The role of chemical contacts in molecular conductance.

Density-functional calculations show that biaryl dithiolates compared with analogues having dicarbene and diisocyanide alligator clips have a lower conductance arising from a lower density of electronic states at the metal electrode Fermi energy. The differences in state density originate from shifts in the energies of molecular orbitals that extend across the molecule to the electrodes. Nonlocal effects consistent with the compounds' electronegativities account for the shifts in orbital energies, beyond the electrostatic potential variations from charge transfer at the metal-molecule interface.