Ultrafast vibrational dynamics of a trigonal planar anionic probe in ionic liquids (ILs): A two-dimensional infrared (2DIR) spectroscopic investigation

A major impediment limiting the widespread application of ionic liquids (ILs) is their high shear viscosity. Incorporation of a tricyanomethanide (TCM^-) anion in ILs leads to low shear viscosity and improvement of several characteristics suitable for large scale applications. However, properties including interactions of TCM^- with the local environment and dynamics of TCM^- have not been thoroughly investigated. Herein, we have studied the ultrafast dynamics of TCM^- in several imidazolium ILs using linear IR and two-dimensional infrared spectroscopy techniques. The spectral diffusion dynamics of the CN stretching modes of TCM^- in all ILs exhibit a nonexponential behavior with a short time component of ∼2 ps and a long time component spanning ∼9 ps to 14 ps. The TCM^- vibrational probe reports a significantly faster relaxation of ILs compared to those observed previously using linear vibrational probes, such as thiocyanate and selenocyanate. Our results indicate a rapid relaxation of the local ion-cage structure embedding the vibrational probe in the ILs. The faster relaxation suggests that the lifetime of the local ion-cage structure decreases in the presence of TCM^- in the ILs. Linear IR spectroscopic results show that the hydrogen-bonding interaction between TCM^- and imidazolium cations in ILs is much weaker. Shorter ion-cage lifetimes together with weaker hydrogen-bonding interactions account for the low shear viscosity of TCM^- based ILs compared to commonly used ILs. In addition, this study demonstrates that TCM^- can be used as a potential vibrational reporter to study the structure and dynamics of ILs and other molecular systems.

Molecular structure and ultrafast dynamics of sodium thiocyanate ion pairs formed in glymes of different lengths

The structure of different sodium–glyme–thiocyanate complexes has been studied by linear and time resolved vibrational spectroscopies.

High-Throughput Two-Dimensional Infrared (2D IR) Spectroscopy Achieved by Interfacing Microfluidic Technology with a High Repetition Rate 2D IR Spectrometer

The precision control of microfluidic technology was successfully interfaced with a 100 kHz two-dimensional infrared (2D IR) spectrometer to observe the sensitivity of the anion cyanate (OCN^-) to the surrounding solvent environment in a high-throughput manner. Producing high-throughput 2D IR spectroscopy measurements allows us to observe the vibrational response of cyanate in mixed solvent environments. Changes in solvation environment around the cyanate ion yield frequency shifts from 2150 to 2165 cm^-1 when moving from a pure dimethylformamide solvent environment to a pure methanol environment. 2D IR spectra were captured laterally across microfluidic devices tailored to produce a tunable gradient to observe the OCN^- vibrational response to mixed solvent environments. These experiments reveal that there is no preferential solvation of cyanate in this system; instead, a more complex local solvent environment is observed.