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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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.
Tschitschibabin, A. E. Über einige phenylierte Derivate des p,p-Ditolyls. Chem. Ber. 40, 1810–1819 (1907).
Gopalakrishna, T. Y., Zeng, W., Lu, X. & Wu, J. From open-shell singlet diradicaloids to polyradicaloids. Chem. Commun. 54, 2186–2199 (2018).
Di Motta, S., Negri, F., Fazzi, D., Castiglioni, C. & Canesi, E. V. Biradicaloid and polyenic character of quinoidal oligothiophenes revealed by the presence of a low-lying double-exciton state. J. Phys. Chem. Lett. 1, 3334–3339 (2010).
Rudebusch, G. E. et al. Diindeno-fusion of an anthracene as a design strategy for stable organic biradicals. Nat. Chem. 8, 753–759 (2016).
Morita, Y., Suzuki, S., Sato, K. & Takui, T. Synthetic organic spin chemistry for structurally well-defined open-shell graphene fragments. Nat. Chem. 3, 197–204 (2011).
Morita, Y. et al. Organic tailored batteries materials using stable open-shell molecules with degenerate frontier orbitals. Nat. Mater. 10, 947–951 (2011).
Nakano, M. et al. Second hyperpolarizability (γ) of singlet diradical system: dependence of γ on the diradical character. J. Phys. Chem. A 109, 885–891 (2005).
Nakano, M. et al. Relationship between third-order nonlinear optical properties and magnetic interactions in open-shell systems: a new paradigm for nonlinear optics. Phys. Rev. Lett. 99, 033001 (2007).
Nakano, M. & Champagne, B. Theoretical design of open-shell singlet molecular systems for nonlinear optics. J. Phys. Chem. Lett. 6, 3236–3256 (2015).
Minami, T. & Nakano, M. Diradical character view of singlet fission. J. Phys. Chem. Lett. 3, 145–150 (2012).
Smith, M. B. & Michl, J. Recent advances in singlet fission. Annu. Rev. Phys. Chem. 64, 361–386 (2013).
Varnavski, O. et al. High yield ultrafast intramolecular singlet exciton fission in a quinoidal bithiophene. J. Phys. Chem. Lett. 6, 1375–1384 (2015).
Hu, P. & Wu, J. Modern zethrene chemistry. Can. J. Chem. 95, 223–233 (2017).
Zeng, W. et al. Super-heptazethrene. Angew. Chem. Int. Ed. 55, 8615–8619 (2016).
Sun, Z. et al. Dibenzoheptazethrene isomers with different biradical characters: an exercise of Clar’s aromatic sextet rule in singlet biradicaloids. J. Am. Chem. Soc. 135, 18229–18236 (2013).
Li, Y. et al. Kinetically blocked heptazethreene and octazethrene: closed-shell or open-shell in the ground state? J. Am. Chem. Soc. 134, 14913–14922 (2012).
Konishi, A., Hirao, Y., Kurata, H., Kubo, T. & Nakano, M. Anthenes: model systems for understanding the edge state of graphene nanoribbons. Pure Appl. Chem. 86, 497–595 (2014).
Konishi, A. et al. Synthesis and characterization of quarteranthene: elucidating the characteristics of the edge state of graphene nanoribbons at the molecular level. J. Am. Chem. Soc. 135, 1430–1437 (2013).
Kubo, T. et al. Four-stage amphoteric redox properties and biradicaloid character of tetra-tert-butyldicyclopenta[b;d]thieno[1,2,3-cd;5,6,7-c′d]diphenalene. Angew. Chem. Int. Ed. 43, 6474–5479 (2004).
Shimizu, A. et al. Alternating covalent bonding interactions in a one-dimensional chain of a phenalenyl-based singlet biradical molecule having Kekulé structures. J. Am. Chem. Soc. 132, 14421–14428 (2010).
Shimizu, A. et al. Aromaticity and π-bond covalency: prominent intermolecular covalent bonding interaction of a Kekulé hydrocarbon with very significant singlet biradical character. Chem. Commun. 48, 5629–5631 (2012).
Frederickson, C. K., Rose, B. D. & Haley, M. M. Explorations of the indenofluorenes and expanded quinoidal analogues. Acc. Chem. Res. 50, 977–987 (2017).
Chase, D. T. et al. 6,12-Diarylindeno[1,2-b]fluorenes: synthesis photophysics, and ambipolar OFETs. J. Am. Chem. Soc. 134, 10349–10352 (2012).
Shimizu, A. et al. Indeno[2,1-b]fluorene: a 20-π-electron hydrocarbon with very low-energy light absorption. Angew. Chem. Int. Ed. 52, 6076–6079 (2013).
Young, B. S. et al. Synthesis and properties of fully-conjugated indacenedithiophenes. Chem. Sci. 5, 1008–1014 (2014).
Marshall, J. L. et al. Indacenodibeznothiophenes: synthesis, optoelectronic properties and materials applications of molecules with strong antiaromatic character. Chem. Sci. 7, 5547–5558 (2016).
Miyoshi, H. et al. Fluoreno[2,3-b]fluorene vs. indeno[2,1-b]fluorene: unusual relationship between the number of π electrons and excitation energy in m-quinodimethane-type singlet diradicaloids. J. Org. Chem. 82, 1380–1388 (2017).
Barker, J. E., Frederickson, C. K., Jones, M. H., Zakharov, L. N. & Haley, M. M. Synthesis and properties of quinoidal fluorenofluorenes. Org. Lett. 19, 5312–5315 (2017).
Casado, J. Para-quinodimethanes: a unified review of the quinoidal-versus-aromatic competition and its implications. Top. Curr. Chem. 375, 73 (2017).
Zeng, Z. & Wu, J. Stable π-extended p-quinodimethanes: synthesis and tunable ground states. Chem. Rec. 15, 322–328 (2015).
Zeng, Z. et al. Pushing extended p-quinodimethanes to the limit: stable tetracyano-oligo(N-annulated perylene)quiniodimethanes with tunable ground states. J. Am. Chem. Soc. 135, 6363–6371 (2013).
Bendikov, M. et al. Oligoacenes: theoretical predictions of open-shell diradical ground states. J. Am. Chem. Soc. 126, 7416–7417 (2004).
Jiang, D. E. & Dai, S. Electronic ground state of higher acenes. J. Phys. Chem. 112, 332–335 (2008).
Purushothaman, B., Bruzek, M., Parkin, S. R., Miller, A. & Anthony, J. E. Synthesis and structural characterization of crystalline nonacenes. Angew. Chem. Int. Ed. 50, 7013–7017 (2011).
Kubo, T. Recent progress in quinoidal singlet biradical molecules. Chem. Lett. 4, 111–122 (2015).
Sun, Z., Zeng, Z. & Wu, J. Extended zethrenes, p-quinodimethanes and periacenes with a biradical ground state. Acc. Chem. Res. 47, 2582–2591 (2014).
Abe, M. Diradicals. Chem. Rev. 113, 7011–7088 (2013).
Nakano, M. Electronic structure of open-shell singlet molecules: diradical character viewpoint. Top. Curr. Chem. 375, 47 (2017).
Zeng, Z. et al. Pro-aromatic and anti-aromatic π-conjugated molecules: an irresistible wish to become diradicals. Chem. Soc. Rev. 44, 6578–6596 (2015).
Clar, E. The Aromatic Sextet (Wiley, London, 1972).
Yamaguchi, K. The electronic structure of biradicals in the unrestricted Hartree–Fock approximation. Chem. Phys. Lett. 33, 330–335 (1975).
Zeng, W. et al. Phenalenyl-fused porphyrins with different ground states. Chem. Sci. 6, 2427–2433 (2015).
Shi, X. et al. Benzo-thia-fused [n]thienoacenequinodimethanes with small to moderate diradical characters: the role of pro-aromaticity versus antiaromatity. Chem. Sci. 7, 3036–3046 (2016).
Frisch, M. J. et al. Gaussian 09, Revision B.01 (Gaussian, 2009).
Fukuda, K., Nagami, T., Fujiyoshi, J. & Nakano, M. Interplay between open-shell character, aromaticity, and second hyperpolarizablilities in indenofluorenes. J. Phys. Chem. A 119, 10620–10627 (2015).
Bernard, Y. A., Shao, Y. & Krylov, A. I. General formulation of spin-flip time-dependent density functional theory using non-collinear kernels: theory, implementation, and benchmarks. J. Chem. Phys. 136, 204103 (2012).
Shao, Y. et al. Advances in molecular quantum chemistry contained the Q-chem 4 program package. Mol. Phys. 113, 184–215 (2014).
Knall, A. et al. Naphthacenodithiophene based polymers—new members of the acenodithiophene family exhibiting high mobility and power conversion efficiency. Adv. Funct. Mater. 26, 6961–6969 (2016).
Nakagawa, H., Kawai, S., Nakashima, T. & Kawai, T. Synthesis of photochemical reaction of photochromic terarylene having a leaving methoxy group. Org. Lett. 11, 1475–1478 (2009).
Schleyer, Pv. R. et al. Dissected nucleus-independent chemical shift analysis of π-aromaticity and antiaromaticity. Org. Lett. 3, 2465–2468 (2001).
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.
The authors declare no competing interests.
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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
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Dressler, J.J., Teraoka, M., Espejo, G.L. et al. Thiophene and its sulfur inhibit indenoindenodibenzothiophene diradicals from low-energy lying thermal triplets. Nature Chem 10, 1134–1140 (2018). https://doi.org/10.1038/s41557-018-0133-5
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