Metal–Adsorbate Interactions Modulate Plasmonic Reactivity of Chemisorbed Nitrophenyl Derivatives

Abstract

Energetic hot electrons generated upon nonradiative decay of localized plasmons in metallic nanostructures can be effectively harnessed to catalyze photochemical transformations of molecular adsorbates through unique reaction pathways. When designing metal–adsorbate hybrid systems for hot electron-driven photocatalysis, both the intrinsic plasmonic properties of metallic photocatalysts and the chemical nature of metal–adsorbate interactions should be taken into careful considerations. In this work, we show that the reactivity of nitrophenyl derivative adsorbates on Ag nanoparticle surfaces toward plasmon-driven reductive coupling reactions is intimately tied to the bonding nature of molecular chemisorption. We focus on the comparative studies of three representative nitrophenyl derivatives, specifically para-nitrothiophenol, para-nitrophenylacetylene, and para-nitrophenylisocyanide, which covalently interact with the Ag photocatalysts using chemically distinct surface-anchoring groups. Taking full advantage of the unique time-resolving and molecular fingerprinting capabilities offered by surface-enhanced Raman spectroscopy, we have been able to precisely correlate the chemical nature of metal–adsorbate interactions to the kinetic characteristics of molecular transformations under a broad range of reaction conditions. Although the kinetic features of the coupling reactions change substantially upon variation of the excitation wavelength, the light illumination power, and the pH of the reaction medium, we have consistently observed that the plasmonic reactivity of the nitrophenyl derivative adsorbates drops drastically, as reflected by significant decrease in both reaction rates and yields, when the bonding modes dominating the metal–adsorbate interactions are switched from σ-donation to π-back-donation.