Inhomogeneous and Complex Interfacial Electron-Transfer Dynamics: A Single-Molecule Perspective

Interfacial electron transfer (ET) plays a critical role in surface chemistry, catalysis, and solar energy conversion, such as solar photovoltaic and solar fuel science and technology. Molecular-level information on the energy and electron flow between molecules and substrate surfaces as a function of surface site geometry and molecular structure is imperative for understanding the interfacial ET mechanism and dynamics. The intrinsic complexity of the interfacial ET dynamics often presents a major challenge for conventional ensemble-averaged measurements because of the fact that the molecule–substrate interactions are inhomogeneous, involving heterogeneous local environments, especially at an individual molecule level. Beyond the conventional ensemble-averaged studies, real-time single-molecule approaches have been demonstrated to be powerful in dissecting the complex, fluctuating, and often intermittent interfacial ET dynamics. In this Review, we will focus our discussion on the importance of single-molecule studies of interfacial ET dynamics involving detailed analysis of the fluctuations and inhomogeneity of the driving force, electronic and vibrational coupling, solvent and vibrational relaxation energy, and local electronic work function, mostly using our recent publications as examples.