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 (b(2)) was evaluated as a function of R. An interplanar resonance integral (beta(1) + beta(2)) was estimated from b(2) and the magnitude of a red shift of T-1 (Delta E(T-1)). b(2) and beta(1) + beta(2) correlated well with both of Delta E(T-1) 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.