Solvent-Limited Ion-Coupled Electron Transfer and Monolayer Thiol Stability in Au144 Cluster Films

Voltammetric investigations were carried out for Au-144 cluster films protected by 1-hexanethiol (C6S) and 2-phenylethanethiol (PET) in acetonitrile (0.1 M TBAPF(6)) and in water (0.1 M KPF6). The C6S-protected Au-144 cluster films show single electron charging behavior both in acetonitrile and water electrolyte systems. Whereas, the PET-protected Au-144 cluster films show charging behavior only in acetonitrile and not in water, although both electrolyte systems contain a common hydrophobic anion (PF6-). This discrepancy is attributed to solvent-limited ion-coupled electron-transfer phenomena. Furthermore, spectroelectrochemistry was employed to study the thermal and electrochemical stability of PET on curved/3D (Au-144 cluster films) and flat/2D (self-assembled monolayers (SAMs) of PET on a polycrystalline planar Au electrode) Au surfaces. At 4 mW laser power, the SAMs of the curved system remained stable; however, in the flat system, they irreversibly desorb from the surface. This was ascribed to the relative stability differences of the PET monolayer originating from the existence of different Au-S structures on the two types of Au surfaces.