Electrochemical STM Tip-Enhanced Raman Spectroscopy Study of Electron Transfer Reactions of Covalently Tethered Chromophores on Au(111)

The ability to study electron transfer reactions at the solid–liquid interface with nanometer resolution has the potential to critically improve our understanding of electrocatalytic processes. However, few techniques are capable of studying electrode surfaces in situ at the nanoscale. We study the redox reactions of Nile Blue (NB) covalently tethered to an Au(111) electrode using in situ tip-enhanced Raman spectroscopy (TERS) and show that TERS amplitude decreases reversibly as NB is reduced. The potential dependent TERS intensity allows us to associate an electrochemical wave with the loss of electronic resonance of NB and another with the peak of fluorescence of tethered NB, which we tentatively attribute to the disassembly of on-surface NB aggregates. The study of the electrochemical activity of immobile adsorbates at the solid–liquid interface with TERS is an essential step toward the realization of in situ spectroscopic mapping at the nanoscale.