高效有机电致荧光材料中新型电子给体的开发与应用

In the organic electroluminescence (EL) field, organic fluorescent molecules with a D-π-A skeleton have gained increasing attention for their low cost and the potential for realizing an internal quantum efficiency of 100%. For the moment, relative to a variety of excellent electron-acceptors (A), the electron-donors (D) are still very limited, mainly referring to two classic structure types of carbazole and diphenylamine, as well as their derivatives. Thus, there is a lack of another typical D group which is capable of finding itself a universal utility in the EL application, and this to a large extent restricts the development of organic EL materials and devices. To solve this dilemma, this project is supposed to propose a new type of D group, pyrrolo[3,2-b]pyrrole, which has recently made a breakthrough in its synthesis methodology and owns a huge room for molecular derivation. The research here will focus on three respects: designing and synthesizing a series of center-symmetrical multi-ad D-π-A compounds based on the pyrrolo[3,2-b]pyrrole core; ascertaining the influence rules of the molecular structure features, such as the peripheral A groups’ species, substituting positon and number, on their optical and electronic physical properties; realizing fluorescent OLEDs with high quantum efficiencies using these pyrrolo[3,2-b]pyrrole -based molecules. This project will extend the structure system of the organic EL materials, and provide new theoretical and experimental basis for designing low-cost and high-performance organic EL materials.

在有机电致发光领域，D-π-A构型的有机荧光分子因为廉价的成本和实现100%内量子效率的潜力，受到了越来越多的关注。相对于目前种类繁多的优良电子受体A，电子给体D的种类仍然非常有限，主要是沿用咔唑和二苯胺这两类经典结构及它们的衍生体。因而尚且缺少第三类能够普适于电致发光应用的D基团，而这在很大程度上限制了电致发光材料和器件的发展。针对上述问题，本申请拟引入近期在合成方法上有了突破并且具有巨大分子衍生空间的新型电子给体—吡咯并[3,2-b]吡咯。研究内容包含三方面：设计、合成系列以吡咯并[3,2-b]吡咯为核心的点中心对称的多元D-π-A化合物；探明外围A取代的种类、位置、数目等结构因素对分子光电物理性质的影响规律；实现基于吡咯并[3,2-b]吡咯分子的高量子效率的荧光OLED器件。本项目将拓宽有机电致发光材料的结构体系，为设计高效、廉价的有机电致发光材料提供一些理论和实验上的新依据。

近年来D-A型分子在OLED应用中受到越来越多的关注，因元素电负性的差异，A基团的种类已有很多，而与之形成鲜明反差的是针对新型D基团的开发明显落后，主要仍在使用咔唑和二苯胺这两类经典的D基团以及他们的衍生体。本研究以吡咯并[3,2-b]吡咯作为新型电子给体基团，衍生合成了系列D-A型荧光分子，光谱覆盖蓝、绿、红三基色，从电子受体A的拉电子能力、共轭程度以及数量引起的空间排斥作用等角度，归纳总结光谱性质与分子结构的关系。其中，BTZPP在经济型溶液法OLED器件中实现了3.4%的外量子效率，处在同类型器件（溶液法红光器件）的前列水平。但是项目执行过程中发现吡咯并[3,2-b]吡咯类分子的热稳定性较差，不适合用真空蒸镀的方法制作结构更加复杂的器件，因而后期我们转向开发新型高三重态能级D-A分子材料。本研究也提供了一种普适、便捷、高产率的合成策略，制备芴基9位sp3碳上同时修饰D和A基团的高三重态能级双极分子材料，D和A基团的种类可变化，因而为OLED应用提供了系列高效敏化蓝绿光TADF的主体材料以及高效发光激基复合物的给体材料，其中三元体系的绿光激基复合物实现了24%的最高外量子效率。上述研究工作将为未来OLED应用中D-A型功能分子的设计提供一定的参考思路。