Multiple resonance delayed fluorescence emitter with C3 symmetry for high-performance solution-processed OLEDs

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2024-08, Vol.493, p.152857, Article 152857
• Main Authors: Zhuang, Xuming, Liang, Jie, Song, Xiaoxian, Wang, Qingyang, Bi, Hai, Liang, Baoyan, Wang, Yue
• Format: Article
• Language: English
• Subjects: Multiple resonance; Narrowband emission; Organic light-emitting diodes; Solution-processed; Thermally activated delayed fluorescence
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2024.152857

A unique molecular design paradigm aimed at developing solution-processed multiple resonance-induced thermally activated delayed fluorescence (MR-TADF) materials is proposed here, the solution processing ability could be enhanced by integrating three MR-building blocks. When utilized as an emitter in solution-processed organic light-emitting diodes (sOLEDs), the synthesized TriBNCz molecule demonstrates a narrow emission spectrum with full width at half maximum (FWHM) of 27 nm. Furthermore, through a sensitization strategy, the sOLED device achieves impressive maximum external quantum efficiency (EQE) of 28.8 % and maintains 26.1 % at 1000cd/m−2, with an FWHM of 30 nm and Commission Internationale de I’Éclairage (CIE) coordinates of (0.103, 0.497). [Display omitted] •A novel narrowband multiple resonance delayed fluorescence emitter is developed through the integration of MR-building blocks;•A higher kRISC has been achieved owing to the mixed SRCT and LRCT characteristic of excited states as well as multiple charge transfer channels;•Quite high maximum EQE of 28.8 % and a high-level EQE of 26.1 % at 1000 cd/m2, with an FWHM of 30 nm have been realized. Solution-processed organic materials that exhibit both high emission efficiency and narrowband emission characteristics are rare, and the performance of corresponding solution-processed organic light-emitting diodes (sOLEDs) remains inadequate for practical applications. This study proposes a proof-of-concept design aimed at enhancing both solution processing capability and emission efficiency in multiple-resonance induced thermally activated delayed fluorescence (MR-TADF) materials through the integration of multiple emitting units. A unique emitter named TriBNCz is synthesized and characterized, incorporating three MR-building blocks onto a single phenyl ring, resulting in sky-blue emission with a peak at 490 nm and a small full width at half maximum (FWHM) of 25 nm. Significant improvements in solution processing attributes, including solubility and film-forming properties, are achieved. Moreover, except for the MR effect of the excited states, long-range charge transfer properties of excited states are also obtained. The multiple charge transfer channels contribute to higher rate of reverse intersystem crossing (kRISC). The optimized sOLED device exhibits a maximum external quantum efficiency (EQEmax) of 17.8 %. Furthermore, by employing 5TCzBN as a sensitizer, the sensitized sOLED achieves an EQEmax of