Ruthenium Tris-bipyridine Single-Molecule Junctions with Multiple Joint Configurations.

Single-molecule junctions are of particular interest in molecular electronics. To realize molecular electronic devices, it is crucial that functional single-molecule junctions are connected to each other by using joint units on the atomic scale. However, good joint units have not been reported because controlling the charge transport directions through the junctions is not trivial. Here, we report a joint unit that controls and changes the charge transport directions through the junctions, by using a ruthenium-tris-bipyridine (RuBpy) complex. The RuBpy single-molecule junction was fabricated with scanning tunnelling microscopy-based break junction techniques. The RuBpy single-molecule junction showed two distinct high and low conductance states. The two states were characterized by the conductance measurement, the correlation analysis, and the comparative experiment of bipyridine (Bpy), which is the ligand unit of RuBpy. We demonstrate that the Ru complex has multiple charge transport paths, where the charge is carried vertically and horizontally through the complex depending on the path.