A Molecular Engineering Approach to Conformationally Regulated Conductance Dualism in a Molecular Junction

One key aspect for the development of functional molecular electronic devices is the ability to precisely tune and reversibly switch the conductance of individual molecules in electrode-molecule-electrode junctions in response to external stimuli. In this work, we present a new approach to access molecular switches by deliberately controlling the flexibility in the molecular backbone. We here describe two new conductance switches based on bis(triarylamines) that rely on the reversible toggling between two conformers, each associated with vastly different conductances. By molecular design, we were able to realize an on/off ratio G_high/G_low of ~10³, which is one of the largest values reported to date. Flicker noise analysis and molecular transport calculations indicate that on/off switching relies on a change of the conduction pathway and vast differences in molecule-electrode coupling. We thereby provide a new scaffold for further development of molecular conductance switches that are both efficient and easily refined.