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

In 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 BmimBF(4)/propylene carbonate are presented. A slight bathochromic shift was observed in the steady-state spectra upon increasing the IL molar fraction x(IL). The time correlated photon counting TCSPC and fluorescence upconversion techniques were used to obtain the experimental solvation response functions (SRFs). The SRFs were found to be multi-exponential and the average solvation times increased with x(IL). The MD simulations were performed to help the interpretation of the experimental data. An unprecedentedly good agreement between the measured and the calculated SRFs was achieved. The partition of the coulombic energy of interaction between the atoms of C153 and cations, anions and PC molecules provides a deep understanding 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 in function of x(IL), and represent the previously established regimes of IL/MS mixtures: electrolyte solution (x(IL)< 0.2) and lubricated IL (x(IL) > 0.2). These results will be of crucial interest for the understanding of the molecular rearrangements occurring in IL/MS electrolyte models for dye sensitized solar cells (DSSCs) after photo-excitation. (C) 2021 Published by Elsevier B.V.

Automated summary

This article investigates the solvation in IL/MS mixtures using steady-state and time-resolved measurements of coumarin 153 in BmimBF(4)/propylene carbonate. The experimental results showed a lengthening of solvation times with increasing IL molar fraction, with IL dominating the slow portion of the solvation response. MD simulations provided a deep understanding and excellent agreement with experimental data, shedding light on the molecular rearrangements in different IL/MS mixture regimes.