Effect of molecular aggregation on the photo-induced anisotropy in amorphous polymethacrylate bearing an aminonitroazobenzene moiety

We investigated H-type molecular aggregation in a simply spin-coated amorphous homopolymer film of polymethacrylate containing push-pull azobenzene moieties. It was found that the aggregate formation was strongly influenced by thermal treatment and that the aggregate created in the polymer film could be easily disrupted by irradiation of a linearly polarized light. In the first writing cycle of aggregated polymer film, photo-induced birefringence showed a steep increase to the highest value followed by a gradual decrease to the certain asymptotic value under longer irradiation of a linearly polarized light. This unique behavior could be attributed to the cooperative motion and the disruption of the aggregated molecules under continuous irradiation of light.