SimCP3-An advanced homologue of SimCP2 as a Solution-Processed small molecular host material for blue phosphorescence organic Light-Emitting diodes

Article abstract of DOI:10.3390/molecules21101315

We have overcome the synthetic difficulty of 9,90,90 0,90 0 0,90 0 0 0,90 0 0 0 0-((phenylsilanetriyl) tris(benzene-5,3,1-Triyl))hexakis(9H-carbazole) (SimCP3) an advanced homologue of previously known SimCP2 as a solution-processed, high triplet gap ener

Full text of DOI:10.3390/molecules21101315

molecules
Article
SimCP3—An Advanced Homologue of SimCP2
as a Solution-Processed Small Molecular Host
Material for Blue Phosphorescence Organic
Light-Emitting Diodes
Yi-Ting Lee 1, Yung-Ting Chang 2, Cheng-Lung Wu 2, Jan Golder 3, Chin-Ti Chen 2,3,
*
and Chao-Tsen Chen 1,
*
1
Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan; likewithyou@gmail.com
Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan; eveningtin@gmail.com (Y.-T.C.);
cdstant@yahoo.com.tw (C.-L.W.)
Department of Applied Chemistry, National Chiao Tung University, Hsinchu 30050, Taiwan;
jangolder@gmx.net
2
3
*
Correspondences: chintchen@gate.sinica.edu.tw (C.-Ti Chen); chenct@ntu.edu.tw (C.-Tsen Chen);
Tel.: +886-2-2789-8542 (C.-Ti Chen); +886-2-3366-4200 (C.-Tsen Chen)
Academic Editor: Jwo-Huei Jou
Received: 5 September 2016; Accepted: 27 September 2016; Published: 30 September 2016
Abstract: We have overcome the synthetic difficulty of 9,90,900,9000,90000,900000-((phenylsilanetriyl)
tris(benzene-5,3,1-triyl))hexakis(9H-carbazole) (SimCP3) an advanced homologue of previously
known SimCP2 as a solution-processed, high triplet gap energy host material for a blue
phosphorescence dopant. A series of organic light-emitting diodes based on blue phosphorescence
dopant iridium (III) bis(4,6-difluorophenylpyridinato)picolate, FIrpic, were fabricated and tested to
demonstrate the validity of solution-processed SimCP3 in the device fabrication.
Keywords: solution process; molecular host material; high triplet gap energy; SimCP2; blue
phosphorescence OLED
1. Introduction
An increasing number of high-performance blue phosphorescence organic light-emitting
diodes (OLEDs) can be found in literature reports. Although remarkable electroluminescence
(EL) efficiency as high as ~27%, ~51 lm/W, or ~54 cd/A based on sky-blue phosphorescence
dopant iridium (III) bis(4,6-difluorophenylpyridinato)picolate (FIrpic) has been achieved [1–7],
vacuum-thermal-evaporation is a common device fabrication process, but it is not favorable
for mass production or large panel fabrication. Accordingly, for more desirable production or
fabrication process, there have been a number of solution-processable small molecular host materials
for blue phosphorescence organic light-emitting diodes in recent years [8–14]. We and others
have developed and demonstrated bis(3,5-di(9H-carbazol-9-yl)phenyl)diphenylsilane (SimCP2
in Scheme 1) as one of high-performance solution-processable small molecular host materials
for yellow, green, and blue phosphorescence OLEDs [15–22]. More recently, SimCP2 hosted
FIrpic OLEDs were reported as having EL efficiency reaching ~11%, ~11 lm/W, or 23 cd/A [23].
Nevertheless, the EL of these FIrpic OLEDs with solution-processed light-emitting layer is far less
efficient than those OLEDs fabricated by vacuum-thermal-evaporation. For blue phosphorescence
OLEDs, solution-processable small molecular hosts with a high triplet energy gap (ET) greater than
2.6 eV of the benchmark sky-blue FIrpic are still rare and highly demanded in the field. As our
ongoing effort to develop high-performance solution-processable small molecular host materials
Molecules 2016, 21, 1315; doi:10.3390/molecules21101315
www.mdpi.com/journal/molecules

Molecules 2016, 21, 1315
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for blue phosphorescence OLEDs, we have recently overcome synthetic difficulties and successfully
prepared
9,90,900,9000,90000,900000-((phenylsilanetriyl)tris(benzene-5,3,1-triyl))hexakis(9H-carbazole)
SimCP3) (Scheme 1) as an advanced homologue of SimCP2. Herein, we report the synthesis and
(
characterization of SimCP3 in full detail. A series of SimCP3-hosted OLEDs are fabricated and tested
to demonstrate its viability as a solution-processed host material for sky-blue phosphorescence OLEDs.
Scheme 1. Chemical structure of SimCP2 and SimCP3. MM2 energy minimized structures (by Chem
3D) are shown on the right, respectively.
2. Results and Discussion
In our earlier reports [16
SimCP) and SimCP2 were synthesized in a similar method (Scheme 2). Either chlorotripheylsilane
,24,
25], both 9,90-(5-(triphenylsilyl)-1,3-phenylene)bis(9H-carbazole)
(
or dichlorodiphenylsilane was reacted with monolithiated 1,3,5-tribromobenzene to furnish
1,3-dibromophenyl substituted thriphenylsilane and bis-1,3-dibromophenyl substituted diphenylsilane,
respectively. The silane compounds were then brought to a palladium-catalyzed amination reaction
with excess amount of carbazole. Both SimCP and SimCP2 were obtained with a reasonable isolation
yield of 54% and ~40%, respectively, in the final amination reaction. It is conceivable that the reaction
yields will be lower than that of SimCP2 if the higher homologue SimCP3 is prepared by a same
reaction sequence shown in Scheme 2.
Scheme 2. Synthetic preparation of SimCP and SimCP2.
Due to the much more partial amination products formed in the reaction of synthesizing
SimCP3, we obtained a series of product mixtures, which were hard to separate by column
chromatography. In addition, the purification of SimCP3 required a tedious process in order to
remove the excess amount of carbazole used in the reaction. Alternatively, we have been able to
synthesize SimCP by using mono-lithiated 9,90-(5-bromo-1,3-phenylene)bis(9H-carbazole) (BrmCP)
to react with chlorotripheylsilane. However, the same synthetic approach has been problematic in
the preparation of SimCP2 and SimCP3, even though a very recent literature has reported the same
synthetic approach in the preparation of SimCP2 and SimCP3
[23]. We also tried the approach of
Grignard reaction (Mg instead of n-butyllithium), but it did not work out well either. It seems to us

Molecules 2016, 21, 1315
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that either lithiated or magnesiated BrmCP is relatively unstable under the reaction condition. In the
case of SimCP2 and SimCP3, the chance of either lithiated or magnesiated BrmCP reacting more than
once with dichlorophenylsilane or trichlorophenylsilane is rather low. In addition, the reaction is quite
sensitive to the purity of dichlorophenylsilane or trichlorophenylsilane, which is prone to hydrolysis
and generates hydrochloric acid that is detrimental to the reaction. Finally, we were able to synthesize
and isolate pure SimCP3 in multi-gram scale via reaction with sodium metal, i.e., a Würtz–Fittig-type
coupling reaction between chlorosilane and aryl halide (Scheme 3) [26,27]. Instead of a carbon anion of
BrmCP, a more feasible silyl anion of trichlorophenylsilne is involved in the coupling reaction.
Scheme 3. Synthesis of SimCP3 from BrmCP via Würtz–Fittig reaction.
To facilitate the SimCP3 preparation, we improved the synthesis of BrmCP with a significantly
better isolation yield of >90% [12
was furnished in only modest yields around 30% due to the competition reaction of the potential
silicon–silicon bond formation of oligosilane or polysilane [29 30]. However, the desired product
,28]. Regarding the Würtz–Fittig-type coupling reaction, SimCP3
,
was much easier to isolate from the product mixture. In this reaction, we also observed silanol
side products, although they were readily removed by column chromatography. In addition, there
was no excess amount of carbazole involved in the reaction; hence, no extra purification process
was required for SimCP3. These are the main advantages of the Würtz–Fittig reaction over other
synthetic methods of preparing SimCP3. Several spectroscopic and physical methods were used to
characterize the homogeneity of thin film and the necessary optoelectronic properties of SimCP3 as a
solution-processable host material for FIrpic OLEDs.
First, as shown in Figure 1,◦SimCP3 is very thermally stable with a thermal decomposition
temperature (Td) as high as 620 C, where 5% weight loss was determined by thermogravimetric
analysis (TGA) under a nitrogen atmosphere. Second, SimCP3 exhibits amorphous or semi-amorphous
characteristic based on the thermograms of differential scanning calorimetry (DSC). As shown in
Figure 1, SimCP3 has melting temperatures (Tm), crystallization temperatures (Tc), and glass transition
◦
temperatures (Tg) of 330, 223, and 174 C, respectively. Two very weak exothermic signals around 290
◦
and 330 C may be the inhibited crystallization process of thermally annealed SimCP3. The Tm and Tc
of SimCP3 disappeared, and Tg was observed after the first heating scan, indicative of the amorphous
tendency of SimCP3.
Tm 330 o
C
100
80
60
40
20
0
st
Heating
Cooling
1
o
2nd
3rd
T
= 620 C
Tc 223 o
C
d
1st
2nd
3rd
Tg 174 o
C
100 200 300 400 500 600 700 800 900
100 150 200 250 300 350 400
Temperature (oC)
o
Temperature ( C)
(a)
(b)
Figure 1. TGA (a) and DSC (b) thermograms of SimCP3.

Molecules 2016, 21, 1315
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Similarly, amorphous or semi-amorphous characteristics are evident from the X-ray diffraction
(XRD) spectrum (Figure 2a) of the solution-casting thin film of SimCP3. The XRD spectrum is basically
a featureless halo, indicative of an amorphous nature. Macroscopically, the homogeneity of the solution
spin-coated SimCP3 thin film is evident from the photoluminescence (PL) images of the neat film and
FIrpic-doped SimiCP3 thin films (Figure 2b), which show uniform color and no sign of agglomeration
or phase separation. Microscopically, atomic force microscopy (AFM) demonstrated the homogenous
and flat surface morphology of SimCP3 thin films with or without a FIrpic dopant (Figure 3). Whereas
thin film of poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) had a
higher surface roughness of 0.68 nm, a rather small values of root-mean-square (RMS) roughness of
0.25 and 0.33 nm was observed for the thin film of SimCP3 and SimCP3:FIrpic (10 wt %), respectively.
Regarding the flatness of the thin films, none of the discernable features in AFM surface images
had a height over 5.5 nm, 2.1 nm, and 2.7 nm, for PEDOT:PSS, SimCP3, and SimCP3:Firpic thin
films, respectively.
(a)
2000
1500
1000
500
5
10 15 20 25 30 35 40 45 50 55 60
2 Theta (degree)
Figure 2.
(a) XRD spectra of the solution drop-casting thin film of SimCP3 on silicon wafer; (b) PL
images of solution spin-coated thin films of SimCP3: FIrpic (~10 wt %) and SimCP3.
(a)
(b)
(c)
Figure 3.
5
×
5
µ
m AFM images of ITO/PEDOT:PSS (
a); ITO/PEDOT:PSS/SimCP3 (b); and
ITO/PEDOT:PSS/SimCP3:FIrpic (10 wt %) (c).
The most important property of the host material for a blue phosphorescence dopant such as
FIrpic is ET. We estimated the ET of SimCP3 as a neat thin film with time-gated acquisition PL spectra
at low temperatures (Figure 4a,b). From spectra with either variable delayed time or variable low
temperature, it can be confirmed that the emission band with a
λ
max
around 400 nm is the delayed
fluorescence and a
λ
max
around 525 nm is the phosphorescence. By taking the onset wavelength
of the high energy edge of phosphorescence bands, we obtain ~461–468 nm (2.69–2.65 eV) as the
optical energy gap for ET. From our measurements, the ET of SimCP3 is sufficiently larger than that of
FIrpic, ensuring triplet state exciton on the phosphorescence dopant rather than its host SimCP3. The
UV-visible absorption and fluorescence spectra of SimCP3 in solution are illustrated in Figure 4c.

Molecules 2016, 21, 1315
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60000
50000
40000
30000
20000
10000
0
Neat film @14 K
Delayed time
1 ms
Neat film @ 121 ms delayed time
Temperature
200000
180000
160000
140000
120000
100000
80000
60000
40000
20000
0
(a)
(b)
250K
200K
150K
100K
50K
14K
7 ms
13 ms
22 ms
28 ms
468 nm
461 nm
350 400 450 500 550 600 650 700 750
350 400 450 500 550 600 650 700 750
Wavelength (nm)
Wavelength (nm)
140000
120000
100000
80000
60000
40000
20000
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
UV-Visible absorption
Fluorescence
in CH2Cl2
(c)
368 nm
347 nm
250 300 350 400 450 500 550 600
Wavelength (nm)
Figure 4.
(
a) Variable time-gated PL spectra of SimCP3 thin film; (
b) Variable temperature, 121 msec
time-delayed PL spectra of SimCP3 thin film; (
SimCP3 in dichloromethane solution.
c) Room temperature absorption and PL spectra of
Knowing an optical energy gap of 3.57 eV (347 nm shown in Figure 4c) and the HOMO
energy level of 5.95 eV (Figure 5a), which was acquired by a low-energy photoelectron spectrometer
Riken-Keiki AC-2, the LUMO energy level of SimCP3 can thus be calculated as ~2.4 eV. Together
with the HOMO and LUMO energy levels and ET of TAPC (hole transporting or electron blocking
material) [31,32], FIrpic [32], and TmPyPB (electron transporting or hole blocking material) [33], the
energy level alignment of materials involved in OLEDs is depicted in Figure 5b. Therefore, TAPC,
SimCP3, and TmPyPB all have HOMO and LUMO energy levels that encompass those of FIrpic,
and FIrpic has the smallest ET among all materials involved in the OLED fabrication. This is a
good set of materials enabling the confinement of triplet exciton on the FIrpic phosphorescence
dopant. Accordingly, we fabricated three types of FIrpic OLED having SimCP3 as a solution-processed
host material: a single-layer device (SL)—ITO/PEDOT:PSS/SimCP3:FIrpic/CsF/Al—a bilayer
device (BL)—ITO/PEDOT:PSS/SimCP3:FIrpic/TmPyBP/CsF/Al—and a trilayer device (TL)—ITO/
PEDOT:PSS/TAPC/SimCP3:FIrpic/TmPyBP/CsF/Al. After optimization, the dopant concentration
of FIrpic was 4 wt % in all three devices. Except for TmPyBP and CsF/Al cathode, each thin film layer
of such FIrpic OLEDs was fabricated by solution process, i.e., the spin-coating method.
12
(a)
11
10
9
8
7
6
5
4
5.95 eV
3
2
1
0
5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0 6.1 6.2 6.3 6.4 6.5
Energy (eV)
Figure 5.
(a) Low-energy photoelectron spectra of SimCP3; (b) Energy level alignment of materials
involved in OLEDs.

Molecules 2016, 21, 1315
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EL characteristics of SL, BL, and TL devices are summarized in Figure 6 and Table 1. All three
devices exhibit typical sky-blue emissions of FIrpic with a max of ~468 nm, although a variation of
λ
emission shoulder band around 500 nm (Figure 6a) was observed. Since both BL and TL devices
have a similar intensity of the shoulder band and are both more intense than that of the SL device,
it can be logically inferred that TmPyPB effectively blocks the triplet exciton of FIrpic, confining the
charge recombination mostly in the SimCP3:FIrpic light-emitting layer (i.e., farther away from the
cathode surface) [19]. Therefore, the same reason can be ascribed to the low EL efficiency of the SL
device (Figure 6b,c), where the triplet exciton of FIrpic generates in an area too close to the cathode
surface and hence is prone to being quenched. Similarly, the TAPC of the TL device plays a role
of inhibiting triplet exciton from contacting the anode of the device. Therefore, the EL efficiency
of the TL device is promoted further when compared with the BL device. The maximum external
quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of the TL device are ~9%,
~20 cd/A, and 12 lm/W, respectively. However, the TL device has the lowest current density and the
highest turn-on voltage—around 5 V at 1 cd/m2 (see Figure 6d)—among the three devices. This can
be attributed to the two exciton blocking layers in the device, which limits the current density and
elevates the driving voltage of the device. Nevertheless, all three devices exhibited relatively mild
efficiency roll-off. Even at the high brightness of 3000 cd/m2 (about 38, 30, and 19 mA/cm2 of the SL,
BL, and TL devices), an EQE of 3.6%, 4.5%, and 7.4% were achieved by the SL, BL, and TL devices,
which are 95%, 62%, and 81% of the maximum EL efficiency, respectively (Figure 6c). Compared with
those of vacuum-thermal-evaporation OLEDs [
is relatively modest.
2,
4], the efficiency roll-off observed for the three devices
100
SL
BL
TL
(b)
(a)
SL
BL
TL
1.0
0.5
0.0
10
10
1
1
400
450
500
550
600
650
0
10 20 30 40 50 60 70 80 90 100
Current Density (mA/cm2)
Wavelength (nm)
10000
1000
100
10
10000
1000
100
(c)
SL
BL
TL
(d)
SL
BL
TL
10
1
10
1
0.1
0
10 20 30 40 50 60 70 80 90 100
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14
Current Density (mA/cm2)
Voltage (V)
Figure 6. Electroluminescence characteristics of SimCP3-hosted FIrpic OLEDs. ) EL spectra
(a
at ~10 volt; ) Current density dependent current efficiency and power efficiency; (c) Current density
(b
dependent external quantum efficiency; (d) Voltage dependent current density and brightness.
Table 1. Electroluminescence characteristics of SimCP3-hosted FIrpic OLEDs.
a
CE c (cd/A)
EQE e (%)
b
f
Lmax (cd/m2)
PE d (lm/W)
CIEx,y
Device
λmax (nm)
Von (V)
SL
BL
TL
472, 492
476, 500
476, 500
5.0
4.5
5.0
8078
9440
8880
7.7, 7.0, 7.7
16.0, 12.7, 10.8
19.6, 18.0, 17.4
3.4, 3.4, 3.0
11.1, 7.2, 5.2
12.3, 9.5, 7.3
3.8, 3.4, 3.8
7.3, 5.8, 4.9
9.1, 8.4, 8.1
0.15, 0.32
0.16, 0.34
0.16, 0.34
a
b
c
Turn-on voltage of 10 cd/m2 (Von).
Maximum luminance.
Current efficiency: maximum, at 100,
and 1000 cd/m2, respectively. Power efficiency: maximum, at 100, and 1000 cd/m2, respectively. External
d
e
quantum efficiency: maximum, at 100, and 1000 cd/m2, respectively. Measured at ~10 volt.
f

Molecules 2016, 21, 1315
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3. Materials and Methods
3.1. General Instrumentation
1H- and 13C-NMR spectra including distortionless enhancement by polarization (DEPT) were
measured on a Bruker AV-400 MHz or AV-500 MHz NMR Fourier transform spectrometer (Bruker,
Billerica, MA, USA) at room temperature. Elemental analyses (on a FLASHEA 1112 Series, Thermo
Electron Corporation, Waltham, MA, USA), matrix-assisted laser desorption/ionization time-of-flight
mass spectroscopy (MALDI-TOF MS, The New UltraflextremeTM, Bremen, Germany), and fast
atom bombardment (FAB) mass spectroscopy (FAB-MS, JMS-700 double focusing mass spectrometer,
JEOL, Tokyo, Japan) were performed by the Elemental Analyses Laboratory and Mass Spectroscopic
Laboratory, respectively, in-house service of the Institute of Chemistry, Academic Sinica. Infrared
absorption spectra were recorded on a Varian 640-IR FT-IR spectrometer (Palo Alto, CA, USA). The
sample of SimCP3 was ground together with KBr powder and compressed into a thin disc. Thermal
0
decomposition temperatures (Td s) of the host materials were measured by thermogravimetric analysis
0
(TGA) using Perkin-Elmer TGA-7 analyzer systems (Waltham, MA, USA). Melting temperatures (Tm s),
0
0
crystallization temperatures (Tc s), and glass transition temperatures (Tg s) of the host materials were
measured by differential scanning calorimetry◦(DSC) using Perkin-Elmer DSC-6 analyzer systems
(Waltham, MA, USA), using a scan rate of 10 C/min. The X-ray diffraction measurement of the
solution-casting thin film was carried out by using a Bruker D8 Advance diffractometer (Billerica,
MA, USA) equipped with a Lynxeye detector. The radiation used was a monochromatic Cu K
α
bea‘m of wavelength = 0.154 nm. AFM measurements were carried out with XE-100 from Park
λ
Systems (Suwon, South Korea) using a non-contact mode to obtain topography images of the thin
films, which were prepared by a spin-coating chlorobenzene solution of SimCP3 or SimCP3:FIrpic
on a PEDOT:PSS-coated ITO-glass substrate. UV-visible absorption spectra were recorded on a
Hewlett-Packard 8453 diode array spectrophotometer (Palo Alto, CA, USA). Room temperature
fluorescence spectra were recorded on a Hitachi fluorescence spectrophotometer F-4500 (Tokyo, Japan).
The ionization potentials (or HOMO energy levels) of SimCP3 were determined with a low energy
photo-electron spectrometer (Riken-Keiki AC-2, Riken Keiki Co., Ltd., Tokyo, Japan). LUMO energy
levels were estimated by subtracting the optical energy gap (Eg) from HOMO energy levels. Eg was
determined by the on-set absorption energy from the absorption spectra of the materials as thin
film. To measure the triplet energy gap (ET) of a thin film sample, we established a system with a
temperature control of Model 350 (LakeShore Company, Westerville, OH, USA) as low as 10 K by
Model 22C/350C Cryodyne Refrigerators (Janis Research Company, Woburn, MA, USA) and a tunable
laser with excitation wavelengths of 213, 266, 355, 532, and 1064 nm (Brilliant B laser, Quantel Company,
Newbury, Berkshire, UK), which was coupled with a time-delay controller of LP920 flash photolysis
spectrometer (Edinburgh Instrument, Kirkton Campus, Livingston, England). We also acquired
the triplet energy gap of SimCP3 in frozen 2-Me-THF by using Fluorolog III photoluminescence
spectrometer (Kirkton Campus, Livingston, UK), which was equipped a xenon lamp as excitation
light source.
3.2. Device Fabrication and Performance Measurements
The ITO substrate was purchased from Buwon Precision Sciences (Taoyuan, Taiwan with a
sheet resistance around 25
Ω/sq and a thickness of 100 nm. The hole transport layer—PEDOT:PSS
(CH8000)—was purchased from Sigma-Aldrich (St. Louis, MO, USA). The blue phosphorescence
dopant FIrpic, the electron transport layer of TmPyPB, and the hole transport layer of TAPC were
obtained commercially from Lumtec (Hsinchu, Taiwan). The indium tin oxide (ITO) su◦bstrates were
pre-coated with the PEDOT:PSS hole transporting layer (HTL) and baked in the air at 150 C for 10 min.
Blends of SimCP3 and FIrpic in chlorobenzene were spin-coated on ITO/PEDOT:PSS. The active layer
◦
was then annealed at 90 C for 30 min. After spin-coating the active single-layer, the TmPyPB
(50 nm), an ultrathin CsF (2 nm) interfacial layer, and then an aluminum cathode (100 nm) were

Molecules 2016, 21, 1315
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vacuum-thermal deposited. In the triple-layer device, a thin layer (~20 nm) of T◦APC was spin-coated
first on PEDOT:PSS. In this case, TAPC layer was thermally annealed at 90 C for 10 min before
spin-coating SimCP3:FIrpic. A surface profiler (Dektak 150, Veeco Instruments, Plainview, NY, USA)
was used for calibrating the thickness of HTL and the active layer. After the deposition of the cathode,
the devices were hermetically sealed with glass and UV-cured resins in a glove box (O2 and H2O
concentration below 0.1 ppm). The device’s active area was 0.04 cm2 and was defined by the self-made
shadow mask applied in the cathode deposition. Current density and voltage characteristics were
measured by a dc current–voltage source meter (Keithley 2400, Tektronix, Beaverton, OR, USA), and
the device brightness (or electroluminance, cd/m2) and EL spectra were monitored and recorded with
a spectrophotometer (PR650; Photo Research, Syracuse, NY, USA). The EQE of OLEDs was calculated
from the luminance, current density, and the EL spectra, assuming the EL of the OLED is isotropic, i.e.,
a Lambertian emission [34].
3.3. Materials Preparation
All chemical and reagents were obtained from commercial suppliers and used without further
purification. Solvents were purified according to the standard procedures. Unless specified condition,
all reaction were performed under a nitrogen atmosphere using standard Schlenk techniques. Materials
involved in OLED fabrication, 4,40-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC), and
3,30-(50-(3-(pyridin-3-yl)phenyl)-[1,10:30,100-terphenyl]-3,300-diyl)dipyridine (TmPyPB) were purchased
from Lumtec (Hsinchu, Taiwan) and Ultra Fine Chemical Technology Corp. (Degussa, Dusseldorf,
Germany), respectively. They were used as received without further purification.
Synthesis and characterization of 9,90-(5-Bromo-1,3-phenylene)bis(9H-carbazole), BrmCP. The synthesis
and isolation of BrmCP are modified from a known procedure of a patent report [28]. To an anhydrous
DMF solution (200 mL) containing sodium hydride (60% suspension in oil, 13 g, 0.31 mole), carbazole
(52 g, 0.31 mol) was slowly added. The mixture was stirred for 1 h at room temperature. After cooling
in an ice bath, 3,5-difluorobromobenzene (12 mL, 0.1 mol) was added dropwise. The solution mixture
was then heated at 130 ◦C for 12 h. After cooling, an excess amount of ethanol–water mixture (10:1)
was added and stirred, resulting in white precipitates. The product was isolated by suction filtration,
and further purification was achieved by zone-temperature sublimation to afford white solid (44.7 g,
1
92%). H-NMR (400 MHz, CDCl3):
δ
(ppm) 8.13 (d, 4H, J = 7.6 Hz), 7.85 (s, 2H), 7.78 (s, 1H), 7.53 (d,
(ppm)
4H, J = 7.6 Hz), 7.45 (t, 4H, J = 7.6 Hz), 7.32 (t, 4H, J = 7.6 Hz). 13C-NMR (100 MHz, CDCl3):
δ
140.72, 140.55, 128.89, 126.58, 124.32, 124.18, 124.04, 120.98, 120.77, 109.81. MALDI-HRMS: calcd MW
486.0726, m/z = 486.0705 (M+).
Synthesis and characterization of 9,90,900,9000,90000,900000-((phenylsilanetriyl)tris(benzene-5,1,3-triyl))
hexakis(9H-carbazole) (SimCP3). To a refluxing toluene (4 mL), sodium metal (0.2 g, 8.3 mmol) was
added. The mixture was stirred for 10 min. Then, BrmCP (2.0 g, 4.0 mmol) and trichloro(phenyl)silane
(0.2 mL, 1.3 mmol) dissolved in toluene (4 mL) were added slowly to the refluxing toluene
containing sodium metal through an additional funnel. After 3 h of reaction, the reaction solution
was cooled to room temperature and an excess amount of methanol was added. The resulting
precipitations were isolated by suction filtration and subjected to column chromatography (silica
gel, dichloromethane/hexanes: 2/3). A white solid was obtained with a yield of 34% (0.6 g). FT-IR
(λ
, cm−1): 3044 (w), 3013 (w), 1623 (w), 1580 (s), 1490 (m), 1480 (m), 1447(s), 1416 (m), 1374 (m), 1330
(s), 1309 (s), 1227 (s), 1191 (m), 1155 (m), 1120 (m), 1098 (w), 1027 (w), 1002 (w), 959 (w), 923 (w), 904
(w), 882 (w), 840 (w), 798 (w), 778 (w), 746 (s), 706 (s), 722 (s). UV-Vis (CH2Cl2):
δ (ppm) 8.07–8.03 (m, 18H), 7.87 (m, 5H),
7.48–7.47 (m, 3H), 7.27 (d, 12H, J = 8.4 Hz), 7.15 (t, 12H, J = 7.6 Hz), 7.00 (t, 12H, J = 7.6 Hz). 13C- and
λ
293, 311, 325,
max
339 (3.61 × 104 cm−1·M−1). 1H-NMR (400 MHz, CDCl3):
DEPT NMR (125 MHz, CDCl3):
δ (ppm) 140.54, 140.04, 137.07, 136.27 (DEPT-90), 133.69, 132.92
(DEPT-90), 131.40 (DEPT-90), 129.19 (DEPT-90), 127.27 (DEPT-90), 126.47 (DEPT-90), 123.89, 120.74

Molecules 2016, 21, 1315
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(DEPT-90), 120.62 (DEPT-90), 109.62 (DEPT-90). MALDI-HRMS: calcd MW 1326.4800, m/z = 1326.4757
(M+). Anal. Found (calcd) for C96H62N6Si: C 86.66 (86.85), H 4.92 (4.71), N 6.37 (6.33).
4. Conclusions
In summary, we have overcome the synthetic difficulty of SimCP3, an advanced homologue of
previously known SimCP2. We have examined the amorphous nature and the spectroscopic properties
(HOMO and LUMO energy levels as well as the triplet energy gap) of SimCP3. Three sky-blue
phosphorescence OLEDs have been fabricated with a SimCP3:FIrpic light-emitting layer, which
was spin-coated from solution. A trilayer device exhibits the highest EL efficiency of ~9%, ~20 cd/A,
or ~12 lm/W, demonstrating the viability of SimCP3 as a solution-processed host material for sky-blue
phosphorescence OLEDs.
Acknowledgments: We thank the Ministry of Science and Technology (MOST 103-2113-M-001-021-MY3),
Academia Sinica, and National Taiwan University for financial support. We acknowledge Jiun-Haw Lee of
National Taiwan University in the calculation of EQE of the OLEDs in this work.
Author Contributions: Chin-Ti Chen and Chao-Tsen Chen conceived and designed the experiments;
Cheng-Lung Wu, Yung-Ting Chang, Jan Golder, and Yi-Ting Lee performed the experiments; Yung-Ting Chang
and Yi-Ting Lee analyzed the data; Chin-Ti Chen and Chao-Tsen Chen wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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Sample Availability: Samples of SimCP3 are available from the authors.
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2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC-BY) license (http://creativecommons.org/licenses/by/4.0/).