PHOTORESPONSIVE ION-CONDUCTING BEHAVIOR OF POLYSILOXANES CARRYING A CROWNED AZOBENZENE MOIETY AT THE SIDE-CHAIN

Three polysiloxane derivatives carrying a crowned azobenzene, that is, an azobenzene derivative with a crown ether moiety, at the side chain have been designed to enhance aggregation of the crowned azobenzene molecules. Crowned azobenzene polysiloxanes 1 and 2 exhibited a smectic liquid crystal phase, whereas their corresponding monomeric crowned azobenzenes did not. Polymer composite films containing one of the crowned azobenzene polysiloxanes and an alkali-metal salt underwent remarkable photoinduced ionic-conductivity switching, which is ascribable to structural changes in its highly-oriented side chains, induced by isomerization of its azobenzene moiety. The ionic conductivity was drastically decreased by UV light and then restored to the initial value by visible light. The photochemical switching tendency of ionic conductivity for the crowned azobenzene polysiloxane systems is opposed to that for the corresponding monomeric systems. The photoresponse mechanism is also discussed.