High efficiency non-dopant blue organic light-emitting diodes based on anthracene-based fluorophores with molecular design of charge transport and red-shifted emission proof

Article abstract of DOI:10.1039/c4tc00876f

A new series of 9,10-diphenylanthracene (DPA)-based blue fluorophores have been synthesized and characterized for organic light-emitting diode (OLED) applications. These fluorophores have a bulky substituent, such as triphenylsilane in TPSDPA and mesityle

Full text of DOI:10.1039/c4tc00876f

Volume 2 Number 35 21 September 2014 Pages 7143–7438
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
www.rsc.org/MaterialsC
ISSN 2050-7526
PAPER
Chin-Ti Chen, Chao-Tsen Chen, Chi-Jung Su et al.
High efficiency non-dopant blue organic light-emitting diodes based
on anthracene-based fluorophores with molecular design of charge
transport and red-shifted emission proof

Journal of
Materials Chemistry C
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PAPER
High efficiency non-dopant blue organic light-
emitting diodes based on anthracene-based
fluorophores with molecular design of charge
transport and red-shifted emission proof
Cite this: J. Mater. Chem. C, 2014, 2,
7188
a
a
Cheng-Lung Wu,ab Che-Hong Chang,ac Yung-Ting Chang, Chin-Ti Chen,
*
b
c
*
*
Chao-Tsen Chen and Chi-Jung Su
A new series of 9,10-diphenylanthracene (DPA)-based blue fluorophores have been synthesized and
characterized for organic light-emitting diode (OLED) applications. These fluorophores have a bulky
substituent, such as triphenylsilane in TPSDPA and mesitylene in TMPDPA, on the C-2 position. The C-2
substituent also includes electron transporting diphenylphosphine oxide in PPODPA and dimesitylene
borane in BMTDPA, or hole transporting N-phenylnaphthalen-1-amine in NPADPA. For TMPDPA blue
fluorophores, 9,10-diphenyl substituents of the anthracene core are further attached to hole-
transporting 9H-carbazole in CBZDPA and electron-transporting 2-phenyl-1,3,4-oxadiazole in OXDDPA.
Absorption and emission spectroscopic properties of all DPA-derived fluorophores, either in solution or
in the condensed phase, were fully characterized and the HOMO/LUMO energy levels of these
fluorophores were determined. The frontier molecular orbitals of the DPA derivatives were analysed by
theoretical methods to determine the possible intramolecular charge transfer (ICT) characteristics.
Whereas the blue emission is best preserved in TMPDPA, in which the non-conjugated bulky mesitylene
group suppresses red-shifted emissions, the ICT is attributed to the deterioration in the emissions of
NPADPA and BMTDPA. In the solid state, PPODPA suffered from red-shifted and weakened emissions
because of adverse crystallization, which is promoted by the dipolar nature of the diphenylphosphine
oxide substituent. Non-dopant OLEDs were fabricated with DPA, TPSDPA, TMPDPA, PPODPA, CBZDPA,
and OXDDPA. Except for PPODPA, the electroluminescence efficiency of these DPA derivatives was
significantly improved compared with that of the DPA OLEDs. In particular, CBZDPA and OXDDPA
OLEDs exhibited the best external quantum efficiency of 4.5% and 4.0% with a true blue colour, with
CIEx,y coordinates of (0.17, 0.17) and (0.16, 0.18), respectively. The improved electroluminescence
efficiency can be attributed to the molecular charge transport design of CBZDPA and OXDDPA.
Received 29th April 2014
Accepted 6th July 2014
DOI: 10.1039/c4tc00876f
www.rsc.org/MaterialsC
emitters are still relatively rare. More critically, true-blue phos-
phorescent emitters with high photoluminescent quantum
Introduction
efficiency that are stable enough for practical applications are
rarer still.1–5
Organic light-emitting diodes (OLEDs) remain a subject of
intense investigation because of their potential applications in
high-quality at-panel displays and solid state lighting, with
some consumer devices such as cell phones and digital cameras
incorporating OLED screens already available in the market-
place. OLEDs for full colour displays are showing great promise,
and require red, green, and blue-emitting materials. However,
highly efficient true-blue (Commission Internationale de
Therefore, use of blue electrouorescent materials has been
revived and they are in high demand for energy-saving solid-
state lighting that uses hybrid white OLEDs.6–9 Anthracene has
been widely regarded as an attractive building block and start-
ing material for blue uorescence OLEDs,10–60 because its
derivatives usually have a high uorescence quantum yield and
wide energy band-gap in solution. However, the planarity of
anthracene means it is prone to aggregation in the solid state,
which causes uorescence quenching and emission wavelength
red-shiing. For example, two perpendicular phenyl substitu-
ents at the C-9 and C-10 positions of 9,10-diphenylanthracene
(DPA) cannot completely overcome the uorescence quenching
and red-shiing problems through the steric hindrance
´
l'Eclairage coordinate (CIEx,y) of y < 0.20) phosphorescent
aInstitute of Chemistry, Academia Sinica, Taipei 11529, Taiwan. E-mail: chintchen@
gate.sinica.edu.tw; Fax: +886 2 27831237; Tel: +886 2 27898542
bDepartment of Chemistry, National Taiwan University, Taipei 10617, Taiwan
cSchool of Medical Applied Chemistry, Chung Shan Medical University, Taichung
40201, Taiwan
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Fig. 1 Left: chemical structure of DPA derivatives. Right: solution (dichloromethane) and solid state fluorescence image of, from left to right,
DPA, TMPDPA, TPSDPA, PPODPA, BMTDPA, NPADPA, CBZDPA, and OXDDPA.
approach.10 The bulky substituent at the C-2 position of DPA with different electrophiles to give TPSDPA (2a), PPODPA (2b),
can further prevent the molecule from aggregating, and thus and BMTDPA (2c). In contrast, NPADPA (2d) was obtained from
improve the performance of OLEDs further.13,14 However, red- 1 via Pd-catalyzed amination with N-phenylnaphthalen-1-
shied emissions are still observed in many 2-substituted DPA amine. CBZDPA (6a), TMPDPA (6b), and OXDDPA (6c) were
derivatives.
synthesized through a three-step procedure. Firstly, 2-bro-
In this research, in order to reduce the emission red-shiing moanthracene (3) was coupled to 2,4,6-trimethylboronic acid
in solution as well as in the solid state, we have synthesized and via a Suzuki–Miyaura coupling reaction to give 2-(1,3,5-trime-
systematically examined a series of chemical functionalities thylphenyl)anthracene (4). Secondly, compound 4 was bromi-
with steric hindrance at the C-2 position of DPA. We used nated at the C-9 and C-10 positions using N-bromosuccinamide
mesitylene (TMP), triphenylsilane (TPS), diphenylphosphine (NBS). Thirdly, the resulting 9,10-dibromo-2-(1,3,5-trimethyl-
oxide (PPO), dimesitylborane (BMT), and N-phenylnaphthalen- phenyl) anthracene (5) was converted to CBZDPA, TMPDPA, or
1-amine (NPA) groups in TMPDPA, TPSDPA, PPODPA, BMTDPA, OXDDPA via the Suzuki–Miyaura coupling reaction with a pre-
and NPADPA, respectively (Fig. 1).
synthesized boronic ester or boronic acid. The compounds were
Moreover, by introducing a charge transporting moiety of readily puried by column chromatography. Further purica-
either 9H-carbazole (CBZ) or 2-phenyl-1,3,4-oxadiazole (OXD) on tion of materials by gradient sublimation was necessary prior to
the phenyl substituent at the C-9 and C-10 positions of device fabrication. All these DPA derivatives were fully charac-
1
TMPDPA, the performance of OLEDs based on either CBZDPA terized by H-NMR and 13C-NMR and mass spectrometry and
or OXDDPA was signicantly improved in terms of electrolu- the data obtained were consistent with the proposed chemical
minescence (EL) efficiency with little compromise of the purity structures.
of the blue colour (Fig. 1).
Thermal properties
Results and discussion
The thermal properties of these DPA derivatives were charac-
terized by using thermogravimetric analysis (TGA) and differ-
Synthesis
As shown in Scheme 1, 2-bromo-9,10-diphenylanthracene (1) ential scanning calorimetry (DSC). All key data are shown in
was lithiated with n-butyllithium at ꢀ78 ꢁC, followed by reaction Fig. 2 and Table 1. TMPDPA, TPSDPA, PPODPA, BMTDPA and
Scheme 1 Reagents and conditions: (i) (a) nBuLi, ether, ꢀ78 ꢁC, 45 min, (b) chlorotriphenylsilane, ꢀ78 ꢁC / RT, 12 h, (ii) (a) n-BuLi, ether, ꢀ78 ꢁC,
45 min, (b) chlorodiphenylphosphine, ꢀ78 ꢁC / RT, 12 h, (c) H2O2, 12 h, (iii) (a) n-BuLi, THF, ꢀ78 ꢁC, 45 min, (b) dimesitylboron fluoride, ꢀ78 ꢁC
/ RT, 12 h, (iv) N-phenylnaphthalen-1-amine, NaOtBu, P(t-Bu)3, Pd(OAC)2, xylene, 120 ꢁC, 16 h, (v) 2,4,6-trimethylphenylboronic acid, catalyst:
Pd(PPh3)4, 2 M K2CO3(aq), ethanol, toluene, 80 ꢁC, 12 h, (vi) NBS, CHCl3, 50 ꢁC, 2 h, (vii) phenylboronic acid or pinacolborane derivative of 9-
phenyl-9H-carbazole or 2,5-diphenyl-1,3,4-oxadiazole, catalyst: Pd(PPh3)4, 2 M K2CO3(aq), ethanol, toluene, 80 ꢁC, 12 h.
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Fig. 2 DSC thermograms of DPA, TMPDPA, TPSDPA, PPODPA, BMTDPA, NPADPA, CBZDPA, and OXDDPA.
Table 1 Optical and thermal properties of DPA-based derivatives
Solution
Solid
lmax
ab
a
d
DPA
derivatives
l
, lab
,
lmaxb, lmaxc, lm ax
(nm)
,
max on set
(nm)
Ffc (%)
(nm)
Ff (%)
Tg (ꢁC)
Tc (ꢁC)
Tm (ꢁC)
Td (ꢁC)
LUMO/HOMOf (eV)
e
DPA
375, 410
378, 413
380, 421
384, 420
413, 460
429, 473
379, 417
379, 413
432, 433, 433
438, 438, 439
443, 446, 444
448, 452, 450
473, 480, 490
490, 502, 507
442, 442, 445
443, 443, 446
90
90
86
83
61
33
94
88
442
444
456
487
499
513
459
461
ꢂ60
ꢂ40
ꢂ70
ꢂ30
ꢂ50
ꢂ20
ꢂ60
ꢂ70
165
253
227
277
289
315
332
361
398
378
335
416
449
2.87/5.81
3.04/5.94
2.96/5.93
3.04/5.90
3.23/5.87
3.20/5.46
3.07/5.94
2.86/5.74
e
TMPDPA
TPSDPA
PPODPA
BMTDPA
NPADPA
CBZDPA
OXDDPA
109
97
104
104
97
189
202
e
220
e
e
e
e
e
e
188
162
In THF. b In toluene. c In dichloromethane. d In DMF. e Not observed. f Highest occupied molecular orbit (HOMO) energy was determined using
an AC-2 photoelectron spectrometer (Riken Keiki); lowest unoccupied molecular orbital (LUMO) energy was determined as the lowest photo-
excitation state energy from the onset absorption energy of the thin lm absorption spectra.
a
NPADPA, which were C-2 modied DPA derivatives, exhibited the vacuum thermal deposition process in OLED fabrication.
high decomposition temperatures (Td, corresponding to 5% Among these DPA derivatives, including the parent DPA, a
weight loss) of 332, 361, 398, 378, and 335 ꢁC, respectively. distinct exothermic signal for the crystallization temperature
Furthermore, CBZDPA and OXDDPA have even higher decom- (Tc) was only identied for DPA, TPSDPA, and PPODPA. Of these
position temperatures of 416 and 449 ꢁC, respectively. Based on three compounds, only PPODPA possesses bipolar characteris-
the high Td, all these DPA derivatives are capable of enduring tics because of the electron decient diphenylphosphine oxide
7190 | J. Mater. Chem. C, 2014, 2, 7188–7200
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moiety. The crystallization features of the bipolar material are shiing of the absorption and emission spectra in the solid
particularly undesirable for light emission in OLED state, when compared with DPA in solution. In its solid state the
applications.
Ff of DPA is ꢂ60%, which is reasonably good but it is a
The glass transition (Tg) values of CBZDPA and OXDDPA signicant decrease from the value of ꢂ90% obtained for DPA
were 188 and 162 ꢁC, respectively, which were much higher than in solution. This is very common for planar polycyclic aromatic
ꢁ
those for the other derivatives (Tg around 97–109 C). In addi- hydrocarbons such as DPA. The spectroscopic features
tion to NPADPA, CBZDPA and OXDDPA were the only two DPA (including vibronic structures) observed for DPA are attributed
derivatives where both the melting (Tm) and crystallization (Tc) to the p–p* electronic transition and its corresponding energy
temperatures were not detected (less than 350–400 ꢁC). The is sensitive to the molecular interactions (p–p molecular
superior thermal properties of CBZDPA and OXDDPA could stacking) in the condensed phase.
increase the phase stability of the amorphous thin lm, which
Among the C-2 modied DPA derivatives, the broadening
is benecial to the operation lifetime and possibly the efficiency and red-shiing of spectroscopic features is signicantly sup-
of the devices. From the thermal property studies, the structural pressed, especially in TMPDPA. Based on the present results,
features of CBZDPA and OXDDPA were identied as the most the sterically hindered mesityl group at the C-2 position is a very
effective for use in OLEDs.
effective structural feature for preserving the deep blue uo-
rescence color of DPA derivatives in the solid state. The C-2
modied DPA derivatives, TPSDPA, PPODPA, BMTDPA, and
NPADPA, are designed along these lines. However, the absorp-
tion and emission spectra are signicantly red-shied, which is
detrimental to the purity of the blue color, particularly for
PPODPA, BMTDPA, and NPADPA. Based on these spectroscopic
observations, it was deduced that the broadening and red-
shiing spectroscopic features of these DPA derivatives are
caused by various factors.
Absorption and emission spectroscopic characterization
The absorption and emission spectra of DPA derivatives were
studied in various solvents [toluene, dichloromethane, dime-
thylformamide (DMF), and tetrahydrofuran (THF)] as well as in
solid thin lms, which were prepared by spin-coating a
dichloromethane solution on to quartz plates. As shown in
Fig. 3, the parent compound, DPA, exhibits broadening and red-
Fig. 3 The absorption and photoluminescence (PL) spectra of DPA and DPA derivatives in solution and in the condensed phase.
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It was not expected that the triphenylsilyl group would not be both in solution and in the solid state, all the DPA derivatives
as effective as the mesityl group in preventing the spectra of DPA reported here exhibit common typical aggregation caused-
from broadening or red-shiing in the solid state. However, it quenching emission instead of aggregation-induced emission
ab
was noticed that both the solution l
and lm ax of TPSDPA are or aggregation-induced enhanced emission.64–66
max
ab
substantially longer than those of TMPDPA, which has a l
and
max
lmax only slightly longer than those of DPA (Table 1). The more
red-shied spectra observed for TPSDPA than for TMPDPA can be
ascribed to the s-conjugation of the silyl group. In the solid state,
the molecular packing of TPSDPA probably intensies the s-
conjugation and further red-shis the emission spectra.
However, the molecular packing slightly reduces its solid state Ff.
It remains as high as ꢂ70%, slightly less than the 86% obtained
for TPSDPA in solution. In terms of Ff, TPSDPA is different from
TMPDPA, where the uorescence is signicantly quenched in the
solid state with a solid state Ff of only ꢂ40%, which is much
smaller than the 90% obtained in solution. Based on this, it is
thought that the pronounced red-shiing in the thin lm or
powder emission spectra of PPODPA may also be explained by
molecular packing, because its solution lmax is at a relatively
short wavelength (448–452 nm vs. 487 nm in the solid state). In
addition, the molecular packing of PPODPA may be the factor
that reduces its solid state Ff to 30%, which is signicantly lower
than the solution Ff of 83% (Table 1). Potentially, excimer
formation may arise from the molecular packing of PPODPA.
These solid state properties make PPODPA an unsuitable blue
light-emitting material for OLEDs.
On the other hand, the relatively long wavelength for the
solution lmax observed for both BMTDPA and NPADPA can be
attributed to the electronic effect of the N-phenylnaphthalen-1-
amine p-donor and the dimesitylborane p-acceptor, respec-
tively. In other words, the intramolecular charge transfer (ICT),
which is lower in energy when compared with that of the p–p*
transition, contributes to the electronic transition process. The
less well resolved vibronic bands observed in the absorption
spectra (Fig. 3) of BMTDPA and NPADPA are consistent with our
conclusion. In addition, BMTDPA and NPADPA are the two DPA
derivatives that show the most distinct uorescence sol-
vatochromism trend (Table 1), which is also consistent with the
ICT that we propose above. Otherwise, the low Ff and solvent-
dependent PL wavelength may be attributed to photoinduced
electron transfer, which has been observed for arylamine-
substituted electron decient uorophores.61–63 In fact, NPADPA
has the lowest Ff of 33% and 20%, in solution and solid state,
respectively, among the DPA derivatives in the present study.
Since TMPDPA has the least broadening and red-shiing of
the DPA derivatives in its spectra, it was chosen for further
functionalization for charge transport, i.e., for hole transport in
CBZDPA and electron transport in OXDDPA. Based on the well-
resolved vibronic bands in the absorption spectra and the
relatively high solid state Ff of 60% and 70%, respectively,
Theoretical estimation of frontier molecular orbitals
The molecular structures of DPA, TPSDPA, TMDDPA, PPODPA,
BMTDPA, NPADPA, CBZDPA, and OXDDPA were optimized by
applying density functional theory (DFT) with the hybrid B3LYP
functional and 6-31G* basis set. With the optimized structure,
the electronic ground states of these DPA derivatives were
calculated using DFT with the hybrid B3LYP functional and
6-31G* basis set.67 The singlet excited states of these DPA
derivatives were studied with time-dependent density func-
tional theory by using the hybrid B3LPY functional.68 All
calculations were performed with a developmental version of Q-
Chem soware.69 We display a comparison of the correspond-
ing HOMO and LUMO of these DPA derivatives in the S0 state,
where materials are in the gas phase to approximate the solu-
tion state instead of in the condensed phase. Because electronic
excitation from the HOMO to the LUMO produces the rst
singlet excited state S1 (a Franck–Condon excited state), the
orbital features presented in Fig. 4 provide important clues
towards understanding the nature of the optically accessible
rst excited state.
From the contour plots of DPA, TMPDPA, TPSDPA, and
PPODPA, both the HOMO and LUMO consist mainly of the
p-conjugation of the anthracene core. Similar HOMO/LUMO
contour plots were found for OXDDPA with little p-conjugation
extended into substituents on the C-9 and C-10 positions. In
contrast, the HOMO and/or the LUMO of BMTDPA and NPADPA
were signicantly extended beyond the anthracene core into
N-phenylnaphthalen-1-amine and dimesitylborane, respec-
tively. These theoretical ndings are consistent with the ICT
proposed from the spectroscopic characterization described in
the previous section.
Considering the large twist angle (dihedral angle ꢂ80ꢁ)
between the phenyl ring and anthracene core, it is surprising
that the p-conjugation shown by the HOMO contour plots of
CBZDPA actually expands extensively into one of the phenyl-
oxadiazole substituents on the C-9 and C-10 positions, whereas
the p-conjugation of the LUMO is pretty much conned to the
anthracene core. The implication from the theoretical results
for CBZDPA is somewhat contradictory to the experimental
spectroscopy results, i.e., well-resolved vibronic absorption
bands in solution, no clear trend in uorescence sol-
vatochromism, and a reasonable solution Ff.
Characterization of OLEDs and charge transport
(Fig. 3 and Table 1), it can be reasonably deduced that there is All OLEDs were fabricated by the sequential thermal vacuum
little ICT involved in the spectroscopic electronic transitions of deposition of a thin lm layer of the organic material and LiF–Al
ab
max
both CBZDPA and OXDDPA. The solution absorption, l , and as the nal cathode electrode on indium tin oxide (ITO)-coated
emission, lmax, of both CBZDPA and OXDDPA are nearly as glass substrate. Excluding BMTDPA and NPADPA, which were
short as those of TMPDPA (Fig. 3 and Table 1), indicating there spectroscopically unsatisfactory, six devices were fabricated
is limited p-conjugation between the charge transport substit- from six blue DPA derivatives, with the device conguration of
uent and the anthracene core. Finally, based on the Ff data, ITO/NPB (30 nm)/TCTA (10 nm)/DPAs (30 nm)/TPBI (30 nm)/LiF
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Fig. 4 Calculated spatial distributions of the HOMO and LUMO of DPA and DPA derivatives.
(1 nm)/Al, where 4,40-bis[N-(1-naphthyl)-N-phenyl-1-amino]- satisfactory blue colour (all y-values are less than 0.20, Table 2).
biphenyl (NPB) is a common hole-transporting layer, 2,20,200- However, the EL spectrum of PPODPA is signicantly worse and
(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBI) is a its 1931 CIEx,y (0.22, 0.37) indicates that it is not a blue OLED
common electron-transporting layer, and LiF–Al were used as because of its unsatisfactory colour purity.
the electron injecting layer and cathode. In each device,
For EL efficiency, both TMPDPA and TPSDPA OLEDs greatly
between the NPB and DPA light-emitting layers, there is a thin outperform the DPA OLED with just a small compromise in the
layer of tris(4-carbazoyl-9-ylphenyl)amine (TCTA), which serves purity of the blue color. In fact, the current density and
multiple functions, including as a hole-transporting layer, brightness of TMPDPA and TPSDPA OLEDs are far superior to
exciton blocking layer, and in smoothing the alignment of the that of the DPA OLED (Fig. 5). More specically, the EL effi-
HOMO energy levels inside the device. Such interlayers can ciency of the TPSDPA OLED is better than the TMPDPA OLED,
decrease the turn-on voltage and enhance the charge recombi- which can be mostly attributed to the higher Ff of TPSDPA than
nation of the device. The device performances are summarized TMPDPA in the solid state. Nevertheless, the purity of the blue
in Fig. 5 and the corresponding data are listed in Table 2.
color (1931 CIEx,y in Table 2) of the TMPDPA OLED is slightly
In accordance with its solid state PL, TMPDPA exhibits the better than that of the TPSDPA OLED. For PPODPA, the OLED
deepest blue EL, with a wavelength (444 nm) nearly as short as performance is inferior in all aspects, including current density,
that of DPA (442 nm) and an EL band width (66 nm) nearly as brightness, blue colour purity, and EL efficiency (Fig. 5). The
narrow as that of DPA (56 nm). Therefore, the 1931 CIEx,y of the unsatisfactory performance of the PPODPA OLED is mainly
DPA and TMPDPA OLEDs are a comparable deep blue; (0.15, because of its poor Ff and red-shied emission in the solid
0.05) and (0.17, 0.10), respectively. The EL spectra of TPSDPA, state, which can be attributed to its bipolar structure that
CBZDPA, and OXDDPA are slightly red-shied and broadened, promotes its crystallization in the solid state. PPODPA is the one
although the 1931 CIEx,y chromaticity of these devices remains a of two DPA derivatives here that shows a Tc in the thermal
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Fig. 5 Electroluminescence characteristics of DPA and DPA derivatives.
Table 2 Characteristics of OLEDsa
Efficiency at 100 and
DPA
derivatives
Turn-on
Max. luminance,
voltage (V)
Max. efficiencyc
lmax EL,
1931 CIE
1000 cd mꢀ2
voltageb (V)
(%, cd Aꢀ1, lm Wꢀ1
)
fwhmd (nm)
chromaticity (x, y)d
(%, cd Aꢀ1, lm Wꢀ1
)
DPA
3.5
4.0
3.5
4.0
3.5
3.5
1134, 15
1477, 15
4501, 15
7891, 15
3377, 15
6985, 15
1.5, 0.7, 0.4
3.0, 2.5, 1.9
3.8, 4.4, 3.8
0.7, 2.5, 1.1
4.5, 5.7, 3.9
4.0, 5.2, 5.1
440, 56
444, 66
458, 76
496, 96
454, 72
460, 78
(0.15, 0.05)
(0.17, 0.10)
(0.16, 0.15)
(0.22, 0.37)
(0.17, 0.17)
(0.16, 0.18)
1.6, 0.8, 0.4; 0.3, 0.7, 0.2
2.8, 2.4, 1.5; 1.1, 0.8, 0.3
3.7, 4.2, 2.8; 2.9, 3.2, 1.4
0.6, 1.7, 0.9; 1.1, 2.5, 0.9
4.5, 5.6, 3.7; 3.3, 4.0, 1.8
4.0, 5.2, 3.6; 3.6, 4.7, 2.3
TMPDPA
TPSDPA
PPODPA
CBZDPA
OXDDPA
a
b
c
ITO/NPB (30 nm)/TCTA (10 nm)/9,10-DPA based derivatives (30 nm)/TPBI (30 nm)/LiF (1 nm)/Al. With electroluminance at 1 cd mꢀ2
.
At a
current density of 1 mA cmꢀ2
for 1931 CIE chromaticity.
.
fwhm denotes full-width-at-half-maximum and the EL spectra were recorded at 8.0 V and the same EL spectra
d
property measurements (see Fig. 2). Following our previous OLED exhibits an EL efficiency of only 2.8% and 1.1% at an EL
analysis of the spectroscopic data of PPODPA, excimer forma- of 100 and 1000 cd mꢀ2, respectively. At rst glance, the much
tion is highly probable in the non-doped device. This explains higher solid state Ff of CBZDPA and OXDDPA than that of
the low solid state Ff and thus, the low brightness, the low TMPDPA provides a logical explanation for the improved EL
current density because of the charge trapping nature of the efficiency of these OLEDs. Furthermore, we think that the
excimer, and the long EL wavelength and thus the poor 1931 charge transport molecular structures of CBZDPA and OXDDPA
CIEx,y for blue purity.
also contribute to the enhancement of the EL efficiency.
From their structures, CBZDPA and OXDDPA are considered
In order to understand the hole and electron transporting
as derivatives of TMPDPA with charge transporting moieties on properties of TMPDPA, CBZDPA, and OXDDPA, we also fabri-
their phenyl rings at the C-9 and C-10 positions of the anthra- cated two kinds of single-charge carrier-dominated devices70 for
cene core. The EL efficiency of the CBZDPA and OXDDPA OLEDs exploring the nature of the material charge carrier in terms of
is drastically improved in comparison with that of the TMPDPA the current density of these devices. The hole-dominated device
OLEDs (Fig. 5 and Table 2). OLEDs exhibit an EL efficiency of has a conguration of ITO/NPB (40 nm)/TCTA (10 nm)/DPA
4.5% and 4.0% at an EL of 100 cd mꢀ2, respectively; and 3.3% derivative (50 nm)/NPB (20 nm)/Al (100 nm). The electron-
and 3.6% at an EL of 1000 cd mꢀ2, respectively. The TMPDPA dominated device has a conguration of ITO/BCP (10 nm)/DPA
7194 | J. Mater. Chem. C, 2014, 2, 7188–7200
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Fig. 6 Current density–voltage (I–V) characteristics of the hole-dominated device (left) and the electron-dominated device (right).
derivative (50 nm)/TPBI (20 nm)/LiF (1 nm)/Al (100 nm). As high as 100 mA cmꢀ2. Like OXDDPA, diphenylphosphine oxide-
shown in the inset of Fig. 6, we used a high-lying LUMO NPB to bearing PPODPA is bipolar and has potential for electron
limit the electron carrier in the hole-dominated device and a transport.
low-lying HOMO BCP and TPBI to limit the hole carrier in the
electron-dominated device. One should note that the current
density of a single-charge carrier-dominated device is deter-
Conclusions
mined by several factors: the hole injection barrier between the
electrode and organic layers, the difference in the HOMO energy
levels between adjacent organic layers, and the charge mobility
of each organic layer. In this case, the HOMO energy levels of
TMPDPA and CBZDPA are very similar, which implies that the
current density of the hole-dominated device depends solely on
the hole-mobility of the blue emitter. The HOMO energy level of
OXDDPA is about 0.20 to 0.23 eV higher than the other two,
which implies that it should be easier for the hole carrier to pass
through the device. Considering all the factors, the current
density of the device indicates that the hole mobility of the three
DPA derivatives is in the order CBZDPA > TMPDPA > OXDDPA.
The current density of the electron-dominated device is similar
but in reverse order. The LUMO energy levels of TMPDPA,
CBZDPA, and OXDDPA are all lower than the LUMO energy level
of TPBI (2.7 eV), which implies that there is no apparent elec-
tron injection barrier at the interface of the two layers. The
magnitude of the current density clearly decreases in the order
OXDDPA > TMPDPA > CBZDPA, which is in accordance with the
anticipated order of the electron mobility of the material based
on the electron decient structural features.
The charge transporting properties of light-emitting mate-
rials is one of the paramount factors in enhancing the EL effi-
ciency and reducing the efficiency roll-off of non-doped OLEDs
such as those used in the present study. Whereas the hole
transporting nature of CBZDPA enhances the EL efficiency in
the low to medium current density range, the electron trans-
porting nature of OXDDPA enhances the EL efficiency in the
high current density range. This difference in current density-
dependent EL efficiency enhancement makes CBZDPA the most
efficient EL in the low current density range although OXDDPA
becomes the most efficient EL in the high current density range
(Fig. 5). The efficiency roll-off is more pronounced in the
CBZDPA OLED than in the OXDDPA OLED, which is consistent
with our conclusions. In addition, from the experimental
results for the PPODPA EL efficiency (Fig. 5 and Table 2), there is
no efficiency roll-off, rather a “roll-up” at current densities as
In summary, we have synthesized and characterized a series of
DPA derivatives, TPSDPA, TMDDPA, PPODPA, BMTDPA,
NPADPA, CBZDPA, and OXDDPA. Some of these new uo-
rophores are capable of emitting EL nearly as blue as the EL
from DPA. All these DPA derivatives are designed with a bulky or
sterically hindered substituent at the C-2 position to prevent the
solid state emission from red-shiing and broadening. In
addition to one failure, PPODPA, which tends to crystallize and
form excimers in the condensed phase, the emission of
BMTDPA and NPADPA were strongly quenched and red-shied
because of the ICT. The non-doped OLEDs fabricated with
charge transport moiety-bearing CBZDPA or OXDDPA exhibited
the highest external quantum efficiencies of 4.5% and 4.0%,
respectively, of all the OLEDs, including the DPA OLED, which
was only 1.5% with the same device structure. The charge
transporting properties of CBZDPA and OXDDPA were veried
by the current density of hole-dominated and electron-domi-
nated devices. We have successfully demonstrated that the
mesityl group on the C-2 position is excellent in preserving the
deep blue uorescence of DPA in the solid state. The EL effi-
ciency of DPA OLEDs have been greatly improved by incorpo-
rating charge transporting moieties on the phenyl rings at the
C-9 and C-10 positions of the anthracene core.
Experimental
General information
UV-visible electronic absorption spectra were recorded on a
Hewlett-Packard 8453 diode array spectrophotometer. Fluores-
cence spectra were obtained on a Hitachi F-5400 uorescence
spectrophotometer with excitation at 380 nm. The solution
uorescence quantum yields of the compounds of interest were
determined relative to that of DPA in dichloromethane at 298 K
(Ff ¼ 0.9).44 The solid-state uorescence quantum yields (Ff) of
the blue emitters were determined by the integrating sphere
method.71,72 The ionization potentials (or HOMO energy levels)
of DPA derivatives were determined by a low-energy Riken Keiki
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AC-2 photo-electron spectrometer. LUMO energy levels were phenyl]-9H-carbazole,78 and 2-phenyl-5-(3-(4,4,5,5-tetramethyl-
estimated by subtracting the energy (DE) from the HOMO 1,3,2-dioxaborolan-2-yl)phenyl)-1,3,4-oxadiazole41 were prepared
energy levels. DE was determined by the onset absorption according to methods in the literature. For the materials used in
energy from the absorption spectra of the thin lm materials. device fabrication, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline
DSC analysis was performed under a nitrogen atmosphere on a (BCP) was commercially available. NPB79 TPBI80 and TCTA81 were
Perkin-Elmer DSC-7 differential scanning calorimeter, using a prepared via published methods and were subjected to gradient
scan rate of 10 ꢁC minꢀ1. TGA was carried out on a Perkin-Elmer sublimation prior to use.
DSC-7 thermogravimetric analyzer to determine the decompo-
sition temperatures (Td) of the compounds under a nitrogen
9,10-Diphenyl-(2-triphenylsilanyl)anthracene (TPSDPA, 2a)
atmosphere, using a scan rate of 10 ꢁC minꢀ1. 1H-NMR and 13C-
NMR spectra were recorded on a Bruker AV-400 or Bruker AV-III To a dry diethyl ether solution (60 mL) of 2-bromo-9,10-diphenyl-
400 MHz instrument, using deuterated chloroform (CDCl3) as anthracene (0.96 g, 2.35 mmol) was added n-BuLi (1.66 mL,
the internal standard. Electroionization-high-resolution mass 4.16 mmol, 2.5 M in hexane) slowly at ꢀ78 ꢁC. The mixture was
spectrometric (EI-HRMS) measurements were obtained from stirred for 45 min under a nitrogen atmosphere. Chloro-
the Mass Spectroscopic Laboratory in-house service of the triphenylsilane (1.0 g, 3.39 mmol) in diethyl ether (10 mL) was
Institute of Chemistry, using a Jeol JMS-700 double focusing added dropwise at ꢀ78 ꢁC and the mixture was stirred at room
mass spectrometer.
temperature for 12 h. Aer the reaction was quenched with
water, the mixture was extracted with dichloromethane. The
organic layer was dried with magnesium sulfate. Aer removal
of the drying agent, the organic solution was evaporated to
dryness under reduced pressure. The resulting solid was puri-
ed by using column chromatography (silica gel, 10% CH2Cl2–
Fabrication and characterization of light-emitting diodes
OLED devices were fabricated by thermal vacuum deposition.
The substrate was ITO coated glass (Shinan SNP, Taiwan) with a
sheet resistance of #30 U sqꢀ1. The pretreatment of ITO
included routine chemical cleaning using detergent, deionized
water, acetone, and isopropyl alcohol in sequence, followed by
oxygen plasma cleaning. The thermal evaporation of organic
materials was carried out using a CRYOTEC-10 at a chamber
pressure of 10ꢀ6 Torr. The thickness of each layer was deter-
mined by a quartz thickness monitor (Sycon STM-100/MF and
Sycon STM-2XM). The LiF–Al cathode was prepared rst by
1
hexane) to give TPSDPA (0.7 g, 44%) as a white solid. H-NMR
(400 MHz, CDCl3): d (ppm): 7.93 (s, 1H), 7.71–7.65 (m, 3H), 7.59–
7.45 (m, 13H), 7.38–7.24 (m, 17H). 13C-NMR (100 MHz, CDCl3): d
(ppm): 138.96, 138.42, 137.84, 136.82, 136.26, 134.08, 131.34,
131.08, 130.98, 130.52, 130.28, 130.03, 129.92, 129.44, 129.24,
128.37, 128.15, 127.79, 126.92, 125.69, 125.27, 124.93. EI-HRMS:
calculated 588.2273, m/z ¼ 588.2270 (M+).
˚
thermal deposition of a LiF thin lm (10 A) followed by the
˚
deposition of Al (1000 A) as the top layer. The thickness of each
9,10-Diphenyl-(2-diphenylphosphinyl)anthracene
(PPODPA, 2b)
layer of material was determined as described previously. The
devices were all encapsulated with glass slides, which were
attached to the device by UV-cured epoxy glue. The effective size
of the emitting diode was 4.00 mm2, which was signicantly
smaller than the active area of the photodiode detector, a
condition known as “under-lling”, which satised the
measurement protocol.73 This is one of the most conventional
ways of measuring the EL efficiency of OLEDs, although
sometimes experimental errors may arise because of the non-
Lambertian emission of OLEDs.74 Current–voltage–luminance
(I–V–L) measurements were made simultaneously using a
Keithley 2400 source meter and a Newport 1835-C optical meter
equipped with a Newport 818-ST silicon photodiode. The
measurements of the devices were made at room temperature
under ambient conditions. The EL was measured using the
Hitachi F-5400 uorescence spectrophotometer by blocking the
incident light.
To a dry THF solution (60 mL) of 2-bromo-9,10-diphenylan-
thracene (1.0 g, 2.45 mmol) was added n-BuLi (1.96 mL, 4.90
mmol, 2.5 M in hexane) slowly at ꢀ78 ꢁC. The mixture was
stirred for 45 min under a nitrogen atmosphere. Chloro-
triphenylphosphine (1.6 mL, 7.1 mmol) was added dropwise at
ꢀ78 ꢁC and the mixture was stirred at room temperature for 6 h.
Aer the reaction was quenched with water, the mixture was
extracted with dichloromethane. The separated organic layer
was evaporated to dryness under reduced pressure. The solid
residue was re-dissolved in CH2Cl2 (10 mL) and was treated with
H2O2 (10 mL, 30 wt% in H2O) and stirred for another 24 h. The
separated organic layer was dried with magnesium sulfate. Aer
removal of the drying agent, the organic solution was evapo-
rated to dryness under reduced pressure. The resulting solid
was puried by using column chromatography (silica gel, 10%
CH2Cl2–EtOAc) to give PPODPA (0.4 g, 30%) as a light yellow
solid. 1H-NMR (400 MHz, CDCl3): d (ppm): 7.86–7.28 (d, J ¼ 0.8
Hz, 1H), 7.58–7.68 (m, 3H), 7.60–7.33 (m, 22H), 7.29–7.26 (m,
Synthesis of materials
Unless specied, all reactions were performed under a nitrogen 2H). 13C-NMR (100 MHz CDCl3): d (ppm): 139.08, 138.39, 137.73,
atmosphere using standard Schlenk techniques. All commercially 137.29, 134.50, 134.39, 132.73, 132.06, 131.96, 131.75, 131.32,
available chemical reagents were used directly without further 131.21, 130.98, 130.36, 130.25, 129.35, 128.53, 128.42, 128.35,
purication. Compounds such as 2-bromo-9,10-diphenylan- 128.30, 127.75, 127.58, 127.46, 127.30, 127.03, 126.12, 125.57,
thracene (1),75 2-bromoanthracene (3),76 2,4,6-trimethylphenyl- 124.97, 124.87. EI-HRMS: calculated 530.1800, m/z
¼
boronic acid,77 9-[4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)- 530.1801 (M+).
7196 | J. Mater. Chem. C, 2014, 2, 7188–7200
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ꢁ
80 C for 12 h. Aer the reaction was cooled to room tempera-
ture, toluene was removed under reduced pressure and the
residue was extracted with dichloromethane and H2O. The
organic layer was dried with magnesium sulfate. Aer removal
of the drying agent, the organic solution was evaporated to
dryness under reduced pressure. The resulting solid was puri-
ed by using column chromatography (silica gel, hexane) to give
2-(1,3,5-trimethylphenyl)anthracene (0.15 g, 55%) as a white
9,10-Diphenyl-(2-dimesitylboranyl)anthracene (BMTDPA, 2c)
To a dry THF solution (30 mL) of 2-bromo-9,10-diphenylan-
thracene (0.4 g, 0.98 mmol) was added n-BuLi (1.1 mL, 2.84
mmol, 2.5 M in hexane) slowly at ꢀ78 ꢁC. The mixture was
stirred for 45 min under a nitrogen atmosphere. Dimesityl-
boron uoride (0.86 g, 3.23 mmol) in THF (5 mL) was added
dropwise at ꢀ78 ꢁC and the mixture was stirred at room
temperature for 12 h. Aer the reaction was quenched by water,
the mixture was extracted with dichloromethane. The organic
layer was dried with magnesium sulfate. Aer removal of the
drying agent, the organic solution was evaporated to dryness
under reduced pressure. The resulting solid was puried by
using column chromatography (silica gel, hexane) to give
BMTDPA (0.12 g, 21%) as a yellow-green solid. 1H-NMR (400
MHz, CDCl3): d (ppm): 7.83 (s, 1H), 7.78–7.75 (d, J ¼ 8.4 Hz, 1H),
7.71–7.69 (d, J ¼ 8 Hz, 1H), 7.59–7.47 (m, 6H), 7.42–7.29 (m, 8H),
6.73 (s, 4H), 2.28 (s, 6H), 1.97 (s, 12H). 13C-NMR (75 MHz,
CDCl3): d (ppm): 141.69, 140.48, 140.03, 139.75, 138.87, 138.20,
136.47, 133.90, 131.28, 130.58, 129.65, 129.54, 128.32, 127.92,
127.41, 127.27, 126.91, 125.67, 125.48, 124.86, 123.63,
122.72, 23.42, 21.12. EI-HRMS: calculated 578.3145, m/z ¼
578.3141 (M+).
1
solid. H-NMR (400 MHz, CDCl3): d (ppm): 8.63–8.56 (m, 3H),
8.37 (s, 1H), 7.63–7.60 (m, 2H), 7.45–7.42 (dd, J ¼ 1.2 Hz, 1H),
7.00 (s, 2H), 2.36 (s, 3H), 2.06 (s, 6H). 13C-NMR (125 MHz,
CDCl3): d (ppm): 138.81, 138.09, 136.71, 136.11, 131.89, 131.69,
130.65, 128.16, 128.05, 127.91, 127.72, 126.03, 125.77, 125.38,
125.23, 21.02, 20.74. Fast atom bombardment-MS: calculated
296.16, m/z ¼ 296.2 (M+).
9,10-Dibromo-2-(1,3,5-trimethylphenyl)anthracene (5)
To a chloroform solution (2 mL) was added 2-(1,3,5-trimethyl-
phenyl) anthracene (0.2 g, 0.67 mmol) and N-bromosuccini-
mide (0.33 g, 1.87 mmol) and the resulting mixture was stirred
at 50 ꢁC for 2 h under a nitrogen atmosphere. Aer the reaction
was cooled to room temperature, the mixture was poured into 2
N NaOH(aq) and extracted with dichloromethane. The organic
layer was dried with magnesium sulfate. Aer removal of the
drying agent, the organic solution was evaporated to dryness
under reduced pressure. The residue was puried by using
column chromatography (silica gel, hexane) to give 9,10-
dibromo-2-(1,3,5-trimethylphenyl) anthracene (0.2 g, 65%) as a
yellow solid. 1H-NMR (400 MHz, CDCl3): d (ppm): 8.63–8.56 (m,
3H), 8.37 (s, 1H), 7.63–7.60 (m, 2H), 7.45–7.42 (dd, J ¼ 1.2 Hz,
1H), 7.00 (s, 2H), 2.36 (s, 3H), 2.06 (s, 6H). 13C-NMR (125 MHz,
CDCl3): d (ppm): 140.36, 137.94, 137.17, 135.95, 131.26, 130.98,
130.10, 129.98, 129.75, 128.44, 128.30, 128.24, 128.19, 128.05,
127.45, 127.30, 123.4, 123.33, 21.00, 20.78. Matrix-assisted
laser desorption/ionization (MALDI)-MS: calculated 451.98,
m/z ¼ 451.9 (M+).
9,10-Diphenyl-(2-phenylnaphthalen-1-amino)anthracene
(NPADPA, 2d)
To a mixture of N-phenylnaphthalen-1-amine (0.64 g, 2.94
mmol), 2-bromo-9,10-diphenylanthracene (0.8 g, 1.96 mmol),
sodium tert-butoxide (0.22 g, 2.35 mmol), and palladium acetate
(0.01 g, 0.05 mmol) in xylene (7 mL), was added tri-tert-butyl-
phosphine (0.05 mL, 0.2 mmol) and the mixture was stirred at
ꢁ
120 C for 16 h. Aer the reaction was cooled to room temper-
ature, the xylene was removed under reduced pressure. The
residue was extracted with dichloromethane and H2O. The
organic layer was dried with magnesium sulfate. Aer removal
of the drying agent, the organic solution was evaporated to
dryness under reduced pressure. The resulting solid was puri-
ed by using column chromatography (silica gel, 10% CH2Cl2–
hexane) to give NPADPA (0.91 g, 84%) as a yellow solid. 1H-NMR
(400 MHz, CDCl3): d (ppm): 7.88–7.84 (t, J ¼ 8 Hz, 2H), 7.72–7.70
(d, J ¼ 8 Hz, 1H), 7.65–7.61 (m, 2H), 7.57–7.54 (t, J ¼ 4 Hz, 2H),
7.51–7.45 (m, 4H), 7.43–7.41 (d, J ¼ 8 Hz, 1H), 7.37–7.33 (t, J ¼ 8
Hz, 1H), 7.29–7.14 (m, 10H), 7.09–7.07 (d, J ¼ 8 Hz, 4H), 6.95–
6.91 (t, J ¼ 8 Hz, 1H), 6.86–6.85 (d, J ¼ 12 Hz, 1H). 13C-NMR (100
MHz, CDCl3): d (ppm): 147.65, 144.56, 143.14, 139.09, 138.53,
136.78, 135.23, 131.24, 131.04, 130.80, 130.15, 128.96, 128.29,
127.87, 127.78, 127.35, 127.00, 126.84, 126.65, 126.40, 126.23,
126.07, 125.95, 124.99, 124.17, 124.00, 122.54, 122.46, 122.32,
114.46. EI-HRMS: calculated 547.2300, m/z ¼ 547.2292 (M+).
9,10-Bis(4-carbazole)phenylene-2-(1,3,5-trimethylphenyl)
anthracene (CBZDPA, 6a)
This compound was prepared by a similar method to that of
9,10-diphenyl-2-(1,3,5-trimethylphenyl) anthracene, except that
9-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-9H-
carbazole (0.37 g, 0.99 mmol), two drops of Aliquat 336 and
triphenylphosphine (0.034 g, 0.13 mmol) were added to the
reaction and the reaction continued for 24 h. A mixed solvent of
15% EtOAc–hexane was used as the eluent for column chro-
matography. CBZDPA was obtained as a white solid (0.15 g,
1
60%). H-NMR (400 MHz, CDCl3): d (ppm): 8.21–8.17 (m, 4H),
7.94–7.85 (m, 4H), 7.74–7.66 (m, 7H), 7.53–7.46 (m, 6H), 7.38–
7.29 (m, 5H), 6.97 (s, 1H), 2.32 (s, 3H), 2.09 (s, 6H). 13C-NMR
(100 MHz, CDCl3): d (ppm): 140.91, 140.77, 138.77, 138.16,
2-(1,3,5-Trimethylphenyl)anthracene (4)
To a deoxygenated mixture of 2-bromoanthracene (0.18 g, 0.70 138.02, 137.88, 137.22, 136.91, 136.36, 136.16, 132.86, 132.74,
mmol), 2,4,6-trimethylphenylboronic acid (0.2 g, 0.77 mmol), 130.45, 130.04, 129.00, 128.33, 128.18, 127.66, 127.43, 127.00,
K2CO3(aq) (1.2 mL, 2.31 mmol, 2 M in H2O), and ethanol (1 mL) 126.88, 126.82, 126.73, 126.05, 125.98, 125.55, 125.39, 123.58,
in toluene (5 mL) was added tetrakis(triphenylphosphine) 120.42, 120.33, 120.14, 120.10, 110.10, 109.95, 20.99, 20.96. EI-
palladium (0.04 g, 0.04 mmol) and the mixture was stirred at HRMS: calculated 778.3348, m/z ¼ 778.3329 (M+).
This journal is © The Royal Society of Chemistry 2014
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3 H. Fu, Y.-M. Cheng, P.-T. Chou and Y. Chi, Mater. Today,
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9,10-Diphenyl-2-(1,3,5-trimethylphenyl)anthracene
(TMPDPA, 6b)
4 C.-H. Yang, M. Mauro, F. Polo, S. Watanabe, I. Muenster,
To a deoxygenated mixture of 9,10-dibromo-2-(1,3,5-trimethyl-
phenyl)anthracene (0.2 g, 0.44 mmol), phenylboronic acid (0.13
g, 1.1 mmol), K2CO3(aq) (1.2 mL, 2.31 mmol, 2 M in H2O), and
ethanol (0.5 mL) in toluene (2.2 mL) was added tetrakis-
(triphenylphosphine)palladium (0.04 g, 0.04 mmol) and the
¨
R. Frohlich and L. D. Cola, Chem. Mater., 2012, 24, 3684.
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¨
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ꢁ
resulting mixture was stirred at 80 C for 12 h. Aer cooling to
room temperature, the toluene solvent was removed under
reduced pressure and the residue was extracted with dichloro-
methane and water. The organic layer was dried with magne-
sium sulfate. Aer removal of the drying agent, the organic
solution was evaporated to dryness under reduced pressure.
The resulting solid was puried by using column chromatog-
raphy (silica gel, 10% dichloromethane–hexane) to give
TMPDPA (0.1 g, 50%) as a white solid. 1H-NMR (400 MHz,
CDCl3): d (ppm): 7.74–7.59 (m, 6H), 7.56–7.44 (m, 10H), 7.32–
7.30 (m, 2H), 7.15–7.12 (dd, J ¼ 4 Hz, 1H), 6.90 (s, 2H), 2.29 (s,
3H), 1.99 (s, 6H). 13C-NMR (100 MHz, CDCl3): d (ppm): 139.14,
137.35, 137.00, 136.65, 136.14, 133.57, 133.07, 132.17, 131.38,
131.26, 130.16, 129.97, 129.86, 128.86, 128.41, 128.14, 127.57,
127.46, 126.91, 126.09, 125.00, 124.88, 123.38. EI-HRMS:
calculated 448.2191, m/z ¼ 448.2197 (M+).
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9,10-Bis[3-(3-phenyl-2,4,5-oxadiazole)phenylene]-2-(1,3,5-
trimethylohenyl)anthracene (OXDDPA, 6c)
This compound was prepared by a similar method to that of
TMPDPA, except that 2-phenyl-5-(3-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)phenyl)-1,3,4-oxadiazole (1.91 g, 5.5 mmol)
was used in the reaction. In addition, a mixed solvent of 20%
EtOAc–hexane was used as the eluent for column chromatog-
raphy. OXDDPA was obtained as a white solid (1.2 g, 74%). 1H-
NMR (400 MHz, CDCl3): d (ppm): 8.41–8.38 (m, 1H), 8.31–8.30
(s, J ¼ 4 Hz, 2H), 8.25 (s, 1H), 8.12–8.08 (t, J ¼ 8 Hz, 4H), 7.84–
7.80 (dt, J ¼ 8 Hz, 1H), 7.76–7.66 (m, 6H), 7.52–7.47 (m, 7H),
7.39–7.36 (m, 2H), 7.23–7.19 (d, J ¼ 4 Hz, 1H), 6.89–6.86 (d, J ¼
12 Hz, 2H), 2.25 (s, 3H), 2.00 (s, 6H). 13C-NMR (100 MHz,
CDCl3): d (ppm): 164.70, 164.47, 140.13, 140.01, 138.46, 138.09,
136.85, 135.97, 135.85, 134.59, 134.53, 131.70, 130.01, 129.87,
129.76, 129.53, 129.43, 129.01, 128.81, 128.21, 126.91, 126.63,
126.46, 126.28, 125.64, 125.52, 124.46, 123.85, 20.82. EI-HRMS:
calculated 736.2838, m/z ¼ 736.2845 (M+).
23 S.-K. Kim, B. Yang, Y. Ma, J.-Y. Lee and J. Park, J. Mater.
Chem., 2008, 18, 3376.
24 L. Wang, W.-Y. Wong, M.-F. Lin, W.-K. Wong, K.-W. Cheah,
H.-L. Tam and C. H. Chen, J. Mater. Chem., 2008, 18,
4529.
Acknowledgements
This work was partially supported by the National Science
Council (NSC 101-2113-M-001-004-MY2), Academia Sinica, and
the National Taiwan University. Supporting personnel from
Chung Shan Medical University are acknowledged.
25 S. Tao, Y. Zhou, C.-S. Lee, S.-T. Lee, D. Huang and X. Zhang,
J. Phys. Chem. C, 2008, 112, 14603.
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