Position effect based on anthracene core for OLED emitters

Article abstract of DOI:10.1166/jnn.2016.11056

Green-orange emitters based on anthracene core have been successfully synthesized by substitution with triphenylamine side group in the 9,10 or 2,6 positions. There are larger blue shifts in the UV-visible absorption and PL spectra of the synthesized 2,6-substituted derivative compared to the 9,10-substituted derivative. When the synthesized compounds were used as emitting layers in non-doped OLED devices, a related trend was observed in their optical properties. In particular, the OLED device containing the 2,6-substituted derivative was found to exhibit excellent characteristics, with maximum EL emission at 518 nm, pure green emission with CIE coordinates of (0.334, 0.604), and external quantum efficiency of 2.83%.

Full text of DOI:10.1166/jnn.2016.11056

Article
Journal of
Nanoscience and Nanotechnology
Vol. 16, 3045–3048, 2016
Copyright © 2016 American Scientific Publishers
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Position Effect Based on Anthracene
Core for OLED Emitters
∗
Hyeonmi Kang, Hwangyu Shin, Beomjin Kim, and Jongwook Park
Department of Chemistry, The Catholic University of Korea, Bucheon, 420-743, Korea
Green-orange emitters based on anthracene core have been successfully synthesized by substi-
tution with triphenylamine side group in the 9,10 or 2,6 positions. There are larger blue shifts in
the UV-visible absorption and PL spectra of the synthesized 2,6-substituted derivative compared to
the 9,10-substituted derivative. When the synthesized compounds were used as emitting layers in
non-doped OLED devices, a related trend was observed in their optical properties. In particular, the
OLED device containing the 2,6-substituted derivative was found to exhibit excellent characteristics,
with maximum EL emission at 518 nm, pure green emission with CIE coordinates of (0.334, 0.604),
and external quantum efficiency of 2.83%.
Keywords: OLED, Anthracene, Green-Orange Emission, Link-Position, Density Functional
Calculation.
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1
. INTRODUCTION
IP: 211.103.163.74 On: Mo np ,o 2s i1t i oM na br e 2t w0 1e e6 n0c 5o : r1e 8 a: n2 d6 side groups, it would be helpful
Copyright: American S icn iec na ts i ef i co fP mu bo l li es ch ue l re sdesign for OLED emitter.
The interest in organic functional materials based on
Although varying the substitution positions of side
groups on emitting cores offers important information
about the intrinsic properties of the molecules, it is dif-
ficult to change substitution positions of the side group
for most emitting cores (e.g., fluorene, bifluorene and
ꢀ
-conjugated molecules has been rapidly growing in
diverse fields. Many remarkable results have been reported,
especially in the field of optoelectronics (organic light-
emitting diodes [OLEDs], solar cells, and organic thin-
1
–8
film transistors [OTFTs]. Many researchers are engaged
in ongoing efforts to systematically elucidate the corre-
lation between their molecular structures and properties,
with the aim of developing materials with good perfor-
mance and stability for particular optoelectronic applica-
tions. Most existing studies of emitters use molecules with
excellent fluorescence characteristics such as anthracene,
pyrene, and fluorene as core or side moieties. Many
studies have investigated the use of anthracene as the
core of emitting materials since they have high PL
efficiencies.
1
0–19
anthracene).
In this study, bromoanthracenes for which
Br is substituted into the 9,10 or 2,6 positions were syn-
thesized and used as precursors of two derivatives. This
process allowed for synthesis of two compounds with dif-
ferent link-position of side group by substituting tripheny-
lamine as an electron donating group with vinyl group in
the 9,10 and 2,6 positions of anthracene (Scheme 1). And
the synthesis method is shown in Scheme 2.
2
. EXPERIMENTAL DETAILS
Anthracene derivatives synthesized as emitting materi-
als mainly substituted the side group in the 9,10 positions
of anthracene. This is because substitution of 9,10 posi-
tions is relatively easy due to higher reactivity. However,
many interests have been recently focused on link posi-
2
2
4
.1. Synthesis
.1.1. Synthesis of DPAS
.66 g of diphenylamine (27.5 mmol), 11.6 g of sodium-
tert-butoxide and 0.84 g of Pd (dba) (0.46 mmol) were
dissolved in 130 ml of anhydrous toluene in a round
flask with nitrogen substitution. 3 ml of 4-bromosyrene
2
3
9
tion of emitters inside. In this study, position effect of
anthracene was examined by substituting the same side
group in other positions of anthracene. If emission wave-
length and efficiency can be expected according to link
(
22.9 mmol) and 0.2 ml of tri-tert-butylphosphine were
added before reacting the solution for 1 hour at room tem-
perature. 2 ml of HCl was added after the reaction. The
solution was extracted using dichloromethane and mois-
∗
Author to whom correspondence should be addressed.
ture was removed by MgSO . The product was refined
4
J. Nanosci. Nanotechnol. 2016, Vol. 16, No. 3
1533-4880/2016/16/3045/004
doi:10.1166/jnn.2016.11056
3045

Position Effect Based on Anthracene Core for OLED Emitters
Kang et al.
Scheme 1. Chemical structures of 9,10-DSAn and 2,6-DSAn.
Scheme 2. Synthetic routes for 9,10-DSAn and 2,6-DSAn.
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by column chromatography to oI bP t a: i2n 1 51 . .31 0g 3 o. 1f 6w 3h. i7t e4 sOo nl i :d Mon 2, . 21 .14 .M Sa yrn 2t h0 e1 s 6i s0 o5f : 19 8, 1: 02 -6D SAn
Copyright: American Scientific Publishers
(
yield: 71%).
1.5 g of 9,10-dibromoanthracene (4.5 mmol), 2.85 g of
DPAS (10.7 mmol), 0.9 g of Na CO and 0.2 g of Pd(OAc)
1H-NMR (300 MHz, DMSO, ꢁ): 7.35 (d, 2H), 7.31
t, 4H), 7.04 (m, 6H), 6.93 (d, 2H), 6.67 (q, 1H), 5.70
d, 1H), 5.16 (d, 1H).
2
3
2
(
(
were added to a round flask for nitrogen substitution. After
adding 150 ml of DMF, the solution was allowed to react
for 3 hours at 90 C. The solution was extracted using
ꢀ
2
.1.2. Synthesis of 2,6-DBAQ
chloroform and water, and moisture was removed using
Solution made by dissolving 3.44
diaminoanthraquinone (14 mmol) in 50 ml of anhydrous
acetonitrile was dropped to the mixture of 7.76 g of CuBr
35 mmol) and 5.16 ml of t-BuNO at 65 C. 200 ml of
g
of 2,6-
MgSO . The product was refined by column chromatogra-
4
phy to obtain 1.73 g of yellow solid (yield: 53%).
2
ꢀ
(
2
HCl was added after the reaction. The solution was washed
sufficiently and filtered using ethanol and water. The pre-
cipitate was dissolved in chloroform and re-filtered after
adding MgSO . The solvent was removed by evaporation
4
and the product was re-precipitated with chloroform and
MeOH to obtain 3.1 g of brown solid (yield: 58%).
1
H-NMR (300 MHz, CDCl , ꢁ): 8.43 (s, 2H), 8.17
3
(
d, 2H), 7.95 (d, 2H).
2
.1.3. Synthesis of 2,6-DBA
3
g of 2,6-DBAQ (8.2 mmol), 170 ml of AcOH, 20 ml
of HBr and 15 ml of H PO were sequentially added to a
3
2
ꢀ
round flask and refluxed at 140 C. After 5 days of reac-
tion, the solution was washed and filtered using ice water
and ethanol to obtain 1.46 g of solid (yield: 53%).
1
H-NMR (300 MHz, CDCl , ꢁ): 8.31 (s, 2H), 8.18
3
Figure 1. Normalized UV-Vis. and PL spectra of 9,10-DSAn and 2,6-
(
s, 2H), 7.90 (d, 2H), 7.56 (d, 2H).
DSAn in film state.
3046
J. Nanosci. Nanotechnol. 16, 3045–3048, 2016

Kang et al.
Position Effect Based on Anthracene Core for OLED Emitters
Table I. Optical, electrical and thermal properties of the synthesized compounds.
a
max
a
max
b
max
b
max
b
c
exp
UV
(
PL
UV
PL
FWHM
(nm)
HOMO
(eV)
LUMO
(eV)
ꢂE
(eV)
Tm
ꢀ
Td
ꢀ
nm)
(nm)
(nm)
(nm)
( C)
( C)
9
2
,10-DSAn
,6-DSAn
426
421
552
503
432
426
459
589
530
102ꢃ4
91ꢃ7
5.46
5.45
3.04
2.94
2.42
2.51
262.7
265.7
406
430
443
Notes: aSolution in THF (1ꢃ00×10−5 M). bFilm on glass. cExperimental band gaps.
was used for photo-luminescence (PL) spectroscopy. Ther-
mal degradation temperature (T ) of the compounds was
d
measured by thermo-gravimetric analysis (TGA) using
SDP-TGA2960 (TA instrument). The HOMO energy lev-
els were determined with ultraviolet photoelectron yield
spectroscopy (Riken Keiki AC-2). The LUMO energy lev-
els were derived from the HOMO energy levels and the
band gaps. All DFT calculations (B3LYP/6-311G(d)) were
performed with the Gaussian09 program.
3
. RESULTS AND DISCUSSION
The UV-Visible absorption spectra and photoluminescence
PL) spectra are shown in Figure 1, and the spectral
(
features are summarized in Table I. In the PL spectra, max-
imum peak of 2,6-DSAn and 9,10-DSAn was 530 nm and
Figure 2. Electronic density distributions of the frontier molecular
orbitals of the anthracene core (a) and of 9,10-DSAn and 2,6-DSAn (b).
5
89 nm, showing maximum difference of about 59 nm. As
1
a result, the emission spectrum of 2,6-DSAn showed green
color and 9,10-DSAn exhibited orange color. These find-
H-NMR (300 MHz, THF-d , ꢁ): 8.42 (q, 4H) 8.95
8
(
(
d, 2H), 7.64 (d, 4H),D7 e. 4l i 6v e (r qe ,d4 bHy ) ,P 7u .b2 l 7i s h( ti n, g8 HT )e ,c 7h .n1 o2 logy to: Adelaide Theological Library
ings suggest that changing the substitution position alters
d, 12H), 7.02 (t, 4H), 6.89 (d, I2PH :) 2. 11.103.163.74 On: Mon, 21 Mar 2016 05:18:26
the intrinsic optical properties of the molecule. Figure 2
Copyright: American Scientific Publishers
shows HOMO and LUMO orbitals of 9,10-DSAn and 2,6-
DSAn based on calculation of DFT. While 9,10-DSAn
has HOMO and LUMO electron distributions similar to
anthracene, 2,6-DSAn shows electron distributions differ-
ent from electron density distributions of anthracene. 2,6-
DSAn has relatively shorter conjugation length compared
to 9,10-DSAn due to relatively low electron distribution at
carbon atom of 2,6-DSAn. This makes 2,6-DSAn to pos-
sess emission with shorter wavelength than 9,10-DSAn.
Such result agrees with the larger band gap shown by 2,6-
DSAn compared to 9,10-DSAn, as shown in Table I.
Comparing the full widths at half maximum (FWHM)
of 9,10-DSAn and 2,6-DSAn in film state, FWHM of
2
0
.1.5. Synthesis of 2,6-DSAn
.5 g of 2,6-dibromoanthracene (1.49 mmol), 0.95 g of
DPAS (3.5 mmol), 0.3 g of Na CO3 and 0.04 g of
Pd(OAc) were added to a round flask for nitrogen sub-
stitution. After adding 50 ml of DMF, the solution was
allowed to react for 2 hours at 130 C. The solution
was extracted using chloroform and water, and moisture
was removed using MgSO . The product was refined by
column chromatography to obtain 0.53 g of yellow solid
2
2
ꢀ
4
(
yield: 50%).
1
H-NMR (300 MHz, THF-d , ꢁ): 8.35 (s, 2H), 7.96
8
(
(
m, 4H), 7.82 (d, 2H), 7.51 (d, 4H), 7.27 (m, 12H), 7.06
m, 16H).
2
,6-DSAn is smaller than 9,10-DSAn by more than 10
nm. The sharper spectrum of 2,6-DSAn is probably
because 2,6-DSAn has fewer electron transition states than
9,10-DSAn.
2
.2. Measurements
1
10
The H-NMR spectra were recorded on Bruker Avance
3
00 spectrometers. The optical absorption spectra were
To determine whether the changes with substitution
position in the intrinsic molecular properties are reflected
in OLED performance, non-doped OLED devices were
obtained by HP 8453 UV-VIS-NIR spectrometer. Perkin
Elmer luminescence spectrometer LS50 (Xenon flash tube)
Table II. EL performances of multi-layered devices. Device: ITO/2-TNATA (60 nm)/NPB (15 nm)/9,10-DSAn or 2,6-DSAn (35 nm)/Alq (20 nm)/LiF
3
2
(1 nm)/Al (200 nm) at 10 mA/cm .
Compounds
Volt (V)
L.E. (cd/A)
P.E. (lm/W)
E.Q.E. (%)
Elmax (nm)
CIE (x, y)
9
2
,10-DSAn
,6-DSAn
5.92
6.12
2.68
8.71
1.61
4.95
1.50
2.83
600
518
(0.540, 0.452)
(0.334, 0.604)
J. Nanosci. Nanotechnol. 16, 3045–3048, 2016
3047

Position Effect Based on Anthracene Core for OLED Emitters
Kang et al.
4
. CONCLUSION
Two new anthracene derivatives were successfully synthe-
sized by substituting triphenylamine and vinyl group with
anthracene core in different positions. Despite the same
core and side group, 2,6-DSAn showed greater blue shift
of the PL spectra compared to 9,10-DSAn in thin film
state by different link-position. 9,10-DSAn showed orange
emission and 2,6-DSAn showed green emission. Conjuga-
tion length was shortened when the side group is substi-
tuted in the 2,6 positions compared to 9,10 positions. In
particular, luminescence efficiency was greatly improved
from 2.68 cd/A in 9,10-DSAn to 8.71 cd/A in 2,6-DSAn,
and the EL spectrum was blue-shifted by about 80 nm.
Acknowledgment: This research was supported by a
grant from the Technology Development Program for
Strategic Core Materials funded by the Ministry of Trade,
Industry and Energy, Republic of Korea (Project No.
1
0047758). This research was supported by a grant from
the Fundamental R&D Program for Core Technology of
Materials funded by the Ministry of Trade, Industry and
Energy, Republic of Korea (Project No. 10050215).
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,10-DSAn. This trend in the EL spectra is in good agree-
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region observed in the PL spectra of the thin films. Fur-
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nm, which is much narrower than 12 nm of 9,10-DSAn.
Such narrow emission spectrum can emit pure color, which
becomes an advantage for emitting materials.
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quantum efficiency is 2.68 cd/A and 1.50% for 9,10-
DSAn, and 8.71 cd/A and 2.83% for 2,6-DSAn. Espe-
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Received: 17 June 2014. Accepted: 1 September 2014.
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