Structure Determination in Bulk Films of Two-Dimensional Covalent Organic Frameworks

Two-dimensional covalent organic framework materials (2D COFs) are being studied for their potential to act as porous, high-surface-area host structures for catalysts and sensors, and as functional membranes in energy storage devices, water filters, chemical separators, etc. A key requirement for achieving the desired chemical, physical, and mechanical properties in these films is the formation of a well-ordered framework structure as dictated by the functionality and stoichiometry of the component monomers. However, the bulk organization of the individual 2D macromolecules into larger ensembles will also certainly play an important role in determining the final properties. In this work, bulk films made from trifunctional 1,3,5-tris(4-aminophenyl)benzene (TAPB) and difunctional terephthaldehyde (PDA) are interrogated using combined small-angle and wide-angle X-ray scattering. This technique provides information not only on the hexagonal lattice structure of the 2D COF, but also on the stacking of the individual 2D molecules and the overall size and orientation of the ensembles. X-ray scattering combined with in situ heating provides insight into the stability of the crystalline ensembles as well. Current results on this effort will be presented.