A novel kind of dimmer (excimer)-induced-AIE compound 2- phenylisothiazolo[5,4-b]pyridin-3(2H)-one as high selective bisulfite anion probe

Article abstract of DOI:10.1016/j.tet.2013.07.038

An interesting dimmer (excimer)-induced-AIE characteristic of 2-phenylisothiazolo[5,4-b]pyridin-3(2H)-one was observed. By using a ring-opening reaction, we developed a novel fluorescent probe based on sub-micron particles of 2-phenylisothiazolo[5,4-b]pyridin-3(2H)-one in water.

Full text of DOI:10.1016/j.tet.2013.07.038

Tetrahedron 69 (2013) 8250e8254
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A novel kind of dimmer (excimer)-induced-AIE compound 2-
phenylisothiazolo[5,4-b]pyridin-3(2H)-one as high selective bisulfite
anion probe
,
b
a,
Bingchuan Yang a, Xiaoyi Niu a, Zixiao Huang a, Cuihua Zhao a , Yang Liu , Chen Ma
*
*
a School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China
b State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
An interesting dimmer (excimer)-induced-AIE characteristic of 2-phenylisothiazolo[5,4-b]pyridin-3(2H)-
one was observed. By using a ring-opening reaction, we developed a novel fluorescent probe based on
sub-micron particles of 2-phenylisothiazolo[5,4-b]pyridin-3(2H)-one in water.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 11 March 2013
Received in revised form 4 July 2013
Accepted 8 July 2013
Available online 17 July 2013
Keywords:
2-Phenylisothiazolo[5,4-b]pyridin-3(2H)-
one
AIE
Bisulfite anion
Probe
X-ray crystallographic analysis
1. Introduction
Aggregation-Induce Emission Enhancement (AIEE)8 characteristic. It
was non-emissive in good solvent (THF), but in poor solvent (water/
Since 2001, a series of aggregation-induced emission (AIE) ma-
terials were found, such as Hexaphenylsilole (HPS),1 1,1,2,2-
Tetraphenylethene (TPE),2 1-methyl-pentaphenyl silole (MPPS)3
and so on. Unlike normal fluorescence materials, these com-
pounds have higher emission intensity in high concentration so-
lution and solid state compared with that in the dilute solution.
After formation of aggregation, the fluorescence emission is in-
tensified instead of quenched. These special materials show the
new synthetic direction of fluorescence materials. And by using
their aggregation-induced emission characteristics, new kinds of
biological sensors have been designed, such as BSA probe, DNA
probe,4 and CO2 probe.5
Isothiazolidin-3-one is a common bioactive skeleton. It is an in-
hibitor for cartilage breakdown6 and HATs (histone acetyltransfer-
ase).7 A lot of research about the bioactivity of isothiazolidin-3-one
has been done, but its photometric characteristics remain un-
explored. Recently, during the synthesis of benzothiazepine
compounds, we unexpectedly found that one of our intermediate
products 2-phenylisothiazolo[5,4-b]pyridin-3(2H)-ones had potential
THF) its emission gradually became intensified. Based on this unique
characteristic and a ring-opening reaction, we developed a novel fast
fluorescent sensor for bisulfite anion.
Bisulfite is usually used as preservative for foods, beverages, and
pharmaceutical products. It acts like antioxidant, antimicrobial
agent and enzyme inhibitor during production and storage.9e12 But
recent research discovered that certain concentration levels of bi-
sulfite can cause asthmatic attacks, oculonasal symptoms, and al-
lergic reaction in some sulfite-sensitive individuals.13 So the levels
of bisulfite and sulfur dioxide in food and medicine are rigorously
limited in many countries. In China, the levels of bisulfite in wine
and beer are confined to 0.05 mg kgꢀ1 (calculated as SO2).14
Therefore, it is very important to develop a quick, low cost, sensi-
tive and selective method for bisulfite determination.
To detect sulfite in foods, the Monier-Williams method15 is still
the official method. Although many other analytical techniques are
available for the determination of bisulfite, such as spectrofluo-
rometry,16 electro chemical methods,17 chromatography,18 enzy-
matic techniques,19 sulfite biosensors,20 and ion chromatography21
with indirect UV detection method, most of which either are not
selective enough, or need tedious pretreatment and complicated
instruments. So it is still a challenge to find an easy and quick de-
termination method. Herein, we reported the design and synthesis
* Corresponding authors. Tel.: þ86 531 8836 3756; fax: þ86 531 8856 4464 (C.Z.);
tel.: þ86 531 8836 4464; fax: þ86 531 8856 4464 (C.M.); e-mail addresses:
chzhao@sdu.edu.cn (C. Zhao), chenma@sdu.edu.cn (C. Ma).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.07.038

B. Yang et al. / Tetrahedron 69 (2013) 8250e8254
8251
of 2-phenylisothiazolo[5,4-b]pyridin-3(2H)-one, which can act as
a high sensitive and selective sensor for rapid and efficient de-
tection of bisulfite in water.
2. Results and discussion
2.1. Synthesis of isothiazolidin-3-one derivatives and photo-
physical studies
The synthesis has been published by Monge,22 but we changed
it into a one-pot reaction. To investigate the compound’s AIE
characteristic formation mechanism,23e25 two important electronic
effects of the compound 1a were tested. First, we tested the
Intramolecular Charge Transfer (ICT) effect of the compound 1a.26
Second, the assembling structure of the molecule in poor solvent
(THF/water) was investigated.
Compounds (1aed) were synthesized to identify the ICT effect
in the molecule (Scheme 1). The fluorescence microscope images
(ISO 200) of these compounds are shown in Fig.1. The configuration
of 1a was determined by X-ray crystallographic analysis (Fig. 2).
After electron-donating group was introduced to the molecule, the
emission was bathochromic-shifted. When electron-withdrawing
group was added, the emission was hypsochromic-shifted. When
we changed the ring from pyridine to benzene, the pushepull
intramolecular electron effect was ruined, and the luminescence
apparently reduced (Fig. 3).
Fig. 2. X-ray structure of compound 1a.
1000
800
600
400
200
0
1a
1b
1c
1d
350
400
450
500
550
600
650
Wavelength (nm)
Fig. 3. Fluorescence emission spectra of 1aed (10 M) in THF/water (1/99, v/v).
m
Scheme 1. Synthesis and absolute quantum yields determined by a calibrated in-
tegrating sphere system of fused isothiazolidin-3-ones 1.
Fig. 4. Ball-and-Stick model of 1a and HOMO/LUMO imagines of 1a calculated by
Gaussian 03 program using the B3LYP method with the 6-31G (d) basis set.
energy was wasted in energy-consuming and non-radiative decay
pathways were suppressed, so luminescence became stronger.
The AIE characteristics of compound 1a were investigated in
THF/water (from 100/0 to 1/99, v/v) shown in Figs. 5 and 6. In pure
THF, the luminescence was so weak that it was even undetected by
the naked eyes. However as the water fraction rose to 99%, the
fluorescence emission became very strong. The fluorescence in-
tensity increased by 225 times compared with that in pure THF.
It was because that high percentage of poor solvent in the so-
lution made the molecules aggregate into sub-micron particles.
After sub-micron particles were formed, the emission progressively
intensified.
Fig. 1. Fluorescence microscope images (ISO 200) of compounds 1aed.
Meanwhile, after molecule’s ring changed from pyridine to
benzene, the formation of the dimmer became more difficult. There
was another important reason that 1a showed better fluorescence
than 1d. As we can see in Fig. 4, two molecules formed a dimmer via
intermolecular N/S and N/N bonds in the crystal. When the
dimmers were excited, they would turn into excimers without ar-
rangement changes, and when the excimers returned to ground
state, no repulsive interactions generated either. As a result, no
The sub-micron particles of compound 1a in THF/water solution
(1/99, v/v) were graphed by polarized light microscope and tested
by non-invasive back-scatter (NIBS, Fig. 7). The size of sub-micron
particles was measured as about 266.7 nm, and crystal anisotropy
was observed significantly, the colour of sub-micron particles
changed from red to green. This proved that molecules formed
dimmer and then grew into microcrystal after aggregation. It is just
the same as what happened in the solid.

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B. Yang et al. / Tetrahedron 69 (2013) 8250e8254
7000
6000
5000
4000
3000
2000
1000
0
fw (vol%)
0
10
30
50
70
80
90
95
99
350
400
450
500
550
600
650
700
Wavelength/nm
Fig. 8. 1H NMR spectral change of probe 1a and the product of 1a with bisulfate.
After the conjugated
chemical shifts of the benzene protons were observed. The pyridine
and benzene protons at around 8.40, 7.44, 7.36 were dramatically
shifted to 7.72, 7.15, 7.00 (Fig. 8) and the active hydrogen signal
was also observed at 11.20. The intermediate was also tested by
p-system was destroyed, significant
d
Fig. 5. Emission spectra (excitation at 350 nm) and fluorescent images of 1a in THF/
water mixtures with different water fractions (fw).
d
d
mass spectrometry. The intermediate has a [(MþH)þ] of 231.0605
m/z (Fig. S26) while the probe has a [(MþH)þ] of 229.0425 m/z
(Fig. S16). According to the experimental data above, the possible
reaction mechanism is a ring-opening reaction of 1a with bisulfite
anion.
250
200
150
100
50
2.3. pH dependence
Firstly, the effect of pH on the probe was tested from 0.17 to 9.08
in THF/water (1/99, v/v). Different pH was obtained by mixing 1 M
hydrochloric acid and 0.1 M NaOH solution at specific volume ratios
buffered by 20 mM HEPES. As we can see from Fig. 9, the fluores-
cence was relatively stable when pH was between 7.00 and 9.08, and
the emission raised slightly after solution became acidic. When pH
was less than 2.27, the emission decreased quickly, and the emission
at pH 2.27 was about five times stronger than that of at pH 0.17. At
last we chose a relatively stable pH 7.20 for our analytical system.
0
0
20
40
60
80
100
Water fraction
Fig. 6. I/I0 of 1a in THF/water mixtures with different water fractions (fw).
4000
3500
3000
2500
2000
1500
1000
500
Fig. 7. Non-Invasive Back-scatter (NIBS) result of 1a (10 mM) in THF/water (1/99, v/v)
buffered by 20 mM HEPES at pH 7.0.
0
0
2
4
6
8
10
PH
2.2. Mechanism study
Fig. 9. Effect of pH on the fluorescent intensity of the probe.
After the test of AIE characteristics, we moved on to explore the
uses of this type of molecules as HSO3 probe based on the ring-
ꢀ
2.4. Selective detection over other anions
opening reaction utilizing 1a as a representative compound. The
reaction was verified by 1H NMR in CDCl3 with tetramethylsilane
(TMS) as internal standard. The chemical shift changes of hydro-
gens marked by squares were shown in Fig. 8.
ꢀ
Secondly, the selectivity of the analytical system for HSO3 was
compared to other anions, such as Fꢀ, Clꢀ, Brꢀ, Iꢀ, ClO3ꢀ, ClO4
,
ꢀ

B. Yang et al. / Tetrahedron 69 (2013) 8250e8254
8253
ꢀ
NO3ꢀ, SO42ꢀ, CO32ꢀ, PO43ꢀ, ꢀAcꢀ, HCO3ꢀ, HSO4 shown in Fig. 10.
We can see that only HSO3 can cause the decrease of probe’s
emission. All the tests were investigated in THF/water (1/99, v/v)
solution with 1ꢁ10ꢀ4 M probe and 20 equiv of anions. The ana-
ꢀ
lytical system showed highly selectivity for HSO3
.
3500
3000
2500
2000
-
-
Probe,F-,Cl-,Br-,I-,ClO3 ,ClO4 ,
-
3-
NO3 ,SO42-,CO32-,PO4
,
1500
1000
500
0
Ac-,HCO3 ,HSO4
-
-
Fig. 12. Fluorescence emission (excitation at 350 nm) of 1a (10
HSO3 (0e1.3 equiv) in THF/water solution (1/999, v/v) buffered by 20 mM HEPES at
pH 7.2.
m
M) titrated with
ꢀ
-
HSO3
350
400
450
500
550
600
650
Wavelength/nm
Fig. 10. Fluorescence emission spectra (excitation at 350 nm) of 100
m
M 1a in THF/
ꢀ
water (v/v, 1/99) mixtures buffered by 20 mM HEPES at pH 7.20 with 20 equivꢀHSO3
,
Fꢀ, Clꢀ, Brꢀ, Iꢀ, ClO3ꢀ, ClO4ꢀ, NO3ꢀ, SO42ꢀ, CO32ꢀ, PO43ꢀ, Acꢀ, HCO3ꢀ, HSO4
.
2.5. Kinetics characteristic
Thirdly, the fluorescence kinetics characteristic was stꢀudied and
the results are shown in Fig. 11. After adding the HSO3 into the
solution, the fluorescence of the solution quenched in 10 s. Com-
pared to the other determination systems for bisulfite anion, the
response speed is excellent.
800
700
600
500
400
300
200
Fig. 13. Calibration graph for bisulfite anion. Working conditions: pH 7.20, reaction
time 10 s.
3. Conclusions
In summary, we have investigated AIE mechanism of 2-
phenylisothiazolo[5,4-b]pyridin-3(2H)-one, and have verified the
ICT effect has great influence on the luminescence. Through crystal
analysis and theoretical calculation, we finally confirmed the
dimmer (excimer)-induced-AIE mechanism. By using this AIE
compound, we developed a high sensitive and selective sub-micron
particle bisulfite anion probe. Because of the high response speed
and simplicity for analysis, we believe this probe may be applied in
a variety of real samples in the future.
0
50 100 150 200 250 300 350 400 450 500 550 600 650
Time (s)
Fig. 11. Fluorescence kinetics graph (excitation at 350 nm) of 1a (10
with HSO3 (1 equiv) in THF/water solution (1/999, v/v) buffered by 20 mM HEPES at
pH 7.2.
mM) titrated
4. Experimental section
4.1. General
ꢀ
2.6. Work curve
All chemicals purchased were used without purification. THF of
analytical grade and de-ionized water were used throughout the
experiment as solvents. 1H NMR spectra were recorded on
a Bruker Avance 400 (400 MHz) or 300 (300 MHz) spectrometer,
using CDCl3 as solvent and tetramethylsilane (TMS) as internal
standard. 13C NMR spectra were recorded on a Bruker Avance
100 (100 MHz) or 75 (75 MHz) spectrometer, using CDCl3 as
Figs 12 and 13 show titration curve and linear correlation for
ꢀ
HSO3 at the concentration between 0.5 and 6.0
mM, R¼0.99573
(n¼12). According to IUPAC, the detection limit was calculated as
0.39 M and a relative standard deviation of 0.9% was measured for
5.0 M of bisulfite (Fig. 13).
m
m

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B. Yang et al. / Tetrahedron 69 (2013) 8250e8254
solvent and tetramethylsilane (TMS) as internal standard. Melting
points were determined on an XD-4 digital micro melting point
apparatus. HEPES buffer solutions (pH 7.2) were prepared using
20 mM HEPES and the proper amount of aqueous sodium hy-
droxide using a pH meter. HRMS spectra were determined on a Q-
TOF6510 spectrograph (Agilent). Single crystal X-ray diffraction
was made on a Rigaku RAXIS-SPIDER IP diffractometer at 50 kV
120.1. HRMS calcd for C13H9N2OS[(MþH)þ], 228.0438; found,
228.0472.
Acknowledgements
We are grateful to National Natural Science Foundation of China
(Nos. 21172131, 21272141, 21072117) for financial support of this
research.
and 20 mA and data collection was performed at 293 K by using
ꢀ
graphite-monochromated Mo-K
a
radiation (
l
¼0.71073 A). The
nanoparticle diameter was measured by the Zetasizer 2000
(Marven, UK). Fluorescent measurements were collected on
a Hitachi F-4500 luminescence spectrophotometer with a 150 W
Xe lamp. Calculations were conducted by using the Gaussian 03
program.
Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.07.038.
References and notes
4.2. General experimental procedure for the preparation of 2-
phenylisothiazolo[5,4-b]pyridin-3(2H)-one (1a)
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was refluxed for 2.5 h (oil bath). The mixture was evaporated in
vacuo, and the solvent and thionyl chloride were removed, yellow
solid was obtained. The yellow solid was dissolved by CH2Cl2
(50 mL), then aniline (1.86 g, 20 mmol) dissolved in 30 mL CH2Cl2
was added dropwise to the ice bath solution. The mixture was
stirred overnight, then H2O (100 mL) was added and the mixture
was filtered and extracted with CH2Cl2 (3ꢁ50 mL). The combined
organic layers were washed by chilled water (3ꢁ100 mL), dried by
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purified by flash chromatography on silica gel (hexane/
EtOAc¼5:1). Compound 1a was obtained as white plate crystals
(1.96 g, 43%).
4.2.1. 2-Phenylisothiazolo[5,4-b]pyridin-3(2H)-one
(1a). White
crystal, mp 137e138 ꢂC, yield 43%. 1H NMR (300 MHz, CDCl3)
d
8.81 (dd, 1H, J¼1.5, 4.8 Hz), 8.40 (d, 1H, J¼8.1 Hz), 7.70 (d, 2H,
J¼7.5 Hz), 7.50 (t, 2H, J¼7.8 Hz), 7.44 (t, 1H, J¼3.9 Hz). 13C NMR
(75 MHz, CDCl3)
d 162.5, 161.9, 154.0, 136.7, 135.3, 129.5, 127.5,
124.9, 121.0. HRMS calcd for C12H8N2OS [(MþH)þ], 229.0391;
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4.2.2. 2-(4-Methoxyphenyl)isothiazolo[5,4-b]
(1b). Yellow acicular crystal, yield 40%, mp 169e171 ꢂC. 1H
NMR (300 MHz, CDCl3)
pyridine-3(2H)-one
d
8.80 (d, 1H, J¼3.3 Hz), 8.34 (dd, 1H,
J¼1.2, 7.8 Hz), 7.58e7.53 (m, 2H), 7.40 (dd, 1H, J¼4.6, 7.8 Hz),
7.02e6.97 (m, 2H), 3.85 (s, 1H). 13C NMR (100 MHz, CDCl3)
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d
162.7, 162.0, 159.0, 153.9, 135.2, 129.0, 121.0, 119.6, 114.7, 55.6.
HRMS calcd for
259.0536.
C
13H10N2O2S [(MþH)þ], 259.0497; found,
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(1c). White acicular crystal, mp 188e190 ꢂC, yield 33%. 1H NMR
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(300 MHz, CDCl3)
7.8 Hz), 7.68e7.63 (m, 2H), 7.42 (dd, 1H, J¼4.8, 7.8), 7.21e7.16 (m,
2H). 13C NMR (100 MHz, CDCl3)
d
8.83 (dd, 1H, J¼1.2, 4.8 Hz), 8.36 (dd, 1H, J¼1.2,
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Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
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Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
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Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
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Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-
Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03,
Revision B.01; Gaussian: Pittsburgh, PA, 2003.
d
162.7 (d, JCeF¼12 Hz), 161.8, 160.3,
154.1, 135.4, 133.0, 132.4 (d, JCeF¼2.9 Hz), 127.1 (d, JCeF¼8.5 Hz),
121.1, 119.5, 116.5 (d, JCeF¼23 Hz). HRMS calcd for C12H7FN2OS
[(MþH)þ], 247.0297; found, 247.0334.
4.2.4. 2-Phenylbenzo[d]isothiazol-3(2H)-one (1d). White crystal,
yield 31%. 1H NMR (400 MHz, CDCl3)
d
8.11 (d, 1H, J¼7.8 Hz),
7.73e7.70 (m, 2H), 7.69e7.65 (m, 1H), 7.59 (d, 1H, J¼8.0 Hz),
7.52e7.43 (m, 3H), 7.32 (t, 1H, J¼7.4 Hz). 13C NMR (75 MHz, CDCl3)
d
164.1, 139.9, 137.3, 132.3, 129.4, 127.2, 127.0, 125.8, 124.9, 124.6,