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

Abstract

This article reports the synthesis and photoresponsive properties of a hyperbranched azo polymer containing 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 photoinduced 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/cm²). The azo chromophores introduced by post-azo-coupling reaction at the para-positions of the peripheral azobenzenes shows a significant effect on the SRG inscription rate. The hyperbranched azo polymers can potentially be used for applications such as reversible optical data storage, photoswitch, sensors, and other photo-driven devices.