Photochemical phase transition behaviour of polymer azobenzene liquid crystals with flexible siloxane units as a side-chain spacer

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Abstract
The influence of the spacer structure on the photochemical phase transition behaviour was explored for azobenzene polymer liquid crystals (azo-PLCs) possessing siloxane spacers in the polymer side chain, and for analogue without the siloxane spacer. The photochemical phase transition 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 trans-cis photoisomerization behaviour of the azobenzene moieties. These results were interpreted in terms of stabilization of the alignment of the mesogens in the liquid crystalline phase by the siloxane spacer, since the siloxane chain is one of the most flexible spacers and decouples the motion of the polymer backbone from that of the aligned mesogens. Furthermore, the response of the azo-PLCs in the photochemical phase transition was evaluated by means of a laser pulse. The phase transition occurred in 300 mus for both samples.