Overcoming the bottleneck of d-band holes in plasmonic photocatalysis through molecular electronic coupling

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.