Novel mercury sensor based on water soluble styrylindolium dye

Article abstract of DOI:10.1016/j.dyepig.2012.09.010

A novel water soluble Hg²⁺-selective chemosensor using a styrylindolium dye as both colorimetric and fluorometric reporting group has been synthesized and characterized. The chemosensor exhibits a specific Hg ²⁺ selectivity to discriminate between Hg²⁺ and chemically close ions by using a NO₂S₂ chelating unit as the ion binding site. Due to the Hg²⁺-induced intramolecular charge transfer, the chemosensor shows a visible colorimetric change from red to yellow, leading to potential production of both visual and fluorometric detection of Hg ²⁺ cation both in water and in aqueous ethanol solutions.

Full text of DOI:10.1016/j.dyepig.2012.09.010

Dyes and Pigments 96 (2013) 424e429
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Novel mercury sensor based on water soluble styrylindolium dye
,
a
a
,
,
*
Yuanyuan Li a, Fangfang Wei a, Yan Lu a , Song He , Liancheng Zhao b, Xianshun Zeng a
*
a Key Laboratory of Display Materials & Photoelectric Devices, Ministry of Education, School of Materials Science & Engineering, Tianjin University of Technology, Tianjin 300384,
China
b School of Materials Science and Engineering, Institute of Information Functional Materials& Devices, Harbin Institute of Technology, Harbin 150001, China
a r t i c l e i n f o
a b s t r a c t
A novel water soluble Hg2þ-selective chemosensor using a styrylindolium dye as both colorimetric and
fluorometric reporting group has been synthesized and characterized. The chemosensor exhibits
a specific Hg2þ selectivity to discriminate between Hg2þ and chemically close ions by using a NO2S2
chelating unit as the ion binding site. Due to the Hg2þ-induced intramolecular charge transfer, the
chemosensor shows a visible colorimetric change from red to yellow, leading to potential production of
both visual and fluorometric detection of Hg2þ cation both in water and in aqueous ethanol solutions.
Ó 2012 Elsevier Ltd. All rights reserved.
Article history:
Received 5 February 2012
Received in revised form
14 September 2012
Accepted 17 September 2012
Available online 26 September 2012
Keywords:
Styrylindolium
Dye
Sensor
Fluorescence
Mercury
Intramolecular charge transfer
1. Introduction
due to their excellent spectroscopic properties including high
molar extinction coefficient (ε w 104 Mꢀ1 cmꢀ1), reasonable fluo-
Chromo- and fluoro-ionophores combined by an organic dye as
a signaling unit and an ionophore as an ionic binding moiety within
a single molecule provide a basis for the development of supra-
molecular ionic devices. Many excellent ionic devices have been
developed for the detection of various ions based on different
signaling mechanisms, such as photo-induced electron transfer
(PET) [1e5], internal charge transfer (ICT) [6e13], fluorescence
resonance energy transfer (FRET) [14] and excimer [15,16].
Amongst these, the chemosensors which exhibit spectrum signal
changes along with an obvious color change which provide for
a rapid judgment for ion sensing, in particular, have received great
attention. Herein, we aim to develop a novel visual chemosensor for
Hg2þ. It was known that the electronic property of an ICT sensor
(e.g. UVevisible and fluorescent emission spectra) is very sensitive
to the presence of ions. The feature may facilitate the kind of che-
mosensors to detect targeted ions by direct visual observation.
Hemicyanine-based dyes have found applications in many fields,
such as the study of complex biological systems as molecular
probes and photosensitizers in dye-sensitized solar cells [17,18],
rescence quantum yield and the properties of significant spectral
signal changes under external environmental stimuli. By the careful
design of the ionic binding unit conjugated with the styryl dye,
some hemicyanine dye-based chemosensors have also been
developed by using ICT signaling mechanisms in recent years. For
example, styrylbenzothiazolium dye with a crown ether as binding
unit was developed for Mg2þ [19], Agþ, Hg2þ [20,21] and Ba2þ
sensing [22]. Boronic acid grafted styrylpyridinium dyes were used
as cyanide fluorogenic chemosensors [23]. Merocyanine forms of
spiropyran derivatives, such as the styrylindolium dye [24] and
styrylbenzothiazolium dye [25], were also developed as Cu2þ- and
Hg2þ-sensitive chemosensors, respectively.
The chemosensor based on para-N-substituted styrylindolium
dyes has potential application as a direct visual ion sensor due to
the obvious color change before and after the ion binding event. As
shown in Scheme 1, due to intramolecular charge transfer between
two nitrogen atoms within the chemosensor, the chemosensor
exhibited the absorption and the emission in long-wavelength
regions because of the equilibrium between the benzenoid form (A)
and the quinoid form (B) (Scheme 1) in the absence of ions. Upon
the addition of a metal ion, the fact that the lone pairs of the
substituted nitrogen atom located on the para-position of the styryl
dye participated in the ligation with the ion prevented the intra-
molecular charge transfer, which led to the absorption band of the
* Corresponding author. Tel.: þ86 22 6021 6748; fax: þ86 22 6021 5226.
E-mail address: xshzeng@tjut.edu.cn (X. Zeng).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.09.010

Y. Li et al. / Dyes and Pigments 96 (2013) 424e429
425
2-mercaptoethanol (3.2 mL) was added in one portion. The reaction
mixture was stirred for 12 h at 80 ꢂC under nitrogen atmosphere. The
reaction mixture was diluted with water (100 mL) and extracted
with dichloromethane (5 ꢁ 50 mL). The combined organic phasewas
dried over MgSO4. After filtration, the filtrate was condensed to
dryness. The residue was purified by column chromatography (SiO2,
CH2Cl2/EtOAc, 4:1, v/v). The product was obtained as a viscous oil
(0.924 g) in 28.0% yield; MS (EI) m/z [M þ H]þ: 329.11(Calcd); Found:
329.12; IR(KBr): 3369, 2930, 2872, 1660, 1592, 1522, 1400, 1343,
Scheme 1. The equilibrium between the benzenoid form (A) and the quinoid form (B).
.
1281, 1167, 1045, 1007, 926, 815 cmꢀ1 1H NMR (400 MHz, CDCl3,
chemosensor being shifted to shorter wavelength with an associ-
ated color change.
ppm)
d
9.70 (s, 1H), 7.71 (d, J ¼ 8.8 Hz, 2H), 6.68 (d, J ¼ 8.8 Hz, 2H),
In the present work, a novel styrylindolium dye-based, water
soluble, colorimetric and fluorometric chemosensor 3 was reported
3.78 (t, J ¼ 6 Hz, 4H), 3.64 (t, J ¼ 7.6 Hz, 4H), 2.78 (t, J ¼ 7.2 Hz, 8H),
2.75 (s, 2H); 13C NMR (100 MHz, CDCl3, ppm): 190.41, 151.61, 132.50,
125.89, 111.13, 61.41, 51.54, 35.44, 29.20; Anal. Calcd for
C15H23NO3S2$0.75H2O: C 52.53%, H 7.20%, N 4.08%; Found: C 52.60%,
H 7.37%, N 3.93%.
as Hg2þ-selective chemosensor. The chemosensor
3 involves
a styrylindolium dye moiety and a NS2O2 ionophore. The NS2O2
ionophore located on the para-position of the styryl dye possesses
strong affinity toward the heavy metal ions similar to pendant or
crown ether systems as reported in our previous work [26e28]. The
chemosensor 3 shows a remarkably high selectivity to discriminate
between Hg2þ and chemically close ions in conjunction with
a visible colorimetric change from red to light yellow, leading to
production of both visual and fluorometric detection of the Hg2þ
ion due to the ligation of the electron-donor aniline nitrogen with
the Hg2þ ion promoting a strong intramolecular charge transfer
(ICT).
2.4. Preparation of the chemosensor tetrafluoroborate of 2-{2-[4-
N,N’-bis(2-hydroxyethylthio-ethyl)aminophenyl]ethenyl}-1,3,3’-
trimethylindoline 3
To a 50 mL round-bottomed flask, was charged N-methyl-
2,3,3’-trimethylindolium iodide (0.51 g, 1.55 mmol), compound 2
(0.462 g, 1.54 mmol) and ethanol (8 mL). The reaction suspension
was flushed with nitrogen for 20 min, and then stirred for 14 h at
95 ꢂC. After cooling, the reaction mixture was condensed to
dryness. The residue was purified by column chromatography
(SiO2, CH2Cl2/EtOH, 10:1, v/v). The product was obtained as red
powder (0.824 g) in 87.7% yield. The product was dissolved in
ethanol (20 mL) and dichloromethane (20 mL), and then NaBF4
(1 g) was added. The reaction mixture was stirred at 50 ꢂC for 2.5 h
in dark. The solid inorganic salts were filtered out. The filtrate was
condensed to dryness. The residue was dried under vacuum to get
a red powder (0.883 g) in 99% yield. HRMS: m/z [M þ H]þ 485.2291
(Calcd); Found: 485.2295; IR(KBr), 3354, 3025, 2918, 2861, 1571,
1521, 1466, 1402, 1283, 1173, 1109, 1046, 980, 931, 786, 752,
2. Experimental
2.1. Materials and instruments
All solvents and reagents (analytical grade and spectroscopic
grade) were obtained commercially and used as received unless
otherwise mentioned. pH measurements were carried out on
a Mettler Toledo MP 220 pH meter. NMR spectra were recorded on
a Bruker spectrometer at 400 (1H NMR) MHz and 100 (13C NMR)
MHz. Chemical shifts (d values) were reported in ppm down field
from internal Me4Si (1H and 13C NMR). EI mass spectra were
recorded on a VG ZAB-HS mass spectrometer (VG, U. K.). High-
resolution mass spectra (HRMS) were acquired on an Agilent
6510 Q-TOF LC/MS instrument (Agilent Technologies, Palo Alto, CA)
equipped with an electrospray ionization (ESI) source. Elemental
analyses were performed on a Vanio-EL elemental analyzer (Ana-
lysensystem GmbH, Germany). UV absorption spectra were recor-
ded on a UV-3600 UVeVIS spectrophotometer (Shimadzu, Japan).
Fluorescence measurements were performed using an F-4600
fluorescence spectrophotometer (Hitachi, Japan) and a quartz cell
(1 cm ꢁ 1 cm). Melting points were recorded on a Boethius Block
apparatus and are uncorrected.
717 cmꢀ1
.
1H NMR (400 MHz, D2O, ppm): 8.15 (d, J ¼ 1.2 Hz, 2H),
8.06 (s, 1H), 7.49e7.32 (m, 5H), 6.91 (d, J ¼ 8.8 Hz, 2H), 4.16 (s, 3H),
3.86 (t, J ¼ 5.8 Hz, 4H), 3.75 (t, J ¼ 7.8 Hz, 4H), 2.91e2.78 (m, 8H),
1.79 (s, 6H); 13C NMR (100 MHz, DMSO, ppm): 179.74, 153.57,
151.99, 142.35, 141.71, 133.81, 128.45, 127.50, 122.47, 122.30, 113.44,
112.00, 105.48, 60.83, 50.47, 34.00, 32.92, 28.67, 25.90. Anal. Calcd
for C27H37BF4N2O2S2: C 56.64%, H 6.51%, N 4.89%; Found: C 56.88%,
H 6.43%, N 4.70%.
3. Results and discussion
3.1. The molecular design and preparation of the chemosensor 3
2.2. General spectroscopic methods
We present here a novel, highly sensitive fluorescent chemo-
sensor based on a styrylindolium dye (Scheme 2), which displayed
high Hg2þ selectivity both in water and ethanol/water mixture by
using the internal charge-transfer (ICT) mechanism. The chemo-
sensor 3 composed of an electron-donor aniline moiety and an
electron acceptor that in this case is a styrylindolium dye where the
electron-donor nitrogen atom, sulfur atoms and the hydroxyl
oxygen atoms provide the mercury-coordinating elements [29,30].
The chemosensor 3 was synthesized from 1 through two steps. As
shown in Scheme 1, aldehyde 2 was obtained by the reaction of 1
with sodium salt of 2-mercaptoethanol prepared in the presence of
Na2CO3 as a base. Then, 3 was readily prepared in 99% yield by the
condensation of N-methyl-2,3,3’-trimethylindolium iodide with 2
in ethanol under refluxed. The anion exchange was carried out by
refluxing the ethanol solutions 3 with excess NaBF4. The structure
of 3 was confirmed by MS, NMR and elemental analyses.
Metal ions and the chemosensor 3 were dissolved in deionized
water and ethanol to obtain 10 mM stock solutions, respectively.
Before spectroscopic measurements, the solution was freshly
prepared by diluting the high concentration the stock solution to
the required concentration. All of the experiments were conducted
at standard barometric pressure and room temperature.
2.3. Synthesis of 4-(N,N-(bis-(2-hydroxyethylthiaethyl))
benzaldehyde) 2
To a 250 mL reactor, was added sodium carbonate (2.1 g,
19.8 mmol), tetrahydrofuran (50 mL), water (20 mL) and4-(N,N-(bis-
(2-chloro-ethyl))benzaldehyde) 1 (2.46 g, 10 mmol). The reaction
mixture was flushed with nitrogen for 20 min, and then

426
Y. Li et al. / Dyes and Pigments 96 (2013) 424e429
Scheme 2. The preparation of chemosensor 3.
3.2. UVeVis evaluation of metal binding interaction
The chemosensor 3 is soluble in H2O or in aqueous ethanol.
Therefore, the sensing behavior was carried out both in water and
in ethanol/water systems for comparison the differences of the
binding ability of 3 toward metal ions in different solvent systems,
which may provide more valuable information for new receptor
design. Fig. 1 displays the absorption spectra of the chemosensor 3
in the presence and absence of a variety of environmentally and
biologically relevant metal ions. The UV/Vis spectra of 3 both in H2O
and in aqueous ethanol show the characteristic intense charge-
transfer band occurring in the long-wavelength region between
425 and 600 nm, which centered at 540 nm in water
(ε ¼ 8.7 ꢁ 104 Mꢀ1 cmꢀ1
) and 525 nm in EtOH/H2O (1:1, v/v)
(ε ¼ 7.8 ꢁ 104 Mꢀ1 cmꢀ1) (Fig. 1a and 1b). As shown in Fig. 1a and
1b, upon addition 50 equivalents of Hg2þ, the absorbance band
over 500 nm vanished drastically, while the one around 400 nm
increased significantly. There was over a 30-fold decrease in
absorbance at ca. 530 nm and with a large enhancement factor
(over 15-fold) of absorbance at ca. 400 nm upon the addition of 50
equivalents of Hg2þ. This interesting feature revealed that 3 can
serve as selective visual chemosensor for Hg2þ (Fig. S1). Upon
Fig. 1. UVevis responses of chemosensor 3 (10 mM) upon the addition of the nitrate
salts (50.0 equiv) of Naþ, Kþ, NH4þ, Mg2þ, Ca2þ, Pb2þ, Hg2þ, Co2þ, Cd2þ, Zn2þ, Ni2þ, Cu2þ
Cr3þ, Fe3þ and Agþ (a) in ethanol/H2O (1:1, v/v) and (b) in H2O.
,
406 nm in aqueous ethanol and 400 nm in water increased signif-
icantly. Meanwhile, the isosbestic points at 466 nm in EtOH/H2O
(1:1, v/v) and 455 nm in H2O were observed indicated the forma-
tion of a new complex between 3 and Hg2þ. The changes of the
absorbance at ca. 530 nm and at ca. 400 nm with the increase of
[Hg2þ] were shown in the inset of Fig. 2a and 2b. It is important to
note that a 1:1 stoichiometry for the 3ꢃHg2þ complex was
confirmed by Job’s plot analysis [32], where the decrease of the
absorbance at 525 nm was plotted against mole fractions of 3 under
the conditions of a constant total concentration of [3] þ [Hg2þ]. As
such, the concentration of the 3ꢃHg2þ complex approached
a maximum when the molar fraction of [3]/[Hg2þ] was about 1
addition the other metal ions such as Kþ, Naþ, NH4þ, Al3þ, Co2þ, Fe3þ
,
Pb2þ, Cu2þ, Zn2þ, Cd2þ, Ni2þ, Ca2þ, Mg2þ, no significant changes in
the UV spectra were observed both in H2O and in aqueous ethanol
(Fig. 1), except for Agþ which displays a slight decrease of the
absorbance at 540 nm. The large changes in the spectrum by the
addition of Hg2þ implied that the electron-donor aniline nitrogen
participated the ligation with the Hg2þ ion which promoted intra-
molecular charge-transfer (ICT) process occurred as shown in
Scheme 3. The unique absorption change by the addition of Hg2þ
implied that the chemosensor 3 was efficiently binding with Hg2þ
selectively. Normally, free Hg2þ only exists in strong acidic media
(pH < 2), while at pH > 2, Hg2þ usually exists in the form of
Hg(OH)þ[31]. Therefore, the high selectivity can be rationalized
that the Hg(OH)þ was not only selectively entrapped by the NS2O2
chelating unit but also further stabilized by the formation of
intramolecular OeH$$O hydrogen bonds as shown in Scheme 3.
To obtain further insight into the binding of Hg2þ with 3, the
absorption spectra of 3 upon titration with Hg2þ were recorded in
H2O (Fig. 2a). For comparison the binding ability of 3 with Hg2þ, the
absorption spectra of 3 upon titration with Hg2þ were also recorded
in aqueous ethanol (ethanol/water, 1:1, v/v) solutions (Fig. 2b).
With the addition of Hg2þ, the absorbance at 540 nm in aqueous
ethanol and 525 nm in water decreased sharply, while the band at
Scheme 3. The equilibrium between the benzenoid form and the quinoid form of 3
and the coordination model of 3 and Hg2þ
.

Y. Li et al. / Dyes and Pigments 96 (2013) 424e429
427
Fig. 3. Fluorescence spectra of
3
(10
m
M) upon the addition of the nitrate salts
(10 equiv.) of Naþ, Kþ, NHþ4 , Agþ, Mg2þ, Ca2þ, Pb2þ, Hg2þ, Co2þ, Cd2þ, Zn2þ, Ni2þ, Cu2þ
,
Cr3þ, Fe3þ, and Al3þ in H2O (lex ¼ 520 nm).
Fig. 2. Absorbance spectra of 3 (10 mM) (a) in H2O and (b) in EtOH/H2O (1:1, v/v) in the
presence of different amounts of Hg2þ. (a) [Hg2þ]/[3]: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18 in EtOH/H2O (1:1, v/v), Inset: the changes of the absorbance at
540 nm and absorbance at 406 nm as a function of Hg2þ concentration. (b) [Hg2þ]/[3]:
0, 1, 2, 3, 4, 6, 8, 10, 14, 18, 23, 28, 33, 38 in H2O, Inset: the changes of the absorbance at
525 nm and absorbance at 400 nm as a function of Hg2þ concentration.
(Fig. S2). From the changes in Hg2þ-dependent absorption inten-
sity, the detection limit was estimated to be 1.5 ꢁ10ꢀ7 M in water
(Fig. S3).
3.3. Metal ion binding studies by fluorescence titration
Subsequently, the nitrate salts of Kþ, Naþ, NH4þ, Al3þ, Co2þ, Fe3þ
,
Pb2þ, Agþ, Cu2þ, Zn2þ, Cd2þ, Ni2þ, Ca2þ, Mg2þ and Hg2þ ions were
used to evaluate the metal ion binding property and selectivity of
the chemosensor 3 (10
shown in Fig. 3, an emission band centered at 590 nm of the free
chemosensor 3 (10 M) was observed. Upon the addition of 10
equivalents of Naþ, Kþ, NH4þ, Mg2þ, Ca2þ, Pb2þ, Co2þ, Cd2þ, Zn2þ
mM) by fluorescence spectra in H2O. As
m
,
Ni2þ, Cr3þ, Fe3þ, and Al3þ, no obvious effect on the fluorescence
emissions were observed, whereas Agþ responded with weak
decrease in the fluorescent intensity. In contrast, the addition of
Hg2þ resulted in a significant diminution of the emission intensity
at 590 nm. The fact that 3 showed a strong fluorescence diminution
only with Hg2þ among the various metal ions examined indicated
that 3 displayed a high Hg2þ selectivity. The fluorescence spectra
were obtained by excitation of the hemicyanine fluorophore at
520 nm.
Fig. 4. Fluorescent titration spectra. (a)
3
(10
m
M) in the presence of different
concentrations of Hg2þ in water, [Hg2þ] ¼ 0, 6, 16, 21, 26, 31, 36, 41, 46, 51, 56, 61, 71, 81,
91, 101, 121, 151, 201, 251 equivalents. Inset: Fluorescent intensity Fi as a function of
Hg2þ concentration. lex ¼ 530 nm, (b) 3 (10
mM) in the presence of different concen-
trations of Hg2þ in ethanol/water (1:1, v/v), [Hg2þ] ¼ 0, 30, 45, 55, 65, 75, 90, 100, 110,
120, 130, 140, 150, 170, 200, 250, 300, 350, 400 equivalents. Inset: Fluorescent intensity
(Fi) as a function of Hg2þ concentration. lex ¼ 530 nm.

428
Y. Li et al. / Dyes and Pigments 96 (2013) 424e429
Fig. 5. (I0 ꢀ I)/(I0) ratio of fluorescence intensity of 3 (10
m
M) upon the addition of 50 equivalents Hg2þ in the presence of 50 equivalents background metal ions. (a) In H2O and (b) in
EtOH/H2O (1:1, v/v) solution.
Fig. 6. pH profiles of the absorption intensities of 3 (10 m
M) in the absence and presence of Hg2þ (10 eqv.) in EtOH/H2O (1:1, v/v) (a) and in H2O (b).
To achieve a binding constant (K) via fluorescence titration, the
titrations were conducted in H2O solutions. Fig. 4a shows the
gradual change of the fluorescence spectra of 3 upon addition of
Hg2þ, clear “on-off” fluorescence changes of 3 to Hg2þ were
observed. When Hg2þ was added to the solution, a significant
decrease of the fluorescence intensity at 590 nm and with a blue
shift to 576 nm was observed. The quenching is found to follow
a BenesieHildebrand equation. A linear dependence of the ratio of
fluorescent intensity [3][Hg2þ]/(F0 ꢀ Fi) at 590 nm as a function of
Hg2þ concentration assumed a 1:1 stoichiometry for the 3ꢃHg2þ
complex. The binding constant derived from the fluorogenic titra-
tions was found to be 3.46 ꢁ 104 Mꢀ1 (R ¼ 0.992) in water. For
comparison, the fluorometric titrations of 3 with Hg2þ were also
recorded in aqueous ethanol (ethanol/water, 1:1, v/v) solutions
(Fig. 4b). The binding constant was found to be 1.17 ꢁ 104 Mꢀ1
(R ¼ 0.994) in aqueous ethanol, indicating that the binding ability of
3 in aqueous ethanol is weaker than that in water. From the changes
in Hg2þ-dependent fluorescence intensity, the detection limit was
estimated to be 1.0 ꢁ 10ꢀ7 M (Fig. S4) [33], indicating that the limit
of detection of 3 to Hg2þ met the discharge limits for industrial
waste water according to the China SA standard [34].
color change is observed in the presence of metal ions other than
Hg2þ. When 50 equivalents of Hg2þ are added to these solutions,
the red color disappears immediately and the spectra are almost
identical to that obtained in the presence of Hg2þ alone. The results
demonstrated that the chemosensor 3 is able to discriminate
between Hg2þ and chemically close ions, especially Agþ which is
common interfering ion in many cases. Obviously, the remarkable
sensitivity for fluorescent detection of Hg2þ can be available using
the chemosensor 3 even in the presence of coexisting metal ions.
3.5. pH profiles of chemosensor 3
For practical applicability, the proper pH condition of the che-
mosensor 3 was evaluated in the presence and absence of Hg2þ by
absorption spectra. The absorption intensities at different pH
values of the free and Hg2þ-bound forms of 3 in EtOH/H2O (1:1, v/v)
and in water are shown in Fig. 6. As can be seen from Fig. 6,
absorption intensities are essentially insensitive to pH in the pH
range of 3e10 in both cases. Thus, the chemosensor 3 can be used
for Hg2þ detection in a wide pH range, which is convenient for the
practical application.
3.4. Selective binding of Hg2þ
4. Conclusion
To explore further the utility of the chemosensor 3 as an ion-
In conclusion, a styrylindolium dye with a NS2O2 ionophore on
the para-position of the styryl moiety has been successfully
designed and synthesized as a Hg2þ-selective chemosensor by
taking advantage of the ICT mechanism. Results revealed that the
chemosensor 3 could be used as an efficient Hg2þ-selective fluo-
rescent and chromogenic chemosensor both in aqueous ethanol
solution and in water. The detection limit for Hg2þ was determined
as 1.0 ꢁ 10ꢀ7 M. The chemosensor shows a remarkably high selec-
tivity to discriminate between Hg2þ and chemically close ions in
selective fluorescent chemosensor for Hg2þ
, ion interference
experiments were carried out both in H2O and in aqueous ethanol
(ethanol/water, 1:1, v/v) solvent systems for evaluation of the
sensing ability of 3 toward Hg2þ in the presence of 50 equivalents of
a series of background metal ions. The results are shown in Fig. 5.
No interference was observed in H2O in the presence of 50 equiv-
alents of a series of metal ions (Fig. 5a). It showed the same
tendency in aqueous ethanol (Fig. 5b). In both cases, almost no

Y. Li et al. / Dyes and Pigments 96 (2013) 424e429
429
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Acknowledgments
This work was sponsored by the NNSFC (21272172, 20972111,
21074093, 21004044), NCET-09-0894, SRF for ROCS, SEM, the NSFT
(12JCZDJC21000) and the State Key Lab. Elemental-Organic Chem-
istry at Nankai University (No. 1103).
Appendix A. Supplementary data
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.dyepig.2012.09.010
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