Enormously Enhanced Rectifying Performances by Modification of Carbon Chains for D−σ–A Molecular Devices

By using the carbon chain as the end group attached to either the left or right side or both sides of the D−σ–A molecule, we investigate theoretically its rectifying performance. Interestingly, the currently reported highest rectification ratio, 408, with the density functional calculations for a unimolecule device with metal electrodes can be obtained when both carbon chains are symmetrically attached to both sides of the D−σ–A molecule. Our finding implies that to greatly promote rectifying characteristics of the D−σ–A molecule the suitable end-group engineering might be a key issue, and increasing geometrical asymmetries of a molecule may not be the only effective way.