Radiation stability of cations in ionic liquids. 2. Improved radiation resistance through charge delocalization in 1-benzylpyridinium.

Hydrophobic room-temperature ionic liquids (ILs) hold promise as replacements for molecular diluents for processing of used nuclear fuel as well as for the development of alternative separations processes, provided that the solvent can be made resistant to ionizing radiation. We demonstrate that 1-benzylpyridinium cations are uniquely suited as radiation resistant cations due to the occurrence of charge delocalization in both their reduced and oxidized forms in the ILs. It is suggested that the excess electron and hole in the latter ILs are stabilized through the formation of π-electron sandwich dimers that are analogous to the well-known dimer radical cations of aromatic molecules. This charge delocalization dramatically reduces the yield of fragmentation by deprotonation and the loss of benzyl arms, thereby providing a synthetic path to radiation resistant ILs that are suitable for nuclear fuel processing.