Ethynyl-capped hyperbranched conjugated polytriazole: Click polymerization, clickable modification, and aggregation-enhanced emission

Article abstract of DOI:10.1021/ma3017037

Cu(I)-catalyzed azide-alkyne click polymerization, developed based on the click reaction, has become a powerful tool for the construction of functional polytriazoles with linear and hyperbranched structures. This method has, however, rarely been used for

Full text of DOI:10.1021/ma3017037

Article
pubs.acs.org/Macromolecules
Ethynyl-Capped Hyperbranched Conjugated Polytriazole: Click
Polymerization, Clickable Modification, and Aggregation-Enhanced
Emission
Jian Wang,† Ju Mei,† Engui Zhao,‡ Zhegang Song,‡ Anjun Qin,*,† Jing Zhi Sun,*,†
and Ben Zhong Tang*,†,‡
†MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering,
Zhejiang University, Hangzhou 310027, China
‡Department of Chemistry, Institute for Advanced Study, Institute of Molecular Functional Materials, State Key Laboratory of
Molecular Neuroscience, and Division of Biomedical Engineering, The Hong Kong University of Science & Technology, Clear Water
Bay, Kowloon, Hong Kong, China
S
* Supporting Information
ABSTRACT: Cu(I)-catalyzed azide−alkyne click polymer-
ization, developed based on the click reaction, has become a
powerful tool for the construction of functional polytriazoles
with linear and hyperbranched structures. This method has,
however, rarely been used for the preparation of functional
hyperbranched conjugated polytriazoles (hb-CPTA). In this
paper, soluble ethynyl-capped hb-CPTA with weight-averaged
molecular weight of 39 500 was synthesized in high yield
(84.4%) by the Cu(I)-catalyzed azide−alkyne click polymer-
ization of tetraphenylethene containing diazide [1,2-bis(4-
azidophenyl)-1,2-diphenylethene] and tetrayne [1,1,2,2-
tetrakis(4-ethynylphenyl)ethane] in equal concentration. By
taking advantage of the ethynyl groups on its periphery, the
polymer could be efficiently postfunctionalized by azide−alkyne and thiol−yne click reactions. The polymers are thermally stable
and loss 5% of their weights at temperatures higher than 340.0 °C. hb-CPTA also possesses high char yield (74.8%) at 800 °C.
The polymers feature the unique characteristics of aggregation-enhanced emission. Furthermore, the PL intensities of the hb-
CPTA and thiol−yne postfunctionalized polytriazoles increase linearly with water fraction in THF/water mixtures. Thanks to
their rigid structures, the polymers could be fabricated into unimolecular nanoparticles with sizes of ca. 100 nm. Thus, this paper
provides a powerful method to synthesize soluble ethynyl-capped hyperbranched polymers, which could be a useful platform for
preparation of versatile functional polymers via postreactions.
pot procedure, making them particularly desirable candidates
for bulk-material and large-scale applications in diverse areas,
such as nanoscale catalysis, drug delivery, and adhesive
coatings.6 With persistent efforts of the scientists, various
polymerization methods, such as polycondensation, polycyclo-
trimerization, and polycoupling reactions, have been developed
and functional hyperbranched polymers have been obtained.7
Besides the harsh reaction conditions required in these
polymerizations, the resultant hyperbranched polymers bearing
emissive units, such as triphenylamine, fluorene, and carbazole
in their branches or on their periphery, generally suffer from an
upsetting “aggregation-caused quenching” (ACQ) effect; that
is, their intense emission in dilute solution is weakened or even
annihilated in condensed phases resulting from energy transfer
INTRODUCTION
■
Cu(I)-catalyzed azide−alkyne click reaction, reported inde-
pendently by Sharpless and Meldal and co-workers in 2002,1
has become a versatile and powerful synthetic tool with
applicability in diverse areas including bioconjugate synthesis
and surface modification, etc.2 It enjoys the advantages of high
efficiency, regioselectivity, mild reaction conditions, atom
economy, and tolerance to functional groups and has great
potential to be developed into a powerful polymerization
method. It does have been utilized in polymers science but with
emphasis on the postfunctionalization of preformed polymers.3
We and others have endeavored to develop the click reaction
into a click polymerization. Functional linear polytriazoles and
dendrimers have been successfully prepared;4,5 the hyper-
branched polymers were, however, rarely reported by this
powerful tool.
Received: August 12, 2012
Although structurally imperfect, a hyperbranched polymer
can be facilely synthesized via a single-step reaction by a one-
Revised: September 12, 2012
© XXXX American Chemical Society
A
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Scheme 1. Synthetic Route to Diazide BATPE
Scheme 2. Synthetic Route to Tetrayne TETPE
and the formation of excimers and exciplexes.8 This undesirable
ACQ effect greatly hinders their further broad applications in
optoelectronic devices, fluorescent chemosensors, and biop-
robes since the light-emitting hyperbranched polymers are
always applied in solid or aggregate states.9 Thus, preparation
of hyperbranched polymers whose emission intensity could be
enhanced instead of being decreased in the solid or aggregate
states by efficient polymerization method with mild reaction
conditions is highly desirable.
(A2) and tetrayne TETPE (B4) (Schemes 1 and 2). Through
adjusting the monomer stoichiometry, ethynyl-capped 1,4-
regioregular hb-CPTA with satisfactory molecular weight (Mw:
39 500) was obtained in high yield (84.4%) (Scheme 3), which
Scheme 3. Schematic Illustration of Synthetic Route to
Ethynyl-Capped Hyperbranched Conjugated Polytriazole
(hb-CPTA) (SA = Sodium Ascorbate)
We have recently discovered an abnormal photophysical
phenomenon of “aggregation-induced emission” (AIE), which
is exactly opposite to the ACQ effect.10 A serious of propeller-
shaped luminogens, such as silole and tetraphenylethene
(TPE), are nonemissive when molecularly dissolved but
induced to emit efficiently by aggregate formation. Restriction
of intramolecular rotation (RIR) of the multiple phenyl rotors
in the aggregates has been proven experimentally and
theoretically as the main cause for the AIE effect.11 With the
novel AIE effect, researchers can buoyantly take advantage of
aggregate formation, instead of painfully fighting against the
nature process of molecule aggregation. Thanks to their unique
AIE characteristics, the molecules have been found to serve as
chemosensors, bioprobes, stimuli-responsive nanomaterials,
and active layers of efficient organic light-emitting diodes.12
During the course of developing click chemistry into a
powerful click polymerization, we have succeeded in prepara-
tion of linear and hyperbranched polytriazoles with advanced
properties, including AIE or aggregation-enhanced emission
(AEE) characteristics.13 However, the AIE or AEE-active
conjugated hyperbranched polytriazoles, which are expected
to perform better than the nonconjugated ones in fluorescent
sensor and bioimaging applications as well as organic light-
emitting diodes, etc.,14 are rarely reported.
enables us to postmodify it by azide−alkyne and thiol−yne
click reactions. Photoluminescence measurements showed that
hb-CPTA and its postmodified products are AEE active with
high solid state quantum yields up to 93.5%.
RESULTS AND DISCUSSION
■
In this paper, we report the preparation and postfunction-
alization of the first example of soluble AEE-active hyper-
branched conjugated polytriazole (hb-CPTA) by the facile and
efficient Cu(I)-catalyzed click polymerization of diazide BATPE
Monomer Preparation. Different from our previous A2 +
B3 strategy, we adopted an A2 + B4 monomer pairs to construct
hb-CPTA by click polymerization.15 TPE cored 1,2-bis(4-
azidophenyl)-1,2-diphenylethene (A2, BATPE) and 1,1,2,2-
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tetrakis(4-ethynylphenyl)ethane (B4, TETPE) were thus
designed and synthesized. The reaction of 1,2-bis(4-bromo-
phenyl)-1,2-diphenylethene (1) and tosylazide (2) in the
presence of n-BuLi readily furnish BATPE in satisfactory yield
(Scheme 1), whereas TETPE was prepared with following
routes: McMurry homocoupling of 4,4′-bis(trimethylsilyl)-
benzophenone (4), synthesized by Sonogashira reaction of
4,4′-dibromobenzophenone (3) and (trimethylsilyl)acetylene,
in the presence of TiCl4, and zinc powder in tetrahedrofuran
(THF) afforded TPE derivative 5. Desilylation of 5 by KOH in
methanol and THF mixture furnished TETPE as pale yellow
solid (Scheme 2). The monomer structures were confirmed by
spectroscopic analyses (see Supporting Information for detailed
characterization data; their high-resolution spectra are shown in
Table 1. Time Courses of the Click Polymerization of
BATPE and TETPE
a
b
b
no.
t (h)
yield (%)
Mw
PDI
1
2
3
4
5
6
1.0
2.0
49.6
75.2
81.6
83.7
84.4
85.3
6 500
15 900
31 100
38 900
39 500
47 100
2.35
4.33
4.36
4.73
4.64
5.22
3.0
4.0
5.0
12.0
a
Polymerizations were carried out in THF/Et3N (v/v = 10:1) mixture
at 60 °C under nitrogen using CuSO4/sodium ascorbate as catalyst
b
system; [BATPE] = [TETPE] = 0.018 M. Relative value estimated by
GPC in THF of the basis of a linear polystyrene calibration, PDI =
Mw/Mn.
1
Figures S1 and S2). The H NMR spectrum of BATPE (inset
of Figure 3B) indicated that it is composed of almost equivalent
E/Z-isomers. We have tried to separate them to obtain pure E-
or Z-BATPE but failed probably due to their high similarities in
molecular structures and polarities. Thanks to the symmetry of
TETPE, needle-shaped single crystal suitable for X-ray
structure analysis could be easily grown from its chloroform
solution by slow evaporation of solvent (Figure 1 and Table
S1), which provided a direct proof of the structure of TETPE.
dichloromethane, chloroform, and N,N-dimethylformamide
(DMF), but partially soluble in dimethyl sulfoxide (DMSO).
Meanwhile, under the same polymerization conditions, gelation
was observed within 4 h if equal molar amounts of ethynyl and
azide groups were used. These interesting results confirm the
practicability of our assumption.
Encouraged by the preliminary results and to make the click
polymerization more efficient, we thus systematically inves-
tigated its time courses. As can be seen from Table 1, the yields
and Mws of hb-CPTA increased rapidly with the reaction time
in the first 3 h. Afterward, the increase of both of them slowed
down. Thus, 5 h was adopted as the optimal reaction time. It is
worth mentioning that the click polymerization possesses
excellent repeatability, giving quite similar results under the
same polymerization conditions.
Structural Characterization. Thanks to its good solubility,
hb-CPTA was fully characterized spectroscopically, and
satisfactory analysis data corresponding to its expected
molecular structure were obtained. The IR spectra of hb-
CPTA and its monomers are shown in Figure 2. The C−H
Figure 1. ORTEP drawing of TETPE.
Click Polymerization. The difficulty in the preparation of
hyperbranched polymers is the solubility especially for the A2 +
B4 monomer strategy with equal reactive functional groups
because the gelation is an ineluctable problem. One of the
solutions is to quench the polymerization reaction before the
gel points which are unfortunately very difficult to predict and
control.16 Given the efficiency and step-growth mechanism of
Cu(I)-catalyzed azide−alkyne click polymerization,4 we as-
sumed that if equal concentrations of A2 (BATPE) and B4
(TETPE) were used, the azide groups would be consumed
rapidly during the polymerization, making the resultant
polymer end-capped with the ethynyl groups, and thus no
gelation would occur.
Figure 2. IR spectra of (A) TETPE, (B) BATPE, and (C) hb-CPTA.
We first tried the click polymerization of BATPE and TETPE
with the same concentration in the presence of the classical
CuSO4/sodium ascorbate catalyst system in THF/triethyl-
amine mixture with minimal amount of water (Scheme 3 and
Scheme S1). Delightfully, no gelation took place even the
polymerization was stirred at 60 °C for 12 h under nitrogen and
hb-CPTA, whose structure is schematically shown in Scheme 3,
with Mw of 47 100 was obtained in excellent yield (85.3%)
(Table 1, no. 6). It is worth noting that hb-CPTA is soluble in
most of common used organic solvent, such as THF,
stretching vibration of TETPE is observed at 3291 cm−1, which
becomes moderate after click polymerization, suggesting that a
large number of ethynyl groups remained on the periphery of
hb-CPTA. The azide groups of BATPE exhibit a strong
absorption band at 2122 cm−1 which almost disappeared after
reaction. The weak peak at 2107 cm−1 could be attributed to
CC stretching vibration, indicating that the hb-CPTA is end-
capped with ethynyl groups on its periphery (cf. Scheme 3).
C
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Scheme 4. Synthetic Routes for the Model Compounds (SA = Sodium Ascorbate)
NMR spectroscopy could provide more valuable information
for the illustration of the polymer structure. To facilitate the
structure characterization of hb-CPTA, model compound M1
was designed and synthesized by click reaction of 1,4-
ethynylphenyl)-1,2,2-triphenylethene (named METPE, Scheme
S2) and 1-(4-azidophenyl)-1,2,2-triphenylethene (named
MATPE, Scheme S3 under the same reaction conditions
(Scheme 4).
intensity keeps relatively strong in the hb-CPTA (1′, Figure
3D). Meanwhile, the resonance of phenyl proton ortho to the
azide groups of BATPE occurs at δ 6.72−6.78 (4), which are
well-separated and make it possible to discriminate whether the
azides are used up or not after click polymerization (Figure
3B). These resonance peaks are hardly observed in the
spectrum of hb-CPTA, indicating that azide groups were
almost consumed. By comparison with the model compound
M1, the peak at δ 8.07 (a′) in the spectrum of hb-CPTA
(Figure 3D) could be readily assigned to the proton resonance
of the formed 1,4-disubstituted 1,2,3-triazoles (Figure 3C).
Because of the electron deficiency and high polarity of triazole
unit, the resonation of its adjacent phenyl protons were shifted
down filed at δ 7.63 (b′) and 7.52 (c′) as demonstrated in the
spectrum of M1.
1
Figure 3 shows the H NMR spectra of hb-CPTA and its
monomers (TETPE and BATPE) as well as its model
compound (M1) in CDCl3. The peak (1) of the ethynyl
group of TETPE was resonates at δ 3.07 (Figure 3A), whose
Furthermore, 13C NMR spectrum of hb-CPTA shows strong
resonated peaks of ethynyl carbon atoms at δ 83.6 and 77.8
(Figure S3), which means considerable ethynyl groups were
remained in the polymer. All the other resonance peaks could
be assigned according to the 13C NMR spectrum of M1. These
results further substantiate the conclusion drawn from the IR
analysis.
Determination of Degree of Polymerization (DP).
According to the structural characterization, hb-CPTA is
composed of TPE and triazole units, and terminal ethynyl
groups (Scheme 3), which enable us to evaluate its degree of
polymerization (DP) instead of the hardly assessed degree of
branching.
Thanks to the rigid conjugated structure of hb-CPTA, the
possibility of intramolecular cyclization is believed to be
extremely low. Thus, to simplify the calculation, we assume
that no loop structures were formed during the click
polymerization. When carefully investigating the process of
click polymerization of BATPE and TETPE, we could find that,
except for the first produced triazole that accompanied by two
TPE units, one triazole formation corresponds to one TPE unit
increase. In other words, the number of TPE is one more than
that of triazole in hb-CPTA. On the basis of this finding, we
could assume that the total number of TPE units in hb-CPTA is
n, and that stemmed from TETPE is x. Then, the number of
triazole units would be n − 1, and that of TPE from BATPE is n
− x.
Accordingly, an equation could be established as follows:
At
Ap
n − 1
16x + 18(n − x)
Figure 3. 1H NMR spectra of (A) TETPE, (B) BATPE, (C) M1, and
(D) hb-CPTA in CDCl3. The solvent peaks are marked with asterisks.
=
(1)
D
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where At and Ap are the integrated areas of proton resonated
peaks of the triazole and phenyl units in hb-CPTA, respectively.
From the structure characterization, we also concluded that
almost all the azides were transformed to the triazole units.
Thus, a relationship between the numbers of triazole and the
used BATPE could be established:
postfunctionalization of hyperbranched conjugated polymers is
rare.
Here, we show examples of modification of the periphery of
hb-CPTA by the azide−alkyne and thiol−yne click reactions
(Scheme 5). Thanks to the same catalyst system, monoazide-
a
Scheme 5. Click Modification of hb-CPTA
2(n − x) = n − 1
(2)
When substituted eq 2 to eq 1, eq 3 could be deduced:
At
Ap
n − 1
17n − 1
=
(3)
As the solvent peak of CDCl3 could influence the integral of
resonance peaks of aromatic protons, the 1H NMR spectrum of
hb-CPTA in DCM-d2 was measured. As shown in Figure S4,
the integral ratio of At to Ap was obtained as 1/17.10.
Introducing this value into eq 3, the DP of hb-CPTA is
calculated to be 161, from which the number of TPE from
TETPE (x) is deduced to be 81 and that from BATPE is 80.
Thus, the number-average molecular weight of hb-CPTA (Mn)
could be derived from eq 4:
a
The spheres are symbolized as hyperbranched conjugated polymers.
functionalized poly(ethylene glycol) (PEG-N3, Scheme S4)
could be added after the click polymerization in one-pot and
PEG-functionalized hb-CPTA; i.e., hb-CPTA-A was produced
after an additional 12 h. Interestingly, hb-CPTA-A is completely
soluble in DMSO but partially in THF because of the attached
PEG segments. Furthermore, the Mw of hb-CPTA-A (204500)
is much higher than that of hb-CPTA (89 600) with the same
measurement conditions using DMF as eluent, indicating that
the PEG segments have been successfully grafted on the
periphery of hb-CPTA.
Mn = xMTETPE + (n − x)MBATPE = 67800
(4)
where MTETPE and MBATPE are the formula weights of TETPE
and BATPE, respectively.
Comparing with the Mn value estimated by GPC, the
calculated one is ca. 8 times higher (eq 5) probably because of
the globular architecture of the hyperbranched polymer, which
normally makes its molecular weight underestimated.17
Mn(NMR)
Since the thiol is a common functional group existing widely
in biomolecules, including amino acid (e.g., cysteine),
polypeptide (e.g., glutathione), and protein (e.g., bovine
serum albumin), etc., the thiol−yne click reaction has special
potential in biological fields and thus drawn much attention in
recent years.21 Attracted by this efficient click reaction,22 we
employed pentanethiol as a representative thiol compound to
end-cap hb-CPTA. The alkyl sulfide-functionalized hb-CPTA,
i.e., hb-CPTA-T, was thus produced after they reacted in DMF
at 80 °C for 24 h in the presence of AIBN, a radical initiator
(Scheme 5). The solubility of the production is even better
than its parent polymer probably due to the alkyl chain
attachment. Furthermore, the enhancement of Mw (67 400)
also suggests the success of the thiol−yne reaction.
Spectroscopic structural characterization of hb-CPTA-A and
hb-CPTA-T could give a clearer vision of the click reactions. As
shown in Figure 4, the C−H and CC stretching vibrations
of hb-CPTA disappeared in the IR spectra of hb-CPTA-A and
hb-CPTA-T, indicating that all the remained ethynyl groups
have been consumed after click reactions. Meanwhile, the
strengthened absorption bands at 2869 and 1108 cm−1 for hb-
CPTA-A and 2925 and 2856 cm−1 for hb-CPTA-T, which are
assigned to the PEG and alkyl chain vibrations, respectively,
verified that these segments have been successfully grafted onto
the peripheries of hb-CPTA.
67800
8500
=
= 7.98
Mn(GPC)
(5)
In addition, based on the calculated results, the theoretical
ratio of the number of proton in remained triple bonds to that
in triazole could be deduced by eq 6.
N
Nt
81 × 4 − 80 × 2
e
=
= 1.025
160
(6)
where Ne and Nt are the number of remained triple bonds and
formed triazole units. The value was thus obtained as 1.025,
whereas the experimental ratio from the integrated areas of
corresponding peaks in the spectrum of hb-CPTA is 0.96
(Figure S4). These two ratios are quite close within the
experimental error, verifying that our assumption is reasonable
and the DP calculation is reliable.
Clickable Modification. Surface modification has been a
hot topic in nano- and biomaterial areas because properties of
the materials are related to or even dependent on their surface
composition.18 One remarkable feature of hyperbranched
polymers is their numerous terminal functional groups on the
periphery (surface) which enable to generate versatile
functions. For example, attaching of water-soluble segments
or biomolecules could make hyperbranched polymers amphi-
philic or biocompatible and facilitate their practical applications.
The hb-CPTA is end-capped with ethynyl groups according
to its structural characterization, which makes it promising to
modify by various acetylene reactions, such as azide−alkyne
and thiol−yne click reactions.19 These reactions have been
utilized to modify the periphery of hyperbranched polymers
with partially or nonconjugated structures.20 However, the
Similar results could be obtained from the NMR spectra of
the polymers. To facilitate the structural characterization of hb-
CPTA-A and hb-CPTA-T, their model compounds M2 and M3
were synthesized under the same reaction conditions (Scheme
4). Figure 5 shows the 1H NMR spectra of hb-CPTA-A and its
parent polymer hb-CPTA as well as its model compound M2.
The ethynyl protons of hb-CPTA resonated at δ 3.07 are hardly
E
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The complete consumption of ethynyl groups in the thiol−
yne click reaction of hb-CPTA and pentanethiol was also
1
proven by the H NMR spectrum. As can be seen from Figure
6, the resonance of ethynyl protons at δ 3.07 could never be
Figure 4. IR spectra of (A) hb-CPTA, (B) hb-CPTA-A, and (C) hb-
CPTA-T.
1
Figure 6. H NMR spectra of (A) hb-CPTA, (B) M3, and (C) hb-
CPTA-T in CDCl3. The solvent peaks are marked with asterisks.
found in the spectrum of hb-CPTA-T. The new peaks at δ 6.66,
6.35, and 6.21 may be stemmed from the vinyl groups,23
indicating that only one thiol was added to one alkyne. This is
an interesting and abnormal result because it was reported that
the radical-mediated thiol−yne click reaction allows two thiols
to add to one alkyne.21,22 In order to prove our assumption, the
model reaction was carried out, and only was sole product of
M3 obtained (Scheme 4). Moreover, the increase of the
amount of AIBN and pentanethiol did not affect the
1
composition of product. In the H NMR spectrum of M3,
1
Figure 5. H NMR spectra of (A) hb-CPTA, (B) M2, and (C) hb-
the integrated area of the vinyl protons is equal to that of the
alkyl ones adjacent to the sulfur atom, further substantiating
that one thiol was added to one alkyne. The reason could be
that the conjugation of the hb-CPTA deactivates the vinyl
sulfide group and makes further addition quite difficult. It is
worth noting that the E/Z isomers of generated vinyl units of
hb-CPTA-T could be identified clearly with the help of the
spectrum of M3, which was calculated to be 85/15.23 The 13C
NMR of hb-CPTA-T (Figure S5) also confirmed that hb-CPTA
could be efficiently functionalized by the radical-mediated
thiol−yne click reaction.
Thermal Stability. The thermal properties of three
polytriazoles were evaluated by thermogravimetric analysis
(TGA) under nitrogen (Figure 7). The hb-CPTA is thermally
stable and loses 5% of its weight at temperature (Td) of 363.3
°C. More importantly, the char yield of hb-CPTA was as high
as 74.8% at 800 °C, which make it promising carbon sources for
graphene, carbon nanotube, etc. Such a high Td value and char
CPTA-A in CDCl3. The solvent peaks are marked with asterisks.
observed in the spectrum of hb-CPTA-A. Meanwhile, new
peaks at δ 4.55−3.34, which could be assigned to the PEG
segments according to that of M2, were emerged. Furthermore,
the resonance of protons from the new formed triazole
appeared at δ 7.94 (b′), indicating that the ethynyl groups on
the periphery of hb-CPTA have been completely transformed
into triazoles and the efficiency of click reaction reaches 100%.
The 13C NMR spectra (Figure S5) also showed that the
ethynyl carbon atoms of hb-CPTA resonated at δ 83.6 and 77.8
completely disappeared after reaction, and new peaks emerged
at δ 71.9−50.3, which are assigned to the resonance of carbon
from PEG segment. These results confirm again that the hb-
CPTA has been completely modified on its periphery via
azide−alkyne click reaction.
F
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the contained TPE units, the THF solutions of hb-CPTA, hb-
CPTA-A, and hb-CPTA-T are emissive with maximum peaks at
512, 509, and 524 nm, respectively, which are also redder than
that of our previously reported partially conjugated hyper-
branched polytriazoles (490 nm).13a
TPE is a typical AIE-active luminogen, whereas the hb-
CPTA, hb-CPTA-A, and hb-CPTA-T containing TPE units are
AEE-active. The PL spectra of hb-CPTA in THF/water
mixtures with different water fraction (fw) are shown in Figure
9A as an example. The UV spectra of hb-CPTA in pure THF
Figure 7. TGA thermograms of hb-CPTA, hb-CPTA-A, and hb-
CPTA-T recorded under nitrogen at a heating rate of 20 °C/min.
yield might be attributed to the aromatic conjugated structure
of and readily cross-linked triple bonds in hb-CPTA.24
The Td values of hb-CPTA-A and hb-CPTA-T lowered
compared to that of hb-CPTA, but they are still higher than
340.0 °C. Their char yields at 800 °C, however, decreased
dramatically to 48.8 and 58.2%, respectively, owing to the
involved PEG and alkyl chains, which could be pyrolyzed at
elevated temperature.
Aggregation-Enhanced Emission. We first measured the
absorption spectra of these polytriazoles (Figure S6). hb-CPTA
exhibits two absorption peaks at 282 and 340 nm. Furthermore,
its maximum absorption is bathochromically shifted by 7 nm
compared to our previously reported TPE containing partially
conjugated hyperbranched polytriazoles due to its fully
conjugated feature.13a Meanwhile, the absorption of hb-
CPTA-A is peaked at 287 and 340 nm, indicating that the
formed triazole units exert little influence over the polymer
conjugation, whereas the introduction of the vinyl sulfide
groups to hb-CPTA greatly change the absorption behavior. hb-
CPTA-T exhibits only one absorption peak at 328 nm, but its
spectrum is tailed to a longer wavelength compared to that of
hb-CPTA and hb-CPTA-A.25 The trend is also observed in
their photoluminescence (PL) spectra (Figure 8). Thanks to
Figure 9. (A) PL spectra of hb-CPTA in the THF/water mixtures with
different water fraction (fw). Concentration: 10 μg/mL; excitation
wavelength: 340 nm. (B) Changes in the quantum yields (ΦF) of hb-
CPTA, hb-CPTA-A, and hb-CPTA-T with fw in the THF/water
mixtures; ΦF was estimated using quinine sulfate in 0.05 M H2SO4
(ΦF = 54.6%) as standard.
and THF/water mixtures show similar profiles, except for the
spectral tails in the long wavelength region which are ascribed
to the formation of aggregates with high fw (Figure S7). When
excited at 340 nm, the PL intensity starts to increase even at a
low fw of 10% and keeps to rise with gradual addition of water
but without a noticeable shift in the emission maximum. The
PL spectra of hb-CPTA-A and hb-CPTA-T in THF/water
mixtures share similar processes (Figure S8). Interestingly, due
to hydrophilic property of PEG containing hb-CPTA-A which
is verified by the contact angle measurement (Figure S9), its
water solubility is enhanced. Thus, its PL intensity decreases
when 10% water is added. Afterward, its emission is slowly
intensified until the fw higher than 50%.
Figure 8. Normalized PL spectra of hb-CPTA, hb-CPTA-A, and hb-
CPTA-T in THF. Concentration: 10 μg/mL; excitation wavelength:
340 nm.
The fluorescence quantum yields (ΦF) of three polymers in
the THF/water mixtures were measured, and their changing
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trajectories are shown in Figure 9B. The ΦF values of hb-CPTA,
hb-CPTA-A, and hb-CPTA-T in THF are 4.31, 5.04, and
3.83%, respectively. Thanks to the rigid structures, the ΦF
values of hb-CPTA and hb-CPTA-T increase linearly with
gradual addition of water, whereas the ΦF value of hb-CPTA-A
decreases to 4.57% in THF/water mixture with an fw of 10%
and then increases swiftly after fw > 50%. At an fw of 90%, the
ΦF values of hb-CPTA, hb-CPTA-A, and hb-CPTA-T are
increased to 23.83, 33.48, and 20.01%, respectively. It is worth
noting that the absolute ΦF values of their thin films measured
by a calibrated integrated sphere were recorded to be 65.2, 93.5,
and 60.2%, respectively, which enable them to find broad
application in optoelectronic and biological fields.
the polymers, and the size distribution of the particles comes
from the distribution of molecule weights. Thanks to the
contained TPE units, the nanoparticles are all emissive. As can
be seen from Figure 10, the particles with bluish-green (for hb-
CPTA and hb-CPTA-A in Figures 10B and 10D, respectively)
to green (for hb-CPTA-T in Figure 10F) emission just like an
array of stars in the sky could be clearly observed upon
excitation with a UV light. Because of the rigid conjugated
structure, the single-molecular fluorescent nanoparticles of the
polymers may hold good shape persistence with suitable sizes
(around 100 nm) for potential biological applications, such as
drug carrier and fluorescence tracing.
Polymer Morphology. Our synthesized AEE-active hyper-
branched polymers possess rigid structures; thus, their
morphology was examined by the transmission electron
microscope (TEM) and fluorescence microscope. The samples
were prepared directly by drop-coating the dilute chloroform
solutions (0.1 μg/mL) of three polytriazoles onto copper grids.
As shown in Figure 10, the particle sizes of hb-CPTA are
CONCLUSION
■
Soluble ethynyl-capped hyperbranched conjugated polytriazole
hb-CPTA with high molecular weight was first constructed in
high yield via Cu(I)-catalyzed azide−alkyne click polymer-
ization of BATPE and TETPE in equal concentrations. Thanks
to the large amount of ethynyl groups on the periphery, hb-
CPTA could be facilely modified by alkyne-based click
reactions. The PEG segment was facilely introduced onto the
polymer via azide−alkyne click reaction in one pot, whereas
pentanethiol could be efficiently reacted with the remained
ethynyl group of hb-CPTA through radical-mediated thiol−yne
click reaction. Furthermore, one thiol was found to react with
only one ethynyl group probably due to the conjugation effect
of the polymer. The polytriazoles are thermal stable and hb-
CPTA shows high char yield of 74.8% at 800 °C. The polymers
are emissive in their solutions, and their luminescence
intensified in aggregate or solid states, demonstrating a unique
AEE feature. Thanks to the rigid structures, the polymers can
form unimolecular nanoparticles from their dilute solutions
with diameters around 100 nm.
The above results indicate that hb-CPTA is a novel clickable
fluorescent platform, onto which various functional groups or
biomolecules could be grafted efficiently, which will be sure to
find wide applications in biological and optoelectronic fields,
etc.
EXPERIMENTAL SECTION
■
Materials. Unless otherwise stated, all the chemicals used in this
study were purchased from Acros or Alfa and used as received without
further purification. The radical initiator 2,2′-azobis(2-methylpropioni-
trile) (AIBN) was recrystallized from ethanol before use. Tetrahy-
drofuran (THF) was distilled from sodium benzophenone ketyl under
nitrogen immediately prior to use. Triethylamine (TEA) was distilled
and dried over potassium hydroxide. DMF was extra-dry grade.
Figure 10. TEM and fluorescent images of (A, B) hb-CPTA, (C, D)
hb-CPTA-A, and (E, F) hb-CPTA-T. Samples prepared from their
chloroform solution directly, concentration: 0.1 μg/mL. The
fluorescent images of the nanoparticles were taken under a
fluorescence microscope with a 337 nm excitation.
1
Instruments. H and 13C NMR spectra were measured on Bruker
DMX-500 and Varian NMR-300 spectrometer in CDCl3 or CD2Cl2
using tetramethylsilane (TMS; δ = 0) as internal reference. FT-IR
spectra were recorded on a Bruker Vector 22 spectrometer. Melting
points (Tm) were measured on a Perkin-Elmer DSC-7 under nitrogen
at a heating rate of 10 °C/min. Elemental analysis was performed on a
ThermoFinnigan Flash EA1112. MALDI-TOF mass spectra were
taken on a GCT Premier CAB048 mass spectrometer. Single-crystal X-
ray diffraction intensity data were collected at 173 K on an Xcalibur,
Sapphire3, Gemini ultra kappa diffractometer with graphite mono-
chromated Cu Kα X-ray radiation. Empirical absorption correction
was done by using spherical harmonics, implemented in SCALE3
ABSPACK scaling algorithm. CrysAlisPro, Agilent Technologies,
Version 1.171.35.19. The structure solution was measured using XS
(Sheldrick 2008), and the structure refinement was conducted using
XL (Sheldrick 2008) suite of X-ray programs. Relative number (Mn)
and weight-average (Mw) molecular weights and polydispersity indices
(PDI) of the polymers were estimated by a Waters PL-GPC-50 gel
relatively uniform with diameters around 70−100 nm (Figure
10A). After postclick reactions, the particle sizes increase
slightly, to 90−120 nm for hb-CPTA-A (Figure 10C) and 80−
100 nm for hb-CPTA-T (Figure 10E). The increase of the
particle sizes of hb-CPTA-A and hb-CPTA-T stemmed from
the attached PEG segments and alkyl chains, respectively.
Their morphology in concentrated solutions (1.0 μg/mL)
was tested as well. Though few polymer aggregates were
observed, a large number of particles were found to have sizes
identical to those from dilute solutions (Figure S10), suggesting
that nanoparticles are probably formed from an unimolecule of
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permeation chromatography (GPC) system equipped with refractive
index (RI) detector, using a set of monodisperse polystyrenes or
poly(methyl methacrylate) (PMMA) as calibration standards and
THF or DMF as the eluents at a flow rate of 1.0 mL/min. Thermal
stabilities were evaluated by measuring thermogravimetric analysis
(TGA) thermograms on a Perkin-Elmer TGA 7 under dry nitrogen at
a heating rate of 20 °C/min. UV−vis spectra were measured on a
Varian VARY 100 Bio UV−vis spectrophotometer. Photolumines-
cence (PL) spectra were recorded on a Shimadzu RF-5301PC
spectrofluorophotometer. Fluorescence quantum yields (ΦF) were
estimated using quinine sulfate in 0.05 M sulfuric acid (ΦF = 54.6%) as
standard. The absorbance of the solutions was kept around 0.05 to
avoid internal filter effect. The ΦF of spin-coated thin films of the
polymers was recorded by a calibrated integrating sphere on a Photon
Technology International time-resolved fluorescence spectroscopy.26
Contact angle was measured on DSA100. The morphology of the
polymers was checked by a JEOL JEM-1200EX electron microscope
(TEM, 80 kV). Fluorescence micrographs were taken on a Zeiss
Axiovert 200 microscope equipped with a 100× oil immersion
objective.
For the AEE measurement, a stock solution of a polymer in THF
(0.1 mg/mL) was prepared. Aliquots of this stock solution were
transferred into volumetric flasks (10 mL), into which appropriate
volumes of THF and water were added dropwise under vigorous
stirring to give 10 μg/mL solutions with different water contents (fw =
0−90%). UV and PL spectra were measured immediately after the
solutions were prepared.
Monomer Preparation. The synthetic routes to TETPE and
BATPE are shown in Scheme 1. One of the starting materials of 1,2-
bis(4-bromophenyl)-1,2-diphenylethene (4) was prepared according
to our previously published procedures.13a
organic layer was combined and washed with water and brine and then
dried over MgSO4. After filtration and solvent evaporation, the crude
product was purified by a silica gel column chromatography using
petroleum ether/DCM (100:1 by volume) mixture as eluent. Pale
yellow solid of TETPE was obtained in 86.8% yield (2.231 g). Tm:
155.5 °C. IR (KBr) ν (cm−1): 3291 (C−H stretching), 3032, 2104
(CC stretching), 1600, 1499, 1402, 1225, 1109, 1016, 841, 737, 642.
1H NMR (500 MHz, CDCl3) δ (TMS, ppm): 7.24 (d, 8H), 6.93 (d,
8H), 3.07 (s, 4H, HC). 13C NMR (125 MHz, CDCl3) δ (ppm):
143.3, 140.9, 131.8, 131.3, 120.7, 83.5 (C−Ar), 77.9 (C−H).
Anal. Calcd for C34H20: C, 95.30; H, 4.70. Found: C, 94.96; H, 4.75.
HRMS (MALDI-TOF), m/z calcd C34H20: 428.1565; found:
428.1567.
1,2-Bis(4-azidophenyl)-1,2-diphenylethene (BATPE). Into a
250 mL round-bottom flask was placed 1,2-bis(4-bromophenyl)-1,2-
diphenylethene (4, 3.677 g, 7.5 mmol). The flask was evacuated under
vacuum and flushed with dry nitrogen three times. After THF (80 mL)
was added, the solution was cooled down to −78 °C, into which n-
BuLi (11.25 mL, 18 mmol, 1.6 M in hexane) was added dropwise. The
mixture was kept at −78 °C for 2 h and then 3.550 g (18 mmol) of 4-
methylbenzenesulfonyl azide (5, see the detailed procedure in the
Supporting Information) dissolved in 20 mL of THF was added into
the flask dropwise. After reacting at −78 °C for 1 h, the mixture was
warmed slowly to room temperature and stirred overnight. Afterward,
saturated NH4Cl solution (100 mL) was added to quench the reaction,
and THF was evaporated. Then, DCM was added to extract the
product three times. The organic layer was combined and washed with
water and brine and dried over MgSO4. After filtration and solvent
evaporation, the crude product was purified by a silica gel column
chromatography using petroleum ether as eluent. Pale yellow solid of
BATPE was obtained in 71.3% yield (2.216 g). Tm: 118.7 °C. IR (KBr)
ν (cm−1): 3054, 2122 (N3 stretching), 1600, 1501, 1291, 1181, 1112,
4,4′-Bis(trimethylsilyl)benzophenone (2). Into a 500 mL
round-bottom flask was added PdCl2(PPh3)2 (561.5 mg, 0.8 mmol),
CuI (304.8 mg, 1.6 mmol), PPh3 (629.5 mg, 2.4 mmol), and 4,4′-
dibromobenzophenone (1) (6.8 g, 20 mmol), and then a mixture of
THF/TEA (1:1 v/v) (200 mL) under nitrogen. After the solution
became homogeneous, trimethylsilylacetylene (7.07 mL, 50 mmol)
was injected. The solution was allowed to react at 50 °C for 24 h, after
which the formed solid was removed by filtration and washed with
diethyl ether. The filtrate was concentrated by a rotary evaporator, and
the crude product was purified by a silica gel column chromatography
using petroleum ether/ethyl acetate mixture (100:1 by volume) as
1
832, 754, 700. H NMR (500 MHz, CDCl3) δ (TMS, ppm): 7.12−
7.08 (m, 6H), 6.99 (m, 8H) 6.78−6.74 (q, 4H, Ar−H proton ortho to
the azido group). 13C NMR (125 MHz, CDCl3) δ (ppm): 143.3,
140.5, 140.2, 138.2−138.1, 132.8, 131.3, 128.0−127.8, 126.8−126.7,
118.5−118.4. Anal. Calcd for C26H18N6: C, 75.35; H, 4.38; N, 20.28.
Found: C, 75.41; H, 4.52; N, 20.37. HRMS (MALDI-TOF), m/z calcd
C26H18N6: 414.1593; found: 414.1593.
Polymer Synthesis. hb-CPTA was synthesized via the well-
established Cu(I)-catalyzed click polymerization (Scheme S1) of
diazide BATPE (A2) and tetrayne TETPE (B4) with the same
concentration.
1
eluent. White solid of 2 was obtained in 89.7% yield (6.720 g). H
NMR (300 MHz, CDCl3) δ (TMS, ppm): 7.69 (d, 4H), 7.54 (d, 4H),
0.27 (s, 18H). 13C NMR (75 MHz, CDCl3) δ (ppm): 195.3, 136.8,
132.0, 129.9, 127.6, 104.1, 98.2, and −0.03.
Click Polymerization. Into a 25 mL Schlenk tube was placed
equivalent molar amount of BATPE (41.4 mg, 0.1 mmol) and TETPE
(42.9 mg, 0.1 mmol). After being evacuated and refilled with dry
nitrogen three times, THF (5 mL) and TEA (0.5 mL) were injected
into the tube. When the monomers were completely dissolved, freshly
prepared aqueous solutions of sodium ascorbate (1 M, 40 μL, 10 mol
% of ethynyl group) and CuSO4 (1 M, 20 μL, 5 mol % of ethynyl
group) were added subsequently under vigorous stirring. The reaction
mixture was stirred at 60 °C under nitrogen for 5 h. After cooled to
room temperature, the resultant mixture was diluted with 5 mL of
THF and then added dropwise into 300 mL of methanol acidified with
1 mL of a saturated NH4Cl solution through a cotton filter under
stirring. The precipitate was allowed to stand for 1 h and then filtered.
The obtained polymer was dissolved again in chloroform and washed
with water three times to remove the residual catalysts. The polymer
solution was dried over MgSO4, concentrated, and precipitated into
300 mL of hexane. The precipitate was allowed to stand again for 1 h,
collected by filtration, and dried over vacuum at room temperature to a
constant weight. Yellow solid of hb-CPTA was obtained in 84.4% yield
(71.2 mg). Mw 39 500; PDI 4.64 (THF as the eluent). Mw 89 600; PDI
6.67 (DMF as the eluent). IR (KBr) ν (cm−1): 3294 (C−H
stretching), 3052, 2107 (CC stretching), 1602, 1516, 1495, 1226,
1,1,2,2-Tetrakis(4-(trimethylsilylethynyl)phenyl)ethene (3).
Into a 500 mL two-necked round-bottom equipped with a reflux
condenser was placed 2 (5.994 g, 16 mmol) and zinc dust (3.137 g, 48
mmol). The flask was evacuated under vacuum and flushed with dry
nitrogen three times. After THF (200 mL) was added, the mixture was
cooled down to 0 °C, into which TiCl4 (4.552 g, 2.64 mL, 24 mmol)
was added dropwise, then warmed slowly to room temperature, and
refluxed overnight. Afterward, the reaction mixture was cooled to
room temperature, filtered, and washed with diethyl ether. After most
of the solvent was evaporated, the filtrate was poured into 1 M HCl
solution (100 mL) and extracted by DCM three times. The organic
layer was combined and washed with brine and water and then dried
over MgSO4. After filtration and solvent evaporation, the crude
product was purified by a silica gel column chromatography using
petroleum ether as eluent. Pale yellow solid of 3 was obtained in 75.4%
yield (4.326 g). 1H NMR (300 MHz, CDCl3) δ (TMS, ppm): 7.18 (d,
8H), 6.86 (d, 8H), 0.22 (s, 36H). 13C NMR (75 MHz, CDCl3) δ
(ppm): 143.2, 140.9, 131.7, 131.3, 121.7, 105.0, 95.0, and 0.07.
1,1,2,2-Tetrakis(4-ethynylphenyl)ethane (TETPE). Into a 500
mL round-bottom flask was placed 3 (4.304 g, 6 mmol) and THF
(100 mL). Then KOH (5.376 g, 96 mmol) dissolved in methanol (100
mL) was added. The mixture was stirred at room temperature
overnight. After most of the solvent was evaporated, 1 M HCl solution
(100 mL) was added and then extracted by DCM three times. The
1
1033, 841, 758, 701. H NMR (500 MHz, CDCl3) δ (TMS, ppm):
1
8.07, 7.63, 7.52, 7.23−6.97, 3.07−3.02 (HC). H NMR (500 MHz,
CD2Cl2) δ (TMS, ppm): 8.02, 7.53, 7.41, 7.14−6.86, 3.00−2.96
(HC). 13C NMR (125 MHz, CDCl3) δ (ppm): 148.0, 144.1,
143.8−143.5, 142.7, 141.2, 140.7, 140.5, 135.4, 135.2, 132.7, 132.0−
I
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131.8, 131.3, 128.8, 128.3, 128.0, 127.3, 125.4, 120.7, 120.6, 120.0,
119.8, 117.6, 83.6 (C−Ar), 77.8 (C−H).
saturated NH4Cl solution through a cotton filter under stirring. The
precipitate was allowed to stand for 1 h and then filtered. The obtained
polymer was dissolved again in a proper amount of chloroform, dried
over MgSO4, and then precipitated into 300 mL of hexane. The
precipitate was allowed to stand again for 1 h, collected by filtration,
washed with methanol three times, and dried over vacuum at room
temperature to a constant weight. Pale yellow solid of hb-CPTA-A
(115.0 mg) was obtained. Mw 204 500; PDI 6.81 (DMF as the eluent).
IR (KBr) ν (cm−1): 3053, 2869, 1605, 1515, 1492, 1350, 1228, 1108,
Preparation of Model Compounds. The detailed synthetic
procedures for the starting materials of 1-(4-ethynylphenyl)-1,2,2-
triphenylethene (METPE) (Scheme S2) and 1-(4-azidophenyl)-1,2,2-
triphenylethene (MATPE) (Scheme S3) are given in the Supporting
Information.
1,4-Bis(4-(1,2,2-triphenylvinyl)phenyl)-1H-1,2,3-triazole
(M1). The main procedures of the preparation of model compound
M1 are similar to those of hb-CPTA. Equal amounts of METPE (71.3
mg, 0.2 mmol) and MATPE (74.7 mg, 0.2 mmol) were used as
reactants. After the reaction mixture was stirred at room temperature
under nitrogen overnight, THF and TEA were evaporated and the
residue was extracted with DCM. The organic layer was washed
sequentially with saturated NH4Cl solution, water, and brine and then
dried over MgSO4. After filtration and solvent evaporation, the crude
product was purified by a silica gel column using DCM as eluent.
White solid of M1 was obtained in 82.4% yield (120.3 mg). IR (KBr) ν
(cm−1): 3053, 1601, 1516, 1491, 1231, 1031, 823, 758, 700. 1H NMR
(500 MHz, CDCl3) δ (TMS, ppm): 8.02 (s, 1H), 7.60 (d, 2H), 7.48
(d, 2H), 7.17 (d, 2H), 7.10 (m, 20H), 7.03 (m, 12H). 13C NMR (125
MHz, CDCl3) δ (ppm): 148.2, 144.6, 144.0, 143.66, 143.6, 143.5,
143.3, 143.26, 143.15, 142.3, 141.4, 140.4, 139.4, 135.0, 132.7, 131.9,
131.4−131.26, 128.2, 128.0, 127.9, 127.8, 127.76, 127.7, 126.9, 126.8,
126.76, 126.6, 126.57, 126.5, 125.2, 119.7, 117.4.
1
1035, 843, 762, 703. H NMR (500 MHz, CDCl3) δ (TMS, ppm):
8.11, 7.94, 7.61−7.52, 7.15−7.04, 4.55, 3.88, 3.59, 3.34. 13C NMR (125
MHz, CDCl3) δ (ppm): 148.1, 147.4, 144.0−143.2, 142.7, 140.7,
135.3, 132.6, 132.1−131.9, 131.3, 128.3, 128.0, 127.3, 125.6−125.2,
121.1, 119.7, 117.6, 71.9, 70.5, 69.6, 59.0, 50.3.
Modification via Thiol−Yne Click Reaction. Pentanethiol was
adopted as a representative thiol compound to modify hb-CPTA.
Into a 25 mL Schlenk tube were placed hb-CPTA (50.0 mg) and
AIBN (3.3 mg, 0.02 mmol). After being evacuated and refilled with dry
nitrogen three times, DMF (5 mL) was injected into the tube. When
the polymer was completely dissolved, pentanethiol (41.7 mg, 49 μL,
0.4 mmol) was added via a syringe. The reaction mixture was stirred at
80 °C under nitrogen for 24 h. After cooled to room temperature, the
resultant mixture was diluted with 5 mL of THF and then added
dropwise into 300 mL of methanol through a cotton filter under
stirring. The precipitate was allowed to stand for 1 h and then filtered.
The obtained polymer was dissolved again in a proper amount of
chloroform, dried over MgSO4, and precipitated into 300 mL of
hexane. The precipitate was allowed to stand again for 1 h, collected by
filtration, and dried over vacuum at room temperature to a constant
weight. Orange-yellow solid of hb-CPTA-T (65.0 mg) was obtained.
Mw 67 400; PDI 5.90 (THF as the eluent). IR (KBr) ν (cm−1): 3022,
1-(Poly(ethylene glycol) monomethyl ether)-4-(4-(1,2,2-
triphenylvinyl)phenyl)-1H-1,2,3-triazole (M2). The main proce-
dure of the preparation of model compound M2 was synthesized from
METPE and PEG-N3 by the similar procedures of M1, during which
excess amount of METPE was used to facilitate the purification. The
crude product was purified by a silica gel column using ethyl acetate as
eluent. Pale yellow solid of M2 was obtained in 74.2% yield (108.5
mg). IR (KBr) ν (cm−1): 3054, 2872, 1598, 1491, 1449, 1355, 1255,
1
2925, 2856, 1593, 1516, 1493, 1228, 1032, 841, 702. H NMR (500
MHz, CDCl3) δ (TMS, ppm): 8.05, 7.62, 7.52, 7.15−6.97, 6.66, 6.35,
6.21, 2.76, 1.67, 1.35, 0.89. 13C NMR (125 MHz, CDCl3) δ (ppm):
148.2, 144.0, 142.7, 142.1, 141.9, 140.7, 135.5, 135.4, 135.3, 132.8−
132.6, 132.1, 131.8, 131.3, 128.3, 128.1, 128.0, 127.3, 126.2, 125.6−
125.2, 124.9, 120.0, 119.7, 117.6−117.5, 32.6, 31.0, 29.2, 22.3, 14.0.
1
1109, 1035, 853, 759, 702. H NMR (500 MHz, CDCl3) δ (TMS,
ppm): 7.92 (s, 1H), 7.57 (d, 2H), 7.03 (m, 17H), 4.54 (t, 2H), 3.87 (t,
2H), 3.59 (m, 24H), 3.51 (m, 2H), 3.34 (m, 3H). 13C NMR (125
MHz, CDCl3) δ (ppm): 147.4, 143.6−143.5, 141.2, 140.4, 131.7,
131.3, 131.26, 128.7, 127.7−127.6, 126.5−126.4, 124.9, 120.9, 71.8,
70.5−70.4, 69.5, 59.0, 50.3.
ASSOCIATED CONTENT
* Supporting Information
■
Pentyl(4-(1,2,2-triphenylvinyl)styryl)sulfane (M3). Into a 25
mL Schlenk tube was placed METPE (71.3 mg, 0.2 mmol) and AIBN
(4.0 mg, 0.024 mmol, 5 mol % of thiol). After being evacuated and
refilled with dry nitrogen three times, DMF (5 mL) was injected into
the tube. When the reactants were completely dissolved, pentanethiol
(50.0 mg, 59 μL, 0.48 mmol) was added using a syringe. The reaction
mixture was then stirred at 80 °C under nitrogen for 24 h. DMF was
evaporated, and the crude product was purified by a silica gel column
using petroleum ether as eluent. All emissive products were collected
and pale yellow solid of M3 was obtained in 85.2% yield (78.5 mg). IR
(KBr) ν (cm−1): 3022, 2925, 2857, 1593, 1494, 1270, 1028, 932, 699.
1H NMR (500 MHz, CDCl3) δ (TMS, ppm): 7.22 (d, Ar−H proton
adjacent to the Z-vinylene unit) and 6.92 (d, Ar−H proton adjacent to
the E-vinylene unit) (2H), 7.10−6.99 (m, 17H), 6.62 (d, =C−H
proton from the E-vinylene unit) and 6.29 (d, =C−H proton from the
Z-vinylene unit) (1H), 6.33 (d, =C−H proton from the E-vinylene
unit) and 6.16 (d, =C−H proton from the Z-vinylene unit) (1H), 2.73
(t, 2H), 1.65 (m, 2H), 1.34 (m, 4H), 0.88 (t, 3H). 13C NMR (125
MHz, CDCl3) δ (ppm): 143.8, 143.7, 142.3, 142.0, 140.9, 140.7, 135.2,
131.7, 131.5, 131.4, 128.0, 127.8−127.7, 127.5, 126.5−126.4, 125.2,
125.0, 124.8, 32.7, 31.1, 29.2, 22.4, 14.1.
Modification via Azide−Alkyne Click Reaction. Monoazide-
functionalized poly(ethylene glycol) (PEG-N3, Scheme S4 and the
detailed synthetic procedures are given in the Supporting Information)
was used as the modification agent.
After the polymerization mixture of BATPE and TETPE was stirred
at 60 °C for 5 h, a THF solution of PEG-N3 (1 mL, 150 mg, about 0.4
mmol) was injected into the tube. The resultant mixture was then
stirred at 60 °C for an additional 12 h. After cooled to room
temperature, the resultant mixture was diluted with 5 mL of THF and
then added dropwise into 300 mL of methanol acidified with 1 mL of a
S
Scheme of click polymerization; detailed procedures and
characterization data for PEG-N3, METPE, and MATPE;
crystal data and structure refinement for TETPE; HRMS
1
spectra of TETPE and BATPE; H NMR spectra of hb-CPTA
in DCM-d2; 13C NMR spectra of monomers, model
compounds, and polymers; normalized UV spectra of the
polymers in THF; UV and PL spectra for the polymers in
THF/water mixtures; contact angle results; TEM images of
samples made from chloroform solution with concentration of
1.0 μg/mL. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: qinaj@zju.edu.cn (A.Q.); sunjz@zju.edu.cn (J.Z.S.);
tangbenz@ust.hk (B.Z.T.).
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Prof. Yuguang Ma and Dr. Ping Lu for the
measurement of the solid-state quantum yields. This work was
partly supported by the Natural National Science Foundation
of China (21174120, 21074113, 20974028, and 20974098), the
Ministry of Science and Technology of China
(2009CB623605), the Research Grants Council of Hong
J
dx.doi.org/10.1021/ma3017037 | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
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