Blue emitters based on Anthracene-Aryl-Anthracene moieties end-capped with 1-naphthyl groups for organic light-emitting diodes

Article abstract of DOI:10.1166/jnn.2015.10392

We have designed emitters based on Anthracene-Aryl-Anthracene moieties end-capped with 1-naphthyl groups. In particular, a device showed blue EL properties with luminous and power efficiencies of 1.95 cd/A and 0.93 lm/W at 200 cd/m² respectively, and CIE coordinates of (0.16,0.10) at 7.0 V.

Full text of DOI:10.1166/jnn.2015.10392

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Nanoscience and Nanotechnology
Vol. 15, 5242–5245, 2015
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Blue Emitters Based on Anthracene-Aryl-Anthracene
Moieties End-Capped with 1-Naphthyl Groups for
Organic Light-Emitting Diodes
Soo Na Park1, Hye Jeong Kim1, Song Eun Lee2, Seok Jae Lee2,
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
We have designed emitters based on Anthracene-Aryl-Anthracene moieties end-capped with
1-naphthyl groups. In particular, a device showed blue EL properties with luminous and power effi-
ciencies of 1.95 cd/A and 0.93 lm/W at 200 cd/m2 respectively, and CIE coordinates of (0.16, 0.10)
at 7.0 V.
Keywords: Organic Light-Emitting Diode, Blue Fluorescence, Anthracene, Suzuki Reaction.
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1. INTRODUCTION
2. EXPERIMENTAL DETAILS
2.1. Synthesis
Organic light-emitting diodes (OLED) have been attract-
ing considerable attention due to its potential applications
in organic flat-panel displays and solid-state lighting.1 For
full-color display applications, blue, green, and red emit-
ters that have high emission, efficiencies and color purity
are required. Particularly, it is needed to be improved
EL efficiencies and color purity of blue emitting mate-
rials for the practical applications.2ꢀ3 In this study, we
have designed and synthesized four emitters 1–4 based
on Anthracene-Aryl-Anthracene moieties end-capped with
1-naphthyl groups. Anthracene derivatives have excel-
lent photoluminescence (PL) and thermal stability as an
emitting material.4ꢀ5 Furthermore, the end-capping groups
of compounds 1–4 such as 1-naphthyl groups would
induce the non-planar structural features of compounds
1–4, which prevent the intermolecular interaction and the
self-aggregation in solid state devices. Furthermore, two
anthracene moieties end-capped with 1-naphtyl groups in
compounds 1–4 were connected through by the various
aryl-spacer groups such as m-phenylene, p-phenylene, 1,4-
biphenylene and 2,7-dimethylfluorene. Therefore, com-
pounds 1–4 may expect to be excellent candidates in
efficient OLEDs.
General Procedure for the Suzuki Cross Coupling Reac-
tion 9-(1-naphthyl)anthracen-10-yl-boronic acid (2.4 mol)
and the corresponding aryl bromides (1.0 mol), Pd(PPh3ꢁ4
(0.04 mol), aqueous 2.0 M Na2CO3 (10.0 mol), ethanol,
and toluene were mixed in a flask. The mixture was
refluxed for 4 h. After the reaction was completed, water
was added to quench the reaction. After cooling, the crude
solid was collected by filtration, washed with water and
ethanol. The product was purified recrystallization from
CH2Cl2/EtOH.
2.1.1. 1,3-bis(10-(naphthalen-1-yl)anthracen-9-yl)
Benzene (1)
1H-NMR (500 MHz, CDCl3ꢁ [ꢂ ppm]: 8.06 (s, 8 H),
8.01–7.92 (m, 3 H), 7.80–7.77 (m, 3 H), 7.72–7.68 (m,
3 H), 7.62 (s, 1 H), 7.52–7.45 (m, 13 H), 7.14–7.05 (m,
3 H). MS (APCI+) m/z 682 (M+).
2.1.2. 1,4-bis(9-(1-naphthyl)anthracene-10-yl)
Benzene (2)
1H-NMR (300 MHz, CDCl3ꢁ [ꢂ ppm]: 8.12 (d, J = 8.1 Hz,
3 H), 8.06 (d, J = 8.4 Hz, 5 H), 7.86 (dd, J = 6.9 Hz, 3 H),
7.82 (dd, J = 6.6 Hz, 2 H), 7.77 (t, J = 7.5 Hz, 3 H), 7.65
∗Authors to whom correspondence should be addressed.
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doi:10.1166/jnn.2015.10392

Park et al.
Blue Emitters Based on Anthracene-Aryl-Anthracene Moieties End-Capped with 1-Naphthyl Groups for OLED
Table I. Optical properties of compounds (1–4).
(a)
Compound UV PLa PLb FWHM HOMO LUMO Eg
ꢂc
Br
Br
1
2
3
4
398 417 442
398 417 442
377 419 442
396 425 442
44
50
49
49
−5ꢃ85 −2ꢃ68 3ꢃ17 0ꢃ58
−5ꢃ82 −2ꢃ76 3ꢃ06 0ꢃ84
−5ꢃ88 −2ꢃ83 3ꢃ05 0ꢃ77
−5ꢃ85 −2ꢃ73 3ꢃ12 0ꢃ46
1 (70%)
2 (74%)
(a)
(a)
Br
Br
Notes: aCH2Cl2 solution (10−5 M); bThin film; cUsing DPA(9,10-
diphenylanthracene) as a standard; ꢄex = 360 nm (ꢂ = 0.90 in CH2Cl2ꢀ.
1.0
Br
Br
1
2
3
4
0.8
3 (86%)
0.6
(a)
Br
Br
0.4
0.2
0.0
4 (86%)
Scheme 1. Structure and synthetic routes of compounds (1–4). (a)
9-(1-naphthyl)anthracen-10-yl-boronic acid, Pd(PPh3ꢀ4, 2 M Na2CO3,
Toluene, EtOH, reflux, 4 h.
400
450
500
550
600
650
700
750
Wavelength [nm]
(dd, J = 6.6 Hz, 2 H), 7.53–7.47 (m, 10 H), 7.33–7.26 (m,
6 H). MS (APCI+) m/z 682 (M+).
Figure 2. EL spectra of the devices (1–4).
2.1.3. 4,4ꢀ-bis(9-(1-naphthyl)anthracene-10-
yl)Biphenyl (3)
1H-NMR (500 MHz, CDCl3) [ꢁ ppm]: 8.10–8.03 (m, 8 H),
7.92 (d, J = 8.7 Hz, 4 H), 7.77–7.69 (m, 6 H), 7.63 (dd,
J = 6.9 Hz, 2 H), 7.53–7.47 (m, 6 H), 7.42–7.37 (m, 4 H),
7.29–7.23 (m, 8 H). MS (APCI+) m/z 759 (M+).
J = 6.5 Hz, 4 H), 7.28–7.26 (m, 4 H), 7.23–7.21 (m, 4 H).
MS (APCI+ꢀ m/z 799 (M+ꢀ.
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2.2. OLED Fabrication and Measurement
Copyright: American Scientific Publishers
For fabricating OLEDs, indium-tin-oxide (ITO) thin films
coated on glass substrates were used, which was 30 square
of the sheet resistivity, and 100 nm of thickness. The
ITO-coated glass was cleaned in an ultrasonic bath by
the following sequence: acetone, methyl alcohol, distilled
water, and stored in isopropyl alcohol for 48 h and dried
by a N2 gas gun. The substrates were treated by O2 plasma
under 2.0×10−2 torr at 125 W for 2 min. All organic mate-
rials and metals were deposited under high vacuum (5 ×
10−7 torr). The OLEDs were fabricated in the following
sequence: ITO/4,4ꢀ-Bis(N -(1-naphthyl)-N -phenylamino)
2.1.4. 10-(9,9-dimethyl-2-(10-(naphthalen-1-
yl)anthracen-9-yl)-9H-fluoren-7-yl)-9-
(naphthalen-1-yl)Anthracene (4)
1H-NMR (500 MHz, CDCl3ꢀ [ꢁ ppm]: 8.13 (t, J = 7.5 Hz,
2 H), 8.10 (d, J = 8.5 Hz, 2 H), 8.04 (d, J = 8.0 Hz,
2 H), 7.91 (d, J = 9.0 Hz, 4 H), 7.74–7.70 (m, 4 H),
7.63–7.60 (m, 4 H), 7.50–7.48 (m, 6 H), 7.40–7.36 (dd,
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
1(UV)
2(UV)
3(UV)
4(UV)
DPA(UV)
1(PL)
4.0
1 (LE)
2 (LE)
3 (LE)
4 (LE)
1 (PE)
2 (PE)
3 (PE)
4 (PE)
2.5
2.0
1.5
1.0
0.5
3.5
3.0
2.5
2.0
1.5
1.0
0.5
2(PL)
3(PL)
4(PL)
DPA(PL)
350
400
450
500
550
0
1500
3000
4500
6000
Wavelength [nm]
Luminance [cd/m2]
Figure 1. The absorption spectra and emission spectra in solution of
blue materials (1–4).
Figure 3. Luminous efficiencies and power efficiencies as a function of
luminance for the devices (1–4).
J. Nanosci. Nanotechnol. 15, 5242–5245, 2015
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Blue Emitters Based on Anthracene-Aryl-Anthracene Moieties End-Capped with 1-Naphthyl Groups for OLED
Park et al.
Table II. EL properties of devices (1–4).
Device
ꢀmax [nm]
Ja [mA/cm2]
La [cd/m2]
LEb/c [cd/A]
PEb/c [lm/W]
CIEd (xꢁy)
1
2
3
4
442, 498, 537
442
553
442, 538
74
147
225
150
1513
2781
4009
2798
2.10/2.06
1.97/1.95
3.32/3.32
3.91/3.90
1.09/0.91
1.27/0.93
2.49/1.90
2.63/2.08
(0.23, 0.26)
(0.16, 0.10)
(0.41, 0.54)
(0.30, 0.45)
Notes: aCurrent density and luminance at 9.0 V; bMaximum values; cAt 200 cd/m2; dCommission Internationale d’Énclairage (CIE) at 7.0 V.
biphenyl (NPB) (50 nm)/Blue emitting materials (1–
4) (40 nm)/Tris(8-hydroxyquinolinato)aluminium (Alq3ꢂ
(15 nm)/Lithium quinolate (Liq) (2 nm)/Al (100 nm),
NPB as the hole-transporting layer, Alq3 as the electron-
transporting layer, and Liq:Al as the composite cathode.
All EL properties of the OLEDs were measured with a
Keithly 2400, Chroma meter CS-1000A. Electroluminance
was measured using a Roper Scientific Pro 300i.
due to forming significant portions of electromers or elec-
troplexes with the CIE coordinates of (0.41, 0.54) and
(0.30, 0.45), respectively at a driving voltage of 7.0 V.
Intriguingly, the degree of the electroplexes at the the
Alq3/Emission layer interface formation in OLED devices
are greatly dependent on the structural changes of the emit-
ting materials with the similar HOMO/LUMO energy lev-
els within 0.15 eV.
The luminous and power efficiencies and external quan-
tum efficiencies of devices 1–4 as a function of the lumi-
nance are shown in Figure 3 and Table II.
3. RESULTS AND DISCUSSION
Scheme 1 shows the synthetic route of the designed
blue fluorescent materials 1–4 and its structures. The
compounds 1–4 were synthesized using the Suzuki cross
coupling reaction between the 9-(1-naphthyl)anthracenyl-
10-boronic acid and the corresponding aryl bromides with
moderate yields (70–86%).
The devices 1–4 exhibited the luminous efficiencies of
2.06, 1.95, 3.32 and 3.90 cd/A and the power efficiencies
of 0.91, 0.93, 1.90 and 2.08 lm/W at 200 cd/m2, respec-
tively. Interestingly, devices 3 and 4 have the better EL
efficiencies than devices 1 and 2. Presumably, the effi-
cient formation of electromers or electroplexes in devices 3
and 4 would contribute to the improved EL efficiencies in
Figure 1 shows the UV-vis absorption and PL emission
spectra of compoundDsel1iv–e4reind dbiychPluorbolimshetinhagnTeescohluntoiolongsy to: Chinese University of Hong Kong
comparison with the devices 1 and 2.5
IP: 109.161.209.100 On: Mon, 07 Dec 2015 15:33:06
and on quartz plate films. The absorption spectra of com-
Copyright: American Scientific Publishers
pounds 1–4 in CH2Cl2 solution show the characteristic
vibronic band from the transitions of anthracene group.6
As shown in Table I, compounds 1–4 showed blue emis-
sion with maximum emission wavelengths at 417, 417, 419
and 425 nm in solution. Compared to the PL spectra of
compound 1 and 2, compounds 3 and 4 showed red-shifts
(2 and 8 nm) due to the longer ꢃ-conjugation lengths.
Solid state PL wavelengths of compound 1–4 showed red
shifts rather than solution PL wavelengths (ca. 14–27 nm)
due to the solid state effect.7
Figure 2 shows the EL spectra of devices 1–4. Device 2
shows the EL spectrum with the maximum peak at
442 nm. This device exhibits the deep blue emission with
the CIE coordinates of (0.16, 0.10). However, the EL spec-
tra of the other devices 1, 3 and 4 show the interest-
ing features. Device 1 shows the main emission peak at
442 nm and the small shoulder peaks at 498 and 537 nm
with the CIE coordinates of (0.23, 0.13). In some multi-
layer OLEDs, a bimolecular recombination state called an
electromers or electroplexes were usually formed at rela-
tively high electric fields.8 The existence of the electromers
or electroplexes in OLEDs usually leads to a red-shifted
and broadened emission spectrum.9 Therefore, this result
imply the possibility of formation of a species such as
an electromers or electroplexes during the electrolumines-
cence process in device 1.10 The devices 3 and 4 exhibits
mainly the greenish emission at 553 nm and 538 nm
4. CONCLUSION
In this study, we have synthesized two anthracene-
containing blue emitters 1–4 based on Anthracene-Aryl-
Anthracene moieties using Suzuki cross coupling reaction.
Their EL properties were investigated by fabrication of
multilayered OLEDs. All devices showed efficient EL effi-
ciencies from blue to green emissions. Particularly, the
device 2 showed the efficient deep-blue emission with
CIEꢄxꢁyꢂ coordinates of (0.16, 0.10) at 7 V, 1.95 cd/A
and 0.93 lm/W at 200 cd/m2 respectively. These results
suggest that anthracene derivatives with 1-naphtyl groups
have excellent electroluminescent properties in efficient
OLEDs.
Acknowledgment: This research was supported by the
MSIP (Ministry of Science, ICT&Future Planning), Korea,
under the ITRC (Information Technology Research Cen-
ter) support program NIPA-2013-(H0301-13-1004) super-
vised by the NIPA (National IT Industry Promotion
Agency).
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Blue Emitters Based on Anthracene-Aryl-Anthracene Moieties End-Capped with 1-Naphthyl Groups for OLED
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Received: 22 November 2013. Accepted: 9 May 2014.
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