New thiazolothiazole derivatives as fluorescent chemosensors for Cr 3 and Al3

Article abstract of DOI:10.1016/j.dyepig.2012.02.005

Two new 2,5-diarylthiazolo[5,4-d]thiazole derivatives bearing ethylene oxide moieties were synthesized. Their photophysical and electrochemical properties as well as binding properties towards various metal ions were examined. Thiazole derivative 1 showed large fluorescent enhancements with Cr³ and Al³. On the other hand, thiazole derivative 2 displayed a selective fluorescent change with Cr³ among the metal ions examined. As far as we are aware of, these are the first examples of thiazolothiazole derivatives as fluorescent chemosensors for metal ions.

Full text of DOI:10.1016/j.dyepig.2012.02.005

Dyes and Pigments 94 (2012) 423e426
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
New thiazolothiazole derivatives as fluorescent chemosensors for Cr3þ
and Al3þ
,
,
,
,
a,b,
*
Ji Young Jung a 1, Su Jung Han b 1, Jihyun Chun b 1, Chongmok Lee b , Juyoung Yoon
*
a Department of Bioinspired Science (WCU), Ewha Womans University, Seoul 120-750, Republic of Korea
b Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new 2,5-diarylthiazolo[5,4-d]thiazole derivatives bearing ethylene oxide moieties were synthesized.
Received 4 January 2012
Received in revised form
5 February 2012
Accepted 7 February 2012
Available online 22 February 2012
Their photophysical and electrochemical properties as well as binding properties towards various metal
ions were examined. Thiazole derivative 1 showed large fluorescent enhancements with Cr3þ and Al3þ
.
On the other hand, thiazole derivative 2 displayed a selective fluorescent change with Cr3þ among the
metal ions examined. As far as we are aware of, these are the first examples of thiazolothiazole deriv-
atives as fluorescent chemosensors for metal ions.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Fluorescent chemosensors
Thiazolothiazole
Sensing chromium ion
Sensing Aluminium ion
Ratiometric sensor
Fluorescent probe
1. Introduction
importance of Cr3þ, only few reports are available regarding
fluorescent detection of Cr3þ [18e23]. On the other hand, the
Numerous organic molecules and polymers that exhibit elec-
troluminescence (EL) or have electron transporting properties have
been reported [1,2]. Especially, 2,5-diarylthiazolo[5,4-d]thiazoles
have been actively utilized for field-effect transistors [3], two-
photon-absorption (TPA) active materials as nonlinear optical
chromophores [4], electroluminescent polymer [5], etc [6].
However, thiazolothiazole derivatives have not been explored as
fluorescent chemosensors [7e14] for metal ions.
widespread use of aluminum in food additives and aluminum-
based pharmaceuticals often expose people to Al3þ. There are
a few fluorescent chemosensors have been reported for the
detection of Al3þ [24e29].
Herein, two new thiazolothiazole derivatives (1 and 2) were
synthesized, in which ether binding units were introduced (Fig. 1).
Photophysical and electrochemical properties of these new deriv-
atives were examined. In addition, compound 2 displayed selective
fluorescence “Off-On” change upon the addition of Cr3þ. On the
other hand, compound 1 bearing shorter ethylene oxide unit
showed large fluorescent enhancements with Cr3þ and Al3þ among
the metal ions examined.
Chromium (Cr3þ) ion is not only an essential nutrient for
humans, but also plays an important role in the metabolism of
carbohydrates, lipids, proteins, and nucleic acids [15]. The defi-
ciency of chromium is known to lead to a variety of disease,
including diabetes and cardiovascular disease [16]. At the mean
time, chromium is an environmental pollutant and its build-up
due to various industrial and agricultural activities is a matter
of concern [17]. In spite of the biological and environmental
2. Experimental
2.1. Materials and equipments
Unless otherwise noted, materials were obtained from
commercial suppliers and were used without further purification.
Flash chromatography was carried out on silica gel 60 (230e400
mesh). 1H NMR and 13C-NMR spectra were recorded using
250 MHz NMR or 500 MHz NMR. Compound 3 was synthesized
following the reported procedure [30].
* Corresponding authors. Department of Chemistry and Nano Science, Ewha
Womans University, Seoul 120-750, Republic of Korea. Tel.: þ82 2 3277 2400;
fax: þ82 2 3277 3419.
E-mail addresses: cmlee@ewha.ac.kr (C. Lee), jyoon@ewha.ac.kr (J. Yoon).
1
Contributed equally to this work.
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2012.02.005

424
J.Y. Jung et al. / Dyes and Pigments 94 (2012) 423e426
S
O
O
O
O
NH2
O
O
O
H2N
O
O
O
N
S
N
S
N
S
N
N
S
S
DMF, reflux
34 %
H
S
S
N
O
4
1
O
O
2
O
1
O
O
O
O
O
S
S
N
N
S
O
O
O
NH2
O
H2N
N
S
N
O
S
3
DMF, reflux
42 %
S
H
Fig. 1. Structures of the thiazolothiazole derivatives 1e3.
5
O
2
O
2.2. Synthesis
O
2.2.1. Compound 1
Scheme 1. Synthesis of the thiazolothiazole derivatives 1e2.
Procedure A. 2-(2-Methoxyethoxy)benzaldehyde (0.75 g,
4.16 mmol) was added to dithiooxamide (0.25 g, 2.08 mmol) in
20 mL DMF. The reaction was refluxed for 20 h, then the solvent was
evaporated. The crude product was purified by column chroma-
tography using ethyl acetate-hexane (2:1) as eluent to give
compound 1 as yellow powder (0.31 g, 34%). Mp: 203 ꢀC; 1H NMR
probe stock solution into a test tube, adding an appropriate aliquot
of each metal stock, and diluting the solution to 3 mL with CH3CN
and CHCl3. The absorption and fluorescence properties of 1 were
tested in CH3CN:CHCl3 (4:1, v/v) and those of 2 were examined in
CH3CN.
(CDCl3, 250 MHz)
d
8.40 (dd,1H, J ¼ 9.0 Hz and 2.0 Hz), 7.33 (m, 1H),
7.05 (dd, 1H, J ¼ 17.3 Hz and 1.2 Hz), 7.00 (t, 1H, J ¼ 11.6 Hz), 4.31 (t,
2H, J ¼ 5.3 Hz), 3.92 (t, 2H, J ¼ 5.75 Hz), 3.58 (s, 3H); 13C NMR
3. Results and discussion
(CDCl3,125 MHz) d 163.7,155.9,152.1,131.1,128.7,123.3, 121.6,112.6,
71.1, 68.7, 59.6; HRMS (FAB) C22H23O4N2S2 ¼ 443.1099, found
3.1. Synthesis
443.1104 (M þ H)þ.
The synthetic routes of new thiazolothiazole derivatives 1 and 2
are shown in Scheme 1. The corresponding aldehyde, such as 2-(2-
methoxyethoxy)benzaldehyde (for 1) was added to dithiooxamide
in 20 mL DMF, which was then refluxed for 20 h. After the solvent
was evaporated, the crude product was purified by column chro-
matography using ethyl acetate-hexane (2:1) as eluent to give
compound 1 as yellow powder in 34% yield. For compound 2, the
corresponding aldehyde 2-[2-(2-methoxyethoxy)ethoxy]benzal-
dehyde 6, was synthesized following the reported procedure [24].
In a similar way, the corresponding aldehyde 6 was reacted with
dithiooxamide to give 2 in 42% yield. Compounds 1 and 2 were fully
characterized by 1H NMR, 13C NMR (see supporting information)
and high resolution FAB mass spectroscopy.
2.2.2. Compound 2
Procedure A was applied to 2-[2-(2-methoxyethoxy)ethoxy]
benzaldehyde 5 (1.47 g, 6.57 mmol) and dithiooxamide (0.15 g,
1.13 mmol) in 20 mL DMF to give compound 2 as yellow powder
(1.46 g, 42%). Mp: 134 ꢀC; 1H NMR (CDCl3, 250 MHz)
d 8.38 (dd, 1H,
J ¼ 9.0 Hz and 2.0 Hz), 7.35 (t, 1H, J ¼ 8.9 Hz), 7.04 (m, 2H), 4.41 (t,
2H, J ¼ 5.3 Hz) 3.84 (t, 2H, J ¼ 5.75 Hz), 3.83 (m, 2H) 3.63 (m, 2H)
1.49 (s, 3H); 13C NMR (CDCl3, 125 MHz)
d 163.7, 155.6, 152.2, 131.1,
128.7, 123.3, 121.6, 112.6, 72.2, 71.1, 69.7, 68.7, 59.3; HRMS (FAB)
C26H21O6N2S2 ¼ 531.1624, found 531.1630 (M þ H)þ.
2.3. Electrochemical study
Cyclic voltammetry (CV) experiments were carried out in the
appropriate solutions containing electroactive compounds and
0.1 M tetrabutylammonium perchlorates at room temperature using
a BAS 100B electrochemical analyzer in a glove-box. A Pt disk (dia.
1.6 mm) and Pt wire, and Ag|AgNO3 (0.1 M) were used as working,
counter, and reference electrodes, respectively. All the potential
values were calibrated versus the ferrocene/ferrocenium (Fc|Fcþ)
redox couple and then corrected to the saturated calomel electrode
(SCE) on the basis of an Fc|Fcþ redox potential of 0.28 V and 0.16 V
versus SCE in CH3CN/DMSO mixed solution and CH2Cl2, respectively.
The potential scan rate was 0.1 V/s.
3.2. Quantum efficiencies and CV data
The absorption and fluorescence spectra of compounds 1 and 2
were examined in DMSO and CH2Cl2 solutions at room tempera-
ture. The relative quantum efficiencies were determined using 9,10-
Table 1
Cyclic voltammetric data for 1e3.a,b
Epa/Epc
Ered
Eg (eV)
lmax (nm)f
1240/lmax (eV)
Eox
1
2
3
ꢁ1.76/ꢁ1.83a
ꢁ1.76/ꢁ1.83a
ꢁ1.60/ꢁ1.67a
.c/ꢁ1.96b
.c/ꢁ1.96b
.c/ꢁ1.83b
3.13d
3.13d
3.43e
390
390
371
3.18
3.18
3.33
2.4. UV and fluorescent study with metal ions
a
b
c
d
e
f
3þ
Stock solutions (0.01 M) of the perchlorate salts of Al3þ, Cr
,
,
CVs were recorded in CH3CN:DMSO (1:1)/0.1 M TBAP.
CVs were recorded in CH2Cl2/0.1 M TBAP.
It is hard to measure the value because of lack of reversibility.
Calculated from the CVs in CH3CN:DMSO (1:1)/0.1 M TBAP.
Calculated from the CVs in CH2Cl2/0.1 M TBAP.
Measured in CH2Cl2.
Agþ, Fe2þ, Ca2þ, Cd2þ, Co2þ, Cu2þ, Hg2þ, Kþ, Liþ, Csþ, Mg2þ, Mn2þ
Naþ, Ni2þ, Pb2þ, Zn2þ ions in CH3CN were prepared. Stock solutions
of 1 and 2 (0.1 mM) were also prepared in CH3CN and CHCl3,
respectively. Test solutions were prepared by placing 300 mL of the

J.Y. Jung et al. / Dyes and Pigments 94 (2012) 423e426
425
Fig. 4. Fluorescent change of 2 (1 ꢂ 10ꢁ5 M, CH3CN) upon adding of 0e30 equiv. of
Cr3þ ion, excitation at 420 nm (Inset: Job plot for 2 with Cr3þ ion. The line show 1:1
stoichiometry.).
Fig. 2. Fluorescent spectra (excitation at 420 nm) of 1 (1 ꢂ 10ꢁ5 M) in CH3CN:CHCl3
(4:1, v/v) upon addition of 5 equiv. of metal ions.
diphenylanthracene in degassed hexane (
F
¼ 0.96) as a reference
3.3. UV absorption and fluorescence study with metal ions
compound. In DMSO, the relative quantum efficiencies and
maximum wavelength for fluorescence were 33% (lmax ¼ 423 nm)
and 23% (lmax ¼ 423 nm) for compound 1 and 2, respectively. In
CH2Cl2, those were observed as 38% (lmax ¼ 428 nm) and 43%
The absorption and fluorescence properties of 2 were tested in
CH3CN. On the other hand, compound
1 was examined in
CH3CN:CHCl3 (4:1, v/v) due to the solubility problem. Compound 1
and 2 showed major absorption bands at 368 nm (Fig. S1) and at
(lmax ¼ 428 nm) for compound 1 and 2, respectively. Quantum
367 nm (Fig. S2), respectively. Perchlorate salts of Al3þ, Cr , Agþ,
3þ
efficiencies of these derivatives were in the range of 23%e43%.
The electrochemical properties of compounds 1-3 by CV
measurements are summarized in Table 1, where the Eox and Ered
values are known to be related to the HOMO and LUMO energy
levels, respectively [31,32]. CVs were carried out both in CH3CN/
DMSO mixture and CH2Cl2 due to the potential window and solu-
bility where reduction was well-defined in the former solvent
while oxidation in the latter one as shown in Figs. S5 and S6. The CV
of 3 and that of 1 resemble each other bearing the same electro-
active structural body except ether linkage. It is notable that
electron-donating properties of ether substituents in 1 and 2,
where reduction and oxidation waves shifted to the negative
potential by 0.16 V (recorded in CH3CN/DMSO mixture) and 0.30 V
(recorded in CH2Cl2), respectively. The reversibility of the oxidation
wave of 3 was also improved by electron-donating substituent of 1
due to stabilization of radical cation of 1 (Fig. S6). Overall, the band
gap values from CV reveal good agreement with those from
absorption wavelength within 0.1 eV.
Fe2þ, Ca2þ, Cd2þ, Co2þ, Cu2þ, Hg2þ, Kþ, Liþ, Csþ, Mg2þ, Mn2þ, Naþ,
Ni2þ, Pb2þ, Zn2þ were used for the metal ion binding study. Cr3þ
and Al3þ induced internal charge transfer peaks around 420 nm in
UV spectra of 1 and 2 as shown in Figs. S1 and S2. The fluorescence
spectra were obtained by exciting thiazole derivatives 1 and 2 at
420 nm. When 5 equiv. of metal ions were added, 1 showed large
fluorescence enhancements with Cr3þ and Al3þ while Fe2þ, Cu2þ
and Pb2þ induced relatively smaller enhancements (Fig. 2). On the
contrary, compound 2 showed a selective “Off-On” fluorescence
change (w200 fold) with Cr3þ among the various metal ions
examined even though there was a small fluorescence enhance-
ment with Al3þ (Fig. 3).
The fluorescence titrations of 1 with Cr3þ and Al3þ are explained
in Figs. S11 and S12. The association constants (Ka) of 1 with Cr3þ
and Al3þ were calculated as 6.99 ꢂ 10ꢁ4 Mꢁ1 and 9.29 ꢂ 10ꢁ4 Mꢁ1
,
Fig. 3. Fluorescent spectra (excitation at 420 nm) of 2 (1 ꢂ 10ꢁ5 M) in CH3CN upon
Fig. 5. Fluorescent change of 2 (1 ꢂ 10ꢁ5 M, CH3CN) upon adding of 0e30 equiv. of
addition of 5 equiv. of metal ions.
Cr3þ ion, excitation at 370 nm.

426
J.Y. Jung et al. / Dyes and Pigments 94 (2012) 423e426
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In current study, we synthesized two new thiazolothiazole
derivatives (1 and 2), in which ether binding units were introduced.
Photophysical and electrochemical properties of these new deriv-
atives were examined. In addition, compound 2 displayed a selec-
tive fluorescence “Off-On” change upon the addition of Cr3þ. On the
other hand, compound 1 bearing shorter ethylene oxide unit
showed large fluorescent enhancements with Cr3þ and Al3þ among
the metal ions examined. As far as we are aware of, these are the
first examples of thiazolothiazole based fluorescent chemosensors
for metal ions.
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Acknowledgements
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This work was supported by National Research Foundation of
Korea Grant funded by the Korean Government (2011-0020450,
2011-0001334) and WCU program (R31-2008-000-10010-0). This
work was also supported by the Ewha Global Top 5 Grant 2011 of
Ewha Womans University. Mass spectral data were obtained from
the Korea Basic Science Institute on a Jeol JMS 700 high resolution
mass spectrometer.
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3759e68.
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.dyepig.2012.02.005.
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