Synthesis of novel coumarin containing conjugated fluorescent polymers by Suzuki cross-coupling reactions and their chemosensing studies for iron and mercury ions

Article abstract of DOI:10.1016/j.polymer.2021.123415

Conjugated fluorescent polymers are very useful materials for chemical and biochemical sensors. Herein we report the synthesis of four novel conjugated coumarin-containing fluorescent co-polymers (P1–P4) by palladium catalyzed Suzuki-Miyaura cross-couplin

Full text of DOI:10.1016/j.polymer.2021.123415

Polymer 218 (2021) 123415
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Polymer
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Synthesis of novel coumarin containing conjugated fluorescent polymers by
Suzuki cross-coupling reactions and their chemosensing studies for iron and
mercury ions
Prabhas Bhaumick, Asim Jana, Lokman H. Choudhury*
Department of Chemistry, Indian Institute of Technology Patna, Patna, 801106, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Conjugated fluorescent polymers are very useful materials for chemical and biochemical sensors. Herein we
report the synthesis of four novel conjugated coumarin-containing fluorescent co-polymers (P1–P4) by palladium
catalyzed Suzuki-Miyaura cross-coupling reaction. 4-Methyl/phenyl coumarin ditriflates and diboronic acids
such as benzene-1,4-diboronic acid and 9,9-dioctylfluorene-2,7-diboronic acid were used as coupling partners.
All the polymers were well-characterized using NMR and gel permeation chromatography. TGA studies revealed
that these polymers are stable over 300 ◦C. The photophysical properties of these novel polymers were studied by
UV–Vis and fluorescence spectroscopy. Among these four polymers, polymer P3 having 4-methylcoumarin and
dioctylfluorene as alternating monomers showed intense fluorescence with 0.73 quantum yield in the DMF
medium. Polymer P3 was also found as selective fluorescence “turned-off” chemosensor for the detection of Hg
(II) and Fe(II)/Fe(III) ions over the other metal ions dissolved in water.
Pd-catalysis
Highly fluorescent coumarin containing
conjugated copolymers
Selective turn-off sensor for Hg2+ and Fe2+
Fe3+
/
Suzuki coupling
Boronic acid
1. Introduction
7-diboronic acid bis(1,3-propanediol) ester monomers [12]. Using
similar polycoupling, synthesis of copolymer poly(9,9-dihexadecyl flu-
′
′
´
Conjugated polymers are important synthetic materials with wide
applications in solar cells [1], organic light-emitting diodes [2],
thin-film transistors [3], fluorescence imaging [4], electro chromic
materials [5], photocatalyst [6], as well as in chemosensors [7].
Specially, fluorescent conjugated polymers are very useful materials for
chemosensing studies. Considering the easy preparation, rigid structure,
and high sensitivity due to the molecular wire effect of conjugated
polymers, the design and development of novel fluorescent conjugated
polymers has remained a popular and very useful research topic [8]. In
addition to these, polymer-based chemosensors often show better
selectivity and binding efficiency due to the presence of multiple
recognition sites for analytes in the polymer backbones [9]. Metal
catalyzed coupling reaction is one of the most widely used strategies for
the synthesis of conjugated polymers [10]. Recently, Zhao and Tang
et al. reported synthesis of through-space conjugated polymers by
Suzuki and Stille coupling reactions, and studied their optical and
explosive detection properties [11]. Foster and Turner et al. reported
synthesis of spherical and rod-like conjugated nanoparticles in emul-
sions from the palladium catalyzed Suzukiꢀ Miyaura cross-coupling re-
actions of different dibromoarenes and 9,9-dioctylfluorene-2,
orene-2,7-diyl-alt-2,2 -bithiophene-5,5 -diyl)s was reported by Cimrova
et al. under microwave conditions and studied their electroluminescent
properties [13]. Likewise, Wang et al. reported a novel conjugated
polymer having coumarin, carbazole, fluorene and phenylene moieties
for the naked-eye detection of DNA [14]. From this literature survey, we
realized the potential and scope of conjugated polymers and its useful-
ness as chemosensors.
Rapid detection of environmentally harmful and biologically
important metal ions dissolved in water has remained an ever-enduring
topic in the field of chemosensing [15]. Considering the advantage of
polymers over the small molecule-based chemosensors, recently atten-
tion has been shifted towards developing novel polymers for the selec-
tive detection of transition and heavy metals [16]. Water pollution due
to the presence of excess amounts of dissolved metal ions is a major
concern for the health of humans and other living organisms [17].
Although metals are very important in various biochemical reactions,
however, excess intake of metal ions such as iron and mercury are very
harmful, toxic and can cause severe health issues [18]. In view of these,
an effective method for the detection of these ions in very low concen-
tration in the aqueous medium has lots of scopes. Fluorescence
* Corresponding author.
E-mail addresses: lokman@iitp.ac.in, lokman.iitp@gmail.com (L.H. Choudhury).
https://doi.org/10.1016/j.polymer.2021.123415
Received 26 February 2020; Received in revised form 6 January 2021; Accepted 10 January 2021
Available online 15 January 2021
0032-3861/© 2021 Elsevier Ltd. All rights reserved.

P. Bhaumick et al.
Polymer 218 (2021) 123415
spectroscopy is a relatively simple and highly sensitive tool for chemo-
sensing studies [19]. Recently, many methods have been developed for
the detection of iron [20] and mercury [21] ions using either small
molecule or polymers as fluorescent chemosensors. However, to the best
shows higher molecular weights [26].
Next, polymer P1 was characterized by 1H NMR in DMSO‑d6 and
solid-state 13C NMR. For the characterization of the polymer P1, we first
compared the 1H NMR peak positions of various protons of the polymer
with 1H NMR of the model compound MD-1. In the model compound,
CH3 attached with the coumarin ring at 4-position appears at 1.79 ppm,
and in the polymer P1 corresponding peak appears at 1.77 ppm. Simi-
larly, the = CH proton of the coumarin ring appears at 6.19 ppm, and in
polymer P1 corresponding peak appears at 6.32 ppm. In the solid-state
13C NMR, the presence of one peak at 24.4 ppm is due to the –CH3 group
attached with coumarin ring and carbonyl carbon appears at 159.78
ppm. These informations confirmed the presence of the coumarin moi-
ety in the polymer backbone. In the 1H NMR of polymer P1, the presence
of another three peaks in the aromatic region implies the presence of an
aryl linker connected with the coumarin moiety. In the FTIR spectra of
of our knowledge, there is no report of
a single fluorescent
polymer-based chemosensor for the simultaneous detection of iron and
mercury ions dissolved in water. Thus, in continuation of our work on
synthesis and studies of fluorescent molecules and chemosensors [22],
we were motivated to develop a novel fluorescent conjugated polymer to
use as fluoroprobe for the detection of important metal ions such as iron
and mercury dissolved in water.
Although polymers with coumarin as pendant are known in the
literature with diverse applications [23] however, to the best of our
knowledge, conjugated polymers having only coumarin-fluorene or
coumarin-arene in alternating copolymers are not yet explored. In this
paper, we are reporting the synthesis of four novel coumarin containing
conjugated fluorescent copolymers by palladium-catalyzed Suzu-
kiꢀ Miyaura cross-coupling reaction of coumarin ditriflate and diboronic
acids and studied their photophysical properties and thermal stabilities.
We have also studied the chemosensing properties of one of the
polymers.
–
the model compound C O stretching appears at 1733, and in the
–
ꢀ 1
–
–
polymer P1 corresponding C O appears at 1701 cm
.
After having this successful result for the polymer P1, next this
Suzuki polycoupling strategy was applied for the preparation of another
polymer P2, using M-2 and benzene 1,4-diboronic acid as monomers. In
this case also a similar result was observed. Similarly, another two
conjugated polymers P3 and P4 were prepared by replacing benzene-
1,4-diboronic acid with 9,9-dioctylfluorene-2,7-diboronic acid and
taking monomers M-1 and M-2 respectively under the standard reaction
conditions (Scheme 3). After preparing 1these conjugated polymers, we
characterized all of them by recording H NMR in DMSO‑d6 or CDCl3
and solid-state 13C NMR. The detailed reaction procedure and charac-
terization data are given in the experimental section and the NMR
spectra of all these polymers are shown in the supporting information.
Thermal stability is one of the very important parameters for
assessing the usefulness of a polymer and deciding its applications in
harsh conditions. To check the thermal stability of our newly synthe-
sized polymers, thermogravimetric analysis (TGA) was performed using
2. Results and discussion
Initially, pre-monomers (dihydroxy coumarin derivatives) PM-1
(where R = Me) and PM-2 (R = Ph) were prepared using iodine medi-
ated reaction of phloroglucinol dihydrate (1) and β-keto esters 2a and 2b
(ethyl acetoacetate or ethyl benzoyl acetate) under neat conditions
following literature reported procedure [24]. Then these two
pre-monomers were converted to the corresponding ditriflates M-1 and
M-2 by reacting with trifluoromethanesulfonic anhydride in the pres-
ence of pyridine as a base in dichloromethane medium at room tem-
perature (Scheme 1). Next, all these synthesized pre-monomers and
monomers were fully characterized by recording melting point, IR
spectroscopy, 1H and 13C NMR as well as by HRMS.
◦
an SDTQ600 (TA Instruments) at a scan rate of 10 C/min under ni-
trogen flow (100 mL/min). The initial decomposition temperature at
◦
◦
which 5% weight loss of the initial weight of P1 was found at 450 C
Before trying the Suzuki poly coupling reaction, a model reaction
was tried by reacting monomer M-1 with 2.0 equivalents of phenyl-
boronic acid in the presence of palladium acetate as catalyst. Interest-
ingly, this model reaction provided our desired biscoupling product MD-
1 with 58% yield within 24.0 h (Scheme 2). This compound was then
while P2, P3 and P4 are stable in the range between 300 and 320 C
(Fig. 1).
2.1. Optical properties
1
characterized by recording IR, H & 13C NMR as well as by recording
HRMS. Langer et al. also prepared this biscoupling product MD-1 using
Pd(PPh3)4 as catalyst, and K3PO4 as base in toluene–1,4-dioxane (1:1)
solvent system [25].
The absorption and emission properties of these newly synthesized
coumarin based polymers were studied in DMF solution. The absorption
peaks of P1, P2, P3, and P4 appear between 335 and 350 nm as shown in
With the success of this biscoupling reaction with monomer M-1,
next, we tried polymerization reaction of M-1 with benzene-1,4-
diboronic acid for the preparation of coumarin containing conjugated
polymer P1 having alternate coumarin-arene monomers. The optimi-
zation table for the preparation of polymer P1 under various reaction
conditions is shown in Table 1. Among all the screened reactions, entry
8, Table 1 using 10-mol% Pd catalyst in dioxane-water medium (20:1 v/
v) at 120 ◦C for 72 h provided the best result in terms of yield obtained
and molecular weight of the polymer. The average molecular weights
(Mw and Mn) of this polymer were determined by GPC in DMF medium.
It is noteworthy to mention that GPC technique has some limitations for
determining molecular weights of rigid-rod polymers, which often
Fig. 2a, which may be due to the π-π* transition of the conjugated
backbone. All the polymers (P1 to P4) exhibit emission peaks in the
range of 407–425 nm in fluorescence spectroscopy (Fig. 2b).
Next, the fluorescence quantum yields (Φf) of these four polymers
(P1 to P4) were measured in DMF medium, and observed quantum
yields were found in the range of 16–73% (Table 2).
Next, considering the high fluorescence quantum yield of P3 poly-
mer, we wanted to explore this polymer as a fluorescent probe for se-
lective metal ion detection from drinking water. Before, screening the
chemosensing properties of P3, we have recorded UV–Vis and fluores-
cence spectra of this polymer in different concentrations. The absor-
bance and the fluorescence intensity were found gradually increasing
Scheme 1. Preparation of pre-monomer and monomers.
2

P. Bhaumick et al.
Polymer 218 (2021) 123415
Scheme 2. Pd catalyzed Suzuki biscoupling of M-1 with two equivalents of phenylboronic acid.
Table 1
Optimization of reaction conditions for the preparation of polymer P1.a
Entry
Pd(OAc)2 (mol%)
Solvent
Temp./oC
Reaction time/h
Mn
Mw
PDI
% Yield
1
1
1,4-Dioxane
70
24
24
48
48
48
48
48
72
72
72
400
559
1.39
1.47
1.18
1.2
25
30
46
56
58
57
68
85
54
59
2
2
1,4-Dioxane
70
521
768
3
10
10
10
10
10
10
10
10
1,4-Dioxane
80
3778
4171
4384
4370
5319
5934
3820
3950
4495
5019
5043
5054
6857
12231
4423
4018
4
1,4-Dioxane-water(20:1)
1,4-Dioxane-water (20:1)
1,4-Dioxane-water(20:1)
1,4-Dioxane-water(20:1)
1,4-Dioxane-water (20:1)
THF
80
5
90
1.15
1.16
1.29
2.06
1.15
1.01
6
100
120
120
120
120
7
8
9
10
DMF
a
Reaction conditions: M-1 (0.5 mmol), benzene 1,4-diboronic acid (0.5 mmol), Pd(OAc)2, PPh3 heating under sealed conditions.
Scheme 3. Synthetic routes to coumarin containing fluorescent polymers P1
to P4.
with the increase in the concentration of P3 from 1 to 15 μg/mL (Fig. 3a
and b).
Next, to check whether P3 will show any solvatochromic effect, we
recorded the UV–Vis and fluorescence spectra of polymer P3 in four
different solvents THF, chloroform, DMSO, and DMF. In all the four
solvents, a very similar kind of absorption pattern having absorption
maxima at 345 nm was observed (Fig. 4a). The fluorescence spectra of
P3, in DMSO, DMF, and CHCl3 showed emission maxima at 425 nm
whereas THF showed at 442 nm (Fig. 4b). On the other hand, the
fluorescence intensity of P3 was found similar in DMF and THF. Inter-
estingly, fluorescence intensity slightly decreased in DMSO, and
increased in CHCl3 medium. We also calculated the quantum yields of
P3 in these four different solvents and the results are summarized in
Table 3.
Fig. 1. Thermograms of polymers P1, P2, P3 and P4.
After having these results in hand, the recognition ability of P3 to-
ward different metal-cations such as Zn2+, Mg2+, Cu2+, Fe3+, Cd2+
,
Ni2+, Mn2+, Na+, K+, Al3+, Co2+, Hg2+ as well as anions like SO24-, Brꢀ ,
NO2ꢀ , Clꢀ , Nꢀ3 , Iꢀ , SO32-, CO23-, NOꢀ3 and Fꢀ which are generally found in
the water were studied by the naked eyes, UV–Vis and fluorescence
spectroscopic methods. In the naked eye, the solution of P3 in DMF is
3

P. Bhaumick et al.
Polymer 218 (2021) 123415
Fig. 2. (a) UV–vis spectra and (b) Fluorescence spectra of polymers P1, P2, P3 and P4 in DMF with a concentration of 2.5 μg/mL.
Table 2
Molecular weight and fluorescence quantum yields of polymers in DMF medium.
Sr. No.
Polymer
Mw (g/mol)
DP
PDI
Yield (%)
Excitation λex(nm)
As
Emission
Stokes’ shift (nm)
Φf
λemmax (nm)
1.
2.
3.
4.
P1
P2
P3
P4
12231
5778
6963
6337
52
19
12
10
2.06
1.19
1.48
1.22
85
78
80
82
339
360
345
340
0.48
0.32
0.25
0.21
416
423
425
407
77
63
63
67
0.16
0.18
0.73
0.49
Fig. 3. (a) UV–Vis spectra of polymer P3 in DMF medium at different concentrations, (b) The fluorescence spectra of polymer P3 in DMF at different concentrations.
colourless, however, on the addition of Fe2+ solution a faint pink colour
and on the addition of Fe3+ solution, the colour of the polymer solution
changed to light brown colour. On the other hand, a sharp colour
change from colourless to yellow for Hg2+ was observed, whereas other
metal ions did not show any colour change under visible light. Inter-
estingly, under the UV light fluorescence quenching because of these
three ions were clearly visible (Fig. 5, second row).
in Fig. 6.
Similarly, fluorescence spectra of polymer P3 in the DMF medium in
the absence of any quencher, and in the presence of salts having
different anions as well as in the presence of Fe(III) is shown in Fig. 7.
From these studies, it was evident that P3 is a selective “turn-off”
fluorescent sensor for Fe3+/2+ and Hg2+ ions. Next, to understand the
counter ion effects, we recorded the fluorescence spectra of P3 solution
in the presence of metal ion solutions of the same concentrations having
different counterions. Fe(III) salts having chloride, nitrate and sulphate
as counterions showed very similar type of quenching with P3 solution
in DMF as shown in Fig. 8.
Next, we have studied the fluorescence property of P3 in DMF so-
lution using a spectro -fluorimeter. The fluorescence properties of
polymer P3 in DMF medium in absence of any metal ions as well as in
the presence of various cations with 10 μg/mL concentration are shown
4

P. Bhaumick et al.
Polymer 218 (2021) 123415
Fig. 4. (a) UV–Vis spectra of polymer P3 (1 μg/mL) in different solvents, (b) Fluorescence spectra of polymer P3 (1 μg/mL) in different solvents.
were prepared and the fluorescence measurements were performed at
room temperature (Figs. 11a, 12a and 13a). LOD was calculated by using
the linear regression method, and the fluorescence recovery graph was
obtained by plotting (F0–F)/F0 against metal-ion concentration. The
Table 3
Quantum yields of P3 in different solvents.
Solvent
λabsmax (nm)
Excitation λex(nm)
As
Emission
Φf
λemmax(nm)
linear range was obtained within 3–13
μ
g/mL of Fe3+ concentration
DMF
345
345
345
345
345
345
345
345
0.145
0.151
0.166
0.164
425
425
442
425
73
69
66
78
(Fig. 11b). The linear equation was fitted as Y = 0.0257X - 0.0316 with a
linear correlation coefficient of R2 = 0.9967. For Fe2+, the linear range
DMSO
THF
was found within 1–11
μg/mL concentration (Fig. 12b). The linear
CHCl3
equation was fitted as Y = 0.024X - 0.0031 with a correlation coefficient
of R2 = 0.9946. Similarly, the linear range was obtained within 1–19
μg/
mL of Hg2+ concentration (Fig. 13b). For Hg2+, the linear equation was
Similarly, for the Fe(II), effects of counter ions were checked, by
taking iron (II) salts having chloride, sulphate and bromide as counter
ions. In this case, also, we did not find any significant change in fluo-
rescence quenching due to the different counterions as shown in Fig. 9.
Interestingly, in the case of mercury sensing, we found that
quenching of fluorescence in the presence of Hg(OAc)2 is more as
compared to Hg(NO3)3 (Fig. 10). This difference in quenching properties
may be due to the reactive nature of Hg(NO3)3 which undergo fast hy-
drolysis in water to give a turbid solution.
fitted as Y = 0.011X+0.0073 with a correlation coefficient of R2
=
0.9978. The limit of detection was obtained by the following equation
3σ/m (Where σ is the standard error of the blank for 11 replicate mea-
surements and m is the slope of calibration curve). The LOD for Fe3+
=
1.25
μ
M, Fe2+ = 2.9
μ
M and for Hg2+ = 2.98
μM were obtained.
Next, to understand the quenching process, the Stern-Volmer con-
stants were calculated using the equation F0/F = 1 + KSV [Q] [27]. Here
F0 and F are the fluorescence intensities in the absence and presence of
metal-ion respectively. [Q] is the metal-ion concentration and KSV is the
Stern-Volmer constant. The linear fitting of the plot F0/F vs [Q] gives the
slope KSV. The KSV for Fe (III) was found to be 7.65 × 103 L molꢀ 1, for Fe
(II) 4.13 × 103 L molꢀ 1 and for Hg(II) 3.54 × 103 L molꢀ 1 (obtained from
Fig. 14a, b and c). This indicates that these three metal ions have binding
affinity towards the polymer. In addition to these, from the life time
2.2. Limit of detection (LOD) calculation
To calculate the limit of detection for these three cations, solutions of
P3 (concentration 1 μg/mL in DMF) with a varying concentration of
Fe3+ (1–100
μ
g/mL), Fe2+ (1–188
μ
g/mL) and Hg2+ (1–200
μg/mL)
Fig. 5. The change of colour of P3 solution in DMF (10 μg/mL) on addition of 50 μL different metal-ion solutions (4.0 mM) (above) and the quenching of fluo-
rescence intensity under the uv light (bellow). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of
this article.)
5

P. Bhaumick et al.
Polymer 218 (2021) 123415
Fig. 6. Fluorescence spectra of P3 in DMF (1
μ
g/mL) in the absence and
g/mL).
Fig. 8. Fluorescence spectra of P3 in DMF (2.5
μg/mL) in the presence of
presence of various metal ions dissolved in water (10
μ
different Fe(III) salts having 0.1 mM concentration.
Fig. 9. Fluorescence spectra of P3 in DMF (2.5
μg/mL) in the presence of
Fig. 7. Fluorescence spectra of P3 in the DMF medium(1.0 μg/mL), measured
different 0.1 mM Fe(II) solutions.
in the absence and presence of aqueous solutions of different salts with different
anions and Fe3+ containing solution having 10
μg/mL concentration.
by weakly interacting with the ester moieties of the coumarin ring. Next,
to further prove that quenching of fluorescence of polymer P3 is due to
aggregation caused quenching (ACQ), we have recorded both absorp-
tion and emission spectra of P3 in the highly soluble DMF medium as
well as in mixtures of DMF-water mixtures. Interestingly, we found that
initially, absorption increases with an increase in water content, and
after that further increase do not give any significant change in ab-
sorption (Supporting information Fig. S2). On the other hand fluores-
cence emission drastically reduces in the presence of higher amount of
water, a poor solvent which forces polymers to have aggregation and
precipitation by hydrophobic interaction (Supporting information,
Fig. S3). Finally, we recorded the UV–visible spectrum of P3 solution in
DMF in the presence of Hg2+ and Fe3+ solutions with different con-
centrations (see supporting information, Fig S4, and S5). Interestingly,
we found that in both cases absorptions gradually increase with
increasing the quencher concentrations. Based on the literature reports
[28,29] and our present studies by using UV–vis and fluorescence
spectroscopy we proposed that quenching of fluorescence of polymer P3
measurement we found that the average fluorescence lifetime of poly-
mer P3 is 0.86 ns in the absence of any quencher. We did not observe any
significant change in the fluorescence lifetime of P3 in the presence of
Hg2+ and Fe3+ solutions (Fig. 15a and b). This clearly indicates that the
quenching of fluorescence of P3 by Hg2+ and by Fe3+ is static in nature
(see Table 4).
To further investigate the quencing mechanism we considered fluo-
rescence quencing of model substrate MD1 in the presence of Hg(II) and
Fe(III) solutions. Interestingly, our model compound MD1 also showed a
similar type of quenching pattern of polymer P3 in the presence of Hg(II)
and Fe(III) solutions. The fluorescence intensity of MD1 was found
decreasing with the increase of concentration of both Hg(II) and Fe(III)
solutions as shown in Fig. 16a and b. The decrease in fluorescence in-
tensity of MD1 with an increase in the concentration of quenchers (Hg2+
or Fe3+) may be due to the selective ion induced aggregation caused
quenching(ACQ). We believe that these cations help to form aggregates
6

P. Bhaumick et al.
Polymer 218 (2021) 123415
purifications. Benzene-1,4-diboronic acid, 9,9-Dioctylfluorene-2,7-
diboronic acid, phloroglucinol, ethyl acetoacetate and palladium ace-
tate were purchased from Sigma-Aldrich. Ethylbenzoyl acetate, tri-
fluoromethane sulfonic anhydride and potassium tert-butoxide were
purchased from TCI chemicals. Chloroform-d and DMSO‑d6 were pur-
chased from Sigma-Aldrich. The monomers were prepared using re-
ported methods. The progress of the reactions was monitored by TLC.
The purification of premonomers and monomers as well as the products
of the model reactions were done by silica gel column chromatography
using ethyl acetate/hexane (in different ratios) solvent system as mobile
phase.
3.2. Instrumentation
FTIR spectra were recorded by ATR mode with the absorption in cmꢀ 1
.
NMR spectra of all compounds were recorded in a Bruker 400 MHz in-
strument. 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were
recorded in either in DMSO‑d6 or CDCl3 as solvent. To define the multi-
plicities: s = singlet; d = doublet; t = triplet; m = multiplet; dd (doublet of
doublets); td (triplet of doublets); bs (broad singlet), coupling constants (J,
in Hz) has been used as abbreviations. Solid-state 13C cross-polarization
magic angle spinning (CP-MAS) NMR spectra were recorded at a spin-
ning rate of 8 kHz and CP contact time of 2 ms with a delay time of 2s.
BRUKER Impact HD mass spectrometer (Impact HD UHR-TOF, ESI with
positive mode) was used for the HRMS data. Melting points were recorded
using an SRS EZ-Melt automated melting point apparatus by capillary
methods without correction. The average molecular weights and poly-
dispersity of polymers (sample concentration:1 mg/mL in DMF) were
determined using Agilent PL-GPC 50 integrated GPC instrument using
DMF as eluent and the molecular weight of polymer sample were calcu-
lated using standard calibration curve based on polystyrene standards at a
flow rate of 1.0 mL/min. Thermal stability (TGA) analysis was performed
using SDTQ600 (TA Instruments) at a scan rate 10 ◦C/min under nitrogen
flow (100 mL/min). Absorption measurements were done by using
Shimadzu-UV2550 spectrophotometer using 1 cm path-length quartz cu-
vettes. Fluorescence emission spectra were measured using Fluoromax-4P
spectrofluorometer (Horiba Jobin Yvon). The fluorescence lifetime was
measured using picosecond time-correlated single photon counting
(TCSPC) technique by a time-resolved fluorescence spectrophotometer
(LifeSpec-II, Edinburgh Instruments, UK).
Fig. 10. Fluorescence spectra of P3 (2.5 μg/mL) in the presence of different
0.1 mM Hg (II) salt solutions.
in the presence of quenchers Hg and Fe ions is due to the ion induced
aggregation caused quenching.
Solubility of polymers at room temperature: The solubility of our
synthesized coumarin containing polymers were checked in various
solvents and their results are summarized below: Copolymers P1 and P2,
where coumarin is connected with phenyl linker are not soluble in most
of the organic solvents except polar aprotic solvents such as DMF, DMSO
and THF. Both P1 and P2 were found sparingly soluble in acetonitrile
and 1,4-dioxane. However, other two polymers P3 and P4 having
dioctyl fluorene (having hydrophobic chain) as one of the monomer
showed better solubility and was found soluble in most of the organic
solvents as shown in Table 5.
3. Experimental section
3.1. Materials and methods
All starting materials, solvents, and the catalyst were purchased from
commercial suppliers and were used as such without further
Fig. 11. (a). Fluorescence spectra of P3 (1.0
μ
g/mL) in DMF measured with increasing concentration of Fe3+ ion, (b). The plot of (F0–F)/F0 vs Fe3+concentration.
Inset: The linear range of the plot with Fe3+ concentration over the range of 3–13
μg/mL.
7

P. Bhaumick et al.
Polymer 218 (2021) 123415
Fig. 12. (a). Fluorescence spectra of P3 (1
μ
g/mL) in DMF measured with increasing concentration of Fe2+ ion. (b) The plot of (F0–F)/F0 vs Fe2+ concentration. Inset:
The linear range of the plot with Fe2+ concentration over the range of 1–11
μg/mL.
Fig. 13. (a). Fluorescence spectra of P3 (1
μ
g/mL) in DMF medium measured with increasing concentration of Hg2+ ion. (b) The plot of (F0–F)/F0 vs Hg2+ con-
centration. Inset: The linear range of the plot with Hg2+ concentration over the range of 1–19
μg/mL.
4. Synthesis of premonomers (PM-1,PM-2)
5,7-dihydroxy-4-phenyl-2H-chromen-2-one (PM-2). Same pro-
cedure of PM-1was followed for the synthesis of PM-2 and the product
was purified by column chromatography. Yield 75%; brick red solid; mp
242–245 ◦C. IR (ATR) 3305, 3184, 1665, 1610, 1587, 1550, 1367, 1234,
1139, 1059, 945, 823, 696, 560 cmꢀ 1. 1H NMR (400 MHz, DMSO‑d6) δ
10.44 (bs, 1H, OH), 10.17 (bs, 1H, OH), 7.37–7.32 (m, 5H, Ar), 6.27 (d,
5,7-dihydroxy-4-methyl-2H-chromen-2-one (PM-1). In a 50 mL
round bottom flask 10.0 mmol of phloroglucinol, 10.0 mmol of ethyl
acetoacetate and 100 mg of iodine were stirred at 80 ◦C. The reaction
was monitored by TLC, after the completion of the reaction, the reaction
mixture was cooled and poured into ice and iodine was neutralised by
using 20.0 mL 10% sodium thiosulphate solution. The light yellow
precipitate was filtered and washed with water for several times and
allowed to dry. The air dried product was further dried under vacuum
and purified by recrystallization in hot ethanol.
J = 2.0 Hz, 1H, Ar), 6.16 (d, J = 2.0 Hz, 1H, Ar), 5.74 (s, 1H, Ar) ppm.13
C
NMR (100 MHz, DMSO‑d6) δ 161.8, 160.0, 157.2, 156.8, 156.1, 139.6,
127.9, 127.5, 127.4, 110.2, 100.7, 99.2, 94.7 ppm. HRMS (ESI-TOF): m/
z [M + H]+ calcd for C15H11O4 255.0652; found 255.0663.
Yield 92%; white solid; mp 260–264 ◦C. IR (ATR) 3421, 3112, 1662,
1616, 1547, 1509, 1376, 1359, 1298, 1234, 1156, 1075, 823, 754, 638
cmꢀ 1. 1H NMR (400 MHz, DMSO‑d6) δ 10.52 (s, 1H, OH), 10.29 (s, 1H,
OH), 6.25 (d, J = 4.0 Hz, 1H, Ar), 6.16 (d, J = 4.0 Hz, 1H, Ar), 5.84 (d, J
= 2.0 Hz, 1H, Ar), 2.48 (s, 3H, CH3) ppm.13C NMR (100 MHz, DMSO‑d6)
δ 161.1, 160.1, 158.0, 156.5, 155.0, 108.9, 102.1, 99.1, 94.5, 23.5 ppm.
HRMS (ESI-TOF): m/z [M + H]+ calcd for C10H9O4 193.0495; found
193.0504.
5. Synthesis of monomers (M-1 and M-2)
Trifluoro-methanesulfonic acid 4-methyl-2-oxo-6-trifluorome-
thanesulfonyloxy-2H-chromen-8-yl ester (M-1). 5.0 mmol of PM-1
was taken in a 50.0 mL two necked round bottom flask equipped with
a magnetic stir bar and flashed with nitrogen gas three times then 20.0
mL dichloromethane and 20.0 mmol of pyridine were injected and the
reaction mixture was placed on an ice bath with the constant stirring for
8

P. Bhaumick et al.
Polymer 218 (2021) 123415
Fig. 14a. Linear fitting of the plot F0/F vs Fe3+ concentration for calculating
Fig. 15a. The time-resolved fluorescence emission spectra of polymer P3 (1
μ
g/mL) in the absence and in presence of Hg2+ (150
μМ) in DMF. The red line
Stern-Volmer constant KSV
.
plot (IRF) shows the instrument response function. (For interpretation of the
references to colour in this figure legend, the reader is referred to the Web
version of this article.)
Fig. 14b. Linear fitting of the plot F0/F vs Fe2+ concentration for calculating
Stern-Volmer constant KSV
.
Fig. 15b. The time-resolved fluorescence emission spectra of polymer P3(1
μ
g/
mL) in the absence and in presence of Fe3+ (150
μМ) in DMF. The red line plot
(IRF) shows the instrument response function. (For interpretation of the refer-
ences to colour in this figure legend, the reader is referred to the Web version of
this article.)
Table 4
Fluorescence life time data.
Sample Name
τ1 (ns)
τ2 (ns)
a1
a2
(
τ
)
χ2
(nsa)verage
P3
0.45
0.46
0.47
1.24
1.20
1.22
0.48
0.48
0.52
0.52
0.52
0.48
0.86
0.84
0.83
0.99
1.04
1.03
P3þHg2þ
P3þFe3þ
15 min to keep the temperature bellow
5
◦C. Next, tri-
fluoromethanesulfonic anhydride (15.0 mmol) was added drop wise by
syringe. After the addition, the reaction was kept stirring at room tem-
perature for 2 h. After the completion of the reaction, the reaction
mixture was poured into 20.0 mL water and extracted by adding 2x 20
mL dichloromethane. The organic layer was collected using a separating
funnel and washed three times with water and 10% HCl solution. The
Fig. 14c. Linear fitting of the plot F0/F vs Hg2+ concentration for calculating
Stern-Volmer constant KSV
.
9

P. Bhaumick et al.
Polymer 218 (2021) 123415
Fig. 16. (a) Fluorescence spectra of model compound MD1 (2.5
μ
g/mL) in DMF in the presence of Hg(II) solutions at different concentrations (left). (b) Fluorescence
spectra of model compound MD1(2.5 μg/mL) in DMF in the presence of Fe(III) solutions at different concentrations (right).
Table 5
Solubility of the polymers P1–P4 (mg/mL) in different solvents.
Polymer
CHCl3
DCM
DMF
THF
DMSO
WATER
Methanol
ACN
1,4-Dioxane
P1
P2
P3
P4
X
X
430
400
840
770
160
161
460
410
200
190
50
X
X
X
X
X
X
X
X
12
10
45
41
35
X
X
30
170
165
190
180
480
360
43
X = insoluble.
combined organic extracts were dried over anhydrous Na2SO4. The
solvent was removed by rotavapor and the crude product was finally
purified by column chromatography. After purification, a white crys-
talline compound was obtained.
water. The tube was sealed properly and the reaction was continued for
◦
24 h at 120 C. After completion of the reaction, 30.0 mL water was
added to the reaction mixture and extracted with ethylacetate 3 x 20.0
mL. The combined organic layer was collected and dried over sodium
sulphate and filtered. Finally, the solvent was removed using rotavapour
and the crude product was purified by column chromatography using a
mixture of ethyl acetate and hexane.
Yield 75%; white solid; mp 126–130 ◦C. IR (ATR) 1726, 1613, 1431,
1200, 1127, 1055, 991, 835, 795, 757, 728, 705, 659, cmꢀ 1. 1H NMR
(400 MHz, DMSO‑d6) 8.01 (d, J = 2.0 Hz, 1H, Ar), 7.70 (d, J = 4.0 Hz,
1H, Ar), 6.66 (s, 1H, Ar), 2.56 (s, 3H, CH3) ppm.13C NMR (100 MHz,
DMSO‑d6) δ 157.6, 154.9, 149.0, 148.9, 145.2, 126.6, 119.0, 114.6,
112.1, 111.9, 21.9 ppm. 19F NMR (376 MHz, DMSO‑d6) δ ꢀ 72.28,
ꢀ 72.50 ppm. HRMS (ESI-TOF): m/z [M + H]+ calcd for C12H7F6O8S2
456.9481; found 456.9507.
4-methyl-5,7-diphenyl-2H-chromen-2-one (MD-1). Yield 58%;
white solid; mp 126–128 ◦C. IR (ATR) 3060, 2928, 2852, 1733, 1208,
1601, 1503, 1427, 1355, 1222, 1140, 1001, 964, 856, 825, 699 cmꢀ 1. 1H
NMR (400 MHz, CDCl3) δ 7.66–7.61 (m, 3H, Ar), 7.48–7.41 (m, 6H, Ar),
7.39–7.36 (m, 3H, Ar), 6.19 (s, 1H, Ar), 1.79 (s, 3H, CH3) ppm.13C NMR
(100 MHz, CDCl3) δ 155.3, 154.2, 143.4, 142.4, 142.3, 138.9, 129.6,
129.4, 129.0, 128.44, 128.37, 127.5, 126.8, 120.8, 117.7, 115.1, 24.4
ppm. HRMS (ESI-TOF): m/z [M + H]+ calcd for C22H16O2 313.1223;
found 313.1229.
Trifluoro-methanesulfonic acid 2-oxo-4-phenyl-8-trifluorome-
thanesulfonyloxy-2H-chromen-6-yl ester(M-2). Same procedure as
mentioned for M-1 was followed for M-2. Yield 70%; white solid; mp
92–96 ◦C. IR (ATR) 1741, 1610, 1428, 1353, 1208, 1130, 1110, 1041,
997, 887, 818, 705, 586 cmꢀ 1. 1H NMR (400 MHz, DMSO‑d6) δ 8.13 (d,
J = 2.0 Hz, 1H, Ar), 7.84 (d, J = 2.0 Hz, 1H, Ar), 7.51–7.48 (m, 5H, Ar),
6.61 (s, 1H, Ar) ppm.13C NMR (100 MHz, DMSO‑d6) δ 157.5, 155.2,
150.6, 149.3, 144.8, 135.3, 129.9, 128.3, 120.2, 119.8, 119.3, 113.8,
113.3, 112.2 ppm. 19F NMR (376 MHz, DMSO‑d6) δ ꢀ 72.09, ꢀ 72.32
ppm. HRMS (ESI-TOF): m/z [M + H]+ calcd for C17H9F6O8S2 518.9638;
found 518.9666.
7. Procedure for the synthesis of polymers (P1, P2, P3 and P4)
Monomer M-1/M-2 (0.5 mmol) was taken in a 10.0 mL sealed tube
equipped with a magnetic stirrer and 3.0 mL of 1,4-dioxane. The solu-
◦
tion was then heated to 65 C and palladium acetate (10 mol%) and
triphenylphosphine (20 mol%) were added. After 10 min, 0.5 mmol of
benzene-1,4-diboronic/9,9-dioctylfluorene-2,7-diboronic acid and 1.5
mmol of K2CO3 was added to the reaction mixture followed by four
drops of water. The tube was sealed properly and the reaction was kept
at 120 ◦C under constant stirring for 72 h. After 72 h, methanol was used
for the precipitation of the polymer. All the polymers were characterized
by recording 1H and 13C NMR as well as GPC (1H and 13C NMR of all
these polymers as well as GPC data are given in supporting
information.).
6. Procedure for the synthesis of model compound (MD-1)
Monomer M-1 (0.5 mmol) was transferred to a 10.0 mL sealed tube
equipped with a magnetic stirrer and 2.0 mL of 1,4-dioxane. To this
solution palladium acetate (10 mol%) and triphenylphosphine (20 mol
%) were added. The reaction mixture was kept at 65 ◦C under stirring
conditions. After 10 min, 1.0 mmol of phenylboronic acid and 1.5 mmol
of K2CO3 was added to the reaction mixture followed by four drops of
P1: IR (ATR) 3417, 3033, 2981, 2932, 2342, 2097, 1701, 1600,
10

P. Bhaumick et al.
Polymer 218 (2021) 123415
(b) K. Li, B. Liu, Polymer encapsulated conjugated polymernanoparticles for fluo
rescence bioimaging, J. Mater. Chem. 22 (2012) 1257–1264;
(c) S. Kim, C.-K. Lim, J. Na, Y.-D. Lee, K. Kim, K. Choi, J.F. Leary, I.C. Kwon,
Conjugated polymernanoparticles for biomedical in vivo imaging, Chem. Commun.
46 (2010) 1617–1619.
1438, 1389, 1352, 1297, 1236, 1190, 1138, 1083, 1029, 965, 936, 829
cmꢀ 1. 1H NMR (400 MHz, DMSO‑d6) δ 7.93 (bs), 7.83 (bs), 7.51(bs),
6.32 (bs), 1.77 (bs) ppm.13C NMR (solid state) δ 159.8, 154.6, 140.9,
127.2, 116.4, 23.7 ppm.
[5] (a) P.M. Beaujuge, J.R. Reynolds, Color control in π-conjugated organic polymers
P2: IR (ATR) 3059, 3027, 2926, 2325, 1716, 1603, 1444, 1389,
1352, 1257, 1190, 1121, 1078, 1034, 976, 869, 829, 757, 696, 642
cmꢀ 1. 1 H NMR (400 MHz, DMSO‑d6) δ 8.04–7.83 (m), 7.68–7.55 (m),
7.47–7.41 (m), 7.28 (bs), 7.08(bs), 7.04(bs), 6.99 (bs) ppm.13C NMR
(solid state) δ 156.3, 140.3, 127.7, 114.9 ppm.
for use in electrochromic devices, Chem. Rev. 110 (2010) 268–320;
(b) M. Hui Chua, Q. Zhu, T. Tang, K.W. Shah, J. Xu, Diversity of electron acceptor
groups in donor–acceptor type electrochromic conjugated polymers, Sol. Energy
Mater. Sol. Cells 197 (2019) 32–75.
[6] G. Zhang, Z.-A. Lan, X. Wang, Conjugated polymers: catalysts for photocatalytic
hydrogen evolution, Angew. Chem. Int. Ed. 55 (2016) 15712–15727.
[7] D.T. McQuade, A.E. Pullen, T.M. Swager, Conjugated polymer-based chemical
sensors, Chem. Rev. 100 (2000) 2537–2574.
P3: IR (ATR) 2923, 2851, 1701, 1603, 1459, 1404, 1375, 1352,
1260, 1179, 1121, 1078, 1003, 818, 737, 722, 693 cmꢀ 1. 1H NMR (400
MHz, CDCl3) δ 7.81 (bs), 7.65 (bs), 7.55–7.48 (m), 7.34 (bs), 2.05, 1.09,
0.80 ppm.13C NMR (solid state) δ 151.6, 140.8, 127.1, 120.0, 55.5, 40.7,
29.9, 23.0, 14.2 ppm.
[8] (a) C. Kim, Y.J. Gwon, J. Kim, T.S. Lee, Synthesis of fluorescent conjugated
polymer nanoparticles and their immobilization on a substrate for white light
emission, Polym. Chem. 9 (2018) 5671–5679;
(b) K. Lee, L.K. Povlich, J. Kim, Recent advances in fluorescent and colorimetric
conjugated polymer-based biosensors, Analyst 135 (2010) 2179–2189;
(c) M. Xu, T. Wang, P. Gao, L. Zhao, L. Zhou, D. Hua, Highly fluorescent
conjugated microporous polymers for concurrent adsorption and detection of
uranium, J. Mater. Chem. A 7 (2019) 11214–11222;
P4: IR (ATR) 3515, 3062, 3012, 2926, 2854, 1701, 1609, 1493,
1462, 1438, 1409, 1306, 1213, 1167, 1118, 1046, 999, 910, 817, 751,
722, 693, 667, 549 cmꢀ 1. 1H NMR (400 MHz, CDCl3) δ 7.78 (bs),
7.68–7.60 (m), 7.50–7.43(m), 2.08, 1.10, 0.80 ppm.13C NMR (100 MHz,
CDCl3) δ 155.8, 145.7, 132.4, 132.3, 132.1, 130.0, 129.4, 128.9, 128.7,
128.2, 127.6, 127.3, 126.3, 121.6, 55.6, 40.5, 31.9, 30.1, 29.3, 24.0,
22.7, 14.2 ppm.
(d) T.M. Swager, The molecular wire approach to sensory signal amplification,
Acc. Chem. Res. 31 (1998) 201–207.
[9] H.N. Kim, Z. Guo, W. Zhu, J. Yoon, H. Tian, Recent progress on polymer-based
fluorescent and colorimetric chemosensors, Chem. Soc. Rev. 40 (2011) 79–93.
[10] (a) S. Lightowler, M. Hird, Palladium-catalyzed cross-coupling reactions in the
synthesis of novel aromatic polymers, Chem. Mater. 16 (2004) 3963–3971;
(b) Z. Bao, W. Chan, L. Yu, Synthesis of conjugated polymer by the stille coupling
reaction, Chem. Mater. 5 (1993) 2–3;
8. Conclusion
(c) T. Yamamoto, Cross-coupling reactions for preparation of π-conjugated
polymers, J. Organomet. Chem. 653 (2002) 195–199.
In summary, we have reported synthesis of four novel coumarin
containing conjugated polymers by using palladium catalyzed poly
coupling reaction of coumarin ditriflate and diboronic acids. These
novel polymers showed good thermal stability. The photophysical
properties of these conjugated polymers were studied by UV–Vis and
fluorescence spectroscopy. Polymer P-3 was found selective chemo-
sensor for the detection of iron (II and III) and mercury (II) ions dis-
solved in water medium both by colorimetric and fluorometric analysis.
[11] Y. Zhang, P. Shen, B. He, W. Luo, Z. Zhao, B.Z. Tang, New fluorescent through-
space conjugated polymers: synthesis, optical properties and explosive detection,
Polym. Chem. 9 (2018) 558–564.
[12] D. Muenmart, A.B. Foster, A. Harvey, M.-T. Chen, O. Navarro, V. Promarak, M.
C. McCairn, J.M. Behrendt, M.L. Turner, Conjugated polymer nanoparticles by
Suzuki–Miyaura cross-coupling reactions in an emulsion at room temperature,
Macromolecules 47 (2014) 6531–6539.
´
[13] V. Dzhabarov, D. Výprachtický, V. Cimrova, Microwave-assisted and conventional
synthesis, photophysics and electroluminescence of poly(9,9-dihexadecylfluorene-
2,7-diyl-alt-2,2′-bithiophene-5,5′-diyl), Eur. Polym. J. 98 (2018) 420–429.
[14] D. Ye, L. Wang, H. Li, J. Zhou, D. Cao, Synthesis of coumarin-containing
conjugated polymer for naked-eye detection of DNA and cellular imaging, Sensor.
Actuator. 181 (2013) 234–243.
Declaration of competing interest
[15] K.P. Carter, A.M. Young, A.E. Palmer, Fluorescent sensors for measuring metal ions
in living systems, Chem. Rev. 114 (2014) 4564–4601;
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
(b) W.-W. Zhao, J.-J. Xua, H.-Y. Chena, Photoelectrochemical detection of metal
ions, Analyst 141 (2016) 4262–4271.
[16] (a) M. Likun, L. Xingfen, F. Quli, H. Wei, Detection of metal ions based on
conjugated fluorescent polymers, Prog. Chem. 22 (2010) 2338–2352;
(b) M. Kimura, T. Horai, K. Hanabusa, H. Shirai, Fluorescence chemosensor for
metal ions using conjugated polymers, Adv. Mater. 10 (1998) 459–462;
(c) X. Lou, Y. Zhang, S. Li, D. Ou, Z. Wan, J. Qin, Z. Li, A new polyfluorene bearing
pyridine moieties: a sensitive fluorescent chemosensor for metal ions and cyanide,
Polym. Chem. 3 (2012) 1446–1452;
Acknowledgement
We are thankful to SERB DST for the financial assistance with
sanction no (EMR/2016/003706) for this work. P. B is grateful to SERB
DST for his fellowship. The authors are also thankful to IIT Patna for
providing general research facilities for conducting this work.
(d) D. Yang, C. Dai, Y. Hu, S. Liu, L. Weng, Z. Luo, Y. Cheng, L. Wang, A new
polymer-based fluorescent chemosensor incorporating propane-1,3-Dione and 2,5-
diethynylbenzene moieties for detection of copper(II) and iron(III), Polymers 9
(2017) 267.
[17] M. Lu, Y. Deng, Y. Luo, J. Lv, T. Li, J.X.S.-W. Chen, J. Wang, Graphene
aerogel–metal–organic framework-based electrochemical method for simultaneous
detection of multiple heavy-metal ions, Anal. Chem. 91 (2019) 888–895.
[18] (a) S. Yoon, E.W. Miller, Q. He, P.H. Do, C.J. Chang, A bright and specific
fluorescent sensor for mercury in water, cells, and tissue, Angew. Chem. Int. Ed. 46
(2007) 6658–6661;
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.polymer.2021.123415.
(b) X. Liu, Y. Tang, L. Wang, J. Zhang, S. Song, C. Fan, S. Wang, Optical detection
of mercury(II) in aqueous solutions by using conjugated polymers and label-free
oligonucleotides, Adv. Mater. 19 (2007) 1471–1474;
References
(c) R. Eid, N.T.T. Arab, M.T. Greenwood, Iron mediated toxicity and programmed
cell death: a review and a re-examination of existing paradigms, Biochim. Biophys.
Acta 1864 (2017) 399–430.
[1] (a) S. Günes, H. Neugebauer, N.S. Sariciftci, Conjugated polymer-based organic
solar cells, Chem. Rev. 107 (2007) 1324–1338;
(b) Y.-J. Cheng, S.-H. Yang, C.-S. Hsu, Synthesis of conjugated polymers for
organic solar cell applications, Chem. Rev. 109 (2009) 5868–5923;
[19] D. Wu, A.C. Sedgwick, T. Gunnlaugsson, E.U. Akkaya, J. Yoon, T.D. James,
Fluorescent chemosensors: the past, present and future, Chem. Soc. Rev. 46 (2017)
7105–7123.
(c) A. Facchetti, π-conjugated polymers for organic electronics and photovoltaic
cell applications, Chem. Mater. 23 (2011) 3733–3758;
[20] (a) G.T. Selvan, C. Varadaraju, R.T. Selvan, I.V.M.V. Enoch, P.M. Selvakumar, On/
off fluorescent chemosensor for selective detection of divalent iron and copper
ions: molecular logic operation and protein binding, ACS Omega 3 (2018)
7985–7992;
(d) J.-T. Chen, C.-S. Hsu, Conjugated polymer nanostructures for organic solar cell
applications, Polym. Chem. 2 (2011) 2707–2722.
[2] (a) A.C. Grimsdale, K.L. Chan, R.E. Martin, P.G. Jokisz, A.B. Holmes, Synthesis of
light-emitting conjugated polymers for applications in electroluminescent devices,
Chem. Rev. 109 (2009) 897–1091;
(b) S. Sen, S. Sarkar, B. Chattopadhyay, A. Moirangthem, A. Basu, K. Dharad,
P. Chattopadhyay, A ratiometric fluorescent chemosensor for iron: discrimin ation
of Fe2+ and Fe3+ and living cell application,, Analyst 137 (2012) 3335–3342;
(c) L.-J. Fan, W.E. Jones, A highly selective and sensitive inorganic/organic hybrid
polymer fluorescence “Turn-on” chemosensory system for iron cations, J. Am.
Chem. Soc. 128 (2006) 6784–6785;
(b) L. Dai, B. Winkler, L. Dong, L. Tong, A.W.H. Mau, Conjugated polymers for
light-emitting applications, Adv. Mater. 13 (2001) 915–925.
´
[3] A.R. Murphy, J.M.J. Frechet, Organic semiconducting oligomers for use in thin film
transistors, Chem. Rev. 107 (2007) 1066–1096.
[4] (a) C. Zhu, L. Liu, Q. Yang, F. Lv, S. Wang, Water-soluble conjugated polymers for
imaging, diagnosis, and therapy, Chem. Rev. 112 (2012) 4687–4735;
(d) J.H. Kang, C. Kim, Colorimetric detection of iron and fluorescence detection of
11

P. Bhaumick et al.
Polymer 218 (2021) 123415
zinc and cadmium by a chemosensor containing a bio-friendly octopamine,
(d) M.N. Khan, S. Pal, T. Parvin, L.H. Choudhury, A simple and efficient method
for the facile access of highly functionalized pyridines and their fluorescence
property studies, RSC Adv. 2 (2012) 12305–12314.
Photochem. Photobiol. Sci. 17 (2018) 442–452;
(e) C. Luo, Y. Liu, Q. Zhang, X. Cai, Hyperbranched conjugated polymers contain
-ing 1,3-butadiene units: metal-free catalyzed synthesis and selective chemosensors
for Fe3+ ions, RSC Adv. 7 (2017) 12269–12276;
[23] (a) S.R. Trenor, A.R. Shultz, B.J. Love, T.E. Long, Coumarins in polymers: from
light harvesting to photo-cross-linkable tissue scaffolds, Chem. Rev. 104 (2004)
3059–3078;
(f) H. Nawaz, W. Tian, J. Zhang, R. Jia, Z. Chen, J. Zhang, Cellulose-based sensor
containing phenanthroline for the highly selective and rapid detection of Fe2+ ions
with naked eye and fluorescent dual modes, ACS Appl. Mater. Interfaces 10 (2018)
2114–2121.
´
(b) D. Gindre, K. Iliopoulos, O. Krupka, M. Evrard, E. Champigny, M. Salle,
Coumarin-containing polymers for high density non-linear optical data storage,
Molecules 21 (2016) 147;
[21] (a) D. Giri, A. Bankura, S.K. Patra, Poly(benzodithieno-imidazole-alt-carbazole)
(c) J. He, Y. Zhao, Y. Zhao, Photoinduced bending of a coumarin-containing
supramolecular polymer, Soft Matter 5 (2009) 308–310.
based π-conjugated copolymers: highly selective and sensitive turn-off fluorescent
probes for Hg2+, Polymer 158 (2018) 338–353;
[24] D. Prajapati, R.C. Boruah, M. Gohain, An Improved Process for the Production of
Substituted 4-Methyl Coumarin, 2012. Indian Patent 250805, Feb. 3.
[25] N. Eleya, Z. Khaddour, T. Patonay, P. Langer, Efficient synthesis of arylated
coumarins by site-selective Suzuki–Miyaura cross-coupling reactions of the bis
(triflate) of 4-methyl-5,7-dihydroxycoumarin, Synlett 23 (2012) 223–226.
[26] H.L. Ricks, U.H. Choudry, A.R. Marshall, U.H.F. Bunz, Rod vs Coil: molecular
weight comparison of a poly(dialkyl-p-phenyleneethynylene) with its reduced poly
(2,5-dialkyl-p-xylylene), Macromolecules 36 (2003) 1424–1425.
(b) Y. Si, X. Wang, Y. Li, K. Chen, J. Wang, J. Yu, H. Wang, B. Ding, Optimized
colorimetric sensor strip for mercury(II) assay using hierarchical nostructured
conjugated polymers, J. Mater. Chem. A 2 (2014) 645–652;
(c) J. Ding, H. Li, Y. Xie, Q. Peng, Q. Li, Z. Li, Reaction-based conjugated polymer
fluorescent probe for mercury(II): good sensing performance with “turn-on” signal
output, Polym. Chem. 8 (2017) 2221–2226.
[22] (a) A. Mahata, P. Bhaumick, A.K. Panday, R. Yadav, T. Parvin, L.H. Choudhury,
Multicomponent synthesis of diphenyl 1,3-thiazole-barbituric acid hybrids and
their fluorescence property studies, New J. Chem. (2020), https://doi.org/
10.1039/D0NJ00406E;
[27] S.W. Thomas, G.D. Joly, T.M. Swager, Chemical sensors based on amplifying
fluorescent conjugated polymers, Chem. Rev. 107 (2007) 1339–1386.
[28] B. Liu, Y. Bao, H. Wang, F. Du, J. Tian, Q. Li, T. Wang, R. Bai, An efficient
conjugated polymer sensor based on the aggregation-induced fluorescence
quenching mechanism for the specific detection of palladium and platinum ions,
J. Mater. Chem. 22 (2012) 3555–3561.
(b) M.N. Khan, S. Pal, S. Karamthulla, L.H. Choudhury, Multicomponent reactions
for facile access to coumarin-fused dihydroquinolines and quinolines: synthesis and
photophysical studies, New J. Chem. 38 (2014) 4722–4729;
(c) R. Dwivedi, D.P. Singh, B.S. Chauhan, S. Srikrishna, A.K. Panday, L. H
Choudhury, V.P. Singh, Intracellular application and logic gate behavior of a ‘turn
off-on-off’ type probe for selective detection of Al3+ and Fꢀ ions in pure aqueous
medium, Sensor. Actuator. 258 (2018) 881–894;
[29] J. Yang, D. Wu, D. Xie, F. Feng, K.S. Schanze, Ion-induced aggregation of
conjugated polyelectrolytes studied by fluorescence correlation spectroscopy,
J. Phys. Chem. B 117 (2013) 16314–16324.
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