Single-component Polyfluorene Electrolytes Bearing Different Counterions for White Light-emitting Electrochemical Cells

A series of polyfluorene (PF) electrolytes bearing Br−, BF4−, or PF6− counterions were synthesized and characterized. 2,1,3-benzoselenadiazole moieties were incorporated into polymer main chains to produce single-component white light-emitting polymers. The thermal stability of Br-containing ionic PF was decreased because of the Hofmann elimination occurred at higher temperature. By replacing Br− with BF4− or PF6− counterions, the thermal stability of polymers was significantly improved. UV-vis absorption and photoluminescence spectra revealed that Br-containing ionic PF generates blue shift in methanol, while BF4 and PF6-containing ionic PFs show blue shift in acetonitrile. Electrochemical analysis revealed that oxidation potentials of BF4 and PF6-containing ionic PFs were decreased, resulting in increase in HOMO and LUMO levels. The optimized spin-coated light-emitting electrochemical cell (LEC) with the configuration of ITO/PEDOT/polymer/Ag showed a maximum luminescence efficiency of 1.56 lm/W at a low operation bias of 3 V. The single-component LEC device exhibited pure white light emission with CIE’1931 coordinates approaching (0.33, 0.33) and high color rendering index (CRI > 85), referring to its potential use in solid-state-lighting application.

本研究合成并表征了一系列带有Br⁻、BF₄⁻或PF₆⁻抗衡离子的聚芴（polyfluorene, PF）电解质。将2,1,3-苯并硒二唑基团引入聚合物主链，成功制备出单组分白光发射聚合物。含Br⁻的离子型聚芴的热稳定性有所下降，原因是其在较高温度下发生了霍夫曼消除反应；将抗衡离子由Br⁻替换为BF₄⁻或PF₆⁻后，聚合物的热稳定性得到显著提升。紫外-可见吸收光谱与光致发光光谱测试结果表明，含Br⁻的离子型聚芴在甲醇溶剂中发生蓝移，而含BF₄⁻与PF₆⁻的离子型聚芴则在乙腈溶剂中出现蓝移。电化学分析结果显示，含BF₄⁻与PF₆⁻的离子型聚芴的氧化电势有所降低，导致其最高占据分子轨道（Highest Occupied Molecular Orbital, HOMO）与最低未占据分子轨道（Lowest Unoccupied Molecular Orbital, LUMO）能级升高。采用氧化铟锡（indium tin oxide, ITO）/聚(3,4-乙烯二氧噻吩)（poly(3,4-ethylenedioxythiophene), PEDOT）/聚合物/银结构的优化旋涂型发光电化学池（light-emitting electrochemical cell, LEC），在3 V低工作偏压下实现了1.56 lm/W的最大发光效率。该单组分LEC器件可发射纯白光，其CIE 1931色坐标接近(0.33, 0.33)，且具有较高的显色指数（color rendering index, CRI > 85），表明其在固态照明领域具备应用潜力。