Greatly enhanced intermolecular π-dimer formation of a porphyrin trimer radical trications through multiple πbonds

Atsuro Takai, Claude P. Gros, Jean Michel Barbe, Shunichi Fukuzumi

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A trefoil-like porphyrin trimer linked by triphenylamine (TPA-TPZn 3) was synthesized. A three-electron oxidation of TPA-TPZn 3 forms a radical trication (TPA-TPZn33+), in which each porphyrin ring undergoes a one-electron oxidation. The radical trication TPA-TPZn33+ spontaneously dimerizes to afford (TPA-TPZn3)26+ in CH2Cl2. The characteristic charge-resonance band due to the charge delocalization over the πsystem of (TPA-TPZn3)26+ was observed in the NIR region. The initial oxidation potential of TPA-TPZn3 is negatively shifted relative to that of the corresponding monomer porphyrin, which results from the stabilization of the oxidized state of TPA-TPZn 3 associated with the dimerization. The thermodynamic parameters (i.e., ΔH, ΔS, and ΔG) for the formation of (TPA-TPZn 3)26+ were determined by measuring Vis/NIR spectra at various temperatures. The formation constant of (TPA-TPZn 3)26+ is significantly larger than that of the radical cation dimer of the corresponding monomer porphyrin (e.g., over 2000-fold at 233K). The electronic states were investigated using EPR spectroscopic analysis. The greatly enhanced dimerization of TPA-TPZn 33+ results from multiple π-bond formation between the porphyrin radical cations. Multiple π bonds: A three-electron oxidation of a trefoil-like porphyrin trimer generates a radical trication, which spontaneously dimerizes. The dimerization of the trimer is much more favorable relative to the corresponding monomer, which results from the intermolecular multiple π-bond formation between porphyrin radical cations of the trimer (see picture).

Original languageEnglish
Pages (from-to)3420-3428
Number of pages9
JournalChemistry - A European Journal
Issue number12
StatePublished - 14 Mar 2011


  • dimerization
  • electron transfer
  • electronic structure
  • multiple bonds
  • pi interactions


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