Self-assembly and thermodynamic synthesis of rotaxane dendrimers and related structures

Leung, Ken Cham‐Fai; Lau, Kwun‐Ngai

doi:10.1039/b9py00380k

Cited by 51 publications

(28 citation statements)

References 142 publications

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“…The 1 H NMR spectra of these dendrimers, especially G 3 and G 4 , showed no proton signals from the terminal acetylenes that would signal structural defects formed during the growth processes. The peaks ascribed to the protons on the linear axle of the rotaxanes were located in a range (below 0.0 ppm) similar to that of [2]rotaxane precursor 1. This result indicates that the structure of the rotaxane was not destroyed during the growth process.…”

Section: Significancementioning

confidence: 71%

“…The rotaxane building blocks must be stable enough to handle and incorporate repeatedly during the growth processes. We used organometallic [2] rotaxane 1 (Fig. 2) as the basic precursor for the divergent dendrimer growth for the following reasons: (i) 1 can be quickly synthesized by using Ogoshi's available pillar [5]arene and its neutral alkyl chain guest (20)(21)(22); (ii) 1 contains a platinum-acetylide unit that prevents the macrocycle from escaping the thread; (iii) 1 can react with a free alkyne to generate a stable organometallic bond in good yield under mild conditions (23)(24)(25); (iv) 1 contains protected alkynes that can be gently exposed for dendrimer growth; and…”

Section: Resultsmentioning

confidence: 99%

“…The building block 1 proved stable and soluble in common solvents during the dendrimer growth processes. Unlike classic charged rotaxane systems that are constructed by incorporating either charged macrocyclic wheels or axles, organometallic [2]rotaxane 1 is neutral, which simplifies the subsequent reaction and purification processes. The growth processes relied on a Cu(I)-catalyzed coupling reaction of 1 with the corresponding polyacetylene precursors.…”

Section: Significancementioning

confidence: 99%

“…We synthesized organometallic [2]rotaxane 1 in a few steps, as indicated in SI Appendix, Scheme S1. The rotaxane formation step proceeded in good yield (86%) from three components and allowed the preparation of 1 on gram scales.…”

Section: Significancementioning

confidence: 99%

“…D endritic molecules containing rotaxane components are a recently developed subset of mechanically bonded supermolecules (1)(2)(3). The combination of the characteristics of both rotaxanes (sliding and rotary motion) and dendrimers (repetitive branching with each generation) provides the resultant rotaxane dendrimers with unusual topological features and potentially useful properties.…”

mentioning

confidence: 99%

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Organometallic rotaxane dendrimers with fourth-generation mechanically interlocked branches

Wang

Chen

Wang

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

136

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Mechanically interlocked molecules, such as catenanes, rotaxanes, and knots, have applications in information storage, switching devices, and chemical catalysis. Rotaxanes are dumbbell-shaped molecules that are threaded through a large ring, and the relative motion of the two components along each other can respond to external stimuli. Multiple rotaxane units can amplify responsiveness, and repetitively branched molecules-dendrimers-can serve as vehicles for assembly of many rotaxanes on single, monodisperse compounds. Here, we report the synthesis of higher-generation rotaxane dendrimers by a divergent approach. Linkages were introduced as spacer elements to reduce crowding and to facilitate rotaxane motion, even at the congested periphery of the compounds up to the fourth generation. The structures were characterized by 1D multinuclear ( 1 H, 13 C, and 31 P) and 2D NMR spectroscopy, MALDI-TOF-MS, gel permeation chromatography (GPC), and microscopy-based methods including atomic force microscopy (AFM) and transmission electron microscopy (TEM). AFM and TEM studies of rotaxane dendrimers vs. model dendrimers show that the rotaxane units enhance the rigidity and reduce the tendency of these assemblies to collapse by self-folding. Surface functionalization of the dendrimers with ferrocenes as termini produced electrochemically active assemblies. The preparation of dendrimers with a well-defined topological structure, enhanced rigidity, and diverse functional groups opens previously unidentified avenues for the application of these materials in molecular electronics and materials science.rotaxane dendrimer | controllable divergent approach | platinum acetylide | surface modification | dynamic supramolecular systems D endritic molecules containing rotaxane components are a recently developed subset of mechanically bonded supermolecules (1-3). The combination of the characteristics of both rotaxanes (sliding and rotary motion) and dendrimers (repetitive branching with each generation) provides the resultant rotaxane dendrimers with unusual topological features and potentially useful properties. For example, the introduction of stimuli-responsive rotaxanes (4) such as muscle-like bistable rotaxanes or daisy chains can impart switchable features to the resultant dendrimers that are "smart" to external inputs. The applications of dendrimers in materials science (5, 6) suggest that rotaxane dendrimers could serve as supramolecular dynamic materials.A variety of rotaxane dendrimers have been designed and constructed over the past few years. For examples, mechanically interlocked units were used either as cores or end groups, by Vögtle and coworkers (7), Stoddart and coworkers (8-13), Gibson et al. (14), Kim and coworkers (15,16), and Kaifer and coworkers (17,18). Compared with these simpler systems, rotaxane dendrimers with interlocking ring components on the branches or at the branch points are rare. Specifically, Kim et al. (16) and Leung et al. (19) have reported the only two cases of rotaxane branched dendrimers u...

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Section: Significancementioning

confidence: 71%