C?H Direct Arylated 6H-Indolo[2,3-b]quinoxaline Derivative as a Thickness-Dependent Hole-Injection Layer

Article abstract of DOI:10.1002/asia.201700112

A novel perfluoro-1,4-phenylenyl 6H-indolo[2,3-b]quinoxaline derivative (TFBIQ) was designed and synthesized by using a C?H direct arylation method. The optoelectrical properties of the obtained TFBIQ were fully characterized by UV/Vis spectroscopy, photoluminescence spectroscopy, cyclic voltammetry, and a group of Alq₃-based green organic light-emitting diodes (OLEDs). Device A, which used 0.5 nm-thick TFBIQ as the interfacial modification layer, exhibited the five best advantages of device performance including a minimum turn-on voltage as low as 3.1 V, a maximum luminescence intensity as high as 26564 cd m^?2, a highest current density value of 348.9 mA cm^?2 at a voltage of 11 V, the smallest efficiency roll-off, as well as the greatest power efficiency of 1.46 lm W^?1 relative to all of the other tested devices with thicker TFBIQ and also 10 nm-thick MoO₃ as hole-injection layers (HILs). As a promising candidate for an organic HIL material, the as-prepared TFBIQ exhibited a strong thickness effect on the performance of corresponding OLEDs. Furthermore, the theoretical calculated vertical ionization potential of the fluorinated TFBIQ suggests better anti-oxidation stability than that of the non-fluorinated structure.

Full text of DOI:10.1002/asia.201700112

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: C-H Direct Arylated 6H-Indolo[2,3-b]quinoxaline Derivative as
Thickness-Dependent Hole Injection Layer
Authors: Dai Dong, Da Fang, Hairong Li, Caixia Zhu, Xianghua Zhao,
Jiewei Li, Lingzhi Jin, Linghai Xie, Lin Chen, Jianfeng Zhao,
Hongmei Zhang, and Wei HUANG
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Asian J. 10.1002/asia.201700112
Link to VoR: http://dx.doi.org/10.1002/asia.201700112
A Journal of
A sister journal of Angewandte Chemie
and Chemistry – A European Journal

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
C-H Direct Arylated 6H-Indolo[2,3-b]quinoxaline Derivative as
Thickness-Dependent Hole Injection Layer
a
b
a
a
c
a
b
b
Dai Dong, Da Fang, Hairong Li, Caixia Zhu, Xianghua Zhao, Jiewei Li, Lingzhi Jin, Linghai Xie,
Lin Chen, Jianfeng Zhao,*a,b Hongmei Zhang,* Wei Huang*
d
b
a,b
Abstract:
A
novel
perfluoro-1,4-phenylenyl
6H-indolo[2,3- hole between the active layers.10, 11 Especially, the electron–hole
b]quinoxaline derivative (TFBIQ) was designed and synthesized balance between the active layers determines the specific
using a C-H direct arylation method. The optoelectrical properties of performance of the sandwiched-like light-emitting device. It has
the obtained TFBIQ were fully characterized by ultraviolet-visible been proved that the modification of the electrode/organic
spectroscopy, photoluminescence spectroscopy, cyclic voltammetry,
and a group of Alq
-based green organic light-emitting diodes the device performance.12-14 Therefore, it is significant to develop
OLEDs). Device A using 0.5 nm-thick TFBIQ as the interfacial suitable HIL materials inserted between the hole transport layer
interface could exert influence on the carrier injection to improve
3
(
modification layer exhibits the best five advantages of device and the transparent anode to optimize the charge injection and
performance including the lowest minimum turn-on voltage as low as transport balance.15-17 Up to now, a few but insufficient organic
.1 V, the maximum luminescence intensity as high as 26564 cd m , HIL materials including 2-TNATA, m-MTDATA,18 CuPc,19 and
the highest current density value as 348.9 mA cm-2 at the voltage of PEDOT:PSS12 have been developed to compete with the non-
1 V, the smallest efficiency rolling-off, as well as the biggest power renewable inorganic HIL materials.20-23 In this situation, it is
efficiency as 1.46 lm W-1 prior to all of other devices with thicker emergent to discover more novel, low cost, eco-friendly, and
TFBIQ and also 10 nm-thick MoO as hole injection layers (HIL). As large-scale preparative organic HIL materials. However, there
-2
3
1
3
a promising candidate as organic HIL material, the as-prepared are few reports about the application of 6H-indolo[2,3-
TFBIQ exhibits a strong thickness effect on the performance of b]quinoxaline derivatives (IQs) as the HIL material. Since the
corresponding OLEDs. Besides, the theoretical calculated vertical discovery,24 IQs have not only many significant applications in
Ionization potential of the fluorinated TFBIQ presents a clue for a biochemistry and medicinal chemistry25-29 but also in recent
better anti-oxidation stability than that of the non-fluorinated material science as electron transport and light-emitting layers of
structure.
organic electronic devices30-35 due to their unique π-conjugated
structures and exceptional stabilities. Although the synthetic
methods and mechanisms have been systematically studied,36-
3
8
the related C-C coupling methods are usually not eco-
friendly32, 35 due to the more toxic organic tin reagents or harsh
Introduction
organic lithium reagents than C-H direct arylation.39, 40 Therefore,
During the past decades, organic light-emitting diodes
the competitive research and development of eco-friendly
(
OLEDs) have attracted an enormous research engagement
organic HIL materials represent an effective strategy for green
because of their prosper applications in the fields of solid-state
lighting and flexible optoelectronic displays.1-4 In order to
increase the illuminated efficiency of emitting devices, great
improvements have been achieved including optimizing device
structures, exploring novel emitting materials5-8 and adjusting the
and sustainable electronics.41, 42
9
carrier buffer ability by enhancing the transport of electron than
[
a]
b]
D. Dong, H. Li, C. Zhu, J. Li, J. Zhao, W. Huang
Key Laboratory of Flexible Electronics (KLOFE) & Institute of
Advanced Materials (IAM), Jiangsu National Synergetic Innovation
Center for Advanced Materials (SICAM)
Nanjing Tech University (NanjingTech), 30 South Puzhu Road,
Nanjing 211816, P.R. China
E-mail: iamwhuang@njtech.edu.cn
[
D. Fang, L. Jin, L. Xie, H. Zhang
Key Laboratory for Organic Electronics & Information Displays
(KLOEID) and Institute of Advanced Materials, Nanjing University of
Posts & Telecommunications, Nanjing 210023, P.R. China
E-mail: iamhmzhang@njupt.edu.cn
[
c]
d]
X. Zhao
College of Chemistry and Chemical Engineering, Xinyang Normal
University, Xinyang 464000, Henan, China
L. Chen
[
Nanjing Polytechnic Institute
Nanjing 210048
Scheme 1. The synthetic routine of TFBIQ, i) o-phenylenediamine, HOAc,
120 ℃ ,
N
2
,
over night; ii) 3-(bromomethyl)heptane, tetrabutyl ammonium
CO , DMF, 140 ℃ , 5h; iii) Pd(OAc) , P(t-Bu) Me-HBF , K CO
, 10h.
P.R. China
bromide, K
3
,
2
3
2
2
4
2
N,N-dimethyl acetamide, 150℃, N
2
Supporting information for this article is given via a link at the end of
the document.
1
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
In this work, we reported a novel hole injection layer material
based
phenylene)bis(6-(2-ethylhexyl)-6H-indolo[2,3-b]quinoxaline)
TFBIQ) presented in Scheme 1. The molecule structure of
on
IQ
derivative
entitled
9,9'-(perfluoro-1,4-
(
TFBIQ contains two IQ moieties and a bridged perfluoro-1,4-
phenylene group jointed by a facile C-H direct arylation.41, 43-46
Symmetrical tetrafluoro-substituted phenylene would promisingly
endow TFBIQ with low vertical Ionization potential (IPv) leading
to its anti-oxidation property (Table S1). The optoelectrical
properties, film morphologies, and thermal properties of TFBIQ
were measured by UV-visible (UV-vis), photoluminescence (PL)
spectra, cyclic voltammetry (CV), atomic force microscopy
(
AFM), thermo-gravimetric analysis (TGA), and differential
scanning calorimetry (DSC) analysis. We also fabricated several
green OLEDs to verify the usability test of TFBIQ as the HIL.
Figure 1. UV-vis and PL spectra in chloroform (1.0×10-5 mol L ) and in thin
-1
film of TFBIQ.
Results and Discussion
Table 1. Physical and thermal properties of TFBIQ.
Materials
λ
abs
λ
max,em
HOMO/
Gapopt
[eV]
g d
T /T
Synthesis. The synthesis of the IQ derivatives were
accomplished as illustrated in Scheme 1. 9-BrIQ was prepared
by the acid catalyzed cyclocondensation47-49 from bromoisatin
and o-phenylenediamine as a yellow precipitate in 84% yield
which was directly used for the next step without further
[nm]
[nm]
471
LUMO[eV]
[℃]
TFBIQ
357, 408
5.96 / 3.21
2.75
N.D./411
purification. 9-BrC
from IQ and 3-(bromomethyl)heptane in the presence of K
in DMF with a yield of 50%. The target molecule TFBIQ was
obtained through the C-H direct arylation from 9-BrC IQ and
as the catalyst in
5% yield avoided the reported toxic and harsh condition. The
8
IQ was obtained via a N-alkylation reaction
2
CO
3
8
1,2,4,5-tetrafluorobenzene using Pd(OAc)
2
4
obtained chemicals were confirmed by 1H-NMR spectroscopy
and MALDI-TOF mass spectroscopy in good agreement with the
molecular structures presented in Scheme 1.
Photophysical properties. As presented in Figure 1 and Table
1, the photophysical behaviors of TFBIQ have been examined
by measuring absorption and fluorescence spectra in chloroform
solution with a concentration of 1.0×10-5 mol L-1 and solid film.
TFBIQ in solution exhibited two absorption bands at 360 nm and
410 nm. The optical energy gap was calculated as 2.75 eV in
solution. There was about 4 nm redshift for TFBIQ from 471 nm
in solution to 475 nm in solid film indicating the existence of a
rigid π-conjugation. Cyclic voltammetry (CV) (Figure 2b) was
measured to estimate highest occupied molecular orbital
(
HOMO) and lowest unoccupied molecular orbital (LUMO).
HOMO value was calculated to be -5.96 eV from the oxidation
potential according to the empirical equation HOMO = -[4.4 +
E
ox].50 The LUMO value was subsequently calculated to be -3.21
eV according to the optical energy gap measured from the
optical edge listed in Table 1. The HOMO level of TFBIQ is
4
4'
lower than the reported value of N ,N -di(naphthalen-1-yl)-
4
4'
N ,N -diphenyl-[1,1'-biphenyl]-4,4'-diamine (NPB) and work
function of indium tin oxide (ITO)51 hinting the potential use as
the HIL in OLEDs.
Figure 2. (a) Cyclic voltammogram recorded for TFBIQ in dichloromethane; (b,
c) Wave functions for the HOMO and LUMO of TFBIQ molecule.
2
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
The DFT calculation was performed to understand the
electronic structure of TFBIQ as shown in Figure 2b and 2c. The
HOMO delocalizes over the whole conjugated backbone
including indole, quinoxaline and perfluoro-1,4-phenylene.
LUMO just localizes on two quinoxaline moieties. The vertical
Ionization potential (IPv) for the fluorinated TFBIQ is -7.38 eV
Table 2. The structures of the OLEDs showing the different layer thickness of
TFBIQ-HIL and MoO
3
used in the devices.
Devices
A
Structures
3
ITO/TFBIQ (0.5 nm)/NPB (80 nm)/Alq (60 nm)/LiF (0.7
nm)/Al (120 nm)
B
C
D
X
3
ITO/TFBIQ (1 nm)/NPB (80 nm)/Alq (60 nm)/LiF (0.7
(
Table S1) which is high enough to prevent TFBIQ from the
oxidization. Besides, the IPv of TFBIQ is higher than the non-
fluorinated BIQ which hints TFBIQ could potentially adjust and
buffer the hole-injection behavior. The hole reorganization
energy of TFBIQ is 0.50 eV lower than 0.57 eV of BIQ indicating
a smaller energy loss for the hole transfer. Both of the two
properties suggest that fluorinated TFBIQ is much more suitable
for HIL material than non-fluorinated BIQ. TFBIQ also exhibits
nm)/Al (120 nm)
3
ITO/TFBIQ (1.5 nm)/NPB (80 nm)/Alq (60 nm)/LiF (0.7
nm)/Al (120 nm)
ITO/TFBIQ (2 nm)/NPB (80 nm)/Alq (60 nm)/LiF (0.7
3
nm)/Al (120 nm)
ITO/MoO
3
3
(10 nm)/NPB (80 nm)/Alq (60 nm)/LiF (0.7
nm)/Al (120 nm)
good thermal stability with
temperature (T ) due to the high molecular weight and the rigid
backbone. The value corresponding to 5% weight loss was
11℃ for TFBIQ (Table 1, Figure S5, S6).
a
very high decomposition
d
Electroluminescent (EL) performance. In order to evaluate the
ability of TFBIQ to adjust the electron/hole injection and the
transport balance, five OLED devices were fabricated using
4
TFBIQ or MoO
.5 to 2 nm (Device A, B, C, and D) for the former and 10 nm
Device X) for the latter, respectively. Their EL characteristics
were measured using general device configuration of
ITO/TFBIQ or MoO /NPB (80 nm)/Alq (60 nm)/LiF (0.7 nm)/Al
120 nm) as shown in Figure 3a. Their device structures and
3
as the HIL materials with thickness from 0.5, 1,
1
(
a
3
3
(
corresponding characteristics were listed in Table 2 and Table 3.
For comparison, the only difference between these devices is
the alternative HIL materials with different thickness.
Table 3. The summary of OLEDs characteristics.
b)
LEmaxb)
(cd A-1)
PEmaxb)
V
on
L
max
EQEmax
c)
CIE
Device
(
V)a)
(cd m-2)
(lm W-1)
(x, y)d)
A/0.5nm
B/1nm
3.1
3.5
4.9
6.5
3.1
26564
22451
20008
19768
22183
4.10
4.21
4.10
4.05
5.04
1.46
1.29
1.09
0.95
2.12
1.36
1.45
1.58
1.41
-
0.30,0.55
0.30,0.55
0.30 0.55
0.31,0.54
0.30 0.55
C/1.5nm
D/2nm
X/10 nm
a)
on, Turn-on voltages at 1 cd m-2; b)
V
L
max, maximum luminance; PEmax
,
,
maximum power efficiency; LEmax, maximum luminance efficiency; c) EQEmax
maximum external quantum efficiency; d) CIE coordinates were recorded at 9
V for devices A-D.
Figure 4 presents the current density–voltage–luminance (J–
V–L),
and
luminance
efficiency–luminance
(LE–L)
characteristics with the main parameters tabulated in Table 3.
As shown in the J–V–L graph and parameters in Table 3, device
A and B using 0.5 nm- and 1 nm-thick TFBIQ as the interfacial
modification layer exhibit a good minimum turn-on voltage (Von
)
-2
as low as 3.1 V and 3.5 V at 1 cd m . These two values are
almost the same as 3.1 V which is the same as the Von value of
3
device X with 10 nm-thick MoO , respectively. Especially, the
maximum luminescence intensity (Figure 4a, rightwards arrows)
reaches as high as 26564 cd m-2 of device A surpassing over
2
2451 cd m-2 of device B and also 22183 cd m-2 of device X with
MoO as the HIL. Besides, at the voltage of 11 V, the current
density (J) (Figure 4a, leftwards arrows) of devices A-D were
3
-2
-2
-2
-2
348.9 mA cm , 137.7 mA cm , 21.1 mA cm , 5.4 mA cm ,
respectively. It is obvious that device A exhibits the best J which
is 2.1 times than the corresponding value as 167.7 mA cm-2 of
device X. When the thickness of TFBIQ increased to 1.5 nm and
Figure 3. (a) Schematic configuration of the OLEDs; (b) Energy band
diagrams of the OLEDs; (c) molecule structures of organic materials.
3
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
Figure 4. The (a) J–V–L characteristics of devices A-D, X; (b) luminance
efficiency–luminance characteristics of devices A-D, X; (c) power efficiency–
luminance characteristics of devices A-D, X.
2
nm, the Von values of device C and D reach as high as 4.9 V
and 6.5 V. It is indicated that these turn-on voltages of TFBIQ
HIL based OLEDs have strong dependence on the HIL
thickness. Meanwhile, the corresponding maximum luminance
efficiencies (LE) measured on devices A-D were rather close as
As shown in Figure 4b and Table 3, it is found that devices A-
D with the thinner TFBIQ as the HIL exhibited better device
stability with reduced efficiency rolling-off. At the same
-1
-1
-1
-1
high as 4.10 cd A , 4.21 cd A , 4.10 cd A , and 4.05 cd A ,
respectively, reaching 4/5 of the LEmax value as 5.04 cd A-1 of
device X (Figure 4b, Table 3).
-2
luminance intensity of 19000 cd m , there were 89.3%, 78.3%,
0.2%, and 73.3% efficiency rolling-off while the LE of TFBIQ in
8
devices A-D reaching 3.66, 3.30, 3.29 and 2.97 cd A-1 compared
to their LEmax, respectively. Among them, Device A presented
the best device stability quite close to 89.2% efficiency rolling-off
of device X when its LE arrived at 4.50 cd A-1 divided by its LEmax
-1
(
5.04 cd A ). As shown in Figure 4c, device A exhibited the best
performance of PEmax as 1.46 lm W-1 larger than the values from
.29, 1.09 to 0.95 lm W-1 of device B, C, and D presenting a
1
gradually reasonable rolling-off. However, the external quantum
efficiency (EQE) of device A reached 1.36% which is lower than
that of other three device B, C and D with higher EQE as 1.45%,
1.58%, and 1.41%, respectively.
Figure 5. AFM topographic (a-d), height (e-h), and inset roughness images of
vapor deposited TFBIQ on Si substrates with four different thickness: 0.5 nm
(a, e), 1 nm (b, f), 1.5 nm (c, g), and 2 nm (d, g).
Figure 6. EL spectra of devices A-D at 9 V.
The operating voltage exhibited an obvious growth trend while
the LE and PE values show a decreasing tendency. It is
indicated that the optimized thickness of 0.5 nm was the most
suitable
physical
parameter
leading
to
the
best
electroluminescent performance of hole injective TFBIQ-based
devices. It should be noted that the similar but lower HOMO
4
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
levels -5.96 eV of TFBIQ than -5.4 eV of NPB leading to the
enhanced hole balance and transfer from TFBIQ-modificated
ITO to higher energy stated NPB layer. Meanwhile, the quite
evaporated to dryness. The residue was purified by silica gel column
chromatography using petroleum ether/ethyl acetate mixed solvent as
eluent. A yellow solid as 9-BrC
8
IQ with a yield of 50% was obtained after
1
drying in vacuum oven. H NMR (400 MHz, CDCl
3
) δ 8.61 (s, 1H), 8.29 (d,
close HOMO level of TFBIQ to that of MoO
a reasonable explanation for the comparative performance
3
(-5.6 eV)51 suggests
J = 8.4 Hz, 1H), 8.13 (d, J = 8.4 Hz, 1H), 7.77 (t, J = 8.5 Hz, 2H), 7.69 (t,
J = 8.3 Hz, 1H), 7.35 (d, J = 8.6 Hz, 1H), 4.35 (d, J = 7.5 Hz, 2H), 2.15 (m,
(
Table 3) of TFBIQ-based OLED devices.
1
H), 1.51 – 1.27 (m, 6H), 1.25 (m, 2H)., 0.94 (t, J = 7.5 Hz, 3H), 0.85 (t, J
7.2 Hz, 3H); 13C NMR (100 MHz, CDCl
) δ 145.90, 143.14, 140.89,
139.38, 138.39, 133.19, 129.38, 128.96 , 127.98, 126.09, 125.26, 121.07,
13.44, 111.09, 45.53, 38.49, 30.66, 28.48, 24.11, 22.92, 13.95 , 10.63.
GC-MS calculated for C22 , 410.35; found 410.9.
=
3
Figure 5 presents the AFM 5 μm × 5 μm topographic images
1
(
5a-d) and phase images (5e-g) of the vapor deposited TFBIQ
H
24BrN
3
films with the thickness from 0.5 nm, 1 nm, 1.5 nm to 2 nm on
bare Si substrates under vacuum with quite similar roughness
and gradually increased thickness shown by the inset images.
All the surface morphologies are determined as quite similar
smoothing patterns without remarkable grain domains which are
favorable for the homogeneous interface modification of ITO
electrode. The modificated interface impedes the lateral TFBIQ
molecular diffusion and suppresses the TFBIQ molecular
crystallization implying the degradation of device stability. Figure
Synthesis of 9,9'-(perfluoro-1,4-phenylene)bis(6-(2-ethylhexyl)-6H-
indolo[2,3-b] quinoxaline) (TFBIQ). 50 ml round-bottom flask
containing a magnetic stirring bar was flame-dried under vacuum and
filled with nitrogen after cooling to room temperature. 9-BrC IQ (410 mg,
mmol), K CO (345 mg, 2.5 mmol), Pd(OAc) (11 mg, 0.05 mmol), and
P(t-Bu) Me-HBF (25 mg, 0.1 mmol) were added to this vessel. The flask
A
8
1
2
3
2
2
4
was evacuated and backfilled with nitrogen for 3 times. Then, 1,2,4,5-
tetrafluorobenzene (120 mg, 0.8mmol) and the solvent N,N-
dimethylacetamide (10 ml) were added with stirring at room temperature
for several minutes. The flask was then placed into oil bath, heated to
6
shows the EL spectra of devices A-D driven at 9 V. It is clearly
seen that the Alq green light emission (peaking at ~515 nm)
3
150 ℃ and refluxed overnight. After cooling to room temperature, the
can be observed in all devices.
reaction mixture was poured into saturated NaCl solution, stirred for 1 h,
and then extracted with dichloromethane. The organic layer was dried
2 4
over anhydrous Na SO , filtered and evaporated to dryness. The crude
Conclusions
product was purified by flash column chromatography using petroleum
ether/ethyl acetate mixed solvent as eluent, to afford a desired product
TFBIQ after drying in vacuum oven, 182 mg, yield 45%. 1H NMR (400
In summary,
derivative TFBIQ synthesized via the palladium-catalyzed C-H
direct arylation was successfully used as the HIL in Alq based
a
fluorinated 6H-indolo[2,3-b]quinoxaline
MHz, CDCl
3
) δ 8.74 (s, 2H), 8.35 (d, J = 8.4, Hz, 2H), 8.17 (d, J = 8.5 Hz,
2
2
1
6
H), 7.90 (d, J = 8.4 Hz, 2H), 7.80 (t, J = 8.4 Hz, 2H), 7.72 (t, J = 8.2 Hz,
3
H), 7.64 (d, J = 8.2 Hz, 2H), 4.45 (d, J = 7.5 Hz, 4H), 2.30-2.20 (m, 2H),
.46 (m, 12H), 1.29 (m, 4H), 1.00 (t, J = 7.4 Hz, 6H), 0.89 (t, J = 7.2 Hz,
green electroluminescent devices. When the thickness ranges
from 0.5 nm to 1 nm, device A with 0.5 nm-thick TFBIQ as the
HIL exhibits the best device performance, especially, in the four
aspects of Von, Lmax, J and the lowest efficiency rolling-off close
H); 13C NMR (100 MHz, CDCl
3
) δ 146.34, 144.78, 140.86, 139.48 (d, J
= 8.8 Hz), 132.58, 129.45, 128.90, 128.05 , 126.16, 124.63, 119.82 (d, J
= 9.4 Hz), 109.91, 45.65, 38.65, 30.74, 28.54, 24.19, 23.01, 14.01, 10.67.
to that of device X with MoO
3
as the HIL. These results reveal
48 4 6
MALDI-TOF MS: calcd for C50H F N 808.95, found 811.74.
that TFBIQ would be a pioneer IQ-based molecule for a new
series of highly performed HIL materials suitable for green and
sustainable organic light-emitting diodes.
Methods. 1H NMR and 13C NMR spectra were measured on a Bruker
ARX 400 spectrometer. The UV-vis absorption and fluorescence spectra
were recorded on
a
Shimadzu UV-1750 and Hitachi F-4600
spectrophotometer, respectively. MS were collected on MALDI TOF2
AXIMA mass spectrometer. The glass transition temperatures of
compounds were determined under a nitrogen atmosphere by DSC using
Experimental Section
a
NETZSCH DSC214 Polyma instrument. The decomposition
Materials.
butyl)ammonium bromide (TBAB), Pd(OAc)
4
and P(t-Bu) Me-HBF were purchased from Nanjing Fountain Global
5-Bromoisatin,
3-(bromomethyl)heptane,
tetra(n-
temperature corresponding to 5% weight loss was conducted on a
METTLER TOLEDO TGA2 thermal analyzer. Density function theory
(DFT) at the B3LYP/6-31G(d)52 level was implemented to optimize the
geometry and calculate the electronic structure of the rigid TFBIQ
molecular structure in Gaussian 09 software53 to relax the structure
fully.54 Cyclic voltammetry experiment was carried out using a three-
electrode system employing a glassy carbon electrode as the working
electrode, a Ag/Ag+ electrode as the reference electrode, and a Pt wire
as the counter electrode. The redox potentials were measured in
2
, 1,2,4,5-tetrafluorobenzene
2
Displays and ENERGY CHEMICIAL. Other reagents and solvents were
purchased from Sinophorm Chemical Reagent Co., Ltd. All solvents were
used without further purification.
Synthesis of 9-bromo-6H-indolo[2,3-b]quinoxaline (9-BrIQ).
mixture of 5-bromoisatin (2.26 g, 10 mmol), benzene-1,2-diamine (1.62 g,
5 mmol) and acetic acid (60 ml) under nitrogen atmosphere was heated
A
4 6
dichloromethane, using 0.1 M n-Bu NPF as the supporting electrolyte
1
-1
with a scan rate of 100 mV s .
at 80 ℃ and stirred over night. After cooling to room temperature, the
reaction mixture was filtered, dried in vacuum oven and gave a yellow
solid 2.43 g with a yield of 84%. The solid was directly used for the next
step.
Electroluminescent tests. The commercial ITO-coated glass substrates
with a sheet resistance of around 10 Ω/m2 were used as the anode,
which were successively rinsed with detergent, de-ionized water, acetone,
and isopropyl alcohol in an ultrasonic bath for 15 min, respectively. The
cleaned and dried ITO glass substrates were treated with oxygen plasma
Synthesis of 9-bromo-6-(2-ethylhexyl)-6H-indolo[2,3-b]quinoxaline
(
9-BrC
5 mmol), and TBAB (0.32 g, 1 mmol) were dissolved with 20 ml of DMF
in a 100 ml round-bottom flask. K CO (4.14 g, 30 mmol) was then added
8
IQ). 9-BrIQ (2.98 g, 10 mmol), 3-(bromomethyl)heptane (3.10 g,
o
for 5 min. The TFBIQ was evaporated at 220 C with four thickness from
1
0
.5, 1, 1.5 to 2 nm. The OLEDs were prepared by thermal evaporation in
a high-vacuum system with the pressure less than 5×10-4 Pa. TFBIQ,
NPB, Alq , 0.7 nm LiF and 120 nm Al were evaporated onto ITO in turn.
2
3
to the solution. The mixture was stirred at 140℃ for 5 h. After cooling to
ambient temperature the solution was poured into saturated NaCl
solution, stirred for 30 min, and then extracted with dichloromethane. The
3
The evaporation rates were monitored by frequency counter, and
calibrated by Dektak 6 M Profiler (Veeco). The overlap area between ITO
4
combined organic layer was dried over anhydrous MgSO , filter and
5
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
and Al electrodes was 16 mm2 as the emissive size of devices. The
25. J. Harmenberg, B. Wahren, J. Bergman, S. Akerfeldt, L. Lundblad,
Antimicrob. Agents Chemother. 1988, 32, 1720-1724.
devices have the same 80 nm NPB, 60 nm Alq
Al. Figure 3 shows the energy level diagrams of the fabricated devices
and the molecular structures of TFBIQ, Alq and NPB used in these
3
, 0.7 nm LiF, and 120 nm
26. J. Harmenberg, A. Akessonjohansson, A. Graslund, T. Malmfors, J.
Bergman, B. Wahren, S. Akerfeldt, L. Lundblad, S. Cox, Antivir. Res.
1991, 15, 193-204.
3
devices. The current–voltage-brightness characteristics were measured
by using a Keithley source measurement unit (Keithley 2400 and Keithley
27. K. Manna, Y. K. Agrawal, Bioorg. Med. Chem. Lett. 2009, 19, 2688-2692.
28. N. R. Pai, D. A. Pusalkar, J. Chem. Pharm. Res. 2010, 2, 485-493.
29. L. W. Deady, A. J. Kaye, G. J. Finlay, B. C. Baguley, W. A. Denny, J. Med.
Chem. 1997, 40, 2040-2046.
2000) with a calibrated silicon photodiode. All devices were measured
without encapsulation at room temperature.
3
0. C. H. Fan, P. P. Sun, T. H. Su, C. H. Cheng, Adv. Mater. 2011, 23, 2981-
985.
1. P. Tyagi, A. Venkateswararao, K. R. J. Thomas, J. Org. Chem. 2011, 76,
571-4581.
2
Acknowledgements
3
4
We thank the 973 program (2015CB932200), the National
Natural Science Foundation of China (NSFC, 21502091,
32. K. R. J. Thomas, P. Tyagi, J. Org. Chem. 2010, 75, 8100-8111.
33. T. H. Su, C. H. Fan, Y. H. Ou-Yang, L. C. Hsu, C. H. Cheng, J. Mater.
Chem. C 2013, 1, 5084-5092.
6
1274065, 21603104, 21003706), and the Natural Science
Foundation of Jiangsu Province (BK20130912 and
4KJB430017) and Ministry of Education and Synergetic
34. A. Venkateswararao, P. Tyagi, K. R. J. Thomas, P. W. Chen, K. C. Ho,
Tetrahedron 2014, 70, 6318-6327.
1
35. X. Qian, H. H. Gao, Y. Z. Zhu, L. Lu, J. Y. Zheng, J. Power Sources 2015,
Innovation Center for Organic Electronics and Information
Displays for financial support.
2
80, 573-580.
36. E. Schunk, L. Marchlewski, Ber. 1895, 28, 2525-2531.
3
7. A. V. Ivashchenko, V. M. Dziomko, Russ. Chem. Rev. 1977, 46, 115-120.
8. R. Dowlatabadi, A. Khalaj, S. Rahimian, M. Montazeri, M. Amini, A.
Shahverdi, E. Mahjub, Synth. Commun. 2011, 41, 1650-1658.
3
Keywords: C-H direct arylation • 6H-indolo[2,3-b]quinoxaline •
hole injection layer • OLED •
39. A. J. Payne, J. S. J. McCahill, G. C. Welch, Dyes And Pigments 2015,
123, 139-146.
References:
40. J. R. Pouliot, F. Grenier, J. T. Blaskovits, S. Beaupre, M. Leclerc, Chem.
Rev. 2016, 116, 14225-14274.
4
1. M. L. Sun, W. S. Zhu, Z. S. Zhang, C. J. Ou, L. H. Xie, Y. Yang, Y. Qian,
Y. Zhao, W. Huang, J. Mater. Chem. C 2015, 3, 94-99.
1
.
.
S. Reineke, F. Lindner, G. Schwartz, N. Seidler, K. Walzer, B. Lussem, K.
Leo, Nature 2009, 459, 234-238.
42. C. Tang, R. Bi, Y. Tao, F. Wang, X. Cao, S. Wang, T. Jiang, C. Zhong, H.
Zhang, W. Huang, Chem. Commun. 2015, 51, 1650-1653.
2
T. L. Chiu, Y. P. Hsiao, Y. T. Chuang, C. M. Lai, H. C. Ho, Org. Electron.
2014, 15, 785-791.
4
4
4
3. W. Lu, J. Kuwabara, T. Kanbara, Macromolecules 2011, 44, 1252-1255.
4. M. Wakioka, Y. Kitano, F. Ozawa, Macromolecules 2013, 46, 370-374.
5. Q. H. Feng, Y. I. Han, M. N. Yu, B. Li, Y. Wei, L. H. Xie, W. Huang, Chin.
J. Polym. Sci. 2017, 35, 87-97.
3
.
.
T. Matsushima, C. Adachi, Appl. Phys. Lett. 2006, 89, 253506.
4
C. F. Qiu, H. Y. Chen, M. Wong, H. S. Kwok, IEEE T. Electron Dev. 2002,
49, 1540-1544.
5
6
7
8
.
.
.
.
.
M. K. Leung, Y. H. Hsieh, T. Y. Kuo, P. T. Chou, J. H. Lee, T. L. Chiu, H.
J. Chen, Org. Lett. 2013, 15, 4694-4697.
46. L. Wang, G. W. Zhang, C. J. Ou, L. H. Xie, J. Y. Lin, Y. Y. Liu, W. Huang,
Org. Lett. 2014, 16, 1748-1751.
C. C. Lee, M. K. Leung, P. Y. Lee, T. L. Chiu, J. H. Lee, C. Liu, P. T.
Chou, Macromolecules 2012, 45, 751-765.
4
7. J. F. Zhao, J. I. Wong, J. K. Gao, G. Li, G. C. Xing, H. C. Zhang, T. C.
Sum, H. Y. Yang, Y. L. Zhao, S. L. A. Kjelleberg, W. Huang, S. C. J. Loo,
Q. C. Zhang, RSC Adv. 2014, 4, 17822-17831.
Q. Wang, J. Ding, D. Ma, Y. Cheng, L. Wang, X. Jing, F. Wang, Adv.
Funct. Mater. 2009, 19, 84-95.
4
8. J. B. Li, Q. C. Zhang, ACS Appl. Mater. Inter. 2015, 7, 28049-28062.
9. J. B. Li, S. Chen, Z. L. Wang, Q. C. Zhang, Chem. Rec. 2016, 16, 1518-
Y. J. Pu, G. Nakata, F. Satoh, H. Sasabe, D. Yokoyama, J. Kido, Adv.
Mater. 2012, 24, 1765-1770.
4
1530.
9
1
T. L. Chiu, P. Y. Lee, Int. J. Mol. Sci. 2012, 13, 7575-7585.
5
0. G. Li, H. M. Duong, Z. Zhang, J. Xiao, L. Liu, Y. Zhao, H. Zhang, F. Huo,
S. Li, J. Ma, F. Wudl, Q. Zhang, Chem. Commun. 2012, 48, 5974-5976.
1. H. M. Zhang, Q. Fu, W. J. Zeng, D. G. Ma, J. Mater. Chem. C 2014, 2,
0. K. Udagawa, H. Sasabe, C. Cai, J. Kido, Adv. Mater. 2014, 26, 5062-
066.
5
5
11. J. J. Huang, M. K. Leung, T. L. Chiu, Y. T. Chuang, P. T. Chou, Y. H.
9620-9624.
Hung, Org. Lett. 2014, 16, 5398-5401.
5
2. C. T. Lee, W. T. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785-789
3. G. W. T. M. J. Frisch, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H.
Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G.
Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L.
Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J.
Dannenberg, S. Dapprich, A. D. Daniels,O¨ . Farkas, J. B. Foresman, J. V.
Ortiz, J. Cioslowski and D. J. Fox, , Gaussian 09, Revision B.1, Gaussian,
Inc., Wallingford CT, 2009.
1
2. M. Shakutsui, H. Matsuura, K. Fujita, Org. Electron. 2009, 10, 834-842.
3. S. R. Tseng, S. C. Lin, H. F. Meng, H. H. Liao, C. H. Yeh, H. C. Lai, S. F.
Horng, C. S. Hsu, Appl. Phys. Lett. 2006, 88, 163501.
5
1
14. J. Chen, D. Ma, Chem. Phys. 2006, 325, 225-230.
15. S. K. Kim, C. J. Lee, I. N. Kang, J. H. Lee, J. W. Park, Thin Solid Films
2006, 509, 132-136.
16. T. Ye, M. Zhu, J. Chen, Q. Fu, F. Zhao, C. Shi, Y. Hu, D. Ma. C. Yang, J.
Mater. Chem. 2012, 22, 6413-6418.
1
7. Y. Zhao, J. Chen, W. Chen, D. Ma, J. Appl. Phys. 2012, 111, 043716.
8. Y. Shirota, Y. Kuwabara, D. Okuda, R. Okuda, H. Ogawa, H. Inada, T.
Wakimoto, H. Nakada, Y. Yonemoto, S. Kawami, K. Imai, J. Lumin., 1997,
1
7
2-4, 985-991.
9. S. A. VanSlyke, C. H. Chen, C. W. Tang, Appl. Phys. Lett. 1996, 69,
160-2162.
1
2
2
2
0. M. G. Helander, Z. B. Wang, J. Qiu, M. T. Greiner, D. P. Puzzo, Z. W. Liu,
Z. H. Lu, Science 2011, 332, 944-947.
54. J. Zhao, J. I. Wong, C. Wang, J. Gao, V. Z. Y. Ng, H. Y. Yang, S. C. J.
1. C. Xu, P. Cai, X. Zhang, Z. Zhang, X. Xue, J. Xiong, J. Zhang, Sol.
Energy Mater. Sol. Cells 2017, 159, 136-142.
Loo, Q. Zhang, Chem. Asian J. 2013, 8, 665-669.
22. F. Wang, X. Qiao, T. Xiong, D. Ma, Org. Electron. 2008, 9, 985-993.
23. Z. Hongmei, X. Jianjian, Z. Wenjin, H. Wei, Displays 2014, 35, 171-175.
24. O.Hinsberg, Ber. 1886, 19, 483-488.
6
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
FULL PAPER
Direct arylation: Symmetrical
Dai Dong, Da Fang, Hairong Li,
Caixia Zhu, Xianghua Zhao,
Jiewei Li, Lingzhi Jin, Linghai
Xie, Lin Chen, Jianfeng Zhao,*
Hongmei Zhang,* Wei Huang*
6H-indolo[2,3-b]quinoxaline
derivative implanted with
tetrafluoro-p-phenylene plays
as an effective hole injection
layer material in organic light
emitting devices.
Page No. – Page No.
C-H Direct Arylated 6H-
Indolo[2,3-b]quinoxaline
Derivative as Thickness-
Dependent Hole Injection Layer
7
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
Supporting Information for
C-H Direct Arylated 6H-Indolo[2,3-b]quinoxaline Derivative as
Thickness-Dependent Hole Injection Layer
a
b
a
a
c
a
b
b
Dai Dong, Da Fang, Hairong Li, Caixia Zhu, Xianghua Zhao, Jiewei Li, Lingzhi Jin, Linghai Xie,
Lin Chen, Jianfeng Zhao,*a,b Hongmei Zhang,* Wei Huang*
d
b
a,b
a.Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM), Jiangsu National Synergetic
Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road,
Nanjing 211816, P.R. China
b.
Key Laboratory for Organic Electronics & Information Displays (KLOEID) and Institute of Advanced Materials, Nanjing
University of Posts & Telecommunications, Nanjing 210023, P.R. China
c.
College of Chemistry and Chemical Engineering, Xinyang Normal University, Xinyang 464000, Henan, China
Nanjing Polytechnic Institute, Nanjing 210048, P.R. China
d.
Contents:
Figure S1. GC-MS of 9-BrC
8
IQ
IQ
1
Figure S2. H NMR of 9-BrC
8
Figure S3. MALDI-TOF MS of TFBIQ
1
Figure S4. H NMR of TFBIQ
Figure S5. TGA curve of TFBIQ
Figure S6. DSC curve of TFBIQ
Table S1. Theoratical calculation of TFBIQ vs non-fluorinated BIQ
8
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
%
296.8
1
00
3
12.8
5
0
0
5
5.0
90.0
100
128.9
230.9
17.9
4
10.9
423.8
2
176.9
255.9
250
351.9 381.9
350
1
54.9
325.9
465.8 497.8
5
0
150
200
300
400
450
500
Figure S1. GC-MS of 9-BrC
8
IQ
1
Figure S2. H NMR of 9-BrC
8
IQ
9
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
Figure S3. MALDI-TOF MS of TFBIQ
1
0
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
1
Figure S4. H NMR of TFBIQ
Figure S5. TGA curve of TFBIQ
1
1
This article is protected by copyright. All rights reserved.

Chemistry - An Asian Journal
10.1002/asia.201700112
FULL PAPER
Figure S6. DSC curve of TFBIQ
Table S1. Theoratical calculation of the symmetrical tetrafluorinated TFBIQ vs non fluorinated one.
Energy level
TFBIQ
BIQ
Ground
Ground+
cation
Cation0
IPv
-2111.12214103
-2110.85099264
-2110.85934041
-2111.11223742
-1714.31059972
-1714.05179844
-1714.06233165
-1714.30033133
-7.378327299646 (eV) -7.042345150592
IP
Hole
Reorganization 0.496645601732 (eV) 0.56604065824
energy
Method
wb97xd/6-31g(d)
wb97xd/6-31g(d)
1
2
This article is protected by copyright. All rights reserved.