A simple strategy to achieve efficient thermally activated delayed fluorescent emitters via enhancing electron donating ability of donors

作者：Liu, He^*; Li, Jiafang; Li, Ganggang; Zhang, Bing; Zhan, Qun; Liu, Zhiwen; Zhou, Changjiang; Li, Kai; Wang, Zhiming; Yang, Chuluo^*

来源：Dyes and Pigments, 2020, 180: 108521.

DOI：10.1016/j.dyepig.2020.108521

• Enhancing electron donating ability
• Carbazole
• Thermally activated delayed fluorescent emitter
• Organic light emitting diode

Simultaneously achieving both effective reverse intersystem crossing (RISC) process and high values of radiative decay rate (k(r))/photoluminescent quantum yield (PLOY) are critical for efficient thermally activated delayed fluorescent (TADF) emitters. The separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) through typical molecular geometry tuning method guarantees a small Delta E-ST but results in disfavored oscillator strength for fluorescent decay. Herein, a simple method is provided to facilitate the reverse intersystem crossing (RISC) of TADF emitters via enhancing electron donating property of donors rather than twisting the donor-acceptor configuration. Three molecules, namely Me-Cz, Me-MOC and Me-DOC, are designed and synthesized. The introduction of methoxy group enhances the electron-donating ability of carbazole. The stabilized charge transfer state features a reduced splitting energy between the first singlet and triplet excited state, thus activating TADF process. Consequently, the molecules Me-DOC and Me-MOC achieve good external quantum efficiency of 18.6% and 12.4% in electroluminescent devices.