Florida State University researchers have identified a molecular pathway that limits the efficiency of certain photochemical reactions, offering new insight that could inform future advances in chemical manufacturing and pharmaceuticals.
The study, led by Bryan Kudisch, an assistant professor in the Department of Chemistry and Biochemistry, focused on ligand-to-metal photocatalysts. These are molecules designed to use light energy to accelerate chemical reactions. Although theoretically these molecules should efficiently harness light for reactivity, experimental results have shown otherwise.
Published in the Journal of the American Chemical Society, the research reveals that after absorbing light energy, these molecules quickly shift into a less energetic state before they can break chemical bonds—a necessary step for catalyzing reactions. As a result, most of the absorbed energy is redirected away from bond-breaking.
“Even though the molecule is absorbing the light and it’s getting the energy, it doesn’t always do the thing that you want it to do, which is to rip itself in half and catalyze some photochemical reaction,” said Kudisch.
Graduate researcher Rachel Weiss explained further: “Whenever you give something a lot of energy, the thing that it wants to do is get rid of it. The two ways that this system has is to either break the bond or rearrange its electrons, and it just tends to go in the rearranging pathway much more often.” In their study examples, about 85% of molecules followed this electron-rearrangement path instead of breaking bonds.
This behavior means that while ligand-to-metal charge transfer molecules do react when exposed to light with other materials present, their efficiency remains much lower than expected. The missing energy does not radiate as heat or light but instead gets funneled into rearranging electrons within the molecule.
Understanding this mechanism could be significant for industrial applications such as pharmaceutical production. Faster chemical reactions could lead to increased output and improved economics for large-scale manufacturing processes. “Right now, we don’t know what determines the path these molecules use, but it implies we can make these reactions five or ten times faster,” Kudisch said. He added: “The economics of making a molecule depends on how much time is needed for a reaction to occur. The faster your reactions are, the more products you can make.”
The research received support from both Florida State University and the American Chemical Society Petroleum Research Fund.
