Efficient thermally activated delayed fluorescence(TADF)emitters have an important application for organic light-emitting diodes(OLEDs).However,due to the limitations of the energy gap law,the development of efficient red TADF emitters with wavelengthsover 600 nm is chal-lenging.Herein,a novel rigid larger conjugated planar acceptor dibenzo[f,h]pyrido[3,4-b]quinoxaline(DBPQ)had been designed,and three TADF materials,namely DBPQtCz,DBPQDMAC and DBPQPXZ,were synthesized by connecting with different donors(tCz,DMAC and PXZ)to DBPQ.With the enhancement of electron-donating ability of the corresponding donors,the emission wavelengths of DBPQtCz,DBPQDMAC and DBPQPXZ were significantly red-shifted and turned from green,red to deep-red.The OLED based on DBPQDMAC obtained maximum exter-nal quantum efficiency(EQEmax)up to 16.0％,and the peak electroluminescent(EL)of 612 nm,while the EQEmax of DBPQPXZ is 3.2％,and the peak EL is 658 nm.Meanwhile,the OLEDs based on DBPQtCz,DBPQDMAC and DBPQPXZ achieved extremely low turn-on voltages of 2.4,2.5 and 2.8 V,respectively.
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