Electronic Properties of a Phenylacetylene Molecular Junction with Dithiocarboxylate Anchoring Group

The electronic transport properties of a kind of phenylacetylene compound (4-mercaptophenyl)-phenylacetylene (MPPA) are studied by the first-principles method. A dithiocarboxylate conjugated linker (–CS₂) is used to anchor the molecule to one gold electrode. Rectification behavior is observed, which is mainly brought about by the asymmetrical coupling of electrodes to the molecule. There is a drastic increase in current as the electrode-electrode distance is reduced, and the rectification ratio increases by 40% as the electrode-electrode distance is diminished from 16 ? to 15.7 ?. For comparison, we also perform simulations with the –CS₂ linker replaced by thiol linkage. It shows an obvious reduction in current. We find that the stronger interface coupling induced by the –CS₂ linker broadens transmission resonances near the Fermi energy, which leads to the current enhancement of the molecular junction with –CS₂ linker.