Dispersion Interactions in Condensed Phases and inside Molecular Containers

Area of Science:

• Supramolecular Chemistry
• Physical Organic Chemistry
• Computational Chemistry

Background:

• London dispersion interactions (LDIs) are fundamental to intermolecular forces in supramolecular systems and solutions.
• The Slater-Kirkwood formula links LDIs to molecular polarizability (α) and interaction distance (R⁻⁶), but gas-phase assumptions don't always translate to condensed phases.
• Bulk polarizabilities, accessible via refractive index or solvatochromic probes, are more relevant for solution-phase association phenomena.

Purpose of the Study:

• To investigate the role of molecular polarizability in London dispersion interactions (LDIs) within condensed phases, specifically in the microenvironments of macrocyclic hosts.
• To explore the applicability of gas-phase LDI concepts to solution-phase phenomena and host-guest chemistry.
• To demonstrate the utility of cucurbit[n]urils (CBn) as model systems for studying LDIs and their influence on binding and reactivity.

Main Methods:

• Utilized experimental measurements (refractive index, solvatochromic probes) to determine bulk polarizabilities of solvents and macrocyclic cavities.
• Employed cucurbit[n]urils (CBn) as model host systems to encapsulate various guests (hydrocarbons, noble gases, aromatics).
• Leveraged computational approaches (quantum-chemical, molecular dynamics) and gas-phase studies of host-guest complexes.

Main Results:

• Demonstrated that bulk polarizabilities, not just molecular polarizabilities, are critical for understanding LDIs in solution.
• Showcased CBn macrocycles as privileged receptors with unique internal microenvironments influencing LDI strength and selectivity.
• Highlighted CB5's ability to bind noble gases, CB8's capacity to tune interactions with aromatic guests, and gas-phase studies revealing isolated LDI effects.

Conclusions:

• The relationship between molecular polarizability and LDIs is complex and context-dependent, especially in condensed phases and confined environments.
• Cucurbit[n]urils (CBn) provide versatile platforms for dissecting and controlling London dispersion interactions in host-guest systems.
• Understanding LDIs in macrocyclic cavities is crucial for designing selective receptors and studying fundamental intermolecular forces.