Photochemistry, Spin, and Molecular Motion: Connections through Magnetic Resonance

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With this award, the Chemical Structure, Dynamics and Mechanisms B (CSDM-B) Program of the Division of Chemistry is funding Professor Malcolm D. E. Forbes at Bowling Green State University to study how molecules move in confined spaces on the nanometer scale. With specially designed spectroscopic measurements, the Forbes laboratory investigates the location and mobility of molecules confined to thin polymer films, such as those making up household paint coatings, as well as other structures like microbubbles, which are used as delivery vehicles for cancer therapy. Recently, this group has applied these techniques to study a class of materials called "structured fluids." These fluids have many practical applications in the food and oil industries, but the underlying fundamental principles describing the flow of these materials under stress is poorly understood. Forbes and his coworkers are attempting to provide a rigorous quantitative footing for how the viscosities of structured liquids change in response to a stress. Dr. Forbes co-chairs the 2015 Gordon Research Conference on Photochemistry and he currently serves as President of the Inter-American Photochemical Society (I-APS), working with the Society to promote UNESCO?s "Year of Light" in 2015. The Forbes laboratory uses steady-state and time-resolved electron paramagnetic resonance (SSEPR and TREPR) spectroscopies at multiple frequencies, coupled to pulsed lasers or continuous wavelength (CW) light sources to create photogenerated radical pairs in confined environments such as vesicles and in heterogeneous media such as non-Newtonian fluids. With rigorous spectral simulation routines, the group is able to extract structural data (hyperfine couplings and exchange interactions), kinetic parameters (rate constants and activation energies), and molecular dynamics information. Systems currently under investigation include: 1) singlet oxygen reactivity and topology in heterogeneous structures (micelles and vesicles), 2) polymer chain dynamics in solutions, emulsions, and thin films, 3) coordination compounds such as light-harvesting copper complexes and water-splitting ruthenium catalysts, and 4) the molecular basis of rheological phenomena such as viscosity modification. The well-established "nanoreactor model" for the TREPR line shapes of mobile spin correlated radical pairs (SCRPs) is being refined for radicals located in colloidal systems such as pluronic micelles and mixed surfactant vesicles. These experiments provide detailed information about the mobility and ordering of small molecules over a wide range of time scales.The Forbes laboratory has strong interactions with scientists from overseas (Russia, Mexico, China and Austria).