silver(I) with high selectivity and sensitivity

Accepted Manuscript A Luminescent Cd(II)-MOF as Recyclable Bi-responsive Sensor for Detecting TNP and Iron(III)/Silver(I) with High Selectivity and Sensitivity Jinsong Hu, Ke Wu, Shengju Dong, Mingdong Zheng PII: DOI: Reference:

S0277-5387(18)30411-X https://doi.org/10.1016/j.poly.2018.07.024 POLY 13289

To appear in:

Polyhedron

Received Date: Revised Date: Accepted Date:

29 May 2018 1 July 2018 14 July 2018

Please cite this article as: J. Hu, K. Wu, S. Dong, M. Zheng, A Luminescent Cd(II)-MOF as Recyclable Bi-responsive Sensor for Detecting TNP and Iron(III)/Silver(I) with High Selectivity and Sensitivity, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.07.024

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A Luminescent Cd(Ⅱ)-MOF as Recyclable Bi-responsive Sensor for Detecting TNP and Iron(III)/Silver(I) with High Selectivity and Sensitivity Jinsong Hu*, a, b, c a

Ke Wua

Shengju Donga

Mingdong Zheng*, a

School of Chemical Engineering, Anhui University of Science and Technology,

Huainan 232001, P. R. China; b

Key Lab of Novel Thin Film Solar Cells, Chinese Academy of Sciences Hefei

Institute of Physical Science, Chinese Academy of Sciences; c

Key Laboratory of Photochemical Conversion and Optoelectronic Material, TIPC,

CAS. E-mail: [email protected], [email protected] ABSTRACT:

A

new

three

dimensional

framework

{[Cd2(BPDPE)2(chdc)2(H2O)2]·4H2O}n (1) (BPDPE = 4,4′-bis(pyridyl)diphenyl ether H2chdc =1,4-cyclohexanedicarboxylic acid ) has been successfully synthesized and characterized. In this complex, the chdc2- adopts tran- configuration, was linked by three types of Cd ions to form wave-like 2D layer with hexagonal grids. The 2D layers are linked by meso-helical chains Cdn(BPDPE)n to form a 3D framework. It is surprised find that complex 1 can highly sensitive sense 2, 4, 6-trinitrophenol (TNP) through luminescence quenching effect, the quenching constant is up to 2.794×105 M-1. In addition, complex 1 also presents highly sensitive fluorescent sensor for detecting Fe3+ and Ag+ ions. The quenching constants are 2.893×104 M-1 and

1.483×104 M-1. Furthermore, the quenching mechanisms of complex 1 as multifunctional sensor have been studied. Key words: Metal-organic frameworks; 2, 4, 6-Trinitrophenol; Metal ions; Fluorescence sensing 1. Introduction Nowadays, how to rapidly detect hazardous organic and heavy metal ions has been an important challenge for environmental protection [1-3], homeland security [4-6] and human health [7-9]. Nitro aromatic explosives have a widely applications in chemical

industry

[10,11],

2,4,6-trinitrophenol

2,4,6-trinitrotoluene

(TNT),

2,6-dinitrotoluene

(TNP),

nitrobenzene

(2,6-DNT),

(NB),

2,4-dinitrotoluene

(2,4-DNT), 2-nitrotoluene (2-NT), 3-nitrotoluene (3-NT) and 4-nitrotoluene (4-NT) are the most widely used explosives in industrial production, all of which do harm to the environment and social safety [12]. TNP have got a lot of attentions due to its high power and really danger. However, some current commercial detecting techniques, such as nuclear magnetic resonance (NMR) [13], atomic absorption spectrometry (AAS) [14], mass spectrometry (MS) [15], are difficult to meet the needs of the real-time detection because of the complication and time-consuming. Therefore, it is a challenging research issue to explore new methods for rapidly and selectively detecting nitro aromatic explosives and heavy-metal ions easily and real-time. Among various metal ions, Fe3+ ion is an important metal ion in living organisms, which plays a critical role in delivering and exchanging oxygen in the blood. It is also an important component of hemoglobin and many enzymes and an activator of the

redox enzyme. Both deficiency and excess of Fe3+ ions can induce various disorders such as liver disease, heart disease, cancer and Parkinson’s disease [16]. Thus, it is very important to detect Fe3+ for assessing human health. Currently, luminescent MOFs (LMOFs) have received some attentions as chemical sensors because of their high selectivity and sensitivity, quick response, and recoverability [17-19]. LMOFs with suitable luminescence intensity and emission area could be used as sensor to detect nitro aromatic explosives and metal ions, their donor abilities can be efficiently enhanced upon the excitation, which further increases the electrostatic interaction between LMOFs and analysts through the exciting migration [20-23]. But part of LMOFs can not keep their framework stable in the water for long time, this limits the applications of MOF in luminescent sensing, so the MOFs were often used to detect nitro explosives and metal ions in organic solvents. Recently, we are interested our research in constructing LMOFs and exploring their applications on luminescent sensing. Combination of the environmental protection

and

our

research

work,

{[Cd2(BPDPE)2(chdc)2(H2O)2]ˑ4H2O}n

in

this

paper,

a

new

MOF

(BPDPE=4,4′-bis(pyridyl)diphenyl

ether,

H2chdc=1,4-cyclohexanedicarboxylic acid) was synthesized. The luminescence sensing properties for nitro aromatic explosives and metal ions are investigated systematically. The results show that {[Cd2(BPDPE)2(chdc)2(H2O)2]·4H2O}n has a good performance on detecting nitro aromatic explosive TNP and metal ions Fe3+ or Ag+ with high selectivity and sensitivity.

2. Experimental 2.1 Materials and physical methods 4,4′-bis(pyridyl)diphenyl ether (BPDPE) was synthesized similar to our previous reported procedure [24], the solvents, reagents and nitro explosives are commercially available without any further purification. Elemental analyses about C, H and N were performed on Perkin-Elmer 240C. FT-IR spectra were carried out with KBr pellets (500 mg KBr with 5 mg sample) in the 400-4000 cm-1 region. Powder X-ray diffraction (PXRD) date were recorded by using Bruker D8 Advance X-ray diffractometer with Cu-Kα radiation (I=1.5418 Å) where the X-ray tube was operated at 40 kV and 40 mA. The liquid photoluminescence measurement was recorded on a F-4600 fluorescence spectrophotometer. Solid luminescent spectra were recorded with a SHIMAZU VF-320 X-ray fluorescence spectrophotometer at room temperature. The as-synthesized sample was characterized by thermogravimetric analysis (TGA) on a Perkin Elmer thermogravimetric analyzer Pyris 1 TGA up to 1073K using a heating rate of 10 K min-1 under N2 atmosphere. 2.2 Synthesis of {[Cd2(BPDPE)2(chdc)2(H2O)2]·4H2O}n (1) Cd(NO3)2·4H2O (30.8 mg 0.1 mmol), 1,4-cyclohexanedicarboxylic acid (17 mg 0.1 mmol) and 4,4′-bis(pyridyl)diphenyl ether (BPDPE (32.4 mg 0.1 mmol)) were dissloved in DMF (1 ml) and H2O (2 ml) after ultrasound 20 min and then transferred into a 20.0 ml Teflon-lined stainless-steel reaction vessel, the reaction was heated at 100 ℃ for 48 h in a oven. After cooling to room temperature, colorless crystals are obtained. Yield = 53% (according to BPDPE). Anal. Calcd for C60H64O16N4Cd2: C,

54.50; H, 4.84; N, 4.24 %; Found: C, 54.44; H, 4.65; N, 4.25 %. IR(KBr, cm-1): 3378 (s), 3236 (s), 2462 (m), 1734 (s), 1680 (s), 1586 (vs), 1552 (vs), 1492 (vs), 1383 (vs), 1330 (vs), 1256 (vs), 1229 (vs), 1168 (s), 1073 (s), 1033 (s), 1006 (s), 879 (m), 824 (vs), 737 (m), 656 (m), 596 (s), 562 (m), 501(s) (Figure S1 in SI). 2.3 X-ray crystallography X-ray crystallographic data of 1 was collected at room temperature using epoxy-coated crystals mounted on glass fiber. All measurements were made on a Bruker Apex Smart CCD diffractometer with graphite-monochromated Mo–K radiation ( = 0.71073 Å). The structures of 1 are solved by direct method, and the non-hydrogen atoms are located from the trial structure and then refined anisotropically with SHELXTL using a full-matrix least-squares procedure based on F2 values [25], The hydrogen atom positions are fixed geometrically at calculated distances and allowed to ride on the parent atoms. The distributions of peaks in the channels are chemically featureless to refine using conventional discrete-atom models. To resolve these issues, the contributions of the electron density by the remaining water molecules are removed by the SQUEEZE routine in PLATON [26]. The relevant crystallographic data are presented in Table 1, the selected bond lengths and angles are given in Table S1. 2.4 Thermal analysis and XRD result To characterize the complex more fully in terms of thermal stability, the thermal behavior was studied by TGA (Figure S2 in SI). Complex 1 has a 8.7 % weight loss is observed from 100 to 300 °C, which belongs to the loss of the coordinated and lattice

water molecules, the network collapses at 360°C. The thermal behavior shows complex 1 has good stability. To confirm whether the crystal structure is truly representative of the bulk materials, PXRD experiment was carried out, the PXRD experimental and computer-simulated patterns show that the bulk synthesized materials have high purity (Figure S3 in SI). 2.5 Luminescence measurements 2 mg of fine powder of 1 was added to 2 mL different organic solvents (methanol, DMA, DMF, THF, trichloromethane, dichloromethane, acetonitrile, 1-propanol, NB), after ultrasonic treatment for one hour, the powder of 1 was well-dispersed into these solvents to form a stable turbid solution. In order to study the sensing abilities towards nitro aromatic explosives more details, fluorescence titration experiments were carried out. The powder of 1 was dispersed in DMF (1 mg/1 ml), and then gradual add 1 mM stock solutions of nitro aromatics, such as TNP, TNT, 2-NT, 3-NT, 4-NT, 2,4-DNT, 2,6-DNT, and NB. Similarly, to investigate the fluorescence sensing for different metal ions. 2 mg complex 1 was dispersed in 1 mM DMF of M(NO3)x (M= Ag+, Na+, Mn2+, Fe3+, Cd2+, Co2+, Ca2+, Li+, K+, Cr3+, Al3+, Cu2+, Mg2+, Pb2+, Ni2+, and Zn2+). All fluorescence dates were record at room temperature. 3. Result and discussion 3.1 Crystal structure description There are three types of coordination environments around the Cd(II) ions in the unit (Figure 1a). Cd1 and Cd3 have similar coordination environments and reside in

an octahedral coordination sphere, which are defined by two carboxylic oxygen atoms from two different chdc2- anions, two coordinated water oxygen atoms at the equatorial position, and two coordinated N atoms from BPDPE at the axial position. Cd2 is six-coordinated defined by four oxygen atoms from three different chdc2anions and two nitrogen atoms from two BPDPE ligands. The average bond lengths of Cd-O and Cd-N are 2.290(4) Å and 2.344(4) Å. In complex 1, each Cd(II) cation coordinates to BPDPE to form an infinitely meso-helical chain along b axis with the distances of neighboring Cd(II) are 19.018 and 19.057 Å (Figure 1b). Every two Cd2(II) ions were connected by carboxylates to generate binuclear Cd cluster. The chdc2- adopts tran- configuration, linked three types of Cd(II) ions to form wave-like 2D layer containing hexagonal grids with the size of ~22.520 × 21.864 Å (Figure 1c). The 2D layers are linked by meso-helical chains to form a 3D framework (Figure 1d). From the b axis, each hexagonal grid was occupied by four BPDPE. A better insight into the nature of this intricate framework is provided by topology analysis. The Cd1 and Cd3(II) centers can be regarded as 4-connected nodes with the chdc2- anions and BPDPE acting as linkers, the binuclear Cd cluster as 6-connect nodes. The whole structure is thus represented as a scu network topology (with the Schläfli symbol {416.612}{44.62}2) (Figure 1e).

(a)

(b)

(c)

(d)

(e)

Figure 1. (a) Coordination environment of the Cd(II) ion. The hydrogen atoms are omitted for clarity. Symmetry codes: #1 = 1-x, 2-y, 1-z; #2 = 4-x, 1-y, -z; #3 = 2+x,y,z; #4 = 2-x, 1-y, -z; #5 = 1-x, 3-y, 3-z; #6 = 2-x, 2-y, 2-z; #5 = -1+x, 1+y, 1+z; (b) A view of meso-helical chain composed by BPDPE and Cd(II) ions; (c) A view of the wavelike 2D sheet bychdc2- and Cd(II) ions along the b axis; (d) A view of 3D

framework along the b axis; (e) Schematic representation 3D framework with scu network topology. 3.2 Fluorescence properties of 1 As we all know, MOF contains d10 Cd(II) cation and conjugated ligands are potential fluorescent materials [27], to determine whether 1 can be serve as a fluorescent material, the soild-state luminescent property of 1 was studied at room temperature. As show in Figure 2, the maximum emission peak of 1 was observed at ~363nm (ex=310nm), displaying a small red shift compare with BPDPE (Δ=6 nm), so the emissions of 1 is mainly attributed to the ligand to ligand charge transfer of BPDPE.

BPDPE Complex 1

320

340

360

380

400

Wavelength (nm) Figure 2. Solid-state photoluminescence spectra of BPDPE and complex 1. 3.3 Nitro aromatic explosives sensing of complex 1

Intensity (a.u.)

250 200 150 100 50 0 2-NT

TNT

TNP

Figure 3. Fluorescence intensities of 1 in the DMF with the addition of nitro explosives (1 mM).

Intensity (a.u.)

3000

0 L 2 L 4L 6L 8 L 10 L 30 L 50 L 70 L 90 L 120 L 160 L

2000

1000

1 L 3L 5L 7L 9L 20 L 40 L 60L 80L 100L 140L 180L

0

350

400

450

500

550

Wavelength (nm) Figure 4. Luminescent quenching of 1 dispersed in DMF with gradual addition of 1 mM solution of TNP.

0.9

R2=0.996 Ksv=2.794×105 M-1

I /I-1 0

0.6

0.3

0.0 0

1

2

3

-6 Concentration (10 M) Figure 5. The S-V plot of TNP. The fluorescent intensities of complex 1 was investigated in different organic solvents. As shown in Figure S4, complex 1 display the stronger emissions intensities in THF, CH2Cl2 and CH3CN, exhibiting medium intensities in CHCl3, CH3OH, DMA, DMF and 1-propanol, while the luminescent intensity shows a complete quenching in NB. Inspired by these results, complex 1 could be acted as a potential luminescent material to detect nitro explosives. In order to study the sensing ability of complex 1 towards many nitro explosives, fluorescence titration experiments were carried out by gradual addition of 1 mM solutions of various nitro explosives. As shown in Figure 3 and Figure S5, NB, 2,6-NT, 4-DNT only partially affect the emission intensities; TNT, 3-NT, 2-NT, 2.4-DNT have medium affection for the emission intensities, while 1 shows a rapid and complete fluorescence quenching upon the gradual addition of TNP. In fact, these nitro explosives weaken the emission intensities of 1 with the following

order: TNP > TNT > 2-NT > 3-NT > 2,4-DNT > 4-NT > 2,6-DNT > NB. To further study the luminescent quenching efficiency, t

t rn−

lm r (S-V) was used to

calculate the quenching efficiency of 1 to TNP, the equation is I0/I = 1 +Ksv[Q] [28], where I0 is the fluorescence intensity when TNP concentration [Q]=0, I is the fluorescence intensity at different TNP concentration [Q], and Ksv is the quenching constant. The results reveal that fluorescence intensities was significantly decreased when TNP act as quencher, the quenching efficient was up to 90.71% when adding 180 μL 1 mM TNP (Figure 4), the S-V plots exists a good linear relationship between the luminescence intensities and the low concentration of TNP (0-2.991×10-6 mol/L), and correlation coefficient is up to 0.996. Whereas the S-V curve subsequently deviates from the linear relationship at higher concentrations. According to the S-V equation, the Ksv value is up to 2.794×105 M-1 (Figure 5 ). To best of my knowledge, the Ksv in this work is larger than most of LMOFs sensors (Table 2). To further study whether other nitro explosive can disturb the quenching selectivity of TNP, the luminescent intensities was investigated with the existence of other nitro explosives. The results show that when 1×10-3 M TNP acted as a quencher was gradient added into nitro explosive solutions of DMF, the fluorescence intensities also significantly decreased, even for TNT, the quenching effect is still pretty obvious (Figure S6-S12). As shown in Figure 6, with the addition of different nitro explosives, 2-NT, 3-NT, TNT shown a slight effect on the fluorescence intensity of complex 1; 2,4-DNT, 4-NT, NB and 2,6-DNT shown a negligible effect; while TNP displayed most excellent quenching effect. Which clearly demonstrates that of complex 1 is an excellent highly

selective sensor for detecting TNP .

10

6 4

I0 /I-1

8

2

Co

80 0 7 0 nc 6 0 en 5 0 tra 4 t

ion

(1 0 -

30

6 M

20

)

10

T 0 2-N NP T T 3-N NT 2, T 4-N 4-DN T T N 2,6 B -D NT

Figure 6. Stern-Volmer plot of I0/I-1 versus different nitro explosives concentration in DMF. Table 2. Quenching constants for TNP detection. #

Complexes

Ksv (M-1)

Ref.

1

[Cd(L6)(L7)]2·H2O

3.7 ×104

[29]

2

[Cd(L12)(L13)]n

2.68×104

[30]

3

[Cd(3-bpd)(N(CN)2)2]n

7.16×104

[31]

4

{[Cd(IPA)(L)]}n

1.35×104

[32]

5

[Tb(L11)(OH)]·(x solvent)

3.37×104

[33]

6

[Eu(L9)H2O]n

2.95×104

[34]

7

[Cd5(TCA)4(H2O)2]n

9.5×104

[35]

8

[Cd3(NTB)2(DMA)3]·2DMA

2.0×104

[36]

9

{[Cd3(SDB)3(TIB)](H2O)2(1,4-dioxane)(G)x}n

2.43×104

[37]

10 [Cd2(NDC)(PCA)2]n

3.42×104

[38]

11 [NH2(CH3)2][Zn4O(bpt)2(bdc-NH2)0.5]·5DMF

6.19×104

[39]

12 {[Cd(IPA)(L14)]}n

1.35×104

[40]

13 [{Cd(fdc)(bpee)1.5}·3(H2O)] n

6.64×104

[41]

14 [Cd2(Lws)(OH)]n

2.23×104

[42]

15 {[Cd1.5(TPO)(bipy)1.5]·3H2O}2n

2.28×105

[43]

16 {[Cd4(hbhdpy)2(bdc)3(DMA)2]·(H2O)4}n

2.5×104

[44]

{[Cd4(hbhdpy)2(bdc-NH2)3(DMA)2]·(H2O)4}n

4.8×104 2.794×105

17 {[Cd2(BPDPE)2(chdc)2(H2O)2]·4H2O}n

This work

Additionally, the recyclability of 1 in TNP was investigated, followed by washing with DMF for several times. The intensities of 1 have not significantly changed after being used for five times (Figure 7). At the same time, PXRD pattern of the original is completely consistent with the recovered samples with five times of quenching and recovery, showing the good recyclability and high stability of 1 (Figure S3 in SI).

Intensity (a.u.)

2500 2000 1500 1000 500 0

1

2

3

4

5

Number of Cycles Figure 7. The changes of emission intensities of 1 after four recycles in 1 mM TNP.

As we all known, resonance energy transfer (RET) and photo-induced electron transfer (PET) could be seen as two reasonable explanation for the sensing mechanism. From the electron transfer point of view, the lowest unoccupied molecular orbitals (LUMOs) of nitro explosives are lower than the condition band (CB) of MOFs (Table S2), especially TNP, because it has the lowest LUMOs among these nitro explosives [45-47]. The electronic will transfer from the valence band to the LUMOs of nitro explosives easily after a light excitation. Beside the energy-transfer mechanism could be a reason for emission quenching. The quenching efficiency could be effect by the spectral overlap between the absorption of nitro explosive and the emission spectrum of LMOFs, TNP reveals a relatively wide absorbance and the absorption region is from 300 to 500 nm when excited (Figure 8). which coincides with the emission spectrum of 1. Therefore, the stronger quenching effect can be achieved through the energy transfer process.

Absorbance

2,4-DNT 4-NT NB TNP TNT 2,6-DNT 2-NT 3-NT Complex 1

350

400

450

500

550

600

Wavelength (nm) Figure 8. UV-vis spectra of different nitro compound in DMF solution. 3.4 Detection of metal cations

To investigate the fluorescence sensing performances of complex 1 to metal cation, the fluorescence sensing experiments of 1 dispersed in 1×10-3 M DMF solutions of metal ions M(NO3)x (M= Ag+, Na+, Fe3+, Cd2+, Co2+, Mn2+, Ca2+，Li+, K+, Cr3+, Al3+, Cu2+, Mg2+, Pb2+, Ni2+, and Zn2+) were recorded under excitation of 310 nm. As shown in Figure S13, fluorescence intensities of different metal ions for complex 1 are distinct. Interestingly, the fluorescence intensities of complex 1 were almost completely quenching after the adding of Fe3+ or Ag+. To further understand the ability of 1 for detecting Fe3+ and Ag+, the relationship between the metal concentrations and the fluorescence intensities were investigated. As shown in Figure 9a, the luminescent intensities of 1 are gradually weaken when the amount of 5 mM Fe3+ ions was increased, the quenching efficiency is 91.42 % when the volume is up to 70 μL. As shown in Figure 9b, the Stern-Volmer plot for Fe3+ exhibits a good liner correlation at low concentrations (0-22.394×10-6 mol/L), and correlation coefficient is up to 0.992, the value of Ksv is estimated to be 2.983×104 M-1. To best of our knowledge, the Ksv in this work is larger than most of LMOFs sensors (Table 3). Similarly, with the amount of 5 mM Ag+ cation was added, the quenching effects rate is 90.18% when the volume is up to 240 μL (Figure 10a), the Stern-Volmer plot for Ag+ also exhibits a good liner correlation at low concentrations (0-22.394×10-6 mol/L), and correlation coefficient is up to 0.998, the Ksv can be calculated as 1.483×104 M-1 for Ag+ (Figure 10b). So complex 1 can be acted as a sensitive fluorescent sensor material for the quantitative detection of Fe3+ and Ag+ ions. To further study whether other metal ions can disturb the quenching selectivity

of Fe3+, the luminescent intensities was investigated with the existence of other metal ions, such as Cu2+ and Ca2+, which can weak the intensities of complex 1 partially. The results show that when 5×10-3 M Fe3+ acted as a quencher was gradient added into Cu2+ and Ca2+ solutions of DMF, the fluorescence intensities were also significantly decreased (Figure S14 and S15) Table 3. A comparison of MOF-based luminescent probes for the detection of Fe3+ ions. Ksv (M-1)

#

Fluorescent Material

Ref.

1

{[Tb4(OH)4(DSOA)2(H2O)8].(H2O)8}n

3.543×104

[48]

2

{(Me2NH2)[Tb(OBA)2]∙(Hatz)∙(H2O)1.5}n

3.4×104

[49]

3

[Zn2(TPOM)(NDC)2]·3.5H2O

1.9×104

[50]

4

[Tb(TBOT)(H2O)](H2O)4(DMF)(NMP)0.5

5.51 × 103

[51]

5

[Zr6O4(OH)4(C8H2O4S2)6]·DMF·18H2O

4.41×103

[52]

6

{[Tb(TATAB)(H2O)2]·NMP·H2O}n

3.6×103

[53]

7

[Zn2(L1)2(bpe)2(H2O)2]

2395

[54]

8

{[Cd(5-asba)(bimb)]}n

1.78×104

[55]

9

{[Eu2L1.5(H2O)2EtOH]∙DMF}n

2.9×103

[56]

10

{[Zn(oba)(L)0.5]·dma}n

9.3×103

[57]

11

{[Cd2(BPDPE)2(chdc)2(H2O)2]·4H2O}n

2.983×104

This work

Based on the above results, the possible quenching mechanisms of 1 for sensing metal ions might be the competition absorption of the excitation energy between the Fe3+, Ag+ and metal organic frameworks due to their weak interactions [58], as shown in Figure S16, the excitation spectrum of 1 and the UV−vis absorption spectrum of Fe3+ and Ag+ have a extensive spectral overlap, which can be served as a explanation.

Intensity (a.u.)

(a)3000 0 μL 2 μL 4 μL 6 μL 8 μL 10 μL 30 μL 50 μL 70 μL

2000

1000

1 μL 3 μL 5 μL 7 μL 9 μL 20 μL 40 μL 60 μL

0 350

400

450

500

550

600

Wavelength (nm)

(a)

2

R =0.992 4

-1

Ksv = 2.983  10 M

I /I-1 0

0.6

0.4

0.2

2

4

6

8

10 12 14 16 18 20 22 24

-6 Concentration (10 M)

Figure 9. (a) Change in emission intensity of 1 with incremental addition of Fe3+ (5 mmol); (b) The Stern−Volmer plot of I0/I-1 versus the Fe3+ concentrations in complex 1 solution;

Intensity (a.u.)

(a)3000 0 μL 2 μL 4 μL 6 μL 8 μL 10 μL 30 μL 50 μL 70 μL 90 μL 140 μL 240 μL

2000

1000

1 μL 3 μL 5 μL 7 μL 9 μL 20 μL 40 μL 60 μL 80 μL 100 μL 180 μL

0 350

400

450

500

Wavelength (nm)

550

600

(b) 2

R =0.998 0.3

4

-1

I /I-1 0

Ksv = 1.483  10 M

0.2

0.1

2

4

6

8

10 12 14 16 18 20 22

-6 Concentration (10 M) Figure 10. (a) The changes of emission intensities with incremental addition of Ag+ (5 mmol); (b) The Stern−Volmer plot of I0/I-1 versus the Ag+ concentrations. 4. Conclusion A new 3D Cd-LMOF was synthesized by hydrothermal reaction, PXRD and TGA indicate it has a good stability. It is noteworthy that complex 1 shows a highly sensitive and selective fluorescence quenching effects for TNP, Fe3+ and Ag+. The quenching mechanisms were studied as well and considered as energy transfer and electron transfer. Further more, complex 1 can be quickly regenerated by simple wash with DMF, exhibiting good recyclability for detecting TNP. These results prove that LMOFs with excellent performance can be rationally designed by importing applicable ligands and metal ions. Future study will be focused on the preparations of new highly selective and sensitive MOF sensors and further understanding of relationships between the structures and properties.

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Table 1. crystal date for Complex 1 Complex

1

Formula

C60H64O16N4Cd2

Formula weight

1321.92

Crystal system

Triclinic

Space group

P-1

a (Å)

10.6406(10)

b (Å)

14.6501(14)

c (Å)

19.6274(19)

α (deg)

106.570(1)

β (deg)

97.798(1)

γ (deg)

92.645(1)

Z

2

V (Å3)

2893.8(5)

Dcalcd(g cm-3)

1.434

(Mo Ka)(mm-1)

0.798

F(000)

1272

theta Min-max (deg)

1.9, 26.0

tot., uniq. data

15908, 11124

R(int)

0.069

observed data [I > 2σ(I)]

9248

R1,wR2 0.0391, 0.1047 ( I > 2σ(I)) S

1.01

min and max resdens (e·Å-3)

-0.86, 1.18

Graphical Abstract-pictogram

10

6 4

I0 /I-1

8

2

Co

80 0 7 0 nc 6 0 en 5 0 tra 4 t

ion

(1 0 -

30

6 M

20

)

10

T 0 2-N NP T T 3-N NT 2, T 4-N 4-DN T T N 2,6 B -D NT

Graphical Abstract-Synopsis

A new Cd(II)-MOFs were synthesized and structurally characterized. Complex 1 is promising bifunctional luminescent probe for highly selective and sensitive sensing TNP and Fe3+ ions through luminescence quenching effect. The quenching mechanisms were studied based on both experiments and calculation.