Efficient red organic light-emitting diodes using 2-(2-(4-Pentylbicyclo[2. 2.2]octan-1-yl)-6-(2-(1,1,7-trimethyl-7-triphenysiliyllethyl-1,2,3,5,6, 7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)vinyl)-4Hpyran- 4-ylidene)malononitrile as a fluorescent red emitter

Article abstract of DOI:10.1080/15421406.2011.599758

The authors have demonstrated red organic light-emitting diodes (OLEDs) using a new fluorescent red emitter, 2-(2-(4-pentylbicyclo[2.2.2]octan-1-yl)-6- (2-(1,1,7-trimethyl- 7-triphenysiliyllethyl-1,2,3,5,6,7-hexahydropyrido[3,2,1- ij]quinolin-9-yl)vinyl)-4Hpyran- 4-ylidene)malononitrile (DCJTPSO), achieved the maximum external quantum efficiency (EQE) of 2.06%, current efficiency (CE) of 3.83 cd/A, and Commision Internationale De L'Eclairage (CIE_x,y) coordinates of (0.58, 0.40) at 0.029 mA/cm² in comparison with control device using 4-(dicyanomethylene)-2-tert-butyl- 6-(1,1,7, 7-tetramethyljulolidin-4-yl-vinyl)- 4H-pyran which showed the maximum EQE of 1.07%, CE of 1.41 cd/A and CIE_x,y coordinates of (0.61, 0.38) at 0.11 mA/cm². This result showed that the high performance of red device using DCJTPSO showed easier electron trapping directly on the emitter molecule. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15421406.2011.599758

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Efficient Red Organic Light-
Emitting Diodes Using 2-(2-(4-
Pentylbicyclo[2.2.2]octan-1-
yl)-6-(2-(1,1,7-trimethyl-7-
triphenysiliyllethyl-1,2,3,5,6,7-
hexahydropyrido[3,2,1-
ij]quinolin-9-yl)vinyl)-4H-pyran-4-
ylidene)malononitrile as a Fluorescent
Red Emitter
a
a
a
a
Bo Min Seo , Ji Hoon Seo , Jun Ho Kim , Jung Sun Park , Kum-
a
a
b
a
Hee Lee , Min Hye Park , Seung Soo Yoon & Young Kwan Kim
a
Department of Information Display , Hongik University , Seoul ,
1
21-791 , Korea
b
Department of Chemistry , Sungkyunkwan University , Suwon ,
Gyungi-do , 440-746 , Koea
Published online: 18 Oct 2011.
To cite this article: Bo Min Seo , Ji Hoon Seo , Jun Ho Kim , Jung Sun Park , Kum-Hee Lee , Min
Hye Park , Seung Soo Yoon & Young Kwan Kim (2011) Efficient Red Organic Light-Emitting Diodes
Using 2-(2-(4-Pentylbicyclo[2.2.2]octan-1-yl)-6-(2-(1,1,7-trimethyl-7-triphenysiliyllethyl-1,2,3,5,6,7-
hexahydropyrido[3,2,1-ij]quinolin-9-yl)vinyl)-4H-pyran-4-ylidene)malononitrile as a Fluorescent Red
Emitter, Molecular Crystals and Liquid Crystals, 550:1, 233-239, DOI: 10.1080/15421406.2011.599758
To link to this article: http://dx.doi.org/10.1080/15421406.2011.599758
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Mol. Cryst. Liq. Cryst., Vol. 550: pp. 233–239, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.599758
Efficient Red Organic Light-Emitting Diodes Using
2
-(2-(4-Pentylbicyclo[2.2.2]octan-1-yl)-6-(2-(1,1,7-
trimethyl-7-triphenysiliyllethyl-1,2,3,5,6,7-
hexahydropyrido[3,2,1-ij]quinolin-9-yl)vinyl)-4H-
pyran-4-ylidene)malononitrile as a Fluorescent
Red Emitter
1
1
1
BO MIN SEO, JI HOON SEO, JUN HO KIM,
1
1
1
JUNG SUN PARK, KUM-HEE LEE, MIN HYE PARK,
SEUNG SOO YOON, AND YOUNG KWAN KIM
2
1,∗
1
Department of Information Display, Hongik University, Seoul 121-791, Korea
Department of Chemistry, Sungkyunkwan University, Suwon,
2
Gyungi-do 440-746, Koea
The authors have demonstrated red organic light-emitting diodes (OLEDs) using a new
fluorescent red emitter, 2-(2-(4-pentylbicyclo[2.2.2]octan-1-yl)-6-(2-(1,1,7-trimethyl-
7
-triphenysiliyllethyl-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)vinyl)-4H-
pyran-4-ylidene)malononitrile (DCJTPSO), achieved the maximum external quantum
efficiency (EQE) of 2.06%, current efficiency (CE) of 3.83 cd/A, and Commision
Internationale De L’Eclairage (CIEx,y) coordinates of (0.58, 0.40) at 0.029 mA/cm2
in comparison with control device using 4-(dicyanomethylene)-2-tert-butyl- 6-(1,1,7,
7
1
-tetramethyljulolidin-4-yl-vinyl)- 4H-pyran which showed the maximum EQE of
.07%, CE of 1.41 cd/A and CIEx,y coordinates of (0.61, 0.38) at 0.11 mA/cm . This
2
result showed that the high performance of red device using DCJTPSO showed easier
electron trapping directly on the emitter molecule.
Keywords light-emitting diode; Red organic lighting emitting diodes; 2-(2-(4-
pentylbicyclo[2.2.2]octan-1-yl)-6-(2-(1,1,7-trimethyl-7-triphenysiliyllethyl-1,2,3,5,6,
7
-hexahydropyrido[3,2,1-ij]quinolin-9-yl)vinyl)-4H-pyran-4-ylidene)malononitrile;
charge carrier trapping directly
Introduction
Since the first application of a multilayer structure in organic light-emitting diodes (OLEDs)
by Tang and Vanslyke, OLEDs have attracted considerable interest due to their easy process-
ability, flexibility, thinness, low operating voltages, high resolution, wide viewing angles,
and fast response time [1]. So OLED have become a technology for the next generation
full color flat-panel displays [2–7]. Many researchers have investigated fluorescent and
phosphorescent green emitters for high device performance in OLED [8, 9]. However, the
fluorescent red and blue emitters have remained to be weaker part in realizing the full color
∗
Corresponding author. E-mail: kimyk@hongik.ac.kr
233

234
B. M. Seo et al.
display with low efficiency and dissatisfied color purity. Therefore, red emitters are still
rare. In this paper, a new red fluorescent material,2-(2-(4-pentylbicyclo[2.2.2]octan-1-yl)-6-
(2-(1,1,7-trimethyl-7-triphenysiliyllethyl-1,2,3,5, 6,7-hexahydropyrido[3,2,1-ij]quinolin-
9-yl)vinyl)-4H-pyran-4-ylidene)malononitrile (DCJTPSO) was sythesized and studied. The
optimized fluorescent red device using DCJTPSO achieved the maximum external quantum
efficiency (EQE) of 2.06%, Current efficiency (CE) of 3.83 cd/A, and Commision Interna-
2
tionale De L’Eclairage (CIEx,y) coordinates of (0.58, 0.40) at 0.029 mA/cm , respectively.
Experimental
Synthesis
Synthesis of (N-2-ethylhexyl)-3(6)-phenothiazinylene vinylene-co-9,10-anthrylene viny-
lene) (KPD-1). Firstly N-(2-ethylhexyl)phenothiazine (EHPZ) was synthesized from the
reaction of phenothiazine (6 g, 0.03 mol) and 2-ethylhexylbromide (5.8 g, 0.03 mol) in
the presence of sodium hydroxide (7.2 g, 0.18 mol) in dimethylsulfoxide (60 ml) at room
temperature for 3 h.11 Yield: 73%. H NMR(CDCl3), δ: 6.87, 7.12 (m, 8H, Ar-H), 3.70 (m,
1
2
H, N-CH2-), 1.93 (t, 1H, CH-), 1.22–1.44 (m, 9H, -CH2-), 0.83–0.87 (m, 6H, -CH3), IR
−1
(KBr), cm : 3064 (Ar CH), 2926 (aliphatic CH), 2857 (N-CH2-), 1593, 1485 (Ar C=C).
N-(2-Ethylhexyl)-3(6)-formylphenothiazine (EHFZ) was synthesized using modified
1
Vilsmeier-Haack formylation in the second step [6, 7]. Yield : 45%, H NMR(CDCl3),
δ: 9.73 (m, 2H, aldehydic hydrogen), 6.88, 7.56 (m, 6H, Ar H), 3.73 (t, 2H, N-CH2-),
−1
1
.17–1.85 (m, 9H, -CH2-, CH-), 0.76–0.82 (m, 6H, -CH3), IR (KBr), cm : 3048 (Ar
CH; weak signal), 2927 (aliphatic CH), 2857 (N-CH2-), 2724 (aldehydic hydrogen), 1688
C=O), 1600, 1465 (Ar C=C).
(
Figure 1. (a) Molecular structure of the key materials used for fabrication. (b) The energy diagram
of the red OLEDs in this study.

Efficient Red OLEDs Using DCJTPSO
235
9
,10-(Chloromethyl)anthracene (4.8 g, 0.014 mol) was reacted with triethylphosphite
◦
(
30g, 0.18 mol) at 120 C for 12 h. The unreacted triethylphosphite was removed under re-
duced pressure. 9,10-Bis(diethoxyphosphinylmethyl)antrhracene (PHAN) was obtained
as yellow crystal. Yield: 92%. H NMR (CDCl3), δ: 7.57, 8.38 (m, 8H, Ar H), 4.23 (d, 8H,
12
1
-
CH2O-P-), 3.84 (m, 4H, Ar-CH2-P), 1.06 (t, 12H, -CH3), IR (KBr), cm-1: 3026 (Ar CH),
2
983 (aliphatic CH), 1251 (P=O).
As presented in Scheme 1 (a), KPD-1 was synthesized with adding potassium tert-
butoxide (4.73 g, 0.04 mol) solution into a mixture of EHFZ (1.70 g, 0.005 mol) and PHAN
1
(
1.20g, 0.0025 mol) in THF, and then stirring at room temperature for 7 h. Yield: 51%, H
−1
NMR (CDCl3), δ: 6.94 (m, 4H, =CH-), IR (KBr), cm : 3021 (Ar CH), 2924 (aliphatic
CH), 2855 (N-CH2-), 1578, 1471 (Ar C=C), 965 (trans vinylene).
Poly(BFMP12-AV) alternating copolymer, as shown in Scheme 1 (b), was obtained by
Horner-Emmons condensation reaction [5, 8, 9].
Fabrication of PLED
Indium tin oxide (ITO)-coated glass was cleaned in an ultrasonic bath by the following se-
quence: in acetone, methanol, distilled water and isopropyl alcohol. Thereafter, pre-cleaned
−
7
2
ITO was treated by O2 plasma with the conditions of 2 × 10 Torr, 125 W for 2 min.
−
All devices were fabricated using the high vacuum (5 × 10 Torr) thermal evaporation
of organic materials onto the surface of the ITO-coated glass substrate (15 ꢀ/sq, emitting
area was 3 mm x 3 mm). The deposition rates were 1.0 ∼ 1.1 Å/sec for organic materials
and 0.1 Å/sec for lithium quinolate (Liq), respectively. After the deposition of the organic
layers without a vacuum break the Al cathode was deposited at a rate of 10 Å/sec. With
the DC voltage bias, the optical and electrical properties of OLEDs such as the current
density, luminance, CE, and electroluminescence (EL) spectra of the emission characteris-
tics were measured with Keithley 236 and CHROMA METER CS-1000A instruments. The
Figure 2. Current density versus voltage characteristics of device A and B. Inset: Luminance versus
voltage characteristics of device A and B.

236
B. M. Seo et al.
UV-Visible absorption spectra were measured in 1.2-dichloroethane solution (10−5 M) using
a Shimadzu UV-1650PC. The photoluminescence (PL) were obtained in 1.2-dichloroethane
−5
solution (10 M) and thin film using an Amincobrowman series 2 luminescence spec-
trometer. The fluorescent quantum yields were determined in 1.2-dichloroethane solution
at 293 K against 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-
vinyl)-4H-pyran (DCJTB) (Ф = 0.78) as a reference. All measurements were carried out
under ambient conditions at room temperature.
Figure 3. (a) EQE versus current density characteristics of device A and B. (b) CE versus current
density characteristics of device A and B.

Efficient Red OLEDs Using DCJTPSO
237
Figure 4. (a) UV/visible absorption spectrum of DCJTB and PL spectrum of MADN. (b) UV/visible
absorption spectrum of DCJTPSO and PL spectrum of MADN.
Results and Discussion
Figure 1 (a) shows the molecular structure of key materials used for fabrication, 2-
methyl-9, 10-di(2-naphthyl)anthracene (MADN), DCJTB (device A), and DCJTPSO (de-
vice B), respectively. Figure 1 (b) shows energy level diagram of two devices with
the structure of ITO/N,N’-bis(naphthalen-1-yl)-N,N’-bis(phenyl)-benzidine (NPB) (500
Å)/DCJTB:MADN (300 Å, 5%, device A) or DCJTPSO:MADN (300 Å, 5%, device
B)/bis-(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminium (BAlq) (300 Å)/Liq(20
Å)/Al(1000 Å), respectively. The doping concentrations of DCJTB and DCJTPSO in
MADN were optimized to 5%, respectively. NPB, MADN, BAlq and Liq were used for hole
transporting layer, red host, electron transporting layer (ETL), and electron injection layer,
respectively. DCJTB and DCJTPSO were also used for fluorescent red emitter, respectively.
Figure 2 shows current density versus voltage characteristics of device A and B. Inset
Fig 2 shows luminance versus voltage characteristics of device A and B. Device A and B

238
B. M. Seo et al.
Figure 5. (a) CIEx,y coordinates versus voltage characteristics of device A and B from 5 to 12 V.
b) EL spectra of device A and B at 1000 cd/m2.
(
2
showed the current density of 50.1 and 265 mA/cm at 13 V, respectively. Seeing that the
highest occupied molecular orbital and the lowest occupied molecular of red dopant, the
carrier injection barrier are 0.5 eV for electrons and only 0 eV for holes. From the electron
carrier point of view, there is the direct electron injection from the ETL to the red emitter.
Also the red device B using DCJTPSO showed higher current density than that of the red
device A with same device structure.
This result showed carrier injection of the devices B is better than that of the device
A. Figure 3 (a) and (b) show the EQE and CE versus current density characteristics of two
devices. Device A and B had a maximum EQE of 1.07 and 2.06% and CE of 1.41 and 3.83
2
cd/A at 0.11, 0.03 mA/cm , respectively. They also exhibited a EQE of 0.84 and 1.49% and
2
CE of 1.13 and 2. 90 cd/A at 10 mA/cm , respectively.

Efficient Red OLEDs Using DCJTPSO
239
Figure 4 (a) and (b) show the UV/visible absorption spectra of DCJTB (device A) and
DCJTPSO (device B) and PL spectrum of MADN, respectively. The UV/visible absorption
of DCJTPSO and PL spectra MADN showed almost the same spectra overlap in comparison
of them of DCJTB and MADN. This result indicated similar efficient F o¨ rster singlet energy
transfer from MADN to the red emitter.
However, PL quantum yield of DCJTPSO(0.97) showed higher than that of
DCJTB(0.78). As a result, the performance of the red device B using the DCJTPSO is
better performance than that of the red device A with same device structure.
Figure 5 (a) shows the CIEx,y coordinates changes of two devices from 5 to 12 V.
Devices A and B showed CIEx,y coordinates of (0.61, 0.39) and (0.58, 0.41) at 13 and 9 V,
respectively.
2
Figure 5 (b) shows the EL spectra of two devices at 1000 cd/m . Device A and B had
a red peak at 615 and 601 nm for DCJTB and DCJTPSO, respectively. Device A showed
more redwish emission than device B.
Conclusions
In this study, we demonstrated efficient red OLEDs using a new fluorescent red emitter,
DCJTPSO. The optimaized red device using DCJTPSO showed higher EQE of 2 times and
CE of 2.7 times than control red device using DCJTB. This result indicated similar efficient
F o¨ rster singlet energy transfer from MADN to the red device using DCJTB or DCJTPSO
because the UV/visible absorption of DCJTPSO and PL spectra MADN showed almost
the same spectra overlap in comparison with them of DCJTB and MADN. However, PL
quantum yield of DCJTPSO(0.97) showed higher than that of DCJTB(0.78). This process
of device B on charge easier electron trapping directly on the emitter molecule also resulted
in a more efficient performance than that of device A.
As a result, the performance of the red device B using the DCJTPSO is better than that
of the red device A with same device structure.
Acknowledgment
This work was supported by 2009 Hongik University Reserch Fund and the ERC program
of the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea
Ministry of Education, Science and Technology (MEST) and (No. R11-2007-045-03001-0).
References
[
[
[
1] C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett. 51, 913 (1987).
2] J. Kido, K. Hongawa, K. Okuyama, and K. Nagai, Appl. Phys. Lett. 64, 815 (1994).
3] J. H. Seo, J. H. Kim, J. H. Seo, G. W. Hyung, J. H. Park, K. H. Lee, S. S. Yoon, and Y. K. Kim,
Appl. Phys. Lett. 90, 203507 (2007).
[
[
[
[
4] Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson, and S. R. Forrest, Nature, 440, 908
(2006).
5] M. H. Ho, Y. S. Wu, S. W. Wen, M. T. Lee, T. M. Chen, C. H. Chen, K. C. Kwok, S. K. So, K. T.
Yeung, Y. K. Cheng, and Z. Q. Gao, Appl. Phys. Lett. 89, 252903 (2006).
6] J. R. Sheats, H. Antoniadis, M. Hueschen, W. Leonard, J. Miller, R. Moon, D. Roitman, and A.
Stocking, Science 273, 884 (1996).
7] L. Zhou, A. Wanga, S. Wu, J. Sun, S. Park, and T. N. Jackson, Appl. Phys. Lett. 88, 083502
(2006).
[
[
8] G. Yu, J. Cao, J. Hummelen, F. Wudl, and A. J. Heeger, Science 270, 1789 (1995).
9] G. Yu, Y. Cao, J. Wang, J. McElvain, and A. J. Heeger, Synth. Met. 102, 904 (1999).