# Tuning Covalent Organic Frameworks via Nucleophilic Aromatic Substitution

## TL;DR

Scientists developed a method to modify covalent organic frameworks using nucleophilic substitution, creating materials with new properties like redox activity and extended light absorption.

## Contribution

A versatile method for tuning COFs via nucleophilic aromatic substitution with O-, S-, and N-based nucleophiles is introduced.

## Key findings

- COF-EG, COF-Fc, and COF-Cz show unique properties like hydrophilicity, redox activity, and extended absorption.
- The optical bandgap of COF-Cz is significantly reduced to 1.9 eV compared to the starting COF-F material.
- The method allows for the attachment of bulky functional groups while maintaining the COF's ordered structure.

## Abstract

A family of covalent organic frameworks (COFs) with tuned properties has been prepared through nucleophilic aromatic substitution (SNAr) from a fluorinated imine‐linked COF (COF‐F). The method has proved useful for O‐, S‐, and N‐based nucleophiles, including bifunctional molecules, leading to average degrees of substitution (DS) ranging from 34% to 87%. COF‐EG, COF‐Fc, and COF‐Cz containing ethylene glycol (DS = 49%), ferrocene (DS = 23%), or carbazole (DS = 34%) moieties, respectively, have been prepared, showcasing the versatility of the methodology. The introduction of these functional molecules on the framework provides unique properties to the organic material, while maintaining the ordered structure. COF‐EG is highly crystalline, porous, and hydrophilic, while COF‐Fc shows a broad redox profile characteristic of the ferrocene/ferrocenium couple, which is covalently attached to the hexagonal framework. The optical properties of the new family of compounds are also greatly influenced by the substitution, with COF‐Cz featuring a remarkably extended absorption profile beyond 700 nm and an optical bandgap of 1.9 eV, significantly reduced compared to the 2.6 eV of the starting fluorinated COF‐F material and the rest of the substituted materials in the range of 2.1–2.5 eV.

The direct nucleophilic aromatic substitution reaction on a fluorinated covalent organic framework leads to functional materials bearing bulky pendant groups such as carbazole or ferrocene. The method is versatile, suitable for O‐, S‐, and N‐based nucleophiles, and provides a unique conjugated structure containing electron‐withdrawing fluorine atoms and electron‐donating groups.© 2026 WILEY‐VCH GmbH