Effect of Solvent Uptake on Morphology in TAPB-PDA COFs

In the bulk, covalent organic frameworks (COFs) are able to form morphologies in which the individual two-dimensional molecules stack into crystallites reminiscent of tactoids in layered silicate clay minerals. Imine-linked, aromatic COFs formed from 1,3,5-tris(4-aminophenyl)benzene (TAPB) and terephthaldehyde (PDA) monomers have a molecular structure in which the TAPB nodes and PDA linkers form planar structures with a regular array of hexagonally-shaped openings. When stacked in an “eclipsed” arrangement, the hexagonal openings in the molecules create columnar pores oriented normal to the plane of the molecule. As such, bulk COFs have promise in applications like filtration, in which a liquid carrying a solute penetrates into the pores, allowing the solute to be selectively altered or bound. Because functionality would depend on morphology, it is important to understand the effect of solvent uptake on morphology. In this presentation, results will be presented for experiments in which small-angle X-ray scattering (SAXS) has been used to monitor morphology of bulk TAPB-PDA COFs in situ as a function of saturation with ethanol or water, and subsequent characterization to determine changes to morphology after the ethanol or water removal.