Near Threshold Excited State Dynamics in Nucleobases and Related Compounds

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In this project, funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Prof. de Vries at the University of California Santa Barbara will study how isolated DNA bases respond to ultraviolet (UV) light. Understanding the response of DNA bases to UV radiation is critical for both practical and fundamental reasons. Nucleobase photochemistry following UV absorption constitutes a fundamental step in radiation induced DNA damage. The extremely efficient response of the nucleobases to absorption of ultraviolet light is often described as nature's strategy to protect the building blocks of life against UV photodamage. UV photo-selection may have played a key role in prebiotic chemistry on an early earth. These same processes also find applications in a variety of modern materials. This project will focus on gas phase spectroscopy of nucleobases and their clusters in the picosecond time domain and close to the threshold for absorption. Experiments will study the excited state processes with the isomer specificity afforded by double resonant spectroscopy in the gas phase and in the sub-nanosecond time domain. Collaboration with computational chemists will provide comparison of the results with quantum chemical modeling. Choosing low energy excitation wavelengths will make the work most sensitive to the details of the relaxation processes. This approach will make it possible to directly investigate the key mechanisms of the response of nucleobases to UV irradiation so this research will contribute to the most basic understanding of fundamental processes that govern the molecular building blocks of life. These topics, in combination with cutting-edge laser and computational techniques, lend themselves extraordinary well to outreach activities that will be based in this work, which also provides for the training of both undergraduate and graduate students in the design and construction of advanced experimental instrumentation, complex computer simulation, and conducting fundamental research.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.