High performance aniline vapor detection based on multi-branched fluorescent triphenylamine-benzothiadiazole derivatives: Branch effect and aggregation control of the sensing performance

Article abstract of DOI:10.1039/c2jm30933e

A series of benzothiadiazole-pyridine branched triphenylamine derivatives TPA1BP, TPA2BP and TPA3BP have been designed and synthesized to sense aniline vapor with distinguished sensitivity, selectivity and repeatability via photoinduced electron transfer (PET). Suitable energy levels ensure the high selectivity to aniline for all three sensory materials. However, the aggregations of the three materials in the film state on a quartz substrate increase along with the branches, which highly deteriorate the sensing performance for less efficient fluorescence, lower contact area and inferior vapor penetration. The oriented ZnO nanorod array is introduced as the substrate to eliminate the aggregation and enhance the sensing performance, because of its high surface-to-volume ratio and 3D structure. Therefore, the cooperative effect that the sensing performance of TPAnBP increases with the number of branches could be observed; fluorescence intensities of the films on the nano-substrate are 34%, 45% and 54% quenched for TPA1BP, TPA2BP and TPA3BP, respectively, after exposure to 300 ppm aniline vapor for less than 5 s. Moreover, the fluorescences of all three sensory materials are almost 100% recovered by eluting with fresh air for 20 s and could be reused immediately. The detection limits are predicted to be 1 ppm for TPA1BP, 100 ppb for TPA2BP and 1 ppb for TPA3BP according to the fitted plot, demonstrating a significant cooperative effect of the molecular branches.

Full text of DOI:10.1039/c2jm30933e

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PAPER
High performance aniline vapor detection based on multi-branched fluorescent
triphenylamine-benzothiadiazole derivatives: branch effect and aggregation
control of the sensing performance†
a
Liqi Shi,ab Chao He,ab Defeng Zhu, Qingguo He, a Yang Li,c Yan Chen,c Yuxi Sun,d Yanyan Fu,a Dan Wen,ab
*
a
Huimin Cao and Jiangong Cheng
a
*
Received 15th February 2012, Accepted 4th April 2012
DOI: 10.1039/c2jm30933e
A series of benzothiadiazole-pyridine branched triphenylamine derivatives TPA1BP, TPA2BP and
TPA3BP have been designed and synthesized to sense aniline vapor with distinguished sensitivity,
selectivity and repeatability via photoinduced electron transfer (PET). Suitable energy levels ensure the
high selectivity to aniline for all three sensory materials. However, the aggregations of the three
materials in the film state on a quartz substrate increase along with the branches, which highly
deteriorate the sensing performance for less efficient fluorescence, lower contact area and inferior vapor
penetration. The oriented ZnO nanorod array is introduced as the substrate to eliminate the
aggregation and enhance the sensing performance, because of its high surface-to-volume ratio and 3D
structure. Therefore, the cooperative effect that the sensing performance of TPAnBP increases with the
number of branches could be observed; fluorescence intensities of the films on the nano-substrate are
34%, 45% and 54% quenched for TPA1BP, TPA2BP and TPA3BP, respectively, after exposure to
300 ppm aniline vapor for less than 5 s. Moreover, the fluorescences of all three sensory materials are
almost 100% recovered by eluting with fresh air for 20 s and could be reused immediately. The detection
limits are predicted to be 1 ppm for TPA1BP, 100 ppb for TPA2BP and 1 ppb for TPA3BP according to
the fitted plot, demonstrating a significant cooperative effect of the molecular branches.
such as pre-concentration of the samples by extraction. Fluo-
1. Introduction
rescent chemosensors have great advantages over other methods
due to their high sensitivity, easy performance and fast response
that are capable for real-time monitoring.19 These fluorescent
chemosensors are mostly based on fluorescence quenching or the
recovery of the active materials by interaction with analytes.
Many fluorescent sensors utilizing polymers or small molecules
as active materials have been developed such as explosive
sensors,20,21 ion sensors22,23 and biomolecule sensors.24,25
However, it was seldom reported on fluorescent chemosensors
which are capable of the real-time detection of volatile aniline
with excellent sensitivity, selectivity and reversibility.26–29
The detection of organic amines has received more attention
recently as many amines have been considered as pollutants and
as toxic to human health.1–7 Aniline and its derivatives are widely
used in manufacturing dyes, rubber and agrochemicals, and
exposure to aniline is suspected to result in carcinogenicity.8,9
Thus, numerous analytical procedures have been developed for
the detection of aniline and its derivatives, including spectrom-
etry,10,11 chromatography12–15 and electrochemistry16–18 methods.
Though many of them have had much success, most of them
suffer from time-consuming and tedious sample pre-workup
In this contribution, we report on a series of sensory materials
with a donor–acceptor (D–A) conjugated structure for aniline
vapor detection, which is based on fluorescence quenching via the
mechanism of PET from aniline to the sensory material. The as-
synthesized compounds (TPAnBP, n ¼ 1, 2, 3, Scheme 1) had
triphenylamine (TPA) as the core and benzothiadiazole-pyridine
(BP) as branch substitutes. 2,1,3-Benzothiadiazole (BT) has been
widely used in various optoelectronic materials to tune the
HOMO–LUMO levels and the energy gap, owing to its electron-
withdrawing capability.30–36 Here, the TPA and BP unit were
coupled into one molecule to tune the energy levels and make it
qualify for the PET process. The survey of the branched structure
aState Key Lab of Transducer Technology, Shanghai Institute of
Microsystem and Information Technology, Chinese Academy of Sciences,
Changning Road 865, Shanghai 200050, China. E-mail: hqg@mail.sim.
ac.cn; jgcheng@mail.sim.ac.cn; Fax: + 86 21 62511070 8934; Tel: + 86
21 62511070 8936
bGraduate School of the Chinese Academy of Sciences, Yuquan Road 19,
Beijing 100039
cSchool of Environmental Science and Engineering, DongHua University,
Yanan Road 1882, Shanghai 200051, China
dResearch center of New Energy
University, Mianyang 621000, P.R. China
& Materials, Mianyang Normal
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c2jm30933e
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Scheme 1 Synthetic routes for TPAnBP (n ¼ 1, 2, 3).
lies in two aspects. Firstly, the electrons could delocalize over all
2. Results and discussion
conjugated branches in such multi-branched D–A structures
across the central TPA unit, which leads to cooperative effects
such as increased two-photon absorption cross section and
electroluminescence performance.37–39 For fluorescent sensory
materials, the cooperative effects of multi-branched structures
may also amplify the quenching signal compared with its mono-
branched counterparts. Secondly, the branch effect may be
designed to control the morphology of the film sensor and
deepen the understanding of the relationship between molecular
aggregation and sensing properties. More conjugated branches
may lead to different intermolecular packing modes in the solid
state as they tend to form an amorphous state with more
branches.40 The packing mode may play a critical role in its
sensory performance since the sensing process requires a large
contact area and a suitable interaction distance to enhance the
efficiency of electron transfer. In the film state, serious self-
aggregation may also cause poor vapor penetration, a small
contact area and low fluorescence intensity.
2.1. Synthesis
The synthetic procedure was illustrated in Scheme 1. Compound
1 was obtained from the Stille coupling of 2-(tributylstannyl)
pyridine and 4,7-dibromo-2,1,3-benzothiadiazole in 27% yield.
NBS and Br2 were used to brominate triphenylamine (TPA),
affording 2, 3 and 4 in yields of 91%, 88% and 66%, respectively.
Compounds 2, 3 and 4 were subjected to halogen–lithium
exchange and the subsequent reaction with 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane to give 5, 6 and 7 in 68%, 47%
and 57% yield, respectively. Suzuki–Miyaura cross-coupling of 1
and 5 resulted in TPA1BP (yield, 73%). Similar reactions of 6 and
7 with 1 yielded compounds TPA2BP (38.5%) and TPA3BP
(55.4%), respectively. The chemical structures of all compounds
1
were verified using H NMR spectroscopy and MALDI-TOF
mass spectrometry. The detailed synthetic route is summarized in
the supporting information.†
All of the three compounds TPAnBP (n ¼ 1, 2, 3) showed
strong fluorescence both in solution and in film state, and the
fluorescence could be quenched upon exposure to aniline vapor.
The high selectivity to aniline was demonstrated and attributed
to the appropriate energy levels for electron transfer from aniline
to the photoexcited state of TPAnBP. Furthermore, introducing
a nano-structure as the film substrate could effectively inhibit the
multi-branch induced aggregation, as well as bringing about
a fast response (within 5 s) and high reversibility (almost 100%
reversible by eluting with air for less than 20 s) to aniline vapor
for all three sensory materials. Moreover, the sensory perfor-
mance, especially the limit of detection, exponentially increased
along with the branches, indicating the strong cooperativity of
the branches; namely, TPA3BP showed the best sensory
performance for aniline detection with a limit as low as 1 ppb.
2.2. Optical and electrochemical properties
The absorption and emission spectra of TPAnBP (n ¼ 1, 2, 3) in
both solution and film were illustrated in Fig. 1, and the data
were summarized in Table 1. The spectra of the three materials
were all normalized to the maximum absorption or emission
intensity of TPA3BP whether in solution or film state. In Fig. 1a,
the absorbance of the three materials increased along with the
number of BP units both in solution (intensity ratio, 1 : 2 : 3) and
in film (1 : 1.4 : 1.9), suggesting that the molar extinction coef-
ficient increased by introducing more BP units into the one
molecule. In the film state, the absorption peaks of the three
materials red shifted by 16, 20 and 23 nm compared to those of
their solution states, indicating that molecular aggregation
occurred in the films and the aggregation tended to be more
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2.3. Sensory properties
Fig. 2 showed the energy levels and Stern–Volmer plots of
TPAnBP for different amines.4a,41 The HOMO levels of TPAnBP
were all slightly lower than that of aniline, which ensured the
PET from aniline to TPAnBP. The PET from aniline to the
photoexcited state of TPAnBP resulted in fluorescence quench-
ing. However, for other amines, such as triethylamine, hexyl-
amine, cyclohexylamine, benzylamine and p-nitroaniline, their
HOMO energy levels were lower than that of TPAnBP, therefore
no fluorescence quenching was found. It should be noted that the
PET between p-methylaniline and TPAnBP led to a much lower
quenching efficiency in contrast to aniline, which might be
attributed to its much higher HOMO level. The selective optical
response of TPAnBP ensured its application in aniline detection.
Fig. 3 illustrated the fluorescence responses of TPAnBP (n ¼ 1,
2, 3) to aniline vapor in the film state on quartz substrate.
TPA1BP showed a much higher quenching efficiency than
TPA2BP and TPA3BP. About 35% of the fluorescence of
TPA1BP is quenched after the first 10 s of exposure to saturated
vapor of aniline (860 ppm) and it increased to 50% upon further
exposure for 50 s. However, TPA2BP and TPA3BP gave similar
quenching efficiencies which are only 8% quenched within the
first 10 s, and increased to 24% and 27% with further exposure for
50 s, respectively. As the energy levels and molecular structures
of TPAnBP are similar, the decreased quenching efficiency from
TPA1BP to TPA3BP could arise from the morphology difference
of the films.
Fig. 1 UV-vis absorption (a) and emission (b) spectra of TPAnBP (n ¼
1, 2, 3) in chloroform solution (1 ꢁ 10ꢀ5 M) and film. The films were spin-
casted from their chloroform solution. The spectra of the three
compounds in (a) and (b) were measured under the same conditions.
severe with more branches. The emission intensity of TPAnBP
(n ¼ 1, 2, 3) in solution increased (1 : 1.7 : 2.2, shown in Fig. 1b)
due to the successively enhanced extinction coefficient (Table 1).
However, in the film state, TPAnBP showed comparable emis-
sion intensities, indicating that aggregation took place with the
increase of branches. The detailed morphology effect was dis-
cussed in the following investigation.
The electrochemical behavior of TPAnBP (n ¼ 1, 2, 3) was
characterized and their cyclic voltammetric curves were shown in
Fig. S1.† The onset oxidation/reduction potentials of TPAnBP
(n ¼ 1, 2, 3) were estimated to be 0.92/ꢀ1.32V, 0.94/ꢀ1.31V and
0.96/ꢀ1.30V vs. SCE, respectively. The HOMO/LUMO energy
levels and energy bandgap (Eg) of the three compounds were
calculated as shown in Table 1.
Fig. 2 HOMO (p) and LUMO (p*) energy levels of TPA1BP and
different amines. The inset shows the Stern–Volmer plots of TPA1BP
(10ꢀ4 M in THF) in the presence of different amines.
Table 1 Optical and electrochemical properties of TPAnBP (n ¼ 1, 2, 3)
Absa, lmax/nm
PLa, lmax/nm
Solution
Film
Solution
Film
HOMOb/eV
LUMOb/eV
Egb/eV
F
TPA1BP
TPA2BP
TPA3BP
450
459
463
466
479
486
591
591
591
576
586
595
ꢀ5.66
ꢀ5.68
ꢀ5.70
ꢀ3.42
ꢀ3.43
ꢀ3.44
2.24
2.25
2.26
0.51
0.50
0.55
a
b
The excitation light wavelength was at 460 nm, and the films were spin-casted from their chloroform solution on a quartz plate. HOMO ¼
onset
onset
ꢀe(Eox
+ 4.741) (eV), LUMO ¼ ꢀe(Ered
+ 4.741) (eV), Eg ¼ LUMO ꢀ HOMO.
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aggregations in TPA2BP and TPA3BP were attributed to the
increase of the BP units which caused strong intermolecular
interactions via heteroatom contacts and/or p–p interactions of
the thiadiazole-containing compounds. That is, the increased
self-aggregation from TPA1BP to TPA3BP not only resulted in
the low fluorescence intensity as we discussed above, but also
induced a poor sensory response due to poor vapor penetration
and a small contact area of the sensory films.
To eliminate the aggregation of the as-prepared film sensor,
a nano-structured substrate was introduced since its high area-
to-volume ratio could ensure the good dispersion and de-aggre-
gation of the TPAnBP molecules and provide more contact sites
for the sensory materials.42,43 Besides, as we reported recently,
nanorod arrays could bring about a significant enhancement of
the fluorescence intensity and sensing performance for their
optical modulation of the nanorod waveguide.43
In this work, the sensor device was fabricated by a simple spin-
coating of TPAnBP solution onto the vertically oriented ZnO
nanorods arrays (ꢂ1.2 mm height, possessing uniform nanorods
of ꢂ80 nm in diameter). Here, the same concentrations of
TPAnBP (n ¼ 1, 2, 3) were taken as those used on the quartz
substrate. As shown in Fig. 4, all structures exhibited uniform
verticality, enough voids and a smooth surface, which ensured
high efficient light transmission and quick diffusion of vapor
molecules. No obvious morphological differences could be found
after coating. In particular, no aggregation of TPA3BP appeared
with the introduction of nanorod arrays, which strongly supports
our assumption. Top-view images were presented in Fig. S2.†
Fig. 5 presented the real time-course fluorescence responses of
TPAnBP (n ¼ 1, 2, 3) films on nano-substrates to aniline vapors
of different concentrations. As expected, TPAnBP (n ¼ 1, 2, 3)
films on the nano-substrates displayed very fast responses and
were almost 100% reversible to aniline vapor in Fig. 5a. In
contrast to the best sensory performance of Fig. 3 that only 50%
was quenched after exposure to 860 ppm aniline vapor for 50 s,
the fluorescence of the film on the nano-substrate was 34%, 45%
and 54% quenched for TPA1BP, TPA2BP and TPA3BP after
exposure to 300 ppm aniline vapor for less than 5 s, respectively.
This result indicated that the aggregation could be controlled by
introducing the ZnO nanorod array. The increased BP unit of
TPA2BP and TPA3BP is advantageous for the enhanced sensi-
tivity. Quantum-chemical calculations (Fig. S3†) indicated that
the electrons in the HOMO orbital delocalized across the three
Fig. 3 The time-course fluorescence responses of TPAnBP (n ¼ 1, 2, 3)
films on quartz to aniline saturated vapor at 25 ꢃC and their corre-
sponding SEM images.
These morphology differences were investigated by scanning
electron microscopy (SEM) images of TPAnBP (n ¼ 1, 2, 3)
coated from their chloroform solutions (7 ꢁ 10ꢀ4 M). The SEM
image showed that on a quartz substrate, TPA1BP formed
a relatively smooth film except for a few points of imperfection.
TPA2BP became separated lumps and triple-branched TPA3BP
evolved into nano-sticks with a diameter of ꢂ200 nm. The severe
Fig. 4 Cross-view images of the nanorod structures (a–c) before and
(d–f) after TPAnBP (n ¼ 1, 2, 3) coating (scale bar is 1 mm).
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Fig. 6 Fluorescence responses of the TPA3BP films on nano-substrates
after exposure to 300 ppm of various amines and solvent vapors for 5 s.
branch effect existed in the branched sensing system. The selec-
tivity test proved that other amines and common solvent vapors
(Fig. 6) caused no quenching for all the sensory devices.
4. Conclusions
In summary, three benzothiadiazole-pyridine branched triphe-
nylamine derivatives have been synthesized and characterized for
aniline sensing. The HOMO/LUMO levels of the molecules were
tuned to achieve a selective PET from aniline to the analytes. All
of the three compounds showed strong fluorescence with
a quantum efficiency as high as ꢂ0.5 in solution. However, with
the increase of the BP moiety, severe aggregation in the film
occurred, which retards the vapor penetration and decreases the
active contact area. A nano-structured substrate was used to
decrease the aggregation and increase the sensing performance.
TPA3BP showed a 100 and 1000 fold decreased limit of detection
over its bi-branched and mono-branched counterparts to aniline
vapor when casted on a nano-structure for its multi-branched
structure. A significant improvement of the sensory property,
attributed to the controlled aggregation via the nano-structured
substrate, also suggests that besides the molecular structure,
morphology control is considered more important in sensory
material and device design. The designed and synthetic strategy
presents a simple and practical approach to construct fluores-
cence chemosensors for environmental pollutant detection and
monitoring.
Fig. 5 (a). Time-course fluorescence responses of TPAnBP (n ¼ 1, 2, 3)
films on nano-substrates to the different concentrations of aniline vapor:
all the first exposures were at 300 ppm, after elution with air, the next
exposure was at a half-diluted concentration of the previous vapor. All
the emission intensities were monitored at 570 nm. (b) Fluorescence
quenching efficiency (1 ꢀ I/I0) as a function of the vapor pressure of
aniline, fitted with the Langmuir equation.
branches, except for the pyridyl part, proving that the coopera-
tive effect would contribute to the enhanced sensitivity in
TPA3BP. Moreover, the fluorescence of all the sensory films was
almost 100% recovered by eluting with air for 20 s and the
recovered film sensor could be reused immediately.
To determine the detection limit, the aniline vapor was diluted
with air every time by half in the subsequent continuous sensing
test, and the fluorescence quenching efficiency of TPAnBP (n ¼ 1,
2, 3) as a function of the vapor pressure of aniline was illustrated,
as shown in Fig. 5b. The quenching data of each film sensor is
well-fitted by the Langmuir equation and the detection limit can
be extrapolated to be ꢂ1 ppm for TPA1BP, ꢂ100 ppb for
TPA2BP and ꢂ1 ppb for TPA3BP according to the fitted plot, if
the triple multiple signal to noise ratio of the fluorescent detec-
tion device was considered as 0.01. Whereas, in the latest reports,
a well-calibrated photodetector can detect intensity changes as
low as 0.1%,4a,4b the detection limit of TPA3BP could be deter-
mined as 1 ppt. Such a 10 and 100 fold detection limit difference
from TPA1BP to TPA3BP means a significant cooperative
Experimental
Synthesis
4-Bromo-7-(2-pyridinyl)-2,1,3-benzothiadiazole (1). A 250 mL
three-necked round-bottomed flask was charged with 4,7-
dibromo-2,1,3-benzothiadiazole (4.8 g, 16.3 mmol) and
Pd(PPh3)4 (0.95 g, 0.82 mmol) under argon, then a toluene
solution (120 mL) of 2-(tributylstannyl)pyridine (6 g,16.25
mmol) was added. The reaction mixture was heated to reflux at
117 ꢃC and stirred for 12 h. After being cooled to room
temperature, the mixture was washed with saturated aqueous
NaCl (100 mL) and the organic layer was separated and dried
over anhydrous MgSO4. The solvent was removed and the
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residue was purified by column chromatography to afford
1
a yellow solid (1.28 g, 27%). H NMR (500 M, CDCl3, ppm)
4,40-(Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl))triphe-
nylamine (6). To a THF solution of 3 (2 g, 5 mmol), n-BuLi
(7 mL, 19.6 mmol) was added under argon and stirred for 1 h at
ꢀ78 ꢃC; then 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxabor-
olane (4.4 mL, 4.0 g, 21.36 mmol) was added dropwise. After
stirring at this temperature for 1 h, the mixture was cooled to
room temperature and reacted for 12 h. The mixture was
quenched with water (20 mL) and extracted with CHCl2, and the
organic layer was dried over anhydrous MgSO4. The solvent was
removed and the residue was pre-purified by column chroma-
tography followed by recrystallization in methanol to afford
d 8.77 (d, 1H, J ¼ 4 Hz), 8.63 (d, 1H, J ¼ 7.5 Hz), 8.36 (d, 1H, J ¼
8 Hz), 8.00 (d, 1H, 7.5Hz), 7.87 (m, 1H), 7.26 (m, 1H); MALDI-
TOF MS: m/z 292.
4-Bromotriphenylamine (2). A solution of NBS (3.63 g, 20.4
mmol) in DMF (40 mL) was added dropwise into a solution of
triphenylamine (5.0 g, 20.35 mmol) in DMF (60 mL), and then
stirred at 0 ꢃC for 4 h. The solvent was removed, the residue was
washed with water (150 mL) and saturated aqueous NaCl
(100 mL), and the organic layer was dried over anhydrous MgSO4.
Then the solvent was removed and the residue was purified by
silica gel chromatography eluted with petroleum ether to get
pellucid liquid (6 g, 91%). 1H NMR (500 M, CDCl3, ppm) d 7.31
(d, 2H, J ¼ 8.5 Hz), 7.24 (t, 4H, 7.5Hz), 7.07 (d, 4H, J ¼ 8 Hz), 7.02
(t, 2H, J ¼ 7.5HZ), 6.93 (m, 2H); MALDI-TOF MS: m/z 323.
1
a white solid (1.15 g, 47%). H NMR (500 MHz, CDCl3, ppm)
d 7.66 (d, 4H, J ¼ 8.35 Hz), 7.27 (s, 1H), 7.24 (s, 1H), 7.09 (d, 3H,
J ¼ 7.8 Hz), 7.04 (d, 4H, J ¼ 8.45 Hz), 1.33 (s, 24H); MALDI-
TOF MS: m/z 497.2.
4,40,400-(Tri(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl))tri-
phenylamine (7). To a THF solution of 4 (2.0g, 4.2 mmol), n-BuLi
(1.54 g, 24.5 mmol) was added under argon and stirring for 1 h at
ꢀ78 ꢃC, then 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxabor-
olane (5.5 mL, 5.0 g, 26.7 mmol) was added dropwise. After
stirring at this temperature for 1 h, the mixture was cooled to
room temperature and reacted for 12 h. The mixture was
quenched with water (20 mL) and extracted with CHCl2, and the
organic layer was dried over anhydrous MgSO4. The solvent was
removed and the residue was purified by recrystallization in
4,40-(Dibromo)triphenylamine (3). A solution of NBS (7.26 g,
40.8 mmol) in DMF (80 mL) was added dropwise into a solution
of triphenylamine (5.0g, 20.35 mmol) in DMF (60 mL), and then
stirred at 0 ꢃC for 4 h. The solvent was removed, the residue was
washed with water (150 mL), saturated aqueous NaCl (100 mL),
and the organic layer was dried over anhydrous MgSO4. Then
the solvent was removed and the residue was purified by silica gel
chromatography eluted with petroleum ether to get pellucid
liquid (7.2 g, 88%). 1H NMR (500 MHz, CDCl3, ppm) d 7.31 (m,
4H), 7.24 (m, 2H), 7.05 (m, 3H), 6.91 (m, 4H); MALDI-TOF
MS: m/z 400.9.
1
methanol to afford a white solid (1.5g, 57%). H NMR (500
MHz, CDCl3, ppm) d 7.67 (d, 6H, J ¼ 8.45 Hz), 7.06 (d, 6H, J ¼
8.45 Hz), 1.34(s, 36H); MALDI-TOF MS: m/z 623.4.
4,40,400-(Tribromo)triphenylamine (4). A 250 mL three-necked
round-bottomed flask charged with triphenylamine (5.0120 g,
20.4 mmol), and chloroform (100 mL). A solution of Br2
(3.25 mL, 0.0634 mol) in chloroform (20 mL) was added drop-
wise under UV irradiation. The reaction solution turned from
purple red to green. The reaction solution was stirring at room
temperature for 24 h under UV irradiation. Then the mixture was
extracted with CHCl3 (30 mL), and washed with NaOH (2 M aq)
and water. The organic layer was separated and dried over
anhydrous MgSO4. The solvent was removed and the residue was
pre-purified by column chromatography eluted with chloroform
and followed by recrystallization in hexane to get a pellucid solid
(6.45 g, 66%). 1H NMR (500 MHz, CDCl3, ppm) d 7.34 (m, 6H),
6.91 (m, 6H); MALDI-TOF MS: m/z 478.8.
4-(4-(Pyridine-2-yl)-2,1,3-benzothiadiazol-7-yl)triphenylamine
(TPA1BP). To a flask of 5 (0.5 g, 1.3 mmol), 1 (400 mg, 1.37
mmol) and Pd(PPh3)4 (20 mg, 0.017 mmol), saturated aqueous
K2CO3 (1 mL) and toluene (20 mL) were injected under argon.
The mixture was heated to reflux for 48 h. After being cooled to
room temperature, the mixture was washed with water (40 mL),
and extracted with CH2Cl2 (100 mL). The organic layer was
separated and dried over anhydrous MgSO4. The solvent was
removed and the residue was purified by recrystallization in
1
methanol to afford a red solid (449 mg, 73%). H NMR (500
MHz, CDCl3, ppm) d 8.79 (d, 1H, J ¼ 4.5 Hz), 8.69 (d, 1H,
7.5Hz), 8.52 (d, 1H, 7.5Hz), 7.87 (m, 3H), 7.83 (d, 1H, J ¼ 7.5
Hz), 7.33 (m, 1H), 7.28 (m, 4H), 7.19 (m, 6H), 7.06 (t, 2H, J ¼ 7.5
Hz); MALDI-TOF MS: m/z 456.
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)triphenylamine
(5). To a THF solution of 2 (2 g, 6.2 mmol), n-BuLi (5 mL, 0.88 g,
14 mmol) was added under argon and stirring for 1 h at ꢀ78 ꢃC,
4,40-(Bis(4-(pyridine-2-yl)-2,1,3-benzothiadiazol-7-yl))triphe-
nylamine (TPA2BP). To a flask of 6 (0.2 g, 0.41 mmol), 1
(270 mg, 0.93 mmol) and Pd(PPh3)4 (20 mg, 0.017 mmol), satu-
rated aqueous K2CO3 (1 ml) and toluene (20 mL) were injected
under argon. The reaction mixture was heated to reflux for 48 h.
After being cooled to room temperature, the mixture was washed
with water (40 mL), and extracted with CH2Cl2 (100 mL). The
organic layer was separated and dried over anhydrous MgSO4.
The solvent was removed and the residue was purified by
recrystallization in methanol to afford a red solid (103 mg,
then
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(2.8 mL, 2.55 g, 13.6 mmol) was added dropwise, after stirring at
this temperature for 1 h, the mixture was cooled to room
temperature and reacted for 12 h. The mixture was quenched
with water (20 mL) and extracted with CHCl2, and the organic
layer was dried over anhydrous MgSO4. The solvent was
removed and the residue was pre-purified by column chroma-
tography followed by recrystallization in methanol to get a white
solid (1.56 g, 68%). 1H NMR (500 MHz, CDCl3, d (ppm)) d 7.65
(d, 2H, 8.5Hz), 7.23 (m, 4H), 7.09 (d, 4H, J ¼ 7.5 Hz), 7.01 (m,
4H); MALDI-TOF MS: m/z 371.
1
38.5%). H NMR (500 MHz, CDCl3, ppm) d 8.79 (d, 2H, J ¼
4.65 Hz), 8.69 (d, 2H, J ¼ 8 Hz), 8.53 (d, 2H, J ¼ 7.45 Hz), 7.95
(d, 4H, J ¼ 8.6 Hz), 7.86 (m, 4H), 7.29 (m, 10H), 7.12 (t, 1H, J ¼
7.25 Hz); MALDI-TOF MS: m/z 667.1.
11634 | J. Mater. Chem., 2012, 22, 11629–11635
This journal is ª The Royal Society of Chemistry 2012

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4,40,400-(Tri(4-(pyridine-2-yl)-2,1,3-benzothiadiazol-7-yl))tri-
phenylamine (TPA3BP). To a flask of 7 (0.2 g, 0.32 mmol), 1
(326mg, 1.12 mmol) and Pd(PPh3)4 (20 mg, 0.017 mmol), satu-
rated aqueous K2CO3 (1 mL) and toluene (20 mL) were injected
under argon. The reaction mixture was heated to reflux for 48 h.
After being cooled to room temperature, the mixture was washed
with water (40 mL), and extracted with CH2Cl2 (100 mL). The
organic layer was separated and dried over anhydrous MgSO4.
The solvent was removed and the residue was purified by
recrystallization in methanol to afford a red solid (155 mg,
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55.4%). H NMR (500 MHz, CDCl3, ppm) d 8.81 (d, 3H, J ¼
4 Hz), 8.71 (d, 3H, J ¼ 8 Hz), 8.56 (d, 3H, J ¼ 7.5 Hz), 8.01 (d,
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(m, 3H); MALDI-TOF MS: m/z 878.1.
Acknowledgements
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The authors are thankful for the financial support from the
National Nature Sciences Foundation of China (No. 51003118,
50973128, 61007066), the research programs from the Ministry
of Science and Technology of China (No. 2009BAK64B03,
2012BAK07B03), the Shanghai Science and Technology
Committee (No. 11JC1414700).
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