Researchers from Linköping University have used computer simulations to show how stable aromatic molecules can change when exposed to light. The findings could have long-term applications in various industries, including molecular machinery, medicine, and solar energy storage.
Everyone knows that petrol smells nice. This is because it contains the aromatic molecule benzene. And aromatic molecules don’t just smell nice: they have many useful chemical properties. Our discovery means that we can add more properties.
Bo Durbeej, Professor, Computational Physics, Linköping University
Normal organic chemistry allows for the use of heat to initiate reactions. However, an aromatic molecule is a persistent hydrocarbon, and it is challenging to ignite interactions between such molecules and others just by heating.
This happens as a result of the molecule’s existing optimum energy state. On the other hand, an aromatic molecule can develop in a process very quickly.
Now, Linköping University researchers have demonstrated through computer simulations that it is feasible to light-activate aromatic compounds. These kinds of reactions are referred to as photochemical reactions.
Durbeej added, “It is possible to add more energy using light than using heat. In this case, light can help an aromatic molecule to become antiaromatic, and thus highly reactive. This is a new way to control photochemical reactions using the aromaticity of the molecules.”
When the study was published, the outcome was deemed significant enough to be featured on the front cover of the Journal of Organic Chemistry. It could be used in a variety of contexts in the long run.
The research group of Bo Durbeej focuses on solar energy storage applications, but he also sees promise in molecular machines, molecular synthesis, and photopharmacology. In the latter case, it might selectively activate aromatic drug molecules using light at a location in the body where the optimal therapeutic effect is desired.
“In some cases, it is not possible to supply heat without harming surrounding structures, such as body tissue. It should, however, be possible to supply light,” further stated Durbeej.
Extends the Concept
By looking at the inverse connection in the simulations, the researchers examined the idea that the loss of aromaticity caused increased reactivity. In this instance, scientists began with an unstable antiaromatic molecule and then simulated subjecting it to light irradiation.
The result was the creation of an aromatic compound, and the researchers observed that the reactivity was lost as they had predicted.
Durbeej added, “Our discovery extends the concept of ‘aromaticity’, and we have shown that we can use this concept in organic photochemistry.”
The Olle Engkvist Foundation, the Swedish Research Council, Forsk, and the Carl Trygger Foundation provided funding for the study. The calculations were done at Linköping University’s National Supercomputer Center with assistance from the Swedish National Infrastructure for Computing (SNIC).
Oruganti, B., et al. (2022) Modulating the Photocyclization Reactivity of Diarylethenes through Changes in the Excited-State Aromaticity of the π-Linker. Journal of Organic Chemistry. doi:10.1021/acs.joc.2c01172.