Elucidation of Selectivity for Silver Ion Based on Metal-Induced H-Type Aggregation of Fluorescent Receptor

Article abstract of DOI:10.1007/s10895-020-02520-3

In present work, a new substituted phthalonitrile derivative was prepared by the nucleophilic displacement reaction and then highly soluble zinc phthalocyanine (ZnPc) with four peripheral 1-hydroxyhexan-3-ylthio groups was synthesized by cyclotetramerization and characterized by FTIR, ¹H and ¹³C NMRs spectroscopies, fluorescence and UV–vis measurements. The optical property and quantum yield of ZnPc were elucidated in mixed solvent of ethanol/water with varying compositions. The pH-dependent fluorescence and absorbance spectra of ZnPc in the absence and presence of Ag⁺ ions were obtained to elucidate the optimum pH value that is convenient for stable complex formation in predetermined mixture. A comparative study for recognition of Ag⁺ ion has been carried out to evaluate the effect of the solution parameters on selective sensing ability of ZnPc as a fluorescent receptor. Interference effect was investigated by spectrofluorometric titration based on fluorescence quenching of ZnPc upon addition of Ag⁺ ion in the presence of foreign metal ions. Stepwise complexation/decomplexation cycles with Na₂S-titration by fluorescence quenching/enhancement were investigated to establish the reversible response rate and reusability of ZnPc toward Ag⁺ ions.

Full text of DOI:10.1007/s10895-020-02520-3

Journal of Fluorescence
https://doi.org/10.1007/s10895-020-02520-3
ORIGINAL ARTICLE
Elucidation of Selectivity for Silver Ion Based on Metal-Induced
H-Type Aggregation of Fluorescent Receptor
Taner Arslan1 & Merve Umutlu1 & Orhan Güney1
Received: 18 December 2019 /Accepted: 14 February 2020
#
Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract
In present work, a new substituted phthalonitrile derivative was prepared by the nucleophilic displacement reaction and then highly
soluble zinc phthalocyanine (ZnPc) with four peripheral 1-hydroxyhexan-3-ylthio groups was synthesized by cyclotetramerization
and characterized by FTIR, 1H and 13C NMRs spectroscopies, fluorescence and UV–vis measurements. The optical property and
quantum yield of ZnPc were elucidated in mixed solvent of ethanol/water with varying compositions. The pH-dependent fluores-
cence and absorbance spectra of ZnPc in the absence and presence of Ag+ ions were obtained to elucidate the optimum pH value that
is convenient for stable complex formation in predetermined mixture. A comparative study for recognition of Ag+ ion has been
carried out to evaluate the effect of the solution parameters on selective sensing ability of ZnPc as a fluorescent receptor. Interference
effect was investigated by spectrofluorometric titration based on fluorescence quenching of ZnPc upon addition of Ag+ ion in the
presence of foreign metal ions. Stepwise complexation/decomplexation cycles with Na2S-titration by fluorescence quenching/
enhancement were investigated to establish the reversible response rate and reusability of ZnPc toward Ag+ ions.
.
.
.
Keywords Fluorescent receptor Silver ion Selective sensing H-type aggregation
Introduction
of inductively coupled plasma - atomic emission spectrometry
[7], inductively coupled plasma - mass spectrometry [8],
atomic absorption spectrometry [9, 10], high performance liq-
uid chromatography [11, 12], X-ray fluorescence [13], strip-
ping voltammetry [14] and potentiometry [15]. However,
these techniques require expensive equipment and profession-
al operators, interferences from sample matrix, need sample
preparation procedures, long analysis time. An accomplished
sample pretreatment and preparation procedure for these ana-
lytical techniques depends on the preconcentration and sepa-
ration from interfering matrix for the accurate detection of
analyte. Various preconcentration methods have been devel-
oped for silver ion, including solid phase extraction [16],
liquid–liquid extraction [17] and cloud point extraction [18].
However, although these methods have simple operations,
there are also limitations such as high solvent usage, low
selectivity, low yield and recoveries and poor reproducibil-
ity of enrichment and isolation [19]. For this reason, there
is a need for alternative and practical solutions that require
fast, reliable, low cost, and less specialized expertise for
silver ion determination. The development of selective
chemosensors for heavy metal ions due to the importance
of their usage in industrial applications and environmental
impact become important in recent years. It is very impor-
tant to determine low concentrations of metal ions by
Silver has a special economic value compared to other heavy
metal atoms and it is used in many field of applications such as
electronic, electroplating, mirroring, chemistry, dentistry, medical
equipment and jewelry industries [1]. The widespread use of
silver applications causes an increase of silver ion in environmen-
tal samples [2]. On the other hand, biological molecules such as
nitrogen, oxygen and sulfur containing proteins and enzymes can
form complexes with silver ion [3]. For example, it can constitute
stable complex with sulfhydryl group of cysteine and sulfur atom
of methionine [4]. Exposure high level or long period of silver in
the body can cause toxicological consequences for bones, kid-
ney, liver and skin disease such as argyria or argyrosis [3, 5, 6].
Diverse analytical and electrochemical determination
methods have been reported for silver ion with the inclusion
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s10895-020-02520-3) contains supplementary
material, which is available to authorized users.
* Orhan Güney
oguney@itu.edu.tr
1
Departments of Chemistry, Istanbul Technical University, 34469
Maslak, Istanbul, Turkey

J Fluoresc
simple fluorescence technique with high sensitivity, good
selectivity, short response time and real time monitoring.
Phthalocyanines (Pcs) are macrocyclic and aromatic
organic dye compounds with a stable two-dimensional
π-electron system which has high inertness, high thermal
stability and low soluble properties [20]. These com-
pounds have been widespread used in automotive paints,
textile, paper and printing industries as a dyestuff due to
their intense blue-green color [21]. Due to the attractive
and tunable photophysical and photochemical properties,
Pcs were used in many applications including solar cells
[22], liquid crystals [23], catalysts [24], photodynamic
cancer therapy [25], and sensor [26, 27]. These macrocy-
clic molecules including a metallic core are classified as
metallo phthalocyanines and their photophysical proper-
ties are influenced by the nature of the central metal ion
[28]. Some metal ions can play a major role in decrease
molecular aggregation and increase the solubility of Pcs,
besides; especially diamagnetic metals can change optical
limiting and photosensitive properties of Pcs [29, 30].
In the present article, the ligand 4-(1-hydroxyhexan-3-
ylthio)-phthalonitrile and its tetra-substituted
zincphthalocyanine (ZnPc) were synthesized and character-
ized by elemental analysis, FTIR, 1H and 13C NMRs, fluores-
cence and UV–vis spectral data. The optimum pH and com-
position of mixture were elucidated to ensure the selective
sensing of Ag+ ions in complex mixture. A remarkable
quenching in fluorescence of ZnPc was observed upon titra-
tion with Ag+ ions in the presence of interference metal ions.
The reversible response of ZnPc toward Ag + ion was
established by the Na2S-titration where enhancement in fluo-
rescence of ZnPc was observed upon decomplexation.
Zn(OAc)2, potassium carbonate (K2CO3), silver nitrate
(AgNO3), mercury nitrate monohydrate (Hg(NO3)2.H2O),
lead nitrate (Pb(NO3)2), strontium nitrate (Sr(NO3)2), magne-
sium nitrate hexahydrate (Mg(NO3)2.6H2O), cadmium nitrate
tetrahydrate (Cd(NO3)2.4H2O), nickel nitrate hexahydrate
(Ni(NO3)2.6H2O), barium nitrate (Ba(NO3)2), iron nitrate
nonahydrate (Fe(NO3)3.9H2O) were obtained from Alfa
Aesar (Lancaster, UK). Chromatography was performed with
silica gel (Merck grade 60 and sephadex) from Aldrich. All
solvents and other reagents were analytical grade and used
without purification.
Apparatus
Attenuated Total Reflectance-Fourier Transform Infrared
(ATR-FTIR) of the samples was recorded on an Agilent
Cary 630 FTIR spectrometer and pH of the solutions was
measured with a VWR 730P pH meter. The fluorescence
spectra were obtained by using a Varian Cary-Eclipse
spectrophotometer controlled by a PC. VWR UV-
1600PC Spectrometer was used for the recording of
1
UV–visible spectra of samples. H NMR and 13C NMR
spectra were recorded on an Agilent VNMRS 500 MHz
spectrometer instruments.
Synthesis and Characterization of ZnPc
Prior to synthesis of ZnPc, 3-(1-hydroxyhexan-3-
ylthio)phthalonitrile (HTPN) was synthesized as follows.
Briefly, 6.0 mmol of 3-mercapto-1-hexanol dissolved in
5.0 mL of DMF and the 8.5 mmol of K2CO3 was added
into solution, and then 6.00 mmol of 3-nitrophthalonitrile
dissolved in 5.0 mL of DMF and added into the first
solution dropwise at 40 °C under N2 atmosphere. The
mixture was stirred adequately under these conditions
for 24 h. At the end of the reaction, the mixture was
cooled down and poured into a 150 mL of ice water for
precipitation of the product (Scheme 1). The precipitate
was dissolved in chloroform and washed with 2.5%
NaHCO3 and anhydrous Na2SO4 in order to remove the
impurities. Finally, chloroform was evaporated and
Experimental
Chemicals
3-mercapto-1-hexanol, 3-nitrophthalonitrile and 1,8-
Diazabicyclo[5.4.0]undec-7-ene (DBU) were purchased from
Sigma-Aldrich (Darmstadt, Germany). Zinc acetate
Scheme 1 Synthesis route of
ZnPc i: K2CO3, 3-mercapto-1-
hexanol, DMF, 40 °C, 2 days, ii:
Anhydrous Zn(OAc)2, DBU,
170 °C, 8 h.

J Fluoresc
Fig. 1 Absorption (A) and fluo-
rescence (B) spectra of ZnPc de-
pending on composition of
ethanol-water mixture. Insets:
Absorbance value at 706 nm (A)
and emission intensity at 720 nm
(B) upon change in percentage of
water in mixture
product was obtained after the silica gel column chroma-
tography (CHCl3: MeOH (95: 5) eluent). For the synthesis
of ZnPc, 300 mg of HTPN and 60 μL of DBU were
powdered in a stamped tube and heated to reflux at
170 °C under N2 atmosphere. After adequately stirring
for 30 min, 48 mg of anhydrous Zn(OAc)2 was added into
mixture. At the end of the heating and stirring for 8 h, the
product was cooled down to the room temperature and
washed with hot heptane, a mixture of isopropanol-water
and acetonitrile, respectively in order to remove the im-
purities. Finally, the product was obtained after the two
silica gel column chromatography (THF: MeOH (50:1 v/
v) eluent), (CHCl3: MeOH (20:1 v/v) eluent) and washed
with hexane and diethyl ether (Scheme 1).
Result and Discussions
Photophysical Property of ZnPc in Solvent Mixture
Absorption and fluorescence emission spectra of ZnPc in
ethanol-water mixture with different ratio were obtained to
elucidate the optimal composition of solution which is oppor-
tune for metal ion detection in aqueous buffer solution for
sensor application in environmental analysis. As can be seen
from Fig. 1A, absorbance of ZnPc diminishes with increasing
water content in mixture due to the aggregation of ZnPc mol-
ecules since hydrophobic character of solution decreases.
However, a red shift occurs in peak maximum of ZnPc due
to the diminution in energy level of electron transition of Pc
ring caused by increment in electron conjugation [26]. On the
other hand, fluorescence emission of ZnPc was quenched with
increase in water content in mixture and peak maximum
shifted from 723 to 716 nm due to increase in HOMO and
LUMO band gap energy (Fig. 1B).
FT-IR (ATR) ν, cm−1: 2922, 2860 (scissoring vibrations of
CH2-O), 1719 (Aliph-H), 1598 (C=C), 1482, 1434, 1382,
1297 (in-plane and out-of-plane bending bands of CO-H),
1093, 1035 (wagging vibrations of CH2-O) 905, 813, 745,
1
680. H NMR (DMSO-d6) δ, ppm: 9.21(d, br, 1H, Phenyl
H4), 9.15 (m, br, 1H, Phenyl H5), 8.15 (d, br, 1H, Phenyl
H6), 4.78 (s, br, 1H, -CH2-OH), 3.93 (t, br, 2H, -CH2-OH),
3.80 (m, br, 1H, CH2CH-S), 3.32 (DMSO), 2.02–1.88 (m, br,
2H, CH2CH2CH-S), 1.73–1.61 (q, br, 2H, CH2CH2CH-S),
1.58–1.51 (m, br, 2H, CH2CH2CH3), 1.05 (t, br, 3H, CH3).
13C NMR (DMSO-d6) δ, ppm: 151.02 (S-Ar-C3), 136.36 (Ar-
C5), 130.11 (Ar-C4), 129.45 (Ar-C6), 128.55 (Ar-C1), 127.21
(Ar-C2), 121.86 (Ar-CN), 58.85 (-CH2-OH), 40.94 (DMSO),
38.13 (CH2CH2-OH), 37.25 (CH-S), 30.99 (CH2CH2CH3),
29.65 (CH2CH2CH3), 14.56 (CH3).
Fluorescence quantum yield of ZnPc in ethanol-water mix-
ture with different composition was determined by means of
Table 1 Quantum yield of ZnPc upon solvent composition
Ethanol-water
%
Absorption
Maxima (nm)
Emission
Maxima (nm)
Quantum
Yield
80:20
60:40
40:60
20:80
706
706
721
726
724
722
717
713
5.73 × 10−2
5.28 × 10−2
6.83 × 10−3
5.64 × 10−4
Fig. 2 The effect of pH on fluorescence emission intensity of ZnPc at
720 nm in the absence (a) and the presence (b) of Ag+ ion

J Fluoresc
Fig. 3 The formation of H-type
aggregation of ZnPc upon titra-
tion with Ag+ ions
measurement of unknown sample against a standard, zinc-
phthalocyanine without peripheral substituents, (Φf = 0.18 in
DMSO) under identical conditions [31].
The fluorescence quantum yields of both the sample
and standard are calculated using Eq. 1 upon excitation
at the same wavelength [32],
formation with silver ion and optimal pH span for deter-
mination of Ag+ ion is 7.0–11.0. The absorption spectra
of ZnPc were also obtained depending on pH of the mix-
ture (Fig. S2). When the fluorescence emission and absor-
bance intensities compared, similar spectrophotometric
behavior was observed upon change in pH (Fig. S3).
AstðλexÞ ∫λ FZnPcðλemÞ n2
em
ZnPc
n2st
Metal Ion Binding Titrations in Ethanol
ΦZnPc ¼ Φst
ð1Þ
AZnPcðλexÞ
∫
λem
FstðλemÞ
It is well established that the sulphur donor atoms bound
on the periphery of the metal-free or metallo Pcs complex
are optically sensitive to soft metal ions including Ag+ ion
[26]. Sulphur heteroatoms are capable to complex with
the soft metals and these complexes are readily monitored
by fluorescence and UV-vis spectroscopy due to forma-
tions of aggregates. Phthalocyanines have high aggrega-
tions inclination because of core 18 π electron interaction
each other and the solubility of aggregated molecules de-
creases in many solvents [33]. There are two types of
aggregations, which are J-type (edge to edge) and H-
type (face to face), varying upon the position and nature
Where, Ast and AZnPc are absorbances of standard and ZnPc
at the respective excitation wavelength, Fst(λem)and
FZnPc(λem)are integrals of fluorescence, and nst and nZnPc are
refractive indexes of solvent used for standard and ZnPc.
Fluorescence quantum yield of ZnPc calculated in each sol-
vent mixture is shown in Table 1.
As seen from Table 1, quantum yield of ZnPc decreases
with increase in water content in mixture due to the ascending
hydrophilic character of mixture which encourages the forma-
tion of aggregated ZnPc molecules.
The Effect of pH on Spectral Property of ZnPc
Since ZnPc has convenient quantum yield in ethanol /
water (3/2; v/v) mixture, the pH effect on fluorescence
signal of ZnPc in the absence and presence of Ag+ ions
were investigated (Fig. S1). Emission intensity of ZnPc at
720 nm obtained from each spectrum was depicted as a
function of pH (Fig. 2).
As seen from Fig. 2, pronounced decrease in emission
intensity was observed at pH from 6.0 to 1.4 since the
reduction of conjugation upon protonation of nitrogen
atoms in Pc ring. Fluorescence intensity reached to max-
imum at pH 7.0, and remained stable at higher pH values.
On the other hand, fluorescence of ZnPc in the presence
of Ag+ ion was prominently quenched in wide range of
pH (11.0–4.0) due to the complex formation which pro-
motes the aggregation. Moreover, same emission values
were obtained in the pH range from 4.0 to 1.4, indicating
that protonation of Pc ring could not allow to complex
Fig. 4 Comparison of fluorescence quenching of 10 μM ZnPc at 720 nm
in ethanol solution depending on concentration of different metal ions; a)
Pb2+ b) Hg2+ and c) Ag+

J Fluoresc
Fig. 5 Change in fluorescence spectra of 10 μM ZnPc in ethanol/buffer
(3/2; v/v) mixture at pH 7.2 upon addition of a) 0, b) 4.0, c) 8.0, d)15.7, e)
31, f) 45.8, g) 60.1, h) 74, i) 90.9, j) 107, k) 137.9, l) 166.7 μM A) Ag+
and B) Hg2+. C) Comparison of fluorescence quenching ratio of ZnPc at
720 nm depending on concentration of Hg2+ (a) and Ag+ (b)
of the substituent. However, hypsochromic and
bathochromic shifts are related to generation of H-type
and J-type aggregations, respectively [34]. The selective
and reversible binding capability of ZnPc with some se-
lected metal ions such as Ag+, Hg2+ and Pb2+ in pure
ethanol solution have been tested with spectrofluorometric
titrations (Fig. S4). As seen from Fig. S4, the fluorescence
intensity of ZnPc strongly diminished with gradual addi-
tions of both Ag+ and Hg2+ ions and color of solution
slightly changed from green to greenish-blue depending
on the metal ion concentrations, indicating the formation
of aggregated structures which decreases solubility due to
the formation of species such as dimer, trimer, tetramer,
etc. [35]. In addition, fluorescence peak maximum shifted
from 723 to 714 nm, revealing the formation of H-type
aggregation, which causes to increase in the HOMO-
LUMO band gap energy, resulting in blue shift in fluores-
cence emission (Fig. 3).
revealed that Ag+ or Hg2+ ion-induced ZnPc aggregation,
which is responsible for amplified fluorescence
quenching, takes place in ethanol solution.
Titrations in Ethanol-Buffer Mixture at Different pH
Spectrofluorometric titrations in ethanol-buffer mixtures
with different pH values were carried out to elucidate the
optimum solution parameters for selective sensing of Ag+
in the presence of Hg2+, which exhibits fluorescence
quenching similar to that of Ag+ in ethanol solution
(Fig. 5). When titration was carried out in a mixture at
pH 7.2, fluorescence of ZnPc strongly diminished with
gradual addition of both Ag+ and Hg2+ but peak maximum
of ZnPc shifted from 721 to 712 nm in the case of Ag+
(Fig. 5A), whereas shift from 721 to 716 nm was observed
in the case of Hg2+ (Fig. 5B). It could be seen that there
was a significant difference in fluorescence quenching in
the range from 4 μM to 100 μM between Ag+ and Hg2+ but
beyond this concentration range, both of metal ions pro-
cured same degree of fluorescence quenching (Fig. 5C).
On the other hand, emission intensity of ZnPc slightly
diminished upon titration with Pb2+ ion in wade range of
concentration scale and spectral shift in fluorescence
spectrum of ZnPc was not observed (Fig. S4C). Figure 4
Fig. 6 Change in fluorescence spectra of 10 μM ZnPc in ethanol/buffer
(60/40, v/v) pH 11 mixture upon addition of a) 0, b) 4.0, c) 8.0, d)15.7, e)
31, f) 45.8, g) 60.1, h) 74, i) 90.9, j) 107, k) 137.9, l) 166.7 μM A) Ag+
and B) Hg2+. C) Comparison in fluorescence quenching ratio of ZnPc at
710 nm for different amount of a) Hg2+ and b) Ag+

J Fluoresc
Fig. 7 Plot of ln ΔF versus ln[M]0(A) and Stern-Volmer plot of ZnPc (B) for the fluorescence quenching of ZnPc upon addition of different concentra-
F
tions of Ag+ and Hg2+ in ethanol-buffer solution (3:2 v/v) at pH 11.0
On the other hand, when the fluorometric titrations were
carried out in ethanol/buffer mixture at pH 11.0, it was ob-
served that fluorescence of ZnPc was strongly quenched upon
increase in concentrations of Ag+ ion compared with that of
Hg2+ and peak maximum shifted from 710 to 703 nm
(Fig. 6A). Meanwhile, slightly decrease in fluorescence of
ZnPc with gradual additions of Hg2+ indicated that interaction
between ZnPc and Hg2+ diminished at basic solution. This
might be due to the formation of water-insoluble compounds
of Hg2+ ion at high pH value of solution (Fig. 6B).
Furthermore, insignificant spectral shift in fluorescence spec-
trum of ZnPc was observed in the presence of Hg2+. On the
other hand, when the results obtained in mixture at pH 11.0
were compared, significant difference in fluorescence
quenching between Ag+ and Hg2+ was observed and revealed
that selective sensing of Ag+ could be managed (Fig. 6C).
and K1 is the equilibrium constant of complex. On the other
hand, the fluorescence quenching process of ZnPc induced by
Ag+ and Hg2+ was fitted to the Stern-Volmer equation.
F0
F
¼ 1 þ Ksv½Mzþ
Š
ð4Þ
Where Ksv represents the Stern-Volmer quenching constant
and [Mz+] is the concentrations of metal ions.
Spectrofluorometric titrations revealed that the most no-
ticeable interfering metal ion is Hg2+ during the analysis of
Ag+ ion. Therefore, binding parameters were evaluated up-
on spectrofluorometric titration of ZnPc with both Ag+ and
Hg2+ ions. The plots of ln ΔF/F versus ln[Mz+]0 for the
fluorescence quenching of ZnPc with both Ag+ and Hg2+
were shown upon carring on titration in pure ethanol and
ethanol/buffer (pH 7.2) solutions (Fig. S5 and S6) and in
ethanol/buffer (pH 11.0) solution (Fig. 7). The characteris-
tic binding parameter, n was obtained from linear regres-
sion analysis in Fig. 7A. The number n of the quencher
[Mz+] bound to a ZnPc was around 1.0, indicating that a
complex with molecular ratio of 1:1 was formed between
ZnPc and metal ions. The quenching constant Ksv for the
quencher, [Mz+] being bound to a ZnPc was about power of
105, demonstrating that a very strong interaction exists
Binding Stoichiometry
The complex formation between ZnPc and n moles of
metal ion, Mz+ as a quencher (Ag+ or Hg2+) is shown
below in Eq.(2).
ZnPc þ nMzþ⇄ZnPc−Mznþ
ð2Þ
Based on the stoichiometric reaction, Eq. (3) below
was derived and steps of derivation were shown in the
supporting information.
Table 2 Binding parameters ZnPc with Ag+ and Hg2+ at different pH
and composition of solution
Medium
Ethanol
Metal ions
n
Ksv (L/mol)
ΔF
F
¼ nln½MzþŠ0 þ lnK1
ð3Þ
Ag+
Hg2+
Ag+
Hg2+
Ag+
Hg2+
1.70
1.47
0.89
1.72
1.22
1.56
4.18 × 105
3.21 × 105
1.08 × 105
1.90 × 104
1.70 × 105
6.80 × 103
ln
In this equation, ΔF is the difference in the fluorescence
Ethanol/buffer
pH 7.2
intensity of F0 and F, which indicates the fluorescence inten-
sities of ZnPc in the absence and presence of the metal ion,
respectively. Where [Mz+]0is initial concentrations of metal
ion, n is the numbers of metal ion bound to a ZnPc molecule
Ethanol/buffer
pH 11.0

J Fluoresc
Fig. 8 A) Enhancement of
fluorescent intensity of ZnPc
(10 μM) complexed with Ag+
(50 μM) in ethanol/water (3/2, v/
v) solution upon addition of Na2S
concentration (0/0, 50/0, 50/100,
150/100 μM, respectively). B)
Complexation/decomplexation
cycles in ethanol/buffer (pH 11.0)
solution with ZnPc and Ag+ by
addition 50 μM of Na2S
between metal ions and ZnPc. As seen from Fig. 7B, the
fluorescence quenching data of ZnPc is well suited to Eq.
(4) in the concentration range of 2.0 × 10−6–1.0 × 10−4
mol/L metal ions and the linear regression coefficients
were found to be 0.9976 for Ag+ and 0.9885 for Hg2+.
As seen from Table 2, the mole number of metal ions
for one mole of ZnPc and quenching constant for both
Ag+ and Hg2+ were not much different in pure ethanol
solution. In ethanol/buffer mixture at pH 7.2, quenching
constant of Ag+ is 10 times higher than that of Hg2+
although the number of Hg2+ bound to ZnPc is twofold
higher than that of Ag+ ion. On the other hand, quenching
constant of Ag+ is distinctly higher than that of Hg2+ in
ethanol/buffer solution at pH 11.0, showing that aggrega-
tion of ZnPc is higher in the presence of Ag+ ion.
Ag+ (50 μM) in order to demonstrate the reversibility of
ZnPc as a sensor, [36]. The experimental results revealed
that the fluorescence emission of ZnPc was enhanced ac-
companying with shift in peak maximum from 712 nm to
721 nm upon interaction of Ag+ with Na2S, resulting in
decomplexation of ZnPc with Ag+ (Fig. 8A). The further
addition of Ag+ ions (higher than 50 μM) did not change
the emission intensity, demonstrating the reversible inter-
action of ZnPc with Ag + ions. The loss of sensitivity was
small when complexation/decomplexation cycles were re-
peated at least four times (Fig. 8B).
Selectivity of ZnPc for Ag+
Two groups of experiments were carried out to demonstrate
the selectivity of ZnPc toward other environmentally impor-
tant cation species. As shown in Fig. 9, the addition of metal
ions such as Hg2+, Ba2+, Ni2+, Cd2+, Co2+, Sr2+, Mg2+, Fe3+
and Pb2+ produced a nominal change in the emission ratio of
ZnPc due to their low affinity in solution at pH 11.0. On the
other hand, a remarkable quenching in fluorescence was ob-
served upon addition of same number of equivalents of Ag+ in
similar conditions.
The Reversibility of the Interaction between ZnPc
and Ag+
Sodium sulfide (Na2S), which has potent affinity for Ag+,
was added into the solution containing ZnPc (10 μM) and
The results revealed that ZnPc can discriminate Ag+ ion in
the presence of interfering metal ions in predetermined solu-
tion. Additional study was carried out to evaluate the selectiv-
ity of the ZnPc in the presence of Ag+ and other possible
interference ions by recording the change in fluorescence re-
sponse. As seen from Fig. 9, the emission signal of ZnPc
slightly influenced by sequential addition of other metal ions,
indicating the selective sensing of Ag+ in the presence of
foreign metal ions.
The analytical performance of our method was compared
with those of previously reported methods for Ag+ detection.
As summarized in Table 3, limit of detection (LOD) of this
method was comparable to other methods. Our method is
additionally cost-effective because of the reusability of ZnPc
as a sensor and the entire detection time was only ∼3 min.
Moreover, the material developed in this method exhibited
high selectivity due to elucidated optimal spectrofluorometric
titration conditions.
Fig. 9 A) Normalized fluorescence response, F/F0 of ZnPc (10 μM) upon
addition of 50 μM of various metal ions in ethanol/buffer (60/40, v/v)
solution at pH 11.0. B) Fluorescence response of ZnPc (10 μM) to 50 μM
of Ag + in ethanol/buffer (3/2, v/v) solution containing 50 μM of various
metal ions. λex = 630 nm and λem = 720 nm

J Fluoresc
Table 3 Comparison of ZnPc as a sensor with other methods for detection of Ag+
Detection System
Methods
LOD (μmol L−1
)
References
Pyridine-based chemosensor
Fluorescence enhancement
Fluorescence quenching
Fluorescence quenching
4.18
3.0
[37]
[38]
[39]
Schiff base based on naphthalimide probe
BINOL-based cyclophane
chemosensor
8.0
2-(2-hydroxyphenyl) benzothiazole probe
Fluorescence enhancement
Fluorescence quenching
Fluorescence quenching
1.7
[40]
NBD-armed thiacalix [4] arene-based chemosensor
Phthalocyanine-based sensor
0.65
0.86
[41]
This work
7. Hosoba M, Oshita K, Katarina RK, Takayanagi T, Oshima M,
Motomizu S (2009) Synthesis of novel chitosan resin possessing
histidine moiety and its application to the determination of trace
silver by ICP-AES coupled with triplet automated-pretreatment
system. Anal Chim Acta 639(1):51–56. https://doi.org/10.1016/j.
aca.2009.02.050
8. Valverde F, Costas M, Pena F, Lavilla I, Bendicho C (2008)
Determination of total silver and silver species in coastal seawater
by inductively-coupled plasma mass spectrometry after batch sorp-
tion experiments with Chelex-100 resin. Chem Spec Bioavailab
20(4):217–226. https://doi.org/10.3184/095422908X381306
9. Ghanei-Motlagh M, Fayazi M, Taher MA, Jalalinejad A (2016)
Application of magnetic nanocomposite modified with a thiourea
based ligand for the preconcentration and trace detection of silver(I)
ions by electrothermal atomic absorption spectrometry. Chem Eng J
290:53–62. https://doi.org/10.1016/j.cej.2016.01.025
Conclusion
We have synthesized and characterized a new peripherally
functionalized zinc phthalocyanine bearing (1-hydroxyhexan-
3-ylthio)-substituents (ZnPc). Fluorescence emission of ZnPc
was distinctly quenched in the presence of Ag+ ions upon
strong complex formation, showing that the recognizing mech-
anism is presumably due to Ag+ ions-induced H-type aggrega-
tion which plays a major role in the intensified fluorescence
quenching. The reversible response of ZnPc toward Ag+ ion
was established upon addition of complex-disrupting substance
into same solution. It could be inferred that ZnPc could be used
as a reversible fluorescent chemosensor for selective sensing of
Ag+ ion in the presence of competing metal ions in ethanol/
buffer (3/2, v/v) solution at pH 11.0.
10. Daşbaşı T, Saçmacı Ş, Şahan S, Kartal Ş, Ülgen A (2013) Synthesis,
characterization and application of a new chelating resin for on-line
separation, preconcentration and determination of Ag(I) by flame
atomic absorption spectrometry. Talanta 103:1–7. https://doi.org/
10.1016/j.talanta.2012.09.017
Acknowledgments This work was supported by Research Fund of the
Istanbul Technical University (BAP, Project Number: 38142).
11. Sötebier CA, Weidner SM, Jakubowski N, Panne U, Bettmer J
(2016) Separation and quantification of silver nanoparticles and
silver ions using reversed phase high performance liquid chroma-
tography coupled to inductively coupled plasma mass spectrometry
in combination with isotope dilution analysis. J Chromatogr A
1468:102–108. https://doi.org/10.1016/j.chroma.2016.09.028
12. Hanley TA, Saadawi R, Zhang P, Caruso JA, Landero-Figueroa J
(2014) Separation of silver ions and starch modified silver nanopar-
ticles using high performance liquid chromatography with ultravi-
olet and inductively coupled mass spectrometric detection.
Spectrochim Acta, Part B 100:173–179. https://doi.org/10.1016/j.
sab.2014.08.022
References
1. Ahamed MEH, Mbianda XY, Mulaba-Bafubiandi AF, Marjanovic
L (2013) Ion imprinted polymers for the selective extraction of
silver(I) ions in aqueous media: kinetic modeling and isotherm
studies. React Funct Polym 73(3):474–483. https://doi.org/10.
1016/j.reactfunctpolym.2012.11.011
2. Jacobson AR, McBride MB, Baveye P, Steenhuis TS (2005)
Environmental factors determining the trace-level sorption of silver
and thallium to soils. Sci Total Environ 345(1):191–205. https://doi.
org/10.1016/j.scitotenv.2004.10.027
3. Saidur MR, Aziz ARA, Basirun WJ (2017) Recent advances in
DNA-based electrochemical biosensors for heavy metal ion detec-
tion: a review. Biosens Bioelectron 90:125–139. https://doi.org/10.
1016/j.bios.2016.11.039
13. Sánchez-Pomales G, Mudalige TK, Lim J-H, Linder SW (2013)
Rapid determination of silver in Nanobased liquid dietary supple-
ments using a portable X-ray fluorescence analyzer. J Agric Food
Chem 61(30):7250–7257. https://doi.org/10.1021/jf402018t
14. Tashkhourian J, Javadi S, Ana FN (2011) Anodic stripping
voltammetric determination of silver ion at a carbon paste electrode
modified with carbon nanotubes. Microchim Acta 173(1):79–84.
https://doi.org/10.1007/s00604-010-0528-5
4. Li H, Michael Siu KW, Guevremont R, Le Blanc JCY (1997)
Complexes of silver(I) with peptides and proteins as produced in
electrospray mass spectrometry. J Am Soc Mass Spectrom 8(8):
781–792. https://doi.org/10.1016/S1044-0305(97)84130-X
5. Martin S, Griswold W (2009) Human health effects of heavy
metals. Environmental Science and Technology briefs for citizens
15:1–6
6. Panyala RN, Pena-Mendez ME, Havel J (2008) Silver or silver
nanoparticles: a hazardous threat to the environment and human
health? J Appl Biomed 6(3):117–129
15. Afkhami A, Shirzadmehr A, Madrakian T, Bagheri H (2015) New
nano-composite potentiometric sensor composed of graphene nano-
sheets/thionine/molecular wire for nanomolar detection of silver ion
in various real samples. Talanta 131:548–555. https://doi.org/10.
1016/j.talanta.2014.08.004
16. Abdolmohammad-Zadeh H, Javan Z (2015) Silica-coated Mn3O4
nanoparticles coated with an ionic liquid for use in solid phase
extraction of silver(I) ions prior to their determination by AAS.
Microchim Acta 182(7):1447–1456. https://doi.org/10.1007/
s00604-015-1468-x

J Fluoresc
17. Rastegarzadeh S, Pourreza N, Larki A (2015) Determination of
trace silver in water, wastewater and ore samples using dispersive
liquid–liquid microextraction coupled with flame atomic absorption
spectrometry. J Ind Eng Chem 24:297–301. https://doi.org/10.
1016/j.jiec.2014.09.045
30. Bıyıklıoğlu Z, Durmuş M, Kantekin H (2010) Synthesis,
photophysical and photochemical properties of quinoline substitut-
ed zinc (II) phthalocyanines and their quaternized derivatives. J
Photoch Photobio A 211(1):32–41. https://doi.org/10.1016/j.
jphotochem.2010.01.018
18. Tavallali H, Yazdandoust S, Yazdandoust M (2010) Cloud point
extraction for the Preconcentration of silver and palladium in real
samples and determination by atomic absorption spectrometry.
CLEAN – Soil, Air, Water 38(3):242–247. https://doi.org/10.
1002/clen.200900207
19. Rawa-Adkonis M, Wolska L, Przyjazny A, Namieśnik J (2006)
Sources of errors associated with the determination of PAH and
PCB Analytes in water samples. Anal Lett 39(11):2317–2331.
https://doi.org/10.1080/00032710600755793
20. Wong RCH, Lo P-C, Ng DKP (2019) Stimuli responsive
phthalocyanine-based fluorescent probes and photosensitizers.
Coord Chem Rev 379:30–46. https://doi.org/10.1016/j.ccr.
2017.10.006
31. Nyokong T (2007) Effects of substituents on the photochemical and
photophysical properties of main group metal phthalocyanines.
Coord Chem Rev 251(13):1707–1722. https://doi.org/10.1016/j.
ccr.2006.11.011
32. Uzumcu AT, Guney O, Okay O (2018) Monitoring the instant cre-
ation of a new fluorescent signal for evaluation of DNA conforma-
tion based on intercalation complex. J Fluoresc 28(6):1325–1332.
https://doi.org/10.1007/s10895-018-2294-4
33. Günsel A, Bilgiçli AT, Kırbaç E, Güney S, Kandaz M (2015) Water
soluble quarternizable gallium and indium phthalocyanines bearing
quinoline 5-sulfonic acid: synthesis, aggregation, photophysical
and electrochemical studies. J Photoch Photobio A 310:155–164.
https://doi.org/10.1016/j.jphotochem.2015.05.018
21. Gregory P (2000) Industrial applications of phthalocyanines. J
Porphyrins Phthalocyanines 04(04):432–437. https://doi.org/10.
1002/(SICI)1099-1409(200006/07)4:4<432::AID-JPP254>3.0.
CO;2-N
22. Urbani M, Ragoussi M-E, Nazeeruddin MK, Torres T (2019)
Phthalocyanines for dye-sensitized solar cells. Coord Chem Rev
381:1–64. https://doi.org/10.1016/j.ccr.2018.10.007
23. Kong S, Song Y, Bai L, Tang X, Meng F (2019) Supramolecular
complexes based on liquid-crystalline polysiloxanes and copper
phthalocyanine. Polym Int 68(3):377–384. https://doi.org/10.
1002/pi.5720
34. Raj MR, Margabandu R, Mangalaraja RV, Anandan S (2017)
Influence of imide-substituents on the H-type aggregates of
perylene diimides bearing cetyloxy side-chains at bay positions.
Soft Matter 13(48):9179–9191. https://doi.org/10.1039/
C7SM01918A
35. Güzel E, Güney S, Kandaz M (2015) One pot reaction and three
type products; 1(4),8(11)-15(18),22(25) adjacent azine attached as
macrocyclically mono, bunk-type (dimer) and polymeric metallo
phthalocyanines; synthesis, spectroscopy, and electrochemistry.
Dyes Pigments 113:416–425. https://doi.org/10.1016/j.dyepig.
2014.08.019
24. Choi J, Wagner P, Gambhir S, Jalili R, MacFarlane DR, Wallace
GG, Officer DL (2019) Steric modification of a cobalt
Phthalocyanine/Graphene catalyst to give enhanced and stable elec-
trochemical CO2 reduction to CO. ACS Energy Letters 4(3):666–
672. https://doi.org/10.1021/acsenergylett.8b02355
25. Kuzyniak W, Ermilov EA, Atilla D, Gürek AG, Nitzsche B,
Derkow K, Hoffmann B, Steinemann G, Ahsen V, Höpfner M
(2016) Tetra-triethyleneoxysulfonyl substituted zinc phthalocya-
nine for photodynamic cancer therapy. Photodiagn Photodyn Ther
13:148–157. https://doi.org/10.1016/j.pdpdt.2015.07.001
26. Kandaz M, Güney O, Senkal FB (2009) Fluorescent
chemosensor for Ag(I) based on amplified fluorescence
quenching of a new phthalocyanine bearing derivative of
benzofuran. Polyhedron 28(14):3110–3114. https://doi.org/
10.1016/j.poly.2009.06.058
36. Smith DS, Bell RA, Valliant J, Kramer JR (2004) Determination of
strong ligand sites in sewage effluent-impacted waters by compet-
itive ligand titration with silver. Environmental science & technol-
ogy 38(7):2120–2125. https://doi.org/10.1021/es035045p
37. Annaraj B, Neelakantan MA (2014) Water-soluble pyridine-based
colorimetric chemosensor for naked eye detection of silver ions:
design, synthesis, spectral and theoretical investigation. Anal
Meth 6(24):9610–9615. https://doi.org/10.1039/C4AY01592D
38. Zhou Y, Zhou H, Ma T, Zhang J, Niu J (2012) A new Schiff base
based on vanillin and naphthalimide as a fluorescent probe for Ag+
in aqueous solution. Spectrochim Acta A 88:56–59. https://doi.org/
10.1016/j.saa.2011.11.054
39. Hou J-T, Zhang Q-F, Xu B-Y, Lu Q-S, Liu Q, Zhang J, Yu X-Q
(2011) A novel BINOL-based cyclophane via click chemistry: syn-
thesis and its applications for sensing silver ions. Tetrahedron Lett
52(38):4927–4930. https://doi.org/10.1016/j.tetlet.2011.07.050
40. Hwang KS, Park KY, Kim DB, Chang S-K (2017) Fluorescence
sensing of Ag+ ions by desulfurization of an acetylthiourea deriv-
ative of 2-(2-hydroxyphenyl)benzothiazole. Dyes Pigments 147:
413–419. https://doi.org/10.1016/j.dyepig.2017.08.041
27. Çağlar Y, Saka ET, Alp H, Kantekin H, Ocak Ü, Ocak M
(2016) A simple Spectrofluorimetric method based on
quenching of a nickel(II)-Phthalocyanine complex to deter-
mine Iron (III). J Fluoresc 26(4):1381–1389. https://doi.org/
10.1007/s10895-016-1829-9
28. Matshitse R, Nyokong T (2018) Singlet oxygen generating
properties of different sizes of charged Graphene quantum
41. Fu Y, Mu L, Zeng X, Zhao J-L, Redshaw C, Ni X-L, Yamato T
(2013) An NBD-armed thiacalix[4]arene-derived colorimetric and
fluorometric chemosensor for Ag+: a metal–ligand receptor of an-
ions. Dalton Trans 42(10):3552–3560. https://doi.org/10.1039/
C2DT32115G
d o t N a n o c o n j u g a t e s w i t h
a p o s i t i v e l y c h a rg e d
Phthalocyanine. J Fluoresc 28(3):827–838. https://doi.org/10.
1007/s10895-018-2247-y
29. Hanack M, Schneider T, Barthel M, Shirk JS, Flom SR, Pong RGS
(2001) Indium phthalocyanines and naphthalocyanines for optical
limiting. Coord Chem Rev 219-221:235–258. https://doi.org/10.
1016/S0010-8545(01)00327-7
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