Modeling of the energies and splitting of the Qx and Qy bands in positional isomers of zinc pyridinoporphyrazines by TDDFT approach: can TDDFT help distinguishing the structural isomers?

Electronic structures, energies and splitting of the Qx and Qy bands for positional isomers of zinc mono-, di-, tri-, and tetra pyridinoporphyrazines as well as parent zinc phthalocyanine were investigated using density functional theory (DFT) and time-dependent (TD) DFT approaches. The influence of the Hartree-Fock exchange on excited state energies and Qx and Qy bands splitting were studied using GGA BP86 and hybrid B3LYP and PBE1PBE exchange-correlation functionals. Solvent effects were estimated using the polarized continuum model (PCM) approach and cyclohexane, toluene, or DMSO as solvents. It was found that general trends in the Qx and Qy band energies and splitting correlate very well with the available experimental data on pyridinoporphyrazines and follow the trends in HOMO-LUMO and HOMO-LUMO+1 energy gaps as well as LUMO-LUMO+1 splitting. TDDFT trends allow estimation of the Qx and Qy band energies and splitting in unknown tripyridinoporphyrazines and in individual positional isomers of tetrapyridinoporphyrazines.