Theoretical studies on the structure and dynamics of room-temperature ionic liquids

<p>In this thesis, we present our studies on the structure and dynamics of novel Room-Temperature Ionic Liquids. Through our computer simulations we demonstrate that the kinetics of photo induced electron transfer reaction between S1 and S2 states of Crystal Violet Lactone in N-propyl-N-methylpyrrolidiniumbis(trifluoromethylsulfonyl)imide room temperature ionic liquid is local solvent environment dependent, because emission time scales are smaller than solvent relaxation time scales. This behavior is characteristic of ionic liquids but uncommon in conventional solvents. Therefore ionic liquids open a window of opportunity for manipulating the outcome of chemical reactions simply by tuning the initial excitation wavelength.</p> <p>We performed Molecular dynamics simulations of mixtures of 1-hexyl-3-methyl imidazoliumhexafluorophosphate and water in order to investigate how small amounts of water affect the translational and rotational dynamics of ionic liquids. We find that water is closely associated with the anions and that its presence enhances both the translational and rotational dynamics of the ionic liquid. In agreement with experiments, we find that the fluorescence spectra of Coumarin-153 is red-shifted because of the presence of water. Small amounts of water enhance the speed of relaxation of the solvent surrounding the solute probe after photo-excitation, but only at a local environment level. Interconversion between environments still occurs on a long time scale compared with the fluorescence lifetime of the probe.</p> <p>To interpret the features of x-ray scattering structure factor of room temperature ionic liquids we introduce a set of general theoretical partitions of real and reciprocal space correlations that allow for unambiguous analysis of all intra- and inter-ionic contributions to the structure function and coherent scattering intensity. Through our simulations we could explain the origin of various peaks in the x-ray structure function of methyltributylammonium bis(trifluoromethylsulfonyl)amide.</p> <p>In order understand the origin of the first sharp diffraction peak in the x ray structure factor of Imidazolium based ionic liquids, we use several different computational techniques to thoroughly dissect the atomistic components giving rise to the low frequency first sharp diffraction peak as well as other features in the structure function (S(q)). By understanding how S(q) changes as Imidazolium based ionic systems undergo solid-liquid phase transition, and by artificially perturbing the liquid structure in a way that directly couples to the intensity of the first sharp diffraction peak, we are able to identify in a rigorous way its geometric origin.</p>