Large Photoinduced Refractive Index Changes of Transparent Polymer Films Containing Photoeliminable Diazo and Azido Groups

Abstract

We measured photoinduced refractive index changes of polymer films containing various compounds, such as α-diazoketone derivatives, azide derivatives, and others which induce the loss of nitrogen molecules during photoirradiation. PMMA films containing 20 wt % of 2-diazo-1-indanone (2DI) and β-azidostyrene (β-AS) showed large refractive index changes of 0.015 during photolysis, keeping transparency throughout the entire visible region. The fact that the chemical structure of the substituents at α-position of the diazo group and hence the resonance effect do not affect the photoinduced changes in refractive indices much indicates the major contribution of the elimination effect of nitrogen molecules to the refractive index changes. Azide derivatives except for β-AS showed small refractive index changes which may be related to the chemical structure of the photoproducts. Discussion is given on the estimation of the molar refraction and the contribution of the changes in electronic structure and in density t...