Thermally　activated　delayed　fluorescence　(TADF)　molecules,　which　can　realize　100%　internal　quantum　efficiency　without　using　noble　metals,　have　emerged　as　the　third-generation　organic　light　emitting-diode　(OLED)　emitters.　However,　high-efficiency　red　TADF　materials　are　still　rare　because　of　their　restricted　molecular　design　based　on　the　energy-gap　law.　Herein,　two　new　TADF　emitters,　2,3-bis　(dimethylacridin　phenyl)　quinoxaline-4,4　＇-dicyanobenzene　(DMAC-QCN)　and　2,3-bis　(phenoxazine　phenyl)　quinoxaline-4,4　＇-dicyanobenzene　(PXZ-QCN)　are　designed　and　synthesized.　Both　investigated　compounds　exhibit　significant　TADF　characteristics　with　small　energy　gap　(Delta　E-ST)　between　the　lowest　excited　singlet　and　triplet　states,　short　delayed　fluorescence　lifetimes,　excellent　thermal　stability　and　high　photoluminescence　quantum　yields.　The　vacuum-deposited　OLEDs　utilizing　DMAC-QCN　and　PXZ-QCN　as　emitters　display　yellow　and　red　electroluminescence　with　emission　peaks　at　545　and　604　nm,　and　maximum　external　quantum　efficiencies　(EQEs)　of　17.3%　and　15.6%,　respectively.　Notably,　the　PXZ-QCN-based　device　shows　a　small　efficiency　roll-off　of　14.1%　(EQE　=　13.4%)　even　at　a　practical　high　luminance　of　1000　cd　m(-2).