化学
分子内力
电致发光
量子产额
接受者
荧光
光化学
单重态
二苯胺
分子
有机发光二极管
量子效率
激发态
蒽醌
立体化学
原子物理学
光电子学
材料科学
有机化学
物理
量子力学
图层(电子)
凝聚态物理
作者
Qisheng Zhang,Hirokazu Kuwabara,William J. Potscavage,Shuping Huang,Yasuhiro Hatae,T. Shibata,Chihaya Adachi
摘要
Red fluorescent molecules suffer from large, non-radiative internal conversion rates (kIC) governed by the energy gap law. To design efficient red thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs), a large fluorescence rate (kF) as well as a small energy difference between the lowest singlet and triplet excited states (ΔEST) is necessary. Herein, we demonstrated that increasing the distance between donor (D) and acceptor (A) in intramolecular-charge-transfer molecules is a promising strategy for simultaneously achieving small ΔEST and large kF. Four D-Ph-A-Ph-D-type molecules with an anthraquinone acceptor, phenyl (Ph) bridge, and various donors were designed, synthesized, and compared with corresponding D-A-D-type molecules. Yellow to red TADF was observed from all of them. The kF and ΔEST values determined from the measurements of quantum yield and lifetime of the fluorescence and TADF components are in good agreement with those predicted by corrected time-dependent density functional theory and are approximatively proportional to the square of the cosine of the theoretical twisting angles between each subunit. However, the introduction of a Ph-bridge was found to enhance kF without increasing ΔEST. Molecular simulation revealed a twisting and stretching motion of the N–C bond in the D-A-type molecules, which is thought to lower ΔEST and kF but raise kIC, that was experimentally confirmed in both solution and doped film. OLEDs containing D-Ph-A-Ph-D-type molecules with diphenylamine and bis(4-biphenyl)amine donors demonstrated maximum external quantum efficiencies of 12.5% and 9.0% with emission peaks at 624 and 637 nm, respectively.
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