Search results for "Rotaxanes"
showing 10 items of 18 documents
Synthesis of [5]Rotaxanes Containing Bi- and Tridentate Coordination Sites in the Axis
2010
A new example of a linear [5]rotaxane has been synthesized by using the traditional "gathering-and-threading" approach but based on an unusual axle incorporating a symmetrical bis(bidentate) chelating fragment built on a 4,7-phenanthroline core. The stoppering reaction is particularly noteworthy since, instead of using a trivial bulky stopper as precursor to the blocking group, two semistoppered copper-complexed [2]pseudorotaxanes (namely [2]semirotaxanes) are used, which leads to the desired [5]rotaxane in good yield. The efficiency of the method relies on the use of "click" chemistry, with its very mild conditions, and on the protection by a transition-metal (copper(I)) of the various coo…
Photocontrolled On-Surface Pseudorotaxane Formation with Well-Ordered Macrocycle Multilayers.
2016
The photoinduced pseudorotaxane formation between a photoresponsive axle and a tetralactam macrocycle was investigated in solution and on glass surfaces with immobilized multilayers of macrocycles. In the course of this reaction, a novel photoswitchable binding station with azobenzene as the photoswitchable unit and diketopiperazine as the binding station was synthesized and studied by NMR and UV/Vis spectroscopy. Glass surfaces have been functionalized with pyridine-terminated SAMs and subsequently with multilayers of macrocycles through layer-by-layer self assembly. A preferred orientation of the macrocycles could be confirmed by NEXAFS spectroscopy. The photocontrolled deposition of the …
A modular "toolbox" approach to flexible branched multimacrocyclic hosts as precursors for multiply interlocked architectures.
2008
Tetralactam macrocycles can be functionalized by a variety of cross-coupling reactions. A modular “toolbox” strategy is presented that allows 1) several tetralactam macrocycles to be covalently connected with each other or with a central spacer, 2) the macrocycles to be substituted with or connected to different chromophores, and 3) metal-coordination sites to be attached to the macrocycles. With this approach a series of different oligo-macrocyclic hosts was obtained with great structural diversity and enormous potential for further functionalization. Rotaxanes made on the basis of these macrocycles have been synthesized to demonstrate their utility in building more complex supramolecular …
Photoinduced Electron Transfer in Multiporphyrinic Interlocked Structures: The Effect of Copper(I) Coordination in the Central Site
2004
Photoinduced processes have been determined in a [2]catenane containing a zinc(II) porphyrin, a gold(III) porphyrin, and two free phenanthroline binding sites, Zn-Au(+), and in the corresponding copper(I) phenanthroline complex, Zn-Cu(+)-Au(+). In acetonitrile solution Zn-Au(+) is present in two different conformations: an extended one, L, which accounts for 40 % of the total, and a compact one, S. In the L conformation, the electron transfer from the excited state of the Zn porphyrin to the gold-porphyrin unit (k = 1.3x10(9) s(-1)) is followed by a slow recombination (k = 8.3x10(7) s(-1)) to the ground state. The processes in the S conformation cannot be clearly resolved but a charge-separ…
Selectivity of cyclodextrins as a parameter to tune the formation of pseudorotaxanes and micelles supramolecular assemblies. A systematic SANS study
2011
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich. This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively. We studied the formation of polypseudorotaxanes formed with cyclodextrins (CDs) threading a copolymer chain that forms self-assembled structures in water. The size of the CD cavity was chosen such that it is block selective with respect to the formation of inclusion complexes and therefore in terms of altering the structure of the copolymer self-assemblies in a systematic fashio…
Cyclic [2]Pseudorotaxane Tetramers Consisting of Two Rigid Rods Threaded through Two Bis-Macrocycles: Copper(I)-Templated Synthesis and X-ray Structu…
2008
Variously substituted coordinating rigid rods have been synthesized which incorporate a central 4,7-phenanthroline nucleus attached to two 2-pyridyl groups via its 3 and 8 positions, so as to yield bis-bidentate chelates, the two-coordinating axes of the chelates being parallel to one another. Regardless of the nature of the substituents borne by the rods, the copper(I)-induced threading reaction of two such rods through the rings of two bis-macrocycles affords in a quantitative yield the 4-copper(I) threaded assembly. The [2]pseudorotaxane tetramers thus obtained have been fully characterized in solution and, for one of them, an X-ray structure could be obtained, confirming the threaded na…
Ion-Pairing Effects in the Self-Assembly of a Fluorescent Pseudorotaxane
2006
Herein we report on the self-assembly, in a low polarity solvent, of a pseudorotaxane species comprising binaphthyl-26-crown-8 (BN26C8) as the macrocyclic host and anthracenyl-benzylammonium as the threadlike positively charged guest (ABH+). Absorption and luminescence data reveal a very efficient energy transfer process occurring from the binaphthyl to the anthracene singlet excited states. The self-assembly is highly dependent on the nature of the counteranion confirming the crucial role played by it in the competition between the self-assembly process and the formation of ion pairs (ABH+X-). This behavior can be readily evidenced in dilute solutions from the analysis of the luminescence …
Autonomous artificial nanomotor powered by sunlight
2006
Light excitation powers the reversible shuttling movement of the ring component of a rotaxane between two stations located at a 1.3-nm distance on its dumbbell-shaped component. The photoinduced shuttling movement, which occurs in solution, is based on a “four-stroke” synchronized sequence of electronic and nuclear processes. At room temperature the deactivation time of the high-energy charge-transfer state obtained by light excitation is ≈10 μs, and the time period required for the ring-displacement process is on the order of 100 μs. The rotaxane behaves as an autonomous linear motor and operates with a quantum efficiency up to ≈12%. The investigated system is a unique example of an artif…
Pillar[5]arene-Diketopyrrolopyrrole Fluorescent Copolymer: A Promising Recognition and Adsorption Material for Adiponitrile by Selective Formation of…
2017
Conjugated pillar[5]arene-diketopyrrolopyrrole copolymer (P1) is synthesized by the copolymerization of a difunctionalized pillar[5]arene and a diketopyrrolopyrrole-based monomer, which shows large extinction coefficients (1.1 × 104 m-1 cm-1 ) at 519 nm and strong emission at 587 nm. P1 exhibits very strong host-guest binding affinity towards adiponitrile but low binding affinity towards 1,4-dihalobutane and 1,4-bis(imidazol-1-yl)butane. Such an enhanced selectivity is first found in the polypseudorotaxane between pillararene and neutral guests in organic solution and is successfully used for the recognition and adsorption of adiponitrile by the formation of a P1-adiponitrile polypseudorota…
Chelate Cooperativity and Spacer Length Effects on the Assembly Thermodynamics and Kinetics of Divalent Pseudorotaxanes
2011
Homo- and heterodivalent crown-ammonium pseudorotaxanes with different spacers connecting the two axle ammonium binding sites have been synthesized and characterized by NMR spectroscopy and ESI mass spectrometry. The homodivalent pseudorotaxanes are investigated with respect to the thermodynamics of divalent binding and to chelate cooperativity. The shortest spacer exhibits a chelate cooperativity much stronger than that of the longer spacers. On the basis of crystal structure, this can be explained by a noninnocent spacer, which contributes to the binding strength in addition to the two binding sites. Already very subtle changes in the spacer length, i.e., the introduction of an additional…