Selective Interrogation of polar and nonpolar regions in room temperature ionic liquids

Description:
Room temperature ionic liquids (RTILs) are molten salts with low vapor pressure, high thermal and chemical stability and a wide electrochemical window. RTILs have been studied in a number of ways, both experimental and theoretical, and it has emerged that organization in these media over length scales ranging from ca. 10 nm to ca. 50 μm has been seen. Dilution studies of RTILs have demonstrated persistent aggregation of RTIL ion pairs to relatively high dilutions, consistent with such binary systems existing as a nanoscale heterogeneous system. We report here on the binary system 1-Decyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (DMPyrr+TFSI-) diluted with 1-decanol. Both the RTIL cation and the molecular liquid have a C10 aliphatic chain. The intent is to produce a system with comparatively isolated polar and nonpolar regions, which we probe selectively with polar (cresyl violet cation) and nonpolar (perylene) chromophores.
We use spatially-resolved, time-resolved fluorescence anisotropy decay measurements to characterize the rotational diffusion dynamics of the two chromophores in the binary RTIL-decanol system. We found bi-exponential anisotropy decay for both chromophores in neat DMPyrr+TFSI-, consistent with their rotation as oblate rotors. While perylene maintains biexponential anisotropy decay from neat DMPyrr+TFSI- to neat diluent, CV+ exhibits a biexponential decay up to 75 mole% of 1-decanol, then the anisotropy decay becomes a single exponential, demonstrating a change to a prolate rotor shape. These data demonstrate long-range order in this binary system, consistent with non-polar regions of lamellar structure and substantial clustering of RTILs dominated by the polar headgroups. The order seen in this system is more extensive and dilution-resistant than what has been seen in other RTIL-molecular liquid binary systems.

Speaker: Md Iqbal Hossain - Michigan State University
Md Iqbal Hossain is a Ph.D. candidate at the Department of Chemistry, Michigan State University, and works under the supervision of Professor Gary J. Blanchard. We work on the interface of liquid and charged surface. We focus on the deep inside on the local and long range order in Room Temperature Ionic Liquids (RTILs) using Fluorescence Anisotropic Decay Imaging (FADI), Time-Correlated Single Photon Counting (TCSPC), and Second Harmonic Generation Sepctroscopy.