TADF molecules with π-extended acceptors for simplified high-efficiency blue and white organic light-emitting diodes

Carbazole-benzonitrile derivatives (CzBNs) are promising high-efficiency and stable blue thermally activated delayed fluorescence (TADF) materials in organic light-emitting diodes (OLEDs), which, however, strongly rely on multiple-donor structures. Here, we demonstrate a strategic implementation of extending the acceptor π-system with parapositioned π-conjugation tails in fewer donor structures, producing a simple and versatile approach to enhance performances of CzBNs. This molecular structure not only enhances TADF properties by delocalizing the frontier molecular orbital distribution and facilitating states mixing but also improves outcoupling efficiency from the preferential horizontal emitting dipole orientation. The proof-of-concept blue emitter affords monochromic devices peaking at 469 nm with a remarkable maximum external quantum efficiency (EQEmax) of 35.7%. Furthermore, simplified bicolor and tricolor white OLEDs using the same compound as emitting host achieve impressive EQEmaxs of 29.3% and 21.1%, respectively. The state-of-the-art performances of both blue and white fluorescent devices validate the superiority of this molecular design strategy