sln-Topological Covalent Organic Frameworks with Shape Dimorphism and Dipolar Rotors
Xiaohan Wang1, Syunto Goto1,2, Takejiro Ogawa3,4
1Laboratory for Zero-Carbon Energy, Institute of Science Tokyo, Tokyo 152-8550, Japan.
Journal of the American Chemical Society
|August 14, 2025
Summary
Researchers created novel covalent organic frameworks (COFs) with a unique sln topology and controllable crystal shapes. These frameworks incorporate dipolar rotors, enabling potential applications in molecular memories and other fields.
Area of Science:
- Materials Science
- Supramolecular Chemistry
- Crystallography
Background:
- Covalent Organic Frameworks (COFs) are crystalline porous polymers with diverse applications.
- Controlling COF crystal morphology and incorporating functional groups remains a challenge.
- Exploring novel topologies like 'sln' is crucial for expanding COF capabilities.
Purpose of the Study:
- To synthesize and characterize the first COFs with the sln topology.
- To demonstrate shape control of COF crystals with identical composition and topology.
- To integrate dipolar rotors into 3D COFs for external-field responsiveness.
Main Methods:
- Synthesis of a novel hexaarylbenzene building block with 1,2-difluorophenyl groups.
- Solution-based crystallization to achieve shape dimorphism (hexagonal prism TK-COF-P and membrane TK-COF-M).
- Powder X-ray diffraction, dielectric measurements, and 19F NMR relaxation studies for structural and dynamic analysis.
Main Results:
- First report of COFs exhibiting the sln topology.
- Demonstration of shape dimorphism (prismatic and membrane) in COFs with identical chemical composition and sln topology.
- Identification of conformational isomerism linked to crystal shape.
- Successful installation of dipolar rotors responsive to electric fields at elevated temperatures.
Conclusions:
- The study expands the diversity of COF topologies and crystal morphologies.
- Shape dimorphism in COFs is linked to conformational isomerism.
- The developed COFs with tunable rotor dynamics offer a platform for advanced functional materials, particularly for room-temperature applications like molecular memories.
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