Theory of electron transport through single molecules of polyaniline

We present theoretical results for the electron transport properties of the organic molecule polyaniline, especially leucoemeraldine (LEB), the fully reduced form. The electron tunnelling characteristics of these chain-like molecules are described by their complex band-structure. We explore how the bandgap and tunnelling decay parameter beta depend on the oxidation state of the molecule and on the torsion angle between rings. It is found that the metal Fermi level lies near the HOMO for gold contacts with a single leucoemeraldine molecule, which results in non- linear I-V characteristics. The conductance of a hepta-aniline (LEB) oligomer is obtained from a first-principles I-V curve and compared with the recent experimental results. We examine the effect of stretching of the molecule on its conductance to explain the discrepancy between the theoretical simulations and single-molecule conductance measurement experiment.