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Greatly Enhanced Intermolecular π‐Dimer Formation of a Porphyrin Trimer Radical Trications through Multiple π Bonds
Author(s) -
Takai Atsuro,
Gros Claude P.,
Barbe JeanMichel,
Fukuzumi Shunichi
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002822
Subject(s) - porphyrin , trimer , chemistry , dimer , photochemistry , triphenylamine , electron paramagnetic resonance , monomer , radical ion , delocalized electron , nuclear magnetic resonance , polymer , organic chemistry , ion , physics
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‐TPZn 3 3+ ), in which each porphyrin ring undergoes a one‐electron oxidation. The radical trication TPA‐TPZn 3 3+ spontaneously dimerizes to afford (TPA‐TPZn 3 ) 2 6+ in CH 2 Cl 2 . The characteristic charge‐resonance band due to the charge delocalization over the π system of (TPA‐TPZn 3 ) 2 6+ was observed in the NIR region. The initial oxidation potential of TPA‐TPZn 3 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., Δ H , Δ S , and Δ G ) for the formation of (TPA‐TPZn 3 ) 2 6+ were determined by measuring Vis/NIR spectra at various temperatures. The formation constant of (TPA‐TPZn 3 ) 2 6+ is significantly larger than that of the radical cation dimer of the corresponding monomer porphyrin (e.g., over 2000‐fold at 233 K). The electronic states were investigated using EPR spectroscopic analysis. The greatly enhanced dimerization of TPA‐TPZn 3 3+ results from multiple π‐bond formation between the porphyrin radical cations.