Unprecedented hunt: Molecules with memory at room temperature

Tarragona (Spain), October 26th^th 2022 – A new paradigm has emerged at ICIQ showing that thermal hysteresis is still maintained for single molecules in liquid solution. This was a really complex and long journey, where clearly the expertise and knowledge of a team of three research groups was the key to success.

Hysteresis is the tendency of a material to retain one of its properties even when the stimulus that created it disappears. An illustrative case is when iron is exposed to a magnetic field. It remains magnetized indefinitely until some energy is transferred to the system (e.g. a magnetic field in the opposite direction). This magnetic storage effect is the basis for recording information on some types of hard drives.

The advantage of small components that can store information is obvious in terms of space requirements and energy consumption. So far, single-molecule magnets (SMMs) have been developed, promising molecular materials that represent the ultimate device for miniaturization. However, they required very low temperatures (−193 °C) to function properly, as the magnetic memory effect is quickly lost through thermal activation at the nanoscale.

The occurrence of a memory effect at the single-molecule level, even with dilution, was found in a spin-crossover molecule (SCO), a polyanionic iron complex. The classical, well-accepted elastic model for SCO systems ruled out the occurrence of molecular bistability since a memory effect would only be allowed if a bulk crystallographic phase transition occurs. Thus, this discovery breaks previous expectations.

The presence of the memory effect in this polyanion at around room temperature has been confirmed by a large amount of supplementary experimental evidence, including magnetic and spectroscopic techniques, both in dilute solid mixtures and in the liquid phase. All consistently showed the occurrence of a true single molecule memory effect. After almost eight years, these results represent successful teamwork by the groups of Prof. José Ramón Galán-Mascarós, Prof. Mónica H. Pérez-Temprano and Prof. Julio Lloret-Fillol.

“Extraordinary claims require extraordinary evidence, which could only be provided by a complementary effort of multiple techniques and multiple backgrounds. ICIQ, but we were fortunate to put together a unique, interdisciplinary team,” says Galán-Mascarós. “Our many years of experience using NMR to elucidate reaction mechanisms in organometallic chemistry was key to investigating this new phenomenon. A completely different problem that we were able to successfully tackle with a fresh mind and a broader view,” concludes Prof. Pérez-Temprano.

The computational analysis led by Prof. Eliseo Ruiz (University of Barcelona) identified the origin of this novel phenomenon in the appearance of strong intra- and supramolecular interactions, capable of slowing down the relaxation processes at the single-molecule level, opening a kinetic thermal hysteresis . Apparently, the previous SCO theory is not disproved, but the occurrence of this unexpected molecular property could not be predicted up to this moment.

The discovery of this slow relaxation process, which seemed impossible, is now basic research, but these results can certainly represent a revolution in the field of spin transition phenomena, since single SCO molecules open up exclusive possibilities for molecular data storage at technologically relevant temperatures. A new method of storing multifunctional (optical or magnetic) information has emerged, suggesting that this is the tip of a large iceberg of new possibilities.

The impossible is the science that has yet to be discovered and at ICIQ an impossible has been brought to light.

Reference article:

Moneo-Corcuera, A., Nieto-Castro, D., Cirera, J., Gómez, V., Sanjosé-Orduna, J., Casadevall, C., Molnár, G., Bousseksou, A., Parella, T. , Martínez-Agudo, JM, Lloret-Fillol, J., Pérez-Temprano, MH, Ruiz, E. & Galán-Mascarós, JR Near-room temperature molecular memory in a polyanionic iron complex. chem. https://doi.org/10.1016/j.chempr.2022.09.025