Integrative Self‐Sorting: One‐Pot Synthesis of a Hetero[4]rotaxane from a Daisy‐Chain‐Containing Hetero[4]pseudorotaxane

The structural complexity of mechanically interlocked molecules are very attractive to chemists owing to the challenges they present. In this article, novel mechanically interlocked molecules with a daisy‐chain‐containing hetero[4]rotaxane motif were efficiently synthesized. In addition, a novel integrative self‐sorting strategy is demonstrated, involving an ABB‐type (A for host, dibenzo‐24‐crown‐8 (DB24C8), and B for guest, ammonium salt sites) monomer and a macrocycle host, benzo‐21‐crown‐7 (B21C7), in which the assembled species in hydrogen‐bonding‐supported solvent only includes a novel daisy‐chain‐containing hetero[4]pseudorotaxane. The found self‐sorting process involves the integrative recognition between B21C7 macrocycles and carefully designed components simultaneously containing two types of secondary ammonium ions and a host molecule, DB24C8 crown ether. The self‐sorting strategy is integrative to undertake self‐recognition behavior to form one single species of pseudorotaxane compared with the previous report. This self‐sorting system can be used for the efficient one‐pot synthesis of a daisy‐chain‐containing hetero[4]rotaxane in a good yield. The structure of hetero[4]rotaxane was confirmed by ¹H NMR spectroscopy and high‐resolution electrospray ionization (HR‐ESI) mass spectrometry.     

Binding of secondary dialkylammonium salts by pyrido-21-crown-7

Pyrido-21-crown-7 (P21C7) has been synthesized and shown to form [2]pseudorotaxanes spontaneously with secondary dialkylammonium ions. These complexes are stronger than their benzo-21-crown-7 counterparts and much stronger than their dibenzo-24-crown-8 counterparts. Based on this new P21C7/secondary dialkylammonium salt recognition motif, a [2]rotaxane terminated by phenyl groups as stoppers has been successfully constructed using the threading-followed-by-stoppering technique.     

[5]Rotaxane,linear polymer and supramolecular organic framework constructed by nor-seco-cucurbit[10]uril-based ternary complexation

Here we use nor-seco-cucurbit[10]uril (ns-CB[10]) based ternary complexation to construct [5]rotaxane, linear supramolecular dynamic rotaxane polymers and cubic 3D supramolecular organic framework. A [5]rotaxane is constructed by ns-CB[10], TMeCB[6] and short linear derivatives of 4,4′-bipyridinium (M2). ns-CB[10], CB[7] and long linear derivatives of 4,4′-bipyridinium (M3) self-assemble into a linear supramolecular dynamic rotaxane polymer. ns-CB[10] and tetracationic tetrahedral monomer self-assemble and form a three-dimensional supramolecular organic framework. The above results demonstrate that ns-CB[10]-based ternary complexation is a versatile platform to build various supramolecular systems.     

Design and synthesis of self-included pillar[5]arene-based bis-[1]rotaxanes

Two strategies for the design of new pillar[5]arene-based mechanically self-interlocked molecules (MSMs) are reported here. The first strategy is based on the construction of an intermediate pseudo[1]rotaxane followed by the desired bis-[1]rotaxane. The other one is based on the construction of the desired bis-[1]-rotaxane directly via a condensation reaction through host-guest interactions between a mono-functionalized pillar[5]arene and the axle. This compound has interesting self-assembly properties in methanol and some extended applications of this compound will be reported in the near future.     

Synthesis of a pH‐Sensitive Hetero[4]Rotaxane Molecular Machine that Combines [c2]Daisy and [2]Rotaxane Arrangements

The synthesis of a novel pH‐sensitive hetero[4]rotaxane molecular machine through a self‐sorting strategy is reported. The original tetra‐interlocked molecular architecture combines a [c2]daisy chain scaffold linked to two [2]rotaxane units. Actuation of the system through pH variation is possible thanks to the specific interactions of the dibenzo‐24‐crown‐8 (DB24C8) macrocycles for ammonium, anilinium, and triazolium molecular stations. Selective deprotonation of the anilinium moieties triggers shuttling of the unsubstituted DB24C8 along the [2]rotaxane units.     

Pseudo[n,m]rotaxanes of Cucurbit[7/8]uril and Viologen‐Naphthalene Derivative: A Precise Definition of Rotaxane

Rotaxane is a kind of classic supramolecule, which is usually constructed from a number of macrocycles and one axis molecule. Herein, we have expanded the supramolecular structure of [n]rotaxane to offer a precise definition of (pseudo)[n,m]rotaxane for accurately describing the two kinds of (pseudo)rotaxanes structures, which are self‐assembled from cucurbit[7/8]uril (CB[7/8]) and viologen‐naphthalene derivative, respectively. Furthermore, these CB‐based pseudorotaxanes exhibit varied photophysical properties, stimuli‐responsive behavior triggered by competitive guest, and self‐sorting behavior.     

Synthesis of thiophene-capped [2]rotaxanes

Two types of thiophene-capped [2]rotaxanes, i.e., bithienyl (2T)- and bis(3,4-ethylenedioxythiophene)-yl (BEDOT)-capped [2]rotaxanes, were synthesized. The electron-deficient cyclophane of cyclobis(paraquat-p-phenylene) (CBPQT⁴⁺) was used as a macrocycle. Association constants for inclusion complexation of 2T- and BEDOT-derivatives with CBPQT⁴⁺ were obtained by ¹H NMR titration. Due to the donor-acceptor charge transfer absorption band, 2T- and BEDOT-capped [2]rotaxanes have red and green colors, respectively. On the basis of electrochemical analysis, we confirmed that only BEDOT-capped [2]rotaxane is a promising candidate for [3]rotaxane synthesis through oxidation coupling of the thiophene unit.     

A Flexible Copper(I)‐Complexed [4]Rotaxane Containing Two Face‐to‐Face Porphyrinic Plates that Behaves as a Distensible Receptor

A new cyclic [4]rotaxane composed of two flexible bis‐macrocycles and two rigid axles is described. Each bis‐macrocycle consists of two rings attached to antipodal meso positions of a central Zn porphyrin through single C? C bonds. Each ring incorporates a 2,9‐diphenyl‐1,10‐phenanthroline chelation site. The axles contain two coplanar bidentate sites derived from the 2,2′‐bipyridine motif. The building blocks were assembled by using a one‐pot threading‐and‐stoppering reaction, which afforded the [4]rotaxane in 50 % yield. The “gathering‐and‐threading” effect of copper(I) was utilised in the formation of a [4]pseudorotaxane, which was immediately converted to the corresponding [4]rotaxane by a quadruple CuAAC stoppering reaction. The rotaxane contains two face‐to‐face zinc porphyrins, which allowed the coordination of ditopic guest substrates. The rotaxane host showed remarkable flexibility and was able to adjust its conformation to the guest size. It can be distended and accommodate rod‐like guests of 2.6 to 15.8 Å in length.     

Highly stable pseudo[2]rotaxanes co-driven by crown ether-ammonium and donor-acceptor interactions

Bis-p-phenylene-34-crown-10 derivatives 1 and 2, bearing one and two dibenzo[24]crown-8 units, respectively, and 4,4′-dipyridinium derivatives of 3·3PF₆ and of 4·4PF₆, bearing one and two ammonium groups, respectively, have been synthesized from readily available starting materials. ¹H NMR and UV-vis studies reveal that in polar acetonitrile 1 binds 3·3PF₆ to produce pseudo[2]rotaxane 1·3·3PF₆ by making use of one donor-acceptor and one electrostatic interaction, whereas 2 binds 4·4PF₆ to form pseudo[2]rotaxane 2·4·4PF₆ through one donor-acceptor and two electrostatic interactions. The association constants of the two pseudorotaxanes have been determined by the UV-vis titration method to be 9.1 (±1.0)×10³ M⁻¹ and 6.5 (±0.7)×10⁵ M⁻¹, respectively. The high stability of the new pseudo[2]rotaxanes has been ascribed to the cooperative interaction of the two different non-covalent forces.     

A [3]rotaxane with two porphyrinic plates acting as an adaptable receptor

Following a multistep procedure, the copper(I)-templated strategy allowed preparation of a multifunctional [3]rotaxane. The dumbbell consists of a central two-bidentate chelate unit and two terminal stoppers. The two rings threaded on the rotaxane axis consist each of a 1,10-phenanthroline-incorporating macrocycle, rigidly connected to an appended zinc-complexed porphyrin. The copper(I) template can be removed, affording a free rotaxane whose two rings can glide freely along the axis and spin around it. The dumbbell being very long (approximately 85 A in its extended conformation from one stopper to the other), the porphyrin-porphyrin distance can be varied over a wide range. The two porphyrinic plates constitute the key elements of a receptor able to complex various guests between the plates. The ability of the threaded rings to move freely makes the host perfectly adjustable, allowing capture of geometrically very different guests. The copper(I)-complexed rotaxane also acts as an efficient receptor, although its adaptability is obviously more limited than that of its free rotaxane counterpart.     

Electron Transfer and Switching in Rigid [2]Rotaxanes Adsorbed on TiO2 Nanoparticles

Bistable [2]rotaxanes have been attached through a bulky tripodal linker to the surface of titanium dioxide nanoparticles and studied by cyclic voltammetry and spectroelectrochemical methods. The axle component in the [2]rotaxane contains two viologen sites, V₁ and V₂, interconnected by a rigid terphenylene bridge. In their parent dication states, V₁²⁺ and V₂²⁺ can both accommodate a crown ether ring, C, but are not equivalent in terms of their affinity towards C and have different electrochemical reduction potentials. The geometry and size of the tripodal linker help to maintain a perpendicular [2]rotaxane orientation at the surface and to avoid unwanted side‐to‐side interactions. When the rigid [2]rotaxane or its corresponding axle are adsorbed on a TiO₂ nanoparticle, viologen V₂²⁺ is reduced at significantly more negative potentials (?0.3 V) than in flexible analogues that contain aliphatic bridges between V₁ and V₂. These overpotentials are analysed in terms of electron‐transfer rates and a donor–bridge–acceptor (D–B–A) formalism, in which D is the doubly reduced viologen, V₁⁰, adjacent to the TiO₂ surface (TiO₂–V₁⁰), B is the terphenylene bridge and A is viologen V₂²⁺. We have also found that, in contrast with earlier findings in solution, no molecular shuttling occurs in rigid [2]rotaxane adsorbed at the surface. The observations were explained by the relative position of the viologen stations within the electrical double layer, screening of V₂²⁺ by the counterions and high capacity of the medium, which reduces the mobility of the crown ether. The results are useful in transposing of solution‐based molecular switches to the interface or in the design and understanding of the properties of systems comprising electroactive and/or interlocked molecules adsorbed at the nanostructured TiO₂ surface.     

Fluorescence Modulation in Tribranched Switchable [4]Rotaxanes

Two novel tribranched [4]rotaxanes with a 1,3,5‐triphenylene core and three rotaxane arms have been designed, synthesized, and characterized by ¹H and ¹³C NMR spectroscopies and HR‐ESI mass spectrometry. [4]Rotaxanes 1 and 2 each possess the same three‐armed skeleton. Each arm incorporates two distinguishable binding sites for a dibenzo[24]crown‐8 ring, namely a dibenzylammonium site and an N‐methyltriazolium site, and is terminated by a 4‐morpholino‐naphthalimide fluorophore as a stopper. [4]Rotaxane 1 has three di‐ferrocene‐functionalized dibenzo[24]crown‐8 rings whereas 2 has three simple dibenzo[24]crown‐8 rings interlocked with the thread component. Uniform shuttling motions of the three macrocycles in both 1 and 2 can be driven by external acid–base stimuli, which were confirmed by ¹H NMR spectroscopy. However, [4]rotaxanes 1 and 2 show distinct modes of fluorescence modulation in response to external acid–base stimuli. [4]Rotaxane 1 exhibits a remarkable fluorescence decrease in response to the addition of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) as a base, which can displace the ferrocene‐functionalized macrocycle from the dibenzylammonium station to the N‐methyltriazolium station. In contrast, the fluorescence intensity of [4]rotaxane 2 showed an enhancement with the addition of DBU. Time‐resolved fluorescence measurements have been performed. The different photoinduced electron‐transfer processes responsible for the fluorescence changes in the two molecular systems are discussed. Topological structures of this kind have significant potential for the design and construction of large and complex assemblies with controllable functions.     

Boron coordination compounds derived from 2-phenyl-benzimidazole and 2-phenyl-benzotriazole bidentate ligands

The syntheses and structural analyses of a series of boron heterocycles derived from 2-(1H-benzimidazol-2-yl)-phenylamine (1), 2-(1H-benzimidazol-2-yl)-phenol (2), 2-(1H-benzimidazol-2-yl)-benzenedisulfide (3), 2-[3-(1,1,1,3,-tetramethyl-butyl)-phenyl]-2H-benzotriazole (4), 2-[3,5-bis-(1-methyl-1-phenylethyl)-phenyl]-2H-benzotriazole (5) and (C₆H₅)₂BOH or BF₃·OEt₂ are reported. The new boron compounds: diphenyl-[2-(1H-benzimidazol-2-yl-κN)-phenylamide-κN]-boron (6), diphenyl-[2-(1H-benzimidazol-2-yl-κN)-phenolate-κO]-boron (7), diphenyl-[2-(1H-benzimidazol-2-yl-κN)-benzenethiolate-κS]-boron (8), diphenyl-[2-(2H-benzotriazol-2-yl-κN)-4-(1,1,3,3-tetramethyl-butyl)-phenolate-κO]-boron (9), diphenyl-[2-(2H-benzotriazol-2-yl-κN)-4,6-(1-methyl-1-phenylethyl)-phenolate-κO]-boron (10), difluoro-[2-(1H-benzimidazol-2-yl-κN)-phenolate-κO]-boron (11), difluoro-[2-(2H-benzotriazol-2-yl-κN)-4-(1,1,3,3-tetramethylbutyl)-phenolate-κO]-boron (12) and difluoro-[2-(2H-benzotriazol-2-yl-κN)-4,6-(1-methyl-1-phenylethyl)-phenolate-κO]-boron (13) have four fused rings, with boron included in a six-membered ring and bound to N, O or S atoms and strongly coordinated by a nitrogen atom from the imidazole or triazole rings. Their structures are zwitterionic, with a negative charge on the boron and a delocalized positive charge on the ligand. Compounds 6-12 were studied by NMR, IR, mass spectrometry, and 6-10 and 12 by X-ray diffraction analyses.     

Threaded structures based on the recognition of 1,5-dinaphtho-crown ethers to paraquat and vinylogous viologen derivatives: host–guest complexations,X-ray crystal structures,and self-assembly superstructures

Host–guest complexation between two 1,5-dinaphtho-crown ethers and two paraquat derivatives has been studied. By self-assembly of 1,5-dinaphtho-44-crown-12 (DNP44C12) 1 with vinylogous viologen 4, a linear [2]pseudorotaxane array forms in the solid state by PF₆⁻ anion linkages. Moreover, the complexation between 1,5-dinaphtho-50-crown-14 (DNP50C14) 2 and paraquat 3 also leads to the formation of a linear [2]pseudorotaxane superstructure in the solid state driven by π–π stacking.     

Untersuchungen an Polyhalogeniden. XXVII. Über Tetra(n-propyl)ammoniumpolyiodide (n-Pr4N)In mit n = 3, 5, 7: Darstellung und strukturelle Charakterisierung eines Triiodids (n-Pr4N)I3, eines Pentaiodids (n-Pr4N)I5 und eines Heptaiodids (n-Pr4N)I7

Studies of Polyhalides. 27. On Tetra(n-propyl)ammonium Polyiodides (n-Pr₄N)I_n with n = 3, 5, 7: Preparation and Crystal Structures of a Triiodide (n-Pr₄N)I₃, a Pentaiodide (n-Pr₄N)I₅, and a Heptaiodide (n-Pr₄N)I₇ [(n-C₃H₇)₄N]I₃, [(n-C₃H₇)₄N]I₅ and [(n-C₃H₇)₄N]I₇ have been prepared by the reaction of tetra(n-propyl)ammoniumiodide [(n-C₃H₇)₄N]I with iodine I₂ in ethanol. Their crystal structures have been determined by single crystal X-ray diffraction methods. The triiodide is built up from layers of the quarternary ammonium ions n-Pr₄N⁺ and from two independent differently packed centrosymmetric triiodide ions I₃^? which alternate with each other along [100]. The pentaiodide ion forms slightly puckered almost squared nets perpendicular [001] of iodide ions which are connected with four iodine molecules by secondary bonds. The meshes from twelve iodine atoms include the cations. The centrosymmetric Z-shaped heptaiodide ion is built up from a linear symmetric triiodide ion and two iodine molecules forming twisted rope ladders along [001] which are separated by stacks of cations.     

Introducing negative charges into bis-p-phenylene crown ethers: a study of bipyridinium-based [2]pseudorotaxanes and [2]rotaxanes

This paper describes novel host-guest systems comprising viologen cations (guests) and the derivatives of bis-para-phenylene-34-crown-10 (hosts) with anionic groups COO(-) or SO(3)(-). The structure of the resulting charge-compensated host-guest complexes, their association constants and their electrochemical behaviour have been studied. In the solid state, the viologen cations thread the negatively charged crown ethers forming electroneutral zwitterion-like [2]pseudorotaxane salts; in solution this threaded geometry is preserved. The association constants of [2]pseudorotaxane salts incorporating the 1,1'-diethylviologen moiety in solution are significantly higher than those of previously reported analogues. The extrapolated association free energies in non-aqueous media exceed -40 kJ mol(-1) at 25 degrees C. This significant increase of the interaction free energy makes these compounds stable even in aqueous solutions. The association constants of [2]pseudorotaxane salts incorporating sterically more hindered 1,1'-diethyl-3,3'-dimethylviologen moieties are significantly lower. Structurally related [2]rotaxane salts, in which the oppositely charged ionic components are mechanically interlocked, have been prepared in good yields. It has been shown that [2]rotaxane salts incorporating anti-isomers of bisfunctionalised crown ethers are cycloenantiomeric. In both [2]pseudorotaxane and [2]rotaxane salts, the electrostatic interactions between the viologen moieties and the negatively charged crown ethers lead to very significant negative shifts of viologen reduction potentials up to 450 mV. The findings of the present study are valuable for the design of nanoscale molecular electronic devices.     

pH-Switched fluorescent pseudorotaxane assembly of cucurbit[7]uril with bispyridinium ethylene derivatives

¹H NMR spectra and fluorescence analysis revealed that the molecular shuttle and pseudorotaxane assembly of Q[7] with guest G²⁺ can be significantly switched via protonation and deprotonation of the terminal carboxylates of the guest.     

Formation of pseudo[3]rotaxanes containing calix-bis-crowns and secondary ammonium ions and their thermodynamic stabilities in a solution: preorganization by second macrocycle and nonallosteric behavior exhibited by large crown cavities

This Letter describes the formation of pseudo[3]rotaxanes containing calix[4]-bis-crowns, exhibiting a 1,3-alternate conformation and large crown cavities, and secondary ammonium ions. The first and second association constants of pseudo[3]rotaxane formation are moderate (K₁ = 175, K₂ = 100 M⁻¹) and are higher than that of the corresponding pseudo[2]rotaxane (K = 24 M⁻¹), consisting of a calix[4]-mono-crown and the same secondary ammonium ion.     

Energy Transfer and Concentration‐Dependent Conformational Modulation: A Porphyrin‐Containing [3]Rotaxane

A zinc porphyrin‐containing [3]rotaxane A was synthesized through a copper(I)‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction. Energy donors and acceptor porphyrin were introduced to dibenzo[24]crown‐8 (DB24C8) and dibenzyl ammonium (DBA) units of [3]rotaxane A to understand the intramolecular energy transfer process. Investigations of the photophysical properties of [3]rotaxane A demonstrated that the intramolecular efficient energy transfer readily occurred from the donors on the wheels to the porphyrin center on the axis. The fluorescence of energy donors in the region of 400 to 450 nm was efficiently absorbed by the porphyrin acceptor under irradiation at 345 nm, and finally a red light emission at about 600 nm was achieved. Further investigation indicated that the conformation of [3]rotaxane A was self‐modulated by changing its concentration in CH₂Cl₂. The triazole groups on the wheel coordinated or uncoordinated to Zn²⁺ through intramolecular self‐coordination with the change in the concentration of [3]rotaxane A in CH₂Cl₂. Therefore, this conformational change was reversible in a non‐coordinating solvent such as CH₂Cl₂ but inhibited in a coordinating solvent such as THF. Such interesting behaviors were rarely observed in porphyrin derivatives. This self‐modulation feature opens up the possibility of controlling molecular conformation by varying concentration.     

Efficient Intramolecular Energy Transfer between Two Fluorophores in a Bis‐Branched [3]Rotaxane

A bis‐branched [3]rotaxane, with two [2]rotaxane arms separated by an oligo(para‐phenylenevinylene) (OPV) fluorophore, was designed and investigated. Each [2]rotaxane arm employed a difluoroboradiaza‐s‐indacene (BODIPY) dye‐functionalized dibenzo[24]crown‐8 macrocycle interlocked onto a dibenzylammonium in the rod part. The chemical structure of the [3]rotaxane was confirmed and characterized by ¹H and ¹³C NMR spectroscopy and high‐resolution ESI mass spectrometry. The photophysical properties of [3]rotaxane and its reference systems were investigated through UV/Vis absorption, fluorescence, and time‐resolved fluorescence spectroscopy. An efficient energy‐transfer process in [3]rotaxane occurred from the OPV donor to the BODIPY acceptor because of the large overlap between the absorption spectrum of the BODIPY moiety and the emission spectrum of the OPV fluorophore; this shows the important potential of this system for designing functional molecular systems.