Recent advances in single crystal COFs from synthesis to applications

Covalent organic frameworks (COFs) are crystalline porous polymers constructed from organic building blocks through dynamic covalent bonds. Their tunable structures, permanent porosity, and high chemical stability have enabled a wide range of applications across separation, electronics, and catalysis. While most COFs exist as polycrystalline powders, the development of single-crystal COFs (scCOFs) has unlocked new opportunities for precise structural characterization and property optimization. However, synthesizing scCOFs remains challenging due to the delicate balance between nucleation and crystal growth. This Highlight review surveys six key strategies for scCOF synthesis, including modulator-controlled growth, template- or additive-guided crystallization, interfacial synthesis, linker-directed design, rapid crystallization, and post-synthetic transformation. We further discuss emerging applications of scCOFs in separation, thermal conductivity, catalysts, electronics, and photonics, emphasizing how their long-range order and structural uniformity provide unique advantages. Overall, this review provides a concise, synthesis-focused overview that links structural control in scCOFs to application-relevant performance.