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

Abstract

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.