A new conjugated light-emitting AB copolymer containing alternating fluorene and naphthalene units, poly{(9,9-di-n-octylfluorenediyl vinylene)-alt-[1,5-(2,6-dioctyloxy)naphthalene vinylene]} (PFV-alt-PNV), was synthesized via Horner-Emmons polymerization. The polymer is completely soluble in common organic solvents and exhibits good thermal stability up to 400 °C. UV-visible, fluorescence and photoluminescence measurements of the copolymer show peak maxima at 427, 500 and 526 nm, respectively. A light-emitting device containing the new polymer was fabricated using a simple indium tin oxide configuration: (ITO)/PEDOT:PSS/PFV-alt-PNV/Al. Measurements of current versus electric field were carried out, with an onset of light emission occurring at 2.5 V. The electroluminescence brightness was observed to reach a maximum of 5000 cd m -2 . Copyright © 2011 Society of Chemical Industry Defect-free poly{(9,9-di-n-octylfluorenediyl vinylene)-alt-[1,5-(2,6-dioctyloxy)naphthalene vinylene]} (PFV-alt-PNV) was prepared via Horner-Emmons coupling. A light-emitting ITO/PEDOT:PSS/PFV-alt-PNV/Al device showed a turn-on voltage of 2.5 V and a maximum electroluminescence brightness of 5000 cd m -2 . © 2011 Society of Chemical Industry.