A novel Hg2+ fluorescence sensor TPE-TSC based on aggregation-induced emission

Article abstract of DOI:10.1080/10426507.2018.1487428

A fluorescent sensor TPE-TSC with aggregation induced emission (AIE) characteristic is synthesized for detecting Hg²⁺ by attaching thiosemicarbazide (TSC) unit into tetraphenylethylene (TPE) group. TPE-TSC exhibits intense green emission in DMS

Full text of DOI:10.1080/10426507.2018.1487428

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
2+
A novel Hg fluorescence sensor TPE-TSC based on
aggregation-induced emission
Jie Ma, Yulan Zeng, Luliang Yan, Bingkun Chen, Mengya Sun, Zhenhua Liu &
Shuping Zhang
To cite this article: Jie Ma, Yulan Zeng, Luliang Yan, Bingkun Chen, Mengya Sun, Zhenhua
2+
Liu & Shuping Zhang (2018): A novel Hg fluorescence sensor TPE-TSC based on
aggregation-induced emission, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2018.1487428
To link to this article: https://doi.org/10.1080/10426507.2018.1487428
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Jul 2018.
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2
+
A novel Hg fluorescence sensor TPE-TSC based on aggregation-induced emission
Jie Ma*,Yulan Zeng, Luliang Yan, Bingkun Chen,Mengya Sun,Zhenhua Liu andShuping Zhang
*Corresponding author Jie Ma: School of Science, University of Shanghai for Science and
Technology, Shanghai, 200093, P. R. China，e-mail: majie@usst.edu.cn
Luliang Yan, Bingkun Chen：School of Science, University of Shanghai for Science and
Technology, Shanghai, 200093, P. R. China
Abstract: A fluorescent sensor TPE-TSC with aggregation induced emission (AIE)
2
+
characteristic is synthesized for detecting Hg by attaching thiosemicarbazide (TSC)
unit into tetraphenylethylene (TPE) group. TPE-TSC exhibits intense green emission
in DMSO/H O (V:V=1:9) solution with the formation of the aggregation. TPE-TSC
2
2
+
shows outstanding fluorescence quenching toward Hg over other metal ions due to
the formation of complex TPE-TSC/Hg with a 2:1 binding ratio. The detection limit
of TPE-TSC for Hg is 1×10 mol·L .
2
+
2
+
-5
-1
2
+
Keywords: Hg ；Tetraphenylethylene；Mannich reaction；Aggregation induced
emission (AIE).
Introduction
Fluorescence-based sensors have recently attracted considerable attention due to
1
their ability in detecting heavy metal ions . Among these heavy metal ions, mercury is
regarded as one of the most toxic ones, and even at the ppm level it has a detrimental
effect on the cardiovascular system, kidneys, the immune system as well as the central
2
, 3
nervous system in humans . Compared with most traditional analytical methods,
4
such as inductively coupled plasma mass spectrometry , atomic absorption
5
6
spectroscopy and electrochemical analysis , fluorescence sensors for mercury
7
detection can have high sensitivity and facile operation . For these reasons, many
fluorescence sensors for detecting mercury in the aqueous medium have been
8
9
designed, which are based on the photo induced electron transfer , energy transfer ,
1
0
and internal charge transfer mechanisms. However, many of the known fluorescence
sensors show low sensitivity to mercury in high concentration or aggregation due to
the aggregation-caused quenchin g（ ACQ） . In addition, fluorescent sensors based on
1
1
the aggregation induced emission (AIE) are rarely designed and applied for mercury
1
2
detection .
Herein, we report the design and synthesis of a new fluorescent sensor TPE-TSC
2
+
for the highly selective detection of Hg , where the AIE-active tetraphenylethylene
TPE) group is modified with the thiosemicarbazide (TSC) unit based on the Mannich
reaction. TPE-TSC can aggregate and emit intense green radiation in the DMSO/H O
(
2
2
+
(
V:V=1:9) solution. In the presence of Hg , the fluorescence emission intensity of
TPE-TSC decreases gradually and is eventually quenches by increasing the ion
concentration. Meanwhile, TPE-TSC responds highly selectively and sensitively
2
+
toward Hg in aqueous medium. Thus, we provide an alternative approach for the
design and construction of a new type of ion-fluorescence probe.

Results and discussion
The synthesis of TPE-TSC is outlined in Scheme 1. 4-(1, 2, 2-triphenylvinyl)
benzaldehyde (compound 1 is first prepared from the reaction between
bromo-triphenylethylene and 4-formylphenylboronic acid in the presence of a
catalytic amount of Pd(PPh ) under the reflux in toluene. TPE-TSC is then efficiently
3
4
synthesized from compound 1 and thiosemicarbazide (TSC) through the Mannich
reaction. The chemical structures of these as-synthesized compounds are confirmed
1
13
by H-NMR, C-NMR and HRMS spectroscopic methods．
Scheme 1 Structure and synthetic of compound 1 and TPE-TSC.
-4
-1
Figure 1 TPE-TSC (1×10 mol·L in DMSO) with different fractions of water.
TPE-TSC is soluble in DMSO but not in water. The AIE characteristics of
TPE-TSC was investigated in the DMSO-H O mixture with varying water fraction.
2
As shown in Figure 1, when the water fraction in the DMSO-H O mixture increases
2
from 10% to 80%, TPE-TSC shows almost no fluorescence emission. However,
TPE-TSC shows strong fluorescence emission when the water fraction is above 90%.
Based on the above AIE behavior of TPE-TSC, further fluorescence experiments were
carried out in the DMSO/H O (V:V=1:9) mixture as the solvent.
2

-
4
-1
Figure 2 Fluorescence spectra of TPE-TSC (1×10 mol·L ) in DMSO/H O (V:V=1:9) in the
2
2+
presence of Hg (from 0 to 0.7 equiv). The plot of the fluorescence intensity at 492 nm (λ = 364
ex
2+
nm) vs the concentration of Hg .
Figure 2 shows the change in the fluorescence spectrum of TPE-TSC upon
2
+
titration with the Hg ion. TPE-TSC shows strong emission at 492 nm in the
DMSO/H O (V:V=1:9) mixture. However, intensity of the fluorescence emission of
2
2
+
TPE-TSC gradually decreases with the increasing concentration of Hg . In fact, the
fluorescence emission intensity of the mixture decreases almost linearly with the
relavite coefficient (R ) of ~0.973 when the concentration of Hg change from 0 to
2
2+
-5
-1
-5
-1
2
.5×10 mol∙L . When the ion concentration is beyond 3×10 mol∙L , the
fluorescence quenching phenonema of the mixed system was observed because of
hardly detected fluorescence emission. This should be attributed to the formation of
2+
complex TPE-TSC/Hg with fluorescence quenching in mixtures solvent. In
2
+
-5
-1
addition ,TPE-TSC responses toward Hg at as low as 1×10 mol∙L .
-4
-1
Figure 3 The fluorescence responses of TPE-TSC (1×10 mol·L ) upon addition of various
-3
-1
2+
-4
-1
metal ions (1×10 mol·L , 10 equiv) in the absence and presence of Hg (2×10 mol·L , 2
equiv) in DMSO/H O (V:V=1:9). (Black bars: TPE-TSC with other metals, red bars: TPE-TSC
2
2+
with other metals and Hg (λ = 364 nm).
ex

Figure 4 Fluorescent intensity of 1 in DMSO/H O (1:9, v/v) in the presence of 10.0 equiv of
2
different anions.
2
+
TPE-TSC shows selective fluorescence properties toward Hg over other metal
ions. As shown in Figure 3. For better comparison, fourteen metal ions at the same
concentration were added into the TPE-TSC and DMSO/H O (V:V=1:9) mixed media,
2
and the fluorescence intensity of these TPE-TSC media show different features. When
+
3+
2+
2+
2+
2+
2+
3+
2+
2+
2+
other metal ions such as Na , Cr , Ni , Pb , Zn , Ba , Co , Fe , Cd , Ca , Fe ,
2
+
2+
2+
Mg , Mn and Hg were added to the aqueous solution of TPE-TSC, the
fluorescence of the media was not quenched, whereas Na , Cr and Fe can enhance
the fluorescence intensity. Pb and Fe ions slightly weakens the fluorescence of
TPE-TSC. On the other hand, TPE-TSC significantly quenches the fluorescence
response to Hg . Competitative experiments was performed by adding Hg into the
+
3+
3+
2
+
2+
2
+
2+
solution of TPE-TSC in DMSO/H O (V:V=1:9) in the presence of other metal ions.
2
The result is shown in Figure. 3. As expected, other metal ions have almost no effect
2
+
on the fluorescence intensity in the presence of Hg suggesting the exclusive
2
+
selectivity of TPE-TSC toward Hg . Meanwhile, some other anions were
investigated and found to have nearly no influence on the fluorescence intensity as
shown in Figure 4. Thus, our experimental results show that the as-prepared TPE-TSC
2
+
can be used as highly selective and sensitive fluorescence sensor for the Hg ion in
the DMSO/H O (V:V=1:9) media.
2
2+
Scheme 2 Proposed binding mode of TPE-TSC with Hg

1
-3
-1
Figure 5 Partial H-NMR spectra (400 MHz) of TPE-TSC (1×10 mol·L ) in DMSO-d /D O (1:9,
6
2
+
v/v) in the presence of increasing amounts of Ag : 0; 0.1; 0.2; 0.3; 0.4; 0.5 equiv [from (1) to (6)].
2
+
Figure 6 HR-MS spectrum of the complex TPE-TSC/Hg
2
+ 1
For determining the exact binding sites between TPE-TSC and Hg , H-NMR
2
+
titration of TPE-TSC with Hg was carried out in the DMSO-d /D O (V:V=1:9)
6
2
2
+
media. As shown in Figure 5, When adding Hg (from 0 to 0.5 equiv) to the
TPE-TSC solution, the chemical shifts of thiosemicarbazide protons H and H and
a
b
the aldehyde proton H exhibit an upfield shift. Moreover, The signals of the H and
c
b
H protons are gradually upfield-shifted from 8.14 ppm to 7.91 ppm and 11.37ppm to
c
2
+
1
1.23 ppm when increasing the amount of Hg from 0 to 0.5 equiv, respectively. The
signal of the H proton becomes weaker after the gradual addition of Hg . The
2
+
a
chemical shifts of all the protons show that their chemical environments are changed
2
+
upon coordination of TPE-TSC with Hg . The change in the fluoresence signals
illustrate that the N atom connected to the aldehyde unit and the atom on the

2
+
thiosemicarbazide unit are bound to Hg . Based on these results, the coordination
2
+
structure of TPE-TSC with Hg is proposed as shown in Scheme 2. Furthermore, the
structure of this complex was further studied by high resolution mass spectrometry.
2
+
As shown in Figure 6, the complex TPE-TSC/Hg (m/z=1068) gives a molecular ion
peak[M-1] at 1067, which confirms the coordination type in Scheme 2.
Conclusions
2
+
In conclusion, a novel Hg fluorescent sensor TPE-TSC was synthesized by attaching
a thiosemicarbazide unit into the tetraphenylethylene group. TPE-TSC shows the
aggregation induced emission characteristic in the DMSO-H O media. TPE-TSC also
2
2
+
shows outstanding fluorescence quenching property toward Hg over other metal
2
+
ions due to the formation of the TPE-TSC/Hg complex with a 2:1 binding ratio. The
2
+
-5
-1
detection limit of TPE-TSC for Hg was found to be below 1×10 mol·L . The
fluorescence properties of TPE-TSC indicate that it has the potential for detecting
2
+
Hg in extremely low concentration in natural drainage system.
Experimental
All chemical reagents was purchased as analytic grade. TPE-TSC and Compound 1
were synthesized as shown below. The stock solutions of metal ions were prepared
-3
-1
(
1×10 mol·L , H O) from NaCl, NaNO , Na SO , AcONa, K CO , CrCl ·6H O,
2 3 2 4 2 3 3 2
NiCl , (CH COO) Pb·3H O, ZnSO ·7H O, BaCl , Co(NO ) ·6H O, FeCl ·6H O,
2
3
2
2
4
2
2
3 2
2
3
2
CdCl ·5H O, Hg(NO ) , CaCO , FeSO ·7H O, MgSO , and MnCl ·4H O with
2
2
3 2
1
3
4
2
4
2
2
13
doubly distilled water. H-NMR and C-NMR spectra were measured on a Bruker
spectrometer (operating at 400 and 100 MHz, respectively) at 298 K using DMSO-d6
as the solvent. UV-vis spectra were recorded using Shimadzu UV3600. TLC analysis
was carried on silica gel plates, and column chromatography was performed over
silica gel (mesh 200–300).
Synthesis of 2-(4-(1,2,2-triphenylvinyl)benzylidene)hydrazine-1-carbothioamide
(TPE-TSC)
Compound 2 (1.0 g, 2.77 mol) was dissolved in ethanol (20 ml) and
thiosemicarbazide (0.28 g, 3.05 mol) in methanol (15 mL) was added, followed by
dropwise addition of glacial acetic acid (0.4 mL). The mixture was stirred at 80 °C for
1
2 h. the solution was cooled and a precipitate was formed. The solid was separated
by filtration, washed with ice-cooled water, and dried under reduced pressure to yield
1
1
(1.1 g, 92%). H-NMR (DMSO-d , 400 MHz, ppm): δ 6.97-7.02 (m, 8H), 7.11-7.18
6
(m, 9H), 7.11-7.18 (m, 17H), 7.55-7.57 (d, J=8.4Hz, 2H), 7.92-7.95 (d, J=12.8Hz, 2H),
8
.14 (s, 1H), 11.37 (s, 1H).
1
3
C-NMR ((DMSO-d , 100 MHz, ppm): δ 127.0, 127.1, 127.2, 128.2, 128.3, 128.4,
6
1
31.0, 131.1, 131.2, 131.5, 132.8, 140.5, 141.7, 142.3, 143.3, 143.4, 143.5, 145.2.
-
HR-MS: [M-H] . Cal.:433.57, found: 432.2072.
Synthesis of 4-(1, 2, 2-triphenylvinyl) benzaldehyde (compound 1)
4
-formylphenylboronic acid (1.35 g, 9 mmol)，bromotriphenylethylene (2.01 g, 6
mmol), TBAB (0.19 g, 0.6 mmol) and 1.2 M potassium carbonate aqueous solution
40 mL) were added to a solution of toluene (40 mL). <AQ Authors to check this
(

previous senstence at proofing as the language was not clear </AQ> The mixture was
stirred at room temperature for 30 min under N gas followed by the addition of
2
-3
Pd(PPh ) (60 mg, 5.3×10 mmol). After that the mixture was heated to 90 °C for 24
3
4
h. The solution was poured into water and extracted with ethyl acetate. The organic
layer was dried over anhydrous sodium sulfate, filtered and concentrated. The residue
was purified by column chromatography with CH Cl /n-hexane (v/v = 1:3) as an
2
2
1
eluent to afford yellow powder with a yield of 90.1%. H-NMR ((DMSO-d , 400
6
MHz, ppm): δ 6.98-7.02 (m, 6H), 7.14-7.17 (m, 9H), 7.18-7.20 (d, J=7.9Hz, 2H),
7
.67-7.69 (d, J=8.2Hz, 2H), 9.89 (s, 1H).
1
3
C-NMR ((DMSO-d , 100 MHz, ppm): δ 127.3, 127.5, 128.3, 128.4, 128.5, 129.5,
6
1
31.0, 131.1, 131.9, 134.6, 140.1, 142.8, 142.9, 134.0, 143.1, 150.1, 192.87. ESI-MS:
+
[
M+H] . Cal.: 361.15, found: 361.3.
Acknowledgments
The authors are thankful to the Natural Science Foundation of Shanghai
(No.15ZR1428500) and the National Natural Science Foundation of China (No.
2
0906061) for financial supports.
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