Substituted Diindenopyrazinediones with symmetrical Polyalkyl-carbazole for high-efficiency blueish green solution-processable OLED

Article abstract of DOI:10.1016/j.dyepig.2017.04.003

Much effort has been devoted to design and synthesize this solution-processable OLEDs, Some significant advances have been achieved with the power efficiencies. However, most of them still lag behind those of evaporated non-doping OLEDs. Two novel peripheral Polyalkyl-carbazole substituted Diindeno-pyrazinediones have been developed for highly-efficient and solution-processable OLEDs. Provide high efficient materials for the solution-processed to reduce costs of OLEDs. By fine-tuning their carriers transfer and injection barriers, solution-processed device based on DTPADIPY-TCz shows highly efficient bluish green emission with a maximum power efficiency (PE) of 6.88?lm?W^?1, which is among the highest reported to date for solution-processable fluorescent OLEDs with a relatively low efficiency roll-off.

Full text of DOI:10.1016/j.dyepig.2017.04.003

Accepted Manuscript
Substituted Diindenopyrazinediones with Polyalkyl-carbazole symmetrically for high-
efficiency bluish green solution-processable OLED
Lei Zhang, Yongqi Bai, Zhiyang Liu, Weigang Jiang, Tao Lei, Rongjuan Yang, Amjad
Islam, Yumei Zhang, Xinhua Ouyang, Ziyi Ge
PII:
S0143-7208(17)30416-3
10.1016/j.dyepig.2017.04.003
DYPI 5897
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 28 February 2017
Revised Date: 1 April 2017
Accepted Date: 1 April 2017
Please cite this article as: Zhang L, Bai Y, Liu Z, Jiang W, Lei T, Yang R, Islam A, Zhang Y, Ouyang X,
Ge Z, Substituted Diindenopyrazinediones with Polyalkyl-carbazole symmetrically for high-efficiency
bluish green solution-processable OLED, Dyes and Pigments (2017), doi: 10.1016/j.dyepig.2017.04.003.
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ACCEPTED MANUSCRIPT
Substituted Diindenopyrazinediones with Polyalkyl-
carbazole symmetrically for High-efficiency bluish
green Solution-processable OLED
a,c
a
a
a
a
a
Lei Zhang , Yongqi Bai , Zhiyang Liu , Weigang Jiang , Tao Lei , Rongjuan Yang , Amjad
a
b
a
*a
Islam , Yumei Zhang , Xinhua Ouyang , Ziyi Ge
a
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences,
Ningbo 315201, P. R. China
b
State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua
University
c
Nano Science and Technology Institute, University of Science and Technology of China, Suzhou
2
*
15123, China
Corresponding author: E-mail: geziyi@nimte.ac.cn
ABSTRACT: Much effort has been devoted to design and synthesize this solution-processable
OLEDs, Some significant advances have been achieved with the power efficiencies. However,
most of them still lag behind those of evaporated non-doping OLEDs. Two novel peripheral
Polyalkyl-carbazole substituted Diindeno-pyrazinediones have been developed for highly-
efficient and solution-processable OLEDs. Provide high efficient materials for the solution-
processed to reduce costs of OLEDs. By fine-tuning their carriers transfer and injection barriers,
solution-processed device based on DTPADIPY-TCz shows highly efficient bluish green
1

ACCEPTED MANUSCRIPT
−
1
emission with a maximum power efficiency (PE) of 6.88 lm W , which is among the highest
reported to date for solution-processable fluorescent OLEDs with a relatively low efficiency
roll-off.
KEYWORDS: Peripheral substituted; Solution-processable OLEDs; Deep blue emitting; Low
turn-on voltage; Low efficiency roll-off
TOC GRAPHICS
1
. Introduction
As we all know, Organic Light Emitting Diodes (OLEDs) will become the next generation
display technology replace liquid crystal. This commercial application has also been put on the
agenda, many manufacturers have begun to layout OLED production line, but its manufacturing
technique of thermal evaporation process consume huge energy and is complicated. The low
2

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energy consumption of solution-processing technology can realize large-area flexible OLED
devices, reduced cost, environment-friendly and large-scale. It is one of the important measures
to reduce the energy crisis by means of the science. Solution-processable organic light-emitting
diodes (OLEDs) have been attracting extensive study due to their simple processes, low costs
[
1-3]
and large-area fabrication.
single or double-layer architectures due to the restriction of intermixing of layers.
single-layer non-dopant devices, their performance usually is inferior to their counterparts of
Generally, solution-processable OLEDs were constructed with a
[
4-6]
For the
[
7-9]
evaporated OLEDs.
While these double-layer structure devices, evaporated an electron-
transporting or hole-blocking layer behind the solution-processed emitters, show similar
[
10,11]
efficiencies with vacuum-deposited OLEDs.
Considering these solution-processable devices
without hole-transporting layer, it is highly desirable to develop novel emitters with excellent
hole transport and low injecting barriers. In the past decades, much effort has been devoted to
[
12]
design and synthesize this kind of materials. Some significant advances have been achieved
-1 [13]
with the maximal power efficiencies of ~5 lm W . However, most of them still lag behind
those of evaporated OLEDs. Therefore, the preparation of novel materials with high fluorescent
quantum yield, balanced charge injection and transfer properties still remains one of the most
active and challenging areas. Peripheral substitution has been demonstrated as one of effective
methods to improve transfer and luminescence, some of them exhibited excellent results for
[
14]
solution-processable OLEDs.
To date, almost of them are mainly concentrated on fluorene
[
15]
and its derivatives, which can be substituted easily on the 9,9’-positions of fluorene. However,
an undesired green emission would be found in these devices due to the excimer/interchain
[
16]
aggregates and the keto defects.
In this respect, diindenopyrazinedione (DIPY) and its
derivatives, another intermediates having two positions for the substitution of peripheral groups,
3

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have been used as efficient blue emission and n-type organic field-effect transistors (OFET) with
-
1
2
-1 -1 [17,18]
excellent performance (efficiencies, 2.01 cd A and 4.6%; mobility, 0.17 cm V s ).
However, DIPY core possessing rigid and planar structures facilitates to form molecular stacking
[
19]
in their film states,
quenching the luminescence and limiting their applications for the
solution-processable OLEDs. In this regard, the development of novel DIPY derivatives,
[
20]
containing some twisted structures to tune their aggregation of intermolecular interaction in
film states and twist four carbazole units through alkyl chains attached to the core and peripheral
[
21]
groups four long alkyl chains to improve their solubility are critically important for the high-
efficient and low-cost OLEDs.
In this work, two novel DIPY derivatives, 2,8-bis(7-(9H-carbazol-9-yl)-9,9-Dioctyl-9H-
fluoren-2-yl)-6,6,12,12-Tetrak-is (6-(9H-carbazol-9-yl)hexyl)-6,12-Dihydrodiindeno[1,2-b:1',2'-
e]pyrazine (DCzDIPY-TCz) and 4,4'-((6,6,12,12-Tetrakis(6-(9H-carbazol-9-yl)hexyl)-6,12-
Dihydrodiindeno[1,2-b:1',2'-e]pyrazine-2,8-diyl)bis(9,9-Dioctyl-9H-fluorene-7,2-diyl))bis(N,N-
Diphenylaniline) (DTPADIPY-TCz) were designed and synthesized by introducing four
peripheral carbazole to regulate their energy levels for the charge transfer and injection (Scheme
1
.). Their absorptive, emissive, thermal and electrochemical properties were investigated and
showed ideal performance for electroluminescence emitters. Solution-processed double-layer
devices based on these peripheral DIPYs show efficient blue and bluish green emission with a
−
1
maximum power efficiency (PE) of 6.88 lm W and a relatively low efficiency roll-off, which is
among the highest performance for solution-processable fluorescent OLEDs.
4

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Scheme 1. Synthetic routes for DCzDIPY-TCz and DTPADIPY-TCz
2
. Experimental section
2
.1. Material and method
1
13
H NMR spectra were recorded on a Bruker DRX-400 spectrometer at 400 MHz and C
NMR were recorded on the same spectrometer at 400 MHz. ESI-MS was measured on a
FINNIGAN Trace DSQ mass spectrometer. The elemental analyses were tested on a
5

ACCEPTED MANUSCRIPT
PerkineElmer 2400 II elemental analyzer. Absorption and fluorescence spectra were done on a
Shimadzu UV-2550 and Shimadzu RF-5301PC spectrophotometers. All the chemicals were
purchased from local suppliers or TCI and used as received without further purification. The
reactions were sensitive to water or oxygen and performed under argon atmosphere.
2
.2. Synthesis
Syntheses of 5-Bromo-2,3-dihydro-2-(hydroxyimino)inden-1-one (1). 5-bromo-indanone
(25 g, 118.5 mmol), concentrated hydrochloric acid and toluene (120 mL) were mixed and
stirred at room temperature in a 500 mL round flask. Amylnitrite (16.6 g, 142 mmol) was slowly
o
added and the mixture was heated to 40 C for 5 hours. The reactant was filtered and rinsed with
1
CH OH, Pale power 1 was obtain with the yield of 71% (20.2 g). H NMR (400 MHz, CDCl ) δ
3
3
[ppm] 3.78(s, 2H), 7.67(d, 2H, J=5.25 Hz), 7.89(s, 1H), 12.73(s, 1H).
Synthesis of 2,8-Dibromo-6,12-dihydrodiindeno[1,2-b:1,2-e]pyrazine (2). To a 500 mL
round flask, the synthesized 1 (3.1 g, 12.5 mmol) and sodium dithionite (7.24 g, 41.6 mmol)
were mixed with EtOH (13 mL). In the nitrogen atmosphere, 28% ammonia solution (26 mL)
o
was added and stirred at 95 C for 24 h. When the reaction was finished, it was cooled and then
more distilled water (100 mL) was added. After stirring, the mixture was filtered and sufficiently
1
rinsed with CH
3
OH, diethyl ether and then 2 was obtained. The yield was 62 %. H NMR (400
MHz, CDCl ) δ [ppm] 4.06（s, 4H）, 7.63-7.67(d, 2H, J=6.01 Hz), 7.8 (s, 2 H), 7.96-8.00(d,
3
2
H, J=6.83 Hz).
Synthesis of 2,8-Dibromo-6,12-dihydrodiindeno[1,2-b:1,2-e]pyrazine (3). To a 100 mL
round flask, the synthesized 2 (0.84 g, 2 mmol), tetra-n-butyl ammonium bromide (0.12 g, 0.4
mmol) and KOH (0.66 g, 12 mmol) were put in 25 ml DMSO and stirred the mixture for 0.5 h at
room temperature. Then, 9-(6-bromohexyl)- 9H-carbazole (5.28 g, 16 mmol) was added for three
6

ACCEPTED MANUSCRIPT
o
times with the time interval of 20 min. After that, the mixture was heated to 55 C for 20 h.
When the reaction was finished, the mixture was washed with water. The organic solution was
dried with MgSO , purified with chromatography on silica gel. The white power was obtained
4
1
with the yield of 0.34 g, 12%. H NMR (400 MHz, CDCl ) δ [ppm] 0.5-0.8(m, 8H), 0.98-1.15(m,
3
1
6 H), 1.60-1.67 (m, 8 H), 1.89 (t, 4 H, J=11.36 Hz), 2.17 (t, 4 H, J=11.50 Hz), 4.10 (t, 8 H,
J=6.48 Hz), 7.15-7.27 (m, 16 H), 7.36-7.42(m, 8 H), 7.54-7.61(m, 4H), 7.93(d, 2H, J=3.90 Hz),
+
8
7
.06(d, 2H, J=3.80Hz). ESI-MS (m/z): 1410.3, 1411.2. (M +1). Anal. Calcd for C90
H86Br
2
N
6
: C,
6.58; H, 6.14; N, 5.95; Found: C, 76.51; H, 6.07; N, 6.01.
Synthesis of 9-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)-9H-carbazole (4). Carbazole (5 g, 30
mmol), 2,7-dibromo-9,9-dioctyl-9H-fluorene (22 g, 40 mmol), CuI (1 g, 5.2 mmol), K CO (6.2
g, 45 mmol), 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU, 2 ml), 18-crown-6
2
3
(0.32 g, 1.2 mmol) were put in 100 mL flask with 50 mmol dichlorobenzene. The mixture was
o
heated to 170 C for 24 h on the nitrogen atmosphere. After reaction, the solvent was removed
1
and purified by chromatography on silica gel. Yield, 38%. H NMR (400 MHz, CDCl ) δ [ppm]
3
0
7
6
.74-0.90 (m, 10H), 1.1-1.3(m, 20H), 1.97-2.06 (m, 4H), 7.32-7.39 (m, 2H), 7.43-7.50 (m, 4H),
.53-7.61 (m, 4H), 7.64-7.70 (m, 1H), 7.89-7.94 (m, 1H), 8.21(d, 2H, J=3.6 Hz); ESI-MS (m/z):
+
33.1, 635.3 (M +1).
Synthesis of 4-(7-bromo-9,9-dioctyl-9H-fluoren-2-yl)-N,N-diphenylaniline (5). 2,7-
dibromo-9,9-dioctyl-9H-fluorene (8.2 g, 15 mmol), (4-(diphenylamino)phenyl)- boronic acid
2.9 g, 10 mmol) and PdCl (PPh )2 (100 mg, 0.14 mmol) was added to a 250 ml flask. The
CO (aq, 20 ml) were added under argon atmosphere. The mixture
(
2
3
toluene (50 ml) and 2M K
2
3
o
was stirred at 100 C for 24 h. After cooling, extraction with DCM, the organic layer was
collected and dried with MgSO . The solvent was removed under reduced pressure and the crude
4
7

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product was absorbed onto silica. Chromatography on silica gel with gradient elution (PE/DCM)
1
and a white solid was gotten (3.5 g, yield, 49%). H NMR (400 MHz, CDCl ), δ [ppm]: 10.1 (s,
3
1
4
H), 7.91 (d, 2H, J=8.14 Hz), 7.71 (d, 2H, J=8.40 Hz), 7.50 (d, 2H, J=8.67 Hz), 7.30-7.24 (m,
+
+
H), 7.13 (d, 6H, J=7.36 Hz), 7.06 (t, 2H, J=7.35 Hz). ESI-MS (m/z): 350.1 (M +H ); ESI-MS
+
(
m/z): 711.2, 713.1 (M +1).
Synthesis of 9-(9,9-dioctyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H- fluoren-2-
yl)-9H-carbazole (6). 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi(1,3,2-dioxaborolane) (3.15 g, 9
mmol), PdCl (dppf) (0.22 g, 0.27 mmol) and Potassium acetate (2.52 g, 27 mmol) were put into
2
a two-neck round-bottom flask equipped with a stirrer and reflux condenser. 1,4-dioxane (40
mL) was added and the mixture was stirred under nitrogen for 10 min. After that compound 4
o
(
3.2 g，5.0 mmol) was added and the mixture was kept at 85 C for 10 h. After cooling to room
temperature, the mixture was extracted with ethyl acetate followed by purification by column
chromatography on silica gel with ethyl acetate/hexane (v/v, 1:3) as the eluent to offer a white
1
solid. Yield: 3.3 g, 97%. H NMR (400 MHz, CDCl ) δ [ppm] 0.69-0.87 (m, 10H), 1.05-1.25(m,
3
2
0H), 1.44 (s, 12H), 1.96-2.14 (m, 4H), 7.33 (t, 2H, J= 6.84 Hz), 7.42-7.50 (m, 4H), 7.53-7.59
(m, 2H), 7.78-7.86 (m, 2H), 7.87-8.0 (m, 2H), 8.20 (d, 2H, J= 3.6 Hz); ESI-MS (m/z): 682.2
+
(
M +1).
Synthesis of 4-(9,9-dioctyl-7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H- fluoren-2-
yl)-N,N-diphenylaniline (7). The synthetic process of compound 7 is the same with the way of
1
compound 6. Yield: 6.22 g, 91%. H NMR (400 MHz, CDCl ) δ [ppm] 0.65-0.74 (m, 4H), 0.81-
3
0
.88 (m, 6H), 1.04-1.26 (m, 20H), 1.45 (s, 12H), 2.0-2.12 (m, 4H), 7.08 (t, 2H, J=7.11Hz), 7.18-
8

ACCEPTED MANUSCRIPT
7
.24 (m, 6H), 7.29-7.35 (m, 4H), 7.57-7.64 (m, 4H), 7.73-7.90 (m, 4H); ESI-MS (m/z): 759.2
+
(
M +1).
Synthesis
of
2,8-bis(7-(9H-carbazol-9-yl)-9,9-dioctyl-9H-fluoren-2-yl)-6,6,12,12-
tetrakis(6-(9H-carbazol-9-yl)hexyl)-6,12-dihydrodiindeno[1,2-b:1',2'-e]pyrazine
(DCzDIPY-TCz). The synthetic process of DCzDIPY-TCz is the same with the way of
1
compound 5. Yield: 0.363 g, 46%. H NMR (400 MHz, CDCl ) δ [ppm] 0.68-0.91 (m, 28H),
3
1
8
7
8
1
1
2
.10-1.23 (m, 56H), 1.60-1.68 (m, 8H), 2.05-2.18 (m, 12H), 2.33-2.45 (m, 4H), 4.04-4.14 (m,
H), 7.16 (t, 8H, J= 7.33 Hz), 7.21-7.26 (m, 8H), 7.36 (t, 12H, J= 7.47 Hz), 7.45-7.54 (m, 10 H),
.60-7.65 (m, 4H), 7.73-7.80 (m, 6H), 7.84 (d, 2H, J= 4.01 Hz), 7.92 (d, 2H, J= 3.89Hz), 7.99-
1
3
3
.09 (m, 10H), 8.23 (d, 2H, J=4.01Hz); C NMR (100 MHz, CDCl ) δ [ppm] 152.9, 152.0,
50.9, 142.8, 141.1, 140.4, 140.3, 139.9, 137.8, 136.6, 126.6, 125.9, 125.5, 123.4, 122.7, 121.9,
21.5, 121.0, 120.2, 119.9, 118.6, 109.8, 108.5, 55.6, 53.0, 42.7, 40.3, 38.4, 31.8, 30.0, 29.5,
+
9.3, 29.2, 28.7, 26.6, 24.0, 22.6, 14.1; ESI-MS (m/z): 2361.3 (M +1); Anal. Calcd for
C H N : C, 87.49; H, 7.77; N, 4.75; Found: C, 87.51; H, 7.71; N, 4.78.
172 182
8
Synthesis of 4,4'-((6,6,12,12-tetrakis(6-(9H-carbazol-9-yl)hexyl)-6,12-dihydrodi- indeno[1,2-
b:1',2'-e]pyrazine-2,8-diyl)bis(9,9-dioctyl-9H-fluorene-7,2-diyl))bis(N,N-diphenylaniline) （
DTPADIPY-TCz). The synthetic process of DTPADIPY-TCz is the same with the way of
1
compound 5. Yield: 0.454 g, 52%. H NMR (400 MHz, CDCl ) δ [ppm] 0.58-0.88 (m, 28H),
3
1
8
.04-1.24 (m, 56H), 1.60-1.68 (m, 8H), 1.09-2.20 (m, 12H), 2.30-2.44 (m, 4H), 4.04-4.14 (m,
H), 7.11-7.26 (m, 28H ), 7.29-7.37 (m, 18H), 7.59-7.64 (m, 8H), 7.67-7.88 (m, 14H), 8.01-8.08
1
3
(
m, 8H), 8.19-8.25 (m, 2H)。 C NMR (100 MHz, CDCl ) δ [ppm] 151.9, 151.7, 150.8, 150.7,
3
1
1
2
8
47.7, 147.1, 142.9, 140.6, 140.2, 139.7, 139.5, 135.5, 129.3, 127.8, 126.3, 125.5, 124.4, 124.0,
22.7, 121.5, 121.0, 120.2, 118.6, 108.5, 55.4, 53.0, 42.8, 40.4, 38.4, 31.8, 30.0, 29.7, 29.5, 29.2,
+
8.6, 26.6, 23.9, 22.6, 14.2; ESI-MS (m/z): 2517.2 (M +1); Anal. Calcd for C184
7.78; H, 7.77; N, 4.45; Found: C, 87.72; H, 7.75; N, 4.53.
194 8
H N : C,
9

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3
. Results and discussion
3
.1 Synthesis
The synthetic routes of DCzDIPY-TCz and DTPADIPY-TCz are shown in Scheme 1. The
synthesis process consists of three steps and two steps of precursor preparation process, then the
target molecules were prepared with a Suzuki coupling of 6,6,12,12-Tetrakis(6-(9H-carbazol-9-
yl)hex-yl)-2,8-Dibromo-6,12-Dihydrodiindeno[1,2-b:1',2'-e]pyrazine (3) and 9-(9,9-dioctyl-7-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-fluoren-2-yl)-9H-carbazole (6), 4-(9,9-dioctyl-
7
-(4,4,5,5-Tetramethyl-1,3,2-Dioxaborolan-2-yl)-9H-fluoren-2-yl)-N,N-Diphenylaniline (7).All
1
13
of the compounds were identified with H NMR, C NMR, mass spectrometry, spectroscopy,
and elemental analysis.
3
.2 Theoretical calculations
To see clearly their geometrical structures and electron density distributions, density
functional theory (DFT) calculations were performed with the B3LYP/6-31G(d, p) basis set by
using the Gaussian 03 program. Their ground geometries and electron densities of HOMOs and
LUMOs are shown in Figure 1. Obviously, both of them have two large torsion angles in the
optimized geometries, one is between the DIPY core and the fluorene planes, another locates on
the fluorene plane and carbazole/triphenylamine. There large angles are beneficial for
[
22]
suppressing their fluorescent quenching induced by the aggregation in the solid states. The
calculated HOMOs and LUMOs of DCzDIPY-TCz and DTPA DIPY-TCz are separately
distributed on the triphenylamine fluorene/carbazole fluorene and the DIPY units, respecttively.
The separation of the HOMO and LUMO is efficient for carrier transfer and balance in the
[
23]
emitter layers of OLEDs.
10

ACCEPTED MANUSCRIPT
HOMO(631)/-5.24 eV
LUMO(632)/-2.16 eV
HOMO(677)/-4.91 eV
LUMO(678)/-2.03 eV
Figure 1. The HOMO and LUMO electron cloud spatial distributions of DCzDIPY-TCz and
DTPADIPY-TCz using Gaussian 03 program calculations.
3
.3 Thermal properties
Figure 2a plots the cures of thermal gravimetric analysis (TGA) and differential scanning
calorimetry (DSC). As shown in the profiles of TGA, DCzDIPY-TCz and DTPADIPY-TCz
exhibit suitable thermal stability with 5% weight loss at a temperature of ~373 °C. The results
suggest both of them are stable for fabricating electroluminescent devices. As shown in the insert
Figure 2a, it can be seen that both of them have an endothermic peak at ~104 °C corresponding
to glass transition, implying the formation of amorphous film at temperatures below 104 °C with
spin-coating method.
3
.4 Electrochemical properties
11

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Electrochemical properties of DCzDIPY-TCz and DTPADIPY-TCz were tested by cyclic
voltammetry (CV) and their voltammogram was presented in Figure 2b. Both of them displayed
similarly reversible oxidation behaviors owing to the homologous oxidation of triphenyl-amine
ox
and carbazole units. Their HOMO levels are estimated from the onset of oxidation potentials (E
vs. saturated calomel electrode) with the values of −5.45 eV (DTPADIPY-TCz) and −5.55 eV
(DCzDIPY-TCz). Their LUMO levels are calculated from the absorption onsets (film
absorption) and HOMOs. The values are −2.82 eV for DTPADIPY-TCz and −2.88 eV for
DCzDIPY-TCz, respectively.
DTPADIPY-TCz
DCzDIPY-TCz
(a)
1
00
(b)
9
8
7
6
5
0
0
0
0
0
o
1
06
C
DTPADIPY-TCz
DCzDIPY-TCz
o
04 C
1
8
0
100
120
140
160
o
Temperature ( C)
1
00
200 300
400
500
0.0
0.2
0.4
0.6
0.8
1.0
1.2
o
Temperature ( C)
Potential Vs. SEC
Figure 2. a) TGA and DSC (insert) profiles of DCzDIPY-TCz and DTPADIPY-TCz; b) Cyclic
voltammogram of DCzDIPY-TCz and DTPADIPY-TCz vs SEC.
3
.5 Photophysical properties
UV-vis absorption, photoluminescence (PL) spectra in solution and film of DCzDIPY-TCz
and DTPADIPY-TCz are shown in Figure 3. Both of them have two similar absorption located at
420 nm and ~350 nm, indicating the same electronic transitions. Compared with their
~
absorption in solution and film, a red-shift about 20 nm is observed due to the molecular
aggregation in their film states. In accordance with the onset of their film absorptions, their
optical band gaps are 2.67 eV for DCzDIPY-TCz and 2.63 eV for DTPADIPY-TCz. The
12

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maximum film PL peaks of DCzDIPY-TCz and DTPADIPY-TCz are in the range of 450−480
nm. DTPADIPY-TCz shows a bathochromic emission about 20 nm in comparison with its
counterpart DCzDIPY-TCz, which can be attributed to the strong electron-donating property of
triphenylamine. Additionally, their solution emission appears obvious solvatochromic shift with
the changes of solvent polarity (Figure 3b and Figure S1), suggesting the occurrence of charge
[
24]
transfer on photoexcitation. In particular, we can see that the FWHM of DTPADIPY-TCz in
dichloromethane broadens while redshifts by 20 nm relative to THF, possibly due to the different
dynamic processes in dichloromethane. The phosphor is excited to produce a dipole moment,
causing the dichloromethane molecules to be disturbed and reassembled into a particular solvent
cage. It is possible that the special solvent cage of this phosphor in dichloromethane make the PL
spectrum different.
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
DCzDIPY-TCz Sol.
DCzDIPY-TCz Film
DTPADIPY-TCz Sol.
DTPADIPY-TCz Film
DCzDIPY-TCz Film
DTPADIPY-TCz Sol.
1.0
0.8
(
a)
(b)
DTPADIPY-TCz
Hexane
THF
DCM
Methno
l
0.6
0.4
0.2
0.0
3
00
350
400
450
500
550
600
650
700
4
00
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
Figure 3. a) UV−vis absorption in solution and film, PL spectra in film; b) PL spectra of T
DTPADIPY-TCz in different solvents.
3
.6 Electroluminescence
13

ACCEPTED MANUSCRIPT
The electroluminescent properties were investigated by fabricating the solution-processed
double-layer devices with the structure of ITO/PEDOT:PSS(40 nm)/DCzDIPY-TCz or
DTPADIPY-TCz (40 nm)/TPBi (50 nm)/LiF (1 nm)Al (120 nm), in which ITO, PEDOT:PSS
and TPBI are abbreviations of indium tin oxide, poly(3,4-ethyl-enedioxythiophene): polystyrene
sulfonate, and 1,3,5-tris(N-phenyl-benzimidazol-2-yl)benzene, respectively. The current
density− voltage−luminance, efficiencies-brightness, and electroluminescent (EL) characteristics
are shown in Figure 4 and Figure S2. Their EL spectra shows typical emissions from DCzDIPY-
TCz and DTPADIPY-TCz compared with their PL ones, suggesting that carriers recombination
is effectively restricted in DCzDIPY-TCz and DTPADIPY-TCz. The device using DCzDIPY-
TCz as emitter exhibits blue electroluminescence with CIE coordinates of (0.24, 0.14) and a
-1
maximum power efficiency (PE) of 0.35 lm W . While the device based on DTPADIPY-TCz
-1
shows better device efficiencies with a maximum PE of 2.20 lm W , which is a higher level
[
25,26]
among the reported to date for solution-processable fluorescent OLEDs.
As we can see in
Figure 4 e), the maximum external quantum efficiency (EQE) of DCzDIPY-TCz and
DTPADIPY-TCz are 0.53 and 1.15%, respectively. They all exhibited a low efficiency roll-off
-2
blow 1000 cd m , TPA efficiency roll-off smaller, especially. As the strong interaction between
triphenylamine with DIPY, the EL of DTPADIPY-TCz shifts to be a bluish green emission with
CIE coordinates of (0.21, 0.35). In comparison with their PEs, DTPADIPY-TCz-based device is
twice higher than that of DCzDIPY-TCz by only replacing carbazole to triphenylamine. This
may be attributed to the difference of hole injection barriers (the interface of
PEDOT:PSS/emitting-layer) and carriers transfer. Due to the different hole injection barriers,
their turn-on voltages alter largely with 3.8 V for DTPADIPY-TCz and 5.5 V for DCzDIPY-
14

ACCEPTED MANUSCRIPT
TCz. Carriers transfer properties were also important to the high power efficiency. To find hole
and electron transfer characteristics of
TPA
CZ
(b)
10
1
(a)
1
00
- - - TPA
CZ
400
300
200
100
3
2
1
10
10
10
DTPADIPY-TCz
DCzDIPY-TCz
1
0
0
0
1
.1
.01
1
E-3
0.1
1E-4
10000
1
10
100
1000
2)
3
4
5
6
7
8
9
Voltage (V)
Brightness
(
cd/m
2
1
0
1
2
3
4
5
1
0
1
.0
.8
.6
.4
.2
.0
(
d)
(c)
DTPADIPY-TCz
DCzDIPY-TCz
10
0
DTPADPIY-TCz
10
-
0
0
0
0
10
-
-
-
-
10
10
10
10
hole-only
electron-only
400
500
600
700
0
2
4
6
8
10
Wavelength (nm)
Voltage (V)
10
DTPADIPY-TCz
DCzDIPY-Cz
1
0.1
0.01
1
10
100
1000
2)
10000
Luminance (cd/m
15

ACCEPTED MANUSCRIPT
Figure 4. a) Current density−voltage−luminance characteristics; b) Current efficiency and power
efficiency versus brightness curves; c) Electroluminescent spectra of DCzDIPY-TCz and
DTPADIPY-TCz; d) Current density−voltage profiles of hole-only and electron-only devices of
DTPADIPY-TCz; e) V-EQE characteristics of DCzDIPY-TCz and DTPADIPY-TCz-based
single-layer OLEDs.
-2
-2
at 100 cd m
at 1000 cd m
a
CEmax PEmax
b
V
on
EQEmax CIE
-1 (%) (x, y)
CE PE
cd (lm
CE PE
(cd (lm
Device
Cz
(
cd (lm
V
EQE V
(%) (V)
EQE
(%)
(V)
-1
A ) W )
(
(V)
-1
-1
-1
-1
A ) W )
A ) W )
5.49 0.83 0.35 0.53
0.243,0.142 6.65 0.56 0.35 0.35 7.67 0.83 0.34 0.53
TPA 3.84 2.49 2.20 1.15
0.207,0.349 5.18 2.36 1.43 1.09 6.74 1.90 0.89 0.91
-2
-2
a: at the luminance of 1 cd m ; b: at the current density of 10 mA cm .
Table 1. Electroluminescent characteristics of the devices with DCzDIPY-TCz and DTPADIPY-
TCz-based.
DTPADIPY-TCz, we also fabricated the hole-only and electron-only devices with configurations
of ITO/PEDOT:PSS (40 nm)/DTPADIPY-TCz (40 nm)/MnO (10 nm)/Al (100 nm) and
3
ITO/Al(100 nm)/DTPADIPY-TCz (40 nm)/TPBi (50 nm)/LiF (1 nm)/Al (100nm) (see the
Figure. 4d). Because the environment of the device is low electric field conditions, the device
structure containing only hole or electron transport material is prepared, and the hole or electron
transport capacity is measured by steady current current-voltage method. In other words, it is
examined whether their carrier mobility is matched and the carrier mobility follows the
ꢈ
ꢁ
ꢇ
following formula: ꢀ = ꢃ ꢃ ꢆ . The L is the carrier mobility, ε and ε are dielectric constants,
ꢄ ꢅ
ꢊ
r
0
ꢂ
ꢉ
J is current density, V is applied voltage, and d is device thickness. Then we use the Origin
16

ACCEPTED MANUSCRIPT
software according to Figure 4 d) to calculate the electron and hole mobility. The electron
-4
-2
-4
-2
mobility is 4.98ꢀ10 cm /V⦁S, and the hole mobility is 1.68ꢀ10 cm /V⦁S. Thus, their carrier
mobility is very similar, indicating that DTPADIPY-TCz-based devices exhibit balanced holes
and electrons transport. Therefore, the balanced carriers transfer and suitable hole injection
barrier collectively contribute to the improvement of power efficiency. Notably, at high
-2
brightness of 100 and 1000 cd m , the power efficiencies of DTPADIPY-TCz still keep as 1.43
-1
-1
-1
-1
lm W and 0.89 lm W , DCzDIPY-TCz still keep as 0.35 lm W and 0.34 lm W , respectively,
implying a relatively low efficiency roll-off.
4
. Conclusions
In conclusion, two novel peripheral carbazole substituted Diindenopyrazinediones have
been demonstrated for high-efficient and solution-processable OLEDs. By fine-tuning their
carriers transfer and hole injection barriers, double-layer solution-processed device based on
DTPADIPY-TCz shows highly efficient bluish green emission with a maximum power
−
1
efficiency (PE) of 2.30 lm W and a relatively low efficiency roll-off. Our results show that
peripheral carbazole substituted Diindenopyrazinediones could be used as a promising unit for
constructing efficient emitters of solution-processed OLEDs to reduce the cost of
industrialization.
Acknowledgments
This work was financially supported from National Natural Science Foundation of China
(
21574144, 21674123, 51273209), National Key Research and Development Plan (2016YFB040
000), Zhejiang Provincial Natural Science Foundation of China (LR16B040002), CAS
Interdisciplinary Innovation Team, Ningbo Municipal Science and Technology Innovative
1
17

ACCEPTED MANUSCRIPT
Research Team (2015B11002, 2016A610277), State Key Laboratory for Modification of
Chemical Fibers and Polymer Materials, Donghua University.
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Highlights
1
. We have designed and synthesized two kinds of solution-processable Substituted
Diindenopyrazinediones with Polyalkyl-carbazole symmetrically blue fluorescent
OLED materials with novel structure and improved carrier transport and
luminescence properties.
2
. Solution-processed device based on DTPADIPY-TCz shows highly efficient bluish
green emission with a maximum power efficiency (PE) and current efficiency (CE) of
−1
-1
2
.20 lm W and 2.49 cd A , which is still the initial 40% and 76% of power
2
efficiency and current efficiency even at 1000 cd/m . Means that the two molecules
with very low efficiency roll-off.
3
. By fine-tuning their carries transfer and injection barriers, solution-processed
device based on DTPADIPY-TCz shows highly efficient blue emission and a
relatively low efficiency roll-off of external quantum efficiency(EQE).