Amido-Schiff base derivatives as colorimetric fluoride sensor: Effect of nitro substitution on the sensitivity and color change

Article abstract of DOI:10.1016/j.saa.2015.04.025

A series of Schiff bases synthesized by the condensation of benzohydrazide and -NO₂ substituted benzaldehyde have been used as selective fluoride ion sensor. Test paper coated with these synthetic Schiff bases (test kits) can detect fluoride io

Full text of DOI:10.1016/j.saa.2015.04.025

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 869–874
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Amido-Schiff base derivatives as colorimetric fluoride sensor: Effect
of nitro substitution on the sensitivity and color change
a
b,
⇑
a
a,
⇑
Soumen Ghosh , Md. Akhtarul Alam , Aniruddha Ganguly , Nikhil Guchhait
a
Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata 700 009, India
Department of Chemistry, Aliah University, DN-18, Sector-V, Saltlake, Kolkata 700091, India
b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Amido-Schiff base derivatives (1, 2 and 3) can detect fluoride ion selectively through visual color change
in both solution phase and solid phase.
ꢀ
Synthesized colorimetric sensors for
detection of biologically important
anions.
ꢀ
Color change of the sensor in
presence of F was detected by
ꢁ
1
+F-
2+F-
3+F-
naked-eye.
ꢀ
ꢀ
Used of sensors as test kit for the
detection of fluoride ion.
Nitro group positional dependency on
sensitivity and color change of the
sensors.
1
+F-
2+F-
3+F-
4+F-
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of Schiff bases synthesized by the condensation of benzohydrazide and –NO2 substituted ben-
zaldehyde have been used as selective fluoride ion sensor. Test paper coated with these synthetic
Schiff bases (test kits) can detect fluoride ion selectively with a drastic color change and detection can
be achieved by just using the naked-eye without the help of any optical instrument. Interestingly, the
Received 27 September 2014
Received in revised form 1 April 2015
Accepted 16 April 2015
Available online 2 May 2015
position of –NO
2
group in the amido Schiff bases has an effect on the sensitivity as well as on the change
of color of species.
Keywords:
Ó 2015 Elsevier B.V. All rights reserved.
Colorimetric sensing
Fluoride detection
Amido-Schiff base
Nitro-substitution
Test kits
Introduction
due to its beneficial effects in human physiology [1–6]. Moreover,
fluoride ion acts as an active constituent in most of the drug mole-
cules and is used for the treatment of hypnotics, anesthetics, psy-
chiatric drugs and cockroach poisons [7–8]. Because of significant
importances, detection of fluoride with a easily synthesized recep-
tor and minimal instrumental assistance is highly desirable
towards practical applications. For this purpose colorimetric
chemosensor is of great interest in recent years [9–11]. In general,
a colorimetric chemosensor is composed of two main fragments,
In the past two decades there have been a great deal of works
focused on the design and synthesis of artificial receptors for selec-
tive detection of anions because of their crucial role in the biolog-
ical, medical and environmental sciences. In particular,
development of chemosensors for fluoride ion are quite intriguing
⇑
Corresponding authors. Tel.: +91 33 23508386; fax: +91 33 23519755
N. Guchhait).
E-mail addresses: alam_iitg@yahoo.com (M.A. Alam), nguchhait@yahoo.com
(
1) a binding sites that interact with anions and (2) a signaling part
(
(
connected to the binding site which can show the color changes in
the anion recognition phenomenon [12–14].
N. Guchhait).
http://dx.doi.org/10.1016/j.saa.2015.04.025
386-1425/Ó 2015 Elsevier B.V. All rights reserved.
1

8
70
S. Ghosh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 869–874
With regard to the above facts, the receptors with a combina-
temperature. After 30 min very light yellow solid was obtained.
tion of different types of anion-binding groups (e.g. amide,
urea/thiourea, pyrrole and imidazolium groups) and nitro-phenyl
as the signaling unit have been explored [15–19]. However, most
of them suffer from interference of other anions. Specifically, dis-
The product thus obtained was filtered and then dried under vac-
1
6
uum (yield: 0.320 g, 76%). H NMR in d -DMSO, 300 MHz, d
(ppm): 12.21 (s, 1H, –CONH–), 8.86 (s, 1H, ACH@NA), 8.12 (d,
J = 7.5 Hz,1H), 8.06 (d, J = 8.2 Hz,1H), 7.92 (d, J = 7.2 Hz,2H), 7.81
ꢁ
ꢁ
13
crimination of fluoride from H
2
PO
4
and AcO with similar basicity
(t, J = 7.5 Hz, 1H), 7.67 (t, J = 7.5 Hz, 1H), 7.52–7.42 (m, 3H),
C
is rather problematic [20–22]. Furthermore, these receptors are
commonly used in solution which significantly restrict their uses.
It is still a challenge to design and synthesize artificial receptor
with high selectivity and sensitivity for fluoride ion both in solid
and solution phase. Inspite of these limitations, detection of fluo-
ride in solid state using test kit have attracted increasing attention
because of their practical application. Till now, the reports on test
kit for the detection of fluoride are limited [23–25].
NMR (75.5 MHz, -DMSO, 20 °C) d (ppm): 124.78, 127.21,
d
6
128.15, 128.76, 130.91, 131.29, 133.43, 133.87, 143.61, 148.39,
162.88. IR (KBr): 3158.5, 3016.6, 2848.6, 1652.4, 1646.1, 1566.9,
ꢁ1
1526.0, 1344.8, 1306.1, 1293.8, 1152.4, 1074.4 cm
.
Receptor 2. Sythesis of N-(3-nitrobenzylidene)benzohydrazide
Receptor 2 was prepared by similar procedure as was done in
To overcome this problem we have synthesized and character-
ized a series of simple benzohydrazide derived Schiff bases as
molecular receptor. These newly designed molecules selectively
detect fluoride ion by naked-eye as well as by change in the optical
signal monitored by UV–Vis spectroscopy. Interestingly, test paper
case of compound 1. Here m-nitrobenzaldehyde is used instead
1
of o-nitrobenzaldehyde (yield: 70%).
6
H NMR in d -DMSO,
300 MHz, d (ppm): 12.12 (s, 1H, –CONH–), 8.54 (s, 2H, ACH@NA,
o-ArH-NO ), 8.25 (d, J = 7.5 Hz, 1H), 8.14 (d, J = 7.5 Hz,1H), 7.91
(d, J = 7.2 Hz, 2H), 7.74 (t, J = 7.5 Hz, 1H), 7.62–7.50 (m, 3H),
NMR (75.5 MHz, -DMSO, 20 °C) (ppm): 124.28, 127.21,
2
13
C
coated with the above amido-Schiff base (test kits) can recognize
d
6
d
ꢁ
F
ion visually. Here we have shown that the color change and sen-
128.05, 128.66, 131.11, 131.89, 134.13, 134.87, 143.41, 148.31,
sitivity of the sensors depend on the position of nitro-group in the
signaling unit.
161.78. IR (KBr): 3207.6, 3071.1, 1654.4, 1650, 1560.2, 1517.2,
ꢁ1
1353.4, 1280.0, 1137.3, 1075.1 cm
.
Experimental
Receptor 3. Synthesis of N-(4-nitrobenzylidene)benzohydrazide
Using similar procedure receptor 3 was prepared by using
Instrumentation
1
p-nitrobenzaldehyde (yield: 80%). H NMR in d
6
-DMSO, 300 MHz,
d (ppm): 12.16 (s, 1H, –CONH–), 8.52 (s, 1H, ACH@NA), 8.28 (d,
J = 8.1 Hz, 2H), 7.98 (d, J = 8.1 Hz, 2H), 7.91 (d, J = 7.5 Hz, 2H),
Electronic absorption spectra were recorded by a Hitachi UV–
Vis (Model U-3501) spectrophotometer. IR spectra (KBr pellet,
1
3
ꢁ
1
7.61–7.51 (m, 3H). C NMR (75.5 MHz, d
6
-DMSO, 20 °C) d (ppm):
4
000–400 cm ) were recorded on a Parkin Elmer modal 782 infra-
ꢁ1
1
124.58, 127.41, 128.54, 129.16, 130.81, 131.29, 132.83, 133.67,
red spectrophotometer (resolution 4 cm ). H NMR spectra were
recorded on a Bruker, Avance 300 spectrometer, where chemical
shifts (d in ppm) were determined with respect to tetramethylsi-
lane (TMS) as internal standards.
1
1
42.91, 148.09, 161.88. IR (KBr): 3176.7, 3017.9, 2836.6, 1654.1,
ꢁ1
647.5, 1569.8, 1522.7, 1343.3, 1305.9, 1150.7, 1104.1 cm
.
Receptor 4. Sythesis of N-benzylidenebenzohydrazide
Using similar procedure benzaldehyde is used for the prepara-
Reagents
1
6
tion of receptor 4. (yield: 74%). H NMR in d -DMSO, 300 MHz, d
All reagents and solvents were used as received from commer-
cial sources without further purification. Benzoic acid, hydrazine
and o/m/p substituted benzaldehyde were purchased from Sigma
Aldrich Chemicals. Spectroscopic grade solvents were purchased
from Spectrochem and were used after proper distillation. The
(
ppm): 11.86 (s, 1H, –CONH–), 8.44 (s, 1H, ACH@NA), 7.90 (d,
13
J = 7.2 Hz, 2H), 7.72 (d, J = 5.1 Hz, 2H), 7.58–7.44 (m, 6H);
NMR (75.5 MHz, -DMSO, 20 °C) (ppm): 127.32, 127.82,
28.71, 129.07, 130.32, 131.99, 133.63, 134.52, 148.08, 164.05. IR
KBr): 3180.98, 3059.9, 3028.50, 2836.68, 1640.51, 1600.60,
C
d
6
d
1
(
1
1
+
ꢁ
4
anions, tetrabutylammonium fluoride (Bu N F ) hydrate (98%),
577.28, 1551.95, 1486.50, 1446.28, 1363.80, 1140.92,
+
ꢁ
tetrabutylammonium acetate (Bu
monium dihydrogenphosphate (Bu
4
N AcO ) (97%), tetrabutylam-
ꢁ1
057.82 cm
.
+
ꢁ
4
4
N H
2
PO ) (97%), tetrabutylam-
+
ꢁ
monium chloride (Bu
4
N Cl ) hydrate (98%), tetrabutylammonium
bromide (Bu N Br ) (98%), tetrabutylammonium bromide
4
N I ) (98%) tetrabutylammonium sulfite (Bu
and tetrabutylammonium Nitrate (Bu
+
ꢁ
Results and discussion
+
ꢁ
+
ꢁ
3
(
Bu
4
4
N HSO
N NO )
) (97%),
+
ꢁ
4
3
(97%), were
As shown in Scheme 1, Schiff bases (1, 2, 3 and 4) have been
synthesized following two steps. Firstly, benzohydrazide has been
synthesized from the ester of benzoic acid, then condensation with
four different aldehydes (o-nitro benzaldehyde, m-nitro benzalde-
hyde, p-nitro benzaldehyde and benzaldehyde) produced the cor-
responding Schiff bases. All these Schiff bases (1, 2, 3 and 4) have
been characterized by H, C NMR and IR spectroscopic methods.
The H NMR spectra of receptors 1, 2, 3 and 4 show two character-
istic peaks in the range of 11.85–12.21 ppm and 8.44–8.86 ppm
which are attributed to the protons of amido and imino groups,
respectively (Figs. S1–S4). In case of compound 2 the peak at
received from Sigma–Aldrich Chemical Company Pvt. Ltd.
Synthesis
Benzoic acid hydrazide
The benzoic acid hydrazides were prepared according to the lit-
erature procedure [26,27] by refluxing ethyl benzoate (0.1 mol)
with hydrazine hydrate (0.15 mol) in presence of ethanol for 12 h
then the reaction mixture was allow to cool. The solid product
was collected by filtration. The crude product was crystallized from
ethanol.
1
13
1
8
.54 ppm of ACH@NA is merged with the ortho hydrogen of the
m-nitro substituted aromatic ring. The presence of amide (–CO–)
Receptor 1. Synthesis of N-(2-nitrobenzylidene)benzohydrazide
Benzoic acid hydrazide (0.200 g, 1.47 mmol) was reacted with
o-nitrobenzaldehyde (0.300 g, 2.0 mmol) in methanol at room
and imino groups (ACH@NA) in the molecules is confirmed by
the vibrations at 1654 and 1647 cm , respectively, in the FT-IR
spectrum [23].
ꢁ1

S. Ghosh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 869–874
871
R2
R3
O
R1
NH2
NH
O
MeOH
Reflux
R
3
N
+
R2
N
H
OHC
R
1
Scheme 1. Syntheses of receptor 1, 2, 3 and 4.
Naked-eye detection of anions
pattern is slightly different as was observed in case of receptor 1.
No shoulder band was observed in case of receptor 3. Fig. 3 shows
The anion binding study of the receptors (10ꢁ5 M) have been
investigated by naked eye in acetonitrile solvent. In this experi-
ment, visual inspection of receptors 1 and 3 show a vivid color
the change in UV–Vis spectra of receptor 3 (1.0 ꢂ 10 M) during
ꢁ6
ꢁ
ꢁ
titration with F ion. Upon addition of F ion the peak of the recep-
tors at 330 nm decreases its intensity and a new peak at 466 nm
appears with an isosbestic point at 370 nm exhibiting a color
change from colorless to red. Interestingly, the band position of
the fluoride complex of 3 is in the red side than the fluoride com-
plex of 1 which indicates more stabilization of the system. During
complexation steric crowding in the ortho substituted nitro com-
pound (receptor 1) may insist the nitro group to be twisted form
thereby reducing the resonance stabilization of the complex lead-
ing to blue sided absorption band. It is important to mention that
ꢁ
ꢁ5
change from colorless to red upon addition of F ion (10 M) to
their acetonitrile solution (Figs. 1 and S5). But in the same experi-
mental condition receptor 2 shows a color change from colorless to
yellow (Fig. S6). The color of the solutions are intensified with
ꢁ
increasing F ion concentration. It is to mention that the color
intensity between compound 1 and compound 3 cannot be distin-
ꢁ
guished visually by addition of F ion. On the contrary, other
ꢁ
ꢁ ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
3
anions such as CH COO , H PO , Cl , Br , I , HSO and NO do
3 2 4 3
not respond under the similar experimental condition. That means
the interaction of these anions with the receptors is too small to
show any observable change. As expected the compound 4 does
not show any color change in presence of any of the anions men-
the UV–Vis response of receptor 1 and 3 is different on addition of
ꢁ
F
ion in contrast with the ‘‘naked eye’’ experiment which cannot
ꢁ
distinguish between receptor 1 and 3 in presence of F ion.
In absence of anions, receptor 2 (N-(3-nitrobenzylidene)benzoh
ydrazide, 1.0 ꢂ 10 M) exhibits a strong band at 290 nm. On addi-
ꢁ5
tioned above (Fig. S7). Therefore, among the four receptors only
ꢁ
ꢁ
1
, 2 and 3 can detect F selectively (Fig. S8).
tion of F ion to receptor 2 the absorbance at 290 nm decreases and
a new absorbance band appears at 365 nm with a distinct isos-
bestic point at 370 nm (Fig. 4) showing a visual color change from
colorless to yellow. The band position of fluoride complex of recep-
tor 2 compared to the band position of fluoride complex of com-
pound 1 and 3 indicates that complex of receptor 2 is least
stable. Weaker acidity of the amide proton may be the reason.
In UV–Vis spectra receptor 4 (N-benzylidenebenzohydrazide)
shows a strong peak at 290 nm (Fig. S12). With the addition of
UV–Vis spectroscopic titration
In order to understand the interaction between the anions and
the receptors properly, UV–Vis experiment has been monitored in
acetonitrile solvent. Receptor 1 (N-(2-nitrobenzylidene)benzohydra
zide) exhibits a strong absorption band at 274 nm and a shoulder
ꢁ
at 343 nm (Fig. 2). Upon adding increasing amount of F ion to 1
ꢁ
ꢁ6
increasing amount of F ion no spectral modification has been
observed which indicates there is no interaction between the
(
1.0 ꢂ 10 M) in CH
3
CN solution, the peak at 274 nm gradually
decreases, shoulder band slightly is shifted to red with increasing
intensity and a new broad absorption peak at 440 nm appears
accompanied by a visual color change from colorless to red color
solution. Spectral change clearly indicates interaction of receptor
with fluoride ion and the obvious choice is the formation of com-
plex between the receptor and the fluoride ion indicated by the
presence of a distinct isobestic point at 317 nm. In case of receptor
receptor 4 and fluoride ion. Under similar experimental condition,
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
3
on addition of other anions such as AcO , H
2
PO
4
, Cl , Br , I , HSO
ꢁ
and NO
3
no noticeable spectral changes were observed with 1, 2,3
and 4 indicating no interaction or complexation of these anions
with the above the compounds (Figs. S9–S12). The appreciable
spectral changes of 1, 2 and 3 in presence of fluoride also indicate
that it can detect fluoride ion selectively (Figs. 5 and S13, S14).
3
(N-(4-nitrobenzylidene)benzohydrazide) the UV–Vis spectral
Fig. 1. Naked-eye color change of receptor 1 (1.0 ꢂ 10ꢁ5 M) after addition of 2 equivalent of various anions in CH
3
CN.

8
72
S. Ghosh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 869–874
nꢁ
mnꢁ
where [X ], [L], and [(X
added, compounds and the complex between fluoride and the com-
pounds, respectively. A , A and A indicate optical density or absor-
m
L)
] are the concentration of fluoride
0
1
bance at a particular wavelength of the compounds without
fluoride, absorbance after adding fluoride at every successive step
and excess amount of anion added, respectively. The terms K, m
and n are binding constant or association constant of the complex,
moles of fluoride and charge of fluoride, respectively. The binding
ꢁ1
ꢁ2
constant or association constant K (M or M ) is determined from
the ratio of intercept and slope of Benesi–Hildebrand plot of the
optical density. As shown in Fig. 2 (inset), the Benesi–Hildebrand
ꢁ
ꢁ
(
B–H) plot of 1/[A ꢁ A
0
] vs 1/[F ] for the titration of 1 and F ion
provides a straight line, indicating 1:1 complex formation with
4
ꢁ1
association constant (K) 1.8 ꢂ 10 M . Receptor 2 and 3 can also
form 1:1 adduct with fluoride having association constants
3
4
1
.62 ꢂ 10 and 1.24 ꢂ 10 respectively (Figs. 3 and 4 (inset)). The
association constant values of all the three fluoride complexes
clearly indicate that the stability of the complex of 1 and 3 is com-
parable and higher than the complex of compound 2.
ꢁ
6
ꢁ
Fig. 2. UV–Vis spectral changes of receptor 1 (1.0 ꢂ 10 M) upon addition of F ion
ꢁ
(
0–2 equiv.) in CH
3
CN. Inset: B–H plot for the titration of 1 with F ion.
1
H NMR titration spectra
Determination of stoichiometries and association constants
To further look into the binding nature of the receptors and
1
anions, H NMR titration experiments have been performed in
1
With the help of UV–Vis titration the stoichiometry and the
association constant between the compounds and fluoride has
been calculated. The binding constants (K) of all the three com-
d
6
-DMSO. H NMR titration experiment of 1 shows (Fig. 6) that
the proton H
tor 1 disappears on adding TBAF (1 equiv.) as a result of fast proton
exchange. The signal at d 8.05 for H corresponding to nitro phenyl
group is slightly shifted to upfield. On further addition of 2 equiv.
a
at d 12.11 ppm corresponding to –NH peak of recep-
ꢁ
pounds (1, 2 and 3) and F complexes have been determined by
d
using Benesi–Hildebrand (B–H) relation [28,29]. The complexation
ꢁ
between the receptors and F ion takes place following the given
of F ions the H
of the phenyl ring. At 5 equivalent of F ions the H
d
proton is found to merge with the H
e
and H
proton is fur-
f
proton
ꢁ
complexation equilibrium
d
ther shifted to upfield direction and then is separated from the H
e
L þ mXnꢁ $ ðX
LÞmnꢁ
m
ꢁ
and H
f
proton. As the concentration of F ion has been increased
from 1 equiv. to 5 equiv., the signal at d 8.78 corresponding to
imine proton H is slowly upfielded owing to the formation of exo-
mnꢁ
½
ðX
m
LÞ
ꢃ
m
K ¼
b
nꢁ
½
Lꢃ½X ꢃ
cyclic double bond during detection process. The upfield shift of
aromatic protons may be explained in terms of deprotonation of
the amide proton which leads to increase in electron density over
the receptor and as a consequence upfield shift is observed.
In case of receptor 3 the –NH peak at d 12.17 vanishes with the
Benesi–Hildebrand relation with m = 1 for 1:1 complex can be
expressed in terms of optical density (A) as follow
nꢁ
A
0
þ A
1
K½X
ꢃ
A ¼
Or;
nꢁ
1
1
þ K½X
ꢃ
addition of TBAF (1 equiv.) during H NMR titration (Fig. 7). In the
same time a slight upfield shift of H
d
proton (d 7.99) of nitro phenyl
1
1
ꢁ A
1
group is observed. As a result the peak of H and H proton merge
d
e
¼
þ
ðA ꢁ A ÞK½Xnꢁꢃ
ðA ꢁ A
0
Þ
ðA
1
0
Þ
together at d 7.91 ppm. On further addition of TBAF (2 equiv.), the
proton is shifted again in the upfield direction. Finally, on
1
0
H
d
ꢁ
6
ꢁ
ꢁ5
ꢁ
Fig. 3. UV–Vis spectral changes of receptor 3 (1.0 ꢂ 10 M) upon addition of F ion
Fig. 4. UV–Vis spectral changes of receptor 2 (1.0 ꢂ 10 M) upon addition of F ion
ꢁ
ꢁ
(
0–2 equiv.) in CH
3
CN. Inset: B–H plot for the titration of 3 with F ion.
(0–2 equiv.) in CH
3
CN. (Inset) B–H plot for the titration of 2 with F ion.

S. Ghosh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 869–874
873
0
0
.20
.15
0
.10
.05
0
0
.00
1
ꢁ
6
Fig. 5. Change in absorbance (k at 440 nm) of 1 (10 M) upon addition of different
anions in acetonitrile solvent.
Fig. 7. Partial 1H NMR spectra of compound 3 in DMSO-d
during addition of 0–5
6
equivalent of fluoride ion.
aromatic protons. However on addition of 5 equivalent of TBAF the
proton is shifted to upfield and separated from the H proton
Fig. S15).
1H NMR titration experiments of 4 shows that the proton H
1.86 ppm corresponding to –NH of receptor 4 is present till the
H
c
b
(
a
at d
1
addition of 1 equivalent of TBAF. When excess amount of fluoride
is added –NH peak disappears with no observable shift of the aro-
matic protons.
Analyzing the results of 1H NMR titration and UV–Vis titration
the binding mechanism of receptors can be proposed by consider-
ing the detection process as a two step process. Initially, hydrogen
ꢁ
bonding occurs between the –NH– proton and F ion to form 1:1
adduct and then –NH– proton gets deprotonated resulting in
increase of electron density over the receptor. As a result charge
separation is introduced in the receptor which causes intramolec-
ular charge transfer (ICT) between the electron deficient –NO
2
group and electron rich –N to show the UV–Vis and colorimetric
changes [30–32].
Fig. 6. Partial 1H NMR spectra of compound 1 in DMSO-d
after addition of 0–5
6
equivalent of fluoride ion.
addition of 5 equiv of TBAF, the H
the right side of H proton.
Now the H NMR titration of compound 2 shows a slight different
result. For compound 2 both the imineproton (H ) and aromatic pro-
ton H appear as singlet at d 8.55 ppm. When one equivalent of TBAF
d
proton appears prominently on
e
1
NO3
-
HSO -
H PO4- Cl-
F-
OAc-
3
2
1
b
c
is added to the solution of compound 2 the –NH peak at d 12.12 does
ꢁ4
Fig. 8. Color change of test paper containing 1 (10 M) in presence of different
not vinish completely and there is no significant shifts of the
anions.

8
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S. Ghosh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 149 (2015) 869–874
Acknowledgment
S.G. & A.G. would like to acknowledge UGC and CSIR for
Fellowship. M.A.A. thanks DST, Govt. of West Bengal, India
Project No. 376 (sanc.)/ST/P/S&T/9G-16/2013) for support.
(
HSO - NO3-
H PO4- Cl-
OAc-
3
F-
2
1
Appendix A. Supplementary data
Fig. 9. Color change of test paper containing 2 (10ꢁ4 M) in presence of different
anions.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2015.04.025.
References
2
In case of receptor 1 and 3 the electron deficient –NO group is
in ortho and para position of the phenyl ring, respectively. As a
result better charge separation occurs which influences the ICT
process resulting a color change from colorless to deep red
[
1] J.A. Weatherell, A.S. Hallsworth, C. Robinson, Arch. Oral Biol. 18 (1973) 1175–
1189.
[2] E.D. Eanes, I. Zipkin, R.A. Harper, A.S. Posner, Arch. Oral Biol. 10 (1965) 161–
73.
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1
(Schemes S1 and S3). In contrast, the receptor 2 possess –NO
2
[
group in meta position which has less influence on the ICT process
and shows yellow color (Scheme S2). ICT process does not occur in
receptor 4 due to the absence of –NO group in the phenyl unit. As
2
1
[
[
5] E.D. Eanes, A.H. Reddi, Metab. Bone Dis. Relat. 2 (1979) 3–10.
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a result no color change has been observed.
(
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[
3
Visual color changes on test papers
[
[
[
[
10] D.A. Jose, D.K. Kumar, B. Ganguly, A. Das, Org. Lett. 6 (2004) 3445–3448.
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On the basis of the above observation, we have investigated the
potential practical applications of 1 as an anion sensor. To explore
this, we have prepared test kits using Whatman-40 test paper
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Velmurugan, Tetrahedron Lett. 46 (2005) 7255–7258.
ꢁ4
coated with CH
3
CN solution of 1 (1 ꢂ 10 M) and then dried in
air (test kits). For the detection of anion, the acetonitrile solution
[
14] S. Dalapati, M.A. Alam, S. Jana, R. Saha, N. Guchhait, Sens. Actuators B 162
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ꢁ
4
of anions (1 ꢂ 10 M) has been dropped onto the test paper and
(
ꢁ
dried in hot air. Interestingly, only F ion exhibits a bright red color
[15] P.D. Beer, P.A. Gale, Angew. Chem. Int. Ed. 40 (2001) 486–516.
[16] P.A. Gale, Coord. Chem. Rev. 240 (2003) 191–221.
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
3
(
NO
Fig. 8). Other anions such as AcO , H
2
PO
4
, Cl , Br , I , HSO
, and
[
17] V. Amendola, D. E.-Gomez, L. Fabbriaai, M. Lichhelli, Acc. Chem. Res. 39 (2006)
43–353.
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ꢁ
3
do not show any naked eye detectable color changes.
3
Under similar experimental condition test paper coated with
[
[
19] P.A. Gale, R. Quesada, Coord. Chem. Rev. 250 (2006) 3200–3218.
20] Y.M. Hijji, B. Barare, A.P. Kennedy, R. Butcher, Sens. Actuators B (Chem.) 136
compound 2 exhibites yellow color (Fig. 9), but compound 3 coated
ꢁ
test paper (test kits) exhibites bright red color in presence of F ion
(
2009) 297–302.
ꢁ
(Fig. S16). In contrast, receptor 4 cannot be used as test kit for F
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Spectrosc. 129 (2014) 499–508.
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Part A Mol. Biomol. Spectrosc. 102 (2013) 314–318.
ion. This experiment support that compounds 1–3 have the
ꢁ
capability to detect F ion in solid state.
[
[
[
[
23] Z. Lin, Y. Zhao, C. Duan, B. Zhang, Z. Bai, Dalton Trans. (2006) 3678–3684.
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Conclusion
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_
[
27] P. Cıkla, S.G. Küçükgüzel, I. Küçükgüzel, S. Rollas, E. De Clercq, C. Pannecouque,
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In summary, we have demonstrated that benzohydrazide base
Schiff base 1–3 having electron deficient –NO
2
group in different
[
ꢁ
position (ortho, meta and para) can selectively detect F ion by
changing color, which can be visible by ‘‘naked-eye’’ without any
spectroscopic instrumentation both in solution and solid sup-
ported materials (test kits). This easy to prepare, cheap test kit
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4778–4781.
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[
[
(
1999) 10438–10439.
ꢁ
would be advantageous to detect F ion in economically poor
[32] H.H. Hammud, A. Ghannoum, M.S. Masoud, Spectrochim. Acta Part A Mol.
Biomol. Spectrosc. 63 (2006) 255–265.
and underdeveloped regions in the world.