Kusakabe Yu, Wada Yoshimasa, Misono Tomoya, Suzuki Katsuaki, Shizu Katsuyuki, Kaji Hironori
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
ACS Omega. 2022 May 4;7(19):16740-16745. doi: 10.1021/acsomega.2c01308. eCollection 2022 May 17.
The members of the imidazole family have been widely used for electron transporting, host, conventional fluorescent, and phosphorescent materials. Although the imidazole core also has great potential as an acceptor segment of deep-blue thermally activated delayed fluorescence (TADF) owing to its high triplet energy, the emission color of imidazole-based TADF organic light-emitting diodes (OLEDs) has so far been limited to blue to green. In this work, four acridan-imidazole systems are theoretically designed aiming for deep- or pure-blue emitters. All four emitters exhibit deep-blue to blue emission owing to the high energy levels of the lowest excited singlet states, exhibiting coordinates of Commission Internationale de l'Eclairage coordinates between 0.06 and 0.26. The molecule composed of a trifluoromethyl-substituted benzimidazole acceptor in combination with a tetramethyl-9,10-dihydroacridine donor (named MAc-FBI) achieves a high maximum external quantum efficiency (EQE) of 13.7% in its application to vacuum-processed OLEDs. The emitter has high solubility even in ecofriendly nonhalogenated solvents, which motivates us to fabricate solution-processed MAc-FBI-based OLEDs, resulting in an even higher EQE of 16.1%.
咪唑家族的成员已被广泛用于电子传输、主体、传统荧光和磷光材料。尽管咪唑核心由于其高三重态能量，作为深蓝色热激活延迟荧光（TADF）的受体片段也具有很大潜力，但迄今为止，基于咪唑的TADF有机发光二极管（OLED）的发射颜色仅限于蓝色到绿色。在这项工作中，理论上设计了四种吖啶-咪唑体系，旨在获得深蓝光或纯蓝光发射体。由于最低激发单重态的高能级，所有四种发射体均呈现深蓝光到蓝光发射，其国际照明委员会（CIE）坐标在0.06至0.26之间。由三氟甲基取代的苯并咪唑受体与四甲基-9,10-二氢吖啶供体组成的分子（命名为MAc-FBI）在应用于真空处理的OLED时，实现了13.7%的高最大外量子效率（EQE）。该发射体即使在环保型无卤溶剂中也具有高溶解性，这促使我们制备基于溶液处理的MAc-FBI的OLED，其EQE甚至更高，达到16.1%。
