Controlled oligomeric guest stacking by cucurbiturils in water

Area of Science:

• Supramolecular Chemistry
• Host-Guest Chemistry
• Organic Synthesis

Background:

• Previous work established a viologen-phenylene-imidazole (VPI) guest molecule forming 2:2 complexes with cucurbit[8]uril (CB[8]) and 2:3 complexes with cucurbit[10]uril (CB[10]).
• Understanding the structural requirements for specific host-guest complex stoichiometry is crucial for designing predictable self-assembly processes.

Purpose of the Study:

• To investigate how structural modifications of the VPI guest molecule influence its complexation behavior with CB[8] and CB[10].
• To synthesize and characterize VPI analogues, T-VPI and VPI-N, to probe the effects of hydrophobicity and extended aromatic systems on complex formation.

Main Methods:

• Synthesis of two VPI analogues: T-VPI (tolyl-substituted) and VPI-N (naphthalene-fused).
• Complexation studies with CB[8] and CB[10] using Nuclear Magnetic Resonance (NMR) spectroscopy, including Diffusion Ordered Spectroscopy (DOSY).
• UV-vis and fluorescence spectroscopy to confirm complex formation and investigate electronic interactions.

Main Results:

• VPI-N formed well-defined 2:2 complexes with CB[8] and 2:3 complexes with CB[10].
• T-VPI formed 2:2 complexes with CB[8], but no well-defined complex with CB[10].
• DOSY NMR indicated more stable 2:2 complexes with CB[8] for more hydrophobic guests. Host-stabilized charge-transfer interactions were observed via UV-vis and fluorescence spectroscopy.

Conclusions:

• Structural modifications of the guest molecule significantly impact the stoichiometry and stability of cucurbituril complexes.
• Hydrophobicity plays a key role in the stability of 2:2 complexes with CB[8].
• The choice of host (CB[8] or CB[10]) and guest structure allows for controlled self-assembly into specific quaternary or quinary host-guest architectures.