Synthesis of single-walled carbon nanotubes with long conjugated segments

[ Instrument Network Instrument R & D ] Carbon nanotubes can be considered as all-carbon-based tubular conjugated polymers containing only sp2 bonded atoms. However, to date, no conjugated polymers with specific diameter carbon nanotube segments have been reported. Recently, Professor Du Pingwu's group at the University of Science and Technology of China has synthesized a long conjugated segment of a single-chiral index single-walled carbon nanotube through precise molecular design and studied its electron and hole transport properties.

Carbon nanotubes, as one-dimensional nanomaterials, are lightweight and have a hexagonal structure with perfect connections. They have many unusual mechanical, electrical, and chemical properties. In recent years, with the deepening of the research on carbon nanotubes and nanomaterials, its broad application prospects have been continuously shown.

The carbon atoms in carbon nanotubes are mainly sp2 hybrids. At the same time, the hexagonal grid structure is bent to a certain extent to form a spatial topology. Certain sp3 hybrid bonds can be formed, that is, the chemical bonds formed have both sp2 and sp3 mixture Hybrid state, and these p orbitals overlap each other outside the carbon nanotube graphene sheet to form highly delocalized large π bonds. The large π bonds on the outer surface of carbon nanotubes are carbon nanotubes and some conjugated The chemical basis of macromolecule recombination with non-covalent bonds.

Pure carbon nanotube materials with a single diameter and chirality have important application potential in the field of nanotechnology and electronics, but the synthesis of such carbon nanotubes is an important challenge in the fields of synthetic chemistry and materials chemistry. The method of catalyst surface-mediated growth has shown great potential in the preparation of carbon nanotubes, but the purity of nanotubes has always been an insurmountable problem. From the perspective of precise structure control, the bottom-up method is one of the ideal strategies for preparing single-chiral high-purity carbon nanotubes. The typical ring-paraphenylene structure can be regarded as the shortest Fragments, long conjugate extension of their structure, is expected to obtain new functional materials structurally close to carbon nanotubes.

In this work, the researchers cleverly introduced a bifunctional structure to a curved conjugated small molecule carbon ring based on previous work on the synthesis and physical properties of new carbon nanotube structures. Subsequently, the fragment was extended in one dimension by a nickel-catalyzed coupling reaction, and a [8,8] single-walled carbon nanotube long conjugated segment with a determined diameter was constructed. Gel permeation chromatography and nuclear magnetic resonance were used. The characterization methods such as UV, IR and Raman spectroscopy confirmed that the long conjugated polymer of carbon nanotubes was successfully synthesized.

Conjugated polymers have strong light-capturing capabilities and can be used to amplify fluorescent sensing signals. They have played an increasingly important role in disease diagnosis and biological detection. In recent years, the application of conjugated polymers in cell- and animal-level fluorescence imaging and biomedical fields has also received great attention. With the support of the National Natural Science Foundation of China and the Ministry of Science and Technology, researchers in the Key Laboratory of Organic Solids of the Institute of Chemistry of the Chinese Academy of Sciences have made a series of new progress in the field of conjugated polymer design and biomedical applications.

The wide-angle ray diffraction test was used to find that the polymer solid film had obvious diffraction rings and showed a certain degree of crystallinity. Comparing the absorption, fluorescence, and fluorescence decay curves of the monomer and the conjugated polymer, it was found that the photophysical properties of the polymer were greatly improved due to the increase in the degree of conjugation. The carrier mobility test results show that the polymer has the ability to transport electrons and holes simultaneously, which are μe ～ 2.0 × 10-5 cm2 · V-1 · S-1 and μh ～ 1.2 × 10-5 cm2 · V-1 · S-1.

The long conjugated segment is the first conjugated polymer compound in the world to be structurally close to an armchair-type single-walled carbon nanotube. The results reported in this article realize the synthesis of a new long conjugate structure of single-walled carbon nanotubes with specific diameters, provide corresponding conjugated polymer templates for the preparation of ultra-pure single-walled carbon nanotubes, and build a single chiral carbon for the solution method The preparation and properties of nanotubes provide important reference.

Source: University of Science and Technology of China, Encyclopedia