Asymmetric sky-blue thermally-activated delayed fluorescence emitters bearing tris(triazolo)triazine moiety for solution-processable organic light-emitting diodes

An efficient blue thermally-activated delayed fluorescence (TADF) emitter is still a challenge in solution-processed organic light-emitting diodes (OLEDs). In this contribution, two asymmetric molecules, TTT-Ac and TTT-2Ac were synthesized and characterized, in which the tris(triazolo)triazine (TTT) fragment is used as the acceptor core and different numbers of acridine (Ac, one or two) units are considered as the donor unit. Both compounds display clear TADF character, concomitant with the emission between 420 and 450 nm in a doped PMMA film. Compared to TTT-2Ac, TTT-Ac shows blue-shifted emission due to its weaker intramolecular charge transfer effect. The solution-processed OLEDs achieve a maximum external quantum efficiency (EQE(max)) of 9.26% and 8.10% with the emission peak at about 470 nm for TTT-Ac and TTT-2Ac, respectively. Furthermore, the TTT-Ac-based solution-processed OLED exhibits an EQE(max) of 10.01% after optimization of the emitter thickness. This research focuses on the molecular structure-property relationship of TTT-based molecules, which enriches the TTT-based solution-processable sky-blue TADF emitter.