Discrete stacking of aromatic oligoamide macrocycles.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Controlling the self-assembly of disc- and ring-shaped molecules into discrete structures is a significant challenge in supramolecular chemistry.
• Precise structural control is typically easier with closed assemblies compared to open-ended stacking systems.

Purpose of the Study:

• To report the successful discrete stacking of rigid aromatic oligoamide macrocycles.
• To investigate the formation, structure, and potential applications of these self-assembled oligomers.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy, including 1D (1)H, 2D nuclear Overhauser effect (NOE), and diffusion-ordered NMR spectroscopy (DOSY).
• Quantum-chemical calculations to determine the stability of different oligomeric stack configurations.
• X-ray crystallography to elucidate the precise three-dimensional structure of the assembled tetramers.

Main Results:

• Aggregation of the oligoamide macrocycles plateaued at increasing concentrations, forming discrete oligomers.
• Quantum-chemical calculations identified the tetramer as the most stable oligomeric stack.
• X-ray crystallography confirmed a tetrameric stack of identical molecules adopting two distinct conformations, featuring a defined length and an internal pore.

Conclusions:

• The study presents a rare example of conformation-regulated supramolecular oligomerization.
• The discrete tetrameric stacks and their higher-order assemblies possess defined structures and internal pores, suitable for guest encapsulation.
• These findings open avenues for new nanotechnological applications utilizing these precisely controlled supramolecular structures.