부산대학교 도서관

The distributions of electron-transfer dynamics in dye-sensitized TiO2films are probed using single-molecule microscopy. The time-dependent emission (i.e., blinking dynamics) of rhodamine 6G (R6G) and rhodamine B (RB) sensitized TiO2films are quantified by constructing cumulative distribution functions of emissive (“on”) and nonemissive (“off”) events. Maximum likelihood estimation (MLE) methods and quantitative goodness-of-fit tests based on the Kolmogorov–Smirnov (KS) statistics are used to establish the best fit to the photophysical data. The on-time distributions for R6G and RB on TiO2are fit by power laws, but only for emissive durations that last longer than ∼0.7 s. Furthermore, large variations in the power-law exponents are observed when using least-squares fitting as compared to the combined MLE and KS-test approach. The off-time distributions for molecules on TiO2and glass are not consistent with power laws and are instead well represented by log-normal distributions. Our observations support the hypothesis that electron-transfer processes are responsible for blinking on TiO2as well as glass substrates. Furthermore, the on-time and off-time distributions are sensitive to the chromophore as well as the substrate. To understand the origin of these power-law and log-normal distributions, single-molecule blinking dynamics are modeled using Monte Carlo simulations based on a three-level system with the rate constants for population and depopulation of the nonemissive state being log-normally distributed (i.e., Albery model). In this framework, the rate constants for FET and BET are log-normally distributed, consistent with a Gaussian distribution of activation energies.