Structural and Photoisomerization Cross Studies of Polar Photochromic Monomeric Glasses Forming Surface Relief Gratings

Abstract

A novel class of photochromic materials based on polar azo derivatives containing functionalized biphenyl substituents has been synthesized. Once melt and cooled, these compounds formed amorphous transparent monomeric materials whose glass transition temperatures depend mainly on the bulkiness of the biphenyl substituent; by contrast, a change in polarity, evidenced by absorption spectroscopy and DFT calculations, exerts insignificant influence. Photoisomerization of the azo groups occurred both in solution and thin films; the rate constants of the thermal back-relaxation in both media increase with compound polarity. Photoconversion yields display smaller values in solid state than in solution, due to more packed surroundings; surprisingly, they increase substantially with the monomer bulkiness, despite raising Tgs. Comparative dynamic surface relief grating writings and AFM surface modulation measurements of irradiated thin films showed that the efficiency of the writing process improves dramatically fo...