Steady-state and time-resolved fluorescence behavior of coumarin-153 in a hydrophobic ionic liquid and ionic liquid–toluene mixture

Abstract

Steady-state and time-resolved fluorescence behavior of C-153 in neat ultra hydrophobic 1-(2-methoxyethyl)-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate and its mixture with toluene has been investigated. Steady-state absorption and emission spectral behavior of C-153 is found not to be affected by the nonpolar cosolvent. Time-resolved fluorescence anisotropy measurements show that the rotational diffusion of the probe becomes faster in presence of toluene. Solvation dynamics in ionic liquid–toluene mixtures is found to be biphasic, and the average solvation time is found to decrease with the addition of nonpolar cosolvent to the ionic liquid. A significant blue shift of the time-zero maximum of fluorescence spectrum upon addition of toluene indicates a more nonpolar environment around C-153 at the initial stage of dynamics in the mixed solvent system. A comparison of the dynamics of solvation data in ionic liquid and ionic liquid–toluene mixture suggests that toluene can effectively penetrate into the ionic liquid-rich cybotactic region of the probe. This is explained in terms of favorable hydrophobic interaction between ionic liquid and toluene.