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Effects of Electron Affinity and Steric Hindrance of the Trifluoromethyl Group on the π-Bridge in Designing Blue Thermally Activated Delayed Fluorescence Emitters.
Chemistry - A European Journal ( IF 3.9 ) Pub Date : 2020-03-24 , DOI: 10.1002/chem.202000926 Huiting Li 1, 2 , Jiuyan Li 1 , Di Liu 1 , Tingting Huang 1 , Deli Li 1
Chemistry - A European Journal ( IF 3.9 ) Pub Date : 2020-03-24 , DOI: 10.1002/chem.202000926 Huiting Li 1, 2 , Jiuyan Li 1 , Di Liu 1 , Tingting Huang 1 , Deli Li 1
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To explore the correlation of the acceptor electron affinity and the molecular conformation to the thermally activated delayed fluorescence (TADF) feature, a series of d-π-A molecules were designed and synthesized with triazine (Trz) as the acceptor (A) and carbazole (Cz) or tert-butylcarbazole (BuCz) as the donor (D). On the phenylene bridge between D and A, methyl or trifluoromethyl was incorporated close either to D or to A to tune the molecular conformation and the electron-withdrawing ability of acceptor. Both the twist angles and the singlet and triplet energy difference (ΔEST ) were observed strongly dependent on the type and position of the substituent on the π-bridge. Only those molecules with trifluoromethyl locating close to the D side, namely TrzCz-CF3 and TrzBuCz-CF3 , exhibit TADF feature, verifying that both sufficient electron affinity of the A unit and large dihedral angle between D and the π-bridge are necessary to ensure the occurrence of TADF. The blue organic light-emitting diodes fabricated with TrzCz-CF3 and TrzBuCz-CF3 achieved external quantum efficiencies of 9.40 % and 14.22 % with CIE coordinates of (0.19, 0.23) and (0.18, 0.29) respectively. This study provides practical design strategy for blue TADF materials particularly when planar and less crowded group is used as donor.
中文翻译：
在设计蓝色热活化延迟荧光发射体时，三氟甲基的电子亲和力和位阻对π桥的影响。
为了探索受体电子亲和力和分子构象与热活化延迟荧光（TADF）特征的相关性，设计并合成了一系列以三嗪（Trz）为受体（A）和咔唑的d-π-A分子（Cz）或叔丁基咔唑（BuCz）作为供体（D）。在D和A之间的亚苯基桥上，靠近D或A并入甲基或三氟甲基，以调节受体的分子构象和吸电子能力。观察到扭曲角以及单线态和三线态能量差（ΔEST）都强烈依赖于π桥上取代基的类型和位置。只有那些三氟甲基位于D侧附近的分子，即TrzCz-CF3和TrzBuCz-CF3才显示TADF特征，验证了A单元的足够的电子亲和力以及D与π桥之间的大二面角对于确保TADF的发生都是必要的。用TrzCz-CF3和TrzBuCz-CF3制成的蓝色有机发光二极管的外部量子效率为9.40％和14.22％，CIE坐标分别为（0.19，0.23）和（0.18，0.29）。这项研究为蓝色TADF材料提供了实用的设计策略，尤其是在使用平面且较不拥挤的基团作为供体时。
更新日期：2020-03-24
中文翻译：
在设计蓝色热活化延迟荧光发射体时，三氟甲基的电子亲和力和位阻对π桥的影响。
为了探索受体电子亲和力和分子构象与热活化延迟荧光（TADF）特征的相关性，设计并合成了一系列以三嗪（Trz）为受体（A）和咔唑的d-π-A分子（Cz）或叔丁基咔唑（BuCz）作为供体（D）。在D和A之间的亚苯基桥上，靠近D或A并入甲基或三氟甲基，以调节受体的分子构象和吸电子能力。观察到扭曲角以及单线态和三线态能量差（ΔEST）都强烈依赖于π桥上取代基的类型和位置。只有那些三氟甲基位于D侧附近的分子，即TrzCz-CF3和TrzBuCz-CF3才显示TADF特征，验证了A单元的足够的电子亲和力以及D与π桥之间的大二面角对于确保TADF的发生都是必要的。用TrzCz-CF3和TrzBuCz-CF3制成的蓝色有机发光二极管的外部量子效率为9.40％和14.22％，CIE坐标分别为（0.19，0.23）和（0.18，0.29）。这项研究为蓝色TADF材料提供了实用的设计策略，尤其是在使用平面且较不拥挤的基团作为供体时。
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