Fluorene-based phosphine oxide host materials for blue electrophosphorescence: an effective strategy for a high triplet energy level.-猫眼课题宝

DOI：

10.1002/chem.201003434

发表时间：

2011-02

期刊：

Chemistry

影响因子：

通讯作者：

中科院分区：

文献类型：

作者：

Donghui Yu;Yongbiao Zhao;Hui Xu;Chunmiao Han;Dongge Ma;Zhaopeng Deng;Shan Gao;Pengfei Yan

电致磷光由于其单重态和三重态激子的内量子效率可达100%而引起了人们的极大兴趣。基于电致磷光材料的磷光体有机发光二极管（PHOLED）可以应用于高能效的平板显示器，也是下一代固态照明的有希望的候选者。[1]然而，三重态激子的较长寿命增加了三重态-三重态湮灭和浓度猝灭的可能性。为了提高器件的性能，一个有效的方法是在主体材料中掺杂荧光粉。[2]然而，稳定和高效的蓝光发射PHOLED的创建仍然是一个重大的挑战。[3]对于发蓝光的电致磷光掺杂体系，向客体（例如双（4，6-二氟苯基吡啶基-N，C2）吡啶基铱（FIrpic））的有效正能量转移需要主体的非常高的第一三重态能级（T1）（T1% 3.0eV）。[4]除了高T1之外，低操作电压是要求宿主的优异载流子注入/传输能力的另一重要因素。[3a-e]通常，高T1需要小的共轭面积，这对载流子注入和传输能力是有害的。因此，如何开发具有高T1和优异载流子注入/输运能力的高效基质材料是高性能蓝光PHOLED的关键问题。为了扩大共辄面积，大多数主体被设计为引入内消旋、扭曲或绝缘键，例如N，N-二咔唑基-3，5-苯（mCP [4]）、9，9 '-（2，2'-二甲基联苯-4，4 '-二基）双（9 H-咔唑）（CDBP [5]）和四芳基硅烷衍生物。[6]然而，咔唑衍生物的电子注入能力差，或硅的电惯性[7a]引起载流子注入/传输能力不平衡，这增加了工作电压。近年来，一些芳基氧化膦（APO）衍生物显示出优异的蓝光PHOLED基质特性，引起了人们的极大兴趣。[7]结果表明，载脂蛋白O宿主的T1由分子中的发色团决定。此外，与其他绝缘系统相比，P= O部分可以有效地将分子固定，以实现对最低未占分子轨道（LUMO）的贡献。[7b]因此，APO可以支持有效的载流子注入/传输能力和高T1。然而，对于迄今为止报道的几乎所有APO主体，P= O部分沿分子的长轴沿着直接键合到发色团;例如，芴的2，7-取代，[7 b，f-h]咔唑的3，6-取代，[7a]和二苯并呋喃的2，8-取代。[7c]这种结构在维持高T1方面是无效的，因为P= O键仍然可以稍微减小能隙和激发能级。[7a因此，高性能APO主体的关键问题之一是开发PO部分和发色团的合适连接模式以保持高T1并促进主体的进一步多官能化。最近，我们报道了一种新的载脂蛋白O主机与邻位连接的氧化膦部分。[8]这证明了不对称结构在保持高T1和使发色团偏振方面是上级的。为了进一步提高载脂蛋白O主体的T1，我们认为发色团和氧化膦部分的间接连接可能是另一种有效的策略。本文设计了两种基于芴的APO主体9-（4 '-丁基苯基）-9-（二苯基磷酰基苯基）芴（FSPO）和9，9-双（二苯基磷酰基苯基）芴（FDPO），并对其进行了表征。

Electrophosphorescence has attracted much interest, with the potential of 100% internal quantum efficiency, generated from both singlet and triplet excitons. Phosphorescent organic light-emitting diodes (PHOLEDs) based on electrophosphorescent materials can be applied to highly energyefficient, flat-panel displays and are also promising candidates for the next generation of solid-state lighting.[1] However, the longer lifetime of triplet excitons increases the possibility of triplet–triplet annihilation and concentration quenching. To improve the device performance, an effective approach is doping the phosphors in host materials.[2] Nevertheless, the creation of stable and efficient blue-emitting PHOLEDs remains a significant challenge.[3] For blue-emitting electrophosphorescent doping systems, the efficient, positive-energy transfer to the guest (such as bis (4, 6-difluorophenylpyridinato-N, C2) picolinatoiridium (FIrpic)) requires a very high first triplet energy level (T1) of the host (T1% 3.0 eV).[4] Besides the high T1, a low operating voltage is another significant factor that requires an excellent carrier injection/transporting ability of the host.[3a–e] Usually, a high T1 requires a small conjugated area, which is detrimental to the carrier injection and transporting ability. Therefore, the key issue for high-performance blue-emitting PHOLEDs is how to develop efficient host materials with a high T1 and excellent carrier injection/transporting ability. To expand the conjugated area, most of the hosts are designed to incorporate meso, twisted, or insulating linkages, such as N, N-dicarbazoyl-3, 5-benzene (mCP [4]), 9, 9’-(2, 2’-dimethylbiphenyl-4, 4’-diyl) bis (9H-carbazole)(CDBP [5]), and tetraaryl silane derivatives.[6] However, the poor electron-injection ability of carbazole derivatives, or the electrical inertia of silicon,[7a] induces an unbalanced carrier injection/transporting ability, which increases the operating voltage. Recently, a number of aryl phosphine oxides (APO) derivatives have shown excellent host characteristics for blue-emitting PHOLEDs and attracted intense interest.[7] Results indicate that the T1 of the APO hosts is determined by the chromophores in the molecules. Furthermore, in contrast to other insulating systems, the P= O moieties can efficiently polarize the molecules to enable contributions to the lowest unoccupied molecular orbital (LUMO).[7b] Therefore, APOs can support both an efficient carrier injection/transporting ability and a high T1. Nevertheless, for nearly all of the APO hosts reported so far, the P= O moieties are directly bonded to the chromophores along the long axis of the molecules; for example, the 2, 7-substitution of fluorene,[7b, f–h] the 3, 6-substitution of carbazole,[7a] and the 2, 8-substitution of dibenzofuran.[7c] Such structures are ineffective in maintaining a high T1 because the P= O bond can still slightly reduce the energy gap and the excited levels.[7a, d, e] Therefore, one of the key problems for high-performance APO hosts is the development of a suitable linkage mode of PO moieties and chromophores to preserve a high T1 and facilitate further multifunctionalization of the hosts. Recently, we reported a novel APO host with an ortho-linked phosphine oxide moiety.[8] This proved that the unsymmetrical structure is superior in maintaining a high T1 and polarizing the chromophore. To further improve the T1 of the APO hosts, we believed that an indirect linkage of the chromophore and phosphine oxide moieties may be another effective strategy. Herein, two fluorene-based APO hosts, 9-(4’-butylphenyl)-9-(diphenylphosphorylphenyl) fluorene (FSPO) and 9, 9-bis (diphenylphosphorylphenyl) fluorene (FDPO) were designed and …

Fluorene-based phosphine oxide host materials for blue electrophosphorescence: an effective strategy for a high triplet energy level.

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