PHOTOINDUCED PROTON DISORDER IN PENTACENE-DOPED BENZOIC-ACID CRYSTALS - A MODEL SYSTEM FOR HOLE-BURNING IN GLASSES

Electronic excitation of dye molecules dissolved in benzoic acid host crystals leads to the appearance of a great variety of metastable defect structures in which the acid protons of the host are displaced from their stable position. Detailed investigations using selectively deuterated pentacene molecules as guests show that reversible hydrogen transfer reactions between the host and the guest are responsible for the appearance of these defects. The ensemble of pentacene molecules in defect environments can be regarded as a disordered solid. This ensemble exhibits many of the characteristics which are commonly observed for dye molecules dissolved in glasses, such as photoinduced and spontaneous site relaxation processes (hole burning, spectral diffusion, etc.). This ensemble, therefore, represents in many regards a model of these more complex amorphous systems.