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

Shunichi Fukuzumi, Kei Ohkubo, Masatoshi Ishida, Christian Preihs, Bo Chen, Weston Thatcher Borden, Dongho Kim, Jonathan L. Sessler

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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 H333+, 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.

Original languageEnglish (US)
Pages (from-to)9780-9783
Number of pages4
JournalJournal of the American Chemical Society
Volume137
Issue number31
DOIs
StatePublished - Aug 12 2015

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All Science Journal Classification (ASJC) codes

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

Cite this

Fukuzumi, S., Ohkubo, K., Ishida, M., Preihs, C., Chen, B., Borden, W. T., Kim, D., & Sessler, J. L. (2015). Formation of Ground State Triplet Diradicals from Annulated Rosarin Derivatives by Triprotonation. Journal of the American Chemical Society, 137(31), 9780-9783. https://doi.org/10.1021/jacs.5b05309