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Dynamic holographic gratings were investigated with thin films of polymer azobenzene liquid crystals by periodic induction of photochemical nematic-to-isotropic phase transition. On irradiation of writing beams (488 nm), multiple diffraction beams of a reading beam (633 nm) were immediately observed. The first-order diffraction efficiency reached to a maximum value within several tens of milliseconds: the rise time was approximately 50 ms for PM6AB2 films and 30 ms for PA6ABCN films. Quite large modulation in refractive index (∼0.08) was obtained in both polymer films. Studies on effects of temperature and light intensity on the grating formation suggested that photochemical reactions of azobenzene moieties followed by photochemical phase transition in bright fringes of the interference pattern would be responsible for the formation of holographic gratings. By turning on and off the writing beams, the diffraction beams could be switched dynamically without significant fatigue.

Photosensitive polyimides (PIs) as an alignment layer induced optical switching of nematic liquid crystal (NLC) on photoirradiation at 366 nm. The orientation of NLC molecule was changed from homogeneous to homeotropic alignment on photoirradiation with a dc electric field as a bias. The optical switching behavior of NLC was largely affected by the chemical structures of PIs.

Photochemical phase transition of push-pull type azobenzene liquid crystal (LC), which contains both an electron donor and an acceptor in both ends of the azobenzene moiety, has been explored. Polymer azobenzene LCs were prepared, which show nematic (N) LC behavior in the trans form while no LC phase in the cis isomer. Photoirradiation of a very thin film of the azobenzene LCs (∼ 200 nm) in the trans form resulted in disappearance of the N phase due to transcis photoisomerization of each mesogen, and the N phase recovered quickly when the irradiated sample was kept in the dark because of cis-trans thermal isomerization and reorientation of trans-azobenzenes. Time-resolved measurements by the use of a laser pulse (355 nm; 10 ns FWHM) revealed that the N to isotropic (I) phase transition took place in 200 μs. The thermal I-N phase transition of the push-pull type azobenzene LC occurred in 800 ms at 135 °C. This response is faster by one order of magnitude than the response of azobenzene LCs without charge-transfer interaction.

The photochemical phase-transition behavior of polymer liquid crystals (LCs) containing azobenzene moieties with strong donor−acceptor substituents has been investigated. Copolymers of a mesogen and a donor−acceptor azobenzene were prepared. Photoirradiation of a thin film of the polymer LCs (100−200 nm thickness) in the nematic (N) phase caused an N-to-isotropic (I) phase transition due to trans−cis photoisomerization of the azobenzene moiety, and the N phase recovered rapidly when photoirradiation was ceased because of cis−trans thermal back-isomerization. Time-resolved measurements with a laser pulse (532 nm; 10 ns, fwhm) revealed that the N−I phase transition took place in 300 μs. The thermal recovery of the N phase in the polymer LC with a donor−acceptor azobenzene, which stabilized the LC phase, occurred in 8 ms at 146 °C. This response of the recovery is 103 times faster than that of non-donor−acceptor azobenzene LCs. In a sample that showed a smectic (S) phase, however, no photochemical phase tran...

Dynamic holographic grating by means of photochemical nematic-to-isotropic phase transition has been studied in a polymer liquid crystal containing an azobenzene moiety with strong donor−acceptor substituents in the side chain. Periodical change in the phase structure was caused reversibly by trans−cis photoisomerization and cis−trans thermal back-isomerization of the azobenzene moiety and led to formation of the dynamic grating following change in refractive index on the order of 10-2. The production and removal of the grating with a narrow fringe spacing of 1.4 μm was achieved within ∼150 and ∼190 ms, respectively. Moreover, the optical switching behavior of the holographic diffraction was observed repeatedly by turning on and off the writing beams.

Norbornene polymerization via “vinyl addition” proceeded with (t-BuNSiMe2Flu)TiMe2 (1) in the presence of various cocatalysts [methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and Ph3CB(...

Copolymerizations of propene with 1,5-hexadiene and 1,7-octadiene were carried out with isospecific rac-dimethylsilylenebis(indenyl)zirconium dichloride (1) and syndiospecific diphenylmethylene(cyclopentadienyl)(9-fluorenyl)zirconium dichloride (2) combined with methylaluminoxane. Microstructures of the copolymers were determined by 1 H NMR, 13 C NMR, and DEPT (distortionless enhancement of polarization transfer) spectroscopies. Incorporation of nonconjugated dienes in the copolymer was higher with 2 than with 1. Intramolecular cycloaddition of the nonconjugated dienes proceeded regardless of the catalysts. Stereoselectivity in cycloaddition of 1,5-hexadiene was investigated based on the structures of isolated methylene-1,3-cyclopentane units. It was found that 1,5-hexadiene was inserted stereospecifically by enantiomorphic site control with both catalysts. The diastereoselectivity of the cyclization step of 1,2-inserted 1,5-hexadiene was, however, found to be independent of stereospecificity of the catalyst. The cyclization selectivity of 1,5-hexadiene copolymerization was higher than that of 1,7-octadiene copolymerization. 1 gave the copolymers with higher selective in cyclization than 2 in the propene/1,5-hexadiene copolymerization, while the opposite tendency was observed in the propene/1,7-octadiene copolymerization. Decrease of cyclization selectivity was observed with the increases of 1,5-hexadiene and 1,7-octadiene concentration in both copolymerizations. Propene insertion could disturb the cyclization of 1,2-inserted dienes, which declined the cyclization selectivity of the copolymers, except propene/1,5-hexadiene copolymerization with 2.

The in situ photopolymerization behavior of a ferroelectric liquid-crystalline (FLC) monomer possessing a chiral moiety is discussed on the basis of molecular alignment in the liquid-crystalline phase. In an early stage of polymerization, the polymerizability of the FLC monomers was highest in the ferroelectric chiral smectic C (SmC*) phase in the absence of an external electric field. The polymerization behavior was found to depend mainly on the molecular alignment in the initial state of polymerization. In contrast, in the late stage of polymerization, the polymerization behavior of the FLC monomers was governed by their diffusion rather than their alignment. This may be due to the change in the phase structure during in situ polymerization. In addition, the alignment of the photopolymerized FLC was evaluated by optical polarizing microscopy. It was found that the application of an electric field to the FLC monomer resulted in the appearance of the immobilized SmC * phase, in which all mesogens of the resulting FLC polymer were aligned in one direction, leading to the formation of a monodomain of LC phase.

We prepared a polymer liquid crystal (PLC) with ortho-substituted azobenzene to explore the effect of the structure of the photochromic unit on the formation of holographic grating. On this behavior, a remarkable difference was observed between two materials. Grating formation of the ortho-substituted azobenzene moiety proceeded faster than that of common azobenzene analogs without substituents at the ortho position. This result is explained in terms of the stability of the LC phase structure. We investigated the relationship between alignment behavior and change of the diffracted light intensity. The result shows that in the ortho-substituted azobenzene sample, the diffraction efficiency showed maximum when orientational relaxation is completed in a bright area of the interference pattern.

Propene polymerization was conducted with titanocene (Cp 2 TiMe 2 . Cp * 2 TiMe 2 ; Cp = η 5 -C 5 H 5 , Cp * = η 5 -C5Me5)/organoborane (B(C 6 F 5 ) 3 , Ph 3 CB(C 6 F 5 ) 4 ) catalysts at -50°C using toluene as a solvent. The polymer obtained with Cp 2 TiMe 2 /Ph 3 CB(C 6 F 5 ) 4 is less isotactic than that obtained with Cp 2 TiMe 2 /B(C 6 F 5 ) 3 . However, the isospecificity of the former catalyst is improved with respect to that of the latter one when a toluene/CH 2 Cl 2 mixture is used as a solvent instead of toluene. As similar enhancement in isospecificity was observed when alkylaluminium is added to the polymerization system. On the other hand, only Ph 3 CB(C 6 F 5 ) 4 is an efficient cocatalyst for the propene polymerization with Cp * 2 TiMe 2 . The polymer obtained with Cp * 2 TiMe 2 /Ph 3 CB(C6F5)4 as catalyst is atactic, even in the presence of CH 2 Cl 2 or alkylaluminium. Based on these results, the stereospecificity of achiral titanocenes is discussed.

Vinyl monomers having a Schiff-base structure were synthesized and their thermal and photopolymerization behavior was explored for different phases of the monomers. It was found that conversion of the monomers increased with temperature in the nematic phase, while it decreased in the isotropic phase. This result suggests that the polymerization behavior may be affected by the molecular alignment. Arrhenius plots for the initial rates of photopolymerization showed a straight line, while those of thermal polymerization changed in slope at the nematic–isotropic phase transition temperature. For MBEA, the number-average molecular weight of the polymer produced by thermal polymerization in the nematic phase was higher than that in the isotropic phase. For ABBA, it was observed that birefringence partially remained in the polymer produced in the nematic phase, although polymer produced by solution polymerization showed no liquid-crystalline phase. In addition, the orientation of the crosslinked polymer obtained by photopolymerization was better than that of the polymer produced by thermal polymerization.

A series of side-chain polymer liquid crystals (PLCs) of 6-[4-(4-ethylphenyl)diazenylphenyloxy]hexyl methacrylate and 4‘-[6-(methacryloyloxy)hexyloxy]-4-cyanobiphenyl were synthesized and characterized. The effects of contents of the azo units and the wavelength of irradiation light on photoinduced alignment behavior were investigated. On irradiation of linearly polarized light (LPL) at 366 nm directly, alignment change was induced only in the PLC with 6 mol % azo units (P6), while phase transition took place in the other PLCs with higher contents of the azo units. On irradiation of LPL at 436 nm directly, alignment was induced with a fair efficiency in P15 and P35, low efficient alignment was observed in P6 and P100, and no alignment change was induced in P55 and P75, which exhibited a homeotropic state. A high alignment efficiency was achieved in all PLCs by using another method: irradiation with 366 nm unpolarized light at first and then with 436 nm LPL. The alignment change induced by this method was...

The alignment of a nematic liquid crystal (LC) could be induced by three polyimide (PI) films exposed to linearly polarized ultraviolet (UV) light of long wavelength (366 nm). The alignment could also be modified by changing the direction of polarization of the linearly polarized light (LPL). Infrared (IR) and UV-visible spectroscopy indicated that among the three PI films the PI with a benzophenone moiety and the PI with a diphenyl methane moiety were sensitive to UV radiation and susceptible to remarkable ablation after irradiation with LPL in air. Polarized UV-visible spectroscopy indicated that dichroism of the PI films was caused by LPL and altered by changing the polarization of the LPL. Furthermore, the PI films irradiated under vacuum showed little reduction in intensity of IR bands, which is in sharp contrast to the marked decreases in samples irradiated in atmospheres containing oxygen. This proves that oxygen is necessary to the ablative process of the PI films. Our results indicate that the mechanism of LC alignment on the photosensitive PI films is photoinduced anisotropic oxidative ablation of the PI films. In contrast, the PI film with a diphenyl ether moiety was quite stable under similar irradiation conditions even though the irradiated PI film could also induce alignment of the LC molecules.

ピコ秒レーザーパルスを励起光源として, 高分子アゾベンゼン液晶薄膜の液晶相-等方相相転移 (光相転移) に要する光応答について検討を行った. 時間分解測定の結果, パルス照射直後アゾベンゼン液晶は液晶状態における複屈折を瞬時に消失し, 約200nsで等方相へと相転移することが明らかとなった. これは尖頭出力の大きなレーザーパルスを用いることで, 液晶性を発現しないアゾベンゼンシス体を効率よく生成できることに基づく. またこの高分子アゾベンゼン液晶はレーザーパワー, 温度によらずナノ秒オーダーの光応答を示すことも明らかとなった. 高分子液晶を用いたナノ秒光応答は本系が初めてであり, 高分子アゾベンゼン液晶をフォトニクス材料へ用いる有用性を大いに示す結果である.

Unique characteristics were observed in phase-type gratings that were formed in a polymer azobenzene liquid-crystal (PALC) film. Generation of sinusoidal variation of the surface of the film was confirmed by atomic force microscopy. However, comparison of the diffraction efficiency with the surface modulation revealed that the gratings could not be characterized only as conventional surface-relief gratings. In the glassy state of the film, moderate efficiency (∼18%) was obtained with large surface modulation (68−76 nm), whereas the gratings recorded in the nematic (N) phase showed high diffraction efficiency (∼28%) with slight surface modulation (33−53 nm). The diffraction efficiency was enhanced in the liquid-crystalline phase. Dynamics of the first-order diffraction beam exhibited that the grating formation was associated with photochemical phase transition of PALC. It was assumed that the isotropic (I) phases were formed by photochemical reaction of azobenzene moieties in the interference pattern at an...

Photochemical phase transition behavior of polymer liquid crystals (LCs) with donor−acceptor azobenzene moieties which contain both electron-donating and -accepting substituents at the 4,4‘-positions has been explored. Polymer azobenzene LCs were prepared which show nematic (N) LC behavior in the trans form but no LC phase in the cis isomer. Photoirradiation of a thin film of the azobenzene LCs (∼200 nm) in the trans form resulted in disappearance of the N phase due to trans−cis photoisomerization of each mesogen, and the initial N phase was recovered when the irradiated sample was kept in the dark because of cis−trans thermal isomerization and reorientation of trans-azobenzenes. Time-resolved measurements with a laser pulse (355 nm; 10 ns, fwhm) revealed that the N-to-isotropic (I) phase transition took place in 200 μs. The thermal I−N phase transition of a donor−acceptor azobenzene LC with an acrylate main chain occurred in 800 ms at 135 °C. This response is faster by one order of magnitude than the res...

An anisotropy was induced in initial isotropic (polydomain) polymer liquid crystal MACB-CNAB6 by using linearly polarized light at 366 nm. The alignment processes induced at various temperatures and various intensities of irradiation light were analyzed by using a biexponential function (as shown in text). It was found that the alignment process involved two response modes: a fast response mode and a slow one. The fast response mode was associated with the angular-dependent trans – cis photoisomerization and the preliminary alignment of mesogens, while the slow one was attributed to the position adjustment of the mesogens to obtain well-aligned monodomain. The writing rate and the induced anisotropy increased with increase in temperature and in light intensity at low intensity of the irradiation light. Combined with photochemical phase transition processes, optical switching and image storage were realized in the polymer liquid crystal.

Photochemical phase transition behavior triggered by photoisomerization of a guest azobenzene doped in nematic (N) liquid-crystalline (LC) domains was investigated in isotropic (I) acrylate polymers with alkyl side chains on their surfaces. These polymer/LC composite films were prepared by in situ thermal polymerization-induced phase separation method (thermal PIPS) from their starting mixtures containing a di- and a mono-functional acrylate monomer. Strong light-scattering states of the intrinsic composite films were transformed into complete transparent states by photochemical N–I phase transition of the LC domains within the polymer matrices that was induced by the trans–cis photoisomerization. Recovery process from the transparent state to the initial light-scattering state was strongly influenced by the alkyl side chains. While the composite film with short alkyl side chain acted as an all-optical switching material because the optical switching could be achieved reversibly and repeatedly between the two different optical states, the composite films with long alkyl side chain showed an ability of optical image storage with high contrast based on light-scattering mode.

We studied the dynamic behavior of director--reorientation induced by linearly polarized light in an oligothiophene-doped liquid crystal (LC) by transmission-mode analyses and the Z-scan measurement. An in-plane reorientation process occurred and LC molecules tended to reorient parallel to the polarization of incident light in the case of low-intensity irradiation. The thermal effect due to absorption affects the reorientation behavior largely in the case of high-intensity irradiation.

Propene polymerization was conducted with TiCl4/(Lewis base)/MgCl2-Cp2TiMe2 catalysts in the presence of ethyl benzoate (EB) and/or 2,2-diisobutyl-1,3-dimethoxypropane (DBDMP). The addition of small amounts of these Lewis bases to MgCl2 before supporting TiCl4 decreased the amount of Ti in the catalyst and improved catalyst isospecificity. The results suggested that the Lewis base is selectively coordinated on the MgCl2 surface where aspecific sites had been formed. The addition of the Lewis bases during the polymerization increased polymerization rate followed by rapid deactivation. Deactivation was second order on the polymerization rate and the deactivation rate constant depended on both structure and amount of the Lewis base. GPC analysis of the produced polymers indicated that the addition of the Lewis bases increased the molecular weight of isotactic polypropene (IPP). Polydispersity depended on the Lewis base: it became narrower by EB and broader by DBDMP. The 13C NMR spectra of IPPs revealed that EB improved the microtacticity of IPP more effectively than DBDMP. ESR spectra of the catalysts indicated that the amount of isolated Ti3+ species increased in the presence of EB.

Photochemical, reversible modulation of a dielectric constant of liquid crystals was demonstrated. This novel method of readout of photonic information as electric output is based on the principle of photochemically triggered phase transition in liquid crystals. Thus, the phase transition of a host liquid crystal, 4-cyano-4'-pentylbiphenyl (5CB), was induced by a partial photo-isomerization of a small amount of 4-butyl-4'-methoxyazobenzene (BMAB) doped in as a perturber. This isothermal phase transition brought about a change in the dielectric constants. The change in the dielectric constants is reversible corresponding to the trans-cis photoisomerization.