Evaluation of charge resonance character in the excited triplet dimers studied by time-resolved electron paramagnetic resonance: Aromatic ring-bridged porphyrin dimers

Zero-field splittings (zfs) of the lowest excited triplet states were obtained by time-resolved EPR for aromatic ring-bridged porphyrin dimers having different interplanar distances. The zfs parameter D (=-3Z/2) of the dimer decreased with decreasing the interplanar distance (R). From comparison of the D value of the dimer with that of the corresponding monomer, a contribution of CR character (b²) was evaluated as a function of R. An interplanar resonance integral (β₁ + β₂) was estimated from b² and the magnitude of a red shift of T₁ (ΔE(T₁)). b² and β₁ + β₂ correlated well with both of ΔE(T₁) and the triplet lifetime in the dimer. All the results were interpreted well in terms of delocalization of excitation over the dimer molecule, namely the charge resonance interaction.