期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 134, 期 35, 页码 14513-14525出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja3050579
关键词
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资金
- BMRC-NMRC [10/1/21/19/642]
- MOE Tier 2 grant [MOE2011-T2-2-130]
- IMRE [IMRE/10-1P0509]
- WCU (World Class University) programs [R32-2010-10217-0]
- AFSOR/APARD grant [FA2386-09-1-4092]
- KAUST
- Ministerio de Educacion y Ciencia (MEC) of Spain
- FEDER funds [CTQ2009-10098, PO9-4708]
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 FeCl3 and/or concentrated H2SO4. The open-shell 2-OS also exhibited a large two-photon absorption (TPA) cross section (760 GM at 1200 nm).
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