Structural isomerization of individual molecules using a scanning tunneling microscope probe

An international research team has succeeded for the first time in controlling the chirality of individual molecules using structural isomerization. The team, led by NIMS, the Graduate School of Science of Osaka University and the Nano Life Science Institute of Kanazawa University (WPI-NanoLSI), also successfully synthesized highly reactive diradicals with two unpaired electrons. They accomplished these tasks using a low-temperature scanning tunneling microscope probe.

The research is published in the journal Natural communications.

It is generally quite difficult to control the chirality of individual molecular units and to synthesize extremely reactive diradicals in organic chemistry; this has prevented detailed study of the electronic and magnetic properties of diradicals. These problems inspired the development of chemical reaction techniques to control the structures of individual molecules on the surface.

The research team recently developed a technique that allows them to controllably change the chirality of specific individual molecular units in a three-dimensional nanostructure. They achieved this by exciting a target molecular unit with a tunneling current from a scanning tunneling microscope probe at low temperature and ultra-high vacuum conditions.

By precisely controlling the 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 the molecular units into three different configurations: two different stereoisomers and a diradical. Finally, the team demonstrated the controllability and reproducibility of 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.

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

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 Researcher, NG, CBRM, NIMS), Oscar Custance (Director 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).