Photoinduced Anisotropy in Poly(Methyl Methacrylate)/Sudan Red III Thin Films

Abstract

The dynamic behavior of photoinduced optical anisotropy of amorphous PMMA/ Sudan Red III thin films has been investigated using the pump-probe method. The results showed that the anisotropy increased rapidly in an exponential fashion in the first seconds of pumping, so that a photostationary state was reached as a result of the photoisomerization process cycles. The anisotropy relaxation phase decreased exponentially in a slow manner, which means the anisotropy did not disappear instantaneously when the irradiation was switched off. Evidence of the existence of the Angular Hole Burning (AHB) and the Angular Redistribution (AR) effects in the Sudan Red III molecules in the PMMA polymeric host is presented. The relative photoinduced optical anisotropy was calculated. The results showed that, at room temperature, the thermal isotropic relaxation of the photoisomer was negligible compared to the anisotropic reverse photoisomerization that occurred as soon as the pump beam was cut-off.