Encapsulation of Trimethine Cyanine in Cucurbit[8]uril: Solution versus Solid-State Inclusion Behavior

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Photophysics

Background:

• Polymethine cyanine dyes exhibit unique spectral properties in aqueous solutions.
• Macrocyclic receptors can influence dye behavior through host-guest interactions.
• Cucurbiturils are a class of macrocyclic hosts known for their binding capabilities.

Purpose of the Study:

• To investigate the impact of cucurbit[8]uril (CB[8]) on the spectral properties and aggregation of a trimethine indocyanine dye (Cy3) in water.
• To characterize the host-guest complex formed between CB[8] and Cy3.
• To explore the potential for supramolecular polymer formation.

Main Methods:

• Solution studies utilizing spectroscopic techniques (UV-Vis absorption, fluorescence).
• Calorimetric measurements to determine binding thermodynamics.
• Nuclear Magnetic Resonance (NMR) spectroscopy to study complex formation.
• Single-crystal X-ray diffraction to elucidate solid-state structure.

Main Results:

• Cucurbit[8]uril (CB[8]) effectively disrupts pre-existing aggregates of cyanine dye (Cy3) in aqueous solution.
• A stable 1:1 host-guest complex is formed between CB[8] and Cy3 with a high association constant (1.5 × 10^6 M^-1).
• At higher concentrations, CB[8]-Cy3 interactions promote the slow formation of a supramolecular polymer, leading to precipitation.
• X-ray crystallography confirms the 1:1 stoichiometry of the polymer in the solid state.

Conclusions:

• Host-guest complexation with cucurbit[8]uril is a viable strategy to control cyanine dye aggregation and spectral properties in water.
• The observed supramolecular polymer formation highlights the potential for designing novel self-assembled materials based on cucurbituril-dye interactions.
• Understanding these interactions is crucial for applications in sensing, imaging, and materials science.