First-principles study of the electron transport through conjugated molecular wires with different carbon backbones

The nonequilibrium Green’s function approach in combination with density-functional theory is used to perform ab initio quantum-mechanical calculations of the electron transport properties of polyacetylene, polythiophene, poly(phenylene vinylene), poly(p-phenylene ethynylene), and poly(p-phenylene) molecules sandwiched between two gold electrodes. The results demonstrate that the conjugation path has a profound effect on the electron transport property of the molecular wires. Among the five molecular wires, polyacetylene is the most conductive one. The conductivities of the five molecular wires decrease with an order of polyacetylene > polythiophene > poly(phenylene vinylene) > poly(p-phenylene ethynylene) > poly(p-phenylene). The conductivities of polyacetylene and polythiophene are much higher than those of poly(phenylene vinylene), poly(p-phenylene ethynylene), and poly(p-phenylene). The difference of electron transport behaviors of these molecular wires are analyzed in terms of the electronic structures, the transmission spectra, and the spatial distributions of molecular orbitals.

► Electron transport through single π-conjugated molecules is discussed.
► Carbon backbone has a profound effect on the electron transport property.
► Polyacetylene is the most conductive one among the five conjugated molecules.
► Spatial distribution of MPSH orbitals is crucial for electron transport.