Rapid Prediction of Energy Level Alignment and Conductance of Single‐Molecule Junctions Through Intramolecular Dipole Moment

Abstract

AbstractHow substituents affect the conductance of single‐molecule junctions has been a subject of ongoing debate. Here, a comparative study on the transport properties across a broader range of experimentally proposed and representative π‐conjugated molecular systems, each characterized by prototypical backbone motifs with distinct terminal groups and featuring a range of substituents is conducted. Employing the non‐equilibrium Green's function method within density functional theory, this investigation reveals a significant impact on junction conductance due to asymmetric characteristics arising from both electronic and spatial effects induced by the di‐substituents of phenanthrene analogs with C═C or B─N motifs. Remarkably, a linear correlation is uncovered, either negative or positive, between the dipole moment of the molecules and the junction conductance, contingent upon whether the transport is governed by the highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO) states. Furthermore, the validity of this proposed dipole moment descriptor is substantiated across various substituted series, including 2,7‐dipyridylfluorene, oligo(phenylene ethynylene), and 1,4‐diaminobenzene. These findings underscore the pivotal role of individual molecular dipole moment, easily determinable, in offering precise predictive insight into the conductance of intricate molecular junctions.