PHOTOCHEMICAL PHASE-TRANSITION BEHAVIOR OF POLYMER AZOBENZENE LIQUID-CRYSTALS WITH FLEXIBLE SILOXANE UNITS AS A SIDE-CHAIN SPACER

The influence of the spacer structure on the photochemical phase trans ition behaviour was explored for azobenzene polymer liquid crystals (a zo-PLCs) possessing siloxane spacers in the polymer side chain, and fo r analogue without the siloxane spacer. The photochemical phase transi tion of the azo-PLC with the siloxane spacer was found to proceed less effectively than that of the azo-PLC without the siloxane spacer. It was also confirmed that the spacer structure does not affect the ti an s-cis photoisomerization behaviour of the azobenzene moieties. These r esults were interpreted in terms of stabilization of the alignment of the mesogens in the liquid crystalline phase by the siloxane spacer, s ince the siloxane chain is one of the most flexible spacers and decoup les the motion of the polymer backbone from that of the aligned mesoge ns. Furthermore, the response of the azo-PLCs in the photochemical pha se transition was evaluated by means of a laser pulse. The phase trans ition occurred in similar to 300 mu s for both samples.