Researchers at the University of Basel have reached an important milestone in their quest to produce more sustainable luminescent materials and catalysts for the conversion of sunlight into other forms of energy. Based on the inexpensive metal manganese, they have developed a new class of compounds with excellent properties that until now have been found mainly in compounds of precious metals.

Now, for the first time, a team led by a professor from the University of Basel and his doctoral students has succeeded in producing manganese complexes that glow, in which exposure to light results in the same reactions as in ruthenium or iridium compounds. Currently, the new manganese complexes perform worse than the iridium compounds in terms of luminescence efficiency. However, the light-driven reactions required for artificial photosynthesis, such as energy and electron transfer reactions, are carried out at high speeds. This is due to the special structure of the new complexes, which leads to an immediate charge transfer from the manganese to its direct binding partner upon excitation by light. The design principles of such complexes have been used for certain types of solar cells, although so far it has mainly featured compounds of noble metals, sometimes complexes based on the less expensive metal copper.

The absorption of light energy usually causes greater deformation in complexes made of cheaper metals than in compounds of precious metals. As a result, these complexes begin to vibrate and a large portion of the absorbed light energy is lost. The researchers were able to suppress these distortions and vibrations by adding tailored molecular components to the complexes to force the manganese into a rigid environment. This design principle also increased the stability of the resulting compound and its resistance to the decomposition process.

To date, no one has succeeded in creating molecular complexes of manganese that can glow in solution at room temperature and have these specific reaction properties. This opens up new opportunities outside the field of precious metals. In future research projects, it is hoped to improve the luminescence properties of new manganese complexes and to immobilize them on suitable semiconductor materials for use in solar cells. Other possible improvements include water-soluble variants of manganese complexes that have the potential to replace ruthenium or iridium compounds in photodynamic therapies used to treat cancer.