Direct Observation of Electric-Field-Catalyzed Imine Cleavage by Single-Molecule Conductance

The controllable cleavage of robust imine bonds, which is a fundamental process in dynamic covalent chemistry, remains a critical challenge due to the inherent conflict between bond stability and reversibility. Although the electric field has been proven as a promising catalyst for bond cleavage, achieving the reaction under a well-defined and controllable ultrahigh electric field (UEF) is still experimentally inaccessible. Herein, the scanning tunneling microscopy break junction (STM-BJ) technique is employed as a dual-functional platform that simultaneously provides a tunable UEF (∼109 V/m) and monitors bond cleavage reactions via single-molecule conductance. The imine bonds embedded in the conjugated structure reveal negligible cleavage under field-free conditions, whereas the single-molecule conductance measurements reveal that the UEF markedly promotes cleavage in both polar and nonpolar solvents. The kinetic investigations indicate that the bond cleavage is governed by solvent polarity and electric field strength. Theoretical calculations confirm that the UEF decisively lowers the energy barrier through a cooperative hydrolysis pathway. This work provides direct evidence for the bond cleavage under an electric field and a strategy for manipulating dynamic covalent bonds.