Electronic Structure of Porphyrins. I. SCF-MO-CI Calculation Based on π-Electron Approximation

The electronic structure and electronic spectra of metal free and metal porphyrins have been investigated by the MO method. In order to elucidate the effect of electron correlation on the electronic transitions, a new approximation for electron repulsion integral has been examined. For metal free porphyrin, the effect of hydrogen bondings on the electronic transitions has also been investigated. In metal porphyrin, the present calculation showed that almost two units of charges are transferred from the ligand porphyrin to the central metal ion through σ-type co-ordination bond. A satisfactory agreement between the calculated results and the experimental data was obtained when a new expression for electron repulsion integral, in which the effect of electron correlation is considered, was used. It was found that the Soret band of metal free porphyrin consists of almost degenerated Bx and By species.