A quantum circuit rule for interference effects in single-molecule electrical junctions

TL;DR

This study establishes a quantum circuit rule linking interference effects to conductance in oligo(phenyleneethynylene) molecules, combining experimental and theoretical insights to reveal how molecular structure influences electrical properties.

Contribution

It introduces a quantum circuit rule for interference effects in single-molecule conductance, validated through experiments and theoretical analysis of specific aromatic molecules.

Findings

Conductance is dominated by quantum interference in the central ring.

The conductance ratios follow a specific quantum circuit rule.

The contribution of the central ring is independent of anchor group connectivity.

Abstract

A quantum circuit rule for combining quantum interference (QI) effects in the conductive properties of oligo(phenyleneethynylene) (OPE)-type molecules possessing three aromatic rings was investigated both experimentally and theoretically. Molecules were of the type X-Y-X, where X represents pyridyl anchors with para (p), meta (m) or ortho (o) connectivities and Y represents a phenyl ring with p and m connectivities. The conductances GXmX (GXpX) of molecules of the form X-m-X (X-p-X), with meta (para) connections in the central ring were predominantly lower (higher), irrespective of the meta, para, or ortho nature of the anchor groups X, demonstrating that conductance is dominated by the nature of QI in the central ring Y. The single-molecule conductances were found to satisfy the quantum circuit rule Gppp/Gpmp = Gmpm/Gmmm. This demonstrates that the contribution to the conductance from the central ring is independent of the para versus meta nature of the anchor groups.