pH‐Controlled Reversible Formation of a Supramolecular Hyperbranched Polymer Showing Fluorescence Switching

A π‐conjugated AB₂ monomer 1 with a dibenzo[24]crown‐8 (DB24C8) ring and two secondary amine centres has been synthesised. Treatment of a solution of 1 in dichloromethane with trifluoroacetic acid (TFA) leads to protonation of the amine groups, and then the DB24C8 rings are threaded by the dialkylammonium ion centres of other monomer molecules, leading to the formation of a supramolecular hyperbranched polymer, TFA‐ 1 . Rather strong π–π stacking interactions between the conjugated cores are evident in this polymer. The supramolecular hyperbranched polymer (SHP) can be completely depolymerised by adding a slight excess of N‐tert‐butyl‐N′,N′,N′′,N′′,N′′′,N′′′‐hexamethylphosphorimidic triamide, tetrabutylammonium fluoride, or tetrabutylammonium acetate. The acid–base‐controlled process induces a reversible change in the fluorescence intensities of the solutions due to the controllable presence of the π–π stacking interactions between the conjugated cores. This dynamic behaviour is significant with respect to “smart” supramolecular polymer materials.     

Translational isomerism in a [3]catenane and a [3]rotaxane

[structure: see text] Post-assembly covalent modification using Wittig chemistry of [2]rotaxane ylides, wherein NH(2)(+) centers in the dumbbell-shaped components are recognized by dibenzo[24]crown-8 (DB24C8) rings, has afforded a [3]catenane and a [3]rotaxane with a precise and synthetically prescribed shortage of DB24C8 rings. The nondegenerate pairs of translational isomers present in both of these interlocked molecular compounds provide the fundamental platform on which to construct sensory devices and nanochemomechanical systems.     

Metal-organic rotaxane frameworks; MORFs

Linear exodentate pyridinium ligands such as 1,2-bis(4,4'-bipyridinium)ethane or its bis N-oxide derivative can be used as axles for the formation of [2]pseudorotaxanes utilising 24-membered crown ethers such as dibenzo-24-crown-8 ether (DB24C8) as the wheel. These [2]pseudorotaxanes can be used to construct coordination networks using transition or lanthanide metal ions as the connecting nodes. 1-, 2- and 3D metal-organic rotaxane frameworks (MORFs) are possible. The resulting materials contain mechanically interlocked units and may be the forerunners of unique solids which contain machine-like components in an ordered array.     

Which One is Bulkier: The 3,5‐Dimethylphenyl or the 2,6‐Dimethylphenyl Group? Development of Size‐Complementary Molecular and Macromolecular [2]Rotaxanes

We developed novel size‐complementary molecular and macromolecular rotaxanes using a 2,6‐dimethylphenyl terminal group as the axle‐end‐cap group in dibenzo‐24‐crown‐8‐ether (DB24C8)‐based rotaxanes, where the 2,6‐dimethylphenyl group was found to be less bulky than the 3,5‐dimethylphenyl group. A series of molecular and macromolecular [2]rotaxanes that bear a 2,6‐dimethylphenyl group as the axle‐end‐cap were synthesized using unsubstituted and fluorine‐substituted DB24C8. Base‐induced decomposition into their constituent components confirmed the occurrence of deslipping, which supports the size‐complementarity of these rotaxanes. The deslipping rate was independent of the axle length but dependent on the DB24C8 substituents. A kinetic study indicated the rate‐determining step was that in which the wheel is getting over the end‐cap group, and deslipping proceeded via a hopping‐over mechanism. Finally, the present deslipping behavior was applied to a stimulus‐degradable polymer as an example for the versatile utility of this concept in the context of stimulus‐responsive materials.     

An Interlocked Figure-of-Eight Molecular Shuttle

Here is reported the synthesis and characterization of an interlocked figure-of-eight rotaxane molecular shuttle from a dibenzo-24-crown-8 (DB24C8) derivative. This latter bears two molecular chains, whose extremities are able to react together by click chemistry. One of the two substituting chain holds an ammonium function aimed at driving the self-entanglement through the complexation of the DB24C8 moiety. In the targeted figure-of-eight rotaxane, shuttling of the DB24C8 along the threaded axle from the best ammonium station to the weaker binding site triazolium was performed through deprotonation or deprotonation-then-carbamoylation of the ammonium. This way, two discrete co-conformational states were obtained, in which the folding and size of the two loops could be changed.     

The Mechanical Strength of a Mechanical Bond: Sonochemical Polymer Mechanochemistry of Poly(catenane) Copolymers

Topological molecular connections and structures, including physical entanglements in polymer networks, knots along polymer chains, and rotaxanes in sliding ring gels, have important consequences for the physical properties of polymeric materials. Often these topologies contribute through their ability to bear mechanical stress, but experimental measures of their relative mechanical strength are rare. Here, we use sonochemical polymer mechanochemistry to assess the relative mechanical strength of a multicatenane copolymer relative to copolymers of cyclic and linear analogs. The relative mechanical strengths are obtained by comparing the limiting molecular weights (M_lim) and contour lengths (L_lim) of the polymers under pulsed ultrasound of their dilute solutions. The values of M_lim and L_lim, and thus the inferred mechanical strengths of the polymers, are effectively identical. The mechanical bonds of the catenanes are therefore as strong, or stronger, mechanically as the covalent bonds along the polymer backbone.     

Dimensional dependence of electronic structure of fullerene polymers

Fullerene polymers made of C(60) are systematically investigated by means of a first-principles pseudopotential approach within the local density approximation of the density functional theory. We assume 10 different structures of fullerene polymers. The first three are C(60) polymer networks cross-linked by [2+2] cycloadditional four-membered rings, and the other seven are composed of peanut-shaped fused C(60) polymer chains cross-linked by either seven-membered rings or eight-membered rings. Owing to the overlap of wave functions as well as the hybrid networks of sp(2)-like (3-fold coordinated) and sp(3)-like (4-fold coordinated) carbon atoms, the electronic structure is considerably different from each other. We find that the resulting electronic structure is either semiconductor or semimetal depending on the spatial dimensionality of materials.     

Conductance study of the thermodynamics of ammonium ion complexes with several crown ethers in acetonitrile solution

A conductance study concerning the interaction between ammonium ion and several crown ethers in acetonitrile solution has been carried out at different temperatures. The stability constants of the resulting 11 complexes at various temperatures were determined from the molar conductance-mole ratio data and found to vary in the order DC18C6>18C6>DB30C10>DB21C7>DB24C8>DB18C6>15C5>B15C5. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants. The influence on the thermodynamic data of different parameters such as cavity size and dimensionality of crown ethers, nature of substituents in the polyether ring, conformations of the free and complexed ligands, solvent-ligand interaction and number of N–H bonds available for hydrogen bonding are discussed.     

2]Pseudorotaxanes, [2]rotaxanes and metal-organic rotaxane frameworks containing tetra-substituted dibenzo[24]crown-8 wheels

[2]Pseudorotaxanes, [2]rotaxanes and metal-organic rotaxane framework materials that utilise DB24C8 as the wheel component are well known and structural variations based on changing the axle component are common. Studies in which the DB24C8 wheel is structurally modified are much more limited. Herein, is described the synthesis of symmetrical DB24C8 analogues containing four CH(2)OR (R = CH(2)CH(2)CH(3), CH(2)(C(6)H(5)), C(6)H(5) and C(6)H(4)(4-COOEt)) substituents on the 4 and 5 positions of the aromatic rings. The effect of these molecular appendages on the stability and structures of the interpenetrated and interlocked molecules derived from these new wheels is described. The major effects are an increase in association constants for the formation of [2]pseudorotaxanes relative to DB24C8, the crystal packing of [2]rotaxanes and a change on the internal structure of a 2D MORF (R = C(6)H(5)) compared to DB24C8.     

Conductance study of ammonium complexes with several crown ethers and cryptands in nitrobenzene,acetonitrile and dimethylformamide solutions

The formation of ammonium complexes with several crown ethers and cryptands in nitrobenzene, acetonitrile and dimethylformamide solutions was investigated by conductometry at 25°C. Stability constants of the resulting 1:1 complexes sere determined from the molar conductance-mole ratio data and found to vary in the order DC18C6>18C6>DB30C10>DB21C7>DB24C8>DB18C6>15C5>B15C5>12C4, in the case of crown complexes, and in the order C222>C221>C211>C22>C21 for the ammonium cryptates. The stabilities of the complexes varied inversely with the Gutmann donicity of the solvents. Influences of the number of members in the macrocycle, nature of the substituents in the polyether ring, cavity size and dimensionality, conformations of the free and complexed ligands and number of N⁺–H bonds available for hydrogen bonding are discussed.     

A Multiple‐Responsive Self‐Healing Supramolecular Polymer Gel Network Based on Multiple Orthogonal Interactions

Supramolecular polymer networks have attracted considerable attention not only due to their topological importance but also because they can show some fantastic properties such as stimuli‐responsiveness and self‐healing. Although various supramolecular networks are constructed by supramolecular chemists based on different non‐covalent interactions, supramolecular polymer networks based on multiple orthogonal interactions are still rare. Here, a supramolecular polymer network is presented on the basis of the host–guest interactions between dibenzo‐24‐crown‐8 (DB24C8) and dibenzylammonium salts (DBAS), the metal–ligand coordination interactions between terpyridine and Zn(OTf)₂, and between 1,2,3‐triazole and PdCl₂(PhCN)₂. The topology of the networks can be easily tuned from monomer to main‐chain supramolecular polymer and then to the supramolecular networks. This process is well studied by various characterization methods such as ¹H NMR, UV–vis, DOSY, viscosity, and rheological measurements. More importantly, a supramolecular gel is obtained at high concentrations of the supramolecular networks, which demonstrates both stimuli‐responsiveness and self‐healing properties.

     

Main‐Chain Linear Polyrotaxanes: Synthesis,Characterization, and Conformational Modulation

Two functional main‐chain linear polyrotaxanes, one a covalent polymeric chain that threads through many macrocycles ( P1 ) and the other a poly[n]rotaxane chain that is composed of many repeating rotaxane units ( P2 ), were synthesized by employing strong crown‐ether/ammonium‐based ( DB24C8 / DBA ) host–guest interactions and click chemistry. Energy transfer between the wheel and axle units in both polyrotaxanes was used to provide insight into the conformational information of their resulting polyrotaxanes. Steady‐state and time‐resolved spectroscopy were performed to understand the conformation differences between polymers P1 and P2 in solution. Additional investigations by using dynamic/static light scattering and atomic force microscopy illustrated that polymer P1 was unbending and had a rigid rod‐like structure, whilst polymer P2 was curved and flexible. This flexible topology facilitated the self‐assembly of polymer P2 into relatively large ball‐shaped particles. In addition, the energy transfer between the wheel and axle units was controlled by the addition of specific anions or base. The anion‐induced energy enhancement was attributed to a change in electrostatic interactions between the polymer chains. The base‐driven molecular shuttle broke the DB24C8 / DBA host–guest interactions. These results confirm that both intra‐ and intermolecular electrostatic interactions are crucial for modulating conformational topology, which determines the assembly of polyrotaxanes in solution.     

Conductance Study of the Thermodynamics of Binding of Some Macrocyclic Polyethers with Tl+ Ion in Dimethylformamide-Acetonitrile Mixtures

The complexation reactions between Tl⁺ ion and dibenzo-30-crown-10 (DB30C10), dibenzo-24-crown-8 (DB24C8), dibenzo-21-crown-7 (DB21C7), and aza-18-crown-6 (A18C6) were studied in different dimethylformamide-acetonitrile mixtures at various temperatures. The formation constants of the resulting 1 : 1 complexes were determined from the molar conductance-mole ratio data and found to vary in the order A18C6 > DB30C10 > DB21C7 > DB24C8. The enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants.     

Exploratory,Regression, and Neural Network Analysis of the Stability of Cation Coronates in Selected Pure Solvents

Russian Journal of General Chemistry - Exploratory, regression, and neural network analysis of the stability constants of crown ether [12C4, 16C5, (CH3)216C5, DB21C7, DB24C8, DCH24C8, DB30C10] 1 :...     

Is the tert-butyl group bulky enough to end-cap a pseudorotaxane with a 24-crown-8-ether wheel?

Although rotaxane chemists have long believed that the tert-butyl group is bulkier than the cavity of dibenzo-24-crown-8-ether (DB24C8), it is essentially smaller than the cavity of DB24C8. The tert-butyl (or 4-tert-butylphenyl) group can actually function as an end-cap of DB24C8-based rotaxanes when the intercomponent interaction is effectively operative. When such attractive interaction is removed, deslippage occurs. [structure: see text]     

The influence of macrocyclic polyether constitution upon ammonium ion/crown ether recognition processes

Secondary dialkylammonium (R2NH2+) ions are bound readily by dibenzo[24]crown-8 (DB24C8) to form threaded complexes, namely [2]pseudo-rotaxanes. The effect of replacing one or both of the catechol rings in DB24C8 with resorcinol rings upon the crown ether's ability to bind R2NH2+ ions has now been investigated. When only one aromatic ring is changed from catechol to resorcinol, a crown ether with a [25]crown-8 constitution is created-namely benzometaphenylene[25]crown-8 (BMP25C8). A [2]pseudorotaxane is formed in the solid state when BMP25C8 is co-crystallized with dibenzylammonium hexafluorophosphate, as evidenced by its X-ray crystal structure. Furthermore, this crown ether has been shown to bind R2NH2+ ions in solution, an observation which has been exploited in the synthesis of the first BMP25C8-containing [2]rotaxane. The methodology employed to generate this [2]rotaxane--the reaction of an amine with an isocyanate to form a urea--was tested initially on a system incorporating DB24C8 and was shown to work efficiently. Both [2]rotaxanes have been fully characterized by 1H and 13C NMR spectroscopies, FAB mass spectrometry and X-ray crystallography. Interestingly, the unsymmetrical nature of the dumbbell-shaped component in each of the two [2]rotaxanes renders each face of the encircling macrocyclic polyether diastereotopic, a feature that is apparent upon inspection of their 1H NMR spectra. The resonances associated with the diastereotopic protons on each face of the macrorings are well enough resolved to enable the faces of the crown ethers to be readily identified with respect to their protons by 1H NMR spectroscopy. Unambiguous assignments can be made as a result of the fact that the protons on each face of the macrocyclic polyether experience a unique set of through-space interactions, as evidenced by T-ROESY experiments. Additionally, the two-dimensional NMR analyses are in agreement with the X-ray crystallographic studies performed on these [2]rotaxanes, indicating that the crown ethers are located intimately around the NH2+ centers as expected. Replacement of both catechol rings in the DB24C8 constitution with resorcinol rings results in a crown ether with a [26]crown-8 constitution--namely bismetaphenylene[26]crown-8 (BMP26CS). All the evidence to date points to the fact that this further change in constitution results in a crown ether that does not bind R2NH2+ ions in either the solution or solid states.     

<Superscript>133</Superscript>Cs NMR Study of Cs<Superscript>+</Superscript> Ion Complexes with Dibenzo-24-crown-8, Dicyclohexano-24-crown-8 and Dibenzo-30-crown-10 in Binary Acetonitrile-Nitromethane Mixtures

Complexation of the cesium ion with the macrocyclic ligands: dibenzo-24-crown-8 (DB24C8), dicyclohexano-24-crown-8 (DC24C8) and dibenzo-30-crown-10 (DB30C10) was studied in binary acetonitrile-nitromethane mixtures by ¹³³Cs NMR spectroscopy. The ¹³³Cs chemical shift data indicated that the cesium cation forms 1:1 cation:ligand complexes with DB24C8 and DB30C10 but forms 2:1, 1:1 and 1:2 cation:ligand complexes with DC24C8 in acetonitrile-nitromethane mixtures. The formation constants of the complexes were calculated from the computer fitting of the chemical shift mole ratio data. The results show that the complex formation constants with the Cs⁺ cation vary in the order DC24C8>DB24C8∼DB30C10. It was found that the stability of the resulting complexes increases with increasing nitromethane concentration in the solvent mixture.     

Novel biobased photo‐crosslinked polymer networks prepared from vegetable oil and 2,5‐furan diacrylate

Novel biobased crosslinked polymer networks were prepared from vegetable oil with 2,5‐furan diacrylate as a difunctional stiffener through UV photopolymerization, and the mechanical properties of the resulting films were evaluated. The vegetable oil raw materials used were acrylated epoxidized soybean oil (AESO), acrylated castor oil (ACO), and acrylated 7,10‐dihydroxy‐8(E)‐octadecenoic acid (ADOD). 2,5‐Furan dicarboxylic acid (FDCA), which can be synthesized through the oxidative dehydration of C6 sugars, was identified by the US Department of Energy as one of 12 priority chemicals for establishing the green chemistry industry of the future. 2,5‐Furan dimethanol (bis‐hydroxymethylfuran), which can be derived from FDCA, was used as a starting material to synthesize 2,5‐furan diacrylate, which was used as a biobased comonomer along with AESO, ACO, or ADOD to form photo‐crosslinked polymer networks. The synthesis of acrylate derivatives was confirmed using FT‐IR and ¹H‐NMR spectroscopic techniques. The composition of the reaction mixture was changed to obtain crosslinked polymer networks with various mechanical properties. The addition of 2,5‐furan diacrylate increased the tensile strengths of the polymer films by up to 1.4–4.2 times relative to those obtained without the addition. These fully biobased polymers derived from vegetable oil and sugar can be used as environmentally friendly renewable materials for various applications to replace the existing petroleum‐based polymers currently used. Copyright © 2013 John Wiley & Sons, Ltd.     

烯碳材料改性有机高性能纤维：制备、性能及应用

有机高性能纤维是全球化纤工业的重要发展方向之一。提升现有纤维力学性能的同时研发新型结构功能一体化的纤维对提升我国在航天航空等领域的国际地位具有重要意义。以石墨烯和碳纳米管为代表的烯碳材料具备优异的力、电、热学等性能,可用于改性传统有机高性能纤维。通过制备不同物化性质的烯碳材料并设计合理的改性方式,可将烯碳材料优异的性能传递到传统纤维中,形成具备更高力、电、热学等性能的烯碳材料改性有机高性能纤维。本文首先综述了烯碳材料改性有机高性能纤维的制备方式,包括烯碳材料的分散与功能化、烯碳材料对有机高性能纤维的改性方法,阐述了烯碳材料改性有机高性能纤维的力、电、热学等性能以及烯碳材料的增强机理,进而总结了烯碳材料改性有机高性能纤维的应用,并对其现存的挑战和未来的发展做出展望。     

Chemical and electrochemical formation of pseudorotaxanes composed of alkyl(ferrocenylmethyl)ammmonium and dibenzo[24]crown-8

Protonation of p-xylylaminomethylferrocene (1) and n-hexylaminomethylferrocene (2) by HCl and NH(4)PF(6) forms the ferrocenylmethyl(alkyl)ammonium salt. Inclusion of the compounds by dibenzo[24]crown-8 (DB24C8) produces [2]pseudorotaxanes, [(DB24C8)(1-H)](+)(PF(6)) and [(DB24C8)(2-H)](+)(PF(6)), respectively. X-ray diffraction of the former product indicates an interlocked structure composed of the axis and the macrocyclic molecule. Intermolecular N-H...O and C-H...O interactions and stacking of the aromatic planes are observed. [(DB24C8)(1-H)](+)(PF(6)), in the solid state, is characterized by IR spectroscopy and elemental analyses. A similar reaction of 1,1'-bis(p-xylylaminomethyl)ferrocene (3) forms a mixture of [2] and [3]pseudorotaxanes, [(DB24C8)(3-H(2))](2+)(PF(6))(2) and [(DB24C8)(2)(3-H(2))](2+)(PF(6))(2). The latter product having two DB24C8 molecules is isolated and characterized by X-ray crystallography. Formation of these pseudorotaxanes in a CD(3)CN solution is evidenced by (1)H NMR and mass spectrometry. Electrochemical oxidation of 1-3 at 0.4 V (vs Ag(+)/Ag) in the presence of TEMPOH (1-hydroxy-2,2,6,6-tetramethylpiperidine) and DB24C8 affords the corresponding pseudorotaxanes. The ESR spectrum of the reaction mixture indicates the formation of a TEMPO radical in high yield. Details of the conversion of the dialkylamino group of the ligand to the dialkylammonium group are investigated by using a flow electrolysis method linked to spectroscopic measurements. The proposed mechanism for the reaction involves the ferrocenium species, formed by initial oxidation, which undergoes electron transfer from nitrogen to the Fe(III) center, producing a cation radical at the nitrogen. Transfer of hydrogen from TEMPOH to the cation radical and inclusion of the resulting dialkylammonium species by DB24C8 yields the pseudorotaxanes.