Can a Covalent-Organic Framework Sustain Structural Integrity during Activation? Microscopic Insight from Molecular Simulation.

Covalent-organic frameworks (COFs) have emerged as versatile nanoporous materials in a wide variety of domains. However, their practical applications are hindered by activation, as solvent evacuation may cause structural collapse. In this study, we investigate whether an imine-based COF can sustain structural integrity during activation by six different solvents (dimethyl sulfoxide, dimethylformamide, acetone, methanol, hexane, and perfluorohexane). From molecular simulation, nanocavity is observed to form in the COF upon solvent evacuation, thus inducing contractive stress. The magnitude of contractive stress is revealed to quantitatively correlate with the surface tension of solvent, indicating that the cohesive force of solvent plays a key role in governing evacuation. Then, the mechanical strength of the COF is estimated to assess the likelihood of structural integrity/collapse during activation. Among six solvents, we predict that hexane and perfluorohexane enable successful activation of the COF at 80 °C and sustain structural integrity, while the other four solvents cause structural collapse. These predictions agree remarkably well with experimental observations. From the bottom up, this study provides microscopic insight into the solvent-induced structural collapse, offering fundamental guidance in properly selecting solvents for activation and designing stable COFs for practical applications.