Dynamics of solvation and rotational relaxation of Coumarin 153 in 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6]–water mixtures

The Stokes’ shift of Coumarin 153 is reported at room temperature to probe the solvation dynamics in [bmim][PF6]–water mixtures. The steady state spectra show that with gradual addition of water polarity of the mixed solvent increases. The high viscosity of the medium is responsible for the slow solvation in the neat [bmim][PF6]. The solvation occurs in two separated time regimes within our instrument response. The fast and slow components of the solvation is originating due to local motion and diffusional motions of the ions. The viscosity of the [bmim][PF6]–water mixtures is gradually decreasing with addition of water. The probable cause may be due to the decrease in electrostatic attraction between the ions and consequently the solvation time gradually decreases with increase in water content in the mixed solvents. With the gradual addition of water in neat [bmim][PF6] the rotational relaxation time becomes faster.