Molecular structure and visible absorption maximum of cobalt phthalocyanine: Quantum calculations via semi-empirical methods

The geometrical molecular structure of cobalt phthalocyanine was first optimized using the semi-empirical PM3 method and the electronic spectrum was then calculated using the ZINDO/S method. The results showed that the visible absorption maximum of cobalt phthalocyanine was precisely predicted by setting the π–π overlap weighting factor parameter in the ZINDO/S method at 0.793. Furthermore, the study of molecular orbitals indicates that the visible absorption maximum corresponds to electronic transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital. The splitting of the visible absorption maximum is related to the splitting of the doubly degenerated eg molecular orbital.