Modulating Aryl Azide Photolysis: Synthesis of a Room-Temperature Phosphorescent Carboline in Cucurbit[7]uril Host

Cucurbit[7]uril (CB7), a supramolecular host, is employed to control the pathway of photolysis of an aryl azide in an aqueous medium. Normally, photolysis of aryl azides in bulk water culminates predominantly in the formation of azepine derivatives via intramolecular rearrangement. Remarkably, however, when this process unfolds within the protective confinement of the CB7 cavity, it results in a carboline derivative, as a consequence of a C─H amination reaction. The resulting carboline caged by CB7 reveals long-lived room temperature phosphorescence (RTP) in the solid state, with lifetimes extending up to 2.1 s. These findings underscore the potential of supramolecular hosts to modulate the photolysis of aryl azides and to facilitate novel phosphorescent materials.

Stimuli-responsive mechanically interlocked molecules constructed from cucurbit[n]uril homologues and derivatives

Cucurbit[n]uril supramolecular chemistry has developed rapidly since 2001 when different cucurbit[n]uril homologues (Q[n]) were successfully separated in pure form. The combination of Q[n] cavity size and various types of external stimuli has given birth to numerous types of Q[n]-based mechanically interlocked molecules (MIMs), including (pseudo)rotaxanes, catenanes, dendrimers and poly(pseudo)rotaxanes. In this review article, the important advances in the field of Q[n]-based MIMs over the past two decades are highlighted. This review also describes examples of heterowheel (pseudo)rotaxanes and poly(pseudo)rotaxanes involving Q[n]s, and reflects on the opportunities and challenges of constructing Q[n]-based stimuli-responsive MIMs.

Symmetrical-Tetramethyl-Cucurbit[6]uril-Driven Movement of Cucurbit[7]uril Gives Rise to Heterowheel [4]Pseudorotaxanes

Two novel heterowheel [4]pseudorotaxanes consisting of cucurbit[7]uril (Q[7]) and symmetrical-tetramethyl-cucurbit[6]uril (TMeQ[6]) were constructed via the multirecognition mechanism, in which Q[7] can rotate freely around the horizontal axis, while TMeQ[6] cannot. In the construction process, due to strong repulsive forces between carbonyl portals of two neighboring wheels, the dethreading and movement of the wheels along the axle was observed. The dissociation of the [4]pseudorotaxanes was also discussed.

Efficient catenane synthesis by cucurbit[6]uril-mediated azide-alkyne cycloaddition

We report here the efficient synthesis of a series of [3]catenanes featuring the use of cucurbit[6]uril to simultaneously mediate the mechanical and covalent bond formations. By coupling the mechanical interlocking with covalent macrocyclization, formation of topological isomers is eliminated and the [3]catenanes are formed exclusively in good yields. The efficient access to these [3]catenanes and the presence of other recognition units render them promising building blocks for the construction of other high-order interlocked structures.

Molecular Snuggle and Stretch of a Tetraammonium Chain in the Construction of a Hetero-[4]pseudorotaxane with CyclopentanoQ[6] and Classical Q[7]

A hetero-[4]pseudorotaxane was designed to perform a molecular machine function of contraction and expansion utilizing the binding features of CyP₆Q[6] and classical Q[7]. First, the effect on guest binding of equatorial substitution on Q[6]'s was examined by comparing Me₄Q[6] and CyP₆Q[6] against classical Q[6] using eight guest molecules varying in shape, size, neutrality, or cations. Second, the binding data provided optimal structural features for the design of a tetraammonium ion chain to effect the synthesis of the hetero-[4]pseudorotaxane. Finally, the hetero-[4]pseudorotaxane was constructed, and the order of component placement was examined for function and thermodynamic stability in relation to component order on the molecular axle.

Five-Component Self-Assembly of Cucurbituril-Based Hetero-pseudorotaxanes

[5]Pseudorotaxanes can be obtained by self-sorting using heteroditopic guests and various cucurbituril homologues as hosts. The assembly and chemically induced disassembly of the pseudorotaxanes can be monitored by measuring the fluorescence of the anthracene guest in solution. Mass spectral evidence for the supramolecular assemblies is obtained in the gas phase. The disassembly in the gas phase can be achieved by collision-induced dissociation leading to the corresponding [2]- and [3]pseudorotaxanes.

Thermal responsiveness and binding affinity of cucurbit[7]uril terminal poly(N-isopropylacrylamide)

The introduction of CB[7] and guests raised the LCST of PNIPAM significantly, and CB[7]-PNIPAM maintained the high binding affinity of CB[7].

A Kinetic Self-Sorting Approach to Heterocircuit [3]Rotaxanes

In this proof-of-concept study, an active-template coupling is used to demonstrate a novel kinetic self-sorting process. This process iteratively increases the yield of the target heterocircuit [3]rotaxane product at the expense of other threaded species.

Facile syntheses of [3]-, [4]- and [6]catenanes templated by orthogonal supramolecular interactions

A branched [6]catenane was synthesised under aqueous conditions in high yield using orthogonal supramolecular interactions as a template.

A water soluble [6]catenane consisting of two interlocking [3]catenanes was synthesised in 91% yield using readily accessible precursors. The new strategy features the simultaneous use of orthogonal Cu⁺–phenanthroline and CB[6]–ammonium interactions for preorganising the precursors and the efficient CB[6]-catalysed azide–alkyne cycloaddition as bond forming reactions for ring closing, resulting in high structural complexity and fidelity of the products without compromising interlocking efficiency. A related [4]catenane with three different types of macrocycles was also obtained in good yield.

One-pot synthesis of a [c2]daisy-chain-containing hetero[4]rotaxane via a self-sorting strategy

The construction and efficient synthesis of hetero[n]rotaxanes with high structural complexity are always attractive challenges. Herein, we demonstrate a facile one-pot preparation of a hetero[4]rotaxane, by employing a self-sorting strategy, which contains an interpenetrated dibenzo-24-crown-8 (DB24C8) based [c2]daisy chain structure and is ended with a benzo-21-crown-7 (B21C7) based rotaxane at each side. The key to the design involved encoding the selective threading using a steric hindrance-related "language", where highly selective self-assemblies occurred in a three-component self-sorting process, which included the threading of a benzylalkylammonium into a B21C7 and interpenetrated dimerized formation of a DB24C8 based [c2]daisy chain simultaneously; the precise pre-assembled system resulted in the efficient synthesis of hetero[4]rotaxane with a high-level of structural complexity under the "CuAAC" reaction.

Cucurbiturils: from synthesis to high-affinity binding and catalysis

Major developments in the synthesis of cucurbiturils and applications related to their high-affinity binding and catalysis have recently taken place.

Self-sorting behavior of a four-component host–guest system and its incorporation into a linear supramolecular alternating copolymer

Self-sorting behavior of a four-component host–guest system was found, which could be utilized to construct a linear supramolecular alternating copolymer.

Use of cleavable coordinating rings as protective groups in the synthesis of a rotaxane with an axis that incorporates more chelating groups than threaded macrocycles

A new methodology allowing preparation of a linear "unsaturated" [3]rotaxane consisting of an axis incorporating more coordination sites than threaded rings was developed. It was based on the preliminary synthesis of a "saturated" [5]rotaxane consisting of a four-chelating site axis threaded through four macrocyclic components, two of them being cleavable rings incorporating a lactone function and the two others being "secure" non-cleavable rings. The stoppering reaction was based on click chemistry. Subsequently, cleavage and removal of the two lactone-containing macrocycles from the [5]rotaxane in basic medium afforded the desired "unsaturated" [3]rotaxane in quantitative yield.

Narcissistic versus social self-sorting of oligophenyleneethynylene derivatives: from isodesmic self-assembly to cooperative co-assembly

Narcissistic versus social! The self-assembly of two structurally related oligophenyleneethynylene derivatives featuring polar or nonpolar peripheral chains is reported. Their remarkable narcissistic versus social self-sorting behaviour in aqueous media can be controlled by concentration and solvent changes.

Reassembly self-sorting triggered by heterodimerization

We report herein a five-component self-sorted system comprising molecular clips that form heterodimers 1·4 and 8·11, and homodimer 14·14 in C(6)D(5)CD(3)/CDCl(3). The three component self-sorting mixture comprising 1·1, 8·8, and 14·14 undergoes triggered reassembly self-sorting upon addition of 4·4 and 11·11.