Atomic-scale sensing by single molecule conformational transitions*

Typical molecular transitions occur between two intrinsic states in a double-well potential. Herein we show that a single molecule can exhibit multiple states in different environment of an atomic-scale cavity. Taking advantage of the sub-angstrom resolution of the scanning tunneling microscope (STM), we report the strong spatial sensitivity of conformational transitions of a single pyrrolidine molecule adsorbed on Cu(001) terrace, Cu₂N monolayer islands, and one-dimensional (1D) Cu row between Cu₂N islands. The molecule exhibits two-level switching on Cu(001), three-level on Cu₂N, and reversible transitions between two-level and three-level on 1D Cu row. Furthermore, the surface anisotropy of the Cu row leads to long time-scale for the molecular switching between two-level and three-level transitions. The transition rate and the population and lifetime of the molecular levels exhibit high sensitivity on the local environment. These results extend our knowledge of molecule–substrate interaction and demonstrate the realization of multiple-level states in a single molecule for processing quantum information and as molecular switches.

 

Research is supported by the Office of Naval Research under Grant No. N00014-20-1-2475.