The copolymerization of 3-methylthiophene (MeT) and fluorene (FE) was successfully achieved in boron trifluoride diethyl etherate by the direct anodic oxidation of the monomer mixtures on a platinum electrode. The optimal feed ratio together with the best suitable potential for their copolymerization was determined. The as-formed copolymer films, which were copolymerized with a feed ratio of FE/MeT = 2:1 at a constant potential of 1.3 V (vs a saturated calomel electrode), had the advantages of both poly(3-methylthiophene) and polyfluorene, such as good electrochemical behavior, high conductivity, excellent thermal stability, and high film quality. The structure of the copolymer was investigated with ultraviolet-visible, infrared spectroscopy, and thermal analysis. Fluorescence spectroscopy studies revealed that the dedoped copolymer film in the solid state was a good blue-light emitter with a strong emission at 435 nm and a shoulder at 459 nm. The emitting properties of the copolymer could be tuned by parameters during the electrochemical polymerization, such as the applied potential and monomer feed ratio. (c) 2006 Wiley Periodicals, Inc.