Fluorescence excitation of single molecules

Abstract

Small volumes of a pentacene-doped p-terphenyl crystal are studied by fluorescence excitation. Excitation lines of single molecules of impurities are resolved, as is shown by the features of the single molecule lines and confirmed by the autocorrelation properties of the emitted light. Following the excitation lines as the temperature is changed, we observe various behaviors. In particular, one behavior is most simply explained by postulating a coupled two-level system in the molecule’s neighborhood.