Suzuki Katsuaki, Kaji Hironori
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
J Am Chem Soc. 2023 Aug 2;145(30):16324-16329. doi: 10.1021/jacs.3c05204. Epub 2023 Jul 24.
The torsion angle between donor and acceptor segments of a thermally activated delayed fluorescence (TADF) molecule is one of the most critical factors in determining the performance of TADF-based organic light-emitting diodes (OLEDs) because the torsion angle affects not only the energy gap between the singlet and triplet but also the oscillator strength and spin-orbit coupling. However, the torsion angle is difficult to analyze, because organic molecules are in an amorphous state in OLEDs. Here, we determined the torsion angle of a highly efficient TADF emitter, DACT-II, in an amorphous state by dynamic nuclear polarization enhanced solid-state NMR measurements. From the experimentally obtained chemical shift principal values of N on carbazole, we determined the average torsion angle to be 52°. Such quantification of the torsion angles in TADF molecules in amorphous solids will provide deep insight into the TADF mechanism in amorphous OLEDs.
热激活延迟荧光（TADF）分子的供体和受体片段之间的扭转角是决定基于TADF的有机发光二极管（OLED）性能的最关键因素之一，因为扭转角不仅影响单重态和三重态之间的能隙，还影响振子强度和自旋-轨道耦合。然而，由于有机分子在OLED中处于非晶态，扭转角难以分析。在这里，我们通过动态核极化增强固态核磁共振测量确定了高效TADF发射体DACT-II在非晶态下的扭转角。从实验获得的咔唑上N的化学位移主值，我们确定平均扭转角为52°。对非晶态固体中TADF分子扭转角的这种量化将为深入了解非晶态OLED中的TADF机制提供帮助。
