Molecular vibrations are a powerful tool for investigating chemical systems. Changes in a molecule’s structure or environment cause shifts in its characteristic vibrational signature, and monitoring these shifts lets us probe the chemical dynamics of the system.
In my graduate work, I developed several new tools for using ultrafast vibrational spectroscopy to investigate molecular structure and dynamics at interfaces:
First, I developed new tools based on two-dimensional infrared spectroscopy (2D IR) to investigate electron transfer in dye-sensitized solar cells.
2D IR enabled us to show that the dye molecules aggregate on the surfaces in these systems, and by rapidly exciting an electronic transition in the middle of our 2D IR experiments, we were able to show that these heterogeneities can dramatically affect electron transfer rates.
Second, I developed a class of tools that fell under the umbrella of vibrational sum-frequency generation, or SFG.
In SFG, a series of laser pulses selects out the vibrational signatures of just the molecules at the interface. By combining the interface-selectivity of SFG with the dynamical sensitivity of 2D IR, we obtained the first direct measurements of the vibrational dynamics of small molecules and proteins adsorbed to solid surfaces, which let us draw important conclusions about their structures and solvation environments. I also developed new theoretical methods to inform the design and interpretation of these experiments.