PHOTORESPONSIVE IONIC-CONDUCTIVITY OF POLYMER COMPOSITE FILMS CONTAINING AZOBENZENE LIQUID-CRYSTAL

Ionic-conductivity control by external stimulation was investigated with thin composite films consisting of poly(vinyl chloride), azobenzene liquid crystal 1, and LiClO4 (or its 12-crown-4 complex). On heating the composite film, a significant jump in the ionic conductivity was attained around TKN (transition temperature from crystal to nematic states) of 1. The ionic-conductivity change is attributable to the phase transition of 1, which in turn enhances the mobility of ionic species in the film. UV light irradiation on the composite film caused photoisomerization from trans to cis forms of the azobenzene derivative, which in turn led to its phase transition from crystal state (below the TKN) or nematic state (above the TKN) to isotropic liquid state, thus augmenting the ionic conductivity of the composite film by more than 2 orders of magnitude compared with that under dark conditions. Visible light irradiation after the UV irradiation promoted cis-to-trans isomerization of 1, diminishing the UV-enhanced ionic conductivity of the composite film, especially at room temperature, to the initial ionic conductivity. Alternating irradiation by UV and visible lights afforded reversible ionic-conductivity switching in the composite film. A novel type of electrostatic imaging process was realized by using the photoresponsive ion-conducting composite film of 1. © 1990 American Chemical Society.