Prof. Mantas Šimėnas from Vilnius University (VU) expressed that the recent awarding of the Nobel Prize in Chemistry for metal–organic frameworks (MOFs) was anticipated among physicists. He stated, “Nobel recognition in this field was long expected – it”s a major area not only in chemistry but also in physics.” Prof. Šimėnas has dedicated over ten years to studying these hybrid materials, which are composed of metal centers and organic linkers, resulting in intricate porous structures. His research on enhancing electron paramagnetic resonance (EPR) techniques for MOF studies recently secured €2.5 million in funding from the European Research Council (ERC).
MOFs have emerged as a critical focus in materials science, offering potential advancements in gas capture, storage, catalysis, and quantum devices. The Nobel Prize in Chemistry was awarded to pioneers in MOF research, including Prof. Susumu Kitagawa, Prof. Omar Yaghi, and Prof. Richard Robson. Prof. Kitagawa has collaborated with Prof. Šimėnas on a scientific publication. Reflecting on their partnership, Prof. Šimėnas recalled, “A decade ago, when I was still a doctoral student, my supervisor, Prof. Jūras Banys, and I attended the Pacifichem conference in Hawaii, where I met a member of Kitagawa”s research team. Our discussion sparked the idea of collaborating.”
This collaboration led to a paper published in The Journal of Physical Chemistry, demonstrating how “guest” molecules within MOF pores could influence a material”s magnetic properties. For Prof. Šimėnas, the experience of working with such a renowned researcher was invaluable. He stated, “If someone had asked me back then whether he would one day gain recognition from the Nobel Committee, I would have said a firm “yes” without hesitation.”
Despite the Nobel Prize focusing on the creation of MOF structures, it is physicists like those at VU who clarify these materials” behaviors. The faculty concentrates on the properties of MOFs, examining how they interact with their environment and how their structural, electrical, and magnetic features evolve. Prof. Šimėnas explained, “When we introduce gas molecules into the pores of these materials, we can observe how they attach to the metal centres and how this affects the magnetic properties. When the molecules are released, everything returns to its initial state. These reversible changes make it possible to design sensitive gas sensors.”
To analyze these materials, researchers utilize two complementary techniques: EPR spectroscopy and dielectric spectroscopy. EPR spectroscopy allows for the observation of subtle magnetic forces between atoms within a crystal lattice, revealing how these centers react to external influences like temperature shifts or gas molecule penetration. This technique provides insights into the fundamental aspects of magnetism, catalysis, or gas absorption.
In contrast, dielectric spectroscopy offers a broader perspective, illustrating how the entire hybrid structure, comprised of organic linkers, responds to an electric field. It captures the movement and oscillation of these linkers when the material interacts with external conditions. “We use EPR to investigate metal centres and dielectric spectroscopy to examine linkers,” noted Prof. Šimėnas, emphasizing the dual approach that enables a comprehensive understanding of the hybrid system.
Interestingly, some MOF structures demonstrate ferroelectric properties, aligning them with functional electronic materials that integrate electric and magnetic domains. Consequently, materials crafted by chemists become subjects of physical experimentation within VU laboratories, enhancing the understanding of material behaviors and revealing new avenues for application.
During his doctoral research, Prof. Šimėnas explored a denser MOF structure characterized by narrow pores. He recalled an instance when an unexpected signal in an EPR spectrum puzzled him and his supervisor. This mystery led them to consult leading EPR experts in Switzerland and Germany. They ultimately identified the phenomenon as rotational tunneling of methyl groups, a quantum effect where a chemical group rotates through a barrier.
This groundbreaking observation, the first of its kind utilizing pulsed EPR, was published in Science Advances and marked a significant milestone for physics research in Lithuania. Prof. Šimėnas noted the relevance of this discovery to the Nobel Prize in Physics, which recognized tunneling phenomena at a macroscopic scale. While past laureates investigated similar principles broadly, the VU physicists examined them at the molecular level, unveiling another manifestation of quantum effects in materials.
While MOFs remain a vital area of study, Prof. Šimėnas” current research interests have shifted towards next-generation hybrid structures and quantum technology applications. He mentioned, “While we did a lot of MOF research five to ten years ago, now we”re more focused on hybrid perovskites – materials that, like MOFs, contain metal centres but have entirely different electronic properties.” These advanced materials promise to enhance the efficiency and affordability of solar cells and LEDs.
The ERC Starting Grant significantly supports this research, providing Prof. Šimėnas with €2.5 million for a project aimed at improving EPR spectroscopy sensitivity. This funding equips him and his team to innovate methods for analyzing hybrid materials and quantum effects. “Vilnius University now has one of the most advanced EPR laboratories and strong partnerships stretching from Germany and the UK to the US and Japan. We strive to compete on a global scale – not just in terms of equipment but also in terms of ideas,” concluded Prof. Šimėnas.
