Rotational mobility and rate of photoisomerization of spin-labeled azobenzenes in glassy polystyrene

The rate of photochemical isomerization of azobenzene derivatives dispersed in glassy polystyrene has been measured along with rotational mobility of reacting molecules. For this purpose bifunctional probe molecules carrying a paramagnetic nitroxide fragment and a photochromic azobenzene moiety were used. The kinetics of photoisomerization was followed by monitoring the change in the UV–Vis absorbance spectra. Rotational mobility was determined by numerical simulation of the ESR spectra. It has been shown that in the matrix of glassy polystyrene amplitudes of high-frequency angular displacements (quasi-librations) correlate with the rate of photochemical trans–cis isomerization.