Photoinduced refractive index change of polymer films containing mesoionic sulfur-substituted phenyloxatriazolones

We measured photoinduced refractive index changes (see Figure) of polymer films containing various sulfur-containing mesoionic compounds. PMMA films containing 30 wt.% of 3-phenyl-1,2,3,4-thiatriazole-5-thione (3PTTT) showed refractive index changes of -0.036 during photoirradiation, at a wavelength far from the resonant region. An increase in the number of sulfur atoms in the mesoionic compounds doped in PMMA films resulted in the increase in refractive index changes during photoirradiation. The estimation and comparison of the changes in specific refraction and densities of the systems suggest that the change in electronic structure mainly contributes to the refractive index changes of the film in the case of 3PTTT, while the changes in both electronic structure and density equally contribute to the refractive index change in the film with 3-phenyl-1,2,3,4-oxatriazole-5-thione (3POTT).