Synthesis of thionaphthalimides and their dual Hg2+-selective signaling by desulfurization of thioimides

Article abstract of DOI:10.1016/j.dyepig.2012.08.007

A series of new thionaphthalimide derivatives were prepared, and their Hg²⁺-selective signaling behavior was investigated in aqueous acetonitrile solution. A monothionaphthalimide (anti) exhibited pronounced Hg²⁺-selective chromogenic signaling behavior through a solution color change from red to yellow, which was easily detectable by eye. It (anti) also showed prominent off-on type Hg²⁺-selective fluorescent signaling behavior. The signaling is due to the Hg²⁺-assisted desulfurization of the thioimide to its imide structure. The presence of other common metal ions did not interfere with the Hg²⁺-signaling of the monothionaphthalimide (anti). The detection limit of monothionaphthalimide (anti) for the determination of Hg²⁺ ions in 30% aqueous acetonitrile was estimated to be 2.7 μM.

Full text of DOI:10.1016/j.dyepig.2012.08.007

Dyes and Pigments 96 (2013) 170e175
Contents lists available at SciVerse ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
2
þ
Synthesis of thionaphthalimides and their dual Hg -selective signaling by
desulfurization of thioimides
Jung Ok Moon, Myung Gil Choi, Taihao Sun, Jong-In Choe, Suk-Kyu Chang*
Department of Chemistry, Chung-Ang University, Seoul 156-756, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
A series of new thionaphthalimide derivatives were prepared, and their Hg2þ-selective signaling
Article history:
Received 3 June 2012
Received in revised form
behavior was investigated in aqueous acetonitrile solution. A monothionaphthalimide (anti) exhibited
2þ
pronounced Hg -selective chromogenic signaling behavior through a solution color change from red to
31 July 2012
2þ
yellow, which was easily detectable by eye. It (anti) also showed prominent off-on type Hg -selective
Accepted 1 August 2012
Available online 9 August 2012
fluorescent signaling behavior. The signaling is due to the Hg2 -assisted desulfurization of the thioimide
þ
2þ
to its imide structure. The presence of other common metal ions did not interfere with the Hg
signaling of the monothionaphthalimide (anti). The detection limit of monothionaphthalimide (anti) for
-
Keywords:
the determination of Hg2 ions in 30% aqueous acetonitrile was estimated to be 2.7
þ
mM.
2
þ
Hg ion
Ó 2012 Elsevier Ltd. All rights reserved.
Colorimetry
Fluorogenic signaling
Desulfurization
Thionaphthalimide
Ratiometry
1
. Introduction
colorimetric and fluorescent sensors for a variety of important
cations [18] and anions [19]. For cation sensors, efficient receptors
were connected to this fluorophore via the amino functionality of
the aryl ring. The absorption and emission spectra of the resulting
probes were highly modulated upon binding of cations to the
Development of smart sensors or probes for the selective
sensing and visualization of important metal ions has attracted
considerable research interest [1,2]. In particular, signaling of Hg
and related species is crucial from both an industrial and ecological
viewpoint due to the high impact of these species on the envi-
ronment [3]. A number of Hg -selective signaling systems have
been designed based on a variety of platforms, including sophisti-
cated chemical and biological tools such as DNA [4], gold nano-
particles [5], and oligonucleotides [6]. However, small molecule-
based sensors remain attractive due to their ease of synthesis and
versatility for structural optimization by systematic modification
2
þ
þ
respective binding sites, consisting of tertiary amines for H [20],
þ
crown ether type receptor for K [21], iminodiacetate or cyclam for
2
þ
2þ
2þ
Zn [22,23], and picolyl amine for Cu sensing [24]. On the other
hand, anion sensors have been designed by combining urea or
thiourea binding sites to this fluorophore.
The photophysical properties of the naphthalimide moiety are
known to be finely tunable through structural modifications.
Naphthalimide fluorescence is sensitive to substituents on the
naphthalimide fluorophore. In general, an amino substituent on the
aromatic ring enhances the quantum yield of the resulting naph-
thalimide [25]. In addition, thionation is known to cause fluores-
cence quenching of the naphthalimide moiety, and also results in
a large red-shifted absorption [26]. Utilizing the expected unique
changes caused by metal ion-induced desulfurization of the thio-
imide moiety, we developed a new colorimetric and fluorogenic
[7]. Recently, reaction-based signaling methods have attracted
substantial research interest [8]. They are particularly suitable for
the selective signaling of Hg ions, and various sulfur-containing
2
þ
systems utilizing thiophilicity of the probe and specific reactions
with Hg2 were successfully designed [9,10]. In particular, desul-
þ
furization of thiocarbonyl groups has been used for the design of
Hg -selective probes, exemplified by thioamide [11,12], thio-
coumarin [13], and thione probes [14e16].
2
þ
2
þ
signaling system for Hg ions in aqueous environment.
The 1,8-naphthalimide structure is a versatile scaffold, which
has been utilized in the design of dyes and therapeutics [17]. It has
also been widely used as a signaling moiety in the construction of
2. Experimental section
General: 4-Bromo-1,8-naphthalic anhydride and Lawesson’s
reagent were purchased from Aldrich Chemical Co. All solvents
were spectroscopic grade and obtained from Aldrich Chemical Co.
*
Corresponding author. Tel.: þ82 2 820 5199; fax: þ82 2 825 4736.
E-mail address: skchang@cau.ac.kr (S.-K. Chang).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.08.007

J.O. Moon et al. / Dyes and Pigments 96 (2013) 170e175
171
1H NMR (600 MHz) and 13C NMR (150 MHz) spectra were measured
on a Varian VNS spectrometer and were referenced to the residual
solvent signal. Column chromatography was performed with silica
gel (230e400 mesh). UVevis spectra were recorded using a Jasco V-
118.9, 106.7, 54.7, 43.6, 31.0, 27.4, 20.3, 20.1, 13.8; HRMS (FAB); m/z
þ
calcd for C20
. Results and discussion
Thionaphthalimides 2e4 were prepared by the reaction of 4-
H
25
N
2
S
2
[M þ H] : 357.1454, found 357.1455.
3
5
50 spectrophotometer equipped with a Peltier temperature
controller. Fluorescence spectra were measured with a PTI Quan-
taMaster steady-state spectrofluorometer. Mass spectra were
measured with a JEOL JMS-700W mass spectrometer.
bromo-1,8-naphthalic anhydride with n-butylamine followed by
thionation with Lawesson’s reagent (Scheme 1). Reaction of 4-
bromo-1,8-naphthalic anhydride with butylamine yielded 4-
butylamino-butylnaphthalimide 1 (EtOH, reflux, 87%) [27]. Subse-
quent reaction of imide 1 with Lawesson’s reagent (1.5 equiv,
toluene, reflux) afforded mono- and di-thio derivatives 2e4. Opti-
mization of the reaction to prepare monothionated products using
limited amounts of Lawesson’s reagent was attempted, but the two
monothio isomers 2 and 3 were consistently obtained in similar
ratios. The structures of monothio derivatives 2 and 3 were
assigned based on COSY and HMBC experiments (Figs. S1 and S2,
Supplementary Data).
2.1. Preparation of 1
n-Butylamine (2.97 mL, 30 mmol) was added to a solution of 4-
bromo-1,8-naphthalic anhydride (0.277 g, 1 mmol) in 30 mL of
ethanol, and the mixture was heated under reflux for 1 day. After
cooling to room temperature, volatiles were evaporated under
reduced pressure, and the residue was partitioned between CH
and water. The organic phase was separated, washed with 1 N HCl
to remove excess n-butylamine, and dried with anhydrous MgSO
After evaporation, the crude product was purified by column
2 2
Cl
4
.
The UVevis absorption behavior of compounds 1-4 demon-
strated that thio derivatization resulted in a significant red-shift in
the absorption spectra (Fig. 1). Compound 1 showed a strong
absorption band at 439 nm in 30% aqueous acetonitrile solution.
Monothio-functionalized imides 2 and 3 revealed largely red-
shifted (Dl ¼ 68 and 81 nm) absorption bands at 507 and
1
chromatography (silica gel, CH
2
Cl
2
). Yield
¼
87%;
H NMR
(
600 MHz, CDCl
3
) d
8.56 (dd, J ¼ 7.3 and 1.0 Hz, 1H), 8.45 (d,
J ¼ 8.4 Hz, 1H), 8.07 (dd, J ¼ 8.5 and 1.0 Hz, 1H), 7.59 (dd, J ¼ 7.3 and
8
4
.5 Hz, 1H), 6.71 (d, J ¼ 8.4 Hz, 1H), 5.25 (br t, J ¼ 5.0 Hz, 1H),
.17e4.14 (m, 2H), 3.42e3.38 (m, 2H), 1.82e1.77 (m, 2H), 1.73e1.68
(
7
(
m, 2H), 1.53 (tq, J ¼ 14.9 and 7.4 Hz, 2H), 1.43 (tq, J ¼ 14.9 and
520 nm, respectively. On the other hand, dithio-functionalized
13
.4 Hz, 2H), 1.02 (t, J ¼ 7.4 Hz, 3H), 0.96 (t, J ¼ 7.4 Hz, 3H); C NMR
derivative 4 exhibited a much greater red-shifted (Dl ¼ 138 nm)
band at 577 nm. We investigated the possible use of these thio
derivatives as probes for targeted metal ions, especially thiophilic
150 MHz, CDCl 164.7, 164.1, 149.4, 134.4, 131.0, 129.8, 125.6,
3
) d
1
24.6, 123.2, 120.1, 110.3, 104.3, 43.4, 40.0, 31.0, 30.3, 20.4, 20.3, 13.9,
þ
13.8; HRMS (FAB); m/z calcd for C20
H
25
N
2
O
2
[M þ H] : 325.1911,
þ
2þ
2þ
metal ions such as Ag , Cd , and Hg . Among these thioimides,
found 325.1919.
monothio derivative 2 showed relatively optimized signaling
2
þ
behavior for Hg ions in terms of selectivity and signaling time.
Therefore, subsequent experiments were performed using mono-
2.2. Preparation of 2, 3, and 4
2
þ
thio derivative 2 as the Hg -selective probe.
Lawesson’s reagent (0.606 g, 1.5 mmol) was added to a solution
2þ
Compound 2 showed highly selective Hg signaling behavior in
of 1 (0.324 g, 1.0 mmol) in toluene (40 mL), and the solution was
heated under reflux for 1 day. The solvent was evaporated under
reduced pressure, and the crude product was purified by flash
3
0% aqueous acetonitrile solution (Fig. 2). Upon interaction with 30
2þ
equiv of Hg ions, the absorption band of 2 at 507 nm disappeared,
and a new strong band at 439 nm appeared. The solution color
column chromatography (silica gel, CH
2
Cl
2
)
to yield thio-
2þ
concomitantly changed from red to yellow. The signaling of Hg by
functionalized products 2e4.
2
was fast, reaching completion within 5 min after sample prepa-
1
2
: Yield: 42%, R
f
¼ 0.41 (CH
2
Cl
2
), H NMR (600 MHz, CDCl
3
)
d
9.10
ration, while the solution of only probe 2 was not responsive at
(
dd, J ¼ 7.7 and 1.0 Hz, 1H), 8.46 (d, J ¼ 8.5 Hz, 1H), 8.03 (dd, J ¼ 8.2
all, even after 6 h of sample preparation (Fig. S3, Supplementary
and 1.0 Hz, 1H), 7.53 (dd, J ¼ 8.2 and 7.7 Hz, 1H), 6.72 (d, J ¼ 8.5 Hz,
2þ
Data). The Hg -induced shift in the absorption maximum was
1
2
H), 5.29 (br t, J ¼ 4.9 Hz, 1H), 4.76e4.73 (m, 2H), 3.43e3.39 (m,
H), 1.83e1.78 (m, 4H), 1.54 (tq, J ¼ 14.9 and 7.4 Hz, 2H), 1.47 (tq,
pronounced, and the signaling could be followed by ratiometry. The
absorbance ratio of the two characteristic wavelengths at 439 and
J ¼ 14.9 and 7.4 Hz, 2H), 1.03 (t, J ¼ 7.4 Hz, 3H), 0.99 (t, J ¼ 7.4 Hz,
507 nm (A439/A507) of 2 varied 155-fold from 0.23 for probe 2 alone
13
3
H); C NMR (150 MHz, CDCl
3
) d 192.5, 162.0, 149.9, 141.1, 132.2,
128.1, 125.8, 124.9, 123.4, 119.2, 117.9, 105.7, 46.8, 43.5, 31.0, 29.0,
2
0.4, 20.3, 13.9, 13.8; HRMS (FAB); m/z calcd for C20
H
25
N
2
OS
þ
[M þ H] : 341.1688, found 341.1688.
3
: Yield: 37%, R
f
¼ 0.51 (CH
2 2 3
Cl )
), 1H NMR (600 MHz, CDCl
d
8.96 (d, J ¼ 8.8 Hz, 1H), 8.54 (dd, J ¼ 7.4 and 1.0 Hz, 1H), 8.00 (dd,
J ¼ 8.3 and 1.0 Hz, 1H), 7.55 (dd, J ¼ 8.3 and 7.4 Hz, 1H), 6.66 (d,
J ¼ 8.8 Hz, 1H), 5.39 (br s, 1H), 4.76e4.73 (m, 2H), 3.41 (t, J ¼ 7.2 Hz,
2
0
H), 1.83e1.78 (m, 4H), 1.54e1.47 (m, 4H), 1.03 (t, J ¼ 7.4 Hz, 3H),
13
.99 (t, J ¼ 7.4 Hz, 3H); C NMR (150 MHz, CDCl
3
) d 194.2, 161.4,
149.6, 137.0, 135.6, 128.2, 128.0, 125.4, 124.8, 120.0, 110.5, 105.0, 47.2,
4
C
3.4, 31.0, 28.6, 20.4, 20.3, 13.9, 13.8; HRMS (FAB); m/z calcd for
þ
20
H
4
25
N
2
OS [M þ H] : 341.1682, found 341.1689.
1
: Yield: 8%, R
dd, J ¼ 7.8 and 1.0 Hz, 1H), 8.84 (d, J ¼ 9.0 Hz, 1H), 7.91 (dd, J ¼ 8.4
and 1.0 Hz, 1H), 7.43 (dd, J ¼ 7.8 and 8.4 Hz, 1H), 6.63 (d, J ¼ 9.0 Hz,
H), 5.43 (br t, J ¼ 4.8 Hz, 2H), 5.29 (br s, 1H), 3.42e3.38 (m, 2H),
.96e1.91 (m, 2H), 1.83e1.78 (m, 2H), 1.55e1.47 (m, 4H), 1.03 (t,
f
¼ 0.83 (CH
2 2 3
Cl ), H NMR (600 MHz, CDCl ) d 8.94
(
1
1
13
J ¼ 7.4 Hz, 3H), 1.01 (t, J ¼ 7.4 Hz, 3H); C NMR (150 MHz, CDCl
3
)
d
190.2, 188.4, 150.1, 142.6, 138.5, 129.8, 125.4, 125.2, 124.8, 119.8,
Scheme 1. Preparation of thionaphthalimides 2e4.

172
J.O. Moon et al. / Dyes and Pigments 96 (2013) 170e175
0
0
0
.25
350
2
0
3
03
300
250
200
0.2
3
15
2 + Hg(II)
2
1
0
5
0
.15
1
2
only,
+ other metal ions
0.1
150
00
2
4
1
4
60
500
540
580
620
660
700
740
.05
Wavelength (nm)
50
1
.00
1.081.08 1.061.111.24 1.261.391.37 1.291.49 1.401.441.30 1.49
0
3
0
50
400
450
500
550
600
650
700
Wavelength (nm)
ꢁ
5
Fig. 1. UVevis spectra of 1e4. [1] ¼ [2] ¼ [3] ¼ [4] ¼ 1.0 ꢀ 10 M in a mixture of
CH CN and acetate buffer solution (pH 4.8, 10 mM), (7:3, v/v).
Fig. 3. Fluorescence intensity ratio I/I
o
of 2 at 537 nm in the presence of various metal
3
ꢁ
6
nþ
ꢁ4
ions. [2] ¼ 5.0 ꢀ 10 M. [M ] ¼ 1.5 ꢀ 10 M. In a mixture of CH
3
CN and acetate
buffer solution (pH 4.8, 10 mM), (7:3, v/v).
in the presence of various metal ions.
l
ex ¼ 460 nm. Inset: fluorescence spectra of
2
to 36.2 for 2 in the presence of 30 equiv of Hg2þ ions. The ratio A439
507 for other surveyed metal ions varied in a narrow range
/
A
3
þ
2þ
between 0.22 for Fe to 0.25 for Cu ions. On the other hand,
thiocarbonyl group of the thionaphthalimide fluorophore [26].
Upon interaction with various metal ions, probe 2 exhibited largely
upon treatment with Hg2 ions, the absorption band of 3 at 520 nm
disappeared, and a new band appeared instantly at 505 nm. The
absorption band at 505 nm is due to the complex formed between 3
þ
2þ
enhanced fluorescence emission exclusively with Hg ions. The
fluorescence intensity ratio in the presence and absence of added
2
þ
and Hg ions, which was confirmed by the treatment of the 3-
Hg system with iodide ions (Fig. S4, Supplementary Data). When
iodide was added to 3-Hg system, the absorption band became
that of 3. Subsequent addition of Hg
metal ions of 2 (I/I
almost no signaling, and the ratio I/I
o
) at 537 nm was 303. Other metal ions revealed
varied in a narrow range
between 1.06 for K and 1.49 for Cu ions. We also tested another
2
þ
o
2
þ
þ
2þ
3þ
2
þ
to this mixture, the
þ
thiophilic metal ions of Au and Au , and found that these gold
ions exhibited considerable signaling behavior (Fig. S6,
Supplementary Data). In fact, gold ions readily desulfurize the
thiocarbonyl group of thiocoumarins [28].
2
þ
absorption spectrum of 3-Hg system was restored again. In the
2
þ
presence of Hg ions, compound 3 first forms relatively stable
complex with Hg2 , and subsequently the desulfurization of thio-
þ
carbonyl group occurred slowly (Fig. S5(a), Supplementary Data). In
Signaling is due to the conversion of thioimide 2 to imide 1
2þ
the case of dithio-derivative 4, upon interaction with Hg ions, it
was rapidly desulfurized to yield monothio-derivative 3, which was
subsequently desulfurized slowly to 1 as discussed above. The
desulfurization was not completed even after 2 days and consid-
erable decomposition of thio-drivative was occurred (Fig. S5(b),
Supplementary Data).
2þ
2þ
induced by Hg
ions. Hg -induced conversion of 2 to 1 as
depicted in Scheme 2 was confirmed by NMR, UVevis, and fluo-
1
rescence measurements. The H NMR spectrum of 2 in the presence
2þ
of 10 equiv of Hg ions was almost identical to that of 1 (Fig. S7,
Supplementary Data). The resonances of the aromatic protons of
at 8.95 and 8.69 ppm disappeared, and new resonances at 8.66
2
2
þ
Selective fluorescence signaling of Hg ions with probe 2 was
also tested by observing changes in the probe fluorescence in the
presence of 30 equiv of various metal ions (Fig. 3). Probe 2 revealed
a very weak fluorescence due to efficient quenching by the
and 8.43 ppm for these protons of 1 were observed. More defini-
13
tively, the C NMR resonance of the thiocarbonyl carbon of 2 at
1
93 ppm disappeared, and a carbonyl carbon signal of 1 at 164 ppm
was observed (Fig. 4). UVevis and fluorescence measurements also
supported this transformation; the UVevis and fluorescence
2
þ
spectra of 2 in the presence of 30 equiv of Hg ions were almost
identical to those of 1 (Figs. S8 and S9, Supplementary Data).
4
3
3
2
2
1
1
0
5
0
5
0
5
0
5
0
3
6.2
0
0
0
0
0
0
.25
.20
.15
.10
.05
.00
2þ
For possible practical applications of 2, Hg -selective signaling
2 only,
2 + other metal
ions
2 + Hg(II)
of the probe in the presence of other common coexisting metal ions
2
þ
was studied (Fig. 5). Signaling of Hg by 2 was not affected by the
presence of other surveyed metal ions as a background. The fluo-
rescence intensity ratio of 2 in the presence and absence of metal
ions (IHg(II) þ other metal ion/IHg(II)) at 537 nm was observed in a narrow
2
þ
þ
range: 0.96 for Co and 1.00 for Na (Fig. S10, Supplementary
Data).
350
400
450
500
550
600
650
2þ
The quantitative Hg signaling behavior of 2 was investigated
Wavelength (nm)
by measuring concentration-dependent fluorescence changes
(Fig. 6). The fluorescence intensity at 537 nm increased almost
0
.23
0.23 0.23 0.24 0.24 0.24 0.24 0.22 0.23 0.23 0.25 0.24 0.23 0.24 0.23
2
þ
ꢁ4
linearly up to 20 equiv of Hg ions (1.0 ꢀ 10 M) (inset of Fig. 6)
without any significant changes in the fluorescence profile. From
these concentration-dependent fluorescence changes, the detec-
2
þ
in 30% aqueous
tion limit of 2 for the determination of Hg
acetonitrile was estimated to be 2.7 M [29].
The effects of pH on the signaling behavior of 2 toward Hg
ions in pH varying between 4 and 9 were measured. The pH of the
Fig. 2. Absorbance ratio
A
439/A507 of
ꢁ4
2
in the presence of various metal ions.
CN and acetate buffer
ꢁ
5
nþ
m
[
2] ¼ 1.0 ꢀ 10 M. [M ] ¼ 3.0 ꢀ 10 M. In a mixture of CH
3
2þ
solution (pH 4.8, 10 mM), (7:3, v/v). Inset: UVevis absorption spectra of 2 in the
presence of various metal ions.

J.O. Moon et al. / Dyes and Pigments 96 (2013) 170e175
173
Scheme 2. Hg2 signaling of thionaphthalimide 2.
þ
Fig. 4. Partial 13C NMR spectra of 2, 2 þ Hg2þ, and 1 þ Hg2þ in deuterated acetate buffered D
(1:9). [1] ¼ [2] ¼ 2.5 ꢀ 10ꢁ2 M. [Hg(OAc)
] ¼ 2.5 ꢀ 10ꢁ1 M.
2
O/DMSO-d
6
2
solution was fixed by using a series of buffer solutions. As can be
seen in Fig. S11 (Supplementary Data), the signaling was relatively
independent of the solution pH between 4 and 6, but the signaling
behavior deteriorated significantly in basic media above pH 8. On
the other hand, the fluorescence spectrum of naphthalimide 1,
Supplementary Data). The differences in signaling behavior of the
two isomers of monothionaphthalimides 2 and 3 might be due to
2
þ
the different affinity of these thio derivatives for the target Hg
2
þ
ions. Because the Hg -induced desulfurization was initiated by the
coordinative interaction of Hg ions with the sulfur atom of the
thiocarbonyl function, we tried to explain the reactivity differences
by comparing the C NMR chemical shifts of 2 and 3. The carbon
resonance of the thiocarbonyl function of 2 (anti) was observed at
2
þ
2
þ
which is the product of the desulfurization of 2-Hg system, was
almost independent of the solution pH between 4 and 9. Therefore,
we supposed that the desulfurization of thionaphthalimide 2 by
13
2
þ
Hg ions has a strong pH-dependency and the signaling decreased
d 192.5 ppm (Fig. 7). On the other hand, that of 3 (syn) appeared at
2
þ
as the pH increased, as in other Hg -selective probes using metal
ion induced desulfurization processes [30,31].
somewhat deshielded 194.2 ppm. The carbon resonance of
carbonyl group is known to be dependent on the polarizability and
partial charge of the carbonyl oxygen atom [32]. Therefore, we
postulated that the carbon resonance of the more electron-rich
Between the two monothio derivatives 2 and 3, the signaling
speed of compound 2 was much faster than compound 3 (Fig. S3,
3
03 302 304 301
300
299
297
299 299
2
97
297
298 295
2
93 292
20
3
2
2
1
1
00
50
00
50
00
20
15
18
16
14
12
10
8
6
4
2
0
[Hg2+
]
10
5
0
0
20
40
60 +80 100
2
Equiv of Hg
5
0
1
0
460
500
540
580
620
660
700
740
+
2 + Hg(II)
Wavelength (nm)
2
þ
2þ
ꢁ6
Fig. 5. Effects of various metal ions on the fluorescence signaling of Hg ions by 2.
Fig. 6. Hg -concentration dependent fluorescence changes of 2. [2] ¼ 5.0 ꢀ 10 M in
ꢁ
6
2þ
ꢁ4
nþ
ꢁ3
[
2] ¼ 5.0 ꢀ 10 M, [Hg ] ¼ 1.5 ꢀ 10 M [M ] ¼ 1.0 ꢀ 10 M in a mixture of CH
3
CN
a
mixture of CH
3
CN and acetate buffer solution (pH 4.8, 10 mM), (7:3, v/v).
and acetate buffer solution (pH 4.8, 10 mM), (7:3, v/v).
l
ex ¼ 460 nm.
l
ex ¼ 460 nm. Inset shows the changes in fluorescence intensity at 537 nm.

174
J.O. Moon et al. / Dyes and Pigments 96 (2013) 170e175
Fig. 7. Partial 13C NMR spectra of 2 and 3 in CDCl
.
3
[4] Lee JS, Han MS, Mirkin CA. Colorimetric detection of mercuric ion (Hg2 ) in
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þ
thiocarbonyl group of 2 having more electron-rich sulfur will
appear in higher field. Therefore, the signaling speed toward Hg
2
þ
ions of compound 2 having more electron-rich sulfur atom was
much faster than compound 3. In the designed compounds, the
presence of butylamine on naphthyl ring of the 2 has two important
roles; induction of differences in desulfurization rate between 2
and 3 as well as the enhancement in fluorescence quantum yield
[
5] Huang CC, Chang HT. Selective gold-nanoparticle-based “turn-on” fluorescent
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8332e8.
[6] Ono A, Togashi H. Highly selective oligonucleotide-based sensor for mercu-
ry(II) in aqueous solutions. Angew Chem Int Ed 2004;43:4300e2.
[7] Kobayashi H, Ogawa M, Alford R, Choyke PL, Urano Y. New strategies for
fluorescent probe design in medical diagnostic imaging. Chem Rev 2010;110:
[25] of the probe 2 itself as discussed earlier.
2620e40.
[
[
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This work was supported by a fund from Korea Research
Foundation of Korean government (2012-0002403).
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