Cylindrically Shaped Carbon Molecule：(6,6)Carbon Nanobelt

Carbon nanobelts were proposed as general term for carbon molecules with a cylindrical structure consisting solely of fused benzene rings, first recorded and described in the literature in 1954.¹⁾ Thereafter, various cylindrical shaped carbon molecules have been proposed, and many researchers have challenged their synthesis methods in part due to the difficulty and reproduceability.²⁾ After the discovery of carbon nanotubes in 1991,³⁾ carbon nanobelts were found to be a partial structure of the carbon nanotube wall and began to garner more and more attention. To date, there have been no effective syntheses of carbon nanobelts, largely in part due to the bent nature of each benzene unit.

Itami and Segawa et al. have succeeded in the first chemical synthesis of 1 in 2017. The synthetic method of converting of an unstrained cyclic molecule into a cylindrical shape structure from p-xylene can be completed in 11 steps.⁴⁾

The cylindrical shape of 1 was confirmed by X-ray crystallography, and its fundamental optoelectronic properties were elucidated by ultraviolet-visible (UV) absorption and fluorescence spectroscopic studies. These analyses demonstrated the properties of the carbon nanobelt with respect to its electric conductivity, light absorption and emission. Raman spectroscopy further demonstrated that carbon nanobelts have characteristics very similar to that of a carbon nanotube.⁴⁾

Carbon nanobelts are expected to open the path for the synthesis of single-structured carbon nanotubes and the development of new functional materials, which will likely be instrumental in the next generation nanocarbon science. One noteworthy property of 1 is that it exhibits red fluorescence, which can be applied toward electronic devices as light emitting materials and as organic semiconductors. Furthermore, if a single-structured carbon nanotube can be obtained by using carbon nanobelt as a template, a wide range of applications are expected to emerge such as a light weight and stretchable display, a power saving super-integrated CPU, and highly efficient batteries and solar cells.

Figure 1. (6,6)Carbon Nanobelt (1)

Figure 2. (6,6)Carbon Nanotube (Schematic Diagram)

Scheme 1.