Mixed-linker approach employing a flexible monomer for constructing highly crystalline multiple-component covalent organic frameworks

Covalent organic frameworks (COFs) are emerging as promising materials across diverse fields, including catalysis, gas storage, water harvesting, and energy storage. Traditionally, COF development relies on the two-component synthesis approach, where two organic monomers with specific reactive sites are strategically combined to form well-ordered frameworks in specific topologies. Although this approach has been effective, it inherently restricts the structural diversity of COFs unless new linkers are introduced, limiting the range of properties achievable. A more flexible and increasingly popular approach in COF synthesis is the use of multicomponent reactions and mixed linker strategies, incorporating three or more organic monomers into a single COF. While researchers have primarily focused on reaction pathways for synthesizing multiple-component COFs, one area that remains relatively underexplored is the use of flexible linkers within these strategies. This study addresses this gap by selecting a flexible amine linker and combining it with four distinct aldehyde linkers in various combinations. This approach allows us to successfully synthesize fifteen different highly crystalline COF materials, including two-component, along with three, four, and five-component COFs. A comparative study of photocatalytic performance between the two-component with the five-component COF demonstrated that increased structural functionalities leads to higher surface area, enhanced visible-light absorption, and consequently enhanced photocatalytic activity in the oxidative conversion of aryl phenylboronic acid to phenol.