Synthesis and properties of novel aggregation-induced emission compounds with combined tetraphenylethylene and dicarbazolyl triphenylethylene moieties

Article abstract of DOI:10.1039/c0jm02824j

A novel class of compounds containing tetraphenylethylene and dicarbazolyl triphenylethylene moieties combined with different spacers is synthesized. The compounds exhibit high thermal stabilities and aggregation-induced emission properties. The different

Full text of DOI:10.1039/c0jm02824j

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www.rsc.org/materials | Journal of Materials Chemistry
Synthesis and properties of novel aggregation-induced emission compounds
with combined tetraphenylethylene and dicarbazolyl triphenylethylene
moieties†
*
Xiqi Zhang, Zhenguo Chi, Haiyin Li, Bingjia Xu, Xiaofang Li, Siwei Liu, Yi Zhang and Jiarui Xu
*
Received 26th August 2010, Accepted 19th October 2010
DOI: 10.1039/c0jm02824j
A novel class of compounds containing tetraphenylethylene and dicarbazolyl triphenylethylene
moieties combined with different spacers is synthesized. The compounds exhibit high thermal stabilities
and aggregation-induced emission properties. The different spacers lead to differences in spatial
conformation structures and spatial electron distributions, and markedly affect the thermal and
photophysical properties of the compounds. The size of the aggregates formed in water–THF mixtures
decreases with increasing water fractions. The time-resolved emission decay behaviors of the
synthesized compounds in water–THF mixtures with water fractions from 60% to 99% show three
relaxation pathways in their fluorescence decays.
methodology, and also aim to design materials with potential
technological applications.
Introduction
Organic luminescent materials with aggregation-induced emis-
sion (AIE) properties have attracted considerable attention
because of their potential application in electroluminescence
devices and chemosensors. Since the first AIE compound 1-
methyl-1,2,3,4,5-pentaphenylsilole was reported in 2001 by
Tang’s group,1 aggregation-caused quenching (ACQ) is no
longer the almost insurmountable obstacle it once was. Since
then, a large number of AIE compounds have been developed by
various research groups, examples of which include silole,
1,1,2,2-tetraphenylethene (TPE) and 1-cyano-trans-1,2-bis-(4-
methylbiphenyl)ethylene (CN-MBE) derivatives.2
In this article, we present the synthesis of three new
compounds, in which tetraphenylethene combines dicarbazolyl
triphenylethylene units with different spacers, and their thermal
and optoelectronic properties are also investigated. These
compounds exhibit aggregation-induced emission properties and
high levels of thermal stabilities, which make them promising
candidates as luminescent materials for electroluminescence
applications.
Results and discussion
The thermal stability of organic materials is very important for
the stability and lifetime of electroluminescence devices because
the heat generated during the electroluminescent process could
affect material morphology and device performance. This could
eventually cause permanent damage to the device. Hence,
a relatively high glass transition temperature (Tg) is essential for
emissive materials used in optoelectronic applications. Recently,
the synthesis and application of carbazole derivatives as emissive
materials have been of great interest for chemists and material
scientists due to their high thermal stabilities, charge-transport
properties and luminescence.3 Therefore, we have endeavored to
attach carbazole moieties onto AIE materials, and recently
reported a new kind of AIE molecules, triphenylethylene
carbazole derivatives.4 These derivatives exhibit excellent
thermal and device properties, moreover, most of which have
strong blue light emission capabilities. Thus, we are extending
these studies by combining dicarbazolyl triphenylethylene and
tetraphenylethene units into a single compound via synthetic
Synthesis methods
The target compounds were synthesized according to the routes
depicted in Scheme 1. The target compounds possessed
a common structural feature, that is, each molecule could be
divided into two parts: the tetraphenylethylene and the dicar-
bazolyl triphenylethylene moieties. However, the linker con-
necting these two moieties was varied. For P4Bc2, the two
moieties shared one phenyl ring, and for P5Bc2 and P6Bc2, the
two parts were linked by a C–C single bond and a phenylene
group, respectively. Thus, to study the influence of the linker on
the properties of the compounds is one of our main purposes.
The synthesis of TPE-PBr was a straightforward (two steps)
procedure using readily available starting material diphenyl-
methane. The hydroxy intermediate, TPE-P(OH)Br, was used
without further purification in the next step. And TPE-PBr was
obtained by the dehydration reaction of TPE-P(OH)Br in the
presence of p-toluenesulfonic acid. TPE-Br was synthesized
according to a literature method5 and TBE-Br was purchased
from a commercial source. The aryl boronic acid C2B was
synthesized starting from carbazole according to our previous
procedure.4 The chemical structures of these products were
confirmed with proton and carbon-13 nuclear magnetic reso-
nance spectra (1H NMR and 13C NMR), high resolution mass
spectrometry and elementary analysis.
PCFM Lab and DSAPM Lab, FCM Institute, State Key Laboratory of
Optoelectronic Materials and Technologies, School of Chemistry and
Chemical Engineering, Sun Yat-sen University, Guangzhou, 510275,
China. E-mail: chizhg@mail.sysu.edu.cn; xjr@mail.sysu.edu.cn; Fax:
+86 20 84112222; Tel: +86 20 84111081
† Electronic supplementary information (ESI) available: Fig. S1–S4. See
DOI: 10.1039/c0jm02824j
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Fig. 1 TGA curves of the compounds.
their melts. Amorphous materials possessing high Tg should have
better chances of retaining film morphology during device
operation.
It is well-known that an organic molecule may have many
conformational structures. However, among these structures, the
most stable one governs the space structure of the molecule,
which affects the planarity of the molecular structure and inter-
molecular packing. The above geometrical factor would directly
affect some physical properties of the compound, such as thermal
transition temperatures (Tg, Tm, etc.) and optical properties (UV,
PL, etc.). The geometrical structures of the isolated molecules of
the compounds in the ground states were optimized on the basis
of B3LYP/6-31G calculations using Gaussian 03.6 To evaluate
the degree of planarity of these systems, the dihedral angles were
measured and are summarized in Table 2. Fig. 3 shows the
position of each plane.
Scheme 1 Synthetic routes for the compounds.
Thermal and photophysical properties
Thermal properties were investigated by thermal gravimetric
analysis (TGA) and differential scanning calorimetry (DSC), and
are summarized in Table 1. The compounds exhibited high
thermal stabilities. The decomposition temperatures with 5%
weight loss under N2 atmosphere (Td) of P4Bc2, P5Bc2 and P6Bc2
ꢀ
were 496, 538 and 562 C, respectively (Fig. 1). The Td values
The results of calculation clearly reveal that the molecules are
not planar. In P5Bc2 and P6Bc2, the six dihedral angles are the
same, which indicates that the dicarbazolyl triphenylethylene
moieties in P5Bc2 and P6Bc2 exhibit the same degree of planarity,
that is why these two compounds show similar crystallization
behavior from their solutions as reflected in their first heating
DSC curves. Although the dihedral angles B2–B3, B2–B4 and
B3–B5 in the three compounds are the same, and B1–B2 and B1–
B3 are close, the dihedral angle values of B4–B5 differ greatly in
P4Bc2 and P5Bc2 (P6Bc2), with values of 19ꢀ and 87ꢀ. This means
that the two carbazole groups in P4Bc2 are almost coplanar,
however, they are perpendicular to each other in P5Bc2 (P6Bc2).
This indicates that P4Bc2 has better co-planarity than P5Bc2 and
P6Bc2, which leads to larger conjugation and higher rigidity. The
high rigidity of the molecular structure of P4Bc2 may be the
reason why the compound cannot form crystals from its solution.
It is well-known that it is not easy to arrange a bulky rigid
molecule into a crystal lattice.
increased with the increasing size of the linkers. High glass
transition temperatures (Tg) were essential for emissive materials
used to improve stability and lifetime of devices. ꢀThe Tg values of
P4Bc2, P5Bc2 and P6Bc2 were 126, 156 and 170 C, respectively.
The high Tg were attributed to the effect of the bulky carbazolyl
groups. As expected, Tg values increased with the increasing
linker sizes.
The DSC curves of the samples in the first and second heating
runs are shown in Fig. 2. In the first heating run, the DSC curves
of P5Bc2 and P6Bc2 showed obvious crystalline melting peaks at
263 and 305 ꢀC, respectively. However, for P4Bc2, no melting
peak could be detected under the same condition, which indicates
that the compound had lower crystallizability from solution than
that of P5Bc2 and P6Bc2. In the second heating run, only the glass
transition could be observed for each compound. This indicates
that the compounds had very low tendency to crystallize from
Table 1 Thermal and optical properties of the compounds
To further study the relationship between their molecular
structures and photophysical properties, we investigated the
photophysical properties of these compounds by UV-Vis
absorption spectroscopy (UV) in solution and photo-
luminescence spectroscopy (PL) in both solution and solid state.
The data are summarized in Table 1.
b
Tg/ꢀC Tm/ꢀC Td/ꢀC lema/nm labsb/nm lemb/nm FFL (%) FFLc (%)
P4Bc2 126 NA 496 490
P5Bc2 156 263 538 456
P6Bc2 170 305 562 460
343
343
344
474
461
462
0.09
0.24
0.32
1.1
2.6
3.4
a
b
Determined in solid powder. Determined in dichloromethane.
Determined in cyclohexane.
c
Fig. 4 outlines the UV absorption and PL emission spectra of
the compounds in dichloromethane (10 mM). The shapes and
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Fig. 4 UV (left) and PL (right) spectra of the compounds in dichloro-
methane (10 mM).
Fig. 2 DSC curves upon the first and the second heating runs with 10 ꢀC
minꢂ1 heating rate.
yield is lower. As is well-known, the molecular size and effect of
steric hindrance will affect the rotation and a larger molecule
should have lower freedom of rotation. Therefore, the data of
FFL are arranged in the order of P6Bc2 > P5Bc2 > P4Bc2. Fig. 5
shows the PL spectra of the compounds in solid powders.
Comparing the PL spectra of the compounds from solutions to
corresponding solid powders, it can be observed that the
maximum emission wavelengths (lem) of P5Bc2 and P6Bc2 are
very close to each other (ꢁ460 nm) and there are only slight lem
blue-shifts (2–5 nm), suggesting weak intermolecular interac-
tions. However, the lem of the P4Bc2 in solution and in solid
powder were 474 and 490 nm, respectively. The lem are much
longer than those of P5Bc2 and P6Bc2 in either solutions or solid
powders. For example, compared to P5Bc2 in solid powder, the
lem of P4Bc2 was red-shifted by 34 nm.
Table 2 Some dihedral angle parameters of the compounds
Dihedral angles
P4Bc2 (deg.)
P5Bc2 (deg.)
P6Bc2 (deg.)
B1–B2
B1–B3
B2–B3
B2–B4
B3–B5
B4–B5
56
70
76
55
55
19
60
64
76
55
55
87
60
64
76
55
55
87
It is well-known that the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital (LUMO),
which are related to the redox potentials, are two important
parameters for electroluminescent materials because of their
relationship with the hole/electron-injecting capability of organic
light-emitting devices. Besides, the energy levels are related to the
level of difficulty of p-electron transitions, which is directly
reflected in UV and PL spectra. To measure the HOMO levels of
the synthesized compounds, cyclic voltammetry (CV) was carried
out. The CV curve of P5Bc2 is shown in Fig. 6. The CV curves for
Fig. 3 Schematic diagram for the optimization geometries of the
compounds (R represents the tetraphenylethylene moiety).
maximum absorption wavelengths (labs) of UV spectra are very
similar. There were two main absorption bands in all the
compounds: one located at ca. 343 nm and the other located at
ca. 293 nm.
The PL emission intensities of the compounds in 10 mM
dichloromethane solutions increased in the order of P6Bc2
>
P5Bc2 > P4Bc2, and the fluorescence quantum yields (FFL) also
increased according to this order, either in dichloromethane
solutions or in cyclohexane solutions. Although P4Bc2 has the
largest conjugation and highest rigidity among the three
compounds as mentioned above, it exhibits the lowest FFL
because AIE compounds are special systems which are different
from the common dyes. In solution, if the phenyl rings or groups
in an AIE molecule rotate more freely, its fluorescent quantum
Fig. 5 PL spectra of the compounds in solid powders.
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had a dense electron distribution. Comparing the electron
distributions in the LUMO orbitals, the electron distribution
density in the tetraphenylethylene moiety was rather high in
P4Bc2. However, the tetraphenylethylene moieties in P5Bc2 and
P6Bc2 had almost no electron distribution. Thus, based on the
theoretical calculations, it is clear that the different electron
distributions of the compounds led to their different emission
properties.
AIE properties
To determine whether the compounds have aggregation-induced
emission properties, the UV absorption and PL emission
behaviors of their diluted mixtures were studied in a mixture of
water–THF with different water fractions. Since the compounds
were insoluble in water and soluble in THF, increasing the water
fraction in the mixed solvent could change their existing forms
from a solution in pure THF to the aggregated particles in the
mixtures, which will result in changes in their UV and PL spectra.
The PL spectra of 10 mM of P5Bc2 in water–THF mixtures
with different water contents are shown in Fig. 8 as an example
(the others are shown in Fig. S2). For P5Bc2 in pure THF and in
the mixtures with water fraction <50% very weak PL intensity is
exhibited and almost no photoluminescence signals can be
detected. However, the fluorescent intensity was significantly
enhanced when the water fraction exceeded 50%. For the series
of compounds, when the water fraction was >60%, the PL
intensity slightly decreased with increasing water fraction up to
80%. A dramatic enhancement in luminescence was observed
when the water fraction was up to 90%. While the PL intensity in
pure THF was only 3 (a.u.), it was boosted to ꢁ241 (a.u.) in 99%
water–THF mixture, an enhancement of about 80 times. Similar
effects were observed for the other compounds. This increase in
Fig. 6 CV curve of P5Bc2 in dichloromethane.
P4Bc2 and P6Bc2 are provided in the Electronic Supplementary
Information (Fig. S1). The HOMO energy levels were obtained
using onset oxidation potentials. The energy band gaps (DEg) of
the compounds were estimated from the onset wavelength of
their UV absorptions. The LUMO energy levels were obtained
from the HOMO energy and the energy band gap (DEg
HOMO ꢂ LUMO).
¼
The HOMO, LUMO and DEg values are listed in Table 3. The
DEg values of the compounds were found to be in the range of
2.99–3.04 eV. Comparing the DEg values of three compounds,
the DEg of P4Bc2 was the lowest (2.99 eV), which means that the
p-electron transition of P4Bc2 was the easiest. This may be the
major reason why the P4Bc2 exhibited the longest PL emission
wavelength among the compounds.
To gain insights into differences in the photophysical proper-
ties of the compounds, quantum mechanical computations were
carried out using the Gaussian 03 program.6 On the basis of the
density functional method at the B3LYP/6-31G level after opti-
mizing the structure, the HOMO and LUMO of these
compounds were obtained, as shown in Fig. 7. The calculated
values are also summarized in Table 3 in brackets. As can be seen
from Table 3, the experimental values are not in good agreement
with the calculated values. P4Bc2 had a larger dipole moment
(2.1616 Debye) than P5Bc2 and P6Bc2. As expected, P5Bc2 and
P6Bc2 showed similar electron distributions in either their
HOMO or LUMO orbitals. This may be the reason why P5Bc2
and P6Bc2 exhibited very close UV and PL spectra. However, in
either the HOMO or LUMO orbital, the electron distributions of
P4Bc2 were significantly different from P5Bc2 and P6Bc2. On the
HOMO orbital of P4Bc2, the electron distributions in the two
carbazole groups had equal opportunities. However, for P5Bc2
and P6Bc2, the electron distributions in the two carbazole groups
were different. The carbazole group on the molecular backbone
Table 3 Energy levels of the compoundsa
Dipole moment
(Debye)
HOMO/eV
LUMO/eV
OEg/eV
P4Bc2
P5Bc2
P6Bc2
5.53 (5.17)
5.54 (5.20)
5.55 (5.20)
2.54 (1.71)
2.52 (1.71)
2.53 (1.74)
2.99 (3.46)
3.04 (3.49)
3.02 (3.46)
2.1616
2.0779
2.0140
a
Fig. 7 Calculated spatial electron distributions of LUMO and HOMO
Data in parentheses obtained from theoretical calculation.
of the compounds.
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addition of more water. We thus measured the particle size using
a laser light scattering system. The effective diameters (EDs) and
polydispersity indexes (PDIs) are summarized in Table 4. To
demonstrate the ED changes in the particles more visually, we
plotted the changes in ED versus water fractions in the water–
THF mixtures (Fig. 10). When the water fraction is <60%, the
instrument system could not detect any particles. As can be seen
from Fig. 10, the ED values decreased with increasing water
fraction. In other words, the size of the aggregation particle
became smaller. This indicates that the decrease in FFL in Stage
(3) was not merely caused by the size of particles.
The emission images of the compounds in pure THF and 99%
water fraction mixtures under 365 nm UV illumination are
shown in Fig. 11. The compounds in 99% water fraction of
water–THF mixture exhibited strong blue emissions. However,
in pure THF, the emissions were very weak.
Fig. 8 PL spectra of P5Bc2 in water–THF mixtures (10 mM).
As an example, the absorption spectra of P5Bc2 in the water–
THF mixtures (10 mM) are shown in Fig. 12 (the others are
shown in Fig. S3). The spectral profile was markedly changed
when the water fraction was >50% in the water–THF mixture.
The spectra showed absorption tails extending well into the long
wavelength region. This indicates that the molecules had aggre-
gated into nanoparticles in the mixtures. It was considered that
the Mie effect of nanoparticles could cause such leveling-off of
tails in the absorption spectra.
PL intensity can be attributed to an AIE effect caused by the
formation of molecular aggregates, in which the restriction of
intramolecular rotations leads to increased fluorescent emission.
To quantitatively estimate the AIE process, the PL quantum
yields (FFL) were calculated for the compounds in the water–
THF mixtures with different water fractions using 9,10-diphe-
nylanthracene as the reference (Fig. 9). The FFL curves could be
divided into four stages according to water fraction (x): (1) 0–
50%, almost no change; (2) 50% < x # 60%, slight increase; (3)
60% < x #80%, slight decrease; and (4) >80%, significant
increase. The variation of the FFL values with the water fractions
was in accordance with that of PL intensity. Compared to the
FFL obtained in pure THF, the FFL of P4Bc2, P5Bc2 and P6Bc2 in
water–THF mixtures with 99% water fraction increased 200-,
190- and 121-fold, respectively. For example, in THF, the FFL of
P4Bc2 was 0.14%; but in water–THF mixtures with 99% water
fraction, the FFL was 28%.
Recently, a time-resolved fluorescence technique was used to
elucidate the mechanism of AIE. It was found that most of the
addition of water to an AIE solution led to a change in the
emission lifetime of AIE and that excited molecule decay
occurred through two relaxation pathways.8,9 In solution, the
decay was through a rapid pathway, and in aggregation it was
mainly through a slow one. To the best of our knowledge, there
are few three decay pathways reported for the AIE system.10
Time-resolved emission decay behaviors of the synthesized
compounds in water–THF mixtures with water fractions from
60% to 99% were studied in this article. As an example, the time-
resolved fluorescence curves of P5Bc2 are illustrated in Fig. 13
(the others are shown in Fig. S4), and the lifetime data are
summarized in Table 5. As can be seen from the table, there are
three relaxation pathways in their fluorescence decays. This
implies that the time-resolved PL spectra of the compounds
include independent emissions from the segments with different
p-conjugation lengths because multiple lifetimes have been
detected. For these three compounds, different pathways played
As the water fraction was increased, decreases in PL intensity
and FFL were often observed, such as in Stage (3), in some AIE
compounds with AIE properties. The reasons for these remain
unclear. Li et al.7 considered that the reason was the decreasing
number of emissive molecules located at the surface of the
aggregates as the aggregates increase in size upon increasing
amounts of water being added to the mixtures. In other words,
after aggregation, the particle size further increased after the
Table 4 Effective diameter and polydispersity index of the compounds
in water–THF mixtures with different water fractiona
P4Bc2
P5Bc2
P6Bc2
Water (v%)
ED
PDI
ED
PDI
ED
PDI
<60
60
70
80
90
95
99
N/A
N/A
N/A
N/A
N/A
N/A
996.1
466.6
235.7
227.3
189.9
173.6
0.230
0.055
0.166
0.162
0.140
0.200
1069.7
388.0
291.1
250.8
189.6
154.5
0.211
0.042
0.108
0.189
0.150
0.198
570.1
369.4
326.5
245.7
194.4
157.3
0.043
0.032
0.012
0.076
0.118
0.073
a
Fig. 9 PL quantum yields of the compounds in water–THF mixtures
with water fraction (10 mM).
ED: Effective diameter (nm); PDI: Polydispersity index.
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Fig. 13 Time-resolved emission decay curves of P5Bc2.
Fig. 10 Effective diameters of the compounds in water–THF mixtures
with water fraction (10 mM). Note: <60%, the instrument system could
not detect any particles.
increasing water fractions in the solvent mixture, the weighted
mean lifetimes <s> exhibited V-shape changes (Fig. 14) in
accordance with the changes of PL intensities and quantum
yields, which may due to the combined action of the increasing
solvent polarity and the molecular aggregation.
Conclusions
A novel class of AIE compounds containing tetraphenylethylene
and dicarbazolyl triphenylethylene moieties combined with
different spacers was synthesized. The compounds possessed
high thermal stability with Tg of 126–170 ꢀC and Td of 496–562
ꢀC. The different spacers led to differences in spatial conforma-
tion structures and spatial electron distributions, and markedly
affected the thermal and photophysical properties of the
compounds synthesized. The size of the aggregated particles
formed from the water–THF mixtures decreased with increasing
water fractions. Studies of the time-resolved emission decay
behaviors of the synthesized compounds in water–THF mixtures
showed that there exist three relaxation pathways in their fluo-
rescence decay processes.
Fig. 11 Emission images of the compounds taken under 365 nm UV
illumination at room temperature in THF solution and 99% water frac-
tion (v%) (10 mM).
Table 5 Fluorescence decay parameters of the compounds in water–
THF mixtures with different water fractions
Water (v%) s1/ns s2/ns s3/ns A1
A2
A3
<s>/ns
P4Bc2 60
70
0.16 1.43 8.84 0.39 0.51 0.10 1.68
0.11 1.18 8.08 0.69 0.20 0.11 1.20
0.07 0.69 5.19 0.65 0.30 0.05 0.51
0.14 0.99 2.14 0.15 0.54 0.31 1.22
0.09 1.11 2.23 0.05 0.32 0.63 1.76
0.09 1.19 2.34 0.05 0.33 0.62 1.85
0.17 1.03 7.89 0.69 0.21 0.10 1.12
0.10 0.94 7.12 0.75 0.16 0.09 0.87
0.08 0.79 4.46 0.62 0.36 0.02 0.42
0.28 1.12 2.68 0.22 0.64 0.14 1.15
0.11 1.05 2.06 0.09 0.49 0.42 1.39
0.12 1.15 2.16 0.06 0.46 0.48 1.57
0.01 0.70 6.90 0.84 0.12 0.04 0.37
0.01 0.59 6.04 0.79 0.17 0.04 0.35
0.03 0.55 4.00 0.68 0.30 0.02 0.27
0.04 1.07 1.73 0.15 0.54 0.31 1.12
0.12 1.18 2.69 0.15 0.65 0.20 1.32
0.07 1.24 2.51 0.12 0.60 0.28 1.46
80
90
95
99
P5Bc2 60
70
80
90
95
99
Fig. 12 UV-Vis absorption spectra of P5Bc2 in water–THF mixtures
with different volume fractions of water (10 mM).
P6Bc2 60
different predominant roles. For example, in the mixture with
60% water fraction, the excited molecules of P4Bc2 mainly decay
through the second pathway (A2 ¼ 0.51). However, for P5Bc2
and P6Bc2, the excited states mainly decay through the first
pathway with A1 ¼ 0.69 and A1 ¼ 0.84, respectively. With
70
80
90
95
99
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occupied molecular orbital (LUMO/HOMO) energy gaps DEg
for the compounds were estimated from the absorption edge of
UV-Vis absorption spectra.
The sizes of the particles of the compounds in THF–water
mixtures were determined using a ZetaPALS dynamic light
scattering system (Brookhaven, ZetaPALS Zeta Potential
Analyzer).
The water–THF mixtures with different water fractions were
prepared by slowly adding distilled water into the THF solution
of samples under ultrasound at room temperature. For example,
a 70% water fraction mixture was prepared in a volumetric flask
by adding 7 mL distilled water into 3 mL THF solution of the
sample. The concentrations of all samples were adjusted to 10
mM after adding distilled water.
Fig. 14 Relationship between the weighted mean lifetimes of the
synthesized compounds and the water fractions in water–THF mixtures.
Synthesis of TPE-PBr
A 2.2 M solution of n-butyllithium in hexane (23.8 mmol, 10.8
mL) was added into a solution of diphenylmethane ꢀ(4.00 g, 23.8
mmol) in anhydrous tetrahydrofuran (50 mL) at 0 C under an
argon atmosphere. After stirring for 1 h at that temperature, the
4-(4-bromophenyl)benzophenone (6.41 g, 19.0 mmol) was added
and the reaction mixture was stirred for 10 h allowing the
temperature to rise gradually to room temperature. Then the
reaction was quenched with an aqueous solution of ammonium
chloride and the mixture was extracted with dichloromethane.
The organic layer was evaporated after drying with anhydrous
sodium sulfate and the resulting crude product was dissolved in
toluene (100 mL). The p-toluenesulfonic acid (1.00 g, 5.8 mmol)
was added, and the mixture was refluxed overnight and cooled to
room temperature. The mixture was evaporated and the crude
product was purified by silica gel column chromatography using
n-hexane as eluent to yield a light green powder (4.15 g, 45%). 1H
NMR (300 MHz, CDCl3) dppm: 7.49 (d, 2H), 7.38 (d, 2H), 7.28
(d, 2H), 7.12–6.98 (m, 17H). FT-IR (KBr) n/cmꢂ1: 3025, 1595,
1478, 813, 764, 699, 578. HRMS (EI), m/z: 488 ([M]+, calcd for
C32H23Br, 488); Anal. calc. for C32H23Br: C 78.85, H 4.76, Br
16.39; Found: C 78.78, H 4.72.
Experimental
Bromotriphenylethylene, diphenylmethane, 4-bromobenzophe-
none, 4-(4-bromophenyl)benzophenone, n-butyl-lithium in
hexane (2.2 M), tetrakis(triphenylphosphine)palladium(0), p-
toluenesulfonic acid, tricaprylylmethyl-ammonium chloride
(Aliquat 336) and tetrabutylammonium perchlorate (electro-
chemical grade) purchased from Alfa Aesar were used as
received. All other reagents and solvents were purchased as
analytical grade from Guangzhou Dongzheng Company (China)
and used without further purification. Tetrahydrofuran (THF)
was distilled from sodium/benzophenone. Ultra-pure water was
used in the experiments. TPE-Br5 and C2B4 were synthesized
according to the literature methods.
1H NMR and 13C NMR spectra were measured on a Mercury-
Plus 300 spectrometer [CDCl3 or DMSO-d6 as solvent and tet-
ramethylsilane (TMS) as the internal standard]. Mass spectra
(MS) were measured on a Thermo MAT95XP-HRMS spec-
trometer. Elemental analyses (EA) were performed with an
Elementar Vario EL elemental analyzer. Fluorescence spectra
were measured on a Shimadzu RF-5301pc spectrometer with
a slit width of 1.5 nm for both excitation and emission. Time-
resolved emission decay behaviors were done with an Endin-
burgh Instruments Ltd spectrometer (FLSP920) and the data
were processed according to the literature method.8 Differential
scanning calorimetry (DSC) curves were obtained with
a NETZSCH thermal analyzer (DSC 204) at heating and cooling
Synthesis of C2B
To a stirred solution of C2Br (6.0 g, 9.0 mmol) in anhydrous THF
(100 mL) was added n-butyllithium solution in hexane (2.2 M, 6
mL, 13.2 mmol) dropwise slowly at ꢂ78 ꢀC. The mixture was
stirred at ꢂ78 ꢀC under Ar gas for an additional 5 h. B(OCH3)3
(2.2 mL) was added quickly at ꢂ78 ꢀC and the mixture was
stirred overnight allowing the temperature to rise gradually to
room temperature. Water (40 mL) was added and then acidified
with conc. HCl. The mixture was stirred for a further 2 h. The
product was extracted into ethyl acetate (3 ꢃ 50 mL). The
organic layer was separated and dried over anhydrous sodium
sulfate. After removing the solvent under reduced pressure, the
residue was chromatographed on a silica gel column with
acetone/CH2Cl2 (1 : 20 by volume) as eluent to give C2B (2.1 g,
rates of 10 C minꢂ1 under N2 atmosphere. Thermogravimetric
ꢀ
analyses (TGA) were performed with a thermal analyzer (TA
Instruments Inc. A50) under N2 atmosphere with a heating rate
of 20 C minꢂ1. The fluorescence quantum yields (F) of all the
ꢀ
compounds in different solvents or THF–water mixtures were
evaluated using 9,10-diphenylanthracene as in reference 11.
Cyclic voltammetry (CV) measurement was carried out on
a Shanghai Chenhua electrochemical workstation CHI660C in
a three-electrode cell with a Pt disk counter electrode, a Ag/AgCl
reference electrode, and a glassy carbon working electrode. All
CV measurements were performed under an inert argon atmo-
sphere with supporting electrolyte of 0.1 M n-Bu4NClO4 in
dichloromethane at a scan rate of 100 mV sꢂ1 using ferrocene as
standard. The lowest unoccupied molecular orbital/highest
1
55% yield). H NMR (300 MHz, DMSO-d6) dppm: 7.14 (s, 1H),
7.25–7.58 (m, 16 H), 7.62–7.78 (m, 8 H), 7.98 (s, 2 H, –B(OH)2),
8.20–8.30 (m, 4 H); MS (EI), m/z: 586 ([Mꢂ(B(OH)2)]+, calcd for
C44H29, 585); Anal. calc. for C44H31BN2O2: C 83.81, H 4.96, N
4.44; Found: C 83.64, H 4.89, N 4.48.
1794 | J. Mater. Chem., 2011, 21, 1788–1796
This journal is ª The Royal Society of Chemistry 2011

View Article Online
1
Synthesis of P4Bc2
47% yield). H NMR (300 MHz, CDCl3) dppm: 7.02–7.17 (m,
16H), 7.2–7.36 (m, 8H), 7.37–7.73 (m, 24H), 8.17 (d, 4H, J ¼ 7.5
Hz); 13C NMR (75 MHz, CDCl3) dppm: 143.90, 143.11, 142.36,
142.08, 141.56, 141.38, 141.20, 140.93, 140.66, 139.87, 139.50,
138.38, 137.42, 136.38, 132.21, 132.04, 131.61, 131.54, 130.39,
129.16, 128.53, 127.96, 127.59, 127.42, 127.34, 127.04, 126.82,
126.71, 136.23, 123.73, 120.62, 120.32, 110.09, 110.02; MS (EI)
calcd. for C76H52N2 992, found 992; Anal. calc. for C76H52N2: C
91.90, H 5.28, N 2.82; Found: C 91.85, H 5.21, N 2.78.
Bromotriphenylethylene (0.24 g, 7.16 ꢃ 10ꢂ4 mol) and C2B (0.30
g, 4.76 ꢃ 10ꢂ4 mol) were dissolved in the mixture of toluene (20
mL), Aliquat 336 (5 drops) and 2 M potassium carbonate
aqueous solution (5 mL). The mixture was stirred at room
temperature for 0.5 h under Ar gas followed by adding Pd(PPh3)4
(0.010 g, 8.70 ꢃ 10ꢂ6 mol) and then heated to 90 ꢀC for 24 h.
After that the mixture was poured into water and extracted three
times with ethyl acetate. The organic layer was dried over
anhydrous sodium sulfate. After removing the solvent under
reduced pressure, the residue was chromatographed on a silica
gel column with n-hexane–CH2Cl2 (3 : 1 by volume) as eluent to
Acknowledgements
The authors gratefully acknowledge the financial support from
the National Natural Science Foundation of China (Grant
numbers: 50773096 and 51073177), the Start-up Fund for
Recruiting Professionals from ‘‘985 Project’’ of SYSU, the
Science and Technology Planning Project of Guangdong Prov-
give P4Bc2 (0.22 g, 55% yield). 1H NMR (300 MHz, CDCl3) dppm
6.92 (s, 4H), 6.95–7.18 (m, 16H), 7.27–7.36 (m, 4H), 7.41–7.67
(m, 16H), 8.13–8.21 (m, 4H); 13C NMR (75 MHz, CDCl3) dppm
:
:
143.84, 143.74, 143.62, 143.08, 142.21, 141.50, 140.92, 140.70,
139.40, 137.28, 137.15, 135.34, 132.23, 131.50, 131.33, 129.62,
129.14, 127.85, 127.46, 126.97, 126.72, 126.18, 123.66, 120.56,
120.24, 110.08; MS (EI) calcd. for C64H44N2 840, found 840;
Anal. calc. for C64H44N2: C 91.40, H 5.27, N 3.33; Found: C
91.29, H 5.30, N 3.28.
ince,
China
(Grant
numbers:
2007A010500001-2,
2008B090500196), Construction Project for University-Industry
cooperation platform for Flat Panel Display from The
Commission of Economy and Informatization of Guangdong
Province (Grant numbers: 20081203) and the Open Research
Fund of State Key Laboratory of Optoelectronic Materials and
Technologies.
Synthesis of P5Bc2
1-Bromo-4-(1,2,2-triphenylethenyl)benzene (0.295 g, 7.17 ꢃ 10ꢂ4
mol) and C2B (0.30 g, 4.76 ꢃ 10ꢂ4 mol) were dissolved in the
mixture of toluene (20 mL), Aliquat 336 (5 drops) and 2 M
potassium carbonate aqueous solution (5 mL). The mixture was
stirred at room temperature for 0.5 h under Ar gas followed by
adding Pd(PPh3)4 (0.010 g, 8.70 ꢃ 10ꢂ6 mol) and then heated to
90 ꢀC for 24 h. After that the mixture was poured into water and
extracted three times with ethyl acetate. The organic layer was
dried over anhydrous sodium sulfate. After removing the solvent
under reduced pressure, the residue was chromatographed on
a silica gel column with n-hexane–CH2Cl2 (3 : 1 by volume) as
Notes and references
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(m, 7H), 7.40–7.72 (m, 18H), 8.17 (d, 4H, J ¼ 7.8 Hz); 13C NMR
(75 MHz, CDCl3) dppm: 143.86, 143.17, 142.08, 141.39, 141.08,
140.92, 140.62, 139.44, 138.19, 137.39, 137.32, 136.16, 133.32,
132.20, 132.03, 131.51, 130.26, 129.31, 129.12, 127.93, 127.88,
127.83, 127.56, 127.02, 126.66, 126.18, 123.70, 120.59, 120.27,
110.08, 110.01; MS (EI) calcd. for C70H48N2 916, found 916;
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91.71, H 5.23, N 2.97.
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Synthesis of P6Bc2
TPE-PBr (0.35 g, 7.18 ꢃ 10ꢂ4 mol) and C2B (0.30 g, 4.76 ꢃ 10ꢂ4
mol) were dissolved in the mixture of toluene (20 mL), Aliquat
336 (5 drops) and 2 M potassium carbonate aqueous solution (5
mL). The mixture was stirred at room temperature for 0.5 h
under Ar gas followed by adding Pd(PPh3)4 (0.010 g, 8.70 ꢃ 10ꢂ6
ꢀ
mol) and then heated to 90 C for 24 h. After that the mixture
was poured into water and extracted three times with ethyl
acetate. The organic layer was dried over anhydrous sodium
sulfate. After removing the solvent under reduced pressure, the
residue was chromatographed on a silica gel column with n-
hexane–CH2Cl2 (6 : 1 by volume) as eluent to give P6Bc2 (0.22 g,
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This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 1788–1796 | 1795

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1796 | J. Mater. Chem., 2011, 21, 1788–1796
This journal is ª The Royal Society of Chemistry 2011