Time-dependent density functional calculations on the electronic absorption spectra of an asymmetric meso-substituted porphyrin and its zinc complex

In the present work, the time-dependent density functional theory (TD-DFT) is applied to study the electronic transitions which give rise to the near-ultraviolet−visible (near-UV−vis) optical absorptions of 3,4-dimethyl-N-{2-[10,15,20-tris-(3,5-di-tert-butyl-phenyl)-porphyrin-5-yl]-phenyl} benzamide (H2P−O34) and its zinc complex ZnP−O34. Optimizations of the molecular structures were performed using the GGA type Perdew−Burke−Ernzerhof exchange-correlation functional. Excitation energies and oscillator strengths were obtained from the TD-DFT calculations. Calculations were also carried out by using the BP and B3LYP functionals. A large number of electronic transitions are responsible for the optical absorptions in the near-UV−vis region. It was also found that distortions induced to the porphyrin ring by the substituents contribute