Structural isomerization of individual molecules using a scanning tunneling microscope probe

1. An international research team led by NIMS, the Osaka University Graduate School of Science and the Kanazawa University Nano Life Science Institute (WPI-NanoLSI) has succeeded for the first time in controlling the chirality of individual molecules through structural isomerization. The team also succeeded in synthesizing highly reactive diradicals with two unpaired electrons. These achievements were made using a scanning tunneling microscope probe at low temperatures.

2. It is usually quite challenging to control the chirality of individual molecular units and synthesize extremely reactive diradicals in organic chemistry, preventing detailed investigation of the electronic and magnetic properties of diradicals. These issues had inspired the development of chemical reaction techniques to control structures of individual molecules on surface.

3. This research team recently developed a technique, which allows them to modify the chirality of specific individual molecular units in a three-dimensional nanostructure in a controlled manner. This was achieved by exciting a target molecular unit with tunneling current from a scanning tunneling microscope probe at low temperature under ultrahigh vacuum conditions. By precisely controlling current injection parameters (e.g., the molecular site, at which the tunneling current is injected at a given applied voltage), the team was able to rearrange molecular units into three different configurations: two different stereoisomers and a diradical. Finally, the team demonstrated the controllability and reproducibility of the structural isomerization by encoding ASCII characters (reading “NanoProbe Grp. NIMS©”) using binary and ternary values in a series of one-dimensional molecular arrays with each array representing a single character (figure).

4. In future research, the team plans to fabricate novel carbon nanostructures composed of designer molecular units, whose configurations are controlled via the structural isomerization technique developed in this project. In addition, the team will explore the possibility of creating quantum materials, in which radical molecular units lead magnetic exchange couplings between the units as designed—a quantum mechanical effect.

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5. This project was carried out by a research team consisting of Shigeki Kawai (Leader, Nanoprobe Group (NG), Center for Basic Research on Materials (CBRM), NIMS), Zhangyu Yuan (Junior Researcher, NG, CBRM, NIMS), Kewei Sun (ICYS Research Fellow, NG, CBRM, NIMS), Oscar Custance (Managing Researcher, NG, CBRM, NIMS), Takashi Kubo (Professor, Department of Chemistry, Graduate School of Science, Osaka University) and Adam S. Foster (Professor, Nano Life Science Institute, Kanazawa University; also Professor, Aalto University).
This work was supported in part by the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Scientific Research (grant number: 22H00285), the Academy of Finland project 346824, and the World Premier Internal Research Center Initiative (WPI), MEXT, Japan.

6. This research was published in the November 25, 2023 issue of Nature Communications (vol. 14).