Synthesis, fluorescence properties and selective Cr(III) recognition of tetraaryl imidazole derivatives bearing thiazole group

Article abstract of DOI:10.1016/j.cclet.2013.01.031

Three tetraaryl imidazole derivatives 5a-5c bearing thiazole groups were synthesized in the presence of [Bmin]Br by one-pot reaction and their structures were fully characterized by the ¹H NMR, IR, MS and elemental analysis. The results of UV-v

Full text of DOI:10.1016/j.cclet.2013.01.031

G Model
CCLET-2445; No. of Pages 3
Chinese Chemical Letters xxx (2013) xxx–xxx
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Chinese Chemical Letters
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Original article
Synthesis, fluorescence properties and selective Cr(III) recognition of tetraaryl
imidazole derivatives bearing thiazole group
*
Bing Zhao , Ya-Cui Zhou, Meng-Jiao Fan, Zhi-Yu Li, Li-Yan Wang, Qi-Gang Deng
Chemistry and Chemical Engineering Institute, Qiqihar University, Qiqihar 161006, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Three tetraaryl imidazole derivatives 5a–5c bearing thiazole groups were synthesized in the presence of
[Bmin]Br by one-pot reaction and their structures were fully characterized by the 1H NMR, IR, MS and
elemental analysis. The results of UV–vis spectra and fluorescent spectra upon metal ions complexation
show that compound 5a displays high selectivity and sensitivity for Cr3+ ions. The complexation ratio of
compound 5a and Cr3+ is 1:1.
Received 28 November 2012
Received in revised form 27 December 2012
Accepted 5 January 2013
Available online xxx
ß 2013 Bing Zhao. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords:
Tetraaryl imidazole
Thiazole
Fluorescent
Selectivity Cr3+
1. Introduction
properties of tri- or tetra- phenylimidazole derivatives [8] has
been reported, which means that multiarylimidazole derivatives
Because of its simplicity and sensitivity, selective fluorimetric
detection of heavy and transition metal ions is much better than
other detection techniques such as electrochemical [1] and
potentiometric ones [2]. In the recent past, much attention has
been paid to the design and synthesis of colorimetric/fluorescent
chemosensors for the selective and efficient detection of biologi-
can exhibit favorable optical properties and be used to construct
highly sensitive fluorescent chemisensors for sensing and imaging
of metal ions.
In the present paper we summarized a comprehensive study of
the tetraaryl imidazole derivatives bearing thiazole group synthe-
sized by one-pot and their structures were characterized by IR, 1H-
NMR, MS and elemental analyses. The metal-binding properties
toward cations show compound 5a displays a highly selective and
sensitive response toward Cr3+ in CH2Cl2.
cally and chemically important cations [3] (e.g. Cu2+, Fe3+, Cr3+
,
Pb2+, Hg2+, etc.). Among the transition-metal ions, Cr3+ is of great
importance and plays an indispensable role in the growth and
development of living systems [4]. However, the reported
chemosensors for fluorescent detection of Cr3+ are still rare due
to the lack of a proper selective ionophore for Cr3+ [5]. So, it is
urgent to synthesize the fluorescence chemosensors and investi-
gate systematically the specific detection of Cr3+ especially for
aqueous systems.
2. Experimental
All reagents were purchased from Aladdin and were used
without further purification. Thin layer chromatography (TLC) was
carried out on alumina backed plates coated with Merck gel F254.
IR spectra (KBr) were recorded on a Perkin Elmer FTIR. 1H NMR
spectra were recorded at room temperature on a Bruker Avance-
400 NMR spectrometer. Chemical ionization (CI) mass spectrome-
try was performed using Agilent 1100 LC/MS. Elemental analyses
were made with a CHN CODRDER MT-3. The UV–vis spectra were
measured using a Lambda-900 spectrometer. The fluorescence
emission spectra were measured using a LS-55 spectrometer.
Synthesis of tetraaryl imidazole compounds 5a–5c: Benzil
(1 mmol), aldehyde (1 mmol), 2-aminothiazole (1 mmol), and
ammonium acetate (1 mmol) were added to 1-butyl-3-methyli-
midazolium {[Bmin]Br} (0.5 g) without another solvent. The
mixture was heated to 140 8C and stirred at temperature for
Imidazole derivatives, as ligands for transition metal ions, have
widely employed in coordination chemistry and supra-molecular
chemistry [6]. They have displayed significant analytical applica-
tions utilizing their fluorescence and chemiluminescence
properties [7]. Most imidazole molecules based fluorescent
chemosensors have been designed and investigated based on
appreciable changes in fluorescence upon binding of metal ion.
Some research about the photoluminescent and chemiluminescent
* Corresponding author.
E-mail address: zhao_submit@yahoo.com.cn (B. Zhao).
1001-8417/$ – see front matter ß 2013 Bing Zhao. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2013.01.031
Please cite this article in press as: B. Zhao, et al., Synthesis, fluorescence properties and selective Cr(III) recognition of tetraaryl imidazole
derivatives bearing thiazole group, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.01.031

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CCLET-2445; No. of Pages 3
2
B. Zhao et al. / Chinese Chemical Letters xxx (2013) xxx–xxx
about 10 h until the reaction was completed (monitored by TLC).
After this, the mixture was cooled to room temperature, water
(20 mL) was added and stirred magnetically for 30 min. Insoluble
products were filtered off and dried. The crude products were
purified by silica gel column chromatography (EtOAc-petroleum
ether) to afford the pure products 5a–5c.
0.8
0.6
0.4
0.2
0.0
Cr3+
5a, Ca2+, Cd2+, Cu2+, Hg2+,
Mn2+, Ni2+, Pb2+, Zn2+, Fe3+,
Na+, Al3+, Mg2+, Ag+
2,4,5-Triphenyl-1-(thiazol-2-yl)-1H-imidazole (5a): Yield: 71%.
mp 268–270 8C; IR (KBr, cmꢀ1):
v
3037, 1601, 1488, 1461, 1320,
1257, 766, and 697. 1H NMR (400 MHz, CDCl3):
d
7.99 (d, 2H,
J = 7.2 Hz), 7.50 (d, 4H, J = 7.2 Hz), 7.44–7.39 (m, 4H), 7.36–7.29 (m,
5H), 7.27–7.26 (m, 2H). MS (m/z): 380.5 (M+H+). Anal. calcd. for
300
350
400
450
C
24H17N3S (%): C, 75.96; H, 4.52; N, 11.07. Found: C, 75.84; H, 4.67;
N, 10.99.
2-(4-Chlorophenyl)-4,5-diphenyl-1-(thiazol-2-yl)-1H-imidazole
(5b): Yield: 68%. mp 134–136 8C; IR (KBr, cmꢀ1):
3063, 1603,
1486, 1437, 1317, 830, 765, and 696. 1H NMR (400 MHz, CDCl3):
Wavelength/nm
Fig. 1. UV–vis spectra of compound 5a (10
m
mol/L) upon addition of various metal
v
ions (10
m
mol/L) in CH2Cl2.
d
800
8.05 (d, 2H, J = 7.2 Hz), 7.44 (d, 4H, J = 7.2 Hz), 7.34 (d, 4H,
J = 8.0 Hz), 7.30–7.26 (m, 4H), 7.24–7.21 (m, 4H). MS (m/z): 415.1
(M+H+). Anal. calcd. for C24H16ClN3S (%): C, 69.64; H, 3.90; N, 10.15.
Found: C, 69.81; H, 4.03; N, 10.27.
Cr3+
600
400
2-(4-Methoxyphenyl)-4,5-diphenyl-1-(thiazol-2-yl)-1H-imidaz-
ole (5c): Yield: 67%. mp 205–207 8C; IR (KBr, cmꢀ1):
v
3030, 2922,
2838, 1608, 1497, 1449, 1290, 1176, 1130, 829, and 695. 1H NMR
(400 MHz, CDCl3): 7.86 (d, 2H, J = 7.2 Hz), 7.55 (d, 4H, J = 7.2 Hz),
d
Fe3+
200
5a
7.35 (d, 4H, J = 4.8 Hz), 7.31 (m, 4H), 6.97 (d, 2H, J = 7.2 Hz), 3.85 (s,
3H). MS (m/z): 410.4 (M+H+). Anal. calcd. for C25H19N3OS (%): C,
73.32; H, 4.68; N, 10.26. Found: C, 73.49; H, 4.49; N, 10.35.
Recovery of ILs: After the reaction was completed, the insoluble
solid was isolated and the water in which [Bmin]Br was soluble
was evaporated and then washed by ethyl acetate three times
(8 mL ꢁ 3 mL), and dried under reduced pressure. [Bmin]Br was
recovered in yield of 95% and reused in next time.
0
300
400
500
600
700
Wavelength/nm
Fig. 2. Fluorescence emission spectra of compound 5a upon addition of various
metal ions (10 mol/L) in CH2Cl2.
m
3. Results and discussion
similar results were obtained for the studies of compound 5b and
5c). Preliminary complexation properties of compound 5a were
investigated in CH2Cl2 toward various heavy and transition metal
cations by UV–vis spectroscope. As shown in Fig. 1, the maximum
absorption band at 304 nm showed the formation of metal
complexation. An obvious change of absorption intensity was
observed on the spectroscopic investigation of addition of Cr3+ and
the original peak was significantly strengthened. The change of this
intensity preliminarily implied that the compound 5a could
Tetraaryl imidiazole derivatives bearing thiazole groups were
prepared using a conventional one-pot four component reaction as
outlined in Scheme 1. Benzil was prepared according to the
literature [9]. Benzaldehydes, 2-aminothiazole and ammonium
acetate were obtained from commercial resources without
purification. The crude products were synthesized by the reaction
of benzil (1 mmol), benzaldehydes (1 mmol), 2-aminothiazole
(1 mmol) and ammonium acetate (1 mmol) in presence of 1-butyl-
3-methylimidazolium {[Bmin]Br} (0.5 g) without another solvent
and were purified by silica gel column chromatography (EtOAc-
petroleum ether) to form the final compounds 5a–5c in moderate
yields. The structures were characterized by 1H NMR, IR, elemental
analysis and MS. One thing to be mentioned was that ILs, [Bmin]Br,
as a solvent could be recovered and reused after the simple
workup.
selectively recognize Cr3+
.
Selectivity is a very important parameter for evaluating the
performance of a fluorescence sensor. For further clarification of
the bonding properties, the fluorescence behavior of the com-
pound 5a was examined in the presence of various metal cations.
Fluorescence emission spectra of 5a (1.0 ꢁ 10ꢀ5 mol/L) in CH2Cl2
with 2 equiv. metal cations were shown in Fig. 2. Compound 5a
exhibited very low background fluorescence emission at 406 nm.
The fluorescence was slightly influenced by the addition of Fe3+
with a small enhancement in fluorescence. Addition of Cr3+ to
compound 5a gives rise to a significant fluorescence enhancement.
The corresponding changes in the fluorescence spectra in the
presence of different metal ions were caused by the PET process in
The complexation properties of compound 5a–5c were studied
to various heavy metal and transition metal cations, including Ca2+
Cd2+, Cu2+, Hg2+, Mn2+, Ni2+, Pb2+, Zn2+, Fe3+, Na+, Al3+, Mg2+, Ag+,
Cr3+, by UV–vis and fluorescence spectra and the results show that
compound 5a demonstrates selective recognition of Cr3+ (the
,
S
O
N
O
N
+
H
ILs
140 ºC
N
N
+
+
NH4OAc
NH
2
R
S
O
R
R
H
5a
5b Cl
2
4
1
3 a~c
5 a~c
5c OCH
3
Scheme 1. One-pot synthesis of tetraaryl imidazole derivatives bearing thiazole group.
Please cite this article in press as: B. Zhao, et al., Synthesis, fluorescence properties and selective Cr(III) recognition of tetraaryl imidazole
derivatives bearing thiazole group, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.01.031

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CCLET-2445; No. of Pages 3
B. Zhao et al. / Chinese Chemical Letters xxx (2013) xxx–xxx
3
[(0 ꢀ 3) ꢁ 10ꢀ5 mol/L]. The strong changes of compound 5a in
its absorption intensity upon the addition of increasing amounts of
Cr3+ might be ascribed to the interaction of Cr3+ with the lone pair
electron of the N and S atoms in the imidazole derivative bearing
thiazole group.
350
300
250
200
150
100
50
4. Conclusion
In summary, the tetraaryl imidazole derivatives 5a–5c bearing
thiazole group have been synthesized in presence of [Bmin]Br by
one-pot reaction and the results of the complexation properties
toward to metal cations show that compound 5a exhibits high
0
0.0
0.2
0.4
0.6
0.8
1.0
Mole Fraction of Cr3+
selectivity and sensitivity for Cr3+
.
Fig. 3. Job’s plot for determining the stoichiometry of receptor 5a and Cr3+ ion in
CH2Cl2, I and I0 are the fluorescence intensity of 5a in the presence and absence of
Acknowledgments
Cr3+
,
respectively, the total concentration of 5a and Cr3+ ion is 0.1 mmol/L
(
l
ex = 358 nm).
This work was supported by the Science Fund for Young
Scholars of Heilongjiang Province of China (No. QC2009C61), the
Program for Young Teachers’ Scientific Research at Qiqihar
University (No. 2012K-Z09) and Qiqihar University Graduate
Innovation Fund Grants (No. YJSCX2011-026X).
Cr3+/10-5mol/L
1000
800
600
400
200
0
3.0
2.5
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
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Please cite this article in press as: B. Zhao, et al., Synthesis, fluorescence properties and selective Cr(III) recognition of tetraaryl imidazole
derivatives bearing thiazole group, Chin. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.cclet.2013.01.031