Light-driven method puts notoriously reactive hydrogen atoms to work for chemical synthesis

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Hydrogen is the simplest element in the periodic table, consisting of just one proton and one electron. In chemistry, however, the smallest of atoms is anything but simple.

First produced by Nobel laureate Irving Langmuir over a century ago, single hydrogen atoms (H•) are so reactive that they are almost impossible to prepare and use. In an international collaborative effort, researchers at the Max Planck Institute of Colloids and Interfaces, University College London and Imperial College London have found a solution to this problem. Using light, they generate hydrogen atoms under mild conditions and use them to reduce organic molecules without metals.

Their findings have been published in the Journal of the American Chemical Society. In the laboratory, chemists frequently encounter hydrogen as H₂: two hydrogen atoms firmly bonded together. The molecule is stable, and its use in synthetic chemistry is widespread.

A single hydrogen atom, on the other hand, is a completely different story. "From a chemical point of view, a hydrogen atom is incredibly simple, but it is also extremely reactive," says Nils J. Flodén, first author of the study at the Max Planck Institute of Colloids and Interfaces.

"Therefore, we had to find a way to generate hydrogen atoms under conditions where we can channel their reactivity to do what we want." For their new approach, the researchers use light. They combine hydrazine with a thiophenol derivative and then expose the mixture to light. The light provides the necessary energy to trigger an electron transfer between the two molecules.

The investigations suggest that the electron transfer results in the formation of a short-lived intermediate belonging to the broader class of so-called Rydberg radicals. Their lifetime is only around 13 picoseconds, which corresponds to 13 trillionths of a second. While Rydberg atoms are crucial in quantum computing, in this work the decay of a Rydberg molecule is used to release a hydrogen radical.