Efficient deep-blue and white organic light-emitting diodes based on triphenylsilane-substituted anthracene derivatives

Article abstract of DOI:10.1039/c1jm12097b

A series of anthracene derivatives with a triphenylsilane end-capping group, (9,9-dimethyl-2-(10-phenylanthracen-9-yl)-9H-fluoren-7-yl)triphenylsilane (PAFTPS), 9,10-bis(9,9-dimethyl-2-(triphenylsilyl)-9H-fluoren-7-yl)anthracene (BFPSA), (9,9-dimethyl-2-(9,10-diphenylanthracen-2-yl)-9H-fluoren-7-yl) triphenylsilane (DPA-2FTPS), and (9,10-eiphenylanthracen-2-yl)triphenylsilane (DPA-2TPS), have been designed, synthesized, and characterized. A device incorporating PAFTPS as the emissive layer exhibited a high external quantum efficiency of 2.02% at 20 mA cm^-2 with color coordinates of (0.152, 0.072) as a non-doped blue emitter. At even higher efficiency, an external quantum efficiency up to 2.32% at 20 mA cm^-2 with color coordinates of (0.155, 0.076) was obtained when doped with the blue fluorescent material, 3-(N-phenylcarbazol)vinyl-p-terphenyl (PCVtPh). Furthermore, an efficient white OLED with an external quantum efficiency, a luminous efficiency and color coordinates of 4.18%, 9.14 cd A^-1 at 1000 cd m^-2 and (0.43, 0.41) at 1000 cd m^-2 was demonstrated by exploiting this highly efficient blue fluorescent material (PAFTPS) as a host in the blue emitting layer.

Full text of DOI:10.1039/c1jm12097b

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PAPER
Efficient deep-blue and white organic light-emitting diodes based on
triphenylsilane-substituted anthracene derivatives
a
Kum Hee Lee, Jeong Keun Park, Ji Hoon Seo, Se Won Park, Young Sik Kim, Young Kwan Kim
a
b
b
b
b
*
*
a
*
and Seung Soo Yoon
Received 12th May 2011, Accepted 4th July 2011
DOI: 10.1039/c1jm12097b
A series of anthracene derivatives with a triphenylsilane end-capping group, (9,9-dimethyl-2-(10-
phenylanthracen-9-yl)-9H-fluoren-7-yl)triphenylsilane (PAFTPS), 9,10-bis(9,9-dimethyl-2-
(triphenylsilyl)-9H-fluoren-7-yl)anthracene (BFPSA), (9,9-dimethyl-2-(9,10-diphenylanthracen-2-yl)-
9H-fluoren-7-yl)triphenylsilane (DPA-2FTPS), and (9,10-eiphenylanthracen-2-yl)triphenylsilane
(DPA-2TPS), have been designed, synthesized, and characterized. A device incorporating PAFTPS as
the emissive layer exhibited a high external quantum efficiency of 2.02% at 20 mA cmꢀ2 with color
coordinates of (0.152, 0.072) as a non-doped blue emitter. At even higher efficiency, an external
quantum efficiency up to 2.32% at 20 mA cmꢀ2 with color coordinates of (0.155, 0.076) was obtained
when doped with the blue fluorescent material, 3-(N-phenylcarbazol)vinyl-p-terphenyl (PCVtPh).
Furthermore, an efficient white OLED with an external quantum efficiency, a luminous efficiency and
color coordinates of 4.18%, 9.14 cd Aꢀ1 at 1000 cd mꢀ2 and (0.43, 0.41) at 1000 cd mꢀ2 was
demonstrated by exploiting this highly efficient blue fluorescent material (PAFTPS) as a host in the
blue emitting layer.
of 7.18% and CIE coordinates of (0.156, 0.088).13 Also, Lee and
Char et al. published an excellent blue host material containing
silicon-cored anthracene with an external quantum efficiency
(EQE) of 6.3% and CIE coordinates of (0.142, 0.149).14
Introduction
Since the first report by Tang and Vanslyke, there has been huge
progress in organic light-emitting diodes (OLEDs) because of
their potential applications in full-color flat-panel displays and
solid-state illumination sources.1,2 Therefore, OLED perfor-
mance has improved remarkably over the past decade.3–6 For
full-color displays, it is essential to have the three primary colors,
red, green and blue. However, because of the wide band-gap of
blue emitters, blue OLEDs show relatively poor performance
compared to red and green OLEDs. For this reason, in the
development of new OLEDs, the progress in highly efficient blue-
light emitters with good color purity is a great challenge.
Up to now, anthracene derivatives have been used widely to
fabricate highly efficient OLEDs due to their outstanding pho-
toluminescence (PL) and electroluminescence (EL) proper-
ties.10,12,15,16 Among these anthracene derivatives, 9,10-
diphenylanthracene (DPA) is an attractive material for its unity
fluorescence quantum efficiency in a dilute solution and high
fluorescence in the solid state. However, it is extremely difficult to
produce dense films or vapor deposited thin films which tend to
crystallize, resulting in a rough surface, grain boundaries or pin
holes that can lead to current leakage or catastrophic device
failure.17,18 In general, amorphous thin films (in OLEDs) with
high glass transition temperatures (Tg) are less vulnerable to
heat, resulting in more stable devices performance.19 Conse-
quently, light-emitting materials with high Tg values are desired
to retain the film morphology during operation of the device. In
this study, triphenylsilane end-capping groups were introduced
to the anthracene skeleton to improve the thermal properties,
while keeping their advantageous electronic and optical charac-
teristics. The non-planar molecular structure would prevent the
close-packing of the molecules in the solid state and enable the
formation of smooth and pinhole-free thin films.10
Recently, a range of blue emitters have been developed for
highly efficient blue OLEDs.7–9 However, there were few highly
efficient deep-blue OLEDs with a CIEy coordinate <0.10, which
can be matched to be the national television system committee
(NTSC) standard blue (0.14, 0.08).10–12 Therefore, many
researchers aim to develop deep blue-light emitters. Particularly,
Park et al. reported anthracene derivatives that contain bulky
side groups with an excellent external quantum efficiency (EQE)
aDepartment of Chemistry, Sungkyunkwan University, Suwon, 440-746,
Korea. E-mail: ssyoon@skku.edu; Fax: +82 31 290 7075; Tel: +82 31
290 7071
bDepartment of Information Display, Hongik University, Seoul, 121-791,
Korea. E-mail: kimyk@hongik.ac.kr; Fax: +82 2 3141 8928; Tel: +82 2
3142 3750
This paper reports the synthesis and full characterization of
a series of triphenylsilane-substituted anthracene derivatives,
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(9,9-dimethyl-2-(10-phenylanthracen-9-yl)-9H-fluoren-7-yl)tri-
phenylsilane (PAFTPS), 9,10-bis(9,9-dimethyl-2-(triphenylsilyl)-
9H-fluoren-7-yl)anthracene (BFPSA), (9,9-dimethyl-2-(9,10-
diphenylanthracen-2-yl)-9H-fluoren-7-yl)triphenylsilane (DPA-
2FTPS),
and
(9,10-diphenylanthracen-2-yl)triphenylsilane
(DPA-2TPS), as blue host materials for OLEDs. A (9,9-
dimethyl-9H-fluoren-7-yl) triphenylsilyl or triphenylsilyl group
was introduced to various positions of the anthracene skeleton to
cause molecular non-planarity. The non-planarity of the
molecular structure effectively suppresses the intermolecular
interactions, reduces concentration quenching and facilitates the
formation of stable, amorphous films. To examine the EL
properties of materials PAFTPS, BFPSA, DPA-2FTPS and
DPA-2TPS, multilayered OLEDs were fabricated using these
blue materials as the emitting layer (non-doped) and host
material for 40-[2-(2-diphenylamino-9,9-diethyl-9H-fluoren-7-yl)
vinyl]-p-terphenyl (PFVtPh)20 (doped) and 3-(N-phenylcarbazol)
vinyl-p-terphenyl (PCVtPh)21 (doped). Furthermore, to expand
the applicability of these blue emitting materials PAFTPS,
BFPSA, DPA-2FTPS and DPA-2TPS, a white OLED device
with the two complementary color emitting layers (e.g., sky-blue
and orange) was fabricated. Among many possible OLED device
structures to generate white emission from OLEDs based on two
complementary colors including a p/n type junction in an
asymmetric tandem OLED in series and multi-doping in a single
host in single unit OLEDs,22,23 an OLED device with the struc-
ture of the sequential stacking of two complementary color
emitting layers in single unit OLEDs using PAFTPS as a sky-
blue emitting host material is described.
Scheme 1 Synthetic routes to host materials and structure of the dopant
materials. Reagents: (i) n-BuLi, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-
dioxaborane, THF; (ii) Pd(PPh3)4, 2 M K2CO3, Toluene, Aliquat 336;
(iii) n-BuLi, THF.
Results and discussion
In this study, we present an integrated investigation encom-
passing density functional theory (DFT) molecular modeling,
material synthesis, and device characterization based on a series
of anthracene derivatives with triphenylsilane end-capping
groups. Scheme 1 shows the synthetic route of the newly designed
host compounds and the structure of the dopant compounds.
The host compounds PAFTPS, BFPSA, DPA-2FTPS and DPA-
2TPS were synthesized by Suzuki cross-coupling reactions
between 4,4,5,5-tetramethyl-2-(9,9-dimethyl-2-(triphenylsilyl)-
9H-fluoren-7-yl)-1,3,2-dioxaborolane and the corresponding
arylanthryl bromide compound in moderate yield.
376, 379, 388 and 380 nm, respectively. In addition, the
maximum emission wavelengths of PAFTPS, BFPSA, DPA-
2FTPS, and DPA-2TPS were observed at 426, 438, 430 and 420
nm, respectively. Compared to the UV-vis and PL spectrum of
PAFTPS, DPA-2FTPS showed bathochromic shifts due to the
lengthened p-conjugation by the 2-position of the anthracene
group. With the same 2-position of the anthracene unit, a red
shift in the absorption and PL maxima of DPA-2FTPS was
observed compared to DPA-2TPS. This is likely due to an
increase in conjugation because of the incorporated spacer of the
planar fluorene molecule. The full width at half maximum
(FWHM) values of the PL spectra ranged from 51 to 54 nm. Blue
emitters PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS
showed high quantum yields of 0.68, 0.67, 0.68, and 0.84,
respectively. Therefore, these compounds are excellent candi-
dates for use as efficient blue-emitting materials in OLEDs. As
shown in Fig. 1(c), the emission spectra of the PAFTPS, BFPSA,
DPA-2FTPS, and DPA-2TPS in thin films were red-shifted
compared to those in a CH2Cl2 solution due to the solid-state
effect.24 Fig. 1(b), which shows the good spectral overlap between
the absorption of PFVtPh and the emission of materials
PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS, suggests
adequate energy transfer from PAFTPS, BFPSA, DPA-2FTPS,
After purification by column chromatography and recrystal-
lization, these newly synthesized blue-emitting materials were
purified further by train sublimation at a reduced pressure below
1.33 Pa and fully characterized with 1H- and 13C-NMR, infrared,
mass spectrometry and element analysis. High-pressure liquid
chromatography analysis was carried out to check the purity of
materials. These analyses revealed that the purity of blue-emit-
ting materials is at least above 99.0%.
Fig. 1(a) shows the UV-vis absorption spectra of the blue
fluorescent materials PAFTPS, BFPSA, DPA-2FTPS, and
DPA-2TPS in dichloromethane. Fig. 1(b) and 1(c) show the PL
emission spectra of the blue fluorescent materials PAFTPS,
BFPSA, DPA-2FTPS and DPA-2TPS in dichloromethane and
quartz plates. Table 1 summarizes the results. In the UV-vis
absorption spectra, the maximum absorption wavelengths of
PAFTPS, BFPSA, DPA-2FTPS and DPA-2TPS appeared at
€
and DPA-2TPS to PFVtPh by Forster energy transfer would
occur. It indicates that PAFTPS, BFPSA, DPA-2FTPS and
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Table 1 Physical properties of the blue materials
PAFTPS
BFPSA
DPA-2FTPS
DPA-2TPS
Tg/Td/ꢁC
140/368
376
426/438
52/42
0.68
ꢀ5.86
ꢀ2.84
3.02
94/490
379
438/451
54/47
0.67
ꢀ5.83
ꢀ2.89
2.94
141/440
388
430/461
51/49
0.68
ꢀ5.65
ꢀ2.77
2.88
89/358
380
420/434
52/43
0.84
ꢀ5.90
ꢀ2.95
2.95
labs,max/nma
lem,max/nma b
,
FWHMa b
,
c
FFL
HOMOd
LUMO
Eg
e
a
Maximum absorption and emission wavelength, measured in CH2Cl2
b
c
solution (ca. 1 ꢂ 10ꢀ5 M). Measured in the film. Fluorescence
quantum yields in CH2Cl2 solution, using DPA as a standard; (F ¼
d
0.90, lex ¼ 360 nm). The HOMO energy level was determined by
e
a low-energy photoelectron spectrometer (Riken-Keiki, AC-2). Eg is
the band-gap energy estimated from the intersection of the absorption
and emission spectra.
were estimated to be ꢀ5.86, ꢀ5.83, ꢀ5.65, and ꢀ5.90 eV,
respectively. The optical energy band gaps (Eg) for these mate-
rials were 3.02, 2.94, 2.88, and 2.95 eV, respectively, as deter-
mined from the absorption spectra. The LUMO energy levels of
compounds 1, 2, 3, and 4 were calculated to be ꢀ2.84, ꢀ2.89,
ꢀ2.77, and ꢀ2.95 eV, respectively, by subtracting the optical
band gaps from the HOMO energy levels.
DFT calculations have been performed to characterize the 3D
geometries and the frontier molecular orbital energy levels of
PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS at the B3LYP/
6-31G* level by using the Gaussian 03 program.25 The calculated
geometries of PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS
in Fig. 2 show the non-planarity of their molecular structures
because of the tetrahedral environment of the tetraphenylsilane
group. The non-planar molecular structure provides steric
hindrance that prevents the intermolecular interactions between
p-systems and suppresses molecular recrystallization, which
improves the morphological stability.
Fig. 1 (a) UV-Vis absorption in CH2Cl2, (b) PL emission spectra of blue
materials in CH2Cl2, and (c) PL emission spectra of blue materials in thin
films.
DPA-2TPS perform well as host materials in OLED devices with
the PFVtPh dopant material.
The highest occupied molecular orbital (HOMO) levels were
measured using a photoelectron spectrometer (Riken-Keiki AC-
2), and the lowest unoccupied molecular orbital (LUMO) levels
were calculated by subtracting the corresponding optical band
gap energies from the HOMO values. The HOMO energy levels
of compounds PAFTPS, BFPSA, DPA-2FTPS and DPA-2TPS
Fig. 2 Three-dimensional structures and calculated HOMO and LUMO
density maps of blue materials.
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temperatures (Tg) of compounds PAFTPS, BFPSA, DPA-
2FTPS, and DPA-2TPS were determined to be 140, 94, 141, and
89 ꢁC, respectively, by DSC in the second heating scans. The high
stability of the amorphous glass state of these compounds was
attributed to the non-planarity of their molecular structures.
These results clearly show that compounds PAFTPS and DPA-
2FTPS have good thermal stability and very desirable charac-
teristics for OLEDs stability.
To evaluate the applicability of these blue fluorescent materials
(PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS) as an
Fig. 3 Energy-level diagrams of non-doped devices 1A–4A.
As shown in Fig. 2, the spatial distributions of electron
densities in the HOMO and LUMO for PAFTPS, BFPSA, DPA-
2FTPS, and DPA-2TPS are mostly localized on the anthracene
moiety. It implies that the absorption and emission process may
only be attributed to the p–p* transition centered at the
anthracene moiety. The HOMO level is increased with the
increase in the number of fluorene groups on the anthracene
molecule from PAFTPS to BFPSA, since the conjugation length
of the 9-position of anthracene ring is increased. Apparently, for
anthracene such a conjugation effect is stronger for substitution
at the 2-, 3-, 6-, and 7-positions than for substitution at the 9- and
10-positions. These results are compatible with the trend of
photophysical properties of PAFTPS, BFPSA, DPA-2FTPS,
and DPA-2TPS. The calculated HOMO energy levels of
PAFTPS, BFPSA, DPA-2FTPS and DPA-2TPS were ꢀ5.09,
ꢀ5.08, ꢀ5.04, and ꢀ5.11 eV, respectively, which is in good
agreement with the experimental values.
The thermal properties of PAFTPS, BFPSA, DPA-2FTPS,
and DPA-2TPS were measured by thermogravimetric analysis
(TGA) and differential scanning calorimetry (DSC), and are
listed in Table 1. The decomposition temperatures (Td), which
correspond to a 5% weight loss upon heating during TGA, of
blue materials PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS
were 368, 490, 440, and 358 ꢁC, respectively. The glass
Fig. 5 (a) J–V characteristics, (b) luminous efficiencies, and (c) external
quantum efficiencies as a function of current density for the non-doped
devices (1A–4A).
Fig. 4 EL spectra of the device 1A–4A at 8 V.
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emitting layer, non-doped blue emitting devices (1A–4A) were
fabricated with the following structure: ITO/NPB (50 nm)/blue
materials (30 nm)/Bphen (30 nm)/Liq (2 nm)/Al (100 nm). Fig. 3
shows the HOMO and LUMO energy levels of the blue fluo-
rescent materials, along with those of the other materials used in
electroluminescence devices, including ITO, NPB, Bphen and
Liq:Al.
The EL spectra of 1A–4A showed blue emission with peaks at
447, 446, 463 and 448 nm, respectively, as shown in Fig. 4.
Narrow EL peaks in the 1A–4A devices with FWHMs of 55, 56,
60, and 62 nm, respectively, were observed. At a driving voltage
of 8 V, the CIE coordinates of devices 2A and 3A were (0.159,
0.121) and (0.160, 0.134), respectively. In particular, the CIE
coordinates of devices 1A and 4A were (0.152, 0.072) and (0.154,
0.092), which is close to the NTSC standard blue color.
Fig. 5 shows the current density–voltage (J–V), luminous
efficiencies (LE), power efficiencies (PE), and external quantum
efficiencies (EQE) of devices 1A–4A, respectively. Table 2 lists
the EL properties of devices 1A–4A with the low turn-on voltages
<4.8 V. Device 1A exhibited the highest external quantum effi-
ciency of 2.02% (1.39 cd Aꢀ1) at 20 mA cmꢀ2 with a maximum
luminance of 1347 cd mꢀ2, which is higher than the 1.62, 1.29,
and 1.43% obtained for devices 2A, 3A, and 4A, respectively.
Interestingly, devices 1A–4A showed improved external quantum
efficiencies compared to the device using a common blue emitting
material MADN. This suggests that the non-planar molecular
structure of triphenylsilane-substituted anthracene derivatives
can effectually hinder intermolecular aggregation and prevent
the close-packing of the molecules, which can lead to enhanced
EL efficiency.
To enhance the EL efficiencies further, these materials
(PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS) were doped
with blue dopant materials (PFVtPh and PCVtPh) at 8 wt% in
Fig. 6 EL spectra of blue OLEDs at 8 V of the doped device; (a) 1B–4B;
and (b) 1C–4C.
Table 2 EL performance characteristics of A devices (non-doped)
LEa b/cd Aꢀ1
PEa b/lm Wꢀ1
EQEa b (%)
La/cd mꢀ2
Ja/mA cmꢀ2
Vonc/V
FWHMd
ELd/nm
CIEd (x, y)
,
,
,
Devices
MADN
1A
2A
3A
4A
1.24/0.98
1.73/1.39
3.01/1.72
1.73/1.52
1.89/1.22
0.98/0.46
1.26/0.69
1.84/0.67
1.22/0.73
1.41/0.62
1.35/1.25
2.42/2.02
2.67/1.62
1.41/1.29
2.06/1.43
935
1347
852
1595
981
145
202
135
215
184
4.0
4.2
4.8
4.0
4.2
55
55
56
60
63
442
447
446
463
448
(0.153, 0.080)
(0.152, 0.072)
(0.159, 0.121)
(0.160, 0.134)
(0.154, 0.092)
a
c
d
Maximum values. b At 20 mA cmꢀ2
.
Turn-on voltage at 1 cd mꢀ2
.
At 8 V.
Table 3 EL performance characteristics of B and C devices (doped)
LEa b/cd Aꢀ1
PEa b/lm Wꢀ1
EQEa b (%)
La/cd mꢀ2
Ja/mA cmꢀ2
Vonc/V
FWHMd
ELd/nm
CIEd (x, y)
,
,
,
Devices
1B
2B
3B
4B
1C
2C
3C
4C
5.17/3.91
3.03/1.71
4.71/3.58
4.76/3.71
2.61/1.68
3.19/2.11
3.19/1.86
0.94/0.94
4.20/1.76
2.62/0.84
4.72/2.01
4.31/2.01
2.41/0.85
2.51/0.95
2.95/0.96
0.66/0.59
3.87/2.96
1.60/0.93
3.23/2.49
3.41/2.70
3.37/2.32
2.19/1.54
2.63/1.64
0.91/0.91
3334
792
178
120
196
174
174
159
149
186
3.8
3.4
3.0
3.2
3.6
4.0
3.4
3.4
57
81
63
60
52
64
62
65
451
457
454
457
437
456
460
448
(0.154, 0.159)
(0.223, 0.266)
(0.159, 0.174)
(0.151, 0.174)
(0.155, 0.076)
(0.169, 0.166)
(0.158, 0.128)
(0.163, 0.115)
2341
2577
1301
1245
1036
899
a
c
d
Maximum values. b At 20 mA cmꢀ2
.
Turn-on voltage at 1 cd mꢀ2
.
At 8 V.
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the same device structure, respectively. Table 3 lists the EL
properties of devices 1B–4C. In terms of the EL efficiency, the B
devices with PFVtPh as the dopant material were more effective
than the C devices with PCVtPh as the dopant material.
Fig. 6 shows the EL spectra of the devices B (8 wt% PFVtPh-
doped) and C (8 wt% PCVtPh-doped). Fig. 7 shows the J–V, LE,
and EQE of the doped devices (1B–4C), respectively. Compared
to the corresponding non-doped devices, all B devices using
PFVtPh as a dopant showed improved EL efficiency, whereas the
CIE-coordinates were red-shifted. This suggests that the EL
emissions of the B devices originate from the emission of PFVtPh
As shown in Fig. 1(b), the emission spectra of the host mate-
rials 1–4 overlapped better with the absorption spectra of
€
PFVtPh than those of PCVtPh. This indicates that Forster-type
€
by Forster type energy transfer between the dopant and corre-
energy transfer enables PFVtPh to accept energy from the host
materials 1–4 more effectively than PCVtPh. This leads to the
improved EL efficiency of device B compared to device C,
because the emissions from devices 1B–4C using host-dopant
sponding hosts. The change in CIE coordinates of the B devices
would contribute to the differences in the solvation state in solid-
state devices using different hosts. Device 1B, which used the
(9,9-dimethyl-9H-fluoren-7-yl) triphenylsilyl end-capping group
at the 9-position of the anthracene group (PAFTPS) as a host,
exhibited the highest EQE of 2.96% with a luminous efficiency
and a power efficiency of 3.91 cd Aꢀ1 and 1.76 lm Wꢀ1 at 20 mA
cmꢀ2, respectively, which is higher than the corresponding values
of 0.93%, 2.49%, and 2.70% for devices 2B, 3B, and 4B. At
a driving voltage of 8 V, the CIE coordinates of device 1B were
(0.154, 0.159). In the case of device C, the best EQE of 2.32%
with a luminous efficiency and a power efficiency of 1.68 cd Aꢀ1
and 0.85 lm Wꢀ1 at 20 mA cmꢀ2, respectively, was obtained in
device 1C, which used PAFTPS as a host. In particular, the CIE
coordinates of device 1C (0.155, 0.076) were similar to the
standard blue emission recommended by the NTSC. As a result,
devices 1A, 1B and 1C using PAFTPS showed higher EL
performance and color purity in all devices. Interestingly, the EL
spectra of device 2B showed shoulder peaks at 594 and 650 nm,
which are different from the BFPSA host device. The shoulder
peak emission observed in device 2B might be due not only to an
excimer from the intermolecular interactions but also to the
exciplex in the device interfaces as a result of the ineffective
energy transfer from BFPSA to the dopant.
€
emitting systems originate from dopant materials by Forster-
type energy transfer from the host to dopant.11
Efficient blue emitting materials are needed to realize efficient
white light emission from OLEDs. Among the blue emitting
materials (PAFTPS, BFPSA, DPA-2FTPS, and DPA-2TPS) in
this study, PAFTPS is the most suitable candidate owing to its
high EL efficiency and color purity. Multilayered WOLEDs were
fabricated with the device 1D structure as follows: ITO/DNTPD
Fig. 7 (a) J–V characteristics, (b) luminous efficiencies, and (c) external
quantum efficiencies as a function of current density for the doped
devices (1B–4C).
Fig. 8 External quantum efficiency–current density curves of the
WOLEDs fabricated from DAF-ph and PAFTPS (inset) EL spectra of
the WOLEDs at 1000 cd mꢀ2
.
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(60 nm)/NPB (20 nm)/CBP:iridium(III) bis(5-acetyl-2-phenyl-
pyridine)acetylacetonate (Ir(acppy)2acac) (8 wt%, 5 nm)/CBP
(5 nm)/PAFTPS: 1,4-bis(2-diphenylamino-9,9-diethylfluoren-
7-ylethenyl)benzene (DAF-ph) (5 wt%, 25 nm)/Bphen (30 nm)/
Liq (2.0 nm)/Al (100 nm). In this study, the blue material DAF-
ph was used as a dopant in a PAFTPS host in the blue emitting
layer.26 In addition, CBP was used as the host material for the
dopant and Ir(acppy)2(acac) in the red emitting layer.27 Fig. 8
compounds were measured using a low-energy photo-electron
spectrometer (Riken-Keiki, AC-2). The LUMO energy levels
were estimated by subtracting the energy band gap from the
HOMO energy levels. The energy band gap was determined by
the on-set absorption energy from the absorption spectra of the
materials. The thermal properties were measured by thermog-
ravimetric analysis (TGA) (DTA-TGA, TA-4000) and differen-
tial scanning calorimetry (DSC) (Mettler Toledo; DSC 822)
under N2 at a heating rate of 10 ꢁC minꢀ1. A heat-cold-heat
shows the EQE and EL spectra of the WOLEDs at 1000 cd mꢀ2
.
Device 1D with CIE coordinates of (0.43, 0.41) exhibited
a luminous efficiency, a power efficiency and an external
quantum efficiency of 9.14 cd Aꢀ1, 3.44 lm Wꢀ1 and 4.18%,
respectively, at 1000 cd mꢀ2. This study demonstrates that an
anthracene derivative PAFTPS has excellent properties for effi-
cient blue fluorescent OLEDs as well as white OLEDs.
method was used with an initial heating rate of 10 ꢁC minꢀ1
,
rapidly quenched-cooled in liquid nitrogen, and finally heated at
ꢁ
a rate of 10 C minꢀ1
.
General procedure for the Suzuki cross-coupling reaction
4,4,5,5-Tetramethyl-2-(9,9-dimethyl-2-(triphenylsilyl)-9H-flu-
oren-7-yl)-1,3,2-dioxaborolane (1.2 or 2.4 mol) and the corre-
sponding arylanthryl bromide derivatives (1.0 mol), Pd(PPh3)4
(0.04 mol), aqueous 2.0 M K2CO3 (10.0 mol), Aliquat 336 (0.1
mol), and toluene were mixed in a flask, and heated under reflux
for 4 h. After the reaction was complete, the reaction mixture was
extracted with ethyl acetate and washed with water. The organic
layer was dried with anhydrous MgSO4 and filtered with silica
gel. The solution was then evaporated. The crude product was
then recrystallized from CH2Cl2/EtOH.
Conclusions
Four anthracene derivatives with triphenylsilane end-capping
groups, which have enhanced thermal and morphological
stability, were synthesized. The PAFTPS-based non-doped
device exhibited efficient blue emission with CIE coordinates of
(0.152, 0.072), which are very close to the NTSC standard. In
addition, an efficient deep blue OLED with color coordinates of
(0.155, 0.076) was obtained using PAFTPS as a host and 3-(N-
phenylcarbazol)vinyl-p-terphenyl (PCVtPh) as a blue dopant.
Furthermore, an efficient white OLED with a external quantum
efficiency, luminous efficiency and color coordinates of 4.18%,
9.14 cd Aꢀ1 at and (0.43, 0.41) at 1000 cd mꢀ2 was fabricated by
exploiting this highly efficient blue fluorescent material
(PAFTPS) as a host in the blue emitting layer.
(9,9-Dimethyl-2-(10-phenylanthracen-9-yl)-9H-fluoren-7-yl)tri-
phenylsilane (PAFTPS). Yield: 89%, 1H-NMR (300 MHz,
CDCl3): d (ppm) 7.96 (d, J ¼ 7.5 Hz, 1H), 7.85 (d, J ¼ 7.5 Hz,
1H), 7.79 (dd, J ¼ 3.3 Hz, 6.9 Hz, 2H), 7.73–7.69 (m, 3H), 7.65
(dd, J ¼ 1.8 Hz, 8.1 Hz, 7H), 7.61–7.55 (m, 4H), 7.51–7.46 (m,
4H), 7.45–7.41 (m, 7H), 7.40–7.38 (m, 1H), 7.33 (dd, J ¼ 3.3, 6.9
Hz, 4H), 1.51 (s, 6H). 13C-NMR (75 MHz, CDCl3): d (ppm)
154.5, 153.4, 140.8, 139.3, 138.7, 138.5, 137.8, 137.4, 136.7, 135.7,
134.8, 133.2, 131.6, 130.7, 130.5, 130.2, 130.1, 129.9, 128.7, 128.2,
127.7, 127.3, 126.1, 125.3, 125.2, 120.5, 119.8, 47.3, 27.4. FT-IR
(ATR cmꢀ1): 2981, 2972, 1738, 1429, 1387, 1055, 1033, 1013, 771,
703; MS (FAB+, m/z): 704 [M+]; Anal. Calcd: C, 90.30; H, 5.72.
Found: C, 89.18; H, 6.05%.
Experimental section
General information
Unless stated otherwise all solvents were dried using standard
procedures and all reagents were used as received from
commercial sources. All reactions were performed under a N2
atmosphere. 9,10-Dibromoanthracene, 2-bromo-9,10-dipheny-
lanthracene (D), and chlorotriphenylsilane were used as received
from Aldrich or TCI. (2-Bromo-9,9-dimethyl-9H-fluoren-7-yl)
triphenylsilane (A),28 10-bromo-9-phenylanthracene (C),29 40-[2-
(2-diphenylamino-9,9-diethyl-9H-fluoren-7-yl)vinyl]-p-terphenyl
9,10-Bis(9,9-dimethyl-2-(triphenylsilyl)-9H-fluoren-7-yl)anth-
racene (BFPSA). Yield: 86%, 1H NMR (300 MHz, CDCl3):
d (ppm) 7.97 (d, J ¼ 7.8 Hz, 2H), 7.86 (d, J ¼ 7.2 Hz, 2H), 7.79
(dd, J ¼ 3.3 Hz, 6.9 Hz, 4H), 7.30 (s, 2H), 7.67–7.63 (m, 12H),
7.61–7.60 (m, 2H), 7.56 (d, J ¼ 6.9 Hz, 2H), 7.49–7.38 (m, 20H),
7.35 (dd, J ¼ 3.3 Hz, 6.9 Hz, 4H), 1.52 (s, 12H); 13C NMR (75
MHz, CDCl3): d (ppm) 154.5, 153.4, 140.7, 138.7, 138.5, 137.8;
136.7, 135.7, 134.8, 133.2, 130.7, 130.4, 130.3, 129.8, 128.1, 127.3,
125.3, 120.4, 119.8, 47.3, 27.4; FT-IR (ATR, cmꢀ1): 2970, 1738,
1366, 1217, 1108, 815, 770, 746, 700; MS (FAB+, m/z): 1078 [M+];
Anal. Calcd: C, 89.01; H, 5.79. Found: C, 87.53; H, 5.96%.
(PFVtPh),20
and
3-(N-phenylcarbazol)vinyl-p-terphenyl
(PCVtPh)21 were prepared using a method reported elsewhere.
The 1H- and 13C-nuclear magnetic resonance (NMR) spectra
were recorded on a Varian Unity Inova 300Nb spectrometer. All
FT-IR spectra were recorded using a Bruker VERTEX70 FT-IR
spectrometer. Elemental analysis (EA) was measured using an
EA 1108 spectrometer. The low resolution mass spectra were
measured using a Jeol JMS-AX505WA spectrometer in FAB
mode and a JMS-T100TD (AccuTOF-TLC) in positive ion
mode. The UV-Vis absorption and photoluminescence spectra of
the newly designed host materials were measured in a CH2Cl2
solution (10ꢀ5 M) using a Shimadzu UV-1650PC and an Amin-
cobrowman series 2 luminescence spectrometer. The fluorescent
quantum yields were determined in a CH2Cl2 solution at 293 K
against 9,10-diphenylanthracene as the standard (F ¼ 0.90).30
The ionization potentials (or HOMO energy levels) of the
(9,9-Dimethyl-2-(9,10-diphenylanthracen-2-yl)-9H-fluoren-7-yl)-
triphenylsilane (DPA-2FTPS). Yield: 82%, 1H NMR (300 MHz,
CDCl3): d (ppm) 7.95 (s, 1H), 7.80 (d, J ¼ 9.1 Hz, 1H), 7.71–7.65
(m, 7H), 7.60 (d, J ¼ 7.5 Hz, 11H), 7.55–7.53 (m, 5H), 7.52–7.50
(m, 2H), 7.44–7.38 (m, 5H), 7.37–7.32 (m, 6H), 1.42 (s, 6H); 13
C
NMR (75 MHz, CDCl3): d (ppm) 154.8, 153.4, 140.9, 140.5,
139.3, 139.2, 138.6, 137.9, 137.7, 137.3, 136.7, 135.7, 134.7, 133.1,
13646 | J. Mater. Chem., 2011, 21, 13640–13648
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131.7, 131.6, 130.6, 130.4, 130.2, 129.8, 129.3, 128.7, 128.1, 127.9,
127.8, 127.3, 127.2, 126.7, 125.4, 125.3, 124.8, 121.8, 120.9, 119.8,
47.2, 27.4; FT-IR (ATR, cmꢀ1): 2970, 1739, 1428, 1374, 1108,
817, 744, 699; MS (FAB+, m/z): 780 [M+]; Anal. Calcd: C, 90.73;
H, 5.68. Found: C, 89.6; H, 5.85%.
Acknowledgements
This research was supported by Basic Science Research Program
through the NRF funded by the Ministry of Education, Science
and Technology (20110004655).
(9,10-Diphenylanthracen-2-yl)triphenylsilane
(DPA-2TPS).
Notes and references
1
Yield: 55%, H NMR (300 MHz, CDCl3): d (ppm) 7.94 (s, 1H),
7.74–7.67 (m, 3H), 7.61–7.52 (m, 4H), 7.50–7.47 (m, 8H), 7.39
(dd, J ¼ 2.4 Hz, 6.6 Hz, 5H), 7.36–7.28 (m, 10H), 7.26–7.25 (m,
1H); 13C NMR (75 MHz, CDCl3): d (ppm) 138.1, 136.5, 134.2,
131.6, 131.3, 130.5, 129.7, 129.4, 128.6, 128.4, 128.0, 127.7, 127.4,
127.2, 125.9, 125.5, 125.2; FT-IR (ATR, cmꢀ1): 2970, 2948, 1739,
1366, 1217, 1033, 760, 746, 697 cmꢀ1; MS (EI+, m/z): 589 [M+ H];
Anal. Calcd: C, 89.75; H, 5.48. Found: C, 87.4; H, 5.92.
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2-isopropoxy-4,4,5,5,-tetramethyl-1,3,2-dioxaborolane
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153.4, 142.2, 140.7, 136.7, 135.5, 134.7, 134.1, 133.8, 130.7, 129.8,
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following sequence: acetone, methyl alcohol, distilled water. The
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€
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(50 nm)/blue-emitting materials (30 nm)/4,7-diphenyl-1,10-phe-
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were measured using a Keithley 2400, Chroma meter CS-1000A.
The electroluminance was measured using a Roper Scientific
Pro 300i.
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