An approach to develop chemical intuition for atomistic electron transport calculations using basis set rotations

Transmission mechanism and quantum interference in fused thienoacenes coupling to Au electrodes through the thiophene rings

So far, quantum interference in molecular devices where the anchors are inseparable parts of the whole molecule has been seldom discussed. In this article, we perform first-principles calculations on the electronic transmission properties of a series of Au-thienoacene-Au junctions where the molecule interacts with electrodes through the S atoms in thiophene rings in a fused-ring system. The calculated binding energy of the Au-S interaction is highly dependent on the substitution sites of the thiophene rings, which agrees with the experimental report that the Au-S interaction is too weak to form a junction for some molecules. The electronic coupling at the molecule-electrode contact is also affected by the molecular structure. To distinguish the coupling mechanism, we show the importance of investigating the electron distribution of frontier molecular orbitals in combination with the percentage of the π system in the partial density of states on the S atoms. Because of the difference in electronic coupling, comparison between molecules should be done with care. On the other hand, conductance suppression due to the destructive quantum interference originating from the molecular topology is demonstrated by comparing the properties of isomers with similar molecule-electrode coupling.

The Role of Through-Space Interactions in Modulating Constructive and Destructive Interference Effects in Benzene

Quantum interference effects, whether constructive or destructive, are key to predicting and understanding the electrical conductance of single molecules. Here, through theory and experiment, we investigate a family of benzene-like molecules that exhibit both constructive and destructive interference effects arising due to more than one contact between the molecule and each electrode. In particular, we demonstrate that the π-system of meta-coupled benzene can exhibit constructive interference and its para-coupled analog can exhibit destructive interference, and vice versa, depending on the specific through-space interactions. As a peculiarity, this allows a meta-coupled benzene molecule to exhibit higher conductance than a para-coupled benzene. Our results provide design principles for molecular electronic components with high sensitivity to through-space interactions and demonstrate that increasing the number of contacts between the molecule and electrodes can both increase and decrease the conductance.

Probing the Conductance of the σ-System of Bipyridine Using Destructive Interference

Guidelines to predict trends in the electrical conductance of molecules have been developed for the π-system of conjugated systems. Little is known, however, about the conductance of the underlying σ-systems because the π-system usually dominates the transport. Here we study a family of bipyridine-based molecules using STM-break junction experiments and density functional theory transport calculations. We use different lengths and substitution patterns to probe the role of both the σ-system and the π-system in controlling conductance. By exploiting the destructive interference feature found in the π-system of the meta-coupled six-membered aromatic rings, we show that the conductance of the σ-system of a meta-coupled molecule can be probed directly and can even exceed that of its para-coupled analog. These results add to the understanding of the conductance through the chemically hidden σ-electrons.