Synthesis of chiral plasmonic nanorods via regulating seed-chiral ligand interactions and their application in Ag⁺-enhanced photochemical oxidation of 4-aminothiophenol

Chiral seeded growth, an extension of seed-mediated growth incorporating chiral ligands, has emerged as a robust method for synthesizing chiral plasmonic nanoparticles. This study introduces a pre-adsorption step, i.e., incubating achiral seeds with chiral ligand prior to chiral growth, to better regulate seed-chiral ligand interactions. Using achiral gold nanorods (AuNRs) as seeds and cysteine (Cys) as the chiral ligand, we explore how this incubation step controls the chiral growth of alloy shells. Our results indicate that a small amount of Cys on the rod surface plays a critical role in initiating chiral growth, which can be fine-tuned by adjusting incubation parameters. Leveraging the large surface area and strong local field enhancement of the resulting chiral plasmonic nanorods, we investigated Ag⁺-enhanced formation of 4,4’-dimercaptoazobenzene (DMAB) via plasmon-mediated oxidative coupling of 4-aminothiophenol (4-ATP). Rather than activating adsorbed oxygen species, we propose that silver ions complex with the amino groups of adsorbed 4-ATP molecules, bringing two 4-ATP molecules into a favorable reaction configuration and thereby promoting the coupling reaction. This work not only reveals a new mechanism for Ag⁺-enhanced oxidative dimerization of 4-ATP but also highlights the crucial role of reactant configuration in on-surface reactions.