The synthesis and highly sensitive detection of water content in THF using a novel solvatochromic AIE polymer containing diketopyrrolopyrrole and triphenylamine

Article abstract of DOI:10.1039/c6nj00192k

A novel electron donor-acceptor polymer (N1) containing diketopyrrolopyrrole as an electron acceptor and triphenylamine as an electron donor has been designed and synthesized. N1 is shown to possess the remarkable dual properties of solvatochromism and aggregation-induced emission (AIE). Importantly, N1 is found to serve as a fluorescence indicator for the qualitative and quantitative detection of low-level water in THF. Moreover, the quaternization of N1 by CH₃I gave ammonium-salt P1. A selective fluorescence turn-on probe for bovine serum albumin (BSA) detection and quantification is developed by taking advantage of the aggregating process of P1. It is found that the intrinsic weak fluorescence of P1 in DMSO/PBS (1:1, v/v) increases to 2.9-fold after the addition of 50 μM BSA through electrostatic complexation and hydrophobic interaction.

Full text of DOI:10.1039/c6nj00192k

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Synthesis and highly sensitive detection of water content in THF
using a novel solvatachromic AIE polymer containing
diketopyrrolopyrrole and triphenylamine
Lingyun Wang a*, Lingling Yanga, Lin Li b*, Derong Cao a
a
School of Chemistry and Chemical Engineering, State Key Laboratory of
Luminescent Materials and Devices, South China University of Technology,
Guangzhou, China, 510641
b
School of Food Science and Engineering, South China University of Technology,
Guangzhou, China, 510641
*Corresponding author: Tel. +86 20 87110245; fax: +86 20 87110245. Eꢀmail:
lingyun@scut.edu.cn; felinli@scut.edu.cn

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Abstract:
A novel electron donorꢀacceptor polymer (N1) containing diketopyrrolopyrrole as
electron acceptor and triphenylamine as electron donor has been designed and
synthesized. N1 is shown to possess the remarkable dual properties of
solvatochromism and aggregationꢀinduced emission (AIE). Importantly, N1 is found
to serve as a fluorescent indicator for the qualitative and quantitative detection of
lowꢀlevel water in THF. Moreover, the quaternization of N1 by CH3I gave
ammoniumꢀsalt P1. A selective fluorescence turnꢀon probe for bovine serum albumin
(BSA) detection and quantification is developed by taking advantage of the
aggregating process of P1. It is found that the intrinsic weak fluorescence of P1 in
DMSO/PBS (1:1, v/v) increases to 2.9ꢀfold after addition of 50 ꢁM BSA through
electrostatic complexation and hydrophobic interaction.
Keywords: Aggregation induced emission (AIE), Diketopyrrolopyrrole,
triphenylamine, Intramolecular charge transfer (ICT), Solvatochromism

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1. Introduction
Aggregationꢀinduced emission (AIE) is a newly developed phenomenon that is
exactly opposite to the aggregationꢀcaused quenching (ACQ) effect observed with
some conventional luminophores. Luminogens with AIE characteristic have emerged
as promising materials for fabricating bioꢀprobes for their incredible emission
efficiency upon interaction with biomolecules in aqueous solutions.1 The
waterꢀsoluble and redꢀemitting AIEꢀactive systems are highly desirable due to their
minimal photoꢀdamage to living cells and deep tissue penetration.2 In principle,
redꢀemitting dyes come from a narrowed energyꢀgap, which can be realized by two
strategies. One is by extending the π ꢀconjugation system such as those observed for
large planar conjugated molecules. However, planar structures often present ACQ
effect due to intermolecular π−π stacking. Another is by introducing strong electron
donor (D) and acceptor (A) groups into a conjugated luminogen to concomitantly
drive up the HOMO and pull down the LUMO.3 Moreover, the building of electron
donor–acceptor structure is an effective way to improve luminescent property of
fluorophores,4, 5 which increases its dipole moment and as a result the molecule
becomes sensitive to its environment.
Diketopyrrolopyrrole (DPP) dyes offer distinctive advantages relative to other
organic dyes, including high fluorescence quantum yields, good light and thermal
stability. In particular, DPP dyes can emit brilliant redꢀfluorescence after specific
structural modification, which makes them better to be applied in biosensors.
Therefore, DPP would be a good candidate for developing redꢀemitting material.

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Significant advancements have been made in the development of new fluorescent
probes based on DPP in recent years.6 However, it is a great challenge to sustain the
efficient emission of DPPꢀbased compounds in aggregated states due to the serious
intermolecular π – π stacking. To overcome this problem, it is a rational strategy to
attach bulky or AIE substituents onto DPP to hinder the ACQ effect, but still very
limited.7 In our recent work, two new redꢀemitting AIEꢀactive DPP compounds were
synthesized, where the introduction of anthranone successfully converted DPP dye
from ACQ to AIE.8
On the other hand, triphenylamine (TPA) has recently become a material with great
prospects due to its AIE properties.9 Moreover, TPA as a conventional electron
donating group is frequently employed to generate various compounds with electron
donor–acceptor structure.10ꢀ12 Recently, Liu’s and Hua’s groups investigated
biocompatible nanoparticles based on DPP with aggregationꢀinduced red/NIR
emission for in vivo twoꢀphoton fluorescence imaging, where propellerꢀlike starburst
TPA as a strong donor tethered to the central DPP acceptor via vinyl arm.13 However,
most of the AIE systems especially those containing TPA moieties developed so far
displaying both AIE and solvatochromism are still quite limited and possess
lowꢀmolecular weights. For practical applications, the polymer with high molecular
weight and good filmꢀforming capacity would be desirable. Preparation of polymers
with AIE features may help to solve ACQ problem and meanwhile impart polymers
with new properties and practical applications. Moreover, due to the “signal
amplification effect” of the conjugated polymer chains, AIE polymers enjoy superior

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sensitivity when work in the application of chemoꢀ and bioꢀsensors compared with
AIE small molecules. At the same time, the superior stability and strong emission
efficiency of polymer enable longꢀterm tracking of the cell for bioimaging
applications. Therefore, the development of longꢀwavelength AIEꢀactive polymers
with pronounced solvatochromic effect and probably higher sensitivity and larger
responses to external stimuli, is still a challenging task.
Herein, a novel conjugated polymer (N1) has been designed and synthesized, as
shown in Scheme 1. In the molecular design, the TPA group is introduced because it
can act not only as a strong electronꢀdonor group to induce intramolecular charge
transfer (ICT) transition but also as an activator for AIE. It was thus expected that N1
possesses intense ICT effect, which bestow N1 with pronounced solvatochromism.
Indeed, N1 exhibit strong solventꢀdependent fluorescence and AIE behaviour.
Importantly, the emission band of N1 was effectively quenched upon addition of
increasing concentration of water in THF. So, N1 can serve as a fluorescent indicator
for the qualitative and quantitative detection of lowꢀlevel water in THF. N1 was
further treated with CH3I at room temperature to afford its ionized product (P1). Due
to the multivalent interactions of P1 with negative bovine serum albumin (BSA), P1
shows superamplification effect in the emission enhancement of its nanoaggregates
and works as sensitive and selective fluorescence “turnꢀon” probe for BSA
quantitation.
2. Experimental

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2.1. Chemicals and instruments
Tetrahydrofuran (THF) and dioxane was distilled under normal pressure from
sodium under argon immediately prior to use. Other solvents and chemicals were
obtained from commercially available resources without further purification.
Compound 3 was synthesized by the published paper .14
1H and 13C NMR spectra were measured on Bruker Avance III 400 MHz (in CDCl3
or in DMSOꢀd6, TMS as internal standard). Fourier transform infrared (FTꢀIR) spectra
were recorded on an RFXꢀ65A (Analect Co.) spectrometer. The UVꢀvis absorption
spectra were recorded using a Helios Alpha UVꢀVis scanning spectrophotometer.
Fluorescence spectra were obtained with a Hitachi Fꢀ4500 FL spectrophotometer with
quartz cuvette (path length = 1cm). The fluorescence spectra were obtained by
excitation at 500 nm and the excitation and emission slit widths were 10 nm and 20
nm, respectively.
2.2. Synthesis of Monomer 1
Compound
3
(0.223 g, 0.5 mmol), KOAc (0.276 g,
2
mmol),
bis(pinacolato)diboron (507 mg, 2 mmol) and Pd(dppf)2Cl2 were mixed in anhydrous
dioxane. Then the mixture was heated under reflux for 24 h under argon. After
cooling, the solvent was removed under reduced pressure. The crude produce was
purified by column chromatography (petroleum ether: CH2Cl2: ethyl acetate =5:4:0.3)
1
on silica gel to afford orange solid in 46.2% yield. H NMR (CDCl3, 400 MHz, δ,
ppm): 8.00 (d, J=8.0 Hz, 4H), 7.80 (d, J=8.0 Hz, 4H), 3.77 (t, J=4.0 Hz, 4H), 3.34 (t,

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J=4.0 Hz, 4H), 1.79ꢀ1.76 (m, 4H), 1.68ꢀ1.55 (m, 6H), 1.39 (s, 24H), 1.28ꢀ1.23 (m,
6H). 13C NMR (CDCl3, 100 MHz, δ, ppm): 162.5, 162.4, 148.4, 147.4, 135.1, 132.3,
130.5, 130.0, 127.7, 126.9, 125.9, 110.2, 110.0, 84.2, 41.6, 33.6, 32.5, 29.2, 27.6, 25.8,
24.9. TOFꢀMS m/z: 867.289 [M+H]+.
Monomer 2 was synthesized according to the previous literature.15 1H NMR
(CDCl3, 400 MHz, δ, ppm): 7.31 (d, J=8.0 Hz, 4H), 7.03 (d, J=8.0 Hz, 2H), 6.90 (d,
J=8.0 Hz, 4H), 6.86 (d, J=8.0 Hz, 2H), 3.94 (t, J=8.0 Hz, 2H), 1.82ꢀ1.76 (m, 2H),
1.49ꢀ1.46 (m, 2H), 1.38ꢀ1.36 (m, 4H), 0.93 (t, J=8.0 Hz, 3H). 13C NMR (CDCl3, 100
MHz, δ, ppm): 156.4, 146.9, 139.5, 132.2, 127.4, 124.3, 115.6, 114.5, 68.3, 31.6, 29.3,
25.8, 22.6, 14.1. TOFꢀMS m/z: 502.892 [M+H]+.
Synthesis of N1.
To a solution of THF (15 mL), Monomer 1 (216 mg, 0.25 mmol), Monomer 2
(125.75 mg, 0.25 mmol) and Pd(Pph3)4 (28.9 mg, 0.025 mmol) were added. The
mixture was deoxygenated by purging with purified N2 gas and then K2CO3 (2 mol/L,
4.5 mL) was injected. The mixture was heated at 50◦C for 18 h under N2. After cooled,
the mixture was poured into water, extracted with CH2Cl2 three times and then washed
with water and EDTA solution in sequence. The concentrated solution was dropwise
added into methanol. The precipitate was collected by filtration from methanol and
dried under vacuum to yield N1 (177 mg, 72%) as a deep red solid. GPC: Mw= 9751,
Mn=7548, PDI=1.29. 1H NMR (CDCl3, 400 MHz, δ, ppm): 7.90ꢀ7.88 (m, 2H),
7.76ꢀ7.72 (m, 4H), 7.57ꢀ7.51 (m, 2H), 7.40ꢀ7.33 (m, 4H), 7.20ꢀ6.86 (m, 8H),

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3.97ꢀ3.94 (m, 2H), 3.83 (br, 2H), 3.30 (br, 6H), 1.81ꢀ1.67 (m, 10H), 1.45ꢀ1.26 (m,
14H), 0.91 (br, 3H).
The ionization of N1 was realized by adding 1 mL trimethylamine to a solution of
N1 (100 mg) in 10 mL CHCl3 and stirring for 24 h at room temperature. The polymer
precipitate was collected and washed with THF, and then dried under vacuum to yield
1
P1 (85 mg). H NMR (DMSOꢀd6, 400 MHz, δ, ppm): 8.18ꢀ6.62 (m, 20H), 4.04ꢀ3.61
(m, 10H), 3.02ꢀ2.78 (m, 24H), 1.49ꢀ0.91 (m, 21H).
2.3. Preparation of aggregates
Stock solutions of N1 were prepared in DMF, with a concentration of 0.1 mM. An
aliquot (1 mL) of the stock solution was transferred to a 25 mL erlenmeyer flask. After
adding an appropriate amount of DMF, water was added dropwise under vigorous
stirring to furnish 10 ꢁM solution with water fractions (fw) of 0–90 vol %.
2.4 Discrimination of BSA
The discrimination of BSA was carried out in a solvent system of DMSO:PBS=1:1
(v/v). The fluorescence BSA titrations were carried out by sequentially adding
0ꢀ200µL aliquots of BSA solution (5×10ꢀ4 M) to a 20µL stock solution of P1 followed
by addition of 980 µmL DMSO and an aqueous PBS buffer to acquire a solution of
2.0 mL.
3. Results and discussion
3.1. Synthesis and structural characterization

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The synthetic routes of Monomer 1 are shown in Scheme 1, and the key compound
3 was synthesized according to the literature.14 Monomer 1 bearing two pinacol
boronate groups was accomplished by the Pdꢀcatalyzed Suzuki reaction of 3 with
bis(pinacolato)diboron in the presence of catalytic amounts of Pd(dppf)Cl2 and
potassium acetate. Monomer 2 was synthesized according to the previous literature.15
Monomer 1 and Monomer 2 were carefully characterized by proton and carbon
nuclear magnetic resonance spectroscopy (1H, 13C NMR) and high resolution mass
spectroscopy (MSꢀTOF) (see the ESI, Figs. S1ꢀS2 for the details). The neutral
precursor polymer N1 was synthesized by Suzuki coupling reaction of Monomer 1
and Monomer 2. As shown in Fig.1, Monomer 1 shows a strong singlet at 1.39 ppm
corresponding to the methyl proton of boryl. However, this singlet does not appeared
in the 1H NMR spectrum of N1, implying the successful polymerization of Monomer
1 and Monomer 2. N1 is soluble in common organic solvents such as
dichloromethane, chloroform, and THF. The ionization of N1 was realized by treating
N1 with trimethylamine at room temperature for 24 h to generate P1 in order to
improve the water solubility and provide the positive charged ammonium binding
sites for the electrostatic interaction between the P1 and negative analytes. P1 is
readily soluble in dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO).
3.2 Solvatochromic effect of N1
TPA is wellꢀknown to be very effective πꢀelectronꢀdonating group with high donor
strength. In the TPA–DPP structural framing of N1, TPA was the donor part while

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DPP served as the acceptor part. Consequently, the excitation of the ICT state induced
a charge shift from the donor to the acceptor part, which would cause significant
solvatochromism. Fig. 2a exhibits the normalization absorption of N1 in the different
solvent. For N1, the absorption spectral maximum is dependent on the solvent polarity;
the magnitude of the solvatochromic shift from ethyl acetate (499 nm) to CHCl3 (522
nm) is 23 nm. Thus, various colors in different solvents are present (Fig. 2b).
As the solvent polarity increases, this interaction becomes stronger, resulting in
emission at lower energies or longer wavelengths. With increasing the solvent polarity,
N1 exhibits polarityꢀdependent solvatochromism of fluorescence (Fig. 3a). In dioxane
and toluene, N1 emits strong yellow fluorescence with the same emission peak at 602
nm. The emission maxima further redꢀshifts to 620, 625 and 611 nm in CH2Cl2,
CHCl3 and THF, respectively. However, blueꢀshifted maxima emission peaks at 576,
598 and 591 nm in acetone, ethyl acetate and DMF are observed, respectively. In
more polar solvents such as DMF, the fluorescence of N1 is nearly completely
quenched. Such changes in fluorescence spectra indicate that the excited state has a
larger dipole moment than the ground state. Accordingly, N1 in various solvents
exhibited dramatic fluorescent color variations under illumination with 365 nm light.
Strong yellow emission in toluene and dioxane, weak redꢀorange emission in
chloroform, CH2Cl2, and THF were observed. While in more polar solvents such as
DMF and acetonitrile, the emission becomes very weak due to the promotion of ICT
process (Fig. 3b).

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3.3 AIE behaviours of N1
To investigate the AIE properties of N1, we employed anhydrous DMF as the good
solvent and water as the poor solvent. The emission spectra of N1 in DMF and
DMF/water mixture solutions were recorded (Fig. 4a). Clearly, the fluorescent
intensity of N1 is rather weak in pure DMF solution. However, the fluorescent
intensity increases dramatically when the water content is above 80%. As the water
content reachs 90%, the photoluminescence intensity is boosted to the maximum.
Eventually, the emission intensity of N1 is approximately 7 folds higher than its
molecularly dispersed species in DMF (Fig. 4b). The apparent emission enhancement
of N1 is thus induced by aggregation, verifying its AIE nature owing to the restricted
intramolecular motions mechanism: large amount of water resulted in formation of
aggregated nanoparticles, which subsequently impeded the intramolecular rotations of
the aromatic rotors of N1 and endowed the aggregates with intense emission.
Moreover, compared to the pure DMF solution of N1, the emission maximum of
the aggregates blueꢀshifted from 625 nm to 600 nm, and the emission color changed
from red to orange (Fig. 4c). The weak and redder emission in pure DMF solution
implied the existence of largeꢀamplitude relaxation in the excited state, such as
intramolecular charge transfer (ICT). Nevertheless, aggregation forced the molecules
to reside in an apolar environment which is unfavourable for ICT process, resulting in
the blue shift of the emission maximum and was also helpful for the light emission. In
contrast to the fluorescence, the absorption spectra of N1 were redꢀshifted (508 to 522
nm) and broadened upon addition of water, due to the nanoaggregated structure of the

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molecules (see the ESI, Fig. S3). Meanwhile, the levelꢀoff tails in the visible region of
the absorption spectra clearly indicated the formation of aggregates.
3.4 Detection of low-level water in THF by N1
The qualitative and quantitative detection of lowꢀlevel water content as impurity in
organic solvents is of great significance in several fields of chemistry and industrial
processes such as pharmaceutical manufacturing, food processing, paper production,
biomedical and environmental monitoring.16 Particularly using fluorescence methods,
parameters such as lifetime, intensity and wavelength ratiometric sensing have been
widely studied and applied for detection of water content in organic solvents.17
Clearly, the fluorescence emission of N1 is highly sensitive to solvent polarity
according to the above discussions. Therefore, we further investigated its emission
behaviour in nonꢀhydrogenꢀbond donating waterꢀmiscible solvents, i.e., THF. As
shown in Fig. S4 (see the ESI), the absorption spectra of N1 in THF solution
underwent slight changes from pure THF to THF containing 10% (v/v) water,
indicating that neither solvent polarity nor hydrogen bonding has a significant
influence on the absorption spectra. In contrast, upon further addition of water in THF
solution, the emission of N1 is effectively quenched and that of N1 is gradually
diminished along with blueꢀshift from 603 nm to 590 nm (Fig. 5a). These phenomena
can be attributed to the cooperative effect of the solvent polarity and the ICT effect.
Fig. 5b shows in details how the measured fluorescent intensity changes as a function
of water content in the THF solution of N1. As can be seen from the graph (Fig. 5b),

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the fluorescent intensity of N1 decreases dramatically when the water content is
below 2.00% (v/v): the reduction in relative fluorescence intensity reaches nearly 53%,
whereas such effect became moderate when the water content is higher than 2.00%
(v/v). More importantly, the fluorescent intensity of N1 as a function of water content
shows a good linear relationship below 2.00% (v/v), and the detection limit of N1 for
water is determined as 0.005% in THF. In comparison with reported solvatochromic
dyes for the detection of water in organic solvents,18, 19 the detection limit of N1 is
high, demonstrating that N1 is sensitive to lowꢀlevel water content in THF. It can be
also utilized to quantitatively detect lowꢀlevel water content in organic solvents.
3.5 The photophysical properties of P1
The addition of p oor solvent (such as THF or methanol) to the solution of P1 in
DMSO fails to make P1 aggregate, possibly because of its amphiphilic nature.20
Hence, the increasing viscosity is investigated to study whether P1 possesses AIE
effect. As shown in Fig. 6, the emission intensity of P1 in glycerol/DMSO mixture
(9:1, v/v) is about 1.15ꢀfold higher than that in DMSO, which implies that P1 is
AIEꢀactive. These phenomena occur because high viscosity can hamper
intramolecular rotation, leading to the closure of the nonradiative decay channel and
thus enhanced fluorescence emission.
3.6 P1 serves as a probe for detecting BSA

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The “traditional” polymer bioprobes usually operate in a light “turnꢀoff” mode due
to the emission quenching caused by the electron and/or energy transfers between the
polymer chains and the bioanalytes. It will be better if the bioprobes can work in a
fluorescence “turnꢀon” mode, which enjoys such advantages as high detection
sensitivity, reduced falseꢀpositive signals, and visual recognition or discrimination
with the naked eyes.
P1 is positively charged and should show affinity toward negatively charged
biopolymers. Bovine serum albumin (BSA), which contains hydrophobic binding
sites in its native folding structure and has a negative charge (the isoelectric point is
about 4.7) in water medium at neutral pH, can bind with P1 through electrostatic and
hydrophobic interaction. Considering the optical properties of P1, we infer P1 would
be suitable for application as a fluorescence turnꢀon probe for BSA based on
controllable aggregation processes through hydrophobic effect and electrostatic
interaction and tuning the π…π stacking interactions by BSA. To explore the
possibility of utilizing P1 for protein assay, its emission spectra in the absence and
presence of BSA are measured. Fig. 7 shows the FL spectral changes in P1 before and
after the addition of BSA. P1 is weakly luminescent in DMSO/PBS (v/v, 1/1);
however, the FL intensity of the buffer solution of P1 increases gradually when BSA
is introduced. For instance, the FL intensity of P1 at 570 nm is enhanced to 2.9ꢀfold
after the concentration of BSA reaches 50 ꢁM.
In the BSA concentration range of 0ꢀ1 ꢁM, the I/I0ꢀ1 vs [BSA] plot follows a linear
relationship with an outstanding “goodnessꢀofꢀfit” (R2 = 0.994). The detection limit is

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0.0038 ꢁM, demonstrating that P1 can function as a biological probe for BSA
quantification at subppm level. In comparison with reported small molecular AIE
8
system for the detection of BSA , the detection limit of P1 was high. This can be
attributed to explanations: (1) the “signal amplification effect” of the conjugated
polymer makes P1 to be more sensitive to BSA; (2) The native BSA contains
hydrophobic binding sites such as hydrophobic pockets in folding structures. P1 has
more suitable size and structure to enter the hydrophobic pockets and bind to BSA,
which benefit the stronger interaction with BSA.
In order to further verify that the enhancement of the fluorescence intensity of P1 is
ascribed to the formation of aggregates of P1 with BSA, the corresponding sizes were
studied by using dynamic light scattering (DLS) before and after the addition of BSA
(Fig. 8). The mean diameter of P1 in the mixture of DMSO/PBS (v/v, 1/1) is 589 nm
while the mean diameter increases to 917 nm as 50 ꢁM BSA is introduced. Moreover,
Fig. S5 (see the ESI) demonstrates the changes in the absorption spectrum of P1 (20
ꢁM) in the absence and presence of BSA. P1 has absorbance maxima peak at 537 nm.
A levelꢀoff tail is observed in the presence of BSA, further indicating that the
formation of aggregates.
3.7. The selectivity of P1 for detecting BSA
As compared with significant fluorescence response induced by BSA, however, no
significant changes in P1 fluorescence intensity as well as emission maxima peak
position is observed after addition of the same concentration of negative charged

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biological species such as alkaline phosphatase (ALP), DNA and other anions (Cl−,
−
−
3−
Br−, I−, NO3 , AcO−, CO3 and PO4 ) (Fig. 9). The conventional reported protein
21
detection methods exhibit various responses for different proteins , which results in
poor selectivity. These differences are related to the amino acid sequence, pI, protein
structure and the presence of certain side chains that can dramatically alter the
proteins response and their hydrophobicity 22. BSA appears to be the most
“hydrophobic” proteins among these proteins/ enzymes used, while ALP, DNA are
less ‘hydrophobic’ proteins and hence have lower binding affnity for P1. Herein, in
the buffer solutions, the cationic amphiphilic P1 bind to BSA via supramolecular
interactions such as electrostatic interaction and the hydrophobic effect. For the native
BSA, it contains hydrophobic binding sites such as hydrophobic pockets. When P1
bind to the hydrophobic regions of BSA chains and enter into the hydrophobic
pockets of their folding structures, the intramolecular rotations of P1 are frozen,
inducing them to emit as aggregation does. All these findings suggested that P1 can
serve as a selective probe for discriminating BSA.
4. Conclusions
A diketopyrrolopyrrole and triphenylamine containing conjugated polymer N1 and
its ionized product P1 were designed and synthesized. N1 displays ICT fluorescence
in different solvents and AIE characteristic. The emission intensity of N1 is
approximately 7 folds higher in DMF/H2O (1/9, v/v) than its molecularly dispersed
species in DMF. Moreover, N1 could be utilized as a fluorescent probe for the

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qualitative detection of lowꢀevel water content in THF. In particular, the low detection
limit (0.005% in THF) enables it a supersensitive water sensor for pratical
applications. Furthermore, P1 can function as a fluorescence “turn on” probe for
discriminating BSA. Other biological species bearing negative charge such as DNA,
ATP and anions have no significant effect on the fluorescence of P1, indicating that
P1 has good selectivity for BSA.

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Acknowledgements
The supports by National Basic Research Program of China (2012CB720801),
National Natural Science Foundation of China (No. 21274045), the Fundamental
Research Funds for the Central Universities (2015ZZ037) and the Natural Science
Foundation of Guangdong Province (2015A030313209, 2016A030311034) are
gratefully acknowledged.

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Br
Br
H
N
O
N
N
O
Br
O
O
Br
Br
CH2OH
CH2OH
Br
O
O
Br
t-C H OK
Br
O
N
NH2SO3H
NMP, 60
℃,
O
t-C5H11ONa
t-C5H11OH
H
4 9
Br
CN
CN
2
1
Br
Br
3
OC6H13
OC6H13
O
B
O
N
O
bis(pinacolato)diboron
KOAc, Pd(Dppf)2Cl2
N
Br
N
Br
N
O
100 0
C
,Ar
O
C6H12Br
B
O
N
O
Monomer 2
O
Pd(PPh3)4, K2CO3, THF
N , 50
N
Br
BrC6H12
℃, 18h
2
Monomer 1
N1
OC6H13
N
Br
C6H12
N
N(CH3)3, CHCl3
N
O
O
N
NC6H12
P1
Br
Scheme 1. Synthesis of N1 and P1.

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Figure captions
Fig. 1. The 1H NMR spectra of Monomer 1, Monomer 2 and N1.
Fig. 2. (a) The normalized UVꢀvis spectra and (b) photographs of N1 in different
solvent.
Fig. 3. (a) The normalized emission spectra of and (b) photographs of N1 in different
solvent under UV irridiation.
Fig. 4 (a) Emission spectra of N1 (10 ꢁM) in DMF/H2O (λex = 500 nm); (b) Plots of
relative emission intensity enhancement factors versus water fractions; (c) Emission
photographs of N1 in DMF/H2O mixtures with different water fractions at 365 nm UV
irradiation.)
Fig. 5 (a) Emission spectra of N1 (10 ꢁM) in THF/H2O (λex = 500 nm); (b) Plots of
relative emission intensity (I/I0) versus water fractions.
Fig. 6. Emission spectra of P1 (20 ꢁM) in various glycerol–DMSO mixture (λex = 500
nm)
Fig.7. Emission spectra of P1 (20 ꢁM) in various amount of BSA (λex= 500 nm) in
DMSO/PBS mixture (1:1, v/v). Inset: photogragh of P1 in the presence and absence
of BSA).
Fig. 8. Particle size distribution of P1 (20 ꢁM) in DMSO/PBS mixture (1:1, v/v) in
the absence (a) and presence (b) of 50 ꢁM BSA.
Fig.9. The fluorescence spectra of P1 (10 ꢁM) in presence of 50 ꢁM DNA, ATP and
anions.

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Fig. 1. The 1H NMR spectra of Monomer 1, Monomer 2 and N1.

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toluene
CH2Cl2
(a)
1.0
0.8
0.6
0.4
0.2
0.0
CHCl3
ethyl acetate
THF
acetone
dioxane
DMF
400
500
600
Wavelength (nm)
Fig. 2. (a) The normalized UVꢀvis spectra and (b) photographs of N1 in different
solvent.

New Journal of Chemistry
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(a)
1.0
0.8
0.6
0.4
0.2
0.0
toluene
CH2Cl2
CHCl3
ethyl acetate
THF
acetone
dioxane
DMF
550
600
650
700
750
800
Wavelength (nm)
Fig. 3. (a) The normalized emission spectra of and (b) photographs of N1 in different
solvent under UV irridiation.

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350
300
250
200
150
100
50
(b)
0
60
Water fraction (%)
0
20
80
40
Fig. 4 (a) Emission spectra of N1 (10 ꢁM) in DMF/H2O (λex = 500 nm); (b) Plots of
relative emission intensity enhancement factors versus water fractions; (c) Emission
photographs of N1 in DMF/H2O mixtures with different water fractions at 365 nm UV
irradiation.)

New Journal of Chemistry
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(b)
1.0
0.8
0.6
0.4
0.2
0.0
0
2
4
6
8
10
Water content (%)
Fig. 5 (a) Emission spectra of N1 (10 ꢁM) in THF/H2O (λex = 500 nm); (b) Plots of
relative emission intensity (I/I0) versus water fractions.

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100
80
60
40
20
0
0% glycerol
50% glycerol
90% glycerol
550
600
650
700
750
800
Wavelength (nm)
Fig. 6. Emission spectra of P1 (20 ꢁM) in various glycerol–DMSO mixture (λex = 500
nm)