Synthetic Molecular Motors and Mechanical Machines

The synthesis of four shape‐switchable macrocycles comprising different peripheral substituents is described. The macrocycles 1–4 consist of m‐terphenyl semicircles interlinked by two azo joints. These macrocycles were assembled from nitro‐functionalized m‐terphenyl moieties through reductive dimerization. The semicircles were assembled through Suzuki cross‐coupling reactions. The molecular weights of the macrocycles were determined by vapour pressure osmometry, because mass spectrometry failed in the cases of 2 and 3. The E → Z photoisomerization reactions were analysed by UV/Vis spectroscopy complemented by 1H NMR studies. A very slow thermal back‐reaction indicated considerable stabilization of the Z isomer. The reduced efficiency of the thermal back‐reaction probably arises from the reduced degree of freedom due to the mechanical interlinking of the two azo groups. The photostationary state consisted of all‐Z (85 %) and all‐E isomers (15 %). The E → Z transformation induced by irradiation displayed simple exponential kinetics, which indicates pairwise switching of the two azo groups in a macrocycle, at least on the timescale under investigation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

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“…Usually the cis isomer is thermally less stable, so cis trans thermal isomerization takes place at room temperature in the dark. [49]- [51] …”

Section: Photophysical Properties Of Azo Compoundsmentioning

confidence: 99%

Shape‐Switchable Azo‐Macrocycles

et al. 2009

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“…It has to be admitted that mechanically bonded macromolecules with precisely controlled structures are not yet producible on a gram scale, using routine synthetic procedures. Several comprehensive review articles have been published [15][16][17] on mechanically bonded macromolecules, in addition to the extensive review literature 11,18 now available on MIMs themselves.…”

Section: Introductionmentioning

confidence: 99%

Mechanically bonded macromolecules

et al. 2010

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Mechanically bonded macromolecules constitute a class of challenging synthetic targets in polymer science. The controllable intramolecular motions of mechanical bonds, in combination with the processability and useful physical and mechanical properties of macromolecules, ultimately ensure their potential for applications in materials science, nanotechnology and medicine. This tutorial review describes the syntheses and properties of a library of diverse mechanically bonded macromolecules, which covers (i) main-chain, side-chain, bridged, and pendant oligo/polycatenanes, (ii) main-chain oligo/polyrotaxanes, (iii) poly[c2]daisy chains, and finally (iv) mechanically interlocked dendrimers. A variety of highly efficient synthetic protocols-including template-directed assembly, step-growth polymerisation, quantitative conjugation, etc.-were employed in the construction of these mechanically interlocked architectures. Some of these structures, i.e., side-chain polycatenanes and poly[c2]daisy chains, undergo controllable molecular switching in a manner similar to their small molecular counterparts. The challenges posed by the syntheses of polycatenanes and polyrotaxanes with high molecular weights are contemplated.

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“…1 Nowadays, studies on macroscopic thermal motion of soft matters received attentions from the viewpoint of biomimetics. 2,3 Next key step for soft matters is to create a material whose macroscopic motion is controlled by external 15 stimuli.…”

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confidence: 99%

Macroscopic motion of supramolecular assemblies actuated by photoisomerization of azobenzene derivatives

et al. 2013

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Submillimetre size self-assemblies composed of oleate and azobenzene derivatives show forceful motions such as screwtype coiling-recoiling motion by photoirradiation.In the past half century, many molecular-level machines which 10 change their molecular structure upon exposure to stimuli have been reported. 1 Nowadays, studies on macroscopic thermal motion of soft matters received attentions from the viewpoint of biomimetics. 2,3 Next key step for soft matters is to create a material whose macroscopic motion is controlled by external 15 stimuli. 4 One of the strategies is to create soft materials consisting of subunits sensitive to external inputs, for instance, the photoinduced bending of polymer films consisted of azobenzene derivatives. 5,6 Another strategy is to create soft materials in which macroscopic motions of molecular assemblies 20 are actuated by small amount of molecular machines. 7 To date, there are few reports describing macroscopic mechanical behaviour based on the latter strategy. 8 Here, we report reversible and spatially controlled macroscopic motion of oleate assembles which have submillimetre length. 25Mixtures of oleic acid (1H) and oleate (1 -) ( Fig. 1) are capable of self-assembly in aqueous solution. The morphology of the mixture depends on pH and ionic strength (I). [9][10][11] In I = 0.1 pH 8-10 aqueous media, oleates form vesicles (Fig. 2a). Between pH 7 and 8, they form several complex aggregates called "blocks" that 30 exhibit an inverted hexagonal phase 12 (Fig. 2b). In the transition region, helical and straight multilayer assemblies are coexisted with vesicles and blocks. 11 It is considered that the shape of assembly depends on the ratio of 1H and 1 -in each assembly. According to the microscopic observations of shape and 35 dynamics described in Ref. 11, the helical assemblies are sufficiently flexible to change their macroscopic helical pitch and curvature, but are also elastic because of the highly-ordered stacking structure of oleate molecules in the assembly. As demonstrated in Fig. 3, the helical assemblies exhibit a highly 40 elastic response to mechanical stress. We assumed that this softness and elasticity of the self-assembly is suitable to the spatially moving material in which motion of molecular machine should be propagated.Azobenzene derivatives 2-5 ( Fig. 1) display reversible 2-5 by addition of 70 mM KH 2 PO 4 -K 2 HPO 4 buffer solution (1.0 mL) and sonication for 20 min. A 125 µL aliquot of each suspension containing one of 2-5 was placed in a sealed microscope slide and incubated for 1 day at 25°C. All 60 azobenzene derivatives dissolved into oleate assemblies. The pH range required for formation of helical assemblies was slightly lowered by the addition of 2-5. 14 Helical assemblies were formed when pH 7.3 buffer solution was used as the dispersing medium (the pH of the dispersion was approximately 7.5); pH 65 values of buffer solution higher than 7.3 resulted in vesicle formation, and pH values lower than 7.3 led to the formation of

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Synthetic Molecular Motors and Mechanical Machines

Cited by 2,518 publications

References 1,594 publications

Shape‐Switchable Azo‐Macrocycles

Shape‐Switchable Azo‐Macrocycles

Mechanically bonded macromolecules

Macroscopic motion of supramolecular assemblies actuated by photoisomerization of azobenzene derivatives

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