A heterocycle fusing strategy for simple construction of efficient solution-processable pure-red thermally activated delayed fluorescence emitters

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2022-11, Vol.1 (42), p.15981-15988
• Main Authors: Gong, Xu, Xiang, Yepeng, Ning, Weimin, Zhan, Lisi, Gong, Shaolong, Xie, Guohua, Yang, Chuluo
• Format: Article
• Language: English
• Subjects: Catalysts; Dehydration; Emitters; Energy gap; Fluorescence; Optical properties; Organic light emitting diodes; Quantum efficiency; Substitution reactions; Thiadiazoles
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc02089k

The development of solution-processable pure-red thermally activated delayed fluorescence (TADF) emitters remains a challenging task in the field of organic light-emitting diodes (OLEDs). Here two strong electron acceptor moieties, acenaphtho[1,2- b ][1,2,5]oxadiazolo[3,4- e ]pyrazine ( ANOP ) and acenaphtho[1,2- b ][1,2,5]thiadiazolo[3,4- e ]pyrazine ( ANTP ), were designed and synthesized by fusing 1,2,5-oxadiazole or 1,2,5-thiadiazole on an acenaphtho[1,2- b ]pyrazine unit through a simple and catalyst-free dehydration cyclization reaction. Combined with rigid electron-donating units, 9,9-dimethyl-9,10-dihydroacridine ( DMAC ) and 2,7-dimethyl-10 H spiro[acridine-9,9′-fluorene] ( MeFAC ), four solution-processable pure-red TADF emitters, ANOP-DMAC , ANOP-MeFAC , ANTP-DMAC , and ANTP-MeFAC , were designed and prepared through catalyst-free nucleophilic substitution reactions. The rational molecular design principles endow all the emitters with small singlet-triplet energy gaps (Δ E ST ), prominent TADF character, red emission, and moderate Φ PL s. The optical, electrochemical, and film morphological properties of all the emitters were systematically investigated. As a consequence, the ANTP-DMAC -based OLED realized a maximum external quantum efficiency of 6.8% with a peak wavelength at 630 nm and Commission International de l'Eclairage 1931 (CIE1931) coordinates of (0.59, 0.40), which is among one of the highest device performances for solution-processed pure-red TADF OLEDs. A heterocycle fusing strategy is demonstrated to construct solution-processable red thermally activated delayed fluorescence emitters. The resulting pure-red organic light-emitting diodes deliver a high external quantum efficiency of 6.8%.