Near-Field Enhanced Photochemistry of Single Molecules in a Scanning Tunneling Microscope Junction

Abstract

Optical near-field excitation of metallic nanostructures can be used to enhance photochemical reactions. The enhancement under visible light illumination is of particular interest because it can facilitate the use of sunlight to promote photocatalytic chemical and energy conversion. However, few studies have yet addressed optical near-field induced chemistry, in particular at the single-molecule level. In this Letter, we report the near-field enhanced tautomerization of porphycene on a Cu(111) surface in a scanning tunneling microscope (STM) junction. The light-induced tautomerization is mediated by photogenerated carriers in the Cu substrate. It is revealed that the reaction cross section is significantly enhanced in the presence of a Au tip compared to the far-field induced process. The strong enhancement occurs in the red and near-infrared spectral range for Au tips, whereas a W tip shows a much weaker enhancement, suggesting that excitation of the localized plasmon resonance contributes to the process. Additionally, using the precise tip-surface distance control of the STM, the near-field enhanced tautomerization is examined in and out of the tunneling regime. Our results suggest that the enhancement is attributed to the increased carrier generation rate via decay of the excited near-field in the STM junction. Additionally, optically excited tunneling electrons also contribute to the process in the tunneling regime.

Mechanistic Studies of Plasmon Chemistry on Metal Catalysts

“…[51,52,39] Hydrogenation to form CH 4 was achieved based on the dissociation of HCO to generate CH, followed by further hydrogenation. [51,52,39] Hydrogenation to form CH 4 was achieved based on the dissociation of HCO to generate CH, followed by further hydrogenation.…”

“…[51,52,39] Hydrogenation to form CH 4 was achieved based on the dissociation of HCO to generate CH, followed by further hydrogenation. [39] [39] …”

“…Theb ond dissociation of R À H( R= C, N, O) was also reported. [51,52,39] Hydrogenation to form CH 4 was achieved based on the dissociation of HCO to generate CH, followed by further hydrogenation. [52] Thet automerization of porphycene molecules,i ncluding the dissociation of NÀHb onds induced by the plasmon, was visualized with UHV-photon-STM (Figure 4d).…”

“…Ap ioneering study applied time-resolved TERS to plasmon chemistry to monitor the formation of DMAB from pNTP. [38,39] An ultrahigh vacuum condition and the atomically well-defined surfaces of metal single crystals are necessary to obtain molecular-scale mechanistic insights.T hese allow the electronic structure of the molecules adsorbed on metal surfaces to be investigated with ac ombination of STM experiments and density functional theory (DFT) calculations.T he findings obtained using the STM provide deep insights into the mechanisms of the plasmon-induced chemical reactions at the single-molecule level that cannot be accessed by the conventional macroscopic analysis methods. [35,36,37] Recently,ascanning tunneling microscope combined with optical excitation (photon-STM) was applied to observe plasmon-induced chemical reactions at as ingle-molecule level.…”

“…[35,36,37] Recently,ascanning tunneling microscope combined with optical excitation (photon-STM) was applied to observe plasmon-induced chemical reactions at as ingle-molecule level. [38,39] An ultrahigh vacuum condition and the atomically well-defined surfaces of metal single crystals are necessary to obtain molecular-scale mechanistic insights.T hese allow the electronic structure of the molecules adsorbed on metal surfaces to be investigated with ac ombination of STM experiments and density functional theory (DFT) calculations.T he findings obtained using the STM provide deep insights into the mechanisms of the plasmon-induced chemical reactions at the single-molecule level that cannot be accessed by the conventional macroscopic analysis methods.…”