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

Abstract

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 the degree of polymerization of more than 15 showed a strong circular dichroism with the 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.