Achieving non-doped deep-blue OLEDs by applying bipolar imidazole derivatives

Article abstract of DOI:10.1016/j.orgel.2019.03.044

In this work, we designed and synthesized two novel bipolar deep-blue emitting materials, 2-(4'-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)-1 (4(tri-fluoromethyl) phenyl)-1H-phenanthro[9,10-d] imidazole (CzB-FMPPI) and 9-(4'-(4,5-diphenyl-1 (4-(trifluoromethyl) phenyl)-1H-imidazole-2-yl)-[1,1′-biphenyl]-4-yl)-9H-carbazole (CzB-FMPIM). Among them, carbazole and phenanthroimidazole are bridged linkage by the biphenyl ring and act as electron-donating part. The CF₃-substituted phenyl ring applies as strong electron-withdrawing moiety. The exhibit highly twisted molecular configuration of two compounds efficiently shorten π-conjugation and inhibit intermolecular interaction, resulting in superior thermal stability and deep blue emission. High decomposition temperature of 431 °C and 414 °C, glass transition temperature of 150 °C and 135 °C for CzB-FMPPI and CzB-FMPIM, respectively, had been achieved. As a consequence of breaking the conjugation of phenanthroimidazole chromophore, CzB-FMPIM achieves an 8 nm blue-shifted emission compared with CzB-FMPPI. CzB-FMPPI exhibits a higher relative fluorescence quantum yield of 92.5% than 83.3% of CzB-FMPIM. Moreover, bipolar property was observed in both compound and homogeneous amorphous films were deposited and applied in the non-doped deep-blue OLEDs. The devices based on two emitters showed maximum luminance of 6667 cd/m² and 3084 cd/m², maximum EQE of 4.10% and 3.17%, respectively. Commission International de l'éclairage (CIE) coordinates of CzB-FMPIM based device achieved (0.15, 0.07) which is extremely close to the NTSC standard blue CIE (0.14, 0.08).

Full text of DOI:10.1016/j.orgel.2019.03.044

Accepted Manuscript
Achieving non-doped deep-blue OLEDs by applying bipolar imidazole derivatives
Yi Jia, Sen Wu, Yuteng Zhang, Shigen Fan, Xiaoming Zhao, Hongli Liu, Xiaofei Dong,
Shirong Wang, Xianggao Li
PII:
S1566-1199(19)30153-3
DOI:
https://doi.org/10.1016/j.orgel.2019.03.044
ORGELE 5182
Reference:
To appear in: Organic Electronics
Received Date: 23 January 2019
Revised Date: 12 March 2019
Accepted Date: 24 March 2019
Please cite this article as: Y. Jia, S. Wu, Y. Zhang, S. Fan, X. Zhao, H. Liu, X. Dong, S. Wang, X. Li,
Achieving non-doped deep-blue OLEDs by applying bipolar imidazole derivatives, Organic Electronics
(2019), doi: https://doi.org/10.1016/j.orgel.2019.03.044.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Achieving non-doped deep-blue OLEDs by applying bipolar
imidazole derivatives
Yi Jiaa,b, Sen Wua,b, Yuteng Zhanga,b Shigen Fana,b, Xiaoming Zhaoa,b, Hongli Liua,b*,
,
Xiaofei Donga,b, Shirong Wanga,b, Xianggao Lia,b*
a Tianjin University, School of Chemical Engineering and Technology, Tianjin 300072,
China
b Collaborative Innovation Center of Chemical Science and Engineering, Tianjin
300072, China
corresponding author email: lixianggao@tju.edu.cn
Abstract: In this work, we designed and synthesized two novel bipolar deep-blue
emitting materials, 2-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)-1 (4(tri-fluoromethyl)
phenyl)-1H-phenanthro[9,10-d] imidazole (CzB-FMPPI) and 9-(4'-(4,5-diphenyl-1
(4-(trifluoromethyl)
phenyl)-1H-imidazol-2-yl)-[1,1'-biphenyl]-4-yl)-9H-carbazole
(CzB-FMPIM). Among them, carbazole and phenanthroimidazole are bridged linkage
by the biphenyl ring and act as electron-donating part. The CF3-substituted phenyl ring
applies as strong electron-withdrawing moiety. The exhibit highly twisted molecular
configuration of two compounds efficiently shorten π-conjugation and inhibit
intermolecular interaction, resulting in superior thermal stability and deep blue
emission. High decomposition temperature of 431 °C and 414 °C, glass transition
temperature of 150 °C and 135 °C for CzB-FMPPI and CzB-FMPIM, respectively, had
been achieved. As a consequence of breaking the conjugation of phenanthroimidazole
chromophore, CzB-FMPIM achieves a 8 nm blue-shifted emission compared with
CzB-FMPPI. CzB-FMPPI exhibits a higher relative fluorescence quantum yield of 92.5%
than 83.3% of CzB-FMPIM. Moreover, bipolar property was observed in both
compound and homogeneous amorphous films were deposited and applied in the
non-doped deep-blue OLEDs. The devices based on two emitters showed maximum
luminance of 6667 cd/m2 and 3084 cd/m2, maximum EQE of 4.10% and 3.17%,

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respectively. Commission International de l'Éclairage (CIE) coordinates of
CzB-FMPIM based device achieved (0.15, 0.07) which is extremely close to the NTSC
standard blue CIE (0.14, 0.08).
Keywords: Bipolar, Deep-blue emission, Twisted configuration, Phenanthroimidazole,
Non-doped OLEDs.
1. Introduction
[1]
Organic light emitting diodes (OLEDs) have already been applied in several
fields due to their preeminent advantages. [2-5] However, the great potential prospect in
the full-color flat-panel display and solid-state lighting [6, 7] make it still a hot field and
attracts scientists’ attention from worldwide. To fulfil the full-color display, three
basic colors (RGB) are crucial. In recent years, a lot of efforts have been devoted to
achieve highly efficient green, red and blue emitters with outstanding color purity and
stability. So far, the green and red emitters have already met the needs for practical
[8-12]
application.
Nevertheless, excellent blue emitters are still on the pursuing list in
terms of efficiency and stability. [13-15] In particular, deep-blue emitter [16, 17] is of great
significance and play a key role in OLEDs devices because of its multi-function, such
as efficiently decreasing the power consumption, increasing the color gamut and being
utilized to be a host for other long-wavelength emitters. [18-20]
In the long term of developing ideal materials for OLEDs, phosphorescent and
thermally activated delayed fluorescent (TADF) emitters are welcome among the
researchers. OLEDs devices based on these materials theoretically could harvest all
excitons to emit photons, thereby achieve a high external quantum efficiency (EQE). [2,
3, 21-23]
However, to realize commercialization, the barriers stand in front of
phosphorescent material is the high cost caused by transition metal complexes, server
efficiency roll-off and poor stability. [24, 25] The requirement for TADF-based OLEDs is
the host-guest doping system to reduce triplet-triplet annihilation and weaken the
efficiency roll-off at high voltage, but this will give rise to complicated device
fabrication technique and raising the cost. Thus, blue fluorescent emitters are still
considered as the competitive candidates for stable non-doped OLEDs devices.
Constructing bipolar molecules is one of the effective ways to develop highly

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efficient deep-blue emitting materials. Chun-Sing Lee’s group lately reported a series
of bipolar blue emitting materials, in which the best non-doped OLEDs performance
based on TPAPOPPI shows an EQEmax of 6.69% and CIE coordinates of (0.152,
[4]
0.095).
Zuolun Zhang had demonstrated a non-doped OLEDs device using
mTPE-DPI as emitting layer achieved EQE of 3.69% with CIE coordinate of (0.15,
[26]
0.14).
Lei Wang’s group showed a DPACPhTPI-based non-doped device exhibits
[27]
CIE of (0.156, 0.047), and a EQE of 3.5%.
C. Huang’s group got a high EQE of
[28]
5.8% for non-doped OLEDs based on CPBPMCN with CIE of (0.15, 0.08).
Generally, bipolar material could transport both holes and electrons, so that achieve a
better balanced charge carriers and broaden exciton recombination region,
consequently improve the device performance. The strategy to construct bipolar
materials is to introduce electron donors and electron acceptors into the molecules. [29,
30] Nevertheless, the intramolecular charge transfer (ICT) between D and A will lower
photoluminescence quantum yields (PLQYs) and lead to a red-shift emission.
Therefore, it is absolutely imperative to choose appropriate donors and acceptors to
regulate the ICT aiming at getting ideal deep-blue bipolar emitters. Carbazole unit is
usually selected as donor originating from its moderate electron-donating properties,
good carriers transporting ability, and good thermal stability. [31] Phenanthroimidazole
is also regarded as an ideal building block in designing a blue emitting material owing
to the high thermal stability and bipolar transporting properties. Meanwhile, the ICT
could be alleviated by modifying appropriate Donor or Acceptor on
Phenanthroimidazole moiety. [32]
Based on the ideas above, we designed and synthesized the molecule
CzB-FMPPI and CzB-FMPIM. In which, carbazole and phenanthroimidazole serves
as electron-donating unit. The CF3-substituted phenyl ring applies as strong
electron-withdrawing moiety and could also trigger blue shifted emission. [33, 34] The
carbazole and phenanthroimidazole are bridged linkage by the biphenyl with moderate
twist angle, maintaining molecular conjugation and high PLQYs. Furthermore,
compared to CzB-FMPPI, CzB-FMPIM fulfils deeper blue emission by breaking the
conjugation of phenanthroimidazole chromophore, but at the cost of thermal stability

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to some extent. The two compounds CzB-FMPPI and CzB-FMPIM exhibit good
thermal stability with glass transition temperature (Tg) of 150 °C and 135 °C,
decomposition temperature (Td) of 431 °C and 414 °C, respectively. What’s more, both
compounds have bipolar properties demonstrated by single-carrier devices and
reorganization energy calculation. The non-doped OLEDs devices based on two
emitters showed maximum luminance of 6667 cd/m2 and 3084 cd/m2, CIE coordinates
of (0.15, 0.12) and (0.15, 0.07), maximum EQE of 4.10% and 3.17%, respectively.
Comprehensively speaking, the overall performance of the devices based on the both
compounds are comparable to the non-doped deep-blue OLEDs with CIEy≈0.1
reported to date. [14, 35, 36]
2. Experimental section
2.1 Material
All the reagents and solvents used in this paper were purchased from
manufacturers without further processing. THF was freshly distilled from
sodium/benzophenone under argon (Ar) atmosphere before use.
2.2 Genernal procedures
1H and 13C NMR measurements were conducted on a Bruker ACF400 (400 MHz)
spectrometer. High resolution mass spectra (HRMS) data were obtained on a Bruker
MicrOTOF-Q II. Absorption spectra and Photoluminescence spectra were recorded on
a Thermo Evolution 300 UV-Vis spectrophotometer and a Hitachi F-4500 fluorescence
spectrophotometer, respectively. Fluorescence quantum yield (Φf) was determined by
using quinine sulfate solution in 0.01 M H2SO4 (Φf = 0.54) as a reference. DSC
measurement was studied on a TA Q20 instrument operated at a heating rate of
10 °C/min from 25 °C to 350 °C in N2. TGA was recorded on a METTLER TOLEDO
TGA/DSC1 Thermogravimetric Analyzer at the heating rate of 10 °C /min from 30 °C
to 800 °C in N2. The transient PL spectrum was performed by FLS980 fluorescence
spectrometer. X-ray diffraction spectra were recorded on a Rigaku Miniflex 600 with
2θ range of 3°-20°, scanning at a rate of 1°/min. crystallography of CzB-FMPPI was
collected at the temperature of 113 K on a Rigaku XtaLAB P200 diffractometer
equipped with graphite-monochromated Mo Ka radiation (λ = 0.71073 Å). The

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structure was solved with the SHELXL-97 program, and the refinement was performed
by a full-matrix least-squares technique based on F2 with the SHELXL-97 program
2.3 OLEDs fabrication and characterization
ITO-coated glasses with a sheet resistance of 30 ꢀ per square were used as
substrates. Before device fabrication, the ITO glass substrates were cleaned with
deionized water, isopropanol, acetone and ethanol in succession, and then dried with
nitrogen and treated with oxygen plasma for 5 min. ITO glass substrates were
spin-coated with a layer of PEDOT: PSS (~40 nm) colloidal solution on the ITO side at
3000 rpm, followed with baking at 140°C for 20 min, and then transferred into a
thermal evaporation system with a pressure of 7×10-4 Pa. Then, all organic functional
layers were sequentially deposited onto the ITO substrates at a rate of 0.3-1.0 Å/s.
Finally, 1 nm LiF and 100 nm Al were deposited onto the substrate at the rate of 0.2 Å/s
and 10 Å/s, respectively. The thicknesses and deposition rates of film were controlled
by a quartz crystal thickness monitor. The EL spectra, luminance of device, and CIE
coordinates were measured with Konicaminolta CS-2000. The current-voltage
characteristics were recorded using a Keithley 2400 SourceMeter under ambient
atmosphere.
2.4 Synthesis and characterizations
Scheme 1. Molecular structures and synthetic routes of CzB-FMPPI and CzB-FMPIM
The molecular structure and synthetic routes were shown in Scheme 1. Firstly,

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9-(4-bromophenyl)-9H-carbazole was prepared by classical Ullmann reaction, then
reacted with boric acid esters to get the (4-(9H-carbazol-9-yl) phenyl) boronic acid.[37]
2-(4-bromophenyl)-1-(4-(trifluoromethyl) phenyl)-1H-phenanthro[9,10-d] imidazole
and 2-(4-bromophenyl)-4,5-diphenyl-1-(4-(trifluoromethyl) phenyl)-1H-imidazole
were prepared by a method previously reported.[38] The final compounds were
successfully prepared by Suzuki cross-coupling reaction. The target compounds were
fully characterized by NMR and HRMS. Detailed reaction procedures are shown in
supporting information.
3. Result and discussion
3.1 X-ray crystal structure and packing mode
Fig. 1 single crystal structure (a) and packing fromat (b) of CzB-FMPPI.
The molecular structure and intermolecular interaction were investigated by
X-ray crystal diffraction. The single crystal of CzB-FMPPI was prepared by slow
volatilization of dichloromethane. (Crystal data of CzB-FMPPI has been submitted to
the Cambridge Crystallographic Data Centre and the CCDC deposition number is:
1891230). The single crystal structure and packing pattern are displayed in Fig. 1. The
data of CzB-FMPPI crystal are summarized in Table S1. As shown in Fig. 1a. The

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CzB-FMPPI exhibits a twisted steric configuration with dihedral angles of 42.28°
between carbazole plane and adjacent benzene ring, 87.89° between
phenanthroimidazole plane and the side benzene ring, 50.12° between the
phenanthroimidazole plane and the adjacent benzene ring, and 38.73° between the
bridging biphenyl group, respectively. The packing details are demonstrated in Fig. 1b.
Two neighboring parallel carbazole can be observed to have a certain extent overlap
with a rather long distance of 3.388 Å, indicating a weak π-π intermolecular interaction
might exist. The carbazole chromophore is also perpendicular to the benzene ring
linked with the –CF3 group, a rather weak edge-to-face intermolecular interaction
with CH/π distance about 2.8 Å could be found. Moreover, the hydrogen on carbazole
is bonded with the phenanthroimidazole by a N/H interaction (d = 2.631 Å). The
biphenyl group mainly has a certain distance (d ≈ 2.8 Å) with phenanthroimidazole
plane, besides, also a comparable distance with carbazole plane. To sum up, the
molecule was successfully synthesized to be a twisted configuration. Such twist
structure suppressed strong π-π intermolecular interaction in some extent, which may
decrease aggregation induced fluorescence quenching in film state.[39] The
CzB-FMPPI is promising to apply in a non-doped OLEDs as emitter.
3.2 optical properties
Fig. 2 Normalized UV-Vis spectra and PL spectra of CzB-FMPPI and CzB-FMPIM in dilute
DMF and in neat film
The UV-vis and photoluminescence spectrum of CzB-FMPPI and CzB-FMPIM
in DMF and films were recorded to study their photophysical properties (Fig. 2). Both
two compounds have similar absorption profile. The peak at 294 nm could be

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[40, 41]
assigned to n-π* transition of carbazole.
The absorption band around 340 nm
may originate from π-π* transition between substitute benzene ring and the imidazole
unit. [42]The unique shoulder-peak at 365nm of CzB-FMPPI is generated by the n-π*
transition of phenanthroimidazole chromophore. [42]
Fig. 3 The lifetime measurement of CzB-FMPPI (a) and CzB-FMPIM (b) in degassed THF
by using time-correlated single photon counting method
As shown in the photoluminescent spectrum (Fig. 2), both compounds exhibit
strong blue emission with maximum emission peak at 423 nm and 415 nm in dilute
DMF solution, and at 440 nm and 415 nm in neat film for CzB-FMPPI and
CzB-FMPIM, respectively. Compared with CzB-FMPPI, CzB-FMPIM exhibit a 8 nm
blue-shift in solution, which could be attributed to the small π-conjugation backbone
of noncoplanar 1,4,5-triphenyl-1H-imidazole. Meanwhile, this noncoplanar structure
of CzB-FMPIM also inhibits the intermolecular stacking in solid state, hence reduce
the aggregation caused fluorescence quenching. The relative fluorescence quantum
yield of CzB-FMPPI and CzB-FMPIM were investigated in THF to be 92.5% and 83.3%

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using quinine sulfate (0.01 M dilute H2SO4, Φf = 0.54) [43] as a standard.
To verify whether the TADF process contributes to the PL spectrum, transient PL
decay curve in 10-6 M degassed THF were investigated by time-correlated single
photon counting method. Both spectra reveal a mono-exponential PL decay with a
short lifetime of 1.41 ns for CzB-FMPPI and 1.44 ns for CzB-FMPIM, respectively
(Fig. 3). As it was known, TADF molecules usually exhibit two-exponential lifetime:
a fast PL decay for nanoseconds and a delayed fluorescence decay for hundreds of
microseconds. [15] This phenomenon indicates that no triplet excitons contribute to PL
decay by thermally activated reverse intersystem crossing (RISC).
Subsequently, combined with PLQYs and transient PL lifetimes. the radiative
rate constants (kf) and nonradiative rate constants (knf) were calculated to investigate
the excited state nature. The data are displayed in Table S3. The kf is 12-fold higher
than its knf for CzB-FMPPI (6.54×108/S, 0.53×108/S), 5-fold higher for CzB-FMPIM
(5.76×108/S, 1.15×108/S). The higher kf rate indicate that the radiative process is
predominant in light emission, as a result obain high PLQYs.
3.3 Thermal properties and morphology
Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)
were studied. As shown in Fig. S1, the Td and Tg for CzB-FMPPI are 431 °C and 150 °C,
which are higher than 414 °C and 135 °C of CzB-FMPIM, respectively. The better
thermal stability of CzB-FMPPI could be attributed to its larger rigidity of
phenanthroimidazole chromophore.
Fig. 4 X-ray diffraction spectra of ITO, CzB-MOPPI and CzB-FMPIM thin film on ITO substrate

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To study the film property of the compound in solid state, the X-ray diffraction
(XRD) spectrum was performed as shown in Fig. 4. All films were prepared by vacuum
deposition. Both compounds exhibit featureless pattern compare to ITO substrate
before and after annealing for 24 h at 90 °C. Such character implies these compounds
are capable of forming homogeneously amorphous films during thermal deposition.[44,
45]
3.4 Electrochemical properties
Photoelectron yield spectroscopy was employed to estimate the HOMO (the
highest occupied molecular orbital) of two compounds (Fig. S2). The HOMO of
CzB-FMPPI is -5.62 eV and CzB-FMPIM is -5.87 eV, respectively. The LUMO (the
lowest unoccupied molecular orbital) of CzB-FMPPI (-2.36 eV) and CzB-FMPIM
(-2.54 eV) were calculated by uniting HOMO energy level with optical band gap (Eg).
Herein, the optical band gaps were determined by the λonset of absorption spectrum.
Details are summarized in the Table 1.
Table 1 Basic properties of CzB-FMPPI and CzB-FMPIM
a
a
b
e
Td/Tg
λabs
λem
λem
Фfc
HOMOd LUMOd
Eg
(eV) （ns）
τf
Compound
( )
(nm)
(nm) (nm)
(%)
(eV)
(eV)
CzB-FMPPI
CzB-FMPIM
431/ 150
414/ 135
294, 343, 364
423
440
415
92.5
83.3
-5.62
-2.36
3.16
3.33
1.41
1.44
294,331
415
-5.87
-2.54
a
b
c
Absorption and PL: measured in 10-5 M DMF. Absorption and PL: measured in neat film. Photoluminescent
quantum yield (PLQY) measured using quinine sulfate as standard. d Measured by photoelectron yield spectroscopy.
e Optical band gap determined from the absorption onset in DMF. f Prompt PL lifetime in THF
3.5 Theoretical calculation
Density functional theory (DFT) calculation at B3LYP/6-31G(d) level was
carried out to get a deeper understanding of the electronic properties. The
electron-cloud distributions of frontier molecular orbitals are demonstrated in Fig. 5.
Interruption of phenanthroimidazole conjugated plane has no effect on HOMO and
LUMO distributions of the two compounds. The HOMO nearly spread on the whole
molecules except the N1-connected benzene ring with trifluoromethyl. While the
LUMO mainly locate on the biphenyl and N1-connected benzene ring, as well as a

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little residue on phenanthroimidazole. Both LUMO and HOMO occupied on imidazole
cycle, this might contribute to the electronic dual nature of imidazole. Bonding
different chromophores on the two nitrogen atoms in imidazole ring will lead to
different bipolar properties: it is a weak electron donor when bonding with a strong
acceptor and a weak acceptor otherwise. [46, 47]The Large HOMO-LUMO overlap is
responsible for their high fluorescence quantum yield. [48] The HOMO energy levels
were calculated to be -5.27 eV and -5.27 eV, LUMO energy levels were -1.54 eV and
-1.46 eV for CzB-FMPPI and CzB-FMPIM, respectively.
Fig. 5 DFT calculated HOMO (upper) and LUMO (bottom) of CzB-FMPPI (a) and
CzB-FMPIM (b)
The reorganization energy calculation was also conducted to study the bipolar
properties of the compounds. Detailed data were summarized in Table S2. The hole
reorganization energy was defined to be 0.182 eV and 0.222 eV, while the electron
reorganization energy were 0.462 eV and 0.468 eV for CzB-FMPPI and CzB-FMPIM,
respectively. Such results indicate both compounds are capable of transporting hole and
electron, which could contribute to good device performance. However, the hole
reorganization energy of two compounds are smaller than the electron reorganization
energy, implying both compounds perform better hole transport ability. Besides,
CzB-FMPPI shows a lower hole reorganization energy than CzB-FMPIM, suggesting
CzB-FMPPI own superior hole tansport ability.
3.6 Carrier transporting characteristics
To further study the charge transporting capacity of two compounds, single

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carrier devices with structure of ITO/NPB (10 nm)/(CzB-FMPPI or CzB-FMPIM) (30
nm)/NPB (10 nm)/Al (100 nm) (hole-only device) and ITO/TPBi (10
nm)/(CzB-FMPPI or CzB-FMPIM) (30 nm)/TPBi (10 nm)/LiF (1 nm)/Al (100 nm)
(electron-only device) were fabricated. As displayed in Fig.6, all of the devices show
high current density at low operated voltages, indicating that both compounds are
capable of transporting electrons and holes. In addition, the hole-only devices exhibit
a higher current density than electron-only device at a relatively high voltage. Such
characteristics agrees with the reorganization energy calculation. Besides, the curves
of CzB-FMPPI reveal a smaller current-density difference between single carrier
devices at high voltage, implying the balance of charge carrier mobility. It is assumed
that the CzB-FMPPI-based blue OLEDs should possess the better performance. The
ohmic conduction regime in low applied voltage and space-charge limited conduction
regime in high applied voltage could be observed for both compounds in Figure 6,
suggesting a good Ohmic (or quasi-Ohmic) contact between the organic layer and the
metal electrode.

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Fig. 6 Current density versus voltage characteristics of single carrier devices of CzB-FMPPI (a) and
CzB-FMPIM (b)
3.7 Electroluminescence investigations
Non-doped OLEDs devices are fabricated with a simple structure of
ITO/PEDOT:PSS (40 nm)/NPB (25 nm)/(CzB-FMPPI/CzB-FMPIM) (30 nm)/TPBi
(20 nm)/LiF (1 nm)/Al (100 nm) to evaluate their EL performance. The device
structure and materials energy level are displayed in Fig. 7. ITO was anode,
PEDOT:PSS was hole injection layer fabricated by spin coating, NPB was
hole-transporting layer, TPBi was electron-transporting layer, LiF/Al act as electron
injection layer and cathode. The energy level diagrams and device structure are
displayed in Figure 5b. Key device parameters are summarized in table 2.
Fig. 7 a) the device structure; b) energy level diagrams of the materials used in OLEDs; c)
molecular structures of the compounds used in device
Table 2 Non-doped OLEDs device performances based on CzB-FMPPI and CzB-FMPIM
a
b
c
e
Von
CEmax
Lmax
EQEd
(%)
λEL
CIEf
Compound
(V)
4.0
3.6
(cd/A)
3.17
(cd/m2)
(nm)
441
425
(x, y)
CzB-FMPPI
CzB-FMPIM
6667
4.10
3.17
0.15, 0.12
0.15, 0.07
1.55
3084
a Turn-on voltage recorded at the luminance of 1 cd m2. b Maximum luminous efficiency. c Maximum luminance. d
Maximum external quantum efficiency. e Maximum peak of EL spectra. f Measured at 8 V.
As shown in the table 2, the device based on CzB-FMPIM has a lower turn on

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voltage (Von) of 3.6 V (recorded at the luminance of 1 cd/m2) than 4.0 V of device
based on CzB-FMPPI. Presumably, such phenomenon might be attributed to the low
electron-injection barrier of 0.16 eV from TPBi to emitting layer. What’s more, the
non-doped device based on CzB-FMPPI demonstrate a bigger maximum luminance
(Lmax) of 6667 cd/m2, a better maximum CE (current efficiency) of 3.17 cd/A than that
of 3084 cd/m2, 1.55 cd/A for non-doped device based on CzB-FMPPI. The result
might benefit from the higher PLQY and radiative relaxation rate of CzB-FMPPI. The
external quantum efficiency (EQE) value are estimated to be 4.10 % and 3.17 % for
devices based on CzB-FMPPI and CzB-FMPIM, respectively.
Fig. 8 a) Current density-voltage-luminance curves; b) Current density-current efficiency curves; c)
the plots of current density versus EQE; d) Normalized electronluminance spectrum of the devices,
inset EL spectra at 5V, 8V, 10V, and 12V.
Apparently, as shown in Fig. 8d, both non-doped devices exhibit deep-blue
emission at the wavelength of 441 nm and 425 nm for CzB-FMPPI and CzB-FMPIM,
respectively. The former emission peak is the same as its PL emission in film,
indicating the EL emission is from the emitting layer. In the meantime, the broadened

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emission at long wavelength could be generated from excimer or exciplex.[49, 50] The
CIE coordinates of two devices based on CzB-FMPPI and CzB-FMPIM are (0.15,
0.12) and (0.15, 0.07), in which the lower CIEy for CzB-FMPIM-based device is
consistent with the original design idea. Not only the CIE coordinates are extremely
close to the NTSC standard blue, but also their emission spectra are also stable along
with the voltage increasing from 5 V to 12 V (Fig. 8d). what’s more, the devices based
on CzB-FMPIM suffers a more severe efficiency roll-off than CzB-FMPPI, that’s
because the hole injection barrier between NPB and CzB-FMPIM (0.57 eV) is bigger
than that of CzB-FMPPI and NPB (0.32 eV), bigger hole injection barrier would
block the hole from transporting to emissive layer at high voltage, leading to a severe
efficiency roll-off.
In order to verify whether TADF or HLCT process contribute to the high EL
performance, first we measured the fluorescence and phosphorescence curves of two
compounds in toluene (shown in Fig. S4), the ꢁEST are calculated to be 0.57 and 0.70
eV based on the onset of FL and Phos. curves for CzB-FMPPI and CzB-FMPIM,
respectively. The ꢁEST of two emitters are so much bigger than sufficiently small S-T
energy gap (＜0.2 eV) to efficiently active the RISC process in TADF mechanism.[51]
The big HOMO-LUMO overlap of two emitters in the DFT calculation (Fig. 5) also
[15]
could not meet the requirement of reducing ꢁEST to support a TADF process.
In
fact, the transient fluorescence of two compounds in degassed tetrahydrofuran (Fig. 3)
exhibit single exponential PL decay without any delayed fluorescence, which is
featureless from typical TADF emitters. [51]On the contrary, it might be the integration
[30]
of HLCT state.
So, we studied the FL of two emitters in different solvents, the
absorption and fluorescence spectrum of two compounds are shown in Fig. S5. In the
low-polar solvent like hexane, both compounds show a LE-like character because of
the shoulder peak caused by their vibrational fine structure. The FL of CzB-FMPPI
and CzB-FMPIM all demonstrate an obvious solvatochromic shift, indicating a
[32, 52]
typical CT feature of their emissive state.
To better understand the
solvatochromic effect, the Stokes shift (va-vf) versus the orientation polarizability f (ε,
n) was fitted in more solvents according to the Lippert-Mataga model (Fig. S5c, f). [53]

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Both compounds show two independent linear relationships, indicating two different
excited states happened in the emissive progress. The excited state dipole moment ꢀe
are calculated to be 10.0 and 8.9 D in low-polarity solvents, 22.7 and 21.2 D in
high-polarity solvents for CzB-FMPPI and CzB-FMPIM, respectively. The small ꢀe
can be attributed to the LE-based HLCT state, whereas the large ꢀe can be treated as
the CT-dominated HLCT state. In which, the ꢀe of CzB-FMPPI is bigger than that of
CzB-FMPIM in low-polar solvents, implying the radiation transition rate and
fluorescence quantum yield of former compound is higher than the latter one, leading
to a better EL performance of CzB-FMPPI than that of CzB-FMPIM. Such results are
coincidence with the experiments above.
4. Conclusion
In conclusion, two novel bipolar deep-blue emitters CzB-FMPPI and
CzB-FMPIM were successfully synthesized and systematically investigated. In
comparison with CzB-FMPPI, CzB-FMPIM realized a deeper blue emission through
decrease the conjugation area of phenanthroimidazole chromophore. Both compounds
exhibited high fluorescence quantum yield, good thermal stability and bipolar
properties. Their distinct properties were all ascribed to their diverse twisted molecular
configuration, which accord with our prospection. What’s more, the non-doped OLEDs
devices based on these two molecules showed deep blue emission. Especially
CzB-FMPIM-based OELDs presented CIE coordinates of (0.15, 0.07), which is
extremely close to the NTSC standard blue. The maximum luminance of OLEDs
devices are 6667 cd/m2 and 3084 cd/m2, maximum EQE of 4.10% and 3.17% for
CzB-FMPPI and CzB-FMPIM, respectively. We believe that these experimental data
will provide the guideline for future molecule design and achieving highly-efficient
deep-blue OLEDs.
Acknowledgements
This work is supported by the National Key Research and Development Program
of China (2016YFB0401303), the National Natural Science Foundation of China (No.
21676188) and the Key Projects in Natural Science Foundation of Tianjin

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(16JCZDJC37100). The calculation in this work was supported by high performance
computing center of Tianjin University, China.
Reference
[1] C.W. Tang, S.A. VanSlyke, Organic electroluminescent diodes, Applied Physics
Letters, 51 (1987) 913-915.
[2] Y. Im, S.Y. Byun, J.H. Kim, D.R. Lee, C.S. Oh, K.S. Yook, J.Y. Lee, Recent Progress in
High-Efficiency Blue-Light-Emitting Materials for Organic Light-Emitting Diodes,
Advanced Functional Materials, 27 (2017) 1603007.
[3] M. Zhu, C. Yang, Blue fluorescent emitters: design tactics and applications in
organic light-emitting diodes, Chemical Society Reviews, 42 (2013) 4963-4976.
[4] Z.-L. Zhu, S.-F. Ni, W.-C. Chen, M. Chen, J.-J. Zhu, Y. Yuan, Q.-X. Tong, F.-L. Wong,
C.-S. Lee, Tuning electrical properties of phenanthroimidazole derivatives to
construct multifunctional deep-blue electroluminescent materials, Journal of
Materials Chemistry C, 6 (2018) 3584-3592.
[5] S. Zhang, L. Yao, Q. Peng, W. Li, Y. Pan, R. Xiao, Y. Gao, C. Gu, Z. Wang, P. Lu, F. Li, S.
Su, B. Yang, Y. Ma, Achieving a Significantly Increased Efficiency in Nondoped Pure
Blue Fluorescent OLED: A Quasi-Equivalent Hybridized Excited State, Advanced
Functional Materials, 25 (2015) 1755-1762.
[6] B.W. D'Andrade, S.R. Forrest, White Organic Light-Emitting Devices for Solid-State
Lighting, Advanced Materials, 16 (2004) 1585-1595.
[7] H. Sasabe, J. Kido, Development of high performance OLEDs for general lighting,
Journal of Materials Chemistry C, 1 (2013) 1699-1707.
[8] H.-H. Chou, C.-H. Cheng, A Highly Efficient Universal Bipolar Host for Blue, Green,
and Red Phosphorescent OLEDs, Advanced Materials, 22 (2010) 2468-2471.
[9] S. Gong, Y. Chen, J. Luo, C. Yang, C. Zhong, J. Qin, D. Ma, Bipolar Tetraarylsilanes as
Universal Hosts for Blue, Green, Orange, and White Electrophosphorescence with
High Efficiency and Low Efficiency Roll-Off, Advanced Functional Materials, 21 (2011)
1168-1178.
[10] C.-H. Chen, L.-C. Hsu, P. Rajamalli, Y.-W. Chang, F.-I. Wu, C.-Y. Liao, M.-J. Chiu, P.-Y.
Chou, M.-J. Huang, L.-K. Chu, C.-H. Cheng, Highly efficient orange and deep-red
organic light emitting diodes with long operational lifetimes using carbazole–
quinoline based bipolar host materials, Journal of Materials Chemistry C, 2 (2014)
6183-6191.
[11] C.-H. Fan, P. Sun, T.-H. Su, C.-H. Cheng, Host and Dopant Materials for Idealized
Deep-Red Organic Electrophosphorescence Devices, Advanced Materials, 23 (2011)
2981-2985.
[12] G. Zhou, C.-L. Ho, W.-Y. Wong, Q. Wang, D. Ma, L. Wang, Z. Lin, T.B. Marder, A.
Beeby, Manipulating Charge-Transfer Character with Electron-Withdrawing
Main-Group Moieties for the Color Tuning of Iridium Electrophosphors, Advanced
Functional Materials, 18 (2008) 499-511.
[13] G. Mallesham, C. Swetha, S. Niveditha, M.E. Mohanty, N.J. Babu, A. Kumar, K.
Bhanuprakash, V.J. Rao, Phosphine oxide functionalized pyrenes as efficient blue light
emitting multifunctional materials for organic light emitting diodes, Journal of

ACCEPTED MANUSCRIPT
Materials Chemistry C, 3 (2015) 1208-1224.
[14] S. Peng, Y. Zhao, C. Fu, X. Pu, L. Zhou, Y. Huang, Z. Lu, Acquiring
High-Performance Deep-Blue OLED Emitters through an Unexpected Blueshift
Color-Tuning Effect Induced by Electron-Donating -OMe Substituents, Chemistry – A
European Journal, 24 (2018) 8056-8060.
[15] Y. Liu, C. Li, Z. Ren, S. Yan, M.R. Bryce, All-organic thermally activated delayed
fluorescence materials for organic light-emitting diodes, Nature Reviews Materials, 3
(2018) 18020.
[16] X. Xu, X. Li, S. Wang, J. Ding, L. Wang, Deep-blue emitting
poly[spiro(dibenzoazasiline-10′,9-silafluorene)] for power-efficient PLEDs, Journal of
Materials Chemistry C, 6 (2018) 9599-9606.
[17] J. Rao, C. Zhao, Y. Wang, K. Bai, S. Wang, J. Ding, L. Wang, Achieving Deep-Blue
Thermally Activated Delayed Fluorescence in Nondoped Organic Light-Emitting
Diodes through a Spiro-Blocking Strategy, ACS Omega, 4 (2019) 1861-1867.
[18] Y. Sun, N.C. Giebink, H. Kanno, B. Ma, M.E. Thompson, S.R. Forrest, Management
of singlet and triplet excitons for efficient white organic light-emitting devices,
Nature, 440 (2006) 908.
[19] S.J. Lee, J.S. Park, K.-J. Yoon, Y.-I. Kim, S.-H. Jin, S.K. Kang, Y.-S. Gal, S. Kang, J.Y.
Lee, J.-W. Kang, S.-H. Lee, H.-D. Park, J.-J. Kim, High-Efficiency Deep-Blue
Light-Emitting Diodes Based on Phenylquinoline/Carbazole-Based Compounds,
Advanced Functional Materials, 18 (2008) 3922-3930.
[20] C.-J. Zheng, J. Wang, J. Ye, M.-F. Lo, X.-K. Liu, M.-K. Fung, X.-H. Zhang, C.-S. Lee,
Novel Efficient Blue Fluorophors with Small Singlet-Triplet Splitting: Hosts for Highly
Efficient Fluorescence and Phosphorescence Hybrid WOLEDs with Simplified
Structure, Advanced Materials, 25 (2013) 2205-2211.
[21] Y. Tao, K. Yuan, T. Chen, P. Xu, H. Li, R. Chen, C. Zheng, L. Zhang, W. Huang,
Thermally Activated Delayed Fluorescence Materials Towards the Breakthrough of
Organoelectronics, Advanced Materials, 26 (2014) 7931-7958.
[22] Z. Zhao, G. Yu, Q. Chang, X. Liu, Y. Liu, L. Wang, Z. Liu, Z. Bian, W. Liu, C. Huang,
Carbazolylphosphines and carbazolylphosphine oxides: facilely synthesized host
materials with tunable mobilities and high triplet energy levels for blue
phosphorescent OLEDs, Journal of Materials Chemistry C, 5 (2017) 7344-7351.
[23] S.-R. Park, S.-M. Kim, J.-H. Kang, J.-H. Lee, M.C. Suh, Bipolar host materials with
carbazole and dipyridylamine groups showing high triplet energy for blue
phosphorescent organic light emitting diodes, Dyes and Pigments, 141 (2017)
217-224.
[24] S. Schmidbauer, A. Hohenleutner, B. König, Chemical Degradation in Organic
Light-Emitting Devices: Mechanisms and Implications for the Design of New
Materials, Advanced Materials, 25 (2013) 2114-2129.
[25] Y. Feng, X. Zhuang, D. Zhu, Y. Liu, Y. Wang, M.R. Bryce, Rational design and
characterization of heteroleptic phosphorescent iridium(iii) complexes for highly
efficient deep-blue OLEDs, Journal of Materials Chemistry C, 4 (2016) 10246-10252.
[26] C. Li, J. Wei, J. Han, Z. Li, X. Song, Z. Zhang, J. Zhang, Y. Wang, Efficient deep-blue
OLEDs based on phenanthro[9,10-d]imidazole-containing emitters with AIE and

ACCEPTED MANUSCRIPT
bipolar transporting properties, Journal of Materials Chemistry C, 4 (2016)
10120-10129.
[27] Z. Huang, B. Wang, Q. Zhang, S. Xiang, X. Lv, L. Ma, B. Yang, Y. Gao, L. Wang,
Highly twisted bipolar emitter for efficient nondoped deep-blue electroluminescence,
Dyes and Pigments, 140 (2017) 328-336.
[28] Y. Tan, Z. Zhao, L. Shang, Y. Liu, C. Wei, J. Li, H. Wei, Z. Liu, Z. Bian, C. Huang, A
novel bipolar D–π–A type phenanthroimidazole/carbazole hybrid material for high
efficiency nondoped deep-blue organic light-emitting diodes with NTSC CIEy and low
efficiency roll-off, Journal of Materials Chemistry C, 5 (2017) 11901-11909.
[29] A.L. Fisher, K.E. Linton, K.T. Kamtekar, C. Pearson, M.R. Bryce, M.C. Petty, Efficient
Deep-Blue Electroluminescence from an Ambipolar Fluorescent Emitter in a
Single-Active-Layer Device, Chemistry of Materials, 23 (2011) 1640-1642.
[30] B. Liu, Z.-W. Yu, D. He, Z.-L. Zhu, J. Zheng, Y.-D. Yu, W.-F. Xie, Q.-X. Tong, C.-S. Lee,
Ambipolar D–A type bifunctional materials with hybridized local and charge-transfer
excited state for high performance electroluminescence with EQE of 7.20% and CIEy
∼ 0.06, Journal of Materials Chemistry C, 5 (2017) 5402-5410.
[31] Y. Li, Z. Wang, X. Li, G. Xie, D. Chen, Y.-F. Wang, C.-C. Lo, A. Lien, J. Peng, Y. Cao,
S.-J. Su, Highly Efficient Spiro[fluorene-9,9′-thioxanthene] Core Derived Blue Emitters
and Fluorescent/Phosphorescent Hybrid White Organic Light-Emitting Diodes,
Chemistry of Materials, 27 (2015) 1100-1109.
[32] W. Li, D. Liu, F. Shen, D. Ma, Z. Wang, T. Feng, Y. Xu, B. Yang, Y. Ma, A Twisting
Donor-Acceptor Molecule with an Intercrossed Excited State for Highly Efficient,
Deep-Blue Electroluminescence, Advanced Functional Materials, 22 (2012)
2797-2803.
[33] Y. Chen, J. Guo, X. Wu, D. Jia, F. Tong, Color-tuning aggregation-induced emission
of o-Carborane-bis(1,3,5-triaryl-2-pyrazoline) triads: Preparation and investigation of
the photophysics, Dyes and Pigments, 148 (2018) 180-188.
[34] K. Kokado, Y. Chujo, Multicolor Tuning of Aggregation-Induced Emission through
Substituent Variation of Diphenyl-o-carborane, The Journal of Organic Chemistry, 76
(2011) 316-319.
[35] W. Sun, N. Zhou, Y. Xiao, S. Wang, X. Li, Novel carbazolyl-substituted
spiro[acridine-9,9′-fluorene] derivatives as deep-blue emitting materials for OLED
applications, Dyes and Pigments, 154 (2018) 30-37.
[36] H. Liu, Q. Bai, W. Li, Y. Guo, L. Yao, Y. Gao, J. Li, P. Lu, B. Yang, Y. Ma, Efficient
deep-blue non-doped organic light-emitting diode with improved roll-off of efficiency
based on hybrid local and charge-transfer excited state, RSC Advances, 6 (2016)
70085-70090.
[37] J. You, G. Li, Z. Wang, Starburst dendrimers consisting of triphenylamine core
and 9-phenylcarbazole-based dendrons: synthesis and properties, Organic &
Biomolecular Chemistry, 10 (2012) 9481-9490.
[38] Y. Zhang, J.-H. Wang, J. Zheng, D. Li, A Br-substituted phenanthroimidazole
derivative with aggregation induced emission from intermolecular halogen–hydrogen
interactions, Chemical Communications, 51 (2015) 6350-6353.
[39] Y. Zhang, S.-L. Lai, Q.-X. Tong, M.-F. Lo, T.-W. Ng, M.-Y. Chan, Z.-C. Wen, J. He, K.-S.

ACCEPTED MANUSCRIPT
Jeff, X.-L. Tang, W.-M. Liu, C.-C. Ko, P.-F. Wang, C.-S. Lee, High Efficiency Nondoped
Deep-Blue Organic Light Emitting Devices Based on Imidazole-π-triphenylamine
Derivatives, Chemistry of Materials, 24 (2012) 61-70.
[40] L. Zhao, S. Wang, S. Shao, J. Ding, L. Wang, X. Jing, F. Wang, Stable and efficient
deep-blue
terfluorenes
functionalized
with
carbazole
dendrons for
solution-processed organic light-emitting diodes, Journal of Materials Chemistry C, 3
(2015) 8895-8903.
[41] Y. Huang, X. Du, S. Tao, X. Yang, C.-J. Zheng, X. Zhang, C.-S. Lee, High efficiency
non-doped deep-blue and fluorescent/phosphorescent white organic light-emitting
diodes based on an anthracene derivative, Synthetic Metals, 203 (2015) 49-53.
[42] Z. Gao, Z. Wang, T. Shan, Y. Liu, F. Shen, Y. Pan, H. Zhang, X. He, P. Lu, B. Yang, Y.
Ma,
High-efficiency
deep
blue
fluorescent
emitters
based
on
phenanthro[9,10-d]imidazole substituted carbazole and their applications in organic
light emitting diodes, Organic Electronics, 15 (2014) 2667-2676.
[43] P. Kotchapradist, N. Prachumrak, R. Tarsang, S. Jungsuttiwong, T. Keawin, T.
Sudyoadsuk, V. Promarak, Pyrene-functionalized carbazole derivatives as non-doped
blue emitters for highly efficient blue organic light-emitting diodes, Journal of
Materials Chemistry C, 1 (2013) 4916-4924.
[44] S. Fan, J. You, Y. Miao, H. Wang, Q. Bai, X. Liu, X. Li, S. Wang, A bipolar emitting
material for high efficient non-doped fluorescent organic light-emitting diode
approaching standard deep blue, Dyes and Pigments, 129 (2016) 34-42.
[45] Y. Zhang, X. Wang, X. Li, S. Wang, Y. Pan, Z. Zhong, L. Ying, Y. Xiao, A thermally
cross-linked hole-transporting film with the remarkable solvent resistance for
solution-processed OLEDs, Organic Electronics, 57 (2018) 345-351.
[46] Y. Yuan, J.-X. Chen, F. Lu, Q.-X. Tong, Q.-D. Yang, H.-W. Mo, T.-W. Ng, F.-L. Wong,
Z.-Q. Guo, J. Ye, Z. Chen, X.-H. Zhang, C.-S. Lee, Bipolar Phenanthroimidazole
Derivatives Containing Bulky Polyaromatic Hydrocarbons for Nondoped Blue
Electroluminescence Devices with High Efficiency and Low Efficiency Roll-Off,
Chemistry of Materials, 25 (2013) 4957-4965.
[47] H. Liu, P. Chen, D. Hu, X. Tang, Y. Pan, H. Zhang, W. Zhang, X. Han, Q. Bai, P. Lu, Y.
Ma, Separation of Electrical and Optical Energy Gaps: Selectively Adjusting the
Electrical and Optical Properties for a Highly Efficient Blue Emitter, Chemistry – A
European Journal, 20 (2014) 2149-2153.
[48] Z. Chen, X.-K. Liu, C.-J. Zheng, J. Ye, X.-Y. Li, F. Li, X.-M. Ou, X.-H. Zhang, A
high-efficiency hybrid white organic light-emitting diode enabled by a new blue
fluorophor, Journal of Materials Chemistry C, 3 (2015) 4283-4289.
[49] C. Liu, Y. Li, Y. Li, C. Yang, H. Wu, J. Qin, Y. Cao, Efficient Solution-Processed
Deep-Blue Organic Light-Emitting Diodes Based on Multibranched Oligofluorenes
with a Phosphine Oxide Center, Chemistry of Materials, 25 (2013) 3320-3327.
[50] C. Liu, Q. Fu, Y. Zou, C. Yang, D. Ma, J. Qin, Low Turn-on Voltage,
High-Power-Efficiency, Solution-Processed Deep-Blue Organic Light-Emitting Diodes
Based on Starburst Oligofluorenes with Diphenylamine End-Capper to Enhance the
HOMO Level, Chemistry of Materials, 26 (2014) 3074-3083.
[51] S. Hirata, Y. Sakai, K. Masui, H. Tanaka, S.Y. Lee, H. Nomura, N. Nakamura, M.

ACCEPTED MANUSCRIPT
Yasumatsu, H. Nakanotani, Q. Zhang, Highly efficient blue electroluminescence based
on thermally activated delayed fluorescence, Nature materials, 14 (2015) 330.
[52] X. Han, Q. Bai, L. Yao, H. Liu, Y. Gao, J. Li, L. Liu, Y. Liu, X. Li, P. Lu, Highly Efficient
Solid-State Near-Infrared Emitting Material Based on Triphenylamine and
Diphenylfumaronitrile with an EQE of 2.58% in Nondoped Organic Light-Emitting
Diode, Advanced Functional Materials, 25 (2015) 7521-7529.
[53] Z.R. Grabowski, K. Rotkiewicz, W. Rettig, Structural changes accompanying
intramolecular electron transfer: focus on twisted intramolecular charge-transfer
states and structures, Chemical reviews, 103 (2003) 3899-4032.

ACCEPTED MANUSCRIPT
Two donor-acceptor type deep blue fluorescent materials were firstly designed and
synthesized.
Compounds exhibit high fluorescence quantum yield, good thermal stability and
bipolar properties.
Non-doped good-performance deep-blue OLED devices with CIE of (0.15, 0.07) were
achieved.