Conductance Switching in an Asymmetric Single-Molecule Junction

Electric switching in a single-molecule junction based on the asymmetric C₆₀ pyrrolidine tris-acid (CPTA) molecule was demonstrated using nanogap electrodes spin-coated with a CPTA thin film. Among the embedded molecules, those closest to the cathode were preferentially activated during two-terminal conductance measurements, exhibiting reproducible bistable switching between low- and high-conductance states at room temperature. The CPTA molecule was anchored to the cathode via a carboxyl ligand, while the opposing electrode was positioned to allow modulation of the molecule-electrode distance by an applied bias voltage. This configuration enabled two distinct transport regimes: metal-fullerene conduction in the high-conductance state and through-space tunneling across a metal-CPTA-vacuum-metal junction in the low-conductance state. Analysis of the high-conductance state using the single-level tunneling transport model confirmed that charge transport occurred through a single molecule, despite the film-based fabrication. In the low-conductance state, transition voltage spectroscopy revealed that the junction asymmetry parameter was strongly dependent on the through-space distance between the fullerene cage and the opposing electrode, offering insight into structural modulation during switching.