TECHNOLOGY FOCUS - POLYMERS - Preparation (claimed): A sulfur-containing polycyclic compound chosen from 4,8-di-thiophen-2-yl-benzo(1,2-b;4, 5-b')dithiophene-type compound of formula (IIIa), 5,10-di-thiophen-2-yl-3,8-dithia-dicyclopenta(a,f)naphthalene-type compound of formula (IIIb), and 4,8-diphenyl-benzo(1,2-b;4,5-b')dithiophene-type compound of formula (IIIc), and bromine-containing thieno-pyrrole-type compound of formula (IVa) or (IVb) are reacted in presence of palladium catalyst and organic solvent under inert atmosphere to obtain polycyclic compound (I) or (II). Preferred Process: The preparation of polycyclic compound (I) or (II) further comprises purification process which involves cooling the reactant mixture to room temperature, adding methanol to precipitate, collecting precipitate by filtration, passing through Soxhlet extractor, carrying out methanol-, acetone-, n-hexane- and chloroform-extraction, evaporating portion of solvent, adding methanol after the precipitation, and collecting the precipitate by filtration. The bromine-containing thieno-pyrrole-type compound (IVb) is obtained by reacting bromine-containing thieno-pyrrole-type compound of formula (V) and tin-containing compounds (VIa)-(VIc) under inert atmosphere in presence of palladium catalyst, and reacting obtained reaction product with N-bromosuccinimide. The reaction product of bromine-containing thieno-pyrrole-type compound (V) and tin-containing compounds (VIa)-(VIc), is added with mixed solution containing chloroform and trifluoroacetic acid, reacted and N-bromosuccinimide is added. Preferred Composition: The palladium catalyst is tetrakis(triphenylphosphine)palladium. The molar ratio of compounds (IIIa)-(IIIc) and bromine-containing thieno-pyrrole-type compound (IVa) is 1:1-1.5:1, preferably 1:1. The molar ratio of compounds (IIIa)-(IIIc) and bromine-containing thieno-pyrrole-type compound (IVb) is 1:1-1.5:1, preferably 1:1. The molar ratio of palladium catalyst and compounds (IIIa)-(IIIc) is 0.02-0.05:1, preferably 0.02:1. The organic solvent is toluene, chlorobenzene and/or o-dichlorobenzene. The molar ratio of bromine-containing thieno-pyrrole-type compound (V) and tin-containing compounds (VIa)-(VIc) is 2:1. The molar ratio of bromine-containing thieno-pyrrole-type compound (V) and palladium catalyst is 0.02:1. Preferred Condition: The compounds (IIIa)-(IIIc) and compound (IVa) or (IVb) are reacted at 100-120 degrees C, preferably 120 degrees C for 12-48 hours, preferably 24 hours.