Hiroyuki Isobe, Professor, Department of Chemistry

Taisuke Matsuno, Assistant Professor, Department of Chemistry

Key Points of Presentation

• We have created a molecular bearing by combining a tubular molecule and a smallest diamond molecule.
• The tubular molecule is the "outer frame" and the smallest diamond molecule is the "inner rotor," creating a "molecular bearing," a small molecular machine.
• When the rotational speed of this molecular bearing was measured, it was found that ultrafast rotation, with a rotational frequency in the terahertz range, can be realized in a solid body. It is expected to be deployed in terahertz science and technology, which has been the focus of much attention recently.

 

Summary of the announcement

A research group led by Professor Hiroyuki Isobe at the Graduate School of Science, The University of Tokyo, has created a small molecular machine called a "molecular bearing ^{(Note 1)} " by combining a tubular molecule and a smallest diamond molecule (adamantane). The tubular molecule is mainly made of ^{sp2 carbon(Note 2)}, and the smallest diamond molecule is mainly ^{made ofsp3 carbon(Note 3)}, making it a hybrid nanocarbon created by combining different types of carbon atoms. The smallest diamond molecule inside this hybrid nanocarbon rotates at ultrahigh speed in the solid state, and it was found that "the rotation frequency is in the terahertz region. The utilization of terahertz frequency has been attracting attention as a new technology and science in various fields, and this is the first clear evidence that ultrafast rotation in this region can be realized by rotating molecules in a solid. The research group has also clarified that this ultrafast rotation is the result of "inertial rotation" of molecules, and that the rotational motion of molecules in solids, which had been trapped in "Brownian motion (diffusive motion)," can be made ultrafast by becoming inertial rotation.

The research results were published in the international journal Nature Communications on August 25, 2021.

 

Publication details

There are different types of carbon atoms, and ^{sp2 carbon andsp3 carbon} are known as typical examples. ^{sp2 carbon} is a type of carbon atom that forms fullerenes and carbon nanotubes, and has recently been explored as the basic structure of nanocarbons ^{(Note 4)}. Diamonds are known as a representative example of ^{sp3 carbon}, and nanodiamonds, which are "small diamonds," have recently been attracting attention as a new nanocarbon material, Nanodiamonds, which are "small diamonds," are beginning to attract attention as a new nanocarbon material. Naturally, many researchers have begun to wonder, "What kind of nanocarbon material would be produced by combining sp2 ^{carbon andsp3 carbon}? This "hybrid nanocarbon material combining ^{sp2 andsp3 car} bons" had begun to be investigated in the fields of materials science and theoretical science, but so far it has been an enigmatic material with conflicting experimental and theoretical results.

This time, the research group succeeded for the first time in the world in making "hybrid nanocarbons combining ^{sp2 carbon andsp3 carbon} " appear as ^a molecular substance ^{(Note 5)} (Figure 1). Then, by making it a molecular substance with a clear composition and structure, we were able to explore its fundamental physical properties, and as a result, we found an unusual rotational behavior called "ultrafast molecular rotation in the terahertz region.

Figure 1 : Crystal structure of molecular bearings made from hybrid nanocarbons. Red is ^{sp2 carbon and} gray is ^{sp3 carbon}. The smallest nanodiamond molecule trapped inside the tubular molecule is rotating at ultrafast terahertz speeds in the solid.

 

The research group first assembled a "molecular bearing" by trapping adamantane, known as the "smallest diamond molecule," inside a tubular molecule (Figure 2). Then, they examined the solid by the technique of nuclear magnetic resonance spectroscopy (NMR ^{(Note 6)} ) and found that the smallest diamond molecule inside rotates at ultrahigh speeds, reaching the "terahertz rotation frequency" region by "inertial rotation" at high temperatures. This is the highest rotational frequency ever recorded in a solid-state rotation of a molecular machine.

Figure 2: How hybrid nanocarbons are assembled. Molecular bearings are assembled simply by mixing two substances in solution.

 

Terahertz frequency is attracting attention as a new technology and science in various fields. The fact that it has been clearly demonstrated that ultrafast rotation in this region can be realized by molecular rotation in solids raises expectations for the design and synthesis of various terahertz molecular materials.

This research was conducted as part of a Grant-in-Aid for Scientific Research, and the state-of-the-art facilities at SPring-8 BL38B1 and Photon Factory (PF) BL17A of the Institute for Materials Structure Science, High Energy Accelerator Research Organization (KEK), were utilized for molecular structure determination using X-ray diffraction. In addition, some of the solid-state NMR instruments are used in the state-of-the-art facilities of the Microstructure Analysis Platform of the National Institute for Materials Science (Nanotechnology Platform, a commissioned research project of the Ministry of Education, Culture, Sports, Science and Technology of Japan).

 

Name of Researcher	Affiliation
Taisuke Matsuno	Assistant Professor, Graduate School of Science, The University of Tokyo
Seiya Terasaki	Graduate Student, Graduate School of Science, The University of Tokyo
Kanako Kogashi	Graduate Student, Graduate School of Science, Tohoku University
Ryosuke Katsuno	Graduate Student, Graduate School of Science, The University of Tokyo
Hiroyuki Isobe	Professor, Graduate School of Science, The University of Tokyo

 

 

Journal

Journal name	Nature Communications
Title of paper	A hybrid molecular peapod of sp2- and sp3-nanocarbons enabling ultrafast terahertz rotations （A hybrid molecular peapod of sp2- and sp3-nanocarbons enabling ultrafast terahertz rotations)
Authors	Taisuke Matsuno*, Seiya Terasaki, Kanako Kogashi, Ryosuke Katsuno & Hiroyuki Isobe* (authors)
DOI Number	10.1038/s41467-021-25358-0
URL	https://www.nature.com/articles/s41467-021-25358-0 (Open access article, so anyone can read it free of charge.)