Cyano azobenzene polymer films: Photo-induced reorientation and birefringence behaviors with linear and circular polarized light

Photo-induced behavior of polymethacrylate polymer, with cyano azobenzene side group, was studied. The photoisomerization process occurs in cyano azo polymer, by illumination of a film with polarized and unpolarized light. The illumination of the polymer film with light results in color change, the color of film gets darker. This is in opposition to common azo polymers in which the result of illumination is a photo-bleaching. Study of spectrum changes of a dilute polymer solution shows that the color change under pump beam illumination is not due to interaction between dye molecules. Time evaluation of probe beam absorption induced by Ar⁺ laser pump beam shows the fast change in population of isomers at higher light powers. Light induced birefringence (LIB) experiments with high power pump beams shows uncommon new features. A high long-term stability of LIB is demonstrated when the polymer film is kept in the dark. Not only a circular polarized light cannot erase the birefringence but it also induces anisotropy in polymer film. It appears that this is relevant of a phase transition in the polymer film.