A highly selective and sensitive ESIPT-based coumarin-triazole polymer for the ratiometric detection of Hg2+

Article abstract of DOI:10.1039/c9nj01366k

A novel fluorescent polymer for Hg²⁺ recognition was developed based on the phototautomerism mechanism of 7-hydroxycoumarin in aqueous solution. The developed system showed higher sensitivity and specificity towards Hg²⁺ in the acetonitrile/water mixture over various other metal ions, with a significant fluorescence quenching of the main emission band. It was shown that the presence of Hg²⁺ affects the chemical equilibrium of the 7-hydroxycoumarin phototautomers through the excited state intramolecular proton transfer (ESIPT) mechanism, which results in ratiometric fluorescence response upon stepwise addition of Hg²⁺. The occurrence of ESIPT mechanism was explained based on a comparison of the ¹H NMR spectra of the starting alkynylated coumarin (4) in a non-polar aprotic solvent (CDCl₃) and in a polar aprotic solvent (DMSO-d₆). This was further confirmed by ¹H NMR of 4 upon stepwise addition of Hg²⁺ in a polar aprotic solvent (DMSO-d₆). From titration experiments, a higher sensitivity with a detection limit at the nanomolar level (50 nM) was observed and the response was fast and reversible. The real applications of the developed system were investigated in real samples and satisfactory results were obtained for both fresh and lake water samples.

Full text of DOI:10.1039/c9nj01366k

View Article Online
View Journal
NJC
New Journal of Chemistry
Accepted Manuscript
A journal for new directions in chemistry
This article can be cited before page numbers have been issued, to do this please use: J. M. V.
Ngororabanga, Z. Tshentu and N. Mama, New J. Chem., 2019, DOI: 10.1039/C9NJ01366K.
Volume 42
Number
March 2018
Pages 3963-4776
This is an Accepted Manuscript, which has been through the
6
21
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
New Journal of Chemistry
rsc.li/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1144-2546
PAPER
Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
rsc.li/njc

Page 1 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
A highly selective and sensitive ESIPT-based coumarin
D
-
O
t
I
r
: 1
i
0
a
.10
z
39
o
/C9NJ01366K
l
e
polymer for the ratiometric detection of Hg2+
Jean Marie Vianney Ngororabanga*, Zenixole R. Tshentu and Neliswa Mama
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Department of Chemistry, Nelson Mandela University, Port Elizabeth, 6031, South Africa
ABSTRACT
A novel fluorescent polymer for Hg2+ recognition was developed based on the
phototautomerism mechanism of 7-hydroxycoumarin in aqueous solution. The developed
2
+
system showed higher sensitivity and specificity towards Hg in acetonitrile/water mixture
over various other metal ions, with a significant fluorescence quenching of the main emission
band. It was shown that the presence of Hg2+ affects the chemical equilibrium of the 7-
hydroxycoumarin phototautomers through excited state intramolecular proton transfer
(
ESIPT) mechanism, which results in ratiometric fluorescence response upon stepwise
2+
addition of Hg . The occurrence of ESIPT mechanism was explained based on a comparison
1
of the H NMR spectra of the starting alkynylated coumarin (4) in non-polar aprotic solvent
1
(
CDCl ) and in polar aprotic solvent (DMSO-d ). This was further confirmed by H NMR of
3
6
4
upon stepwise addition of Hg2+ in polar aprotic solvent (DMSO-d ). From titration
6
experiments, a higher sensitivity with a detection limit at the nanomolar level (50 nM) was
observed and the response was fast and reversible. The real applications of the developed
system were investigated in real samples and satisfactory results were obtained for both fresh
and lake water samples.
Keywords: ESIPT, ratiometric signal, phototautomerism, 7-hydroxycoumarin
*
Corresponding author. Tel.: +27415042684/+27719836342.
Email addresses: s212438700@mandela.ac.za and ngororajv@gmail.com
1

New Journal of Chemistry
Page 2 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01366K
1
. Introduction
Over the past few decades, much interest has been drawn towards the development of
artificial probes for detecting and recognition of heavy transition metal (HTM) ions mainly
due to their detrimental effects on human being and other living species [1]. Among HTM,
Hg2+ has been highlighted as the most dangerous heavy metal ion and a global pollutant that
poses serious hazards to human well-being and the environment. Thus, mercury pollution has
become a serious worldwide environmental concern due to its high toxicity and prevalence in
the environment from various human activities, industrial and natural source [2]. In nature,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
mercury occurs in various forms such as elemental, ionic (Hg2+ and Hg ) and organic
+
2
+
mercury. The most common ionic form of mercury (Hg ) is highly corrosive with
carcinogenic properties and high cellular toxicity [3]. However, both elemental and ionic
forms may be assimilated and turned into organomercury (methyl mercury being the most
common) by aerobic bacteria [4]. The resultant lipophilic organomercury may enter through
the food chain and bio-accumulate in human systems, causing serious irreversible damages to
the immune, central nervous and urinary systems [5].
The toxicity of mercury and its derivatives is mostly related to their high affinity towards
thiols [6], the main component of protein, enzymes and DNA. This interaction interrupts
living cell activities and eventually leads to the cell dysfunction. Because of this high toxicity
the levels of Hg2+ are strictly regulated and a provisional tolerable weekly intake of
methylmercury is 1.6 g/kg body weight according to the joint Food and Agriculture
Organization and Wold Health Organization (FAO/WHO) Expert Committee on Food
Additive (JECFA) [7]. Therefore, a high demand in the development of reliable and
convenient techniques for sensing and monitoring the level of mercury in both environmental
and biological systems is obvious.
Over the last few years, several conventional techniques have been developed for the
recognition and quantification of mercury and its derivatives in environmental and biological
systems. These include cold-vapour atomic fluorescence spectroscopy (CV-AFS) [8], cold-
vapour atomic absorption spectroscopy (CV-AAS) [9], inductively coupled plasma-atomic
emission spectroscopy (ICP-AES) [10], inductively coupled plasma-mass spectroscopy (ICP-
MS) [11], anodic stripping voltammetry [12], surface-enhanced Raman scattering (SERS)
[
13], liquid chromatography (LC) [14], gas chromatography (GC) [15], colorimetric and
2

Page 3 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01366K
fluorometric assays. Among them, fluorometric methods are the most attractive owing to
their obvious sensitivity, low limit of detection and ease operational techniques [16]. Thus, a
substantial effort has been recently dedicated to the production of fluorescence-based probes
2
+
for the detections of Hg and a number of fluorescent small-organic molecules and polymers
with different binding sites for Hg2+ have been developed [17]. However, most of the
fluorescent probes developed so far, are not suitable for practical applications because Hg2+
detection is mainly based on fluorescence quenching mechanism which can be impacted by
other factors such as environmental, instrumental efficiency and probe concentrations [18].
On the contrary, ratiometric-based fluorescent probes can offer self-calibration effect which
can eliminate the interfering elements by using the ratio of the two absorption/emission bands
at different wavelengths [19]. Despite the advantages, a small number of ratiometric-based
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2+
fluorescent probes for the detection of Hg have been reported so far and most of them have
shown some shortcomings such as relatively low sensitivity, low selectivity and difficult
synthetic procedures [20].
The excited state intramolecular proton transfer (ESIPT) has recently become one of the
mechanisms that contributed significantly in the development of the ratiometric fluorescent
probes [21]. ESIPT based probes are known to have beneficial photophysical properties such
as intense lumiscence, photostability and large Stoke’s shifts [22]. The latter offers some
advantages such as a minimized self-absorption and complete absence of the interferences
from auto-fluorescence, which makes them suitable for use in the bioimaging applications
[23]. Though the mechanism has been successfully used in the detection of various analytes
2
+
[
24], very few ESIPT based probes have been developed for Hg detection. Furthermore, all
ESIPT probes developed so far are based on the deprotection of vinylether of the sensing
2+
system via Hg -promoted hydrolysis reaction. This results in keto form through the ESIPT
mechanism [25]. However, this process affects reversible detection of theses probes as their
2
+
original structures are hydrolyzed by Hg .
Inspired by the optical properties of 7-hydroxycoumarin in aqueous solutions, its excellent
chromogenic and fluorogenic properties, we developed herein an ESIPT based polymeric
fluorescent sensing system for Hg2+ using 7-hydrocoumarin as fluorophore. The
incorporation of the fluorophore into the polymeric material was successfully achieved
through structure modifications of coumarin backbone which led to an alkyne-funtionalized
molecule. The latter was incorporated into the azide-functionalized polymer via a well-known
3

New Journal of Chemistry
Page 4 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01366K
Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (CuAAC) to form a fluorescent
2
+
polymer with Hg binding sites [26]. The resulted polymers displayed high sensitivity and
2
+
ratiometric response towards Hg ions and the binding processes were reversible.
2
. Materials and methods
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
.1. Materials
Chemical suppliers (Sigma-Aldrich and Merck) provided the reagents and solvents required
for this research at their analytical grades and were used as received. A stock solution of P2
-3
(
7 x 10 g/L) was prepared in acetonitrile (50 ml) from its pure solid sample. Metal ion
solutions (0.01 M) were prepared using millipore water and same water was used throughout
2
+
the spectroscopic studies. The Fe stock solution was prepared using sulphate salt while the
rest of metal ion stock solutions were obtained from nitrate salts. The titration experiments of
metal ion of interest were conducted in a 3 ml quartz cuvette using a diluted aqueous solution
of P2. Spectroscopic data were recorded after each addition of an aliquot of the particular
metal ion solution.
2
.2. Measurements
The Bruker Avance DPX 400 (400 MHz) with TMS as an internal standard was applied to
record all H NMR and 13C NMR spectra. All FT-IR spectra were collected on Bruker
Platinum Tensor 27 ATR-IR spectrophotometer with Opus software (version 6.5.6). The
molecular weight of the polymers was determined through size exclusion chromatography
(SEC) experiments using poly(methyl methacrylate) (PMMA) as a standard. The experiment
were conducted in dimethylacetamide at 40 °C using a flow rate of 0.5 mL/min. The
chemical composition of synthesized compounds was evaluated based on elemental analysis
and Vario EL (Elementar Analysensystem GmbH) instrument was applied to evaluate
carbon, hydrogen and nitrogen content. The Perkin Elmer Lambda 35 was used to record UV-
Vis absorption spectra while the Perkin Elmer LS 45 was used for emission spectra and the
experiments were conducted at room temperature. The real sample analysis was performed
using Perkin Elmer Avio 200 ICP-OES.
1
2
.3. Synthesis of polymer P2
The synthesis of coumarin derivatives (2, 3) and polymer (P1) were achieved following the
reported literature procedures [27].
4

Page 5 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01366K
2
.3.1. Synthesis of 7-Hydroxy-8-(1-hydroxybut-3-ynyl)-4-methyl-2H-chromen-2-one (4)
Zinc powder (0.26 g, 4 mmol) was suspended in THF (20 ml) and a mixture was vigorous
stirred for 15 min at room temperature. To this mixture, propagyl bromide (0.45 g, 4 mmol)
in THF (10 ml) was added and a reaction was further stirred at room temperature for 1h. Then
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
compound (3) (1.00 g, 4 mmol) in THF (5 ml) was added. The reaction mixture was stirred
o
overnight at 60 C and saturated NH Cl was added. After 1 h, zinc residues were filtrated and
4
hydrochloric acid (10 ml, 10%) was added. THF layer was collected and the solvent was
evaporated on rotary vapour. The residues were dissolved in dichloromethane (50 ml) and
zinc residue were removed by the washing with water (3 x 50 ml). The organic layer was
dried and the solvent was evaporated under reduced pressure. The resulting crude product
was purified using column chromatography over silica gel (Hexane: EtOAc, 70:30) and a
o
-1
white solid product was produced in 43% yield. m.p. 147-152 C. IR ѵ , (cm ): 3359 (O-
max
1
H), 3255 (≡C-H), 1685 (C=O), 1597 (C=C). H NMR (CDCl , 400 MHz): δ = 7.53 (d, J =
3
8
2
.84 Hz, 1H), 6.94 (d, J = 8.84 Hz, 1H), 6.19 (s, 1H), 5.44 (s, 1H), 4.9 (s, 1H), 4.52 (s, 1H),
13
.77 (dd, J = 14, 2H), 2.71 (s, 1H), 2.43 (s, 3H). C NMR (CDCl , 400 MHz): δ = 160.63,
3
155.58, 152.97, 152.28, 151.12, 125.59, 114.02, 113.35, 112.09, 95.48, 57.98, 33.64, 18.82.
.3.2. Synthesis of P2
2
A mixture of P1 (0.07g ), compound 4 (1 mmol), CuSO .5H O (0.054 mmol), sodium
4
2
ascorbate
(0.15
mmol)
and
polydentate
ligand
PMDTA
(N,N,N′,N′′,N′′-
pentamethyldiethylenetriamine) (0.15 mmol) in THF (30 ml) was stirred at room
temperature for 48 hrs. The suspended solid polymers were collected trough filtration,
washed with water and dried under vacuum to give polymer (P2) in 85% yields.
3
. Result and discussion
3. 1. Synthesis of coumarin (4) and polymer (P2)
Coumarin 4 was successfully synthesized in three steps from resorcinol as shown in Scheme
1. Coumarin 2 and 3 were obtained according to the reported method, [27] and an alkyne
functionality was incorporated into coumarin using a well-know zinc mediated regioselective
Barbier reaction of the propargylic bromide [28], to afford coumarin 4 in good yield. The
latter was incorporated into the azide-functionalized polymer P1 under a Cu(I)-mediated
click reaction conditions [29], to yield coumarin-functionalized polymer (P2).
5

New Journal of Chemistry
Page 6 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
CHO
View Article Online
DOI: 10.1039/C9NJ01366K
HO
OH
HO
O
O
HO
O
O
b
a
1
2
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
c
n
n
OH
O
O
HO
P1
N3
N
N
N
Cu(I)
4
O
HO
HO
O
P2
o
Scheme 1. Total synthesis of P2: (a) Conc. H SO , CH COCH COOC H , 0 C;
2
4
3
2
2
5
(
b) Hexamethylenetetramine, AcOH (reflux); (c) Zn, THF, propargyl bromide, NH Cl(aq);
4
(
d) CuSO .5H O, NaAsc and PMDTA.
4
2
The structures of coumarin 4 and polymer P2 were characterized by mass, FT-IR and NMR
spectroscopies (Figure S1-S4). The degree of functionalization was determined from azide
group peaks on the FT-IR spectra of P1 and P2 using the peak height method [30], and was
found to be 73 %. Furthermore, from SEC experiments of the synthesized polymer (P2), an
4
average molecular weight of 2.16 x 10 g/mol and molecular mass distribution (dispersity
index) of 2.18 were obtained.
3
.2. UV-Vis absorption studies
The chemosensing capability of P2 was initially tested using UV-Vis spectral analysis. The
experiments were conducted at room temperature by adding the aliquots of selected metal
+
+
2+
3+
3+
2+
2+
2+
2+
3+
2+
2+
2+
+
2+
ions (Ag , Na , Ca , Cr , Al , Cd , Ba , Cu , Co , Fe , Hg , Fe , Zn , Li , Ni and
2+
Pb ) to the P2 acetonitrile/water (7:3) solution. However, no one of the tested metal ions
2
+
effected a detectable change in the absorption spectral of P2. The addition of Hg aliquots
to the acetonitrile/water (7:3) solution of P2 (Figure 1b) led to a gradually decrease in the
absorption spectrum of P2 with a weak absorption response. The latter signals the existence
6

Page 7 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01366K
of the singlet state (ESIPT) mechanism as in steady state spectra, the absorption of the ESIPT
dye metal complex is usually similar to that of the parent chromophore [31]. A weak
2
+
absorption response upon Hg addition was also observed for the small molecule 4 (Figure
a).
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-5
Figure 1: Changes in the absorption spectra of (a) 4 (4.6 x 10 M) (b) P2 (0.03 g/L) in
2
+
-5
acetonitrile/water (7:3) upon addition of Hg aliquots (from 0  to 6 x 10 
.3. Fluorescence studies
3
To further investigate the chemosensing ability of P2, the emission spectral analysis was
performed. The latter was conducted at the excitation wavelength of 330 nm, under similar
conditions and the same set of ion as in the UV-Vis spectral analysis. Notable in Figure 2a,
only Hg2+ induced an obvious spectral alteration in P2 emission band at 330 nm with a
fluorescence quenching response. Furthermore, Three emission bands were detected in the
quenched spectrum at 390 nm, 453nm and 480 nm. The quenching response upon Hg2+
addition can be ascribed to the heavy atom effect which reduces the lifetime of the singlet
2
+
state of the fluorophore and -philic nature of Hg which is normally associated with the
quenching metal ions [32].
7

New Journal of Chemistry
Page 8 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01366K
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-5
Figure 2: (a) Emission spectra of P2 (2.33 x 10 g/L) in the presence of the aliquot of various
+
+
2+
3+
3+
2+
2+
2+
2+
3+
2+
2+
2+
+
metal ions (Ag , Na , Ca , Cr , Al , Cd , Ba , Cu , Co , Fe , Hg , Fe , Zn , Li ,
Ni2+ and Pb ) (0.01 M). (b) Changes in the emission spectra of P2 (2.33 x 10 g/L)
2+
-5
2
+
obtained during the titration with Hg (From 0 M to 0.62 M). The inset shows the changes
2+
in I /I as a function of Hg concentration (where I and I480 are fluorescence intensities
4
80 390
390
at 390 nm and 480 nm). All spectra were recorded in acetonitrile/water (7:3) at 330 nm.
2+
To further investigate the emission properties of P2 in the presence of Hg , the fluorescence
2
+
response of P2 was investigated using different concentration of Hg . Figure 2b
demonstrates the variations in the emission spectra of P2 upon continuous addition of Hg2+
aliquots. Notably, the addition of Hg2+ aliquots from 0 to 0.62 M led to a progressive
reduction of the emission band at 390 nm and a gradual increase of a new emission peak at
480 nm with a clear isoemission point at 445 nm suggesting a measurable ratiometric
emission response. As the addition of Hg2+ continued, another emission peak at 453 nm
appeared just before the saturation point. The ratio of the two fluorescence intensities
(
I /I ) exhibited a notable change from 0.13 to 2.57 (19 fold enhancement) and a linear
480 390
2
+
response between the emission intensity ratios (I /I ) and concentration of Hg was
4
80 390
noticed in the range of 0.3-0.5 M (Figure 2 inset). Since the sigmoidal calibration curve
2
+
was obtained from the plot of fluorescence signals versus the concentration of Hg , the
theoretical detection limit of P2 was estimated using modified IUPAC method for calculating
-8
detection limit [33], therefore the detection limit was calculated to be 5 x 10 M. This
suggests that P2 could act as potential highly sensitive ratiometric chemosensor for
2+
qualitative and quantitative detection of Hg ions.
8

Page 9 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01366K
For a novel fluorescent probe to be applied in natural samples (biological and environment),
the stability of the complex with a target analyte is vital. Thus, the stability of P2-Hg2+
complex was examined in the presence of other potentially competing metal ions. As
2
+
presented in Figure 3b, the fluorescence quenching caused by Hg ions was not remarkably
changed by the presence of other common metal ions. This suggests that P2 could offer
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
+
specific selectivity towards Hg in the existence of other common metal ions.
-7
-5
Figure 3: Emission responses of (a) 4 (2 x 10 M) and (b) P2 (2.33 x 10 g/L) after adding
the aliquots of various metal ions (0.01 M) (blue bars) and after adding an equimolar of Hg2+
(0.01 M) and common metal ions (0.01 M) (red bars) in acetonitrile/water (7:3). Excitation
was performed at 330 nm.
2
+
3
.4. Mechanism of Hg detection by P2
2+
To understand the mechanism behind Hg recognition, the fluorescence response of 4 was
studied through a continuous addition of Hg2+ aliquots under similar conditions as P2
titration experiments in section 3.3. As shown in Figure 4a, a progressive reduction of the
emission band at 390 nm, a gradual increase of the emission band at 480 nm and appearance
of another emission band at 455 nm were noticed. These observations are similar to the ones
obtained in its corresponding polymer P2 (Figure 2b).
9

New Journal of Chemistry
Page 10 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01366K
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
-
7
2+
Figure 4: (a) Emission spectra of 4 (2 x 10 M) upon addition of Hg aliquots (0 M – 1
2+

M). The inset indicates the changes in I /I as a function of Hg concentration. (b) A
480 390
Job’s plot for 4-Hg2+ complexation in acetonitrile/water (7:3) with a constant total
-7
concentration of 2 x 10 M. All spectra were recorded in acetonitrile/water (7:3) at 330 nm.
The spectral observations can be rationalized based on optical properties of 7-
hydroxycoumarin in aqueous solutions. In an aqueous environment, 7-hydroxycoumarins are
known to have four characteristic emission bands depending on the pH of the environment.
The different emission bands are due to phototautomerisation attributed to the four possible
species as shown in Scheme 2 [34]. In highly basic solutions (pH≥11), the anionic form 8 is
only existing species, while in highly acidic solutions (pH≤4) cationic form 6 is dominant. At
moderate pH range, three species (5, 7 and 8) coexist which results in three emission bands
[
34]. It was also reported that in non-polar aprotic solvents like chloroform, the neutral form
5
is dominant [35].
O
O
OH
7
-
OH+
O
O
O
HO
O
6
8
HO
O
O
5
1
0

Page 11 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01366K
Scheme 2: Phototautomerisation of 7-hydroxycoumarins
1
Thus, to verify the formation of the species, H NMR of 4 was investigated in non-polar
aprotic solvent (CDCl ) and polar aprotic solvent (DMSO-d ). As shown in Figure S5,
3
6
proton signals from CDCl showed the presence of the neutral form of 4 while in DMSO, a
3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
new doublet signal appeared at 5.5 ppm and it was assigned to the proton k of the tautomeric
form. This indicates that in polar solvents more than one form exists. This also explains the
appearance of three emissions bands in the emission spectra of both 4 and P2 during stepwise
2
+
addition of Hg aliquots as a mixture of polar aprotic solvent (acetonitrile) and polar protic
solvent (water) was used.
2
+
1
To further understand the interaction between 4 and Hg , the changes in H NMR of 4 was
2
+
examined in the presence of increasing amounts of Hg . As presented in Figure 5, the
2+
addition of Hg aliquots in DMSO-d solution of 4 caused a disappearance of the doublet at
6
5.5 ppm assigned to proton k of the tautomer. The proton signal at 2.58 ppm assigned to
2
+
2+
terminal alkyne proton was also affected by the addition of Hg . This indicates that Hg
interacts with tautomeric form 9 and convert it back to the neutral form 4 through the excited
state intramolecular proton transfer (ESIPT) mechanism (Scheme 3). Since Hg2+ binding
increase the electron withdrawing capability of the carbonyl group, the resulting complex
emit at long wavelength as push-pull effect in coumarin system increases [36].
1
2+
Figure 5: Changes in the H NMR signal of 4 with increasing amounts of Hg in DMSOd .
6
2
+
The binding stoichiometry between 4 and Hg was investigated using Job’s plot which was
constructed using a continuous variation method [37]. Notable in Figure 4b, the minimum
1
1

New Journal of Chemistry
Page 12 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01366K
emission intensity was attained at molar fractions of 0.5 indicating 1:1 stoicchiometric ratio
2
+
of 4-Hg complex. From the Job’s plot and spectroscopic information above, the interaction
2
+
mechanism between 4 and Hg can be summarized in Scheme 3. Since P2 exhibits similar
2
+
emission responses as 4 towards Hg , it is believed that the interchain interactions in the
polymer do not significantly affect the complexation process. Thus, P2 is expected to follow
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
+
2+
the same mechanism as 4 to complex Hg . The binding constants (Ka) of 4 and P2 with Hg
were evaluated graphically using the Benesi-Hildebrand equation [38]. From the slope and
6
-1
intercept of the line (Figure S6 a and b), Ka were determined to be 1.5 x 10 M and 2.1 x
6
-1
1
0 M for 4 and P2 respectively. The variation in binding constant signals a high affinity
associated with the polymeric sensing material than the small molecule counterpart.
H
O
H
O
X
X
OH
Hg2+
Hg2+
O
O
OH
-
Hg2+
O
O
O
HO
O
O
9
10
11
2+
Scheme 3: A schematic representation of 4-Hg interaction.
2
+
2+
Since 4 displayed ratiometric response towards Hg , the stability of its Hg complex was
examined in the presence of other potential competing metal ions. Notable in Figure 3a, the
2
+
quenching of the emission spectrum caused by Hg ions in acetonitrile/water solution of 4
was not considerably altered by the existence of one molar equivalent of other metal ions,
indicating that 4 could offer specific selectivity towards Hg2+ in the presence of common
metal ions as its polymer counterpart.
3.5. Reversibility and response time
With the purpose of exploring the reusability of the proposed chemosensor, an excess of
ethylenediaminetetraacetic acid (EDTA) was mixed with the acetonitrile/water solution
2
+
containing P2/4-Hg species. As shown in the Figure 6, the addition of the multidentate
ligand (EDTA) resulted in an increased emission intensity at 455 nm in 4 and 453 in P2. This
indicates that, the binding process between P2/4 and Hg2+ are reversible. However, the
resulting species are not the neutral form of 4, but the ionic form instead. This observation is
in agreement with the reports in the literature which state that the addition of alkylamine to
1
2

Page 13 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01366K
the alcoholic and the aqueous solution of 7-hydrocoumarins results only in anionic species
due to the higher ionizing ability of those solvents [34]. The response times of 4 and P1 were
studied in acetonitrile/water solution and in both systems the chemical interactions which
2
+
lead to a detectable change in the presence of Hg took place within 1 min. This suggests
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2+
that 4 and P1 can be used in real time detection of Hg ions.
2+
2+
Figure 6: Reversibility of binding process between (a) 4 and Hg and (b) P2 and Hg .
3
.8. Comparative studies with reported probes
2
+
To underline the impact of this work to the sensing of Hg , the proposed system was
compared with recently reported ratiometric fluorescent systems in term of sensitivity, ligand
to metal ion affinity and reversibility of the interaction. As shown in Table 1, most of
recently developed ratiometric fluorescent systems are reaction-based probes that results in
the chemical structure modifications of the original system. These modifications affect the
binding sites in the sensing system and consequently the reversibility of the interaction. In
contrast, the newly developed system (P2) exhibited a reversibility of the interaction with
2+
Hg and its sensitivity is comparable or superior to that of recently developed ratiometric
fluorescent systems.
1
3

New Journal of Chemistry
Page 14 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table 1: Comparison of P2 with recently reported ratiometric fluorescent systems for HgV2i+ew Article Online
DOI: 10.1039/C9NJ01366K
-
1
Proposed sensors
LOD (M)
K (M )
Detection signal Reversible Ref
a
This
Ratiometric
P4
5 x 10-8
2.1 x 106

work
[39]
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
fluorescence
H2N
2.7 x 10-8
Ratiometric
fluorescence
X
N
S
S
-
-
O
N
O
O
Ratiometric
fluorescence
X
N
. 8 x 10-9
7
[40]
N
S
S
Ratiometric
fluorescence
X
X
5.2 x 10-7
9 x 10-8
-
[41]
[42]
N
H
O
O
Ratiometric
fluorescence
S
N
-
-
S
O
O
N
N
N
Ratiometric
fluorescence
2
1
.3 x 10-7
.2 x 10-8

[43]
[44]
O2N
NH
O
O
O
Ratiometric
fluorescence
X
X
N
O
-
-
O
N
O
NH2
Ratiometric
fluorescence
6
x 10-9
[45]
N
3.9. Application of P2 in practical water samples
2+
To validate the practical application of P2 as a potential Hg chemosensor, we applied the
proposed chemosensor in the evaluation of Hg2+ in natural water samples (tap and lake
water). Tap water was collected from water pipes at Nelson Mandela University chemistry
laboratory while lake water was collected from North End Lake (Port Elizabeth, South
Africa). Both samples were initially digested with nitric acid and analyzed by the Inductively
Coupled Plasma-Optical Emission Spectroscopy (ICP-OES). However, a minimal amount of
2
+
Hg was detected in both tap water (0.084 ppm) and lake water sample (0.179 ppm). To
1
4

Page 15 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
2+
View Article Online
DOI: 10.1039/C9NJ01366K
facilitate fluorescence analysis, both samples were spiked with Hg standards and the results
are presented in Table 2. Notable, the analytical analysis of the two samples using P2
provided satisfactory results for both spiked tap and lake water. These indicate that the
2
+
proposed chemosensor could be an ideal tool for detecting Hg in natural water samples.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
+
Table 2. Evaluation of Hg (ppm) in real samples (standard deviations are given in
parenthesis, n = 3). Calibration range (1ppm-5 ppm).
Samples
ICP-OES analysis (ppm)
4.18 (0.008)
Fluorescence analysis (ppm)
4.71 (0.24)
Spiked lake water
Spiked tap water
3.41 (0.02)
3.39 (0.21)
4
. Conclusion
In summary, a novel fluorescent polymer P2 incorporating 7-hydoxycounmarin as
fluorophore and triazole as a linker was successfully designed and synthesized. The addition
2
+
of Hg into P2 acetonitrille/water solution resulted in three distinctive emission bands which
were assigned to phototautomersim species of 7-hydroxycoumarin unit. The stepwise
addition of Hg2+ showed that P2 can act as highly sensitive ratiometric fluorescent
2
+
chemosensor for quantitative recognition of Hg ions and the signal were not significantly
changed by the existence of common metal ions. The mechanism of Hg2+ detection was
investigated by comparing the fluorescence responses of the alkyne functionalized molecule
2
+
and its polymer in the presence of Hg and it was concluded that ESIPT mechanism is the
basis of ratiometric signals. The proposed system was compared with recently reported
ratiometric fluorescent systems and comparable or superior properties to that of recently
developed ratiometric fluorescent systems were observed. Furthermore, the newly developed
sensing system was also applied in the evaluation of Hg2+ in natural water samples and
satisfactory results were obtained. We believe, this work will significantly promote the
development of novel ratiometric materials for metal ions recognition.
5
. Conflict of interest
There is no conflict of interest to declare.
1
5

New Journal of Chemistry
Page 16 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/C9NJ01366K
6
. Acknowledgments
For this work, we acknowledge the Nelson Mandela University (NMU) for funding and
facilities to carry out this project.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
7
. References
1
. Y. Ding, Y. Tang, W. Zhu and Y. Xie, Chem. Soc. Rev., 2015, 44, 1101-1112; b) B.
Valeur and I. Leray, Coordin. Chem. Rev., 2000, 205, 3-40; c) A. P. De Silva, H. N.
Gunaratne, T. Gunnlaugsson, A. J. Huxley, C. P. McCoy, J. T. Rademacher and T. E.
Rice, Chem. Rev., 1997, 97, 1515-1566; d) V. Amendola, L. Fabbrizzi, F. Foti, M.
Licchelli, C. Mangano, P. Pallavicini, A. Poggi, D. Sacchi and A. Taglietti, Coordin.
Chem. Rev., 2006, 250, 273-299; e), A. P De Silva, D. B. Fox, A. J. Huxley and T. S.
Moody, Coordin. Chem. Rev., 2000, 205, 41-57.
2. (a) A. Renzoni, F. Zino and E. Franchi, Environ. Res., 1998, 77, 68-72; (b) O. Malm,
Environ. Res., 1998, 77, 73-78; (c) H. N. Kim, M. H. Lee, H. J. Kim, J. S. Kim and J.
Yoon, Chem. Soc. Rev., 2008, 37, 1465-1472.
3. J. S. Lee, M. S. Han, C. A. Mirkin. Angew Chem. Int. Ed. 2007, 46, 4093–4096.
4
5
6
. a) I. Onyido, A. R. Norris and E. Buncel, Chem. Rev., 2004, 104, 5911–29; b) F. Baldi,
M. Filippelli and G. Olson, J. Microb. Ecol., 1989, 17, 263–274.
. P. Holmes, K. A. F. James, and L. S. Levy, Sci. Total Environ., 2009, 408, 171-182; b)
M. C. Houston, J. Clin. Hypertens., 2011, 13, 621-627.
. (a) J. Liu, Y.-Q. Sun, P. Wang, J. Zhang and W. Guo, Analyst, 2013, 138, 2654; (b) S.
Pal, J. Hatai, M. Samanta, A. Shaurya and S. Bandyopadhyay, Org. Biomol. Chem., 2014,
1
2, 1072-1078.
7. P. Li, X. Feng and G. Qiu, Int. J. Environ. Res. Public Health, 2010, 72666-2691.
8
9
. (a) X. Ai, Y. Wang, X. Hou, L. Yang, C. Zheng and L. Wu, Analyst, 2013, 138, 3494-
501; (b) M. J. de Silva, A. P. S. Paim, M. F. Pimentel, M. L. Cervera and M. de la
3
Guardia, Anal. Chim. Acta, 2010, 667, 43-48.
. (a) N. H. Khdary and A. G. Howard, Analyst, 2011, 136, 3004-3009; (b) Z. Liu, Z. Zhu,
H. Zheng and S. Hu, Anal. Chem., 2012, 84, 10170-10170; (c) Z. A. Chandio, F. N.
Talpur, H. Khan, H. I. Afridi, G. Q. Khaskheli and M. A. Mughal, RSC Adv., 2014, 4,
3326-333.
1
6

Page 17 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
1
1
0. (a) S. Ma, Q. Chen, H. Li, P. Wang, S. M. Islam, Q. Gu, X. Yang and M. G. Kanatzidis, J.
DOI: 10.1039/C9NJ01366K
Mater. Chem. A, 2014, 2, 10280- 10289; (b) H. Zhou, X. Lv, L. Zhang, A. Gong, A. Wu,
Z. Liang, G. Peng and H. Lin, J. Mater. Chem. C, 2014, 2, 9625-9630.
1. (a) Z. Zhang, J. Li, X. Song, J. Ma and L. Chen, RSC Adv., 2014, 4, 46444-46453; (b) T.
Yordanova, P. Vasileva, I. Karadjova and D. Nihtianova, Analyst, 2014, 139, 1532-1540.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
12. P. Ugo, L. Mortto, P. Bertoneell, J. Wang, Electroanalysis, 1998, 10, 1017–1021.
1
3. a) S. J. Lee and M. Moskovits, Nano Lett., 2011, 11, 145-150; b) Y. Du, R. Liu, B. Liu,
S. Wang, M.-Y. Han and Z. Zhang, Anal. Chem. 2013, 85, 3160-3165.
1
4. a) Z. Gao and X. Ma, Anal. Chim. Acta, 2011, 70250-55; b) Y. Gao, Z. Shi, Z. Long, P.
Wu, C. Zhen and X. Hou, Microchem. J., 2012, 1031-14.
1
1
5. K. Leopold, M. Foulkes and P. Worsfold, Anal. Chim. Acta, 2010, 663127-138.
6. a) A. Thakur, D. Mandal and S. Ghosh, Anal. Chem., 2013, 85, 1665–1674; b) J. Wu, W.
Liu, J. Ge, H. Zhang and P. Wang, Chem. Soc. Rev., 2011, 40, 3483–3495.
7. a) X. Qian and Z. Xu, Chem. Soc. Rev., 2015, 44, 4487-4493; b) A. Balamurugan and H.
Lee, Macromolecules, 2015, 48, 1048-1054; c) J. Song, M. Huai, C. Wang, Z. Xu, Y.
Zhao and Y. Ye, Spectrochim Acta A, 2015, 139, 549-554; d) H. Cheng and Y. Qian,
Sens. Actuators B, 2015, 219, 57-64; e) Q. Q. Rui, Y. Zhou, Y. Fang and C. Yao,
Spectrochim. Acta A, 2016, 209-218.
1
1
1
8. a) X. D. Jiang, J. Zhao, Q. Li, C. L. Sun, J. Guan, G. T. Sun, and L. J. Xiao, Dyes Pigm.,
2
2
016, 125, 136-141; b) W. Shi, Y. Chen, X. Chen, Z. Xie and Y. Hui, Inorg. Chim. Acta,
016, 445, 149-54.
9. a) X. Zhang, Y. Xiao and X. Qian, Angew. Chem., Int. Ed., 2008, 47, 8025–8029; b) C.-
Y. Li, X.-B. Zhang, L. Qiao, Y. Zhao, C.-M. He, S.-Y. Huan, L.-M. Lu, L.-X. Jian, G.-L.
Shen and R.-Q. Yu, Anal. Chem., 2009, 81, 9993–10001; c) Z.-X. Han, X.-B. Zhang, Z.
Li, Y.-J. Gong, X.-Y. Wu, Z. Jin, C.-M. He, L.-X. Jian, J. Zhang, G.-L. Shen and R.-Q.
Yu, Anal. Chem., 2010, 82, 3108–3113.
2
2
0. a) Z. Wang, D. Zhang and D. Zhu, Anal. Chim. Acta, 2005, 549, 10–13; a) E. M. Nolan
and S. J. Lippard, J. Am. Chem. Soc., 2007, 129, 5910–5918. b) M. Suresh, S. Mishra, S.
K. Mishra, E. Suresh, A. K. Mandal, A. Shrivastav and A. Das, Org. Lett., 2009, 11,
2
740–2743. c) X. Cheng, Q. Li, J. Qin and Z. Li, ACS Appl. Mater. Interfaces, 2010, 2,
1066–1072.
1. J. Zhao, S. Ji, Y. Chen, H. Guo and P. Yang, Phys. Chem. Chem. Phys., 2012, 14, 8803–
8
817.
1
7

New Journal of Chemistry
Page 18 of 20
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
2
2. a) M. J. Paterson, M. A. Robb, L. Blancafort and A. D. DeBellis, J. Phys. Chem. A, 2005,
DOI: 10.1039/C9NJ01366K
109, 7527–7537; b) H. Yao and T. Funada, Chem. Commun., 2014, 50, 2748–2750; c) K.
C. Tang, M. J. Chang, T. Y. Lin, H. A. Pan, T. C. Fang, K. Y. Chen, W. Y. Hung, Y. H.
Hsu and P. T. Chou, J. Am. Chem. Soc., 2011, 133, 17738-17745.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
23. a) B. Liu, J. Wang, G. Zhang, R. Bai and Y. Pang, ACS Appl. Mater. Interfaces, 2014, 6,
402–4407; b) S. Goswami, A. Manna, S. Paul, A. K. Maity, P. Saha, C. K. Quah and H.-
4
K. Fun, RSC Adv., 2014, 4, 34572–34576; c) S. Goswami, A. Manna, M. Mondal and D.
Sarkar, RSC Adv., 2014, 4, 62639–62643; d) S. Goswami, A. Manna, S. Paul, A. K. Das,
P. K. Nandi, A. K. Maity and P. Saha, Tetrahedron Lett., 2014, 55, 490–494; e) D. Dahal,
L. McDonald, X. Bi, C. Abeywickrama, F. Gombedza, M. Konopka, S. Parushuri and Y.
Pang, Chem. Commun., 2017, 53, 3697-3700; f) B. Gu, L. Huang, N. Mi, P. Yin, Y.
Zhang, X. Tu, X. Luo, S. Luo and S. Yao, Analyst, 2015, 140, 2778-2784.
24. a) M. Santra, B. Roy and K. H. Ahn, Org. Lett., 2011, 13, 3422–3425; b) B. Gu, L.
Huang, N. Mi, P. Yin, Y. Zhang, X. Tu, X. Luo, S. Luo and S. Yao, Analyst, 2015, 140,
2
778–2784.
25. a) R. Hu, J. Feng, D. Hu, S. Wang, S. Li, Y. Li and G. Yang, Angew. Chem., Int. Ed.,
010, 49, 4915–4918; b) D. P. Murale, H. Kim, W. S. Choi and D. G. Churchill, Org.
Lett., 2013, 15, 3946–3949; c) M. Santra, B. Roy and K. H. Ahn, Org. Lett., 2011, 13,
422–3425; d) S. Goswami, A. Manna, S. Paul, A. K. Das, K. Aich and P. K. Nandi,
2
3
Chem. Commun., 2013, 49, 2912–2914.
2
2
6. a) V. V. RostovtsevL. G., Green, V. V. Fokin and K. B. Sharpless, Angew. Chem. Int.
Ed., 2002, 412596–2599.
7. a) J. C. Qin, T. R. Li, B. D. Wang, Z. Y Yang and L. Fan, Spectrochim. Acta A, 2014,
133, 38-43. C; b) F. Chen, G. Liu, Y. Shi, P. Xi, J. Cheng, J. Hong, R. hen, X. Yao, D.
Bai, Z. Zeng, Talanta, 2014, 124, 139-145.
2
8. a) J. C. Qin, T. R. Li, B. D. Wang, Z. Y Yang and L. Fan, Spectrochim. Acta A, 2014,
133, 38-43; b) A. Jõgi and U. Mäeorg, Molecules, 2001, 6, 964-968.
9. M. Meldal, C. W. Tornøe, Chem. Rev., 2008, 108, 2952-3015.
0. P. K. Adapa, L. G. Schonenau, T. Canam, and T. Dumonceaux, J. Agric. Sci. Technol.,
2
3
2
011, 1, 177-188.
31. J. Wu, W. Liu, J. Ge, H. Zhang and P. Wang, Chem. Soc. Rev., 2011, 40, 3483-3495.
3
2. a) D. S. McClure, J. Chem. Phys., 1952, 20, 682-686; b) H. Masuhara, H. Shioyama, T.
Saito, K. Hamada, S. Yasoshima and N. Mataga, J. Phys. Chem., 1984, 88, 5868–5873; c)
1
8

Page 19 of 20
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/C9NJ01366K
M. Bassetti, B. Floris and G. Spadafora, J. Org. Chem., 1986, 51, 4140-4143; d) R. C.
Larock, L. D. Burns, S. Varaprath and C. E. Russell, Organometallics, 1987, 6, 1780-
1
5
789; e) M. Nishizawa, H. Imagawa and H. Yamamoto, Org. Biomol. Chem., 2010, 8,
11-521.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
3. M. D. Fernández-Ramos, L. Cuardos-Rodríguez, E. Arroyo-Guerrero, L. F. Capitán-
Vallvey, Anal. Bioanal. Chem., 2011, 401, 2881-2889.
3
3
3
4. T. Moriya, B. Chem. Soc. Jpn., 1983, 56, 6-14.
5. T. Moriya, B. Chem. Soc. Jpn., 1988, 61, 1873-1886.
6. C. J. Wheelock, J, Am. Chem. Soc., 1959, 81, 1348-1352.
37. J. S. Renny, L. L. Tomasevich, E. H. Tallmadge and D. B. Collum, Angew. Chem., Int.
Ed. 2013, 52, 11998–12013.
3
8. a) H. A. Benesi and J. H. Hildebrand, J. Am. Chem. Soc. 1949, 71 2703–2707. b) M.
Barra, C. Bohne and J. C. Scaiano, J. Am. Chem. Soc. 1990, 112, 8075–8579. c) L.
Wang, D. Ye and D. Cao, Spectrochim. Acta, Part A, 2012, 90, 40-44.
3
9. S.L. Pan, K. Li, L.L. Li, M.Y. Li, L. Shi, Y.H Liu and X.Q. Yu, Chem. Commun., 2018,
5
4, 4955-4958 RSC.
40. B. Gu, L. Huang, N. Mi, P. Yin, Y. Zhang, X. Tu, X. Luo, S. Luo and S. Yao, Analyst,
015, 140, 2778-2784.
1. J. Hu, Z. Hu, S. Liu, Q. Zhang, H.W Gao and K. Uvdal, Sens. Actuators, B-Chem., 2016,
30, 639-644.
2. X. Cheng, S. Qu, L. Xiao, W. Li and P. He, J. Photochem. Photobiol. A: Chem., 2018,
64, 503-509.
2
4
4
4
4
4
2
3
3. Y. Zhang, H. Chen, D. Chen, D. Wu, Z. Chen, J. Zhang, X. Chen, S. Liu and J. Yin, Sens.
Actuators, B-Chem., 2016, 224, 907-914.
4. Y. Jiao, X. Liu, L. Zhou, H. He, P. Zhou and C. Duan, Sens. and Actuators B-Chem,
2
017, 247, 950-956.
5. M. Nagy, S.L. Kovács, T. Nagy, D. Rácz, M. Zsuga and S. Kéki, Talanta, 2019, 201, 165-
173.
1
9

New Journal of Chemistry
Page 20 of 20
View Article Online
DOI: 10.1039/C9NJ01366K
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table of content entry
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
R
OH
O
O
OH
H
R
O
Hg2+
*
9
T (S )
1
ESIPT
HO
O
O
*
C (S )
1
Hg2+
y
g
r
Complexemission
e
H
n
Absorption Emission
R
R
E
OH
O
Hg2+
O
O-
EDTA
O
O
C(So) HO
O
T (S )
9
o
R
OH
O
O
OH
2
+
A reversible ESIPT based system for the detection of Hg was developed. The system exhibited
better properties compared to that of recently developed ratiometric fluorescent systems.