My research group studies complex molecular systems using ultrafast multi-dimensional infrared and UV/Vis methods. The properties of systems, such as molecular complexes, hydrogen bonding liquids, organic ionic liquids, proteins, liquid crystals, or supercooled liquids depend on molecular level dynamics and intermolecular interactions. Bulk properties are frequently a very poor guide to understanding the molecular level details that determine the nature of a chemical process and its dynamics. Because molecules are small, molecular motions are inherently very fast. Recent advances in methodology developed in our labs make it possible for us to observe important processes as they occur. These measurements act like stop-action photography. To focus on a particular aspect of a time evolving system, we employ sequences of ultrashort pulses of light as the basis for non-linear methods such as ultrafast infrared multidimensional vibrational echoes, optical Kerr effect methods, and ultrafast transient absorption experiments.

We are using ultrafast 2D IR vibrational echo spectroscopy and other multi-dimensional IR methods, which we have pioneered, to study dynamics of molecular complexes, water confined on nm lengths scales with a variety of topologies, organic ionic liquids, and proteins. We can probe the structural transformations of these systems. The methods are somewhat akin to multidimensional NMR, but they probe molecular structural evolution in real time on the relevant fast time scales. We are examining the formation and dissociation of organic solute-solvent complexes and molecular isomerization. We are obtaining direct information on how nanoscopic confinement of water changes its properties, a topic of great importance in chemistry, biology, geology, and materials. In proteins, we are using the vibrational echo methods to study dynamics and the relationship among dynamics, structure, and function. We are measuring how binding of a substrate influences enzyme dynamics by looking at the motions of the enzyme and the substrate. Using artificial amino acids we are tagging proteins and peptide chains to study dynamics of proteins at different points along the protein folding curve. We are also developing and applying theory to these problems frequently in collaboration with top theoreticians.

We are studying dynamics in complex liquids, in particular organic ionic liquids, liquid crystals, supercooled liquids and the glass transition, as well as in influence of small quantities of water on liquid dynamics. Using ultrafast optical heterodyne detected optical Kerr effect methods, we can follow processes from tens of femtoseconds to ten microseconds. Our ability to look over such a wide range of time scales is unprecedented. The change in molecular dynamics when a system undergoes a phase change is of fundamental and practical importance. We are developing detailed theory as the companion to the experiments.

We are studying photo-induced proton transfer in nanoscopic water environments such as polyelectrolyte fuel cell membranes, using ultrafast UV/Vis absorption and fluorescence and multidimensional IR measurements to understand the proton transfer and other processes and how they are influenced by nanoscopic confinement. We want to understand the role of the solvent and the systems topology on proton transfer dynamics.

1) "Ion-Water Hydrogen Bond Switching Observed with 2D IR Vibrational Echo Chemical Exchange Spectroscopy," D.E. Moilanen, D. Wong, D.E. Rosenfeld, E.E. Fenn, and M.D. Fayer, Proc. Nat. Acad. Sci. U.S.A., 106, 375-380 (2009).

2) "Direct Observation of Fast Protein Conformational Switching," H. Ishikawa, K. Kwak, J.K. Chung, S. Kim and M.D. Fayer, Proc. Nat. Acad. Sci. U.S.A., 105, 8619-8624 (2008).

3) "Geometry and Nanolength Scales vs. Interface Interactions: Water Dynamics in AOT Lamellar Structures and Reverse Micelles," D.E. Moilanen, E.E. Fenn, D. Wong, and M.D. Fayer, J. Am. Chem. Soc., 131, 8318-8328 (2009).

4) "Water at the Surfaces of Aligned Phospholipid Multi-Bilayer Model Membranes Probed with Ultrafast Vibrational Spectroscopy," W. Zhao, D.E. Moilanen, E.E. Fenn, and M.D. Fayer, J. Am. Chem. Soc., 130, 13927-13937 (2008).

5) "Proton Transfer and Proton Concentrations in Protonated Nafion Fuel Cell Membranes," D.B. Spry and M.D. Fayer, J. Chem. Phys. B, 113 , 10210-10221 (2009).

6) "Solute-Solvent Complex Kinetics and Thermodynamics Probe by 2D-IR Vibrational Echo Chemical Exchange Spectroscopy," J. Zheng and M.D. Fayer, J. Phys. Chem. B, 112, 10221-10227 (2008).

7) "Dynamics in Supercooled Ionic Organic Liquids and Mode Coupling Theory Analysis," J. Li, I. Wang, K. Fruchey, and M.D. Fayer, J. Phys. Chem. A, 110, 10384-10391 (2006).

8) "Water Dynamics and Proton Transfer in Nafion Fuel Cell Membranes," David E. Moilanen, D.B. Spry, and M. D. Fayer, Langmuir, 24, 3690-3698 (2007).