Chiral polymers based on thiophenes functionalized at the 3-position with a pendant containing a stereogenic sulfur atom. Synthetic and structural aspects

Abstract

The first synthesis of new, chiral polythiophenes functionalized at the 3-position of the thiophene ring with a pendant containing a stereogenic sulfur atom of sulfoxides, sulfoximines or sulfinates was developed. Chemical oxidative polymerization with FeCl₃ or Fe(ClO₄)₃ was successfully applied for their synthesis. It has been found that FeCl₃-induced polymerization of monomers functionalized with an optically active sulfoxide substituent (according to the Sugimoto procedure), leading to regioirregular, α-α′ couplings in the polythiophene backbone, yields polymeric materials with a racemized pendant. On the other hand, those polymers in which the stereogenic sulfur atom located in the sulfoxide moiety remains optically active were obtained using Fe(ClO₄)₃ as a suitable substitute for FeCl₃. In addition, FeCl₃-induced polymerization of monomers functionalized with an optically active sulfoximine substituent gave regiorandom polythiophenes without the racemized stereogenic sulfur centre of a pendant. The structures of the isolated polymeric materials were characterized by various spectroscopic techniques (NMR, IR, UV–vis and fluorescence), and their optical activity was confirmed by polarimetric measurements and CD analysis. Incorporation of a long hydrocarbon side chain to enhance the solubility of the polymers was verified, and the results on this topic were also discussed.