Trap-Engineered Divergent Synthesis of Covalent Organic Frameworks with Distinct Structures and Functions

The crystallization of covalent organic frameworks (COFs) has long been constrained by kinetic trapping, with conventional research primarily focusing on eliminating such nonequilibrium states to improve crystallinity. In contrast, this study proposed an innovative strategy that leveraged kinetic trapping as a key variable for tuning COF structures and functionalities. Through solubility engineering guided by environmental parameters, we achieved, for the first time, precise switching among three competitive growth pathways: the thermodynamic ground-state imine framework (T-nC4-IM), a hydrogen-bond-directed metastable crystalline phase (T-nC4-HOF), and a kinetically trapped intermediate (T-nC4-INT). This work demonstrated that hydrogen-bond-directed assembly could surpass covalent polymerization as the dominant pathway, resulting in the formation of an uncommon, metastable tubular crystal phase. Moreover, variations in kinetic trapping significantly modulated the pore ordering and functional performance of the final products. By combining solvent polarity and temperature gradient experiments, a thermodynamic-kinetic competition model was established. External energy input enabled the system to overcome kinetic limitations of metastable states, facilitating a thermodynamically driven reconstruction of the covalent network. Owing to its high crystallinity and electron-rich framework, T-nC4-IM exhibited a substantially enhanced triiodide (I₃^-) adsorption capacity, surpassing those of T-nC4-HOF and T-nC4-INT by more than 45%. This strategy was successfully extended to C3/iC4 alkyl chain-modified monomers, providing a general guideline for the programmable synthesis of COFs and opening avenues for the treatment of radioactive iodine pollution.