The synthesis, aggregation, and optical properties of a chiral, regioregular polythiophene, substituted with a conjugated substituent, are described. The polymer was prepared using a Stille coupling reaction. The fact that the side-chain contributes to the absorption (UV-vis), emission (fluorescence), and redox behavior (cyclic voltammetry) of the material demonstrates that the substituent contributes to the electronic properties. It was shown that the conjugated side-chain chirally stacks in conditions in which the polymer backbone aggregates, which demonstrates the ability of conjugated polymers to induce a (chiral) lamellar organization of conjugated moieties, present in their side-chain. The aggregation of both the side-chain and the backbone was monitored using UV-vis and CD spectroscopy. Finally, it is shown that the conjugated side-chain can selectively be oxidized, without oxidizing the polythiophene backbone. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1891-1900, 2009