Solvation Dynamics and Proton Transfer in Diethylaminohydroxyflavone.

Area of Science:

• Photochemistry
• Chemical Kinetics
• Spectroscopy

Background:

• 4 '-N,N-Diethylamino-3-hydroxyflavone (DEAHF) exhibits dual fluorescence, useful for ratiometric sensing.
• Excited-state intramolecular proton transfer (ESIPT) in DEAHF is sensitive to solvent properties.

Purpose of the Study:

• To investigate the unusual proposed dependence of DEAHF's proton transfer rate on solvent relaxation.
• To test if rapid solvation retards the reaction rate.

Main Methods:

• Femtosecond Kerr-gated emission spectroscopy was used to measure DEAHF reaction kinetics.
• DEAHF kinetics were studied in propylene carbonate (PC) + acetonitrile (ACN) mixtures.
• Solvent polarity was kept constant while solvation times were varied.

Main Results:

• DEAHF reaction kinetics were multiexponential with components around 2 ps and 30 ps.
• Average reaction times increased with increasing acetonitrile mole fraction.
• This trend contradicts the composition dependence of solvation times.

Conclusions:

• The results support the hypothesis that polar solvation dynamics unusually retard the excited-state intramolecular proton transfer in DEAHF.
• Solvent friction does not affect reaction rates in nonpolar n-alkane solvents.