Proton-transfer-mediated interfacial electronic engineering for molecular assembly

In the field of molecular assembly at metal-organic interfaces, precisely controlling interfacial electronic structures and bonding strength remains a fundamental challenge that governs the performance of corrosion protection, catalysis, and molecular electronics. However, the mechanistic link between solution pH, proton-transfer events, and the resulting interfacial electronic states has not been systematically elucidated. In this paper, the aminopropyltrimethoxysilane corrosion protection system on a copper surface is used as a model to reveal the universal mechanism where solution pH, as a key external control parameter, precisely regulates the electronic structure of the interface and macroscopic properties by driving molecular proton-transfer processes. It was found that the film prepared under weakly alkaline conditions (pH 9) exhibited excellent protective performance, with a low-frequency impedance modulus of 1.77×106 Ω·cm2 and a protection efficiency exceeding 99%. Surface analysis and theoretical calculations indicate that under acidic conditions, protonation of amino groups (-NH3+) leads to a broadened energy gap and diminished electron-donating capability of the molecule, severely weakening interfacial bonding. In contrast, under alkaline conditions, ionization of the silanol group (Si-O-) reduces the energy gap while substantially enhancing reactivity and electron transfer capability of the molecular, which synergizes with non-protonated amino groups to form strong N-Cu coordination bonds, thereby obtaining a high binding energy (131.4 kJ/mol) and a dense protective layer. Organosilane films offer eco-friendly corrosion protection for copper, replacing chromate treatments. Here, the authors show that pH controls the corrosion protection of aminopropyltrimethoxysilane films on copper, with optimal performance at pH 9.