Ultrasensitive dicyanoisophorone-based near-infrared fluorescent probe for rapid and specific detection of thiophenols in river water

Article abstract of DOI:10.1007/s11164-018-3448-3

Thiophenols are a class of highly toxic pollutant compounds, which can cause severe damage to the central nervous system and other nervous systems after long-term exposure. Therefore, it is of significance to develop an effective method to detect trace thiophenols in the environment. Herein, we synthesized a dicyanoisophorone-based near-infrared fluorescent probe (probe 1) with large stokes shift (λ_em ? λ_abs = 203?nm) for the selective detection of thiophenols. Probe 1 exhibited very high response speed (less than 200 S), sensitivity, and selectivity towards thiophenols, regardless of the presence of aliphatic thiols and other analytes. The detection limit was as low as 3.4?nM and the signal-to-background ratio of fluorescence intensity reached 30. Moreover, probe 1 displayed ultrasensitivity and high reliability in the quantitative detection of trace thiophenol in three river water samples.

Full text of DOI:10.1007/s11164-018-3448-3

Res Chem Intermed
https://doi.org/10.1007/s11164-018-3448-3
Ultrasensitive dicyanoisophorone-based near-infrared
fluorescent probe for rapid and specific detection
of thiophenols in river water
1
2
1
2
2
•
Shunzhou Chang
2
Changdong Han
2
Jinlong Zhang
•
Kaiqiang Xiang
Zhizhong Zhang
•
•
Wei Ming
Baozhu Tian
•
Xiaojun Cheng
2
•
•
Received: 27 March 2018 / Accepted: 21 April 2018
Ó Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract Thiophenols are a class of highly toxic pollutant compounds, which can
cause severe damage to the central nervous system and other nervous systems after
long-term exposure. Therefore, it is of significance to develop an effective method
to detect trace thiophenols in the environment. Herein, we synthesized a dicya-
noisophorone-based near-infrared fluorescent probe (probe 1) with large stokes shift
(
kem - kabs = 203 nm) for the selective detection of thiophenols. Probe 1 exhibited
very high response speed (less than 200 S), sensitivity, and selectivity towards
thiophenols, regardless of the presence of aliphatic thiols and other analytes. The
detection limit was as low as 3.4 nM and the signal-to-background ratio of fluo-
rescence intensity reached 30. Moreover, probe 1 displayed ultrasensitivity and high
reliability in the quantitative detection of trace thiophenol in three river water
samples.
Keywords Fluorescence probe Á Thiophenols Á Ultrasensitive Á Near-infrared
(
NIR)
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
18-3448-3) contains supplementary material, which is available to authorized users.
0
&
Baozhu Tian
baozhutian@ecust.edu.cn
Zhizhong Zhang
Zhangzhizhong333@sina.com
Jinlong Zhang
jlzhang@ecust.edu.cn
1
2
Research Institute of Physical and Chemical Engineering of Nuclear Industry, 168 JinTang
Road, Tianjin 300180, People’s Republic of China
Key Lab 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, People’s Republic of China
123

S. Chang et al.
Introduction
Thiols (including aliphaticthiols and thiophenols) are widely used in the fields of
chemical, biological, and environmental sciences [1, 2]. Thereinto, aliphaticthiols
(
including cysteine, homocysteine, and glutathione) have aroused tremendous
interest due to their essential roles in many physiological processes of living
organisms [3–8]. On the contrary, thiophenols are also considered to be a class of
highly toxic compounds to organisms, in spite of their wide applications in raw
materials and intermediates. In this regard, the median lethal concentration (LC )
5
0
of thiophenols for fish is 0.01 - 0.4 mM [9, 10]. Long-term intake of superfluous
thiophenols can lead to severe damage to the central nervous system, shortness of
breath, muscular weakness, and even death [9, 11]. Consequently, it is very
necessary to exploit a highly sensitive and selective detection technique to identify
toxic thiophenols and aliphaticthiols [12, 13]. In recent years, fluorescent detection
has attracted much attention owing to its simple operation, high sensitivity, and real-
time imaging [14, 15]. However, most fluorescent probes are unable to distinguish
aliphatic thiols and thiophenols, due to their low selectivity to the two types of thiols
[
thiophenols over aliphatic thiols through S Ar process [1]. Therein, 4-chloro-7-
16–18]. In 2007, Wang et al. first reported a new fluorescent probe for recognizing
N
nitro-2,1,3-benzoxadiazole was used as the fluorophore and 2,4-dinitrobenzenesul-
fonyl (DNBS) as the response unit. This probe showed high selectivity for the
detection of thiophenols in spite of the drawbacks of low sensitivity. Subsequently,
Lin et al. explored a 3-benzothiazole coumarin-based fluorescent probe for the
detection of thiolphenols via the thiolysis of a dinitrophenyl ether [19]. This probe
shows excellent selectivity and the detection limit reaches as low as 1.8 nM. In
2
014, Yang et al. reported a new type of fluorescent probe for the detection of
thiophenols via an intramolecular charge transfer mechanism, which exhibited high
selectivity and sensitivity in the quantitative determination of thiophenols in
biological systems [20]. However, all three examples suffered from short emission
wavelength, which limited its real application.
So far, the thiolphenol probes based on S Ar mechanism have been studied for
N
1
0 years [21–30], but most of these probes still suffer from the following two main
shortages: one is the low sensitivity, which limits their applications in low
concentration of thiophenols; the other is that these probes mostly emit in the UV to
green light region, which always leads to the interference between excitation light
and emission light. Herein, it is of considerable importance to develop the highly
sensitive fluorescence probes for recognizing thiophenols that emit in NIR light
region, because the NIR fluorescence detection has unique advantages such as deep
tissue penetration, light scattering decrease, autofluorescence reduction, and optical
transparency increase [31–36].
Dicyanoisophorone-based fluorescent dyes are well recognized as an excellent
fluorophore in the field of functional fluorescent materials due to their excellent
spectroscopic characteristics, such as internal charge transfer (ICT), emission at
NIR region, and large Stokes shift [37–42]. In the previous work, we have made
some exploration in the synthesis and application of this type of fluorescence
1
23

Ultrasensitive dicyanoisophorone-based near-infrared…
materials [37, 43]. Herein, we designed a novel NIR fluorescence probe (probe 1)
for recognition of thiophenols (Scheme 1). As expected, probe 1 exhibited a turn-on
response around 658 nm, high sensitivity and selectivity, and large stokes shift
(203 nm). Moreover, probe 1 was also successfully applied in the quantitative
detection of low concentration of thiophenols in the three river water samples.
Experimental
Synthesis
Synthesis of compound A
4
-Fluorobenzaldehyde (2.0 mL, 18.6 mmol) and piperazine (6.0 g, 69.6 mmol)
were dissolved in 2-methoxyethanol (25 mL). The mixture solution was refluxed for
h and poured into 200 mL of water to obtain a yellow precipitate. After filtration,
3
the yellow solid was further purified by silica column chromatography using
dichloromethane/methanol (50/1, v/v) as the eluent to give a light yellow solid
1
Compound A, 2.3 g, 65%). H-NMR (400 MHz, CDCl ): 9.78 (s, 1H), 7.76 (d,
(
J = 8 Hz, 2 H), 6.92 (d, J = 8 Hz, 2 H), 3.36 (t, J = 4 Hz, 4 H), 3.02 (t, J = 4 Hz, 4
3
1
3
H) (Fig. S1). C-NMR (100 MHz, CDCl ): 190.48, 155.41, 131.86, 127.05, 113.48,
3
4
8.19, 45.81 (Fig. S2).
Synthesis of compound B
Under a nitrogen atmosphere, compound A (380 mg, 2.0 mmol) and dicyanoiso-
phorone (372 mg, 2 mmol) were dissolved in toluene (20 mL), followed by addition
of piperidine (0.5 mL) and acetic acid (0.5 mL). The mixture was refluxed for 8 h
and then concentrated under vacuum. Finally, the residue was purified by silica gel
column chromatography with dichloromethane/methanol as the eluent (20/1, v/v) to
1
give a red solid (Compound B, 316 mg, 42%) H-NMR (400 MHz, CDCl ): 7.56 (d,
3
J = 8 Hz, 2 H), 7.20 (d, J = 8 Hz, 2 H), 6.94 (d, J = 8 Hz, 2 H), 6.78 (s, 1H), 3.21
(
t, J = 4 Hz, 4 H), 2.83 (t, J = 4 Hz, 4 H), 2.58 (s, 2H), 2.51 (s, 2H), 1.01 (s, 6H)
Scheme 1 Synthetic route of probe 1
123

S. Chang et al.
1
3
(
Fig. S3). C-NMR (100 MHz, CDCl ): 169.32, 154.63, 151.76, 137.10, 129.13,
3
1
2
27.11, 126.31, 122.39, 115.60, 113.91, 113.14, 47.46, 44.22, 43.00, 39.21, 32.03,
8.06, 22.59 (Fig. S4).
Synthesis of probe 1
Compound B (107 mg, 0.3 mmol) and triethylamine (0.5 mL) was dissolved in
1
chloride (80 mg, 0.3 mmol) and CH Cl (5 mL) was added dropwise to the solution
5 mL of CH Cl at 0 °C. Then, a mixture solution of 2,4-dinitrobenzenesulfonyl
2
2
2
2
and stirred for 30 min. The mixture was warmed to room temperature for another
0 h, followed by removal under vacuum and purification by silica column
chromatography (probe 1, dichloromethane/methanol = 30/1, v/v) to obtained a red
1
1
solid. (68 mg, yield: 11%). H-NMR (400 MHz, CDCl ): 9.01 (d, J = 8 Hz, 1 H),
3
8
H), 6.96 (d, J = 12 Hz, 2 H), 6.79 (s, 1H), 3.41 (t, J = 4 Hz, 4 H), 3.36 (t, J = 4 Hz,
.58 (d, J = 8 Hz, 1 H), 8.31 (d, J = 8 Hz, 1 H), 7.57 (d, J = 8 Hz, 2 H), 7.21 (s, 2
1
3
H), 2.58 (s, 2H), 2.51 (s, 2H), 1.00 (s, 6H) (Fig. S5). C-NMR (100 MHz,
4
CDCl ): 172.28, 170.04, 156.99, 152.07, 138.59, 129.51, 125.40, 120.85, 114.32,
3
1
13.49, 73.83, 47.46, 44.86, 42.27, 38.15, 31.62, 27.42, 21.35 (Fig. S6). HRMS
-
(
ESI): calcd. For [C H N O S–H] 587.1713; found 587.1710 (Fig. S7).
29 28 6 6
Characterization
1
13
H NMR and C NMR spectra were performed on a Bruker AM400 NMR
spectrometer with TMS as the internal standard. High resolution mass spectrum
HRMS) was recorded on a Waters LCT Premier XE spectrometer. Absorption
(
spectra and fluorescence spectra were recorded on a SHIMADZU UV-2450
spectrophotometer and SHIMADZU RF-5301PC fluorescence spectrophotometer at
room temperature, respectively.
2
Measurements of HS in water samples
We collected three various water samples from Qingchun River, Huangpu River,
and Changjiang River. The water samples were filtered first, then the pH was
modulated in terms of PBS buffer solution (20 mM, pH 7.4). Finally, each water
sample (3 mL, containing 5 lM probe 1) was spiked with different concentrations
(
0, 0.1, 0.4, 0.7, 1 lM) of thiophenol solutions.
Results and discussion
Synthesis route
The synthetic routes of probe 1 and its intermediates compound A and compound
B are illustrated in Scheme 1. The key intermediate dicyanoisophorone was
synthesized according to our established procedures [35, 43]. The detailed synthetic
procedures for compound A, compound B and probe 1 are described as follows.
1
23

Ultrasensitive dicyanoisophorone-based near-infrared…
Absorption and fluorescence properties
We firstly examined the absorption and emission spectra of probe 1 (5 lM) in the
absence and presence of thiophenol in PBS buffer. As shown in Fig. 1a, b, the free
probe 1 (5 lM) displayed an absorption band at 450 nm and a relatively weak
emission peak at 596 nm. Upon addition of four equivalents of thiophenol, a new
absorption band at 455 nm appeared. Although the absorption spectra between
probe 1 and compound 2 only had a slight difference, their fluorescence spectra
exhibited a significant difference. As showed in Fig. 1b, a strong emission
enhancement at 658 nm appeared, which is ascribed to the cleavage of 2,4-
dinitrobenzenesulfonyl (DNBS). Moreover, a remarkable large stokes shift of
2
03 nm (kabs = 455 nm, kem = 658 nm) was observed. The large stokes shift is
Fig. 1 UV–vis absorption (a) and fluorescence spectra (b) of probe 1 (5 lM) upon addition of
thiophenol (20 lM). All spectra were recorded in DMSO/PBS buffer solution (20/80, v/v, pH = 7.4,
20 mM). kex = 455 nm; slit width = 5/5 nm. The inset of Fig. 1b is the color change of probe 1 in
DMSO/PBS buffer solution after addition of thiophenol (20 lM) under UV (365 nm) light irradiation
123

S. Chang et al.
generally desired in fluorescence microscopy studies, because the large gap between
the excitation wavelength and the emission wavelength can effectively diminish the
measurement error caused by the excitation light and scattered light [32].
Additionally, the signal-to-background ratio can be achieved 30.4 (t = 0, Fluores-
cence Intensity = 22.4; t = 180 s, Fluorescence Intensity = 681.2), implying that
probe 1 is quiet sensitive for thiophenol detection.
Response kinetics
The reaction kinetics of probe 1 in presence of thiophenol was investigated and is
displayed in Fig. 2. In absence of thiophenol, almost no fluorescence can be
detected throughout the detection process. Under different concentrations of
thiophenol (0–20 lM), the fluorescence emission response speed was extremely fast
(
less than 160 s), which is allowed for real time detection. To verify whether our
probe can work at low level of organic solvent, the influences of different ratios of
DMSO (1, 5, 10, 20, 30, 40%) on the fluorescence response of probe 1 toward
thiolphenol were also investigated. As shown in Fig. S8, probe 1 was effective at
low level (1%) of organic solvent, indicating that probe 1 can be potentially used in
water-rich detection system.
Effect of pH
As shown in Fig. 3, the emission band of probe 1 at 658 nm showed almost no
change in the pH range from 2 to 12 in the absence of thiophenol, indicating that
probe 1 is quiet stable. The emission band at 658 nm showed a remarkable increase
in the pH range from 2 to 6 with thiophenol, which can be attributed to protonation
of amino group [34] (Scheme 2). Then the fluorescence intensity had almost no
Fig. 2 Change of fluorescence intensities of probe 1 (5 lM) at 658 nm as a function of reaction time
under different thiophenol concentrations (0, 1, 4, 7, 10, 20 lM) in DMSO/PBS buffer solution (20/80,
v/v, pH = 7.4, 20 mM). kex = 455 nm; slit width = 5/5 nm
1
23

Ultrasensitive dicyanoisophorone-based near-infrared…
Fig. 3 Effect of pH on the fluorescence intensity of probe 1(5 lM) at 658 nm in DMSO/PBS buffer
solution (20/80, v/v, pH = 7.4, 20 mM) with (filled circle) and without (filled square) thiophenol
(20 lM). kex = 455 nm; slit width = 5/5 nm
Scheme 2 Proposed reaction
mechanism of detecting
thiophenol
change in the pH range from 6 to 8. These results suggested that probe 1 is
suitable for detection of thiophenols in both environmental and biological systems.
Sensitivity
The fluorescence titration experiments was investigated in PBS buffer solution
(
containing 20% DMSO, pH = 7.4, 20 mM). As shown in Fig. 4, probe 1 exhibited
a weak fluorescence band at 596 nm without thiophenol. The intensity of emission
band at 658 nm was strong enhanced upon addition of thiophenol from 0 to 30 lM.
Figure 4b shows the plot of emission band at 658 nm versus thiophenol
123

S. Chang et al.
Fig. 4 Fluorescence spectra (a) of probe 1 (5 lM) in the presence of different concentrations of
thiophenol (0–30 lM) in DMSO/PBS buffer solution (20/80, v/v, pH = 7.4, 20 mM). b Fluorescence
intensity at 658 nm as a function of thiophenol concentration (0–10 lM). kex = 455 nm; slit width = 5/
5
nm
concentration. Notably, a good correlation coefficient of 0.992 was obtained when
the thiophenol concentration was in the range of 0–10 lM, suggesting that probe 1
could be used for the quantitative detection of thiophenol. The detection limit of
probe 1 for thiophenol was determined to be 3.4 nM (3r/j). Moreover, a
considerable fluorescence enhancement was also observed upon addition of
thiophenol from 0 to 1 lM (Fig. S9). All these results indicated that probe 1 is
ultrasensitive and quite suitable to detect low concentrations of thiophenol
quantitatively compared to previously reported thiophenol probes (Table S1).
1
23

Ultrasensitive dicyanoisophorone-based near-infrared…
Fig. 5 a Fluorescence spectra of probe 1 toward various species: (1) Blank, (2) C
HS (100 lM); (4) GSH (100 lM); (5) Cys (100 lM); (6) Hcy (100 lM); (7) OHCH
6
H
5
SH (20 lM); (3)
CH SH (100 lM);
(100 lM); (11) p–NO
SH (20 lM); (14) p–NH
-
2
2
(
(
(
8) (CH
20 lM); (12) p–CH
3
)
3
CSH (100 lM); (9) C
6
H
5
OH (100 lM); (10) C
6
H
5
NH
2
2
–C
–C
6
H
H
4
4
SH
SH
3
O–C SH (20 lM); (13) p–CH
6
H
4
3
–C
6
H
4
2
6
20 lM). b Corresponding fluorescence intensity at 658 nm in the presence of different species. Inset
B: Color change of probe 1 in DMSO/PBS buffer solution (20/80, v/v, pH = 7.4, 20 mM) after addition
of various species. kex = 455 nm; slit width = 5/5 nm
Response mechanism
According to previous reported literatures, the fluorescence enhancement of probe 1
in the presence of thiophenol implies the formation of compound 2. To verify the
proposed reaction mechanism, mass spectra were measured to confirm reaction
product of probe 1 and thiophenol. As shown in Fig. S10, the reaction product of
probe 1–thiophenol is confirmed by HRMS, in which the dominant peaks at m/
z = 359.2242 (calcd. 359.2236) and 291.0434 (calcd. 291.0440) correspond to
?
?
[probe 1–thiophenol ? H] and [DNS–thiophenol ? H] , respectively. Addition-
ally, both absorbance and fluorescence spectra of probe 1–thiophenol adduct were
123

S. Chang et al.
Table 1 Determination of thiophenol concentrations in water samples
Sample
Concentration of spiked
thiophenol (lM)
Concentration of recovered
thiophenol (lM)
Recovery
(%)
Changjiang river
water
0
Not detected
0.09 ± 0.12
0.46 ± 0.04
0.71 ± 0.21
0.97 ± 0.06
Not detected
0.89 ± 0.15
0.43 ± 0.06
0.74 ± 0.16
1.04 ± 0.32
Not detected
0.11 ± 0.13
0.42 ± 0.11
0.72 ± 0.09
0.98 ± 0.18
–
0
0
0
1
0
0
0
0
1
0
0
0
0
1
.1
.4
.7
90
115
101
97
Huangpu river
water
–
.1
.4
.7
89
107
106
104
–
Qingchun river
water
.1
.4
.7
110
105
103
98
consistent with compound 2 (Fig. S11). All these results suggested that the reaction
process of probe 1 toward thiophenol follows the sulfonamide cleavage mechanism
mediated by thiophenol (Scheme 2).
Selectivity
To evaluate the selectivity of probe 1 toward thiophenol, we examined the
fluorescence spectra of probe 1 toward various species including thiophenol
derivatives (C H SH, p–CH –C H SH, p–NH –C H SH, p–NO –C H SH, p–
6
5
3
6
4
2
6
4
2
6 4
CH O–C H SH), aliphatic thiols (Cys, Hcy, GSH, (CH ) CSH, and OHCH CH
2-
3
6
4
3 3
2
-
SH), and various interfering substances such as nucleophilic species (HS ,
C H OH, C H NH ), various anions and metal ions (NaF, NaCl, NaBr, NaI,
NaOAc, Na SO , Na HSO , Na S, KCl, ZnCl , FeCl , AlCl , CuCl , Co(NO ) ,
6
5
6
5
2
2
3
2
3
2
2
-
3
3
2
3 3
-
HgCl ), and some oxygen species (H O , ClO , ClO ). As shown in Fig. 5, the
2
2
2
4
fluorescence intensity of probe 1 exhibited a significant enhancement upon addition
of thiophenols including C H SH, p–CH –C H SH, p–NH –C H SH, and p–
CH O–C H SH. Exceptionally, probe 1 cannot respond to p–NO –C H SH, which
6
5
3
6
5
2
6 5
3
6
5
2
6 4
is due to the existence of strong a electron-withdrawing NO group [12, 25, 29]. p–
2
-
NO –C H S showed very low activity in the S Ar reaction toward sulfonamide
2
6
4
N
-
sulfur
because of its relatively large local softness (S
) value [44]. As shown in Fig. 5
and Fig. S12, probe 1 displayed slight response to other species except for
thiophenols, indicating that probe 1 has a very high selectivity to thiophenols. From
the insets of Fig. 5 and Fig. S11, it can be seen that probe 1 exhibits a significant
fluorescence enhancement in the presence of thiophenols (except for p–NO2–
C H SH). To investigate the influence of coexisting species to probe 1, the
6
4
1
23

Ultrasensitive dicyanoisophorone-based near-infrared…
fluorescence spectra of probe 1 in the presence of both thiophenols (20 lM) and
other species (100 lM) were examined. As shown in Fig. S13 and Fig. S14, probe 1
displayed excellent selectivity to thiophenols and anti-interference ability in the co-
existence of various species. As for the selectivity of probe 1 toward thiophenols
over aliphatic thiols, it is relative to the weak nucleophilicity of probe 1. Since the
pK value of aliphatic thiols is about 8.5, whereas that of thiophenols is around 6.5
a
[
45] the probe 1 preferentially reacts with thiophenols rather than aliphatic thiols.
Determination of the thiophenols in water samples
Considering the toxicity of thiophenols as environmental pollutants, we investigated
the feasibility of probe 1 for analysing the thiophenols in environmental water
samples. Three water samples were obtained from Changjiang River, Huang-Pu
River of Shanghai, and Qing-Chun River of East China University of Science and
Technology. These water samples were filtered before analysis, then spiked with
different concentrations of thiophenols (0, 0.1, 0.4, 0.7, 1 lM). Then, the
fluorescence intensities for different samples at 658 nm were collected. As
displayed in Table 1 and Fig. 6, for all of the three river water samples, the
Fig. 6 a–c Linear plots of fluorescence intensity changes of probe 1 at 658 nm against the spiked
concentrations of PhSH from 0 to 10 lM for ‘‘Changjiang River water’’ (a), ‘‘Huang-Pu River water’’
(
b) and ‘‘Qing-Chun River water’’ (c). d Fluorescent intensities of probe 1 (5 lM) toward different
concentrations of thiophenol in ‘‘Qing-Chun River water’’, ‘‘Huang-Pu River water’’ and ‘‘Changjiang
River water’’. All results were conducted in DMSO/PBS buffer solution (20/80, v/v, pH = 7.4, 20 mM).
kex = 455 nm; slit width = 5/5 nm
123

S. Chang et al.
fluorescent intensities at 658 nm showed good linear relationships to the spiked
thiophenol concentrations (0–1 lM). These results demonstrated that probe 1 is
ultrasensitive and has a potential application in quantitative detection of extremely
-
7
small amount (10 ) of thiophenol in real water samples.
Conclusion
In summary, we have synthesized a new near-infrared (NIR) fluorescent probe
(
probe 1) for the highly selective detection of thiophenols. On the basis of the highly
efficient cleavage reaction mediated by thiophenols, probe 1 showed high response
speed, sensitivity, and selectivity toward thiophenols (except for p–NO -C H SH)
2
6 4
under room temperature. Probe 1 shows a large stokes shift (203 nm) and
significantly enhanced fluorescence intensity which can be easily distinguished by
naked eyes. The detection limit was as low as 3.4 nM and the corresponding signal-
to-background ratio reached 30.4. Additionally, probe 1 showed good anti-
interference ability in the co-existence of the environmental and biologic species.
Moreover, probe 1 was ultrasensitive and successfully used in the quantitative
detection of thiophenol in three river water samples.
Acknowledgements This work has been supported by the National Natural Science Foundation of China
(21573069) and the Research Fund of Education of the People’s Republic of China (JPPT-125-4-076).
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