DFT Study on Structural Distortion and Vibronic Coupling of Vanadyl Porphyrin Anion and Cation

The geometries of one-electron reduced/oxidized species (TOP^-/VOP⁺) of vanadyl por-phyrin (VOP) have been calculated with PBE1PBE method. The results show that for both VOP^- and VOP⁺ the ground states are triplet, in which one of the two unpaired electron occupies the d_xy orbital of the V atom while the other occupies the π-orbital of porphyrin ring. Thus both VOP^- and VOP⁺ can be considered as π-radicals. The ground state of neutral VOP molecule is doublet with the unpaired electron occupying d_xy orbital of V atom. In contract to the C_4v symmetry of neutral VOP molecule, VOP^- anion has a "rectangular" distorted C_2v structure due to Jahn-Teller effect. The linear vibronic coupling constants for the Jahn-Teller active modes of TOP^- were evaluated and the node patterns of frontier KS orbitals are used to explain the reason why the distortion occurs along specific modes. The ground state VOP⁺ has a porphyrin ring with pronounced bond length alternation due to pseudo-Jahn-Teller effect, causing its symmetry declined from C_4v to C₄. The bond length alternation is well explained with the node patterns of re-constructed frontier KS orbitals.