Characterization of the molecular reorientational dynamics of the neat ionic liquid 1-butyl-3-methylimidazolium bromide in the super cooled state using 1H and 13C NMR spectroscopy

The (13)C spectra and (13)C longitudinal relaxation times (T(1)) were measured to investigate the segmental motion of the neat ionic liquid 1-butyl-3-methylimidazolium bromide ([bmim]Br) in the super cooled state. The (13)C signals of the imidazole ring significantly broadened at 283 K, whereas many other signals were unchanged. In the process of lowering temperature, the [bmim]Br changed to the solid state at ca 273 K without showing the rapid phase transition. Only the (13)C signal of the terminal methyl group in the butyl chain was still observed at 263 K, indicating that the motion of the imidazole ring was extremely restricted, whereas the methyl group in the butyl chain was active even in the solid state. The (13)C-T(1) values measured as a function of temperature also supported the discrete segmental motions of the [bmim](+) cation.