Photochemical Phase Transition Behavior of Highly Birefringent Azotolane Liquid-Crystalline Polymer Films: Effects of the Position of the Tolane Group and the Donor−Acceptor Substituent in the Mesogen

Abstract

Highly birefringent liquid-crystalline polymers (LCPs) containing an azobenzene group directly connected to a tolane moiety (azotolane moiety) were synthesized. Attention was focused on the effect of the position of the tolane moiety in the mesogenic azotolane group and the donor−acceptor substituent on photochemical phase transition behavior. In solution, cis−trans back-isomerization of the LCP containing azotolane moieties with a donor−acceptor was faster than that of LCPs having no acceptor groups. All the LCP films showed a homogeneous alignment and very high values of birefringence (about 0.4 at 633 nm). In the LCPs with a conventional azotolane moiety, a large change in birefringence (above 0.35) was induced repeatedly by irradiation of UV light. Furthermore, we investigated photoswitching behavior at telecommunication wavelength (1550 nm) based on the photochemical phase transition by irradiation of UV light.