Solid, liquid or gaseous: these are the different states that matter takes according to external parameters such as temperature and pressure. Let us think of water: in fluid states it cannot be handled like a material, instead ice can even be sculpted. However, when cold, all the matter freezes and stiffens: the molecules themselves move only minimally or very slowly, instead for a solid material to be active it must be endowed with a certain degree of mobility, typical of liquids. The real challenge is to design and build a material from its molecular elements to go into the territory where the boundaries between the states of matter are mixed to have the advantages that each of them can give: a dynamic solid state component can have consequences absolutely innovative on the final properties of the material.
Thanks to the collaboration of a group of researchers from the Department of Materials Science of the University of Milan-Bicocca led by Prof. Piero Sozzani, professor of Industrial Chemistry, and with the collaboration of the Physics Department of the University of Pavia, it was possible obtain a highly porous crystalline material (Metal-Organic Framework, MOF) in which molecular rotors with a record rotation speed in the Gigahertz regime still at 2K (-271 °C) have been inserted. These fast solid-state rotors are supported by a fixed crystalline scaffold that acts as a stator. The high porosity of the MOFs is such that each rotating molecular group has a lot of empty space around it and, therefore, cannot be negatively affected by the crystalline surroundings. The results of this research were recently published in Nature Chemistry in the article entitled "Fast motion of molecular rotors in metal-organic framework struts at very low temperatures" (doi: 10.1038 / s41557-020-0495-3).