Spectroscopically\nElucidating the Local Proton-Coupled\nElectron Transfer Loop from Amino to Nitro Groups via the Au Surface\nin a N<sub>2</sub> Atmosphere

Proton-coupled electron transfer\n(PCET) has been significant\nin\nunderstanding the reactions in solution. In a solid–gas interface,\nit remains a challenge to identify electron transfer or proton transfer\nintermediates. Here, in a Au/N<sub>2</sub> interface, we regulated\nand characterized the PCET from <i>p</i>-aminothiophenol\n(PATP) to <i>p</i>-nitrothiophenol (PNTP) in the plasmon-mediated\nconversion to <i>p</i>,<i>p′</i>-dimercaptoazobenzene\nby variable-temperature surface-enhanced Raman spectroscopy. The Raman\nbands of PATP and PNTP characteristically blue shifted and red shifted\nas the laser wavelength- and power density-regulated PCET from PATP\nto PNTP, respectively. These characteristic Raman band shifts were\nwell reproduced by the density functional theoretical simulations\nof positively charged PATP and negatively charged PNTP, which explicitly\nevidenced the electron transfer intermediates of PATP or PNTP on the\nAu surface. PCET did not occur in the temperature cycle between 100\nand 370 K without laser illumination. These results demonstrated a\ncharacteristic local PCET loop composed of electron transfer between\nPATP/PNTP and Au followed by intermolecular proton transfer between\nPATP and PNTP and the significance of conducting electron transfer\non Au.