Dynamic imaging reveals subnanometer gap distance controls electron transfer processes at plasmonic nanointerfaces.

Understanding electron transfer dynamics at subnanometer gaps between nanomaterial interfaces and electrodes is crucial for applications in catalysis, electrochemistry, and nanophotonics. However, experimentally visualizing and correlating electron transfer processes with dynamic nanoscale gap evolution remains challenging. Here, we use plasmonic scattering interferometric microscopy (PSIM) combined with nanoelectrochemical modulation to dynamically probe electron transfer processes at interfaces between Au nanoparticles and an Au electrode in real time, achieving subnanometer resolution. By tuning interfacial chemical forces and validating our observations through simulations, we correlate the electron transfer-related optical signatures with entry into the nanogap coupling regime. These findings highlight gap distance as the primary determinant of heterogeneous electron transfer at nanomaterial interfaces. This work provides a direct experimental framework for probing nanoscale electron transfer dynamics at optical frequencies, with implications for the rational design of advanced electrocatalytic interfaces, nano-sensing platforms, and optoelectronic devices.