Researchers at Linköping University have used computer simulations to show that stable aromatic molecules can become reactive after absorbing light. The results, published in the Journal of Organic Chemistrymay have long-term applications in areas such as solar energy storage, pharmacology, and molecular machines.
“Everyone knows that gasoline smells good. That’s because it contains the aromatic molecule benzene. And aromatic molecules don’t just smell good: they have many useful chemical properties. Our discovery means we can add more properties,” says Bo Durbeej, Professor of Computational Physics at Linköping University.
In normal organic chemistry, heat can be used to start reactions. However, an aromatic molecule is a stable hydrocarbon and it is difficult to initiate reactions between such molecules and others simply by heating. Because the molecule is already in an optimal energy state. In contrast, a reaction in which an aromatic molecule is formed proceeds extremely easily.
Researchers at Linköping University have now shown using computer simulations that it is possible to activate aromatic molecules with light. Reactions of this type are known as photochemical reactions.
“It is possible to supply more energy with light than with heat. In this case, light can help an aromatic molecule to become anti-aromatic and thus highly reactive. This is a new way to control photochemical reactions via the aromaticity of the molecules,” says Bo Durbeej.
The result was important enough to be recognized on the cover of the Journal of Organic Chemistry when it was published. In the long term, there are potential applications in many areas. Bo Durbeej’s research group focuses on applications in solar energy storage, but he also sees potential in molecular machines, molecular synthesis and photopharmacology. With the latter application, it is possible to activate drugs with aromatic groups in a targeted manner at a site in the body where the pharmacological effect is desired.
“In some cases, it is not possible to apply heat without damaging surrounding structures such as body tissue. However, it should be possible to add light,” says Bo Durbeej.
The researchers tested the hypothesis that it was the loss of aromaticity that led to the increased reactivity by examining the opposite ratio in the simulations. In this case, they assumed an antiaromatic unstable molecule and simulated exposure to light irradiation. This resulted in the formation of an aromatic compound and, as expected, the researchers saw that reactivity was lost.
“Our discovery extends the concept of ‘aromaticity’ and we have shown that we can apply this concept to organic photochemistry,” says Bo Durbeej.
The study was funded by the Olle Engkvist Foundation, the Swedish Research Council, ÅForsk and the Carl Trygger Foundation. The calculations were performed at the National Supercomputer Center at Linköping University with support from the Swedish National Infrastructure for Computing (SNIC).