Optical activity of heteroaromatic conjugated polymer films prepared by asymmetric electrochemical polymerization in cholesteric liquid crystals: Structural function for chiral induction

We electrochemically polymerized various achiral heteroaromatic monomers in left-handed helical cholesteric liquid crystal (CLC) media. Circular dichroism (CD) spectroscopy revealed that most of the resulting conjugated polymer films exhibited both the first negative and second positive Cotton effects near their absorption maxima. This indicates left-handed helical aggregation of the conjugated main chains, which is consistent with left-handed helical order of the CLC. This result suggests that the left-handed helical CLC environment induced left-handed helical aggregation of the polymers during the electrodeposition. However, CD intensity of the polymers depends on the structure of the parent monomers. Systematic investigation of the relationship between monomer structures and optical activity of the polymers indicates that linearity of the conjugated main chains and excluded volume interaction between the monomers and the CLC are important factors for producing optical activity of the polymers.