Multiple-resonance thermally activated delayed fluorescence (MR-TADF) materials can exhibit narrow-spectrum characteristics owing to the inhibition of rotation within the molecules. However, the excited states of these MR-TADF materials, which influence the spin–orbit couplings (SOCs) and device efficiencies of organic light-emitting diodes (OLEDs), have not been investigated to date. In this study, we synthesized MR-TADF materials tDABNA-TP, tDABNA-DN, and tDABNA-DOB by incorporating characteristic neutral, donor, and acceptor pendants into 2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (tDABNA). To determine the effect of pendant engineering, we investigated the excited states of the MR-TADF materials, including their singlet and triplet excited states, calculated the SOCs for their optimal reverse intersystem crossing pathways, and determined their maximum external quantum efficiencies (EQE_max) in OLEDs. The OLED with the emitter bearing the neutral pendant (tDABNA-TP) exhibited the highest EQE_max of 20.7% among those with the emitters bearing the donor (16.6%) and acceptor (12.4%) pendants, with a narrow emission range of 472–492 nm. Furthermore, the device with the tDABNA-TP emitter exhibited an operating lifetime of 196 h, which was 1.42- and 1.92-fold longer than those of the devices with the tDABNA-DN and tDABNA-DOB emitters, respectively. Our findings will promote research on the pendant engineering of MR-TADF-based OLEDs.

中文翻译：

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多共振热激活延迟荧光中的悬垂工程，以产生电荷转移和局部激发态特性


由于抑制分子内的旋转，多共振热激活延迟荧光 （MR-TADF） 材料可以表现出窄光谱特性。然而，这些 MR-TADF 材料的激发态会影响有机发光二极管 （OLED） 的自旋轨道耦合 （SOC） 和器件效率，迄今为止尚未得到研究。在这项研究中，我们通过将特征中性、供体和受体胶束掺入 2,12-二叔丁基-5,9-双（4-（叔丁基）苯基）-5,9-二氢-5,9-二氮杂-13b-硼氧基[3,2,1-de]蒽 （tDABNA） 中，合成了 MR-TADF 材料 tDABNA-TP、tDABNA-DN 和 tDABNA-DOB。为了确定悬垂工程的效果，我们研究了 MR-TADF 材料的激发态，包括它们的单重态和三重态激发态，计算了其最佳反向系统间交叉路径的 SOC，并确定了它们在 OLED 中的最大外部量子效率 （EQE_max）。在带有供体 （16.6%） 和受体 （12.4%） 悬垂的发射器的 OLED 中，带有中性悬垂 （tDABNA-TP） 的 OLED 表现出最高的 EQE_最大值，为 20.7%，发射范围狭窄，为 472-492 nm。此外，带有 tDABNA-TP 发射器的设备的使用寿命为 196 小时，分别比带有 tDABNA-DN 和 tDABNA-DOB 发射器的设备长 1.42 倍和 1.92 倍。我们的研究结果将促进对基于 MR-TADF 的 OLED 的悬垂工程的研究。