscous behaviour is present), the dynamic viscosity of the is similar to the time–temperature superposition of the viscoelastic behaviour of amorphous polymers.15 DGEBA0.49–D400 reactive system is ten times higher than that of the DGEBA0.03–D400 system at any conversion The reference curve being that of DGEBA0.49, Fig. 7 shows that the TI–N, N–I (POM) curves can be accurately superimposed (Fig. 10). Thus, if the two PDLC systems are compared at the same conversion after the cloud point (x–xcp is fixed), the real by applying a conversion shift factor of a(30 °C)=0.09. We checked that the same shift factor can be applied to superim- epoxy conversion is smaller with the high molar mass DGEBA, but the diameter is smaller.This means that the main eVect pose the TN–I (DSC) curves at 30 °C. At 100 °C, a shift factor of a(100 °C)=0.23 (Fig. 8) is calculated to superimpose the that accounts for the particle size is the viscosity of the reaction medium. TN–I (DSC) curves. 1694 J.Mater. Chem., 1998, 8(8), 1691–1695MDGEBA0.49=479 g mol-1. Then, a 50 wt.% LC mixture was chosen and the eVect of the epoxy molar mass was characterized over the course of polymerisation. In our PDLC systems, we illustrate the influence of molar mass using two parameters: the thermodynamic stability of the reacting mixture (illustrated by temperature–conversion phase diagrams obtained by both DSC or POM) and the viscosity of the reaction medium at the cloud point.For the same isothermal cure (30 or 100 °C), the cloud point conversion is lowered with increasing epoxy molar mass and the phase separation is enhanced. The decrease in miscibility resulting from a decrease in entropy is the major parameter that aVects phase separation during polycondensation.Furthermore, the temperature– conversion diagrams (isotropic–nematic and nematic–isotropic transition temperatures) are shown to obey master curves Fig. 9 Evolution of liquid crystal droplet average diameter as when the epoxy molar mass is varied. On the other hand, the a function of ‘reduced’ conversion (x-xcp) at 30°C: (#) viscosity of the reaction medium at the cloud point is the DGEBA0.03–D400/E7 and ($) DGEBA0.49–D400/E7.parameter that aVects the morphology evolution and the final size of the LC droplets. References 1 J. L. West, Mol. Cryst. L iq. Cryst., 1988, 157, 427. 2 L. A. Utracki, Polymer Alloys and Blends, Hanser, 1990. 3 Y. Hirai and S. Niyama, SPIE, 1990, 1257, 2. 4 B. K. Kim, Y. S. Ok and C. H. Choi, J. Polym. Sci., Part B: Polym.Phys., 1995, 33, 707. 5 H. Ono and N. Kawatsuki, Polym. Bull., 1995, 35, 364. 6 T. Kyu, C. Shen and H. W. Chin, Mol. Cryst. L iq. Cryst., 1996, 287, 27. 7 H.Masood Siddiqi, M. Dumon, J. P. Eloundou and J. P. Pascault, Polymer, 1996, 37, 4795. 8 H.Masood Siddiqi, M. Dumon and J. P. Pascault,Mol. Cryst. L iq. Cryst. , 1998, in the press. 9 J. P. Eloundou, M. Fe� ve, J.F. Ge�rard, D. Harran and J. P. Fig. 10 Real part of dynamic viscosity g¾ (log10 plot) as a function Pascault, Macromolecules, 1996, 29, 6907. of conversion at 60 °C. Various angular frequencies were used. 10 J. P. Eloundou, . Ge�rard, D. Harran and J. P. Pascault, DGEBA0.49–D400: (+) 1, (&) 10, (2) 25, ($) 100 rad s-1. Macromolecules, 1996, 29, 6917. DGEBA0.03–D400: (6) 1, (%) 10, (1) 25, (#) 100 rad s-1. 11 K. Dusek, M. Ilavsky and S. Lunak, J. Polym. Sci., Polym. Symp., 1975, 53, 29. 12 J. Borrajo, C. Riccardi, R. J. J. Williams, H. Masood Siddiqi, Conclusion M. Dumon and J. P. Pascault, Polymer, 1998, 39, 845. Two epoxy monomers (DGEBA0.03 and DGEBA0.49) 13 T. G. Fox, Bull. Am. Chem. Soc., 1956, 2, 123. 14 C. W. Macosko and D. R. Miller, Macromolecules, 1976, 9, 199. diVering by their molar mass were compared in an epoxy– 15 Introduction to polymer viscoelasticity, ed. J. J. Aklonis and amine based PDLC. In this study the amine was kept the W. J. Macknight, Wiley Interscience, 1982. same. Firstly, before polymerisation, pseudo-binary tempera- 16 S. Montarnal, Ph.D. Thesis, INSA de Lyon, 1987, p. 190. ture–composition phase diagrams between the epoxy–amine 17 R. J. J. Williams, B. A. Rozenberg and J. P. Pascault, Adv. Polym. monomers and a LC (nematic E7) show that the solubility Sci., 1997, 128, 95. limit of the LC is considerably reduced when the epoxy monomer molar mass is increased from MDGEBA0.03=348.5 to Paper 8/01857J; Received 6thMarch, 1998 J. Mater. Chem., 1998, 8(8), 1691–1695 16

ISSN:0959-9428    

DOI:10.1039/a801857j

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 Polyion-complexed assemblies of diacetylenic carboxylic acid with triblock polyamine carrying a boronic acid-functionalized segment Masazo Niwa,*† Tadahiro Ishida, Tomoki Kato and Nobuyuki Higashi* Department of Molecular Science & T echnology, Faculty of Engineering, Doshisha University, Kyotanabe, Kyoto 610-0321, Japan The polyion complex of 10,12-pentacosadiynoic acid 1 and a novel ABA-type triblock polyamine 2, containing phenylboronic acid groups as sugar-responsive sites, has been prepared. Monolayer properties of the complex 2/1 are examined by measuring surface pressure (p)–area (A) isotherms on water.The p–A curves are found to vary drastically by changing pH in the subphase, suggesting the conformational change of the copolymer segment of 2 containing phenylboronic acid groups and/or deformation of the polyion complex of 2/1.Polymerizations of the complex monolayer of 2/1 are carried out upon UV irradiation, resulting in successful production of polydiacetylene with a blue form under optimum conditions of pH, temperature, substrate, surface pressure and so on. When the polymerized 2/1 LB film deposited on a quartz plate is immersed in aqueous solutions of various diol compounds such as sugars and nucleosides, a remarkable spectral variation due to blue to red color phase change of the polydiacetylene matrices is observed, implying binding of the diol compounds to the phenylboronic acid moieties located at the LB film surface.The extent of the spectral variation of the LB film seems to be proportional to the binding ability for the diol compounds.We report the photopolymerization of mono- and multi-layers polyion-complexed diacetylene mono- and multi-layers and their response to diol compounds. of polyion-complexed diacetylenic carboxylic acids with a triblock polyamine containing phenylboronic acid groups, and their interaction with diol compounds.Polyion complexation Results and Discussion of ionic amphiphiles and oppositely charged polyions at the air–water interface is one of the most fascinating techniques Preparation and characterization of polyion complex for stabilization and facilitated deposition of monolayers.1 We have shown in previous papers14 that bis(isopropylxan- Such polyion-complexed Langmuir–Blodgett (LB) films have thogen) disulfide (BX) serves as an photoinitiator–transfer been found to be stable in water.Another merit of the polyion agent–terminator for the photopolymerization of vinyl mon- complexation is to incorporate a functional polymer segment omers and that the resulting polymers contain an isopropyl- into the polyions.1 xanthate group as a photoinitiatable site at each end of the In this paper, we employed 10,12-pentacosadiynoic acid 1 polymer chain.When a second vinyl monomer is polymerized as an ionic amphiphile and prepared freshly an ABA-type using these macro-photoinitiators, ABA-type triblock polymers triblock polymer 2 composed of poly(2-dimethylaminoethyl are formed. In the same manner, a triblock polymer of 2 was methacrylate) (PDAM) segments and a copolymer segment freshly prepared.At first, a copolymer containing a photosensi- made from DAM and m-methacrylamido phenylboronic acid tive isopropyl xanthate group at each end of the copolymer (MPB) as a polyion (Fig. 1). The copolymer segment is chain was prepared by photopolymerization of MPB and expected to serve as a sugar-responsive site since boronic acid DAM (151 in molar ratio) in the presence of BX.DAM was has been demonstrated to form stable complexes with diol then polymerized by the copolymer as a macro-photoinitiator compounds including poly(vinyl alcohol), glucose and sorbiupon UV irradiation. As a result, a triblock polymer with tol.2–5 The introduction of tertiary amino groups into the segment lengths of n=39 and m=19 and with a copolymer copolymer segment is to facilitate sp3-hybridization of the composition of 151 was obtained.To elucidate the eVect of boron atom, which should enhance the complexation with incorporation of DAM unit into the copolymer segment, the these diol compounds.5,6 The topotactic polymerization of pKa value of the boronic acid moiety was measured in water diacetylene is well known to be acutely sensitive to the by means of pH titration.From the titration curve (data not molecular order of molecular assemblies.7 Thus, such a strinshown), the pKa value was estimated to be 7.1. A phototitration gent requirement for eYcient photopolymerization of diacetymethod was also applied to this polymer to determine pKa, lenes provides an excellent test of the ordering in polyionsince the absorption maximum of the phenylboronic acid complexed mono- and multi-layer films.Additionally, the moiety showed a red shift on going from a neutral to anionic resultant polydiacetylene films have unique optical properties; species. The pKa value (7.0) determined was consistent with the conjugated backbone of alternating double and triple that (7.1) obtained via pH titration.The results imply that the bonds gives rise to intense absorptions in the visible spectrum. pKa value of phenylboronic acid moiety is successfully lowered In single crystals or LB films,8 these materials are known to in the presence of tertiary amino groups, since the pKa of undergo blue to red color transitions due to various environmonomeric phenylboronic acid is estimated to be 8.8.The mental perturbations.9–12 Recently, Reichert et al.13 prepared interaction of the phenylboronic acid moiety of 2 with D- a sialic acid-modified polydiacetylenic liposome that could fructose, a typical diol compound, in water was subsequently specifically bind to influenza virus particles and could report examined via 11B NMR spectroscopy.Fig. 2 shows 11B NMR the binding event by undergoing a visible color change. The spectra of 2 before and after addition of D-fructose at pH 7.1. present paper will describe the polymerization behavior of our The spectrum obtained in the absence of D-fructose gives a peak at d 10 that can be assigned to the free (sp2-hybridized) boronic acid.15 By adding a large excess of D-fructose, a new †E-mail: mniwa@mail.doshisha.ac.jp J.Mater. Chem., 1998, 8(8), 1697–1701 1697Fig. 1 Chemical structure of diacetylenic polyion complexes containing sugar-responsive sites Fig. 2 11B NMR spectra of triblock polymer 2 (a) before and (b) after addition of D-fructose in D2O–H2O (154 v/v) at pH 7.1 and 30 °C. The external standard is B(OCH3)3. peak appears at d -11.8 and simultaneously the peak at d 10 disappears.Such a drastic upfield shift has been demonstrated to be due to formation of a boronate ester with the diol moiety Fig. 3 (a) Surface pressure (p)–area (A) isotherms for (i) 2/1 and (ii) 3/1 complexes on pure water at pH 5.8 and 20 °C. (b) pH dependence of of D-fructose.16 p–A isotherms of the 2/1 complex at 20 °C and (i) pH 3.0, (ii ) pH 5.0 The polyion complex 2/1 was prepared by mixing equivalent and (iii) pH 9.9.amounts of methanolic solutions of 1 (20 mM) and 2 (20 unit mM of DAM in A segments). The chemical composition of the 2/1 complex thus obtained was estimated by 1H NMR specthat of 3/1, probably due to the existence of the copolymer troscopy. The ratio of the content of 1 to that of DAM units segment in 2.Fig. 3(b) shows the pH dependence of the p–A in the A segments of 2 was calculated, by assuming that 1 curve of the 2/1 complex. The p–A curve measured at pH 10 would predominantly complex with DAM units of the A almost fits that at pH 5.8. The pKa value of 1 in water was 5.5 segments but not with DAM units of the B segment (copolymer by pH titration. Therefore, at pH 10 electrostatic interactions segment), because the DAM units located in the B segment would predominate between 1 and 2 because 1 is in the should complex with the vicinal MPB unit through formation deprotonated carboxylate anion form at higher pH.At pH 5.8, of a charge transfer complex.5,6 On the basis of the area ratio where 1 might be in both carboxylate anion and protonated of the signal of v-CH3 in 1 to that of N-CH3 in polymer 2, free carboxylic acid forms since the pKa value of 1 is close to the ratio of [1]5[DAM units in the A segment] was evaluated the subphase pH, hydrogen bonding as well as electrostatic to be 0.9751, which supports the molecular structure of the interactions can be considered to contribute to the stability of polymer complex 2/1 drawn in Fig. 1. the complex of 1 and 2, as illustrated in Fig. 3. Lowering the pH in the subphase below the pKa of 1 (pH 3) causes a drastic Photopolymerization of polyion-complexed monolayers contraction and a drop in collapse pressure of the monolayer, which is very similar to those of a pure monolayer of 1 under The monolayer properties of the polymer complex 2/1 thus obtained were examined by measuring surface pressure (p)–area the same conditions (data not shown), implying deformation of the complex due to protonation of the carboxylic acid of 1.(A) isotherms on water. Fig. 3(a) displays a p–A isotherm of the 2/1 complex on pure water (pH 5.8) at 20 °C. The p–A Subsequently, photopolymerizations of the complex monolayer of 2/1 were carried out at pH 5.8.Fig. 4 depicts UV–VIS curve of the 3/1 complex without the boronic acid-carrying copolymer segment is also shown for comparison. The mono- spectral changes of the monolayer on water upon UV irradiation at 5 °C and a constant surface pressure of layer of 2/1 is found to considerably expand, compared with 1698 J. Mater. Chem., 1998, 8(8), 1697–1701upon UV irradiation and yields the more highly conjugated blue polymer, although the existence of the less conjugated red form cannot be excluded.In Fig. 5, the absorbance change upon UV irradiation is also shown for the 2/1 monolayer at a lower surface pressure of 25 mN m-1. There is no absorption peak in the range of 400–700 nm even after 80 s irradiation, indicating that no polymerization reaction occurred, probably due to the less ordered diacetylene molecular packing in the monolayer to be polymerized.Such an ordered molecular packing in the monolayer is readily predicted to depend on temperature. In fact, when the same experiment under a surface pressure of 35 mN m-1 was performed at 15 °C, the polymerization did not proceed at all because of lowering of the crystallinity of the monolayer due to thermal molecular motion.The photopolymerization of diacetylenic monolayers has been known to be considerably aVected by interface conditions, and in particular the LB films deposited from the monolayers onto solid substrates have provided a blue form-rich polydi- Fig. 4 Absorption spectral change of the 2/1 complex monolayer on acetylene due to suppression of molecular motion.19 pure water upon UV irradiation at 5 °C.The surface pressure was Accordingly, our polyion complex monolayer was transferred kept constant at 35 mN m-1 throughout irradiation. onto a quartz plate, and its polymerization behavior was examined. The hydrophobic quartz plate, prepared by coating 35 mN m-1, just before the collapses pressure. The appearance a thin layer (ca. 100 A ° ) of poly(dimethylsiloxane) prior to use, of the absorption peaks in the UV–VIS spectra indicates that was lowered at a speed of 50 mm min-1 through the monolayer the photopolymerization of monomer took place upon UV on a subphase at 35 mN m-1 and 5 °C, and a one-layer LB irradiation, since there is no absorption peak of the monomeric film, in which the polyion 2 of the complex is exposed to the 2/1 monolayer in an observed wavelength range of 400–700 nm water phase, was deposited on each side of the quartz plate.before exposure to UV light. The remarkable absorption peak The transfer ratio was close to unity. Fig. 6 displays the at 640 nm and the weak and broad shoulder at around 580 nm, absorption spectra of the 2/1 LB film as a function of which are assigned to the p–p* transition (excitonic absorption) irradiation time.Only the absorption peaks at 640 and 580 nm and the phonon sideband of polydiacetylene, respectively,17 are found to appear with polymerization, implying that the were observed. Polydiacetylene, which shows an absorption produced polydiacetylene takes the highly conjugated blue peak at 640 nm, is designated as the blue form.18 In the form.This result is diVerent from that of the monolayer on spectra, other characteristic absorption peaks at 540 and water. To elucidate the influence of the surface pressure at 500 nm were also observed, which are assigned to the p–p* which the monolayer was transferred onto the substrate, the transition and the phonon sideband of the polydiacetylene red same irradiation experiment was performed for a LB film form, respectively.18 It has been reported on the basis of prepared at a lower surface pressure of 25 mN m-1.Exposure spectroscopic analysis that the electronic structure of the of the film to UV light for times up to 180 s revealed no polydiacetylene red form is diVerent from that of the blue absorption peak due to polymerization in the wavelength form.Such a diVerence in the electronic structure has been range of 400–700 nm (data not shown), which is the same demonstrated to stem from the delocalization length of the presult as was observed for the monolayer on water. The electrons; i.e. the red form has a shorter delocalization length temperature dependence of the polymerization was, however, than the blue form.Fig. 5 shows the UV irradiation time diVerent between the LB monolayer on a solid substrate and dependence of the absorbance at 640 nm, according to the the monolayer on water. Fig. 7 shows the UV irradiation time absorption spectra in Fig. 4. The absorbance at 640 nm dependence of the absorbance at 640 nm at 5 and 20 °C. Even increases rapidly in the early stages of irradiation and saturates at 20 °C, interestingly, the polymerization proceeds smoothly, upon further irradiation, indicating that the polymerization following an almost identical profile to that at 5 °C.This result reaction of 2/1 is almost complete after 80 s irradiation. It is clearly demonstrates that the polyion-complexed diacetylene significant that a diacetylenic monolayer complexed with a molecules in the deposited LB film have much reduced thermal polyion such as 2 causes smooth and rapid polymerization molecular motion compared to those in the monolayer on Fig. 5 UV irradiation time dependence of the absorbance at 640 nm Fig. 6 Absorption spectra of the 2/1 complex LB film deposited on a for the 2/1 complex monolayer at 5 °C. The surface pressure was kept constant at (a) 35 or (b) 25mNm-1.quartz plate at 35 mN m-1 as a function of UV irradiation time at 5 °C J. Mater. Chem., 1998, 8(8), 1697–1701 1699Fig. 9 The absorbance ratio of A640/A545 of the polymerized 2/1 complex LB film as a function of immersion time into various Fig. 7 UV irradiation time dependence of the absorbance at 640 nm nucleoside solutions ([nucleoside]=10 mM, pH 7.1): (a) thymidine; (b) for the 2/1 complex LB films at (a) 5 and (b) 20°C adenosine; (c) guanosine; (d) cytidine; and (e) uridine.water, and are in a suYciently crystalline state to allow eVective Subsequently, the interaction of the polymerized 2/1 LB film topotactic polymerization. with nucleosides of adenosine, uridine, cytidine and guanosine was examined, since boronic acid is known to interact specifi- Interaction of polymerized LB film with diol compounds cally with nucleosides having cis-diol moieties. Fig. 9 summar- Fig. 8 shows the spectral change when the polymerized one- izes the immersion time dependence of the absorbance ratio layer 2/1 LB film was immersed in an aqueous solution of D- at 640 and 545 nm (A640/A545).The data for thymidine, which fructose (10 mM) for 30 min at pH 7.1 and 20 °C. On the basis has two OH groups in a trans-conformation on the ribose of 11B NMR spectroscopy, D-fructose has been already found residue, were included for comparison. The value of A640/A545 to form boronate esters with phenylboronic acid in water. In is found to show only a slight decrease upon immersion into the spectrum before immersion, absorption peaks appear at the thymidine solution. On the other hand, the ratios for 640 and 585 nm due to the highly conjugated blue polymer.nucleosides containing cis-diol moieties decrease drastically, Upon immersion, these peaks are found to decrease and the reflecting specific interaction of the boronic acid units of the peak at 545 nm, based on the less conjugated red form, copolymer segment with these nucleosides.The changes in increases. When the same experiment was performed for the A640/A545 reach a plateau after 20 min. There is a small but polymerized LB film of the 3/1 complex without the phenyl- significant diVerence in the total change of the ratio of A640/A545 boronic acid-containing copolymer segment, no spectral among nucleosides, i.e.the total ratio change for nucleosides change was observed. Previous studies have also suggested having a pyrimidine ring seems to be slightly larger than that that color transitions in polydiacetylenes arise from changes for nucleosides having a purine ring. We do not have any in the eVective conjugation length of the polydiacetylene conclusive evidence so far to explain this phenomenon.backbone12,20 and that the electronic structure of the polymer Finally, the reversibility of such an interaction between the backbone is strongly coupled to side chain conformation.21,22 boronic acid units and nucleosides was evaluated via treatment Therefore, the observed spectral change for our polydiacetylene with an acidic solution (pH 3.0), since at such a low pH the triblock polyion complex 2/1 LB film must be considered as boronic acid adopts the sp2 hydrized free form, and the follows.First, D-fructose interacts with the boronic acid units boronate ester with the nucleoside should be hydrolysed. of the copolymer segment, and then a specific binding of D- Fig. 10 displays the ratio change upon immersing the LB film fructose causes a conformational variation of the copolymer with adenosine, a typical nucleoside, into water at pH 3.0.The segment that is transmitted to the polydiacetylene matrices ratio is clearly found to return immediately to its original along the polyion chain; as a result, this perturbs the eVective value, implying that adenosine desorbs from the copolymer conjugation length of the polydiacetylene.Fig. 10 Reversible change of the ratio of A640/A545 of the polymerized Fig. 8 Absorption spectra of the polymerized 2/1 complex LB film (a) before and (b) after immersion into the D-fructose solution 2/1 complex LB film by immersion into (a) adenosine solution at 7.1 and (b) water at pH 3.0 ([D-fructose]=10 mM, pH 7.1) for 30 min 1700 J. Mater.Chem., 1998, 8(8), 1697–1701segment, which recovers the original conformation and eVective Instruments and measurements conjugation length of the polydiacetylene backbone. A low pressure Hg lamp was used as a source of UV light. UV–VIS spectra were recorded on a UV-2100 spectrophotometer (Shimadzu Co. Ltd.,). 11B NMR spectra were recorded at 30 °C using a JEOL JNM GX-400 spectrometer.External Conclusions B(OCH3)3 was used as a reference. The monolayers were obtained by spreading a benzene We have demonstrated that polymerized LB films complexed solution (about 1 mg cm-3) of diacetylenic compound on with a phenylboronic acid-functionalized triblock polycation purified water (Milli-Q system,Millipore Ltd.). Twenty minutes are biomolecular materials that contain both a molecular after spreading, the monolayer was compressed continuously recognition function (phenylboronic acid group-incorporated with a rate of 1.20 cm2 s-1.Wilhelmy’s plate method and a copolymer segment) and a detection moiety (polydiacetylene Teflon-coated trough with a microprocessor-controlled film segment). The binding of diol compounds is transmitted to the balance [FSD-50 (USI system Ltd., Japan) with a precision of polydiacetylene matrices along polyion chains and transduced 0.01 mN m-1] were used for surface pressure measurements.to a visible color change detected by absorption spectroscopy. The pH in the subphase was adjusted with aqueous HCl It is noteworthy that such a color change can take place and KOH. reversibly in response to the binding of diol compounds.These findings are due to the combined properties of the functional References segment-carrying polyion and the perturbation-sensitive electronic structure of polydiacetylene. 1 (a) M. Niwa, A. Mukai and N. Higashi, L angmuir, 1990, 6, 1432; (b) M. Niwa, A. Mukai and N. Higashi, Macromolecules, 1991, 24, 3314; (c) N. Higashi, M. Sunada and M.Niwa, L angmuir, 1995, 11, 1864. 2 G.WulV , Pure Appl. Chem., 1982, 54, 2093. Experimental 3 H. Schott, E. RudloV, P. Schmidt, R. Roychoudhury and H. Ko� ssel, Biochemistry, 1973, 12, 932. Materials 4 H. L. Weith, J. L. Weibers and P. T. Gilham, Biochemistry, 1970, 9, 4396. DAM, 10,12-pentacosadiynoic acid 1, D-fructose and nucleos- 5 P. R. Westmark, L. S. Valencia and B. D.J. Smith, ides were purchased from Wako Chemical Co. (Japan). MPB Chromatographia, 1994, A664, 123. was prepared by reaction of m-aminophenylboronic acid and 6 S. Kitano, I. Hisamitsu, Y. Koyama, K. Kataoka, T. Okano and methacryloyl chloride. Y. Sakurai, Polym. Adv. T echnol., 1991, 2, 261. 7 B. Tieke, G. Wegner, D. Naegele and H. Ringsdorf, Angew. Chem., The triblock polymer 2 was prepared according to the 1976, 88, 805.manner reported previously.1 The photopolymerization of 8 D. Day and H. Ringsdorf, J. Polym. Sci., Polym. L ett. Ed., 1978, MPB and DAM was carried out in the presence of bis(isoprop- 16, 205. ylxanthogen) disulfide (BX) upon UV irradiation in acetone 9 R. R. Chance, G. N. Patel, J. D. Witt, J. Chem. Phys., 1979, 71, 206. 10 R. A. Nallicheri and M.F. Rubner,Macromolecules, 1991, 24, 517. at 30 °C for 9 h. The precipitate was washed with acetone 11 N. Mino, H. Tamura and K. Ogawa, L angmuir, 1992, 8, 594. several times and dried in vacuo to give a white powder. The 12 R. R. Chance,Macromolecules, 1980, 13, 369. copolymer composition (x) and segment length (n) was deter- 13 A. Reichert, J. O. Nagy, W. Spevak and D.Charych, J. Am. Chem. mined by 1H NMR spectroscopy. By using the copolymer thus Soc., 1995, 117, 829. obtained as a macrophotoinitiator, DAM was polymerized 14 (a)M. Niwa, T. Matsumoto and H. Izumi, J.Macromol. Sci.-Chem., 1987, A24, 567; (b) M. Niwa, Y. Sako and M. Simizu, J. Macromol. upon UV irradiation in MeOH at 30 °C for 8 h. The resultant Sci.-Chem., 1987, A24, 1315; (c) M.Niwa, N. Higashi, M. Simizu triblock copolymer was purified by repeated reprecipitation and T. Matsumoto, Makromol. Chem., 1988, 189, 2187. from acetone (solvent) and hexane (nonsolvent) and dried in 15 M. Mikami and S. Shinkai, Chem. L ett., 1995, 603. vacuo. The segment length (m) was determined by 1H NMR 16 H. Suenaga, K. Nakashima and S. Shinkai, J. Chem. Soc., Chem. Commun., 1995, 29. spectroscopy. The homopolymer of DAM 3 was prepared by 17 Y. Tokura, Y. Oowaki, Y. Kaneko, T. Koda and T. Mitani, J. Phys. polymerization initiated with AIBN in acetone at 60 °C. Soc. Jpn., 1984, 53, 4054. Polyion complexes were prepared as follows. Equivalent 18 G. Lieser, B. Tieke and G. Wegner, T hin Solid Films, 1980, 68, 77. amounts of a methanolic solution of 1 (10,12-pentacosadiynoic 19 K. Kuriyama, H. Kikuchi and T. Kajiyama, L angmuir, 1996, 12, acid) and of 2 or 3 were mixed at 40 °C and then cooled to 2283. 20 N. Mino, H. Tamura and K. Ogawa, L angmuir, 1991, 7, 2336. room temperature. The mixtures were poured into benzene 21 W. H. Beckham and F. M. Rubner,Macromolecules, 1993, 26, 5192. and the precipitates produced were washed with benzene 22 H. Tanaka, A. M. Gomez, E. A. Tonelli and M. Thakur, several times and dried in vacuo to give a white powder. The Macromolecules, 1989, 22, 1208. stoichiometric composition of these complexes was evaluated by 1H NMR spectroscopy. Paper 8/01657G; Received 27th February, 1998 J. Mater. Chem., 1998, 8(8), 1697–1701 17

ISSN:0959-9428    

DOI:10.1039/a801657g

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 Structure and physical properties of a hydrogen-bonded self-assembled material composed of a carbamoylmethyl substituted TTF derivative Go Ono,a Akira Izuoka,a Tadashi Sugawara*a and Yoko Sugawarab aDepartment of Basic Science, Graduate School of Arts and Sciences, the University of T okyo, Komaba,Meguro, T okyo 153, Japan bSchool of Science, Kitasato University, Sagamihara, Kanagawa 288, Japan Crystal structures of the carbamoylmethyl substituted TTF derivative AMET are characterized by polymeric hydrogen bonding between amide groups.As a result, the TTF moieties stack in parallel even in the neutral crystal. The nNH absorbtions of neutral AMET at 3426 and 3184 cm-1 show shifts to lower wavenumber, Dk, of 37 and 58 cm-1, respectively, at 4.1 GPa.Therefore the shrinkage of the NMH,O distance is estimated to be ca. 0.04 A ° at this pressure. The pressure dependence of the IR spectra of iodine-doped samples at doping ratios of less than 45% was exactly the same as that for a neutral sample, suggesting that the hydrogen bonding pattern is not aVected significantly upon doping. Although crystalline AMET is an insulator in the neutral state (srt=ca. 10-8 S cm-1), the conductivity is enhanced by a factor of 107 upon iodine doping of 45 mol% (srt=1.2×10-1 S cm-1). Furthermore, the conductivity increases as a function of the external pressure, and the srt of a 5% iodine-doped sample increased three-fold at 1.0 GPa. The enhanced conductivity of iodinedoped samples may be ascribed to the increase in the overlap between the donor moieties based on the shrinkage of the hydrogen bond of the carbamoylmethyl group.Construction of molecular self-assemblies has become a current topic of interest in materials chemistry.1 Although various sophisticated molecular architectures are now known, the number of molecular assemblies which exhibit prominent functionalities is still limited.In this respect, it may be interesting to design a novel organic donor as a building block for the self-assembly, the functionalities of which can be controlled by means of external stimuli.2 It is well-known that organic donors, e.g. perylene, TTF, BEDT-TTF and TMTSF, prefer to align in a herringbone structure in the neutral state in order to avoid electronic Fig. 1 Crystal structure of benzamide viewed along the c axis repulsion between p-electron rich donor molecules.3 On the other hand, when the donors are partially oxidized, they tend the direction of the hydrogen bond is restricted to the horito stack one above the other, with intermolecular contacts zontal direction with reference to the donor plane. Thus the between heavy atoms, e.g. sulfur or selenium.The heteroatom packing pattern is not significantly influenced by the hydrogen contacts, then, construct conduction paths by themselves, as bond of the thioamide group. long as the HOMO of the donor has reasonably large Recently, we have prepared BEDT-TTF derivative AMET coeYcients on these heteroatoms.4 If a stacking structure can 1 carrying a carbamoylmethyl group (CH2CONH2).The be obtained even for the neutral donors by means of specific diVerence in the conformations of the hydrogen-bonding intermolecular forces, the molecular assembly is expected to groups between thioamide TTF and AMET may be explained exhibit controllable transportational phenomena by hole- by the presence of a methylene unit between the amide group doping, application of an external pressure, etc.and the donor moiety; the hydrogen bond in AMET is expected In this respect, we were intrigued by the hydrogen-bonded to be formed perpendicular to the donor plane due to the flexibility of the carbamoylmethyl group. crystal structures of primary amides.5,6 The crystal structure In the present paper, the hydrogen-bonding scheme of of benzamide is characterized by a one-dimensional chain neutral crystals of AMET is investigated by X-ray crystallog- composed of a doubly hydrogen-bonded dimers; the dimer is raphy and IR spectroscopy.The conducting behavior of iodine- formed via one of the amide hydrogens, while the other amide doped AMET is measured as a function of the doping ratio. hydrogen forms a polymeric hydrogen-bonded chain6 (Fig. 1). The change in the hydrogen-bonding scheme of the iodine- Moreover, the one-dimensional arrangement of the phenyl ring doped sample is also examined by IR spectroscopy. Finally of benzamide in the crystal is entirely diVerent from a typical the eVect of external pressure on the conductivity and the herring-bone type packing, as observed in crystals of aromatic hydrogen bonding scheme of AMET is investigated with hydrocarbons. Hydrogen-bonded molecular assemblies conreference to the possible pressure control of the transportation structed using amide groups, therefore, are likely to be eVective properties of hydrogen-bonded organic conducting materials.for regulating the structure of molecular self-assemblies composed of organic donors. Bryce and co-workers reported a TTF derivative substituted Experimental with a thioamide group.7 Although a polymeric hydrogen- Materials bonded chain is constructed by the thioamide groups, the packing of the donor moieties is of a herringbone type.Since Syntheses of zinc chelate 8,8,9 4,5-ethylenedithio-1,3-dithiol-2- one 28 and 4-acetylthio-5-methylthio-1,3-dithiole-2-thione 510 the thioamide group is directly attached to the donor moiety, J.Mater. Chem., 1998, 8(8), 1703–1709 1703were performed according to published procedures. washed with 100 ml saturated aqueous NaHCO3 and 100 ml of water twice. The solution was dried over anhydrous MgSO4 Tetrahydrofuran (THF) was distilled over sodium metal in the presence of benzophenone prior to use under a nitrogen and filtered, and the solvent was evaporated under reduced pressure.The product was purified by column chromatography atmosphere. Methanol was distilled under a nitrogen atmosphere after an addition of sodium metal. Dichloromethane and with silica gel using chloroform–hexane (151) as eluent. Evaporation of the solvent gave 3 as a yellow oil (4.00 g, 1,1,2-trichloroethane were treated with sulfuric acid, then washed with saturated aqueous NaHCO3, water and brine, 13.5 mmol, 95%); dH(CDCl3) 1.29 (t, J=7.3 Hz, 3H), 2.48 (s, 3H), 2.69 (t, J=7.3 Hz, 2H), 3.10 (t, J=7.3 Hz, 2H), 4.18 (q, successively.The solvents were distilled after being dried over CaCl2 for several hours at room temperature. Acetone, 2- J=7.3 Hz, 2H); nmax(KBr)/cm-1 2982 and 2924 (CH2), 1733 (CNO, ester), 1669 (CNO, 1,3-dithiol-2-one), 1425 (CNC), bromoethanol and 1,3-dibromopropane were treated with K2CO3 and distilled.Triethyl phosphite was dried over sodium 1186 and 1022 (CMO), 741 (CMSMC). metal and distilled under a nitrogen atmosphere. All other reagents were used as purchased without further purification. 4,5-Ethylenedithio-4¾-(2-ethoxycarbonylethylthio)-5¾- Gel permeation chromatography was performed using an methylthiotetrathiafulvalene 4.In a 100 ml round-bottomed, LC-08 instrument (Japan Analytical Industry Co., Ltd.) short-necked flask fitted with an air condenser, 2 (2.81 g, equipped with JAIGEL-1H and -2H columns. Chloroform was 13.5 mmol) and 3 (4.00 g, 13.5 mmol) were dissolved in 20 ml used as eluent. of triethyl phosphite.The mixture was heated in an oil bath at 110 °C with stirring for 3 h under nitrogen. The solvent and Cyclic voltammetry triethyl phosphate were then evaporated under reduced pressure at 100 °C. The resulting red residue was extracted with Cyclic voltammograms (CVs) were measured in dichlorochloroform and filtered oV with suction to remove BEDT- methane in the presence of tetrabutylammonium perchlorate TTF. The product 4 was separated from homo-coupled TTF (0.1 mol l-1) as electrolyte with a platinum working electrode derivatives by silica gel column chromatography using using a potentiostat/galvanostat HAB 151 (HOKUTO dichloromethane–hexane (357) as eluent.Evaporation of the DENKO Ltd.). An Ag/AgCl electrode was used as the reference solvent gave 4 as red oil (1.76 g, 3.72 mmol, 23%); dH(CDCl3) electrode.The scanning rate was 200 mV s-1. 1.27 (t, J=7.3 Hz, 3H), 2.47 (s, 3H), 2.65 (t, J=7.3 Hz, 2H), 3.04 (t, J=7.3 Hz, 2H), 3.30 (s, 4H), 4.16 (q, J=7.3 Hz, 2H); Spectral measurements nmax(KBr)/cm-1 2969 and 2921 (CH2), 1731 (CNO), 1417 1H NMR spectra were measured using a JEOL GSX-270 (CNC), 1183 and 1022 (CMO), 773 (CMSMC). spectrometer; chemical shifts in CDCl3 solution are reported in d units relative to tetramethylsilane as internal standard. 4,5-Ethylenedithio-4¾-carbamoylmethylthio-5¾- UV–VIS–NIR spectra were measured using a Nihon Bunko methylthiotetrathiafulvalene 1. In a 50 ml round-bottomed, V-570 series UV–VIS–NIR spectrometer using KBr pellets. short-necked flask fitted with a dropping funnel, 4 (781 mg, Infrared spectra were recorded using a Perkin-Elmer 1400 1.65 mmol) and 2-bromoacetamide (1.13 g, 8.25 mmol) were series infrared spectrometer using KBr pellets.The pressure dissolved in 50 ml of methanol–dichloromethane (951), the dependence of the IR spectra was measured by pressing a KBr flask being cooled with an ice bath. To this solution was added pellet using a diamond anvil cell.dropwise sodium methoxide (357 mg, 6.60 mmol) in 5 ml of methanol with stirring under nitrogen. The resulting red solu- Preparation tion was stirred for 12 h at room temperature. The mixture 4-(2-Ethoxycarbonylethylthio)-5-methylthio-1,3-dithiole-2- was filtered oV with suction and the residue was dissolved in thione 6. In a 200 ml round-bottomed, short-necked flask fitted chloroform to remove sodium bromide.The orange solution with a dropping funnel, 4-acetylthio-5-methylthio-1,3-dithiole- was washed with 50 ml of saturated aqueous NaHCO3 and 2-thione 5 (3.60 g, 15.1 mmol) was dissolved in 100 ml of 50 ml of water twice. The mixture was dried over anhydrous methanol, and the flask was cooled with an ice bath. To this MgSO4 and filtered, and then the solvent was evaporated.The solution was added dropwise sodium methoxide (820 mg, crude product was recrystallized from chloroform to give 1 as 15.1 mmol) in 20 ml of methanol with stirring under nitrogen. orange needles (673 mg, 1.57 mmol, 98%); mp 139 °C; The resulting red solution was stirred for 1 h at room tempera- dH(CDCl3) 2.48 (s, 3H), 3.31 (s, 4H), 3.50 (s, 2H), 6.85 (s, 2H); ture.The solution was cooled with an ice bath again, and ethyl nmax(KBr)/cm-1 3426, 3285, 3257 and 3184 (NH2), 2976 and 3-bromopropionate (2.73 g, 15.1 mmol) in 20 ml of methanol 2921 (CH2), 1664 (CNO), 1601 (NH2), 1483 (CNC, center), was added under nitrogen. The mixture was stirred for 12 h at 1407 (CNC, peripheral), 1370 (CMN), 774 (CMSMC), 587 room temperature. The solvent was evaporated and the residue (NMCNO) (Calc.for C11H11ONS8: C, 30.75; H, 2.58; N, 3.26; was extracted with dichloromethane to remove sodium bro- S, 59.69. Found C, 30.57; H, 2.57; N, 3.49; S, 60.00%). mide. The orange solution was washed with 150 ml of saturated aqueous NaHCO3 and 150 ml of water twice. The mixture was General procedure for preparing iodine-doped samples of dried over anhydrous MgSO4 and filtered, and then the solvent AMET was evaporated. The product, 4-(2-ethoxycarbonylethylthio)- 5-methylthio-1,3-dithiole-2-thione 6, was obtained as a yellow Doping of the crystals of AMET with iodine was carried out oil (4.45 g, 14.2 mmol, 93%); dH (CDCl3) 1.28 (t, J=7.3 Hz, using the following procedure.The crystals of AMET were 3H), 2.53 (s, 3H), 2.70 (t, J=7.3 Hz, 2H), 3.11 (t, J=7.3 Hz, ground in a mortar with a pestle of agate. Then, the obtained 2H), 4.19 (q, J=7.3 Hz, 2H); nmax(KBr)/cm-1 2982, 2928 crystallites were added to carbon tetrachloride containing a (CH2), 1733 (CNO, ester), 1423 (CNC), 1029 (CNS), 744 given amount of iodine and the suspension was stirred for 2 h (CMSMC).at room temperature. The purple color of the suspension faded completely, indicating that the dissolved iodine had been homogeneously absorbed by the crystallites of AMET.The 4-(2-Ethoxycarbonylethylthio)-5-methylthio-1,3-dithiole-2- one 3. In a 200 ml round-bottomed, short-necked flask, (4.45 g, color of the crystallites of AMET changed from orange to black upon iodine doping. Doping of iodine into crystals of 14.2 mmol) and mercury(II) acetate (13.60 g, 42.7 mmol) were dissolved in 20 ml of acetic acid and 60 ml of chloroform.The BEDT-TTF also carried out according to the same procedure. The doping ratio was evaluated via the increased weight of the mixture was stirred for 3 h at room temperature. The mixture was filtered to remove mercury salts, and the filtrate was doped sample. 1704 J. Mater. Chem., 1998, 8(8), 1703–1709X-Ray crystallographic analysis samples of AMET was measured by pressing a pellet of crystallites of AMET using a Be–Cu cell: DEMNUM S-20 A single crystal of AMET was mounted on a Rigaku AFC-5 (Daikin Industries Co, Ltd.) was used as a pressure transmitfour- circle diVractometer using graphite mono-chromatized ting medium. Mo-Ka radiation (l=0.7107A° ).The crystal system is orthorhombic, space group Pca21 (#29), and the cell constants Results and Discussion refined with 20 reflections (4<2h<25°) are a=15.193(2), b= 4.7566(8), c=23.472(3) A ° , V=1696.2(4) A ° 3. Intensity data Preparation of AMET were measured at ambient temperature; v scan (4<2h45°) and v–2h scan (45<2h<55°), scan speed 4 degrees min-1, The preparative route to AMET 1 is shown in Scheme 1.The key reaction is the hetero-coupling between ethylenedithio 0<h<19, 0<k<30, 0<l<6. Three standard reflections (8 0 0, 0 14 0 and 0 4 2) were measured for every 100 reflections, ketone 2 and unsymmetrically substituted ketone 3 carrying an ethoxycarbonylethylthio group. After the coupling, the with no significant variations throughout the data collection; among 2417 reflections measured (4<2h<55°), 2312 were protecting group is eYciently removed by sodium methoxide via a retro-Michael addition mechanism (Scheme 2).The unique (Rint=0.010). The structure was solved by direct methods using SIR9211 ethoxycarbonylethyl group is, therefore, considered to be an excellent protecting group for a thiolate in the coupling and expanded using Fourier techniques.12 The non-hydrogen atoms were refined anisotropically. The hydrogen atom coordi- procedure.13 The thiolate is reacted with 2-bromoacetamide to aVord carbamoylmethylthio-substituted TTF derivative 1.The nates were refined, their isotropic B values being fixed. The refinement of the structure was performed by a full-matrix yield of each step is reasonably high, and the total yield starting from [Zn(dmit)2] (Et4N)2 8 is 4–7%.Single crystals least-squares method based on 1607 observed reflections [I>3.00s(I)]. Final refinement with anisotropic thermal fac- of neutral AMET were obtained by slow evaporation of a chloroform solution. tors for all atoms; 223 parameters, R=0.032 and Rw=0.032; w=1/s2(Fo); S=0.03, max.(shift/e.s.d)=0.09, max. and min. The donating ability of AMET was estimated via redox potentials determined by cyclic voltammetry. Two oxidation heights in final diVerence Fourier map 0.27, -0.25 e A ° -3. The atomic scattering factors used throughout the analysis were waves were measured: E1/2OX1=0.51 V (reversible) and E1/2OX2=0.84 V (irreversible). These values were practically the obtained from International Tables for X-ray Crystallography (1974).All calculations were performed using the teXsan same as those of BEDT-TTF [E1/2OX1=0.51 V (reversible) and E1/2OX2=0.85 V (irreversible)]. This result suggests that intro- crystallographic software package from the Molecular Structure Corporation. duction of a carbamoylmethyl group does not aVect the donating ability of BEDT-TTF.Full crystallographic details, excluding structure factors, have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Information for Authors, J. Mater. Chem., Crystal structure of AMET 1998, Issue 1. Any request to the CCDC for this material The crystal structure of AMET is shown in Fig. 2. The long should quote the full literature citation and the reference molecular axes of the AMET molecules are aligned in parallel number 1145/100.along the a axis, being inclined by ca. 40°, and they are flipped alternately along the c axis. The conformation (t1, t2, t3, see Measurements of electric conductivity Electric conductivities were measured by a four or two probe method. Gold wires (25 mm w) were attached to the sample with gold paste.The sample was fixed in the chamber of a homemade cryostat and cooled slowly. The temperature was measured using a (0.03atom% Fe)-gold-Chromel thermocouple. The activation energies of the semiconducting samples were estimated by the slope of the straight line, obtained via a semilogarithmic plot of the conductivity vs.temperature. The C S– R R CH2CH2 C O OEt O OEt CH2=CH-COOEt –H+ S R CH2CH2 S – Scheme 2 Generation of a thiolate anion via retro-Michael addition pressure dependence of the conductivity of iodine-doped SAc SMe S S S S SMe O S S S S S SMe S S S S S S S SMe S S S SCH2CONH2 S S S SCOPh SCOPh S S O S S S S S S S S S S Zn S S 98% 75% vii 4 2 + 3 ii 85% iv iii 95% 3 AMET 1 32% (NEt4)2 i 91% 2 vi 23% 93% iii v 8 5 S SMe S S S COOEt 6 COOEt 7 COOEt Scheme 1 Reagents and conditions: i, BzCl, acetone, room temp., 3 h; ii, NaOMe, MeOH, 0 °C, 1 h, then BrCH2CH2Br, MeOH, room temp., 12 h; iii, Hg(OAc)2, CHCl3, room temp., 3 h; iv, AcCl, acetone, -5 °C, 2 h, then MeI, acetone, room temp., 1 h; v, NaOMe, MeOH, 0 °C, 1 h, then BrCH2CH2COOEt, MeOH, room temp, 8 h; vi, P(OEt)3, 110 °C, 3 h; vii, NaOMe, MeOH, 0 °C, 1 h, then BrCH2CONH2, MeOH, room temp., 4 h J.Mater. Chem., 1998, 8(8), 1703–1709 1705Fig. 2 Crystal structure of AMET viewed along the b axis Fig. 5 The NMH,O hydrogen bond (2.80 A° ; dotted line) and NMH,S intermolecular interaction (3.52 A ° ; broken line) of AMET Fig. 3) of the carbamoylmethyl group of AMET is (-sc)-(+sc)- (+sc).The donor moiety has a concave shape, and the dihedral angles between the tetrathioethylene moieties of the central short in spite of the electronic repulsion between the p-electrons part and of the two edge parts are 22.3 and 13.1°, respectively of the donor moieties. This structure is in sharp contrast to (Fig. 3). No disorder was observed at the ethylenedithio group. the herringbone structure of a neutral crystal of BEDT-TTF The carbamoylmethyl group forms a one-dimensional molecules.3 hydrogen-bonded chain along the b axis (Fig. 4). The hydrogen Primary amides, in general, form a double hydrogen-bonded bond distance of NMH,O is 2.80 A ° ; this value is approxi- chain utilizing the two hydrogen atoms of the amide group mately an average distance for hydrogen bonds of amide (Fig. 1).5,6 In the case of the hydrogen-bonded crystal of groups.14 As a result of these hydrogen bonds, the AMET AMET, however, only one of the hydrogen atoms of the amide moieties form columnar stacks along the b axis. The shortest group participates in a polymeric hydrogen bond. The other S,S contact in this column is 3.76 A ° . The distance is fairly amide hydrogen is found in close proximity to the sulfur atom of a methylthio group belonging to an AMET molecule in an adjacent column.A weak NMH,S hydrogen bond is, thus, considered to be formed, with an N,S distance of 3.52 A ° (Fig. 5). It should be noted that the hydrogen-bonded chain runs perpendicular to the stacking of the donors. Since the carbamoylmethyl group of AMET has conformational flexibility due to the methylene unit between the amide group and the donor moiety, the amide group can bend to give a (-sc)- (+sc)-(+sc) conformation.Although the donor AMET moieties are stacked in parallel, the conductivity of the neutral crystal is not appreciably high, especially compared with the neutral crystal of tetrakis(decylthio)- TTF.15 In the case of tetrakis(decylthio)-TTF, a onedimensional stack of TTF moieties is achieved due to the dispersion force of the alkyl groups.This eVect is called a ‘fastener eVect’ in order to stress the importance of the disper- Fig. 3 Conformation of the carbamoylmethyl group of AMET sion force of the long alkyl chains. The S,S distance within a column of tetrakis(decylthio)-TTF molecules can be as short as 3.5 A ° , and an exceptionally low resistivity (2.7×105 V cm) was recorded for a crystal of the neutral donor.Compared with tetrakis(decylthio)-TTF, the resistivity of neutral AMET is much higher (ca. 108 V cm). This may be explained by the slightly longer S,S contacts in neutral AMET and the inclined stacking of donor moieties. Pressure dependence of IR spectra of undoped and iodine-doped AMET In order to obtain information on the hydrogen-bonding pattern of the carbamoylmethyl group of AMET, especially under an external pressure, IR spectra of KBr pellets of neutral and iodine-doped AMET were recorded.The stretching modes of the amide group, nNH and nC=O (Amide I), and the deformation mode, dN–C–O, were chosen as key bands for this purpose. The four NMH stretching bands, presumably resulting from site-splitting, were observed at 3426, 3285, 3257 and 3184 cm-1 (Fig. 6). Based on the assignments of acetamide,16 the absorptions at 1664 and 587 cm-1 were assigned to the nC=O stretching (Amide I) and the NMCNO deformation (dN–C–O), Fig. 4 Hydrogen-bonding scheme of AMET. The NMH,O distance is 2.80 A ° respectively. 1706 J. Mater. Chem., 1998, 8(8), 1703–1709Fig. 7 UV–VIS spectra of AMET and iodine-doped samples; (a) neutral sample, (b) 12% I2-doped sample, (c) 32% I2-doped sample Fig. 6 Pressure dependence of IR spectrum of neutral AMET (nNH UV–VIS spectra of undoped and iodine-doped AMET region) The UV–VIS spectra of iodine-doped AMET were recorded in order to examine the electronic structure of the doped sample (Fig. 7). While the spectrum of neutral AMET showed When an external pressure was applied to the neutral sample, absorption maxima at 400 and 490 nm, a broad absorption nNH at 3426 and 3184 cm-1 showed small shifts to lower band at 930 nm was observed for the doped samples. This wavenumber, Dk, of 37 and 58 cm-1, respectively, at 4.1 GPa characteristic broad band can be assigned to the charge (Fig. 6), whereas the peaks at 3258 and 3257 cm-1 were transfer band. relatively unaVected. On the other hand, nC=O at 1664 cm-1 Besides the CT band, two absorption bands at 285 and showed a shift to higher wavenumber of 5 cm-1. The dN–C–O 380 nm were recognized. The former band may be assigned to at 578 cm-1 was also shifted to higher wavenumber by the absorption of I- and the latter to I3-, respectively, judging 60 cm-1.from reference spectra for these species.19 Thus, the doped These results suggest that the N,O hydrogen bond distance iodine is converted to the counter ions I- and I3-, which are becomes shorter when an external pressure was applied, and considered to be in equilibrium with each other. that the NMH hydrogen is shifted towards the oxygen atom, resulting in weakening of the NMH band.On the other hand, EVect of doping on the conductivities of neutral AMET and the dN–C–O (in plane) deformation peak showed a shift to higher BEDT-TTF wavenumber. This is because the force constant of the bending mode of the NMCNO group becomes larger due to the shorter The conductivities of pellets of neutral and iodine-doped hydrogen bond.Nakamoto et al. proposed a relation between AMET were measured as a function of the doping ratio a shift to lower wavenumber of the nNH stretching (Dk/cm-1) (mol%). Although the conductivity of neutral AMET is as low and a shortening of the hydrogen-bonded distance (Dd/A ° ), as srt=ca. 10-8 S cm-1, it is enhanced remarkably as the Dd=7.7×10-4×Dk.17 According to the above equation, the doping ratio increases. The conductivity of the 5% doped shrinkage in the NMH,O distance of AMET is estimated to sample is 2×10-4 S cm-1, 104 times larger than that of neutral be 0.04 A ° at 4.1 GPa.AMET. The maximum value of the conductivity (1.2×10-1 The pressure dependence of nNH and dN–C–O was also exam- S cm-1) was obtained at a doping ratio of 45% (Fig. 8). ined for the 5% iodine-doped sample.The nNH and dN–C–O Although the maximum value of the conductivity of iodineabsorptions showed shifts of -24 and +66 cm-1 respectively doped BEDT-TTF (srt=4×10-3 S cm-1) is also obtained at under 4.0 GPa. The shifts in nNH and dN–C–O are found to a doping ratio of 45%, the value is 102 times smaller than the exhibit the same tendencies as those of the neutral sample.maximum value for iodine-doped AMET. This result strongly suggests that the hydrogen-bonded scheme Some poly(vinyl-TTF) polymers have been synthesised in is not perturbed significantly, at least up to a doping ratio of order to obtain conducting polymers carrying donor units.20 5%. For doping ratios higher than 45% a new absorption Although these polymers were oxidized with bromine or peak, assigned to nC=O of a more weakly hydrogen-bonded TCNQ, the doped polymers exhibited poor conductivities amide group, appeared at 1685 cm-1.This may be explained (srt<10-8 S cm-1). The failure to obtain high conducting by the partial disruption of the uniform polymeric hydrogenpolymers may be ascribed to the diYculty of maintaining a bonded chain due to heavy doping.In other words, the face-to-face stack of donors along the backbone of the polymer. hydrogen bonded chain supports the columnar stacking of On the other hand, the donor units of AMET are arranged in donors as long as the doping ratio does not exceed ca. 45%. a face-to-face stack along the hydrogen-bonded chain formed It is well-documented that, in the IR spectrum of crystalline by the amide units, and the stacking structure is reasonably N-methylacetamide, the intensity of the small peak near amide unperturbed by doping or the application of high pressures, II (1525 cm-1) increases pronouncedly at lower temperatures.18 as judged from the IR spectra of the doped samples.This side-band peak is possibly assigned to the resonance line between the amide II and the lattice phonons, the intensity of Pressure dependence of the conductivities of iodine-doped which is enhanced due to the polaron along the hydrogen- AMET bonded chain, although the origin of the side-band peak is still disputed.In crystals of AMET, such coupling has not The conductivities of 5 and 37% iodine-doped AMET samples under atmospheric pressure showed semiconducting behavior been detected so far.If a coupling between polaronic migration and the transportational phenomena is observed, a new physi- in the temperature range of 300–150 K. The activation energies of the 5 and 37% doped samples under atmospheric pressure cal property might be explored, leading to a novel functionality characteristic of the hydrogen-bonded conductive materials. were evaluated to be Ea=0.2 and 0.09 eV, respectively.J. Mater. Chem., 1998, 8(8), 1703–1709 1707Fig. 10 External pressure dependence of activation energy of the ($) 5 and (#) 37% iodine-doped sample of AMET salts.21 Since the conductivity was measured using pellets, the possibility of a change in the contact resistance between crystallites cannot be ruled out.Fig. 8 Conductivity of the iodine-doped sample of ($) AMET and (#) BEDT-TTF Conclusion In the case of the 5% doped sample, the external pressure According to the IR spectroscopic analysis of the hydrogen dependence of the conductivity was almost linear, and the bond formed by the carbamoylmethyl group of AMET, this conductivity under 1.0 GPa was about 3.5 times larger than group appears to be eVective in maintaining the hydrogenthat under atmospheric pressure (Fig. 9) on the left scale). bonded chain even in the doped sample under high pressure. However, the increase in conductivity of the 37% doped Furthermore, the hydrogen bond distance is sensitive to the sample reached saturation at around 0.3 GPa (Fig. 9, on the applied pressure. Such an eVect may be derived from the right scale). The external pressure dependence of the activation polymeric hydrogen bond network, which is formed parallel energy of the iodine-doped sample was also examined (Fig. 10). to the p-stacking of the donor moieties. The activation energy of the 5% doped sample decreased to It is to be stressed that the donor stacking is realized by Ea=0.1 eV under 0.7 GPa, showing a minimum value at this simply introducing a carbamoylmethyl group into the donor pressure.On the other hand, the activation energy of the 37% moiety. This hydrogen-bonded molecular assembly composed doped sample was relatively unaVected by the application of of AMET is, therefore, appropriate for manifesting pressureexternal pressure. sensitive conducting properties under hole-doped conditions.The increase of the conductivity of iodine-doped AMET may be mainly rationalized by a decrease in the inter-donor This work was partly supported by CREST of JST. The distance within the stack, coupled with the shortening of the authors are indebted to Professor Tokura of the University hydrogen bond distance of the amide groups. The degree of of Tokyo, JRCAT, and Professor Moritomo of Nagoya increase of the srt value is of about the same order as those of University for the measurement of the IR spectra of AMET the TTF–TCNQ, (BEDT-TTF)2Cu(NCS)2 and (TMTSF)2PF6 under high pressures.The authors also thank Dr Matsushita, Tokyo Metropolitan University, for discussions concerning the preparation of AMET. References 1 For a review see: J. R. Fredericks and A.D. Hamilton, in Comprehensive Supramolecular Chemistry, ed, J. L. Atwood, J. E. D. Davies, D. D. MacNicol and F. Vo� gtle, Pergamon, Oxford, 1996, vol. 9, pp. 565–594. 2 M. Jørgensen, K. Bechgaard, T. Bjørnholm, P. Sommer-Larsen, L. G. Hansen and K. Schaumburg, J. Org. Chem., 1994, 59, 5877. 3 H. Kobayashi, A. Kobayashi, Y. Sasaki, G. Saito and H. Inokuchi, Bull. Chem.Soc. Jpn., 1986, 59, 301. 4 Y. Deng, A. J. Illies, M. A. James, M. L. McKee and M. Peschke, J. Am. Chem. Soc., 1995, 117, 420. 5 L. Leiaerowitz and A. T. Hagler, Proc. R. Soc. L ond., 1983, A388, 133; C. C. F. Blake and R. W. H. Small, Acta Crystallogr., 1972, B28, 2201; Q. Gao, G. A. JeVrey, J. R. Ruble and R. K. McMullan, Acta Crystallogr., 1991, B47, 742. 6 W. C. Hamilton, Acta Crystallogr., 1965, 18, 866; W.A. Denne and W. H. Small, Acta Crystallogr., 1971, B27, 1094. 7 P. Blanchard, K. Boubekeur, M. Salle�, G. Duguay, M. Jubault, A. Gorgues, J. D. Martin, E. Canadell, P. Auban-Senzier, Fig. 9 External pressure dependence of conductivity of the ($) 5 and D. Je�rome and P. Batail, Adv. Mater., 1992, 4, 579; A. S. Batsanov, M. R. Bryce, G. Cooke, A.S. Dhindsa, J. N. Heaton, (#) 37% iodine-doped sample of AMET 1708 J. Mater. Chem., 1998, 8(8), 1703–1709J. A. K. Howard, A. J. Moore and M. C. Petty, Chem.Mater., 1994, 15 H. Inokuchi, G. Saito, P. Wu, K. Seki, T. B. Tang, T. Mori, K. Imaeda, K. Enoki, Y. Higuchi, K. Inaka and N. Yasuoka, Chem. 6, 1419; For a review see: M. R. Bryce, J. Mater. Chem., 1995, 5, 1481. L ett., 1986, 1263; N.Ueno, H. Kurosu, K. Seki, G. Saito, K. Sugita and H. Inokuchi,Mol. Cryst. L iq. Cryst., 1992, 218, 171. 8 G. Steimecke, R. Kirmse and E. Hoyer, Z. Chem., 1975, 15, 28. 9 G. Steimecke, H-J. Sieler, R. Kirmse and E. Hoyer, Phosphorus 16 I. Suzuki, Bull. Chem. Soc. Jpn., 1962, 35, 1279; T. Uno, K. Machida and Y. Saito, Bull. Chem. Soc. Jpn., 1969, 42, 897. Sulfur, 1979, 7, 49. 10 A. Izuoka, R. Kumai and T. Sugawara, Chem. L ett., 1992, 285. 17 K. Nakamoto, M. Margoshes and R. E. Rundle, J. Am. Chem. Soc., 1955, 77, 6480. 11 A. Altomare, M. C. Burla, M. Camalli, M. Cascarano, C. Giacovazzo, A. Guagliadi and G. Polidori, J. Appl. Crystallogr., 18 G. Araki, K. Suzuki, H. Nakayama and K. Ishii, Phys. Rev. B, 1991, 43, 12 662. 1994, 27, 435. 19 A. D. Awtrey and R. E. Connick, J. Am. Chem. Soc., 1951, 73, 1842. 12 T he DIRDIF-94 program system, P. T. Beurskens, G. Admirraal, 20 D. C. Green and R. W. Allen, J. Chem. Soc., Chem. Commun., 1978, G. Beurskens, W. P. Bosman, R. de Gelder, R. Israel and 832; M. L. Kaplan, R. C. Haddon, F. Wudl and E. D. Feit, J. Org. J. M. M. Smits, in T echnical Report of the Crystallography Chem., 1978, 43, 4642; C. U. Pittman Jr., M. Ueda and Y. F. Liang, L aboratory, 1994, University of Nijmegen, The Netherlands. J. Org. Chem., 1979, 44. 13 G. Ono, M. M. Matsushita, A. Izuoka and T. Sugawara, 63rd 21 A. Andrieux, H. J. Schulz, D. Je�rome and K. Bechgaard, J. Phys. NationalMeeting of the Chemical Society of Japan, Abstracts, 1993, L ett., 1979, 40, L-385; T. Takahashi, T. Ohyama, T. Harada, p. 147; Other protecting groups of a thiolate anion, see: K. Kanoda, K. Murata and G. Saito, in T he Physics and Chemistry N. Svenstrup, K. M. Rasmussen, T. K. Hansen and J. Becher, of Organic Superconductors, ed. G. Saito and S. Kagoshima, Synthesis, 1994, 809; J. Lau, O. Simonsoen and J. Becher, Synthesis, Springer-Verlag, Berlin, 1990, pp. 107–110; P. Day, in T he Physics 1995, 521. and Chemistry of Organic Superconductors, ed. G. Saito and 14 T he Hydrogen Bond, ed. G. C. Pimentel and A. L. McClellan, S. Kagoshima, Springer-Verlag, Berlin, 1990, pp. 8–14. W. H. Freeman and co., San Francisco, 1960, pp. 285–290; G. A. JeVrey and W. Saenger, Hydrogen bonding in biological structures, Springer-Verlag, 1994, New York. Paper 8/00509E; Received 19th January 1998 J. Mater. Chem., 1998, 8(8), 1703–1709 17

ISSN:0959-9428    

DOI:10.1039/a800509e

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 Preparation, structures and physical properties of k-type twodimensional conductors based on unsymmetrical extended tetrathiafulvalene: 2-cyclopentanylidene-1,3-dithiolo[4,5-d]-4,5- ethylenedithiotetrathiafulvalene (CPDTET) Hideki Fujiwara,†a Yohji Misaki,*a Masateru Taniguchi,a Tokio Yamabe,a Tadashi Kawamoto,b Takehiko Mori,b Hatsumi Moric and Shoji Tanakac aDepartment of Molecular Engineering, Graduate School of Engineering, Kyoto University, Yoshida, Kyoto 606–8501, Japan bDepartment of Organic and Polymeric Materials, Faculty of Engineering, T okyo Institute of T echnology, O-okayama, T okyo 152–8552, Japan cInternational Superconductivity T echnology Center, Shinonome, T okyo 135–0062, Japan Several cation radical salts of an unsymmetrical donor, 2-cyclopentanylidene-1,3-dithiolo[4,5-d]-4¾,5¾- ethylenedithiotetrathiafulvalene (CPDTET) have been prepared.Most salts with octahedral (AsF6-, SbF6-, NbF6- and TaF6-) and linear (I3-) anions showed high conductivity (srt=100–102 S cm-1) and metallic conductive behaviour around room temperature. Among them, the AsF6- salt displayed metallic temperature dependence down to 4.2 K, while the SbF6- and TaF6- salts exhibited metal-to-semiconductor transitions at 200 and 140 K, respectively.The AsF6- and SbF6- salts have a k-type donor arrangement in which two donor molecules are strongly dimerized in a ‘head-to-head’ manner. The calculated Fermi surfaces of these salts are two-dimensional folded circles. Measurement of the thermoelectric power suggests that the AsF6- salt is a normal metal, however, the SbF6- salt has an almost half-filled band structure at room temperature and a small energy gap opens at low temperature.The measurements of magnetic susceptibility indicate that these two salts exhibited Pauli-paramagnetic temperature independence characteristic of metallic materials, though they also showed weak antiferromagnetic interaction.The diVerences between AsF6- and SbF6- salts are also discussed and the origin of the metal-to-semiconductor transition is clarified. In the search for new organic conductors the symmetrical TTF analogue CPDTET, where CPDTET is 2-cyclopentanylidene- 1,3-dithiolo[4,5-d]-4¾,5¾-ethylenedithio-TTF.‡10 donors bis(ethylenedithio)-TTF (BEDT-TTF) and tetramethyltetraselenafulvalene (TMTSF) have played an important role and to date have yielded many superconductors.1,2 On the other hand, the discovery of organic superconductors based on multisulfur unsymmetrical donors, methylenedithio- TTF (MDT-TTF)3 and dimethylethylenedithio(dithiadiselenafulvalene) (DMET)4 has greatly stimulated interest in preparing new classes of unsymmetrical TTF donors.In the course of exploring new substituents we have focused on the 1,3- dithiol-2-ylidene group as a promising substituent for realizing the two-dimensional arrangement of donor molecules required for stable organic metals.5 Among newly synthesized TTF derivatives fused with 1,3-dithiol-2-ylidenes,5–7 we have found that an unsymmetrical derivative 2-isopropylidene-1,3-dithiolo[ 4,5-d]-4,5¾-ethylenedithio-TTF‡(MeDTET) has yielded several cation radical salts retaining metallic conductivity down Experimental to low temperature, and (MeDTET)3PF6TCEx has the so- Synthesis and electrocrystallization called ‘k-type’ donor arrangement in the conducting sheet.8 The realization of a k-type structure has been recognized to CPDTET was prepared according to the literature,6b and was be the most promising strategy for yielding new organic recrystallized from chlorobenzene before preparation of the superconductors.9 In this context, investigation of the physical cation radical salts.Single crystals of CPDTET salts were properties of cation radical salts based on modified MeDTET electrochemically grown in the presence of the corresponding derivatives is of considerable interest.In this article, we describe tetra-n-butylammonium salts at a controlled current11 of the preparation, crystal and electronic structures, transport 0.2–0.5 mA in chlorobenzene containing a small amount of and magnetic properties of cation radical salts of a MeDTET EtOH (10%, v/v) at 25 °C for about two weeks. The I3- salt was obtained by mixing hot chlorobenzene solutions of the donor and tetra-n-butylammonium triiodide.Their composi- †Present address: Institute for Molecular Science, Myodaiji, Okazaki tions were determined by energy dispersion spectroscopy 444–8585, Japan. (EDS) from the ratio of sulfur and the elements designated in ‡IUPAC names: 2-(5-isopropylidene[1,3]dithiolo[4,5-d]dithiol-2- parentheses in Table 1, except for the AsF6- and SbF6- salts ylidene)-5,6-dihydro[1,3]dithiolo[4,5-b][1,4]dithiine (MeDTET) whose compositions were determined by X-ray crystal struc- and 2-(5-cyclopentylidene [1,3]dithiolo[4,5-d]dithiol-2-ylidene)-5,6- dihydro[1,3]dithiolo[4,5-b][1,4]dithiine (CPDTET).ture analysis. J. Mater. Chem., 1998, 8(8), 1711–1717 1711Table 1 Composition and electrical properties of CPDTET (Anion)x impurities (0.55 mol% for AsF6- salt, 0.11 mol% for SbF6- salt).anion xa srt/S cm-1 b conducting behaviour ClO4- 0.60 (Cl ) 0.037 Ea=0.15 eV Results and Discussion PF6- 0.42 (P)c 0.015 Ea=0.13 eV AsF6- 0.36d 27 Metallic 4.2 K Conducting properties SbF6- 0.44d 4.2 TM-I #200 K The electrical properties of CPDTET salts are summarized in NbF6- 0.58 (Nb) 140 Metallic 90 Ke Table 1.The tetrahedral ClO4- salt was a semiconductor with TaF6- 0.37 (Ta) 21 TM-I #140 K I3- 0.30(I) 7.1 Metallic 4.2 K a large activation energy (0.15 eV). In contrast most salts with octahedral (AsF6-, SbF6-, NbF6 - and TaF6-) and linear aDetermined by energy dispersion spectroscopy from the ratio of (I3-) anions showed comparatively high conductivity (srt= sulfur and the elements designated in parentheses.bMeasured on a 100–102 S cm-1), all of which exhibited metallic temperature single crystal using four-probe method. cContains a solvent (PhCl)0.22. dependence around room temperature. Exceptionally the PF6- dDetermined by X-ray structure analysis. eCracked at this temperature. salt was a semiconductor probably due to a diVerent crystal structure containing a small amount of chlorobenzene which Electrical transport measurements was detected by electron dispersion spectroscopy.The con- Resistivity measurements were performed by a four-probe ducting behaviour of the metallic salts is shown in Fig. 1. method along the crystal plane (//bc plane) with gold wire and Among the metallic salts with octahedral anions, the AsF6- gold paste.High pressure measurements were carried out by salts displayed metal-like temperature dependence down to using a clamp type cell. The indicated value of applied pressure 4.2 K though they showed a few resistivity jumps and the is 3 kbar less than the pressure applied at room temperature resistivity increased a little at low temperature.On the other because the pressure is decreased at low temperatures due to hand, the SbF6- and TaF6- salts exhibited metal-to-semiconthe freezing of the daphne oil as pressure medium. ductor transitions at 200 and 140 K, respectively. However, Thermoelectric power was measured along the crystal plane their activation energy after the transition is very small as described in the literature.12 (~0.002 eV), indicating the resulting energy gap is tiny.The resistivity of the SbF6- and TaF6- salts was measured under Crystal structure determination applied pressure. The values decreased almost linearly with increasing pressure. The resistivity at 5.3–5.6 kbar was about The black plate-like crystals of AsF6- and SbF6- salts were half of the ambient-pressure value.Furthermore the SbF6- used for X-ray crystal structure analysis. Crystal and experand TaF6- salts retained metallic behaviour down to low imental data are shown in Table 2.§ Data collection and temperatures under an applied pressure of 5.3–5.6 kbar (Fig. 2). refinement methods are as follows; Rigaku AFC7R The linear I3- salt also showed a relatively high conductivity diVractometer, v/2h mode up to 2h=60°, v scan speed 16.0 (srt=7 S cm-1) and exhibited metallic temperature dependence deg min-1, graphite monochromated Mo-Ka radiation (l= down to 4.2 K though the resistivity slightly increased at low 0.71069 A ° ).No decay correction was applied. The structure temperature. was solved by a direct method (SIR92 for the AsF6- and SHELXS86 for the SbF6- salts, respectively).13 The atomic X-Ray crystal structures of cation radical salts scattering factors were taken from the International Tables for X-ray Crystallography.14 Some non-hydrogen atoms (S, As Among the cation radical salts obtained so far, single crystal and Sb) were refined anisotropically, while the rest were refined X-ray structure analysis was carried out for the AsF6- and isotropically using full-matrix least-squares methods.The pos- SbF6- salts. These two salts have the same space group (Cc) itions of C(18) and C(19) atoms and hydrogen atoms were and are isostructural. There are two crystallographically indenot refined. pendent CPDTET molecules (A and B) in a unit cell. On the other hand, one anion is located in a general position. From Band structure calculations the population analysis the donor to anion ratio was refined to be 250.72 for the AsF6- salt and 250.87 for the SbF6- salt, The transfer integrals, band structure and Fermi surface were indicating an anion site defect.16 The donor structures and calculated by a tight-binding method based on the extended atomic numbering schemes of the AsF6- salt are shown in Hu�ckel approximation.15 Electron paramagnetic resonance Electron paramagnetic resonance spectra were measured on a single crystal which was mounted on the cut flat face of a Teflon rod using a small amount of silicon grease and was placed in an evacuated quartz tube.The applied microwave power was 0.1 mW and the modulation field was 10 G. Static magnetic susceptibility Measurements of magnetic susceptibility were carried out on the warming process using a Quantum Design MPMS-2 SQUID magnetometer in field of 1 T.The data were corrected for the diamagnetic contribution estimated from the Pascal’s constants (xdia=-5.37×10-4 emu mol-1 for AsF6- salt, xdia=-5.68×10-4 emu mol-1 for SbF6- salt) and Curie §Full crystallographic details, excluding structure factors, have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Information for Authors, J. Mater. Chem., 1998, Issue 1. Any Fig. 1 Temperature dependence of normalized electrical resistivity of request to the CCDC for this material should quote the full literature citation and the reference number 1145/104. CPDTET salts in the cooling run 1712 J. Mater. Chem., 1998, 8(8), 1711–1717Table 2 Crystallographic data for CPDTET salts (CPDTET)2(AsF6)0.72 (CPDTET)2(SbF6)0.87 formula As0.72C28F4.32H24S16 C28F5.22H24S16Sb0.87 formula weight 1009.47 1078.55 crystal system monoclinic monoclinic space group Cc Cc Z 4 4 a/A ° 40.900(2) 41.17(3) b/A ° 8.192(2) 8.29(2) c/A° 11.372(2) 11.27(1) b/A ° 99.92(1) 100.0(1) V /A ° 3753(1) 3786(8) Dcalc/g cm-3 1.786 1.892 F(000) 2053.00 2157.40 dimensions/mm3 0.36×0.30×0.02 0.40×0.30×0.01 m(MoKa)/cm-1 16.25 15.70 v scan width 1.68+0.30 tanh 1.63+0.30 tanh reflections measured 5899 5170 unique reflections 5824 5094 reflections used 2406 1809 I/s(I) 3 2 Rint 0.022 0.060 R 0.077 0.074 Rw 0.079 0.081 GOF 3.38 1.47 Fig. 2 Temperature dependence of normalized resistivity of the SbF6- and TaF6- salts under applied pressure Fig. 3.In molecule A, the molecular plane is almost flat, but its cyclopentanylidene ring is bent downwards with a dihedral angle of 9.6° and has a slightly staggered conformation. The C–C bond lengths of the ethylenedithio group are very short [1.35(6) and 1.30(4) A ° ] compared with the usual C–C single Fig. 3 ORTEP drawing and atomic numbering scheme of bond length (about 1.51 A ° ) and the carbon atoms have a large (CPDTET)2(AsF6)0.72: (a) molecule A and (b) side view, (c) molecule temperature factor, indicating the conformational flexibility of B and (d) side view the ethylene bridge.On the other hand, molecule B is also almost planar, but its ethylenedithio ring is bent upwards with a dihedral angle of 9.9° at the S(13)–S(14) position and the neighboring dimers as is usually observed in k-type salts.The shortest distance is 3.36(1) A ° . The overlap mode in the dimer cyclopentanylidene ring is slightly twisted. The crystal structure is shown in Fig. 4. Two neighboring donor layers are related is the so-called ‘ring-over-bond’ type and the interplanar distance within the dimer is 3.60 A ° . The slip distance of the to each other with the symmetry operation (x+1/2, y+1/2, z) in the unit cell, which are separated by the anion sheets TTF skeleton along the molecular long axis is 1.6 A ° .Interestingly, the donor molecules A and B are dimerized in a [Fig. 4(a)]. All the donors in the crystal are oriented in the same direction. Molecules A and B form a dimer and each ‘head-to-head’ manner (Fig. 5) unlike other k-type salts of unsymmetrical donors like (MeDTET)3PF6TCEx,8 (MDT- dimer is orthogonally arranged in the conducting sheet [(Fig. 4(b)]. The donor array of the present salts is classified TTF)2AuI2,3b and (DMET)2AuBr24b in which two donor molecules are arranged in a ‘head-to-tail’ manner to avoid the as the so-called k-type. Short intermolecular S–S contacts less than the sum of the van der Waals radii (3.70 A° ) are also steric hindrance of the flexible ethylenedithio or methylenedithio groups.As mentioned above, the CPDTET molecule has indicated in the caption of [Fig. 4(b)]. They exist only between J. Mater. Chem., 1998, 8(8), 1711–1717 1713Electronic band structure and Fermi surface The dispersion relation and Fermi surfaces of the AsF6- and SbF6- salts were calculated by a tight-binding method based on the extended Hu�ckel approximation on a donor layer (bc plane) [(Fig. 4(b)]. As shown in Table 3, the overlap integrals between molecules arranged parallel to each other ( p and b) are two or three times larger than those between molecules perpendicularly arranged (q, r, c1 and c2). Large intradimer overlap integrals ( p=20.0×10-3 for the AsF6- salt and p= 21.3×10-3 for the SbF6- salt) indicate strong dimerization compared with (MeDTET)3PF6TCEx ( p=13.4×10-3).8a In the k-type CPDTET salts, two donor molecules are dimerized in the ‘head-to-head’ manner.As a result, the eVective overlap area of the TTF skeleton is much wider (about twice) than that of k-type MeDTET salts in which two donors stack in the ‘head-to-tail’ manner.Furthermore the calculated coeYcients of atomic orbitals of the inner four sulfur atoms in TTF skeleton are two to four times larger than those of the peripheral four sulfur atoms. Therefore these large intradimer overlap integrals of the CPDTET salts are derived from this larger eVective overlap area of the TTF skeleton by ‘head-tohead’ overlap.Because of this strong dimerization, the upper two bands and the lower ones are completely separated (Fig. 6). The energy gap in both the salts is 0.08 eV. The band dispersion is degenerate on the ZM zone boundary as a result of existence of a c-glide plane. The Fermi surface is essentially a twodimensional circle but is folded and closed on theZMboundary similar to the case of k-(BEDT-TTF)2I3.17 Thermoelectric power The measurement of thermoelectric power was carried out for the AsF6- and SbF6- salts to clarify the origin of the metalto- semiconductor transition of the SbF6- salt.Fig. 7 shows the temperature dependence of thermoelectric power of these Fig. 4 Crystal structure of (CPDTET)2(AsF6)0.72 (a) viewed along the salts. The AsF6- salt exhibited almost T -linear temperature b-axis and (b) viewed along the molecular long axis. Short intermolecu- dependence to zero thermoelectric power, which is characterlar S–S contacts (3.70 A ° ): b S(7)–S(16) 3.386(9) A ° ; c1 S(5)–S(8) istic of normal metalsthe other hand, the SbF6- salt has 3.66(1) A ° and S(7)–S(8) 3.59(1) A ° ; c2 S(9)–S(12) 3.69 (1) A ° and a very small room temperature thermoelectric power (+1.4 mV S(15)–S(16) 3.36 (1) A ° ; r S(8)–S(14) 3.51 (1) A ° .K-1) compared with that of metallic AsF6- salt (+6.9 mV K-1). These thermoelectric powers are too small for a quarter- Table 3 Intermolecular overlap integrals (×10-3) of k-type CPDTET salts and (MeDTET)3PF6TCEx AsF6- salt SbF6- salt (MeDTET)3PF6TCEx p 20.0 21.3 13.4 b 13.0 13.7 9.5 q 5.0 5.9 4.6 r 3.8 2.8 4.6 c1 6.6 7.7 6.3 c2 4.2 4.3 6.3 Fig. 5 Overlap mode in a dimer of (CPDTET)2(AsF6)0.72: (a) projected onto the molecular plane and (b) the side view sterically flexible cyclopentanylidene and ethylenedithio groups on both ends of the molecule, in contrast to the case of MeDTET, and the steric hindrance of dimerization is not relieved even if the dimer adopts the head-to-tail arrangement. Fig. 6 Energy band structure and Fermi surface of Therefore we think that CPDTET adopts the head-to-head (CPDTET)2(AsF6)0.72 where C, Y, Z and M refer to the reciprocal dimerization mode to increase the eVective overlap area of the lattice points (0, 0, 0), (0, b*/2, 0), (0, 0, c*/2) and (0, b*/.2, c*/2), molecules and to stabilize the electronic state with van der respectively, and kb and kc are the wave vectors along the b* and c* axes, respectively Waals attractive force. 1714 J. Mater. Chem., 1998, 8(8), 1711–1717magnetic field approximately perpendicular to the conducting plane. As shown in Fig. 9, the DHpp values of these salts are almost constant down to about 150 K and decrease monotonically to 30–40 G below 150 K. In the usual k-type BEDTTTF salts, the DHpp value increases with decreasing temperature in a metallic region like metallic Cu(NCS)2-, Cu(CN)[N(CN)2]- and Hg2.89Br82- salts.18 On the other hand, the DHpp value decreases with lowering temperature in a semiconducting region when the low-dimensional antiferromagnetic short range order increases like the case of the semiconducting Cu[N(CN)2]Cl- salt.19 Thus we think that weak antiferromagnetic interaction emerges below room temperature in the k-type CPDTET salts.The degree of decrease is not so much and an apparent antiferromagnetic transition was not observed. The EPR intensities are estimated from the DHpp and amplitude (Im) using the known approximation; Intensity=Im×(DHpp)2. The calculated intensities tend to decrease from room temperature with decreasing temperature and also show the existence of a weak antiferromagnetic interaction (Fig. 10). However the data points are very scat- Fig. 7 Temperature dependence of thermoelectric power of the AsF6- tered due to the weak and broad line shapes and precise and SbF6- salts filled band structure and indicate the band structures of these salts are nearly half-filled and a small amount of positive carriers play a role in the electric conduction.Furthermore the thermoelectric power of the SbF6- salt showed very weak temperature dependence down to 160 K, and then it decreased T -linearly and exhibited a small negative value (~-2 mV K-1) below 100 K, suggesting that the band structure of the SbF6- salt is very close to half-filled and a small gap opens in the low temperature region. EPR Studies The angular dependence of the EPR spectra of the new k-type salt was measured by rotating the crystal in the cavity by use of a goniometer at room temperature.The angular dependence for the SbF6- salt is shown in Fig. 8. When the static magnetic field was applied parallel to the crystal plane (// bc plane), the peak-to-peak line width (DHpp) and g-value show the minimum value (68 G and g=2.001).In contrast, they exhibited maximum values (89 G and g=2.007) with the magnetic field perpendicular to the conducting plane. At the maximum point the static magnetic field is approximately parallel to the long Fig. 9 Temperature dependence of peak-to-peak line width (DHpp) of molecular axis of the donor molecule.These large DHpp values the AsF6- and SbF6- salts are characteristic of the k-type arrangement of donor molecules.1c Variable temperature EPR measurements have been carried out for the AsF6- and SbF6- salts to about 2 K with the Fig. 10 Temperature dependence of normalized spin susceptibility of Fig. 8 Angular dependence of peak-to-peak line width (DHpp) and gvalue of the SbF6- salt the AsF6- and SbF6- salts J.Mater. Chem., 1998, 8(8), 1711–1717 1715metal-to-semiconductor transition at 200 K. The semiconducting state of the SbF6- salt had a very small energy gap of 0.002 eV and was suppressed by an applied pressure of 5.6 kbar. The thermoelectric powers of these salts are too small for a quarter-filled band structure and indicate the band structures of these salts are nearly half-filled.The temperature dependence of the thermoelectric powers showed that the AsF6- salt is a normal metal, but the band structure of the SbF6- salt is very nearly half-filled and a small gap opens at the low temperature region. On the other hand, the magnetic measurements of these two salts showed similar temperature dependent behaviour of the magnetic susceptibilities and weak antiferromagnetic interaction.So where is the diVerence between the two salts? All these results are concluded as follows; (1) the band structure of the SbF6- is very close to half-filled and shows a metal–semiconducting transition due to the strong electron correlation, (2) the AsF6- salt has a similar crystal structure to the SbF6- salt and is also aVected by the strong electron correlation, but the band filling is far from half-filled because there are more anion defects than in the case of the SbF6- salt, and so this avoids the semiconducting transition.We Fig. 11 Temperature dependence of static magnetic susceptibility of think that the electronic states of these two salts are nearly the AsF6- and SbF6- salts the same and the only diVerence between the two salts is the occupancy of the anion sites which determines the possibility information about the interaction could not be obtained from of the semiconducting transition derived from the strong the EPR intensities.electron correlation. Static magnetic susceptibilities Conclusion The magnetic susceptibilities of the AsF6- and SbF6- salts We have prepared several cation radical salts of the unsymwere also measured on a SQUID magnetometer at 1 T because metrical donor, 2-cyclopentanylidene-1,3-dithiolo[4,5-d]-4,5- the spin susceptibility of these salts could not be exactly ethylenedithio-TTF (CPDTET).Most salts showed comparaestimated from the EPR measurements due to the weak and tively high room temperature conductivity and metallic conbroad line shapes.The room temperature susceptibilities are ductive behaviour around room temperature. These results 3.48 x 10-4 emu mol-1 for the AsF6- salt and 3.74×10-4 indicate that CPDTET could yield many organic metals stable emu mol-1 for the SbF6- salt after correction for diamagnetic down to low temperatures. The X-ray crystal structure analysis contributions and Curie impurities. These values are close to of the AsF6- and SbF6- salts reveals that they have k-type each other and correspond to that of normal metallic material arrangement in the conducting sheets.It is noted that these but the value for the SbF6- salt is slightly higher than that salts are the first example of cation radical salts of unsymmetrifor the AsF6- salt.The temperature dependence of these cal donors in which the donors are dimerized in a head-tosusceptibilities is shown in Fig. 11. They are weakly temperahead manner. The band calculation indicated the upper two ture-dependent, namely, they decrease slightly with decreasing bands and lower ones are completely separated because of the temperature, indicating the weak antiferromagnetic interaction strongly dimerized structure derived from the head-to-head as discussed in the EPR study.The degree of this decrease for overlap mode. The calculated Fermi surfaces are two-dimenthe SbF6- salt is 15% and is higher than that for the AsF6- sional circles as is often shown by superconducting k-type salt (10%). These results suggest that these two salts have BEDT-TTF salts.The measurements of transport and magnetic similar magnetic properties but the SbF6- salt shows slightly properties have been performed to discuss the diVerences stronger electron correlation and antiferromagnetic interaction between the AsF6- and SbF6- salts. We have also discussed than the metallic AsF6- salt. Though the correction for Curie the origin of the metal–semiconducting transition of the SbF6- impurities has been performed, the susceptibilities increase at salt and indicated that the anion content determines the low temperature.We think that this increase may be derived possibility of a semiconducting transition caused by the strong from the spin localization by lattice defects and this localization electron correlation. Anyway CPDTET has yielded many seems to cause the slight increase in resistivity of the AsF6- metallic salts and shown an unusual crystal structure and salt as is shown in Fig. 1. interesting physical properties. Thus we think CPDTET would be a suitable donor for researching organic metals in the future. Comparison of AsF6- salt and SbF6- salt This work is partially supported by Grants-in-Aid for Scientific Here we discuss the diVerences between the AsF6- and SbF6- Research No. 06243215, 07232219, and 00063275 from the salts. They are isostructural and the donors have a k-type Ministry of Education, Science, and Culture of Japan. One of arrangement in the conducting sheet. From the population the authors (H. F.) is indebted to the JSPS Research analysis there are some defects of the anion site.The electronic Fellowships for Young Scientists. structure calculation indicated the upper two bands and lower ones are perfectly separated because of the strongly dimerized structure derived from the head-to-head overlap mode. This References situation makes the upper band eVectively half-filled and yields 1 (a) T. Ishiguro and K. Yamaji, Organic Superconductors, Springer- a strong electron-correlated system when the donor to anion Verlag, Berlin, Heidelberg, 1990; (b) T he Physics and Chemistry of ratio is 251.20 Though the AsF6- and SbF6- salts have the Organic Superconductors, ed. G.Saito and S. Kagoshima, Springer- same k-type crystal structure and similar closed Fermi surface, Verlag, Berlin, Heidelberg, 1990; (c) J. M. Williams, J.R. Ferraro, the transport properties of these two salts are very diVerent; R. J. Thorn, K. D. Carlson, U. Geiser, H. H.Wang, A. M. Kini and that is, the AsF6- salt displayed metallic temperature depen- M.-H. Whangbo, Organic Superconductors, Prentice Hall, New Jersey, 1992. dence down to 4.2 K, whereas the SbF6- salt exhibited the 1716 J. Mater. Chem., 1998, 8(8), 1711–17172 Recent Proceedings of International Conferences: (a) Synth.Met., T. Yamabe, T. Mori, H. Mori and S. Tanaka, Mol. Cryst. L iq. Cryst., 1996, 284, 329. 1995, 69–71, ed. Y. W. Park and H. Lee; (b) Synth. Met., 1997, 11 H. Anzai, J. M. Delrieu, S. Takasaki, S. Nakatsuji and J. Yamada, 84–86, ed. Z. V. Vardeny and A. J. Epstein. J. Cryst. Growth, 1995, 154, 145. 3 (a) G. C. Papavassiliou, G.A. Mousdis, J. S. Zambounis, A. Terzis, 12 T. Mori, H. Inokuchi, A. Kobayashi, R. Kato and H. Kobayashi, A. Hountas, B. Hilti, C. W. Mayer and J. PfeiVer, Synth. Met., Phys. Rev. B, 1988, 38, 5913. 1988, 27, B379; (b) A. M. Kini, M. A. Beno, D. Son, H. H. Wang, 13 (a) A. Altomare, M. C. Burla, M. Camalli, M. Cascarano, K. D. Carlson, L. C. Porter, U. Welp, B. A. Vogt, J.M. Williams, C. Giacovazzo, A. Guagliardi, G. Polidori, J. Appl. Crystallogr., D. Jung, M. Evain, M.-H. Whangbo, D. L. Overmyer and 1994, 27, 432; (b) G. M. Sheldrick, in Crystallographic Computing J. E. Schirber, Solid State Commun., 1989, 69, 503. 3, Oxford University Press, 1985, p. 175. 4 (a) K. Kikuchi, M. Kikuchi, T. Namiki, K. Saito, I. Ikemoto, 14 D. T. Cromer and J.T. Waber, International T ables for X-ray K. Murata, T. Ishiguro and K. Kobayashi, Chem. L ett., 1987, 931; Crystallography, vol. 4, Kynoch Press, Birmingham, 1974. (b) K. Kikuchi, Y. Honda, Y. Ishikawa, K. Saito, I. Ikemoto, 15 T. Mori, A. Kobayashi, Y. Sasaki, H. Kobayashi, G. Saito and K. Murata, H. Anzai and T. Ishiguro, Solid State Commun., 1988, H. Inokuchi, Bull. Chem. Soc.Jpn., 1984, 57, 627. 66, 405. 16 The final R value is much lower than that of the 251 assumption 5 Y. Misaki, H. Nishikawa, K. Kawakami, T. Uehara and for the AsF6- salt (0.092 to 0.077) and for the SbF6- salt (0.081 T. Yamabe, T etrahedron L ett., 1992, 33, 4321. to 0.074). 6 (a) Y. Misaki, H. Nishikawa, H. Fujiwara, K. Kawakami, 17 D. Jung, M. Evain, J. J. Novoa, M.-H. Whangbo, M. A. Beno, T. Yamabe, H. Yamochi and G. Saito, J. Chem. Soc., Chem. A. M. Kini, A. J. Schultz, J. M. Williams and P. J. Nigrey, Inorg. Commun., 1992, 1408; (b) Y. Misaki, K. Kawakami, H. Nishikawa, Chem. 1989, 28, 4516. H. Fujiwara, T. Yamabe and M. Shiro, Chem. L ett., 1993, 445. 18 (a) H. Urayama, H. Yamochi, G. Saito, S. Sato, T. Sugano, 7 S. Aonuma, Y. Okano, H. Sawa, R. Kato and H. Kobayashi, M. Kinoshita, A. Kawamoto, J. Tanaka, T. Inabe, T. Mori, J. Chem. Soc., Chem. Commun., 1992, 1193. Y. Maruyama, H. Inokuchi and K. Oshima, Synth. Met., 1988, 27, 8 (a) Y. Misaki, H. Nishikawa, T. Yamabe, T. Mori, H. Inokuchi, A393; (b) H. H. Wang, B. A. Vogt, U. Geiser, M. A. Beno, H. Mori and S. Tanaka, Chem. L ett., 1993, 1341; (b) Y. Misaki, K. D. Carlson, S. Kleinjan, H. Thorup and J. M. Williams, Mol. H. Nishikawa, H. Fujiwara, T. Yamabe, T. Mori, H. Mori and Cryst. L iq. Cryst., 1990, 181, 135. S. Tanaka, Synth.Met., 1995, 70, 1151. 19 M. Kubota, G. Saito, H. Ito, T. Ishiguro and N. Kojima, Mol. 9 (a) G. Saito, Phosphorus, Sulfur and Silicon, 1992, 67, 345; (b) Cryst. L iq. Cryst., 1996, 284, 367. H. Yamochi, T. Komatsu, N. Matsukawa, G. Saito, T. Mori, 20 T. Komatsu, N. Matsukawa, T. Inoue and G. Saito, J. Phys. Soc. Jpn., 1996, 65, 1340. M. Kusunoki and K. Sakaguchi, J. Am. Chem. Soc., 1993, 115, 11 319. 10 Preliminary proceeding: H. Fujiwara, T. Miura, Y. Misaki, Paper 8/01375F; Received 17th February, 1998 J. Mater. Chem., 1998, 8(8), 1711–1717 1717

ISSN:0959-9428    

DOI:10.1039/a801375f

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 The synthesis, redox properties and X-ray crystal structures of two new tetrathiafulvalene-thiophene donors Peter J. Skabara,*a† Klaus Mu�llen,a Martin R. Bryce,b Judith A. K. Howardb and Andrei S. Batsanovb aMax-Planck Institut fu� r Polymerforschung, Ackermannweg 10, D-55128Mainz, Germany bDepartment of Chemistry, University of Durham, Durham, UK DH1 3L E The functionalisation of tetrathiafulvalene with thiophene units is reported via the synthesis of two multiredox compounds 4 and 5.The two molecules represent a fused structure (4) and a TTF-thiophene system directly linked by a single bond (5); both compounds are endowed with ‘free’ 2,5-positions within the thiophene ring, making them accessible to polymerisation reactions. The solution electrochemistry of 4 and 5 reveals the redox properties of the two components: a three-stage oxidation process is seen in each case.Charge-transfer complexes have been prepared, using TCNQ or TCNQF4 as the electron acceptor, with conductivities in the range of 10-4 to 0.22 S cm-1. Compounds 4 and 5 have been studied by X-ray crystallography; the former exhibits kappa-packing whilst the latter shows a high degree of conjugation between the two donor moieties.The outstanding redox properties of the p-electron donor of these eVorts has been manifold: improving donor ability by lowering oxidation potentials, integrating potential highly mag- tetrathiafulvalene (TTF) 1, and its derivatives, are well documented; many charge-transfer salts incorporating TTF units netic components, and producing materials capable of intramolecular charge-transfer have all been realised.Examples of exhibit metallic conductivity and even superconductivity.1 TTF itself undergoes oxidation to the radical cation 2 and dication such TTF systems incorporate other electron donors (e.g. ferrocene,4 pyrrole,5 selenophene,6 thiophene7 and phthalo- 3 via two reversible single-electron processes (E1/2=+0.34 and +0.71 V vs.Ag/AgCl in acetonitrile, respectively). Generally, cyanines)8 and electron acceptors (e.g. C60).9 The inclusion of TTF into redox-active polymeric materials is also a fascinating the oxidation of TTF compounds can be achieved by one of the following methods: (i) complexation with suitable electron prospect.To this end, several attempts have been made at polymerising TTF-thiophene monomers, with only few acceptors (e.g. tetracyano-p-quinodimethane, TCNQ); (ii) via electrochemical techniques; (iii) by exposing the material to reported to be successful.7d,e In a previous communication, we have described the iodine vapour—a practice more commonly employed in the development of TTF-containing Langmuir–Blodgett (LB) synthesis and electrochemistry of a novel fused TTF-thiophene donor 4.10 In this paper, we present this work and the X-ray films.The principal interest in TTF compounds focuses on the electronic behaviour of the corresponding stable radical inter- crystal structure of 4 in detail, together with the synthesis, redox properties and X-ray structure of a new donor system, mediates which, as open-shell species, are directly associated with potential magnetic and conducting properties. 4-(3-thienyl)tetrathiafulvalene 5. Both compounds 4 and 5 are precursors to potentially fascinating polymer materials, however, herein we concentrate mainly on the p-electron donor ability of the two species. S S S S S S S S S S S S 1 2 3 • + ++ Scheme 1 Since the discovery of tetrathiafulvalene,2 a multitude of S S S S S S S H13C6S H13C6S S S S 4 5 TTF derivatives have been reported in the literature.This fact can be attributed to the meritorious donor ability and exceptional synthetic versatility of the molecule and its related 1,3- Results and Discussion dithiole half-unit.3 Among the TTF family of compounds are numerous examples of highly ordered solid state structures, Synthesis of TTF-thiophene donors whose self-assembly is usually promoted by intermolecular The preparation of 4 (Scheme 2) was achieved using an non-bonding chalcogen–chalcogen interactions providing a alternative route for the synthesis of the trithiocarbonate closely knit network of molecules with reduced intermolecular species 9.11 Conversion of diol 612 to the dibromide 7 proceeded distances and electronic band-type superstructures.If the in 70% yield. Formation of the cyclic thioether 813 (78%), material comprises radical charged species, either as compofollowed by dehydrogenation with DDQ gave the thiophene nents in charge-transfer (CT) complexes or radical ion salts, derivative 9 (96%), which was finally oxidised to compound then the formation of partially filled HOMO bands can lead 1011 by treatment with mercuric acetate in 98% yield.The to high levels of conductivity. cross-coupling of half-units 10 and 13 in the presence of triethyl In recent years, several groups have prepared TTF systems phosphite gave 4 in 20–30% yield, together with significant covalently linked to other redox-active molecules.The purpose amounts of self-coupled products. (Ketone 13, containing hexylthio side chains for improved solubility, was obtained *E-mail: P.J.Skabara@shu.ac.uk using known synthetic methodology, via compounds 11 and †Current address: Division of Chemistry, SheYeld Hallam University, SheYeld, UK S1 1WB 12.)14 J. Mater. Chem., 1998, 8(8), 1719–1724 1719Table 1 Cyclic voltammetric data for TTF 1 and compounds 4 and 5 compound E11/2/V E21/2/V E31/2/V TTF 1a +0.23 +0.62 — TTF 1b +0.34 +0.71 — 4a +0.46 +0.83 +2.18 5b +0.42 +0.79 +2.34c Data were obtained in dichloromethanea or acetonitrileb vs.Ag/AgCl, 20 °C (except 4, -30 °C), under argon, 0.1 M TBAPF6 supporting electrolyte, 0.01 M substrate, 100 mV s-1 scan rate with iR compensation. All waves represent a reversible single-electron process, except cwhich is irreversible.the TTF moiety in each donor species) are slightly raised compared to those of TTF, indicating an electron withdrawing eVect of the pendant thiophene units. The oxidation potential of 4 may also be raised slightly by the presence of the alkylthio substituents.16 Unsurprisingly, the E1/2 values for compound 5 are almost identical to those of 4-(2-thienyl )tetrathiafulvalene (E1/2=+0.41 and +0.80 V).7b Further substitution of TTF by thienyl groups has a detrimental eVect on the donor ability of the TTF unit: positive shifts of 170 mV (E11/2) and 130 mV (E21/2) have been reported between the higher substituted analogues 4,5-bis(2-thienyl)tetrathiafulvalene and 4,4¾,5,5¾- tetrakis(2-thienyl)tetrathiafulvalene.7c A third single-electron oxidation process is also observed for each of the donors 4 and 5 and is assigned to the thiophene component (the peak oxidation potential for unsubstituted thiophene is 2.06 V).17 Whereas this oxidation wave is reversible for compound 4, the same is found to be irreversible for 3-thienylTTF 5.S S H13C6S SC6 H13 S S S S S S PhC(O)S PhC(O)S S S S H13C6S H13C6S S S S HO HO S S S Br Br S S S S S S S S S S O S S S O H13C6S H13C6S (v) (iv) (iii) (ii) (i) 4 10 9 8 7 6 + (vi) (vii) 11 12 13 Our failure to produce polymeric materials from either 4 or Scheme 2 Reagents and conditions: (i) CBr4, PPh3, dichloromethane; (ii) Na2S·9H2O, ethanol–water; (iii) DDQ, toluene, reflux, 1.5 h; 5 under electrochemical conditions is mirrored by a number (iv) Hg(OAc)2, acetic acid–chloroform; (v) NaOEt, EtOH, -10 °C, of groups who have tried to form polythiophenes bearing the then C6H13Br; (vi) Hg(OAc)2, acetic acid–chloroform; (vii) P(OEt)3, TTF moiety.There are several possible reasons for this: (i) 90 °C, 6 h anodic polymerisation of thiophene involves the coupling of thiophene cation radicals.18 It has been hypothesised that TTF Compound 5 was prepared using standard Suzuki coupling may act as a radical scavenger towards the thiophene unit,7e methods (Scheme 3). 4-Iodotetrathiafulvalene15 14 was reacted thereby stabilising the thiophene radical cation and inhibiting in the presence of Pd(PPh3)4 with thiophene-3-boronic acid, the polymerisation sequence.In this instancee charged using Ba(OH)2 as base and a 1:1 mixture of monoglyme and species is allowed to diVuse away from the electrode surface water as the solvent. The reaction, which was allowed to stir to form soluble oligomers in solution. A similar behaviour in at 80 °C in the dark and under nitrogen for several hours, stabilisation is believed to predominate for (alkylthio)thioa Vorded the product 5 in 31% yield.phenes: attempts at electropolymerising 3-(methylthio)-, 3-(ethylthio)- and 3,4-bis(ethylthio)-thiophenes have either Solution electrochemistry failed,19 or resulted in the formation of soluble oligomers,20 due to the electron donating (and thus stabilising) eVects of The cyclic voltammetric data for compounds 4 and 5 are the b(b¾) alkylthio side chains.(ii) The oxidation potentials of collated in Table 1, together with data for TTF 1, for comparithe thiophene units in compounds 4 and 5 are higher than son. With both TTF-thiophene donors, two fully reversible that of thiophene; this is most probably due to the coulombic single-electron waves are observed, corresponding to E11/2 and repulsion of the tricationic species generated in each case.In E21/2. These values (which are attributed to the behaviour of deference to polymerisation, these unusual triply charged molecules may be suYciently unstable to react with either the solvent or the anion in solution to form by-products. This phenomenon has been observed previously in derivatised thiophene monomers with high oxidation potentials.21 Further evidence to support this theory can be seen in the cyclic voltammogram of 4,10 which reveals an additional unexpected solitary cathodic peak at +1.46 V, suggesting some decomposition of the starting material.(iii ) Of the two types of TTFthiophene systems known to polymerise under electrochemical conditions,7d,e both polymerisations have been performed using nitrobenzene as the solvent; when other solvents were employed, no polymeric materials were obtained.The strategy behind this choice of solvent utilises the acceptor ability of S S S S S S S S S I S S S S 1 14 5 (i) (ii) nitrobenzene itself. It is believed that TTF forms a charge- Scheme 3 Reagents and conditions: (i) Lithium diisopropylamide, transfer complex with the individual solvent molecules, thus THF, -78 °C, then C6F13I; (ii) Pd(PPh3)4, Ba(OH)2 , decreasing the radical scavenging ability of the TTF moiety CH3OCH2CH2OCH3–H2O (151), thiophene-3-boronic acid, 80 °C, 24 h and allowing the thiophene unit to undergo polymerisation.7e 1720 J.Mater. Chem., 1998, 8(8), 1719–1724Table 2 Room temperature conductivity values and nitrile stretching frequencies of CT complexes of 1, 4 and 5 donor acceptor ratio sa/S cm-1 n(CN)/cm-1 TTF 1 TCNQ 151 0.13 2202 4 TCNQ 151 3.0×10-4 2206 4 TCNQF4 151 6.7×10-3 2191 5 TCNQ 151 0.22 2188 aConductivity measurements were carried out using two-probe apparatus on compressed pellets.23 The values given above represent the averages of five measurements of each CT complex.However, on using these solvent conditions with monomers 4 and 5, a dark precipitate formed at the anode in each experiment, indicating the formation of charge-transfer matter instead of polymerisation taking place. Charge-transfer complexes An alternative method for the polymerisation of thiophene derivatives involves the addition of a strong acceptor.This has been demonstrated byWudl et al.,22 who prepared poly(iso- Fig. 1 Molecule 4, showing 50% probability elipsoids and its inversion equivalent thianaphthene) via the oxidation of isothianaphthene by TCNQ. When compound 4 was treated with TCNQ and TCNQF4, the precipitate which formed in each case was found to be a CT complex (MALDI-TOF mass spectroscopy indicated the presence of monomer units, rather than oligomeric or polymeric species). A CT salt was also isolated when 4-(3- thienyl)TTF 5 was reacted with TCNQ.The conductivity values of the complexes (all of which are of 151 stoichiometry as judged by CHN analysis), were measured using two-probe apparatus23 and the results are collated in Table 2 (TTF–TCNQ was also measured and used as a standard for our equipment). Complex 5–TCNQ gave a conductivity slightly higher than that of TTF–TCNQ, whilst the complexes of donor 4 gave conductivity values several orders of magnitude lower, in the semiconductor range.The CN stretching frequencies of the above complexes are also given in Table 2. The CN peak for TTF–TCNQ (2202 cm-1) is shifted with respect to that of neutral TCNQ (2222 cm-1), and this is due to the influence of the delocalised radical anion in the former.24 The shift in CN frequencies of the complexes of 4 and 5 are commensurate with those of reduced TCNQ and TCNQF4 moieties (2226 cm-1 for neutral TCNQF4), providing further evidence of charge-transfer material.X-Ray crystallography Molecule 4 (Fig. 1) has a non-crystallographic mirror Fig. 2 Kappa-packing of 4 (hexyl groups omitted); projection on the symmetry. Its TTF-thiophene moiety adopts a boat confor- (1 0 1) plane, showing S,S contacts <3.6 A ° mation, folding along the S(2),S(3) and S(4),S(5) vectors by 10.8 and 16.3°, respectively.Both hexyl chains adopt almost ideal all-trans conformations. Molecules related via an inversion centre form rather loose dimers, overlapping with their parallel fused-ring systems (interplanar separation of 3.75 A ° ).The dimers are arranged into a kappa-type layer (Fig. 2), wherein each molecule participates in two S,S contacts closer than twice the van der Waals radius of sulfur (1.81 A ° ),25 S(2),S(5¾) (and its equivalent) of 3.56 A ° . Other S,S contacts are in the range of 3.70–3.85 A ° . The layers are eVectively separated from each other by hexyl chains, stretched in general normally to TTF-thiophene systems.In molecule 5 (Fig. 3) the TTF moiety is folded by 10.5° along the S(1),S(2) vector. The planar thiophene ring is nearly coplanar with the S(1)C(2)C(3)S(2) moiety. The C(2)MC(13) bond distance of 1.457(8) A°is typical for ‘conjugated’ single C(sp2)MC(sp2) bonds (mean 1.455 A ° )26 and much shorter than non-conjugated ones (1.478 A ° )26 indicating a Fig. 3 Molecular structure of 5, showing 50% probability elipsoids. considerable interaction between the p-electron systems of the The S/C(11) was refined as 85% sulfur and 15% carbon, S/C(15) vice versa thiophene and the TTF. The thiophene ring is disordered over J. Mater. Chem., 1998, 8(8), 1719–1724 1721Table 3 Crystal data and experimental details compound 4 5 formula C20H28S7 C10H6S5 M 492.84 286.45 symmetry monoclinic monoclinic T/K 150 293 l/A° 1.54184 0.71073 a/A ° 17.113(2) 5.886(1) b/A ° 12.259(2) 8.617(1) c/A ° 12.338(2) 23.146(2) b (°) 110.42(1) 93.06(1) U/A ° 3 2425.8(7) 1172.3(3) space group P21/c P21/c Z 4 4 m/cm-1 60.4 9.5 Dc/g cm-3 1.35 1.62 crystal size/mm 0.22×0.35×0.35 0.03×0.30×0.50 2hmax(°) 150 50.6 Fig. 4 Crystal packing diagram of 5 data total 4957 4766 data unique 4150 1880 data observed, I>2s(I) 3478 1387 two orientations, diVering by the 180° rotation around the Rint before/after abs.corr. 0.066, 0.047 0.077, 0.048 C(2)MC(13) bond, thus the observed bond distances in that absorption correction analyticala integrationb transmission min, max 0.16, 0.40 0.68, 0.97 ring are not meaningful. The crystal packing of 5 (Fig. 4) no. of refined variables 356 137 shows a perpendicular motif without short intermolecular wR(F2), all data 0.147 0.214 contacts. All S,S contacts are 3.8 A° , except one (3.51 A° ) R(F), obs. data 0.039 0.061 between S(4) and its inversion equivalent atom. Drmax,min/e A° -3 0.36, -0.32 0.46, -0.41 aTEXSAN software (ref. 28). bSHELXTL software (ref. 27). Conclusions The synthesis of two new tetrathiafulvalene-thiophene systems S(2)MC(3) bond (the thiophene and dithiole rings overlap- 4 and 5 has been described.Under oxidative conditions, the ping), did not produce a consistent refinement. The disordered propensity to form non-coupling charged intermediates, rather S and C atoms in overlapping positions were refined as a than oligomeric or polymeric species, is supported by the fact single atom.All H atoms were refined in isotropic approxi- that compounds 4 and 5 form stable CT materials on reaction mation (4) or were treated as ‘riding’ (5). Crystal data and with TCNQ and TCNQF4. The X-ray crystal structures of 4 experimental details are listed in Table 3; atomic coordinates and 5, however, oVer some interesting features: compound 4 and thermal parameters, bond distances and angles have been crystallises with a high degree of order between the molecules, deposited at the Cambridge Crystallographic Data Centre procured by an extensive network of close S,S intermolecular (CCDC); see Information for Authors, J.Mater. Chem., 1998, contacts, whilst compound 5 exhibits a high degree of p- Issue 1.Any request to the CCDC for this material should delocalisation between the two donor units. Either of these quote the full literature citation and the reference number characteristics could be beneficial to the corresponding poly- 1145/103. Selected bond lengths are given in Table 4. mer systems by: (i) increasing the dimensionality of the polymer material via the interaction of chalcogens between the chains, General and (ii) integrating the TTF moiety into the electronic behaviour of the polythiophene backbone, on the basis of a highly Melting points were recorded on a Kofler hot-stage microscope conjugated TTF-thiophene link. In view of these results, our apparatus and are uncorrected. 1H and 13C NMR spectra were current eVorts involve the synthesis of 2,5-dihalothiophene recorded on a Varian Gemini 200 instrument.Infrared spectra analogues of 4 and 5 as a means of functionalisation for chemical polymerisation. Table 4 Selected bond distances in A ° in 4 and 5 Compound 4 Experimental S(1)–C(1) 1.714(3) S(1)–C(4) 1.719(3) X-Ray crystallography S(2)–C(2) 1.752(3) S(2)–C(5) 1.762(3) The single-crystal X-ray diVraction experiment for 4 was S(3)–C(3) 1.760(3) S(3)–C(5) 1.767(3) S(4)–C(6) 1.759(3) S(4)–C(7) 1.769(3) carried out on a Rikagu AFC6S 4-circle diVractometer (2h/v S(5)–C(8) 1.761(3) S(5)–C(6) 1.761(3) scan mode), using graphite monochromated Cu-Ka radiation S(6)–C(7) 1.744(3) S(6)–C(9) 1.814(3) and an Oxford Cryosystems open-flow N2 cryostat.For 5, the S(7)–C(8) 1.751(3) S(7)–C(15) 1.817(4) experiment was performed on a Siemens SMART 3-circle C(1)–C(2) 1.357(3) C(2)–C(3) 1.425(4) diVractometer with a CCD area detector, using graphite mon- C(3)–C(4) 1.352(4) C(5)–C(6) 1.331(4) ochromated Mo-Ka radiation.A hemisphere of the reciprocal C(7)–C(8) 1.346(4) space was scanned by v in frames of 0.3°. Both structures were Compound 5 solved by direct methods and refined by full-matrix least squares against F2 of all data, using SHELXTL software.27 All S(1)–C(1) 1.764(6) S(1)–C(2) 1.768(5) non-H atoms were refined with anisotropic displacement par- S(2)–C(3) 1.707(5) S(2)–C(1) 1.740(6) ameters.In 5 the thiophene ring is disordered over two S(3)–C(5) 1.730(6) S(3)–C(4) 1.755(6) orientations in which the sulfur atom occupies the positions S(4)–C(6) 1.722(7) S(4)–C(4) 1.744(6) S/C(11)–C/S(15) 1.651(7) S/C(11)–C(12) 1.706(5) 11 and 15, with the occupancies of 85(1) and 15(1)%, respect- C/S(15)–C(14) 1.453(8) C(1)–C(4) 1.363(8) ively.Other possible models of disorder, such as the partial C(2)–C(3) 1.414(8) C(2)–C(13) 1.457(8) presence of the a-thiophene substituent (i.e. sulfur in the C(5)–C(6) 1.348(9) C(12)–C(13) 1.459(8) positions 12 or 14) and the rotation of the whole molecule by C(13)–C(14) 1.480(7) 180° around the axis through S(1) and the midpoint of the 1722 J.Mater. Chem., 1998, 8(8), 1719–1724were recorded on a Nicolet FTIR spectrometer and mass (CDCl3) 136.0, 127.5, 113.8, 112.1, 112.0, 36.3, 31.3, 29.7, 28.2, 22.5 and 14.0; nmax (KBr)/cm-1 3087.8, 2948.3, 2922.7, 2853.6, spectra were determined with a Fison Instruments Trio 2000 or a Zab2-SE-FPD (VG Instruments). Elemental analyses 1459.5 and 768.8.were performed on a Carlo-Erba Strumentazione instrument. Cyclic voltammetry was performed using a BAS CV50W 4-(3-Thienyl )tetrathiafulvalene 5 voltammetric analyser, using freshly distilled dichloromethane To a stirred solution of thiophene-3-boronic acid (0.22 g, or acetonitrile as the solvent, with iR compensation.The 1.72 mmol) in dimethoxyethane–water (100 ml, 151 v/v), was syntheses of compounds 813 and 911 were achieved using added 4-iodotetrathiafulvalene15a 14 (0.63 g, 1.91 mmol). After alternative methods to those reported previously. the addition of barium hydroxide (0.5 g, 2.91 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.05 g, 0.04 mmol), 4,5-Bis(bromomethyl )-1,3-dithiole-2-thione 7 the reaction was stirred at 80 °C in the dark, under nitrogen, To a suspension of 612 (2.00 g, 10.31 mmol) in dry dichloro- for 24 h.Dichloromethane (200 ml) was added and the methane (300 ml), under nitrogen, was added carbon tetrabro- resulting mixture was washed with water. The organic layer mide (6.85 g, 20.63 mmol). Whilst stirring, a solution of was separated, dried (MgSO4) and evaporated.The residue triphenylphosphine (5.40 g, 20.61 mmol) in dry dichloro- was chromatographed (silica gel ), using dichloromethane– methane (100 ml) was added over 45 min. Evaporation of the hexane (153 v/v) as the eluent to aVord the product. solvent gave an oily brown residue, which was chromato- Recrystallisation from dichloromethane–hexane gave orange graphed using silica gel and dichloromethane–hexane (152 v/v) crystals (0.15 g, 31% yield); mp 95–97 °C; m/z (EI) 286 (M+); as the eluent.The product was recrystallised from dichloro- HRMS found 285.9076, C10H6S5 requires 285.9073; dH (CDCl3) methane–hexane to give a bright yellow solid (2.31 g, 70% 7.34 (1H, dd), 7.20 (2H, m), 6.43 (1H, s) and 6.34 (2H, s); dC yield); mp 124–126 °C (Found: C, 18.9; H, 1.3%; C5H4Br2S3 (CDCl3) 133.8, 131.1, 127.0, 125.6, 122.6, 119.4 and 113.6; nmax requires C, 18.8; H, 1.3%); m/z (FD) 320 (M+); dH (CDCl3) (KBr)/cm-1 3070.0, 2924.6, 2856.9, 1458.5, 870.8, 748.7 and 4.33 (s); dC (CDCl3) 208.4, 139.7 and 20.6; nmax (KBr)/cm-1 643.2. 3023.3, 2960.5, 1198.5, 1058.2, 594.3 and 514.4. General method for the preparation of CT complexes 4,6-Dihydrothieno[3,4-d]-1,3-dithiole-2-thione 8 To a solution of the donor (1 equiv.) in refluxing dichloro- A solution of 7 (2.00 g, 6.25 mmol) in THF–ethanol (250 ml, methane (for compound 4), or acetonitrile (for compound 5), 451 v/v) and a solution of sodium sulfide nonahydrate (1.50 g, was added a hot solution of TCNQ or TCNQF4 (1 equiv.) 6.25 mmol) in water–ethanol (250 ml, 45:1 v/v), were added in the same solvent.The mixture was heated gently at reflux simultaneously, over 45 min, to ethanol (200 ml) with vigorous for 10 min before allowing to cool. After several hours the stirring. Evaporation of the solvent aVorded a yellow solid charge-transfer material was collected by filtration. residue, which was leached with dichloromethane (3×150 ml). The resulting solution was washed with water, separated, dried Complex 4–TCNQ. Analysis found: C, 54.9; H, 4.7; N, 7.7%; (MgSO4) and evaporated to leave a yellow solid.C32H32N4S7 (a 151 complex) requires C, 55.1; H, 4.6; N, 8.0%; Recrystallisation from hexane–dichloromethane gave a yellow nmax (KBr)/cm-1 2921.6, 2852.2, 2206.2, 1508.1, 1469.5, 1423.2, crystalline solid (0.94 g, 78% yield); mp 131–133 °C (Found: 1313.3, 1186.0 and 767.5.C, 31.5; H, 2.1%. C5H4S4 requires C, 31.2; H, 2.1%); m/z (EI) 192 (M+); dH (CDCl3) 4.03 (s); dC (CDCl3) 217.4, 138.6 and Complex 4–TCNQF4. Analysis found: C, 49.9; H, 3.7; N, 35.1; nmax (KBr)/cm-1 2919.0, 2839.5, 1638.6, 1080.4, 1041.4 7.5%; C32H28F4N4S7 (a 151 complex) requires C, 50.0; H, 3.7; and 507.3.N, 7.3%; nmax (KBr)/cm-1 2926.7, 2856.8, 2191.1, 1630.4, 1386.4, 1313.6, 776.9 and 484.5. Thieno[3,4-d]-1,3-dithiole-2-thione 9 To a solution of 8 (1.00 g, 5.21 mmol), under nitrogen in dry Complex 5–TCNQ. Analysis found: C, 53.3; H, 2.0; N, toluene (150 ml), was added 2,3-dichloro-5,6-dicyano-1,4- 11.1%; C22H10N4S5 (a 151 complex) requires C, 53.9; H, 2.1; benzoquinone (1.30 g, 5.73 mmol); the mixture was allowed to N, 11.4%; nmax (KBr)/cm-1 3062.4, 2925.9, 2187.9, 1642.1, reflux for 1.5 h.After evaporation of the solvent, the product 1314.8, 1122.5, 1084.1, 687.2 and 431.9. was extracted with dichloromethane (3×150 ml). The solution was washed with water (5×200ml), separated, dried (MgSO4), We thank the Max-Planck Society for funding P.J.S.and The and the residue chromatographed using silica gel and ethyl Royal Society of Chemistry for funding A.S.B.; P.J.S. also acetate–light petroleum (153 v/v) as the eluting solvent. thanks The Royal Society of Chemistry for equipment related Recrystallisation from ethyl acetate–light petroleum aVorded to conductivity measurements. the product as an orange solid (0.95 g, 96% yield); mp 139–141 °C ( lit.,29 142 °C).Note added in proof: After submission of this manuscript, the electropolymerisation of TTF-functionalised bithiophene 2-[4,5-Bis(hexylthio)-1,3-dithiol-2-ylidene]thieno[3,4-d]-1,3- derivatives was reported: L. Huchet, S. Akoudad and J. Roncali, dithiole 4 Adv. Mater., 1998, 10, 541. Compounds 1011 (0.75 g, 4.32 mmol) and 13 (2.25 g, 6.43 mmol) were added to neat freshly distilled triethyl References phosphite (10 ml ); the mixture was heated to 90 °C and left to stir at this temperature for 6 h.After cooling, the solution was 1 Recent reviews: (a) M. R. Bryce, J. Mater. Chem., 1995, 5, 1481; chromatographed (silica gel ), using hexane as the eluting (b) J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, H.H. Wang, A. M. Kini and M.-H. Whangbo, Organic solvent to remove triethyl phosphite, followed by dichloro- Superconductors (Including Fullerenes); Synthesis, Structure, methane–hexane (153 v/v) to isolate the product. Properties and T heory, Prentice Hall, Englewood CliVs, NJ, 1992; Recrystallisation from dichloromethane–acetonitrile aVorded (c) G. Schukat and E.Fangha�nel, Sulfur Rep., 1993, 14, 245. bright yellow needles (0.53 g, 25% yield); mp 73–74 °C (Found 2 (a) F. Wudl, G. M. Smith and E. J. Hufnagel, J. Chem. Soc., Chem. C, 48.4; H, 5.7%; C20H28S7 requires C, 48.7; H, 5.7%); m/z Commun., 1970, 1453; (b) S. Hu� nig, G. Kiesslich, D. Scheutzow, (FD) 492 (M+); dH (CDCl3) 6.88 (2H, s), 2.83 (4H, t, J 7.2 Hz), R. Zahradnik and P. Carsky, Int.J. Sulfur Chem. C, 1971, 6, 109; (c) G. Kiesslich, Ph.D. Thesis, University ofWu� rzburg, 1968. 1.65 (4H, m), 1.32 (12H, m) and 0.90 (6H, t, J 6.4 Hz); dC J. Mater. Chem., 1998, 8(8), 1719–1724 17233 Recent synthetic reviews: (a) M. C. Grossel and S. C. Weston, 7249; C. Rovira, J. Veciana, N. Santalo� , J. Tarre�s, J. Cirujeda, E. Molins, J. Llorca and E. Espinosa, J.Org. Chem., 1994, 59, 3307. Contemp. Org. Synth., 1994, 1, 367; (b) N. Svenstrup and J. Becher, Synthesis, 1995, 215. 14 G. Saito, Pure Appl. Chem., 1987, 59, 999. 15 (a) C. S. Wang, A. Ellern, V. Khodorkovsky, J. Bernstein and 4 A. J. Moore, P. J. Skabara, M. R. Bryce, A. S. Batsanov, J. A. K. Howard and S. T. A. K. Daley, J. Chem. Soc., Chem. J. Y. Becker, J. Chem. Soc., Chem.Commun., 1994, 983; (b) A. S. Batsanov, A. J. Moore, N. Robertson, A. Green, M. R. Commun., 1993, 417; M. R. Bryce, P. J. Skabara, A. J. Moore, A. S. Batsanov, J. A. K. Howard and V. J. Hoy, T etrahedron, 1997, Bryce, J. A. K. Howard and A. E. Underhill, J.Mater. Chem., 1997, 7, 387. 53, 17781. 5 K. Zong, W. Chen, M. P. Cava and R. D. Rogers, J. Org. Chem., 16 (a) D. L. Lichtenberger, R.L. Johnston, K. Hinkelmann, T. Suzuki and F. Wudl, J. Am. Chem. Soc., 1990, 112, 3302; (b) A. J. Moore 1996, 61, 8117. 6 (a) R. Ketcham, A.-B. Ho� rnfeldt and S. Gronowitz, J. Org. Chem., and M. R. Bryce, J. Chem. Soc., Chem. Commun., 1991, 1638. 17 R. J. Waltman, J. Bargon and A. F. Diaz, J. Phys. Chem., 1983, 1984, 49, 1117; (b) C. S. Wang, A. Ellern, J. Y. Becker and J.Bernstein, Adv. Mater., 1995, 7, 644. 87, 1459. 18 J. Roncali, Chem. Rev., 1992, 92, 711. 7 (a) P. Shu, L. Chiang, T. Emge, D. Holt, T. Kistenmacher, M. Lee, J. Stokes, T. Poehler, A. Bloch and D. Cowan, J. Chem. Soc., Chem. 19 J. P. Ruiz, K. Nayak, D. S. Marynick and J. R. Reynolds, Macromolecules, 1989, 22, 1231. Commun., 1981, 920; (b) M. Iyoda, Y. Kuwatani, N. Ueno and M. Oda, J.Chem. Soc., Chem. Commun., 1992, 158; (c) A. Charlton, 20 S. Tanaka, M. Sato and K. Kaeriyama, Synth.Met., 1988, 25, 277. 21 R. J.Waltman and J. Bargon, Can. J. Chem., 1986, 64, 76. A. E. Underhill, G. Williams, M. Kalaji, P. J. Murphy, K. M. Abdul Malik and M. B. Hursthouse, J. Org. Chem., 1997, 62, 3098; 22 F. Wudl, M. Kobayashi and A. J. Heeger, J. Org. Chem., 1984, 49, 3382.(d)M. R. Bryce, A. D. Chissel, J. Gopal, P. Kathirgamanathan and D. Parker, Synth. Met., 1991, 39, 397; (e) C. Thobie-Gautier, 23 F.Wudl and M. R. Bryce, J. Chem. Educ., 1990, 67, 717. 24 J. S. Chappel, A. N. Bloch, W. A. Bryden, M. Maxfield, A. Gorgues, M. Jubault and J. Roncali, Macromolecules, 1993, 26, 4094; ( f ) for a general review see J. Roncali, J.Mater. Chem., 1997, T.O. Poehler and D. O. Cowan, J. Am. Chem. Soc., 1981, 103, 2442. Exceptions to the linear dependence of the nitrile stretching 7, 2307; ( g) T. Yamamoto and T. Shimizu, J. Mater. Chem., 1997, frequency with the degree of CT in TCNQ salts have been noted 7, 1967. on several occasions: F. Bigoli, P. Deplano, F. A. Devillanova, 8 (a)M. J. Cook, G. Cooke and A. Jafari-Fini, Chem. Commun., 1996, A. Girlando, V. Lippolis, M.-L. Mercuri, M.-A. Pellinghelli and 1925; (b) M. A. Blower, M. R. Bryce and W. Devonport, Adv. E. F. Trogu, J.Mater. Chem., 1998, 8, 1145, and references therein. Mater., 1996, 8, 63. 25 R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100, 7384. 9 (a)M. Prato, M. Maggini, C. Giacometti, G. Scorrano, G. Sandona` 26 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen and G. Farina, T etrahedron, 1996, 52, 5221; (b) N. Martý�n, and R. Taylor, J. Chem. Soc., Perkin T rans. 2, 1987, Suppl., 1. L. Sa�nchez, C. Seoane, R. Andreu, J. Garý�n and J. Orduna, 27 G. M. Sheldrick, SHELXTL, Version 5, Siemens Analytical T etrahedron L ett., 1996, 33, 5979; (c) J. Llacay, M. Mas, E. Molins, Instruments, Madison, WI, USA, 1995. J. Veciana, D. Powell and C. Rovira, Chem. Commun., 1997, 659. 28 TEXSAN, TEXRAY Structural Analysis Package, Molecular 10 P. J. Skabara and K. Mu� llen, Synth. Met., 1997, 84, 345. Structure Corporation, TheWoodlands, TX77381, USA. 11 L. Chiang, P. Shu, D. Holt and D. Cowan, J. Org. Chem., 1983, 29 S. Gronowitz and P. Moses, Acta Chem. Scand., 1962, 16, 105. 48, 4713. 12 M. A. Fox and H.-L. Pan, J. Org. Chem., 1994, 59, 6519. 13 C. Rovira, N. Santalo� and J. Veciana, T etrahedron L ett., 1989, 30, Paper 8/03027H; Received 23rd April, 1998 1724 J. Mater. Chem., 1998,

ISSN:0959-9428    

DOI:10.1039/a803027h

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 Versatile optical materials: fluorescence, non-linear optical and mesogenic properties of selected 2-pyrazoline derivatives Joaquý�n Barbera� ,a Koen Clays,b Raquel Gime�nez,a Stephan Houbrechts,b Andre� Persoonsb and Jose� Luis Serrano*a aDepartamento de Quý�mica Orga�nica-CSIC, Facultad de Ciencias-ICMA, Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain bDepartment of Chemistry, L aboratory of Chemical and Biological Dynamics, Katholieke Universiteit L euven, Celestijnenlaan 200D, B-3001 L euven, Belgium A study of the structure–property relationships in a series of 3-(4-n-decyloxyphenyl)-1-( p-X-phenyl)-2-pyrazolines has been performed.By simply changing the substituent in the 1-phenyl ring we were able to tune the physical properties of the compounds.If this ring is non-substituted or substituted with a 4-methoxy, 4-chloro or 4-carboxy group, the pyrazoline compounds are fluorescent. If the ring is 4-nitro- or 2,4-dinitro-substituted, the compounds have interesting second-order non-linear optical properties. The first hyperpolarizability has been measured using the Hyper-Rayleigh Scattering technique in solution.The 4-nitro derivative displays liquid crystalline behaviour, showing a monotropic smectic A phase with a partial bilayer structure due to an antiparallel arrangement of molecules as confirmed by X-ray studies in the mesophase. show the 1,3-diaryl-2-pyrazolines to be very promising mate- Introduction rials for second-order non-linear optics.8a,b Moreover, measure- Materials with optical properties are very interesting for appli- ments of the electrooptic half-wave voltage have shown cations in many areas of technology, including fluorescent the potential of pyrazolines as high eYciency electrooptic materials which have been extensively used as optical bright- materials.8c eners, fluorescent dyes and scintillators.1 Non-linear optical In order to promote mesomorphism in these structures we (NLO) materials have also attracted great interest for appli- have introduced an n-decyloxy substituent as a terminal chain cations in optical signal processing such as frequency doubling, in the 4-position of one of the aromatic rings (Scheme 1).amplifiers, modulators for laser technology, data storage and Moreover, this group increases the solubility of the pyrazoline telecommunications.2 derivatives in organic solvents and favours the necessary Organic compounds are being extensively studied for non- arrangements to obtain LB films.9 linear optical properties, as molecular materials, and their In the other aromatic ring we have introduced a variety of properties are highly dependent on their structural character- groups such as H, OCH3, COOH and NO2, in order to study istics.For second-harmonic generation, organic materials have the influence of both acceptor and donor groups on the optical to show a high first hyperpolarizability (b) and also possess a and mesogenic properties of the compounds. non-centrosymmetric organization in order to achieve a macro- In total, seven new compounds have been synthesised in scopic eVect.To obtain this particular arrangement several order to investigate the points outlined above. approaches are possible and these include the use of crystals, poled polymers, Langmuir–Blodgett (LB) films and liquid crystals. Moreover, organic compounds have other advantages Results and Discussion such as low dielectric constants, low switching times and easy processability.3 Synthesis Typical organic molecules with large hyperpolarizabilities The synthetic route to the compounds is shown in Scheme 1.are systems with donor and acceptor groups separated by a Compounds 2–6 were prepared by the reaction of 4-n-decyloxy- conjugated system (p-system) such as benzene, stilbene or phenyl vinyl ketone 1 with the appropriately substituted phe- stilbazolium.2,4–6 nylhydrazine (route c), by adapting literature methods.10 The aim of the work described in this paper is to obtain Ethanol was chosen as the solvent at a temperature of 30–40 °C molecular materials that combine NLO, fluorescent and mesoto ensure the dissolution of the reactants and the precipitation genic properties. The existence of mesogenic properties helps of the cyclised products.The use of acid catalysis (acetic acid) the macroscopic molecular orientations which are very importfavours cyclisation as opposed to the formation of phenyl- ant to both optical and technical applications.3c In this context, hydrazone derivatives or Michael addition products. we have introduced the structural characteristics of organic The reaction follows a general mechanism that was studied NLO materials into molecules that exhibit fluorescent properby Coispeau and Elguero.11 1,2-Addition of the primary nitro- ties.For these reasons, we have prepared new organic comgen atom of the phenylhydrazine occurs at the carbonyl group pounds with the 1,3-diphenyl-2-pyrazoline group as the pof compound 1, followed by cyclisation by means of an system.These compounds show fluorescent properties1a,b,7 and, electrocyclic reaction involving six electrons. by means of relatively straightforward synthetic procedures, When X=COOH and NO2 (compounds 5 and 6), the allow the introduction of suitable substituents for the nucleophilic power of the secondary nitrogen atom of the promotion of second-order non-linear optical properties.phenylhydrazine derivative is diminished due to the presence Molecular calculations (CNDO) have been carried out and of an electron withdrawing substituent, whereas the primary nitrogen atom is aVected to a lesser extent. As a consequence, the carboxy derivative needed a longer reaction time and, in *E-mail: joseluis@posta.unizar.es J.Mater. Chem., 1998, 8(8), 1725–1730 1725OH OC10H21 C10H21O O C10H21O N N X X H2N-NH NO2 H2N-NH NO2 C10H21O N N NO2 C10H21O NH N NO2 NO2 O2N C10H21O N N H NO2 F NO2 O 1 a b c d e H OCH3 Cl COOH NO2 X = 23456 7 8 Scheme 1 Synthetic routes to the pyrazoline and phenylhydrazone compounds the nitro derivative, the yield is lower than in the other explained by the presence of the nitro groups, which cause a non-radiative deactivation of the excited state due to a rapid compounds. dissipation of electronic energy.14 In addition to this, the When the phenylhydrazine bears two electron withdrawing hydrazone system present in compound 8 is less rigid and has groups, as in the 2,4-dinitrophenylhydrazine, route c proved more rotational freedom than pyrazoline systems.unsuccessful even after heating under reflux for several hours. We can observe (Table 1) a relationship between the acceptor Indeed this method led to the formation of a phenylhydrazone character of the substituent X and the emission wavelength derivative resulting from the attack of a molecule of 2,4- (lem). The stronger the acceptor character of X, the lower lem. dinitrophenylhydrazine on the carbonyl group and of a mol- On the other hand, the opposite tendency is observed for the ecule of ethanol on the double bond (route e, compound 8).It intensities of the emission maxima (I/c in Table 1): the stronger has been reported that 2,4-dinitrophenylhydrazones can only the acceptor character of X, the higher the intensity. be cyclised under extreme conditions (boiling acetic acid Generally, the groups that produce a higher bathochromic containing hydrobromic acid).12 eVect and higher molar absorptivity in the absorption spectrum Therefore, compound 7 was synthesised in two consecutive exhibit a stronger emission, except for the compound with X= steps (route d).In the first step 3-(4-decyloxyphenyl)-2-pyraz- OCH3, which has a slighty larger absorption lmax but weaker oline is generated in situ to react react with 1-fluoro-2,4- fluorescent emission than the compound with X=H.These dinitrobenzene by a nucleophilic aromatic substitution using results can be accounted for by structural and electronic eVects. an adaptation of described methods.13 When the acceptor strength of X increases, the molecular planarity increases because the contribution of resonance form Absorbance and fluorescence propeich the N1 atom has an sp2 character, becomes greater.In order to compare the absorbance and fluorescence proper- The quantum yields of compounds 2–5 are high (see Table 1). ties of these compounds we recorded the absorbance spectra The values are relative to quinine sulfate (QF=0.55)15 and and the emission spectra in solution in THF.The pyrazoline have been obtained at an excitation wavelength of 340 nm. derivatives 2–5 exhibit fluorescent emission. The data for these Compound 2 (X=H) displays the highest value (0.80). The fluorescent compounds are given in Table 1, and an example quantum yield trend is diVerent from the I/c trend. This could of these spectra is given in Fig. 1. The concentrations of the be due to the diVerences between the irradiation wavelength solutions were of the order of 10-7 M, except for the methoxy (340 nm) and the absorption maxima (lmax) of each compound. derivative (compound 3), which needed solutions ten or The Stokes shift (diVerence between absorption and fluoreshundred times more concentrated. cence maxima) increases as the donor character of X increases.On the other hand, no significant emission was found for The fact that electron-donor substituents induce higher the nitro derivatives (pyrazolines 6 and 7, and phenylhydrazone Stokes shifts is in agreement with previous studies on related pyrazolines.1a,b 8). The lack of fluorescence in these compounds could be 1726 J. Mater. Chem., 1998, 8(8), 1725–1730Table 1 Absorption and emission UV–visible spectral data of 2-pyrazolines 2–5 (in THF) lmax log ea log eb c/M×10-7 lem/ Stokes shift/ Compound /nm (lmax) (340 nm) (em)c nm I/cd cm-1e QF f 2 355 4.30 4.24 5.4 426 1700 4695 0.80 3 360 4.26 4.21 15.9 454 740 5750 0.55 4 357 4.33 4.27 4.6 424 1740 4425 0.70 5 369, 387sh 4.54 4.31 2.7 413 2700 3885 0.66 aExtinction coeYcient at the absorption maximum wavelength.bExtinction coeYcient at the excitation wavelength. cConcentration of the solution in which the emission spectrum has been performed. dIntensity maximum normalised to a concentration of 1×10-5 M. eDiVerence between the absorption and emission maxima in wavenumbers. fQuantum yield relative to quinine sulfate (QF=0.55).sh: shoulder. were measured in chloroform solution relative to standard solutions of p-nitroaniline ( p-NA) in the same solvent (bp-NA=23×10-30 esu). The absorption spectra in chloroform and the quadratic coeYcient as a function of molar concentration in the same solvent are shown in Fig. 2 and 3 respectively for compounds 6–8. The absorption maxima and b values for compounds 6–8 are given in Table 2.We would have expected that compound 7, bearing two nitro groups in the ortho- and para-positions, would have a b value higher than that of compound 6, bearing only one nitro group in the para-position. This would be expected because Fig. 1 Excitation spectrum (- - -) and emission spectrum (—) for compound 5 Fig. 2 Normalised UV–visible spectra of the nitro derivatives in chloroform: (—) compound 6, (- - -) compound 7 and (· · · · · · ·) compound 8) O N N X R O N N R O N N R X X X = acceptor group A X = donor group C B Resonance forms of the 1-(p-X-phenyl)-3-(p-alkoxyphenyl)-2- pyrazoline Non-linear optical properties The first hyperpolarizability (b) of each of the nitro derivatives (compounds 6–8) was measured using the Hyper-Rayleigh Scattering (HRS) technique.16 This technique relies on the fact that a small part of an intense Nd-YAG laser pulse at optical frequency v (1064 nm) is scattered at 2v (532 nm) due to local orientational fluctuations of the molecules.Because the HRS signal is directly proportional to b2, only absolute values of b can be deduced. A detailed description of the experimental set-up has been described elsewhere.17 We were unable to measure the first hyperpolarizability for the other pyrazoline derivatives (2–5) because of the interference of the HRS signal with another incoherent process: multiphoton fluorescence in the region of 532 nm.If we consider compounds 6–8 as asymmetric conjugated p-electron systems with donor and acceptor groups in the 4-position, bzzz is by far the largest component of bHRS.18 The Fig. 3 Quadratic coeYcient (I2w /Iw2) versus molar concentration plot b0 values (extrapolated to infinite wavelengths) have been of the nitro derivatives at room temperature in chloroform (1064 nm): ($) compound 6, (+) compound 7 and (2) compound 8 calculated according to the two-level model.19 The bHRS values J. Mater. Chem., 1998, 8(8), 1725–1730 1727Table 2 Absorption maxima (in CHCl3) and first hyperpolarizabilities (1064 nm, CHCl3) of the nitro derivatives. lmax/ bHRS b0HRS Compound nm log e (×10-30 esu) (×10-30 esu) 6 430 4.5 393 114 7 424 4.4 215 66 8 396 4.4 130 51 the intramolecular charge transfer should be higher in the first case, and therefore, the lowest transition energy should be lower (i.e.lmax should be higher).However, the absorbance spectra show that compound 7 absorbs at a wavelength lower than compound 6. This eVect has already been seen in other related compounds such as 1-(4-nitrophenyl)-2-pyrazoline and 1-(2,4-dinitrophenyl)-2-pyrazoline.13b This phenomenon indicates that there is more eYcient charge transfer in compound Fig. 4 DSC thermogram for compound 6; solid line: first heating; 6 than in compound 7, which can be explained by a higher dashed line: first cooling degree of planarity and higher resonance eVect in the mononitro derivative.Indeed, the presence of a second nitro group complete (-20 °C at 10°Cmin-1). In the second heating cycle in the ortho-position of the phenyl ring (compound 7) must a cold crystallization takes place and the sample melts again cause a decrease in the charge transfer due to the deviation at a similar temperature to the first scan (Fig. 4).from planarity of the phenyl ring at the N1 position due to The poor mesogenic behaviour of the compounds in this steric eVects. The eVect of this is a decrease in b with respect series could be due to the fact that their molecular structure to compound 6.To verify this, we tried to grow crystals of deviates significantly from linearity. Indeed, in the crystal these pyrazolines but all eVorts proved unsuccesful. The crystal structure of 1,3-diphenyl-2-pyrazoline the angle between the structure analysis of similar molecules, such as 1-(2¾,4¾-dinitroaxis of the phenyl rings is 35°.23 phenyl)pyrazole20 and 4-bromo-1-(2¾,4¾-dinitrophenyl)pyra- The fact that compound 6 is the only derivative with liquid zole,21 taken from the literature reveal that the nitro group in crystalline properties is probably due to the aforementioned the ortho-position is not conjugated with its phenyl ring (the eVect that the nitro group induces a planar structure with dihedral angles are 69 and 65° respectively).Moreover, the conjugation throughout the whole molecule.Furthermore, the dihedral angles between the pyrazole ring and the phenyl ring presence of terminal groups possessing a large dipole moment are 27 and 22° respectively, higher than the 19° of a similar is known to make intermolecular interactions stronger through compound with only one nitro group in the para-position, dimer associations leading to an antiparallel arrangement.24 4-bromo-3-methyl-1-(4¾-nitrophenyl)pyrazole.22 This is supported by the X-ray diVraction study of the super- The b value of the hydrazone derivative (compound 8) is cooled mesophase of compound 6 at room temperature, which lower than those measured in the pyrazoline derivatives. This confirms its smectic structure with a layer thickness d=37 A ° .indicates that, in terms on NLO properties, the pyrazoline If we compare this value with the molecular length estimated derivatives are better systems than the hydrazone derivative, from Dreiding stereomodels, assuming an all-trans confor- due to the presence of the heterocyclic ring which prevents the mation of the hydrocarbon chain, L=29.5 A ° , we can conclude conformational freedom of the CNN–N atoms of the hydrathat the mesophase has a partial-bilayer structure (SAd zone, thus enhancing the conjugation and, consequently, b.mesophase). Although compound 5 also has an acceptor group in the 4- Mesogenic properties position, it is not mesogenic. The existence of dimers in benzoic The thermal behaviour of all the compounds has been studied acid derivatives due to hydrogen bonding is a well known by polarizing optical microscopy and diVerential scanning phenomenon that leads to liquid crystalline behaviour in calorimetry (DSC).All the compounds melt to give an isotropic systems such as 4-alkoxybenzoic acids.25 This type of associliquid (see Table 3). However, compound 6 showsmesomorphic ation is present in compound 5 in the solid state (an IR band behaviour on cooling, displaying a monotropic smectic A is present at 1676 cm-1, which is typical for a hydrogen phase.The texture of this mesophase is typically fan-shaped. bonded COOH). However, this association leads to a much The compound melts at 93 °C on heating and shows hysteresis higher melting point in compound 5 than in all the other in the cooling scan, with the smectic A phase appearing at pyrazoline derivatives (see Table 3).These strong interactions 71 °C and remaining metastable until the cooling cycle is in the solid could be responsible for the lack of liquid crystallinity. Table 3 Optical, thermal and thermodynamical properties of 2- Experimental pyrazolines 2–8 General methods Compound Transitiona T / °C (DH/kJ mol-1) All compounds have been characterised satisfactorily by 2 C–I 108 elemental analysis, 1H NMR and IR spectroscopy and mass 3 C–I 161 spectrometry.Microanalyses were performed with a Perkin- 4 C–I 143 5 C–I 239 Elmer 240C microanalyser. 1H NMR spectra were recorded 6 C–I 93.1 (31.0) on a Varian Unity 300 spectrometer; coupling constants J are I–SA 71.4 (-1.3) given in Hz.IR spectra were obtained on a Perkin-Elmer 1600 7 C–I 162 (FTIR series) spectrometer. Mass spectra were obtained on a 8 C–I 106 VG Autospec EBE (FAB+, 3-NBA matrix). Absorption spectra were obtained on a Kontron Uvikon 940 Spectrophotometer. aC–I: crystal–isotropic liquid transition; I–SA: isotropic liquid–smectic A mesophase transition Fluorescence spectra were obtained on a Perkin-Elmer 1728 J.Mater. Chem., 1998, 8(8), 1725–1730LS-50 Luminometer using quartz cells with a 1 cm optical J 8.5, 2H), 6.88 (d, J 8.3, 2H), 7.07 (d, J 8.3, 2H), 7.63 (d, J 8.5, 2H). MS m/z (%): 408 (100, [M+]). path-length. The quantum yields were measured using quinine sulfate as the standard (QF=0.5) at an excitation wavelength of 340 nm. The melting points and the optical textures of the 1-(4¾-Chlorophenyl )-3-(4-n-decyloxyphenyl-2-pyrazoline 4 mesophase were studied with an Olympus polarizing micro- This compound was synthesized from 4-chlorophenylhydrazine scope equipped with a Linkam THMS 600 heating-cooling chlorhydrate and 1 and purified using the same procedure as stage and a TMS 91 central processor.The transition temperadescribed for compound 3.Yield: 45%. Mp 143 °C. Anal. calc. tures were measured by diVerential scanning calorimetry with for C25H33ON2Cl: C, 72.73; H, 8.00; N, 6.79. Found: C, 72.51; a TA Instruments 2000 calorimeter operated at a scanning H, 7.94; N, 6.79%. IR (Nujol, NaCl): n(CNN) 1604, n(CNC rate of 10 °C min-1. The apparatus was calibrated with indium arom.) 1510, n(CMO) 1261 cm-1. 1H NMR (CDCl3, 293 K): (156.6 °C, 28.4 J g-1) as the standard. X-ray diVraction patterns d 0.88 (t, J 7.3, 3H), 1.27–1.46 (m, 14H), 1.76–1.79 (m, 2H), were obtained using a Pinhole camera (Anton-Paar) operating 3.23 (t, J 10.1, 2H), 3.81 (t, J 10.1, 2H), 3.98 (t, J 6.5, 2H), with a point-focused Ni-filtered Cu-Ka beam. The sample was 6.90 (d, J 8.1, 2H), 7.02 (d, J 8.1, 2H), 7.22 (t, J 8.1, 2H), 7.65 held in Lindemann glass capillaries (1 mm diameter) and (d, J 8.1, 2H). MS m/z (%): 412 (100, [M+]).heated with a variable-temperature attachment. The diVraction pattern was collected on flat photographic film. 1-(4¾-Carboxyphenyl )-3-(4-n-decyloxyphenyl )-2-pyrazoline 5 4-n-Decyloxyphenyl vinyl ketone 1 A solution of 2 mmol (0.30 g) of 4-hydrazinobenzoic acid in 15 ml of hot absolute ethanol was added to a solution of 67 mmol (8.94 g) of aluminum chloride and 65 mmol (5.88 g) 2 mmol (0.58 g) of 1 in 10 ml of absolute ethanol.A drop of of acryloyl chloride were suspended in 150 ml of dry carbon acetic acid was added and the mixture was stirred at 40 °C for tetrachloride and cooled in an ice bath. 65 mmol (15.21 g) of 4 h. The yellow precipitate was filtered oV and washed several decyl phenyl ether was added dropwise and the mixture was times with hot ethanol.Yield. 50%. Mp 239 °C. Anal. calc. for stirred for 2 h. The red mixture was poured into a suspension C26H34O3N2: C, 73.93; H, 8.06; N, 6.63. Found: C, 73.63; H, of calcium chloride in water. The aqueous layer was discarded 7.94; N, 6.47%. IR (Nujol, NaCl): n(CNO) 1676, n(CNN) and the organic layer washed with saturated aqueous sodium 1606, n(CNC arom.) 1511, n(CMO) 1258 cm-1. 1H NMR hydrogen carbonate, dried over calcium chloride, and the (CDCl3, 293K): d 0.86 (t, J 7.3, 3H), 1.25–1.50 (m, 14H), solvent removed under reduced pressure. The residue was 1.75–1.77 (m, 2H), 3.29 (t, J 10.4, 2H), 3.90 (t, J 10.4, 2H), purified by column chromatography on silica gel using hex- 3.93 (t, J 7.1, 2H), 6.91 (d, J 9.0, 2H), 7.06 (d, J 8.7, 2H), 7.68 ane–ethyl acetate (2051) as the eluent.Yield: 50%. Mp 36 °C. (d, J 9.0, 2H), 7.99 (d, J 8.7, 2H). MS m/z (%): 422 (100, Anal. calc. for C19H28O2: C, 79.17; H, 9.72. Found: C, 78.94; [M+]), 261 (63). H, 10.31%. IR (Nujol, NaCl): n(CNO) 1664, n(CNC) 1602, n(CNC arom.) 1509 cm-1. 1H NMR (CDCl3, 293 K): d 0.86 3-(4¾-n-Decyloxyphenyl )-1-(4-nitrophenyl )-2-pyrazoline 6 (t, J 6.8, 3H), 1.25–1.44 (m, 14H), 1.75–1.80 (m, 2H), 4.00 (t, J 6.6, 2H), 5.85 (d, J 10.5, 1H), 6.41 (d, J 17.0, 1H), 6.92 This compound was synthesized from 4-nitrophenylhydrazine (d, J 8.8, 2H), 7.16 (dd, J 16.8, J 10.1, 1H), 7.94 (d, J 8.6, and 1 using the same procedure as described for compound 5. 2H). MS m/z (%): 289 (43, [M+]), 261 (100). The reaction mixture was stirred for 6 h at 40 °C. The solvent was evaporated and the crude product purified by column chromatography on silica gel using hexane–ethyl acetate (151) 3-(4¾-n-Decyloxyphenyl )-1-phenyl-2-pyrazoline 2 as the eluent. Yield: 30%. Mp (DSC) 93 °C (I 71°C SmA on 2 mmol (0.58 g) of 1 was dissolved in 20 ml of absolute ethanol cooling).Anal. calc. for C25H33O3N3: C, 70.92; H, 7.80; N, and 2 mmol (0.22 g) of phenylhydrazine. A drop of acetic acid 9.93. Found: C, 70.44; H, 7.63; N, 10.06%. IR (Nujol, NaCl): was added and the mixture was stirred at room temperature n(CNN) 1593, n(CNC arom.) 1507, n(NO2) 1299, n(CMO) for two hours. The yellow precipitate was filtered oV under 1246 cm-1. 1H NMR (CDCl3, 293 K): d 0.88 (t, J 7.1, 3H), vacuum and recrystallized from ethanol.Yield: 55%. Mp 1.20–1.34 (m, 14H), 1.78–1.80 (m, 2H), 3.36 (t, J 10.2, 2H), 108 °C. Anal. calc. for C25H34ON2: C, 79.36; H, 8.99; N, 7.41. 3.98 (t, J 10.2, 2H), 4.00 (t, J 6.6, 2H), 6.94 (d, J 9.0, 2H), 7.03 Found: C, 79.04; H, 8.58; N, 7.45%. IR (Nujol, NaCl): n(CNN) (d, J 9.2, 2H), 7.69 (d, J 9.5, 2H), 8.18 (d, J 9.5, 2H).MS m/z 1600, n(CNC arom.) 1501, n(CMO) 1258 cm-1. 1H NMR (%): 423 (100, [M+]). (CDCl3, 293 K): d 0.89 (t, J 6.8, 3H), 1.28–1.50 (m, 14H), 1.76–1.83 (m, 2H), 3.23 (t, J 10.2, 2H), 3.86 (t, J 10.2, 2H), 3-(4¾-n-Decyloxyphenyl )-1-(2, 4-dinitrophenyl )-2-pyrazoline 7 3.98 (t, J 6.5, 2H), 6.87 (t, J 7.8, 1H), 6.91 (d, J 8.7, 2H), 7.12 (d, J 7.8, 2H), 7.26 (t, 2H), 7.67 (d, J 8.8, 2H).MS m/z (%): 1.39 mmol (0.4 g) of 1 was added to a solution of 4.17 mmol (0.26 ml, 80%) of hydrazine hydrate in 10 ml of absolute ethanol. 378 (100, [M+]), 237 (27). This reaction was carried out under an argon atmosphere. The reaction mixture was heated under reflux for 3 h. Distillation 3-(4¾-n-Decyloxyphenyl )-1-(4-methoxyphenyl-2-pyrazoline 3 under argon aVorded ethanol, water and hydrazine.The white residue of 3-(4¾-decyloxyphenyl)-2-pyrazoline was suspended in 2 mmol (0.35 g) of 4-methoxyphenylhydrazine chlorhydrate was dissolved in a mixture of ethanol–water (551) and a 10 ml of absolute ethanol and placed into an ice bath. 70 mmol (130 mg) of 2,4-dinitrofluorobenzene was added. The dinitrophe- solution of 2 mmol (80 mg) of sodium hydroxide in 5 ml of ethanol was added.The mixture was poured into a solution nyl derivative precipitated instantaneously. The suspension was stirred for 3 h and the orange precipitate was filtered oV and of 2 mmol (0.58 g) of 1 in 15 ml of ethanol. Several drops of acetic acid were added (until pH=5) and the reaction mixture recrystallized from ethanol. Yield: 55%. Mp 162 °C. Anal.calc. for C25H32O5N4: C, 64.10; H, 6.84; N, 11.96. Found: C, 64.04; was stirred for two hours at 40 °C. The yellow precipitate was filtered oV under vacuum and recrystallized from acetonitrile. H, 6.94; N, 11.88%. IR (Nujol, NaCl ): n(CNN) 1603, n(CNC arom.) 1510, n(NO2) 1306, n(CMO) 1252 cm-1. 1H NMR Yield: 50%. Mp 161 °C. Anal. calc. for C26H36O2N2: C, 76.47; H, 8.82; N, 6.86. Found: C, 76.04; H, 7.91; N, 6.92%.IR (Nujol, (CDCl3, 293K): d 0.86 (t, J 6.6, 3H), 1.26–1.44 (m, 14H), 1.75–1.80 (m, 2H), 3.35 (t, J 9.6, 2H), 3.95 (t, J 9.6, 2H), 3.97 NaCl): n(CNN) 1604, n(CNC arom.) 1510, n(CMO) 1251 cm-1. 1H NMR (CDCl3, 293 K): d 0.87 (t, J 7.3, 3H), (t, J 6.3, 2H), 6.90 (d, J 8.8, 2H), 7.06 (d, J 9.3, 1H), 7.59 (d, J 8.8, 2H), 8.20 (dd, J 9.3, J 2.5, 1H), 8.46 (d, J 2.5, 1H).MS 1.25–1.55 (m, 14H), 1.75–1.77 (m, 2H), 3.18 (t, J 10.0, 2H), 3.77 (t, J 10.0, 2H), 3.77 (s, 3H), 3.96 (t, J 6.6, 2H), 6.86 (d, m/z (%): 468 (100, [M+]). J. Mater. Chem., 1998, 8(8), 1725–1730 1729Chemical Society, Washington DC, 1983; (b) Materials for N1-[4¾-Decyloxy-a-(2-ethoxyethyl )benzylidene]-N2-(2,4- Nonlinear Optics: Chemical Perspectives, ed.S. R. Marder, dinitrophenyl )hydrazine 8 J. E. Sohn and G. D. Stucky, ACS Symposium Series 455, American Chemical Society, Washington DC, 1991; (c) Molecular Nonlinear A mixture of 8 mmol (2.30 g) of 1, 8 mmol (1.58 g) of 2,4- Optics, ed. J. Zyss, Academic Press, New York, 1994. dinitrophenylhydrazine, 60 ml of absolute ethanol and several 3 (a) D. J. Williams, Angew.Chem., Int. Ed. Engl., 1984, 23, 690; drops of acetic acid was heated under reflux for 12 h. The (b) Nonlinear Optical Properties of Organic Molecules and Crystals; mixture was evaporated to dryness and the orange solid was ed. D. S. Chemla, J. Zyss, Academic Press., Orlando, 1987; purified by column chromatography on silica gel using hex- (c) Introduction to Nonlinear Optical EVects in Molecules and ane–ethyl acetate (1551) as the eluent and recrystallized from Polymers; ed.P. N. Prasad and D. J. Williams, John Wiley and Sons, New York, 1991. ethanol. Yield: 30%. Mp 106 °C. Anal. calc. for C27H38O6N4: 4 J. L. Oudar and D. S. Chemla, J. Chem. Phys., 1977, 66, 2664. C, 63.03; H, 7.39; N, 10.89. Found: C, 62.98; H, 7.42; N, 10.95%. 5 J. L. Oudar, J. Chem.Phys., 1977, 67, 446. IR (Nujol, NaCl): n(NH) 3278, n(CNN) 1615, n(NO2) 1615, 6 (a) L.-T. Cheng, W. Tam, S. H. Stevenson, G. R. Meredith, n(CNC arom.) 1508, n(NO2) 1326, 1307, n(CMO) 1250 cm-1. G. Rikken and S. R. Marder, J. Phys. Chem., 1991, 95, 10 631; 1H NMR (CDCl3, 293 K): d 0.86 (t, J 6.6, 3H), 1.1 (t, J 7.0, (b) L.-T. Cheng, W. Tam, S. H. Stevenson, G. R. Meredith, G. Rikken and S.R. Marder, J. Phys. Chem., 1991, 95, 10 643. 3H), 1.25–1.40 (m, 12H), 1.4–1.5 (m, 12H), 1.77–1.82 (m, 2H), 7 (a) H. Stra�hle, W. Seitz and H. Gu� sten, Ber. Bunsen-Ges. Phys. 3.13 (t, J 5.6, 2H), 3.51 (q, J 7.0, 2H), 3.78 (t, J 5.6, 2H), 4.00 Chem., 1976, 80, 288; (b) H.Gu� sten, G. Heinrich and H. Fru� hbeis, (t, J 6.6, 2H), 6.93 (d, J 8.9, 2H), 7.80 (d, J 9.1, 2H), 7.59 (d, Ber.Bunsenges. Phys. Chem., 1977, 81, 810; (c) H. Gu� sten, J 8.8, 2H), 7.99 (d, J 9.6, 1H), 8.27 (dd, J 9.6, J 2.6, 1H), 9.13 P. Schuster and W. Seitz, J. Phys. Chem., 1978, 82, 459. (d, J 2.6, 1H), 11.88 (s, 1H). MS m/z (%): 515 (100, [M+]), 8 (a) J. O. Morley and D. Pugh, in Organic Materials for Nonlinear 332 (67). Optics., ed. R. A. Hann and D. Bloor, Spec. Publ. R. Soc.Chem. 69, Kent, 1989, p. 28; (b) J. O. Morley, V. J. Docherty and D. Pugh, J. Mol. Electron., 1989, 5, 117; (c) S. Allen, in Organic Materials for Conclusions Nonlinear Optics., ed. R. A. Hann and D. Bloor, Spec. Publ. R. Soc. Chem. 69, Kent, 1989, p. 137. The pyrazoline structure has shown a special ability to strongly 9 Y. R. Peterson, in Molecular Electronics, ed. O. J. Ashwell, interact with UV and visible radiation in both linear and non- Research Studies Press LTD, Exeter, 1992, ch. 3. 10 R. S. Theobald, in Rodd’s Chemistry of Carbon Compounds, 2nd linear optical senses. Thus, the compounds with the terminal Edition, ed. S. CoVey and M. F. Ansell, Vol. 4, Heterocyclic groups OCH3, H, Cl and COOH behave as fluorescent mate- Compounds, Part C, ed. M. F. Ansell, Elsevier, New York, 1986; rials with large Stokes shifts and high quantum yields.The ch. 1. nitro derivatives exhibit significant bo values measured by the 11 G. Coispeau and J. Elguero, Bull. Soc. Chim. Fr., 1970, 2717. HRS technique. Surprisingly, the compound with only one 12 L. Chambers, M. L. Willard, J. Am. Chem. Soc., 1962, 82, 3373. nitro group shows a higher first hyperpolarizability than that 13 (a) S.G. Beech, J. H. Turnbull and W. Wilson, J. Chem. Soc., 1952, 4686; (b) J. Elguero and R. Jacquier, Bull. Soc. Chim. Fr., 1966, 610. with two nitro groups. All of these optical phenomena can be 14 N. Rajalakshimi, in Ultra-V iolet and V isible Spectroscopy. explained on the basis of structural factors. Furthermore, these Chemical Applications, ed.C. N. R. Rao, 2nd edn., Butterworth, compounds tend to be oriented in a parallel form behaving as London, 1967, ch. 10. promising promesogenic materials. Elongation of the central 15 G. C. Guilbaut, in Practical Fluorescence, 2nd edn., ed. unit could provide the desirable liquid crystal properties. The G. C. Guilbaut, Marcel Dekker, New York, 1990, p. 16. combination in the same structure of all these properties 16 (a) R.W.Terhune, P. D. Maker and C. M. Savage, Phys. Rev. L ett., 1965, 14, 681; (b) K. Clays and A. Persoons, Phys. Rev. L ett, 1991, can open new technological applications for these classical 66, 2980. materials. 17 K. Clays and A. Persoons, Rev. Sci. Instrum. 1992, 63, 3285. 18 K. Clays, A. Persoons and L. De Maeyer, Modern Nonlinear We thank Drs J.Galba�n and S. de Marcos (Universidad de Optics, ed. M. Evans and S. Kielich, Adv. Chem. Phys. Ser., Vol. 85, Zaragoza) for performing fluorescence measurements. This Part 3,Wiley, New York, 1993. 19 (a) J. L. Oudar, and D.S. Chemla, J. Chem. Phys., 1977, 66, 2664; work was supported by the Comisio�n Interministerial de (b) S. J. Lalama and A. F. Garito, Phys. Rev. A, 1979, 20, 1179. Ciencia y Tecnologia� (projects MAT94-0717-CO2-01 and 20 F. R. Fronczek, F. J. Parodi and N. H. Fischer, Acta Crystallogr., MAT96-1073-CO2-02), the Programa Europa CAI-DGA (col- Sect. C, 1989, 45, 2027. laborative visit of R. G. to Leuven) and the Diputacio�n General 21 J. L. Galigne and J. Falgueirettes, Acta Crystallogr., Sect. B, 1969, de Arago�n (Research studentship to R. G.). S. H. is a Research 25, 1637. Assistant and K. C. is a Senior Research Associate of the Fund 22 J. Lapasset and J. Falgueirettes, Acta Crystallogr., Sect. B, 1972, 28, 791. for Scientific Research—Flanders (FWO-V). 23 B. DuYn, Acta Crystallogr., Sect. B, 1968, 24, 1256. 24 (a) Smectic L iquid Crystals, ed. G. W. Gray and J. W. G. Goodby, Leonard Hill, Glasgow, 1984, pp. 6–8; ( b) A. J. Leadbetter, References T hermotropic L iquid Crystals (Critical Reports on Applied Chemistry, Vol. 22), ed. G. W. Gray, Wiley, Chichester, 1987, 1 (a) A.Wagner, C. W. Schellhammer and S. Petersen, Angew. Chem., pp. 12–15. Int. Ed. Engl., 1966, 5, 699; (b) C. D’Ambrosio, H. Leutz, M. Taufer 25 (a) C. M. Paleoew. Chem., Int. Ed. Engl., 1995, and H. Gu� sten, Appl. Spectrosc., 1991, 45, 484; (c) L uminescent 34, 1696; (b) Molecular Structure and the Properties of L iquid Materials, ed. G. Blasse and B. C. Grabmaier, Springer-Verlag, Crystals, ed. G. W. Gray, Academic Press, New York, 1985, p. 147. Berlin, 1994. 2 (a) Nonlinear Optical Properties of Organic and Polymeric Materials, ed. D. J. Williams, ACS Symposium Series 233, American Paper 8/02070A; Received 16thMarch, 1998 1730 J. Mater. Chem., 1998, 8(8), 1725–17

ISSN:0959-9428    

DOI:10.1039/a802070a

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 Photoelectric response of ITO electrode sensitized by single-layer C60- aminodicarboxylate derivative C60(C7H13NO4) Wen Zhang, Liangbing Gan and Chunhui Huang*† State Key L aboratory of Rare Earth Material Chemistry and Applications, Peking University, Beijing 100871, P.R. China A single layer of an amphiphilic C60-aminodicarboxylate (C60AC) derivative has been fabricated on semiconducting transparent ITO electrodes with transfer ratios of about 0.90±0.05 at 25 mN m-1 by the Langmuir–Blodgett (LB) technique.The photoelectric response of the modified electrodes has been investigated under a nitrogen atmosphere. The photocurrent action spectrum shows that the excited C60AC acts as a photoactive species in the photoinduced electron transfer process.Factors such as the intensity of the irradiation, concentration of reducing agent in the electrolyte solution and bias voltage have been studied. The results indicate that electrons flow from the electrolyte through LB film to the ITO electrode. The quantum yield is 3.0% under favorable conditions. C60 and its derivatives are good electron acceptors.1–3 Electron 80 mmol) and methyl chloroacetate (8.68 g, 80 mmol).The mixture was stirred at room temperature for 12 h, then refluxed transfer from various amines2 and semiconductor colloids3 to for another 12 h. The pH of the solution was adjusted with photoexcited singlet and triplet C60 has been reported. Cast sodium carbonate to 8.5, then filtered. One eighth of the filtrate films of C60 on metal electrode surfaces have been found to was taken and diluted with methanol to 50 ml.This solution, act as n-type semiconductors.4 C60 and C70 embedded within containing about 5 mmol of nitrilotriacetate, was added to a a lipid membrane can act both as photosensitizers for eYcient C60 solution (72 mg, 0.1 mmol) in toluene (250 ml). To make electron transfer from a donor and mediators for electron the solution homogeneous, more methanol was added (ca.transport across the membrane.5 However, photoelectric 30–50 ml ). The reaction flask was fitted with a condenser. The investigations on fullerene LB films are still rare. Monolayer mixture was irradiated for 2.5 h with two 150 W high pressure films of C60 are very sensitive to vibration, aggregate easily fluorescent bulbs (of the type used in Beijing street lights).The and are diYcult to transfer onto solid substrates due to the solution began to reflux after 1 h of photolysis. The solution very high hydrophobicity of the rigid ball-shaped molecules. was treated with water twice (20 ml each time) to remove some The introduction of hydrophilic groups into the close-caged water soluble components.The organic solvents were evapor- molecule can enhance the stability of these Langmuir films. ated. The residue was chromotographed on silica gel using Some monolayers of C60 derivatives were obtained and transtoluene as eluent. Unreacted C60 (40 mg, 0.055 mmol) and ferred onto hydrophilically pretreated substrates by carefully C60AC (6.7 mg, 0.007 mmol) were eluted as well-separated controlling the experimental conditions.6 When amphiphilic bands.dH(400 MHz, CDCl3–CS2) 3.76 (s, 6H), 4.15 (s, 4H), C60 derivatives are deposited onto conducting or semiconduct- 4.72 (s, 2H), 7.11 (s, 1H); dC(100.6 MHz, CDCl3–CS2) 170.16 ing electrodes by LB techniques to form organized assemblies, (2CO2Me), 154.36, 154.19, 147.07 (1C), 146.95, 146.88 (1C), eVective electron transfer between the materials and the elec- 146.44, 146.12, 146.04, 145.91, 145.86, 145.50, 145.28, 145.11, trode may be expected.It has been reported that aggregates 145.07, 145.05, 144.46, 144.18, 142.96, 142.31, 142.27, 142.07, formed in Langmuir–Blodgett films at the air–water interface 141.81, 141.68, 141.42, 141.40, 141.36, 140.08, 139.84, 135.92, possess photophysical properties that are significantly diVerent 135.63 (all signals represent 2C except those indicated), 68.13 from the monomers.7 Previous work in our laboratory has (CH), 67.10, 57.35 (CH2), 56.09 (CH3), 51.17 (CH2) (DEPT shown that C60-pyrrolidine derivatives can generate anodic spectra located the H containing carbons); nmax/cm-1 527, 574, photocurrents, the magnitude of which depends on the struc- 998, 1012, 1144, 1169, 1203, 1261, 1384, 1411, 1429, 1742; m/z ture of the introduced groups.8 Here we report the film (FDMS) 895 (M++1); lmax(CHCl3)/nm 257 (with shoulder formation properties of a new C60-aminodicarboxylate derivacentered at 328), 434 [Found (Calc.) for C67H13O4N: C, 90.20 tive (C60AC) and the photoelectric response of its single-layer (89.83); H, 1.30 (1.46); N 1.38% (1.56%)].modified ITO electrodes. The dependence of the photocurrent on some factors that may enhance or decrease the observed LB film preparation photocurrent was investigated. A possible mechanism for electron transfer is proposed. Single layers of C60AC were obtained using a NIMA 622 computer-controlled Langmuir trough (UK).The subphase was deionized water (20±1 °C, pH 5.6, >18 V). A solution of Experimental C60AC (6 ml, 1.5×10-5 mol dm-3 in chloroform) was carefully Materials and sample preparation added dropwise to the subphase over 1 h. After evaporation of the solvent (ca. 30 min) the monolayer was compressed. The Ascorbic acid (AA) was reagent grade and recrystallized from monolayer was deposited onto a hydrophilically pretreated water before use.Chloroform was purified by distillation. transparent indium-tin oxide (ITO) glass substrate at a rate Deionized water was purified by passing through an EASY of 5 mm min-1 (vertical dipping) under a constant surface pure RF compact ultrapure water system (Barnstead Co. US). pressure 25 mN m-1. The transfer ratio was 0.90±0.05.C60AC was prepared by the process shown in Scheme 1. To a solution of iminodiacetic acid (5.32 g, 40 mmol) in methanol Photoelectrochemical and electrochemical measurements (250 ml) was added anhydrous sodium carbonate (8.48 g, The photocurrent measurements were carried out using a model 600 voltammetric analyzer (CH Instruments Inc., US) †E-mail: hch@chemms.chem.pku.edu.cn J.Mater. Chem., 1998, 8(8), 1731–1734 1731Scheme 1 and a 500 W xenon lamp (Ushio Electric, Japan). A series of limiting area per molecule, obtained by extrapolation of the rising portion of the isotherm to p=0, was 95 A ° 2 molecule-1. filters (Toshiba, Japan) with certain band passes were used to obtain diVerent wavelengths of incident light. The intensity of This value is in good agreement with that of C60O,6b indicating that the substituted group does not aVect the distances between incident light was measured by a power and energy meter (Scientech 372, boulder Co., US).The IR light was filtered the molecule at the air–water interface and that a monolayer is probably formed. This is reasonable if the hydrophilic group throughout the experiment with a Toshiba IRA-25s filter (Japan).A three-electrode cell having a flat window for illumi- is arranged under the water surface and only the hydrophobic fullerene ball stands on the surface. The film could be easily nation of the working electrode was used. The counterelectrode was Pt wire and the reference was a saturated calomel transferred on to a hydrophilic ITO plate. electrode.The C60AC LB film modified ITO electrode was used as the working electrode. KCl solution (0.1 mol dm-3) Photoelectric response of the LB films was used as the electrolyte solution. Because oxygen could A typical photocurrent response of a single-layer C60AC film suppress the photocurrent, all experiments were carried out as a function of excitation wavelengths is shown in Fig. 2. The under a nitrogen atmosphere. At least eight independent absorption spectrum is also shown. Owing to a large forbidden monolayer-modified electrodes were used for each experiment gap (3.8 eV9), the background anodic photocurrent due to to test the reproducibility of the photocurrent data. ITO excitation was negligibly small in the visible region. Since Cyclic voltammograms were measured on a PAR-270 the absorbencies of C60-pyrrolidine films on a quartz substrate Electrochemical Analysis System (US).A three-electrode conin the near-ultraviolet region are several times higher than figuration was used throughout. A polished platinum electrode those in the visible region,10,6a 404 nm was chosen as the (0.5 mm diameter) was used as the working electrode. The exciting source throughout the experiment.At this wavelength counter and reference electrodes were platinum wire and the anodic photocurrent of bare ITO is below 4 nA. Ag/AgCl, respectively. The concentration of C60AC was The photocurrent was measured under nitrogen atmosphere. 1.0×10-4 mol dm-3. In the cyclic voltammetry experiment, a If oxygen was bubbled through the electrolyte, ca. 40% of the ferrocene/ferrocenium couple (FC/FC+) was used as the internal photocurrent could be suppressed. However, this process is standard. All measurements were performed at ambient temreversible in the case of C60AC. When nitrogen was bubbled perature under a nitrogen atmosphere in a 0.1 mol dm-3 again to remove oxygen, the photocurrent rose gradually to chloroform solution of Bun4NPF6.the value before addition of oxygen. Under a nitrogen atmosphere, an anodic photocurrent ranging from 38–52 nA was Results and Discussions observed when the C60AC-modified electrodes were illuminated by 404 nm light of 2.10 mW cm-2 intensity (after transmitting Modification of ITO electrodes the ITO electrode) for a series of eight independent samples (Table 1). The quantum yield is ca. 0.76%. The action spectrum The p–A isotherm of C60AC (Fig. 1) shows that it can form stable films on an aqueous subphase due to the two hydrophilic resembles the absorption spectrum, which indicates that C60AC is the photoactive species. ester groups and the nitrogen atom in the molecule. The The photocurrent ranges of C60AC without a bias voltage or electron donor overlap to quite an extent (Table 1).This Fig. 2 (+) Photocurrent (0.1 mol dm-3 KCl, pH 5.6, no bias voltage, Fig. 1 Surface pressure–area (p–A) isotherm of C60AC at the air– light intensity=2.10 mW cm-2, l=404 nm) and (full line) absorption spectrum for a monolayer of C60AC on ITO water interface (293±1 K, pH 5.6) 1732 J. Mater. Chem., 1998, 8(8), 1731–1734Table 1 Three sets of data from eight independent modified electrodes photocurrenta/nA KCl, no KCl, no KCl, Samples bias, no AA bias, AA bias, AA 1 49 86 180 2 47 80 182 3 52 92 180 4 50 84 181 5 46 86 179 6 39 90 180 7 44 94 183 8 35 92 183 av. 45 88 181 a[KCl]=0.1 mol dm-3, bias=0.2 V, [AA]=38 mmol dm-3. Fig. 4 Photocurrent as a function of ascorbic acid concentration for LB film of C60AC on ITO (0.1 mol dm-3 KCl, no bias voltage, light may be due to the influence of the produced oxygen, the intensity=2.10 mW cm-2, l=404 nm) release rate of oxygen from the electrolyte solution and the diVerent adsorption abilities of oxygen on the surface of the is stable in the presence of AA and on/oV switching of the modified electrodes.light can be repeated tens of times with very little attenuation (Fig. 5).Characteristics of photocurrent versus voltage and light intensity In order to determine the direction of the current flow, the Mechanism of photocurrent generation from the C60AC–ITO eVect of bias voltage was investigated. A linear relationship electrode with a slope of 0.10 nA mV-1 between the observed photo- In order to examine the electron transfer process for the anodic current and the bias voltage in the range -0.35 to 0.4V vs.photocurrent, the energies of the relevant electronic states must SCE was observed (Fig. 3). The photocurrent increases as the be estimated. The redox energy level for the excited state of positive bias of the electrode increases. This is a result of the C60AC, E# (*C60AC/C60AC.-), is situated above the E# applied positive voltage having the same polarity to the (C60AC/C60AC.-) level by the excitation energy D*E.11 photocurrent.A linear relationship between the photocurrent and light intensity (from 0.28 to 2.10 mW cm-2) is also E#(*C60AC/C60AC·-)=E#(C60AC/C60AC·-)+D*E observed. The photocurrent increases as the light intensity Since the functionalization of C60 leads only to a minor change increases.Photocurrent saturation was not observed. It may in the excitation energy,12 and the reduction potential of the be that the intensities used cannot supply enough photons to make all molecules active and contribute to photocurrent. EVect of an electron donor in the electrolyte solution The eVect of the electron donor (AA) also gives evidence for the direction of electron transfer.The photocurrent increases with the concentration increase of AA in the electrolyte, and a limiting value at high concentration (beginning at ca. 38 mmol dm-3, Fig. 4) is reached. This indicates that the quantum yield for eVective electron transfer is higher in the presence of the reducing agent. Under the favorable conditions determined above, e.g. 0.2 V bias and 38 mmol dm-3 AA, the photocurrent at 404 nm was four times higher than in pure 0.1 mol dm-3 KCl electrolyte solution.The quantum yield of single-layer C60AC can be increased to 3.0%. The photocurrent Fig. 5 Representative photocurrent obtained from a C60AC monolayer- modified electrode (0.2 V bias voltage, 38 mmol dm-3 AA, 0.1 mol dm-3 KCl electrolyte solution, light intensity=2.10 mW cm-2, l=404 nm) Table 2 Half-wave potentialsa of C60 and its derivatives by cyclic voltammetry potential/V Compound E0/-1 E-1/-2 E-2/-3 ref.C60 -1.13 -1.50 -1.95 13 C60(C3H4O) -1.23 -1.58 -2.11 13 C60(C4H8O2) -1.21 -1.57 -2.11 13 C60AC -1.26 -1.76 -2.22 this work Fig. 3 Photocurrent vs. electrode potential for LB film of C60AC on ITO (0.1 mol dm-3 KCl, pH 5.6, light intensity=2.10 mW cm-2, aV vs.ferrocene/ferrocenium couple. Bun4NPF6 (0.1 mol dm-3) in chloroform. Scan rate=0.1 V s-1. l=404 nm) J. Mater. Chem., 1998, 8(8), 1731–1734 1733ground state of C60AC is only negatively shifted 0.13 V com- photoactive electrode. The photocurrent spectrum clearly indicates that C60AC acts as the photoactive species. The anodic pared with C60 (Table 2),13 the reduction potential of *C60AC photocurrent increases when AA is added or a positive bias is expected to be slightly lower than that of *C60 (ca. 1.01 V voltage is applied, indicating that electrons flow from the for 3C60/C60.-; 1.44 V vs. SCE for 1C60/C60.-).12 Note that electrolyte through the LB film to the ITO. These results show these data are based on solution values rather than aggregates that single-layer sensitized semiconductor electrodes made in a closely packed film, for which the appropriate parameters from fullerene derivatives can initiate eVective photoinduced are unknown.electron transfer. It should be emphasized that the photocurrent of the LB films were measured in aqueous KCl (except for the experi- Financial support from the National Natural Science ments on the eVect of AA) without any additional reducing Foundation of China (29571004, 29671001) is gratefully agent.The excited state of C60AC must have been reduced by acknowledged. H2O. The possible reaction scheme is then given by: C60ACCA hn *C60AC References 1 R. J. Sension, A. Z. Szarka, G. R. Smith and R. M. Hochetrasser, *C60AC+H2OCA(C60AC)·-+O2 Chem. Phys. L ett., 1991, 185, 179.or *C60AC+AACA(C60AC)·-+AA·+ 2 J. W. Arbogast, C. S. Foote and M. Kao, J. Am. Chem. Soc., 1992, 114, 2277. (C60AC)·-CAC60AC+e- 3 P. V. Kamat, J. Am. Chem. Soc., 1991, 113, 9705. 4 B. Miller, J. M. Rosamilia, G. Dabbagh, R. Tycko, R. C. Haddon, When irradiated the C60AC molecules are excited to the excited A. J. Muller, W. Wilson, D. W. Murphy and A. F. Hebard, J.Am. state, *C60AC is reduced to the anion by water because the Chem. Soc., 1991, 113, 6291. reduction potential of *C60AC is higher than the reduction 5 (a) R. V. Bensasson, J. L. Garaud, S. Leach, G. Miquel and P. Seta, Chem. Phys. L ett., 1993, 210, 141; (b) S. F. Niu and D. Mauzerall, potential of H2O (EO2/H2O=0.66 V vs. SCE at pH 5.6). The J. Am. Chem. Soc., 1996, 118, 5791.electron transfer from C60AC.- to the electrode completes the 6 (a) D. J. Zhou, L. B. Gan, C. P. Luo, H. S. Tan, C. H. Huang, circuit for the observed photocurrent. When an electron donor G. Q. Yao, X. S. Zhao, Z. F. Liu, X. H. Xia and P. Zhang, J. Phys. (AA) is added to the electrolyte, it gives electrons to the C60AC Chem., 1996, 100, 3150; (b) N. C. Maliszewskyj and P. A.Heiney, more readily than water because the reduction potential of AA L angmuir, 1993, 9, 1439. 7 Y. M. Wang, P. V. Kamat and L. K. Patterson, J. Phys. Chem., (-0.21 V vs. SCE) is lower than EO2/H2O. 1993, 97, 8793. The suppression of the photocurrent in the presence of 8 C. P. Luo, C. H. Huang, L. B. Gan, D. J. Zhou, W. S. Xia, oxygen may be due to two processes: (i) the quenching of Q.K. Zhuang, Y. L. Zhao and Y. Y. Huang, J. Phys. Chem., 1996, 3C60AC14 or (ii ) the trapping of photogenerated conduction 100, 16 685. electrons.11 It is well-known that in solution the excited singlet 9 N. Balasubramanian and A. Subrahmanyam, J. Phys. D: Appl. state of fullerenes is eYciently converted to the excited triplet Phys., 1989, 22, 206. 10 L. B. Gan, D. J. Zhou, C. P. Luo and C. H. Huang, J. Phys. Chem., state by rapid and quantitative intersystem crossing.12 1994, 98, 12 459. However, in a closely packed assembly singlet–singlet annihil- 11 T. Takizawa, T. Watanabe and K. Honda, J. Phys. Chem., 1978, ation may predominate. The detailed mechanism is still being 82, 1391. investigated. 12 D. M. Guldi and K. D. Asmus, J. Phys. Chem. A, 1997, 101, 1472. 13 T. Suzuki, Y. Maruyama, T. Akasaka, W. Ando, K. Kobayashi and S. Nagase, J. Am. Chem. Soc., 1994, 116, 1359. Conclusion 14 J. W. Arbogast, A. P. Darmanyan, C. S. Foote, Y. Rubin, F. N. Diederich, M. M. Alvarez, S. J. Anz and R. L. Whetten, A new amphiphilic C60-aminodicarboxylate derivative was J. Phys. Chem., 1991, 95, 11. shown to readily form stable films at the air–water interface which can be deposited onto an ITO substrate to form a Paper 8/00359I; Received 13th January, 1998 1734 J. Mater. Chem., 1998, 8(8), 1731–1734

ISSN:0959-9428    

DOI:10.1039/a800359i

出版商:RSC    

年代:1998

数据来源: RSC