Graduate Student Shea Martin

"Combining Experiment and Computation to Solve Complex Problems in Photochemistry"

Light-driven reactions are an attractive method of accessing novel chemistry. Their broad applicability to industrial process and renewable energy research makes understanding their mechanisms extremely desirable. Steady-state and time resolved spectroscopic experiments provide a powerful window into the complex behavior of photoactive species. Those results can be made even more powerful by rationalizing the quantum-mechanical nature of the observed phenomena using theoretical modeling. This seminar will focus on three projects in which I fused advanced spectroscopic techniques with DFT-level computational chemistry to describe complex processes that drive unexpected photochemistry. First, a novel Re(I) bipyridine complex, which was developed as a model system for photoinduced proton-coupled electron transfer (PCET), was found to exhibit an unexpected biexponential photoluminescence decay. Spectroscopic and computational results show that this phenomenon occurs via rearrangement into discrete and asymmetric geometrical isomers in the excited state. A deeper understanding of the role of protons in this complex will provide key insight for its use in future PCET studies. Second, three Pd(II) biladiene complexes that were developed as candidate drugs for photodynamic therapy (PDT) were observed to produce excitation wavelength-dependent kinetics when measured with transient absorption spectroscopy. I discovered that this behavior arises from excited-state photophysics which facilitate unusual high-energy intersystem crossing into triplet excited states. Access to high-energy triplet states is rare and will enable new and interesting possibilities for these molecules in other challenging chemical reactions that employ triplet photochemistry. Finally, a series of pyridine-based azo dyes displayed trans to cis photoisomerization that was unexpectedly disabled when protonated at a site far from the azo bond. Significant alterations to excited-state potential energy landscapes when protonated rationalized the drastically different conformational changes in the presence of acid. Increasing the understanding of azo dye photophysics is crucial for industries such as textile pigmentation and wastewater treatment.

1. Shea M. Martin, Amanda N. Oldacre, Craig A. Pointer, Tao Huang, Gil M. Repa, Lisa A. Fredin, and Elizabeth R. Young “Proton-controlled non-exponential photoluminescence in a pyridylamidine-substituted Re(I) complex” Dalton Trans., 2021, 50, 7265-7276
2. Shea M. Martin, Gil Repa, Robert C. Hamburger, Craig Pointer, Kaytlin Ward, Nhan Pham, Maxwell I. Martin, Joel Rosenthal, Lisa A. Fredin, Elizabeth R. Young. “Elucidation of Complex Triplet Excited State Dynamics in Pd(II) Biladiene Tetrapyrroles” Physical Chemistry Chemical Physics, 2023, 25, 2179-2189
3. Shea M. Martin, Zachary J. Knepp, Ing Angsara Thongchai, Kiera Englehart, Keyri Sorto, Athina Jaffer, Lisa A. Fredin, Elizabeth R. Young. “The Doorstop Proton: Acid-controlled Photoisomerization in Pyridine-Based Azo Dyes” Manuscript in preparation.