Electrochemically Tunable Chemical Interface Damping in Methyl Viologen-Modified Single Gold Nanorods

Chemical interface damping (CID) provides an important indicator of plasmon-induced direct charge transfer, but the role of molecular redox states in controlling this process remains poorly understood. Here, we investigate CID in individual methyl viologen (MV)-modified gold nanorods using single-particle hyper-spectroelectrochemistry. Correlated single-particle scattering measurements show a pronounced plasmon resonance energy (Eres) dependence and strong CID under reduction potentials, while both the Eres dependence and CID magnitude are weaker under oxidation potentials. Our model suggests that resonant charge transfer channels are energetically allowed for both MV redox states, but their distinct redox-dependent responses originate from differences in the broadening of adsorbate-derived interfacial states, which govern both the magnitude and the Eres dependence of CID. These results illustrate that electrochemical redox control can tune plasmon-induced direct charge transfer by modulating not only energetic alignment but also by broadening interfacial states resulting from Au-adsorbate coupling. This work highlights redox-dependent interfacial state engineering as a promising strategy for enhancing plasmon-induced direct charge transfer chemistry.