Synthesis and electroluminescence properties of new dual-core derivatives

Article abstract of DOI:10.1166/jnn.2018.14948

New blue emitting materials based on dual core concept, TP-AF-TP and TP-HAF-TP were synthesized through boronylation and Suzuki coupling reactions. In the thin film state, TP-AF-TP and TP-HAF-TP exhibited maximum PL values at 445 and 440 nm, respectively. A non-doped OLED device based on TP-AF-TP and TP-HAF-TP showed current efficiency of 3.16 and 2.67 cd/A, respectively. TP-AF-TP exhibited a higher EL efficiency than that of TP-HAF-TP.

Full text of DOI:10.1166/jnn.2018.14948

Article
Journal of
Nanoscience and Nanotechnology
Vol. 18, 2166–2170, 2018
Copyright © 2018 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Synthesis and Electroluminescence Properties of
New Dual-Core Derivatives
1
2
1
1
1ꢀ∗
Hayoon Lee , Sunmi Lee , Hyocheol Jung , Seokwoo Kang , and Jongwook Park
1Department of Chemical Engineering, Kyung Hee University, Gyeonggi, 17104, Korea
Central Research Institute, KISCO, 69, Yangcheon-ro 75-gil, Gangseo, Seoul 07537, Korea
2
New blue emitting materials based on dual core concept, TP-AF-TP and TP-HAF-TP were synthe-
sized through boronylation and Suzuki coupling reactions. In the thin film state, TP-AF-TP and TP-
HAF-TP exhibited maximum PL values at 445 and 440 nm, respectively. A non-doped OLED device
based on TP-AF-TP and TP-HAF-TP showed current efficiency of 3.16 and 2.67 cd/A, respectively.
TP-AF-TP exhibited a higher EL efficiency than that of TP-HAF-TP.
Keywords: Organic Light Emitting Diodes, Emitting Material Layer, Fluorescence, Dual Core.
IP: 88.161.78.101 On: Mon, 18 Jun 2018 08:02:08
1
. INTRODUCTION
2. EXPERIMENTAL DETAILS
Copyright: American Scientific Publishers
Since the study of organic light-emitting diodes (OLEDs)
began, OLED have received much attention because of
their potential applications in full color flat panel dis-
2.1. Synthesis
The structures and synthetic routes of compounds are
shown in Scheme 1. Compounds (1), (2), and (3) were
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1
7
plays and next generation lighting. In order to fabricate
synthesized according to the literature.
full color OLED displays, we need high performance red,
green, and blue-light emitters with high electrolumines-
cence efficiencies and pure color coordinates.
2.1.1. 2,7-Dibromo-9,9-Diethyl-9H-Fluorene (4)
In a 250 mL round-bottom flask, 2,7-dibromo-9H-fluorene
5.0 g (15 mmol), KOC(CH3ꢁ3 4.1 g (37 mmol) were
added and then dissolved in anhydrous dimethylsulfox-
ide (DMSO) 100 mL, and then stirred. While maintain-
Many studies of blue emitters have investigated with
high PL efficiencies such as anthracene, pyrene, and
fluorene.2 In our previous study, we reported new dual
–4
5
ꢀ6
ꢁ
core chromophores containing anthracene and pyrene.
ing the reaction temperature at 0 C, ethyl iodide 3.0 mL
Compounds based on dual cores have advantages such as
the prevention of excimer formation and improvements in
the efficiency and lifetime of devices.
(37 mmol) was slowly added to the reaction mixture. After
the reaction had finished, distilled water was added and
then stirred. After filtering of the crude product, it was
In this study, anthracene and fluorene chromophores
as dual core (AF core) were introduced and substituted
ethyl and heptyl groups on fluorene. 9-(9,9-diethyl-7-[1,1 ;
recrystallized with hexane. (85% yield).
1
H-NMR (300 MHz, CDCl ꢁ: ꢂ (ppm) 7.54 (dd, 2H),
3
ꢀ
7.47 (m, 4H), 2.03 (q, 4H), 0.34 (t, 6H).
ꢀ
ꢀꢀ ꢀ
3
[
,1 ]terphenyl-5 -yl-9H-fluoren-2-yl)-10-fluoren-2-yl)-10-
ꢀ
ꢀ
ꢀꢀ
ꢀ
1,1 ;-3 ,1 ]ter phenyl-5 -yl-anthracene (TP-AF-TP) with
2.1.2. 2,7-Dibromo-9,9-Diheptyl-9H-Fluorene (5)
ꢀ
the ethyl-substituted structure and 9-(9,9-diheptyl-7-[1,1 ;
In a 250 mL round-bottom flask, 2,7-dibromo-9H-fluorene
10 g (31 mmol) and KOC(CH3ꢁ3 8.4 g (74 mmol)
were added and dissolved in DMSO 200 mL, and then
ꢀ
ꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀ
ꢀꢀ
3
5
,1 ]terphenyl-5 -yl-9H-fluoren-2-yl)-10-[1,1 ;3 ,1 ]terphenyl-
-yl-anthracene (TP-HAF-TP) with the heptyl-substituted
ꢁ
structure were newly synthesized. Multilayered EL devices
were fabricated using these materials.
stirred. After maintaining reaction temperature at 0 C,
1-bromoheptane 11.7 ml (74 mmol) was added and then
the reaction was performed for about 18 h. After filtering
of the crude product, it was recrystallized with methanol.
(65% yield).
∗
Author to whom correspondence should be addressed.
2166
J. Nanosci. Nanotechnol. 2018, Vol. 18, No. 3
1533-4880/2018/18/2166/005
doi:10.1166/jnn.2018.14948

Lee et al.
Synthesis and Electroluminescence Properties of New Dual-Core Derivatives
IP: 88.161.78.101 On: Mon, 18 Jun 2018 08:02:08
Copyright: American Scientific Publishers
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Scheme 1. Synthetic routes of TP-AF-TP and TP-HAF-TP.
1
H-NMR (300 MHz, CDCl ꢁ: ꢂ (ppm) 7.50–7.60
and distilled water, and the organic layer was dried with
3
(
(
m, 2H), 7.35–7.55 (m, 4H), 1.70–2.00 (m, 4H), 0.90–1.45
m, 16H), 0.70–0.85 (m, 6H), 0.40–0.75 (m, 4H).
MgSO . After column refinement of the compound with
4
chloroform:hex = 1:10, it was reprecipitated with chloro-
form and methanol. (70% yield).
2
.1.3. 9-(7-Bromo-9,9-diethyl-9H-fluoren-2-yl)-
Anthracene (6)
1H-NMR (300 MHz, THF): ꢂ (ppm) 8.56 (s, 1H), 8.09
(
d, 2H), 8.00 (d, 1H), 7.81 (d, 1H), 7.70 (d, 2H), 7.67 (d,
In a 500 mL round-bottom flask, (4) 3.0 g (7.9 mmol),
3) 2.1 g (9.5 mmol), Pd(PPh3ꢁ4 0.37 g (0.31 mmol)
1
H), 7.57 (dd, 1H), 7.46 (m, 4H), 7.35 (m, 2H).
(
were added and dissolved in anhydrous toluene 270 mL
and anhydrous ethanol 30 mL, and then stirred. While
maintaining the nitrogen condition, the reaction temper-
2
.1.4. 9-(7-Bromo-9,9-diheptyl-9H-fluoren-2-yl)-
Anthracene (7)
ꢁ
This compound was synthesized with the same method
as for compound (6) by using (5) 0.50 g (1.0 mmol).
(30% yield).
ature is raised to 110 C, and then 2 M K CO 20 mL
2
3
(
39 mmol) was added to the reaction mixture. After the
reaction had finished, it was extracted with chloroform
J. Nanosci. Nanotechnol. 18, 2166–2170, 2018
2167

Synthesis and Electroluminescence Properties of New Dual-Core Derivatives
Lee et al.
1H-NMR (300 MHz, THF): ꢂ (ppm) 8.40–8.60 (s,
H), 8.00–8.20 (d, 2H), 7.80–7.95 (d, 2H), 7.60–7.75
m, 3H), 7.25–7.55 (m, 8H), 1.85–2.05 (m, 4H), 1.00–1.45
m, 16H), 0.55–0.95 (m, 10H).
2.1.8. 9-(9,9-diheptyl-7-[1,1 ;3 ,1 ]terphenyl-5 -yl-9H-
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
(
(
fluoren-2-yl)-10-[1,1 ;3 ,1 ]terphenyl-5 -yl-
anthracene (TP-HAF-TP)
This compound was synthesized with the same method
as for TP-AF-TP by using (9) 0.16 g (0.23 mmol). (57%
yield).
2
.1.5. 9-Bromo-10-(7-bromo-9,9-diethyl-9H-fluoren-2-
yl)-anthracene (8)
1
H-NMR (300 MHz, CDCl ꢁ: ꢂ (ppm) 8.15–8.25 (m,
3
2
1
H), 8.05–8.15 (m, 2H), 7.95–8.05 (m, 2H), 7.85–7.95 (m,
0H), 7.75–7.85 (m, 3H), 7.65–7.75 (m, 3H), 7.50–7.60
In a 500 mL round-bottom flask, (6) 1.0 g (2.1 mmol)
was added and dissolved in chloroform 200 mL and then
stirred. NBS 0.45 g (2.5 mmol) was added to the reac-
(
m, 8H), 7.35–7.50 (m, 10H).
tion mixture. After maintaining the reaction temperature at
ꢁ
3. RESULTS AND DISCUSSION
4
0 C, acetic acid 20 mL was added to the reaction mix-
The optical properties of TP-AF-TP and TP-HAF- TP are
summarized in Table I. In solution state, TP-AF-TP and
TP-HAF-TP exhibited the same UV-Vis. absorption at 322,
ture. After the reaction had finished, it was extracted with
chloroform and distilled water and the organic layer was
dried with MgSO . The compound was reprecipitated with
4
chloroform and ethanol. (84% yield).
1H-NMR (300 MHz, THF): ꢂ (ppm) 8.56 (s, 1H), 8.09
Table I. Optical properties of synthesized materials.
(
(
(
d, 2H), 8.00 (d, 1H), 7.81 (d, 1H), 7.70 (d, 2H), 7.64
d, 1H), 7.57 (dd, 1H), 7.46 (m, 4H), 7.35 (m, 2H), 2.13
q, 4H), 0.47 (t, 6H).
Solution
Film
Compound
TP-AF-TP
UVmax (nm) PLmax (nm) UVmax (nm) PLmax (nm)
322, 379, 399
TP-HAF-TP 322, 379, 399
440
440
323, 380, 401
323, 380, 402
445
440
2
.1.6. 9-Bromo-10-(7-bromo-9,9-diheptyl-9H-fluoren-2-
yl)-anthracene (9)
This compound was synthesized with the same method
as for compound (8) by using (7) 0.50 g (0.80 mmol).
IP: 88.161.78.101 On: Mon, 18 Jun 2018 08:02:08
Copyright: American Scientific Publishers
(
29% yield).
1
H-NMR (300 MHz, CDCl ꢁ : ꢂ (ppm) 8 D. 5 e0 l–i v8 e. 8r e0 d by Ingenta
3
(
d, 2H), ꢂ 7.85–7.95 (m, 1H) 7.65–7.75 (m, 2H),
ꢂ 7.60–7.65 (m, 2H), 7.50–7.60 (m, 2H), ꢂ 7.30–7.50
m, 5H), 1.80–2.10 (m, 4H), ꢂ 0.90–1.35 (m, 16H),
(
0
.60–0.90 (m, 10H).
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
ꢀ
2
.1.7. 9-(9,9-diethyl-7-[1,1 ;3 ,1 ]terphenyl-5 -yl-9H-
ꢀ
ꢀ
ꢀ
fluoren-2-yl)-10-[1,1 ;3 ,1 ]terphenyl-5 -yl-
anthracene (TP-AF-TP)
In a 500 mL round-bottom flask, (8) 0.50 g (0.9 mmol),
(
(
2) 0.80 g (2.3 mmol), palladium(II) acetate 0.05 g
0.07 mmol), tricyclohexylphosphine 0.04 g (0.14 mmol)
were added and dissolved in anhydrous toluene 150 mL,
and then stirred. While maintaining the nitrogen condition,
ꢁ
after increasing the reaction temperature to 110 C, (Et)
4
NOH 6.0 mL was added to the reaction mixture. After
the reaction had finished, it was extracted with chloro-
form and distilled water, and the organic layer was dried
with MgSO . After column refinement of the compound
4
with EA:Hex = 1:15, it was re-precipitated with THF and
methanol (78% yield).
1H-NMR (300 MHz, THF): ꢂ (ppm) 8.17 (t, 1H), 8.09
(
(
(
d, 1H), 8.04 (d, 1H), 7.98 (d, 2H), 7.89 (m, 16H), 7.76
t, 1H), 7.53 (m, 10H), 7.40 (m, 8H), 2.25(m, 4H), 0.57
t, 6H).
Figure 1. UV-vis and PL spectra of synthesized materials: (a) in CHCl
solution (1ꢃ0×10− M), (b) in the thin film state.
3
5
2168
J. Nanosci. Nanotechnol. 18, 2166–2170, 2018

Lee et al.
Synthesis and Electroluminescence Properties of New Dual-Core Derivatives
Table II. EL performance of non-doped OLED at 10 mA/cm2.
3
79, 399 nm (Fig. 1(a)). This is similar to the shape of
UV-Vis absorption peak unique to anthracene.
Volt (V)
C.E. (cd/A)
P.E. (lm/W)
ELmax (nm)
This indicates that the absorption mainly occurred in
anthracene among AF core containing anthracene and flu-
orene. Also, substituted heptyl group does not affect the
conjugation length of TP-HAF-TP. For the same reason,
maximum PL of TP-AF-TP and TP-HAF-TP in solution
state appeared the same at 440 nm.
TP-AF-TP
TP-HAF-TP
7.88
8.17
3.16
2.67
1.38
1.15
459
457
group substituted in TP-AF-TP, thus effectively preventing
the intermolecular packing.
7
In general, the film state has closer distances between
molecules in film state than in solution state, showing red-
shift. In film state, however, TP-AF-TP and TP-HAF-TP
showed UV-Vis. absorption at 323 380, 401 nm, and this is
similar to the results in solution state (Fig. 1(b)). The dihe-
dral angle between dual chromophores such as AF core is
TP-AF-TP and TP-HAF-TP were used as the emit-
ting layer in order to produce non-doped OLED with
the following structure: ITO/2-TNATA (60 nm)/NPB
(
(
15 nm)/EML (35 nm)/Alq3 (20 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
ꢁ
6
known to be about 90 .
layer (HTL). Alq was used as the electron transporting
3
Accordingly, when it goes from solution state to film
state, it has a small degree of red-shift by preventing the
intermolecular packing. In film state, maximum PL of TP-
AF-TP and TP-HAF-TP were observed to be 445 and
layer (ETL), LiF as the electron injection layer (EIL), and
ITO and Al were respectively used as anode and cathode.
The OLED properties are summarized in Figure 2 and
Table II. TP-AF-TP showed high efficiency with current
efficiency of 3.16 cd/A, power efficiency of 1.38 lm/W
and maximum EL of 459 nm, which higher than those of
TP-HAF-TP. TP-HAF-TP had an efficiency with current
efficiency of 2.67 cd/A, power efficiency of 1.15 lm/W and
maximum EL of 457 nm.
4
5
40 nm, respectively. TP-AF-TP exhibited red-shift about
nm compared to TP-HAF-TP. It also showed red-shift
about 5 nm compared to maximum PL of solution state.
In contrast TP-HAF-TP had a same maximum PL value
in solution state and in film state. This is because heptyl
group substituted in TP-HAF-TP was bulkier than ethyl
As shown in Figure 1, intermolecular interactions were
effectively suppressed by the introduction of bulky hep-
tyl group. However, the absorption and luminescence of
IP: 88.161.78.101 On: Mon, 18 Jun 2018 08:02:08
TP-AF-TP and TP-HAF-TP appear mainly in anthracene.
Copyright: American Scientific Publishers
It probably means that ethyl and heptyl group substituted
Delivered by Ingenta
fluorene activated non-radiative process such as vibration
and rotation in molecule. Therefore, TP-HAF-TP sub-
stituted heptyl group with larger molecular motion than
ethyl group, exhibited lower EL efficiency than that of
TP-AF-TP.
4
. CONCLUSION
Using dual chromophores of anthracene and fluorene, blue
emitting materials of TP-AF-TP and TP-HAF-TP were
synthesized. TP-AF-TP and TP-HAF-TP showed maxi-
mum PL values at 445 and 440 nm in film state.
This is because heptyl group substituted in TP-HAF-TP
was bulkier than ethyl group substituted in TP-AF-TP, thus
more effectively preventing the intermolecular packing.
A non-doped OLED device based on TP-AF-TP showed
current efficiency of 3.16 cd/A and power efficiency of
1
.38 lm/W, exhibiting a higher efficiency than that of
TP-HAF-TP. It probably means heptyl group substituted
in TP-HAF-TP activated more non-radiative process than
ethyl group substituted in TP-AF-TP.
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. 10047758). This research was supported by Basic
Figure 2. EL characteristics of devices: (a) I–V –L curves, (b) Current
efficiency versus current density.
J. Nanosci. Nanotechnol. 18, 2166–2170, 2018
2169

Synthesis and Electroluminescence Properties of New Dual-Core Derivatives
Lee et al.
Science Research Program through the National Research
Foundation of Korea (NRF) funded by the Ministry of
Education (No. 2016R1D1A1B03931477).
3. R. Zhang, Y. Zhao, T. Zhang, L. Xu, and Z. Ni, Dyes and Pigments
130, 106 (2016).
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J. Rault-Berthelot, and C. Poriel, J. Mater. Chem. C 4, 1692 (2016).
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Received: 10 December 2016. Accepted: 23 February 2017.
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J. Nanosci. Nanotechnol. 18, 2166–2170, 2018