Solution-processable organic fluorescent dyes for multicolor emission in organic light emitting diodes

Article abstract of DOI:10.1039/b806160b

Four novel fluorescent dyes, bis(difluorenyl)amino-substituted carbazole 1, pyrene 2, perylene 3, and benzothiadiazole 4, were synthesized by C-N cross-coupling with a palladium catalyst. These dyes are soluble in common organic solvents, and their uniform films were formed by spin-coating from their solutions. Their glass transition temperatures were sufficiently high (120-181°C) to form amorphous films for organic light emitting diodes. These solution processable dyes exhibited strong photoluminescence (PL) in the film form (1: sky blue, 2: blue-green, 3: yellow, and 4: deep red). Optical and electrochemical properties of the compounds were investigated with photoelectron spectroscopy and cyclic voltammetry. The energy levels obtained from both measurements were in good agreement, and those levels were related to the electronic properties of the central core; the electron-donating carbazole compound showed the lowest ionization potential and the electron-withdrawing benzothiadiazole compound showed the largest electron affinity. Simple double layer devices were prepared with these fluorescent dyes as emitting layer and bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminium(iii) (BAlq) as a common hole blocking layer for each color. Electroluminescence colors were the same as those of the PL spectra in each compound. These multicolor electroluminescences show that these conjugated oligomers can be candidates for solution processable light emitting materials for OLEDs as well as conjugated polymers or dendrimers.

Full text of DOI:10.1039/b806160b

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Solution-processable organic fluorescent dyes for multicolor emission
in organic light emitting diodes†
*
Yong-Jin Pu, Makoto Higashidate, Ken-ichi Nakayama and Junji Kido
*
Received 11th April 2008, Accepted 11th June 2008
First published as an Advance Article on the web 24th July 2008
DOI: 10.1039/b806160b
Four novel fluorescent dyes, bis(difluorenyl)amino-substituted carbazole 1, pyrene 2, perylene 3, and
benzothiadiazole 4, were synthesized by C–N cross-coupling with a palladium catalyst. These dyes are
soluble in common organic solvents, and their uniform films were formed by spin-coating from their
solutions. Their glass transition temperatures were sufficiently high (120–181 ꢀC) to form amorphous
films for organic light emitting diodes. These solution processable dyes exhibited strong
photoluminescence (PL) in the film form (1: sky blue, 2: blue-green, 3: yellow, and 4: deep red).
Optical and electrochemical properties of the compounds were investigated with photoelectron
spectroscopy and cyclic voltammetry. The energy levels obtained from both measurements were in
good agreement, and those levels were related to the electronic properties of the central core; the
electron-donating carbazole compound showed the lowest ionization potential and the electron-
withdrawing benzothiadiazole compound showed the largest electron affinity. Simple double layer
devices were prepared with these fluorescent dyes as emitting layer and bis(2-methyl-8-quinolinolato)
(4-phenylphenolato)aluminium(III) (BAlq) as a common hole blocking layer for each color.
Electroluminescence colors were the same as those of the PL spectra in each compound. These
multicolor electroluminescences show that these conjugated oligomers can be candidates for solution
processable light emitting materials for OLEDs as well as conjugated polymers or dendrimers.
compounds, the emitting color can be easily controlled by a kind
Introduction
of central dye, and outer fluorene oligomers can sterically
prevent excimer formation between the emitting cores in a neat
film. Successive deposition of the hole-transporting layer and the
emitting layer in solution processes is still difficult because of
their solubility problems. Therefore these compounds are
designed to contain triarylamine units to have both hole-
transporting and emitting properties. On the other hand, dry
deposition of the electron transporting layer onto the solution
processed emitting layer is much easier than using a wet process.
For practical application, the electron transporting layer has to
be common for each color pixel to be deposited without
a shadow mask like the deposition of cathode metal. We used
bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminium(III)
(BAlq) as an common electron transporting layer in the same
thickness for each emitting dye.
Solution processes such as spin-coating, inkjet-printing, or
spray-coating for organic light emitting diodes (OLEDs) are still
fascinating due to their potential advantages for the production
of large area devices at low cost, although dry deposition
processes under vacuum are far ahead of solution processes from
the commercialization point of view. Conjugated polymers have
been extensively studied as solution processable emitting
materials for OLEDs since 1990.1 Precise control of molecular
weight, end-group structure, and regioregular structure of the
conjugated polymers for OLED has been established, but it is not
possible to purify structural defects in
a polymer chain
thoroughly. However, monodisperse conjugated oligomers are
able to have no structural defects and better purity from
conventional purification methods such as column chromatog-
raphy, recrystallization, and sublimation, and they can show
a high glass transition temperature and a good film forming
ability. While fluorescent or phosphorescent dendrimers with
well-defined molecular structure and monodisperse molecular
weight have been developed for solution processed OLEDs,2–5
there have been few reports on the conjugated oligomers as
solution processable electroluminescent dyes.6–9 In this research,
we designed bis(difluorenyl)amino-substituted fluorescent dyes
1–4 as solution processable light-emitting dyes. In these
Results and discussion
Synthesis
Four fluorescent dyes 1–4 were synthesized by palladium-
catalyzed cross-coupling reaction between excess 2-(20-bromo-90,
90-diethylfluoren-70-yl)-9,9-diethylfluorene and 3-amino-N-
ethylcarbazole for 1, 1-aminopyrene for 2, 3-aminoperylene for
3, and 4-amino-2,1,3-benzothiadiazole for 4 (Scheme 1). Their
1
structures were fully characterized by H-NMR spectroscopy,
Department of Organic Device Engineering, Yamagata University,
Yonezawa, Yamagata, 992-8510, Japan. E-mail: pu@yz.yamagata-u.ac.
jp; kid@yz.yamagata-u.ac.jp
matrix-assisted laser desorption/ionization time-of-flight
(MALDI) mass spectrometry (MS), and elemental analysis. All
compounds were purified by column chromatography, and then
† Electronic supplementary information (ESI) available: Further
synthesis details. See DOI: 10.1039/b806160b
thoroughly purified with
a train sublimation for OLED
This journal is ª The Royal Society of Chemistry 2008
J. Mater. Chem., 2008, 18, 4183–4188 | 4183

View Article Online
Scheme 1 Synthesis of the compounds.
application. These sublimable properties are one of the advan-
tages of these materials compared with conjugated polymers
from the purity point of view, because it is difficult to separate
low molecular weight impurities having similar polarity to the
target compounds by column chromatography. In practice, such
impurities are regarded as detrimental to device stability.
under nitrogen atmosphere. All the compounds except 4 showed
higher Ffilm values than that of tris(8-quinolinolato)aluminium
(Alq3) film (22%) which was determined under the same
conditions (Table 1).
Electrochemical properties
Ionization potentials (Ip) were measured by photoelectron
spectroscopy.10 Compound 1 showed the lowest Ip due to the
electron-donating properties of the carbazole group, and
compound 2 showed the highest Ip due to the electron-
withdrawing properties of the benzothiadiazole group. The order
of Ip among the compounds is in good agreement with that of the
redox potentials in anodic scan mode from cyclic voltammetry
(CV) (Table 2). Generally, it is hard to measure electron affinities
(Ea) of organic compounds. The tentative Ea values were
Thermal and optical properties
Decomposition temperatures at 5 wt% loss of the compounds
were over 400 ꢀC from thermogravimetric analysis (TGA). Glass
transitions appeared at 154 ꢀC for 1, 142 ꢀC for 2, 181 ꢀC for 3,
and 120 ꢀC for 4 in differential scanning calorimetry (DSC)
measurements. These results ensure that these compounds can be
sufficiently amorphous films to be used in OLED devices. All the
compounds are soluble in toluene, THF, and 1,2-dichroloethane,
and their uniform films were formed by spin-coating from their
solutions. UV absorption and PL spectra of the solutions and the
films on a quartz substrate were measured. PL spectra of the
films showed the emission color derived from the central dye
(1: sky blue, 2: blue-green, 3: yellow, 4: deep red). The outer
oligofluorene groups did not affect the emission color because
they have a wider energy gap than that of the central dye. The
p-conjugations of the fluorene groups and the central dye seem
to not be fully delocalized. PL quantum efficiencies (Ffilm) of the
films were determined by using an integrating sphere system
estimated from the difference of Ip and optical band gap (EOPT
)
which is obtained from the UV absorption edge of the film. The
order of Ea values are also consistent with that of redox poten-
tials in cathodic scan mode from CV. The energy diagrams are
shown in Fig. 1. In particular, in the energy levels corresponding
to the highest occupied molecular orbital (HOMO) level, the Ip
and redox potential values of each compounds are very similar,
compared with those in the energy levels corresponding to the
lowest unoccupied molecular orbital (LUMO) level. These are
because all the compounds have a common arylamine moiety
Table 1 Thermal and optical characteristics of compounds 1–4
UV/nm (log 3)
PL/nm
Tg/ꢀC
Td5%/ꢀC
toluene
THF
film
toluene
445
THF
467
film (F (%))
EL/nm
459
1
154
471
368 (4.78), 406 (4.84)
317 (4.85), 368 (4.83),
406 (4.89)
394 (4.96)
398 (4.81), 489 (4.33)
349 (4.73), 379 (4.82)
318, 378, 401
461 (34)
2
3
4
142
181
120
452
487
448
396 (4.95)
398 (4.65), 494 (4.19)
348 (4.83), 378 (4.89)
324, 397
401, 498
320, 356, 380
480
550
643
508
584
673
491 (40)
571 (23)
643 (10)
490
572
635
4184 | J. Mater. Chem., 2008, 18, 4183–4188
This journal is ª The Royal Society of Chemistry 2008

View Article Online
Table 2 Electrochemical properties of compounds 1–4
Ip/eV
Ea/eV
EOPTg/eV
Eanode a/V
Ecathode b/V
EEC c/V
1/2
1/2
g
1
2
3
4
5.29
5.52
5.41
5.62
2.48
3.01
3.09
3.49
2.81
2.51
2.32
2.13
0.11 (5.29)
0.29 (5.47)
0.24 (5.42)
0.38 (5.56)
ꢁ2.58 (2.60)
ꢁ2.33d (2.85)
ꢁ2.12 (3.06)
ꢁ1.89 (3.29)
2.69
2.62
2.36
2.27
a
In the parentheses, calculated HOMO energy levels (eV) based on the Ip of compound 1 are shown.b In the parentheses, calculated LUMO energy
levels (eV) based on the Ip of compound 1 are shown.c Electrochemically obtained bandgap: EEC ¼ Eanode1/2 ꢁ Ecathode
.
1/2
Measured by differential pulse
d
g
voltammetry. The redox wave of CV was irreversible.
´
the Commission Internationale de L’Eclairage (CIE) chroma-
ticity coordinate of compound 4 was dependent on current
density. The EL spectrum of 4 showed another emission around
480 nm derived from BAlq under high current density (Fig. 2).
These results suggest that a part of injected holes can go into the
BAlq layer because the Ip value of 4 (5.62 eV) is close to that
of BAlq (6.0 eV) and charge recombination partially occurred in
the BAlq layer. Carbazole dye 1 showed the highest current
density and luminance among the compounds in Fig. 3, probably
because of better hole injection due to its high Ip and because of
efficient electron blocking by its high Ea. Driving voltages and
efficiencies of the devices are shown in Table 3. The red emitting
device containing 4 exhibited the lowest external quantum
efficiencies (EQE, h) among the devices. Current densities of 4
were as high as those of 2 and 3, but luminance values of 4 were
lower than the others probably because of its lowest PL efficiency
among the dyes. The EQE values around 1% of the other devices
(1–3) are reasonably high in limited and same device configura-
tions, which is using a common electron-transporting material in
the same thickness for the different colors. Even the lowest EQE
(0.60%) of 4 should be considered high because the theoretical
EQE may be 0.625% if the out-coupling efficiency and the ratio of
singlet and triplet excitons are 25% and the charge recombination
ratio is 100%. Recently ratios of singlet and triplet excitons higher
than 25% in fluorescent conjugated polymers, and theoretical
calculations of the ratio in model conjugated oligomers have been
reported.11 Conjugated oligomers having relatively large
molecular weights would be interesting as experimental model
compounds to investigate the singlet–triplet exciton ratio.
Fig. 1 Energy diagrams of compounds 1–4 measured by photoelectron
spectroscopy (solid lines) and cyclic voltammetry (dotted lines). The
values in parentheses are the energy levels estimated by cyclic voltam-
metry.
resulting in similar HOMO levels, while the LUMO levels are
derived from the different central dyes.
OLED performance
Light emitting devices with the configuration ITO/poly(3,4-
ethylenedioxythiophene) (PEDOT) : poly(styrene sulfonic acid)
(PSS) (40 nm)/1–4 (50 nm)/BAlq (50 nm)/LiF (0.5 nm)/Al
(100 nm) were fabricated. PEDOT:PSS and the emitting layer
were deposited by spin-coating in open atmosphere. BAlq and
LiF/Al layers were deposited by evaporation under vacuum
successively using two independent vacuum chambers for BAlq
and for LiF/Al. EL spectra of the compounds are in good
agreement with the PL spectra of the films. The EL spectrum and
Fig. 2 EL spectra (a) and CIE coordinates (b) under 1 mA cmꢁ2 (circles) and 25 mA cmꢁ2 (triangles).
This journal is ª The Royal Society of Chemistry 2008
J. Mater. Chem., 2008, 18, 4183–4188 | 4185

View Article Online
Fig. 3 (a) Current density–voltage and (b) luminance–voltage plots of OLEDs with the different dyes 1–4.
Table 3 Turn-on voltages at 1 cd mꢁ2 and efficiencies at 100 cd mꢁ2 and 1000 cd mꢁ2 of the devices
100 cd mꢁ2
1000 cd mꢁ2
1 cd mꢁ2
E/V
Compound
E/V
h/lm Wꢁ1
h/cd Aꢁ1
h (%)
E/V
h/lm Wꢁ1
h/cd Aꢁ1
h (%)
1
2
3
4
3.05
3.79
3.64
4.21
5.44
6.21
6.07
8.06
1.29
1.32
1.42
0.24
2.22
2.61
2.75
0.61
1.35
1.06
0.93
0.60
8.37
8.60
8.65
10.84
1.61
1.32
0.75
0.14
1.57
2.60
2.07
0.50
0.95
1.06
0.71
0.46
Measurements
Conclusion
The 1H NMR spectra were measured in deuterated solvents with
a JEOL ECX 400 MHz spectrometer. Elemental analyses were
carried out in the Elemental Analysis Service, Yamagata
University, Japan. MALDI mass spectra were recorded on
a Applied Biosystems Voyager DE-Pro from dithranol in posi-
tive linear mode. Thermogravimetric analyses were performed on
a SII EXSTAR 6000 and a TGA/DTA 62000. Differential
scanning calorimetry (DSC) was performed on a Perkin-Elmer
Diamond DSC7. Ionization potentials were measured with
photoelectron spectroscopy in air (PESA) using a RIKEN
KEIKI AC-3. UV-visible absorption spectra were recorded as
solutions in THF with a Shimadzu UV-3150 spectrometer. PL
spectra were recorded using a Jobin Yvon Fluoromax-2
fluorometer. PL quantum efficiencies were measured with an
integral sphere system Hamamatsu C9920-01 under nitrogen.
Electrochemistry was performed using a BAS Electrochemical
Analyzer 660B. All measurements were performed at room
temperature on samples dissolved in dry benzonitrile with 0.1 M
tetra-n-butylammonium tetrafluoroborate as the electrolyte. The
sample concentration was 1 mM, and a platinum working
We have synthesized novel fluorescent dyes, bis(difluo-
renyl)amino-substituted carbazole, pyrene, perylene, and
benzothiadiazole derivatives, via palladium catalyzed C–N
coupling. These dyes are soluble in common organic solvents,
and have sufficiently high glass transition temperatures
(120–181 ꢀC) to form amorphous films. The energy levels of the
compounds were related to the electronic properties of the
central core: the electron-donating carbazole compound showed
the lowest ionization potential and the electron-withdrawing
benzothiadiazole compound showed the largest electron affinity
in the compounds. The emitting colors were also reflected from
the central core in the dyes, and they ranged from sky blue to
deep red. Simple double layer devices from a solution process
showed the same emission colors as PL, and their external
quantum efficiencies were around 1%. Multicolor emissions from
conjugated oligomer dyes having well-defined structures were
achieved in OLEDs fabricated from a solution process.
Experimental
electrode, platinum counter electrode in 0.1
M tetra-n-
Materials
butylammonium tetrafluoroborate in the same solvent as used
for the sample, and a Ag/0.01 M AgNO3 in acetonitrile reference
electrode were used. The scan rate was 100 mV sꢁ1. The solutions
were deoxygenated with argon. The ferrocenium/ferrocene
couple was used as standard. All potentials are quoted relative to
the ferrocenium/ferrocene couple. The EL devices were
fabricated on indium tin oxide (ITO) coated glass substrates,
ultrasonicated sequentially in detergent, methanol, 2-propanol
2-(20-Bromo-90,90-diethylfluoren-70-yl)-9,9-diethylfluorene and
3-aminoperylene were synthesized according to literature
reports12 and their synthesis details are described in ESI.†
3-Amino-N-ethylcarbazole, 1-aminopyrene and 4-amino-2,1,
3-benzothiadiazole were purchased from TCI Japan.
Tris(dibenzylideneacetone)dipalladium and 1,10-bis(diphenyl-
phosphino)ferrocene were purchased from Sigma Aldrich Japan.
4186 | J. Mater. Chem., 2008, 18, 4183–4188
This journal is ª The Royal Society of Chemistry 2008

View Article Online
and acetone, and exposed to UV-ozone ambient for 20 min. A
hole-injecting layer, PEDOT:PSS, was spin-coated onto the ITO
substrates and annealed at 160 ꢀC for 15 min under vacuum. The
emissive layers were prepared by spin-coating from 1,2-dichlo-
roethane solution. Layer thickness calibration was performed
using a Dektak 3 surface profilometer. A BAlq layer was formed
on the emitting layer by vacuum evaporation under 2 ꢂ 10ꢁ4 Pa.
Lithium fluoride and aluminium were finally deposited under
1 ꢂ 10ꢁ3 Pa as a cathode through a shadow mask, and its active
area was 5 ꢂ 5 mm2. The EL spectra were measured on
a Hamamatsu photonic multichannel analyzer PMA-11. The
current–voltage (I–V) characteristics and luminance were
measured using a Keithley 2400 Source Meter and a Konika
Minolta CS-200, respectively. External quantum efficiencies were
m), 7.74 (2H, d, J ¼ 6.3 Hz), 7.75 (2H, d, J ¼ 7.7 Hz), 7.90–8.22
(9H, m). MALDI-MS m/z Calcd: 1097.59 (100.0%), 1098.59
(91.2%), 1099.60 (41.6%), 1100.60 (12.4%), 1101.60 (2.7%).
Found: 1097.66 (100%), 1098.68 (99%), 1099.64 (55%), 1100.63
(19%), 1101.82 (5%). Elemental Anal. Calcd for C84H75N1: C,
91.84; H, 6.88; N, 1.28. Found C, 91.48; H, 7.50; N, 1.15%.
3
A
mixture of 2-(20-bromo-90,90-diethylfluorene-70-yl)-9,9-
diethylfluorene (2.57 g, 4.93 mmol), 3-aminoperylene (0.438 g,
1.64 mmol), sodium tert-butoxide (0.473 g, 4.92 mmol),
tris(dibenxylideneacetone)dipalladium (75 mg, 0.082 mmol),
1,10-bis(diphenylphosphino)ferrocene (91 mg, 0.164 mmol), and
toluene (100 cm3) was degassed and placed under nitrogen, and
then heated at 100 ꢀC for 32 h. The mixture was allowed to cool
to room temperature and then toluene was added. The organic
layer was washed with water, dried over magnesium sulfate, and
filtered. The solvent was removed and the residue was purified by
column chromatography over silica using a n-hexane : toluene
mixture (3 : 1) as eluent to give 3 (0.51 g, 27%). 1H-NMR
(400 MHz, CD2Cl2, ppm) d 0.34 (12H, t, J ¼ 7.3 Hz), 0.42 (12H,
t, J ¼ 7.7 Hz), 1.89–1.98 (4H, m), 2.04–2.12 (12H, m), 6.97 (2H,
s), 7.29–7.36 (9H, m), 7.49–7.87 (22H, m), 8.19 (2H, d, J ¼
7.1 Hz), 8.24 (2H, d, J ¼ 7.3 Hz). MALDI-MS m/z Calcd:
1147.61 (100.0%), 1148.61 (96.1%), 1149.61 (45.1%), 1150.62
(14.3%), 1151.62 (3.3%). Found: 1147.66 (100%), 1148.69
(106%), 1149.68 (67%), 1150.68 (27%), 1151.71 (8%). Elemental
Anal. Calcd for C88H77N1: C, 92.02; H, 6.76; N, 1.22. Found C,
91.42; H, 6.75; N, 1.26%.
calculated assuming
a Lambertian emission pattern and
considering all spectral features in the visible range.
1
A
mixture of 2-(20-bromo-90,90-diethylfluorene-70-yl)-9,9-
diethylfluorene (1.00 g, 1.92 mmol), 3-amino-N-ethylcarbazole
(0.135 g, 0.642 mmol), sodium tert-butoxide (0.185 g,
1.93 mmol), tris(dibenxylideneacetone)dipalladium (29 mg,
0.032 mmol), 1,10-bis(diphenylphosphino)ferrocene (36 mg,
0.065 mmol), and toluene (100 cm3) was degassed and placed
under nitrogen, and then heated at 100 ꢀC for 32 h. The mixture
was allowed to cool to room temperature and then toluene was
added. The organic layer was washed with water, dried over
magnesium sulfate, and filtered. The solvent was removed and
the residue was purified by column chromatography over silica
using a n-hexane : toluene mixture (2 : 1) as eluent to give 1 (0.39
1
g, 56%). H-NMR (400 MHz, d6-DMSO, ppm) d 0.32 (12H, t,
4
J ¼ 7.25 Hz), 0.42 (12H, t, J ¼ 6.8 Hz), 1.42 (3H, t, J ¼ 6.8 Hz),
1.89–1.99 (4H, m), 2.06–2.23 (12H, m), 4.73 (2H, d, J ¼ 6.3 Hz),
7.00 (2H, d, J ¼ 8.2 Hz), 7.18 (1H, t, J ¼ 7.5 Hz), 7.23 (2H, s),
7.35–7.38 (5H, m), 7.47–7.51 (3H, m), 7.64–7.93 (18H, m), 8.07,
8.08 (2H, s). MALDI-MS m/z Calcd: 1090.62 (100.0%), 1091.62
(89.6%), 1092.62 (39.5%), 1093.63 (11.6%), 1094.63 (2.5%).
Found: 1090.26 (100%), 1091.32 (92%), 1092.24 (52%), 1093.30
(22%), 1094.34 (6%). Elemental Anal. Calcd for C82H78N2: C,
90.23; H, 7.20; N, 2.57. Found: C, 90.15; H, 7.43; N, 2.48%.
A mixture of 2-(20-bromo-90,90-diethylfluorene-70-yl)-9,9-diethyl-
fluorene (0.78 g, 1.5 mmol), 4-amino-2,1,3-benzothiadiazole
(76 mg, 0.50 mmol), sodium tert-butoxide (0.144 g, 1.5 mmol),
tris(dibenxylideneacetone)dipalladium (23 mg, 0.025 mmol),
1,10-bis(diphenylphosphino)ferrocene (0.139 g, 0.25 mmol), and
toluene (200 cm3) was degassed and placed under nitrogen, and
then heated at 100 ꢀC for 32 h. The mixture was allowed to cool to
room temperature and then toluene was added. The organic layer
was washed with water, dried over magnesium sulfate, and
filtered. The solvent was removed and the residue was purified by
column chromatography over silica using a n-hexane : toluene
mixture (1 : 3) as eluent to give 4 (0.22 g, 43%). 1H-NMR
(400 MHz, d6-DMSO, ppm) d 0.34 (12H, t, J ¼ 7.25 Hz), 0.39
(12H, t, J ¼ 7.25 Hz), 1.89–1.97 (4H, m), 2.09–2.20 (12H, m), 7.05
(1H, d, J ¼ 2.2 Hz), 7.07 (1H, d, J ¼ 1.8 Hz), 7.19 (2H, d, J ¼ 1.8
Hz), 7.32 (1H, d, J ¼ 6.3 Hz), 7.36–7.42 (4H, m), 7.47–7.50 (2H,
m), 7.70–7.93 (18H, m). MALDI-MS m/z Calcd: 1031.5 (100.0%),
1032.5 (82.7%), 1033.5 (38.3%), 1034.5 (12.8%), 1035.5 (3.3%).
Found: 1031.3 (100%), 1032.3 (96%), 1033.3 (61%), 1034.3 (25%),
1035.4 (9%). Elemental Anal. Calcd for C74H69N3S1: C, 86.09; H,
6.74; N, 4.07; S, 3.11. Found: C, 86.28; H, 6.96; N, 3.82; S, 2.78%.
2
A
mixture of 2-(20-bromo-90,90-diethylfluorene-70-yl)-9,9-
diethylfluorene (1.50 g, 2.88 mmol), 1-aminopyrene (0.209 g,
0.962 mmol), sodium tert-butoxide (0.277 g, 2.88 mmol),
tris(dibenxylideneacetone)dipalladium (44 mg, 0.048 mmol),
1,10-bis(diphenylphosphino)ferrocene (53 mg, 0.096 mmol), and
toluene (200 cm3) was degassed and placed under nitrogen, and
then heated at 100 ꢀC for 32 h. The mixture was allowed to cool
to room temperature and then toluene was added. The organic
layer was washed with water, dried over magnesium sulfate, and
filtered. The solvent was removed and the residue was purified by
column chromatography over silica using a n-hexane : toluene
mixture (1 : 1) as eluent to give 2 (0.51 g, 48%). 1H-NMR
(400 MHz, CD2Cl2, ppm) d 0.34 (12H, t, J ¼ 7.25 Hz), 0.44 (12H,
t, J ¼ 7.25 Hz), 1.89–1.98 (4H, m), 2.03–2.17 (12H, m), 6.90 (2H,
s), 7.29–7.36 (8H, m), 7.54 (2H, d, J ¼ 8.2 Hz), 7.61–7.65 (10H,
References
1 J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature,
1990, 347, 539.
This journal is ª The Royal Society of Chemistry 2008
J. Mater. Chem., 2008, 18, 4183–4188 | 4187

View Article Online
2 S. C. Lo, N. A. H. Male, J. P. J. Markham, S. W. Magennis,
P. L. Burn, O. V. Salata and I. D. W. Samuel, Adv. Mater., 2002,
14, 975.
3 J. P. J. Markham, S. C. Lo, S. W. Magennis, P. L. Burn and
I. D. W. Samuel, Appl. Phys. Lett., 2002, 80, 2645.
4 P. L. Burn, S. C. Lo and I. D. W. Samuel, Adv. Mater., 2007, 19, 1675.
5 S. C. Lo and P. L. Burn, Chem. Rev., 2007, 107, 1097.
6 J. P. J. Markham, E. B. Namdas, T. D. Anthopoulos,
I. D. W. Samuel, G. J. Richards and P. L. Burn, Appl. Phys. Lett.,
2004, 85, 1463.
10 A RIKEN KEIKI AC-3 was used for the photoelectron spectroscopy
in atmospheric conditions. Although ultraviolet photoelectron
spectroscopy in high vacuum is necessary to analyze a precise
density of states of a organic semiconductor, this apparatus is
useful to estimate the HOMO level of the compounds conveniently.
Some of the obtained values (eV) by this measurement are: 5.55
for N,N0-di(naphthalen-1-yl)-N,N0-diphenylbenzidine (a-NPD), 5.93
for Alq3, 6.10 for 4,40-N,N0-dicarbazolylbiphenyl (CBP), 5.36 for
fac-tris(2-phenylpyridinyl)iridium (Ir(ppy)3), and 6.49 for 2,9-
dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP).
7 A. C. A. Chen, S. W. Culligan, Y. H. Geng, S. H. Chen, K. P. Klubek,
K. M. Vaeth and C. W. Tang, Adv. Mater., 2004, 16, 783.
8 Y. H. Geng, A. C. A. Chen, J. J. Ou, S. H. Chen, K. Klubek,
K. M. Vaeth and C. W. Tang, Chem. Mater., 2003, 15, 4352.
9 S. W. Culligan, Y. H. Geng, S. H. Chen, K. Klubek, K. M. Vaeth and
C. W. Tang, Adv. Mater., 2003, 15, 1176.
11 (a) M. Wohlgenannt, K. Tandon, S. Mazumdar, S. Ramasesha
and Z. V. Vardeny, Nature, 2001, 409, 494; (b) D. Beljonne,
´
A. Ye, Z. Shuai and J.-L. Bredas, Adv. Funct. Mater., 2004, 14,
684.
12 T. Li, T. Yamamoto, H.-L. Lan and J. Kido, Polym. Adv. Technol.,
2004, 15, 266.
4188 | J. Mater. Chem., 2008, 18, 4183–4188
This journal is ª The Royal Society of Chemistry 2008