Divergent Nanotube Synthesis through Reversible Macrocycle Assembly

Abstract

Metrics & MoreArticle RecommendationsCONSPECTUS: Nanotubes offer a unique combination of structural precision, tunable interior environments, and high aspect ratios that will be useful for many applications. Despite these desirable attributes, widespread explorations into the properties and applications of chemically designed nanotubes have been limited by challenges related to their synthesis. This realization has motivated developing a unified synthetic nanotube design, which would enable wide-reaching explorations into onedimensional molecular architectures. In principle, supramolecular polymerization is a viable method to prepare such systems, but historically, this approach has yielded materials with poor mechanical properties and/or low aspect ratios whose chemical diversity is limited. This Account describes the development of an acid-mediated approach to macrocycle assembly that overcomes these limitations to yield robust, yet reversible, high-aspect-ratio nanotubes. Imine-linked macrocycles are prepared in high yield from readily accessible precursors by coupling dynamic imine exchange to an out-of-equilibrium macrocycle stacking event. Upon protonation, these macrocycles assemble into high-aspect-ratio nanotubes through electrostatic, solvophobic, and π−π interactions. The interplay between covalent and noncovalent processes are critical to guide macrocycle synthesis and assembly. Including basic pyridine groups into the macrocycle backbone leads to cooperative assembly, even in the presence of <1 equiv of acid per macrocycle. This design was elaborated to enable a general onepot nanotube synthesis from many functional aromatic dialdehydes. The development of structure−property relationships for nanotube assembly strength and ion conductivity are made possible because protonation-induced macrocycle assembly is modular and robust. For instance, supramolecular interactions endow synthetic nanotubes with robust cohesion and mechanical properties that surpass many covalent linear polymers. Tailoring the nanotube interior using site-selective chemical functionalization results in ion-conducting materials. Pyridinium-based nanotubes universally exhibit the ability to conduct protons and nanotubes functionalized with interior glycol groups promote efficient Li-ion transport. Overall, this versatile class of one-dimensional nanostructures shows substantial promise to merge the desirable properties of carbon nanotubes and biological filaments, all while being synthetically tailorable for many designed applications.

Self-assembled Macrocycles: Design Strategies and Emerging Functions

“…However, dynamic covalent chemistry (DCC), which involves reversible bond formation, gives a better yield of macrocycles through a thermodynamically controlled path and has error-correction capabilities. With this strategy, Dichtel and co-workers used DCC to prepare several imine-based rigid macrocycles in nearly quantitative yields from simple and multiple components. − Particularly, the reaction of 2,4,6-triphenylpyridine diamine (DAPP) with various aromatic dialdehydes yielded distinct pentagonal [5+5], hexagonal [3+3], and diamond-shaped [2+2] macrocycles, which self-assembled into high-aspect-ratio nanotubes upon protonation under mild conditions (Figure a) . They found that macrocycle self-assembly relied significantly on the protonation of imine, which occurs at a higher acid concentration.…”

Covalent-coordination driven hierarchical assembly of tubular frameworks

“…In recent years, the assembly of covalent linkage-based nanotubular structures has gained growing attention because of their improved mechanical properties and molecular sieving performance [29][30][31][32][33][34] . Nevertheless, a bottom-up method for the hierarchical assembly of covalent linkagebased nanotubular materials, e.g., nanotube-aligned frameworks, remains elusive 35 .…”

Controlling the crystal packing and morphology of metal–organic macrocycles through side-chain modification

“…Large macrocycles that self-assemble into extended nanotubular structures provide a fertile middle ground in between molecules and materials. [1][2][3][4][5] As molecules, macrocycles offer processability along with the ability to tune chemical structure with atomic precision. As materials, they possess multifunctional pore channels that can be used to mimic biological water channels, 6 selectively transport molecules, 7,8 conduct ions, [9][10][11][12] and host chemical reactions.…”