Scientists uncover a hidden power in a common metal

Researchers at Johannes Gutenberg University Mainz (JGU) have now created a new metal complex built from manganese, a widely available and inexpensive element. "This metal complex sets a new standard in photochemistry: it combines a record-breaking excited-state lifetime with simple synthesis," explained Professor Katja Heinze of the JGU Department of Chemistry. "It thus offers a powerful and sustainable alternative to the noble metal complexes that have long dominated light-driven chemistry." The study recently appeared in Nature Communications.

A One Step Route to a High Performance Manganese Complex

Manganese is more than 100,000 times more common on Earth than ruthenium, yet it has rarely been used successfully in photochemical systems. Two major obstacles held it back: most manganese complexes required a long, complicated synthesis involving nine or ten steps, and they typically had very short excited-state lifetimes.

"The newly developed manganese complex overcomes both challenges," said Dr. Nathan East, a former doctoral student in the Heinze group who carried out the initial synthesis. The team created the material directly from commercially available ingredients in a single synthesis step.

To fine-tune the behavior of the complex, the researchers combined manganese with a ligand that adjusts its electronic properties. According to Sandra Kronenberger, who investigated the complex as a doctoral student in the Heinze group at the Max Planck Graduate Center (MPGC), mixing a colorless manganese salt with a colorless ligand produced an unexpectedly intense purple solution resembling ink. She noted that this striking color indicated that the complex had formed in an unusual way.

Dr. Christoph Förster, who contributed quantum chemical calculations, emphasized that the complex does far more than simply look unusual. Its ability to absorb light is extremely strong, giving it a very high chance of capturing incoming light particles. As a result, it uses light energy with exceptional efficiency.

Record Setting Excited State Behavior

"The lifetime of the complex of 190 nanoseconds is also remarkable. This is two orders of magnitude longer than any previously known complexes containing common metals such as iron or manganese," said Dr. Robert Naumann, the lead spectroscopist who analyzed how the excited state behaves using luminescence spectroscopy. In photochemistry, light energizes the catalyst, and the excited catalyst must encounter another molecule through diffusion in order to pass along an electron. Because this encounter can take several nanoseconds, a long lasting excited state is essential.

The researchers also confirmed that the complex performs this key step. "We were able to detect the initial product of the photoreaction -- the electron transfer that occurred -- and thus prove that the complex reacts as desired," said Professor Heinze.

Potential for Scalable Clean Energy Photochemistry

This advancement broadens the possibilities for sustainable photochemical systems. With its simple, scalable synthesis, strong light absorption, stable photophysical characteristics, and long lived excited state, the manganese-based material could support future large scale photochemical applications. Such capabilities may be especially promising for technologies related to sustainable hydrogen production.