Ionic Liquids: Not only Structurally but also Dynamically Heterogeneous

In recent years, the complex and heterogeneous structure of ionic liqs. was demonstrated; however, the consequences on the dynamics have remained elusive. Here, the authors use femtosecond IR spectroscopy to elucidate the local structural dynamics in protic alkylammonium-based ionic liqs. The structural relaxation after an ultrafast temp. increase, following vibrational excitation and subsequent relaxation of the N-D (or N-H) stretching vibration, is found to vary substantially between the ionic and hydrophobic subdomains. The dynamics in the ionic domains are virtually unaffected by the alkyl chain length and is, therefore, decoupled from viscosity. Equilibration within the hydrophobic subdomains, as evident from the dynamics of the C-H stretching vibration, is faster than that in the ionic domains and shows a remarkably low thermal activation. [on SciFinder(R)