Highly efficient pyrene blue emitters for OLEDs based on substitution position effect

Article abstract of DOI:10.1016/j.dyepig.2018.05.024

To investigate the effect of substitution position of the side group on a pyrene core, three derivatives having a triphenylbenzene group as a bulky side group at the 1,6-position, 4,9-position, and 1,8-position were successfully synthesized: 1,6-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (1,6-DTBP), 4,9-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (4,9-DTBP), and 1,8-bis(5′-phenyl-[1,1':3′,1″-terphenyl]-4-yl)pyrene (1,8-DTBP). The three synthesized materials showed excellent thermal stability with a high T_g of >140 °C and a high T_d of >500 °C. Due to the highly twisted structure of 1,8-DTBP in the film state, the absolute photoluminescence quantum yield value was improved. Of the three synthesized materials used as an emitter in a non-doped organic light-emitting diode device, 1,8-DTBP showed highly efficient electroluminescence performance, with a luminance efficiency of 6.89 cd/A, power efficiency of 3.03 lm/W, and external quantum efficiency of 7.10% at 10 mA/cm². In addition, 4,9-DTBP showed a deep-blue emission of CIE x, y (0.158, 0.063) suitable for HD-TV.

Full text of DOI:10.1016/j.dyepig.2018.05.024

Accepted Manuscript
Highly efficient pyrene blue emitters for OLEDs based on substitution position effect
Mina Jung, Jaehyun Lee, Hyocheol Jung, Seokwoo Kang, Atsushi Wakamiya,
Jongwook Park
PII:
S0143-7208(18)30608-9
10.1016/j.dyepig.2018.05.024
DYPI 6753
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 19 March 2018
Revised Date: 12 May 2018
Accepted Date: 13 May 2018
Please cite this article as: Jung M, Lee J, Jung H, Kang S, Wakamiya A, Park J, Highly efficient pyrene
blue emitters for OLEDs based on substitution position effect, Dyes and Pigments (2018), doi: 10.1016/
j.dyepig.2018.05.024.
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ACCEPTED MANUSCRIPT
Highly Efficient Pyrene Blue Emitters for OLEDs Based on Substitution
Position Effect
Mina Jung , Jaehyun Leea,c1, Hyocheol Jung , Seokwoo Kang , Atsushi Wakamiya , Jongwook Park *
aDepartment of Chemistry/Display Research Center, The Catholic University of Korea
bDepartment of Chemical Engineering, Kyung Hee University, Gyeonggi, 17104, Korea
cInstitute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan
a1
b
b
c
b
*E-mail: jongpark@khu.ac.kr
1Mina Jung and Jaehyun Lee contributed equally to this work as the first coauthor
Abstract
To investigate the effect of substitution position of the side group on a pyrene core, three derivatives
having a triphenylbenzene group as a bulky side group at the 1,6-position, 4,9-position, and 1,8-position
were successfully synthesized: 1,6-bis(5'-phenyl-[1,1':3',1''-terphenyl]-4-yl)pyrene (1,6-DTBP), 4,9-bis(5'-
phenyl-[1,1':3',1''-terphenyl]-4-yl)pyrene (4,9-DTBP), and 1,8-bis(5'-phenyl-[1,1':3',1''-terphenyl]-4-yl)pyrene
(
1,8-DTBP). The three synthesized materials showed excellent thermal stability with a high T of >140 ℃
g
and a high T of >500 ℃. Due to the highly twisted structure of 1,8-DTBP in the film state, the absolute
d
photoluminescence quantum yield value was improved. Of the three synthesized materials used as an
emitter in a non-doped organic light-emitting diode device, 1,8-DTBP showed highly efficient
electroluminescence performance, with a luminance efficiency of 6.89 cd/A, power efficiency of 3.03 lm/W,
2
and external quantum efficiency of 7.10% at 10 mA/cm . In addition, 4,9-DTBP showed a deep-blue
emission of CIE x, y (0.158, 0.063) suitable for HD-TV.
1
. Introduction
In the past two decades, interest in π-conjugated compounds in the optoelectronic field, such as organic
light-emitting diodes (OLEDs), organic thin film transistors (OTFTs), and organic photovoltaic cells (OPVCs),
has increased dramatically. [1-3] In particular, OLEDs have been intensively studied due to potential
applications such as full-color flat-panel displays, next-generation lighting, and flexible displays. [4] The
current research trends in OLED technologies have focused on optimizing device structure and

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developing new emitting materials. Among the various development methods for OLEDs, new blue-
emitting materials that satisfy high electroluminescence (EL) efficiencies, good thermal stability, long
device lifetime, and pure color coordinates remains a hot button issue. [5]
Predicting the properties of emitting materials and finding effective ways to develop high-performance
materials depends on the relationship between molecular structure and properties. [6, 7] These molecular
structures consist of core groups and side groups. As a core group, for example, anthracene and pyrene
are typically used as blue light-emitting materials, and a variety of derivatives combined side groups have
been reported in the blue light-emitting field. [8] Among the many blue emitters using core and side
groups, substitution positions can affect optical and electrical properties including conjugation length,
electronic state, photophysical properties, and intramolecular and intermolecular interactions. [9]
Therefore, when designing the emitting material, an understanding of the substitution position effect is
needed. However, few studies have investigated substitution positions between core and side groups and
their effects. Therefore, we report the efficiency and color purity of blue light emitters when using
different link positions with the same core and side groups.
In our previous study, the m-terphenyl side groups were introduced in the ortho, meta, and para link
positions on 6,12-dihydro-diindeno [1,2-b; 1', 2'-e] pyrazine (indenopyrazine) and the optical and EL
properties were investigated according to changes in the substitution position. [10] Larger blue shifts in
the UV–visible (UV-vis) absorption and photoluminescence (PL) spectra occur in the synthesized ortho-
and para-substituted derivatives compared to the meta-substituted derivative. In particular, the OLED
device containing the para-substituted derivative exhibited excellent characteristics, with maximum EL
emission at 423 nm, a full width at half maximum of 42 nm, pure violet emission with CIE coordinates
(0.173, 0.063), and an external quantum efficiency of 1.88%.
The pyrene core group is one of the most efficient core groups among organic compounds, and has
been used to replace anthracene recently due to advantages such as high quantum efficiency and thermal
and chemical stability. [11] With regard to the link positions of pyrene, the 1, 3, 6, and 8 positions are
easily accessible in organic synthesis, as established in previous research. [12] However, because of the
synthetic challenge, research on pyrene derivatives in terms of the 4 and 9 positions has been not been

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investigated. Also, it is very difficult to separate 1,6 and 1,8 disubstituted pyrene derivatives because of
chemical similarity of two compounds. Especially, we introduce 1,8 disubstituted pyrene in this study
which has twisted chemical structure. Thus, pyrene derivatives which are substituted for various positions,
can provide not only numerous new chromophores but also an effective strategy for performance
optimization of pyrene-based emitters.
In this study, we successfully synthesized Br-substituted pyrene compounds at the 1,6, 4,9, and 1,8
positions to investigate the effect of each substitution position on the pyrene core group. The
triphenylbenzene group was selected for use as a bulky side group and was substituted at each position
to synthesize three derivatives: 1,6-bis(5'-phenyl-[1,1':3',1''-terphenyl]-4-yl)pyrene (1,6-DTBP), 4,9-bis(5'-
phenyl-[1,1':3',1''-terphenyl]-4-yl)pyrene (4,9-DTBP), 1,8-bis(5'-phenyl-[1,1':3',1''-terphenyl]-4-yl)pyrene (1,8-
DTBP). The optical properties of the three compounds were compared with the EL properties of non-
doped OLED devices using as the emitting layer (EML).
2
. Experimental
2
.1. Synthesis
Compound 1. 1,3,5-Tribromobenzene (20.0 g, 63.5 mmol), phenyl boronic acid (18.8 g, 154 mmol), and
Pd(PPh ) (3.75 g, 3.25 mmol) were added to 300 mL of anhydrous THF. Then, 2M K CO solution (100 mL),
3
4
2
3
which was dissolved in H O, was added to the reaction mixture. The mixture was heated to 65 ℃ for 12 h
2
under nitrogen. After completion of the reaction, the reaction mixture was extracted with CHCl and water.
3
The organic layer was dried with anhydrous MgSO and filtered. The solvent was evaporated. The product
4
was isolated via silica gel column chromatography by using CHCl : n-hexane (1 : 20) as the eluent to
3
1
afford a white solid (12.4 g, 63%). H-NMR (300 MHz, CDCl ): δ= 7.70 (s, 3H), 7.60 (d, 4H), 7.44(t, 4H), 7.36
3
(t, 2H); EI+-Mass: 310.
Compound 2. Compound 1 (12.0 g, 38.8 mmol) was added to 300 mL of anhydrous THF and stirred at
78℃ under a nitrogen atmosphere, then 2 M n-BuLi (29.0 mL, 58.1 mmol) was added to the reaction
−
mixture. Next, isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (11.9 mL, 58.1 mmol) was added to the
reaction mixture after 30 min. After the reaction was finished, the reaction mixture was extracted with
diethyl ether and water. The organic layer was dried with anhydrous MgSO and filtered. The solvent was
4
evaporated. The residue was re-dissolved in CHCl and MeOH was added to the solution. The precipitate
3

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1
was filtered and washed with MeOH to afford a white solid (12.9 g, 93%). H-NMR (300 MHz, CDCl ): δ=
3
8
.03 (s, 2H), 7.90 (s, 1H), 7.69 (d, 4H), 7.44(t, 4H), 7.35 (t, 2H), 1.37 (s, 12H); EI+-Mass: 356.
Compound 3. 1,4-dibromobenzene (1.65 g, 7.00 mmol), compound 2 (2.49 g, 7.00 mmol), and Pd(PPh3)4
0.40 g, 0.35 mmol) were added to 100 mL of anhydrous THF. Then, 2M K CO solution (20 mL), which
(
2
3
was dissolved in H O, was added to the reaction mixture. The reaction mixture was heated to 65°C for 12
2
h under nitrogen. After the reaction was finished, the reaction mixture was extracted with CHCl and water.
3
The organic layer was dried with anhydrous MgSO and filtered. The solvent was evaporated. The product
4
was isolated by silica gel column chromatography using CHCl : n-hexane (1 : 10) eluent to afford a white
3
1
solid (2.07 g, Yield 77%). H-NMR (300 MHz, CDCl ): δ= 7.80 (s, 1H), 7.74 (s, 2H), 7.69 (d, 4H), 7.58 (m, 4H),
3
7
.48 (t, 4H), 7.39 (t, 2H); EI+-Mass: 384.
Compound 4. Compound 3 (3.00 g, 7.79 mmol) was added to 13 mL of anhydrous THF and stirred at
78 ℃ under a nitrogen atmosphere, then 2 M n-BuLi (5.85 mL, 11.7 mmol) was added to the reaction
−
mixture. Next, isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (3.18 mL, 15.6 mmol) was added to the
reaction mixture after 30 min. After the reaction was finished, the reaction mixture was extracted with
ethyl acetate and water. The organic layer was dried with anhydrous MgSO and filtered. The solvent was
4
removed by evaporation. The product was purified by silica gel column chromatography using THF : n-
1
hexane (1 : 10) eluent to afford a white solid (3.01 g, 89%). H -NMR (300 MHz, CDCl ): δ = 7.94 (d, 2H),
3
7
.79 (m, 3H), 7.69 (m, 6H), 7.46 (t, 4H), 7.37 (t, 2H), 1.24 (d, 12H); EI+-Mass: 432.
Compounds 5 and 6. Bromine (10.0 mL, 195 mmol) in CHCl (500 mL) was dropped into a solution of
3
pyrene (20.0 g, 98.9 mmol) in CHCl (500 mL) over 5 h while stirring. The precipitate was collected after
3
1
2 h and recrystallized from xylene to give compound 5 (5.01 g, 14%) and compound 6 (2.17 g, 6%).
1
Compound 5: H-NMR (300 MHz, CDCl ): δ = 8.46 (d, 2H), 8.26 (d, 2H), 8.11 (d, 2H), 8.05 (d, 2H); EI+-
3
1
Mass: 360. Compound 6: H-NMR (300 MHz, CDCl ): δ = 8.56 (s, 2H), 8.27 (d, 2H), 8.05 (m, 4H); EI+-Mass:
3
3
60.
1
,6-DTBP. Compound 5 (1.00 g, 2.78 mmol), compound 4 (2.63 g, 6.08 mmol), Pd(OAc) (0.06 g, 0.28
2
mmol), and (cyclohexyl) P (0.12 g, 0.42 mmol) were added to 30 mL of anhydrous THF and 170 mL of
3
anhydrous toluene mixture. Then tetraethylammonium hydroxide (20 wt%) (35 mL) was added to the
reaction mixture at 50 ℃. The mixture was heated to 80 ℃ for 2 h under nitrogen. After the reaction was
finished, the reaction mixture was filtered. The product was isolated using silica gel column
chromatography with CHCl as the solvent. The eluent was removed by evaporation. Recrystallization of
3
1
the residue from CHCl afforded a beige solid product (0.51 g, 23%). H-NMR (300 MHz, [D ]THF): δ= 8.33
3
8
(
m, 4H), 8.16 (d, 2H), 8.07 (d, 2H), 8.05 (m, 8H), 7.93 (s, 2H), 7.86 (m, 12H), 7.52 (t, 8H), 7.41 (t, 4H); 13C-
NMR data could not be obtained because of the low solubility of the 1,6-DTBP; TOF-MS 810.3 m/z.
1
,8-DTBP. Compound 6 (1.00 g, 2.78 mmol), compound 4 (2.63 g, 6.08 mmol), Pd(OAc) (0.06 g, 0.28
2
mmol), and (cyclohexyl) P (0.12 g, 0.42 mmol) were added to 30 mL of anhydrous THF and 170 mL of
3

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anhydrous toluene mixture. Then tetraethylammonium hydroxide (20 wt%) (35 mL) was added to the
reaction mixture at 50 ℃. The mixture was heated to 80 ℃ for 2 h under nitrogen. After the reaction was
finished, the reaction mixture was extracted with CHCl3 and water. The organic layer was dried with
anhydrous MgSO and filtered. The solvent was evaporated. The product was isolated by silica gel column
4
1
chromatography using the CHCl : n-hexane (1 : 10) eluent to afford a beige solid (1.51 g, 67%). H-NMR
3
(
300 MHz, [D ]THF): δ= 8.35 (d, 2H), 8.29 (s, 2H), 8.20 (s, 2H), 8.11 (d, 2H), 8.03 (m, 8H), 7.92 (s, 2H), 7.83
8
(
m, 12H), 7.50 (t, 8H), 7.39 (t, 4H); 13C-NMR (125 MHz, CDCl ): δ= 142.63, 142.10, 141.31, 140.58, 140.20,
3
1
1
37.30, 131.28, 131.20, 129.04, 128.57, 127.89, 127.75, 127.69, 127.54, 127.48, 125.63, 125.48, 125.33,
25.10; HRMS (EI, m/z): [M+] calcd for C64H42, 810.3287; found, 810.3291; elemental analysis calcd (%)
for C64H42: C 94.78, H 5.22; found: C 94.39, H 5.31%.
Compound 7. Pyrene (20.0 g, 98.9 mmol) was added to 500 mL of 1-pentanol and stirred while refluxing.
3
2.0 g of sodium was slowly added for 1 h and additionally stirred for 2 h. Temperature was reduced to
room temperature and the solution was extracted using water. After vaporizing the solvent, ethanol was
1
used for recrystallization to obtain a white solid (9.25 g, 45%). H-NMR (300 MHz, CDCl ): δ= 7.12 (s, 4H),
3
3
.04 (t, 8H), 2.00 (m, 4H); EI+-Mass: 208.
Compound 8. Compound 7 (42.0 g, 144 mmol) was added to 100 mL of CH Cl and stirred. 15 mL of Br
2
2
2
was added to 30 mL of CH Cl , and this solution was slowly added by dropping. After 30 minutes of
2
2
1
reaction, the material to be extracted was filtered. A white solid was obtained (16.9 g, 32%). H-NMR (300
MHz, CDCl ): δ= 7.40 (s, 2H), 3.06 (t, 4H), 2.97 (t, 4H), 1.99 (m, 4H), EI+-Mass: 366.
3
Compound 9. Compound 8 (12.0 g, 32.8 mmol) and 22.3 g of DDQ were added to 240 mL of anhydrous
toluene under nitrogen atmosphere and stirred for reflux. After 4 h of reaction, the temperature was
reduced to room temperature. The solution was refined by column chromatography using CHCl . The
3
1
solvent was vaporized and recrystallized using CHCl . A yellow solid was obtained (4.51 g, 38%). H-NMR
3
(
300 MHz, CDCl ): δ= 8.57 (d, 2H), 8.40 (s, 2H), 8.13 (d, 2H), 8.04 (t, 2H); EI+-Mass: 360.
3
4
,9-DTBP. Compound 9 (1.00 g, 2.78 mmol), compound 4 (2.63 g, 6.08 mmol), Pd(OAc) (0.06 g, 0.28
2
mmol), and (cyclohexyl) P (0.12 g, 0.42 mmol) were added to 30 mL of anhydrous THF and 170 mL of
3
anhydrous toluene mixture. Then tetraethylammonium hydroxide (20 wt%) (35 mL) was added to the
reaction mixture at 50 ℃. The mixture was heated to 80 ℃ for 2 h under nitrogen. After the reaction was
finished, the reaction mixture was extracted with CHCl3 and water. The organic layer was dried with
anhydrous MgSO and filtered, and the solvent was evaporated. The product was isolated by silica gel
4
column chromatography using a CHCl : n-hexane (1 : 10) eluent to produce a beige solid (1.15 g, 51%).
3
1
H-NMR (300 MHz, [D ]THF): δ= 8.35 (m, 4H), 8.20 (s, 2H), 8.07 (m, 10H), 7.94 (s, 2H), 7.87 (m, 12H), 7.53
8
(
t, 8H), 7.41 (t, 4H); 13C-NMR (125 MHz, CDCl ): δ= 142.67, 142.17, 141.33, 140.56, 140.27, 139.16, 131.26,
3
1
30.81, 130.54, 129.07, 128.31, 127.78, 127.57, 126.27, 125.67, 125.53, 125.37, 124.81, 124.06; HRMS (EI,
m/z): [M+] calcd for C64H42, 810.3287; found, 810.3291; elemental analysis calcd (%) for C64H42: C 94.78,

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H 5.22; found: C 94.48, H 5.29%.
2
.2. Measurements and OLED fabrication
1
3
1
C NMR data of the 1,6-DTBP could not be obtained because of the very low solubility. The H-NMR
spectra and 13C-NMR spectra were recorded on Bruker Avance 300 (300 MHz for 1H) and JEOL ECA 500
+
+
(
125 MHz for 13C) spectrometers. The FAB -mass and EI -spectra were recorded on a JEOL, JMS-
AX505WA, HP5890 series II. The optical absorption spectra were obtained using a Lambda 1050
UV/vis/NIR spectrometer (PerkinElmer). A PerkinElmer luminescence spectrometer LS50 (Xenon flash tube)
was used to perform photoluminescence (PL) spectroscopy. PL quantum yield was measured by an
absolute PL quantum yield measurement system (QM-400 Spectrofluorometer). The glass-transition
temperatures (T ) of the compounds were determined with differential scanning calorimetry (DSC) under a
g
nitrogen atmosphere by using a DSC4000 (PerkinElmer). Degradation temperatures (T ) were determined
d
with thermogravimetric analysis (TGA) using a TGA4000 (PerkinElmer). HOMO energy levels were
determined by ultraviolet photoelectron yield spectroscopy (Riken Keiki AC-2). LUMO energy levels were
derived from HOMO energy levels and band gaps. The redox potentials of the compounds were
determined with cyclic voltammetry (CV) using IVIUM STAT system. The synthesized materials were
dissolved in acetonitrile with 0.1M tetrabutylammonium perchlorate as an electrolyte. We used a carbon
working electrode, a platinum wire counter electrode and a saturated Ag/AgCl reference electrode.
Ferrocene was used for potential calibration. DFT calculations for optimization of the geometries were
conducted using the Gaussian 09 program. [13]
In each of the EL devices, N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) was used for the
hole transport and injection layer (HTL), tris(4-carbazoyl-9-ylphenyl)amine (TCTA) was used for the hole
transport and electron blocking layer, one of the synthetic materials 1,6-DTBP, 1,8-DTBP, and 4,9-DTBP was
used as the EML, 1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (TPBi) was used for the electron
transport and hole blocking layer (ETL), lithium fluoride (LiF) was used for the electron injection layer (EIL),
and ITO was used as the anode and aluminum (Al) as the cathode. All organic layers were deposited
under 10-6 Torr, with a rate of deposition of 1.0 Å/s to create an emitting area of 4 mm . LiF and
aluminum layers were continuously deposited under the same vacuum conditions. Luminance efficiency
data for the fabricated EL devices were obtained using a Keithley 2400 electrometer. Light intensities were
obtained with a Minolta CS-1000A. The operational stability of the devices was measured under
encapsulation in a glove box.
2
3
. Results and Discussion
Fig. 1 and Scheme 1 show the chemical structure and synthetic methods of the synthesized materials.

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1,6-DTBP
4,9-DTBP
1,8-DTBP
Fig. 1 Chemical structures of the pyrene derivatives.
OH
OH
Br
B
Br
Br
Br
Pd(PPh3)4, 2 M K2CO3
n-BuLi, THF
Pd(PPh3)4, 2 M K2CO3
n-BuLi, THF
Br
Br
Bpin
Br
Bpin
THF, reflux, 12 h
–78 °C to rt, 3 h
THF, reflux, 12 h
–78 °C to rt, 3 h
1
2
3
4
Bpin
Br
Br
4
Br2, CHCl3
5
Pd(OAc)2, PPh3, (Et)4NOH
toluene, 80 °C, 2 h
rt, 5 h
Br
1,6-DTBP
Br
6
1,8-DTBP
Bpin
Br
Br
4
Na, 1-pentanol
reflux, 3 h
Br2, CH2Cl2
rt, 30 min
DDQ, toluene
reflux, 4 h
Pd(OAC)2, PPh3, (Et)4NOH
toluene, 80 °C, 2 h
Br
Br
7
8
9
4,9-DTBP
Scheme 1. Synthetic routes of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP.
In this study, optical characteristics and OLED performance according to different substitution positions
were observed with the same core and side groups. Pyrene chromophore was used as the core group in
a blue OLED emitter and a triphenylbenzene group was used as a side group to reduce intermolecular

ACCEPTED MANUSCRIPT
interactions and to prevent excimer formation through a bulky chemical structure. The substitution
position was either 1,6, 4,9, or 1,8, with 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP, respectively, synthesized as
model compounds. In organic synthesis, conventional Suzuki-Miyaura cross-coupling reactions and
boronylation were used. In particular, the bromination of pyrene resulted in two isomers, 1,6-
dibromopyrene and 1,8-dibromopyrene. These two isomers were purified several times through
recrystallization. 4,9-Dibromopyrene cannot be synthesized by direct bromination due to its
regioselectivity. In order to obtain 4,9-dibromopyrene, it was synthesized from pyrene through the three
synthetic steps shown in Scheme 1. [14] All compounds were purified by recrystallization and column
chromatography. The synthesized compounds were characterized using nuclear magnetic resonance (NMR)
spectroscopy, mass spectroscopy, and elemental analysis. The synthetic methods are described in more
detail in the Experimental section.
(a) 1.0
(b) 1.0
1,6-DTBP
4,9-DTBP
1,8-DTBP
1,6-DTBP
4,9-DTBP
1,8-DTBP
0
0
0
0
0
.8
.6
.4
.2
.0
0.8
0.6
0.4
0.2
0.0
3
00
350
400
450
500
300 350 400 450 500 550 600 650 700
Wavelength(nm)
Wavelength(nm)
Fig. 2 (a) UV-vis absorption and (b) PL spectra of 1 ⅹ10-5 M THF solution for the synthesized materials.

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(a) 1.0
(b) 1.0
1,6-DTBP
4,9-DTBP
1,8-DTBP
1,6-DTBP
4,9-DTBP
1,8-DTBP
0
0
0
0
0
.8
.6
.4
.2
.0
0.8
0.6
0.4
0.2
0.0
3
00
350
400
450
500
300 350 400 450 500 550 600 650 700
Wavelength(nm)
Wavelength(nm)
Fig. 3 (a) UV-vis absorption and (b) PL spectra of the vacuum-deposited film for the synthesized materials.
-5
Fig. 2 and 3 show the UV-vis absorption and PL spectra of the synthesized compounds in 1 x 10 M THF
solution and vacuum-deposited film states. Table 1 summarizes the optical properties, absolute
photoluminescence quantum yield, energy levels of molecular orbitals, and thermal properties of
synthesized compounds. The tendencies of the UV-vis absorption and PL spectra were similar in the
solution and film states. The photophysical properties of 1,6-DTBP and 1,8-DTBP were similar, and 4,9-
DTBP showed a relatively blue-shifted absorption and PL spectrum. The UVmax and PLmax of 1,6-DTBP and
1
,8-DTBP in the THF solution were the same at 365 nm and 425 nm, and were 373 nm and 461 nm for
the film state, respectively. 4,9-DTBP exhibited UVmax of 349 nm and PLmax of 384 nm in the solution state,
and UVmax of 358 nm and PLmax of 428 nm in the film state, respectively. The PL spectra in various
solvents in order to investigate the intramolecular charge transfer of compounds were shown in Fig S1.
Stokes shifts of three compounds in various solvents were small. The blue-shifted value of 4,9-DTBP can
be explained by the π-electron partition of pyrene, which was reported by A. T. Balabana et al. [15] As
shown in Fig. 4, the relative π-electron partition values are described in pyrene. The upper and lower
phenyl rings inside of pyrene have an π-electron partition value of 4.67, while the value of the two phenyl
rings in the middle of pyrene is 3.33, indicating relatively deficient π-electron partition.

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Fig. 4 the π-electron partition of pyrene.
Table 1. Physical properties of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP.
Solutiona
λmax
Film on glass
λmax
HO
MOd
(eV)
LU
Band
gap
λmax
abs
λmax
abs
Tg
Td
FWHMb
FWHMb
Φfc
MOe
(eV)
Compounds
PL
PL
(℃)
(℃)
(
nm)
(nm)
(eV)
(
nm)
(nm)
(nm)
(nm)
1,6-DTBP
4,9-DTBP
1,8-DTBP
365
425
54
35
54
373
358
373
461
428
461
68
46
43
55
69
−
5.70
5.78
5.69
−
2.76
2.65
2.74
2.94
3.13
2.95
159
146
142
508
530
527
349
365
384, 405
−
−
−
−
425
54
aMeasured in 1 x 10-5 M THF. Full width at half maximum of PL. Absolute photoluminescence quantum yield in neat
b
c
d
e
films. Ultraviolet photoelectron spectroscopy (Riken-keiki, AC-2). LUMO obtained from HOMO and the optical band
gap.
The FWHM values of 1,6-DTBP, 1,8-DTBP, and 4,9-DTBP in solution state were 54 nm, 54 nm, and 35 nm,
respectively, and 4,9-DTBP had the narrowest PL spectrum among the three compounds. In case of the
film state, the FWHM values of 1,6-DTBP, 1,8-DTBP, and 4,9-DTBP were 68 nm, 54 nm, and 46 nm. 1,8-
DTBP in the film state had the same FWHM value, while the other two compounds exhibited increased
FWHM values in the film state.
Fig. 5 shows the calculation results of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP using the B3LYP / 6-31G (d)
level. In the side view of the optimized molecular structure, 1,6-DTBP had a more planar structure than
the other two materials. On the other hand, in the case of 4,9-DTBP and 1,8-DTBP, the pyrene core and
triphenylbenzene side group were highly twisted. Such a highly twisted structure prevents intermolecular
interactions in the film state. [16] This difference in intermolecular interactions may also affect the
absolute photoluminescence quantum yields (PLQYs), which were 43%, 55%, and 69% for 1,6-DTBP, 4,9-
DTBP and 1,8-DTBP, respectively.
As shown in Table 1, The highest occupied molecular orbital (HOMO), lowest unoccupied molecular

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orbital (LUMO) and band gap of the synthesized materials were −5.70 eV, −2.76 eV, and 2.94 eV for 1,6-
DTBP, −5.69 eV, −2.74 eV, and 2.95 eV for 1,8-DTBP, and −5.78 eV, −2.65 eV, and 3.13 eV for 4,9-DTBP,
respectively. In the calculation results of Fig. 5, the electron density distributions of HOMO and LUMO of
the newly synthesized materials were mainly localized to the pyrene core. Also, the tendency of the
calculation results for HOMO, LUMO, and band gap was similar to those obtained by experiments. The CV
of the compounds were measured to further investigate their electrochemical properties as shown in Fig.
S2. HOMO level calculated by CV results were −5.95 eV for 1,6-DTBP, −6.02 eV for 4,9-DTBP, and −5.98
eV for 1,8-DTBP, respectively.
Fig. 5 Pictorial presentation of the frontier orbitals, a plot of the Kohn-Sham HOMO and LUMO energy
levels for pyrene, triphenylbenzene (TB), 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP (calculated at the B3LYP/6-
3
1G(d) level of theory).

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To determine the thermal properties of the synthesized molecules, thermogravimetric analysis (TGA)
and differential scanning calorimetry (DSC) were used as shown in Fig. 6 and Table 1. OLED materials
require high thermal stability. Materials with a high glass transition temperature (T ) and decomposition
g
temperature (T ) are advantageous in that their morphology does not easily change due to the heat
d
generated during OLED device operation. [17] As shown in Table 1, T of the newly synthesized materials
d
showed excellent thermal stability over 500 ℃. In the case of T , 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP had
g
high values of 159 ℃, 146 ℃, and 142 ℃. These values indicated better thermal properties than Tg
(120 ℃) of MADN, which is a well-known blue-emitting material with an anthracene core.
1
00
1
4
1
,6-DTBP
,9-DTBP
,8-DTBP
80
60
40
20
1
00
200
300
400
500
600
o
Temperature ( C)
Fig. 6 TGA curves of the synthesized materials.
In order to observe the change in EL performance according to the substitution position on the pyrene
core, an OLED device was fabricated using the synthesized materials as non-doped EMLs according to the
following structure: ITO / NPB (40 nm) / TCTA (20 nm) / EML (30 nm) / TPBi (20 nm) / LiF (1 nm) / Al (200
nm). NPB was used as the hole transport layer, and the TCTA layer played a hole transport and electron
blocking role. TPBi was used as the electron transport and hole blocking layers. Emitting materials were
used as a single layer with a non-doped structure. The OLED device properties and luminance – current
density plot are summarized in Fig. 7, Fig. 8, Table 2, and Fig S3.

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Fig. 7 EL characteristics of devices using 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP as EMLs: (a) energy levels of
materials, (b) EL spectra.
8
7
6
5
4
3
2
1
0
8
7
6
5
4
3
2
1
0
(
a)
(b)
1
4
1
,6-DTBP
,9-DTBP
,8-DTBP
1,6-DTBP
4,9-DTBP
1,8-DTBP
0
20
40
60
80
100
0
20
40
60
80
100
2
2
Current Density (mA/cm )
Current Density (mA/cm )
Fig. 8 EL performance of devices using 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP as EMLs: (a) luminance
efficiency versus current density, (b) external quantum efficiency versus current density.
Fig. 7 (a) shows the energy levels of the organic materials used in OLED devices. The HOMO and LUMO
levels of the synthesized materials matched the HOMO levels of the carrier transporting materials. Fig. 7
(b) shows the EL spectra of the EL device. The ELmax of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP exhibited similar
maximum values to the PL spectrum at 455 nm, 433 nm, and 456 nm, respectively. Such a maximum
emission wavelength value suggests that the light emission of the device is generated from the
synthesized material within under normal device operation. In Fig. 8, 1,8-DTBP showed higher efficiency
than 1,6-DTBP or 4,9-DTBP.

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Table 2. The EL performance of the ITO / NPB (40 nm) / TCTA (20 nm) / EML (30 nm) / TPBi (20 nm) / LiF
/
Al device.
λmax EL
nm)
Compounds
Von (V)a
L (cd/m2)b
LE (Cd/A)b
PE (lm/W)b
EQE (%)b
CIE (x,y)b
(
1
4
1
,6-DTBP
,9-DTBP
,8-DTBP
4.0
4.2
4.0
182
158
1.82
1.58
6.89
1.08
0.92
3.03
1.59
3.47
7.10
(0.168, 0.152)
(0.158, 0.063)
(0.151, 0.125)
455
433
456
689
a
Turn-on voltage at 1 cd/m2.
b
Luminance, luminance efficiency, power efficiency, external quantum
efficiency, Commission Internationale de l’Eclairage at 10 mA/cm2.
Table 2 shows the turn-on voltage, luminance efficiency (LE), power efficiency (PE), external quantum
efficiency (EQE), and color coordinates values for OLED devices based on the three materials. 1,6-DTBP
had a turn-on voltage of 4.0 V, LE of 1.82 cd/A, PE of 1.08 lm/W, EQE of 1.59%, and color coordinate of
(
0.168, 0.152). For 4,9-DTBP and 1,8-DTBP, these values were 4.2 V, 1.58 cd/A, 0.92 lm/W, 3.47%, and
0.158, 0.063), and 4.0 V, 6.89 cd/A, 3.03 lm/W, 7.10%, and (0.151, 0.125), respectively. All three materials
(
exhibited a similar turn-on voltage of 4.0 V at 1 cd/m2.
The LE of 1,8-DTBP showed the highest efficiency of 6.89 cd/A among the three materials. This can be
explained by the suppressed intermolecular interactions and consequent high PLQY of 69%, which are
related to the bulky triphenyl benzene group. The PE of 1,8-DTBP was 3.03 lm/W, which was three times
higher than those of the other two materials. The EQE value was generally affected by the LE and CIE
coordinate values. Thus, 1,8-DTBP exhibited an excellent EQE of 7.10%, which was approximately 4.5 times
higher than that of 1,6-DTBP. As shown in Fig. 9, in the case of mobile phones, attaining a blue color
requires a y value of 0.15 or less for the color coordinates and high definition (HD)-TV requires a y value
of 0.08 or less. Three compounds met the requirement specifications of mobile phones in case of color
purity. Also, although EL efficiency of 4,9-DTBP was lower than that of 1,8-DTBP, the color coordinate y
value was 0.063, showing excellent color purity exceeding 0.08.

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Fig. 9 CIE x, y values of the synthesized compounds: (a) y value of 0.15 for mobile phone specifications,
(b) y value of 0.08 for HD-TV specifications.
4
. Conclusion
1
,6-DTBP, 4,9-DTBP, and 1,8-DTBP were successfully synthesized using a pyrene core group and triphenyl
benzene side group with different link positions. The PLQYs of the 1,6-DTBP, 4,9-DTBP and 1,8-DTBP
materials were 43%, 55%, and 69%, respectively. 1,8-DTBP showed the highest PLQY value among the
three compounds, likely due to its highly twisted structure. When these synthesized materials were
applied to non-doped OLEDs as an EML, the EQE of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP was 1.59%, 3.47%,
and 7.10%. 1,8-DTBP showed remarkably improved EL performance for blue emission. In addition, 4,9-
DTBP had a deep-blue emission of CIE x, y (0.158, 0.063), satisfying the HD-TV requirements due to its
wide band gap. These results are expected to contribute to the development of new blue-emitting
materials.
Acknowledgements
This research was supported by the National R&D Program through the National Research Foundation of
Korea (NRF) funded by the Ministry of Science & ICT (No. 2017M3A7B4041699). This research was
supported by the Basic Science Research Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education (No. 2017R1D1A1A09082138).

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Supporting Information
Highly Efficient Pyrene Blue Emitters for OLEDs Based on Substitution
Position Effect
Mina Jung , Jaehyun Leea,c1, Hyocheol Jung , Seokwoo Kang , Atsushi Wakamiya , Jongwook Park *
aDepartment of Chemistry/Display Research Center, The Catholic University of Korea
bDepartment of Chemical Engineering, Kyung Hee University, Gyeonggi, 17104, Korea
cInstitute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan
a1
b
b
c
b
*E-mail: jongpark@khu.ac.kr
1Mina Jung and Jaehyun Lee contributed equally to this work as the first coauthor

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(a) 1.0
Toluene
THF
DMSO
(b) 1.0
Toluene
THF
DMSO
(c) 1.0
Toluene
THF
DMSO
Fig.
S1
0
0
0
0
0
.8
.6
.4
.2
.0
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
Solvato-
chromism in
various
solvents of
3
00 350 400 450 500 550 600 650 700
300 350 400 450 500 550 600 650 700
300 350 400 450 500 550 600 650 700
Wavelength(nm)
Wavelength(nm)
Wavelength(nm)
(a)
1,6-
DTBP, (b) 4,9-DTBP, and (c) 1,8-DTBP.
Fig. S2 CV
(
a)
(b)
(c)
1,6-DTBP
4,9-DTBP
1,8-DTBP
curves of (a)
1
,6-DTBP,
(b) 4,9-
DTBP, and
c) 1,8-
DTBP: 0.1M
as an
solvent, Ag/AgCl reference
(
0
.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
0.5
1.0
1.5
2.0
2.5
3.0
Voltage (V)
Voltage (V)
Voltage (V)
tetrabutylammonium
perchlorate
electrolyte,
electrode.
acetonitrile
6000
1
,6-DTBP
4,9-DTBP
,8-DTBP
5
4
3
2
1
000
000
000
000
000
0
1
0
20
40
60
80
100
2
Current Density (mA/cm )

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Fig. S3 Luminance – current density plots of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP devices.

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-
1,6-DTBP, 4,9-DTBP, and 1,8-DTBP were successfully synthesized using a pyrene core group and
triphenyl benzene side group with different link positions.
-
-
The EQE value of 1,6-DTBP, 4,9-DTBP, and 1,8-DTBP was 1.59%, 3.47%, and 7.10%.
4,9-DTBP had a deep-blue emission of CIE x, y (0.158, 0.063), satisfying the HD-TV requirements
due to its wide band gap.