Density Functional Theory Based Configuration Interaction Calculations on the Electronic Spectra of Free-Base Porphyrin, Chlorin, Bacteriochlorin, and cis- and trans-Isobacteriochlorin

Configuration interaction calculations with single excitations based on density functional theory (DFT/SCI) provide a reasonably accurate description of the electronic spectra of prototype porphyrin-type molecules at modest computational cost. The calculations reproduce the experimentally observed Q−B energy splitting, differences in Q and B oscillator strengths, and the intensification, relative to porphyrin, of Q x bands of hydroporphyrins. In all cases, the DFT/SCI results are in comparable or better agreement with experiment, compared to recent ab initio CASPT2, SAC−CI, and STEOM-CCSD calculations.