New soluble poly(aryleneethynylene)s consisting of electron-accepting benzothiadiazole units and electron-donating dialkoxybenzene units. Synthesis, molecular assembly, orientation on substrates, and electrochemical and optical properties

A new class of poly(aryleneethynylene)s containing an aryl heterocyclic structure were prepared in the yield of higher than 80% by polycondensation between 4,7-dibromo-2,1,3-benzothiadiazole and 2,5-dialkoxy-1,4-diethynylbenzenes with different long side chains using Pd(PPh3)(4) and CuI as the catalysts in the presence of triethylamine. All these polymers had a number-average molecular weight, M., higher than 12 000 and showed good solubility in chloroform. The polymers were photoluminescent in chloroform and showed metallic luster in the solid state. X-ray diffraction patterns of the powder and cast film (on a platinum plate) of the polymers revealed that the polymers assumed a pi-stacked structure in the solid state, and the polymer molecules in the film were ordered on the surface of the platinum plate.