Strong colorfast blue photo- and electroluminescence is reported for random high molecular weight poly(fluorene-co-anthracene)s, prepared via the nickel-mediated copolymerization of the corresponding aryl dibromides. The incorporation of anthracene into the main chain is demonstrated to completely suppress excimer formation-a major drawback of many planar pi-systems. Poly(fluorene)s are attractive as active components of organic light-emitting diodes (LEDs) because of their thermal and chemical stability and exceptionally high fluorescence quantum yields.