3-Benzoyl-4H-chromen-4-one: A novel twisted acceptor for highly efficient thermally activated delayed fluorescence emitters

In this work, a novel twisted 3-benzoyl-4H-chromen-4-one (BZC) acceptor is reported and a BZC-based thermally activated delayed fluorescence (TADF) emitter, 3-(4-(10H-phenoxazin-10-yl)benzoyl)-4H-chromen-4-one (BZC-PXZ), is developed. The unique structure of BZC endows BZC-PXZ with favorable molecular and stacking structures. First, the small and twisted structure of BZC group not only brings about large dihedral angle (88.78 degrees) between donor and acceptor groups, but also efficiently prevents pi center dot center dot center dot pi interaction. Second, the three oxygen atoms of BZC group bring about abundant weak intermolecular interactions which can enhance the charge-transporting ability of BZC-PXZ and facilitate the exciton recombination on it. As a result, BZC-PXZ exhibits small singlet-triplet energy splitting (0.02 eV) and high photoluminescence quantum yield (93%) simultaneously. Meanwhile, the BZC-PXZ-based device displays high efficiency (64.6 cd/A, 69.0 lm/VV, 21.3%), high exciton utilization efficiency (77.2%) and low roll-off of efficiencies even at ultralow doped concentration of 1%. These results demonstrate that BZC group is a good acceptor for developing high-performance TADF emitters.