Pillar[5]arene Based Conjugated Microporous ... - ACS Publications

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Pillar[5]arene Based Conjugated Microporous Polymers for Propane/ Methane Separation through Host−Guest Complexation Siddulu Naidu Talapaneni,† Daeok Kim,† Gokhan Barin,‡ Onur Buyukcakir,† Sang Hyun Je,† and Ali Coskun*,†,§ †

Graduate School of Energy, Environment, Water and Sustainability (EEWS), Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea ‡ Department of Chemistry, University of California, Berkeley, Berkeley, California 94720, United States § Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Republic of Korea S Supporting Information *

ABSTRACT: We present an efficient strategy for the preparation of conjugated microporous polymers incorporating pillar[5]arenes (P5-CMPs) with surface areas up to 400 m2 g−1 via Pd-catalyzed Sonogashira−Hagihara cross-coupling reaction of triflate functionalized pillar[5]arene with 1,4-diethynylbenzene and 4,4′-diethynyl-1,1′-biphenyl linkers. In an effort to transfer intrinsic properties of pillar[5]arene, that is its ability to form strong host−guest complexes with linear hydrocarbons in solution, into the solid-state, we investigated the affinity of P5CMPs toward propane gas. Unlike previously reported porous solids, which showed isosteric heats of adsorption (Qst) for propane in the range of 32.9−36.9 kJ mol−1 at zero coverage and increasing Qst with rising loading due to intermolecular interactions between propane molecules, we observed very high Qst values up to 53 kJ mol−1 at zero coverage, which gradually decreased to ∼35 kJ mol−1 with increasing loadings. This observation indicates strong supramolecular host−guest complexation between propane and pillar[5]arene via multiple C−H/π interactions, i.e., “macrocyclic effect” arising from the ideal size match of kinetic diameter of propane to the cavity of pillar[5]arene. This approach also allowed us to introduce thermodynamic selectivity for the separation of saturated hydrocarbons with low polarizability. High affinity of P5-CMPs for propane facilitated its efficient breakthrough separation from a simulated natural gas mixture (methane:propane, 9:1) at 298 K.

1. INTRODUCTION Selective separation of higher hydrocarbons from natural gas streams is extremely important due to the high value of these hydrocarbons as chemical feedstocks and safety concerns arising from the partial dissolution/softening of plastic pipes and flow meters by the liquid slugs of condensed highermolecular-weight hydrocarbons. Moreover, these higher hydrocarbons such as propane can also cause photochemical smog, which under direct sunlight can lead to the formation of several hazardous chemicals. To date, cryogenic distillation, swing adsorption, and rectification processes have been usually employed in the context of commercial separation of hydrocarbons from natural gas streams.1−3 However, these commercial methods are extremely cost-intensive in terms of both capital and energy input, mainly due to the operation requirements of very low temperatures and high pressures during the separation process.2 Separation by adsorption, which can be applied in both liquid and gas phases, is one of the most efficient and economical alternatives to the commercial methods.3 In this case, the separation is achieved by controlling © 2016 American Chemical Society

the affinity of target compounds toward the sorbent, whereby the kinetic effects like shape and size selectivity as well as enthalpic or entropic factors constitutes the elements of driving force. In recent years, the application of porous materials such as metal−organic frameworks (MOFs), zeolites, and microporous polymers for gas separation has become a promising alternative to other conventional separation techniques as these materials could potentially decrease required capital and energy input while minimizing the environmental impact.3 These separation methods generally take advantage of high surface area, large pore volume, and tunable pore topologies along with the selective chemical interactions with unsaturated carbon− carbon bonds, such as the absorptive separations involving coordination with open metal sites.3−11 However, designing selective sorbents for alkanes is rather difficult due to their low polarizability arising from the presence of only C−C and C−H Received: April 25, 2016 Revised: May 31, 2016 Published: June 1, 2016 4460

DOI: 10.1021/acs.chemmater.6b01667 Chem. Mater. 2016, 28, 4460−4466

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Chemistry of Materials bonds, which renders their interactions with the solid sorbents such as zeolites and MOFs rather weak.12 One possible direction to address these issues is to resort to supramolecular host−guest interactions by incorporating macrocyclic hosts into the porous frameworks, which will imbue the resulting porous polymer with properties arising from the inherent host−guest chemistry of macrocyclic units. As these materials could potentially inherit unique molecular recognition properties of macrocycles, the guest selectivity of resulting materials can be tailored through size and shape of the host and through various noncovalent interactions. Pillar[n]arenes13,14 composed of hydroquinone units linked in the para position through methylene bridges are a new type of emerging cyclophane hosts, which were first introduced by Ogoshi and co-workers in 2008.13−20 Pillar[n]arenes’ unique structural characteristics and properties such as facile preparation, structural tunability, well-defined rigid structure, and π-electron rich cavity, as well as intriguing and peculiar guest complexation capabilities, have given them outstanding abilities to bind selectively various kinds of neutral and πelectron deficient guest molecules. Such features facilitated the construction of many interesting supramolecular systems such as cyclic dimers,21,22 self-inclusion complexes, chemosensors,23−25 supramolecular polymers, fibers and gels,26−33 responsive supramolecular networks,22,34,35 drug delivery systems,36,37 molecular switches,38,39 MOFs,40 and transmembrane channels.41,42 Among all the pillar[n]arenes, pillar[5]arene has been shown to exhibit higher affinity and shape/ size-selectivity toward n-alkanes compared to other branched or cyclic alkanes via host−guest interactions in organic solvents.43 In an effort to transfer these unique features of pillar[5]arenes into MOFs, Stoddart et al. have synthesized a highly crystalline Zn-based MOF incorporating pillar[5]ane units located on the organic struts as docking sites for electron-deficient guest molecules.40 More recently, Tan and co-workers have prepared a low-density, crystalline, porous supramolecular organic framework (SOF) from perhydroxyl-pillar[5]arene (P5, i.e., P5-SOF), which formed a 3D open network held together by intermolecular hydrogen bonds and showed permanent porosity, good thermal stability, reversible sorption, and high CO2/CH4 selectivity mainly arising from the limited diffusion of CH4 into the densely packed network structure. It is, however, important to note that while these are promising examples, the lack of water stability in these systems presents an important challenge for their application in practical gas adsorption or separation applications.44 Microporous polymers have emerged as promising candidates for gas separation applications, due to their (1) permanent porosity, (2) structural tunability, which allows control over textural properties and gas affinity, and (3) their high thermal and water stabilities. Conjugated microporous polymers (CMPs), which were first prepared by Cooper and co-workers using Sonogashira−Hagihara cross-coupling chemistry, have exhibited relatively high BET surfaces areas (500− 800 m2 g−1) and shown exceptional physicochemical stability. CMPs have already been utilized for adsorption and separation, environmental protection, heterogeneous catalysis, and so on.45−47 Modularity of their synthesis along with their water stability renders CMPs as ideal platforms for the incorporation of macrocylic hosts such as pillar[5]arenes, in which the presence of macrocyclic units is expected to introduce molecular recognition ability into the resulting microporous polymers and enable affinity-based separation through host−

Figure 1. Chemical structures of perhydroxy- and pertriflatedpillar[5]arenes along with the synthesis of pillar[5]arene-based conjugated microporous polymers (P5-CMPs) via Pd-catalyzed Sonogashira−Hagihara cross-coupling reaction. Inset: X-ray crystal structure of perhydroxy pillar[5]arene.

guest interactions.48 In this direction, herein, we report (Figure 1) the preparation of pillar[5]arene based conjugated microporous polymers (P5-CMPs) by reacting triflate functionalized pillar[5]arene with 1,4-diethynylbenzene (P5-CMP-1) and 4,4′diethynyl-1,1′-biphenyl (P5-CMP-2) via Pd-catalyzed Sonogashira cross-coupling reaction. P5-CMP-1 and -2 showed BET surface areas of 400 and 345 m2 g−1, respectively. P5-CMPs exhibited very high affinity and selectivity toward propane when compared to methane. Importantly, high isosteric heat of adsorption (Qst) for propane up to 53 kJ mol−1 at zero coverage clearly demonstrates the presence of host−guest interactions and the macrocyclic effect, which leads to exceptional methane/ propane breakthrough separation at 298 K. Moreover, unlike other porous materials, which show increasing Qst with increasing loading amounts due to van der Waals interactions between propane molecules, we observed decreasing Qst with increasing loading amount, an indication of confinement of propane molecules within the cavity of pillar[5]arenes. Notably, we introduced thermodynamic selectivity via host−guest complexation for the separation of saturated hydrocarbons with low polarizability.

2. EXPERIMENTAL SECTION 2.1. General Synthetic Procedure for P5-CMPs. In a typical reaction, triflate functionalized pillar[5]arene40,49 (200 mg, 0.1 mmol) and 0.6 mmol of corresponding phenyl acetylene were added into a 25 mL Schlenk flask and dissolved in an anhydrous predegassed solvent mixture (5 mL, toluene/DIPEA; 1:1) under Ar atmosphere. Then, the mixture was heated to 80 °C. When the reaction mixture reached the target temperature, a suspension of bis(triphenylphosphine)palladium(II) dichloride (15.0 mg, 0.02 mmol) and copper(I) iodide (6 mg, 0.03 mmol) in an anhydrous toluene (1.0 mL), was added. The final reaction mixture was stirred at 80 °C under argon atmosphere for 48 h. After cooling to room temperature, the resulting precipitate was 4461


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Chemistry of Materials filtered and washed extensively with toluene (3 × 10 mL), THF (3 × 10 mL), methanol (3 × 10 mL), acetone (1 × 10 mL), and diethyl ether (1 × 10 mL). Further purification of the polymer was achieved by Soxhlet extraction (methanol) for 72 h. The product was dried under vacuum for 24 h at 70 °C (yield, 70.5%). 2.2. Measurements. Solid-state cross-polarization magic angle spinning (CP/MAS) 13C NMR spectra of polymers were measured on a Bruker Digital Avance III HD 400 WB (400 MHz) NMR spectrometer at ambient temperature with a magic angle spinning rate of 7.0 kHz. Fourier transform infrared spectroscopy (FT-IR) spectra were recorded in ATR mode by using a Shimadzu FT-IR spectrometer. Thermogravimetric analysis (TGA) was performed by using a NETZSCH-TG 209 F3 instrument, and the samples were heated up to 800 °C at a rate of 10 °C min−1 under air and N2 atmosphere for each sample. The scanning electron microscopy (SEM) analyses were performed using a Hitachi S-4800 FE-SEM instrument at 2.0−10 kV. Elemental analyses (C, H, N) were recorded on a FlashEA 2000 (Series) [C,H,N,S] elemental analyzer. Powder Xray diffraction (PXRD) analyses of samples were carried out over the 2θ range of 5° to 80° on a Bruker AXS D8 Discover multipurpose high power X-ray diffractometer. The surface area and pore size distribution analysis of samples were performed with a Micrometrics 3Flex Surface Characterization Analyzer by Ar adsorption and desorption at 87 K. All of the samples were degassed at 100 °C for 16 h under vacuum prior to the analysis. The specific surface areas of samples were calculated using the BET and Langmuir model in the pressure range where the term V(1 − P/P0) continuously increases with P/P0 in the Rouquerol plot. The pore size distributions of samples were calculated from argon isotherms according to nonlocal density functional theory (NLDFT) method using a zeolite cylindrical pore model. Gas adsorption experiments were performed for both methane (99.99% purity) and propane (99.5% purity) gases at designated temperatures on a Micromeritics 3Flex gas adsorption analyzer.

3. RESULTS AND DISCUSSION 3.1. Synthesis and Structural Characterization. The synthesis of perhydroxyl-pillar[5]arene was achieved by following the previously reported literature procedure.40,49 The synthesis of pertriflated pillar[5]arene was achieved (Figures S1−S6) by reacting perhydroxyl-pillar[5]arene with trifluoromethanesulfonic anhydride in CH2Cl2 for 18 h at 30 °C. Ogoshi and co-workers49 showed that pertriflated pillar[5]arene can undergo efficient Pd-catalyzed Sonogashira− Hagihara cross-coupling with ethynylbenzene to give a highly conjugated and fluorescence pillar[5]arene derivative.49 To obtain P5-CMPs, we have reacted pertriflated pillar[5]arene with 1,4-diethynylbenzene and 4,4′-diethynyl-1,1′-biphenyl (Figure 1) in a 1:1 solvent mixture of toluene:DIPEA at 80 °C for 48 h to obtain P5-CMP-1 and P5-CMP-2, respectively. The P5-CMPs were obtained as gray colored powders and were found to be completely insoluble in common organic solvents, indicating the formation of a cross-linked network structure. In addition, P5-CMPs also showed high stability toward dilute solutions of HCl and NaOH. The scanning electron microscopy (SEM) analysis was performed (Figure S7) in order to investigate the bulk scale morphology of P5-CMPs. P5-CMPs showed fibrous structures with width of approximately 300 nm and length of several micrometers. The broad featureless PXRD patterns of P5-CMPs verify (Figure S8) their amorphous nature. TGA analysis of P5-CMPs revealed (Figure S9) thermal stabilities up to 350 °C under air. The molecular level connectivity of P5-CMPs was assessed (Figure 2) by FT-IR and the solid-state cross-polarization magic angle spinning (CP/MAS) 13C NMR spectroscopy. The infrared spectra of P5-CMP-1 and -2 showed (Figure 2a)

Figure 2. (a) FT-IR spectra of pertriflated-pillar[5]arene, 1,4diethynylbenzene, P5-CMP-1 and -2. (b) Solid-state CP-MAS 13C NMR spectra of P5-CMP-1 and -2 along with the corresponding peak assignments. The spectra were recorded with a contact time of 2 ms, a relaxation time of 5 s, and a spinning frequency of 7 kHz. The carbonyl carbon of glycine was used as an external chemical shift reference for the 13C NMR.

antisymmetric and symmetric stretching vibrations of the −CH2− moieties of the pillar[5]arenes in the P5-CMPs at 2924 and 2854 cm−1 respectively.37 A first lower absorption band in the range of 650−1200 cm−1 was attributed to the benzene ring vibration and the second peak (1400−1650 cm−1) was assigned to the sp2 benzene stretching vibrations.37 We have also observed the corresponding peak for the CC stretching at 2250 cm−1.45−47 The complete disappearance of ethynyl and −SO3 stretching bands at 3250 and 1000 cm−1, respectively, indicates efficient formation of the corresponding P5-CMPs. The formation of P5-CMPs was further verified using solidstate CP-MAS 13C NMR analysis. We ascribed the broad chemical shift located at 35 ppm to the aliphatic methylene moiety (−CH2−) in the backbone of pillar[5]arene core.49 Moreover, the peaks at 91 and 98 ppm were assigned as sphybridized −CArCCCAr− moiety, thus clearly demonstrating the successful formation of P5-CMPs.49 The observed appearance of resonances between 124 and 150 ppm ascribed to sp2 carbons of the phenyl rings.45,46 As expected, the solidstate 13C NMR spectrum of P5-CMP-1 was found to be similar to that of P5-CMP-2, which showed increased population of 4462


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therms of P5-CMPs showed slight hysteresis loop in the desorption. The presence of H4 hysteresis loop in P5-CMP-1 upon desorption could be attributed to the pore network effects, interaction of gas molecules with micropore surfaces, and to the swelling of the framework as commonly observed for the cages, CMPs, PIMs, and GNRs.50,51 The specific surface areas of P5-CMPs estimated from the Ar adsorption isotherm using the Brunauer−Emmett−Teller (BET) model, in which the pressure ranges were determined according to the Rouquerol plots (Figures S10 and S11), were found (Table 1) to be 400 and 345 m2 g−1 for P5-CMP-1 and -2, respectively. Although both P5-CMPs showed similar Ar adsorption− desorption isotherms, we observed a lower surface area for P5CMP-2. This result was attributed to the interpenetration of the framework arising from longer linker length, which could limit the accessibility of micropores within the framework.52,53 P5CMPs showed uniform pore size distribution mainly in the micropore region with a pore width maxima located at about 6 Å. Importantly, this value is in good agreement with the recently reported supramolecular pillar[5]arane frameworks,44 thus proving both existence and accessibility of pillar[5]arene cavities within P5-CMPs. We then investigated P5-CMPs ability to separate propane from methane under the simulated (methane:propane, 9:1) natural gas conditions. It is important to note that although propane’s kinetic diameter (∼4.3 Å) is an ideal fit to the cavity of pillar[5]arene, that of methane is too small (3.8 Å),12 thus rendering pillar[5]arenes as ideal candidates for the affinity based separation of propane. To assess the affinity of P5-CMPs toward methane and propane, we have carried out (Figure 4a,d) single component gas uptake measurements up to 1 bar at 288, 298, and 308 K for methane, at 298, 313, and 323 K for propane, respectively. Because of the higher specific surface area of P5-CMP-1 compared to that of the P5-CMP-2, we observed higher methane and propane uptake capacities of 0.177 and 1.12 mmol g−1 at 298 K and 1 bar, respectively. P5-CMP-2 showed methane and propane adsorption capacities of 0.13 and 0.87 mmol g−1 at 298 K and 1 bar, respectively. The high affinity of propane toward P5-CMPs can be further verified by the (Qst) data, which were calculated (Figure 4b,e) from the propane adsorption data at 288, 298, and 308 K and best fitted by a dual-site Langmuir−Freundlich model. Importantly, porous solids such as HKUST-1, Zeolite 13X, and MOF-74 typically have Qst values for propane in the range of 32.9−36.9 kJ mol−1 at zero coverage.54 In addition, the Qst values for propane was shown to gradually increase up to 55 kJ mol−1 at higher loadings, mainly due to pronounced intermolecular van der Waals interactions between propane molecules.12,54 Interestingly, we have observed an opposite trend for P5-CMPs. At zero coverage, Qst values up to 53 kJ mol−1 were obtained for propane, an indication of strong supramolecular host−guest complexation between propane and pillar[5]arene via multiple C−H/π interactions. This behavior

carbon resonances in the range of 124 and 150 ppm arising from the biphenyl linker. It is noteworthy to mention that we did not detect any resonances in the range of 75 to 85 ppm, which is generally observed for the quaternary ethynyl carbon atom (−CCH), thus suggesting the complete consumption of phenylethynyl monomers during the course of polymerization reaction.46 The porosity of P5-CMPs was investigated (Figure 3) by argon adsorption/desorption analyses at 87 K. All samples were

Figure 3. (a) Argon uptake isotherms (filled and empty symbols represent adsorption and desorption, respectively) at 87 K and (b) NLDFT pore size distributions of P5-CMP-1 and P5-CMP-2.

activated at 100 °C for 16 h prior to gas uptake measurements in order to remove any trapped gases, solvent molecules, and moisture. P5-CMPs exhibited reversible type I gas sorption isotherms. The observed rapid gas uptake at relatively lowpressure range (below P/P0 ≤ 0.01) indicates the presence of permanent microporosity in P5-CMPs. Ar adsorption iso-

Table 1. Textural Properties Including Surface Areas and Corresponding Pore Volumes of P5-CMPs sample name

SBETa (m2 g−1)

Langmuir (m2 g−1)

Vmicrob (cm3 g−1)

dmicroc (nm)

Sext (m2 g−1)

Smicrod (m2 g−1)

Vtotale (cm3 g−1)

P5-CMP-1 P5-CMP-2

400 345

720 581

0.06 0.07

0.60 0.60

202 126

198 219

0.13 0.11

a

Brunauer−Emmett−Teller (BET) surface areas were calculated over the pressure range (P/P0) 0.01−0.12. bMicropore volume calculated using the t-plot method. cMicropore diameter calculated from NLDFT method. dMicropore surface area calculated from the adsorption isotherms using the tplot method. eTotal pore volume obtained at P/P0 = 0.99. 4463


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Figure 4. Propane/methane single component gas uptake isotherms of P5-CMP-1 (a, b) and -2 (d, e) up to 1 bar at 298, 313, and 323 K for propane and at 288, 298, and 308 K for methane along with their corresponding isosteric heats of adsorption (Qst) data. Breakthrough experiments of P5CMP-1 (c) and P5-CMP-2 (f) for a binary methane/propane (9:1) gas mixture with a total flow 1 sccm at 298 K, 22 kPa. We note that the relatively delayed breakthrough time of P5-CMP-1 compared to P5-CMP-2 is attributed to the difference in the amount of adsorbents loaded into the testing columns: P5-CMP-1 (137 mg) and P5-CMP-2 (83.5 mg).

from continuous flow of methane/propane mixture. The adsorption capacities of P5-CMP-1 and P5-CMP-2 were calculated to be 0.51 and 0.47 mmol g−1, respectively. These results indicate that the intrinsic cavities of pillar[5]arene can be effectively utilized for affinity based separation of saturated hydrocarbons via supramolecular host−guest interactions, thus allowing us to transfer intrinsic properties of supramolecular hosts into the microporous polymers for gas separation applications.

can be attributed to the macrocyclic effect arising from the ideal size match of kinetic diameter of propane to the cavity of pillar[5]arene. Moreover, decreasing Qst values with increasing loading amounts of propane was observed. This result can be explained by the confinement of propane molecules within the cavity, which leads to a very high Qst at zero coverage; however, following the saturation of pillar[5]arene hosts, a narrow pore size distribution of P5-CMPs still limits intermolecular interactions between propane molecules, thus leading to the Qst values of 33−35 kJ mol−1 at high gas loadings.12 In the case of methane, however, we have observed a much lower Qst value of 20 kJ mol−1, which was obtained by fitting isotherm data using a single-site Langmuir model. In addition, unlike propane, we observed a slight increase in the Qst values with rising loadings presumably due to intermolecular interactions between methane molecules, which in turn indicates the lack of confinement for methane within the cavity of pillar[5]arene due to its smaller size. We calculated (Figure S16) the selectivity by using the ideal adsorbed solution theory (IAST) for propane/methane mixture of 10:90 to simulate natural gas conditions. The IAST selectivities of P5-CMP-1 and -2 were found to be 180, 189 at 298 K, 1 bar. Interestingly, we observed increasing selectivity with increasing loading presumably due to the high affinity of propane toward the pillar[5]arene cavity, which limits the diffusion of CH4 into the sorbent. To test real adsorption-based separation performance of P5-CMPs under the simulated natural gas conditions, breakthrough experiments were carried out (Figure 4c,f) using a binary methane and propane mixture with a molar ratio of 9:1. For the breakthrough experiments, the gas mixture was flowed over a packed bed of P5-CMPs with a total flow of 1 sccm at 298 K, 22 kPa. Before the breakthrough times at 15.6 and 8.7 min for P5-CMP-1 and P5-CMP-2, respectively, both P5-CMPs exhibited complete, selective adsorption of propane

4. CONCLUSION We have successfully demonstrated the synthesis of conjugated microporous polymers incorporating pillar[5]arene macrocycles and shown that the intrinsic properties of these macrocycles, i.e., their ability to bind long-chain linear hydrocarbons in solution via host−guest complexation, can be transferred into the solid-state in the form of microporous polymers and used in the affinity-based separation of saturated hydrocarbons such as propane from a natural gas mixture. Importantly, we introduced thermodynamic selectivity for the separation of saturated hydrocarbons from each other, which is rather difficult to achieve due to their low polarizability. Considering the vast number of host−guest complexes reported in the literature, this approach could pave the way for the preparation microporous polymers for selective encapsulation and separation of desired target guests from complex mixtures.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.6b01667. 4464


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(13) Ogoshi, T.; Kanai, S.; Fujinami, S.; Yamagishi, T.-a.; Nakamoto, Y. Para-bridged symmetrical pillar[5]arenes: Their lewis acid catalyzed synthesis and host−guest property. J. Am. Chem. Soc. 2008, 130, 5022−5023. (14) Ogoshi, T.; Aoki, T.; Kitajima, K.; Fujinami, S.; Yamagishi, T.-a.; Nakamoto, Y. Facile, rapid, and high-yield synthesis of pillar[5]arene from commercially available reagents and its X-ray crystal structure. J. Org. Chem. 2011, 76, 328−331. (15) Huang, F.; Gibson, H. W. Polypseudorotaxanes and polyrotaxanes. Prog. Polym. Sci. 2005, 30, 982−1018. (16) Elemans, J. A. A. W.; van Hameren, R.; Nolte, R. J. M.; Rowan, A. E. Molecular materials by self-assembly of porphyrins, phthalocyanines, and perylenes. Adv. Mater. 2006, 18, 1251−1266. (17) Jiang, W.; Schalley, C. A. Integrative self-sorting is a programming language for high level self-assembly. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 10425−10429. (18) Vinciguerra, B.; Cao, L.; Cannon, J. R.; Zavalij, P. Y.; Fenselau, C.; Isaacs, L. Synthesis and self-assembly processes of monofunctionalized cucurbit[7]uril. J. Am. Chem. Soc. 2012, 134, 13133−13140. (19) Yan, X.; Wang, F.; Zheng, B.; Huang, F. Stimuli-responsive supramolecular polymeric materials. Chem. Soc. Rev. 2012, 41, 6042− 6065. (20) Liu, K.; Kang, Y.; Wang, Z.; Zhang, X. 25th anniversary article: Reversible and adaptive functional supramolecular materials: “Noncovalent interaction” matters. Adv. Mater. 2013, 25, 5530−5548. (21) Wang, X.; Han, K.; Li, J.; Jia, X.; Li, C. Pillar[5]arene-neutral guest recognition based supramolecular alternating copolymer containing [c2]daisy chain and bis-pillar[5]arene units. Polym. Chem. 2013, 4, 3998−4003. (22) Wang, K.; Wang, C.-Y.; Zhang, Y.; Zhang, S. X.-A.; Yang, B.; Yang, Y.-W. Ditopic pillar[5]arene-based fluorescence enhancement material mediated by [c2]daisy chain formation. Chem. Commun. 2014, 50, 9458−9461. (23) Yu, G.; Zhang, Z.; Han, C.; Xue, M.; Zhou, Q.; Huang, F. A non-symmetric pillar[5]arene-based selective anion receptor for fluoride. Chem. Commun. 2012, 48, 2958−2960. (24) Li, C.; Ma, J.; Zhao, L.; Zhang, Y.; Yu, Y.; Shu, X.; Li, J.; Jia, X. Molecular selective binding of basic amino acids by a water-soluble pillar[5]arene. Chem. Commun. 2013, 49, 1924−1926. (25) Zhang, Z.; Zhao, Q.; Yuan, J.; Antonietti, M.; Huang, F. A hybrid porous material from a pillar[5]arene and a poly(ionic liquid): Selective adsorption of n-alkylene diols. Chem. Commun. 2014, 50, 2595−2597. (26) Zhang, Z.; Luo, Y.; Chen, J.; Dong, S.; Yu, Y.; Ma, Z.; Huang, F. Formation of linear supramolecular polymers that is driven by C-H···π interactions in solution and in the solid state. Angew. Chem., Int. Ed. 2011, 50, 1397−1401. (27) Hu, X.-Y.; Wu, X.; Wang, S.; Chen, D.; Xia, W.; Lin, C.; Pan, Y.; Wang, L. Pillar[5]arene-based supramolecular polypseudorotaxane polymer networks constructed by orthogonal self-assembly. Polym. Chem. 2013, 4, 4292−4297. (28) Wang, X.; Deng, H.; Li, J.; Zheng, K.; Jia, X.; Li, C. A neutral supramolecular hyperbranched polymer fabricated from an ab2-type copillar[5]arene. Macromol. Rapid Commun. 2013, 34, 1856−1862. (29) Wang, K.; Wang, C.-Y.; Wang, Y.; Li, H.; Bao, C.-Y.; Liu, J.-Y.; Zhang, S. X.-A.; Yang, Y.-W. Electrospun nanofibers and multiresponsive supramolecular assemblies constructed from a pillar[5]arene-based receptor. Chem. Commun. 2013, 49, 10528−10530. (30) Li, C.; Han, K.; Li, J.; Zhang, Y.; Chen, W.; Yu, Y.; Jia, X. Supramolecular polymers based on efficient pillar[5]areneneutral guest motifs. Chem. - Eur. J. 2013, 19, 11892−11897. (31) Li, Z.-Y.; Zhang, Y.; Zhang, C.-W.; Chen, L.-J.; Wang, C.; Tan, H.; Yu, Y.; Li, X.; Yang, H.-B. Cross-linked supramolecular polymer gels constructed from discrete multi-pillar[5]arene metallacycles and their multiple stimuli-responsive behavior. J. Am. Chem. Soc. 2014, 136, 8577−8589. (32) Song, N.; Chen, D.-X.; Qiu, Y.-C.; Yang, X.-Y.; Xu, B.; Tian, W.; Yang, Y.-W. Stimuli-responsive blue fluorescent supramolecular

Experimental methods, synthetic procedures, and additional structural and spectroscopic data (PDF).

AUTHOR INFORMATION

Corresponding Author

*A. Coskun. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a National Research Foundation of Korea (NRF) Grant funded by the Korea government (MEST; NRF-2014R1A4A1003712) and the BK21 PLUS program. The collection and analysis of gas adsorption data were supported through the Center for Gas Separations Relevant to Clean Energy Technologies, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award DE-SC0001015. G.B. thanks the Miller Institute for Basic Research in Science for a postdoctoral fellowship. We thank Prof. J. R. Long for use of gas adsorption analyzer to obtain propane isotherms.

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REFERENCES

(1) Karan, S.; Jiang, Z.; Livingston, A. G. Sub−10 nm polyamide nanofilms with ultrafast solvent transport for molecular separation. Science 2015, 348, 1347−1351. (2) Safarik, D. J.; Eldridge, R. B. Olefin/paraffin separations by reactive absorption: A review. Ind. Eng. Chem. Res. 1998, 37, 2571− 2581. (3) Herm, Z. R.; Bloch, E. D.; Long, J. R. Hydrocarbon separations in metal−organic frameworks. Chem. Mater. 2014, 26, 323−338. (4) Kim, J.; Lin, L.-C.; Martin, R. L.; Swisher, J. A.; Haranczyk, M.; Smit, B. Large-scale computational screening of zeolites for ethane/ ethene separation. Langmuir 2012, 28, 11914−11919. (5) Li, K.; Olson, D. H.; Seidel, J.; Emge, T. J.; Gong, H.; Zeng, H.; Li, J. Zeolitic imidazolate frameworks for kinetic separation of propane and propene. J. Am. Chem. Soc. 2009, 131, 10368−10369. (6) Bux, H.; Chmelik, C.; Krishna, R.; Caro, J. Ethene/ethane separation by the MOF membrane ZIF-8: Molecular correlation of permeation, adsorption, diffusion. J. Membr. Sci. 2011, 369, 284−289. (7) Lee, C. Y.; Bae, Y.-S.; Jeong, N. C.; Farha, O. K.; Sarjeant, A. A.; Stern, C. L.; Nickias, P.; Snurr, R. Q.; Hupp, J. T.; Nguyen, S. T. Kinetic separation of propene and propane in metal−organic frameworks: Controlling diffusion rates in plate-shaped crystals via tuning of pore apertures and crystallite aspect ratios. J. Am. Chem. Soc. 2011, 133, 5228−5231. (8) Li, B.; Zhang, Y.; Krishna, R.; Yao, K.; Han, Y.; Wu, Z.; Ma, D.; Shi, Z.; Pham, T.; Space, B.; Liu, J.; Thallapally, P. K.; Liu, J.; Chrzanowski, M.; Ma, S. Introduction of π-complexation into porous aromatic framework for highly selective adsorption of ethylene over ethane. J. Am. Chem. Soc. 2014, 136, 8654−8660. (9) Slater, A. G.; Cooper, A. I. Function-led design of new porous materials. Science 2015, 348, aaa8075. (10) Assen, A. H.; Belmabkhout, Y.; Adil, K.; Bhatt, P. M.; Xue, D.X.; Jiang, H.; Eddaoudi, M. Ultra-tuning of the rare-earth fcu-mof aperture size for selective molecular exclusion of branched paraffins. Angew. Chem., Int. Ed. 2015, 54, 14353−14358. (11) Huang, L.; Cao, D. Selective adsorption of olefin-paraffin on diamond-like frameworks: Diamondyne and paf-302. J. Mater. Chem. A 2013, 1, 9433−9439. (12) Geier, S. J.; Mason, J. A.; Bloch, E. D.; Queen, W. L.; Hudson, M. R.; Brown, C. M.; Long, J. R. Selective adsorption of ethylene over ethane and propylene over propane in the metal-organic frameworks m2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Zn). Chem. Sci. 2013, 4, 2054− 2061. 4465


Article

Chemistry of Materials polymers based on a pillar[5]arene tetramer. Chem. Commun. 2014, 50, 8231−8234. (33) Li, C. Pillararene-based supramolecular polymers: From molecular recognition to polymeric aggregates. Chem. Commun. 2014, 50, 12420−12433. (34) Song, N.; Chen, D.-X.; Xia, M.-C.; Qiu, X.-L.; Ma, K.; Xu, B.; Tian, W.; Yang, Y.-W. Supramolecular assembly-induced yellow emission of 9,10-distyrylanthracene bridged bis(pillar[5]arene)s. Chem. Commun. 2015, 51, 5526−5529. (35) Yang, J.; Li, Z.; Zhou, Y.; Yu, G. Construction of a pillar[5]arene-based linear supramolecular polymer and a photoresponsive supramolecular network. Polym. Chem. 2014, 5, 6645− 6650. (36) Yu, G.; Yu, W.; Mao, Z.; Gao, C.; Huang, F. A pillararene-based ternary drug-delivery system with photocontrolled anticancer drug release. Small 2015, 11, 919−925. (37) Yao, Y.; Xue, M.; Chen, J.; Zhang, M.; Huang, F. An amphiphilic pillar[5]arene: Synthesis, controllable self-assembly in water, and application in calcein release and tnt adsorption. J. Am. Chem. Soc. 2012, 134, 15712−15715. (38) Dong, S.; Yuan, J.; Huang, F. A pillar[5]arene/imidazolium [2]rotaxane: Solvent- and thermo-driven molecular motions and supramolecular gel formation. Chem. Sci. 2014, 5, 247−252. (39) Shu, X.; Chen, W.; Hou, D.; Meng, Q.; Zheng, R.; Li, C. Novel binding regioselectivity in the interpenetration of a non-symmetric axle into a non-symmetric pillar[5]arene wheel. Chem. Commun. 2014, 50, 4820−4823. (40) Strutt, N. L.; Fairen-Jimenez, D.; Iehl, J.; Lalonde, M. B.; Snurr, R. Q.; Farha, O. K.; Hupp, J. T.; Stoddart, J. F. Incorporation of an a1/ a2-difunctionalized pillar[5]arene into a metal−organic framework. J. Am. Chem. Soc. 2012, 134, 17436−17439. (41) Si, W.; Xin, P.; Li, Z.-T.; Hou, J.-L. Tubular unimolecular transmembrane channels: Construction strategy and transport activities. Acc. Chem. Res. 2015, 48, 1612−1619. (42) Si, W.; Chen, L.; Hu, X.-B.; Tang, G.; Chen, Z.; Hou, J.-L.; Li, Z.-T. Selective artificial transmembrane channels for protons by formation of water wires. Angew. Chem., Int. Ed. 2011, 50, 12564− 12568. (43) Ogoshi, T.; Sueto, R.; Yoshikoshi, K.; Sakata, Y.; Akine, S.; Yamagishi, T.-A. Host−guest complexation of perethylated pillar[5]arene with alkanes in the crystal state. Angew. Chem., Int. Ed. 2015, 54, 9849−9852. (44) Tan, L.-L.; Li, H.; Tao, Y.; Zhang, S. X.-A.; Wang, B.; Yang, Y.W. Pillar[5]arene-based supramolecular organic frameworks for highly selective co2-capture at ambient conditions. Adv. Mater. 2014, 26, 7027−7031. (45) Jiang, J.-X.; Su, F.; Trewin, A.; Wood, C. D.; Campbell, N. L.; Niu, H.; Dickinson, C.; Ganin, A. Y.; Rosseinsky, M. J.; Khimyak, Y. Z.; Cooper, A. I. Conjugated microporous poly(aryleneethynylene) networks. Angew. Chem., Int. Ed. 2007, 46, 8574−8578. (46) Jiang, J.-X.; Su, F.; Niu, H.; Wood, C. D.; Campbell, N. L.; Khimyak, Y. Z.; Cooper, A. I. Conjugated microporous poly(phenylene butadiynylene)s. Chem. Commun. 2008, 486−488. (47) Dawson, R.; Laybourn, A.; Clowes, R.; Khimyak, Y. Z.; Adams, D. J.; Cooper, A. I. Functionalized conjugated microporous polymers. Macromolecules 2009, 42, 8809−8816. (48) Alsbaiee, A.; Smith, B. J.; Xiao, L.; Ling, Y.; Helbling, D. E.; Dichtel, W. R. Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer. Nature 2016, 529, 190−194. (49) Ogoshi, T.; Umeda, K.; Yamagishi, T.-a.; Nakamoto, Y. Through-space [small pi]-delocalized pillar[5]arene. Chem. Commun. 2009, 4874−4876. (50) Buyukcakir, O.; Seo, Y.; Coskun, A. Thinking outside the cage: Controlling the extrinsic porosity and gas uptake properties of shapepersistent molecular cages in nanoporous polymers. Chem. Mater. 2015, 27, 4149−4155. (51) Byun, Y.; Coskun, A. Bottom-up approach for the synthesis of a three-dimensional nanoporous graphene nanoribbon framework and its gas sorption properties. Chem. Mater. 2015, 27, 2576−2583.

(52) Srinivas, G.; Burress, J. W.; Ford, J.; Yildirim, T. Porous graphene oxide frameworks: Synthesis and gas sorption properties. J. Mater. Chem. 2011, 21, 11323−11329. (53) Song, K. S.; Coskun, A. Catalyst-free synthesis of porous graphene networks as efficient sorbents for co2 and h2. ChemPlusChem 2015, 80, 1127−1132. (54) Bao, Z.; Alnemrat, S.; Yu, L.; Vasiliev, I.; Ren, Q.; Lu, X.; Deng, S. Adsorption of ethane, ethylene, propane, and propylene on a magnesium-based metal−organic framework. Langmuir 2011, 27, 13554−13562.

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