Highly efficient non-doped deep-blue organic light-emitting diodes by employing a highly rigid skeleton

Article abstract of DOI:10.1016/j.dyepig.2018.05.071

Two novel deep-blue emitters based on a highly rigid unit, IDC-PA and IDC-Py, were prepared by respectively introducing the 7,7-dimethyl-5-phenyl-5,7-dihydro indeno [2,1-b] carbazole (IDC) unit with anthracene and pyrene derivatives. The emitters exhibit

Full text of DOI:10.1016/j.dyepig.2018.05.071

Accepted Manuscript
Highly efficient non-doped deep-blue organic light-emitting diodes by employing a
highly rigid skeleton
Ye-Xin Zhang, Yi-Yuan, Qiang Wang, Yun Hu, Aziz Khan, Zuo-Quan Jiang, Liang-
Sheng Liao
PII:
S0143-7208(18)30545-X
10.1016/j.dyepig.2018.05.071
DYPI 6800
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 12 March 2018
Revised Date: 28 May 2018
Accepted Date: 29 May 2018
Please cite this article as: Zhang Y-X, Yi-Yuan , Wang Q, Hu Y, Khan A, Jiang Z-Q, Liao L-S, Highly
efficient non-doped deep-blue organic light-emitting diodes by employing a highly rigid skeleton, Dyes
and Pigments (2018), doi: 10.1016/j.dyepig.2018.05.071.
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ACCEPTED MANUSCRIPT
Highly Efficient Non-doped Deep-blue Organic Light-Emitting Diodes
by Employing a Highly Rigid Skeleton
Ye-Xin Zhang, Yi-Yuan, Qiang Wang, Yun Hu, Aziz Khan, Zuo-Quan Jiang,* Liang-
Sheng Liao.*
Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of
Functional Nano & Soft Materials (FUNSOM), and Collaborative Innovation Center of
Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu 215123,
China
* Corresponding authors.
E-mail addresses: zqjiang@suda.edu.cn (Z.-Q. Jiang), lsliao@suda.edu.cn (L.-S. Liao).
1 Tel.: +86-521-65880093; fax: +86-521-658808220
2 Tel.: +86-521-65880945; fax: +86-521-658808220
Abstract
Two novel deep-blue emitters based on a highly rigid unit, IDC-PA and IDC-Py, were
prepared by respectively introducing the 7,7-dimethyl-5-phenyl-5,7-dihydro indeno [2,1-
b] carbazole (IDC) unit with anthracene and pyrene derivatives. The emitters exhibit high
quantum efficiency, excellent thermal stability, narrow full width at half maximum and
deep-blue emission. Moreover, the IDC-PA and IDC-Py-based devices demonstrated
maximum EQEs of 4.41% and 6.08% and maintain 4.35% and 5.35% as applied in non-
doped devices even at the brightness of 5000 cd m-2 with CIE coordinates of (0.15, 0.10)
and (0.15, 0.08), respectively.
Keywords
Fluorescent OLED; Non-doped; High Rigidity; Deep-blue.

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1. Introduction
Organic light-emitting diodes (OLEDs) have drawn considerable attention due to the
potential application in future illuminations and information displays, such as residential
lamps, automobile tail lights, TVs and computer monitors.1,2 Therefore, many material
systems have been explored over the past decades for the goal of highly efficient OLED
emitters with fluorescence,3-7 phosphorescence,8-12 or thermally activated delayed
fluorescence (TADF).13-16 The fluorescent emitters were firstly investigated covering the
whole visible region, but the maximum internal quantum efficiency is limited to 25%
because they can only harvest singlet excitons. This fact promotes researchers to develop
phosphorescent or TADF emitters which can harness all the electron-generated excitons
in theory. The phosphorescent dyes, however, are limited by the high cost of noble metal
elements and it is difficult to achieve deep-blue emission, i.e. giving a Commission
International de l'Eclairge “y” coordinate (CIEy) < 0.15.17 This problem can be partly
ascribed to the host-guest doping system for the application of phosphorescent and TADF
emitters. Given a deep-blue emitter, a wider band-gap host is necessary to prevent any
energy back transfer. However, the consequence is that the carrier injection from
neighboring transport layer to the emitting layer could be very tough. On the other hand,
the TADF materials with deep-blue emission for OLEDs are still lacking,18 and they also
faced the challenge in reducing the efficiency roll-off at high operation luminance.
According to the standard of National Television System Committee (NTSC), the CIEy
of blue emission should be further limited to 0.08. In this regard, the fluorescent emitters
regenerated new interest because they could be used without host and the molecular
design aiming for deep-blue emitters with low efficiency roll-off could be achievable.19-25

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Anthracene and pyrene are two important candidate blocks for fluorescent blue emitters
because of their high quantum efficiency, good carrier mobility, and chemical stability.26-
33
However, the anthracene and pyrene derivatives also suffer from aggregation induced
red-shift due to intermolecular packing in the film state, which is ascribed to their plate-
like structure. In this work, we report the synthesis and characterization of two new
fluorescent dyes, named IDC-PA and IDC-Py, to introduce highly rigid skeleton unit, 7,7-
dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (IDC), which can effectively
alleviate the aggregation effect. They also exhibit good thermal stability and show strong
blue emission in both solution and film. Both of dyes can act as the emitters in non-doped
OLEDs without any hole-injection layers, giving the maximum external quantum
efficiency (EQE) of 4.41% for IDC-PA and 6.08% for IDC-Py, respectively.
Consequently, they present deep-blue electroluminescence, for which the CIEys are 0.10
and 0.08, subsequently.
2.
Experimental
2.1. Chemicals and Characterization
All reagents used in the synthesis procedure were purchased from Shanghai Titan
Scientific Co., Ltd without further purification. THF was purified by PURE SOLV
(Innovative Technology) purification system. Tris (4-(9H-carbazol-9-yl) phenyl)amine
(TCTA), N,N'-bis-(1-naphthalenyl)-N,N'-bis-phenyl-(1,1'-biphenyl)-4,4' diamine (NPB),
1,3,5-tris(1-phenyl-1H-benzimidazole-2-yl)benzene (TPBi), 8-Hydroxyquinolinolato-
1
lithium (Liq) and aluminum (Al) were purchased from Lumtec Company. H NMR
spectra were recorded using Bruker 400 MHz and 600 MHz NMR instrument, while 13C

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NMR spectra were recorded on an Agilent DD2-600 MHz NMR instrument. Mass
spectra were recorded on a Thermo ISQ mass spectrometer using a direct exposure probe.
UV-Vis absorption spectra were recorded on a Perkin Elmer Lambda 750
spectrophotometer. PL spectra were recorded on a Hitachi F-4600 fluorescence
spectrophotometer. Differential scanning calorimetry (DSC) was performed on a TA
DSC 2010 unit at a heating rate of 10 K min-1 under nitrogen. Thermogravimetric
analysis (TGA) was performed on a TA SDT 2960 instrument at a heating rate of 10 K
min-1 under nitrogen. Elemental Analysis (EA) was determined by ELEMENTAL Vario
III elemental analyzer. The film surface morphologies were evaluated by atomic force
microscopy (AFM, Multimode V, Veeco). Ultraviolet photoelectron spectroscopy (UPS)
measurement was carried out in a Kratos AXIS UltraDLD ultrahigh vacuum (UHV)
surface analysis system. The electroluminescence (EL) and current density-voltage (J–V)
characteristics of the devices were measured using a constant current source meter unit
(Keithley 2400s Source Meter) equipped with a photometer (Photo Research PR 655
spectrophotometer).
2.2. Synthetic Process
2.2.1 Methyl 2-(9-phenyl-9H-carbazol-3-yl) benzoate (1)
(9-phenyl-9H-carbazol-3-yl) boronic acid (10.0 g, 34.8 mmol), methyl 2-iodobenzoate
(10.0 g, 38.3 mmol), K2CO3 (2M in water, 20 mL) and Pd(PPh3)4 (0.4 g, 0.35 mmol) were
dissolved in toluene (120 mL), the mixture was stirred at 100 oC under nitrogen for 48 h.
After cooling to room temperature, the organic phase was separated and concentrated.
The residue was purified by silica gel column chromatography using an eluent mixture of
dichloromethane and petroleum ether in the volume ratio of 1:2 to give a white solid with

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10.1 g (yield: 83.6%). 1H NMR (600 MHz, DMSO-d6) δ 8.29 (d, J = 7.8 Hz, 1H), 8.22
(d, J = 1.2 Hz, 1H), 7.77 (dd, J = 7.8, 1.2 Hz, 1H), 7.71 (t, J = 7.8 Hz, 2H), 7.67 – 7.64
(m, 3H), 7.57 (dd, J = 7.8, 2.4 Hz, 2H), 7.51 – 7.44 (m, 2H), 7.42 (d, J = 1.2 Hz, 1H),
7.40 (s, 1H), 7.32 (ddd, J = 14.4, 8.4, 1.2 Hz, 2H), 3.59 (s, 3H). 13C NMR (CDCl3, 400
MHz) (δ, ppm): 169.66, 142.94, 141.27, 140.20, 137.66, 133.21, 131.25, 131.17, 129.90,
129.71, 127.50, 127.08, 126.73, 126.70, 126.08, 123.43, 123.36, 120.36, 120.04, 119.94,
109.90, 109.35, 52.03. Anal. calcd for C26H19NO2 (%): C, 82.74; H, 5.07; N, 3.71. Found:
C, 82.41; H, 5.25; N, 3.52. MS (EI) m/z: 377.21 [M+].
2.2.2 2-(2-(9-phenyl-9H-carbazol-3-yl) phenyl) propan-2-ol (2)
2-(9-phenyl-9H-carbazol-3-yl)benzoate (4.0 g, 10.6 mmol) was dissolved in anhydrous
tetrahydrofuran, CH3MgCl (2M in THF, 21 mL, 42.4 mmol) was added dropwise at room
temperature, the mixture was heated up to 65 °C and kept at same temperature for 10
hours under nitrogen atmosphere. After cooling to room temperature, the reaction was
quenched with NH4Cl solution. The organic layer was dried by anhydrous sodium sulfate,
and concentrated. The residue was purified by silica gel column chromatography using an
eluent mixture of ethyl acetate and petroleum ether in the volume ratio of 1:4, a white
amorphous powder was obtained with 2.9 g (yield:72.5%). 1H NMR (600 MHz, DMSO-
d6) δ 8.26 (d, J = 7.8 Hz, 1H), 8.11 (s, 1H), 7.88 (d, J = 7.8 Hz, 1H), 7.73 – 7.66 (m, 4H),
7.56 (t, J = 7.2 Hz, 1H), 7.47 – 7.42 (m, 1H), 7.40 (d, J = 8.4 Hz, 1H), 7.36 (s, 2H), 7.31
(dd, J = 8.4, 1.6 Hz, 1H), 7.28 (t, J = 7.2 Hz, 1H), 7.24 (t, J = 7.2 Hz, 1H), 7.08 (d, J =
13
6.0 Hz, 1H), 4.86 (s, 1H), 1.24 (s, 6H). C NMR (CDCl3, 400 MHz) (
δ
, ppm): 146.64,
141.35, 140.47, 139.93, 137.58, 135.12, 132.96, 127.66, 127.57, 127.33, 127.10, 126.25,

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125.98, 125.78, 123.12, 122.86, 121.09, 120.39, 120.08, 109.94, 109.09, 74.24, 32.70.
Anal. calcd for C27H23NO (%): C, 85.91; H, 6.14; N, 3.71. Found: C, 85.85; H, 6.25; N,
3.62. MS (EI) m/z: 377.53 [M+].
2.2.3 7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (3)
2-(2-(9-phenyl-9H-carbazol-3-yl)phenyl)propan-2-ol (3.8 g, 10.0 mmol) was dissolved in
dichloromethane (50 mL) and cooled to 0 oC, a mixture of polyphosphoric acid (3.0 g) in
o
methanesulfonic acid (2 mL) was also added and left for 1 hour at 0 C, ethanol (100
o
mL) was added, and heated up to 80 C and kept it for 2 h. Dichloromethane was
evaporated and a colorless precipitate was filtered off, washed twice with methanol which
gives a white solid with 2.7 g (yield: 75.0%). 1H NMR (400 MHz, CDCl3) δ 8.55 (d, J =
7.6 Hz, 1H), 7.81 (d, J = 8.4 Hz, 1H), 7.74 (d, J = 7.2 Hz, 1H), 7.66 – 7.51 (m, 6H), 7.45
13
– 7.31 (m, 6H), 1.93 (s, 6H). C NMR (CDCl3, 400 MHz) (
δ
, ppm): 154.04, 147.99,
145.95, 141.75, 141.71, 139.74, 137.59, 131.98, 129.94, 127.86, 126.87, 125.95, 125.55,
124.49, 122.16, 121.73, 119.88, 119.22, 118.81, 118.03, 109.96, 108.90, 47.97, 24.08.
Anal. calcd for C27H21N (%): C, 90.21; H, 5.89; N, 3.90. Found: C, 90.35; H, 5.68; N,
3.97. MS (EI) m/z: 359.29 [M+].
2.2.4 2-bromo-7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (4)
7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (7.5 g, 20.9 mmol) was
dissolved in N,N-dimethylformamide, while N-bromosuccinimide (3.7 g, 20.9 mmol) was
added over the course of 30 min at room temperature in the dark, The mixture was stirred
for 8 h and poured into the Na2CO3 solution (3M, 1 L). The product was extracted with

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dichloromethane, and the organic phase was separated and concentrated. The residue was
recrystallized to give the product as a white solid with 8.3 g (yield: 92%). 1H NMR (600
MHz, CDCl3) δ 8.60 (s, 1H), 7.82 (d, J = 8.4 Hz, 1H), 7.73 (d, J = 7.2 Hz, 1H), 7.63 (d, J
= 7.8 Hz, 2H), 7.54 (d, J = 7.2 Hz, 4H), 7.50 (d, J = 9.6 Hz, 1H), 7.40 – 7.29 (m, 4H),
13
1.89 (s, 6H). C NMR (CDCl3, 400 MHz) (
δ
, ppm): 153.92, 148.13, 141.99, 140.40,
139.46, 137.14, 132.38, 130.07, 128.26, 128.20, 127.75, 127.18, 126.96, 126.86, 126.18,
123.48, 122.21, 118.90, 118.75, 112.57, 111.35, 109.14, 48.00, 24.17. Anal. calcd for
C27H20BrN (%): C, 73.98; H, 4.60; N, 3.20. Found: C, 73.85; H, 4.68; N, 3.02. MS (EI)
m/z: 437.31 [M+].
2.2.5 7,7-dimethyl-5-phenyl-2-(10-phenylanthracen-9-yl)-5,7-dihydroindeno [2,1-
b]carbazole
(IDC-PA)
and
7,7-dimethyl-5-phenyl-2-(pyren-1-yl)-5,7-
dihydroindeno[2,1-b]carbazole (IDC-Py)
2-bromo-7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (0.9 g, 2.0 mmol),
1.5 equivalent of arylboronic acid, 2M K2CO3 (10 mL), and Pd(PPh3)4 (0.023 g, 0.02
o
mmol) were added to 1,4-dioxane (80 mL), and stirred at 100 C for 12 h under nitrogen
atmosphere. The organic layer was concentrated and purified by silica gel column
chromatography using an eluent mixture of dichloromethane and petroleum ether in the
volume ratio of 1:3, which give a white powder with 0.96 g (yields: 77%) and 0.84 g
o
(yields: 73%), respectively. IDC-PA: mp: 334 C (760 mmHg). IR (KBr): v 3062, 2955,
1
1595, 1505, 1452, 1388, 1298, 1230, 763, 752 cm-1. H NMR (600 MHz, CDCl3) δ 8.65
(s, 1H), 7.92 (d, J = 8.4 Hz, 2H), 7.85 (d, J = 8.4 Hz, 1H), 7.77 – 7.69 (m, 8H), 7.62 (dd,
J = 15.6, 7.8 Hz, 4H), 7.59 – 7.55 (m, 3H), 7.45 (d, J = 8.4 Hz, 1H), 7.41 (d, J = 7.2 Hz,

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13
1H), 7.36 – 7.31 (m, 6H), 7.26 (d, J = 7.2 Hz, 1H), 1.77 (s, 6H). C NMR (CDCl3, 400
MHz) ( , ppm): 154.10, 148.23, 142.22, 141.12, 139.69, 138.65, 137.64, 132.93, 132.25,
δ
131.60, 131.11, 130.37, 130.07, 128.89, 128.35, 128.19, 128.04, 127.89, 127.49, 127.43,
127.30, 126.90, 126.64, 126.03, 126.02, 125.58, 125.03, 124.75, 124.73, 122.20, 118.86,
118.32, 109.91, 109.12, 48.07, 24.16. Anal. calcd for C47H33N (%): C, 92.27; H, 5.44; N,
2.29. Found: C, 92.31; H, 5.17; N, 2.52. MS (EI) m/z: 611.46 [M+].
o
IDC-Py: mp: 288 C (760 mmHg). IR (KBr): v 3045, 2966, 1600, 1500, 1457, 1382,
1
1288, 1230, 810, 752 cm-1. H NMR (600 MHz, CDCl3) δ 8.78 (s, 1H), 8.39 (d, J = 9.0
Hz, 1H), 8.30 (d, J = 7.8 Hz, 1H), 8.22 (d, J = 7.2 Hz, 1H), 8.20 – 8.09 (m, 5H), 7.85 (d,
J = 8.4 Hz, 1H), 7.76 – 7.70 (m, 3H), 7.70 – 7.65 (m, 4H), 7.56 (dd, J = 10.2, 6.0 Hz,
2H), 7.43 (dd, J = 9.6, 4.2 Hz, 2H), 7.34 (d, J = 7.2 Hz, 1H), 7.29 – 7.26 (m, 1H), 1.87 (s,
6H). 13C NMR (CDCl3, 400 MHz) (
δ, ppm): 154.10, 148.20, 142.13, 141.20, 139.67,
139.19, 137.96, 137.67, 136.95, 132.20, 131.39, 131.35, 130.55, 130.35, 130.05, 130.01,
129.21, 128.41, 128.01, 127.91, 127.44, 127.36, 127.31, 127.27, 127.24, 126.98, 126.92,
126.86, 125.97, 125.00, 124.97, 124.87, 122.16, 121.83, 119.18, 118.83, 118.31, 109.87,
109.10, 48.05, 24.06. Anal. calcd for C43H29N (%): C, 92.27; H, 5.22; N, 2.50. Found: C,
92.39; H, 5.27; N, 2.34. MS (EI) m/z: 559.39.
3. Results and discussions
The synthetic routes to IDC-PA and IDC-Py are illustrated in scheme 1. Methyl 2-(9-
phenyl-9H-carbazol-3-yl) benzoate is prepared by Suzuki Miyaura coupling reaction with
more than 80% yield. The precursor of tertiary alcohol is afforded by the nucleophilic
addition process. The chemical equilibrium of isomers can achieve directional

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development by strictly controlling the temperature and the acid ratio in the process of
dehydration. After the high yield electrophilic substitution reaction and the Suzuki
Miyaura coupling reaction, IDC-PA and IDC-Py are prepared.
Fig. 1 shows the optimized structure of IDC-PA and IDC-Py. Density functional theory
(DFT) calculations are carried out with Gaussian 09 using a B3LYP method with a basis
set of 6-31G(d). The dihedral angles between IDC and phenylanthracene/pyrene are
81.08o and 53.08o for IDC-PA and IDC-Py, respectively. The large steric hindrance
structures provide the possibility to restrain the aggregation effect.
UV-Vis absorption and photoluminescence (PL) spectra of IDC-PA and IDC-Py in the
dilute dichloromethane solution are shown in Fig. 2. Three absorption peaks at 358, 375,
and 397 nm, are attributed to the vibrational structure of the anthracene unit of IDC-PA.
The absorption peak around 350 nm of IDC-Py is due to π–π* transition derived from the
conjugated substituted pyrene backbone. The optical energy gaps are 2.93 and 3.07 eV
for IDC-PA and IDC-Py, respectively, which are determined from the UV-Vis absorption
edges. The emission maximum (λem) of IDC-PA and IDC-Py are 450 and 439 nm in dilute
CH2Cl2 solution, and the counterparts are 453 nm and 443 nm in films. The negligible
red-shit indicates there are almost no intermolecular interactions in the films. As
expected, the aggregation effect is suppressed by the twisted chemical structures. The
morphologies of IDC-PA and IDC-Py film are also measured by AFM, the surface
roughness values (in Root Mean Square, RMS) of the vacuum evaporated films are 0.63
and 0.97 nm for IDC-PA and IDC-Py, respectively (see Fig. S13). The PL quantum yields
in dichloromethane solution are estimated to be 0.84 and 0.78 by using 9,10-
diphenylanthrancene as the reference. 34

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The thermal properties of the two 3-monosubstituted compounds were evaluated using
thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) (see Fig.
3). Both the compounds were found to be highly stable under a nitrogen atmosphere, and
o
with thermal decomposition temperature (Td, 5% weight-loss) at 424 and 389 C, for
IDC-PA and IDC-Py, respectively, showing the stable nature of the material to compete
for the temperature of vacuum vapor deposition. During the second DSC traces of heating
(10 K min-1), the glass transition temperatures were observed at 186 and 157 oC for IDC-
PA and IDC-Py.
Ultraviolet photoelectron spectroscopy (UPS) with a helium lamp emitting at 21.2 eV is
used to ascertain the HOMO energy levels. As shown in Fig. 4, from the ionization
potential (HOMO-edge position) and the secondary cut-off regions of the UPS spectra,
the HOMO energy levels of IDC-PA and IDC-Py are -5.69 and -5.57 eV, respectively.
The bandgaps are determined to be -2.93 and -3.07 eV, thus the LUMO levels of IDC-PA
and IDC-Py are determined to be -2.76 and -2.50 eV, respectively. All the pertinent data
of IDC-PA and IDC-Py are summarized in Table 1.
To investigate the electroluminescence (EL) properties, non-doped devices were
fabricated with a structure of ITO/NPB (70 nm)/TCTA (10 nm)/Emitter (20 nm)/TPBi
(40 nm)/Liq (1 nm)/Al (100 nm). Fig. 5 shows the energy level diagram of devices, NBP
and TPBi are respectively used as the hole-transporting layer and the electron-
transporting layer, and TCTA is adopted as a buffer for confining excitons within the
emitting layer. Fig. 6a gives current density (J)-voltage (V)-luminance characteristics (L)
of blue OLEDs, the turn-on voltages (the driving voltage with the brightness of 1 cd/m2)
of the devices are 3.50 and 3.51 V for IDC-PA and IDC-Py-based devices, respectively. A

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relatively low opening voltage can be obtained without a hole-injection layer, which may
attribute to the two materials possessing a good carrier injection and transportation. Fig.
S14 exhibits the EL emission spectra of the blue OLEDs at different voltages. It can be
seen that the EL spectra and the PL spectra are almost the same, which suggests that the
EL can be attributed to the emission from the singlet excited state. In addition, the full
width at half maximum (FWHM) of the EL spectra is 58 and 56 nm for IDC-PA and IDC-
Py-based device, respectively. The emission peaks are 452 and 440 nm, the corresponding
color coordinates are (0.15, 0.10) and (0.15, 0.08). The stability of the spectra is also very
impressive because the electroluminescent peaks of the device do not show any drift even
at a higher voltage. In our non-doped devices, the long wavelength emission is not
observed, which is due to the non-planar molecular structure with a greater steric
hindrance of the materials. Fig. 6b shows the current and external quantum efficiencies of
IDC-PA and IDC-Py-based blue devices at different voltages. The maximum current and
external quantum efficiencies for the IDC-PA-based device are 4.80 cd A-1 and 4.41%,
-1
whereas those for the IDC-Py-based device are 4.13 cd A and 6.08%, respectively.
Interestingly, the IDC-Py-based device has a lower current efficiency, but a higher
external quantum efficiency, just owing to the minor difference of CIEy values. It is
noteworthy that the external quantum efficiency roll-off from 1000 cd m-2 to 5000 cd m-2
of the IDC-PA-based device is extremely low, with the value of 0.7%. The detailed
device performance parameters are summarized in Table 2. To further understand the
origin of the high EQEs, we study the excited state energy levels of the emitters by time-
dependent density functional theory (TD-DFT), the calculated results are summarized in
Table S1. The triplet energy (T1) levels of IDC-PA and IDC-Py are 1.77 and 2.08 eV,

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respectively, which can be ascribed to the transition in the anthracene and pyrene units. In
a triplet-triplet annihilation (TTA) process, twice the T1 should be higher than its singlet
energy (S1), and the energy should near with any of highly excited Sn (n > 1) to ensure the
exothermic energy transfer to S1. In Fig. S15, twice T1 energy levels of IDC-PA and IDC-
Py are close to corresponding S3 and S9, respectively, which may achieve the efficient
energy transfer to S1 by Förster energy transfer. Historically, anthracence and pyrene
chromophores are widely reported in TTA-based devices.35-38 Therefore, the highy
efficient OLEDs may be ascribed to the efficient up-conversion of triplet excitons
through TTA.
4. Conclusion
In summary, we have designed and synthesized two novel deep-blue emitters with highly
rigid structures and also successfully suppressed the negative aggregation effect. Both of
these compounds exhibit good thermal stability and excellent quantum yield, which
provide a potential to develop them as the emitter of OLEDs. The simple non-doped
devices based on these emitters exhibit high efficiencies of up to 4.80 and 4.13 cd A-1,
and maximum EQEs of 4.41% and 6.08% with CIE coordinates of (0.15, 0.10) and (0.15,
0.08) for IDC-PA and IDC-Py-based devices. In particular, the devices also maintain
almost negligible efficiency roll-off, even at the very high brightness of 5000 cd m-2.
These results provide a strategy of molecular design to achieve deep-blue emission in the
non-doped device.
Acknowledgments
The authors acknowledge the financial support from the National Natural Science Foundation of
China (Grant No. 21572152 and 61575136). This work was also funded by the Collaborative

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Innovation Centre of Suzhou Nano Science and Technology (Nano-CIC), by the Priority
Academic Program Development of Jiangsu Higher Education Institutions (PAPD), by the “111”
Project of The State Administration of Foreign Experts Affairs of China, and by Yunnan
Provincial Research Funds on College-Enterprise Collaboration (No. 2015IB016)
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Scheme 1. Syntheses of IDC-PA and IDC-Py.
Table 1. The photophysical and thermal properties of IDC-PA and IDC-Py.
a)
d)
λabs
λem (ФF)a)
(nm)
Td
Tg
HOMO b)
LUMO c)
(eV)
Eg
(nm)
(oC) (oC) (eV)
(eV)
2.93
3.07
289, 375, 397
278, 310, 350
450 (0.84)
424
389
186
157
-5.69
-5.57
-2.76
IDC-PA
IDC-Py
439 (0.78)
-2.50
a)
b)
c)
d)
Measured in dichloromethane solution; measured by UPS; calculated using HOMO and Eg;
the onsets of the UV−Vis absorption edges.
Table 2. Electroluminescence characteristics of the devices.
Device
IDC-PA
IDC-Py
V a) (V)
3.50
ηcb) (cd A-1)
4.80, 4.75, 4.62
4.13, 4.11, 3.64
ηextb) (%)
CIE(x,y)
(0.15, 0.10)
(0.15, 0.08)
4.41, 4.38, 4.35
6.08, 6.05, 5.35
3.51
a) Turn-on voltage. b) Current efficiency (ηc) and external quantum efficiency (ηext ) in the order of
maximum, at 1000 cd m-2 and at 5000 cd m-2.

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Fig. 1. Optimized structures of IDC-PA and IDC-Py obtained at B3LYP/6-31G* level.
Fig. 2. Absorption and photoluminescence spectra of IDC-PA and IDC-Py in solution, inset:
photoluminescence spectra of IDC-PA and IDC-Py in films.
Fig. 3. TGA curves of IDC-PA and IDC-Py measured at a heating rate of 10 K min-1. Inset: DSC
traces measured at a heating rate of 10 K min-1.

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Fig. 4. The ultraviolet photoelectron spectroscopy (UPS) spectra of IDC-PA and IDC-Py.
Fig. 5. The energy level diagram of the non-doped blue OLEDs.

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Fig. 6. a. Current density-voltage-luminance characteristics; b. the current efficiency and EQE versus
voltage.

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Table of Contents

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Supporting Information for:
Highly Efficient Non-doped Deep-blue Organic Light-Emitting Diodes
by Employing a Highly Rigid Skeleton
Ye-Xin Zhang, Yi-Yuan, Qiang Wang, Yun Hu, Aziz Khan, Zuo-Quan Jiang,* Liang-
Sheng Liao.*
Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of
Functional Nano & Soft Materials (FUNSOM), and Collaborative Innovation Center of
Suzhou Nano Science and Technology, Soochow University, Suzhou, Jiangsu 215123,
China
Fig. S1. 1H NMR spectrum of methyl 2-(9-phenyl-9H-carbazol-3-yl) benzoate (1).

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Fig. S2. 13C NMR spectrum of methyl 2-(9-phenyl-9H-carbazol-3-yl) benzoate (1).
Fig. S3. 1H NMR spectrum of 2-(2-(9-phenyl-9H-carbazol-3-yl) phenyl) propan-2-ol (2).

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Fig. S4. 13C NMR spectrum of 2-(2-(9-phenyl-9H-carbazol-3-yl) phenyl) propan-2-ol (2).

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Fig. S5. 1H NMR spectrum of 7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (3).
Fig. S6. 13C NMR spectrum of 7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (3).

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Fig. S7. 1H NMR spectrum of 2-bromo-7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (4).
Fig. S8. 13C NMR spectrum of 2-bromo-7,7-dimethyl-5-phenyl-5,7-dihydroindeno[2,1-b]carbazole (4).

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Fig. S9. 1H NMR spectrum of IDC-PA.
Fig. S10. 13C NMR spectrum of IDC-PA.

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Fig. S11. 1H NMR spectrum of IDC-Py.
Fig. S12. 13C NMR spectrum of IDC-Py.