含咔唑和芳基膦氧的双极性蓝光聚螺芴的合成与表征

Synthesis and Characterization of Bipolar Blue-emitting Poly(spirobifluorene)s Containing Carbazole and Arylphosphine Oxide

采用Suzuki聚合方法,设计合成了一系列含咔唑和芳基膦氧的双极性蓝光聚螺芴PSFCzPO10、PSFCzPO20和PSFCzPO30.和仅含有咔唑单元的参比聚合物Cz-PSF相比,芳基膦氧的引入,在保证最高占据分子轨道(HOMO)能级基本不变的情况下,能够有效地降低聚合物的最低未占分子轨道(LUMO)能级,从而在一定程度上实现载流子的双极性传输.因此,PSFCzPO10获得了最优的单层器件性能,电流效率为1.19 cd A^(-1),比Cz-PSF(0.39 cd A^(-1))提高了将近2倍.在此基础上,采用醇溶性的电子传输材料作为电子传输层,通过正交溶剂法,成功地组装了PSFCzPO10的全溶液加工型多层器件,电流效率进一步增加到1.93 cd A^(-1).同时,它的电致发光光谱几乎不受驱动电压的影响,色坐标为(0.16,0.14),表现出良好的蓝光光谱稳定性.

A series of bipolar blue-emitting poly（spirobifluorene）s,named PSFCzPO10,PSFCzPO20 and PSFCzPO30,have been designed and synthesized via Suzuki polycondensation,where carbazole and arylphosphine oxide are incorporated as the hole-and electron-transporting units,respectively.These resultant poly（spirobifluorene）s are thermally stable with decomposition temperatures up to 380 oC and no glass transition or melting behaviors are observed in the range of 25-280 ℃,which are beneficial for the fabrication of long-trem PLEDs.Moreover,compared to the reference polymer Cz-PSF only containing carbazole,the introduction of the arylphosphine oxide unit does not obviously affect their photoluminescence（PL） and the corresponding PL quantum yields of PSFCzPO10-PSFCzPO30 in solid states.However,with increasing content of the arylphosphine oxide,the lowest unoccupied molecular orbital（LUMO） levels are lowered from-2.22 eV for Cz-PSF to-2.68 eV for PSFCzPO30,whereas the highest occupied molecular orbital（HOMO） levels remain nearly unchanged（-5.39 ～-5.40 eV）.This trend implies the favored electron injection and transporting although the hole injection barriers seem to be the same for all the polymers.That is,the bipolar transporting and thus charge balance to some degree are within our expectation for PSFCzPO10-PSFCzPO30.Among them,PSFCzPO10 exhibits the best current efficiency of 1.19 cd A^-1 based on a single-layer device structure,which is about twofolds higher than that of Cz-PSF（0.39 cd A^-1）.In addition,with PSFCzPO10 as the emitting layer and TPPO as the alcohol-soluble electron-transporting layer,the corresponding all-solution-processed multilayer device is successfully assembled through orthogonal sequential solvent processing.And its current efficiency is further up to 1.93 cd A^-1 together with CIE coordinates of（0.16,0.14）.Meanwhile,the electroluminescence is nearly independent of the driving voltages,indicative of the good blue spectral stability.These results clearly demonstrate that the bipolar design is a promising strategy to improve the efficiency and stability of blue-emitting poly（spirobifluorene）s applied in PLEDs.