A new colorimetric and ratiometric fluorescent probe for selective recognition of cyanide in aqueous media

Article abstract of DOI:10.1016/j.saa.2019.03.063

A simple naphthopyran derivative (L) has been synthesized as a colorimetric and ratiometric fluorescent probe for cyanide sensing in the aqueous DMSO medium and paper strips. The nucleophilic addition of CN^? to this probe blocks the π-conjugation and the intramolecular charge transfer (ICT) transition between naphthopyran and benzoindolium moieties and consequently results in remarkable color and spectral changes. Upon addition of cyanide, L displayed a ratiometric fluorescence response with a blue shift of the peak position and a noticeable color change from fuchsia to colorless within 90 s. The probe exhibits high selectivity and sensitivity toward CN^? over other anions and the detection limit was calculated to be 7.56 × 10^?7 M, which is well below the WHO cyanide standard in drinking water (1.9 μM). In addition, the excitation and emission of the probe were within the visible wavelength range, which could benefit an application of the probe in an inexpensive portable cyanide sensor. The sensing ability of L has been successfully applied in real water samples. Furthermore, test strips based on L were fabricated, which can act as convenient and efficient test kits for detecting CN^?.

Full text of DOI:10.1016/j.saa.2019.03.063

Accepted Manuscript
A new colorimetric and ratiometric fluorescent probe for selective
recognition of cyanide in aqueous media
Zhen Ming Dong, Hong Ren, Jia Na Wang, Jian Bin Chao, Yu
Wang
PII:
S1386-1425(19)30301-4
https://doi.org/10.1016/j.saa.2019.03.063
SAA 16953
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
To appear in:
Received date: 21 November 2018
Revised date:
Accepted
date:
25 February 2019
1
8 March 2019
Please cite this article as: Z.M. Dong, H. Ren, J.N. Wang, et al., A new colorimetric
and ratiometric fluorescent probe for selective recognition of cyanide in aqueous media,
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, https://doi.org/
1
0.1016/j.saa.2019.03.063
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ACCEPTED MANUSCRIPT
A New Colorimetric and Ratiometric Fluorescent Probe for Selective
Recognition of Cyanide in Aqueous Media
Zhen Ming Dong, Hong Ren, Jia Na Wang, Jian Bin Chao, Yu Wang
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China
ABSTRACT A simple naphthopyran derivative (L) has been synthesized as a colorimetric and
ratiometric fluorescent probe for cyanide sensing in the aqueous DMSO medium and paper strips.
-
The nucleophilic addition of CN to this probe blocks the π-conjugation and the intramolecular
charge transfer (ICT) transition between naphthopyran and benzoindolium moieties and
consequently results in remarkable color and spectral changes. Upon addition of cyanide, L
displayed a ratiometric fluorescence response with a blue shift of the peak position and a
noticeable color change from fuchsia to colorless within 90 s. The probe exhibits high selectivity
-
and sensitivity toward CN over other anions and the detection limit was calculated to be
-7
7
.56×10 M, which is well below the WHO cyanide standard in drinking water (1.9 µM). In
addition, the excitation and emission of the probe were within the visible wavelength range, which
could benefit an application of the probe in an inexpensive portable cyanide sensor. The sensing
ability of L has been successfully applied in real water samples. Furthermore, test strips based on
L were fabricated, which can act as convenient and efficient test kits for detecting CN-.
Keywords: Ratiometric; Fluorescence; Colorimetric; Probe; Cyanide anion
∗
Corresponding author. Tel.: +86 351 7010588; fax: +86 351 7011688.
E-mail: wangyu1168@sxu.edu.cn (Y. Wang).

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1. Introduction
As an important chemical, cyanide has been widely used in many industries such as mining,
electroplating, gold extraction and synthetic fiber production [1]. Besides, some organisms
including bacteria, fungi and algae produce cyanide ions as part of their nitrogen metabolic
pathways [2]. Consequently, the increasing cyanide contamination in our living environment and
ecosystem has created great concerns because cyanide is one of the most fatal toxic anions and
fast-acting poisons to humans. Cyanide can strongly bind at the heme unit of cytochrome c in its
active site and thereby destroy the central respiratory system of the body, leading to various types
of physiological disorders like convulsions, loss of consciousness and eventually death [3]. For
these toxic effects, the World Health Organization (WHO) has suggested a permissible limit of 0.2
ppm (ca.1.9μM) in drinking water [4]. Owing to the toxicological and environmental concern, the
selective, sensitive detection of cyanide is significantly important for the biological, industrial,
environmental, and practical applications.
Currently, designing a fluorescent sensor for anions is of great interest [5]. Until now, in the
field of cyanide sensing, many chemosensors have been developed, wherein the sensing
mechanism is based on hydrogen-bonding interaction, metal complex ensemble displacement,
anion induced deprotonation, nucleophilic addition reaction, etc. [2, 5-23]. Despite having many
cyanide sensors, some limitations still exist, such as long response time, low sensitivity,
complicated synthesis process, the need for short UV light excitation, etc. In particular, many of
the reported probes are based on fluorescence measurement at a single wavelength and ratiometric
-
fluorescent probes for CN are still very limited [24-39]. In fact, ratiometric sensing is more
favorable because the measurement of emission intensities at two different wavelengths can
reduce the impact of external factors and therefore greatly improve the reliability of the
measurements. Thus, developing new ratiometric probes for cyanide with high sensitivity is highly
desirable.
Altering intramolecular charge transfer (ICT) of fluorophores is an effective strategy to
design ratiometric fluorescent sensors for anions since ICT can cause both intensity changes and
spectral shift. Based on ICT sensing mechanism, we herein report a highly selective and reliable
-
ratiometric fluorescence probe for the recognition of CN . The probe is composed of
naphthopyran-3-carboxaldehyde and a highly activated benzo[e]indolium ion acceptor linked

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through a carbon–carbon double bond, which exhibits a strong intramolecular charge transfer (ICT)
process from electron-rich naphthopyran to the benzo[e]indolium moiety through the double bond
-
conjugated spacer. The facile nucleophilic attack of CN toward the benzo[e]indolium group
interrupts the extensive π-conjugation and thereby hinders the ICT process, leading to dramatic
changes in the color as well as shifts in absorption and emission maxima. The observed
ratiometric changes enabled both qualitative and quantitative detection of cyanide in aqueous
media. Furthermore, a filter paper-based strip was prepared for the naked-eye detection of cyanide
under both visible light and UV irradiation.
2
2
. Experimental
.1. Chemicals and instrumentation
2
-Hydroxy-1-naphthaldehyde (98%) was purchased from Energy Chemical (Shanghai,
China). 1,1,2-Trimethyl-1H-benzo[e]indole (98%) was obtained from Aladdin Industrial
Corporation(Shanghai, China). Iodoethane (99%) was from Shanghai Macklin Biochemical
Technology Co., Ltd (Shanghai, China). Other needed reagents were commercially available at
analytical grade and used as received. Stock solutions of anions were prepared by dissolving
appropriate amounts of their sodium or potassium salts in water. Deionized double distilled water
was used throughout the study.
A UV-2450 spectrophotometer (Shimadzu, Japan) was used for UV-vis absorption
measurements. A Hitachi FL-4600 spectrofluorimeter (Tokyo, Japan) was used for fluorometric
1
measurements. H-NMR spectra were recorded on a Bruker AVANCE III HD 600 MHz
spectrometer. High resolution mass spectra of receptor L and the L–CN adduct were obtained on a
Q Exactive mass spectrometer (Thermo Fisher Scientific). The pH measurements were carried out
using a pHS-3C acidometer (Shanghai Precision &Scientific Instrument Co., Ltd, China).
2.2. Synthesis of the probe L
As illustrated in Scheme 1, the synthesis of probe L was accomplished in three steps.
2H-benzo[h]chromene-3-carbaldehyde was prepared according to the literature method [40]. A
1
golden-yellow solid was obtained. H NMR (DMSO-d6) δ(ppm): 9.72 (s, 1H), 8.44 (s, 1H), 8.24
(d, J=8.7, 1H), 8.00 (d, J=9.0, 1H), 7.92 (d, J=8.4, 1H), 7.63 (t, J=7.8, 1H), 7.46 (t, J=7.5, 1H),
7.19 (d, J=9.0, 1H), 5.05 (s, 2H). 1-ethyl-2,3,3-trimethylbenzo[e]indolium iodide was synthesized
1
according to literature reports[41]. A gray purple solid was obtained. H NMR (DMSO-d6) δ(ppm):

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8
1
.38 (d, J=8.4, 1H), 8.31 (d, J=9.0, 1H), 8.23 (d, J=8.1, 1H), 8.17 (d, J=9.0, 1H), 7.79 (t, J=7.2,
H), 7.73 (t, J=7.5, 1H), 4.63 (q, J=7.2, 2H), 2.95 (s, 3H), 1.76 (s, 6H), 1.51 (t, J=7.5, 3H). In the
last
step,
2H-benzo[h]chromene-3-carbaldehyde
(0.11
g,
0.5
mmol)
and
1-ethyl-2,3,3-trimethylbenzo[e] indolium iodide (0.19 g, 0.5 mmol) was dissolved in 3 mL of
ethanol. Then a catalytic amount of piperidine (5 µL) was added. After addition, the reaction
mixture was refluxed for 6 h and then cooled to room temperature. The dark-purple precipitate
1
obtained was filtered and washed with cold ethanol (2 × 1 ml). Yield = (0.23 g) 84%. H NMR
(DMSO-d
6
) δ(ppm): 8.67 (s, 1H), 8.46 (t, J=9.4, 2H), 8.31 (d, J=8.8, 1H), 8.25 (q, J=8.5, 2H), 8.12
(d, J=8.8, 1H), 8.04 (d, J=9.0, 1H), 7.97 (d, J=8.2, 1H), 7.83 (t, J=7.6, 1H), 7.73 (m, 2H), 7.52 (t,
J=7.5, 1H), 7.27 (d, J=8.8, 1H), 7.01 (d, J=16.3, 1H), 5.48 (s, 2H), 4.78 (q, J=7.2, 2H), 2.05 (s, 6H),
1
3
1
1
1
.51 (t, J=7.2, 3H). C NMR (DMSO-d ): 181.37, 155.80, 150.16, 138.75, 138.68, 136.60, 134.79,
6
33.58, 131.60, 130.73, 130.52, 129.58, 129.49, 129.18, 128.92, 128.71, 127.62, 127.30, 125.38,
23.66, 122.14, 117.94, 116.04, 113.55, 110.69, 64.64, 53.99, 42.59, 26.01, 14.21. HRMS(ESI): calcd.
+
for C31H
28NO 430.21654, found 430.21671.
Scheme1 The synthesis of probe L
.3. Sample preparation for the spectroscopic studies
2
-3
A stock solution of probe L (1.0×10 M) was prepared in DMSO. Stock solutions of anions
-2
(
1.0×10 M) were prepared in deionized water. Absorption and fluorescence spectra of L were
-
recorded in the absence and presence of different anions including CN in 10 mM HEPES buffer
DMSO/water=3:2 v/v (pH 7.4). Typically, for the titration, the probe and different anion
sodium/potassium salts were mixed in such a way to get the final concentration of the probe to be
20μM with the preferred concentration of the anion.
3
3
. Results and discussion
.1 Spectroscopic and Selectivity Studies of Anions
The sensing behavior of sensor L was investigated by monitoring its UV-visible and

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fluorescence spectra in the presence of various anions in DMSO/water (3:2 v/v, pH 7.4). The
solution of L appears fuchsia and its UV–vis spectrum exhibits a strong ICT band at 538 nm.
-
Upon addition of various anions, only CN induces a significant change in the absorption spectra
-
of L. Fig. 1a shows the ICT peak of L disappeared in the presence of CN with concomitant
change in color from fuchsia to colorless. Some absorption decrease at 538 nm was also shown by
2
-
-
S ions. However, the change is very small in comparison to the decrease with CN and also no
2
-
obvious color change was detected upon addition of S (Fig. 1c). Moreover, in the competing
-
experiment, the spectral responses and color change of the probe L toward CN ions was hardly
affected by other competing anions (Fig. 2a). Furthermore, addition of common metal ions such as
+
2+
+
2+
3+
2+
2+
2+
2+
2+
2+
2+
3+
+
3+
K , Ca , Na , Mg , Al , Zn , Cd , Cu , Hg , Pb , Ni , Co , Fe , Ag and Cr hardly
influenced the spectral nature of probe L as depicted in Fig. 2b. Thus, the interferences from metal
ions can be eliminated. Due to its excellent colorimetric responsive characteristic property, L
-
could be easily utilized for detection of CN with the naked eye.
2
Fig. 1 (a) UV-vis absorption and (b) Emission spectra of L (20 μM) in DMSO-H O (3:2, v/v, HEPES, pH 7.4) in
the presence and absence of various anions (80 μM). Inset: Amplification within 538-800nm in fluorescence
spectra. (c) and (d) The color and fluorescence change of L upon the addition of various anions (4 equiv.). All the
images were obtained 1.5 min after the addition of the anions.
-
To validate the selectivity of L toward CN , fluorescence spectrum of L was also studied in
presence of other anions. Upon excitation at 413 nm, probe L exhibited a strong emission band at
525nm and a broad centered weak emission band at λmax~680 nm (Fig. 1b), which could be

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attributed to emission of naphthopyran moiety and the ICT emission, respectively. The large
Stokes shift observed can be attributed to the extended π-conjugation and ICT transition in the
probe molecule. The charge transfer emission at ~680nm is quenched while significant
-
fluorescence emission enhancement at 525 nm has been observed in presence of CN . The
-
dramatic fluorescence quenching at ~680 nm of the probe L is specific in case of CN addition.
-
2-
The only anion that showed response toward the probe L along with CN was S , but this
-
interference was ignored due to the instantaneous colorimetric response in the case of CN ions
which clearly discerned it from S2- ions. Under a UV-lamp of 365 nm, the weak fuchsia
fluorescence color of L changed to a strong greenish fluorescence only in the presence of cyanide
ions, which is well discriminated from L in presence of other anions as shown in Fig. 1d.
-
Fig. 2 (a) UV-vis absorption spectra of L upon addition of CN in the presence of interfered anions and (b) UV-vis
-
5
-
n-
−5
absorption spectra of L in the presence of metal ions. [L]=2.0×10 M, [CN ]=[A ]=8.0×10 M, [metal
-
4
ions]=1.0×10 M.
-
To further elucidate the selectivity of the probe L with CN , competitive experiments were
-
executed by the addition of anions (4 equiv.) to the solution of L containing CN ions (4 equiv.).
-
There was no obvious interference of other anions in the detection of CN (Fig. 3). As shown in
-
Fig. 3b, the fluorescence intensity of [L-CN ] remained unchanged in the presence of an excess of
-
other anions. This clearly illustrates the excellent selectivity of L toward CN compared to other
-
anions, which can be attributed to the strong nucleophilicity of CN . Thus, L proved to be an
-
excellent fluorescent probe for CN ions over other competitive anions.

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-
Fig. 3 (a) Emission spectra of L upon addition of CN in the presence of interfered anions and (b) Fluorescence
-
5
-
n-
−5
intensity of L in the presence of interfered anions. [L]=2.0×10 M, [CN ]=[A ]=8.0×10 M.
-
3
.2 The CN sensing property
-
Fig. 4 (a) Absorption spectra and (b) fluorescence titration of L (20 μM) with varying concentration of CN (up to 4
equiv.). Inset in (b): Amplification within 638-800nm in fluorescence spectra and the ratiometric calibration curve
-
(
I
525nm/I680nm) as a function of CN concentration.
-
The sensing behavior of L toward CN was further studied through UV-Vis and fluorescence
-
titrations. Upon the addition of consecutive amounts of CN , an obvious decrease in the
absorbance at 538 nm occurred and concomitantly intensity of the peak at 367 nm increased (Fig.
4a). An isosbestic point was observed at 413 nm, demonstrating the formation of a new compound.
-
Notably, the ratio of A367/A538 increased ~11-fold in the presence of 4 equiv. CN . Moreover, the
-
gradual addition of CN elicited a significant increase in the emission at 525 nm and decrease in
the emission at 680 nm accompanied by a distinct isoemissive point at 638 nm (Fig. 4b). When 1
−
equiv. CN was added, the emission ratio (F525/F680) of the probe changed dramatically from 8.0 to
19.7. These spectral changes are in agreement with a nucleophilic addition mechanism. The probe
-
L could potentially undergo nucleophilic attack by CN , which would block the π-conjugation and
ICT transition between naphthopyran and benzoindolium moieties and consequently induces a
ratiometric fluorescence change with a large emission shift.

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-
Fig. 5 The pseudo first-order kinetic fitting plot of the reaction of L (20 μM ) with CN (80 μM)
The response time is an important practical parameter. Time-dependent absorbance change of
-
the probe L upon addition 4.0 equiv. of CN was thus investigated. After adding cyanide ions, the
absorption band at 538 nm decreased immediately and the absorbance reached a plateau within
about 90 s, and remained constant thereafter. This result suggests that probe L is a ‘‘fast response’’
-
probe for cyanide and may be suitable for real-time sensing of CN in environmental systems.
Moreover, Fig. 5 displayed that the nucleophilic reaction obeyed a typical pseudo-first-order with
-1
a rate constant (kobs) of 0.0429 s .
-
-5
-
-5
Fig. 6 Effect of pH on fluorescence of L and L+CN . [L]=2.0×10 M, [CN ]=8.0×10 M.
The effect of pH on probe L and its sensing process was examined over a wide pH range. Fig.
6
depicts the changes in the fluorescence intensity of L at 525 nm in the absence and presence of
-
-
CN ion.Probe L showed efficient fluorescence response toward CN over a pH range of 5.0–8.0,
-
indicating that L was suitable for the CN detection in biological medium and in most neutral
environmental samples.
Under optimal experiment conditions, the emission ratios (I525nm/I680 nm) were linearly
-
−5
2
proportional to the concentration of CN in the range of 0–2.0×10 M (R = 0.9913) (Fig. 4b),
-
which allows the determination of CN concentration ratiometrically. The limit of detection was
calculated by dividing three times standard deviation of the blank sample with the slope of the
-7
calibration curve, and was calculated to be 7.56×10 M. In addition, the emission intensity at 525

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-
−5
2
nm was linear in relation to CN concentrations in the range of 0–2.0×10 M (R = 0.9931), with a
-8
detection limit of 1.02×10 M.
-
Table 1 Comparison of some fluorescence ratiometric probes for CN detection
Refs.
Testing media
λex(nm)
-
Response time
30 min
8 min
10 min
90s
LOD(M)
2.4×10-7
7.5×10-7
2.1×10-6
1.5×10-6
4.08×10-7
7.1×10-9
9.0×10-8
2.3×10-7
5.52×10-8
2.7×10-8
2.3×10-7
7.56×10-7
2
2
3
3
3
3
3
3
3
3
3
8
9
0
1
2
3
4
5
6
7
8
buffer-CH
3
CN (v/v, 1/4)
THF
-
THF-H
2
O (v/v, 9/1)
-
DMSO-H
2
O (v/v, 5/95)
411
340
360
330
340
325
480
390
413
buffer-DMSO (v/v, 4/6)
10min
5s
3 2
CH CN-H O (v/v, 1/9)
DMSO-H
2
O (v/v, 1/9)
2 min
10 min
-
DMSO
buffer-DMSO (v/v, 99/1)
EtOH
6s
DMSO-H
2
2
O (v/v, 1/9)
O (v/v, 3/2)
60 min
90s
This work
DMSO-H
-
Not mentioned.
The novelty of L was checked by comparing with the analytical results of some recently
-
published fluorescence ratiometric probes for CN , which revealed that the probe L showed
comparable/superior analytical performance. In terms of sensitivity, the proposed method is not
the best. However, the detection limits are much lower than the limit recommended in the World
Health Organization (WHO) guidelines for drinking water (1.9 μM), indicating that the probe may
-
be sensitive enough for the detection of CN in environmental samples. Compared with the probe
in our previous report [34], the important features of the present probe include its more facile
synthesis, faster response and longer excitation wavelength in the visible region, which could
-
benefit an application of this probe in an inexpensive portable CN sensor.

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3.3. Sensing mechanism
-
Fig. 7 Job’s plot from the emission intensity changes for L and CN complexation.
-
Based on the spectral changes, we propose that the nucleophilic addition of CN toward L
results in the breaking of the extensive π-conjugation, thereby blocking the ICT process. The
reaction mechanism of the present system was further investigated using Job’s plot, ESI-MS and
NMR. Job's plot analysis of the fluorescence titration spectra indicated L reacted with cyanide in a
1:1 stoichiometric manner (Fig. 7). The molecular ion peak appeared in HRMS spectra for
L+CN+H at m/z 457.22677 [calcd., m/z: 457.22799], clearly supporting the formation of a 1 : 1
stoichiometric reaction product (Fig. 8).
Fig. 8 ESI-MS spectrum of the product formed upon reaction of L with CN-.
-
1
The interaction mechanism of L with CN was further investigated through H NMR titrations
1
in DMSO-d6 solvent. The H NMR spectrum of free receptor L (Fig. 9) showed signals at 4.78
and 1.51 ppm corresponding to the ethyl protons attached to the quaternary N (marked as Hc and
-
He). After the addition of CN ions, these two protons disappeared, while new upfield signals
appeared at 4.26 ppm and 1.37ppm, respectively. The proton signals of pyran ring (Ha and Hb)
and the methyl group of indole ring (Hd) also shifted upfield. These changes revealed a

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nucleophilic addition mechanism, i.e. cyanide was added to the C atom of C=N bond of the
benzoindolium moiety. The nucleophilic addition of cyanide results in an augmentation of electron
density in the entire molecule and causes a shielding effect leading to upfield shifts of protons. It
is worthy to note that the Hd proton splits into two peaks (Hd’ and Hd’’), indicating that the two
methyl groups become non-equivalent after addition of cyanide.
1
-
Fig. 9 The H NMR spectral changes observed for L upon the addition of various amounts of CN in DMSO-d
6
and
a plausible mode of the interaction of L with CN-.
3.4. Real water sample analysis and Paper strip experiment
-
Table2 Determination of CN in water samples
-
-
CN added
CN found
Recovery
(%)
R.S.D.
Samples
-
6
-6
(
10 M)
(10 M)
(n = 5) (%)
Tap water1
Tap water 2
Tap water 3
Tap water 4
River water1
River water 2
River water 3
River water 4
0
－
－
95.5
105.6
100.4
－
－
2.00
10.0
18.0
0
1.91
10.56
18.08
－
1.83
1.42
0.45
－
2.00
10.0
18.0
1.93
9.56
17.76
96.5
95.6
98.7
2.27
1.87
1.42
−
Encouraged by the excellent selectivity and sensitivity of L toward CN sensing, we
−
investigated the ability of the probe to detect CN ions in three water samples. The assessment was

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determined by the spike and recovery method. The samples were spiked with various
concentrations of cyanide and tested using the developed assay. The recovery for the cyanide
sensing experiments ranges from 95.5 to 105.6% with low RSD values, indicating that the probe L
−
has great potential for the monitoring of CN concentration in water solutions.
To facilitate the real time application of probe L, test strips were also prepared and dipped in
cyanide solutions of known concentrations, followed by air drying. As shown in Fig. 10, the
-
visible color changes of the probe in the presence of CN ions can be observed under both visible
light and under UV-illumination at 365 nm. These results showed that the L-based test strips can
-
quickly and conveniently detect CN in an aqueous medium without any spectroscopic
instrumentation.
Fig. 10 Color and emission changes of L-based test strips before and after addition of CN-.
4. Conclusions
-
In summary, a ratiometric fluorescent probe for the recognition of CN was developed,
-
which displays colorimetric and fluorescence dual responses toward CN over other anions in
neutral aqueous medium. A hypsochromic shift both in the absorbance and emission spectra
occurs as a result of ICT suppression due to the nucleophilic addition of cyanide to L. The limit
-7
of detection was calculated to be 7.56×10 M. These behaviors of L, i.e. working in neutral
aqueous media, functioning in a ratiometric mode, displaying high selectivity and rapid response
(90s), and being excitable by visible light, make L a promising candidate as a selective
-
colorimetric and ratiometric fluorescent probe to detect CN ions in the biological and
environmental monitoring works. The probe was successfully applied in the analysis of real
samples with satisfactory results. Moreover, the L-based test strips can quickly and conveniently
-
detect CN in an aqueous medium without resorting to any spectroscopic instrumentation.
Acknowledgments
This work was financially supported by the National Natural Foundations of China

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(
No.21475080), the Research Project Supported by Shanxi Scholarship Council of China
2017-Key1), and the Project Sponsored by the Scientific Research Foundation for the Returned
(
Overseas Chinese Scholars, State Education Ministry.
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Graphical abstract

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Highlights
•
•
•
•
•
Novel probe L was synthesized and characterized.
L exhibits ratiometric and Turn-on fluorescence changes with cyanide ions.
The probe can be excited with visible light.
The response time is 90s.
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Test strips were fabricated for detecting CN in water samples.