title: Formation of Ground State Triplet Diradicals from Annulated Rosarin Derivatives by Triprotonation.
abstract: Annulated rosarins, β,β'-bridged hexaphyrin(1.0.1.0.1.0) derivatives 1-3, are formally 24 π-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 H₃3(3+), a distance of 3.6 Å between the two unpaired electrons was estimated. The temperature dependence of the singlet-triplet 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.
authors.affiliation: †Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA and SENTAN, Japan Science and Technology (JST), Suita, Osaka 565-0871, Japan.|‡Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.|§Faculty of Science and Engineering, ALCA, SENTAN, Japan Science and Technology Agency (JST), Meijo University, Nagoya, Aichi 468-0073, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.affiliation: †Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA and SENTAN, Japan Science and Technology (JST), Suita, Osaka 565-0871, Japan.|‡Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.affiliation: ∥Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Ishida
authors.affiliation: ⊥Department of Chemistry, The University of Texas, Austin, Texas 78712-1224, United States.
authors.forename: Christian
authors.initials: C
authors.lastname: Preihs
authors.affiliation: #Department of Chemistry and the Center for Advanced, Scientific Computing and Modeling, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5070, United States.
authors.forename: Bo
authors.initials: B
authors.lastname: Chen
authors.affiliation: #Department of Chemistry and the Center for Advanced, Scientific Computing and Modeling, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5070, United States.
authors.forename: Weston Thatcher
authors.initials: WT
authors.lastname: Borden
authors.affiliation: ∥Department of Chemistry, Yonsei University, Seoul 120-749, Korea.
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.affiliation: ∥Department of Chemistry, Yonsei University, Seoul 120-749, Korea.|⊥Department of Chemistry, The University of Texas, Austin, Texas 78712-1224, United States.
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler