Highly thermally-stable 4,4′-bis(4″-triphenylsilylphenyl)-1,1′- binaphthalene as the ultraviolet amplified spontaneous emitter, efficient host and deep-blue emitting material

Article abstract of DOI:10.1016/j.dyepig.2016.03.034

We report herein the synthesis and characterization of an efficient versatile binaphthyl derivative, 4,4′-bis(4″-triphenylsilylphenyl)-1,1′-binaphthalene (SiBN) with a high glass transition temperature of 159.3 °C. Its role as a lasing dye was demonstrated by the amplified spontaneous emission, which exhibited an ultraviolet peak of 397 nm with a low threshold of 20 μJ/pulse. Meanwhile, the lasing film and blue electroluminescent device employing this novel binaphthyl derivative as the host showed superior performances to the reference based on the conventional host 4,4′-bis(carbazol-9-yl)biphenyl. Finally, extremely stable colour-tunable deep-blue (436 nm/472 nm) organic electroluminescent devices based on SiBN were demonstrated with very high brightness (>7521.2 cd/m²) and high external quantum efficiencies (1.90% for 436 nm and 4.66% for 472 nm emission). The development of such functional versatility materials will be an effective method for reducing the cost of organic photoelectric devices.

Full text of DOI:10.1016/j.dyepig.2016.03.034

Dyes and Pigments 130 (2016) 266e272
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Highly thermally-stable 4,40-bis(400-triphenylsilylphenyl)-1,10-
binaphthalene as the ultraviolet amplified spontaneous emitter,
efficient host and deep-blue emitting material
, c,
Weiling Li a, Tao Xu a, Guo Chen a, Hao Zhang a, Xicun Gao b **, Xuehua Zhou c,
Haifang Huang b, Heliang Fan b, Miao Cai d, Xiaowen Zhang d, Lianqiao Yang a,
,
*
Wenqing Zhu a, Bin Wei a
a Key Laboratory of Advanced Display and System Applications, Ministry of Education, Shanghai University, 149 Yanchang Road, Shanghai 200072, PR China
b School of Petroleum and Chemical Engineering, Qinzhou University, 12 Coastal Avenue, Qinzhou 535000, PR China
c Department of Chemistry, School of Science, Nanchang University, 999 Xue-Fu Road, Hong-Gu-Tan New District, Nanchang 330031, PR China
d School of Mechanical & Electrical Engineering, Guilin University of Electronic Technology, 1 Jinji Road, Guilin 541004, PR China
a r t i c l e i n f o
a b s t r a c t
We report herein the synthesis and characterization of an efficient versatile binaphthyl derivative, 4,40-
Article history:
bis(400-triphenylsilylphenyl)-1,10-binaphthalene (SiBN) with
a
high glass transition temperature of
159.3 ꢀC. Its role as a lasing dye was demonstrated by the amplified spontaneous emission, which
exhibited an ultraviolet peak of 397 nm with a low threshold of 20 J/pulse. Meanwhile, the lasing film
Received 11 December 2015
Received in revised form
9 March 2016
Accepted 18 March 2016
Available online 21 March 2016
m
and blue electroluminescent device employing this novel binaphthyl derivative as the host showed
superior performances to the reference based on the conventional host 4,40-bis(carbazol-9-yl)biphenyl.
Finally, extremely stable colour-tunable deep-blue (436 nm/472 nm) organic electroluminescent devices
based on SiBN were demonstrated with very high brightness (>7521.2 cd/m2) and high external quan-
tum efficiencies (1.90% for 436 nm and 4.66% for 472 nm emission). The development of such functional
versatility materials will be an effective method for reducing the cost of organic photoelectric devices.
© 2016 Elsevier Ltd. All rights reserved.
Keywords:
Highly thermal stability
Versatile material
Ultraviolet lasing dye
Hosting material
Colour-tunable OLED
1. Introduction
bis(p-N,N-diphenyl-aminosty-ryl)-benzene (DSA-ph) and 4,40-
bis(2,2-diphenylvinyl)-1,19-biphenyl (DPVBi) are two well-known
Recently, much progress on the developments of materials and
advanced device structures in organic light-emitting diodes
(OLEDs) [1e4] and white OLEDs (WOLEDs) [5,6] has been achieved.
OLEDs are potential candidates for display and lighting market
because of their various advantages such as excellent image quality,
light weight, easy manufacturability, low cost, large-area, and
flexibility. In order to fabricate full-colour OLED displays, three
basic colours, red, green and blue are needed. However, the blue
emission is more difficult to produce due to its intrinsic charac-
teristic of a wider gap, impeding faster development of the OLED
technology. Considerable efforts in terms of efficiency and colour
purity are being made to resolve this problem in blue emission. P-
commercialized blue emitting compounds. However, they have
low glass transition temperatures (Tg) of 89 ꢀC and 64 ꢀC, which
could lead to recrystallization or film roughing after long operation
or storage. Such recrystallization results in a much shorter device
operational lifetime in contrast to the longer lifetime based on
green and red materials. In addition, DSA-ph can only play one role
of a emitter, while some multi-functional materials such as tris(8-
hydroxyquinoline)aluminum (Alq3), is bi-functional by combining
the role of both an emitter and an electron transporter [7e9]. Some
recent results have confirmed that the instability of the cationic
Alq3 species was one of the major device-degradation factors for
small-molecule Alq3-based OLEDs [10e12]. It is thus necessary to
develop a multi-functional and stable blue emitting material to
meet the demands of full-colour displays.
Our group has reported three kinds of molecular materials with
* Corresponding author.
a
binaphthyl backbone (BN1: 400,4000-N,N-diphenylamine-4,40-
** Corresponding author. School of Petroleum and Chemical Engineering, Qinzhou
University, 12 Coastal Avenue, Qinzhou 535000, PR China.
E-mail addresses: gaoxicun1@hotmail.com (X. Gao), bwei@shu.edu.cn (B. Wei).
diphenyl-1,10-binaphthyl;
BN2:
400,4000-(9H-9-carbazole)-4,40-
http://dx.doi.org/10.1016/j.dyepig.2016.03.034
0143-7208/© 2016 Elsevier Ltd. All rights reserved.

W. Li et al. / Dyes and Pigments 130 (2016) 266e272
267
diphenyl-1,10-binaphthyl; and BN3: 4,40-bis(9-(p-fluorophenyl)-
9H-3-carbazolyl))-1,10- binaphthyl) in 2010 [13]. They function as
highly efficient hole-transport, host and deep-blue-emitting ma-
terials. Recent reports revealed that some of them were also good
lasing dyes [14,15]. Be enlightened by the significant enhancement
of 3,5-di(N-carbazolyl) tetraphenyl-silane (SimCP) in thermal sta-
bility compared with N,Nʼ-dicarbazolyl-3,5-benzene (mCP) [16], we
designed and synthesized a molecule with a binaphthyl backbone
modified by triphenylsilylphenyl. In 2011 and 2014, Pavel et al. and
Yanʼs group reported two kinds of triphenylsilyl-contained hosting
materials for blue electrophosphorescence respectively, indicating
that materials with the functional group of triphenylsilylphenyl can
be good blue hosting materials [17,18]. In addition, although similar
functional materials as (1-methyl-1,2,3,4,5-pentaphenylsilole and
into a 500 mL three-necked round-bottom flask. n-butyllithium
(0.052 mol, 32.4 mL) was added dropwise. The solution had been
stirred 1 h. Trimethyl borate (0.12 mol, 13.36 mL) was added
quickly. The reaction was continued at ꢁ78 ꢀC for 3e4 h, and it was
warmed to room temperature overnight. The reaction mixture was
poured into an ice-water beaker, and 100 mL 2 N hydrochloric acid
was slowly added. The reaction continued for 4 h. The organic
phase was separated, and the aqueous phase (80 mL ꢂ 3) was
extracted with petroleum ether, then the combined organic phases
were distilled in the rotary distiller. The residue was purified by
column chromatography [Silica gel (200e400 mesh), eluent: V
(petroleum ether): V (ethyl acetate) ¼ 5: 1], a white solid was ob-
tained (14.0 g, yield: 92%, Mp: 213e216 ꢀC.)
poly(dimethylsilylene-p-
phenylene-vinylene-(2,5-dibutoxy-p-
2.1.3. Synthesis of SiBN
phenylene)) have been reported by Tang et al. [19] and Had-
ziioannou's [20] group, the efficiencies reported were still low with
EQE no more than 0.65%. Furthermore, Si-containing blue organic
emitting material was rarely reported. Silicon is one of the most
abundant elements in the earth; compared with the compounds
containing rare earth metals, making Si compounds more available.
This versatile material consisting of easy Si-containing elements
brings convenience to the design of device architecture and is more
cost-efficient, which can further pave the way to the booming of
organic photoelectric devices.
In this paper, a novel and versatile silicon-containing binaphthyl
derivative, 4,40-bis(400- triphenylsilylphenyl)-1,10-binaphthalene
(SiBN) was synthesized. The excellent thermal stability of SiBN was
demonstrated by the high Tg of 159.3 ꢀC; the low amplified stim-
ulated emission (ASE) of SiBN which was peaking at ultraviolet
Under
nitrogen,
4-(triphenylsilyl)phenylboronic
acid
(0.024 mol, 9.13 g), 4,40- diiodo-1,10-binaphthalene (0.01 mol,
5.06 g), tetrakis (triphenyl phosphine) palladium (0) (6 mmol,
0.69 g), toluene (100 mL), ethanol (10 mL) and potassium carbonate
solution (2 mol/L, 20 mL) were added to a 250 mL three necked
round-bottom flask. The reaction was slowly heated to reflux for
14 h, and then cooled to room temperature. The organic phase was
separated with the aqueous layer by toluene (80 mL ꢂ 3) and the
organic phase was evaporated to dryness. The residual was purified
by column chromatography [silica gel (200e400 mesh), eluent: V
(petroleum ether): V (ethyl acetate) ¼ 30: 1]. The resulting white
solid was further purified by train sublimation, 7.40 g, yield: 80.1%,
M.p: 174e175 ꢀC. 1HNMR (400 MHz,CDCl3, TMS):
d
¼ 8.09e8.07 (d,
J ¼ 8.4 Hz, 2 H),7.76e7.74 (d, J ¼ 8.00 Hz, 4 H),7.68e7.67 (d,
J ¼ 6.00 Hz, 12 H), 7.64e7.62 (d,J ¼ 7.6 Hz, 4 H);7.60e7.58
(t,J ¼ 3.2 Hz, 6 H); 7.52e7.50 (m, 20 H). 7.35e7.33 (t, J ¼ 3.8 Hz, 2 H).
Anal. Calcd for C68H50Si2 (%): C, 88.27; H, 5.33; Found: C, 88.46; H,
5.46. The molecule structure is represented in Fig. 1a.
region had a threshold of 20 mJ/pulse. It was shown that SiBN was
very suitable as a host by comparing with a commonly used host,
4,40-bis(carbazol-9-yl)biphenyl (CBP). Finally, we obtained two
colour-tunable blue OLEDs based on SiBN, peaking at 436 nm and
472 nm with the maximum efficiencies of 2.63 cd/A (1.90%) and
9.38 cd/A (4.66%), respectively. To our best knowledge, we got one
of the highest reported efficiencies of OLED based on Si-containing
blue material.
2.2. The fabrication of thin films and devices
A variety of characterizations were performed on SiBN neat thin
films, including the absorption, photoluminescence (PL) spectra
and the ASE. Moreover, CBP:3 wt% BUBD-1 and SiBN:3 wt% BUBD-1
thin films were optically pumped to investigate the hosting char-
acteristics of SiBN, while BUBD-1 (N,Nʼ-(4,4ʼ-(1E, 1ʼE)-2,2’-(1,4-
phenylene) bis(ethene-2,1-diyl)bis(4,1-phenyl-ene))-bis(2-ethyl-
6-methyl-N-phenylaniline)) was a bluish-green lasing dye [21].
Two sets of OLEDs were fabricated to study the hosting ability of
SiBN (referred to Devices A and B) and discuss the EL characteristics
of SiBN (defined as Devices C and D). The architectures of these
devices were as follows:
Device A: ITO/2T-NATA (25 nm)/NPB (5 nm)/TCTA (10 nm)/CBP:
5 wt%DSA-ph (20 nm)/TPBi (30 nm)/Liq (1 nm)/Al; Device B: ITO/
2T-NATA (25 nm)/NPB (5 nm)/TCTA (10 nm)/SiBN: 5 wt%DSA-ph
(20 nm)/TPBi (30 nm)/Liq (1 nm)/Al; Device C: ITO/HAT-CN
(30 nm)/NPB (10 nm)/AND: 1 wt%SiBN (20 nm)/Bphen (30 nm)/
Liq (1 nm)/Al; Device D: ITO/HAT-CN (30 nm)/NPB (10 nm)/AND: 5
wt%SiBN (20 nm)/TPBi (30 nm)/Liq (1 nm)/Al; Where ITO is indium
tin oxide; 4,40,400-tris(N-(naphthalene-2-yl)-N-phenyl-amino) tri-
phenylamine (2T-NATA) and 1,4,5,8,9,11-hexaazatriphenylene-
hexacarbonitrile (HAT-CN) were used as hole injection layers. N,N0-
di(naphthalen-1-yl)-N,N0- diphenyl-benzidine (NPB) and 4,40,400-
tris-(N-carbazolyl)-triphenlyamine (TCTA) acted as hole trans-
portation layers, while 1,3,5-tris(N-phenylbenzimiazole-2-yl)ben-
zene (TPBi) and 4,7-diphenyl-1,10-phenanthroline (Bphen)
performed as the electron transportation layers and the hole
blocking layers to confine the carriers within the emitting region
due to their excellent hole-blocking and high electron transport
ability. Finally, Liq (8-hydroxyquinolato-lithium) was used to
2. Experimental
2.1. Synthetic procedures
2.1.1. Synthesis of 4-bromophenyl-triphenylsilane
1,4-dibromobenzene (0.015 mol, 3.54 g) and 60 mL anhydrous
tetrahydrofuran were added into a 150 ml three-neck flask, under
nitrogen. At ꢁ78 ꢀC, n-butyl lithium was added dropwise into the
flask. The solution had been stirred 1 h, then, triphenyl chlorosilane
was added quickly (0.017 mol, 4.87 g). The reaction was kept under
the same temperature for 4 h, and the solution was warmed to
room temperature overnight. The reaction liquid was extracted
with anhydrous diethyl ether, the combined organic phase was
rotary evaporated and the residue was purified by column chro-
matography [silica gel (200e400 mesh)] with pure petroleum ether
as eluent. White solid was obtained (5.29 g), yeild: 85.1%, Mp:
160e161 ꢀC.
1HNMR(400 MHz,CDCl3):
d
7.56 ~ 7.53 (t, J ¼ 5.60 Hz, 6 H),
7.53e7.51 (d, J ¼ 8.00 Hz, 2 H), 7.49e7.46 (t, J ¼ 5.40 Hz, 2 H),
7.45e7.37 (m, 9 H).
Anal. Calcd for C24H19Br (%): C, 69.39; H, 4.61; Found: C, 69.73;
H, 3.57.
2.1.2. Synthesis of 4-(triphenylsilyl)phenylboronic acid
4-bromophenyl-triphenylsilane (0.04 mol, 16.60 g) and 200 mL
anhydrous tetrahydrofuran were added under nitrogen, at ꢁ78 ꢀC,

268
W. Li et al. / Dyes and Pigments 130 (2016) 266e272
Fig. 1. (a) The molecular structure of SiBN. The architectures of (b) Device A, Device B, (c) Device C and (d) Device D.
modify the cathode.
All devices were fabricated in conventional vacuum chamber by
thermal evaporation of organic layers onto a clean glass substrate
stability of the samples under a nitrogen atmosphere was deter-
mined by measuring their weight loss during heating at a rate of
10 ꢀC minꢁ1 from 100 ꢀC to 900 ꢀC. The lifetime measurements
were carried out under a nitrogen atmosphere at room temperature
without device encapsulation. The water and oxygen levels of the
glove box were 0.3 ppm and 5.8 ppm in the testing process.
coated with an ITO (150 nm thick, 15
U per sheet) layer. Prior to use,
the substrates were degreased in an ultrasonic bath by the
following sequence: in detergent, de-ionized water, acetone, iso-
propanol, and then cleaned in a UV-ozone chamber for 15 min. The
typical deposition rates, monitored by oscillating quartz, were
0.6 Å/s and 5.0 Å/s for organic materials and Al, respectively. The
device active area which was defined by the overlap between the
electrodes was 4 mm2 in all cases.
3. Results and discussion
3.1. Thermal stability
The thermal properties of SiBN were measured by DSC and TGA
under nitrogen atmosphere, as it is shown in Fig. 2. Tg of SiBN was
2.3. Measurement
The PL spectra were measured by using a FLSP 920 spectrometer
series. The electroluminescence (EL) spectra and Commission
Internationale de L'Eclairage (CIE) coordinates of the devices were
measured by a Photo Research PR-650 spectra scan spectropho-
tometer while the currentevoltage characteristics were measured
by a Keithley 2400 source-meter. The measurements were carried
out in the dark at room temperature without device encapsulation.
When we studied the ASE characteristics of SiBN, the thin film was
optically pumped with a Nd:YAG laser (FTSS 355-50,CryLaS) at an
excitation wavelength of
l
¼ 355 nm with a pulse width of about
1 ns and at a repetition rate of 100 Hz by focusing the excitation
light with an irradiation area of 2.5 mm ꢂ 9 mm. A cylindrical lens
and neutral density filters were used to adjust the excitation in-
tensities. The emission radiation was collected from the edge of the
film into an optical fiber connected to a spectrometer. Differential
scanning calorimetry (DSC) was performed on a TA Q2000 Differ-
ential Scanning Calorimeter at a heating rate of 10 ꢀC minꢁ1 from
40 ꢀC to 250 ꢀC under nitrogen atmosphere. The Tg was determined
from the second heating scan. The mogravimetric analysis (TGA)
was performed with a NETZSCH 209F3 instrument. The thermal
Fig. 2. DSC and TGA measurements of SiBN.

W. Li et al. / Dyes and Pigments 130 (2016) 266e272
269
measured to be 159.3 ꢀC, which was higher than those of the
commonly used organic materials, such as TCTA (151 ꢀC) [22,23],
CBP (62 ꢀC) [24] and TPBi (124 ꢀC) [25]. The decomposition tem-
perature (Td) of such material reached 480.7 ꢀC. These high thermal
stabilities derived from the molecular structure of the bulky
binaphthyl backbone that impeded the stretching and rotating of
the molecules and absorbed the thermal energy.
were investigated by developing thin films with different mixing
concentration of AND and SiBN. As it is shown in Figure S1, the
emission at 468 nm which was considered as an excimer emission
reduced when the doping concentration was decreased. In addi-
tion, the PL quantum yield of the SiBN neat film reached 69.05%.
These photophysical characteristics were important because they
were the cornerstone of SiBN-based OLEDs [27].
The morphologies of 50 nm neat thin films with annealing at
room temperature, 200 ꢀC and 300 ꢀC were analyzed by mean of
Atomic Force Microscope. As a result, the roughness of SiBN thin
films annealing at different temperatures were 1.441 nm, 0.9066
and 0.9697 nm, respectively. Such small morphological changes
demonstrate the high thermal stability of SiBN thin film. Absorp-
tion spectra of these films were measured, as shown in Fig. 3, while
no change was observed after the subsequent annealing, indicating
that SiBN molecules remained stable in high-temperature
environments.
It is known that 2-phenyl-5-biphenyl-1,3,4-oxadiazole (PBD) is
not only a transporting material but also a ultraviolet lasing dye.
However, the threshold of PBD is as high as several mJ/pulse when
the PBD-doped silica sample peaks at 365 nm [28], and PBD can be
easily crystallized because its Tg was only 60 ꢀC [29]. Herein, an ASE
threshold of 20 mJ/pulse of SiBN was demonstrated with peak at
397 nm, indicating an ultraviolet lasing. In Fig. 4a, when a 60 nm
SiBN thin film was pumped under low optical power excitation,
very broad ASE spectra could be observed at the spectral centres of
around 430 nm; when the excitation power exceeded 20 mJ/pulse,
the emission intensity increased dramatically, while the full width
at half maximum (FWHM) decreased sharply as shown in Fig. 4b.
The peak of ASE spectra around 397 nm deviated from the PL
shoulder of 415 nm, this could be explained by the mode selection
of slab waveguide. Moreover, the FWHM decreased to 6.6 nm when
3.2. PL properties and as a lasing dye
In Fig. 3, SiBN showed a strong emission in the deep blue region
which peaked at 468 nm with a strong shoulder of 415 nm, while
the absorption peaked at 323 nm. The PL spectrum of SiBN with a
peak at 468 nm was different from those of the common organic
materials (such as DSA-ph) with the most intense 0e0 vibronic
band at highest-energy side, followed by next intense 0e1 vibronic
band, and continued to the third intense 0e2 vibronic band with
decreasing photon energy. The PL spectra were changing regularly
as the annealing temperature increasing: as the temperature
increasing, the emission at 468 nm decreased and the emission at
415 nm enhanced correspondingly as the result demonstrated in
Fig. 3.
The emission at 468 nm originated from excimer formation in
SiBN neat thin film. This phenomenon would be contributed to the
large configuration space of SiBN molecules in its original state. The
planarized degree of these molecules were inclined to decrease
when the temperature increased, making them less likely to form
excimer at the wavelength of 468 nm. This is the reason for the
decrease in emission at 468 nm with the increase in annealing
temperatures in Fig. 3. It is known that the excimer emission is
related to the concentration to a large extent, and it is easier to
forming excimer in the thin films with a higher doping concen-
tration [26]. In order to confirm such assumption, the PL spectra
a pump intensity of 40
mJ/pulse was employed.
3.3. As a hosting material
It is reported that materials with Si-containing groups and novel
molecular structures are not only efficient blue-emitting materials
due to their high luminescence efficiency, easy isolation and puri-
fication and high quality of colour of the emitted light but also have
unique electronic properties [19]. SiBN could be applied as a host
material for one lasing dye. In this work, the ASE properties of CBP
and SiBN thin films doped with 3wt%BUBD-1 were investigated to
study the hosting ability of SiBN for a lasing dye. In general, the
overall principle of this study was cascaded energy transfer: the
hosting material absorbed the pump energy and transferred to the
guest, while the guest produced ASE. The dependences of the
output intensity of the emission spectra on the pump intensity for
the corresponding thin films were shown in Fig. 5b. We observed
the spectra narrowing in both cases, as shown in Fig. 5a, but SiBN
doped with 3wt%BUBD-1 showed a lower threshold which was
commonly regarded as a crucial parameter in ASE. The thresholds
are 1.7 and 1.5
mJ/pulse for CBP: 3wt%BUBD-1 and SiBN: 3wt%
BUBD-1 thin films, respectively. Furthermore, in Fig. 5b the ASE
intensity of SiBN: 3wt%BUBD-1 thin film was higher than that of
Fig. 3. The absorption and PL spectra of SiBN thin films annealing at room temperature
(black), 200 ꢀC (orange) and 300 ꢀC (blue) for 30 min. (For interpretation of the ref-
erences to colour in this figure legend, the reader is referred to the web version of this
article.)
Fig. 4. (a) The ASE spectra of the SiBN neat thin film pumped with increasing exci-
tation energy. (b) The measurement of FWHM and peak intensity versus the increasing
pump intensities, and the dash or dot lines correspond to the operation below and
above ASE threshold and were guides for the eye.

270
W. Li et al. / Dyes and Pigments 130 (2016) 266e272
Fig. 5. (a) The PL spectrum of BUBD-1 and the ASE spectra of CBP: 3wt%BUBD-1 and SiBN: 3wt%BUBD-1 under different pump intensity. (b) The measurements of the output
intensity of the emission spectra on the pump intensity for CBP: 3wt%BUBD-1 and SiBN: 3wt% BUBD-1 thin films, and the lines correspond to the operation below and above ASE
threshold are guides for the eye.
CBP: 3wt%BUBD-1 thin film at the same pump intensity. Therefore,
the SiBN served as a good bridge between the primary pump light
and the final guest.
current density-voltage-luminance curves of the two devices, and
the curves of current efficiency and power efficiency versus lumi-
nance were plotted in Fig. 6b.
The hosting ability of this novel stable material in EL were
proposed by fabricating an OLED doping with 5 wt% DSA-ph (De-
vice B), and a device applying CBP as the hosting material with the
same structure was developed severing as reference (Device A).
3.4. As an emitting material
Here, the role of light-emitting of SiBN was investigated, and
two colour-tunable OLEDs employing SiBN as fluorescent emitters,
as shown in Fig. 1c and d, were fabricated. SiBN exhibited special
emission of excimer in PL, and we also obtained interesting phe-
nomena in EL as follow. As shown in Fig. 7c, the emission spectrum
of Device C peaked at 436 nm, corresponding to a deep blue light,
with a CIE of (0.171, 0.149), while the spectrum of Device D peaked
at 472 nm with a CIE of (0.176, 0.286). It was uncommon that there
were two kinds of colours in the OLEDs using the same emissive
material. We found that the two peaks of EL emission of two de-
vices were quite agreeable to the peaks of PL, as shown in Fig. 7c.
These made easily considered that the EL peak of 472 nm in Device
D might origin from the excimer emission as mentioned in PL: the
EL peak of 436 nm in Device C fitted the peak of 415 nm in PL. Sort
of colour shifts of SiBN might result from the interaction between
SiBN and the hosting material. Thereby, we could get colour-
tuneable blue OLEDs by adjusting the structures. The peak effi-
ciencies of Devices C and D were 1.90% for 436 nm and 4.66% for
472 nm emission. To our best knowledge, we got one of the highest
reported efficiencies of OLED based on Si-containing blue material.
Detailed performance of Devices C and D were summarized in
Table 2.
High brightness in blue OLEDs can hardly be achieved due to the
efficiency roll-off phenomenon. Remarkably, Devices C and D ach-
ieved very high brightness of 7521.2 cd/m2 and 17236.8 cd/m2
which were quite considerable compared with the brightness of
deep blue phosphorescent OLEDs with very high brightness pub-
lished recently [30]. It has been demonstrated that Devices C and D
were highly stable, especially Device C. Since the current efficiency
was 2.40 cd/A at the luminance of 100 cd/m2, while they were
2.35 cd/A at 1000 cd/m2 and 2.30 cd/A at 5000 cd/m2. When the
luminance was 5000 cd/m2, the current efficiency only decreased
by 12.5% compared with the maximum value. Also, the EQE versus
luminance performance curve was smooth as the results
€
Rather large Forster transfer radii of ~2.98 and ~3.17 nm were
estimated for CBP:DSA-ph and SiBN:DSA-ph emissive layer
matrices based on the large spectral overlap between the absorp-
tion spectrum of the guest and the PL spectra of the hosts, sug-
gesting that efficient FRETs were possible. The detailed results are
summarized in Table 1.
It was demonstrated that Device B showed superior perfor-
mance than Device A. Device B showed maximum efficiencies of
6.53% and 15.63 cd/A while they were 2.51% and 6.61 cd/A for
Device A. Besides, as shown in Fig. 6a, Device B obtained much
higher maximum luminance (11043.6 cd/m2) than Device A
(7238.0 cd/m2), which could be attributed to the high thermal
stability of SiBN. Higher current density outputted higher lumi-
nance, but correspondingly, higher Joule heat as well; so materials
that higher stable could stand higher Joule heat, and thus exhibiting
higher luminance which was a crucial issue for OLED. In addition,
we have performed experiments to study the lifetime of these
devices. The lifetime was found to be significantly improved by
using SiBN as the host compared to that one using CBP, as it is
shown in Fig. 6c. The initial brightness of both devices was 3000 cd/
m2, while they lasted 45 min and 1350 min for Devices A and B,
respectively, until the brightness decreased to 1500 cd/m2. As a
result, SiBN was well qualified for the role of the hosting compared
with the most commonly hosting material (CBP). Fig. 6a gave the
Table 1
The summary of the performances of devices using SiBN as hosting materials. In the
table, CE, PE, EQE and L are the abbreviations for current efficiency, power efficiency,
external quantum efficiency and luminance, respectively.
CEmax(cd/A)
PEmax(lm/W)
EQEmax(%)
Lmax(cd/m2)
Device A
Device B
6.61
15.63
2.66
10.91
2.51
6.53
7238.0
11043.6

W. Li et al. / Dyes and Pigments 130 (2016) 266e272
271
Fig. 6. (a) The current density-voltage-luminance characteristics of the Devices A and
B. (b) The curves of current efficiency and power efficiency versus different luminance.
(c) The device lifetimes of Devices A and B.
Fig. 7. (a) The characteristics of luminance evoltageecurrent density. (b) The current
efficiency and the EQE are plotted against luminance. (c) The spectra of Devices C and
D, and the inset is the CIE coordinates of the spectra.
with a high Tg of 159.3 ꢀC and a high Td of 480.7 ꢀC. The ASE of SiBN
thin film peaking at 397 nm was obtained with a threshold of 20 mJ/
demonstrated in Fig. 7b. We considered that such performance was
ascribed to the high Tg of SiBN, which helped to stay good thin-film
morphology even at high current density and thus promising the
stability of the device we fabricated.
pulse. It was shown that SiBN was adequate to the role of hosting
material, since it exhibited superior performance in OLED and ASE
compared to the commonly used hosting material (CBP). In addi-
tion, extremely stable colour-tunable blue OLEDs with very high
brightness (>7521.2 cd/m2) peaking at 436 nm and 472 nm were
developed, exhibiting maximum current efficiencies of 2.63 cd/A
and 9.38 cd/A, respectively.
4. Conclusions
In summary, we have synthesized a highly stable and versatile
material of binaphthyl derivative, namely SiBN. The thermal and
photophysical characteristics of SiBN, including Tg, Td, absorption,
PL and quantum yield and lasing properties, were investigated. It
was demonstrated that SiBN exhibited significant thermal stability,

272
W. Li et al. / Dyes and Pigments 130 (2016) 266e272
Table 2
The summary of the performances of devices using SiBN as emissive materials. In the table, V, CE, PE and L are the abbreviations for voltage, current efficiency, power efficiency
and luminance, respectively.
Units
Vturn-on
V
CEmax
(cd/A)
aCE
bCE
cCE
dCE
PEmax (lm/W)
EQEmax (%)
Lmax (cd/m2)
Device C
Device D
3.5
3.5
2.63
9.38
2.40
8.30
2.35
7.49
2.30
6.87
/
2.36
7.19
1.90
4.66
7521.2
17236.8
6.65
a
Measured at the luminance of 100 cd/m2.
Measured at the luminance 1000 cd/m2.
Measured at the luminance 5000 cd/m2.
Measured at the luminance 10,000 cd/m2.
b
c
d
TED.2009.2034505.
Acknowledgments
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Electron 2009;10:1417e23. http://dx.doi.org/10.1016/j.orgel.2009.08.026.
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This work was financially supported by the “973” program
(2015CB655005), the National Natural Scientific Foundation of
China (61136003, 51505270, 61565003), the Science and Technol-
ogy Committee of Shanghai (15590500500), and the Guangxi Key
Laboratory of Manufacturing System and Advanced Manufacturing
Technology (No. 14045-15-014K).
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Appendix A. Supplementary data
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