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Development of red thermally activated delayed fluorescence (TADF) emitters has been lagging behind when compared with those of blue and green fluorophores, especially for solution-processable ones. In this work, two novel orange-red TADF emitters 3,6-di(10 H -phenoxazin-10-yl)dibenzo a, c phenazine (DBPZ-DPXZ) and 10,10′-(11,12-bis(3,5-di- tert -butylphenyl)dibenzo a, c phenazine-3,6-diyl)bis(10 H -phenoxazine) ( t DBBPZ-DPXZ) are developed. A high-performance orange-red TADF emitter, DBPZ-DPXZ, is first prepared by connecting a rigid acceptor and two rigid donor segments. While this design strategy endows DBPZ-DPXZ with an excellent TADF performance leading to a vacuum-processed organic light-emitting diode (OLED) with a high external quantum efficiency (EQE) of 17.8%, the rigid segments limit its solubility and applications in solution-processed devices. Based on this prototype, t DBBPZ-DPXZ is designed with the addition of 3,5-di- tert -butylphenyl groups to boost its solubility with barely an influence on the photophysical properties. In particular, t DBBPZ-DPXZ maintains nearly an identical photoluminescence quantum yield of 83% and singlet–triplet energy splitting of 0.03 eV with EQE of 17.0% in a vacuum-processed orange-red OLED. Furthermore, it can be applied on the orange-red solution-processed OLED realizing an EQE as high as 10.1%, representing one of the state-of-the-art results of the reported orange-red solution-processed TADF-OLEDs. This work provides an effective strategy to address the conflicting requirements between high efficiency and good solubility and develop efficient soluble orange-red TADF emitters.
Chen et al. (Mon,) studied this question.