Preparation of side-on bisazobenzene-containing homopolymers and block copolymers via ATRP and studies on their photoisomerization and photoalignment behaviors

The preparation of a series of novel homopolymers and copolymers containing bisazobenzene chromophores with side-on structure in the side chains via atom transfer radical polymerization (ATRP) were presented. UV-vis spectra of the thin films of these polymers under irradiation of 488 nm Ar⁺ laser suggested that the photoisomerization of the bisazobenzene chromophores happened mainly on one of the two azo groups in the bisazobenzene chromophores with similar probability due to their side-on structure. Good photoalignment behaviors of these polymers were proved by photoinduced birefringence measurements because side-on structure permitted the two azo groups in the bisazobenzene chromophores both participated in the trans-cis-trans photoisomerization cycles equally to induce the whole chromophore reorientation. Furthermore, the reorientation axis located at the middle of chromophore decreased the sweep volume during photoalignment. The impetus for this study was to evaluate the photoisomerization and photoalignment process of side-on bisazobenzene-containing polymers and to find possible applications in the photosensitive devices.