Liu Tiangeng, Deng Chao, Duan Ke, Tsuboi Taiju, Niu Sheng, Wang Dan, Zhang Qisheng
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China.
State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China.
ACS Appl Mater Interfaces. 2022 May 18;14(19):22332-22340. doi: 10.1021/acsami.2c02623. Epub 2022 May 5.
Blue-emitting organic light-emitting diodes (OLEDs) fall significantly behind other OLEDs in operational stability. To better understand the key factors governing the stability of blue OLEDs employing thermally activated delayed fluorescence (TADF), nine efficient sky-blue to green TADF emitters with different frontier orbital energy levels and different TADF lifetimes have been designed and synthesized on the basis of charge-transfer (CT) acridine/phenyltriazine derivatives. Among them, ToDMAC-TRZ, a molecule composed of a 9,9-dimethyl-2,7-di--tolyl-9,10-dihydroacridine donor and a 2,4,6-triphenyl-1,3,5-triazine acceptor, shows a quantum yield of nearly 1 and a TADF lifetime as short as 0.59 μs in thin film. However, the stability of OLEDs is independent of the frontier orbital energy levels and TADF lifetime of the emitter. In contrast, the device half-life is found to decrease by five-sixths as the 0-0 energy of the singlet excitons increases by about 0.06 eV, which can be well-explained by the Arrhenius equation employing a photoreaction model. Whether in photoluminescence or electroluminescence, the contribution of long-lifetime triplet excitons to degradation is much lower than expected, which can be accounted for by how the solid-state solvation effect reduces the energy of the CT state and how most molecules have a low-lying locally excited triplet state.
发蓝光的有机发光二极管（OLED）在运行稳定性方面明显落后于其他OLED。为了更好地理解影响采用热激活延迟荧光（TADF）的蓝光OLED稳定性的关键因素，基于电荷转移（CT）吖啶/苯基三嗪衍生物，设计并合成了九种具有不同前沿轨道能级和不同TADF寿命的高效天蓝色至绿色TADF发光体。其中，由9,9-二甲基-2,7-二-对甲苯基-9,10-二氢吖啶供体和2,4,6-三苯基-1,3,5-三嗪受体组成的分子ToDMAC-TRZ在薄膜中的量子产率接近1，TADF寿命短至0.59 μs。然而，OLED的稳定性与发光体的前沿轨道能级和TADF寿命无关。相反，当单重态激子的0-0能量增加约0.06 eV时，器件半衰期会缩短六分之五，这可以通过采用光反应模型的阿仑尼乌斯方程得到很好的解释。无论是在光致发光还是电致发光中，长寿命三重态激子对降解的贡献都远低于预期，这可以通过固态溶剂化效应如何降低CT态的能量以及大多数分子如何具有低能的局域激发三重态来解释。
