Density functional theory study of the electronic absorption spectrum of Mg-porphyrin and Mg-etioporphyrin-I

The electronic absorption spectra of magnesium porphyrin (MgP) and magnesium etioporphyrin I (MgEtioP) have been studied at the density functional theory level using the time-dependent perturbation theory approach. The optimization of the molecular structures was carried out using the Becke-Perdew functional and split-valence quality basis sets augmented by polarization functions. The first excitation energy for MgP and MgEtioP are 2.21 and 2.19 eV, respectively, as compared to the experimental value of 2.14 eV for MgEtioP. For higher excited states, the excitation energies of MgEtioP an about 0.2-0.3 eV smaller than for MgP. (C) 2000 Elsevier Science B.V. All rights reserved.