Theoretical study on electronic spectrum properties of group 12 bis-metal (II) complexes of [26]hexaphyrin(1.1.1.1.1.1)

The electronic absorption spectra of group 12 bis-metal (II) complexes of [26]hexaphyrin(1.1.1.1.1.1) were systematically investigated using the localized density matrix (LDM) method and the time-dependent density functional theory (TD-DFT). The results show that the LDM method is a reliable approach for determining the electronic transition properties of the complexes and substantially reduces the computational cost. By analyzing the changes in energy and frontier molecular orbitals, this study found that bis-Hg (II) hexaphyrin forms rectangle-shaped complexes easily whereas bis-Zn (II) hexaphyrin and bis-Cd (II) hexaphyrin are more likely to form dumbbell-shaped complexes. In the R-shaped complexes, the absorption characteristics mostly represent Q-like bands from intra-ligand charge transfer transitions of the 26π macrocycle conjugate system, whereas in the D-shaped complexes, the absorption characteristics exhibit B-like bands from ligand-to-metal charge transfer and ligand-to-ligand charge transfer transitions. In addition, the introduction of group 12 transition metals (II) leads to red shifts in the R-shaped complexes and blue shifts in the D-shaped complexes in the spectra of these metal complexes. Moreover, the transition properties of the D-shaped complexes show that the contribution from segmental phenyl rings is even more important at the B-like bands compared with those of the R-shaped complexes in the meso-carbons.