Structural isomers are a well-known class of compounds in organic chemistry. These substances have the same chemical formula but different arrangements of atoms, leading to significant variations in chemical and physical properties. Covalent organic frameworks (COFs) are an emerging class of crystalline, porous organic material. Since they were first reported about in 2005, hundreds of new COF structures have been reported with many applications as conductors, semiconductors, catalysts, etc. However, research focused on studying the properties of structural isomers in COFs still hasn’t been explored. In this work, we’re presenting the design, synthesis, and characterization of a novel COF named TAPA-PDA COF. Comparing the properties of TAPA-PDA COF with that of its structural isomers IISERP-COF2, we were able to demonstrate that a small difference in structure can lead to significant changes in properties of these materials. Specifically, TAPA-PDA COF is an imine-based COF formed from the solvothermal reaction between Tris(4-aminophenyl)amine and Terephthalaldehyde. Its structural isomer IISERP-COF2 can be synthesized from Tris(4-formylphenyl)amine and 1,4-Diaminobenzene. The only difference between the two COFs in their structures is the position of the imine C=N bond. Both of these materials, after activation to remove excess solvents, formed a different crystal phase (β-phase) as compared with the as-synthesized phase (α-phase). Interestingly, the transition between α and β is totally reversible for TAPA-PDA COF but only partially reversible for IISERP-COF2. Significantly, the optical properties of these materials are considerably different in terms of color, UV-Vis absorbance, and fluorescence emission. Lastly, preliminary study indicated that both TAPA-PDA COF and IISERP-COF2 process significantly distinct hydrophobic/hydrophilic properties as IISERP-COF2 was reported as a super-hydrophobic material, TAPA-PDA COF is hydrophilic. In conclusion, based on the study of TAPA-PDA COF and IISERP-COF2, we demonstrated that COF structural isomers can have vastly different properties despite a minor alteration in their structures.

Exploring structural isomers in covalent organic frameworks

ACS Spring Meeting 2021

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