Highly Selective and Sensitive Colorimetric and Fluorescent Chemosensors for Rapid Detection of Cyanide Anions in Aqueous Medium: Investigation on Supramolecular Recognition of Tweezer?shaped Salophenes

Article abstract of DOI:10.1007/s10895-021-02738-9

Three tweezer?shaped salophenes having catechols (1), phenols (2) and anisoles (3) units in conjunction to the dipodal Schiff bases have been applied for the optical sensing of cyanide (CNˉ) ions in CH₃CN-H₂O (7:3) as solvent of choi

Full text of DOI:10.1007/s10895-021-02738-9

Journal of Fluorescence (2021) 31:1085–1097
https://doi.org/10.1007/s10895-021-02738-9
ORIGINAL ARTICLE
Highly Selective and Sensitive Colorimetric and Fluorescent
Chemosensors for Rapid Detection of Cyanide Anions in Aqueous
Medium: Investigation on Supramolecular Recognition
of Tweezer‑shaped Salophenes
Hossein Reza Darabi1 & Ramo Nazarian1 & Sepideh Alizadeh1 & Kioumars Aghapoor1 & Leila Ebadinia1
Received: 9 March 2021 /Accepted: 3 May 2021
/ Published online: 8 May 2021
#
The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021
Abstract
Three tweezer‑shaped salophenes having catechols (1), phenols (2) and anisoles (3) units in conjunction to the dipodal Schiff
bases have been applied for the optical sensing of cyanide (CN¯) ions in CH3CN-H2O (7:3) as solvent of choice. Among them,
compounds 1 and 2 recognized CN¯, relying on distinct color and spectral changes. They are easy-to-use probes that exhibit
extremely high sensitivity (limit of detection = 1–10 nM), rapid response (5 s) and excellent selectivity. Moreover, the visual
detection and concentration determination of CN¯ by solution test kits of both sensors are the advantages for the practical
applications. Based on the fluorescence and NMR spectroscopy, as well as the OH¯ and reversibility experiments, the explicit
effect of hydroxyl groups on sensing and as well the different recognition of 1 and 2 toward CN¯ ions was proved. While probe 1
senses CN¯ via deprotonation, probe 2 recognizes it through an intramolecular aldimine condensation cyclization, leading to
formation of anions of dihydroxyquinoxaline 4. This chemodosimetry is being reported for the first time in a Schiff’s base.
Furthermore, the similarity of fluorescence and NMR responses of 2 and 4 toward CN¯ supports the proposed process.
.
.
.
.
Keywords Salophenes Schiff base Cyanide sensing IACC process Test kits
Introduction
control of CN¯ in various sources of water, under the WHO
allowable level, is an important duty [6]. Therefore, the devel-
opment of new optical chemosensors for this hypertoxic ion is
a paramount challenge.
Although there are numerous efficient optical
chemosensors to recognize CN¯ in various samples, the de-
sign of an accurate, cost-effective, easily synthesized and fast-
response sensor for on-site CN¯ detection is still urgently
needed [7–9]. Therefore, the monitoring of remote polluted
sites can be easily achieved by portable sensitive and selective
optical sensors in countering environmental crisis.
Schiff bases, shown as S1-S13 in Table 1, have been re-
cently applied as optical chemosensors for the detection of
CN¯. As clear in their structures, the imine groups are located
at the ortho position of the hydroxyl groups with a possible
intramolecular hydrogen bonds (O-H…N = C) [10].
According to the intrinsic nature of CN¯, both imine and hy-
droxyl groups of these Schiff bases are important binding site
for CN¯ recognition. In this regard, the imine groups in the
structures of S1-S8 have been activated through the
resonance-assisted hydrogen bonds to promote the
Supramolecular chemistry is a relatively young area of inter-
disciplinary field of science in which the design of receptors is
a main principle for making nonbonding supramolecular in-
teractions with substrates. In order to produce high levels of
affinity and selectivity, the binding ability of receptors is re-
lated to mutual size, shape, rigidity and binding sites with
analytes [1, 2].
The inevitable widespread use of cyanide ion (CN¯) in
various modern industries, such as the polymer industry and
gold extraction process, has polluted water resources
[3–5]. Given that CN¯ has the capability to suppress the trans-
portation process of oxygen in human body, the concentration
* Hossein Reza Darabi
darabi@ccerci.ac.ir; r_darabi@yahoo.com
1
Nano & Organic Synthesis Laboratory, Chemistry & Chemical
Engineering Research Center of Iran, Pajoohesh Blvd., km 17, Karaj
Hwy, 14968-13151 Tehran, Iran

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J Fluoresc (2021) 31:1085–1097
nucleophilic addition of CN¯ on imine groups [11–17]. In
contrast, CN¯ sensing of S9-S13 is taken place via the depro-
tonation of hydroxyl groups in which imines are remained
inert [18–22].
propose that the sensing mechanism of 1 and 2 is taken place
in different ways.
The supramolecular recognition of salophenes 1–3 and
their analogues for coordination with various metal ions have
been already investigated [23–28]. However, there is no report
on evaluation of these dipodal Schiff bases for sensing of
CN¯, whileas they have suitable coordinating sites like imine
and hydroxyl moeities in their tweezer-shaped architecture
(Scheme 1).
Among probes S1-S13 listed in Table 1, the dipodal probes
S7-S9 have the closest architecture to 1–3. While S7 and S8
undergo deprotonation followed by nucleophilic attack of
CN¯ to imine bond via Strecker’s reaction mechanism, [17]
the CN¯ sensing of S9 is taken place via deprotonation follow-
ed by disaggregation [18].
Results and Discussion
The compounds 1 and 2 were simply synthesized by the con-
densation reaction of 1,2-diaminobenzene with 2,3-dihydroxy
benzaldehyde, [23, 24] or 2-hydroxy benzaldehyde [25] re-
spectively (Schemes S1 and S2). The known compound 4 has
been also prepared from the reaction of NaCN with 2 for 48–
64 h stirring at room temperature under harsh reaction condi-
tion [26–28]. The synthesis routes are drawn in Schemes S1-
S3. All products were characterized by H NMR measure-
ments which are identical to those of the reported data (Figs.
S1-S3).
1
For a long time, we have been interested to the design and
synthesis of various supramolecular based chemosensors
[29–40]. In this regards, we have designed and synthesized
some optical receptors for sensing of CN¯ which are based on
the different recognition mechanism, such as deprotonation,
[37, 38] metal-replacement [39] and aggregation induced
emission [40].
We herein report the CN¯ sensing of salophenes 1–3 by
optical methods. Among them, compounds 1 and 2 recog-
nized CN¯ which bolded the critical role of hydroxyl groups.
Both sensors are applicable in buffer solutions and show high-
ly selectivity, very low detection limit (1–10 nM) and rapid
response toward CN¯. As for practical applications, the solu-
tion test kits of both probes was successful for quantitative
measurment of CN¯. Moreover, the various experimental data
Optical Response of 1 Toward CN¯ Ion
To investigate the optical response of 1 to CN¯ ion, a solution
of NaCN was gradually added to CH3CN : H2O buffered
solution (7:3, pH 7.4) of 1 and after each addition the absorp-
tion and emission spectra were recorded.
The UV–vis spectra of 1 exhibits two absorption peaks at
290 and 321 nm which are assigned to the π–π* and n–π*
transition of the C = C and C = N bonds. When CN¯ (0–1.5
equiv.) is added into the buffer solution of 1, the intensity of
original peaks gradually reduced, whereas a new peak/
shoulder at 410 nm appeared (Fig. 1a). At the same time, a
clear isosbestic point at 355 nm is formed to indicate a distinct
interaction between 1 and CN¯. This spectral change is sup-
ported by the color change of solutions from colorless to
Scheme 1 Structure of
compounds 1–4
N
OH
N
N
N
OH
OCH3 OCH3
OH
OH
1
3
N
N
N
NH
NaCN
OH
OH
OH
OH
2
4

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Table 1 Detection of CN¯ by Schiff base probes S1-S13 (N.A.= Nucleophilic addition; D.P.= Deprotonation)
Probe
Substrate
Complex
Process
Ref
Solvent system Mechanism
DL
S1
DMSO:H2O
N.A.
Irreversible
14 pM
11
S2
S3
S4
DMSO:H2O
DMSO:H2O
N.A.
N.A.
Irreversible
Irreversible
Irreversible
3.1 nM
35 µM
12
13
14
DMSO:H2O
N.A.
105 µM
S5
S6
DMSO:H2O
CH3CN:H2O
N.A.
N.A.
Irreversible
Irreversible
77 nM
15
16
1.9 µM
S7
S8
Irreversible
Irreversible
17
17
DMSO:H2O
DMSO:H2O
N.A.
D.P.
3 µM
1.65 µM
DMSO:H2O
EtOH:H2O
D.P.
D.P.
55 nM
S9
Reversible
Reversible
18
19
0.28 µM
S10
DMSO:H2O
CH3CN:H2O
CH3CN:H2O
D.P.
D.P.
D.P.
210 µM
1.2 µM
S11
S12
S13
Reversible
Reversible
Reversible
20
21
22
1.65 µM
yellow (the inset of Fig. 1a). Therefore, the observed
bathochromic shift suggests that the transition of
intramolecular charge transfer (ICT) band is occurred through
the deprotonation of the chemosensor 1 by CN¯ [19–21, 41].

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Fig. 1 a Absorbance and
b emission spectra of 1 (0.015
μM) upon addition of CN¯ ions
(0–1.5 equiv.) in CH3CN : H2O
buffered solution (7:3, pH 7.4)
Compound 1 displays a single fluorescence emission band
at 442 nm when excited at 400 nm. Upon the addition of CN¯
(0–1.5 equiv.) to the solution of 1, this emission peak is grad-
ually increased with a virtually unchanged emission shift
(Fig. 1b) and a more intensive green emission color which is
perceptible to the naked eyes under 365 nm UV light (the inset
of Fig. 1b). In contrast, other anions do not induce such chang-
es (Fig. S4). The fluorescence enhancement might be attribut-
ed to the deprotonation of hydroxyl groups, through which an
ICT process (from hydroxyl anion to the electron-deficient
imine groups) can be improved [37].
The binding mode of 1 with CN¯ was measured by Job plot
analysis and gave a 1:1 stoichiometry (Fig. 2a and b). The
optical response of 1 fits well with the Stern-Volmer equation
to confirm the strong interaction between 1 and CN¯ (Fig. 2c
and d). The binding constants (Ka) were calculated using the
Benesi-Hildebrand equation and found 2.8 × 103 and 1.0 ×
105 M− 1 by UV-vis and Fluorescence methods, respectively.
According to calculations, a high sensitivity by fluorescence
(LOD = 1.2 nM) and UV–vis (LOD = 2.3 nM) methods were
obtained which are much lower than the maximum allowable
level of CN¯ ions in drinking water (1.9 μM) set by the WHO
[6].
To evaluate the interference of CN¯ with the following
sodium anions (NO2 , NO3 , SCN¯, HS¯, S2−, Br¯, Cl¯, F¯,
¯
¯
¯
¯
¯
¯
¯
¯
2−
I¯, H2PO4 , IO3 , IO4 , ClO4 , BrO3 , ClO3 , MoO42−, SO3
,
S2O32−, S2O42−, S2O52−, SO42−) competitive experiments by
UV-vis (Fig. 3a) and fluorescence (Fig. 3b) spectroscopy were
carried out and showed no interference between CN¯ and
other anions. Moreover, as the other anions, except CN¯, did
not induce the solution color change, the interference between
CN¯ and other anions is distinctable via solution color under
naked eye (Fig. 3c and d). It means that among other anions,
CN¯ has the most basic and least hydrogen bonding character
which might deprotonate the protons of catechol rings,
resulting in the color change of solution [37, 38].
On the other hand, it was found that addition of different
chloride cations (Li+, Na+, Ca2+, Ba2+, Sr2+, K+, Mg2+, Al3+,
Cu2+, Cd2+, Co2+, Fe3+, Ni2+, Hg2+, Ag+, Mn2+, Pb2+, Zr4+) to
solutions of 1 did not interfer the CN¯ sensing (Fig. S5). The
high selectivity of CN¯ over cations confirmed that the depro-
tonation process is superior to metal complexation.
To figure out the interaction between 1 and CN¯, 1H NMR
measurements were first performed in the presence of NaCN,
as shown in Fig. 4a. When 1 equiv. of CN¯ was added to the
solutions of 1 in DMSO-d6, the corresponding signals of the
Fig. 2 Job plots for the binding of
1 and CN¯ based on absorbance
(a) and emission (b) titrations.
The changes in absorbance (c)
and emission (d) intensity of 1
upon CN¯ addition

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Fig. 3 Competition of CNˉ with
various anions under a UV-vis
measurements and
b fluorescence. c visual and
d fluorescence images of 1 (1
equiv.) in the presence of 10
equiv. of various sodium anions
CH3CN : H2O buffered solution
(7:3, pH 7.4). (From A to U: Fˉ,
Clˉ, Brˉ, Iˉ, NO2ˉ, NO3ˉ, IO3ˉ,
IO4ˉ, ClO3ˉ, ClO4ˉ, SCNˉ, CNˉ,
H2PO4ˉ, S²ˉ, SHˉ, SO3ˉ, SO4²ˉ,
S2O3²ˉ, S2O4²ˉ, S2O5²ˉ, BrO3ˉ,
MoO4²ˉ)
OH protons at 10.5 and 13.5 ppm vanished, confirming the 1H
NMR result is consistent with the Job’s plot result. At the
same time, the imine peak shifted upfield slightly from 8.7
to 8.5 ppm to show that this functional group is inert to CN¯
ions. Meanwhile, the peaks of aromatic rings showed upfield
shield to different extent, indicating the increase of electron
density through charge delocalization in the conjugated sys-
tem [42]. In addition, no new peak related to formation of
Fig. 4 a 1H NMR spectra of 1 in
the presence of 1 equiv. of CN¯. b
and c The emission and
absorption response of 1 to OH¯
and CN¯ ions in CH3CN:H2O
(7:3)

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Scheme 2 Proposed recognition
mechanism for sensor 1 and its
reversibility route
amine was observed to show that the nucleophilic addition of
CN¯ to the imine moiety did not occur.
fluorescence peak at 466 nm was blue-shifted to 446 nm
(Fig. 5b). This spectral changes is consistent with distinct
color change of solution, as shown in inset of Fig. 5b. It is
inferred that sensor 2 is converted to a new emissive product,
shown as compound 4, through which the electronic property
has been changed. This change is evidenced by the non-linear
emission response 2 to CN¯, as shown in inset of Fig. 5b.
The binding mode of 2 with CN¯ was measured by Job plot
analysis and gave a 1:1 stoichiometry (Fig. S6). The calculat-
ed detection limit by fluorescence (2 μM) is remarkably lower
than that of UV–vis (10 nM). However, using of emission
intensity ratio (I466/I446) method improved the ratiometric de-
tection of CN¯ (0.9 μM, Fig. S7). In contrast, a linear response
was observed in the 10–30 μM range and a detection limit as
low as 8.2 nM was obtained.
To further support of CN¯ sensing mechanism, the interac-
tion between 1 and alkaline base (OH¯) as a good blank sam-
ple for CN¯ was investigated. As shown in Fig. 4b, c, the
addition of OH¯ or CN¯ to 1 gave the identical emission
and absorption spectrum to support the deprotonation mecha-
nism of 1 [37, 38].
Based on the experimental data, 1 can recognize CN¯ via
its tetradentate site which formed between four hydroxyl
groups. As depicted in Scheme 2, this binding site prohibits
the nucleophilic attack of CN¯ on imine groups.
Optical Response of 2 Toward CN¯ Ion
To examine the selectivity, probe 2 was incubated with
The binding ability of 2 toward CN¯ ions was also studied in
CH3CN : H2O buffered solution (7:3, pH 7.4) by UV–vis and
fluorescence spectroscopy (Fig. 5).
The absorbance response of 2 to different amounts of CN¯
are depicted in Fig. 5a. When 20 equiv. of CN¯ was gradually
added to 2, the intensity of the absorption band at 320 nm
decreases. At the same time, a new shoulder at 417 nm togeth-
er with a clear isosbestic point at 370 nm was observed. These
spectral changes is consistent with a distinct color change
from colorless to pale yellow, as shown in Fig. 6c.
various anion species including (CN¯, NO2 , NO3 , SCN¯,
−
−
¯
−
HS¯, S2−, Br¯, Cl¯, F¯, I¯, H2PO4 , IO3−, IO4−, ClO4
,
,
BrO3 , ClO3 , MoO42−, SO32−, S2O32−, S2O42−, S2O5
¯
−
2−
SO42−). Among them, only CN¯ responded to 2 (Fig. 6a and
b) with a distinct color and spectral change in solution (6 C,
6D and Fig. S8). We therefore assume CN¯ selectivity of the
dosimeter 2 over anions and cations (Fig. S9) is due to its
unique reaction pathway, as shown in Scheme 3.
1
To investigate the reaction pathway of 2 with CN¯, H
NMR measurement was carried out in DMSO-d6 (Fig. 7a).
When 1 equiv. of CN¯ was added to solution of 2, the protons
of hydroxyls and imines at 13 and 8.9 ppm, respectively,
The fluorescence response of 2 to CN¯ is more distinctable
than its corresponding UV − vis spectrum. Upon addition of
CN¯ ions (0–30 equiv.) to a solution of 2 (0.015 μM), the
Fig. 5 Absorbance (a) and
emission (b) spectra of 2
(0.015μM) upon addition of CN¯
ions (0–30 equiv.) in CH3CN :
H2O buffered solution (7:3, pH
7.4)

J Fluoresc (2021) 31:1085–1097
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Fig. 6 Competition of CNˉ with various anions under fluorescence (a)
and UV-vis (b) measurements. Visual (c) and fluorescence (d) images of
2 (1 equiv.) in the presence of 10 equiv. of various sodium anions CH3CN
: H2O buffered solution (7:3, pH 7.4). (From A to U: Fˉ, Clˉ, Brˉ, Iˉ, NO2ˉ,
NO3ˉ, IO3ˉ, IO4ˉ, ClO3ˉ, ClO4ˉ, SCNˉ, CNˉ, H2PO4ˉ, S²ˉ, SHˉ, SO3ˉ,
SO4²ˉ, S2O3²ˉ, S2O4²ˉ, S2O5²ˉ, BrO3ˉ, MoO4²ˉ)
disappeared. Moreover, all the protons of aromatic rings ex-
hibited an upfield shield on different levels. At the same time,
a new broad peak at 4.5 ppm, related to the amine protons,
appeared as attributed to the nucleophilic attack on imine
moeities.
NMR and fluorescence changes of 2 and 4 in the presence of
CN¯ is identical (Fig. 8b), confirming the CN¯ sensing of 2 is
happened via 4.
Compound 4 has two emission peaks at 470 and 520 nm
(Fig. 9). Upon addition of CN¯ (0–1.0 equiv.) to a solution of
4, the peak at 520 nm gradually disappeared. At the same time,
the peak intensity at 470 nm was gradually increased. This
unique feature can be attributed to gradual breaking of intra-
molecular hydrogen bonds of 4 followed by the deprotonation
process. This response is fast and show highly sensitivity to
CN¯ (LOD = 6.5 nM) with significant color change from yel-
low to blue under 365 nm UV light (below inset of Fig. 9) with
a binding constant of 5 × 103 M− 1 between 4 and CN¯. On the
other hand, UV-vis spectroscopy was not suitable method,
because no absorption changes appeared when CN¯ was
added to 4 (Fig. S15).
Furthermore, the interaction between 2 and CN¯ was stud-
ied by the OH¯ test. As shown in Fig. 7b, the emission peaks
of 2 in the presence of CN¯ and OH¯ in CH3CN:H2O (7:3),
unlike those of probe 1, are differ to each other. This differ-
ence is also observable by UV-vis spectroscopy Fig. 7c, with
an improvement in MeOH:H2O (7:3) to show that recognition
mechanism of CN¯ by 1 and 2 is taken place in different route.
As a result, NMR and OH¯ data support the formation of a
new compound 4 through the route depicted in Scheme 3.
Accordingly, an equivalent mixture of 2 and CN¯ in
MeOH was reacted at room temperature for 1 h and gave
quantitative yield of dihydroxyquinoxaline 4. The structure
of 4 was well supported by 1H NMR and mass spectroscopy
Based on the mentioned spectral data, we depicted the
sensing mechanism in Scheme 3. Therefore, CN¯ attacks to
the first aldimine group to form a cyano-adduct intermediate.
1
(Figs. S3 and S11) [26, 27]. As shown in Figs. 7 and 8, H
Scheme 3 Proposed recognition
mechanism for sensors 2 and 4
(the color changes are observable
under UV light 365 nm)

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Fig. 7 a 1H NMR spectra of 2 in
the presence of 1 equiv. of CN¯. b
and c The emission and
absorbance response of 2 to OH¯
and CN¯ ions in MeOH:H2O
(7:3)
The suitable distance between two aldimine groups of 2 pro-
moted the intramolecular aldimine condensation cyclization
(IACC) process on this intermediate, followed by formation
of product 4. On the other hand, The obtained spectral data by
4 in the presence of CN¯ is similar to those of 2 to confirm that
the CN¯ sensing of 2 is occured via 4.
Taking the structures of 2 and 3, the comparison of their
respective behavior to CN¯ may give clues about the proposed
mechanism. In this regard, no obvious color and spectral
changes for 3 was observed even in a large excess of CN¯.
Therefore, the phenolic hydrogen may activate the imines
groups of 2 through an intramolecular hydrogen bond [43].
Effect of Solvents on CN¯Sensing
It is well known that solvents play a fundamental role in bind-
ing processes between host and guest [44]. In this study, to
assess the impact of solvents on UV-vis and fluorescence
spectroscopy of probes, CH3CN, MeOH and DMF together
with their aqueous solutions were selected. As shown in Fig.
S12, the absorption and emission spectroscopy of each com-
pound, except absorption of 4, is almost similar in all solvents.
In contrast, the response of these compounds to CN¯ is sol-
vent dependent, as shown in Table S1 and Figs. S13-S15. It
was found that DMF solutions are not suitable solvents for
Fig. 8 a 1H NMR of 4 in the presence of 1 equiv. of CN¯. b The comparison of fluorescence response of 2 and 4 to CN¯ ions

J Fluoresc (2021) 31:1085–1097
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we set all measurements at buffer pH = 7.4 which is applicable
for biological samples.
Reversibility Experiment
The reversibility between 1 and CN¯ or 2 and CN¯ were
evaluated by the HCl addition experiments. When 1 equiv.
of HCl was added to the mixture of 1 and CN¯, the solution
color changed from yellow to colorless (Fig. 11a). The color
change was confirmed by the disappearance of the absorbance
shoulder at 417 nm, suggesting the reversible deprotonation-
protonation cycle after several cycles.
In contrast, probe 2 shows the irreversible behavior under
the similar experiment to suggest a nucleophilic reaction was
taken place on it.
Fig. 9 Emission spectra of 4 (0.1 μM) upon addition of CN¯ ions (0–1
equiv.) in 30 % aqueous CH3CN
The reversibility of probe 1 was also studied on silica gel
plates. As shown in Fig. 11b, a colorless test strip was pre-
pared by immersing TLC plate into MeOH solution of 1 (10−
4 M). When this colorless paper was immersed into solution of
CN¯ (10− 4 M), a yellow color appeared on it. This yellow
color subsequently returned back to original color of 1 when
plate immersed into solution of HCl (10− 4 M). These results
showed that sensor 1 can work well in both solution and solid
state as portable kits for CN¯ analysis.
CN¯ sensing because of the insignificant spectral changes of
probes. On the other hand, solutions of MeOH or CH3CN
bold the spectral response of probes in the presence of CN¯.
At the same time, the absorption and color response of MeOH
solutions of 2 to CN¯ becomes more outstanding which is
suitable for quantitative experiments (see Figs. 7c and 12),
whileas the calculated DLs for CN¯ is above the level of
WHO (2 μM as discussed in 2.4.3). Regarding the spectral
response and DLs, therefore, CH3CN : H2O (7:3) is the sol-
vent of choice for sensing tests of all probes. Notably, the
addition of more amount of H2O in CH3CN led to decreased
solubility of probes in solutions.
Solution Kit Tests
The performance of 1 and 2 for qualitative detection of CN¯
was evaluated. As shown in Fig. 12, the gradual color change
from colorless to yellow with the addition of various concen-
trations of CN¯ was detectable by both probes.
Practical Application
pH Dependence
The visual color changes are accompanied with gradual
increasing of absorption shoulder/peak of 1 in 30 % aqueous
CH3CN (Fig. 12a and c). In contrast, the observation of grad-
ual color change of 2 in 30 % aqueous CH3CN was almost
impossible. Therefore, the measurements were carried out in
30 % aqueous MeOH which showed an improvement in grad-
ual color and spectral changes (Fig. 12b and d). Although
aqueous MeOH is suitable solvent for the qualitative study,
Since the pH variation effects the charge distribution on a
molecule, it can change the absorbance and fluorescence re-
sponse of the probes. To check the versatility of probes 1 and
2 in different pH, the effects of pH on these probes and their
complexes with CN¯ by UV-vis and fluorescence spectrosco-
py were also studied. As shown in Fig. 10 and Fig. S10, the
detection can work well in the pH range 5.0–8.0. Accordingly,
Fig. 10 The effect of pH on the
emission of 1 (a) and 2 (b) with
and without CN¯ ions

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Fig. 11 a Reversibility of 1
through UV-vis spectra and visual
color change upon alternate addi-
tion of CN¯ and HCl.
b Photographs of 1 after the se-
quential immersion into water
solution of CN¯ and HCl on test
strips under visible light
its calculated detection limit is far above the guidelines of
WHO (2.0 μM) [6].
dihydroxyquinoxaline 4. This distinguished response is relat-
ed to the specific binding sites of 1 and 2. Finally, it was found
that the calculated detection limits of these probes are signif-
icantly superior to those of all reported S1-S13 (Table 1).
Conclusions
The study on optical responses of salophenes 1–3 toward CN¯
showed that hydroxyl groups are playing critical roles in the
recognition of this anion. Therefore, probes 1 and 2 are prom-
ising CN¯ indicators in terms of their ease-of-use, highly se-
lectivity, very low detection limit (1–10 nM), visual and emis-
sion color change together with rapid response. Moreover, the
solution test kits of 1 and 2 for quantitative measurment of
CN¯ was successful. On the other hand, the recognition mech-
anism of CN¯ by 1 and 2 is different as evidenced by fluores-
cence, OH¯ test, reversibility experiment and 1H NMR mea-
surements. Therefore, probe 1 senses CN¯ via deprotonation
process, whiles 2 recognizes CN¯ via intramolecular aldimine
condensation cyclization, leading to formation of
Experimental
Materials and Instrumentation
All chemical reagents and solvents were of analytical
grade and commercially available. The fluorescence spec-
tra were carried out on a Jasco FP-6500 spectrofluorime-
ter. The absorbance spectra were recorded on an Agilent
8453 UV-Vis spectrophotometer. Mass spectra were ob-
tained on a Fisons instrument. H NMR was measured by
Varian 400 MHz. Infrared spectra were recorded on a
Perkin Elmer 883 spectrometer.
1
Fig. 12 Absorbance peaks and
colorimetric changes of 1 in 30 %
aqueous CH3CN (a and c) and 2
in 30 % aqueous MeOH (b and d)
upon addition of various
concentrations of CN¯

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Synthesis of 4
1H NMR of Probes 1, 2 and 4 in the Presence of CN¯
A mixture of compound 2 (1 mmol) and NaCN (8 mmol) in
MeOH was stirred at room temperature for 60 min. After
removing of MeOH, the solid was extracted with chloroform.
The organic layer was dried over sodium sulfate. The orange
product 4 was purified by column chromatography and gave
80 % yield.
Each of compounds 1, 2 and 4 was added to the NMR tube
and then dissolved in DMSO-d6. Then, 1 equiv. of dissolved
NaCN in DMSO-d6 was added to each solution of receptors.
After shaking them for a minute, 1H NMR spectra were mea-
sured at room temperature.
Dihydroxyquinoxaline 4: IR (KBr, cm-1): 3400 (O-H),
2921 (C-H), 1610 (C = N), 1470 (C = C), 1226 (C-N); 1 H
NMR (DMSO-d6): δ 14.92 (s, 1 H), 10.17 (s, 1 H), 7.44 (d,
1 H), 7.36–7.17 (m, 2 H), 7.06 (t, 1 H), 6.94 (m, 4 H), 6.79 (t,
1 H), 6.63 (m, 3 H), 6.23 (s, 1 H).; MS (EI), m/z (rel. intensity
%) 317 (M+, 100 %), 299 (10 %), 223 (75 %), 196 (60 %).
Supplementary Information The online version contains supplementary
material available at https://doi.org/10.1007/s10895-021-02738-9.
Author Contributions All authors contributed to the study conception
and design. Sepideh Alizadeh: contributed to the synthesis and initial
analysis in this study; Ramo Nazarian: contributed significantly to anal-
ysis and manuscript preparation; Leila Ebadinia: performed the data anal-
yses; Kiomars Aghapoor: helped perform the analysis with constructive
discussions.
Fluorescence and UV-vis Titration Measurements of
Probes with NaCN
Data Availability The data and materials used or analysed during the
current study are available from the corresponding author on reasonable
request.
Caution CN¯ solutions are also very toxic! All the experi-
ments are strongly recommended to do with respiratory pro-
tection under good fume hood. Keep any remaining CN¯ so-
lution in alkaline solution of ferrous sulfate (pH > 9).
Declarations
Competing Interests The authors have declared that no competing
interests exist.
Receptors 1 or 2 or 4 were dissolved in 100 mL of CH3CN :
H2O buffered system (7:3, pH 7.4) to make the final concen-
tration of 0.3 μM.
0–100 μL of the NaCN solution (0.5 μM) was transferred
to the receptor 1 solution prepared above.
0–300 μL of the NaCN solution (24 μM) was transferred to
the receptor 2 solution prepared above.
0–70 μL of the NaCN solution (0.2 μM) was transferred to
the receptor 4 solution prepared above.
References
1. Davis F, Higson S (2011) Macrocycles: construction, chemistry
and nanotechnology applications. Wiley, Chennai
2. Brnjas-Kraljevi J, Pifat-Mrzljak G (2011) Supramolecular structure
and function 10. Springer, Dordrecht
3. Kulig KW (1991) Cyanide Toxicity. US. Department of Health and
Human Services, Atlanta
4. Young C, Tidwell L, Anderson C (2001) Cyanide: social, industrial
and economic aspects. Minerals, Metals and Materials Society,
Warrendale
After mixing the above solutions for a few seconds,
Fluorescence and UV-vis spectra of 1 or 2 or 4 were measured
at room temperature.
5. Acheampong MA, Meulepas RJW, Lens PNL (2010) Removal of
heavy metals and cyanide from gold mine wastewater. J Chem
Technol Biotechnol 5:590–613
6. Guidelines for Drinking Water Quality (2008) WHO guidelines
values for chemicals that are of health significance in drinking
water, 3rd edn. WHO Press, Geneva
Determination of the Detection Limit
To determine the signal-to-noise ratio (S/N), the absorbance
and emission intensities of 1 or 2 or 4 in the presence of NaCN
were measured 5 times and the standard deviation of the blank
measurements was determined. The measurement of the ab-
sorbance was performed in the presence of NaCN ions, and
the mean intensity was plotted as a concentration of NaCN to
determine the slope. The detection limit (DL) was calculated
using the following equation:
7. Xu Z, Chen X, Kim HN, Yoon J (2010) Sensors for the optical
detection of cyanide ion. Chem Soc Rev 39:127–137
8. Wang F, Wang L, Chen X, Yoon J (2014) Recent progress in the
development of fluorometric and colorimetric chemosensors for
detection of cyanide ions. Chem Soc Rev 43:4312–4324
9. Saleem M, Lee KH (2015) Optical sensor: a promising strategy for
environmental and biomedical monitoring of ionic species. RSC
Adv 5:72150–72287
10. Berhanu AL, Gaurav I, Mohiuddin AK, Malik JS, Aulakh V,
Kumar KH, Kim (2019) A review of the applications of Schiff
bases as optical chemical sensors. Trends Anal Chem 116:74–91
11. Zhang P, Shi BB, Wei TB, Zhang YM, Lin Q, Yao H, You XM
(2013) A naphtholic Schiff base for highly selective sensing of
cyanide via different channels in aqueous solution. Dyes Pigm 99:
857–862
DL ¼ 3σ=m
where σ is the standard deviation of the intensity of 1, 2 and 4
in the presence of NaCN and m is the slope between the
intensity (A0/A) or (I0/I) and concentration (Ct).

1096
J Fluoresc (2021) 31:1085–1097
12. Li Q, Zhang Jh, Cai Y, Qu Wj, G y. Gao, Lin Q, Yao H, Zhang YM,
Wei TB (2015) A facile colorimetric and fluorescent cyanide
chemosensor: utilization of the nucleophilic addition induced by
resonance-assisted hydrogen bond. Tetrahedron 71:857–862
13. Lee JJ, Lee SY, Bok KH, Kim C (2015) A new dual-
channel chemosensor based on chemodosimeter approach
for detecting cyanide in aqueous solution: a combination of
experimental and theoretical studies. J Fluoresc 25:1449–
1459
28. Gorginpour F, Zali-Boeini H, Amiri Rudbari H (2021) A
quinoxaline-based porous organic polymer containing copper
nanoparticles CuNPs@Q-POP as a robust nanocatalyst toward
C–N coupling reaction. RSC Adv 11:3655–3665
29. Darabi HR, Kargar M, Hajipoor R, Abouali N, Aghapoor K,
Jadidi K, Notash B, Sayahi H (2016) Synthesis and structure
of 2,6-bis(2-methoxyphenyl)dithiazolo[4,5-b:5′,4′-e]pyridine)
as a novel fluorescent sensor: different recognition of transi-
tion metal ions and proton. Tet Lett 57:256–259
14. Lee HJ, Park SJ, Sin HJ, Na YJ, Kim C (2015) A selective color-
imetric chemosensor with an electron-withdrawing group for multi-
analytes CN–and F–. New J Chem 39:3900–3907
15. Leng YL, Zhang JH, Li Q, Zhang YM, Lin Q, Yao H, Wei TB
(2016) A highly sensitive colorimetric chemodosimeter for cyanide
anion by Michael addition based on a coumarin derivative. New J
Chem 40:8607–8613
30. Darabi HR, Mirzakhani M, Aghapoor K, Faraji L, Sakhaee N,
Jadidi K (2013) A structure-activity relationship study on the
Wacker oxidation of stilbenes at ambient condition. J Organomet
Chem 740:131–134
31. Kawase T, Tanaka K, Fujiwara, N, Darabi HR, Oda M (2003)
Complexation of a carbon nanoring with fullerenes. Angew Chem
Int Ed Engl 42:1624-1628
16. Udhayakumari D, Velmathi S, Boobalan MS (2015) Novel
chemosensor for multiple target anions: The detection of F–and
CN– ion via different approach. J Fluor Chem 175:180–184
17. Sharma S, Hundal MS, Hundal G (2013) Dual channel
chromo/fluorogenic chemosensors for cyanide and fluoride
ions – an example of in situ acid catalysis of the Strecker
reaction for cyanide ion chemodosimetry. Org Biomol Chem
11:654–661
18. Bhalla V, Pramanik S, Kumar M (2013) Cyanide modulated fluo-
rescent supramolecular assembly of a hexaphenylbenzene deriva-
tive for detection of trinitrotoluene at the attogram level. Chem
Commun 49:895–897
19. Rezaeian K, Khanmohammadi H, Gholizadeh S, Dogaheh (2018)
Studies on a multifunctional chromo-fluorogenic sensor for dual
channel recognition of Zn2+ and CN− ions in aqueous media: mim-
icking multiple molecular logic gates and memory devices. New J
Chem 42:2158–2166
32. Darabi HR, Darestani Farahani A, Karouei MH, Aghapoor K,
Firouzi R, Herges R, Mohebbi AR, Naether C (2012) Cup-shaped
E,E-Stilbenophane: synthesis, crystal structure and supramolecular
chemistry. Supramol Chem 24:653–657
33. Darabi HR, Azimzadeh M, Motamedi A, Firouzi R, Herges R,
Mohebbi AR, Nasseri S, Naether C (2009) Synthesis, crystal struc-
ture and silver complexation of a novel saddle-shaped
stilbenophane: NMR and theoretical study on the complex.
Supramol Chem 21:632–837
34. Darabi HR, Sobhani L, Rastgar S, Aghapoor K, Amini SK,
Zadmard R, Jadidi K, Notash B (2019) Synthesis, characterization
and selective Cu2+ recognition of novel E– and Z–stilbenophanes.
Supramol Chem 31:45–51
35. Darabi HR, Khatamifar E, Aghapoor K, Sayahi H, Firouzi R (2017)
Practical and theoretical aspects of Wacker oxidation of
tolanophanes: synthesis and characterization of novel diketonic
cyclophanes. Appl Organometal Chem 31:e3812
20. Ryu KY, Lee JJ, Kim JA, Park DY, Kim C (2016) Colorimetric
chemosensor for multiple targets, Cu2+, CN− and S2−. RSC Adv 6:
16586–16597
21. HY, Lee SA, Na YJ, Park GJ, Kim C (2015) A colorimetric Schiff
base chemosensor for CN− by naked-eye in aqueous solution. Inorg
Chem Commun 54:73–76
22. Mohammadi A, Jabbari J (2016) Simple naked-eye colorimetric
chemosensor based on Schiff-base for selective sensing of cyanide
and fluoride ions. Can J Chem 94:631–636
36. Darabi HR, Mirzakhani M, Aghapoor K (2015) The supramolecu-
lar effect of stilbenophanes on the Wacker oxidation progress: a
structure-activity relationship study. J Organometal Chem 786:
10–13
37. Assadollahnejad N, Kargar M, Darabi HR, Abouali N, Jamshidi S,
Sharifi A, Aghapoor K, Sayahi H (2019) A new ratiometric, color-
imetric and ‘‘turn-on’’ fluorescent chemosensor for the detection of
cyanide ions based on a phenol–bisthiazolopyridine hybrid. New J
Chem 43:13001-13009
38. Kargar M, Darabi HR, Sharifi A, Mostashari A (2020) A new
chromogenic and fluorescent chemosensor based on a naphthol–
bisthiazolopyridine hybrid: a fast response and selective detection
of multiple targets, silver, cyanide, sulfide, and hydrogen sulfide
ions and gaseous H2S. Analyst 145:2319–2330
39. Ebadinia L, Darabi HR, Ramazani A (2020) Optical detection of
cyanide by palladium(II)-dithiazolopyridine probe at the parts per
billion level. Phosphurous Sulfur Silicon 195:620
40. Nazarian R, Darabi HR, Aghapoor K, Firouzi R, Sayahi H
(2020) A highly sensitive “ON–OFF” optical sensor for the
selective detection of cyanide ions in 100% aqueous solu-
tions based on hydrogen bonding and water assisted aggre-
gation induced emission. Chem Commun 56:8992-8995
41. Kumari N, Jha S, Bhattacharya SJ (2011) Colorimetric probes
based on anthraimidazolediones for selective sensing of fluoride
and cyanide ion via intramolecular charge transfer. J Org Chem
76:8215–8222
23. Olea-Román D, Bélanger-Desmarais N, Flores-Álamo M, Bazán C,
Thouin F, Reber C, Castillo-Blum SE (2015) Spectroscopic studies
of lanthanide complexes of varying nuclearity based on a
compartmentalised ligand. Dalton Trans 44:17175–17188
24. Joshu L, Benítez H, Jiménez-Cruz P, Cureño-Hernández KE,
Solano-Peralta A, Flores-Álamo M, Flores-Parra A, Gracia-Mora
I, Castillo-Blum SE (2018) [VIVO]2+ complexes: Structure, unusual
magnetic properties and cytotoxic effect. Inorg Chim Acta 480:
197–206
25. . Mota VZ, de Carvalho GSG, Corbi PP, Bergamini FRG, Formiga
ALB, Diniz R, Freitas MCR, Cuin A, da Silva AD (2012) Crystal
structure and theoretical studies of the keto-enol isomerism of N,N′-
bis(salicylidene)-o-phenylenediamine (salophen). Spectrochim
Acta A Mol Biomol Spectrosc 99:110–115
26. Reich BJE, Justice AK, Beckstead BT, Reibenspies JH, Miller SA
(2004) Cyanide-Catalyzed Cyclizations via Aldimine Coupling. J
Org Chem 69:1357–1359
27. Reich BJE, Greenwald EE, Justice AK, Beckstead BT,
Reibenspies JH, North SW, Miller SA (2005) Ene-diamine
versus Imine-amine Isomeric Preferences. J Org Chem 70:
8409–8416
42. Wei TB, Yan GT, Li H, Zhu YR, Shi BB, Lin Q, Yao H, Zhang YM
(2016) A highly sensitive and selective “turn-on” fluorescence sen-
sor for rapid detection of cyanide ions in aqueous solution.
Supramol Chem 28:720–726

J Fluoresc (2021) 31:1085–1097
1097
43. Albayrak C, Odabasoglu M, Büyükgüngör O, Lönnecke P (2004)
5-(2-Chlorophenyldiazenyl) salicylaldehyde and 4-(2-
chlorophenyldiazenyl)-2-{[tris (hydroxymethyl) methyl]
aminomethylene} cyclohexa-3, 5-dien-1 (2H)-one. Acta
Crystallogr C60:o318–o320
44. Beer PD, Gale PA (2001) Anion recognition and sensing: the state
of the art and future perspectives. Angew Chem Int Ed 40:486-516
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