Theoretical study of donor-π-bridge-acceptor unimolecular electric rectifier

The electrical rectifying properties of a single-molecule nanowire from the type donor-pi-bridge-acceptor are investigated by means of the nonequilibrium Green's function method, combined with density functional theory (NEGF-DFT). The investigated nanowire is an oligo-1,4-phenylene ethylene with pi-donor and pi-acceptor groups attached on opposite sides of the molecule. The donor and acceptor wires are separated by a pi-bridge, in contrast to the Aviram-Ratner rectifier, which is a donor-sigma-bridge-acceptor diode. A model more similar to the real molecular electronic device is considered with relaxation of the molecular geometry, under the interaction with external electric field, taking into account its influence on the electronic properties of the nanowire. An asymmetric current-bias (I-V) diagram is observed, with a conductance ratio of 7. The analysis of the spatial distribution of frontier orbitals, the highest occupied molecular orbital-lowest unoccupied molecular orbital ( HOMO-LUMO) gaps, and the transmission spectra give an inside view of the observed results.