In the traditional molecular design of thermally activated delayed fluorescence (TADF) emitters composed of electron-donor and electron-acceptor moieties, achieving a small singlet-triplet energy gap (ΔE ) in strongly twisted structures usually translates into a small fluorescence oscillator strength, which can significantly decrease the emission quantum yield and limit efficiency in organic light-emitting diode devices. Here, based on the results of quantum-chemical calculations on TADF emitters composed of carbazole donor and 2,4,6-triphenyl-1,3,5-triazine acceptor moieties, a new strategy is proposed for the molecular design of efficient TADF emitters that combine a small ΔE with a large fluorescence oscillator strength. Since this strategy goes beyond the traditional framework of structurally twisted, charge-transfer type emitters, importantly, it opens the way for coplanar molecules to be efficient TADF emitters. Here, a new emitter, composed of azatriangulene and diphenyltriazine moieties, is theoretically designed, which is coplanar due to intramolecular H-bonding interactions. The synthesis of this hexamethylazatriangulene-triazine (HMAT-TRZ) emitter and its preliminary photophysical characterizations point to HMAT-TRZ as a potential efficient TADF emitter.

With the aim of achieving high‐performance thermally activated delayed fluorescence, a series of trioxoazatriangulene derivatives are systematically developed by modifying the donor substituents. The emission colors are shifted from green to greenish‐yellow and to yellow with rather broad spectral widths of 70–95 nm by introducing carbazole, triphenylamine, or diphenylamine donor units, indicating that each emission originates from a charge‐transfer transition. On the other hand, the trioxoazatriangulene modified with three diphenylamines shows orange emission with a narrow emission spectrum (45 nm), suggesting that the transition mainly originates from a multiple resonance effect.