Response of a Hydrogen-Bonded Liquid Crystal to an Applied Electric

anhydride of benzyl-l-glutamate monomers on soft flexible substrates. Hatice Duran , Basit Yameen , Hadayat Ullah Khan , Renate Förch , Wolfgang ...
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Langmuir 1997, 13, 576-580

Response of a Hydrogen-Bonded Liquid Crystal to an Applied Electric Field Accelerated by a Poly(γ-benzyl L-glutamate) Chemical Reaction Alignment Film Shigeru Machida,*,† Taeko I. Urano,† Kenji Sano,† and Takashi Kato‡ Materials and Devices Research Laboratories, Toshiba Corporation, 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210, Japan, and Department of Chemistry and Biotechnology, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan Received June 24, 1996. In Final Form: October 29, 1996X Poly(γ-benzyl L-glutamate) (PBLG) was bonded covalently to a flat substrate, and it formed an aligned dipole layer (PBLG-CRA film). Using the PBLG-CRA film as an orienting film for a nematic hydrogenbonded liquid crystalline complex, 6OBA-9Py (formed from 4-(hexyloxy)benzoic acid (6OBA) and 4-nonylpyridine (9Py)), complexes, not only in the vicinity of the CRA film but also in the bulk layer, were able to respond more rapidly to an applied electric field when using a rubbed polyimide film, and they became responsive at frequencies in the MHz region. We conclude that the PBLG-CRA film has a dynamic orienting force, that dipole-dipole interaction takes place between the interfacial 6OBA-9Py complexes and the PBLG molecules, and that the movement of the interfacial 6OBA-9Py complexes is smoothly transferred to the bulk layer because the electric state of the complex 6OBA-9Py in the bulk changes under the influence of the CRA film.

Introduction Nematic liquid crystal molecules typically consist of rigid parts called mesogenic cores and terminal groups, and they have a moderate self-assembling ability. Although they aggregate to form small domains and scatter light without an orienting force, they are able to make an oriented monodomain under the influence of an orienting film for the liquid crystal, such as a polyimide film treated by the rubbing technique or a surface treated with a surfactant which has long alkyl chains.1,2 The rubbed polyimide film endows liquid crystal molecules with a homogeneous orientation in the rubbed direction. On the other hand, surfactant (e.g., octadecyltriethoxysilane) treated surfaces invest them with a homeotropic orientation (orientation in the direction of the substrate normal). In both cases, the orienting force for liquid crystals is unidirectional and constant. Using the reversible change of the orientation of the liquid crystal from one stable state to another upon the application and removal of an electric field is the basis for nematic liquid crystal display devices.3-7 The movement of nematic liquid crystals induced by an external electric field is always influenced by the static orienting force originating from the typical substrate. While the electric field is applied, the orienting force of the film interferes with the response of liquid crystal molecules to the electric field. After the removal of the electric field, the orienting force acts as the force for reorienting the liquid crystals to the initial state. It is impossible for typical orienting films to accelerate the †

Toshiba Corporation. The University of Tokyo. X Abstract published in Advance ACS Abstracts, January 1, 1997. ‡

(1) Gray, G., Ed. Thermotropic Liquid Crystals; Wiely: Chichester, 1987. (2) Bauer, G. In The Physics and Chemistry of Liquid Crystal Devices; Sprokel, G. J., Ed.; Plenum: New York, 1980, 61. (3) Snell, A. J.; Mackenzie, K. D.; Spear, W. E.; Comber, P. G. L.; Hughes, A. J. Appl. Phys. 1981, 24, 357. (4) Scheffer, T. J.; Nehring, J. Appl. Phys. Lett. 1984, 45, 1021. (5) Katoh, K.; Endo, Y.; Akatsuka, M.; Ohgawara, M.; Sawada, K. Jpn. J. Appl. Phys. Part 1, 1987, 26, L1784. (6) Kinugawa, K.; Kando, Y.; Kanasaki, M. Inf. Dis. Dig. 1986, 122. (7) Khoo, I. C.; Wu, S. T. Optics and Nonlinear Optics of Liquid Crystals; World Scientific: London, 1993.

movement of the liquid crystal molecules in both directions upon application and removal of the electric field due to the static orienting forces. The poly(γ-benzyl L-glutamate) (PBLG) molecule has a rigid conformation due to its R-helical structure8 and has a very large dipole moment (1590 D, MW 100 000) in the direction of the long molecular axis.9 If the large dipole moments of the PBLG molecules are aligned, the monolayer is expected to exhibit specific electric functions. We have proposed a new concept for preparing highly oriented organic thin films by chemical reaction, which we call the chemical reaction alignment (CRA) method,10 and we reported that PBLG molecules bind covalently to a flat substrate via carbonyl end groups and that they form an oriented dipole layer which has a three-dimensional chiral conformation. We call this a PBLG-CRA film.11,12 Although the PBLG molecules in the CRA film form many small domains and are aligned at an angle of about 57° from the substrate normal in each domain, the domains do not have any planar orientation along with the substrate. Using the PBLG-CRA film as an orienting film for 4-n-pentyl-4'-cyanobiphenyl (5CB), 5CB molecules in the vicinity of the PBLG-CRA film (interfacial 5CB molecules) can respond to an applied electric field more rapidly than in the case of using a rubbed polyimide film because the CRA film has a dynamic orienting force which can be switched off and on with the application and removal of the electric field, which was measured by means of time-resolved infrared spectroscopy. The interfacial 5CB molecules are aligned under the strong orienting force of the CRA film when no electric field is applied. An application of an electric field affects the electric property and/or alignment of PBLG molecules in the CRA film through the interaction between its dipole moment and the electric field, resulting in the decrease in its orienting force. It would take about 0.5 ms for the CRA film to lose (8) Elliot, A. Poly-R-Amino Acids; Marcel Dekker: New York, 1967. (9) Wada, A. J. Chem. Phys. 1960, 33, 822. (10) Sano, K.; Machida, S.; Sasaki, H.; Yoshiki, M.; Mori, Y. Chem. Lett. 1992, 1477. (11) Machida, S.; Sano, K.; Sasaki, H.; Yoshiki, M.; Mori, Y. J. Chem. Soc., Chem. Commun. 1992, 1626. (12) Machida, S.; Sano, K.; Sunohara, K.; Kawata, Y.; Mori, Y. J. Chem. Soc., Chem. Commun. 1992, 1628.

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its orienting force since the orienting force would originate from the organized structure of PBLG molecules in the film. At T ≈ 0.5 ms, the 5CB molecules can make a large and quick reorientation under a small or no anchoring force of the CRA film. After the removal of the electric field, the CRA film recovers its orienting force instantly and affects it to the 5CB molecules.13 Generally, typical nematic liquid crystals are responsive to an applied electric field mainly due to dielectric anisotropy (∆) because molecules with a dipole moment as large as that of 5CB molecule are located in a position symmetrically inverted to each other so as to minimize unfavorable dipolar repulsions.14,15 However, since the time-response curve of the 5CB molecules in the vicinity of the CRA film to an applied electric field varied with the polarity of the external electric field and the 5CB molecules themselves were responsive at frequencies in the MHz region,16,17 we concluded that the interfacial 5CB molecules do not form antiparallel pairs and exist as isolated molecules with large dipole moments under the influence of the PBLG molecules in the CRA film. In the bulk, the response of the 5CB molecules to an applied electric field was scarcely accelerated because the 5CB molecules there were not influenced by the CRA film and they formed antiparallel pairs. We, therefore, concluded that a dipoledipole interaction between interfacial 5CB molecules and PBLG molecules was essential to accelerate the response of the 5CB molecules to the external electric field. If nematic liquid crystals, which have large dipole moments and do not form antiparallel pairs, are used instead of the 5CB molecules, the response of the liquid crystal molecules in the bulk to an external electric field is expected to be accelerated under the influence of the PBLG-CRA film. Kato and co-workers have reported that supramolecular liquid crystalline complexes could be obtained due to the molecular self-assembly of carboxylic acid and pyridine fragments through intermolecular hydrogen bonding.18-20 The complex consisting of 4-alkoxybenzoic acid, operating as a H-bonding donor and 4-alkylpyridine, serving as a H-bonding acceptor, shows nematic phases near room temperature.21 Electrooptic effects in a twisted nematic cell were observed for these room-temperature hydrogenbonded liquid crystals.21 Furthermore, the hydrogen bonding between the carboxylic acid derivative and the pyridine derivative was of a nonionic type with a doubleminimum potential energy, which was confirmed by infrared measurement.22 Generally, if liquid crystals are themselves ionic compounds or if ionic impurities exist in a liquid crystal cell, the effective internal electric field applied to the liquid crystals is reduced owing to the formation of an electric double layer.23-27 Consequently, ionic compounds cannot (13) Urano, T. I.; Machida, S.; Sano, K. J. Chem. Soc., Chem. Commun. 1994, 231. (14) Liebert, L. Liquid Crystals (Solid State Physics Suppl. 14); Academic Press: New York, 1978; 109. (15) Schadt, M.; von Planta, C. J. Chem. Phys. 1975, 63, 4379. (16) Urano, T. I.; Machida, S.; Sano, K. Chem. Phys. Lett. 1995, 242, 471. (17) Machida, S.; Urano, T. I.; Sano, K.; Kawata, Y.; Sunohara, K.; Sasaki, H.; Yoshiki, M.; Mori, Y. Langmuir 1995, 11, 4838. (18) Kato, T. In Handbook of Liquid Crystals; Demus, D., Goodby, J. W., Gray, G. W., Spiess, H. W., Vill, V., Eds.; VCH: Weinheim, in press. (19) Kato, T.; Frechet, J. M. J. J. Am. Chem. Soc. 1989, 111, 8533. (20) Kato, T.; Frechet, J. M. J.; Wilson, P. G.; Saito, T.; Uryu, T.; Fujishima, A.; Jin, C.; Kaneuchi, F. Chem. Mater. 1993, 5, 1094. (21) Kato, T.; Fukumasa, M.; Frechet, J. M. J. Chem. Mater. 1995, 7, 368. (22) Kato, T.; Uryu, T.; Kaneuchi, F.; Jin, C.; Frechet, J. M. J. Liq. Cryst. 1993, 14, 1311. (23) Cognard, J. J. J. Electroanal. Chem. 1984, 160, 305.

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be used as materials for liquid crystal display devices because the ability of the device deteriorates. However, since the hydrogen-bonded liquid crystalline complexes as described above are nonionic compounds, they are considered to be applicable as materials for nematic liquid crystal display devices. Furthermore, they have large dipole moments and are expected not to form antiparallel pairs. In the present study, we have prepared a new hydrogenbonded liquid crystal complex which consists of 4-hexyloxybenzoic acid (6OBA) and 4-nonylpyridine (9Py). The response of the complex (6OBA-9Py) to an applied electric field accelerated by a PBLG-CRA film has been measured by time-resolved infrared spectroscopy. Furthermore, the electric influence of the PBLG-CRA film on complex 6OBA-9Py in the bulk has been evaluated by the dependence of the response on the frequency of the external electric field. Experimental Section (A) Preparation of PBLG-CRA Film. Substrate. Si (100) substrates for time-resolved infrared spectroscopy were polished with a 0.25 µm diamond polisher and washed with acetone and water repeatedly. Flat glass plates for the observation of the texture were washed several times with acetone and water. The substrates were treated with pH 1 HCl aqueous solution for 24 h before reaction with a silane coupling agent in order to make the substrates hydrophilic. Treatment with Silane Coupling Agent. Typically, the substrate surface was treated with the silane coupling agent in acidic solution (pH 4) at 5 wt% concentration for 24 h. (N-(2-Aminoethyl)-(3-aminopropyl)methyldimethoxysilane (TSL8345, Toshiba Silicone) was used as the silane coupling agent because it has moderate reactivity and is easy to treat. Preparation of PBLG-CRA Film. The samples for timeresolved infrared measurement were prepared using PBLG (MW 116 000). Typically, preparation was as follows. PBLG (1 g) was dissolved in methylene chloride (100 mL) with an excess of dicyclohexylcarbodiimide (DCC 1 g) at 0 °C. The substrates treated with the silane coupling agent were immersed in the solution very gently and left for 1 week at room temperature. The substrates were then washed several times with methylene chloride and acetone. (B) Preparation of a Hydrogen-Bonded Liquid Crystal Cell. Synthesis of 4-Nonylpyridine. 4-Nonylpyridine was prepared using the method of Comins and Abudullar.28 Pyridine (24.2 mL, 0.3 mol), CuI (1.9 g, 10 mmol), and 200 mL of dry THF were placed in a 500 mL flask under a nitrogen atmosphere. The solution was cooled to -20 °C. Ethyl chloroformate (19.2 mL, 0.2 mol) was added to the solution over a period of 5 min with stirring. After 10 min, nonylmagnesium chloride (37.5 g, 0.2 mol) in 160 mL of dry diethyl ether was added dropwise over a period of 20 min. The mixture was stirred for 1 h at -20 °C and 15 min at room temperature. Then, 20% NH4Cl aqueous solution was added and the organic layer was washed with water, 10% hydrochloric acid, water, and saturated NaCl solution. After it was dried over MgSO4, the ether solution of the crude dihydropyridine derivative was filtrated and evaporated to yield a yellow crude oil. The oil was treated with sulfur (6.4 g, 0.2 mol) at 190 °C for 50 min under a nitrogen atmosphere. The reaction mixture was cooled and dissolved in 300 mL of dry diethyl ether. The product was extracted with three 100 mL portions of 10% hydrochloric acid. The solution was then treated with saturated K2CO3 aqueous solution to render the solution alkaline. The crude 4-nonylpyridine was extracted with diethyl ether. The solution was dried over anhydrous K2CO3, filtered, and evaporated to dryness. The crude product was vacuum distilled twice (24) Mada, H.; Osajima, K. J. Appl. Phys. 1986, 60, 3111. (25) Naito, H.; Okuda, M. Phys. Rev. A: At. Mol., Opt. Phys. 1991, 44, R3434. (26) Sugimura, A.; Matsui, N.; Takahashi, Y.; Sonomura, H.; Naito, H.; Okuda, M. Phys. Rev. B: Condens. Matter 1991, 43, 8272. (27) Oh-e, M.; Kondo, K.; Kando, Y. Liq. Cryst. 1994, 17, 95. (28) Comins, D. L.; Abdullah, A. H. J. Org. Chem. 1982, 47, 4315.

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to give 8.54 g (14%) of 4-nonylpyridine as a colorless liquid: bp 98-100 °C (0.42 Torr); 1H-NMR (CDCl3) δ 0.88 (t, 3H), 1.26 (m, 12H), 1.62 (m, 2H), 2.59 (t, 2H), 7.10 (d, 2H), 8.47 (d, 2H). Preparation of 6OBA-9Py. The equimolar amounts of 4-nonylpyridine (9Py) and 4-(hexyloxy)benzoic acid (6OBA) were mixed, heated to the isotropic state, and then cooled to room temperature. Characterization of 6OBA-9Py. An Olympus BH-2 polarized microscope equipped with a Mettler FP82HT hot stage was used for visual observation. DSC measurement was performed on a Seiko I DSC 110 at both heating and cooling rates of 5 C min-1. Preparation of 6OBA-9Py Cell. The liquid crystal cell was prepared by a typical method. A polyimide film (AL1051 for thin film transistor (TFT) liquid crystal displays, Japan, Synthetic Rubber Corporation, Ltd.) was used for the opposite film of the PBLG-CRA film. The cell gap was adjusted with a spacer powder of 6 µm which was mixed with an epoxide adhesive agent. 6OBA9Py was injected into the cell in the isotropic state. (C) Evaluation of Response of 6OBA-9Py to an Applied Electric Field. Time-Resolved Infrared Measurement. The block diagram of the system for AC-coupled dispersive timeresolved infrared spectroscopy is given in ref 29. It consists of a dispersive infrared spectrometer (Hitachi I-3000), a photoconductive MCT detector (EG&G Judson J15D16), an ultra low noise preamplifier (NF SB-17480), a main amplifier (NF 5305), a digital sampling oscilloscope (Tektronix TDS520), and a computer (NEC PC9801DA). The preamplifier is AC-coupled to the MCT detector and amplifies only the AC signal induced by the applied electric field generated by a multifunctional synthesizer (NF 1940) and an amplifier (NF 4005). High sensitivity of 10-6 in the absorbance change, which is sufficiently high for precise observation of the orientation of liquid crystal molecules, is achieved with a time resolution of 10 µs. The digital sampling oscilloscope is used for the measurement of the time response of a certain infrared band at a fixed wavenumber which corresponds to an individual motion of the corresponding functional group. For example, by fixing the spectrometer at 1605 cm-1, the response of the ring stretching band of the phenyl group can be monitored directly.

Results and Discussions Features of LC Cell Using PBLG-CRA Film. Using the PBLG-CRA film as an orienting film for liquid crystal, a chiral director field in the achiral nematic liquid crystal phase was induced and a characteristic texture of the nematic liquid crystal, which we call the spiral texture, was observed besides the Schlieren texture. Since disclination lines passed through the center of the spiral texture, the liquid crystal molecules in the CRA cell did not have a homogeneous orientation and the induced chiral director field was quite different from a twist-nematic mode.12 A homogeneous unidirectional orientation of the liquid crystal molecules is necessary for the precise measurement of the anchoring energy and pretilt angle. Although we attempted to endow the PBLG molecules with an unidirectional orientation by rubbed technique, the conformation of PBLG changed from an R-helical structure to a random coil structure by the local heat of friction. Therefore, the rubbed CRA film was no longer the oriented dipole layer because the large dipole moment of PBLG is due to the R-helical structure, and the measured anchoring energy and pretilt angle are considered to be quite different from those of the CRA dipole layer. Physical Properties of 6OBA-9Py. The complex 6OBA9Py (molecular ratio, 1:1) exhibited a smectic A phase from 37 to 44 °C and a nematic phase from 44 to 58 °C on heating. Upon cooling, isotropic-nematic, nematicsmectic A, and smectic A-smectic C transitions were observed at 58, 40, and 37 °C. The complex crystallized at 26 °C. The corresponding DSC thermogram of the 6OBA-9Py complexes is shown in Figure 1. (29) Urano T. I.; Hamaguchi, H. Appl. Spectrosc. 1993, 47, 2108.

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Figure 1. DSC thermogram of 6OBA-9Py complex (molecular ratio, 1:1).

The response of liquid crystal cells will depend on material properties, such as dielectric anisotropy, elastic constants, and rotational viscosity, as well as the applied field. Hydrogen-bonded liquid crystals have dynamic properties due to the intermolecular hydrogen bonds, including rearrangement of the hydrogen bonds and movement around the hydrogen bonds induced by an applied electric field. Therefore, the static values of the material properties are not helpful in interpreting the response behavior in this case, which uses hydrogenbonded liquid crystals. The time-resolved measurements of the material properties, however, are very difficult due to the rapidity of the structural change of the hydrogenbonded liquid crystal. Time-Resolved Infrared Measurement. By using polarized monochromated IR light, an individual motion of a functional group can be monitored through the absorbance change of the corresponding IR band. Common time responses to an electric field were observed for functional groups in the rigid part of the liquid crystal molecule, indicating that they move synchronously in an electric field like a rigid rod. In the case of the 6OBA9Py complex, the ring stretching band of the phenyl group (1605 cm-1) was selected as the probe to monitor the motion of the complex because the band is parallel to the complex’s long axis. In order to clarify the contribution of the orienting film for complex 6OBA-9Py to the complex’s response to an applied electric field, three kinds of liquid crystal cells were prepared as follows: Cells A and B employed the PBLG-CRA film as the orienting film for the complex. The opposite substrate for cell A was coated with a nonrubbed polyimide film which did not possess an orienting force. As for cell B, the opposite substrate of the PBLG-CRA film was coated with a rubbed polyimide film which possessed a unidirectional and static orienting force. Cell C as the control cell had two rubbed polyimide films arranged antiparallel to each other. The time-resolved infrared measurement was carried out, keeping the cell temperature at 52 °C. The complex 6OBA-9Py exhibited a stable nematic phase at that temperature. Liquid crystals anchored by an orienting film are able to move when an electric field above the threshold voltage is applied, and at the beginning of the reorientational process, the interfacial liquid crystal molecules respond more rapidly than those in the bulk under the electric influence of an orienting film. Therefore, the absorbance change of a probe functional group induced by the electric field at around the threshold voltage corresponds mainly to the movement of the interfacial liquid crystals.29 In order to investigate the movement of the interfacial 6OBA-9Py complexes, the time responses of the cells to

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Figure 2. Absorbance change at 1605 cm-1 to burst electric fields of 2 ms width (pulse ratio +15 V:-15 V ) 1:1, repetition rate 4 kHz, interval of burst electric field 18 ms) in the cases of using cells A, B, and C.

the applied electric field at around the threshold voltage (15 V) were measured. Figure 2 shows the absorbance change (∆Abs) of the 1605 cm-1 band to burst electric fields of 2 ms width (pulse ratio +15 V:-15 V ) 1:1, repetition rate 4 kHz, interval of burst electric field 18 ms) in the cases of cells A, B, and C. The waveform of the applied electric field is also depicted in Figure 2. The movement of the 6OBA-9Py complexes induced by the applied electric field of pulse ratio +15 V:-15 V ) 1:1 is estimated to be about (10-3 - 10-2)° in angle. The absorbance change of cell A was about 2.1 times larger than that of cell B and about 3.0 times larger than that of cell C with the same voltage. Since this tendency is similar to that observed in the case of interfacial 5CB molecules, the response of the 6OBA-9Py complexes in the vicinity of the CRA film is considered to be accelerated by the same mechanism as that in the case of the interfacial 5CB molecules. Concerning cell B, the static and unidirectional orienting force of the rubbed polyimide film interfered with the movement of the interfacial 6OBA9Py complexes induced by the electric field. Therefore, the response of complex 6OBA-9Py of cell B to the external electric field was slower than that of cell A. The movement of complex 6OBA-9Py in the bulk can be monitored by measuring the time responses of the 1605 cm-1 band to the applied electric field of much higher voltage (45 V). Figure 3 shows the absorbance change (∆Abs) to burst electric fields of 2 ms width (pulse ratio +45 V:-45 V) 1:1, repetition rate 4 kHz, interval of burst electric field 18 ms) in the cases of cells A, B, and C. Even in the case of the applied electric field of pulse ratio +45 V:-45 V ) 1:1, although the data gave information about the 6OBA-9Py complexes in the bulk, the movement was no more than several degrees in angle. The absorbance change of cell A was about 1.4 times larger than that of cell B and about 6.6 times larger than that of cell C at the same voltage. The same tendency of the time-response curves as that in the case of interfacial 6OBA-9Py complexes was observed. Interestingly, the difference of the movement of complex 6OBA-9Py in the bulk between the PBLG cells (cells A and B) and cell C was larger than that of the interfacial complexes. This fact is very significant because

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Figure 3. Absorbance change at 1605 cm-1 to burst electric fields of 2 ms width (pulse ratio +45 V:-45 V ) 1:1, repetition rate 4 kHz, interval of burst electric field 18 ms) in the cases of using cells A, B, and C.

Figure 4. Absorbance change at 1605 cm-1 after applying burst electric fields of 2 ms width at various frequencies (pulse ratio +45 V:-45 V ) 1:1, interval of burst electric field 18 ms) in the cases of using cells A, B, and C.

the response of the 5CB molecules in the bulk to the applied electric field was not accelerated by the PBLG-CRA film. The authors propose a hypothesis which is consistent with these phenomena as described below: PBLG molecules in the CRA film are reversibly responsive to an external electric field and the orienting force of the CRA film can be switched off and on with the application and removal of the electric field, respectively. Dipole-dipole interaction takes place between the PBLG molecules in the CRA-aligned dipole layer and the interfacial 6OBA9Py complexes, and the rapid movement of the interfacial 6OBA-9Py complexes is smoothly transferred to the bulk layer due to the change of the electric state of complex 6OBA-9Py induced by the PBLG-CRA film. In order to clarify the electric influence of PBLG-CRA film to the 6OBA-9Py complexes in the bulk, the time responses of the cells to the applied electric field at various frequencies were measured. Figure 4 shows the absorbance change (∆Abs) of the ring stretching band of phenyl group after applying burst electric fields of 2 ms width (pulse ratio +45 V:-45 V) 1:1, interval of burst electric field 18 ms) at various frequencies in the cases of cell’s A, B, and C.

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Complex 6OBA-9Py in the bulk of Cell C were not responsive to the applied electric field in the kHz region. On the other hand, in the cases of using PBLG-CRA film as the orienting film (Cells A and B), complex 6OBA-9Py not only in the interfacial area but also in the bulk could respond to the electric field at much higher frequencies in the MHz region. This phenomenon could not be explained by the static pretilt angle endowed by the PBLG-CRA film, and the phenomenon strongly indicated that the electric state of complex 6OBA-9Py in the bulk was changed under the influence of the PBLG-CRA film. Conclusion PBLG molecules in CRA film were reversibly responsive to an external electric field due to the large dipole moments, and the orienting force of the CRA film could be switched off and on with the application and removal of the electric field. The 5CB molecules in the vicinity of the PBLG-CRA film were able to respond more rapidly to an external electric field than in the case of using a rubbed polyimide film which has a static orienting force. However, the movement of the 5CB molecules in the bulk was not accelerated using a PBLG-CRA film because the 5CB molecules in the bulk were not influenced by the CRA dipole layer and formed antiparallel pairs, canceling out the dipole moments.

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On the other hand, complex 6OBA-9Py in the bulk was able to respond more rapidly (at frequencies in the MHz region) to an applied electric field where a PBLGCRA film was used than when a rubbed polyimide film was used. Hydrogen-bonded liquid crystals have characteristic properties due to the intermolecular hydrogen bonds, including the rearrangement of the hydrogen bonds, and movement around the hydrogen bonds is expected to be induced by an applied electric field. We conclude that the response of the interfacial 6OBA-9Py complexes to an applied electric field is accelerated by the same mechanism as that in the case of the interfacial 5CB molecules, and the movement of the interfacial 6OBA9Py complexes is smoothly transferred to the bulk layer owing to the change of the electric state of complex 6OBA9Py under the influence of the PBLG-CRA film. Further investigation concerning the movement of 6OBA-9Py complexes induced by an applied electric field is now in progress by time-resolved infrared spectroscopy. Acknowledgment. This work was partially supported by a grant-in-aid for Development of Scientific Research (Grant 07555675) to T.K. by the Ministry of Education, Science, Sports, and Culture. Partial financial support by the Iketani Science and Technology Foundation to T.K. is also gratefully acknowledged. LA960626W