Making stable aromatic molecules reactive with light

Reactions of this type are known as photochemical reactions.

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Aromatic molecules don’t just smell nice: they have many useful chemical properties. A discovery by Linköping University is adding more properties to them.

Scientists have shown that it is possible to activate aromatic molecules using light. Using computer simulations, they have shown that stable aromatic molecules can become reactive after absorbing light. These types of reactions are known as photochemical reactions.

An aromatic molecule is a stable hydrocarbon; however, it is difficult to initiate reactions between such molecules and others simply by heating. This is a result of the molecule’s existing optimum energy state. On the other hand, an aromatic molecule can arise in a process very quickly.

Bo Durbeej, professor of computational physics at Linköping University, said, “It is possible to add more energy using light than 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.”

Besides having potential applications in the storage of solar energy, the discovery could also be useful in molecular machines, molecular synthesis, and phytopharmacology. In the latter case, it might be able to selectively activate aromatic drug molecules using light at a site in the body where the desired pharmacological effect is desired.

Bo Durbeej said, “In some cases, it’s impossible to supply heat without harming surrounding structures, such as body tissue. It should, however, be possible to supply light.”

By looking at the inverse connection in the simulations, the scientists investigated 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.

Bo Durbeej said“Our discovery extends the concept of ‘aromaticity,’ and we have shown that we can use this concept in organic photochemistry.”

Journal Reference:

  1. Baswanth Oruganti*, Jun Wang, and Bo Durbeej* et al. Modulating the Photocyclization Reactivity of Diarylethenes through Changes in the Excited-State Aromaticity of the π-Linker. American Chemical Society. DOI: 10.1021/acs.joc.2c01172
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