Photon Interaction Frequency Is Essential to Maximize Plasmon-Driven Charge Transfer

Due to their light-harvesting properties and energetic nanoscale environments, plasmonic materials are powerful photocatalysts, initiating chemical reactions through processes including plasmon-to-molecule charge transfer. However, the impact that different excitation conditions have on the yield and efficiency of charge transfer is not well understood. Here, we investigate how photon interaction frequency, defined as the average time between photon interactions in a single plasmonic hotspot, impacts the plasmon-driven reduction of methyl viologen. We found that simply increasing the photon interaction frequency did not proportionally increase the reduction yield. Instead, photon interaction frequency combined with modulated illumination impacts the charge transfer yield. For continuous wave illumination with periodic illumination, the charge transfer yield was negligible. Conversely, pulsed excitation with intermittent dark periods led to high reaction efficiencies, likely by suppressing competing processes, such as electron-hole annihilation. Our work highlights the importance of excitation conditions on plasmon-driven charge transfer reaction yields.