Spectroscopic probes of plasmon-driven chemical reactions

Plasmonic materials are highly promising catalysts for driving energetically unfavorable chemical reactions with sunlight, due to their large optical cross sections and ability to generate a number of hot holes and electrons. However, the efficiencies of most plasmon-driven processes are quite low, likely due to the lack of mechanistic understanding of the underlying physical processes. Plasmons can concentrate electromagnetic fields, can generate highly energetic electrons and holes, and can heat up local environments. An understanding of the energy partitioning into each of these processes is crucial to the design of plasmonic photocatalysts which are optimized for chemical selectivity. Here I'll discuss our development of ultrafast surface-enhanced Raman spectroscopy (SERS) to probe the contributions of plasmon-generated hot electron transfer, heating, and vibrational energy transfer on timescales relevant to photocatalysis. Specifically, we are able to quantify plasmon-driven charge transfer processes by monitoring the rate and yield of reduced molecular adsorbates, as well as monitoring energy transfer and heating processes through ultrafast Raman thermometry. These efforts in developing a fundamental understanding of plasmon-mediated processes in molecules will ultimately aid in the rational design of cost-effective plasmonic materials capable of driving industrially relevant chemistries using solar radiation.