A highly selective fluorescent chemosensor for Al(III) ions based on 2-hydroxy-1-naphthaldehyde derivative

Article abstract of DOI:10.1139/cjc-2018-0141

This manuscript reports the synthesis and fluorescent chemosensor property of a Schiff base derivative, 4-[(2-hydroxy-1-naphthyl) methylideneamino]benzoic acid (H₂L). The fluorescence spectrum shows that H₂L exhibits a highly selecti

Full text of DOI:10.1139/cjc-2018-0141

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Title page
Title: A highly selective fluorescent chemosensor for Al(III) ions based
on 2-hydroxy-1-naphthaldehyde derivative
Author: Jiayi Sun, Min Zhang , Changyan Sun *
Address: Beijing Key Laboratory for Science and Application of
Functional Molecular and Crystalline Materials, School of Chemistry and
Biological Engineering, University of Science and Technology Beijing,
Beijing, 100083, China
Corresponding author: Changyan Sun, E-mail: cysun@ustb.edu.cn,
Telephone: 86-010-62333871, Fax: 86-010-62332126

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Abstract:
This manuscript reports the synthesis and fluorescent chemosensor
property of a Schiff base derivative 4-[(2-hydroxy-1-naphthyl)
methylideneamino]benzoic acid (H2L). Fluorescence spectrum shows that
H2L exhibits a highly selective and sensitive recognition for Al3+ ions in
N,N′-dimethylformamide/water (DMF/H2O, 1/1, v/v). The fluorescence
titration experiments and electrospray ionization mass spectrometry
1
(ESI-MS) show that H2L and Al3+ ions form a 1:1 complex. H NMR
titration results prove that H2L coordinates to Al3+ ions with carboxylate,
hydroxyl groups, and imine groups, and the probable sensing mechanism
may be ESIPT process.

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A highly selective fluorescent chemosensor for Al(III)
ions based on 2-hydroxy-1-naphthaldehyde derivative
Jiayi Sun, Min Zhang , Changyan Sun *
Beijing Key Laboratory for Science and Application of Functional Molecular and
Crystalline Materials, School of Chemistry and Biological Engineering, University of
Science and Technology Beijing, Beijing, 100083, China
Abstract
This manuscript reports the synthesis and fluorescent chemosensor
property of a Schiff base derivative 4-[(2-hydroxy-1-naphthyl)
methylideneamino]benzoic acid (H2L). Fluorescence spectrum shows that
H2L exhibits a highly selective and sensitive recognition for Al3+ ions in
N,N′-dimethylformamide/water (DMF/H2O, 1/1, v/v). The fluorescence
titration experiments and electrospray ionization mass spectrometry
1
(ESI-MS) show that H2L and Al3+ ions form a 1:1 complex. H NMR
titration results prove that H2L coordinates to Al3+ ions with carboxylate,
hydroxyl groups, and imine groups, and the probable sensing mechanism
may be ESIPT process.
Keywords: Schiff base; fluorescent chemosensors; Al3+ ions; ESIPT
process
1. Introduction
Aluminum is widely used in the fields of food additives, water
treatment, and the production of light alloys.1-3 It can easily enter human
body through food and water.4-5 According to a WHO report, the average

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daily intake of aluminum is about 3-10 mg/day. Excessive Al3+ ions may
lead to diseases such as anemia, Alzheimer’s disease, bone and joint
diseases.6-9 Thus the detection of Al3+ ions has attracted widespread
attention.
Analytical techniques such as atomic absorption spectrometry,10
inductively coupled plasma mass spectroscopy (ICP–MS),11
electrochemical method,12 and fluorescent chemosensors have been
reported for the detection of Al3+ ions.13 Among these analytical
techniques, fluorescent chemosensors have got significant attentions
because of their high selectivity, high sensitivity and simple operation.14
Recently, a large number of fluorescent chemosensors for Al3+ ions have
been reported.15-17 But most of them require complicated synthesis.
Therefore, it is important to develop new chemosensors which is easily
prepared and has high selectivity and sensitivity for Al3+ ions.
Schiff bases are known as one kind of classical ligand which can form
stable complexes with not only transition metal ions, but also rare earth
metal ions. Considering their strong coordination ability and simple
synthesis, quite a lot of chemosensors based on Schiff bases have been
reported to detect multiple kinds of metal ions such as Zn2+ ions, Cu2+
ions, Hg2+ ions and Al3+ ions.18-26
4-[(2-Hydroxy-1-naphthyl)methylideneamino]benzoic acid (H2L) is a
typical Schiff base derived from 2-hydroxy-1-naphthaldehyde. A.

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Mehmet reported its structure in 2008.27 But after that, there is no further
study about this Schiff base. In its structure, it has nitrogen and oxygen
donating atoms which are favorable to coordinate with metal ions.
Through intramolecular hydrogen bonding, a six-membered ring can be
formed which is the typical structure for excited-state intramolecular
proton transfer (ESIPT) process to probe metal ions.28,29 In this
manuscript, experiments were performed to study the chemosensor
property of H2L and the experimental results show that H2L has high
selectivity and sensitivity for Al3+ ions in N,N′-dimethylformamide/water.
2. Experimental
2.1 Materials and measurements
All reagents for synthesis were obtained commercially. The infrared
spectra were studied on a Digilab FTIR-8400S spectrophotometer.
Elemental analyses (CHN) were recorded using a Vario EL elemental
analyzer. Fluorescence spectra were performed on a F-4500 fluorescence
spectrophotometer with a xenon lamp as the excitation source. Mass
1
spectra were measured on a Bruker esquire 6000 spectrometer. HNMR
spectra were recorded on a Bruker DPX 400 MHz spectrometer with
DMF-d7 as solvents and TMS as an internal reference of analytical grade.
2.2 Synthesis of H2L
Scheme 1 shows the synthesis route of H2L. A mixture of

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4-aminobenzoic acid (0.0137 g, 0.1 mmol), 2-hydroxy-1-naphthaldehyde
(0.0172 g, 0.1 mmol), N, N′-dimethylformamide (1 ml), ethanol (3 mL)
and deionized water (1 ml) was sealed in a 25 mL vessel and then heated
to 100 °C for 5 h. After standing in room temperature for two days, yellow
needle-shaped crystals of H2L were obtained. Yield: 0.025g (86.0%). Anal.
calcd for C18H13NO3 (%): C, 74.15; N, 4.81; H, 4.46. Found: C, 74.15; N,
4.88; H, 4.42. (IR, KBr, cm−1): 3437(w), 2361(w), 1678(m), 1625(m),
1583(m), 1534(m), 1428(m), 1290(s), 1208(m), 1150(m), 1121(m),
929(w), 852(m), 819(m), 766(m), 737(m).1H NMR (DMSO-d6, 400 MHz):
δ = 15.50 (s, 1H,-OH), 10.96 (s, 1H, -COOH), 9.86 (d, 1H, C=N),
8.59-8.61(d, 1H), 8.12-8.15 (d, 2H), 7.94-7.96 (d, 1H), 7.84-7.86 (d, 2H),
7.64-7.68 (d, 1H), 7.52-7.56(t, 1H), 7.40-7.42 (t, 1H), 7.06-7.08 (d, 1H).
ESI-MS: m/z: 292.4. The structure of H2L is the similar as that reported in
2008. 27
NH2
CHO
OH
CH
H
+
N
COOH
O
COOH
Scheme. 1. Synthesis rout of chemosensor H2L
2.3 General experiment
In the titration experiments, stock solutions of the chlorate salts of K+,
Ag+，Ca2+, Mg2+, Ba2+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+, Fe3+, and the

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nitrate salts of Ag+, Al3+ in DMF/H2O (v/v, 1/1, 0.2mM) were prepared.
And H2L was dissolved in DMF/H2O (v/v, 1/1, 0.2mM). Test solutions
contained the same amount of H2L and the ions. The excitation
wavelength was 295 nm. And all the slit widths were 5.0 nm.
3. Results and discussion
3.1 Fluorescence response of H2L to metal ions
Fig. 1 shows the fluorescence spectra of H2L in DMF/H2O (v/v, 1/1)
upon the addition of 1.0 equiv. of different kinds of metal ions. It can be
seen that with the addition of 1.0 equiv. of K+，Ag+，Ca2+，Mg2+，Ba2+,
Mn2+，Co2+，Ni2+，Zn2+，Cd2+，Hg2+ or Fe3+ ions into H2L, no obvious
fluorescence response could be observed. However, with the addition of
1.0 equiv. of Al3+ ions, the fluorescence intensity was enhanced about
11-fold, which indicates a high selectivity of H2L for Al3+ ions.
To investigate the practical utility of H2L in detecting Al3+ ions in
DMF/H2O, competitive fluorescence titration was performed. H2L was
treated with 1.0 equiv. of Al3+ ions in the presence of 1.0 equiv. of other
metal ions. Fig. 2 shows the experimental results. It can be seen that there
are no interference for the detection of Al3+ ions in the presence of other
metal ions. This indicates that H2L has high selectivity for Al3+ ions.
3.2 Binding ratio
In order to investigate the interactions of H2L with Al3+ ions, the
fluorescence titration experiment was conducted with different

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concentrations of H2L in DMF/H2O (1:1, v/v). As shown in Fig. 3, the
emission intensity of H2L gradually increases with the addition of Al3+
ions until the equiv. of Al3+ ions is equal to H2L. Upon the further
addition of Al3+ ions, the intensity of H2L tends to be the same. The Job’s
plot (see the inset in Fig. 3) also shows that when the molar fraction of
Al3+ ions is 0.5, the fluorescence intensity reaches the highest. This
indicates that H2L and Al3+ ions form a 1:1 complex, which can be further
proved by the results of the electrospray ionization mass spectrometry. As
shown in Fig. 4, the peak at 369.6 (m/z) can be attributed to
[Al(L)(H2O)3]+ (calcd. m/z 370.2). The association constants were
estimated to be 1.8x104 by using the Benesi-Hildebrand equation.30 And
the detection limit of H2L for Al3+ ions can be calculated with the basis of
3s/k by fluorescence titration.31,32 From the fluorescence titration, the
detection limit was 8.8x10-6 M, which were comparable to the reported
(10-6 mol) in the literature.33,34 These results demonstrated that H2L is
highly selective and sensitive for Al3+ ions.
3.3 pH effect
The sensitivity of H2L for Al3+ ions at different pH was studied in DMF
solution. The pH values of the solution were adjusted by NaOH and HCl.
Fig. 5 shows the fluorescence intensity of H2L with the addition of Al3+
ions in different pH. It can be seen that in the pH range of 4-11, H2L
shows high sensitivity for Al3+ ions. So it is not necessary to adjust the

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pH and the further studies were performed with the solution of H2L in
DMF/H2O (v/v, 1/1) which was in the pH of 6.
3.4 Reversibility
Experiments were conducted to detect the reversibility of H2L. As
shown in Fig. 6, the fluorescence of H2L was increased by the addition of
1.0 equiv. of Al3+ ions. But when1.0 equiv. of EDTA anions were added
into the mixture of H2L and Al3+ ions, the fluorescence of the mixture
decreased. This can be attributed to the coordination interaction between
Al3+ ions and EDTA anions, which releases H2L. While adding more Al3+
ions, the fluorescence of H2L was increased again. These experiments
show that H2L has good reversibility in the detection of Al3+ ions.
3.5 Sensing mechanism
1
To further study the detailed complexation of H2L with Al3+ ions, H
NMR titrations have been performed by the concomitant addition of H2L
1
into Al3+ ions in deuterated reagents. Fig. 7a shows the H NMR
spectrum of H2L in DMF-d7. The hydroxyl proton locating at 15.59 ppm
is characteristic of an intramolecular hydrogen bond, the proton peak of
carboxylate is at 11.00 ppm, and the proton peak of imine group is at 9.86
1
ppm. Figs. 7b, 7c and 7d are the H NMR spectra of Al3+ ions with the
addition of 0.5 to 2.0 equiv. of H2L. Comparing with Fig. 7a, with the

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addition of Al3+ ions, the proton signals of carboxylate and hydroxyl
groups became weak and disappeared, which means that carboxylate and
hydroxyl groups may be deprotonated and involved in coordination. The
proton signals of imine group at 9.86 ppm was shifted to a singlet at 9.74
ppm, which indicates that the imine group may be involved in
coordination. Comparing with Fig. 7c, there were no significant changes
with the proton peaks upon the addition of 2.0 equiv of H2L to Al3+ ions
(Fig. 7d). These results suggest that H2L and Al3+ ions form a 1:1
complex, and H2L coordinates to Al3+ ions with carboxylate, hydroxyl
groups, and imine groups. This tridentate coordination fashion can inhibit
the excited-state intramolecular proton transfer (ESIPT) process thus the
fluorescence emission of H2L can be enhanced.
4. Conclusion
This manuscript reports the synthesis and characterization of a Schiff
base fluorescent chemosensor, 4-[(2-hydroxy-1-naphth)methyleneamino]
benzoic acid. This chemosensor can be used to detect Al3+ ions in DMF/
H2O (1/1, v/v) and the detect limit is 8.8x10-6 M. The ESIPT mechanism
can be used to explain the detection for Al3+ ions.
Acknowledgements
This project is supported by National Nature Science Foundation of
China (21101013) and Beijing Higher Education Young Elite Teacher

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Project (YETP0393).
References
(1) Jang, Y. K.; Nam, U. C.; Kwon, H. L.; Hwang, I. H.; Kim, C. Dyes Pigm. 2013,
99(1), 6. doi:10.1016/j.dyepig.2013.04.002.
(2) Barcelo, J.; Poschenrieder, C. Environ. Exp. Bot. 2002, 48, 75. doi:10.1016/
S0098-8472(02)00013-8.
(3) Gupta, V. K.; Singh, A. K.; Kumawat, L. K. Sensor. Actuat. B-Chem. 2014, 195
98. doi: 10.1016/j.snb.2013.12.092.
(4) Berthon, G. Coord. Chem. Rev. 2002, 228, 319. doi: 10.1016/ S0010-8545(02)
00021-8.
(5) Yousef, M. I.; EI-Morsy, A. M. A.; Hassan, M. S. Toxicology 2005, 215, 97.
doi:10.1016/j.tox.2005.06.025.
(6) Liu, B.; Wang, P. F.; Chai, J.; Hu, X. Q.; Gao, T.; Chao, J. B.; Chen, T. G.; Yang,
B. S. Spectrochim. Acta A 2016, 168, 98. doi:10.1016/j.saa.2016.06.002.
(7) Chatterjee, N.; Maity, S. B.; Samadder, A.; Mukherjee, P.; Bukhsh, A. R. K.;
Bharadwaj, P. K. RSC Adv. 2016, 6, 17995. doi: 10.1039/c5ra23968k.
(8) Kumawat, L. K.; Mergu, N.; Asif, M.; Gupta, V. K. Sens. Actuators B 2016, 231,
847. doi:10.1016/j.snb.2016.03.062.
(9) Gupta, V. K.; Mergu, N.; Kumawat, L. K.; Singh, A. K.; TALANTA. 2015, 144, 80.
doi. 10.1016/j.talanta.2015.05.053.
(10) Frankowski, M.; Frankowska, A. Z.; Siepak, J. Talanta 2010, 80, 2120.
doi:10.1016/j.talanta.2009.11.018.
(11) Sanz-Medel, A.; Cabezuelo, A. B. S.; Milăcĭc, R.; Polak, T. B. Coord. Chem.
Rev. 2002, 228, 373. doi:10.1016/S0010-8545(02)00085-1.
(12) Gupta, V. K.; Ganjali, M. R.; Norouzi, P.; Khani, H.; Nayak, A.; Agarwal, S.
Crit. Rev. Anal. Chem., 2011, 41, 282. doi: 10.1080/10408347.2011.589773.
(13) Naskar, B.; Modak, R.; Sikdar, Y.; Maiti, D. K.; Bauza, A.; Frontera, A.;
Katarkar, A.; Chaudhuri, K.; Goswami, S. Sens. Actuators B 2017, 239, 1194.
doi:10.1016/j.snb.2016.08.148.
(14) Valeur, B.; Leray, I. Coord. Chem. Rev. 2000, 205, 30. doi:10.1016/ S0010-
8545(00)00246-0.
(15) Hossain, S. M.; Singh, K.; Lakma, A.; Pradhan, R. N.; Singh, A. K. Sens.
Actuators B 2017, 239, 1109. doi:10.1016/j.snb.2016.08.093.
(16) Torawane, P.; Tayade, K.; Bothra, S.; Sahoo, S. K.; Singh, N.; Borse, A.; Kuwar,
A. Sens. Actuators B., 2016, 222, 562. doi:10.1016/j.snb.2015.08.104.
(17) Sheet, S. K.; Sen, B.; Thounaojam, R.; Aguan, K.; Khatua, S. J. Photoch.
Photobio. A: Chem. 2017, 332, 101. doi:10.1016/j.jphotochem.2016.08.019.
(18) Wang, Y.; Mao, P.D.; Wu, W.N.; Mao, X.J.; Fan, Y.C.; Zhao, X.L.; Xu, Z.Q.;
Xu, Z.H. Sens. Actuators B 2018, 255, 3085. doi:10.1016/j.snb.2017.09.133.
(19) Ding, W. H.; Cao, W.; Zheng, X. J.; Fang, D. C.; Wong, W. T.; Jin, L. P. Inorg.
Chem. 2013, 52, 7320. doi:10.1021/ic401028u

Page 12 of 17
(20) Fu, Y. L.; Fan, C. B.; Liu, G.; Pu, S. Z. Sens. Actuators B 2017, 239, 295.
doi:10.1016/j.snb.2016.08.020.
(21) Li, J.; Yin, C.; Huo, F. Dyes Pigm. 2016, 131, 100. doi: 10.1016/j.dyepig.
2016.03.043.
(22) Singh, R.; Das, G. Sens. Actuators B 2018, 255, 478. doi:10.1016/j.snb. 2017.
08.072.
(23) Kumar, G.G.V.; Kesavan, M.P.; Sivaraman, G.; Annaraj, J.; Anitha, K.;
Tamilselvi, A.; Athimoolam, S.; Sridhar, B.; Rajesh, J. Sens. Actuators B 2018,
255, 3235. doi:10.1039/c7nj03784h.
(24) Zhou, D.; Sun, C.Y.; Chen, C.; Cui, X.N.; Li, W.J. J. Mol. Struct., 2015, 1079,
315. doi:10.1016/j.molstruc.2014.09.050.
(25) Patil, R.; Moirangthem, A.; Butcher, R.; Singh, N.; Basu, A.; Tayade, K.; Fegade,
U.; Hundiwale, D.; Kuwar, A. Dalton Trans., 2014, 43, 2895. doi:10.1039/
c3dt52770k.
(26) Xiong, J.J.; Huang, P.C.; Zhou, X.; Wu, F.Y. Sens. Actuators B, 2016, 232, 673.
doi:10.1016/j.snb.2016.04.004.
(27) Mehmet, A.; Ozturk,Y.S.; Mohamed, A.A.; Vickie, M. Acta Crystallogr. E 2008,
64(4), o682.
(28) McDonald, L.; Wang, J.F.; Alexander, N.; Li, H.; Liu, T.B.; Pang, Y. J. Phys.
Chem. B 2016, 120 (4), 766. doi:10.1021/acs.jpcb.5b10909.
(29) Budzá, Š.; Jacquemin, D. J. Phys. Chem. B 2016, 120(27), 6730. doi:10.1021/
acs.jpcb.6b04474.
(30) Parker, C. A.; Rees, W. Analyst, 1960, 85(1013), 587. doi:10.1039/ AN9608
500587.
(31) Gabe, Y.; Urano, Y.; Kikuchi, K.; Kojima, H.; Nagano, T. J. Am. Chem. Soc.
2004, 126(10), 3357. doi:10.1021/ja037944j.
(32) Liu, J.; Lu, Y. Angew Chem. 2007, 119(40), 7731. doi:10.1002/ange.200702006.
(33) Shellaiah, M.; Wu, Y.H.; Lin, H.C. Analyst 2013, 138, 2931. doi:10.1039/
c3an36840h.
(34) Singh, P.; Tiwari, K.; Mishra, M.; Srivastava, N.; Saha, S. Sens. Actuators B
2013, 82, 546. doi:10.1016/j.snb.2013.03.083.

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Figure Captions
Fig. 1. Fluorescence spectra of H2L (0.2mM) upon addition of 1.0 equiv. of metal
ions in DMF/H2O (v/v, 1/1).
Fig. 2. Fluorescence intensity of H2L with Al3+ ions in the presence of other metal
ions. Red bars: solutions of H2L (0.2 mM) with 1.0 equiv. of metal ions stated.
Green bars: solutions of H2L (0.2 mM) with 1.0 equiv of Al3+and other metal
ions stated.
Fig.3. Fluorescence titration profiles (λ ex = 295 nm) of H2L (0.2 mM) in the presence
of increasing amounts of Al3+ in the range of 0-3 equiv. in DMF/H2O. Inset. The
emission intensity of H2L with the increasing amounts of Al3+ ions in the range
of 0-3 equiv. and Job’s plot.
Fig.4. Mass spectrum of H2LwithAl3+ions
Fig.5. Effect of pH towards the fluorescence intensity of H2L (0.2mM) for Al3+ ions.
Fig. 6. The reversibility experiment of the probe H2L (0.2 mM) with Al3+ (10.0 mM)
ions in DMF/H2O (v/v=1/1).
Fig. 7.1H NMR spectra in DMSF-d7: (a) H2L only; (b) Al3+and 0.5 equiv. of H2L; (c)
(b) Al3+ and 1.0 equiv. of H2L; (d) Al3+ and 2.0 equiv. of H2L.

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H2L
400
300
200
100
0
Ca2+
Zn2+
Cd2+
Hg2+
K+
Ni2+
Mg2+
Mn2+
Ag+
Fe3+
Al3+
Ba2+
Co2+
350
400
450
Wavelength（nm)
Fig. 1. Fluorescence spectra of H2L (0.2mM) upon addition of 1.0 equiv. of metal ions in
DMF/H2O (v/v, 1/1).
600
500
400
300
200
100
0
L
Al3+
Ca2+
Zn2+
Cd2+
Hg2+
K+
Ni2+
Mg2+ Mn2+ Ag2+
Fe3+
Ba2+
Co2+
Fig. 2. Fluorescence intensity of H2L with Al3+ ions in the presence of other metal ions. Red bars:
solutions of H2L (0.2 mM) with 1.0 equiv. of metal ions stated. Green bars: solutions of H2L (0.2
mM) with 1.0 equiv of Al3+and other metal ions stated.

Page 15 of 17
Fig.3. Fluorescence titration profiles (λ ex = 295 nm) of H2L (0.2 mM) in the presence of
increasing amounts of Al3+ in the range of 0-3 equiv. in DMF/H2O. Inset. The emission intensity
of H2L with the increasing amounts of Al3+ ions in the range of 0-3 equiv. and Job’s plot.
2000
1500
1000
500
0
369.644
300
320
340
360
380
400
m/z
Fig.4. Mass spectrum of H2LwithAl3+ions

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2800
2600
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
pH
Fig.5. Effect of pH towards the fluorescence intensity of H2L (0.2mM) for Al3+ ions.
2500
3+
H L+Al
2
2000
1500
1000
500
0
3+
3+
H L+Al +EDTA+Al
2
3+
H L+Al +EDTA
2
H L
2
300
350
400
450
500
550
600
650
700
750
wavelength
Fig. 6. The reversibility experiment of the probe H2L (0.2 mM) with Al3+ (10.0 mM)
ions in DMF/H2O (v/v=1/1).

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Fig. 7.1H NMR spectra in DMSF-d7: (a) H2L only; (b) Al3+and 0.5 equiv. of H2L; (c) (b) Al3+ and
1.0 equiv. of H2L; (d) Al3+ and 2.0 equiv. of H2L.