Thermal recovery and spectral diffusion of photochemical holes in polymorphic systems

Abstract

We present comparative investigations of doped benzophenone in its glass and crystal phases by using thermal cycling hole burning techniques. Chlorin and s-tetrazine were used as probe molecules. We measured the distribution of reactive barriers and the spectral diffusion behavior in both phases. The distribution in the glass is broad and is well described by a Gaussian. In the crystal, there are rather well-defined barriers, yet they are different for different sites. The respective kinetics is exponential and its temperature dependence is Arrhenius-like in contrast to the glass phase. Thermally induced spectral diffusion broadening in the glass phase is strong and shows the pattern well known from other organic glasses. In the crystal, it is much weaker, yet it is not completely absent. The experiments seem to indicate a threshold temperature ∼40 K.