Crosslinked fluorescent conjugated polymer nanoparticles for high performance explosive sensing in aqueous media

Article abstract of DOI:10.1016/j.dyepig.2018.06.018

In this work, water dispersible crosslinked fluorescent poly(triphenylamine-co-benzothiadiazole)s (PTPABT) nanoparticles have been synthesized via Suzuki-type coupling (A₃ + B₂) in a toluene/water miniemulsion. Dialysis method was us

Full text of DOI:10.1016/j.dyepig.2018.06.018

Accepted Manuscript
Crosslinked fluorescent conjugated polymer nanoparticles for high performance
explosive sensing in aqueous media
Wenyue Dong, Zhihua Ma, Qian Duan, Teng Fei
PII:
S0143-7208(18)30877-5
10.1016/j.dyepig.2018.06.018
DYPI 6823
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 19 April 2018
Revised Date: 29 May 2018
Accepted Date: 11 June 2018
Please cite this article as: Dong W, Ma Z, Duan Q, Fei T, Crosslinked fluorescent conjugated polymer
nanoparticles for high performance explosive sensing in aqueous media, Dyes and Pigments (2018),
doi: 10.1016/j.dyepig.2018.06.018.
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ACCEPTED MANUSCRIPT
Crosslinked fluorescent conjugated polymer nanoparticles for high performance explosive
sensing in aqueous media
Wenyue Donga, Zhihua Maa, Qian Duana,*, Teng Feib,*
a
School of Materials Science and Engineering, Changchun University of Science and
Technology, Changchun 130022, P.R. China
b
State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and
Engineering, Jilin University, Changchun 130012, P.R. China
*Corresponding author:
duanqian@cust.edu.cn (Q. Duan)
feiteng@jlu.edu.cn (T. Fei)
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Abstract
In this work, water dispersible crosslinked fluorescent poly(triphenylamine-co-benzothiadiazole)s
(PTPABT) nanoparticles have been synthesized via Suzuki-type coupling (A3 + B2) in a
toluene/water miniemulsion. Dialysis method was used to purify the PTPABT nanoparticles with
a diameter range of 40-70 nm. The good dispersion property of the polymer in water could be
attributed to the small sizes of the PTPABT nanoparticles. The obtained PTPABT nanoparticles
possess microporous characteristic and display bright red emission in aqueous solution, which
makes them possible to detect the nitro-aromatic explosive in aqueous media by monitoring the
photoluminescence. The sensing property of the polymer nanoparticles towards 1,3,5-
trinitrobenzene (TNB) in aqueous media has been researched, resulting a Stern-Volmer
quenching constant Ksv of 1.22×104 M-1. The most attractive character of the conjugated polymer
nanoparticles is the combination of both physical stability and solution-processability, thus
making them good candidates for sensors and optoelectronic applications.
Keywords Polymerization in miniemulsion; Crosslinked fluorescent polymer; Porous
nanoparticles; Explosive detection
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1. Introduction
The detection of nitro-aromatic explosives is of great importance for global security and
environmental protection in the past few decades [1,2]. It is well known that nitro-aromatic
explosives are not only dangerous component in landmines but also identified as pollutants in soil
or water, which may cause harmful damage to human nerves and visceral organs [3-5]. Therefore,
the realization of the detection of nitro-aromatic explosives in aqueous phase is very attractive
and important [6-10]. Different methods have been developed to detect nitro-aromatic explosives
in vapor or solution, such as gas chromatography [11], ion mobility spectrometry [12],
electrochemical method [13,14], field-effect transistor and photoluminescence (PL) sensing based
on various fluorescent materials (e.g. conjugated polymers) [15-21]. Among them, PL sensing
has drawn the most attention for its high sensitivity, stability and easy operation. Because of the
strong electron-accepting capacity of nitro-aromatic compounds, the excited states of fluorescent
materials could be affected when treating with nitro-aromatic molecules, thus leading to the PL
quenching [22,23]. In most cases, the fluorescent conjugated polymers with high PL quantum
yield (PLQY) possess low polarity, thus when detecting nitro-aromatic explosives in aqueous
media by monitoring the PL, conjugated materials have to face a serious dispersion issue. A lot of
efforts have been paid to solve this problem. For example, the occurrence of water soluble
conjugated polymeric materials with strong polar groups brought the possibility for aqueous
phase PL sensing [24,25]. The preparation of nanoparticles is another effective way, with
dispersing fluorescent materials in aqueous media, including small sized conjugated polymers
nanoparticles [26,27], carbon-based quantum dots or nanosheets [28,29]. Especially, aggregation
induced emission (AIE)-active polymer nanoparticles have been widely used to detect nitro-
aromatic explosives in mixed organic-aqueous solution or pure aqueous solution for their high
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PLQYs in the aggregated state [30-34]. In addition, polymer films with stable crosslinked
chemical structure could be used in aqueous media as well [35,36].
Conjugated microporous polymers (CMPs) are promising candidates for the applications in gas
desorption [37], heterogeneous catalysis [38], energy storage [39] etc., because of their large
specific surface area and multiple reactive sites for molecular recognition [40]. Especially, CMPs
exhibited a great potential in the field of fluorescence sensing, due to their good fluorescent
property and intrinsic porosity. However, the CMPs synthesized from conventional
polymerization methods are normally insoluble powders, which are difficult to process and even
more difficult to realize aqueous phase detection. In this work, a CMP poly(triphenylamine-co-
benzothiadiazole)s (PTPABT) nanoparticles with good dispersibility were prepared by Suzuki-
type coupling (A3 + B2) in a toluene/water miniemulsion, followed by dialysis purification to
obtain surfactant-free PTPABT nanoparticles. Unlike completely insoluble porous conjugated
polymer solids synthesized by conventional Suzuki coupling, the obtained PTPABT
nanoparticles with average sizes of 40-70 nm could be readily dispersed in both aqueous and
organic solvents. The sensing properties of the PTPABT nanoparticles towards 1,3,5-
trinitrobenzene (TNB) in pure aqueous media were researched.
2. Experimental
CAUTION! 1,3,5-Trinitrobenzene (TNB) is highly explosive and should be handled carefully
only in small amounts.
2.1 General information
The fourier transform infrared spectroscopy (FT-IR) of PTPABT was obtained on a WQF-
510A FT-IR spectrometer with KBr pellet as the reference. 1H NMR spectra were recorded on a
Bruker AVANCE 400 or AVANCEIII 600, with tetramethylsilane (TMS) as an internal standard.
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Atmospheric Pressure Laser Ionization (APLI) measurement was carried out on a Bruker
Daltronik Bremen with micrOTOF. Thermal gravimetric analysis (TGA) was undertaken on a
TGA/DSC1 STAR System (Mettler Toledo) at a heating rate of 10 °C/min and an argon (Ar)
flow rate of 50 mL/min. Nitrogen isotherms were obtained at 77 K on a Micromeritics Tri-star
o
3000 analyzer. Samples were pretreated by degassing for 12 h at 150 C. The morphology was
observed by field emission scanning electron microscopy (FE-SEM) on a JSM-6700F electron
microscope (JEOL, Japan). AFM measurement was performed using a dilnnova microscope from
Bruker in the tapping mode at room temperature under ambient conditions. An ALV/CGS-3 light
scattering spectrometer equipped with an ALV/LSE-7004 multiplet digital correlator was used in
the Dynamic Light Scattering (DLS) measurement. UV-visible absorption spectra were recorded
on a Jasco V-670 spectrometer, and PL spectra on a HORIBA Scientific FluroMax-4. The PLQY
of PTPABT dispersion was measured with an integrating sphere. The HOMO (highest occupied
molecular orbital) levels were estimated on a Surface Analyzer MODEL AC-2 on RIKEN, given
as the threshold where photoelectron emission first occurs.
2.2 Materials
All chemicals and reagents were used as received from commercial sources without further
purification. The water used throughout all experiments was purified through a Millipore system.
The used organic solvents were purified according to standard procedures.
2.2.1 Synthesis of PTPABT nanoparticles
2.2.1.1 Synthesis of tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amine
1.93 g (4.00 mmol) Of tris(4-bromophenyl)amine was dissolved in anhydrous tetrahydrofuran
o
(THF) (60 mL), the solution was degassed and stirred at -78 C. 4.86 mL (13.61 mmol) Of n-
butyllithium solution (n-BuLi, 2.8 M in hexane) was added to the above mixture under Ar
o
atmosphere and the resulting solution was stirred for 2 h at -78 C. 5.83 mL (28.58 mmol) Of 2-
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isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane was added to the solution and the mixture
was kept at -78 °C for another 1 hour and then stirred at room temperature for 48 h. The reaction
was quenched with water, and the organic layer was extracted with dichloromethane (DCM).
After dried over MgSO4, the solution was concentrated and the solvent mixture of DCM/hexane
(3:2) was used as eluent for silica gel column chromatography to isolate the product. The
obtained product was further purified by recrystallization from chloroform (CHCl3)/ethanol to
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give a white solid in 55% yield. H NMR (600 MHz, C2D2Cl4): δ (ppm) 1.30 (s, 36H), 7.03 (d,
6H), 7.64 (d, 6H). MS (APLI): m/z calcd 623.3778; found 623.3667.
2.2.1.2 Synthesis of PTPABT nanoparticles by Suzuki-type coupling in miniemulsion
187 mg (0.30 mmol) Of tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amine, 132
mg (0.45 mmol) of 4,7-dibromobenzo[c][1,2,5]thiadiazole and 10 mg (0.009 mmol) of
tetrakis(triphenylphosphine) palladium(0) (Pd(PPh3)4) were dissolved in toluene (20 mL). 248 mg
(1.80 mmol) Of K2CO3 and 200 mg (0.69 mmol) of sodium dodecyl sulfate (SDS) were dissolved
in water (2 mL) with stirring and sonification. The aqueous phase was then added to the organic
phase and the mixture was ultrasonicated for 2 min to prepare a stable miniemulsion. Afterwards,
the miniemulsion was heated at 85 oC under Ar atmosphere for 24 h. The obtained red dispersion
was stirred open to air for 1 day to evaporate toluene and then dialyzed in deionized water for 15
days to remove the surfactant and unreacted monomers using a semi-permeable dialysis
membrane with a cutoff of average Mn 3500 g/mol.
To obtain solid PTPABT for characterization, the orange dispersion after polymerization was
poured into a saturated NaCl aqueous solution, and CHCl3 and ethanol were added to the mixture.
The organic layer was separated and concentrated by rotary evaporation. The residue was
precipitated into methanol and finally the solid was collected by centrifugation. The yield is 85%.
2.2.2 Synthesis of PTPABT solid powder by conventional Suzuki coupling
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187 mg (0.30 mmol) Of tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amine, 132
mg (0.45 mmol) of 4,7-dibromobenzo[c][1,2,5]thiadiazole, 0.69 g (5 mmol) of K2CO3 and 16 mg
(0.014 mmol) of Pd(PPh3)4 were dissolved in toluene (7.5 mL) and water (2.5 mL). The mixture
o
was degassed and then heated at 95 C for 24 h. The precipitate was collected by filtration and
washed with water, methanol, acetone and DCM, respectively. Finally the obtained red solid was
washed by Soxhlet extractor with methanol, acetone, ethyl acetate and DCM for 1 day each,
respectively. The yield for PTPABT powder is 90%.
3. Results and discussion
3.1 Synthesis and characterizations
Herein, we prepared well-defined nanoparticles by Suzuki-type polymerization in
miniemulsion followed by dialysis treatment, as shown in Scheme 1. Tris(4-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)phenyl)amine was obtained by the treatment of tris(4-
bromophenyl)amine with an excess of n-BuLi followed by the addition of 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane. 4,7-Dibromobenzo[c][1,2,5]thiadiazole was synthesized
according to the reported procedures [41]. The Suzuki-type polymerization was controlled
between monomer A3, tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)amine, and
monomer B2, 4,7-dibromobenzo[c][1,2,5]thiadiazole in a water/toluene miniemulsion, with
Pd(PPh3)4 as the catalyst, K2CO3 as the base and SDS as the surfactant, respectively. The two
compounds (A3 and B2) were chosen as the monomers for the polymerization because of their
intrinsic crosslinking ability and good fluorescence nature as building blocks. After the reaction
o
at 85 C for 24 h, stable PTPABT nanoparticles dispersion could be obtained. Dialysis treatment
in deionized water was applied to purify the product and resulted in stable aqueous dispersion
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with uniform nanoparticles. It is worthy to note that the obtained nanoparticles could be dispersed
not only in water but also in common organic solvents, such as THF, DCM and CHCl3 etc.
Scheme 1. Synthesis route to nanoparticles composed of triphenylamine-based porous polymer
PTPABT.
The conventional Suzuki polymerization in toluene for PTPABT was also done with the same
monomers for comparison. In the miniemulsion polymerization, there were no solid precipitates
even after the reaction at 85 oC for 24 h. However, red precipitates were observed in ca. 3 h in the
conventional Suzuki polymerization, and more precipitates emerged with increasing
polymerization time. The reaction of the used monomers (A3 + B2) results in the polymer chains
with crosslinked structure, which would precipitate from the toluene solution when the
aggregates become big enough. The obtained crosslinked polymer powder could not be dissolved
or dispersed in common organic solvents, thus limiting the application in PL sensing as film or in
solution.
The structure of PTPABT was determined by FT-IR measurement. As shown in Fig. 1,
PTPABT nanoparticles and PTPABT powder show almost identical peaks, demonstrating the
similar chemical structures with different polymerization methods. The peaks at 1592, 1507 and
1474 cm-1 come from the C=C stretching of the phenyl rings, while the C-H stretching of the
phenyl rings occurs at 1264, 1184, 1087, 817, 654 and 585 cm-1. The peaks at 1352 and 1317
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cm-1 are attributed to the C-N vibration of aromatic tertiary amine. And the S-N vibration occurs
at 882 cm-1.
Fig. 1. The FT-IR spectra of PTPABT nanoparticles and PTPABT powder.
Further characterization of PTPABT nanoparticles was carried out by 1H NMR measurements.
1
The H NMR spectra of the two monomers and PTPABT in 1,1,2,2-tetrachloroethane-d2
(C2D2Cl4) were shown in Fig. 2. The two monomers show clear chemical structure with exact
1
1
assignments of hydrogen atoms from their H NMR spectra. As for the polymer, H NMR
spectrum is complicated compared with the monomers, because of the highly crosslinked
chemical structure. Importantly, it is necessary to note that there are no obvious signals of the
monomers in the spectrum of PTPABT, thus demonstrating the successful preparation of polymer
PTPABT nanoparticles.
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1
Fig. 2. The H NMR spectra of the two monomers and the polymer PTPABT nanoparticles in
C2D2Cl4.
3.2 Thermal property
In order to investigate the thermal stability property of the obtained polymer nanoparticles,
TGA of PTPABT nanoparticles was measured under Ar atmosphere. There was no obvious
decomposition before 250 oC and a 6% weight loss occurred at the temperature of 329 oC. These
data demonstrate the good thermal stability of the crosslinked PTPABT framework, which is
important for the practical application.
3.3 Porous structure
The surface areas were measured to confirm their porous structures. As shown in Fig. 3, N2
sorption isotherms were carried out at 77 K. The Brunauer-Emmett-Teller (BET) surface areas of
PTPABT nanoparticles and powder from N2 physisorption are 66 and 32 m2/g, respectively and
the pore volumes are 0.31 and 0.20 cm3/g, respectively. The pore size of PTPABT nanoparticles
was determined to be ca. 1.46 nm. These results demonstrate the CMP nanoparticles have been
obtained. The final surface areas are not high because of the structures of the monomers, however,
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the obvious increase of surface area of the PTPABT nanoparticles compared with the powder
from conventional polymerization demonstrates that it is beneficial to obtain porous structure via
the miniemulsion method, because much denser structures may be generated in the process of
crosslinking polymerization in the organic solvent.
Fig. 3. The nitrogen adsorption/desorption curves of PTPABT (a) nanoparticles and (b) powder
samples at 77 K. Inset shows the pore width distribution profile of PTPABT nanoparticles.
The morphology of PTPABT nanoparticles was assessed by SEM and AFM measurements.
The PTPABT dispersion was deposited on a silicon plate for SEM (Fig. 4a). The SEM image
demonstrates well-defined nanoparticles have been obtained. At the same time, a thin film was
obtained by spin-coating PTPABT dispersion on a quartz plate and used for AFM. The 3-
dimensional AFM image is shown in Fig. 4b, which indicates a 3-dimensional graph of the
nanoparticles covered surface over an area of 5 µm × 5 µm. The diameters of the obtained
nanoparticles range from 40 to 70 nm. Fig. 4c shows the DLS characterization of PTPABT
nanoparticles, and the average hydrodynamic radius (Rh) was measured as 42.2 nm.
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Fig. 4. (a) SEM image of PTPABT nanoparticles. (b) 3-Dimensional AFM image of PTPABT
nanoparticles spin-coated on a quartz plate. (c) The hydrodynamic radius distribution of PTPABT
aqueous dispersion.
3.4 Photophysical properties
The UV-visible absorption and PL spectra of PTPABT nanoparticles in aqueous solution are
shown in Fig. 5a. The maximum absorption peak locates at 323 nm and there is a broad
absorption band around 483 nm, which are corresponding to the TPA and BT structures,
respectively. The solution shows red emission peaking at 617 nm, due to the complete intra-
molecular energy transfer from TPA to BT. The UV-visible absorption and PL spectra of
PTPABT film are shown in Fig. 5b. The film shows similar absorption and PL emission with that
in aqueous solution, with a slight red shift in absorption and a broader PL spectrum, which can be
attributed to the aggregation of the nanoparticles in the solid state.
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Fig. 5. The normalized UV-visible absorption and PL spectra of PTPABT (a) in aqueous solution
(0.03 mg/mL, excitation wavelength for PL: 483 nm) and (b) as film (excitation wavelength for
PL: 483 nm).
PTPABT owns the intra-molecular charge transfer (ICT) characteristic because of its typical
donor-acceptor chemical structure, which is demonstrated by the obvious solvatochromism for
PTPABT nanoparticles as shown in Fig. 6. The emission gets red-shifted as the solvent
permittivity increases, with the maximum PL wavelength from 612 nm in toluene to 670 nm in
acetone, and the corresponding full width at half maximum also increases from 118 nm in toluene
to 179 nm in acetone.
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Fig. 6. The normalized PL spectra of PTPABT nanoparticles in different solvents (excitation
wavelength for PL: 483 nm).
3.5 Explosive detection based on PTPABT nanoparticles
For the good dispersion of the obtained fluorescent CMP nanoparticles in pure aqueous
solution, polymer PTPABT nanoparticles show a possible application for the detection of nitro-
aromatic explosives in aqueous media. The aqueous PTPABT dispersion was diluted to a
concentration of 0.03 mg/mL for carrying out the PL sensing towards TNB. The PL quantum
yield of the PTPABT nanoparticles aqueous solution was determined to be 0.55% with an
integrating sphere. Different amounts of TNB (0.05-2 µmol) were added into the PTPABT
aqueous solution (0.03 mg/mL, 2 mL), and the PL emissions were recorded with an excitation
wavelength of 480 nm, as shown in Fig. 7a. The emission intensity of the PTPABT aqueous
dispersion decreases progressively with the increasing content of TNB. The limit of detection
was calculated to be 1.9×
10-5 M [42]. It is noteworthy that as the content of TNB increases, the
PL spectra are blue-shifted from 617 nm (0 mol TNB) to 596 nm (1 µmol TNB) while the
intensity decreases. In contrast, pure THF was added into the solution and no blue-shift in the PL
spectra occurred. Therefore, the blue-shift in the sensing experiment may be attributed to the
interaction between PTPABT nanoparticles and TNB molecules.
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Fig. 7. (a) Evolution of emission spectra of PTPABT dispersion (0.03 mg/mL in 2 mL water)
with increasing amounts of TNB. The content of TNB from top to bottom is 0, 0.05, 0.1, 0.2, 0.3,
0.4, 0.5, 0.6, 0.8, 1.0 and 2.0 µmol, respectively. (b) Stern-Volmer plots of PL intensity (I0/I-1) of
PTPABT dispersion vs. TNB concentration of 0.025-0.45 mM.
The PL quenching of PTPABT dispersion towards TNB shows a linear response in the Stern-
Volmer plots in the range of 0.025-0.45 mM with a correlation coefficient R square of 0.9963. A
linear regression equation of (I0/I) − 1 = −0.30 + [1.22×104] CTNB is obtained (Fig. 7b). The
Stern-Volmer quenching constant Ksv is high among the PL sensing towards the explosives in
water [27,43-51]. The electron-rich TPA moities in polymer PTPABT and the porous spherical
structure of the polymer nanoparticles are beneficial for the interaction of PTPABT with TNB
explosive and the diffusion/transport of the TNB analyte inside the polymer nanoparticles, thus
leading to the high sensitivity in TNB detection.
Actually, few reports have focused on red-emissive materials for nitro-aromatic explosives
detection. Since the basic working principle for PL sensing towards nitro-aromatics is the charge
transfer from the LUMO of sensing materials to that of explosives, most of the sensing materials
own much higher LUMO than the explosives, and the corresponding band gaps usually result in
blue or green emission. For the sensing mechanism based on PTPABT dispersion, there is no
overlap between the absorption spectrum of TNB and the emission spectrum of PTPABT
aqueous dispersion (Fig. 8a), indicating the PL quenching is not attributed to Förster-type energy
transfer between PTPABT and TNB. On the other hand, the HOMO of PTPABT was estimated
to be ca. -5.4 eV (AC-2 method), and combining the optical band gap (2.2 eV) from the onset of
its UV-visible absorption, the LUMO of PTPABT is calculated to be ca. -3.2 eV, which is very
close to that of TNB (-3.1 eV). Since there is no big barrier between the LUMO of conjugated
polymer PTPABT and electron-deficient explosive TNB analyte, it is considered that the photo-
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induced electron transfer could easily happen between PTPABT and TNB (Fig. 8b), which would
hinder the radiative transition of PTPABT, thus resulting in an effective fluorescence quenching
[52-56].
Fig. 8. (a) Normalized absorption spectrum of TNB and PL spectrum of PTPABT aqueous
dispersion. (b) Schematic representation of the excited state electron-transfer process from
PTPABT to TNB.
To test the onsite detection of nitro-aromatic explosives based on PTPABT nanoparticles,
paper strips with the deposits of PTPABT were prepared by dipping the filter paper into the
PTPABT dispersion, followed by drying them in air. The original test paper and the papers after
dropping TNB solution with different concentrations under UV irradiation are shown in Fig. 9.
When a TNB solution (concentration: 0.001, 0.005, 0.01, 0.05, 0.1 and 0.2 mg/mL, respectively)
was dropped onto the test paper, the fluorescence of the PTPABT paper was quenched
progressively. Importantly, the quenching effect can be recognized when TNB concentration is as
low as 0.001 mg/mL, which shows the feasible detection of micromolar TNB concentrations. In
addition, the sensing behavior of PTPABT test paper towards TNB vapor was checked as well,
with the strip over TNB powder for 5 min. From Fig. 9, it can be seen that the fluorescence of
PTPABT was distinctly quenched. Therefore, the obtained PTPABT nanoparticles demonstrated
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a great potential for fabricating solid sensor and realizing onsite detection towards nitro-aromatic
explosives.
Fig. 9. Paper strips of PTPABT before and after dropping a TNB solution (0.001, 0.005, 0.01,
0.05, 0.1 and 0.2 mg/mL, respectively) and over TNB powder for 5 min.
4. Conclusions
Porous conjugated polymer PTPABT nanoparticles with stable structure and good
dispersibility in pure aqueous media were prepared via Suzuki-type coupling in a miniemulsion
with consecutive dialysis process. The PTPABT nanoparticles display intra-molecular charge
transfer excited states with red-emission in aqueous dispersion. The electron-rich TPA units
inside PTPABT and stable porous structure make the polymer nanoparticles promising for the
detection of electron-deficient nitro-aromatic compounds. PTPABT aqueous dispersion has been
used to detect the TNB analyte and exhibits a high sensitivity towards TNB with a Stern-Volmer
quenching constant Ksv of 1.22×104 M-1. This method opens a new way for the fabrication of
stable polymer nanoparticles and realizing various sensors in pure aqueous media.
Acknowledgements
The authors would like to thank the financial support from Science and Technology Research
Project of the Education Department of Jilin Province (No. JJKH20181119KJ) and Natural
Science Fund Project of Changchun University of Science and Technology (No. XQNJJ-2017-15;
XQNJJ-2017-14).
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Declaration of interest
The authors declare no conflict of interest.
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References
[1] S.W. Zhang, T.M. Swager, Fluorescent detection of chemical warfare agents: Functional
group specific ratiometric chemosensors, J. Am. Chem. Soc. 125 (2003) 3420-3421.
[2] X. Sun, Y. Wang, Y. Lei, Fluorescence based explosive detection: From mechanisms to
sensory materials, Chem. Soc. Rev. 44 (2015) 8019-8061.
[3] J. Huang, J. Gu, Z. Meng, X. Jia, K. Xi, Signal enhancement of sensing nitroaromatics based
on highly sensitive polymer dots, Nanoscale 7 (2015) 15413-15420.
[4] Y. Geng, M.A. Ali, A.J. Clulow, S. Fan, P.L. Burn, I.R. Gentle, P. Meredith, P.E. Shaw,
Unambiguous detection of nitrated explosive vapours by fluorescence quenching of
dendrimer films, Nat. Commun. 6 (2015) 8240.
[5] R.S. Aparna, J.S.A. Devi, P. Sachidanandan, S. George, Polyethylene imine capped copper
nanoclusters- fluorescent and colorimetric onsite sensor for the trace level detection of TNT,
Sens. Actuators B: Chem. 254 (2018) 811-819.
[6] M.K. Chahal, M. Sankar, 1,8-Naphthyridine-based fluorescent receptors for picric acid
detection in aqueous media, Anal. Methods 7 (2015) 10272-10279.
[7] R. Dalapati, S. Biswas, Post-synthetic modification of a metal-organic framework with
fluorescent-tag for dual naked-eye sensing in aqueous medium, Sens. Actuators B: Chem.
239 (2017) 759-767.
[8] W. Huang, E. Smarsly, J. Han, M. Bender, K. Seehafer, I. Wacker, R.R. Schroder, U.H.
Bunz, Truxene-based hyperbranched conjugated polymers: fluorescent micelles detect
explosives in water, ACS Appl. Mater. Interfaces 9 (2017) 3068-3074.
[9] S.S. Nagarkar, A.V. Desai, S.K. Ghosh, A fluorescent metal-organic framework for highly
selective detection of nitro explosives in the aqueous phase, Chem. Commun. 50 (2014)
8915-8918.
19

ACCEPTED MANUSCRIPT
[10]A.S. Tanwar, S. Hussain, A.H. Malik, M.A. Afroz, P.K. Iyer, Inner filter effect based
selective detection of nitroexplosive-picric acid in aqueous solution and solid support using
conjugated polymer, ACS Sensors 1 (2016) 1070-1077.
[11]M. Elsner, M.A. Jochmann, T.B. Hofstetter, D. Hunkeler, A. Bernstein, T.C. Schmidt, A.
Schimmelmann, Current challenges in compound-specific stable isotope analysis of
environmental organic contaminants, Anal. Bioanal. Chem. 403 (2012) 2471-2491.
[12]M. Najarro, M.E.D. Morris, M.E. Staymates, R. Fletcher, G. Gillen, Optimized thermal
desorption for improved sensitivity in trace explosives detection by ion mobility
spectrometry, Analyst 137 (2012) 2614-2622.
[13]H. Ma, F. Li, P. Li, H. Wang, M. Zhang, G. Zhang, M. Baumgarten, K. Müllen, A
dendrimer-based electropolymerized microporous film: Multifunctional, reversible, and
highly sensitive fluorescent probe, Adv. Funct. Mater. 26 (2016) 2025-2031.
[14]C. Gu, N. Huang, Y. Wu, H. Xu, D. Jiang, Design of highly photofunctional porous polymer
films with controlled thickness and prominent microporosity, Angew. Chem. Int. Ed. 54
(2015) 11540-11544.
[15]S. Bandyopadhyay, P. Pallavi, A.G. Anil, A. Patra, Fabrication of porous organic polymers
in the form of powder, soluble in organic solvents and nanoparticles: a unique platform for
gas adsorption and efficient chemosensing, Polym. Chem. 6 (2015) 3775-3780.
[16]Y. Salinas, R. Martinez-Manez, M.D. Marcos, F. Sancenon, A.M. Castero, M. Parra, S. Gil,
Optical chemosensors and reagents to detect explosives, Chem. Soc. Rev. 41 (2012) 1261-
1296.
[17]X.-S. Ma, D.-H. Wang, Y.-Z. Cui, F.-R. Tao, Y.-T. Wang, T.-D. Li, A novel hydrophilic
conjugated polymer containing hydroxyl groups: Syntheses and sensing performance for
NACs in aqueous solution, Sens. Actuators B: Chem. 251 (2017) 851-857.
20

ACCEPTED MANUSCRIPT
[18] W.-Q. Song, Y.-Z. Cui, F.-R. Tao, J.-K. Xu, T.-D. Li, A.-Q. Wang, Conjugated polymers
based on poly(fluorenylene ethynylene)s: Syntheses and sensing performance for
nitroaromatics, Opt. Mater. 42 (2015) 225-232.
[19]J.S. Yang, T.M. Swager, Fluorescent porous polymer films as TNT chemosensors: Electronic
and structural effects, J. Am. Chem. Soc. 120 (1998) 11864-11873.
[20]W. Dong, Y. Pan, M. Fritsch, U. Scherf, High sensitivity sensing of nitroaromatic explosive
vapors based on polytriphenylamines with AIE-active tetraphenylethylene side groups, J.
Polym. Sci., Part A: Polym. Chem. 53 (2015) 1753-1761.
[21]D.T. McQuade, A.E. Pullen, T.M. Swager, Conjugated polymer-based chemical sensors,
Chem. Rev. 100 (2000) 2537-2574.
[22]M.E. Germain, M.J. Knapp, Discrimination of nitroaromatics and explosives mimics by a
fluorescent Zn(salicyladimine) sensor array, J. Am. Chem. Soc. 130 (2008) 5422-5423.
[23]B. Xu, X. Wu, H. Li, H. Tong, L. Wang, Selective detection of TNT and picric acid by
conjugated polymer film sensors with donor-acceptor architecture, Macromolecules 44 (2011)
5089-5092.
[24]J. Liu, H. Mi, M. Guan, Y. Huan, Q. Fei, Z. Zhang, G. Feng, Preparation and application of
novel fluorescence chemical sensor for determining trace levels of picronitric acid based on
water soluble conjugated polymer, Chem. J. Chinese U. 38 (2017) 2163-2168.
[25]C. Liu, Q. Zhang, N. An, J. Wang, L. Zhao, Y. Lu, A new water-soluble polythiophene
derivative as a probe for real-time monitoring adenosine 5’-triphosphatase activity in
lysosome of living cells, Talanta 182 (2018) 396-404.
[26]J. Pecher, S. Mecking, Nanoparticles of conjugated polymers, Chem. Rev. 110 (2010) 6260-
6279.
21

ACCEPTED MANUSCRIPT
[27]X. Wu, H. Hang, H. Li, Y. Chen, H. Tong, L. Wang, Water-dispersible hyperbranched
conjugated polymer nanoparticles with sulfonate terminal groups for amplified fluorescence
sensing of trace TNT in aqueous solution, Mater. Chem. Front. 1 (2017) 1875-1880.
[28]L. Lin, M. Rong, S. Lu, X. Song, Y. Zong, J. Yan, Y. Wang, X. Chen, A facile synthesis of
highly luminescent nitrogen-doped graphene quantum dots for the detection of 2,4,6-
trinitrophenol in aqueous solution, Nanoscale 7 (2015) 1872-1878.
[29]M. Rong, L. Lin, X. Song, T. Zhao, Y. Zhong, J. Yan, Y. Wang, X. Chen, A label-free
fluorescence sensing approach for selective and sensitive detection of 2,4,6-trinitrophenol
(TNP) in aqueous solution using graphitic carbon nitride nanosheets, Anal. Chem. 87 (2015)
1288-1296.
[30]W. Dong, J. Pina, Y. Pan, E. Preis, J.S. Seixas de Melo, U. Scherf, Polycarbazoles and
polytriphenylamines showing aggregation induced emission (AIE) and intramolecular charge
transfer (ICT) behavior for the optical detection of nitroaromatic compounds, Polymer 76
(2015) 173-181.
[31]Y.-W. Wu, A.-J. Qin, B.Z. Tang, AIE-active polymers for explosive detection, Chin. J.
Polym. Sci. 35 (2016) 141-154.
[32]Z. Zhao, T. Jiang, Y. Guo, L. Ding, B. He, Z. Chang, J.W.Y. Lam, J. Liu, C.Y.K. Chan, P.
Lu, L. Xu, H. Qiu, B.Z. Tang, Silole-containing poly(silylenevinylene)s: Synthesis,
characterization, aggregation-enhanced emission, and explosive detection, J. Polym. Sci.,
Part A: Polym. Chem. 50 (2012) 2265-2274.
[33] N. Tripathi, S. Sandhu, P. Singh, A. Mahajan, M. Kaur, S. Kumar, Dansyl conjugated
tripodal AIEEgen for highly selective detection of 2,4,6-trinitrophenol in water and solid
state, Sens. Actuators B: Chem. 231 (2016) 79-87.
22

ACCEPTED MANUSCRIPT
[34]W. Dong, T. Fei, A. Palma-Cando, U. Scherf, Aggregation induced emission and amplified
explosive detection of tetraphenylethylene substituted polycarbazoles, Polym. Chem. 5 (2014)
4048-4053.
[35]H. Nie, Y. Lv, L. Yao, Y. Pan, Y. Zhao, P. Li, G. Sun, Y. Ma, M. Zhang, Fluorescence
detection of trace TNT by novel cross-linking electropolymerized films both in vapor and
aqueous medium, J. Hazard. Mater. 264 (2014) 474-480.
[36]C. Gu, N. Huang, J. Gao, F. Xu, Y. Xu, D. Jiang, Controlled synthesis of conjugated
microporous polymer films: Versatile platforms for highly sensitive and label-free chemo-
and biosensing, Angew. Chem. Int. Ed. 53 (2014) 4850-4855.
[37]X. Liu, Y. Xu, Z. Guo, A. Nagai, D. Jiang, Super absorbent conjugated microporous
polymers: A synergistic structural effect on the exceptional uptake of amines, Chem.
Commun. 49 (2013) 3233-3235.
[38]K. Zhang, D. kopetzki, P.H. Seeberger, M. Antonietti, F. Vilela, Surface area control and
photocatalytic activity of conjugated microporous poly(benzothiadiazole) networks, Angew.
Chem. Int. Ed. 52 (2013) 1432-1436.
[39]Y. Kou, Y. Xu, Z. Guo, D. Jiang, Supercapacitive energy storage and electric power supply
using an aza-fused
8753-8757.
π-conjugated microporous framework, Angew. Chem. Int. Ed. 50 (2011)
[40]K. Wu, J. Guo. C. Wang, Dispersible and discrete metalloporphyrin-based CMP
nanoparticles enabling colorimetric detection and quantitation of gaseous SO2, Chem.
Commun. 50 (2014) 695-697.
[41]W. Dong, S. Xue, P. Lu, J. Deng, D. Zhao, C. Gu, Y. Ma, Functionality of peripheral side
chain for enhanced performance of conjugated polymer-F8BT as an example, J. Polym. Sci.,
Part A: Polym. Chem. 49 (2011) 4549-4555.
23

ACCEPTED MANUSCRIPT
[42]M. Shortreed, R. Kopelman, M. Kuhn, B. Hoyland, Fluorescent fiber-optic calcium sensor
for physiological measurements, Anal. Chem. 68 (1996) 1414-1418.
[43]B. Parmar, Y. Rachuri, K.K. Bisht, R. Laiya, E. Suresh, Mechanochemical and conventional
synthesis of Zn(II)/Cd(II) luminescent coordination polymers: dual sensing probe for
selective detection of chromate anions and TNP in aqueous phase, Inorg. Chem. 56 (2017)
2627-2638.
[44]D. Fu, N. Wang, H. Fan, T. Shu, S. Yue, Luminescent two-dimensional CdII coordination
polymer for selective sensing Fe3+ and 2,4,6-trinitrophenol with high sensitivity in water,
Inorg. Chem. Commun. 86 (2017) 262-266.
[45]S. Kumari, S. Joshi, T.C. Cordova-Sintjago, D.D. Pant, R. Sakhuja, Highly sensitive
fluorescent imidazolium-based sensors for nanomolar detection of explosive picric acid in
aqueous medium, Sens. Actuators B: Chem. 229 (2016) 599-608.
[46]X. Sun, J. He, Y. Meng, L. Zhang, S. Zhang, X. Ma, S. Dey, J. Zhao, Y. Lei, Microwave-
assisted ultrafast and facile synthesis of fluorescent carbon nanoparticles from a single
precursor: preparation, characterization and their application for the highly selective
detection of explosive picric acid, J. Mater. Chem. A 4 (2016) 4161-4171.
[47]X.-Y. Guo, F. Zhao, J.-J. Liu, Z.-L. Liu, Y.-Q. Wang, An ultrastable zinc(II)-organic
framework as a recyclable multi-responsive luminescent sensor for Cr(III), Cr(VI) and 4-
nitrophenol in the aqueous phase with high selectivity and sensitivity, J. Mater. Chem. A 5
(2017) 20035-20043.
[48]B. Wang, X.-L. Lv, D. Feng, L.-H. Xie, J. Zhang, M. Li, Y. Xie, J.-R. Li, H.-C. Zhou, Highly
stable Zr(IV)-based metal-organic frameworks for the detection and removal of antibiotics
and organic explosives in water, J. Am. Chem. Soc. 138 (2016) 6204-6216.
24

ACCEPTED MANUSCRIPT
[49]Z. Luo, B. Liu, S. Si, Y. Lin, C.S. Luo, C. Pan, C. Zhao, L. Wang, A fluorescent
chemosensor based on nonplanar donor-acceptor structure for highly sensitive and selective
detection of picric acid in water, Dyes Pigments 143 (2017) 463-469.
[50]R.N. Gillanders, I.A. Campbell, J.M.E. Glackin, I.D.W. Samuel, G.A. Turnbull, Ormosil-
coated conjugated polymers for the detection of explosives in aqueous environments, Talanta
179 (2018) 426-429.
[51]T. Wang, N. Zhang, R. Bai, Y. Bao, Aggregation-enhanced FRET-active conjugated polymer
nanoparticles for picric acid sensing in aqueous solution, J. Mater. Chem. C 6 (2018) 266-
270.
[52]M. Gao, Y. Wu, B. Chen, B. He, H. Nie, T. Li, F. Wu, W. Zhou, J. Zhou, Z. Zhao,
Di(naphthalen-2-yl)-1,2-diphenylethene-based conjugated polymers: aggregation-enhanced
emission and explosive detection, Polym. Chem. 6 (2015) 7641-7645.
[53]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.
[54]J. Wang, B. Li, D. Xin, R. Hu, Z. Zhao, A. Qin, B.Z. Tang, Superbase catalyzed regio-
selective polyhydroalkoxylation of alkynes: a facile route towards functional poly(vinyl
ether)s, Polym. Chem. 8 (2017) 2713-2722.
[55]Z. Zhao, Y. Guo, T. Jiang, Z. Chang, J.W.Y. Lam, L. Xu, H. Qiu, B.Z. Tang, A fully
substituted 3-silolene functions as promising building block for hyperbranched
poly(silylenevinylene), Macromol. Rapid Commun. 33 (2012) 1074-1079.
[56]X.-G. Liu, C.-L. Tao, H.-Q. Yu, B. Chen, Z. Liu, G.-P. Zhu, Z. Zhao, L. Shen, B.Z. Tang, A
new luminescent metal-organic framework based on dicarboxyl-substituted
25

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tetraphenylethene for efficient detection of nitro-containing explosives and antibiotics in
aqueous media, J. Mater. Chem. C 6 (2018) 2983-2988.
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Highlights:
Crosslinked PTPABT nanoparticles were synthesized by Suzuki coupling in
miniemulsion.
PTPABT nanoparticles can be well dispersed in both water and common organic
solvents.
The uniform PTPABT nanoparticles own stable and porous structure.
The PTPABT dispersion can realize aqueous TNB detection with high sensitivity.