Bartkowski Krzysztof, Zimmermann Crocomo Paola, Kochman Michał Andrzej, Kumar Dharmandra, Kubas Adam, Data Przemysław, Lindner Marcin
Institute of Organic Chemistry, Polish Academy of Sciences Kasprzaka 44/52 Warsaw 01-224 Poland
Faculty of Chemistry, Silesian University of Technology M. Strzody 9 Gliwice 44-100 Poland
Chem Sci. 2022 Jul 21;13(34):10119-10128. doi: 10.1039/d2sc03342a. eCollection 2022 Aug 31.
Hyperfluorescence (HF), a relatively new phenomenon utilizing the transfer of excitons between two luminophores, requires careful pairwise tuning of molecular energy levels and is proposed to be the crucial step towards the development of new, highly effective OLED systems. To date, barely few HF yellow emitters with desired narrowband emission but moderate external quantum efficiency (EQE < 20%) have been reported. This is because a systematic strategy embracing both Förster resonance energy transfer (FRET) and triplet to singlet (TTS) transition as complementary mechanisms for effective exciton transfer has not yet been proposed. Herein, we present a rational approach, which allows, through subtle structural modification, a pair of compounds built from the same donor and acceptor subunits, but with varied communication between these ambipolar fragments, to be obtained. The TADF-active dopant is based on a naphthalimide scaffold linked to the nitrogen of a carbazole moiety, which through the introduction of an additional bond leads not only to π-cloud enlargement, but also rigidifies and inhibits the rotation of the donor. This structural change prevents TADF, and guides bandgaps and excited state energies to simultaneously pursue FRET and TTS processes. New OLED devices utilizing the presented emitters show excellent external quantum efficiency (up to 27%) and a narrow full width at half maximum (40 nm), which is a consequence of very good alignment of energy levels. The presented design principles prove that only a minor structural modification is needed to obtain commercially applicable dyes for HF OLED devices.
超荧光（HF）是一种利用两个发光体之间激子转移的相对较新的现象，需要仔细地对分子能级进行成对调节，并且被认为是开发新型高效有机发光二极管（OLED）系统的关键步骤。迄今为止，仅有少数具有所需窄带发射但外部量子效率适中（EQE < 20%）的HF黄色发光体被报道。这是因为尚未提出一种将福斯特共振能量转移（FRET）和三重态到单重态（TTS）跃迁作为有效激子转移的互补机制的系统策略。在此，我们提出一种合理的方法，通过微妙的结构修饰，可以获得一对由相同供体和受体亚基构建但这些双极性片段之间具有不同连通性的化合物。具有热激活延迟荧光（TADF）活性的掺杂剂基于与咔唑部分的氮相连的萘酰亚胺支架，通过引入额外的键，不仅导致π云扩展，还使供体刚性化并抑制其旋转。这种结构变化阻止了TADF，并引导带隙和激发态能量同时追求FRET和TTS过程。使用所提出的发光体的新型OLED器件显示出优异的外部量子效率（高达27%）和半高宽窄（40 nm），这是能级非常良好匹配的结果。所提出的设计原则证明，只需进行微小的结构修饰就能获得适用于HF OLED器件的商业可用染料。
