Effects of Nitridation and Vinylation of Imidazolium Rings on Hydrogen Bonding Interactions, π-π-Stacking Structures, and Dynamical Heterogeneities in Imidazolium and Triazolium Ionic Liquids

Extensive atomistic simulations have been performed to investigate how nitridation and vinylation of cations affect hydrogen bonding structures and dynamics, pi-pi-stacking interactions between cation-ring planes, and translational and rotational dynamics of ion species in ionic liquids (ILs) consisting of bis(trifluoromethylsulfonyl)imide anions coupled with either imidazolium or triazolium cations. Both nitridation and vinylation of cations have remarkable effects on molecular electrostatic potential contours of cations and polarities of cation-ring hydrogen atoms, leading to distinct structures and dynamics in their hydrogen bonding associations with representative atoms in anions and in triazolium cations. Both imidazolium- and triazolium-ring planes exhibit varied pi-pi-stacking structures depending on nitridation positions on imidazolium rings. The vinyl-substituted cations have more prominent pi-pi-stacking interactions than their methyl-based counterparts because of the formation of pi-conjugated ring vinyl moieties. Polar and apolar groups in ion species exhibit remarkable translational and rotational dynamics and distinct diffusion distributions in IL matrices at different timescales. The nitridation and vinylation of cations lead to enhanced deviation of translational mobilities of ion species from Gaussian behavior, and cations have a higher degree of dynamical heterogeneity than their coupled anions.