TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): Copolymer (I) is prepared by adding 4,4'-dibromo-6,6'-diiodo-2,1,3-benzothiadiazole of formula (II), acetylenic compound of formula (III), first catalyst and base into first solvent, reacting under inert gas environment at 130 degrees C for 4 hours to obtain compound 3 of formula (IV), adding compound 4 of formula (V) into second solvent under inert gas environment, adding butyl lithium, reacting at - 78 degrees C for 1-2 hours, adding tributyltin chloride at - 78 degrees C, reacting for 1 hour, heating to room temperature for 6 hours, performing column chromatography using neutral alumina to obtain compound 5 of formula (VI), adding compound 3, compound 5 and second catalyst into third solvent under inert gas environment, and reacting at 50-120 degrees C for 6-100 hours to obtain diselenothiopene-benzodiazepine(benzothiadiazole) copolymer. The mole ratio of 4,4'-dibromo-6,6'-diiodo-2,1,3-benzothiadiazole and acetylenic compound is 1:2. The mole ratio of base and acetylenic compound is 1:1. The mole ratio of compound 4 and butyl lithium is 1:2. The molar amount of tributyltin chloride is 2 times the molar amount of compound 4. The mole ratio of compound 3 and compound 5 is 1:1.5-1.5:1.R1,R2=1-20C alkyl;R3,R4=H or 1-20C alkyl; andn=1-100.The 4,4'-dibromo-6,6'-diiodo-2,1,3-benzothiadiazole is prepared by adding compound E of formula (VII) into thionyl chloride, stirring, adding pyridine dropwise at 85 degrees C, reacting under reflux to obtain compound F' of formula (VIII), adding hydrobromic acid, reacting under reflux at 127 degrees C for 30 minutes, adding liquid bromine dropwise, reacting under reflux to obtain compound G of formula (IX), adding copper catalyst and N,N-dimethylformamide solvent, reacting by heating to 120 degrees C for 3 hours to obtain compound H' of formula (X), adding tin(II) chloride and tetrahydrofuran solvent, reacting under reflux by heating to 100 degrees C for 10 hours, and stopping reaction to obtain 4,4'-dibromo-6,6'-diiodo-2,1,3-benzothiadiazole. Preferred Component: The first catalyst is palladium(II) acetate. The second catalyst is tris(dibenzylideneacetone)dipalladium(0), tetrakis(triphenylphosphine)palladium(0) or bis(triphenylphosphine)palladium(II) dichloride, preferably bis(triphenylphosphine)palladium(II) dichloride. The base is tributylnitride. The acetylenic compound is 2,6,13,17-tetramethyl-9-octadecyne, 2,6-dimethyl-9-triacontyne or 2-pentyne. The first solvent is dimethylformamide. The second solvent is tetrahydrofuran. The third solvent is tetrahydrofuran, ethylene glycol dimethyl ether, diethyl ether, benzene or toluene. Preferred Composition: The molar amount of first catalyst is 10% of 4,4'-dibromo-6,6'-diiodo-2,1,3-benzothiadiazole. The molar amount of second catalyst is 0.05-20% of compound 3.