Effect of Structure of Photoresponsive Molecules on Photochemical Phase Transition of Liquid Crystals III. Photochemical Phase Transition Behaviors of Photochromic Azobenzene Guest/Ester Host Mixtures

Abstract

Sixteen azobenzene derivatives were used as guests in an ester-type host liquid crystal (LC), 4-hexy- loxyphenyl-4′-ethyl-cyclohexanecarboxylate (ECH 206), and were examined on their ability to induce the photochemical isothermal phase transition of the guest/host mixtures. Attention was focused on the effect of the mesogenic 4-cyanobiphenyl (CB) groups covalently incorporated at one end or at both ends of the azobenzene derivatives through flexible methylene spacers in order to enhance the interaction of the guest molecules with the matrix LC. Distinct odd-even effect of the methylene spacers was observed on the orientational ordering of the guests in the ECH 206 matrix, which was demonstrated by the order parameters of the mixtures evaluated by UV dichroism. The photochemical phase transition was found to occur more effectively in the mixtures with the guests of higher orientational ordering in the host.