ROOM-TEMPERATURE FLUORESCENCE CHARACTERISTICS OF SINGLE DYE MOLECULESADSORBED ON A GLASS-SURFACE

Measurements of the total fluorescence and fluorescence spectra from s ingle carbocyanine dye molecules (DiIC(12)) as a function of time reve al a wide range of phenomena. Discrete jumps in the fluorescence inten sity 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 st ate potential minima are accessed by twists of the chromophore backbon e that alter the quantum efficiency of emission as well as the emissio n spectrum. Monte Carlo simulations based on this model are shown whic h qualitatively match experimental data. In addition, we observed emis sion spectra which range in shape from narrow, well-separated vibronic bands to a broad, featureless band. The distribution of emission para meters from different molecules, not obtained from ensemble measuremen ts, indicates an abundance of distinct nanoenvironments of the glass s urface sampled by the adsorbed molecules. (C) 1998 American Institute of Physics. [S0021-9606(98)00441-3].