Increasing electron transporting properties and horizontal molecular orientation: Via meta -position of nitrogen for (A)n-D-(A)n structured terpyridine electron-transporting material

Article abstract of DOI:10.1039/c9tc03787j

The electron-transporting materials (ETMs) with excellent electron injection (EI) and electron transporting properties are prerequisites for highly efficient organic light-emitting diodes (OLEDs). In this work, we report a novel ETM, 2,7-di([3,2′:6′,3′′-terpyridin]-4′-yl)-9,9′-spirobifluorene (27-mTPSF), which is synthesized by combining electron-withdrawing terpyridine (TPY) moieties with rigid twisted spirobifluorene. This rigid twisted structure helps to maintain the morphological stability of the amorphous film and contributes to the enhancement of the device lifetime. The nitrogen atom at the meta-position on the peripheral pyridine in 27-mTPSF can enhance the horizontal molecular orientation and the electron-transporting property. A green phosphorescent OLED (PhOLED) based on tris[2-(p-tolyl)pyridine]iridium(iii) (Ir(mppy)₃) as the emitter and 27-mTPSF as ETM displayed a maximum external quantum efficiency (EQE) of 23.1%, and a half-life (T₅₀) of 77, 4330 and 243495 h at an initial luminance of 10000, 1000 and 100 cd m^-2, respectively, which are significantly superior to those of the device based on the conventional ETM 1,3,5-tris(N-phenylbenzimid azol-2-yl-benzene (TPBi). These results indicate a potential application for the (A)_n-D-(A)_n structured terpyridine ETMs.

Full text of DOI:10.1039/c9tc03787j

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Materials for optical, magnetic and electronic devices
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Nosang V. Myung, Yong-Ho Choa et al.
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Page 1 of 8
J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
View Article Online
DOI: 10.1039/C9TC03787J
ARTICLE
To Increase Electron Transporting Properties and horizontal
molecular orientation via a Meta-Position of Nitrogen for “(A)n–
D–(A)n” Structured Terpyridine Electron-Transporting Material†
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
b
c
c
a
Xuan Guo, Mengying Bian, Fang Lv, Yuanxun Wang, Zifeng Zhao, Zuqiang Bian, Bo Qu, Lixin
*a
*a
DOI: 10.1039/x0xx00000x
Xiao and Zhijian Chen
The electron-transporting materials (ETM) with excellent electron injection (EI) and electron transporting properties are
prerequisites for highly efficient organic light-emitting diodes (OLEDs). In this work, we report a novel ETM, 2,7-di([3,2':6',3''-
terpyridin]-4'-yl)-9,9'-spirobifluorene (27-mTPSF), which is synthesized by combining electron-withdrawing terpyridine (TPY)
moieties with rigid twisted spirobifluorene. This rigid twisted structure helps to maintain the morphological stability of
amorphous film and contributes to the enhancement of the device lifetime. The nitrogen atom at the meta-position on the
peripheral pyridine in 27-mTPSF can enhance the horizontal molecular orientation and the electron-transporting property.
A green phosphorescent OLED (PhOLED) based on tris[2-(p-tolyl)pyridine]iridium(III) (Ir(mppy)
3
) as the emitter and 27-
mTPSF as ETM displayed a maximum external quantum efficiency (EQE) of 23.1%, and a half-life (T50) of 77, 4330 and 243
-2
4
95 h at an initial luminance of 10 000, 1000 and 100 cd m , which are significantly superior to those of the device based
on the conventional ETM 1,3,5-tris(N-phenylbenzimid azol-2-yl-benzene (TPBi). These results indicate a potential application
for the “(A)n–D–(A)n” structured terpyridine ETMs.
deposition process, further influencing the electron-
1
4, 15
Introduction
transporting properties of ETM in the film state.
Based on our previous works, the nitrogen atom on the
peripheral pyridine in 27-TPSF was changed from ortho to meta
position, synthesizing the ETM of 27-mTPSF which used
Organic light-emitting diodes (OLEDs) have attracted extensive
interests of the researchers’ due to the wide applications in the
new field of solid-state lighting sources and flexible display
devices.1 In order to achieve highly efficient OLEDs, developing
excellent electron-transporting materials plays an important
3
,2':6',3''-TPY. The analysis of spectroscopic ellipsometry
-4
confirmed that the 3,2':6',3''-TPY resulted in better horizontal
orientation than 2,2':6',2''-TPY, leading to higher electron-
transporting ability of 27-mTPSF. The electron mobility of 27-
mTPSF is nearly three times higher than that of 27-TPSF. A green
PhOLED based on 27-mTPSF achieved a maximum EQE of 23.1%,
and a T50 of 77, 4330, and 243 495 h at an initial luminance of
5
-7
role. Because of the strong electron-withdrawing property,
terpyridine (TPY) has been recognized as a useful tridentate
ligand for ETM.8
,
9
The spirobifluorene with rigid twisted
structure can guarantee a high triplet energy (E ) and a high
glass transition temperature (T ), which is beneficial to
maintaining the morphological stability.
a long-lived ETM with a “(Acceptor) -Donor-(Acceptor)
D-(A) ”) structure, 2,7-di([2,2':6',2''-terpyridin]-4'-yl)-9,9'-
spirobifluorene (27-TPSF), by combining two TPY moieties and
T
g
-2
1
0 000, 1000, and 100 cd m , revealing superior performance
1
0, 11
We have reported
n
“ (“(A) -
over the conventional ETM TPBi.
n
n
n
Results and Discussions
Synthesis and Characterization
1
2
a spirobifluorene moiety (Figure S1). Kido et al. recently
reported that the nitrogen atom in the pyridine could form
inter- and intramolecular CH···N weak hydrogen bond (H-bond)
network with the surrounding hydrogen atoms. Therefore the
position of the nitrogen atom on the peripheral pyridine in TPY
could greatly affect the horizontal orientation of ETM during
The synthesis procedure of 27-mTPSF is shown in Scheme 1. TPY
was linked to spirobifluorene through Suzuki coupling reaction
by Pd catalysts, the same as our pervious report. 27-mTPSF
was sublimated before use, and characterized by H NMR,
1
3
12
1
13
C
NMR, electrospray ionization mass spectroscopy (ESI-MS),
elemental analysis and single-crystal analysis (as shown in
supporting information).
a. State Key Laboratory for Mesoscopic Physics and Department of Physics, Peking
University, Beijing 100871, People’s Republic of China
b.
Valiant Corporation, Shandong 264006, P. R. China
c.
Beijing National Laboratory for Molecular Sciences, State Key Laboratory of Rare
Earth Materials Chemistry and Applications, College of Chemistry and Molecular
Engineering, Peking University, Beijing 100871, P. R. China
†
Electronic Supplementary Information (ESI) available. CCDC 1907643. For ESI and
crystallographic data in CIF or other electronic format see DOI: 10.1039/x0xx00000x
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DOI: 10.1039/C9TC03787J
Scheme 1. The synthesis process of the 27-mTPSF.
Photophysical Properties
Theoretical Calculations and Electrochemical Properties
The room-temperature UV/vis absorption and fluorescence The theoretical calculations were carried out by Gaussian 09
-5
3
spectra of 27-mTPSF in chloroform (CHCl ) (10 M) and film software with the 6-31G(d,p) basis set to obtain the energies,
state are shown in Figure 1. In solution, the absorption of 27- and orbital distributions of the highest occupied molecular
mTPSF showed three different peaks at 297 nm, 309 nm and orbital (HOMO) and the lowest unoccupied molecular orbital
3
38 nm. The two peaks of 297 nm and 309 nm were caused by (LUMO) levels. As shown in Figure 2a, the HOMO of 27-mTPSF
1
6
the π–π* transition of the fluorene units in spirobifluorene.
was mainly located at the electron-rich spirobifluorene moiety.
The peak of 338nm was attributed to the electronic coupling Nevertheless, the LUMO was extended to the TPY, leading to
1
0, 17
between the spirobifluorene and the two TPY components.
high electron mobility. The calculated HOMO and LUMO
Since the twisted structure of spirobifluorene inhibited the energies of 27-mTPSF were -5.9 and -2.0 eV, respectively. The
formation of π–π stacking of 27-mTPSF, the absorption of 27- total self-consistent field density for 27-mTPSF (as shown in
mTPSF film exhibited a small red shift, which shift to 300 nm, Figure 2b) was calculated using the electrostatic potential (ESP)
2
2
3
13 nm, and 343 nm, respectively. The onset of the absorption method and indicated that the negative charge accumulated
spectra of 27-mTPSF was about 379 nm, which amounted to an around nitrogen atoms in the heteroaromatic ring, which
optical band gap (Eop) of 3.3 eV. The photoluminescence (PL) promoted the interaction between nitrogen and lithium, when
peaks were measured at 376 nm, 394 nm in solution and red using LiF as an electron injecting material, thereby effectively
2
3
shift to be 390 nm, 408 nm in film due to the π-conjugation increased the electron injection (EI). The spin density
extension.1
2
8, 19
The phosphorescence spectrum of 27-mTPSF in distribution (SDD) of the first triplet state of 27-mTPSF was also
-5
1
-methyl-tetrahydrofuran (10 M) was measured at 77 K. The calculated (Figure 2c), which showed that the T state was
highest energy peak of this emission was located at 511 nm, localized over the spirobifluorene and extended to the core
then the triplet energy of 27-mTPSF was calculated to be
2
0, 21
approximately 2.42 eV (Table 1),
the emitter of Ir(mppy) (T = 2.4 eV).
a little higher than that of
3
1
(
a)
b)
HOMO
LUMO
(
(c)
SCF
SDD of T
1
(d)
Figure 2. a) The HOMO and the LUMO distributions of 27-mTPSF. b) The isosurface of 27-
mTPSF ESP. c) The distribution of the triplet density. d) The CV curves for 27-mTPSF at a
scan rate of 100 mV s-1 (inset: multiple CV of 27-mTPSF in DMSO with 10 cycles).
Figure 1. Absorption, fluorescence, and phosphorescence spectra of 27-mTPSF
2
| J. Name., 2012, 00, 1-3
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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ARTICLE
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DOI: 10.1039/C9TC03787J
Table 1. Physical properties of 27-mTPSF.
a)
b)
a)
b)
c)
d)
c)
d)
Material
λ
abs [nm]
λ
abs [nm]
λ
PL [nm]
λ
PL [nm]
T
g
[℃]
HOMO /HOMO [eV]
LUMO /LUMO [eV]
E
T
[eV]
2
7-mTPSF
279,309,338
300,313,343
376,394
390,408
186
-6.0/-6.0
-2.7/-2.5
2.42
a)Measured in CHCl
; b)Measured in neat film; c)Measured using photoelectron spectrometer (Riken AC-2), LUMOc) = HOMOc) + E ; d)Measured using CV
g
3
g
pyridine. However, SDD did not extend to the peripheral transition temperature (T ) is 186 °C (as shown in Figure S3),
pyridine, indicating that the quenching of the excitons occurred which was higher than those commonly used electron transport
5
through the Dexter transfer mechanism could be effectively materials such as TPBi (T
reduced.24
To further confirmed the HOMO and LUMO energy levels of structure.
7-mTPSF, the cyclic voltammetry (CV) measurement was The surface morphology of the 27-mTPSF film obtained by
g
= 124 °C). High T
g
was due to the fact
that the 27-mTPSF had a spirobifluorene with a rigid and twisted
2
adopted, as shown in Figure 2e. The HOMO and LUMO energy thermal evaporation was measured by atomic force microscopy
levels were obtained by comparing the onset potentials for (AFM) with tapping mode. The surface roughness of 50 nm-thick
reduction and oxidation of 27-mTPSF in solution with ferrocene film deposited on silica glass exhibited a root-mean-square
2
5
(
4.8 eV below vacuum). The HOMO energy level of 27-mTPSF roughness (Rrms) of only 0.466 nm (as shown in Figure 3). The
was determined to be -6.0 eV with an empirical formula (EHOMO smooth surface morphology was derived from the inhibition of
2
6
=
- (Eox – EFc/Fc+) eV + (-4.8) eV) , and the LUMO energy level was molecule aggregation due to rigid twisted structure of
figured to be -2.5 eV with the formula (ELUMO = - (Ere – EFc/Fc+) eV spirobifluorene.
(-4.8) eV). Meanwhile, the HOMO energy level of 27-mTPSF in
film state was measured by Riken AC-2 to be -6.0 eV, consistent Electron Transport Property and Molecular Orientation
+
g
with the measurement result of CV. But combined with E , the
In order to study the electron-transporting property of 27-
mTPSF, electron-dominant devices with structure of ITO/BCP
LUMO of 27-mTPSF was calculated to be -2.7 eV, slightly deeper
than the result of CV, which was caused by differences between
solution and film state. During the reduction measurement
repeated 10 times (inset of Figure 2e), the reduction peak of 27-
mTPSF did not show an evident shift, indicating that its anion
unities had excellent stability, which was a prerequisite for a
stable OLED device during operation.
(10 nm)/27-mTPSF or 27-TPSF or TPBi (30 nm)/LiF/Al were
fabricated. Figure 4a shows that the current density of the 27-
mTPSF based device was higher than that of the 27-TPSF and
TPBi based devices at the same voltage. This may be due to the
nitrogen atom on the peripheral pyridine in the 27-mTPSF in the
meta-position, which could form weak intermolecular H-bonds
compared to the nitrogen atom in the ortho-position in 27-
Thermal Properties and Film Morphology
The thermal properties of 27-mTPSF were studied under a
nitrogen atmosphere. The result of thermogravimetric analysis
(
d
TGA) indicated decomposition temperature (T ) of 27-mTPSF
(a)
as high as 475 °C (as shown in Figure S2). The measurement of
the differential scanning calorimetry (DSC) showed that glass-
(b)
Figure 4. a) Current density-voltage characteristics of electron-dominant devices:
ITO/BCP (10 nm)/27-mTPSF or 27-TPSF or TPBi (30 nm)/LiF/Al. b) (Color online) ordinary
Figure 3. 3D topography image and Rrms value of 50 nm thick film of 27-mTPF on silica
and extraordinary refractive indices (n
and extinction coefficients (k and k , blue solid and dashed lines, respectively) of 27-
TPSF and 27-mTPSF determined by VASE.
o e
and n , red solid and dashed lines, respectively)
glass.
o
e
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Page 4 of 8
ARTICLE
Journal Name
TPSF, thereby enhancing the horizontal molecular orientation the device based on Ir complexes.31 The thickness of each layer
View Article Online
1
3, 14
DOI: 10.1039/C9TC03787J
was adjusted and the optimal device structures are listed as
and the electron-transporting property.
The horizontal molecular orientation was confirmed by the follows (Figure. 5)
measurement of variable angle spectroscopic ellipsometry
Device A: ITO/HAT-CN (2 nm)/NPB (60 nm)/TCTA (5 nm)/
(7 wt%, 20 nm)/TPBi (45 nm)/LiF/Al
Device B: ITO/HAT-CN (2 nm)/NPB (40 nm)/TCTA (5nm)/
) of the 27-TPSF and 27-mTPSF were DIC-TRZ: Ir(mppy) (7 wt%, 20 nm)/27-mTPSF(65 nm)/LiF/Al
determined using the uniaxial anisotropic model, as shown in Device C: ITO/HAT-CN (2 nm)/TAPC (60 nm)/TCTA (5nm)/
Figure 4b. The difference between k and k indicated a DIC-TRZ: Ir(mppy) (7 wt%, 20 nm)/27-mTPSF(55 nm)/LiF/Al
VASE).2
7-29
The ordinary (horizontal) and extraordinary DIC-TRZ: Ir(mppy)
and n ) and extinction
(
(
3
vertical) refractive indices (n
and k
o
e
coefficients (k
o
e
3
o
e
3
significant dipole orientation in the horizontal direction. We where HAT-CN is dipyrazino[2,3-f:2’’,3’’-h]quinoxaline-
quantified the anisotropy of the film by the ensemble average 2,3,6,7,10,11-hexacarbonitrile as the hole injection layer, NPB is
3
0
of the orientation angle of the dipole moments,
4,4’-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl, TAPC is 1,1-
bis[4-[N,N-di(p-tolyl)-amino]phenyl]-cyclohexane, TCTA is
tris(4-(9H-carbazol-9-yl)phenyl)-amine as the hole transporting
layer and DIC-TRZ is 2,4-diphenyl-6-bis(12-phenylindolo)[2,3-a]-
carbazole-11-yl)-1,3,5-triazine as the host material. A 20nm
푚푎푥
푚푎푥
2
푘
푒
― 푘
표
1
2
<
cos 휃 > =
+
(1)
푚푎푥
+ 2푘 푚표 푎푥
3
3
푘
푒
where <···> is the ensemble average, θ is the angle between the
molecular long axis and the direction perpendicular to the
are the extraordinary and
ordinary extinction coefficients at the peak wavelength,
respectively. As a result, 27-mTPSF exhibits a < cos 휃 > value
of 0.08, which is smaller than that of 27-TPSF ( < cos 휃 > =
.12). These results indicated that the 27-mTPSF molecule in
film state had more horizontal orientation compared to 27-
TPSF, which was beneficial to increasing the electron mobility of
ETMs.
푚푎푥
푚푎푥
layer of emitting material (EM) consisted of Ir(mppy) (7 wt%),
3
substrate surface, and 푘
and 푘
푒
표
codeposited with the TADF host material DIC-TRZ. TPBi and 27-
mTPSF were used as electron transporting material.
2
2
As shown in Figure 6 and Table 2, the turn-on voltage (at 1
-2
cd m ) of device B was 2.3 V, which was significantly lower than
that of device A (3 V). And the PE, max of device B was 88.0 lm
0
-1
W , which was much higher than that of device A (55.0 lm
-1
W ). Meanwhile, the current density of device B was also
greater than that of device A, which verified that the electron
injection and electron-transporting properties of 27-mTPSF
Device Performance
The OLEDs were fabricated using 27-mTPSF, 27-TPSF and TPBi
as an ETM respectively. Ir complexes was selected as the
(a)
(b)
(c)
(d)
(e)
(f)
Figure 6. a) Current density-voltage and luminance-voltage, b) power efficiency-
luminance, c) current efficiency-luminance, d) external quantum efficiency- luminance
curves of Device A, Device B and Device C, and e) The lifetimes of devices measured at
-2
an initial luminance of 10 000 cd m , f) electroluminescence (EL) spectra obtained from
Figure 5. Chemical structures, and energy diagram of materials.
Device A, Device B and Device C.
phosphorescent emitter on account of high EQE exhibited by
4
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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DOI: 10.1039/C9TC03787J
ARTICLE
Table 2. List of device performances
a)
CE, max/1000/10 000 [cd A-1]
b)
PE, max/1000/10 000 [lm W-1]
b)
b)
c)
V
on [V]



ext, max/1000/10 000 [%]
CIE (x,y)
A
B
C
3.0
2.3
2.5
63.5/63.0/56.0
68.2/66.8/53.2
80.7/80.7/55.2
55.0/29.9/17.7
88.0/70.0/24.6
94.9/70.4/17.8
18.3/18.3/16.1
20.4/19.4/15.3
23.1/23.1/15.8
(0.31, 0.62)
(0.32, 0.62)
(0.31, 0.62)
a)At 1 cd m-2; b)Maximum, at 1000 cd m , at 10 000 cd m ; c)At 100 cd m-2.
-2
-2
were superior to those of TPBi. The Von of device B was also
lower than the gap of Ir(mppy) . This kind of sub-gap
3
Conclusions
luminescence may be due to Auger-type electroluminescence
In summary, we had synthesized an electron-transporting
material by combining a rigid twisted spirobifluorene with
electron-withdrawing TPY moieties. The VASE analyses
demonstrated that the nitrogen atom on the peripheral
up-conversion.3
2, 33
Moreover, device B achieved a maximum
-1
current efficiency (CE, max) of 68.2 cd A and ext, max of 20.4%,
which was higher than those of device A with aCE, max of 63.5
-1
cd A and ext, max of 18.3%. However, it is worth noting that
device B showed a stronger roll-off of CE and ext with
pyridine of the 27-mTPSF in the meta-position was helpful to
enhance the horizontal molecular orientation, which could
increase the electron-transporting property. Green PhOLEDs
with 27-mTPSF as ETM were fabricated, which exhibited a Von
of 2.3 V and an ext, max of 23.1%. Under constant current
-2
brightness increased up to 10 000 cd m compared to those of
device A. One of the dominant mechanisms for this efficiency
roll-off at high brightness in phosphorescent emitter systems
3
4
was charge carrier imbalance. In order to confirm the exciton
confinement ability of 27-mTPSF, the exciton lifetimes of the
-2
operation at an initial luminescence of 10 000 cd m , the T50 of
Ir(mppy)
Ir(mppy)
3
in the DIC-TRZ: Ir(mppy)
(8 wt%, 30nm)/27-mTPSF(50nm) films had been
3
(8 wt%, 30nm) and DIC-TRZ:
7
1
7 h was achieved with 27-mTPSF, corresponding to 4330 h at
000 cd m and 243 495 h at 100 cd m . The results were better
3
-2
-2
measured as shown in Figure S5. No obvious exciton quenching
was observed in the decay curve, demonstrating the relatively
good exciton confinement ability of 27-mTPSF. Furthermore, as
than those of the commonly used ETM (TPBi) based device,
which indicated that 27-mTPSF possesses superior electron
injection and electron-transporting properties, and could be a
potential ETM.
2
shown in Figure 6e, at an initial luminance of 10 000 cd m , 27-
mTPSF based device exhibited a lifetime T50 of 77 h, which is
higher than that of 45 h achieved by TPBi based device,
indicating long-term stability of 27-mTPSF. By adopting a
degradation acceleration factor that relates luminance to Experimental
3
5
lifetime, viz
General
H NMR and 13C NMR spectra were measured on Bruker 500
The
푛
1
0 000 푐푑 푚―2
000 푐푑 푚―2
1000 푐푑 푚―2) = 푇50
10 000 푐푑 푚―2
1
푇
50
(
(
)
×
(2)
[
]
1
MHz NMR spectrometer. ESI-MS in positive ion mode was
recorded on a Bruker Solarix XR Fourier Transform Ion Cyclotron
Resonance Mass Spectrometer. Elemental analyse was
performed on a VARIO elemental analyzer from Elementar
Analysensysteme GmbH. Under nitrogen atmosphere at a
With n = 1.75, the speculated lifetimes are 4330 h at an initial
-
2
-2
luminance of 1000 cd m (243 495 h at 100 cd m ).
In order to further obtain the carrier balance in the device,
we replaced the hole-transporting material from NPB to TAPC
to fabricate device C. Despite a slight increase in the turn-on
voltage of device C, the CE, max, PE, max and ext, max were
significantly increased. As shown in Figure 6, device C showed a
maximum CE of 80.7 cd A , a maximum PE of 94.9 lm W and a
maximum EQE of 23.1%. An EQE of more than 20% indicated
that the balance of electron and hole injection was achieved in
device C at a low current. But unfortunately, the same as device
B, the roll-off ofCE and ext were severe at high brightness. The
cause of this phenomenon required further research.
−1
heating rate of 10 °C min , DSC was measured on a Perkin-
Elmer Diamond DSC Pyris instrument while TGA was recorded
on a SEIKO EXSTAR 6000 TG/DTA 6200 unit. UV–vis absorption
spectra were performed on a Perkin-Elmer Lambda 35
spectrometer. Emission spectra were measured by using Hitachi
F7000 fluorescence spectrophotometer. CV was measured
-1
-1
using
a
CHI600C
voltammetric
analyzer
with
tetrabutylammonium hexafluorophosphate (TBAPF
6
, 0.1 M) as
the supporting electrolyte and ferrocene as an internal
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
Page 6 of 8
ARTICLE
standard, in a nitrogen-purged dichloromethane (CH
Journal Name
2
Cl
2
) or C, 84.81; H, 4.40; N, 10.79. Found: C, 84.15; H, 4.43; N, 10.75.
View Article Online
DOI: 10.1039/C9TC03787J
DMSO solution at room temperature. A platinum working Melting point: 388 ℃.
electrode, a platinum wire auxiliary electrode, and a Ag/AgCl
wire pseudo reference electrode make up the conventional Device Fabrication
three electrodes. HOMO level in film state was estimated by The indium-tin-oxide (ITO) patterned anode with a sheet
using atmospheric ultraviolet photoelectron spectroscopy resistance of 14Ω- was commercially available. Before the
1
(Rikken Keiki AC-2). The surface roughness of the film was deposition of organic layers, the ITO substrate was cleaned with
measured on a conductive atomic force microscope (CAFM, deionized water, acetone, and ethanol in sequence,
SEIKO SPA300HV). The VASE measurement was performed on a successively. The organic and cathode layers were evaporated
spectroscopic ellipsometer (UVISEL, Horiba). The current in different chambers, the base pressure of which is lower than
−5
2
density, voltage, and luminance characteristics of OLEDs were 8 × 10 Pa. The active area for all devices was 4 mm . The
obtained by using absolute ηext measurement system (C9920- organic and Al layers were thermally evaporated at a rate of
−1
−1
1
2, Hamamatsu Photonics) with the photonic multichannel 0.1–0.2 nm s , while that of LiF layer was 0.01 nm s .
analyzer (PMA-12, Hamamatsu Photonics) and a computer
controlled Keithley 2400 Sourcemeter unit with a calibrated
silicon diode.
Conflicts of interest
There are no conflicts to declare.
Materials
3
HAT-CN, TAPC, NPB, TCTA, DIC-TRZ, Ir(mppy) , and TPBi were
commercially available and used without further purification.
Acknowledgements
This work was supported by the National Key Basic Research
and Development Program of China (No. 2016YFB0401000) and
the National Natural Science Foundation of China (11574009,
U1605244, 61575005, 11574013, 61775004, 11527901).
Sythesis and Characterization
Synthesis of 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)-9,9’-spirobifluorene(1):
30.0 mmol), bis(pinacolato)diboron (90.0 mmol), KOAc (120.0
mmol) and Pd(PPh (0.3 mmol) were mixed in a flask
2,7-dibromo-9,9’-spirobifluorene
(
3 4
)
containing nitrogen-saturated 1,4-dioxane (300 mL). The
resulting mixture was heated to 90-95 ℃ and reacted for 5.0 h.
Then 200 mL cold water was added into the solvent for eluting
to give a gray solid mixture after cooling to room temperature.
The residue was purified by column chromatography using
petroleum ether as the eluent, and the isolate was recrystallized
from THF:petroleum ether (1:5) to give white pure solid.
Synthesis of 27-mTPSF: Compund (1) (2.20 mmol), 4’-bromo-
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This journal is © The Royal Society of Chemistry 20xx
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J. Name., 2013, 00, 1-3 | 7
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Journal of Materials Chemistry C
Page 8 of 8
View Article Online
DOI: 10.1039/C9TC03787J
A “(A) -D-(A) ” structured terpyridine electron-transporting material with nitrogen atom in meta-
n
n
position for long-lived and highly efficient TADF-PhOLEDs