AbstractVoltammetric investigations were carried out for Au144 cluster films protected by 1‐hexanethiol (C6S) and 2‐phenylethanethiol (PET) in acetonitrile (0.1 M TBAPF6) and in water (0.1 M KPF6). The C6S‐protected Au144 cluster films show single electron charging behavior both in acetonitrile and water electrolyte systems. Whereas, the PET‐protected Au144 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 (Au144 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.