Synthesis of Isoindigo-Based and Porphyrin-Based Linkers for Advanced Covalent and Metal Organic Frameworks

Abstract

Isoindigo, an electron deficient planar conjugated and structurally rigid organic dye, has garnered substantial promise as a versatile building block in the field of reticular chemistry and material science. Due to this linker’s capacity for tunable functionalization, we are exploring it in the fabrication of covalent organic frameworks (COFs) and metal organic frameworks (MOFs). Motivated by the exceptional electronic properties of its core, isoindigo is leveraged in this project to create a diverse library of organic linkers encompassing dialdehydes, fluorinated, tetraaldehydes, and terpyridine functionalized derivatives. We have also explored a porphyrin-based macrocyclic linker in COFs. By varying the alkylation substituents, additional tunability is achieved. The feasibility of these linkers to be integrated into COFs confirmed its efficiency by the incorporation of our synthesized (E)-4,4'-(1,1'-dihexyl-2,2'-dioxo-[3,3'-biindolinylidene]-6,6'diyl) dibenzaldehyde linker with the electron rich 4,4’,4’’-(1,3,5-triazine-2,4,6-triyl)-trianiline moiety through an imine linkage to form I-TTA COF via donor-acceptor chemistry. I-TTA demonstrated promising electrocatalytic applicability in water-splitting mechanisms requiring lower overpotentials than most benchtop catalysts and providing a subtle hint about the multifaceted capabilities these linkers exhibit once incorporated into extended frameworks. Additionally, one of the synthesized tetraaldehyde linkers was utilized in the synthesis of a highly porous and crystalline imine-based COF. Consequently, these COFs can offer substantial benefits in industrial applications compared to their metal-containing counterparts, by promoting sustainability through the reduced use of toxic metals and lowering costs via the use of abundant, reusable, and stable, organic frameworks. Inspired by the superior photocatalytic activity and robustness of I-TTA, each linker in the synthesized library will be screened for COFs or MOFs synthesis under diverse reaction conditions, with emphasis on structural, electronic, optical, and photocatalytic properties.