Photo-optical properties of amorphous and crystalline films of azobenzene-containing photochromes with bent-shaped molecular structure

A comparative study of the photo-optical properties and the photo-orientation processes in thin films of the bent-shaped azobenzene-containing compounds with different molecular structure was performed. For this purpose three new compounds were designed and prepared: two of these compounds with a symmetric bent-shaped molecular structure incorporate two azobenzene chromophores with different length of alkyl chains (6 and 8 methylene units), the third bent-shaped compound possesses only one azobenzene fragment. The effect of molecular and supramolecular structure, thermal prehistory of the films, wavelengths of the excitation light on the photo-optical properties, photoorientation processes and films morphology was revealed. It was shown that UV-irradiation leads to E-Z isomerization of azobenzene fragments in both amorphousized and crystalline films of the synthesized substances. This process is partially suppressed in crystalline films, but, nevertheless, UV-irradiation of the bichromophoric compounds results in transition from crystalline to amorphous state and decrease in the surface roughness. Irradiation of amorphousized films with polarized visible and UV-light induces the photoorientation of chromophores in direction perpendicular to the polarization plane of the incident light. Relatively high values of photoinduced dichroism in the bent-shaped compounds (D similar to 0.60-0.65) are comparable with other azobenzene-containing rod-shaped systems. Photoinduced isothermal melting and photoorientation processes could be served for the photo-optical data recording and storage. (C) 2015 Elsevier B.V. All rights reserved.