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.