Molecular electrochemistry of monolayer-protected clusters

In sufficiently small monolayer-protected clusters (MPCs), quantum-confinement effects are responsible for the emergency of distinct electrochemical behaviors. Careful voltammetric analysis of MPCs allows, e.g., estimating HOMO–LUMO gaps, detecting effects caused by selective modification of the monolayer or the metal atoms, assessing the physical properties of the monolayer, and enabling a precise understanding of their electron-transfer properties, whether in solution, in unconventional media, in membranes, at soft interfaces, or in films. To achieve this knowledge, key factors are the preparation of MPCs with atomic precision, accurate control of core composition and charge state, and a molecular understanding of the dynamic interface between metal core and the surrounding medium. MPCs show electrochemical properties that span from those of common redox molecules to self-assembled monolayers on metal surfaces, but also display some unique features.