Liquid Crystal Photonics : Effect of Structure of Phothochromic Moieties on Optical Alignment Process in Polymer Liquid Crystals

Abstract

Polymer liquid crystals (PLCs) with donor-acceptor type azobenzcne moieties (CNAB6) or common azobenzene moieties (AB6) in the side chain were synthesized Homogeneous alignment in the PLCs was induced by using linearly polarized light at 366 nm. Induced order parameter was measured at various irradiation temperaturres by using polarized UV spectroscopy. It was found that the alignment behavior was dependent on the structure of the azobenzene groups. The writing rate of AB6 was higher than that of CNAB6. When the writing light was switched off, discrete increase of the transmittance (positive relaxation) was observed in AB6, while no relaxation in CNAB6. The writing process of CNAB6 can be well dcscibed by a biexponential function. The behavior of azobenzene moieties during the alignment process was investigated. Higher concentration of cis-azobenzene was produced in AB6 during the alignment process. It is one of the reasons for higher writing rate and positive relaxation of AB6.