Synthesis, Photophysics, and Electroluminescence of Copolyfluorenes Containing Jacketed and Silyl Units

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• 作者：Ping Wang ; Qian Yang ; Hao Jin ; Wanli Liu ; Zhihao Shen ; Xiaofang Chen ; Xinghe Fan ; Dechun Zou ; Qifeng Zhou
• 刊名：Macromolecules
• 出版年：2008
• 出版时间：November 25, 2008
• 年：2008
• 卷：41
• 期：22
• 页码：8354-8359
• 全文大小：313K
• 年卷期：v.41,no.22(November 25, 2008)
• ISSN：1520-5835

文摘

New copolyfluorenes (PSiC8OF0PSiC8OF50) composed of 9,9-dioctylfluorene, jacketed units 2,5-bis[(5-octyloxy-phenyl)-1,3,4- oxadiazole]-1-(3,5-dibromophenyl)-benzene (35C8) and 2,5-bis(trimethylsilyl)benzene were synthesized by palladium-catalyzed Suzuki coupling reaction. They were characterized by GPC, ¹H 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 °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 56 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 −5.59−6.07 eV and −2.60−3.01 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 PSiC8OF10PSiC8OF50 showed emissions between them. This indicates that copolymer PSiC8OF5 could be a good candidate for blue light-emitting materials.