Synthesis of Liquid-Crystalline Extended Viologens their Photoresponsive Behavior

Abstract

N,N'-dialkyl-4,4'-bipyridinium salts (viologen) are generally reduced by the action of an electric field or photo-irradiation. It is expected that viologens with two long alkyl chains show liquid crystal (LC). In thisstudy, extended viologens that an aromatic ring was inserted between two pyridine rings were synthesized. It was found that the viscosity of the extended viologens was lower as compared with that of general viologens, and the extended viologens exhibited mesophases. In result, the photochromism was notobserved in the extended viologen films, however the LC-Isotropic transition temperature was lowered after irradiation with UV light.