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A novel coumarin-pyrazole-triazine based fluorescence chemosensor for fluoride detection via deprotonation process: Experimental and theoretical studies
Accepted Manuscript A novel coumarin-pyrazole-triazine based fluorescence chemosensor for fluoride detection via deprotonation process: Experimental and theoretical studies Ergin Yalçın, Meltem Alkış, Nurgül Seferoğlu, Zeynel Seferoğlu PII:
S0022-2860(17)31530-2
DOI:
10.1016/j.molstruc.2017.11.042
Reference:
MOLSTR 24529
To appear in:
Journal of Molecular Structure
Received Date: 23 May 2017 Revised Date:
9 November 2017
Accepted Date: 10 November 2017
Please cite this article as: E. Yalçın, M. Alkış, Nurgü. Seferoğlu, Z. Seferoğlu, A novel coumarinpyrazole-triazine based fluorescence chemosensor for fluoride detection via deprotonation process: Experimental and theoretical studies, Journal of Molecular Structure (2017), doi: 10.1016/ j.molstruc.2017.11.042. 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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Graphical Abstract
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A novel coumarin-pyrazole-triazine based fluorescence chemosensor for fluoride detection via deprotonation process: Experimental and theoretical studies
a
Gazi University, Department of Chemistry, 06500 Ankara, Turkey
Gazi University, Advanced Technology Department, Inst. Sci. &Technol., Ankara, Turkey
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b
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Ergin Yalçına,*, Meltem Alkışa, Nurgül Seferoğlub and Zeynel Seferoğlua,*
Abstract
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A novel fluorescence coumarin-pyrazole-triazine based chemosensor (CPT) bearing 5hydroxypyrazole as a receptoric part was synthesized and characterized by using IR, 1H/13C NMR and HRMS for the purpose of recognition of anions in DMSO. The most stable tautomeric form of CPT was determined by experimental techniques and theoretical
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calculations. The selectivity and sensitivity of CPT towards anions (CN−, F−, Cl−, Br−, I−, AcO−, HSO4−, H2PO4− and ClO4−) were determined using spectrophotometric and 1H NMR titration techniques as the experimental approach, and the results were explained by
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employing theoretical calculations. It was found to be suitable for the selective detection of F− in the presence of CN− and AcO− as competing anions. In addition, CPT exhibits significant
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“light-up” effect after interaction with TFA in CH2Cl2. Keywords: Coumarin, pyrazole, triazine, fluorescence chemosensor, anion sensor, acid sensitive dyes, DFT.
*Corresponding authors Tel.: +90 312 2021525; fax: +90 312 2122279 *E-mail
addresses:
[email protected]
(E.Yalçın),
[email protected]
(Z.
Seferoğlu).
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1. Introduction
In natural environment and organisms include many important anion such as Fluoride,
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Chloride, Acetate etc. and they play critical role in environmental, biological, and chemical processes [1-33]. Therefore, especially in the last decade, sensing and recognition of anions, and any analyte such as amino acid, DNA, etc., have become a highly hot topic of interest to
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scientist who study on host/guest, supramolecular and organic chemistry
So far, there are many methods for anion detection and sensing techniques with colorimetric
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and fluorometric chemosensors by using spectrophotometer, spectrofluorimeter and NMR equipment. Chemosensors interact with anions via some mechanisms, including reaction based and strong hydrogen bonding interaction. The interactions between chemosensor and ligand via H-bonding, with NH or OH part of receptoric moiety, are widely used because they
[34-38].
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can be prepared easily with short reaction time, and have high sensitivity to specific anions
In our previous study [39], we combined three important heterocyclic rings for obtaining
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stable H-bonding fluorescent pyrazole moiety for selective detection of Fluoride anion. We obtained selectivity towards Fluoride at the stoichiometric ratio of 1:1 in this study. In our
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current study, we used triazine instead of pyridine to increase selectivity towards Fluoride and designed new fluorescent chemosensor for selective detection of Fluoride. We combined three biologically important heterocyclic compounds; (i) 7-diethylaminocoumarin, which is the signaling unit (fluorophore/chromophore); (ii) Pyrazole, which is bound to the coumarin ring at the 3-position as receptoric part; (iii) Triazine is important part for stabilisation of enol tautomer via H-bonding between pyrazole and triazine moieties.
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ACCEPTED MANUSCRIPT The fluorescence chemosensor (CPT) was synthesized using both conventional and Microwave Irradiation (MWI) methods, and its structure characterized using FT-IR, UV-vis, 1
H NMR, 13C NMR and HRMS techniques. The effect of solvents with different polarities on
the UV-vis absorption and emission spectra of CPT were investigated in detail. In addition,
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the anion recognition properties of CPT towards F− in the presence of CN−, Cl−, Br−, I−, AcO−, HSO4−, H2PO4− and ClO4− (their n-Bu4N+ salts, TBA) were studied experimentally by the UV-vis, fluorescence, 1H NMR spectroscopic methods and naked-eye detection. The kind
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of interaction between CPT and the anions was also investigated by the quantum mechanical
2. Experimental
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2.1. Materials and instrumentation
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calculations at the level of density functional theory (DFT and TD-DFT).
Reagents, anions and solvents used in all steps of the synthesis and measurements were procured from Sigma Aldrich USA, and used as commercial grade without further
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purification. Deuterated solvent (DMSO-d6) for NMR studies were obtained from Merck Germany. Melting points were determined using Electrothermal 9200 melting point
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apparatus. Nuclear magnetic resonance (1H/13C NMR/anion titrations) spectra were recorded on a Bruker Ultrashield 300 MHz NMR spectrometer. Mass spectra was recorded on a Waters LCT Premier XE (TOF MS) mass spectrometer. Ultraviolet-visible (UV-vis) absorption spectra were recorded on a Shimadzu UV-1800 UV-VIS Spectrophotometer. Fluorescence spectra were recorded on a HITACHI F-7000 FL Spectrofluorophotometer. Anions used for all measurements were obtained as tetrabutylammonium salts (F−, Cl−, Br−, I−, AcO−, CN−, H2PO4−, HSO4−, ClO4−) and their solvents were prepared in DMSO as analytical grade.
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ACCEPTED MANUSCRIPT Thermal analysis was performed with a Shimadzu DTG-60H system, up to 500 °C (10 °C min−1) under a dynamic nitrogen atmosphere (15 mL min−1). 2.2. Synthesis and characterization of CPT with conventional method
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3 (197 mg, 1 mmol) was added slowly, under N2 atmosphere, to a stirred solution of 1 (317 mg, 1 mmol) in toluene (20 mL). The mixture was left under reflux for 48 hours. After the period, the mixture was cooled to room temperature. The product obtained was filtered and
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the orange solid was washed with small amount of hot dioxane (5 mL) to obtain pure compound CPT. (Yield: 181 mg, 39 %, mp: 266-268 ⁰C). FT-IR ʋmax (cm-1), 3315 (O-H),
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2966 (C-H), 1713 (C=O), 1617 (C=C), 1592 (C=N). 1H-NMR (DMSO-d6, 300 MHz) δ (ppm): 13.40 (s, 1H), 8.40 (s, 1H), 7.65 (d, J = 8.9 Hz), 6.75 (dd, J=8.9, J=2.4 Hz, 1H), 6.60 (d, J= 2.7, 1H), 6.15 (s, 1H), 3.46 (q, J= 6.9, 4H), 3.20 ( s, 12H), 1.14 (t, J = 6.9 Hz).
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NMR (DMSO-d6, 75 MHz) δ (ppm): δ 163.5, 162.0, 160.7, 158.0, 156.7, 150.9, 149.3, 140.0,
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129.6, 112.4, 109.1, 108.7, 97.0, 89.1, 67.1, 44.9, 36.6, 36.6, 12.5. TOF-MS (m/z) (M-H)+ calculated for C23H29N8O3: 465.2363; found 465.2342.
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2.2.1. Synthesis of CPT using MWI
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A mixture of 3 (197 mg, 1 mmol), 1 (317 mg, 1 mmol), and 1 mL Acetic acid, was placed in a microwave tube, and then stirred for 4 min. at 270 W, 130 ºC. After the period, the tube was cooled, and water (20 mL) was added to the mixture and filtered. The obtained orange solid, in this manner, was suitable most synthetic purposes. An analytical sample was further purified by washing of CPT in a small amount of hot dioxane. Yield: 195 mg, 42%.
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2.2.2. UV-vis, fluorimetric, and 1H NMR titration measurements of CPT with all studied
2.2.2.1. UV-vis and fluorimetric titration experiments
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anions
A stock solution (10 mL, 1x10-3 M) of CPT and stock solutions (1 mL, 1x10-2 M) of
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tetrabutylammonium (TBA) salts of each of the anions were prepared in DMSO. For UV-vis titration, the final solution containing 20 µL of CPT and 1980 µL of DMSO was prepared and
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transferred into a glass cell to obtain a final concentration of 1x10-5 M of CPT. For fluorimetric titration, the stock solution of CPT was (10 mL, 1x10-5 M) and stock solutions of TBA salts were (1 mL, 1x10-4 M) and the final concentration was 1x10-7 M in DMSO in the same way. 2-40 mL of the salts of TBA solution (1x10-2 M) were transferred to the solution of
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each chemosensor (1x10-5 M) prepared above, into the glass cell. After mixing them for a few seconds, UV-vis absorption spectra were taken at room temperature (25 oC). TBA salts of F−, Cl−, Br−, I−, AcO−, CN−, H2PO4−, HSO4−, and ClO4− (1x10-2 M) were dissolved in DMSO (1
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mL). In all experiments, any changes in the UV-vis and emission spectra of CPT were recorded upon the addition of TBA salts while the ligand concentration was maintained at
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1x10-5 M (for UV-vis titration) and 1x10-7 M (for fluorimetric titration).
2.2.2.2. 1H NMR titration experiment
For 1H NMR titrations, two stock solutions were prepared in DMSO-d6, one containing the sensor (1x10-2 M) only, and the other containing an appropriate concentration of all studied
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Quantum yield of fluorescence for CPT was calculated with equation (a). Coumarin 153 in EtOH was used as reference to compare the obtained results. In this experiment, DMSO was used as a solvent for the calculation of fluorescence quantum yield of CPT with the
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arrangements of the device with slit width of 5 nm for both excitation and emission, and the
obtained using following equation; Φs = Φr
(a)
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PMT voltage was 700 V for computation. The quantum yield of fluorescence, Φs, was
From equation (a); s and r represent sample and reference, respectively, A is the abbreviation for excitation wavelength of absorbance, I is the height of emission intensity, and n is the
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index of refraction, change depends on current solvent for the sample and the reference. The quantum yield of Coumarin 153 was obtained as Φr= 0.38 in EtOH, nDMSO: 1.479 , nEtOH:
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1.362
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2.4. Computational Details
The calculations were carried out using Gaussian 09 software package [40].
In the
calculations, Becke’s three-parameter exact-exchange functional (B3), combined with the gradient-corrected correlation functional of Lee–Yang–Parr (LYP) of the density functional theory methods (B3LYP) [41-43] were used with 631+G(d,p) basis set. Vibrational frequency calculations were performed on all optimized structures to verify the structures at true minima.
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3.1. Synthesis and spectroscopic characterization of CPT
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3. Results and discussion
Compounds 1, 2, and 3 were synthesized using literature methods [44-46] and characterized
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by melting points (for 1 and 3), and 1H NMR, 13C NMR, and HRMS (for 4). The reaction of methyl 3-[7-(diethylamino)-2-oxo-2H-chromen-3-yl]-3-oxopropanoate (1) with 2-hydrazino-
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4,6-bis-(dimethylamino)-s-triazine (3) in the presence of toluene gave CPT (Scheme 1).
Scheme 1 is here
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CPT was characterized using 1H NMR, 13C NMR, and HRMS, and was found to be thermally stable up to 321 oC (Supplementary data, Figures S1-9). CPT was exclusively obtained as the enol tautomer (Scheme 2), as confirmed by; (a) a single clear absorption band in solvents
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of various polarity (Figure 1), and (b) 1H NMR chemical shift of the aromatic proton on the
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pyrazole ring at 6.20 ppm (in DMSO-d6) and absence of signal of pyrazolone methylene proton. This result is also confirmed by
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C-NMR data (Supplementary data, Figures S6
and S7) [39].
Scheme 1 is here Figure 1 is here
The absorption and emission spectra of CPT were studied in various solvents and the absorption and emission maxima were recorded in the ranges of 412-426 nm and 467-501 nm,
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Figure 1-3 are here
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3.2. Anion sensing properties of CPT by UV-vis and fluorimetric titrations
The anion-CPT interaction study was performed using UV-vis absorption spectroscopy in
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DMSO against F−, Cl−, Br−, I−, AcO−, CN−, H2PO4−, HSO4−, and ClO4− anions with tetrabutylammonium (TBA) as the counter cation (Figure 4).
The absorption maximum of CPT observed at 426 nm in DMSO and shifted hypsochromically upon addition of 20 equiv of F− to the solution of CPT and a new band was
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observed at λ=408 nm (Fig. 5). The observed hypsochromic shift can be from electrostatic interaction between CPT and F− that leads to the deprotonation of the acidic proton on pyrazole -OH function and extinguishes the –OH•••N H–bond. After deprotonation, a
was
obtained
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negative charge is created on the pyrazole ring and hereby the observed hypsochromic shift because
of
decreasing
intramolecular
charge
transfer
from
7-
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diethylaminocoumarin core to the pyrazole ring [24]. For competitive anions such as AcO− and CN−, similar results were observed. However, chemosensor CPT was more sensitive to F− as compared to its sensitivity towards both AcO− and CN− at the stoichiometric ratios of 1:1 and 1:20 (Figure 4 and Supplementary data, Figures S10 and S12). CPT displayed an emission maximum at 476 nm in DMSO with a high intensity that gradually decreased upon titration with F− (Figure 5). The light-off of the emission, presumably via breaking of the pyrazole O–H bond and hence –OH•••N H–bond, by F− is the targeted anion sensing action.
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Figure 4 and 5 are here
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albeit not as effective (Supplementary data, Figures S11 and S13).
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The determination of reversibility and reusability of a chemosenser is quite an important property, as well as its usability in practical application with real sample. Therefore, in our
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efforts on the identification of CPT, we investigated its reversibility and reusability. Systematic titration of CPT in the presence of F−, upon addition of increasing amounts of TFA (0−20 equiv) shifted the absorption band from 404 to 426 nm (Figure 6). The determination colour differences of anion-ligand interection can be determined by the
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naked eye or by using a portable UV lamp. In our study, we investigated interaction of CPT with studied anions and obtained distinctive colour and fluorescent change after anion-CPT interaction. The chemosensor CPT displayed a colour change from yellow to red upon
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addition of F−, whereas a yellow-to-light orange colour change was observed in the case of CN− and AcO− (Figure 7). The results showed that CPT can be used as a ‘‘naked-eye’’ probe
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for F− in DMSO. In addition to this, the emission quenching in CPT was observed only in the presence of F− in same solvent. No significant colour or emission changes were observed by the naked eye and under portable UV lamp upon the addition of the other anions.
Figures 6 and 7 are here
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Upon addition of 5 equiv of F−, the proton of the pyrazole ring, originally at 6.16 ppm, promptly shifted up-field to 4.97 ppm, suggesting an accumulation of negative charge surrounding the pyrazole proton (Figure 8). This response is due to deprotonation of CPT upon interaction of F− with the enolic -OH group. It is important that a new signal at 16.15
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ppm (JHF=121 Hz) after addition of 4 equiv of F− was observed and indicated the creation of
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bifluoride (FHF-) ion. Thus FHF- is generated through abstraction of the OH proton by F− that simultaneously broke the intramolecular OH•••N H–bond as well. AcO−, CN− and H2PO4− showed analogous, albeit less pronounced 1H NMR chemical shift changes at 5.12, 5.03 and 6.02 ppm, respectively, when compared to F− (Figure 9). This difference is presumably due to the lower basicity of AcO−, CN− and H2PO4−, compared to F−. It was not observed any
and ClO4−) (Figure 9).
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changing in spectrum for pyrazole proton regarding the rest of the anions (Cl−, Br−, I−, HSO4−,
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Figures 8 and 9 are here
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3.4. Acidochromic properties
The determination of pH change in any medium with fluorescent light-up probe has attracted considerable attention subject field in recently. In our synthesized molecule, the presence of many nitrogen atoms in coumarin-pyrazole-triazine hybrid compound prompted us to study the possibility of protonation of this compound in CH2Cl2. Therefore, the protonation effect on spectroscopic properties of CPT in CH2Cl2 solution was studied. Solution of CPT in CH2Cl2 (10 µM) added trifluoroacetic acid (TFA) shifted the absorption maximum from 419 10
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observed, while significant increase in the emission intensity was observed even by the naked-eye (Figure 10). Therefore, it may be used for the development of a light-up probe for
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Figures 10 is here
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determining pH differences in biological samples after determination of pKa value in water.
2.5 Computational Results
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2.5.1 The stability of possible tautomeric forms
The calculated relative energies corresponding to total energies of the three tautomeric forms of CPT are given in Table 1. The enol tautomer appears more stable than the two keto
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tautomers (keto A and keto B) with the energy difference of 3.43 kcal/mol and 3.20 kcal/mol
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in gas phase, and 3.31 kcal/mol and 0.78 kcal/mol for keto A and keto B forms, respectively. In the following calculations, to obtain an insight into the deprotonation of CPT, the enol form was used.
Table 1 is here
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The optimized structures of the enol form CPT, CPT-F− and CPT-CN− are shown in Figure 11. There is a formation of an intramolecular O-H…N hydrogen bond between OH and
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triazin, with O-H and H…N distances of 0.997 Å and 1.719 Å, respectively, in enol form of CPT (Table 2). It should be noted that the presence of the intramolecular O-H…N hydrogen bond resulted in the stability of the enol tautomer. CPT is planar with the dihedral C3-C2-C1-
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N29 = -177.65o between coumarin and pyrazole rings, and N29-N30-C33-N36 = -179.23o between pyrazole and triazin rings. After the molecule interacted with the anions F− and CN−,
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there were no significant changes in the geometry of the dihedrals with C3-C2-C1-N29 = 178.98o and N29-N30-C33-N36 = -179.23o for CN-, whereas the planarity was broken for F−, in which the geometry of coumarin and pyrazole rings did not change with the dihedral C3C2-C1-N29 = -174.31o, but the dihedral angle between the pyrazole and the triazin rings was
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found to be -159.24 o. These structural changes can be the reason for the hypsochromic shifts in the absorption spectra and the quenching of the emission spectra. TD-DFT calculations were performed on the ground state geometry structures CPT, CPT-F−
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and CPT-CN−, in DMSO, to get a further information about electronic transitions using the molecular orbitals. The obtained results are summarized in Table 3. The calculated
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hypsochromic shifts are 13 nm and 16 nm for the interaction with CN− and F−, respectively, consistent with experimental value of F− (18 nm). The calculated frontier orbitals are shown in Figure 12. For CPT, the main transition is from HOMO to LUMO and the electron density in the HOMO is localized on coumarin moiety with the contributions of pyrazole and Et2N moieties. After deprotonation with F−, and CN−, the electron density of the HOMO was distributed over only the pyrazole moiety while the LUMO was based on the coumarin moiety. Upon excitation of the CPT-F− and CPT-CN−, an electron would have been
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Figure 12 is here
4. Conclusions
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We reported a novel example of a coumarin-based tautomer stabilization, yielding an efficient chemosensor for anion detection, with remarkable sensitivity for fluoride at the stoichiometric
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ratio of 1:20. The results showed clear visible colorimetric changes, and emission quenching in CPT were observed in the presence of F− in polar aprotic DMSO. It has high fluorescent property in acidic environment, therefore CPT can detect pH visually by fluorescence change and can be used as a candidate for the development of light up probe in pH imaging in living
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cells. As a result, the chemosensor CPT was more sensitive towards F− and H+ than our
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previous published chemosensor [39] which bearing pyridine instead of triazine.
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Acknowledgements
We are grateful to The Scientific and Technological Research Council of TURKEY for providing financial support (Project Grant No: 113Z895) for this study.
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ACCEPTED MANUSCRIPT Supplementary material
Supplementary data (Copies of 1H NMR, 13C NMR, HRMS and absorption spectra on anionschemosensor interactions Figs. S1–S13) associated with this article can be found, in the
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online version, at…..
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[32] K.Tayade, S. K. Sahoo, A. Singh, N. Singh, P. Mahulikar, S.Attarde, A. Kuwar, Sensors and Actuators B: Chemical, 202 (2014) 1333-1337.
[33] D. Sharma, A. Moirangthem, S. M. Roy, A.S.K. Kumar, J. P. Nandre, U. D.Patil, A.
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Basu, S. K.Sahoo, Journal of Photochemistry and Photobiology B: Biology, 148 (2015) 37-
S.-H. Kim, S.-Y. Lee, S.-Y. Gwon, J.-S. Bae, Y.-A. Son, Journal of Photochemistry
R. Manivannan, A. Satheshkumar, E.-S. H. El-Mossalamy, L. M. Al-Harbi, S. A.
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[35]
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and Photobiology A: Chemistry 217 (1) (2011) 224-227.
Kosa, K. P. Elango, New Journal of Chem. 39 (5) (2015) 3936-3947. [36] 768.
S. H. Mashraqui, S. S. Ghorpade, S. Tripathi, S. Britto, Tet. Lett. 53 (7) (2012) 765-
[37] J. Shao, H. Lin, M. Yu, Z. Cai, H. Lin, Talanta. 75 (2) (2008) 551-555. [38] Y. Shiraishi, H. Maehara, T. Sugii, D. Wang, T. Hirai, Tet. Lett. 50 (29) (2009) 42934296.
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ACCEPTED MANUSCRIPT [39] M. Alkış, D. Pekyılmaz, E. Yalçın, B. Aydıner, Y. Dede, Z. Seferoğlu, Dyes Pigments 141 (2017) 493-500. [40] M. J. Frisch, G. W. T., H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P.
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Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers,
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K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
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Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, and D. J. Fox, 1988, 37, 785. Lee, C.; Yang, W.; Parr, R. G., Physical review B. 1988, 37 (2), 785.
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[41]
[42] Becke, A. D., The Journal of chemical physics. 1993, 98 (7), 5648-5652. [43] Stephens, P.; Devlin, F.; Chabalowski, C.; Frisch, M. J., The Journal of Physical
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Chemistry. 1994, 98 (45), 11623-11627.
Y. Zhou, J. F. Zhang, Yoon, J. Chemical Reviews. 114 (10) (2014) 5511-5571.
[45]
A. Baliani, G. J. Bueno, M. L. Stewart, V. Yardley, R. Brun, M. P. Barrett, I. H.
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[44]
Gilbert, Journal of Med Chem. 48 (17) (2005) 5570-5579. [46]
M.-Z. Zhao, Y.-W. Zhang, F. Yuan, Y. Deng, J.-X. Liu, Y.-L. Zhou, X.-X. Zhang,
Talanta. 144 (2015) 992-997. [47] B. Valeur, M. N. Berberan-Santos, Molecular fluorescence: principles and applications, John Wiley & Sons: 2012;
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CAPTIONS Tables Captions
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Table 1. The relative energies for enol, keto A and keto B tautomeric forms of CPT. Table 2. Hydrogen bond geometry (Å, o) for the enol tautomer of CPT.
Table 3. Calculated absorption wavelengths (λmax) for CPT, CPT-F- and CPT-CN- in
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DMSO. The oscillator strengths (f) and the contributions (c) are given in parentheses.
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Scheme Captions
Scheme 1. Synthetic pathway of CPT; i: EtOH, piperidine, reflux; ii: dimethylamine, acetone; iii: Hydrazine monohydrate (65 %), THF, reflux; iv: toluene, reflux.
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Figure Captions
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Scheme 2. Favoured tautomers and intramolecular H-bonds.
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Fig. 1. UV-vis spectra of CPT in various solvents. Fig. 2. Emission spectra of CPT in various solvents. Fig. 3. Normalized Emission spectra of CPT in various solvents. Fig. 4. UV-vis titration spectra of CPT (c= 2 µM) upon addition of 1 equiv of various anions in DMSO.
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of increasing amount of TFA (0−20 equiv) in DMSO, (1 equiv = 2 µM ).
Fig. 7. Photographs of CPT (c=1 mM in DMSO) upon addition of 1 equiv studied anions
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(c=10 mM in DMSO) under ambient light (top), under UV light (bottom, 365 nm).
Fig. 8. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with TBAF solution in DMSO-d6.
studied solution in DMSO-d6.
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Fig. 9. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with 4 equiv of TBA salts of anions
Fig. 10. UV–vis titration (left, 10 µM in CH2Cl2) and Fluorescence emission titration (λexc.=478 nm, right, 0.1 µM in CH2Cl2) spectrum of CPT upon the addition in the range of 1
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with 20 equiv of TFA. (1 equiv = 2 µM ).
Fig. 11. The optimized geometries of CPT, CPT-F- and CPT-CN-.
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Fig. 12. The frontier orbital of CPT, CPT-F- and CPT-CN-.
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ACCEPTED MANUSCRIPT Table 1. The relative energies for enol, keto A and keto B tautomeric forms of CPT. Gas
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E ∆E Enol -1556.582943 0.00 Keto A -1556.577474 3.43 Keto B -1556.577851 3.20
DMSO E ∆E -1556.608057 0.00 -1556.603412 2.91 -1556.606816 0.78
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Table 2. Hydrogen bond geometry (Å, o) for the enol tautomer of CPT. D-H. . .A D-H(Å) H. . .A(Å) D. . .A (Å) ∠D-H. . .A (o) O-H…N 0.997 1.719 2.61 145.9
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Table 3. Calculated absorption wavelengths (λmax) for CPT, CPT-F- and CPT-CN- in DMSO. The oscillator strengths (f) and the contributions (c) are given in parentheses. λmaxexp.(nm) 426 408 419
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CPT CPT-FCPT-CN-
λmax(nm), f 419 (0.9960) 403 (0.9060) 406 (0.9686)
Transition, c HOMO→LUMO (98.5%) HOMO→LUMO (93.4%) HOMO→LUMO (96.5%)
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Fig. 1. UV-vis spectra of CPT in various solvents.
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Fig. 2. Emission spectra of CPT in various solvents.
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Fig. 3. Normalized Emission spectra of CPT in various solvents.
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Fig. 4. UV-vis titration spectra of CPT (c= 2 µM) upon addition of 1 equiv of various anions in DMSO.
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Fig. 5. UV–vis titration (top) and Fluorescence emission titration (bottom) spectrum of CPT
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with TBAF in DMSO, (λexc.=426 nm, c=10 µM for UV–vis titration, c=0.1 µM for Fluorescence emission titration), (1 equiv = 2 µM ).
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Fig. 6. Absorption spectra of CPT (c= 10 µM) in the presence of F− (20 equiv) upon addition of increasing amount of TFA (0−20 equiv) in DMSO, (1 equiv = 2 µM ).
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Fig. 7. Photographs of CPT (c=1 mM in DMSO) upon addition of 1 equiv studied anions
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(c=10 mM in DMSO) under ambient light (top), under UV light (bottom, 365 nm).
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Fig. 8. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with TBAF solution in DMSO-d6.
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Fig. 9. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with 4 equiv of TBA salts of anions studied solution in DMSO-d6.
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Fig. 10. UV–vis titration (left, 10 µM in CH2Cl2) and Fluorescence emission titration (λexc.=478 nm, right, 0.1 µM in CH2Cl2) spectrum of CPT upon the addition in the range of 1
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with 20 equiv of TFA. (1 equiv = 2 µM ).
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CPT
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CPT-F-
CPT-CN-
Fig. 11. The optimized geometries of CPT, CPT-F- and CPT-CN-.
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HOMO
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CPT
LUMO
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CPT-F-
HOMO
LUMO
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CPT-CN-
HOMO
LUMO
Fig. 12. The frontier orbital of CPT, CPT-F- and CPT-CN-.
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Scheme 1. Synthetic pathway of CPT; i: EtOH, piperidine, reflux; ii: dimethylamine,
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acetone; iii: Hydrazine monohydrate (65 %), THF, reflux; iv: toluene, reflux.
Scheme 2. Favoured tautomers and intramolecular H-bonds.
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Highlights •
A novel fluorescence coumarin-pyrazole-pyridine triad (CPT) was synthesized and
•
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characterized for detection of anions. CPT has remarkable sensitivity for fluoride detection in DMSO at the stoichiometric ratio of 1:20. CPT exhibits acidochromic property.
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Significant “light-up” effect was observed after interaction with TFA in CH2Cl2.
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CPT can be used as promising candidate for the development of light up probe in
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acidic environment.
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S0022-2860(17)31530-2
DOI:
10.1016/j.molstruc.2017.11.042
Reference:
MOLSTR 24529
To appear in:
Journal of Molecular Structure
Received Date: 23 May 2017 Revised Date:
9 November 2017
Accepted Date: 10 November 2017
Please cite this article as: E. Yalçın, M. Alkış, Nurgü. Seferoğlu, Z. Seferoğlu, A novel coumarinpyrazole-triazine based fluorescence chemosensor for fluoride detection via deprotonation process: Experimental and theoretical studies, Journal of Molecular Structure (2017), doi: 10.1016/ j.molstruc.2017.11.042. 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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Graphical Abstract
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A novel coumarin-pyrazole-triazine based fluorescence chemosensor for fluoride detection via deprotonation process: Experimental and theoretical studies
a
Gazi University, Department of Chemistry, 06500 Ankara, Turkey
Gazi University, Advanced Technology Department, Inst. Sci. &Technol., Ankara, Turkey
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b
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Ergin Yalçına,*, Meltem Alkışa, Nurgül Seferoğlub and Zeynel Seferoğlua,*
Abstract
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A novel fluorescence coumarin-pyrazole-triazine based chemosensor (CPT) bearing 5hydroxypyrazole as a receptoric part was synthesized and characterized by using IR, 1H/13C NMR and HRMS for the purpose of recognition of anions in DMSO. The most stable tautomeric form of CPT was determined by experimental techniques and theoretical
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calculations. The selectivity and sensitivity of CPT towards anions (CN−, F−, Cl−, Br−, I−, AcO−, HSO4−, H2PO4− and ClO4−) were determined using spectrophotometric and 1H NMR titration techniques as the experimental approach, and the results were explained by
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employing theoretical calculations. It was found to be suitable for the selective detection of F− in the presence of CN− and AcO− as competing anions. In addition, CPT exhibits significant
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“light-up” effect after interaction with TFA in CH2Cl2. Keywords: Coumarin, pyrazole, triazine, fluorescence chemosensor, anion sensor, acid sensitive dyes, DFT.
*Corresponding authors Tel.: +90 312 2021525; fax: +90 312 2122279 *E-mail
addresses:
[email protected]
(E.Yalçın),
[email protected]
(Z.
Seferoğlu).
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1. Introduction
In natural environment and organisms include many important anion such as Fluoride,
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Chloride, Acetate etc. and they play critical role in environmental, biological, and chemical processes [1-33]. Therefore, especially in the last decade, sensing and recognition of anions, and any analyte such as amino acid, DNA, etc., have become a highly hot topic of interest to
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scientist who study on host/guest, supramolecular and organic chemistry
So far, there are many methods for anion detection and sensing techniques with colorimetric
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and fluorometric chemosensors by using spectrophotometer, spectrofluorimeter and NMR equipment. Chemosensors interact with anions via some mechanisms, including reaction based and strong hydrogen bonding interaction. The interactions between chemosensor and ligand via H-bonding, with NH or OH part of receptoric moiety, are widely used because they
[34-38].
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can be prepared easily with short reaction time, and have high sensitivity to specific anions
In our previous study [39], we combined three important heterocyclic rings for obtaining
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stable H-bonding fluorescent pyrazole moiety for selective detection of Fluoride anion. We obtained selectivity towards Fluoride at the stoichiometric ratio of 1:1 in this study. In our
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current study, we used triazine instead of pyridine to increase selectivity towards Fluoride and designed new fluorescent chemosensor for selective detection of Fluoride. We combined three biologically important heterocyclic compounds; (i) 7-diethylaminocoumarin, which is the signaling unit (fluorophore/chromophore); (ii) Pyrazole, which is bound to the coumarin ring at the 3-position as receptoric part; (iii) Triazine is important part for stabilisation of enol tautomer via H-bonding between pyrazole and triazine moieties.
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ACCEPTED MANUSCRIPT The fluorescence chemosensor (CPT) was synthesized using both conventional and Microwave Irradiation (MWI) methods, and its structure characterized using FT-IR, UV-vis, 1
H NMR, 13C NMR and HRMS techniques. The effect of solvents with different polarities on
the UV-vis absorption and emission spectra of CPT were investigated in detail. In addition,
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the anion recognition properties of CPT towards F− in the presence of CN−, Cl−, Br−, I−, AcO−, HSO4−, H2PO4− and ClO4− (their n-Bu4N+ salts, TBA) were studied experimentally by the UV-vis, fluorescence, 1H NMR spectroscopic methods and naked-eye detection. The kind
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of interaction between CPT and the anions was also investigated by the quantum mechanical
2. Experimental
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2.1. Materials and instrumentation
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calculations at the level of density functional theory (DFT and TD-DFT).
Reagents, anions and solvents used in all steps of the synthesis and measurements were procured from Sigma Aldrich USA, and used as commercial grade without further
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purification. Deuterated solvent (DMSO-d6) for NMR studies were obtained from Merck Germany. Melting points were determined using Electrothermal 9200 melting point
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apparatus. Nuclear magnetic resonance (1H/13C NMR/anion titrations) spectra were recorded on a Bruker Ultrashield 300 MHz NMR spectrometer. Mass spectra was recorded on a Waters LCT Premier XE (TOF MS) mass spectrometer. Ultraviolet-visible (UV-vis) absorption spectra were recorded on a Shimadzu UV-1800 UV-VIS Spectrophotometer. Fluorescence spectra were recorded on a HITACHI F-7000 FL Spectrofluorophotometer. Anions used for all measurements were obtained as tetrabutylammonium salts (F−, Cl−, Br−, I−, AcO−, CN−, H2PO4−, HSO4−, ClO4−) and their solvents were prepared in DMSO as analytical grade.
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3 (197 mg, 1 mmol) was added slowly, under N2 atmosphere, to a stirred solution of 1 (317 mg, 1 mmol) in toluene (20 mL). The mixture was left under reflux for 48 hours. After the period, the mixture was cooled to room temperature. The product obtained was filtered and
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the orange solid was washed with small amount of hot dioxane (5 mL) to obtain pure compound CPT. (Yield: 181 mg, 39 %, mp: 266-268 ⁰C). FT-IR ʋmax (cm-1), 3315 (O-H),
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2966 (C-H), 1713 (C=O), 1617 (C=C), 1592 (C=N). 1H-NMR (DMSO-d6, 300 MHz) δ (ppm): 13.40 (s, 1H), 8.40 (s, 1H), 7.65 (d, J = 8.9 Hz), 6.75 (dd, J=8.9, J=2.4 Hz, 1H), 6.60 (d, J= 2.7, 1H), 6.15 (s, 1H), 3.46 (q, J= 6.9, 4H), 3.20 ( s, 12H), 1.14 (t, J = 6.9 Hz).
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NMR (DMSO-d6, 75 MHz) δ (ppm): δ 163.5, 162.0, 160.7, 158.0, 156.7, 150.9, 149.3, 140.0,
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129.6, 112.4, 109.1, 108.7, 97.0, 89.1, 67.1, 44.9, 36.6, 36.6, 12.5. TOF-MS (m/z) (M-H)+ calculated for C23H29N8O3: 465.2363; found 465.2342.
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2.2.1. Synthesis of CPT using MWI
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A mixture of 3 (197 mg, 1 mmol), 1 (317 mg, 1 mmol), and 1 mL Acetic acid, was placed in a microwave tube, and then stirred for 4 min. at 270 W, 130 ºC. After the period, the tube was cooled, and water (20 mL) was added to the mixture and filtered. The obtained orange solid, in this manner, was suitable most synthetic purposes. An analytical sample was further purified by washing of CPT in a small amount of hot dioxane. Yield: 195 mg, 42%.
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2.2.2. UV-vis, fluorimetric, and 1H NMR titration measurements of CPT with all studied
2.2.2.1. UV-vis and fluorimetric titration experiments
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anions
A stock solution (10 mL, 1x10-3 M) of CPT and stock solutions (1 mL, 1x10-2 M) of
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tetrabutylammonium (TBA) salts of each of the anions were prepared in DMSO. For UV-vis titration, the final solution containing 20 µL of CPT and 1980 µL of DMSO was prepared and
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transferred into a glass cell to obtain a final concentration of 1x10-5 M of CPT. For fluorimetric titration, the stock solution of CPT was (10 mL, 1x10-5 M) and stock solutions of TBA salts were (1 mL, 1x10-4 M) and the final concentration was 1x10-7 M in DMSO in the same way. 2-40 mL of the salts of TBA solution (1x10-2 M) were transferred to the solution of
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each chemosensor (1x10-5 M) prepared above, into the glass cell. After mixing them for a few seconds, UV-vis absorption spectra were taken at room temperature (25 oC). TBA salts of F−, Cl−, Br−, I−, AcO−, CN−, H2PO4−, HSO4−, and ClO4− (1x10-2 M) were dissolved in DMSO (1
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mL). In all experiments, any changes in the UV-vis and emission spectra of CPT were recorded upon the addition of TBA salts while the ligand concentration was maintained at
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1x10-5 M (for UV-vis titration) and 1x10-7 M (for fluorimetric titration).
2.2.2.2. 1H NMR titration experiment
For 1H NMR titrations, two stock solutions were prepared in DMSO-d6, one containing the sensor (1x10-2 M) only, and the other containing an appropriate concentration of all studied
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Quantum yield of fluorescence for CPT was calculated with equation (a). Coumarin 153 in EtOH was used as reference to compare the obtained results. In this experiment, DMSO was used as a solvent for the calculation of fluorescence quantum yield of CPT with the
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arrangements of the device with slit width of 5 nm for both excitation and emission, and the
obtained using following equation; Φs = Φr
(a)
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PMT voltage was 700 V for computation. The quantum yield of fluorescence, Φs, was
From equation (a); s and r represent sample and reference, respectively, A is the abbreviation for excitation wavelength of absorbance, I is the height of emission intensity, and n is the
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index of refraction, change depends on current solvent for the sample and the reference. The quantum yield of Coumarin 153 was obtained as Φr= 0.38 in EtOH, nDMSO: 1.479 , nEtOH:
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2.4. Computational Details
The calculations were carried out using Gaussian 09 software package [40].
In the
calculations, Becke’s three-parameter exact-exchange functional (B3), combined with the gradient-corrected correlation functional of Lee–Yang–Parr (LYP) of the density functional theory methods (B3LYP) [41-43] were used with 631+G(d,p) basis set. Vibrational frequency calculations were performed on all optimized structures to verify the structures at true minima.
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3.1. Synthesis and spectroscopic characterization of CPT
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3. Results and discussion
Compounds 1, 2, and 3 were synthesized using literature methods [44-46] and characterized
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by melting points (for 1 and 3), and 1H NMR, 13C NMR, and HRMS (for 4). The reaction of methyl 3-[7-(diethylamino)-2-oxo-2H-chromen-3-yl]-3-oxopropanoate (1) with 2-hydrazino-
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4,6-bis-(dimethylamino)-s-triazine (3) in the presence of toluene gave CPT (Scheme 1).
Scheme 1 is here
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CPT was characterized using 1H NMR, 13C NMR, and HRMS, and was found to be thermally stable up to 321 oC (Supplementary data, Figures S1-9). CPT was exclusively obtained as the enol tautomer (Scheme 2), as confirmed by; (a) a single clear absorption band in solvents
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of various polarity (Figure 1), and (b) 1H NMR chemical shift of the aromatic proton on the
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pyrazole ring at 6.20 ppm (in DMSO-d6) and absence of signal of pyrazolone methylene proton. This result is also confirmed by
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C-NMR data (Supplementary data, Figures S6
and S7) [39].
Scheme 1 is here Figure 1 is here
The absorption and emission spectra of CPT were studied in various solvents and the absorption and emission maxima were recorded in the ranges of 412-426 nm and 467-501 nm,
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Figure 1-3 are here
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3.2. Anion sensing properties of CPT by UV-vis and fluorimetric titrations
The anion-CPT interaction study was performed using UV-vis absorption spectroscopy in
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DMSO against F−, Cl−, Br−, I−, AcO−, CN−, H2PO4−, HSO4−, and ClO4− anions with tetrabutylammonium (TBA) as the counter cation (Figure 4).
The absorption maximum of CPT observed at 426 nm in DMSO and shifted hypsochromically upon addition of 20 equiv of F− to the solution of CPT and a new band was
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observed at λ=408 nm (Fig. 5). The observed hypsochromic shift can be from electrostatic interaction between CPT and F− that leads to the deprotonation of the acidic proton on pyrazole -OH function and extinguishes the –OH•••N H–bond. After deprotonation, a
was
obtained
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negative charge is created on the pyrazole ring and hereby the observed hypsochromic shift because
of
decreasing
intramolecular
charge
transfer
from
7-
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diethylaminocoumarin core to the pyrazole ring [24]. For competitive anions such as AcO− and CN−, similar results were observed. However, chemosensor CPT was more sensitive to F− as compared to its sensitivity towards both AcO− and CN− at the stoichiometric ratios of 1:1 and 1:20 (Figure 4 and Supplementary data, Figures S10 and S12). CPT displayed an emission maximum at 476 nm in DMSO with a high intensity that gradually decreased upon titration with F− (Figure 5). The light-off of the emission, presumably via breaking of the pyrazole O–H bond and hence –OH•••N H–bond, by F− is the targeted anion sensing action.
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Figure 4 and 5 are here
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albeit not as effective (Supplementary data, Figures S11 and S13).
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The determination of reversibility and reusability of a chemosenser is quite an important property, as well as its usability in practical application with real sample. Therefore, in our
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efforts on the identification of CPT, we investigated its reversibility and reusability. Systematic titration of CPT in the presence of F−, upon addition of increasing amounts of TFA (0−20 equiv) shifted the absorption band from 404 to 426 nm (Figure 6). The determination colour differences of anion-ligand interection can be determined by the
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naked eye or by using a portable UV lamp. In our study, we investigated interaction of CPT with studied anions and obtained distinctive colour and fluorescent change after anion-CPT interaction. The chemosensor CPT displayed a colour change from yellow to red upon
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addition of F−, whereas a yellow-to-light orange colour change was observed in the case of CN− and AcO− (Figure 7). The results showed that CPT can be used as a ‘‘naked-eye’’ probe
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for F− in DMSO. In addition to this, the emission quenching in CPT was observed only in the presence of F− in same solvent. No significant colour or emission changes were observed by the naked eye and under portable UV lamp upon the addition of the other anions.
Figures 6 and 7 are here
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Upon addition of 5 equiv of F−, the proton of the pyrazole ring, originally at 6.16 ppm, promptly shifted up-field to 4.97 ppm, suggesting an accumulation of negative charge surrounding the pyrazole proton (Figure 8). This response is due to deprotonation of CPT upon interaction of F− with the enolic -OH group. It is important that a new signal at 16.15
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ppm (JHF=121 Hz) after addition of 4 equiv of F− was observed and indicated the creation of
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bifluoride (FHF-) ion. Thus FHF- is generated through abstraction of the OH proton by F− that simultaneously broke the intramolecular OH•••N H–bond as well. AcO−, CN− and H2PO4− showed analogous, albeit less pronounced 1H NMR chemical shift changes at 5.12, 5.03 and 6.02 ppm, respectively, when compared to F− (Figure 9). This difference is presumably due to the lower basicity of AcO−, CN− and H2PO4−, compared to F−. It was not observed any
and ClO4−) (Figure 9).
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changing in spectrum for pyrazole proton regarding the rest of the anions (Cl−, Br−, I−, HSO4−,
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Figures 8 and 9 are here
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3.4. Acidochromic properties
The determination of pH change in any medium with fluorescent light-up probe has attracted considerable attention subject field in recently. In our synthesized molecule, the presence of many nitrogen atoms in coumarin-pyrazole-triazine hybrid compound prompted us to study the possibility of protonation of this compound in CH2Cl2. Therefore, the protonation effect on spectroscopic properties of CPT in CH2Cl2 solution was studied. Solution of CPT in CH2Cl2 (10 µM) added trifluoroacetic acid (TFA) shifted the absorption maximum from 419 10
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observed, while significant increase in the emission intensity was observed even by the naked-eye (Figure 10). Therefore, it may be used for the development of a light-up probe for
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Figures 10 is here
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determining pH differences in biological samples after determination of pKa value in water.
2.5 Computational Results
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2.5.1 The stability of possible tautomeric forms
The calculated relative energies corresponding to total energies of the three tautomeric forms of CPT are given in Table 1. The enol tautomer appears more stable than the two keto
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tautomers (keto A and keto B) with the energy difference of 3.43 kcal/mol and 3.20 kcal/mol
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in gas phase, and 3.31 kcal/mol and 0.78 kcal/mol for keto A and keto B forms, respectively. In the following calculations, to obtain an insight into the deprotonation of CPT, the enol form was used.
Table 1 is here
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ACCEPTED MANUSCRIPT 2.5.2 The theoretical results of the interaction of CPT with F− and CN−
The optimized structures of the enol form CPT, CPT-F− and CPT-CN− are shown in Figure 11. There is a formation of an intramolecular O-H…N hydrogen bond between OH and
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triazin, with O-H and H…N distances of 0.997 Å and 1.719 Å, respectively, in enol form of CPT (Table 2). It should be noted that the presence of the intramolecular O-H…N hydrogen bond resulted in the stability of the enol tautomer. CPT is planar with the dihedral C3-C2-C1-
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N29 = -177.65o between coumarin and pyrazole rings, and N29-N30-C33-N36 = -179.23o between pyrazole and triazin rings. After the molecule interacted with the anions F− and CN−,
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there were no significant changes in the geometry of the dihedrals with C3-C2-C1-N29 = 178.98o and N29-N30-C33-N36 = -179.23o for CN-, whereas the planarity was broken for F−, in which the geometry of coumarin and pyrazole rings did not change with the dihedral C3C2-C1-N29 = -174.31o, but the dihedral angle between the pyrazole and the triazin rings was
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found to be -159.24 o. These structural changes can be the reason for the hypsochromic shifts in the absorption spectra and the quenching of the emission spectra. TD-DFT calculations were performed on the ground state geometry structures CPT, CPT-F−
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and CPT-CN−, in DMSO, to get a further information about electronic transitions using the molecular orbitals. The obtained results are summarized in Table 3. The calculated
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hypsochromic shifts are 13 nm and 16 nm for the interaction with CN− and F−, respectively, consistent with experimental value of F− (18 nm). The calculated frontier orbitals are shown in Figure 12. For CPT, the main transition is from HOMO to LUMO and the electron density in the HOMO is localized on coumarin moiety with the contributions of pyrazole and Et2N moieties. After deprotonation with F−, and CN−, the electron density of the HOMO was distributed over only the pyrazole moiety while the LUMO was based on the coumarin moiety. Upon excitation of the CPT-F− and CPT-CN−, an electron would have been
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Figure 12 is here
4. Conclusions
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We reported a novel example of a coumarin-based tautomer stabilization, yielding an efficient chemosensor for anion detection, with remarkable sensitivity for fluoride at the stoichiometric
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ratio of 1:20. The results showed clear visible colorimetric changes, and emission quenching in CPT were observed in the presence of F− in polar aprotic DMSO. It has high fluorescent property in acidic environment, therefore CPT can detect pH visually by fluorescence change and can be used as a candidate for the development of light up probe in pH imaging in living
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cells. As a result, the chemosensor CPT was more sensitive towards F− and H+ than our
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previous published chemosensor [39] which bearing pyridine instead of triazine.
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Acknowledgements
We are grateful to The Scientific and Technological Research Council of TURKEY for providing financial support (Project Grant No: 113Z895) for this study.
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ACCEPTED MANUSCRIPT Supplementary material
Supplementary data (Copies of 1H NMR, 13C NMR, HRMS and absorption spectra on anionschemosensor interactions Figs. S1–S13) associated with this article can be found, in the
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online version, at…..
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CAPTIONS Tables Captions
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Table 1. The relative energies for enol, keto A and keto B tautomeric forms of CPT. Table 2. Hydrogen bond geometry (Å, o) for the enol tautomer of CPT.
Table 3. Calculated absorption wavelengths (λmax) for CPT, CPT-F- and CPT-CN- in
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DMSO. The oscillator strengths (f) and the contributions (c) are given in parentheses.
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Scheme Captions
Scheme 1. Synthetic pathway of CPT; i: EtOH, piperidine, reflux; ii: dimethylamine, acetone; iii: Hydrazine monohydrate (65 %), THF, reflux; iv: toluene, reflux.
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Figure Captions
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Scheme 2. Favoured tautomers and intramolecular H-bonds.
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Fig. 1. UV-vis spectra of CPT in various solvents. Fig. 2. Emission spectra of CPT in various solvents. Fig. 3. Normalized Emission spectra of CPT in various solvents. Fig. 4. UV-vis titration spectra of CPT (c= 2 µM) upon addition of 1 equiv of various anions in DMSO.
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ACCEPTED MANUSCRIPT Fig. 5. UV–vis titration (top) and Fluorescence emission titration (bottom) spectrum of CPT with TBAF in DMSO, (λexc.=426 nm, c=10 µM for UV–vis titration, c=0.1 µM for Fluorescence emission titration), (1 equiv = 2 µM ). Fig. 6. Absorption spectra of CPT (c= 10 µM) in the presence of F− (20 equiv) upon addition
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of increasing amount of TFA (0−20 equiv) in DMSO, (1 equiv = 2 µM ).
Fig. 7. Photographs of CPT (c=1 mM in DMSO) upon addition of 1 equiv studied anions
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(c=10 mM in DMSO) under ambient light (top), under UV light (bottom, 365 nm).
Fig. 8. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with TBAF solution in DMSO-d6.
studied solution in DMSO-d6.
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Fig. 9. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with 4 equiv of TBA salts of anions
Fig. 10. UV–vis titration (left, 10 µM in CH2Cl2) and Fluorescence emission titration (λexc.=478 nm, right, 0.1 µM in CH2Cl2) spectrum of CPT upon the addition in the range of 1
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with 20 equiv of TFA. (1 equiv = 2 µM ).
Fig. 11. The optimized geometries of CPT, CPT-F- and CPT-CN-.
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Fig. 12. The frontier orbital of CPT, CPT-F- and CPT-CN-.
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ACCEPTED MANUSCRIPT Table 1. The relative energies for enol, keto A and keto B tautomeric forms of CPT. Gas
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E ∆E Enol -1556.582943 0.00 Keto A -1556.577474 3.43 Keto B -1556.577851 3.20
DMSO E ∆E -1556.608057 0.00 -1556.603412 2.91 -1556.606816 0.78
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Table 2. Hydrogen bond geometry (Å, o) for the enol tautomer of CPT. D-H. . .A D-H(Å) H. . .A(Å) D. . .A (Å) ∠D-H. . .A (o) O-H…N 0.997 1.719 2.61 145.9
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Table 3. Calculated absorption wavelengths (λmax) for CPT, CPT-F- and CPT-CN- in DMSO. The oscillator strengths (f) and the contributions (c) are given in parentheses. λmaxexp.(nm) 426 408 419
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CPT CPT-FCPT-CN-
λmax(nm), f 419 (0.9960) 403 (0.9060) 406 (0.9686)
Transition, c HOMO→LUMO (98.5%) HOMO→LUMO (93.4%) HOMO→LUMO (96.5%)
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Fig. 1. UV-vis spectra of CPT in various solvents.
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Fig. 2. Emission spectra of CPT in various solvents.
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Fig. 3. Normalized Emission spectra of CPT in various solvents.
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Fig. 4. UV-vis titration spectra of CPT (c= 2 µM) upon addition of 1 equiv of various anions in DMSO.
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Fig. 5. UV–vis titration (top) and Fluorescence emission titration (bottom) spectrum of CPT
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with TBAF in DMSO, (λexc.=426 nm, c=10 µM for UV–vis titration, c=0.1 µM for Fluorescence emission titration), (1 equiv = 2 µM ).
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Fig. 6. Absorption spectra of CPT (c= 10 µM) in the presence of F− (20 equiv) upon addition of increasing amount of TFA (0−20 equiv) in DMSO, (1 equiv = 2 µM ).
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Fig. 7. Photographs of CPT (c=1 mM in DMSO) upon addition of 1 equiv studied anions
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Fig. 8. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with TBAF solution in DMSO-d6.
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Fig. 9. Partial 1H NMR (300 MHz) titration of 1 (10 mM) with 4 equiv of TBA salts of anions studied solution in DMSO-d6.
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Fig. 10. UV–vis titration (left, 10 µM in CH2Cl2) and Fluorescence emission titration (λexc.=478 nm, right, 0.1 µM in CH2Cl2) spectrum of CPT upon the addition in the range of 1
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CPT
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Fig. 11. The optimized geometries of CPT, CPT-F- and CPT-CN-.
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HOMO
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CPT
LUMO
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CPT-F-
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Fig. 12. The frontier orbital of CPT, CPT-F- and CPT-CN-.
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Scheme 1. Synthetic pathway of CPT; i: EtOH, piperidine, reflux; ii: dimethylamine,
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Scheme 2. Favoured tautomers and intramolecular H-bonds.
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Highlights •
A novel fluorescence coumarin-pyrazole-pyridine triad (CPT) was synthesized and
•
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characterized for detection of anions. CPT has remarkable sensitivity for fluoride detection in DMSO at the stoichiometric ratio of 1:20. CPT exhibits acidochromic property.
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Significant “light-up” effect was observed after interaction with TFA in CH2Cl2.
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CPT can be used as promising candidate for the development of light up probe in
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acidic environment.
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•