The present invention is directed to a method for preparing a 4,7-bis(5-halothien-2-yl)-2,1,3-benzothiadiazole, more particularly, 4,7-bis(5-bromothien-2-yl)-2,1,3-benzothiadiazole, and a precursor therefor, namely, a 4,7-bis(thien-2-yl)-2,1,3-benzothiadiazole. The precursor is prepared by contacting in the presence of a palladium catalyst and a solvent a 4,7-dihalo-2,1,3-benzothiadiazole with a thienyl group adding reagent, which can either be a 2-thienylzinc halide, a 2-thienylmagnesium halide, or a 2-thiopheneboronic acid, under such conditions as to form 4,7-bis(thien-2-yl)-2,1,3-benzothiadiazole. The precursor can then be halogenated, preferably brominated, to form the desired dibrominated product, which is a particularly suitable monomer for the preparation of a copolymer of a 9,9-disubstituted fluorene. This copolymer is useful, for example, in polymeric light emitting diode (pLED) applications.