The use of plasmonic materials to drive chemical reactions represents an exciting approach in the development of efficient light-driven energy storage and conversion devices.  A mechanistic understanding of photoreactions occurring at plasmonic surfaces is currently lacking, but is likely to involve some combination of hot electron transfer, highly localized temperature gradients, and/or modification of excited state potential energy surfaces. We discuss our efforts to directly follow structural changes in reacting molecular plasmonic systems through the use of time-resolved surface-enhanced Raman spectroscopy (TR-SERS).  TR-SERS is a pump-probe technique which provides ultrafast structural information on reacting molecules following plasmon excitation.This talk will focus on our current efforts in using the TR-SERS technique to determine the mechanism of two plasmonically-enhanced chemical reactions: photoisomerization in a push-pull azobenzene, and light-driven organic pollutant degradation.  In both systems, we investigate the role of hot electrons in driving the photochemistry on the timescale of the fundamental bond-stretching and bond-breaking processes. By obtaining time-resolved structural snapshots of these reacting molecules, the impact of the plasmon on the reaction rate, coordinate, and yield is determined.The development and application of this highly-enhancing, surface-specific ultrafast spectroscopic technique provides a molecular-level understanding of the effect of excited plasmons on proximal chemical reactions.  We anticipate our results should lead to design insight into efficient and cost-effective plasmonically-enhanced devices for energy harvesting, storage, and conversion.

Determining the mechanism of plasmon-driven reactions with time-resolved surface-enhanced Raman spectroscopy

248th National Meeting (2014)

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