New poly(N-substituted dithieno[3,2-b:2',3'-d]pyrrole)s (PDTPs) with high molecular weights, good yields, and increased solubility were prepared, and their supramolecular behavior was studied. The polymers differ in their polymerization method (using chemical oxidants, Stille-couplings, or a Yamamoto-type polymerization) and the bulkiness of the side chain. The solubility of the polymer depends on the bulkiness of the side chains employed, while the yield and, to a lesser extent, the molecular weight depend on the polymerization method. In general, Stille-couplings proved to be the best polymerization method for PDTPs. The higher molecular weight polymers showed more defined voltammograms, higher lambda(max) together with the presence of a vibronic fine-structure, and higher fluorescence yields than lower molecular weight materials. In solution, the polymers are present as highly conjugated rigid rods, which, upon transition to films or in nonsolvents, poorly aggregate. The stacking is more complicated in high molecular weight polymers than in low molecular weight samples.