The lifetime, coupling, and localization of electronic states in molecular films near metal electrodes fundamentally determine their propensity to act as precursors or reactants in chemical reactions, crucial for a detailed understanding of charge transport and degradation mechanisms in batteries. We investigated the formation dynamics of small polarons and their role as intermediate electronic states in thin films of dimethyl sulfoxide (DMSO) on Cu(111) using time- and angle-resolved two-photon photoemission spectroscopy. Upon photoexcitation, a delocalized and strongly coupled DMSO electronic state is initially populated two monolayers from the Cu surface, followed by a dynamic increase in binding energy and electronic state localization, forming a small polaron on a 200 fs timescale. This localized state is a precursor state for an extremely long-lived and weakly-coupled surface-bound electronic state with a lifetime of several seconds and, thus, thirteen orders of magnitude longer than the small polaron. Our findings highlight the importance of interfacial electronic states near metal surfaces for electrochemical reactions despite their femtosecond lifetimes, as they are crucial precursors for long-lived, reactive states of solvents and electrolytes. I will also discuss experimental developments in my laboratory for probing how nanoscale material heterogeneity determines excited state lifetimes, coupling, and transport dynamics.

Tracing from femtoseconds to seconds the dynamics of electronic states at a model electrode-electrolyte interface

2019 Fall National Meeting

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