Highly efficient blue organic light-emitting diodes based on 2-(diphenylamino)fluoren-7-ylvinylarene derivatives that bear a tert-butyl group

Article abstract of DOI:10.1002/chem.201100304

Blue fluorescent materials with a 2-(diphenylamino)fluoren-7-ylvinylarene emitting unit and tert-butyl-based blocking units were synthesized. The photophysical properties of these materials, including UV/Vis absorption, photoluminescent properties, and HO

Full text of DOI:10.1002/chem.201100304

DOI: 10.1002/chem.201100304
Highly Efficient Blue Organic Light-Emitting Diodes Based on
2-(Diphenylamino)fluoren-7-ylvinylarene Derivatives that Bear a tert-Butyl
Group
AHCTUNGTRENNUNG
Kum Hee Lee,[a] Young Soo Kwon,[a] Jin Yong Lee,[a] Sunwoo Kang,[a]
Kyoung Soo Yook,[b] Soon Ok Jeon,[b] Jun Yeob Lee,*[b] and Seung Soo Yoon*[a]
Abstract: Blue fluorescent materials
with a 2-(diphenylamino)fluoren-7-ylvi-
nylarene emitting unit and tert-butyl-
based blocking units were synthesized.
The photophysical properties of these
materials, including UV/Vis absorption,
biphenyl, and blue materials doped in
2-methyl-9,10-di(2-naphthyl)anthra-
cene/tris(8-quinolinolato)aluminum/
LiF/Al. All devices exhibit highly effi-
cient blue electroluminescence with
high external quantum efficiency (3.20–
7.72% at 20 mAcmꢀ2). A deep-blue
device with Commission Internationale
de lꢀEclairage (CIE) coordinates of
(0.15, 0.11) that uses 7-[2-(3’,5’-di-tert-
butylbiphenyl-4-yl)vinyl]-9,9-diethyl-2-
N-(3,5-di-tert-butylphenyl)-2,4-difluoro-
benzenamino-9H-fluorene as a dopant
in the emitting layer showed a lumi-
nous efficiency and external quantum
efficiency of 3.95 cdAꢀ1 and 4.23% at
20 mAcmꢀ2, respectively. Furthermore,
a highly efficient sky-blue device that
uses the dopant 7-{2-[2-(3,5-di-tert-bu-
tylphenyl)-9,9’-spirobifluorene-7-yl]vin-
yl}-9,9-diethyl-2-N,N-diphenylamino-
9H-fluorene exhibited a luminous effi-
ciency and high quantum efficiency of
10.3 cdAꢀ1 and 7.7% at 20 mAcmꢀ2,
respectively, with CIE coordinates of
(0.15, 0.20).
photoluminescent
properties,
and
HOMO–LUMO energy levels, were
characterized and rationalized with
quantum-mechanical DFT calculations.
The electroluminescent properties of
these molecules were examined
through the fabrication of multilayer
devices with a structure of indium–tin
oxide, 4,4’-bis{N-[4-(N,N-di-m-tolylami-
no)phenyl]-N-phenylamino}biphenyl,
4’-bis[N-(1-naphthyl)-N-phenylamino]-
Keywords: density functional calcu-
lations
· luminescence · organic
light-emitting diodes · photophysics ·
quantum chemistry
Introduction
ting material needs to be developed to reduce OLED power
consumption and increase the color range. Deep blue-emit-
ting materials with a Commission Internationale de lꢀEclair-
age y coordinate value (CIE y) of <0.15 are important not
only for full-color displays, but also for solid-state lighting.[5]
However, it is difficult to design deep-blue-emitting mate-
rials with high efficiency, saturated color purity, and long op-
eration times due to the wide bandgap of blue materials. Se-
rious efforts to develop such materials have included host
and dopant materials, such as diaryanthracenes,[6] di-
In recent years, organic light-emitting diodes (OLEDs) have
attracted considerable attention due to their potential appli-
cations in full-color, flat-panel displays and space illumina-
tion.[1,2] Red, green, and blue primary emitters are needed
to produce full-color OLEDs for displays or lighting. High
efficiency and saturated color have been achieved for red
and green light-emitting materials.[3,4] However, blue devices
require further improvement in their efficiency and color
index. In particular, a highly efficient, pure deep-blue-emit-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
[a] Dr. K. H. Lee, Y. S. Kwon, Prof. J. Y. Lee, S. Kang, Prof. S. S. Yoon
Department of Chemistry, Sungkyunkwan University
300 Cheoncheon-dong, Jangan-gu, Suwon
Gyeonggi, 440-746 (Korea)
ACHTUNGTRENNUNG
blue dopant known as BD-1 has high efficiency and a pure
blue color.[10] A current efficiency of 5.4 cdAꢀ1 with CIE co-
ordinates of (0.14, 0.13) and external quantum efficiency of
5.1% were demonstrated by doping BD-1 in 2-methyl-9,10-
di(2-naphthyl)anthracene (MADN). Unfortunately, blue
dopant materials based on aromatic amine units suffer
color-shifting problems at high doping concentrations due to
intermolecular interactions between the dopant materials.
Other than BD-1, few studies have reported deep-blue
dopant materials with high efficiencies and a pure blue
color.[11]
Fax : (+82)31-290-7075
E-mail: ssyoon@skku.edu
[b] K. S. Yook, S. O. Jeon, Prof. J. Y. Lee
Department of Polymer Science and Engineering
Dankook University
126, Jukjeon-dong, Suji-gu, Yongin
Gyeonggi, 448-701 (Korea)
E-mail: leej17@dankook.ac.kr
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100304.
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Chem. Eur. J. 2011, 17, 12994 – 13006

FULL PAPER
Fluorene moieties, such as alkylated fluorene, indeno-
fluorene, and spirobifluorene, are expected to be good elec-
troluminescent (EL) building units for OLED materials be-
cause fluorene-based core units have excellent fluorescent
properties[12–15] as well as good morphological, thermal, and
electrochemical stability.[15–19] Furthermore, fluorene moiet-
ies can be substituted easily with a range of functional
groups,[20] and the fine-tuning of their EL properties though
structural modification is relatively simple. However, only a
few systematic studies have examined the EL properties of
blue-emitting materials based on fluorene derivatives.
This paper reports the synthesis and electroluminescent
properties of a series of newly designed, deep-blue-emitting
materials based on 2-(diphenylamino)fluoren-7-ylvinylarene
derivatives (1–14). In these materials, the diphenylamino-
fluorene core was combined with a vinylarene unit, thereby
providing an extended conjugated structure to obtain a
deep-blue color and enhanced light-emitting efficiency given
the wide bandgap of the fluorene unit. The steric hindrance
of the tert-butyl-based blocking group could prevent inter-
molecular interactions between the dopant materials and
contribute to the high efficiency and deep-blue color, even
at high doping concentrations.
Among the fourteen different blue materials studied,
compound 1 had a 2-(diphenylamino)fluoren-7-ylstyrene
emitting core without any blocking groups, whereas five
other materials had the same emitting core with four differ-
ent tert-butyl-substituted blocking groups: 3,5-di-tert-butyl-
phenyl; 3,7-di-tert-butylnaphthyl; 2,7-di-tert-butyl-9,9-dieth-
yl-4-fluorenyl; 4,4’-di-tert-butyl-2-biphenyl; and 3,5-bis(3’,5’-
di-tert-butylphenyl)phenyl, which are shown here as com-
pounds 2, 3, 4, 5, and 6, respectively, to examine their effects
on the device performance of blue fluorescent OLEDs. In
addition, two different arenes, such as fluorene and spirobi-
fluorene, between the 2-(diphenylamino)fluoren-7-ylvinyl
moiety and 3,5-di-tert-butylphenyl blocking groups were in-
troduced in blue fluorescent materials 7 and 8 to determine
the substituent effect on the fluorophore. Furthermore, com-
pounds 9, 10, and 11, which were obtained by replacing di-
ethylfluorene in compound 2 with spirobifluorene, diphenyl-
fluorene, and spiroindanylfluorene, respectively, were stud-
ied to confirm the substituent effect on the 9,9-positions of
the diphenylaminofluorene moiety. Finally, in compounds
12, 13, and 14, fluorine with electron-withdrawing ability
and a tert-butyl group with electron-donating ability were in-
troduced to the diphenyl moiety to examine the electronic
and steric effects on the EL performances of the devices
using them. In this study, blue OLEDs with high efficiency,
deep-blue color chromaticity, and stable CIE coordinates
were developed using these novel blue materials based on
the a 2-(diphenylamino)fluoren-7-ylvinylarene unit with a
tert-butyl blocking group.
Results and Discussion
Synthesis and characterization: Scheme 1 and Scheme 2
summarize the syntheses of the blue fluorescent materials
(1–14). The blue-emitting materials (1, 2, 4, 5, 6, 7, and 8)
were prepared in moderate yield by the Horner–Wads-
worth–Emmons reaction between [7-(diphenylamino)-9,9-di-
ethylfluorene-2-yl]methylphosphonate and the correspond-
ing aldehyde compounds, such as 15–19, which were synthe-
sized from the Suzuki cross-coupling of 4-formylphenylbor-
onic acid or 3,5-di-tert-butylphenylboronic ester, with the
corresponding bromo intermediates. Compound 3 was pre-
pared by Suzuki cross-coupling between 7-(diphenylamino)-
2-(4-bromostyryl)-9,9-diethyl-9H-fluorene and 3,7-di-tert-bu-
Chem. Eur. J. 2011, 17, 12994 – 13006
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S. S. Yoon, J. Y. Lee et al.
Scheme 1. The synthetic routes to blue fluorescent materials (1–8). Reagents: a) [Pd
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Scheme 2. The synthetic routes to blue fluorescent materials (9–14). Reagents: a) 20, KOtBu/THF; and b) [Pd2ACHTNUGTRNNEUG(dba)3], PACHTUGNTREN(NUGN tBu)3, NaOtBu, toluene.
tylnaphthalenyl-1-boronic acid. Compounds 9, 10, and 11
were prepared by synthetic routes consisting of the Horner–
Wadsworth–Emmons reaction between diethyl (3’,5’-di-tert-
butylbiphenyl)-4-methylphosphonate (20) and the corre-
sponding aldehyde compounds, followed by Buchwald–Hart-
wig cross-coupling with diphenylamine.[21] Finally, Buch-
wald–Hartwig cross-coupling between 2-bromo-9,9-diethyl-
7-[2-(3’,5’-di-tert-butylbiphenyl-4-yl)vinyl]-9H-fluorene (25)
and the corresponding diarylamine (26, 27, and 28) afforded
the blue-emitting materials (12, 13, and 14) in moderate
yield. After the conventional purifications, such as column
chromatography and recrystallization, these newly synthe-
sized blue-emitting materials (1–14) were purified further by
train sublimation under reduced pressure (<10ꢀ3 torr) and
1
fully characterized by H and 13C NMR spectroscopy, infra-
red (IR), elemental analysis, and low- and high-resolution
mass spectrometry. High-pressure liquid chromatography
(HPLC) was carried out to examine the purity of materials.
These analyses revealed that the blue-emitting materials (1–
14) is at least >99.0% pure.
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Blue Organic LEDs
FULL PAPER
Photophysical properties: The UV/Vis absorption and pho-
toluminescence (PL) spectra of the synthesized blue materi-
als were obtained in dichloromethane (Figure 1). Com-
pounds 1–6, 9, 10, and 12 showed similar UV/Vis spectra, re-
gardless of blocking groups and substituents on the 9,9-posi-
tions of the diphenylaminofluorene moiety. These observa-
tions suggest that the substituents did not have a significant
effect on the UV/Vis absorption; UV/Vis light was absorbed
mostly by the 2-diphenylaminofluorene-7-ylstyrene core
units. The edge of the UV/Vis spectra of these dopant mate-
rials, which was used to calculate the bandgap, revealed a
similar bandgap of around 2.90 eV in materials 1–6, 9, 10,
and 12, even though small substituent-dependent differences
were observed. Compared to compound 2, the maximum
peaks of the UV/Vis absorption spectra of compounds 7 and
8 were observed at 397 and 398 nm on account of the ex-
tended p-conjugation length of the chromophores. Com-
pared to compound 2 with only hydrogen atoms on the di-
phenyl moiety, the maximum peak of the UV/Vis absorption
spectrum of compound 12 with three electron-donating tert-
butyl units was redshifted by 10 nm, whereas that of com-
pound 13 with two electron-withdrawing fluorine atoms ex-
hibited a blueshift of 6 nm. Interestingly, compound 14 with
both electron-donating tert-butyl units and electron-with-
drawing fluorine atoms on the diphenyl moiety showed a
similar maximum peak of the UV/Vis absorption spectrum
to compound 12. As will be seen below in the quantum-me-
chanical calculation section, the electron densities of
HOMO in the blue materials (1–14) are concentrated on di-
phenylamine moieties, whereas those of LUMO are spread
over the other moiety of materials. Therefore, the electron-
donating or -withdrawing groups on the phenyl group of the
diphenylamine moiety would affect the energy levels of the
HOMO more significantly than the LUMO of this type of
material. Therefore, electron-donating groups on compound
12 decrease the energy bandgap by the increasing HOMO
energy level of compound 12, and thus induce a redshift in
the UV/Vis absorption spectrum compared to compound 2,
whereas the electron-withdrawing groups on compound 13
increase the energy bandgap by lowering HOMO energy
level of compound 13 and inducing a blueshift in the UV/
Vis absorption spectrum relative to compound 2. In com-
pound 14, the effects of the electron-donating and -with-
drawing groups are cancelled out, and its UV/Vis absorption
spectrum is similar to that of compound 2. The UV/Vis ab-
sorption spectra of blue materials (1–14) overlapped well
with the PL emission spectra of a common blue host,
MADN. This suggests that energy transfer between MADN
and these materials is quite efficient and MADN is a good
host in OLED devices using these materials as dopants.
The maximum peaks of the PL spectra of compounds 2–5
were 476 nm, whereas that of compound 1, without any
blocking groups, had a maximum peak of 478 nm. The red-
shift of the emission peaks was attributed to the extended
conjugation structure of compound 1, as shown below in the
molecular calculation. Interestingly, compound 6 showed a
hypsochromic shift in the emission peak of 4 nm relative to
the PL spectrum of compound 2 due to the shortening of
the p-conjugation length by meta substitution, not para sub-
stitution, of 3,5-di-tert-butylbenzene. In the case of com-
pounds 12, 13, and 14, the PL spectra showed similar trends
to the UV/Vis absorption spectra. Therefore, in compound
12, a redshift of 24 nm occurred when the tert-butyl group
was added to the diphenyl moiety of compound 2. In con-
trast, compound 13 exhibited hypsochromic shift (14 nm)
relative to compound 2 due to the increased electron-with-
drawing effect by the fluorine atoms. In addition, the PL
spectrum of compound 14 is similar to that of compound 2.
The PL quantum yield of materials (1–14) were measured to
Figure 1. UV and PL spectra of blue fluorescent materials (1–14).
Chem. Eur. J. 2011, 17, 12994 – 13006
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S. S. Yoon, J. Y. Lee et al.
have a quantum yield >0.60, thereby indicating that the di-
phenylaminofluorene-based core was an efficient emitting
unit, and thus high efficiency could be expected in a blue
device that used these materials. Figure 1 shows the PL
spectra of the blue materials (1–14) in thin solid film on
quartz plates. All the blue materials (1–14) showed a nar-
rower full width at half-maximum (fwhm; 10–41 nm) in the
film than in solution. The narrower emission bands in the
films suggest that these materials could have improved color
purity in solid-state OLED devices. Table 1 lists the basic
physical properties of these materials.
Table 1. Physical properties of the compounds 1–14.
Dopants UV lmax PL lmax
fwhm
HOMO LUMO
Eg
F[c]
[nm][a]
[nm][a,b] [nm][a,b]
1
2
3
4
5
6
7
8
388
388
386
386
386
385
397
398
390
390
390
398
382
386
478/470
476/473
476/471
476/471
476/480
472/457
482/484
492/488
474/476
477/480
482/480
500/476
462/470
470/464
76/35
74/64
74/52
73/49
73/65
71/50
74/50
76/50
77/48
72/52
75/56
77/66
73/52
73/53
ꢀ5.43
ꢀ5.45
ꢀ5.55
ꢀ5.47
ꢀ5.57
ꢀ5.59
ꢀ5.44
ꢀ5.47
ꢀ5.53
ꢀ5.51
ꢀ5.50
ꢀ5.29
ꢀ5.70
ꢀ5.63
ꢀ2.54
ꢀ2.55
ꢀ2.62
ꢀ2.55
ꢀ2.64
ꢀ2.67
ꢀ2.61
ꢀ2.66
ꢀ2.62
ꢀ2.63
ꢀ2.63
ꢀ2.48
ꢀ2.75
ꢀ2.72
2.89 0.95
2.90 0.94
2.93 0.97
2.92 0.91
2.93 0.97
2.92 0.82
2.83 0.81
2.81 0.97
2.91 0.86
2.88 0.99
2.87 0.95
2.81 0.79
2.95 0.62
2.91 0.62
9
10
11
12
13
14
Figure 2. Energy-level diagram of the materials used in the devices.
[a] In CH2Cl2 (ꢁ1ꢂ10ꢀ5 m). [b] In neat film. [c] Quantum yield using
BDAVBi as a standard; lex =360 nm (F=0.86 in CH2Cl2).
ces, including indium–tin oxide (ITO); 4,4’-bis{N-[4-(N,N-di-
m-tolylamino)phenyl]-N-phenylamino}biphenyl (DNTPD);
4’-bis[N-(1-naphthyl)-N-phenylamino]biphenyl
(NPB);
Measurement of the energy levels of the materials: The
HOMO energy levels of these materials were estimated
using an AC-2 photoelectron spectrometer to show that the
HOMO energy levels of compounds 1–11 varied from ꢀ5.43
to ꢀ5.59 eV, respectively (Table 1). The LUMO energy
levels, which were calculated by subtracting the optical
bandgaps from the HOMO energy levels, ranged from
ꢀ2.54 and ꢀ2.66 eV. The energy bandgap of the blue fluo-
rescent materials (1–14) ranged from 2.81 to 2.95 eV, which
are narrower than the 3.0 eV for MADN, thereby demon-
strating the suitability of compounds 1–14 and MADN to
act as dopants and hosts, respectively, in blue OLEDs. Inter-
estingly, when the electron-donating tert-butyl groups were
added to the diphenylaminofluorene group of compound 12,
the energy bandgap became 2.81 eV, which is 0.09 eV nar-
rower than that of compound 2. In addition, compared to
the energy bandgap of compound 2 (2.90 eV), the energy
bandgap of 13 became 2.95 eV when electron-withdrawing
fluorine atoms were added to the diphenylaminofluorene
group of compound 13. The energy bandgap of compound
14 (2.91 eV) is similar to that of compound 2. These results
are in good agreement with the trends observed in the ab-
sorption and emission spectra, and the quantum mechanical
calculations. Figure 2 shows the HOMO and LUMO energy
levels of blue fluorescent materials (1–14), along with the
other materials employed here in electroluminescent devi-
MADN; tris(8-quinolinolato)aluminum (Alq3); and LiF:Al.
Quantum-mechanical calculation of electronic structures: To
better understand the observed photophysical properties of
the organic light-emitting diode materials at the molecular
level, density functional theory (DFT) calculations for com-
pounds 1–14 were carried out using the nonlocal density
functional of Beckeꢀs three parameters and employing the
Lee–Yang–Parr functional (B3LYP) with 6-31G* basis sets
using a suite of Gaussian 03 programs.[22] The calculations
showed that the dihedral angles between the fluorene
(linked with diphenyl amine or substituted diphenyl amine
moiety) and benzene (linked with styryl) moieties were 9.18,
7.89, 7.33, 9.33, 6.54, 3.89, 3.43, 0.30, 3.14, 1.02, 0.82, and
1.588 for compounds 1–6 and 9–14, respectively. For com-
pounds 7 and 8, the calculated dihedral angles between the
fluorene (linked with diphenyl amine) and fluorene (spiro-
fluorene) were 1.68 and 0.618, respectively. The calculated
dihedral angles between benzene (linked with styryl) and
substituents for compounds 1–6 and 9–14 were 36.7, 37.9,
53.8, 58.7, 50.5, 39.9, 37.2, 37.6, 37.0, 37.4, 37.7, and 37.98, re-
spectively. For compounds 7 and 8, the calculated dihedral
angles between fluorene (spirofluorene) and the substituents
were 37.9 and 37.48, respectively, and the substituents of all
of the compounds were out of plane. Figure 3 presents the
HOMOs and LUMOs for compounds 1–14. The shapes of
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Chem. Eur. J. 2011, 17, 12994 – 13006

Blue Organic LEDs
FULL PAPER
compounds 1–14; the results
are listed in Table 2. The excita-
tion energies calculated for
compounds 1–6 are 2.8715,
2.8890, 2.8799, 2.9022, 2.9024,
and 2.9523 eV, respectively,
which correspond to the ab-
sorption wavelengths of 431.78,
429.16, 430.52, 427.21, 427.18,
and 419.96 nm, respectively.
The calculated HOMO–LUMO
gaps for compounds 2–6 are
larger than that of compound 1
because the LUMO for com-
pound 1 shows more delocaliza-
tion than compounds 2–6. In
other words, the energy level of
the LUMO for compounds 2–6
is higher than that of compound
1, thereby resulting in large
HOMO–LUMO gap values.
The HOMO–LUMO gaps of
compounds 7 and 8 are smaller
than those of compounds 1–5
because the lengths of the chro-
mophores of compounds 7 and
8 are longer than those of com-
pounds 1–5. The HOMO–
LUMO gaps of compounds 7
and 8 are 2.7988 and 2.7832 eV,
respectively, which correspond
to absorption wavelengths of
443.0 and 445.47 nm. The
HOMO–LUMO gaps of com-
pounds 9–11 are 2.8780, 2.8703,
and 2.8808 eV, which corre-
spond to the absorption wave-
Figure 3. B3LYP/6-31G*-calculated HOMOs and LUMOs orbitals of blue fluorescent materials (1–14).
the HOMOs and LUMOs for all the compounds appear
similar. In the HOMOs of compounds 1–6 and 9–14, the
electrons are distributed over the 2-diphenylaminofluoren
(spirofluoren, diphenylfluoren, indanylfluoren)-7-ylstyrene
moiety, whereas in the LUMOs, they are distributed over
the fluoren-7-ylvinylarene moieties. For compounds 7 and 8,
the HOMO electrons are distributed over the 2-diphenyla-
minofluoren-7-ylfluorene and 2-diphenylaminofluoren-7-yl-
spirobifluorene moieties, respectively, whereas the LUMO
electrons are distributed over the fluoren-7-ylvinylarenes.
The electrons in the HOMOs for compounds 13 and 14 are
distributed over the 2-N-2,4-difluorophenyl-N-phenylamino-
7-ylstyrene moiety and 2-N-2,4-difluorophenyl-N-3,5-di-tert-
butylphenylaminofluoren-7-ylstyrene moiety, whereas the
electrons in the LUMOs are distributed over the fluoren-7-
ylvinylarene moieties.
lengths of 430.80, 431.96, and 430.39 nm, respectively. For
Table 2. Oscillation strength and electronic transition for compounds 1–
14.
Compound
Oscillation
strength
Transition
([%])
labs,max
[nm][a]
labs,max
[nm][b]
1
2
3
4
5
6
7
8
1.3833
1.4986
1.4781
1.4547
1.4245
1.2833
1.9494
1.9070
1.4867
1.4494
1.5151
1.4412
1.6363
1.5687
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
HOMO to LUMO (100)
431.78
429.16
430.52
427.21
427.18
419.96
443.00
445.47
430.80
431.96
430.39
440.84
420.38
426.81
388
388
386
386
386
385
397
398
390
390
390
398
382
386
9
10
11
12
13
14
Time-dependent DFT (TD-DFT) calculations were car-
ried out at the optimized geometries to investigate the elec-
tronic transition energies and properties. The HOMO!
LUMO transition contributes solely to the excitations for
[a] Calculated absorption wavelength. [b] Measured absorption wave-
length.
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S. S. Yoon, J. Y. Lee et al.
compounds 12–14, the calculated HOMO–LUMO gaps are
2.8125, 2.9493, and 2.9049 eV, respectively, which correspond
to the absorption wavelengths of 440.84, 420.38, and
426.81 nm, respectively. The absorption wavelengths of com-
pounds 12–14 are shifted by 10.68, ꢀ8.78, and ꢀ2.35 nm, re-
spectively, relative to compound 2. In compound 12, elec-
tron-donating tert-butyl groups are substituted in the high-
electron-density moiety (biphenyl amino moiety) of the
HOMO. Hence, the HOMO–LUMO gap is narrower than
that of compound 2 due to the growth of the HOMO
energy level. In the case of compound 13, fluorine substitu-
ent lowers the energy level of HOMO and increases the
HOMO–LUMO gap. For compound 14, the electron-donat-
ing tert-butyl substituent leads to an increase in the HOMO
energy level, whereas the fluorine atom extracts the electron
density and lowers the energy level of the HOMO. There-
fore, HOMO–LUMO gap of compounds 14 and 2 are simi-
lar. These results are in good agreement with the experi-
mentally observed absorption wavelengths.
Electroluminescence properties: The device performance of
the blue fluorescent materials (1–14) was examined by
doping these materials in the MADN host at a 5–15% con-
centration, with the following device structure: ITO/
DNTPD (60 nm)/NPB (30 nm)/1–14 doped in MADN
(30 nm)/Alq3 (20 nm)/LiF (1.0 nm)/Al (200 nm). Table 3
summarizes the device performances, and Figure 4 presents
the EL spectra of the blue device with a 5% doping concen-
tration (1A–14A). All devices
exhibited blue emission with
emission peaks between 441
Table 3. EL performance characteristics of devices 1–14.
[a]
[b]
[c]
[e]
Devices
Dopants
[(wt%)]
hL
hP
hext
L[d]
Von
EL[f]
CIE (x, y)[f]
and 484 nm. The contribution
of the host MADN to the elec-
troluminescence (EL) emission
can be excluded because of the
superior EL performance of de-
vices 1A–14A relative to that
of a similar device using only
MADN as the emitting layer.
This suggests that the EL emis-
sion of devices 1A–14A origi-
nates from the emissions of
dopants 1–14 through Forster-
type energy transfer between
the dopants and MADN host.
With the exception of devices
7A, 8A, and 12A, which have
a wider energy bandgap than
the others, eleven devices A
showed deep-blue colors with a
y CIE coordinate <0.16 due to
the blue-emitting diphenylami-
ACHTUNGTRENNUNG
MADN only
1A
1B
1C
2A
2B
2C
3A
3B
3C
4A
4B
4C
5A
5B
5C
6A
6B
6C
7A
7B
7C
8A
8B
8C
2.4
1.28
3.11
3.03
3.00
3.10
2.84
2.81
2.17
2.19
1.76
2.11
2.39
2.43
2.18
1.71
1.35
2.13
2.17
1.97
4.67
4.27
4.02
5.11
5.42
5.23
2.90
3.17
3.20
2.56
2.89
3.34
3.27
3.48
3.61
3.54
3.96
3.81
1.54
1.71
1.76
1.96
2.32
2.18
1.96
5.27
4.92
4.31
5.17
4.47
4.14
3.96
3.82
2.84
3.39
3.58
3.81
4.13
3.37
2.25
3.89
3.86
3.60
6.83
5.48
4.56
7.67
7.72
7.27
4.97
5.43
4.91
4.21
4.68
5.35
5.41
5.12
5.08
4.97
5.00
5.14
3.20
3.56
3.55
4.23
4.53
3.98
160
6.0
5.0
5.0
4.5
4.5
4.5
4.5
5.0
5.0
5.0
4.0
4.5
4.5
5.0
5.0
5.0
5.0
4.5
5.0
4.5
4.5
4.5
5.5
5.5
5.5
5.0
5.0
5.0
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.0
4.0
6.0
6.0
6.0
6.0
5.0
4.5
462
(0.15, 0.16)
(0.15, 0.16)
(0.15, 0.18)
(0.15, 0.19)
(0.15, 0.13)
(0.15, 0.14)
(0.15, 0.15)
(0.15, 0.13)
(0.15,0.14)
(0.15,0.17)
(0.15, 0.14)
(0.14, 0.15)
(0.14, 0.15)
(0.15, 0.13)
(0.15,0.13)
(0.15,0.14)
(0.15, 0.12)
(0.15, 0.13)
(0.15, 0.15)
(0.15, 0.17)
(0.15,0.19)
(0.15,0.20)
(0.15, 0.20)
(0.15, 0.20)
(0.15, 0.21)
(0.15, 0.15)
(0.15,0.16)
(0.15,0.17)
(0.15, 0.14)
(0.15, 0.15)
(0.15, 0.15)
(0.15, 0.15)
(0.15, 0.17)
(0.14, 0.16)
(0.14, 0.17)
(0.14, 0.19)
(0.14, 0.19)
(0.15, 0.15)
(0.15,0.16)
(0.15,0.17)
(0.15, 0.11)
(0.15, 0.13)
(0.15, 0.13)
1 (5)
6.28
6.31
5.75
5.42
5.07
4.85
4.09
4.12
3.01
3.81
4.21
4.42
4.18
3.41
2.54
3.82
4.06
3.69
8.44
8.58
7.55
10.3
10.9
10.5
5.85
6.61
6.20
4.79
5.40
6.25
6.12
6.38
6.24
6.24
6.84
6.85
3.54
4.16
4.26
3.95
4.50
4.07
4081
3102
5617
10200
7623
9502
4847
4852
5430
5151
6903
5346
3406
1652
1167
3543
5155
4648
13550
14860
14790
5651
5750
6512
4477
4029
5185
6849
6604
11440
7341
9536
17190
14350
17670
27280
612.7
451.2
459.1
3299
4004
4713
455, 474
457, 477
458, 478
451
452, 472
453, 472
450
451
453
450
452, 472
454, 472
449
449
450
1 (10)
1 (15)
2 (5)
2 (10)
2 (15)
3 (5)
3 (10)
3 (15)
4 (5)
4 (10)
4 (15)
5 (5)
5 (10)
5 (15)
6 (5)
6 (10)
6 (15)
7 (5)
7 (10)
7 (15)
8 (5)
8 (10)
8 (15)
9 (5)
9 (10)
9 (15)
10 (5)
10 (10)
10 (15)
11 (5)
11 (10)
11 (15)
12 (5)
12 (10)
12 (15)
13 (5)
13 (10)
13 (15)
14 (5)
14 (10)
14 (15)
447
448, 461
447, 463
456
458
459
458, 482
460, 484
461, 484
449, 472
450, 473
451, 474
449, 472
449, 473
449, 473
451, 473
453, 476
454, 476
456, 481
457, 481
457, 481
443, 463
443, 464
443, 465
443, 462
444, 465
444, 466
nofluorene-7-ylstyrene
core
unit. However, the CIEs of the
devices were dependent on the
blocking groups of the dopant
materials. For example, device
1A that used compound 1 with-
9A
9B
9C
10A
10B
10C
11A
11B
11C
12A
12B
12C
13A
13B
13C
14A
14B
14C
out
a blocking group as a
dopant showed a y CIE of 0.16,
whereas devices A that used
dopant materials 2–6, 9–11, 13,
and 14 with tert-butyl-based
blocking groups showed a y co-
ordinate of <0.15, thus indicat-
ing a blueshift in the CIE color
coordinates of the devices due
to the introduction of a block-
ing group on the dopants.
These blueshifts could be ex-
plained by the protection of the
[a] Luminous efficiency [cdAꢀ1] at 20 mAcmꢀ2. [b] Power efficiency [lmWꢀ1] at 20 mAcmꢀ2. [c] External
quantum efficiency [%] at 20 mAcmꢀ2. [d] Luminance [cdmꢀ2] at 8 V. [e] Turn-on voltage at 1 cdmꢀ2. [f] CIE
x, y coordinates at 8.0 V.
13000
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Chem. Eur. J. 2011, 17, 12994 – 13006

Blue Organic LEDs
FULL PAPER
Figure 4. EL spectra of blue OLEDs (1A–14A) at 8 V.
Figure 5. a) Comparison of the current efficiency of devices using 1 and 4
depending on doping concentration. b) EL spectra of the devices using 1
and 4 depending on doping concentration
emitting core of the dopants by the bulky tert-butyl-based
blocking groups, which suppressed the intermolecular inter-
actions between the dopant materials. The reduced interac-
tions led to a blueshift in the emission peaks observed in the
EL spectra of the devices that used them as dopants
(Figure 4). Among devices 1A–14A, device 14A, which
used compound 14 as a dopant, showed the best CIE coordi-
nates of (0.15, 0.11). In addition, the compound 6-doped
device 6A exhibited deep-blue emission with CIE coordi-
nates of (0.15, 0.12).
The effects of the tert-butyl-based blocking group was
confirmed by an examination of the performance of the de-
vices built using compounds 1 and 4 in terms of their doping
concentrations, as shown in Table 3 and Figure 5a. In gener-
al, the external quantum efficiency (EQE) of the blue fluo-
rescent materials decreases at high doping concentrations
due to concentration-quenching effects with the optimum
doping being observed at approximately 5% in most
cases.[23] A similar result was obtained in devices that used
compound 1 as a dopant, in which the quantum yield de-
creased with increasing doping concentration. The EQEs of
the compound 1 doped devices at 5 and 15% concentrations
were 5.3 and 4.2%, respectively. However, the efficiency of
the devices that used compound 4 as a dopant improved at
high doping concentrations. The EQEs of the compound 4
doped devices at 5 and 15% concentrations were 3.4 and
3.8%, respectively, and showed >10% improvement at
higher doping concentrations. The improved EQE of the de-
vices that used compound 4 as a dopant at higher doping
concentrations suggests that the hydrocarbon-based, nonpo-
lar blocking groups of compound 4 reduces the level of mo-
lecular aggregation in the emitting layer and suppresses self-
quenching, even at concentrations as high as 15%. The EL
spectra of the devices that used compounds 1 and 4 as dop-
ants support this notion, as shown in Figure 5b. In devices
that used compound 4 as a dopant, there was little change in
the EL spectra with various doping concentrations, but the
spectral intensity between 480 and 700 nm was higher in the
devices that used compound 1 as a dopant at higher concen-
trations. This increased EL emission peak intensity was at-
tributed to intermolecular interactions of the dopant materi-
als. The CIE coordinates of devices 4 were (0.15, 0.14) and
(0.14, 0.15) at a 5 and 15% doping concentration, respec-
tively, whereas the CIE of devices 1 were (0.15, 0.16) and
(0.15, 0.19) at a 5 and 15% doping concentration, respec-
tively. Therefore, the tert-butyl-based blocking group is ef-
fective in keeping the EL spectra constant at longer wave-
lengths, irrespective of the doping concentration, and in al-
lowing high efficiency even at high concentrations.
Interestingly, in the devices that used compound 2 as a
dopant, tert-butyl-based blocking groups, such as 3,5-di-tert-
Chem. Eur. J. 2011, 17, 12994 – 13006
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13001

S. S. Yoon, J. Y. Lee et al.
butylbenzene, do not play an important role in the EL effi-
ciency because the EL efficiencies of the devices that used
compounds 1 and 2 as a dopant were similar (Figure 6). This
suggests that in contrast to 2,7-di-tert-butyl-9,9-diethyl-4-flu-
orenyl group of compound 4, the 3,5-di-tert-butylbenzene
group of compound 2 is not bulky enough to affect molecu-
lar aggregation and EL efficiencies of the devices that used
compound 2 as a dopant. Interestingly, the devices that used
compounds 6, 10, 11, 12, and 14 as dopants exhibited the ef-
fects of a tert-butyl-based blocking group on the EL efficien-
cies. In particular, the EQEs of the compound 10 doped de-
vices at 5 and 15% concentrations were 4.2 and 5.4%, re-
spectively, and showed a 29% improvement at higher
doping concentrations. In addition, the EQEs of the devices
that used compounds 6, 11, 12, and 14 as dopants at 5 and
15% concentrations were in a similar range within 7.5%, re-
spectively, whereas the EQEs of the device that used com-
pound 2 as a dopant at a 15% concentration decreased by
20% relative to that at a 5% concentration. This suggests
that the introduction of additional groups to compound 2
would increase the molecular size of compounds 6, 10, 11,
12, and 14 and reduce the level of molecular aggregation in
the emitting layer of the devices that used them as dopants,
even at concentrations as high as 15%, as shown in devices
that used compound 4 as a dopant.
renyl group, 4,4’-di-tert-butyl-2-biphenyl group, and the 3,5-
bis(3’,5’-di-tert-butylphenyl)phenyl group decreased the
EQE by 30, 52, 25, and 33% (2B versus 3B, 4B, 5B, and
6B), respectively. In addition, the substitution of diethyl
groups at the 9,9 positions of the fluorene moiety of dopant
2 to diphenyl groups, spirodiphenyl groups and spiroindanyl
influenced the EL efficiency of the devices that used them
as dopants (2B versus 9B, 10B, and 11B). For example, rel-
ative to device 2B, the EQEs of devices 9B and 10B de-
creased by 3.9 and 19%, respectively, whereas the EQE of
device 11B increased by 4.6%. Furthermore, the additional
tert-butyl groups and fluorine atoms in the diphenylamine
moiety of compound 2 significantly altered the EL efficiency
of the devices. For example, relative to device 2B, devices
12B, 13B, and 14B showed a 3.9, 38, and 18% decrease in
the EQE, respectively. These observations reflect the com-
plex aspects of the host–dopant system in the emitting layer
of the OLED devices.
Among devices 1A–14A, devices 7A and 8A showed the
highest EQE, whereas the CIE coordinates of devices 7A
and 8A indicated a redshift (0.04 and 0.07) from that of
device 2A in the CIE y coordinate due to an extension of
the p-conjugation length by fluorene and spirobifluorene.
The best luminous efficiency and EQE were achieved in
device 8A, with 10.3 cdAꢀ1 and 7.67% at 20 mAcmꢀ2, re-
spectively. This increase in efficiency might be partially due
to the differences in the effectiveness of exciton formation
on dopant materials through energy transfer between the
MADN host material and dopants 7 and 8 within devices
7A and 8A, respectively. Among dopants 1–14, the degree
The EL efficiencies of devices show complex correlations
with the molecular structure of the blue dopants in the emit-
ting layer. First of all, a change of the tert-butyl blocking
group from the 3,5-di-tert-butylphenyl group to the 3,7-di-
tert-butylnaphthyl group, 2,7-di-tert-butyl-9,9-diethyl-4-fluo-
Figure 6. I–V–L characteristics of devices 2A–2C (closed symbols: current density; open symbols: luminance) and the efficiency versus current density
relationship for devices 2A, 8A, and 14A.
13002
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Chem. Eur. J. 2011, 17, 12994 – 13006

Blue Organic LEDs
FULL PAPER
of overlap between the absorption spectra of dopants 7 and
8 and the emission spectra of MADN host was most effec-
tive, as shown in Figure 1. These observations suggest that
exciton formation on the dopant materials was most effec-
tive in devices 7A and 8A through energy transfer between
the MADN host material and dopants 7 and 8. Therefore,
the improved efficiencies in devices 7A and 8A suggest that
effective energy transfer between the host and dopant play
an important role in the highly efficient blue OLEDs. In
particular, relative to device 7A, the EQE and luminous ef-
ficiency of device 8A increased by 12 and 22%, respectively.
The higher quantum yield of dopant 8 (0.97) than that of
dopant 7 (0.81) may have contributed partially to the im-
proved EL performance. Moreover, in device 8, the effect of
the suppression of self-quenching by the spirobifluorene
moiety in dopant 8 may have partially contributed to the im-
proved EL performance, because the EL efficiencies of
device 8A do not decrease significantly at higher doping
concentrations. Interestingly, the EL efficiency of device
12A was not high as that of devices 7A and 8A despite the
overlap of the emission spectra of the MADN host, with the
absorption spectra of dopant 12 being as effective as that of
dopants 7 and 8. Presumably, compared to compounds 7 and
8, the higher HOMO energy level of compound 12 would
facilitate the hole-trapping process in device 12A. This
would prevent effective exciton formation on the dopant
through an energy-transfer process, and reduce the EL effi-
ciency of device 12A relative to devices 7A and 8A.
Among devices 1A–14A, devices 13A showed the lowest
EQE, with 3.20% at 20 mAcmꢀ2. This low efficiency might
be attributed partially to the ineffective exciton formation
on dopant 13 in device 13A through the energy-transfer
process because, among dopants 1–14, the degree of overlap
between the absorption spectra of dopant 13 and the emis-
sion spectra of the MADN host was the least effective, as
shown in Figure 1. In addition, the low quantum yield of
dopant 13 (0.62) might have contributed partially to the re-
duced EL efficiency of device 13A. The rather improved ef-
ficiency of the device 14 is due to improved charge balance
by the electron trapping by the dopant 14. The charge trap-
ping also affected the turn-on voltage of the device in addi-
tion to the charge-transport properties of the dopant. The
turn-on voltage was defined as the voltage at 1 cdmꢀ2,
which was different depending on the dopant materials be-
cause of the different charge-transport properties of the
dopant materials and the different charge trapping caused
by different HOMO and LUMO levels.
spective of the doping concentrations from 5 to 15% due to
the effects of the tert-butyl-based blocking group. The EL
spectra were insensitive to the doping concentrations and
high efficiency was obtained, even at high concentrations,
due to the blocking group. Therefore, a blue fluorescent
device with high efficiency and stable CIE coordinates can
be fabricated regardless of the doping concentration by
combining a highly efficient 2-(diphenylamino)fluoren-7-yl-
styrene emitting unit and tert-butyl-based blocking groups.
In addition, highly efficient sky-blue materials were devel-
oped that bore 2-(diphenylamino)fluoren-7-ylvinylarene
emitting units and tert-butyl-based blocking units. Efficient,
sky-blue emission with a quantum efficiency of 7.72% was
obtained using the core 2-(diphenylamino)fluoren-7-ylvinyl-
spirobifluorene-emitting unit. The introduction of bulky
building units, such as spirobifluorene to the emitting core
(2 versus 8), improved the current efficiency of the OLEDs
by 90%. When the tert-butyl group and fluorine were com-
bined and added to the diphenylaminofluorene group of
compound 14, device 14A exhibited a deep-blue emission of
0.11, which is superior to that of device 13A (0.15). A deep-
blue device with CIE coordinates of (0.15, 0.11) that used
compound 14 as a dopant in the emitting layer showed a lu-
minous efficiency of 3.95 cdAꢀ1 and an external quantum ef-
ficiency of 4.23% at 20 mAcmꢀ2. These results clearly dem-
onstrate the excellent properties of fluorene derivatives with
suitable substituents for applications in blue-emitting mate-
rials in OLEDs.
Experimental Section
Synthesis and characterization: All reactions were performed under ni-
trogen and the solvents were dried and distilled from the appropriate
drying agents prior to use. Commercially available reagents were used
without further purification unless stated otherwise. 4-Diphenylcarboxal-
dehyde, 4-formylphenylboronic acid, 3,5-di-tert-butylaniline, and 1-
bromo-4-tert-butylbenzene were used as received from Aldrich or TCI. 7-
(Diphenylamino)-9,9-diethyl-9H-fluorene-2-carbaldehyde,[24] 7-(diphenyl-
AHCTUNGTRENNUNG
amino)-2-(4-bromostyryl)-9,9-diethyl-9H-fluorene,[24] diethyl (4-bromo-
benzyl)methylphosphonate,[25] 4-bromo-2,7-di-tert-butyl-9,9-diethylfluor-
ene,[26] 2-bromo-4,4’-di-tert-butylbiphenyl,[27] 3,7-di-tert-butylnaphthalenyl-
1-boronic acid,[28] 3’,5’-di-tert-butylbiphenyl-4-carbaldehyde,[29] 7-bromo-
9,9-diethylfluorene-2-carbACHTUNGTRNEUNG
aldehyde,[30] 7-bromospirobifluorene-2-carbal-
dehyde,[31] 2-(3,5-di-tert-butylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lane,[32] 7-bromo-9,9-diphenyl-9H-fluorene-2-carbaldehyde,[33] 2,7-dibro-
mo-1’,3’-dihydrospiro[9H-fluorene-9,2’-(2H)indene],[34] and 7-(diphenyl-
AHCTUNGTRENNUNG
amino)-9,9-diethylfluorene-2-ylmethylphosphonate[35] were prepared
using previously published methods. The 1H and 13C NMR spectra were
obtained using a Varian (Unity Inova 300Nb) spectrometer at 300 MHz.
The FTIR spectra were acquired using a VERTEX 70 spectrometer. The
low- and high-resolution mass spectra were obtained using either a Jeol
JMS-AX505WA spectrometer in FAB mode, a Jeol JMS-600 spectrome-
ter in EI mode, or a JMS-T100TD (AccuTOF-TLC) spectrometer in pos-
itive-ion mode. Elemental analysis (EA) was performed using an EA
1108 spectrometer. The UV/Vis absorption spectra were measured using
a Shinco S-3100 spectrometer, and the PL spectra were measured using
an Aminco–Bowman Series 2 luminescence spectrometer. The UV/Vis
and PL spectra were measured in 10ꢀ5 m dilute dichloromethane solu-
tions. The fluorescent quantum yield was determined for solutions of the
compounds in dichloromethane at 293 K using BDAVBi as a reference
(F=0.86).[8] The ionization potentials (or HOMO energy levels) of the
Conclusion
Highly efficient blue fluorescent materials were developed
with 2-(diphenylamino)fluoren-7-ylvinylarene emitting units
and tert-butyl-based blocking units. Efficient, deep blue
emission with an external quantum efficiency of 5.17% was
obtained using a core 2-(diphenylamino)fluoren-7-ylstyrene
emitting unit. Stable CIE coordinates were achieved irre-
Chem. Eur. J. 2011, 17, 12994 – 13006
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
13003

S. S. Yoon, J. Y. Lee et al.
blue material thin films were determined by UV photoemission spectros-
copy using a Surface Analyzer model AC-2 (Riken-Keiki AC-2). The
LUMO energy levels were estimated by subtracting the bandgap energy
from the HOMO energy levels. The energy gaps were determined by the
on-set absorption energy based on the absorption spectra of the materi-
als.
8.5 Hz, 5H), 7.31–7.23 (m, 10H), 7.18–7.12 (m, 8H), 7.07–6.99 (m, 6H),
6.93 (d, J=8.2 Hz, 2H), 2.06–1.94 (m, 4H), 1.39 (s, 9H), 1.31 (s, 9H),
0.41 ppm (t, J=7.0 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=151.9,
151.0, 150.7, 150.6, 149.7, 149.6, 148.3, 147.4, 141.4, 139.0, 136.7, 136.3,
136.0, 135.9, 130.0, 129.5, 129.4, 127.7, 126.5, 126.2, 125.8, 124.1, 123.9,
123.4, 122.7, 121.8, 120.8, 120.6, 119.7, 119.6, 119.5, 118.9, 56.3, 55.5, 35.1,
35.0, 33.2, 33.0, 31.9, 31.8, 8.9, 8.8 ppm; FTIR (ATR): n˜ =3029, 2961,
1594, 1511, 1494, 1361, 1334, 1278, 1231, 1216, 1202, 957, 876, 823, 752,
696 cmꢀ1; MS (FAB+): m/z: 823 [M+]; HRMS (FAB+): m/z calcd for
C62H65N: 823.5117 [M+]; found: 823.5117; elemental analysis calcd (%)
for C62H65N: C 90.35, H 7.95, N 1.70; found: C 90.41, H 7.93, N 1.67.
Compound 1: KO
dropwise to mixture of 7-(diphenylamino)-9,9-diethylfluorene-2-yl-
ACHTUNGTRENNUNGmethylphosphonate (1.13 g, 2.10 mmol) and diphenylcarboxaldehyde
ACHTUNGTRENNUNG(tBu) (2.40 mL, 1.0m, 2.40 mmol) in THF was added
a
(0.360 g, 2.00 mmol) in anhydrous THF (20.0 mL) at 08C under nitrogen.
The reaction mixture was stirred for 15 min at 08C followed by 1 h at
room temperature, quenched with water, extracted with ethyl acetate,
and washed twice with water. The combined organic layers were dried
over MgSO4 and the solvent was removed under reduced pressure. The
residue was purified by silica gel column chromatography using ethyl ace-
tate/hexane (1:20 v/v) and subsequent recrystallization from CH2Cl2/
MeOH to produce 1 (0.520 g, 45% yield). M.p. 214–2168C; 1H NMR
(300 MHz, CDCl3): d=7.65–7.59 (m, 7H), 7.56 (d, J=8.2 Hz, 1H), 7.50
(d, J=1.3 Hz, 1H), 7.47–7.42 (m, 3H), 7.34 (t, J=7.3 Hz, 1H), 7.28–7.20
(m, 6H), 7.14–7.10 (m, 5H), 7.05 (d, J=1.0 Hz, 1H), 7.01 (t, J=7.3 Hz,
2H), 1.96 (q, J=7.2 Hz, 4H), 0.39 ppm (t, J=7.3 Hz, 6H); 13C NMR
(75 MHz, CDCl3): d=151.9, 150.7, 148.2, 147.5, 141.5, 140.9, 140.3, 136.9,
136.6, 135.8, 129.7, 129.4, 129.0, 127.6, 127.5, 127.3, 127.1, 126.2, 124.1,
123.9, 122.7, 120.8, 120.6, 119.6, 119.5, 56.3, 33.0, 8.9 ppm; FTIR (ATR):
1
Compound 5: Yield: 0.430 g, 47%; m.p. 110–1128C; H NMR (300 MHz,
CDCl3): d=7.58 (d, J=7.8 Hz, 1H), 7.55 (d, J=8.2 Hz, 1H), 7.47–7.37
(m, 7H), 7.29–7.22 (m, 6H), 7.18–7.08 (m, 11H), 7.04 (d, J=1.8 Hz, 1H),
7.00 (t, J=7.3 Hz, 2H), 2.00–1.89 (m, 4H), 1.40 (s, 9H), 1.30 (s, 9H),
0.37 ppm (t, J=7.3 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=151.8,
150.6, 150.4, 149.4, 148.2, 147.4, 141.7, 141.4, 139.9, 138.5, 137.8, 136.6,
135.9, 135.8, 130.7, 130.5, 130.1, 129.7, 129.4, 129.2, 127.8, 127.6, 126.2,
125.0, 124.8, 124.1, 123.9, 122.7, 120.7, 120.6, 119.6, 119.5, 56.3, 34.9, 34.7,
33.0, 31.7, 31.6, 8.8 ppm; FTIR (ATR): n˜ =3028, 2963, 1586, 1487, 1466,
1362, 1278, 1228, 1204, 960, 824, 756, 746, 695 cmꢀ1; MS (FAB+): m/z:
755 [M+]; HRMS (FAB+): m/z calcd for C57H57N: 755.4491 [M+]; found:
755.4479; elemental analysis calcd (%) for C57H57N: C 90.55, H 7.60, N
1.85; found: C 90.61, H 7.58, N 1.82.
n˜ =3029, 2969, 1586, 1487, 1468, 1334, 1299, 1267, 962, 822, 758, 696 cmꢀ1
;
1
Compound 6: Yield: 0.468 g, 27%; m.p. 132–1348C; H NMR (300 MHz,
MS (EI+): m/z: 567 [M+]; HRMS (EI+): m/z calcd for C43H37N: 567.2926
[M+]; found: 567.2924; elemental analysis calcd (%) for C43H37N: C
90.96, H 6.57, N 2.47; found: C 90.91, H 6.59, N 2.45.
CDCl3): d=7.69–7.62 (m, 5H), 7.60 (s, 1H), 7.57 (d, J=8.2 Hz, 2H), 7.53
(s, 1H), 7.50 (s, 6H), 7.30 (s, 2H), 7.24–7.23 (m, 2H), 7.13–7.11 (m, 5H),
7.05–6.99 (m, 3H), 2.05–1.89 (m, 4H), 1.41 (s, 36H), 0.39 ppm (t, J=
7.2 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=151.8, 151.5, 150.7, 148.2,
147.5, 143.7, 141.5, 141.1, 138.5, 136.6, 135.8, 130.2, 129.4, 127.9, 126.6,
126.3, 124.6, 124.1, 123.9, 122.7, 122.2, 121.9, 120.8, 120.6, 119.6, 119.5,
56.3, 35.3, 33.0, 31.8, 8.8 ppm; FTIR (ATR): n˜ =2963, 2870, 1588, 1494,
1467, 1278, 1249, 867, 752, 713, 697 cmꢀ1; MS (FAB+): m/z: 868 [M+];
HRMS (FAB+): m/z calcd for C65H73N: 867.5743 [M+]; found: 867.5738;
elemental analysis calcd (%) for C65H73N: C 89.91, H 8.47, N 1.61; found:
C 89.78, H 8.39, N 1.57.
Compound 7: Yield: 0.450 g, 40%; m.p. 246–2488C; 1H NMR (300 MHz,
CDCl3): d=7.76–7.70 (m, 3H), 7.62–7.46 (m, 12H), 7.28–7.23 (m, 4H),
7.13 (d, J=7.9 Hz, 4H), 7.05–6.98 (m, 4H), 2.15–1.91 (m, 8H), 1.41 (s,
18H), 0.41–0.33 ppm (m, 12H); 13C NMR (75 MHz, CDCl3): d=151.8,
151.4, 151.0, 150.6, 148.3, 147.4, 141.7, 141.4, 141.3, 141.2, 140.5, 136.7,
136.1, 129.4, 128.8, 128.5, 126.7, 126.1, 126.0, 124.1, 123.9, 122.7, 122.1,
121.9, 121.6, 120.9, 120.8, 120.6, 120.1, 1120.0, 119.6, 119.6, 56.4, 56.3,
35.3, 33.1, 33.0, 31.8, 8.9, 8.8 ppm; FTIR (ATR): n˜ =2967, 2876, 1592,
1492, 1469, 1324, 1273, 1216, 1203, 964, 873, 817, 745, 696, 660 cmꢀ1; MS
(FAB+): m/z: 823 [M+]; HRMS (FAB+): m/z calcd for C62H65N:
823.5117 [M+]; found: 823.5131; elemental analysis calcd (%) for
C62H65N: C 90.35, H 7.95, N 1.70; found: C 90.30, H 7.98, N 1.67.
1
Compound 2: Yield: 0.420 g, 67%; m.p. 200–2028C; H NMR (300 MHz,
CDCl3): d=7.65–7.59 (m, 5H), 7.56 (d, J=8.2 Hz, 1H), 7.51 (d, J=
1.2 Hz, 1H), 7.48–7.44 (m, 4H), 7.23 (m, 4H), 7.21 (d, J=2.8 Hz, 2H),
7.14–7.10 (m, 5H), 7.05 (d, J=2.1 Hz, 1H), 7.01 (t, J=7.2 Hz, 2H), 1.96
(q, J=7.4 Hz, 4H), 1.40 (s, 18H), 0.39 ppm (t, J=7.3 Hz, 6H); 13C NMR
(75 MHz, CDCl3): d=151.9, 151.4, 150.7, 148.3, 147.5, 141.6, 141.4, 140.4,
136.7, 136.6, 135.9, 129.4, 127.9, 127.5, 127.0, 126.2, 124.1, 123.9, 122.7,
121.7, 121.6, 120.8, 120.6, 119.6, 119.5, 56.3, 35.2, 33.0, 31.8, 8.9 ppm;
FTIR (ATR): n˜ =3026, 2965, 2869, 1593, 1492, 1468, 1330, 1321, 1307,
1276, 1246, 963, 877, 857, 819, 757, 743, 694, 663 cmꢀ1; MS (EI+): m/z:
679 [M+]; HRMS (EI+): m/z calcd for C51H53N: 679.4178 [M+]; found:
679.4182; elemental analysis calcd (%) for C51H53N: C 90.08, H 7.86, N
2.06; found: C 90.12, H 7.84, N 2.05.
Compound 3: Toluene (10.0 mL), EtOH (3.00 mL), and a K2CO3 solution
(3.4 mL of 2.0m) were added stepwise to a 30.0 mL, two-necked, round-
bottomed flask that contained 7-(diphenylamino)-2-(4-bromostyryl)-9,9-
diethyl-9H-fluorene (0.390 g, 0.680 mmol), [3,7-bis(1,1-dimethylethyl)-1-
naphthalenyl]boronic acid (0.300 g, 0.820 mmol), and tetrakis(triphenyl-
phosphine)palladium(0) (31.0 mg, 0.0270 mmol). The reaction mixture
was heated under reflux at 1208C for 3 h. The mixture was then extracted
with ethyl acetate and washed with water. The combined organic layers
were dried with anhydrous MgSO4, filtered, and the solvent was removed
by evaporation to dryness. The residue was purified by silica gel column
chromatography using dichloromethane/hexane (1:3 v/v) to produce com-
pound 3 (0.350 g 73% yield). M.p. 226–2288C; 1H NMR (300 MHz,
CDCl3): d=7.90 (d, J=1.6 Hz, 1H), 7.83 (d, J=8.7 Hz, 1H), 7.75 (d, J=
1.6 Hz, 1H), 7.68 (d, J=8.2 Hz, 2H), 7.64–7.50 (m, 8H), 7.29–7.23 (m,
6H), 7.18–7.10 (m, 5H), 7.06 (d, J=2.1 Hz, 1H), 7.01 (t, J=6.9 Hz, 2H),
1.97 (q, J=7.4 Hz, 4H), 1.44 (s, 9H), 1.32 (s, 9H), 0.40 ppm (t, J=7.0 Hz,
6H); 13C NMR (75 MHz, CDCl3): d=151.9, 150.7, 148.4, 148.3 147.7,
147.5, 141.5, 140.7, 139.7, 136.7, 136.6, 135.9, 132.3, 130.7, 129.7, 129.6,
129.4, 128.9, 128.2, 127.8, 127.6, 126.6, 126.5, 126.2, 124.7, 124.1, 123.9,
122.7, 122.5, 120.8, 120.6, 119.6, 56.3, 35.2, 35.1, 33.0, 31.6, 31.5, 8.9 ppm;
FTIR (ATR): n˜ =3029, 2964, 1591, 1493, 1466, 1332, 1278, 962, 881, 823,
811, 752, 695 cmꢀ1; MS (FAB+): m/z: 729 [M+]; HRMS (FAB+): m/z
calcd for C55H55N: 729.4335 [M+]; found: 729.4342; elemental analysis
calcd (%) for C55H55N: C 90.49, H 7.56, N 1.92; found: C 90.41, H 7.55,
N 1.95.
1
Compound 8: Yield: 0.370 g, 45%; m.p. 254–2568C; H NMR (300 MHz,
CDCl3): d=7.89 (d, J=6.9 Hz, 2H), 7.85 (d, J=8.1 Hz, 1H), 7.61–7.50
(m, 4H), 7.41–7.31 (m, 5H), 7.26–7.20 (m, 6H), 7.16–7.06 (m, 8H), 7.01–
6.97 (m, 5H), 6.87 (s, 2H), 6.84 (d, J=7.6 Hz, 2H), 1.90–1.85 (m, 4H),
1.29 (s, 18H), 0.31 ppm (t, J=7.2 Hz, 6H); 13C NMR (75 MHz, CDCl3):
d=151.8, 151.2, 150.5, 150.1, 149.7, 149.0, 148.2, 147.4, 142.6, 142.1, 141.3,
141.1, 140.9, 140.8, 137.6, 136.7, 135.8, 129.4, 129.1, 128.2, 128.0, 127.7,
126.6, 126.0, 124.6, 124.4, 124.1, 123.9, 123.3, 122.7, 122.0, 121.9, 121.6,
120.7, 120.5, 120.4, 120.3, 120.2, 119.6, 119.4, 76.8, 66.3, 56.2, 35.1, 32.9,
31.7, 8.8 ppm; FTIR (ATR): n˜ =3025, 2965, 2873, 1594, 1493, 1466, 1447,
1362, 1278, 1230, 1216, 1205, 961, 872, 816, 752, 696, 660, 639 cmꢀ1; MS
(FAB+): m/z: 917 [M+]; HRMS (FAB+): m/z calcd for C70H63N:
917.4961 [M+]; found: 917.4961; elemental analysis calcd (%) for
C70H63N: C 91.56, H 6.92, N 1.53; found: C 91.62, H 6.89, N 1.49.
Compound 9: Compound 21 (0.400 g, 0.870 mmol), diphenylamine
(0.203 g, 1.00 mmol), [Pd2ACHTNUTRGNE(NUG dba)3] (dba=dibenzylideneacetone; 40.0 mg,
43.0 mmol), sodium tert-butoxide (0.167 g, 1.74 mmol), and tri-tert-butyl-
phosphine (24.0 mg, 80.0 mmol) were mixed in a two-necked, round-bot-
tomed flask that contained toluene (30.0 mL). The mixture was heated
under reflux for 4 h under argon. Water was added to the mixture and
1
Compound 4: Yield: 0.420 g, 46%; m.p. 218–2208C; H NMR (300 MHz,
CDCl3): d=7.64 (t, J=8.3 Hz, 4H), 7.57 (d, J=8.1 Hz, 2H), 7.52 (d, J=
13004
www.chemeurj.org
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 12994 – 13006

Blue Organic LEDs
FULL PAPER
the solution was extracted with toluene. The combined organic extracts
were dried (MgSO4) and concentrated. Column chromatography on silica
gel (hexane/dichloromethane, 5:1) afforded compound 9 (0.250 g, 55%
yield). M.p. 138–1408C; 1H NMR (300 MHz, CDCl3): d=7.77 (d, J=
7.4 Hz, 2H), 7.70 (d, J=7.9 Hz, 1H), 7.65 (d, J=8.2 Hz, 1H), 7.52–7.49
(m, 3H), 7.43–7.40 (m, 5H), 7.33 (t, J=7.3 Hz, 1H), 7.18–7.06 (m, 7H),
7.01–6.92 (m, 8H), 6.88–6.83 (m, 4H), 6.54 (s, 1H), 1.36 ppm (s, 18H);
13C NMR (75 MHz, CDCl3): d=151.4, 150.8, 149.6, 149.0, 147.9, 147.8,
142.0, 141.6, 141.5, 140.4, 136.7, 136.6, 136.4, 129.3, 128.7, 128.1, 128.0,
127.9, 127.0, 124.3, 124.1, 122.9, 122.0, 121.7, 120.9, 120.4, 120.1, 119.9,
66.1, 35.3, 31.8 ppm; FTIR (ATR): n˜ =2961, 1594, 1482, 1467, 1303, 1270,
820, 744, 698 cmꢀ1; MS (FAB+): m/z: 773 [M+]; HRMS-TOF: m/z calcd
for C56H52N: 774.4100 [M++H]; found: 774.4115; elemental analysis
calcd (%) for C56H52N: C 91.55, H 6.64, N 1.81; found: C 91.50, H 6.65,
N 1.79.
Compound 10: Yield: 0.260 g, 76%; m.p. 140–1428C; 1H NMR
(300 MHz, CDCl3): d=7.66 (d, J=7.9 Hz, 1H), 7.59–7.53 (m, 6H), 7.50
(s, 2H), 7.44 (s, 3H), 7.22–7.18 (m, 12H), 7.12–7.05 (m, 7H), 7.03–6.06
(m, 4H), 1.39 ppm (s, 18H); 13C NMR (75 MHz, CDCl3): d=153.2,
151.6, 151.4, 147.8, 145.0, 141.7, 140.4, 140.0, 136.4, 136.3, 134.5, 129.4,
129.1, 128.5, 128.4, 128.3, 127.8, 126.9, 126.8, 126.4, 124.6, 124.5, 123.3,
123.1, 121.8, 121.7, 120.9, 120.0, 68.2, 56.6, 35.2, 31.8 ppm; FTIR (ATR):
n˜ =3030, 2963, 1591, 1491, 1468, 1282, 963, 7523, 697 cmꢀ1; MS (FAB+):
m/z: 775 [M+]; HRMS (FAB+): m/z calcd for C59H53N: 775.4178 [M+];
found: 775.4177; elemental analysis calcd (%) for C59H53N: C 91.31, H
6.88, N 1.80; found: C 91.35, H 6.83, N 1.79.
18H), 1.25 (s, 18H), 0.36 ppm (t, J=7.2 Hz, 6H); 13C NMR (75 MHz,
CDCl3): d=160.7 (dd, J
242.1 Hz), 151.6, 151.3, 151.2, 150.1, 146.9, 146.5, 141.4, 141.3, 140.2,
136.4, 135.7, 135.4, 131.4 (d, J(F,C)=6.6 Hz), 130.0 (d, J(F,C)=9.4 Hz),
129.2, 127.7, 127.1, 126.7, 125.9, 121.5, 120.8, 120.5, 120.2, 119.2, 116.5,
111.9 (d, J(F,C)=22.1 Hz), 105.3 (dd, J(F,C)=23.8, 26.0 Hz), 56.1, 35.1,
ACHUTGTNRENNUG(F,C)=11.0, 257.6 Hz), 157.4 (dd, JACHTUNGTERN(NUGN F,C)=11.8,
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
34.9, 32.9, 31.6, 31.4, 8.63 ppm; FTIR (ATR): n˜ =2963, 1593, 1505, 1465,
1428, 1141, 859, 823, 711 cmꢀ1; MS (FAB+): m/z: 828 [M+]; HRMS
(FAB+): m/z calcd for C59H67F2N: 827.5242 [M+]; found: 827.5238; ele-
mental analysis calcd (%) for C59H67F2N: C 85.57, H 8.15, N 1.69; found:
C 85.07, H 8.01, N 1.61.
Device fabrication and characterization: The device configuration of the
blue devices was indium–tin oxide (ITO, 150 nm)/N,N’-diphenyl-N,N’-bis-
[4-(phenyl-m-tolylamino)phenyl]biphenyl-4,4’-diamine (DNTPD, 60 nm)/
N,N’-di(1-naphthyl)-N,N’-diphenylbenzidine (NPB, 30 nm)/MADN:do-
pants (30 nm)/tris(8-hydroxyquinoline) aluminium (Alq3, 20 nm)/LiF
(1.0 nm)/Al (200 nm). DNTPD and NPB were hole-injection and hole-
transport materials, respectively. Alq3 was used as an electron-transport
layer and LiF/Al as a cathode. All organic materials except for dopants
were deposited at a deposition rate of 1 ꢃsꢀ1. Current (I)/voltage (V)/lu-
minance (L) characteristics and electroluminescence (EL) spectra of the
devices were measured using a Keithley 2400 source measurement unit
and CS 1000A spectrophotometer.
Compound 11: Yield: 0.220 g, 56%; m.p. 122–1248C; 1H NMR
(300 MHz, CDCl3): d=7.60 (t, J=7.3 Hz, 2H), 7.52 (t, J=7.9 Hz, 5H),
7.43 (s, 3H), 7.27–7.20 (m, 8H), 7.11–7.08 (m, 6H), 7.05–6.95 (m, 5H),
3.44 (d, J=16 Hz, 2H), 3.33 (d, J=16 Hz, 2H), 1.38 ppm (s, 18H);
13C NMR (75 MHz, CDCl3): d=154.0, 153.8, 151.4, 148.0, 147.9, 142.8,
141.6, 140.4, 139.1, 136.5, 136.2, 134.4, 129.5, 129.1, 127.9, 127.6, 127.1,
126.9, 126.1, 124.9, 124.5, 123.3, 123.1, 121.7, 120.6, 120.3, 119.6, 118.3,
57.3, 45.8, 35.2, 31.8 ppm; FTIR (ATR): n˜ =3028, 2963, 1589, 1490, 1467,
1297, 963, 898, 750, 696 cmꢀ1; MS (FAB+): m/z: 725 [M+]; HRMS
(FAB+): m/z calcd for C55H51N: 725.4022 [M+]; found: 725.4016; elemen-
tal analysis calcd (%) for C55H51N: C 90.99, H 7.08, N 1.93; found: C
90.91, H 7.10, N 1.91.
Compound 12: Yield: 0.432 g, 53%; m.p. 120–1228C; 1H NMR
(300 MHz, CDCl3): d=7.61 (s, 4H), 7.54 (d, J=8.2 Hz, 1H), 7.50–7.44
(m, 7H), 7.26–7.23 (m, 4H), 7.22 (s, 1H), 7.13–7.06 (m, 3H), 6.97 (s, 2H),
2.04–1.89 (m, 4H), 1.40 (s, 18H), 1.33 (s, 9H), 1.25 (s, 18H), 0.37 ppm (t,
J=7.3 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=151.7, 151.4, 141.6,
140.4, 136.7, 129.5, 127.9, 127.2, 126.9, 126.0, 123.4, 121.7, 119.4, 118.7,
116.6, 56.3, 35.2, 35.1, 34.5, 33.1, 31.8, 31.7, 31.6, 8.9 ppm; FTIR (ATR):
n˜ =2963, 2868, 1593, 1512, 1466, 1248, 822, 710 cmꢀ1; MS (FAB+): m/z:
847 [M+]; HRMS-TOF: m/z calcd for C68H78N: 848.6134 [M++H];
found: 848.6127; elemental analysis calcd (%) for C68H78N: C 89.20, H
9.15, N 1.65; found: C 89.15, H 9.18, N 1.62.
Acknowledgements
This research was supported by Basic Science Research Program through
the National Research Foundation of Korea (NRF) funded by the Minis-
try of Education, Science and Technology (20100007370). J.Y. Lee ac-
knowledges the NRF (grant no. 2010-0001630) funded by MEST, Repub-
lic of Korea. J.Y. Lee acknowledges the financial support from the Fun-
damental R&D Program for Core Technology of Materials (grant no.
M2009010025) funded by the MKE, GRRC program of Gyeonggi Prov-
ince (GRRC Dankook2010-B01: Materials Development for High-Effi-
ciency Solid-State Lighting) and Development of Core Technologies for
Organic Materials Applicable to OLED Lighting with High Color Ren-
dering Index by MKE.
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Compound 13: Yield: 0.328 g, 68%; m.p. 190–1928C; 1H NMR
(300 MHz, CDCl3): d=7.61 (s, 4H), 7.58 (s, 1H), 7.56 (d, J=8.1 Hz,
1H), 7.49 (d, J=7.8 Hz, 1H), 7.46–7.44 (m, 4H), 7.28–7.24 (m, 2H), 7.23
(s, 1H), 7.21–7.19 (m, 2H), 7.03–6.99 (m, 4H), 6.98–6.95 (m, 1H), 6.88
(d, J=8.1 Hz, 2H), 1.99–1.91 (m, 4H), 1.38 (s, 18H), 0.36 ppm (t, J=
7.2 Hz, 6H); 13C NMR (75 MHz, CDCl3): d=160.0 (dd, J
247.3 Hz), 158.4 (dd, J(F,C)=12.2, 254.3 Hz), 151.7, 151.2, 150.4, 147.4,
146.5, 141.4, 141.2, 140.2, 136.4, 136.3, 135.7, 131.1 (dd, J(F,C)=3.9,
10.5 Hz), 129.9 (d, J(F,C)=9.4 Hz), 129.2, 127.7, 127.3, 126.8, 125.9, 122.2,
121.7, 121.5, 120.5, 120.4, 119.3, 117.5, 112.0 (dd, J(F,C)=3.8, 22.4 Hz),
105.5 (dd, J(F,C)=23.8, 26 Hz), 56.1, 35.0, 32.8, 31.6, 8.6 ppm; FTIR
ACHTUNGTRENUN(NG F,C)=11.0,
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
(ATR): n˜ =2964, 1595, 1503, 1467, 1264, 1144, 944, 853, 821, 741, 711,
695 cmꢀ1; MS (FAB+): m/z: 715 [M+]; HRMS (FAB+): m/z calcd for
C51H51F2N: 715.3990 [M+]; found: 715.3985; elemental analysis calcd (%)
for C51H51F2N: C 85.56, H 7.18, N 1.96; found: C 85.12, H 7.02, N 1.91.
Compound 14: Yield: 0.200 g, 79%; m.p. 212–2148C; 1H NMR
(300 MHz, CDCl3): d=7.61 (s, 4H), 7.58 (s, 1H), 7.53 (d, J=8.2 Hz,
2H), 7.48 (d, J=8.2 Hz, 1H), 7.45–7.43 (m, 4H), 7.22 (d, J=2.0 Hz, 1H),
7.07 (t, J=1.6 Hz, 1H), 6.88–6.83 (m, 5H), 2.08–1.85 (m, 4H), 1.39 (s,
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