Synthesis of new bis-benzylidene-hydrazides as a sensitive chromogenic sensor for naked-eye detection of CNˉ and AcOˉ ions

Article abstract of DOI:10.1016/j.tet.2018.07.050

Some new bis-benzylidene-hydrazides were synthesized via a condensation reaction of the corresponding azo dyes with adipic acid dihydrazide. All compounds because of the three possible stereoisomers showed four sets of signals in NMR. The anion recognition studies exhibited that the nitro bis-benzylidene-hydrazide derivative acts as a highly sensitive and selective chromogenic sensor for naked-eye detection of CNˉ and AcOˉ ions, with a distinct color change from yellow to blue and yellow to purple, respectively. The limit of detection (LOD) was found for 1d toward CNˉ to be 1.1 μM. The result of the Job's plot indicated stoichiometry of binding between chemosensor and anions is found to be 1:2.

Full text of DOI:10.1016/j.tet.2018.07.050

Accepted Manuscript
Synthesis of new bis-benzylidene-hydrazides as a sensitive chromogenic sensor for
naked-eye detection of CN¯ and AcO¯ ions
Ammar Sheykhi-Estalkhjani, Nosrat O. Mahmoodi, Asieh Yahyazadeh, Meysam
Pasandideh Nadamani
PII:
S0040-4020(18)30916-5
10.1016/j.tet.2018.07.050
TET 29710
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 9 June 2018
Revised Date: 14 July 2018
Accepted Date: 27 July 2018
Please cite this article as: Sheykhi-Estalkhjani A, Mahmoodi NO, Yahyazadeh A, Nadamani MP,
Synthesis of new bis-benzylidene-hydrazides as a sensitive chromogenic sensor for naked-eye
detection of CN¯ and AcO¯ ions, Tetrahedron (2018), doi: 10.1016/j.tet.2018.07.050.
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Synthesis of new bis-benzylidene-hydrazides as a
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sensitive chromogenic sensor for naked-eye detection
of CN¯ and AcO¯ ions
Ammar Sheykhi-Estalkhjani, Nosrat O. Mahmoodi, Asieh Yahyazadeh, Meysam Pasandideh Nadamani
Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 41335-1914, Rasht, Iran

1
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Tetrahedron
journal homepage: www.elsevier.com
Synthesis of new bis-benzylidene-hydrazides as a sensitive chromogenic sensor for
naked-eye detection of CN¯ and AcO¯ ions
a
a,
a,

Ammar Sheykhi-Estalkhjani , Nosrat O. Mahmoodi , Asieh Yahyazadeh * and Meysam Pasandideh
Nadamania
a Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 41335-1914, Rasht, Iran
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Some new bis-benzylidene-hydrazides were synthesized via a condensation reaction of the
corresponding azo dyes with adipic acid dihydrazide. All compounds because of the three
possible stereoisomers showed four sets of signals in NMR. The anion recognition studies
exhibited that the nitro bis-benzylidene-hydrazide derivative acts as a highly sensitive and
selective chromogenic sensor for naked-eye detection of CN¯ and AcO¯ ions, with a distinct
color change from yellow to blue and yellow to purple, respectively. The limit of detection
(LOD) was found for 1d toward CN¯ to be 1.1 μM. The result of the Job’s plot indicated
stoichiometry of binding between chemosensor and anions is found to be 1:2.
Available online
Keywords:
Azo dye
Benzylidene
Chemosensor
Hydrazide
2018 Elsevier Ltd. All rights reserved.
Naked-eye detection
1. Introduction
sophisticated technical equipment is required to perform these
measurements and being naked eye visible.
The anions play essential roles in medical diagnostics,
physiology, industrial and environmental processes. Among the
various anions, CN¯ is one of the most worried anions, because it
could be absorbed through lungs, gastrointestinal tract and skin,
leading to vomiting, convulsion, loss of consciousness, and
eventual death.1–3 In spite of its extreme toxicity, today cyanide is
still extensively used in the gold and silver mining industry,
plastic manufacturing, electroplating and resin industry.4–6 To
detect CN¯, several methods have been developed by means of
different experimental procedures and detection techniques, for
example chromatography, voltammetric, spectrophotography,
potentiometric, electrochemical, optical methods and flow
injection analysis technique.7–18 Colorimetric methods have been
actively studied in recent years because of conveniently and
easily monitor target ions with the naked eye, quick response
rates and at relatively low costs.19–28 In the light of the above
mentioned facts, it is necessary to design of molecules that can
recognize, respond to, or sense anions selectively through visible,
electrochemical and optical responses.
In consideration of these characteristics, and in continuation of
our previous works,34–38 The synthesis, characterization and
sensing properties of some new colorimetric bis-benzylidene-
hydrazide receptors 1a-1h for visual detection of CN¯ and AcO¯
ions was described (Scheme 1). The sensing processes can be
realized by naked-eye detection, with a color change from yellow
to blue and yellow to purple in presence of CN¯ and AcO¯ ions,
respectively.
2. Results and discussion
2.1. Synthesis and Spectral studies
Our approach involves, the convenient one-pot, multi-component
synthesis of bis-benzylidene-hydrazide receptors (1a-1h) through
a condensation reaction of one equivalent of adipic acid
dihydrazide (3) and two equivalents of premade azo-aldehyde
dyes (2a-2h) as shown in Scheme 1. The azo-aldehyde dye
precursors (2a-2h) separately were synthesized by reaction of o-
vanillin or salicylaldehyde with benzene diazonium chloride salts
that in sequence made by diazotization of corresponding
aniline derivatives. The structure of products has been well
characterized by FT-IR, UV-Vis, NMR spectroscopies and
elemental analyses (see Table 1 and supporting data). The NMR
spectra of (1a-1h) were recorded in DMSO at 25 °C. All of the
Over the last decade, chromogenic chemosensors based on a
new azophenol-create colorimetric sensor shows a selective
detection for specifically identify anions.29–33 The advantage of
these sensors is real-time monitoring, rapidity and no
———
 Corresponding authors. E-mail addresses: mahmoodi@guilan.ac.ir (N. O. Mahmoodi), Tel: +981333320912; yahyazadeh@guilan.ac.ir (A.
Yahyazadeh)

2
Tetrahedron
1
synthesized compounds showed four sets of signals in H NMR
As shown in Fig. 1 & Fig. 2, each of the two hydrogens
marked with green and orange colors shows four sets of signals.
Two signals of the same intensity (with an area under each peak
approximately equal to 1.79) are related to syn and anti
conformers of structure 1aʹ. The syn/anti isomer was found to be
the predominant conformer, followed by the syn/syn and anti/anti
conformers, respectively. In fact, there are two equal conformers
of 1aʹ-s/a (22.4%) and 1aʹ-a/s (22.4%) with total amount of
(44.8%) and two other isomers 1a-s/s (40.1%) and 1aʺ-a/a
(15.1%). The presence of 1a, 1aʹ and 1aʺ stereoisomers confirmed
by interpretation of 1H and 13C NMR and presented in
experimental section.
ACCEPTED MANUSCRIPT
duo to the three possible stereoisomers syn/syn, syn/anti (or
anti/syn) and anti/anti with respect to the amide bonds.39 The two
syn/anti or anti/syn isomers are actually the same isomer with
two set of signals attribute to syn- and anti-moieties separately.
Fig. 1 designates the structures of the stereoisomers of bis-
benzylidene-hydrazide 1a interpreted base on the FT-IR and
NMR spectra.
Scheme 1. Synthesis of bis-benzylidene-hydrazides
Fig. 1. Structures of three stereoisomers of bis-benzylidene-
hydrazide 1a
Table 1. The properties of target bis-benzylidene-hydrazide
receptors 1a-1h
λmax(nm)
(DMSO)
Yielda
(%)
Product Picture
mp (°C)
1a
2 H-syn
1a
295, 387
296-297 dec
82
80
83
77
84
1a
2 H-syn
1aʹ
1a ʹ
2 H-syn
2 H-anti
1aʹ
2 H-anti
1a ʹ
1b
1c
1d
1e
287, 337, 370
315, 350, 378
285, 317, 396
306, 356, 380
291-292 dec
297-298
2 H-syn
1aʹʹ
2 H-anti
1aʹʹ
2 H-anti
306-307 dec
277-278
Fig. 2. 1HNMR spectra of compound 1a; four sets of signals
related to three stereoisomers 1a:1aʹ: 1aʺ with a ratio of 40.1:
44.8: 15.1%
1f
288, 379
247-248
276-277
273-274
88
70
75
2.2. Colorimetric sensing of CN¯and AcO¯
1g
308, 383
The electronic absorption spectra of bis-benzylidene-
hydrazide receptors (1a-1h), were measured in DMSO at a 3
×10−5 M concentration, the results are summarized in Table 1.
The electronic absorption spectra of 1a-1h display mainly two
bands with different shoulders (Fig. 3). The first UV band located
at 285-317 nm can be assigned to the moderate energy π→π*
transition of the aromatic rings and the second band at 370-396
1h
309, 357, 387
a Isolated yields.

3
nm is due to low energy π→π* transition.40 Compound 1f in
1
1d Free
1d Free
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DMSO display a broadband at 432-550 nm assigned to an n→π*
NO2-
a
1d+NO2¯
1d
C
+
N
cO
A
C
-
N¯
cO¯
1d+I¯
electronic transition of azo-aromatic chromophore and
intramolecular charge transfer interaction.
1d
I
A
+
-
0.8
0.6
0.4
0.2
0
Br
1d+Br¯
1d+Cl¯
Cl
F
1d+F¯
1d HPO24PO4
1d CO3¯
CO
1d
̅
H2
+
1
+H
H 3
1a
N
+
O
N
3
2
O3¯
2
1b
1
C
d
O
+
3
C
O 3
-
¯
1d+
S2-
S2¯
0.8
2
1c
HPO4-
1d+HPO4
¯
HSO4-
1d+HSO4¯
1d
0.6
ClO4-
1d+ClO4¯
1e
1f
0.4
1g
265
1
365
465
565
665
765
Wavelength (nm)
1h
0.2
1d + anions
b
̅
1d + anions + CN
0
240
340
440
540
640
740
0.8
Wavelength (nm)
0.6
0.4
0.2
0
Fig. 3. Absorption spectra character of 1a-1h in DMSO
As an initial test, we surveyed sensitivity of receptors 1a-1h
towards anions upon addition of 10 equivalents of various anions,
including CO2 , NO¯, AcO¯, NO¯, CN¯, F¯, Cl¯, Br¯, I¯,
¯
3
3
2
3
H PO¯, HCO¯ and S2 in DMSO/H2O (9/1). Receptor 1d
¯
2
4
showed superb sensitivity to CN¯ and AcO¯ among these anions.
The sensitivity of receptor 1d is attributed to increase of its anion
stability due to the electron-withdrawing power of the p-nitro
group substituents that powerfully extended the π-conjugation
length. As shown in Fig. 4, receptor 1d upon addition of CN¯
and AcO¯, compared to other anions that display a remarkable
and immediate colorimetric response from yellow to blue and
yellow to purple, respectively.
1d + anions
c
1
0.8
0.6
0.4
0.2
0
̅
1d + anions + AcO
Fig. 4. The color change observed by naked-eye of receptor
1d (3 × 10−5 M) upon addition of 10 equiv. of various ions in
DMSO/H2O (9/1)
Furthermore, UV-Vis absorption spectral responses of
receptor 1d (3 × 10−5 M in DMSO/H2O (9/1)) upon addition of
10 equiv. of different anions were also investigated (Fig. 5).
Addition of CN¯ and AcO¯ ions had an intense effect on the
electronic spectrum of 1d and induced a new absorption peak
appeared at 591 and 515 nm, respectively. However, when other
anions were added no significant change was observed.
Fig. 5. a) UV-Vis absorption spectra of 1d (3 × 10−5 M) in the
presence of 10 equiv. of various anions in DMSO/H2O (9/1).
Effect of competitive anions (10 equiv.) on the interaction of;
b) 1d/CN¯ (10 equiv.) and c) 1d/AcO¯ (10 equiv.)
The effect of pH on the host-guest binding affinity of receptor
1d was considered. The absorption band of receptor 1d at 591 nm
was recognized to the formation of the 1d-CN complex under
various pH conditions. As revealed in Fig. 6, in pH less than 4,
the color of the solution remained unchanged (yellow) and no
absorption band was appeared at 591 nm. This phenomenon
confirms that the complex 1d-CN was not prepared. As the pH
rose from 4 to 12, the absorption band at 591 nm intensified
rapidly and the color of the solution turned to dark blue. The
result confirmed that 1d is a very sensitive sensor especially at
basic pH and this will encompass the development of new pH-
selective sensor.
In other efforts, the superior selectivity of 1d as a colorimetric
chemosensor for the detection of CN¯ in the presence of various
competing anions was considered as illustrated in Fig. 4b. In the
presence of other excess anions (10 equiv.), premade sensor 1d
(1 equiv.) and CN¯ (10 equiv.), the absorption intensity of final
solution was exhibited. The UV-Vis spectra revealed that the
presence of other interfering anions up to 10 equiv. had no effect
on the absorbance intensity of CN¯, with the exception of AcO¯
(Fig. 5b). A similar competition test (same as above) was
repeated for AcO¯ (10 equiv.), premade sensor 1d (1 equiv.) in
the presence of other anions (10 equiv.), the UV-Vis spectra
revealed that the presence of other interfering anions had no
effect on the absorbance intensity of AcO¯ (Fig. 5c). However,
these experiments illustrated that the intraction of AcO¯ is
slightly greater than CN¯ verses 1d.
The UV-Vis absorption spectral responses of 1d in
DMSO/H2O (9/1) upon gradual addition of 10 equivalents of
CN¯ and AcO¯ ions were investigated Fig. 7 & Fig. 8. Free 1d
indicated absorptions at 285, 317 and 396 nm. Upon gradual
addition of CN¯ to 1d, these absorptions slightly decreased and a

4
Tetrahedron
examined, which was roughly the same as the observed changes
ACCEPTED MANUSCRIPT
1
0.8
0.6
0.4
0.2
0
upon the addition of CN¯ (Fig. 8). The difference between AcO¯
1d + CN
1d
¯
and CN¯ is the color change of solution from yellow to purple for
AcO¯ and yellow to dark blue for CN¯, respectively. As well,
upon the addition of CN¯, the bathochromic shift and higher
intensity of new absorption peak in comparison to AcO¯ were
observed (See Figs. 7 and 8).
The result of the Job’s plot of UV-Vis titration of 1d with
CN¯ indicate that the stoichiometric ratio inferred to be 1:2 (Fig.
9). The same result was confirmed by 1H NMR titration obtained
from average integration of the singlet signals of the OH and NH
protons related to 1d verses 1d + 2 equiv. CN¯ at δ 11.04-11.99
1
2
4
6
8
10
12
ppm (Fig. 10). Furthermore, the H NMR spectra revealed that
PH
the chemosensor recognition of CN¯ rely on the H-bonds, this
deprotonation evidently directed to color change.
Fig. 6. Effect of pH on the UV-Vis spectra of sensor 1d (3 ×
10−5 M) and 1d containing CN¯ ion at 591 nm
1
0.8
0.6
0.4
0.2
0
new emerged remarkably growth centered at 591 nm and the
intensity was steadily enhanced until the amount of CN¯ reached
10 equivalents with simultaneously decreasing of the peaks at
285, 317 and 396 nm. Meanwhile, the color of the solution
changed from yellow to blue, allowing naked-eye detection of
CN¯. These changes can be attributed to the increase of
intramolecular charge transfer (ICT) due to the strong interaction
between CN¯ ion with hydroxyl groups of receptor 1d and the
deprotonation effect. In other efforts, the absorption spectral
changes of 1d upon gradual addition of AcO¯ ion were also
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
[CN¯]/([1d]+[CN¯])
Fig. 9. Job’s plot for stoichiometry of binding between
receptor 1d with CN¯ in DMSO/H2O (9/1) (λ = 591 nm)
CN¯
̅
1d + 2 equiv. CN
NH and OH
f
Fig. 7. UV-Vis absorption spectra of sensor 1d (3 × 10−5 M in
DMSO/H2O (9/1)) upon addition of CN¯ (0-10 equiv.). Inset
showing the binding isotherm at selected wavelengths
1d
f
NH and OH
1
AcO¯
Fig. 10. Partial 1H NMR spectra of 1d and 1d + 2 equiv. CN¯
in DMSO-d6
0.8
0.6
0.4
0.2
0
The world health organization (WHO) has set the maximum
safe concentration for cyanide in drinking water at 1.9 μM. The
limit of detection (LOD) was evaluated with the equation LOD =
3σ/s and was found for 1d toward CN¯ to be 1.1 μM which is
lower than the maximum value of cyanide permitted by WHO in
drinking water (see supporting data).
260
360
460
560
660
760
2.3. Antibacterial activity
Wavelength (nm)
Fig. 8. UV-Vis absorption spectra of sensor 1d (3 × 10−5 M in
DMSO/H2O (9/1)) upon addition of AcO¯ (0-10 equiv.). Inset
showing the binding isotherm at selected wavelengths
The In vitro antibacterial activity of compounds 1a–1h was
evaluated against Gram-negative and Gram-positive bacteria
including: Micrococcus luteus (M. luteus), Staphylococcus

5
aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas
(HRMS) were obtained on a Finnigan MAT 95, EI: 70 eV,
R:10000.
ACCEPTED MANUSCRIPT
aeruginosa (Ps. aeruginosa) by zone inhibition method.
Tetracycline and Ampicillin were used as standard drugs and
DMSO was used as a solvent. The concentration of compounds
was 1 mg/mL in DMSO. The Results are shown in Table 2 that
the compound importance antibacterial activity against
Micrococcus luteus is: 1b > 1f > 1a > 1c > 1d = 1h > 1e = 1g.
Compound 1b indicate higher antibacterial activity than standard
drugs. Compounds 1c and 1h showed similar antibacterial
activity as ampicillin. Whereas, none of the compounds had
antibacterial activity verses Ps. aeruginosa.
4.2. General procedure for the synthesis of bis-benzylidene-
hydrazides 1a-1h
Azo dye, 2a-2h, (2 mmol) was dissolved in absolute EtOH
(10-15 ml) and the solution was stirred vigorously for 10 min at
reflux condition. Then adipic dihydrazide acid 3 (0.174 g, 1
mmol) was added and the mixture stirred at reflux condition. The
progress of the reaction was monitored by TLC (EtOAc:n-
hexane, 1:3). The reaction was completed after 1 h and the
product was collected by filtration, washed with EtOH and
recrystallized from DMF/H2O.
Table 2. Antibacterial assay of 1a-1h as a zone of inhibition
(mm)
4.2.1. N'1 ,N'6 -bis((E)-2-hydroxy-5-((E)-
Antibacterial activity (mm)
Compound
M. luteus
S. aureus
E. coli
Ps. aeruginosa
phenyldiazenyl)benzylidene)adipohydrazide (1a)
Yield: 82%, mp 296-297 °C; FT-IR (KBr, υ/cm-1): 3450 (O–
H), 3201 (N–H), 3051 (aromatic C–H), 2941 (aliphatic C–H),
1664 (C=O), 1615 (C=N), 1545 (C=C), 1484 (N=N), 1275 (C-
O). 1H NMR (DMSO-d6, 400 MHz, ppm): syn/syn isomer,
40.1%: 11.76 (s, 4H, He and Hc), 8.51 (s, 2H, Hd), 8.20 (d, J = 2.4
Hz, 2H, Hh), 7.91-7.78 (m, 6H, Hg, Hi), 7.61-7.49 (m, 6H, Hk,
Hl), 7.13-7.04 (m, 2H, Hf), 2.34-2.29 (m, 4H, Hb), 1.73-1.66 (m,
4H, Ha); syn/anti and/or anti/syn isomers, 44.8%: 11.76 (s, 2H,
He or Hc), 11.38 (s, 1H, He or Hc), 10.98 (br, 1H, He or Hc), 8.48
(s, 1H, Hd (syn)), 8.37 (s, 1H, Hd (anti)), 8.28 (d, J = 2.8 Hz, 1H, Hh
(anti)), 8.18 (d, J = 2.4 Hz, 1H, Hh (syn)), 7.91-7.78 (m, 6H, Hg, Hi),
7.61-7.49 (m, 6H, Hk, Hl), 7.13-7.04 (m, 2H, Hf), 2.73-2.70 (m,
2H, Hb (anti)), 2.34-2.29 (m, 2H, Hb (syn)), 1.73-1.66 (m, 8H, Ha);
anti/anti isomer, 15.1%: 11.37 (s, 2H, He or Hc), 10.98 (br, 2H,
He or Hc), 8.35 (s, 2H, Hd), 8.26 (d, J = 2.8 Hz, 2H, Hh), 7.91-
7.78 (m, 6H, Hg, Hi), 7.61-7.49 (m, 6H, Hk, Hl), 7.13-7.04 (m,
2H, Hf), 2.73-2.70 (m, 4H, Hb), 1.73-1.66 (m, 4H, Ha). 13C NMR
(100 MHz, DMSO-d6, ppm): 174.47, 174.39, 169.03, 168.99,
160.57, 159.77, 152.48, 145.62, 145.54, 145.14, 139.74, 131.33,
131.26, 129.86, 129.74, 126.24, 124.89, 123.84, 122.76, 122.54,
121.45, 120.13, 117.68, 117.42, 34.43, 34.31, 32.40, 32.18,
25.25, 25.13, 24.56, 24.32. Anal. Calcd. For C32H30N8O4 (%): C,
65.07; H, 5.12; N, 18.97. Found: C, 65.14; H, 5.08; N, 18.91.
HRMS-ESI (m/z) calcd. for C32H31N8O4 [M + H]+ 591.2463,
found 591.2467.
1a
1b
1c
1d
1e
1f
20
10
-
-
28
18
16
10
24
10
16
16
8
4
8
-
-
-
4
-
-
-
-
4
8
-
-
1g
1h
-
-
8
-
-
Tetracycline 25
21
22
21
8
19
0
Ampicillin
27
3. Conclusion
Here, some new bis-benzylidene-hydrazide derivatives were
successfully synthesized via a simple reaction between adipic
acid dihydrazide and azo-coupled to o-vanillin or salicylaldehyde
precursors. The anion recognition studies exhibited that 1d acts
as a highly sensitive and selective chromogenic sensor for naked-
eye detection of CN¯ and AcO¯ ions. Upon the addition of CN¯
and AcO¯ ions, the solution was changed immediately from
yellow to blue and yellow to purple, respectively. In addition, the
1H NMR spectra revealed chemosensor recognition of CN¯ via
H-bonds, this deprotonation evidently directed to color change.
For 1d toward CN¯, the LOD was found to be 1.1 μM .The Job’s
4.2.2. N'1 ,N'6 -bis((E)-2-hydroxy-5-((E)-p-
tolyldiazenyl)benzylidene)adipohydrazide (1b)
Yield: 80%, mp 291-292 °C; FT-IR (KBr, υ/cm-1): 3447 (O–
H), 3202 (N–H), 3066 (aromatic C–H), 2955 (aliphatic C–H),
1668 (C=O), 1617 (C=N), 1558 (C=C), 1489 (N=N), 1274 (C–
1
plot
titration
of
1d
toward
CN¯
indicated
O). H NMR (400 MHz, DMSO-d6)  (ppm): syn/syn isomer,
a stoichiometry of binding between sensor and anions to be 1:2.
39.1%: 11.75 (s, 2H, He or Hc), 11.74 (s, 2H, He or Hc), 8.50 (s,
2H, Hd), 8.17 (d, J = 2.4 Hz, 2H, Hh), 7.88-7.69 (m, 6H, Hg, Hi),
7.40-7.32 (m, 4H, Hk), 7.12-7.04 (m, 2H, Hf), 2.33-2.29 (m, 4H,
Hb), 2.41 (s, 6H, Hl), 1.74-1.65 (m, 4H, Ha); syn/anti and/or
anti/syn isomers, 47.4%: 11.75 (s, 1H, He or Hc), 11.74 (s, 1H, He
or Hc), 11.37 (s, 1H, He or Hc), 10.93 (s, 1H, He or Hc), 8.47 (s,
1H, Hd (syn)), 8.36 (s, 1H, Hd (anti)), 8.26 (d, J = 2.8 Hz, 1H, Hh
(anti)), 8.15 (d, J = 2.4 Hz, 1H, Hh (syn)), 7.88-7.69 (m, 6H, Hg, Hi),
7.40-7.32 (m, 4H, Hk), 7.12-7.04 (m, 2H, Hf), 2.73-2.69 (m, 2H,
Hb (anti)), 2.33-2.29 (m, 2H, Hb (syn)), 2.41 (s, 3H, Hl (syn or anti)), 2.35
(s, 3H, Hl (syn or anti)), 1.74-1.65 (m, 3H, Ha); anti/anti isomer,
13.5%: 11.36 (s, 2H, He or Hc), 10.89 (s, 2H, He or Hc), 8.35 (s,
2H, Hd), 8.23 (d, J = 2.8 Hz, 2H, Hh), 7.88-7.69 (m, 6H, Hg, Hi),
7.40-7.32 (m, 4H, Hk), 7.12-7.04 (m, 2H, Hf), 2.73-2.69 (m, 4H,
Hb), 2.39 (s, 6H, Hl), 1.74-1.65 (m, 4H, Ha). 13C NMR (100 MHz,
DMSO-d6, ppm): 168.98, 160.30, 150.55, 145.56, 145.14,
141.50, 130.40, 126.17, 123.52, 122.77, 120.09, 117.65, 34.30,
25.12, 21.48. Anal. Calcd. For C34H34N8O4 (%): C, 66.01; H,
4. Experimental section
4.1. Materials and apparatus
Adipic acid dihydrazide (3) was purchased from Merck and
used without further purification. The azo dyes (2a-2h) used as a
precursor were synthesized according to our previously reported
procedures.35 Melting points were measured by electrothermal
9100s apparatus and were uncorrected. The FT-IR spectra were
recorded on a Bruker Vector 22 in the region of 400–4000 cm−1
in KBr pellets. The absorption spectra of bis-benzylidene-
hydrazides were
measured by Shimadzu UV-2100
spectrophotometer in the range 200–800 nm (DMSO/H2O (9:1), c
= 3 × 10−5 M, cell path length 1 cm). H and 13C NMR spectra
1
were measured with Bruker Avance 400 MHz spectrometer using
DMSO-d6 as solvent. The CHN analyses were performed on a
Vario-ELIII elemental analyzer. High resolution mass spectra

6
Tetrahedron
ACCEPTED MANUSCRIPT
5.54; N, 18.11. Found: C, 65.95; H, 5.50; N, 18.18. HRMS-ESI
6H, H ), 2.34-2.30 (m, 4H, H ), 1.74-1.66 (m, 4H, H ); syn/anti
f
b
a
(m/z) calcd. for C34H35N8O4 [M + H]+ 619.2776, found 619.2781.
4.2.3. N'1 ,N'6 -bis((E)-5-((E)-(4-ethylphenyl)
diazenyl)-2-hydroxybenzylidene)adipohydrazide
(1c)
and/or anti/syn isomers, 47.2%: 11.77 (s, 1H, Hc (syn) or He (syn)),
11.57 (br, 1H, Hc (syn) or He (syn)), 11.39 (m, 1H, Hc (anti) or He (anti)),
10.36 (br, 1H, Hc (anti) or He (anti)), 8.49 (s, 1H, Hd (syn)), 8.41 (s, 1H,
Hd (anti)), 7.98 (d, J = 2.4 Hz, 1H, Hh (anti)), 7.90-7.79 (m, 5H, Hh
(syn), Hi), 7.62-7.50 (m, 7H, Hg (syn), Hk, Hl), 7.48 (d, J = 2 Hz, 1H,
Hg (anti)), 3.96-3.91 (m, 6H, Hf), 2.77-2.70 (m, 2H, Hb (anti)), 2.34-
2.30 (m, 2H, Hb (syn)), 1.74-1.66 (m, 4H, Ha); anti/anti isomer,
13.3%: 11.38 (m, 2H, Hc), 10.36 (br, 2H, He), 8.39 (s, 2H, Hd),
7.96 (d, J = 2 Hz, 2H, Hh), 7.90-7.79 (m, 4H, Hi), 7.62-7.50 (m,
6H, Hk, Hl), 7.43 (d, J = 2.4 Hz, 2H, Hg), 3.96-3.91 (m, 6H, Hf),
2.77-2.70 (m, 4H, Hb), 1.74-1.66 (m, 4H, Ha). 13C NMR (100
MHz, DMSO-d6, ppm): 174.51, 174.41, 169.01, 168.96, 152.44,
152.34, 150.75, 149.77, 149.27, 145.31, 145.22, 145.11, 139.66,
139.55, 131.32, 129.90, 129.76, 122.77, 121.06, 119.54, 119.39,
118.07, 104.43, 102.70, 56.47, 56.41, 34.44, 34.31, 32.32, 32.11,
25.19, 25.11, 24.51, 24.30. Anal. Calcd. For C34H34N8O6 (%): C,
62.67; H, 5.26; N, 17.25. Found: C, 62.58; H, 5.18; N, 17.33.
HRMS-ESI (m/z) calcd. for C34H35N8O6 [M + H]+ 651.2674,
found 651.2679.
Yield: 83%, mp 297-298 °C; FT-IR (KBr, υ/cm-1): 3449(O–
H), 3259 (N–H), 3055 (aromatic C–H), 2963-2870 (aliphatic C–
H), 1657 (C=O), 1617 (C=N), 1550 (C=C), 1484 (N=N), 1274
(C–O). 1H NMR (400 MHz, DMSO-d6)  (ppm): syn/syn isomer,
39.5%: 11.76-11.74 (m, 4H, He or Hc), 8.50 (s, 2H, Hd), 8.17 (d, J
= 2.4 Hz, 2H, Hh), 7.89-7.71 (m, 6H, Hi, Hg), 7.43-7.34 (m, 4H,
Hk), 7.12-7.04 (m, 2H, Hf), 2.74-2.62 (m, 4H, Hl), 2.35-2.29 (m,
4H, Hb), 1.74-1.65 (m, 4H, Ha), 1.24 (t, J = 7.6 Hz, 6H, Hm);
syn/anti and/or anti/syn isomers, 48%: 11.76-11.74 (m, 2H, He or
Hc), 11.37 (s, 1H, He or Hc), 10.92 (br, 1H, He or Hc), 8.48 (s, 1H,
Hd (syn)), 8.36 (s, 1H, Hd (anti)), 8.26 (d, J = 2.4 Hz, 1H, Hh (anti)),
8.16 (d, J = 2.4 Hz, 1H, Hh (syn)), 7.89-7.71 (m, 6H, Hi, Hg), 7.43-
7.34 (m, 4H, Hk), 7.12-7.04 (m, 2H, Hf), 2.74-2.62 (m, 6H, Hl, Hb
(anti)), 2.35-2.29 (m, 2H, Hb (syn)), 1.74-1.65 (m, 4H, Ha), 1.24 (t, J
= 7.6 Hz, 3H, Hm (syn or anti)), 1.18 (t, J = 7.6 Hz, 3H, Hm (syn or anti));
anti/anti isomer, 12.5%: 11.37 (s, 2H, He or Hc), 10.92 (br, 2H, He
or Hc), 8.35 (s, 2H, Hd), 8.23 (d, J = 2.4 Hz, 2H, Hh), 7.89-7.71
(m, 6H, Hi, Hg), 7.43-7.34 (m, 4H, Hk), 7.12-7.04 (m, 2H, Hf),
2.74-2.62 (m, 8H, Hl, Hb), 1.74-1.65 (m, 4H, Ha), 1.24 (t, J = 7.6
Hz, 6H, Hm). 13C NMR (100 MHz, DMSO-d6, ppm): 174.46,
174.43, 169.02, 168.97, 160.32, 159.50, 150.76, 150.69, 147.61,
147.52, 145.65, 145.59, 145.21, 139.78, 139.70, 129.20, 129.16,
129.06, 126.11, 125.01, 124.80, 123.64, 122.85, 122.25, 122.01,
121.47, 121.40, 120.10, 117.65, 117.37, 34.39, 34.30, 32.40,
32.26, 28.52, 28.47, 25.28, 25.12, 24.58, 24.39, 15.82, 15.76.
Anal. Calcd. For C36H38N8O4 (%): C, 66.86; H, 5.92; N, 17.33.
Found: C, 66.95; H, 5.98; N, 17.29. HRMS-ESI (m/z) calcd. for
C36H39N8O4 [M + H]+ 647.3089, found 647.3093.
4.2.6. N'1 ,N'6 -bis((E)-5-((E)-(4-ethylphenyl)
diazenyl)-2-hydroxy-3-methoxybenzylidene)
adipohydrazide (1f)
Yield: 88%, mp 247-248 °C; FT-IR (KBr, υ/cm-1): 3416 (O–
H), 3198 (N–H), 3056 (aromatic C–H), 2961-2870 (aliphatic C–
H), 1670 (C=O), 1606 (C=N), 1547 (C=C), 1460 (N=N), 1267
(C–O). 1H NMR (400 MHz, DMSO-d6)  (ppm): syn/syn isomer,
37.3%: 11.76 (s, 2H, Hc), 11.53 (br, 2H, He), 8.51 (s, 2H, Hd),
7.86-7.73 (m, 6H, Hh, Hi), 7.54 (d, J = 2.4 Hz, 2H, Hg), 7.44-7.34
(m, 4H, Hk), 3.96-3.91 (m, 6H, Hf), 2.75-2.63 (m, 4H, Hl), 2.36-
2.30 (m, 4H, Hb), 1.76-1.66 (m, 4H, Ha), 1.25 (t, J = 7.6 Hz, 6H,
Hm); syn/anti and/or anti/syn isomers, 48.5%: 11.76 (s, 1H, Hc (syn)
or He (syn)), 11.53 (br, 1H, Hc (syn) or He (syn)),11.38 (s, 1H, Hc (anti) or He
(anti)), 10.30 (br, 1H, Hc (anti) or He (anti)), 8.49 (s, 1H, Hd (syn)), 8.41 (s,
1H, Hd (anti)), 7.96 (d, J = 2.4 Hz, 1H, Hh (anti)), 7.86-7.73 (m, 5H,
Hh (syn), Hi), 7.52 (d, J = 2.4 Hz, 1H, Hg (syn)), 7.47 (d, J = 2.4 Hz,
1H, Hg (anti)), 7.44-7.34 (m, 4H, Hk), 3.96-3.91 (m, 6H, Hf), 2.75-
2.63 (m, 6H, Hl, Hb (anti)), 2.36-2.30 (m, 2H, Hb (syn)), 1.76-1.66 (m,
4H, Ha), 1.25 (t, J = 7.6 Hz, 3H, Hm), 1.20 (t, J = 7.6 Hz, 3H,
Hm); anti/anti isomer, 14.2%: 11.37 (s, 2H, Hc), 10.30 (br, 2H,
He), 8.40 (s, 2H, Hd), 7.93 (d, J = 2.4 Hz, 2H, Hh), 7.85-7.73 (m,
4H, Hi), 7.44-7.34 (m, 6H, Hg, Hk), 3.96-3.91 (m, 6H, Hf), 2.75-
2.63 (m, 8H, Hl, Hb), 1.76-1.66 (m, 4H, Ha), 1.25 (t, J = 7.6 Hz,
6H, Hm). 13C NMR (100 MHz, DMSO-d6, ppm): 174.48, 174.42,
168.98, 168.94, 150.71, 150.65, 150.45, 149.44, 149.24, 147.58,
147.52, 147.41, 145.37, 145.25, 145.15, 139.63, 129.22, 129.06,
122.87, 121.06, 119.50, 119.03, 117.65, 117.44, 104.51, 102.97,
102.76, 56.47, 56.41, 34.40, 34.30, 32.32, 32.18, 28.52, 25.22,
25.11, 24.52, 24.37, 15.81, 15.76. Anal. Calcd. For C38H42N8O6
(%): C, 64.57; H, 5.99; N, 15.85. Found: C, 64.51; H, 6.05; N,
15.97. HRMS-ESI (m/z) calcd. for C38H43N8O6 [M + H]+
707.3300, found 707.3304.
4.2.4. N'1 ,N'6 -bis((E)-2-hydroxy-5-((E)-(4-
nitrophenyl)diazenyl)benzylidene)adipohydrazide
(1d)
Yield: 77%, mp 306-307 °C; FT-IR (KBr, υ/cm-1): 3447 (O–
H), 3212 (N–H), 3053 (aromatic C–H), 2953 (aliphatic C–H),
1662 (C=O), 1613 (C=N), 1545 (C=C), 1517 (NO2 asymmetric),
1483 (N=N), 1341 (NO2 symmetric), 1284 (C–O). 1H NMR (400
MHz, DMSO-d6)  (ppm): syn/syn isomer, 35.4%: 11.99 (s, 2H,
Hc or He), 11.79 (s, 2H, Hc or He), 8.56-8.20 (m, 8H, Hd, Hh, Hk),
8.10-7.70 (m, 6H, Hg, Hi), 7.18-7.10 (m, 2H, Hf), 2.36-2.30 (m,
4H, Hb), 1.77-1.68 (m, 4H, Ha); syn/anti and/or anti/syn isomers,
47.9%: 11.94 (s, 1H, Hc (syn) or He (syn)), 11.76 (s, 1H, Hc (syn) or He
(syn)), 11.40 (s, 1H, Hc (anti) or He (anti)), 11.24 (s, 1H, Hc (anti) or He (anti)),
8.56-8.20 (m, 8H, Hd, Hh, Hk), 8.10-7.70 (m, 6H, Hg, Hi), 7.18-
7.10 (m, 2H, Hf), 2.75-2.68 (m, 2H, Hb (anti)), 2.36-2.30 (m, 2H,
Hb (syn)), 1.77-1.68 (m, 4H, Ha); anti/anti isomer, 16.7%: 11.36 (s,
2H, Hc or He), 11.03 (s, 2H, Hc or He), 8.56-8.20 (m, 8H, Hd, Hh,
Hk), 8.10-7.70 (m, 6H, Hg, Hi), 7.18-7.10 (m, 2H, Hf), 2.75-2.68
(m, 4H, Hb), 1.77-1.68 (m, 4H, Ha). The product shows low
solubility in any appropriate solvents to allow for structural
characterization using 13C NMR. Anal. Calcd. For C32H28N10O8
(%): C, 56.47; H, 4.15; N, 20.58. Found: C, 56.55; H, 4.11; N,
20.51. HRMS-ESI (m/z) calcd. for C32H29N10O8 [M + H]+
681.2164, found 681.2161.
4.2.7. N'1 ,N'6 -bis((E)-5-((E)-(4-chlorophenyl)
diazenyl)-2-hydroxy-3-methoxybenzylidene)
adipohydrazide (1g)
Yield: 70%, mp 276-277 °C; FT-IR (KBr, υ/cm-1): 3441 (O–
H), 3187 (N–H), 3044 (aromatic C–H), 2958 and 2930 (aliphatic
C–H), 1657 (C=O), 1605 (C=N), 1539 (C=C), 1465 (N=N), 1268
4.2.5. N'1 ,N'6 -bis((E)-2-hydroxy-3-methoxy-5-((E)-
phenyldiazenyl)benzylidene) adipohydrazide (1e)
Yield: 84%, mp 277-278 °C; FT-IR (KBr, υ/cm-1): 3450 (O–
H), 3087 (aromatic C–H), 2991-2944 (aliphatic C–H), 1670
(C=O), 1581 (C=C), 1461(N=N), 1270 (C–O), 768, 691. 1H
NMR (400 MHz, DMSO-d6)  (ppm): syn/syn isomer, 39.5%:
11.77 (s, 2H, Hc or He), 11.57 (br, 2H, He), 8.51 (s, 2H, Hd), 7.90-
7.79 (m, 6H, Hh, Hi), 7.62-7.50 (m, 8H, Hg, Hk, Hl), 3.96-3.91 (m,
1
(C–O), 751 (C-Cl). H NMR (400 MHz, DMSO-d6)  (ppm):
syn/syn isomer, 34.6%: 11.72 (s, 2H, He), 11.33 (s, 2H, Hc), 8.48
(s, 2H, Hd), 7.87-7.74 (m, 6H, Hh, Hi), 7.62-7.35 (m, 6H, Hg, Hk),
3.90-3.86 (m, 6 H, Hf), 2.31-2.30 (m, 4H, Hb), 1.72-1.66 (m, 4H,
Ha); syn/anti and/or anti/syn isomers, 47.7%: 11.72 (s, 2H, He or
Hc), 11.33 (s, 2H, He or Hc), 8.45 (s, 1H, Hd (syn)), 8.39 (s, 1H, Hd
(anti)), 7.95 (d, J = 7.2 Hz, 1H, Hh (anti)), 7.87-7.74 (m, 5H, Hh (syn)
,

7
10.
Xie, Y.; Ding, Y.; Li, X.; Wang, C.; Hill, J. P.; Ariga, K.; Zhang,
H ), 7.62-7.35 (m, 6H, H , H ), 3.90-3.86 (m, 6H, H ), 2.73-2.68
ACCEPTED MANUSCRIPT
i
g
k
f
W.; Zhu, W. Chem. Commun. 2012, 48, 11513.
Wu, C.; Wang, J.; Shen, J.; Zhang, C.; Wu, Z.; Zhou, H.
Tetrahedron 2017, 73, 5715.
Feng, E.; Fan, C.; Wang, N.; Liu, G.; Pu, S. Dye. Pigment. 2017.
Park, G. J.; Hwang, I. H.; Song, E. J.; Kim, H.; Kim, C.
Tetrahedron 2014, 70, 2822.
Xu, Z.; Chen, X.; Kim, H. N.; Yoon, J. Chem. Soc. Rev. 2010, 39,
127.
Park, S.; Kim, H.-J. Chem. Commun. 2010, 46, 9197.
(m, 2H, Hb (anti)), 2.31-2.30 (m, 2H, Hb (syn)), 1.72-1.66 (m, 4H,
Ha); anti/anti isomer, 17.7%: 11.72 (s, 2H, He), 11.33 (s, 2H, Hc),
8.37 (s, 2H, Hd), 7.93 (d, J = 7.2 Hz, 2H, Hh), 7.87-7.74 (m, 4H,
Hi), 7.62-7.35 (m, 6H, Hg, Hk), 3.90-3.86 (m, 6 H, Hf), 2.73-2.68
(m, 4H, Hb), 1.72-1.66 (m, 4H, Ha). 13C NMR (100 MHz,
DMSO-d6, ppm): 173.96, 173.83, 168.50, 168.44, 150.62,
150.55, 150.43, 149.12, 148.96, 144.96, 143.95, 139.31, 139.08,
134.83, 134.76, 129.41, 129.23, 123.76, 120.52, 119.97, 119.92,
118.99, 118.44, 118.31, 103.43, 101.83, 101.74, 55.83, 55.78,
33.89, 33.76, 31.76, 31.60, 24.68, 24.60, 24.00, 23.80. Anal.
Calcd. For C34H32Cl2N8O6 (%): C, 56.75; H, 4.48; N, 15.57.
Found: C, 56.83; H, 4.41; N, 15.66. HRMS-ESI (m/z) calcd. for
C34H33Cl2N8O6 [M + H]+ 719.1895, found 719.1893.
11.
12.
13.
14.
15.
16.
Lin, Q.; Liu, L.; Zheng, F.; Mao, P.-P.; Liu, J.; Zhang, Y.-M.; Yao,
H.; Wei, T.-B. Tetrahedron 2017, 73, 5307.
17.
Saha, S.; Ghosh, A.; Mahato, P.; Mishra, S. K. S.; Mishra, S. K. S.;
Suresh, E.; Das, S.; Das, A. Org. Lett. 2010, 12, 3406.
Christison, T. T.; Rohrer, J. S. J. Chromatogr. A 2007, 1155, 31.
Mahapatra, A. K.; Karmakar, P.; Roy, J.; Manna, S.; Maiti, K.;
Sahoo, P.; Mandal, D. RSC Adv. 2015, 5, 37935.
Tümay, S. O.; Okutan, E.; Sengul, I. F.; Özcan, E.; Kandemir, H.;
Doruk, T.; Çetin, M.; Çoşut, B. Polyhedron 2016, 117, 161.
Wei, T.; Li, J.; Bai, C.; Lin, Q.; Yao, H.; Xie, Y.; Zhang, Y. Sci.
China Chem. 2013, 56, 923.
Zhang, X.; Guo, X.; Yuan, H.; Jia, X.; Dai, B. Dye. Pigment. 2018.
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Pigment. 2018, 149, 491.
Jang, H. J.; Ahn, H. M.; Kim, M. S.; Kim, C. Tetrahedron 2017, 73,
6624.
Kim, M. S.; Jung, J. M.; Kang, J. H.; Ahn, H. M.; Kim, P.-G.; Kim,
C. Tetrahedron 2017, 73, 4750.
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18.
19.
20.
21.
4.2.8. N'1 ,N'6 -bis((E)-5-((E)-(4-bromophenyl)
diazenyl)-2-hydroxy-3-methoxybenzylidene)
adipohydrazide (1h)
Yield: 75%, mp 273-274 °C; FT-IR (KBr, υ/cm-1): 3450 (O–H),
3189 (N–H), 3043 (aromatic C–H), 2928 (aliphatic C–H), 1656
22.
23.
1
(C=O), 1606 (C=N), 1539 (C=C), 1463(N=N), 1268(C–O). H
24.
25.
NMR (400 MHz, DMSO-d6)  (ppm): syn/syn isomer, : 11.76 (s,
2H, He), 11.38-11.37 (m, 2H, Hc), 8.50 (s, 2H, Hd), 7.89 (d, J =
2.4 Hz, 2H, Hh), 7.84-7.70 (m, 8H, Hi, Hk), 7.52 (d, J = 2.4 Hz,
2H, Hg), 3.93-3.89 (m, 6 H, Hf), 2.34-2.29 (m, 4H, Hb), 1.74-1.66
(m, 4H, Ha); syn/anti and/or anti/syn isomers, : 11.76 (s, 2H, He or
Hc), 11.38-11.37 (m, 2H, He or Hc), 8.48 (s, 1H, Hd (syn)), 8.40 (s,
1H, Hd (anti)), 7.98 (d, J = 2.4 Hz, 1H, Hh (anti)), 7.86 (d, J = 2.4 Hz,
1H, Hh (syn)), 7.84-7.70 (m, 8H, Hi, Hk), 7.52(d, J = 2.4 Hz, 1H,
Hg (syn)), 7.46 (d, J = 2.4 Hz, 1H, Hg (anti)), 3.93-3.89 (m, 6H, Hf),
2.75-2.69 (m, 2H, Hb (anti)), 2.34-2.29 (m, 2H, Hb (anti)), 1.74-1.66
(m, 4H, Ha); anti/anti isomer, : 11.76 (s, 2H, He), 11.38-11.37 (m,
2H, Hc), 8.38 (s, 2H, Hd), 7.95 (d, J = 2.4 Hz, 2H, Hh), 7.84-7.70
(m, 8H, Hi, Hk), 7.39 (d, J = 2.4 Hz, 2H, Hg), 3.93-3.89 (m, 6 H,
Hf), 2.75-2.69 (m, 4H, Hb), 1.74-1.66 (m, 4H, Ha). 13C NMR (100
MHz, DMSO-d6, ppm): 174.51, 174.38, 169.00, 168.94, 151.33,
149.36, 145.26, 144.87, 139.60, 139.43, 132.89, 132.72, 124.61,
124.46, 121.08, 120.00, 119.52, 118.66, 104.18, 102.48, 102.32,
56.53, 56.38, 56.35, 34.43, 34.31, 32.27, 32.12, 25.18, 25.10,
24.50, 24.31. Anal. Calcd. For C34H32Br2N8O6 (%): C, 50.51; H,
3.99; N, 13.86. Found: C, 50.59; H, 4.07; N, 13.82. HRMS-ESI
(m/z) calcd. for C34H33Br2N8O6 [M + H]+ 807.0884, found
807.0890.
26.
27.
28.
29.
30.
Orojloo, M.; Amani, S. Comptes Rendus Chim. 2017, 20, 415.
Mohammadi, A.; Yaghoubi, S. Sensors Actuators B Chem. 2017,
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32.
Rezaeian, K.; Khanmohammadi, H. New J. Chem. 2015, 39, 2081.
Yeap, G.-Y.; Hrishikesan, E.; Chan, Y.-H.; Mahmood, W. A. K.
Tetrahedron 2017, 73, 5517.
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34.
Isaad, J.; El Achari, A. Tetrahedron 2011, 67, 5678.
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Mahmoodi, N. O.; Rahimi, S.; Pasandideh Nadamani, M. Dye.
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Acknowledgments
We thank the Research Committee of the University of Guilan
for the partial support given to this study.
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ACCEPTED MANUSCRIPT
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Eight new bis-benzylidene-hydrazides synthesized and characterized.
Chemosensor 1d acts as highly sensitive chromogenic sensor for CN¯ and AcO¯ ions.
Bis-benzylidene-hydrazides exhibit three stereoisomers: syn/syn, anti/syn and anti/anti
isomers.
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The 1H NMR spectra revealed chemosensor recognition of CN¯ via H-bonds.
The LOD for 1d toward CN¯ found to be 1.1 µM.
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For nitro bis-benzylidene-hydrazide derivative + CN¯ ratio of binding chemosensor:
anion is ~ 1:2.
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