Mechanically Programmable Tristate Molecular Switching Through Controlled Fullerene Assembly

Multistate control of electrical conductance at the molecular scale is essential for extending molecular electronics beyond binary functionality. Here we demonstrate a mechanically programmable and fully reversible tristate molecular junction based on the controlled assembly of fullerene (C₆₀) molecules. Using the scanning tunneling microscope-break junction technique, we identify three discrete and well-separated conductance states spanning more than four orders of magnitude, which can be repeatedly accessed by mechanical push-pull modulation of the junction. Low-temperature scanning tunneling microscopy, together with noise analysis and transport calculations, shows that the states originate from controlled stacking of one, two, and three C₆₀ molecules. Owing to the spherical geometry and isotropic π-electron delocalization of C₆₀, the conductance is largely insensitive to molecular orientation and contact rearrangements, enabling robust and configuration-insensitive multistate transport. This work establishes mechanically controlled intermolecular assembly as a general route to deterministic multistate molecular switching, with relevance to adaptive and neuromorphic-inspired electronic systems.