Density Functional Theory Study of the Solvent Effects on Electronic Transition Energies of Porphyrins

Abstract

We have calculated the solvent effects on the ground state and the lowest triplet state absorption spectra of meso-tetraphenylporphyrin (TPP), meso-tetrakis(p-sulfonatophenyl)porphyrin (TSPP) and their diprotonated forms (H4TPP and H4TSPP) in thirty-nine different solvent using time-dependent-DFT density functional theory (TD-DFT) coupled with CPCM method. The results of the calculations show that the Q-bands and Soret-bands (or B-bands) in the absorption spectra of these compounds substantially change as function of solvent dielectric constant (ε) up to 20.493 (acetone), but become stabile in high polar solvents with dielectric constants ε > 20. The relative shifts in the B-bands are more significant than that in the Q-bands. The magnitude of the shifts in the spectral position of the Q and B bands are in the following order: H4TSPP > H4TPP > TPP > TSPP for the B-bands and H4TSPP > H4TPP > TSPP > TPP for the Q-bands. We also have determined that the energy-gaps between the B/Q-bands and their nearest triplet states are also solvent dependent for ε < ~ 20.493.