New five-membered ring pi-conjugated polymers composed of 2,2'-bithiophene and 4,4'-dialkyl-2,2'-bithiazole units were prepared. The polymers were soluble in 1,2-dichlorobenzene and showed a UV-vis peak at about 490 nm above 120 degrees C. Cooling the solution led to the appearance of new UV-vis peaks at 550 and 600 nm, which were considered to originate from self-assembled polymer molecules. Powder XRD (X-ray diffraction) data supported a well-stacked solid structure of the polymers and a highly ordered structure of a polymer film formed on a quartz glass substrate. These data revealed a strong tendency of the new polymers to self-assemble and to form an aligned structure on the surface of the substrates. (c) 2006 Elsevier Ltd. All rights reserved.