Stimuli-Responsive Aggregation-Induced Delayed Fluorescence Emitters Featuring the Asymmetric D–A Structure with a Novel Diarylketone Acceptor Toward Efficient OLEDs with Negligible Efficiency Roll-Off

Abstract

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%.

A multifunctional luminescent material based on quinoxaline and triphenylamine groups: polymorphism, mechanochromic luminescence, and applications in high-efficiency fluorescent OLEDs

“…10–13 Additionally, it is an effective way to investigate crystal-packing and structure–property relationships. 14,15 Z. Chi reported a chromophore with phenoxazine and phenothiazine as donors (D) and diphenyl sulfone as an acceptor (A), realizing full-color emission, peaking in the range of 469 nm to 583 nm, from ten individual single crystals, ranging from normal fluorescence to room-temperature phosphorescence. 16…”

Twisted Biphenyl‐Diimide Derivatives with Aggregation‐Induced Emission and Thermally Activated Delayed Fluorescence for High Performance OLEDs

“…Meanwhile, the EL spectra resembled to the FL spectra of the two emitters revealed that the EL really stemmed from the emitting layers. [ 57 ]…”

Aggregation‐induced emission: Red and near‐infrared organic light‐emitting diodes

“…In 2020, Yang et al 127 reported two D–A type aggregation‐induced delayed fluorescence (AIDF) emitters, pipd ‐BZ‐PXZ, pipd ‐BZ‐PTZ (Figure 10A), where a fused N‐heterocycle (imid‐azo[1,2‐a]pyridin‐2‐yl(phenyl), pipd ) and diarylketone acceptor served as acceptor, and phenoxazine (PXZ), phenothiazine (PTZ) group functioned as donors respectively. Owing to the embedded two nitrogen atoms, the pipd exhibited very strong electron‐withdraw ability, which favors the ICT effect and red‐shifted emission.…”

“…(A) Chemical structure of pipd ‐BZ‐PXZ and pipd ‐BZ‐PTZ; (B) PL spectra of pipd ‐BZ‐PXZ in THF/water mixtures with various f w ; (C) plots of I / I 0 versus f w (red) and emission wavelength change (blue) upon increasing the water content, I 0 stands for the PL intensity in THF, and the inset presents PL images under f w of 0%, 50%, and 99%, respectively; (D) chemical structure of BenCN‐PXZ and BDCN‐PXZ; (E) EL spectra measured at 10 mA cm −2 from the doped OLED based on emitters of BenCN‐PXZ (5 wt% in CBP) and BDCN‐PXZ (20 wt% in CBP); (F) EQE versus luminance plots of the two OLED devices. Reproduced (Adapted) with permission 127,128 . Copyright 2020, American Chemical Society.…”