Electrochemical TERS Elucidates Potential‐Induced Molecular Reorientation of Adenine/Au(111)

Electrochemical surface activity arises from the interaction and geometric arrangement of molecules at electrified interfaces. We present a novel electrochemical tip‐enhanced Raman spectroscope that can access the vibrational fingerprint of less than 100 small, non‐resonant molecules adsorbed at atomically flat Au electrodes to study their adsorption geometry and chemical reactivity as a function of the applied potential. Combining experimental and simulation data for adenine/Au(111), we conclude that protonated physisorbed adenine adopts a tilted orientation at low potentials, whereas it is vertically adsorbed around the potential of zero charge. Further potential increase induces adenine deprotonation and reorientation to a planar configuration. The extension of EC‐TERS to the study of adsorbate reorientation significantly broadens the applicability of this advanced spectroelectrochemical tool for the nanoscale characterization of a full range of electrochemical interfaces. Superficial changes: High‐sensitivity electrochemical tip‐enhanced Raman spectroscopy in combination with DFT calculations allows the potential‐induced reorientation and chemical conversion of small, non‐resonant molecules at a single‐crystal Au electrode to be monitored in situ. With this unique methodological development, nanoscale chemical information becomes accessible for a full range of (solid/liquid) electrochemical systems.