Source: China University of Science and Technology News


Curved carbon solenoid only appears in theoretical prediction, and the quasi-synthesis and properties of this kind of material have never been reported in literature. Professor Du Pingwu's research group at the University of Science and Technology of China has realized the first curved carbon nanosolenoid material with Riemannian surface, which fills the gap in the field of molecular-based curved carbon spiral materials. The research results were recently published in the international academic journal Nature Communications as "Synthesis of a magnetic pi-extended carbon nanosolenoid with Riemann. surfaces "(Nat.Commun.2022, 13, 1239).

Molecular based carbon materials, due to their unique geometric shape caused by the rich physical and chemical properties (including mechanical properties, electrical conductivity, absorption and luminescence properties, etc.), have received extensive attention. An atomic graphene plane spirals continuously around a line perpendicular to the base plane, which can be thought of as closely following the Riemannian surface (i.e. log z type). As a famous mathematical object, the Riemann surface (FIG. 1a) was proposed to predict the single range of a multivalued analytic function. From each local point, they look like a complex plane, but the overall topology may deviate from the plane, making it look like a ball or ring, or even a spiral with a more complex and beautiful topology. Riemann surfaces not only play a crucial role in the development of modern mathematics, but also provide new insights into the design and synthesis of multifunctional curved carbon materials. Theoretical predictions show that carbon solenoids with a Riemannian surface can act as quantum conductors, generating large magnetic fields and inductances when a voltage is applied. However, achieving such helical topologies with large conjugate extensions is a major challenge.

FIG. 1. a) Example of carbon nanosolenoids predicted by theory; b) Synthesized three-dimensional π-extended twisted carbon nanosoles (CNS) materials.

Recently, the research team used a quasi-bottom-up synthesis method to successfully construct the first large conjugated metal-free carbon nanosolenoid (CNS, FIG. 1b) material with Riemannian surface by reasonably designing and synthesizing suitable molecular precursors to achieve the helix distortion of the target molecule. Combined with multi-scale experimental characterization and theoretical analysis, the structural characteristics and properties of carbon nanosols were systematically studied. Solid state NMR spectroscopy, Fourier transform infrared (FIG. 2a), XPS and Raman were used to confirm that the material has a large conjugated π-extended structure. Low-dose high-resolution integrated differential phase-contrast scanning transmission electron microscopy (iDPC-STEM, FIG. 2c-e) imaging shows the molecular structure of a single-stranded helix with a pitch of ~0.4 nm and a width of ~2.7 nm. The ultraviolet visible absorption, fluorescence and time-resolved photoluminescence spectra show that it has rich visible light absorption properties. Notably, CNS has a low optical band gap of 1.97 eV and a strong red photoluminescence. The ground state electronic structure and magnetic behavior of CNS have been studied by EPR, SQUID and theoretical calculations. The magnetic test results show that CNS contains a large number of free radical single electrons at room temperature, showing a strong EPR magnetic signal, and has paramagnetic response and complex magnetic ordered behavior at low temperatures (FIG. 2f-g).

This work expands the scope of SP2-carbon allotrope materials, a quasi-π-extended carbon solenoid material, which provides the possibility for researchers to deeply explore its physical properties, and provides the experimental basis for developing a variety of spiral carbon materials in electronic materials, quantum materials, and spintronic devices. Wang Jinyi, PhD student, Department of Materials Science and Engineering, School of Chemistry and Materials Science, University of Science and Technology of China, and Professor Zhu Yihan and Professor Zhuang Guilin, Zhejiang University of Technology, are co-first authors of the paper. Professor Du Pingwu is the single corresponding author of the paper. This research was supported by the National Natural Science Foundation of China (21971229, U1932214), the Major Research Program of the Ministry of Science and Technology (2017YFA0402800), the Frontier Collaborative Innovation Center for Energy Materials Chemistry, and the National Research Center for Microscale Matter Science in Hefei.

Attached article link: https://www.nature.com/articles/s41467-022-28870-z