Photochromic properties of azo dye polymer thin films: evidence of an additional reversible mechanism of molecular behaviour

Abstract

Photoinduced refractive index and absorption anisotropies in thin films of an azo dye polymer have been carried out by pump-probe experiments. A refractive index change of $\Delta $n=-0.04 was obtained by independently measuring the two indices, parallel and perpendicular to pump light polarization. A long-term stability of the induced birefringence and a reversible photoinduced memory effect have been observed. The experimental results cannot be completely explained by the proposed photoisomerization models to describe the process involved.