Photoacids are a well-known class of molecules studied almost exclusively by the ultrafast organic photochemistry community. Jillian is very familiar with organic photoacids, because they were crucial in her elucidation of hydrogen evolution mechanisms at cobalt–diglyoxime coordination compound electrocatalysts. My group is using photoacids as dye sensitizers in light-driven ion pumps fabricated from ion-exchange membranes, a concept that we invented several years ago for various applications including solar desalination of salt water. For my talk, I will first cover the brief history of this new class of materials, and then I will share my group’s efforts to understand the fundamental photochemistry and photophysics of organic photoacids dissolved in solution and covalently bound to polymers such as nanoporous poly(ethylene terephthalate) and several ion-exchange membranes I will present simulations results from our Marcus-like micro-kinetic models for the photoacid sensitization cycle, which strongly suggest that when a photo-liberated proton cage escapes from a photoacid, the conjugate base of the photoacid generates a hydroxide via regeneration by water. While hydroxide generation from photoacids has not been previously reported, this proposed mechanism is very similar to typical electron-transfer dye sensitization cycles. Results from these simulations will be complemented by experimental data to support the proposed kinetic processes. In honor of Jillian’s work on quantum dot nanocrystals, I will also share my group’s efforts to demonstrate the first quantum dot photoacids. Using several recently developed photo-iono-chemical techniques and a large suite of electrochemical and spectroscopic measurements, we have strong evidence that CdSe quantum dots containing a mixed-ligand surface of solubilizing 2-mercaptoethanesulfonate groups and 4-mercaptophenol donor groups are photoacidic. Collectively, this body of work represents an entirely new direction in photochemical energy conversion and storage, where a more complete understanding of the underlying fundamental mechanisms may help enable technologies to better the health of our planet.

Understanding the photoacid sensitization cycle and cause of photovoltaic action in light-driven ion pumps

2019 Spring National Meeting

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