Scientists create largest molecular rotor in solid-state

Researchers are challenging the conventional notion of solid materials being rigid and immobile by exploring the integration of moving parts within solids. This innovative approach has paved the way for the creation of extraordinary materials like amphidynamic crystals, which blend rigid and mobile components. These crystals’ properties can be manipulated by controlling the rotation of molecules within them.

A team led by Associate Professor Mingoo Jin from the Institute for Chemical Reaction Design and Discovery at Hokkaido University has achieved a remarkable feat in this realm. They have successfully demonstrated the largest operational molecular rotor in the solid-state, breaking size records in the process. This molecular rotor consists of a central rotating molecule connected to stationary stator molecules, resembling a wheel and axle connected to a car frame. What sets this study apart is that the crystal they used features a molecular rotor, pentiptycene, which is almost 40% larger in diameter than previous solid-state rotors.

Credit: Rempei Ando, et al. Angewandte Chemie International Edition. August 31, 2023

Creating enough free space within the solid to allow the rotation of such a large molecule was a significant challenge. To address this, the team synthesized concave, umbrella-like metal complexes that shield the rotor molecule from unwanted interactions with neighboring molecules in the crystal. They achieved the necessary space by attaching an exceptionally large, bulky molecule to the metal atom of the stator, drawing inspiration from the protective space inside an egg.

Experimental and simulated nuclear magnetic resonance spectra of the crystal indicated that the giant molecular rotor rotates in 90-degree intervals at a frequency ranging from 100 to 400 kHz.

This groundbreaking work expands the possibilities of molecular motion within solids, opening new avenues for the development of amphidynamic crystals and potentially leading to the creation of novel functional materials with distinctive properties. Professor Jin envisions that the pentiptycene rotators used in this study, with their various pocket sites, could accommodate different guest compounds, including luminophores. This versatility could facilitate the development of highly functional and sophisticated optical or luminescent solid-state materials.

Source: Hokkaido University

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