Amine-Linked Single Molecule Circuits: Systematic Trends Across Molecular Families

TL;DR

This paper reviews single molecule junction conductance measurements with amine linkers, unifies the bonding and tunneling mechanisms through DFT calculations, and compares theoretical trends with experimental data across various molecules.

Contribution

It provides a systematic analysis of conductance trends in amine-linked molecules and introduces a theoretical framework that explains experimental variability and bonding characteristics.

Findings

Conductance varies from 10^-7 G0 to 10^-2 G0.

Theoretical trends agree within a factor of two with experiments.

Bonding involves donor-acceptor interactions with gold atoms.

Abstract

A comprehensive review is presented of single molecule junction conductance measurements across families of molecules measured while breaking a gold point contact in a solution of molecules with amine end groups. A theoretical framework unifies the picture for the amine-gold link bonding and the tunnel coupling through the junction using Density Functional Theory based calculations. The reproducible electrical characteristics and utility for many molecules is shown to result from the selective binding between the gold electrodes and amine link groups through a donor-acceptor bond to undercoordinated gold atoms. While the bond energy is modest, the maximum force sustained by the junction is comparable to, but less than, that required to break gold point contacts. The calculated tunnel coupling provides conductance trends for all 41 molecule measurements presented here, as well as insight into the variability of conductance due to the conformational changes within molecules with torsional degrees of freedom. The calculated trends agree to within a factor of two of the measured values for conductance ranging from 10-7 G0 to 10-2 G0, where G0 is the quantum of conductance (2e2/h).