Dependence of Single Molecule Junction Conductance on Molecular Conformation

TL;DR

This study demonstrates that the conductance of single biphenyl molecular junctions decreases with increasing twist angle, confirming theoretical predictions and highlighting the importance of molecular conformation in nanoscale electronic devices.

Contribution

The paper provides experimental evidence linking molecular conformation to conductance in single-molecule junctions using amine link groups.

Findings

Conductance decreases with increasing twist angle.

Results are consistent with cosine squared theoretical relation.

Seven biphenyl derivatives show a clear correlation.

Abstract

The conductance of a single metal-molecule-metal junction depends critically on the conformations of the molecule. In the simple case of a biphenyl, two phenyl rings linked together by a single C-C bond, the conductance is expected to depend on the relative twist angle between the two rings, with the planar conformation having the highest conductance. A number of different techniques have measured the conductance of metal-molecule(s)-metal junctions. However, the conductance variation from junction to junction has made it difficult to verify even the simplest predictions about how molecules should behave in unimolecular devices. Here, using amine link groups to form single molecule junctions, we show a clear correlation between molecule conformation and junction conductance in a series of seven biphenyl molecules with different ring substitutions that alter the twist angle of the molecules. We find that the conductance for the series decreases with increasing twist angle, consistent with a cosine squared relation predicted theoretically for transport through pi-conjugated systems.