Reversion of the in-plane reorientation direction of mesogenic groups has been observed for the first time in novel polymethacrylate liquid crystal (PLC) films substituted with a 4-methoxycinnamoyloxybiphenyl side group. The reversion was generated by irradiation with linearly polarized ultraviolet (LPUV) light and a subsequent annealing. Irradiation with LPUV light induces negative optical anisotropy of the films as a result of an axis-selective photoreaction of the side groups. The direction of the thermally enhanced reorientation is dependent on the degree of photoreaction and the distribution of photoproducts, while the induced orientational order in both directions, S, was larger than 0.5. The distribution of photoproducts in PLC films has been analyzed to elucidate their contribution to the thermally enhanced reorientation behavior. Initially upon photoreaction, thermal enhancement of the photoinduced negative optical anisotropy was observed. However, when the degree of photodimerization was 15% or greater, the direction of the thermally enhanced reorientation was found to be parallel to the polarization direction (E) of LPUV light. It is concluded that a small amount of photoproduct plays a role in the thermal amplification of the photoinduced negative optical anisotropy in a manner identical to that of PLC with azobenzene side groups. In contrast, photodimerized mesogenic groups generated reversion of the orientational direction and enhancement of positive optical anisotropy of the film through annealing.

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The photoinduced orientation in polymethacrylate, which has a hexamethylene spacer group terminated with a 4-oxycinnamic acid in its side chain (P6CAM), is explored using linearly polarized ultraviolet (LPUV) light irradiation. Because of the hydrogen- (H-) bonding among the cinnamic acid groups, P6CAM exhibits a liquid crystalline phase, and the axis-selective photoreaction of the cinnamic acid moiety generates the optical anisotropy of the film. When the exposed film is annealed or a virgin film is exposed to LPUV light at elevated temperatures, molecular reorientation both perpendicular and parallel to the polarization (E) of LPUV light is achieved, and the generated birefringence is 0.15. The orientation behavior of the film is determined by polarization UV and FTIR spectroscopies. Furthermore, the molecular orientation is erased by annealing at elevated temperature, while reexposing to LPUV light reorganizes the orientation. Finally, homogeneous alignment control of low-molecular liquid crystals on P6CAM films is demonstrated both perpendicular and parallel to E by adjusting the exposure energy.

A novel photo‐crosslinkable polymer liquid crystal (PCP‐LC), in which a high molecular orientation has been achieved by irradiation with UV light and thermal treatment, is presented. Two types of optical birefringent film have been obtained whereby the orientational order is controlled by the irradiation angle and polarization of the UV light. The Figure shows the viewing angle dependence of the two films between crossed polarizers.