Force-driven single-molecule transformations through tip-mediated stabilization of transition states.

Mechanochemistry uses mechanical forces to drive chemical transformations, offering an energy-efficient alternative to traditional thermal, optical, or electrical reaction pathways. At the single-molecule scale, controlling structural changes with mechanical stimuli is fundamental for developing nanoscale devices and understanding chemical reactivity. In conventional single-molecule reactions driven by light or electrical currents, energy is supplied through one-way excitation processes, requiring the single-event energy input to exceed the activation energy barrier. Here we show that mechanically driven single-molecule reactions can bypass this limitation, proceeding with a net energy cost below the activation energy. By using atomic force microscopy to induce the structural inversion of individual, bowl-shaped sumanene molecules on a gold surface, we measure the mechanical energy spent during the transformation. The net energy cost is significantly lower than the theoretical activation energy. This sub-barrier reaction occurs because attractive van der Waals forces from the mesoscopic tip body stabilize the transition state more effectively than the final state. Our findings demonstrate a distinct energetic mechanism in mechanochemistry, highlighting alternative strategies for energy-efficient molecular manipulation.