Pathway Complexity in the Stacking of Imine-Linked Macrocycles Related to Two-Dimensional Covalent Organic Frameworks

Abstract

2019): Pathway Complexity in the Stacking of Imine-linked Macrocycles Related to Two-Dimensional Covalent Organic Frameworks. ChemRxiv. Preprint.This work reports on the assembly of imine-linked macrocycles that serve as models of two-dimensional covalent organic frameworks (2D COFs). Interlayer interactions play an important role in the formation of 2DCOFs, yet the effect of monomer structure on COF formation, crystallinity, and susceptibility to exfoliation are not well understood. For example, monomers with both electron-rich and electron-poor π-electron systems have been proposed to strengthen interlayer inter-actions and improve crystallinity. Here we probe these effects by studying the stacking behavior of imine-linked macrocycles that represent discrete models of 2D COFs.Specifically, macrocycles based on terephthaldehyde (PDA) or 2,5-dimethoxyterephthaldehyde (DMPDA) stack upon cooling molecularly dissolved solutions. Both macrocycles assemble cooperatively with similar ΔHe values of -97 kJ/mol and -101 kJ/mol, respectively, although the DMPDA macrocycle assembly process showed a more straightforward temperature dependence. Circular dichroism spectroscopy performed on macrocycles bearing chiral side chains revealed a helix reversion process for the PDA macrocycles that was not observed for the DMPDA macrocycles.Given the structural similarity of these monomers, these findings demonstrate that the stacking processes associated with nanotubes derived from these macrocycles, as well as for the corresponding COFs, are complex and susceptible to kinetic traps, casting doubt on the relevance of thermodynamic arguments for improving materials quality. File list (3) download file view on ChemRxiv 2019_03_ChemRxiv_MacrocycleAssembly_Wang_Manus... (6.99 MiB) download file view on ChemRxiv 2019_03_ChemRxiv_MacrocycleAssembly_Wang_SI.pdf (2.98 MiB) download file view on ChemRxiv TOC3.tiff (177.29 KiB)

Cooperative Self‐Assembly of Pyridine‐2,6‐Diimine‐Linked Macrocycles into Mechanically Robust Nanotubes

“…[23] Theh igh modulus of the NT-NF is presumably due to the interplay of multiple intermolecular forces,s uch as the electrostatic interactions that govern the initial assembly event, the hydrophobic interactions of the decyloxy side chains that are forced into close proximity,aswell as the p-p interactions present from macrocycle self-assembly. [24][25][26][27][28] This work establishes that imine-linked macrocycles, which are readily designed and prepared, assemble into high-aspect ratio nanotubes under mild conditions when they contain easily protonatable groups.T he enhanced basicity of the pyridine moiety compared to the imine linkages in the first inverse chromonic liquid crystal macrocycles enables assembly to proceed through the formation of pyridinium ions,i nstead of hydrolytically unstable iminium ions.T he assembly of MC 1 under sub-stoichiometric acid loadings is highly cooperative,a sd emonstrated by GPC measurements of macrocycle disappearance as well as fluorescence spec-troscopy.T he assembled nanotubes were processed into NT-NF via touch-spinning.T he resulting fibers demonstrated aY oungsm odulus of 1.33 GPa, exceeding that of several covalently linked polymers and biological filaments.M acrocycles that relied on protonating the imines with excess CF 3 CO 2 Hd id not form nanofibers suitable for mechanical testing.These findings demonstrate ageneral design principle for the synthesis of macrocycle assembles under mild conditions,a swell as the ability to touch-spin nanofibers of robust supramolecular assemblies.…”

Total scattering reveals the hidden stacking disorder in a 2D covalent organic framework

“…The geometry of specic linker molecules can generate ordered layer stacking by offering a templating effect during the growth of new layers, [7][8][9][10][11] as thermodynamics generally govern the arrangement of linker and small oligomer molecules. On the other hand, because the stacking energy is too high to be overcome at typical reaction temperatures, 4,[12][13][14] layer aggregation, as opposed to linker and oligomer adsorption, is effectively irreversible, which results in stacking disorder in most COFs. The in-plane disorder can also be caused by exible linkers and inuences stacking interactions, leading to further out-of-plane disorder.…”

Diverse Proton-Conducting Nanotubes via a Tandem Macrocyclization and Assembly Strategy

“…40 The shorter C-N bonds result in a decreased bite angle between the two reactive amines from 120° to 108°, leading to the realization of a pentagonal structure. This approach yielded structurally and electronically diverse macrocycles using terephthalaldehyde (PDA), 2,3,5,6tetrafluoroterephthalaldehyde (F4-PDA), 41-42 2,5-dimethoxyterephthalaldheyde (DiOMe-PDA), [43][44] and 9,10-anthracenedicarboxaldehyde (9,10-ADA) monomers (Schemes S19-22). [45][46] Lastly, we prepared a diamond shaped [2+2] macrocycle from DAPP and 4,4′-(1,10-phenanthroline-2,9-diyl)dibenzaldehyde…”