Poly(9,9-dioctylfluorene-co-fluorenone) with 1% fluorenone, (PFO-F(1%)), was synthesized as a model compound to investigate the optical and electrical effects of fluorenone defects in poly(9,9-dioctylfluorenyl-2,7-diyl), PFO. Photoluminescence (PL) studies indicate efficient Förster energy transfer from PFO to fluorenone “impurities” which are responsible for the pronounced green emission from PFO-F(1%). In electroluminescence (EL), the more pronounced green emission from PFO-F(1%) results from a combination of Förster energy transfer, charge carrier trapping, and relatively easy injection (from the electrodes) of carriers into the fluorenone traps.