image: In a tetrahydrofuran/water solvent system with a water content of 70%, the toroidal topological structures formed by molecular assembly were observed via atomic force microscopy.
Credit: Jie Lu
As an important class of chiral assemblies, cyclic topological nanostructures such as toroids and Möbius strips have attracted significant attention in supramolecular chemistry. However, the assembly of macrocyclic molecules into well-defined chiral toroidal or Möbius strip topologies remains rarely reported. Now, writing in the journal National science review, a team of researchers designed chiral amphiphilic pillar[5]arene derivatives by conjugating enantiomeric glutamide units to the macrocyclic framework. Using assembly strategies such as the anti-solvent method, they achieved the construction of chiral topological toroid from chiral macrocyclic molecules. Furthermore, a systematic investigation was conducted on the chiroptical properties of these assembled topological architectures.
In THF/water mixed solvents, these compounds spontaneously organized into chiral toroidal nanostructures and Möbius strip-like nanorings through synergistic non-covalent interactions, including hydrogen bonding, van der Waals forces, and π-π stacking. The assembly process exhibited intriguing solvent-dependent evolution: small amounts of water led to the formation of stable bilayer vesicles, while 70% of water content made the vesicles to transform into toroidal topologies, with some adopting distinct Möbius strip-like structures through dynamic reconfiguration of intermolecular interactions.
Notably, the resulting nanostructures displayed structure-dependent luminescent properties. Only the toroidal assemblies exhibited strong blue circularly polarized luminescence (CPL), while the other aggregated forms showed no CPL activity. Furthermore, these chiral toroids could serve as supramolecular templates to induce achiral fluorescent blue or red dyes to emit as CPL, a phenomenon unattainable with the conventional assemblies.
This work establishes a novel strategy for constructing hierarchical chiral topologies from macrocyclic building blocks, spanning from molecular to nanoscale. In addition, it demonstrates precise control over chiroptical properties through solvent-mediated structural regulation, opening new possibilities for designing functional chiral nanomaterials.