Fully unsaturated fluoranthene-type ladder polymers (PFA : polyfluoranthene) recently synthesized by Schluter et al. show a high. degree of pi-electron localization. Variation of the size of the two oligoacenic components separated by the characteristic five-membered ring, however, can lead to more delocalized structures with small (few tenths of an electronvolt) band gaps and can be used for engineering the electronic properties. Charge transfer produces bipolaronic defect states in these polymers; sp(3) defects produce polaronic defects. Interpretation of the differences between the published absorption spectra for two members of the PFA family is also given.