A new approach to prepare efficient blue AIE emitters for undoped OLEDs

Article abstract of DOI:10.1002/chem.201303522

Two aggregation-induced emission active luminogens (TPE-pTPA and TPE-mTPA) were successfully synthesized. For comparison, another six similar compounds were prepared. Because of the introduced hole-dominated triphenylamine (TPA), fluorene groups with high luminous efficiency, and unconjugated linkages, the π conjugation length of the obtained luminogens is effectively restricted to ensure their blue emission. The undoped organic light-emitting diodes based on TPE-pTPA and TPE-mTPA exhibited blue or deep-blue emissions, low turn-on voltages (3 V), and high electroluminescence efficiencies with L_max, η_C,max, and η_P,max values of up to 26 697 cd m^-2, 3.37 cd A^-1, and 2.40 Lm W^-1. By adding the hole-dominated triphenylamine (TPA) and fluorene groups with high luminous efficiency to the tetraphenylethene (TPE) moiety through unconjugated linkages, the π conjugation lengths of the fluorophores are effectively restricted to ensure deep-blue emission. Two of the undoped OLEDs exhibit blue and deep-blue emissions with good electroluminescence efficiencies.

Full text of DOI:10.1002/chem.201303522

DOI: 10.1002/chem.201303522
Full Paper
&
Aggregation-Induced Emission
A New Approach to Prepare Efficient Blue AIE Emitters for
Undoped OLEDs**
Jing Huang,[a] Runli Tang,[a] Tian Zhang,[a] Qianqian Li,[a] Gui Yu,[b] Shuyi Xie,[a] Yunqi Liu,*[b]
Shanghui Ye,*[c] Jingui Qin,[a] and Zhen Li*[a]
Abstract: Two aggregation-induced emission active lumino-
gens (TPE–pTPA and TPE–mTPA) were successfully synthe-
sized. For comparison, another six similar compounds were
prepared. Because of the introduced hole-dominated triphe-
nylamine (TPA), fluorene groups with high luminous efficien-
cy, and unconjugated linkages, the p conjugation length of
the obtained luminogens is effectively restricted to ensure
their blue emission. The undoped organic light-emitting
diodes based on TPE–pTPA and TPE–mTPA exhibited blue or
deep-blue emissions, low turn-on voltages (3 V), and high
electroluminescence efficiencies with Lmax, hC,max, and hP,max
values of up to 26697 cdmÀ2, 3.37 cdAÀ1, and 2.40 LmWÀ1.
Introduction
formances, new design strategies should be explored in addi-
tion to the traditional approaches.
Over the past few decades, following the achievements of the
Kodak group, there has been great progress in the field of or-
ganic light-emitting diodes (OLEDs).[1] To realize full-color dis-
plays, it is essential to obtain red-, green-, and blue-emitters
with high thermal stability, good electroluminescence (EL) effi-
ciencies, and color purity. However, due to the intrinsic large
band gap in blue luminogens, the performance of blue OLEDs
is often inferior to that of their red and green counterparts.[2–3]
Therefore, the development of blue-emitting materials with
both high efficiencies and good color purity becomes particu-
larly important.[4] In 2007, Cheng et al. reported efficient un-
doped deep-blue OLEDs with current efficiencies of up to
5.6 cdAÀ1 by utilizing anthracene derivatives as emitters.[5]
However, to further develop blue luminogens with good per-
On the other hand, when fabricated as thin solid films in
practical applications (including the aforementioned OLEDs),
most emitters suffer badly from the notorious aggregation-
caused quenching (ACQ) effect.[6] Considerable research has
been performed to mitigate the ACQ effect,[7] for example, by
using guest–host doped emitter systems, blending with trans-
parent polymers or the attachment of bulky alicyclics. Never-
theless, there are still some side effects, including additional
complexity and cost for device fabrication, jeopardizing the
electronic conjugation in the emitters.
In 2001, the group of Benzhong Tang discovered an “abnor-
mal” phenomenon: a series of propeller-like molecules turned
from faint fluorophores in solution to strong emitters in the
aggregated form.[8] It was exactly the opposite of the ACQ
effect and is known as aggregation-induced emission (AIE).[9]
The Tang group have also rationalized the restriction of intra-
molecular rotation (IMR) as the main cause for the AIE effect.[9]
Consequently, AIE-active luminogens exhibit great potential in
the field of OLEDs due to their unique luminescent characteris-
tics.[10] Among the reported AIE fluorophores, tetraphenyle-
thene (TPE) was a prototype molecule because of its facile syn-
thesis and splendid AIE effect.[11] Recently, a lot of efficient
solid-state emitters have been constructed by using TPE as the
key building block (see the Supporting Information).[12] Never-
theless, blue AIE-active luminogens are still very scarce: if TPE
is simply linked to other aromatic groups, the intrinsic exten-
sion of the p conjugation results in green–blue, green or even
longer wavelength emission, although TPE itself is a blue emit-
ter with poor performance. Similar cases have been reported
for other AIE emitters.[12c–n] Thus, it is still a challenge to design
AIE fluorophores with both blue emission and good electro-
luminescent performance.
[a] J. Huang, R. Tang, T. Zhang, Prof. Q. Li, S. Xie, Prof. J. Qin, Prof. Z. Li
Department of Chemistry, Hubei Key Laboratory on
Organic and Polymeric Opto-Electronic Materials
Wuhan University, Wuhan 430072 (P.R. China)
Fax: (+86)27-68756757
E-mail: lizhen@whu.edu.cn
lichemlab@163.com
[b] Prof. G. Yu, Prof. Y. Liu
Organic Solids Laboratories, Institute of Chemistry
The Chinese Academy of Sciences
Beijing 100080 (P.R. China)
E-mail: liuyq@iccas.ac.cn
[c] Dr. S. Ye
Key Laboratory for Organic Electronics and
Information Displays (KLOEID)
Institute of Advanced Materials (IAM)
Nanjing University of Posts and Telecommunications
Nanjing 210046 (P.R. China)
E-mail: yeshh@iccas.ac.cn
[**] AIE=aggregation-induced emission, OLED=organic light-emitting diodes.
Previously, we have reported several TPE-based blue-light
emitters by tuning the conjugation between different con-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201303522.
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a fluorene core through the unconjugated 9,9’-positions, and
the twisted conformations should effectively control the exten-
sion of the p conjugation to ensure the blue emission of the
emitters and hamper the close packing of the adjacent mole-
cules, preventing the formation of species detrimental to the
emission. Furthermore, the conjugation of the whole mole-
cules could be partially tuned by the meta- and para-linking
mode of the TPE moiety and the phenyl ring at the 9-position
of fluorene. The theoretical calculations confirmed the twisted
conformation and special electron cloud distribution. For com-
parison, we have incorporated a toluene group instead of tri-
phenylamine, lengthened the conjugation in the molecules,
and obtained six other compounds, TPE–ptol, TPE–mtol, TPE–
2ptol, TPE–2mtol, TPE–2pTPA, and TPE–2mTPA. The device per-
formance has confirmed the validity of our design idea: when
fabricated as emissive layers in undoped OLEDs, both TPE–
pTPA and TPE–mTPA exhibit deep-blue emission with current
efficiencies of up to 3.37 cdAÀ1 and CIE (CIE=commission in-
ternational de l’eclairage) coordinates of (0.16, 0.16) and (0.15,
0.15). More excitingly, owing to the lower energy barriers be-
tween emitters and adjacent layers, the luminescence of the
devices has been greatly enhanced (up to 26697 cdmÀ2), ac-
companied with lower turn-on voltages of approximately 3 V.
Although the device performance was inferior to those of the
best deep-blue emitters, it is believed that better electrolumi-
nescence data could be obtained through rational molecular
design and further device optimization. Herein, we would like
to present the synthesis, characterization, photophysical prop-
erties, theoretical calculations, and OLED performances of
these TPE-based luminogens in detail.
struction blocks through different approaches.[13] For example,
SFTPE and TPE–2Cz were constructed from the TPE moiety and
twisted spirofluorene or carbazole by either sharing one
phenyl ring or linking through a carbon–nitrogen bond. The
undoped EL devices based on these two luminophors exhibit-
ed blue emissions at approximately 460 nm and enhanced effi-
ciencies up to 3.33 cdAÀ1. In addition, we have obtained four
deep-blue AIE luminogens, which were simply constructed Results and Discussion
from two TPE groups with different linking positions. The con-
Synthesis
jugation was effectively controlled, and all of the molecules ex-
hibited deep-blue emission ranging from 435 to 459 nm and
good electroluminescence efficiencies of up to 2.8 cdAÀ1
The synthetic route to TPE–pTPA, TPE–mTPA, and six other de-
.
rivatives is illustrated in Scheme 1. Compounds 1 and 2 were
prepared from 9-fluorenone and 1,4- or 1,3-dibromobenzene
in the presence of n-butyllithium according to literature proce-
dures.[14,15] After dehydration with the aid of concentrated sul-
furic acid or boron trifluoride diethyl etherate, the key inter-
mediates 3–6 were obtained in good yields. The syntheses of
the TPE boronic esters and diboronic esters were started from
4-bromobenzophenone and 4,4’-dibromobenzophenone and
completed in three steps.[12e,16] The final products were con-
veniently produced by the palladium-catalyzed Suzuki cou-
pling reaction of the corresponding aromatic bromides and
boronic esters with yields ranging from 60.4 to 85.9%. The
compounds were all purified by column chromatography on
silica gel by using petroleum ether–dichloromethane as the
Thus, to further realize our design ideas and develop new
blue AIE systems we incorporated triphenylamine (TPA) and
fluorene into the TPE moiety through an unconjugated linking
mode and obtained two blue emitters, TPE–pTPA and TPE–
mTPA. It was expected that the introduction of fluorene,
a known deep-blue-emitting building block, could contribute
to the EL efficiencies of the emitters, while the hole-dominated
triphenylamine group could enhance the hole mobility, and
thus decrease the turn-on voltages of the devices. In addition,
these two aromatic moieties would also make the two emitters
more rigid and thermally stable. TPE and TPA were linked to
1
eluent and were fully characterized by H and 13C NMR spec-
troscopy, mass spectrometry, and elemental analysis.
As reported in the literature, the spirofluorene group has
often been utilized in conjugated molecules instead of the
normal fluorene group to hamper the possible aggregation
and intermolecular p–p interactions due to the presence of
the sp3-hybridized spiro carbon atom.[15] Inspired by this, in
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from the TPA group, and the
possible improved emission effi-
ciency from the fluorene moiet-
ies. Thus, the design idea for
TPE–pTPA and TPE–mTPA should
be considered to be a new ap-
proach for the further develop-
ment of AIE-active blue and
deep-blue emitters.
Optical properties
All eight molecules have good
solubility in common organic
solvents, such as dichlorome-
thane, chloroform, and tetrahy-
drofuran (THF), but are insoluble
in water. Figure S1 in the Sup-
porting Information shows their
absorption spectra in THF. The
UV/Vis spectra of TPE–ptol and
TPE–mtol are similar, with
maxima at 324 and 323 nm, re-
spectively. The spectra of TPE–
pTPA and TPE–mTPA, however,
are considerably blueshifted (309
and 310 nm) and have higher
absorptivity than those of TPE–
ptol and TPE–mtol, suggesting
that they possess lower conjuga-
tion. This is a reasonable suppo-
sition. The conformation of TPE–
pTPA and TPE–mTPA should be
more twisted due to the nonpla-
nar and bulky triphenylamine
group, leading to their shorter
effective conjugation lengths.
Moreover, the similar maximum
absorptions of TPE–pTPA and
TPE–mTPA indicated that they
TPE–pTPA and TPE–mTPA, the TPE and TPA moieties were com-
bined into one molecule through the sp3-hybridized carbon
atom of a fluorene block. The twisted structure would avoid
the possible intermolecular p–p interactions to a large degree.
Furthermore, due to the presence of the sp3-hybridized carbon
atom, there were very weak conjugation effects among the
three main construction blocks in TPE–pTPA and TPE–mTPA,
that is, the TPA, fluorene, and TPE groups. Actually, these three
units could emit deep-blue light or even shorter wavelengths.
Thus, the special linking mode would not lead to the conjuga-
tion effects throughout the molecule, but retain the properties
of the three moieties. To subtly adjust the structure further, the
linking position of the TPE group was either the meta- or para-
position, with the aim of controlling the weak conjugation ef-
fects and extent of twisting in the structure. In comparison
with the TPE molecule, there were some advantages of TPE–
pTPA and TPE–mTPA, such as the good hole mobility derived
possess similar conjugation lengths. It was originally expected
that the different linking mode might lead to a different inter-
molecular conjugation pattern, as mentioned in the introduc-
tion, due to their different degree of twisting of the aromatic
rings. However, the almost identical absorption behavior does
not agree with this theory. The reason for this might be that
these two luminogens possess a highly twisted structure, and
thus, the difference caused by the different linking mode could
be nearly canceled out by the twisted structure. Interestingly,
different phenomena were observed for the other four fluoro-
phores, TPE–2pTPA, TPE–2mTPA, TPE–2ptol, and TPE–2mtol
with similar peak maxima in the range 304–307 nm. Perhaps,
the aryl groups attached to the TPE core make the phenyl
rings of TPE more twisted, thus affecting the conjugation in
the molecules.
To investigate the AIE properties of these new luminogens,
their fluorescent behavior was recorded. THF and water were
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for AIE luminogens, the emitting
behavior is, generally, different
from that in the thin solid film,
possibly due to the different ap-
proaches for the preparation of
the thin films. In our previous re-
search, the EL spectra of blue
AIE luminogens are considerably
blueshifted in comparison to
their corresponding PL spectra,
as a result of the crystalline
state of the luminophors in the
emitting devices.[11] The phe-
nomenon is known as “crys-
tallization-induced
blueshifted
emission.”[9a,11] Furthermore, the
key reason for this phenomenon
is the highly twisted structure.
Here, with a twisted conforma-
tion, TPE–pTPA and TPE–mTPA
should exhibit considerably blue-
Scheme 1. Synthetic routes to the TPE–Ar luminogens.
chosen as the solvent pair due to their miscibility. They are all
nearly nonemissive when molecularly dissolved in pure THF,
but become strongly emissive in the aggregated state. Fig-
ures 1 and 2 clearly show the PL change, quantum yield, and
fluorescent images of the fluorophores in THF and THF/water
mixtures. Taking TPE–pTPA and TPE–mTPA as examples, the PL
curves are virtually flat lines parallel to the abscissa, demon-
strating that they are faint emitters in the solution state. When
a large amount of water is added, the aggregates form step by
step. For TPE–pTPA, when the water fraction of the solvent is
over 60%, the fluorescence intensity increases rapidly, indicat-
ing the formation of aggregates. At a water fraction (fw) of
99%, the PL intensity is over 420 times that in pure THF. The
quantitative enhancement of emission was evaluated by the
PL quantum yields (FF) by using 9,10-diphenylanthracene as
the standard. From a solution in pure THF to the aggregated
state in a 99% aqueous mixture, the FF values of TPE–pTPA in-
creased from nearly 0 to 32.8%. Similar PL behaviors were also
observed for the other six fluorophores. However, for TPE–
mTPA, when the water fraction was increased from 70 to 80%,
the PL peak redshifts from 440 to 485 nm, which is probably
caused by the morphological change from the aggregated,
amorphous form to the crystalline state. As TPE–mTPA is more
twisted than TPE–pTPA, the aggregates should be crystallized
more easily, confirming the subtle adjustment of their emitting
properties by accurate modification of the structure through
the different linking position.
Closer inspection of the PL spectra of the luminogens in the
solid state was carried out because they should be fabricated
as thin solid films in the OLEDs. As shown in Figure 3, all of the
films exhibit sky-blue emission ranging from 470 to 481 nm.
The PL peaks of the films are almost the same as the values
obtained from the corresponding PL spectra of the aggregates
in the 99% water fraction, suggesting the aggregates in fw =
99% are in the amorphous state. It should be pointed out that
Figure 1. Plots of the fluorescence quantum yields determined in THF/H2O
solutions by using 9,10-diphenylanthracene (F=90% in cyclohexane) as the
internal standard versus the fraction of water in the solvent. Insets: photo-
graphs of the TPE–Ar luminogens in the THF/water mixture (fw =99%) taken
under the illumination of a 365 nm UV lamp. Excitation wavelengths [nm]:
320 for TPE–ptol and TPE–mtol, and 310 for the other six fluorophores.
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Figure 2. PL spectra of a) TPE–pTPA and b) TPE–mTPA in THF/H2O mixtures
with different water fractions. Concentration [mM]: 10; excitation wavelength
[nm]: 310.
Figure 3. The PL spectra of the films of the TPE–Ar luminogens. The thin
films were spin-coated onto ITO glass from dilute THF solutions with con-
centrations of 1 mgmLÀ1. Excitation wavelengths [nm]: 320 for TPE–2pTPA
and TPE–2mTPA, 350 for TPE–2ptol and 340 for the rest of the fluorophores.
shifted EL emission, rather than the sky-blue emission shown
in the PL spectra of spin-coated thin films. In fact, the PL spec-
trum of TPE–mTPA (Figure 2), when the water fraction is 70%,
partially disclosed this possibility. Thus, unlike the sky-blue
emission of the thin films (Figure 3), blue, even deep-blue,
emissions could still be achieved in the LED devices.
Table 1. The thermal, electrochemical, and photophysical data of the
TPE–Ar luminogens.
PL lmax
FF
lmax,abs
[a]
[c]
[d]
[e]
Td Tg[b] Eg
EHOMO ELUMO aggr[f] film aggr[f] soln[g]
[8C] [8C] [eV[ [eV]
[eV]
[nm] [nm] [%]
[nm]
Thermal properties
TPE–ptol
TPE–mtol
TPE–pTPA
TPE–mTPA 450
TPE–2ptol 517
409 82 3.28 À5.49 À2.21 486
391 80 3.29 À5.53 À2.24 479
451 106 3.37 À5.22 À1.85 480
479 17.9 324
474 21.6 323
476 32.8 309
477 30.1 310
481 26.5 307
476 29.6 307
480 20.7 305
470 24.8 304
Good thermal stability of an emitter is closely related to the
process of vacuum deposition and the operating stability of
the LED devices. The thermal properties of all of the new com-
pounds were determined by thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) measurements. As
depicted in Figure S2 in the Supporting Information and
Table 1, because of the bulky and rigid structures of the TPE,
triphenylamine, and fluorene groups, all of the fluorophores
are thermally stable with Td values (5% weight loss) in the
range 391–5498C. Clearly, compounds 13–16 possess higher
thermal stability than compounds 9–12, possibly due to the
longer molecular structures and larger molecular weights.
Moreover, as a result of their more rigid structures, all of the
triphenylamine-substituted compounds have higher Td values
than the toluene-substituted ones. In addition, molecules with
the meta-linking mode of TPE and the phenyl ring at the 9-po-
sition of fluorene are less stable than the analogues with the
–
–
3.38 À5.22 À1.84 478
3.20 À5.46 À2.26 492
TPE–2mtol 492 110 3.21 À5.49 À2.28 483
TPE–2pTPA 549 174 3.33 À5.21 À1.88 490
TPE–2mTPA 506
–
3.36 À5.14 À1.78 480
[a] 5% weight-loss temperature measured by TGA under N2. [b] Glass-
transition temperature measured by DSC under N2. [c] Band gap estimat-
ed from the optical absorption band edge of the solution. [d] Calculated
from the onset oxidation potentials of the compounds. [e] Estimated by
using the empirical equation ELUMO =EHOMO +Eg. [f] Determined in THF/
H2O=1:99. [g] Observed from absorption spectra in dilute THF (10 mM).
para-linking mode as a result of their more twisted conforma-
tions. Among these compounds, TPE–2pTPA possesses the
highest thermal stability and exhibits a glass-transition temper-
ature (Tg) of 1748C. With the thermal and morphological stabil-
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ity of these compounds, homogeneous and stable amorphous
thin films should be possible to be obtained by vacuum depo-
sition, which is desirable for OLEDs with high stability and
efficiency.
Electrochemical properties
Cyclic voltammetry (CV) was carried out to investigate the elec-
trochemical behavior of these materials. The HOMO energy
levels were estimated from the onset oxidation potentials ac-
cording to the equation HOMO=À(4.8+Eox) eV, whereas the
LUMO energy levels were obtained from the optical band gap
energies (estimated from the onset wavelengths of the UV ab-
sorptions) and the HOMO values. The HOMO values for TPE–
pTPA and TPE–mTPA (À5.22 eV for both) are higher than those
of TPE–ptol and TPE–mtol (À5.49 and À5.53 eV), suggesting
that they possess better hole-transporting properties due to
the introduction of the triphenylamine unit. Furthermore, the
higher band gap energies of TPE–pTPA and TPE–mTPA (3.37
and 3.38 eV) have clearly demonstrated their shorter effective
conjugation lengths, which is closely related to their twisted
conformations. Therefore, it could be rationalized that the
turn-on voltages of TPE–pTPA and TPE–mTPA will be decreased
in comparison with those of TPE–ptol and TPE–mtol. As seen
in Table 1, the other four luminogens, TPE–pTPA, TPE–mTPA,
TPE–ptol, and TPE–mtol, are in the same situation. They all pos-
sess longer conjugation lengths than the aforementioned
ones, which will result in redshifted EL emissions.
Theoretical calculations
To better understand the correlation between the structure
and photophysical properties, as well as the OLED per-
formance, density functional theory (DFT) calculations (B3LYP/
6-31g*) were conducted to obtain the orbital distributions of
the HOMO and LUMO energy levels. As shown in Figure 4, for
Electroluminescence
The efficient solid-state emission and good thermal and mor-
phological stability of these luminogens prompted us to inves-
tigate their electroluminescence properties. Undoped multilay-
er OLEDs with configurations of indium tin oxide/polyethylene-
dioxythiophene–polystyrene sulfonic acid (ITO/PEDOT:PSS,
30 nm)/NPB (1,4-bis(1-naphthylphenylamino)biphenyl, 30 nm)/
EML (emissive layer, 10–30 nm)/TPBI (1,3,5-tris(N-phenylbenzi-
Figure 4. Calculated molecular orbital amplitude plots of HOMO and LUMO
levels of the TPE–Ar luminogens.
toluene-substituted compounds TPE–2ptol, TPE–2mtol, TPE–
ptol, and TPE–mtol, the electron clouds of the HOMOs and
LUMOs are all located on the TPE moieties, showing their weak
intramolecular charge transfer and corresponding to their
lower absorbance shown in the UV/Vis spectra (see the Sup-
porting Information, Figure S1). However, the electron distribu-
tions of the HOMO and LUMO orbitals are centralized on TPE
and triphenylamine separately for the TPA-substituted com-
pounds, that is, TPE–2pTPA, TPE–2mTPA, TPE–pTPA, and TPE–
mTPA, suggesting the electron-donating properties of triphe-
nylamine, and thus their better hole-transporting ability. Fur-
ther inspection of their optimized molecular structures was
carried out. From Figure S4 in the Supporting Information, we
can see that the dihedral angles between the toluene group or
the triphenylamine and fluorene plane are all over 758, sug-
gesting weak conjugation. This is consistent with our synthetic
idea of combining the classically fluorescent moieties together
without bringing about the side effect of lengthened conjuga-
tion. Moreover, the bulky nonplanar triphenylamine makes the
molecules more twisted. This is beneficial for decreasing the
intermolecular p–p stacking compared to the toluene-substi-
tuted compounds, leading to crystallization-induced blueshift-
ed emission for TPE–pTPA and TPE–mTPA.
midizol-2-yl)benzene,
10 nm)/Alq3
(tris(8-oxoquinoline)
aluminum(III), 30 nm)/Ca:Ag(100 nm) were fabricated in which
NPB and TPBI work as the hole-transporting and hole-blocking
layers, respectively, PEDOT:PSS was used to smooth the ITO
surface and decrease the hole injection barrier, and the AIE lu-
minogens served as emitters.
As summarized in Table 2, the devices based on the four tri-
phenylamine-containing emitters (TPE–pTPA, TPE–mTPA, TPE–
2pTPA, and TPE–2mTPA) possess lower turn-on voltages (3.0–
3.6 V) and higher current densities than those of the toluene-
substituted compounds (3.9–4.5 V), reflecting their smaller in-
jection barriers from transporting layers. This confirmed that
the TPA moieties were beneficial for increasing the hole-trans-
porting capability compared to toluene moieties, which is con-
sistent with our design idea. As shown in the current-density–
voltage–luminance (J–V–L) curves (Figure 5a), the current den-
sities increase rapidly as the voltage increases. All of the devi-
ces containing TPA-based emitters show better EL efficiencies
than the toluene-based compounds. In detail, devices based
on TPE–ptol and TPE–mtol exhibit maximum luminances (Lmax
)
of 8540 and 10494 cdmÀ2, maximum current efficiencies
(hC,max) of 1.64 and 2.18 cdAÀ1, and maximum power efficien-
cies (hP,max) of 0.70 and 0.96 ImWÀ1, respectively. As expected,
much better EL performances were observed for TPE–pTPA
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and TPE–mTPA with Lmax, hC,max, and hP,max values of 26697 and
14854 cdmÀ2, 3.37 and 2.76 cdAÀ1, and 2.40 and 1.80 LmWÀ1,
respectively, showing more efficient carrier transport and exci-
ton combination in the emissive layer. Interestingly, although
the chemical structures of TPE–pTPA and TPE–mTPA are similar,
their device performance is quite different. This is reasonable;
the conformation of TPE–pTPA is more planar than that of
TPE–mTPA, which is good for carrier transport when serving as
an emitter. Furthermore, as TPE and TPA or toluene groups are
linked to the fluorene core through the 9,9’-positions, the mol-
ecules are quite twisted, and the p-conjugation lengths are ef-
fectively controlled. Thus, all four emitters exhibit deep-blue
emission with EL peaks at 448–451 nm. From the CIE coordi-
nates, devices made from TPE–mtol (0.16, 0.14) and TPE–mTPA
(0.15, 0.15) are bluer than those made from TPE–ptol and TPE–
pTPA because the meta-linkage of TPE and the fluorene core
contributes less to the elongation of the conjugation than the
para-linkage, as evidenced by our previous study.[13c] Compared
to TPE alone, the incorporation of TPA and fluorene not only
could increase the thermal stability, but also could greatly en-
hance the OLED performance without sacrificing the deep-blue
emission because of the special linking mode through the sp3-
hybridized carbon atom, as discussed above.
Table 2. EL performance of the TPE–Ar luminogens.[a]
lEL
Von
[V]
Lmax
[cdmÀ2
hC,max
[cdAÀ1
hP,max
CIE
[x,y]
[nm]
]
]
[lm/W]
TPE–pTPA
TPE–mTPA
TPE–ptol
TPE–mtol
TPE–2ptol
TPE–2mtol
TPE–2pTPA
TPE–2mTPA
448
451
448
450
511
484
488
489
3.0
3.3
4.5
3.9
3.9
3.9
3.3
3.6
26697
14854
8540
10494
9578
7382
14173
10275
3.37
2.76
1.64
2.18
1.68
1.37
5.65
4.24
2.40
1.80
0.70
0.96
0.39
0.57
3.68
2.10
0.16, 0.16
0.15, 0.15
0.16, 0.19
0.16, 0.14
0.17, 0.24
0.16, 0.27
0.19, 0.31
0.14, 0.28
[a] Abbreviations: Von =turn-on voltage at 1 cdmÀ2, Lmax =maximum lumi-
nance, hC,max and hP,max =maximum current and power efficiencies, respec-
tively. CIE=commission international de l’eclairage coordinates.
Moreover, as the conjugation lengths are effectively length-
ened, the OLED performance of TPE–2pTPA and TPE–2mTPA is
greatly enhanced with Lmax, hC,max, and hP,max values of 14173
and 10275 cdmÀ2
, , and 3.68 and
5.65 and 4.64 cdAÀ1
2.10 LmWÀ1, respectively (Figure 6). However, their EL emis-
sions are no longer in the deep-blue region, with EL peaks at
488 and 489 nm, and CIE coordinates of (0.19, 0.31) and (0.14,
0.28), demonstrating the difficulty of generating AIE emitters
with both deep-blue emission and high OLED efficiencies.
TPE–2ptol and TPE–2mtol possess worse device performance,
probably due to the imbalance between charge injection and
transportation in OLEDs. In comparison with the PL spectra of
these four disubstituted TPE derivatives, the EL spectra exhibit
some redshifting. This phenomenon is totally different from in
the monosubstituted TPE compounds, including TPE–pTPA,
TPE–mTPA, TPE–mtol, and TPE–ptol, which could not be ex-
plained only by the transformation from the crystalline state to
the amorphous one. Analyzing their structures carefully, the re-
sults could be understood. In the four disubstituted TPE deriv-
atives (TPE–2pTPA, TPE–2mTPA, TPE–2ptol, and TPE–2mtol), the
p systems are much longer than those of in the monosubsti-
tuted compounds. Thus, in the compacted films of LED devices
their coplanarity might be better than that in the loosely ag-
gregated nanoparticles in a 90% water/THF solution or in spin-
coated films, which would lead to the redshifted emission as
a result of the enhanced conjugation throughout the molecule.
On the other hand, as shown in Table 1, the PL emission wave-
lengths of these four disubstituted TPE derivatives in thin films
are blueshifted in comparison with those in the aggregated
state due to the transformation from the amorphous state to
the crystalline one. Thus, in the compacted films of LED devi-
ces, there are two conflicting parameters, coplanarity and
states (amorphous vs. crystalline). From these results, coplanar-
ity is the main parameter causing the redshifted emission. As
Figure 5. a) Current-density–voltage–luminance characteristics of multilayer
EL devices of TPE–pTPA, TPE–mTPA, TPE–ptol, and TPE–mtol. b) Change in
current efficiency with current density in multilayer EL devices. c) EL spectra
of the devices. Device configurations: ITO/PEDOT:PSS (30 nm)/NPB (30 nm)/
EML (15 nm)/TPBI (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Ca:Ag (100 nm).
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As is known, it is difficult to obtain blue and deep-blue emit-
ters with good EL performance. Definitely, a lot of excellent AIE
emitters could be obtained by attaching the TPE moiety to
classical molecules, such as pyrene,[12d,k] anthracene,[12a–b,k] and
fluorene[12h], because the nonplanar TPE molecule could sup-
press the intermolecular p–p stacking of the molecules, al-
though TPE itself is a weak emitter. However, it will certainly
result in the intrinsic extension of the conjugation length
through common linkage modes. The good device per-
formance and deep-blue emission of TPE–pTPA and TPE–mTPA
have fulfilled our synthetic idea of utilizing less- or unconjugat-
ed linking modes, and shed some light on our further rational
molecular design.
Conclusion
In this work, we have successfully synthesized two deep-blue
fluorophores, TPE–pTPA and TPE–mTPA, and also another six
molecules with toluene groups or different conjugation
lengths for comparison. All of the luminogens show splendid
AIE effects and exhibit good thermal and morphological stabili-
ty due to the bulky aromatic groups. By incorporating hole-
dominated triphenylamine, fluorine groups with high luminous
efficiency, and the TPE moiety together through unconjugated
linkages, we partially overcame the intrinsic inconsistency be-
tween high efficiencies and deep-blue emission for construct-
ing AIE-active blue luminogens. When fabricated as emissive
layers in OLEDs, TPE–pTPA and TPE–mTPA exhibit the best EL
performance with Lmax, hC,max, and hP,max values of up to
26697 cdmÀ2, 3.37 cdAÀ1, and 2.40 LmWÀ1, and CIE coordi-
nates of (0.16, 0.16) and (0.15, 0.15), respectively, suggesting
the more efficient carrier transport and exciton combination in
these devices and less effective conjugation lengths compared
to other emitters. Evidently, the electroluminescence properties
of TPE could be greatly enhanced without sacrificing the deep-
blue emission through rational molecular design. By utilizing
this design idea, we believe that more efficient blue or deep-
blue TPE-based emitters will be developed and find applica-
tions in OLEDs.
Figure 6. a) Current-density–voltage–luminance characteristics of multilayer
EL devices of TPE–2pTPA, TPE–2mTPA, TPE–2ptol, and TPE–2mtol. b) Change
in current efficiency with current density in multilayer EL devices. c) EL spec-
tra of the devices. Device configurations: ITO/PEDOT:PSS (30 nm)/NPB
(30 nm)/EML (15 nm)/TPBI (10 nm)/Alq3 (30 nm)/LiF (1 nm)/Ca:Ag (100 nm).
Experimental Section
Preparation of the compounds
All other chemicals and reagents were obtained from commercial
sources and used as received. Solvents for chemical synthesis were
purified according to standard procedures. Compounds 3–6 were
synthesized according to literature procedures.[1]
to the cases of the four monosubstituted TPE derivatives, the
coplanarity and different state compete; fortunately, the trans-
formation from the amorphous to the crystalline state contrib-
utes considerably to the blueshifted EL emissions for these rel-
atively shorter p systems and lower molecular weights. These
phenomena have never been observed for AIE luminogens
with blue or deep-blue emission, possibly due to their shorter
p systems. However, the results obtained here remind us of an-
other point in the design of AIE luminogens with blue and
deep-blue emissions: the possibly improved coplanarity of the
AIE luminogens in the compacted thin films of LED devices de-
rived from long p systems.
Synthesis of compound 7
A solution of n-butyllithium in hexane (2.3m, 15.0 mmol, 6.5 mL)
was added to a solution of 4-bromotetraphenylethene (2, 4.12 g,
10.0 mmol) in anhydrous tetrahydrofuran (60 mL) at À788C under
an atmosphere of argon. 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
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layers were combined and dried over anhydrous sodium sulfate.
After filtration and evaporation of the solvent, the crude product
was purified by silica gel column chromatography using petroleum
ether (60–908C)/dichloromethane (5:1 v/v) as the eluent. A white
powder (7) was obtained in a yield of 60% (2.30 g). 1H NMR
(300 MHz, CDCl3): d=7.55–7.52 (m, 2H), 7.08–7.01 (m, 17H),
1.31 ppm (s, 12H).
TPE–pTPA
1
White powder (yield: 84.6%). M.p.: 155–1588C; H NMR (300 MHz,
CDCl3): d=7.78–7.76 (m, 1H), 7.44–7.34 (m, 6H), 7.30–7.19 (m,
14H), 7.07–7.05 (m, 21H), 6.98–6.96 (m, 1H), 6.92–6.89 ppm (m,
2H); 13C NMR (75 MHz, CDCl3): d=151.7, 147.8, 146.7, 145.1, 143.8,
142.7, 141.1, 140.6, 140.5, 139.5, 138.9, 138.6, 131.9, 131.7, 129.5,
128.9, 128.4, 127.6, 126.8, 126.2, 124.6, 123.4, 122.7, 120.5 ppm; IR
(thin film): n˜ =2958, 2886, 1726, 1492, 1188, 1068, 956, 851,
700 cmÀ1; MS (EI): m/z calcd for C63H45N: 816.04; found: 816.13
[M+]; elemental analysis calcd (%) for C63H45N: C 92.73, H 5.56, N
1.72; found: C 92.45, H 5.18, N 1.71.
Synthesis of compound 8
A mixture of 4,4’-dibromotetraphenylethene (3, 4.90 g, 10 mmol),
4,4,4’,4’,5,5,5’,5’-octamethyl-2,2’-bi(1,3,2-dioxaborolane)
(6.35 g,
TPE–mTPA
25 mmol), potassium acetate (6.87 g, 70 mmol), and [Pd(dppf)Cl2]
(0.15 g, 0.2 mmol) in anhydrous 1,4-dioxane (80 mL) was heated at
reflux under N2 for 12 h, and then water (20 mL) was added. The
crude product was extracted into ethyl acetate, washed with
water, and dried over anhydrous sodium sulfate. After removing
the solvent under reduced pressure, the residue was purified by
column chromatography using petroleum ether (60–908C)/ethyl
acetate (10:1 v/v) as the eluent. A white powder (8) was obtained
White powder (yield: 70.5%). M.p.: not observed; 1H NMR
(300 MHz, CDCl3): d=7.77–7.75 (m, 1H), 7.45–7.34 (m, 3H), 7.26–
7.19 (m, 24H), 7.10–6.98 (m, 16H), 6.91–6.88 ppm (m, 1H); 13C NMR
(75 MHz, CDCl3): d=151.4, 147.8, 146.7, 146.4, 143.9, 142.9, 141.2,
140.6, 140.4, 140.2, 139.7, 138.9, 131.9, 131.5, 129.3, 129.1, 128.0,
127.9, 127.8, 127.7, 126.6, 126.4, 125.4, 124.5, 123.3, 122.9,
120.4 ppm; IR (thin film): n˜ =2958, 2883, 1721, 1491, 1188, 1066,
963, 852, 745, 698 cmÀ1; MS (EI): m/z calcd for C63H45N: 816.04;
found: 816.09 [M+]; elemental analysis calcd (%) for C63H45N: C
92.73, H 5.56, N 1.72; found: C 92.37, H 5.51, N 1.81.
1
in a yield of 68.9% (4.2 g). H NMR (300 MHz, CDCl3): d=7.53–7.47
(m, 4H), 7.11–7.09 (m, 4H), 7.07–7.05 (m, 6H), 7.00–6.98 (m, 4H),
1.27 ppm (s, 24H).
TPE–2ptol
General procedure for the synthesis of TPE–ptol, TPE–mtol,
TPE–pTPA, TPE–mTPA, TPE–2ptol, TPE–2mtol, TPE–2pTPA,
and TPE–2mTPA
1
White powder (yield: 60.4%). M.p.: 204–2078C; H NMR (300 MHz,
CDCl3): d=7.87–7.85 (m, 4H), 7.48–7.45 (m, 12H), 7.38–7.27 (m,
30H), 7.17–7.04 (m, 4H), 2.38 ppm (s, 6H); 13C NMR (75 MHz,
CDCl3): d=151.4, 145.2, 143.9, 143.0, 142.8, 141.3, 140.2, 138.9,
138.5, 136.4, 132.0, 131.5, 129.1, 128.6, 128.2, 127.9, 127.6, 126.7,
126.6, 126.4, 126.2, 126.1, 120.3, 21.2 ppm; IR (thin film): n˜ =2960,
2891, 1716, 1640, 1442, 1368, 1346, 1322, 1190, 1065, 963, 927,
849 cmÀ1; MALDI-TOF: m/z calcd for C78H56: 992.4382; found:
992.4396 [M+]; elemental analysis calcd (%) for C78H56: C 94.32, H
5.68; found: C 94.01, H 5.81.
TPE–ptol
A
mixture of 3 (412 mg, 1 mmol), 7 (463 mg, 1.01 mmol),
[Pd(PPh3)4] (60 mg), and potassium hydroxide (280 mg, 5 mmol) in
THF (15 mL) and distilled water (5 mL) was heated at reflux for two
days under N2 in a Schlenk tube (50 mL). The mixture was extract-
ed with dichloromethane. The combined organic extracts were
dried over anhydrous Na2SO4 and concentrated by rotary evapora-
tion. The crude product was purified by column chromatography
on silica gel using dichloromethane/petroleum ether (1:50 v/v) as
the eluent. A white powder was obtained in a yield of 69.4%
TPE–2mtol
1
White powder (yield: 84.5%). M.p.: 206–2098C; H NMR (300 MHz,
1
(460 mg). M.p.: 108–1108C; H NMR (300 MHz, CDCl3): d=7.77–7.75
CDCl3): d=7.77–7.75 (m, 4H), 7.42–7.33 (m, 13H), 7.28–7.18 (m,
10H), 7.08–7.03 (m, 11H), 7.02–7.00 (m, 12H), 2.29 ppm (s, 6H);
13C NMR (75 MHz, CDCl3): d=151.5, 146.7, 144.0, 143.1, 140.4,
139.1, 136.5, 132.0, 131.6, 129.2, 128.3, 128.0, 127.7, 127.3, 126.8,
126.5, 126.4, 125.5, 120.4, 21.2 ppm; IR (thin film): n˜ =2960, 2890,
(m, 2H), 7.38–7.32 (m, 6H), 7.23–7.20 (m, 4H), 7.09–7.04 (m, 23H),
2.29 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=151.4, 145.3, 143.9,
143.8, 143.0, 142.8, 141.2, 140.7, 140.3, 138.9, 138.5, 136.5, 131.9,
131.6, 131.5, 129.2, 128.7, 128.2, 127.9, 127.8, 127.6, 126.8, 126.6,
126.3, 126.2, 120.4, 21.2 ppm; IR (thin film): n˜ =2959, 2886, 1722,
1443, 1188, 1064, 962, 845 cmÀ1; MS (EI): m/z calcd for C52H38:
662.86; found: 662.17 [M+]; elemental analysis calcd (%) for C52H38:
C 94.22, H 5.78; found: C 94.45, H 5.72.
1722, 1643, 1442, 1368, 1344, 1190, 1066, 963, 926, 850 cmÀ1
;
MALDI-TOF: m/z calcd for C78H56: 992.4382; found: 992.4370 [M+];
elemental analysis calcd (%) for C78H56: C 94.32, H 5.68; found: C
93.88, H 5.31.
TPE–2pTPA
TPE–mtol
Light-yellow powder (yield: 85.9%). M.p.: 217–2208C; 1H NMR
(300 MHz, CDCl3): d=7.77–7.75 (m, 4H), 7.45–7.33 (m, 11H), 7.29–
7.26 (m, 11H), 7.22–7.17 (m, 15), 7.09–7.04 (m, 25H), 6.98–
6.88 ppm (m, 4H); 13C NMR (75 MHz, CDCl3): d=151.5, 147.9, 146.4,
145.3, 142.9, 140.3, 139.7, 138.6, 132.0, 131.6, 129.4, 129.1, 128.7,
127.9, 127.7, 126.8, 126.4, 126.2, 124.6, 123.4, 123.0, 120.4 ppm; IR
(thin film): n˜ =2959, 2886, 1715, 1443, 1346, 1188, 1060, 960,
854 cmÀ1; MALDI-TOF: m/z calcd for C100H70N2: 1298.5539; found:
1298.5559 [M+]; elemental analysis calcd (%) for C100H70N2: C 92.42,
H 5.43, N 2.16; elemental analysis calcd (%) for C100H70N2: C 92.40,
H 5.18, N 1.88.
White powder (yield: 69.4%). M.p.: not observed; 1H NMR
(300 MHz, CDCl3): d=7.78–7.75 (m, 2H), 7.38–7.33 (m, 6H), 7.23–
7.20 (m, 4H), 7.09–7.05 (m, 23H), 2.29 ppm (s, 3H); 13C NMR
(75 MHz, CDCl3): d=151.4, 146.7, 143.9, 143.8, 143.1, 142.9, 141.1,
140.6, 140.5, 140.3, 138.9, 136.4, 131.9, 131.5, 129.1, 128.1, 127.9,
127.8, 127.6, 127.2, 126.6, 126.4, 126.3, 125.4, 120.3, 21.2 ppm; IR
(thin film): n˜ =2959, 2890, 1722, 1442, 1190, 1064, 966, 851 cmÀ1
;
MS (EI): m/z calcd for C52H38: 662.86; found: 662.16 [M+]; elemental
analysis calcd (%) for C52H38: C 94.22, H 5.78; found: C 94.37, H
5.36.
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J. W. Hong, G. C. Bazan, K. W. Plaxco, A. J. Heeger, Proc. Natl. Acad. Sci.
USA 2003, 100, 6297–6301; d) S.-F. Lim, R. H. Friend, I. D. Rees, J. Li, Y.
Ma, K. Robinson, A. B. Holms, E. Hennebicq, D. Beljonne, F. Cacialli, Adv.
Funct. Mater. 2005, 15, 981–988.
TPE–2mTPA
Light-yellow powder (yield: 80.5%). M.p.: 190–1928C; 1H NMR
(300 MHz, CDCl3): d=7.61–7.57 (m, 4H), 7.25–7.13 (m, 9H), 7.11–
7.08 (m, 19H), 7.05–7.00 (m, 8H), 6.88–6.80 (m, 27H), 6.81–
6.70 ppm (m, 3H); 13C NMR (75 MHz, CDCl3): d=151.5, 147.9, 144.0,
140.4, 132.0, 131.6, 129.4, 129.2, 128.8, 128.0, 127.7, 126.8, 126.5,
125.5, 124.6, 123.3, 123.0, 120.4 ppm; IR (thin film): n˜ =2959, 2888,
1715, 1590, 1489, 1446, 1189, 1061, 959, 747 cmÀ1; MALDI-TOF: m/z
calcd for C100H70N2: 1298.5539: found: 1298.5586 [M+]; elemental
analysis calcd (%) for C100H70N2: C 92.42, H 5.43, N 2.16; found: C
92.18, H 5.72, N 2.19.
[8] J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu, H. S. Kwok, X.
Zhan, Y. Liu, D. Zhu, B. Z. Tang, Chem. Commun. 2001, 1740–1741.
[9] a) J. Chen, B. Xu, X. Ouyang, B. Z. Tang, Y. Cao, J. Phys. Chem. A 2004,
108, 7522–7526; b) Z. Li, Y. Dong, B. Mi, Y. Tang, H. Tong, P. Dong,
J. W. Y. Lam, Y. Ren, H. H. Y. Sun, K. Wong, P. Gao, I. D. Williams, H. S.
Kwok, B. Z. Tang, J. Phys. Chem. B 2005, 109, 10061–10066; c) Y. Ren,
J. W. Y. Lam, Y. Dong, B. Z. Tang, K. S. Wong, J. Phys. Chem. B 2005, 109,
1135–1140; d) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009,
4332–4353; e) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Soc. Rev. 2011, 40,
5361–5388.
[10] Z. Zhao, J. W. Y. Lam, B. Z. Tang, J. Mater. Chem. 2012, 22, 23726–23740.
[11] Y. Dong, J. W. Y. Lam, A. Qin, J. Liu, Z. Li, B. Z. Tang, Appl. Phys. Lett.
2007, 91, 011111.
Acknowledgements
[12] a) S. K. Kim, Y. Park, I. N. Kang, J. W. Park, J. Mater. Chem. 2007, 17,
4670–4678; b) P. Shih, C. Y. Chuang, C. H. Chien, E. W. G. Diau, C. F. Shu,
Adv. Funct. Mater. 2007, 17, 3141–3146; c) Z. Zhao, S. Chen, X. Shen, F.
Mahtab, Y. Yu, P. Lu, J. W. Y. Lam, H. S. Kwok, B. Z. Tang, Chem. Commun.
2010, 46, 686–688; d) Z. Zhao, S. Chen, J. W. Y. Lam, P. Lu, Y. Zhong,
K. S. Wong, H. S. Kwok, B. Z. Tang, Chem. Commun. 2010, 46, 2221–
2223; e) W. Z. Yuan, P. Lu, S. Chen, J. W. Y. Lam, Z. Wang, Y. Liu, H. S.
Kwok, Y. Ma, B. Z. Tang, Adv. Mater. 2010, 22, 2159–2163; f) Z. Zhao,
J. W. Y. Lam, C. Y. K. Chan, S. Chen, J. Liu, P. Lu, M. Rodriguez, J. L. Maldo-
nado, G. Ramos-Ortiz, H. H. Y. Sung, I. D. Williams, H. Su, K. S. Wong, Y.
Ma, H. S. Kwok, H. Qiu, B. Z. Tang, Adv. Mater. 2011, 23, 5430–5435; g) Y.
Liu, S. Chen, J. W. Y. Lam, P. Lu, R. T. K. Kwok, F. Mahtab, H. S. Kwok, B. Z.
Tang, Chem. Mater. 2011, 23, 2536–2544; h) Z. Zhao, C. Deng, S. Chen,
J. W. Y. Lam, W. Qin, P. Lu, Z. Wang, H. S. Kwok, Y. Ma, H. Qiu, B. Z. Tang,
Chem. Commun. 2011, 47, 8847–8849; i) W. Z. Yuan, S. Chen, J. W. Y.
Lam, C. Deng, P. Lu, H. H.-Y. Sung, I. D. Williams, H. S. Kwok, Y. Zhang,
B. Z. Tang, Chem. Commun. 2011, 47, 11216–11218; j) Z. Zhao, P. Lu,
J. W. Y. Lam, Z. Wang, C. Y. K. Chan, H. H. Y. Sung, I. D. Williams, Y. Ma,
B. Z. Tang, Chem. Sci. 2011, 2, 672–675; k) C. Y. K. Chan, Z. Zhao, J. W. Y.
Lam, J. Liu, S. Chen, P. Lu, F. Mahtab, X. Chen, H. H. Y. Sung, H. S. Kwok,
Y. Ma, I. D. Williams, K. S. Wong, B. Z. Tang, Adv. Funct. Mater. 2012, 22,
378–389; l) Z. Chang, Y. Jiang, B. He, J. Chen, Z. Yang, P. Lu, H. S. Kwok,
Z. Zhao, H. Qiu, B. Z. Tang, Chem. Commun. 2013, 49, 594–596.
[13] a) J. Huang, X. Yang, J. Wang, C. Zhong, L. Wang, J. Qin, Z. Li, J. Mater.
Chem. 2012, 22, 2478–2484; b) J. Huang, N. Sun, J. Yang, R. Tang, Q. Li,
D. Ma, J. Qin, Z. Li, J. Mater. Chem. 2012, 22, 12001–12007; c) J. Huang,
N. Sun, Y. Dong, R. Tang, P. Lu, P. Cai, Q. Li, D. Ma, J. Qin, Z. Li, Adv.
Funct. Mater. 2013, 23, 2329–2337.
We are grateful to the National Fundamental Key Research Pro-
gram (2013CB834701) and the National Natural Science Foun-
dation of China (21161160556, 61106017) for financial support.
Keywords: aggregation-induced emission · blue emitters ·
luminescence
·
organic
light-emitting
diodes
·
tetraphenylethene
[1] a) C. W. Tang, S. A. Vanslyke, Appl. Phys. Lett. 1987, 51, 913–915; b) C.
Adachi, T. Tsutsui, S. Saito, Appl. Phys. Lett. 1989, 55, 1489–1491;
c) M. A. Baldo, M. E. Thompson, S. R. Forrest, Nature 2000, 403, 750–
753; d) B. W. D’Andrade, S. R. Forrest, Adv. Mater. 2004, 16, 1585–1595;
e) P. L. Burn, S. C. Lo, I. D. W. Samuel, Adv. Mater. 2007, 19, 1675–1688.
[2] a) L. M. Leung, W. Y. Lo, S. K. So, K. M. Lee, W. K. Choi, J. Am. Chem. Soc.
2000, 122, 5640–5641.
[3] a) L. H. Chan, R. H. Lee, C. F. Hsieh, H. C. Yeh, C. T. Chen, J. Am. Chem.
Soc. 2002, 124, 6469–6479; b) M. T. Lee, C. H. Liao, C. H. Tasi, C. H. Chen,
Adv. Mater. 2005, 17, 2493–2497; c) B. C. Krummacher, V. E. Choong,
M. K. Mathsi, S. A. Choulis, F. Jermann, T. Fiedler, M. Zachau, Appl. Phys.
Lett. 2006, 88, 113506; d) R. C. Chiechi, R. J. Tseng, F. Marchioni, Y. Yang,
F. Wudl, Adv. Mater. 2006, 18, 325–328; e) T. P. I. Saragi, T. Spehr, A. Sie-
bert, T. F. Lieker, J. Salbeck, Chem. Rev. 2007, 107, 1011–1065; f) Y. Y. Lyu,
J. Kwak, O. Kwon, S. H. Lee, D. Kim, C. Lee, K. Char, Adv. Mater. 2008, 20,
2720–2729; g) K. T. Kamtekar, A. P. Monkman, M. R. Bryce, Adv. Mater.
2010, 22, 572–582.
[4] a) Y.-H. Kim, H.-C. Jeong, S.-H. Kim, K. Yang, S.-K. Kwon, Adv. Funct.
Mater. 2005, 15, 1799–1805; b) I. Cho, S. H. Kim, J. H. Kim, S. Park, S. Y.
Park, J. Mater. Chem. 2012, 22, 123–129; c) S. H. Kim, I. Cho, M. K. Sim,
S. Park, S. Y. Park, J. Mater. Chem. 2011, 21, 9139–9148; d) H. Park, J.
Lee, I. Kang, H. Y. Chu, J. I. Lee, S. K. Kwon, Y. H. Kim, J. Mater. Chem.
2012, 22, 2695–2700.
[5] K. C. Wu, P. J. Ku, C. S. Lin, H. T. Shih, F. I. Wu, M. J. Huang, J. J. Lin, I. C.
Chen, C. H. Cheng, Adv. Funct. Mater. 2008, 18, 67–75.
[6] a) S. W. Thomas III, G. D. Joly, T. M. Swager, Chem. Rev. 2007, 107, 1339–
1386; b) A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz, A. B.
Holmes, Chem. Rev. 2009, 109, 897–1091.
[14] S. O. Kim, K. H. Lee, G. Y. Kim, J. H. Seo, Y. K. Kim, S. S. Yoon, Synth. Met.
2010, 160, 1259–1265.
[15] a) K. T. Wong, Y. Y. Chien, R. T. Chen, C. F. Wang, Y. T. Lin, H. H. Chiang,
P. Y. Hsieh, C. C. Wu, C. H. Chou, Y. O. Su, G. H. Lee, S. M. Peng, J. Am.
Chem. Soc. 2002, 124, 11576–11577; b) H. H. Huang, C. Prabhakar, K. C.
Tang, P. T. Chou, G. J. Huang, J. S. Yang, J. Am. Chem. Soc. 2011, 133,
8028–8039.
[16] X. Zhou, H. Li, Z. Chi, X. Zhang, J. Zhang, B. Xu, Y. Zhang, S. Liu, J. Xu,
New J. Chem. 2012, 36, 685–693.
[7] a) M. T. Lee, H. H. Chen, C. H. Liao, C. H. Tsai, C. H. Chen, Appl. Phys. Lett.
2004, 85, 3301–3303; b) S. Hecht, J. M. J. Frechet, Angew. Chem. 2001,
113, 76–94; Angew. Chem. Int. Ed. 2001, 40, 74–91; c) C. Fan, S. Wang,
Received: September 6, 2013
Revised: January 15, 2014
Published online on March 24, 2014
Chem. Eur. J. 2014, 20, 5317 – 5326
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