Multidimensional Spectroscopic Studies of Condensed Phase Dynamics

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With this award, the Chemical Structure, Dynamics and Mechanisms A program is funding the research of Graham Fleming of the University of California Berkeley to develop two new experimental methods to study the way energy flows through individual molecules, even if that flow is affected by the solvent the molecules might be dissolved in. Molecules in living tissue, for example, are always surrounded by a great deal of water and other substances that affect the way those molecules absorb energy from light and redistribute it. The influence of the water or other solvent can be quite large, and currently available experimental techniques are unable to separate the effects of the solvent from the molecule of interest. In this project, two new methods are being developed. The first method, which is called "two dimensional electronic-vibrational spectroscopy," or 2D-EV, will enable the investigators to directly observe the flow of light energy in, for example, a green plant as it undergoes the process of photosynthesis. The second new technique being developed in this work, known as "two dimensional fluorescence-detected coherent spectroscopy," or 2D-FDCS will more directly measure the influence of the solvent (usually water) on the molecule of interest. This work is having a broad impact on scientific infrastructure through the development of new devices so solve problems ranging from biology to materials science. Students at all levels will participate, including young students from local schools in the Oakland area who might not otherwise have the opportunity to consider a career in science.This project has two aims: (1) to investigate electronic-vibrational coupling; and (2) to understand the role of the solvent environment in preserving quantum coherence. To achieve these aims, two new methodologies are being developed. The first of the new methodologies involves the construction of a new two-dimensional spectroscopic technique, 2D-EV, used to elucidate the involvement and role of nuclear motions in molecular and nanomaterial electronic dynamics. This technique measures the interplay between electronic and vibrational coordinates by correlating the electronic (visible) spectrum with a second dimension, the (mid) infrared spectrum of the system, as a function of waiting time. The ability to follow the ultrafast temporal evolution of both electronic and vibrational degrees of freedom allows the study of coupling between electronic and nuclear dynamics in, for example, regions of the potential surface where the Born-Oppenheimer approximation breaks down, such as in situations where conical intersections occur. By providing a site-sensitive tag, the method is, thus, enabling direct exploration of energy flow pathways. The second new technique, 2D-FDCS, aims to extend photon echo and related techniques to small ensembles and, eventually, single molecules. This method can be used to detect weak signals from small ensembles and single molecule nanoparticles and is allowing a sampling of fluctuations as well as the distribution of environmental frequencies. The result is new insight into the role of the solvent environment in destroying quantum phase and the degree to which the ensemble average masks the true microscopic dynamics. The group is also using theoretical methods to interpret their experiments and inform new directions for study.