A novel near-infrared chemosensor for mercury ion detection based on D-A structure of triphenylamine and benzothiadiazole

Article abstract of DOI:10.1016/j.tet.2017.03.088

A novel near infrared ratiometric fluorescent chemosensor based on triphenylamine, thiophene and benzothiadiazole has been developed. The emission wavelength of sensor DTPAT-BT-S was in the near infrared region. The wavelength changed from 656?nm to 723?n

Full text of DOI:10.1016/j.tet.2017.03.088

Tetrahedron 73 (2017) 2824e2830
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A novel near-infrared chemosensor for mercury ion detection based
on D-A structure of triphenylamine and benzothiadiazole
Qisong Zhang, Jian Zhang, Hujin Zuo, Chengyun Wang, Yongjia Shen*
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel near infrared ratiometric fluorescent chemosensor based on triphenylamine, thiophene and
benzothiadiazole has been developed. The emission wavelength of sensor DTPAT-BT-S was in the near
infrared region. The wavelength changed from 656 nm to 723 nm, and got a rather long stokes shift about
170 nm. The sensor showed a very high selectivity towards Hg2þ ions.
Received 10 February 2017
Received in revised form
27 March 2017
Accepted 31 March 2017
Available online 1 April 2017
© 2017 Elsevier Ltd. All rights reserved.
Keywords:
Ratiometric
Near-infrared
Triphenylamine
Benzothiadiazole
Mercury-sensing
1. Introduction
These compounds consist of electron donating (D) and electron
accepting (A) components connected by a
p conjugation bridge,
The development of highly sensitive and selective chemical
sensors for heavy metal ions or toxic elements has been received
considerable attention owing to their quick response, operation
simplicity, low cost, non-destructive and real-time monitoring.1,2
These metals usually play important a role in living systems and
have potential high toxicity in environment and Biosystems.3e6
Mercury, one of the common toxic elements in the environment,
contaminates the atmosphere, soil and water ubiquitously. The
accumulation of mercury ion in human body could induce various
diseases, such as prenatal brain damage, serious cognitive, motion
disorders and minamata disease.7e9
have been used in a vast array of organic electronic materials
including field effect transistors, light emitting diodes, fluorescent
sensors and so on. The modular nature of donor-acceptor systems
means they can offer an exceptional tunability by altering the donor
acceptor groups or even
p bridge to produce the desired properties.
A colorimetric and ratiometric chemosensor with D-A-D struc-
ture has been developed by our group in the previous work.25 It
showed a fluorescence wavelength around 600 nm, and changed
into 650 nm when added with Hg2þ. The fluorescence wavelength
could hardly reach the near infrared region, so we planned to
modify the molecule to make a bathochromic shift. The most effi-
Moreover, new fluorescent chemosensors are preferred for a
ratiometric response due to the ratio between two emission in-
tensities, which can correct the sensor analytic concentration as
well as environmental effects such as polarity, photo-bleaching and
temperature. Although many efforts has been done to develop
ratiometric chemosensors for Hg2þ, very few near infrared che-
cient way to make a bathochromic shift is to extend the p conju-
gation of molecule. According to the research of Wang26 we knew
that thiophene had great merits in tuning the energy gap of the D-
p-A-p-D type of chromophores as it can extend the p conjugation
and promote or stabilize the quinoid structure. Indeed, the fluo-
rescence wavelength shifted about 80 nm when inserted with the
bridge of thiophene.
p
mosensors exhibited a sensitive ratiometric response to Hg2þ 10ꢀ19
.
Therefore, it is highly expected to develop reversible ratiometric
We have developed such a near-infrared ratiometric fluorescent
chemosensor DTPAT-BT-S (4,40-(5,50-(5-(bis(ethylthio)methyl)
benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(thiophene-5,2-diyl))
chemosensors that detect Hg2þ 20ꢀ24
.
bis(N,N-diphenylaniline)) by the strategy of extending
p conjuga-
tion of D-A structure with triphenylamine and benzothiadiazole.
The emission wavelength of sensor DTPAT-BT-S was extended to
* Corresponding author.
E-mail address: yjshen@ecust.edu.cn (Y. Shen).
http://dx.doi.org/10.1016/j.tet.2017.03.088
0040-4020/© 2017 Elsevier Ltd. All rights reserved.

Q. Zhang et al. / Tetrahedron 73 (2017) 2824e2830
2825
the near infrared region (over 650 nm) along with a large Stokes
shifts (170 nm).
Hg2þ caused the red shift (about 70 nm) in the emission spectrum,
the majority of which was found in the near infrared region
(>650 nm).
The development of novel chromophores with appropriate units
for selective detection remains an important goal for Hg2þ sensors.
Herein, we have designed and synthesized a novel sensor system
utilizing mercury-promoted desulfurization reaction as outlined in
Scheme 1. The DTPAT-BT-S was prepared as red solid with a high
yield (78%). The structure of DTPAT-BT-S was fully confirmed by
NMR spectroscopy and mass spectrometry.
4. Selectivity
Excess metal ion salts (2 equiv.) of Kþ, Naþ, Agþ, Co2þ, Mn2þ
,
Zn2þ, Ca2þ, Pb2þ, Ni2þ, Mg2þ, Cu2þ, Cr3þ, Al3þ, Fe3þ were added to
the sensor to investigate the selectivity. However, only the Hg2þ
promoted a bathochromic shift in the UVevis absorbance from
489 nm to 535 nm under identical conditions (Fig. 4).
2. Experimental
Fig. 5 showed the fluorescent intensity spectra of sensor DTPAT-
BT-S when added with different metal ions. Similarly, the fluores-
cent intensity band centered at 656 nm decreased and band
centered at 723 nm increased only when the Hg2þ was added.
As can be seen in Fig. 6, the results of Hg2þ competitive exper-
iments showed Hg2þ was not influenced by other metal ions (Kþ,
2.1. Materials
All chemical reagents and solvents were purchased from com-
mercial suppliers and were used without further purification un-
less otherwise mentioned. Tetrahydrofuran was dried with metal
sodium and fresh-distilled prior to use. All moisture-sensitive and
air-sensitive reactions were carried out under argon atmosphere.
Inorganic salts including NaNO3, KNO3, AgNO3, CoCl2$6H2O, Ca(N-
Naþ, Agþ, Co2þ, Mn2þ, Zn2þ, Ca2þ, Pb2þ, Ni2þ, Mg2þ, Cu2þ, Cr3þ
Al3þ Fe3þ). Sensor showed high Hg2þ selectivity chemo-
,
,
a
dosimetric response even under other metal ions. The selectivity
indicated that sensor DTPAT-BT-S, maintained at a concentration of
O3)2$4H2O,
Cu(NO3)2$3H2O,
Pb(NO3)2,
Ni(NO3)2$6H2O,
CrCl3,
Zn(NO3)2$6H2O,
Fe(NO3)3$9H2O,
Al(NO3)3$9H2O,
10
m
M, can be used for the analysis of micromolar concentrations of
.
MnSO4$2H2O, MgSO4, and Hg(ClO4)2$3H2O were dissolved in wa-
Hg2þ
ter, before use.
5. Detection limit
2.2. Instrumentation
The detection limit of the fluorescent spectrum changes calcu-
1H NMR and 13C NMR spectra were measured on a Bruker AM-
400 spectrometer using d-chloroform as a solvent and tetrame-
lated on the basis of 3
s/K, where
s
is the relative standard devia-
tion and K is the slope of the calibration curve. So the detection
thylsilane (TMS,
d
¼ 0 ppm) as an internal standard. The UVevis
limit was determined to be 0.36
Fig. 7.
m
M for Hg2þ, which can be seen in
spectra were recorded on a Varian CARY 100 spectrophotometer at
room temperature. Fluorescence-emission was detected on Varian
Cary Eclipse spectrophotometer at room temperature in a mixed
solvent of THF/H2O (99:1, v/v). The structure of DTPAT-BT-S con-
tained triphenylamine, thiophene and benzothiadiazole moieties
was synthesized as Scheme 2. The detailed information can be seen
in ESI.
For the avoidance of doubt, although so many cations (Kþ, Naþ,
Agþ, Co2þ, Mn2þ, Zn2þ, Ca2þ, Pb2þ, Ni2þ, Mg2þ, Cu2þ, Cr3þ, Al3þ
,
Fe3þ) were tested for selectivity, we cannot exclude the interfer-
ence of other thiophile ions, such as Cd2þ, Auþ and so on. The
mercury ions reacted with DTPAT-BT-S in such a short time that the
response time of all the experiments was in several seconds.
6. Fluorescence quantum yield
3. Titration
As shown in Fig. 1, the UV/vis spectrum of sensor DTPAT-BT-S
alone showed a maximum characteristic absorption peak at
489 nm (responsible for the red color of the solution) due to the
The quantum yield of sensor DTPAT-BT-S in THF was observed to
be 0.112, and the quantum yield of the production DTPAT-BT-Ald (In
Scheme 3) was 0.0665. Rh 6G (Rhodamine 6G) in ethanol (4 ¼ 0.89,
lex ¼ 495 nm) was used as the standard.
structure (D-p-A-p-D) of triphenylamine and benzothiadiazole.
Upon addition of increasing concentration of Hg2þ, a new absorp-
tion band centered at 535 nm appeared, with an isosbestic point
appearing at about 503 nm attributed to the desulfurization reac-
tion of DTPAT-BT-S. Hence, the color of the solution changes
simultaneously from red to violet, which is perceptible to the naked
eye (Fig. 3).
Fluorescence quantum yield was determined in each case by
comparing the corrected spectrum with that of Rhodamine 6G
(
fF ¼ 0.95) in EtOH by taking the area under total emission using
the following equation:
ꢀ
ꢁ
2
FsAR hs
F As hR
R
fs ¼ fR
As shown in Fig. 2, upon excitation at 587 nm, the sensor
showed a band centered at 656 nm. Upon addition of Hg2þ the
fluorescence intensity at around 656 nm was reduced evidently and
a new band centered at 723 nm was produced. Thus, addition of
where fS and fR are the radiative quantum yields, FS and FR are the
area under the fluorescence spectra, AS and AR are the absorbance
Scheme 1. Reaction of sensor DTPAT-BT-S with Hg2þ
.

2826
Q. Zhang et al. / Tetrahedron 73 (2017) 2824e2830
Scheme 2. Synthetic route of sensor DTPAT-BT-S.
(at the excited wavelength) of the respective sample and the
reference; hS and hR are the refractive indices of the solvent used
for the sample and the reference.
dithioacetal signal at 1.19 ppm (Ha), 2.61 ppm (Hb) and 5.6 ppm (Hc)
of adjacent CeH bond, which was disappeared finally with the
addition of 3.5 equiv. of Hg2þ, while a new signal increased at
10.4 ppm (Hf), corresponding to the proton of aldehyde. Also the
original aromatic protons showed a downfield shift, which was in
accordance with previous studies that dithioacetal (Donor)
changed into aldehyde (acceptor).
7. Sensing mechanism
To demonstrate the mechanism which the sensor follows, we
analyzed accordingly with 1H NMR titration. Fig. 8 shows the 1H
NMR of DTPAT-BT-S upon the addition of Hg2þ in a solution
(CDCl3/DMSO-d6 99:1 [v/v]). Scheme 3 shows the mechanism of
reaction. The addition of Hg2þ resulted in a slow oxidation of the
8. Conclusions
In summary, a novel near infrared ratiometric Hg2þ probe

Q. Zhang et al. / Tetrahedron 73 (2017) 2824e2830
2827
Fig. 1. Absorption spectra of DTPAT-BT-S (1 ꢁ 10ꢀ5 M) in a THF/H2O (99:1 [v/v]) upon
Fig. 4. Absorption spectra of DTPAT-BT-S (1 ꢁ 10ꢀ5 M) in a THF/H2O (99:1 [v/v]) upon
gradual addition of increasing amounts of Hg2þ ions (from 0 to 1.4 equiv.).
addition of 2.0 equiv. of various cations.
Fig. 5. Emission spectra (lex ¼ 587 nm) of DTPAT-BT-S (1 ꢁ 10ꢀ5 M) in a THF/H2O (99:1
Fig. 2. Emission spectra of DTPAT-BT-S (1 ꢁ 10ꢀ5 M) in a THF/H2O (99:1 [v/v]) solution
upon gradual addition of increasing amounts of Hg2þ ions (from 0 to 1.4 equiv.).
[v/v]) upon addition of 2.0 equiv. of various cations.
Fig. 6. The fluorescence responses of DTPAT-BT-S (1 ꢁ 10ꢀ5 M) upon the addition of
2.0 equiv. of Hg2þ and other interfering cations in a THF/H2O (99:1 [v/v]) solution at
25 ꢂC (DTPAT-BT-S þ other cations, red bar; DTPAT-BT-S þ other cations þ Hg2þ, violet
bar).
Fig. 3. Naked-eye visible and fluorescent
(
lex
¼
365 nm) images of DTPA-BT-S
(1 ꢁ 10ꢀ5 M) upon the addition of 2.0 equiv. of Hg2þ and other interfering cations in
a THF/H2O (99:1 [v/v]) at 25 ꢂC.
manipulates ICT (intramolecular charge transfer) to afford an
emission bands shift for ratiometric detection of Hg2þ. DTPAT-BT-S
could react, in principle, with 1.4 equiv. of Hg2þ. Furthermore, the
oxidation of Hg2þ to the dithioacetal moiety induces a conspicuous
emission spectra change (band centered at 656 nm shifted to
723 nm), and it has a large stokes shift about 170 nm. The detection
(DTPAT-BT-S), containing triphenylamine (donor), thiophene (p)
and benzothiadiazole (acceptor) was designed and synthesized,
and this is a new strategy for Hg2þ detection. The modulation of
such electron features in the context of aldehyde revealing process

2828
Q. Zhang et al. / Tetrahedron 73 (2017) 2824e2830
Fig. 7. The ratio (I723/I656) of DTPAT-BT-S (1 ꢁ 10ꢀ5 M) upon the addition of Hg2þ (from
0.4 to 1 equiv.).
Fig. 8. 1H NMR spectra changes of DTPAT-BT-S in a solution (CDCl3/DMSO-d6 99:1 [v/
v]), upon the addition of Hg2þ ions.
sodium and distilled immediately prior to use. All moisture-
sensitive and air-sensitive reactions were carried out under argon
atmosphere.
1H NMR and 13C NMR spectra were measured on a Bruker AM-
400 spectrometer using d-chloroform as a solvent and tetrame-
thylsilane (TMS,
d
¼ 0 ppm) as an internal standard. The UVevis
spectra were recorded on a Varian CARY 100 spectrophotometer at
room temperature. Fluorescence-emission was detected on the
Varian Cary Eclipse spectrophotometer at room temperature in
acetonitrile.
9.1. Synthesis
9.1.1. Synthesis of 5-methylbenzo[c][1,2,5]thiadiazole (1)
To a 250 mL three-neck flask were added commercial 4-
methylbenzene-1,2-diamine (3.75 g, 0.03 mol), 60 mL of CH2Cl2
and, trimethylamine (13.14 g, 0.13 mol). The solution was stirred
until total dissolution of the diamine Sulfurous dichloride (11.47 g,
0.10 mol) was added dropwise very slowly and the mixture refluxed
for 5 h. After quenching the reaction with 1 mol/L sodium hy-
droxide solution, the solvent was extracted
3 times with
dichloromethane (30 mL) and removed by rotary evaporation. The
residue was purified by silica gel column chromatography using
pure petroleum ether as eluant to collect a brown needle solid,
yield 3.69 g (82%). m.p. 33e34 ꢂC; 1H NMR (CDCl3, 400 MHz, TMS):
Scheme 3. Mechanism of DTPAT-BT-S desulfurization reaction.
d
7.88 (d,1H, J ¼ 9 Hz), 7.76 (s, 1H), 7.43 (d, 1H, J ¼ 9 Hz), 2.55 (s, 3H);
13C NMR (CDCl3, 100 MHz, TMS):
d 155.31, 153.54, 139.94, 132.41,
120.66, 119.76, 21.91; EI-MS [Mþ] Calcd. 150.0252, Found 150.0251.
limit of the fluorescent spectrum changes calculated on the basis of
3s/K is 0.36 m
M for Hg2þ. Comparing to the competitive experi-
ments, DTPAT-BT-S showed fast response, good selectivity and
outstanding anti-interference performance.
9.1.2. Synthesis of 4,7-dibromo-5-methylbenzo[c][1,2,5]thiadiazole
(2)
To a 250 mL three-neck flask was added 5-methyl-benzothia-
diazole (6.0 g, 0.04 mol) and HBr (75 mL, 47%). A solution con-
taining Br2 (22.21 g, 0.12 mol) in HBr (10 mL) was added dropwise
very slowly. After addition was complete, solution was stirred and
heated under reflux for 6 h. Precipitation of a lot of solid was noted.
After the reaction was cooled to room temperature, sufficient
9. Materials and instrumentation
All chemical reagents and solvents were purchased from com-
mercial suppliers and were used without further purification un-
less it is noted by other way. Tetrahydrofuran was dried with metal

Q. Zhang et al. / Tetrahedron 73 (2017) 2824e2830
2829
saturated solution of sodium bisulfite was added to consume excess
100 MHz, TMS):
d
154.00, 150.30, 138.57, 136.30, 135.45, 129.80,
liquid bromine. The mixture was filtrated and washed with water.
The solid was then washed once with cold Et2O and dried and the
residue purified by silica gel column chromatography using pure
petroleum ether as eluent to collect a pale yellow powder, yield
0.612 g (71%); m.p. 150e151 ꢂC; 1H NMR (CDCl3, 400 MHz, TMS):
129.12, 128.64, 127.09, 126.64, 125.78, 123.42, 114.54, 114.37, 30.26;
EI-MS [Mþ] Calcd.547.7321, Found 547.7323.
9.1.6. Synthesis of 4,7-bis(5-bromothiophen-2-yl)benzo[c][1,2,5]
thiadiazole-5-carbaldehyde(6)
d
7.78 (s, 1H), 2.62 (s, 3H); 13C NMR (CDCl3, 100 MHz, TMS):
d
153.41,
5-(bromomethyl)-4,7-bis(5-bromothiophen-2-yl)benzo[c]
[1,2,5]thiadiazole (1.1 g, 2 mmol) and DMSO (30 mL) was added to a
100 mL three-neck flask. After refluxed for 30 min, the mixture was
extracted with water and dichloromethane. The solvent was
removed by rotary evaporation, and the residue was purified by
silica gel column chromatography using petroleum ether-CH2Cl2
(2:1 (v/v)) as eluent to give a red powder, yield 0.45 g (46%); m.p.
151.53, 140.43, 135.14, 114.22, 112.60, 22.67; EI-MS [Mþ] Calcd.
305.8462, Found 305.8461.
9.1.3. Synthesis of 5-methyl-4,7-di(thiophen-2-yl)benzo[c][1,2,5]
thiadiazole(3)
To a mixture of 4,7-dibromo-5-methylbenzo[c][1,2,5]thiadia-
zole (1.5 g, 4.8 mmol) in THF (20 mL) and aqueous 2 M potassium
carbonate solution (25 mL) was added thiophen-2-ylboronic acid
(1.84 g, 14.4 mmol) in THF (20 mL) under an argon atmosphere.
211e212 ꢂC; 1H NMR (CDCl3, 400 MHz, TMS):
1H), 7.91 (d, 2H, J ¼ 4 Hz), 7.23 (d, 1H, J ¼ 4 Hz), 7.19e7.16 (m, 2H);
13C NMR (CDCl3, 100 MHz, TMS):
189.73, 153.64, 138.55, 133.16,
d 10.18 (s, 1H), 8.31 (s,
d
Subsequently,
tetrakis(triphenylphosphine)palladium
(0)
132.80, 132.08, 129.84, 129.33, 129.01, 127.35, 125.57, 121.39, 117.30,
28.68; EI-MS [Mþ] Calcd. 483.8009, Found 489.8003.
(261.9 mg, 0.23 mmol) was added to the mixture. After the mixture
was refluxed for 12 h, the reaction mixture was poured into water
and extracted with dichloromethane. The organic layer was dried
over anhydrous sodium sulfate and evaporated to dryness. The
residue was purified by silica gel column chromatography using
petroleum ether-CH2Cl2 (4:1 (v/v)) as eluent to give a bright yellow
powder, yield 1.25 g (83%); m.p. 112e113 ꢂC; 1H NMR (CDCl3,
400 MHz, TMS):
J ¼ 4 Hz), 7.47 (d, 1H, J ¼ 4 Hz), 7.32 (d, 1H, J ¼ 4 Hz), 7.24e7.21 (m,
2H), 2.61 (s, 3H); 13C NMR (CDCl3, 100 MHz, TMS):
155.89, 151.04,
9.1.7. Synthesis of 4,7-bis(5-(4-(diphenylamino)phenyl)thiophen-2-
yl)benzo[c][1,2,5]thiadiazole-5-carbaldehyde(7)
To a mixture of 4,7-bis(5-bromothiophen-2-yl)benzo[c][1,2,5]
thiadiazole-5-carbaldehyde (0.49 g, 1 mmol) in THF (20 mL) and
aqueous 2 M potassium carbonate solution (25 mL) was added 4-
diphenylaminophenylboronic acid (0.9 g, 3 mmol) in THF (20 mL)
d
8.14 (d, 1H, J ¼ 4 Hz), 7.82 (s, 1H), 7.54 (d, 1H,
under
an
argon
atmosphere.
Subsequently,
tetrakis(-
d
triphenylphosphine)palladium (0) (78.58 mg, 0.068 mmol) was
added to the mixture. After the mixture was refluxed for 12 h, the
reaction mixture was poured into water and extracted with
dichloromethane. The organic layer was dried over anhydrous so-
dium sulfate and evaporated to dryness. The residue was purified
by silica gel column chromatography using petroleum ether-CH2Cl2
(2:1 (v/v)) as eluent to give a violet powder, yield 0.6 g (74%); m.p.
139.07, 138.19, 136.90, 129.82, 129.08, 128.05, 127.86, 126.96, 126.90,
126.80, 126.07, 124.42, 21.14; EI-MS [Mþ] Calcd. 314.0006, Found
314.0005.
9.1.4. Synthesis of 4,7-bis(5-bromothiophen-2-yl)-5-methylbenzo
[c][1,2,5]thiadiazole(4)
5-methyl-4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole
(3.2 g, 0.01 mol) was dissolved to dichloromethane (30 mL) into a
250 mL three-neck flask. A solution containing Br2 (3.3 g, 0.02 mol)
in dichloromethane (10 mL) was added dropwise very slowly. After
addition was completed, solution was stirred under reflux for
30 min. Precipitation of a lot of orange solid was noted. After the
reaction was finished, sufficient saturated solution of sodium
bisulfite was added to consume excess liquid bromine. The mixture
was extracted with dichloromethane and washed with water. The
residue was purified by silica gel column chromatography using
ether-CH2Cl2 (4:1 (v/v)) as eluent to collect an orange powder, yield
3.8 g (81%); m.p. > 160e162 ꢂC; 1H NMR (CDCl3, 400 MHz, TMS):
208e209 ꢂC; 1H NMR (CDCl3, 400 MHz, TMS):
d 10.40 (s, 1H), 8.42
(s, 1H), 8.19 (d, 1H, J ¼ 4 Hz), 7.58 (dd, 4H, J1 ¼ 4 Hz, J2 ¼ 8 Hz),
7.38e7.26 (m, 11H), 7.16e7.07 (m, 16H); 13C NMR (CDCl3, 100 MHz,
TMS): d 191.54, 155.00, 153.89, 150.02, 148.17, 147.35, 147.28, 146.68,
134.26, 133.56, 131.16, 129.71, 129.41, 129.38, 127.20, 126.85, 126.68,
124.84, 124.74, 123.46, 123.34, 123.14, 122.53, 29.70; EI-MS [Mþ]
Calcd. 814.1895, Found 814.1893.
9.1.8. Synthesis of 4,40-(5,50-(5-(bis(ethylthio)methyl)benzo[c]
[1,2,5]thiadiazole-4,7-diyl)bis(thiophene-5,2-diyl))bis(N,N-
diphenylaniline) (8)
After 4,7-bis(5-(4-(diphenylamino)phenyl)thiophen-2-yl)benzo
[c][1,2,5]thiadiazole-5-carbaldehyde (0.2 g, 0.25 mmol) was dis-
solved in DCM (30 mL) with a 100 mL three-neck flask, a solution
containing p-toluenesulfonic acid (0.017 g, 0.1 mmol) and ethane-
thiol (0.043 g, 0.7 mmol) was added, and the reaction mixture was
stirred at 25 ꢂC under an argon atmosphere overnight. The solvent
was removed by rotary evaporation, and the residue was purified
by silica gel column chromatography using petroleum ether-CH2Cl2
(1:1 (v/v)) as eluent to give a red powder, yield 0.18 g (78%); m.p.
d
7.84 (d, 1H, J ¼ 4 Hz), 7.72 (s, 1H), 7.17 (dd, 2H, J1 ¼ 4 Hz, J2 ¼ 8 Hz),
7.08 (d, 1H, J ¼ 4 Hz), 2.61 (s, 3H); 13C NMR (CDCl3, 100 MHz, TMS):
d
150.62, 140.22, 138.38, 138.24, 130.77, 129.84, 129.54, 129.17,
127.72, 125.46, 123.71, 114.81, 114.09, 99.99, 21.21; EI-MS [Mþ]
Calcd. 469.8216, Found 469.8220.
9.1.5. Synthesis of 5-(bromomethyl)-4,7-bis(5-bromothiophen-2-yl)
benzo[c][1,2,5]thiadiazole(5)
A mixture of 4,7-bis(5-bromothiophen-2-yl)-5-methylbenzo[c]
[1,2,5]thiadiazole (4.7 g, 0.01 mol), N-bromosuccinimide (NBS;
2.13 g, 0.012 mol) and benzoyl peroxide (BPO; 300 mg, 1.3 mmol)
was added to a 100 mL three-neck flask, which was dissolved in
carbon tetrachloride (100 mL). The mixture was heated at reflux for
17 h under argon atmosphere. The solution was filtered and the
filtrate concentrated by rotary evaporation. The residues were pu-
rified by silica gel column chromatography using petroleum ether-
CH2Cl2 (4:1 (v/v)) as eluent to give a reddish orange solid, yield
4.26 g (77%); m.p. 186e188 ꢂC; 1H NMR (CDCl3, 400 MHz, TMS):
241e242 ꢂC; 1H NMR (CDCl3, 400 MHz, TMS):
d 8.35 (s, 1H), 8.14 (d,
1H, J ¼ 4 Hz), 7.58 (dd, 4H, J1 ¼ 20 Hz, J2 ¼ 8 Hz), 7.35e7.29 (m, 11H),
7.16e7.04 (m, 16H), 5.57 (s, 1H), 2.61 (m, 4H), 1.19 (t, 6H); 13C NMR
(CDCl3, 100 MHz, TMS):
d 155.36, 151.50, 147.66, 147.41, 146.90,
146.16, 140.93, 137.26, 133.44, 130.57, 129.36, 129.25, 128.02, 127.87,
127.32, 126.70, 125.95, 124.64, 123.47, 123.25, 123.24,123.12, 122.95,
122.20, 29.70, 26.71,14.48; ESI-MS [MþNaþ] Calcd. 921.2242, Found
921.2248.
Acknowledgements
d
7.88 (s, 1H), 7.86 (d, 1H J ¼ 4 Hz), 7.30 (d, 1H, J ¼ 4 Hz), 7.22 (d, 1H,
J ¼ 4 Hz), 7.19 (d, 1H, J ¼ 4 Hz), 4.71 (s, 2H), 13C NMR (CDCl3,
The project was supported by National Natural Science

2830
Q. Zhang et al. / Tetrahedron 73 (2017) 2824e2830
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