A new Schiff base based on vanillin and naphthalimide as a fluorescent probe for Ag+ in aqueous solution

Article abstract of DOI:10.1016/j.saa.2011.11.054

A new Schiff base based on vanillin and naphthalimide was designed and synthesized as fluorescent probe. The probe showed high selectivity for Ag ⁺ over other metal ions such as Pb²⁺, Na⁺, K⁺, Cd²⁺, B

Full text of DOI:10.1016/j.saa.2011.11.054

Spectrochimica Acta Part A 88 (2012) 56–59
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
A new Schiff base based on vanillin and naphthalimide as a fluorescent probe for
Ag+ in aqueous solution
Yanmei Zhou∗, Hua Zhou, Tongsen Ma, Junli Zhang, Jingyang Niu∗
Institute of Environmental and Analytical Sciences, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new Schiff base based on vanillin and naphthalimide was designed and synthesized as fluorescent probe.
The probe showed high selectivity for Ag+ over other metal ions such as Pb2+, Na+, K+, Cd2+, Ba2+, Cr3+
,
Received 14 September 2011
Received in revised form
19 November 2011
Zn2+, Cu2+, Ni2+, Ca2+, Al3+ and Mg2+ in aqueous solution. A new fluorescence emission was observed at
682 nm in the presence of Ag+ ion. The fluorescence intensity quenched with increasing the concentration
of Ag+ at 682 nm. The method of job’s plot confirmed the 1:2 complex between Ag+ and probe, and the
mechanism was proposed.
Accepted 24 November 2011
Keywords:
Schiff base
Naphthalimide
Vanillin
© 2011 Elsevier B.V. All rights reserved.
Ag+
1. Introduction
tion. The probe showed high selectivity for Ag+, and the job’s plot
confirmed the formation of 1:2 between Ag+ and probe.
Fluorescent chemosensors are very important in chemistry,
biology and medicine. There are several strategies in the
design of environment-sensitive fluorophores agents based on
these donor–acceptor systems like 4-dimethylamino phthalim-
ide and 4-amino-1,8-naphthalimide [1]. It is well known that
1,8-naphthalimide derivatives are sensitive to the environment
because of the substituted functional groups, especially aromatic
groups. Because of their strongly fluorescence and good photosta-
bility, 1,8-naphthalimide derivatives have been used in a number
of areas, including polymer materials [2,3], anticancer agents [4,5],
fluorescent markers in biology [6], fluorescence probes [7–11] and
light emitting diodes [12].
2. Experimental
2.1. Reagents
All the chemicals and organic solvents were of analytical grade.
The solution of metal ions was prepared from their nitrate salts
and chloride salts of analytical grade. The value of pH was adjusted
by HCl (0.1 mol L−1 and 1 mol L−1) and NaOH (0.1 mol L−1 and
1 mol L−1) at room temperature.
Schiff bases are a large class of organic compounds being
from condensation reaction of aromatic aldehyde and amine [13].
Vanillin was used as a flavoring agent in foods, but there was only
a few reports about its ability of combined with metal ions [14].
Herein, our job designed and synthesized a Schiff base based on
vanillin and 1,8-naphthalimide.
2.2. Apparatus
IR spectra were recorded on Nicolet AVATAR360 infrared spec-
trometer and pellets were made by using KBr. The MS spectra
were performed on Bruker ESQUIRE LC–MS. 1H NMR spectra were
recorded using Bruker AVANCE-400 spectrometer operating at
400 MHz. UV–vis spectra were recorded using Hitachi U-4100 Spec-
trophotometer. The fluorescence spectra were taken on Hitachi
F-7000FL Spectrophotometer.
The structure was characterized by FTIR, Mass and 1H NMR spec-
tra analysis. Then the influence of solvents and pH on its absorption
spectra was investigated. The coordination of metal ions and the
probe was investigated by fluorescence emission in aqueous solu-
2.3. Synthesis of the probe of 4DVN
The synthesis of 4DVN was shown in Scheme 1.
4-Bromo-N-hydroxyethyl-1,8-naphthalimide: It was synthesized
by 4-bromo-1, 8-naphthalimide and ethanolamine followed the
∗
Corresponding authors. Tel.: +86 378 2868833x3422; fax: +86 378 3881589.
E-mail addresses: zhouyanmei@henu.edu.cn (Y. Zhou), jyniu@henu.edu.cn
(J. Niu).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.11.054

Y. Zhou et al. / Spectrochimica Acta Part A 88 (2012) 56–59
57
Fig. 1. Absorption spectra of 4DVN in different solvents (C = 1.0 × 10−5 mol L−1).
3.3. The effect of pH on the fluorescence spectra
Scheme 1. Synthesis of 4DVN.
The fluorescence spectra of different values of pH were pre-
sented in Fig. 3. The fluorescence emission of probe in acidic
medium is low with a maximum at 540 nm. During the transition
from acidic to alkali pH, the fluorescence intensity increased and
the maximum fluorescence emission was shifted by 5 nm [18]. It
can be seen that fluorescence kept tiny intensity between pH 2 and
6, but changed sharply after pH 8, which was because the C N dou-
ble bond of Schiff base damaged in a low or high pH value [19]. So
the experiment followed was carried out in nearly neutral solution
of pH 6.8.
literature [15]. Yield: 94%. m.p. 199–201 ◦C. IR(KBr pellet, cm−1):
3387, 1698, 1568, 1375, 778.
4-Hydrazine-N-hydroxyethyl-1,8-naphthalimide:
4-Bromo-
N-hydroxyethyl-1,8-naphthalimide (2.00 g) and 12.5 mL 80%
hydrazine hydrate in 30 mL ethanol were heated under reflux for
4 h. After cooling to room temperature, the precipitated product
was filtered, washed with ethanol and dried, 1.63 g orange crystal
obtained [16]. Yield: 96%. m.p. 197–199 ◦C. IR (KBr pellet, cm−1):
3475, 3376, 1578, 1631, 1390, 775.
4-Vanillin-N-hydroxyethyl-1,8-naphthalimide (4DVN): Vanillin
(0.19 g)
and
4-hydrazine-N-hydroxyethyl-1,8-naphthalimide
3.4. Fluorescence evaluation of metal binding interaction
(0.34 g) was added in 40 mL ethanol. Then the mixture solution
was stirred and heated under reflux for 6 h. After cooling to room
temperature, the solid product was filtered. After purification
0.38 g red powder was obtained [17]. Yield: 75%. m.p. 212–214 ◦C.
IR (KBr pellet, cm−1): 3462, 1578, 1387. Ms: m/z: 428 ([M+Na]+).
1H NMR (DMSO-d6): 9.501 (s, 1H), 8.724 (b, 1H), 8.423 (b, 1H),
8.306 (b, 2H), 7.716 (t, 1H), 7.652 (b, 1H), 7.391 (s, 1H), 7.156 (dd,
1H), 6.873 (d, 1H), 5.749 (s, 1H), 4.119 (t, 2H), 4.801 (t, 1H), 3.896
(s, 3H), 3.606 (q, 2H).
The photophysical sensitivity of 4DVN towards physiological
and environmental relevant metal ions, Ag+, Pb2+, Na+, K+, Cd2+
,
Ba2+, Cr3+, Zn2+, Cu2+, Ni2+, Ca2+, Al3+ and Mg2+ were studied. The
fluorescence spectrum of 4DVN displayed at 540 nm (ꢀex = 455 nm)
with 1 equiv. metal ions. As can bee seen in Fig. 4, the fluorescence
profile of the probe remained essentially invariant to added Pb2+
,
Na+, K+, Cd2+, Ba2+, Cr3+, Zn2+, Cu2+, Ni2+, Ca2+, Al3+ and Mg2+. It
implies that there are none or very poor affinities of these metal ions
3. Results and discussion
3.1. The influence of solvents on UV–vis spectra
The influence of solvents on the absorption spectra was deter-
mined. It can be seen clearly from Fig. 1 that the maximum
absorption in H2O, ethanol and DMF were all located at 472 nm.
While the maximum absorption in acetone and chloroform has a
blue shift in a range of 12 nm, respectively. Taking into account of
the economic cost and practical application, the experiments were
carried out in aqueous solution.
3.2. The effect of pH on UV–vis spectra
The effect of pH on its absorption spectra was studied in a range
from 2 to 12. As shown in Fig. 2, the value of pH played an impor-
tant role in the absorption spectra. The maximum absorption was
located at 475 nm, with the transition from pH 2 to 8. But the maxi-
mum absorption has various red shifts after pH 8. The solution took
on different colors between pH 8–12, which implied the probe was
sensitive to high pH.
Fig. 2. Absorption spectra of 4DVN in various pH (C = 1.0 × 10−5 mol L−1).

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Y. Zhou et al. / Spectrochimica Acta Part A 88 (2012) 56–59
Fig. 3. Fluorescence spectra of 4DVN in various pH (C = 1 × 10−5 mol L−1
ꢀex = 455 nm).
,
Fig. 5. Fluorescence spectra of 4DVN at different concentration of Ag+
(C4DVN = 1.0 × 10−5 mol L−1, ꢀex = 455 nm).
towards the probe. To our surprise, a new fluorescence emission
was observed at 682 nm when 1 equiv. Ag+ was added.
The fluorescence spectra with different concentrations of Ag+
ions were also studied and shown in Fig. 5. It can be seen clearly
that the fluorescence emission decreased by increasing the con-
centration of Ag+ from 1.0 × 10−5 mol L−1 to 7.0 × 10−5 mol L−1. A
linear relationship for Ag+ detection under the optimum conditions
was obtained at 682 nm with a correlation coefficient of 0.9913.
The regression equation is I682 = 11.4143 − 1.1961C (10−5 mol L−1
)
shown in Fig. 6. Based on the definition of detection limit, the limit
of detection for Ag+ is up to 3.0 × 10−6 mol L−1
.
3.5. The mechanism of the complex coordination
The stoichiometry of the complex was obtained according
to the job’s plot method [20], with a total concentration of
1 × 10−4 mol L−1 Ag+ and 4DVN. It established that the maximum
fluorescence was about 0.33 shown in Fig. 7, indicating the 1:2
stoichiometry between Ag+ and 4DVN.
Thus, a possible structure of Ag+ and 4DVN complex could be
proposed and was shown in Fig. 8. The electron density of the naph-
thalimide is very high due to the electron donors at 4-position.
Fig. 6. The linear relationship of the fluorescence intensity at 682 nm (ꢀex = 455 nm).
Fig. 7. Job’s plot for Ag+-4DVN system ([Ag+] + [4DVN] = 1.0 × 10−4 mol L−1).
Fig. 4. Fluorescence spectra of 4DVN and in the presence of metal ions in aqueous
solution (C4DVN = Cmetal = 1 × 10−5 mol L−1, ꢀex = 455 nm).

Y. Zhou et al. / Spectrochimica Acta Part A 88 (2012) 56–59
59
in aqueous solution. We believe that this work would help to extend
the development of vanillin and naphthalimide in fluorescent probe
for metal ion.
Acknowledgements
The authors thank the Key Scientific and Technological Project of
Henan Province (112102310360) and the Natural Science Research
Project of Henan Province Education Department (2011A610005).
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4. Conclusion
In conclusion, we have designed and synthesized a new probe
based on vanillin and 1,8-naphthalimide. The overall study results
confirmed the successful synthesis of 4DVN. It was promising to be
a probe for high pH. The coordination of metal ions and probe was
studied, and it showed high selectivity for Ag+ over other metal ions
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