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.
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The data that support the findings were acquired using a custom instrument controlled by custom software (Igor Pro, Wavemetrics). The software is available from the corresponding authors upon reasonable request.
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This work was supported in part by the National Science Foundation under grant DMR-1807580. J.Z.L. thanks the A*STAR Graduate Academy in Singapore for a graduate fellowship. S.G. was supported by a National Science Foundation Graduate Research Fellowship under grant DGE-1644869. C.R.P. was supported by a National Defense Science and Engineering Graduate Fellowship. X.Y. and G.L. acknowledge the Analysis and Testing Center of Beijing Institute of Technology for characterization in NMR and high-resolution mass spectrometry. X.Y. acknowledges the Beijing Institute of Technology Research Fund Program for Young Scholars. G.L. thanks the Project of the Science Funds of Jiangxi Education Office (GJJ180629) and the Project of Jiangxi Science and Technology Normal University (2016XJZD009) for financial support. J.W. and F.E. thank M. Camarasa-Gomez for helpful discussions. J.W. and F.E. acknowledge the Gauss Centre for Supercomputing for providing computational resources on SuperMUC-NG at the Leibniz Supercomputing Centre under project ID pn72pa. The work in Regensburg was supported by the Deutsche Forschungsgemeinschaft (German Research Foundation) through project ID 314695032 (SFB 1277, subprojects A03 and B01).
The authors declare no competing interests.
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Li, L., Low, J.Z., Wilhelm, J. et al. Highly conducting single-molecule topological insulators based on mono- and di-radical cations. Nat. Chem. 14, 1061–1067 (2022). https://doi.org/10.1038/s41557-022-00978-1