  The solid-state structures of organic charge transfer (CT) salts are critical
in determining their mode of charge transport, and hence their unusual
electrical properties, which range from semiconducting through metallic to
superconducting. In contrast, using both theory and experiment, we show here
that the conductance of metal | single molecule | metal junctions involving
aromatic donor moieties (dialkylterthiophene, dialkylbenzene) increase by over
an order of magnitude upon formation of charge transfer (CT) complexes with
tetracyanoethylene (TCNE). This enhancement occurs because CT complex formation
creates a new resonance in the transmission function, close to the metal
contact Fermi energy, that is a signal of room-temperature quantum
interference.
