Abstract: Theoretical investigation has been performed on electron transport properties of 4, 4'- diamino biphenyl based molecules that are sandwiched between two gold surfaces. Dependence of the molecular electronic structure of the gold–molecule complex on the external electric field is studied too. The electronic conduction has been analyzed from the change in the shape of molecular orbital and the evolution of the HOMO–LUMO gap of the gold-molecule complex under the influence of the electric filed. Density functional calculations are performed to analyze the conduction process through various aromatic bridges in a donor–bridge–donor molecular wire through frontier molecular orbital analysis. According to Systematic study on the molecular orbital populations, five and six member hetero-aromatic rings (electron-rich) in the conduction path are inserted between the donor–donor complexes. Values of Potential barrier (PB) that have been determined experimentally and reached the conclusion is mentioned later in this paper.