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 amorph ous homopolymer film of polymethacrylate containing push-pull azobenzene mo ieties. It was found that the aggregate formation was strongly influenced b y thermal treatment and that the aggregate created in the polymer film coul d 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 decreas e to the certain asymptotic value under longer irradiation of a linearly po larized light. This unique behavior could be attributed to the cooperative motion and the disruption of the aggregated molecules under continuous irra diation of light.