For more than half a century, the scientific contributions of Dr. Michael Kasha have impacted all aspects of molecular photochemistry and photophysics. Some of his works include heavy-atom effects, Kasha’s rule, the assignment of electronic transition, and the triplet excited states in organic molecules. The latter is particularly important in applications ranging from molecular photon upconversion to organic light emitting diodes. Interestingly, by fate or by chance, a majority of the work in the Hanson research group at Florida State University, the academic home of Michael Kasha, revolves around the generation of triplet excited states in organic molecules. In this presentation we will recount some of our efforts to harness triplet excited state to facilitate organic transformations. We will start by discussing the use of triplet sensitized isomerization of stilbene for the conversion of photon energy into mechanical work in photomechanical polymers. Accessing the triplet state of these polymers enables the use of lower energy light and more efficient light to work conversion. Then we will describe the use of excited state proton transfer (ESPT) via the triplet excited state in catalytic and enantioselective protonation of prochiral substrates as well as enantioenrichment atropisomers via chiral group directed isomerization. The triplet excited state is key to these processes because the long lifetime enables diffusion limited bimolecular reactions and they can be excited using low energy light via sensitization.

Facilitating organic transformations via triplet excited states

ACS Spring 2022

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