Extremely high and readily tunable optical activity in a poly(phenylacetylene) with small-size amino-acid pendant groups

A poly(phenylacetylene) (PPA) derivative with small-size amino acid pendant is synthesized by Rh complexes. The resulting polymer showed a very high specific rotation and Cotton effect in chloroform, suggesting that a predominant one-handed helical conformation is adopted by the PPA backbone of 2. Such high value may be related to the hydrogen bonding between the polymer chains. The sign of specific rotation and Cotton effect in 2 are readily tunable by changing solvents. [α]_D²⁰ and molar ellipticity of 2 are not only-solvent dependent but also molecular weight sensitive, which is rarely reported in optically active PPAs.