Mechanically controlled binary conductance switching of a single-molecule junction

Molecular-scale components are expected to be central to the realization of nanoscale electronic devices1–3. Although molecu-lar-scale switching has been reported in atomic quantum point contacts4–6, single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through mol-ecular design. To date, switching in single-molecule junctions has been attributed to changes in the conformation or charge state of the molecule7–12. Here, we demonstrate reversible binary switching in a single-molecule junction by mechanical control of the metal–molecule contact geometry. We show that 4,4’-bipyridine–gold single-molecule junctions can be reversibly switched between two conductance states through repeated junction elongation and compression. Using first-prin-ciples calculations, we attribute the different measured conduc-tance states to distinct contact geometries at the flexibl