Reversible conductance transitions are demonstrated on the molecular scale in a complex of 3-nitrobenzal malononitrile and 1,4-phenylenediamine, by application of local electric field pulses. Both macroscopic and local current-voltage (I-V) measurements show similar electrical bistability behavior. The mechanism of the electrical bistability is discussed.

Two popular models of the gold-4,4 bipyridine (44BPD)-gold molecular junction, i.e., the direct contact of the 44BPD molecule with the Au(111) surface and the intermediary contact through one extra gold atom on each side, were studied using density functional theory calculations under periodic boundary conditions. The relative position of the Fermi level is changed by the extra gold atom from well below the LUMO(lowest unoccupied molecular orbital) of the 44BPD molecule in the direct contact model to within the energy range of theLUMOin the intermediary contact model, indicating that the local structure of the contact can significantly affect the conducting characteristics of the junction. The dependence of the molecule–electrode interaction on the interface structure was also investigated in details.

The conductance of a benzene molecule connected to two ruthenium (Ru) electrodes through two C(H) anchoring groups is investigated using a self-consistent ab initio approach that combines the non-equilibrium Green's function formalism with density functional theory. Our calculations demonstrate that a nearly perfect conductance with magnitude exceeding 84% of the conductance quantum GO can be obtained when the two C(H) anchoring groups are bonded to a Ru adatom on the Ru(0001) surface, independently from whether this is a Ru@C double bond or a Ru„C triple bond. Both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the benzene backbone interact with the Ru-C p bonds in the contact region to form efficient charge transport channels, illustrating the high conducting nature of benzene.

The conductance of a single 1,4-diisocyanatobenzene molecule sandwiched between twosingle-walled carbon nanotube (SWCNT) electrodes are studied using a fully self-consistentab initio approach which combines nonequilibrium Green's function formalism with densityfunctional theory calculations. Several metallic zigzag and armchair SWCNTs with differentdiameters are used as electrodes; dangling bonds at their open ends are terminated with hydrogenatoms. Within the energy range of a few eV of the Fermi energy, all the SWCNT electrodes couplestrongly only with the frontier molecular orbitals that are related to nonlocal π bonds. Although thechirality of SWCNT electrodes has significant influences on this coupling and thus the molecularconductance, the diameter of electrodes, the distance, and the torsion angle between electrodes haveonly minor influences on the conductance, showing the advantage of using SWCNTs as theelectrodes for molecular electronic devices.

The conductance of a family of ruthenium-octene-ruthenium molecular junctions with different πconjugation are investigated using a fully self-consistent ab initio approach which combines thenonequilibrium Green's function formalism with density functional theory. Our calculationsdemonstrate that the continuity of the π conjugation in the contact region as well as along themolecular backbone affects the junction conductance significantly, showing the advantage of usingthe ruthenium-carbon double bond as the linkage of conjugated organic molecules.