Electron Irradiation-driven charge state modulation in metal-intercalated SAMs

Metal ion intercalation provides a powerful strategy to modulate the physical and electronic properties of molecular self-assembled monolayers (SAMs), with the charge state of the intercalated metal ions playing a critical role in determining system functionality. Here, we demonstrate that electron irradiation can be employed as an external stimulus to control the charge state of metal ions within π-conjugated molecular SAMs on Au (111) substrates. Using copper-intercalated 5,5′-bis(mercaptomethyl)-2,2′-bipyridine (BPD) −based SAMs as a model system, we systematically investigate the effect of electron beam exposure on the valence state of copper ions. X-ray photoelectron spectroscopy reveals a progressive conversion of Cu2⁺ to Cu⁺ under electron irradiation, attributed to irradiation-induced molecular rearrangements that lower the metal coordination. Density functional theory calculations further indicate that external electrons promote crosslinking patterns stabilizing twofold metal coordination. These findings establish electron irradiation as a versatile tool for post-synthetic charge state modulation in metal-intercalated SAMs, enabling new routes to tailor nanoscale molecular electronic devices.