Hybrid density functional theory (DFT) calculations have been carried out for oligomer species of a fused porphyrin, denoted by P(n), where n represents the number of porphyrin rings in the oligomer, to elucidate the electronic structures at ground and excited states. A polymer of fused porphyrin (p-Por) was also investigated using one-dimensional periodic boundary conditions (PBC) for comparison. It was found that the lowest energy band is located below 0.6 eV in the case of oligomers larger than n = 8, which corresponds to a band gap of p-Por. Carrier transport pathways in p-Por were discussed on the basis of theoretical results. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.