Fluorescent Aromatic Tag-Functionalized MOFs for ... - ACS Publications

Article pubs.acs.org/IC

Fluorescent Aromatic Tag-Functionalized MOFs for Highly Selective Sensing of Metal Ions and Small Organic Molecules Si-Si Zhao, Jin Yang,* Ying-Ying Liu, and Jian-Fang Ma* Key Lab of Polyoxometalate Science, Department of Chemistry, Northeast Normal University, Changchun 130024, People’s Republic of China S Supporting Information *

ABSTRACT: By varying the fluorescent tags of resorcin[4]arenebased tetracarboxylic acids from phenyl to naphthyl, two highly luminescent metal−organic frameworks (MOFs), namely, [Zn2(TPC4A)(DMF)(H2O)4]·3H2O (1) and [(CH3)2NH2]2[Zn(TNC4A)]·4H2O (2), were successfully achieved (TPC4A = 2,8,14,20-tetra-phenyl-6,12,18,24-tetra-methoxy-4,10,16,22-tetracarboxy-methoxy-resorcin[4]arene and TNC4A = 2,8,14,20-tetra1-naphthal-6,12,18,24-tetra- methoxy-4,10,16,22-tetra-carboxymethoxy-resorcin[4]arene). Compound 1 features a unique 2D network, while 2 exhibits a fascinating 3D framework. The highly selective detection of small organic molecules as well as Fe2+ and Fe3+ was performed for 1 and 2 as fluorescent sensors. Remarkably, luminescent 1 and 2 were used as sensory materials for the sensing of various amine vapors with high selectivity and rapid response. Most strikingly, clear fluorescence “on−off” switch-functions toward small organic molecules as well as amine vapors were also explored for luminescent 1 and 2.

■

INTRODUCTION Currently, much effort has been devoted to rapid detection of hazardous chemicals, such as toxic metal ions and volatile small organic molecules, because of their widespread societal concern related to human health and environment.1−4 In this regard, detection of volatile organic amines is of great interest owing to increasing content found in wastewater or soil as well as in the areas of food safety and medical diagnosis.5,6 Thereby, various types of analytical tools, such as chromatography and other instrumental analyses, have been utilized for the detection of volatile organic amines, but very few facile methods for the detection of organic amine species have been successfully realized thus far.7,8 With the increase of organic amines in packaged food, especially fish and meat, the vapor detection of organic amines becomes specially attractive; however, much less progress has been made in the vapor detection of organic amines than in solution.9,10 Usually, the vapor pressures of the organic amines are very low at room temperature, and therefore the facile fluorescence detection of these trace amine vapors is much more difficult than that of the liquid ones, and still is a challenge now.11 Metal−organic framework (MOF) sensors for the detection of small organic molecules have received increasing attention, but luminescent MOF switches showing fluorescence “on−off” switch-functions involving amine vapor sensing have not been explored until now.12,13 It needs to be mentioned that sensing and detection of metal ions also play a significant role in life science, medicinal science, environmental science, and the nuclear industry.14−17 As a vital kind of element, iron (Fe2+ and Fe3+), has an indispensable role in © XXXX American Chemical Society

biological processes involving enzymes, proteins, and transcriptional events.18 Thus, in the case of human health, selective sensing or detection of irons over other metal ions is of great importance. However, until now, only a few fluorescent sensors that select Fe3+ over Fe2+ have been reported.19,20 Particularly, selective sensing of Fe2+ and Fe3+ with MOFs, simultaneously, without the interference of other mixed metal ions through fluorescence quenching is a significant but challenging task, and still remains exceedingly rare.21−23 In recent times, MOFs, as a class of crystalline materials, have been used to explore their promising applications such as catalysis, gas adsorption, light-emitting devices, and chemical sensors.24−27 In this context, luminescent MOFs have attracted a growing amount of attention primarily owing to their potential applications as fluorescence sensors.28 For the luminescent MOF-based sensors, the most common detection method is a change in their fluorescence intensity.29,30 For example, analyte molecules quench the excited states of metal ions or fluorescent organic linkers, thereby turning off or reducing the luminescent intensity of the parent MOFs.31,32 Generally, the selectivity and sensitivity of the luminescent detection is mainly dependent on the electron density of the MOFs as well as the ability of the MOFs to donate electrons.33 Introducing electron-rich πconjugated fluorescent ligands could give rise to luminescence in the backbone of the MOFs. Thus, MOFs constructed by Received: November 17, 2015

A

DOI: 10.1021/acs.inorgchem.5b02666 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Chart 1. Synthetic Process of Resorcin[4]arene-Functionalized Tetracarboxylic Acids TPC4A and TNC4A

diffractometer using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Absorption corrections were performed by a multiscan method. The structures were solved by direct methods using SHELXTL and were refined by full matrix least-squares on F2 using SHELX-97 within WINGX.35−37 Non-hydrogen atoms were refined with anisotropic displacement parameters during the final cycles. Hydrogen atoms of the organic molecules were placed by geometrical considerations. Because solvent molecules in the crystal are highly disordered, the SQUEEZE function in PLATON was utilized to remove residual electron density.38 Crystallographic data and structure refinements for 1 and 2 are given in Table 1. Selected bond lengths and angles are provided in Tables S1 and S2.

organic ligands with chromophores are excellent candidates for the fluorescence sensors.34 With this in mind, we initiate a new strategy of utilizing aromatic moieties as fluorescent tags to tune the sensitivity and selectivity of MOFs for detection of small organic molecules, organic amines, and metal ions. In this work, two newly designed resorcin[4]arene-functionalized tetracarboxylic acids, 2,8,14,20tetra-phenyl-6,12,18,24-tetra-methoxy-4,10,16,22-tetra-carboxymethoxy-resorcin[4]arene (TPC4A) and 2,8,14,20-tetra-1naphthal-6,12,18,24-tetra- methoxy-4,10,16,22-tetra-carboxymethoxy-resorcin[4]arene (TNC4A), with increasing π-electron density in the aromatic tags from phenyl to naphthyl (Chart 1), have been prepared, characterized, and employed in the syntheses of two new luminescent active MOFs, [Zn2(TPC4A)(DMF)(H2O)4]·3H2O (1) and [(CH3)2NH2]2[Zn(TNC4A)]· 4H2O (2). The introduction of these aromatic tags into MOFs was anticipated to adjust the selectivity and sensitivity for the detection of organic amines and metal ions. The luminescent studies indicate that 1 and 2 are capable of highly selective sensing of amine vapors as well as highly selective detection of Fe2+ and Fe3+. Remarkably, 1 and 2 exhibit good “on−off” switchfunctions for the probing of small organic molecules as well as amine vapors.

■

Table 1. Crystal Data and Structure Refinements for 1 and 2 formula Mr space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z Dc (g/cm3) GOF on F2 R1 [I > 2σ(I)] wR2 (all data) Rint

EXPERIMENTAL SECTION

Materials and Methods. All reagents and solvents used in the experiments were purchased from commercial sources. FT-IR spectra were recorded on a Mattson Alpha Centauri spectrometer. A PerkinElmer 240C elemental analyzer was used to determine the C, H, and N elemental contents. The powder X-ray diffraction (PXRD) patterns were measured on a Rigaku Dmax 2000 X-ray diffractometer with graphite monochromatized Cu Kα radiation (λ = 0.154 nm). Thermogravimetric analysis (TGA) was measured under nitrogen gas by using a NETZSCH STA 449F3 TG instrument. The luminescent spectra were determined with an Edinburgh FLSP920 fluorescence spectrometer. Diffuse reflectivity spectra were collected with a Cary 500 spectrophotometer. X-ray Crystallography. Single-crystal X-ray data of 1 and 2 were collected at 293 K on a Oxford Diffraction Gemini R Ultra

1

2

C67H72NO24Zn2 1406.00 P1̅ 13.3690(11) 16.1200(13) 16.4590(11) 78.684(6) 83.297(6) 72.579(7) 3312.2(4) 2 1.410 1.226 0.1238 0.2978 0.0692

C84H84N2O20Zn 1506.90 C2/c 27.694(2) 15.8734(11) 18.5692(15) 90 110.079(9) 90 7666.8(10) 4 1.306 1.167 0.0926 0.2469 0.0518

Sensing of Various Amine Vapors. The as-synthesized samples were ground and used for vapor sensing experiments. For each experiment, a 20 mg portion of the samples was placed into a small beaker (10 mL), and then exposed to various amine vapors (15 mL) for 24 h in a sealed container. The sample beaker was then taken out from the container and sealed, and emission spectra were measured. For the “turn-off” experiments toward triethylamine vapors, the same MOF B


Article

Inorganic Chemistry

Figure 1. (a) Coordination environments of the Zn(II) atoms in 1 (hydrogen atoms and lattice water molecules are omitted for clarity). Symmetry code: (#1) −x + 1, −y + 1, −z. (b) View of the coordination modes of TPC4A ligands in 1. (c) View of the 2D network of 1. sample (20 mg) was placed into several small beakers for parallel experiments, and then exposed to triethylamine vapor for different times. The sealed samples were quickly measured for their emission spectra in the solid state. For the “turn on” experiments toward triethylamine vapors, the sample (20 mg) was placed into a small beaker (10 mL), and then exposed to triethylamine vapors in a sealed container for 24 h. Then the sample beaker was taken out from the container and

exposed to atmospheres. The emission spectra for the solid sample were measured at different exposing time. Syntheses of TPC4A and TNC4A. The TPC4A and TNC4A ligands were achieved by following the literature procedure.39,40 A mixture of 3-methoxyphenol (12.41 g, 100 mmol), dichloromethane (200 mL), and benzaldehyde (10.61 g, 100 mmol) was stirred while being cooled in an ice bath for 0.5 h with dropwise addition of BF3·OEt2 C


Article

Inorganic Chemistry

Figure 2. (a) Coordination environment of the Zn(II) atom in 2 (hydrogen atoms and lattice water molecules are omitted for clarity). Symmetry codes: (#1) x − 1/2, −y + 3/2, z − 1/2; (#2) −x + 3/2, y − 1/2, −z + 3/2; (#3) −x + 1, −y + 1, −z + 1. (b) View of the coordination mode of TNC4A ligand in 2. (c) View of the 3D framework of 2. Synthesis of [Zn2(TPC4A)(DMF)(H2O)4]·3H2O (1). Zn(NO3)2·6H2O (0.012 g, 0.04 mmol), TPC4A (0.020 g, 0.02 mmol), DMF (4 mL), and distilled water (4 mL) were placed in a Teflon reactor (15 mL) and heated at 100 °C for 3 days. Colorless crystals of 1 were isolated in a 52% yield based on Zn(II) after the mixture was cooled to room temperature. Anal. Calcd for C67H72NO24Zn2 (Mr = 1406.00): C, 57.23; H, 5.16; N, 0.99. Found C, 57.38; H, 5.12; N, 1.02. IR data (KBr, cm−1): 3450 (m), 3024 (m), 2931 (m), 1651 (w), 1611 (w), 1500 (w), 1448 (w), 1399 (m), 1288 (w), 1192 (w), 1159 (m), 1104 (m), 1054 (m), 926 (s), 848 (s),812 (s), 755 (s), 701(m), 583 (s), 527 (s). Synthesis of [(CH3)2NH2]2[Zn(TNC4A)]·4H2O (2). The preparation of 2 was similar to that of 1. Typically, a mixture of TNC4A (0.025 g, 0.02 mmol) and Zn(NO3)2·6H2O (0.014 g, 0.05 mmol) was dissolved in mixed DMF (6 mL) and distilled water (2 mL). The mixture was maintained in a Teflon reactor (15 mL) at 100 °C for 3 days. Then colorless crystals of 2 were isolated in a 48% yield based on Zn(II). Anal. Calcd for C84H84N2O20Zn (Mr = 1506.90): C, 66.95; H, 5.61; N, 1.86. Found C, 67. 21; H, 5.53; N, 1.89. IR data (KBr, cm−1): 3444 (s), 3046 (m), 2929 (m), 2832 (m), 1654 (w), 1614 (w), 1503 (w), 1462 (w), 1445 (w), 1393 (w), 1283 (w), 1191 (w), 1169 (m), 1156 (m), 1104 (w), 1055 (w),1024 (m), 925 (s), 889 (s), 858 (s), 818 (m), 800 (m), 789 (m), 771 (m), 733 (s), 698 (s), 663 (s), 647 (s), 594 (s), 516 (s)

(15 mL). The mixture was maintained at room temperature and stirred overnight. The product was then washed using CH2Cl2. The crude product of the precursor 2,8,14,20-tetra-phenyl-6,12,18,24-tetra-methoxy-4,10,16,22-tetra-carboxy-methoxy-resorcin[4]arene (L1) was achieved in 78% yield after evaporation of the solvent. The synthesis of 2,8,14,20-tetra-1-naphthal-6,12,18,24-tetra-methoxy-4,10,16,22tetra-carboxy-methoxy-resorcin[4]arene (L2) is similar to that of the former (yield 59%). A mixture of L1 (16.96 g, 20 mmol), anhydrous K2CO3 (55.28 g, 400 mmol), methyl chloroacetate (17.36 g, 160 mmol), KI (0.15 g, 0.90 mmol), and CH3CN (300 mL) was heated in a water bath for 48 h under nitrogen gas. After filtration of the mixture, the solvent was removed with the rotary evaporator. Then, the extraction was conducted three times by addition of the saturated K2CO3 aqueous solution and chloroform (200 mL) to the dry solid. The mixture was recrystallized in methanol after removal of the chloroform. Then, tetrahydrofuran (150 mL), sodium hydroxide (4 g, 100 mmol), and water (150 mL) were poured into the isolated products, and refluxed for 8 h. The solvent was removed by water bath, and 500 mL of water was then added. With HCl (1.0 mol L−1), the pH value of the mixture was adjusted to 1−2, and pale green solid of TPC4A was achieved in a 60% yield. Anal. Calcd for C64H56O16 (Mr = 1081.12): C, 71.10; H, 5.22. Found: C, 70.49; H, 5.31. The TNC4A was prepared by using a synthetic method similar to that for TPC4A in a 53% yield. Anal. Calcd for C80H64O16 (Mr = 1281.35): C, 74.99; H, 5.03. Found: C, 74.37; H, 5.16. D


Article

Inorganic Chemistry

Figure 3. Solid-state emission spectra of TPC4A, TNC4A, 1, and 2.

■

RESULTS AND DISCUSSION Structural Description of [Zn2(TPC4A)(DMF)(H2O)4]· 3H2O (1). Compound 1 crystallizes in the triclinic space group P1̅. The SQUEEZE function in PLATON was utilized during the refinement of 1 owing to the highly disordered solvents.38 Thermogravimetric analysis and elemental analysis demonstrate the presence of three lattice water molecules (Figure S1). As shown in Figure 1a, the asymmetric unit of 1 is composed of two Zn(II) cations, two unique half-occupied TPC4A ligands, one coordination DMF molecule, four coordination water molecules, and three lattice water molecules. Zn1 is coordinated by four carboxylate oxygen atoms of four TPC4A anions in a distorted tetrahedral coordination sphere, while Zn2 is six-coordinated by one carboxylate oxygen atom of one TPC4A, four water oxygen atoms, and one DMF oxygen atom, showing a distorted octahedral coordination environment. Notably, the two TPC4A ligands exhibit different coordination manners: one TPC4A bridges six Zn(II) atoms, while the other TPC4A links four Zn(II) atoms (Figure 1b). In this manner, adjacent Zn(II) atoms are alternately linked by two different types of TPC4A ligands into a charming 2D network (Figure 1c). The calculated free volume is 9.5% by PLATON analysis after removal of the solvent molecules.38 Structural Description of [(CH3)2NH2]2[Zn(TNC4A)]· 4H2O (2). Compound 2 crystallizes in the monoclinic space group C2/c. The SQUEEZE function in PLATON was used during the refinement of 2 due to the highly disordered solvents.38 Thermogravimetric analysis and elemental analysis indicate the presence of one [H2N(CH3)2]+ cation and two free waters in the asymmetric unit (Figure S2). The asymmetric unit of 2 contains one-half-occupied Zn(II) atom, one-half-occupied TNC4A ligand, one [H2N(CH3)2]+ cation, and two lattice

waters, as illustrated in Figure 2a. Each Zn(II) atom exhibits a tetrahedral coordination geometry, completed by four carboxylate oxygen atoms of four different TNC4A anions (Figure 2b). Strikingly, each TNC4A ligand bridges four Zn(II) atoms to furnish a charming 3D framework with an open channel along the c axis, in which the [H2N(CH3)2]+ cations and water molecules are located (Figure 2c). The calculated free volume is 22.7% by PLATON analysis after removal of the solvent molecules.38 Topologically, if both Zn(II) atom and TNC4A ligand are regarded as 4-connected nodes, respectively, the overall framework of 2 can be described as a 3D 4-connected (42)(84) net (Figure S3). Luminescent Properties. Luminescent MOFs with d10 metals have received immense attention in materials science because of their widespread applications in detection and sensing, labeling, and optoelectronic display devices.41−45 Thus, the luminescent behaviors of the ligands (TPC4A and TNC4A) and MOFs (1 and 2) were studied in the solid state at room temperature. As illustrated in Figure 3, the free TPC4A and TNC4A exhibit emission peaks at 325 (λex = 295 nm) and 371 nm (λex = 322 nm), respectively, which are usually derived from π* → π or π* → n transitions.46,47 It is noteworthy that the emission peak of the TNC4A ligand is red-shifted by 46 nm in comparison with that of the free TPC4A in the solid state. A possible explanation for this red shift involves increasing order of π-electron density in the resorcin[4]arene-based tags from phenyl to naphthyl.48,49 The luminescent spectra of 1 and 2 exhibit strong emission peaks at 325 nm (λex = 295 nm) and 375 nm (λex = 322 nm), respectively. The emission peaks of 1 and 2 are very close to the corresponding free TPC4A and TNC4A ligands, respectively. Thereby, their emissions are probably ascribed to the ligandbased luminescence.50,51 E


Article

Inorganic Chemistry

Figure 4. Emission spectra and intensities for 1 (a) and 2 (b) in aqueous solutions of different metal ions.

Selective Sensing of Fe2+ and Fe3+. Metal ion sensing and detection are of great significance because some metal ions are highly related to the environment and human health.52−54 Therefore, much effort has been currently devoted to detection of metal ions utilizing luminescent MOF-based sensors.55,56 In this study, the luminescent 1 and 2 were used to sense metal ions. In order to identify the potential of 1 and 2 toward sensing of metal ions, their crystalline samples were simply soaked in aqueous solutions of 0.01 mol L−1 MClx (M = Ca2+, Cd2+, Mn2+, Ni2+, Mg2+, Co2+, Na+, K+, Zn2+, Al3+, Cu2+, Fe2+, and Fe3+) to give the metal ion incorporated suspensions of MOFs for luminescence measurements. Emission intensities of the different suspensions strongly depend on the incorporated metal ions, as shown in Figure 4. For the different suspensions of 1, the Ca2+, Cd2+, Mn2+, Ni2+, Mg2+, and Co2+ ions enhance the luminescence intensity, whereas the metal ions such as Al3+, Cu2+, Fe2+, and Fe3+ produce varying degrees of luminescent quenching effects (Figure 4a). In the case of the different suspensions of 2, the luminescent intensity is enhanced when the Mg2+, Na+, K+, and Ca2+ are involved. In contrast, the interaction with Mn2+, Co2+, Ni2+, Cu2+, Fe2+, and Fe3+ ions drastically decreased the luminescence intensity (Figure 4b). The rest of the tested metal ions such as Cd2+ and Zn2+ result in a little bit of change in the luminescent intensity. The different quenching effects on the luminescent changes completely correspond to the variation tendency of the emission spectra, as illustrated in Figure 4. Notably, although both the Fe2+ and Fe3+ ions greatly quench the emissions of 1 and 2, their emission intensities are slightly different and can be distinguished under UV light. As shown in Figure 4, Fe2+ can quench the emission of 1 and 2, causing the

luminescence decrease. However, under the same condition, Fe3+ ions can completely quench the emission of the MOFs, which leads to the dark under UV light, as illustrated in Figure 4. In other words, the suspensions of 1 and 2 exhibit the selective sensing of the Fe2+ and Fe3+. Notably, there exist some shifts of the emission peaks of 2 in aqueous solutions of different metal ions, which probably accounts for the coordination interactions between guest metal ions and ligands/MOFs.33,57,58 The concentration-dependent luminescent sensing of Fe2+ and Fe3+ were also examined (see the Supporting Information). To determine whether 1 and 2 act as a highly selective luminescent sensor for Fe2+ and Fe3+, their selectivity detection and anti-interference sensing ability were further performed by the competing experiments. Typically, some mixed metal ions (each 0.01 mol L−1) were added consecutively into a suspension of 1 or 2 under the same conditions (Figures S4−S10). As shown in Figures 5 and 6, no significant emission intensity changes for 1 and 2 were observed in the presence of mixed metal ions. In other words, the quenching selectivity toward Fe2+ and Fe3+ does not show great interference by the addition of other metal ions. The results further confirm the ability of 1 and 2 to sense Fe2+ and Fe3+ with high selectivity even in the presence of other metal ions. To identify the luminescent quenching process toward metal ions, UV−vis absorption spectra of 1 and 2 as well as metal ions were measured. As illustrated in Figure S11, the Fe3+ ions in aqueous solution reveal a strong absorption band from 256 to 405 nm, whereas no apparent absorption bands were observed for the remaining metal ions in aqueous solutions. For 1 and 2, the strong absorption bands are also in the range 200−330 nm F


Article

Inorganic Chemistry

various mixed solvents are further investigated. In this study, the suspensions of 1 and 2 were achieved by soaking the finely ground samples of 1 and 2 (3 mg) into equal amounts of mixed solvents (3 mL), respectively (Figures S13−S28). As depicted in Figure 8, there are no apparent emission intensity changes for 1 upon mixing of acetone with equal amounts of other solvents. The relatively low interference is observed for the detection of acetone using 2 in the presence of aforesaid other potential interfering solvents, as illustrated in Figure 9. The competition experiments indicate that 1 and 2, especially 1, can be used as a highly selective sensor for acetone over other organic solvents. Moreover, the quenching effect of acetone has been further studied for the suspensions of 1 and 2. The as-synthesized samples of 1 and 2 were dispersed in ethanol as the standard suspension, and the content of acetone was gradually enhanced to monitor the emission response. As shown in Figure 10a, the luminescent performance of 1 with various concentrations of acetone from 0 to 5 vol % was measured. For the ethanol suspension of 1, an apparent decrease in the fluorescence intensity was observed with addition of acetone. Drastically, the fluorescence almost disappeared at the acetone content of 5 vol %, indicating that efficient fluorescent quenching of 1 is diffusioncontrolled by acetone. Moreover, the luminescent performance of 2 was also conducted in various concentrations of acetone from 0 to 100 vol %. As depicted in Figure 10b, the luminescent intensity of 2 decreases with the increasing concentration of acetone. At the acetone content of 100 vol %, the emission of suspension of 2 disappeared. Notably, the limit detection of acetone is determined as 5 vol % for 1, which is much better than 2. The luminescent “on−off” responses toward the different solvents were also concisely studied (see the Supporting Information). In order to understand the luminescent quenching mechanism of 1 and 2 toward small organic molecules, their UV−vis spectra were determined. As shown in Figure S29, there is a strong absorption band ranging from 250 to 315 nm for acetone solvent. Nevertheless, no apparent absorption bands were found for the remaining organic solvents. The absorption bands for 1 and 2 were also observed in the ranges 200−310 and 200−350 nm, respectively. Clearly, the absorption band of 1 is completely overlapped by the acetone solvents, yielding sensitive luminescent quenching with the addition of acetone solvents. Nevertheless, the absorption band of 2 is partially mantled by the acetone solvents, leading to relatively weak luminescent quenching under similar conditions.66 It also can be inferred that, after the samples of 1 and 2 were soaked in acetone solvents, their free guest molecules are gradually replaced by acetones, and the luminescence intensities of their suspensions are quenched accordingly.67,68 Sensing of Amine Vapors. The increasing content of volatile organic amines has been found in soil, wastewater, and food, which are very toxic to environments and human beings.69 Thereby, rapid probing of volatile organic amines is of great significance from the viewpoint of human health and environmental protection.70 Among various analytical tools for detection of amine vapors, the fluorescent chemosensor is an advantageous detection device with a high signal output, low cost, and simple detection.71,72 Notably, most of the explored MOFs exhibit only a single “turn-on” or “turn-off” luminescent response for small organic molecules thus far.73,74 Particularly, the fluorescent “on− off” MOFs for detecting amine vapors have not been exported thus far.75,76 Considering the excellent luminescent behaviors of 1 and 2, it will be of interest that their samples were used to detect

Figure 5. Emission intensities of 1 in aqueous solutions of mixed metal ions. The concentration of Fe2+, Fe3+, and other metal cations was 0.01 mol L−1, respectively. Mix: mixture of Al3+ and Cu2+.

Figure 6. Emission intensities of 2 in aqueous solutions of mixed metal cations. The concentration of Fe2+, Fe3+, and other metal ions was 0.01 mol·L−1, respectively. Mix: mixture of Mn2+, Co2+, and Ni2+.

(Figure S12). Clearly, the absorption bands of 1 and 2 are completely mantled by the Fe3+ ions in aqueous solution, resulting in a drastic decrease in luminescence intensities or even quenching.59 Sensing of Small Organic Molecules. Currently, small organic molecules have received increasing concerns because of their environmental biological hazards and human health risks.60,61 Hence, there exists an extensive interest in the sensing and recognition of small organic molecules.62,63 In this context, a MOFs-based luminescent switch showing a clearly sensory “on− off” effect is particularly interesting, and is exceeding rare.64,65 In this study, the fluorescent properties of 1 and 2 in diverse solvents have been investigated to examine their potential “on− off” sensing of small organic molecules. Typically, 1 and 2 (3 mg) were soaked into 3 mL of methanol, ethanol, 1-propanol, 2propanol, DMF, THF, acetone, and acetonitrile, respectively. The mixtures were then vigorously agitated using ultrasound to give the suspensions of 1 and 2. As shown in Figure 7, the luminescent intensities of 1 and 2 strongly depend on the solvents, particularly with regard to acetone, which shows the most serious quenching effect. The rest of the organic solvents have relatively weak effects on the emissions of 1 and 2. To demonstrate whether the acetone can completely quench the emission of 1 and 2, their emission performances in the G


Article

Inorganic Chemistry

Figure 7. Emission spectra and intensities for 1 (a) and 2 (b) in different organic solvents.

Figure 9. Emission intensities of 2 in various equal amounts of solvents. Mix: mixture of methanol, ethanol, 1-propanol, 2-propanol, DMF, THF, and acetonitrile.

Figure 8. Emission intensities of 1 in various equal amounts of solvents. Mix: mixture of methanol, ethanol, 1-propanol, 2-propanol, DMF, THF, and acetonitrile.

amine vapors as potential fluorescent sensors, such as methylamine (CH3NH2), ethylamine (C2H5NH2), propylamine (C3H7NH2), butylamine (C4H9NH2), ammonium hydroxide (NH 3 ·H 2 O), diethylamine ((C 2 H 5 ) 2 NH), triethylamine (C2H5)3N), and aniline (C6H5NH2). During the amine vapor

sensing experiments, the as-synthesized samples of 1 or 2 (20 mg) were ground and placed into a glass tube (5 mL), and then exposed to various amine vapors for 24 h in a sealed container. The sample tube was then taken out from the container and sealed, and their emission spectra were measured. As depicted in H


Article

Inorganic Chemistry

Figure 10. Emission spectra for 1 and 2 in different concentrations of acetone.

Figure 11. Emission spectra and intensities for 1 (a) and 2 (b) in various amine vapors.

effective quencher in liquid media for that reported compound. It can be inferred that the guest−host interactions between the guest molecules and the framework act as a significant role in the fluorescence responses of the different guests. To fully identify the luminescent “on−off” responses of 1 and 2 as luminescent sensors toward triethylamine vapors, the timedependent fluorescence profiles of 1 and 2 upon exposure to the triethylamine vapors and atmospheres have been investigated, respectively. As shown in Figures 12 and 13, a luminescent sensor setup was designed. The time-dependent luminescent quenching experiments toward triethylamine vapors were performed in the

Figure 11, the sensing experiments show that amine vapors act as fluorescent quenchers for 1 and 2 with apparently differential sensitivity. The order of quenching efficiency is C4H9NH2 < (C2H5)2NH < C6H5NH2 < C3H7NH2 < C2H5NH2 < NH3·H2O < CH3NH2 < (C2H5)3N for 1, and C3H7NH2 < C4H9NH2 < (C2H5)3N < C6H5NH2 < C2H5NH2 < CH3NH2 < NH3·H2O < (C2H5)2NH for 2. Obviously, the triethylamine shows the most effective quenching efficiency in vapor media. It is noteworthy that the reported luminescent compound {[EuL2(H2O)3](NO3)} (L = 4-(pyrimidin-5-yl)benzoate) also exhibits selective sensing of amine vapors.9 Nevertheless, aniline is the most I


Article

Inorganic Chemistry

Figure 12. Luminescent “on−off” process for 1 under triethylamine vapor (a) and atmosphere conditions (b), respectively.

induced fluorescent quenching was nearly unaffected in the background of 1 equiv of other amines. The result suggests that 1 and 2 have high sensitivity and selectivity toward triethylamine detection than other amine vapors. For clarification of the process of the quenching effect of amine vapors, their UV−vis absorption spectra were recorded. Triethylamine shows a UV absorption band from 200 to 310 nm, and aniline displays a strong absorption band ranging from 200 to 325 nm. However, no obvious absorption bands are found for other amines in this range. Obviously, the absorption peaks of 1 and 2 are almost mantled by the wide absorptions of both triethylamine and aniline (Figure S46), while no other amines absorb at this wavelength. Although the absorption bands of both triethylamine and aniline overlapped the ones of 1 and 2, they behave with different luminescent quenching effects on 1 and 2, which probably accounts for the different sizes of amine vapors. Usually, the ability of energy-transfer between guest molecules and framework also could affect the sensitivity of luminescent sensory MOFs.78 Thereby, the size-effect of guest molecules is a significant factor concerning the fluorescence responses of the framework.79 It is possible that the guest amine molecules, such as aniline with large size, whose diffusion is probably constrained by the framework, show a relatively weak effect on the luminescent quenching.9,80 Therefore, we could conclude that the luminescent 1 and 2 exhibit a striking size-selectivity for the probing of various amine vapors.

designed luminescent sensor setup. The result demonstrates that the luminescent intensities of 1 and 2 under the triethylamine vapors gradually decrease with increasing time. The luminescent quenching efficiency of triethylamine vapors reaches to a maximum in 60 min with a quenching percentage of more than 56.97% and 89.93% for 1 and 2, respectively (Figures 12 and 13 and Figure S30). Notably, after 24 h, the quenching percentage of 2 reached to 96.16%, while 1 shows no apparently quenching increase (Figure S30). The result suggests that 2 shows a remarkable selectivity and sensitivity for the sensing of various amine vapors, especially triethylamine vapor. Most strikingly, after the sample tubes of 1 and 2 under the triethylamine vapors were taken out from the container and exposed to the atmosphere, the luminescent intensities of 1 and 2 are gradually enhanced with an interesting luminescent “on−off” process. For 1, the luminescent percentage reached to 90.93% upon exposure to atmosphere after 24 h (Figure 12b and Figure S31a), and luminescent percentage of 79.59% was recovered for 2 after 48 h (Figure 13b and Figure S31b). It is interesting to note that such a luminescent switch for the amine vapors, exhibiting clearly two switch-functions of fluorescent quenching and enhancement effects, has not been explored before.77 Thus, the luminescent materials of 1 and 2 will be promising luminescent sensors for amine vapors, especially triethylamine vapors. To confirm the effective triethylamine detection for 1 and 2, competition experiments were further performed in the presence of other amine vapors. The luminescent quenching experiments of 1 and 2 are determined after they are, respectively, exposed to triethylamine and 1 equiv of other amine, as shown in Figures S32−S45. As illustrated in Figures 14 and 15, the triethylamine-

■

CONCLUSION In summary, two charming luminescent 2D and 3D MOFs were constructed by resorcin[4]arene-based tetracarboxylic acids with J


Article

Inorganic Chemistry

Figure 13. Luminescent “on−off” process for 2 under triethylamine vapor (a) and atmosphere conditions (b), respectively.

Figure 15. Emission intensities of 2 in two mixed amine vapors with 1:1 ratio.

Figure 14. Emission intensities of 1 in two mixed amine vapors with 1:1 ratio.

increasing aromatic tags. The luminescent sensing studies demonstrate that 1 and 2 are capable of highly selective detection of small organic molecules and amine vapors as well as highly selective sensing of Fe2+ and Fe3+ through fluorescent quenching. Remarkably, the luminescent materials of 1 and 2 reveal high selectivity and sensitivity for detecting trace amine vapors, especially triethylamine vapor. Most strikingly, 1 and 2

also exhibit clear fluorescent “on−off” switch-functions for sensing of small organic molecules and amine vapors with potential applications from environmental and health points of view. Further research centered on making fluorescent MOFbased “on−off” switches for more straightforward sensing of amine vapors and metal ions is underway in our laboratory. K


Article

Inorganic Chemistry

■

(21) Chen, Z.; Sun, Y.; Zhang, L.; Sun, D.; Liu, F.; Meng, Q.; Wang, R.; Sun, D. Chem. Commun. 2013, 49, 11557−11559. (22) Wu, Z.-L.; Dong, J.; Ni, W.-Y.; Zhang, B.-W.; Cui, J.-Z.; Zhao, B. Inorg. Chem. 2015, 54, 5266−5272. (23) Xu, H.; Hu, H.-C.; Cao, C.-S.; Zhao, B. Inorg. Chem. 2015, 54, 4585−4587. (24) Zhang, Z.; Chen, Y.; He, S.; Zhang, J.; Xu, X.; Yang, Y.; Nosheen, F.; Saleem, F.; He, W.; Wang, X. Angew. Chem., Int. Ed. 2014, 53, 12517−12521. (25) Dong, M.-J.; Zhao, M.; Ou, S.; Zou, C.; Wu, C.-D. Angew. Chem., Int. Ed. 2014, 53, 1575−1579. (26) Al-Maythalony, B. A.; Shekhah, O.; Swaidan, R.; Belmabkhout, Y.; Pinnau, I.; Eddaoudi, M. J. Am. Chem. Soc. 2015, 137, 1754−1757. (27) Cheng, J.; Ma, X.; Zhang, Y.; Liu, J.; Zhou, X.; Xiang, H. Inorg. Chem. 2014, 53, 3210−3219. (28) Kado, S.; Otani, H.; Nakahara, Y.; Kimura, K. Chem. Commun. 2013, 49, 886−888. (29) Wang, J.-H.; Li, M.; Li, D. Chem. Sci. 2013, 4, 1793−1801. (30) Lv, L.−L.; Yang, J.; Zhang, H.-M.; Liu, Y.-Y.; Ma, J.-F. Inorg. Chem. 2015, 54, 1744−1755. (31) Singha, D. K.; Mahata, P. Inorg. Chem. 2015, 54, 6373−6379. (32) Yi, F.-Y.; Wang, Y.; Li, J.-P.; Wu, D.; Lan, Y.-Q.; Sun, Z.-M. Mater. Horiz. 2015, 2, 245−251. (33) Hu, Z.; Deibert, B. J.; Li, J. Chem. Soc. Rev. 2014, 43, 5815−5840. (34) Wu, W.; Wu, W.; Ji, S.; Guo, H.; Song, P.; Han, K.; Chi, L.; Shao, J.; Zhao, J. J. Mater. Chem. 2010, 20, 9775−9786. (35) Sheldrick, G. M. SHELXL-97, Programs for X-ray Crystal Structure Solution; University of Göttingen: Göttingen, Germany, 1997. (36) Sheldrick, G. M. SHELXL-97, Programs for X-ray Crystal Structure Refinement; University of Göttingen: Göttingen, Germany, 1997. (37) Farrugia, L. J. WINGX: A Windows Program for Crystal Structure Analysis; University of Glasgow: Glasgow, U.K., 1988. (38) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7−13. (39) Klaes, M.; Agena, C.; Köhler, M.; Inoue, M.; Wada, T.; Inoue, Y.; Mattay, J. Eur. J. Org. Chem. 2003, 2003, 1404−1409. (40) McIldowie, M. J.; Mocerino, M.; Ogden, M. I.; Skelton, B. W. Tetrahedron 2007, 63, 10817−10825. (41) Cui, Y.; Yue, Y.; Qian, G.; Chen, B. Chem. Rev. 2012, 112, 1126− 1162. (42) Rocha, J.; Carlos, L. D.; Paz, F. A. A.; Ananias, D. Chem. Soc. Rev. 2011, 40, 926−940. (43) Ranft, A.; Niekiel, F.; Pavlichenko, I.; Stock, N.; Lotsch, B. V. Chem. Mater. 2015, 27, 1961−1970. (44) Fang, J. M.; Leng, F.; Zhao, X. J.; Hu, X. L.; Li, Y. F. Analyst 2014, 139, 801−806. (45) Li, J.; Yang, J.; Liu, Y.-Y.; Ma, J.-F. Chem. - Eur. J. 2015, 21, 4413− 4421. (46) Wu, H.; Liu, H.-Y.; Liu, Y.-Y.; Yang, J.; Liu, B.; Ma, J.-F. Chem. Commun. 2011, 47, 1818−1820. (47) Zhang, L.-P.; Ma, J.-F.; Yang, J.; Pang, Y.-Y.; Ma, J.-C. Inorg. Chem. 2010, 49, 1535−1550. (48) Barbon, S. M.; Staroverov, V. N.; Gilroy, J. B. J. Org. Chem. 2015, 80, 5226−5235. (49) Du, B.-S.; Lin, C.-H.; Chi, Y.; Hung, J.-Y.; Chung, M.-W.; Lin, T.Y.; Lee, G.-H.; Wong, K.-T.; Chou, P.-T.; Hung, W.-Y.; Chiu, H.-C. Inorg. Chem. 2010, 49, 8713−8723. (50) Bauer, C. A.; Timofeeva, T. V.; Settersten, T. B.; Patterson, B. D.; Liu, V. H.; Simmons, B. A.; Allendorf, M. D. J. Am. Chem. Soc. 2007, 129, 7136−7144. (51) Wang, Y.; Yang, J.; Liu, Y.-Y.; Ma, J.-F. Chem. - Eur. J. 2013, 19, 14591−14599. (52) Formica, M.; Fusi, V.; Giorgi, L.; Micheloni, M. Coord. Chem. Rev. 2012, 256, 170−192. (53) Huang, D.; Niu, C.; Ruan, M.; Wang, X.; Zeng, G.; Deng, C. Environ. Sci. Technol. 2013, 47, 4392−4398. (54) Hirayama, T.; Okuda, K.; Nagasawa, H. Chem. Sci. 2013, 4, 1250− 1256. (55) You, Y.; Cho, S.; Nam, W. Inorg. Chem. 2014, 53, 1804−1815.

ASSOCIATED CONTENT

S Supporting Information *

Crystallograpic data in CIF format. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02666. IR spectra, UV−vis absorption spectra, thermal gravimetric analysis curves, powder X-ray diffraction (PXRD) patterns, luminescent spectra, and selected bond lengths and angles for 1 and 2 (PDF) Crystallographic details for 1 (CIF) Crystallographic details for 2 (CIF)

■

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Fax: +86-431-85098620. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (Grants 21277022, 21371030, 21301026, and 21471029).

■

REFERENCES

(1) Diehl, K. L.; Anslyn, E. V. Chem. Soc. Rev. 2013, 42, 8596−8611. (2) Zhang, X.; Wang, W.; Hu, Z.; Wang, G.; Uvdal, K. Coord. Chem. Rev. 2015, 284, 206−235. (3) Hester, R. E.; Harrison, R. M. Volatile Organic Compounds in the Atmosphere; Royal Society of Chemistry: Cambridge, U.K., 1995. (4) Lin, H.; Jang, M.; Suslick, K. S. J. Am. Chem. Soc. 2011, 133, 16786− 16789. (5) Huang, W.; Besar, K.; LeCover, R.; Rule, A. M.; Breysse, P. N.; Katz, H. E. J. Am. Chem. Soc. 2012, 134, 14650−14653. (6) Yue, E.; Ma, X.; Zhang, Y.; Zhang, Y.; Duan, R.; Ji, H.; Li, J.; Che, Y.; Zhao, J. Chem. Commun. 2014, 50, 13596−13599. (7) Rochat, S.; Swager, T. M. Angew. Chem., Int. Ed. 2014, 53, 9792− 9796. (8) Meng, D.; Yang, S.; Sun, D.; Zeng, Y.; Sun, J.; Li, Y.; Yan, S.; Huang, Y.; Bielawski, C. W.; Geng, J. Chem. Sci. 2014, 5, 3130−3134. (9) Chen, J.; Yi, F.-Y.; Yu, H.; Jiao, S.; Pang, G.; Sun, Z.-M. Chem. Commun. 2014, 50, 10506−10509. (10) Pablos, J. L.; Vallejos, S.; Muñoz, A.; Rojo, M. J.; Serna, F.; García, F. C.; García, J. M. Chem. - Eur. J. 2015, 21, 8733−8736. (11) Wang, J.-H.; Li, M.; Li, D. Chem. Sci. 2013, 4, 1793−1801. (12) Shustova, N. B.; Cozzolino, A. F.; Reineke, S.; Baldo, M.; Dinca, M. J. Am. Chem. Soc. 2013, 135, 13326−13329. (13) Pais, V. F.; Remón, P.; Collado, D.; Andréasson, J.; PérezInestrosa, E.; Pischel, U. Org. Lett. 2011, 13, 5572−5575. (14) Xiang, Z.; Fang, C.; Leng, S.; Cao, D. J. Mater. Chem. A 2014, 2, 7662−7665. (15) Joseph, R.; Chinta, J. P.; Rao, C. P. Inorg. Chem. 2011, 50, 7050− 7058. (16) Rivasseau, C.; Farhi, E.; Atteia, A.; Couté, A.; Gromova, M.; Cyr, D. G. S.; Boisson, A.; Féret, A.-S.; Compagnon, E.; Bligny, R. Energy Environ. Sci. 2013, 6, 1230−1239. (17) Seela, F.; Jawalekar, A. M.; Chi, L.; Zhong, D. Chem. Biodiversity 2005, 2, 84−90. (18) Xu, X.-Y.; Yan, B. ACS Appl. Mater. Interfaces 2015, 7, 721−729. (19) Saleh, S. M.; Ali, R.; Wolfbeis, O. S. Chem. - Eur. J. 2011, 17, 14611−14617. (20) Nadella, S.; Selvakumar, P. M.; Suresh, E.; Subramanian, P. S.; Albrecht, M.; Giese, M.; Fröhlich, R. Chem. - Eur. J. 2012, 18, 16784− 16792. L


Article

Inorganic Chemistry (56) Dong, X.-Y.; Wang, R.; Wang, J.-Z.; Zang, S.-Q.; Mak, T. C. W. J. Mater. Chem. A 2015, 3, 641−647. (57) He, H.; Song, Y.; Sun, F.; Bian, Z.; Gao, L.; Zhu, G. J. J. Mater. Chem. A 2015, 3, 16598−16603. (58) Pramanik, S.; Hu, Z. C.; Zhang, X.; Zheng, C.; Kelly, S.; Li, J. Chem. - Eur. J. 2013, 19, 15964−15971. (59) Zhou, J.-M.; Shi, W.; Li, H.-M.; Li, H.; Cheng, P. J. Phys. Chem. C 2014, 118, 416−426. (60) Nagarkar, S. S.; Joarder, B.; Chaudhari, A. K.; Mukherjee, S.; Ghosh, S. K. Angew. Chem., Int. Ed. 2013, 52, 2881−2885. (61) Voutchkova, A. M.; Osimitz, T. G.; Anastas, P. T. Chem. Rev. 2010, 110, 5845−5882. (62) Zhou, J.-M.; Shi, W.; Xu, N.; Cheng, P. Inorg. Chem. 2013, 52, 8082−8090. (63) Helmbrecht, C.; Lützenkirchen-Hecht, D.; Frank, W. Nanoscale 2015, 7, 4978−4983. (64) Tang, Y.; Yang, H.-R.; Sun, H.-B.; Liu, S.-J.; Wang, J.-X.; Zhao, Q.; Liu, X.-M.; Xu, W.-J.; Li, S.-B.; Huang, W. Chem. - Eur. J. 2013, 19, 1311−1319. (65) Kwon, J. E.; Lee, S.; You, Y.; Baek, K.-H.; Ohkubo, K.; Cho, J.; Fukuzumi, S.; Shin, I.; Park, S. Y.; Nam, W. Inorg. Chem. 2012, 51, 8760−8774. (66) Yi, F.-Y.; Yang, W.; Sun, Z.-M. J. Mater. Chem. 2012, 22, 23201− 23209. (67) Chen, B.; Yang, Y.; Zapata, F.; Lin, G.; Qian, G.; Lobkovsky, E. B. Adv. Mater. 2007, 19, 1693−1696. (68) Liu, F.-H.; Qin, C.; Ding, Y.; Wu, H.; Shao, K.-Z.; Su, Z.-M. Dalton Trans. 2015, 44, 1754−1760. (69) Rampfl, M.; Mair, S.; Mayer, F.; Sedlbauer, K.; Breuer, K.; Niessner, R. Environ. Sci. Technol. 2008, 42, 5217−5222. (70) Shen, X.; Yan, B. J. Mater. Chem. C 2015, 3, 7038−7044. (71) Oliveri, I. P.; Malandrino, G.; Di Bella, S. Inorg. Chem. 2014, 53, 9771−9777. (72) Lee, M. H.; Yoon, B.; Kim, J. S.; Sessler, J. L. Chem. Sci. 2013, 4, 4121−4126. (73) Douvali, A.; Tsipis, A. C.; Eliseeva, S. V.; Petoud, S.; Papaefstathiou, G. S.; Malliakas, C. D.; Papadas, I.; Armatas, G. S.; Margiolaki, I.; Kanatzidis, M. G.; Lazarides, T.; Manos, M. J. Angew. Chem., Int. Ed. 2015, 54, 1651−1656. (74) Freimuth, L.; Christoffers, J. Chem. - Eur. J. 2015, 21, 8214−8221. (75) He, C.; He, Q.; Deng, C.; Shi, L.; Zhu, D.; Fu, Y.; Cao, H.; Cheng, J. Chem. Commun. 2010, 46, 7536−7538. (76) Heier, P.; Boscher, N. D.; Choquet, P.; Heinze, K. Inorg. Chem. 2014, 53, 11086−11095. (77) Nastasi, F.; Puntoriero, F.; Palmeri, N.; Cavallaro, S.; Campagna, S.; Lanza, S. Chem. Commun. 2007, 4740−4742. (78) Mameli, M.; Aragoni, M. C.; Arca, M.; Atzori, M.; Bencini, A.; Bazzicalupi, C.; Blake, A. J.; Caltagirone, C.; Devillanova, F. A.; Garau, A.; Hursthouse, M. B.; Isaia, F.; Lippolis, V.; Valtancoli, B. Inorg. Chem. 2009, 48, 9236−9249. (79) Jiang, B.-P.; Guo, D.-S.; Liu, Y. J. Org. Chem. 2011, 76, 6101− 6107. (80) Saitow, K.; Suemori, H.; Tamamitsu, H. Chem. Commun. 2014, 50, 1137−1140.

M


Fluorescent Aromatic Tag-Functionalized MOFs for ... - ACS Publications

Recommend Documents