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

Electron irradiation offers controllable tuning of SAM electronic behavior. • Metal ion intercalation tunes SAM physical and electronic properties. • Electron irradiation converts Cu 2+ to Cu + via structural rearrangement. • XPS confirms Cu charge state modulation under irradiation. • DFT shows crosslinking favors twofold metal ion coordination. • Quantum transport links metal ion charge state to SAM conductivity. • Pre-irradiated SAMs promote Cu + stabilization after ion insertion. • Electron irradiation offers controllable tuning of SAM electronic behavior. 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.