Synthesis and light emitting properties of fluorene-carbazole-based conjugated copolymers

A novel series of soluble conjugated copolymers comprised of 9,9′-bis(2-ethylhexylfluorene) and comonomer included carbazole moiety, 3,6-bis[1-{4-bromobenz(1-cyanovinylene)}]-9-(2-ethylhexyl)-carbazole (BCEC), were synthesized by nickel-catalyzed Yamamoto coupling reaction. The resulting copolymers exhibit good solubility in common organic solvents such as chloroform, chlorobenzene, etc. and good thermal stability. The copolymers are also easily cast in thin film on glass substrate. By means of the feed ratio, the electronic and optical properties of the polymers were tuned. The UV-Vis spectra of polymers exhibit absorption band at about 382nm. These polymers showed photoluminescence (PL) maxima at 466 and 479nm, respectively. The electroluminescence (EL) spectrum results were similar to the PL spectra. However, the EL spectra showed the possibility of the white light emission through the electroplex emission around 700nm from the single polymer device. The EL spectra of the devices were little changed with the various current densities.