Pore surface engineering in covalent organic frameworks

TLDR

Covalent organic frameworks are porous materials with precisely tunable pore size and geometry, but controlling their pore surface remains a challenge. The study introduces a protocol for pore surface engineering of COFs that enables controlled composition and density of organic groups in the pore walls. The protocol uses azide‑functionalized building blocks incorporated into COFs, followed by quantitative click reactions with alkynes to install desired organic groups at controlled densities on the pore walls. The click‑based protocol successfully generates diverse, well‑defined surface chemistries in COFs, demonstrating its utility for creating pre‑designed pore compositions and functions.

Abstract

Covalent organic frameworks (COFs) are a class of important porous materials that allow atomically precise integration of building blocks to achieve pre-designable pore size and geometry; however, pore surface engineering in COFs remains challenging. Here we introduce pore surface engineering to COF chemistry, which allows the controlled functionalization of COF pore walls with organic groups. This functionalization is made possible by the use of azide-appended building blocks for the synthesis of COFs with walls to which a designable content of azide units is anchored. The azide units can then undergo a quantitative click reaction with alkynes to produce pore surfaces with desired groups and preferred densities. The diversity of click reactions performed shows that the protocol is compatible with the development of various specific surfaces in COFs. Therefore, this methodology constitutes a step in the pore surface engineering of COFs to realize pre-designed compositions, components and functions. Covalent organic frameworks form a porous skeleton with a precise pore size and geometry, but control of the pore surface is challenging. Here, a protocol is introduced for pore surface engineering of covalent organic frameworks, allowing the control of composition and density of organic groups in the pores.