A highly selective naked-eye and fluorescent probe for fluoride ion based on 1,8-naphalimide and benzothizazole

Article abstract of DOI:10.1016/j.dyepig.2017.02.008

Based on benzothizazole and 1,8-naphalimide, a novel colorimetric and fluorescent probe (probe 1) for fluoride ion was synthesized by Schiff base reaction. The striking yellow-to-blue color change of the probe 1 in the CH₃CN was observed with the naked eyes only in presence of F^? among the eight anions (F^?, Cl^?, Br^?, I^?, NO₃^?, HSO₄^?, H₂PO₄^?, AcO^?). Besides that, upon addition of F^?, both of the absorption and emission peaks shifted to near-infrared region (NIR) (>600?nm) in UV–vis and fluorescent spectra, and the detection limit reached as low as 0.41?μM. Furthermore, the ¹H NMR titration and theoretical calculation based on TD-DFT indicated that the fluoride ion induced deprotonation of the probe 1 through hydrogen bonding interaction between amino group of probe 1 and fluoride ion.

Full text of DOI:10.1016/j.dyepig.2017.02.008

Accepted Manuscript
A highly selective naked-eye and fluorescent probe for fluoride ion based on 1,8-
naphalimide and benzothizazole
Xiaoxing Chen, Taohua Leng, Chengyun Wang, Yongjia Shen, Weihong Zhu
PII:
S0143-7208(16)31410-3
10.1016/j.dyepig.2017.02.008
DYPI 5785
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 14 December 2016
Revised Date: 6 February 2017
Accepted Date: 7 February 2017
Please cite this article as: Chen X, Leng T, Wang C, Shen Y, Zhu W, A highly selective naked-eye and
fluorescent probe for fluoride ion based on 1,8-naphalimide and benzothizazole, Dyes and Pigments
(2017), doi: 10.1016/j.dyepig.2017.02.008.
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ACCEPTED MANUSCRIPT
Graphical Abstract
A highly selective naked-eye and fluorescent probe for fluoride ion based
on 1,8-naphalimide and benzothizazole
Xiaoxing Chen, Taohua Leng, Chengyun Wang , Yongjia Shen, and Weihong Zhu
A novel near-infrared fluorescent probe with high sensitivity and selectivity for fluoride ion
has been fabricated.

ACCEPTED MANUSCRIPT
A highly selective naked-eye and fluorescent
probe for fluoride ion based on 1,8-naphalimide and
benzothizazole
Xiaoxing Chen a, Taohua Leng b, Chengyun Wang a, , Yongjia Shena, and Weihong Zhu a,*
a Shanghai Key Laboratory of Functional Materials Chemistry, Key Laboratory for Advanced
Materials and Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East
China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China
b National Food Quality Supervision and Inspection Center (Shanghai) / Shanghai Institute of
Quality Inspection and Technical Research, Shanghai 200233, China.
Abstract
Based on benzothizazole and 1,8-naphalimide, a novel colorimetric and fluorescent
probe (probe 1) for fluoride ion was synthesized by Schiff base reaction. The striking
yellow-to-blue color change of the probe 1 in the CH3CN was observed with the
naked eyes only in presence of F- among the eight anions (F-, Cl-, Br-, I-, NO3 , HSO4 ,
-
-
-
H2PO4 , AcO-). Besides that, upon addition of F-, both of the absorption and emission
peaks shifted to near-infrared region (NIR) (>600 nm) in UV-vis and fluorescent
spectra, and the detection limit reached as low as 0.41µM. Furthermore, the 1H NMR
titration and theoretical calculation based on TD-DFT indicated that the fluoride ion
induced deprotonation of the probe 1 through hydrogen bonding interaction between
Corresponding author. Tel./fax: +86-021-64252967; e-mail: cywang@ecust.edu.cn; whzhu@ecust.edu.cn

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amino group of probe 1 and fluoride ion.
Key words
Fluoride ion; fluorescent probe; 1, 8-napthalimide; benzothizazole
1. Introduction
In recent years, the design of methods to selectively recognize and detect various
anions has emerged as a research area of great importance [1-4] due to the major roles
of the anions in chemical, biological and environmental assays [5-7]. Among the
various anions, fluoride ion, with the smallest ionic radius, highest charge density and
a hard Lewis basic nature [8-10], is closely associated with human health. For
example, excessive intake of fluoride could induce many diseases such as fluorosis,
urolithiasis, acute gastric, kidney problems and even cancer [11]. In addition, fluoride
has also been applied in military areas such as nuclear weapon manufacture [2] and
nerve gas monitor [12, 13]. As a result, convenient and efficient detection techniques
for fluoride ion have attracted great attention and many achievements have been
reported [14-20]. Compared with the traditional detection techniques including
electrode method and 19F-NMR analysis [21], colorimetric and fluorescent probe
methods have drawn increasing attention from scientists who are devoted to studying
host/guest and supramolecular chemistry because of their operational simplicity, high
sensitivity, low detection limit and bioimaging analysis in vivo, even in living cells
[22-25]. Up to date, some probes for fluoride ion have been developed, most of which
are mainly based on molecular interactions between the receptor and fluoride [26],

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such as hydrogen bonding [26-32], B-F complexation [1, 33-35] and desilylation of
Si-O/Si-C bonds [36-39].
Among them, probes for fluoride ion based on hydrogen bond generally utilize the
N-H of urea, sulfonamide, pyrrole, indole and amide. However, probes used the
hydrazone as hydrogen bond donor are rare. In some case, these receptors may also
-
respond to other anions like H2PO4 and AcO- or only show colorimetric responses to
fluoride ion. Thus, it is extremely necessary to develop the colorimetric and
fluorescent probe with high selectivity.
In this paper, a new hydrazone receptor (probe 1) containing 1,8-naphthalimide and
benzothiazole was designed and synthesized through Schiff base reaction (Scheme 1).
As one of the classical fluorophore, 1,8-naphthalimide has been widely used by
various receptors due to its many excellent properties, such as good photostability,
high fluorescence quantum yields, large Stokes’ shift. In addition, benzothiazole was
chosen to append to the –NH-N= moiety for two main reasons: (i) the presence of the
benzothiazole as electron-withdrawing substituent group is expected to enhance the
acidity and propitious to deprotonation of probe 1 as consequence; (ii) The
benzothiazole unit can broaden conjugation structure of the system after
deprotonation of probe 1. According to the ICT mechanism, probe 1 maybe show
peaks red-shifts and intensity changes in UV-vis and fluorescent spectra [2], therefore
it can be used as probe for F-. Actually, Probe 1 showed high selectivity for fluoride
ion through the deprotonation action, and it could detect fluoride ion by ratiometric
colorimetric and fluorescent methods which was observable with the naked eyes

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within 10 s, the detection limit reached as low as 0.41µM.
Insert Scheme 1 here
2. Experimental section
All the starting materials, reagents and solvents were AR grade and purchased from
1
J&K chemical Co., which were received without further purification. H and 13C
NMR spectra were measured on a Bruker AM-400 spectrometer at room temperature
using d-chloroform or DMSO-d6 as a solvent and tetramethylsilane (TMS, δ= 0 ppm)
as an internal standard. The UV-vis spectra were recorded on a Nicolet CARY 100
and the fluorescence spectra were measured on a CARY Eclipse. The stock solutions
of probe 1 (1.0 × 10-5mol/L) were prepared in DMSO solution. The TBA salts (F-, Cl-,
B-, I-, NO3 , HSO4 , H2PO4 , AcO-) solutions were prepared at a concentration of 0.01
mol/L in CH3CN solution. Different equivalents of TAB salts were added to the probe
1 and their corresponding UV-vis and fluorescence spectra were recorded at room
temperature. Probe 1 (1.0 × 10-5mol/L in CH3CN) was titrated with fluoride anion (as
tetrabutylammonium salts) by addition of increasing equivalents of anion in
DMSO-d6 solution. The energies and oscillator strengths with 80-120 lowest energy
electronic transitions were obtained using time-dependent DFT (TD-DFT) with
Becker’s three parameterized Lee-Yang-Par(B3LYP) exchange functional with
6-31G(d) and 6-31G**+Lanl2DZ basis sets.
-
-
-
2.1 Synthesis of 4-bromo-N-butyl-1,8-naphthalimide (compound 2)
The mixture of 4-bromo-1,8-naphthalic anhydride (5.000 g, 18.000 mmol) (70 mL)

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and 1-aminobutane (1.700 g, 23.400 mmol) in ethanol was refluxed for 6 h under
nitrogen atmosphere. The mixture was then cooled to the room temperature and
filtered. The filter cake was washed three times with ethanol and the crude product
was recrystallized from ethanol to obtained a pale yellow solid [40] (5.220 g, 87%).1H
NMR (400 MHz, DMSO-d6, TMS): δH 8.54-8.49 (m, 2H)ꢀ8.30 (d, J=7.6 Hz, 1H),
8.19 (d, J=7.6 Hz, 1H), 7.97 (t, J=7.2 Hz, 1H), 4.02 (t, J=7.2 Hz, 2H), 1.61 (m, 2H),
1.41-1.31 (m, 2H), 0.93 (t, J=7.6 Hz, 3H). 13C NMR (100 MHz, DMSO-d6) δC
162.639, 162.588, 132.377, 131.374, 131.172, 130.750, 129.545, 128.986, 128.592,
127.993, 122.491, 121.712, 29.492, 19.776, 13.665.
2.2 Synthesis of 4-hydrazine hydrate-N-butyl-1,8-naphthalimide (compound 3)
4-Bromo-N-butyl-1,8-naphthalimide (3.300 g, 10.000 mmol) and 2.5 mL hydrazine
hydrate (85%, w/w) were added into 50 mL ethylene glycol monomethyl ether and the
mixture was refluxed for 6 h. After cooled to the room temperature, the mixture was
poured into 80 mL water and the precipitated solid was filtered, dried in vacuum to
give a red solid [14] (2.250 g, 80%).1H NMR (400 MHz, DMSO-d6, TMS): δH 9.12 (s,
1H), 8.61 (d, J= 8.4 Hz, 1H), 8.41 (d, J= 7.2 Hz, 1H), 8.28 (d, J= 8.8 Hz, 1H), 7.63 (t,
J=7.6 Hz, 1H), 7.24 (d, J=7 Hz, 1H), 4.67 (s, 2H), 4.01 (t, J=7.2Hz, 2H), 1.58 (m, 2H),
13
1.33 (m, 2H), 0.92 (t, J= 7.2 Hz, 3H). C NMR (100 MHz, DMSO-d6) δC 163.695,
162.843, 153.108, 134.108, 130.461, 129.213, 128.142, 124.008, 121.668, 118.346,
107.330, 103.910, 29.805, 19.826, 13.717.
2.3 Synthesis of benzo[d]thiazol-2-ylmethanol (compound 4)

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To mixture of 2-aminobenzenethiol (25.000 g, 0.200 mol) and glycolic acid (46.000 g,
0.600 mol) was added HCl (4 N, 60 mL). The reaction was allowed to proceed under
reflux at 100 °C for 6 h prior to being quenched with saturated aqueous sodium
bicarbonate. The solution was extracted three times with ethyl acetate. The combined
extracts were evaporated in vacuum to give the crude product. The crude product was
purified by chromatography on a silica gel column with DCM/MeOH (100/2, v/v) as
1
the eluent to yield compound 4 [41] (3.630 g, 11%). H NMR (400 MHz, CDCl3,
TMS): δH 7.97 (d, J=8.0 Hz, 1H), 7.88 (d, J=7.6 Hz, 1H), 7.47 (t, J=7.2 Hz, 1H), 7.38
(t, J=7.2 Hz, 1H), 5.75 (br, 1H), 5.08 (s, 2H). 13C NMR (100 MHz, CDCl3) δC
173.635, 152.634, 134.528, 126.218, 125.099, 122.569, 121.841, 62.237.
2.4 Synthesis of Benzothiazole-2-carbaldehyde (compound 5)
To a solution of benzothiazol-2-ylmethanol (1.650 g, 10.000 mmol) in methylene
chloride (40mL) was added DMP (4.600 g, 31.000 mmol), and the reaction was
allowed to proceed with stirring at 4 °C for 1 h prior to being quenched with saturated
aqueous sodium thiosulfate solution. The subsequent mixture was extracted three
times with methylene chloride. The combined organic extracts were dried with
anhydrous magnesium sulfate and concentrated. The crude product was purified by
chromatography on a silica gel column, eluting with DCM/MeOH (100/1, v/v) to
yield the product benzothiazole-2-carbaldehyde [41] (0.650 g ,40%). 1H NMR (400
MHz, CDCl3, TMS): δH 10.18 (s,1H), 8.25 (d, J=7.6 Hz, 1H), 8.02 (d, J=7.6 Hz, 1H),
13
7.61 (m, 2H). C NMR (100 MHz, CDCl3) δC 184.432, 164.377, 135.263, 127.359,
126.966, 124.728, 121.649.

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2.5 Synthesis of probe 1
A
mixture of benzothiazole-2-carbaldehyde (1.630 g, 1.000 mmol),
4-hydrazinehydrate-N-butyl-1,8-naphthalimide (0.283g, 1.000 mmol) and a drop of
acetic acid was heated to reflux for 4 h in 10 ml ethanol. After cooling to the room
temperature, many precipitates were formed. The precipitates were collected through
filtration and recrystallized from ethanol to give pale yellow probe 1 (0.359 g, 84%).
MP: 194.5-195.5 °C. 1H NMR (400 MHz, DMSO-d6, TMS): δH 12.05 (s, 1H), 8.78 (d,
J=8.4 Hz, 1H), 8.68 (s, 1H), 8.52 (d, J=7.2 Hz, 1H), 8.02 (d, J=8.0 Hz, 1H), 7.87 (t,
J=8.4 Hz, 1H), 7.73 (d, J=8.4 Hz, 1H), 7.57-7.47 (m, 2H), 4.03 (t, J=7.2 Hz, 2H),
1.61 (m, 2H), 1.35 (m, 2H), 0.93 (t, J=7.2 Hz, 3H). IR (KBr: v (cm-1)): 3445, 3222,
2960, 1682, 1647, 1587, 1566, 1387, 1242, 1120, 1020. HRMS (EI): m/z Calcd for
C24H20N4O2S1 [M]-, 428.1307; found, 428.1308. Anal. Calcd for C24H20N4O2S1: C,
67.27; H, 4.70; N, 13.07%. Found: C, 67.23; H, 4.66; N, 13.11%.
3. Results and discussion
3.1 Colorimetric analysis
The interactions of probe 1 with various anions (F-, Cl-, Br-, I-, NO3 , HSO4 , H2PO4 ,
AcO-) were firstly investigated in CH3CN through colorimetric analysis. These anions
mentioned were prepared in TBA salts form. Upon addition of 5 equiv of fluoride
anion, the solution color of probe 1 (1.0 × 10-5mol/L in CH3CN) changed from yellow
to blue under ambient light and fluorescence color of probe 1 changed from green to
red under a UV lamp at 365 nm, yet no appreciable color changes were observed
-
-
-
-
-
-
when 5 equiv of other anions (Cl-, Br-, I-, NO3 , HSO4 , H2PO4 , AcO-) were added

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(Fig.1). Thus, the detection of probe 1 for F- can be observed through naked eyes.
Insert Fig. 1 here
3.2 UV-vis and fluorescence emission studies in CH3CN
-
-
The interactions between probe 1 and various anions (F-, Cl-, Br-, I-, NO3 , HSO4 ,
-
H2PO4 , AcO-) were studied by UV-vis absorption and fluorescence titration. The
titrations were carried out in CH3CN by addition of 0.01 mol/L corresponding anions
(F-, Cl-, Br-, I-, NO3 , HSO4 , H2PO4 , AcO-) to solution of probe 1 (1.0 × 10-5 mol/L).
As shown in Fig 2a, probe 1 possessed a certainly strong absorption band centered at
445 nm. Upon the addition of F-, the intensity of absorbance at 445 nm decreased
gradually while a new peak at 620 nm appeared and developed. And then, the band
reached the maxima at 5 equiv of F-. Meanwhile, five clear isosbestic points were
observed at 248 nm, 280 nm, 334 nm, 381 nm and 494 nm, indicating that only one
product was generated during the titration process. Besides, the fluorescence titrations
(Fig.2b) demonstrated that probe 1 exhibited emission at 505 nm when it was excited
at 410 nm. When F- was added to the solution of probe 1, a drastic decrease of
emission at 505 nm and the emergence of a red-shifted emission band centered at 660
nm in near-infrared (NIR) region, were observed with a clear iso-emission point at
629 nm. These UV-vis and fluorescence spectral changes could be attributed to the
hydrogen-bond interaction between F- with the amino proton of probe 1 and the
following deprotonation of amino group [2] (Scheme 2). Analogous UV-vis and
-
-
-

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-
fluorescence experiments were also carried out with other anions (Cl-, Br-, I-, NO3 ,
-
-
HSO4 , H2PO4 , AcO-) (Fig. 3a, Fig. 3b and blue bars of Fig. S1). Upon addition of 50
equiv of these anions, only AcO- showed dinky interference while other anions have
no interference in the detection of F- with UV-vis and fluorescence spectroscopy
methods. To further assess its utility as an F- selective probe, its UV-vis spectra
response to F- in presence of other anions was also tested. The test results were the
same as the results mentioned above (white bars of Fig. S1). These results strongly
indicated that probe 1 can detect F- as a colorimetric and fluorescent probe with high
selectivity.
Insert Fig. 2 here
Insert Scheme 2 here
Insert Fig. 3 here
3.3 Determination of the stoichiometric ratio and association constant
Continuous variation methods were applied to determine the stoichiometric ratio of
probe 1 with fluoride ion. A Job-plot (Fig. 4a) of probe 1 with fluoride ion in CH3CN
showed the maxima at 0.5 of [F-] / ([F-] + [probe 1]). The phenomenon indicated that
the probe 1 associated with fluoride ion in 1:1 ratio during the initial stage of the
reaction. The binding stoichiometry of probe 1 with fluoride ion also calculated by the
Benesi-Hildebrand equation:
A0 is the absorbance of free probe 1, A∞ is the absorbance treated with excess amount
of F-, A is the absorbance treated with a certain concentration of fluoride ion, K is the

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binding constant (M-1) and [F-]0 is the concentration of fluoride ion (M). The plot of 1/
(A-A0) against 1/ [F-]0 showed linear relationship (R=0.994) (Fig. 4b), indicating that
probe 1 bound to fluoride ion in 1:1 stoichiometry. The association constant K
between probe 1 and fluoride ion was determined from the ratio of intercept/slope to
be 1.46 × 104 M-1.
Insert Fig. 4 here
3.4 Detection mechanism
The proposed binding mechanism of probe 1 with F- is shown in Scheme 2. To
1
interpret F- sensing mechanism of probe 1, H NMR titration experiments were
1
carried out in DMSO-d6. Fig. 5 showed partial H NMR spectrum of interaction of
probe 1 and F-. The signal of NH proton decreased and became broader after the
addition of 0.05 equiv F-, implying that fluoride ion could complex with probe 1
because of the hydrogen–bond interactions existed between amino proton of probe 1
and fluoride at low concentration of TBAF. On the further addition of more than 2
equiv of F-, the resonance signal of the N-H proton disappeared. Meanwhile the
chemical shift values of aromatic protons occurred to slightly changes. These results
suggested that the amino group of probe 1 would be deprotonated when the F-
concentration turned higher.
Insert Fig. 5 here
To further interpret the interaction between the F- and probe 1, theoretical calculations
based on time-dependent density functional theory (TD-DFT) were carried out. As

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shown in Table 1 and Table 2, the highest occupied molecular orbitals (HOMO) of
probe 1 and 1+F- were located at the conjugated units of probe 1, and the lowest
unoccupied molecular orbitals (LUMO) of the probe 1 and 1+F- were mainly located
at the 1,8-naphthalimide unit. The strongest absorption at 445 nm of probe 1
contributed to the charge transfer transition from benzothiazole to 1, 8-naphthalimide.
After adding fluoride ion, the charge of product 1+F- transferred from the amino
group to the 1,8-naphthalimide unit, which could be used to explain the new
absorption at 620 nm. In addition, Fig. S2 and Table S1 (See in ESI) clearly showed
that the calculated UV-vis spectra of probe 1 and 1+F- were in agreement with the
experimental results, implying that the sensing mechanism that we proposed is
reasonable.
Insert Table 1 here
Insert Table 2 here
4. Conclusion
In summary, a ratiometric colorimetric and fluorescent receptor (probe 1) for fluoride
ion was designed and synthesized via Schiff base reaction. Probe 1 shows good
selectivity, high sensitivity, and fast response to fluoride ion. Moreover, it presents
dramatic color change, which can be observed directly by naked eyes and displays
optical response in near-infrared (NIR) region (>600 nm) after addition of fluoride ion
in 10 s. We believe these characteristics of probe 1 are very important and promising
in the sensing fluoride ion.

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Acknowledgments
The authors are grateful to financial support from the National Natural Science
Foundation of China (No. 21576087) and Natural Science Foundation of Shanghai
(16ZR1408000).
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Structure-Activity
Relationship
and
Pharmacokinetic
Studies
of
1,5-Diheterorylp-enta-1,4-dien-3-ones: A Class of Promising Curcumin-Based
Anticancer Agents. J Med Chem 2015;58(11):4713-26.

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Scheme captions:
Scheme 1 Synthetic route of probe 1
Scheme 2 Proposed sensing mechanism toward F-

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Scheme 1 Synthetic route of probe 1
Scheme 2 Proposed sensing mechanism toward F-

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Table captions:
Table 1. Computed energy levels of frontier molecular orbitals
Table 2. Calculated surfaces of HOMO-1, HOMO, LUMO, and LUMO+1 of probe 1
and 1+F-

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Table 1
Computed energy levels of frontier molecular orbitals
HOMO-1(eV) HOMO(eV)
LOMO(eV)
LUMO+1(eV) HOMO-LUMO(e
V)
Probe 1
1+F-
-6.56
-5.79
-5.66
-4.51
-2.54
-2.02
-1.85
3.12
-1.09
2.49
Table 2
Calculated surfaces of HOMO-1, HOMO, LUMO, and LUMO+1 of probe 1 and 1+F-
HOMO-1
HOMO
LUMO
LUMO+1
Probe 1
1+F-

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Figure captions:
Fig. 1 Color changes of probe 1 (1.0 × 10-5 mol/L in CH3CN) with the addition of 5
equiv of various anions (0.01 mol/L in CH3CN) (Cl-, Br-, I-, F-, NO3 , HSO4 , H2PO4 ,
-
-
-
AcO-) under ambient light (top) and a UV lamp at 365 nm (bottom)
Fig. 2 (a) UV-vis absorption and (b) emission spectra of probe 1 (1.0 × 10-5mol/L in
CH3CN) in presence of TBAF (0.01mol/L in CH3CN)
Fig. 3 (a) UV-vis absorption and (b) emission spectra of probe 1 (1.0 × 10-5mol/L in
CH3CN) in the present of 50 equiv of other anions (Cl-, Br-, I-, NO3 , HSO4 , H2PO4 ,
AcO-) (0.01mol/L in CH3CN) and 5 equiv of F- (0.01mol/L in CH3CN).
Fig. 4 (a) Job’s plot for complexation of probe 1 (620nm) with F- determined by
UV-vis absorbance in CH3CN ([F-] + [probe 1]) = 1.0 × 10-5mol/L at 298 K. (b)
Benesi-Hildebrand plot of UV-vis titration results probe 1 (1.0 × 10-5mol/L) at 445
nm with F- (0.01 mol/L).
-
-
-
1
Fig. 5. H NMR titration spectra of probe 1 in DMSO-d6 in presence of various
equivalents of TBAF.

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Fig. 1 Color changes of probe 1 (1.0 × 10-5 mol/L in CH3CN) with the addition of 5
equiv of various anions (0.01 mol/L in CH3CN) (Cl-, Br-, I-, F-, NO3 , HSO4 , H2PO4 ,
-
-
-
AcO-) under ambient light (top) and a UV lamp at 365 nm (bottom)

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Fig. 2 (a) UV-vis absorption and (b) emission spectra of probe 1 (1.0 × 10-5mol/L in
CH3CN ) in presence of TBAF (0.01mol/L in CH3CN)
Fig. 3 (a) UV-vis absorption and (b) emission spectra of probe 1 (1.0 × 10-5mol/L in

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-
-
-
CH3CN) in the present of 50 equiv of other anions (Cl-, Br-, I-, NO3 , HSO4 , H2PO4 ,
AcO- ) (0.01mol/L in CH3CN) and 5 equiv of F- (0.01mol/L in CH3CN).
Fig. 4 (a) Job’s plot for complexation of probe 1 (620nm) with F- determined by
UV-vis absorbance in CH3CN ([F-] + [probe 1]) = 1.0 × 10-5mol/L at 298 K. (b)
Benesi-Hildebrand plot of UV-vis titration results probe 1 (1.0 × 10-5mol/L) at 445
nm with F- (0.01 mol/L).

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1
Fig. 5. H NMR titration spectra of probe 1 in DMSO-d6 in presence of various
equivalents of TBAF.

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Highlights
ꢀ The obvious color and fluorescence changes can be observed with naked
eyes.
ꢀ Probe 1 possesses good selectivity, low detection limit and fast response for
F-.
ꢀ Probe 1 displays ratiometric optical response to F- in near-infrared (NIR)
region