Enhanced proton conductivity in azole-functionalized three-dimensional crystalline covalent organic frameworks

Area of Science:

• Materials Science
• Chemistry
• Crystallography

Background:

• Proton conduction in covalent organic frameworks (COFs) is poorly understood due to polycrystalline disorder.
• Existing post-synthetic modification (PSM) methods often use solvents, limiting pore accessibility and functionalization precision.

Purpose of the Study:

• To develop a solvent-free melt-phase PSM strategy for precise functionalization of 3D single-crystalline COFs.
• To establish structure-property relationships for anhydrous proton conduction in functionalized COFs.

Main Methods:

• A novel solvent-free melt-phase post-synthetic modification (PSM) was employed.
• Three-dimensional single-crystalline COF-300 was functionalized with azole groups.
• Atomic-resolution crystallography, DFT calculations, and conductivity measurements were utilized.

Main Results:

• The PSM strategy successfully converted imine bonds to amine linkages and covalently anchored proton-conductive azoles.
• Azole-functionalized COFs exhibited anhydrous superprotonic conductivity up to 4.35 × 10^-3 S cm^-1 at 170°C.
• Low activation energies (0.153-0.186 eV) and rigid hydrogen-bond networks were observed, correlating with efficient proton transport.

Conclusions:

• The solvent-free melt-phase PSM is a versatile platform for functionalizing crystalline porous materials.
• Precise functionalization enables the design of COFs with tailored proton conductivity.
• This work clarifies proton conduction mechanisms in single-crystal COFs.