Defect‐Free Synthesis of a Fully π‐Conjugated Helical Ladder Polymer and Resolution into a Pair of Enantiomeric Helical Ladders

• Published in: Angewandte Chemie International Edition 2023-05, Vol.62 (20), p.e202301962-n/a
• Main Authors: Ikai, Tomoyuki, Miyoshi, Sayaka, Oki, Kosuke, Saha, Ranajit, Hijikata, Yuh, Yashima, Eiji
• Format: Article
• Language: English
• Subjects: Alkynes; Circular dichroism; Defect-Free; Defects; Degree of polymerization; Dichroism; Enantioseparation; Fully π-Conjugation; Helical Ladder Polymers; Ladders; Molecular dynamics; Nanotechnology devices; Optical activity; Polymers; Synthesis; Thermal stability
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202301962

Fully π‐conjugated ladder polymers with a spiral geometry represent a new class of helical polymers with great potential for organic nanodevices, but there is no precedent for an optically active helical ladder polymer totally composed of achiral units. We now report the defect‐free synthesis and resolution of a fully π‐conjugated helical ladder polymer with a rigid helical cavity, which has been achieved by quantitative and chemoselective acid‐promoted alkyne benzannulations of a rationally designed, random‐coil achiral polymer followed by chromatographic enantioseparation. Because of a sufficiently high helix‐inversion barrier, the isolated excess one‐handed helical ladder polymer with a degree of polymerization of more than 15 showed a strong circular dichroism with a dissymmetry factor of up to 1.7×10−2 and is thermally stable, maintaining its optical activity in solution even at 100 °C, as well‐supported by molecular dynamics simulation. Quantitative and chemoselective helical ladderization of a rationally designed random‐coil polymer followed by chromatographic enantioseparation has led to a fully π‐conjugated optically active helical ladder polymer composed entirely of achiral units. The sufficiently high helix‐inversion barrier makes the helical ladder polymer with an excess of one‐handed helicity thermally stable, maintaining its optical activity in solution even at 100 °C.