Highly efficient dual anthracene core derivatives through optimizing side groups for blue emission

Article abstract of DOI:10.1016/j.dyepig.2017.06.053

TP-AA-TPB, TP-AA-TPB, TPB-AA-TPB, TP-AA-DPA, TP-AA-TPA, and TPB-AA-TPA were synthesized using a 9,9'-bianthracene (AA core). Through a systematic side group change, we optimized the dual-core chromophore system and investigated the relationship between the core and the side groups. The ultraviolet-visible (UV-Vis) absorption of the six materials showed an intrinsic absorption peaks of anthracene in the range of 360 nm–410 nm and photoluminescence (PL) emission in the blue region. The minimum decomposition temperatures (T_d) was 425 °C, the minimum melting temperatures (T_m) was 335 °C, and the minimum glass transition temperatures (T_g) was 176 °C. We achieved excellent overall electroluminescence (EL) efficiency in non-doped OLED devices using the six synthesized materials as emitting layer (EML). TPB-AA-TPA synthesized through size and polarity optimization of the side groups on the AA core had a current efficiency of 8.97 cd/A, power efficiency of 4.43 lm/W, external quantum efficiency (EQE) of 6.37%, and Commission Internationale de L'Eclairage coordinates (CIE) of (0.14, 0.19). TPB-AA-TPA also maintained blue emission and realized the highest EL efficiency among the six synthesized materials.

Full text of DOI:10.1016/j.dyepig.2017.06.053

Dyes and Pigments 146 (2017) 27e36
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Highly efficient dual anthracene core derivatives through optimizing
side groups for blue emission
,
,
Hayoon Lee a 1, Minjin Jo b 1, Garam Yang b, Hyocheol Jung a, Seokwoo Kang a,
Jongwook Park a
,
*
a Department of Chemical Engineering, College of Engineering, Kyung Hee University, Youngin, Gyeonggi, 17104, Republic of Korea
b Department of Chemistry, The Catholic University of Korea, Bucheon, Gyeonggi, 14662, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
TP-AA-TPB, TP-AA-TPB, TPB-AA-TPB, TP-AA-DPA, TP-AA-TPA, and TPB-AA-TPA were synthesized using a
9,9'-bianthracene (AA core). Through a systematic side group change, we optimized the dual-core
chromophore system and investigated the relationship between the core and the side groups. The
ultraviolet-visible (UV-Vis) absorption of the six materials showed an intrinsic absorption peaks of
anthracene in the range of 360 nme410 nm and photoluminescence (PL) emission in the blue region. The
minimum decomposition temperatures (Td) was 425 ꢀC, the minimum melting temperatures (Tm) was
335 ꢀC, and the minimum glass transition temperatures (Tg) was 176 ꢀC. We achieved excellent overall
electroluminescence (EL) efficiency in non-doped OLED devices using the six synthesized materials as
emitting layer (EML). TPB-AA-TPA synthesized through size and polarity optimization of the side groups
on the AA core had a current efficiency of 8.97 cd/A, power efficiency of 4.43 lm/W, external quantum
efficiency (EQE) of 6.37%, and Commission Internationale de L'Eclairage coordinates (CIE) of (0.14, 0.19).
TPB-AA-TPA also maintained blue emission and realized the highest EL efficiency among the six syn-
thesized materials.
Received 27 April 2017
Received in revised form
23 May 2017
Accepted 21 June 2017
Available online 23 June 2017
Keywords:
OLED
EML
Blue emission
Core-side concept
9,9'-bianthracene
© 2017 Published by Elsevier Ltd.
1. Introduction
material should use a lower triplet energy level (T1) than the
singlet energy level (S1) of the fluorescent material, and it is diffi-
Since the first reported organic light-emitting diodes (OLEDs) by
Tang and Van Slyke, OLEDs are now attracting attention in the
market, such as for mobile phone and TV display and solid-state
lighting because of their potentials as next generation applica-
tions [1]. These OLEDs require red, green, and blue emitting ma-
terials to realize a full color display. In particular, blue emitting
materials require a wide energy band gap, which causes high
charge injection barriers in the device, thus blue OLED devices are
relatively inferior to green and red in terms of electroluminescence
(EL) efficiency and device lifetime [2e15].
The emitting materials can be divided into fluorescent materials
and phosphorescent materials. In the case of a blue-emitting ma-
terial with a wide energy band gap, fluorescent materials show
higher efficiency, greater color gamut, and a longer lifetime than
phosphorescent materials [16]. The phosphorescent blue-emitting
cult to develop a phosphorescent blue emitting material because of
the limits in achieving a molecular structure with a high T1 level
[17,18].
In order to solve these problems, many fluorescent blue-
emitting materials have been synthesized to improve the effi-
ciency and the long lifetime. However, development of blue emit-
ting materials with a pure color and high efficiency is still required.
We systematically designed the structure of a fluorescent emitting
material, synthesized it using the core-side concept, and reported
the properties accordingly [9,10,19]. The core group is responsible
for the main absorption and emission roles of the final compound,
and the side groups capable of controlling the size, arrangement,
and polarity of the final molecule are symmetrically or asymmet-
rically arranged.
We have also reported a systematic study of the derivatives of
dual and triple cores composed of two or three chromophores
compared to single core group derivatives [11,12,20,21]. In the case
of a dual core, relatively higher quantum efficiency is shown in
photoluminescence (PL) and EL compared to a single core, and the
* Corresponding author.
E-mail address: jongpark@khu.ac.kr (J. Park).
Hayoon Lee and Minjin Jo contributed equally to this work as the first coauthor.
1
http://dx.doi.org/10.1016/j.dyepig.2017.06.053
0143-7208/© 2017 Published by Elsevier Ltd.

28
H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
results of the research on relatively longer lifetime and its theo-
retical explanation are also reported. Dual core and triple core
studies have been reported using anthracene and pyrene groups.
However, this study proposes a homogeneous dual core system. A
homogeneous dual core can be composed of chromophore such as
anthracene, pyrene, chrysene, carbazole, or fluorene. Among these,
anthracene is a representative blue chromophore with a wide band
gap, high fluorescence quantum yield, and good thermal stability.
In this study, we used anthracene group as a homogeneous dual
core. The homogeneous dual core used here is 9,9'-bianthracene,
defined as the AA core, and differs from conventional heteroge-
neous dual core chromophores. In the AA core, two anthracenes are
connected to a single bond at the 9 and 90 positions. According to
the crystallographic information, the dihedral angle formed by the
two anthracene is approximately 89.4ꢀ due to strongly repulsive
hydrogen atoms located at the 1,10 and 8,80 positions [22]. In
addition, in an electronically decoupled structure with an orthog-
onal structure in the ground state, like the AA core, strong elec-
tronic interaction is observed for the relaxed state of the excited
state [23e25]. Thus, the AA core can have its own high PL efficiency.
Aromatic side groups with different sizes and aromatic amine
side groups with the electron donating effect were used on the AA
core, unlike in previous studies. We also studied side group opti-
mization for the AA core by systematically changing the side group
symmetrically or asymmetrically. The m-terphenyl group (TP) and
triphenylbenzene (TPB) were used as bulky aromatic side groups,
and diphenylamine (DPA) and triphenylamine (TPA) were used as
aromatic amine side groups with the electron donating effect. The
six materials synthesized were 10,10'-di([1,1':30,100-terphenyl]-5'-
yl)-9,9'-bianthracene (TP-AA-TP); 10-([1,1':30,100-terphenyl]-5'-yl)-
10'-(5'-phenyl-[1,1':30,100-terphenyl]-4-yl)-9,9'-bianthracene (TP-
67.32 mmol), and Pd(PPh3)4 (2.12 g, 1.84 mmol) were added to
anhydrous tetrahydrofuran (THF) solution (200 mL) under nitro-
gen. Then, 2 M K2CO3 solution (95 mL) dissolved in H2O was added
to the reaction mixture at 50 ꢀC. The mixture was refluxed for 4 h.
After the reaction was complete, the reaction mixture was extrac-
ted with chloroform and water. The organic layer was dried with
anhydrous MgSO4 and filtered. The solution was evaporated. The
product was isolated with silica gel column chromatography using
chloroform: n-hexane (1:20) as the eluent to obtain a white solid
(5.68 g, 60%). 1H NMR (300 MHz, CDCl3, 25 ꢀC, TMS):
3H), 7.62 (d, J ¼ 6.9, 4H), 7.47 (t, J ¼ 6.9, 4H), 7.39 (t, J ¼ 7.2, 2H).
Compound [2]
2-([1,1':3′,100-terphenyl]-5'-yl)-4,4,5,5-
d (ppm) 7.70 (s,
tetramethyl-1,3,2-dioxaborolane compound [1] (5 g, 16.2 mmol)
was added to anhydrous THF solution (200 mL) under nitrogen.
Then, 2.0 M n-butyllithium (9.7 mL, 19.5 mmol) was added slowly
at
ꢁ78
ꢀC.
Next,
isopropoxy-4,4,5,5-tetramethyl-1,3,2-
dioxaborolane (4.65 mL, 24.3 mmol) was added to the reaction
mixture, and the mixture was stirred at room temperature. After
the reaction was complete, the reaction mixture was extracted with
chloroform and water. The organic layer was dried with anhydrous
MgSO4 and filtered. The mixture was evaporated. The residue was
re-dissolved in chloroform and added to excess methanol. The
precipitate was filtered and washed with methanol to obtain a
white solid (5.19 g, 90%). 1H NMR (300 MHz, CDCl3, 25 ꢀC, TMS):
d
(ppm) 8.03 (s, 2H), 7.90 (s, 1H), 7.69 (d, J ¼ 6.9, 4H), 7.45 (t, J ¼ 7.2,
4H), 7.35 (t, J ¼ 7.5, 2H), 1.37 (s, 12H).
Compound [3] 4-bromo-5'-phenyl-1,1':3′,100-terphenyl com-
pound [2] (3.5 g, 9.82 mmol), 1,4-dibromobenzene (3.3 g,
13.2 mmol), and Pd(PPh3)4 (0.4 g, 0.34 mmol) were added to
anhydrous THF solution (30 mL) under nitrogen. Then, 2 M K2CO3
solution (3.0 mL) dissolved in H2O was added to the reaction
mixture at 50 ꢀC. The mixture was refluxed overnight under ni-
trogen. After the reaction was complete, the reaction mixture was
extracted with chloroform and water. The organic layer was dried
with anhydrous MgSO4 and filtered. The solution was evaporated.
The product was isolated with silica gel column chromatography
using chloroform: n-hexane (1:5) as the eluent to obtain a white
solid (2.01 g, 53%). 1H NMR (300 MHz, [D6]DMSO, 25 ꢀC, TMS):
AA-TPB);
10,10'-bis(5'-phenyl-[1,1':30,100-terphenyl]-4-yl)-9,9'-
bianthracene (TPB-AA-TPB); 10'-([1,1':30,100-terphenyl]-5'-yl)-N,N-
diphenyl-[9,9'-bianthracen]-10-amine
(TP-AA-DPA);
4-(10'-
([1,1':30,100-terphenyl]-5'-yl)-[9,9'-bianthracen]-10-yl)-N,N-diphe-
nylaniline (TP-AA-TPA); N,N-diphenyl-4-(10'-(5'-phenyl-[1,1':30,100-
terphenyl]-4-yl)-[9,9'-bianthracen]-10-yl)aniline
(Scheme 1).
(TPB-AA-TPA)
d
(ppm) 7.90e7.84 (m, 9H), 7.70 (d, J ¼ 8.7, 2H), 7.51 (t, J ¼ 7.2, 4H),
7.41 (t, J ¼ 7.2, 2H).
2. Experimental
Compound [4] 9,9'-bianthracene anthraquinone (10 g,
48 mmol) and zinc powder (25 g, 33 mmol) were dissolved in acetic
acid (240 mL). Then, HCl (60 mL) was added slowly at 50 ꢀC. The
mixture was refluxed overnight. After the reaction was complete,
the mixture was cooled at room temperature. The mixture was
filtered and washed with methanol. The residue was re-dissolved in
chloroform and added to excess ethanol. The precipitate was
2.1. Synthesis
13C NMR data of the Type (B) materials could not be obtained
because of the very low solubilities.
Compound
[1]
5'-bromo-1,1':3′,100-terphenyl
1,3,5-
tribromobenzene (10 g, 30.60 mmol), phenylboronic acid (8.22 g,
Scheme 1. Chemical structures of the synthesized compounds.

H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
29
filtered and washed with ethanol to obtain a beige solid (5.10 g,
30%). 1H NMR (300 MHz, CDCl3, 25 ꢀC, TMS):
(ppm) 8.68 (s, 2H),
8.16 (d, J ¼ 8.7, 4H), 7.44 (t, J ¼ 7.8, 4H), 7.16e7.06 (m, 8H).
with silica gel column chromatography using chloroform: n-hexane
(1:5) as the eluent to obtain a white solid (1.27 g, 84%). 1H NMR
d
(300 MHz, CDCl3, 25 ꢀC, TMS):
d
(ppm) 8.70 (s, 1H), 8.18 (d, J ¼ 8.7,
Compound [5] 10,10'-dibromo-9,9'-bianthracene compound
[4] (5.0 g, 14.1 mmol) and N-bromosuccinimide (NBS), (5.52 g,
31.0 mmol) were added to chloroform (300 mL), and then acetic
acid (50 mL) was added to the reaction mixture. The mixture was
refluxed for 3 h. After the reaction was complete, the reaction
mixture was extracted with chloroform and water. The organic
layer was dried with anhydrous MgSO4 and filtered. The solution
was evaporated. The residue was re-dissolved in chloroform and
added to excess ethanol. The precipitate was filtered and washed
with ethanol to obtain a yellow solid (6.64 g, 92%). 1H NMR
2H), 8.08 (s, 1H), 7.99 (d, J ¼ 8.7, 2H), 7.88 (s, 2H) 7.83 (d, J ¼ 8.4, 4H),
7.53e7.32 (m, 10H), 7.21e7.13 (m, 8H).
Compound [10] 10-([1,1':3′,100-terphenyl]-5'-yl)-10'-bromo-
9,9'-bianthracene compound [9] (1.28 g, 2.2 mmol) and NBS
(0.47 g, 2.64 mmol) were added to chloroform (170 mL), and acetic
acid (25 mL) was added to the reaction mixture. The mixture was
refluxed for 4 h. After the reaction was complete, the reaction
mixture was extracted with chloroform and water. The organic
layer was dried with anhydrous MgSO4 and filtered. The solution
was evaporated. The residue was re-dissolved in chloroform and
added to excess ethanol. The precipitate was filtered and washed
with ethanol to obtain a yellow solid (1.41 g, 97%). 1H NMR
(300 MHz, CDCl3, 25 ꢀC, TMS):
J ¼ 7.5, 4H), 7.18 (t, J ¼ 9.0, 4H), 7.08 (d, J ¼ 7.5, 4H).
Compound [6] 10,10'-bis(4,4,5,5-tetramethyl-1,3,2-
d
(ppm) 8.72 (d, J ¼ 9.0, 4H), 7.58 (t,
(300 MHz, [D8]THF, 25 ꢀC):
d
(ppm) 8.73 (d, J ¼ 9.0, 2H), 8.21 (s, 1H),
dioxaborolan-2-yl)-9,9'-bianthracene compound [5] (10 g,
19.5 mmol) was added to anhydrous THF solution (400 mL) under
nitrogen. Then, 2.0 M n-butyllithium (22 mL, 39.2 mmol) was
added slowly at ꢁ78 ꢀC. Next, isopropoxy-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (8.0 mL, 39.2 mmol) was added to the reaction
mixture and stirred at room temperature. After the reaction was
finished, the reaction mixture was extracted with chloroform and
water. The organic layer was dried with anhydrous MgSO4 and
filtered. The mixture was evaporated. The product was isolated
with silica gel column chromatography using chloroform: n-hexane
(1:2) as the eluent to obtain a white solid (4.26 g, 36%). 1H NMR
7.98 (d, J ¼ 9.0, 2H), 7.91e7.87 (m, 6H), 7.63 (t, J ¼ 7.5, 2H), 7.48 (t,
J ¼ 7.5, 4H), 7.40e7.32 (m, 4H), 7.27e7.07 (m, 8H).
Compound [11] 10-(5'-phenyl-[1,1':3′,100-terphenyl]-4-yl)-
9,9'-bianthracene compound [8] (2.50 g, 5.2 mmol), compound [3]
(2.41 g, 6.42 mmol), and Pd(PPh3)4 (0.24 g, 0.21 mmol) were added
to anhydrous toluene solution (600 mL) and anhydrous ethanol
(400 mL) under nitrogen. Then, 2 M K2CO3 solution (100 mL) dis-
solved in H2O was added to the reaction mixture at 50 ꢀC. After the
reaction was complete, the reaction mixture was extracted with
chloroform and water. The organic layer was dried with anhydrous
MgSO4 and filtered. The solution was evaporated. The product was
isolated with silica gel column chromatography using chloroform:
n-hexane (1:5) as the eluent to obtain a white solid (2.40 g, 73%). 1H
(300 MHz, CDCl3, 25 ꢀC, TMS):
J ¼ 7.8, 4H), 7.10e7.02 (m, 8H), 1.65 (s, 24H).
d
(ppm) 8.50 (d, J ¼ 8.7, 4H), 7.43 (t,
Compound [7] 10-bromo-9,9'-bianthracene compound [4]
(5.0 g, 14.1 mmol) and NBS (2.76 g, 15.5 mmol) were added to
chloroform (300 mL), and acetic acid (15 mL) was added to the
reaction mixture. The mixture was refluxed for 2 h. After the re-
action was complete, the reaction mixture was extracted with
chloroform and water. The organic layer was dried with anhydrous
MgSO4 and filtered. The solution was evaporated. The residue was
re-dissolved in chloroform and added to excess ethanol. The pre-
cipitate was filtered and washed with ethanol to obtain a yellow
solid (4.89 g, 80%). 1H NMR (300 MHz, [D8]THF, 25 ꢀC, TMS):
NMR (300 MHz, [D6]DMSO, 25 ꢀC):
d (ppm) 8.92 (s, 1H), 8.32 (d,
J ¼ 8.7, 2H), 8.26 (d, J ¼ 8.1, 2H), 8.15 (s, 2H), 7.99 (d, J ¼ 8.7, 5H), 7.85
(d, J ¼ 8.7, 2H), 7.78 (d, J ¼ 8.1, 2H), 7.58e7.52 (m, 6H), 7.45 (t, J ¼ 7.5,
4H), 7.31e7.21 (m, 4H), 7.01 (t, J ¼ 9.3, 4H).
Compound
[12]
10-bromo-10'-(5'-phenyl-[1,1':3′,100-ter-
phenyl]-4-yl)-9,9'-bianthracene compound [11] (1.4 g, 2.13 mmol)
and NBS (0.42 g, 2.34 mmol) were added to chloroform (140 mL),
and then acetic acid (20 mL) was added to the reaction mixture.
After the reaction was complete, the reaction mixture was extrac-
ted with chloroform and water. The organic layer was dried with
anhydrous MgSO4 and filtered. The solution was evaporated. The
residue was re-dissolved in chloroform and added to excess
ethanol. The precipitate was filtered and washed with ethanol to
obtain a beige solid (1.54 g, 98%). 1H NMR (300 MHz, [D6]DMSO,
d
(ppm) 8.78 (s, 1H), 8.70 (d, J ¼ 9.0, 2H), 8.19 (d, J ¼ 8.4, 2H), 7.59 (t,
J ¼ 7.8, 2H), 7.46 (t, J ¼ 7.8, 2H), 7.21e6.99 (m, 8H).
Compound [8] 2-([9,9'-bianthracen]-10-yl)-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane compound [7] (10 g,
19.5 mmol) was added to anhydrous THF solution (400 mL) under
nitrogen. Then, 11.7 mL of 2.0 M n-butyllithium (23 mmol) was
added slowly at ꢁ78 ꢀC. Next, 4 mL of isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (27.3 mmol) was added to the
reaction mixture and stirred at room temperature. After the reac-
tion was complete, the reaction mixture was extracted with chlo-
roform and water. The organic layer was dried with anhydrous
MgSO4 and filtered. The mixture was evaporated. The product was
isolated with silica gel column chromatography using chloroform:
n-hexane (1:2) as the eluent to obtain a white solid (3.36 g, 36%). 1H
25 ꢀC):
d
(ppm) 8.68 (d, J ¼ 8.7, 2H), 8.27 (d, J ¼ 8.4, 2H), 8.15 (s, 2H),
7.99 (d, J ¼ 8.4, 5H), 7.86 (d, J ¼ 8.7, 2H), 7.79e7.72 (m, 4H), 7.56 (t,
J ¼ 7.2, 4H), 7.45 (t, J ¼ 7.2, 4H), 7.38 (t, J ¼ 8.7, 2H), 7.28 (t, J ¼ 7.5,
2H) 7.12 (d, J ¼ 9.0, 2H), 7.01 (d, J ¼ 9.0, 2H).
Compound [13] N,N-diphenyl-4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)aniline
(4-Bromo-phenyl)-diphenyl-amine
(8.0 g, 24.7 mmol) was added to anhydrous THF solution (300 mL)
under nitrogen. Then, 2.0 M n-butyllithium (18.54 mL, 25.4 mmol)
was added slowly at ꢁ78 ꢀC. Next, triethylborate (5.89 mL,
25.4 mmol) was added to the reaction mixture, followed by HCl
(4.53 mL, 49.4 mmol) at room temperature. After the reaction was
complete, the reaction mixture was extracted with ethyl acetate
(EA) and water. The organic layer was dried with anhydrous MgSO4
and filtered. The mixture was evaporated. The residue was re-
dissolved in THF and added to hexane. The precipitate was
filtered and washed with hexane to obtain a white solid (5.0 g, 70%).
NMR (300 MHz, CDCl3, 25 ꢀC, TMS):
d (ppm) 8.66 (s, 1H), 8.52 (d,
J ¼ 8.7, 2H), 8.15 (d, J ¼ 8.7, 2H), 7.47e7.40 (m, 4H), 7.14e7.05 (m,
8H), 1.66 (s, 12H).
Compound [9] 10-([1,1':3′,100-terphenyl]-5'-yl)-9,9'-bian-
thracene compound [8] (1.25 g, 2.60 mmol), compound [1] (1.02 g,
3.31 mmol), and Pd(PPh3)4 (0.18 g, 0.15 mmol) were added to
anhydrous THF solution (150 mL) under nitrogen. Then, 2 M K2CO3
solution (15 mL) dissolved in H2O was added to the reaction
mixture at 50 ꢀC and refluxed overnight. After the reaction was
complete, the reaction mixture was extracted with chloroform and
water. The organic layer was dried with anhydrous MgSO4 and
filtered. The solution was evaporated. The product was isolated
1H NMR (300 MHz, [D8]THF, 25 ꢀC):
d
(ppm) 7.67 (d, J ¼ 8.4, 2H),
7.21 (t, J ¼ 8.4, 4H), 7.06e6.95 (m, 10H).
Compound[TP-AA-TP] 10,10'-di([1,1':3′,100-terphenyl]-5'-yl)-
9,9'-bianthracene compound [6] (1.0 g, 1.65 mmol), compound [1]
(1.12 g, 3.62 mmol), Pd(OAC)2 (0.022 g, 0.10 mmol), and tricyclo-
hexylphosphine (0.056 g, 0.20 mmol) were added to anhydrous

30
H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
toluene (200 mL) and anhydrous ethanol (140 mL) solution. Then,
(Et)4NOH (20 wt%, 35 mL) was added to the reaction mixture at
50 ꢀC. The mixture was refluxed for 4 h under nitrogen. After the
reaction was complete, the reaction mixture was extracted with
chloroform and water. The organic layer was dried with anhydrous
MgSO4 and filtered. The solution was evaporated. The product was
isolated with silica gel column chromatography using chloroform:
n-hexane (1:3) as the eluent to obtain a white solid (0.98 g, 73%). 1H
with silica gel column chromatography using toluene: n-hexane
(1:3) as the eluent to obtain a white solid (0.26 g, 26%) 1H NMR
(300 MHz, [D6]DMSO, 25 ꢀC):
d (ppm) 8.25e8.22 (m, 3H), 7.98e7.90
(m, 8H), 7.55e7.41 (m, 10H), 7.33e7.24 (m, 8H), 7.19e7.11 (m, 8H),
6.97 (t, J ¼ 7.2, 2H); HRMS (FAB-MS, m/z): calcd. for C58H39N,
749.3083; found, 749.3082 [M]þ. Anal. calcd for C58H39N: C 92.89,
H 5.24, N 1.87; found: C 92.50, H 5.48, N 1.83%.
Compound[TP-AA-TPA] 4-(10'-([1,1':3′,100-terphenyl]-5'-yl)-
[9,9'-bianthracen]-10-yl)-N,N-diphenylaniline compound [10]
(1.57 g, 2.39 mmol), compound [13] (0.85 g, 2.86 mmol), Pd(OAC)2
(0.032 g, 0.14 mmol), and tricyclohexylphosphine (0.04 g,
0.14 mmol) were added to anhydrous THF (110 mL) solution. Then,
(Et)4NOH (20 wt%, 11 mL) was added to the reaction mixture at
50 ꢀC. The mixture was refluxed for 1 h under nitrogen. After the
reaction was finished, the reaction mixture was extracted with
chloroform and water. The organic layer was dried with anhydrous
MgSO4 and filtered. The solution was evaporated. The product was
isolated with silica gel column chromatography using chloroform:
n-hexane (1:6) as the eluent to obtain a white solid (0.59 g, 30%). 1H
NMR (300 MHz, [D8]THF, 25 ꢀC):
d (ppm) 8.21 (s, 2H), 8.01 (d,
J ¼ 9.0, 4H), 7.95 (s, 4H), 7.91 (d, J ¼ 7.2, 8H), 7.49 (t, J ¼ 7.2, 8H), 7.37
(t, J ¼ 9.3, 8H), 7.25e7.15 (m, 8H); 13C NMR (75 MHz, [D8]THF,
25 ꢀC):
d (ppm) 142.61, 141.22, 140.73, 138.28, 134.01, 131.98, 130.77,
129.46, 129.24, 128.04, 127.70, 127.35, 126.06, 125.91, 125.29; HRMS
(FAB-MS, m/z): calcd. for C64H42, 810.3287; found, 810.3286 [M]þ.
Anal. calcd for C64H42: C 94.78, H 5.22; found: C 90.19, H 5.34%.
Compound[TP-AA-TPB] 10-([1,1':3′,100-terphenyl]-5'-yl)-10'-
(5'-phenyl-[1,1':3′,100-terphenyl]-4-yl)-9,9'-bianthracene
com-
pound [12] (0.6 g, 0.81 mmol), compound [2] (0.35 g, 0.97 mmol),
and Pd(PPh3)4 (0.03 g, 0.024 mmol) were added to anhydrous
toluene solution (300 mL) and anhydrous ethanol (200 mL) under
nitrogen. Then, 2 M K2CO3 solution (50 mL) dissolved in H2O was
added to the reaction mixture at 50 ꢀC. After the reaction was
complete, the reaction mixture was extracted with chloroform and
water. The organic layer was dried with anhydrous MgSO4 and
filtered. The solution was evaporated. The product was isolated
with silica gel column chromatography using chloroform: n-hexane
(1:3) as the eluent to obtain a white solid (0.55 g, 76%). 1H NMR
NMR (300 MHz, [D8]THF, 25 ꢀC):
d
(ppm) 8.21 (s,1H), 7.99 (d, J ¼ 9.0,
4H), 7.94 (s, 2H), 7.90 (d, J ¼ 7.2, 4H), 7.51e7.46 (m, 6H), 7.40e7.27
(m, 16H), 7.21e7.06 (m, 10H); HRMS (FAB-MS, m/z): calcd. for
C
64H43N, 825.3396; found, 825.3394 [M]þ. Anal. calcd for C64H43N:
C 93.06, H 5.25, N 1.70; found: C 92.66, H 5.24, N 1.69%.
Compound[TPB-AA-TPA]
N,N-diphenyl-4-(10'-(5'-phenyl-
[1,1':3′,100-terphenyl]-4-yl)-[9,9'-bianthracen]-10-yl)aniline
compound [12] (0.5 g, 0.68 mmol), compound [13] (0.26 g,
0.82 mmol), Pd(OAC)2 (0.012 g, 0.054 mmol), and tricyclohex-
ylphosphine (0.015 g, 0.054 mmol) were added to anhydrous THF
(130 mL) solution. Then, (Et)4NOH (20 wt%,14 mL) was added to the
reaction mixture at 50 ꢀC. The mixture was refluxed for 3 h under
nitrogen. After the reaction was complete, the reaction mixture was
extracted with chloroform and water. The organic layer was dried
with anhydrous MgSO4 and filtered. The solution was evaporated.
The product was isolated with silica gel column chromatography
using toluene: n-hexane (1:2) as the eluent to obtain a beige solid
(300 MHz, [D8]THF, 25 ꢀC):
d
(ppm) 8.22 (s, 1H), 8.18 (d, J ¼ 8.1, 2H),
8.13 (s, 2H), 8.01e7.87 (m, 15H), 7.78 (d, J ¼ 8.1, 2H), 7.53e7.46 (m,
8H), 7.42e7.34 (m, 8H), 7.24e7.15 (m, 8H); 13C NMR (75 MHz, [D8]
THF, 25 ꢀC):
d (ppm) 140.61, 140.22, 140.09, 139.27, 138.83, 138.72,
138.34, 136.51, 135.88, 135.73, 131.61, 131.58, 130.01, 129.59, 128.37,
127.08, 126.85, 126.82, 125.65, 125.53, 124.98, 123.68, 123.65,
123.53, 123.40, 122.98; HRMS (FAB-MS, m/z): calcd. for C70H46
,
886.3600; found, 886.3604 [M]þ. Anal. calcd for C70H46: C 94.77, H
5.23; found: C 94.48, H 5.39%.
Compound[TPB-AA-TPB] 10,10'-bis(5'-phenyl-[1,1':3′,100-ter-
phenyl]-4-yl)-9,9'-bianthracene compound [6] (3.0 g, 4.95 mmol),
compound [3] (4.58 g, 11.88 mmol), Pd(OAC)2 (0.03 g, 0.15 mmol),
and tricyclohexylphosphine (0.08 g, 0.3 mmol) were added to
anhydrous toluene (50 mL) and anhydrous ethanol (20 mL) solu-
tion. Then (Et)4NOH (20 wt%, 15 mL) was added to the reaction
mixture at 50 ꢀC. The mixture was refluxed for 4 h under nitrogen.
After the reaction was complete, the reaction mixture was extrac-
ted with chloroform and water. The organic layer was dried with
anhydrous MgSO4 and filtered. The solution was evaporated. The
product was isolated with silica gel column chromatography using
chloroform: n-hexane (1:2) as the eluent to obtain a white solid
(0.50 g, 81%). 1H NMR (300 MHz, [D6]DMSO, 25 ꢀC):
d (ppm) 8.27 (d,
J ¼ 8.4, 2H), 8.16 (s, 2H), 7.99 (d, J ¼ 8.1, 5H), 7.90 (t, J ¼ 8.7, 4H), 7.80
(d, J ¼ 8.4, 2H), 7.58e7.41 (m, 16H), 7.31e7.25 (m, 10H), 7.18 (t,
J ¼ 2.1, 2H), 7.13 (d, J ¼ 9.0, 4H); HRMS (FAB-MS, m/z): calcd. for
C
70H47N, 901.3709; found, 901.3712 [M]þ. Anal. calcd for C70H47N:
C 93.20, H 5.25, N 1.55; found: C 92.97, H 5.28, N 1.62%.
2.2. Measurements and OLED fabrication
Reagents and solvents were purchased as reagent grade and
used without further purification. Analytical TLC was carried out on
Merck 60 F254 silica gel plate, and column chromatography was
performed on Merck 60 silica gel (230e400 mesh). The 1H NMR
and 13C NMR spectra were recorded on Bruker Avance 300 spec-
trometers. The FABþ-mass and EIþ-spectra were recorded on a
JMS-600W, JMS-700, 6890 Series and Flash1112, Flash2000. The
optical UV-Vis absorption spectra were obtained using a Lambda
1050 UV/Vis/NIR spectrometer (Perkin Elmer). A Perkin-Elmer
luminescence spectrometer LS55 (Xenon flash tube) was used to
perform PL spectroscopy. The glass transition temperatures (Tg) of
the compounds were DSC under a nitrogen atmosphere using a DSC
4000 (Perkin Elmer). Samples were heated to 360 ꢀC or 400 ꢀC at a
rate of 10 ꢀC/min, cooled at 10 ꢀC/min, and then heated again under
the same heating condition used in the initial heating process. Td of
the compounds were measured with TGA using a TGA4000 (Perkin
Elmer). Samples were heated to 800 ꢀC at a rate of 10 ꢀC/min. The
HOMO energy levels were determined with ultraviolet photoelec-
tron yield spectroscopy (Riken Keiki AC-2). The LUMO energy levels
were derived from the HOMO energy levels and the band gaps. For
(3.58 g, 75%). 1H NMR (300 MHz, [D8]THF, 25 ꢀC):
d (ppm) 8.19e8.13
(m, 8H), 7.98 (s, 2H), 7.94 (s, 2H), 7.91e7.87 (m, 10H), 7.78 (d, J ¼ 8.4,
4H), 7.51 (t, J ¼ 7.2, 8H), 7.42e7.34 (m, 8H), 7.24e7.15 (m, 8H); 13C
NMR (75 MHz, [D8]THF, 25 ꢀC):
d (ppm) 143.00, 143.48, 141.67,
141.11, 138.90, 138.12, 133.96, 132.40, 131.97, 130.76, 129.21, 127.92,
127.69, 127.63, 127.40, 126.05, 125.79; HRMS (FAB-MS, m/z): calcd.
for C76H50, 962.3913; found, 962.3905 [M]þ. Anal. calcd for C76H50
:
C 94.77, H 5.23; found: C 93.44, H 5.24%.
Compound[TP-AA-DPA] 10'-([1,1':3′,100-terphenyl]-5'-yl)-N,N-
diphenyl-[9,9'-bianthracen]-10-amine compound [10] (0.87 g,
1.32 mmol), diphenylamine (0.27 g, 1.58 mmol), Pd(OAC)2 (0.009 g,
0.04 mmol), sodium tert-butoxide (0.38 g, 3.95 mmol), and 1.0 M
tri-tert-butlyphosphine in toluene (0.08 mL) were added to anhy-
drous toluene (180 mL) solution under nitrogen. After the reaction
was complete, the reaction mixture was extracted with EA and
water. The organic layer was dried with anhydrous MgSO4 and
filtered. The solution was evaporated. The product was isolated

H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
31
the EL devices, all organic layers were deposited under 10ꢁ6 torr,
with a rate of deposition of 1 Å/s to give an emitting area of 4 mm2.
The LiF and aluminum layers were continuously deposited under
the same vacuum conditions. The current-voltage-luminance (I-V-
L) characteristics of the fabricated EL devices were obtained with a
Keithley 2400 electrometer. Light intensities were obtained with a
Minolta CS-1000A. To calibrate the EQE values considering the
angular dependence, emission angular distributions were also
measured. The operational stabilities of the devices were measured
under encapsulation in a glovebox. Delayed fluorescence under
electrical pulse excitations was measured using a function gener-
ator (Agilent 33220A) and an amplified Si photodetector (Thorlabs
PDA8A).
are summarized in Fig. 1 and Table 1. In the solution and film states,
the ultraviolet-visible (UV-Vis) absorption shapes of the six syn-
thesized materials, which have the intrinsic pattern of anthracene,
mainly presented in the range of 360 nme410 nm (Fig. 1). The
highly twisted structure prevents increase in the conjugation
length of AA itself so that the UV-Vis absorption spectrum and the
PL spectrum of AA derivative are similar to those of a single
anthracene core derivative [9,10,22]. Unlike the other five mate-
rials, TP-AA-DPA(4) had a different UV-Vis absorption peak at
approximately 450 nm in the solution and film states. This is
thought to be the UV-Vis absorption peak due to the intramolecular
charge transfer, which occurs only when the aromatic amine group
is directly substituted in anthracene [26e30].
In solution state, TP-AA-TP(1), TP-AA-TPB(2), and TPB-AA-
TPB(3) (Type (A)), the PL maximum values were similar, with the
values of 434, 433, and 433 nm, respectively. In the cases of TP-AA-
DPA(4), TP-AA-TPA(5), and TPB-AA-TPA(6) (Type (B)), the PL
maximum values of 494, 458, and 458 nm, respectively, were red-
shifted compared to those of Type (A). We can compare the PL
maximum values of Type (A) with an aromatic ring composed of
only carbon and hydrogen as a side group and those of Type (B) in
which an amine group is substituted for the phenyl ring of Type (A).
In solution state, TP-AA-DPA(4) was red-shifted approximately
60 nm compared to TP-AA-TP(1), and TP-AA-TPA(5) and TPB-AA-
TPA(6) were red-shifted approximately 25 nm compared to TP-
AA-TPB(2) and TPB-AA-TPB(3). This is interpreted to be a result of
the electron donating effect of the substituted aromatic amine side
groups. In the case of TP-AA-DPA(4), in which DPA was substituted
3. Results and discussion
3.1. Synthesis and optical properties
AA dual core was prepared by reduction coupling of 9-
anthraquinone using zinc, and other reactions used boronylation,
bromination, and Suzuki aryl-aryl coupling reactions. The synthesis
methods are described in more detail in Scheme 2 and the exper-
imental section. All synthesized materials were purified with rep-
recipitation and the column chromatography method. The
synthesized compounds were characterized using nuclear mag-
netic resonance (NMR) spectroscopy, elemental analysis, and FAB
mass analysis.
The optical and thermal properties of the synthesized materials
Scheme 2. Synthetic routes of synthesized compounds.

32
H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
Fig. 1. UV-Vis absorption spectra and PL spectra of synthesized materials: (a) and (b) 1.0 ꢂ 10ꢁ5 M toluene solution; (c) and (d) vacuum-deposited film state.
Table 1
Optical and thermal properties of the synthesized materials.
Compounds
Solutiona
Film on glassb
HO
LU
MO
(eV)
Band gap
(ev)
Tg
(ꢀC)
Tm
(ꢀC)
Td
(ꢀC)
MOc
(eV)
UV
(nm)
PL
(nm)
UV
(nm)
PL
(nm)
TP-AA-TP
361,381,403
361,381,403
361,382,404
361,380,400,444
361,382,404
362,382,404
434
433
433
494
458
458
365,385,407
366,386,408
366,386,408
365,384,403,450
366,386,408
367,387,409
449
453
464,499
503
469
ꢁ5.78
ꢁ5.68
ꢁ5.68
ꢁ5.61
ꢁ5.59
ꢁ5.60
ꢁ2.88
ꢁ2.78
ꢁ2.79
ꢁ3.05
ꢁ2.86
ꢁ2.85
2.90
2.90
2.89
2.56
2.73
2.75
176
203
206
192
e
427
418
425
424
335
371
465
516
525
425
470
520
TP-AA-TPB
TPB-AA-TPB
TP-AA-DPA
TP-AA-TPA
TPB-AA-TPA
469
e
a
1.00 ꢂ 10ꢁ5 M toluene solution.
b
c
Film thickness is 50 nm on the glass.
Ultraviolet photoelectron spectroscopy.
to maximize the electron donating effect in the AA core, the PL
maximum value was the most highly red-shifted. However, when
TPA was substituted, one phenyl ring was positioned between the
core and the DPA side group, resulting in a reduction of the electron
donating effect of DPA and a smaller red-shift of substituted DPA.
Generally, the PL maximum value in the film state is red-shifted
as the distance between the molecules becomes closer than in the
solution state. The film PL maximum values of TP-AA-TP(1), TP-AA-
TPB(2), and TPB-AA-TPB(3) were 449, 453, and 464 nm, respec-
tively. The PL maximum values for the film state of TP-AA-TP(1), TP-
AA-TPB(2), and TPB-AA-TPB(3) were red-shifted by 15, 20, and
31 nm compared to the PL maximum values of the solution state. In
addition, when the substituted side group was changed from TP to
TPB, the intermolecular conjugation length was increased by the
added phenyl ring in the side group, and the PL maximum value
shifted from 449 nm to 453 nm and 464 nm. TPB-AA-TPB(3)

H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
33
showed the emission of the excimer peak at 499 nm in addition to
464 nm. When the size of the side group is properly matched with
the size of the whole molecule, the excimer may be generated in
the film state, inducing the orientation of the molecule, which was
shown previously [20]. PL spectra change with increasing concen-
tration, excitation spectra, and time-resolved PL measurement ex-
periments were analyzed to confirm that 499 nm of TPB-AA-TPB(3)
was excimer emission peak.
temperatures (Tm) and the decomposition temperatures (Td) of the
synthesized materials were determined with differential scanning
calorimetry (DSC) and thermogravimetric analysis (TGA) as shown
in Table 1.
In the case of Type (A), HOMO level was ꢁ5.68 eV to ꢁ5.78 eV,
while that of Type (B) was ꢁ5.59 eV to ꢁ5.61 eV. When Type (A)
and Type (B) were compared, Type (B) had a 0.09 eVe0.17 eV higher
HOMO level than that of Type (A). This is the result of the increased
electron donating effect of the aromatic amine group acting on
Type (B).
Firstly, using toluene, PL spectra change at concentrations from
1.0 ꢂ 10ꢁ5 M to 1.0 ꢂ 10ꢁ2 M was measured (Fig. S1, ESI). The
excimer peak is not seen at the diluted concentration (ex:
1.0 ꢂ 10ꢁ5 M); however, as the concentration increases, intermo-
The Td values of the six synthesized material showed that the
higher was the molecular weight, the higher was the Td value. The
order of molecular weight for Type (A) is TPB-AA-TPB(3) > (2)TP-
lecular aggregation,
p-p electron stacking, and the excimer peak
would occur [31,32]. PL maximum value of TPB-AA-TPB(3) was red-
shifted from 433 nm to 462 nm as the concentration increases, and
the excimer peak at 490 nm can be simultaneously observed from
2.5 ꢂ 10ꢁ3 M. Secondly, the excitation spectra of TPB-AA-TPB(3) in
the film state were measured. Excitation spectra were measured
along with the UV-Vis absorption spectrum (Fig. S2, ESI). The UV-
Vis absorption spectrum matched well with the excitation
spectra. The excitation spectra monitored at 464 nm and 499 nm
are very similar, indicating that they arise from the same excitation
pathway. Thirdly, time-resolved PL was measured when TPB-AA-
TPB(3) was in the film state. The excimer generally has a longer
decay lifetime than the original peak material [33]. The average
decay rate of TPB-AA-TPB(3) was 0.93 ns at 464 nm and 2.03 ns at
499 nm, and the decay lifetime at 499 nm was relatively longer
(Fig. S3, ESI) [19e21]. From these three experimental results, PL
emission at 499 nm for TPB-AA-TPB(3) was determined to be the
excimer peak.
In the film states of TP-AA-DPA(4), TP-AA-TPA(5), and TPB-AA-
TPA(6), which are Type (B), the PL maximum value was red shif-
ted from that of Type (A) and showed PL maximum values at
503 nm, 469 nm, and 469 nm, respectively. This trend was similar
to that seen in the solution state. When the film PL maximum
values were compared with the solution PL maximum values of
Type (B), they were red-shifted 9 nme11 nm. It was relatively red-
shifted less than Type (A) which was approximately red-shifted
15 nme31 nm. Since Type (B) with a polar aromatic amine side
group has different interactions depending on the polarity of sol-
vent compared to Type (A), a change in the PL maximum value
mainly occurs in the solution state [10].
AA- TPB
>
TP-AA-TP(1), and that of Td values is
525 ꢀC > 516 ꢀC > 465 ꢀC. In the case of Type (B), the molecular
weights were determined to be in the order of TPB-AA-TPA(6) > TP-
AA-TPA(5) > TP-AA-DPA(4), and Td values were in the order of
520 ꢀC > 470 ꢀC > 425 ꢀC. All Td values of the synthesized materials
showed high thermal stability with a minimum value of 425 ꢀC. The
Td values of these materials showed an increase of 28 ꢀCe128 ꢀC
above the Td value of 397 ꢀC for MADN, which is one of the
commercially used blue emitting materials.
Tm values of the six synthesized materials had a minimum of
335 ꢀC, and Tg values were high at a minimum of 176 ꢀC. It was
confirmed that the six materials had higher Tm values by a mini-
mum of 80 ꢀC and Tg values by a minimum of 56 ꢀC than those of
MADN, which has a Tm of 255 ꢀC and Tg of 120 ꢀC. In Type (A), Tm
values of TP-AA-TP(1) and TPB-AA-TPB(3), which has symmetric
side groups, were 427 ꢀC and 425 ꢀC, respectively. These are higher
than the Tm of 418 ꢀC for TP-AA-TPB(2), which has an asymmetric
side group. This difference comes from the symmetry of the
molecules.
The Tg value increased to 176 ꢀC, 203 ꢀC, and 206 ꢀC for TP-AA-
TP(1), TP-AA-TPB(2), and TPB-AA-TPB(3), respectively, as the mo-
lecular weight increased. When the Tg values of TP-AA-TP(1) and
TP-AA-DPA(4) were compared, TP-AA-DPA(4) was approximately
191 ꢀC, which was higher by approximately 15 ꢀC than the Tg value
of TP-AA-TP(1). This is presumably due to the generated dipole in
the TP-AA-DPA(4) molecule. It is thought that these highly thermal
characteristics can implement a stable device whose morphology
does not easily change due to the heat generated from the opera-
tion of OLED device [34].
When the film PL maximum values of Type(A) and Type (B) were
compared, TP-AA-DPA(4) was red-shifted approximately 54 nm
compared to TP-AA-TP(1). TP-AA-TPA(5) and TPB-AA-TPA(6) were
red-shifted approximately 16 nm and 5 nm compared to TP-AA-
TPB(2) and TPB-AA-TPB(3), respectively. This is due to the elec-
tron donating effect of the substituted aromatic amine side group.
When DPA is substituted, it is the most red-shifted, and TP-AA-
DPA(4) emitted in the green region. When replacing TPA, the
donating effect of electrons is slightly reduced compared to DPA
due to the phenyl ring substituting directly to the core, and it is not
significantly red-shifted. Therefore, TP-AA-TPA(5) and TPB-AA-
TPA(6) were able to maintain emission in the blue region, similar
to Type (A).
3.3. Electroluminescence properties
Using the six synthesized materials as an emitting layer (EML), a
non-doped device was fabricated with the following structure: ITO/
tris(N-(naphthalen-2-yl)-N-phenyl-amino)triphenylamine
(2-
TNATA) (60 nm)/N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzi-
dine (NPB) (15 nm)/EML (synthesized compounds, 30 nm)/8-
hydroxyquinoline aluminum (Alq3) (15 nm)/LiF (1 nm)/Al
(200 nm). Here, 2-TNATA was used as the hole injection layer (HIL),
and NPB was used as the hole transporting layer (HTL). Alq3 was
used as the electron transporting layer (ETL), LiF as the electron
injection layer (EIL), and ITO and Al were used as the anode and
cathode, respectively. The measured EL results are summarized in
Table 2.
3.2. Electrical and thermal properties
Overall, the operating voltage of Type (B) was lower than that of
Type (A). This is because the difference in HOMO energy level be-
tween NPB used as the HTL and Type (B) was 0.19 eVe0.21 eV and
was less than the 0.28 eVe0.38 eV difference between NPB and
Type (A). It is easy to induce hole injection from NPB to Type (B).
Also, the difference in LUMO energy level between Alq3 used as the
ETL and Type (B) was 0.05 eVe0.14 eV and was less than the
0.12 eVe0.23 eV difference between Alq3 and Type (A). It is also
The HOMO levels were determined by photoelectron spectros-
copy using an ultraviolet light energy source. The LUMO energy
levels were obtained from the HOMO levels and the optical band
gaps (Table 1). The optical band gaps were derived by determining
the absorption edges from plots of (hn) vs. (ahn a, h, and n
)2, where
are the absorbance, Planck's constant, and the frequency of light,
respectively. The glass transition temperatures (Tg), the melting

34
H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
Table 2
green color as the film PL.
EL performances: ITO/2-TNATA (60 nm)/NPB (15 nm)/EML (30 nm)/Alq3 (15 nm)/LiF
TP-AA-TPA(5) showed relatively lower efficiency than TP-AA-
DPA(4), with a current efficiency of 6.78 cd/A, power efficiency of
3.55 lm/W, and EQE of 4.72%. However, the weak donating effect of
the side group made it possible to maintain the emission of the blue
region with an EL maximum value of 466 nm and CIE of (0.15, 0.20).
TPB-AA-TPA(6) showed the highest efficiency among the six syn-
thesized materials, with a current efficiency of 8.97 cd/A, power
efficiency of 4.43 lm/W, and EQE of 6.37%. And the EL maximum
and CIE values of TPB-AA-TPA(6) was 466 nm and (0.14, 0.19), which
is blue emission. This result came from that the electron donating
effect and the size effect of the side group were optimized.
These EL results of synthesized materials overall showed high
performance. Especially, TPB-AA-TPA(6) has higher EL efficiency
compared to previous studies using AA core. Z. Li et al. and Y. Yu
et al. reported blue emitting materials with a current efficiency of
3.05 cd/A and EQE of 5.02% by introducing fluoro and tri-
fluoromethyl electron withdrawing side groups in AA derivatives
[40e42]. P. Zhang et al. introduced the chromophore, carbazole, as
a side group on the AA to obtain a current efficiency of 3.2 cd/A and
EQE of 3.4% and J.Y. Song et al. developed AA derivatives substituted
with triphenylsilane with a current efficiency of 2.76 cd/A and EQE
of 1.82% [43,44].
Comparing TP-AA-TP(1) with TP-AA-DPA(4), the EL efficiency of
TP-AA-DPA(4) is 1.8 times higher than that of TP-AA-TP(1) because
it increased due to the electron donating effect of the aromatic
amine side group. However, the EL maximum value of TP-AA-
DPA(4) is red-shifted 51 nm, and using DPA as a side group in the
AA core can increase the EL efficiency but presents difficulties with
blue emission [10,19]. Thus, it is necessary to add one or more
phenyl rings between the core and the side group in order to
optimize the electron donating effect and maintain the blue
emission. As a result, when TP-AA-TPA(5) is compared with TP-AA-
DPA(4), TP-AA-TPA(5) is blue-shifted 35 nm and has an EL
maximum value at 466 nm.
(1 nm)/Al (200 nm) at 10 mA/cm2.
EMLs
Operating ELmax
Current
efficiency efficiency (%)
(cd/A)
Power
EQE CIE
voltage
(V)
(nm)
(x,y)
(lm/W)
TP-AA-TP
TP-AA-TPB
TPB-AA-TPB 8.15
TP-AA-DPA
TP-AA-TPA
7.33
7.69
450
455
4.27
5.10
2.00
2.33
1.14
3.79
3.55
4.43
4.26 (0.15,0.12)
4.02 (0.17,0.15)
1.50 (0.21,0.29)
3.17 (0.19,0.52)
4.71 (0.15,0.20)
6.37 (0.14,0.19)
469,499 2.72
7.08
6.66
501
466
466
7.79
6.78
8.97
TPB-AA-TPA 7.00
easier to induce electron injection from Alq3 to Type (B) than Type
(A) (Fig. 2(a)).
Comparing the EL maximum value with the PL maximum value
showed a similar range of 450 nme501 nm. In the case of TPB-AA-
TPB(3), the excimer band appeared at 499 nm, as in the PL spec-
trum, and all materials excluding TP-AA-DPA(4) showed an EL
spectrum in the blue region (Fig. 2(b)).
The results of EL efficiencies and Commission Internationale de
L'Eclairage coordinates (CIE) are as follows. For Type (A), TP-AA-
TP(1) showed a current efficiency of 4.27 cd/A, power efficiency
of 2.00 lm/W, and external quantum efficiency (EQE) of 4.26%. TP-
AA-TPB(2) had a current efficiency of 5.10 cd/A, which is about
1.2 times higher than that of TP-AA-TP(1), power efficiency of
2.33 lm/W, and EQE of 4.02% (Fig. 3).
This is because TPB with a larger size than TP shows the bulky
size effect of side group. Also, due to the higher relative PL quantum
efficiency of TPB than that of TP, TP-AA-TPB(2) has a higher current
efficiency than TP-AA-TP(1) [9,19,35,36]. As a result, the power ef-
ficiency of TP-AA-TPB(2) was also increased compared to TP-AA-
TP(1).
TPB-AA-TPB(3) had a current efficiency of 2.72 cd/A, power ef-
ficiency of 1.14 lm/W, and EQE of 1.50%. This material showed an
excimer peak in both the EL spectrum and the PL spectrum. In
general, the material that shows an excimer has low EL efficiency,
and it can be interpreted as indicating many non-radiative decay
pathways [37e39]. Therefore, in the case of TPB-AA-TPB(3), the
three kinds of device EL efficiencies are low.
Also, comparing TP-AA-TPB(2) with TPB-AA-TPA(5), the EL
maximum value of TP-AA-TPA(5) was red-shifted 11 nm, but blue
emission could still be maintained, and the EL efficiency of TP-AA-
TPA(5) increased 1.3 times compared to the value of TP-AA-TPB(2).
Comparison of TPB-AA-TPB(3) and TPB-AA-TPA(6) showed that
TPB-AA-TPA(6) was increased the current efficiency by 3.2 times
compared to that of TPB-AA-TPB(3). The efficiency of TPB-AA-
TPA(6) was increased by preventing the excimer from asymmetri-
cally replacing side groups and optimizing the electron donating
effect of the side group. When TPB-AA-TPA(6) was compared with
For Type (B), TP-AA-DPA(4) showed a high current efficiency of
7.79 cd/A, power efficiency of 3.79 lm/W, and EQE of 3.17% due to
the electron donating effect of the aromatic amine side group.
However, with the strong donating effect of the side group, the EL
maximum and CIE values were 501 nm and (0.19, 0.52) indicating
Fig. 2. EL characteristics of devices using the synthetic materials as EML: (a) energy diagram and (b) EL spectra.

H. Lee et al. / Dyes and Pigments 146 (2017) 27e36
35
Fig. 3. EL characteristics of devices using the synthetic materials as EML: (a) IeVeL character, (b) current efficiency against current density, (c) power efficiency against current
density, and (d) external quantum efficiency against current density.
TP-AA-TPA(5), TPB-AA-TPA(6) was increased the efficiency
approximately 1.2 times higher than TP-AA-TPA(5). This is because
TPB has not only a larger side group size than TP, more efficiently
prevents intermolecular packing, but also the higher relative PL
quantum efficiency of TPB than that of TP [9,19,35,36].
Materials substituted with TPA in this series as a whole showed
high EL efficiency, especially for maintaining blue emission. That is,
when TPA, which is an aromatic amine side group, is substituted on
the AA core, the EL efficiency can be increased, and blue emission
can be maintained. Further, by replacing the bulky aromatic side
group of TPB with relatively high PL quantum efficiency, the EL
efficiency of the final molecule can be increased. Therefore, TPB-
AA-TPA(6) was maximized the EL efficiency using the AA core by
optimizing side groups for blue emitting materials.
group and aromatic amine side group, showed not only blue
emission but also the highest EL efficiency among the six synthe-
sized materials with a current efficiency of 8.97 cd/A, power effi-
ciency of 4.43 lm/W, and EQE of 6.37%. The results show that the
size and electron donating effect of the side group were optimized.
Studies of such systematic changes between the core and side
groups of molecular structures will help to increase EL efficiency
and obtain optimized OLED data.
Acknowledgements
This research was supported by a grant from the Technology
Development Program for Strategic Core Materials funded by the
Ministry of Trade, Industry & Energy, Republic of Korea (Project No.
10047758). This research was supported by Basic Science Research
Program through the National Research Foundation of Korea fun-
ded by the Ministry of Education (No. 2016R1D1A1B03931477).
4. Conclusions
In this study, we synthesized six materials by systematically
changing the side groups on the AA core and optimized EL emission
wavelength and EL efficiency. TP-AA-TP(1), TP-AA-TPB(2), and TPB-
AA-TPB(3) of Type (A), which are composed of only carbon and
hydrogen, and TP-AA-DPA(4), TP-AA-TPA(5), and TPB-AA-TPA(6) of
Type (B), which have substituted aromatic amine groups as side
groups. Type (B) showed higher overall EL efficiency than Type (A)
due to the electron donating effect of the substituted aromatic
amine side group. Particularly, TPB-AA-TPA(6) with a bulky size
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2017.06.053.
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