Composition Dependent Stokes Shift Dynamics in Binary Mixtures of 1-Butyl-3-methylimidazolium Tetrafluoroborate with Water and Acetonitrile: Quantitative Comparison between Theory and Complete Measurements

Abstract

Here we predict, using a semimolecular theory, the Stokes shift dynamics of a dipolar solute in binary mixtures of an ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), with water (H2O) and acetonitrile (CH3CN), and compare with the experimental results. The latter are from the recent measurements that combined broad-band fluorescence up-conversion (FLUPS) with time-correlated single photon counting (TCSPC) techniques and used coumarin 153 (C153) as a solute probe. Nine different compositions of ([Bmim][BF4] + H2O) and ([Bmim][BF4] + CH3CN) binary mixtures are considered for the extensive comparison between theory and experiments. Two separate model calculations have been performed using the available experimental frequency dependent dielectric function, ε(ω). These calculations semiquantitatively reproduce the experimentally observed (i) IL mole fraction dependence of dynamic Stokes shifts in these mixtures, (ii) composition dependence of average fast, slow, and solvation times, (iii) viscosity dependence of slow times, and (iv) the nonlinear dependence of average solvation times on experimental inverse conductivity. Variations of the calculated dynamics on water dipole moment values (gas phase or liquid phase) and sensitivity to different measurements of ε(ω) for ([Bmim][BF4] + H2O) mixtures are examined. In addition, the importance of the missing contribution to experimental ε(ω) from high frequency collective solvent intermolecular modes for generating the experimentally observed sub-picosecond solvation response in these (IL + polar solvent) binary mixtures has been explored.

Interaction and dynamics of (alkylamide + electrolyte) deep eutectics: Dependence on alkyl chain-length, temperature, and anion identity

“…It would be interesting to explore how the jumplike dynamics modifies itself in presence of mono and divalent ions in these DEs, 100 and how such a decoupling of dynamics from medium viscosity affects a simple chemical reaction, for example, cis-trans isomerisation reaction 101 in these media. Complete measurements of Stokes shift dynamics and dielectric relaxation similar to what has been done for (ionic liquid + polar solvent) binary mixtures, 102, 103 and interpreting them using molecular theories [104][105][106] and simulations 107 are therefore necessary for a detailed understanding of interaction and dynamics of these complex yet fascinating solvent systems.…”

Fluorescence response of a dipolar organic solute in a dicationic ionic liquid (IL): is the behavior of dicationic IL different from that of usual monocationic IL?

“…The absence of the ultrafast component in the case of the dicationic ionic liquid possibly indicates that the origin of the ultrafast component is related to the dipolar rotation of the imidazolium cation, the findings that have been already discussed in a few recent studies. [39][40][41][42] However, we would also like to stress that further investigation possibly exploiting molecular dynamics simulation might be required to rationalize the observed behavior.…”

Coumarin 153 Dynamics in Ethylammonium Nitrate: The Effects of Dilution with Methanol

“…Dynamic anisotropy measurements yield a different measure of solute-solvent interactions through examining the viscosity coupling (microscopic friction) to the solvent system. In IL systems, solvation dynamics have been described using computer simulations [15][16][17][18][19][20], Stokes shift measurements [21][22][23][24][25][26][27][28], and rotational dynamics [21,22,29] measurements. The basic starting point for comparisons from these measurements is to use the results to evaluate the solution behavior against simple hydrodynamic theory, e.g., Debye-Stokes-Einstein (DSE) behavior [30].…”

“…In neat ILs, ion-dipole (i.e., IL-solute) forces are typically the most significant interactions [26,34,35] but solvent-solvent interactions such as occurs through ion-ion interactions, dispersion forces, and dipolar forces also contribute to the overall IL solvation characteristics [14,20,26,36,37]. A molecular cosolvent adds more complexity by introducing additional forces that depends on the nature of the chosen cosolvent/IL pair, which has been discussed using a theoretical perspective [27,28]. In both neat ILs and IL/solvent mixtures one expects the solvation dynamics to be responsive to the varying types of molecular interactions; however, this is not always the case [24,25,35,38,39].…”