An important impact of the molecule-electrode couplings asymmetry on the efficiency of bias-driven redox processes in molecular junctions

TL;DR

This paper demonstrates that asymmetric molecule-electrode couplings in molecular junctions significantly enhance the efficiency of bias-driven redox processes, guiding better nanofabrication strategies for molecular electronics.

Contribution

It provides a general theoretical argument favoring asymmetric coupling and electrochemical environments for improved control over molecular redox states in junctions.

Findings

Asymmetric coupling enhances redox process efficiency.

Electrochemical environments offer advantages over dry setups.

Guidelines for optimal nanofabrication of molecular junctions.

Abstract

Two recent experimental (Li, J.~\emphj{et al}, \emph{Proc.\ Natl.\ Acad.\ Sci.\ U.~S.~A.} {\bf 2014}, 111, 1282-1287) and theoretical studies (B\^aldea, I, \emph{Phys.\ Chem.\ Chem.\ Phys.}\ {\bf 2014}, 16, 25942-25949) have addressed the problem of tuning molecular charge and vibrational properties of single molecules embedded in nanojunctions. These are molecular characteristics escaping so far to an efficient experimental control in broad ranges. Here, we present a general argument demonstrating why, out of various experimental platforms possible, those wherein active molecules are asymmetrically coupled to electrodes are to be preferred to those symmetrically coupled for achieving a(n almost) complete redox process, and why electrochemical environment has advantages over "dry" setups. This study aims at helping to nanofabricate molecular junctions using the most appropriate platforms enabling the broadest possible bias-driven control of the redox state and vibrational modes of single molecules linked to electrodes.