Novel synthesized azo-benzylidene-thiourea as dual naked-eye chemosensor for selective detection of Hg2+ and CNˉ ions

Article abstract of DOI:10.1016/j.jphotochem.2020.112365

Seven novel chemosensors contain azo chromophore and phenylthiourea, were synthesized and applied as colorimetric probes in aqueous solutions of dimethyl sulfoxide. The anion recognition studies exhibited that the synthesized azo dye derivatives act as a

Full text of DOI:10.1016/j.jphotochem.2020.112365

JournalofPhotochemistry&PhotobiologyA:Chemistry391(2020)112365
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Journal of Photochemistry & Photobiology A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Novel synthesized azo-benzylidene-thiourea as dual naked-eye chemosensor
for selective detection of Hg2+ and CN¯ ions
Hamide Hosseinjani-Pirdehia, Nosrat O. Mahmoodib,*, Meysam Pasandideh Nadamanib,
Amir Taheric,*
a Department of Chemistry, Tarbiat Modares University, 14115-175, Tehran, Iran
b Department of Chemistry, Faculty of Sciences, University of Guilan, 41335-1914, Iran
c Interdisciplinary Technologies Department, Breast Cancer Research Center, Motamed Cancer Institute, ACECR, Tehran, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords:
Colorimetric probe
Dual sensor
Ion sensing
Naked-eye detection
Seven novel chemosensors contain azo chromophore and phenylthiourea, were synthesized and applied as
colorimetric probes in aqueous solutions of dimethyl sulfoxide. The anion recognition studies exhibited that the
synthesized azo dye derivatives act as a highly dual-sensitive and selective chromogenic sensor for naked-eye
detection of Hg2+ and CN¯ ions, with a different color change from yellow to colorless and yellow to red,
respectively. The limit of detection (LOD) was found for 3c toward Hg2+ and CN¯ ions to be 4.89 μM and 2.23
μM, respectively. The result of the Job's plot indicating that the stoichiometry binding ratios of compound 3c to
Hg2+ is 1:1 and to CN¯ is 1:2. These results were confirmed by 1H NMR titration experiments.
1. Introduction
equipment required, and relatively low costs [21–29]. Colorimetric
chemosensors based on azo chromophore with high sensitivity display a
Cations and anions play important roles in industrial, biological and
environmental processes. Among the various cations, Hg2+ is one of the
most toxic environmental pollutants and threatens human beings and
living organisms. Mercury as heavy metal can be bioaccumulated
through the food chain and causes strongly damage to the central
nervous system and other organs by the blood-brain barrier even at
very low concentrations [1–3]. Among the various anions, CN¯ is one of
the most worrisome anions because it can be absorbed through skin,
gastrointestinal tract and lungs, resulting in vomiting, convulsion, loss
of consciousness, and eventual death [4–10]. Despite its severe toxicity,
cyanide is still extensively produced and used in various industrial
processes such as electroplating and resin industry, plastic manu-
facturing and the silver and gold mining industry [11,12]. Therefore,
considering the public health concerns, the development of sensitive
and selective chemosensors is necessary for detection of Hg2+ and CN¯
in aqueous solution. To detect Hg2+ and CN¯, several methods including
atomic absorption, voltammetric, chromatographic, potentiometric,
spectrophotography, electrochemical, optical methods and flow injec-
tion analysis technique have been developed [13–20]. Among the dif-
ferent methods, colorimetric chemosensors have been widely used in
recent years because of their advantages, such as conveniently and
easily being naked-eye detectable, quick response rates, lack of
selective detection for sensing Hg2+ and CN¯ in aqueous media
[30–33]. The advantage of these sensors is strong photophysical prop-
erties, real-time monitoring, coordination ability with metal ions, ra-
pidity and and being naked-eye visible.
In consideration of these characteristics, we designed dual-func-
tional naked-eye chemosensors 3a-3 g based on azo dyes for visual
detection of Hg2+ and CN¯ ions (Scheme 1). The sensing processes can
be recognized by naked-eye detection, with a color change from yellow
to colorless and yellow to red in presence of Hg2+ and CN¯ ions, re-
spectively. Furthermore, the prepared strip papers of chemosensors
make the qualitative sensing of the ions available.
2. Experimental
2.1. Materials and apparatus
All chemicals, solvents and salts such as sodium salts of F¯, Cl¯, Br¯,
I¯, H2PO4 , NO2 , NO3 , CN¯, SCN¯, SO42− and chloride salts of Li+, Na+
,
¯
¯
¯
K+, Cu+, Cu2+, Hg2+, Ca2+, Ba2+, Ni2+, Mn2+, Co2+, Mn2+ and Al3+
were prepared from Merck, Alpha Aesar and Samchun companies.
Melting points measured on an Electrothermal 9100 apparatus. IR
spectra were recorded as KBr pellets on
a NICOLET FTIR 100
⁎ Corresponding authors.
E-mail addresses: mahmoodi@guilan.ac.ir (N.O. Mahmoodi), ataheri@ibcrc.ir (A. Taheri).
https://doi.org/10.1016/j.jphotochem.2020.112365
Received 8 December 2019; Received in revised form 5 January 2020; Accepted 7 January 2020
Availableonline09January2020
1010-6030/©2020ElsevierB.V.Allrightsreserved.

H. Hosseinjani-Pirdehi, et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry391(2020)112365
Scheme 1. Synthesis of compounds 3a-3 g.
was added and the mixture stirred for 2 h at room temperature. The
orange to red azo products were obtained by filtration and washed with
cold EtOH.
2.2.1. 1-{2-[(2-Hydroxy-5-phenylazo-benzylidene)-amino]-phenyl}-3-
phenyl-thiourea (3a)
Orange solid; Yield = 285.0 mg (63.2 %); M.p. = 208–212 °C; FT-IR
(KBr) (Cm−1): 3468 (s), 3414 (s), 3256 (s), 3154 (s), 1616 (s), 1591
(m), 1541 (m), 1480 (m), 1400 (s); ESI-MS m/z (%) = 315 (67), 301
(73), 209 (82), 150 (82), 105 (12), 93 (39), 77 (100); 1H NMR
(300 MHz, DMSO-d6) δ (ppm): 13.48 (1H, s), 9.92 (1H, s), 9.51 (1H, s),
9.07 (1H, s), 8.33 (1H, d, J = 2.4 Hz), 8.01 (1H, dd, J = 2.4, 9.0 Hz),
7.83 (2H, dd, J = 1.5, 7.4 Hz), 7.65-7.44 (7H, m), 7.40-7.26 (4H, m),
7.15 (1H, d, J = 8.7 Hz), 7.09 (1H, t, J = 7.4 Hz); 13C NMR (75 MHz,
DMSO-d6) δ (ppm): 180.2, 163.6, 162.6, 151.9, 144.7, 143.5, 139.2,
133.3, 130.9, 129.4, 128.5, 127.8, 127.7, 127.0, 126.9, 124.6, 123.9,
123.8, 122.2, 119.8, 119.0, 118.0. Anal. Calcd. For C26H21N5OS (%): C,
69.16; H, 4.69; N, 15.51. Found: C, 69.09; H, 4.64; N, 15.60.
Fig. 1. Solvent effect according to H2O percentage.
spectrometer. 1H NMR (500 MHz), 1H NMR (300 MHz) and 13C NMR
(126 MHz), 13C NMR (75 MHz) spectra were obtained using Bruker
DRX-500 AVANCE and Bruker DRX-300 AVANCE spectrometers. All
NMR spectra at room temperature were recorded in DMSO-d6. Mass
spectra were recorded on a FINNIGAN-MATT 8430 mass spectrometer
operating at an ionization potential of 70 eV. Important mass fragments
were interpreted and their structures were reported in the supporting
information. The CHN analyses were performed on a Vario-ELIII ele-
mental analyzer. Ultraviolet-Visible (UV–vis) spectra were recorded
with a Rayleigh UV-2601 double-beam spectrophotometer.
2.2.2. 1-(2-{[2-Hydroxy-5-(3-nitro-phenylazo)-benzylidene]-amino}-
phenyl)-3-phenyl-thiourea (3b)
Red solid; Yield = 444.9 mg (89.7 %); M.p. = 203–205 °C; FT-IR
(KBr) (Cm−1): 3470 (m), 3413 (m), 3147 (m), 1618 (s), 1590 (m), 1540
(m), 1516 (s), 1401 (s), 1342 (s); ESI-MS m/z (%) = 346 (100), 196
(98), 150 (81), 122 (19), 93 (49); 1H NMR (300 MHz, DMSO-d6) δ
(ppm): 13.80 (1H, s), 9.95 (1H, s), 9.53 (1H, s), 9.09 (1H, s), 8.41 (3H,
m), 8.07 (1H, d, J = 2.4 Hz), 8.02 (2H, d, J = 9.0 Hz), 7.62 (1H, dd,
J = 2.1, 7.7 Hz), 7.47 (3H, d, J = 7.5 Hz), 7.35- 7.26 (4H, m), 7.16 (1H,
d, J = 9.0 Hz), 7.09 (1H, t, J = 7.5 Hz); 13C NMR (75 MHz, DMSO-d6) δ
(ppm): 180.2, 165.4, 162.2, 155.3, 147.9, 144.6, 143.0, 139.1, 133.3,
129.3, 128.5, 127.8, 127.3, 127.2, 127.0, 125.1 (2C), 124.6, 123.9,
123.1 (2C), 119.7, 118.9, 118.6. Anal. Calcd. For C26H20N6O3S (%): C,
62.89; H, 4.06; N, 16.93. Found: C, 62.78; H, 4.01; N, 17.01.
2.2. General procedure for the synthesis of phenylthiourea-based azo dye
3a-3 g
Related azo dye 1a-1 g were prepared based on the reported pro-
cedure in literature [34,35]. 1-(2-aminophenyl)-3-phenylthiourea 2
simply prepared by mixing o-phenylenediamine and phenyl iso-
thiocyanate (1:1) in CH2Cl2. After 30 min white crystals generated,
filtered and used for the next step. The azo dye (1 mmol) and compound
2 (1 mmol) were added to a 25 ml round bottom flask. Then 10 ml EtOH
2.2.3. 1-(2-{[2-Hydroxy-5-(4-nitro-phenylazo)-benzylidene]-amino}-
phenyl)-3-phenyl-thiourea (3c)
Dark orange solid; Yield = 359.6 mg (72.5 %); M.p. = 205–207 °C;
FT-IR (KBr) (Cm−1): 3469 (m), 3412 (m), 3160 (m), 1618 (s), 1590
(m), 1516 (s), 1402 (s), 1342 (s); ESI-MS m/z (%) = 346 (100), 196
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H. Hosseinjani-Pirdehi, et al.
JournalofPhotochemistry&PhotobiologyA:Chemistry391(2020)112365
Fig. 2. Color changing after the addition of various ions (10 equiv.) to the solutions of 3c (5.0 μM) in H2O-DMSO (2:1 v/v).
Fig. 4. The UV-Vis absorbance of probes 3a-3 g (5.0 μM) after the addition of
Fig. 3. UV–vis spectral responses (A) and absorbance values (B) of probe 3c
(5.0 μM) after the addition of 10 equiv. of different ions in H2O-DMSO (2:1 v/
v).
10 equiv. of Hg2+ ions (A) or CN¯ ions (B) in H2O-DMSO (2:1 v/v).
118.6. Anal. Calcd. For C26H20N6O3S (%): C, 62.89; H, 4.06; N, 16.93.
Found: C, 62.83; H, 3.98; N, 17.02.
(61), 150 (29), 93 (21); 1H NMR (300 MHz, DMSO-d6) δ (ppm): 13.75
(1H, s), 9.95 (1H, s), 9.53 (1H, s), 9.09 (1H, s), 8.41 (3H, m), 8.07 (1H,
d, J = 2.4 Hz), 8.02 (2H, d, J = 9.0 Hz), 7.62 (1H, dd, J = 2.1, 7.7 Hz),
7.47 (3H, d, J = 7.5 Hz), 7.35- 7.26 (4H, m), 7.16 (1H, d, J = 9.0 Hz),
7.09 (1H, t, J = 7.5 Hz); 13C NMR (75 MHz, DMSO-d6) δ (ppm): 180.2,
165.5, 162.2, 155.3, 148.0, 144.5, 143.4, 139.1, 133.3, 129.3, 128.5,
127.8, 127.4, 127.2, 127.0, 125.1, 124.5, 123.9, 123.0, 119.7, 118.9,
2.2.4. 1-(2-{[5-(3-Chloro-phenylazo)-2-hydroxy-benzylidene]-amino}-
phenyl)-3-phenyl-thiourea (3d)
Red solid; Yield = 240.1 mg (49.4 %); M.p. = 196–200 °C; FT-IR
(KBr) (Cm−1): 3466 (m), 3414 (m), 3267 (m), 3157 (s), 1616 (s), 1590
(m), 1540 (s), 1480 (m), 1400 (m); ESI-MS m/z (%) = 335 (71), 196
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JournalofPhotochemistry&PhotobiologyA:Chemistry391(2020)112365
Fig. 5. Ion interference with Hg2+ ions at 280 nm (A) and CN¯ ions at 480 nm
(B).
Fig. 7. The UV–Vis changes of the chemosensor 3c (5.0 μM) with various
amounts of Hg2+ ions (10 equiv.) (A) and CN¯ ions (10 equiv.) (B).
2.2.5. 1-(2-{[5-(4-Chloro-phenylazo)-2-hydroxy-benzylidene]-amino}-
phenyl)-3-phenyl-thiourea (3e)
Pale orange; Yield =332.4 mg (68.4 %); M.p. = 193–195 °C; FT-IR
(KBr) (Cm−1): 3466 (m), 3414 (m), 3163 (s), 1616 (s), 1590 (m), 1478
(s), 1399 (s); ESI-MS m/z (%) = 335 (3), 260 (100), 149 (63), 139 (33),
121 (87), 111 (85), 93 (48), 77 (29); 1H NMR (300 MHz, DMSO-d6) δ
(ppm): 13.63 (1H, s), 10.36 (1H, s), 9.95 (1H, s), 9.53 (1H, s), 9.06 (1H,
s), 8.31 (1H, s), 8.17 (1H, d, J = 1.8 Hz), 8.01 (1H, dd, J = 1.8, 8.7 Hz),
7.99 (1H, dd, J = 1.5, 8.7 Hz), 7.85 (3H, d, J = 8.4 Hz), 7.34- 7.26 (6H,
m), 7.22- 7.04 (2H, m); 13C NMR (75 MHz, DMSO-d6) δ (ppm): 180.2,
164.0, 162.5, 150.5, 144.6, 143.4, 139.2, 135.3, 133.3, 129.7, 129.5,
128.5, 128.2, 127.7, 124.6, 124.0, 123.9, 122.7, 119.8, 119.0, 118.5,
118.2. Anal. Calcd. For C26H20ClN5OS (%): C, 64.26; H, 4.15; N, 14.41.
Found: C, 64.14; H, 4.19; N, 14.48.
2.2.6. 1-{2-[(2-Hydroxy-5-p-tolylazo-benzylidene)-amino]-phenyl}-3-
phenyl-thiourea (3f)
Fig. 6. UV–Vis spectra of 3c with simultaneous addition of CN¯ and Hg2+ ions
in H2O-DMSO (2:1 v/v) solution.
Red solid; Yield = 249.7 mg (53.7 %); M.p. = 214–215 °C; FT-IR
(KBr) (Cm−1): 3425 (m), 3416 (m), 3260 (s), 3155 (s), 1615 (s), 1591
(m), 1541 (m), 1480 (m), 1400 (s); ESI-MS m/z (%) = 329 (18), 315
(90), 196 (100), 150 (65), 119 (16), 93 (45), 91 (47); 1H NMR
(300 MHz, DMSO-d6) δ (ppm): 13.44 (1H, s), 9.94 (1H, s), 9.53 (1H, s),
9.06 (1H, s), 8.29 (1H, d, 2.4 Hz), 7.98 (1H, dd, 2.4, 9.0 Hz), 7.77 (2H,
d, J = 8.1 Hz), 7.64 (1H, dd, J = 2.4, 6.9 Hz), 7.46 (3H, d, J = 7.5 Hz),
7.39- 7.26 (6H, m), 7.14 (1H, d, J = 9.0 Hz), 7.09 (1H, t, J = 7.4 Hz),
2.39 (3H, s); 13C NMR (75 MHz, DMSO-d6) δ (ppm): 180.2, 163.3,
162.7, 150.0, 144.7, 143.6, 141.1, 139.2, 133.3, 129.9, 128.5, 127.7,
127.0, 127.0, 127.0 (2C), 124.6, 123.9, 122.3, 119.8, 119.4, 117.9,
21.0. Anal. Calcd. For C27H23N5OS (%): C, 69.66; H, 4.98; N, 15.04.
(100), 150 (92), 111 (11), 93 (36), 77 (30); 1H NMR (300 MHz, DMSO-
d6) δ (ppm): 13.72 (1H, s), 9.93 (1H, s), 9.53 (1H, s), 9.10 (1H, s), 8.35
(1H, d, J = 2.4 Hz), 8.02 (1H, dd, J = 2.7, 8.85 Hz), 7.68 (2H, dt,
J = 1.5, 7.7 Hz), 7.61 (1H, dd, J = 2.1, 7.2 Hz), 7.54 (1H, dd, J = 1.9,
7.4 Hz), 7.47 (4H, t, J = 7.5 Hz), 7.36- 7.26 (4H, m), 7.17 (1H, d,
J = 9.0 Hz), 7.09 (1H, t, J = 7.5 Hz); 13C NMR (75 MHz, DMSO-d6) δ
(ppm): 180.2, 164.6, 162.5, 147.9, 144.9, 143.3, 139.1, 133.4, 133.3,
130.1, 129.1, 128.5, 128.3, 128.1, 127.8, 127.1, 127.0, 126.8, 124.6,
123.9, 119.4, 119.0, 118.4, 117.5. Anal. Calcd. For C26H20ClN5OS (%):
C, 64.26; H, 4.15; N, 14.41. Found: C, 64.22; H, 4.07; N, 14.53.
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JournalofPhotochemistry&PhotobiologyA:Chemistry391(2020)112365
using any catalyst in moderately good yields and candidates as sensing
performance (Scheme 1).
3.2. Colorimetric and UV–vis spectral studies
3.2.1. Solvent
At the first step, with the goal of choosing the best ratio of H2O-
DMSO, the UV absorption of compound 3c was measured in the dif-
ferent percent of H2O-DMSO media. The results indicated, with a minor
difference, 66.7 % H2O will be the best (Fig. 1).
3.2.2. Ion sensing
In order to investigate the colorimetric behavior of the novel dyes
3a-3 g, their ability to sensing sodium salts of F¯, Cl¯, Br¯, I¯, H2PO4 ,
¯
¯
¯
NO2 , NO3 , CN¯, SCN¯, SO42− and chloride salts of Li+, Na+, K+, Cu+
,
Cu2+, Hg2+, Ca2+, Ba2+, Ni2+, Mn2+, Co2+, Mn2+ and Al3+ were
investigated by UV–vis absorption spectrometry in H2O-DMSO (2:1, v/
v) solution (Fig. 2).
Among the synthesized dyes 3a-3 g, probes with electron-with-
drawing groups (NO2 and Cl) 3b-3e compared with electron-donner
groups (Me and Et) 3f, 3 g represented distinct colorimetric response
upon addition of 10 equiv. CN¯ and Hg2+
.
Upon the addition of CN¯ and Hg2+ ions, a remarkable color change
from yellow to red (bathochromic shift) and yellow to colorless (hyp-
sochromic shift) were monitored respectively (Fig. 2). All of the
synthesis probes except 3d under similar conditions shown a compar-
able sensing behavior towards Hg2+ ion. Even though the 3e and 3b
showed higher absorbance than 3c towards Hg2+ ion, the 3c was se-
lected in comparison to them due to the highest selectivity to both
Hg2+ and CN¯ ions as shown in Fig. 4. Additionally, the absorption
intensity at 280 nm for 3c after the addition of CN¯ remained un-
changed. However, for 3e and 3b the absorption intensity at 280 nm
increased. This phenomenon initiated the inaccuracy in Hg2+ mea-
surement. Our investigation revealed that synthesized probe 3c can be
used as ‘naked-eye’ CN¯ and Hg2+ indicators.
Fig. 8. Job's plot between probe 3c, Hg2+ (A) and CN¯ (B) ions in H2O-DMSO
solution (2:1 v/v).
The UV–vis spectra of chemosensor 3c in H2O-DMSO (2:1) showed
an absorption band with the ⌊max centered at 365 nm, which is attrib-
uted to intramolecular charge transfer (ICT) of azo skeleton (π to π٭
and/or n to π٭) (Fig. 3). Immediately after interaction of probe 3c with
CN¯ or Hg2+ ions, the new ICT bands were observed at 480 nm (Δλ max
=115 nm) or 280 nm (Δλ max=85 nm) respectively. As it can be ob-
served, these bands have not appeared for other ions.
Unlike previous reports concerning on the bifunctional response of
azo-based dyes to CN¯/F¯ [36,37], CN¯/OAc¯ [30] and CN¯/Cu2+
[33,38] all synthesized probes 3a-3 g selectively response to CN¯/Hg2+
(Fig. 4).
In continues, the effect of competitive anions and cations (10 equiv.)
on the interaction of 3c/Hg2+ and 3c/CN¯ was examined in the pre-
sence of Hg2+, CN¯ ions and other species (Fig. 5). The UV–vis spectra
revealed that the presence of other interfering ions up to 10 equiv. had
no effect on the absorbance intensity of Hg2+ at 280 nm or CN¯ at
480 nm (Fig. 5).
Found: C, 69.60; H, 4.89; N, 15.08.
2.2.7. 1-(2-{[5-(4-Ethyl-phenylazo)-2-hydroxy-benzylidene]-amino}-
phenyl)-3-phenyl-thiourea (3 g)
Orange solid; Yield = 249.7 mg (57.4 %); M.p. = 213–215 °C; FT-IR
(KBr) (Cm−1): 3468 (s), 3414 (s), 3261 (s), 3156 (s), 1617 (s), 1592
(m), 1541 (m), 1481 (m), 1400 (s); ESI-MS m/z (%) = 329 (94), 196
(99), 150 (100), 135 (39), 93 (51), 77 (40); 1H NMR (300 MHz, DMSO-
d6) δ (ppm): 13.44 (1H, s), 9.93 (1H, s), 9.52 (1H, s), 9.06 (1H, s), 8.30
(1H, d, J = 2.1 Hz), 7.99 (1H, dd, J = 2.4, 9.0 Hz), 7.79 (1H, d,
J = 8.1 Hz), 7.63 (1H, dd, J = 2.4, 6.6 Hz), 7.48- 7.40 (5H, m), 7.34-
7.26 (4H, m), 7.14 (1H, d, J = 9.0 Hz), 7.09 (1H, t, J = 7.2 Hz), 2.69
(2H, quin. J = 7.5 Hz), 1.22 (3H, t, J = 7.5 Hz); 13C NMR (75 MHz,
DMSO-d6) δ (ppm): 180.2, 163.3, 162.7, 150.2, 147.2, 144.7, 143.6,
139.2, 133.3, 128.8, 128.5, 127.7, 127.6, 127.0, 127.0, 126.9, 124.6,
123.9, 122.4, 119.8, 119.0, 118.0, 28.1, 15.3. Anal. Calcd. For
Moreover, the simultaneous addition of CN¯ and Hg2+ ions effect on
the sensing behavior of compound 3c (5.0 μM) was examined (Fig. 6).
The simultaneous addition of Hg2+ and CN¯ (same equiv.) led to a color
change from yellow to colorless, which demonstrates the Hg2+ ions can
be chiefly detected by the designed chemosensor under the same con-
ditions. Upon the titration of 3c-CN¯ (10 equiv. CN¯) with different con.
of Hg2+, the red color of the solution remained almost unchanged up to
2.1 equiv. of Hg2+. In higher con. of 2.1 equiv. the absorption peak at
480 nm decrease while simultaneously, the absorption peak at 280 nm
increased. Addition of 2.2–10 equiv. of Hg2+ demonstrated with the
naked-eye color change from red to colorless (Fig. 6). These phenomena
confirm the formation of the stable mercury-cyanide complex [Hg
(CN)x]n− and releasing of compound 3c in the solution. Moreover, the
addition of excess Hg2+ ions to this solution changed it to colorless.
C
28H25N5OS (%): C, 70.12; H, 5.25; N, 14.60. Found: C, 70.07; H, 5.22;
N, 14.72.
3. Result and discussion
3.1. Chemistry
With our background on chemosensors designing [7], the presence
of OH, NH and C]S functional groups on probes can increase the re-
activity toward Hg2+ and CN¯ ions. For this purpose, we designed seven
novel azo dyes 3a-3 g containing thiourea moiety prepared straight-
forwardly by condensation of corresponding premade azo compound 1
and 1-(2-aminophenyl)-3-phenylthiourea 2 in EtOH at r.t. without
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JournalofPhotochemistry&PhotobiologyA:Chemistry391(2020)112365
Fig. 9. 1H NMR spectra of compound 3c, 3c + 2 equiv. CN¯ and 3c + 1 equiv. Hg2+ in DMSO-d6.
In order to gain more information about the sensing behavior of the
compound 3c to CN¯ and Hg2+, the UV–Vis spectrophotometric titra-
tions experiment was performed. As shown in Fig. 7A, upon the
addition of Hg2+ ions (10 equiv.) to the solution of compound 3c (5.0
μM), a new absorption band appeared at 280 nm, which gradually
growth with increasing concentration of Hg2+. In the other case, with
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JournalofPhotochemistry&PhotobiologyA:Chemistry391(2020)112365
Fig. 10. Photographs of the test strips with compound 3c for detecting CN¯ and Hg2+ ions in aqueous solution.
CN¯ ions (10 equiv.) addition to compound 3c solution (5.0 μM) the
absorption band at 365 nm slowly decreased and a new absorption band
appeared at 480 nm (Fig. 7B). The measured limit of detection
(LOD = 3σ/m) for CN¯ and Hg2+ were 2.23 μM and 4.89 μM, respec-
tively.
Funding
Funding was received for this work.
Declaration of Competing Interest
No conflict of interest exists.
Acknowledgments
The binding stoichiometry of compound 3c with Hg2+ and CN¯ were
determined by Job's plot analyses via analyzing the changes in ab-
sorption intensity with different Hg2+ and CN¯ concentration (Fig. 8).
The maximum absorption at selected wavelengths (480 nm for 3c-CN¯
and 280 nm for 3c-Hg2+) was observed when the mole fraction of Hg2+
and CN¯ ions reached about 0.50 and 0.63 respectively, indicating that
the binding ratio of compound 3c to Hg2+ is 1:1 and to CN¯ is 1:2.
The same result was confirmed by 1H NMR titration obtained from
average integration of 3c-Hg2+ and 3c-CN¯ carried out in DMSO-d6
solution. As shown in Fig. 9, before the addition of CN¯ and Hg2+ ions,
the phenolic proton at 13.77 ppm as a broad signal, the thioamide
protons at 9.95 and 9.53 ppm, as well as imine proton at 9.09 ppm as
sharp singlets, were observed. However, after the addition of CN¯ the
thioamide protons appeared at 10.00 and 9.55 ppm, the phenolic
The authors are grateful to the Tarbiat Modares University for the
financial support of this research work. We would like to thank our
colleagues at Motamed Cancer Institute and University of Guilan for
providing a good contribution to all aspects of the project.
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.jphotochem.2020.
112365.
proton at 13.77 ppm disappeared and
a new signal grew in at
10.28 ppm, which can be attributed to the = NeNH hydrazone tauto-
meric form [37,39]. In the case of Hg2+ (1 eqiv.), a significant shift for
the OH band (∼ 2 ppm) and a small shift for NH groups were observed.
Therefore, the results of 1H NMR titration, point to the complexation of
compound 3c with Hg2+ and deprotonation of the hydroxyl group
during the CN¯ sensing process.
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