Captodative Radicals Enable the Coexistence of Monomer and Dimer Single-Molecule Junctions with 100-Fold Difference in Conductance

High Resolution Image Download MS PowerPoint Slide Atomic-scale manipulation of chemical bond cleavage and formation offers significant advantages of extending the reaction controllability to the single-molecule regime and enabling the elucidation of fundamental reaction mechanisms. Herein, we drive reactions between two chemical species, open-shell monomeric radicals and closed-shell dimers in single-molecule junctions. Both monomers and dimers form a C−Au covalently linked highly conducting junction in situ, with the conductance being about 100× higher than that of the dimer junction. First-principles calculations suggest that the substitution groups on the carbon in the C(sp 3 )−Au linkage bond effectively tunes the molecular junction conductance. Notably, captodative radicals enable the formation of weakly bonded spin–spin interactions in solution, yielding diamagnetic dimers, and we can reversibly switch between the dimer and the weakly bonded radical pair by mechanically controlling the gap between the two electrodes.