A homologous series of donor-substituted oligothiophenes 5, 7, and 9 bearing pyrrolidino groups in the "outer" beta-positions were synthesized up to a quaterthiophene. The physical properties were investigated in dependence on the chain length of the conjugated system. Due to the substitution pattern, even the longer oligomers exhibit good film forming properties and could be electropolymerized to the corresponding donor-substituted polythiophenes P5, P7, and P9, which promise a pure stereoregular structure. The electronic properties of both oligomers and polymers were found to be strongly dominated by the donor strength of the substituents.