Photoinduced Reorientation and Multiple Optical Data Storage in Photo-Cross-Linkable Liquid Crystalline Copolymer Films Using 405 nm Light

New polymethacrylate liquid crystalline copolymers, which are comprised of photo-cross-linkable 4-(4-methoxycinnamoyloxy)biphenyl (MCB) and photosensitizing 4-nitrobiphenyl (NB) or 4-nitrophenyl (NP) side groups, were synthesized. The irradiation with linearly polarized (LP) 405 nm light was performed to investigate the photoinduced reorientation behavior of the thin films. On the basis of the polarization-preserved excited energy transfer from the photosensitizing groups to the MCB groups, a photoinduced optical anisotropy due to the axis-selective photoreaction of the MCB groups accompanied the photoreaction of the film. In all cases, annealing the film reversely amplified the photoinduced optical anisotropy and an in-plane order parameter greater than 0.7 was achieved for the NB-containing copolymer films. The axis-selectivity of the photoabsorption of the photosensitizing groups and the effective energy transfer played important roles in generating the large photoinduced optical anisotropy and the effective thermal enhancement. Finally, it was demonstrated that the orientation direction of the mesogenic side groups controlled the multiple optical information storage in a thin film.