Single-molecule detection fluorescence of surface-bound species in vacuum

We have performed single-molecule fluorescence detection of DiIC(12) molecu les adsorbed on a solid substrate where the surrounding pressure is control led. The triplet lifetimes are significantly longer (4-100 ms) and far more easily observed at moderate vacuum pressures than in air(typically < 100 m u s) The photobleaching rate also decreases by over an order of magnitude i n vacuum. In addition, we have observed fluctuations in the intersystem cro ssing rate and the triplet lifetime for a single molecule, consistent with our previous observations, in this same system in air, of hopping between t wo or more molecular configurations, each with its own time-averaged intens ity. (C) 1999 Elsevier Science B.V. All rights reserved.