4.7 Article

Isomeric thermally activated delayed fluorescence emitters based on a quinolino[3,2,1-de]acridine-5,9-dione multiple resonance core and carbazole substituent

期刊

MATERIALS CHEMISTRY FRONTIERS
卷 6, 期 7, 页码 966-972

出版社

ROYAL SOC CHEMISTRY
DOI: 10.1039/d1qm01588e

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资金

  1. National Natural Science Foundation of China [51773141, 51873139, 61961160731, 62175171, 22175124]
  2. Suzhou Science and Technology Plan Project [SYG202010]
  3. Suzhou Key Laboratory of Functional Nano & Soft Materials, Collaborative Innovation Center of Suzhou Nano Science Technology
  4. 111 Project
  5. Joint International Research Laboratory of Carbon-Based Functional Materials and Devices

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This study investigates the influence of linking moieties on the efficiency of MR-TADF emitters. The results show that weakening the D-A interaction between the substituents and the MR core can enhance the photoluminescence quantum yield and external quantum efficiency of the emitters.
The color purity of the pixels is an essential indicator in organic light-emitting diode (OLED) commercial displays. Since the two important parameters of high color purity and efficiency can be achieved simultaneously, multiple resonance thermally activated delayed fluorescence (MR-TADF) emitters have achieved rapid development. Recently, there has been a lot of research work on connecting various donor (D) moieties to the existing MR core, but few studies on how the linking moiety affects the efficiency of MR-TADF emitters. To figure out the influence of substituents on the MR-TADF system, we developed three isomers QAOCz1, QAOCz2, and QAOCz3, which are constructed with the same moieties of 3,11-diphenylquinolino[3,2,1-de]acridine-5,9-dione and 9-phenyl-9H-carbazole (PhCz) by different site connections. Through reasonable adjustments of the substitution site, the donor-acceptor (D-A) interaction of the isomers gradually weakened and molecular rigidity gradually increased. As a result, their singlet-triplet energy gap (Delta E-ST) gradually decreased and their photoluminescence quantum yield (PLQY) gradually rose. QAOCz3 with the weakest D-A interaction successfully achieves a much higher PLQY of 98.9% and a smaller Delta E-ST of 0.16 eV. The QAOCz3 based OLED not only realizes the best maximum external quantum efficiency (EQE) of 21.1% but also has the narrowest full-width at half maximum (FWHM) of 40 nm. This work shows that weakening the D-A interaction between the substituents and the MR core by a spacer group is of great significance for the construction of efficient MR-TADF emitters.

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