A poly-pseudorotaxane constructed by threading pillar[5]arene onto an ion-pair recognition-based calix[4]pyrrole supramolecular polymer

The ion-pair recognition ability of calix[4]pyrrole was utilized to form a multicomponent monomeric assembly and a linear supramolecular polymer via concurrent anion and bis-cation complexation. The inherent dynamic interactions of these assemblies were further used to construct pseudorotaxanes in monomeric and supramolecular polymer forms with pillar[5]arene.

Noncovalently bound and mechanically interlocked systems using pillar[n]arenes

Pillar[n]arenes are pillar-shaped macrocyclic compounds owing to the methylene bridges linking the para-positions of the units. Owing to their unique pillar-shaped structures, these compounds exhibit various excellent properties compared with other cyclic host molecules, such as versatile functionality using various organic synthesis techniques, substituent-dependent solubility, cavity-size-dependent host-guest properties in organic media, and unit rotation along with planar chiral inversion. These advantages have enabled the high-yield synthesis and rational design of pillar[n]arene-based mechanically interlocked molecules (MIMs). In particular, new types of pillar[n]arene-based MIMs that can dynamically convert between interlocked and unlocked states through unit rotation have been produced. The highly symmetrical pillar-shaped structures of pillar[n]arenes result in simple NMR spectra, which are useful for studying the motion of pillar[n]arene wheels in MIMs and creating sophisticated MIMs with higher-order structures. The creation and application of polymeric MIMs based on pillar[n]arenes is also discussed.

Anion-Responsive Pseudo[3]rotaxane from a Difunctionalized Pillar[4]arene[1]quinone and a Bis-Imidazolium Cation

Synthesis of a new functionalized pillar[4]arene[1]quinone and its host-guest complexation with a bis-imidazolium dication was demonstrated. 1D/2D NMR spectroscopic analyses and high-resolution mass spectrometric analyses showed the formation of the pseudo[3]rotaxane assembly upon host-guest complexation. ¹H NMR titration experiments revealed the role of hydrogen bonding motifs in bringing positive cooperativity by comparing the binding constants for the host-guest complexation of pillar[4]arene[1]quinone with a bis-imidazolium guest. Anion-responsiveness of the pseudo[3]rotaxane assembly was also demonstrated.

Recent advances in the development of rotaxanes and pseudorotaxanes based on pillar[n]arenes: from construction to application

This article summarizes recent advances in the development of rotaxanes and pseudorotaxanes based on pillar[n]arenes: from construction to application.

A light-driven molecular machine based on stiff stilbene

We report a new molecular design for optically triggered nm-scale translation of a submolecular component relative to another.

Calix[5]arene Through-the-Annulus Threading of Dialkylammonium Guests Weakly Paired to the TFPB Anion

Through-the-annulus threading of calix[5]arene penta-O-ethers by dialkylammonium cations coupled to the loosely coordinating superweak TFPB^- anion has been achieved. ¹H NMR titration data show that preorganization of the calix[5]arene scaffold leads to great thermodynamic stability of the pseudorotaxane complexes as well as to a favorable threading kinetic. Thus, calix[5]arene 1c, bearing tert-butyl groups at the wide rim, was threaded by all of the cations under study (with the exception of the dibenzylammonium 2b⁺) more tightly than the other derivatives under investigation (K_a's up to 2.02 ± 0.2 × 10⁵ M^-1) because of its preorganized cone conformation. According to DFT calculations, van der Waals interactions between the tert-butyl groups of 1c and the alkyl chain of the cationic axle are likely responsible for the remarkable stability observed. The threading of the calix[5]arene wheels with the asymmetric pentylbenzylammonium axle 2c⁺ led to the toposelective formation of the endo-pentylpseudorotaxane stereoisomer in agreement with the known "endo-alkyl rule". Owing to the steric hindrance of the axle phenyl group, the threading of the guest was seen to occur in a unidirectional fashion through the calixarene narrow rim.

Formation of a series of stable pillar[5]arene-based pseudo[1]-rotaxanes and their [1]rotaxanes in the crystal state

A series of mono-amide-functionalized pillar[5]arenes with different lengths of N-ω-aminoalkyl groups as the side chain on the rim were designed and synthesized, which all formed pseudo[1]rotaxanes in the crystal state. And these pseudo[1]rotaxanes could be transformed into [1]rotaxanes or open forms in the crystal state. In addition, they were also studied in solution by (1)H NMR spectroscopy.

Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry

In 2008, we reported a new class of pillar-shaped macrocyclic hosts, known as "pillar[n]arenes". Today, pillar[n]arenes are recognized as key players in supramolecular chemistry because of their facile synthesis, unique pillar shape, versatile functionality, interesting host-guest properties, and original supramolecular assembly characteristics, which have resulted in numerous electrochemical and biomedical material applications. In this Review, we have provided historical background to macrocyclic chemistry, followed by a detailed discussion of the fundamental properties of pillar[n]arenes, including their synthesis, structure, and host-guest properties. Furthermore, we have discussed the applications of pillar[n]arenes to materials science, as well as their applications in supramolecular chemistry, in terms of their fundamental properties. Finally, we have described the future perspectives of pillar[n]arene chemistry. We hope that this Review will provide a useful reference for researchers working in the field and inspire discoveries concerning pillar[n]arene chemistry.

Efficient complexation between pillar[5]arenes and neutral guests: from host–guest chemistry to functional materials

This feature article covers the molecular recognition of pillar[5]arenes and neutral guests, and its application in making supramolecular structures, polymers and functional materials.

A pillar[6]arene-based [2]pseudorotaxane in solution and in the solid state and its photo-responsive self-assembly behavior in solution

A pillar[6]arene-based [2]pseudorotaxane was constructed in solution and studied in the solid state, and its photo-responsive self-assembly behavior in solution was investigated.

Bis-urea macrocycles with a deep cavity

Two bis-urea macrocycles with a deep cavity demonstrate an enzyme-like binding, and the influence of dipole alignments on molecular recognition.