Helix Induction and Inversion of Polymeric Foldamer Regulated by the Single Enantiomers

This is the authors' abstract. We don't add key points for this paper.

Generally, a single enantiomer can induce a foldamer into a preferred‐handed helix, while another condition is required for the helical inversion. Herein, it is found that the helix induction and subsequent inversion of poly(m‐phenylene diethynylene)‐based foldamer bearing aza‐18‐crown‐6 pendants (Poly‐1) can be realized by increasing the concentration of sterically hindered l‐amino acid perchlorate salts. When the amount of chiral enantiomers is small, one enantiomer tends to complex with two non‐adjacent aza‐18‐crown‐6 rings via three N+H···O hydrogen bonds in a sandwich mode. Notably, the transition dipole moment is perpendicular to the aza‐18‐crown‐6 ring, so that the induced helical chirality in Poly‐1 backbone is opposite to the chirality of enantiomers. When the amount of chiral enantiomers is large enough, each aza‐18‐crown‐6 is occupied by one enantiomer, which causes the transition dipole moment in a parallel direction to aza‐18‐crown‐6 ring. In this case, the increased steric hindrance can facilitate the inversion of screw sense of Poly‐1 backbone, which is directed by chiral center of enantiomers. As a result, a helix inversion has been achieved successfully. This work not only provides a novel strategy for regulating the two‐stage folded helical conformations by the single enantiomers, but opens a window to develop chiral recognition materials.