Nonlinear Optical Studies of Condensed Phase Dynamics

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Graham Fleming at the University of California is supported by the Experimental Physical Chemistry Program to continue his experimental studies of dynamics in complex condensed phase systems. Ultrafast resonant and non-resonant spectroscopy will be used to achieve an improved understanding of electronic interactions and electronic-phonon interactions in multichromophore systems, in particular the development of experimental methods that probe orbital mixing and electronic coherence. Specific plans include the extension of resonant photon echo spectroscopy to more complex systems such as reacting systems, proteins, and optically active polymers such as dendrimeric light harvesting complexes and conducting polymers. As well, the mechanisms of nonpolar solvation will be explored. In another project, two-dimensional Raman spectroscopy will be used to clarify coupling mechanisms between different nuclear motions. Enhancements to this technique, including the use of polarization to enhance relative contributions to the signal, will be sought to achieve the capability to retrieve structural information from the two-dimensional data. Many important chemical and biological processes occur in solution, where the species of interest are surrounded completely by large numbers of solvent molecules. The rapid time scales of molecular motion in solution make these processes amenable to exploration by ultrafast laser techniques. Theory and experiment have evolved to the extent that useful complex systems can now be studied effectively. Outcomes from these studies are expected to impact the understanding of solution phenomena in biological systems, including folding and unfolding transitions in proteins.