Distribution of 1-Butyl-3-methylimidazolium Bistrifluoromethylsulfonimide in Mesoporous Silica As a Function of Pore Filling

Rotational dynamics of the ionic liquid (IL) 1-butyl-3-methylimidazolium bistrifluoromethylsulfonimide, [C4mim][Tf2N], 1, as a neat liquid, and confined in mesoporous silica were investigated by 1H spin–spin (T2) and spin–lattice (T1) relaxation measurements and 13C NMR spectroscopy. Translational dynamics (self-diffusion) were monitored via the diffusion coefficient, D, obtained with 1H pulsed field gradient NMR measurements. These data were used to determine the distribution of 1 in the pores of KIT-6, a mesoporous silica with a bicontinuous gyroid pore structure, as a function of filling fraction. Relaxation studies performed as a function of filling factor and temperature reveal a dynamic heterogeneity in both translational and rotational motions for 1 at filling factors, f = 0.2–1.0 (f = 1 corresponds to fully filled pores). Spin–lattice and spin–spin relaxation times reveal that the motion of 1 in silica mesopores conforms to that expected for a two-dimensional relaxation model. The relaxation dynam...