Fluorimetric detections of nitroaromatic explosives by polyaromatic imine conjugates

Accepted Manuscript Fluorimetric detections of nitroaromatic explosives by polyaromatic imine conjugates Muhammet Kose, Hilal Kırpık, Aysegul Kose PII:

S0022-2860(19)30255-8

DOI:

https://doi.org/10.1016/j.molstruc.2019.03.003

Reference:

MOLSTR 26272

To appear in:

Journal of Molecular Structure

Received Date: 10 December 2018 Revised Date:

8 February 2019

Accepted Date: 2 March 2019

Please cite this article as: M. Kose, H. Kırpık, A. Kose, Fluorimetric detections of nitroaromatic explosives by polyaromatic imine conjugates, Journal of Molecular Structure (2019), doi: https:// doi.org/10.1016/j.molstruc.2019.03.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Fluorimetric detections of nitroaromatic explosives by polyaromatic imine conjugates

1

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Muhammet Kose1*, Hilal Kırpık1, Aysegul Kose2

Chemistry Department, Kahramanmaras Sutcu Imam University, 46100, Kahramanmaras, Turkey 2

Bioengineering Department, Kahramanmaras Sutcu Imam University, 46100,

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Kahramanmaras, Turkey

Abstract

In this study, new hydrazide-imine conjugates (1-3) containing polyaromatic groups (pyrene, anthracene or phenanthrene) were prepared and used as fluorescent probes for the sensing of nitro-aromatic compounds. The compounds were structurally characterized by single crystal X-ray diffraction studies. X-ray analysis showed that the polyaromatic moieties

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of the compounds play an important role for the crystal packing of the structure. The compounds exhibit aggregation induced emissions (AIE) due to π-π stacking of poly aromatic groups of the compounds. This, in turn, effects the color coordinates (CIE) of the compounds. The fluorimetric sensing of nitrobenzene (NB), 4-nitrophenol (NP), 2,4-dinitrophenol (DNP)

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and 2,4,6-trinitrophenol (TNP) were studied by photoluminescence spectroscopy. Fluorimetric titrations showed that the nitro-aromatic compounds showed a quenching effect

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in the emission band of the probes due to the photoinduced electron transfer (PET) or fluorescence resonance energy transfer (FRET). The compounds showed better sensitivity towards nitrobenzene (NB) with low LOD values. Quenching constants for NB detections are 2.20 × 105 for (1), 5.49 × 105 for (2) and 7.86 × 105 for (3), respectively.

Keywords: Fluorimetric sensing; Nitro-aromatic; hydrazide-imine conjugates; polyaromatic moiety Corresponding author* e-mail address: [email protected] & [email protected] 1

ACCEPTED MANUSCRIPT 1.

Introduction Nitro-aromatic compounds (NACs) are most commonly used organic compounds in the

production of industrial products [1, 2]. However, the excessive usage of these compounds results several environment issues such as pollution of soil, rivers and spring water [3-5]. Due to its acidic nature and high solubility in water, 2,4,6-trinitrophenol (TNP), also known as

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picric acid, pollutes ground water as well as irrigation lands [6]. Picric acid can result in severe health problems [7]. Nitroaromatic compounds such as nitrobenzene (NB), 4nitrophenol (NP), 2,4-dinitrophenol (DNP),

2,4,6-trinitrophenol (TNP) and 2,4,6-

trinitrotoluene (TNT) are are organic compounds which have nitro groups (-NO2) and the

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main ingredient of explosives [8]. The weapon manufacture plants and unexploded mine fields are the main cause the environmental contamination of these compounds [9]. The nitroaromatic explosives are hazardous to human beings. Long term exposure to these compounds

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can lead to headache, nausea, vomiting, sweating, dizziness, liver damage and dermatitis; and they have negative impacts on central nervous and cardiovascular systems [10-12]. Due to the security, human health and environmental impacts, the rapid and selective sensing of nitro-aromatic explosives in the gas phase as well as in solution have received considerable attention [13-15]. In the field applications, sniffer dogs are usually used for the

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detection of nitroaromatic explosives [16]. Additionally, several instrumental methods such as liquid chromatography, mass spectrometry, fluorescence and Raman spectroscopy have been employed for the recognition of nitro-aromatic explosives [17-20]. Recently, an interesting semiconductor-based sensor was introduced as electronic nose for the detection of nitro-

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aromatics [21]. The instrumental techniques have several disadvantages such as a certain cost and not conveniently applied in real field applications. Fluorescent compounds have been applied as fluorimetric probes for the recognition of nitro-aromatic compounds in both solid and

solutions

[22-25].

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state

Due

to

their

several

advantages

such

as

high

selectivity/sensitivity, fast response, and easy preparation, tuneable fluorescent molecules show promising chemosensors properties [26-28]. Nitro-aromatic compounds are not inherently fluorescent, yet, these compounds quench the emission band of fluorescent materials via inter-molecular charge transfer mechanism. Several fluorophore molecules have been

designed

for

the

detection

of

nitro-aromatic

compounds.

These

include

monomers/oligomers/ polymers with highly delocalized π-electrons, quantum/carbon dots, coordination polymers [29-33]. Pyrene, anthracene and naphthalene appended polyaromatic compounds have also used fluorescent probes for the sensitive detection of nitro-aromatic compounds [34-36]. 2

ACCEPTED MANUSCRIPT In our group, we reported naphthalene group containing organic fluorescent molecules and metal organic frameworks for the selective detection of harmful nitro-aromatic compounds [37, 38]. In the current study, three new polyaromatic compounds were prepared for fluorimetric detections of nitro-aromatics. The new probes were characterized by the

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spectroscopic and analytical methods. Molecular structures of the new compounds were investigated by X-ray diffraction studies. Fluorimetric sensing properties of the compounds towards nitrobenzene (NB), 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP) and trinitrophenol (TNP) were studied. Experimental

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2.

2.1. General materials

and

solvents

(1-pyrene

carboxaldehyde,

9-anthracene

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Starting

carboxaldehyde, 9-phenanthrene carboxaldehyde and salicylic hydrazide) were purchased from Sigma Aldrich and used as received. FT-IR spectra were measured on a Perkin Elmer Spectrum 100 FT-IR. The electronic spectra were taken on a Perkin Elmer Lambda 45 spectrophotometer. The fluorescence spectra were obtained on a Perkin Elmer LS55

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luminescence spectrometer. 2.2. Synthesis of the probes (1-3)

A methanol solution (10 mL) of salicylic hydrazide (2 mmol, 0.304 g) was added to a refluxing solution of polyaromatic aldehydes [1-pyrene carboxaldehyde (2 mmol, 0.461 g), 9-

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anthracene carboxaldehyde (2 mmol, 0.412 g) or 9-phenanthrene carboxaldehyde (2 mmol, 0.412 g)] in methanol (20 mL). The clear reaction solution was refluxed for 4 h and cooled to

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room temperature. Upon cooling precipitates formed were filtered and dried under vacuum. (1): Color: Yellow, Yield: 87.24%. Elemental analysis: Calc. For C24H16N2O2 (M.W.:364.39): C, 79.11; H, 4.43; N, 7.69. Found: C, 78.93; H, 4.28; N, 7.32%. 1H NMR (DMSO-d6); 12.06 (s, 1H, NH), 11.90 (s, 1H, OH), 9.54 (s, 1H, CH=N), 8.89 (d, 1H, CHpyrene), 8.60 (d, 1H, CHpyrene), 8.38 (m, 4H, CHpyrene), 8.29 (q, 2H, CHpyrene), 8.15 (t, 1H, CHpyrene), 7.98 (d, 1H, CHphenyl), 7.52 (t, 1H, CHphenyl), 7.05 (m, 2H, CHphenyl). IR (ATR, cm1

): 3200, 3038, 1639, 1605, 1580, 1537, 1454, 1376, 1295, 1223, 1148, 1075, 925, 848, 754,

714, 608, 527. (2): Color: Yellow, Yield: 66.16%. Elemental analysis: Calc. For C22H16N2O2·H2O·CH3OH (M.W.:390.43): C, 70.75; H, 5.68; N, 7.17. Found: C, 70.41; H, 5.18; N, 6.82%. 1H NMR 3

ACCEPTED MANUSCRIPT (DMSO-d6); 12.18 (s, 1H, NH), 11.91 (s, 1H, OH), 9.70 (s, 1H, CH=N), 8.76 (m, 3H, CHanthracene), 8.20 (d, 2H, CHanthracene), 7.99 (d, 1H, CHanthracene), 7.66-7.53 (m, 4H, CHanthracenephenyl),

7.49 (t, 1H, CHphenyl), 7.02 (m, 2H, CHphenyl). IR (ATR, cm-1): 3228, 3025, 1634, 1591,

1543, 1488, 1441, 1306, 1226, 1077, 890, 753, 727, 612, 516. (3): Color: White, Yield: 79.26%. Elemental analysis: Calc. For C22H16N2O2 (M.W.:340.37):

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C, 77.63; H, 4.74; N, 8.23. Found: C, 77.19; H, 4.42; N, 7.95%. 1H NMR (DMSO-d6); 12.01(s, 1H, NH), 11.85 (s, 1H, OH), 9.14 (s, 1H, CH=N), 9.10 (m, 1H, CHphenanthrene), 8.97 (m, 1H, CHphenanthrene), 8.89 (d, 1H, CHphenanthrene), 8.30 (s, 1H, CHphenanthrene), 7.98 (d, 1H, CHphenanthrene), 7.80 (d, 1H, CHphenanthrene), 7.74 (m, 3H, CHphenanthrene), 7.70 (m, 1H, CHphenyl), IR (ATR, cm-1): 3203, 3064, 1635, 1606,

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7.50 (t, 1H, CHphenyl), 7.02 (m, 2H, CHphenyl).

1519, 1492, 1394, 1348, 1306, 1246, 1215, 1142, 943, 908, 751, 725, 625, 557.

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2.3. X-ray structure solution and refinement

X-ray diffraction data for compounds (1-3) were collected at 293(2) K) on a Bruker D8 QUEST diffractometer using Mo-Kα radiation (λ= 0.71073 Å). Data reduction was performed using Bruker SAINT [39]. SHELXS97 was used to solve and SHELXL2014/6 to refine the structures [40]. The structure of the compounds (1-3) were solved by direct methods

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and refined on F2 using all the reflections. All the non-hydrogen atoms were refined using anisotropic atomic displacement parameters. The hydrogen atoms belong to carbon and oxygen atoms were located at calculated positions using a riding model. The crystallographic data for the compounds are listed in Table 1. Bond distances, angles and hydrogen bond

Results and discussion

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parameters are given in the supplementary file.

3.1. Chemistry

In this work, three new polyaromatic groups containing fluorophores were

synthesized and characterized by 1H-NMR, FT-IR spectra and elemental analysis. Molecular structures of the compounds were determined by X-ray diffraction studies. The Schiff base condensation reaction of polyaromatic carboxaldehydes (1-pyrene carboxaldehyde, 9anthracene carboxaldehyde or 9-phenanthrene carboxaldehyde) and salicylic hydrazide gave the compounds (1-3) and proposed structures were shown in Fig. 1. The new π-extended polyaromatic compounds are soluble in MeOH, DMF and DMSO, partially soluble in chloroform and ethanol and not soluble in diethyl ether and water. The FT-IR spectra of the 4

ACCEPTED MANUSCRIPT receptor compounds were measured, and the data are listed in the experimental section. In the spectra of the compounds, the characteristic carbonyl group ν(C=O) stretching was observed at 1639-1634 cm-1 range. The compounds showed a sharp peak due to the imine bond stretching’s ν(C=N) at around 1606-1591 cm-1, confirming the proposed structures. 3.2. X-ray structures of (1-3)

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Single crystals of the compounds for the X-ray diffraction experiments were grown from slow evaporation of methanol solution of the compounds. Single crystal X-ray diffraction data indicate that compound (1) has been crystallized in Orthorhombic unit cell with Pca21 space group. Molecular structure of (1) is shown in Fig. 2. The molecule

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comprises pyrene and phenol moieties linked by imine-hydrazide unit. The imine (C8=N2) and carbonyl group (C7=O2) bond distances are 1.269(6) and 1.236(5) Å, respectively and

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within the expected double distances. The pyrene and phenolic hydrazide unit are translocated with respect to the imine bond (C8=N2). In the molecular unit, the pyrene and phenol moieties are not in the same plane making a dihedral angle of 35.721(15)°. In the structure, there is an intramolecular hydrogen bond between hydrazide group nitrogen (NH) and phenolic oxygen atom (NH····OPh). The phenolic group involves in a bifurcated intermolecular hydrogen bonding (as donor) with imine nitrogen and carbonyl group oxygen

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atoms forming a hydrogen bond chain along the b axis. The hydrogen bonded chains are further connected by π-π stacking interactions between the pyrene units. One edge of the pyrene moiety (C11/C16) stacks with another edge of the pyrene unit of an adjacent molecule and these contacts are further extended with their respective plane to form 3D supramolecular

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network. The π-π stacking interactions are shown in Fig. 3. The structure of compound (2) was solved in Monoclinic unit cell and P21/c space

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group. The asymmetric unit contains one (2) molecule, one methanol and one water solvates. The molecule comprises an anthracene and a phenol moiety linked by imine-hydrazide group. Interestingly, the anthracene and phenolic hydrazide group are in cis-configuration with respect to the imine bond (C8=N2). The cis-configuration the compound may be due the steric hindrance of anthracene hydrogen atoms and/or intermolecular interactions within the crystal structure. In the structure, there is a intramolecular hydrogen bond between the hydrazide group nitrogen (NH) and phenolic oxygen atom (NH····OPh). Molecules of (2) involves in hydrogen bonding interactions with methanol and water solvates. Each water molecule bridges two (2) molecules via hydrogen bonds (as donor) with the hydrazide group carbonyl group (C=O) and imine nitrogen (CH=N). The methanol solvate makes two 5

ACCEPTED MANUSCRIPT hydrogen bonds (as donor with water molecule and as acceptor with phenolic group). The hydrogen bond contacts form 2D hydrogen bonded network. Molecules are further linked by face to face π-π stacking interactions between the anthracene units with the centroid-centroid distance of 3.837 Å. Compound (3) was found to crystallize in Orthorhombic unit cell with Pbca space

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group. The molecule contains a phenanthrene and phenolic hydrazide group linked by an imine bond. The phenanthrene and phenolic hydrazide group are in trans arrangement with respect to the imine bond (C=N). The phenanthrene and phenol units are not in the same plane with the dihedral angle of 68.14(6)°. The molecules form a 1D hydrogen bond network along

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the b axis via PhOH····O=C and PhOH····N hydrogen bonds. Molecules also show an intramolecular hydrogen bonding between hydrazide group and the phenolic group

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(NH····OPh). Molecules are further linked by π-π stacking interactions between the phenanthrene units forming a 3D supramolecular structure. 3.3. Absorption and photoluminescence studies

Absorption spectra of the compounds (1-3) were studied in both DMF solution and solid state. The UV-vis spectra of the compounds in MeOH and DMF solvents (10-5 M) are presented in Fig. 4 and absorption maximums are listed in Table 2. In MeOH, a broad

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absorption band was observed at 350 nm (λmax). This band is assigned to the π→π* transition. In DMF which is more polar solvent than MeOH, the absorption band of the compound showed a red shift (λmax = 365 nm) with a shoulder band. The bands may be due to

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overlapping π→π* transition of the pyrene unit. The compound also exhibits a weak absorption band in the range of 420-450 nm due to the n→π* transitions of hydrazide-imine functionalized pyrene unit. In the solid state, the absorption band due to the π→π* transition

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showed a blue shift compared to the DMF and MeOH solutions. In the absorption spectra, two broad bands at 288 and 338 nm (λmax) are assigned to the π→π* transition of pyrene and phenyl units. The band at 416 nm (λmax) is due to the n→π* transition. In MeOH, the compound (2) shows two absorption bands at 305 and 375 nm (λmax). These absorption bands were assigned to the π→π* transition of anthracene unit with vibrational characteristics. In DMF, the compound showed very similar absorption bands except a new weak band at 430 nm (λmax). The new band may be due to the the existence of keto-enamine tautomer in DMF solution [41]. In the solid state, compound (2) shows similar absorption spectra to the spectrum in DMF solution, yet, the absorption bands shifted to lower wavelengths (blue shift).

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ACCEPTED MANUSCRIPT Compound (3) showed a strong absorption band (λmax = 335) in MeOH due to π→π* electronic transitions of phenanthrene moieties. The π→π* absorption band slightly red shifted (λmax = 440 nm) in DMF. Moreover, a new weaker band was observed at 400 nm (λmax) due to the presence of the keto-enamine tautomer in DMF solution [41]. The photoluminescence emission spectra of the compounds were investigated at 25 °C

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in MeOH, DMF solutions and solid state. Emission spectra of the compounds (1-3) are shown in Fig. 5. The maximum excitation and emission wavelengths (nm) are given Table 1. In DMF, compound (1) shows a strong emission band with a shoulder peak in the range of 370550 nm upon excitation at 339 nm. The imine compounds generally show weak or no

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fluorescence. However, the introduction of highly conjugated polyaromatic units to the imine compounds may cause aggregation induced emissions (AIE) due to π-π stacking of poly aromatic groups of the compounds in solutions [42, 43]. In MeOH, the emission band of the

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compound was observed at higher wavelength resulting in higher Stokes shift (100 nm). In the solid state, while the excitation band shifted to lower wavelength, the emission band was observed at the higher wavelength compared to the emission band in DMF or MeOH resulting in a higher stokes shift (176 nm). The large Stokes shift in the solid state may be due to greater intermolecular interactions in solid state. In DMF solution, compounds 2 and 3 exhibit

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a large emission band with shoulder bands upon excited at 320 and 308 nm, respectively. The shoulder bands in the emission spectra of 2 and 3 may be due to the vibrational progression of the main emission bands. However, the emission bands of 2 and 3 are much narrower when MeOH was used as solvent (Fig. 5). Additionally, emission bands in MeOH much stronger

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than in DMF. In the solid state, compounds (2&3) shows higher stokes shift values compared to the values in DMF solution. The larger Stokes shifts in solid state may be due to the charge

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transfer in the crystal packing of the compounds. The colors of the new polyaromatic group containing compounds (1-3) in solid state were obtained via the Commission Internationale de L'Eclairage (CIE) coordinates using emission spectra [44]. The 1931 CIE chromatic color coordinates of the compounds are given in Fig. 6 & Table 2. The CIE coordinates (x, y) for compound 1 (λexc. = 309 nm) were 0.1390 and 0.3490 showing a greenish-blue color (cyan). The anthracene polyaromatic group containing compound (2) emits a yellow-green light upon exciting at 315 nm with color coordinates of 0.2527 for x and 0.5860 for y. When compound 3 is excited at 345 nm, it emits a lavender blue light with color coordinates (x, y) of 0.1662 and 0.1744, respectively. The similar compounds with different polyaromatic groups showed different light emitting and 7

ACCEPTED MANUSCRIPT this suggest that the π-electron delocalization is an important factor for light emitting. These materials have potentials in light emitting diodes (LED). 3.4. Fluorimetric detection of nitroaromatic compounds The nitro-aromatic compounds contain the electron-withdrawing nitro moieties which

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have empty π* orbital with low energy. The nitro groups are keen to accept electrons from highly π-electron localized luminescent materials [14, 45]. Therefore, the emission band of the luminescent materials can be quenched by nitro-aromatic compounds via photoinduced electron transfer (PET) or fluorescence resonance energy transfer (FRET) [45]. This

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observation has led to design chemical probes for the fluorimetric detections of nitraromatic compounds. The fluorescent probes can interact with nitro-aromatic compounds via strong hydrogen bond interactions or π-π interactions.

Number luminescent systems such as

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quantum dots, lanthanide-doped compound, fluorescent dye-based materials, metal-organic frameworks (MOF), π-electron rich monomers/polymers have been employed for the selective sensing of nitroaromatic compound [46-50]. There are still some drawbacks (such as cost, ease of synthesis, re-usability, toxicity and biodegradability) of fluorescent systems for the detection of nitro-aromatic compounds. In our group, we have designed pamoic acid-

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based monomers and Bi(III) based metal-organic coordination polymer and used as fluorescent probes for the detection of nitro-aromatic compounds in solution media [37, 38]. In continuation of our work for design and fluorimetric sensing of nitro-aromatic compounds, three π-electron rich hydrazide-imine compounds (1-3) were prepared.

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Compound (1) shows two emission bands in the range of 370-500 nm in DMF (λExc = 339 nm). Nitro-aromatic compounds [nitrobenzene (NB), 4-nitrophenol (NP), 2,4-

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dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP)] were gradually added to the DMF solution of (1) [concentration (1) kept constant] and the emission bands of (1) were monitored by photoluminescence spectroscopy (Fig. 7). When 10 µM nitro-aromatic compounds (NB, NP and DNP) were added to a DMF solution of (1), the emission band was quenched by 58%, 8% and 9%, respectively. 10 µM addition of TNP did not cause a quenching in the emission band of (1). However, further addition of TNP shows a quenching effect. The gradual addition of NB, NP, DNP and TNP decreased the emission intensity. 100 µM NB addition almost 100% quenched the emission band (turn off) while NP, DNP and TNP caused approximately 37%, 93% and 31% quenching. The quenching effect of NB and DNP are higher that NP and TNP. This may be better interaction of those nitro-aromatic compounds with the probe (1). 8

ACCEPTED MANUSCRIPT The nitro-aromatic compounds can interact with the probes (1-3) via hydrogen bonding (NH····O2N- or OH····O2N-) and π-π interactions between the electron deficient nitroaromatics and π-electron rich polyaromatic rings (pyrene, anthracene or phenanthrene). Those intermolecular interactions can allow the photoinduced electron transfer (PET) or fluorescence resonance energy transfer (FRET) which can result in quenching in the emission

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band. Compound (2) emits light at 350-550 nm range when excited at 320 nm. The emission band of the probe (2) shifted higher wavelength values (red shift) upon addition nitroaromatic compounds. The red shift may be due to the charge transfer during the excited state.

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10 µM addition of NB, NP, DNP and TNP, the emission band of (2) was quenched by 80%, 13%, 34% and 24%, respectively. As shown in compound (1), NB showed better quenching effect for compound (2). The 100 µM addition of NB almost 100% quenched the emission

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band while DNP caused approximately 80% quenching effect. The incremental addition of NB, NP, DNP and TNP caused a red shift in the emission band of compound (3). The first addition of NB (10 µM) caused a dramatic quenching (by 90%) and 60 µM addition almost turn the emission off. The NP, DNP and TNP also show quenching effect but with lower values. 100 µM addition of NP, DNP and TNP decreased the emission intensity of the probe

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(3) with the quenching effect of 81%, 50% and 69%, respectively. The quenching efficiencies of nitro-aromatics (100 µM) are summarized in Fig. 8. Nitrobenzene (NB) showed better quenching values than the other nitroaromatic compounds used. DNP also exhibited

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considerable quenching effect for compound (1) and (3). The efficiency of chemosensing properties of probes (1-3) were compared using the

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quenching efficiency which is obtained by using the Stern-Volmer (SV) equation [51], I0/I = 1 + Ksv[A]

Where I0: fluorescence intensity with no nitro-aromatic compounds, I: fluorescence intensity after addition of nitro-aromatic compounds, [A]: concentration of nitro-aromatic compounds, and Ksv: Quenching constant (M−1). The quenching constant (Ksv) is a common tool to evaluate and compare the efficiency of a florescent probes. Ksv can be accurately obtained once linear graph is obtained the I0/I vs [A] plot. Ksv graphs for probe (1) for NB, NP, DNP and TNP is shown in Fig. 9. The quenching constant (Ksv) calculated for the new fluorimetric probes (1-3) against NB, NP, DNP and TNP are listed in Table 3. 9

ACCEPTED MANUSCRIPT The quenching constant order for the detections of NB, NP, DNP and TNP is NB > DNP TNP > NP for probe (1), NB > TNP > NP > DNP for probe (2) and NB > NP > DNP > TNP for probe (3). All three probes were found to have the highest sensitivity for NB with higher Ksv (M-1) values which are lower than our previous reported probes (Pam-Et and Bi(III) complex) [37, 38]. Compound (2) exhibited good sensitivity for NP with Ksv value of

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3.96 × 104 M-1. For TNP, compounds showed comparable quenching constant values to Zr(IV) complex and yet lower than pyrene-thiourea compound and Bi(III) complex [36-38, 52]. The detection limit (LOD) for the flurorimetric detections of nitro-aromatic compounds was obtained by using the following equation:

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LOD = 3σ /k (σ: standard, k: slope)

The LOD values are listed in the supplementary file. The compound (3) exhibited the

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lowest LOD value for NB with 0.013 µM. The lower LOD and high quenching constant value for NB showed the high sensitivity of the probes (1-3) for the fluorescent sensing of NB in DMF solution. 4.

Conclusions

Three new hydrazide-imine conjugates (1-3) having polyaromatic groups (pyrene,

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anthracene or phenanthrene) were prepared and their structures were determined by X-ray diffraction studies. The compounds were used as a fluorimetric probes for the sensing of nitroaromatic compounds [nitrobenzene (NB), 4-nitrophenol (NP), 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP). The quenching efficiency of nitrobenzene (NB) were found to

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be higher than the other nitro-aromatics used. The compound (3) exhibited the lowest LOD

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value for NB with 0.013 µM.

Acknowledgments

We are grateful to The Research Unit of Kahramanmaras Sutcu Imam University for the financial support for this work. The authors also acknowledge to Scientific and Technological Research Application and Research Center, Sino University, Turkey, for the use of the Bruker D8 QUEST diffractometer. Supplementary Information CCDC 1848538-1848540 contain the supplementary crystallographic data for compounds (3-1), respectively. The data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, by e−mailing [email protected], or by 10

ACCEPTED MANUSCRIPT contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK. Fax: +44(0)1223−336033. References A. Esteve-Nunez, A. Caballero, J. L. Ramos, Biological Degradation of 2,4,6Trinitrotoluene, Microbio. & Mol. Bio. Rev. 65(3) (2001) 335–352.

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ACCEPTED MANUSCRIPT explosives, TrAC - Trends Anal. Chem. 65 (2015) 13–21. [15] E. V. Verbitskiy, A.A. Baranova, K.I. Lugovik, K.O. Khokhlov, E.M. Cheprakova, M.Z. Shafikov, G.L. Rusinov, O.N. Chupakhin, V.N. Charushin, New 4,5di(hetero)arylpyrimidines as sensing elements for detection of nitroaromatic explosives in vapor phase, Dye. Pigment. 137 (2017) 360–371.

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[23] T. Chattopadhyay, S. Chatterjee, I. Majumder, S. Ghosh, S. Yoon, E. Sim, Fluorometric detection of nitroaromatics by fluorescent lead complexes: A spectroscopic assessment of detection mechanism, Spectrochim. Acta - Part A Mol. Biomol. Spectrosc. 194 (2018) 222–229.

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[24] S. Maity, M. Shyamal, P. Mazumdar, G.P. Sahoo, R. Maity, G. Salgado-Morán, A. Misra, Solvatochromism and turn-off fluorescence sensing property of N,N′-bis(3pentyl)perylene-3, 4, 9, 10-bis(dicarboximide) towards nitroaromatics and photophysical study of its microstructures, J. Mol. Liq. 224 (2016) 255–264. [25] Q. Fu, Y. Zhang, B. Liu, F. Guo, and 1 , 2-diphenylethylenediamine moieties : Structure and its fl uorescence-based detection of nitroaromatics, J. Mol. Struct. 1171 (2018) 69–75. [26] T. Naddo, Y. Che, W. Zhang, K. Balakrishnan, X. Yang, M. Yen, J. Zhao, J.S. Moore, L. Zang, Detection of explosives with a fluorescent nanofibril film, J. Am. Chem. Soc. 129 (2007) 6978–6979. [27] A.K. Chaudhari, S.S. Nagarkar, B. Joarder, S.K. Ghosh, A Continuous π‑Stacked Starfish Array of Two-Dimensional Luminescent MOF for Detection of Nitro Explosives, Cryst. Growth Des. 13 (8) (2013) 3716-3721. 12

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[38] O. Gungor, M. Kose, Selective detections of nitroaromatic explosives by monomeric and polymeric Bi(III) complexes, Sensors Actuators, B Chem. 264 (2018) 363–371. [39] Bruker, APEX2 and SAINT, (1998) Bruker AXS Inc., Madison, Wisconsin, USA, [40] G.M. Sheldrick, A short history of SHELX, Acta Crystallogr. Sect. A Found. Crystallogr.,. 64 (2007) 112–122. [41] M. Odabasoglu, C. Albayrak, B. Kosar, O. Buyukgungor, Synthesis, spectroscopic characterizations and quantum chemical computational studies of (Z)-4-[(E)-ptolyldiazenyl]-6-[(2-hydroxyphenylamino)methylene]-2-methoxycyclohexa-2,4dienone, Spectrochim. Acta Part (A) 92 (2012) 357-364. [42] M. Shellaiah, Y. H. Wu, A. Singh, M.V.R. Raju, H.C. Lin, Novel pyreneand anthracene-based Schiff base derivatives as Cu2+and Fe3+ fluorescence turn-on sensors and for aggregation induced emissions, J. Mater. Chem. A, 1(4) (2013) 13101318. 13

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[51] S.S. Nagarkar, A. V. Desai, P. Samanta, S.K. Ghosh, Aqueous phase selective detection of 2,4,6-trinitrophenol using a fluorescent metal–organic framework with a pendant recognition site, Dalt. Trans. 44 (2015) 15175–15180.

14

ACCEPTED MANUSCRIPT H N N O

OH

H N N

OH

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O

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(1)

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(2)

H N

N

O

OH

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(3)

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Fig. 1 The structures of fluorescent probes (1-3).

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(1)

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(3)

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(2)

Fig. 2 Molecular structures of the compounds (1-3). Hydrogen bonds are shown as dashed lines.

(1)

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(3)

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(2)

Fig. 3 π-π stacking interactions in compounds (1-3).

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Fig. 4 UV-Vis spectra of the compounds (10-5 M).

Compound (1) -5 M) (10 ACCEPTED

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DMF

300 200

370

470 Wavelength (nm)

450

570

Compound (2) (10-5 M)

DMF 300

150

0 350 450 Wavelength (nm)

550

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250

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MeOH

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100 0

Intensity (a.u.)

365 nm

MeOH

SC

Intensity (a.u.)

400

Compound (3) (10-5 M)

200

EP

MeOH

100

0 280

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Intensity (a.u.)

DMF

380 480 Wavelength (nm)

580

Fig. 5 Emission spectra of the compounds in DMF solution and solid state.

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Fig. 6 The CIE 1931 chromaticity plot for compounds (1-3) in solid state.

ACCEPTED MANUSCRIPT K1(1) 10 µM NB

400

K1(1) 10 µM NP 20 µM NP 30 µM NP 40 µM NP 50 µM NP 60 µM NP 70 µM NP 80 µM NP

300

20 µM NB

50 µM NB 60 µM NB

200

70 µM NB 80 µM NB

200

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Intensity (a.u.)

Intensity (a.u.)

30 µM NB 40 µM NB

300

100

90 µM NB

100

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100 µM NB 0

370

0 370

420

470

520

470

K1 (1)

(1) K1

30 µM DNP

30 µM TNP

50 µM DNP 60 µM DNP 70 µM DNP

0 370

395

420

445

Wavelength (nm)

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100

470

495

80 µM DNP

Intensity (a.u.)

20 µM TNP

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Intensity (a.u.)

20 µM DNP 40 µM DNP

200

10 µM TNP

300

10 µM DNP

300

520

Wavelength (nm)

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Wavelength (nm)

420

40 µM TNP

200

50 µM TNP 60 µM TNP 100

70 µM TNP

90 µM DNP

80 µM TNP

100 µM DNP 0

520

545

370

420

470

Wavelength (nm)

Fig. 7 The emission spectra of (1) in DMF (10-5 M) upon addition of different nitroaromatic concentrations in DMF (λExc = 339 nm).

520

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100 90

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70 60 50 40

SC

% Quenching

80

30

10 0 (1) (2) (3)

NP 70.95 81.44 82.14

DNP 92.63 57.72 89.53

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TNP 72.92 39.84 69.98

NB 99.58 98.99 98.54

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Fig. 8 Fluorescence quenching of compounds (1-3) for detecting different nitro-aromatic compounds at room temperature (Condition:1 mL DMF (10-5 M) solution of compounds (1-3) and 1 mL analyte solvent (100 µM)).

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K1 (1)

4

KSV = 2.20x105 M-1 R² = 0.9919

KSV = 2.10x104 M-1 R² = 0.9889

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12.00

I0/I

I0/I

8.00 2

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4.00

0

0.00 20 NB (µM) K1 4.32x104

KSV = R² = 0.9817

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3.00 M-1

EP

I0/I

2.00

0.00 0

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1.00

20 DNP (µM)

0

40

40

20

40 NP (µM)

60

80

K1

4 KSV = 2.19x104 M-1 R² = 0.988 I0/I

0

2

0 0

20

40 60 TNP (µM)

80

100

Fig. 9 The Stern-Volmer plots of (1) with NB, NP, DNP and TNP. The solid lines were fitted to the concentration-resolved data using the SternVolmer equation.

ACCEPTED MANUSCRIPT Table 1 Crystallographic data for the compounds. (1)

(2)·H2O·CH3OH

(3)

Empirical formula Formula weight Crystal color Crystal system Space group

C24H16N2O2 364.39 Yellow Orthorhombic Pca21

C23H22N2O4 390.42 Yellow Monoclinic P21/c

C22H16N2O2 340.37 White Orthorhombic Pbca

Unit cell a (Å) b (Å) c (Å)

12.5349(16) 4.9539(6) 28.323(3) 90

9.6845(2)

90

11.3670(3) 12.5738(3) 24.3749(7) 90

90 90

100.025(3) 90

90 90

1758.8(4) 4

1992.62(9) 4

3483.82(16) 8

0.089 17855 99.9 % 3716 [0.0766] 0.0666, 0.1300 0.0919, 0.1383

0.090 25125 99.8% 4867 [0.0268] 0.0510, 0.1270 0.0771, 0.1434

0.084 44620 99.9 % 4415 [0.0727] 0.0648, 0.1488 0.1174, 0.1706

1848540

1848539

1848538

Volume (Å3) Z Abs. coeff. (mm-1) Refl. collected

R1, wR2 [I>2σ (I)] R1, wR2 (all data)

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CCDC number

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Completeness to θ= 25.242° Ind. Refl. [Rint]

SC

17.3584(4)

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α (°) β (°) γ (°)

12.0370(3)

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Identification code

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Table 2 The absorption and excitation/emission data for the compounds.

In MeOH

Solid state

365 305, 375, 430 340, 400

350 305, 375 335

288, 338, 416 305, 329, 365, 379, 420 293, 306, 377, 384

In DMF Ex. Em. 339 404, 429 320 434, 482 308 410, 492

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In DMF

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Photoluminescence

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(1) (2) (3)

UV-vis absorption

In MeOH Ex. Em. 350 450 339 426 330 422

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Compound

1931 color coordinates Solid state Ex. Em. 309 485 315 522 340 443

x 0.1390 0.2527 0.1662

y 0.3490 0.5860 0.1744

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Table 3 Ksv values for the detection of nitroaromatic compounds.

Compound

NB

NP

DNP

SC

KSV M-1 (R2)

TNP

Ref.

2.20 × 105 (0.9919)

2.10 × 104 (0.9889)

4.32 × 104 (0.9817)

2.19 × 104 (0.9880)

This work

(2)

5.49 × 105 (0.9838)

3.33 × 104 (0.9849)

1.61 × 104 (0.9970)

6.80 × 103 (0.9831)

This work

(3)

7.86 × 105 (0.9899)

3.96 × 104 (0.9865)

2.34 × 104 (0.9753)

2.33 × 104 (0.9805)

This work

-

-

1.03 × 107

5.20 × 103

Bi(III) complex

2.96 × 106

Zr(IV) complex

-

6

-

4 .0 × 10

[36]

6.20 × 104

-

[37]

3.22 × 105

4.16 × 105

1.87 × 106

[38]

-

-

5.80 × 104

[52]

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Pyrene linked Thiourea Pam-Et

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(1)

ACCEPTED MANUSCRIPT Highlights


New hydrazide-imine conjugates were prepared.
The compounds showed angregation induced emission (AIE).
The polyaromatic moieties changed the color coordinates (CIE).

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The compounds were used as fluorescent probes for the sensing of nitroaromatics.


The compounds showed better sensitivity towards nitrobenzene (NB) with low

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LOD values.