Beyond single-molecule chemistry for electrified interfaces using molecule polaritons

Abstract

Abstract This review introduces the preparation, observation, and characterization of systems of molecule polaritons. We summarize recent progress by our group on the control of molecular properties in the spaces of various optical cavities, such as plasmonic metal nanostructures and Fabry–Perot mirrors. After stating our motivations, we introduce topics on single-molecule observations based on surface-enhanced Raman scattering (SERS) spectroscopy. Our original findings are not limited to the ultrasensitive detection of molecules/materials, but include unique resonant enhancements of SERS through exotic electronic excitation processes at electrified interfaces. Comprehensive analyses of SERS spectra provide novel routes to electronic excitation using plasmonic metal nanostructures. This behavior leads to the distinct photoenergy conversion based on excited electrons and holes with anomalous electrochemical potentials. Such unique resonant electronic excitation emerges as a large optical force that can be used to manipulate small single molecules on surfaces in solution, even at room temperature. We also introduce systems for examining unique interactions between molecules and the optical modes of cavities, from single molecules to molecular ensembles. Plasmonic surface lattices and Fabry–Perot mirrors allow the formation of electronic and vibrational strong coupling states, respectively, showing unique properties of molecule polaritons, even under dark conditions, i.e. without photoillumination.