Quinoline-based aggregation-induced delayed fluorescence materials for highly efficient non-doped organic light-emitting diodes

Three new emitters,namely 10,10'-(quinoline-2,8-diyl)bis(10 H-phenoxazine)(Fene),10,10'-(quinoline-2,8-diyl)bis(10 H-phenothiazine)(Fens) and 10,10'-(quinoline-2,8-diyl)bis(9,9-dimethyl-9,10-dihydroacridine)(Yad),featuring quinoline as a new electron acceptor have been designed and conveniently synthesized.These emitters possessed small singlet-triplet splitting energy(ΔEst) and twisted structures,which not only endowed them show thermally activated delayed fluorescence(TADF)properties but also afforded a remarkable aggregation-induced emission(AIE) feature.Moreover,they also showed aggregation-induced delayed fluorescence(AIDF) property and good photoluminescence(PL) property,which are the ideal emitters for non-doped organic light-emitting diodes(OLEDs).Furthermore,high-performance non-doped OLEDs based on Fene,Fens and Yad were achieved,and excelle nt maximum external quantum efficiencies(EQE_(max)) of 14,9%,13.1% and 17,4%,respectively,were obtained.It was also found that all devices exhibited relatively low turn-on voltages ranging from 3.0 V to3.2 V probably due to their twisted conformation and the AIDF properties.These results demonstrated the quinoline-based emitters could have a promising application in non-doped OLEDs.     

Rational Design of a Near-infrared Fluorescent Material with High Solid-state Efficiency,Aggregation-induced Emission and Live Cell Imaging Property

Near-infrared(NIR) fluorescent materials with high photoluminescent quantum yields(PLQYs) have wide application prospects. Therefore, we design and synthesize a D-A type NIR organic molecule, TPATHCNE, in which triphenylamine and thiophene are utilized as the donors and fumaronitrile is applied as the acceptor. We systematically investigate its molecular structure and photophysical property. TPATHCNE shows high T_gof 110℃ and T_d of 385℃ and displays an aggregation-induced emission(AIE) property. A narrow optical bandgap of 1.65 eV is obtained. The non-doped film of TPATHCNE exhibits a high PLQY of 40.3% with an emission peak at 732 nm, which is among the best values of NIR emitters. When TPATHCNE is applied in organic light-emitting diode(OLED), the electroluminescent peak is located at 716 nm with a maximum external quantum efficiency of 0.83%. With the potential in cell imaging, the polystyrene maleic anhydride(PMSA) modified TPATHCNE nanoparticles(NPs) emit strong fluorescence when labeling HeLa cancer cells, suggesting that TPATHCNE can be used as a fluorescent carrier for specific staining or drug delivery for cellular imaging. TPATHCNE NPs fabricated by bovine serum protein(BSA) are cultivated with mononuclear yeast cells, and the intense intracellular red fluorescence indicates that it can be adopted as a specific stain for imaging.     

Coumarin-cored carbazole dendrimers as solution-processed non-doped green emitters for electroluminescent devices

A series of green-emitting thiophenyl coumarin-cored carbazole dendrimers containing carbazole dendrons up to the third generation as substituent were synthesized and characterization. Their optical, thermal, electrochemical, and electroluminescent properties as non-doped solution-processed light-emitters for OLEDs were investigated. By incorporating carbazole dendrons in the molecule, we are able to reduce the crystallization and retain the high emissive ability of a planar thiophenyl coumarin fluorescent core in the solid state as well as improve the thermal stability of the material. These dendrimers showed a bright-green fluorescence and can form morphologically stable amorphous thin films with glass-transition temperatures as high as 285 °C. Simple structured solution-processed OLEDs using these materials as hole-transporting non-doped emitters and BCP as a buffer layer emit a stable green electroluminescence (λ_EL=502–526 nm) with high luminance efficiencies (up to 7.92 cd/A at 7.39 mA/cm²) and high green color purity (CIE=0.26, 0.62, which are close to the pure green color).     

Structural Controls of Tetraphenylbenzene-based AIEgens for Non-doped Deep Blue Organic Light-emitting Diodes

Aggregation-induced emission(AIE)has emerged as a new concept,giving highly efficient solid-state photoluminescence.Particularly,AIE luminogens(AIEgens)with deep blue emission(400–450 nm)have displayed salient advantages for non-doped organic light-emitting diodes(OLEDs).However,deep blue emitters with Commission Internationale de L’Eclairage(CIE)coordinates less than 0.08 are still rare.In this review,we outline the latest achievements in the molecular guidelines based on the AIE core of tetraphenylbenzene(TPB)for developing efficient deep blue AIEgens.We provide insights into the construction of deep blue emitters with high horizontal orientation by regulating the length of the linear molecule.We also discuss the luminescence mechanisms of these AIEgens-based OLEDs by using the magnetic field effects measurements.Finally,a summary of the challenges and perspectives of deep blue AIEgens for non-doped OLEDs is also presented.     

甲基修饰的咔唑/二苯砜基AIE-TADF蓝光材料及其OLED器件

以四甲基咔唑为电子给体(D)、 二苯砜为电子受体(A)构建了具有D-A-D结构的纯有机咔唑/二苯砜衍生物——9,9'-[磺酰基双(3,1-亚苯基)]双(1,3,6,8-四甲基-9H-咔唑)(TMe-mSOCz). 对所合成材料的光物理性能研究表明, TMe-mSOCz表现出明显的聚集诱导发射(AIE)和热激活延迟荧光(TADF), 延迟寿命和延迟荧光占比分别为2.26 μs和47.7%, 并具有良好的电化学稳定性和热稳定性. 基于TMe-mSOCz作为非掺杂发光层制备了有机发光二极管(OLED)器件, 其启亮电压(V_on)为3.5 V, 最大外量子效率为5.63%, 国际照明委员会(CIE)坐标为(0.18, 0.26). 在1000 cd/m²亮度下, 非掺杂器件的效率滚降非常小(7.1%), 色彩稳定性较好, 其具有窄的半峰宽(FWHM=72 nm). 研究结果表明, 在传统TADF分子给受体间引入甲基修饰有利于开发具有AIE特性与更高效的D-A-D型TADF分子, 这为基于AIE-TADF分子开发新型OLED器件提供了新途径.     

氟取代噻咯衍生物结构和光电性能的理论研究

采用密度泛函理论在B3LYP/6-31G(d)水平上计算了1,1-二甲基-2,3,4,5-四苯基噻咯(PSP)及其8种氟取代衍生物的几何结构与光电性质. 计算结果表明, 2,5位苯基上氟取代对PSP结构和光电性质的影响主要由氟原子的取代位置决定, 而取代基个数的增加能加强相关影响. 苯基上邻对位氟取代对分子构型影响较大, 导致HOMO-LUMO能隙增大, 光谱显著蓝移; 而间位氟取代显示诱导作用突出, 使2,5位侧链吸电子能力增强, 同时LUMO能级降低, 电子亲和势增大更有利于电子的注入.     

Triplet fusion delayed fluorescence materials for OLEDs

The development of fluorescent materials capable of harvesting triplet excitons efficiently is of great importance in achieving high-performance low-cost organic light-emitting diodes (OLEDs). Among the three mechanisms converting triplet to singlet excitons, triplet fusion delayed fluorescence (TFDF) plays a key role in the demonstration of highly efficient and reliable OLEDs, especially blue devices, for practice applications. This review focuses on the recent development of TFDF materials and their applications in OLEDs. Fundamental TFDF mechanism, molecular design principles, and the structure-property relationship of TFDF materials with a particular emphasis on their different excited state characters, are presented and discussed. Moreover, the future perspectives and ongoing challenges of TFDF materials are also highlighted.     

Photo- and electroluminescent properties of cyano-substituted styryl derivatives and synthesis of CN-PPV model compounds containing an alkoxy spacer for OLEDs

The series of cyano-substituted model compounds 18-20 for organic light emitting diodes (OLEDs) was prepared through Knoevenagel condensation reactions between the dialdehydes 3,6,9 and the differently substituted acetonitrile derivatives 11,16,17. The influence of the different substituents on the optical properties of the resulting α-cyanostyryl compounds 18-20 was investigated. Another series of dimeric cyano-substituted styryl compounds 26-28 were prepared, in which a flexible, nonconjugated spacer is present between the two cyanostyryl moieties. The spacer isolates the π-conjugated portions of dimeric compounds 26-28, improves their solubility in common organic solvents, and decreases their tendency to crystallize. These features are favorable for producing efficient luminescent films in OLEDs devices.     

Comparative study of photoelectric properties of a copolymer and the corresponding homopolymers based on poly(3-alkylthiophene)s

As semiconducting materials in organic light-emitting devices (OLEDs), a novel, highly soluble poly[(3-octylthiophene)-co-(3-(2-ethyl-1-hexylthiophene))] (P3OTIOT) and the corresponding homopolymers (poly(3-octylthiophene) (P3OT) and poly(3-isooctylthiophene) (P3IOT)) were prepared by an FeCl₃-oxidative approach to compare their photoelectric properties. Characterization of the polymers included FT-IR, ¹H NMR, gel permeation chromatography (GPC), thermo-gravimetric analysis (TGA), UV-vis spectroscopy, photoluminescence (PL) and electroluminescence (EL). P3OTIOT and P3OT depicted excellent solubility in common organic solvents. TGA studies showed that all of the materials exhibited very good thermal stabilities, losing 5% of their weight on heating to 300 °C. The optical property investigations showed that the band-gap energy of P3OTIOT was similar to that of P3OT (2.43 eV) at 2.45 eV and 6% lower than that of P3IOT (2.6 eV) in CHCl₃ solution. In PL spectra, the emission maxima of P3OTIOT and P3IOT were 50 nm and 130 nm blue-shifted with respect to that of P3OT, respectively. However, the PL intensity of P3OTIOT was seven times higher than that of P3OT. Single layer polymer light-emitting devices (PLEDs) with the ITO/polymer/Ag configurations were fabricated by the spin-coating method with P3OT, P3IOT and P3OTIOT as the EL materials, which exhibited red (650 nm), orange-red (610 nm) and yellow-green (525 nm) EL, respectively. The external EL quantum efficiencies (QE) of P3IOT and P3OTIOT devices are 6.4 × 10⁻³% and 5.1 × 10⁻³% which are about five and four times higher than that of the P3OT device (1.2 × 10⁻³%), respectively. The turn-on voltage of the P3OTIOT device (5 V) is between that of the P3OT (4.5 V) and P3IOT (6 V) devices. These results indicated that the P3OTIOT combined the photoelectric properties of P3OT and P3IOT with excellent solubility, processability, low band-gap energy, high QE and low turn-on voltage in the PLEDs, and they might be excellent polymeric materials for applications in organic light-emitting diodes, light-emitting electrochemical cells and polymer solar cells.     

Pure red electrophosphorescence from polymer light-emitting diodes doped with highly emissive bis-cyclometalated iridium(III) complexes

In order to develop highly emissive red phosphorescent materials for OLED application, novel bis-cyclometalated iridium(III) complexes were developed using the 1-(dibenzo[b,d]furan-4-yl)isoquinolinato-N,C^3′ (dbfiq) cyclometalating ligand. When 1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dionate (bdbp) is employed as an ancillary ligand, Ir(dbfiq)₂(bdbp) 1 exhibits red photoluminescence (PL) at 640 nm with a quantum yield (Φ_PL) of 0.61 (in toluene, 298 K). Replacement of bdbp to dipivaloylmethanate (dpm) and acetylacetonate (acac) (Ir(dbfiq)₂(dpm) 2 and Ir(dbfiq)₂(acac) 3, respectively) does not affect the PL spectrum, but reduces Φ_PL to 0.55 and 0.49 for 2 and 3, respectively. Similar tendency is also found in the doped poly(methyl methacrylate) (PMMA) film, and 1 is more emissive (Φ_PL = 0.17) than 2 and 3 (Φ_PL = 0.08 and 0.06, respectively). Using 1 as a phosphorescent dopant, polymer light-emitting diodes (PLEDs) were fabricated, of which structure was ITO/PEDOT:PSS (40 nm)/PVCz:1:PBD (100 nm)/CsF (1 nm)/Al (250 nm). Pure red electroluminescence (EL) is obtained from the fabricated PLEDs, affording a CIE chromaticity coordinate of (0.68, 0.31). When 0.51 mol% of 1 is incorporated in the PVCz-based emitting layer, the PLED shows maximum luminance of 7270 cd m⁻² at 16.5 V, power efficiency of 1.4 lm W⁻¹ at 7.5 V, and external quantum efficiency of 6.4% at 9.0 V. PLEDs with the same structure and components were also fabricated using 2 and 3, and their device characteristics were investigated. In proportion to the PL quantum yields, 1 affords better device performance than 2 and 3. Owing to four butoxy groups introduced to the bdbp ligand, 1 exhibits high solubility in organic solvents such as chloroform and toluene, and thus, is an excellent red phosphorescent dopant for solution-processed OLEDs.     

一种新型苯乙烯衍生物的光致发光与电致发光

对一种新型苯乙烯衍生物的光致发光和电致发光进行了研究。１－９－蒽基－４－氯甲基－２,５－二甲氧基苯的溶液随浓度的增大,其单体荧光逐渐减弱而激基复合物发光逐渐增强。在薄膜状态只有激基复合物荧光,表明在溶液和薄膜状态下均存在单体向激基复合物的能量转移过程,用分子间距离越近,能量转移效率越高。以该化合物制成的单层二极管器件,其电致发光光谱随电压增强从激基复合物发光逐渐转变为激复合发光。     

抗菌医药左氧氟沙星在有机电致发光二极管中的应用

左氧氟沙星(LOFX)是一种知名的抗菌药物, 它的价格非常便宜, 且有成熟的合成和纯化技术. 本文中首次将LOFX作为一种蓝光发光材料和电子传输材料应用于有机电致发光器件(OLED)中. 通过热重分析、UVVis吸收光谱、发射光谱以及循环伏安曲线详细地表征了LOFX的热学及光物理特性. LOFX有高的分解温度,为327 ℃; HOMO、LUMO能级分别为-6.2 和-3.2 eV, 光学带隙为3.0 eV. 以LOFX作为客体材料, 掺杂在主体材料4,4'-二(9-咔唑)联苯(CBP)中制备了蓝光OLED, 该器件的电致发光(EL)发射峰位于452 nm, 最大亮度为2315 cd·m^-2. 进一步, 选择8-羟基喹啉铝(Alq₃)作为参考材料, 分别以LOFX和Alq₃作为电子传输材料制备了结构相同的单载流子器件和绿色磷光OLED. 在相同的电压下, 以LOFX作为电子传输材料的单载流子器件的电流密度比以Alq₃作为电子传输材料的单载流子器件更高. 同时, 以LOFX作为电子传输材料的绿色磷光OLED获得更高的器件效率. 从这些EL性能可以看出, LOFX同时也是一很好的电子传输材料.     

New Electroactive Polymers with Electronically Isolated 4,7-Diarylfluorene Chromophores as Positive Charge Transporting Layer Materials for OLEDs

A group of polyethers containing electroactive pendent 4,7-diarylfluorene chromophores have been prepared by the multi-step synthetic route. Full characterization of their structures has been presented. The polymeric materials represent derivatives of high thermal stability with initial thermal degradation temperatures in a range of 392–397 °C. Glass transition temperatures of the amorphous polymers range from 28 °C to 63 °C and depend on structures of the 4,7-diarylfluorene chromophores. Electron photoemission spectra of thin layers of the electroactive derivatives showed ionization potentials in the range of 5.8–6.0 eV. Hole injecting/transporting properties of the prepared polymeric materials were confirmed during formation of organic light-emitting diodes with tris(quinolin-8-olato)aluminium (Alq₃) as a green emitter, which also serves as an electron transporting layer. The device using hole-transporting polymer with electronically isolated 2,7-di(4-biphenyl)fluorene chromophores demonstrated the best overall performance with low turn on voltage of 3 V, high current efficiency exceeding 1.7 cd/A, and with maximum brightness over 200 cd/m². The organic light-emitting diode (OLED) characteristics were measured in non-optimized test devices. The efficiencies could be further improved by an optimization of device structure, formation conditions, and encapsulation of the devices.     

Asymmetric Thermally Activated Delayed Fluorescence Materials Rendering High-performance OLEDs Through both Thermal Evaporation and Solution-processing

Exploring high-efficiency thermally activated delayed fluorescence(TADF) materials is of great importance regarding to organic light-emitting diode(OLED). Herein, we present a design strategy for developing asymmetric TADF materials based on a diphenyl sulfone-phenoxazine structure, resulting in efficient TADF emitters(CzPXZ and t-CzPXZ) with aggregation-induced emission properties, while t-CzPXZ is modified with tert-butyl groups. The two compounds exhibit high solid-state luminescence, efficient TADF, and significantly impressive device performances by both thermal evaporation and solution processing. For an instance, CzPXZ and t-CzPXZ enable the thermally-evaporated OLEDs with high external quantum efficiencies(EQEs) of over 20%. Meanwhile, t-CzPXZ allows the solution-processed device with a high EQE of 16.3% with low-efficiency roll-off, attributing to the enhanced molecular solubility and suppressed excitons quenching through tert-butyl modification on t-CzPXZ. The results reveal that the proposed asymmetric structure is a promising approach for developing high-efficiency TADF materials and OLEDs.     

含噻吩单元的硅芴共聚物的合成及其蓝色电致发光性能

将少量(摩尔分数为1%—3％)含噻吩的窄带隙单体和宽带隙硅芴单体进行共聚, 合成了聚{9,9-二己基-3,6-硅芴-co-[2,5-二(2-甲基苯撑-4-基)-噻吩]}和聚{9,9-二己基-3,6-硅芴-co-[2,5-二(2-苯撑-4-基)-噻吩]}两类硅芴共聚物, 通过紫外-可见吸收光谱、光致发光光谱, 并制作聚合物发光二极管器件测试电致发光光谱等手段, 系统表征了两类硅芴共聚物材料的性能. 实验结果表明, 噻吩的加入形成了新的蓝色发光中心, 并且实现了从硅芴链段到含噻吩发光中心的有效能量转移. 通过增加发光中心结构的空间位阻来减小其共轭程度, 可以使聚合物的PL和EL光谱发生较大蓝移. 最终得到了效率为0.46%和色坐标(CIE)为(0.19, 0.16)的蓝光LED器件.     

二咔唑四苯乙烯多功能发光化合物的合成与性能

合成了一种新型的具有压致荧光变色效应的聚集诱导增强发光(PAIE)化合物二咔唑四苯乙烯; 通过核磁共振、质谱和元素分析等手段对其进行了结构表征; 利用紫外吸收光谱、荧光发射光谱、热分析和X射线衍射等手段研究了化合物的基本性能. 实验结果表明, 随着水含量的增加, 该化合物溶液荧光强度增强了171倍, 荧光量子产率提高了100倍, 表现出明显的聚集诱导增强发光效应; 在外界因素作用下该化合物固体样品可实现结晶态与无定形态的相互转变. 结晶态的荧光发射波长为450 nm, 无定形态为480 nm, 相差30 nm, 说明该化合物具有明显的压致荧光变色效应; 将该化合物用于制备发光器件, 未经优化的器件亮度达2438 cd/m², 电流效率为2.87 cd/A, 流明效率为1.81 lm/W. 该化合物是一种多功能材料.     

Four-coordinate boron compounds derived from 2-(2-pyridyl)phenol ligand as novel hole-blocking materials for phosphorescent OLEDs

Four-coordinate boron compounds of Ph₂B · 1 (2) and (C₆F₅)₃B(1 · H) (3) were prepared from the reaction of 2-(2-pyridyl)phenol (1 · H) ligand with triarylborane starting materials, BPh₃ and B(C₆F₅)₃, respectively, and tested as hole-blocking layer (HBL) materials in phosphorescent OLEDs. While the crystal structure of 2 reveals the pseudo-tetrahedral geometry around the boron center with bidentate [N,O] chelation by 1, 3 is characterized as the zwitterionic four-coordinate system where the ligand 1 · H acts as monodentate [O] chelator with N-protonation. UV-Vis absorption and PL spectra of 2 and 3 are consistent with the ligand-centered, HOMO-LUMO electronic transitions with charge transfer from a phenoxide ring to a pyridine, which was further supported by time dependent DFT calculation for 2. Both compounds are found to possess the HOMO-LUMO energy gap of 3.1 eV appropriate for hole-blocking materials for phosphorescent OLEDs. The devices incorporating 2 and 3 as HBL materials displayed stable green phosphorescence of Ir(ppy)₃ (ppy = 2-phenylpyridine) with low turn-on voltage of 3.2 and 3.4 V, respectively, indicating that 2 and 3 function as HBL materials. Although both devices show the short lifetime (<1 h) probably owing to the low thermal stability, the device based on 2 displays better performances in terms of luminance, power and luminance efficiency, and external quantum efficiency in a wide range of current densities (0.1-100 mA/cm²) than the reference device incorporating BAlq as HBL materials.     

Fluorescence quenching detection of peanut agglutinin based on photoluminescent silole-core carbosilane dendrimer peripherally functionalized with lactose

A glycocluster peripherally functionalized with a lactose (Lac: Galβ1→4Glcβ1–) derivative possessing a silole moiety as a luminophore was synthesized. The photoluminescence spectrum of the glycocluster showed extremely strong emission at 474 nm and the absolute quantum yield was estimated to be 92% in distilled water. The emission intensity was decreased by increasing the amount of peanut agglutinin (PNA), a lactose-binding lectin, and plots of the relative fluorescence intensity revealed a decline of 95% in emission intensity. Fluorescence quenching of the glycocluster upon mixing with PNA could be easily observed by the naked eye under UV irradiation, whereas no distinct change in fluorescence properties of the glycocluster was observed when wheat germ agglutinin (WGA) was employed.     

二苯胺取代吖啶衍生物发光材料的合成、表征及电致发光性能

设计合成了2个苯胺取代吖啶衍生物N3,N3,N6,N6-四苯基吖啶基-3,6-二胺(1)和N3,N3,N6,N6-四对甲苯基吖啶基-3,6-二胺(2),通过化学修饰在吖啶核的两端引入二苯胺取代基可以调节化合物的能级和堆积结构等性质,从而使这些吖啶衍生物具有良好的发光性能,可用于制备电致发光器件.基于吖啶衍生物为掺杂发光材料制备的电致发光器件均呈现绿光发射,器件开启电压较低(2.4 V),以化合物1和2制备的器件最高功率效率分别为4.9和8.2 lm/W.考察了其光物理、电化学、热学和荧光量子效率等性能.结果表明,化合物1和2具有较高的量子效率及匹配的能级结构,这是获得较高电致发光效率的基础.     

金属纳米粒子增强有机光电器件性能研究进展

金属纳米粒子以其特殊的体积效应、量子尺寸效应、表面效应和宏观量子隧道效应提供了诸多优异的光学和电学性能.实验表明,利用金属纳米粒子的光学和电学效应可以有效提升有机光电器件的综合性能.目前在有机发光二极管器件中流明效率最好的增强效果为150%,在有机光伏器件中功率转换效率最好的增强效果为70%,特别是在一些高效有机光电器件中的成功应用,虽然增强的比例相对较低,但是器件效率基数大,最终得到的器件性能相当优异.这些性能提升的主要机理包括表面增强荧光、等离激元光捕获、能量转移、电学效应、散射效应等.本文以金属纳米粒子的表面等离子体共振效应和电学效应为主线,按照不同纳米粒子及器件中的修饰位置进行分类,系统总结了金属纳米粒子提高有机发光二极管器件和有机光伏器件性能方面的工作.针对纳米粒子的局域表面等离子共振效应作用范围小,增强波长单一等问题,总结了一些新的设计思路如远场增强效应、纳米粒子和激子剖面的调控与匹配及散射增强效应等,希望为进一步的结构设计提供帮助.