A highly selective fluorescent sensor for mercury (II) ion based on Bodipy and Calix[4]arene bearing triazolenaphthylene groups; synthesis and photophysical investigations

Article abstract of DOI:10.1016/j.jphotochem.2017.09.022

A highly selective and sensitive fluorescent sensor for mercury ion has been obtained from a combination of Bodipy and Calix[4]arene derived by click chemistry. The structural characterization of all compounds had been carried out by FT-IR, ¹H

Full text of DOI:10.1016/j.jphotochem.2017.09.022

Accepted Manuscript
Title: A highly selective fluorescent sensor for mercury (II)
ion based on Bodipy and Calix[4]arene bearing
triazolenaphthylene groups; synthesis and photophysical
investigations
Authors: Mine Sulak, Ahmed Nuri Kursunlu, Burcu Girgin,
¨
¨
Ozlem Ozen Karakus¸, Ersin Gu¨ler
PII:
S1010-6030(17)30258-7
DOI:
Reference:
http://dx.doi.org/10.1016/j.jphotochem.2017.09.022
JPC 10867
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
25-2-2017
9-9-2017
10-9-2017
¨
Please cite this article as: Mine Sulak, Ahmed Nuri Kursunlu, Burcu Girgin, Ozlem
¨
Ozen Karakus¸, Ersin Gu¨ler, A highly selective fluorescent sensor for mercury (II)
ion based on Bodipy and Calix[4]arene bearing triazolenaphthylene groups; synthesis
and photophysical investigations, Journal of Photochemistry and Photobiology A:
Chemistryhttp://dx.doi.org/10.1016/j.jphotochem.2017.09.022
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A highly selective fluorescent sensor for mercury (II) ion based on Bodipy and Calix[4]arene
bearing triazolenaphthylene groups; synthesis and photophysical investigations
Mine Sulak2, Ahmed Nuri Kursunlu1*, Burcu Girgin3, Özlem Özen Karakuş3, Ersin Güler1
1Department of Chemistry, University of Selcuk, Campus, 42075, Konya, Turkey
2Department of Organic Agricultural Management School of Applied Sciences, Pamukkale
University, 20017, Denizli, Turkey
3 Department of Chemistry, Pamukkale University, 20017, Denizli, Turkey
*Corresponding author:
E-mail address: ankursunlu@gmail.com (A.N.Kurşunlu)
Phone: +90 332 223 3876 Konya/Turkey
Graphical abstract
Highlights
 A highly selective and sensitive fluorescent sensor for mercury ion has been obtained from a
combination of Bodipy and Calix[4]arene derived by click chemistry.
 Calix [4]-B can potentially serve a sensitive and selective ratiometric sensor for Hg (I).
 This chemosensor was performed by various spectroscopic methods.
1

Abstract
A highly selective and sensitive fluorescent sensor for mercury ion has been obtained
from a combination of Bodipy and Calix[4]arene derived by click chemistry. The structural
1
13
characterization of all compounds had been carried out by FT-IR, H-NMR, C-NMR, MS,
elemental analysis or melting point. Calix[4]-B including a calix[4]arene and two Bodipy units
is a good fluorescent sensor for Hg(II). It can be explained by the coordination between
mercury and the triazole rings. In a co-solvent of methanol and water, the complexation ratio
for Calix[4]-B/Hg(II) was determined as 1:1 and the binding constant was found to be 3.42 ×
10 7 M−1. The detection of Hg (II) by Calix[4]-B works selectively in aqueous methanol mixture.
Keywords: Bodipy, Calix[4]arene, fluorescence, sensor, mercury, complex
Introduction
Sensors have a great importance in the detection of heavy metal ions due to their
serious hazards toward the environment and biological systems [1-4]. Among transition metal
ions, Hg (II) ion is a heavy metal that can cause harmful effects on the living organisms and
environment owing to its high toxicitiy [5-8]. Mercury ions in the polluting water accumulate
in the living cells by a soft-hard acid-base interaction, therefore, the removal and detection of
2

Hg (II) ion is important and necessary [9-12]. The researchers had published to some reports
on Hg (II) ion sensors over last decade [13, 14].
On the other hand, the fluorescent probes (a class of chemosensors) are crucial for a
lot of applications such as food analysis, process control, and medical diagnosis. The
fluorescent chemosensors have to include both the detection of ionophore and the signaling
of fluorophore units. The signaling units can convert into a signal expressed as the differences
in the photophysical characteristics of the chemosensor, electron, charge (ICT) or energy
transfer (PET) [15-17]. The chemosensors based-on cryptands, calixarene, cyclodextrins and
crown-ether have received a remarkable attention in supramolecular chemistry [18-20]. These
compounds can include some aromatic groups such as naphthalene, anthracene, pyrene,
rhodamine, dansyl and BODIPY as a fluorescent probe [21-29].
Cu(I)-catalyzed 1,3-dipolar cycloaddition reaction, known as “click reaction”, was
reported by Meldal [30] and Sharpless [31], which five members heterocyclic 1,2,3-triazole
occurred from the reaction between an organic azide and a terminal alkyne. In addition, it has
also been demonstrated that the triazoles formed during the coupling reactions are excellent
cation binding motifs [32,33].
This study reports to the synthesis of a calix[4]arene derived by the reaction of an azide
and an alkyne to form a triazole binding site. Moreover, a Bodipy derivative with alkyl chloride
terminal was prepared. Calix[4]arene based-on dual triazole-naphthalene and a Bodipy
derivative were combined as ionophore group and fluorescent unit, respectively. The
photophysical studies of target compound show that the sensor can be selectively used to the
detection of Hg (II) ion in presence of other ones.
3

Experimental Section
2.1. Instruments and materials
13
1H and C-NMR spectra were recorded on Varian 400 MHz NMR. The infrared spectra
were obtained from Bruker Fourier Transform Infrared FTIR (ATR). All components were
supplied from Sigma-Aldrich (MO, USA), Fisher Scientific (USA) and Acros Organics (USA) in
analytical grade and used as received, unless otherwise stated. The absorption data were
recorded by Perkin Elmer Lambda 25 UV–vis spectrophotometer at room temperature. The
emission results were taken from Perkin Elmer LS 55 spectrofluorimeter. The emission slits
were set at 3 nm in a fixed excitation. The amounts of carbon, hydrogen and nitrogen were
performed by using a TruSpec elemental analyzer. The solutions of Calix[4]-B (5x10-7 M) and
metal cation (1.10-5 M) were mixed.
2.2. The synthesis of 5,11,17,23-tetra-t-butyl-25,26-bis(O-propargyl)calix[4]arene (2)
p-tert-butylcalix[4]arene was classically synthesized as a known procedure [23].
Potassium carbonate (0.510 g, 3.69 mmol) and p-tert-butylcalix[4]arene (1 g, 1.54 mmol) was
dissolved in acetone (100 mL) and stirred at room temperature for 1 h. Propargyl bromide
(0.616 g, 5.18 mmol) was dropwise added into the mixture over 30 min. The reaction mixture
was refluxed for 24 h and then allowed to cool down to room temperature. The mixture was
then filtered over Celite to the removing of the insoluble particles and the filtrate was
concentrated by a rotary evaporator. 50 mL of HCl (2 M) was added to the concentrated
reaction mixture, and the product was extracted with dichloromethane/water (3 x 50 mL) for
three times. The combined organic extracts were successively washed with water and brine
(50 mL), dried over anhydrous Na2SO4, filtered, and evaporated to dryness in vacuum. The
4

crude product was recrystallized from CH2Cl2/CH3OH to afford 2 as a white solid (Yield, 82%).
mp 120–130 ◦C [34,35]. 1H N-MR (CDCl3, 400 MHz): 8.33 (s, 2H, OH), 7.04–7.00 (m, 8H, Ph-H),
4.81 (m, 4H, OCH2), 4.37 (d, J = 13.4 Hz, 4H, Ph-CH2-Ph), 3.40 (d, J = 13.2 Hz, 4H, Ph-CH2-Ph),
3.38 (d, J = 13.5 Hz, 2H, Ph-CH2-Ph), 2.67 (t, J = 2.4 Hz, 2H, OCH2-CC-H), 1.24 (s, 18H, t-Bu), 1.17
(s, 18H, t-Bu); MS m/z for C50H60O4: 724.45 [M+H]+.
2.3. The synthesis of 1-Azidonaphthalene (4)
An ice-cold solution of sodium nitrite (210 mg, 3 mmol) in water was dropwise added
to a cold solution of aryl amine (143 mg, 1 mmol) (3) in the concentrated hydrochloric acid in
water (50 mL) at 0 oC over 10 min. The reaction mixture was slowly stirred for 10 min before
an ice cold solution of sodium azide (195 mg, 3 mmol) in water (50 mL) was dropwise added
o
at 0 C over 10 min. After the mixture was stirred for 15 min. The resulting mixture was
extracted with diethylether (3 x 20 mL) [36]. The organic layer was washed with water (3x 100
mL) and brine solution, dried over anhydrous Na2SO4, and then concentrated to pure aryl azide
4 (152 mg, yield 90%). 1H- NMR (CDCl3, 400 MHz): 8.0-8.2 (m, 3H, Ph-H ), 7.4–7.9 (m, 4H, Ph-
H).
2.4. The synthesis of calix[4]arene-click-1-Azidonaphthalene (5)
5,11,17,23-tetra-t-butyl-25,26-bis(O-propargyl)calix[4]arene (0.15g, 0.20 mmol) was
solved in toluene (20 mL). A mixture of 4 (0.067 g, 0.40 mmol), CuI (0.021g, 0.11 mmol) and
triethylamine (0.165 mL, 1.19 mmol) in DMF (20 mL) was added to this solution and refluxed
for 24 h. The mixture was extracted with CHCl3 /water for three times and the organic phase
was combined. The organic phase was dried over MgSO4 and the solvent was evaporated to
give the solid crude product [20]. The solid product was eluted with ethyl acetate/hexane (v/v,
5

1:1) mixture and gave 5 (0.45 g, 72%) as a white solid, mp 241-242 ◦C; Rf = 0.3, ethyl
acetate/hexane (v/v, 1:3). 1H NMR (CDCl3, 400 MHz): 7.84 (s, 2H, OH), 7.75 (s, 2H, CCHN), 7.0-
7.23 (m, 10H, naphthalene -H), 6.85 (d, J =2.4 Hz, 2H, Ph-H), 6.67 (d, J = 2.3 Hz, 2H, Ph-H), 7.04
(d, J = 2.3 Hz, 2H, Ph-H), 7.00 (d, J = 2.3 Hz, 2H, Ph-H), 4.93 (s, J = 11.5 Hz, 4H, OCH2), 3.91 (d, J
= 12.7 Hz, 4H, Ph- CH2-Ph), 2.93 (d, J = 12.9 Hz, 4H, Ph-CH2-Ph),.0.91 (s, 18H, t-Bu), 0.64 (s, 18H,
t-Bu). Anal.Calc. for (%) C70H74N6O4: C, 79.06; H, 7.01; N, 7.90; Found; C, 79.46; H, 7.41; N, 7.77.
2.5. The synthesis of 8-{4-(chloromethyl)phenyl}-2,6-diethyl-4,4-difluoro-1,3,5,7-
tetramethyl-4-bora-3a,4a-diaza-s-indacene (6)
6 was synthesized according to a known procedure [37,38]. 4-(chloromethyl)benzoyl
chloride (0.938 g, 5 mmol) was added to a solution of 2,4-dimethyl-3-ethylpyrrole (1.35 mL,
10 mmol ) in dry DCM (80 mL) at room temperature and under dark/N2 medium. The solution
was stirred at 55 oC for 3 h. After the cooling of the mixture, triethylamine (TEA) (5 equiv.) was
injected to the residual solid, the mixture was stirred at room temperature for 1 h in inert
medium and then BF3.OEt2 (8 equiv.) was added. The mixture was refluxed at 55 oC for 3 h and
the final product was purified on column (petrolium ether-EtOAc; in 7:1). A red solid (0.885 g
Yield 43%). 1H-NMR [400 MHz, CDCl3]: ¹H NMR [400 MHz, CDCl3]: 7.41 (d, J = 2.3 Hz, 2H, Ph-
H), 7.18 (d, J = 2.3 Hz, 2H, Ph-H), 4.63 (s, 2H, CH2), 2.44 (s, 6H, CH3) 2.21 (q, 4H, CH2) 1.27 (s,
6H, CH3) 0.89 (t, 6H, CH3).13C NMR [100 MHz, CDCl3]: δ (ppm); 153.81, 139.42, 138.42, 136.12,
135.81, 132.83, 130.62, 129.02, 128.78, 45.59, 17.07, 14.43, 12.43, 11.62. Anal.Calc. for (%)
C24H28N2F2ClB: C, 67.23; H, 6.58; N, 6.53; Found: C, 66.97; H, 6.98; N, 6.22. MS for
C24H28N2F2ClB m/z: 428.2 [M+H]+.
6

2.6. The synthesis of Calix[4]-B
Calix[4]-B was prepared according to a known procedure [37] and purified by some
purification techniques. A solution of potassium iodide (50 mg, 3 equiv.) in 10 mL dry DMF was
poured to the solution of 5 (106 mg, 1 mmol) in 50 mL chloroform. The mixture was stirred at
95 oC for 24 hours. Chloro-Bodipy (86 mg, 2 mmol) and N,N-Diisopropylethylamine (DIPEA) (2
equiv.) was added to this mixture and was refluxed for 72 hours. The reaction mixture was
poured to ice and the suspension was extracted with dichloromethane for five times (3 x 30
mL). The organic phase was evaporated and the purification of crude product was carried out
with a mixture of ethylacetate/petroleum ether (1:2) in column, a red-orange solid was
obtained (114 mg Yield: 62%).1H NMR (CDCl3, 400 MHz): 7.68 (d, J = 2.4 Hz, 2H, Ph-H) , 7.25
(d, J = 2.3 Hz, 4H, Ph-H), 7.20 (d, J = 2.3 Hz, 4H, Ph-H), 7.0-7.12 (m, 10H, naphthalene -H), 6.92
(s, , 2H, CCHN), 6.68 (d, J = 2.3 Hz, 2H, Ph-H), 6.48 (d, J = 2.3 Hz, 2H, Ph-H), 6.42 (d, J = 2.3 Hz,
2H, Ph-H), 5.38 (s, J= 11.5 Hz, 4H, OCH2), 4.92 (s, 4H, CH2), 4.28 (dd, J = 12.8 Hz, 2H, Ph- CH2-
Ph), 4.08 (dd, J = 12.8 Hz, 2H, Ph- CH2-Ph), 3.25 (d, J = 12.8 Hz, 2H, Ph- CH2-Ph), 3.17 (d, J = 12.8
Hz, 2H, Ph- CH2-Ph), 2.50 (s, 12H, CH3), 2.20 (q, 8H, CH2), 1.21 (s, 12H, CH3) , 1.17 (s, 18H, t-
13
Bu), 1.11 (s, 18H, t-Bu), 0.93 (t, 12H, CH3). C-NMR [100 MHz, CDCl3]: (ppm); 154.6, 147.2,
145.1, 143.2, 141.2, 139.2, 136.8, 135.2, 134.6, 134.0, 132.2, 132.1, 130.1, 129.8, 128.8, 128.1,
126.7, 126,0, 125.7, 125.0, 122.2, 120.0, 73.2, 71.2, 35.5, 32.5, 30.7, 18.3, 17.7, 14.3, 12.3,
11.6. Anal.Calc. for (%) C118H128B2F4N10O4: C, 76.69; H, 6.98; N, 7.58; Found: C, 76.82; H, 6.99;
N, 7.50. MS for 1848,02 [M+H]+.
7

i
HO
OH OH
1
OH
OH
2
O
OH
O
O
O
OH
OH
ii
N
N
N
N
NH2
N3
N
N
iii
4
3
5
F
F
B
N
N
F
F
F
F
N
N
O
O
OH
OH
B
N
B
N
+
iv
N
N
O
O
O
O
2
N
N
N
N
N
N
N
N
N
N
Cl
6
5
Calix [4]-B
Scheme 1. The preparing process of Calix [4]-B. (i) NaH, propargyl bromide, DMF, 70 ◦C, 2 h; (ii) 1-
azidonaphthalene (4), CuI, Toluene/50 ◦C, 1 d;(iii) NaNO2/HCl, NaN3/H2O, r.t., 15 min. (iv) DIPEA
3. Results and Discussion
3.1. The synthesis and characterization of compounds
8

The synthetic pathway for ligand, Calix [4]-B, was given in Scheme 1. The compound 2
was synthesized by the reaction of p-tert-butylcalix[4]arene and propargyl bromide in the
presence of NaH in DMF. The compound 5 was obtained by a click reaction with Cu(I)-catalysis
between 3 and 4, which prepared from the diazotization of 1-aminonaphthalene. The target
molecule, Calix [4]-B, was synthesized by the dually binding of chloro-Bodipy to 5 in presence
of DIPEA. The structure of compounds synthesized in this work was characterized by 1H-NMR
spectra as well as Fourier Transform Infrared FTIR (ATR) and elemental analyses. The mass
measurement was recorded by a Bruker Compass Data Analysis 4.0 (ESI-TOF-MS) (The mass
spectrometers used were a micrOTOFQ and a maXis quadrupole time-of-flight mass
spectrometer).
In FT-IR spectrum of 5, the peaks were observed at 3367 cm-1, 3057 cm-1, 2964 cm-1,
1598 cm-1, 1515 cm-1 and 1481 cm−1 which can be referred to aromatic νO-H, aromatic νC-H,
aliphatic νC-H, imine νC=N, νC-N and alkene νC=C, respectively. In spectrum of Calix [4]-B, new
bands were especially observed around 1750 cm-1 that the peaks assigned to the νC=N
vibrations of Bodipy.
1H-NMR spectrum of 5 exhibits the evanescence of three terminal CCH hydrogens
originally found in 2 leaving the new singlet peak revealing around δ = 6.91 ppm referring to
1
two protons of the newly formed triazole skeleton. H-NMR spectrum of 5 showed to two
doublet-doublet signals at δ 3.98 and 2.90 ppm. These signals can be ascribed to a classical
methylene-bridge protons of calix[4]arenes in 5 owing to its C2v symmetry. These signals
1
appeared as four doublets in H-NMR spectrum of Calix [4]-B. These differences can be
explained by the different conformation of two Bodipy fragments due to the steric hindrance
occurred between Bodipy and triazoyl-naphtalene units. Therefore, the molecular symmetry
9

of Calix [4]-B can be asserted as Cs. On the other hand, the peak -CH2 of compound 6 at 4.63
ppm prominently shifted to 4.92 ppm depending on the effect of an electronegative atom and
electron attractive groups. Other peak values of 6 and 5 around 0-2.5 ppm and aromatic area
slightly changed and some signals hidden because of the overlapped peaks.
3.2. The spectroscopic studies of Calix [4]-B
As referred to previously, the synthesis of calixarenes containing ionophore groups is
crucial in fluorescent sensor applications. Therefore, Calix [4]-B have been substituted with
naphtalene groups and Bodipy units exhibiting ligand property and fluorescence character,
respectively.
The fluorescence, excitation and absorption properties of Calix [4]-B were investigated
in presence of some metal cations [Ga(III), Gd(III), Ni(II), Zn (II), Cu (II), Co (II), Cd (II), Cr (III),
Mn (II), Yb (III), Hg (II), Ag (I), Tb (III)]. The concentrations of ligand and metal cations were
adjusted as 5.10-7 M and 1.10-5 M, respectively.
In the fluorescence spectrum, we get to the band of Calix [4]-B with the longest
wavelength as a reference that it appeared at 535 nm. Upon the addition of metal cations, a
quenching effect was only observed in presence of Hg(II) ion. Other cations slightly affected
to the emission intensity of Calix [4]-B. The evident change in the fluorescence intensity of
sensor can be depended on the interaction between Calix [4]-B and Hg (II) ion. Compound 5
consists of two parts; the receptor fluorophore (Bodipy). Calix [4]-B has an efficient form
binding sites of metal ion. The fluorescence measurements show that Hg (II) is most likely to
bind Calix [4]-B via two N-atom pairs of the triazole ring. Actually, the complex formation was
10

supported by the cavity occurred by the derivatization of calix[4]arene. The cationic size,
charge and nature of donor atoms play a crucial role in the selective interaction of compound
Calix [4]-B with only Hg (II) over other metal ions [Ga(III), Gd(III), Ni(II), Zn (II), Cu (II), Co (II),
Cd (II), Cr (III), Mn (II), Yb (III), Ag (I), Tb (III)].
On the other hand, naphthyl derivatives are known as an effective precursor for the
preparing of different fluorescent sensors due to its donor as well as acceptor sites [39].
Although the naphthyl groups have a good fluorescence character, they have a much lower
emission wavelength (around 400 nm) and intensity when they compared with Bodipy (≥ 500
nm) [37,38]. However, in this study, both Bodipy units and naphthyl ring act as an electron
donor toward Hg (II) ion. Therefore, the fluorescence intensity of Calix[4]-B bearing two
naphthyl and two Bodipy fluorophores decreased in presence of Hg (II) ion. This turn-off
fluorescence change indicated that an energy transfer carried out from the Bodipy-naphthyl
excimer to mercury ion. In particular, calix[4]arene unit has attracted as a considerable
interest because they form efficient excimer signal by the strong intramolecular π-π
interactions between the two naphthyl groups.
The excitation spectra of Calix[4]-B and mixtures were performed at the fixed emission
(535 nm). The excitation spectra specially show a So-S1 band between 300-450 nm due to they
have the lowest energy absorption features. The excitation curves of Calix[4]-B and Calix[4]-
B/metal solutions in MeOH/H2O mixture (v/v, 9:1) were obtained in the fixed emission (535
nm) (Fig.2). The five bands were observed in all spectra of the mixtures. The excitation curves
almost superimposed except of Calix[4]-B/Hg(II) mixture. Although the excitations spectra are
close for the Hg complex and the free ligand, the all excitation mounds of Calix[4]-B
11

broadened in presence of Hg (II) cation owing to the strong ligand character of two
triazolylnaphthalene units.
The absorption spectra of Calix [4]-B and Calix [4]-B/metal cations mixture were
shown in Fig 3. The used metal cations [Ga(III), Gd(III), Ni(II), Zn (II), Cu (II), Co (II), Cd (II), Cr (III), Mn
(II), Yb (III), Ag (I), Tb (III)] did not affect to the absorption properties of Calix [4]-B. Therefore, the
absorption curves Calix [4]-B and Calix [4]-B/metal cations [except of Hg (II)] were
represented with yellow cloudy-line. However, Hg (II) ion caused evidently to a blue-shift and
the band of Bodipy (522 nm) and π-π transitions (around 360 nm) of Calix [4]-B appeared in
lower wavelengths. A complexation reaction mechanism can be proposed between ligand and
metal ion that mercury ion is encapsulated by calix-triazole-bodipy with triangle cavity. The
shift in absorption bands can be explained with internal charge transfer (ICT) from Bodipy
units. Uv-vis studies, just as the fluorescence and excitation, Calix [4]-B can be used as an
effective fluorescent sensor in the selective and sensitive detection of Hg (II) ion. So, Calix [4]-
B has a more attractive performance for the detection of mercury ion when compared to
previous papers [40].
Job plot analysis was used for determine of the complex stoichiometry between
Calix[4]-B and Hg (II). The mixtures of Calix[4]-B with Hg (II) approached a maximum when the
molar fraction of ligand/metal cation was around 0.50, indicating a 1:1 ratio between sensor
and mercury ion. The similar studies were carried out by the emission maxima and observed
same ratio between metal and ligand as 1:1. The estimated binding mode of the complex was
given in Fig. 4 that Hg(II) ion coordinated with two triazole fragments.
12

The quantum yields were determined by using rhodamine B as a criterion. The
quantum yield of emission for Calix[4]-B and Calix[4]-B–Hg(II) complex were evaluated as 0.56
and 0.13 in methanol/water (9:1), respectively. The fluorescence quantum yield of Hg (II)
solution (20 equiv.) was lower than of the free ligand. The lower quantum yield shows an
energy transfer from Calix[4]-B to Hg (II) ion).
To determine the association constant, a solution of Calix[4]-B in MeOH:H2O (9:1) was
titrated with a solution of HgCl2 in MeOH:H2O (9:1) due to the solubility requirements (Fig. 5).
The binding constant was calculated by Stern-Volmer relationship.
I0/I=1 + Ka[Q]
where I0 and I are the fluorescence intensities of Calix[4]-B in the absence and presence of
mercury ion, respectively, Ka is the association constant of Calix[4]-B/Hg (II) ion and [Q] is the
concentration of mercury cation. The concentration of Calix[4]-B was kept the constant during
the whole experiment to a reliable measurement. The concentration of mercury salt was 2
times smaller (first mixture) and 19 times smaller (final mixture) that the association constant
of Calix[4]-B/Hg (II) calculated as 3.42 × 10 7 M−1 while other metal ions have lower association
constants range of 2.5 x 104 -2.8 x 105 M−1. The association constant can be depended on the
strong chelating effect of a multi-dentate ligand on mercury ion. The value acceptable for the
fluorescent sensors. Moreover, the quantum yield was calculated as 0.18 for the complex
system.
To better investigate Calix[4]-B (5.10-7 M) as a selective sensor for Hg(II) ion in the practical
applications, the competing ion studies were performed in the presence of Hg (II) ion (1.10-5
M) mixed with Ga(III), Gd(III), Ni(II), Zn (II), Cu (II), Co (II), Cd (II), Cr (III), Mn (II), Yb (III), Hg (II),
13

Ag (I), Tb (III) at 1.10-5 M; as shown in Fig. 6., A remarkable interference in detection of Hg (II)
ion with Calix[4]-B was not observed in the presence of most other competing metal ions
except for the Hg (II) ion. Thus, these results assign that Calix[4]-B can be applied as a selective
sensor for mercury ion in the presence of most competing metal cations.
Moreover, we studied to a sensing response time of the sensor toward various times
of Hg (II) (0-20 minutes) (Fig. 7). By the addition of mercury solution, the fluorescence intensity
of Calix[4]-B quickly decreased and reached to a maximum quenching effect in four minutes.
The fluorescence intensity continued in a stable value after four minute though the increasing
time. The response time is an ideal result for a selective sensor that Calix[4]-B can be applied
for Hg (II) ion.
The peaks -CH2 of compound 5 at 4.95 ppm clearly shifted to 5.38 ppm in the NMR spectrum
of Calix [4]-B depending on the effect of an electron attractive groups. Other peaks of reagents
between 0-2.5 ppm and aromatic area slightly changed and some signals hidden due to the
overlapped peaks. To get first-hand information about the coordinating sites of receptor
1
Calix[4]-B and Hg (II), H-NMR of ligand was performed with Hg(NO3)2 (in DMSO-d6) (Fig. 8).
Upon addition of Hg (II) ion, Calix[4]-B exhibited a considerable changes for the protons close
to the triazole rings and Bodipy units that are supposed to serve as coordination sites. While
-CH2 protons close to the triazole and Bodipy groups appeared at 5.27 and 4.89 ppm, Calix[4]-
B-Hg(II) complex gave singlet peaks for same protons at 5.8 and 5.1 ppm, respectively.
Moreover, -CH protons in triazole ring shifted from 6.91 to 7.43 ppm.
The limit of detection (LOD) was calculated from the standard deviation of the blank and some
parameters that the detection limit affected the accuracy of the model used to predict
14

concentrations from the sole emission peak. LOD was evaluated by the emission intensities
obtained from the mixture of Calix[4]-B (5.10-7 M) and the solutions of Cu (II) in different
concentrations.
LOD= 3σ/F
In there, F is the false of the LOD curve, σ is the standard deviation of the blank solution; The
LOD of Calix[4]-B towards Hg (II) calculated to be 2.8 (±0.2) × 10-7 M. When it compared with
previous papers, Calix[4]-B has a lower LOD that it is useful for the detection of Hg (II) ions in
half aqueous [40, 41].
Conclusion
An efficient sensor, Calix[4]-B, was produced from calix[4]arene−naphthalene
derivative (5) obtained by click reaction and a fluorescent Bodipy with alkyl-chloride terminal.
Calix[4]-B displayed a high selectivity for Hg (II) ion in MeOH/H2O co-solvent. The studied
competing ions [Ga(III), Gd(III), Ni(II), Zn (II), Cu (II), Co (II), Cd (II), Cr (III), Mn (II), Yb (III), Ag
(I), Tb (III)] in the same solution did not cause to any hindrance to the enhancement or
quenching in the fluorescence intensity of Calix[4]-B. The sensor having two azido-
naphthalene groups turns out to have high affinity for Hg(II) and completely is quenched to
the fluorescence intensity of the fluorophore. As result, the sensor, Calix[4]-B, can be usefully
used in the detection of mercury (II) ion.
Acknowledgements
We thank to Selcuk University (BAP) (15401013) for financial support of this work.
15

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18

Figures
Fig.1 The fluorescence spectra (ʎexc= 470 nm, slit:3) of Calix [4]-B (5.10-7 M) and Calix [4]-B/metal
cations (1.10-5 M) in MeOH/H20(v/v, 9:1)
19

Fig.2 The excitation spectra (ʎem= 535 nm, slit: 3) of Calix [4]-B (5.10-7 M) and Calix [4]-B/metal
cations (1.10-5 M) in MeOH/H20(v/v, 9:1)
20

Fig.3 The absorption spectra of Calix [4]-B (5.10-7 M) and Calix [4]-B/metal cations (1.10-5 M) in
MeOH/H20(v/v, 9:1)
21

Fig. 4 Job’s plot for Calix[4]-B (5.0x10−7 M) and Hg (II) complexation in a mixture of MeOH/H2O (9:1,
v/v).
22

Fig.5 Stern-Volmer plot for changes of Calix[4]-B [5.10-7 M in MeOH/H2O (9:1, v/v)] in the
fluorescence intensity by the addition of Hg (II) ion in MeOH/H2O (9:1)
23

Fig. 6 The relative fluorescence intensity changes of Calix[4]-B/Hg(II) mixture [5.10-7 M, 1.10-5 M in
MeOH/H2O (9:1, v/v), respectively] at 298 K in presence of various competing metal ions (1.10-5 M). Io
is emission intensity at 535 nm for free receptors, and I is the emission intensities after adding metal
cations with a fixed excitation at 470 nm.
24

Fig. 7 The effect of response time to the fluorescence intensity of Calix[4]-B [5.10-7 M, 1.10-5 M in
MeOH/H2O (9:1, v/v)] in by the addition of Hg (II) ion [1.10-5 M in MeOH/H2O (9:1, v/v), (ʎem: 535 nm)
25

1
Fig. 8 The complexation of Hg (II) by Calix[4]-B A) H-NMR spectrum of Calix[4]-B with signal
assignment based on 2D spectra (400 MHz, DMSO, 298 K); B) Calix[4]-B–Hg(II) (2 equiv, 400 MHz,
DMSO, 298 K)
26