Protic Ionic Liquids (PILs) build hydrogen bonds between cation and anion leading to the formation of neutral ion pairs or larger aggregates. This is well reflected in their cationic and anionic motional behavior.
The dynamics of both species can be simultaneously investigated by means of NMR relaxometry, provided that cation and anion contain different NMR active nuclei. Therefore, appropriate PILs were investigated by means of Fast Field Cycling 1H and 19F NMR relaxometry dominated by the dipolar relaxation mechanism as well as by high-field 2H NMR relaxometry following the quadrupolar relaxation mechanism as a function of frequencies ranging over five orders of magnitude.
Rotational correlation times, translational diffusion coefficients and reliable coupling parameters for both relaxation mechanisms were determined. The validity of the Bloembergen-Purcell-Pound relaxation model considering solely isotropic rotations was examined for different examples and cases of anisotropic and internal rotations were scrutinized.