Asymmetric current–voltage characteristics of molecular junctions containing bipolar molecules

The asymmetric current–voltage (I–V) curves are computed for a conjugated biphenyl–bipirimidine diblock oligomer with two thiol end groups sandwiched between Au(1 1 1) electrode surfaces. The method is based on density functional theory and self-consistently determines the electronic structure of the molecule coupled to the gold electrodes with varied electrochemical potentials. Spatial asymmetry in the molecule is found to be essential in generating the I–V asymmetry.