Potential controlled redox cycling of 4-aminothiophenol by coupling plasmon mediated chemical reaction with electrochemical reaction

Abstract

The plasmon-mediated chemical reaction (PMCR) is a promising new direction for photocatalysis. By harvesting light through photon-electron interactions using nanostructures of plasmonic metals, chemical reactions of immobilized molecules on the metal surface can be activated. As demonstrated in recent years, the electrode potential (E) applied to the metal surface also provides a unique means for electrosynthesis by changing the local electrostatic field and controlling the electron transfer and redistribution in the molecules immobilized on the electrode surface. Here, as a case study, we studied the E-modulated PMCR of 4-aminothiophenol (4-ATP) confined in the nano junction formed between the gold nanoparticle (AuNP) and gold nanoelectrode (AuNE) by using the time-resolved electrochemical-surface-enhanced Raman spectroscopy (EC-SERS), a powerful tool to track the chemical reaction in-situ on the plasmonic metal surfaces in solution. We demonstrated that the negative E can effectively suppress the plasmon-mediated photo-oxidation of 4-ATP to 4,4-dimercaptoazobenzene (DMAB) and meanwhile activate the EC reduction of DMAB to 4-ATP. We are able to use E to regulate the competition between photo-oxidation and EC reduction and achieve the redox cycling between 4-ATP and DMAB in continuous E cycles. By analyzing the E-modulated dynamic SERS signal changes, we also found the applied E could affect the SERS changes through two intertwined nonreaction and reaction mechanisms. This approach can improve our understanding of the photon-electron-molecule interactions and the interplay between PMCR and EC reactions in plasmonic molecular junctions.