A new selective pyrazoline-based fluorescent chemosensor for Cu 2+ in aqueous solution

Article abstract of DOI:10.1016/j.dyepig.2012.09.019

A new pyrazoline derivate was designed and synthesized. The structure of the pyrazoline was confirmed by single crystal X-ray diffraction and its photophysical properties were studied by absorption and fluorescence spectra. This compound can be used to determine Cu²⁺ ion with high selectivity and sensitivity among a series of cations in aqueous tetrahydrofuran. This sensor forms a 1:1 complex with Cu²⁺ and displays fluorescent quenching.

Full text of DOI:10.1016/j.dyepig.2012.09.019

Dyes and Pigments 96 (2013) 509e515
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
A new selective pyrazoline-based fluorescent chemosensor for Cu2þ in aqueous
solution
,
a
a
a
b,
**
Shengli Hu a , Shushu Zhang , Yang Hu , Qing Tao , Anxin Wu
*
a Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, Department of Chemical and Environmental Engineering, Hubei Normal University, Huangshi 435002, PR China
b Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new pyrazoline derivate was designed and synthesized. The structure of the pyrazoline was confirmed
by single crystal X-ray diffraction and its photophysical properties were studied by absorption and
fluorescence spectra. This compound can be used to determine Cu2þ ion with high selectivity and
sensitivity among a series of cations in aqueous tetrahydrofuran. This sensor forms a 1:1 complex with
Cu2þ and displays fluorescent quenching.
Received 27 July 2012
Received in revised form
25 September 2012
Accepted 27 September 2012
Available online 6 October 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Pyrazoline
Fluorescent sensor
Copper ion detection
Selective
1. Introduction
compounds widely used in fluorescence dyes emitting blue
fluorescence with high fluorescence quantum yield [33,34]; addi-
The selective detection of transition and heavy metal ions is very
important in various fields of chemical and biological science as
well as in the protection of our environment [1]. Cu2þ is an
important transition metal ion because it is not only an environ-
mental pollutant at high concentrations [2,3], but also an essential
trace element for many biological process and systems [4,5].
Therefore, many studies concerning Cu2þ sensing by synthesized
colorimetric/fluorescent probes based on quinoline [6], fluorescein
[7], pyrene [8,9], rhodamine [10e16], azobenzene [17,18], coumarin
[19e21], 1,8-naphthalimide [22e25], anthraquinone [26e29] and
other fluorophores [30,31] have been reported and investigated.
However, there is still an intense demand for new efficient Cu2þ
optical chemosensors, especially those that are simple to synthe-
size, and can work in aqueous solution with high selectivity and
sensitivity; very important factors for potential biological applica-
tions [32]. Studies related to this area are a great challenge and
continue to be of widespread interest.
tionally these compounds have found application in electrolumi-
nescence [35e39]. However, to the best of our knowledge, only
a few examples have been reported on the interactions between
pyrazoline derivatives and zinc ion [40e42]. Herein, we report the
synthesis of two new pyrazoline derivative 1 and 2, and study the
properties of their UVevis absorption and fluorescence emission.
Compound 1 can be used to determine Cu2þ ion with high selec-
tivity and a low detection limit in aqueous solution.
2. Experimental
2.1. Apparatus
NMR spectra were measured on a Varian Mercury 300 spec-
trometer operating at 300 MHz for 1H and 75 MHz for 13C relative to
tetramethylsilane as internal standard.
HRMS were obtained on an Apex-Ultra MS equipped with an
electrospray source. IR spectra were recorded on a PerkineElmer
PE-983 infrared spectrometer as KBr pellets with absorption re-
ported in cmꢀ1. All pH measurements were made with a Model
PHS-3C pH meter (Shanghai, China) and operated at room
temperature about 298 K. Absorption spectra were determined on
UV-2501 PC spectrophotometer. Fluorescence spectra measure-
ments were performed on a FluoroMax-P spectrofluorimeter
equipped with a xenon discharge lamp, 1 cm quartz cells at room
1,3,5-Triaryl-2-pyrazolines, with their rigid but only partly
unsaturated central pyrazoline ring, are well-known fluorescent
* Corresponding author. Tel./fax: þ86 (0) 714 6515602.
** Corresponding author. Tel./fax: þ86 (0) 27 67867773.
E-mail addresses: hushengli168@126.com (S. Hu), chwuax@mail.ccnu.edu.cn
(A. Wu).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.09.019

510
S. Hu et al. / Dyes and Pigments 96 (2013) 509e515
temperature (about 298 K). The X-ray crystal structure determi-
nations of 1 were obtained on a Bruker SMART APEX CCD system.
7.10e7.34 (m, 2H, AreH), 7.41e7.50 (m, 7H, AreH), 7.64e7.67 (m,
1H, AreH); 13C NMR (CDCl3),
(ppm): 163.2, 152.6, 152.5, 141.2,
d
131.7, 131.2, 130.1, 128.9, 128.7, 127.8, 126.5, 125.9, 125.6, 121.8, 120.8,
120.1, 63.6, 43.7; HRMS (ESI): m/z [M þ H]þ calcd for C22H18N3S:
356.1216; found: 356.1217.
2.2. Reagents
Deionized water was used throughout the experiments. All the
reagents were purchased from commercial suppliers and used
without further purification. The salts used in stock solutions of
metal ions were CoCl2$6H2O, ZnCl2, MnCl2$4H2O, KCl, NaCl,
CuCl2$2H2O, NiCl2$6H2O, CdCl2$2H2O, HgCl2, FeCl3$6H2O,
MgCl2$6H2O, CrCl3$6H2O, Pb(NO3)2. HEPES (4-(2-hydroxyethyl)-1-
piperazineethanesulfonic acid) buffer solution (pH ¼ 7.4) was
prepared using 20 mM HEPES, and proper amount of aqueous
sodium hydroxide under adjustment by a pH meter.
2.4. X-ray diffraction analysis of compound 1
Suitable single crystals of 1 for X-ray structural analysis were
obtained by slow evaporation of a solution of 1 in CHCl3eCH3OH
(20:1, v/v) mixture at room temperature. The diffraction data was
collected with a Bruker SMART CCD diffractometer using a graphite
ꢀ
monochromated MoK
a
radiation (
l
¼ 0.71073 A) at 296(2) K. The
structures were solved by direct methods with SHELXS-97 program
and refinements on F2 were performed with SHELXL-97 program
by full-matrix least-squares techniques with anisotropic thermal
parameters for the non-hydrogen atoms. All H atoms were initially
located in a difference Fourier map. All H atoms were placed in
geometrically idealized positions and constrained to ride on their
2.3. Synthesis of pyrazoline derivatives 1 and 2
The synthetic route to compounds 1 and 2 is shown in Scheme 1.
Starting materials 2-hydrazinobenzothiazole (3) [43], chalcone (4)
[44] and chalcone (5) [45] were prepared according to the litera-
ture. To a stirred solution of chalcone (4) and (5) (1.0 mmol) in
AcOH (15 mL) was added 2-hydrazinobenzothiazole (3) (0.165 g,
1.0 mmol). The reaction mixture was heated under reflux for 6 h.
The progress of the reaction was monitored by TLC. After comple-
tion, the reaction mixture was cooled to room temperature and the
solvent was evaporated in vacuo, and the crude product was
washed with water, and consequently recrystallized from ethanol
to afford pure compound 1 as a white solid (24.1 mg, 0.65 mmol,
65%) and compound 2 as a white solid (24.9 mg, 0.70 mmol, 70%).
2-(1-(Benzo[d]thiazol-2-yl)-5-phenyl-4,5-dihydro-1H-pyrazol-
3-yl)phenol (1). M.p.:206e207 ꢁC; IR (nmax, KBr, cmꢀ1): 3214, 1599,
ꢀ
parent atoms, with CeH ¼ 0.93 A and Uiso(H) ¼ 1.2 Ueq(C).
2.5. Binding titration
The stock solutions of 1 and 2(1.0 ꢂ 10ꢀ5 M) were prepared by
dissolving 1 and 2 in THF/water (9:1, v/v) containing HEPES buffer
(10 mM, pH ¼ 7.4), respectively. The cationic stocks were all in H2O
with a concentration of 3.0 ꢂ 10ꢀ3 M for UVevis absorption and
fluorescence spectra analysis. For metal ion absorption and fluo-
rescence titration experiments, each time 3 mL solution of 1 and 2
were filled in a quartz cell of 1 cm optical path length, and we
increased concentrations of metal ions by stepwise addition of
different equivalents using a micro-syringe. After each addition of
Cu2þ ion, the solution was stirred for 3 min. The volume of cationic
1531,1440, 1316, 755; 1H NMR (CDCl3),
d
(ppm): 3.44 (dd,1H, J ¼ 5.4,
5.4 Hz, pyridine-H), 4.05 (dd, 1H, J ¼ 12.0, 12.0 Hz, pyridine-H), 5.81
(dd, 1H, J ¼ 5.1, 5.1 Hz, pyrazoline-H), 6.90e6.93 (m, 1H, AreH),
7.08e7.38 (m, 10H, AreH), 7.52e7.55 (m, 1H, AreH), 7.64e7.67
stock solution added was less than 100
mL with the purpose of
keeping the total volume of testing solution without obvious
change. For all measurements of fluorescence spectra of 1 and 2, the
excitation was at 355 nm and 349 nm, respectively.
(m, 1H, AreH), 10.06 (s, 1H, OH); 13C NMR (CDCl3),
d (ppm):
162.3, 157.5, 154.8, 152.2, 140.6, 131.9, 131.3, 128.9, 128.1, 128.0,
125.9, 125.8, 122.2, 120.8, 120.2, 119.7, 117.1, 115.1, 62.2, 44.1; HRMS
(ESI): m/z [M þ H]þ calcd for C22H18N3OS: 372.1165; found:
372.1168.
3. Results and discussion
2-(3,5-Diphenyl-4,5-dihydropyrazol-1-yl) benzo[d]thiazole (2).
3.1. Synthesis and structural characteristics of 1 and 2
M.p.:186e187 ꢁC; IR (nmax, KBr, cmꢀ1): 3080, 2385, 1601, 1537, 1440,
1274, 1126, 870, 753; 1H NMR (CDCl3),
5.1 Hz, pyridine-H), 3.93 (dd, 1H, J ¼ 11.7, 12.0 Hz, pyridine-H), 5.83
d
(ppm): 3.30 (dd, 1H, J ¼ 5.1,
The 3, 5-diaryl pyrazoline derivative 1 was obtained by the
reaction of chalcone (4) with 2-hydrazinobenzothiazole (3) in
AcOH under reflux. To understand the crucial role of both the
(dd, 1H, J ¼ 5.1, 5.1 Hz, pyrazoline-H), 7.05e7.08 (m, 1H, AreH),
O
N
N
AcOH, reflux
65%
N
N
NHNH2
+
S
S
OH
OH
1
3
4
O
AcOH, reflux
70%
N
N
N
S
5
2
Scheme 1. Synthesis of pyrazoline derivates 1 and 2.

S. Hu et al. / Dyes and Pigments 96 (2013) 509e515
511
Table 1
phenol and thiazole providing a suitable binding site for metal ions,
Crystal structure data and structure refinement for 1.
compound 2 was also prepared from chalcone (5) with 2-
hydrazinobenzothiazole (3) in the same way. The yields of 1 and
2 were 65% and 70%, respectively. The structures of 1 and 2 were
identified by using 1H NMR, IR and MS. The structure of 1 was
further confirmed by X-ray diffraction analysis.
The X-ray molecular view of 1 is shown in Fig. 1. A summary of
crystallographic data collection parameters and refinement
parameters for 1 is compiled in Table 1.
Compound 1 crystallized in an orthorhombic space group Pbcn.
One benzene moiety, one phenol ring and a benzothiazole moiety
are bonded to the pyrazoline ring at the atoms of C8, C10 and N2,
respectively. Consistent with a pronounced electronic interaction,
the bond lengths of C10eC11, N2eC7 are significantly shorter as
would be expected for a single bond. Moreover, the bond lengths of
N2eN3, N3eC10, C8eC9 agree well with the equivalent ones in
similar structures [46]. In the crystal of 1, torsion angle C7eN2e
C8eC17 of 67.9(3)ꢁ shows C7 in the benzothiazole moiety adopts
an synperiplanar conformation with respect to the C17 atom of the
benzene ring. In the asymmetry unit, the pyrazoline ring, phenol
ring and benzothiazole are almost coplanar. And the pyrazoline
ring makes dihedral angles with phenol and thiazole of 5.19(11)ꢁ
and 4.54(12)ꢁ, respectively, while the dihedral angle between pyr-
azoline and benzene moiety is 87.89(10)ꢁ.
Empirical formula
Formula weigh
Temperature
C22H17N3OS
371.45
296(2) K
0.71073
Orthorhombic
Pca2(1)
26.585 (5)
9.5587 (17)
7.0731 (12)
90ꢁ
90ꢁ
90ꢁ
ꢀ
Wavelength (A)
Crystal system
Space group
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a
b
g
3
ꢀ
V (A )
1797.4 (5)
4
Z
Density (calculated)
Index ranges
F(000)
1.373 Mg/m3
ꢀ22 ꢃ h ꢃ 28, ꢀ13 ꢃ k ꢃ 13, ꢀ18 ꢃ l ꢃ 18
776
Crystal size
0.16 ꢂ 0.12 ꢂ 0.05 mm
q
Range for data collection
1.53e25.26ꢁ
Reflections collected
11,100
Independent reflections
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
3253 [R(int) ¼ 0.0351]
0.9902 and 0.9691
3253/1/246
1.063
Absorption correction
None
Final R indices (I > 2
R indices (all data)
Largest diff. peak and hole
s
(I))
R1 ¼ 0.0304, wR2 ¼ 0.0752
R1 ¼ 0.0381, wR2 ¼ 0.0782
ꢀꢀ3
Regarding the crystal structure of 1, there is one intramolecular
O1eH1/N3 hydrogen bond forming a pseudo six-membered ring.
The packing diagram of compound 1 is shown in Fig. 2. The
0.153 and ꢀ0.155 e A
molecules are connected by weak
interaction. Cl5/Cg4 3.661(2) A C18/Cg2 2.998(2) A.
p/p interactions and CeH/p
no hydroxyl group in the phenyl ring and exhibits two broad band
at 294 nm (log
any significant changes in absorption and fluorescence emissions
upon addition to 1 equiv of copper ion as shown in Fig. 3, which
indicates the importance of a phenolic group as a binding site at the
3 position of the pyrazoline ring.
ꢀ
ꢀ
3
¼ 4.69) and 350 nm (log ¼ 4.42), did not revealed
3
3.2. Spectral characteristics
Initial studies on the UVevis absorption and fluorescent emis-
sion revealed that 1 showed selectivity toward Cu2þ ions in THF/
The UVevis absorption spectra of compound 1 (1 ꢂ 10ꢀ5 M) in
the presence of various concentrations of Cu2þ ion (0e3 ꢂ 10ꢀ5 M)
is shown in Fig. 4 and the inset shows the plots of changes in 352
and 400 nm maxima as a function of increasing concentrations of
Cu2þ. The absorbance of compound 1 at 352 nm gradually
decreases with an increasing concentration of Cu2þ ion. Moreover,
two isobestic points appears at 328 nm and 380 nm; new absorp-
tion peaks appear in the range 250e328 nm and 380e450 nm, and
their absorption intensity gradually increases or decreases with the
water (9:1, v/v). As shown in Fig. 3, in the absence of Cu2þ
,
compound 1 exhibits a broad band at 352 nm (log
3
¼ 4.48).
Coordination of copper cation to 1 resulted in the formation of
a new absorption band at 400 nm and synchronous decrease in the
absorption band at 352 nm. In contrast to 1, compound 2, which has
Fig. 1. The molecular structure of compound 1, with displacement ellipsoids drawn at
Fig. 2. A packing diagram for 1, viewed along the a-axis. Dashed lines show arrays of
the 30% probability level.
hydrogen bonds.

512
S. Hu et al. / Dyes and Pigments 96 (2013) 509e515
b
a
294 nm
0.5
294 nm
0.5
0.4
0.3
0.2
0.1
0.0
0.4
0.3
0.2
0.1
0.0
352 nm
350 nm
350 nm
400nm
400
352 nm
275
300
325
350
375
425
450
475
275
300
325
350
375
400
425
450
475
Wavelength (nm)
Wavelength (nm)
d
c
438 nm
1800
1800
1500
1200
900
600
300
0
446 nm
446 nm
1500
1200
900
600
300
0
438 nm
450
375
400
425
475
500
525
550
575
600
375
400
425
450
475
500
525
550
575
600
Wavelength (nm)
Wavelength (nm)
Fig. 3. UVevis spectra of compound 1(d) and 2 (
(10 mM, pH ¼ 7.4). Fluorescence spectra of 1(d) and 2 (
pH ¼ 7.4).
) (1 ꢂ 10ꢀ5 M) (a) in the absence, and (b) in the presence of 1 equiv of CuCl2 in THF/water (9:1, v/v) containing HEPES buffer
) (c) in the absence and (d) in the presence of 1 equiv of CuCl2 in THF/water (9:1, v/v) containing HEPES buffer (10 mM,
addition of Cu2þ ion, respectively. This absorption peak is likely due
to the coordination of compound 1 with Cu2þ ion.
The fluorescence titration spectra of 1 with Cu2þ shows an
emission maximum peak at 438 nm (Fig. 5a). The fluorescence
quantum yield (Fu) of 1 in the absence of Cu2þ was calculated to be
0.20 with respect to quinine sulfate in 0.1 N H2SO4 solution
0.5
0.4
0.3
0.2
0.1
0.0
(
Fs ¼ 0.54) [47]. As Cu2þ ion was gradually titrated, the fluorescence
intensity of compound 1 gradually decreased and when the amount
of Cu2þ ion added was about 1 ꢂ10ꢀ5 M, the fluorescence intensity
almost reached a minimum. The quantum yield of 1 was calculated
to be 0.025 in the presence of Cu2þ ion (1 ꢂ 10ꢀ5 M) and almost
reduced to 12% of the initial one. When more Cu2þ was titrated, the
fluorescence intensity showed negligible changes. The nonlinear
curve fitting of the fluorescence titration (inset) gives a 1:1 stoi-
chiometric ratio between compound 1 and Cu2þ. Moreover, a Job’s
plot [48], which exhibits a maximum at 0.5 M fraction of Cu2þ
,
further indicates that only a 1:1 complex is formed (Fig. 5b). Based
on the above fluorescence titration of 1 with Cu2þ, the association
constant was calculated to be 9.3 ꢂ 104
M
ꢀ1(error limits ꢃ10%)by
275
300
325
350
375
400
425
450
475
a BenesieHildebrand plot [49] (Fig. 6). The detection limit, based on
the definition by IUPAC (CDL ¼ 3 Sb/m) [50], was found to be
8.7 ꢂ 10ꢀ8 M from 10 blank solutions.
Wavelength(nm)
Fig. 4. UVevis titration of compound 1 (1 ꢂ 10ꢀ5 M) in THF/water (9:1, v/v) containing
HEPES buffer (10 mM, pH ¼ 7.4) with increasing amount of Cu2þ (0e3 ꢂ 10ꢀ5 M). Inset:
Absorbance plot of compound 1 against increasing of Cu2þ at lmax 352 and 400 nm.
The selectivity and tolerance of compound 1 for copper ion over
other metal cations were investigated by adding metal cations

S. Hu et al. / Dyes and Pigments 96 (2013) 509e515
513
a
1800
1500
1200
900
600
300
0
438 nm
0
Cu2+
2eq
375
400
425
450
475
500
525
550
575
600
Wavelength (nm)
b
700
600
500
400
300
200
100
0
Fig. 7. UVevis spectral changes of compound 1 (1 ꢂ 10ꢀ5 M) in THF/water (9:1, v/v)
containing HEPES buffer (10 mM, pH ¼ 7.4) upon additions of various metal ions
(1 ꢂ 10ꢀ5 M).
(5 ꢂ 10ꢀ5 M) to the solution of compound 1(1 ꢂ 10ꢀ5 M). As
depicted in Fig. 7, there was no obvious new absorption band at
400 nm and synchronous decrease in the absorption band at
352 nm with any other metal ions.
Fig. 8 shows that Cu2þ produced significant quenching in the
fluorescent emission of 1, the other tested metals only show rela-
tively insignificant changes. This means that sensor 1 has a high
selectivity to Cu2þ ion. And from the photograph shown in Fig. 8,
we can see the stronger blue emission of compound 1 without
addition of Cu2þ ion under the irradiation at 365 nm than with
addition of 1 ꢂ 10ꢀ5 M Cu2þ ion.
0.0
0.2
0.4
0.6
0.8
1.0
X = [ 1] /{ [1] +[ Cu2+] }
To further gauge selectivity for copper ion over other metal ions,
competition experiments of Cu2þ ion mixed with other metal ions
were carried out from fluorescence spectra and the results are
shown in Fig. 9. The fluorescence intensity of 1 (1 ꢂ 10ꢀ5 M) in the
presence of 1 equiv of the Cu2þ ion was almost unaffected by the
Fig. 5. (a)Fluorescence emission spectra of 1 (10ꢀ5 M) was titrated with Cu2þ (0e
2.0 equiv.) in THF/water (9:1, v/v) containing HEPES buffer (10 mM, pH ¼ 7.4). Inset:
variations of fluorescence intensity of compound 1 (10ꢀ5 M) at 438 nm vs. equivalents
of [Cu2þ] [1]. (b) Job’s plot for determining the stoichiometry for 1 and Cu2þ in THF/
addition of 5 equiv of competing metal ions (Kþ, Naþ, Cd2þ, Fe3þ
,
water (9:1, v/v) containing HEPES buffer (10 mM, pH
¼
7.4). Total
concentration ¼ 1.0 ꢂ 10ꢀ5 M.
1800
1, K+,Na+, Cr3+, Mg2+,
0.0040
Mn2+, Ni2+, Pb ,
2
Zn2+, Cd2+, Co2+,
1500
Cu2+, Fe3+, Hg
2+
0.0035
y = 3.12×10-4 + 3.34×10-4x
1200
900
R = 0.99702
0.0030
K
= 9.3×104 M-1
ass
0.0025
0.0020
0.0015
0.0010
0.0005
600
Cu2+
300
0
375
400
425
450
475
500
525
550
575
600
Wavelength (nm)
0
1
2
3
4
5
6
7
8
9
10
11
Fig. 8. Fluorescence spectra of 1 (1 ꢂ 10ꢀ5 M) in THF/water (9:1, v/v) containing HEPES
buffer (10 mM, pH ¼ 7.4) in the presence of different metal ions (1 equiv). Inset: Photos
of 1 in THF/water (9:1, v/v) containing HEPES buffer (10 mM, pH ¼ 7.4) without and
with addition of Cu2þ under the irradiation of UV light at 365 nm.
[ Cu2+] -1/ ×105M-1
Fig. 6. BenesieHildebrand linear analysis plots of 1 at different Cu2þ concentration.

514
S. Hu et al. / Dyes and Pigments 96 (2013) 509e515
1800
1500
1200
900
600
300
0
1eq
EDTA
0
375
400
425
450
475
500
525
550
575
600
Wavelength(nm)
Fig. 11. Fluorescence spectra of 1ꢀCu2þ(10ꢀ5 M in THF/water (9:1, v/v) containing
HEPES buffer (10 mM, pH ¼ 7.4), excitation at 389 nm, buffered by 10 mM HEPES, pH
7.4) upon addition of EDTA (0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 equiv).
Fig. 9. Competitive experiments in the 1 þ Cu2þ system with interfering metal ions.
[1] ¼ 1 ꢂ 10ꢀ5 M, [Cu2þ] ¼ 1 ꢂ 10ꢀ5 M, and [Mnþ] ¼ 5 ꢂ 10ꢀ5 M. Excited at 355 nm and
emission collected at 438 nm.
to the stronger complexation of Cu2þ ion with EDTA than with
sensor 1.
Mn2þ, Mg2þ, Co2þ, Ni2þ, Hg2þ, Pb2þ and Zn2þ). These results sug-
gested that molecule 1 could be used as Cu2þ selective fluorescent
chemosensor.
Additionally, in order to explore the effects of anionic counter-
ions on the sensing behavior of compound 1 to Cu2þ ion, fluores-
cence responses of compound 1 to sulfate, chloride, and nitrate
salts of copper were conducted in the THF/water (9:1, v/v) con-
taining HEPES buffer (10 mM, pH ¼ 7.4). As can be seen from Fig. 10,
there were no obvious changes in the fluorescence responses of
compound 1 to CuSO4, CuCl2, and Cu(NO3)2.
To investigate the mechanism of the fluorescence quenching for
1, Cu2þ may be easily establish coordinative interactions with the
phenol, pyrazoline, and benzo[d]thiazole moiety than other metal
ions examined, the capture of Cu2þ resulted in the electron or
energy transfer from 1 to Cu2þ; thus, 1 showed quenching of the
fluorescence for Cu2þ and provided a high selectivity for Cu2þ over
the other tested metal ions.
4. Conclusion
To gain further insight into the fluorescent signaling behavior of
compound 1 toward Cu2þ ion, the effect of EDTA on the fluores-
cence signaling of the 1ꢀCu2þ system was investigated. When
1 ꢂ 10ꢀ5 M EDTA was added into the 1ꢀCu2þ system, the fluores-
cence intensity increased to the fluorescence intensity of
compound 1 without Cu2þ ion as shown in Fig. 11. This is attributed
In summary, a new highly selective fluorescent sensor based on
a pyrazoline unit was synthesized and used for the determination
of Cu2þ ion with high selectivity and a low detection limit in THF/
water (9:1, v/v) containing HEPES buffer (10 mM, pH ¼ 7.4). This
sensor formed a 1:1 complex with Cu2þ and showed a fluorescent
quenching with good tolerance of other metal ions. Moreover, this
sensor is very sensitive with fluorometric detection limit of
8.7 ꢂ 10ꢀ8 M.
1800
1
1+ CuSO4
Acknowledgments
1500
1200
900
600
300
0
1+ Cu
1+ CuCl2
( NO3)
2
We thank the National Natural Science Foundation of China
(Grant No. 20872042) and the Hubei Province Education Ministry
Foundation of China (Grant No. D20112507) for financial support.
Appendix A. Supplementary material
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2012.09.019.
References
[1] de Silva AP, Gunaratne HQN, Gunnlaugsson T, Huxley AJM, McCoy CP,
Rademacher JT, et al. Signaling recognition events with fluorescent sensors
and switches. Chem Rev 1997;97:1515e66.
[2] High B, Bruce D, Richter MM. Determining copper ions in water using elec-
trochemiluminescence. Anal Chim Acta 2001;449:17e22.
[3] Tapia L, Suazo M, Hodar C, Cambiazo V, Gonzalez M. Copper exposure
modifies the content and distribution of trace metals in mammalian cultured
cells. Biometals 2003;16:169e74.
375
400
425
450
475
500
525
550
575
600
Wavelength(nm)
Fig. 10. Fluorescence spectra of 1 (10ꢀ5 M) in THF/water (9:1, v/v) containing HEPES
buffer (10 mM, pH ¼ 7.4) in the presence of different copper salts (10ꢀ5 M). Excited at
355 nm.

S. Hu et al. / Dyes and Pigments 96 (2013) 509e515
515
[4] Sigel H, editor. Metal ions in biological systems. Properties of copper, vol. 12.
New York: Dekker; 1981.
[28] Kaur N, Kumar S. A differential receptor for selective and quantitative multi-
ion analysis for Co2þ and Ni2þ/Cu2þ. Tetrahedron Lett 2008;49:5067e9.
[29] Wu SP, Du KJ, Sung YM. Colorimetric sensing of Cu (II): Cu (II) induced
deprotonation of an amide responsible for color changes. Dalton Trans 2010;
39:4363e8.
[30] Ballesteros E, Moreno D, Gomez T, Rodriguez T, Rojo J, Garcia-Valverde M,
et al. A new selective chromogenic and turn-on fluorogenic probe for cop-
per(II) in water-acetonitrile 1:1 solution. Org Lett 2009;11:1269e72.
[31] Guo ZQ, Chen WQ, Duan XM. Highly selective visual detection of Cu(II)
utilizing intramolecular hydrogen bond-stabilized merocyanine in aqueous
buffer solution. Org Lett 2010;12:2202e5.
[32] Wang HH, Xue L, Fang ZJ, Li GP, Jiang H. A colorimetric and fluorescent che-
mosensor for copper ions in aqueous media and its application in living cells.
New J Chem 2010;34:1239e42.
[33] Ji SJ, Shi HB. Synthesis and fluorescent property of some novel benzothiazoyl
pyrazoline derivatives containing aromatic heterocycle. Dyes Pigment 2006;
70:246e50.
[5] Waggoner DJ, Bartnikas TB, Gitlin JD. The role of copper in neurodegenerative
disease. Neurobiol Dis 1999;6:221e30.
[6] Park JS, Jeong S, Dho S, Lee M, Song C. Colorimetric sensing of Cu2þ using
a cyclodextrin-dye rotaxane. Dyes Pigment 2010;87:49e54.
[7] Kim MH, Noh JH, Kim S, Ahn S, Chang S-K. The synthesis of crown ether-
appended dichlorofluoresceins and their selective Cu2þ chemosensing. Dyes
Pigment 2009;82:341e6.
[8] Martinez R, Zapata F, Caballero A, Espinosa A, Tarraga A, Molina P. 2-Aza- 1,3-
butadiene derivatives featuring an anthracene or pyrene unit: highly selective
colorimetric and fluorescent signaling of Cu2þ cation. Org Lett 2006;8:3235e8.
[9] Lin WC, Wu CY, Liu ZH, Lin CY, Yen YP. A new selective colorimetric and
fluorescent sensor for Hg2þ and Cu2þ based on a thiourea featuring a pyrene
unit. Talanta 2010;81:1209e15.
[10] Xiang Y, Tong A, Jin P, Ju Y. New fluorescent rhodamine hydrazone chemosensor
for Cu (II) with high selectivity and sensitivity. Org Lett 2006;8:2863e6.
[11] Zeng X, Dong L, Wu C, Mu L, Xue SF, Tao Z. Highly sensitive chemosensor for
Cu(II) and Hg(II) based on the tripodal rhodamine receptor. Sens Actuators B
2009;141:506e10.
[34] Bian B, Ji SJ, Shi HB. Synthesis and fluorescent property of some novel bis-
chromophore compounds containing pyrazoline and naphthalimide groups.
Dyes Pigment 2008;76:348e52.
[12] Chen X, Jou MJ, Lee H, Kou S, Lim J, Nam SW, et al. New fluorescent and
colorimetric chemosensors bearing rhodamine and binaphthyl groups for the
detection of Cu2þ. Sens Actuators B 2009;137:597e602.
[35] Pramanik S, Banerjee P, Sarkar A, Mukherjee A, Mahalanabis KK,
Bhattacharya SC. Spectroscopic investigation of 3-pyrazolyl 2-pyrazoline
derivative in homogeneous solvents. Spectrochim Acta A 2008;71:1327e32.
[36] Pokladko M, Gondek E, Sanetra J, Nizio1 J, Danel A, Kityk IV, et al. Spectral
emission properties of 4-aryloxy-3-methyl-1-phenyl-1Hpyrazolo [3,4-b]
quinolones. Spectrochim Acta A 2009;73:281e5.
[37] Gong ZL, Zheng LW, Zhao BX, Yang DZ, Lv HS, Liu WY, et al. The synthesis, X-
ray crystal structure and optical properties of novel 1, 3,5-triaryl pyrazoline
derivatives. J Photochem Photobiol A 2010;209:49e55.
[13] Zhao M, Yang XF, He S, Wang L. A rhodamine-based chromogenic and fluo-
rescent chemosensor for copper ion in aqueous media. Sens Actuators B 2009;
135:625e31.
[14] Zhou Y, Wang F, Kim Y, Kim SJ, Yoon J. Cu2þ-selective ratiometric and “off-on”
sensor based on the rhodamine derivative bearing pyrene group. Org Lett
2009;11:4442e5.
[15] Xiang Y, Li Z, Chen X, Tong A. Highly sensitive and selective optical chemosensor
for determination of Cu2þ in aqueous solution. Talanta 2008;74:1148e53.
[16] Xu Z, Zhang L, Guo R, Xiang T, Wu C, Zheng Z, et al. A highly sensitive and
selective colorimetric and off-on fluorescent chemosensor for Cu2þ based on
Rhodamine B derivative. Sens Actuators, B 2011;156:546e52.
[17] Lee SJ, Lee SS, Jeong IY, Lee JY, Jung JH. Azobenzene coupled chromogenic
receptors for the selective detection of copper (II) and its application as
a chemosensor kit. Tetrahedron Lett 2007;48:393e6.
[18] Lee SJ, Jung JH, Seo J, Yoon I, Park KM, Lindoy LF, et al. A chromogenic mac-
rocycle exhibiting cation-selective and anion-controlled color change: an
approach to understanding structure-color relationships. Org Lett 2006;8:
1641e3.
[38] Liu WY, Xie YS, Zhao BX, Wang BS, Lv HS, Gong ZL, et al. The synthesis, X-ray
crystal structure and optical properties of novel 5-aryl-1-arylthiazolyl-3-
ferrocenyl-pyrazoline derivatives. J Photochem Photobiol A 2010;214:135e44.
[39] Wang PF, Onozawa-Komatsuzaki N, Himeda Y, Sugihara H, Arakawa H. Kasuga
K.3-(2-Pyridyl)-2-pyrazoline derivatives: novel fluorescent probes for Zn2þ
ion. Tetrahedron Lett 2001;42:9199e201.
[40] Shi HB, Ji SJ, Bian B. Studies on transition metal ions recognition properties of
1-(2-benzothiazole)-3-(2-thiophene)-2-pyrazoline derivatives. Dyes Pigment
2007;73:394e6.
[41] Gong ZL, Zhao BX, Liu WY, Lv HS. A new highly selective “turn on” fluorescent
sensor for zinc ion based on a pyrazoline derivative. J Photochem Photobiol A
2011;218:6e10.
́
́
́
[19] Lin W, Yuan L, Cao X, Tan W, Feng Y. A coumarin-based chromogenic sensor
for transition-metal Ions showing ion-dependent bathochromic shift. Eur J
Org Chem 2008;29:4981e7.
[20] Jung HS, Kwon PS, Lee JW, Kim JI, Hong CS, Kim JW, et al. Coumarin-derived
Cu2þ-selective fluorescence sensor: synthesis, mechanisms, and applications
in living cells. J Am Chem Soc 2009;131:2008e12.
[42] Gong ZL, Ge F, Zhao BX. Novel pyrazoline-based selective fluorescent sensor
for Zn2þ in aqueous media. Sens Actuators B 2011;159:148e53.
[43] Li DF, Jiang GJ, Li JS. Synthesis of 1-(2-benzothiazolyl)-3-phenyl pyrazoline
and its derivatives. Chem J Chin Univ 1990;11:205e7.
[44] Hasan A, Khan KM, Sher M, Maharvi GM, Nawaz SA, Choudhary MI, et al.
Synthesis and inhibitory potential towards acetylcholinesterase butyr-
ylcholinesterase and lipoxygenase of some variably substituted chalcones.
J Enzym Inhib Med Chem 2005;20:41e4.
[45] Budakoti A, Bhat AR, Azam A. Synthesis of new 2-(5-substituted-3-phenyl-2-
pyrazolinyl)-1,3-thiazolino[5,4-b]quinoxaline derivatives and evaluation of
their antiamoebic activity. Eur J Med Chem 2009;44:1317e25.
[46] Fahrni CJ, Yang L, VanDerveer DG. Tuning the photoinduced electron-transfer
thermodynamics in 1,3,5-triaryl-2-pyrazoline fluorophores: X-ray structures,
photophysical characterization, computational analysis, and in vivo evalua-
tion. J Am Chem Soc 2003;125:3799e812.
[47] Crosby GA, Demas JN. Measurement of photoluminescence quantum yields.
Rev J Phys Chem 1971;75:991e4.
[48] Job P. Formation and stability of inorganic complexes in solution. Ann Chim
1928;9:113e203.
[49] Benesi HA, Hildebrand JH. A spectrophotometric investigation of the interac-
tion of iodine with aromatic hydrocarbons. J Am Chem Soc 1949;71:2703e7.
[50] Joshi BP, Park J, Lee WI, Lee KH. Ratiometric and turn-on monitoring for heavy
and transition metal ions in aqueous solution with a fluorescent peptide
sensor. Talanta 2009;78:903e9.
[21] Helal A, Or Rashid MH, Choi CH, Kim HS. Chromogenic and fluorogenic
sensing of Cu2þ based on coumarin. Tetrahedron 2011;67:2794e802.
[22] Xu Z, Xiao Y, Qian X, Cui J, Cui D. Ratiometric and selective fluorescent sensor
for CuII based on internal charge transfer (ICT). Org Lett 2005;7:889e92.
[23] Huang J, Xu Y, Qian X. A colorimetric sensor for Cu2þ in aqueous solution
based on metal ion-induced deprotonation: deprotonation/protonation
mediated by Cu2þ-ligand interactions. Dalton Trans 2009:1761e6.
[24] Xu Z, Pan J, Spring DR, Cui J, Yoon J. Ratiometric fluorescent and colorimetric
sensors for Cu2þ based on 4, 5-disubstituted-1, 8-naphthalimide and sensing
cyanide via Cu2þ displacement approach. Tetrahedron 2010;66:1678e83.
[25] Zhang JF, Zhou Y, Yoon J, Kim Y, Kim SJ, Yoon J. Naphthalimide modified
rhodamine derivative: ratiometric and selective fluorescent sensor for Cu2þ
based on two different approaches. Org Lett 2010;12:3852e5.
[26] Kaur N, Kumar S. Near-IR region absorbing 1,4-diaminoanthracene-9,10-
dione motif based ratiometric chemosensors for Cu2þ. Tetrahedron 2008;64:
3168e75.
[27] Kaur N, Kumar S. Single molecular colorimetric probe for simultaneous esti-
mation of Cu2þ and Ni2þ. Chem Commun 2007:3069e70.