【作者】 田野；

【导师】 张皓；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2023， 博士

【摘要】 发光二极管（LED）作为一种新型固体照明设备,有着发光效率高、响应速度快、可应用场景广泛的优点,吸引了学术界与工业界的广泛研究。一直以来,为了获得更高效、更环保以及更稳定的LED,研究人员致力于开发新型的发光材料。近年来,金属纳米簇由于合成简单、生物相容性好、光色可调以及稳定性好的优点,成为了制备新型LED的备选材料之一。与传统的荧光材料相比,金属纳米簇最大的缺点是其荧光量子产率（PLQY）较低,这使得研究人员难以进一步发展基于金属纳米簇的LED。为了解决该问题,研究人员开发了大量的方法以提升金属纳米簇的发光性能,聚集诱导发光（AIE）便是其中最具代表性的一种。在本论文中,我们根据金属纳米簇的结构特性与应用需求,设计了不同的AIE体系以增强金属纳米簇的荧光,制备了一系列具有较高PLQY的金属纳米簇,并基于这些金属纳米簇分别制作了光致发光LED（PL-LEDs）、电致发光LED（EL-LEDs）以及电致圆偏振LED（CPLEDs）,提升了基于金属纳米簇的LED的器件性能,证明了金属纳米簇作为发光材料在LED领域中具有巨大的应用潜力。在第二章中,我们以N-乙酰-L-半胱氨酸（NAC）为配体,合成了PLQY为0.02%的银纳米簇（NAC-Ag NCs）。随后我们利用配体间的氢键以及疏水相互作用实现了NAC-Ag NCs的组装,制备了PLQY为26.8%的NAC-Ag NCs组装体。进一步的研究表明,组装过程对于NAC-Ag NCs荧光的增强来自两个方面:（1）组装过程抑制了配体的振动转动所带来的非辐射跃迁,提升了辐射跃迁速率;（2）组装过程减小了NAC-Ag NCs的三线态与单线态之间的能垒,促进了三线态激子的反向隙间窜跃,实现了组装诱导的热活化延迟荧光（TADF）发射。由于NAC-Ag NCs组装体可以从溶液中分离,因此其可以作为颜色转换层应用于PL-LEDs之中。组装诱导的TADF发射作为一种新的基于AIE增强金属纳米簇荧光的手段,证实了AIE在提升金属纳米簇的发光性能方面的巨大潜力,也为开发基于金属纳米簇组装体的颜色转换层提供了新的思路。在第三章中,我们将AIE与表面配体工程结合,利用配体间的氢键以及静电相互作用,合成了正四辛基溴化铵（TOAB）、精氨酸（Arg）以及6-氮杂-2-硫代胸腺嘧啶（ATT）三层配体包覆的金纳米簇（TOAB/Arg/ATT-Au NCs）。三层配体包覆的策略在单簇水平上实现了AIE,抑制了金核以及配体的振动所带来的非辐射跃迁,在保持金纳米簇单分散性的同时,将PLQY从2.1%提升至73.4%。此外,三层配体包覆的策略提升了TOAB/Arg/ATT-Au NCs在乙醇中的溶解性,满足了EL-LEDs的制备过程中对于溶液分散性、正交性与浸润性的要求,提高了发光层的薄膜质量。基于TOAB/Arg/ATT-Au NCs的EL-LEDs（Au NCs-LEDs）的最大亮度为1104 cd/m²,最大外量子效率（EQE）为5.1%,其各项性能指标均为目前所报道的Au NCs-LEDs的最高值。本章中所制备的Au NCs-LEDs满足了显示器件中对于亮度以及色纯度的要求,三层配体的包覆的策略也为后续设计基于金属纳米簇的EL-LEDs提供了一种全新的思路。在第四章中,我们以R/S-4-苯基噻唑烷-2-硫酮（R/S-PTLT）为配体,利用重结晶法合成了同时具有AIE以及圆偏振发光（CPL）的银纳米簇（R/S-Ag₆（PTLT）₆NCs）。进一步的研究表明,R/S-Ag₆（PTLT）₆ NCs在聚集态时的PLQY与其在聚集体中的堆积方式密切相关,即紧密且有序的堆积可以实现其AIE效应的增强。因此,我们在R/S-Ag₆（PTLT）₆ NCs的薄膜中引入1,3-双（咔唑-9-基）苯（m CP）作为主体材料,利用m CP和R/S-PTLT之间的π-π相互作用提升了薄膜中R/S-Ag₆（PTLT）₆ NCs堆积的紧密度和有序性,将薄膜的PLQY从40.3%提升至71.0%。此外,m CP的加入也平衡了发光层中电子与空穴的传输速率,抑制了三线态激子的淬灭。以R/S-Ag₆（PTLT）₆ NC/m CP混合薄膜为发光层的CPLEDs的最大亮度为3906 cd/m²,最大EQE为10.0%,不对称因子为-5.3×10^-3/4.7×10^-3,其各项性能指标均为基于金属纳米簇的CPLEDs的最高值。这一全新的主体材料增强AIE的手段为后续进一步提升基于金属纳米簇的CPLEDs以及EL-LEDs的器件性能提供一种有前景的思路。更多还原

【Abstract】 As a kind of solid-state lighting,light-emitting diodes（LEDs）are drawing more and more attention in laboratories and industries because of their attractive luminous efficiency,high-speed response time and wide range of applications.In order to obtain highly-efficient,environmental-friendly and stable LEDs,researchers have been committed to developing new light-emitting materials for a long time.In recent years,metal nanoclusters（MNCs）have attracted a great deal of interest in preparing new LEDs owing to their facile synthesis,tunable emitting color,good biocompatibility and good stability.Compared with traditional light-emitting materials,the biggest shortcoming of MNCs is their low photoluminescent quantum yield（PLQY）.Therefore,the performance of LEDs based on MNCs is still at the initial developmental stage.Researchers have developed many approaches to improve the PLQY of MNCs,the aggregation induced emission（AIE）is the most attractive one.In this paper,we designed different AIE systems to enhance the PL performance of MNCs according to their structure and requirements,and synthesized a series of MNCs with high PLQY.Based on these MNCs,we fabricated highly-efficient photoluminescent LEDs（PL-LEDs）,electroluminescent LEDs（EL-LEDs）and electroluminescent circularly polarized LEDs（CPLEDs）,which exhibited the great potential of metal nanoclusters in LED fields as emitters.In the second chapter,we synthesized sliver nanoclusters（NAC-Ag NCs）with PLQY of 0.02%using N-acetyl-L-cysteine（NAC）as the capping ligand.The hydrogen bond and hydrophobic interactions between ligands were used to achieve self-assembly induced emission.Based on this,we synthesized NAC-Ag NCs self-assemblies with PLQY of 26.8%.Further researches indicated that the mechanism of self-assembly induced emission was attributed to two aspects:（1）The self-assembly inhibited the vibration and rotation of the ligands and promoted the radiative relaxation in the excited state;（2）The self-assembly reduced the energy barrier between the triplet state and singlet state of NAC-Ag NCs,which promoted the reverse intersystem crossing of triplet excitons and realized the thermally activated delayed fluorescent（TADF）.The self-assemblies were separated from solution and applied as the color conversion in PL-LEDs.Such self-assembly induced TADF emission demonstrated the great potential of the AIE effect in enhancing the PL properties of MNCs and provided a new strategy for developing new environmental-friendly color conversions based on metal nanoclusters self-assemblies.In the third chapter,with the combination of AIE and surface ligand engineering,we employed a triplet-layered ligand coordination of gold nanoclusters,from the Au kernel out,the ligands:6-aza-2-thiothymine（ATT）,arginine（Arg）and tetraoctyl ammonium bromide（TOAB）,through hydrogen bonds and electrostatic interactions（TOAB/Arg/ATT-Au NCs）.The triplet-layered ligand coordination of Au NCs achieved AIE at single-cluster level,which suppressed the nonradiative transition in excited state caused by the vibration of the ligands and gold core.The PLQY of gold nanoclusters was improved from 2.1%to 73.4%while the mono-dispersity was maintained.In addition,the good solubility of TOAB/Arg/ATT-Au NCs in ethanol satisfied the solvent requirements of dispersibility,orthogonality and wettability in device fabrication and improved the thin film quality of emitting layer.The EL-LEDs based on TOAB/Arg/ATT-Au NCs（Au NCs-LEDs）exhibited a maximum brightness of 1104cd/m² and a peak external quantum efficiency（EQE）of 5.1%,which was the highest performance among the Au NCs-LEDs.Primarily,the Au NCs-LEDs reported here met the color purity and brightness requirements for display applications,and such a triple ligand engineering strategy broadened the horizons in future design of high-performance metal NC-based EL-LEDs.In the fourth chapter,we synthesized enantiomeric（R/S）-4-phenylthiazolidine-2-thione capped silver（R/S-Ag₆（PTLT）₆）NCs with both AIE and circularly polarized luminescence（CPL）by recrystallization.Further studies indicated that ordered and dense packing arrangements were essential for the R-Ag₆（PTLT）₆ NCs aggregates to fulfill efficient AIE and achieve high PLQY.On this basis,1,3-bis（carbazol-9-yl）benzene（m CP）was introduced as a host molecule and further enhanced the photoluminescence（PL）emission by constructing ordered and dense packing arrangements of the Ag₆（PTLT）₆ NCs in solid films viaπ-πinteractions.The PLQY of solid thin film was increased from 40.3%to 71.0%.As the hybrid solid thin films were employed for CPLEDs,m CP also suppressed the triplet-triplet annihilation and balanced the charge transport.The as-fabricated CPLEDs exhibited a maximum brightness of 3906 cd/m²,a peak EQE of 10.0%and dissymmetry factors of-5.3×10^-3and 4.7×10^-3.As our efforts achieved the MNC-based CPLEDs with best performance,the host molecule enhanced AIE of MNCs provided a promising strategy for fabricating high-performanced MNC-based CPLEDs and EL-LEDs.更多还原