Controlling the Hierarchal Structure of Light-Harvesting Chromophore Aggregates

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In this project supported by the Chemical Structure, Dynamics and Mechanisms Program of the Division of Chemistry, Professor Jeanne McHale and her graduate students will address fundamental questions about the hierarchal structures of light-harvesting chromophore aggregates and their potential to improve the efficiency of solar energy conversion. Based on previous studies of porphyrin aggregates, the PI has developed the hypothesis that molecular flexibility directs local supramolecular structure while environment determines the longer range order. To pursue the objective of controlling and optimizing the optical and energy-transfer properties of light-harvesting aggregates (LHAs), the following four specific aims will be pursued: 1. Use resonance Raman spectroscopy to reveal molecular conformation of flexible carotenoids in aggregates whose supramolecular structure depends on solvent. 2. Prepare LHAs with controlled size and shape using nanostructured metal and metal oxide supports and examine their optical properties using ensemble and single-aggregate resonance Raman spectroscopy. 3. Prepare self-assembled heteroaggregates of energy donors (carotenoids) with energy acceptors (porphyrins) and explore their energy transfer and excited electronic states. 4. Exploit LHAs as energy donors and/or sensitizers for dye-sensitized solar energy conversion to achieve improved light harvesting. These experiments will result in fundamental knowledge required to exploit the extended wavelength response of LHAs in solar photovoltaic devices. The proposal builds on the PI's longstanding research in resonance Raman studies of photoinduced electron transfer, excited state dynamics, and chromophore aggregation, as well as more recent breakthroughs in solar energy conversion using plant pigments. The project will also extend previous education and outreach efforts aimed at broadening participation in science and specifically in solar energy research. The PI and her graduate students will continue to contribute to WSU's outreach program to Native American and Hispanic students: "Pumping up the Math and Science Program." The PI and her students will also partner with the Palouse Clearwater Environmental Institute to grow "solar vegetables" as sources of plant pigments for demonstration solar cells to be used in presentations to local schools and nonprofit groups. It is the goal of both these projects to recruit future scientists to face the technical challenges of powering the planet with sunlight.