High Aspect Ratio Nanotubes Assembled from Macrocyclic Iminium Salts

23 March 2018, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

One-dimensional nanostructures such as carbon nanotubes rely on strong and directional interactions that stabilize their high aspect ratio shapes from fracture. This requirement has precluded making isolated, long, thin organic nanotubes by stacking molecular macrocycles, as their noncovalent stacking interactions are generally too weak. Here we report high aspect ratio (>103), lyotropic nanotubes of stacked, macrocyclic, iminium salts, which are formed by protonation of the corresponding imine-linked macrocycles. Iminium ion formation establishes cohesive interactions that are two orders-of-magnitude stronger than the neutral macrocycles, as estimated by molecular dynamics simulations. Nanotube formation stabilizes the iminium ions, which otherwise rapidly hydrolyze, and is reversed and restored upon addition of bases and acids. Acids generated by irradiating a photoacid generator or sonicating chlorinated solvents also induced nanotube assembly, allowing these nanostructures to be coupled to diverse stimuli, and, once assembled, they can be fixed permanently by crosslinking their pendant alkenes. As the largest, and the first macrocyclic chromonic liquid crystals, macrocyclic iminium salts are easily accessible through a modular design and provide a means to rationally synthesize structures that mimic the morphology and rheology of carbon nanotubes and biological tubules.

Keywords

supramolecular polymerizations
chromonic mesophases
stimuli response property
Self-Assembly Nanostructures

Supplementary materials

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2018 03 Sun ChemRxiv SI
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Supplementary Video S1 Flow responses of lyotroptic nanotubes
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Supplementary Video S2 Simulation of 2 separated MCs with or without protonation
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Supplementary Video S3 Simualtion of 2 stacked MCs with or without protonation
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Supplementary Video S4 Steered molecular dynamics
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Supplementary Video S5 Simulation of 10 stacked MCs
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Supplementary Video S6 Simulation of 10 stacked protonated MCs
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Supplementary Video S7 Reversible formations of nanotubes
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Supplementary Video S8 Light and Sonication induced nanotube assembly
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