FLUORESCENCE-SPECTRA OF SINGLE PENTACENE MOLECULES IN P-TERPHENYL AT 1.7-K

A new optical scheme for single molecule spectroscopy, based on a conf ocal design and a high-quality parabolic mirror enables us to efficien tly 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 con stant from molecule to molecule. Comparison of single-molecule fluores cence spectra to those of O1 and O2 sites, which differ slightly, allo ws unambiguous identification of the molecular site in most cases. Som e molecules present original features which do not appear in O1 and O2 spectra. We think they arise from defect-induced redistribution of in tensity, although we cannot rule out isotopic substitutions completely .