Extreme anti-ohmic conductance enhancement in neutral diradical acene-like molecular junctions

TL;DR

This study demonstrates room-temperature anti-ohmic conductance enhancement in neutral diradical acene-like molecular junctions, driven by topological electronic states and quantum interference, with potential for highly conductive nanoscale wires.

Contribution

It introduces a new class of molecules exhibiting anti-ohmic behavior due to topological states and quantum interference, supported by experimental and theoretical analysis.

Findings

Conductance increases over two orders of magnitude with molecular length.

Anti-ohmic trend is linked to diradical character and topological states.

Synthetic tuning of diradical character can control conductance behavior.

Abstract

We achieve, at room temperature, conductance enhancements over two orders of magnitude in single molecule circuits formed with polycyclic benzoquinoidal (BQn) diradicals upon increasing molecular length by ~0.5 nm. We find that this extreme and atypical anti-ohmic conductance enhancement at longer molecular lengths is due to the diradical character of the molecules, which can be described as a topologically non-trivial electronic state. We adapt the 1D-SSH model originally developed to examine electronic topological order in linear carbon chains to the polycyclic systems studied here and find that it captures the anti-ohmic trends in this molecular series. The mechanism of conductance enhancement with length is revealed to be constructive quantum interference (CQI) between the frontier orbitals with non-trivial topology, which is present in acene-like, but not in linear, molecular systems. Importantly, we predict computationally and measure experimentally that anti-ohmic trends can be engineered through synthetic adjustments of the diradical character of the acene-like molecules. Overall, we achieve an experimentally unprecedented anti-ohmic enhancement and mechanistic insight into electronic transport in a class of materials that we identify here as promising candidates for creating highly conductive and tunable nanoscale wires.