Chiral Organic Cages with a Triple-Stranded Helical Structure Derived from Helicene

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Materials Science

Background:

• Helicenes possess inherent chirality due to their unique helical structure.
• Covalent organic cages (COCs) are porous materials with tunable properties.
• Developing chiral COCs is crucial for enantioselective applications.

Purpose of the Study:

• To synthesize novel covalent organic cages utilizing helicene building blocks.
• To investigate the structural and chiral properties of the resulting COCs.
• To evaluate the enantioselective adsorption capabilities of the chiral COCs.

Main Methods:

• Imine condensation reactions were employed to construct the COCs.
• Proton nuclear magnetic resonance (NMR) spectroscopy was used to confirm structural integrity and diastereotopy.
• Circular dichroism (CD) spectroscopy was utilized to analyze the chiral properties.
• Chiral adsorption experiments were performed using aromatic racemates.

Main Results:

• A [3+2]-type covalent organic cage with a triple-stranded helical structure was successfully synthesized.
• The intrinsic chirality of the helicene units was preserved in the COCs, exhibiting a propeller-like, twisted framework.
• Structural chirality was maintained in solution, evidenced by significant diastereotopy in NMR and distinct Cotton effects in CD spectra.
• The chiral COCs demonstrated notable enantioselectivity in the adsorption of various aromatic racemates.

Conclusions:

• Helicene-based covalent organic cages can be effectively prepared via imine condensation.
• The synthesized COCs exhibit robust structural chirality, retained in solution.
• These chiral organic cages show promise for enantioselective separation and recognition applications.