A new kinetic description of the complex optical behavior in photochromic polymer films

Kinetics of photoinduced birefringence in precolored spirooxazine-doped polymer films pumped with He–Ne laser beams of various powers was investigated in detail. An improved model, elucidating a competition between photo-orientation and photo-isomerization, was precisely presented. Kinetic parameters determined by fitting to the experimental data were analyzed. As He–Ne laser intensity is increased, the thermal rate constants for isomerization and randomization increase in linear and exponential fashions, respectively. Taking these factors into account, the Thermal Effect Model was more suitable for describing the experiment than the Constant Model, indicating that thermal effect of He–Ne laser plays a key role in decreasing the saturated birefringence. According to the Thermal Effect Model, the highest value of the saturated birefringence was obtained at the He–Ne laser power of 6.5 mW in our experiment.