Wavelength Dependence of the Reorientation Efficiency of Azo Dyes in Polymer Matrixes

Irradiation with linearly polarized light of azobenzene-containing polymeric matrixes causes reorientation of azobenzene molecules. In this study, the optical light-induced anisotropy of amorphous poly(alkyl methacrylates) doped with an azo compound was measured at different temperatures and at two irradiation wavelengths. To describe a decrease in the efficiency of anisotropy formation with temperature, a model of molecule reorientation is suggested which includes the probability of molecule reorientation per one isomerization as a basic parameter. The probability of molecule reorientation was found to depend on irradiation wavelength. Comparing the anisotropy time profiles at different irradiation wavelengths, we concluded that, upon each photon absorption, the molecule most likely makes an attempt to reorient even without isomerization, i.e., the reorientation occurs by a mechanism predicted by Persico and co-workers in their theoretical works. Also, we infer that the reorientation is facilitated by the photon energy absorbed by a molecule.