Deciphering Catalytic Reaction Mechanisms and Modulation Dynamics via Single-Molecule Break Junctions

Abstract

Traditional catalytic characterization relies on ensembleaveraged observables that inherently mask the stochastic dynamics and mechanistic heterogeneity of individual reactive events. Single-molecule break junction platforms provide a distinctive operando framework to resolve these processes at the level of individual molecular trajectories. By coupling quantum transport measurements with sub-nanometer confinement, these systems transform molecular conductance from a passive electronic signal into a dynamic probe of reaction-state evolution and elementary-step kinetics. This review evaluates how scanning tunneling microscope break junctions (STM-BJ) and mechanically controllable (MC-BJ) break junctions provide complementary access to statistical state populations and time-resolved dynamics across reaction landscapes. The discussion delineates the conceptual mapping of conductance signatures to metastable intermediates and activated complexes while maintaining a critical focus on interpretative boundaries such as geometric degeneracy and interfacial noise. Beyond mechanistic interrogation, the nanogap environment acts as an active driver of reactivity where external perturbations, including oriented electric fields, electrochemical gating, and mechanical force, can be used to steer catalytic selectivity at the single-site limit. By identifying hidden electronic descriptors, break junction techniques provide specific design principles that could be emulated in bulk materials through coordination engineering and porous support design.