JACS: Japanese chemists have made a breakthrough in the synthesis of single-walled carbon nanoribbons

Since the 21st century, carbon based materials have been playing an important role in the field of materials science because of their excellent physical and chemical properties, especially graphene The other form of graphene, single-walled carbon nanotubes, not only inherits the excellent physical and chemical properties of graphene, but also has higher homogeneity than graphene, so it has greater application potential in energy reserves, semiconductor preparation and other fields It has been decades since the discovery of carbon nanotubes, and its preparation methods are relatively mature At present, the existing synthesis methods include arc method and chemical vapor deposition method, but these methods can not produce high-purity carbon nanotubes, and the structure of nanotubes can not be perfectly controlled In order to solve this problem, scholars have synthesized high-purity single-walled carbon nanotubes with uniform structure through the strategy of "bottom-up" from conjugated aromatic macrocycles As the precursor of carbon nanotubes (CNTs), the synthesis of cylindrical polyaromatic compounds (such as cyclophenylene CPPs, carbon nanobelts CNBS) has attracted the attention of numerous chemists Figure 1 A) CNTs, Recently, chemists yasutosegawa and Kenichiro Itami from Nagoya University in Japan reported a kind of carbon nanobelt, The synthesis method of CNB) has increased the yield of [12] CNB (1) from 1% to 7%, and the author has also applied this method to the synthesis of [16] CNB (2) and [24] CNB (3) (Fig 1) This achievement was published in the Journal of the American Chemical Society (DOI: 10.1021 / JACS 8b06842) under the title of "synthesis and size dependent properties of [12], [16], and [24] carbon nanobelts" Figure 2 Synthesis route of CNBS 2 and 3 (source: J am Chem SOC.) first, the author studied the synthesis of CNBS 2 and 3 (Figure 2) In the synthesis of carbon nanoribbons, xylene was used as the starting material The hexabromo substituted p-xylene 7 was obtained by two steps of reaction, and then the 7 was desymmetrized, which was the first key step of the whole reaction By controlling the reaction conditions, the author successfully obtained the dimethoxy substituted p-xylene bromine 9 by the reaction of 7 with sodium methothane, and then 9 with the hydrolysate 12 through the multi-step Wittig reaction to obtain dimer 15, trimer 16 and tetramer 17 Further polymerization was also attempted, but it was not successful due to solubility In order to obtain more units of polymer, another strategy, macrocyclization, was adopted: through the oligomerization of 18, the octamer 5 and dodecamer 6 containing bromine were obtained in 15% and 3% yields, respectively The coupling reaction from 5 to 2 or 6 to 3 is the second key step of the whole reaction, and it is also a point limiting the whole reaction yield At first, [12] CNB (1) can be directly obtained by the reaction of 4 in the presence of Ni (COD) 2 and 2,2 '- bipyridine However, the author found that the yield of the product obtained by this method will gradually decrease with the extension of reaction time Therefore, the author speculates that 1 may not be stable in this reaction condition So the author changed the ligands of the reaction, reduced the electron cloud density of the nickel center, and made 1 more stable under this condition In this way, the yield of [12] CNB was increased to 7% The yield of 2 and 3 were 1% and 0.06% respectively under the same conditions Fig 3 A) crystal structure of 1, 2 and 3; b) UV and fluorescence spectra of 1, 2 and 3; c) simulation calculation results of 1, 2 and 3 (source: J am Chem SOC.) After obtaining these compounds, the author has carried out structural characterization and property research The molecular structures of 1, 2 and 3 were obtained by single crystal diffraction (Fig 3a) The author found that they are all round, but the shape of 1 is more perfect, while the shape of 2 and 3 is slightly "flat" The diameter of 1 containing 12 aromatic rings is about 8.3 Å, and the maximum diameter of 2 and 3 are 11.2 Å and 17.5 Å, respectively (Fig 3a) The authors speculate that this change in size will inevitably affect their photophysical properties, which is also the case 1 The photophysical properties of 2 and 3 show regular changes with the increase of the number of units: the maximum absorption wavelength moves from 313 nm to 333 nm with the increase of carbon nanoband size (Fig 3b); the ultraviolet weak absorption band moves from 496 nm to 466 nm with the increase of carbon nanoband size (Fig 3B); the maximum fluorescence emission wavelength moves from 524 nm with the increase of carbon nanoband size It moved to 466 nm (Fig 3b) It is worth noting that the half height width of the fluorescence emission peak of 3 is only 6 nm, which indicates that 3 can emit very high purity light (Fig 3b) Highlight: in this paper, the synthesis method of carbon nanoribbons has been improved on the basis of predecessors The yield of [12] CNB has been successfully increased to 7% by nickel catalyzed coupling reaction, and [16] CNB and [24] CNB have been synthesized under the same conditions Full text author: Guillaume povie, yasutomo Segawa, Taishi Nishihara, Yuhei Miyauchi, and Kenichiro Itami