AM I calculations were used to study the charge-separated state of porphyrin analogues as sensitizers. Initial calculations were performed on the donor and acceptor moieties to determine the molecular orbital (MO) energy levels independently. The analogues were modeled by combining the donor and acceptor moieties. The charge-separated state of the porphyrin analogues was analyzed from the MO energy levels of the donor and acceptor moieties, and from the porphyrin analogues (donor-acceptor pairs). MO spatial orientations were also used to elucidate the charge-separated state of the analogues. Our results revealed that the relative positions of the lowest unoccupied molecular orbital (LUMO) levels of the donor and acceptor moieties could predict the MO spatial orientations of the porphyrin analogues, i.e., the donor-acceptor pairs. The LUMO is localized in the acceptor and the highest occupied molecular orbital (HOMO) in the donor region when the difference between LUMOdoor and LUMOacceptor is positive, which indicates a charge-separated state. Of the molecular models, (Zn-5G) had the smallest HOMO-LUMO gap and had a relative difference of 0.16 eV compared to (Zn-1A), which has a known cell efficiency of 4.8%. (c) 2007 Elsevier B.V. All rights reserved.