Solvation dynamics and rotation of coumarin 153 in a new ionic liquid/molecular solvent mixture model: [BMIM][TFSI]/propylene carbonate

Using picosecond time-correlated single photon counting (TCSPC) technique, C-153 fluorescent probe solvation and orientational dynamics in [BMIM][TFSI]/PC mixtures have been investigated. The bi-exponential fit of the solvation response gives tens and hundreds of picoseconds time-components, respectively. Both components are dependent on mixture composition. A characteristic power-law relation between integral solvation times and mixture viscosity has been extracted. As the solvation dynamics is controlled by translational motion, we chose to confront integral solvation times 〈τ_solv〉 of C-153 in [BMIM][TFSI]/PC with the translational diffusion coefficients of BMIM⁺ cations and propylene carbonate molecules, as well as with average rotational times 〈τ_rot〉, obtained measuring time-resolved fluorescence anisotropy. Our results allow to make the hypothesis that the solvation dynamics of C-153 in this mixture is mainly influenced by the cation.