New aggregation-induced emission enhancement materials combined triarylamine and dicarbazolyl triphenylethylene moieties

Article abstract of DOI:10.1039/c0jm00599a

A new class of compounds containing triarylamine and dicarbazolyl triphenylethylene moieties with high thermal stability and aggregation-induced emission enhancement properties was synthesized. The glass transition temperature and 5% weight loss temperatu

Full text of DOI:10.1039/c0jm00599a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
New aggregation-induced emission enhancement materials combined
triarylamine and dicarbazolyl triphenylethylene moieties†
*
Haiyin Li, Zhenguo Chi, Bingjia Xu, Xiqi Zhang, Zhiyong Yang, Xiaofang Li, Siwei Liu, Yi Zhang
*
and Jiarui Xu
Received 4th March 2010, Accepted 27th April 2010
DOI: 10.1039/c0jm00599a
A new class of compounds containing triarylamine and dicarbazolyl triphenylethylene moieties with
high thermal stability and aggregation-induced emission enhancement properties was syntꢀhesized. The
glass transition temperature and 5% weight loss temperature of 3B-TPA are up to 214.3 C and
516.8 ꢀC, respectively. The compounds exhibited significant photoinduced intramolecular charge-
transfer properties. The aggregation considerably affected the p–p* transition and resulted in 6–7 nm
red shift of the p–p* absorption wavelength at the peak in UV-vis spectra. The compounds could emit
intense blue-green light in aggregated states.
morphological stability and optoelectronic properties.6 On the
Introduction
other hand, we have already reported in the recent works a new
class of triphenylethylene carbazole derivatives that displayed
strong blue light emissions, high Tg temperatures and AIE
effects.7 We are thus extending these studies by combining
dicarbazolyl triphenylethylene and triarylamine units into
a single compound via synthetic methodology, and to design
materials with potential technological applications.
Organic luminescent materials with strong solid-state emission
have gained great interest for their important use in the applied
fields of electroluminescence devices.1 The aggregation caused by
the strong intermolecular p–p interaction in the solid state
generally debases or quenches the emission.2 Aggregation
quenching is considered as an intractable problem in the devel-
opment of devices because organic materials are normally used
as thin solid films, and that aggregation inherently accompanies
film formation. Thus, it is highly desirable to develop lumines-
cent materials that emit intense light in the solid state and can
overcome the aggregation-quenching problem. Recently, an
unusual phenomenon, where some luminescent molecules have
enhanced emission in the solid state, referred to as aggregation-
induced emission (AIE)3 or aggregation-induced emission
enhancement (AIEE),4 has been observed. This phenomenon
offers a new path in solving problems on aggregation-caused
quenching.
In this article, we present the synthesis of three new
compounds in which triphenylamine was mono-, di- and tri-
substituted by dicarbazolyl triphenylethylene units. Their
thermal and optoelectronic properties are also discussed. The
compounds exhibited significant photoinduced intramolecular
charge-transfer properties. It was found that the aggregation has
a pronounced effect on the p–p* transition. In particular, the
three compounds have exhibited aggregation-induced emission
enhancement and high levels of thermal stability, which might be
promising as luminescent materials.
Highly electron-rich triarylamines, which are known to have
high hole mobility, have been widely used as hole-transporting
materials in multilayer organic electro-luminescence devices.5
However, triphenylamine (TPA) derivatives have the tendency to
crystallize upon exposure to heat resulting in aggregation-
induced fluorescence quenching of fluorophores, and often
possess low glass transition temperatures (Tg) (i.e., poor
morphological stability), resulting in low reliability when used in
optoelectronic devices. Aggregation quenching and low Tg are
the major reasons for the rare use of TPA derivatives for layer
emission in electroluminescent device applications. Conse-
quently, many structural modifications have been made in
attempts to develop new TPA derivatives that possess high
Results and discussion
Synthesis
The synthetic routes to the desired compounds are illustrated in
Scheme 1. The intermediates 1,7 2,7 4,8 59 and 610were prepared
according to the methods in the literatures. The key intermediate,
3, was prepared from 2 by lithiation with n-butyllithium and
boronation with trimethyl borate (55% yield). However, we
could not obtain compound 3 by Grignard reaction because
compound 2 did not react with magnesium (Mg) and failed to
produce a Grignard reagent. The target compounds, 1B-TPA,
2B-TPA and 3B-TPA, were synthesized by Suzuki coupling
reactions of 3 with the corresponding halogenated triphenyl-
amines 4, 5 and 6 in the presence of a palladium(0) catalyst (36–
53% yield). The products exhibited good solubility in common
organic solvents and were purified by silica gel column chro-
matography using dichloromethane–n-hexane as eluent. Their
chemical structures were confirmed with proton nuclear
magnetic resonance (1H-NMR), high resolution mass
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: UV-vis and PL
spectra, and CV curves of 1B-TPA and 2B-TPA. See DOI:
10.1039/c0jm00599a
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Compared with the mono-substituted 1B-TPA, the Tg of 3B-
TPA was higher by 76.4 ꢀC.
The DSC curves of the samples in the first and second heating
runs are shown in Figs 1 and 2, respectively. In the first heating
run, only compound 1B-TPA exhibited a very small melting
Fig. 1 DSC scans of the synthesized compounds at first heating.
Scheme 1 Synthetic routes to the compounds.
spectrometer (HRMS), Fourier transform infrared spectroscopy
(FT-IR) and elementary analysis (EA).
Thermal properties
The thermal stability of organic materials is critical for their
applications as luminescent emitters because thermal stability
governs the stability and lifetime of devices. If a device is heated
above the Tg of its organic material components, irreversible
failure can occur. Hence, a relatively high Tg is essential for
emissive materials used for optoelectronic applications.
Fig. 2 DSC scans at second heating (samples after cooled from their
melts with a 10 ꢀC minꢁ1 cooling rate).
Thermal properties were investigated by differential scanning
calorimetry (DSC) and thermal gravimetric analysis (TGA). The
Tg values of 1B-TPA, 2B-TPA and 3B-TPA were 137.9, 196.7
and 214.3 ꢀC, respectively, which were much higher than those of
the two reported typical AIE-active compounds, 1-methyl-
1,2,3,4,5-pentaphenylsilole (MPPS, 54 ꢀC) and 1,1,2,3,4,5-hex-
aphenylsilole (HPS, 65 ꢀC).11 The high Tg is attributed to the
effect of the bulky carbazolyl groups. To the best of our
knowledge, the Tg of 3B-TPA is currently the highest reported
for organic luminescent materials with AIE properties. The
highest Tg found for AIE compounds was at 204 ꢀC, which was
reported by Tang.12 As expected, Tg values increased with a rise
in the number of dicarbazolyl triphenylethylene substituents. Tri-
ꢀ
substituted 3B-TPA possessed the highest Tg of up to 214.3 C.
Fig. 3 TGA curves of the compounds.
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transition peak at 236.5 ꢀC. In the second heating run, only
a glass transition could be observed for each compound. This
indicates that the compounds exhibited a very low tendency
towards crystallization, as no melting peak could be detected,
which is ascribed to the starburst structures. Amorphous mate-
rials possessing a high Tg could have a better chance to retain film
morphology during device operation.
The Td of 1B-TPA, 2B-TPA and 3B-TPA (corresponding to
5% weight loss under N2 atmosphere) were 438.5, 487.2 and
516.8 ꢀC, respectively (Fig. 3). The Td values also showed the
same trend as the Tg values, increasing with the rise in the
number of dicarbazolyl triphenylethylene substituents. The tri-
substituted 3B-TPA possessed the highest Td of up to 516.8 ꢀC.
The results indicate that the compounds have a very high
thermal stability, including high Tg and Td. The thermal stability
of organic compounds plays a critical role in both the stability
and lifetime of photoelectric devices. Thus, the high level of
thermal stability suggests that the synthesized compounds might
prove useful for photoelectric materials in fabrication devices.
Fig. 4 UV-vis absorption spectra of 2B-TPA in different solvents
(5 mM).
Table 1 UV data of the compounds in different solvents (5 mM)
1B-TPA
2B-TPA
3/104 l1
3B-TPA
3/104 l1
Optical properties and energy levels
Solv.
l1
l2
l2
l2
3/104
To further study the relationship between their molecular
structures and optical properties, we investigated the optical
properties of these compounds by UV-vis absorption spectros-
copy (UV) and photoluminescence spectroscopy (PL). Different
organic solvents of cyclohexane (CH), toluene (TOL),
dichloromethane (MC), tetrahydrofuran (THF), N,N-dime-
thylformamide (DMF) and dimethyl sulfoxide (DMSO) were
used; herein, these are arranged from the lowest to highest
polarity. Note that the spectra of 2B-TPA are shown in the text
as examples; the others are mentioned in the ESI.†
CH
TOL
MC
THF
DMF
341 368 5.0
342 370 4.4
343 368 4.6
343 368 4.9
344 369 4.9
341 379 7.8
342 384 7.2
343 379 7.6
342 380 7.7
342 381 7.5
343 381 7.5
341 387
—
342 388 11.2
342 386 11.4
341 387 11.8
342 387 11.3
342 390 11.3
DMSO 344 370 4.5
Table 2 PL data of compounds in different solventsa
CH
TOL
MC
THF
DMF
DMSO
Fig. 4 outlines the UV absorption spectra of 2B-TPA in
different solvents (5 mM) (see also the ESI for the absorption
spectra of 1B-TPA and 3B-TPA†). There were two main
absorption bands in all the compounds: one located at 341–
344 nm (l1) corresponding to the absorption of the carbazolyl
segment, and the other located at 368–389 nm (l2) attributed to
p–p* transitions. The UV data are summarized in Table 1. It is
interesting to note that the compounds show almost the same l1
values. However, the l2 and molar absorption coefficient, 3,
values increased with the number of dicarbazolyl triphenyl-
ethylene substituents. For example, in toluene, even if the l1 of
1B-TPA, 2B-TPA and 3B-TPA were the same at 342 nm, their l2
values were 370, 384 and 388 nm and their 3 values were 4.4 ꢂ
104, 7.2 ꢂ 104 and 11.2 ꢂ 104 Mꢁ1 cmꢁ1, respecitvely. As can be
seen from Table 1, solvent polarity had little effect on the
absorption wavelengths of these compounds. Since 3B-TPA has
a relatively low solubility in CH and its concentration cannot
reach 5 mM at room temperature, the 3 in Table 1 and PL
intensity in Table 2 were omitted.
1B-TPA
2B-TPA
3B-TPA
F
l
I
F
l
I
F
l
I
0.57
467
265
0.67
461
419
0.73
456
—
0.38
473
147
0.47
468
304
0.49
465
385
0.25
494
105
0.34
496
226
0.37
498
279
0.22
491
93
0.32
493
216
0.37
495
276
0.17
516
64
0.22
522
124
0.22
524
145
0.19
519
63
0.20
527
113
0.20
529
131
a
F: quantum yield; I: PL intensity (a.u.); l: maximum emission
wavelength.
However, solvent polarity exerted a great effect on the PL
emission, as shown in Fig. 5 and Table 2. The PL intensities (I)
and quantum yield (F) of the solutions of the three compounds
decreased with increasing solvent polarity. The F of 1B-TPA,
2B-TPA and 3B-TPA were 0.57, 0.67 and 0.73 in CH (lowest
polarity, the F were very high), and 0.19, 0.20 and 0.20 in DMSO
(highest polarity), respectively. In CH, the F were approximately
3.0-, 3.4-, and 3.7-fold higher as compared with those in the
Fig. 5 PL emission spectra of 2B-TPA in different solvents (5 mM).
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Fig. 6 Fluorescent images of 2B-TPA dissolved in different solvents
taken under irradiation at 365 nm (5 mM).
DMSO. As illustrated in Fig. 5, the maximum emission wave-
length (l) of each compound progressively shifted to a longer
wavelength when the polarity of the solvent increased from CH
to DMSO. The lem of 1B-TPA, 2B-TPA and 3B-TPA were 467,
461 and 456 nm in CH, and 519, 527 and 529 nm in DMSO,
respectively. Compared with the l in CH solutions, the l values
in DMSO solutions red-shifted by 52, 66 and 73 nm for 1B-TPA,
2B-TPA and 3B-TPA, respectively. The fluorescent images of
2B-TPA dissolved in different solvents taken under irradiation at
365 nm are shown in Fig. 6. As can be seen, the fluorescence
colors completely differ from each other. Thus, the emission
properties of this group of molecules highly depend on the
solvent polarity.
Fig. 7 The calculated spatial distributions of the LUMO and the
HOMO of 1B-TPA.
The large bathochromic shift combined with the decreased F
might be related to the stabilization of the excited state. This
behavior is frequently observed in highly polarized molecules
exhibiting enlarged dipoles and charge-transfer characters in
their excited states referred to as intramolecular charge-transfers
(ICT).13 Since solvent polarity had little effect on the absorption
wavelengths of the compounds, their solvatochromisms might be
caused by photo-induced ICT in the excited state, suggesting that
the ICT excited state had a larger dipolar moment compared
with the ground state, due to substantial charge redistribution.
The photo-induced ICT of the compounds was supported by
the molecular orbital (MO) calculation studies. On the basis of
the density functional method at the HF/3-21G level after opti-
mizing the structure,14 the highest occupied molecular orbitals
(HOMO) and lowest unoccupied molecular orbitals (LUMO) of
1B-TPA were obtained, as shown in Fig. 7. The calculation
results showed that 1B-TPA exhibited the complete separation of
the HOMO and the LUMO. The majority of the electron
distribution of the HOMO was located on the triarylamine
moiety; however, the electron distribution of the LUMO was
located on the triphenylethylene moiety. The complete localiza-
tion of HOMO and LUMO means the HOMO / LUMO
transition becomes a typical photo-induced intramolecular
charge transfer transition, which is desirable for the efficient
energy transfer.15
of the involvement of the ICT mechanism in the AIEE process of
our synthesized compounds.
It is also interesting to note that the number of dicarbazolyl
triphenylethylene substituents exerted little effect on their emis-
sion wavelengths in their solid states. As shown in Fig. 8, the
maximum emission wavelengths (l) of the three compounds were
about 482.7 nm. However, in CH and TOL, the order of the
l values followed the order of 1B-TPA > 2B-TPA > 3B-TPA. In
sharp contrast, in MC, THF, DMF and DMSO, the l values
followed the order of 3B-TPA > 2B-TPA > 1B-TPA.
The highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO), which are related
However, since the solvent polarity has little effect on the
emission of the siloles system, typical AIE compounds included
HPS, MPPS etc, the ICT mechanism has been ruled out in the
AIE and AIEE process of the siloles system.16 The above PL
results in different solvents evidently demonstrate the likelihood
Fig. 8 The PL spectra of the compounds recorded from their TLC
plates.
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Fig. 10 PL spectra of 2B-TPA in water–DMF mixtures (5 mM).
Fig. 9 A CV curve of 2B-TPA in MC.
existing forms from a solution or well-dispersed state in the pure
DMF to the aggregated particles in the mixtures with high water
content.
Table 3 The energy levels of the compounds
The PL spectra of 5 mM 2B-TPA in water–DMF mixtures with
different water contents are shown in Fig. 10. The 2B-TPA in
DMF exhibited a weak PL intensity (ꢃ125 a.u.). However, the
fluorescence intensity was significantly enhanced when the water
fraction exceeded 15%. The enhancement of the fluorescence
intensity from 125 to 245 a.u. was observed as the water fraction
of the water–DMF mixture increased from 15% to 20%. Similar
phenomena were observed for the other two compounds (see the
ESI†). Therefore, the compounds were characterized as AIEE-
active. However, the starting points for the PL enhancement of
1B-TPA, 2B-TPA and 3B-TPA differed from each other and
were at 20, 15 and 10% water fraction, respectively. The reason
for the difference is that the three compounds possessed different
solubilities in the mixed solvents. Clearly, the huge 3B-TPA had
the lowest solubility, and thus, was the one most easily aggre-
gated and precipitated from the mixed solvents.
Compound
HOMO/eV
LUMO/eV
DEg/eV
1B-TPA
2B-TPA
3B-TPA
5.19
5.15
5.12
2.37
2.38
2.37
2.82
2.77
2.75
to the redox potentials, have been identified as two important
parameters for electroluminescent materials because of their
relationship with the hole-/electron-injecting capability of
organic light-emitting devices. To measure the HOMO levels of
the synthesized compounds, CV analyses were carried out. The
CV curve of 2B-TPA, as an example, is shown in Fig. 9 (the other
CV curves are shown in the ESI†). The HOMO energy levels
were obtained using the onset oxidation potential. 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 ¼ HOMO ꢁ LUMO). 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 2.75–2.82 eV, which
is below the value (3 eV) that common organic light materials
possess. As can be seen, the DEg values decreased with an
increase in the number of dicarbazolyl triphenylethylene
substituents. Therefore, compounds 3B-TPA and 1B-TPA
exhibited the narrowest energy band gap and the widest energy
band gap, respectively. HOMO values ranged from 5.12–5.19 eV.
The HOMO values also depended on the number of the dicar-
bazolyl triphenylethylene substituents: the larger the number, the
smaller the HOMO value. However, LUMO values ranged from
2.37–2.38 eV and were very close to each other.
The emission images of 2B-TPA taken under 365 nm UV
illumination at room temperature in pure DMF and mixed
solvents with different water fractions, as well as the TLC thin
film, are shown in Fig. 11. As can be seen, there is a wide
difference in the emissive brightness and color among the
samples. When the water content was up to 20%, the solution
exhibited very strong blue-green emission (Fig. 11b–e).
AIEE properties
To determine whether 1B-TPA, 2B-TPA and 3B-TPA are AIEE
active, the fluorescent behaviors of their diluted mixtures were
studied in a mixture of water–DMF under different water frac-
tions. Since the compounds were insoluble in water, increasing
the water fraction in the mixed solvent could change their
Fig. 11 Emission images of 2B-TPA taken under 365 nm UV illumi-
nation at room temperature in (a) DMF solution, (b) 15%, (c) 20%, (d)
25%, and (e) 90% (water fraction, v%) (5 mM); (f) the TLC plate.
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Moreover, the solid thin film also emitted very strong blue-green
fluorescence (Fig. 11f).
into two kinds of nanoparticle suspensions: crystal particles and
amorphous particles. The former leads to an enhancement in the
intensity of photoluminescence emission, while the latter leads to
a reduction in intensity.7 Thus, the measured overall PL intensity
data depends on the combined actions of the two kinds of
nanoparticles. However, it is hard to control the formation of
nanoparticles in high water content. Thus, the measured
photoluminescence intensity often shows no regularity in high
water content.
Figs 12 and 13 illustrate the PL intensity and maximum
emission wavelength of the compounds. As can be seen in
Fig. 12, the intensities of 2B-TPA and 3B-TPA exhibited a slight
decrease in PL enhancement upon the addition of water before
the starting point, but an increase in the PL intensities of the
three compounds was observed with the further addition of water
after the starting points. After reaching a maximum, the PL
intensities of the three compounds decreased with the increase in
water content. This phenomenon was often observed in some
compounds with AIE or AIEE properties, but the reasons
remain unclear. Thus far, there are two possible explanations for
this phenomenon. First, after the aggregation, only the molecules
on the surface of the nanoparticles emitted light and contributed
to the fluorescence intensity upon excitation, leading to
a decrease in fluorescence intensity. However, the restriction of
intramolecular rotations of the aromatic rings around the
carbon-carbon single bonds in the aggregation state could
enhance light emission. The net outcome of these antagonistic
processes depends on which process plays a predominant role in
affecting the fluorescence behavior of the aggregated molecules.17
Second, when water is added, the solute molecules can aggregate
As shown in Fig. 13, the PL maximum emission wavelength of
the compounds exhibited significant blue shifts after the starting
points of PL enhancement. The blue shifts of 1B-TPA, 2B-TPA
and 3B-TPA in the 90 : 10 (v/v) water–DMF mixture in relation
to the emission in DMF solution were 34, 39 and 39 nm,
respectively. Their maximum emission wavelengths in the 90 : 10
(v/v) water–DMF mixture (483, 484 and 485nm, respectively)
were very close to each other and closer to the emission wave-
lengths of their film samples, mentioned above (482.7 nm).
The absorption spectra of 2B-TPA in the water–DMF
mixtures (5 mM) are shown in Fig. 14. The spectral profile was
markedly changed when >15% water was added to the DMF
solution. The entire spectrum started to increase in absorption,
indicating the formation of nanoscopic aggregates of 2B-TPA.
Fig. 14 UV-vis absorption spectra of 2B-TPA in water–DMF mixtures
with different volume fractions of water (5 mM).
Fig. 12 PL intensities of the compounds in water–DMF mixtures (5
mM).
Fig. 13 PL maximum emission wavelengths of the compounds in water–
DMF mixtures (5 mM).
Fig. 15 The relationship between the absorption peaks (l1 and l2) of the
compounds and water fraction in water–DMF mixtures (5 mM).
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heating and cooling rates of 10 C minꢁ1 under N2 atmosphere.
Thermogravimetric analyses (TGA) were performed with
a thermal analyzer (TA Instruments Inc. A50) under N2 atmo-
sphere with a heating rate of 20 ꢀC minꢁ1. The fluorescence
quantum yields (F) of all the compounds in different solvents or
DMF–water mixtures were evaluated using 9,10-diphenylan-
thracene, as in ref. 19 The solid-state PL spectra of the
compounds on TLC plates (aluminium TLC plate, Merck, Silica
60 F254) were measured according to the literature procedure.20
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 0.1M n-Bu4NClO4 in
dichloromethane at scan rate of 100 mV sꢁ1 using ferrocene (Fc)
as the standard. The lowest unoccupied molecular orbital/highest
occupied molecular orbital (LUMO/HOMO) energy gaps DEg
for the compounds were estimated from the absorption edge of
the UV-vis absorption spectra.
ꢀ
The light scattering, or Mie effect, of the nanoaggregates
suspensions in the solvent mixtures effectively decreased light
transmission in the mixture and caused the apparent high
absorbance and level-off tail in the visible region of the UV
absorption spectrum.18
Fig. 15 shows the relationship between the peak positions of
the two absorption bands, l1 and l2, of the compounds and the
water fraction. It can be seen that the l1 values had almost no
change during water addition. However, l2 exhibited a red-
shifted abrupt change corresponding to the abrupt change in PL
spectra. This indicates that the aggregation has a pronounced
effect on p–p* transitions. The l2 of 1B-TPA, 2B-TPA and 3B-
TPA in the 90 : 10 (v/v) water–DMF mixture in relation to those
in DMF solution red-shifted by 7, 6 and 7 nm, respectively.
Conclusions
A new class of compounds containing dicarbazolyl triphenyl-
ethylene and triarylamine units was synthesized. The compounds
possessed high thermal stability and AIEE properties. The glass
transition temperature and 5% weight loss temperature of the tri-
substituted compound (3B-TPA) are up to 214.3 ꢀC and
516.8 ꢀC, respectively. The Tg value is the highest ever reported to
date for materials with AIE or AIEE properties. The compounds
exhibited photo-induced intramolecular charge-transfer proper-
ties. The PL spectra blue-shifted after aggregation. The aggre-
gation considerably affected the p–p* transition and resulted in
6–7 nm red shift of the p–p* absorption wavelength at the peak
in UV-vis spectra. The number of the dicarbazolyl triphenyl-
ethylene substituents exerted little effect on the emission wave-
lengths of the compounds in the solid state.
The DMF–water mixtures with different water fractions were
prepared by slowly adding distilled water into the DMF 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 DMF solution of the
sample. The concentrations of all of the samples were adjusted to
5 mM after adding distilled water.
Synthesis of 4-(2,2-bis(4-(9H-carbazol-9-yl)phenyl)vinyl)
phenylboronic acid (3)
Compound 2 (6.0 g, 9.0 ꢂ 10ꢁ3 mol) was dissolved in anhydrous
THF (100 mL) and n-butyllithium (2.2 M/hexane, 6 mL, 0.0132
mol) was added, dropwise, under an argon atomosphere at
ꢁ78 ꢀC. After stirring for 5 h, B(OCH3)3 (2.2 mL) was added
quickly at ꢁ78 ꢀC and the mixture was stirred overnight allowing
the temperature to rise gradually to room temperature. Then, the
reaction mixture was acidified with hydrochloric acid (2 M) for
2 h. The mixture was extracted with dichloromethane (3 ꢂ
50 mL) and the organic layer was dried with anhydrous sodium
sulfate. After removing the solvent under reduced pressure, the
crude product was purified by silica gel column chromatography
using acetone/CH2Cl2 (1 : 20, v/v) as eluent to yield 3 (2.1 g,
yield 55%). 1H-NMR (300 MHz, DMSO-d6) d: 7.137 (s,
1 H, >C]CH–), 7.25–7.58 (m, 16 H), 7.62–7.78 (m, 8 H), 7.976
(s, 2 H, –B(OH)2), 8.20–8.30 (m, 4 H, carbazole–H); MS (EI), m/
z: 586 ([M-(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.
Experimental
All starting reagents and chemicals were purchased from Alfa-
Aesar and used as received. Analytical grade N,N-dime-
thylformamide (DMF) was purified by distillation under an inert
nitrogen atmosphere. Tetrahydrofuran (THF) was distilled from
sodium benzophenone. Ultra-pure water was used in the exper-
iments. All other analytical-grade solvents were purchased from
Guangzhou Dongzheng Company and used without further
purification. Intermediates bis(4-(9H-carbazol-9-yl)phenyl)me-
thanone (1) and 9,90-(4,40-(2-(4-bromophenyl)ethene-1,1-diyl)-
bis(4,1-phenylene))bis(9H-carbazole) (2) were synthesized
according to procedures in previously published by us.7 The
halogenated triphenylamines 4-bromo-N,N-diphenylbenzen-
amine (4),8 4-bromo-N-(4-bromo phenyl)-N-phenylbenzenamine
(5)9 and tris(4-iodophenyl)amine (6)10 were prepared according
to the literature procedures.
Proton nuclear magnetic resonance (1H-NMR) spectra were
measured on a Mercury-Plus 300 spectrometer (CDCl3 or
DMSO-d6 as solvent and tetramethylsilane (TMS) as the internal
standard). Mass spectra (MS) were measured on a Thermo
MAT95XP-HRMS spectrometer. 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. Differential scanning calorimetry (DSC) curves were
obtained with a NETZSCH thermal analyzer (DSC 204) at
Synthesis of 40-(2,2-bis(4-(9H-carbazol-9-yl)phenyl)vinyl)-N,N-
diphenylbi phenyl-4-amine (1B-TPA)
Compounds 4 (0.315 g, 0.5 mmol) and 3 (0.162 g, 0.5 mmol) were
dissolved in toluene (15 mL), then K2CO3 (2 M, 1.5 mL) and
Aliquat 336 (5 drops) were added. After stirring for 45 min under
an argon atmosphere, the Pd(PPh3)4 (catalytic amount) was
added and the reaction mixture was stirred at 85 ꢀC for 24 h.
Then, the mixture was cooled to room temperature and extracted
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with dichloromethane–water. The organic layer was collected
and dried with Na2SO4. The crude product was purified by silica
gel column chromatography using n-hexane–CH2Cl2 ¼ 2 : 3 (v/v)
numbers: 50773096, 50473020), the Start-up Fund for Recruiting
Professionals from ‘‘985 Project’’ of SYSU, the Science and
Technology Planning Project of Guangdong Province, China
(Grant numbers: 2007A010500001-2, 2008B090500196),
Construction Project for University-Industry cooperation plat-
form 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.
1
as eluent, to obtain pure product (0.22 g, yield 53%). H-NMR
(300 MHz, CDCl3) d: 7.07 (dd, 4 H, Ph–H), 7.20 (m, 5 H, Ph–H,
>C]CH–), 7.31 (dd, 8 H, carbazole-H, Ph–H), 7.40–7.72 (m,
22 H, carbazole–H, Ph–H), 8.14–8.19 (d, 4 H, carbazole–H); FT-
IR (KBr) n/cmꢁ1: 3030 (Ar and ]C–H stretching), 2922, 2851,
1593, 1513, 1448, 1227, 817, 750, 625; MS (EI), m/z: 829 ([M]+,
calcd for C63H43N3, 829); anal. calc. for C62H43N3: C 89.72, H
5.22, N 5.06; found: C 89.69, H 5.15, N 5.12.
Synthesis of 40-(2,2-bis(4-(9H-carbazol-9-yl)phenyl)vinyl)-
N-(40-(2,2-bis(4-(9H- carbazol-9-yl) phenyl)vinyl)biphenyl-4-yl)-
N-phenylbiphenyl-4-amine (2B-TPA)
Notes and references
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5 (0.15 g, 0.375 mmol) and 3 (0.47 g, 0.75 mmol) were dissolved in
toluene (20 mL), and then K2CO3 (2 M, 2.5 mL) and 5 drops of
Aliquat 336 were added. The mixture was stirred for 45 min
under an argon atmosphere at room temperature. Then the
Pd(PPh3)4 catalyst (catalytic amount) was added and the reac-
tion mixture was stirred at 85 ꢀC for 24 h. After cooling, the
reaction mixture was extracted with dichloromethane–water.
The organic layer was collected and dried with Na2SO4. The
crude product was purified by silica gel column chromatography
(n-hexane–CH2Cl2 ¼ 1: 1, v/v) to obtain pure product (0.19 g,
€
2 (a) A. Dreuw, J. Ploner, L. Lorenz, J. Wachtveitl, J. E. Djanhan,
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yield 36%). H-NMR (300 MHz, CDCl3) d: 7.15–7.25 (m, 7 H),
7.32 (m, 12 H, carbazole–H, Ph–H), 7.40–7.72 (m, 44 H, carba-
zole–H, Ph–H), 8.14–8.19 (d, 8 H, carbazole–H); FT-IR (KBr)
n/cmꢁ1: 3035 (Ar and ]C–H stretching), 1594, 1513, 1448, 1227,
817, 747, 623; MS (FAB), m/z: 1414([M]+, calcd for C106H71N5,
1414); anal. calc. for C106H71N5: C 89.99, H 5.06, N 4.95; found:
C 90.01, H 5.12, N 4.91.
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Synthesis of tris(40-(2,2-bis(4-(9H-carbazol-9-yl) phenyl)vinyl)
biphenyl-4- yl)amine (3B-TPA)
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6 (0.21 g, 0.33 mmol) and 3 (0.63 g, 1.0 mmol) were dissolved in
toluene (25 mL), and then K2CO3 (2 M, 3.0 mL) and 5 drops of
Aliquat 336 were added. The mixture was stirred for 45 min
under an argon atmosphere at room temperature. Then the
Pd(PPh3)4 catalyst (catalytic amount) was added and the reac-
tion mixture was stirred at 85 ꢀC for 48 h. After cooling, the
reaction mixture was extracted with dichloromethane–water.
The organic layer was collected and dried over Na2SO4. The
crude product was purified by silica gel column chromatography
(n-hexane–CH2Cl2 ¼ 2: 3, v/v) to obtain pure product (0.32 g,
ꢀ
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yield 48%). H-NMR (300 MHz, CDCl3) d: 7.20–7.25 (m, 9 H),
7.32 (m, 12 H, carbazole–H, Ph–H), 7.40–7.72 (m, 66 H, carba-
zole–H, Ph–H), 8.14–8.19 (d, 12 H, carbazole–H); FT-IR (KBr)
n/cmꢁ1: 3030 (Ar and ]C–H stretching), 1594, 1508, 1448, 1313,
1227, 812, 747, 720, 623; MS (FAB), m/z: 1999([M]+, calcd for
C150H99N7, 1999); anal. calc. for C150H99N7: C 89.99, H 4.99, N
4.90; found: C 89.95, H 4.94, N 4.96.
Acknowledgements
20 J. Chen, C. C. W. Law, J. W. Y. Lam, Y. Dong, S. M. F. Lo,
I. D. Williams, D. Zhu and B. Z. Tang, Chem. Mater., 2003, 15,
1535.
The authors gratefully acknowledge the financial support from
the National Natural Science Foundation of China (Grant
6110 | J. Mater. Chem., 2010, 20, 6103–6110
This journal is ª The Royal Society of Chemistry 2010