KubarychGroup
“Vibrational Resonance Imaging”
Solvation Dynamics
When a reaction occurs, the solvent responds, and simultaneously plays an active role in determining the dynamics and fate of the chemical event. Traditional methods study only the reacting species. We have studied the first solvation shell directly for the first time!
Watching the First Solvation Shell
We have recently developed a new approach to study precisely these most important solvent molecule directly by devising a three-component system made up of a photoinduced charge-transfer dye (Betaine-30, above), a solvation shell probe (Na+SCN– contact pairs), and a supporting solvent of ethyl acetate. Since the charge-transfer reaction causes a dramatic rearrangement of electrons—something common to most reactions—the local electric field felt by the solvent changes. Via the so-called “Stark effect,” the changing electric field causes a vibrational frequency shift of the NaSCN probes, which we measure using transient IR photon echo spectroscopy.
light
The shape of the signal tells us that the solvent shell molecules are actually aligned with the dye in the ground state.
Dynamic Stark Effect
All reactions in solution involve complicated, yet critical interactions between the species undergoing reaction and the surrounding solvent. It has long been known that the first solvation shell is responsible for the vast majority of relevant dynamics, but due to the small number of solvent molecules there relative to the bulk, it has been essentially impossible to study these key reaction participants. A new method developed by our group is able to track specifically those molecules in the first solvation shell, watching them much as a magnetic resonance imager maps the correlation between proton resonance frequency and inhomogeneous magnetic fields.