Solvation Dynamics in a Prototypical Ionic Liquid + Dipolar Aprotic Liquid Mixture: 1-Butyl-3-methylimidazolium Tetrafluoroborate + Acetonitrile

Abstract

Solvation energies, rotation times, and 100 fs to 20 ns solvation response functions of the solute coumarin 153 (C153) in mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([Im41][BF4]) + acetonitrile (CH3CN) at room temperature (20.5 °C) are reported. Available density, shear viscosity, and electrical conductivity data at 25 °C are also collected and parametrized, and new data on refractive indices and component diffusion coefficients presented. Solvation free energies and reorganization energies associated with the S0 ↔ S1 transition of C153 are slightly (≤15%) larger in neat [Im41][BF4] than in CH3CN. No clear evidence for preferential solvation of C153 in these mixtures is found. Composition-dependent diffusion coefficients (D) of Im41(+) and CH3CN as well as C153 rotation times (τ) are approximately related to solution viscosity (η) as D, τ ∝ η(p) with values of p = -0.88, -0.77, and +0.90, respectively. Spectral/solvation response functions (Sν(t)) are bimodal at all compositions, consisting of a subpicosecond fast component followed by a broadly distributed slower component extending over ps-ns times. Integral solvation times (⟨τ(solv)⟩ = ∫(0)(∞)Sν(t) dt) follow a power law on viscosity for mixturecompositions 0.2 ≤ x(IL) ≤ 1 with p = 0.79. With recent broad-band dielectric measurements [J. Phys. Chem. B 2012, 116, 7509] asinput, a simple dielectric continuum model provides predictions for solvation response functions that correctly capture thedistinctive bimodal character of the observed response. At x(IL) ∼ 1 predicted values of ⟨τ(solv)⟩ are smaller than those observed by a factor of 2-3, but the two become approximately equal at x(IL) = 0.2. Predictions of a recent semimolecular theory [J. Phys. Chem. B 2011, 115, 4011] are less accurate, being uniformly slower than the observed solvation dynamics.

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

“…Composition Dependent Dynamic Stokes Shift: Comparison between Theory and Experiments. Figure 23,45 reproducing well the experimentally observed near-insensitivity to the mole fraction of the dynamic Stokes shift in these binary mixtures. SM calculations, in contrast, predict pronounced nonideal composition dependence, showing a strong deviation from the experimental trend.…”

“…First, both EM and SM calculations predict acceleration of average solvation rate upon addition of polar solvent into IL and can well reproduce the experimentally observed slow long-time dynamics at these compositions. 45 Second, the early time dynamics predicted by the SM calculations is faster than that observed in experiments 45 for all these mixture compositions, while the opposite is predicted by EM calculations. Third, the difference in solvation rates between the neat and mixtures at the initial phase is larger in SM predictions than that in experiments.…”

“…23,45 The prefactor of eq 6 is B = 2(k B T/2π) 2 . c sα 10 (k) denotes the longitudinal component of the wavenumber dependent static structural correlations between the dipolar solute and an ion of type α, given by…”

Translational Diffusion in Mixtures of Imidazolium ILs with Polar Aprotic Molecular Solvents

“…30,57 It should also be pointed out that the diffusion coefficients of all particles vary over 1.5−2 orders of magnitude with concentration. For comparison, data of Hsu et al 58 and the very recent results from Liang et al 44 are included in Figure 1. Absolute values of our diffusion coefficients for cations and solvent molecules compare very well with the literature, and this agreement becomes excellent when relative diffusion coefficients are considered (see Figure 2 and discussion in Section 3.2).…”

Sequence-Dependent Solvation Dynamics of Minor-Groove Bound Ligand Inside Duplex-DNA

“…33−35 TRFSS has been widely used to study solvation dynamics in simple water, 36 ionic liquids, 37,38 proteins, 39,40 DNA, 5,41−50 protein−DNA complexes, 51−53 supramolecular assemblies, 54 and even biological cells. 55,56 TRFSS experiments measure the dynamics of solvation by recording the time-dependent change of electrostatic interaction energy of a probe (here DAPI) with its surrounding charged/dipolar molecules (i.e., water, ions, and DNA).…”