Mechanically Induced Switching Between Orbital- and Fano-Resonance Rectification in a Dual-Anchored Molecular Junction.

Achieving precise control over charge transport through individual molecules is central to advancing single-molecule electronics. In short molecular junctions can exhibit rectification from fundamentally different mechanisms, yet strong sensitivity to contact geometry and electrode-molecule coupling often obscures whether diode behavior arises from asymmetric orbital alignment or quantum interference. Here, we demonstrate dual-mode rectification in a mechanically addressable metal-molecule-metal junction by chemically programming the interface with a heterofunctional scaffold bearing thiol and carboxyl anchors. Using scanning tunneling microscopy break-junction (STM-BJ) measurements under controlled mechanical modulation, we observe two reproducible conductance states that are most consistently assigned to two contact configurations on the basis of converging mechanical, statistical, and theoretical evidence. Current-voltage analysis further shows that the state assigned to the S-Au/COO-Au (thiolate-carboxylate) configuration rectifies through asymmetric molecular-orbital alignment and electrode coupling, whereas the state assigned to the nominally symmetric COO-Au/COO-Au (carboxylate-carboxylate) configuration rectifies via an interference-driven, bias-dependent Fano-resonance pathway. These findings demonstrate that anchored chemical synthons, combined with mechanical control of binding geometry, provide a practical strategy for engineering and directly comparing rectification mechanisms in short single-molecule junctions.