Synthesis and physical properties of new pyrene derivative with bulky side groups for blue emission

Article abstract of DOI:10.1166/jnn.2016.12480

Organic light-emitting diodes (OLEDs) have attracted much attention from academia and industry field because of their various applications such as large area flat-panel displays and lightings. We designed and synthesized new pyrene derivative with 1,6-bis(3',5'-diphenylbiphenyl-4-yl)pyrene (1,6-DTBP) which has bulky side group for intra-twisted structure and blue emission. In solution state, 1,6-DTBP exhibited absorption maximum value of 365 nm and photoluminescence (PL) maximum value of 425 nm. In film state, 1,6-DTBP exhibited absorption maximum value of 373 nm and PL maximum value of 461 nm without excimer band. 1,6-DTBP can be applicable to OLED emitter as a blue emission.

Full text of DOI:10.1166/jnn.2016.12480

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Nanoscience and Nanotechnology
Vol. 16, 8796–8799, 2016
Copyright © 2016 American Scientific Publishers
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Synthesis and Physical Properties of New Pyrene
Derivative with Bulky Side Groups for Blue Emission
Mina Jung, Jaehyun Lee, Hyocheol Jung, and Jongwook Park∗
Department of Chemistry/Display Research Center, The Catholic University of Korea, Bucheon, 420-743, Korea
Organic light-emitting diodes (OLEDs) have attracted much attention from academia and indus-
try field because of their various applications such as large area flat-panel displays and lightings.
We designed and synthesized new pyrene derivative with 1,6-bis(3ꢀ,5ꢀ-diphenylbiphenyl-4-yl)pyrene
(1,6-DTBP) which has bulky side group for intra-twisted structure and blue emission. In solution
state, 1,6-DTBP exhibited absorption maximum value of 365 nm and photoluminescence (PL) max-
imum value of 425 nm. In film state, 1,6-DTBP exhibited absorption maximum value of 373 nm and
PL maximum value of 461 nm without excimer band. 1,6-DTBP can be applicable to OLED emitter
as a blue emission.
Keywords: OLEDs, Pyrene, Blue Fluorescent Emitter, Core-Side Concept.
IP: 46.161.56.174 On: Thu, 26 Apr 2018 07:57:57
1. INTRODUCTION
de l’Eclairage (CIE ꢁ coordinate (0.156, 0.088) than
Copyright: American Scientific Publisherꢀs xꢀy
Organic light-emitting diodes (OLEDs)1–5 based on small
organic molecules are under many intense researches in
view of their promising future for large full color dis-
play applications such as TV and advertising displays.
OLED has been under active researches so far with its
overlooking high potential for use in liquid crystal display
(LCD) backlight and lighting field due to its low power
consumption.6ꢀ7
At the heart of full color display is the development
of stable and highly efficient red, green, and blue (RGB)
emitting materials.8 Among the red, green and blue emit-
ting materials used in OLED, blue ones are character-
ized especially as low efficiency and short device lifetimes
because of its wide band gap. Blue light means that it
includes high energy band gap as well as a steep energy
barrier at the hole and electron injection interfaces inside
of device compared to red and green emitter.
2-methyl-9,10-di(2 -naphthyl)anthracene(MADN).
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Among derivatives used diverse core groups like
anthracene, pyrene, phenanthrene, and chrysene well
known as blue emitting materials, pyrene and its deriva-
tives received the spotlight as they provide high PL
quantum efficiency, thermal and chemical stabilities.10
In this work, we designed and synthesized 1,6-bis(3ꢀ,5ꢀ-
diphenylbiphenyl-4-yl)pyrene (1,6-DTBP) using pyrene
core group with triphenylbenzene group as bulky side
groups for blue emission (see Scheme 1).
2. EXPERIMENTAL DETAILS
2.1. General Experiment
1H-NMR spectra were recorded on Bruker, Advance 300.
The optical absorption spectra were obtained by Lambda
1050 UV-VIS-NIR spectrometer. Perkin Elmer lumines-
cence spectrometer LS50 (Xenon flash tube) was used
for photoluminescence (PL) spectroscopy. HOMO value
was measured by RIKEN Surface analyzer AC-2. MALDI
TOF-TOF 5800 System was used for mass spectroscopy.
OLED device was fabricated as the following structure:
ITO/2-TNATA (60 nm)/NPB (15 nm)/EML (35 nm)/Alq3
(20 nm)/LiF (1 nm)/Al (200 nm), where, 4,4ꢀ,4ꢀꢀ-
Tris(N -(naphthalen-2-yl)-N-phenylamino) triphenylamine
[2-TNATA] as hole injection layer, N ,Nꢀ-bis(naphthalen-
1-yl)-N ,N ꢀ-bis(phenyl)benzidine [NPB] as hole trans-
port layer, and 8-hydroxyquinoline aluminum [Alq3] as
In past research, we have reported new high performance
blue-light emitters based on anthracene core derivatives
using core-side concepts.9 For example, 9,10-bis(3ꢀꢀ,5ꢀꢀ-
diphenylbiphenyl-4ꢀ-yl)anthracene (TAT) was synthesized
using anthracene core group with triphenylbenzene group
as bulky side group. This material has better thermal
properties, a better luminance efficiency, a higher power
efficiency, and a deeper blue Commission Internationale
∗Author to whom correspondence should be addressed.
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1533-4880/2016/16/8796/004
doi:10.1166/jnn.2016.12480

Jung et al.
Synthesis and Physical Properties of New Pyrene Derivative with Bulky Side Groups for Blue Emission
ꢁ
ꢁ
50 C. The mixture was heated to 80 C for 2 h under
nitrogen. After the reaction was complete, the reaction
mixture was filtered. The product was isolated using silica
gel column chromatography with CHCl3 as the solvent.
The eluent was removed by evaporation. Recrystalliza-
tion of the residue from CHCl3 afforded a solid product
(0.16 g, yield 6.92%). 1H-NMR (300 MHz, THF) ꢂ(ppm):
8.33(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). TOF-
MS 810.3 m/z.
Scheme 1. Chemical structure of the synthesized material.
electron transporting and emission layer, lithium fluoride
[LiF] as electron injection layer, ITO as anode and Al as
cathode. The organic layer was vacuum-deposited using
thermal evaporation at a vacuum base pressure of 10−6 torr
and the rate of deposition being 1 Å/s to give an emit-
ting area of 4 mm2, and the Al layer was continuously
deposited under the same vacuum condition. I–V –L char-
acteristic of OLED device and EL spectrum were obtained
using a Keithley 2400 source measure unit and a Minolta
CS-1000A spectrophotometer.
3. RESULTS AND DISCUSSION
The synthesis routes to the 1,6-DTBP are shown in
Scheme 2. In blue emitting material, it has generally core
and side moieties. 1,6-DTBP introduced pyrene as the core
group with high PL quantum yield of 0.65% which is two
times higher than that of anthracene. However, the use
of pyrene as efficient emitters in OLED has been lim-
ited, because the planar structure of pyrene has strong ten-
dency to form excimers in the solid state, which results
in long-wavelength excimers emission with low fluores-
cence quantum yield and emission quenching.11 In order to
prevent this limitation, bulky triphenylbenzene group was
introduced as the side group to pyrene core.
2.2. Synthesis of Tetramethyl-3ꢀ,5ꢀ-Diphenylbiphenyl-
4-yl-[1,3,2]-Dioxaborolane, (Compound [9])
Compound [8] (3 g, 7.78 mmol) was added to 13 mL of
ꢁ
UV-Visible (UV-Vis.) absorption and PL spectra of
the synthesized compound in the THF solution and the
anhydrous THF and stirred at −78 C under a nitrogen
atmosphere, then 2 M n-BuLi (5.83 mL, 11,68 mmol) was
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added to the reaction mixture. Next, isopropoxy-4,4,5,5-
Copyright: American Scientific Publishers
tetramethyl-1,3,2-dioxaborolane (3.24 mL, 15.6 mmol)
Delivered by Ingenta
was added to the reaction mixture after 30 min. After
the reaction was complete, the reaction mixture was
extracted with ethyl acetate and water. The organic layer
was dried with anhydrous MgSO4 and filtered. The sol-
vent was removed by evaporation. The product was puri-
fied by silica gel column chromatography using THF:
n-hexane (1:10) (3.03 g, yield 90%). 1H-NMR (300 MHz,
CDCl3) ꢂ(ppm): 7.94(d, 2H), 7.80(m, 3H), 7.73(m, 6H),
7.51(t, 4H), 7.42(t, 2H), 1.24(d, 12H).
2.3. Synthesis of 1,6-Dibromopyrene (Compound [2])
Bromine (10.0 mL, 195 mmol) in CHCl3 (500 mL) was
dropped into a solution of pyrene (20.0 g, 98.9 mmol) in
CHCl3 (500 mL) over 5 h while stirring. The precipitate
was collected after 12 h and resolved by fractional crys-
1
tallization from xylene (5.01 g, yield 14.07%). H-NMR
(300 MHz, CDCl3) ꢂ(ppm): 8.49(d, 2H), 8.29(d, 2H),
8.15(d, 2H), 8.08(d, 2H).
2.4. Synthesis of 1,6-Bis(3ꢀ,5ꢀ-Diphenylbiphenyl-4-yl)
Pyrene (1,6-DTBP)
Compound [2] (1 g, 2.76 mmol), compound [9] (2.63 g,
6.08 mmol) and Pd(OAc)2 (0.23 g, 0.52 mmol) were
added to 30 mL of anhydrous THF and anhydrous toluene
170 mL mixture. Then tetraethylammonium hydroxide
(20 wt%) (35 mL) was added to the reaction mixture at
Scheme 2. Synthetic routes of 1,6-DTBP.
J. Nanosci. Nanotechnol. 16, 8796–8799, 2016
8797

Synthesis and Physical Properties of New Pyrene Derivative with Bulky Side Groups for Blue Emission
Jung et al.
Figure 2. Electron density distributions of HOMO and LUMO in the
1,6-DTBP calculated with B3LYP/6-31G.
the B3LYP/6-31G level as shown in Figure 2. In the
Figure 1.
UV-Visible absorption and PLIPsp:ec4tr6a.o1f611,6.-5D6T.B1P7: 4(a)Osonlu:-Thu, 26 Apr 2018 07:57:57
tion state in THF (1.0×10−5
optimized structure, 1,6-DTBP has highly twisted core-
M), (b) evaporateCd ofilpmysrtiagteh.t: American Scientific Publishers
side angle of 90.1ꢁ between the pyrene and triphenylben-
Delivered by Ingenta
zene group. Highly twisted structure can prevent excimer
in film state by effectively reducing intermolecular ꢃ–ꢃ
interaction. Therefore, there is no excimer band at PL
spectrum.
evaporated film state were measured as shown in Figure 1
and Table I. In the THF solution state, 1,6-DTBP exhibits
a absorption maximum (UVmaxꢁ value of 365 nm and
PL maximum (PLmaxꢁ value of 425 nm. In film state,
1,6-DTBP showed UVmax of 373 nm and PLmax of 461 nm.
In PL spectrum of film state, excimer emission was not
exhibited. In comparison to solution state, UVmax and
PLmax of film state were respectively red-shifted by 8 nm
and 36 nm, which indicated an increase in conjugation
length in the solid state.12 The increase in conjugation
length might be due to the conformation of solid state
ꢃ-stacked compounds being more planar. Furthermore, the
full widths at half maximum (FWHM) of 1,6-DTBP was
found to be 54 nm in solution state and 68 nm in film
state.
Highest occupied molecular orbital (HOMO) value for
the 1,6-DTBP was measured by AC-2 at −5.70 eV. Opti-
cal band gap of 2.94 eV was calculated from the UV-Vis.
absorption spectrum.
Lowest unoccupied molecular orbital (LUMO) value of
−2.76 eV calculated from the HOMO and optical band
gap. Those data are summarized in Table II.
The device structure was fabricated as ITO/2-TNATA
(60 nm)/NPB (15 nm)/EML (35 nm)/Alq3 (20 nm)/LiF
(1 nm)/Al (200 nm). I–V –L curve was shown in Figure 3.
OLED device based on 1,6-DTBP exhibited luminance
efficiency of 4.19 cd/A. Power efficiency was 1.87 lm/W.
The EL maximum value of 1,6-DTBP was exhibited at
468 nm of blue emission (Fig. 3). In case of CIE value,
1,6-DTBP was shown at (0.16, 0.19).
The molecular structure of 1,6-DTBP was optimized
by using density functional theory (DFT) calculated at
Table I. Optical properties of 1,6-DTBP.
Solutiona
Filmb
Table II. Electrochemical property of 1,6-DTBP.
HOMOa (eV)
LUMOb (eV)
Band gap (eV)
2.94
UVmax
(nm)
PLmax
(nm)
FW HM UVmax
PLmax
(nm)
FW HM
(nm)
(nm)
(nm)
1,6-DTBP
−5.70
−2.76
1,6-DTBP
365
425
54
373
461
68
Notes: a: Ultraviolet photoelectron spectroscopy (Riken-keiki, AC-2), b: LUMO
Notes: a: Solution state of THF (1×10−5 M), b: Film state.
obtained from the HOMO and the optical band gap.
8798
J. Nanosci. Nanotechnol. 16, 8796–8799, 2016

Jung et al.
Synthesis and Physical Properties of New Pyrene Derivative with Bulky Side Groups for Blue Emission
Triphenylbenzene group is a bulky side group introduced
to effectively prevent ꢃ–ꢃ interaction of pyrene and
excimer in film state. 1,6-DTBP in solution state showed
UVmax of 365 nm and PLmax of 425 nm. In film state,
they were 373 nm and 461 nm, respectively. OLED device
based on 1,6-DTBP exhibited luminance efficiency of
4.19 cd/A. Power efficiency was 1.87 lm/W.
Acknowledgments: This research was supported by a
grant from the Fundamental R&D Program for Core Tech-
nology of Materials funded by the Ministry of Trade,
Industry and Energy, Republic of Korea (Project No.
10050215).
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Figure 3. (a) I–V –L data of OLED device, (b) EL spectrum of
OLED device: ITO/2-TNATA (60 nm)/NPIBP(:145 6nm.1)6/E1M.5L6(3.157n4m)O/Anlq:3 Thu,82. 6Y.AIp. rPa2rk0,1J8. H0.7S:o5n7, :J5. 7S. Kang, S. K. Kim, J. H. Lee, and J. W.
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4. CONCLUSION
We designed and synthesized 1,6-DTBP as a new blue
emitting material in OLED with pyrene as the core
group and triphenylbenzene group as the side group.
12. D. Vak, B. Lim, S. H. Lee, and D. Y. Kim, Org. Lett. 7, 4229 (2005).
Received: 20 May 2015. Accepted: 12 August 2015.
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