Nonlinear Optical Studies of Condensed Phase Dynamics

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Graham Fleming of the University of California-Berkeley is supported by the Experimental Physical Chemistry Program to carry out nonlinear optical studies of condensed phase dynamics. New methods to extend two-dimensional (2D) spectroscopic methods into the optical region will be developed, allowing 2D electronic spectroscopy with femtosecond time resolution. This technique, along with the simpler two-color photon echo peak shift technique, will enable the determination of electronic couplings and pathways of relaxation, reveal quantum aspects of ultrafast dynamics, and may enable electronic and spatial structure of molecular complexes to be directly connected. In addition, the nature and geometry of conical intersection seams, thought to control the products of many if not most ultrafast photochemical processes, can be accessed with 2D and combined visible/infrared spectroscopic experiments. The experimental technique involves the generation of independently tunable femtosecond light pulses and Fourier transform photon echo spectroscopy to record the full field of the third-order nonlinear response. Outcomes are expected to influence the understanding and design of molecular complexes and nanostructures for optoelectronic applications. Two-dimensional spectroscopic methods have proved extraordinarily powerful in nuclear magnetic resonance (NMR) spectroscopy, and have become an area of active development in the infrared spectral region for studying how molecules vibrate. The research supported here moves these techniques into the visible light region, creating new opportunities for the understanding of important chemical systems. As a result, critical information is expected to be provided for the design of highly efficient light harvesting devices for solar energy conversion, and the applications of single walled carbon nanotubes in opto-electronic devices. The studies of photochemical reactions are anticipated to influence the use of light-driven chemistry to produce high-value chemicals. This project as well will contribute to the US scientific infrastructure by providing state-of-the-art research training to young scientists at the undergraduate, graduate, and postdoctoral levels.