Photoinduced dichroism and surface-relief-gratings of hyperbranched azo polymers synthesized by azo-coupling reaction

This article reports the synthesis and photores-ponsive properties of a hyperbranched azo polymer contain-ing electron donor-acceptor type azo chromophores both in backbone and peripheral positions.For the synthesis,a hyperbranched azo precursor polymer was synthesized by step-growth polymerization of an AB2 monomer,bis[2-(N-ethylanilino)ethyl]5-aminoisophthalate,through azo-coupling reaction.The hyperbranched precursor polymer was then reacted with the diazonium salt from 4-cyanoaniline to introduce donor-acceptor azo chromophores in the peripheral groups.The resulting azo polymers were characterized by the spectroscopic methods and thermal analysis.The photo-induced dichroism of the hyperbranched polymer was studied and its orientation order parameter was estimated to be 0.063.Thin films of the hyperbranched azo polymers were used to fabricate surface-relief-gratings(SRGs)by exposing them to an interference pattern of Ar^(+)laser beam at modest intensities(150 mW/cm^(2)).The azo chromophores introduced by post-azo-coupling reaction at the para-positions of the peripheral azobenzenes shows a significant effect on the SRG inscrip-tion rate.The hyperbranched azo polymers can potentially be used for applications such as reversible optical data storage,photoswitch,sensors,and other photo-driven devices.