Photoresponsive behavior of two well-defined azo polymers with different electron-withdrawing groups on push—pull azo chromophores

摘要

Two well-defined methacrylate-based azo polymers bearing strong push—pull azo chromophores were synthesized by RAFT polymerization. The polymers contain cyano and carboxyl as electron-withdrawing groups at 4-positions of the azo chromophores. The polymers exhibited significantly different photo-responsive properties on all light-driven motion levels. When irradiated with a linearly polarized laser beam at 532 nm, the cyanoazobenzene-containing polymer showed rapid birefringence growth relative to that of the carboxylazobenzene-containing polymer. When the light was switched off, a much lower orientation decay was observed for the carboxylazobenzene-containing polymer compared with its counterpart. Upon irradiation with the interfering laser beams at these two wavelengths, surface-relief-grating amplitude formed on the film of the cyanoazobenzene-containing polymer and was substantially larger than that for the carboxyl substituted polymer. When the polymer films were irradiated with a homogenous laser beam at 488 and 532 nm, self-structured surface pattern was only detected for the cyanoazobenzene-containing polymer with the 532 nm light irradiation.