States and migration of an excess electron in a pyridinium-based, room-temperature ionic liquid: an ab initio molecular dynamics simulation exploration

The structural and electronic properties of an excess electron (EE) in the ionic liquid (IL) 1-methylpyridinium chloride were explored using ab initio molecular dynamics simulations and quantum chemical calculations to give an overall understanding of the solvation and transport behavior of an EE in this IL. The results show that the EE resides in cation pi*-type orbitals and that the electronic states can be characterized by the alternating appearance of localized and delocalized states during the time evolution. The characters of the EE electronic states are determined by the number of cations contributing to the LUMO of the IL. In a localized state one or two cations contribute to the LUMO of the bulk ionic liquid, while in the delocalized state the IL LUMO is composed of pi*-type orbitals spanning nearly all the cations in the cell. The arrangement and fluctuation-induced changes of the orbital components in the empty band produce an alternation of different states and leads to the migration of the excess electron. These findings can be attributed to the special features of the electronic structures and geometries of the IL, and they can be used to explain similarities and differences between pyridinium-based and imidazolium-based ILs in mediating electron migration.