Interrogating the mechanism of the solvation dynamics in BmimBF4/PC mixtures: A cooperative study employing time-resolved fluorescence and molecular dynamics

International audienceIn this article, the solvation in ionic liquid/molecular solvent (IL/MS) mixtures is investigated. The steady-state and time-resolved measurements of the solvation of coumarin 153 (C153) in BmimBF4/propylenecarbonate are presented. A slight bathochromic shift was observed in the steady-state spectra uponincreasing the IL molar fractionxIL. The time correlated photon counting TCSPC and fluorescence upcon-version techniques were used to obtain the experimental solvation response functions (SRFs). The SRFswere found to be multi-exponential and the average solvation times increased withxIL. The MD simula-tions were performed to help the interpretation of the experimental data. An unprecedentedly goodagreement between the measured and the calculated SRFs was achieved. The partition of the coulombicenergy of interaction between the atoms of C153 and cations, anions and PC molecules provides a deepunderstanding of the time signatures of the mixture components participation in the solvation response.Indeed, the slow portion of the SRFs was found to be dominated by the IL. These time signatures change infunction ofxILand represent the previously established regimes of IL/MS mixtures: electrolyte solution(xIL0.2). These results will be of crucial interest for the understanding ofthe molecular rearrangements occurring in IL/MS electrolyte models for dye sensitized solar cells(DSSCs) after photo-excitation