Sean Garrett-Roe

Ultrafast dynamics; nonlinear spectroscopy; biophysics; solvation dynamics; ion channels; ionic liquids.

The goal of the Garrett-Roe research group is to develop a deep understanding of structure and dynamics in the condensed phase, especially in complex systems. We have established a strong theme in the ultrafast dynamics of ionic liquids, and we are founding a parallel theme for the dynamics of ion-binding peptides.

 Ultrafast vibrational spectroscopy allows us to make “molecular movies” of ionic liquids to understand their physical chemistry and chemical physics to support their application as advanced electrolytes, carbon absorbents, and reaction media.]

Ionic liquids are salts that are molten at room temperature. They are liquids composed of cations and anions with no excess solvent. Ionic liquids are fascinating from both the practical and fundamental points of view. Their low vapor pressure, high thermal stability, and chemical tunability make them “green solvents” whose properties can be tuned for the application at hand. For example, these solvents show promise as reaction media, non-aqueous electrolytes, and carbon capture absorbents.

More than 10¹⁸ ionic liquids are possible, only the smallest fraction of which have been tested. What is missing is the fundamental understanding to guide the exploration of this large chemical space. The competition between intermolecular forces -- electrostatic attraction, dispersion, polarization, and hydrogen bonding -- makes the bulk properties of these fluids difficult to predict from their molecular properties. In the same way that solvation structure and dynamics dictate the behavior of simple liquids, so do they control the properties of this class of complex liquids.

To develop a deeper understanding of the molecular interactions in these complex solvents, we use ultrafast vibrational spectroscopy (2D-IR) to elucidate local structure and dynamics. Ultrafast spectroscopy has the time resolution to resolve intermolecular motions. Vibrational spectroscopy has the advantage of small, well-defined chromophores which can provide local chemical information. A comprehensive understanding of how molecular structure of the ionic liquid's components dictates the solvation dynamics will lead to the insights needed for the rational design and optimization of ionic liquids for many important properties, from their viscosity, to CO₂ solubility, to catalytic properties.