Thermally activated delayed fluorescent (TADF) emitters based on pure organic aromatic compounds aroused much attention in that an internal quantum efficiency of 100% can be achieved by taking advantage of the efficient up-conversion of the triplet excitons. Novel thioxanthone-based TADF emitters, TXO-TPA and TXO-PhCz, were reported. Both emitters exhibited high fluorescent efficiency and small energy gap between the triplet and singlet, affording the high efficient up-conversion process from triplet states to singlet states. Their application in the high performance organic light emitting diodes were investigated in detail. These results made thioxanthone derivatives promising for the application in the future organic flat panel display and solid-state lighting.