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

Abstract

Nanotubes assembled from macrocyclic precursors offer au nique combination of low dimensionality,s tructural rigidity,a nd distinct interior and exterior microenvironments. Usually the weak stackinge nergies of macrocycles limit the length and mechanical strength of the resultant nanotubes. Imine-linked macrocycles were recently found to assemble into high-aspect ratio (> 10 3 ), lyotropic nanotubes in the presence of excess acid. Yetthese harsh conditions are incompatible with many functional groups and processing methods,a nd lower acid loadings instead catalyze macrocycle degradation. Here we report pyridine-2,6-diimine-linked macrocycles that assemble into high-aspect ratio nanotubes in the presence of less than 1equiv of CF 3 CO 2 Hp er macrocycle.A nalysis by gel permeation chromatography and fluorescence spectroscopyrevealed acooperative self-assembly mechanism. The low acid concentrations needed to induce assembly enabled nanofibers to be obtained by touch-spinning, which exhibit higher Youngs moduli (1.33 GPa) than many synthetic polymers and biological filaments.T hese findings represent ab reakthrough in the design of inverse chromonic liquid crystals,asassembly under such mild conditions will enable the design of structurally diverse and mechanically robust nanotubes from synthetically accessible macrocycles.

Ring Size-Dependent Solution Behavior of Macrocycles: Dipole–Dipole Attraction Counteracted by Excluded Volume Repulsion

“…Self-assembly usually results from the interplay of multiple motifs, though many studies focus on one predominant force. − , Self-assembly of merocyanine dyes (dipole moment = 12–19 D) is driven by dipole–dipole interaction but promoted by solvophobicly induced aromatic interactions . The dipole moment of 63 D (Figure a) for the P­( P FpR) 28 macrocycles is sufficiently large for a dipole–dipole attraction (Figure a and c). , Therefore, a self-assembly of this macrocycle would be possible by overcoming the EV repulsion, which can be achieved by introducing an additional self-assembling motif.…”

“…Repulsive interaction, e.g., electrostatic interaction of like-charged electrolytes, is an important motif for biological assemblies and colloidal and supramolecular chemistry. − Excluded volume (EV) prevents molecules in solutions from approaching each other and is a type of repulsive interaction with the strength depending on the molecular structures. − Cyclic molecules are attractive due to a range of interesting properties, , including a larger EV interaction than their linear analogues. , Nevertheless, the role of EV interaction in supramolecular synthesis is rarely studied, and most reported assembling systems focus on various conventional intermolecular interactions, e.g., hydrogen bonding, − π–π stacking, and electrostatic interactions. , …”

“…10,11 Nevertheless, the role of EV interaction in supramolecular synthesis is rarely studied, and most reported assembling systems focus on various conventional intermolecular interactions, e.g., hydrogen bonding, 12−14 π−π stacking, 15 and electrostatic interactions. 16,17 The large EV for synthetic macrocycles, expected based on theoretic calculations, 10,11,18 has not been commonly observed as indicated by low ratios of R g /R h , (R g = radius of gyration; R h = hydrodynamic radius), 19−21 e.g., R g /R h of 0.87−1.06 for cyclic polystyrene. 19 This is explained by the flexible backbone of the macrocycles.…”

“…Self-assembly usually results from the interplay of multiple motifs, though many studies focus on one predominant force. [12][13][14][15][16]34 Self-assembly of merocyanine dyes (dipole moment = 12−19 D) is driven by dipole−dipole interaction but promoted by solvophobicly induced aromatic interactions. 33 The dipole moment of 63 D (Figure 1a) for the P( P FpR) 28 macrocycles is sufficiently large for a dipole−dipole attraction (Figure 1a and 1c).…”

Conformationally Confined Emissive Cationic Macrocycle with Photocontrolled Organelle‐Specific Translocation

“…Along with the rapid development in the past decades, diverse macrocyclic compounds have been created with defined topological structures and elaborate functions, which greatly expand the research scope for nanoscience and have inventive applications in material manufacturing. [ 1 ] However, the commonly used representative macrocycles, including the parent crown ethers, cyclodextrins, and cucurbiturils, are spectroscopically transparent or possess rather weak absorption in the UV–vis region. These factors seriously hinder their development and applications, especially as photoluminescent materials in the biorelated fields.…”