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 (C 60 ) 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 C 60 molecules. Owing to the spherical geometry and isotropic π–electron delocalization of C 60 , 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.