Electron Transport and Redox Reactions in Molecular Electronic Junctions

Abstract

Electron transport through single molecules or collections of molecules oriented in parallel can occur by several mechanisms, including coherent tunneling, activated transfer between potential wells, various "hopping" modes, etc. Given suitable energy levels and sufficiently long charge transport times, reduction or oxidation with accompanying nuclear reorganization can occur to generate "polarons", that is, localized redox centers in the molecule or monolayer. Redox events in molecular junctions are amenable to spectroscopic monitoring in working devices, and can have major effects on the electronic behavior of the junction. Several examples are presented, along with a possible application to molecular memory.

Understanding the charge transport properties of redox active metal–organic conjugated wires

“…Therefore, redox exchange, for which the presence of charge localized redox centers is the perquisite, has been considered in diverse molecular junctions. 77 The study of a single electron transistor reveals that several distinct redox states in the phenylenevinylene oligomer (3.2 nm in length) can be reached with small addition energies, which controls the charge transport properties. 35 According to Nishihara, different redox states for the [Fe(tpy) 2 ] sites in the wire, generated after electron injection from the gold electrode, are responsible for the intra-wire hopping between the [Fe(tpy) 2 ] sites along the wire.…”

Towards Integrated Molecular Electronic Devices: Characterization of Molecular Layer Integrity During Fabrication Processes

“…We have pursued an alternative approach to using self‐assembled monolayers in junction fabrication that relies on covalent modification of carbon electrodes through the electrochemical reduction of aryl diazonium salts 12, 15, 25–29. As detailed in the experimental section, carbon electrodes comprise pyrolyzed photoresist film (PPF), with rms (root mean square) surface roughness of about 0.5 nm.…”

The merger of electrochemistry and molecular electronics

“…One treatment compares the “tunneling time” to the vibrational period, and proposes that reorganization to a radical anion or cation will occur once the tunneling time exceeds the time required for molecular reorganization 132,133. We have reported several examples of redox reactions which occur in molecular junctions, in particular when an oxide tunneling barrier is present 94,98,99,101,103,134,135. Readers will likely recognize that many of the concepts underlying the various transport mechanisms are shared by both electrochemistry and molecular electronics: tunneling, alignment of energy levels, activated electron transfer, redox exchange, and reorganization during redox reactions.…”