Synthesis and anion recognition studies of novel bis (4-hydroxycoumarin) methane azo dyes

Article abstract of DOI:10.1016/j.molstruc.2015.11.013

Four new bis (4-hydroxycoumarin) methane azo dyes were synthesized by the condensation of 4-hydroxycoumarin with four different azo salicylaldehydes and their structures were characterized by FT-IR, ¹H NMR, ¹³C NMR, HRMS. Anion bindi

Full text of DOI:10.1016/j.molstruc.2015.11.013

Accepted Manuscript
Synthesis and anion recognition studies of novel bis (4-hydroxycoumarin) methane
azo dyes
Amorn Panitsiri, Sukanya Tongkhan, Widchaya Radchatawedchakoon, Uthai Sakee
PII:
S0022-2860(15)30418-X
10.1016/j.molstruc.2015.11.013
MOLSTR 21963
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 2 July 2015
Revised Date: 5 November 2015
Accepted Date: 11 November 2015
Please cite this article as: A. Panitsiri, S. Tongkhan, W. Radchatawedchakoon, U. Sakee, Synthesis
and anion recognition studies of novel bis (4-hydroxycoumarin) methane azo dyes, Journal of Molecular
Structure (2015), doi: 10.1016/j.molstruc.2015.11.013.
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ACCEPTED MANUSCRIPT
Graphical abstract
OH
OH
N
O
OH
O
N
N
R2
R1
R1
R1
O
O
H
H
NaNO2, HCl
MeOH / reflux
OH
OH
Na2CO3, H2O
OH
O
R2
N
NH2
R2
O
O
O

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Synthesis and anion recognition studies of novel
bis (4-hydroxycoumarin) methane azo dyes
Amorn Panitsiri, Sukanya Tongkhan, Widchaya Radchatawedchakoon and Uthai
Sakee*
Center of Excellence for Innovation in Chemistry (PERCH-CIC), Department of Chemistry,
Faculty of Science, Mahasarakham University, Mahasarakham 44150, Thailand
Abstract
Four new bis (4-hydroxycoumarin) methane azo dyes were synthesized by the condensation
of 4-hydroxycoumarin with four different azo salicylaldehydes and their structures were
characterized by FT-IR, 1H NMR, 13C NMR, HRMS. Anion binding ability in dimethyl
sulfoxide (DMSO) solutions with tetrabutylammonium (TBA) salts (F−, Cl−, Br−, I−, AcO−
−
and H2PO4 ) was investigated by the naked eye, as well as UV‐visible spectroscopy. The
sensor shows selective recognition towards fluoride and acetate. The binding affinity of the
sensors with fluoride and acetate was calculated using UV–visible spectroscopic technique.
Keywords: anion, sensor, azo, coumarin, synthesis
*Corresponding authors: e-mail address: uthai.s@msu.ac.th
1. Introduction
Azo compounds are widely used as colorants in the textile, printing, cosmetics, drugs,
foods coloring, and other consumer goods. There are about 3000 azo dyes currently in use all
over the world. In general, they can be classified into monoazo-, diazo-, triazo- and polyazo-

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dyes, but the great majority of them are monoazo compounds, which have the common
structure unit of the azo chromophore linking two aromatic systems [1-2]. Another
application is analytical chemistry [3]. On the other hand azo compounds shown biological
activities containing antimicrobial [4-5].
4-Hydroxycoumarin is an important component of numerous synthetic and natural
products with wide-ranging biological activities [6] including anticoagulant [7], spasmolytic
[8], and anti-HIV activities [9, 10]. They are also extensively used as analytical reagents [11,
12].
Anions play a major role in our daily life; being crucial to physiological function as well
as various industrial process [13]. The development of new receptors, sensors and
transporters for anionic species continues to be a rich area of research [14]. Most
chemosensors developed so far are chromogenic and fluorescent sensors, which efficiently
change their photophysical properties in the presence of anions [15]. One of particular
interest in this regard involves the construction of colorimetric anion sensors [16]. Such
sensors allow naked-eye detection of anions without the use of any spectroscopic
instrumentation [17].
In the past few years, some chromogenic sensors based on coumarin have been developed
for cations [18-20] and anions [21]. To date a number of azo-based colorimetric sensors for
anions have been reported [22-25]. Generally, colorimetric chemosensor is made up of two
main fragments, which involve the binding sites that interact with anions either
electrostatically or through hydrogen bonding and the signal parts that connect to the binding
sites either directly or intramolecularly linked which show the color changes in the anion
recognition procession. The anion sensing, simplicity and high selectivity are still challenges
for investigators and they attract much interest. In particular, to develop the naked-eye

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detection technique for the analysts without using any expensive equipment is of great
interest in recent years.
Herein, as a part of our ongoing research on analyst recognition, we designed and
synthesized new and simple anion sensors 3a-d containing both hydrogen-bond-donor group
(4-hydroxycoumarin) and chromogenic unit (azophenyl) and studied their anion recognition
behaviors toward biologically important fluoride and acetate ions over other anions with high
selectivity. In addition, the sensing processes can be realized by the ‘naked-eye’
determination as it has a remarkable color response.
Scheme 1.
2. Experimental
2.1. General
All solvents and reagents were purchased from commercial sources and used as received. IR
spectra were recorded on Perkin Elmer SPECTRUM GX, FT-IR spectrophotometer. Spectra
were recorded as pressed KBr disc. The 1H and 13C NMR spectra were measured with a
Bruker AVANCE 400 spectrometer operating at 400 and 100 MHz, respectively. The
chemical shifts (δ) are reported in ppm, and coupling constants (J) are given in Hz. The
spectra were taken in CD3SOCD3 and the residual solvent signal of CH3SOCH3 at δ 2.50 and
39.5 was used as reference for 1H and 13C NMR spectra, respectively. The HRMS mass
spectra were recorded on micrOTOF spectrometer.
2.2. Synthesis
2.2.1 General procedure for 3a-d synthesis
2.2.1.1 Synthesis derivatives of azo aromatic aldehyde (2a-d)

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The structures of synthesized azo aromatic aldehyde are shown in Scheme 1. A 0 °C solution
I of aniline derivatives (10 mmol) in deionized water (10 mL) and HCl (2 mL) was prepared.
A 0 °C solution II of NaNO2 (15 mmol) in deionized water (5 mL) was dropwised into the
solution I. The mixture was stirred for 10 min. A solution of Na2CO3 (30 mmol) in deionized
water (30 mL) at 0 °C was added aldehyde derivatives 1a or 1b (10 mmol). The solution of
aldehyde derivatives and Na2CO3 was dropwised into the mixture solution of I and II and
then the solution was stirred 2 h in cool bath. The reaction was adjusted the pH to 7 by adding
the solution of HCl. The precipitated products 2a-d were filtered and heated in the oven.
2.2.1.2 Representative procedure for the synthesis of sensors 3a-d
4-Hydroxycoumarin (2 mmol) was added into the solution of azo aromatic aldehydes
2a–d (1 mmol) in methanol (10 mL). The reaction was stirred and refluxed for 12 h. After
heating, the precipitated products 3a–d were filtered and recrystallized from ethanol to afford
a pure product.
Sensor 3a; Orange solid, Yield: 86%; FT-IR (KBr, cm-1)3416,2835 1608, 1535, 1413;
1H NMR (400 MHz, d6-DMSO): δ 6.36 (s, 1H, CH), 6.81 (d, 1H, J = 8.4 Hz, ArH), 7.18-7.28
(m, 4H, ArH), 7.34-7.50 (m, 5H, ArH), 7.6 (d, 1H, J = 8.4 Hz, ArH), 7.72 (d, 2H, J = 8.0 Hz,
ArH), 7.95-7.96 (m, 3H, ArH). 13C NMR (100 MHz, d6-DMSO): 33.08, 103.61, 115.46,
115.52, 119.36, 120.15, 122.52, 122.45, 123.02, 124.39, 127.52, 128.86, 129.05, 129.71,
130.69, 145.23, 152.45, 158.84, 165.95, 168.62; HRMS (m/z): found 533.1398 (calculated:
+
533.1349) for C31H21N2O7 , [MH]+
Sensor 3b; Orange solid, Yield: 81%; FT-IR (KBr, cm-1) 3415, 2836, 1609, 1537,
1420;1H NMR (400 MHz, d6-DMSO): δ 2.37 (s, 3H, CH3), 6.40 (s, 1H, CH), 6.83 (d, 1H, J =
7.2 Hz, ArH), 6.91-7.00 (m, 2H, ArH), 7.14-7.18 (m, 4H, ArH), 7.30-7.40 (m, 3H, ArH), 7.52
(d, 1H, J = 8.0 Hz, ArH), 7.59 (d, 1H, J = 8.0 Hz, ArH), 7.99 (d, 2H, J = 8.0 Hz, ArH), 8.07

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(s, 1H, ArH); 13C NMR (100 MHz, d6-DMSO): 21.30, 33.24, 103.74, 115.74, 116.19, 119.40,
120.05, 120.32, 122.43, 123.50, 124.96, 128.06, 128.68, 130.66, 131.11, 138.68, 146.14,
152.45, 152.86, 158.00, 168.06, 170.89; HRMS (m/z): found 547.1545 (calculated: 547.1505)
+
for C32H23N2O7 , [MH]+
Sensor 3c; Red solid, Yield: 80%; FT-IR (KBr, cm-1) 3450, 2936, 1610, 1543,
1421;1H NMR (400 MHz, d6-DMSO): δ 2.40 (s, 3H, CH3), δ 3.84 (s, 3H, OCH3), 6.42 (s,
1H, CH), 7.18-7.23 (m, 5H, ArH), 7.28-7.35 (m, 4H, ArH), 7.43-7.74 (m, 3H, ArH), 7.98 (d,
2H, J = 7.6 Hz, ArH); 13C NMR (100 MHz, d6-DMSO):21.20, 33.00, 55.79, 97.72, 103.72,
109.86, 115.46, 119.73, 120.32, 122.36, 122.98, 124.37, 124.58, 128.66, 130.52, 130.65,
138.53, 144.68, 147.53, 147.78, 152.51, 166.49, 169.21; HRMS (m/z): found 577.1656
(calculated: 577.1611) for C33H25N2O8 , [MH]+
+
Sensor 3d; Red solid, Yield: 86%; FT-IR (KBr, cm-1) 3451, 2948, 1610, 1540,
1409;1H NMR (400 MHz, d6-DMSO): δ 3.76 (s, 3H, OCH3), 3.83 (s, 3H, OCH3), 6.48 (s,
1H, CH), 6.93 (d, 1H, J = 7.6 Hz, ArH), 7.14-7.22 (m, 6H, ArH), 7.30-7.40 (m, 4H, ArH),
7.82 (s, 1H, ArH), 7.99(d, 2H, J = 8.0 Hz, ArH); 13C NMR (100 MHz, d6-DMSO): 32.90,
55.40, 55.78, 97.85, 103.72, 105.85, 115.58, 116.19, 116.34, 120.34, 123.22, 124.49, 124.83,
127.90, 129.54, 130.85, 144.99, 147.27, 147.34, 152.48, 153.91, 160.14, 167.59, 170.29;
+
HRMS (m/z): found 593.1623 (calculated: 593.1560) for C33H25N2O9 , [MH]+
2.3. UV–vis experiments
Deionized water was used throughout all experiments. All UV–vis spectroscopy was carried
out just after the addition of anions in DMSO or a DMSO/H2O binary solution,while keeping
the sensor concentration constant (2.0×10−5 M) on a Perkin Elmer Lambda25 UV-vis

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−
spectrometer. All anions (AcO−, F−, Cl−, Br−, I− and H2PO4 ) were used as tetra-n-
butylammonium salts
3. Result and discussion
3.1. Synthesis of novel sensors
New four azo dyes having bis-4-hydroxycoumarin, 3a-d have been synthesized via
condensation reaction of 4-hydroxycoumarin with four different azo salicylaldehydes (2a-d)
in methanol in good yield (Scheme 1). General synthetic method for 2a-d was reported in our
previous paper [25]. The resultant products were characterized using standard spectroscopic
techniques. The characteristic IR absorption bands of 3a-d were determined in KBr disk. The
functional groups of these compounds have been identified from the infrared spectrum. The
bands in the region 3415–3451 cm-1 attributed to the (O–H) vibrations. The aliphatic (C–H)
vibration bands were observed in the range of 2835-2948 cm-1.The bands in the region 1608-
1610 cm-1 were assigned to (C=O) lactone carbonyl function of coumarin. Two bands in the
range of 1409-1421 and 1535-1543 cm-1 were assigned to the azo group –N=N–and –C=C–)
(aromatic) stretching, respectively. 1H and 13C NMR spectra of the synthesized azo dyes
having bis-4-hydroxycoumarin were recorded. The formation of 3a-d was confirmed by the
disappearance of aldehyde protons and the appearance of aliphatic methine protons at δ 6.36,
δ 6.40, δ 6.42 and δ 6.48 ppm for 3a, 3b, 3c and 3d, in 1H NMR spectra, respectively. The
13C NMR spectra of these compounds exhibited the signals due to the presence of aromatic,
carbonyl, methine and methyl carbons. The carbonyl carbon shifts were observed in the range
of δ 165.59-170.89 ppm. The appearance of aliphatic methine carbons was observed at
δ 33.08, δ 33.24, δ 33.00 and δ 32.90 ppm for 3a, 3b, 3c and 3d, respectively. All the
aromatic carbon atoms were observed in the range of 97.71-160.14 ppm. Two aliphatic

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signals (δ 21.30 and δ 21.20 ppm for 3b and 3c, respectively) were assigned to the methyl
group carbon atoms. The carbon atom of CH3O- groups was observed at δ 55.79 ppm for 3c
and δ 55.40 and 55.78 ppm for 3d.
3.2. Colorimetric and UV–vis spectroscopic studies
The interaction of the synthesized sensors 3a-d with anions was firstly investigated at room
temperature in DMSO solution by naked eye analysis and UV–vis absorption method and the
anions added as their tetrabutylammonium salts. Visual inspection of the sensors 3a-d with
−
various anions such as AcO−, F−, Cl−, Br−, I− and H2PO4 was carried out through colorimetric
analysis (Fig 1 (a-d)). The color or spectra of 3a-d solution did not change upon addition of 5
equiv. of Cl−, Br− and I−. Noticeable and appreciable color changes were observed when the
sensors 3c and 3d were treated with fluoride and acetate anions, which induce an immediate
color change from yellow to orange yellow for 3c and purple for 3d (Fig 1 (a) and (b)).
−
During the addition of H2PO4 showed the color change from yellow to light orange yellow
for only 3d (Fig 1 (d)). This selectivity of 3c and 3d toward to F− and AcO− may be due to
both the strong basicity of anions and a steric hindrance effect of CH3O- group from the host
[30].
Fig.1.
Different from 3c, 3d contains two methoxy groups, resulting in significant absorption
−
spectrum and color changes (Fig. 1(c and d)) not only for F− and AcO−, but also for H2PO4 ,
bearing OH groups. Consequently, addition of fluorides into the solution of 3c gave
significant bathochromic shift from 382 to 531nm (∆λ = 149 nm), as shown in Table 1 and
Fig 1. (c). Meanwhile, AcO− induced a similar but smaller wavelength change in 3c (∆λ =
103 nm). Although azophenol chromophore and two methoxy groups with a structure in 3d

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−
contributed to its selective sensing of F−, AcO−, and H2PO4 , 3d can not allow for
−
calorimetric differentiation of F−, AcO−, and H2PO4 , in which almost the same wavelength
changes for 3a-d are listed in Table 1. Evidently, the changes in the absorption spectral
profile of 3d is better than other. The most remarkable color based changes were observed
with azophenol-sensor, 3d appended with o-methoxyphenol and p-methoxyazophenyl groups.
The results indicated the methoxy on the azobenzene unit could improve visible sensing
ability.
Table 1.
As the second experiment, to examine the possibility of application of the sensor 3d to
analytical chemistry, the anion recognition ability of receptor 3d was tested in mixed
water/DMSO medium. In general, hydration will terminate the anion sensing behavior, water
the strong competitive solvent in the hydrogen bonding. On addition of different anions, the
receptor able to show visually detectable color changes when the water content was not more
than 10% (v/v) in DMSO (Fig. 2b). In 5%(v/v) aqueous DMSO (Fig. 2a), the presence of
AcO− and F− induced similar changes in UV–vis spectrum of 3d to that observed in pure
DMSO (Fig. 1d) which clearly demonstrate that anions are acting here as a base and giving
rise to the deprotonation upon interaction with the receptor 3d. No remarkable spectral
−
changes of 3d were observed in presence of H2PO4 ,which suggested hydrogen bonding
−
donor solvent destroyed the binding between 3d and H2PO4 .
Fig.2.
The further binding properties of 3d toward F− and AcO− were studied by UV–vis
titration experiments. The stoichiometry between 3d with anions (F− and AcO−) was

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determined by Job’s plot that indicates formation of host–guest complex in 1:1 stoichiometry
(Fig. 3).
Fig.3.
The association constant of 3d with F− and AcO− were calculated based on the UV–
vis titration through the Benesi–Hildebrand equation [26](Fig. 4), which inferred that the
selectivity trends of binding affinities of anions for 3d were determined to be AcO− ( 1.49 x
102 M-1) > F− (0.26 x 102 M-1). The sensor 3d had a higher binding affinity for acetate anion,
which could be rationalized on basis of shape complementarity between the host and the
anionic guests, and higher basicity in compared to F−.
Fig.4.
4. Conclusion
In summary, four new bis (4-hydroxycoumarin) methane azo dyes have been synthesized and
their spectral behaviors and anion recognition properties were fully investigated. The results
indicated that the sensors 3c and 3d can selectively detected F− or AcO− anions. Especially,
compound 3d is capable of naked-eye detecting of F− and AcO− in a straightforward and
inexpensive manner. Further the anion recognition was easily monitored by anion-
complexation induced changes in UV-vis spectroscopic studies. Naked-eyes detectable color
changes for acetate and fluoride were realized successfully in aqueous solution, which made
it possible to detect acetate and fluoride for practical analysis and application.
Acknowledgements
This work was financially supported by PERCH-CIC and Mahasarakham University.
References

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Table 1. The optical response of 3a-d (2×10-5 M) to different anion in DMSO
Anion-induced wavelength changes (λmax/nm)
/cm-1M-1
Compound λmax/nm
ε
AcO¯
F¯
Cl¯
Br¯
I¯
H2PO4¯
3a
3b
3c
366
367
382
401
401
400
2.01×104
2.02×104
1.98×104
1.47×104
1.45×104
1.41×104
109
108
103
152
149
150
134
158
149
154
151
152
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
152
n
n
3d
3da
3db
a Solvent as 5% H2O/DMSO
b Solvent as 10% H2O/DMSO

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Figure Captions
Fig.1. UV–vis absorption spectra of 3a–d (2.0 × 10-5 M) in the presence of 10 equiv of
various anions in DMSO; (a) 3a, (b) 3b, (c) 3c and (d) 3d
Fig.2. UV–vis absorption changes of 3d with various anions (10 equiv); (a) 3d = 2.0 × 10-5 M
in 5% H2O in DMSO and (b) 3d = 2.0 × 10-5 M in 10% H2O in DMSO.
Fig.3. . (a) UV–vis spectrum changes of 3d (2.0 × 10-5 M) upon addition of fluoride anion
(0–12 equiv.) in 5% H2O in DMSO. (b) Job’s plot analysis of 3d-F¯ complex in 5% H2O in
DMSO at 550 nm. (c) UV–vis spectrum changes of 3d (2.0 × 10-5 M) upon addition of
acetate anion (0–12 equiv.) in 5% H2O in DMSO. (d) Job’s plot analysis of 3d-AcO¯
complex in 5% H2O in DMSO at 550 nm.
Fig.4. Benesi–Hildebrand plot assuming 1:1 stoichiometry for association between 3d and (a)
F¯ , (b) AcO¯ anion.

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Fig.1.
(a)
(b)
(d)
(c)
Fig. 2.
(a)
(b)

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Fig. 3.
(a)
(b)
(c)
(d)
Fig. 4.
(a)
(b)

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OH
OH
O
OH
O
N
N
R2
R1
R1
R1
O
O
H
H
NaNO2, HCl
MeOH / reflux
OH
Na2CO3, H2O
N
OH
O
OH
R2
N
NH2
1a; R1 = H
1b; R1 = OCH3
R2
O
O
O
2a; R1 = H, R2 = H
3a; R1 = H, R2 = H
2b; R1 = H, R2 = p-CH3
3b; R1 = H, R2 = p-CH3
2c; R1 = OCH3, R2 = p-CH3
2d; R1 = OCH3, R2 = o-OCH3
3c; R1 = OCH3, R2 = p-CH3
3d; R1 = OCH3, R2 = o-OCH3
Scheme 1. Synthetic procedures for sensors 3a-3d

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Highlights
1) New azo dyes having bis-4-hydroxycoumarin were synthesized for anion sensor
evaluation.
2) It is a very good naked eye detection sensor.