posted on 2020-06-22, 16:34authored byZhiwen Yang, Yingying Zhan, Zhipeng Qiu, Jiajie Zeng, Jingjing Guo, Sheng Hu, Zujin Zhao, Xianwei Li, Shaomin Ji, Yanping Huo, Shi-jian Su
Multifunctional
luminescent materials with aggregation-induced delayed fluorescence
(AIDF) are capable of suppressing concentration-caused emission quenching
and exciton annihilation when used as organic light-emitting diode
(OLED) emitters. In this contribution, three stimuli-responsive AIDF
luminogens, pipd-BZ-PXZ, pipd-BZ-PTZ,
and pipd-BZ-DMAC, featuring a D–A asymmetric
framework based on a fused N-heterocycle diarylketone acceptor (imid-azo[1,2-a]pyridin-2-yl(phenyl)methanone pipd) are
designed and synthesized. Interestingly, pipd-BZ-PTZ
forms two different kinds of crystals (G-crystal and O-crystal) with
distinct intermolecular interactions between pipd moieties. The G-crystal with a looser packing mode presents significant
morphology-dependent stimuli-responsive behavior with a shifted emission
wavelength of 56 nm. Generated by a strong intramolecular charge transfer
effect, pipd-BZ-PXZ and pipd-BZ-PTZ
exhibit orange to red emission in solution and neat films. Both nondoped
and doped devices are fabricated for comparison. Nondoped devices
present moderate performance with external quantum efficiencies and
current efficiency that reach 7.04% and 19.86 cd A–1, respectively, and the corresponding efficiency roll off at 1000
cd m–2 is as small as 2.3%, which is among the best
records of AIDF-OLEDs with an emission wavelength over 570 nm. Doped
devices show better performance with corresponding efficiencies of
up to 55.41 cd A–1 and 15.77%.