Combined Single-Molecule Photon-Stamping Spectroscopy and Femtosecond Transient Absorption Spectroscopy Studies of Interfacial Electron Transfer Dynamics

Abstract

The inhomogeneous interfacial electron transfer (IET) dynamics of 9-phenyl-2,3,7-trihydroxy-6-fluorone (PF)-sensitized TiO(2) nanoparticles (NPs) has been probed by a single-molecule photon-stamping technique as well as ensemble-averaged femtosecond transient absorption spectroscopy. The forward electron transfer (FET) time shows a broad distribution at the single-molecule level, indicating the inhomogeneous interactions and ET reactivity of the PF/TiO(2) NP system. The broad distribution of the FET time is measured to be 0.4 +/- 0.1 ps in the transient absorption and picoseconds to nanoseconds in the photon-stamping measurements. The charge recombination time, having a broad distribution at the single-molecule level, clearly shows a biexponential dynamic behavior in the transient absorption: a fast component of 3.0 +/- 0.1 ps and a slow component of 11.5 +/- 0.5 ns. We suggest that both strong and weak interactions between PF and TiO(2) coexist, and we have proposed two mechanisms to interpret the observed IET dynamics. A single-molecule photon-stamping technique and ensemble-averaged transient absorption spectroscopy provide efficient "zoom-in" and "zoom-out" approaches for probing the IET dynamics. The physical nature of the observed multiexponential or stretched-exponential ET dynamics in the ensemble-averaged experiments, often associated with dynamic and static inhomogeneous ET dynamics, can be identified and analyzed by single-molecule spectroscopy measurements.

Photoluminenscence Blinking Dynamics of Colloidal Quantum Dots in the Presence of Controlled External Electron Traps

“…For our DBA dimers, a P( t off ) exhibiting a stretched exponential dependency at longer times suggests complex charge recombination dynamics 48. Compared with the direct electron tunneling during forward electron transfer, e.g., from QD to fullerene FMH, it is not uncommon to speculate that charge recombination follows more complicated dynamics at the donor–acceptor interface 49…”

Single-molecule, single-particle fluorescence imaging of TiO2-based photocatalytic reactions

“…However, over the past decade, following a pioneering work by Lu and Xie, 130 the single-molecule fluorescence spectroscopy became a powerful analytical technique for studying intramolecular [131][132][133][134][135] and interfacial [136][137][138][139][140][141][142][143][144] ET dynamics in various complex systems.…”

Interfacial Electron Transfer from CdSe/ZnS Quantum Dots to TiO2 Nanoparticles: Size Dependence at the Single‐Molecule Level

“…For instance, conformation changes and reorientation of the adsorbate structure feasibly induces fluctuation in the fluorescence decay times for ET processes, but such detailed dynamic complexity cannot be visualized in ensemble experiments. [42][43][44][45][46][47][48][49][50][51] This work aims to understand ET dynamics of QDs adsorbed on TiO 2 thin films at the single-molecule level. [29][30][31][32][33] Analysis of fluorescence intermittency observed in SMS, or on/off blinking phenomena, has been popular in studies to unveil the dynamic behavior of triplet states, [34][35][36] molecular reorientation, [37] energy transfer, [38][39][40] spectral diffusions, [31,41] and ET.…”

“…[29][30][31][32][33] Analysis of fluorescence intermittency observed in SMS, or on/off blinking phenomena, has been popular in studies to unveil the dynamic behavior of triplet states, [34][35][36] molecular reorientation, [37] energy transfer, [38][39][40] spectral diffusions, [31,41] and ET. [42][43][44][45][46][47][48][49][50][51] This work aims to understand ET dynamics of QDs adsorbed on TiO 2 thin films at the single-molecule level.…”