An electron-transporting 2,5-bis(4-bromophenyl)-1,3,5-oxadiazole (OXD) was incorporated by copolymerization into polyfluorene (PF) end-capped with a 4-bromo-4',4"-dimethyltriphenylamine (TPA) main chains on the Yamamoto coupling method to improve the initial electroluminescence (EL) color stability against applied voltage and the device operation lifetime. The copolymer, PF/OXD-TPA, possessed a high molecular weight enough for film-forming ability and excellent solution-processability, that is, good solubility in common organic solvents such as toluene. An EL device fabricated using this copolymer as a polymeric emission layer allowed the generation of a strong deep-blue EL peaking at 424 nm with a comparatively high EL efficiency of 0.47 cd A -1, and its color was extremely stable against applied voltage within 527 V. The incorporation of OXD units into the PF-TPA system also improved the operation lifetime, although it is not a practical level for displays. The results are probably attributed to the great roles of the incorporated OXD units for disturbing the formation of fluorene excimer sites and for tuning the hole/electron mobility balance..

diphenylsilanes with different alkyl chain lengths (C n = 4 and 8) were synthesized in this work. Conventional 9,9-dialkyl-substituted polyfluorenes (PFs) were modified through copolymerization of the diphenylsilane-containing comonomers by the Suzuki coupling method to improve electroluminescence (EL) color purity. The PF copolymers possessed high molecular weights that were enough for film-forming ability and good solubility in various common organic solvents such as toluene. The incorporation of the diphenylsilane units suppressed effectively the PF-inherent green PL, which is undesirable for the present purpose, with a slight blue-shift of the interesting blue emission band. The results are closely related to a bent and bulky structure at the diphenylsilane units which disturb interchain stacking and a controlled conjugation length along the PF main chains. This effect was observed much more prominently in the EL spectra. Even in the di-n-butyl-substituted PF copolymer which tends to show a strong green excimer emission, the incorporation of the diphenylsilane units completely erased the green EL band. The results suggest that the PF copolymers can be a good candidate as a novel deep-blue emission layer material in EL devices.