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

• The polymer film color changed under illumination of polarized and unpolarized beam.
• The photo-induced birefringence was not erased by circularly polarized light.
• We could induce birefringence in our polymer film by circularly polarized light.
• A sudden increase and relaxation in birefringence curves are due to phase transition.

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.

Despite typical azobenzene polymers, pCNOhomo polymer does not show photo-bleaching during illumination of light. The color of polymer film gets darker during and after illumination of light. This behavior is occurred by illumination of polarized and unpolarized light and the color change remains stable for a long time.Figure optionsDownload high-quality image (103 K)Download as PowerPoint slide