Highly Efficient Red-Orange Delayed Fluorescence Emitters Based on Strong π-Accepting Dibenzophenazine and Dibenzoquinoxaline Cores: toward a Rational Pure-Red OLED Design
Highly Efficient Red-Orange Delayed Fluorescence Emitters Based on Strong π-Accepting Dibenzophenazine and Dibenzoquinoxaline Cores: toward a Rational Pure-Red OLED Design
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DOI：
10.1002/adom.201701147
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发表时间：
2018-03-05
影响因子：
9
通讯作者：
Yasuda, Takuma
中科院分区：
文献类型：
--
作者：
Furue, Ryuhei;Matsuo, Kyohei;Yasuda, Takuma
表现出热激活延迟荧光（TADF）的有机发光材料可以收获用于发光的单重态和三重态激子，导致有机发光二极管（OLED）中的高电致发光（EL）量子效率。然而，高效的红色TADF材料仍然非常罕见，因为它们基于能隙定律的受限分子设计。为了解决这一问题，应策略性地设计可以同时实现大的荧光辐射速率和小的单重态-三重态能量分裂的精细π共轭供体-受体（D-A）系统。在本研究中，为了制备高效的纯红色TADF材料，在D-pi-A分子框架中引入了非常强的π-接受二氰基二苯并[a，c]吩嗪（CNBPz）单元，并与亚苯基连接的对二甲苯基胺或9，9-二甲基吖啶部分结合。稳态和时间分辨的电子物理测量显示，这些CNBPz基分子在溶液和掺杂薄膜中都有强烈的真正的红色TADF发射。结合CNBPz基TADF发光体的OLED实现了所需的高效率的纯红色EL，中心在670 nm处，色坐标为（0.66，0.34），伴随着15.0%的高最大外部EL量子效率。因此，可以得出结论，CNBPz，其扩展的π-共轭和强电子接受特性，是一个特别有用的建筑单元，以设计长波长TADF材料，可以克服固有的能隙定律的障碍。
Organic luminescent materials that exhibit thermally activated delayed fluorescence (TADF) can harvest both singlet and triplet excitons for light emission, leading to high electroluminescence (EL) quantum efficiencies in organic light-emitting diodes (OLEDs). However, efficient red TADF materials are still very rare because of their restricted molecular design based on the energy gap law. To address this issue, elaborate pi-conjugated donor-acceptor (D-A) systems that can simultaneously achieve a large fluorescence radiative rate and small singlet-triplet energy splitting should be strategically designed. In this study, to produce high-efficiency pure-red TADF materials, a remarkably strong pi-accepting dicyanodibenzo[a,c]phenazine (CNBPz) unit has been introduced in a D-pi-A molecular framework, and combined with a phenylene-linked p-ditolylamine or 9,9-dimethylacridan moiety. The steady-state and time-resolved photophysical measurements revealed intense genuine red TADF emissions of these CNBPz-based molecules in both solution and doped thin films. The OLEDs incorporating the CNBPz-based TADF emitters achieve the desired high-efficiency pure-red EL, centered at 670 nm with color coordinates of (0.66, 0.34), accompanied by a high maximum external EL quantum efficiency of 15.0%. Therefore, it is concluded that CNBPz, with its expanded pi-conjugation and strong electron-accepting characteristics, is a particularly useful building unit to design long-wavelength TADF materials that can overcome the intrinsic energy gap law obstacle.