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Title: Stable tetrabenzo-Chichibabin's hydrocarbons: Tunable ground state and unusual transition between their closed-shell and open-shell resonance forms
Authors: 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. 
Issue Date: 5-Sep-2012
Citation: 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. (2012-09-05). 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. ScholarBank@NUS Repository.
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). © 2012 American Chemical Society.
Source Title: Journal of the American Chemical Society
ISSN: 00027863
DOI: 10.1021/ja3050579
Appears in Collections:Staff Publications

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