新型刚性铱(III)配合物的合成及其在有机发光二极管中的应用

The development of emissive materials is one of the key steps for the advances in organic light emitting diode (OLED) technology. Phosphorescent Ir(III) complexes are one type of most popular emitters. Within Ir(III) complexes, the vibration and rotation of ligands around metal ion could lead to the non-radiative decay, which could account in part for the low quantum yields. Herein the rigid bidentate or tridentate ligands were linked together through rigid π bridges to enhance the overall rigidity of Ir(III) complexes, which could lead to high quantum yields, high stability and good color purity, and at meantime reduce concentration-induced luminescence quenching and the production isomers. This project intends to study the dependence of the emission properties of novel Ir(III) complexes on the rigid ligands and to investigate the relationship between the structures of Ir(III) complexes and device performance via the optimization of the structures and electronic properties of multiple-dentate ligands such as the rigidity, planarity and the size of the conjugation system of ligands, and the steric effect of ancillary ligands. This study includes the following sections: (1) the design and synthesis of novel rigid ligands; (2) the preparation and purification of Ir(III) complexes; (3) the selection of suitable host materials to enhance the energy transfer from hosts to dopants; (4) the fabrication and optimization of OLED devices, and the interrogation of the device data and the redesign of novel rigid ligands.

发光材料的发展是有机发光二极管（OLED）技术发展的一个重要环节，其中磷光铱(III)配合物是一类备受关注的发光材料。在铱(III)配合物中配位基团振动和转动引起的非辐射跃迁是导致发光效率降低的一个重要因素。本项目拟通过π桥联基团连接二齿或三齿配位单元来增强铱(III)配合物整体结构的刚性，从而提高发光效率、稳定性和色纯度，同时抑制浓度淬灭效应和减少异构体的形成。本项目拟研究多齿刚性配体的结构和性能（配体的刚性和共面性、配体的配位性能、配位基团的共轭尺度和电子能级、辅助基团的位阻效应等）对铱(III)配合物发光性能的影响，并归纳总结新型刚性铱(III)配合物结构与OLED器件性能之间的关系。本项目的研究内容主要包括（1）新型刚性多齿配体的设计与合成；（2）新型铱(III)配合物的制备、提纯与表征；（3）主客体材料的能级匹配以及能量传输；（4）OLED器件制备、性能分析与材料结构的优化。

自1987年C.W.Tang和S.A.VanSlyke发明有机发光二极管 (OLED) 以来，研究者在其器件物理和相关实际应用方面取得了重大进展。磷光材料通过引入铱(Ⅲ)、铂(Ⅱ)等重原子,可以实现三重态激子到单重态的跃迁，进而达到100%的激子利用。磷光Ir（III）配合物中的刚性配体可以抑制金属离子周围的振动和旋转，最大限度地利用单线态和三线态激子，从而降低非辐射跃迁速率。将大位阻辅助配体用于合成Ir（III）配合物，有利于减弱Ir（III）配合物分子之间的相互作用，从而减少三线态-三线态湮灭和三线态-极化子湮灭。基于Ir-DHBA的器件具有高的外量子效率（EQE）和低效率滚降。在亮度为1000 cd m-2和10 000 cd m-2时，EQE分别为25.3%和22.7%。三线态激子参与的湮灭过程将导致磷光OLED的效率显著下降。热激活延迟荧光（TADF）材料可以通过三线态激子到单线态激子的上转换来降低发光层（EML）中的三线态激子密度。然而，TADF主体材料的三线态激子寿命对效率衰减的影响仍在研究中。受TADF中具有小单线态-三线态能隙以及快速自旋-翻转过程的启发，我们合成了三线态激子寿命短的三嗪-咔唑杂化物（Trz–PhCz），由Trz–PhCz作为主体材料，在10 000 cd m-2时，绿色、黄色、橙色和红色OLED的EQE均超过20%，实现了极低的效率衰减。这项工作对开发低效率滚降的主体材料具有指导意义。