Synthesis of fluorene-based hyperbranched polymers for solution-processable blue, green, red, and white light-emitting devices

For the purpose of making hyperbranched polymer (Hb-Ps)-based red, green, blue, and white polymer light-emitting diodes (PLEDs), three Hb-Ps Hb-terfluorene (Hb-TF), Hb-4,7-bis(9,9′-dioctylfluoren-2-yl)-2,1,3- benzothiodiazole (Hb-BFBT), and Hb-4,7-bis[(9,9′-dioctylfluoren-2-yl)- thien-2-yl]-2,1,3-benzothiodiazole (Hb-BFTBT) were synthesized via [2+2+2] polycyclotrimerization of the corresponding diacetylene-functionalized monomers. All the synthesized polymers showed excellent thermal stability with degradation temperature higher than 355 °C and glass transition temperatures higher than 50 °C. Photoluminance (PL) and electroluminance (EL) spectra of the polymers indicate that Hb-TF, Hb-BFBT, and Hb-BFTBT are blue-green, green, and red emitting materials. Maximum brightness of the double-layer devices of Hb-TF, Hb-BFBT, and Hb-BFTBT with the device configuration of indium tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)/light-emitting polymer/CsF/Al are 48, 42, and 29 cd/m 2; the maximum luminance efficiency of the devices are 0.01, 0.02, and 0.01 cd/A. By using host-guest doped system, saturated red electrophosphorescent devices with a maximum luminance efficiency of 1.61 cd/A were obtained when Hb-TF was used as a host material doped with Os(fptz) 2(PPh 2Me 2) 2 as a guest material. A maximum luminance efficiency of 3.39 cd/A of a red polymer light-emitting device was also reached when Hb-BFTBT was used as the guest in the PFO (Poly(9,9-dioctylfluorene)) host layer. In addition, a series of efficient white devices were, which show low turn-on voltage (3.5 V) with highest luminance efficiency of 4.98 cd/A, maximum brightness of 1185 cd/m 2, and the Commission Internationale de l'Eclairage (CIE) coordinates close to ideal white emission (0.33, 0.33), were prepared by using BFBT as auxiliary dopant. © 2011 Wiley Periodicals, Inc.