Experimental evaluation of diffusion constant in a thin polymer film by triplet lifetime analysis of single molecules

We propose a method for dynamically sensing oxygen concentration in a local nanoscale domain of a thin polymer film using histograms of photon interdetection times of single molecules. By temporally analyzing the histograms, a dynamical change in the triplet lifetime of single molecules in thin polymer films with different thicknesses can be measured with respect to the oxygen concentration in a gas cell. From the time lags for observing the triplet lifetime change in the histograms due to differences in the oxygen diffusion times in the films, we estimate the diffusion constants in a local nanoscale domain of films, which approximately corresponds to the reported values in the bulk film. Thus, we conclude that this method is applicable to in situ nanoscale environmental sensors with high spatial resolution in heterogeneous materials, such as polymer blends, biological cells, and thin-film devices.