Effect of Structure of Photoresponsive Molecules on Photochemical Phase Transition of Liquid Crystals IV. Photochemical Phase Transition Behaviors of Photochromic Azobenzene Guest/ Polymer Liquid Crystal Host Mixtures

Abstract

Sixteen azobenzene derivatives were used as guests in a polymer liquid crystal (PLC) host with side- chain mesogenic phenyl benzoate groups, poly(4′-methoxyphenyl 4-(acryloyloxy)propoxybenzoate (PAPB3), and were examined on their ability to induce the photochemical isothermal phase transition of the guest/host mixtures. Although the rates of photoisomerization of the azobenzene guests were found to be similar to those of the mixtures composed of the same azo guests and a low molecular weight ester-type host, ECH206, the rates of the photochemical phase transition were retarded approximately by one order of magnitude compared to those of the same azo guest/ECH206 mixtures. This was interpreted as a consequence of low mobility of mesogenic moieties in PLC. The effect of mesogenic 4-cyanobiphenyl groups incorporated into the azobenzene guests on the photochemical phase transition behaviors of the guest/host mixtures was discussed with Reference to the effect of the meth-ylene spacer length.

Key Words:

• photochemical phase transition
• azobenzene
• photoisomerization
• order parameter
• guest/host mixture
• polymer liquid crystal