Highly efficient blue light-emitting materials based on arylamine substituted DPVBi derivatives

Article abstract of DOI:10.1166/jnn.2011.4798

A series of arylamine substituted DPVBi derivatives (1-4) were synthesized via the Horner-Wadsworth-Emmons reaction. Their electroluminescent properties were examined by fabricating a multilayer OLED device with the following structure: ITO/DNTPD (40 nm)/

Full text of DOI:10.1166/jnn.2011.4798

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Journal of
Nanoscience and Nanotechnology
Vol. 11, 7250–7253, 2011
Highly Efficient Blue Light-Emitting Materials
Based on Arylamine Substituted DPVBi Derivatives
Suhyun Oh1, Kum Hee Lee1, Ji Hyun Seo2, Young Kwan Kim2ꢀ∗, and Seung Soo Yoon1ꢀ∗
1Department of Chemistry, Sungkyunkwan University, Suwon, 440-746, Korea
2Department of Information Display, Hongik University, Seoul 121-791, Korea
A series of arylamine substituted DPVBi derivatives (1–4) were synthesized via the Horner-
Wadsworth-Emmons reaction. Their electroluminescent properties were examined by fabricating a
multilayer OLED device with the following structure: ITO/DNTPD (40 nm)/NPB (20 nm)/2% DPVBi
derivatives (1–4) doped in MADN (20 nm)/Alq3 (40 nm)/Liq (1.0 nm)/Al. All devices showed efficient
blue emission. In particular, a high efficiency blue OLED was fabricated using compound 1 as a
dopant in the emitting layer. The maximum luminance, luminous efficiency, power efficiency and CIE
coordinates of the blue OLED using compound 1 as a dopant were 16110 cd/m2 at 10 V, 10.1 cd/A
at 20 mA/cm2, 4.37 lm/W at 20 mA/cm2, and (x = 0ꢀ197, y = 0ꢀ358) at 8 V, respectively. Moreover,
a device using compound 4 as the dopant exhibited efficient deep blue emission with a luminance,
luminous efficiency, power efficiency and CIE coordinates of 7005 cd/m2 at 10 V, 6.25 cd/A at
20 mA/cm2, 2.50 lm/W at 20 mA/cm2 and (x = 0ꢀ151, y = 0ꢀ143) at 8 V, respectively.
Keywords: Blue OLEDs, DPVBi Derivatives, Horner-Wadsworth-Emmons Reaction.
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Copyright: American Scientific Publishers
1. INTRODUCTION
groups could prevent intermolecular interactions of the
emitting materials and contribute to high EL efficiency
through the suppression of concentration quenching.6
Among the four different blue materials, compounds
1 and 2 have two diphenylamine groups at the DPVBi
emitting core, whereas the other two materials 3 and 4
had the same emitting core with a diphenylamine and
carbazole group, respectively, to allow an examination of
the amine-substituents effects on device performances of
blue fluorescent OLEDs. As described herein, blue OLEDs
with high efficiency and deep blue color chromaticity
were developed using these novel blue materials based on
DPVBi.
Blue light-emitting materials have attracted considerable
interest in academic and industrial fields for applications to
light-weight, low-cost, flexible large-area OLED (organic
light-emitting diode) displays.1 However, blue-emitting
materials with a high EL efficiency of 3.1–6.5%, deep-blue
color with Commission Internationale de l’Eclairage (CIE)
y coordinate <0.15, and long operational lifetime are dif-
ficult to develop due to the wide bandgap of blue-emitting
materials.2 DPVBi (4,4ꢀ-bis(2,2-diphenylvinyl)biphenyl) is
a deep blue-emitting material for OLEDs with the CIE
coordinates of (0.15, 0.08).3 However, the EL efficiencies
of devices using DPVBi are unsuitable for widespread use.
In addition, DPVBi has a low glass transition temperature
ꢁ
(Tg; ∼64 C) and a tendency to crystallize.4 Therefore,
2. EXPERIMENTAL DETAILS
devices using DPVBi have problems with their operational
lifetime.
2.1. Synthesis of Materials
This paper describes the synthesis and electrolumines-
cent properties of arylamine-substituted DPVBi deriva-
tives (1–4). In these materials, the DPVBi core was
combined with arylamine units, which have enhanced
hole-transporting properties,5 and the EL performances of
the devices using them as emitting materials showed sig-
nificant improvement. Moreover, the bulky 1,1ꢀ-diphenyl
Diethyl (4ꢀ-(2,2,-diphenylvinyl)biphenyl-4-yl) methylphos-
phonate (A)7 (515 mg, 1.06 mmol) and bis[4-(diphenyl-
amino)phenyl]- methanone (B)8 (551 mg, 1.06 mmol) in
THF (35 mL) placed in an ice bath, KOtBu (1.17 mL,
1.17 mmol) was added under N2. The reaction mix-
ture was stirred for 30 min at 0 ꢁC, followed by
1 h at room temperature and quenched with water. It
was extracted twice with CH2Cl2 and washed twice
∗Authors to whom correspondence should be addressed.
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doi:10.1166/jnn.2011.4798

Oh et al.
Highly Efficient Blue Light-Emitting Materials Based on Arylamine Substituted DPVBi Derivatives
with water. The organic layers were dried with anhy-
drous MgSO4 and filtered. The crude mixture was puri-
fied through column chromatography using silica-gel
and recrystallization to give the desired compound. The
tetraethyl biphenyl-4,4ꢀ-diylbis(methylene)diphosphonate
(C),7 (4-(diphenylamino)phenyl)(phenyl)methane (D),9
and (4-(9-carbazole-9-yl)phenyl)(phenyl)methane (E)10
were synthesized as reported previously.
2.2. Device Fabrication and Characterization
For fabricating OLEDs, indium-tin-oxide (ITO) thin
films coated on glass substrates were used, which were
30 ꢃ/square of the sheet resistivity at a 100 nm thick-
ness. The ITO-coated glass was cleaned in an ultrasonic
bath by the following sequences: acetone, methyl alcohol,
distilled water, storage in isopropyl alcohol for 48 h, dry-
ing by an N2 gas gun. The substrates were treated by O2
plasma treatment at 2×10−2 Torr at 125 W for 2 min. All
organic materials and metals were deposited under high
vacuum (5 × 10−7 Torr). The OLEDs fabricated in this
paper had a configuration of ITO/DNTPD (40 nm)/NPB
(20 nm)/MADN: Blue dopants 1–4 (2%, 20 nm)/Alq3
(40 nm)/Liq (1.0 nm)/Al. The CIE coordinates of the
OLEDs were measured with a Keithly 2400, Chroma
meter CS-1000A. Electroluminance was measured using a
Roper Scientific Pro 300i. The UV-vis absorption spectra
were measured in a dichloromethane solution (10−5 M)
using a shimadzu UV-1650PC. The HOMO energy lev-
els were measured with a low-energy photo-electron spec-
trometer (Riken-Keiki, AC-2).The energy band gaps were
determined from the intersection of the absorption and
photoluminescence spectra. LUMO (lowest unoccupied
molecular orbital) energy levels were calculated by sub-
tracting the corresponding optical band gap energies from
the HOMO energy values.
1
1: (Yield: 60%). H-NMR (300 MHz, CDCl3ꢀ: ꢁ ppm
7.37–7.32 (m, 11H), 7.30–7.27 (m, 5H), 7.25–7.23
(m, 6H), 7.14–7.08 (m, 14H), 7.05–6.99 (m, 11H), 6.90
(s, 1H). 13C-NMR (75 MHz, CDCl3ꢀ: ꢁ ppm 147.9, 147.8,
147.5, 147.3, 143.6, 142.9, 142.2, 140.7, 138.5, 137.3,
136.6, 134.5, 131.5, 130.6, 130.2, 130.1, 129.5, 129.0,
128.5, 128.5, 128.0, 127.8, 127.7, 126.5, 126.4, 126.2,
124.8, 124.7, 123.8, 123.3, 123.2. APCI-MS (m/z): 845
[M+]. HRMS [EI+] calcd for C64H48N2: 844.3817, found:
844.3793. Anal. calcd for C 90.96,ꢁH 5.73, N 3.31; found:
C 90.90, H 5.69, N 3.37. mp 229 C.
1
2: (Yield: 72%). H-NMR (CDCl3, 300 MHz): ꢁ ppm
7.43-7.38 (m, 4H), 7.36–7.31 (m, 8H), 7.30–7.21 (m, 8H),
7.20–7.18 (m, 2H), 7.17–7.08 (m, 12H), 7.05–6.97 (m,
12H), 6.94–6.92 (m, 2H). 13C-NMR (75 MHz, CDCl3ꢀ:
ꢁ ppm 147.8, 147.8, 137.3, 134.3, 131.5, 130.6, 130.2,
130.1, 129.5, 129.0, 128.4, 128.0, 127.7, 126.4, 124.8,
123.6, 123.2, 123.2. APCI-MS (m/z): 845 [M+]. HRMS
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[EI+] calcd for C64H48N2: 844.3817, found: 844.3799.
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Anal. calcd for C 92.96, H 5.73, N 3.31; found: C 92.92,
Copyright: American Scientific Publishers
ꢁ
H 5.71, N 3.35. mp 124 C.
3. RESULTS AND DISCUSSION
1
3: (Yield: 35%). H-NMR (CDCl3, 300 MHz): ꢁ ppm
Blue compounds 1–4 were synthesized by Horner-
Wadsworth-Emmons reactions between the phosphonate
compounds and the corresponding carbonyl compounds in
moderate yield,7 as shown in Scheme 1.
Figure 1 presents the UV-vis absorption and photolumi-
nescence (PL) spectra of the blue materials 1–4 in CH2Cl2.
7.40–7.29 (m, 15H), 7.25–7.23 (m, 7H), 7.15–7.12
(m, 6H), 7.09–7.06 (m, 5H), 7.03–6.70 (m, 5H), 6.92
(s, 1H). 13C-NMR (75 MHz, CDCl3ꢀ: ꢁ ppm 147.8, 147.3,
143.7, 143.6, 142.9, 142.7, 140.7, 139.0, 138.8, 137.0,
136.6, 134.3, 131.5, 130.6, 130.2, 130.2, 129.5, 129.0,
128.5, 128.0, 127.8, 127.7, 126.5, 126.4, 124.8, 123.6,
123.2, 123.2. APCI-MS (m/z): 678 [M+]. HRMS [EI+]
calcd for C52H39N: 677.3083, found: 677.3077. Anal. calcd
for C 92.13, H 5.80, N 2.07; found: 92.10, H 5.76, N 2.05.
ꢁ
mp 202 C.
1
4: (Yield: 53%). H-NMR (CDCl3, 300 MHz): ꢁ ppm
8.68–8.65 (d, J = 8ꢂ1 Hz, 2H), 7.85–7.83 (d, J = 7ꢂ8 Hz,
5H), 7.58–7.50 (d, J = 8ꢂ1 Hz, 3H), 7.44–7.35 (m, 9H),
7.19–7.09 (m, 8H), 6.96–6.91 (t, J = 7ꢂ8 Hz, 2H), 6.74–
6.72 (d, J = 7ꢂ8 Hz, 6H), 6.67–6.64 (d, J = 7ꢂ5 Hz,
2H). 13C-NMR (75 MHz, CDCl3): ꢁ ppm 143.6, 143.2,
143.5, 141.0, 140.6, 138.8, 136.8, 136.8, 132.2, 130.6,
130.3, 130.3, 130.2, 129.2, 129.1, 129.0, 128.7, 128.5,
128.0, 127.8, 127.8, 127.4, 126.9, 126.6, 126.5, 126.5,
126.2, 126.2, 123.7, 123.7, 120.6, 120.3, 120.2, 110.1. EI-
MS (m/z): 676 [M+]. HRMS [EI+] calcd for C52H37N:
675.2926, found: 675.2919. Anal. calcd for C 92.41,
H 5.52, N 2.07; found: C 92.38, H 5.47, N 2.12. mp
Scheme 1. Synthetic routes of blue fluorescent materials 1–4. Condi-
ꢁ
114 C.
tion: (a) KOtBu, THF, 0 ꢁC to room temperature, 30 min.
J. Nanosci. Nanotechnol. 11, 7250–7253, 2011
7251

Highly Efficient Blue Light-Emitting Materials Based on Arylamine Substituted DPVBi Derivatives
Oh et al.
Fig. 2. Energy-level diagrams of OLEDs.
molecular aggregation was restrained effectively in com-
pounds 1–4 by the bulky substituent in the DPVBi emitting
core.
The HOMO/LUMO energy levels of compounds 1–4
were −5ꢂ69/ − 2ꢂ71, −5ꢂ61/ − 2ꢂ75, −5ꢂ66/ − 2ꢂ68, and
−5ꢂ94/ − 2ꢂ86 eV, respectively. The bandgap of the blue
materials (1–4) ranged from 2.86 to 3.08 eV. Figure 2
shows the HOMO and LUMO energy levels of blue fluo-
rescent materials (1–4), along with the other materials used
in the electroluminescent devices, including ITO, DNTPD,
NPB, MADN, Alq3, and LiF: Al.
Table II summarizes the electroluminescent properties
of the devices using compound 1–4 as dopants. All devices
exhibited blue emission with a maximum emission wave-
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length from 454 to 472 nm, as shown in Figure 3(a).
Copyright: American Scientific Publishers
Among devices 1–4, device 4 using dopant 4 with a car-
Fig. 1. (a) The absorption and (b) solution and film emission spectra of
compounds 1–4.
bazole moiety showed the deepest blue emission with a
CIEy value <0.15. This is compatible with the results of
PL studies in the solution and thin film states, in which
compound 4 showed the most blue-shifted emission peaks
in both states compared to compounds 1–3. The incorpora-
tion of a carbazole moiety was expected to turn the LUMO
energy level to the increase band gap (average 0.14 eV) of
the light-emitting materials.
Figure 3(b) shows the current density-luminous efficien-
cies (LE) and power efficiencies (PE) characteristics of
devices 1–4. All devices showed efficient blue emission.
The arylamine moieties with the good hole-transporting
properties and the bulky 1,1ꢀ-diphenyl groups of com-
pounds 1–4 would lead to efficient blue emission by
The maximum absorption peaks of compounds 1–4 were
located at 382, 383, 338, and 354 nm, respectively.
Figure 1(a) shows that the UV-vis absorption of the
compounds 1–4 overlapped well with the PL spectrum of
a common blue host MADN. This indicates that host in
OLED devices using these materials as dopants. In the PL
spectra in solution, the maximum emission peaks of com-
pounds 1–4 were observed at 456, 492, 494, and 451 nm,
respectively. In thin film states, the maximum peaks of
compounds 1–4 ranged from 461 to 498 nm, which is sim-
ilar to those in the dilute solution states. This suggests that
Table I. Physical properties of compounds 1–4.
Table II. EL performance characteristic of the doped-devices 1–4.
Compound
1
2
3
4
Device
1
2
3
4
UVꢄamax[nm]
382
465/498
99
5ꢂ69
2ꢂ71
383
492/489
83
5ꢂ61
2ꢂ75
338
494/481
90
5ꢂ66
2ꢂ68
354
451/461
79
5ꢂ94
2ꢂ86
EL
ꢄ
[nm]
472
16110
10ꢂ1b
10ꢂ1c
5ꢂ08b
4ꢂ37c
466
10420
8ꢂ65b
8ꢂ56c
3ꢂ96b
3ꢂ41c
458
454
max
a/b
PLꢄ [nm]
max
La [cd/m2]
LE [cd/A]
7180
6ꢂ12b
6ꢂ08c
2ꢂ86b
2ꢂ53c
7005
6ꢂ27b
6ꢂ25c
2ꢂ72b
2ꢂ50c
FWHM [nm]
HOMO[eV]
LUMO[eV]
Eg
PE [lm/W]
2ꢂ98
0ꢂ035
2ꢂ86
0ꢂ035
2ꢂ98
0ꢂ032
3ꢂ08
0ꢂ081
ꢅc
CIEd (xꢆy) (0.197, 0.358) (0.185, 0.248) (0.161, 0.182) (0.151, 0.143)
aCH2Cl2 solution (10−5 M). bThin solid film. cUsing BDAVBi as a standard; ꢄex
360 nm (ꢅ = 0ꢂ86 in CH2Cl2).
=
aMaximum luminance. Values were obtained at 10 V. bMaximum value. cAt
20 mA/cm2. dCIE (x, y) at 8.0 V.
7252
J. Nanosci. Nanotechnol. 11, 7250–7253, 2011

Oh et al.
Highly Efficient Blue Light-Emitting Materials Based on Arylamine Substituted DPVBi Derivatives
formation on the dopant materials was more effective in
devices 1 and 2 than devices 3 and 4. This indicates that
effective energy transfer between the host and dopant play
an important role in the highly efficient blue OLEDs.
4. CONCLUSION
Blue-emitting dopants based on arylamine substituted
DPVBi derivatives were synthesized. Among those, an
OLED using dopant 1 exhibited highly efficient blue emis-
sion. The device showed the maximum luminance, best
luminous efficiency, power efficiency and CIE coordi-
nates of 16,110 cd/m2 at 10 V, 10.1 cd/A at 20 mA/cm2,
4.37 lm/W at 20 mA/cm2, and (0.197, 0.358) at 8 V. In
addition, the OLED using dopant 4 exhibited a highly
efficient deep blue emission with a maximum luminance,
luminous efficiency and power efficiency of 7,005 cd/m2
at 10 V, 6.25 cd/A, and 2.50 lm/W at 20 mA/cm2. The
peak wavelength of the electroluminescence was 454 nm
with CIE coordinates of (0.151, 0.143) at 8 V.
Acknowledgment: This research was supported by
Basic Science Research Program through the NRF funded
by the Ministry of Education, Science and Technology
(20100007370).
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Received: 20 November 2010. Accepted: 10 March 2011.
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