LEAPS-MPS: Development and Investigation of Visible Light Activated Switches for Water

About This Grant

In this project, funded by the MPS-LEAPS (Launching Early-Career Academic Pathways) Program and managed by the Division of Chemistry, Professor Julie A. Peterson and her students at Bowling Green State University will conduct fundamental investigations on an underexplored photoswitch which undergoes reversible isomerization using visible light in aqueous systems. Photoswitches have possible applications in light-responsive hydrogels and drug delivery systems; however, there is a lack of switches that can reversibly isomerize using visible light in water. Stenhouse salts reversibly switch in water using visible light but the principles that govern their on-target reactivity (i.e., reversible switching) and off-target reactivity (i.e., irreversible rearrangements) are not well understood. Professor Peterson and her students will conduct mechanistic investigations on the on-target and off-target reactivities of Stenhouse salts to establish design principles for new derivatives. Their studies could lead towards the development of Stenhouse salts with highly controlled reactivities for applications in light-responsive drug delivery systems. In addition, this program will increase the engagement of undergraduates through the development of an undergraduate lab on photoswitches and with the external community through the development of STEM-based outreach events at community centers. Professor Peterson and her students will conduct fundamental investigations on the on-target and off-target mechanistic pathways of Stenhouse salt photoswitches, which display negative photochromism upon excitation with visible light. While Stenhouse salts reversibly photoisomerize in protic solvents, including water, they also undergo irreversible thermal rearrangements. Professor Peterson and her students will investigate the underlying photochemical and thermal mechanisms using time-dependent UV-Vis, NMR with in-situ irradiation, and computational methods. The effects of environmental factors (e.g., solvent polarity, pH, presence of additives) on the on-target and off-target reactivities will be determined. New molecules will be synthesized and the impact of structural factors (e.g., electronics, sterics) on on-target and off-target reactivities will be evaluated. Their studies will establish a mechanistic understanding of Stenhouse salt reactivity which may also provide insight into the thermal rearrangements of other common polymethine dyes such as cyanines, merocyanines, and donor-acceptor Stenhouse adducts and establish design principles for derivatives that are hydrolytically stable and have full reversible switching in aqueous systems. 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.