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

We have performed single-molecule fluorescence detection of DiIC12 molecules adsorbed on a solid substrate where the surrounding pressure is controlled. The triplet lifetimes are significantly longer (4–100 ms) and far more easily observed at moderate vacuum pressures than in air (typically <100 μs). The photobleaching rate also decreases by over an order of magnitude in vacuum. In addition, we have observed fluctuations in the intersystem crossing rate and the triplet lifetime for a single molecule, consistent with our previous observations, in this same system in air, of hopping between two or more molecular configurations, each with its own time-averaged intensity.