Two blue thermally activated delayed fluorescence molecules based on bis(phenylsulfonyl)benzene with very small singlet–triplet splitting energy were designed and synthesized by combining 3,6-di-tert-butylcarbazole with 1,4-bis(phenylsulfonyl)benzene and 1,3-bis(phenylsulfonyl)benzene, and a maximum external quantum efficiency of 11.7% was achieved for an electroluminescent device.