X⋅⋅⋅X Halogen Bond‐Induced Supramolecular Helices

Abstract

AbstractThe 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 a challenge 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 21 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−1. Halogen bond induced an opposite helicity compared to the fluorinated species, accompanied by the inversed circularly polarized luminescence.