TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): 2,7-Bis(trimethyl tin)benzo(2,1-b:3,4-b')dithiophene of formula (A), 2,7-dibromobenzo(2,1-b:3,4-b')dithiophene of formula (B) and 5,8-2-(5-bromo-2-thienyl)-2,3-disubstituted-quinoxaline of formula (C) are subjected to Stille coupling reaction in presence of catalyst (a1) and organic solvent (b1) in oxygen-free environment. Preferred Process: The 5,8-2-(5-bromo-2-thienyl)-2,3-disubstituted-quinoxaline is obtained by carrying out hybrid reaction of 3,6-dibromo-O-phenylenediamine and alkyl ethylene dione, forming 5,8-dibromo-2,3-disubstituted-quinoxaline, reacting 5,8-dibromo-2,3-disubstituted-quinoxaline and 3-alkyl-2-boric acid thiophene and anhydrous sodium carbonate in organic solvent (b2) and catalyst (a2). The 5,8-2-(5-bromo-4-alkyl-2-thienyl)-2,3-disubstituted-quinoxaline is formed by reacting N-bromosuccinimide and 5,8-2-(4-alkyl-2-thienyl)-2,3-disubstituted-quinoxaline in mixed solvent of sulfuric acid and trifluoroacetic acid at 10-30 degrees C for 12-48 hours. The 2,7-bis(trimethyl tin)benzo(2,1-b:3,4-b')dithiophene is obtained by reacting 4,5-dialkyl-benzo(2,1-b:3,4-b')dithiophene and butyl lithium in organic solvent (b3) at -78 degrees C to -25 degrees C, and adding trimethyltin chloride to the mixture. The 2,7-dibromobenzo(2,1-b:3,4-b')dithiophene is obtained by reacting N-bromosuccinimide and 4,5-dialkyl- dibromobenzo(2,1-b:3,4-b')dithiophene in mixed solvent of sulfuric acid and trifluoroacetic acid at 10-30 degrees C for 12-48 hours. Preferred Composition: The catalyst (a2) is organic palladium, or mixture of organic palladium and organic phosphor ligand. The organic solvent (b2) is chosen from tetrahydrofuran, ether, methylene chloride, chloroform and ethyl acetate. The content of catalyst (a1) is 0.01-30 mol%. The catalyst (a1) is organic palladium or mixture of organic palladium and organic phosphorus ligand. The organic palladium is chosen from tris(dibenzylideneacetone)dipalladium, tetrakis(triphenylphosphine)palladium or bis(triphenylphosphine)palladiumchloride. The organic phosphor ligand is tri(o-tolyl)phosphine. The mol ratio of organic palladium and organic phosphorus ligand is 1:1-20. The organic solvent (b1) is chosen from tetrahydrofuran, glycol dimethyl ether, benzene, chlorobenzene and methylbenzene. The organic solvent (b3) is chosen from tetrahydrofuran, ether, methylene chloride, chloroform and ethyl acetate.