X…X Halogen Bond-Induced Supramolecular Helices

The halogen bond is the attractive interaction between the electrophilic region of a halogen atom and the nucleophilic region of another molecular entity, emerging as a favorable manner to manipulate supramolecular chirality in self-assemblies. Engineering halogen bonded helical structures remains major challenges due to its sensitivity to solvent polarity and competitive forces like hydrogen bonds. Herein, we report a X …X (X = Cl, Br, I) type weak halogen bond that induces the formation and evolution of supramolecular helical structures both in solid and solution state. The π-conjugated phenylalanine derivatives with F, Cl, Br and I substitution self-assembled into 2 1 helical packing driven by hydrogen bond and halogen bond respectively. The specific molecular geometries of π-conjugated amino acids gave rise to multiple noncovalent forces to stabilize the X…X halogen bond with small bond energies ranging from -0.69 to -1.49 kcal/mol. Halogen bond induced an opposite helicity compared to the fluorinated species, accompanied by the inversed circularly polarized luminescence. The halogen bond could further engineer the helical nanoarchitectures in the mono- and multiple-component coassemblies with melamine, providing a flexible protocol to prepare chiral functional materials. This work unveils the effect of weak X…X type halogen bonds on controlling supramolecular chirality in solid and solution state and offers a strategy to design halogenated chiral functional molecules.