Crystalline C-C and C═C Bond-Linked Chiral Covalent Organic Frameworks
Chen Yuan1, Shiguo Fu1, Kuiwei Yang2
1School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules and State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P. R. China.
Journal of the American Chemical Society
|December 28, 2020
Summary
Synthesizing crystalline covalent organic frameworks (COFs) with C-C bonds is challenging. This study introduces a crystal-to-crystal transformation method, reducing olefin-linked COFs to achieve stable, porous C-C linked frameworks.
Area of Science:
- Materials Science
- Organic Chemistry
- Supramolecular Chemistry
Background:
- Crystalline covalent organic frameworks (COFs) with C-C bonds are highly sought after but difficult to synthesize.
- De novo synthesis of C-C single bonds in COFs often results in amorphous materials.
Purpose of the Study:
- To develop a method for synthesizing crystalline C-C bond-linked COFs.
- To explore crystal-to-crystal transformations for COF modification.
- To investigate the properties and applications of the resulting C-C linked COFs.
Main Methods:
- Knoevenagel polycondensation of chiral tetrabenzaldehyde with dinitrile monomers to form olefin-linked COFs.
- Direct reduction of C═C bonds in the pre-formed COFs to C-C single bonds.
- Characterization using Fourier transform infrared (FTIR) and solid-state 13C NMR spectroscopy.
- Evaluation of porosity, chemical stability, and optical properties.
Main Results:
- Two olefin-linked chiral COFs with 2D layered tetragonal structures were successfully synthesized.
- Reduction yielded crystalline C-C single bond-linked COFs retaining high crystallinity and porosity.
- The reduced COFs demonstrated excellent chemical stability in strong acids and bases.
- Reduced COFs showed blue-shifted emission with enhanced quantum yields and fluorescence lifetimes compared to parent COFs.
Conclusions:
- A novel crystal-to-crystal transformation strategy enables the synthesis of stable, crystalline C-C bond-linked COFs.
- This method overcomes limitations of de novo synthesis for C-C bond formation in COFs.
- The resulting COFs offer tunable optical properties and potential for applications in chiral sensing.
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