The traditional perception of solid materials as rigid and immobile is being challenged by scientists who are exploring ways to incorporate moving parts into solids. This groundbreaking idea has opened up possibilities for the development of exotic materials called amphidynamic crystals. These crystals consist of both rigid and mobile components, and their properties can be altered by controlling molecular rotation within the material. However, achieving motion in solids, especially in crystals, has been a major challenge due to their tightly packed structure. This restricts dynamic motion to molecules of limited size. In a recent study, a team led by Associate Professor Mingoo Jin from Hokkaido University has achieved a significant breakthrough by demonstrating the largest molecular rotor ever shown to be operational in the solid-state.
Traditional molecular rotors consist of a central rotating molecule connected to stationary stator molecules, similar to a wheel and axle connected to a car frame. While previous studies have reported the existence of such systems, this study features a crystalline material with an operational rotor made of the molecule pentiptycene. What sets this rotor apart is its size, as it is nearly 40% larger in diameter than any previous rotors in the solid-state. This size increase marks a significant advancement in the field.
Enabling rotation in such a large molecule required creating enough free space within the solid. To achieve this, the research team synthesized concave, umbrella-like metal complexes that shielded the rotor molecule from unwanted interactions with other molecules in the crystal. By attaching a large, bulky molecule to the metal atom of the stator, they were able to create sufficient space to accommodate the giant rotor. Associate Professor Mingoo Jin drew inspiration for this approach from nature itself, specifically from the way an egg creates a large space and protects its inside with a circular hardcover.
Through a comparison of experimental and simulated nuclear magnetic resonance spectra of the crystal, the study indicated that the giant molecular rotor rotates in 90-degree intervals at a frequency ranging from 100 to 400 kHz. These findings expand the realm of possibilities for molecular motion in the solid-state. They provide a blueprint for further exploration in the development of amphidynamic crystals and could lead to the creation of new functional materials with unparalleled properties.
The pentiptycene rotators utilized in this study have several pocket sites, which opens up avenues for various applications. By capitalizing on the unique characteristics of amphidynamic crystals, scientists can potentially develop advanced materials with properties tailored to specific needs. For example, these materials could be used in the creation of smart sensors or actuators that respond to external stimuli. The controlled molecular rotation within these materials could also lead to the development of more efficient energy storage and conversion devices.
The groundbreaking study led by Associate Professor Mingoo Jin and his team at Hokkaido University has shattered previous size records for molecular motion in solids. By successfully demonstrating the operational capability of a significantly larger molecular rotor, they have pushed the boundaries of what is achievable in this field. This breakthrough unlocks new possibilities for the development of amphidynamic crystals and the creation of unique functional materials. As scientists continue to explore the world of molecular motion in solids, they pave the way for innovative applications that could revolutionize various industries.