Distribution of single molecules in polymer thin films

Distribution of fluorescent dye molecules in polymer thin (100 nm) films was investigated using far-field single-molecule video microscopy, by varying concentrations of dye molecules mixed in the polymer. Histograms of fluorescence photocounts of individual fluorescent spots showed wide distribution, varying in the number of fluorescent spots composed of one, two, three or group of molecules. The number of the molecules present in the fluorescent spots was also ascertained by fluorescence photobleaching experiments. Photocounts associated with maxima of the histograms were found to be independent of the concentrations; however, the number of occurrences associated with more than one molecule decreased with decreasing concentration. By reducing concentration as well as by mixing dye molecules into a polymer solution, fluorescent spots grouping more than one molecule were separated considerably into fluorescent spots including a single-molecule.