The consequence of unpaired electrons in organic molecules has fascinated and confounded chemists for over a century. The study of open-shell molecules has been rekindled in recent years as new synthetic methods, improved spectroscopic techniques and powerful computational tools have been brought to bear on this field. Nonetheless, it is the intrinsic instability of the biradical species that limits the practicality of this research. Here we report the synthesis and characterization of a molecule based on the diindeno[b,i]anthracene framework that exhibits pronounced open-shell character yet possesses remarkable stability. The synthetic route is rapid, efficient and possible on the gram scale. The molecular structure was confirmed through single-crystal X-ray diffraction. From variable-temperature Raman spectroscopy and magnetic susceptibility measurements a thermally accessible triplet excited state was found. Organic field-effect transistor device data show an ambipolar performance with balanced electron and hole mobilities. Our results demonstrate the rational design and synthesis of an air- and temperature-stable biradical compound.
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This work was supported by the US National Science Foundation (CHE-1301485), by the Spanish Government, MINECO (CTQ2012-33733 and CTQ2011-26507), by Junta de Andalucía (P09-FQM-4708) and Generalitat Valenciana (PrometeoII/2014/076), by a Japan Society for the Promotion of Science (JSPS) Research Fellowship for Young Scientists (No. 15J04949), Grant-in-Aid for Scientific Research (A) (No. 25248007) from the JSPS, a Grant-in-Aid for Scientific Research on Innovative Areas ‘Stimuli-Responsive Chemical Species’ (No. A24109002a), ‘π-System Figuration’ (15H00999), ‘Photosynergetics’ (A26107004a), the Strategic Programs for Innovative Research, Ministry of Education, Culture, Sports, Science & Technology, Japan, the Computational Materials Science Initiative, Japan, the Swedish Research Council (project grant 621-2011-4177) and the Swedish National Infrastructure for Computation (NSC, Linköping). K.J. and H.O. thank R. Herges for providing the AICD 2.0.0 program. The authors acknowledge the Biomolecular Mass Spectrometry Core of the Environmental Health Sciences Core Center at Oregon State University (NIH P30ES000210). We thank T. Kubo (Osaka) for insightful discussions.
The authors declare no competing financial interests.
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Rudebusch, G., Zafra, J., Jorner, K. et al. Diindeno-fusion of an anthracene as a design strategy for stable organic biradicals. Nature Chem 8, 753–759 (2016). https://doi.org/10.1038/nchem.2518
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