Linked Covalent Organic Framework - ACS Publications - American

Article Cite This: J. Am. Chem. Soc. 2018, 140, 12922−12929

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Layer-Stacking-Driven Fluorescence in a Two-Dimensional ImineLinked Covalent Organic Framework Pablo Albacete,† Jose ́ I. Martínez,‡ Xing Li,§ Alejandro Loṕ ez-Moreno,∥ Sofıá Mena-Hernando,∥ Ana E. Platero-Prats,*,† Carmen Montoro,† Kian Ping Loh,§ Emilio M. Peŕ ez,*,∥ and Feĺ ix Zamora*,†,∥,⊥,#

J. Am. Chem. Soc. 2018.140:12922-12929. Downloaded from pubs.acs.org by UNIV OF SUNDERLAND on 10/29/18. For personal use only.

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Departamento de Quı ́mica Inorgánica, ⊥Institute for Advanced Research in Chemical Sciences (IAdChem), and #Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain ‡ Departamento de Nanoestructuras, Superficies, Recubrimientos y Astrofı ́sica Molecular, Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC), 28049 Madrid, Spain § Department of Chemistry, Centre for Advanced 2D Materials (CA2DM), National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore ∥ Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, Madrid E-28049, Spain S Supporting Information *

ABSTRACT: Schiff-condensation reactions carried out between 1,6-diaminopyrene (DAP) and the tritopical 1,3,5 benzenetricarbaldehyde (BTCA) or 2,4,6-triformylphloroglucinol (TP) ligands give rise to the formation of twodimensional imine-based covalent-organic frameworks (COFs), named IMDEA-COF-1 and -2, respectively. These materials show dramatic layer-packing-driven fluorescence in solid state arising from the three-dimensional arrangement of the pyrene units among layers. Layer stacking within these 2D-COF materials to give either eclipsed or staggered conformations can be controlled, at an atomic level through chemical design of the building blocks used in their synthesis. Theoretical calculations have been used to rationalize the different preferential packing between both COFs. IMDEA-COF-1 shows green emission with absolute photoluminescence quantum yield of 3.5% in solid state. This material represents the first example of imine-linked 2D-COF showing emission in solid state.

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Decorating porous COF materials with π-conjugated photoelectric units, selectively, is an attractive strategy to develop chemical sensors. Unlike three-dimensional (3D) COF platforms,17 where quenching can be avoided by selecting suitable topologies, the preparation of highly fluorescent 2D-COFs in solid-state still remains a challenge. This is mainly due to the fact that packing is governed by π−π interactions among COF layers. Emission properties are often compromised in layered systems due to aggregation-caused quenching driven by those same π−π interactions. Highly emissive COFs have been obtained using different strategies. On one hand, boronate ester covalent frameworks, of certain structural flexibility, have been designed to form materials consisting on aggregation-induced emission moiety.18,22−24 Submicron particles of imine-based COFs integrating nonplanar pyrene building blocks have shown high photoluminescence (PL) and sensing abilities.25 More recently, solid-state emission has been turned on and tuned via

INTRODUCTION

Two-dimensional covalent organic frameworks (2D-COFs) are crystalline porous architectures resulting from the selfassembling of atomically designed aromatic layers.1 COF materials are constructed through condensation reactions among building blocks with particular geometries and chemistries.2 The selection of COF components allows design not only over chemical composition but also pore sizes and shapes.3−7 As these materials have been mainly explored for applications related to their porosity such as gas storage,8−10 potential for COF chemical functionalization has opened up novel directions such as water treatment,11,12 catalysis,13−16 or optoelectronics.17,18 However, embedding functional molecules into organized platforms often leads to modified properties compared to their performance in solution. In the case of 2D-COFs, layers are exclusively stacked through soft interactions, providing these materials with remarkable structural flexibility.19−21 Therefore, detailed understanding of the structural variety of 2D-COFs is mandatory to truly tailor their ultimate properties. © 2018 American Chemical Society

Received: July 15, 2018 Published: September 14, 2018 12922

DOI: 10.1021/jacs.8b07450 J. Am. Chem. Soc. 2018, 140, 12922−12929

Article

Journal of the American Chemical Society

Figure 1. (a) Schematic representation of the syntheses of IMDEA-COF systems by condensation of a tritopical aldehyde (1,3,5 benzenetricarbaldehyde, where R = H; or 1,3,5-triformilfloroglucionol, where R = OH) and 1,6-diaminopyrene (DAP), showing two possible pore isomers. (b) Comparison of ATR-FTIR data of IMDEA-COF-1 and -2. (c) 13C-MAS NMR spectra of IMDEA-COF-1 and (d) -2 systems.

agreement with the formation of bonds, as it shows a resonance at 155 ppm which corresponds to the imine carbon atom (Figure 1c). ATR-FTIR data collected on the modified IMDEA-COF-2 corroborated the existence of a much more complex chemistry, resulting in broad contributions in the regions related to imine and amine groups. The coexistence of the keto-amine and enol-imine tautomeric forms of IMDEA-COF-2 (Scheme 1)

restriction of intramolecular bond rotation (RIR) in hydrogenbonded hydrazone-based 2D COFs.26 In this way, it is imperative to harness local modifications within 2D-COFs that can result in improved solid-state fluorescence performance for ultimate applications. Herein, we report a novel family of imine-linked 2D-COFs bearing pyrene photoelectric units which show selective stacking-driven fluorescence (named IMDEA-COF materials). We show that structures in which the pyrene units are stacked in staggered fashion are excellent fluorescence emitters in solid state. The opposite behavior is observed for their eclipsed AAstacked counterparts. Interestingly, controlled pyrene-packing can be achieved through chemical modification of the aldehyde building blocks. Combined experimental and theoretical work has been carried out to elucidate the unexpectedly rich structural nature of these systems as well as the energetics for different pore and stacking isomers.

Scheme 1. Enol-Imine/Keto-Amine Tautomerism Observed for IMDEA-COF-2

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RESULTS AND DISCUSSION The syntheses of IMDEA-COF materials were carried out by Schiff condensation between the photoelectric building block 1,6-diaminopyrene (DAP) and the tritopic 1,3,5 benzenetricarbaldehyde (BTCA) or 2,4,6-triformylphloroglucinol (TP) ligands for IMDEA-COF-1 and -2, respectively. Reactions were performed in mixtures of m-cresol (2.6 mL) and glacial acetic acid (0.26 mL), heating at 120 °C for 3 or 7 days, respectively (Figure 1a). Activation of the COF materials to clean the pores of unreacted ligands and solvent was performed with supercritical CO2 (see SI for details about activation procedure). The formation of the IMDEA-COFs was confirmed by solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (CP-MAS NMR) and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopies (Figure 1 and SI Section S2). IMDEA-COF-1 showed characteristic ATR-FTIR signals at 1653 and 1276 cm−1 corresponding to CN and −CN−C stretching bands, respectively. The 13C CP-MAS NMR spectrum is also in good

was clearly identified by 13C CP-MAS NMR spectroscopy (Figure 1d). This COF showed distinctive signals at 182.3 and 146.8 ppm, linked to the carbonyl and the amine carbon atoms, respectively; together with a contribution at 154.5 ppm which corresponds to imine carbon atoms. Powder X-ray Diffraction (PXRD) data collected on the activated IMDEA-COF materials revealed major differences depending on the chemistry of the layers (Figure 2). IMDEACOF-2, bearing electron-donor oxygen groups (Figure 1a), showed a main Bragg diffraction peak at ∼4.3° 2-θ corresponding to the (100) plane. On the contrary, PXRD data of bare IMDEA-COF-1 showed two additional intense peaks at ∼12.3° and ∼13.2° 2θ. TGA showed thermal stability up to ∼300 °C for both IMDEA-COF materials (SI Section S6). These results 12923


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Figure 2. Representation of (a) IMDEA-COF-1 and (b) IMDEA-COF-2 structures, together with the experimental diffraction data against the simulated one for the periodic optimized models following AB- or AA- stacking (i.e., small-pore with corrugated layers and big-pore with flat layers). Peaks are assigned to the corresponding (hkl) planes within the structures. For clarity, only big-pore isomers are represented.

evidenced major structural differences between these two materials. To gain structural insights into the IMDEA-COF materials, the energetics of different models were explored computationally (Table 1). Based on the variable orientation of the imine Table 1. Cohesive Energy Values (Ec) for the Two Pore Isomer in Either Eclipsed or Staggered Conformations COF

pore

stacking

L (Å)

Ec (kcal mol−1)

IMDEA-1 IMDEA-1 IMDEA-1 IMDEA-1 IMDEA-2 IMDEA-2 IMDEA-2 IMDEA-2

small small big big small small big big

AA AB AA AB AA AB AA AB

3.543 3.482 3.760 3.749 3.570 3.637 3.780 3.638

−41.05 −38.28 −42.89 −39.66 −40.36a/−38.742b −14.53a/−16.37b −48.20a/−46.81b −20.99a/−19.83b

Figure 3. Representation of the optimized structures for (a) big- and (b) small-pore isomers for bare IMDEA-COF-1 parallel to the a and c axes (top and bottom, respectively). Accessible pore diameter values were computed with PLATON29 using the optimized periodic models.

a

Enol-imine form. bKeto-amine form.

Steric repulsions hinder the formation of flat layers for the small-pore IMDEA-COF materials (Figure 4a). The observed corrugation of the COF layers is caused by C−H···π weak hydrogen bonds30 found within the framework as determined for the optimized periodic models, resulting in a twisted conformation of the imine-linkage of ca. 30°. This structural feature is common for both of the IMDEA-COF chemistries explored. Interestingly, the relative stability of these two pore conformations (corrugated or flat) significantly depends on the chemistry of the COF layers. The calculations indicated that the formation of the big-pore isomer is energetically favored when using electron-donor-modified building blocks.

bonds27 (Figure 1a), we first computed periodic models of the two pore isomers in the expected more energetically favored AA-stacked-eclipsed conformation (Figure 3).28,29 The optimizations predicted for all cases the most energetically favorable networks having C3 symmetry, with formation of hexagonal-shaped pores. The computational studies indicated that, while the COF layers are virtually flat within the big-pore isomer (accessible pore diameter of ∼14.2 Å), there is an occurrence of an accused corrugation of the COF layers for the small-pore structure (accessible pore diameter of ∼13.1 Å) (Figure 3). 12924


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By comparing experimental against simulated diffraction data, it can be concluded that IMDEA-COF-1 is formed as a mixture of big- and small-pore structures in an AB stacking of the layers. We propose that this material is formed as a mixture of big- and small-pore structures in an AB stacking of the layers based on the broad contribution corresponding to the (100) plane centered at ca. 3.7 Å together with the occurrence of two distinctive peaks linked to the (101) plane (Figure 2a, dashed lines). These results are in good agreement with our computational predictions. Due to the small energy barriers between staggered and eclipsed conformations (i.e., ∼3 kcal mol−1) for IMDEA-COF-1, we propose AB-stacked COFs to be the kinetic products. For IMDEA-COF-2, diffraction data match well with the most stable computationally predicted AAbig-pore conformation (Figure 2b). Furthermore, the structural models for both IMDEA-COF materials match with the N2 adsorption data collected at 77 K for both of them (Figure 5). As it was expected, IMDEA-COF1 shows a low N2 adsorption capacity with a BET value of 78.82 m2 g−1, in comparison with IMDEA-COF-2, with a value of 397.12 m2 g−1.

Figure 4. Representation of IMDEA-COF-2 structures for (a) small pore and (b) big pore conformations, showing two perpendicular orientations. In the case of the small pore COF, steric repulsions hinder the formation of flat layers, resulting in a corrugated structure.

Thus, the big-pore structure is 7.8 kcal mol−1 more stable than its small-pore counterpart for IMDEA-COF-2, while in the unmodified IMDEA-COF-1, this energy barrier is substantially depressed to only 1.8 kcal mol−1 (Table 1). Periodic IMDEA-COF structures in a staggered conformation with AB stacking of the layers were also generated for both pore isomers. These theoretical studies predicted similar stabilization energy values for eclipsed and staggered conformations of IMDEA-COF-1. For this system, AA stacking is slightly more stable than AB stacking, with energies barriers of ca. ∼3 kcal mol−1 for both pore isomers (Table 1). This result points that all the structural configuration explored are likely to coexist experimentally. Contrary, for IMDEACOF-2, computations showed AA stacking to be about ∼40% more stable than AB stacking for both pore forms (Table 1). This result corroborates that, for IMDEA-COF-2, eclipsed conformations are significantly thermodynamically favored. More detailed analyses of the optimized periodic models of IMDEA-COF-2 indicated significantly small energy barriers of ca. 1.5 kcal mol−1 between tautomeric forms, for both pore isomers in AA and AB packing (Figure S4.1 and Table 1). This result corroborated the experimentally observed coexistence of both tautomers of IMDEA-COF-2. Interestingly, when considering a single COF monolayer, the keto-amine form was determined to be significantly more stable than the enolimine counterpart. The calculated energy barriers between tautomeric forms in a single layer were 10.4 and 7.6 kcal mol−1 for small and big pores, respectively (see SI Section S4). Electronic charge distribution DFT-based simulations were carried out to better understand the energetics of these COF structures. The calculations indicated that the electronic charge distribution is highly dependent on the configuration of the pores. While π-conjugation is virtually unaltered for big-pore conformations, remarkable redistribution of the electronic density is observed for the corrugated small-pore counterparts (Figures S4.2 and S4.3). Interestingly, while partial loss of conjugation appears to imply only a minor destabilization for the unmodified IMDEA-COF-1 structures (i.e., small-pore is only ∼7% less stable compared to big-pore for both packing), it does result in a remarkable energy penalty for IMDEA-COF2 structures (i.e., small-pore systems are ∼15% and ∼30% less stable compared to big-pore for AA and AB stacking, respectively) (Table 1). These results pointed electrostatic repulsion between layers to play a noninnocent role on the overall energy of these systems.

Figure 5. N2 adsorption (●,▲) and desorption (○,Δ) for IMDEACOF-1 (orange) and IMDEA-COF-2 (purple).

Both materials show the classic type I isotherm characterized by a sharp uptake under low pressures in the range of P/P0 < 0.003. Also, the Langmuir surface area found for IMDEACOF-1 was 106.51 m2 g−1, whereas for IMDEA-COF-2, it was 541.67 m2 g−1. The pore size distribution of IMDEA-COF-1 and IMDEACOF-2 was calculated based on nonlocal density functional theory (NLDFT), showing in both cases a peak maximum at 14 Å (Figure S7.2), which agrees with the pore size of each single layer predicted from the crystal structure (13−14 Å). The total pore volumes evaluated at P/P0 = 0.90 were 0.05 cm3 g−1 for IMDEA-COF-1 and 0.2 cm3 g−1 for IMDEA-COF-2. The CO2 uptake was 8 and 71.7 mg g−1 for IMDEA-COF-1 and IMDEA-COF-2, respectively, at 298 K and 1 bar; these capacities increased to 50.4 and 149 mg g−1 at 273 K and 1 bar (Figures S7.3 and S7.4). These results indicate that the presence of hydroxyl/keto groups on the wall of the pores originate an enhanced CO2 uptake due to the affinity of this functional group through dipole−hydrogen bonding interaction with CO2. These results are in good agreement with 12925


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Figure 6. (a) Images under visible light of IMDEA-COF-1, IMDEA-Polymer-1, and IMDEA-COF-2 materials (top), images of the same materials under UV 365 nm irradiation (middle), and the corresponding PL spectra (bottom). (b) PL lifetime of IMDEA-COF-1.

those reported for similar materials and make IMDEA-COF-2 an attractive adsorbent with a Qst value of 22 kJ mol−1 at low coverage.31,32 Detailed analyses of the local charges were performed to better understand the electrostatic repulsion between layers for the electron-donor-enriched IMDEA-COF-2 systems (Figures S4.2 and S4.3). By investigating the Löwdin charges of some representative atoms, it can be seen that electronic density is more equally distributed for AA-stacked structures. This fact explains the decreased electrostatic interlayer repulsion and, therefore, stabilization of this packing over the staggered conformation. This would indicate that the main destabilization element is the repulsion between electron-enriched tritopic building blocks. This result is also corroborated by the computed cohesive energies, showing the big-pore AAstacked configuration to be the preferred one. On the contrary, AB-stacking structures can be isolated under kinetic control only if the contribution of the interlayer electrostatic repulsion is not significant (i.e., IMDEA-COF-1). We hypothesize this could be a general phenomenon in COF structures and could help harness layer stacking by chemical modification of COF constituents. While layer stacking in COFs can be tuned through the occurrence intra-interactions within the building blocks,33 the phenomenon seen in the IMDEA-COF systems is certainly remarkable. By incorporation of a small chemical modification in the molecular precursor, formation of structures with eclipsed or staggered 3D arrangement of pyrene groups can be selectively achieved. In order to explore the use of this unique control of the COF structure at a molecular level, we studied the fluorescence properties of these materials in solid-state. As shown in Figure 6b, IMDEA-COF-1 exhibits a green color emission at 501 nm with absolute PL quantum yield of 3.5%. Theoretical calculations of the density of electronic states (DOS) of the four relaxed configurations of IMDEA-COF-1, big and small pores and AA- and AB-stacked structures, and the most important electronic excitation states have been computed confirming the experimental observations (Figure S8.8).

The UV−vis-NIR spectra reveal that the COFs and amorphous counterpart exhibit a redshift absorption compared to the pyrene building unit (SI Section S8). This is probably due to increased conjugation size and π−π stacking-caused charge transfer in these frameworks. In particular, IMDEACOF-1 displays a broad band from 650 to 1400 nm with low absorbance, which might be attributed to the charge transfer between the pyrene unit within the AB-stacked big and small pore structure. Compared to the AA-stacked eclipse structure, the alignment of pyrene units in IMDEA-COF-1 is more random, possibly giving rise to more energy relaxation pathways and thus a broader absorption band. Besides, the low absorbance of the redshift band in IMDEA-COF-1 may suggest that the small population of charge transfer in this material. This is consistent with the PL experiment that we only observe fluorescence in IMDEA-COF-1 but neither in the ordered IMDEA-COF-2 (Figure 6a) nor in the disordered IMDEA-Polymer-1 (Figure S8.7) and the molecular model IMDEA-COF-1 (Figure S8.8).

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CONCLUSIONS

In summary, we have reported a solid-state fluorescent iminelinked 2D-COF material containing pyrene building blocks, named IMDEA-COF-1. This system shows dramatic layerpacking-driven fluorescence in solid-state, arising from the ordered staggered arrangement of the pyrene units along the COF structure. Our computational studies have demonstrated a much more complex structural variation than originally expected for these materials. Due to the two possible orientation of the imine bonds, two different pore isomers with similar cohesive energies could be generated. The bigpore conformer appears as a flat structure, while the small-pore counterpart is corrugated. Layer stacking within these 2D-COF materials to give either eclipsed or staggered conformations can be controlled by chemical decoration of the building blocks with oxygen-electron groups. To the best of our knowledge, IMDEA-COF-1 is the first example of a solid-state fluorescent 2D COF bonded via imine linkages. Compared to the previous reported AA-stacked 2D 12926


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Journal of the American Chemical Society imine COFs34−36 or IMDEA-COF-2 in our work, IMDEACOF-1 with its structure of AB-stacked mixture of big and small pores is able to minimize the π−π interaction between the pyrene units, hence inhibiting the nonradiative energy dissipation via π−π stacking and turning on the fluorescence. Interestingly, the coexistence of the enol-imine/keto-amine tautomers corresponding to the IMDEA-COF-2 has been confirmed by 13C CP-MAS NMR. Calculations corroborate rather similar energies of both tautomers. These findings suggest that in our system the keto-amine form is not fully irreversible. This work provides a new tool for the structural design of imine-linked 2D-COF with strong emissive properties.

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Computational Studies. Density functional theory (DFT) analyses were carrying out using Gaussian 09 code39 within the B3LYP/cc-pVTZ40−42 level of theory. Periodic structural models of the different IMDEA-COFs to be fully optimized with the QUANTUM EXPRESSO plane-wave DFT code.43 Simultaneous full lattice/cell and structure optimizations for the different crystal bulk configurations were carried out. The calculations account for an empirical efficient vdW R-6 correction (DFT+D2 method).44 We have used the GGA-PBE functional to account for the exchange− correlation effects.45 Ultrasoft pseudopotentials have been used to model the ion−electron interaction within the H, C, N, and O atoms.46,47 The Brillouin zones have been sampled by means of optimal Monkhorst−Pack grids.48 The one-electron wave functions are expanded in a basis of plane waves with an energy cutoff of 450 eV for the kinetic energy, which has been adjusted to achieve sufficient accuracy to guarantee a full convergence in total energy and electronic density. All the atomic relaxations were carried out within a conjugate gradient minimization scheme until the maximum force acting on any atom was below 0.05 eV Å−1. Cell shape/size relaxations have been carried out with two different algorithms: a damped dynamics and a bfgs-like relaxation.49−51 These different approaches, tested for different crystal bulk configurations, provide very similar results for cell shape and lattice parameters as well as similar frequencies for the internal vibrations and for the cell oscillations. Optical Properties. Solid-state UV−vis-NIR absorption spectra were measured using Shimadzu UV-3600 UV−vis-NIR spectrophotometer with an integration sphere setup. PL spectra and lifetimes were recorded on a Horiba Fluorolog-3 spectrofluorometer equipped with a FluoroHub R-928 detector. The PL was measured using excitation wavelength of 365 nm from a Tungsten lamp. Lifetimes were recorded using a 374 nm nanoLED as excitation source. Diluted LUDOX HS-40 colloidal silica was used for lifetime prompt measurement. Absolute PL quantum yield (QY were recorded on the HORIBA Fluorolog-3 Photon Counting Spectrofluorometer System with Quanta-φ 6-in. integrating sphere.

EXPERIMENTAL SECTION

Methods. Powder X-ray diffraction (PXRD) data were collected using Panalytical X’Pert PRO diffractometer with Ge primary monochromator and X’Celerator fast detector, using Cu−Kα1 = 1.5406 Å radiation. Attenuated total reflectance Fourier-transform infrared (ATR-FT-IR) spectroscopy data were collected in a PerkinElmer Spectrum 100 with a PIKE Technologies MIRacle Single Reflection Horizontal ATR accessory. Elemental analysis was obtained using LECO CHNS-932 elemental analyzer. 13C Solid-state cross-polarization-magic angle spinning nuclear magnetic resonance (CP-MAS NMR) was carried out on a Bruker AV 400 WB spectrometer. Thermogravimetric analyses of samples were run on a Thermobalance TGA Q 500 thermal gravimetric analyzer with samples held in a platinum pan under nitrogen atmosphere. Gas adsorption isotherms were measured using a Micromeritics ASAP2020 volumetric instrument under static adsorption conditions. Prior to measurement, powdered samples were heated at 323 K overnight and outgassed to 10−6 Torr. Brunauer−Emmet−Teller (BET) and Langmuir analyses were carried out to determine the total specific surfaces areas for the N2 isotherms at 77 K. By using the nonlocal density functional theory (NLDFT) model, the pore volume was derived from the sorption curve. In addition, CO2 isotherms were measured at 273 and 298 K. Synthesis of IMDEA-COF Materials. All chemicals and solvents are commercially available and were used without further purification. Solvents and reagents for the preparation of these materials were dried by usual methods prior to use and typically used under inert gas atmosphere. 1,6-Diaminopyrene (DAP) and 2,4,6-triformylphloroglucinol (TFP) were synthesized as previously reported.37,38 Benzene1,3,5-tricarbaldehyde was commercially available and used as purchased with no further treatment. IMDEA-COF Materials. In a Pyrex tube, 0.12 mmol of the diamine DAP and 0.08 mmol of the trialdehyde BTCA or TFP for IMDEA-COF-1 or -2, respectively, were dissolved in a 10:1 mixture of m-cresol (2.60 mL) and glacial acetic acid (0.26 mL). After three freeze−pump−thaw cycles, the tube was vacuumed and flame-sealed. The mixture was heated to 120 °C for 72 or 168 h for IMDEA-COF1 or -2, respectively. The obtained precipitates were filtered and washed with methanol (3 × 100 mL) and tetrahydrofuran (THF) (3 × 100 mL) and dried in air over 2 days to yield a red product (57% yield). IMDEA-COF-1: Elemental analysis found: C, 74.40; H, 3.99; N, 7.60%. Calculated (C66H36N6·5CH3CO2H): C, 75.17; H, 4.73; N, 6.92%. IMDEA-COF-2: Elemental analysis found: C, 66.68; H, 4.35; N, 6.58%. Calculated (C66H36N6O6·10H2O): C, 66.66; H, 4.75; N, 7.07%. Amorphous IMDEA-COF-1. 27.3 mg (0.12 mmol) of DAP was dissolved in a mixture of m-cresol (1 mL) and glacial acetic acid (0.26 mL), and 12.7 mg (0.08 mmol) of BTCA was dissolved in 1.6 mL of m-cresol. The solutions were subsequently mixed at room temperature, and, shortly after, the formation of a red gel was observed. The gel was washed with methanol (3 × 100 mL) and THF (3 × 100 mL) and dried in air over 48 h to yield a red-brown product (87% yield). Elemental analysis found: C, 73.11; H, 3.97; N, 9.96%. Calculated (C66H36N6·6CH3CO2H): C, 73.57; H, 4.75; N, 6.60%.

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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/jacs.8b07450. Computed atomic coordinates (CIF) Computed atomic coordinates (CIF) Computed atomic coordinates (CIF) Computed atomic coordinates (CIF) Computed atomic coordinates (CIF) Computed atomic coordinates (CIF) Computed atomic coordinates (CIF) Computed atomic coordinates (CIF) Details of sample preparation and activation, X-ray diffraction, ATR-FT-IR, and 13C CP-MAS NMR spectroscopy, TGA, gas sorption, and computational studies (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] *[email protected] ORCID

Xing Li: 0000-0002-5470-1043 Alejandro López-Moreno: 0000-0001-5620-6129 Ana E. Platero-Prats: 0000-0002-2248-2739 Kian Ping Loh: 0000-0002-1491-743X Emilio M. Pérez: 0000-0002-8739-2777 Félix Zamora: 0000-0001-7529-5120 12927


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Journal of the American Chemical Society Notes

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The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Spanish MICINN (MAT2016-77608-C3-1-P) and MINECO (CTQ2014-60541-P and MAT2017-85089-C2-1R) and the European Research Council (ERC-StG-MINT 307609) for financial support. J.I.M. acknowledges the financial support by the “Ramón y Cajal” Program of MINECO (grant RYC-2015-17730) and computing resources from CTI-CSIC. K.P.L. acknowledges NRF-CRP grant no. NRF-CRP16-201502, “Two Dimensional Covalent Organic Framework: Synthesis and Applications”, funded by National Research Foundation, Prime Minister’s Office, Singapore. A.E.P.P. acknowledges a TALENTO grant (2017-T1/IND5148) from Comunidad de Madrid and InterTalentum Marie Skłodowska Curie Actions funding.

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