Carbazole incorporated ratiometric chemosensor for Zn2+

Article abstract of DOI:10.1016/j.saa.2012.12.034

An electron donating carbazole incorporated thiazole (3) based Zn ²⁺ selective intrinsic chemosensor has been synthesized and investigated. It was found that electron donating substituents such as methyl and carbazole on chemosensor (1) produce remarkable red shift in emission upon complexation with Zn²⁺. The sensor shows a selective fluorescence response with Zn²⁺ over biologically relevant cations (Ca ²⁺, Mg²⁺, Na⁺, and K⁺) and biologically non-relevant cations (Cd²⁺, In³⁺ and Ga ³⁺) in an aqueous ethanol system. It also produce an enhancement in the quantum yield and a longer emission wavelength shift on Zn²⁺ binding with the potential of a ratiometric assay.

Full text of DOI:10.1016/j.saa.2012.12.034

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 273–279
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Carbazole incorporated ratiometric chemosensor for Zn2+
⇑
Aasif Helal, Hong-Seok Kim
Department of Applied Chemistry, Kyungpook National University, Daegu 702-701, Republic of Korea
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
An electron donating carbazole
incorporated thiazole-based
chemosensor was prepared.
Sensor showed a selective
fluorescence response with Zn2+ in
an aqueous ethanol system.
It also produce an enhancement in
the quantum yield.
Probe produced a longer emission
wavelength shift on Zn2+ binding
with the potential of a ratiometric
assay.
"
"
"
a r t i c l e i n f o
a b s t r a c t
An electron donating carbazole incorporated thiazole (3) based Zn2+ selective intrinsic chemosensor has
Article history:
Received 13 November 2012
Received in revised form 10 December 2012
Accepted 10 December 2012
Available online 22 December 2012
been synthesized and investigated. It was found that electron donating substituents such as methyl and
carbazole on chemosensor (1) produce remarkable red shift in emission upon complexation with Zn2+
.
The sensor shows a selective fluorescence response with Zn2+ over biologically relevant cations (Ca2+
,
Mg2+, Na+, and K+) and biologically non-relevant cations (Cd2+, In3+ and Ga3+) in an aqueous ethanol sys-
tem. It also produce an enhancement in the quantum yield and a longer emission wavelength shift on
Zn2+ binding with the potential of a ratiometric assay.
Keywords:
Carbazole
Chemosensor
Fluorescence
Ratiometric sensing of Zn2+
ESIPT
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
alone are not sufficient to ensure that a probe will be valuable
for bioimaging analysis in vivo because the fluorescence emission
The design and synthesis of artificial fluorescent chemosensors
for sensing and reporting heavy transition-metal ions has been
receiving considerable attention in recent years [1–5]. Especially,
as the second most abundant transition metal ion in the human
body behind iron, zinc(II) ion, an essential trace element, plays a
significant role in various fundamental biological processes, such
as cellular metabolism, gene expression, DNA repair, apoptosis,
neurotransmission, regulation of metalloenzymes, DNA binding
or recognition and regulation of neurological disorders such as Par-
kinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis,
and epileptic seizures [6–16]. However sensitivity and selectivity
intensity depends on bleaching, optical path length and both the
analyte and the probe concentration. In a cellular environment,
the sensor concentration depends on many factors such as mem-
brane permeability, incubation time and temperature, or variations
in the cell size and also phototransformation, which contributes to
the fluorescence intensity modulation of a system [17,18]. Such
limitations can be solved by using ratiometric probes which not
only display a shift in peak emission upon binding but conse-
quently eliminates likely artifacts caused due to extraneous factors
by self-calibration of two emission bands and can also increase the
dynamic range of fluorescence measurement [19–22]. Popular
mechanisms designed to produce ratiometric changes on Zn2+
binding include (a) ICT (Intramolecular Charge Transfer) [23,24],
(b) FRET (Fluorescence Resonance Energy Transfer) [25,26], (c)
⇑
Corresponding author. Tel.: +82 53 950 5588; fax: +82 53 950 6594.
E-mail address: kimhs@knu.ac.kr (H.-S. Kim).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.12.034

274
A. Helal, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 273–279
CHEF (Chelation-Enhanced Fluorescence) [27], (d) the pyrene
monomer–excimer transformation [28], (e) the chemodosimeter
approach through irreversible chemical reactions [29], (f) the two
fluorophore approach [30], (g) conformational restriction [31], (h)
the self-assembly strategy [32] and (i) ESIPT (Excited-State Intra-
molecular Proton Transfer) [33–35].
hexane); 1H NMR (400 MHz. DMSO-d6) d 2.32 (s, 3H), 6.97 (d,
J = 8.4 Hz, 1H), 7.13 (dd, J = 8.4, 1.5 Hz, 1H), 7.25 (m, 1H), 7.41 (d,
J = 1.0 Hz, 1H), 7.79 (dt, J = 7.6, 1.8 Hz, 1H), 8.00 (d, J = 7.8 Hz,
1H), 8.07 (s, 1H), 8.62 (d, J = 4.8 Hz, 1H) 11.97 (s, 1H, OH); 13C
NMR (100 MHz, DMSO-d6) d 20.9, 116.2, 116.8, 117.9, 121.5,
123.7, 127.7, 129.2, 133.4, 138.1, 149.5, 151.3, 153.8, 154.9,
169.9; Anal. Calcd. for C15H12N2OS: C, 67.14; H, 4.51; N, 10.44; S,
11.95; found C, 67.07; H, 4.44; N, 10.38; S, 11.86.
We have reported some ESIPT based chemosensors in which a
thiazole ring is substituted with a phenol at position 2 and a pyri-
dine, phenyl, or another thiazole phenol moiety at position 4 for its
use as a ratiometric fluorescence sensor of zinc [36,37], anions [38],
or the dual chemosensing of zinc and copper [39], respectively due
to the ion induced inhibition of ESIPT. We also studied the effect of
naphthol based regioisomers on complexation with Zn2+ [40]. Car-
bazole compounds are well-known as potential electron donors
with low oxidation potentials, charge transferring material and
many other electroluminescent activities [41–44]. As an extension
of our previous work in this paper we obtain further useful infor-
mation on the effect of the electron donating substituents on the
phenol–thiazole chromophore skeleton of 1 by fabricating with
our newly designed and synthesized methyl (2) and carbazole
incorporated chemosensor (3).
Synthesis of chemosensor (3)
Carbazole was incorporated into 5-iodosalicyclic acid following
Buchwald reaction by refluxing copper iodide, cyclohexyldiamine,
potassium carbonate, and carbazole in DMF [46]. The resulting car-
bazole ester was converted to compound 7 by the above procedure
[40]. A solution of 7 (100 mg, 0.3 mmol) and 2-(2-bromoace-
tyl)pyridine (72 mg, 0.36 mmol) in ethanol (15 mL) was refluxed
for 2 h. The solvent was removed under vacuum and the residue
was diluted with water and extracted with CH2Cl2. The organic
layer was dried over anhydrous Na2SO4 and concentrated. The res-
idue was purified by SiO2 column chromatography (elution with
EtOAc:hexane-1:3) to give 8 in 85% yield. A solution of BBr3
(290 mg, 1.15 mmol) in dry CH2Cl2 (15 mL) was slowly added to
a solution of 8 (100 mg, 0.23 mmol) in dry CH2Cl2 (15 mL) at
À78 °C for 1 h. The cold bath was removed and the mixture was
stirred at room temperature for 5 h, and then poured into water
and stirred for an additional hour. An aqueous layer was extracted
with CH2Cl2, the organic layer was washed with brine, dried over
anhydrous Na2SO4 and evaporated. The residue was purified by
SiO2 column chromatography (elution with EtOAc:hexane-3:1) to
Experimental
Materials
Analytical grade absolute ethanol was purchased from Merck.
Deionized water (double distilled) was used throughout the exper-
iment as an aqueous layer. All other materials used for synthesis
were purchased from Aldrich Chemical Co. and used without fur-
ther purification. Compound 5 was prepared from 5-methylsalicy-
clic acid [40] and 2-(2-bromoacetyl)pyridine were prepared in
accordance with the procedure in the literature [45]. The solutions
of metal ions were prepared from their perchlorate salts of analyt-
ical grade, and then subsequently diluted to prepare working solu-
tions. HEPES buffer solutions of different pH were prepared using
proper amount of HEPES and KOH (all of analytical grade) under
adjustment by a pH meter.
give
3
in 77% yield. mp 198 °C (CH2Cl2–hexane); 1H NMR
(400 MHz. DMSO-d6) d 7.33–7.28 (m, 2H), 7.37 (m, 2H), 7.44 (q,
J = 7.1 Hz, 1H), 7.55 (m, 2H), 7.76 (t, J = 7.6 Hz, 1H), 8.09 (q,
J = 2.8 Hz, 1H), 8.24 (d, J = 7.8 Hz, 1H), 8.30 (d, J = 7.8 Hz, 1H),
8.37 (s, 1H), 8.46 (t, J = 2.0 Hz, 1H), 8.51 (d, J = 2.0 Hz, 1H), 8.57
(d, J = 5.8 Hz, 1H), 11.76 (s, 1H, OH); 13C NMR (100 MHz, DMSO-
d6) d 109.9, 112.2, 112.6, 118.5, 120.2, 120.9, 121.4, 121.8, 122.8,
124.8, 126.3, 126.6, 127.4, 128.3, 128.8, 129.0, 130.2, 137.9,
139.9, 141.1, 141.5, 149.7, 153.6, 154.9, 155.0, 162.2; Anal. Calcd.
for C26H17N3OS: C, 74.44; H, 4.08; N, 10.02; S, 7.64; found C,
74.40; H, 4.02; N, 9.95; S, 7.55.
Equipment
Melting points were determined using a Thomas–Hoover capil-
lary melting point apparatus and are uncorrected. 1H and 13C NMR
spectra were recorded on a Bruker AM-400 spectrometer using
Me4Si as the internal standard. UV–vis absorption spectra were
determined on a Shimadzu UV-1650PC spectrophotometer. Fluo-
rescence spectra were measured on a Shimadzu RF-5301 fluores-
cence spectrometer equipped with a xenon discharge lamp, 1 cm
quartz cells. All of the measurements were carried out at 298 K.
HR-FAB mass were taken at KBSI Daegu branch.
Synthesis of chemosensor (4)
This compound was obtained from the deprotection of 9, which
was prepared from the reaction of 7 (100 mg, 0.3 mmol) and 2-
bromoacetylphenone (71 mg, 0.35 mmol), with BBr3. Work-up
was as in the above procedure for the preparation of 3. The residue
was purified by SiO2 column chromatography (elution with
EtOAc:hexane-1:2) to give 4 in 85% yield. mp 195 °C (CH2Cl2–hex-
ane); 1H NMR (400 MHz. DMSO-d6) d 7.30–7.25 (m, 3H), 7.35 (m,
5H), 7.39 (d, J = 4.8 Hz, 1H), 7.42 (d, J = 7.3 Hz, 1H), 7.54 (dd,
J = 8.6, 2.8 Hz, 1H), 7.96 (d, J = 7.1 Hz, 1H), 8.19 (s, 1H), 8.23 (d,
J = 7.6 Hz, 2H), 8.44 (d, J = 2.5 Hz, 1H), 11.73 (s, 1H, OH); 13C NMR
(100 MHz, DMSO-d6) 109.9, 110.1, 112.3, 115.9, 118.5, 120.2,
120.9, 121.1, 121.8, 122.8, 124.8, 126.2, 126.4, 126.6, 127.4,
128.4, 128.8, 129.1, 130.1, 134.3, 139.9, 141.1, 141.5, 153.5,
154.9, 155.0, 162.0; Anal. Calcd. for C27H18N2OS: C, 77.49; H,
4.34; N, 6.69; S, 7.66; found C, 77.55; H, 4.25; N, 6.63; S, 7.58.
Synthesis of chemosensor (2)
Compound 5 was prepared from 5-methylsalicylic acid accord-
ing to the reported procedures [40]. Further reaction of 5 (100 mg,
0.3 mmol) and 2-(2-bromoacetyl)pyridine [45] (71 mg, 0.35 mmol)
gave 6 in good yield. A solution of BBr3 (290 mg, 1.15 mmol) in dry
CH2Cl2 (15 mL) was slowly added to a solution of 6 (100 mg,
0.35 mmol) in dry CH2Cl2 (15 mL) at À78 °C for 1 h. The cold bath
was removed and the mixture was stirred at room temperature for
5 h, and then poured into water and stirred for an additional hour.
An aqueous layer was extracted with CH2Cl2, the organic layer was
washed with brine, dried over anhydrous Na2SO4 and evaporated.
The residue was purified by SiO2 column chromatography (elution
with EtOAc:hexane-1:2) to give 2 in 85% yield. mp 170 °C (CH2Cl2–
Synthesis of 3-Zn2+ complex
A
mixture of
3
(100 mg, 0.24 mmol) and Zn(ClO4)2Á6H2O
(147 mg, 0.39 mmol) in ethanol was refluxed for 2 h. The mixture
was cooled to room temperature and the precipitated complex
was filtered. The filtered cake was washed thoroughly with water,

A. Helal, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 273–279
275
ethanol, and dried under vacuum to provide the complex (90 mg,
X
79% yield). HR-FAB mass: calcd. for (C26H16N3OSZn) 482.0306;
found: 482.0305.
1: X = H, Y = N
S
Y
2: X = CH3, Y = N
OH
N
3: X = carbazole, Y = N
4: X = carbazole, Y = C
Results and discussion
Carbazole was introduced in 1 by Buchwald reaction. The hydro-
xyl and the carboxylic acid groups of 5-iodosalicyclic acid was first
protected with dimethylsulfate, the product was then refluxed with
copper iodide, 1,2-diaminocyclohexane, potassium carbonate, and
carbazole in DMF for 24 h. The carbazole incorporated methyl ester
was converted to amide by first deprotection of the ester by alkaline
hydrolysis, and subsequently converting it to acid chloride and then
to amide. Thionation of amide with Lawesson’s reagent gave thio-
amide 6 in good yields. Compound 5 was prepared by the reported
method from 5-methylsalicyclic acid [40]. Thiazole ring formation
was carried out by Hantzsch condensation between thioamides
and 2-(2-bromoacetyl)pyridine [45] for 7 and 8, and 2-bromo-aceto-
phenone to give 9 in ethanol as shown in Scheme 1. Deprotection of
the methoxy group with boron tribromide gave 2, 3, and 4 with
good yields. Analogue 4 was prepared to gain insight into the com-
plexation mode of 3 for Zn2+ (Fig. 1). The structures of 2, 3, and 4
were confirmed by 1H NMR, 13C NMR (Supporting Information S1,
S2, S3, S4, S5 and S6), and elemental analyses data.
Emission tuning via electron donating group has been used in
many cases to achieve the proper region of the spectrum [47]. Be-
cause the highest density HOMOs of the sensor 1 are located on the
phenoxide oxygen [40] and the C5 (para position to the oxygen),
we decided to manipulate the HOMO–LUMO energy gap responsi-
ble for the emission energy via attaching electron-donating groups
(EDG) to the C5-aryl moieties of 1. Moreover the ESIPT process in-
volves the presence of an intramolecular hydrogen bond between
the acidic group (phenol) and the basic group (thiazole nitrogen)
which are in close proximity in the ground state. Upon excitation
to the excited state due to charge transfer from the phenol ring
to the thiazole there occurs a change in the charge density that in-
creases the acidity of the acidic center and the basicity of the basic
center [35].
Fig. 1. Structures of chemosensors 1–4.
increase of a new band at 393 nm (log
e = 3.6, Table 1) due to the
deprotonation of the hydroxyl proton and disruption of the hydro-
gen bonding. The absorption bands at 338 and 393 nm linearly de-
creased and increased, respectively, up to 1 equiv. of zinc (Fig. 3a
inset), indicating the formation of a 1:1 complex. Sensor 2 also
showed a similar behavior with maximal absorption at 337 nm
and 394 nm after addition of the Zn2+ (Fig. 4a).
In both the cases of 3 and 2 the absorption band is red shifted
10 nm as compared to 1 both in the free and complex form due
to the electron donating substituents that reduce the HOMO–
LUMO gap resulting in bathochromic shift (Fig. 2, and Table 1).
Free 3 in water–ethanol system (1:3) buffered by 10 mM HEPES
at pH 7.4 with a concentration level of 20 lM exhibits fluorescence
with two emission peaks at 426 and 537 nm corresponding to the
keto and the enol emission respectively. (UF = 0.15, Table 1) with a
kex at 355 nm. Addition of zinc ion to the solution of 3 causes dis-
appearance of the two fluorescent emission peaks synchronously
and formation of a new peak at 492 nm (UF = 0.27, Table 1) with
isoemission points at 465 and 526 nm (Fig. 3b). Like some of the
benzothiazole derivatives 3 contains an intramolecular hydrogen
bond that undergo ESIPT to yield keto and enol emission from
the proton-transfer tautomer [50,51]. Coordination of zinc re-
moves the phenolic proton and disrupts the ESIPT, thus causing
emission with a normal Stokes’ shift at 492 nm. The peaks at
426, and 492 nm show a linear enhancement and diminution
respectively with the increase of zinc ion concentration up to the
ratio of Zn2+ and sensor 3 concentration is equal to 1:1. However,
when a ratio of 1:1 was reached, higher zinc ion concentration
did not lead to any further emission enhancement (Fig. 3b inset).
Thus the binding mode of 3 with zinc from the results of fluores-
cence titration spectra and Job’s plot (Fig. S-7, SI) showed to be
1:1 with a binding constant 6.8 Â 104 MÀ1 (error estimated to be
The metal-binding behaviors of 2 and 3 were determined by
UV–vis and fluorescence spectroscopic studies. In order to achieve
a physiologically acceptable condition and maintain the amphi-
pathicity of a sensor the photophysical properties of 2 and 3 were
examined in a water–ethanol system (1:3) buffered by 10 mM
610%) (Table 1) [52]. The ratio of fluorescence intensities (F492
F426) (kex = 355 nm) changed from 0.31 to 31.0 (R = 100-fold) with
/
a detection limit of 2.1 lM [53]. Sensor 2 showed a hypsochromic
HEPES at pH 7.4 with a concentration level of 20 lM. First we ob-
tain a comparative photophysical study of the sensors 1, 2, 3, and 4
in aqueous ethanol (Fig. 2).
shift from 517 to 474 nm on complexation with Zn2+ with a bind-
ing constant of 2.6 Â 104 MÀ1 (error estimated to be 610%) (Fig. 4,
and Table 1). The emission results of both 3 and 2 showed a red
shift of 31 nm and 13 nm on complexation with Zn2+ as compared
to 1 (Table 1).
Sensor 3 in the ground state exhibits a maximal absorption
band centered at 338 nm (log
e = 3.7, Table 1) (Fig. 3a). This can
be attributed to a
p
–
pà transition; this is favored by the planar ori-
The selectivity and tolerance of 3 for zinc ion over other biolog-
ically relevant metal cations such as Na+, K+, Mg2+, Ca2+ and non
biologically relevant metal cations were investigated by adding
entation enforced by intramolecular hydrogen bonding [36–
40,48,49]. When titrated by Zn2+ (0–10 equiv.), the intensity of
the maximal absorption band of 3 decreased, with a concomitant
X
X
O
X
Br
S
Y
S
Y
BBr3
NH2
H3CO
N
OH
N
EtOH
H3CO
S
Y = N, C
Y
5: X = CH3
6: X = carbazole
7: X = CH3 Y = N
8: X = carbazole, Y = N
9: X = carbazole, Y = C
2: X = CH3 Y = N
3: X = carbazole, Y = N
4: X = carbazole, Y = C
Scheme 1.

276
A. Helal, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 273–279
0.5
0.4
0.3
0.2
0.1
0.0
1 + Zn2+
2 + Zn2+
3 + Zn2+
4 + Zn2+
1
(a)
(b)
2
3
4
300
350
400
450
500
300
350
400
450
500
400
1 + Zn2+
2 + Zn2+
3 + Zn2+
4 + Zn2+
1
(c)
(d)
2
3
4
300
200
100
0
400
450
500
550
600
650
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 2. UV–visible spectra of 1 (—), 2 ( ), 3 ( ) and 4 ( ) (a) in the absence, (b) in presence of 10 equiv. of Zn(ClO4)2 in H2O:EtOH (1:3) containing HEPES buffer (10 mM, pH
7.4). Fluorescence spectra of 1 (—), 2 ( ), 3 ( ) and 4 ( ) (c) in the absence and (d) in the presence of 10 equiv. of Zn(ClO4)2 in H2O:EtOH (1:3) containing HEPES buffer
(10 mM, pH 7.4). Excitation at kex = 355 nm.
Table 1
Photophysical data and binding constants of 1–4 in H2O:EtOH (1:3).
a
Sensors
Absorption max. nm (log
Free
e
)
Emission max. (nm)
Free
Ka (MÀ1
)
Quantum yield (
U)
Zn2+
Zn2+
Free
Zn2+
1
2
3
4
329 (3.7)
337 (3.7)
338 (3.7)
338 (4.7)
384 (3.8)
394 (3.8)
393 (3.6)
338 (4.7)
502
517
426, 537
422, 538
461
474
492
422, 538
3.2 Â 104
2.6 Â 104
6.8 Â 104
ND
0.04
0.05
0.15
0.11
0.09
0.08
0.27
0.11
a
Quantum yields were obtained using quinine sulfate in 0.5 M H2SO4 as standard.
10 equiv. of metal cations to 20
l
M solution of 3 and studying their
to deprotonation and the signals of Ha, Hb, and Hc shifted downfield
due to the deshielding effect of the metal ion. However, in the case
of protons Hd experienced an upfield shift.
complexation abilities by fluorescence emission. None of the other
cations except Zn2+ induced any distinct emission shift on binding
with any of the sensors, although paramagnetic transition-metal
cations Cu2+, Ni2+, Co2+, Fe2+, and Fe3+ produced complete quenching
on binding with the sensor 3 (Figs. 5a and 6). Moreover in a compet-
itive binding experiment the presence of Na+, K+, Mg2+ and Ca2+
which are abundant in cells, did not interfere with the ratiometric
response to Zn2+, even though their concentrations were 100 times
higher than Zn2+ concentration as illustrated in Fig. 5b. Except in the
cases of Pb2+, Hg2+, Ni2+, Co2+, Fe2+, Fe3+ and Cu2+, where the
enhancement was smaller when compared to the others.
It possibly resulted from pyridine ring-metal p–d orbital inter-
action through space [54]. There was no further change in the
chemical shifts after the addition of more than 1 equiv. of Zn2+ ion.
To gain an insight into the complexation mode of Zn2+ we pre-
pared 4 which in contrast to 3 did not reveal any significant changes
in absorption and fluorescence emission upon addition up to 10
equiv. of Zn2+. This verifies the fact that it is the nitrogen of the pyr-
idine ring that is involved in Zn2+ binding and not the carbazole.
We prepared the complex of 3 with Zn2+ in H2O:EtOH (1:3) and
characterized by HR-FAB mass (Fig. S-8, SI). The HR mass spectra of
3-Zn2+ shows a 1:1 stoichiometry with the molecular ion peak at
m/z 482.0305, which can be assigned as the signal for
[M + Zn À H]+.
The ground state behavior of the zinc complexation and ion rec-
ognition was evaluated in DMSO-d6. A partial 1H NMR spectrum of
3, upon addition of 1 and 2 equiv. of Zn2+ is shown in Fig. 7. Upon
addition of 1 equiv. of Zn2+ the O–H proton peak disappeared due

A. Helal, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 273–279
277
0.5
0.4
0.3
0.2
0.1
0.0
400
(b)
(a)
0.9
0.6
393 nm
0.9
0.6
492 nm
0.3
0.3
0.0
0.0
300
200
100
0
-0.3
-0.6
-0.9
-0.3
-0.6
-0.9
-1.2
0-10 eq
426 nm
0-10 eq
492 nm
338 nm
1.5
Mole fraction of Zn2+
426 nm
0.0
0.5
1.0
2.0
0.0
0.5
1.0
1.5
2.0
Mole fraction of Zn2+
0-10 eq
338 nm
0-10 eq
0-10 eq
393 nm
537 nm
300
350
400
450
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 3. (a) UV–vis and (b) fluorescence titration spectra of 3 (20
lM) with Zn(ClO4)2 (200 lM) in H2O:EtOH (1:3) containing 10 mM HEPES (pH 7.4).
200
0.5
0.9
(b)
(a)
394 nm
0.9
0.6
0.6
0.3
474 nm
0.4
0.3
0.2
0.1
0.0
0.0
0.3
0-10 eq
290 nm
-0.3
-0.6
-0.9
150
0.0
-0.3
-0.6
-0.9
-1.2
337 nm
1.5
Mole fraction of Zn2+
0.0
0.5
1.0
2.0
517 nm
0.0
0.5
1.0
1.5
2.0
0-10 eq
Mole fraction of Zn2+
0-10 eq
337 nm
100
50
0
394 nm
0-10 eq
517 nm
0-10 eq
474 nm
300
350
400
450
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 4. (a) UV–vis and (b) fluorescence titration spectra of 2 (20
lM) with Zn(ClO4)2 (200
lM) in H2O:EtOH (1:3) containing 10 mM HEPES (pH 7.4).
250
400
1+Zn2+ Mn+
(b)
(a)
200
150
100
50
300
Host, Ag+, Ca2+, K+, Na+, Cs+, Rb+,
Mg2+, Cd2+, Al3+, Ga3+, In3+
Zn2+
200
100
Pb2+
Hg2+
Fe2+
Co2+, Cu2+, Ni2+, Fe3+
0
0
n+
2+
+ +
K
+
2+ 2+
2+ 3+
+
3+
2+
2+ 2+
2+ 3+
+
2+
2+
M
=
Zn Na
Cs Cu Ni Co Fe Ag Al Hg Pb Cd Ca Ga Rb Fe Mg
400
450
500
550
600
650
Wavelength (nm)
Fig. 5. (a) Fluorescence spectra of 3 (20 lM) upon addition of 10 equiv. of various metal ions and (b) competitive binding of 3 (20 lM) with 10 equiv. of different metal ions in
H2O:EtOH (1:3) containing HEPES buffer (10 mM, pH 7.4). kex = 355 nm.
introduction of a electron donating carbazole (3) and methyl (2)
red shifted the emission peak of the 3-Zn2+ complex 31 nm and
2-Zn2+ complex 13 nm than 1-Zn2+. Along with the red shift, incor-
poration of carbazole enhanced the quantum yield. Fluorescence is
Conclusion
In summary we chemically modified the intrinsic ratiometric
chemosensor 1 by introducing two electron donating groups. The

278
A. Helal, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 273–279
Fig. 6. Fluorogenic changes of a 20
lM solution of 3 in H2O:EtOH (1:3) containing HEPES buffer (10 mM, pH 7.4) in the presence of 10 equiv. of different cations upon
illumination at 365 nm.
Fig. 7. Partial 1H NMR spectra of 3 with Zn(ClO4)2 in DMSO-d6.
[16] F. Qian, C. Zhang, Y. Zhang, W. He, X. Gao, P. Hu, Z. Guo, J. Am. Chem. Soc. 131
produced by the disruption of ESIPT. We also established that the
strong binding affinity with zinc ion is successfully achieved by
incorporating a pyridine group as the binding ligand into the fluo-
rophore and not the carbazole nitrogen.
(2009) 1460–1468.
[17] D. Srikun, E.W. Miller, D.W. Domaille, C.J. Chang, J. Am. Chem. Soc. 130 (2008)
4596–4597.
[18] K. Komatsu, Y. Urano, H. Kojima, T. Nagano, J. Am. Chem. Soc. 129 (2007)
13447–13454.
[19] Z. Zhou, M. Yu, H. Yang, K. Huang, F. Li, T. Yi, C. Huang, Chem. Commun. (2008)
3387–3389.
[20] Y. Zhang, X. Guo, W. Si, L. Jia, X. Qian, Org. Lett. 10 (2008) 473–476.
[21] M.M. Henary, C.J. Fahrni, J. Phys. Chem. A 106 (2002) 5210–5220.
[22] K. Konig, J. Microsc. 200 (2000) 83–104.
[23] X. Zhou, B. Yu, Y. Guo, X. Tang, H. Zhang, W. Liu, Inorg. Chem. 49 (2010) 4002–
4007.
[24] J.-S. Bae, S.-Y. Gwon, Y.-A. Son, S.-H. Kim, Dyes. Pigm. 83 (2009) 324–327.
[25] J.L. Vinkenborg, T.J. Nicolson, E.A. Bellomo, M.S. Koay, G.A. Rutter, M. Merkx,
Nat. Method 6 (2009) 737–739.
Acknowledgments
This work was supported by the NRF grant funded by MEST in
Korea (NRF-2010-0010070). The Research Institute of Industrial
Technology at Kyungpook National University also supported A.H.
Appendix A. Supplementary material
[26] R.A. Bozym, R.B. Thompson, A.K. Stoddard, C.A. Fierke, ACS Chem. Biol. 1 (2006)
103–110.
[27] N.C. Lim, J.V. Schuster, M.C. Porto, M.A. Tanudra, L. Yao, H.C. Freake, Inorg.
Chem. 44 (2005) 2018–2030.
[28] K. Honda, S.-H. Fujishima, A. Ojida, I. Hamachi, ChemBioChem 8 (2007) 1370–
1372.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.12.034.
[29] Z. Li, M. Yu, L. Zhang, M. Yu, J. Liu, L. Wei, H. Zhang, Chem. Commun. 46 (2010)
7169–7171.
References
[30] C.C. Woodroofe, S.J. Lippard, J. Am. Chem. Soc. 125 (2003) 11458–11459.
[31] A. Ajayaghosh, P. Carol, S. Sreejith, J. Am. Chem. Soc. 127 (2005) 14962–14963.
[32] Z. Wu, Y. Zhang, J.S. Ma, G. Yang, Inorg. Chem. 45 (2006) 3140–3142.
[33] J. Wu, W. Liu, J. Ge, H. Zhang, P. Wang, Chem. Soc. Rev. 40 (2011) 3483–3495.
[34] A. McCarthy, A.A. Ruth, Phys. Chem. Chem. Phys. 13 (2011) 7485–7499.
[35] G. Krishnamoorthy, F.A.S. Chipem, J. Phys. Chem. A 113 (2009) 12063–12070.
[36] A. Helal, H.-S. Kim, Tetrahedron Lett. 50 (2009) 5510–5515.
[37] A. Helal, S.-H. Kim, H.-S. Kim, Tetrahedron 66 (2010) 9925–9932.
[38] A. Helal, N.T.T. Thao, S. Lee, H.-S. Kim, J. Inclusion Phenom, Macro. Chem. 66
(2010) 87–94.
[39] A. Helal, S.H. Lee, S.H. Kim, H.-S. Kim, Tetrahedron Lett. 51 (2010) 3531–3535.
[40] A. Helal, M.H.O. Rashid, C.-H. Choi, H.-S. Kim, Tetrahedron 68 (2012) 647–653.
[41] J.Y. Shen, X.L. Yang, T.H. Huang, J.T. Lin, T.H. Ke, L.Y. Chen, C.C. Wu, M.C.P. Yeh,
Adv. Funct. Mater. 17 (2007) 983–985.
[42] K.R.J. Thomas, M. Velusamy, J.T. Lin, Y.T. Tao, C.H. Chuen, Adv. Funct. Mater. 13
(2004) 387–392.
[43] S. Wang, C. Yu, M.-S. Choi, S.-H. Kim, Dyes. Pigm. 77 (2008) 245–248.
[44] Z. Zhao, X. Xu, H. Wang, P. Lu, G. Yu, Y. Liu, J. Org. Chem. 73 (2008) 594–602.
[45] J.M. Keith, L.A. Gomez, A.J. Barbier, S.J. Wilson, J.D. Boggs, B.L.C. Mazur, L.
Aluisio, T.W. Lovenberg, N.I. Carruthers, Bioorg. Med. Chem. Lett. 17 (2007)
4374–4377.
[46] A. Ueno, T. Kitawaki, N. Chida, Org. Lett. 10 (2008) 1999–2002.
[47] R. Pohl, V.A. Montes, J. Shinar Jr, P. Anzenbacher, J. Org. Chem. 69 (2004) 1723–
1725.
[1] Q.T. Meng, X.L. Zhang, C. He, G.J. He, P. Zhou, C.Y. Duan, Adv. Funct. Mater. 20
(2010) 1903–1909.
[2] M. Ishida, Y. Naruta, F. Tani, Angew. Chem. Int. Ed. 49 (2010) 91–94.
[3] G.J. He, X.L. Zhang, C. He, X.W. Zhao, C.Y. Duan, Tetrahedron 66 (2010) 9762–
9768.
[4] B. Valeur, I. Leray, Coord. Chem. Rev. 205 (2000) 3–40.
[5] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, A.J.M. Huxley, C.P. McCoy, J.T.
Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515–1566.
[6] X.Y. Zhou, B.R. Yu, Y.L. Guo, X.L. Tang, H.H. Zhang, W.S. Liu, Inorg. Chem. 49
(2010) 4002–4007.
[7] Z. Xu, J. Yoon, D.R. Spring, Chem. Soc. Rev. 39 (2010) 1996–2006.
[8] Z. Guo, G.H. Kim, I. Shin, J. Yoon, Biomaterials 33 (2012) 7818–7827.
[9] M. Rouffet, C.A.F. de Oliveira, Y. Udi, A. Agrawal, I. Sagi, J.A. McCammon, S.M.
Cohen, J. Am. Chem. Soc. 132 (2010) 8232–8233.
[10] Z. Xu, K.-H. Baek, H.N. Kim, J. Cui, X. Qian, D.R. Spring, I. Shin, J. Yoon, J. Am.
Chem. Soc. 132 (2010) 601–610.
[11] A.V. Gyulkhandanyan, H.F. Lu, S.C. Lee, A. Bhattacharjee, N. Wijesekara, J.E.M.
Fox, P.E. MacDonald, F. Chimienti, F.F. Dai, M.B. Wheeler, J. Biol. Chem. 283
(2008) 10184–10187.
[12] K. Komatsu, K. Kikuchi, H. Kojima, Y. Urano, T. Nagano, J. Am. Chem. Soc. 127
(2005) 10197–10204.
[13] C.J. Frederickson, J.Y. Koh, A.I. Bush, Nat. Rev. Neurosci. 6 (2005) 449–453.
[14] M.P. Cuajungco, K.Y. Faget, Brain. Res. Rev. 41 (2003) 44–54.
[15] M.M. Yu, Z.X. Li, L.H. Wei, D.H. Wei, M.S. Tang, Org. Lett. 10 (2008) 5115–5118.
[48] S. Wang, Coord. Chem. Rev. 215 (2001) 79–98.

A. Helal, H.-S. Kim / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 273–279
[49] J. Keck, H.E.A. Kramer, H. Port, T. Hirsch, P. Fischer, G. Rytz, J. Phys. Chem. 100 [52] P. Thordarson, Chem. Soc. Rev. 40 (2011) 1305–1323.
279
(1996) 14468–14475.
[50] M.M. Henary, C.J. Fahrni, J. Phys. Chem. A. 106 (2002) 5210–5220.
[51] S. Santra, G. Krishnamoorthy, S.K. Dogra, J. Phys. Chem. A 104 (2000) 476–482.
[53] B. Zhu, X. Zhang, Y. Li, P. Wang, H. Zhang, X. Zhuang, Chem. Commun. 46
(2010) 5710–5712.
[54] C. Lu, Z. Xu, J. Cui, R. Zhang, X. Qian, J. Org. Chem. 72 (2007) 3554–3557.