FRET-based Fluorescent and Colorimetric Probe for Selective Detection of Hg(II) and Cu(II) with Dual-mode

Article abstract of DOI:10.1002/jhet.2863

A dual-function fluorescence resonance energy transfer (FRET)-based fluorescent and colorimetric probe was rationally fabricated from an energy donor coumarin moiety and an energy acceptor rhodamine moiety linked by a thiohydrazide arm for selective detection of Hg²⁺ and Cu²⁺. Two distinct mechanisms were used for the selective detection. Results revealed that probe 1 showed high fluorescent selectivity towards Hg²⁺ and evident colorimetric selectivity for Cu²⁺, which was suitable for ‘naked-eye’ detection.

Full text of DOI:10.1002/jhet.2863

Month 2017 FRET-based Fluorescent and Colorimetric Probe for Selective Detection of
Hg(II) and Cu(II) with Dual-mode
†
†
*
*
Xue Luo, Xu-Dong He, Yuan-Chao Zhao, Chong Chen, Biao Chen, Zhi-Bing Wu, and Pei-Yi Wang
State Key Laboratory Breeding Base of Green Pesticide and Agricultural Bioengineering, Key Laboratory of Green
Pesticide and Agricultural Bioengineering, Ministry of Education, Center for R&D of Fine Chemicals of Guizhou
University, Guiyang, Huaxi District 550025, PR China
*
E-mail: wzb1171@163.com; pywang888@126.com
†The two authors contributed equally to this work.
Additional Supporting Information may be found in the online version of this article.
Received September 27, 2016
DOI 10.1002/jhet.2863
Published online 00 Month 2017 in Wiley Online Library (wileyonlinelibrary.com).
A dual-function fluorescence resonance energy transfer (FRET)-based fluorescent and colorimetric probe
was rationally fabricated from an energy donor coumarin moiety and an energy acceptor rhodamine moiety
linked by a thiohydrazide arm for selective detection of Hg2+ and Cu2+. Two distinct mechanisms were used
for the selective detection. Results revealed that probe 1 showed high fluorescent selectivity towards Hg2+
and evident colorimetric selectivity for Cu2+, which was suitable for ‘naked-eye’ detection.
J. Heterocyclic Chem., 00, 00 (2017).
INTRODUCTION
“turn-on” probe by covalently attaching 5-(benzothiazol-
2-yl)-4-hydroxyisophthalaldehyde onto 8-aminoquinoline;
this probe exhibited high sensitivity towards Hg2+ with a
detection limit down to 0.11 μM [25]. Although many
elaborate chemosensors with single functions can monitor
Hg2+ or Cu2+ individually [26–31], designing dual-
function fluorescent probes for monitoring Hg2+ and Cu2+
is attractive.
Metal binding changes the molecular structure and/or
electronic property of a sensor, which consequently
results in changes in fluorescence properties that can be
detected through monitoring. A number of intensity-
dependent fluorescent sensors have been reported.
However, these sensors still exhibit many limitations,
including inaccurate measurements of fluorescence
intensity, which is influenced by variations in probe
concentration, environmental conditions, instrumental
efficiency and excitation intensity [32,33]. Fluorescence
Detecting heavy metal ions has extensively attracted
attention because qualitative and quantitative assays of
these ions show their direct effect on human health and
the environment. Mercury(II) ion is a dangerous and
toxic pollutant. Accumulation of this ion can damage
the nervous system, kidneys, endocrine system and
brain because of its high affinity towards sulphydryl
groups [1–3]. Copper(II) is another essential trace
element for humans. It is usually present at low
concentration levels in biological systems but plays vital
roles in different physiological and pathological
processes. An elevated level of copper in the liver or
kidney is usually associated with Wilson’s disease,
amyotrophic lateral sclerosis and Menkes syndrome [4,5].
Thus, monitoring the levels of these two metal ions is
necessary.
Numerous strategies have been developed to detect the
two metals, which have led to significant progress in this
field [6–19]. Particularly, chemosensors based on
rhodamine, fluorescein, coumarin, or other functional
chromophores showed promising applications because of
their high selectivity [20], low detection limits [21],
real-time detection [22], and potential biological
applications [23]. Zhang and co-workers [24] reported a
resonance energy transfer (FRET) strategy, as
a
promising platform to solve these problems, has been
widely explored for designing ratiometric and/or
colorimetric fluorescent probes. Zeng and co-workers
designed a FRET-based fluorescent probe with the
fluorescein analogue as the energy acceptor and the
coumarin group as the energy donor. They found that this
sensor with a detection limit of as low as 0.39 μM was
highly selective and sensitive to H2S over other
biologically relevant species [34]. Han and co-workers
employed a phenothiazine donor and a rhodamine
fluorescent “turn-off” sensor towards Cu2+ with
a
detection limit of 4.9 nM in pure water at pH 3.5; this sensor
was based on benzimidazo[2,1-a]benz[de]isoquinoline-7-
one. Bharadwaj and co-workers developed a fluorescent
acceptor to construct
a FRET-directed ratiometric
© 2017 Wiley Periodicals, Inc.

X. Luo, X.-D. He, Y.-C. Zhao, C. Chen, B. Chen, Z.-B. Wu, and P.-Y. Wang
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fluorescent probe with a low detection limit of 9.2 nM for
selective response to Hg2+ [35]. These studies motivate
us to rationally design a FRET-based colorimetric
scaffold 1. In this scaffold, rhodamine moiety served as
the energy acceptor because of its high fluorescence
quantum yields and large absorption coefficients [36,37].
The coumarin group acted as an energy donor because of
its overlaps between its emission spectra and the
absorption spectrum of rhodamine [38,39], and
thiohydrazide moiety served as the binding sites with
metals because of its strong affinity towards Hg2+ and
Cu2+ [40–44]. By combining the donor and the acceptor
Fluorescence spectra of probe 1 with various metal ions.
To examine the selectivity of probe 1 for metal ions, we
employed fluorescence microscopy and UV light. As
shown in Figure 1a, a strong emission peak at 586 nm
was observed upon the addition of Hg2+. This
observation indicates that Hg2+ promoted the spiro-
opening of rhodamine, which occurred after the
interactions between the thiourea moiety and metal ions.
No evident emission peak was observed after adding a
variety of metal ions, including Li+, Na+, K+, Ag+, Mg2+,
Ca2+, Cu2+, Zn2+, Cd2+, Ba2+, Pb2+, Cr3+, Al3+ and Fe3+,
suggesting that Hg2+ can be selectively detected using a
fluorescence microscope at an excitation wavelength of
350 nm (excitation wavelength of coumarin group). In
addition, When Hg2+ (one equivalent) was added into the
mixture of probe 1 and Cu2+ (molar ratio 1:1), the
fluorescence of the solution was significantly enhanced,
suggesting that Hg2+ also can be detected in the presence
of Cu2+ (Fig. S3, supplementary data). Under UV light,
only an orange solution of 1/Hg2+ was observed. This
observation further confirmed that a colorimetric probe
for detecting Hg2+ was developed. The titration of 1 with
Hg2+ showed that the emission intensity at 586 nm was
gradually enhanced with increasing Hg2+ concentration,
reaching a maximum value in the presence of 20 μM
Hg2+ (Fig. 1b). This result shows a good linear detection
range from 2 μM to 10 μM. A 1:2 binding mode of 1
and Hg2+ was revealed by the Job’s plot method (Fig. S4,
supplementary data).
with
a thiohydrazide arm, a FRET system was
constructed for selective detection of Hg2+ and Cu2+
directed by two distinct mechanisms.
RESULTS AND DISCUSSION
Synthesis of probes 1.
As shown in Scheme 1, the
starting reagent 2-hydroxybenzaldehyde was treated
using cyclisation, hydrolysis, chloroformylation, and
substitution reaction to produce an important intermediate
6. Intermediate 7 was also an important intermediate that
was achieved through the condensation reaction between
rhodamine
intermediates
B
and hydrazine hydrate. By mixing
and in CH3CN solvent, target
6
7
1
compound 1 was obtained and characterised by H NMR,
13C NMR and mass spectrometry (Figs. S1–S2,
supplementary data). After adding Hg2+ or Cu2+ into the
solution (EtOH:H2O = 9:1, v/v) of probe 1, the colorless
solution was immediately transformed into pink or
purple, suggesting that a colorimetric probe for selective
detection of Hg2+ and Cu2+ could be fabricated.
UV–vis spectra of probe 1 with various metal ions.
Evident colour changes of probe 1 appeared after adding
Hg2+ or Cu2+. Hence, UV–vis spectrometry was
conducted to monitor the variations. Interestingly, not
only Hg2+ induced obvious absorption at 562 nm but also
Scheme 1. Synthesis route of probes 1 and 2.
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FRET-based Fluorescent and Colorimetric Probe for Selective Detection of Hg(II)
and Cu(II) with Dual-mode
Figure 1. (a) Fluorescence spectrum of 1 (10 μM) in the presence of Hg2+ and various competitive ions (10 μM). Inset photograph shows the fluorescent
detection of Hg2+. (b) Fluorescent titration of 1 (10 μM) with Hg2+ (from 0 to 20 μμ). Inset shows the fluorescence intensity (at 586 nm) as a function of
Hg2+ concentration (λex = 350 nm, slit = 2, EtOH:H2O = 9:1, v/v). [Color figure can be viewed at wileyonlinelibrary.com]
Cu2+ showed evident absorption at 558 nm (Fig. 2a). In the
presence of Cu2+, the color of the mixture changed from
colorless to purple, which was different from the pink
color of 1/Hg2+ or the achromatic color of 1 or 1/other
metals. Therefore, probe 1 was suitable for ‘naked-eye’
detection of Cu2+ (purple colour without fluorescence).
Moreover, the same phenomenon and results could be
observed after treating the probe 1 with Cu2+ bearing
different anions such as SO24-, Cl-, CH3COO-, NO3- ,
indicating that anions could not affect the detection of
Cu2+ (Fig. S5, supplementary data). The titration of 1
with Cu2+ showed that the absorption at 558 nm was
gradually enhanced with increasing Cu2+ concentration,
in which a good linear detection range from 2 μM to 10
μM was observed (Fig. 2b). Moreover, the stoichiometry
between probe 1 and Cu2+ was determined to be 1:2 by
the Job’s plot method (Fig. S6, supplementary data).
disrupt the structure of thiohydrazide unit (Scheme 1;
Figs. S7–8, supplementary data). The selectivity of probe
2 for Hg2+ and Cu2+ was evaluated by fluorescence and
UV–vis spectra under the same conditions as that of
probe 1. The result showed no change in the fluorescent
and UV–vis intensity (Fig. S9, supplementary data), as
well as in the solution color. These results verified the
crucial role of the thiohydrazide unit.
Proposed detection mechanisms of probe 1 for Hg2+ and
Cu2+
.
Two distinct mechanisms were proposed for
selective detection of Hg2+ and Cu2+. In the presence of
Hg2+, ring-opening reaction of the rhodamine B moiety
is induced because the sulphur atom of thiohydrazide
moiety will be deprived, resulting in the formation of a
new oxadiazole moiety. In this irreversible process, the
energy can effectively transfer from the coumarin moiety
to the rhodamine B moiety and consequently gives an
orange fluorescence (Fig. 1a). However, in the presence
of Cu2+, the sulphur atom of thiohydrazide moiety
cannot be deprived. In comparison, the Cu2+-complex
forms between the carbonyl oxygen atom and
Fluorescence and UV–vis spectra of probe 2 with various
metal ions.
To study the role of the thiohydrazide
moiety towards the detection of Hg2+ and Cu2+, we
designed probe 2 by embedding two methylene groups to
Figure 2. (a) Absorption spectrum of 1 (10 μM) in the presence of Cu2+ and various competitive ions (10 μM). Inset photograph shows the visual
detection of Cu2+. (b) Absorbance obtained during the titration of 1 (10 μM) with Cu2+ (from 0 to 20 μμ). Inset shows the absorbance (at 558 nm) as
a function of Cu2+ concentration (EtOH:H2O = 9:1, v/v). [Color figure can be viewed at wileyonlinelibrary.com]
Journal of Heterocyclic Chemistry
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X. Luo, X.-D. He, Y.-C. Zhao, C. Chen, B. Chen, Z.-B. Wu, and P.-Y. Wang
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Figure 3. Proposed detection mechanisms of probe 1 for Hg2+ and Cu2+. [Color figure can be viewed at wileyonlinelibrary.com]
thiohydrazide moiety. This condition induces the
spiro-opening of rhodamine and consequently provides a
purple colour without fluorescence (Fig. 3). Using
electrospray ionisation mass spectrometry, oxadiazole-
containing compound A (found: 654.4) and copper
complex [B+H]+ (found: 814.7) were observed separately,
confirming the above hypothesis (Figs. S10–11,
supplementary data).
spectra were performed on a TU-1900 spectrophotometer
(Beijing Pgeneral Instrument Co., China). The following
abbreviations are used to describe spin multiplicities in 1H
NMR spectra: s = singlet, d = doublet, t = triplet, m = mul-
tiplet, q = quartet.
Experimental section. Synthesis of coumarin-3-carboxylic
acid ethyl ester (3). To a 50 mL flask, 10 g salicylaldehyde
(81.89 mmol), 14.43 g diethyl malonate (90.07 mmol), and
0.5 mL piperidine were added and heated at reflux for 10 h.
Upon completion, the cooled reaction solution was
transferred into a beaker containing 30 mL distilled water
under ice bath. The generated white solid was filtered and
further evaporated to afford the compound coumarin-3-
CONCLUSIONS
In summary, a dual-function FRET-based colorimetric
probe 1 was developed for selective detection of Hg2+ and
Cu2+. Moreover, two different detection mechanisms were
proposed. First, Hg2+ monitoring was conducted by
removing the sulphur atom from the thiohydrazide moiety
and consequently resulted in the formation of a new
oxadiazole moiety. Second, examination of Cu2+ was
directed by constructing a coordination complex. We
expect that our results can offer more applicable and
alternative opportunities for the prediction of these heavy
metal ions.
1
carboxylic acid ethyl ester (3) (10.8 g, yield of 60%). H
NMR (500 MHz, DMSO-d6, ppm) δ 8.76 (s, 1H, CH), 7.93
(d, J = 7.5 Hz, 1H, Ar-H), 7.75 (t, J = 17 Hz, 1H, Ar-H),
7.43 (dd, J = 8.6, 17.0 Hz, 2H, Ar-H), 4.31 (dd, J = 7.5,
14.0 Hz, 2H, CH2), 1.33 (t, J = 14.0 Hz, 3H, CH3); 13C
NMR (125 MHz, DMSO-d6, ppm) δ 163.1, 156.5,
155.1, 149.2, 135.0, 130.8, 125.4, 118.3, 118.2, 116.7,
61.8, 14.6; Anal. Calcd for C12H10O4: C, 66.05; H, 4.62.
Found: C, 66.02; H, 4.60. ESI-MS calcd for m/z =
218.1, found [M+H]+ = 219.2.
Synthesis of coumarin-3-carboxylic acid (4). Compound
(3) (4 g, 18.33 mmol) and NaOH (3 g, 75.01 mmol) were
dissolved in 30 mL of ethanol-water solution, and the
resulting reaction mixture was refluxed for 15 min. The
cooled reaction solution was then transferred into a
beaker, acidized with concentrated hydrochloric acid to
pH=2, followed by filtration and evaporation to produce
the compound coumarin-3-carboxylic acid (4) (4.3 g,
EXPERIMENTAL
Materials.
All chemicals were purchased from
commercial suppliers and used without further
purification. All the solvents were of analytic grade.
Deionized distilled water was used throughout. All the
metal cations were used as their nitrate salts, respectively.
All reactions were magnetically stirred and monitored by
thin-layer chromatography (TLC) using Spectrochem
1
yield 90%). 196-197 °C. H NMR (500 MHz, DMSO-d6,
ppm) δ 13.27 (s, 1H, COOH), 8.76 (s, 1H, CH), 7.93 (d,
J = 7.5 Hz, 1H, Ar-H), 7.75 (t, J = 17.0 Hz, 1H, Ar-H),
7.43 (dd, J = 8.6, 17.0 Hz, 2H, Ar-H); 13C NMR (125
MHz, DMSO-d6, ppm) δ: 164.5, 157.2, 155.0, 148.9,
134.8, 130.7, 125.3, 118.9, 118.5, 116.6; Anal. Calcd for
C10H6O4: C, 63.16; H, 3.18. Found: C, 63.12; H, 3.16.
ESI-MS calcd for m/z = 190.0, found [M+H]+ = 191.1.
Synthesis of rhodamine B hydrazide (7). Rhodamine B
(4.8 g, 10.02 mmol), 8 mL hydrazine hydrate (80% in
water by weight), and 50 mL methanol were added into a
100 mL flask and heated at reflux till the pink color
1
GF254 silica gel coated plates. H and 13C NMR spectra
were measured on a JEOL-ECX 500 NMR spectrometer
at room temperature using TMS as an internal standard.
Mass spectra were recorded by an Agilent LC/MSD Trap
VL mass spectrometer. Elemental analysis was recorded
on an Elementar Vario-III CHN analyzer. Fluorescence
spectra measurements were performed on a Fluoromax-4
spectrofluorimeter (Horiba Trading CO., LTD). UV–vis
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FRET-based Fluorescent and Colorimetric Probe for Selective Detection of Hg(II)
and Cu(II) with Dual-mode
disappeared [45]. Then, the cooled reaction solution was
poured into distilled water and extracted with ethyl
acetate. The combined extracts were dried with sodium
sulfate anhydrous, filtered, and evaporated, giving the
compound rhodamine B hydrazide (7) as a light brown
chromatography with petroleum ether/ethyl acetate as the
eluent to afford 1 (0.1 g, yield: 20%). 1H NMR (500
MHz, CDCl3, ppm) δ 11.63 (s, 1H, CONH), 11.45 (s, 1H,
NHNCO), 8.79 (s, 1H, CH), 8.01 (d, J = 6.9 Hz, 1H, Ph-
H), 7.71 (t, J = 15.0 Hz, 1H, Ph-H), 7.64 (d, J = 5.5 Hz,
1H, Ph-H), 7.52-7.47 (m, 2H, Ph-H), 7.39(dd, J = 8.0,
13.0 Hz, 2H, Ph-H), 7.25 (d, J = 6.9 Hz, 1H, Ph-H), 7.15
(d, J = 7.5 Hz, 1H, N(CH2CH3)2Ph-H), 6.77(s, 1H, N
(CH2CH3)2Ph-H), 6.37-6.33(m, 4H, N(CH2CH3)2Ph-H),
3.35 (d, J = 6.9 Hz, 8H, 4CH2), 1.17 (t, J = 14.0 Hz, 12H,
4CH3); 13C NMR (125 MHz, CDCl3, ppm) δ 180.4,
164.1, 160.3, 155.0, 153.9, 151.8, 151.1, 135.7, 133.4,
130.3, 128.8, 128.4, 125.8, 124.1, 123.9, 118.2, 117.1,
116.4, 108.1, 103.8, 97.7, 66.8, 44.5, 29.6, 12.7; Anal.
Calcd for C39H37N5O5S: C, 68.10; H, 5.42; N, 10.18.
Found: C, 68.12; H, 5.45; N, 10.20. ESI-MS calcd for m/z
= 687.3, found [M+H]+ = 688.4.
1
solid (3.2 g, yield of 70%). H NMR (500 MHz, CDCl3,
ppm) δ 7.93 (d, J = 8.6 Hz, 1H, Ar-H),7.44 (t, J = 6.9 Hz,
2H, Ar-H), 7.10 (d, J = 8.6 Hz, 1H, Ar-H), 6.45 (d, J = 8.6
Hz, 2H, xanthene-H), 6.41 (d, J = 2.3 Hz, 2H, xanthene-
H), 6.28 (dd, J = 2.3, 8.6 Hz, 2H, xanthene-H), 3.60 (s,
2H, NH2), 3.33 (dd, J = 6.9, 14.0 Hz, 8H, 4NCH2CH3),
1.15 (t, J = 14.0, 12H, 4NCH2CH3); 13C NMR (125 MHz,
CDCl3, ppm) δ 166.2, 153.9, 151.6, 148.9, 132.6, 130.1,
128.2, 123.9, 123.1, 108.1, 104.6, 98.0, 66.0, 44.5, 12.7;
Anal. Calcd for C28H32N4O2: C, 73.66; H, 7.06; N, 12.27.
Found: C, 73.63; H, 7.03; N, 12.29. ESI-MS calcd for m/z
= 456.3, found [M+H]+ = 457.4.
Synthesis of rhodamine B ethylenediamine (8). Rhodamine
B (4.8 g, 10.02 mmol), 3.01 g ethylenediamine (50.10 mmol),
and 50 mL ethanol were added into a 100 mL flask and
heated at reflux till the pink color disappeared [46,47].
Then, the cooled reaction solution was poured into
distilled water and extracted with ethyl acetate. The
combined extracts were dried with sodium sulfate
anhydrous, filtered, and evaporated to afford the
compound rhodamine B ethylenediamine (8) as a light
brown solid (3.5 g, yield 72%). 1H NMR (500 MHz,
DMSO-d6, ppm) δ 7.77 (d, J = 4.3 Hz, 1H, Ph-H), 7.48 (t,
J = 8.0 Hz, 2H, Ph-H), 6.99 (d, J = 4.6 Hz, 1H, Ph-H),
6.37 (s, 2H, xanthene-H), 6.35 (d, J = 3.3 Hz, 2H,
xanthene-H), 6.32 (d, J = 8.6 Hz, 2H, xanthene-H), 3.32
(dd, J =6.9, 14.0 Hz, 8H, 4CH2), 2.97 (t, J = 15.0 Hz, 2H,
NCH2), 2.19 (t, J = 15.0 Hz, 2H, CH2NH2), 1.08 (t, J =
14.0 Hz, 12H, 4CH3); 13C NMR (125 MHz, DMSO-d6,
ppm) δ 167.6, 154.1, 153.1, 148.9, 128.8, 128.7, 124.1,
108.6, 105.6, 97.7, 64.5, 40.4, 12.9; Anal. Calcd for
C30H36N4O2: C, 74.35; H, 7.49; N, 11.56. Found: C,
74.32; H, 7.47; N, 11.58. ESI-MS calcd for m/z = 484.3,
found [M+H]+ = 485.4.
Synthesis of probe 2.
To the coumarin-3-carboxylic
isothiocyanate (6) filtrate, compound (8) (0.37 g,
0.76 mmol) was added, and the resulting solution was
kept stirring for 4 h. After removal of the solvent, the
residue was purified by column chromatography with
petroleum ether/ethyl acetate as the eluent to afford 2
1
(0.12 g, yield: 23%). H NMR (500 MHz, CDCl3, ppm)
δ 8.78 (s, 1H, CH), 8.66 (s, 1H, CONH), 7.91 (d, J =
8.6 Hz, 1H, Ph-H), 7.63 (t, J = 17.0 Hz, 2H, Ph-H), 7.43
(dd, J = 3.5, 5.8 Hz, 2H, Ph-H), 7.35 (dd, J = 8.0 Hz,
13.0 Hz, 2H, Ph-H), 7.07 (d, J = 8.0 Hz, 1H, Ph-H),
6.49 (d, J = 9.2 Hz, 2H, N(CH2CH3)2Ph-H), 6.36 (d, J =
2.3 Hz, 2H, N(CH2CH3)2Ph-H), 6.28 (d, J = 2.3 Hz, 1H,
N(CH2CH3)2Ph-H), 3.43 (t,
J
=
12.0 Hz, 2H,
CH2-NHCS), 3.29-3.21 (m, 10H, 5CH2), 2.04 (s, 1H,
CH2N-H), 1.12 (t, J = 14.0 Hz, 12H, 4CH3); 13C NMR
(125MHz, CDCl3, ppm) δ 168.9, 161.5, 161.1, 154.5,
153.8, 153.3, 133.7, 132.5, 131.1, 129.8, 128.9, 128.1,
125.1, 123.9, 123.0, 118.8, 116.6, 108.3, 105.6, 97.9,
65.0, 44.4, 39.6, 38.5, 12.7; Anal. Calcd for
C41H41N5O5S: C, 68.79; H, 5.77; N, 9.78. Found: C,
68.81; H, 5.79; N, 9.79. ESI-MS calcd for m/z = 715.3,
found [M+H]+ = 716.4.
Synthesis of probe 1.
Compound (4) (280 mg, 1.5
mmol) and thionyl chloride (5 mL, 70 mmol) were
successively added into a flask, and refluxed for 7 h.
After that, the excess thionyl chloride was moved out by
distillation, leading to the crude coumarin-3-carboxylic
acyl chloride (5). To the solution of potassium rhodanide
(0.3 g, 3 mmol) dissolving in 8 mL distilled acetonitrile,
compound (5) was added, and kept stirring for 0.5 h at
room temperature. Upon completion, the resulting
solution was filtered to give an orange filtrate (coumarin-
3-carboxylic isothiocyanate (6) filtrate). Without any
purification, compound (7) (0.34 g, 0.76 mmol) was
directly added into the orange filtrate containing
compound (6), and stirred for 4 h. After removal of
the solvent, the residue was purified by column
Procedures for ion detection.
The stock solutions of
probe 1 and 2 (1.0 × 10À3 M) were prepared in ethanol.
Metal ions stock solutions (1.0 × 10À3 M) of the nitrate
salts of Li+, Na+, K+, Ag+, Mg2+, Ca2+, Cu2+, Zn2+,
Cd2+, Ba2+, Hg2+, Pb2+, Cr3+, Al3+, and Fe3+ ions were
prepared in distilled water. The procedures to prepare
samples for fluorescence and UV-vis spectra
measurement were as follows: 100 μL of 1 mM stock
solution of probe was added into a volumetric flask
(10 mL), then appropriate amount of analytes was added
into the volumetric flask and the mixture was diluted to
10 mL with corresponding solvent. Spectral data were
usually recorded at 10 min after the addition of
corresponding solvent.
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Acknowledgments. We acknowledged the financial support of
the Key Technologies R&D Program (2014BAD23B01),
National Natural Science Foundation of China (21372052,
21662009, 21262009), Research Project of Chinese Ministry of
Education (213033A, 20135201110005), Guizhou Province
S&T Program ([2012]6012 and [2011]3016), and Scientific Re-
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sity 2015[34].
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CONFLICTS OF INTEREST
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The authors declare no conflict of interest.
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet