Effect of siloxane spacer on photochemical phase transition behavior of polymer liquid crystals with azobenzene moieties in the side chain

The effect of flexible siloxane spacers on photochemical phase transition behavior was investigated for polymer liquid crystals (PLCs) with an azobenzene group as a photoresponsive moiety in which mesogens (azobenzene and cyanobiphenyl moieties) are attached to the polymer main chain through different types of spacers (siloxane and alkyl chains). The PLC possessing the siloxane spacer and the non-photoresponsive moiety in the same side chain showed a slower response in the photochemical liquid-crystalline (LC) to isotropic (I) phase transition than the analog having the siloxane spacer and the photoresponsive moiety in the side chain. The result indicates that the flexible siloxane spacer stabilizes the phase structure of the LC phase and depresses the propagation of the perturbation due to trans-cis isomerization of the azobenzene in the LC phase. Furthermore, it was also confirmed that the spacer structure did not affect the photoisomerization behavior of the azobenzene moieties.