Synthesis and anion binding studies of azo-Schiff bases: Selective colorimetric fluoride and acetate ion sensors

Article abstract of DOI:10.1016/j.jfluchem.2013.05.010

Two artificial colorimetric sensors, 4-[(E)-phenyldiazenyl]-2-[(E)- (phenylimino)methyl]phenol and 2-{(E)-[(4-nitrophenyl)imino]methyl}-4-[(E)- phenyldiazenyl]phenol, have been synthesized by a two step procedure and characterized. The interactions of the

Full text of DOI:10.1016/j.jfluchem.2013.05.010

Accepted Manuscript
Title: Synthesis and anion binding studies of azo-schiff bases:
Selective colorimetric fluoride and acetate ion sensors
Author: Vijayaraghavan Reena Sivalingam Suganya Sivan
Velmathi
PII:
S0022-1139(13)00189-9
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jfluchem.2013.05.010
FLUOR 8110
To appear in:
FLUOR
Received date:
Revised date:
Accepted date:
22-1-2013
24-4-2013
2-5-2013
Please cite this article as: V. Reena, S. Suganya, S. Velmathi, Synthesis
and anion binding studies of azo-schiff bases: selective colorimetric
fluoride and acetate ion sensors, Journal of Fluorine Chemistry (2013),
http://dx.doi.org/10.1016/j.jfluchem.2013.05.010
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Synthesis and anion binding studies of azo-schiff bases: selective colorimetric fluoride
and acetate ion sensors
*
Vijayaraghavan Reena, Sivalingam Suganya and Sivan Velmathi
Organic and Polymer Synthesis Laboratory, Department of Chemistry,
National Institute of Technology, Tiruchirappalli, Tamil Nadu -620 015, INDIA.
*
Author to whom correspondence should be addressed:
Dr. S. Velmathi [velmathis@nitt.edu] Tel.: 91-431-2503640 Fax: 91-431-2500133
Highlights
Receptor 1 and 2 has been synthesized by a two step procedure and characterized.
Receptors has Azo as signaling unit and hydroxyl group as the binding unit.
Selectively senses fluoride and acetate over other halide ions in stoichiometry of 1:1.
Abstract
Two artificial colorimetric sensors 4-[(E)-phenyldiazenyl]-2-[(E)-(phenylimino)methyl]phenol
and 2-{(E)-[(4-nitrophenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol has been synthesized
Page 1 of 26

by a two step procedure and characterized. The interactions of these receptors with halide ions
are determined by colorimetric, UV-vis and NMR studies. Due to the presence of hydroxyl
moiety as binding site in receptors 1, 2 and nitro group as a signaling unit in receptor 2, both
system displays excellent selectivity and sensitivity for fluoride and acetate ions with intense
yellow and red color changes. The sensors changes its color obviously on addition of the
fluoride and acetate ion and that makes the naked-eye recognition in CH CN solution come true.
3
-
-
Key words: Azo-schiff Bases, naked eye sensing, F and AcO sensors, UV-vis spectroscopy,
binding constant study.
1
. Introduction
Because of anion's crucial role in the biological fields, medical systems and
environmental science a great deal of work has been focused on the design and synthesis of the
selective receptors for anions in the past two decades. As a result, anion recognition has been
developed into a fastest growing branch of supramolecular chemistry [1-2]. Among all the
anions, fluoride ion [3-5] is the biologically active ion and acts as a frequent constituent in most
of the drug molecules and used for the treatment of hypnotics, anesthetics, psychiatric drugs and
cockroach poisons. When the fluoride ion exceeds from its normal level it may cause diseases
like flourosis, thyroid activity depression, bone disorders and also contamination can occur in
Page 2 of 26

drinking water [6-8]. Similarly acetate ions [9-11] also play an important role and it is present in
living system as acetyl coenzyme A. Sodium acetate is used as main ingredient in some
medicines and involves in biological process like enzyme metabolism. Also the production of
acetic acid from fermentation process is the main component present in vinegar used in foods.
Accordingly, how to effectively recognize and sense anions through the naked eye,
electrochemistry and/or optical responses have attracted considerable attention [12-14].
Generally speaking, colorimetric chemosensor are made up of two main fragments, which
involve the binding sites that interact with anions either electrostatically or through hydrogen
bonding, etc., and the signal parts that connect to the binding sites either directly or
intramolecularly linked which show the color changes [15-18] in the anion recognition
procession. With regard to the binding sites, the functional groups such as imine [19], urea [20],
thiourea [21], amide [22], pyrrole (NH) [23], imidazolium [24], hydrazones [25] and hydroxyl
groups [26] are numerously used owing to their capacity to perform as hydrogen donors.
Otherwise, if taking advantage of the electrostatic interaction, the quartenized nitrogen [27] and
positively charged pyridine [28] may be firstly chosen as binding sites. However, among the
colorimetric and optical parts of the receptors for the anion sensing, simplicity and high
selectivity [29-30] are still challenges for investigators and they attract much interests. In
particular, to develop the naked-eye detection technique for the analytes without using any
expensive equipment is of great interest in recent years. Azophenyl as the optical group has been
less explored as the functional group of the sensor molecules in the literature [31-32].
In this paper, we designed and synthesized new and simple anion receptors 1, 2 contains
both hydrogen-bond-donor group (phenolic –OH and imine) as well as chromogenic unit
(azophenyl) and studied its anion recognition behaviors towards biologically important fluoride
Page 3 of 26

and acetate ions over other anions with high selectivity. The recognition is found by forming the
hydrogen bonding at charge-neutral sites. In addition, the sensing processes can be realized by
the ‘naked-eye’ determination as it has a remarkable color response.
2
. Results and discussion
Both the receptors 1 and 2 were synthesized by simple condensation reactions between
1
13
aldehyde and amine. The structure of the receptors 1 and 2 were proved by FTIR, H and C
NMR spectroscopic methods. In the FT-IR spectroscopy we get information about the presence
of functional groups in the compound such as C=C, CH=N etc by the position of absorption
peaks which arise due to stretching vibration of the bonds in the groups. The presence of CH=N
-1
in the molecule is confirmed by the vibrations between 1690-1640 cm and aromatic C=C
-1
1
between 1600-1473 cm in the FT-IR spectrum. In H NMR (Fig 2a, 3a) both the receptors
showed a singlet at around δ 9.2 ppm corresponding to the CH=N proton indicating the
formation of imine and the aromatic protons resonate in the δ 7-8.3 ppm region. The peak around
1
3
δ 13-14 ppm indicates OH proton. It was found that In the case of C NMR spectroscopy CH=N
carbon came as a sharp peak at δ 145-147ppm. Mass spectral analysis confirms the molecular
structure of the compounds synthesized without any ambiguity. M+1 (protonated molecular ion
peak) clearly proves the complete formation of the azo-Schiff bases. We investigated the
interactions of fluoride ion towards receptors 1 and 2 in the ground state by running proton NMR
titrations both in absence and presence of fluoride ion. Generally, the interaction between the
receptor and anions could be explained on the basis of up field shift in aromatic, imine protons
and downfield shift in OH protons. Two main effects occurred in OH proton of receptor in the
presence of anions are hydrogen bonding and deprotonation effects.
Page 4 of 26

1
2
.1. H NMR spectroscopic studies
We investigated the interactions of fluoride ion towards receptors 1 and 2 in the ground
1
state by running H NMR titrations both in absence and presence of fluoride ion. Generally, the
interaction between the receptor and anions could be explained on the basis of up field shift in
aromatic, imine protons and downfield shift in OH protons. Two main effects occurred in OH
proton of receptor in the presence of anions are hydrogen bonding and deprotonation effects.
1
In H NMR spectral titration curves of the receptor 1, the peak at 13.85 ppm, assigned to
OH group, disappears with the addition of 0-2 equiv. of fluoride ion (Fig. 1). The hydroxyl group
was completely deprotonated even with 0.5 equiv. of fluoride ion and a new triplet signal
-
appeared at 15.7-16.4 ppm indicating the formation of HF2 complex. Unlike receptors
containing electron withdrawing group, in azo linked receptor systems the acidity will be
enhanced by azophenyl unit. Y.Li et.al [33] reported azo based phenyl hydrazone as anion
receptor and the proton of OH group is getting deprotonated with the addition of 0.4 equiv. of
acetate ion. Similarly J. Shao et.al [34] reported the deprotonation of OH by fluoride ion with 0.5
-
equiv. and form a HF complex in azo based thiosemicarbazone. Hence the presence of
2
azophenyl unit in receptor 1 will enhance the acidity of OH proton and the deprotonation is
-
mainly occurred at 0.5 equiv. of F ion. Consequently up field shift was observed for imine and
phenyl rings protons due to the increase in the electron density around aromatic system. In case
of receptor 2 also, the similar shifts were observed in presence of 0-2 equiv. of fluoride ion (Fig.
2
). Because, the presence of NO group in receptor 2 is just acting as signaling unit which is not
2
responsible for the increasing the acidity of OH group in receptor 2. These observations clearly
support that anion recognition by both receptor 1, 2 underwent through the deprotonation of the
-
hydroxyl group proton induced by the fluoride anion. In addition OH also involves in the
Page 5 of 26

-
1
deprotonation of OH group in receptor 1, 2 due to the similar basicity as F ion in H NMR (Fig.
-
3
, 4). But the distinct color and UV-vis changes were not observed with OH ion due to the size
-
of OH ion is not adoptable to bind with receptors.
2
.2 Colorimetric and UV-vis studies
The anion binding properties of the synthesized receptor 1 and 2 were investigated by
naked eye analysis and UV–vis titrations at room temperature in CH CN solution. The color
3
change was visualized by naked eye observation and optical response was studied by UV-vis
-5
spectroscopy. In the naked eye experiments, visual inspection of receptor 1 and 2 (5x10 M in
CH CN) showed dramatic color change from light yellow to intense yellow for receptor 1 and
3
-
-
-3
dark red for receptor 2 with the addition of 2 equiv. of F and AcO ions (1.5x10 M) (Fig. 5, 6).
In order to have a deeper understanding of the binding action, UV-vis spectral studies
-
-
were carried out. As we gradually added the F ion into the solution of receptors 1 and 2 (1.5x10
3
M), the absorbance bond centered at 353 nm, ascribed to the charge- transfer in the molecule
35], diminished little by little accompanied with a new band generated at 450 nm, suggesting
[
the formation of the complex between receptor 1 and fluoride ion. The color change from light
yellow to intense yellow and red could be easily detected by the naked eye. Similar changes in
the colorimetric from light yellow to intense yellow for receptor 1 and red color for receptor 2
-
were observed with the addition of 2 equiv. of AcO ion. Consequently, the formation of a new
-
band at 450 nm in the UV-vis spectrum was also observed with the addition of 2 equiv. of AcO
-
-
-
-
ion. On the contrary, the addition of excess amount of other anions like Cl , Br , OH , and H PO
2
4
into the solution of receptors 1 and 2 did not show considerable result in any visible spectrum
Page 6 of 26

responses. There was a well-defined isosbestic point at 390 nm in all cases, which indicated the
-
-
presence of only one type of host–F /AcO ion complexes (Fig. 7, 8).
From the UV-vis absorption measurements, the binding constant of the anion complexes
-
-
of two receptors were calculated using Benesi- Hildebrand (B-H) plot. F /AcO complexes of
3
3
-
-
receptor 1 were (4.996±0.36) x10 , (2.793±0.25) x10 and F /AcO complexes of receptor 2 were
4
4
(
3.206±0.05) x10 and (2.538±0.34) x10 respectively. The Job’s plot (Fig. 9a, 9b) gives a
-
-
stoichiometry of 1:1 for both F / AcO ion complexes of receptor 1 and 2.
A full understanding of the principles that govern anion recognition has not yet
been achieved, it already becomes clear early on that the selectivity for special anions can be
rationalized on the basis of guest basicity and shape complementarities between host and
anionic guests. Actually, it is necessary that the sensor possesses the multiple hydrogen-bonding
interaction offering the high-affinity anion binding sites. In particular, the best selective
-
-
recognition for F and AcO ions was most likely due to its best complementarily between the
anions and receptors among the anions tested.
3
. Conclusion
In summary, simple azo based colorimetric receptors 1 and 2 were successfully
synthesized in high yields. Azophenyl unit was treated as a signaling unit and hydroxyl group
-
-
acted as the binding sites of framework related to receptor 1 and 2 that could detect F and AcO
ions selectively over other anions confirmed by colorimetric and UV-vis spectroscopic methods.
The binding affinity of the receptors 1, 2 and 1:1 stoichiometry of the host-guest complex was
calculated from B-H plot and Job’s plot. The yield of the reactions is good which is an important
aspect of commercial scale along with the simplicity of the synthesis scheme.
Page 7 of 26

4
. Experimental Section
4
.1 Materials and Methods
All reagents for synthesis obtained commercially were used without further purification.
In the titration experiments, all anions were added in the form of tetrabutylammonium (TBA)
salts, which were purchased from Sigma-Aldrich Chemical, stored in a vacuum desiccator
containing self-indicating silica. The cations were added in the form of bivalent salts. 1H NMR
spectra were recorded on a Bruker 400 MHz spectrometer in DMSO-d . FT-IR spectra were
6
measured on a Perkin-Elmer Spectrum One FT-IR spectrometer using KBr plates. UV- vis and
Fluorescence spectra were recorded in 1 cm path length quartz cell on a Shimadzu UV-2600
spectrophotometer and Shimadzu RF-5301 PC spectrofluorophotometer respectively.
-5
A 5x10 M solution of receptors was made up with HPLC grade acetonitrile (CH CN)
3
solvent. UV-vis absorption titrations were carried out by adding 0.2 equiv. aliquots of the titrant
-3
as tetrabutyl ammonium (TBA) halides (1.5x10 M) in CH CN. The UV-vis spectra were
3
recorded after each addition. All reactions were carried out in the atmosphere of purified
nitrogen. They were well characterized by LCMS, NMR spectroscopic methods before using
them in sensor studies.
4
.2 General experimental procedure for the synthesis of the receptors
The intermediate for the receptors 1 and 2 were synthesized according to a reported method [36]
To a solution of aniline (5ml; 0.05 mol) in 5ml of water, was slowly added, 6 ml of 37 % aq. HCl
solution at 0-5 °C with stirring. 20 ml of 20 % aq. NaNO solution was added to the mixture and
2
resulting solution was stirred for 1h, affording a bright yellow solution. Salicylaldehyde (5 ml;
0
.05 mol) was dissolved in a solution comprising 18 g Na CO and 150 ml water and the
2 3
Page 8 of 26

resulting solution of salicylaldehyde was added dropwise to the bright yellow colored solution
over 1h. After stirring for 4h, the reaction mixture was neutralized with HCl, the brown crude
solid was filtered and recrystallized from ethanol to afford pure yellow product. Mp.120℃. The
solid isolated was used to synthesize two sensors by stirring with Aniline (1 mol, Receptor 1)
and nitro aniline (1 mol. Receptor 2) respectively in ethanol for 24 h. The solids are filtered and
then recrystallised from n-hexane (Fig. 10).
Receptor 1: (4-((E)-phenyldiazenyl)-2-((E)-(phenylimino)methyl)phenol)
-1
Yield: 76%. IR (KBr pellets, (cm ): 3445, 3052, 1620, 1594, 1572, 1495, 1485, 1430, 1348,
1
1
286,1184. H NMR (400 MHz, DMSO-d ): δ 13.8 (s, 1H, OH), 9.2 (s, 1H, CH=N), 8.3 (s, 1H,
6
13
Ar), 8.0 (d, 1H, Ar), 7.8 (d, 2H, Ar), 7.4-7.6 (m, 7H, Ar), 7.3 (m, 1H, Ar), 7.1(d, 1H, Ar). C
NMR (100 MHz, DMSO-d ): δ 164.5, 163, 152, 148, 145,132, 130, 130, 129, 128, 128, 123,
6
1
22, 120, 118. LCMS: Calcd: 301.3, Found: 301.5.
Receptor 2: (2-((E)-(4-nitrophenylimino)methyl)-4-((E)-phenyldiazenyl)phenol)
-1
1
Yield: 67%. IR (KBr pellets, (cm ): 3465, 3074, 1617, 1603, 1590, 1518, 1486,1343. H NMR
(
400 MHz, DMSO-d ): δ 12.8 (s, 1H, OH), 9.1 (s, 1H, CH=N), 8.4 (s, 1H, Ar), 8.3 (d, 2H, Ar),
6
1
3
8
.1 (d, 1H, Ar), 7.8 (d, 2H, Ar), 7.5-7.6 (m, 5H, Ar), 7.2 (d, 1H, Ar). C NMR (100 MHz,
DMSO-d ): δ 165, 163, 154, 152, 145, 131, 130, 129, 128, 127, 125, 120, 118, 117, 112. LCMS:
6
Calcd: 346.3, Found: 347.2.
Page 9 of 26

Acknowledgement
One of the authors S.V thanks DRDO for a major sponsored project EPIR/ ER/
1
006004/M/01/1333 dated 23-05-2011for financial assistant.
Page 10 of 26

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Y. Zhou, J. Y. Jung , H. R. Jeon , Y. Kim , S. J. Kim, J. Yoon, Org. Lett. 13 (2011)
2
742–2745.
[20] J. Shao, H. Lin, X. F. Shang, H. M. Chen, H. K. Lin, J. Inclusion Phenom. Macrocyclic
Chem. 59 (2007) 371-375.
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Hyun, J. Org. Chem. 73 (2008) 301-304.
[
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22] S. O. Kang, R. A. Begum, K. B. James, Angew. Chem. Int. Ed. 45 (2006) 7882-7894.
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[36] J. Shao, Dyes Pigments, 87 (2010) 272-276.
Page 13 of 26

List of Figure Captions.
1
Fig. 1. H NMR spectra of receptor
1 in the recorded on a Bruker 400 MHz
spectrometer in DMSO-d . (a) Free receptor
6
1
, (b) 0.5 equiv, (c) 1 equiv, (d)
-
.5 equiv, (e) 2 equiv of F ion.
1
1
Fig. 2. H NMR spectra of receptor
2 in the recorded on a Bruker 400 MHz
spectrometer in DMSO-d . (a) Free receptor
6
2
, (b) 0.5 equiv, (c) 1 equiv, (d)
-
.5 equiv, (e) 2 equiv of F ion.
1
1
Fig. 3. H NMR spectra of receptor
1 in the (a) absence and (b) presence of 2
-
equiv. OH ion recorded on a Bruker 400 MHz spectrometer in DMSO-d .
6
1
Fig. 4. H NMR spectra of receptor
2 in the (a) absence and (b) presence of 2
-
equiv. OH ion recorded on a Bruker 400 MHz spectrometer in DMSO-d .
6
-5
Fig. 5. Color changes of receptor
1 (5x10 M in CH CN) on addition of 2
3
-
3
-
-
-
equiv. of various anions (1.5x10 M in CH CN): R1, R1+F , R1+Cl , R1+Br ,
3
-
R1+AcO , R1+H PO and R1+OH .
-
4
-
2
-5
Fig. 6. Color changes of receptor
2 (5x10 M in CH CN) on addition of 2
3
-
3
-
-
-
equiv. of various anions (1.5x10 M in CH CN): R1, R1+F , R1+Cl , R1+Br ,
3
-
R1+AcO , R1+H PO and R1+OH .
-
4
-
2
-5
Fig. 7. UV-vis titration spectra of receptor
1 (5x10 M in CH CN) on gradual
3
-3
addition of 2 equiv. of (a) fluoride and (b) acetate ions (1.5x10 M in
CH CN).
3
Page 14 of 26

-5
Fig. 8. UV-vis titration spectra of receptor
2 (5x10 M in CH CN) on gradual
3
-3
addition of 2 equiv. of (a) fluoride and (b) acetate ions (1.5x10 M in
CH CN).
3
Fig. 9. Job’s plot for receptor (a)
Fig. 10. Synthesis of receptors
1
and (b)
2.
1
and 2.
Page 15 of 26

1
a
.b
b
c
d
1
.a
e
1
Fig. 1. H NMR spectra of receptor
1 in the recorded on a Bruker 400 MHz
spectrometer in DMSO-d . (a) Free receptor
6
1
, (b) 0.5 equiv, (c) 1 equiv, (d)
-
.5 equiv, (e) 2 equiv of F ion.
1
Page 16 of 26

a
b
2
.a
c
d
e
1
Fig. 2. H NMR spectra of receptor
2 in the recorded on a Bruker 400 MHz
spectrometer in DMSO-d . (a) Free receptor
6
2
, (b) 0.5 equiv, (c) 1 equiv, (d)
-
.5 equiv, (e) 2 equiv of F ion.
1
Page 17 of 26

a
b
1
Fig. 3. H NMR spectra of receptor
1 in the (a) absence and (b) presence of 2
-
equiv. OH ion recorded on a Bruker 400 MHz spectrometer in DMSO-d .
6
Page 18 of 26

a
b
1
Fig. 4. H NMR spectra of receptor
2 in the (a) absence and (b) presence of 2
-
equiv. OH ion recorded on a Bruker 400 MHz spectrometer in DMSO-d .
6
Page 19 of 26

-5
Fig. 5. Color changes of receptor
1 (5x10 M in CH CN) on addition of 2
3
-
3
-
-
equiv. of various anions (1.5x10 M in CH CN): R1, R1+F , R1+Cl , R1+Br ,
-
3
-
R1+AcO , R1+H PO and R1+OH .
-
4
-
2
-5
Fig. 6. Color changes of receptor
2 (5x10 M in CH CN) on addition of 2
3
-
3
-
equiv. of various anions (1.5x10 M in CH CN): R1, R1+F , R1+Cl , R1+Br ,
-
-
3
-
R1+AcO , R1+H PO and R1+OH .
-
4
-
2
Page 20 of 26

0
.6
.5
2
1
1
0
0
0
.0
.6
.2
.8
.4
.0
0
7
.a
0.4
0
.3
.2
0
0.1
-
2
0
eq. F 0.0
0
.0
0.5
1.0
1.5
2.0
no.of eq.
-
eq. F
2
00 250 300 350 400 450 500 550
Wavelength(nm)
0
0
0
.6
.5
.4
2
.0
.6
.2
.8
.4
.0
7
.b
1
1
0
0
0
0.3
0.2
0.1
0.0
0
.0
0.5
1.0
1.5
2.0
-
2
eq. AcO
no.of eq.
-
0
eq. AcO
2
00 250 300 350 400 450 500 550
Wavelength(nm)
Page 21 of 26

-5
Fig. 7. UV-vis titration spectra of receptor
1 (5x10 M in CH CN) on gradual
3
-3
addition of 2 equiv. of (a) fluoride and (b) acetate ions (1.5x10 M in CH CN)
3
1
1
1
1
.6
.4
.2
.0
2
2
1
1
0
0
.5
.0
.5
.0
.5
.0
-
0.8
.6
8
.a
2 eq. F
0
0.4
0.2
-
0
eq. F
0.0
0
.0
0.5
1.0
1.5
2.0
no.of eq.
2
00
300
400
Wavelength(nm)
500
600
1
1
1
0
0
0
0
0
.4
.2
.0
.8
.6
.4
.2
2
1
1
0
0
.0
-
8
.b
2 eq. AcO
.5
.0
.5
.0
-
0
eq. AcO
.0
0
.0
0.5
1.0
1.5
2.0
no.of eq.
2
00
300
400
500
Wavelength(nm)
Page 22 of 26

-5
Fig. 8. UV-vis titration spectra of receptor
2 (5x10 M in CH CN) on gradual
3
-3
addition of 2 equiv. of (a) fluoride and (b) acetate ions (1.5x10 M in CH CN)
3
0
0
0
0
0
0
.2 5
.2 0
.1 5
.1 0
.0 5
.0 0
0.30
.25
.20
.15
.10
.05
.00
9
.b
9
.a
0
0
0
0
0
0
0
.0
0 .2
0 .4
0.6
0.8
-
1.0
0
.0
0.2
0.4
0.6
0.8
1.0
-
Rec/ [(R ec) + (F )]
Rec/ [(Rec) + (F )]
-
Fig. 9. Job’s plot for F complex of receptor (a) 1 and (b) 2
Page 23 of 26

OH
N
OH
N
CHO
N
R
H N
R
2
OH
1
. C H NH , NaNO , HCl
6 5 2 2
2
. Na CO , H O
N
EtOH
N
CHO
2
3
2
Receptor 1: R= H
Receptor 2: R= NO2
Fig. 10. Synthesis of receptors 1 and 2
Page 24 of 26

Graphical Abstract
X-
H
OH
O
N
N
NO2
N
NO2
-
X in AcN
N
N
N
R2
R2+X-
-
-
X=F /OAc
Page 25 of 26

Graphical abstract
Two artificial colorimetric sensors 4-[(E)-phenyldiazenyl]-2-[(E)-(phenylimino)methyl]phenol
and 2-{(E)-[(4-nitrophenyl)imino]methyl}-4-[(E)-phenyldiazenyl]phenol has been synthesized
by a two step procedure and characterized. The interactions of these receptors with anions are
determined by colorimetric, UV-vis and NMR studies. Due to the presence of hydroxyl moiety
as binding site in receptor 1, 2 and nitro group as a signaling unit in receptor 2, both system
displays excellent selectivity and sensitivity for fluoride and acetate ions with intense yellow and
red color changes. The sensors changes its color obviously on addition of the fluoride and acetate
ion and that makes the naked-eye recognition in CH CN solution come true.
3
Page 26 of 26