Plasmonic Hot Carrier-Driven Chemistry Revealed by Dual Raman Thermometry

Plasmonic nanoparticles (NPs) have been employed as nanocatalysts in a myriad of photochemical reactions with the underlying mechanisms divided into two categories: thermal and nonthermal pathways. Differentiating these two pathways is the key to optimizing plasmon-mediated chemistry; however, the challenge of measuring temperature down to the nanoscale hinders the advancement and causes the ongoing debate in the field. Herein, we report an in situ spectroscopic approach that leverages two Raman thermometries─the background of surface-enhanced Raman spectroscopy (plasmonic thermometry) and molecular vibrational fingerprints (molecular thermometry) are used independently to probe the local temperature of NP/molecule hybrid systems. Using gold NP/4-nitrothiophenol as a prototype system, we demonstrate the agreement between the two thermometries and prove the nonthermal pathways for the dimerization of 4-nitrothiophenol. Since the temperatures of both metal NPs and adsorbed molecules are probed simultaneously, the dual Raman thermometry enables a detailed mechanistic understanding of plasmon-mediated chemistry.