OPTICAL MODIFICATION OF A SINGLE IMPURITY MOLECULE IN A SOLID

THE possibility of obtaining information about solids on a truly microscopic scale has stimulated several recent advances in the optical detection and spectroscopy of single impurity centres in solids. For the system composed of pentacene impurity molecules in the crystal p-terphenyl, absorption 1 and fluorescence excitation 2 studies At liquid-helium temperatures have led to direct observations of the lifetime-limited homogeneous linewidth of a single pentacene molecule 3, as well as the surprising observation of spontaneous spectral diffusion in a crystal 4. Spectral diffusion-changes in the resonance frequency of an impurity molecule with time as a result of structural relaxation processes in the molecular environment-is generally expected in amorphous hosts. We report here the observation of optical spectra of single perylene impurity molecules in a polymeric (polyethylene) host. At 1.5 K, individual perylene molecules show the expected spectral diffusion; furthermore, we observe light-induced changes in resonance frequency (that is, persistent spectral hole-burning 5) for certain single molecules. These observations suggest the possibility of optical storage at the single-molecule level.