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Huang R, Phan H, Herng TS, et al. Higher Order π-Conjugated Polycyclic Hydrocarbons with Open-Shell Singlet Ground State: Nonazethrene versus Nonacene. J Am Chem Soc. 2016;138(32):10323-30doi: 10.1021/jacs.6b06188.
Huang, R., Phan, H., Herng, T. S., Hu, P., Zeng, W., Dong, S. Q., Das, S., Shen, Y., Ding, J., Casanova, D., & Wu, J. (2016). Higher Order π-Conjugated Polycyclic Hydrocarbons with Open-Shell Singlet Ground State: Nonazethrene versus Nonacene. Journal of the American Chemical Society, 138(32), 10323-30. https://doi.org/10.1021/jacs.6b06188
Huang, Rui, et al. "Higher Order π-Conjugated Polycyclic Hydrocarbons with Open-Shell Singlet Ground State: Nonazethrene versus Nonacene." Journal of the American Chemical Society vol. 138,32 (2016): 10323-30. doi: https://doi.org/10.1021/jacs.6b06188
Huang R, Phan H, Herng TS, Hu P, Zeng W, Dong SQ, Das S, Shen Y, Ding J, Casanova D, Wu J. Higher Order π-Conjugated Polycyclic Hydrocarbons with Open-Shell Singlet Ground State: Nonazethrene versus Nonacene. J Am Chem Soc. 2016 Aug 17;138(32):10323-30. doi: 10.1021/jacs.6b06188. Epub 2016 Aug 04. PMID: 27435865.
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J Am Chem Soc. 2016 Aug 17;138(32):10323-30. doi: 10.1021/jacs.6b06188. Epub 2016 Aug 04.

Higher Order π-Conjugated Polycyclic Hydrocarbons with Open-Shell Singlet Ground State: Nonazethrene versus Nonacene.

Journal of the American Chemical Society

Rui Huang, Hoa Phan, Tun Seng Herng, Pan Hu, Wangdong Zeng, Shao-Qiang Dong, Soumyajit Das, Yongjia Shen, Jun Ding, David Casanova, Jishan Wu

Affiliations

  1. Department of Chemistry, National University of Singapore , Science Drive 3, 117543, Singapore.
  2. Key Laboratory of Advanced Material, Department of Chemistry, East China University of Science and Technology , 130 Meilong Road, Shanghai, 200237, China.
  3. Department of Materials Science and Engineering, National University of Singapore , 119260, Singapore.
  4. IKERBASQUE - Basque Foundation for Science & Donostia International Physics Center & Kimika Fakultatea, Euskal Herriko Unibertsitatea , Paseo Manuel de Lardizabal, 4, 20018 Dgonostia-San Sebastián, Euskadi, Spain.
  5. Institute of Materials Research and Engineering, A*STAR , 2 Fusionopolis Way, Innovis #08-03, 138634, Singapore.

PMID: 27435865 DOI: 10.1021/jacs.6b06188

Abstract

Higher order acenes (i.e., acenes longer than pentacene) and extended zethrenes (i.e., zethrenes longer than zethrene) are theoretically predicted to have an open-shell singlet ground state, and the radical character is supposed to increase with extension of molecular size. The increasing radical character makes the synthesis of long zethrenes and acenes very challenging, and so far, the longest reported zethrene and acene derivatives are octazethrene and nonacene, respectively. In addition, there is a lack of fundamental understanding of the differences between these two closely related open-shell singlet systems. In this work, we report the first synthesis of a challenging nonazethrene derivative, HR-NZ, and its full structural and physical characterizations including variable temperature NMR, ESR, SQUID, UV-vis-NIR absorption and electrochemical measurements. Compound HR-NZ has an open-shell singlet ground state with a moderate diradical character (y0 = 0.48 based on UCAM-B3LYP calculation) and a small singlet-triplet gap (ΔES-T = -5.2 kcal/mol based on SQUID data), thus showing magnetic activity at room temperature. It also shows amphoteric redox behavior, with a small electrochemical energy gap (1.33 eV). Its electronic structure and physical properties are compared with those of Anthony's nonacene derivative JA-NA and other zethrene derivatives. A more general comparison between higher order acenes and extended zethrenes was also conducted on the basis of ab initio electronic structure calculations, and it was found that zethrenes and acenes have very different spatial localization of the unpaired electrons. As a result, a faster decrease of singlet-triplet energy gap and a faster increase of radical character with increase of the number of benzenoid rings were observed in zethrene series. Our studies reveal that spatial localization of the frontier molecular orbitals play a very important role on the nature of radical character as well as the excitation energy.

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