LUX-INVENTA is a European Research Council-funded project aiming to develop photomagnetic materials – photo-responsive materials that get magnetised by visible light.
The photomagnetic effect is the change of magnetic moment in response to visible light and occurs in compounds called photomagnets. It was coined by the pioneers in the field of molecular magnetism: Hashimoto, Miller, Verdaguer and Dei. Its discovery, however, is a consequence of the seminal work of Hauser et al. on the light-induced excited spin state trapping (LIESST) effect in octahedral iron(II) complexes showing spin crossover (SCO) behaviour.
The photomagnetic effect explained
The term photomagnetic effect applies to all types of magnetic systems responsive to light: diamagnetic, paramagnetic, as well as ferro- and antiferromagnetic. It relies on the observation that absorption of a photon by a specific part of a molecular system (a photomagnetic chromophore) can lead to a series of physical events resulting in a spin state change. This spin state change is directly associated with the change of the magnetisation. In other words, the construction of molecular materials based on photomagnetic chromophores results in compounds that get magnetised when exposed to visible light – the photomagnets.
Currently, photomagnets remain laboratory curiosities due to extremely low temperatures at which they operate, requiring expensive liquid helium cooling. Hence, the major objective of LUX-INVENTA is the design and synthesis of high-temperature photomagnets – paramagnetic compounds that, upon exposure to visible light, become reversibly magnetised at the highest possible temperature – preferably room temperature.
LUX-INVENTA: Advancements in photomagnetic materials
Photocrystallographic and photomagnetic studies performed within LUX-INVENTA extend beyond the current state-of-the-art. This enabled the identification of a high-performance photomagnetic chromophore: heptacyanomolybdate(III) complex anion. A complete experimental and theoretical study performed for its potassium salt revealed photoswitching in the solid state, involving an unprecedented change of the coordination sphere of the molybdenum(III) centre from a 7-coordinated capped trigonal prism to a 6-coordinated octahedron. This transformation induces a spin state and magnetisation changes, paving the way for the development of a new class of photo-switchable high-temperature magnets and nanomagnets. The manuscript has been deposited with the ChemRxiv repository.
Tripak
One of the peak achievements of the LUX-INVENTA research team was the rational design and successful isolation of a completely new and yet very simple organic molecule called tripak. The unique redox properties of tripak enabled its isolation in five different valence states, accommodating up to six additional electrons. These states can be reached by applying a small electrical potential, enabling electro-switching between completely different properties: record strong anion-π binding of halides, molecular qubit behaviour, red fluorescence and chemically unique diradicaloid character. The unique combination of vastly different physical properties enclosed within a compact and elegant molecular framework of tripak makes it highly versatile for applications ranging from quantum technologies and energy storage to molecular sensing. These results were published as an open-access research article in the Cell Press journal Chem.
Moreover, the unique physico-chemical character of tripak sparked an in-depth investigation of other derivatives with similar properties and improved potential for further chemical tuning and modifications.
Significant progress: Expanding the limits
While the goal of achieving room-temperature photomagnetism has yet to be reached, the LUX-INVENTA project has already pushed the limits of photomagnets towards an applicable temperature range and demonstrated a completely new photoswitching mechanism based on a reversible photodissociation reaction occurring in the solid state.
Moreover, the search for novel organic molecules suitable for the observation of charge-transfer induced photomagnetic switching has spawned a unique and yet very simple tripak molecule, which seems to be an extremely versatile platform for the construction of completely new magnetic coordination polymers.
Acknowledgments
Publication of this article has been funded under the Strategic Programme Excellence Initiative at the Jagiellonian University.
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