Charge transfer in molecular conductors -- oxidation or reduction?

TL;DR

This paper explores how charge transfer in molecular conductors depends on the Fermi energy position and contact coupling, affecting oxidation or reduction, with implications for molecular electronic devices.

Contribution

It introduces a level diagram approach to determine charge transfer nature and analyzes transport mechanisms in Tour-Reed switching molecules.

Findings

Charge transfer sign depends on Fermi energy relative to molecular levels.

Coupling strength influences charge transfer behavior.

Transport involves oxidation of HOMO-based levels in specific molecules.

Abstract

We discuss the nature of charge transfer in molecular conductors upon connecting to two metallic contacts and imposing a voltage bias across them. The sign of the charge transfer (oxidation vs. reduction) depends on the position of the metal Fermi energy with respect to the molecular levels. In addition, the charge transfer depends on the strength of the coupling (chemisorption vs. physisorption) with the contacts. A convenient way to establish the nature and onset of the charge transfer and the corresponding features in the I-V is to draw an energy level diagram for each spin species. Starting from such a level diagram, we argue that transport in the Tour-Reed switching molecules, which consist of a central phenyl ring with a nitroamine redox center, involves the oxidation of a highest occupied molecular orbital (HOMO)-based level.