A Photoswitchable Triple Chemosensor for Cyanide Anion Based on Dicyanovinyl-Functionalized Dithienylethene

Article abstract of DOI:10.1002/ejoc.201900369

The development of new sensors for the accurate detection of cyanide anion has attracted more and more attention due to their potential applications in environmental and biological systems. Here, two novel near-infrared (NIR) photochromic compounds 1a and 1b, which were modified by the dicyanovinyl fragment with cyanide recognition function, have been developed. Surprisingly, 1a presented an unprecedented triple sensing performance for cyanide anion (colorimetric-fluorescent-colorimetric), which can be utilized as a potential precision sensor for CN^– in environmental and biological systems. Although 1b did not show triple detection behavior for CN^–, it could recognize CN^– and F^– synchronously and selectively by naked eyes. Moreover, their NIR photochromic behaviors could be modulated by the cyanide anion. Their sensing mechanism for CN^– or F^– was confirmed by absorption spectral studies, NMR titration, and DFT calculations.

Full text of DOI:10.1002/ejoc.201900369

A Journal of
Accepted Article
Title: A photoswitchable triple chemosensor for cyanide anion based
on dicyanovinyl-functionalized dithienylethene
Authors: Ziyong Li, Yijie Dai, Zhiqiang Lu, Yingying Pei, Yufei Song,
Lilei Zhang, and Hui Guo
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201900369
Link to VoR: http://dx.doi.org/10.1002/ejoc.201900369
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10.1002/ejoc.201900369
European Journal of Organic Chemistry
A photoswitchable triple chemosensor for cyanide anion based on
dicyanovinyl-functionalized dithienylethene
Ziyong Li,*[a] Yijie Dai,[a] Zhiqiang Lu,*[b] Yingying Pei,[a] Yufei Song,[a] Lilei Zhang,[b] and Hui Guo*[b]
[a] Key Laboratory of Organic Functional Molecules, Luoyang City, College of Food and Drug, Luoyang Normal University,
Luoyang 471934, P. R. China
[b] College of Chemistry and Chemical Engineering, and Henan Key Laboratory of Function-Oriented Porous Materials,
Luoyang Normal University, Luoyang, 471022, China
Corresponding authors E-mail: liziyong@mails.ccnu.edu.cn; zqlu2000@163.com; guohui0319@nankai.edu.cn.
ABSTRACT
The development of new sensors for the accurate detection of cyanide anion has attracted more and
more attention due to their potential applications in environmental and biological systems. Here, two novel
near-infrared (NIR) photochromic compounds 1a and 1b, which were modified by the dicyanovinyl
fragment with cyanide recognition function, have been developed. Surprisingly, 1a presented an
unprecedented triple sensing performance for cyanide anion (colorimetric-fluorescent-colorimetric), which
can be utilized as a potential precision sensor for CN- in environmental and biological systems. Although
1b did not show triple detection behavior for CN-, it could recognize CN- and F- synchronously and
selectively by naked eyes. Moreover, their NIR photochromic behaviors could be modulated by the
cyanide anion. Their sensing mechanism for CN- or F- was confirmed by absorption spectral studies, NMR
titration and DFT calculations.
Introduction
Cyanide anion plays a significant role in many industrial processes such as fiber manufacturing,
tanning, electroplating, metallurgy and silver or gold extraction.[1] Nevertheless, cyanide is one of the
highly toxic species in environmental and biological systems, which is mainly ascribed to binding with
Fe3+ in metalloenzymes and then disorder some important biological processes like oxidative metabolism
and cellular respiration.[2] It can eventually lead to death once ingested cyanide in excess of 0.05 mg/kg
body weight. In consideration of its extreme toxicity, the World Health Organization (WHO) has
recommended the permissible maximum level of cyanide anion in drinking water to be 1.9 μM.[3] Based on
this, many detection methods based on titrimetric, potentiometric and other techniques have been
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developed for quantitative analysis of cyanide anion.[4] However, the utilization of these methods is limited
owing to their complexity and time-consuming nature. Compared with these conventional detection
methods, colorimetric and fluorescent sensors for cyanide are considered as the superior approach in view
of high selectivity and sensitivity, their simplicity, inexpensive instrumentation and possibility for naked
eye detection.[5] In recent years, a large number of sensing systems for cyanide anion have been largely
developed.[6] To minimize the disturbance of other anions, many colorimetric and fluorescent sensors for
cyanide anion based on nucleophilic addition reaction mechanism have also been reported.[7] However,
most existing sensors can only perform in single style, and only a few can achieve double detection (such
as fluorescent and colorimetric sensing), from which still can not avoid the uncertainity in target anion
detection. In order to avoid the false test results and enhance the detection accuracy to the greatest extent,
it is urgent to develop multiple detection methods for cyanide anion.
As a typical photoswitchable unit, photochromic compounds provide an opportunity for the
realization of multiple detection for cyanide anion because photochromic sensors show advantages in
providing more recognition states and sensing information. Among photochromic materials,
dithienylethene has been extensively studied due to their excellent thermal stability, rapid response and
remarkable fatigue resistance.[8] Recently, various photochromic sensors based on dithienylethene unit
have attracted extensive attention.[9] Among them, most photochromic sensors still exhibit only a single or
dual detection capability for analytes like the traditional sensors. Hence, the development of photochromic
sensor with multiple detection for the accurate detection of CN- is a very meaningful and challenging task.
Herein, we described two novel dicyanovinyl-functionalized dithienylethene derivatives 1a and 1b, in
which dicyanovinyl group not only functioned as electron acceptor (A) but also responded to cyanide
anion. They displayed excellent NIR photochromic properties in CH3CN. Moreover, 1a exhibited an
unprecedented triple sensing performance for cyanide anion (Scheme 1): (1) the ring-open isomer 1a (o)
exhibited colorimetric sensing for CN- (yellow to colorless), which can be defined as the first detection; (2)
the intense yellow fluorescence of 1a (o) was turned off in the presence of CN- (second detection); (3) the
ring-closed isomer 1a (c) displayed NIR colorimetric sensing for CN- (green to purple) (third detection).
Therefore, 1a can be utilized as a photoswitchable triple chemosensor for cyanide anion. Nevertheless, its
analogue 1b just showed dual colorimetric sensing capability for CN-, while the ring-open isomer 1b (o)
can recognize CN- and F- synchronously and selectively by naked eyes. Their sensing mechanism based on
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10.1002/ejoc.201900369
European Journal of Organic Chemistry
the nucleophilic addition reaction was confirmed by absorption spectral studies, NMR titration and DFT
calculations.
Scheme 1. Proposed triple sensing processes of 1a for cyanide anion.
Scheme 2. Synthetic route of dicyanovinyl-functionalized dithienylethene derivatives 1a and 1b.
Results and discussion
Synthesis and characterization
The synthetic route of the dithienylethene derivatives 1a and 1b was outlined in Scheme 2. The
starting material 2 was treated with n-BuLi and tributyl borate in turn, followed by a Suzuki cross-coupling
reaction with 4-bromobenzaldehyde 3 to afford the dialdehyde-functionalized intermediate 4. In the
meanwhile, the continuous treatment of 2 with n-BuLi followed by the addition of DMF generated the
other dialdehyde 5. Subsequently, the target 1a and 1b were prepared by Knoevenagel condensation
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10.1002/ejoc.201900369
European Journal of Organic Chemistry
reaction between the corresponding dialdehydes (4 and 5) and malononitrile 6 in a yield of 85% and 78%
in the presence of K2CO3, respectively. Their chemical structures were confirmed by standard
spectroscopic methods (1H NMR, 13C NMR and HRMS) (Figure S27-S35).
Photochromic properties
The photochromic behaviors of 1a and 1b were firstly explored in CH3CN at room temperature. And
it was found that they underwent photoisomerization between ring-open and ring-closed isomers upon
alternant irradiation with 365 nm and > 600 nm visible light, as shown in Scheme S1. As illustrated in
Figure 1 (A), the ring-open isomer 1a (o) exhibited one distinct absorption bands at 424 nm with ε = 2.60
× 104 cm-1 M-1, which was ascribed to intramolecular π - π* transition.[10] Upon irradiation with UV light (λ
= 365 nm), the yellow solution of 1a (o) turned blue-green, and a new absorption band appeared at 690 nm
(ε = 1.49 × 104 cm-1 M-1), which was due to the formation of the corresponding ring-closed isomer 1a (c).
A well-defined isosbestic point was observed at 474 nm, which implied the two-component photochromic
reaction as illustrated in Scheme S1. The blue-green solution completely bleached upon irradiation with
λ > 600 nm visible light to afford the initial ring-open isomer. Particularly, it displayed good fatigue
resistance and no distinct deterioration (about 5%) was observed after repeating six times (Figure S1). The
cyclization and cycloreversion reaction quantum yields of 1a were measured to 0.431 (φo-c) and 0.0085
(φc-o), respectively. Similar reversible photochromic behaviors were also observed when the acetonitrile
solution of 1b was irradiated under the same conditions, as illustrated in Figure 1 (B), S2, and Table S1.
0.9
0.7
UV
Vis
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UV
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Wavelength / nm
Wavelength / nm
Figure 1. The UV-Vis absorption spectra changes of 1a and 1b with 365 nm UV and > 600 nm visible light irradiation in
CH3CN (2.0×10-5 mol/L) at 298 K. (Inset) Corresponding color changes of 1a and 1b upon photoirradiation. (A) UV-Vis
absorption spectra changes for 1a; (B) UV-Vis absorption spectra changes for 1b.
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Colorimetric sensing for cyanide anion of the ring-open isomers 1a (o) and 1b (o) (First detection)
Initially, the sensing properties of the ring-open isomers 1a (o) and 1b (o) upon addition of various
anions was examined by UV-Vis absorption spectra in CH3CN/H2O (95/5, v/v). As illustrated in Figure 2
(A), upon the addition of 10 equiv. CN-, the absorption band at 424 nm 1a (o) diminished completely and a
new absorption band at 284 nm appeared along with a distinct color change from yellow to colorless
(Figure 2 (C), Scheme S2). Nevertheless, no obvious absorption spectra and color changes were recorded
2-
-
upon addition of other anions (F-, Cl-, Br-, I-, HPO4 , HSO4 , OAc-). Similar colorimetric sensing behavior
for CN- for analogue 1b (o) was observed under the same conditions (Figure 2 (B)). Accidentally, the
absorption maximum at 386 nm for 1b (o) was red-shifted to 474 nm (△λ = 88 nm) upon addition of
fluoride (10 equiv.), and it was remarkable that a pale yellow solution became dark yellow (Figure 2 (D)).
These results indicated that 1a (o) could be utilized for the naked-eye detection of CN- with high selectivity.
And 1b (o) provided a novel method to simultaneously discriminate F- and CN- by different color change.
1.0
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F-
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F-
Cl-
Cl-
Br-
I-
CN-
Br-
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CN-
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-
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-
HPO4
HPO4
F-
HSO4
OAc-
HSO4
OAc-
CN-
CN-
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650
700
250 300 350 400 450 500 550 600 650 700
Wavelength / nm
Wavelength / nm
Figure 2. The UV-Vis absorption spectra changes and the corresponding solution color changes of 1a (o) and 1b (o) (20 μM)
upon the addition of 10 equiv. of different anions in CH3CN/H2O (95/5, v/v). (A) UV-Vis absorption spectra changes of 1a
(o); (B) UV-Vis absorption spectra changes of 1b (o); (C) the corresponding solution color changes of 1a (o); (D) the
corresponding solution color changes of 1b (o).
Subsequently, the UV-Vis titration experiment of 1a (o) upon addition of CN- was investigated
(Figure 3 (A)). Upon the gradual addition of CN- (0-3.0 equiv.) into the solution of 1a (o) (20 μM), the
absorption band at 424 nm gradually decreased and accompanied with a simultaneous increase of
absorption band at 284 nm, which can be explained by the reduction of conjugate degree due to
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European Journal of Organic Chemistry
nucleophilic addition of CN− to dicyanovinyl (C=C) group of 1a (o). Job’s plot experiments revealed a 1:2
binding stoichiometry between sensor 1a (o) and CN- (Figure S3). Furthermore, a distinct isosbestic point
was observed at 334 nm, indicating the formation of the 1a-CN- (o) adduct during the titration process. In
addition, the time-dependence changes in the absorption spectra of 1a (o) upon the addition of CN- (3.0
equiv.) were almost complete within 50 s (Figure S4), indicating high reactivity of 1a (o) and CN-. The
detection limit (DL) of sensor 1a for CN- was estimated to be 0.69 M (Figure S5), which was below the
permissible maximum level of CN- in drinking water (1.9 μM) recommended by World Health
Organization. Similar titration results of cyanide anion for analogue 1b (o) were obtained upon addition of
CN- (as shown in Figure 3 (B), S6-S8, Scheme S3). Compared with 1a (o), the sensor 1b (o) displayed
lower sensitivity and higher detection limit (DL) for CN-.
1.8
CN-
0-3.0 eq
1.6
1.0
CN-
1.4
0-3.0 eq
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1.0
CN-
CN-
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0.0
250
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700
200 250 300 350 400 450 500 550 600 650 700
Wavelength / nm
Wavelength / nm
Figure 3. The UV-Vis absorption spectra changes of 1a (o) and 1b (o) (20 μM) with gradual addition of CN- (0-3.0
equiv.uiv.) in CH3CN/H2O (95/5, v/v). (A) UV-Vis absorption spectra changes of 1a (o); (B) UV-Vis absorption spectra
changes of 1b (o).
1
The mechanism of 1a (o) and 1b (o) in sensing of CN- was confirmed by the H NMR titration
experiments in CDCl3 (Figure S9 and S10). As shown in Figure S9, upon addition of 3.0 equiv. of CN-, the
signal at 7.69 ppm assigned to the vinyl proton (Ha) disappeared completely with a new upfield signal
emerged at 4.30 ppm (Ha’). In addition, the aryl protons Hb and Hc at 1a (o) had an obvious upfield shift
upon CN- addition due to a break in conjugation. And the presence of tertiary carbon (Ca’) in the cyanide
adduct further confirmed sensing mechanism of CN- by the 13C NMR titration experiments (Figure S11
and S12). These investigations strongly revealed that the nucleophilic addition of CN- attacked the vinyl
C=C bond and disrupted the conjugation system, forming the corresponding adduct (Scheme S2 and S3),
which was consistent with the cyanide sensing by such nucleophilic addition mechanism reported in the
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literature. [11] To further explore the mechanism of interaction between photochromic sensors 1a (or 1b)
and CN-, DFT calculations were performed at the B3LYP/6-31G* level of the Gaussian 09 program.[12]
The optimized geometries of free sensor 1a (o) and 1a-CN- (o) adduct were described in Figure S13. 1a (o)
was nearly a sp2 hybridized vinyl group and a rigid planar conformation, which provided an efficient
π-conjugation system, while 1a-CN- (o) adduct had a sp3 hybridized carbon bond and tetrahedral
conformation. Thus the π-conjugation system was effectively interrupted due to the twisted conformation.
Similar optimized geometries for sensor 1b (o) was observed by DFT calculations (Figure S14). Moreover,
it was worth mentioning that the calculated electronic absorption spectra for 1a (o), 1a-CN- (o), 1b (o) and
1b-CN- (o) were similar to the experimental data (Figure S15). Therefore, the DFT theoretical calculations
further verified the experimental results that the CN- was bound to the vinyl group of 1a (o) and 1b (o).
Consequently, the ring-open isomers 1a (o) and 1b (o) exhibited colorimetric sensing for CN-, which can
be defined as the first detection.
Finally, the UV-Vis titration experiment of 1b (o) upon addition of F- was also explored (Figure S16).
Upon the addition of F- (0-5.0 equiv.), the absorption bands at 330 nm and 386 nm gradually decreased
together with the appearance and enhancement of a new absorption peak at 474 nm, which could be
attributed to the elongated conjugation when 1b (o) was treated with fluoride. To further study the fluoride
anion sensing mechanism of 1b (o), the 1H NMR titration experiments for 1b (o) upon addition of F- were
carried out. As illustrated in Figure S17 (A), when 2.0 equiv. F- was added to the solution of 1b (o), the
downfield shift of the vinyl proton resonance signals (Ha) was observed from δ = 7.62 ppm to δ = 9.74
ppm (Ha’), which may be due to the formation of complex (1b (o)-2F-) between 1b (o) and F- (Figure S17
(B)). When the amount of F- reached 5.0 equiv., the vinyl proton signals (Ha or Ha’) disappeared
1
completely and may exist as the deprotonated form (1b (o)2-). However, their absorption spectra and H
NMR titration experiments indicated only 1b (o) could interact with F-, while 1a (o) is inert. This may be
due to the fact that the degree of conjugation (electron density) of 1a (o) is higher than that of 1b (o),
which weaken the hydrogen bond interaction between the vinyl proton of dicyanoethylene groups of 1a (o)
and F-. These results indicated that 1b (o) can serve as a novel “naked-eye” sensor for simultaneous
detection of CN- and F-.
Fluorescent turn-off sensing for cyanide anion of the ring-open isomers 1a (o) (second detection)
The second detection capability of the ring-open isomer 1a (o) to act as a highly selective CN- sensor
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was explored by fluorescence spectroscopy. As depicted in Figure 4 (A), the free 1a (o) in CH3CN-H2O
(95:5 v/v) solution exhibited a moderate yellow fluorescence (Φ = 0.24) with one emission band at 533 nm
(λex = 424 nm). However, the yellow fluorescence decreased gradually upon addition of CN-. As
anticipated, the solution of 1a (o) (20 μM) was almost non-emissive when the concentration of CN-
reached 60 μM. Indeed, such fluorescence quenching can be distinguished with the naked eye as illustrated
in the inset of Figure 4A, where solution photos of 1a (o) in the absence and presence of CN- under 365
UV light were revealed. Moreover, Figure 4 (B) presented the plot of fluorescence intensity at 533 nm vs.
the equivalent of CN-, which showed an almost linear variation. Unfortunately, the ring-open isomer 1b (o)
scarcely displayed fluorescence in the absence or presence of CN-.
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Equivalent of CN-
Wavelength / nm
Figure 4. (A) The fluorescence spectra changes of 1a (o) (20 μM) in the presence of different amounts of CN- (0-3.0
equiv.uiv.) in CH3CN/H2O (95/5, v/v); the inset shows photos of the solution of 1a (o) (20 μM) in the absence (a) or
presence (b) of CN- (3.0 equiv.) under 365 nm UV light. (B) The plot of fluorescence intensity at 533 nm vs. the equivalent
of CN- in CH3CN/H2O (95/5, v/v).
280
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200
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120
80
40
0
Br-
OAc-
F-
2-
-
Cl-
I-
CN- HPO4 HSO4
1a
Figure 5. Variation of the relative fluorescence intensity at 533 nm of 1a (o) (20 μM) in the presence of various anions (10
equiv.) in CH3CN/H2O (95/5, v/v).
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To evaluate the cyanide anion selectivity of 1a (o), the changes of relative fluorescence intensity I0/I
at 533 nm (I0 and I represent the fluorescence intensity of 1a (o) in the absence and presence of anions)
2-
-
upon the addition of various anions (including F-, Cl-, Br-, I-, CN-, HPO4 , HSO4 , OAc-) were studied. As
depicted in Figure 5 and Figure S18, significant fluorescence quenching was detected only after the
addition of CN-, while nearly no emission intensity ratio (I0/I) change was observed in the presence of F-,
2-
-
Cl-, Br-, I-, HPO4 , HSO4 , OAc-. Thus, 1a (o) exhibited high selectivity for cyanide anion by fluorescence
spectra changes, which can be defined as the second detection.
Colorimetric sensing for cyanide anion of the ring-closed isomers 1a (c) and 1b (c) (Third detection)
In recent years, colorimetric sensors have attracted much attention because they can easily be detected
color changes with the naked eye. To the best of our knowledge, almost all of the reported cyanide anion
colorimetric chemosensors worked in the visible region, but there were few examples in the near-infrared
region. Colorimetric chemosensors with near-infrared optical response will be more useful in biological
systems because they can avoid the interference from endogenous chromophores.[13] Subsequently, the
UV-Vis spectra changes of the ring-closed isomers 1a (c) and 1b (c) with NIR absorption in the presence
of CN- were explored. As shown in Figure 6, upon the addition of CN- (0-3.0 equiv.), the NIR absorption
band of 1a (c) at 690 nm gradually decreased while a new peak at 552 nm emerged, which was responsible
for the color change from green to purple. Similarly, the addition of CN- (0-3.0 equiv.) or F- (0-5.0 equiv.)
to the solutions of 1b (c) brought about a decrease in the NIR absorption intensity at 714 nm and formation
of a new absorption band at 558 nm or 550 nm, respectively (Figure S19 and S20). Interestingly, 1b (c)
displayed a different recognition mechanism for fluoride from that of 1b (o). This may be because the
degree of conjugation of 1b (c) is much higher than that of 1b (o), which weakens acidity of the vinyl
proton of 1b (c) compared with that of 1b (o). Thus, the nucleophilic addition of F- may attack the vinyl
C=C bond of 1b (c) easily to form the corresponding adduct (Figure S20). Furthermore, the purple
solutions of 1a-CN- (c) and 1b-CN- (c) were also obtained by directly irradiating the colorless solutions of
1a-CN- (o) and 1b-CN- (o) (Figure S21, Scheme S2 and Scheme S3). And the photochromism of sensor 1b
could also be modulated upon addition of F- (Figure S22). Accordingly, 1a (c) and 1b (c) displayed an
infrequent NIR colorimetric response to cyanide anion with more complicated sensing mechanism, which
can be defined as the third detection.
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European Journal of Organic Chemistry
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
300
400
500
600
700
800
900
1000
Wavelength / nm
Figure 6. The UV-Vis absorption spectra changes of 1a (c) (20 μM) at photostationary state (365 nm) with gradual addition
of CN- (0-3.0 equiv.) in CH3CN/H2O (95/5, v/v).
Owing to the excellent selectivity and high sensitivity of 1a and 1b towards CN- or F-, we further
explored their potential application in river water sample without further processing (from Luoyang Yi
River). [5e] The solution of CN- or F- (1.0 M) was firstly added into the river water sample to obtain the
real water samples containing CN- or F-. Subsequently, these water samples were detected by the changes
in absorption and fluorescence spectra of 1a (o), 1b (o), 1a (c) and 1b (c), respectively, as shown in
Figure S23-26. The detection results were very close to that of our designed solution system, which
indicated that the photochromic sensors 1a and 1b could be applied for detecting CN- or F- in practical
water samples with high accuracy.
Conclusions
In summary, two new acceptor-acceptor type dithienylethene derivatives 1a and 1b, in which
dicyanovinyl group not only functioned as electron acceptor but responded to cyanide anion, have been
successfully developed. And they displayed excellent NIR photochromic properties in CH3CN. Moreover,
1a exhibited an unprecedented triple sensing performance for cyanide anion: (1) the ring-open isomer 1a
(o) exhibited colorimetric sensing for CN- (yellow to colorless), which can be defined as the first detection;
(2) the intense yellow fluorescence of 1a (o) was turned off in the presence of CN- (second detection); (3)
the ring-closed isomer 1a (c) displayed NIR colorimetric sensing for CN- (green to purple) (third detection).
Although 1b did not show triple detection behavior for CN- like 1a, it could recognize CN- and F-
synchronously and selectively by naked eyes. NMR titration and DFT calculations further confirmed the
sensing mechanism for CN- or F-. Moreover, the photochromic sensors 1a and 1b could be applied for
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detecting CN- or F- in practical water samples with high accuracy.
Experimental Section
Materials and apparatus: All manipulations were underway under N2 atmosphere by standard Schlenk
2-
-
techniques unless otherwise stated. All anions (F-, Cl-, Br-, I-, CN-, HPO4 , HSO4 , OAc-) were used as the
tetrabutylammonium salts. Tetrahydrofuran was distilled from sodium/benzophenone. Ethanol was
distilled from magnesium/iodine. Distilled water was utilized in all experiments. The other chemicals and
solvents were used without further purification. The intermediates 2 and 5 were synthesized according to
literature method.[14] The relative quantum yields were determined by the known quantum yields of
1,2-bis(2-methyl-5-phenyl-3 -thienyl)perfluorocyclopentene.[15] 1H and 13C NMR spectra were collected on
German BRUKER AVANCE III 400 MHz. The chemical shifts of 1H and 13C NMR were relative to TMS.
High resolution mass spectra were obtained on SCIEX X-500R QTOF (ESI mode) or Thermo Scientific
TM Q ExactiveTM (ESI mode). UV-Vis absorption spectra were collected on a Persee TU-1810 UV-Vis
spectrophotometer. For the photochromic reaction, UV light irradiation (λ = 365 nm) was carried out by
using a ZF5UV lamp, and visible light irradiation (λ > 600 nm) was carried out by using a LZG 220 V 500
W tungsten lamp with cut-off filters.
2-
-
General procedure: The stock solutions of analytes (F-, Cl-, Br-, I-, CN-, HPO4 , HSO4 , OAc-) were
prepared in distilled water with the concentration of 1.0 mM, which were diluted to desired concentrations
with distilled water as needed. Sensors 1a and 1b were dissolved in CH3CN to afford the stock solution
(1.0 mM) and then diluted with a mixed solution of CH3CN/H2O to prepare the analytical solution (20 μM)
(CH3CN/H2O, 95/5, v/v).
Calculations of detection limit (DL): The detection limits (DL) were measured on the basis of absorption
spectra titration data.
DL = 3δ/k
In which δ was the standard deviation of blank sample, k represented the absolute value of the slope
between absorbance intensity and anion concentration.[16]
Synthesis of intermediate 4: To a solution of 2 (414 mg, 1.0 mmol) in anhydrous tetrahydrofuran (10 mL),
n-BuLi (0.8 mL of 2.5 M solution in hexane, 2.0 mmol) was slowly added under nitrogen at 0 °C and
stirred for 2 h at 0 °C. Then B(OBu)3 (0.82 mL, 3.0 mmol) was added and stirred for another 6 h at room
11
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10.1002/ejoc.201900369
European Journal of Organic Chemistry
temperature, and the solution was directly used in next Suzuki cross coupling reaction without any workup.
Then, the resulting reddish solution was added dropwise to a flask containing 4-bromobenzaldehyde 3 (370
mg, 2.0 mmol), Pd(PPh3)4 (50 mg, 0.041 mmol), ethylene glycol (0.5 mL), tetrahydrofuran (10 mL) and 2
M Na2CO3 solution (10 mL) at 60 °C. Subsequently, the mixture was refluxed for 12 h under N2
atmosphere. The reaction solution was cooled to room temperature and extracted with ethyl acetate (3 × 40
mL), and the combined organic layer was washed with the saturated NaCl solution (2 × 30 mL). The
organic layer was dried over Na2SO4, filtered and concentrated in vacuo. Then the crude product was
purified by column chromatography (petroleum ether / ethyl acetate = 9:1) to give 4 as a light yellow solid
in a yield of 61%. m.p. 81.8 - 83.4 °C. 1H NMR (400 MHz, CDCl3) δ 9.96 (s, 2H), 7.83 (d, J = 8.0 Hz, 4H),
7.63 (d, J = 8.0 Hz, 4H), 7.19 (s, 2H), 2.86 (t, J = 8.0 Hz, 4H), 2.15 - 2.08 (m, 2H), 2.04 (s, 6H). 13C NMR
(100 MHz, CDCl3) δ 191.28, 140.07, 138.17, 137.16, 137.04, 134.80, 134.69, 130.38, 126.03, 125.30,
38.44, 23.01, 14.59. HRMS (ESI-TOF) m/z: [M + Na]+ Calcd for C29H25NaO2S2 491.1115; Found
491.1095.
Synthesis of 1a: To a solution of 4 (468 mg, 1.0 mmol) and malononitrile 6 (1.06 g, 16.0 mmol) in
anhydrous ethanol (10 mL) was added 0.2 mL K2CO3 saturated ethanol solution under N2. The reaction
mixture was refluxed for 4 h. After the solution was cooled to room temperature, the resulting precipitation
was filtered and washed with ethanol (2 mL  2) to give 1a as a yellow solid in a yield of 85 %. m.p. 165.5
- 167.7 °C . 1H NMR (400 MHz, CDCl3) δ 7.88 (d, J = 8.0 Hz, 4H), 7.68 (s, 2H), 7.61 (d, J = 8.0 Hz, 4H),
7.22 (s, 2H), 2.87 (t, J = 8.0 Hz, 4H), 2.17 - 2.09 (m, 2H), 2.05 (s, 6H). 13C NMR (100 MHz, CDCl3) δ
140.47, 138.38, 137.92, 137.65, 135.10, 131.78, 130.58, 129.40, 126.92, 125.73, 125.50, 38.59, 23.16,
14.88. HRMS (ESI-TOF) m/z: [M + Na]+ Calcd for C35H24N4NaS2 587.1340; Found 587.1307.
Synthesis of 1b: 1b was synthesized by an analogous method to 1a as a yellow solid in a yield of 78%.
m.p. 149.5 - 150.4 °C . 1H NMR (400 MHz, CDCl3) δ 7.65 (s, 2H), 7.40 (s, 2H), 2.82 (t, J = 8.0 Hz, 4H), 2.14
(br, s, 8H). 13C NMR (100 MHz, CDCl3) δ 150.43, 148.93, 139.13, 137.91, 135.40, 132.22, 114.09, 113.29,
38.42, 22.99, 15.48. HRMS (ESI-TOF) m/z: [M + Na]+ Calcd for C23H16N4NaS2 435.0709; Found
435.0686.
Supporting Information (see footnote on the first page of this article): Additional UV/Vis, fluorescence,
NMR spectroscopic and mass spectrometric data.
12
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10.1002/ejoc.201900369
European Journal of Organic Chemistry
Acknowledgements
The authors acknowledge financial support from National Natural Science Foundation of China (No.
U1304206) and the Key Scientific Research Project of Higher Education of Henan Province (No.
18A150012, 13A150799).
Keywords: Dithienylethene • Dicyanovinyl • Colorimetric sensor • Fluorescent sensor • Cyanide anion.
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