Homochiral Helicene Covalent Organic Frameworks

While chirality is common in nature, creating synthetic macromolecules with controlled chirality remains a significant challenge. Here we report the synthesis of homochiral frameworks by exploring <i>M</i> and <i>P</i> enantiomers of [7]Helicene as building units to create chiral skeletons. The racemic [7]Helicene was separated into its <i>P</i>-[7]Helicene and <i>M</i>-[7]Helicene enantiomers via chiral column chromatography, which, upon aldol condensation reactions with 1,3,5-trimethyltriazine, form crystalline microporous <i>P</i>-[7]Helicene sp²c-COF-1 and <i>M</i>-[7]Helicene sp²c-COF-1, respectively. The resulting homochiral [7]Helicene sp²c-COFs develop a two-dimensional hexagonal lattice and π-conjugated skeleton linked by a C═C bond, displaying distinct circular dichroism of mirror images. Notably, <i>P</i>-[7]Helicene sp²c-COF-1 and <i>M</i>-[7]Helicene sp²c-COF-1 formed homogeneous thin films upon dispersion in a poly(methyl methacrylate) matrix and greatly enhanced circular dichroism signals and circularly polarized luminescence to reach a luminescence dissymmetry factor as high as 1.2 × 10^-3 at 570 nm. These findings demonstrate a way to homochiral frameworks for chiro-optical applications.