Fluorescence spectra of single pentacene molecules in p-terphenyl at 1.7 K

A new optical scheme for single molecule spectroscopy, based on a confocal design and a high-quality parabolic mirror enables us to efficiently image fluorescence light from single molecules onto the slit of a spectrograph. Owing to the enhanced sensitivity, the emission spectra of single pentacene molecules in a p-terphenyl crystal can be recorded with unprecedented detail. The main spectral lines are remarkably constant from molecule to molecule. Comparison of single-molecule fluorescence spectra to those of O1 and O2 sites, which differ slightly, allows unambiguous identification of the molecular site in most cases. Some molecules present original features which do not appear in O1 and O2 spectra. We think they arise from defect-induced redistribution of intensity, although we cannot rule out isotopic substitutions completely.