This image shows a carbon nanobelt, represented as both a ball-and stick model and a space-filing model. Carbon atoms are orange and gray, and hydrogen atoms are white. Image: ITbM, Nagoya University.
This image shows a carbon nanobelt, represented as both a ball-and stick model and a space-filing model. Carbon atoms are orange and gray, and hydrogen atoms are white. Image: ITbM, Nagoya University.

Chemists have tried to synthesize carbon nanobelts for more than 60 years without success, but in a paper in Science a team at Nagoya University in Japan has now reported the first organic synthesis of a carbon nanobelt. Carbon nanobelts are expected to serve as a useful template for building carbon nanotubes and open up a new field of nanocarbon science.

The new nanobelt, measuring 0.83nm in diameter, was developed by researchers at Nagoya University's JST-ERATO Itami Molecular Nanocarbon Project and Institute of Transformative Bio-Molecules (ITbM). "Nobody knew whether its organic synthesis was even possible or not," says Yasutomo Segawa, a group leader of the JST-ERATO project who had been working on the synthesis of carbon nanobelts for seven and a half years. "However, I had my mind set on the synthesis of this beautiful molecule."

Carbon nanobelts are belt-shaped molecules composed of fused benzene rings, which are aromatic rings consisting of six carbon atoms. They are also segments of carbon nanotubes, which have various applications in electronics and photonics due to their unique physical characteristics.

Current synthesis methods produce carbon nanotubes with inconsistent diameters and sidewall structures, affecting their electrical and optical properties and making it extremely difficult to isolate and purify a single carbon nanotube with a specific diameter, length and sidewall structure. Being able to control precisely the synthesis of structurally-uniform carbon nanotubes will help in the development of novel and highly functional materials.

Carbon nanobelts have been identified as a way to build structurally-uniform carbon nanotubes. However, synthesizing carbon nanobelts is challenging due to their extremely high strain energies. This is because benzene is stable when flat but becomes unstable when distorted by its rings fusing together.

Now, Segawa, together with Guillaume Povie, a postdoctoral researcher of the JST-ERATO project, and Kenichiro Itami, director of the JST-ERATO project and of ITbM, have succeeded in chemically synthesizing a carbon nanobelt from a readily available precursor, p-xylene, in 11 steps. The key to their success is a novel synthetic strategy based on preparing a macrocycle precursor from p-xylene in 10 steps, and then forming the belt-shaped aromatic compound via a coupling reaction mediated by nickel.

"The most difficult part of this research was this key coupling reaction of the macrocycle precursor," explains Povie. "The reaction did not proceed well day after day and it took me three to four months for testing various conditions. I have always believed where there's a will, there's a way."

In 2015, Itami launched a new initiative in the JST-ERATO project to focus specifically on the synthesis of carbon nanobelts. At a so-called ‘belt festival’, various new synthetic routes for the carbon nanobelt were proposed and more than 10 researchers were involved in the project. In September 2016, exactly a year after the start of the festival, the carbon nanobelt structure was finally revealed by X-ray crystallography in front of the Itami group members. Everyone held their breath while staring at the screen during the X-ray analysis, and cheered when the cylindrical shape image of the carbon nanobelt appeared on the screen.

"It was one of the most exciting moments in my life and I will never forget it," says Itami. "Since this is the result of a decade-long study, I greatly appreciate all the past and current members of my group for their support and encouragement. Thanks to their skill, toughness, sense and strong will of all members, we achieved this successful result."

The synthesized carbon nanobelt is a red-colored solid and exhibits a deep red fluorescence. Analysis by X-ray crystallography revealed that the carbon nanobelt has a cylindrical shape, just like carbon nanotubes. The researchers measured its light absorption and emission, electric conductivity and structural rigidity with ultraviolet-visible absorption fluorescence and Raman spectroscopy, as well as theoretical calculations.

"Actually, the synthesis part was finished last August but I could not rest until I was able to confirm the X-ray structure of the carbon nanobelt," says Povie. "I was really happy when I saw the X-ray structure."

The carbon nanobelt will be released to the market in the future. "We are looking forward to discovering new properties and functionalities of the carbon nanobelt with researchers from all over the world," say Segawa and Itami.

This story is adapted from material from Nagoya University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.