A new unsymmetrical azine derivative based on coumarin group as dual-modal sensor for CN? and fluorescent “OFF–ON” for Zn2?+

Article abstract of DOI:10.1016/j.saa.2016.12.009

A simple chemosensor YS based on coumarin group was designed and synthesized. Its structure was determined by single crystal X–ray diffraction analysis. In the presence of cyanide the sensor showed an immediate visible change in color from colorless to pale yellow by naked–eyes and produced a strong blue fluorescence rapidly in DMSO/H₂O (3:7, v/v). The detection limit on fluorescence response of the sensor to CN^? is down to 1.69?×?10^??7?M. In addition YS could show fluorescence turn–on response rapidly for Zn^2?+ over other metals ions such as Fe^3?+, Hg^2?+, Ag⁺, Ca^2?+, Cu^2?+, Co^2?+, Ni^2?+, Cd^2?+, Pb^2?+, Cr^3?+ and Mg^2?+ in aqueous solutions. Notably, this sensor served as a molecular switch, which was controlled by Zn^2?+ and EDTA cyclically. Test strips based on YS were fabricated, which could act as a convenient and efficient CN^? and Zn^2?+ test kit. This chemosensor could achieve the detection of two ions, which need not depend on two different sensors.

Full text of DOI:10.1016/j.saa.2016.12.009

Accepted Manuscript
A new unsymmetrical azine derivative based on coumarin group
as dual-modal sensor for CN− and fluorescent “OFF–ON” for
Zn2+
Jing-Han Hu, You Sun, Jing Qi, Qiao Li, Tai-Bao Wei
PII:
S1386-1425(16)30725-9
doi: 10.1016/j.saa.2016.12.009
SAA 14822
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date:
Revised date:
Accepted date:
27 July 2016
7 December 2016
12 December 2016
Please cite this article as: Jing-Han Hu, You Sun, Jing Qi, Qiao Li, Tai-Bao Wei , A
new unsymmetrical azine derivative based on coumarin group as dual-modal sensor for
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captured as affiliation for all authors. Please check if appropriate. Saa(2016), doi: 10.1016/
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ACCEPTED MANUSCRIPT
A new unsymmetrical azine derivative based on coumarin group
–
as dual-modal sensor for CN and fluorescent “OFF–ON” for
2
+
Zn
a*
a
a
b
b
Jing-Han Hu , You Sun , Jing Qi , Qiao Li , Tai-Bao Wei
a
College of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou, Gansu,
30070, P. R. China
7
E-mail: hujinghan62@163.com
b
College of Chemical and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu,
730070, P. R. China
E-mail address: zhangnwnu@126.com
Abstract:
A simple chemosensor YS based on coumarin group was designed and
synthesized. Its structure was determined by single crystal X–ray diffraction analysis.
In the presence of cyanide the sensor showed an immediate visible change in color
from colorless to pale yellow by naked–eyes and produced a strong blue fluorescence
rapidly in DMSO/H O (3:7, v/v). The detection limit on fluorescence response of the
2
−
-7
sensor to CN is down to 1.69×10 M. In addition YS could show fluorescence turn–
2
+
3+
2+
+
2+
on response rapidly for Zn over other metals ions such as Fe , Hg , Ag , Ca ,
2
+
2+
2+
2+
2+
3+
2+
Cu , Co , Ni , Cd , Pb , Cr and Mg in aqueous solutions. Notably, this sensor
2
+
served as a molecular switch, which was controlled by Zn and EDTA cyclically.
Test strips based on YS were fabricated, which could act as a convenient and efficient
–
2+
CN and Zn test kit. This chemosensor could achieve the detection of two ions,
which need not depend on two different sensors.
−
2+
Keywords: Chemosensor; Coumarin; CN ; Zn ; DFT calculations.
*
Corresponding author: Prof. Jing-Han Hu, E-mail: hujinghan62@163.com, Tel: +86 931 18109460354

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1
. Introduction
Metals and anions both play important roles in daily life [1-3]. If eating some
food by mistake such as cassavas and the kernels of apricot, the toxicity may directly
lead to the death of human. The cyanide which is inhaled into living organisms could
disrupt the mitochondrial electron-transport chain, further cause the decreased
oxidative metabolism and oxygen utilization [4-7]. Even if the cyanide is so
dangerous, they also have widespread use in the synthesis processes of a large amount
of industrial products, such as nitriles, nylon, and fertilizers, as well as electroplating
industry [8-11]. And zinc ion as the second most abundant transition-metal ion often
involve in a variety of physiological and pathological processes for example gene
expression, enzyme regulation, and catalytic function of protein [12-13]. Its most
important applications in industry are producing zinc alloy and as a protective layer of
other metals. Eating some toys surface containing zinc for a long time may lead to
poisoning, which have emesis, diarrhea and other gastrointestinal symptoms. In other
words, limited quantities of zinc are necessary for the living organism however
excessive amounts may damage the life entity. [14-15] Thus, more enthusiastic has
been sparked in exploring efficient methods that can selectively, sensitively and
–
2+
rapidly detect CN and Zn .
At present, optical sensors which have a color or fluorescence change show a lot
of merits, such as low cost, rapid response, convenience, high sensitivity and potential
–
application [16-18]. As far as we known, the combination modes of host–CN usually
include these types: hydrogen boding interaction, deprotonation, addition reaction,
coordination and so on [19-22]. Among these methods, deprotonation as a simple
–
mechanism utilizing acidity of HCN are widely used in detection for CN . In recent
2
+
years, more and more fluorescent sensors for Zn are also reported, but they often

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have interference problems from other metal ions or low water solubility [23-30]. At
present, the sensors for single ion already could not satisfy demand. Hence the
convenient, even multi-objects recognized sensors have become particularly
imperative [31-33].
Our research group has a longstanding interest in molecular recognition [34-37].
–
2+
Furthermore, there are few literatures about simultaneously detecting CN and Zn .
Herein, we designed and synthesized an unsymmetrical azine derivative chemosensor
–
2+
(
YS) for respective recognition of CN and Zn . Sensor YS showed blue fluorescent
−
and UV-vis selectivity for CN in DMSO/H O (3:7, v/v) binary solution over other
2
anions based on a simple deprotonated mechanism. The detection limit of the probe
for the cyanide anion was below the ppm level, which was much lower than the
2
+
permitted limit of cyanide anions. And in the presence of Zn , sensor YS showed a
green fluorescence response at λmax = 510 nm. The coumarin group was introduced as
fluorophore to achieve fluorescent recognition. Differently from the previous reports,
here, we considered whether recyclable project could be achieved by adding of the
EDTA to affect the intramolecular charge of the molecular and induce fluorescence
–
2+
color changes. In addition, compared with other reported sensors for CN and Zn in
the table (In SI), the sensor YS as a simple and inexpensive compound had preferable
sensitivity and water solubility, it was worth mentioning that YS could achieve the
detection of two ions in different mix–aqueous solution. So the compound YS could
–
2+
be used as a potential optical sensor for CN and Zn ions. At the same time, the
1
mechanism of this process was verified by spectroscopic methods including H NMR,
UV–vis, and mass spectrometry.
2
2
. Experimental
.1. Materials and physical methods

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All reagents and solvents were commercially available at analytical grade
without further purification. Double–distilled water was purified by standard methods
−
−
and was used throughout the experiment. Tetrabutylammonium salt of anions (F , Cl ,
−
−
−
−
−
−
3+
2+
Br , I , AcO , H PO , HSO , and ClO ), perchlorate salt of cations (Fe , Hg ,
2
4
4
4
+
2+
2+
2+
2+
2+
2+
2+
3+
2+
Ag , Ca , Cu , Co , Ni , Cd , Pb , Zn , Cr and Mg ), sodium salt of anions
−
−
(
CN and SCN ) and HEPES were purchased from Alfa-Aesar Chemical Reagent Co.
and stored in a vacuum desiccator.
Melting points were measured on an X–4 digital melting-point apparatus. The
infrared spectra were performed on a Digilab FTS–3000 FT–IR spectrophotometer.
1
12
H NMR and C NMR were recorded on a Mercury–400BB at 400 MHz spectra. For
1
H NMR titrations, the sensor of stock solutions was prepared in DMSO–d , the
6
cyanide and zinc ions were prepared in D O. Aliquots of the two solutions were
2
mixed directly in NMR tubes. Electrospray ionization mass spectra (ESI–MS) were
measured on an Agilent 1100 LC–MSD–Trap–VL system. UV–vis spectra were
recorded on a Shimadzu UV–2550 spectrometer. Photoluminescence spectra were
performed on a Shimadzu RF–5301 fluorescence spectrophotometer. The structure of
sensor YS was further confirmed by single–crystal X–ray diffraction.
2
.2. Synthesis of sensor molecule YS
The synthesis route of probe molecule YS is demonstrated in Scheme 1. 4–
methyl–7–hydroxy–8–formyl–coumarin (0.41 g, 2 mmol), salicylaldehyde hydrazone
0.28 g, 2 mmol) and a catalytic amount of acetic acid (AcOH) were combined in hot
(
absolute EtOH (30 mL). The solution was stirred under reflux for 4 h. After cooling to
room temperature, the yellow precipitate was filtered, washed three times with hot
absolute ethanol, then recrystallized with EtOH to obtain a yellowy powdered product
1
YS in 82% yield. (m.p. 248–250°C). H NMR (DMSO–d , 400 MHz) δ: 12.55 (s, 1H,
6

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OH), δ: 10.88 (s, 1H, OH), δ: 9.30 (s, 1H, CH=N), δ: 9.08 (s, 1H, CH=N), δ:
6
.29~7.82 (m, 7H, ArH), δ: 2.51 (t, 3H, CH ) (Fig. S1); ESI–MS calcd for
3
+
+
-1
[
C H N O + H ] 323.32. Found 323.109. (Fig. S2) IR (KBr, cm ) v: 3446.78,
18 15 2 4
2
926.01, 1730.14, 1622.13, 1292.31, 1082.06, 758.02 (Fig. S3). The structure of
sensor YS was further confirmed by single–crystal X–ray diffraction (Fig. 1).
Scheme 1 Synthesis of the sensor molecule YS.
Fig. 1 Single-crystal X-ray structure of sensor YS.
3
3
. Results and Discussion
–
.1 Sensing CN
UV–vis absorption and fluorescence emission spectral response of chemosensor
−
−
−
−
−
−
−
−
–
YS were tested with the anions (F , CI , Br , I , AcO , H PO , HSO , ClO , CN
2
4
4
4
−
−
and SCN ) in DMSO/H O (3:7, v/v) solutions. Only after addition of CN , the
2

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solution of YS resulted in an immediate change in color from colorless to pale yellow.
In the corresponding UV–vis spectrum, a strong absorption band at 310 nm
−
disappeared, while a new band developed at 372 nm (Fig. 2). All examined anions (F ,
−
−
−
−
−
−
−
−
CI , Br , I , AcO , H PO , HSO , ClO , and SCN ) did not cause any obvious
2
4
4
4
color and spectral changes. These results suggested that sensor YS displayed an
−
excellent selectivity for CN over all other anions tested.
Compound YS alone displayed a weak, single fluorescence emission band at 430
nm when excited at 375 nm in DMSO/H O (3:7, v/v). Changes in spectral pattern
2
−
were observed only in the presence of added 50 equiv. of CN , chemosensor YS
produced a strong fluorescence response band and shifted toward 447 nm, and
responded with a dramatic color change from colorless to blue. No change in spectral
pattern for receptor YS in the presence of other anions suggested either a very weak
or no interaction between these anions and the compound (Fig. 3).
-5
Fig. 2 UV–vis spectra changes of YS (210 M) and in the presence of 50 equiv. of
various anions in DMSO/H O (3:7, v/v) binary solution at room temperature. Inset:
2
Color changes observed upon the addition of various anions (50 equiv.) to solutions of
-5
sensor YS (210 M) in DMSO/H O (3:7, v/v) solutions.
2

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-5
Fig. 3 Fluorescence spectra of YS (210 M) and in the presence of 50 equiv. of
various anions in DMSO/H O (3:7, v/v) binary solution at room temperature. Inset:
2
Color changes observed upon the addition of various anions (50 equiv.) to solutions of
-5
sensor YS (210 M) in DMSO/H O (3:7, v/v) solutions under a UV–lamp.
2
–
Fig. 4 (a) UV−vis spectra of YS (5.0 μM) in response to CN (0.0 to 22.4 equiv.) in
-5
DMSO/H O (3:7, v/v) (b) Absorption of YS (2.0×10 M) at 372 nm after adding of
2
various anions.
The absorption spectral changes of YS on addition of cyanide (0.01 M) in
DMSO/H O (3:7, v/v) solutions were shown in Fig. 4a. The absorption band at 310
2
nm decreased, while a new band at 372 nm appeared. A clear isosbestic point at 356
nm indicated an interconversion into single discrete chemical species during the
–
titration process. To validate the selectivity of sensor YS–CN , the some tests were
−
−
−
−
−
−
−
carried out using for other anions including F , CI , Br , I , AcO , H PO , HSO ,
2
4
4

ACCEPTED MANUSCRIPT
−
−
ClO , and SCN . The presence of only those anions caused no change in UV–vis
4
–
spectrum. However, in the presence of CN and the respectively competitive anions
above described, the absorbance changes were similar to that in the presence of only
–
CN . (Fig. 4b)
–
As shown in Fig. 5a, without CN , the sensor had almost no fluorescence, while
the significant increase of the fluorescence intensity of the solution was observed at
–
4
47 nm upon gradual addition of CN . In addition, the interfering anions also did not
influence the fluorescence spectrum. (Fig. 5b) These results indicated that YS was a
–
highly selective CN sensor and had good antijamming capability.
–
Fig. 5 (a) Fluorescence of YS in the presence of different concentration CN (0.0 to
-5
6
.7 equiv.) in DMSO/H O (3:7, v/v) (b) Fluorescence of YS (2.0×10 M) at 372 nm
2
after adding of various anions.
In order to apply in real life, it was very necessary to detect the analytes at low
concentrations. The detection limit of the fluorescence spectra measurements, was
calculated on the basis of 3S /S (where S is the standard deviation of the blank
B
B
solution and S is the slope of the calibration curve), Fig. 6 showed the detection limit
-7
−
of 1.69×10 M for CN , which was far lower than the maximum level for cyanide of
−
6
1
.9×10 M in drinking water from WHO guidelines. Meanwhile, the fluorescence
quantum yields increased from 0.27 to 0.76. (In SI)

ACCEPTED MANUSCRIPT
-5
Fig. 6 Fluorescence detection limit spectra of YS (210 M) in DMSO/H O (3:7, v/v)
2
−
-3
solutions upon adding of a concentration of CN (110 M).
For practical applicability, the fluorescence spectra of the solution of YS at
–
different pH in the absence and presence of CN were recorded. As shown in Fig. S4,
–
without CN , the fluorescence of the solution of YS had no obvious change in the pH
–
range 2–13. However, upon addition of CN , it could work well from 7 to 11.
1
According to H NMR titration experiments were conducted to further
−
investigate the interaction of YS with CN in DMSO-d , as shown in Fig. 8. When 1.0
6
–
1
2
equiv. CN was added, the signal of –OH (coumarin rings) and –OH (benzene rings)
respectively at 12.55 (s, 1H) and 10.88 (s, 1H) ppm had completely disappeared,
which stated clearly the –OH had deprotonation process and the other aromatic ring
1
proton signals gradually shifted to upfield due to the shielding effect. Therefore, H
NMR titration experiments suggested that the validity of the mechanism submitted
and the cause of the fluorescence enhancement presented.
This deprotonation process caused a high charge separation between acceptor
and donor unit in YS, and consequently excellent electron delocalization to
salicylaldehyde hydrazone unit. The excited states in the complexes were stabilized
−
upon the binding of CN , resulting in a bathochromic shift in the absorption band with
−
Dl = 60 nm for YS. Moreover, a new emission band at 533 nm for YS and CN was

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observed. It possibly caused by a large charge separation between salicylaldehyde
hydrazone unit and the coumarin rings resulting in a strong intramolecular charge
transfer (ICT). Consequently, the observed fluorescence enhancement is most likely
caused by the ICT. A schematic illustration was shown in Scheme 2. [38]
1
−
Fig. 7 H NMR titration in DMSO-d upon addition of varying amounts CN .
6
Scheme 2 The proposed reaction mechanism.
Generally, reaction-based chemosensors suffered from a long response time. In
−
our case, the response of YS to CN was found to be very fast (Fig. 8). After addition
−
of a solution of CN , the fluorescence emission intensity of YS in DMSO/H O (3:7,
2
v/v) solutions at 447 nm increased rapidly and reached a plateau in about 30 s. This

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–
result suggested that the recognition profiles of sensor YS with CN was completed
−
nearly instantly, so that CN ions were detected rapidly.
-5
Fig. 8 Fluorescence intensity of a solution of YS (210 M) in DMSO/H O (3:7, v/v)
2
−
solutions at 446 nm after addition of 50 equivalents CN .
The realization of quick response to cyanide is quite meaningful for the sensor in
its practical application in portable sensing devices. To facilitate the use of YS for the
detection of cyanide, test strips were prepared by immersing filter papers into a
DMSO/H O binary solution of YS (0.01 M) following by exposing it to air to dry it.
2
Intriguingly, the fluorescence color can be changed immediately from purple to
mazarine once the test paper was immersed
of
cyanide under UV irradiation (Fig. 9). Thereby, chemosensor YS exhibited excellent
fluorescence sensing performance, which will be very useful for the fabrication of
sensing devices with fast and convenient detection for cyanide and ions.
Fig. 9 Photographs of YS (0.01 M) on test strips (a) only YS, (b) after immersion into
−
water solutions with CN , (c) after immersion into water solutions with other anions,

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−
(
d) after immersion into water solutions with CN and other anions under UV light
respectively.
.2 Sensing Zn
To evaluate recognition studies of YS, Fe , Hg , Ag , Ca , Cu , Co , Ni ,
2
+
3
3
+
2+
+
2+
2+
2+
2+
2
+
2+
2+
3+
2+
Cd , Pb , Zn , Cr and Mg ions were used to measure the selectivity and
sensitivity of probe YS (20 M) in DMSO/H O (pH=7.2, v/v=7:3) HEPES buffer
2
solutions, and fluorescence spectra were recorded upon the addition of 20 equiv. of
2
+
each of these metal ions. Only in the presence of Zn , sensor YS showed a strong
fluorescence response at λmax = 510 nm, which responded with a dramatic color
change from colourless to green by the naked eyes under the UV–lamp (365 nm) as
shown in Fig. 10.
Fig. 10 Fluorescence emission data of YS (20μM) and different metal ions in
DMSO/H O (pH=7.2, v/v=7:3) HEPES buffer solutions. (λ = 475 nm). Inset: Visual
2
ex
2
+
3+
2+
+
2+
fluorescence emissions of sensor YS after the addition of Zn , Fe , Hg , Ag , Ca ,
2
+
2+
2+
2+
2+
3+
2+
Cu , Co , Ni , Cd , Pb , Cr and Mg (20 equiv.) in DMSO/H O (pH=7.2,
2
v/v=7:3) HEPES buffer solutions under the UV–lamp(365 nm).
3
+
To validate the selectivity of YS, the same tests were carried out using Fe ,
2
+
+
2+
2+
2+
2+
2+
2+
3+
2+
Hg , Ag , Ca , Cu , Co , Ni , Cd , Pb , Cr and Mg metal ions. None of these
ions induced any significant changes in the fluorescence spectrum of the sensor. The

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selectivity of YS for zinc ion over other metal ions was examined. Therefore, it was
clear that all potentially competitive metal ions exerted no or little influence on the
fluorescence detection of zinc ion in DMSO/H O (pH=7.2, v/v=7:3) HEPES buffer
2
solutions (Fig. 11).
Fig. 11 Fluorescence emission data of YS and different metal ions in DMSO/H O
2
(pH=7.2, v/v=7:3) HEPES buffer solutions (excitation wavelength = 475 nm).
To further investigate the interaction between YS and zinc ion, the fluorescence
emission spectral variation of YS in DMSO/H O (pH=7.2, v/v=7:3) HEPES buffer
2
solutions was monitored during titrations with different concentrations of zinc ions
from 0.0 to 8.4 equivalents (Fig. 12a). The binding constant K was determined to be
a
3
-1/2
2
0
.91×10 M . Meanwhile, the fluorescence quantum yields increased from 0.27 to
.63. (In SI)
The detection limit is one of the most important parameters in ion sensing. For
many practical purposes, it is very important to detect the analytes at low
2
+
concentrations. The fluorimetric detection limits of sensor YS for Zn were also
2
+
determined. As shown in Fig. S5, the minimum concentration of Zn that could be

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observed though one order of magnitude lower for fluorescence naked eye detection
-5
was 2.010 M by using a UV lamp at 365 nm. In the meantime, the detection limit
of the fluorescence spectra measurements, as calculated on the basis of 3s /S (where
B
sB is the standard deviation of the blank solution and S is the slope of the calibration
-8
2+
curve), Fig. 12b showed a detection limit of approximately 6.1×10 M for Zn . Thus,
2
+
YS can be applied to detect Zn at an extremely low concentration level.
2
+
Fig. 12 (a) Fluorescence spectra of YS-Zn in the presence of different concentration
of zinc ions (0.0–8.4 equiv.) in DMSO/H O (pH=7.2, v/v=7:3) HEPES buffer
2
-5
solutions. (b) Fluorescent detection limit spectra of YS (2.0×10 M) in DMSO/H O
2
(pH=7.2, v/v=7:3) HEPES buffer solutions upon adding of an increasing
2
+
concentration of Zn .
2
+
With the Zn concentration increasing, the fluorescent intensity remarkably
increased at 510 nm. In order to gain an insight into the stoichiometry of the complex,
the method of continuous variations was used as shown in Fig. 13. As expected, when
2
+
the molar fraction of sensor YS-Zn was 0.35, the value approached a maximum,
2
+
which revealed the possible formation of a 1:2 complex between the sensor Zn and
YS.

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2
+
2+
Fig. 13 Job plot of YS and Zn , which indicated that the stoichiometry of YS-Zn
complex was 1:2.
The pH dependence in aqueous media was examined using fluorescence
+
–
emission spectroscopy (Fig. S6). Free YS was insensitive against H and OH . And
2
+
when Zn was added to the buffered solution of YS at different pH values, the results
2
+
indicated that YS binding with Zn occurred effectively in the range of pH = 7–12.In
2
+
order to investigate the reversibility of YS, the addition of Zn to the solution of
sensor YS lead to fluorescence increasing. By addition of EDTA to the solution of
2
+
YS–Zn complex, the emission intensity of YS diminishes. This “Off–On–Off”
switching process could be repeated at several times with little fluorescent efficiency
loss (Fig. 14).
2
+
Fig. 14 Fluorescence study showing reversibility of Zn coordination to YS by
EDTA.

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Generally, reaction-based chemosensors suffer from a long response time. In our
2
+
case, the response of YpriS to Zn was found to be very fast (Fig. S7). After addition
2
+
of a solution of Zn , the fluorescence emission intensity of YS in DMSO/H O
2
(pH=7.2, v/v=7:3) HEPES buffer solutions at 510 nm increased rapidly and reached a
plateau in about 15 s. This result suggested that the recognition profiles of sensor YS
2
+
2+
with Zn was completed nearly instantly, so that Zn ions were detected rapidly.
2
+
1
In order to further validate the conjugation of YS–Zn , we did H–NMR
titration experiments As shown in Fig. 15, after adding 2.0 equivalents of zinc ions,
1
the single –OH of coumarin group peak at 12.55 ppm decreased and gradually
2
+
disappeared, due to binding to electron deficient Zn . Another hydroxyl proton peak
2
+
(
10.88 ppm) was gradually shifted downfield due to the addition of Zn destroying
the intramolecular hydrogen bonding, which was leading to electron density
decreased. The two proton peaks at 9.30 and 9.08 ppm corresponded to the protons of
CH=N showed upfield shift. In addition, the aryl protons also had different changes in
chemical shift.
1
2+
Fig. 15 H NMR titration in DMSO-d upon addition of varying amounts Zn .
6

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2
+
In the ESI-MS spectra of YS–Zn complex, we found a new peak appeared at
2
+
+
7
7
07.08, which coincides well with that for the species [Zn +2 YS -H] (m/z calcd.
2
+
07.11). A Job plot also indicated that Zn and YS ion form 1:2 adduct. Based on the
above findings, we proposed that the reaction mechanism in this system may proceed
through the route depicted in Scheme 3. The existence of hydrogen bonding blocked
intramolecular energy transfer, which was leading to host molecule could not show
2
+
2+
fluorescence. Upon addition of Zn , the chelation of heteroatom with Zn resulted in
2
+
the efficient inhibition for the PET process of the C=N group. As a result, YS-Zn
showed strong fluorescence. [39-40]
2
+
Scheme 3 Proposed mechanism for detection of Zn by YS.
To facilitate the use of YS for the detection of zinc, test strips were prepared by
immersing filter papers into a DMSO/H O binary solution of YS (0.01 M) followed
2
by exposure to air until complete drying. Intriguingly, the fluorescence color could be
changed immediately from purple to grass green once the test paper was immersed
2
+
into an aqueous solution (5 M) of Zn under UV-vis irradiation (Fig. 16). Thereby
the sensor YS exhibited excellent fluorescence sensing performance, which would be
very useful for the fabrication of sensing devices with fast and convenient detection
2
+
for Zn .

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Fig. 16 Photographs of YS (0.01 M) on test strips (a) only YS under UV light, (b)
2
+
after immersion into water solutions with Zn under UV light, (c) after immersion
into water solutions with other anions under UV light, (d) after immersion into water
2
+
solution with Zn and other ions under UV light.
.3 Theoretical calculations
Further to confirm the proposed mechanism of sensor YS with CN and Zn , we
3
−
2+
performed DFT calculations done at the B3LYP/6-311g (2d, p) level of theory. [41-42]
The highest occupied molecular orbital (HOMO) and the lowest unoccupied
–
molecular orbital (LUMO) of YS and the YS-CN complex were investigated and
shown in Fig. 17. Obviously, the HOMO–LUMO energy band gap of YS was 93.74
–
kcal/mol. it was higher than that of YS-CN complex (87.48 kcal/mol), which caused
2
+
the red–shift in the absorption band of YS. The presence of Zn ions in compound
YS caused the change of electron density. And the HOMO–LUMO energy band gap
2
+
of YS was also higher than that of YS-Zn complex (80.78 kcal/mol). These
calculations results were consistent with the experimental results.

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Fig. 17 Density functional theory computed diagrams of LUMOs, HOMOs and
–
energy gaps of YS and YS–CN , blue ball is nitrogen, grey ball is carbon, red ball
both are oxygen and white ball is hydrogen.
Fig. 18 Density functional theory computed diagrams of LUMOs, HOMOs and
2
+
energy gaps of YS and YS–Zn , blue ball is nitrogen, grey ball is carbon, pink or red
ball both are oxygen and white ball is hydrogen.
4
. Conclusion
In conclusion, we have presented a facile, rapid and efficient chemosensor YS,
–
2+
which could recognize CN and Zn with different fluorescence changes and
different mechanisms. Moreover, the detection limit on fluorescence response of the
−
-7
sensor to CN is down to 1.69×10 M, which is far lower than the WHO guideline of
−
6
1
.9×10 M. According to Job’s plot and ESI-MS, binding stoichiometry of
metal/ligand complex was found by fluorescence method as 2:1. In addition, test
strips based on YS were fabricated, which could serve as a practical colorimetric and
−
2+
fluorimetric sensor to detect CN and fluorescent “OFF–ON” for Zn . We believe
this work provides an underlying applications for constructing a fluorescent sensor for
–
2+
highly selective and rapidly recognition of CN and Zn ions based on different
mechanisms respectively in aqueous.

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Acknowledgment
This work was supported by the National Nature Science Foundation of China
no. 21467012).
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A new unsymmetrical azine derivative based on coumarin
–
group as dual-modal sensor for CN and fluorescent “OFF–
2+
ON” for Zn in aqueous media
a†
a
a
b
b
Jing-Han Hu , You Sun , Jing Qi , Qiao Li , Tai-Bao Wei
a
College of Chemical and Biological Engineering, Lanzhou Jiaotong University,
Lanzhou, Gansu, 730070, P. R. China
E-mail: hujinghan62@163.com
b
College of Chemical and Chemical Engineering, Northwest Normal University,
Lanzhou, Gansu, 730070, P. R. China
E-mail address: zhangnwnu@126.com
Graphical abstract: In this work, an unsymmetrical azine derivative chemosensor
–
2+
(
YS) for respective recognition of CN and Zn was designed and synthesized.
Sensor YS exhibited high sensitivity and good selectivity for cyanide and zinc in
aqueous solution.
†
Corresponding author: Prof. Jing-Han Hu, E-mail: hujinghan62@163.com, Tel: +86 931 18109460354

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Highlights
. A structurally simple sensor could achieve the detection of two ions in aqueous
solution.
. This sensor was successfully applied to detect CN by dual-modal and showed
1
−
2
2
+
fluorescence turn-on response rapidly for Zn in aqueous solution.
3
4
. Taking advantage of a simple mechanism of deprotonation.
. Test strips based on YS were fabricated, which could act as a convenient and
–
2+
efficient CN and Zn test kit.