Manganese complexes exhibit for the first time luminescent properties and photocatalytic behavior, mainly associated with noble metal compounds.

Source: Jakob Bige, University of Basel

Manganese can make the conversion of light-emitting materials and sunlight more stable.

Researchers at the University of Basel have reached a milestone in the production of greener light-emitting materials and catalysts for converting sunlight into other forms of energy. Based on cheap metallic manganese, they developed a new class of compounds with promising properties, which until now have been found mainly in noble metal compounds.

Smartphone screens and catalysts for artificial photosynthesis, such as using sunlight to produce fuel, often contain very rare metals. For example, iridium, used in organic light emitting diodes (OLEDs), is rarer than gold or platinum. Ruthenium, used in solar cells, is also one of the rarest stable elements. Due to their rarity, these metals are not only very expensive, but also toxic in many compounds.

Now, for the first time, a team led by Professor Oliver Wenger of the University of Basel and his doctoral student Patrick Hull have succeeded in obtaining luminescent complexes of manganese, in which, when exposed to light, the same reaction with ruthenium occurs. or iridium compounds. The results were published in the journal Nature Chemistry. The advantage of using manganese is that the element is 900,000 times more abundant in the earth's crust than iridium, much less toxic, and much cheaper.

Fast photochemistry

At present, the light output of new manganese complexes is worse than that of iridium complexes. However, the light-driven reactions required for artificial photosynthesis, such as energy and electron transfer reactions, proceed at a high rate. This is due to the special structure of the new complex, which leads to instantaneous charge transfer from manganese to its directly bonded partner upon photoexcitation. This complex design principle has been used in some types of solar cells, although so far it has been characterized mainly by noble metal compounds and sometimes by copper-based less noble metal complexes.

Prevent unwanted vibration

In complexes of inexpensive metals, the absorption of light energy usually causes greater distortion than in noble metal compounds. As a result, the complex begins to vibrate and most of the absorbed light energy is lost. The researchers were able to suppress these twists and turns by adding specially selected molecular components to the complex, thereby forcing the manganese into a harsh environment. This design principle also increases the stability of the resulting compounds and their resistance to decomposition processes.

According to BEnger, so far no one has been able to create a molecular manganese complex that emits light at room temperature and has such special reactive properties. “Patrick Herr and his postdocs have really made a breakthrough in this area, which opens up new possibilities beyond the realm of precious metals.” In future research projects, Wenger and his team hope to improve the properties of the new manganese complexes. emitting properties, and fix it on semiconductor materials suitable for use in solar cells. Other potential improvements include water-soluble variants of manganese complexes that could potentially replace ruthenium or iridium compounds in photodynamic therapy for cancer treatment.