Gating of single molecule junction conductance by charge transfer complex formation

TL;DR

This paper demonstrates that forming charge transfer complexes in metal-molecule-metal junctions significantly enhances conductance by introducing a resonance near the Fermi level, revealing room-temperature quantum interference effects.

Contribution

It shows experimentally and theoretically that charge transfer complex formation can dramatically increase molecular junction conductance through quantum interference.

Findings

Conductance increases by over an order of magnitude upon CT complex formation.

Charge transfer creates a new resonance near the Fermi energy.

Quantum interference effects are observed at room temperature.

Abstract

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.