Two new copolymers, P1 and P2, containing 5,5-bis(dodecyloxymethyl)-5,6-dihydro-4H-cyclopenta[c]thiophene (DCPT) or DCPT-based thiophene trimer (as donor) and 4,4-dibutyl-2,2-bithiazole (BTz, as weak acceptor) have been synthesized. To reduce the steric hindrance and enhance the conjugation, the thiophene spacers have been incorporated between DCPT and BTz in P2, which play an important role in maintaining the side chain ordering and -stacking interactions. Both the polymers showed -stacking with similar distances (approximate to 0.37 nm) but with larger extent in P2. Combination of DCPT with BTz has resulted in low lying HOMO levels for the resulting polymers with significant improvement in oxidative stability. P1 and P2 showed p-type mobility of 0.03 and 0.052 cm(2) V-1 s(-1) with current on/off ratio (I-on/I-off) in the order of 10(4) and 10(3), respectively. These differences in characteristics may be attributed to the variation in donor (D)-acceptor (A) property, supramolecular ordering, extent of -stacking, and film microstructure. The polymers were further characterized by GPC, TGA, DSC, PXRD, cyclic voltammetry, and atomic force microscopy. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4481-4488