Formation of Ground State Triplet Diradicals from Annulated Rosarin Derivatives by Triprotonation

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• 作者：Shunichi Fukuzumi ; Kei Ohkubo ; Masatoshi Ishida ; Christian Preihs ; Bo Chen ; Weston Thatcher Borden ; Dongho Kim ; Jonathan L. Sessler
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：August 12, 2015
• 年：2015
• 卷：137
• 期：31
• 页码：9780-9783
• 全文大小：320K
• ISSN：1520-5126

文摘

Annulated rosarins, 尾,尾鈥?bridged hexaphyrin(1.0.1.0.1.0) derivatives 1鈥?b>3, are formally 24 蟺-electron antiaromatic species. At low temperature, rosarins 2 and 3 are readily triprotonated in the presence of trifluoroacetic acid in dichloromethane to produce ground state triplet diradicals, as inferred from electron paramagnetic resonance (EPR) spectral studies. From an analysis of the fine structure in the EPR spectrum of triprotonated rosarin H₃3³⁺, a distance of 3.6 脜 between the two unpaired electrons was estimated. The temperature dependence of the singlet鈥搕riplet equilibrium was determined by means of an EPR titration. Support for these experimental findings came from calculations carried out at the (U)B3LYP/6-31G* level, which served to predict a very low-lying triplet state for the triprotonated form of a simplified model system 1.