Quantifying Ultrafast Hot Carrier Transfer along a Specific Vibrational Reaction Coordinate at Plasmonic Nanoparticle/Molecule Interfaces

Insight into the transfer of energetic hot carriers (HCs) from plasmonic nanostructures to specific vibrational coordinates of adsorbed molecules is essential for understanding the HC-driven reaction mechanism, yet this process remains incompletely elucidated. Here, using 4-nitrothiophenol (4-NTP) adsorbed on gold nanoparticles (AuNPs) as a model system, we demonstrate that femtosecond visible pump–sum frequency generation vibrational spectroscopy (SFG-VS) probe technique can quantitatively monitor ultrafast interfacial HC injection into 4-NTP molecules following AuNP excitation, by detecting the third-order nonlinear SFG response (χ (3) ) of specific vibrational modes. The HC transfer efficiencies from AuNPs to the NO 2 coordinates are determined to be 45–55% and 21–23% for interband and intraband excitations, respectively, significantly higher than those to the C═C coordinates. A higher HC transfer efficiency is correlated with an enhanced reaction yield. The observed selectivity in HC transfer to specific vibrational coordinates highlights the dominance of nonthermal pathways in plasmonic catalysis.