Highly conducting single-molecule topological insulators based on mono- and di-radical cations

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Liang Li, Jonathan Z. Low, Jan Wilhelm, Guanming Liao, Suman Gunasekaran, Claudia R. Prindle, Rachel L. Starr, Dorothea Golze, Colin Nuckolls, Michael L. Steigerwald, Ferdinand Evers, Luis M. Campos, Xiaodong Yin, Latha Venkataraman

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Nature Chemistry

Single-molecule topological insulators are promising candidates as conducting wires over nanometre length scales. A key advantage is their ability to exhibit quasi-metallic transport, in contrast to conjugated molecular wires which typically exhibit a low conductance that decays as the wire length increases. Here, we study a family of oligophenylene-bridged bis(triarylamines) with tunable and stable mono- or di-radicaloid character. These wires can undergo one- and two-electron chemical oxidations to the corresponding mono-cation and di-cation, respectively. We show that the oxidized wires exhibit reversed conductance decay with increasing length, consistent with the expectation for Su–Schrieffer–Heeger-type one-dimensional topological insulators. The 2.6-nm-long di-cation reported here displays a conductance greater than 0.1G0, where G0 is the conductance quantum, a factor of 5,400 greater than the neutral form. The observed conductance–length relationship is similar between the mono-cation and di-cation series. Density functional theory calculations elucidate how the frontier orbitals and delocalization of radicals facilitate the observed non-classical quasi-metallic behaviour.

 

https://www.nature.com/articles/s41557-022-00978-1