Interfacial Coupling Rewrites the Odd-Even Effect in Molecular Junctions

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/Ga₂O₃ 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.