TPE-embedded butterfly bis-crown ether with controllable conformation and supramolecular chiroptical property

Understanding how subtle structural differences between macrocyclic conformational isomers impact their properties and separation has garnered increasing attention in the field of supramolecular synthetic chemistry. In this work, a series of tetraphenylene (TPE)-embedded butterfly bis-crown ether macrocycles (BCE[n], n = 4-7), comprising two crown ether side rings and a TPE core, are synthesized through intramolecular McMurry coupling. Unexpectedly, the presence of flexible oligoethylene chains with varying lengths are found to influence molecular conformation via multiple intramolecular interactions, resulting in the formation of two stabilized conformers with specific semi-rigid symmetric/asymmetric structures (sym-BCE[n] and asym-BCE[n], n = 5, 6). Moreover, it is noteworthy that neither symmetric nor asymmetric conformers are present in the more rigid BCE[4] or the more flexible BCE[7]. Interestingly, these conformers display distinct fluorescence properties and host-guest binding abilities, and only sym-BCE[5] can serve as a host for chiral polymer binding, resulting in the formation of chiral supramolecular assemblies through host-guest interaction induced chirality. Moreover, both circular dichroism and circularly polarized luminescence signals of the obtained assemblies can be switched off by the addition of sodium ion, suggesting potential applications in the field of dynamic chiral materials.