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

Abstract

How 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.

Screening and Antiscreening Effects in Endohedral Nanotubes

“…It basically consists of the evaluation of the dipole moment from the valence electron density distribution and the nuclei positions, in the analysis of the differential charge density, and for ionic nanostructures, in the calculation of the displacements of positive and negative ions of the nanotube upon encapsulation of a small molecule. It is well-known that dipole moments of molecules and isolated system, and electron density distributions are efficiently and accurately evaluated by DFT (see, for instance, refs and ). The electronic dipole moment of the systems is computed as where − e is the electron charge, n ( r ) the electronic number density, and Z i and R i are the valence and spatial coordinate of the i th ion of the system, respectively.…”