Fluorescent probe dependence of the solvation dynamics in ionic liquid BmimBF4 and propylene carbonate mixtures: a time-resolved fluorescence and quantum chemistry study

Abstract

In this work, steady-state and time-resolved fluorescence experiments on solvation of C153, C102, 4-ANMP and PRODAN fluorescent probes in BmimBF4 and BmimBF4/PC mixtures with a molar fraction of ionic liquid equal to 0.65 and 0.85 are reported. Quantum Chemistry calculations were performed to complete the experimental data interpretation. All the four studied probes exhibit similar solvation dynamics, with their average solvation times following the trend 4-ANMP < C153 ≅ C102 < PRODAN. A specific interactions hypothesis was put forward to explain the slight divergence of 4-ANMP and PRODAN spectra shift. The C153 molecule, showing a big change in dipole moment (8.7 D) upon the photoexcitation, little geometry relaxation upon the excitation due to its rigid structure, small change in dipole moment orientation and relatively small hydrogen bonding ability is thus proved to be the most adequate for use in the study of the solvation dynamics in various environments, including ionic liquids and ionic liquid/molecular solvent mixtures.