Effect of water on the dynamics of room temperature ionic liquids

PHYS 263

Claudio J. Margulis, claudio-margulis@uiowa.edu, Department of Chemistry, University of Iowa, Iowa City, IA 52242
Our recent studies have shown that heterogeneity is the underlying microscopic cause for the recently reported "red-edge effect" (REE) observed in the study of the fluorescence of certain organic probes in novel solvents commonly termed room-temperature ionic liquids. The REE is common of micellar or colloidal systems, that are characterized by microscopic environments which are structurally distinct. In contrast, in ionic liquids, the REE occurs because of the long period during which molecules are trapped in quasistatic local solvent cages. This trapping time, which is long compared to the lifetime of the excited-state probe, induces a set of site-specific spectroscopic responses. Subensembles of fluorescent molecules associated with particular local environments absorb and emit at different frequencies. Water is an important contaminant in room temperature ionic liquids and it affects the spectroscopy of molecules dissolved in them. We present here results showing that water enhances relaxation but only to local minima. Absorption wavelength dependent Stokes Shifts are still observed even in the presence of water.