Article pubs.acs.org/IC
Phase Transformation, Exceptional Quenching Efficiency, and Discriminative Recognition of Nitroaromatic Analytes in Hydrophobic, Nonporous Zn(II) Coordination Frameworks Jeong Hwa Song, Yeonga Kim, Kwang Soo Lim, Dong Won Kang, Woo Ram Lee, and Chang Seop Hong* Department of Chemistry, Research Institute for Natural Sciences, Korea University, Seoul 136-713, Korea S Supporting Information *
ABSTRACT: Five-fold interpenetrated Zn(II) frameworks (1 and 2) have been prepared, and an irreversible phase transformation from 1 to 2 is found to occur through a dissolution−recrystallization process. Compound 1 exhibits the highest quenching efficiency (>96%) for nitrobenzene at 7 ppm among luminescent coordination polymers. Selective discrimination of nitroaromatic molecules including o-nitrophenol (o-NP), p-nitrophenol (p-NP), 2,4dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP) is realized in 1 and 2 as a result of the fact that the framework−analyte interaction affords characteristic emission signals. This observation is the first case of a nonporous coordination framework for such discriminative detection. Notably, significant hydrophobicity is evident in the framework 1 because of its surface roughness, which accounts for the enhanced quenching ability.
■
INTRODUCTION In recent years, vast industrial development has led to serious environmental problems, including air and water pollution. As a result, methods for detection of the levels of these pollutants have gained significant attention. For this purpose, various materials such as polymers, quantum dots, supramolecules, and coordination polymers have been extensively investigated.1 Coordination polymers are formed via the combination of metal ions and organic linkers. Therefore, the structure and functionality of a coordination network can easily be tuned by altering its components. When organic linkers with conjugated π systems are included in the coordination polymers, photoluminescence is induced upon excitation. 2 These luminescent coordination systems can be used as sensory materials for real-world applications. In particular, detection of nitroaromatic compounds is crucial because they are explosive and harmful to human health. Advantageously, these compounds can be readily detected via fluorescence quenching of luminescent frameworks. The sensing mechanism of the systems is related to electron transfer from the framework to electron-deficient analyte.3 The sensing process requires appreciable interactions between the luminescent framework surface and the analyte molecules. Many coordination polymers used for sensing applications have extremely porous surfaces; hence, the target molecules can diffuse into the pores and couple with the pore surface, thereby quenching or enhancing fluorescence. The existent pores within the frameworks can allow for enhanced host−guest interactions in preconcentrated environments. In this case, the diffusion of analyte molecules into the pores filled © XXXX American Chemical Society
by solvents could affect detection sensitivity during the capture of guests, although the facile hydrolysis of the porous framework structures is a drawback.4 Because of the advantageous nature of analyte−pore surface interactions, the sensing performance of porous coordination polymers has been actively explored.5 Although such specific interactions seem to play a role in detection, coordination frameworks with pore sizes smaller than analytes or pores preoccupied by solvent molecules showed similar sensing capabilities associated with not pore internal surfaces but external surfaces.6 Moreover, some nonporous frameworks also demonstrated fluorescence quenching behavior upon exposure to nitroaromatics such as nitrobenzene (NB) for example.7 The NB quenching efficiencies of nonporous coordination frameworks were reported to be comparable to or lower than those of porous frameworks.7a,8 In addition to the significant sensing power of nitroaromatic compounds (NACs), the ability to distinguish among different types of NACs is important for practical sensing applications. In this context, metal−organic frameworks that show selective recognition of NACs have been recently studied, while nonporous frameworks have not been attempted to this aim.6c,8b,9 Hence, if a nonporous framework shows rapid response, high selectivity, sensitivity, recyclability, and discriminative recognition for detecting NACs, the material is expected to be a sustainable platform for detection applications that could show greater resistance to decomposition via hydrolysis as compared Received: September 9, 2016
A
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 1. (a) View of the coordination sphere around a Zn ion of 1. (b) Schematic view of 5-fold interpenetrated dia topology for 1. (c) View of the coordination sphere around a Zn ion of 2. (d) Schematic view of 5-fold interpenetrated net for 2. Color codes: green = Zn, red = O, blue = N, gray = C. All hydrogen atoms are omitted for clarity. by the modified method that was previously reported.10 All chemicals and solvents in the synthesis were of reagent grade and used as received. [Zn(Let)(bpy)] (1). 4,4′-Dipyridyl (11.34 mg, 0.0726 mmol) and H2Let (24 mg, 0.0726 mmol) were put in a 10 mL vial and dissolved in DMF/EtOH (2:2 v/v, 4 mL). After Zn(NO3)2·6H2O (24 mg, 0.0726 mmol) dissolved in H2O (2 mL), it was added to the previous solution and sonicated for 5 min. The vial was sealed and placed in a preheated oven (100 °C) and reacted for 24 h. Colorless crystals were formed, which were washed with hot DMF/EtOH/H2O (1:1:1 v/v/v) and dried in air. Yield: 62%. Anal. Calcd for C28H24N2O6Zn: C, 61.16; H, 4.40; N, 5.09. Found: C, 61.18; H, 4.54; N 5.21. [Zn(Lpr)(bpy)] (2). The procedure identical to the synthesis of 1 was applied for the preparation of 2. H2Lpr (24 mg, 0.0672 mmol) was used instead of H2Let. Yield: 59%. Anal. Calcd for C30H28N2O6Zn: C, 62.34; H, 4.88; N, 4.85. Found: C, 62.53; H, 5.04; N 4.97. Irreversible Phase Transformation from 1 to 2. Crystals of 1 (20 mg, 0.0364 mmol) were immersed in DMF/EtOH/H2O (1:1:1 v/ v/v, 6 mL) containing H2Lpr ligand (39.12 mg, 0.1092 mmol), and a solvothermal reaction was carried out at 100 °C for 72 h. After each reaction, crystals were washed with a hot DMF/EtOH/H2O (1:1:1 v/ v/v) solution and dried in air. These processes were checked by PXRD and single-crystal X-ray diffraction. Anal. Calcd for C30H28N2O6Zn: C, 62.34; H, 4.88; N, 4.85. Found: C, 62.32; H, 4.77; N, 4.81. We selected a single crystal and put it in a glass capillary with DMF/ EtOH/H2O containing H2Lpr. We took photographs of the crystal as the solvothermal reaction proceeded in order to monitor morphology changes of the crystal. Crystallographic Structure Determination. X-ray data for compounds were collected on a Bruker SMART APEXII diffrac-
to a porous coordination polymer. Realization of such sensing properties is challenging and has not been achieved using nonporous coordination networks so far. Herein, we report the synthesis, structures, and sensing properties of two hydrophobic frameworks [Zn(Let)(bpy)] (1; H2Let = 3,3′-diethoxy-[1,1′-biphenyl]-4,4′-dicarboxylic acid; bpy = 4,4′-bipyridine) and [Zn(Lpr)(bpy)] (2; H2Lpr = 3,3′dipropoxy-[1,1′-biphenyl]-4,4′-dicarboxylic acid) with 5-fold interpenetrated three-dimensional networks. Irreversible phase transformation from 1 to 2 occurs via a dissolution− recrystallization process. Surprisingly, the NB quenching efficiency of nonporous framework 1 is exceptionally high; to the best of our knowledge, the quenching efficiency is the highest among those observed with luminescent coordination polymers. We also observed that NACs such as o-nitrophenol (o-NP), p-nitrophenol (p-NP), 2,4-dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP) can be discriminated by 1 and 2 from distinct emission outputs that are responsive to each molecule. This finding is the unique demonstration of a nonporous coordination network to enable discriminative detection. Additionally, 1 shows significant hydrophobicity, with a high contact angle of 133°, because of the surface roughness of the crystal.
■
EXPERIMENTAL SECTION
Reagent. 3,3′-Diethoxybiphenyl-4,4′-dicarboxylic acid (H2Let) and 3,3′-dipropoxybiphenyl-4,4′-dicarboxylic acid (H2Lpr) were prepared B
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry tometer equipped with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Preliminary orientation matrix and cell parameters were determined from three sets of ϕ/ω scans at different starting angles. Data frames were obtained at scan intervals of 0.5° with an exposure time of 10 s per frame. The reflection data were corrected for Lorentz and polarization factors. Absorption corrections were carried out using SADABS.11 The structures of 1 and 2 were solved by direct methods and refined by full-matrix least-squares analysis using anisotropic thermal parameters for non-hydrogen atoms with the SHELXTL program.12 All hydrogen atoms except for hydrogens bound to water oxygens were calculated at idealized positions and refined with the riding models. Crystal data and refinement details of 1 and 2 are given in Table S1. CCDC 147118 (1) and 147119 (2) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Physical Measurement. Elemental analyses for C, H, and N were performed at the Elemental Analysis Service Center of Sogang University. Thermogravimetric analyses were carried out at a ramp rate of 10 °C/min in a Ar flow with a Scinco TGA N-1000 instrument. PXRD data were recorded using Cu Kα (λ = 1.5406 Å) on a Rigaku Ultima III diffractometer with a scan speed of 2°/min and a step size of 0.01°. Surface analysis was performed via atomic force microscopy (AFM) using a XE-100 Park systems in noncontact mode. Scanning electron microscopy (SEM) images were obtained with a JEOL JSM7001F system. Contact angle measurements were conducted by a contact angle analyzer (Phoenix 10). Photoluminescence was measured with a Hitachi F-7000 FL spectrophotometer. Compounds (2 mg) dispersed in 2 mL of DMF were used for the optical measurements. Gas Sorption Measurements. Gas sorption isotherms of compounds were measured using a BEL Belsorp mini II gas adsorption instrument up to 1 atm of gas pressure. The highly pure N2 (99.999%) was used in the sorption experiments. N2 gas isotherms were measured at 77 K. Computational Methods. We carried out density functional theory (DFT) calculations for Let, Lpr, and NACs by using the Gaussian 09W program.13 All compounds studied were fully optimized using the SMD solvation model to correct the solvent effect of DMF.14 M06-2X as a density function and 6-31G(d,p) as a basis set were employed in the calculation.15
Phase Transformation. To investigate the phase transformation, we immersed 1 in a mixed solvent of DMF/EtOH/ H2O containing H2Lpr and conducted solvothermal reactions at 100 °C with increasing reaction time. The PXRD profiles reflect the phase evolution over time (Figure 2a). It is obvious
Figure 2. (a) PXRD patterns of as-synthesized 1, samples after 1, 6, 12, 24, 48, and 72 h, and as-synthesized 2. (b) Relative integration ratio of methyl protons in Let2− and Lpr2− as a function of time.
that the phase of 1 disappeared, followed by the formation of phase 2 after 72 h. This suggests that the Let2− ligands were slowly replaced by the Lpr2− ligands, and the phase transformation from 1 to 2 emerged (Figure 2a). The phase conversion from 1 to 2 did not occur when the reaction proceeded at room temperature, which indicates that the reaction requires appropriate activation energy to enable the structural change (Figures S6 and S7). To elucidate the conversion process, we selected a single crystal and placed it in a narrow homemade glass capillary. After the crystal was soaked in the saturated H2Lpr solution, the capillary was sealed using a torch and placed in an oven preheated to 100 °C to initiate the solvothermal reaction. To monitor the variation in the crystal morphologies, we recorded time-dependent photographs of the crystal (inset of Figure 2b). As the original crystal size slowly decreased, small rod crystals started to grow around the parent crystal of 1. After 72 h, the parent crystal almost disappeared and the rod-shaped crystals became dominant. The cell parameters of the newly formed crystal were verified using single-crystal X-ray crystallography, and the crystal was identified as 2. This result suggests that the transformation process is associated with the dissolution−recrystallization mechanism. To obtain a quantitative conversion ratio, we digested powders and crystals at different reaction times using DMSO-d6 and 48% HF and collected 1H NMR data of them (Figure S8).16 We analyzed the relative portion of the methyl protons of ethoxy and propoxy moieties in the spectra. From the NMR results of the powder samples, it was found that 1 rapidly
■
RESULTS AND DISCUSSION Characterization. Using a solvothermal method, colorless and transparent crystals of 1 (2) were obtained from a mixture of Zn(NO3)2·6H2O, 4,4′-bipyridine, and H2Let (H2Lpr) in DMF/EtOH/H2O (6 mL, v/v/v = 1/1/1). Compounds 1 and 2 crystallize in the triclinic crystal system with space group P-1 and in the orthorhombic system with space group P212121, respectively (Table S1). In the crystal structures, each Zn center adopts a tetrahedral geometry consisting of two N atoms from bpy [Zn−N = 2.0209(4)−2.080(4) Å] and two O atoms from Let/pr2− [Zn−O = 1.9174(3)−1.9629(3) Å]. For topology analysis, the organic spacers of bpy and Let/pr2− are represented by sticks and the Zn atoms are placed at the joints. The simplification procedure allows the structure to be a 4-c uninodal diamond (dia) net with a point symbol of (66) (Figure 1b and 1d). Entanglement of adamantanoid nets leads to the construction of a network architecture with 5-fold interpenetration (Figures S1 and S2). The powder X-ray diffraction (PXRD) profiles of both compounds were well matched with the simulated patterns, indicating the phase purity of the bulk samples (Figure S3). No solvent molecules are included in the frameworks, and hence, there are no void spaces, as confirmed by elemental analysis, thermogravimetric analysis (TGA), and N2 sorption (Figures S4 and S5). C
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry converted to 2 and the 1 h reaction afforded a 50% change (Figure 2b). Subsequently, a phase alteration from 1 to 2 progressed and eventually reached ∼65% after 72 h. Thus, full transformation from 1 to 2 was not achieved even when the reaction time was increased to 96 h (Figure 2b). The ligand replacement was incomplete during the dissolution process probably owing to the passivation of the shell part of the crystal.17 The transformation rate of the crystals was lower than that of the powder samples, which may be attributed to the conversion behavior depending on the grain sizes. In contrast, reverse transformation from 2 to 1 did not proceed under identical solvothermal conditions where 2 and H2Let coexisted, as corroborated by PXRD patterns (Figures S9 and S10). Sensing Properties. In order to examine the sensing features, the photoluminescence (PL) properties of H2Lpr, H2Let, 1, and 2 were measured in both the solid state and the DMF suspension (Figure S11). The solid-state PL spectra showed broad emission peaks at ∼400 nm for the ligands and ∼460 nm for the compounds upon excitation at 275 nm. The emission spectra of 1 and 2 were red shifted compared to those of the ligands, which is a typical phenomenon for the interpenetrated frameworks. 18 When the samples were dispersed in DMF, the emission peaks of both ligands and compounds were blue shifted (∼375 nm) compared to the solid-state fluorescence emission spectra, which is commonly observed in MOF systems containing π-conjugated linkers.19 The emission peaks of ligands and compounds in DMF appeared at the same position (∼375 nm), suggesting that the luminescence in 1 and 2 arises from the ligands. We investigated the quantum yields of 1 and 2. Due to the selfquenching effect arising from the 5-fold interpenetrated systems, the quantum yields of the compounds were small (∼20%). The emission data of 1 and 2 in various solvents such as N,Ndimethylformamide (DMF), chloroform (CHCl3), methanol (MeOH), ethanol (EtOH), and NB showed that the fluorescence of the compounds was selectively quenched by NB (Figure S12). To probe the quenching sensitivity of 1 and 2 toward NB, we used a series of NB solutions in DMF with increasing concentration from 0 to 5000 ppm. The fluorescence intensity decreased as the NB concentration increased (Figure S13). When the quenching efficiency (QE) is defined by (I0 − I)/I0 × 100%, where I0 and I are the luminescence intensities of compounds before and after the addition of NB, the estimated values were found to be 34% (1) and 13% (2) for 1 ppm. Remarkably, 1 exhibited almost complete quenching efficiency at 7 ppm (with QE greater than 96%). To the best of our knowledge, this is the highest QE observed among coordination polymer-based sensory materials for such ultralow concentrations of NB (Figure 3 and Table S2).3b,7,8b,20 The QE for 2 was also significant, with 90% QE at the same concentration of NB. The quenching characteristics of NB were generally tested in porous frameworks, wherein the pores facilitate preconcentration and recognition of a targeted molecule.2b Accordingly, the existent porosity in a sensory material was believed to be of utmost importance for effective detection. It is surprising that the quenching effect of the solids 1 and 2 on NB is exceptionally strong, although both are nonporous frameworks. Such an observation explicitly supports the fact that the surface of the framework with dangling ethoxy or propoxy groups is involved in the superb detection of NB. This finding signifies that nonporous frameworks enable superior response to NB via
Figure 3. Quenching efficiency of 1 (squares) and 2 (diamonds) upon addition of different concentrations of NB. (Inset) Normalized intensity graph of recyclability tests for 1 in the presence of nitrobenzene.
interactions between the analyte and the framework surface. The QE of 1 is greater than that of 2; this may be accounted for by the bulkiness of the dangling groups, which affects the approach of the analyte molecules to the surface. Moreover, the fluorescence intensity of 1 was fully restored by washing the sample once with DMF (inset of Figures 3 and S14). The recovery of NB-containing 1 to the original phase was substantially faster than that observed when using other coordination polymers, in which their fluorescence was restored upon several turns of washing and subsequent immersion.4b,7a The quenching−recovery cycles for 1 were conducted five times without intensity loss, which is important for the sensor reusability. The PXRD profiles collected after the recyclability test indicated that the structure remained intact (Figure S15). The cycling experiment conducted on 2 showed that the initial fluorescence was not recovered after washing the sample with DMF, while the structural integrity was retained (Figure S16). The steric effect of the bulkier propoxy group that limits the analytes from approaching to the framework may be responsible for such poor recyclability. To examine additional sensing properties toward NACs, we chose a series of nitro-substituted phenols such as onitrophenol (o-NP), p-nitrophenol (p-NP), 2,4-dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP). As shown in Figure 4, all NACs showed quenching properties. Due to the similar quenching behaviors of both compounds, we only focused on 1 (PL data of 2 in Figure S17). The emission intensities of all NACs were almost quenched (QE = ∼ 97%) at 100 ppm (Table S3). 1 showed distinguishable fluorescence spectra for different NACs. The emission peaks in the spectra were red shifted for o-NP and p-NP. According to the related research,8b,21 the red-shifted PL peaks of NP originate from the interaction between the framework and the analytes in the excited states. To support this hypothesis, we performed calculations on the analyte (o-NP)−ligand (Let) couple by using density functional theory (DFT). We modeled two possible interaction sites that are located near the benzene rings in the framework and ethoxy group (Figure S18 and Table S4). In both cases, the energy gaps between the HOMO and the LUMO are reduced compared to the Let-only case. This result is consistent with the observation of the red shift in the emission peak for o-NP. Moreover, for p-NP, an additional emission band was clearly observed in the lower energy region around 500 nm (Figure 4b). This peak implies that the exciplex is formed in the excited states through the specific noncovalent D
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry
Figure 4. Fluorescence quenching spectra of 1 dispersed in different concentrations of (a) o-NP, (b) p-NP, (c) DNP, and (d) TNP under λex = 275 nm.
Figure 5. (a) AFM image (2 μm × 2 μm) of a single-crystal surface of 1. Measured root-mean-square (rms) roughness of the crystal is 2.74 nm. Photographs of a water droplet on the powder samples of (b) 1 and (c) 2.
interactions such as hydrogen-bonding and/or π−π contacts.8b,22 Furthermore, 1 showed two distinct emission peaks when DNP and TNP were added (Figure 4c and 4d). It appears that the origin of the peaks is associated with the formation of exciplexes through specific interactions between the framework and the guest molecules, as also found in some coordination frameworks.8b,23 In the PL spectra of Figure 4c and 4d, one band at a higher wavelength more rapidly disappeared than the other band with increasing TNP concentration, while the two bands were gradually reduced in the addition of DNP. From the observed emission properties of NACs tested, the patterns of the fluorescent spectra were different depending on the NACs, which provide discriminative
output signals for selective recognition of analyte molecules. Indeed, all samples have instantaneous response time (a few second) upon the fluorescence measurements. The fluorescence quenching mechanism of compounds toward NACs can be explained by the electron transfer between donor (a framework) and acceptor (NACs).3a,5b The excited electrons from the conduction band of an MOF are suggested to transfer to the valence band of an electrondeficient NAC. The quenching mechanism in the current system (1 and 2) can be similarly interpreted. We speculated that the HOMO of the framework is similar to that of the ligand because the positions of the emission peaks are almost identical to each other. From the DFT calculations, the LUMO E
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
■
of an analyte is lower than the LUMO of the ligand used (Figure S19). Quenching mechanism thereby occurs via electron transfer from LUMO of the framework to LUMO of analytes upon excitation. Figure S20 shows UV-absorption spectra of NACs and fluorescence emission spectra of 1 and 2. The spectral overlap was clearly observed for NACs except for NB. This result indicates that the primary quenching mechanism for NB is based on electron transfer, while the mechanism for the other NACs is associated with the combined effect of electron and energy transfer.24 After being soaked in various analyte solutions for 7 days, the tested compounds retained their structural integrity as confirmed by PXRD patterns (Figure S21). Hydrophobicity. To investigate the structural stability, we immersed the samples in aqueous medium. The structures were maintained even under refluxing water for 7 days (Figure S22). The observed structural stability under such harsh aqueous conditions stems from the nonporous trait of the frameworks. The side groups (ethoxy or propoxy groups) and nonporosity prevent water molecules from accessing the metal core and the interior of the network, thus enhancing resistance to hydrolysis. Note that the superior water stability is beneficial for real-world applications because most coordination polymers are subject to decomposition upon exposure to liquid water.4a To gain more insight into the NB quenching efficiency of 1 and 2, we examined the hydrophobic properties by measuring the contact angles on the single crystals and powder samples of 1 and 2 (Figure 5). While the contact angles on the single crystals were 112° for 1 and 105° for 2, the powder samples had contact angles of 133° for 1 and 119° for 2. The larger contact angle for the powders was also found in a Zn(II)-based porous coordination polymer with a corrugated surface.25 To inspect the roughness of the crystal surface, we performed atomic force microscopy (AFM) and scanning electron microscopy (SEM) analyses (Figures 5a, S23, and S24). The crystal surface of 1 was rougher than that of 2. This result reveals that hydrophobicity can be ascribed to the presence of surface roughness on the crystallites. From the surface properties, the interfacial area of 1 that confers host−analyte (NB) contacts is greater than that of 2, thereby leading to the greater QE for 1 than 2.
■
Article
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02178. Detailed preparations and additional structural and PL data (PDF) X-ray crystallographic files (CIF)
■
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Chang Seop Hong: 0000-0002-4329-4745 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work was supported by a Korea CCS R&D Center (KCRC) grant funded by the Korean government (the Ministry of Science, ICT, and Future Planning (MSIP)) (NRF-2014M1A8A1049253) and the Basic Science Research Program (NRF-2015R1A2A1A10055658). W.R.L was partly supported by a Korea University grant and the Priority Research Centers Program (NRF-20100020209). We are grateful to Prof. H. J. Yoon and Prof. H. Y. Woo in Korea University for helping us measure the contact angles and AFM images.
■
REFERENCES
(1) (a) DeCoste, J. B.; Peterson, G. W. Metal−Organic Frameworks for Air Purification of Toxic Chemicals. Chem. Rev. 2014, 114, 5695− 5727. (b) Sun, X.; Wang, Y.; Lei, Y. Fluorescence based explosive detection: from mechanisms to sensory materials. Chem. Soc. Rev. 2015, 44, 8019−8061. (2) (a) Tanaka, D.; Horike, S.; Kitagawa, S.; Ohba, M.; Hasegawa, M.; Ozawa, Y.; Toriumi, K. Anthracene array-type porous coordination polymer with host−guest charge transfer interactions in excited states. Chem. Commun. 2007, 3142−3144. (b) Hu, Z.; Deibert, B. J.; Li, J. Luminescent metal−organic frameworks for chemical sensing and explosive detection. Chem. Soc. Rev. 2014, 43, 5815−5840. (3) (a) Pramanik, S.; Zheng, C.; Zhang, X.; Emge, T. J.; Li, J. New Microporous Metal-Organic Framework Demonstrating Unique Selectivity for Detection of High Explosives and Aromatic Compounds. J. Am. Chem. Soc. 2011, 133, 4153−4155. (b) Guo, M.; Sun, Z.-M. Solvents control over the degree of interpenetration in metal-organic frameworks and their high sensitivities for detecting nitrobenzene at ppm level. J. Mater. Chem. 2012, 22, 15939−15946. (4) (a) Greathouse, J. A.; Allendorf, M. D. The Interaction of Water with MOF-5 Simulated by Molecular Dynamics. J. Am. Chem. Soc. 2006, 128, 10678−10679. (b) Gong, Y.-N.; Jiang, L.; Lu, T.-B. A highly stable dynamic fluorescent metal−organic framework for selective sensing of nitroaromatic explosives. Chem. Commun. 2013, 49, 11113−11115. (5) (a) Lan, A.; Li, K.; Wu, H.; Olson, D. H.; Emge, T. J.; Ki, W.; Hong, M.; Li, J. A Luminescent Microporous Metal−Organic Framework for the Fast and Reversible Detection of High Explosives. Angew. Chem., Int. Ed. 2009, 48, 2334−2338. (b) Nagarkar, S. S.; Joarder, B.; Chaudhari, A. K.; Mukherjee, S.; Ghosh, S. K. Highly Selective Detection of Nitro Explosives by a Luminescent Metal− Organic Framework. Angew. Chem., Int. Ed. 2013, 52, 2881−2885. (c) Wang, G.-Y.; Yang, L.-L.; Li, Y.; Song, H.; Ruan, W.-J.; Chang, Z.; Bu, X.-H. A luminescent 2D coordination polymer for selective sensing of nitrobenzene. Dalton Trans. 2013, 42, 12865−12868. (d) Kim, T.
CONCLUSIONS
In summary, we prepared two nonporous compounds (1 and 2) that show 5-fold interpenetrated nets. The structural conversion from 1 to 2 irreversibly proceeds via a dissolution−recrystallization mechanism. The quenching efficiency of NB in 1 is remarkable and marks a record high at the given NB concentrations among luminescent coordination frameworks. Nitroaromatic compounds including o-nitrophenol (o-NP), p-nitrophenol (p-NP), 2,4-dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP) are selectively recognized by nonporous 1 and 2, and the analyte-specific interaction with the framework surface accounts for such discriminative detection. Furthermore, the robust solid 1, which was stable under heating water conditions, possesses substantial hydrophobicity attributable to the surface roughness, which is responsible for its NB quenching properties. F
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry K.; Lee, J. H.; Moon, D.; Moon, H. R. Luminescent Li-Based Metal− Organic Framework Tailored for the Selective Detection of Explosive Nitroaromatic Compounds: Direct Observation of Interaction Sites. Inorg. Chem. 2013, 52, 589−595. (e) Ma, D.; Li, B.; Zhou, X.; Zhou, Q.; Liu, K.; Zeng, G.; Li, G.; Shi, Z.; Feng, S. A dual functional MOF as a luminescent sensor for quantitatively detecting the concentration of nitrobenzene and temperature. Chem. Commun. 2013, 49, 8964− 8966. (f) Zhang, Z.; Xiang, S.; Rao, X.; Zheng, Q.; Fronczek, F. R.; Qian, G.; Chen, B. A rod packing microporous metal−organic framework with open metal sites for selective guest sorption and sensing of nitrobenzene. Chem. Commun. 2010, 46, 7205−7207. (g) Zhou, X.; Li, H.; Xiao, H.; Li, L.; Zhao, Q.; Yang, T.; Zuo, J.; Huang, W. A microporous luminescent europium metal−organic framework for nitro explosive sensing. Dalton Trans. 2013, 42, 5718− 5723. (6) (a) Gole, B.; Bar, A. K.; Mukherjee, P. S. Fluorescent metal− organic framework for selective sensing of nitroaromatic explosives. Chem. Commun. 2011, 47, 12137−12139. (b) Nagarkar, S. S.; Joarder, B.; Chaudhari, A. K.; Mukherjee, S.; Ghosh, S. K. Highly Selective Detection of Nitro Explosives by a Luminescent Metal−Organic Framework. Angew. Chem., Int. Ed. 2013, 52, 2881−2885. (c) Asha, K. S.; Bhattacharyya, K.; Mandal, S. Discriminative detection of nitro aromatic explosives by a luminescent metal−organic framework. J. Mater. Chem. C 2014, 2, 10073−10081. (7) (a) Kim, Y.; Song, J. H.; Lee, W. R.; Phang, W. J.; Lim, K. S.; Hong, C. S. Reversible Structural Flexibility and Sensing Properties of a Zn(II) Metal−Organic Framework: Phase Transformation between Interpenetrating 3D Net and 2D Sheet. Cryst. Growth Des. 2014, 14, 1933−1937. (b) Singh, D.; Nagaraja, C. M. A luminescent 3D interpenetrating metal−organic framework for highly selective sensing of nitrobenzene. Dalton Trans. 2014, 43, 17912−17915. (8) (a) Wang, Y.-N.; Zhang, P.; Yu, J.-H.; Xu, J.-Q. 4-(4Carboxyphenoxy)phthalate-based coordination polymers and their application in sensing nitrobenzene. Dalton Trans. 2015, 44, 1655− 1663. (b) Wan, X.-Y.; Jiang, F.-L.; Liu, C.-P.; Zhou, K.; Chen, L.; Gai, Y.-L.; Yang, Y.; Hong, M.-C. Rapid and discriminative detection of nitro aromatic compounds with high sensitivity using two zinc MOFs synthesized through a temperature-modulated method. J. Mater. Chem. A 2015, 3, 22369−22376. (c) Wang, G.-Y.; Song, C.; Kong, D.-M.; Ruan, W.-J.; Chang, Z.; Li, Y. Two luminescent metal−organic frameworks for the sensing of nitroaromatic explosives and DNA strands. J. Mater. Chem. A 2014, 2, 2213−2220. (d) Zhou, E.-L.; Huang, P.; Qin, C.; Shao, K.-Z.; Su, Z.-M. A stable luminescent anionic porous metal−organic framework for moderate adsorption of CO2 and selective detection of nitro explosives. J. Mater. Chem. A 2015, 3, 7224−7228. (9) Zhang, S.-R.; Du, D.-Y.; Qin, J.-S.; Bao, S.-J.; Li, S.-L.; He, W.-W.; Lan, Y.-Q.; Shen, P.; Su, Z.-M. A Fluorescent Sensor for Highly Selective Detection of Nitroaromatic Explosives Based on a 2D, Extremely Stable, Metal-Organic Framework. Chem. - Eur. J. 2014, 20, 3589−3594. (10) Wang, X.-Z.; Zhu, D.-R.; Xu, Y.; Yang, J.; Shen, X.; Zhou, J.; Fei, N.; Ke, X.-K.; Peng, L.-M. Three Novel Metal-Organic Frameworks with Different Topologies Based on 3,30-Dimethoxy-4,40-biphenyldicarboxylic Acid: Syntheses, Structures, and Properties. Cryst. Growth Des. 2010, 10, 887−894. (11) Sheldrick, G. M. SADABS, A program for area detector absorption corrections; University of Göttingen: Germany, 1994. (12) Sheldrick, G. M. SHELXTL, Version 6.12; Bruker Analytical Xray Systems: Inc: Madison, 2000. (13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö .; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09W; Gaussian, Inc.: Wallingford, CT, 2009. (14) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. Universal Solvation Model Based on Solute Electron Density and on a Continuum Model of the Solvent Defined by the Bulk Dielectric Constant and Atomic Surface Tensions. J. Phys. Chem. B 2009, 113, 6378−6396. (15) (a) Steinmann, S. N.; Csonka, G.; Corminboeuf, C. Unified Inter- and Intramolecular Dispersion Correction Formula for Generalized Gradient Approximation Density Functional Theory. J. Chem. Theory Comput. 2009, 5, 2950−2958. (b) Steinmann, S. N.; Piemontesi, C.; Delachat, A.; Corminboeuf, C. Why are the Interaction Energies of Charge-Transfer Complexes Challenging for DFT? J. Chem. Theory Comput. 2012, 8, 1629−1640. (c) Zhao, Y.; Truhlar, D. G. Theor. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215−241. (d) Zhao, Y.; Truhlar, D. G. Computational characterization and modeling of buckyball tweezers: density functional study of concave−convex π···π interactions. Phys. Chem. Chem. Phys. 2008, 10, 2813−2818. (16) Fei, H.; Shin, J.; Meng, Y. S.; Adelhardt, M.; Sutter, J. r.; Meyer, K.; Cohen, S. M. Reusable Oxidation Catalysis Using MetalMonocatecholato Species in a Robust Metal−Organic Framework. J. Am. Chem. Soc. 2014, 136, 4965−4973. (17) Lee, W. R.; Ryu, D. W.; Phang, W. J.; Park, J. H.; Hong, C. S. Charge effect of foreign metal ions and the crystal growth process in hybridized metal−organic frameworks. Chem. Commun. 2012, 48, 10847−10849. (18) Farrusseng, D. Metal-Organic Frameworks: Applications from Catalysis to Gas Storage; John Wiley & Sons, 2011. (19) Stylianou, K. C.; Heck, R.; Chong, S. Y.; Bacsa, J.; Jones, J. T. A.; Khimyak, Y. Z.; Bradshaw, D.; Rosseinsky, M. J. A Guest-Responsive Fluorescent 3D Microporous Metal-Organic Framework Derived from a Long-Lifetime Pyrene Core. J. Am. Chem. Soc. 2010, 132, 4119− 4130. (20) (a) Wang, Y.; Cheng, L.; Liu, Z.-Y.; Wang, X.-G.; Ding, B.; Yin, L.; Zhou, B.-B.; Li, M.-S.; Wang, J.-X.; Zhao, X.-J. An Ideal Detector Composed of Two-Dimensional Cd(II)−Triazole Frameworks for Nitro-Compound Explosives and Potassium Dichromate. Chem. - Eur. J. 2015, 21, 14171−14178. (b) Chen, D.-M.; Ma, X.-Z.; Shi, W.; Cheng, P. Solvent-Induced Topological Diversity of Two Zn(II) Metal−Organic Frameworks and High Sensitivity in Recyclable Detection of Nitrobenzene. Cryst. Growth Des. 2015, 15, 3999− 4004. (c) He, Y.-C.; Zhang, H.-M.; Liu, Y.-Y.; Zhai, Q.-Y.; Shen, Q.-T.; Song, S.-Y.; Ma, J.-F. Luminescent Anionic Metal−Organic Framework with Potential Nitrobenzene Sensing. Cryst. Growth Des. 2014, 14, 3174−3178. (d) Liu, F.-H.; Qin, C.; Ding, Y.; Wu, H.; Shao, K.-Z.; Su, Z.-M. Pillared metal organic frameworks for the luminescence sensing of small molecules and metal ions in aqueous solutions. Dalton Trans. 2015, 44, 1754−1760. (e) Parshamoni, S.; Telangae, J.; Konar, S. Regulation of the pore size by shifting the coordination sites of ligands in two MOFs: enhancement of CO2 uptake and selective sensing of nitrobenzene. Dalton Trans. 2015, 44, 20926−20935. (f) Zhang, S.-R.; Du, D.-Y.; Qin, J.-S.; Li, S.-L.; He, W.-W.; Lan, Y.-Q.; Su, Z.-M. 2D Cd(II)−Lanthanide(III) Heterometallic−Organic Frameworks Based on Metalloligands for Tunable Luminescence and Highly Selective,Sensitive, and Recyclable Detection of Nitrobenzene. Inorg. Chem. 2014, 53, 8105−8113. (g) Li, W.-J.; Lü, J.; Gao, S.-Y.; Li, Q.-H.; Cao, R. Electrochemical preparation of metal−organic framework films for fast detection of nitro explosives. J. Mater. Chem. A 2014, 2, 19473−19478. (h) Tian, D.; Li, Y.; Chen, R.-Y.; Chang, Z.; Wang, G.-Y.; Bu, X.-H. A luminescent metal−organic framework G
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry demonstrating ideal detection ability for nitroaromatic explosives. J. Mater. Chem. A 2014, 2, 1465−1470. (i) Li, Y.; Liu, K.; Li, W.-J.; Guo, A.; Zhao, F.-Y.; Liu, H.; Ruan, W.-J. Coordination Polymer Nanoarchitecture for Nitroaromatic Sensing by Static Quenching Mechanism. J. Phys. Chem. C 2015, 119, 28544−28550. (j) Wang, X.P.; Han, L.-L.; Wang, Z.; Guo, L.-Y.; Sun, D. Microporous Cd(II) metal-organic framework as fluorescent sensor for nitroaromatic explosives at the sub-ppm level. J. Mol. Struct. 2016, 1107, 1−6. (k) Du, J.-L.; Lu, X.; Shen, T.-L.; Li, C.-P.; Mu, Y.-J.; Li, L.-J. A luminescent cadmium metal-organic framework with potential detection of nitroaromatic compounds. Mater. Lett. 2015, 158, 225− 228. (21) (a) Shi, Y.-X.; Hu, F.-L.; Zhang, W.-H.; Lang, J.-P. A unique Zn(II)-based MOF fluorescent probe for the dual detection of nitroaromatics and ketones in water. CrystEngComm 2015, 17, 9404− 9412. (b) Sun, Y.; Wang, S. Conjugated Triarylboryl Donor-Acceptor Systems Supported by 2,2′-Bipyridine: Metal Chelation Impact on Intraligand Charger Transfer Emission, Electron Accepting Ability, and “Turn-on”Fluoride Sensing. Inorg. Chem. 2009, 48, 3755−3767. (22) (a) Tazuke, S. POLYMER BONDED EXCITED COMPLEXES - A POWERFUL APPROACH TO STUDY POLYMER EFFECTS. Makromol. Chem. 1985, 14, 145−159. (b) Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Luminescent metal−organic frameworks. Chem. Soc. Rev. 2009, 38, 1330−1352. (c) Pramanik, S.; Hu, Z.; Zhang, X.; Zheng, C.; Kelly, S.; Li, J. A Systematic Study of Fluorescence-Based Detection of Nitroexplosives and Other Aromatics in the Vapor Phase by Microporous Metal−Organic Frameworks. Chem. - Eur. J. 2013, 19, 15964−15971. (23) (a) Chahal, M. K.; Sankar, M. 1,8-Naphthyridine-based fluorescent receptors for picric acid detection in aqueous media. Anal. Methods 2015, 7, 10272−10279. (b) He, H.; Song, Y.; Sun, F.; Bian, Z.; Gao, L.; Zhu, G. A porous metal−organic framework formed by a V-shaped ligand and Zn(II) ion with highly selective sensing for nitroaromatic explosives. J. Mater. Chem. A 2015, 3, 16598−16603. (c) SK, M.; Biswas, S. A thiadiazole-functionalized Zr(IV)-based metal−organic framework as a highly fluorescent probe for the selective detection of picric acid. CrystEngComm 2016, 18, 3104− 3113. (24) (a) Wang, J.; Mei, J.; Yuan, W.; Lu, P.; Qin, A.; Sun, J.; Ma, Y.; Tang, B. Z. Hyperbranched polytriazoles with high molecular compressibility: aggregation-induced emission and superamplified explosive detection. J. Mater. Chem. 2011, 21, 4056−4059. (b) Wei, W.; Huang, X.; Chen, K.; Tao, Y.; Tang, X. Fluorescent organic− inorganic hybrid polyphosphazene microspheres for the trace detection of nitroaromatic explosives. RSC Adv. 2012, 2, 3765−3771. (25) Rao, K. P.; Higuchi, M.; Sumida, K.; Furukawa, S.; Duan, J.; Kitagawa, S. Design of Superhydrophobic Porous Coordination Polymers through the Introduction of External Surface Corrugation by the Use of an Aromatic Hydrocarbon Building Unit. Angew. Chem., Int. Ed. 2014, 53, 8225−8230.
H
DOI: 10.1021/acs.inorgchem.6b02178 Inorg. Chem. XXXX, XXX, XXX−XXX
