On the role of electromagnetic boundary conditions in single molecule fluorescence lifetime studies of dyes embedded in thin films

Single molecule fluorescence lifetime studies are generally performed in th in polymer films, where the influence of the interface on the behaviour of fluorescing molecules is not negligible. In order to describe this influenc e, we investigate annealed films of different thickness. We show that the d istribution of fluorescence lifetimes of the embedded dyes is shifted to lo wer values as the thickness of the film increases. We explain this shift by simple electromagnetic arguments related to the boundary conditions at the interfaces of the polymer film with air and glass, respectively. The concl usion is that extreme care must be taken in order to interpret single molec ule data with respect to the true chemical nature of the phenomena. (C) 200 1 Elsevier Science B.V. All rights reserved.