Effect of structures of mesogenic groups in azotolane liquid-crystalline polymers on photoresponsive behavior

We have synthesized liquid-crystalline polymers (LCPs) containing a long mesogenic core in which an azobenzene group is directly connected to a tolane moiety (azotolane moiety). To evaluate birefringence of the homogeneously aligned polymer films, the LCP films were placed between a pair of crossed polarizers and the transmittance of a probe beam (633 nm) was carefully measured. Before irradiation with a pumping beam, the values of birefringence were extremely large (about 0.7). Upon irradiation with the pumping beam, the largest change in alignment of the azotolane moieties was observed in P5ATTA which contains two azobenzene moieties in the mesogen core.