Optical Detection of Single Molecules in a Solid: A New Frontier in Optical Spectroscopy?

Four individual pentacene molecules in a p-ter-phenyl crystal gave rise to the fluorescence excitation signals on the right. The excitation energies of three of these molecules do not change with time, whereas the excitation energy of the fourth changes even during the recording of a single spectrum. This high-sensitivity optical experiment, recently described by Moerner et al., might be useful to measure, among other things, dye-matrix interactions in situations of nearly unperturbed equilibrium.