Monitoring the Growth of 2D Imine-linked COF Single Crystals via in situ USAXS

Two-dimensional (2D) covalent organic frameworks (COFs) are highly modular, porous, crystalline polymers. While COFs have several applications, most are synthesized as unoriented aggregates of nanoscale crystallites. Overcoming this challenge, our new synthesis uses a modulator and transimination catalyst to yield single-crystalline, imine-linked 2D COFs in under five minutes as compared to existing month-long syntheses. However, the polymerization itself is not yet well-understood. To investigate key reaction parameters, we will systematically vary our growth conditions and monitor COF formation in situ by ultra-small-angle X-ray scattering at ESRF ID02. We hypothesize that COF single crystals form via simultaneous polymerization and crystallization processes, unlike polycrystalline COFs that polymerize much faster than they crystallize. Collectively, such insights into COF growth will enable rational design of synthetic conditions for single crystals of next generation 2D polymers.