Probing -coupling in molecular junctions

Charge transport characteristics for metal–molecule–metal junctions containing two structurally related -conjugated systems were studied to probe – interactions in molecular junctions. The first molecule contains a typical -conjugated framework derived from phenylene vinylene units, whereas the second has the phenylene vinylene structure interrupted by a [2.2]paracyclophane (pCp) core. Electrochemical investigations were used to characterize the defects and packing density of self-assembled monolayers of the two molecules on gold surfaces and to enable quantitative comparison of their transport characteristics. Current–voltage measurements across molecular junctions containing the two species demonstrate that the pCp moiety yields a highly conductive break in through-bond -conjugation. The observed high conductivity is consistent with density functional theory calculations, which demonstrate strong through-space – coupling across the pCp moiety.