New Colorimetric and Fluorometric Fluoride Ion Probe Based on Anthra[1,9-cd]pyrazol-6(2H)-one

Article abstract of DOI:10.1007/s10895-017-2170-7

New colorimetric and fluorometric fluoride ion probe, anthra[1,9-cd]pyrazol- 6(2H)-one (1), was synthesized by one-step condensation. The probe 1 shows F^?-selective color change from colorless to pink and appearance of red fluorescence. The flu

Full text of DOI:10.1007/s10895-017-2170-7

J Fluoresc
DOI 10.1007/s10895-017-2170-7
ORIGINAL ARTICLE
New Colorimetric and Fluorometric Fluoride Ion Probe Based
on Anthra[1,9-cd]pyrazol-6(2H)-one
Yang Hu1 · Yan-Yan Liu1 · Qiao Li1 · Jing-Yu Sun1 · Sheng-Li Hu1
Received: 25 June 2017 / Accepted: 10 August 2017
© Springer Science+Business Media, LLC 2017
Abstract New colorimetric and fluorometric fluoride
ion probe, anthra[1,9-cd]pyrazol- 6(2H)-one (1), was syn-
thesized by one-step condensation. The probe 1 shows
F−-selective color change from colorless to pink and appear-
ance of red fluorescence. The fluorescence quantum yield of
free probe 1 in DMSO was calculated to be 0.03. After addi-
tion of 15 equiv. of F−, its fluorescence quantum yield can be
increased to 0.37. The analytical detection limit for F− was
2.8×10−7 M. 1H NMR analysis and DFT calculation show
that the F−-induced colorimetric and fluorometric responses
of 1 are driven by deprotonation process.
of lower doses of fluoride can result in dental and skeletal
fluorosis and urolithiasis in humans [2, 6, 7]. In addition,
with the development of industry and the increase in the
number and the scale of enterprises on fluorine products, the
contamination of fluorine becomes more serious. Therefore,
the detection of fluoride is of great importance for biological
and environmental applications.
To date, many methods have been applied to detect fluo-
ride ion (F−) such as the Willard and Wilson method [8],
electrochemistry [9], ion chromatography [10]. Although
these methods are sensitive and accurate, they often require
time-consuming sample preparation steps, sophisticated
instruments, and a large amount of sample. In contrast, a
colorimetric probe could detect the target analytes by the
naked-eye, without the aid of any expensive instruments
[11–14]. On the other hand, fluorescent probes might be the
most attractive method for the detection of F− because of
their high sensitivity, convenience, fast on-site evaluation,
and low cost [15, 16].
Keywords Colorimetric · Fluorometric · Fluoride ion ·
Anthra[1,9-cd]pyrazol-6(2H)-one · Theoretical calculations
Introduction
Fluoride plays vital roles in biological processes and indus-
try. In living organisms, fluoride is an essential trace ele-
ment and shortage of fluoride results in dental caries [1] and
osteoporosis [2]. In the nuclear industry, fluoride can be used
to separate radioactive and non-radioactive substances safely
and easily [3–5]. However, high dose or chronic ingestion
Various colorimetric and/or fluorescent probes for F− had
been developed based on thiourea [17–19], urea [20, 21],
amide [22–24], sulfonamide [25–27], imidazole [28, 29],
indole [30–32], pyrrole [33, 34], phenol [35, 36], and so forth
[37–41]. However, these probe molecules are most often
relatively complex structures and multiple synthetic steps are
required for their preparation. Therefore, constructing a simple,
easy to synthesize, both colorimetric and fluorescent probe
for visualization of F− with high selectivity and sensitivity are
of great challenge and continue to be of widespread interest.
Herein, we report that a simple-structured compound (1),
anthra[1,9-cd]pyrazol- 6(2H)-one, synthesized by one step
condensation (Scheme 1), can be used as a colorimetric and
fluorometric probe for selective fluoride ion sensing. The probe
1 shows F−-induced color change from colorless to pink and
appearance of red fluorescence through deprotonation process.
Electronic supplementary material The online version
of this article (doi:10.1007/s10895-017-2170-7) contains
supplementary material, which is available to authorized users.
* Sheng-Li Hu
hushengli168@hbnu.edu.cn
1
Hubei Key Laboratory of Pollutant Analysis & Reuse
Technology, Hubei Collaborative Innovation Center for Rare
Metal Chemistry, College of Chemistry and Chemical
Engineering, Hubei Normal University, Huangshi 435002,
People’s Republic of China
Vol.:(0123456789)
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131.7, 128.6, 128.5, 128.4, 125.1, 122.4, 122.1, 120.2,
NH
N
O
O
Cl
117.1. EI-MS: 221.06 ([M+H]+).
H2O
H2NNH2
Uv–vis/Fluorescence and 1H NMR Titration Studies
Pyridine, reflux, 9h
O
The stock solutions of 1 (1.0 mM) in DMSO and anions
(10.0 mM) in DMSO as tetrabutylammonium salts were
prepared. The volume of a solution of 1 used in the experi-
ments was 3.0 mL. Titration spectra were recorded by add-
ing corresponding volume of anion solutions to a solution
1
Scheme 1 Synthesis of the probe, 1
1
of 1. H NMR titrations were also performed on a Varian
Experimental
Materials
300 MHz spectrometer at 298 K. The solution of 1 (0.05 M
for F− in DMSO) was titrated by adding known quantities
of concentrated solution of tetrabutylammonium fluoride
(TBAF).
All reagents for synthesis obtained commercially were used
without further purification. In the titration experiments, all
the anions were added in the form of tetrabutylammonium
(TBA) salts, which were purchased from Sigma–Aldrich
Chemical, stored in a vacuum desiccator containing self-
indicating silica and dried fully before using. DMSO was
dried with CaH2 and then distilled in reduced pressure.
Computational Details
Preliminary geometry optimizations were performed
using the WinMOPAC version 3.0 software (Fujitsu Inc.)
at the semi empirical PM3 level, where the optimization
of 1-F− complexes was done using a bound structure, in
which F atoms are directly bound to the NH protons. The
obtained structures were fully refined in the gas-phase
with tight convergence criteria at the DFT level with the
Gaussian 03 package, using the B3LYP/6-31G* basis set
for all atoms.
Apparatus
NMR spectra were measured on a Varian Mercury 300 spec-
trometer operating at 300 MHz for 1H and 75 MHz for 13
C
relative to tetramethylsilane as internal standard. MS spec-
tra were obtained on a Finnigan Trace MS spectrometer.
IR spectra were recorded on a Perkin-Elmer PE-983 infra-
red spectrometer as KBr pellets with absorption reported
in cm−1. Absorption spectra were determined on UV-2501
PC spectrophotometer. Fluorescence spectra measurements
were performed on a Fluoro-Max-P spectrofluorimeter
equipped with a xenon discharge lamp, 1 cm quartz cells at
room temperature (about 298 K).
Results and Discussion
The probe 1 is obtained by refluxing a pyridine solution
containing 1-chloroanthracene-9, 10-dione and hydrazine
monohydrate for 10 h (Scheme 1). The structures of 1
1
were identified by using H and 13C NMR and EI-MS
analyzes.
Synthesis of Probe 1
The anion binding affinities of 1 were investigated in the
−
presence of various anions (F−, Br−, Cl−, I−, AcO−, NO3 ,
HSO4−, and H2PO4−) by using UV–vis and fluorescence
spectroscopy in DMSO solution at 25 μM concentration.
Figure 1 shows the UV–vis spectral changes of 1 (25 μM)
in the presence of different anion (15 eq). As shown in
Fig. 1, the probe 1 exhibited a major absorption band at
400 nm (log ε=4.32). When the F− ion was added, it was
found that a new absorption band appeared at 528 nm (log
ε=2.82), while the intensities of absorption at 400 nm were
decreased correspondingly. At the same time, the solution
changed from colorless to pink (Fig. 2). Other anions did
not cause this change under the same conditions. Accord-
ingly, 1 can serve as a colorimetric fluoride ion probe in
DMSO.
The probe 1 was synthesized according to the reported
method [42]. 1-Chloroanthracene-9, 10-dione (0.33 g,
1.35 mmol) and hydrazine monohydrate (0.06 g, 1.35 mmol)
were dissolved in pyridine (15 mL), the mixture was after
refluxed for 10 h under dry N2. The title compound was
purified by radial chromatography eluting with MeOH/
CH2Cl2 (1:100, volume ratio) to give 1 as a yellow pow-
der. M.p.: 267–268 °C. IR (νmax, KBr, cm−1): 3436, 3079,
1728, 1666, 1638, 769, 741; 1H NMR (300 MHz, CDCl3), δ
(ppm): 13.80(s, 1H, -NH), 8.32(d, J=7.8 Hz, 1H), 8.23(d,
J=7.5 Hz, 1H), 8.03(d, J=8.1 Hz, 1H), 7.97(d, J=7.2 Hz,
1H), 7.84(t, J = 7.5 Hz, 1H), 7.75(t, 1H), 7.63(t, 1H). 13C
NMR (CDCl3), δ (ppm): 182.8, 139.1, 138.3, 133.7, 132.6,
1 3

J Fluoresc
0.25
0.20
0.15
0.10
0.05
0.00
0.25
400nm
-
only , Cl , Br , I , AcO ,
-
-
-
1
-
HSO , NO , and H PO
-
-
0.20
0.15
0.10
0.05
0.00
4
3
2
4
529nm
-
F
20eq
-
F
437nm
363nm
0
350
400
450
500
550
600
650
350
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 3 Absorption titration of 1 (25 μM) with F− (as a n-bu4N+ salt)
Fig. 1 Changes in absorption spectra of 1 (25 μM) measured in
DMSO upon addition of 15 equiv of respective anions (as a n-bu4N+
salt)
in DMSO
The UV–vis absorption spectra of 1 in the presence of
various concentrations of F− ion is shown in Fig. 3. With
increase of F− concentration, the absorption intensity of 1
gradually decreased in 400 nm, along with an increase in
the 528 nm, indicating a red shift of 128 nm. Two clear isos-
bestic points at 363 and 437 nm indicate that a single com-
ponent is produced in response to the interaction between
1 and F−.
-
F
600
500
400
300
Only 1,
-
200
100
0
-
Cl , Br , I , HSO , NO
-
-
-
-
The fluorescence behavior of 1 was observed by exci-
tation at 420 nm in the presence of various anions. As
shown in Fig. 4, upon treatment of 1 with fluoride anion, a
dramatic increase in fluorescence intensity was observed.
In contrast, the addition of AcO− and H2PO4− only led to
slight fluorescence changes in 1; other representative ani-
ons did not cause any significant fluorescence response,
which clearly indicated that 1 could act as a highly selec-
tive fluorescent sensor for fluoride ion over other anions. In
addition, we also observed a selective visual fluorescence
change upon addition of F− to 1 solution over other various
anions (Fig. 5).
A O
C
4
3
-
H PO
2
4
550
575
600
625
650
675
700
725
Wavelength (nm)
Fig. 4 Changes in fluorescence (λex = 420 nm) spectra of 1 (25 μM)
measured in DMSO upon addition of 15 equiv of respective anions
(as a n-bu4N+ salt)
The fluorescence quantum yield (Фu) of 1 in the absence of
Fluorometric titration experiments for 1 were also realized
F− was calculated to be 0.03 with respect to rhodamine B in
by addition of F− at different concentrations in order (Fig. 6).
Fig. 2 Change in color of 1
upon addition of upon addition
of 15 equiv of respective anions
(as a n-bu4N+ salt) in DMSO
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Fig. 5 Visual colour change
of compound 1 upon addition
of upon addition of 15 equiv of
respective anions (as a n-bu4N+
salt) in DMSO under UV light
(λex = 365 nm)
0.011
0.010
0.009
0.008
0.007
0.006
0.005
0.004
0.003
600
500
400
300
200
100
0
y = 0.0017+0.0166x
R = 0.9998
4
=1.02 10 M
-1
K
15 eq
ass
-
F
0
550
575
600
625
650
675
700
725
0.1
0.2
0.3
0.4
0.5
-
1/[F ]
Wavelength (nm)
Fig. 6 Fluorescence (λex = 420 nm) titration of 1 (25 μM) with F−
(as a n-bu4N+ salt) in DMSO
Fig. 7 Benesi–Hildebrand plots (λem=574 nm) of 1 using Eq. 1,
assuming 1:1 stoichiometry for association between 1 and F−
ethanol solution (Фs=0.89) [43]. With increase of F− concen-
tration, the emission intensity increased gradually and when 15
equiv. of F− was added, the emission intensity almost remain
unchanged, and the fluorescence quantum yield was increased
to 0.37.
[F−]0 shows a liner relationship, indicating that 1 asso-
ciates with F− in a 1:1 stoichiometry. The association
constant, K, between 1 and F−, is determined from the
ratio of intercept/slope to be 1.02 × 104 M− 1. The detec-
tion limit, based on the definition by IUPAC (CDL = 3
Sb/m) [45], was found to be 2.8 × 10− 7 M from 10 blank
solutions.
The 1:1 stoichiometry of probe 1 with F− is confirmed
by the Benesi–Hildebrand analysis [44]. When assuming a
1:1 association between 1 and F−, the Benesi–Hildebrand
equation is given as follows:
To test the practical applicability, the competition
experiments of F−mixed with other anions were also car-
ried out from fluorescence spectra and the results were
shown in Fig. 8. When 1 (25 μM) was treated with 15
equiv of F− in the presence of the same concentration
of other anions, the F−- induced fluorescence response
of 1 was almost unaffected by the presence of the other
anions except for AcO− and H2PO4−. The results indicate
that the binding of F− to 1 is much stronger than that of
other anions.
[
]
1
1
1
=
+ 1
Fl − Fl0
Fl∞ − Fl0 K[F−]0
FI0 is the fluorescence intensity of 1, FI∞ is the inten-
sity measured with excess amount of F−, FI is the inten-
sity measured with F−, K is the association constant
(M− 1), and [F−]0 is the concentration of F− added (M). It
can be seen from Fig. 7, the plot of 1/ (FI–FI0) against 1/
The fluoride ion binding to probe 1 was also monitored
by 1H NMR titration studies in DMSO–d6. The systematic
1 3

J Fluoresc
Fig. 8 Fluorescent response of
1 (25 μM) to F− (15 equiv) in
the presence of various anions
(15 equiv) in DMSO (λex
574 nm)
=
changes in 1H NMR signals of 1 upon addition of increas-
ing amounts of fluoride ion were shown in Fig. 9. The
signal of proton on the pyrazolic N–H (Ha) was decreased
significantly to be a broad peak at 13.80 ppm upon addi-
tion of 5 equiv. of fluoride, and disappeared entirely upon
addition of 15 equiv. of fluoride. Furthermore, a typical
triplet influenced by F− was appeared at 16.15 ppm
with a coupling constant J = 120 Hz appeared, which
was ascribed to the FHF− dimer. These observations
indicated that the first added F− establishes an H-bond
interaction with the pyrazolic NH of 1, while an excess
of F− induces the proton transfer reaction [46]. When
e
d
-Ha
c
-Ha
b
-Ha
a
Fig. 9 Change in partial 1H NMR spectra of 1 (25 μM) in DMSO-d6 upon addition of (a) 0, (b) 5.0, (c) 10.0, (d) 15.0, and (e) 20.0 equiv of F−
(as a n-bu4N+salt)
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J Fluoresc
Fig. 10 Optimized geometries
of the receptor–additive com-
plexes at the B3LYP/6- 31G*
level of theory. The selected
bond distances (Å) of the cor-
responding species are shown
2.07
0.99
1.03
1.58
1+F-
1+Cl-
N-H=1.03 Å; H…Cl-=2.07 Å
N-H=1.58 Å; H…F-=0.99 Å
2.34
1.03
1.78
1.03
1+Br-
1+OAc-
N-H=1.03 Å; H…Br-=2.34 Å
N-H=1.03 Å; H…OAc-=1.78 Å
-NH is deprotonated, the electron density is increased.
This leads to the intramolecular charge transfer in the
whole system and the red shift of absorption spectrum.
At the same time, the electron density of aromatic ring
is greatly increased and the hydrogens on aromatic ring
shift upfield significantly. This explains the changes in
the UV–vis titration of 1 with F−.
could conclude from these data the deprotonation of the
acidic pyrazolic N–H protons of sensor 1 and the forma-
tion of HF. In the case of other receptor-additive (sen-
sor–X−, where X− = Cl−, Br−, and OAc−) species, bond
length suggested weak recognition occurred through
weakly hydrogen bonded complexes.
To clarify the mechanism for the changes in absorp-
tion and fluorescence spectra of 1, electronic properties
of ground state and excited state of 1 and 1-F− complex
were also studied by ab initio molecular orbital calcu-
lation. Figure 11 shows the HOMO–LUMO orbitals of
sensor 1 and 1-F− complex, and energy level diagrams
of HOMO and LUMO orbitals of sensor 1 and 1-F− com-
plex. As summarized in Fig. 11, upon F− interaction, the
HOMO and LUMO energy level increases significantly
from − 5.997 to − 1.770 eV and − 2.270 to 1.354 eV,
respectively. As a result of this, the HOMO–LUMO gap
of decreases (3.726→3.124 eV). This may therefore lead
to red shift of the absorption spectrum and an intense
fluorescence enhancement can be observed.
To determine whether the recognition process in the
system was mediated through the hydrogen-bonding
interaction between probe 1 and F− or proton abstraction
from pyrazolic N–H of sensor 1 to the fluoride ion, the
theoretical calculations had been performed exploiting
the density function theory (DFT) calculations, the cal-
culation results are shown in Fig. 10. The N–H distance
was 1.01 Å in the structure of sensor 1, and the H–F
distance was 0.99 Å and the N–H distance was 1.58 Å
in the structure of sensor–F−. And normal H–F bond
and N–H bond distances were generally around 0.92 and
0.98 Å, respectively, whereas a typical NH…F− hydro-
gen– bond distance ranges from 1.73 to 1.77 Å. So, we
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J Fluoresc
LUMO
1.354eV
LUMO
Egap=3.124eV
-2.270eV
Egap=3.726eV
HOMO
-1.770eV
HOMO
-5.997eV
Fig. 11 HOMO–LUMO orbitals of probe 1 and 1-F− complex, and energy level diagrams of HOMO and LUMO orbitals of probe 1 and 1-F−
complex, calculated on the DFT level using a B3LYP/6-31G* level of theory
Conclusion
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