In this study, a novel conjugated polymer, poly(4,4-bis(2-ethylhexyl)-4H-cyclopenta[def]phenanthrene-2,6-vinylene) (PCPPV) has been synthesized and characterized. For the polymerization, Gilch's reaction was applied for the first time with the cyclopenta[def]phenanthrene system. The absorption and emission spectra of PCPPV are red-shifted about 40-50 nm due to the vinylene units when compared with those of poly(2,6-(4,4-bis(2-ethylhex-yl)-4H-cyclopenta[def]phenanthrene)) (PCPP). The solid-state fluorescence is significantly broadened, possibly due to pi-pi interactions introduced by the phenanthrene and vinylene moieties. In solution, as the concentration of polar solvent increased, the photoluminescence (PL) intensity decreased due to quenching and aggregation by the interchain interactions between the conjugated backbones. After annealing the film at 80 degrees C, the PL and electroluminescence (EL) emission spectra exhibited also the quenching and aggregation effects indicating the interchain interactions of PCPPV. The large number of aromatic rings in a unit and the increased planarity achieved through introduction of vinylene units are able to give interchain interactions stronger than fluorene or phenylene units. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5068-5077, 2009