Towards a better understanding of 'delocalized charge' in ionic liquid anions

One of the main characteristics that are attributed to ionic liquids (especially those with a low melting point) is that the anions comprising the ionic liquids possess a certain degree of charge delocalization as compared to anions in traditional molten salts. Based on the proton affinity equilibrium we proposed a new energetic criterion that can be used as a measure of charge delocalization. The proposed proton affinity comparison quantifies the extent to which ionic liquid anions are delocalized. Thus it should lead to a better understanding towards the design of task-specific ionic liquids. Therefore, this criterion can be applied to newly designed anions to assure that the extent of charge delocalization falls within the same range of values on the proton affinity scale as other commonly used ionic liquid anions.