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Abstract
Photochemical phase transition behavior of polymer azobenzene liquid crystals (LCs) was explored by transmission-mode analysis and reflection-mode analysis. Four samples with different structures were used, which show LC behavior in the trans form but no LC phase in the cis isomer. Attention was focused on the effect of the position of the mesogenic azobenzene moiety in the flexible side chain on the photochemical phase transition behavior. Photoirradiation of a thin film of the azobenzene LCs (∼200 nm) in the trans form resulted in the disappearance of the LC phase due to trans-cis photoisomerization of each mesogen. and the LC phase recovered quickly when the irradiated sample was kept in the dark because of thermal cis-trans back-isomerization. In all polymers, the photochemical LC to isotropic (I) phase transition was induced in 100∼200 us on laser pulse irradiation. In the sample with an azobenzene located apart from the main chain of the polymer by a spacer, the LC-I phase transition took place almost completely. In the sample with the azobenzene moiety in the vicinity of the main chain, however, the photochemical phase transition was induced only locally. These phenomena are interpreted in terms of the mobility of the azobenzene moiety in the side chain and the stability of the LC phase.