Multicomponent Polycoupling of Internal Diynes, Aryl Diiodides, and Boronic Acids to Functional Poly(tetraarylethene)s

Article abstract of DOI:10.1021/acs.macromol.5b01946

This paper describes the development of a new three-component polymerization route to functional poly(tetraarylethene)s (PTAEs). The polycoupling reactions of internal diynes, aryl diiodides, and arylboronic acids proceed smoothly in the presence of PdCl₂ and NaF at 70 °C in dimethylformamide, generating PTAEs with promising molecular weights in high yields from different monomers. Most of the PTAEs are soluble in common organic solvents and are thermally stable. Some of the PTAEs exhibit the phenomenon of aggregation-induced emission: their light emission in solution is enhanced by aggregate formation. The tetraphenylethene-containing PTAE can function as a fluorescent chemosensor for detecting Ru³⁺ ions with high sensitivity and specificity. It is also a promising material for the fabrication of fluorescent pattern by photolithography process. All the PTAEs possess good film-forming ability and their thin films exhibit high refractive index (RI = 1.7751-1.6382) at 632.8 nm, whose values are higher than those of commercial polymers such as polycarbonate and polystyrene.

Full text of DOI:10.1021/acs.macromol.5b01946

Article
pubs.acs.org/Macromolecules
Multicomponent Polycoupling of Internal Diynes, Aryl Diiodides, and
Boronic Acids to Functional Poly(tetraarylethene)s
†
,‡
‡
†,‡
,†,‡,§
Yajing Liu, Jesse Roose, Jacky W. Y. Lam, and Ben Zhong Tang*
†
HKUST-Shenzhen Research Institute, No. 9 Yuexing first RD, South Area, Hi-tech Park, Nanshan, Shenzhen 518057, China
‡
Department of Chemistry, Hong Kong Branch of National Engineering Research Center for Tissue Restoration Reconstruction,
Division of Life Science, State Key Laboratory of Molecular Neuroscience, Institute for Advanced Study, Institute of Molecular
Functional Materials, and Division of Biomedical Engineering, The Hong Kong University of Science and Technology, Clear Water
Bay, Kowloon, Hong Kong, China
§
Guangdong Innovative Research Team, SCUT-HKUST Joint Research Laboratory, State Key Laboratory of Luminescent Materials
and Devices, South China University of Technology, Guangzhou 510640, China
*
S Supporting Information
ABSTRACT: This paper describes the development of a new three-component
polymerization route to functional poly(tetraarylethene)s (PTAEs). The
polycoupling reactions of internal diynes, aryl diiodides, and arylboronic acids
proceed smoothly in the presence of PdCl2 and NaF at 70 °C in
dimethylformamide, generating PTAEs with promising molecular weights in high
yields from different monomers. Most of the PTAEs are soluble in common organic
solvents and are thermally stable. Some of the PTAEs exhibit the phenomenon of
aggregation-induced emission: their light emission in solution is enhanced by
aggregate formation. The tetraphenylethene-containing PTAE can function as a
3
+
fluorescent chemosensor for detecting Ru ions with high sensitivity and
specificity. It is also a promising material for the fabrication of fluorescent pattern
by photolithography process. All the PTAEs possess good film-forming ability and
their thin films exhibit high refractive index (RI = 1.7751−1.6382) at 632.8 nm,
whose values are higher than those of commercial polymers such as polycarbonate and polystyrene.
INTRODUCTION
Research on conjugated polymers has been a classic topic for
many decades because of their distinct properties and
promising applications. Among them, polyacetylene, poly(p-
phenylene), and poly(p-phenylenevinylene) (PPV) are the
also equip the polymer with multiple functions. Thus, it is
widely utilized in PPV modification.
■
Various reactions have been developed to synthesize
substituted PPVs with alkyl, alkoxy, or phenyl side chains,
1
5
6
such as Wittig coupling, Knoevenagel condensation and Heck
7
coupling reactions. Polymers generated from Wittig-type
most classical ones (Scheme 1). Despite their outstanding
polycoupling of an aryl dialdehyde and a diylide usually suffer
from low molecular weights, broad polydispersity, and poor
control of diastereoselectivity. Although Knoevenagel poly-
condensation of phenylenediacetonitrile with an aryl dialdehyde
can yield polymers with high molecular weights, side reactions
such as hydrolysis of nitrile groups are a common problem.
Because of its high efficiency, Heck polycoupling of aromatic
dihalides with dialkenes or ethenes appears to be the method of
choice to furnish a myriad of different PPVs. Since alkenes with
substituents are limited, the pendants of the corresponding
polymers are thus generally attached on the phenyl rings.
In 2003, Larock and co-workers reported a palladium-
catalyzed one-step, one-pot three-component coupling reaction
of aryl iodide, internal alkyne and aryl diboronic acid, giving
tetrasubstituted olefins in excellent yields under mild conditions
Scheme 1. Structures of Polyacetylene, Poly(p-phenylene),
and PPV
features like electrical conductivity, these rigid rod-like
polymers are not suitable for most real-world applications
because they all suffer from infusibility and hence low
processability. Taking PPV as an example, many approaches
have been developed to improve its tractability and solubility
2
through, for example, the precursor routes, postpolymerization
3
modification, and attachment of pendant groups to its
4
backbone. However, both pre- and postmodification methods
make the preparation process complicated and may lead to
defects in the polymer structure. Functional pendants, on the
contrary, can not only improve the processability of PPV but
Received: September 5, 2015
Revised: October 31, 2015
Published: November 9, 2015
©
2015 American Chemical Society
8098
DOI: 10.1021/acs.macromol.5b01946
Macromolecules 2015, 48, 8098−8107

Macromolecules
Article
Scheme 2. Polycoupling of Diarylacetylene, Diiodobenzene, and Benzene-1,4-Diboronic Acid
8
with high regio- and stereoselectivity. Based on Larock’s work,
ENF-280C/F UV lamp. Details can be found in our previous
12
9
publication.
Tomita developed the corresponding three-component
polymerization of aryl dihalide, aryl diboronic acid and
diarylacetylene catalyzed by PdCl (PhCN) and KHCO in
007 (Scheme 2). Poly(tetraarylethene) (PTAE) with good
solubility in common organic solvents was successfully
Polymer Synthesis. All the polymerization reactions were
performed using the standard Schlenk technique. A typical
experimental procedure for the polymerization of 1a, 2a, and 3a is
given below as an example. In a 25 mL Schlenk tube equipped with a
magnetic stirrer were dissolved 1a (0.1 mmol), 2a (0.3 mmol), 3a (0.6
2
2
3
2
obtained, but its molecular weight was rather low (M =
mmol), PdCl (0.01 mmol), and NaF (0.6 mmol) in distilled DMF
n
2
2
600). The polymerization was carried out at 100 °C for 24 h,
(10 mL). The mixture was stirred under nitrogen at 70 °C for 18 h.
Afterward, the polymerization reaction was terminated by pouring the
reaction mixture into 150 mL of hexane through a cotton filter to
remove insoluble substances, if any formed, and catalyst residues. The
precipitates were washed with hexane and dried in vacuum overnight
at room temperature until a constant weight was achieved. The
polymer was obtained as a yellow powder. Yield: 42.0% (Table 5, entry
which may set a limit on the monomer scope. Therefore, in this
paper, we aim to modify this polymerization and develop it into
a versatile strategy to synthesize soluble PTAEs with higher
molecular weights and variable structures under mild
conditions.
−1
On the basis of our experience in developing novel synthetic
1
). M = 11200; M /M = 3.93. IR (film), υ (cm ): 3056 (CC),
w
w
n
10
routes to functional polymers, we finally found better
conditions for synthesizing such polymers. PTAEs with fully
or partially conjugated structures and high molecular weights of
up to 18000 can be readily synthesized from readily available
internal diynes and other commercially available monomers in
the presence of PdCl and NaF in dimethylformamide (DMF)
at 70 °C within 18 h. Since the tetraarylethene moieties
2940 (CH ), 2866 (CH ), 1657, 1603, 1510, 1284, 1246, 1175, 1026.
3
2
1
H NMR (CD
Cl , 400 MHz), δ (ppm): 7.50−6.36 (aromatic
2
2
protons), 3.97−3.87 (OCH
protons), 2.30 (CH
protons), 1.75 and
2
3
13
1
1
2
.48 (CH protons). C NMR (CD Cl , 100 MHz), δ (ppm): 159.80,
2
2
2
33.39, 131.76, 130.98, 130.40, 129.92, 128.39, 115.02, 114.14, 68.19,
9.60, 26.25, 21.31.
2
P1b/2a/3a. Yellow powder; yield 66.1% (Table 5, entry 2). M =
w
−1
1
(
1800; M /M = 2.87. IR (film), υ (cm ): 3054 (CC), 2929
w
n
generated in situ are typical chromophores with aggregation-
1
CH ), 2857 (CH ), 1661, 1605, 1509, 1284, 1244, 1175, 1028. H
3
2
11
induced emission (AIE) features, the obtained PTAEs may be
AIE-active as well. Indeed, some of the PTAEs exhibit more
intense fluorescence in the aggregated state than their solutions.
Thus, they are promising as solid-state emission materials and
may find applications as imaging agents or fluorescent sensors.
NMR (CD Cl , 400 MHz), δ (ppm): 7.51−6.43 (aromatic protons),
2
2
3.97−3.76 (OCH protons), 2.45 (CH protons), 2.23, 1.74, and 1.38
2
3
13
(
CH protons). C NMR (CD Cl , 100 MHz), δ (ppm): 159.15,
2
2
2
1
2
35.72, 132.99, 131.39, 128.26, 123.59, 114.48, 67.94, 34.19, 30.29,
5.94, 21.86.
P1c/2a/3a. Yellow powder; yield 43.2% (Table 5, entry 3). M =
w
−1
1
1100; M /M = 1.72. IR (film), υ (cm ): 3054 (CC), 2927
w
n
1
EXPERIMENTAL SECTION
(CH ), 2855 (CH ), 1661, 1603, 1507, 1243, 1175, 1108, 1024. H
3 2
■
NMR (CD Cl , 400 MHz), δ (ppm): 7.67−6.63 (aromatic protons),
2
2
Materials and Instruments. Aryl diiodides, arylboronic acids, and
other reagents were purchased from Aldrich and used as received
without further purification. DMF and other organic solvents were
dried and distilled before use. Monomers 1a−1d were prepared
3
.97−3.74 (OCH protons), 2.36 (CH protons), 2.29, 1.73, and 1.29
2
3
13
(CH protons). C NMR (CD Cl , 100 MHz), δ (ppm): 159.17,
2
2
2
1
35.73, 132.98, 131.39, 128.26, 125.49, 114.48, 67.94, 34.19, 30.29,
12
29.40, 25.98, 21.16.
according to the methods reported in the literatures.
Gel permeation chromatography (GPC) was performed in THF at
P1d/2a/3a. Yellow powder; yield 42.3% (Table 5, entry 4). M =
w
−1
1
8000; M /M = 2.29. IR (film), υ (cm ): 3055 (CC), 3025 (C
−1
w
n
4
0 °C with an elution rate of 1.0 mL min on a Waters GPC system
1
C), 2922 (CH ), 1663, 1597, 1492, 1442, 1400, 1072, 1023. H NMR
3
equipped with a Waters 486 UV−vis detector, a Waters 515 HPLC
pump, a set of Styragel columns (HT3, HT4 and HT6; molecular
weight range 10 −10 ), and a column temperature controller. The
THF solutions of the polymers (about 2 mg mL ) were filtered
through a 0.45 μm PTFE filter before being injected into the GPC
system. IR spectra of the films of the polymers and monomers were
(
(
1
CD Cl , 400 MHz), δ (ppm): 7.94−7.11 (aromatic protons), 2.24
2
2
13
CH protons). C NMR (CD Cl , 100 MHz), δ (ppm): 143.82,
2
7
3
2
2
41.15, 131.66, 128.79, 126.93, 123.60, 121.35, 21.28.
−1
P1a/2a/3b. Yellow powder; yield 62.5% (Table 5, entry 5). M =
w
−1
8
2
1
900; M /M = 2.19. IR (film), υ (cm ): 3055 (CC), 2937 (CH ),
w
n
3
864 (CH ), 2730 (CHO), 1698 (CHO), 1602, 1508, 1283, 1244,
1
2
recorded on a PerkinElmer 16 PC FTIR spectrophotometer. H and
1
014. H NMR (CD Cl , 400 MHz), δ (ppm): 10.04 and 9.88 (CHO
2
2
1
3
C NMR spectra were measured on a Bruker AV 400 spectrometer in
protons), 8.36−6.39 (aromatic protons), 3.88 (OCH protons), 1.69
2
deuterated dimethyl sulfoxide, or dichloromethane. Thermogravimet-
ric analysis (TGA) was carried out on a TA TGA Q5000 in nitrogen at
a heating rate of 10 °C/min. High-resolution mass spectra (HRMS)
were recorded on a GCT premier CAB048 mass spectrometer
operated in MALDI-ToF mode. UV spectra were measured on a
Milton Ray Spectronic 3000 Array spectrophotometer and photo-
luminescence (PL) spectra were recorded on a PerkinElmer LS 55
spectrophotometer. Refractive indices (RI) were measured on a J A
Woollam Variable Angle Ellipsometry System with a wavelength
tunability from 400 to 1000 nm. Photopatterning was conducted in air
at room temperature using 365 nm light obtained from a Spectroline
13
and 1.20 (CH protons). C NMR (CD Cl , 100 MHz), δ (ppm):
2
2
2
1
6
62.74, 159.73, 133.34, 131.70, 128.35, 123.96, 115.34, 114.05, 112.91,
8.36, 36.65, 31.47, 29.55, 25.93, 23.95.
P1c/2b/3a. Red solid; yield 72.0% (Table 5, entry 6). M = 8000;
w
−1
M /M = 1.70. IR (film), υ (cm ): 3055 (CC), 2924 (CH ), 2854
w
n
3
1
(CH ), 1663, 1609, 1509, 1346, 1247, 1178, 1110, 1022. H NMR
2
(CD Cl , 400 MHz), δ (ppm): 7.89−6.61 (aromatic protons), 3.98−
2
2
3.71 (OCH protons), 2.36 (CH protons), 2.25, 1.84, and 1.29 (CH
2
2
3
protons). 13C NMR (CD Cl , 100 MHz), δ (ppm): 163.07, 141.42,
2
2
138.40, 136.23, 135.19, 134.19, 133.34, 131.70, 128.77, 125.80, 114.94,
68.17, 36.74, 31.52, 30.47, 29.78, 26.34, 25.96, 21.72.
8
099
DOI: 10.1021/acs.macromol.5b01946
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Macromolecules
Article
Scheme 3. Palladium-Catalyzed Polycoupling of Internal Diynes, Aryl Diiodides and Aryl Boronic Acids, and Model Reaction
a
Table 1. Solvent Effect on the Polymerization of 1a, 2a and 3a
entry
solvent
DMF
temp (°C)
time (h)
yield (%)
Mw
M /M
w
n
1
2
3
4
5
70
100
100
70
19
48
26
17
17
52.7
52.0
15100
12200
2.33
2.23
b
DMF/H O
2
THF
trace
trace
trace
methanol
toluene
70
a
b
Polymerization under nitrogen in the presence of 10% of PdCl and 6 equiv of NaF. [1a]:[2a]:[3a] = 1:3:6, [1a] = 0.01 M. 4:1 by volume.
2
P1c/2a/3b. Red solid; yield 40.0% (Table 5, entry 7). M = 4800;
δ (TMS, ppm): 144.00, 140.40, 136.04, 131.28, 128.35, 127.57,
126.26, 21.37. HRMS (MALDI−TOF): m/z 346.1719 (M , calcd
346.4636) (Figure S1 in the Supporting Information).
w
−1
+
M /M = 1.31. IR (film), υ (cm ): 3056 (CC), 2925 (CH ), 2854
w
n
3
1
(
CH ), 1601, 1508, 1282, 1174, 1021. H NMR (CD Cl , 400 MHz),
2
2
2
δ (ppm): 10.04 and 9.84 (CHO protons), 7.88−6.40 (aromatic
1
3
protons), 3.95−3.86 (OCH protons), 1.70−1.28 (CH protons).
C
2
2
RESULTS AND DISCUSSION
NMR (CD Cl , 100 MHz), δ (ppm): 133.32, 131.69, 128.58, 114.91,
■
2
2
6
8.51, 29.75, 26.26.
P1c/2a/3c. Red solid; yield 59.9% (Table 5, entry 8). M = 4700;
Polymer Synthesis. To widen the scope of the applicability
of polycoupling of internal diyne, aryl diiodide and boronic acid
to PTAEs, we optimized the reaction conditions using 1a, 2a,
and 3a as model monomers. The effects of different parameters
including solvent, temperature, monomer concentration and
feeding ratio as well as catalyst loading were examined. The
polymerization was first performed in different solvent systems
at different temperatures. Since sodium fluoride shows better
w
−1
M /M = 1.21. IR (film), υ (cm ): 2954, 2924 (CH ), 2854 (CH ),
w
n
3
2
1
1
4
604, 1596, 1508, 1458, 1284, 1246, 1173, 1024. H NMR (CD Cl ,
00 MHz), δ (ppm): 7.73−6.60 (aromatic protons), 4.01−3.89
2 2
(
OCH protons), 1.69, 1.60, 1.42, 1.27, 1.05, and 0.84 (CH protons).
2
2
1
3
C NMR (CD Cl , 100 MHz), δ (ppm): 159.84, 133.38, 131.74,
2
2
1
2
28.79, 124.03, 114.99, 113.94, 111.41, 89.77, 88.25, 68.59, 30.49,
9.70, 27.76, 23.13, 19.93, 14.31.
Model Reaction. Model compound 4 was synthesized by the
solubility in water, the model reaction was carried out in a
8
coupling reaction of diphenylacetylene and 4-methylphenylboronic
acid (Scheme 3). The experimental procedure was similar to that for
DMF/H O mixture as reported (Scheme 3). However, the
2
polymerization performed in pure DMF gives better results
the preparation of P1a/2a/3a except for the fact that DMF/H O
2
than those in DMF/H O mixture (Table 1, entries 1 and 2).
8
2
mixture (4:1 by volume according to the literature ) was used as a
The molecular weight of the PTAE produced in pure DMF
solvent. Light yellow solid; yield 26% (after purification by silica-gel
(
M = 15100) was higher than that (M = 12200) furnished in
w w
column chromatography using hexane/ethyl acetate mixture as the
−
1
1
a DMF/H O mixture. In addition, the use of pure DMF
eluent). IR (film), υ (cm ): 3074, 3050, 3020, 1508, 1489, 1442. H
NMR (400 MHz, CD Cl ), δ (ppm): 7.09, 7.04, and 6.91 (aromatic
2
enables the polymerization to perform at a lower temperature
and complete in a shorter time, presumably due to the better
2
2
13
protons), 2.26 (s, 3H, CH protons). C NMR (100 MHz, CD Cl ),
3
2
2
8
100
DOI: 10.1021/acs.macromol.5b01946
Macromolecules 2015, 48, 8098−8107

Macromolecules
Article
solubility of the polymer in this solvent. In contrast, other
organic solvents including tetrahydrofuran (THF), methanol
and toluene only afford polymers in trace yields (Table 1,
entries 3−5). Subsequently, the influence of temperature on the
polymerization was investigated. As shown in Table 2,
Table 4. Effects of Different Catalysts and Loading on the
Polymerization of 1a, 2a and 3a
a
loading
b
entry
catalyst
PdCl2
(%)
yield (%)
Mw
M /M
S
w
n
1
2
3
4
5
10
5
42.0
59.3
10000
7300
6600
3400
3600
1.90
1.75
1.61
1.16
1.19
√
Δ
√
√
√
PdCl2
Table 2. Temperature Effect on the Polymerization of 1a, 2a,
PdCl2
20
10
10
25.3
a
and 3a
Pd(OAc)2
∼100
16.8
[Pd(PPh ) Cl ]
entry
1
temp (°C)
yield (%)
Mw
M /Mn
3
2
2
w
a
Polymerization at 70 °C in DMF under nitrogen for 18 h (entries 1−
3) and 19 h (entries 4 and 5) in the presence of 10% of catalyst and 6
equiv of NaF. [1a]:[2a]:[3a] = 1:3:6, [1a] = 0.01 M. Solubility (S)
50
70
48.1
52.7
10.4
54.6
6100
15100
3400
1.56
2.33
1.20
1.44
b
2
b
3
4
90
tested in common organic solvents, such as dichloromethane,
chloroform, and tetrahydrofuran: √ = completely soluble, Δ =
partially soluble.
120
4800
a
Polymerization in DMF under nitrogen for 19 h in the presence of
1
0
0% equiv of PdCl and 6 equiv of NaF. [1a]:[2a]:[3a] = 1:3:6, [1a] =
.01 M. Data taken from Table 1, entry 1.
2
b
On the basis of the investigation above, we explored the
monomer scope in order to enrich the molecular structures and
introduce functionality to the polymers. We performed
polymerizations using aromatic internal diynes 1a−1d with
different alkyl chain lengths or TPE luminogenic unit, aryl
diiodides 2a−2b and arylboronic acids 3a−3c carrying different
aryl rings. All the reactions proceed smoothly, generating
increasing the reaction temperature from 70 to 90 °C and
then to 120 °C does not improve the yield or the
polymerization degree (Table 2, entries 2−4), whereas
lowering the temperature to 50 °C decreases the molecular
weight of the resulting polymer generated to 6100 (Table 2,
entry 1). Such result demonstrates that 70 °C is a suitable
temperature for this polymerization.
Traditional polymerization routes involved in preparing PPV
require strict stoichiometric control between the two monomer
pairs. The reaction developed here, however, is tolerant to
stoichiometric imbalance. Theoretically, the molar ratio
between 1a, 2a, and 3a was 1:1:2. However, PTAE with the
highest molecular weight and yield was obtained at a feed ratio
of 1:3:6 (Table 3, entry 1). Thus, an excess amount of
polymers with moderate to high molecular weights (Mw
=
4
700−18000) in moderate yields (40.0−72.0%) (Table 5).
a
Table 5. Polymerization of Different Monomers
b
entry
monomer
[1] (M) yield (%)
Mw
M /M
S
w
n
1
2
3
4
5
6
7
8
1a/2a/3a
1b/2a/3a
1c/2a/3a
1d/2a/3a
1a/2a/3b
1c/2b/3a
1c/2a/3b
1c/2a/3c
0.01
0.02
0.02
0.01
0.01
0.02
0.02
0.02
42.0
66.1
43.2
42.3
62.5
72.0
40.0
59.9
11200
11800
11100
18000
8900
3.93
2.87
1.72
2.29
2.19
1.70
1.31
1.21
√
√
√
√
√
Δ
Table 3. Concentration Effect on the Polymerization of 1a,
a
2a, and 3a
8000
b
4800
Δ
Δ
entry
[1a]
[2a]
[3a]
yield (%)
Mw
M /Mn
w
4700
b
1
0.01
0.01
0.01
0.01
0.03
0.03
0.02
0.02
0.06
0.03
0.06
0.02
52.7
13.2
8.5
15100
5500
5700
5500
2.33
1.48
1.55
1.40
a
Polymerization at 70 °C in DMF under nitrogen for 18 h in the
2
3
4
presence of 10% equiv of catalyst and 6 equiv of NaF. [1]:[2]:[3] =
1
b
:3:6. Solubility (S) tested in common organic solvents, such as
11.0
dichloromethane, chloroform, and tetrahydrofuran: √ = completely
soluble, Δ = partially soluble.
a
Polymerization at 70 °C in DMF under nitrogen for 19 h in the
b
presence of 10% of PdCl . [NaF] = [3a]. Data taken from Table 1,
2
entry 1.
Most of the polymers are soluble in common organic solvents,
except those synthesized from 1c, which may possess a high
molecular weight and hence a low solubility (Table 5, entries
6−8). The moderate yields may be attributed to the production
of terphenyl derivatives as byproducts from the Suzuki coupling
of aryl diiodides and arylboronic acids.
aryldiiodide and aryldiboronic acid seems to assist fast and
complete consumption of the diyne monomer. It is worthy to
note that even when a low monomer concentration 0.01 M was
used, the polymerization also proceeds well.
Palladium complexes are found to be efficient for catalyzing
the coupling reactions of alkyne, aryl iodides and arylboronic
acids. We examined the efficiency of several commonly used
palladium complexes in order to select the most suitable one
for our system. Regarding the molecular weights of the
Structural Characterization. We utilized IR and NMR
techniques to characterize the polymers obtained and model
compound. The IR spectra of polymer P1a/2a/3a and its
monomers 1a, 2a, and 3a as well as the model compound 4 are
1
3
given in Figure 1. The CH and C−O−C stretching vibrations
2
−1
polymers generated, we found that PdCl at a loading of 10%
of 1a are observed at 2941 and 1246 cm , which are also found
in the spectrum of P1a/2a/3a. On the other hand, the spectra
of 4 and P1a/2a/3a show no absorption band at 1346 cm−
related to the B−O stretching vibration of 3a. They both
2
outperformed its cousins (Table 4, entry 1). Reducing the
loading from 10% to 5% generates a polymer in a higher yield
1
(
59.3%), but with a poorer solubility, probably due to the
−
1
formation of high molecular weight species. On the other hand,
raising the catalyst loading leads to a poorer result in terms of
lower yield and molecular weight (Table 4, entry 3). Thus, 10%
exhibit CC stretching absorption bands at around 3050 cm
originated from the transformation of the CC triple bonds of
1a by the polymerization reaction.
1
PdCl was chosen for catalyzing the polymerization in the
Analysis by H NMR spectroscopy gives more detailed
structural information. Figure 2 depicts the H NMR spectra of
2
1
subsequent research.
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Figure 1. IR spectra of (A) 1a, (B) 2a, (C) 3a, (D) 4, and (E) P1a/
2
a/3a.
monomers 1a, 2a, and 3a, model compound 4, and polymer
P1a/2a/3a. The methylene protons of 1a resonate at δ 3.99,
1
.84 and 1.55, which are also found at the same positions in the
1
Figure 2. H NMR spectra of (A) 1a, (B) 2a, (C) 3a, (D) 4, and (E)
P1a/2a/3a in (A, B, D and E) CD Cl and (C) (CD ) SO. The
spectrum of P1a/2a/3a (Figure 2, parts A and E). The
absorption of the methyl group of 3a, on the other hand,
upfield-shifts from δ 2.44 to 2.25 after the model reaction and
polymerization (Figure 2, parts C−E). Meanwhile, the spectra
of 4 and P1a/2a/3a exhibit no resonance of the boronic acid
protons of 3a at δ 8.14. This suggests the complete
consumption of the boronic acid group by the polymerization.
The 13C NMR spectrum of P1a/2a/3a is given in Figure S2.
The spectrum of the polymer shows no triple bond resonances
of 1a at δ 89.82 and 88.18. Instead, it exhibits a peak related to
the methyl carbon absorption of 3a at δ 21.52. No unexpected
signals are detected and all the peaks can be readily assigned by
comparing the spectrum with those of its monomers and model
2
2
3 2
solvent peaks are marked with asterisks.
1
13
compound. Thus, all the H NMR and C NMR data prove
that the polymeric product is indeed P1a/2a/3a, with a
molecular structure as shown in Scheme 3. The IR and NMR
data of other polymers are summarized in the Experimental
Section and all confirm their expected molecular structures.
Thermal Stability. High thermal stability is usually a
prerequisite for polymers to be served as functional materials.
Figure 3 shows the thermal stability of the PTAEs evaluated by
TGA analysis. Most of the polymers retain 30−75% of their
weights after being heated to 800 °C under nitrogen and show
merely 5% weight loss at temperatures between 212−67 °C
Figure 3. TGA thermograms of P1a−1d/2a−2b/3a recorded under
nitrogen at a heating rate of 10 °C/min.
intramolecular charge transfer (ICT) from the electron-rich
tetraarylethene unit to the electron-withdrawing aldehyde
group. The absorption maximum of other polymers locate
within a wavelength range of 325−358 nm (Table 6). P1a/2a/
3a shows a bluer absorption than P1d/2a/3a because of its
nonfully conjugated structure but absorbs at longer wavelength
than P1c/2b/3a because its tetraarylethene moiety may take a
more planar conformation due to the lesser steric hindrance
(
T ). These render them as potential candidates for heat-
d
resistant materials.
Optical Properties. Because of their diverse structures,
polymers P1/2/3 exhibit different optical properties. Figure 4A
shows the absorption spectra of the polymers in THF solutions.
Among the polymers, P1a/2a/3b shows the longest absorption
maximum wavelength at 370 nm, probably due to the
8
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Figure 4. (A) Absorption spectra and (B) normalized PL spectra of P1/2/3 in THF solutions. Excitation wavelength (nm): 340 (P1a/2a/3a), 358
(P1d/2a/3a), 370 (P1a/2a/3b), 325 (P1c/2a/3c), and 326 (P1c/2b/3a).
a
Table 6. Optical Properties of P1/2/3
shown in Figure 5, the THF solution of 4 was barely emissive
under photoexcitation at 312 nm. Addition of a large amount of
water, a poor solvent for 4, into its THF solution aggregate its
molecules and induces it to emit intensity. Clearly, 4 exhibits
the AIE phenomenon.
polymer
λabs (nm)
λem (nm)
P1d/2a/3a
P1a/2a/3a
P1a/2a/3b
P1c/2a/3c
P1c/2b/3a
358
340
370
325
326
531
478
469
416
433
The luminogenic units of polymers P1a/2a/3a and P1d/2a/
3
a are similar to 1,4-bis(1,2,2-triphenylvinyl)benzene, an AIE
16
luminogen. Thus, both polymers are anticipated to show
a
In dilute THF solution. Abbreviation: λabs = absorption maximum;
strong emission in the aggregated state. Unlike 4, both P1a/2a/
λem = emission maximum.
3a and P1d/2a/3a are somewhat emissive in their THF
solutions albeit with a weak intensity. We have proposed that
1
5
between the aryl rings. The corresponding PL spectra are
shown in Figure 4B. Instead of P1a/2a/3b, whose PL is
sensitive to the solvent polarity, the emission maximum of
other polymers seems to be correlated with their conjugation,
with 1d/2a/3a being the reddest emitter.
the restriction of intramolecular motion (RIM) is the main
cause for the AIE effect. The AIE units in the polymers are
linked by covalent bonds and suffer certain steric effect from its
neighbors. These activate their RIM process and thus enable
the polymers to show somewhat light emission in the solution
state (Figure 6). The formation of nanoaggregates upon water
addition into the polymer solutions has further enhanced the
emission intensity. Interestingly, at water content exceeded 80
Tetraphenylethene (TPE) is a luminogen with AIE
characteristic. Being a TPE derivative, model compound 4 is
14
anticipated to be also AIE-active. It is really the case. As
Figure 5. (A) PL spectra of 4 in THF and THF/H O mixtures with different water fractions (f ). Concentration: 10 μM. Excitation wavelength:
2
w
3
12 nm. (B) Plot of relative PL intensity (I/I ) versus the composition of the THF/H O mixture of 4.
0
2
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Figure 6. PL spectra of (A) P1a/2a/3a and (C) P1d/2a/3a in THF and THF/H O mixtures with different water fractions (f ). Concentration
2
w
(μM): 20 (P1a/2a/3a) and 10 (P1d/2a/3a); excitation wavelength (nm): 340 (P1a/2a/3a) and 358 (P1d/2a/3a). (B and D) Plot of the relative
PL intensity (I/I ) as a function of the water fraction in the THF/H O mixture of (B) P1a/2a/3a and (D) P1d/2a/3a. Insets in parts B and D:
0
2
fluorescent photos of P1a/2a/3a and P1d/2a/3a in THF/H O mixtures with different f .
2
w
vol % for P1a/2a/3a and above 70 vol % for P1d/2a/3a, their
emission becomes weaker. Such a phenomenon may result
from the formation of large aggregates in the presence of water,
which reduces the effective solute concentration. P1d/2a/3a
emits at a longer wavelength (529 nm) than P1a/2a/3a (478
nm), probably due to its higher conjugation.
vicinity. This enhances their π−π stacking interactions and
results in PL annihilation. On the other hand, the RIM process
is activated upon aggregate formation, which results in emission
enhancement. The first factor seems to be predominant in P1c/
2b/3a in the aggregated state and thus the observation of PL
drop upon gradual addition of water.
We also investigated the optical properties of P1a/2a/3b,
P1c/2a/3c, and P1c/2b/3a in THF/water mixture. Unlike
P1a/2a/3a and P1d/2a/3a, the strong emission of these
polymers in THF is quenched upon aggregate formation in the
presence of water (Figures S3−S5). The higher the water
content in the THF/water mixture, the weaker is the light
emission. The enhancement of the ICT effect by increasing the
solvent polarity upon water addition in P1a/2a/3b may be
responsible for the emission quenching. The thiophene ring
and triphenylethene unit in P1c/2a/3c may serve as energy
Metal Ion Detection. Ruthenium(III) complexes are
18
19
commonly used catalysts for many oxidation, metathesis,
20
and reduction reactions, but they can potentially cause
corrosion and are irritating to skin, the eyes, and the respiratory
and digestive systems. Therefore, detection and monitoring of
ruthenium(III) ions has become an important safety issue.
However, few papers are available in the literature dealing with
3+
16,21,22
the quantitative fluorescence detection for Ru .
Taking
advantages of the high sensitivity, reliability, and selectivity of
fluorescent sensors and the AIE property of polymer P1d/2a/
3a, we investigated its potential as a fluorescent chemosensor
for Ru3+ ion.
17
acceptor and donor, respectively. When they are in close
proximity in the aggregates, it may lead to emission quenching
via the Fo
̈
rster resonance energy transfer mechanism. The
The emission spectra of P1d/2a/3a in THF/H O mixtures
2
volume shrinkage of the polymer chain of P1c/2b/3a in the
presence of poor solvent may push the phenyl rings in close
(3:7 v/v) containing different amounts of RuCl are given in
3
3
+
Figure 7A. With an increase in the concentration of Ru from
8
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3+
Figure 7. (A) PL spectra of P1d/2a/3a in THF/H O mixtures (3:7 v/v, 10 μM) containing different amounts of Ru . (B) Stern−Volmer plots of
2
3+
3+
relative intensity (I /I) versus the Ru concentration. I = PL intensity in the absence of Ru .
0
0
Figure 8. (A) Selectivity of P1d/2a/3a to different metal ions (0.8 mM in THF) in THF/H O mixture (3:7 by volume, 10 μM). I = intensity in the
2
0
absence of metal ions. Inset: Photographs of P1d/2a/3a in THF/H O mixtures (3:7 by volume) containing different metal ions taken under (upper)
2
daylight and (lower) UV illumination. (B) Normalized emission spectrum of P1d/2a/3a in THF/H O mixture (3:7 by volume) and absorption
2
spectra of metal ions. Concentration: 10 μM (P1d/2a/3a) and 1 mM (metal ions).
0
to 0.8 mM, the emission of the polymer aggregates was
of P1d/2a/3a in THF/H O mixtures (3:7 by volume) with 0.8
2
gradually quenched while the spectral profile remained
unchanged. The Stern−Volmer plots of relative PL intensity
mM of some of these cations. Results show that the emission of
3
+
P1d/2a/3a is only sensitive to the presence of Ru ion, which
is demonstrative of the high specificity of the fluorescent
chemosensor. Different mechanisms have been proposed for
3
+
(
I /I) versus the Ru concentration provides a more detailed
0
picture of the quenching process (Figure 7B). At different
3
+
metal ion concentrations, the quenching constants deduced
from the linear region of the plot varies from 13200 M (0−
such selectivity, such as high reduction potential of Ru
ion,
−1
16a,17,22 21
heteroatom-involved energy transfer and for-
23
−1
−1
0
.3 mM), to 37500 M (0.3−0.6 mM) and then 143600 M3
0.6−0.8 mM). This trend shows that at high Ru
mation of metal complex or coordination effect. In this case,
+
(
the dark color of the aqueous solution of RuCl gives us a hint
3
concentration, the sensing performance of the polymer
becomes higher. Such amplification is attributed to an increase
in the number of binding cavity due to the conformational
that its absorption may be responsible for the emission
annihilation. Thus, we studied the electronic transitions of
RuCl and other metal ions for comparison. As shown in Figure
3
3
+
3+
change caused by Ru ions already bound to the polymer.
In order to investigate the selectivity of the metal ion sensor,
we tested the emission response of the polymer to several other
ions, including Cr , Cu , Fe , Fe , Ni , Co , Rh , Ag ,
Hg , and Zn . Figure 8A illustrates the relative intensity (I /I)
8B, the absorption spectrum of Ru overlaps with the emission
spectrum of P1d/2a/3a at the wavelength range of 400−670
nm. This will lead to the energy transfer from the excited state
3
+
2+
3+
2+
2+
3+
3+
+
3+
of the polymer to the ground state of Ru and hence quench
2+
2+
its emission. In contrast, the onset wavelength of the absorption
0
8
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Macromolecules
Article
spectra of other metal ions is all shorter than 410 nm. Thus,
efficient energy transfer between them and the polymer
aggregates is less likely to occur.
them with many advanced applications such as high-perform-
ance complementary metal-oxide-semiconductor image sen-
sors.
Photopatterning. P1d/2a/3a possesses a good film-
forming capacity and exhibits strong emission in the solid
state. These properties make it promising for the facile
fabrication of nanoscale luminescent patterns. The spin-coated
film of P1d/2a/3a on a silicon wafer was illuminated through a
copper mask by UV light for 10 min. As depicted in Figure 10,
24
Light Refraction. Polymers with high refractive indices
RI) are promising candidates for a variety of photonic
(
applications, such as organic light-emitting diodes, waveguides,
24
lenses and image sensors. Theoretically, polymers with
heteroatoms, polarized aromatic rings and large conjugation
are likely to exhibit high RI values. Our polymers can be
fabricated into uniform films on silica wafers by drop-casting or
spin-coating with thicknesses of 100−300 nm. Their films
exhibit RI of 1.6382−1.7751 at 632.8 nm, whose values are
higher than those of commercial polymers such as polycar-
bonate (n = 1.593−1.576) and polystyrene (n = 1.602−1.589)
2
5
(
Figure 9). In particular, polymer P1d/2a/3a exhibits the
Figure 10. Photopatterns generated by photolithography of a film of
P1d/2a/3a through a copper mask taken under (A) normal light
illumination and (B) UV irradiation. Excitation wavelength: 330−385
nm.
the exposed parts (lines) of the films are photobleached and
thus appear dark upon UV irradiation, while the unexposed
10a
squares still emit brightly. High resolution patterns are thus
discernible under normal light illumination and UV irradiation.
Therefore, this technique proves to be highly efficient and facile
for the construction of photonic and electronic devices as well
27
as biological sensing and probing systems.
Figure 9. Wavelength-dependent refractive indices of thin films of
P1a−d/2a−b/3a−c.
CONCLUSIONS
■
We have successfully developed a highly efficient approach to
prepare poly(tetraarylethene)s by a one-pot one-step palla-
dium-catalyzed three-component polycoupling of internal
diynes, aryl diiodides, and arylboronic acids. This polymer-
ization enjoys the advantages of mild reaction condition, less
highest RI values of 1.9788−1.6917 in the range of 400−1000
nm, thanks to its fully conjugated backbone. The high RI values
of P1/2/3 enable them to be used in a variety of above-
mentioned applications.
Chromatic Dispersion. Chromatic dispersion (D) of a
particular material is related to its wavelength-dependent
28
costly catalyst, and a high tolerance to different functional
groups. The obtained polymers possess distinguished proper-
ties such as good film-forming capability, high refractive indices
and good thermal stability. The strong aggregate/solid state-
emission characteristic of TPE-containing PTAE enables it to
be a promising material for fabricating high-resolution photo-
patterns and serve as a highly sensitive and selective fluorescent
́
refractive index. The Abbe number (ν ) describes the variation
D
of RI as a function of the wavelength. Those with high D values
are not favorable in fabricating optical devices since they will
26
lead to chromic aberration. As shown in Table 7, the ν and
D
the corresponding D values of the polymers fall in the range of
3+
7
.4574−36.7667 and 0.0272−0.1341, respectively. Obviously,
chemosensor for Ru ion. Therefore, this paper demonstrates a
successful strategy for manipulating the properties and
functionalities of polymers via proper structural design. Further
research will be directed to explore monomers with other
functional groups, such as pyrrole and fluorophenyl rings and
potential applications of the resulting polymers as electro-
fluorescent materials for PLED.
the high RI values and low dispersion of the polymers endow
Table 7. Refractive Indices and Chromatic Dispersions of
a
P1/2/3
polymer
n632.8
νD
D
P1a/2a/3a
P1c/2a/3a
P1d/2a/3a
P1c/2b/3a
P1c/2a/3b
P1c/2a/3c
1.6409
1.6806
1.7751
1.6445
1.6382
1.6583
16.9034
12.2429
7.4575
0.0592
0.0817
0.1341
0.0677
0.0565
0.0272
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications Web site. The Supporting Information is
available free of charge on the ACS Publications website at
DOI: 10.1021/acs.macromol.5b01946.
■
*
S
14.7808
17.7115
36.7667
a
Abbreviation: n = refractive index, ν = Abbe
n ), where n , n , and n are the RI values at wavelengths of
C D F C
́
number = (n − 1)/(n
D
D
F
13
HRMS spectrum of 4, C NMR spectra of 1a, 2a, 3a, 4
and P1a/2a/3a, and PL spectra of P1a/2a/3b, P1c/2a/
3c, and P1c/2b/3a (PDF)
−
Fraunhofer D, F, and C spectral lines of 589.2, 486.1, and 656.3 nm,
respectively; D = 1/νD.
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(
b) Sharpless, K. B.; Akashi, K.; Oshima, K. Tetrahedron Lett. 1976,
AUTHOR INFORMATION
■
1
7, 2503−2506.
19) (a) Nelson, D. J.; Manzini, S.; Urbina-Blanco, C. A.; Nolan, S. P.
Chem. Commun. 2014, 50, 10355−10375. (b) Furstner, A. Ruthenium-
Catalyzed Metathesis Reactions in Organic Synthesis. In Alkene
Metathesis in Organic Synthesis, Furstner, A., Ed. Springer: Berlin
and Heidelberg, Germany, 1998; 1, 37−72.
20) (a) Bontemps, S.; Vendier, L.; Sabo-Etienne, S. J. Am. Chem. Soc.
Corresponding Author
(B.Z.T.) E-mail: tangbenz@ust.hk. Telephone: +852-2358-
375. Fax: +852-2358-1594.
(
*
̈
7
̈
Notes
The authors declare no competing financial interest.
(
2
014, 136, 4419−4425. (b) Gutsulyak, D. V.; Nikonov, G. I. Adv.
ACKNOWLEDGMENTS
■
Synth. Catal. 2012, 354, 607−611. (c) Fukuzawa, H.; Ura, Y.; Kataoka,
Y. J. Organomet. Chem. 2011, 696, 3643−3648.
This work was partially supported by the National Basic
Research Program of China (973 Program; 2013CB834701),
the National Science Foundation of China (21490570 and
1490574), the University Grants Committee of Hong Kong
AoE/P-03/08), the Research Grants Council of Hong Kong
16305014, 16303815 and 604913), and the Nissan Chemical
(
21) Deng, H.; Hu, R.; Zhao, E.; Chan, C. Y. K.; Lam, J. W. Y.; Tang,
B. Z. Macromolecules 2014, 47, 4920−4929.
22) Chan, C. Y. K.; Lam, J. W. Y.; Jim, C. K. W.; Sung, H. H. Y.;
Williams, I. D.; Tang, B. Z. Macromolecules 2013, 46, 9494−9506.
23) Kangwanwong, T.; Pluempanupat, W.; Parasuk, W.; E. Keenan,
H.; Songsasen, A. ScienceAsia 2012, 38, 278−282.
(
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Industries, Ltd. B.Z.T. expresses thanks for the support of the
Guangdong Innovative Research Team Program
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