Hg2+ sensing in aqueous solutions: an intramolecular charge transfer emission quenching fluorescent chemosensors

Article abstract of DOI:10.1016/j.tet.2006.06.035

Compounds 4a and 4b, comprising an anthracene moiety as the fluorophore and a pair of dithiocarbamate functionalities as ligating groups, were designed as fluorescent chemosensors for Hg(II). In aqueous solvent systems, upon excitation, in addition to the normal emission bands of locally excited (LE) state of anthracene, both compounds show a prominent pH-independent intramolecular charge transfer (ICT) emissive band, which can be modulated by Hg²⁺ binding. The systems can be exploited to develop a fluorescent sensitive probe for Hg²⁺.

Full text of DOI:10.1016/j.tet.2006.06.035

Tetrahedron 62 (2006) 8379–8383
Hg2+ sensing in aqueous solutions: an intramolecular charge
transfer emission quenching fluorescent chemosensors
*
Sin-Man Cheung and Wing-Hong Chan
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, China
Received 29 March 2006; revised 2 June 2006; accepted 10 June 2006
Available online 7 July 2006
Abstract—Compounds 4a and 4b, comprising an anthracene moiety as the fluorophore and a pair of dithiocarbamate functionalities as
ligating groups, were designed as fluorescent chemosensors for Hg(II). In aqueous solvent systems, upon excitation, in addition to the normal
emission bands of locally excited (LE) state of anthracene, both compounds show a prominent pH-independent intramolecular charge transfer
(ICT) emissive band, which can be modulated by Hg2+ binding. The systems can be exploited to develop a fluorescent sensitive probe
for Hg2+
.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
moiety, and the long wavelength structureless band could
be ascribed to intramolecular charge transfer (ICT) states
between the DTC groups and excited AN. Interestingly,
the relative intensity of these two emissions was found to
be modulated by metal ion binding.
Fluoroionophore design based on ‘fluorophore–spacer–
receptor’ motif has been demonstrated to be an effective
way of developing both anion and cation chemosensors.1
A variety of signal transduction mechanisms are established
to signify the binding event between a receptor and a guest
molecule/ion.2 Particularly, a number of cation chemosen-
sors operated on modulation of dual fluorescence emission
of electron donor–acceptor integrated systems permitting
ratiometric measurement are attractive in sensory applica-
tions.2a,3 Chemosensor exhibiting high selectivity and sensi-
tivity toward a target analyte is in great demand due to its
low cost, ability on real time monitoring, and high through-
put capability. Among all metal analytes detection, mercury
chemosensing has been recently attracted considerable
interests. Mercury is ubiquitous and its potent neurotoxicity
on human warrants the exploration of new methods for
monitoring aqueous Hg2+ in biological, food, and environ-
mental samples.4
2. Results and discussion
On the outset of the investigation, we envisage that DTC is
an effective ligating group for heavy metal ion’s complexa-
tion and the structural environment of DTC in the system
could render the sensors with discriminative binding affini-
ties toward various metal cations. For synthesizing sensors,
the requisite precursor 2 obtained from phenyliminodietha-
nol (1) and TsCl in pyridine was treated with ammonium
N,N-diethyldithiocarbamate and morpholinyldithiocarba-
mate in CH3CN at room temperature for 2 days, affording
the corresponding bis-dithiocarbamate 3a and 3b in 95 and
87% yield, respectively. After building up the metal recep-
tive site, incorporation of a fluorescent moiety on the recep-
tor was achieved by Friedel–Crafts alkylation reaction.
Thus, to complete the synthesis of sensors 4, aluminum
chloride induced Friedel–Crafts alkylation of 3 with 9-chloro-
methylanthracene in refluxing chloroform allowed the
smooth appendage of the anthracene subunit as the fluores-
cent signaling handle (Scheme 1).7
To continue our interests in fluorescent sensor development
on toxic metal monitoring,5 we herein report acceptor–
spacer–donor systems 4a and 4b, in which anthracene
(AN) used as an electron acceptor is linked to a pair of di-
thiocarbamates (DTC) as both metal chelating groups and
electron donors via iminophenylmethylene spacer.6 In aque-
ous media, both systems display dual fluorescence emissive
bands. In which the short wavelength emission bands are
ascribed to the locally excited (LE) state of the anthracene
To probe the best operative conditions for the sensors to ex-
hibit the selective binding of metals, the choice of a proper
aqueous solvent system is our first priority. In that connec-
tion, the fluorescent titration of 4a with Hg2+ in aqueous
acetonitrile (1:1, v/v) was first undertaken. The emission
spectra of the corresponding titration curves reveal the
Keywords: Chemosensors; Mercury probe; Dual fluorescence; Anthracene.
* Corresponding author. Tel.: +852 3411 7076; fax: +852 3411 7348;
e-mail: whchan@hkbu.edu.hk
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.06.035

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S.-M. Cheung, W.-H. Chan / Tetrahedron 62 (2006) 8379–8383
S
S
–
O
O
N
O
OTs
OTs
S
S
N
N
NH
4
+
S
OH
OH
p-TsCl
N
N
N
DMSO
Py
S
2, 85%
3b, 87%
1
S
Cl
Cl
+
Na
–
CH CN
3
N
S
CHCl
3
CHCl
3
S
AlCl
3
AlCl
3
S
N
N
S
OH
OH
N
S
O
O
N
N
S
N
S
S
N
3a, 95%
S
Cl
4c, 56%
4b, 50%
CHCl
3
AlCl
3
S
S
S
N
N
N
S
4a, 74%
Scheme 1. Synthesis of the chemosensors.
dependence of the fluorescent behavior of the sensor on the
metal concentration (Fig. 1A). Increasing the concentration
of Hg2+ from 5ꢀ10ꢁ8 to 2.5ꢀ10ꢁ4 M, the corresponding
titration curves exhibited an increase in the short wavelength
emissive peaks with a concomitant decrease in the long
wavelength structureless emissive peak at 525 nm. A clear
isoemissive point at 455 nm was observed. The long
wavelength emissive peak is conceivably arising from ICT
fluorescence formed between the excited state of the
anthracene moiety and DTC (vide infra). The findings pro-
vide the basis for ratiometric fluorescent determination of
Hg2+. The limit of detection (LOD) for Hg2+ is estimated
to be 1ꢀ10ꢁ8 M with the present system. The responsive
sensitivity of the sensor can be further increased by changing
the solvent system to 1:1 aqueous ethanol. The more polar
solvent system adopted further enhances the intensity of ICT
emissive band as evidenced in the titration experiments
(Fig. 1B). Interestingly, under the same conditions of the
titration experiments, in contrast to that of sensor 4a, sensor
4b responds quite distinctively to Hg2+. As shown in
Figure 2, by increasing the concentration of Hg2+ from
5ꢀ10ꢁ8 to 1.0ꢀ10ꢁ3 M, the corresponding titration curves
exhibit a decrease in ICT fluorescence with the short wave-
length peaks being intact. Conceivably, the two dithiocarba-
mate moieties bearing morpholine ring present in 4b could
confer a more focused metal binding site for the sensor in
such a way that the lone pair of the imino-nitrogen did not
take part in the metal complexation. As a result, metal bind-
ing in 4b would not interfere with the photo-induced electron
transfer (PET) process. In contrast, the imino-nitrogen pres-
ent in 4a could actively participate in the metal binding; the
increase of emissive peaks of LE state is attributed to the
Hg2+ (M)
Hg2+ (M)
B
A
1400
700
0
0
5.0 X 10-8
8.0 X 10-8
1200
2.5 X 10-7
2.5 X 10-6
8.0 X 10-7
600
500
400
300
200
100
0
3.0 X 10-6
5.0 X 10-6
7.5 X 10-6
2.5 X 10-5
5.0 X 10-5
1.0 X 10-4
2.5 X 10-4
8.0 X 10-6
1000
1.0 X 10-5
1.5 X 10-5
4.0 X 10-5
5.0 X 10-4
2.0 X 10-3
800
600
400
200
0
400
450
500
550
600
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
Figure 1. Fluorescence spectra of 4a as a function of [Hg2+] (A) in CH3CN/H2O ¼ 1:1, v/v; (B) in EtOH/H2O ¼ 1:1, v/v. [4a] ¼ 5.0ꢀ10ꢁ6 M.

S.-M. Cheung, W.-H. Chan / Tetrahedron 62 (2006) 8379–8383
8381
1200
1100
1000
900
800
700
600
500
400
300
200
100
Hg2+ (M)
0
5.0 X 10-8
5.0 X 10-7
4.0 X 10-6
8.0 X 10-6
1.5 X 10-5
4.0 X 10-5
8.0 X 10-5
5.0 X 10-4
1.0 X 10-3
350
300
250
200
150
100
50
FLE/417nm
FICT/500nm
0
1
2
3
4
5
6
7
8
9
10 11 12 13
0
400
450
500
550
600
pH
Wavelength (nm)
Figure 4. Effect of pH on the emission peaks of LE state (417 nm) and ICT
(500 nm) peaks of 4b.
Figure 2. Fluorescence spectra of 4b as a function of [Hg2+] in EtOH/
H2O ¼ 1:1, v/v. [4b] ¼ 1.0ꢀ10ꢁ5 M.
indicated that there is no cross response of the sensor to
the pH change of the sensor solution. According to Figure 4,
emissions from both LE and ICT state remain constant over
a wide pH range from 3.5 to 12.5. It is noteworthy that the
anthracene emissive peak of the sensor exists at ‘off state’
when the pH of the solution is greater than 3.2. Considering
the fact that Ag+ ion is seldom found in biological and envi-
ronmental samples, thus in terms of high sensitivity and
selectivity and wide working pH range, sensor 4b possesses
good potential to be used for monitoring the mercury level of
real samples.
reduction of the intrinsic PET process as a result of metal
binding. Apparently, the fine structural environment of the
binding site of sensor can be tuned by a rational design.
The selectivity studies of the sensors substantiate that 4b
with more rigid binding site exhibits a better selectivity
toward Hg2+ among other metal ions. In contrast, sensor
4a is a less selective sensor as shown in Figure 3. Sensor
4b in fact does not respond to other common metal cations
as well as organo-mercury. Further detailed investigation
reveals that sensor 4b also responded sensitively with Ag+.
On the basis of the nonlinear fitting experiments of fluores-
cent titrations, the binding constant of 4b with Ag+ and Hg2+
was determined to be 32.3ꢀ104 and 3.9ꢀ104 Mꢁ1, respec-
tively. The values of binding constants revealed that the sen-
sor forms fairly strong complexes with these metals. On the
other hand, the detection sensitivity of both sensors toward
Hg2+ is excellent with an estimated LOD at 10ꢁ8 M. Metal
ion chemosensors often exhibit pH-dependent emission
and could be problematic in practical operation. To our
delight, pH fluorescent titration experiments on sensor 4b
To shed light for the response mechanism of the sensory
systems, a control molecule 4c without the DTC receptive
groups was synthesized from Friedel–Crafts alkylation
of phenyliminodiethanol and 9-chloromethylanthracene.
No ICT fluorescence was observed in the emission spectra
of 4c in 1:1 aqueous ethanol solution. As shown in Figure 5,
the fluorescent titration curves of 4c exhibit a typical PET
based chemosensor behavior. The fluorescence of the sensor
was completely turned off at 10ꢁ3 M of Hg2+. Thus, the pres-
ence of DTC moieties in sensors 4 is essential for the
4b
4a (A)
4a (B)
9000
80
70
Hg2+ (M)
8000
7000
6000
5000
6.0 X 10-8
1.0 X 10-6
60
50
40
30
20
10
1.0 X 10-5
1.0 X 10-4
5.0 X 10-4
1.0 X 10-3
1.5 X 10-3
2.0 X 10-3
4000
3.0 X 10-3
0
3000
0
2000
1000
0
400
450
500
550
600
ions
Wavelength (nm)
Figure 3. Quenching ratio of 4a and 4b with different ions. Compound 4a
(A) EtOH/H2O ¼ 1:1, v/v; 4a (B) and 4b CH3CN/H2O ¼ 1:1, v/v;
[4a] ¼ 5.0ꢀ10ꢁ6 M; [ion] ¼ 2.5ꢀ10ꢁ4 M; [4b] ¼ 1.0ꢀ10ꢁ5 M.
Figure 5. Fluorescence spectra of 4c as a function of [Hg2+] in EtOH/
H2O ¼ 1:1, v/v. [4c] ¼ 2.0ꢀ10ꢁ5 M.

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S.-M. Cheung, W.-H. Chan / Tetrahedron 62 (2006) 8379–8383
Table 1. Exciplex emissive band of 4a, 4b, and 4c in different solvents,
excitation wavelength ¼ 368 nm
dried over Na2SO4. The solvent was removed by rotary evapo-
ration under vacuum, affording 1 as a colorless oil (0.34 g,
99% yield). dH (270 MHz, CDCl3): 3.33 (s, 2H), 3.58
(t, J¼4.86 Hz, 4H), 3.85 (t, J¼4.86 Hz, 4H), 6.68–6.77
(m, 3H), 7.24 (t, J¼7.83 Hz, 2H).
CH3CN/
EtOH/
DMSO DMSO/
H2O ¼ 1:1 (nm) H2O ¼ 1:1 (nm) (nm)
H2O ¼ 0.5:99.5 (nm)
—
465
4a 525
4b
467
500
—
530
—
3.1.2. Phenyliminodi(ethyltosylate) 2. To a pyridine solu-
tion (5 mL) of 1 (0.5 g, 2.8 mmol), p-toluenesulfonyl chlo-
ride (1.6 g, 8.4 mmol) was added. The reaction mixture
was stirred in an ice bath under N2 for 5 h. Water was added
(30 mL) and products were extracted by CH2Cl2
(3ꢀ30 mL). The organic layer was collected and dried
over Na2SO4. The solvent was removed by rotary evapora-
tion under vacuum. The crude product was recrystallized
in PE to give pure 2 as white crystals (1.15 g, 85% yield).
Mp 72.0–75.0 ꢂC; HRMS m/z calcd for C24H27NO6S2
(M+H)+: 490.1358, found: 490.1357; dH (270 MHz,
CDCl3): 2.42 (s, 6H), 3.55 (t, J¼6.75 Hz, 4H), 4.08 (t,
J¼6.75 Hz, 4H), 6.43 (br d, J¼8.10 Hz, 2H), 6.70 (t, J¼
8.10 Hz, 1H), 7.13 (br d, J¼8.10 Hz, 2H), 7.28 (d, J¼
8.10 Hz, 4H), 7.71 (d, J¼8.10 Hz, 4H); dC (67.8 Hz,
CDCl3): 21.72, 50.18, 66.57, 111.89, 117.46, 127.71,
129.34, 129.76, 132.44, 144.85, 145.55.
occurrence of dual fluorescence emission as compared with
the control experiment conducted by 4c. It is noteworthy that
the fluorescence maximum of the structureless long wave-
length emission of both 4a and 4b is highly solvent depen-
dent (Table 1). Such an observation is consistent with the
characteristics of ICT fluorescence.3 The strong binding
between Hg2+ and the sensors can be rationalized by the
combination of electronic and steric effect. On one hand,
the four sulfur atoms present in the sensors provide strong
affinity to bind heavy metals while on the other hand, the
bulkiness of the two morpholine moiety appended on 4b
defines a semi-rigid cavity favoring a selective binding of
mercury and silver. Upon binding of metal ions by the
DTC groups, the electron density of the receptive site is
greatly reduced, the ICT mechanism between the ‘donor–
receptor’ and the excited state of anthracene is retarded.
3.1.3. Ammonium morpholinyldithiocarbamate. Mor-
pholine (5 mL, 57 mmol) was dissolved in CH3OH
(100 mL). CS2 (5 mL, 83 mmol) and NH4OH (4 mL, 28%)
were added. The reaction mixture was stirred at room tem-
perature for few minutes. Et2O (100 mL) was added. The
product was precipitated and filtered, which was dried under
reduced pressure to afford a pale yellow solid (6.67 g, 70%
yield). dH (270 MHz, DMSO-d6): 3.48 (t, J¼4.05 Hz, 4H),
4.27 (t, J¼4.05 Hz, 4H); dC (67.8 Hz, DMSO-d6): 49.74,
66.12.
In summary, we have demonstrated that the dual fluorescence
characteristics of a new Hg2+-selective fluoroionophore 4b
could be modulated by its interaction with mercury ion.
The excellent selectivity and sensitivity of the sensor toward
Hg2+ and Ag+ are attributed to the combined electronic and
steric effect. The fluorescence measurements for analyzing
the metal content of the solution can be conducted in
un-buffered solutions.
3. Experimental
3.1. General
3.1.4. Phenyliminobis(ethyldiethyldithiocarbamate) 3a.
Compound 2 (1 g, 2 mmol) was dissolved in CH3CN
(40 mL). Sodium diethyldithiocarbamate (1.42 g, 6.3 mmol)
was added. The reaction mixture was stirred under N2 at
room temperature for 2 days. Water (30 mL) was added
and products were extracted with CH2Cl2 (3ꢀ30 mL). The
organic layer was collected and dried over Na2SO4. The sol-
vent was removed by rotary evaporation under vacuum,
affording 3a as white solid (0.9 g, 100% yield). Mp 77–
81 ꢂC; HRMS m/z calcd for C20H33N3S4Na (M+Na)+:
466.1455, found: 466.1459; dH (270 MHz, CDCl3): 1.29 (t,
J¼6.75 Hz, 12H), 3.49–3.54 (m, 4H), 3.67–3.76 (m, 8H),
4.00–4.08 (m, 4H), 6.69 (t, J¼8.10 Hz, 1H), 6.97 (br d,
J¼8.10 Hz, 2H), 7.24 (br d, J¼8.10 Hz, 2H); dC (67.8 Hz,
CDCl3): 11.29, 32.96, 46.46, 49.54, 111.62, 115.91,
128.75, 146.56, 194.07.
Melting point was determined with a MEL-TEMPII melting
1
point apparatus (uncorrected). H and 13C NMR spectra
were recorded on a JOEL EX 270 spectrometer (at 270
and 67.8 MHz, respectively) in DMSO-d6 or CDCl3. Chemi-
cal shifts were registered relatively to Me4Si (in ppm). High-
resolution mass spectra were recorded on a Bruker Autoflex
mass spectrometer (MALDI-TOF) or electrospray ioniza-
tion high-resolution mass spectra on an API Qstar Pulsari
mass spectrometer. Fluorescent emission spectra were col-
lected on a Hitachi F4500 fluorescence spectrophotometer.
Unless specified, all fine chemicals were used as received.
3.1.1. Phenyliminodiethanol 1. To a THF solution (15 mL)
of phenyliminodiacetic acid diethyl ester7 (0.5 g, 1.9 mmol)
in a round bottomed flask immersed in an ice bath, LAH
(0.14 g, 3.6 mmol) was slowly added in two portions. The
reaction mixture was allowed to stir for 10 min and then
refluxed at 80 ꢂC under N2 for 2 h. After the reaction mixture
was cooled to room temperature, the flask was soaked in the
ice bath. H2O (1 mL), NaOH (1 M, 1 mL), and again H2O
(3 mL) were added successively. White solid appeared,
which was filtered off using sinter filter and washed with
several portions of ethyl acetate. The filtrate was extracted
by CH2Cl2 (3ꢀ30 mL). The combined organic layers were
3.1.5. Phenyliminobis(ethyldimorpholinyldithiocarba-
mate) 3b. Compound 2 (0.37 g, 0.8 mmol) was dissolved
in DMSO (8 mL). Ammonium morpholinyldithiocarbamate
(0.38 g, 2.3 mmol) was added. The reaction mixture was
allowed to stir under N2 at room temperature for 2 days.
Water was added and products were extracted with CH2Cl2
(3ꢀ30 mL). Then, the emulsified layer was combined with
satd NH4Cl. H2O (4ꢀ20 mL) was introduced to wash the
organic portion. The organic layer was collected and dried
over Na2SO4. The solvent was removed by rotary evapora-
tion under vacuum. The crude product was purified by

S.-M. Cheung, W.-H. Chan / Tetrahedron 62 (2006) 8379–8383
8383
column chromatography, eluted with PE:EA (1:1) to give 3b
as white solids (0.31 g, 87% yield). Mp 141–143 ꢂC; HRMS
m/z calcd for C20H29N3O2S4 (M+Na)+: 494.1004, found:
494.0953; dH (270 MHz, CDCl3): 3.53–3.59 (m, 4H),
3.68–3.70 (m, 4H), 3.76–3.79 (m, 8H), 3.96–4.00 (m, 4H),
4.30 (m, 4H), 6.73 (t, J¼7.20 Hz, 1H), 6.92 (br d,
J¼7.20 Hz, 2H), 7.26 (br d, J¼7.20 Hz, 2H); dC (67.8 Hz,
CDCl3): 33.37, 49.90, 50.81, 66.22, 112.07, 116.63,
129.33, 146.86, 196.71.
AlCl3 (0.6 g, 4.6 mmol) was added. The reaction mixture
was refluxed at 70 ꢂC under N2 overnight. At the end of
the reaction, NaOH (10 mL, 1 M) was added to the reaction
mixture. Water (30 mL) was added and products were
extracted with CH2Cl2 (3ꢀ30 mL). The organic layer was
collected and dried over Na2SO4. The solvent was removed
by rotary evaporation under vacuum. The crude product was
purified by column chromatography, eluted with EA to
afford the product 4c as yellow solids (0.95 g, 56% yield).
Mp 46.0–47.5 ꢂC; HRMS m/z calcd for C25H25NO2
(M+H)+: 372.1963, found: 372.1958; dH (270 MHz,
CDCl3): 3.34 (t, J¼4.73 Hz, 4H), 3.61 (t, J¼4.73 Hz, 4H),
3.74–3.77 (m, 2H), 4.86 (s, 2H), 6.42 (d, J¼8.10 Hz, 2H),
6.9l (d, J¼8.10 Hz, 2H), 7.38–7.42 (m, 4H), 7.95–7.99 (m,
2H), 8.19–8.22 (m, 2H), 8.36 (s, 1H); dC (67.8 Hz,
CDCl3): 32.37, 55.35, 60.66, 112.60, 114.63, 124.75,
124.79, 125.63, 126.14, 128.76, 128.94, 129.09, 130.29,
131.54, 145.86.
3.1.6. 4-(9-Methylanthracene)phenyliminobis(ethyl-
diethyldithiocarbamate) 4a. Compound 3a (0.23 g,
0.5 mmol) and 9-chloromethylanthracene (0.13 g, 0.6 mmol)
were added in a 50 mL round bottomed flask. Dry CHCl3
was added (10 mL) and then followed by AlCl3 (0.07 g,
0.5 mmol). The reaction mixture was refluxed at 70 ꢂC under
N2 overnight. At the end of the reaction, NaOH (10 mL,
1 M) was added to the reaction mixture. The combined solu-
tion was extracted by CH2Cl2 (3ꢀ30 mL) and H2O. The
organic layer was collected and dried over Na2SO4. The
solvent was removed by rotary evaporation under vacuum.
The crude product was purified by column chromatography,
eluted with PE:EA (6:1) affording the product 4a as yellow
solids (0.24 g, 74% yield). Mp 92.0–93.0 ꢂC; HRMS m/z
calcd for C35H43N3S4 (M+): 633.2339, found: 633.2369;
dH (270 MHz, CDCl3): 1.20 (t, J¼6.75 Hz, 12H), 3.44 (t,
J¼5.40 Hz, 4H), 3.57–3.64 (m, 8H), 3.98 (t, J¼5.40 Hz,
4H), 4.89 (s, 2H), 6.79 (d, J¼8.10 Hz, 2H), 6.98 (d, J¼
8.10 Hz, 2H), 7.40–7.44 (m, 4H), 7.99 (br d, J¼5.40 Hz,
2H), 8.24 (br d, J¼5.40 Hz, 2H), 8.37 (s, 1H); dC (67.8 Hz,
CDCl3): 12.48, 33.48, 46.76, 49.52, 49.94, 112.16, 124.69,
124.88, 125.55, 126.00, 128.82, 128.83, 128.85, 130.28,
131.50, 132.64, 145.27, 194.70.
Acknowledgements
This work was supported by a Faculty Research Grant of the
Hong Kong Baptist University (FRG/04-05/II-18) and a
studentship was provided by the additional UGC bid.
References and notes
1. (a) Fluorescent Chemosensors for Ion and Molecule Recogni-
tion; Czarnik, A. W., Ed.; ACS Symposium Series 538;
American Chemical Society: Washington, DC, 1992; (b)
Chemosensors of Ion and Molecule Recognition; Desvergne,
J. P., Czarnik, A. W., Eds.; Kluwer: Dordrecht, 1997.
2. For review, see: (a) de Silva, A. P.; Nimal Gunaratne, H. Q.;
Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.;
Rademacher, J. T.; Rice, T. E. Chem. Rev. 1997, 97, 1515–
1566; (b) Beer, P. D.; Gale, P. A. Angew. Chem., Int. Ed. 2001,
40, 486–516; (c) Martinez-Manez, R.; Sancenon, F. Chem.
Rev. 2003, 103, 4419–4476.
3. (a) Brouwer, F. Conformational Analysis of Molecules in
Excited States; Waluk, J., Ed.; Wiley-VCH: New York, NY,
2000, Chapter 4, pp 177–235; (b) Yang, J.-S.; Lin, Y.-D.;
Chang, Y.-H.; Wang, S.-S. J. Org. Chem. 2005, 70, 6066–6073
and references therein.
4. For recent selected examples of fluorescent mercury chemosen-
sors: (a) Descalzo, A. B.; Martinez-Manez, R.; Radeglia, R.;
Rurack, K.; Soto, J. J. Am. Chem. Soc. 2003, 125, 3418–3419;
(b) Nolan, E. M.; Lippard, S. J. J. Am. Chem. Soc. 2003, 125,
14270–14271; (c) Guo, X.; Qian, X.; Jia, L. J. Am. Chem. Soc.
2004, 126, 2272–2273; (d) Ono, A.; Togashi, H. Angew.
Chem. Int. Ed. 2004, 43, 4300–4302; (e) Wang, J.; Qian, X.
Chem. Commun. 2006, 109–111.
5. (a) Chan, W.-H.; Yang, R.-H.; Wang, K. Anal. Chim. Acta 2001,
444, 261–269; (b) Shao, N.; Zhang, Y.; Cheung, S.-M.; Yang,
R.-H.; Chan, W.-H.; Mo, T.; Li, K.-A.; Liu, F. Anal. Chem.
2005, 77, 7294–7303.
3.1.7. 4-(9-Methylanthracene)phenyliminobis(ethyl-
dimorpholinyldithiocarbamate) 4b. Compound 3b (0.15 g,
0.3 mmol) and 9-chloromethylanthracene (0.07 g, 0.3 mmol)
were mixed in a 50 mL round bottomed flask. Dry CHCl3
was added (11 mL) and then followed by AlCl3 (0.04 g,
0.3 mmol). The reaction mixture was refluxed at 70 ꢂC under
N2 overnight. At the end of the reaction, NaOH (11 mL,
1 M) was added to the reaction mixture. Water (30 mL)
was added and CH2Cl2 (3ꢀ30 mL) was used for extraction.
The organic layer was collected and dried over Na2SO4. The
solvent was removed by rotary evaporation under vacuum.
The crude product was purified by column chromatography,
eluted with PE:EA (3:1) affording the product 4b as yellow
solids (0.1 g, 50% yield). Mp: 99.0–99.5 ꢂC; HRMS m/z
calcd for C35H39N3O2S4 (M+H)+: 662.2003, found:
662.2002; dH (270 MHz, CDCl3): 3.49 (t, J¼4.05 Hz, 4H),
3.60 (t, J¼4.05 Hz, 4H), 3.70–3.73 (m, 8H), 3.91–3.94 (m,
4H), 4.30–4.33 (m, 4H), 4.91 (s, 2H), 6.75 (d, J¼8.10 Hz,
2H), 7.01 (d, J¼8.10 Hz, 2H), 7.43–7.47 (m, 4H), 8.02 (br
d, J¼5.40 Hz, 2H), 8.25 (br d, J¼5.40 Hz, 2H), 8.41 (s,
1H); dC (67.8 Hz, CDCl3): 32.46, 33.43, 49.92, 51.11,
62.55, 112.17, 124.76, 124.88, 125.66, 126.15, 128.88,
128.96, 129.37, 130.33, 131.56, 132.53, 145.17, 196.73.
6. (a) King, J. N.; Fritz, J. S. Anal. Chem. 1987, 59, 703–708; (b)
Webber, P. R. A.; Drew, M. G. B.; Hibbert, R.; Beer, P. D.
Dalton Trans. 2004, 1127–1135.
7. Gunnlaugsson, T.; Lee, T. C.; Parkesh, R. Org. Lett. 2003, 5,
4065–4068.
3.1.8. 4-(9-Methylanthracene)phenyliminodiethanol 4c.
Compound 1 (0.83 g, 4.6 mmol) and 9-chloromethylanthra-
cene (1.1 g, 4.8 mmol) were mixed in dry CHCl3 (10 mL).