Intramolecular dimer formation reveals anomalous solvation within fluorous solvent perfluorodecalin

Area of Science:

• Physical Chemistry
• Materials Science
• Supramolecular Chemistry

Background:

• Fluorous solvents exhibit unique properties due to fluorine's high electronegativity.
• Solute solvation and aggregation behavior can differ significantly in fluorous versus hydrocarbon solvents.
• 1,3-bis(1-pyrenyl)propane (BPP) is a fluorescent probe known to form intramolecular excimers in hydrocarbon solvents.

Purpose of the Study:

• To investigate the intramolecular aggregation of BPP in a fluorous solvent, perfluorodecalin (PFD).
• To explore the influence of temperature and co-solvents (n-hexane) on BPP aggregation in PFD.
• To understand the role of solvation in fluorous media compared to hydrocarbon solvents.

Main Methods:

• Steady-state fluorescence emission and excitation spectroscopy.
• Time-resolved fluorescence spectroscopy (excited-state emission intensity decay).
• Variable temperature studies (293.15–333.15 K) in PFD and PFD/n-hexane mixtures.

Main Results:

• BPP forms intramolecular excimers in PFD, but also exhibits ground-state aggregation, unlike in hydrocarbon solvents.
• Ground-state aggregation in PFD decreases with increasing temperature.
• Addition of a small mole fraction of n-hexane (0.1) eliminates ground-state aggregation, restoring excited-state-only excimer formation.
• Pyrene probe preferentially solvated by n-hexane in PFD/n-hexane mixtures, supporting poor BPP solvation in PFD.

Conclusions:

• Poor solvation of BPP in PFD is responsible for the observed ground-state aggregation.
• Fluorous solvents induce distinct solute aggregation behaviors compared to traditional hydrocarbon solvents.
• These findings demonstrate unique solubilization and aggregation phenomena in fluorous media.