TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The separating and purifying steps comprise decompressing and distilling (II) and (III), then dripping in methanol, filtering the mixture using a filter, washing the mixture with methanol, then drying, leaching in chloroform and Soxhlet extracting with acetone, and vacuum pumping obtained product. (II) is prepared by adding thieno(2,3-f)benzothiophene-4,8-dione (IV) and 2-dimethoxyphosphoryl-1,3-dithiole compound of formula (V) into an anhydrous tetrahydrofuran solution under the protection of inert gas atmosphere, cooling the mixture at 78 degrees C, slowly adding cyclohexane solution and lithium diisopropylamide, stirring the mixture at 78 degrees C for 2-3 hours, carrying out Wittig-Horner reaction, heat preserving the mixture at room temperature for 0.5-1 hour, continuously reacting for 12-15 hours to obtain 4,8-bis(1,3-dithiol-2-ylidene)thieno(2,3-f)benzothiophene compound of formula (VI), where the mole ratio of lithium diisopropylamide and (V) is 1:1-1.5, and the mole ratio of (IV) and (V) is 1:2-1:2.5, adding obtained (VI) into the anhydrous tetrahydrofuran solution under the protection of inert gas atmosphere, cooling the mixture at 78 degrees C, slowly adding n-hexane solution and n-butyl lithium, stirring the reaction mixture at 78 degrees C for 2-3 hours, then adding trimethyl chloride, heat preserving the mixture at room temperature for 0.5-1 hour, continuously reacting for 20-24 hours, where the mole ratio of n-butyl lithium and (VI) is 2.2:1-2.5:1, and the mole ratio of trimethyl chloride and (VI) is 2:1-2.5:1. (III) is prepared by adding 2,6-dibromo-4H-dithieno(3,2-b;2',3'-d)pyrrole compound of formula (VII) and 2-thioxothiazolidin-4-one compound of formula (VIII) into second solvent in a mole ratio of 1:2-1:2.5, then dropping in aqueous ammonia, heating the dropped mixture, then adding ammonium chloride solution, stirring and refluxing the mixture at 80 degrees C for 2-3 hours, where the mole ratio of (VII) and ammonium hydroxide is 0.05-0.1 l, and the mole ratio of ammonium chloride and (VIII) is 0.7:1-0.9:1.R2 = linear or branched-chain alkyl.Preferred Components: The catalyst comprises organic palladium or organic phosphine ligand. The organic palladium comprises bis(triphenylphosphine)palladium dichloride and tetrakis(triphenylphosphine)palladium in a molar ratio of 1:2-1:20. The organic phosphine ligand is tris(dibenzylidene acetone) dipalladium and tris(2-methylphenyl) phosphine. The mol ratio of organic palladium and (III) is 0.01-5%. The first organic solvent is tetrahydrofuran, N,N-dimethyl formamide or toluene.