Organic Long-Persistent Luminescence from a Thermally Activated Delayed Fluorescence Compound
Organic Long-Persistent Luminescence from a Thermally Activated Delayed Fluorescence Compound
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DOI：
10.1002/adma.202003911
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发表时间：
2020-10-07
影响因子：
29.4
通讯作者：
Samuel, Ifor D. W.
中科院分区：
文献类型：
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作者：
Li, Wenbo;Li, Zhaoning;Samuel, Ifor D. W.
有机长余辉发光(OLPL)是最有前途的长寿命发光方法之一。然而，目前的室温OLPL发射器主要是基于双分子激基络合物体系，通常需要昂贵的小分子如2，8-二(二苯基-磷酰基)二苯并[b，d]噻吩基(PPT)作为受体。本研究设计了一种新型的热激活延迟荧光化合物3-(4-(9H-carbazol-9-yl)phenyl)acenaphtho[1，2-b]pyrazine-8，9-dicarbonitrile(CHPhAP)，该化合物在PPT、2，2‘，2-’‘-(1，3，5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)(TPBi)和聚甲基丙烯酸甲酯(PMMA)等多种已知主体中也显示出OLPL，没有任何激基络合物的形成，在室温下其OLPL持续时间超过1h。结合PMMA制造的低成本和TADF分子的灵活设计，纯有机、大规模、颜色可调和低成本的室温OLPL应用成为可能。此外，我们还发现TADF掺杂薄膜的77K余辉光谱的开始并不一定是确定最低三重态能级的可靠方法。这是因为在一些TADF发射体掺杂的薄膜中，光激发可以产生电荷(电子和空穴)，这些电荷可以在磷光光谱测量过程中重新结合形成单重态激子。因此，在低温下的磷光时间窗中获取的光谱可能由单线态和三线态发射组成。
Organic long-persistent luminescence (OLPL) is one of the most promising methods for long-lived-emission applications. However, present room-temperature OLPL emitters are mainly based on a bimolecular exciplex system which usually needs an expensive small molecule such as 2,8-bis(diphenyl-phosphoryl)dibenzo[b,d]thiophene (PPT) as the acceptor. In this study, a new thermally activated delayed fluorescence (TADF) compound, 3-(4-(9H-carbazol-9-yl)phenyl)acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile (CzPhAP), is designed, which also shows OLPL in many well-known hosts such as PPT, 2,2 ',2 ''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi), and poly(methyl methacrylate) (PMMA), without any exciplex formation, and its OLPL duration reaches more than 1 h at room temperature. Combining the low cost of PMMA manufacture and flexible designs of TADF molecules, pure organic, large-scale, color tunable, and low-cost room-temperature OLPL applications become possible. Moreover, it is found that the onset of the 77 K afterglow spectra from a TADF-emitter-doped film is not necessarily reliable for determining the lowest triplet state energy level. This is because in some TADF-emitter-doped films, optical excitation can generate charges (electron and holes) that can later recombine to form singlet excitons during the phosphorescence spectrum measurement. The spectrum taken in the phosphorescence time window at low temperature may consequently consist of both singlet and triplet emission.