New copolyfluorenes (PSiC8OF0 similar to PSiC8OF50) composed of 9,9-dioctylfluorene, jacketed units 2,5-bis[(5-octyloxy-phenyl)-1,3,4-oxadiazole]-l-(3,5-dibromophenyl)-benzene (35C8) and 2,5-bis(trimethylsilyl)benzene were synthesized by palladium-catalyzed Suzuki coupling reaction. They were characterized by GPC, H-1 NMR, elemental analysis, DSC, TGA, absorption and emission spectroscopy, and cyclic voltammetry (CV). These copolymers were readily soluble in common organic solvents and exhibited high glass transition temperature (up to 173 degrees C). The copolymer films showed absorption peaks from 325 to 337 nm, and PL peaks from 402 to 408 nm with a great blue shift relative to polyfluorene (377 and 432 nm) originated from silyl and jacketed units. The transient PL spectra show a rapid rise in the lifetime, implying a sharp increase in molecular rigidity and an additional long decay time around 5 similar to 6 ns, assigned to an "excimer-like" state, and its contribution increases with the increased jacketed fraction. The HOMO energy levels and LUMO levels changed from -5.59 similar to-6.07. eV and -2.60 similar to-3.01 eV as the incorporation of silyl and jacketed units, which facilitated electron injection. Electroluminescent devices: ITO/PEDOT:PSS/PVK/polymer/TPBI (15nm)/Ca (30 nm)/Ag (80 nm) were fabricated to investigate the influence of jacketed and silyl contents on the emission characteristics. The maximum current efficiency and external quantum efficiency of the PSiC8OF5 device (0.484 cd/A and 1.35%) surpassed those of the PC8OF0 device (0.416 cd/A and 0.51%). The EL emissions of PSiC8OF0 and PSiC8OF5 were bright blue and pure blue with sharp emissions, respectively, while PSiC8OF10 similar to PSiC8OF50 showed emissions between them. This indicates that copolymer PSiC8OF5 could be a good candidate for blue light-emitting materials.