We examine the structure of ionic liquids by spectroscopic methods with smaller probes, electrons and the iodine molecule. Solvated electrons act as the smallest probe for studying the structure of solvents including ionic liquids. We create excess electrons by photoirradiating TMPA-Tf2N (N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl) imide) by a light pulse of 40 fs duration at 240 nm and record the electron solvation process with a 40 fs probe pulse covering the near-infrared region of 950 to 1550 nm. A broad absorption band is observed at 1050 nm immediately after the photoirradiation, indicating the presence of excess electrons. The absorption maximum shifts to the short wavenumber direction by 740 cm-1 in 100 ps, two orders of magnitude slower than in water. Presence of two or more distinctively different solvation environments is suggested from the spectral peak shift that follows a double exponential decay. We estimate the rotational diffusion time of the iodine molecule in molecular and ionic liquids from the polarization Raman spectroscopy. The isotropic and anisotropic components of the iodine Raman band are calculated from the Raman spectra detected with the parallel and perpendicular polarization. Different widths of the isotropic and anisotropic Raman bands reflect the rotational diffusion of the iodine molecule. We estimate the rotational diffusion time of the iodine molecule in 21 molecular solvents and 7 ionic liquids. The rotational relaxation time of the iodine molecule is estimated as 10 ps or longer in the ionic liquids, while it is 1 to 3 ps in alkane solvents.

Structure of ionic liquids examined with smaller probes

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.