Room-temperature fluorescence characteristics of single dye molecules adsorbed on a glass surface

Measurements of the total fluorescence and fluorescence spectra from single carbocyanine dye molecules (DiIC(12)) as a function of time reveal a wide range of phenomena. Discrete jumps in the fluorescence intensity from single molecules on a glass surface have been observed with correlation times spanning several orders of magnitude (1 ms-10 s). We propose a model for these fluctuations in which two or more ground state potential minima are accessed by twists of the chromophore backbone that alter the quantum efficiency of emission as well as the emission spectrum. Monte Carlo simulations based on this model are shown which qualitatively match experimental data. In addition, we observed emission spectra which range in shape from narrow, well-separated vibronic bands to a broad, featureless band. The distribution of emission parameters from different molecules, not obtained from ensemble measurements, indicates an abundance of distinct nanoenvironments of the glass surface sampled by the adsorbed molecules. (C) 1998 American Institute of Physics. [S0021-9606(98)00441-3].