Large photoinduced refractive index changes of transparent polymer films containing photoeliminable diazo and azido groups

We measured photoinduced refractive index changes of polymer films containi ng various compounds, such as alpha-diazoketone derivatives, azide derivati ves, and others which induce the loss of nitrogen molecules during photoirr adiation. PMMA films containing 20 wt % of 2-diazo-1-indanone (2DI) and bet a-azidostyrene (beta-AS) showed large refractive index changes of 0.015 dur ing photolysis, keeping transparency throughout the entire visible region. The fact that the chemical structure of the substituents at alpha-position of the diazo group and hence the resonance effect do not affect the photoin duced changes in refractive indices much indicates the major contribution o f the elimination effect of nitrogen molecules to the refractive index chan ges. Azide derivatives except for beta-AS showed small refractive index cha nges which may be related to the chemical structure of the photoproducts. D iscussion is given on the estimation of the molar refraction and the contri bution of the changes in electronic structure and in density to the refract ive index of the systems.