Two non-doped blue emitters for electroluminescent devices: Preparation, photophysics and electroluminescence

Article abstract of DOI:10.1016/j.dyepig.2016.04.048

Two blue emitters, 2,7-bis(9-benzyl-9H-carbazol-2-yl)pyrene and 2,7-bis(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)pyrene, were synthesized by a Suzuki coupling reaction. Photophysical studies show that the two emitters have excellent optical and electron transfer properties. The emission peaks of the two emitters are 430 nm and 439 nm with 87.5% and 68.6% fluorescence quantum yields in chloroform, respectively. The emitters both have good thermal stability (Td > 330 °C, Tg > 160 °C). Electrochemical Redox properties of the emitters were measured by cyclic voltammetry, and the highest occupied molecular orbital and the lowest unoccupied molecular orbital levels are in good agreement with the results of theoretical calculations. Additionally, non-doped blue organic light-emitting diodes with these emitters have been achieved with the Commission International de l'éclairage (x,y) coordinates of (0.17, 0.11) and (0.16, 0.15) respectively, which are very close to the National Television System Committee standard blue. Remarkably, the performance of device A (2,7-bis(9-benzyl-9H-carbazol-2-yl) pyrene) offers balanced performance and without any significant disadvantages.

Full text of DOI:10.1016/j.dyepig.2016.04.048

Accepted Manuscript
Two non-doped blue emitters for electroluminescent devices: Preparation,
photophysics and electroluminescence
Jiarong Zhu, Ninghua Yin, Liheng Feng
PII:
S0143-7208(16)30177-2
10.1016/j.dyepig.2016.04.048
DYPI 5227
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 25 March 2016
Revised Date: 27 April 2016
Accepted Date: 28 April 2016
Please cite this article as: Zhu J, Yin N, Feng L, Two non-doped blue emitters for electroluminescent
devices: Preparation, photophysics and electroluminescence, Dyes and Pigments (2016), doi: 10.1016/
j.dyepig.2016.04.048.
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ACCEPTED MANUSCRIPT
Two Non-doped Blue Emitters for Electroluminescent Devices:
Preparation, Photophysics and Electroluminescence
Jiarong Zhu, Ninghua Yin, Liheng Feng*
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan, 030006, P.R. China.
E-mail address: lhfeng@sxu.edu.cn (L. Feng); Tel.:+86 351 7010904; Fax: +86 351 7011688.
Abstract: Two blue emitters, 2,7-bis(9-benzyl-9H-carbazol-2-yl)pyrene and 2,7-
bis(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)pyrene, were synthesized by a Suzuki
coupling reaction. Photophysical studies show that the two emitters have excellent
optical and electron transfer properties. The emission peaks of the two emitters are
430 nm and 439 nm with 87.5% and 68.6% fluorescence quantum yields in
o
chloroform, respectively. The emitters both have good thermal stability (Td>330 C,
o
Tg>160 C). Electrochemical Redox properties of the emitters were measured by
cyclic voltammetry, and the highest occupied molecular orbital and the lowest
unoccupied molecular orbital levels are in good agreement with the results of
theoretical calculations. Additionally, non-doped blue organic light-emitting diodes
with these emitters have been achieved with the Commission International de
l’Éclairage (x,y) coordinates of (0.17, 0.11) and (0.16, 0.15) respectively, which are
very close to the National Television System Committee standard blue. Remarkably,
the performance of device A (2,7-bis(9-benzyl-9H-carbazol-2-yl) pyrene) offers
balanced performance and without any significant disadvantages.
Keywords: blue emitter, electroluminescent devices, pyrene, carbazole, oxadiazole
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1. Introduction
Organic light-emitting diodes (OLEDs) have been developed rapidly due to the
advantages of the low drive voltage, high luminance and high efficiency [1-5]. Red,
green and blue light plays a very important role in the full-color display, as they are
the three primary colors. To date, green and red OLEDs materials have been widely
reported [6-15]. Due to the low energy consumption lighting, white OLEDs materials
have also been developed rapidly [16-22]. In comparison with other shades of OLED
materials, it is difficult to obtain high-efficient blue or deep blue OLEDs because of
the necessary wide band gaps. Hence, it is always a large challenge to design and
achieve blue OLEDs. Based on these requirements, recently, the development speed
of blue OLEDs is also very fast and many different types of blue OLEDs have been
reported. Carbazole and its derivatives have been widely used as good hole-transport
materials in the preparation of blue OLEDs [23-28]. Fluorene and its derivatives can
be used as efficient blue emitters in the preparation of blue OLEDs [23, 28-35].
Moreover, chrysene derivatives [36], anthracene derivatives [37-39], triphenylamine
derivatives [40], naphthalene derivatives [41,42] and other simple polymers [43-46]
have also been used in OLEDs. Apart from these organic molecules, some metal
complexes can be also used in OLEDs. Florian [47], Wong [48], Adachi [49] amongst
other researchers have succeeded in using iridium (III) complexes to prepare blue
OLEDs. Moreover, some other transition-metal complexes have also been successful
in OLED applications [50].
Compared with other conjugated aromatic compounds, the pyrene functional group
offers a high quantum yield, excellent electron mobility and hole-injection ability.
However, pyrene itself has a strong tendency towards crystallization. Due to the π-π
stack forming the excited molecule, its fluorescence emission may be red-shifted over
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480 nm and with pyrene derived molecules it is difficult to form a stable amorphous
thin film, which makes pyrene itself unsuitable for blue OLEDs [51,52]. Therefore, it
is imperative to modify pyrene structures with some specific functional groups. Rao
and his coworkers have successfully appended an electron transport group to blue
emitting pyrene derivatives. But the CIEy of these compounds are over 0.2, and the
thermal stability of these compounds are not good [53]. Mullen and his coworkers
successfully prepared a dark blue emitter with pyrene and carbazole units, but the
brightness of corresponding OLED is low (<1000 cd·m-2) [24]. Tao and his coworkers
also prepared pyrene derivatives with 4-(2,2-diphenyl-vinyl)phenyl group [54]. The
performances of combined devices are good, but they are not deep blue OLEDs.
Similarly, other researchers also designed and developed some pyrene derivatives as
blue OLEDs materials [55-58]. These obtained pyrene emitters have their own
particular characteristics, but more or less have their disadvantages, such as either
larger CIEy, lower brightness or emitting violet light. Additionally, hole-transfer and
electron-injection properties of emitters are two important parameters for OLEDs
materials.
Based on the current case, the aim of our work is to achieve excellent blue emitters
with hole-transfer or electron-injection groups. Hence, we designed and synthesized
two novel pyrene emitters with 9-benzyl-9-H-carbazole (hole-transfer group) and 2,5-
diphenyl-1,3,4-oxadiazole (electron-injection group), respectively. The test results of
photophysical and electroluminescence properties display that the two compounds as
emitters of OLEDs emit blue light. Noticeably, the device based on 2,7-bis(9-benzyl-
9H-carbazol-2-yl)pyrene (BCP) emitter has good properties including higher
brightness, pure blue light and good stability.
2. Experimental
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2.1 Materials
Unless otherwise stated, all chemical reagents were obtained from commercial
suppliers and were used without further purification. The following reagents:
Pd(dppf)Cl2, bis(pinacolato)diboron, N-bromosuccinimide, phosphoryl chloride,
Pd(PPh3)4, 4-bromobenzoyl chloride, phenylhydrazine, N-benzylcarbazole and 1,6-
dibromopyrene were all purchased from Aldrich (Steinheim, Germany).
2.2 Characterization
13
1H NMR and C NMR were measured on a Bruker ARX400 spectrometer with
chemical shifts reported as ppm (TMS as an internal standard). The UV-Vis
absorption and fluorescence emission spectra were taken on a HITACHI UH5300 and
F-4600 spectrophotometers, respectively. The excitation and emission slit widths were
both 5.0 nm. High-resolution mass spectra (HRMS) were acquired on an Agilent 6510
Q-TOF LC/MS instrument (Agilent Technologies, Palo Alto, CA) equipped with an
electrospray ionization (ESI) source. IR-spectroscopy measurements were performed
on a FTIR8400S spectrophotometer, using KBr pellets. Elemental analyses were
measured on a EuroVector EA3000 elemental analyzer. The glass transition
temperatures of compounds were determined by DSC using a DSC-Q10 instrument
under a nitrogen atmosphere. The decomposition temperature corresponding to 5 %
weight loss was detected using a Perkine Elmer Pyris 1 TGA thermal analyzer. The
melting points of compounds were recorded on a WRS-3 instrument with a 3 °C/min
heating rate. Cyclic voltammetry (CV) measurements were determined on a three-
electrode AUTOLAB (model PGSTAT30) workstation in a solution of Bu4NClO4
(0.1 M) in acetonitrile at a scan rate of 50 mV/s at room temperature.
2.3 Device fabrication
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The multilayer OLEDs were fabricated by vacuum-deposition method. Organic
layers were fabricated by high-vacuum (5×104 Pa) thermal evaporation onto a glass (3
cm×3 cm) substrate percolated with an ITO layer, which was used as anode. The hole-
transfer layer (HTL) was poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)
(PEDOT: PSS). The electron-blocking layer was 4,4-bis(N-carbazolyl)-1,10-biphenyl
(CBP). The emitting layer was BOP and BCP, respectively. The electron-transport
layer (ETL) was 1,3,5-tris(N-phbenylbenzimidazol-2-yl) benzene (TBPI). The
cathode was LiF/Al. All organic layers were sequentially deposited. Thermal
deposition rates for organic materials, LiF and Al were 0.5 Å·s-1, 0.5·Å s-1and 1.0 Å·s-
1, respectively. The active areas of these devices were 9 mm2. The electroluminescent
spectra were measured on a Hitachi MPF-4 fluorescence spectrometer. The voltage-
current density characteristics of OLEDs were recorded on Keithley 2400 Source
Meter. The characterization of luminance-voltage was measured with a 3645 DC
power supply combined with a 1980 A spot photometer and was recorded
simultaneously. All measurements were done at room temperature.
2.4 Synthesis procedures of BCP and BOP
Compounds
of
9-benzyl-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-
carbazole and 2-phenyl-5-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-
1,3,4-oxadiazole were prepared according to the previous reported works [59-61].
2.4.1 2,7-bis(9-benzyl-9H-carbazol-2-yl)pyrene (BCP)
A mixture with 1,6-dibromopyrene (0.9 g, 2.5 mmol), 9-benzyl-3-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole (1.92 g, 5.0 mmol) in dioxane
(50.0 mL) and 2.0 M K2CO3 (10.0 mL) was stirred for 30 min at room temperature
under nitrogen atmosphere. Then, Pd(PPh3)4 (0.1 g) catalyst was quickly added to the
o
suspension and heated to 110 C for 48 h under nitrogen atmosphere. The reaction
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mixture was cooled to room temperature, poured into the ice water (200 mL), filtered
and then purified by column chromatography on silica gel with dichloromethane
/petroleum ether (1/1, v/v) as the eluant to afford BCP as faint yellow solids (1.149g
1
64.5 %), m.p. 275-277 °C. H NMR (CDCl3, 400 MHz) δ 8.42 (s, 2H), 8.34-8.31 (d,
J=12.0 Hz, 2H), 8.26-8.22 (m, 4H), 8.19-8.06 (m, 6H), 7.76-7.73 (t, J=6.0, 6.0 Hz,
2H), 7.67-7.59 (t, J=8.0, 8.0 Hz, 2H) , 7.56-7.45 (m, 4H), 7.36-7.04 (m, 10H), 5.65 (s,
4H). 13C NMR (CDCl3, 100 MHz) δ 141.21, 140.03, 138.56, 137.18, 132.50, 130.23,
128.87, 128.33, 127.57, 126.54, 126.12, 125.42, 123.24, 122.39, 120.56 , 119.44,
108.70, 46.83. IR (KBr, υcm-1):(arene C-H) 3083, 3030; (aliphatic C-H) 2920, 2856;
(C=C, Ar) 1625, 1601; (C-N, Ar) 1477, 1466. Element Analysis for C54H36N2 (Mol.
Wt.: 712.90) calcd.: C, 90.98; H, 5.09; found: C 91.12; H 4.98. HRMS-ESI for
C54H36N2 (m/z) 713.53 [M+1].
2.4.2 2,7-bis(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)pyrene (BOP)
The BOP was synthezied according to the above method. The crude produce was
purified by column chromatography on silica gel with ethyl acetate/dichloromethane
(1/12, v/v) as the eluant to afford BOP as a pale fawn solid (0.905 g 56.3 %), m.p.
285-287 °C, respectively. 1H NMR (CDCl3, 400 MHz) δ 8.50 (d, J=6.4 Hz, 2H), 8.41
(d, J=4.8, 2H), 8.39-8.25 (m, 8H), 8.14 (d, J=12.0 Hz, 2H), 8.03 (d, J=8.0 Hz, 2H),
7.89 (d, J=8.0 Hz, 4H), 7.62 (m, 6H). 13C NMR (CDCl3, 100 MHz) δ 164.71, 135.34,
131.77, 129.08, 127.00, 126.06, 125.97, 123.89, 84.25, 25.03. IR (KBr, υcm-1): (arene
C-H) 3043; (C=C, Ar) 1612, 1630; (C=N) 1546; (C-O-C) 1078, 1296. Element
Analysis for C44H26N4O2 (Mol. Wt.: 642.72) calcd.: C, 82.23; H, 4.08; N, 8.72; found:
C, 82.48; H, 4.51; N, 8.64; HRMS-ESI for C44H26N4O2 (m/z): 643.48 [M+1].
3. Results and discussion
3.1 Synthesis and photophysical properties of BCP and BOP
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The synthetic routes used to prepare blue emitters BCP and BOP were showed in
Scheme 1. The two compounds also were synthesized by Suzuki coupling reaction
between 1, 6-dibromopyrene and carbazole boric acid ester or oxadiazoles boric acid
ester in the presence of palladium catalyst with 64.5 % and 56.3 % yields, respectively
[59-61]. The structures of BCP and BOP were characterized and verified by 1H NMR,
13C NMR, high resolution mass (HRMS), IR-spectroscopy and elemental analysis
(EA). Due to larger rigid conjugated structures of BCP and BOP, they have poor
solubility in routine organic solvents, for example ethyl acetate, acetone, ethanol,
methanol, diethyl ether, etc.
The photophysical properties of BCP and BOP were studied by UV-Vis absorption
and fluorescence emission techniques. Fig. 1 gives the absorption and emission
spectra of BCP and BOP in CHCl3. As can be seen from Fig. 1, BOP and BCP have
similar absorption and emission peaks, and the peaks are very close. The λmax of
absorption peaks of BCP and BOP are 370 nm and 372 nm, respectively.
Accordingly, the emission peaks of BCP and BOP are 430 nm and 435 nm,
respectively. The energy gaps (Eg) of BCP and BOP were calculated by the empirical
equation [Eg=1240/λabs]. The energy gaps (Eg) of BCP and BOP are 3.33 eV and 3.35
eV, which are very close to the theoretical calculation results 3.34 eV and 3.33 eV,
respectively. Using quinine sulfate in 0.10 M sulfuric acid as the reference, the
fluorescent quantum yields (Φ) of BCP and BOP in CHCl3 are 87.5 % and 68.6 % in
chloroform, respectively. These data indicate that the two compounds can be used as
potential blue emitting materials because they have suitable blue emitting range.
The solvent effects of BCP and BOP were tested by the fluorescence instrument in
different organic solvents (Table S1). As can be seen from the Table S1, the
maximum emission wavelengths (λem) of BCP and BOP are both gradually red-shifted
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with increase of solvent polarity. The result may be explained by the following
reason: the polarity of excited state always is smaller than the ground state because of
the π-π* transition of molecules. Thus, the interaction between the excited state and
polar solvent is larger than the interaction between ground state and polar solvent.
That is to say, the energy difference between the ground state and excited state
becomes small with the increase of solvent polarity. So the emission peaks of BCP
and BOP are red-shifted.
3.2 Thermal properties of BCP and BOP
Good thermal stability of emitter materials plays very important in device
application. The thermal stabilities of BOP and BCP were evaluated by thermal
gravimetric analysis (TGA) with a 5.0 °C/min heating rate and differential scanning
calorimetry (DSC) under nitrogen atmosphere. Due to their large molecular masses
and rigid structures, both compounds showed good thermal stability. The
decomposition temperatures (Td, 5 % weight loss) of BOP and BCP are 353 ºC and
333 ºC with the glass transition temperatures 164 ºC and 170 ºC (Fig. 2), respectively.
These results indicate that BOP and BCP have good stable thermal properties and
high glass transition temperatures, which will contribute to the device performance
(longevity).
3.3 Electrochemical properties
Using cyclic voltammetry (CV) with a saturated calomel electrode as the reference
electrode, we studied the electrochemical properties of BCP and BOP. Under N2
atmosphere, using 0.10 M tetrabutylammonium perchlorate as the supporting
electrolyte, the electrochemical properties of BCP and BOP were studied. Fig. S1 and
Fig. S2 give the electrochemical properties of BOP and BCP, respectively. There is
an oxide peak and a reversible reduction peak in the entire electrochemical window of
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BOP (Fig. S1). The initial oxidation potential is around +0.59 eV, which comes from
the oxidation of the pyrene core and the reversible reduction. And, the reversible
reduction peak is around -1.11 eV, which results from electron injection into the
vacant p-orbital of BOP. That is to say, the electron distribution of LUMO is mainly
on 2,5-diphenyl-1,3,4-oxadiazole moiety, which indicates that BOP can be used as a
good electron-transfer material. The HOMO energy level is -5.33 eV, which can be
calculated by the empirical equation [HOMO=-(Eox+4.5+0.24) eV]. The HOMO
level indicates that the electron distribution is mainly in the pyrene moiety. The
energy gap (Eg) of BOP is 3.33 eV, which is obtained by the equation [Eg=1240/λabs].
The LUMO energy level is -2.00 eV, which is calculated by the HOMO and Eg.
Similarly, the HOMO, LUMO level and Eg of BCP were obtained by the same
calculation methods (Fig. S2). The HOMO, LUMO and Eg of BCP are -5.35 eV, -
2.02 eV and 3.33 eV, respectively. The electron distributions of HOMO and LUMO
for BCP are mainly on the pyrene core. These results indicate that the emission of
BCP mainly comes from the excited state of pyrene core.
3.4 Theoretical calculation
Theoretical calculations have been widely used in many research fields and can
effectively provide a reasonable qualitative indication of the excitation and emission
properties of a conjugated molecule [62, 63]. Using density functional theory (DFT),
the geometries and electron density distributions of the HOMO and LUMO energy
levels of BOP and BCP. Under the DFT/B3LYP/6-31G (d, p) level with using
Gaussian 09 software the geometry in the ground state was optimized. The geometries
and electron density distributions of the HOMO and LUMO energy levels of BOP and
BCP were calculated by density functional theory (DFT) in Fig. 3. As can be seen
from Fig. 3, the HOMO level of BOP is -5.33 eV and the electron density is mainly
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distributed on the pyrene moiety. The LUMO level is -2.00 eV and electron density is
mainly distributed on the oxadiazole moiety. The HOMO and LUMO of BCP is -5.33
eV and -1.99 eV, respectively. But the electron distributions of HOMO and LUMO
for BCP are both mainly on the pyrene moiety. In addition, complete localization of
the HOMO and LUMO is essential for efficient hole and electron transport and the
prevention of reverse energy transfer as well [64].
3.5 Electroluminescence Devices
In order to evaluate BOP and BCP as potential luminescent materials in OLEDs,
multilayers non-doped OLEDs with configurations of A:ITO/PEDOT:PSS(50
nm)/BCP(30 nm)/CBP(5 nm)/TPBI(30 nm)/LiF(1 nm)/Al(200 nm) and B:ITO/
PEDOT:PSS(50 nm)/BOP(30 nm)/CBP(5 nm)/TPBI(30 nm)/LiF(1 nm)/Al(200 nm)
were fabricated. The electroluminescence (EL) spectra of device A and B are
displayed in Fig. 4 and Fig. S3. The emission peaks of BCP and BOP are 450 nm and
440 nm respectively. According to the EL spectra, the electroluminescence
chromaticity coordinates (CIE) of BCP and BOP are (0.17, 0.11) and (0.16, 0.15),
respectively. The results suggest that the two compounds afford deep blue coloured
OLEDs materials and the diode constructed using BCP is much deeper blue than that
using BOP (Fig. 5). From the EL spectra it can also be found that the emission peaks
of BCP and BOP are red-shifted about 10 nm and 15 nm in contrast with their PL
emission peaks in CHCl3. Along with the increase of the voltage, there are almost no
changes of the EL emission wavelengths of device A and device B, which indicates
that both device A and device B are very stable.
The voltage-luminance and voltage-current density curves of device A and device
B are depicted in the Fig. 6(a) and (b), respectively. While the current density-
efficiency and luminance-power efficiency curves are listed in Fig. S4-S5. Based on
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these experiment results, we can find the turn-on voltage, maximum luminance,
maximum current efficiency and maximum power efficiency of device A are 4.6 V,
1975 cd·m-2 (at 9.5 V), 1.08 cd A-1(at 6.2 V) and 0.628 lm·W-1(at 5.2 V), respectively.
Similarly, the turn-on voltage, maximum luminance, maximum current efficiency and
maximum power efficiency of Device B are 4.8 V, 1282 cd·m-2 (at 9.5 V), 0.73 cd·A-
1(at 7.0 V) and 0.328 lm·W-1(at 7.0 V), respectively. Compared to the
electroluminescence data of device A with device B, the performance of device A is
superior to device B. The experimental data indicate that all aspects of device A are
well suited with the application of deep blue OLEDs. It should be pointed out that the
EL performances were obtained in non-optimized test devices under ordinary
laboratory conditions. We believe that the performance of devices will be improved
by optimizing the structures of devices, the layer thickness and process conditions.
4. Conclusion
In summary, we have successfully synthesized and characterized two deep blue-
light emitters (BCP and BOP) by Suzuki coupling reactions. The advantages of
photophysical and electroluminescence properties of the two emitters are as follows:
1) they are both new OLEDs materials with good π-electron delocalization and
conjugation features; 2) The CIEs of BCP and BOP are (0.17, 0.11) and (0.16, 0.15),
which indicates that both of them are deep blue-light emitting materials; 3) They are
comprised of luminophor (pyrene) and electron-transfer group (oxadiazole) or hole-
transport group (carbazole), respectively; 4) Owing to the rigid structures, they have
good thermal stabilities; 5) The performance of device A is balanced and without
obvious disadvantages. In other words, the emitter with hole-transfer group (BCP) is
better than with electron-transport group (BOP) in device application. With the
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optimization of structures and layers thickness, the properties of devices will be
improved and may meet commercial requirements.
Acknowledgment
The work described in this paper was supported by the National Nature Science
Foundation (No. 21571116 and 21371110), the Youth Science Foundation of Shanxi
Province (No. 2014021006) and the Program for the Outstanding Innovative Teams of
Higher Learning Institutions of Shanxi (2013).
Appendix. Supplementary data
Other fluorescence spectroscopy (PDF) associated with this article can be found in
the online version, at doi:
References
[1] Tang CW, Vanslyke SA. Organic electroluminescent diodes. Appl Phys Lett 1987;
51: 913-5.
[2] Chen SF, Deng LL, Xie J, Peng L, Xie LH, Fan QL et al. Recent developments in
top-emitting organic light-emitting diodes. Adv Mater 2010; 22: 5227-39.
[3] Burroughes JH, Bradley DDC, Brown AR, Marks RN, Friend RH, Burn PL et al.
Light-emitting diodes based on conjugated polymers. Nature 1990; 37: 539-41.
[4] Zhu MR, Yang CL. Blue fluorescent emitters: design tactics and applications in
organic light-emitting diodes. Chem Soc Rev 2013; 42: 4963-76.
[5] Reineke S, Lindner F, Schwartz G, Seidler N, Walzer K, Sseml B, et al. White
organic light-emitting diodes with fluorescent tube efficiency. Nature 2009; 459:
234-8.
[6] Bucinskas A, Volyniuk D, Danyliv Y, Grazulevicius JV, Baryshnikov G, Minaev
B, et al. N-annelated perylenes as effective green emitters for OLEDs. RSC Adv
2015; 5: 78150-9.
12

ACCEPTED MANUSCRIPT
[7] Cho YJ, Jeon SK, Chin BD, Yu ES, Lee JY. The design of dual emitting cores for
green thermally activated delayed fluorescent material. Angew Chem Int Ed 2015;
54: 5201-4.
[8] Zhao QH, Zhang WY, Fan ZX, Li JJ, Chen XM, Luo GG, et al. Synthesis and
characterization of high triplet energy polyfluorene bearing m-tetraphenylsilane
segment as a polymer host for green phosphorescent polymer light emitting diodes.
Synth Met 2015; 204: 70-5.
[9] Jankus V, Abdullah K, Griffiths GC, Al-Attar H, Zheng YH, Bryce MR, et al. The
role of exciplex states in phosphorescent OLEDs with poly (vinylcarbazole)
(PVK) host. Org Electron 2015; 20: 97-102.
[10] Zhang S, Xue LS, Jing YM, Liu X, Lu GZ, Liang X, et al. 1-(N-
phenylamino)naphthalene oligomers as novel hole transport materials for highly
efficient green electrophosphorescence. Dyes Pigments 2015; 118: 1-8.
[11] Feng YS, Li P, Zhuang XM, Ye KQ, Peng T, Liu Y, et al. A novel bipolar
phosphorescent host for highly efficient deep-red OLEDs at a wide luminance
range of 1000-10 000 cd/m2. Chem Commun 2015; 51: 12544-47.
[12] Qin W, Lam JWY, Yang ZY, Chen SM, Liang GD, Zhao WJ, et al. Red emissive
AIE luminogens with high hole-transporting properties for efficient non-doped
OLEDs. Chem Commun 2015; 51: 7321-24.
[13] Zhou L, Li LJ, Jiang YL, Cui RZ, Li YN, Zhao XS, et al. Rare earth complex as
electron trapper and energy transfer ladder for efficient red iridium complex
based electroluminescent devices. ACS Appl Mater Interfaces 2015; 7: 16046-53.
[14] Liu J, Miao JS, Wu HB. Efficient solution-processed double-layer red OLEDs
based on a new europium complex with a carbazole group. Luminescence 2015;
30: 393-6.
13

ACCEPTED MANUSCRIPT
[15] Kim JW, Yoo S, Kang JS, Lee SE, Kim YK, Yu HH, et al. Color stable white
phosphorescent organic light emitting diodes with red emissive electron transport
layer. J Appl Phys 2015; 117: 245503.
[16] Farinola GM, Ragni R. Electroluminescent materials for white organic light
emitting diodes. Chem Soc Rev 2011; 40: 3467-82.
[17] Schwartz G, Pfeiffer M, Reineke S, Walzer K, Leo K. Harvesting triplet excitons
from fluorescent blue emitters in white organic light-emitting diodes. Adv Mater
2007; 19: 3672-6.
[18] Wu YS, Hwang SW, Chen HH, Lee MT, Shen WJ, Chen CH. Efficient white
organic light emitting devices with dual emitting layers. Thin Solid Films 2005;
488: 265-9.
[19] Kamtekar KT, Monkman AP, Bryce MR. Recent advances in white organic light-
emitting materials and devices. Adv Mater 2010; 22: 572-82.
[20] Sun Y, Forrest SR. High-efficiency white organic light emitting devices with
three separate phosphorescent emission layers. Appl Phys Lett 2007; 91: 263503.
[21] Schwartz G, Fehse K, Pfeiffer M, Walzer K, Leo K. Highly efficient white
organic light emitting diodes comprising an interlayer to separate fluorescent and
phosphorescent regions. Appl Phys Lett 2006; 89: 083509.
[22] Andrade BWD, Holmes RJ, Forrest SR. Efficient organic electrophosphorescent
white-light-emitting device with a triple doped emissive layer. Adv Mater 2004;
16: 624-8.
[23] Wei Y, Wang WJ, Huang YT, Wang BC, Chen WH, Wua SH, et al. Blue
fluorescent dihydro-indenoindene derivatives with unusual low oxidation
potentials as multifunctional OLED materials. J Mater Chem C 2014; 2: 1779-82.
14

ACCEPTED MANUSCRIPT
[24] Chercka D, Yoo SJ, Baumgarten M, Kim JJ, Mullen K. Pyrene based materials
for exceptionally deep blue OLEDs. J Mater Chem C 2014; 2: 9083-6.
[25] Sasabe H, Toyota N, Nakanishi H, Ishizaka T, Pu YJ, Kido J. 3,3′-bicarbazole-
based host materials for high-efficiency blue phosphorescent OLEDs with
extremely low driving voltage. Adv Mater 2012; 24: 3212-7.
[26] Lin SL, Chan LH, Lee RH, Yen MY, Kuo WJ, Chen CT, et al. Highly efficient
carbazole-p-dimesitylborane bipolar fluorophores for nondoped blue organic
light-emitting diodes. Adv Mater 2008; 20: 3947-52.
[27] Liang ZQ, Chu ZZ, Yang JX, Yuan CX, Tao XT, Zou DC. X-shaped tetra-
substituted pyrenes: synthesis, photophysics, and electroluminescence. Synth
Met 2011; 161: 1691-8.
[28] Huang J, Yang X, Wang JY, Zhong C, Wang L, Qin JG, et al. New
tetraphenylethene-based efficient blue luminophors:aggregation induced
emission and partially controllable emitting color. J Mater Chem 2012; 22: 2478-
84.
[29] Li ZF, Jiao B, Wu ZX, Liu P, Ma L, Lei XL, et al. Fluorinated 9,9′-
spirobifluorene derivatives as host materials for highly efficient blue organic
light-emitting devices. J Mater Chem C 2013; 1: 2183-92.
[30] Tang C, Liu F, Xia YJ, Lin J, Xie LH, Zhong GY, et al. Fluorene-substituted
pyrenes-novel pyrene derivatives as emitters in nondoped blue OLEDs. Org
Electron 2006; 7: 155-62.
[31] Loy DE, Koene BE, Tompson ME. Thermally stable hole-transporting materials
based upon a fluorine core. Adv Funct Mater 2002; 12: 245-49.
15

ACCEPTED MANUSCRIPT
[32] Chiang CL, Tseng SM, Chen CT, Hsu CP, Shu CF. Influence of molecular
dipoles on the photoluminescence and electroluminescence of dipolar
spirobifluorenes. Adv Funct Mater 2008; 18: 248-57.
[33] Tang S, Liu MR, Lu P, Xia H, Li M, Xie ZQ, et al. A molecular glass for deep-
blue organic light-emitting diodes comprising a 9,9′-spirobifluorene core and
peripheral carbazole groups. Adv Funct Mater 2007; 17: 2869-77.
[34] Chen SF, Tian Y, Peng JH, Zhang HR, Feng XJ, Zhang HX, et al. Synthesis and
characterization of arylamino end-capped silafluorenes for blue to deep-blue
organic light-emitting diodes (OLEDs). J Mater Chem C 2015; 3: 6822-30.
[35] Liu C, Gu Y, Fu Q, Sun N, Zhong C, Ma DG, et al. Nondoped deep-blue organic
light-emitting diodes with color stability and very low efficiency roll-off:
solution-processable small-molecule fluorophores by phosphine oxide linkage.
Chem Eur J 2012; 18: 13828-35.
[36] Chung YH, Sheng L, Xing X, Zheng L., Bian MY, Chen ZJ, et al. A pure blue
emitter (CIEy≈0.08) of chrysene derivative with high thermal stability for OLED.
J Mater Chem C 2015; 3: 1794-8.
[37] Wu CL, Chang CH, Chang YT, Chen CT, Chen CT, Su CJ. High efficiency non-
dopant blue organic lightemitting diodes based on anthracene-based fluorophores
with molecular design of charge transport and red-shifted emission proof. J
Mater Chem C 2014; 2: 7188-200.
[38] Wu CH, Chien CH, Hsu FM, Shih P, Shu CF. Efficient non-doped blue-light-
emitting diodes incorporating an anthracene derivative end-capped with fluorene
groups. J Mater Chem 2009; 19: 1464-70.
16

ACCEPTED MANUSCRIPT
[39] Zhu MR, Wang Q, Gu Y, Cao XS, Zhong C, Ma DG, et al. Efficient deep-blue
emitters comprised of an anthracene core and terminal bifunctional groups for
nondoped electroluminescence. J Mater Chem 2011; 21: 6409-15.
[40] Li WJ, Yao L, Liu HC, Wang ZM, Zhang ST, Xiao R, et al. Highly efficient
deep-blue OLED with an extraordinarily narrow FHWM of 35 nm and a y
coordinate <0.05 based on a fully twisting donor–acceptor molecule. J Mater
Chem C 2014; 2: 4733-6.
[41] Hu JY, Pu YJ, Nakata G, Kawata S, Sasabe H, Kido J. A single-molecule
excimer-emitting compound for highly efficient fluorescent organic light-
emitting devices. Chem Commun 2012; 48: 8434-36
[42] Oh HY, Lee CH, Lee S. Efficient blue organic light-emitting diodes using newly-
developed pyrene-based electron transport materials. Org Electron 2009; 10:
163-9.
[43] Giovanella U, Botta C, Galeotti F, Vercelli B, Battiatoc S, Pasini M.
Perfluorinated
polymer
with
unexpectedly
efficient
deep
blue
electroluminescence for full-colour OLED displays and light therapy
applications. J Mater Chem C 2013; 1: 5322-9.
[44] Gao ZQ, Li ZH, Xia PF, Wong MS, Cheah KW, Chen CH. Efficient deep-blue
organic light-emitting diodes: arylamine substituted oligofluorenes. Adv Funct
Mater 2007; 17: 3194-9.
[45] Bacher E, Bayerl M, Rudati P, Reckefuss N, Muller CD, Meerholz K, et al.
Synthesis and characterization of photo-cross-linkable hole-conducting polymers.
Macromolecules 2005; 38: 1640-7.
17

ACCEPTED MANUSCRIPT
[46] Shu CF, Dodda R, Wu FI. Highly efficient blue-light-emitting diodes from
polyfluorene containing bipolar pendant groups. Macromolecules 2003; 36:
6698-703.
[47] Kessler F, Watanabe Y, Sasabe H, Katagiri H, Nazeeruddin MK, Gratzel M, et al.
High-performance pure blue phosphorescent OLED using a novel bis-
heteroleptic iridium (III) complex with fluorinated bipyridyl ligands. J Mater
Chem C 2013; 1: 1070-5.
[48] Zhou GJ, Ho CL, Wong WY, Wang Q, Ma DG, Wang LX, et al. Manipulating
charge-transfer character with electron-withdrawing main-group moieties for the
color tuning of iridium electrophosphors. Adv Func. Mater 2008; 18: 499-511.
[49] Kawamura Y, Goushi K, Brooks J, Brown JJ, Sasabe H, Adachi C, et al. 100%
Phosphorescence quantum efficiency of Ir(III) complexes in organic
semiconductor films. Appl Phys Lett 2005; 86: 071104.
[50] Chi Y, Chou PT. Transition-metal phosphors with cyclometalating ligands:
fundamentals and applications. Chem Soc Rev 2010; 39: 638-55.
[51] Mikroyannidis JA, Fenenko L, Adachi C. Synthesis and photophysical
characteristics
of
2,7-fluorenevinylene-based
trimers
and
their
electroluminescence. J Phys Chem B 2006; 110: 20317-26.
[52] Wu KC, Ku PJ, Lin CS, Shih HT, Wu FI, Huang MJ, et al. The photophysical
properties of dipyrenylbenzenes and their application as exceedingly efficient
blue emitters for electroluminescent devices. Adv Funct Mater 2008; 18: 67-75.
[53] Mallesham G, Swetha C, Niveditha S, Mohanty MEN, Babu J, Kumar A, et al.
Phosphine oxide functionalized pyrenes as efficient blue light emitting
multifunctional materials for organic light emitting diodes. J Mater Chem C
2015; 3: 1208-24.
18

ACCEPTED MANUSCRIPT
[54] Liang ZQ, Chu ZZ, Zou DC, Wang XM, Tao XT. Novel 4-(2, 2-diphenyl-vinyl)-
phenyl substituted pyrene derivatives as efficient emitters for organic light-
emitting diodes. Organic Electronics 2012; 13: 2898-904.
[55] Chan KL, Lim JPF, Yang XH, Dodabalapur A, Jabbour GE, Sellinger A. High-
efficiency pyrene-based blue light emitting diodes: aggregation suppression
using a calixarene 3D-scaffold. Chem Commun 2012; 4: 5106-08.
[56] Wang ZQ, Liu CL, Zheng CJ, Wang WZ, Xu C, Zhu M, et al. Efficient violet
non-doped organic light-emitting device based on a pyrene derivative with novel
molecular structure. Organic Electronics 2015; 23: 179-185.
[57] Zhao ZJ, Chen SM, Lam JWY, Lu P, Zhong YC, Wong KS, et al. Creation of
highly efficient solid emitter by decorating pyrene core with AIE-active
tetraphenylethene peripheries. Chem Commun 2010: 46: 2221-3.
[58] Jeltsch KF, Lupa G, Weitz RT. Materials depth distribution and degradation of a
fIrpic based solution-processed blue OLED. Org Electron 2015; 26: 365-70.
[59] Chen W, Wunderlich B. Nanophase separation of small and large molecules.
Macromol Chem Phys 1999; 200: 283-311.
[60] Ponce MB, Cabrerizo FM, Bonesi SM, Balsells RE. Synthesis and electronic
spectroscopy of bromocarbazoles direct bromination of N- and C-substituted
carbazoles by N-bromosuccinimide or a N-bromosuccinimide/silica gel system.
Helv Chim Acta 2006; 89: 1123-39.
[61] Peng ZH, Bao ZN, Galvin ME. Polymers with bipolar carrier transport abilities
for light emitting diodes. Adv Mater 1998; 10: 680-4.
[62] Belletete M, Morin JF, Leclerc M, Durocher GA. A theoretical, spectroscopic,
and photophysical study of 2,7-carbazolenevinylene. J Phys Chem A 2005; 109:
6953-9.
19

ACCEPTED MANUSCRIPT
[63] Becke AD. Density-functional thermochemistry. III. the role of exact exchange. J
Chem Phys 1993; 98: 5648-52.
[64] Ge Z, Hayakawa T, Ando S, Ueda M, Akiike T, Miyamoto H, et al. Spin-coated
highly efficient phosphorescent organic light-emitting diodes based on bipolar
triphenylamine-benzimidazole derivatives. Adv Funct Mater 2008; 18: 584-90.
The figures and scheme captions
Scheme 1. The synthesis routes of BCP and BOP.
Fig. 1 The UV-vis absorption and fluorescence emission spectra of BCP and BOP in
CHCl3.
Fig. 2 TGA thermogram of BCP and BOP with a heating rate of 5 oC/min under
nitrogen atmosphere, respectively.
Fig. 3 Molecular orbital surfaces of the HOMO and LUMO for BCP and BOP.
Fig. 4 The electroluminescence spectra of BCP and BOP in device A,
(ITO/PEDOT:PSS/BCP/CBP/TPB/LiF/Al).
Fig. 5 The electroluminescence (CIE) chromaticity coordinates of BCP and BOP.
Fig. 6 (a) Plots of voltage versus luminance for blue-light emitting devices A and B,
(b) Plots of voltage versus current density for blue-light emitting devices A and B,
(ITO/PEDOT:PSS/BCP/CBP/TPB/LiF/Al; ITO/PEDOT:PSS/BCP/CBP/TPB/LiF/Al).
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Scheme 1
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Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
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Fig. 5
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Fig. 6
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Two Non-doped Blue Emitters for Electroluminescent Devices:
Preparation, Photophysics and Electroluminescence
Jiarong Zhu, Ninghua Yin, Liheng Feng*
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan, 030006, P.R. China.
E-mail address: lhfeng@sxu.edu.cn (L. Feng); Tel.:+86 351 7010904; Fax: +86 351 7011688.
Highlights
Two novel blue emitting OLED materials were designed and synthesized.
These emitters exhibit good thermal stability and electron transfer properties.
The device with BCP emitter has good optical and electrical characteristics.