Interfacial Coupling Rewrites the Odd–Even Effect in Molecular Junctions

ABSTRACT

When all junction components, including the anchoring group, electrode materials, and molecule–electrode contact, are kept unchanged, changing only the number of molecular repeat units can induce oscillatory conductance, known as the odd–even effect. This effect is viewed as a manifestation of molecular backbone parity. However, whether such parity‐dependent charge transport is intrinsically encoded by the molecular backbone or governed by molecule–electrode interfacial coupling remains unclear. Here, we show that interfacial coupling can program the odd–even conductance trend in molecular junctions. Molecules with odd‐numbered repeat units exhibit higher conductance than their even‐numbered homologues when coupled to EGaIn/Ga ₂ O ₃ electrodes through physical van der Waals interactions. Strikingly, this trend is reversed when strong thiol–Ag chemical bonds dominate the junction interface, while replacing thiol with a weaker amino chemical anchor nearly eliminates the odd–even effect. Beyond conductance, we demonstrate that the formation probability of molecule‐bridged junctions also exhibits a pronounced odd–even effect. Assisted by DFT‐based calculations, we clarify the underlying mechanism, thereby establishing interfacial coupling as a design principle for programming charge transport and improving the formation yield of molecule‐based devices.