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 porphyrin (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 dxy 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 dxy orbital of V atom. In contract to the C4v symmetry of neutral VOP molecule, [VOP] − anion has a “rectangular” distorted C2v 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 C4v to C4. The bond length alternation is well explained with the node patterns of re-constructed frontier KS orbitals.