David Lee Phillips (Physical Seminar)
"Time-Resolved Spectroscopic Studies of Selected Water-Assisted Reactions and Insight Into Their Reaction Mechanisms"
David Lee Phillips, Chair of Physical Chemistry
University of Hong Kong, Department of Chemistry
Host: Art Winter
Abstract: This seminar presents time-resolved spectroscopic results for selected water-assisted photochemical reactions in order to better understand the role of water molecules in the reactions of interest.[1-3] The first part of the talk examines the photochemistry of polyhalomethanes in aqueous solutions to elucidate how halide ions are produced as photoproducts.[1] It was found that water assists the solvation of HX leaving groups to generate the halide ions.[1] The reaction mechanisms for the photochemistry of polyhalomethanes in aqueous solutions were deduced and discussed.[1] The second part then studied Blebbistatin using fs-TA experiments along with photoproduct analysis and DFT calculations and discovered that one blue (400 nm) photon and two-photon near infrared (800 nm) excitation can generate some hydroxyl radicals with potential for use in photochemically activated cancer therapy (PCAT).[2] Further work on several blebbistatin derivatives with various electronic characteristic leaving groups found that more substantial electron-withdrawing leaving groups facilitate heterolysis of the C-O bond that leads to a cationic intermediate and corresponding fragment.[3] Weaker electron-withdrawing leaving groups were found to give a higher proportion of homolysis of the C-O bond, accompanied by the production of some hydroxyl radical.[3] These results suggest that blebbistatin-derived photoprotecting groups have potential to deliver an anti-cancer drug and hydroxyl radicals at the same time which may lead to more efficient photochemotherapy.[2,3]
Bio: David Lee Phillips is recognized for his groundbreaking contributions to physical chemistry, particularly in the areas of ultrafast spectroscopy and reaction dynamics. His research combines time-resolved spectroscopic techniques with quantum mechanical modeling to investigate fleeting chemical intermediates relevant to biological systems and environmental chemistry.
Phillips has provided direct spectroscopic characterization of excited states and intermediates involved in photochemical and chemical damage to DNA nucleobases and oligomers. His work also explores photodeprotection compounds with applications in physiology, drug delivery, and photodynamic therapy, as well as novel photoredox reactions in aqueous solutions. In collaboration with multidisciplinary teams, he contributes to the development of advanced materials for solar cells, OLEDs, and photocatalysts for hydrogen production.
After earning his B.S. in chemistry from Iowa State University in 1984, Phillips completed a Ph.D. in physical chemistry at the University of California, Irvine in 1989 and pursued postdoctoral research in the Department of Chemistry at the University of Rochester. In 1993, he joined the University of Hong Kong’s Department of Chemistry, where he now serves as chair professor of physical chemistry and previously led the department as head from 2006 to 2010.