Effect of Aromatic Coupling on Electronic Transport in Bimolecular Junctions

We have performed a systematic first-principles study on conductance−voltage characteristics of bioligo(phenylene ethynylene)−monothiol molecular junctions as recently reported by Wu et al.[Nature Nanotech.2008, 3, 569]. It is found that the molecular conductance is very sensitive to the vertical distance between two molecules as well as the titled angle between two molecular planes. By comparing with experimental results, key structure parameters for bimolecular junction are determined, indicating that in the experimental devices, the vertical distance between two molecules is around 0.30 nm, the two planar molecules have a cofacial arrangement, and the length of the molecular bridge is about 2.88 nm. The underlying mechanism for electron transport in these aromatically coupled bimolecular junctions has also been discussed.