Hierarchical chirality conversion switched by biaxial halogen bonding

Abstract

Precise control over chirality across hierarchical levels of peptides enriches the toolbox of peptide-based chiroptical materials. In this work, we report a controlled conversion from folded molecular chirality to supramolecular chirality, which can be effectively switched by biaxial halogen bonds. Amino acid segments were conjugated to the bipyridine core as a β-turn to facilitate the formation of parallel β-sheet arrays, which enables intramolecular chirality transfer to the appended pyrenes. This allows for efficient excimer emission and boosted circularly polarized luminescence with a dissymmetry factor of up to 10⁻². The folding structures are self-assembled into nanohelices where supramolecular chirality is dominated by emerged heterochirality in response to the solvent medium. The introduction of hypervalent iodine(III) species binds to the peptide via strong biaxial I⋯N halogen bonds that transform well-ordered helices into amorphous nanoparticles. The biaxial halogen bonding complexation rearranges the assembly with extremely high efficacy, suppressing the supramolecular chirality and recovering the folded molecular chirality, when the chiroptical activities are rationally manipulated. This work unveils the dynamic conversion of artificially folded peptides, which will inspire the design of protocols for peptide- or protein-based chiroptical materials.