Tetraphenylsilane group containing carbazoles as high triplet energy host materials for solution-processable PhOLEDs

Article abstract of DOI:10.3906/kim-1502-73

A series of solution processable, wide band-gap host materials composed of carbazole and tetraphenylsilane groups were designed and synthesized. Their thermal, electrochemical, and photophysical properties were fully investi- gated. The introduction of bulky tetraphenylsilane and tert-butyl groups around the carbazole led to high glass transition temperatures (Tg) between 120 and 204 ° C. The triplet energies (ET ) of the synthesized materials were examined by low temperature (77 K) photoluminescence studies and determined as ET > 2.6 for all compounds. Phosphorescent organic light-emitting devices with the ITO/PEDOT:PSS/EML/TPBi/Cs2CO3 /Al device structure were fabricated by using synthesized materials as the host and two kinds of phosphorescent emitters, FIrpic and Ir(ppy)3 , as the guests. The highest luminous and power efficiency values obtained by using FIrpic were 3.6 cd A -1 and 1.48 lm W -1 , respectively, with commission International de I'Eclairage (CIE) coordinates of (0.17, 0.36), whereas these values were 7.8 cd A -1 and 2.9 lm W -1 for the device structure when Ir(ppy)3 was used as the guest [CIE (0.28, 0.62)].

Full text of DOI:10.3906/kim-1502-73

Turk J Chem
Turkish Journal of Chemistry
(2015) 39: 917 – 929
¨
http://journals.tubitak.gov.tr/chem/
˙
c
⃝ TUBITAK
doi:10.3906/kim-1502-73
Research Article
Tetraphenylsilane group containing carbazoles as high triplet energy host
materials for solution-processable PhOLEDs
∗
¨
˙
¨
Saliha ONER, Ilker ONER, Haydar AKDAG, Canan VARLIKLI
˘
˙
Ege University, Solar Energy Institute, Bornova, Izmir, Turkey
Received: 11.02.2015
•
Accepted/Published Online: 22.05.2015
•
Printed: 30.10.2015
Abstract: A series of solution processable, wide band-gap host materials composed of carbazole and tetraphenylsilane
groups were designed and synthesized. Their thermal, electrochemical, and photophysical properties were fully investi-
gated. The introduction of bulky tetraphenylsilane and tert-butyl groups around the carbazole led to high glass transition
temperatures (Tg) between 120 and 204 ◦ C. The triplet energies (ET ) of the synthesized materials were examined by
low temperature (77 K) photoluminescence studies and determined as ET > 2.6 for all compounds. Phosphorescent
organic light-emitting devices with the ITO/PEDOT:PSS/EML/TPBi/Cs2 CO3 /Al device structure were fabricated by
using synthesized materials as the host and two kinds of phosphorescent emitters, FIrpic and Ir(ppy)3 , as the guests. The
highest luminous and power efficiency values obtained by using FIrpic were 3.6 cd A−1 and 1.48 lm W−1 , respectively,
with commission International de I’Eclairage (CIE) coordinates of (0.17, 0.36), whereas these values were 7.8 cd A−1
and 2.9 lm W−1 for the device structure when Ir(ppy)3 was used as the guest [CIE (0.28, 0.62)].
Key words: Host material, blue and green PhOLEDs, tetraphenylsilane, carbazole
1. Introduction
Phosphorescent organic light emitting diodes (PhOLEDs) have attracted great attention because of their ability
to reach nearly 100% internal quantum efficiency by using both singlet (25%) and triplet (75%) excitons.1−3
In order to prevent triplet–triplet annihilation and concentration quenching, which have hindering effects on
device efficiency, phosphorescent emitters should be doped in a suitable host material.4,5 However, the design
of the host material is very important and several requirements should be met: i) the triplet energy of the
host material should be higher than that of the phosphorescent emitter to prevent exothermic energy transfer
from the emissive dopant to the host material,6 ii) the glass transition temperature of the host material should
be high for good film-forming properties,7,8 iii) the highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) energy levels of the host material and the phosphorescent emitter should
be appropriate for efficient energy transfer,9,10 and iv) the host material should have good charge transporting
properties.
A carbazole group containing 4,4′ -bis(n-carbazolyl)-1,1′ -biphenyl (CBP) host material is widely used
as the host material for PhOLED applications, but the triplet energy of the CBP (ET = 2.56 eV) is lower
than that of the blue phosphorescent FIrpic (ET = 2.65 eV), which hampers device efficiency due to back
∗Correspondence: canan.varlikli@ege.edu.tr, onerilker@gmail.com
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energy transfer.6 Several studies have been conducted on the modification of CBP for increasing triplet energy
and glass transition temperature.11,12 These studies are mainly focused on decreasing the conjugation between
the carbazole groups by creating a twisted structure and/or introduction of a nonconjugated linkage such as
diphenylether, tetraphenylsilane, or sp3 hybridized carbon atoms between the molecular entities.13−19 Among
these, tetraphenysilane-based host materials have been widely used in OLED applications because of their high
triplet energy and high glass transition temperature.20,21 The effective interruption of the π conjugation with
the δ-Si structure ensures a high ET . Moreover, the bulky phenyl groups around the silicon atom increase
the molecular weight and steric hindrance, providing high Tg and better film-forming properties. However,
most of the previously reported tetraphenysilane derivative host-based PhOLEDs have been fabricated by
vacuum deposition method,16,22,23 which is an expensive technique and not suitable for large area applications.
Only a few studies have been reported on solution-processable tetraphenylsilane-based host materials.18,19,24
Furthermore, efficient, solution-processable, and high triplet energy host materials are still needed to be
developed for low cost and simple coating techniques, such as spin coating and inkjet printing.
In this study, we prepared a series of tetraphenylsilane-bridged carbazole compounds named 9,9’-
[(diphenylsilanediyl)bis(4,1-phenylene)]bis-9H-carbazole (DiCzSi), 9,9’-[(diphenylsilanediyl)bis(4,1-phenylene)]
bis(3,6-di-tert-butyl-9H-carbazole) (tBuDiCzSi), 9,9’-[(diphenylsilanediyl)bis(biphenyl-4’,4-diyl)]bis-9H-carba-
zole (DiCzPhSi), and 9,9’-[(diphenylsilanediyl)bis(biphenyl-4’,4-diyl)]bis(3,6-di-tert-butyl-9H-carbazole) (tBu-
DiCzPhSi). The combination of carbazole and tetraphenylsilane groups provided relatively high ET (>2.6 eV)
and high Tg (≥120 ◦ C). Additionally, good solubility of the synthesized materials in organic solvents allowed
their utilization as hosts in solution-processed PhOLEDs. Blue and green light emitting devices are realized by
using the synthesized host materials doped with FIrpic and Ir(ppy)3 as the light emitting layer. The highest
luminous and power efficiency values obtained by using FIrpic were 3.6 cd A−1 and 1.48 lm W−1 , respectively,
whereas these values were 7.8 cd A−1 and 2.9 lm W−1 for the device structure when Ir(ppy)3 was used as the
guest.
2. Results and discussion
2.1. Synthesis
The synthetic route used to obtain the materials is shown in Scheme Firstly, 9H -carbazole (1) was alky-
lated by using the Friedel–Crafts method and 3,6-di-tert-butylcarbazole (2) was obtained. After that, bis(4-
bromophenyl)(diphenyl)silane (3) was obtained by Li-halogen exchange reaction by using n-BuLi at –78 ◦ C.
The Buchwald–Hartwig amination reaction of carbazole and 3,6-di-tert-butylcarbazole with molecule 3 in the
presence of Pd(OAc)2 , P(t-Bu)3 , and K2 CO3 allowed us to obtain the target molecules DiCzSi and tBuDiCzSi.
After that, both 9H -carbazole and 3,6-di-tert-butylcarbazole were reacted with 1-bromo-4-iodobenzene by Ull-
mann coupling in the presence of Cu, 18-crown-6, and K2 CO3 . The brominated derivatives (4 and 5) were then
converted to boronic acids (6 and 7) by using n-BuLi and B(OMe)3 . The Suzuki–Miyaura coupling reaction
between the boronic acids and molecule 3 allowed us to obtain the target molecules DiCzPhSi and tBuDiCzPhSi.
The molecular structures of the intermediates and the target molecules were confirmed by FTIR, 1 H NMR, and
13 C NMR spectroscopy and the results were in good agreement with the proposed structures. Details of the
synthetic routes followed are given in the supplementary (S) section together with the corresponding structural
characterization spectra (Figures S1–S13; on the journal’s website).
918

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R
t-BuCl
NH
NH
AlCl
3
CH Cl
2
2
R
2 (R=tert-butyl)
1
R
R
Pd(OAc)2
P(t-Bu)3
K2CO3
Br
Br
C
Cl Si Cl
Br
Si
Br
N
Si
N
n-BuLi
THF, -78 o
1 or 2
Toluene
3
R
R
R
H
(DiCzSi)
(tBuDiCzSi)
tert-butyl
R
R
R
OH
Br
I
B(OMe)
nBuLi
3
N
Br
NH
N
B
Cu, K CO
2
3
THF, -78 o
C
OH
18-Crown-6
Pd(dppf)Cl2
Cs CO
R
R
R
3
2
4 and 5
3
6 and 7
Toluene/MeOH
R
R
R
Si
N
N
H
(DiCzPhSi)
tert-butyl
(tBuDiCzPhSi)
R
R
Scheme. Molecular structures and the synthetic route for the synthesized materials.
2.2. DSC measurements
The thermal properties of the compounds were studied by differential scanning calorimetry (DSC) measure-
ments. The first heating scan of the DSC thermograms revealed the melting points (Tm) of the compounds
(Figure 1a). Tm values of DiCzSi and DiCzPhSi were determined as 290 ◦ C and 285 ◦ C, respectively. The in-
troduction of tert-butyl groups to 3- and 6- positions of the carbazole greatly increased the melting point to 384
◦ C for tBuDiCzSi and no melting point was observed for tBuDiCzPhSi within the measurement scale (30–400
◦ C). During the second heating scan (Figure 1b), weak endothermic transitions were observed, indicating the
Tg of the compounds, which increased with the increasing molecular weight. Among the compounds, DiCzSi
has the lowest Tg (120 ◦ C), which is still much higher than that of the commonly used host material CBP (Tg
= 62 ◦ C).25 Introduction of the diphenylsilane group into the CBP molecule greatly enhanced the Tg , which
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indicates the positive effect of the nonplanar silicon moiety. Furthermore, the introduction of tert-butyl and
phenyl groups increased the Tg from 120 ◦ C up to 204 ◦ C. With the increasing temperature, crystallization
was observed for DiCzSi and tBuDiCzSi, showing that they have both crystalline and amorphous states. The
Tg of the tBuDiCzPhSi was determined as 337 ◦ C, and no other phase transitions could be detected up to 400
◦ C; therefore, the compound stays in amorphous state. The results showed that all of the synthesized materials
have high thermal stability, which is favorable for obtaining smooth and stable films.19
290 oC
285 oC
DiCzSi
384 oC
DiCzSi
a)
b)
tBuDiCzSi
DiCzPhSi
tBuDiCzPhSi
tBuDiCzSi
DiCzPhSi
tBuDiCzPhSi
T :204 oC
g
T :172 oC
g
T :154 oC
g
T :120 oC
g
T :337 oC
c
T :222 oC
c
Not detected
50
100 150 200 250 300 350
Temperature (°C)
400
50 100 150 200 250 300 350 400
Temperature (°C)
Figure 1. a) The first heating scan of the DSC thermograms, which shows the melting points of the compounds, b) the
second heating scan of the DSC thermograms, which shows the glass transition (Tg) and crystallization temperatures
(Tc) for the synthesized compounds.
2.3. Absorption–photoluminescence studies
The UV-Vis absorption and PL spectra of the compounds were measured in different solvents with different
polarities (Figure 2). The maximum absorption peak at around 290 nm is identical for all compounds and
can be assigned to the carbazole-centered n–π* transition and the absorption band between 310 and 350 nm
is attributed to the π–π* transition of the entire conjugated system.26 The optical band-gap [Eg(opt) ] of the
compounds was calculated from the onset of the UV-Vis absorption spectra, which is around 3.5 eV.
The PL spectra of DiCzSi and tBuDiCzSi are almost identical in CHCl3 solvent, except that the
introduction of the tert-butyl groups caused a red-shift of 7 nm for the latter. The PL spectrum of DiCzPhSi
showed a significant red-shift (ca. 33 nm/in CHCl3 solvent) compared to the DiCzSi counterpart, which is
attributed to the extended π conjugation between the carbazole and tetraphenylsilane units. The PL spectrum
of tBuDiCzPhSi also showed a red-shift (ca. 18 nm/in CHCl3 solvent) compared to the DiCzPhSi counterpart,
which is caused by the introduction of the electron-donating tert-butyl groups. There was no significant
difference between the absorption spectra of the compounds, probably because the molecules were exposed
to the same local environment in the ground and excited states. In contrast, the PL maxima of DiCzPhSi
and tBuDiCzPhSi showed a bathocromic shift with increasing solvent polarity (Figure 2). Actually, this was
expected as the π character in those two compounds is dominant and therefore a solvent polarity increase would
have a dramatic effect on the π*–π relaxation. A summary of the photophysical data is given in Table 1.
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DiCzSi
Toluene
tBuDiCzSi
Toluene
a)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
b)
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
THF
THF
Chloroform
DCM
Chloroform
DCM
0.8
0.6
0.4
0.2
0.0
300
350
400
450
500
550
300
350
400
450
500
550
Wavelength (nm)
Wavelength (nm)
tBuDiCzPhSi
DiCzPhSi
Toluene
THF
d)
c)
1.0
1.0
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
Toluene
THF
Chloroform
DCM
Chloroform
DCM
0.8
0.6
0.4
0.2
0.0
0.8
0.6
0.4
0.2
0.0
300
350
400
450
500
550
300
350
400
450
500
550
Wavelength (nm)
Wavelength (nm)
Figure 2. UV-Vis and PL spectra of the synthesized compounds, a) DiCzSi, b) tBuDiCzSi, c) DiCzPhSi, d) tBu-
DiCzPhSi obtained in different solvents (10−5 M), at room temperature.
Table 1. Physical, optical and electrochemical data for the synthesized compounds.
c
d
f
Tm/Tg/Tca
(◦C)
λbP L
(nm)
ET Eox
(eV) (V)
HOMOe LUMOe Eg(opt)
b
Host material
λabs (nm)
(eV)
(eV)
(eV)
3.54
3.47
3.52
3.45
DiCzSi
tBuDiCzSi
DiCzPhSi
290/120/222 294, 306, 326, 341 347, 362 3.00 1.18
384/172/337 298, 312, 332, 347 354, 370 3.00 1.06
–5.69
–5.57
–5.67
–5.57
–2.15
–2.10
–2.15
–2.12
285/154/NA 294, 314
tBuDiCzPhSi NA/204/NA 298, 324
380
398
2.64 1.16
2.64 1.06
a Tm /Tg /Tc were obtained from the DSC measurements (10 ◦ C min−1 N2 gas flow), b maximum absorption and PL
wavelengths were measured in CHCl3 solution (10−5 M), c triplet energy values were calculated from the maximum
wavelength of the phosphorescence spectra measured in DCM at 77 K, d oxidation potentials were determined from the
onset of the CV curves, e) HOMO energy levels were calculated from the onset of the oxidation potentials, e LUMO
f
energy levels were deduced from the formula LUMO = HOMO + Eg(opt), Eg(opt) were calculated from the onset of the
absorption spectra in CHCl3 solution.
The phosphorescence spectra of the materials were determined by low temperature (77 K) PL measure-
ments in dichloromethane (DCM) (10−5 M solutions). DiCzSi and tBuDiCzSi showed a new emission band
with a maximum peak at around 415 nm, and the emission maximum shifted to ∼470 nm for DiCzPhSi and
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tBuDiCzPhSi (Figure 3). The ET values were estimated to be >2.6 eV by taking the highest-energy peak
of phosphorescence as the transition energy of T1 →S0 , which corresponded to the vibronic 0–0 transition
between these two electronic states.19,27 The ET values of DiCzSi and tBuDiCzSi were calculated as 3.0 eV.
This value is higher than that of the blue phosphorescent emitter FIrpic (ET = 2.65 eV); this meant that they
are suitable hosts for effectively confining the excitons on FIrpic dopant.6 The addition of the –phenyl ring
between the carbazole and tetraphenysilane groups caused a significant red-shift (ca. 54 nm) because of the
extension of the π conjugation, resulting in lower triplet energy for DiCzPhSi and tBuDiCzPhSi (ET = 2.64
eV), which is close to the triplet energy of the green phosphorescent emitter Ir(ppy)3 (ET = 2.4 eV).4 Because
of their suitable ET values, all synthesized host materials were used with the green emitter Ir(ppy)3 , and the
higher triplet energy host materials, DiCzSi and tBuDiCzSi, were used with the blue emitter FIrpic.
2.4. Electrochemical studies
The electrochemical behaviors of the compounds were determined by cyclic voltammetry (CV). All of the
synthesized compounds showed reversible and/or nonreversible oxidation peaks because of the p-type carbazole
groups, and no reduction peak within the electrochemical window (+2/–2 V) was detected. With regard to
the energy level of the ferrocene reference (4.8 eV relative to the vacuum level), the HOMO energy levels were
calculated by using the equation of EHOMO = –e (4.8 + E(ox) – E(F c)), in which Eox was taken from the onset
of the oxidation potential.28 As shown in Figure 4, tBuDiCzSi and tBuDiCzPhSi showed Eox values of around
1.06 V that correspond to a HOMO energy level of –5.57 eV. DiCzSi and DiCzPhSi exhibited a nonreversible
oxidation peak because of the instability of the radical cations of these carbazoles since the electro-active -3 and
-6 positions may have undergone dimerization under the CV scan.29,30 The Eox values were around 1.2 V and
HOMO energy levels were calculated as –5.69 eV and –5.67 eV for DiCzSi and DiCzPhSi, respectively.
-1.5
DiCzSi
1.0
0.8
0.6
0.4
0.2
0.0
DiCzSi
tBuDiCzSi
DiCzPhSi
tBuDiCzSi
DiCzPhSi
tBuDiCzPhSi
-1.0
-0.5
0.0
tBuDiCzPhSi
415 nm
0.5
469 nm
470 nm
1.0
416 nm
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Potential / V
350
400
450
Wavelength (nm)
500
550
Figure 3. Phosphorescence spectra of the synthesized
materials recorded at 77 K in CHCl3 (10−5 M).
Figure 4. Cyclic voltammograms of the synthesized ma-
terials measured in CHCl3 .
CV studies are also important to determine the electrochemical stability of the synthesized compounds,31,32
which has a significant importance in terms of device efficiency.33 The consecutive CV scans (20 cycles) revealed
that the tert-butyl group containing tBuDiCzSi and tBuDiCzPhSi were electrochemically stable and there was
no new wave formation after continuous cycling (Figure S13; on the journal’s website). However, during the
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consecutive CV scans of DiCzSi and DiCzPhSi, the oxidation peak at around 1.2 eV disappeared and a new
wave at around 0.8 eV appeared, due to the oxidation of the carbazole groups.34 The LUMO energy levels
were obtained by using the following equation: LUMO = HOMO + Eg(opt.) , which was around –2.10 eV for all
compounds. The electrochemical data are summarized in Table 1.
2.5. Theoretical calculations
In order to understand the electronic states of the host molecules, density functionalized theory (DFT) cal-
culations were performed by using Gaussian 09 C.01 software.35 The geometry optimizations and frequency
calculations were performed at the level of B3LYP/ cc-pVDZ (any imaginary frequency). Calculated energy
values of density surfaces of the HOMO and LUMO are shown in Figure 5 and Table 2. The triplet energy
(ET ) of the compounds was calculated using time-dependent density functional theory (TD-DFT). The results
revealed that the HOMO and LUMO electron density distributions of the synthesized materials are mainly
localized on the carbazole and tetraphenylsilane fragments, respectively.36 As shown in Figure 5, the highly
twisted configurations of the host molecules allow the separation of HOMO and LUMO, which is favorable for
the efficient hole and electron transporting properties.37 The calculated triplet energy levels were around 3.1
eV for the DiCzSi and tBuDiCzSi, which was consistent with the experimental results (3.0 eV). The ET of the
DiCzPhSi and tBuDiCzPhSi were calculated as 3.03 eV and 2.98 eV, respectively.
Table 2. Calculated energy values of the host materials.
Host material HOMO (eV) LUMO (eV) Eg (eV) S1 (eV) ET (eV)
DiCzSi
tBuDiCzSi
DiCzPhSi
–5.55
–5.34
–5.52
–1.44
–1.05
–1.45
–1.40
4.11
4.29
4.07
3.91
3.83
3.73
3.56
3.44
3.15
3.10
3.03
2.98
tBuDiCzPhSi –5.31
2.6. PhOLED performances
To evaluate the EL properties of the synthesized compounds as solution-processable host materials, we fabricated
blue and green PhOLEDs with the configuration of ITO/PEDOT:PSS (40 nm)/B-EML (or G-EML) (70
nm)/TPBi (20 nm)/Cs2 CO3 (3 nm)/Al (100 nm), where B-EML and G-EML refer to the synthesized host
materials doped with FIrpic and Ir(ppy)3 , respectively. The device architectures are listed in Table 3. The
optimized doping concentrations of FIrpic and Ir(ppy)3 were 15 wt.% and 10 wt.%, respectively.
Table 3. Device names and corresponding structures.
Device name Structures
Device B1
Device B2
Device G1
Device G2
Device G3
Device G4
ITO/PEDOT:PSS/DiCzSi:FIrpic/TPBi/Cs2CO3/Al
ITO/PEDOT:PSS/tBuDiCzSi:FIrpic/TPBi/Cs2CO3/Al
ITO/PEDOT:PSS/DiCzSi:Ir(ppy)3/TPBi/Cs2CO3/Al
ITO/PEDOT:PSS/tBuDiCzSi:Ir(ppy)3/TPBi/Cs2CO3/Al
ITO/PEDOT:PSS/DiCzPhSi:Ir(ppy)3/TPBi/Cs2CO3/Al
ITO/PEDOT:PSS/tBuDiCzPhSi:Ir(ppy)3/TPBi/Cs2CO3/Al
Figure 6 depicts the luminance–voltage–current density (L–V–J) characteristics of blue (devices B1–B2)
and green (devices G1–G4) emitting devices. The turn-on voltages of devices were between 5 and 8 V (taking
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HOMO
LUMO
a
b
c
d
Figure 5. Calculated density surfaces of the molecular orbitals of a) DiCzSi, b) tBuDiCzSi, c) DiCzPhSi, and d)
tBuDiCzPhSi.
924

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1 cd m−2 to be the turn-on standard). Among the blue devices, the rise in the current density of device B1
might be due to a better hole or electron transport within the emitting layer, resulting in lower turn-on voltage.
The same phenomenon was also observed for green devices. The devices with nonsubstituted host materials
(B1, G1, G3) showed higher driving voltages than those of the tert-butyl substituted derivatives (B2, G2, G4).
b)
a)
100
80
60
40
20
0
100
80
60
40
20
0
103
102
101
100
Green OLED; Host:Ir(ppy)
103
102
101
100
3
Blue OLED; Host:FIrpic
DiCzSi, G1
DiCzSi, B1
tBuDiCzSi, G2
DiCzPhSi, G3
tBuDiCzSi, B2
tBuDiCzPhSi, G4
0
2
4
6
8 10
Voltage (V)
12
14
16
0
2
4
6
8
Voltage (V)
10
12
14
c)
Figure 6. The luminance–voltage–current density (L–V –J) characteristics for a) blue PhOLEDs and b) green
PhOLEDs. The symbols apply for luminance (filled) and current density (hollow) of the devices. c) Energy level
diagram of the PhOLEDs, the dashed and dotted lines apply for FIrpic and Ir(ppy)3 , respectively.
The luminous and power efficiency versus current density of blue and green PhOLEDs is shown in Figure
7. Among the blue emitting devices, device B1, which contains DiCzSi as the host material, showed higher
luminous and power efficiency than did device B2, which contains tert-butyl substituted derivative (tBuDiCzSi).
Device B1 exhibited the highest luminous efficiency of 3.6 cd A−1 , the highest power efficiency of 1.48 lm W−1
,
and a maximum brightness of 1324 cd m−2 . These results are in good agreement with the data reported by Hu
et al.22 On the other hand, for green PhOLEDs, device G3 showed higher luminous and power efficiency than
did the other devices, with a maximum luminous efficiency of 7.8 cd A−1 , maximum power efficiency of 2.9 lm
W
−1 , and maximum brightness of 4237 cd m−2 . The EL performances of the devices are summarized in Table
4. Although the introduction of tert-butyl groups increased the Tg , electrochemical stability, and solubility
of the synthesized compounds, the OLED devices with tert-butyl group containing host materials resulted in
lower device efficiencies. The lower efficiency may be attributed to the constrained charge transport caused by
the insulating effect of the tert-butyl groups.38
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8
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Blue OLED; Host:FIrpic
b)
a)
DiCzSi, B1
tBuDiCzSi, B2
6
4
2
0
Green OLED; Host:Ir(ppy)3
DiCzSi, G1
tBuDiCzSi, G2
DiCzPhSi, G3
tBuDiCzPhSi, G4
0
20
40
60
80
100
0
20
40
60
80
100
Current density (mA/cm2)
Current density (mA/cm2)
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Blue OLED; Host:FIrpic
DiCzSi, B1
Green OLED; Host:Ir(ppy)3
c)
d)
DiCzSi, G1
tBuDiCzSi, B2
tBuDiCzSi, G2
DiCzPhSi, G3
tBuDiCzPhSi, G4
0
20
40
60
80
100
0
20
40
60
80
100
Current density (mA/cm2 )
Current density (mA/cm2 )
Figure 7. Luminous efficiency (a,b) and power efficiency (c,d) versus current density characteristics for blue and green
OLEDs.
Table 4. Maximum luminance, current, power, EQE efficiencies and CIE color coordinates of blue devices B1 and B2,
and green devices G1–G4.
Device Vaon Max.
Max. current Max. power Max.
CIE (x, y)
name
(V) luminance efficiency
efficiency
EQE (%) (@ 10 V)
(cd/m2)
1324
642
(cd/A)
3.6
3
(lm/W)
1.48
1
1.5
0.78
2.9
B1
B2
G1
G2
G3
6.4
7.3
6.2
7.8
5.2
5.2
1.72
1.47
1.26
0.8
0.17, 0.36
0.17, 0.34
0.28, 0.62
0.27, 0.62
0.28, 0.62
0.28, 0.62
689
367
4237
1950
4.27
2.65
7.8
2.27
2.26
G4
a
7.6
3
Turn-on voltage
Electroluminescence (EL) spectra of the blue and green devices at 12 V are presented in Figure 8. All of
the devices showed blue and green emission spectra peaking at 475 nm and 510 nm, which originated from the
emission of FIrpic and Ir(ppy)3 , respectively, implying efficient energy transfer from host materials to dopant
molecules.
926

¨
ONER et al./Turk J Chem
Green OLED; Host:Ir(ppy)3
Blue OLED; Host:FIrpic
b)
a)
DiCzSi, G1
DiCzSi, B1
tBuDiCzSi, G2
DiCzPhSi, G3
tBuDiCzPhSi, G4
tBuDiCzSi, B2
400 450 500 550 600 650 700 750 800
Wavelength (nm)
400 450 500 550 600 650 700 750 800
Wavelength (nm)
Figure 8. Electroluminescence spectra of a) blue and b) green devices at 12 V.
In summary, a series of tetraphenylsilane-bridged carbazole-based host molecules, DiCzSi, tBuDiCzSi,
DiCzPhSi, and tBuDiCzPhSi, were synthesized and characterized. The high glass transition temperature (≥120
◦ C) and high triplet energy (>2.6 eV) host materials were used for blue and green PhOLEDs.
By using DiCzSi:FIrpic as the emissive layer (blue PhOLED, color coordinates (0.17, 0.36)), the highest
luminous and power efficiency values of 3.6 cd A−1 and 1.48 lm W−1 , respectively, were obtained. Among the
green PhOLEDs, the DiCzPhSi:Ir(ppy)3 -based device demonstrated the best performance, with a maximum
brightness of 4200 cd m−2 at 12 V and a maximum luminous efficiency of 7.8 cd A−1 at 8 V with the color
coordinates of (0.28, 0.62). The higher efficiencies for the devices with DiCzPhSi:Ir(ppy)3 and tBuDiCzPhSi:
Ir(ppy)3 emissive layers can be attributed to the good triplet energy level match between guest and host.
3. Experimental
3.1. Materials and instruments
Solvents were carefully dried and distilled from appropriate drying agents prior to use. All reactions were
performed under a dry nitrogen atmosphere. Commercially available reagents were supplied from Aldrich
and used without further purification. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)
was purchased from Ossila Company. Cesium carbonate (Cs2 CO3), 2,2′ ,2′′ -(1,3,5-benzinetriyl)-tris(1-phenyl-
1-H -benzimidazole) (TPBi), and fac-tris(2-phenylpyridine)iridium(III) [Ir(ppy)3 ] were provided by Aldrich.
Iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′ ]picolinate [FIrpic] was purchased from ADS Dyes. Tetra-
butyl ammonium hexafluorophosphate (TBAPF6) was purchased from Fluka. Indium tin oxide (ITO) glass
substrates with a sheet resistance of 9–15 Ω sq−1 were provided by LumTec.
1 H NMR and 13 C NMR spectra were measured on a Bruker 400 MHz spectrometer using tetramethylsi-
lane (TMS) as an internal standard. The infrared (IR) spectra were obtained by using a PerkinElmer Spectrum
BX-FTIR spectrophotometer. FAB-MASS measurements were carried out on a Finnigan MAT 95 mass spec-
trometer. UV-Vis, photoluminescence (PL), and phosphorescence emission spectra (77 K) were recorded by
using Lambda 950 UV-Vis-NIR and FLS920P spectrophotometers, respectively. Electrochemical studies were
carried out with a CH Instrument 660 B Model Electrochemical Workstation by using a three-electrode elec-
trochemical cell configuration consisting of a glassy carbon working electrode, Pt wire auxiliary electrode, and
a Ag wire reference electrode with ferrocene/ferrocenium (CP2 Fe/CP2 Fe+) as the internal standard, and 0.1
927

¨
ONER et al./Turk J Chem
M TBAPF6 in CHCl3 was used as the supporting electrolyte. Cyclic voltammograms were obtained at a scan
rate of 100 mV s−1 and the oxidation potentials (Eox) were determined from the onsets of the oxidation peaks.
Thermal properties of the materials were analyzed by the use of a PerkinElmer Pyris 6 DSC instrument.
The heating rate was 10 ◦ C min−1 and the nitrogen flow rate was 10 mL min−1 . Solution-processed coatings
were prepared using a Laurell WS-400B-6NPP-LITE spin coater. Film thicknesses were measured using an
Ambios XP-1 high-resolution surface profiler. Electron transport layer and metal depositions were performed
with a shadow mask using a vacuum evaporator attached to an MBRAUN 200B glovebox system. The
EL spectra and L–V–J curves were obtained using a Keithley 2400 source measurement unit and calibrated
Hamamatsu C9920-12 External Quantum Efficiency (EQE) measurement system.
3.2. Device fabrication and measurement
The OLEDs were fabricated in a structure of indium–tin oxide (ITO)/PEDOT:PSS (40 nm)/emissive layer
(80 nm)/TPBi (20 nm)/Cs2 CO3 (3 nm)/Al (200 nm). Prior to organic layer deposition, the ITO substrates
were cleaned with acetone and isopropanol ultrasonically for 15 min. For all devices, PEDOT:PSS was firstly
spin-coated onto ITO glass substrates as first layer and annealed in a vacuum oven at 120 ◦ C for 30 min to
form a 40-nm film. Following this, the materials for the emission layer were dissolved in chlorobenzene at
a stock density of 10 mg mL−1 (at various doping weight percentages, wt%) and were spin-coated onto the
PEDOT:PSS layer. A 20-nm-thick TPBi was vacuum-deposited on top of the EML at a deposition rate of 0.5
A s−1 . Finally, Cs2 CO3 (3 nm) and Al (200 nm) were deposited onto the emitting layer as cathode by thermal
˚
evaporation under a vacuum of 1 × 10−6 mbar. The emission areas of the devices were 6 mm2 .
Acknowledgments
¨
This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) (Project
˙
#: 113Z253). The authors would like to thank Dr Arma˘gan Kınal for productive discussions on the numerical
¨
˙
˙
calculations, which were performed at TUBITAK ULAKBIM, High Performance and Grid Computing Center
(TRUBA Resources).
˙
The authors are grateful to Prof Dr Sıddık I¸cli, who retired from Ege University Solar Energy Institute
(EU-SEI) in 2014 and made valuable contributions to the organic electronics research infrastructure of EU-SEI.
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929

A tetraphenylsilane group containing carbazoles as high triplet energy host materials for solution-
processable PhOLEDs
Saliha ÖNER, İlker ÖNER**, Haydar AKDAĞ, Canan VARLIKLI
Ege University, Solar Energy Institute, Bornova, İzmir, Turkey
Supplementary (S)
Synthesis:
Synthesis of 3,6-di-tert-butylcarbazole (2): Carbazole (5.01 g, 30 mmol) and AlCl3 (3.99 g, 30 mmol)
were weighed into a 250-mL 3-necked round-bottom flask. Dichloromethane (DCM, 100 mL) was added
to the flask and the solution was cooled to 0 °C with an ice-water bath. tert-Butyl chloride (t-BuCl, 66
mmol, 7.3 mL) was dissolved in DCM (20 mL) and added to the flask dropwise at 0 °C. The resultant
solution was left to stir at room temperature (RT) overnight. Next 100 g of cold water was added to the
reaction mixture and the organic phase was extracted. The water phase was washed with DCM (50 mL)
and the organic phases were combined and dried over MgSO4. After removal of the solvent, the residue
was purified by recrystallization from DCM/petroleum ether mixture and pale white solid was obtained.
Yield: 54%. IR (500–4000 cm–1, KBr pellet): 3415, 2958, 2903, 2864, 1493, 1471, 1392, 1363, 1300,
1
1264, 1250, 820, 617. H NMR (δH, ppm, 400 MHz, CDCl3): 8.07 (s, 2H, Ar); 7.66 (s, 1H, N–H); 7.47–
7.42 (d, J = 8.4 Hz, 2H, Ar); 7.25–7.22 (d, J = 8.8 Hz, 2H, Ar); 1.44 (s, 18H).
Synthesis of bis(4-bromophenyl)(diphenyl)silane (3): 1,4-dibromobenzene (12 mmol, 2.83 g) was
weighed into a 250-mL Schlenk and dissolved in THF (50 mL). The solution was cooled to –78 °C by
using a dry ice/acetone mixture. N-butyllithium (n-BuLi, 2.5 M in hexane, 14.40 mmol, 5.76 mL) was
added dropwise to the Schlenk using a syringe and the solution was stirred at –78 °C for 1 h. After that,
dichloro(diphenyl)silane (5 mmol, 1.05 mL) was added to the Schlenk dropwise and the resultant solution
was stirred at RT overnight. Water (50 mL) was added to the reaction mixture and the THF phase was
extracted. The water phase was washed with DCM (50 mL), and the organic phases collected and dried
over MgSO4. After the removal of the solvents, a white solid was obtained and purified by
recrystallization from the EtOH. Yield: 51%. IR (500–4000 cm–1, KBr pellet): 3065, 3024, 1567, 1549,
1
1477, 1428, 1376, 1301, 1183, 1111, 1062, 1008, 998, 809, 728, 711, 698, 537, 522, 512. H NMR (δH,
ppm, 400 MHz, CDCl3): 7.60–7.52 (m, 8H, Ar); 7.47–7.35 (m, 10H, Ar).
Synthesis of 9,9'-[(diphenylsilanediyl)bis(4,1-phenylene)]bis-9H-carbazole [DiCzSi]: Carbazole (4
mmol, 0.67 g), bis(4-bromophenyl)(diphenyl)silane (2) (2 mmol, 0.99 g), and K2CO3 (8 mmol, 1.10 g)
were weighed into a 50-mL 2-necked round-bottom flask equipped with a reflux condenser. Toluene (20
mL) was added to the reaction flask and degassed by argon for 20 min. Pd(OAc) (0.08 mmol, 18 mg) and
P(t-Bu)3 (0.32 mmol, 65 mg) were weighed in a glovebox and transferred to the reaction flask. The
1

resultant mixture was heated to 80 °C overnight. After cooling, EtOAc (20 mL) was added to the mixture
and the insoluble solid was removed by filtering. Solvents were removed by rotary evaporator and the
crude product was purified by column chromatography from the hexane/DCM (10/1) solvent system.
Yield: 38%. Mp: 290 °C. IR (500–4000 cm–1, KBr pellet): 3049, 3023, 1624, 1618, 1591, 1506, 1478,
1450, 1428, 1361, 1334, 1317, 1228, 1173, 1111, 1096, 1017, 999, 915, 826, 765, 748, 722, 700, 676,
1
525, 536, 520. H NMR (δH, ppm, 400 MHz, CDCl3): 8.19–8.16 (d, J = 8.4 Hz, 4H, Ar); 7.93–7.89 (d, J
= 8.4 Hz, 4H, Ar); 7.78–7.75 (d, J = 8.0 Hz, 4H, Ar); 7.70–7.67 (d, J = 8.4 Hz, 4H, Ar); 7.57–7.43 (m,
14H, Ar); 7.34–7.30 (t, J = 7.6 Hz, 4H, Ar). 13C NMR (δC, ppm, 400 MHz, CDCl3): 140.59; 139.26;
137.92; 136.45; 133.59; 133.20; 130.05; 128.21; 126.29; 125.97; 123.59; 120.34; 120.14; 109.91. MS
(+FAB) m/z: 666.3 (M+H).
Synthesis
of
9,9'-[(diphenylsilanediyl)bis(4,1-phenylene)]bis(3,6-di-tert-butyl-9H-carbazole)
[tBuDiCzSi]: 3,6-di-tert-butylcarbazole (1) (4 mmol, 1.12 g), bis(4-bromophenyl)(diphenyl)silane (2) (2
mmol, 0.99 g), and K2CO3 (8 mmol, 1.10 g) were weighed into a 25-mL 2-necked round-bottom flask
equipped with a reflux condenser. Toluene (20 mL) was added to the reaction flask and degassed by
argon for 20 min. Pd(OAc) (0.08 mmol, 18 mg) and P(t-Bu)3 (0.32 mmol, 65 mg) were weighed in a
glovebox and transferred to the reaction flask. The resultant mixture was heated to 80 °C overnight. After
cooling, EtOAc (20 mL) was added to the mixture and the insoluble solid was removed by filtering.
Solvents were removed by rotary evaporator and the crude product was purified by column
chromatography from the hexane/DCM (10/1) solvent system. Yield: 45%. Mp: 384 °C. IR (500–4000
cm–1, KBr pellet): 2958, 1592, 1488, 1470, 1363, 1324, 1292, 1262, 1232, 1179, 1111, 1077, 880, 840,
807, 739, 703, 537. 1H NMR (δH, ppm, 400 MHz, CDCl3): 8.26 (s, 4H, Ar); 7.99–7.95 (d, J = 7.6 Hz, 4H,
Ar); 7.86–7.82 (d, J = 8.0 Hz, 4H, Ar); 7.78–7.74 (d, J = 8.4 Hz, 4H, Ar); 7.62–7.54 (m, 14H, Ar); 1.57
(s, 36H). 13C NMR (δH, ppm, 400 MHz, CDCl3): 145.79; 143.22; 139.93; 139.11; 138.01; 136.63;
133.93; 132.70; 130.17; 128.36; 126.02; 123.81; 116.43; 109.59; 34.91; 32.21. MS (+FAB) m/z: 890.7
(M+H).
Synthesis of 9-(4-bromophenyl)-9H-carbazole (4): Carbazole (10 mmol, 1.67 g), 1-bromo-4-
iodobenzene (12 mmol, 3.40 g), Cu (10 mmol, 0.64 g), 18-Crown-6 (2 mmol, 0.53 g), and K2CO3 (20
mmol, 2.76 g) were weighed into a 100-mL 2-necked round-bottom flask equipped with a reflux
condenser. DMF (50 mL) was added to the reaction flask and the resultant mixture was heated to reflux
overnight. After cooling, 100 mL of cold water was poured onto the reaction mixture and a yellow
precipitate was obtained. The solid material was filtered under vacuum and the crude product was
purified by column chromatography from the hexane/DCM (10/1) solvent system. Yield: 62%. IR (500–
4000 cm–1, KBr pellet): 3040, 2927, 1596, 1584, 1497, 1479, 1453, 1363, 1335, 1316, 1231, 1181, 1121,
1
1100, 1067, 1009, 827, 750, 726, 709. H NMR (δH, ppm, 400 MHz, CDCl3): 8.18–8.15 (d, J = 8.4 Hz,
2H, Ar); 7.76–7.73 (d, J = 8.4 Hz, 2H, Ar); 7.50–7.30 (m, 8H, Ar).
Synthesis of 9-(4-bromophenyl)-3,6-di-tert-butyl-9H-carbazole (5): 3,6-di-tert-butylcarbazole (1) (6
mmol, 1.67 g), 1-bromo-4-iodobenzene (7.5 mmol, 2.12 g), Cu (10 mmol, 0.64 g), 18-Crown-6 (2 mmol,
0.53 g), and K2CO3 (20 mmol, 2.76 g) were weighed into a 100-mL 2-necked round-bottom flask
equipped with a reflux condenser. DMF (50 mL) was added to the reaction flask and the resultant mixture
2

was heated to reflux overnight. After cooling, 100 mL of cold water was poured onto the reaction mixture
and a yellow precipitate was formed. The solid material was filtered under vacuum and the crude product
was purified by column chromatography from the hexane/DCM (10/1) solvent system. Yield: 62%. IR
(500–4000 cm–1, KBr pellet): 3040, 2927, 1596, 1584, 1497, 1479, 1453, 1363, 1335, 1316, 1231, 1181,
1
1121, 1100, 1067, 1009, 827, 750, 726, 709. H NMR (δH, ppm, 400 MHz, CDCl3): 8.17 (s, 2H, Ar);
7.91–7.89 (d, J = 8.4 Hz, 2H, Ar); 7.70–7.68 (d, J = 8.4 Hz, 2H, Ar); 7.52–7.44 (m, 4H, Ar); 1.49 (s,
18H).
Synthesis of [4-(9H-carbazol-9-yl)phenyl]boronic acid (6): 9-(4-bromophenyl)-3,6-di-tert-butyl-9H-
carbazole (5) (1 mmol, 0.32 g) was added to a 50-mL 2-necked round-bottom flask and dissolved in THF
(20 mL). The solution was cooled to –78 °C by using dry ice/acetone mixture. After cooling, n-BuLi (2.5
M in hexane, 5 mmol, 2 mL) was added to the flask dropwise and the solution was stirred at –78 °C for 1
h. Trimethylborate (5 mmol, 0.56 mL) was added to the flask dropwise and the resultant solution was
stirred at RT overnight. Then 50 mL of cold water was added to the reaction mixture and the THF phase
was separated. The water phase was washed with DCM (50 mL), and the organic phases collected and
dried over MgSO4. After removal of the solvents, a white solid was precipitated from the hexane/EtOAc
mixture. Yield: 44%. IR (500–4000 cm–1, KBr pellet): 3212, 1604, 1559, 1479, 1451, 1412, 1353, 1221,
1196, 1169, 1109, 1016, 741, 719, 692.
Synthesis of [4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl]boronic acid (7): 9-(4-bromophenyl)-3,6-
di-tert-butyl-9H-carbazole (7) (4 mmol, 1.74 g) was added to a 100-mL 2-necked round-bottom flask and
dissolved in THF (50 mL). The solution was cooled to –78 °C by using dry ice/acetone mixture. After
cooling, n-BuLi (2.5 M in hexane, 6 mmol, 2.40 mL) was added to the flask dropwise and the solution
was stirred at –78 °C for 1 h. Trimethylborate (8 mmol, 0.89 mL) was added to the flask dropwise and the
resultant solution was stirred at RT overnight. Then 50 mL of cold water was added to the reaction
mixture and the THF phase was separated. The water phase was washed with DCM (50 mL), and the
organic phases collected and dried over MgSO4. After removal of the solvents, a white solid was
precipitated from the hexane. Yield: 48%. IR (500–4000 cm–1, KBr pellet): 2960, 2904, 2866, 1602,
1560, 1489, 1473, 1420, 1406, 1345, 1324, 1297, 1262, 1232, 1175, 1106, 1083, 878, 842, 812, 752, 741,
708, 692.
Synthesis of 9,9'-[(diphenylsilanediyl)bis(biphenyl-4',4-diyl)]bis-9H-carbazole [DiCzPhSi]: [4-(9H-
carbazol-9-yl)phenyl]boronic acid (6) (1 mmol, 0.29 g), bis(4-bromophenyl)(diphenyl)silane (2) (0.4
mmol, 0.2 g), Cs2CO3 (2 mmol, 0.65 g), and Pd(dppf)Cl2 (0.08 mmol, 65 mg) were weighed in a 25-mL
2-necked round-bottom flask equipped with a reflux condenser. Toluene/MeOH (10/5 mL) solvent
mixture was added to the reaction flask and argon gas was bubbled through the solution for about 20 min.
The resultant solution was heated to 80 °C overnight. After cooling, EtOAc (20 mL) was added to the
mixture and the insoluble solid was removed by filtering. Solvents were removed by rotary evaporator
and the crude product was purified by column chromatography from the hexane/DCM (10/1) solvent
system. Yield: 42%. Mp: 285 °C. IR (500–4000 cm–1, KBr pellet): 3035, 1597, 1521, 1493, 1451, 1426,
1
1364, 1334, 1315, 1228, 1184, 1110, 1004, 816, 752, 723, 712, 626, 559, 531, 521. H NMR (δH, ppm,
400 MHz, CDCl3): 8.19–8.15 (d, J = 8.0 Hz, 4H, Ar); 7.88–7.85 (d, J = 8.4 Hz, 4H, Ar); 7.80–7.74 (m,
3

8H, Ar); 7.72–7.65 (m, 8H, Ar); 7.52–7.42 (m, 14H, Ar); 7.34–7.30 (t, J = 6.8 Hz, 4H, Ar). 13C NMR
(δH, ppm, 400 MHz, CDCl3): 141.36; 140.84; 139.91; 137.17; 137.06; 136.44; 134.03; 133.47; 129.80;
128.51; 128.03; 127.37; 126.60; 125.97; 123.47; 120.32; 120.01; 109.83. MS (+FAB) m/z: 818.4 (M+H).
Synthesis of 9,9'-[(diphenylsilanediyl)bis(biphenyl-4',4-diyl)]bis(3,6-di-tert-butyl-9H-carbazole)
[tBuDiCzPhSi]: [4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl]boronic acid (8) (1 mmol, 0.4 g), bis(4-
bromophenyl)(diphenyl)silane (2) (0.4 mmol, 0.2 g), Cs2CO3 (2 mmol, 0.65 g), and Pd(dppf)Cl2 (0.08
mmol, 65 mg) were weighed in a 25-mL 2-necked round-bottom flask equipped with a reflux condenser.
Toluene/MeOH (10/5 mL) solvent mixture was added to the reaction flask and argon gas was bubbled
through the solution for about 20 min. The resultant solution was heated to 80 °C overnight. After
cooling, EtOAc (20 mL) was added to the mixture and the insoluble solid was removed by filtering.
Solvents were removed by rotary evaporator and the crude product was purified by column
chromatography from the hexane/DCM (10/1) solvent system. Yield: 56%. Mp: na. IR (500–4000 cm–1,
KBr pellet): 3042, 2952, 2907, 2862, 1603, 1522, 1491, 1473, 1364, 1324, 1294, 1261, 1233, 1190, 1111,
1
1004, 879, 810, 769, 725, 699, 611, 530, 511. H NMR (δH, ppm, 400 MHz, CDCl3): 8.18 (s, 4H, Ar);
7.87–7.84 (d, J = 8.4 Hz, 4H, Ar); 7.81–7.75 (m, 8H, Ar); 7.74–7.71 (m, 4H, Ar); 7.69–7.65 (m, 4H, Ar);
7.54–7.43 (m, 14H, Ar); 1.50 (s, 36H). 13C NMR (δH, ppm, 400 MHz, CDCl3): 142.96; 141.45; 139.36;
139.20; 137.70; 137.06; 136.46; 134.10; 133.35; 129.79; 128.39; 128.03; 126.96; 126.57; 123.63; 123.48;
116.25; 109.29; 34.74; 32.03. MS (+FAB) m/z: 1043.6 (M+H).
4

1H NMR and 13C NMR Spectra
Figure S1. 1H NMR spectrum of 3,6-di-tert-butylcarbazole (2).
Figure S2. 1H NMR spectrum of bis(4-bromophenyl)(diphenyl)silane (3).
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Figure S3. 1H NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(4,1-phenylene)]bis-9H-carbazole [DiCzSi].
Figure S4. 13C NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(4,1-phenylene)]bis-9H-carbazole
[DiCzSi].
6

Figure S5. 1H NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(4,1-phenylene)]bis(3,6-di-tert-butyl-9H-
carbazole) [tBuDiCzSi].
Figure S6. 13C NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(4,1-phenylene)]bis(3,6-di-tert-butyl-9H-
carbazole) [tBuDiCzSi].
7

Figure S7. 1H NMR spectrum of 9-(4-bromophenyl)-9H-carbazole (4).
Figure S8. 1H NMR spectrum of 9-(4-bromophenyl)-3,6-di-tert-butyl-9H-carbazole (5).
8

Figure S9. 1H NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(biphenyl-4',4-diyl)]bis-9H-carbazole
[DiCzPhSi].
Figure S10. 13C NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(biphenyl-4',4-diyl)]bis-9H-carbazole
[DiCzPhSi].
9

Figure S11. 1H NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(biphenyl-4',4-diyl)]bis(3,6-di-tert-butyl-
9H-carbazole) [tBuDiCzPhSi].
Figure S12. 13C NMR spectrum of 9,9'-[(diphenylsilanediyl)bis(biphenyl-4',4-diyl)]bis(3,6-di-tert-butyl-
9H-carbazole) [tBuDiCzPhSi].
10

Electrochemical stability
-2.0
-1.6
-1.2
-0.8
-0.4
0.0
tBuDiCzSi
DiCzSi
a)
b)
-1.6
-1.2
-0.8
-0.4
0.0
0.4
0.8
1.2
0.4
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Potential / V
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Potential / V
-0.8
tBuDiCzPhSi
-1.6
d)
DiCzPhSi
c)
-0.6
-0.4
-0.2
0.0
-1.2
-0.8
-0.4
0.0
0.2
0.4
0.6
0.4
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Potential / V
1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
Potential / V
Figure S13. Consecutive cyclic voltammograms (20 cycles) of the synthesized materials, a) DiCzSi,
b) tBuDiCzSi, c) DiCzPhSi, and d) tBuDiCzPhSi measured in CHCl3.
11