Showing papers by "J. Fraser Stoddart published in 2000"
TL;DR: The aim of this review is to present a unified view of the field of molecular machines by focusing on past achievements, present limitations, and future perspectives.
Abstract: The miniaturization of components used in the construction of working devices is being pursued currently by the large-downward (top-down) fabrication. This approach, however, which obliges solid-state physicists and electronic engineers to manipulate progressively smaller and smaller pieces of matter, has its intrinsic limitations. An alternative approach is a small-upward (bottom-up) one, starting from the smallest compositions of matter that have distinct shapes and unique properties-namely molecules. In the context of this particular challenge, chemists have been extending the concept of a macroscopic machine to the molecular level. A molecular-level machine can be defined as an assembly of a distinct number of molecular components that are designed to perform machinelike movements (output) as a result of an appropriate external stimulation (input). In common with their macroscopic counterparts, a molecular machine is characterized by 1) the kind of energy input supplied to make it work, 2) the nature of the movements of its component parts, 3) the way in which its operation can be monitored and controlled, 4) the ability to make it repeat its operation in a cyclic fashion, 5) the timescale needed to complete a full cycle of movements, and 6) the purpose of its operation. Undoubtedly, the best energy inputs to make molecular machines work are photons or electrons. Indeed, with appropriately chosen photochemically and electrochemically driven reactions, it is possible to design and synthesize molecular machines that do work. Moreover, the dramatic increase in our fundamental understanding of self-assembly and self-organizational processes in chemical synthesis has aided and abetted the construction of artificial molecular machines through the development of new methods of noncovalent synthesis and the emergence of supramolecular assistance to covalent synthesis as a uniquely powerful synthetic tool. The aim of this review is to present a unified view of the field of molecular machines by focusing on past achievements, present limitations, and future perspectives. After analyzing a few important examples of natural molecular machines, the most significant developments in the field of artificial molecular machines are highlighted. The systems reviewed include 1) chemical rotors, 2) photochemically and electrochemically induced molecular (conformational) rearrangements, and 3) chemically, photochemically, and electrochemically controllable (co-conformational) motions in interlocked molecules (catenanes and rotaxanes), as well as in coordination and supramolecular complexes, including pseudorotaxanes. Artificial molecular machines based on biomolecules and interfacing artificial molecular machines with surfaces and solid supports are amongst some of the cutting-edge topics featured in this review. The extension of the concept of a machine to the molecular level is of interest not only for the sake of basic research, but also for the growth of nanoscience and the subsequent development of nanotechnology.
2,099 citations
TL;DR: In this paper, a solid state, electronically addressable, bistable [2]catenane-based molecular switching device was fabricated from a single monolayer of the [2]-Catenane, anchored with phospholipid counterions, and sandwiched between an n-type polycrystalline silicon bottom electrode and a metallic top electrode.
Abstract: A solid state, electronically addressable, bistable [2]catenane-based molecular switching device was fabricated from a single monolayer of the [2]catenane, anchored with phospholipid counterions, and sandwiched between an n-type polycrystalline silicon bottom electrode and a metallic top electrode. The device exhibits hysteretic (bistable) current/voltage characteristics. The switch is opened at +2 volts, closed at −2 volts, and read at ∼0.1 volt and may be recycled many times under ambient conditions. A mechanochemical mechanism for the action of the switch is presented and shown to be consistent with temperature-dependent measurements of the device operation.
1,241 citations
TL;DR: In this paper, a bottom-up approach for the construction of kleiner maschines is proposed, in which the Molekulare maschine is constructed in a top-down approach.
Abstract: Die zum Bau kleiner Maschinen notwendige Miniaturisierung von Komponenten erfolgt derzeit nach dem Verkleinerungsprinzip (top-down approach). Diesem Ansatz, der Festkorperphysiker und Elektronikingenieure zwingt, mit immer kleineren Materialbausteinen zu arbeiten, sind allerdings Grenzen gesetzt. Eine Alternative besteht im Vergroserungsprinzip (bottom-up approach), bei dem man von den kleinsten Teilen der Materie mit eindeutiger Form und definierten Eigenschaften, den Molekulen, ausgeht. Vor dem Hintergrund dieser Herausforderung haben Chemiker das Konzept der makroskopischen Maschine auf die molekulare Ebene ubertragen. Eine molekulare Maschine kann als eine Anordnung einer definierten Anzahl von molekularen Komponenten definiert werden, die so konzipiert wurden, dass sie als Reaktion auf geeignete externe Stimulation (input) maschinenahnliche Bewegungen ausfuhren (output). Genau wie ihr makroskopisches Gegenstuck ist eine molekulare Maschine durch folgende Merkmale charakterisiert: 1) die Art der Energie, die ihr zugefuhrt werden muss, damit sie funktioniert, 2) die Art der Bewegungen ihrer Komponenten, 3) die Methoden, durch die ihre Funktionen verfolgt und gesteuert werden konnen, 4) die Moglichkeit der cyclischen Wiederholung, 5) die Zeit, die fur die Durchfuhrung eines vollstandigen Arbeitscyclus benotigt wird, und 6) der Zweck ihrer Funktion. Zweifellos sind Photonen oder Elektronen die besten Energielieferanten fur molekulare Maschinen. So ist es moglich, mit sorgfaltig ausgewahlten photochemischen oder elektrochemischen Reaktionen, funktionierende molekulare Maschinen zu entwerfen und zu synthetisieren. Daruber hinaus hat unser rasch angewachsenes, fundamentales Verstandnis uber die Selbstorganisation und die ihr zugrunde liegenden Prozesse in der chemischen Synthese zum Aufbau kunstlicher molekularer Maschinen beigetragen. Dies geschah vor allem durch die Entwicklung neuer Methoden in der nichtkovalenten Synthese und das Aufkommen der supramolekular unterstutzten kovalenten Synthese als ausgesprochen leistungsfahiges Syntheseprinzip. Ziel dieses Ubersichtsartikels ist eine einheitliche Darstellung des Gebiets der molekularen Maschinen, wobei besonderes Augenmerk auf das in der Vergangenheit Erreichte, auf gegenwartig bestehende Grenzen und auf Zukunftsperspektiven gelegt werden soll. Nach der Beschreibung einiger naturlicher molekularer Maschinen werden die wichtigsten Entwicklungen auf dem Gebiet der kunstlichen molekularen Maschinen vorgestellt. Dabei wird auf folgende Systeme naher eingegangen: 1) chemische Rotoren, 2) photochemisch und elektrochemisch induzierte molekulare (konformative) Umlagerungen und 3) chemisch, photochemisch und elektrochemisch steuerbare (cokonformative) Bewegungen in ineinander greifenden (interlocked) Molekulen (Catenanen und Rotaxanen) sowie in Koordinationsverbindungen und supramolekularen Komplexen (darunter Pseudorotaxanen). Kunstliche, auf Biomolekulen basierende molekulare Maschinen und kunstliche molekulare Maschinen, die auf Oberflachen oder festen Tragern aufgebracht wurden, sind zwei der spannenden Entwicklungen, die besprochen werden. Die Erweiterung des Konzepts einer Maschine auf die molekulare Ebene ist nicht nur fur die Grundlagenforschung von Interesse, sondern auch fur die Weiterentwicklung der Nanowissenschaften und der daraus erwachsenden Nanotechnologie.
386 citations
30 Oct 2000
TL;DR: In this article, the authors describe the design and synthesis of organic synthesis in aqueous media, including asymmetric two-center catalysis, and catalytic asymmetric synthesis of natural products.
Abstract: Design and synthesis - theozymes and catalyst design organic synthesis in aqueous media domino reactions asymmetric two-center catalysis organic reactions in supercritical CO2 separation-built-in organic synthesis catalytic asymmetric synthesis of natural products combinatorial libraries architecture, organization and assembly - carbon - from fullerenes to new allotropes dendritic architecture constructive binding and slippage inclusion phenomena molecular organization molecular devices and material properties - molecular wires molecular devices and machines electron and energy transfer crystal engineering nano technology chemical sensors biological aspects - enzyme mimitics enzyme inhibitors organic synthesis and cell biology.
263 citations
TL;DR: The results have demonstrated that photochemically driven switching can be performed successfully by the sacrificial mechanism, whereas, in the case of the intramolecular mechanism, it would appear that the electronic reset of the system is faster than the ring displacement.
Abstract: A molecular-level abacus-like system driven by light inputs has been designed in the form of a [2]rotaxane, comprising the pi-electron-donating macrocyclic polyether bis-p-phenylene-34-crown-10 (BPP34C10) and a dumbbell-shaped component that contains 1) a Ru(II) polypyridine complex as one of its stoppers in the form of a photoactive unit, 2) a p-terphenyl-type ring system as a rigid spacer, 3) a 4,4'-bipyridinium unit and a 3,3'-dimethyl-4,4'-bipyridinium unit as pi-electron-accepting stations, and 4) a tetraarylmethane group as the second stopper. The synthesis of the [2]rotaxane was accomplished in four successive stages. First of all, the dumbbell-shaped component of the [2]rotaxane was constructed by using conventional synthetic methodology to make 1) the so-called "west-side" comprised of the Ru(II) polypyridine complex linked by a bismethylene spacer to the p-terphenyl-type ring system terminated by a benzylic bromomethyl function and 2) the so-called "east-side" comprised of the tetraarylmethane group, attached by a polyether linkage to the bipyridinium unit, itself joined in turn by a trismethylene spacer to an incipient 3,3'-dimethyl-4,4'-bipyridinium unit. Next, 3) the "west-side" and "east-side" were fused together by means of an alkylation to give the dumbbell-shaped compound, which was 4) finally subjected to a thermodynamically driven slippage reaction, with BPP34C10 as the ring, to afford the [2]rotaxane. The structure of this interlocked molecular compound was characterized by mass spectrometry and NMR spectroscopy, which also established, along with cyclic voltammetry, the co-conformational behavior of the molecular shuttle. The stable translational isomer is the one in which the BPP34C10 component encircles the 4,4'-bipyridinium unit, in keeping with the fact that this station is a better pi-electron acceptor than the other station. This observation raises the question- can the BPP34C10 macrocycle be made to shuttle between the two stations by a sequence of photoinduced electron transfer processes? In order to find an answer to this question, the electrochemical, photophysical, and photochemical (under continuous and pulsed excitation) properties of the [2]rotaxane, its dumbbell-shaped component, and some model compounds containing electro- and photoactive units have been investigated. In an attempt to obtain the photoinduced abacus-like movement of the BPP34C10 macrocycle between the two stations, two strategies have been employed-one was based fully on processes that involved only the rotaxane components (intramolecular mechanism), while the other one required the help of external reactants (sacrificial mechanism). Both mechanisms imply a sequence of four steps (destabilization of the stable translational isomer, macrocyclic ring displacement, electronic reset, and nuclear reset) that have to compete with energy-wasteful steps. The results have demonstrated that photochemically driven switching can be performed successfully by the sacrificial mechanism, whereas, in the case of the intramolecular mechanism, it would appear that the electronic reset of the system is faster than the ring displacement.
260 citations
TL;DR: An acyclic polyether 1a, incorporating a central tetrathiafulvalene (TTF) electron donor unit and two 4-tert-butylphenoxy groups at its termini, has been synthesized and the results obtained in acetonitrile solution can be summarized.
Abstract: An acyclic polyether 1a, incorporating a central tetrathiafulvalene (TTF) electron donor unit and two 4-tert-butylphenoxy groups at its termini, has been synthesized. Two macrocyclic polyethers containing two different electron donors, namely a TTF unit with, in one case, a 1,4-dioxybenzene ring (2a), and, in the other case (2b), a 1,5-dioxynaphthalene ring system, have also been synthesized. These two macrocyclic polyethers have been mechanically interlocked in kinetically controlled template-directed syntheses with cyclobis(paraquat-p-phenylene) cyclophane (34+) to afford the [2]catenanes 2a/34+ and 2b/34+, respectively. X-ray crystallography reveals that the [2]catenane 2b/34+ has the TTF unit of 2b located inside the cavity of 34+. The spectroscopic (UV/vis and 1H NMR) and electrochemical properties of compounds 1a, 2a, 2b, 2a/34+, and 2b/34+ and of the [2]pseudorotaxane 1a·34+ were investigated. The absorption and emission properties of the mono- and dioxidized forms of the TTF unit in these various ...
187 citations
TL;DR: In this paper, a V-shaped compound incorporating two bipyridinium units, which emanate from a central hydrophilic core and bear hydrophobic tetraarylmethane-based stoppers at each end, was designed and synthesized.
Abstract: A V-shaped compound incorporating two bipyridinium units, which emanate from a central hydrophilic core and bear hydrophobic tetraarylmethane-based stoppers at each end, was designed and synthesized. In a thermodynamically controlled self-assembly process in solution, either one or two 1,4-dioxybenzene-based macrocyclic polyethers can be slipped over the bulky stoppers of the V-shaped compound, affording either a [2]rotaxane or a [3]rotaxane, respectively. The parent V-shaped compound and the two rotaxanes incorporate two redox-active bipyridinium units that can be reduced reversibly and two redox-active phenoxy groups in the stoppers that can be oxidized irreversibly. Furthermore, these three compounds have amphiphilic character and, as a result, form stable monolayers at the air/water interface. Langmuir−Blodgett monolayers of these compounds were sandwiched between two electrodes to afford molecule-based solid-state switches. In forward bias mode, the I−V characteristics of the junction are reversible,...
132 citations
TL;DR: In this article, a range of secondary dialkylammonium (R2NH2+) ions have been shown to thread through the cavities of appropriately-sized crown ether compounds to afford interwoven complexes.
Abstract: A range of secondary dialkylammonium (R2NH2+) ions has been shown to thread through the cavities of appropriately-sized crown ether compounds to afford interwoven complexes. X-Ray crystallographic investigations to probe the solid-state properties of these supermolecules have revealed that many subtle factors—e.g., solvent of crystallisation, crown ether conformation and anion interactions—can influence the nature of the overall three-dimensional superstructures. Nonetheless, a family of building blocks—namely R2NH2+ ions and crown ethers—can be generated, which constitute a molecular meccano kit. By mixing and matching these modules in different ways, intricate interwoven supramolecular architectures can be constructed. From relatively simple beginnings—where one R2NH2+ ion is threaded through one monotopic crown ether (dibenzo[24]crown-8)—the designed evolution of the building blocks in the molecular meccano kit has led to more elaborate multiply encircled and/or multiply threaded superstructures. The effects of crown ether constitution, macroring size, and both crown ether as well as R2NH2+ ion substitution, upon the solid-state behaviour of these interwoven complexes have also been examined. A statistical analysis of the hydrogen bonding interactions observed in these systems has been carried out. It reveals that a reasonable correlation exists between N+–H⋯O bond angle and H⋯O bond length. The correlation between C–H⋯O bond angle and H⋯O distance is poor, suggesting that C–H⋯O hydrogen bonding interactions are of secondary importance in determining the co-conformations adopted by these supermolecules.
120 citations
111 citations
TL;DR: Two new [2]rotaxane-based molecular shuttles, in which a mechanically bound dibenzo[24]crown-8 (DB24C8) macroring shunts back and forth between two dialkylammonium recognition sites situated on a chemical dumbbell, have been constructed by a novel synthetic strategy that relies upon the use of the tert-butoxycarbonyl (Boc) protecting group.
Abstract: Two new [2]rotaxane-based molecular shuttles, in which a mechanically bound dibenzo[24]crown-8 (DB24C8) macroring shunts back and forth between two dialkylammonium recognition sites situated on a chemical dumbbell, have been constructed by a novel synthetic strategy that relies upon the use of the tert-butoxycarbonyl (Boc) protecting group. During the syntheses of both molecular shuttles, this protecting group masks a dialkylammonium recognition center which is liberated only after the [2]rotaxane constitution is established. In both cases, the molecular shuttles' other dialkylammonium center is essential for the rotaxane-forming reactions and it ensures that DB24C8 is interpenetrated by threadlike precursors, as a result of noncovalent bonding interactions, to produce [2]pseudorotaxanes which are stoppered subsequently through 1,3-dipolar cycloadditions between azides and bulky acetylenedicarboxylates. The new molecular shuttles have been examined by means of dynamic 1H NMR spectroscopy, which reveals th...
97 citations
TL;DR: The reversible nature of the imine bond formation in CDCl(3) solution has been exploited to exchange substituted for unsubstituted m-phenylenediamine units in hemicarcerand octaimines and acid-catalyzed imine exchange has been shown to provide a novel mechanism whereby ferrocene can be released as an entrapped guest from the hemicarceplex.
TL;DR: Two ammonium ion/crown ether-based [2]rotaxane monomers-each incorporating a dumbbell-shaped component, possessing an exchangeable benzylic triphenylphosphonium stopper, and a ring component bearing an aldehyde function-undergo a sequence of Wittig reactions.
TL;DR: In this article, the optimal ratio of phospholipid to [2] catenane for good Langmuir film formation was determined using Π−A isotherms and isochore measurements.
Abstract: The formation of Langmuir films comprised of (i) dimyristoylphosphatidic acid and a [2]catenane composed of a bisparapheylene-34-crown-10 with its two π-electron-rich hydroquinone rings and the π-electron-deficient cyclophane bis(paraquat-p-phenylene) and (ii) dimyristoylphosphatidic acid and a [2]catenane composed of a macrocyclic polyether containing two hydroquinone rings and an azobenzene unit and the π-electron-deficient cyclophane bis(paraquat-p-phenylene), has been acheived. Utilizing Π−A isotherms and isochore measurements, it is possible to determine the optimum ratio of phospholipid to [2]catenane for good Langmuir film formation and to interpret these experimental findings in terms of intermolecular π−π interactions between the [2]catenane tetracations in the Langmuir films. They have been transferred via the Langmuir−Blodgett technique to hydrophobized quartz supports, and, through a combination of UV−vis spectroscopy and small-angle X-ray scattering (SAXS), it has been established that the La...
TL;DR: 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 and the evidence to date points to the fact that this further change in constitution results in a crown ether that does not bind R 2NH2- ions in either the solution or solid states.
Abstract: 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.
TL;DR: Using dynamic light scattering and nuclear magnetic resonance, it was shown that addition of bis-dibenzylammonium dication initiates aggregation of the silver nanocrystal dispersion by pseudorotaxane assembly.
Abstract: Near size-monodisperse silver nanocrystals stabilized by chemisorption of a mixture of an alkane thiol (85%) and an alkane thiol incorporating a dibenzo-24-crown-8 moiety (15%) have been prepared. Using dynamic light scattering and nuclear magnetic resonance, it is shown that addition of bis-dibenzylammonium dication initiates aggregation of the silver nanocrystal dispersion by pseudorotaxane assembly. It is also shown that addition of excess dibenzylammonium cation or dibenzo-24-crown-8 inhibits further aggregation. This novel demonstration of controlled nanocrystal aggregation points the way toward the programmed assembly of complex nanocrystal architectures in solution.
TL;DR: In this article, the tetracationic cyclophanes cyclobis(paraquat-p-phenylene) and cyclobimax-piphenylene have been used to construct stable electrostatically-linked superstructures of 13 nm Au-colloids.
TL;DR: In this paper, two dumbbell-shaped compounds (8 and 11) were synthesized, each composed of two polyether chains intercepted by a 1,4-dioxybenzene recognition site, terminated by tetraarylmethane-based stoppers, and emanating from a central 9,10- or a 2,6-dioxyanthracene unit.
TL;DR: A rotaxane-like complex, based on a dumbbell-shaped component containing an NH(2)(+) recognition site for a [25]crown-8 ring component and a slippage stopper in the form of a p-(tert-butyl)phenyl group, has been synthesized by a "threading-followed-by-stoppering" approach.
TL;DR: Dipyrido[24]crown-8 (DP24C8) has been synthesized and shown to form [2]pseudorotaxanes spontaneously with dibenzylammonium ions, which have been demonstrated by (1)H NMR spectroscopy to form faster in solution than when the macrocyclic polyether is dibanzo[24].
TL;DR: In the solid state, the macrocyclic polyether, tetrabenzo[24]crown-8 (TB24C8), is an interesting molecule as discussed by the authors.
TL;DR: In this article, three [3] catenanes with cavities large enough to accommodate aromatic guests have been designed and synthesized by means of kinetically controlled self-assembly processes.
Abstract: Three [3]catenanes with cavities large enough to accommodate aromatic guests have been designed and synthesized (yields=5–20 %) by means of kinetically controlled self-assembly processes. The X-ray structural analysis of one of three [3]catenanes confirmed the presence of a rectangular cavity (dimensions=7×11 A) lined by π-electron-rich recognition sites and hydrogen-bond acceptor groups. In spite of their apparently ideal recognition features, none of these [3]catenanes bind guests incorporating a π-electron-deficient bipyridinium unit. However, the template-directed syntheses of the [3]catenanes also produce, in yields of 2–23 %, [2]catenanes incorporating a 1,5-dioxynaphtho[38]crown-10 interlocked with a bipyridinium-based tetracationic cyclophane. The X-ray structural analyses of two of these [2]catenanes revealed that a combination of [π⋅⋅⋅π] and [C−H⋅⋅⋅π] interactions is responsible for the formation of supramolecular homodimers in the solid state. 1H NMR spectroscopic investigations of the four [2]catenanes demonstrated that supramolecular homodimers are also formed (Ka=17–31 M−1, T=185 K) in (CD3)2CO solutions. Dynamic 1H NMR spectroscopy revealed that the 1,5-dioxynaphtho[38]crown-10 and tetracationic cyclophane components in the four [2]catenanes and in the three [3]catenanes circumrotate (ΔGc≠=9-14 kcal mol−1) through each other's cavity in (CD3)2CO. Similarly, the 1,5-dioxynaphthalene and the bipyridinium ring systems rotate (ΔGc≠=10-14 kcal mol−1) about their [O⋅⋅⋅O] and [N⋅⋅⋅N] axes, respectively, in solution.
TL;DR: A dicationic benzylammonium guest threads through the crown ether pendants and the resulting noncovalent, self-assembled pseudorotaxane complex is both stable and has optical properties dependant on temperature.
Abstract: Natural peptide spine and artificial crown ether are blended together to form a hybrid structure. A dicationic benzylammonium guest threads through the crown ether pendants and the resulting noncovalent, self-assembled pseudorotaxane complex, shown schematically in the picture, is both stable and has optical properties dependant on temperature.
TL;DR: The stabilities and complexation kinetics associated with these pseudorotaxanes depend markedly on the nature of the substituents situated on the phenyl rings of the DBA+ ions.
TL;DR: The host-guest adducts display absorption bands in the visible spectral region, characteristic of charge-transfer interactions, and reversible decomplexation/recomplexation takes place upon electrochemical oxidation/reduction of the ferrocene-based unit or upon reduction/oxidation of the tetracationic cyclophane.
Abstract: The tetracationic cyclophane, cyclobis(paraquat-4,4‘-biphenylene), binds 1,1‘-disubstituted ferrocene-based polyethers as a result of (i) [π...π] stacking between the π-electron-deficient bipyridinium units and the π-electron-rich cyclopentadienyl rings and (ii) [C−H...O] hydrogen bonds between the α-bipyridinium hydrogen atoms and the polyether oxygen atoms. However, even the presence of a bulky tetraarylmethane groupwhich is too large to thread through the cavity of the cyclophane hostat the end of each of the two polyether substituents of the ferrocene-containing guest does not discourage adduct formation of the inclusion type. Thus, in these adducts, the ferrocene unit of the guest is located inside the cavity of the host with its two polyether chains protruding outward from the same side of the host. The alternative pseudorotaxane geometry is not observed in solutions of these 1:1 adducts. The host−guest adducts display absorption bands in the visible spectral region, characteristic of charge-transfe...
TL;DR: A linear bis secondary dialkylammonium ion-containing scaffold-based upon an anthracenyl core-has been synthesized and it has been demonstrated that it is possible to dock either one or two dibenzo[24]crown-8 (DB24C8) macrocycles onto this scaffold to afford either a [2]- or [3]pseudorotaxane, respectively.
TL;DR: In this paper, a supramolecular homodimer is formed in solution and in the solid state by a self-complementary catenane incorporating a 1,5-dioxynaphthalene-based macrocyclic polyether interlocked with a bipyridinium-based tetracationic cyclophane.
Abstract: A supramolecular homodimer is formed in solution and in the solid state by a self-complementary [2]catenane incorporating a 1,5-dioxynaphthalene-based macrocyclic polyether interlocked with a bipyridinium-based tetracationic cyclophane (shown schematically). This unique example of self-recognition is the result of a combination of cooperative pi small middle dot small middle dot small middle dotpi and C-H small middle dot small middle dot small middle dotpi interactions.