Organometallic Rotaxane Dendrimers with Fourth-Generation Mechanically Interlocked Branches

Organometallic rotaxane dendrimers with fourth-generation mechanically interlocked branches

Wei Wanga, Li-Jun Chena, Xu-Qing Wanga, Bin Suna,b, Xiaopeng Lib, Yanyan Zhangc, Jiameng Shic, Yihua Yuc, Li Zhangd, Minghua Liud, and Hai-Bo Yanga,1

aShanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, People’s Republic of China; bDepartment of Chemistry and Biochemistry, Texas State University, San Marcos, TX 78666; cShanghai Key Laboratory of Magnetic Resonance, Department of Physics, East China Normal University, Shanghai 200062, People’s Republic of China; and dKey Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100080, People’s Republic of China

Edited by Vivian Wing-Wah Yam, The University of Hong Kong, Hong Kong, China, and approved March 31, 2015 (received for review January 11, 2015) Mechanically interlocked molecules, such as catenanes, rotaxanes, Herein, we describe the synthesis, characterization, and func- and knots, have applications in information storage, switching tionalization of higher-generation (up to fourth-generation) organ- devices, and chemical catalysis. Rotaxanes are dumbbell-shaped ometallic rotaxane branched dendrimers. A divergent strategy was molecules that are threaded through a large ring, and the relative employed for the dendrimer synthesis in which the host–guest motion of the two components along each other can respond to complex of a pillar[5]arene and a neutral alkyl chain were used as external stimuli. Multiple rotaxane units can amplify responsiveness, the rotaxane subunits. The formation of platinum–acetylide bonds — — and repetitively branched molecules dendrimers can serve as vehi- wasthegrowthstepinthesynthesis;it produced satisfactory yields cles for assembly of many rotaxanes on single, monodisperse com- and allowed construction of the targeted structures. The introduction pounds. Here, we report the synthesis of higher-generation rotaxane of macrocyclic wheels enhanced the rigidity of the resultant rotaxane dendrimers by a divergent approach. Linkages were introduced as dendrimers and reduced self-folding. Electrochemically active spacer elements to reduce crowding and to facilitate rotaxane motion, rotaxane dendrimers substituted with different numbered ferrocenes even at the congested periphery of the compounds up to the fourth generation. The structures were characterized by 1D multinuclear (1H, were also prepared by direct surface modification. 13 31 C, and P) and 2D NMR spectroscopy, MALDI-TOF-MS, gel perme- Results and Discussion ation chromatography (GPC), and microscopy-based methods in- Synthesis. cluding atomic force microscopy (AFM) and transmission electron To synthesize rotaxane branched dendrimers, the microscopy (TEM). AFM and TEM studies of rotaxane dendrimers mechanically interlocked functions must be repeating subunits of vs. model dendrimers show that the rotaxane units enhance the the targeted structures. The rotaxane building blocks must be rigidity and reduce the tendency of these assemblies to collapse stable enough to handle and incorporate repeatedly during the by self-folding. Surface functionalization of the dendrimers with growth processes. We used organometallic [2] rotaxane 1 (Fig. 2) ferrocenes as termini produced electrochemically active assemblies. as the basic precursor for the divergent dendrimer growth for CHEMISTRY The preparation of dendrimers with a well-defined topological the following reasons: (i) 1 can be quickly synthesized by using structure, enhanced rigidity, and diverse functional groups opens Ogoshi’s available pillar[5]arene and its neutral alkyl chain guest previously unidentified avenues for the application of these mate- (20–22); (ii) 1 contains a platinum–acetylide unit that prevents rials in molecular electronics and materials science. the macrocycle from escaping the thread; (iii) 1 can react with a free alkyne to generate a stable organometallic bond in good rotaxane dendrimer | controllable divergent approach | platinum yield under mild conditions (23–25); (iv) 1 contains protected acetylide | surface modification | dynamic supramolecular systems alkynes that can be gently exposed for dendrimer growth; and

endritic molecules containing rotaxane components are a Significance Drecently developed subset of mechanically bonded super- – molecules (1 3). The combination of the characteristics of both In this study, the preparation of organometallic rotaxane den- rotaxanes (sliding and rotary motion) and dendrimers (repetitive drimers with a well-defined topological structure and enhanced branching with each generation) provides the resultant rotaxane rigidity was developed. Starting from a simple rotaxane building dendrimers with unusual topological features and potentially use- block, high-generation rotaxane branched dendrimers were syn- ful properties. For example, the introduction of stimuli-responsive thesized and characterized. The fourth-generation structure de- rotaxanes (4) such as muscle-like bistable rotaxanes or daisy chains scribed is among the highest-generation organometallic rotaxane can impart switchable features to the resultant dendrimers that are dendrimers reported to date. The introduction of pillar[5]arene “smart” to external inputs. The applications of dendrimers in rotaxane units activates dynamic features in the dendrimer and materials science (5, 6) suggest that rotaxane dendrimers could enhances the rigidity of each branch of the supermolecules. This serve as supramolecular dynamic materials. research offers a facile approach to the construction of high-gen- A variety of rotaxane dendrimers have been designed and con- eration rotaxane branched dendrimer, which not only enriches the structed over the past few years. For examples, mechanically library of rotaxne dendrimer but also provides the further insight interlocked units were used either as cores or end groups, by Vögtle into their applications as supramolecular dynamic materials. and coworkers (7), Stoddart and coworkers (8–13), Gibson et al. (14), Kim and coworkers (15, 16), and Kaifer and coworkers (17, Author contributions: W.W. and H.-B.Y. designed research; W.W., L.-J.C., X.-Q.W., B.S., X.L., Y.Z., J.S., Y.Y., L.Z., and M.L. performed research; W.W. contributed new reagents/ 18). Compared with these simpler systems, rotaxane dendrimers analytic tools; W.W., X.L., and H.-B.Y. analyzed data; and W.W., X.L., and H.-B.Y. wrote with interlocking ring components on the branches or at the branch the paper. points are rare. Specifically, Kim et al. (16) and Leung et al. (19) The authors declare no conflict of interest. have reported the only two cases of rotaxane branched dendrimers This article is a PNAS Direct Submission. up to the second generation. Third- or higher-generation rotaxane 1To whom correspondence should be addressed. Email: [email protected]. dendrimers equipped with mechanically interlocked functions on This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. the branches (Fig. 1) are unknown to us. 1073/pnas.1500489112/-/DCSupplemental.

www.pnas.org/cgi/doi/10.1073/pnas.1500489112 PNAS | May 5, 2015 | vol. 112 | no. 18 | 5597–5601 Downloaded by guest on October 6, 2021 1,each31P NMR spectrum of the rotaxane dendrimers displayed a downfield shift (Δδ ’ 2.4 ppm), which also supports the formation of platinum–acetylide bonds during dendrimer growth. As in the 1H NMR spectra, different chemical shifts were observed for Rotaxane the phosphine ligands in each generation in the growth of the rotaxane dendrimers, indicating the nonequivalent chemical en- vironment of the phosphorous ligands (SI Appendix, Fig. S80). MALDI-TOF-MS studies were performed on all of the rotaxane dendrimers. The spectra provided direct support for the formation of mechanically interlocked compounds (Fig. 4). For the first-generation rotaxane dendrimer G1, the MALDI-TOF-MS spectrum in reflectron mode exhibited a single peak at m/z = 6,661.5, which was + Rotaxane Dendrimer attributed to [G1 + H] with a theoretical monoisotopic mass at 6,661.9 Da. This peak was isotopically resolved and agreed well with Dendrimer the theoretical distribution. The corresponding peaks were also observed in the MS spectra of the higher-generation rotaxane den- Fig. 1. Schematic representation of a rotaxane dendrimer with mechan- drimers G2 and G3, confirming the synthesis of the targeted ically interlocked moieties incorporated on the branches. compounds. [With increasing molecular weight (for G2, theoretical average Mr = 18,760 Da; for G3, theoretical average Mr = 42,948 v 1 Da), the peaks became broader, with a rational deviation from the ( ) has active alkyne units that can be functionalized to impart theoretical mass in linear acquisition mode. This broadening effect further structural diversity and function. was attributed to the binding of sodium and potassium ions to large We synthesized organometallic [2]rotaxane 1 in a few steps, SI Appendix rotaxane dendrimers, along with the proton signals.] For these high- as indicated in ,SchemeS1. The rotaxane formation step generation architectures, high charge states, i.e., 2+ and/or 3+, were proceeded in good yield (86%) from three components and allowed also observed in MALDI-TOF-MS in addition to singly charged the preparation of 1 on gram scales. The building block 1 proved ions, as shown in Fig. 4 B and C. In the MS spectrum of G3,some stable and soluble in common solvents during the dendrimer growth fragments were observed. Further experiments with stronger laser processes. Unlike classic charged rotaxane systems that are con- power showed that the MS spectrum of G3 produced a higher structed by incorporating either charged macrocyclic wheels or axles, abundance of fragments (SI Appendix,Fig.S40). This indicates that organometallic [2]rotaxane 1 is neutral, which simplifies the sub- such additional peaks may be attributed to the fragments induced in sequent reaction and purification processes. The growth processes either MALDI source or ionization processes (26). For the fourth- relied on a Cu(I)-catalyzed coupling reaction of 1 with the corre- generation rotaxane dendrimer G4, neither MALDI-TOF nor elec- sponding polyacetylene precursors. During this reaction, the bulky trospray ionization-MS provided satisfactory mass data because of phosphine ligands remained inert and the rotaxane remained intact. M = 1 the high molecular mass (theoretical average r 91,254 Da) and Following production of the building block , the divergent G growth of organometallic dendrimers was carried out by in- low ionization efficiency of 4. A gel permeation chromatography (GPC) analysis of G3 and G4 revealed narrow distributions for the corporating mechanically interlocked rotaxanes on the branches M (Fig. 3). The Cu(I)-catalyzed coupling reaction of 1 and 1,3,5-trie- number-averaged molecular weight ( n) and the polydispersity in- dex (PDI) (for G3,PDI= 1.07; for G4,PDI= 1.09; SI Appendix,Figs. thynylbenzene produced the first-generation rotaxane dendrimer G1 S81 and S82). The Mn values clearly increased for each dendrimer at a yield of 79%, where six protected alkynes were located at the G M = G M = A G generation (for 3, n 32,440; for 4, n 48,022), as expected outer periphery of the compound (Fig. 3 ). Deprotection of 1 G with tetrabutylammonium fluoride produced the corresponding for the existence of the fourth-generation rotaxane dendrimer 4. dendrimer G1-YNE, in an 87% yield, which bore six acetylene The “Rotaxane Effect.” The effect of introducing rotaxane units groups. These groups were used to grow the next generation: The into the dendrimers (the “rotaxane effect”) was investigated by coupling of G1-YNE and 1 produced the second-generation rotax- preparing model organometallic dendrimers Gn-c (n = 1, 2, 3) ane dendrimer G2 with nine pillar[5]arene-based rotaxanes on the without pillar[5]arene wheels using a parallel approach (SI Ap- branches in 58% yield. The third- and fourth-generation rotaxane G G pendix, Scheme S2). The absence of the pillar[5]arene wheels dendrimers ( 3 and 4, respectively) were prepared via sequential G -c deprotection−coupling processes, as shown in Fig. 3B. The fourth- resulted in reduced solubility of n in common solvents G (chloroform and THF); the third-generation model dendrimer generation rotaxane dendrimer 4, can be considered as a highly G -c branched [46]rotaxane: 45 rotaxanes located in a dendrimer skele- 3 was the highest-generation dendrimer that could be synthesized. We used electron microscopy methods such as atomic ton of monodisperse distribution. All of the dendrimers G1−G4 were soluble in common solvents such as chloroform, dichloro- force microscopy (AFM) and transmission electron microscopy methane, and THF. The purification of these dendrimers was per- (TEM), to visualize individual supramolecular dendrimers as formed using flash column chromatography and recrystallization.

Rotaxane Dendrimer Characterization. The 1H NMR spectra of these dendrimers, especially G3 and G4, showed no proton signals from the terminal acetylenes that would signal structural Facile and scalable preparation defects formed during the growth processes. The peaks ascribed to the protons on the linear axle of the rotaxanes were located in Neutrality a range (below 0.0 ppm) similar to that of [2]rotaxane precursor Excellent stability and solubility 1 1 . This result indicates that the structure of the rotaxane was not Synthesized in 0.55 g batches in 86% yield destroyed during the growth process. More than one set of peaks Synthesized in 2.07 g batches in 80% yield React ive end sites for dendrimer growth corresponding to the threaded structures was observed for each subsequent generation. In other words, the rotaxane subunits were located on different branches and were nonequivalent Fig. 2. Chemical structure of organometallic [2]rotaxane 1, a key building (SI Appendix, Fig. S79). Compared with [2]rotaxane precursor block in the preparation of the rotaxane dendrimers.

5598 | www.pnas.org/cgi/doi/10.1073/pnas.1500489112 Wang et al. Downloaded by guest on October 6, 2021 A absence of rotaxane subunits. (Note that the rotaxane dendrimers were not completely spherical in solution, and the samples usually exhibited shrinkage on the surface because of solvent loss, which resulted in the measurement of different

CuI, Et2NH, rt, 12h dendrimer sizes using the aforementioned three types of tech- niques. These results are reasonable according to previous re- 79% ports. For example, see ref. 28.) We also used 2D diffusion-

G1 ordered NMR spectroscopy to evaluate the size (hydrodynamic diameter) of the dendrimers in solution. The introduction of the pillar[5]arene wheels resulted in a decrease in the measured weight- averaged diffusion coefficients (D). For example, under the same B conditions, the diffusion coefficient of the rotaxane dendrimer G3 − was found to be 5.83 × 10 11 m2/s, which was significantly smaller −10 2 I II than that of the model dendrimer G3-c (2.19 × 10 m /s). These results support a structural role for the rotaxane subunits G that enhances the rigidity of the branches and the integrated den- 1 G2 drimers. This “rotaxane effect” may also impart stability in their laser G3 desorption/ionization processes in the MALDI-TOF-MS spectra. For instance, under the same characterization conditions, the G1 + exhibited a complete and single molecular ion peak [G1+H] , : (I) (a) TBAF, THF, whereas the corresponding model G1-c displayed additional peak rt. 12h, 87%; (b) CuI, ,EtNH, rt, 12h, 1 2 fragments attributed to degradation of the dendrimer skeleton (see III 58%; (II) ) (a) TBAF, THF, rt. 12h, 67%; SI Appendix G1 SI Appendix G1-c (b) CuI, 1,Et2NH, rt, 12h, 49%; (II) ) (a) ,Fig.S21for and ,Fig.S53for ). TBAF, THF, rt. 12h, 63%; (b) CuI, 1, Et NH, rt, 12h, 83%; 2 Surface Modification. A subsequent study was performed in which the new dendrimers were subjected to surface modification (29)

G4 + [G1+H] Fig. 3. (A) Synthesis of organometallic rotaxane dendrimers G1 by a CuI- A catalyzed coupling reaction of 1 and 1,3,5-triethynylbenzene; (B) schematic of a controllable divergent approach for the synthesis of organometallic

rotaxane dendrimers G2–G4.

described by others (27). These methods can provide structural CHEMISTRY parameters of dendrimers such as their size, conformation, and 6661.5 rigidity, using direct images on a surface. The AFM analysis of G −G 1 4 showed that the average heights gradually increased with 6658 6666 6674 m/z each generation of the rotaxane dendrimers (’1.6 nm for G1; ’2.6 nm for G2; ’3.3 nm for G3;and’6.0 nm for G4), as shown in Fig. 5, although flattened dendrimers were also found on the 3000 4000 5000 6000 7000 m/z surface. The introduction of pillar[5]arene rotaxane subunits 18768 B [G +H]+ apparently increased the rigidity of each branch of the den- 2 [G +Na]+ drimers. We expected that the absence of pillar[5]arene wheels 2 would make the model dendrimers G1-c–G3-c “floppier” compared with the corresponding rotaxane dendrimers when exposed on the surface. The average heights of the model dendrimers G1-c–G3-c were indeed reduced by nearly one-half (’0.8 nm for G1-c; ’1.0 nm for G2-c;and’1.5 nm for G3-c) compared with the AFM data for the corresponding rotaxane dendrimers under the same conditions 9380 + (Fig. 6). The enhanced rigidity induced by the rotaxane subunits was [G2+2H] further confirmed by TEM, showing that the individual rotaxane ∼ G dendrimer structure had a size of 3.0 nm for 3,avalueingood 8000 12000 16000 20000 m/z agreement with the AFM result. However, the TEM image of G3-c 42959 ∼ SI Appendix + showed a corresponding size of only 1.5 nm ( ,Fig.S85). C [G3+H] + Dynamic light scattering (DLS) is also a useful technique for [G3+Na] [G +K]+ determining the dimensions of dendrimers in solution, and we 3 applied it to the new compounds. We were unable to measure the size of the smallest dendrimer G1 using DLS, possibly because the size of G1 was below the measuring limit. A size pro- 2+ [G3+2H] gression was observed with increasing generations for the 2+ [G3+H+Na] 2+ measured hydrodynamic diameters of the higher-generation [G3+H+K] [G +2Na]2+ dendrimers (2.2 nm for G2; 3.5 nm for G3; and 8.7 nm for G4)(SI 21501 3 [G +2K]2+ Appendix, Fig. S84). No obvious size results were obtained in the 3 G -c–G -c DLS studies for the model dendrimers 1 3 , possibly be- 20000 30000 40000 m/z cause the sizes of G1-c–G3-c were all below the measuring limit.

This result is also consistent with dendrimer self-folding in the Fig. 4. MALDI-TOF-MS spectra for rotaxane dendrimers G1 (A), G2 (B), and G3 (C).

Wang et al. PNAS | May 5, 2015 | vol. 112 | no. 18 | 5599 Downloaded by guest on October 6, 2021 repeating units on each branch. The AFM and TEM studies of the rotaxane dendrimers vs. corresponding model dendrimers indicate that pillar[5]arene “wheels” enhance the rigidity of the branches, reducing self-folding and collapse. Functional rotaxane dendrimers substituted with ferrocenes as termini were prepared through surface chemical transformations. The well-defined topological structures, enhanced rigidity, and diverse functional groups of rotaxane dendrimers should provide a platform for investigations of these molecules in molecular electronics and materials science. Materials and Methods General Information. All reagents were commercially available and were used as supplied without further purification. Deuterated solvents were purchased from Cambridge Isotope Laboratory. NMR spectra were recorded on a Bruker DRX 400 (400-MHz) spectrometer. 1H and 13C NMR chemical shifts were reported relative to the residual solvent signals, and 31P{1H} NMR chemical shifts were referenced to an external unlocked sample of 85% (vol/vol)

H3PO4 (δ 0.0). The 2D rotating-frame Overhauser enhancement spectroscopy NMR spectra were recorded on a Bruker DRX500 spectrometer. DLS measurements were performed using a Malvern Zetasizer Nano-ZS light scattering apparatus (Malvern Instruments) with a He–Ne laser (633 nm, 4 mW). The TEM images were obtained using a Philips TECNAI-12 instrument with an accelerating voltage of 120 kV. AFM images were obtained on a Di- mension FastScan (Bruker), using the ScanAsyst mode under ambient conditions. UV−vis spectra were recorded in a quartz cell (with a light path of 10 mm) on a Cary 50Bio UV–vis spectrophotometer. Steady-state fluorescence Fig. 5. AFM images of the rotaxane dendrimers Gn (n = 1, 2, 3, and 4). spectra were recorded using a conventional quartz cell (with a light path of 10 mm) and a Cary Eclipse fluorescence spectrophotometer. MALDI-MS experiments were carried out using a Bruker UltrafleXtreme MALDI TOF/TOF with functional groups. In this study, a triisopropylsilyl-protected mass spectrometer (Bruker Daltonics) equipped with a Smartbeam-II laser. acetylene group was used as the surface group to facilitate Cyclic voltammetry (CV) was performed using a three-electrode cell and a RST dendrimer growth and enable diversity. We chose ferrocene, a electrochemical work station. The working electrode was a glassy carbon disk robust redox function, which has been extensively explored in with surface area of about 7.0 mm2. A saturated calomel electrode was used as applications in the nanoelectronics field (30, 31). The ferrocene reference electrode and a Pt wire as the counterelectrode. The CV measurements subunit was introduced into the rotaxane dendrimers via a were carried out in a dichloromethane solution containing 0.2 M tetra-n-buty- coupling reaction of the ferrocenyl monosubstituted platinum– lammoniumhexafluorophosphate (n-Bu4NPF6). The concentration of redox molecule in solution was 2.00 mM. acetylide complex with the multiple alkyne groups in the respective rotaxane dendritic intermediates (G1-YNE, G2-YNE, and G3- General Procedure for Synthesis of Rotaxane Dendrimers Gn. A mixture of YNE)(SI Appendix, Scheme S3). The resultant heterobimetallic multiyne complexes (1,3,5-triethynylbenzene for G1; G1-YNE for G2; G2-YNE G1-Fc G2-Fc G3-Fc dendrimers, , , and , with 6, 12, and 24 ferro- for G3; and G3-YNE for G4) and 1 (for each terminal acetylene moiety, 1.1 eq cene units, respectively, were characterized by 1D multinuclear 1 was added) in degassed diethylamine was stirred overnight at room (1H, 13C, and 31P) NMR spectroscopy and MALDI-TOF-MS. temperature in the presence of a catalytic amount of CuI (∼5 mol %). The The cyclic voltammogram studies of the ferrocenyl derivatives solvent was evaporated under reduced pressure and purified by column – revealed that the peak current increased systematically with the chromatography on SiO2 using petroleum ether/CH2Cl2 (1:1 0:1) as an eluent increase of the scan rates. The cyclic voltammograms corre- to produce a pale-yellow solid as the target compound (recrystallization was sponding to the one-electron oxidation of ferrocene groups necessary for G3 and G4). yielded cathodic/anodic peak current ratios of ic/ia ∼ 1. The nearly identical cathodic and anodic peak currents, as well as nearly scan rate-independent peak potentials, indicated that the oxidized complexes were chemically stable on the voltammetric timescale and the oxidation of the ferrocene units in each assembly was chemically reversible (SI Appendix, Fig. S87). The multiple ferrocene groups reacted independently, producing a single voltammetric wave, even though more than one electron was transferred in the overall reaction. Conclusions In conclusion, we have reported the synthesis, characterization, and functionalization of a series of organometallic rotaxane dendrimers with mechanically interlocked pillar[5]arene subunits on each branch. We used an organometallic [2]rotaxane precursor, 1, and used sequential coupling–deprotection–coupling processes to obtain organometallic rotaxane dendrimers up to the fourth generation. The largest assembly incorporates 45 rotaxane subunits on the dendritic skeleton in a monodisperse manner. Numerous polymeric rotaxanes, such as rotaxane co-

ordination polymers (32), have been well documented; this study Fig. 6. AFM images of the corresponding model dendrimers Gn-c (n = 1, 2, presents discrete, high-generation rotaxane dendrimers with and 3) without pillar[5]arene wheels.

5600 | www.pnas.org/cgi/doi/10.1073/pnas.1500489112 Wang et al. Downloaded by guest on October 6, 2021 1 G1: Light yellow solid, 79%, H NMR (CDCl3, 400 MHz): δ 7.25 (d, J = 8.8 Hz, 0.48 (m), 0.38 (m), 0.15 (m), −0.04 (m), −0.33 (m), −0.68 (m), −0.77 (m), 31 6H), 7.19 (s, 3H), 7.02 (s, 3H), 6.93 (s, 6H), 6.92 (s, 15H), 6.90 (s, 15H), 6.73 (d, −1.35 (m), −1.77 (m); P NMR (CDCl3, 161.9 MHz): δ 11.44, 11.38 and 11.2; = 13 J 8.8 Hz, 6H), 3.90 (m, 30H), 3.76 (s, 30H), 3.72 (m, 30H), 3.38 (m, 6H), 3.29 C NMR (CDCl3, 100 MHz): δ 158.8, 157.2, 149.69, 149.65, 149.58, 131.8, (m, 6H), 2.21 (m, 36H), 1.89–1.75 (m, 78H), 1.25 (m, 45H), 1.16 (s, 108H), 1.08– 131.6, 128.3, 128.23, 128.16, 127.7, 124.5, 117.9, 114.2, 114.1, 113.8, 113.6, 1.01 (m, 98H), 0.81 (m, 6H), 0.48 (m, 6H), 0.16 (m, 2H), 0.15 (m, 6H), −0.05 106.3, 90.9, 69.78, 69.70, 69.6, 69.5, 68.6, 68.1, 30.9, 30.8, 30.6, 30.4, 30.3, 31 (m, 18H), −0.68 (m, 6H), −0.76 (m, 6H); P NMR (CDCl3, 161.9 MHz): δ 11.4 30.2, 30.1, 29.33, 29.31, 29.27, 29.1, 25.3, 24.0, 23.30, 23.25, 23.22, 23.18, = 13 δ (J 2379.9 Hz); C NMR (CDCl3, 100 MHz): 158.8, 157.1, 149.7, 149.6, 131.8, 18.6, 18.3, 18.07, 18.02, 16.5, 16.4, 16.2, 11.8, 11.3, 10.8, 10.69, 10.65, 10.60, + + + 128.3, 128.2, 127.7, 124.5, 117.9, 114.2, 114.1, 113.8, 106.3, 90.9, 69.7, 69.6, 8.4; MS: (MALDI-TOF-MS) 42,959 (broad, [M+H] ,[M+Na] ,[M+K] ), 21,501 + 68.6, 68.1, 30.59, 30.56, 30.4, 30.1, 29.33, 29.27, 29.1, 25.3, 24.0, 23.3, 23.2, (broad, [M+2H]2 , etc.). 18.6, 18.3, 18.1, 16.5, 16.3, 16.2, 11.8, 11.3, 10.70, 10.66, 8.4; MS: (MALDI-TOF-MS) G : Light yellow solid, 83%, 1H NMR (CDCl , 400 MHz): δ 7.22 (d), 7.18 (s), + + 4 3 6,667.15 ([M H] ). 6.93 (s), 6.92 (s), 6.90 (s), 6.81 (s), 6.73 (d), 6.69 (d), 6.65 (s), 3.90 (m), 3.76 (s), 1 δ = G2: Light yellow solid, 58%, H NMR (CDCl3, 400 MHz): 7.22 (d, J 8.8 Hz), 3.73 (m), 3.38 (m), 3.29 (m), 2.71 (m), 2.22 (m), 1.89–1.68 (m), 1.16 (m), = = 7.19 (s), 7.04 (s), 6.92 (s), 6.92 (s), 6.90 (s), 6.73 (d, J 8.8 Hz), 6.68 (d, J 8.8 Hz), 1.16 (s), 1.12–0.86 (m), 0.82 (m), 0.73 (m), 0.48 (m), 0.37 (m), 0.14 (m), 0.07 (s), 6.64 (s), 3.89 (m), 3.76 (s), 3.74 (m), 3.40 (m), 3.28 (m), 2.71 (m), 2.22 −0.05 (m), −0.33 (m), −0.68 (m), −0.76 (m), −1.34 (m), −1.77 (m); 31P NMR – – – (m, PCH2CH3), 1.87 1.75 (m), 1.26 (m), 1.16 (s), 1.12 0.98 (m), 0.82 (m), 0.73 (m), (CDCl , 161.9 MHz): δ 11.48 and 11.43; 13C NMR (CDCl , 100 MHz): δ 158.8, − − − − − 3 3 0.48 (m), 0.38 (m), 0.15 (m), 0.05 (m), 0.33 (m), 0.69 (m), 0.77 (m), 1.35 (m), 157.1, 149.70, 149.66, 149.60, 131.8, 131.6, 128.31, 128.25, 128.18, 124.5, −1.77 (m); 31P NMR (CDCl , 161.9 MHz): δ 11.5 and 11.3; 13C NMR (CDCl , 3 3 118.0, 114.2, 114.1, 113.8, 113.6, 106.3, 90.9, 90.1, 69.8, 69.7, 69.6, 69.5, 68.6, 100 MHz): δ 158.8, 157.2, 149.70, 149.65, 149.6, 131.8, 131.6, 128.3, 128.23, 68.1, 30.8, 30.6, 30.4, 30.1, 29.69, 29.65, 29.5, 29.3, 29.1, 23.30, 23.25, 23.22, 128.16, 127.7, 124.5, 117.9, 114.2, 114.1, 113.8, 113.6, 106.3, 90.9, 69.7, 69.6, 23.18, 18.6, 18.3, 18.1, 16.5, 16.4, 16.2, 14.1, 11.8, 11.3, 10.8, 10.69, 10.65, 69.5, 68.6, 68.1, 30.9, 30.8, 30.6, 30.4, 30.3, 30.2, 30.1, 29.33, 29.31, 29.27, 10.60, 8.4. 29.1, 25.3, 24.0, 23.30, 23.25, 23.22, 23.18, 18.6, 18.3, 18.1, 16.5, 16.4, 16.2, 11.8, 11.3, 10.8, 10.69, 10.66, 8.4; MS: (MALDI-TOF-MS) 18,768 (broad, + + ACKNOWLEDGMENTS. We thank Prof. Kun Huang at East China Normal [M+H] ,[M+Na] ). University for assistance with the GPC analysis. H.-B.Y. thanks National 1 δ = G3: Light yellow solid, 49%, H NMR (CDCl3, 400 MHz): 7.22 (d, J 8.8 Hz), Natural Science Foundation of China (Grants 21322206, 21132005, and = = 7.19 (s), 7.04 (s), 6.92 (s), 6.92 (s), 6.90 (s), 6.73 (d, J 8.8 Hz), 6.69 (d, J 91027005), the Key Basic Research Project of the Shanghai Science and Tech- 8.8 Hz), 6.64 (s), 3.90 (m), 3.76 (s), 3.73 (m), 3.39 (m), 3.28 (m), 2.72 (m), nology Commission (Grant 13JC1402200), and the Program for Changjiang 2.23 (m), 1.89–1.73 (m), 1.26 (m), 1.16 (s), 1.12–0.98 (m), 0.82 (m), 0.73 (m), Scholars and Innovative Research Team in University for financial support.

1. Lee JW, Kim K (2003) Rotaxane dendrimers. Top Curr Chem 228:111–140. 18. Wang W, Kaifer AE (2006) Electrochemical switching and size selection in cucurbit[8] 2. Leung KCF, Lau KN (2010) Self-assembly and thermodynamic synthesis of rotaxane uril-mediated dendrimer self-assembly. Angew Chem Int Ed Engl 45(42):7042–7046. dendrimers and related structures. Poly Chem 1(7):988–1000. 19. Ho WKW, et al. (2013) Type III-B rotaxane dendrimers. Chem Commun (Camb) 49(92): 3. Rosen BM, et al. (2009) Dendron-mediated self-assembly, disassembly, and self-organization 10781–10783. of complex systems. Chem Rev 109(11):6275–6540. 20. Ogoshi T, Kanai S, Fujinami S, Yamagishi TA, Nakamoto Y (2008) para-Bridged sym- 4. Bruns CJ, Stoddart JF (2014) Rotaxane-based molecular muscles. Acc Chem Res 47(7): metrical pillar[5]arenes: Their Lewis acid catalyzed synthesis and host-guest property. 2186–2199. J Am Chem Soc 130(15):5022–5023. 5. Vögtle F, Richardt G, Werber N (2009) Dendrimer Chemistry: Concepts, Syntheses, 21. Xue M, Yang Y, Chi X, Zhang Z, Huang F (2012) Pillararenes, a new class of macro- Properties, Applications (Wiley-VCH, Weinheim, Germany). cycles for supramolecular chemistry. Acc Chem Res 45(8):1294–1308. 6. Astruc D, Boisselier E, Ornelas C (2010) Dendrimers designed for functions: From physical, 22. Li ZY, et al. (2014) Cross-linked supramolecular polymer gels constructed from discrete photophysical, and supramolecular properties to applications in sensing, catalysis, mo-

multi-pillar[5]arene metallacycles and their multiple stimuli-responsive behavior. CHEMISTRY lecular electronics, photonics, and nanomedicine. Chem Rev 110(4):1857–1959. – 7. Hübner GM, Nachtsheim G, Li QY, Seel C, Vögtle F (2000) The spatial demand of J Am Chem Soc 136(24):8577 8589. dendrimers: Deslipping of rotaxanes. Angew Chem Int Ed Engl 39(7):1269–1272. 23. Wang W, Yang HB (2014) Linear neutral platinum-acetylide moiety: Beyond the links. – 8. Amabilino DB, et al. (1996) Self-assembly of [n]rotaxanes bearing dendritic stoppers. Chem Commun (Camb) 50(40):5171 5186. J Am Chem Soc 118(48):12012–12020. 24. Leininger S, Stang PJ, Huang S (1998) Synthesis and characterization of organo- 9. Elizarov AM, Chiu SH, Glink PT, Stoddart JF (2002) Dendrimer with rotaxane-like platinum dendrimers with 1,3,5-triethynylbenzene building blocks. Organometallics mechanical branching. Org Lett 4(5):679–682. 17(18):3981–3987. 10. Elizarov AM, Chang T, Chiu SH, Stoddart JF (2002) Self-assembly of dendrimers by 25. Onitsuka K, et al. (2004) Convergent synthesis of platinum-acetylide dendrimers. slippage. Org Lett 4(21):3565–3568. Chemistry 10(24):6433–6446. 11. Leung KCF, Aricó F, Cantrill SJ, Stoddart JF (2005) Template-directed dynamic syn- 26. Oesterling I, Müllen K (2007) Multichromophoric polyphenylene dendrimers: Toward thesis of mechanically interlocked dendrimers. J Am Chem Soc 127(16):5808–5810. brilliant light emitters with an increased number of fluorophores. J Am Chem Soc 12. Aprahamian I, et al. (2007) A liquid-crystalline bistable [2]rotaxane. Angew Chem Int 129(15):4595–4605. – Ed Engl 46(25):4675 4679. 27. Ornelas C, Ruiz J, Belin C, Astruc D (2009) Giant dendritic molecular electrochrome 13. Spruell JM, Dichtel WR, Heath JR, Stoddart JF (2008) A one-pot synthesis of consti- batteries with ferrocenyl and pentamethylferrocenyl termini. J Am Chem Soc 131(2): tutionally unsymmetrical rotaxanes using sequential Cu(I)-catalyzed azide-alkyne cy- 590–601. cloadditions. Chemistry 14(14):4168–4177. 28. Kikuchi T, Sato S, Fujita D, Fujita M (2014) Stepwise DNA condensation by a histone- 14. Gibson HW, Yamaguchi N, Hamilton L, Jones JW (2002) Cooperative self-assembly of mimic peptide-coated M L spherical complex. Chem Sci 5(8):3257–3260. dendrimers via pseudorotaxane formation from a homotritopic guest molecule and 12 24 29. Leon JW, Kawa M, Fréchet JM (1996) Isophthalate ester-terminated dendrimers: complementary monotopic host dendrons. J Am Chem Soc 124(17):4653–4665. Versatile nanoscopic building blocks with readily modifiable surface functionalities. 15. Lee JW, Han SC, Kim JH, Ko YH, Kim K (2007) Formation of rotaxane dendrimers by – supramolecular click chemistry. Bull Korean Chem Soc 28(10):1837–1840. J Am Chem Soc 118(37):8847 8859. 16. Kim SY, et al. (2007) Toward high-generation rotaxane dendrimers that incorporate a 30. Astruc D (2012) Electron-transfer processes in dendrimers and their implication in ring component on every branch: Noncovalent synthesis of a dendritic [10]pseudor- biology, catalysis, sensing and nanotechnology. Nat Chem 4(4):255–267. otaxane with 13 molecular components. Chem Asian J 2(6):747–754. 31. Astruc D (2011) Ferrocenyl dendrimers: Multi-electron redox reagents and their ap- 17. Moon K, Grindstaff J, Sobransingh D, Kaifer AE (2004) Cucurbit[8]uril-mediated plications. New J Chem 35(4):764–772. redox-controlled self-assembly of viologen-containing dendrimers. Angew Chem Int 32. Vukotic VN, Loeb SJ (2012) Coordination polymers containing rotaxane linkers. Chem Ed Engl 43(41):5496–5499. Soc Rev 41(18):5896–5906.

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