Van der Waals force modulation towards liquid processable covalent organic frameworks

Covalent Organic Frameworks (COFs) have been widely developed in the fields of catalysis, energy storage, and transformation due to their excellent controllability, stability, and porosity, but the un-processable powder nature imposes limitations. Here, we report the designed synthesis of a liquid processable COF material (termed as COFNTC-Fe) in a variety of organic solvents and alkaline solutions via modulating the van der Waals force approach. Through increasing conjugate structure by extending the number of benzene rings in the reaction monomer, the newly developed COFNTC-Fe obtains lower inter-layer interactions and dissolves faster in the same solution compared with small conjugated materials, i.e., COFBTC-Fe. Our experiments along with molecular dynamics simulations reveal that the COFNTC-Fe can be more easily exfoliated to dissolve due to the smaller van der Waals force in the same solvent. Benefitting from the excellent liquid processability, the newly developed COFs can be directly added into Poly(9-vinylcarbazole) solution to form a uniform transport layer to obtain enhanced hole transport rate and more efficient blue light perovskite light-emitting diodes (perovskite LED) devices. This work, therefore, provides a new preparation approach toward liquid processable COF materials to broaden their applications.