新型蒽基回旋交叉共轭荧光分子体系的构筑及其光电性质研究

Conjugated organic molecules have attracted considerable attention owing to their interesting properties as materials for charge transport, sensing, non linear optics, electronics, and optoelectronics. However, organic electroluminescent materials with good combined performances are still scarce, and there is a demand for the exploitation of new and high-performance organic lumonogens applicable in LEDs. Anthracene and its derivatives have been reused as building blocks for promising functional materials with unique optical and optoelectronic properties, because its derivatives usually have a high fluorescence quantum yield and wide energy band-gap in solution, but the planarity of anthracene means it is prone to aggregation in the solid state and causes fluorescence quenching and emission wavelength red-shifting. In view of advantages of swivel cross structure and 9,10-diarylanthracene, along with development of new structure and principle emissive materials, in this project, we first design, and synthesize anthracene-based swivel cruciforms by linking functional moieties at the ortho- and meta-positions, rather than at the para-position of 9,10-diaryl units to form 2,5-direction conjugation branches, which endows such anthracene-based molecules with more twisted and swivel conformation and less dependent optical and electronic properties among branches and anthracene unit. This structure could suppress the intermolecular π-π interactions and enhance fluorescence emission and adjust the electroluminescent nature. The fluorescent branches could be tuned to be hole- and/or electron-transporting moieties, aggregation-enhanced emission, and twisted donor-acceptor type, which renders the integral materials with unique aggregation behavior, frontier molecular orbital and exciton utilization natures. Such swivel cruciforms are multi-function integration and multi-color emission, novel high-performance electroluminescence materials could be developed. Moreover, the swivel cruciforms based-on 9,10-diarylanthracene have the well-defined structure, good film-forming, high morphological stability, and most of them are solution- processed, which are also suitable for investigation on structure-property relationship.

本项目首次综合利用和发挥回旋交叉结构和9,10-二芳基蒽各自优点，构筑具有独特几何构型和构象的新型蒽基回旋交叉共轭荧光分子体系，研究它们的聚集行为、电致发光性质及结构与性能关系。通过变化9,10-二芳基及在芳基邻位和间位键接不同功能杈体基团，有效降低杈体之间、蒽环之间及蒽环与杈体之间的π-π相互作用，调控材料的聚集行为、荧光光色、载流子传输和电致发光特性，获得高发光体密度、高形态热稳定性、易于合成纯化、包括可溶液加工成膜的多功能集成新结构新原理有机电致荧光齐聚物材料。本项目不仅拓展了蒽基共轭分子和回旋交叉共轭分子的种类、光电特性和应用范围，开辟综合性能优良的新结构新原理有机电致发光材料新途径，而且为揭示分子几何构型和构象及维数等对材料聚集行为和光电性质影响，提供了结构明确、便于构效关系研究的新材料体系。

不同化学组成和结构的共轭有机分子能够重要影响材料的聚集态结构和分子间相互作用，因而显示不同的光电特性。具有大的内旋转位垒的蒽基回旋交叉共分子，存在因分子单键内旋转而引起的基团在空间的不同排布方式，这种构象或旋转异构体同样影响分子内电荷转移、分子间的相互作用和堆积结构，进而影响材料的光电性质。如果能获得稳定和可分离的共轭有机回旋交叉构象异构体，研究它们的聚集态结构和对光电性质的影响，是一个很有意义的不同于以往多晶培养的创新性研究课题。然而，共轭有机分子单键内旋转位垒通常较小，构象异构体很难被预先稳定在特定结构和分离，其设计合成和光电性质鲜见研究报道。本项目以9,10-二苯基蒽为母体，通过在苯环邻位引入电子给/受体等芳基单元，有效调控和强化苯基‒蒽单键的内旋转位垒，首次成功创建和分离出新型顺式（syn-）和反式（anti-）回旋交叉构象异构体，研究构象异构体的光热稳定性及其空间位阻效应，研究构象异构对聚集态结构和光电性质的影响。通过在9,10-二苯基蒽的苯环邻位引入电子给体咔唑、噁二唑和苯基乙烯等位阻基团，得到6对12个可分离的构象异构体。研究了在熔融、真空蒸镀条件下构象的稳定性，借助DSC和核磁共振谱表征，结合内旋转位垒的量子化学计算，研究了构象之间相互转变的可能性和调控途径。发现构象异构几乎不影响溶液的光学吸收和发射性质，但严重影响晶态的光电性质。一种构象异构体晶体堆积呈现压电空间群，相对应的构象异构体往往是非压电空间群堆积结构，压电空间群的晶体表现明亮的力致发光现象。电致发光器件性能表征结果表明，反式构象异构体常常能获得更高的电致发光亮度和电流效率，显示在无定形蒸镀膜状态，順式和反式构象异构体可能已经形成不同的堆积结构，对平面蒽环间的π-π作用有影响，掺杂器件的性能几乎不受掺杂浓度的影响，表现低的启动电压（2.6 V）、高的流明效率（14 lm/W）和大于5%的EQE。本项目不仅发展9,10-二芳基蒽衍生物的新种类和新性质，其构效关系对新型共轭有机光电材料的构筑也有重要的启发和指导意义。