Photoinduced orientation of azo dye in various polymer matrices

Abstract

Photoinduced dichroism in various polymers containing the same azo dye has been studied. "Angular hole burning" and molecular reorientation have been identified by analysis of dichroism dynamics at various probe wavelengths. The glass-transition temperature T(g) is of major relevance for the reorientation of optically active molecules. For low T(g) (below ambient temperature) thermal diffusion impedes anisotropy buildup. For higher T(g) the angular distribution induced by the polarized pump beam is frozen. We propose a simple model based on diffusion rates in trans and cis molecules.

Photoinduced absorption and refraction in azo dye doped PMMA films: the aging effect

“…Thus, the obtained spectral changes confirm the above proposed hypothesis of two mechanisms. Note that similar studies were conducted on hosts having different glass transition temperatures (without taking into account the aging phenomena) [15]. The results obtained there concerning the angular mobility and corresponding excitation mechanisms are in agreement with ours.…”

“…This may significantly increase the angular mobility of azo chromophores. In this case, photoisomerization should be the dominant mechanisms of excitation [15]. In contrast, molecular rotation may be significant for cases when the solvent is evaporated and the rigidity of the matrix is increased (in older samples).…”

Holographic Recording in a Photoactive Elastomer

“…When the writing UV laser is turned on, the photoisomerization in the excited (reactive) areas converts oriented trans-azobenzene into disordered cis-azobenzene, which actually corresponds to an isothermal photochemical phase transition from the LC phase to the isotropic phase. As the azobenzene polymer in the isotropic phase is more fluid than in the LC state, [33] its microdomains are no longer effective as crosslinking points and, consequently, relaxation of oriented PB chains may occur, releasing the stress. As this happens, the stress is no longer uniformly distributed in space as before irradiation, and local structural reorganization may follow to rebalance the stress along the strain direction.…”

Optical non-linearity in Disperse Red 1 dye-doped sol–gel

“…The absorption coefficient of the material can be changed by the same occasion. Using polarized light, one can induce anisotropy leading to birefringence and dichroism [6].…”