Highly luminescent metal-organic frameworks based on an AIE ligand

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Highly luminescent metal-organic frameworks based on an AIE ligand as chemical sensors for nitroaromatic compounds Fang-Ming Wang, Lei Zhou, William P. Lustig, Zhichao Hu, Jun-Feng Li, Bing-Xiang Hu, Li-Zhuang Chen, and Jing Li Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00604 • Publication Date (Web): 11 Jul 2018 Downloaded from http://pubs.acs.org on July 12, 2018

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Crystal Growth & Design

Highly luminescent metal-organic frameworks based on an AIE ligand as chemical sensors for nitroaromatic compounds

Fang-Ming Wang,*a Lei Zhou,a,# William P. Lustig,b,# Zhichao Hu,b Jun-Feng Li,a Bing-Xiang Hu,a Li-Zhuang Chen,*a Jing Li*b

a

School of Environmental and Chemical Engineering, Jiangsu University of Science

and Technology, Zhenjiang 212003, P. R. China. Email: [email protected], [email protected] b

Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor

Road, Piscataway, New Jersey 08854, USA. E-mail: [email protected]

ABSTRACT: Three new luminescent metal organic frameworks (LMOFs) based on d10 metals (Zn2+, Cd2+) and the highly emissive aggregation-induced emission (AIE) ligand 1,1,2,2-tetrakis(4-(4-carboxyphenyl)phenyl)ethene(H4tcbpe) are reported, with the formulas

[Cd(tcbpe)1.5(DMF)(H2O)]·(DMF)6·(C2H5OH)3

(1),

[Zn(tcbpe)(DMF)]·(MeCN) (2), and [Cd(tcbpe)]·(MeCN) (3). Compounds 1 and 2 both emit strong green light with internal quantum yields (IQYs) as high as 66.8% and 65.7%, respectively, while compound 3 emits bluish green light with 37.2% IQY. A solution-phase sensing study shows that 1 has the highest sensitivity to nitroaromatic compounds and demonstrates that it is potentially useful as a luminescence-based chemical sensor. DFT calculations are used to explain the sensing mechanism and relative sensitivity of compound 1 to various nitroaromatic compounds.

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Equal Contributor

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Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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INTRODUCTION Metal-organic frameworks (MOFs) are an important and relatively new class of porous materials that have attracted increasing attention in recent years for their diverse, tunable properties. They have demonstrated great potential for applications in the fields of catalysis, gas storage and separation, sensing, drug delivery, and bio-imaging, among others.1-9 Using luminescent MOFs (LMOFs) to detect poisonous gases and various other hazardous species10-15 has been a particularly popular area of research,

as the presence of these molecules—or potentially any other

molecules—within the material’s pores can alter the LMOF’s luminescence in a variety of easily detectable ways.16-18 Taking advantage of this feature, LMOFs have been effectively used to detect a variety of analytes, with a special emphasis on nitroaromatic compounds that are used in explosives or present as environmental pollutants.19-21 Quickly and effectively sensing the presence of these species is important to ensure homeland security and civilian safety.3, 22 According to previous studies, photoluminescent emission in LMOFs based on d10 metals is most often the result of ligand-centered (LC) or ligand-to-ligand charge transfer (LLCT) processes.3, 5, 23 We have previously reported LMOFs23-25 exhibiting LC emission from the ligand 1,1,2,2-tetrakis(4-(4-carboxyphenyl)phenyl)ethane (H4tcbpe) which contains the classic AIE tetraphenylethylene (TPE) core.26, 27As a continuing study, we have explored the synthesis of d10 metal-based LMOFs with H4tcbpe under different experimental conditions, and now report three new LMOFs consisting of H4tcbpe, d10 metals, and a variety of terminal solvent molecules, namely [Cd(tcbpe)1.5(DMF)(H2O)]·(DMF)6·(EtOH)3

(1,

JUST-3,

or

LMOF-311),

[Zn(tcbpe)(DMF)]·(MeCN) (2, JUST-4, or LMOF-312), and [Cd(tcbpe)]·(MeCN) (3, JUST-5, or LMOF-313). All three compounds were synthesized hydrothermally, and their structures were determined and analyzed by single crystal and powder X-ray diffraction (SXRD and PXRD) methods. Photoluminescence (PL) spectroscopy, thermogravimetric analysis (TGA), and internal quantum yield measurements were carried out to characterize their optical and thermal properties. Fluorescence titrations, coupled with DFT 2


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calculations, revealed that 1 is an effective luminescent sensor for nitroaromatic compounds in DMF suspension by fluorescence quenching, which occurs via a photo-excited electron transfer-based mechanism.

EXPERIMENTAL SECTION Materials and Methods All reagent-grade chemicals and solvents were obtained from commercial sources and used without further purification. The luminescence spectra of the three compounds

in

solid

form

were

recorded

at

room

temperature

on

a

SpectrofluorometerFS5. Powder samples were uniformly coated on glass slides which have no emission in the visible range. Thermogravimetric analyses (TGA) of compounds 1 ~ 3 were carried out on a TA Q5000 analyzer. Crystal samples were loaded onto a platinum pan and heated with a ramp rate of 15 °C min−1 from 30 °C to 800 °C under a nitrogen at 50 ml min−1.The IQYs of the samples were measured on a Hamamatsu C9920-03 absolute quantum yield measurement system with a 150 W xenon monochromatic lamp and a 3.3 inch integrating sphere. Sodium salicylate and YAG:Ce3+ were chosen as the standards with an IQY of 60% (measured 66%) at 360 nm and 95% (measured 99%) at 455 nm, respectively. Powder X-ray diffraction (PXRD) patterns were recorded on an Ultima IV X-ray diffractometer using Cu Kα radiation (λ = 1.5406 Å). The data were collected at room temperature over a 2θ range of 5–50° with a scan speed of 6° min 1 and an operating power of 40 kV and 44 mA. −

Synthesis of Ligand and Compounds Ligand synthesis 1,1,2,2-tetrakis(4-(4-carboxyphenyl)phenyl)ethene(H4tcbpe)

(Fig.S1)

was

synthesized as previously reported.28 Preparation of [Cd(tcbpe)1.5(DMF)(H2O)]·(DMF)6·(EtOH)3 (1) Cd(NO3)2•4H2O (12.3 mg, 0.04 mmol), H4tcbpe (16.2 mg, 0.02 mmol), dimethylformamide (DMF, 1 mL), and ethanol (EtOH, 0.5 mL) were sealed in a glass tube under vacuum and kept at 80 ˚C for two days. Pale yellow crystals of 1 were obtained with a yield of 57% based on H4tcbpe. 3



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Preparation of [Zn(tcbpe)(DMF)]·(MeCN) (2) Zn(NO3)2•6H2O (11.9 mg, 0.04 mmol), H4tcbpe (16.2 mg, 0.02 mmol), DMF (1 mL), and acetonitrile (MeCN, 0.5 mL) were sealed in a glass tube under vacuum and kept at 80 ˚C for two days. Pale yellow crystals of 2 were obtained with a yield of 53% based on H4tcbpe. Preparation of [Cd(tcbpe)]·(MeCN) (3) Cd(NO3)2·4H2O (12.3 mg, 0.04 mmol), H4tcbpe (8.1 mg, 0.01 mmol), DMF (2 mL), acetonitrile (1 mL), and 6 mol/L HNO3 (0.5 mL) were mixed in a 20 ml glass vial, and then were kept at 125˚C for two days. Pale yellow crystals of 3 were obtained with a yield of 46% based on H4tcbpe. Single crystal X-ray diffraction (SXRD) Single crystal diffraction data for 1–3 were collected using a Bruker SMART APEX II CCD diffractometer with graphite-monochromatic Mo Kα radiation (λ = 0.71073 Å). Data processing, including empirical absorption correction, was performed using SADABS. The structures of 1, 2, and 3 were solved by direct methods and refined by the full-matrix method based on F2 by means of the SHELXLTL software package. The SQUEEZE routine within the crystallographic program PLATON was employed to treat the disordered solvent molecules in the crystal. Non-hydrogen atoms were refined anisotropically using all reflections with I>2σ(I). All H atoms were placed at the calculated positions (C–H= 0.930 Å for benzene and 0.960 Å for methyl) and refined riding on the parent atoms with U(H) = 1.2Ueq (bonded C of both benzyl and methyl group atoms) and U(H) = 1.5Ueq (bonded C of the methyl group). CCDC numbers of 1–3 are, respectively, 1544146, 1544145, and 1544144. Fluorescence titration experimental details To examine 1’s capability to sense nitroaromatic compounds, a fluorescence titration experiment was carried out at room temperature. First, a well-dispersed 1 mM suspension of 1 (44.5 mg, 0.02 mmol) in DMF (20 mL) was prepared by ultrasonic stirring for 30 minutes. The suspension of 1 (4 mL) was transferred to a quartz cuvette, and 5µL aliquots of a standard solution of analyte in DMF were 4


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gradually titrated into the suspension with ultrasonic stirring for 1 minute before the test. Emission from the suspension, under 365 nm excitation, was recorded before/after each addition of analyte, with the analyte concentrations ranging from 0-2.5 mM (nitrobenzene, m-nitrotoluene and p-nitrotoluene) and 0-1.25 mM (2,6-dinitrotoluene) over the course of the titration.

Table 1. Crystallographic data for 1, 2, and 3. Empirical formula Formula weight Space group a (Å) b (Å) c (Å) α(o) β(o) γ(o) V (Å3) Z Dc (g/m-3) µ(mm-1) F (000) θ range [ º ] Collected reflections Unique reflections R1 , wR2 [I > 2σ (I)] R1, wR2 [all data] GOF

1 C108H119Cd3N7O24 2236.36 Pbca 17.1330(2) 42.5330(3) 33.8993(3) 90 90 90 24703.0(4) 8 1.203 4.624 6646 4.01-73.12 22231

2 C59H42N2O9Zn2 1053.68 Pna21 42.3285(10) 11.1182(3) 10.3030(3) 90 90 90 4848.8(2) 4 1.443 1.052 2168 2.332-26.989 6800

3 C56H35CdNO8 962.29 P4/ncc 10.2835(4) 10.2835(4) 43.559(4) 90 90 90 4606.4(5) 4 1.328 0.528 1872 2.724-19.487 1408

18732 0.0410, 0.1085

5696 0.0369, 0.0793

894 0.1291, 0.1903

0.0504, 0.1176 1.018

0.0462, 0.0826 0.958

0.1708, 0.2075 1.079

RESULTS AND DISCUSSION Structural and Topological Analysis Compound 1 crystallizes in the orthorhombic system with space group Pbca (Table 1). There are three Cd atoms, one and a half tcbpe ligands, one DMF and two H2O molecules in the asymmetric unit (Fig.1a). Each Cd atom is coordinated to six O atoms (Fig. 1b), forming either an octahedron or a distorted octahedron. Cd03 and 5



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Cd04 coordinate with four oxygen from four tcbpe ligands, one O atom from a coordinated DMF molecule, and one O atom from a coordinated H2O molecule to form a regular octahedron. Cd01 and Cd02 coordinate only with four tcbpe ligands; two ligands are coordinated through monodentate carboxylate groups, while the other two ligands bind in a bidentate fashion to form a distorted octahedron. These CdO6 units are interconnected with each other through bridging carboxylate groups to afford an infinite 1D PBU in the form of a helical chain along the c-axis (Fig.1b). 1 has two 1D channels along the a and c axes with cross-sections measuring 12.1×14.2 Å and 15.8×20.1 Å respectively, and a 55.2% solvent accessible volume calculated by PLATON. The bond distances of Cd-O range from 2.204Å to 2.646Å (Table S1). Simplifying the tcbpe ligand as a 4-c node gives the framework is as a 4-nodal (4, 4, 4, 4)-c net{6^2.7^2.9^2}{6^4.7.8}6{6^6}2(Fig. 1c).

6


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Fig.1 (a) The asymmetric unit of 1, containing three Cd atoms, one and a half tcbpe ligands, one DMF, and two H2O molecules. (b) The octahedral and distorted octahedral coordination spheres formed by Cd2+ and the resulting helical chain running in the c direction. (c) The topological structure of 1 and the two 1D channels running along the a (green) and c (blue) axes. In all structures, hydrogen have been omitted for clarity.

Compound 2 crystallizes in the orthorhombic system with space group Pna21 (Table 1). The asymmetric unit contains one tcbpe ligand, two Zn atoms, one DMF, and one MeCN. 2 is different from previously reported compounds containing the same metal center and ligand.28,

29

The two Zn atoms have four-coordinated and 7



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five-coordinated geometries, and are bridged by three carboxylate groups to form a secondary building unit (SBU). Both Zn coordinate to four tcbpe ligands in a monodentate fashion, while the five-coordinated Zn is also coordinated to an O from a DMF molecule (Fig. 2a). The adjacent clusters are further linked by one carboxylic acid group generating a 3D framework (Fig. 2b). The bond distances of Zn-O range from 1.912 Å to 2.159 Å (Table S1). A 1D channel runs along the a axis, with four tcbpe ligands (each contributing half of a molecule) forming the channel walls and the MeCN solvent molecules located in the center of the channel (Fig. 2c). The cross-section of the channel measures 5.7×5.8 Å. The solvent accessible volume of compound 2 is 16.8% as calculated by PLATON. With the tcbpe ligand simplified as a 4-c node, the framework is a 3-nodal (3, 4, 5)-c net {5^3.8^3} {5^3}{5^4.8^4.9^2} (Fig. 2d).

8


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Fig.2 (a) SBU of 2, showing the two different coordination modes of Zn. (b) The MeCN-loaded 1D channels of 2 running along the a-axis with a cross section of 5.7×5.8 Å.(c) Channel with MeCN solvent molecules located at the center along the a-axis. (d) The topological structure of 2. In all structures, hydrogen have been omitted for clarity.

Single crystal X-ray diffraction studies revealed that 3 crystallizes in the tetragonal system with space group P4/ncc (Table 1). Despite being constructed from the same metal and ligand, the structure of 3 is very different from 1, which demonstrates the strong impact synthesis conditions have on the resulting framework 9



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geometries. In 3, each Cd is tetrahedrally coordinated with four O atoms from monodentate carboxylic acid groups on four tcbpe ligands, forming the primary building unit (PBU). These PBUs are interconnected by ligands to create an overall three-dimensional (3D) net (Fig.3a, b). The bond distances of Cd-O range from 2.361 Å to 2.588 Å (Table S2). Four of these identical nets interpenetrate to generate a 4-fold 3D→3D homo-interpenetrating MOFs (homo-IMOFs),30, 31 which reduces the void space. As expected, the pore size of a single net is 10.5×10.5 Å along the c-axis, but decreases to 4.9×4.9 Å in 3 due to interpenetration (Fig.3 c-d). The vacant space in complex 3 is 14.8%, calculated by PLATON. As indicated by PXRD, 3 is stable when exposed to various solvents (Fig.S7). With the ligand tcbpe simplified as a 4-c node, the framework is a 2-nodal (4, 4)-c net {4^2.8^4} (pts type)(Fig.3e).

Fig.3 (a) PBU of 3, a tetrahedrally coordinated Cd center, and the structure of the ligand tcbpe. (b) The coordination environment of 3, with Cd bonded to four tcbpe molecules. (c) Single net of 3 viewed along the c-axis and the pore space shown in pink. (d) The 4-fold 10


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interpenetration of 3 and 1D channels along the c-axis. (e) The topological structure of 3. In all structures, hydrogen have been omitted for clarity.

Optical Properties The photoluminescence emission spectra of the three compounds were studied at room temperature in their solid form (Fig.4a). 1 and 2 both exhibit green emission, with emission peaks of 513 nm under 373 nm excitation and 505 nm under 408 nm excitation, respectively. 3 exhibits bluish green emission at 480 nm when excited at 408 nm, and the ligand H4tcbpe exhibits yellowish emission peaking at 537 nm when excited at 431 nm. The Commission International de I’Eclairage (CIE) chromaticity coordinates of 1, 2, 3, and H4tcbpe are (0.260, 0.445), (0.246, 0.505), (0.201, 0.360), and (0.351, 0.539) respectively (Fig. 4b). The luminescence lifetimes of these compounds were measured, giving lifetimes are 3.45 ns, 2.58 ns and 1.94 ns for 1, 2, and 3, respectively. Interestingly, the order of their luminescence lifetimes are in trend with their emission peaks and framework porosity. This agrees with earlier reports, which related decreased lifetime in a tcbpe-based LMOF with increased rigidity and higher energy emission.32 In this case, the rigidification of the tcbpe ligand prevents molecular torsion in the excited state, which is the typical relaxation pathway for these structures. Denied this pathway, energy is released as a photon. Increased rigidification further limits the degree of relaxation that occurs after excitation, resulting in shorter lifetimes and higher energy emission. Following solvent removal by heating at 100 °C under vacuum for 12 hours, the location of the emission peaks of compounds 2 and 3 barely changed (Fig. S2), indicating that their emission is largely independent of the encapsulated solvent molecules. Diffuse reflectance spectra of 1-3 were collected at room temperature, and a KM plot was used to estimate the optical band gap (figure S3).

11



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Fig.4 (a) The excitation (dotted) and emission (solid) spectra of 1 (red), 2 (blue), 3 (magenta) and tcbpe (black). (b) CIE coordinates of 1 (red), 2 (blue), 3 (purple) and H4tcbpe (black).

As shown in Table 2, the relatively high IQYs of 1 and 2 make them potentially useful as phosphors or sensors. The highly porous nature of 1 improves its prospects as a sensor material, as it provides a feasible platform for the confinement of, and interaction with, guest molecules. The chemical sensing properties of 1 were therefore studied.

Table 2. The peak emission wavelengths, optical band gaps, internal quantum yields (IQYs), and CIE coordinates of 1–3.

Compound 1 2 3

Emission wavelength 513 nm 505 nm 480 nm

Color green green bluish green

Optical band gap 2.48 eV 2.60 eV 2.64 eV

λex: 365 nm

λex: 455 nm

CIE

66.8% 65.7% 37.2%

48.3% 50.1% 30.2%

0.260, 0.445 0.246, 0.505 0.201, 0.360

To first evaluate the stability of compound 1 in various solvents, solvent exchange was carried out at room temperature by soaking 1 in the exchange solvents for 24 hours, with the solvent refreshed every 4 hours. While the structure of 1 is maintained in DMF, it loses its long-range order when soaked in low boiling point solvents such as acetone, dichloromethane, n-hexane, and methanol (Fig.S4a). As such, DMF was selected as the solvent used in the sensing titrations. A suspension of 1 in DMF was prepared and titrated with the nitroaromatic compounds nitrobenzene, 12


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m-nitrotoluene, p-nitrotoluene, and 2,6-dinitrotoluene. PXRD analysis of 1 before and after the sensing titration demonstrated that the crystallinity of 1 was maintained (Fig. S4b). Upon the gradual addition of these analytes, emission from 1 was strongly quenched. The quenching efficiency was quantified using the Stern−Volmer (SV) equation16, 29, 33-35 I0/I = KSV[Q] + 1 Where Io and I are the luminescent intensities of 1@DMF suspensions before and after the addition of analyte, [Q] is the molar concentration of analyte, and Ksv is the quenching constant used to quantitatively evaluate the sensing efficiency. Using the SV plot (Fig. 5, S8), the Ksv of 2,6-dinitrotoluene was determined to be 2063 M-1. This value is nearly twice that of nitrobenzene (1173 M-1), m-nitrotoluene (1124 M-1) and p-nitrotoluene (1252 M-1), indicating 1 responds more strongly to the presence of 2,6-dinitrotoluene. This is consistent with the quenching mechanism and our DFT calculations. Emission quenching occurs via the photo-induced electron-transfer (PET) mechanism,20,

36-39

in which excited electrons in the

higher-lying LUMO of the fluorescent ligand are transferred into the lower-lying LUMO of the analyte, interrupting and quenching the ligand-centered emission. DFT calculations, using the hybrid functional B3LYP and 6-311++G(3df,3pd) basis set, were performed on the ligand H4tcbpe and the nitroaromatic analyte molecules, demonstrating that the relative positions of their LUMO energy levels are appropriate for PET-mediated emission quenching (Fig. 6). These calculations indicate that 2,6-dinitrotoluene has a lower LUMO energy level than the other three nitroaromatic analytes, giving rise to stronger electron transfer from the excited tcbpe and thereby improving the efficiency of emission quenching in 1.

13



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Fig. 5 The Stern−Volmer curves acquired at λex = 365 nm for nitrobenzene (cyan triangle), m-nitrotoluene (blue triangle), p-nitrotoluene (red dots), and 2,6-dinitrotoluene (black square).

Fig. 6 Calculated LUMO and HOMO energy levels of nitroaromatic compounds and the ligand H4tcbpe at B3LYP/6-311++G(3df,3pd), demonstrating that the elevated position of the tcbpe LUMO relative to the nitroaromatic analyte LUMOs enables PET-based emission 14


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quenching.

To demonstrate the importance of porosity on the ability of an LMOF to function as a sensor material, solvent exchange with nitrobenzene was performed on compounds 1, 2, and 3 (Fig. S5). Emission from 1, already shown to be an effective sensor for nitroaromatic compounds, was completely quenched. However, emission from 2 and 3 was partially maintained, with 2 exhibiting 82% quenching and 3 exhibiting 73.6% quenching. This is in trend with the porosities of each structure, demonstrating the importance of maximizing accessible surface area in a sensor material. As discussed previously, 1 possesses large internal channels with cross-sections measuring 12.1×14.2 Å and 15.8×20.1 Å running along the a and c axes respectively, which are large enough to permit nitroaromatic analyte molecules into the structure. In addition, 1 possesses 55.2% solvent accessible volume as calculated

by

PLATON—significantly

higher

than

the

PLATON-calculated

solvent-accessible volumes of 2 (16.8%) and 3 (14.8%),which likewise have narrower internal channels. To further compare their performance, exposing 1 to a nitrobenzene concentration of just 2 mM during the previously described sensing titration—instead of the high concentration exposure in solvent exchange—was sufficient to induce a response consistent with that caused by solvent exchange in 2 and 3 (Fig. S8). The difference in sensing performance between 1 and 3 underlines another aspect of LMOF sensor design. In 3, large gaps between the tetrahedral CdO4 PBUs allows for four-fold framework interpenetration, greatly restricting the pore volume of the structure. In 1, which is composed of the same ligand and metal, the infinite 1D PBU effectively prevents interpenetration, maintaining the large framework channels. This maximizes the potential interactions between the framework and large analytes like nitroaromatic molecules.

CONCLUSIONS In summary, three new LMOFs based on d10 metals and the AIE-chromophore ligand H4tcbpe have been designed and synthesized, their luminescent properties have been investigated, and their suitability as sensor materials for nitroaromatic 15



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compounds has been investigated. Compared with other reports,19-21, 25 this work uses an AIE-chromophore ligand, which is a fairly reliable method of generating highly luminescent MOFs. The high quantum yields that can be achieved using this strategy are useful in designing optical sensor materials, as increased luminescence intensity permits easier signal detection. Additionally, this work demonstrates the importance of employing LMOFs with the appropriate framework qualities, as the significantly porous 1 shows enhanced performance over 2 and 3, which are chemically similar but differ in topology. The combination of porosity plus strong luminescence in 1 suggests that the material would function effectively as a luminescent sensor. Fluorescence titration experiments show that 1 can efficiently detect nitroaromatic molecules, with an especially high sensitivity for 2,6-dinitrotoluene. DFT calculations were used to explain this special sensitivity as well elucidate as the general quenching mechanism, which is based on the photo-excited transfer of electrons from 1 to the analyte. The results illustrate that 1 has the potential to serve as a simple, low-cost, and efficient chemical sensor for monitoring nitroaromatic compounds.

ASSOCIATED CONTENT Supporting Information Supporting information, including crystallographic data (CIF), selected bond lengths, TGA, powder XRD, and other details, is available free of charge via the internet at http://pubs.acs.org. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS The JUST team would like to thank the support from the National Natural Science Foundation of China (Grant No. 21671084). The RU team acknowledges the partial support from the National Science Foundation via Grant No. DMR-1507210.

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Highly luminescent metal-organic frameworks based on an AIE ligand as chemical sensors for nitroaromatic compounds Fang-Ming Wang,*a Lei Zhou,a,# William P. Lustig,b,# Zhichao Hu,b Jun-Feng Li,a Bing-Xiang Hu,a Li-Zhuang Chen,*a Jing Li*b

a

School of Environmental and Chemical Engineering, Jiangsu University of Science

and Technology, Zhenjiang 212003, P. R. China. Email:[email protected], [email protected] b

Department of Chemistry and Chemical Biology, Rutgers University, 610 Taylor

Road, Piscataway, New Jersey 08854, USA. E-mail: [email protected]

Three strongly luminescent metal organic frameworks (LMOFs) are designed and synthesized based on a highly emissive chromophore ligand. An internal quantum yield as high as 66.8% has been achieved for these LMOFs. Compound 1 is highly porous with a 55.2% porosity and exhibits a high sensitivity toward nitroaromatic species, making it potentially useful as a luminescence-based chemical sensor. 20


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338x190mm (96 x 96 DPI)


Highly luminescent metal-organic frameworks based on an AIE ligand

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