New tetraphenylethene-based efficient blue luminophors: Aggregation induced emission and partially controllable emitting color

Article abstract of DOI:10.1039/c1jm14054j

In this paper, two new TPE-based conjugated molecules, constructed using tetraphenylethene (TPE) and carbazole or spirofluorene moieties, have been successfully prepared. They exhibited aggregation induced emission (AIE) properties, high thermal and morphological stabilities, and low oxidation potential, making them promising properties for optoelectric materials. The fabricated non-doped multilayer OLEDs demonstrate that devices using these luminophors as the emitting layer show relatively good performance, and the device of SFTPE gives a maximum luminance and efficiency of 8196 cd m ^-2 and 3.33 cd A^-1, respectively, with the maximum emission wavelength at about 466 nm, thanks to the adjusted molecular structure and AIE characteristic of TPE.

Full text of DOI:10.1039/c1jm14054j

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PAPER
New tetraphenylethene-based efficient blue luminophors: aggregation induced
emission and partially controllable emitting color†
a
Jing Huang,‡ Xiao Yang,‡ Jinyu Wang, Cheng Zhong, Lei Wang, Jingui Qin and Zhen Li
b
a
a
b
a
a
*
*
Received 19th August 2011, Accepted 18th October 2011
DOI: 10.1039/c1jm14054j
In this paper, two new TPE-based conjugated molecules, constructed using tetraphenylethene (TPE)
and carbazole or spirofluorene moieties, have been successfully prepared. They exhibited aggregation
induced emission (AIE) properties, high thermal and morphological stabilities, and low oxidation
potential, making them promising properties for optoelectric materials. The fabricated non-doped
multilayer OLEDs demonstrate that devices using these luminophors as the emitting layer show
relatively good performance, and the device of SFTPE gives a maximum luminance and efficiency of
8196 cd mꢀ2 and 3.33 cd Aꢀ1, respectively, with the maximum emission wavelength at about 466 nm,
thanks to the adjusted molecular structure and AIE characteristic of TPE.
AIE mechanism to the restriction of intramolecular rotations
(RIR) of the aromatic peripheries against the core in the aggre-
gation state.5b Excitingly, among all the reported AIE molecules,
tetraphenylethene (TPE) (Chart 1) could emit strong blue fluo-
rescence in its solid films. However, its corresponding light-
emitting diode (LED) devices exhibited low efficiency
(0.45 cd Aꢀ1).6 By introducing some aromatic rings, which could
also be considered as the rotators, to the TPE moieties, the
resultant efficiencies could be improved at a large extent
(Chart S1†), but the maximum electroluminescent (EL) emission
wavelengths are much red-shifted, and the emission color was
not blue any longer, due to the prolonged p-conjugation
system.6,7 Then, is it possible to design new TPE-based lumino-
phors with improved efficiency LED devices but still retaining
blue emission?
Introduction
The development of efficient luminophoric materials has
attracted great interest due to their huge applications in flat-
panel displays and lighting.1 Among the three primary color (red,
green, and blue) light-emitting materials, the biggest challenge so
far has still been to obtain efficient and spectrally-stable blue
light emitting materials.2 Generally, the luminophoric materials
are used as solid films in practical applications. The formation of
delocalized excitons or excimers in the solid state, however, often
quenches the emission of organic luminophors, which is partially
why efficient blue luminophors are rare.3 Taking the famous
polyfluorene as an example, it is considered as the most prom-
ising blue emitter, but suffered from the notorious long-wave-
length emission owing to the formation of ketone defects or
excimers/aggregation in the condensed state.4
Analyzing the previous cases carefully, on one side the intro-
duction of the additional aromatic rotators could improve the
LED efficiency, meanwhile, one another side the bonded
aromatic moieties would extend the formed p-conjugation
system, leading to the bathochromic shift of the emission, that is,
no blue emission.8 Thus, perhaps, the balance could be adjusted
accurately by structural modification. Previously, we have
Recently, a novel photophysical phenomenon was observed by
Tang et al.: some conjugated organic molecules were non-
luminescent in their solutions, but once aggregated (either in the
solid state or as nanoparticles) they were strongly fluorescent,
with quantum yields enhanced several hundred times.5 They
named this aggregation induced emission (AIE), and ascribed the
aDepartment of Chemistry, Hubei Key Lab on Organic and Polymeric
Opto-Electronic Materials, Wuhan University, Wuhan, 430072, China.
E-mail: lizhen@whu.edu.cn; lichemlab@163.com; Fax: +86-27-
68755363; Tel: +86-27-68755363
bWuhan National Laboratory for Optoelectronics, School of
Optoelectronic Science and Engineering, Huazhong University of
Science, and Technology, Wuhan, 430074, China. E-mail: lei96wang@
163.com
† Electronic supplementary information (ESI) available: Charts of TPE
and TPE-based molecules, and a new series of indole-based AIEE
luminophors; and the optimized molecular structures of SFTPE and
TPE–2Cz. See DOI: 10.1039/c1jm14054j
Chart 1 The chemical structures and maximum emission wavelengths of
‡ Contributed equally to this manuscript.
TPE, SFTPE and TPE–2Cz.
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successfully developed a new series of indole-based AIEE lumi-
nophors (Chart S2†), through the single Carbon–Nitrogen bond.
In comparison with the traditional Carbon–Carbon bond
reported in the AIE molecules, the conjugation effect of the
Carbon–Nitrogen bond is much less.9 Another possible
approach to decrease the effective conjugation is to link some
group with a more localized p system.
2-bromoiodobenzene and TPE boronic ester, which was
obtained from diphenylmethane in three steps according to the
literature.10 The synthesis of TPE–2Cz started from 4,40-dibro-
mobenzophenone and carbazole by using t-BuOK as the base.
The hydroxy intermediate was not isolated but used directly in
the next step. After the dehydration reaction in the presence of
p-toluenesulfonic acid, TPE–2Cz was yielded. The products were
purified by column chromatography on silica gel using petroleum
Generally, spirofluorene, triphenylamine and carbazole
groups are frequently utilized to construct efficient blue emitters.
The linkage of triphenylamine moieties to TPE has already
demonstrated good performance, regardless of its red-shifted
emission at about 505 nm.6 However, there were no reports
concerning the direct bonding of spirofluorence and carbazole
moieties to a TPE one. Considering all the above points, we
designed two new TPE-based luminophors, SFTPE and TPE–
2Cz (Chart 1), in which spirofluorene group was directly bonded
to TPE moieties, and a carbazolyl one was bonded through the
Carbon–Nitrogen bonds. Thanks to the more localized p system
of spirofluorene and the linkage mode of Carbon–Nitrogen
bond, these two luminophors exhibit blue emission at ꢁ460 nm,
but enhanced efficiencies of their LED devices (as high as 3.33 cd
Aꢀ1). These results partially realized the above idea of the design
of new TPE-based luminophors with improved efficiency of the
LED devices but still having blue emission, shedding some light
on the further development of new blue luminophors with AIE
characteristics. Herein, we would like to present the synthesis,
characterization, photophysical properties, theoretical calcula-
tion and LED device performance of these two TPE-based
luminophors in detail.
1
ether-dichloromethane as eluent and fully characterized by H
and 13C NMR, mass spectrometry, and elemental analysis.
Thermal properties
The thermal properties of the new compounds SFTPE and TPE–
2Cz were investigated by thermal gravimetric analysis (TGA)
and differential scanning calorimetry (DSC). As shown in Fig. 1,
the two compounds exhibited good thermal stability. Their
thermal-decomposition temperatures (Td, corresponding to 5%
weight loss) were determined to be about 334 and 378 ꢂC
(Table 1), respectively. Relatively, TPE–2Cz possessed a slightly
higher thermal stability, indicating that the carbazole moieties
could benefit the stability of the resultant materials, thanks to the
good conjugated planar ring. SFTPE and TPE–2Cz exhibited
relatꢂively high glass transition temperatures (Tg) of 107 and
119 C, respectively, which should be ascribed to the introduc-
tion of rigid spirofluorene and carbazole moieties. Thus, the
good thermal stability with high Td and Tg values would
contribute to the preparation of the homogeneous and stable
amorphous emissive layer in OLED devices.
Results and discussion
Photophysical and AIE properties
Synthesis
Both SFTPE and TPE–2Cz are soluble in common solvents such
as tetrahydrofuran, chloroform and dichloromethane, but
insoluble in water. The absorption spectra of SFTPE and TPE–
2Cz in dilute THF solution were shown in Fig. 2. Their
absorption maximum wavelengths were about 310 and 293 nm,
respectively. These two sharp peaks should be assigned to the
spirofluorene and carbazolyl moieties. Both of these two fluo-
rophors exhibited a relatively flat absorption peak at about
330 nm, which should be the absorptive behavior of the whole
Scheme 1 illustrates the synthetic routes to SFTPE and TPE–
2Cz. SFTPE was synthesized by lithiation and acid-catalyzed
cyclization reactions. As the key intermediate, Compound 3 was
prepared by the palladium-catalyzed Suzuki coupling reaction of
Fig. 1 TGA curves of SFTPE and TPE–2Cz recorded at a heating rate
of 10 ꢂC minꢀ1. Inset: DSC (second heating cycle) measurement recorded
Scheme 1 Synthetic routes to SFTPE and TPE–2Cz.
This journal is ª The Royal Society of Chemistry 2012
at a heating rate of 15 ꢂC minꢀ1
.
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Table 1 The thermal, electrochemical and photophysical data for SFTPE and TPE–2Cz
Td (ꢂC) Tm (ꢂC) Tg (ꢂC) Eg (eV) EHOMO (eV) ELUMO (eV) lmax,abe (nm) PL lmax (aggr)f (nm) PL lmax (film) (nm)
a
b
c
d
SFTPE 334
TPE–2Cz 378
254
303
107
119
3.23
3.29
5.47
5.17
2.24
1.88
310
293
493
443
490
464
a
5% weight loss temperature measured by TGA under N2. b Band gap estimated from optical absorption band edge of the solution. c Calculated from
the onset oxidation potentials of the compounds. d Estimated using empirical equations ELUMO ¼ EHOMO + Eg. e Observed from absorption spectra in
dilute THF solution. f Determined in THF : H2O ¼ 1 : 99 solution.
so red-shifted in comparison with that of TPE. Possibly, their
emission was blue.
Generally, TPE and TPE-based fluorophors possessed AIE
properties. To investigate the possible AIE characteristics of
these two dyes, their fluorescence behavior was studied.
Considering that the good and poor solvents should be miscible,
tetrahydrofuran and water were chosen as the solvent pair. Both
SFTPE and TPE–2Cz were nonemissive when molecularly dis-
solved in organic solvents, however, they became strongly
emissive in the aggregate state. Fig. 3 and Fig. 4 show the PL
spectra of SFTPE and TPE–2Cz in THF–water mixtures with
different water fractions (fw). It was easily seen that in pure THF
solutions their spectra were practically flat lines parallel to the
Fig. 2 UV spectra in THF solution. Concentration (mM): 12.6 and 11
abscissa, confirming that they were nonemissive in the solution
for SFTPE and TPE–2Cz, respectively.
state. When a large amount of water was added, the aggregates of
SFTPE and TPE–2Cz were formed step by step. Interestingly, as
shown in Fig. 3, when the water fraction was as high as 80%, the
molecules. In comparison with that of TPE7 (299 nm), SFTPE
emission intensity of SFTPE was still nearly zero. In our previous
and TPE–2Cz demonstrated red-shifted absorption, confirming
study and those reported in the literature, once the water fraction
that there were some conjugations between the TPE group and
in the mixed solvents was higher than 60%, the AIE luminophors
the spirofluorene or carbazolyl moieties and the p-conjugation
system was elongated. However, compared to those of TPATPE
would exhibit detectable or strong fluorescence. The abnormal
phenomenon of SFTPE was surely related to the special struc-
and 2TPATPE (Chart S1†) at about 360 nm, the extent of red-
ture. Although the crystal structure was not obtained, the
shifted absorptions was much less.7
calculated one with the minimized energy of SFTPE could still
As mentioned in the introduction, the introduction of the
give an explanation. As shown in Chart S3,† the structure was
additional aromatic rotators to TPE could improve the LED
highly twisted, which might provide more room for the rotation
efficiency of the resultant fluorophors, meanwhile, on the other
(or vibration) of the phenyl rings in SFTPE. That was to say,
hand, the bonded aromatic moieties would extend the former
only when the molecules were packed much more tightly, the
p-conjugation system, leading to the bathochromic shifted
aggregation induced emission would be realized. Thus, possibly,
emission of no blue color. To adjust this balance, we designed
the higher water fraction in the mixed solvents could facilitate the
SFTPE and TPE–2Cz, in which the additional aromatic groups
were intelligently linked to the TPE moieties, to possibly decrease
their conjugation with the TPE one. For the spirofluorene, the p
system was liable to localize in the spirofluorene ring itself, and it
was a little difficult to effectively conjugate with other aromatic
ones, thus, in SFTPE, the TPE group has one shared phenyl ring
with the peripheral spirofluorene, with the aim to increase the
rigidity; while in TPE–2Cz, the Carbon–Nitrogen bond was
utilized, based on our previous studies. These were different from
other TPE-based fluorophors, in which other aromatic groups
were generally bonded to TPE moieties directly through the
normal, but with highly efficient conjugation, Carbon–Carbon
bonds (just as TPATPE and 2TPATPE). As a result, partially
Fig. 3 (A) PL spectra of SFTPE in THF–H2O mixtures with different
confirmed by the absorption behavior, the conjugation between
water fractions (fw). Concentration (mM): 12.6; excitation wavelength
the TPE block and the spirofluorene or cabarzolyl one was not
(nm): 340. (B) Plots of fluorescence quantum yields determined in THF–
good, indicating that the extent of conjugation of TPE-based
H2O solutions using 9,10-diphenylanthracene (F ¼ 90% in cyclohexane)
fluorophors could be controlled in some degree. And, the rela-
tively shorter maximum absorptions of SFTPE and TPE–2Cz
could reflect their low band gap, thus, their emission might be not
as standard versus water fractions. Inset in (B): photos of SFTPE in
THF–water mixtures (fw ¼ 0 and 99%) taken under the illumination of
a 365 nm UV lamp.
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Fig. 4 (A) PL spectra of TPE–2Cz in THF–H2O mixtures with different
water fractions. Concentration (mM): 11; excitation wavelength (nm):
346. (B) Plots of fluorescence quantum yields determined in THF–H2O
solutions using 9,10-diphenylanthracene (F ¼ 90% in cyclohexane) as
standard versus water fractions. Inset in (B): photos of TPE–2Cz in THF–
water mixtures (fw ¼ 0 and 90%) taken under the illumination of a 365 nm
UV lamp.
Fig. 5 Calculated molecular orbital amplitude plots of HOMO and
LUMO levels.
the whole molecules, showing the weak intramolecular charge
transfer of SFTPE and TPE–2Cz.
formation of the tightly packed nanoparticles, as a result, leading
to the enhanced emission. The quantitative enhancement of
emission was evaluated by the PL quantum yields (FF), using
9,10-diphenylanthracene as the standard. From pure solution in
THF to aggregate state in 99% aqueous mixture, the FF values of
SFTPE increased from nearly 0 to 0.89.
Electrochemical properties
The electrochemical properties of SFTPE and TPE–2Cz were
investigated by cyclic voltammetry (CV). The HOMO energy
levels were calculated to be 5.47 and 5.17 eV, respectively,
according to the following equation: HOMO ¼ ꢀ(4.8 + Eox) eV,
suggesting that SFTPE possesses better hole-transporting prop-
erties than TPE–2Cz. Their LUMOs could be obtained from
optical band gap energies (estimated from the onset wavelength
of their UV absorptions) and HOMO values, which gave LUMO
values of 2.24 and 1.88 eV, respectively.
Unfortunately, although its absorption was relatively good,
SFTPE exhibited the maximum emission at about 492 nm, which
is not blue. This seemed very bad, however, after being fabricated
into an LED device, the obtained EL spectrum was much blue-
shifted, with the maximum emission at about 466 nm, exactly
blue. We will discuss this point later.
Unlike SFTPE, TPE–2Cz exhibited similar AIE behavior to
the previous materials. When the water fraction reached 70%, the
tested quantum yields increased rapidly, from nearly zero to
29%. The highest quantum yield was achieved when the water
fraction increased to 90%. Accompanying the further increased
water fraction, the quantum yields decreased, due to the
decreased solubility. Fortunately, the emission of TPE–2Cz was
blue, in good accordance with the design idea, confirming that
the conjugation efficiency of the Carbon–Nitrogen bonds was
not good again. It was noted that the maximum emission
wavelength of TPE–2Cz changed in the range of 436–456 nm,
when the water fraction in the mixed solvents changed. This
phenomenon was often observed in the AIE fluorophors, and
should be ascribed to the transformation between the crystal and
amorphous states of the packing order.6,11
Electroluminescence
The electrochemical properties and high quantum yields of
SFTPE and TPE–2Cz in the aggregate state encouraged us to
investigate their electroluminescence properties. Non-doped
multilayer organic light-emitting diodes (OLEDs) were fabri-
cated with configurations of ITO/NPB (60 nm)/SFTPE (30 nm)/
TPBi (20 nm)/LiF (1 nm)/Al (100 nm) and ITO/NPB (40 nm)/
TPE–2Cz (10 nm)/TPBi (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Al
(100 nm) by vacuum deposition. In these OLED devices, NPB,
TPBi and Alq3 worked as hole-transporting, hole-blocking and
electron-transporting layers respectively, and SFTPE and TPE–
2Cz served as emitters.
As shown in Fig. 6, after being fabricated into LED devices,
both SFTPE and TPE–2Cz emit blue light at 466 and 462 nm
with Commission International d’Eclairage (CIE) chromaticity
coordinates of (0.18, 0.24) and (0.17, 0.21), respectively. The
electroluminescence (EL) spectrum of TPE–2Cz is close to the
photoluminescence (PL) spectrum of its film, while for SFTPE,
its EL spectrum is much blue-shifted in comparison with the PL
spectrum of its film (466 nm versus 490 nm). This should be
ascribed to the transformation between the crystal and amor-
phous states of the packing order, and indicates that in the LED
device, the SFTPE was in the crystal state, partially due to its
large rigidity. Thus, although the PL spectrum of SFTPE was not
blue, the output emission of its LED device was blue. These
results realized our thought of the design of blue emitters.
Theoretical calculations
To further understand the correlation between structure and the
physical properties as well as the device performance, quantum
chemistry computations were conducted. The geometries of the
molecules have been optimized using DFT calculations with the
Gaussian 09 program.12 In particular, we used the B3LYP
exchange-correlation functional and a 6-31g* basis set. Fig. 5
shows the optimized geometries and the orbital distributions of
HOMO and LUMO energy levels of SFTPE and TPE–2Cz. The
LUMOs of both molecules were located at the central TPE core.
However, the electron clouds of the HOMOs are dominated by
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devices was relatively stable. This point would surely contribute
to their possible practical applications. The detailed EL perfor-
mances are listed in Table 2. For comparison, the performance of
TPE, obtained from the ref. 6 is also shown in Table 2. The
unsubstituted TPE only showed Lmax and hC, max of 1800 cd mꢀ2
and 0.45 cd Aꢀ1 with a similar device configuration. That is to
say, by the simple modification of TPE with spiroflurene and
carbazole moieties, the device performances of the resultant
SFTPE and TPE–2Cz have been greatly improved. More
importantly, their EL color was within the range of blue light-
emitting, confirming that by rational design the emission
behavior of TPE-based luminophores could be partially
controlled.
Fig. 6 PL and EL spectra of solid thin films of SFTPE and TPE–2Cz.
The thin films were spin-coated onto ITO glass from dilute THF solution
with concentrations of 1 mg mLꢀ1
Conclusions
.
In summary, two TPE-based luminophores, SFTPE and TPE–
2Cz, constructed by the TPE and spirofluorene or carbazole
moieties, were successfully synthesized, which served as emitting
layers in blue OLEDs. These two new compounds were non-
emissive in the solution state, but highly emissive when aggre-
gated. They exhibited high thermal stability with glass transition
temperatures of 109 and 117 ꢂC. Fortunately, by simply changing
the linkage mode of TPE and spirofluorene or carbazole moie-
ties, we have achieved a balance between improved OLED effi-
ciencies and blue light-emission. These two luminophors exhibit
blue emissions at 466 and 462 nm with Commission International
d’Eclairage (CIE) chromaticity coordinates of (0.18, 0.24) and
(0.17, 0.21), and better EL performance is achieved for SFTPE
(Lmax of 8196 cd mꢀ2, hC, max of 3.33 cd Aꢀ1 and hP, max of 2.10 Im
Wꢀ1, respectively). It is believed that, inspired by these prelimi-
nary results, many other TPE-based luminophores with better
performance and blue emission could be further developed.
Fig. 7 (A) Current density–voltage–luminance (J–V–L) characteristics
of multilayer EL device of SFTPE. (B) Changes in power and current
efficiencies with the applied voltage in multilayer EL devices of SFTPE.
Device configuration: ITO/NPB (60 nm)/SFTPE (30 nm)/TPBi (20 nm)/
LiF (1 nm)/Al (100 nm).
Experimental section
Characterization
1H and 13C NMR spectra were measured on a Mecuryvx300
spectrometer. Elemental analyses of carbon, hydrogen, and
nitrogen were performed on a CARLOERBA-1106 micro-
analyzer. Mass spectra were measured on a ZAB 3F-HF mass
spectrophotometer. UV–vis absorption spectra were recorded on
a Shimadzu UV-2500 recording spectrophotometer. Photo-
luminescence spectra were recorded on a Hitachi F-4500 fluo-
rescence spectrophotometer. Differential scanning calorimetry
(DSC) was performed on a NETZSCH DSC 200 PC unit at
a heating rate of 15 ꢂC minꢀ1 from room temperature to 300 ꢂC
under argon. The glass transition temperature (Tg) was deter-
mined from the second heating scan. Thermogravimetric analysis
(TGA) was undertaken with a NETZSCH STA 449C instru-
ment. The thermal stability of the samples under a nitrogen
atmosphere was determꢂined by measuring their weight loss while
Fig. 8 (A) Current density–voltage–luminance characteristics of multi-
layer EL device of TPE–2Cz. (B) Changes in power and current effi-
ciencies with the applied voltage in multilayer EL devices of TPE–2Cz.
Device configuration: ITO/NPB (40 nm)/TPE–2Cz (10 nm)/TPBi
(10 nm)/Alq3 (30 nm)/LiF (1 nm)/Al (100 nm).
As shown in Fig. 7 and Fig. 8, the devices turned on at a low
voltage (2.6 V for SFTPE and 3.3 V for TPE–2Cz). Accompa-
nying the increase of the voltage, the luminance increased
rapidly. The device based on TPE–2Cz exhibits a maximum
luminance (Lmax) of 6179 cd mꢀ2, a maximum current efficiency
heating at a rate of 10 C minꢀ1 from 25 to 600 C. Cyclic vol-
ꢂ
(hC, max) of 2.8 cd Aꢀ1 and a maximum power efficiency (hP, max
)
tammetry (CV) was carried out on a CHI voltammetric analyzer
in a three-electrode cell with a Pt counter electrode, a Ag/AgCl
reference electrode, and a glassy carbon working electrode at
a scan rate of 100 mV sꢀ1 with 0.1 M tetrabutylammonium
perchlorate (purchased from Alfa Aesar) as the supporting
electrolyte, in anhydrous dichloromethane solution purged with
of 2.51 lm Wꢀ1. Better EL performance is observed for SFTPE
with Lmax, hC, max and hP, max of 8196 cd mꢀ2, 3.33 cd Aꢀ1 and
2.10 lm Wꢀ1, respectively. It was noted: while the current density
increased, both of the current and power efficiencies dropped fast
at first, then very slowly, indicating the performance of these
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Table 2 EL performances of SFTPE and TPE–2Cz.a
lEL (nm)
Von (V)
Lmax (cd mꢀ2
)
hP, max (lm Wꢀ1
)
hC, max (cd Aꢀ1
)
CIE (x,y)
SFTPE
TPE-Cz
TPE
466
462
445
2.6
3.3
2.9
8196
6179
1800
2.10
2.51
0.35
3.33
2.80
0.45
0.18, 0.24
0.17, 0.21
—
a
Abbreviations: Von ¼ turn-on voltage at 1 cd mꢀ2, Lmax ¼ maximum luminance, hC, max, and hC, max ¼ maximum power and current efficiency,
respectively. CIE ¼ Commission International de l’Eclairage coordinates.
nitrogen. The potential values obtained in reference to the Ag/
Ag+ electrode were converted to values versus the saturated
calomel electrode (SCE) by means of an internal ferrocenium/
ferrocene (Fc+/Fc) standard.
filtration and solvent evaporation, the crude product was puri-
fied by silica gel column chromatography using petroleum ether/
dichloromethane (v/v 5/1) as eluent. Light yellow powder of 2
1
was obtained in the yield of 60% (2.30 g). H NMR (300 MHz,
CDCl3) d (ppm): 7.55–7.52 (m, 2H), 7.08–7.01 (m, 17H), 1.31
(s, 12H).
Computational details
The geometrical and electronic properties were optimized at
B3LYP/6-31g(d) level using Gaussian 09 program.12 The
molecular orbitals were obtained at the same level of theory.
Synthesis of compound 3
A mixture of 2 (2.34g, 5.1 mmol), 2-bromoiodobenzene (1.420 g,
5 mmol), Pd(PPh3)4 (0.10 g, 4% mmol) and sodium carbonate
(2.65 g, 25 mmol) in 30 mL of THF and 10 mL of distilled water
in a 100 ml Schlenk tube was refluxed for 2 days under argon.
The mixture was extracted with chloroform. The combined
organic extracts were dried over anhydrous Na2SO4 and
concentrated by rotary evaporation. The crude product was
purified by column chromatography on silica gel using
dichloromethane/petroleum ether (v/v 1/2) as eluent to give the
product as a pale yellow powder in the yield of 51% (1.24 g). 1H
NMR (300 MHz, CDCl3) d (ppm): 7.49 (d, J ¼ 7.8 Hz, 1H), 7.36–
7.31 (m, 3H), 7.20–7.07 (m, 19H).
OLED device fabrication and measurement
The hole-transporting material NPB (1,4-bis(1-naph-
thylphenylamino)-biphenyl), electron-transporting materials
1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) and tris(8-
hydroxyquinolinato)aluminium (Alq3) were obtained from
a commercial source. The EL devices were fabricated by vacuum
deposition of the materials at a base pressure of 5 ꢃ 10ꢀ6 Torr
onto glass precoated with a layer of indium tin oxide (ITO) with
a sheet resistance of 25 U squareꢀ1. Before deposition of an
organic layer, the clear ITO substrates were treated with oxgen
plasma for 3 min. The deposition rate of organic compounds was
Synthesis of compound SFTPE
0.9–1.1 A sꢀ1. Finally, a cathode composed of lithium fluoride
ꢀ
Compound 3 (0.2 g, 1.1 mmol) in anhydrous tetrahydrofuran
(10 mL) was treated with n-BuLi (0.3 mL, 2.3 M in hexane,
(1 nm) and aluminium (100 nm) was sequentially deposited onto
the substrate in the vacuum of 10ꢀ5 Torr. The J–V–L of the
devices was measured with a Keithley 2400 Source meter and
PR655. The EL spectra were measured by PR655. All measure-
ments were carried out at room temperature under ambient
conditions.
ꢂ
1.2 mmol) at ꢀ78 C for 30 min, then a solution of 1 (91 mg,
0.5 mmol) in THF (10 mL) was added. After stirring at ꢀ78 ꢂC
for 1 h, the mixture was allowed to warm to room temperature.
The solution was quenched with water and extracted twice with
CH2Cl2. The combined organic extracts were dried over anhy-
drous Na2SO4 and concentrated by rotary evaporation. The
crude product was dissolved in boiling acetic acid (10 ml) and
added concentrated HCl(aq) (0.5 mL). The reaction was allowed
to reflux for 2 h, the organic layer was washed with water and
brine, dried over Na2SO4, and filtered. The precipitate was
purified by column chromatography on silica gel using CH2Cl2/
petroleum ether (v/v 1/1) to give the product as a white powder in
the yield of 62% (0.354g). 1H NMR (300 MHz, CDCl3) d (ppm):
7.74 (d, J ¼ 7.5 Hz, 3H), 7.62 (d, J ¼ 9 Hz, 1H), 7.32 (t, J ¼
7.2 Hz, 3H), 7.10–7.00 (m, 10H), 6.96–6.76 (m, 10 H), 6.582
(t, J ¼ 8.1 Hz, 3H), 6.42 (s, 1H). MS (EI), m/z: 570.12 ([M+], calcd
for C45H30, 570.72). Anal. Calcd for C45H30: C, 94.70; H, 5.30.
Found: C, 94.86; H, 5.43.
Preparation of compounds
All other chemicals and reagents were obtained from commercial
sources and used as received without further purification.
Solvents for chemical synthesis were purified according to the
standard procedures.
Synthesis of compound 2
A 2.3 M solution of n-butyllithium in hexane (15.0 mmol, 6.5mL)
was added to a solution of 1 (4.12 g, 10.0 mmol) in anhydrous
tetrahydrofuran (60 mL) at ꢀ78 ꢂC under an argon atmosphere.
After stirring for 4 h, 2-isopropoxy-4, 4,5,5-tetramethyl-1,3,2-
dioxaborolane (6.1 mL) was added. After 2 h, the mixture was
slowly warmed to room temperature. After stirring overnight,
the reaction was terminated by the addition of brine. The mixture
was extracted with dichloromethane and the organic layer was
combined, and dried with anhydrous sodium sulfate. After
Synthesis of compound 5
Carbazole (16.7 g, 100 mmol) was dissolved in anhydrous DMF
(150 mL) in a flask fitted with a magnetic stirrer and condenser.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 2478–2484 | 2483

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R. C. Chiechi, F. Wudl and Y. Yang, Appl. Phys. Lett., 2010, 88,
093512; (c) K. T. Kamtekar, A. P. Monkman and M. R. Bryce,
Adv. Mater., 2010, 22, 572.
3 (a) A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz and
A. B. Holmes, Chem. Rev., 2009, 109, 897; (b) T. P. I. Saragi,
T. Spehr, A. Siebert, T. Fuhrmann-Lieker and J. Salbeck, Chem.
Rev., 2007, 107, 1011; (c) J. Liu, J. W. Y. Lam and B. Z. Tang,
Chem. Rev., 2009, 109, 5799; (d) A. Iida and S. Yamaguchi, Chem.
Commun., 2009, 3002.
4 (a) Y. Ohmori, M. Uchida, K. Muro and K. Yoshino, Jpn. J. Appl.
Phys., 1991, 11, 1941; (b) M. Fukuda, K. Sawada and K. Yoshino,
J. Polym. Sci., Part A: Polym. Chem., 1993, 101, 2465; (c) Q. Pei
and Y. Yang, J. Am. Chem. Soc., 1996, 31, 7416; (d) M. Ranger
and M. Leclerc, Chem. Commun., 1997, 1597; (e) M. Ranger,
D. Rondeau and M. Leclerc, Macromolecules, 1997, 25, 7686.
5 (a) J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu,
H. S. Kwok, X. Zhan, Y. Liu, D. Zhu and B. Z. Tang, Chem.
Commun., 2001, 1740; (b) Y. Hong, J. W. Y. Lam and B. Z. Tang,
Chem. Commun., 2009, 4332.
Potassium tert-butoxide (11.8 g, 105 mmol) was added and the
mixture was heated at 70 ꢂC for 10 min and bis(4-fluorophenyl)
methanone (10.9 g, 50 mmol) was added, then the resultant
mixture was stirred for 12 h. The mixture was cooled to room
temperature, poured into ice-water, filtered, and the crude
residue was recrystallized from acetone. A white powder was
obtained in the yield of 94% (24.1 g). 1H NMR (300 MHz,
CDCl3) d (ppm): 8.18 (d, J ¼ 6.6 Hz, 8H), 7.81 (d, J ¼ 8.1 Hz,
4H), 7.58 (d, J ¼ 8.1 Hz, 4H), 7.56 (t, J ¼ 7.5 Hz, 4H), 7.35
(t, J ¼ 7.2 Hz, 4H).
Synthesis of compound TPE–2Cz
A 2.3 M solution of n-butyllithium in hexane (2.4 mmol, 1.5 mL)
was added to a solution of diphenylmethane (0.51 g, 3 mmol) in
anhydrous tetrahydrofuran (40 mL) at 0 ꢂC under an argon
6 Y. Dong, J. W. Y. Lam, A. Qin, J. Liu, Z. Li and B. Z. Tang, Appl.
Phys. Lett., 2007, 91, 011111.
atmosphere. After stirring for
1 h at this temperature,
7 Y. Liu, S. Chen, Jacky W. Y. Lam, P. Lu, Ryan T. K. Kwok,
F. Mahtab, H. S. Kwok and B. Z. Tang, Chem. Mater., 2011, 23, 2536.
8 (a) Z. Y. Wang, P. Lu, S. Chen, Jacky W. Y. Lam, Z. Wang, Y. Liu,
H. S. Kwok, Y. Ma and B. Z. Tang, Adv. Mater., 2010, 22, 1; (b)
Z. Zhao, S. Chen, Jacky W. Y. Lam, P. Lu, Y. Zhong, K. S. Wong,
H. S. Kwoka and B. Z. Tang, Chem. Commun., 2010, 46, 2221; (c)
Z. Zhao, S. Chen, Jacky W. Y. Lam, Z. Wang, P. Lu, F. Mahtab,
Herman H. Y. Sung, Ian D. Williams, Y. Ma, H. S. Kwokc and
B. Z. Tang, J. Mater. Chem., 2011, 21, 7210; (d) Z. Zhao, S. Chen,
X. Shen, F. Mahtab, Y. Yu, P. Lu, Jacky W. Y. Lam, H. S. Kwoka
and B. Z. Tang, Chem. Commun., 2010, 46, 686; (e) S. Dong, Z. Li
and J. Qin, J. Phys. Chem. B, 2009, 113, 434.
Compound 5 (1.02 g, 2 mmol) was added. After 2 h, the mixture
was slowly warmed 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 (25 mL).
The p-toluenesulfonic acid (0.10 g, 0.4 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 CH2Cl2/petroleum
ether (v/v 2/1) as eluent to obtain a light green powder in the yield
9 Q. Li, S. Li, S. Yu and J. Qin, J. Phys. Org. Chem., 2009, 22, 241.
10 M. Banerjee, S. J. Emond, S. V. Lindeman and R. Rathore, J. Org.
Chem., 2007, 72, 8054.
1
of 63.4% (0.84 g). H NMR (300 MHz, CDCl3) d (ppm): 8.14–
11 (a) Y. Dong, J. W. Y. Lam, Z. Li, A. Qin, H. Tong, Y. Dong, X. Feng
and B. Z. Tang, J. Inorg. Organomet. Polym. Mater., 2005, 15, 287; (b)
H. Tong, Y. Hong, Y. Dong, Y. Ren, M. Haeussler, J. W. Y. Lam,
K. S. Wong and B. Z. Tang, J. Phys. Chem. B, 2007, 111, 2000; (c)
H. Tong, Y. Dong, Y. Hong, M. Haeussler, J. W. Y. Lam,
H. H. Y. Sung, X. Yu, J. Sun, I. D. Williams, H. S. Kwok and
B. Z. Tang, J. Phys. Chem. C, 2007, 111, 2287; (d) H. Tong,
Y. Hong, Y. Dong, M. Haeussler, Z. Li, J. W. Y. Lam, Y. Dong,
H. H. Y. Sung, I. D. Williams and B. Z. Tang, J. Phys. Chem. B,
2007, 111, 11817.
8.12 (m, 4H), 7.39–7.37 (m, 15H), 7.31–7.18 (m, 15H). 13C NMR
(75 MHz, CDCl3) d (ppm): 143.5, 143.0, 142.7, 141.0, 139.5,
136.2, 133.0, 131.6, 128.1, 127.2, 126.5, 126.1, 123.6, 120.5, 120.2,
110.0. MS (EI), m/z: 662.33 ([M+], calcd for C50H34N2, 662.82).
Anal. Calcd for C50H34N2: C, 90.60; H, 5.17; N, 4.23. Found: C,
90.16; H, 5.47; N, 4.01.
12 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi,
V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth,
P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich,
A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz,
Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson,
W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian 09,
revision E.1, Gaussian, Inc.:Pittsburgh, PA, 2003.
Acknowledgements
We are grateful to the National Science Foundation of China
(no. 21034006), the National Fundamental Key Research
Program (2011CB932702), the Doctoral Fund of Ministry of
Education of China (20100142120049), and the Opening Project
of Key Laboratory of Biomedical Polymers of Ministry of
Education (Wuhan University) (20090401) for financial support.
References
1 (a) C. W. Tang and S. A. Vanslyke, Appl. Phys. Lett., 1987, 51, 913;
(b) M. A. Baldo, M. E. Thompson and S. R. Forrest, Nature, 2000,
403, 750; (c) B. W. D’Andrade and S. R. Forrest, Adv. Mater.,
2004, 16, 1585.
2 (a) T. P. I. Saragi, T. Spehr, A. Siebert, T. Fuhrmann-Lieker and
J. Salbeck, Chem. Rev., 2007, 107, 1011; (b) R. J. Tseng,
2484 | J. Mater. Chem., 2012, 22, 2478–2484
This journal is ª The Royal Society of Chemistry 2012