Dimensionality and\nMolecular Packing Control of Covalent\nOrganic Frameworks through Pendant Group Design

Tuning the dimensions and molecular packing geometry\nof crystalline\norganic frameworks and polymers represents an important challenge\nfor reticular chemistry. Here we show that for extended structures\nmade of 1,3,6,8-tetrakis(4-aminophenyl)pyrene (PyTTA) linked with\nmethoxy group functionalized terephthalaldehyde aldehydes, simple\nsubstituents on the aldehyde linker can have profound structure directing\neffects due to noncovalent interactions. Specifically, reacting 2,3-dimethoxy­terephthalaldehyde\nwith PyTTA gives a 2D covalent organic framework with unique AA-inclined-AA\nstacking and bilayer pyrene motifs, whereas reacting 2,5-dimethoxy­terephthalaldehyde\nwith PyTTA gives a 1D crystalline polymer with AB stacking and isolated\npyrene motifs. Both materials show high crystallinity, allowing for\natomic resolution structure determination using three-dimensional\nelectron diffraction, and the similarity of their fluorescence properties\nshows the electronic structures of pyrene-based extended structures\nmostly depends on the in-plane structures, which is supported by density\nfunctional theory calculations. These two pyrene-based extended structures\nalso show different fluorescence responses to organic vapors due to\ndifferent pore environments. The current work shows the potential\nof noncovalent interactions in the reticular design of functional\norganic materials.