Red fluorescent organic light-emitting diodes (OLEDs) using 4-(1,3-Indanedione-2-yl)-2-(adaman-1-yl)-6-(10-aza-2,3,4,5,6, 7-hexahydronaphtio[1,8-gh]chromen-10(1 H)-one-9-enyl)-4H-pyran

Article abstract of DOI:10.1080/15421406.2012.706551

A red fluorescent material 4-(1,3-Indanedione-2-yl)-2-(adaman-1-yl)-6-(10- aza-2,3,4, 5,6,7-hexahydronaphtio[1,8-gh]chromen-10(1H)-one-9-enyl)-4H-pyran is synthesized and characterized. In this material, four methyl groups and adamantly group are introduced into DCJTB skeleton to increase steric hindrance between red emitters in the emitting layer of devices and thus improve the EL efficiencies by preventing concentration quenching. In particular, a device doped with this material in the emitting layer exhibits the luminous and power efficiencies of 3.58 cd/A and 1.61 lm/W at 20mA/cm², respectively. The CIE coordinates of this device was (0.64, 0.35) at 7.0V. Copyright

Full text of DOI:10.1080/15421406.2012.706551

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Red Fluorescent Organic Light-
Emitting Diodes (OLEDs) using 4-(1,3-
Indanedione-2-yl)-2-(adaman-1-yl)-6-(10-
aza-2,3,4,5,6,7-hexahydronaphtio[1,8-
gh]chromen-10(1H)-one-9-enyl)-4H-
pyran
Heung Soo Jang a , Kum Hee Lee a , Eun Jae Na a , Young Kwan Kim b
& Seung Soo Yoon a
a Department of Chemistry, Sungkyunkwan University, Suwon,
440–746, Korea
b Department of Information Display, Hongik University, Seoul,
121–791, Korea
To cite this article: Heung Soo Jang, Kum Hee Lee, Eun Jae Na, Young Kwan Kim & Seung Soo Yoon
(2012): Red Fluorescent Organic Light-Emitting Diodes (OLEDs) using 4-(1,3-Indanedione-2-yl)-2-
(adaman-1-yl)-6-(10-aza-2,3,4,5,6,7-hexahydronaphtio[1,8-gh]chromen-10(1H)-one-9-enyl)-4H-pyran,
Molecular Crystals and Liquid Crystals, 568:1, 1-7
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Mol. Cryst. Liq. Cryst., Vol. 568: pp. 1–7, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.706551
Red Fluorescent Organic Light-Emitting Diodes
(OLEDs) using 4-(1,3-Indanedione-2-yl)-2-(adaman-
1-yl)-6-(10-aza-2,3,4,5,6,7-hexahydronaphtio[1,8-
gh]chromen-10(1H)-one-9-enyl)-4H-pyran
HEUNG SOO JANG,1 KUM HEE LEE,1 EUN JAE NA,1
YOUNG KWAN KIM,2 AND SEUNG SOO YOON1,∗
1Department of Chemistry, Sungkyunkwan University, Suwon 440–746, Korea
2Department of Information Display, Hongik University, Seoul 121–791, Korea
A red fluorescent material 4-(1,3-Indanedione-2-yl)-2-(adaman-1-yl)-6-(10-aza-2,3,4,
5,6,7-hexahydronaphtio[1,8-gh]chromen-10(1H)-one-9-enyl)-4H-pyran is synthesized
and characterized. In this material, four methyl groups and adamantly group are in-
troduced into DCJTB skeleton to increase steric hindrance between red emitters in the
emitting layer of devices and thus improve the EL efficiencies by preventing concentra-
tion quenching. In particular, a device doped with this material in the emitting layer
exhibits the luminous and power efficiencies of 3.58 cd/A and 1.61 lm/W at 20 mA/cm2,
respectively. The CIE coordinates of this device was (0.64, 0.35) at 7.0V.
Keywords Red Fluorescence; OLEDs; DCJTB derivative; Adamandane; Indanedione
group
Introduction
Organic light-emitting diodes (OLEDs) have attracted considerable attention due to their
potential application in flat panel displays [1]. Among three elemental colors of red, green
and blue for full color display applications, red fluorescent materials are far behind in terms
of efficiency and color purity [2]. The well-known pyran-containing laser dyes based on
DCM (4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran) have been
widely studied [3,4]. In most DCM type emitters, dramatically reduces EL performance due
to concentration quenching. Thus, there had been considerable efforts to developed efficient
red fluorescent materials by preventing excimer and exciplex formation through incorpora-
tion of sterically bulky moieties in the emitters [5]. Particularly, 4-(dicyanomethylene)-2-
tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) represents the most
efficient fluorescent red emitting material for OLEDs [6]. In these material, the bulky sub-
tituents on julolidine and pyran moieties of DCM backbone are incorporated to prevent
concentration quenching between the emitting materials, which lead to the improved EL
efficiencies of devices [7].
∗Address corresponding to Seung Soo Yoon, Department of Chemistry, Sungkyunkwan Univer-
sity, Suwon 440–746, Korea. Tel.: +82 31 290 5971; Fax: +82 31 290 7075. E-mail: ssyoon@skku.edu
[417]/1

2/[418]
H. S. Jang et al.
Scheme 1. Synthesis and structures of Red 1 and DCJTB. (a) NaN(TMS)2. (b) i. H2SO4, ii.1,3-
Indanedione, Ac2O. (c) Piperidine, EtOH.
Nevertheless, their EL performances still need to be improved. Particularly, color
purities of devices using DCJTB is far from ideal [8]. This imply that the more bulky
groups than tert-butyl group in DCJTB is need to improve the EL performances of red
fluorescent OLEDs [9].
In this paper, we describe the synthesis and electroluminescent properties of a
red fluorescent material, 4-(1,3-Indanedione-2-yl)-2-(adaman-1-yl)-6-(10-aza-2,3,4,5,6,7-
hexahydronaphtio[1,8-gh]chromen-10(1H)-one-9-enyl)-4H-pyran (Red 1). In Red 1, four
methyl groups and adamantly group are introduced into DCJTB skeleton to increase steric
hindrance between red emitters in the emitting layer of devices and thus improve the EL
efficiencies by preventing concentration quenching. Furthermore, the additional π con-
jugation groups such as pyran-2-one and 1,3-indanedione are incorporated to increase
the p π -conjugation length and thus improve the color purity of devices using Red 1
[10–12].
Experimental
Materials and Measurement
All commercially available reagents were purchased from Aldrich and TCI and used with-
out further purification. 1H- and 13C-NMR were recorded on a Varian (300 or Unity Inova
300Nb or Unity Inova 500Nb) spectrometer. FT-IR spectra were recorded using a Thermo
Nicolet Avatar 320 FT-IR spectrometer. Low- and high-resolution mass spectra were mea-
sured using a Jeol JMS-AX505WA spectrometer in the FAB mode and a Jeol JMS-600W
spectrometer in the EI mode and a JMS-T100TD (AccuTOF-TLC) in the positive ion mode.
The UV-Vis absorption and photoluminescence spectra of these newly designed red dopants
were measured in a 10−5 M solution of 1,2-dichloroethane. Fluorescent quantum yields
were determined in 1.2-dichloroethane at 293 K against DCJTB = 0.78 [13]. The HOMO
energy levels were measured with low energy photo-electron spectrometry (Riken-Keiki
AC-2). The LUMO energy levels were estimated by subtracting the energy gap from the
HOMO energy levels.

Red Fluorescent Organic Light-Emitting Diodes
[419]/3
Synthesis
Synthesis of 2-methyl-6-(adamantly-1-yl)-4-(1,3-indanedione-2-yl)-4H-pyran. To a solu-
tion of 2.6 g of 1-acetyl-adamantane (14.68 mmol) in 30 mL of THF at −78◦C was added
36.71 mL of 1M NaN(TMS)2 solution in THF. After stirring 1 hr at −78◦C, 4.7 g of
methyl 2-(2-methyl-1,3-dioxolan-2-yl)acetate (29.37 mmol) was added and then heated to
70◦C for 12 hr. The reaction mixture was quenched with NH4Cl aqueous solution and then
extracted with ethyl acetate. Column chromatography using silica gel with the elution of
ethyl acetate and hexane provided 2.2 g of the crude 1-(adamant-1-yl)-4-(2-methyl-1,3-
dioxolan-2-yl)butane-1,3-dione (7.22 mmol, 49.2%). This crude compound was dissolved
in 10 mL of 95% H2SO4 solution and then stirred for 4 hr at room temperature. After the
neutralization with NaHCO3 solution, the reaction mixture was extracted with ethyl acetate.
Without further purification, the crude products were dissolved in 10 mL of acetylanhy-
dride and then 0.5 g of 1, 3-indanedione (3.12 mmol) was added to the reaction mixture.
After refluxing the reaction mixture for 12 hr, the crude products were extracted with
ethyl acetate. Column chromatography using silica gel with the elution of ethyl acetate and
hexane provided 1.7 g of 2-methyl-6-(adamantly-1-yl)-4-(1,3-indanedione-2-yl)-4H-pyran
(4.50 mmol, 62.3%). 1H-NMR (300 MHz, CDCl3): δ (ppm) 5.31 (s, 1H), 5.20 (s, 1H), 1.77
(s, 3H), 1.52 (m, 6H), 1.31 (m, 6H), 1.18 (t, 2H, J = 7.5 Hz), 1.10 (m, 6H), 0.91 (t, 3H,
J = 7.5 Hz); FT-IR (KBr): ν = 2925, 2323, 1587, 1520, 830 cm−1; Mass (EI) m/z = 336
(M+).
Synthesis of Red 1 (4-(1,3-Indanedione-2-yl)-2-(adaman-1-yl)-6-(10-aza-2,3,4,5,6,7-
hexahydronaphtio[1,8-gh]chromen-10(1H)-one-9-enyl)-4H-pyran). To
a
solution
of 0.68 of 6-(10-aza-2,3,4,5,6,7-hexahydronaphtio[1,8-gh]chromen-10(1H)-one)-
g
9-carboaldehyde (2.11 mmol) and 0.79 g of 2-methyl-6-(adamantly-1-yl)-4-(1,3-
indanedione-2-yl)-4H-pyran (2.11 mmol) in 20 mL of EtOH was added 0.83 mL of
piperidine (8.44 mmol) at room temperature. After refluxing under deanstark trap for 5 h,
the resulting crude solid products was filtered and then washed with brine. Recrystallization
from ethyl alcohol provided 0.47 g of Red 1 as reddish solids (0.686 mmol, 32.5%).
1H-NMR (300 MHz, CDCl3): δ (ppm) 7.61 (s, 1H), 7.42 (s, 1H), 6.65 (d, 1H, J = 12.1 Hz),
6.43 (d, 1H, J = 12.0 Hz), 5.45 (s, 1H), 5.15 (s, 1H), 3.45 (m, 2H), 3.23 (m, 2H), 1.91 (m,
2H), 1.45 (m, 12H), 1.31 (m, 12H), 1.21 (s, 6H), 1.11 (t, 2H, J = 7.5 Hz), 1.02 (s, 6H),
0.91 (t, 3H, J = 7.5 Hz); FT-IR (KBr): ν = 2989, 2330, 1582, 1559, 1500 cm−1; Mass
Figure 1. (a) UV-Vis absorption spectra and (b) Photoluminescence spectra of Red 1 and DCJTB.

4/[420]
H. S. Jang et al.
Table 1. Optical properties of Red 1 and DCJTB
[a]
[b]
λmax
[nm]
λmax
[nm]
FWHM
[nm]
HOMO/
LUMO[eV]
Compound
Eg
ꢀ[c]
1
542
511
633
620
80
72
−5.18/−3.09
−5.26/−3.10
2.09
2.16
0.71
0.78
DCJTB
[b]
[a]Maximum absorption and emission wavelength, measured in Cl2CH2CH2Cl2 solution. Ob-
tained from AC-2 and absorption measurement. [c]Using DCJTB as a standard; λex = 500 nm (Фp =
0.78 in Cl2CH2CH2Cl2).
(EI) m/z = 604 (M+); HRMS (EI) calcd for C41H53N3O, 603.4189; found, 603.4178; mp.
258◦C.
Fabrication of OLED
OLEDs using red-light-emitting molecules were fabricated by vacuum (10−6 torr) ther-
mal evaporation onto pre-cleaned ITO coated glass substrates. The device structures were
as follows: (1) ITO/ N,N’-diphenyl-N,N’-(1-napthyl)-(1,1’-biphenyl)-4,4’-diamine (NPB)
(40 nm)/ tris(8-quionlinolato)-aluminium (Alq3) : Red dopant (1, 5 or 10%) (20 nm)/ Alq3
(40 nm)/ Liq (2 nm)/ Al. All of the properties of the OLEDs such as the current density (J),
luminance (L), luminance efficiency (LE), power efficiency (PE), and commission interna-
´
tional de 1’Eclairage (CIE) coordinate characteristics were measured using a Keithly 2400
source measurement unit and a Chroma meter MINOLTA CS-1000A. Electro-luminance
was measured using a Roper Scientific Pro 300i.
Results and Discussion
Synthesis of the red emitter Red 1 began with the preparation of two intermediates by
following the known procedure [14]. DCJTB was prepared by following the standard
procedure [15]. The ultraviolet-visible (UV-Vis) absorption spectra of Red 1 and DCJTB
are shown in Figure 1 (a). The maximum absorption peaks of these materials were 542 and
511 nm, respectively. Figure 1 (a) shows the good overlap between the emission spectra
of a common fluorescent red host material Alq3 and the absorption spectra of Red 1 and
Table 2. EL performance characteristic of devices 1–4
L[a]
Von
LE-J[c]/[d]
(cd/A)
PE[c]/[d]
(lm/W)
EL[e]
(nm)
CIE[e]
(x,y)
[b]
Dopant
Device (doping%) (cd/m2)
(V)
1
2
3
4
Red 1(1)
Red 1 (5)
Red 1 (10)
DCJTB
(1)
10700
2000
340
4.0
5.0
6.0
3.0
3.58/3.61 1.61/1.71
0.54/0.56 0.15/0.29
0.13/0.15 0.03/0.07
2.45/2.52 1.06/1.32
648
656
672
616
(0.64, 0.35)
(0.66, 0.33)
(0.67, 0.32)
(0.60, 0.39)
6300
[a]Maximum luminance at 21.0 V, [b]Turn-on voltage at 1 cd/m2, [c]Value measured at 20 mA/cm2,
[d]Maximum values, [e]Value measured at 7.0 V.

Red Fluorescent Organic Light-Emitting Diodes
[421]/5
Figure 2. (a) Current density-Voltage and (b) Luminance-Voltage characteristics of devices 1–4.
DCJTB. This observation imply that the Fo¨rster Singlet energy transfer from host Alq3 to
red emitter Red 1 and DCJTB would be efficient. Red 1 and DCJTB exhibit efficient red
emissions with maximum emission peaks of 633 and 620 nm, respectively, as shown in
Figure 1 (b). Compared to DCJTB, the maximum emission peak of Red 1 was red-shifted
by 13 nm due to the increase the π-conjugation length of Red 1. The quantum yields of
Red 1 and DCJTB were 0.71 and 0.78, respectively in Table 1.
To explore the electroluminescent properties of Red 1, OLED devices using Red 1
as a dopant in Alq3 host were fabricated. Particularly, to optimize the device structure,
three kinds of devices with the different dopping concentrations such as 1, 5 and 10% were
fabricated. Also, for the comparison, the control device using DCJTB as a dopant in Alq3
host at 1% dopping concentration was fabricated. All electroluminescent data on devices
using Red 1 and DCJTB was summarized in Table 2.
Figure 2 showed the current density-voltage and the luminance-voltage characteristics
of devices. The luminous and power efficiencies of devices are shown in Figure 3. Also,
the EL spectra of devices are shown in Figure 4. The maximum luminous efficiency of
devices 1 and 4 were 3.61 and 2.52 cd/A, respectively. And the maximum power efficiency
of devices 1 and 4 were 1.71 and 1.32 lm/W, respectively. The power efficiency of devices
1 and 4 were 1.61 and 1.06 lm/W at 20 mA/cm2, respectively.
Figure 3. (a) Luminous efficiency-current density and (b) Power efficiencies-current density char-
acteristics of devices 1–4.

6/[422]
H. S. Jang et al.
Figure 4. EL spectra devices of 1–4.
Notably, compared to device 4 using DCJTB, The methyl groups and adamantly
group of dopant Red 1 of device 1 could prevent molecular aggregation and thus reduce
concentration quenching [16]. This would contribute to the improved luminous efficiency
of device 1. Moreover, the other factor is such as the more effective hole trapping de-
vice 1 than device 4. This imply that device 1 prevent hole leakage from emitting layer
into Alq3 layer. Thus more efficient exciton formation at device 1 could contribute to
the improved EL efficiencies of device 1 in comparison to device 4 [17]. In devices 1, 2
and 3 using Red 1 as a dopant at the different dopping concentrations, with the increase
of doping concentration from 1% to 5 and 10%, the luminous and power efficiencies
decreased due to the concentration quenching effect. Notably, the EL spectra of device
1, 2 and 3 showed more red-shift by change of doping concentration. These observat
ions imply that the emission peak around 670 nm might originate from the excimers
of dopant Red 1 and the extent of excimer formation of dopant increased at the higher
doping concentra tion. Compared to device 4 with the CIE coordinates of (0.60 0.39),
device 1 has the improved CIE coordinates of (0.64, 0.35) due to the increase the π-
conjugation length of dopant [18]. Interestingly, compared to device 1, device 2 and 3
showed the further improved CIE coordinates of (0.66, 0.33) and (0.67, 0.32) at 7.0 V,
approaching saturated red emission due to the excimer formation of Red 1 at the higher
dopping concentration. This study demonstrate that Red 1, a DCJTB derivative with mod-
ified julolidine and pyran moieties, is an excellent fluorescent red material for efficient
OLEDs.
Conclusions
we designed and synthesized a new red emitter Red 1 (4-(1,3-Indanedione-2-yl)-2-
(adaman-1-yl)-6-(10-aza-2,3,4,5,6,7-hexahydronaphtio[1,8-gh]chromen-10(1H)-one-9-
enyl)-4H-pyran). A device with Red 1 (1%) showed the luminous and power efficiencies
of 3.58 cd/A and 1.61 lm/W at 20 mA/cm2, respectively. The CIE coordinates of this
device was (0.64, 0.35) at 7.0 V. Compared to a device using DCJTB, this device showed
the improved EL efficiencies due to prevent concentration quenching.

Red Fluorescent Organic Light-Emitting Diodes
[423]/7
Acknowledgment
This research was supported by Basic Science Research Program through the NRF funded
by the Ministry of Education, Science and Technology (20110004655).
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