Influence of alkylene spacer length on photoinduced molecular reorientation and LC alignment behavior in photo-cross-linkable liquid crystalline polymeric films with H-bonded cinnamic acid side groups

Photoinduced reorientation of liquid crystalline polymethacrylates comprised of various lengths of alkylene spacers terminated with 4-oxycinnamic acid in the side chain and low-molecular liquid crystal (LC) alignment on the resultant photoreacted films were investigated using linearly polarized UV light. As the length of the spacer increased, the photoinduced optical anisotropy (ΔA) of the thin films increased, and ΔA increased as the irradiating temperature increased. Exposing the polymeric films in the LC temperature range of the material generated an in-plane molecular reorientation because the small photoinduced ΔA was simultaneously amplified. The low-molecular LCs aligned homogeneously on the photoreacted polymeric films, but the LC alignment direction depended on the alkylene spacer length and the degree of the photoreaction.