Dynamics in a Room-Temperature Ionic Liquid from the Cation Perspective: 2D IR Vibrational Echo Spectroscopy.
Steven A Yamada1, Heather E Bailey1, Amr Tamimi1
1Department of Chemistry Stanford University , Stanford, California 94305, United States.
Journal of the American Chemical Society
|January 19, 2017
Summary
Room-temperature ionic liquid (RTIL) dynamics were studied using 2D IR spectroscopy. A modified cation (2-SeCN-Bmim+) revealed slow structural diffusion, indicating sensitivity to local and long-range liquid motions.
Area of Science:
- Physical Chemistry
- Materials Science
- Spectroscopy
Background:
- Room-temperature ionic liquids (RTILs) exhibit complex dynamics crucial for their applications.
- Understanding molecular motion within RTILs requires advanced spectroscopic techniques.
Purpose of the Study:
- To investigate the dynamic behavior of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BmimNTf2) using vibrational spectroscopy.
- To probe local and collective dynamics of the ionic liquid using a modified cation as a vibrational reporter.
Main Methods:
- Two-dimensional infrared (2D IR) vibrational echo spectroscopy.
- Polarization-selective pump-probe (PSPP) experiments.
- Optical heterodyne-detected optical Kerr effect (OHD-OKE).
Main Results:
- A long time scale structural spectral diffusion component (600 ps) was observed for the modified cation (2-SeCN-Bmim+).
- The anion (SeCN-) sampled its spectral width much faster than the neat liquid's structural randomization time (870 ps).
- Complete orientational randomization of 2-SeCN-Bmim+ occurred at ~900 ps, matching the neat liquid's randomization time.
Conclusions:
- The modified cation (2-SeCN-Bmim+) is sensitive to local ionic liquid motions influencing spectral diffusion.
- Slow, long-range fluctuations govern the complete randomization of the RTIL structure.
- These findings provide insights into the complex dynamics of ionic liquids.
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