Modeling and experimental study of photoinduced anisotropy in hybrid solgel films

Abstract

The mechanism of photoinduced anisotropy through photoisomerization has been studied by measuring photoinduced dichroism and birefringence in solgel silica-based glasses containing an azo dye (Disperse Red 1) and a plasticizer (carbazole). The equations commonly adopted to describe the molecular orientation (Sekkat's theory) have been solved numerically and analytically within two different approximations. The results have been applied to photoinduced birefringence measured with expanded beams, and the dominant mechanisms driving the azo-dye molecular orientation in the investigated materials during both illumination and relaxation have been inferred. The experiments of photoinduced dichroism, performed with nonexpanded beams, suggest that the distribution of times describing the kinetics of the anisotropy formation, usually attributed to inhomogeneities in the chromophore environment, may be ascribed instead to the nonuniform profile of the beams.