The invention relates to a thermal activation delayed fluorescent material with a general formula of the structure shown as the formula (I) or the formula (II). D is one of phenoxazinyl, phenothizainyl, 9,9-dimethyl 
acridine, 9-methyl phenazinyl, 9-phenyl phenazinyl, 4-phenoxazinyl-1-phenyl, 4-phenothizainyl-1-phenyl, 4-(9,9-dimethyl)acridinyl-1-phenyl, 4-(9-methyl)-phenazinyl-1-phenyl, 4-(9-phenyl)phenazinyl-1-phenyl and 3,5-bis-carbazolyl-1-phenyl. The invention further relates to an organic electroluminescent device which comprises a light-emitting layer, and luminescent dye of the light-emitting layer is the thermal activation delayed fluorescent material. The 
singlet state-
triplet state energy gap (
delta EST) of the thermal activation delayed fluorescent material is very small, 
triplet state excitors can be converted into 
singlet state excitors through inverse 
intersystem crossing (RIST) to emit light, and the efficiency and stability of an 
OLED device can be improved. The formula is shown in the description.