Plasmon-Driven Reaction Mechanisms: Hot Electron Transfer versus Plasmon-Pumped Adsorbate Excitation

• Published in: Journal of physical chemistry. C 2019-04, Vol.123 (14), p.8469-8483
• Main Authors: Tesema, Tefera E, Kafle, Bijesh, Habteyes, Terefe G
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b12054

Photochemistry that can be driven at low incident photon flux on optically excited plasmonic nanoparticles is attracting increasing research interest because of the fundamental need to combine surface reaction and in situ spectroscopy as well as the opportunity that plasmon-driven reactions may offer a pathway for efficient conversion of solar energy into fuel. In mechanistic studies of plasmon-driven reactions to date, a great deal of emphasis is given to hot electron transfer. The results summarized in this Feature Article indicate that photochemistry on plasmonic nanoparticles can be induced by hot electron transfer from the nanoparticle to an unoccupied orbital of the adsorbate and/or by plasmon-pumped electron transition from an occupied molecular orbital to an unoccupied molecular orbital of the adsorbate. The branching photochemical reaction of para-aminothiophenol on the plasmonic gold surface depending on the presence of a cetyltrimethylammonium bromide surface ligand that influences the hot electron concentration is used to highlight reactions driven by hot carriers. The importance of plasmon-pumped electronic excitation of adsorbates in initiating surface photochemistry is demonstrated based on the N-demethylation of methylene blue (MB) on gold nanostructures depending on excitation wavelengths. At excitation wavelength that overlaps with the resonances of MB and the gold nanoparticles, conversion of MB to thionine is observed in the presence of oxygen in the atmosphere and water in the surface–molecule complex. Considering that MB is a well-known photosensitizer, this observation suggests that the photochemical N-demethylation reaction involves singlet oxygen that can be generated via energy transfer from the MB triplet excited state to the O2 triplet ground state.