Stable tetrabenzo-Chichibabin's hydrocarbons: Tunable ground state and unusual transition between their closed-shell and open-shell resonance forms

Zebing Zeng, Young Mo Sung, Nina Bao, Davin Tan, Richmond Lee, José L. Zafra, Byung Sun Lee, Masatoshi Ishida, Jun Ding, Juan T. López Navarrete, Yuan Li, Wangdong Zeng, Dongho Kim, Kuo Wei Huang, Richard D. Webster, Juan Casado, Jishan Wu

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Abstract

Stable open-shell polycyclic aromatic hydrocarbons (PAHs) are of fundamental interest due to their unique electronic, optical, and magnetic properties and promising applications in materials sciences. Chichibabin's hydrocarbon as a classical open-shell PAH has been investigated for a long time. However, most of the studies are complicated by their inherent high reactivity. In this work, two new stable benzannulated Chichibabin's hydrocarbons 1-CS and 2-OS were prepared, and their electronic structure and geometry in the ground state were studied by various experiments (steady-state and transient absorption spectra, NMR, electron spin resonance (ESR), superconducting quantum interference device (SQUID), FT Raman, X-ray crystallographic etc.) and density function theory (DFT) calculations. 1-CS and 2-OS exhibited tunable ground states, with a closed-shell quinoidal structure for 1-CS and an open-shell biradical form for 2-OS. Their corresponding excited-state forms 1-OS and 2-CS were also chemically approached and showed different decay processes. The biradical 1-OS displayed an unusually slow decay to the ground state (1-CS) due to a large energy barrier (95 ± 2.5 kJ/mol) arising from severe steric hindrance during the transition from an orthogonal biradical form to a butterfly-like quinoidal form. The quick transition from the quinoidal 2-CS (excited state) to the orthogonal biradicaloid 2-OS (ground state) happened during the attempted synthesis of 2-CS. Compounds 1-CS and 2-OS can be oxidized into stable dications by FeCl 3 and/or concentrated H 2SO 4. The open-shell 2-OS also exhibited a large two-photon absorption (TPA) cross section (760 GM at 1200 nm).

Original languageEnglish
Pages (from-to)14513-14525
Number of pages13
JournalJournal of the American Chemical Society
Volume134
Issue number35
DOIs
Publication statusPublished - 2012 Sep 5

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All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Zeng, Z., Sung, Y. M., Bao, N., Tan, D., Lee, R., Zafra, J. L., Lee, B. S., Ishida, M., Ding, J., López Navarrete, J. T., Li, Y., Zeng, W., Kim, D., Huang, K. W., Webster, R. D., Casado, J., & Wu, J. (2012). Stable tetrabenzo-Chichibabin's hydrocarbons: Tunable ground state and unusual transition between their closed-shell and open-shell resonance forms. Journal of the American Chemical Society, 134(35), 14513-14525. https://doi.org/10.1021/ja3050579