Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Proton Transfer Mechanisms In Protic Ionic Liquids

The focus of this thesis was the investigation of the underlying proton transfer phenomena in a series of ionic liquids (ILs). Four IL systems were examined: prototype imidazolium ILs, cholinium protic ionic liquids (PILs), phospho-amino acid PILs and Aminotris(methylenephosphonic acid) (ATMP). The complex structure and dynamics was explored through accurate, efficient computational approaches using electronic structure calculations, ab initio and semi-empirical molecular dynamics (MD). The short and long range interactions of ILs extend into long time-scales (hundreds of picoseconds); hence Density Functional Tight Binding (DFTB) was selected for the dynamical MD simulations. DFTB is a well-established parametrised method which employs a variable chemical topology with significantly reduced computational time relative to ab initio MD along with a comparable accuracy. A novel part of this thesis was the use of DFTB to extend the simulation time frame sufficiently so that proton transfer events can be adequately sampled (towards thermodynamics). The aim was to ascertain whether proton shuttling can occur in these liquids thus providing a route to develop a dry proton conducting material. Interestingly each of the studied systems display unique characteristics dependent on the cationic or anionic constituent. It has been established that the protic functionality is the determining factor to provide a route for proton migration along with a non-participating counterion ensuring the ionicity of the fluid is unaltered. A computational characterisation of these ILs was performed to explore the role played by protons as fast charge carriers in biocompatible (or at least green) materials.