Polyfluorenes have emerged as the most attractive blue-green emitting polymers due to their high efficiency and good thermal stability. It is well known, however, that strong interchain interactions, e.g. excimer formation, in these polymers can lead to luminescence quenching and color change. To improve the color stability, a copolymer has been prepared by coupling of binaphthyl with dialkyl fluorene. Electroluminescence devices were fabricated using the copolymer as a light-emitting layer, and their opto-electric characteristics were evaluated and compared with a device using the homopolymer. Virtually no difference was found in the photoluminescence spectrum of the copolymer film before and after annealing process, indicating improved thermal stability by introducing binaphthyl into the polymer chain. The linearly polarized electroluminescence was observed from the device using the copolymer even without rubbing the substrate.
