A Dual-Modality Photoswitchable Supramolecular Polymer - Langmuir

Article pubs.acs.org/Langmuir

A Dual-Modality Photoswitchable Supramolecular Polymer Qiwei Zhang, Da-Hui Qu,* Junchen Wu, Xiang Ma, Qiaochun Wang, and He Tian* Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, Shanghai 200237, People’s Republic of China S Supporting Information *

ABSTRACT: Covalent or noncovalent linked polymers with stimuli-responsive properties have been well researched as a kind of advanced functional materials. However, little effort has been devoted to establishing a bridge for switching between covalent polymers and noncovalent polymers. Actually, such unitive system is promising because it can combine their chemical advantages of two types of polymers in a single and tunable platform. Herein, by taking advantage of reversible photodimerization of coumarins and host−guest assemblies with γcyclodextrin (γ-CD), we demonstrate a simple and effective way to construct a dual-modality supramolecular polymer, which can be switched between a noncovalent polymer and its corresponding covalent polymer in response to light stimuli. Moreover, this unique switchable polymer can also be employed to construct a dual-stimuli responsive supramolecular hydrogel with the surfactant cetyl trimethylammonium bromide (CTAB). This methodology establishes a bridge between the two “polymer mansions” and is promising to open a new class of photoswitchable materials. polymer NCP in the presence of γ-cyclodextrin (γ-CD) in water, employing host−guest interaction between γ-CD and two coumarin units. Here, the cavity of γ-CD accommodates two coumarin units due to its large hydrophobic cavity (7.5− 8.3 Å).41 NCP can be converted into its corresponding polypseudorotaxane CP with a covalent polymer backbone upon UV light irradiation at 365 nm, which can lead to highly efficient photoinduced cyclodimerization of coumarin units and generate a stable cyclobutane-based dimer in the cavity of γCD.42 On the contrary, conversion of CP back to NCP can be achieved by UV light irradiation at 254 nm, which can result in the photochemical cleavage of the produced dimer.

1. INTRODUCTION During the past few decades, research on advanced functional materials,1−5 especially materials based on polymers that have environmentally responsive properties, has attracted considerable attention.6−11 Covalent polymers with long or hyperbranched covalent molecular chains have been widely used due to their versatile properties and abilities to withstand environmental changes.12−15 On the other hand, supramolecular polymers,16−24 in which highly directional and ordered polymeric arrays of monomeric units are brought together by reversible noncovalent interactions, such as hydrogen bonding,25−27 metal−ligand coordination,28−30 donor−acceptor interaction,31−33 host−guest recognition,34−36 and π−π stacking,37 have also attracted much attention because of their reversible and stimuli-responsive properties and their potentials for drug delivery systems and self-healing materials. Actually, both covalent polymers and supramolecular nonconvalent polymers have their own advantages. However, to the best of our knowledge, little effort has been devoted to establishing a system that can combine the two types of polymers or switch between them. Such a system is promising in that it may combine the chemical advantages of the two types of polymers in a single molecular platform, and it can also provide a new choice for materials with tunable properties. It is still a formidable challenge to design and construct such a molecular platform. In this Article, we reported the first dual-modality supramolecular polymer that can be switched between a noncovalent polymer and its corresponding covalent polymer in response to light stimuli. The keys in the design of this switching system are host−guest interaction and reversible dimerization of photoactive coumarin moieties.38−40 As shown in Scheme 1, monomer 2, bearing two terminal coumarins separated by a viologen moiety, can form a supramolecular noncovalent © XXXX American Chemical Society

2. EXPERIMENTAL SECTION 2.1. Merterials and General Procedures. Materials. Unless stated otherwise, all reagents were purchased from Sigma-Aldrich or TCI Chemicals and used without further purification. Solvents were purified according to standard laboratory methods. The molecular structures were confirmed using 1H NMR, 13C NMR, and highresolution ESI mass spectroscopy. General. 1H NMR spectra were measured on a Brüker AV-400 spectrometer. 13C and 2D ROESY NMR spectra were measured on a Brüker AV-500 spectrometer. The electronic spray ionization (ESI) high-resolution mass spectra were tested on a HP 5958 mass spectrometer. The UV−vis absorption spectra and fluorescence spectra were obtained on a Varian Cary 100 spectrometer and a Varian Cary Eclipse (1-cm quartz cell was used), respectively. FT-IR spectra were taken on NICOLET 380 FT-IR, Thermo Electron Corp. DLS were measured on MALV RN, ZETA SIZER, model ZEN3600, 25 °C. SEM images were obtained by using an S-4800 instrument (Hitachi) and Nova NanoSEM 450 (droplets of the sample solution (5.0 × 10−5 M) were applied to a mica plate and dried in air at room temperature, and then coated with nano Au in vacuum). TEM images Received: April 2, 2013

A

dx.doi.org/10.1021/la4012444 | Langmuir XXXX, XXX, XXX−XXX

Langmuir

Article

and washed with a small amount of DMF and ethyl acetate and dried in vacuo to provide compound 2 (Scheme 2) as a pale yellow powder (0.95 g, 94% yield), mp 280−282 °C. 1H NMR (400 MHz, D2O): δ 9.07 (d, J = 6.9 Hz, 4H), 8.35 (d, J = 6.8 Hz, 4H), 7.73 (d, J = 9.5 Hz, 2H), 7.38 (d, J = 8.7 Hz, 2H), 6.79 (dd, J = 8.7, 2.4 Hz, 2H), 6.57 (d, J = 2.3 Hz, 2H), 6.10 (d, J = 9.4 Hz, 2H), 4.73 (t, J = 6.5 Hz, 4H), 4.00 (t, J = 5.9 Hz, 4H), 2.32−2.15 (m, 4H), 1.95−1.76 (m, 4H). 13C NMR (125 MHz, DMSO-d6): δ 166.8, 165.5, 160.6, 153.8, 151.1, 149.6, 134.8, 131.9, 117.9, 117.8, 117.6, 106.4, 72.8, 65.7, 32.8, 30.2. HRMS (ESI) (m/z): [M − 2Br]2+/2 calcd for C18H17N1O3, 295.1203; found, 295.1206.

Scheme 1. Schematic Representation for the Preparation of the Supramolecular Noncovalent Polymer NCP by Host− Guest Interaction between Coumarin Derivative 2 and γ-CD, and the Photoswitching between Noncovalent Polymer NCP and Its Corresponding Covalent Polymer CP by Alternating UV Light Irradiation at 365 and 254 nm, Respectively

3. RESULTS AND DISCUSSION The NCP was obtained by mixing 2 and γ-CD ([2]mol:[γCD]mol = 1:1, 8 mM) in water and stirring for 2 h. The complexation behavior of 2 and γ-CD in D2O was validated using NMR spectroscopy. The proton signals of the coumarin moiety in 2 underwent upfield shifts due to the shielding effect of the cavity of γ-CD (Supporting Information, Figure S1). The Δδ values were 0.02, 0.23, 0.26, 0.10, and 0.23 ppm for protons Ha, Hb, Hc, Hd, and He, respectively. Furthermore, 2D ROESY NMR spectrum (Supporting Information, Figure S2) of the complex shows strong NOE signals between the protons Ha−e of coumarin and the inner protons H3 and H5 of γ-CD, which clearly demonstrates that the coumarin moiety of 2 enters into the cavity of γ-CD to form the complex. FT-IR spectrum shows distinct absorption bands as compared to 2 at 800−900, 1600− 1700, 1200−1300, and 1700−1800 cm−1, which correspond to CC out-of-plane hydrogen deformation mode, CC stretching mode, C−O−C asymmetric stretching mode, and −C(O)− stretching mode, respectively. These results also suggest the formation of the inclusion complex (Supporting Information, Figure S3).44 It is well-known that the stoichiometry is very important for host−guest self-assembly supramolecular polymers. So here a Job’s plot was used to confirm the binding stoichiometry between monomer 2 and γ-CD (Figure 1). The total concentration of 2 and γ-CD was fixed at 0.1 mM, while the molar ratio of 2 was varied from 0 to 1. The intensity of the UV/vis absorption peak at 323 nm (the maximum absorption peak of the coumarin moiety) was recorded each time the molar ratio of 2 was changed, so that the dependence of the intensity on the molar ratio of 2 could be determined. The change of the absorption reached a maximum at a ratio of 0.5 for [2]/([2]+[γ-CD]). This result confirms the 1:1 complex between 2 and γ-CD in water, which is consistent with the electrospray mass spectra (see the Supporting Information). Next, we focused on the characterization of the generated supramolecular polymer NCP. Dynamic light-scattering (DLS) measurements were conducted to identify the hydrodynamic diameter (DH) and the concentration dependence of NCP. The

were recorded on a JEOL JEM-1400 apparatus (droplets of the sample solution (5.0 × 10−5 M) were applied to a perforated copper grid (200 mesh) covered with a carbon film). AFM images were measured on Solver P47-PRO, NT-MDT. The photoirradiation was carried on a UV lamp of 6 W in a 1 mm × 1 or 1 cm × 1 cm quartz cell. The distance between the lamp and the sample cell was 1 cm. Photostationary states were ensured by taking UV spectra at distinct intervals until no changes in absorbance were observed. 2.2. Syntheses. 7-(4-Bromobutoxy)-2H-chromen-2-one (1). This compound was synthesized conveniently in one step from commercial materials 7-hydroxyl coumarin and 1,4-dibromobutane according to the literature procedure.43 1,1′-Bis(4-((2-oxo-2H-chromen-7-yl)oxy)butyl)-[4,4′-bipyridine]1,1′-diiumbromide (2). Compound 1 (1 g, 3.4 mmol, 2.5 equiv) and 4,4′-bipyridine (0.21 g, 1.3 mmol, 1 equiv) were dissolved in 10 mL of DMF. The solution was stirred at 80 °C under argon for 12 h and cooled to room temperature. The precipitate was collected by filtration

Scheme 2. Synthesis of Compound 2

B

dx.doi.org/10.1021/la4012444 | Langmuir XXXX, XXX, XXX−XXX

Langmuir

Article

detailed information inside the fibers. As shown in the TEM image in Figure 2b, it can be concluded that the thick fiber actually consists of many thin fibers, which associate together side by side. These structural features again confirmed the formation of linear supramolecular polymer that is selfassembled through noncovalent host−guest interaction. Photoconversion of supramolecular noncovalent polymer NCP into its corresponding covalent polymer CP was confirmed using 1H NMR spectroscopy (Figure 3). Irradiation of NCP in aqueous solution ([2]:[γ-CD] = 1:1, 8 mM, in 0.5 mL of D2O) with 365 nm UV light can result in the photodimerization of the two neighboring coumarin moieties and generate a stable cyclobutane-based dimer in the cavity of γ-CD. Before irradiation, there is only one set of signals (Figure 3a), while after irradiation (Figure 3b−d), there appears two sets of well-defined signals corresponding to the original NCP and produced CP polymers, respectively. The new resonances at 4.00−4.08 (Ha′, Hb′), 5.87−5.95 (He′), and 6.61−6.79 (Hc′, Hd′) ppm were assigned to the formed cyclobutane protons. In the photostationary state (Figure 3d), the integral area of peak Ha at 6.08 ppm decreased from 2.00 to 0.45 as compared to the original state in Figure 3a, so the photoconversion ratio of the dimerization process was calculated as 78%. The 2D ROESY spectrum was applied to study the structure of CP. As shown in Figure S7 in the Supporting Information, strong correlation signals were observed between the inner protons H3 and H5 (δ = 3.48 ppm and 3.60 ppm) of γ-CD and produced cyclobutane protons (Ha′−e′). The new strong NOE cross peaks indicate that the dimerized coumarins of CP are located inside the cavity of γ-CD, which is consistent with the structure in Scheme 1. As a control, the solutions of 2 and the 1:1 mixture of 2 and β-CD were irradiated with 365 nm in the same condition, respectively. Surprisingly, irradiation at 365 nm could not result in any obvious 1H NMR spectral change of the two samples (Supporting Information, Figures S8, S9). These results indicate that both 2 and 2@β-CD complex are photochemically inert in this experimental condition, while γCD can provide a constrained environment and act as a microreactor to keep the two coumarin units in a suitable space, and the cavity of γ-CD can also stabilize the excited singlet state of coumarin from being quenched by bromide ion and facilitate the photoreaction.46 These control experiments, in turn, also proved the formation of the supramolecular structure of NCP in which a γ-CD macrocycle encircles two coumarin units. Furthermore, the FT-IR spectrum also shows the change upon NCP in response to 365 nm UV light (Supporting Information, Figure S10). The absorbance at 1606 cm−1 (CC ring stretch) decreased significantly after irradiation at 365 nm, suggesting the photodimerization of the coumarin moieties. The DLS results of CP (Supporting Information, Figure S11) showed that the hydrodynamic diameter value of the polymer is around 1000 nm. To analyze the morphology of CP intuitively, SEM and TEM images were again performed. As seen in Figure 4a and b, covalent polymer CP still displays linear fibers with a length of over 500 nm, which indicates the 1D nanostructure of polymer CP. Moreover, the reversibility of the switching process between noncovalent polymer NCP and covalent polymer CP was demonstrated using 1H NMR spectroscopy. The photocleavage reaction of cyclobutane moieties occurs at short wavelength (254 nm) irradiation. Irradiation of CP solution with 254 nm UV light resulted in the disappearance of the set of signals corresponding to CP, and the 1H NMR spectrum almost

Figure 1. Job plot for complexation between 2 and γ-CD (total concentration 0.1 mM) based on the UV/vis absorption changes at 323 nm (the maximum absorption peak of the coumarin moiety). The peak at 0.5 confirms 1:1 complexation.

results (Supporting Information, Figure S4) showed that the DH value of the polymer was concentration-dependent and NCP does not form until the concentration is above 0.01 mM. The DH value of NCP can reach over 1000 nm at a concentration above 0.5 mM, which convincingly indicates the formation of highly polymerized supramolecular complexes. The morphology of NCP was investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). As shown in Figure 2a, the SEM image of NCP

Figure 2. (a) SEM image of the linear polymer NCP (droplets of NCP solution on a mica plate, 5.0 × 10−5 M); and (b) TEM image of the linear polymer NCP (droplets of NCP solution on a copper grids, 5.0 × 10−5 M, and negative stained by Phosphotungstic acid).

displays a straight fiber with a length of over 1000 nm, which indicates the formation of linear supramolecular polymer (for more fibers with a length from ca. 450 to 1200 nm, see Supporting Information, Figure S5). In addition, the AFM image of NCP (Supporting Information, Figure S6) shows a rod-like fiber with a length of ca. 670 nm. The 1D nanostructure appears to be 1.7−1.8 nm in height, which is consistent with the size of torus-like γ-CD (the outer diameter of the large rim is 1.69 nm).41 However, the widths of the fibers (Figure 2a, and Supporting Information, Figure S5, S6) are much larger than a single polymer. We ascribe it to the association between the polymer chains, which is very common in cyclodextrin-based polymer systems as mentioned in the literature.45 Because of the different imaging mechanism, transmission electron microscope (TEM) is able to find some C

dx.doi.org/10.1021/la4012444 | Langmuir XXXX, XXX, XXX−XXX

Langmuir

Article

Figure 3. Partial 1H NMR spectra (400 MHz, D2O, 25 °C) of NCP solution irradiated with 365 nm UV light, (a) 0 h, (b) 8 h, (c) 10 h, (d) 16 h, (e) 365 nm for 16 h, and then 254 nm for 8 h. The peaks marked with asterisk correspond to D2O.

Figure 5. Photographic representation of thermal/photo responsive supramolecular hydrogel, (a) CP (16 wt %)−CTAB (3 wt %) aqueous solution at 60 °C, (CP-sol); (b) CP-gel obtained from CP-sol cooled to 15 °C or NCP-sol irradiated by 365 nm UV light for 5 days; and (c) CP-gel irradiated by 254 nm UV light for 4 days, at 15 °C (NCP-sol).

Figure 4. (a) SEM image of the linear polymer CP (droplets of CP solution on a mica plate, 5.0 × 10−5 M); and (b) TEM image of the linear polymer CP (droplets of CP solution on a copper grid, 5.0 × 10−5 M).

NCP-sol, on the contrary, the value of G′ is smaller than G″ in the whole range of the measured strain, indicating that the hydrogel structure has been destroyed. Benefiting from the photoswitching of CP/NCP, the sol−gel transition can also be achieved by UV light, which was confirmed by electron microscopy (Supporting Information, Figure S14). The different gelling ability between NCP and CP is probably ascribed to the fact that CP has a covalent polymer backbone and can act as a physical barrier and restrict CTAB aggregations in or around the polymer network (see SEM/ TEM images, Supporting Information, Figure S14a, S14c). On the other hand, in NCP-CTAB solution, the cavities of part γCDs in NCP are occupied by the alkyl chain of CTAB (see 2D ROESY spectrum, Supporting Information, Figure S15); thus the NCP polymer chains were broken down (Supporting Information, Figure S14b, S14d). As a result, constructing such dual-stimuli responsive hydrogel may expose one of the applications of this switchable supramolecular polymer.

recovered to the original one, indicating a conversion into NCP (Figure 3e). The absorption and fluorescence spectra of the complex, as well, show good reversibility under the alternating UV light irradiation at 365 and 254 nm. This photochemical process is highly reproducible over four cycles according to the fluorescence spectral changes (Supporting Information, Figures S12, S13). Interestingly, this switchable supramolecular polymer could be used to construct a thermally and photochemically dualresponsive hydrogel with the surfactant cetyl trimethylammonium bromide (CTAB) as a cogelator, as shown in Figure 5. An opaque hydrogel (CP-gel) was easily obtained by cooling the transparent aqueous solution (3 wt % CTAB + 16 wt % CP) to 15 °C (Figure 5b), while the mixture of CTAB and NCP aqueous solution cannot form a hydrogel in the same condition. To explore the difference in molecular dynamics of the photo reversible supramolecular gel−sol as well as quantify their mechanical properties, dynamic oscillatory measurements were performed. As shown in Figure 6, strain amplitude sweeps of the sample CP-gel demonstrates an elastic response typical of hydrogels; that is, when in small strain range the storage modulus (G′) stays larger than the loss modulus (G″), and both remain almost constant up to 1% strain. As for sample

4. CONCLUSIONS In summary, by taking advantage of host−guest interactions between γ-CD and coumarin moieties, a self-assembled supramolecular noncovalent polymer was constructed in aqueous solution. This novel polymer can be photochemically converted to the corresponding covalent polymer by UV light D

dx.doi.org/10.1021/la4012444 | Langmuir XXXX, XXX, XXX−XXX

Langmuir

Article

Figure 6. Dynamic oscillatory data for (a) CP-gel and (b) NCP-sol (245 mg/mL, 15 °C), on strain sweep at a frequency of 1 rad s−1. (5) Zhang, K.-D.; Zhou, T.-Y.; Zhao, X.; Jiang, X.-K.; Li, Z.-T. Redoxresponsive reverse vesicles self-assembled by pseudo[2]rotaxanes for tunable dye release. Langmuir 2012, 28, 14839−14844. (6) Zhang, X.; Wang, C. Supramolecular amphiphiles. Chem. Soc. Rev. 2011, 40, 94−101. (7) Chen, G.; Jiang, M. Cyclodextrin-based inclusion complexation bridging supramolecular chemistry and macromolecular self-assembly. Chem. Soc. Rev. 2011, 40, 2254−2266. (8) Aida, T.; Meijer, E. W.; Stupp, S. I. Functional supramolecular polymers. Science 2012, 335, 813−817. (9) Wojtecki, R. J.; Meador, M. A.; Rowan, S. J. Using the dynamic bond to access macroscopically responsive structurally dynamic polymers. Nat. Mater. 2011, 10, 14−27. (10) Du, G.; Moulin, E.; Jouault, N.; Buhler, E.; Giuseppone, N. Muscle-like supramolecular polymers: Integrated motion from thousands of molecular machines. Angew. Chem., Int. Ed. 2012, 51, 12504−12508. (11) Oikonomou, E.; Bokias, G.; Kallitsis, J. K.; Iliopoulos, I. Formation of hybrid wormlike micelles upon mixing cetyl trimethylammonium bromide with poly(methyl methacrylate-cosodium styrenesulfonate) copolymers in aqueous solution. Langmuir 2011, 27, 5054−5061. (12) Iliopoulos, K.; Krupka, O.; Gindre, D.; Sallé, M. Reversible twophoton optical data storage in coumarin-based copolymers. J. Am. Chem. Soc. 2010, 132, 14343−14345. (13) Ouchi, M.; Badi, N.; Lutz, J.-F.; Sawamoto, M. Single-chain technology using discrete synthetic macromolecules. Nat. Chem. 2011, 3, 917−924. (14) Mai, Y.; Eisenberg, A. Self-assembly of block copolymers. Chem. Soc. Rev. 2012, 41, 5969−5985. (15) Jin, H.; Huang, W.; Zhu, X.; Zhou, Y.; Yan, D. Biocompatible or biodegradable hyperbranched polymers: from self-assembly to cytomimetic applications. Chem. Soc. Rev. 2012, 41, 5986−5997. (16) Chen, Y.; Liu, Y. Cyclodextrin-based bioactive supramolecular assemblies. Chem. Soc. Rev. 2010, 39, 495−505. (17) Liu, Y.; Wang, Z.; Zhang, X. Characterization of supramolecular polymers. Chem. Soc. Rev. 2012, 41, 5922−5932. (18) De Greef, T. F. A.; Smulders, M. M. J.; Wolffs, M.; Schenning, A. P. H. J.; Sijbesma, R. P.; Meijer, E. W. Supramolecular polymerization. Chem. Rev. 2009, 109, 5687−5754. (19) Dankers, P. Y. W.; Hermans, T. M.; Baughman, T. W.; Kamikawa, Y.; Kieltyka, R. E.; Bastings, M. M. C.; Janssen, H. M.; Sommerdijk, N. A. J. M.; Larsen, A.; van Luyn, M. J. A.; Bosman, A. W.; Popa, E. R.; Fytas, G.; Meijer, E. W. Hierarchical formation of supramolecular transient networks in water: A modular injectable delivery system. Adv. Mater. 2012, 24, 2703−2709. (20) Li, S.-L.; Xiao, T.; Lin, C.; Wang, L. Advanced supramolecular polymers constructed by orthogonal self-assembly. Chem. Soc. Rev. 2012, 41, 5950−5968. (21) Ma, X.; Sun, R.; Li, W.; Tian, H. Novel electrochemical and pH stimulus-responsive supramolecular polymer with disparate pseudorotaxanes as relevant unimers. Polym. Chem. 2011, 2, 1068−1070.

irradiation at 365 nm, and vice versa (254 nm), due to the reversible photo dimerization and cleavage properties of the coumarin moiety in the cavity of γ-CD. The simplicity and tunability highlights this methodology to construct novel photoswitchable supramolecular noncovalent/covalent polymers. This original concept may also pave the way for chemists in designing switchable materials.

■

ASSOCIATED CONTENT

S Supporting Information *

Experimental details, 1H NMR and 2D ROESY spectra, absorption and fluorescence spectra, IR, AFM, SEM, TEM, and other characterization data mentioned in the text. This material is available free of charge via the Internet at http:// pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (D.-H.Q.); [email protected]. cn (H.T.). Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank the NSFC/China (21272073, 21190033) and National Basic Research 973 Program (2013CB733700). D.H.Q. thanks the Foundation for the Author of National Excellent Doctoral Dissertation of China (200957), the Fok Ying Tong Education Foundation (121069), the Fundamental Research Funds for the Central Universities, and Innovation Program of Shanghai Municipal Education Commission, and the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, for financial support.

■

REFERENCES

(1) Wenz, G.; Han, B.-H.; Muller, A. Cyclodextrin rotaxanes and polyrotaxanes. Chem. Rev. 2006, 106, 782−817. (2) Ma, X.; Tian, H. Bright functional rotaxanes. Chem. Soc. Rev. 2010, 39, 70−80. (3) Avellini, T.; Li, H.; Coskun, A.; Barin, G.; Trabolsi, A.; Basuray, A. N.; Dey, S. K.; Credi, A.; Silvi, S.; Stoddart, J. F.; Venturi, M. Photoinduced memory effect in a redox controllable bistable mechanical molecular switch. Angew. Chem., Int. Ed. 2012, 51, 1611−1615. (4) Hu, J.; Zhang, G.; Liu, S. Enzyme-responsive polymeric assemblies, nanoparticles and hydrogels. Chem. Soc. Rev. 2012, 41, 5933−5949. E

dx.doi.org/10.1021/la4012444 | Langmuir XXXX, XXX, XXX−XXX

Langmuir

Article

(22) Zhu, L.; Lu, M.; Zhang, Q.; Qu, D.; Tian, H. Construction of polypseudorotaxane from low-molecular weight monomers via dual noncovalent interactions. Macromolecules 2011, 44, 4092−4097. (23) Vukotic, V. N.; Loeb, S. J. Coordination polymers containing rotaxane linkers. Chem. Soc. Rev. 2012, 41, 5896−5906. (24) Francisco, K. R.; Dreiss, C. A.; Bouteiller, L.; Sabadini, E. Tuning the visco-elastic properties of bis-urea based supramolecular polymer solutions by adding co-solutes. Langmuir 2012, 28, 14531− 14539. (25) Li, S.-L.; Xiao, T.; Hu, B.; Zhang, Y.; Zhao, F.; Ji, Y.; Yu, Y.; Lin, C.; Wang, L. Formation of polypseudorotaxane networks by crosslinking the quadruple hydrogen bonded linear supramolecular polymers via bisparaquat molecules. Chem. Commun. 2011, 47, 10755−10757. (26) Belowich, M. E.; Valente, C.; Smaldone, R. A.; Friedman, D. C.; Thiel, J.; Cronin, L.; Stoddart, J. F. Positive cooperativity in the template-directed synthesis of monodisperse macromolecules. J. Am. Chem. Soc. 2012, 134, 5243−5261. (27) Momčilović, N.; Clark, P. G.; Boydston, A. J.; Grubbs, R. H. One-pot synthesis of polyrotaxanes via acyclic diene metathesis polymerization of supramolecular monomers. J. Am. Chem. Soc. 2011, 133, 19087−19089. (28) Gröger, G.; Meyer-Zaika, W.; Böttcher, C.; Gröhn, F.; Ruthard, C.; Schmuck, C. Switchable supramolecular polymers from the selfassembly of a small monomer with two orthogonal binding interactions. J. Am. Chem. Soc. 2011, 133, 8961−8971. (29) Whittell, G. R.; Hager, M. D.; Schubert, U. S.; Manners, I. Functional soft materials from metallopolymers and metallosupramolecular polymers. Nat. Mater. 2011, 10, 176−188. (30) Burnworth, M.; Tang, L.; Kumpfer, J. R.; Duncan, A. J.; Beyer, F. L.; Fiore, G. L.; Rowan, S. J.; Weder, C. Optically healable supramolecular polymers. Nature 2011, 472, 334−337. (31) Klajn, R.; Olson, M. A.; Wesson, P. J.; Fang, L.; Coskun, A.; Trabolsi, A.; Soh, S.; Stoddart, J. F.; Grzybowski, B. A. Dynamic hookand-eye nanoparticle sponges. Nat. Chem. 2009, 1, 733−738. (32) Fang, L.; Olson, M. A.; Benitez, D.; Tkatchouk, E.; G., W. A., III; Stoddart, J. F. Mechanically bonded macromolecules. Chem. Soc. Rev. 2010, 39, 17−29. (33) Niu, Z.; Huang, F.; Gibson, H. W. Supramolecular AA−BB-type linear polymers with relatively high molecular weights via the selfassembly of bis(m-phenylene)-32-crown-10 cryptands and a bisparaquat derivative. J. Am. Chem. Soc. 2011, 133, 2836−2839. (34) Zhu, L. L.; Li, X.; Ji, F.-Y.; Ma, X.; Wang, Q.-C.; Tian, H. Photolockable ratiometric viscosity sensitivity of cyclodextrin polypseudorotaxane with light-active rotor graft. Langmuir 2009, 25, 3482−3486. (35) Xu, Y.; Guo, M.; Li, X.; Malkovskiy, A.; Wesdemiotis, C.; Pang, Y. Formation of linear supramolecular polymers that is based on hostguest assembly in water. Chem. Commun. 2011, 47, 8883−8885. (36) Wilson, J. S.; Frampton, M. J.; Michels, J. J.; Sardone, L.; Marletta, G.; Friend, R. H.; Samorì, P.; Anderson, H. L.; Cacialli, F. Supramolecular complexes of conjugated polyelectrolytes with poly(ethylene oxide): Multifunctional luminescent semiconductors exhibiting electronic and ionic transport. Adv. Mater. 2005, 17, 2659− 2663. (37) Liu, Y.; Liu, K.; Wang, Z.; Zhang, X. Host-enhanced π−π interaction for water-soluble supramolecular polymerization. Chem.Eur. J. 2011, 17, 9930−9935. (38) Trenor, S. R.; Shultz, A. R.; Love, B. J.; Long, T. E. Coumarins in polymers: From light harvesting to photo-cross-linkable tissue scaffolds. Chem. Rev. 2004, 104, 3059−3078. (39) Muthuramu, K.; Murthy, V. R. Photodimerization of coumarin in aqueous and micellar media. J. Org. Chem. 1982, 47, 3976−3979. (40) Ramasubbu, N.; Row, T. N. G.; Venkatesan, K.; Ramamurthy, V.; Rao, C. N. R. Photodimerization of coumarins in the solid state. J. Chem. Soc., Chem. Commun. 1982, 178−179. (41) Szejtli, J. Introduction and general overview of cyclodextrin chemistry. Chem. Rev. 1998, 98, 1743−1754.

(42) Moorthy, J. N.; Venkatesan, K.; Weiss, R. G. Photodimerization of coumarins in solid cyclodextrin inclusion complexes. J. Org. Chem. 1992, 57, 3292−3297. (43) Feng, P.; Zhu, J.; Cheng, Z.; Zhang, Z.; Zhu, X. Reversible addition−fragmentation chain transfer polymerization of 7-(4(acryloyloxy)butoxy)coumarin. Polymer 2007, 48, 5859−5866. (44) Tanaka, Y.; Sasaki, S.; Kobayashi, A. Solid-state photoreaction on an inclusion compound of coumarin with β-cyclodextrin. J. Inclusion Phenom. Macrocyclic Chem. 1984, 2, 851−860. (45) Larrañeta, E.; Isasi, J. R. Self-assembled supramolecular gels of reverse poloxamers and cyclodextrins. Langmuir 2012, 28, 12457− 12462. (46) Ramnath, N.; Ramamurthy, V. Photochemical reactions in constrained systems: changes in mode of solubilization due to longchain hydrophobic groups. J. Org. Chem. 1984, 49, 2827−2830.

F

dx.doi.org/10.1021/la4012444 | Langmuir XXXX, XXX, XXX−XXX