Overcoming the bottleneck of d-Band Holes in Plasmonic Photocatalysis through Molecular Electronic Coupling

Abstract

Interband excitation of plasmonic metals generates highly oxidizing d-band holes that, in principle, can drive demanding oxidative transformations. However, their ultrafast relaxation and recombination severely limit their chemical utilization. Here we identify d-band hole extraction as the intrinsic rate-limiting step in interband plasmonic photocatalysis and demonstrate that subtle modulation of metal–ligand electronic coupling provides a quantitative handle to overcome this bottleneck. Using gold nanorods functionalized with electronically distinct yet structurally analogous thiophenol ligands, we combine single-particle spectroscopy, ensemble photocatalysis, and density functional theory to establish a direct correlation between ligand HOMO–metal d-band coupling strength and overall photocatalytic efficiency. Despite comparable morphology and surface coverage, small enhancements in hole-transfer coupling accelerate oxidative charge extraction, suppress recombination, and amplify both reduction and oxidation reaction pathways. Marcus–Hush analysis reveals that hole transport is intrinsically slower than electron transfer by two orders of magnitude, rendering d-band hole extraction the dominant kinetic constraint under interband excitation. These findings establish molecular electronic coupling as a predictive descriptor for controlling d-hole flow and provide a general design principle for exploiting short-lived oxidative equivalents in plasmon-driven chemistry.