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Photoinduced reorientation (photon-mode process) and thermal effects in an oligothiophene-doped liquid crystal (LC) system were investigated by self-diffraction measurements in different experimental configurations. The results obtained in homeotropic sample cells were compared with those obtained in homogeneous cells. Optical Freedericksz transition could be induced by low-intensity light in the homeotropic cell, and the induced birefringence was affected by the thermal effect. No photoinduced reorientation effect was observed in the homogeneous cell in the present experimental configuration; however, due to the thermal modulation of the refractive index of the LC, which arises from light absorption, self-diffraction phenomena could also be observed.

The direction of molecular switching, i.e., the sign of the electro-optic response, in ferroelectric liquid crystals depends on the polarity of the applied electric field as well as on the sign of the spontaneous polarization. Light-induced switching of the molecules by ultraviolet light was found in a photochromic ferroelectric liquid crystal at fixed field polarity. A high contrast image was recorded whose contrast could easily be inverted by reversing the field polarity. Moreover, in the presence of bistable boundary conditions, the optically recorded image can be stored after removal of the electric field. The effect of light-assisted switching in the photochromic ferroelectric liquid crystal seems to be promising for applications such as optical recording, all-optical switches, and image storage.

We attempted formation of holographic gratings in an optically isotropic state of polymer azobenzene liquid-crystal films. On irradiation of writing beams at 488 nm, first-order diffraction beams of a probe beam at 633 nm were immediately observed even though the films exhibited the optically isotropic state. The diffraction beams quickly disappeared by turning off the writing beams. The first-order diffraction efficiency was affected by polarization of the writing beams. When unpolarized light was employed as the writing beams, diffraction beams were hardly observed. On the other hand, the highest diffraction efficiency was obtained with the linearly polarized writing beams. It is speculated that photoinduced alignment of azobenzene moieties in bright fringes of the interference pattern would be responsible for the grating formation. Furthermore, it was found that rubbing treatment slightly enhanced the diffraction efficiency. By turning on and off the writing beams, dynamic control of the diffraction be...

We have demonstrated reversible change in transmittance of composite films, which are composed of an isotropic (I) polymer matrix and a host nematic (N) liquid crystal (LC) containing donor–acceptor type azobenzene LCs (AzoLCs) as photoresponsive molecules, by means of reversible phase transition in the LC domain. The composite films were prepared by in situ thermal polymerization-induced phase separation (PIPS) method from their homogeneous mixtures. Photoisomerization of AzoLCs was induced within the polymer network, and the resultant effect brought about isothermal change in transmittance. The photoinduced reversible and repeatable changes between opaque light scattering and clear transparent states were achieved effectively by irradiation with a monochromatic light at 366 nm. These changes are attributed to photochemical N–I phase transition and rapid thermal I–N phase transition in the host LC domain based on reversible change in molecular sharp of the guest AzoLCs. The optical effects were influenced by such factors as temperature of the composite films in the initial state and photoisomerization ability of the guest AzoLCs. The composite films acted as an optical switching material without polarizers.

The alignment behavior of nematic liquid crystal (LC) on the surface of four types of polyimide (PI) films, three aromatic PIs and a PI with an alicyclic dianhydride, exposed to linearly polarized light of long wavelength (366 nm) was investigated by polarizing microscopy. It was found that the alignment of the LC was induced by all of the exposed PIs and the alignment direction of the LC was perpendicular to the polarization direction of the linearly polarized light. The degree of uniformity of LC alignment increased with increasing exposure energy incident on PI films. To produce the uniform alignment state, the PI with an alicyclic dianhydride had to be exposed to higher energy than aromatic PIs. Ultraviolet (UV) -visible spectroscopy indicated that the absorbance changes of the aromatic PIs were much smaller than that of the PI with an alicyclic dianhydride when uniform alignment of the LC was caused. Furthermore, both UV-visible and infrared spectroscopy showed the change in the absorbance of the aromatic PI with a diphenyl ether diamine was still very small even though it was exposed to linearly polarized light with a large dose. These results demonstrate that the aromatic PIs are more favorable as a photosensitive alignment layer and the uniform alignment of the LC can be induced without significant destruction of the chemical structure of PI with a diphenyl ether diamine.

Hole drift mobilities of films of copolymers of acrylates with side‐chain mesogens and dimeric carbazoles were measured by the time‐of‐flight method. The copolymers were composed of acrylates with side‐chain phenylbenzoate or cyanobiphenyl and acrylates with side‐chain 1,2‐trans‐bis(9H‐carbazol‐9‐yl)cyclobutane (DCZB). Incorporation of the DCZB moiety into the copolymers resulted in homogeneous dispersion of the carrier molecules, but destabilization to a great extent of the liquid‐crystalline phase of the resulting copolymers. The hole drift mobility was found to be enhanced in copolymer films with more ordered structure of the DCZB moieties, indicating that orientation of the active molecules is favorable for the hole transport.

Hole drift mobilities have been measured in films of solid solution of trans‐1,2‐bis(9H‐carbazol‐9‐yl) cyclobutane (DCZB) in various host polymers; polymer liquid crystals (PLCs) and amorphous polymers. The hole drift mobilities were found to depend on the host polymers and be higher in PLCs. The larger mobilities of the DCZB/PLC mixtures have been attributed to the orientational effect of carrier molecules in the host PLCs.

Photochemical regulation of in‐plane alignment of a nematic liquid crystal is presented. A quartz plate surface was modified with 4‐hexyl‐4’‐hexyloxyazobenzene substituted with triethoxysilyl group through a spacer at the 2’ position to introduce the side‐on type azobenzene unit of the surface. A liquid crystal hybrid cell fabricated with the azo‐modified plate was irradiated with linearly polarized visible light for the n‐π* transition. This resulted in the in‐plane reorientation of the liquid crystal molecules to afford homogeneous alignment. Discussion is made on the mechanism of the in‐plane alignment regulation, and the concept of a molecular rotor is proposed.

We present a simple method to record subwavelength gratings (SWGs) in an azobenzene (AZ)-containing liquid-crystalline polymer by preirradiation. Since the cooperative motions of mesogens are eliminated in a cis-AZ-rich isotropic phase by the pretreatment, the subwavelength modulation of surface relief and refractive index (RI) was obtained. The surface relief of less than 10nm and the RI modulation were detected by atomic force microscopy. A large phase retardation and formed birefringence were obtained in the recorded SWGs in which a possible schematic illustration of AZ was proposed.

A liquid-crystalline polymer in the side chain was synthesized through copolymerization of a bipolar carrier-transporting monomer with a liquid-crystalline monomer containing oxadiazole moieties substituted with trifluoromethyl groups. A single-layer light-emitting diode of indium tin oxide (ITO)/copolymer/MgAg emitted white light with a maximum luminous efficiency of 0.1cd∕A. The origin of the white emission in the copolymer is the electroplex between bipolar carrier-transporting moieties and strong electron-withdrawing moieties. Furthermore, a simple multilayer device with configuration of ITO/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid)/copolymer/MgAg device showed white emission with CIE 1931 chromaticity coordinates (x,y): (0.30, 0.33).

The photoinduced change in refractive index of poly(methyl methacrylate) films doped with an azobenzene liquid crystal was measured by the prism-coupling method. Upon irradiation of the film with a high-pressure mercury lamp at 366nm, the coupling angles shifted and then recovered to the initial position by turning off the light. The change in refractive index was found to be 2×10−3, which is attributed to the reversible photoisomerization of the azobenzene moieties.

Hole drift mobilities have been measured in films of solid solutions of trans‐1,2‐bis (9H‐carbazole‐9‐yl) cyclobutane (DCZB) in various polymer binders. The hole drift mobilities differ by more than two orders of magnitude depending on the polymer binder used. In poly (methacrylates) films the hole drift mobility is large and the temperature dependence is small when the glass transition temperature of pure polymer is about 50 °C. The difference in rotational mobility of DCZB molecules is considered as the origin of this binder and temperature dependence on the hole mobility.