Wire-length dependence of the conductance of oligo(p-phenylene) dithiolate wires: A consideration from molecular orbitals

The electrical transmission of a series of oligo(p-phenylene) dithiolate (PDT) wires coupled with gold electrodes is investigated using a Green function method combined with a hybrid density functional method. To investigate how the nonplanarity of the π-backbone affects the electrical transmission, two types of PDT wires with planar and nonplanar forms are compared. The exponential decay of conductance at the Fermi level, G(E_F) = G ₀ exp(-γL), is observed for both forms. The damping factors, γ's, for the planar and nonplanar PDT wires are 0.165 and 0.256 Å^-1, respectively, these values being comparable with experimental data for analogous oligophenylene wires. A possible reason for the slower decay in the planar PDT wires is analyzed in terms of molecular orbitals.