Quantifying the Ultrafast and Steady-State Molecular Reduction Potential of a Plasmonic Photocatalyst

Plasmonic materials are promising photocatalysts as they are well-suited to convert light into hot carriers and heat. Hot electron transfer is suggested as the driving force in many plasmon-driven reactions. However, to date there are no direct molecular measures of the rate and yield of plasmon-to-molecule electron transfer, or energy of these electrons on the timescale of plasmon decay. Here, we use ultrafast and spectroelectrochemical surface-enhanced Raman spectroscopy to quantify electron transfer from a plasmonic substrate to adsorbed methyl viologen molecules. We observe a reduction yield of 2.4 - 3.5 % on the picosecond timescale, with plasmon-induced potentials ranging from -3.1 to -4.5 mV. Excitingly, some of these reduced species are stabilized and persist for tens of minutes. This work provides concrete metrics toward optimizing material-molecule interactions for efficient plasmon-driven photocatalysis.