Semiconducting polymers with moderate HOMO-LUMO energy gaps between 1.5 and 2.0 eV are of increasing attraction as donor components of bulk heterojunction type organic solar cells. The synthesis and characterization of a novel cross-conjugated, aromatic polymer, poly(diindenonaphthalene)PDIN, with a HOMO-LUMO gap of ca. 1.6 eV (lambda(max): 724 nm) in comparison to poly(indenofluorene) PIF, a previously described, structurally related polymer, is presented. the replacement of the central benzene ring of PIF by a naphthalene moiety in PDIN leads to an increase of the optical bandgap energy of ca. 0.16 eV.