Two-dimensional sp2 carbon-conjugated covalent organic frameworks.
Enquan Jin1, Mizue Asada2, Qing Xu1
1Field of Energy and Environment, School of Materials Science, Japan Advanced Institute of Science and Technology, 1-1 Asahidai, Nomi 923-1292, Japan.
Science (New York, N.Y.)
|August 19, 2017
Summary
Researchers created a novel 2D crystalline covalent organic framework (sp2c-COF) using only sp2 carbons. This π-conjugated material exhibits semiconductor properties and can be chemically oxidized to achieve high conductivity and ferromagnetic behavior.
Area of Science:
- Materials Science
- Organic Chemistry
- Condensed Matter Physics
Background:
- Covalent organic frameworks (COFs) are crystalline porous polymers with tunable properties.
- Achieving fully π-conjugated, crystalline COFs from sp2 carbons remains a synthetic challenge.
- Developing novel carbon-based materials with unique electronic and magnetic properties is of significant interest.
Purpose of the Study:
- To synthesize a novel two-dimensional (2D) crystalline covalent organic framework (sp2c-COF) exclusively from sp2 hybridized carbon atoms.
- To investigate the electronic and magnetic properties of the synthesized sp2c-COF, focusing on its π-conjugation, semiconducting behavior, and potential for conductivity enhancement and magnetic ordering.
- To explore the structural characteristics, including the formation of an eclipsed layer framework and the confinement of radicals on pyrene units.
Main Methods:
- Synthesis of sp2c-COF via C=C condensation reactions between tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile.
- Characterization of the 2D crystalline structure and π-conjugation.
- Measurement of the semiconductor band gap (1.9 eV).
- Chemical oxidation to study conductivity enhancement.
- Investigation of radical formation, spin density, and magnetic phase transitions.
Main Results:
- Successfully synthesized a fully π-conjugated 2D crystalline covalent organic framework (sp2c-COF) with an eclipsed layer structure.
- The sp2c-COF demonstrated semiconducting behavior with a discrete band gap of 1.9 eV.
- Chemical oxidation enhanced the material's conductivity by 12 orders of magnitude.
- Formation of a paramagnetic carbon structure with high spin density due to confined radicals on pyrene knots.
- Observation of ferromagnetic phase transition, indicating spin-spin coherence and unidirectional spin alignment.
Conclusions:
- The developed sp2c-COF represents a significant advancement in the design of fully π-conjugated, all-sp2 carbon materials.
- The material's tunable conductivity and ferromagnetic properties open avenues for applications in organic electronics and spintronics.
- The study highlights the potential of rational design in creating novel carbon-based materials with emergent electronic and magnetic functionalities.
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