In this research, we report the regioselective synthesis of methylene-bridged naphthalene oligomers from 2,6-dialkoxyl naphthanene and paraformaldehyde by using p-TsOH as the catalyst and CH2Cl2 as the solvent. The structures were characterized by NMR spectroscopy and X-ray crystallography. Their host–guest chemistry with organic cations was studied, and optimal naphthalene numbers in the oligomers were revealed for different guests. In addition, the reason for the unsuccessful synthesis of methylene-bridged naphthalene macrocycles was discussed.

A series of quaternary ammonium guests have been synthesized, and their binding behavior with oxatub[4]arene have been studied. In particular, remote electronic substituents of the guests can significantly affect the binding affinities mainly through a field/inductive effect by following a linear free energy relationship. More surprisingly, oxatub[4]arene, with a complex conformational network, shows a large amplitude of conformational change in response to the remote electronic substituents on the guests. This novel mode of synthetic molecular recognition may also have biological relevance.

Chiral epoxides are important intermediates in chemistry and biology. The high-throughput screening of asymmetric epoxidation conditions requires fast determination of the absolute configurations and ee values of chiral epoxides. Herein, we report molecular recognition and chiroptical sensing of epoxides in water using endo-functionalized molecular tubes. The absolute configurations and ee values were simultaneously determined by circular dichroism spectroscopy. In addition, real-time monitoring as well as the application to real asymmetric epoxidation was demonstrated. The method is simple, environmentally friendly, and amenable to high-throughput screening.

In this research, we report that the acid/base-switchable molecular shuttle without any photoresponsive group can be controlled photochemically by coupling to the indazole-based photoacid via an intermolecular proton-transfer process. The photocontrolled shuttling of the wheel can be conveniently monitored by following the fluorescent evolution during the photoirradiation.

A phase-selective, bis-urea organogelator with a curved bis-naphthalene core was synthesized and characterized. This gelator is capable of gelating a variety of hydrocarbons and oils. The resulting gels have been characterized by rheology, SEM, and molecular modelling. The gelator can be applied in the powder form for the recovery of a thin layer of petrol oil spill in water.Download high-res image (129KB)Download full-size imageA bis-urea, phase-selective organogelator with a curved bis-naphthalene core is capable of gelating oils, and can be used to recover oil spill in water when applied in the powder form.

Large oxatub[n]arenes (n = 5, 6) have been synthesized and characterized. Their conformational complexity was analyzed and host–guest chemistry was studied. In particular, the rather flexible oxatub[6]arene is able to accommodate C60 and C70 with moderate binding affinities. Computational results suggest that there are different binding affinities to C60 or C70 for each conformer of oxatub[6]arene. This endows oxatub[6]arene with conformational adaptability according to the needs of its guests.

A series of oxatub[4]arenes with different alkyl side chains have been synthesized. The conformational interconversion, molecular recognition and macroscopic self-assembly behaviour of oxatub[4]arene derivatives were investigated. The difference in side chains slightly changes the binding affinities, but results in different self-assembly morphologies at the solid state.

A water-soluble oxatub[4]arene with tri(ethylene oxide) moieties was synthesized. The lower critical solution temperature (LCST) behavior of this macrocyclic receptor was tunable by changing its concentration or by adding an appropriate guest. Most interestingly, the LCST behavior of the host–guest complex showed a response to the presence of the physiological gasotransmitter H2S through nitro group reduction.

The molecular “transformer”, oxatub[4]arene, was found to be able to host a wide range of organic cations. The strong binding ability is believed to originate from its four interconvertible and deep-cavity conformers. The binding behavior of such adaptable receptors may provide implications for molecular recognition in nature.

Four endo-functionalized molecular tubes with urea/thiourea groups in the deep cavities have been synthesized, and their binding ability to neutral molecules studied. Very high binding affinity and selectivity have been achieved, which are rationalized by invoking the shape and electrostatic complementarity and dipole alignment.

•All synthetic routes to naphthol-based molecular receptors are covered.•Synthesis and property of endo-functionalized NaphthoTubes is discussed.•Configurational and conformational complexity is introduced to molecular receptors.Synthetic macrocyclic receptors are the primary workhorses in supramolecular chemistry. In particular, macrocyclic arenes are versatile receptors due to their special binding performances and wide applications. In this Digest, we discussed the recent advances on naphthol-based macrocyclic receptors, with special emphasis on the construction of naphthol-based molecular receptors with high guest binding ability and selectivity, and broad guest binding scope.Figure optionsDownload full-size imageDownload as PowerPoint slide

Large protein-sized synthetic supramolecular architecture is rare and certainly has not yet achieved the structural and functional complexity of biomolecules. As multiple, identical copies of a few building blocks are repetitively used, a highly symmetrical architecture results with limitations in function. In marked contrast, functional structures in nature are often assembled with high geometric precision from many different building blocks. They cooperate in a complex way realizing energy conversion, mechanical motion or transport phenomena. Beyond self-assembly, the structurally and functionally complex biomolecular machines rely on self-sorting to correctly position all subunits through orthogonal recognition sites. Mimicking such self-sorting processes is a promising strategy for supramolecular synthesis – resulting in higher structural complexity and promising access to a more sophisticated function. The term “integrative self-sorting” was coined to describe the strategy to form well-defined assemblies with well-controlled subunit positions. The key process is the incorporation of two or more orthogonal binding motifs into at least some of the subunits. Modularity and programmability based on orthogonal yet similar binding motifs generate diversity and complexity. Integrative self-sorting is thus inherently related to systems chemistry. Depending on the individual binding motifs, (multi-)stimuli responsiveness can be achieved. When different recognition events en route to the final assembly occur on significantly different time scales, kinetic pathway selection is observed. In this account, we review the modularity, programmability, and emergent properties of integrative self-sorting, emphasizing its utility and perspective for complex supramolecular architectures.

There are a large number of synthetic macrocyclic receptors in the literature. No particular one is suitable for all guests or purposes. For a broader guest binding scope or multiple purposes, a macrocycle with multiple interconvertible cavities will be advantageous. Here, we report a naphthalene-based macrocyclic receptor with an adaptable cavity, namely oxatub[4]arene. It has four representative conformations resulting from the flipping of naphthalene rings, each with a deep and well-defined cavity. Different guests select one host conformer or a combination of conformers. All the four conformers have been detected and characterized based on 2D NMR spectra and X-ray single crystal structures. Thermodynamically, these conformers constitute a reservoir, that responds to the structural changes of guests, and thus maximizes the association free energies. This smart macrocycle may provide a new platform for the construction of molecular machines and devices or stimuli-responsive materials.

Three classes of hydrogen-bonded capsules with imperfect walls have been prepared and characterized. The defects reduce the symmetry of the capsules, leading to rich isomerism. The missing hydrogen bonds provide additional flexibility to the capsules and exert an influence on their guest binding properties in different assemblies.

Two configurational isomers of bis-urea macrocycles have been synthesized, and their neutral molecule recognition was studied by X-ray crystallography and 1H NMR experiments. Cooperative action between the deep cavity and the urea groups and the influence of dipole alignments on molecular recognition are discussed.

The rigid and nonchiral bis-naphthalene cleft was used for the first time as a scaffold to build a chiral molecular tweezer. The molecular tweezer and its related compounds have been synthesized and carefully characterized by X-ray crystallography and NMR spectroscopy. Their solid-state structures and molecular recognition properties have also been studied.

The realization of controllable and well-organized self-assembly within multicomponent supramolecular systems (MSSs) is still a great challenge. Herein, we present the construction of multicomponent supramolecular systems with high-level complexity through the combination of orthogonal self-assembly and the self-sorting approach. Driven by the orthogonality of metal–ligand coordination and host–guest interactions in the orthogonal self-assembly as well as directed by multiple molecular codes in the self-sorting process, five types of simple components (up to eighteen precursors) were successfully self-assembled into two novel tris[2]pseudorotaxanes in one pot through a highly selective manner, which were well-characterized by one-dimensional (1-D) and two-dimensional (2-D) multinuclear NMR as well as ESI-TOF-MS.

Four endo-functionalized molecular tubes with urea/thiourea groups in the deep cavities have been synthesized, and their binding ability to neutral molecules studied. Very high binding affinity and selectivity have been achieved, which are rationalized by invoking the shape and electrostatic complementarity and dipole alignment.

There are a large number of synthetic macrocyclic receptors in the literature. No particular one is suitable for all guests or purposes. For a broader guest binding scope or multiple purposes, a macrocycle with multiple interconvertible cavities will be advantageous. Here, we report a naphthalene-based macrocyclic receptor with an adaptable cavity, namely oxatub[4]arene. It has four representative conformations resulting from the flipping of naphthalene rings, each with a deep and well-defined cavity. Different guests select one host conformer or a combination of conformers. All the four conformers have been detected and characterized based on 2D NMR spectra and X-ray single crystal structures. Thermodynamically, these conformers constitute a reservoir, that responds to the structural changes of guests, and thus maximizes the association free energies. This smart macrocycle may provide a new platform for the construction of molecular machines and devices or stimuli-responsive materials.

Two configurational isomers of bis-urea macrocycles have been synthesized, and their neutral molecule recognition was studied by X-ray crystallography and 1H NMR experiments. Cooperative action between the deep cavity and the urea groups and the influence of dipole alignments on molecular recognition are discussed.

The molecular “transformer”, oxatub[4]arene, was found to be able to host a wide range of organic cations. The strong binding ability is believed to originate from its four interconvertible and deep-cavity conformers. The binding behavior of such adaptable receptors may provide implications for molecular recognition in nature.

Large oxatub[n]arenes (n = 5, 6) have been synthesized and characterized. Their conformational complexity was analyzed and host–guest chemistry was studied. In particular, the rather flexible oxatub[6]arene is able to accommodate C60 and C70 with moderate binding affinities. Computational results suggest that there are different binding affinities to C60 or C70 for each conformer of oxatub[6]arene. This endows oxatub[6]arene with conformational adaptability according to the needs of its guests.

The realization of controllable and well-organized self-assembly within multicomponent supramolecular systems (MSSs) is still a great challenge. Herein, we present the construction of multicomponent supramolecular systems with high-level complexity through the combination of orthogonal self-assembly and the self-sorting approach. Driven by the orthogonality of metal–ligand coordination and host–guest interactions in the orthogonal self-assembly as well as directed by multiple molecular codes in the self-sorting process, five types of simple components (up to eighteen precursors) were successfully self-assembled into two novel tris[2]pseudorotaxanes in one pot through a highly selective manner, which were well-characterized by one-dimensional (1-D) and two-dimensional (2-D) multinuclear NMR as well as ESI-TOF-MS.

Large protein-sized synthetic supramolecular architecture is rare and certainly has not yet achieved the structural and functional complexity of biomolecules. As multiple, identical copies of a few building blocks are repetitively used, a highly symmetrical architecture results with limitations in function. In marked contrast, functional structures in nature are often assembled with high geometric precision from many different building blocks. They cooperate in a complex way realizing energy conversion, mechanical motion or transport phenomena. Beyond self-assembly, the structurally and functionally complex biomolecular machines rely on self-sorting to correctly position all subunits through orthogonal recognition sites. Mimicking such self-sorting processes is a promising strategy for supramolecular synthesis – resulting in higher structural complexity and promising access to a more sophisticated function. The term “integrative self-sorting” was coined to describe the strategy to form well-defined assemblies with well-controlled subunit positions. The key process is the incorporation of two or more orthogonal binding motifs into at least some of the subunits. Modularity and programmability based on orthogonal yet similar binding motifs generate diversity and complexity. Integrative self-sorting is thus inherently related to systems chemistry. Depending on the individual binding motifs, (multi-)stimuli responsiveness can be achieved. When different recognition events en route to the final assembly occur on significantly different time scales, kinetic pathway selection is observed. In this account, we review the modularity, programmability, and emergent properties of integrative self-sorting, emphasizing its utility and perspective for complex supramolecular architectures.

Three classes of hydrogen-bonded capsules with imperfect walls have been prepared and characterized. The defects reduce the symmetry of the capsules, leading to rich isomerism. The missing hydrogen bonds provide additional flexibility to the capsules and exert an influence on their guest binding properties in different assemblies.