SPECTRAL DIFFUSION OF SINGLE-MOLECULE FLUORESCENCE - A PROBE OF LOW-FREQUENCY LOCALIZED EXCITATIONS IN DISORDERED CRYSTALS

Spectral diffusion of the transition frequency of single pentacene mol ecules in p-terphenyl crystal was recently observed experimentally. In this Letter we propose a microscopic theoretical model to explain thi s phenomenon. Analysis of the experimental data with our model yields detailed microscopic information about the nature and spatial distribu tion of the localized excitations responsible for the observed spectra l diffusion.