Interlayer interactions in 2D covalent organic frameworks (COFs) have been shown to be important factors in both their formation and bulk properties.  There are many previous examples of controlling interlayer interactions in COFs by tuning the monomer or geometry.  However, the use of hydrogen bonding is much rarer.  The highly directional nature of a hydrogen bonding interaction makes it difficult orient properly in a COF structure.  To accomplish this, we have designed monomers with a non-planar structure that arises from steric crowding, forcing the amide side groups out of plane with the COF sheets orienting the hydrogen bonds between the layers.  The presence of these hydrogen bonds provides significant structural stabilization as demonstrated by comparison to control structures that lack hydrogen bonding capability, resulting in lower surface area and crystallinity.  We have characterized both azine and imine-linked versions of these COFs, named COFamide-1 and -2, respectively, for their surface areas, pore sizes and crystallinity.  In addition to these more conventional characterization methods, we also used variable temperature infrared spectroscopy (VT-IR) methods and van der Waals density functional calculations to directly observe the presence of hydrogen bonding.

Interlayer hydrogen bonding in covalent organic frameworks – design approaches and characterization methods

ACS Fall 2020 Virtual Meeting

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