Many qualitative structure–property correlations between diradical character and emerging molecular properties are known. For example, the increase of diradical character further decreases the singlet–triplet energy gap. Here we show that inclusion of thiophenes within a quinoidal polycyclic hydrocarbon imparts appreciable diradical character yet retains the large singlet–triplet energy gap, a phenomenon that has no precedent in the literature. The low aromatic character of thiophene and its electron-rich nature are the key properties leading to these unique findings. A new indenoindenodibenzothiophene scaffold has been prepared and fully characterized by several spectroscopies, magnetic measurements, solid-state X-ray and state-of-the-art quantum chemical calculations, all corroborating this unique dichotomy between the diradical input and the emerging magnetic properties. New structure–property relationships such as these are not only extremely important in the field of diradical chemistry and organic electronics, but also provide new insights into the versatility of π-electron chemical bonding.

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Data availability

Crystallographic data for the structure reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition no. CCDC 1832752 (10a). Copies of the data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif. All other data supporting the findings of this study are available within the Article and its Supplementary Information, or from the corresponding author upon reasonable request.

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This work was supported by the US National Science Foundation (CHE-1565780), by the Spanish Government, MINECO (CTQ2015-69391-P, CTQ2016-80955 and CTQ2017-87201-P) and Generalitat Valenciana (Prometeo II / 2014 / 076), and by the Japan Society for the Promotion of Science (JSPS, KAKENHI grant nos. JP15J04949, JP25248007, JP17H05157, JP18H01943, JP18J10067 and JP26107004). The authors acknowledge support from the Biomolecular Mass Spectrometry Core of the Environmental Health Sciences Core Center at Oregon State University (NIH P30ES000210). M.N. also thanks King Khalid University for financial support through grant no. RCAMS/KKU/001-16 from the Research Center for Advanced Materials Science at King Khalid University, Kingdom of Saudi Arabia. Theoretical calculations were partly performed at the Research Center for Computational Science, Okazaki, Japan.

Author information


  1. Department of Chemistry & Biochemistry and the Materials Science Institute, University of Oregon, Eugene, OR, USA

    • Justin J. Dressler
    • , Mitsuru Teraoka
    •  & Michael M. Haley
  2. Department of Physical Chemistry, University of Málaga, Málaga, Spain

    • Guzmán L. Espejo
    •  & Juan Casado
  3. Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan

    • Ryohei Kishi
    • , Shota Takamuku
    •  & Masayoshi Nakano
  4. Instituto de Ciencia Molecular, Universidad de Valencia, Paterna, Spain

    • Carlos J. Gómez-García
  5. CAMCOR, University of Oregon, Eugene, OR, USA

    • Lev N. Zakharov
  6. Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan

    • Masayoshi Nakano
  7. Institute for Molecular Science, Myodaiji, Okazaki, Japan

    • Masayoshi Nakano


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J.J.D. and M.T. designed and carried out the experiments. J.J.D. analysed the data and wrote the manuscript. M.M.H. conceived the project and played a critical role in discussions of the experimental design, project direction, experiments and results, and preparation of the manuscript. C.J.G.G. carried out the SQUID magnetic measurements and DSC measurements. G.L.E. acquired and analysed the cyclic voltammetry data and performed the Raman spectroscopic measurements. L.N.Z. acquired and analysed the X-ray crystallographic data. J.C. interpreted the spectroscopic data and co-wrote the paper. R.K., S.T. and M.N. performed the calculations and wrote the discussion on geometry optimization, the open-shell character and the S–T gaps. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Masayoshi Nakano or Juan Casado or Michael M. Haley.

Supplementary information

  1. Supplementary information

    Synthesis details and copies of NMR spectra, variable temperature NMR and SQUID magnetic data, X-ray diffraction details for 10a, cyclic voltammetry and Raman spectroscopy, additional computational details and cartesian coordinates of calculated systems, and a detailed explanation of the relationship between S–T gap and diradical character

  2. Crystallographic data

    CIF for compound 10a; CCDC reference: 1832752

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