The invention discloses a preparation method of a symmetric 
phosphine oxide type TADF organic photoelectric material, and belongs to the field of organic functional materials. 2, 2 '-dinitro-
biphenyl is subjected to stannous 
chloride reduction, amido 
acylation, 
electricity-rich aromatic ring bromination reaction and acid deacylation of a 
protecting group to form free amido, the amido is converted into 5, 5'-dibromo-2, 2 '-diiodo-
biphenyl through a diazonium salt process, then the 5, 5'-dibromo-2, 2 '-diiodo-
biphenyl is converted into 5, 5'-dibromo-2, 2 '-diiodo-biphenyl, and the 5, 5'-dibromo-2, 2 '-diiodo-biphenyl is converted into 5, 5 The preparation method comprises the following steps: carrying out 
lithium-
iodine exchange on 2, 2 '-diiodo-biphenyl, carrying out 
nucleophilic substitution reaction on the 2, 2'-diiodo-biphenyl and 
dichlorophenylphosphine to generate 
phenylphosphine heterobenzoindole, oxidizing the 
phenylphosphine heterobenzoindole to form 
phenylphosphine oxide heterobenzoindole, and carrying out 
coupling reaction on brominated 
aromatic hydrocarbon and heteroaromatic 
hydrocarbon under the 
catalysis of 
copper to synthesize the small organic molecule 
luminescent material with fluorescent 
reactive oxygen species. The 2, 8-diphenothiazinyl-5-phenyl benzoxphosphine heteroindole synthesized by the method has the potential of becoming an organic micromolecule electroluminescent material and being used as a 
photosensitizer for organic photoreaction, and fits the development trend of multifunctional application of organic micromolecule materials.