Anomalous Fluorescence Quenching in Fluorous Solvent-Added Media

Area of Science:

• Physical Chemistry
• Photochemistry
• Supramolecular Chemistry

Background:

• Perfluorocarbons (PFCs) possess unique properties due to fluorine's high electronegativity.
• Fluorous solvents can exhibit anomalous behavior compared to hydrocarbon analogues.
• Understanding solvent effects on fluorescence quenching is crucial for chemical processes.

Purpose of the Study:

• To investigate the influence of perfluorodecalin (PFD) on the fluorescence quenching of polycyclic aromatic hydrocarbons (PAHs).
• To elucidate the role of solvent viscosity and electronic effects in electron/charge transfer processes.
• To compare the behavior of fluorous solvents with hydrocarbon analogues in quenching studies.

Main Methods:

• Systematic variation of perfluorodecalin (PFD) concentration in n-hexane solvent mixtures.
• Measurement of bimolecular quenching rate constants (kq) for PAHs using nitromethane and triethylamine (TEA) as quenchers.
• Analysis of fluorescence quenching dynamics in fluorous and hydrocarbon solvent systems.

Main Results:

• Addition of PFD to n-hexane initially increased kq for PAHs with nitromethane, contrary to expectations.
• This enhancement was attributed to stabilization of partial positive charges on excited PAHs by PFD's electronegative fluorines.
• A decrease in kq was observed in PFD-rich mixtures and in hydrocarbon solvent systems, consistent with increased viscosity and expected behavior.

Conclusions:

• Fluorous media, specifically PFD, can facilitate electron/charge transfer processes in fluorescence quenching.
• The observed effects are a balance between electronic stabilization by fluorine and viscosity effects.
• PFD's unique properties offer new avenues for controlling photochemical reactions and molecular interactions.