Hot Electron-Driven Amide Bond Formation in Plasmonic Nanogaps without Chemical Activation

Plasmonic nanostructures enable light-driven chemical transformations through localized electromagnetic fields and hot-carrier generation. Here, we demonstrate that amide bond formation between carboxylic acids and amines, which is thermodynamically unfavorable under ambient conditions, can be directly driven in plasmonic nanogaps without coupling agents or thermal activation. Under resonant excitation, hot electrons generated in the nanogap activate the carbonyl group within a spatially confined environment, enabling a nucleophilic attack and subsequent bond formation. In situ surface-enhanced Raman spectroscopy reveals the emergence of amide vibrational modes, supported by density functional theory calculations. The reaction exhibits a clear excitation power threshold, is suppressed under off-resonant conditions, and is not induced by thermal heating alone, confirming its nonthermal origin. Furthermore, plasmon-induced nanoparticle aggregation provides independent evidence of covalent bond formation at the nanoscale. These findings establish plasmonic nanogaps as functional reaction environments that enable reactions without coupling agents and demonstrate that nanoscale confinement and localized electronic excitation can drive thermodynamically challenging transformations.