Tubular-Shape Evolution of Microporous Organic...

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Tubular-Shape Evolution of Microporous Organic Networks Jiseul Chun, Ji Hoon Park, Jieun Kim, Sang Moon Lee, Hae Jin Kim, and Seung Uk Son* ,Department of Chemistry and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea Korea Basic Science Institute, Daejeon 350-333, Korea * S Supporting Information ABSTRACT: This work suggests a synthetic method for tubular-shape evolution of amorphous and microporous organic networks. The gradual addition of a dihalo building block to its mixture with tetrakis(4-ethynylphenyl)methane under conventional Sonogashira coupling conditions resulted in the formation of tubular materials. The resulting tubular materials were characterized by scanning and transmission (TEM) electron microscopies, BrunauerEmmettTeller and thermogravimetric analyses, and solid-phase 13 C NMR spectroscopy. In comparison, when the mixture of a dihalo building block and tetrakis(4- ethynylphenyl)methane was heated under conventional Sonogashira coupling conditions, granular materials were formed. We suggest that the tubular-shape evolution is attributed to the dierences of steric situations in networking steps. In TEM, the oriented attachment of the tubular materials was observed. KEYWORDS: porous material, microporous organic network, tube, Sonogashira coupling, shape control, oriented attachment 1. INTRODUCTION During the past decade, amorphous and microporous organic networks (A-MON) have been extensively prepared via diverse organic reactions among building blocks. 1 For example, the Cooper group reported the Sonogashira-coupling-based for- mation of A-MON using multialkynes and multihalides. 2 Usually, related studies have focused on the inner porosity of materials and the resulting high surface area. In addition, by screening of the geometry of the building blocks, the pore sizes and surface areas of A-MONs could be controlled. 2a Recently, several building blocks with tetrahedral geometry have been used as connectors for obtaining A-MONs with 3D inner network structures. 3 However, studies on the outer-shape evolution of A-MONs having 3D inner networking are quite rare, 4 possibly for the following two reasons. First, because the outer shape of A-MONs can be expected to be amorphous, control of the outer shape was not seriously considered. Second, an isotropic shape, such as in spherical materials, can be expected when tetrahedral building blocks were used to induce 3D inner network structure. Thus, the mechanism of the outer-shape evolution of A-MONs has not yet been seriously considered. The outer shape of A-MONs can be a key factor for their physical properties and ultimate applications. For example, the dispersion ability in solvents and the diusion pathway of guest molecules into porous networks can be dependent on the outer shape of A-MONs. 4b In addition, our research group has recently prepared metal oxide incorporated A-MONs for application as anode materials of lithium-ion batteries. 5 The metal oxides were successfully incorporated into microporous networks and showed enhanced stability in maintaining a discharge capacity, possibly because of the structural buering action of the networks. In this case, the outer shape of the composites was important for their performance because the electrochemical reactions occurred on the surface of the materials. In continuous eorts for the synthesis of new functional A- MON materials, we and other groups often encountered mixtures of the conventional spherical granules and intriguing tubular materials (as a minor product). 6 We have tenaciously tried to elucidate the underlying mechanism of anisotropic- shape evolution and ultimately to develop the synthetic process for purely tubular materials. In this work, we report a synthetic method for the tubular-shape evolution of amorphous MONs and suggestions for the underlying mechanism. Received: June 8, 2012 Revised: August 2, 2012 Published: August 21, 2012 Article pubs.acs.org/cm © 2012 American Chemical Society 3458 dx.doi.org/10.1021/cm301786g | Chem. Mater. 2012, 24, 34583463

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Tubular-Shape Evolution of Microporous Organic NetworksJiseul Chun,† Ji Hoon Park,† Jieun Kim,† Sang Moon Lee,‡ Hae Jin Kim,‡ and Seung Uk Son*,†

†Department of Chemistry and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea‡Korea Basic Science Institute, Daejeon 350-333, Korea

*S Supporting Information

ABSTRACT: This work suggests a synthetic method for tubular-shape evolution of amorphous and microporous organicnetworks. The gradual addition of a dihalo building block to its mixture with tetrakis(4-ethynylphenyl)methane underconventional Sonogashira coupling conditions resulted in the formation of tubular materials. The resulting tubular materials werecharacterized by scanning and transmission (TEM) electron microscopies, Brunauer−Emmett−Teller and thermogravimetricanalyses, and solid-phase 13C NMR spectroscopy. In comparison, when the mixture of a dihalo building block and tetrakis(4-ethynylphenyl)methane was heated under conventional Sonogashira coupling conditions, granular materials were formed. Wesuggest that the tubular-shape evolution is attributed to the differences of steric situations in networking steps. In TEM, theoriented attachment of the tubular materials was observed.

KEYWORDS: porous material, microporous organic network, tube, Sonogashira coupling, shape control, oriented attachment

1. INTRODUCTION

During the past decade, amorphous and microporous organicnetworks (A-MON) have been extensively prepared via diverseorganic reactions among building blocks.1 For example, theCooper group reported the Sonogashira-coupling-based for-mation of A-MON using multialkynes and multihalides.2

Usually, related studies have focused on the inner porosity ofmaterials and the resulting high surface area. In addition, byscreening of the geometry of the building blocks, the pore sizesand surface areas of A-MONs could be controlled.2a Recently,several building blocks with tetrahedral geometry have beenused as connectors for obtaining A-MONs with 3D innernetwork structures.3 However, studies on the outer-shapeevolution of A-MONs having 3D inner networking are quiterare,4 possibly for the following two reasons. First, because theouter shape of A-MONs can be expected to be amorphous,control of the outer shape was not seriously considered.Second, an isotropic shape, such as in spherical materials, canbe expected when tetrahedral building blocks were used toinduce 3D inner network structure. Thus, the mechanism of theouter-shape evolution of A-MONs has not yet been seriouslyconsidered.The outer shape of A-MONs can be a key factor for their

physical properties and ultimate applications. For example, thedispersion ability in solvents and the diffusion pathway of guest

molecules into porous networks can be dependent on the outershape of A-MONs.4b In addition, our research group hasrecently prepared metal oxide incorporated A-MONs forapplication as anode materials of lithium-ion batteries.5 Themetal oxides were successfully incorporated into microporousnetworks and showed enhanced stability in maintaining adischarge capacity, possibly because of the structural bufferingaction of the networks. In this case, the outer shape of thecomposites was important for their performance because theelectrochemical reactions occurred on the surface of thematerials.In continuous efforts for the synthesis of new functional A-

MON materials, we and other groups often encounteredmixtures of the conventional spherical granules and intriguingtubular materials (as a minor product).6 We have tenaciouslytried to elucidate the underlying mechanism of anisotropic-shape evolution and ultimately to develop the synthetic processfor purely tubular materials. In this work, we report a syntheticmethod for the tubular-shape evolution of amorphous MONsand suggestions for the underlying mechanism.

Received: June 8, 2012Revised: August 2, 2012Published: August 21, 2012

Article

pubs.acs.org/cm

© 2012 American Chemical Society 3458 dx.doi.org/10.1021/cm301786g | Chem. Mater. 2012, 24, 3458−3463

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2. EXPERIMENTAL SECTIONTransmission electron microscopy (TEM) and high-resolution TEMimages were obtained using a JEOL 2100F unit operated at 200 kV.Samples for TEM were prepared on a copper grid by drop-casting amethylene chloride solution of the materials. The scanning electronmicroscopy (SEM) images were taken by a field-emission scanningelectron microscope (JSM6700F). Powder X-ray diffraction (PXRD)patterns were obtained using a Rigaku MAX-2200 and filtered Cu Kαradiation. Solid-phase 13C NMR spectra were recorded on a Varian600 MHz NOVA600 spectrometer at KBSI (Daegu). Adsorption−desorption isotherm curves for N2 (77 K) were recorded by usingBELSORP II-mini volumetric adsorption equipment. Thermogravi-metric analysis (TGA) curves were obtained by Seiko Exstar 7300.Elemental analysis was performed on a CE EA1110 elemental analysisinstrument.Preparation of Building Block A, Its Methyl Salt, and B. The

building block A, 3,5-bis(4-bromophenyl)pyridine was prepared by themethod in the literature.8 (4-Bromophenyl)acetonitrile (10 g, 0.051mol) and toluene (35 mL) were added to a flame-dried 250 mL two-necked Schlenk flask. A 1.5 M toluene solution (45 mL, 0.068 mol) ofdiisobutylaluminum hydride in a flame-dried dropping funnel wasslowly added to the Schlenk flask at −5 °C. At this temperature, thereaction mixture was stirred for an additional 1.5 h. Ethanol (20 mL)was added to the reaction mixture at −5 °C. Toluene (35 mL) wasadded at 0 °C, and then 1 M sulfuric acid (120 mL) was slowly added.At room temperature, the reaction mixture was extracted with brinethree times and the resultant toluene solution was separated. In a 250mL one-necked Schlenk flask, the toluene solution above andmorpholine (20 mL) were mixed, and the reaction mixture wasstirred overnight. Then, after the solvent was evaporated, the solid wasrecrystallized using cyclohexane and retrieved by centrifugation. Afterwashing with cyclohexane, the resulting solid, 2-(N-morpholino)-4′-bromostyrene, was dried under vacuum. For the preparation ofhexahydra-1,3,5-tri-tert-butyl-1,3,5-triazine, a 37% formaldehyde sol-ution (45 mL) was added dropwise to tert-butylamine (32 mL) in aflame-dried 100 mL one-necked Schlenk flask at 5 °C. The reactionmixture was stirred at room temperature for 2 h. The organic phasewas separated using a separatory funnel, and the remaining water wasremoved using KOH. For the preparation of 3,5-bis(4-bromophenyl)-pyridine (building block A), 2-(N-morpholino)-4′-bromostyrene (3.2g, 12 mmol), hexahydra-1,3,5-tri-tert-butyl-1,3,5-triazine (1.6 g, 6.3mmol), and p-xylene (43 mL) were added to a flame-dried 100 mLtwo-necked Schlenk flask. The reaction mixture was refluxed for 72 h.Then, after cooling to room temperature, the solid was recrystallizedusing hot ethanol. The resulting solid, 3,5-bis(4-bromophenyl)-pyridine, was dried under vacuum. 1H NMR spectrum of the productmatched well with the reported one.8 1H NMR (300 MHz, CDCl3): δ7.79 (d, J = 6.6 Hz, 4H), 7.70 (s, 1H), 7.54 (m, 3H), 7.37 (d, J = 6.6Hz, 4H). For the preparation of methyl salts of building block A, 3,5-bis(4-bromophenyl)pyridine (0.50 g, 1.3 mmol) was suspended inacetonitrile (30 mL) using a flame-dried 50 mL Schlenk flask. After theaddition of methyl iodide (0.24 mL, 3.9 mmol), the reaction mixturewas refluxed overnight. After cooling to room temperature, theprecipitates were separated by filtration, washed with acetone, anddried under vacuum. Characterization data of the methyl salt ofbuilding block A are given. 1H NMR (300 MHz, DMSO-d6): δ 9.41 (s,2H), 9.14 (s, 1H), 7.98 (d, J = 8.7 Hz, 4H), 7.85 (d, J = 8.7 Hz, 4H),4.45 (s, 3H). 13C NMR (75 MHz, DMSO-d6): δ 142.2, 139.3, 138.0,132.4, 134.1, 129.7, 124.1, 48.3. HRMS (FAB). Calcd for C18H14NBr2([M − I]+): m/z 401.9493. Found: m/z 401.9497. The building blockB, tetrakis(4-ethynylphenyl)methane, was prepared by the method inthe literature.3b

Preparation of Tubular A-MONs. In a flame-dried 50 mL two-neck Schlenk flask, 3,5-bis(4-bromophenyl)pyridine (23 mg, 0.060mmol) and tetrakis(4-ethynylphenyl)methane (50 mg, 0.12 mmol)were dissolved in a mixture of toluene (2 mL) and triethylamine (6mL). After the addition of bis(triphenylphosphine)palladiumdichloride (8.4 mg, 0.012 mmol) and copper iodide (2.3 mg, 0.012mmol), the reaction mixture was heated at 90 °C under nitrogen.

Then, 3,5-bis(4-bromophenyl)pyridine (70 mg, 0.18 mmol) in toluene(10 mL) was slowly added to the reaction mixture for 1 h using asyringe pump. After the reaction mixture was stirred for 24 h at 90 °C,the resulting precipitates were retrieved by centrifugation, washed withmethanol, methylene dichloride, and acetone, and dried undervacuum.

Preparation of Granular A-MONs. 3,5-Bis(4-bromophenyl)-pyridine (93 mg, 0.24 mmol) and tetrakis(4-ethynylphenyl)methane(50 mg, 0.12 mmol) were dissolved in a mixture of toluene (12 mL)and triethylamine (6 mL) in a flame-dried 50 mL two-necked Schlenkflask. Copper iodide (2.3 mg, 0.012 mmol) and bis-(triphenylphosphine)palladium dichloride (8.4 mg, 0.012 mmol)were added, and the reaction mixture was heated at 90 °C for 24 hunder nitrogen. The isolated precipitates were washed with methanol,methylene dichloride, and acetone, and dried under vacuum. For thepreparation of granular A-MONs in Figure S1 in the SI, 3,5-bis(4-bromophenyl)-N-methylpyridinium iodide (0.24 mmol) was usedinstead of 3,5-bis(4-bromophenyl)pyridine.

Preparation of the Methyl Adduct of Tubular A-MONs. In aflame-dried 50 mL Schlenk flask, tubular A-MONs (60 mg) weresuspended in acetonitrile (8 mL). After the addition of methyl iodide(1.0 mL, 1.6 mmol), the reaction mixture was heated at 80 °C for 48 h.The resulting precipitates were retrieved by centrifugation, washedwith acetone, and dried under vacuum.

3. RESULTS AND DISCUSSIONBasically, A-MONs in this work were prepared by Sonogashiracoupling between tetrahedral multialkyne building blocks anddihalo building blocks (Scheme 1). In previous observations in

our group, when imidazolium or viologen salt containing dihalobuilding blocks was used, we observed the exclusive formationof tubular materials.4b,7 In comparison, when neutral dihalobuilding blocks such as 1,3- or 1,4-bis(4-iodophenyl)benzenewere used, spherical materials were obtained.5,7 Consideringthis, at first glance, it was speculated that a certain undisclosedassembly related to the ionic character of salt-containing dihalobuilding blocks may exist in a relatively less polar solvent forinduction of the tubular shape.To get more straightforward information by a systematic

approach, we prepared 3,5-bis(4-bromophenyl)pyridine (A).8

By transformation of building block A to its methylpyridiniumsalt form, a change in the outer shape of the materials fromspheres to tubular materials would be expected. However, inboth cases (A and its pyridinium derivative), we obtainedirregular granules (Figure S1 in the SI). In the continuoussearch for synthetic conditions for purely tubular materials,finally, we found that maintaining a subequivalent amount ofdihalo building blocks against tetrahedral building blocks innetworking is a key reaction condition for successful tubular-shape evolution (vide infra). The resulting optimized syntheticprocedure for anisotropic-shape evolution is shown in Scheme1.

Scheme 1. Synthetic Methods for A-MONs in This Study

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First, the conventional method was applied for thepreparation of A-MONs using building block A and tetrakis-(4-ethynylphenyl)methane (B). After 2 equiv of A and 1 equivof B were completely dissolved in a mixture of toluene andtriethylamine, the reaction mixture was heated at 90 °C for 24 husing 5 mol % (PPh3)2PdCl2 and 5 mol % CuI catalysts. Duringthe reaction, dark-yellow precipitates gradually formed. SEM ofthe obtained A-MONs showed irregular granules (Figure 1e).

Second, in a comparison with the conventional method above,when 1.5 equiv of A was slowly added to the mixture of 0.5equiv of A and 1 equiv of B at 90 °C for 1 h by a syringe pumpand the reaction mixture was heated for 24 h, the tubes wereexclusively obtained. Parts a and e of Figure 1 show typicalSEM images of the tubular and granular A-MONs, respectively.The TEM images in Figures 1d and S2 and S4 in the SI showedthe hollow inner space of the tubes.Brunauer−Emmett−Teller (BET) analysis showed the

microporous character of A-MONs (Figures 1b,c and 2a).Interestingly, the tubular A-MON showed a significantly highersurface area value (580 m2/g) than the granular A-MON (506m2/g). In addition, while pore-size distribution patternsobtained by the density functional theory (DFT) methodwere similar, tubular A-MONs showed sharper pore-sizedistribution in a size range of <1 nm (red-circled peak inFigure 1b) compared with that of granular A-MONs (Figure1b,c). TGA and differential scanning calorimetry (DSC)showed that the tubular A-MON was stable up to 290 °C(Figures 2b and S3 in the SI). PXRD studies showed theamorphous character of both tubular and granular A-MONs(Figure 2c). Solid-state 13C NMR spectra of tubular andgranular A-MONs matched well with the expected structure(Figure 2d). Interestingly, the PXRD patterns and 13C NMRspectra of both tubular and granular A-MONs were nearlyidentical with each other.

Actually, the synthetic method for the tubular A-MON wasdevised from an insightful interpretation of tubular materials,which were obtained using salt-containing dihalo buildingblocks even by the conventional synthetic method in Scheme1.4b,7 We speculated that the salt-containing dihalo buildingblocks would have relatively poor solubility and hence mightgradually join in networking with B, which can be related toanisotropic-shape evolution. In the case of building block A inthis study, it has good solubility in the reaction medium used,and thus the anisotropic-shape evolution of A-MONs using A isquite challenging. However, we could induce a similar reactionsituation with the cases of salt-containing dihalo building blocksvia the gradual addition of the soluble A using a syringe pumpto the reaction mixture containing B. Considering this, wescreened the amount of A in the syringe and in the reactionmixture in the Schlenk flask. Figure 3 summarizes the results(see the Experimental Section for the detailed procedure).First, 2 equiv of A was slowly added to 1 equiv of B in a

Schlenk flask for 1 h under conventional Sonogashira couplingconditions, and then the reaction mixture was stirred for 24 h.However, black materials with irregular shape were obtainedpossibly by the self-coupling of B. Second, when 1.75 or 1.5equiv of A was slowly added for 1 h to a mixture of 1 equiv of Band 0.25 or 0.5 equiv of A, respectively, tubular materials wereobtained exclusively. Third, when the amount of A in themixture with 1 equiv of B in the Schlenk flask was increasedfrom 1 to 1.5 and 2 equiv, conventional granules started toform. Through these experiments, the key points could besummarized as follows. To obtain tubular A-MONs withconvincing quality, a partial amount of A is necessary in amixture with B in a Schlenk flask to suppress the self-couplingof B. Although more specific amounts of A in a mixture with 1equiv of B could be screened for further optimization, tubularA-MONs with sufficiently good quality were obtained by thegradual addition of 1.5 equiv of A to a mixture solution of 0.5equiv of A and 1 equiv of B.

Figure 1. SEM image of a tubular A-MON (a), pore-size distributions(based on a DFT method) of tubular (b) and granular (c) A-MONs,TEM image of a tubular A-MON (d), and SEM image of a granular A-MON (e).

Figure 2. (a) N2 adsorption isotherm curves by BET analysis, (b)TGA curves, (c) PXRD patterns, and solid-state 13C NMR spectra oftubular (red) and granular (black) A-MONs.

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The next question was, why were the tubular materialsobtained by the synthetic method in this study? We suggest oneof the candidates of the underlying mechanism for theformation of tubular materials, acknowledging that alternativesuggestions are definitely possible by other scientists.9 Asexplained in Scheme 2, although the tubular A-MON hasamorphous character and the building block B has symmetrictetrahedral geometry, its connection with A for 3D networkingcan be analyzed step by step according to differences in stericsituations. First, the growth of materials in the 1D direction(process a in Scheme 2) can be induced by the 1:1 connection

of B with A. Second, the interconnection of 1D chains to forma 2D network (process b in Scheme 2) is the second preferableone. Third, 3D networking (process c in Scheme 2) occursslowly. Thus, we think that the order of the more facile reactionwill be (1) the formation of a 1D connection, (2)interconnection of 1D chains to 2D networks, and then (3)3D networking. These three processes will occur at the sametime and compete with one another. The kinetic differences inthese processes may result in anisotropic-shape evolution, as isoften observed in the template-free tube formation of inorganicpolymer materials.10

Usually, the formation of tubular materials can be understoodby interconnection of the end parts of 2D plates with certainthickness, the so-called rolling mechanism.10 The inner tubediameters showed a size distribution in the range of 12−40 nm.The formation timing of the tubular structure by a possiblerolling process10 and a ripening process depending on the wallthickness of each tube may be related to the size distribution ofthe inner tube diameters.It can be speculated that the growths in the direction of the

length, diameter, and thickness of the tubular structurecorrespond to the formation of 1D chains, interconnection ofthe chains to 2D networks, and then 3D networking,respectively, as is explained in Scheme 2. This anisotropic-shape evolution can be induced efficiently by the slow additionof A to B. In contrast, if the amount of A exceeds a certainconcentration such as the situation in the conventionalsynthetic method for A-MON in Scheme 1, irregular granulesmay be formed via enhanced random networking.The terminal alkynes are known to show unique IR peaks at

∼3250 cm−1 in IR absorption spectroscopy.11 Thus, wefollowed the reaction process for tubular A-MONs by SEMand IR studies. The reaction mixture was transparent for nearly5 min. When the reaction mixture was quenched after 5 min, ill-defined materials with incomplete tubes were mainly observed.Interestingly, ribbonlike materials were rarely observed (FigureS4 in the SI). It is worth noting that the 2D intermediatematerials were often observed in tube formation through arolling process in material science.10 The materials obtainedafter 30 min showed relatively shorter tubes. As the reactionproceeded, the length of the tube was gradually elongatedthrough oriented attachment12 (vide infra).As shown in Figure 4, the terminal alkynes existed for a

longer time in networking for tubular A-MONs than in that forgranular A-MONs, which means that networking occurredmore gradually in the case of tubular A-MONs. Elementalanalysis for the resulting materials after 24 h showed that morebuilding block A participated in networking in granular A-MONs (1.55 wt % N) than in the case of the tubular one (0.98wt % N), which matches well with the IR results. Thus, itseemed that networking for the granular A-MONs wasrelatively faster and occurred gradually for the tubular A-MONs, which is believed to be the origin of efficientanisotropic-shape evolution in the synthetic method in thisstudy.Another interesting aspect in tubular A-MONs is the

unexpected observation of oriented attachment12 of the tubes.In careful TEM analysis of tubular A-MONs, not only end-to-end (circled with red in Figure 5) but also side-to-sideattachments (circled with blue) of the tubes were frequentlyobserved (Figures 5 and S5 in the SI). Especially, the end-to-end attachment was mainly observed in unsmoothly bent partsof the tubes, which implies that the tubes can be elongated via

Figure 3. SEM images of materials obtained by screening the amountof building block A (the first equiv value in each SEM image) in asyringe with 10 mL of toluene and that (the second equiv value in eachSEM image) in a Schlenk flask with 1 equiv of building block B,respectively. The 0 equiv of A in the last SEM image means that 10 mLof toluene without A was added by a syringe pump. Scale bars in SEMimages correspond to 1 μm.

Scheme 2. Suggested Mechanistic Aspects of Tubular A-MONs

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oriented attachment in the ripening process. Although theoriented attachment process was often reported in the growthprocess of crystalline inorganic nanomaterials,13 its observationin the growth of amorphous organic networks was, as far as weare aware, unprecedented. These observations imply anintriguing fact that, although the PXRD pattern of the tubularA-MON showed typical amorphous character, each side of thetubes in this work has differentiated reactivity toward growth.When the synthetic method for tubular-shape evolution was

applied to other dihalo building blocks such as 2,8-dibromobenzothiophene and 1,3-bis(4-iodophenyl)benzene inplace of building block A, similar tubular materials wereobtained (Figure S6 in the SI). In addition, because the tubularA-MON obtained from building block A contains pyridinerings, model studies of postsynthetic functionalization wereconducted (Figure 6a). When the tubular A-MON was treatedwith excess methyl iodide, broad peaks at 50 and 140 ppmappeared in the solid-state 13C NMR spectrum, indicatinggeneration of the methylpyridinium moieties14 (Figure 6c).

The surface area was decreased from 580 to 470 m2/g (Figure6b). According to SEM and TEM analysis, the original tubularshape was maintained, indicating that tailored functional sitescan be introduced into the tubes (Figure 6d,e).

4. CONCLUSIONSThis study shows an optimized synthetic route for tubularmicroporous organic networks. Under Sonogashira couplingconditions, the gradual addition of 1.5 equiv of 3,5-bis(4-bromophenyl)pyridine to a mixture of 1 equiv of tetrakis(4-ethynylphenyl)methane and 0.5 equiv of 3,5-bis(4-bromophenyl)pyridine by a syringe pump induced tubular-shape evolution of microporous organic networks. Interestingly,the oriented attachment of tubes was observed. It is suggestedthat anisotropic-shape evolution of amorphous organic net-works is attributable to the differences in the steric situations ofnetworking steps. We believe that the synthetic method in thiswork can be extended to other dihalo building blocks.

■ ASSOCIATED CONTENT*S Supporting InformationExperimental details, DSC curves, and additional SEM andTEM images. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: [email protected] authors declare no competing financial interest.

Figure 4. SEM images and IR spectra of tubular and granular A-MONs taken from reaction mixtures after 0.5, 1, and 24 h. Scale barscorrespond to 1 μm. The peaks in the IR spectra indicated by asteriskscorrespond to terminal alkynes.

Figure 5. (a) Illustration and (b) the corresponding TEM image of atypical oriented attachment of the tubular A-MON (also refer toFigure S5 in the SI for more diverse images).

Figure 6. (a) Illustration of methylation of the tubular A-MON and(b) BET, (c) solid-state 13C NMR, (d) SEM and (e) TEMcharacterization of the methyl adduct to the tubular A-MON.

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■ ACKNOWLEDGMENTSThis work was supported by Grants NRF-2009-0084799through the National Research Foundation of Korea fundedby the Ministry of Education, Science and Technology. J.K. isthankful for Grants NRF-2011-0031392 (Priority ResearchCenters Program) and R31-2008-10029 (WCU program).H.J.K. is thankful for the Hydrogen Energy R&D Center, a 21stcentury Frontier Program.

■ REFERENCES(1) Recent reviews on A-MONs: (a) Mckeown, N. B.; Budd, P. M.Chem. Soc. Rev. 2006, 35, 675. (b) Weder, C. Angew. Chem., Int. Ed.2008, 47, 448. (c) Jiang, J.-X.; Cooper, A. I. Top. Curr. Chem. 2010,293, 1. (d) Thomas, A. Angew. Chem., Int. Ed. 2010, 49, 8328.(2) (a) Jiang, J.-X.; Su, F.; Trewin, A.; Wood, C. D.; Niu, H.; Jones, J.T. A.; Khimyak, Y. Z.; Cooper, A. I. J. Am. Chem. Soc. 2008, 130, 7710.(b) Jiang, J.-X.; Laybourn, A.; Clowes, R.; Khimyak, Y. Z.; Bacsa, J.;Higgins, S. J.; Adams, D. J.; Cooper, A. I. Macromolecules 2010, 43,7577.(3) Selected examples: (a) Weber, J.; Thomas, A. J. Am. Chem. Soc.2008, 130, 6334. (b) Yuan, S.; Kirklin, S.; Dorney, B.; Liu, D.-J.; Yu, L.Macromolecules 2009, 42, 1554. (c) Wang, Z.; Zhang, B.; Yu, H.; Sun,L.; Jiao, C.; Liu, W. Chem. Commun. 2010, 46, 7730. (d) Patra, A.;Koenen, J.-M.; Scherf, U. Chem. Commun. 2011, 47, 9612. (e) Zhao,Y.-C.; Zhou, D.; Chen, Q.; Zhang, X.-J.; Bian, X.; Qi, A.-D.; Han, B.-H.Macromolecules 2011, 44, 6382. (f) Xie, Z.; Wang., C.; deKrafft, K. E.;Lin, W. J. Am. Chem. Soc. 2011, 133, 2056.(4) (a) Feng, X.; Liang, Y.; Zhi, L.; Thomas, A.; Wu, D.; Lieberwirth,I.; Kolb, U.; Mullen, K. Adv. Funct. Mater. 2009, 19, 2125. (b) Chen,L.; Honsho, Y.; Seki, S.; Jiang, D. J. Am. Chem. Soc. 2010, 132, 6742.(c) Cho, H. C.; Lee, H. S.; Chun, J.; Lee, S. M.; Kim, H. J.; Son, S. U.Chem. Commun. 2011, 47, 917. (d) Patra, A.; Koenen, J.-M.; Scherf, U.Chem. Commun. 2011, 47, 9612.(5) Lee, H. S.; Choi, J.; Jin, J.; Chun, J.; Lee, S. M.; Kim, H. J.; Son, S.U. Chem. Commun. 2012, 48, 94.(6) (a) 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. Angew. Chem., Int. Ed. 2007, 46, 8574. (b) Hasell, T.;Wood, C. D.; Clowes, R.; Jones, J. T. A.; Khimyak, Y. Z.; Adams, D. J.;Cooper, A. I. Chem. Mater. 2010, 22, 557.(7) Kang, N.; Park, J. H.; Choi, J.; Jin, J.; Chun, J.; Jung, I. G.; Jeong,J.; Park, J.-G.; Lee, S. M.; Kim, H. J.; Son, S. U. Angew. Chem., Int. Ed.2012, 51, 6626.(8) Kumar, A.; Rhodes, R. A.; Spychala, J.; Wilson, W. D.; Boykin, D.W.; Tidwell, R. R.; Dykstra, C. C.; Hall, J. E.; Jones, S. K.; Schinazi, R.F. Eur. J. Med. Chem. 1995, 30, 99.(9) As far as we are aware, there were no mechanistic suggestions fortubular-shape evolution of microporous organic networks.(10) (a) Tenne, R. Angew. Chem., Int. Ed. 2003, 42, 5124. (b) Park, K.H.; Choi, J.; Kim, H. J.; Son, S. U. Chem. Mater. 2007, 19, 3861.(11) Pavia, D. L.; Lampman, G. M.; Kriz, G. S. Introduction toSpectroscopy; Brooks/Cole: Belmont, CA, 2001.(12) (a) Penn, R. L.; Banfield, J. F. Science 1998, 281, 969. (b) Penn,R. L.; Banfield, J. F. Am. Mineral. 1998, 83, 1077.(13) Recent selected examples: (a) O’Sullivan, C.; Gunning, R. D.;Sanyal, A.; Barrett, C. A.; Geaney, H.; Laffir, F. R.; Ahmed, S.; Ryan, K.M. J. Am. Chem. Soc. 2009, 131, 12250. (b) Koh, W.; Bartnik, A. C.;Wise, F. W.; Murray, C. B. J. Am. Chem. Soc. 2010, 132, 3909.(c) Wang, Z.; Schliehe, C.; Wang, T.; Nagaoka, Y.; Cao, Y. C.; Bassett,W. A.; Wu, H.; Fan, H.; Weller, H. J. Am. Chem. Soc. 2011, 133, 14484.(14) The benzyl adduct of the tubular A-MON was also obtained bythe reaction of the tubular A-MON with benzyl bromide instead ofmethyl iodide. It showed a decrease of the surface area from 580 to286 m2/g. However, it is hard to characterize vivid new peaks in itssolid-state 13C NMR spectra because of overlap of the correspondingpeaks of the benzyl moieties with those of the arene and alkynemoieties in the original tubular A-MON.

Chemistry of Materials Article

dx.doi.org/10.1021/cm301786g | Chem. Mater. 2012, 24, 3458−34633463