SPECTRAL DIFFUSION OF SINGLE-MOLECULE LINES IN POLYMERS

The narrow fluorescence excitation lines of single aromatic molecules dissolved in polymers can be used to probe the low-temperature dynamics of the matrix. The shape and width of the spectrum, as well as the fluctuations of the fluorescence intensity of a single molecule can be interpreted in terms of two-level systems in its neighborhood, i.e., the disordered regions of the glass responsible for its specific dynamics at low temperatures. The observed characteristic times of the fluctuations and their dependence on temperature point to tunneling mechanisms, assisted in different ways by acoustical phonons.