Collaborative Research: Investigating Photoinduced Charge Transfer Dynamics Across Molecule-Nanocrystal Interfaces

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Plants use sunlight to convert carbon dioxide into energy rich sugar molecules, in a process known as photosynthesis. The development of artificial photosynthetic systems that could use sunlight to make fuels such as alcohol from carbon dioxide and hydrogen from water would have enormous societal benefit. However, the chemical reactions are complicated and involve multiple electron transfer steps and connecting these steps with the absorption of light remains a challenge. With support from the Chemical Structure, Dynamics and Mechanisms A and Macromolecular, Supramolecular and Nanochemistry programs in the Division of Chemistry, Professors David McCamant, Pengfei Huo, and Kathryn Knowles at University of Rochester are teaming up with Professors Luis Velarde and David Watson at the University at Buffalo, State University of New York and Kacie Liwosz at D'Youville College to study light-induced electron transfer reactions between dye molecules and semiconductor nanoparticles. Working with their students, they grow nanoparticles composed of common minerals such as titanium dioxide and iron oxide and coat them with organic dyes. They then combine sophisticated laser spectroscopies with computer modeling to characterize the electron transfer process that occur when the dye molecules absorb light. In addition to training the next generation of scientists, the team is also running educational workshops in Upward Bound summer schools for high-school students with disadvantaged backgrounds. The summer workshops inspire students' curiosity and enthusiasm about renewable energy and chemistry, as well as encourage them to pursue higher education in STEM fields. Photoinduced interfacial charge transfer is a fundamental process underlying the conversion of solar energy to chemical energy and is particularly important in photocatalytic fuel-forming reactions. Detailed knowledge of the conformation and electronic structure of the ground, photoexcited, and charge separated states of molecular species bound to semiconductor surfaces is critical to a mechanistic understanding of the dynamics of such charge transfer reactions. The project combines interdisciplinary expertise in time-resolved electronic and vibrational spectroscopy, sum-frequency generation spectroscopy, quantum dynamics simulation, and the fabrication and characterization of nanostructured semiconductors. These tools are being applied to three important areas relating to interfacial charge transfer: (i) the role of molecular structure in mediating relaxation and energy transfer pathways that precede interfacial charge transfer, (ii) structure-function relationships between the morphology of wide band-gap p-type semiconductors and hole injection from surface-bound molecular sensitizers, and (iii) structure-function relationships between the morphology of narrow band gap semiconductors and charge transfer to surface-bound molecular hole and electron acceptors, such as catalysts for fuel production. Fundamental mechanistic insights generated by this work could enable the rational design of semiconductor/molecule partner systems with improved performance in photocatalytic generation of fuels from sunlight.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.