Effective management of intramolecular charge transfer to obtain from blue to violet-blue OLEDs based on a couple of phenanthrene isomers

Article abstract of DOI:10.1016/j.dyepig.2015.06.036

Abstract A couple of phenanthrene isomers were designed and synthesized by introducing strong D-π-A structure strategy to manage effectively their intramolecular charge transfer processes for violet-blue emitters. Their physical properties, including UV-vis, photoluminescence, thermal and electrochemistry, were systematically studied. The results were found to be good candidates as emitters for organic light emitting diodes (OLEDs). The devices based on them exhibit deep-blue light emissions with CIE coordinates of (0.15, 0.15) for p-PATPA and violet-blue (0.16, 0.05) for m-PATPA at 100 cd/m², respectively. The violet-blue device shows good performance with external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) of 2.39%, 0.78 cd/A, and 0.72 lm/W, respectively. Furthermore, at the high luminescence, the device still indicated good performance with relative low efficiency roll-off. Our results here successfully provide an efficient design strategy with strong donor and acceptor for violet-blue emitters.

Full text of DOI:10.1016/j.dyepig.2015.06.036

Accepted Manuscript
Effective Management of Intramolecular Charge Transfer to Obtain from Blue to
Violet-blue OLEDs Based on a Couple of Phenanthrene Isomers
Xinhua Ouyang, Xiang-Long Li, Xingye Zhang, Amjad Islam, Ziyi Ge, Shi-Jian Su
PII:
S0143-7208(15)00254-5
10.1016/j.dyepig.2015.06.036
DYPI 4838
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 3 April 2015
Revised Date: 19 June 2015
Accepted Date: 22 June 2015
Please cite this article as: Ouyang X, Li X-L, Zhang X, Islam A, Ge Z, Su S-J, Effective Management
of Intramolecular Charge Transfer to Obtain from Blue to Violet-blue OLEDs Based on a Couple of
Phenanthrene Isomers, Dyes and Pigments (2015), doi: 10.1016/j.dyepig.2015.06.036.
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ACCEPTED MANUSCRIPT
Effective Management of Intramolecular Charge Transfer to Obtain from Blue to
Violet-blue OLEDs Based on a Couple of Phenanthrene Isomers
Keywords: Violet-blue emission, Intramolecular charge transfer, Phenanthrene isomers
1
2
1
1
2
1
Xinhua Ouyang , Xianglong Li , Xingye Zhang , Amjad Islam , Shijian Su *, Ziyi Ge *
A couple of phenanthrene isomers (PATPA) were designed and synthesized by introducing
strong D-π-A structure strategy to manage effectively their intramolecular charge transfer
(
ICT) processes for violet-blue emitters.
1

ACCEPTED MANUSCRIPT
Effective Management of Intramolecular Charge Transfer to Obtain from Blue
to Violet-blue OLEDs Based on a Couple of Phenanthrene Isomers
1
2
1
1
1
Xinhua Ouyang , Xiang-Long Li , Xingye Zhang , Amjad Islam , Ziyi Ge *, Shi-Jian
2
Su *,
1
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of
Sciences, Ningbo 315201, P.R. China
2
State Key Laboratory of Luminescent Materials and Devices (South China University
of Technology) and Institute of Polymer Optoelectronic Materials and Devices, South
China University of Technology, Guangzhou 510640, P.R. China
Corresponding authors: geziyi@nimte.ac.cn (Z. Ge), mssjsu@scut.edu.cn (S. Su)
Abstract: A couple of phenanthrene isomers were designed and synthesized by
introducing strong D-π-A structure strategy to manage effectively their intramolecular
charge transfer processes for violet-blue emitters. Their physical properties, including
UV-vis, photoluminescence, thermal and electrochemistry, were systematically
studied. The results were found to be good candidates as emitters for organic light
emitting diodes (OLEDs). The devices based on them exhibit deep-blue light
emissions with CIE coordinates of (0.15, 0.15) for p-PATPA and violet-blue (0.16,
2
0
.05) for m-PATPA at 100 cd/m , respectively. The violet-blue device shows good
performance with external quantum efficiency (EQE), current efficiency (CE), and
power efficiency (PE) of 2.39%, 0.78 cd/A, and 0.72 lm/W, respectively. Furthermore,
at the high luminescence, the device still indicated good performance with relative
1

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low efficiency roll-off. Our results here successfully provide an efficient design
strategy with strong donor and acceptor for violet-blue emitters.
Keywords Violet-blue emission, Intramolecular charge transfer, Phenanthrene
isomers
Introduction
Blue organic light-emitting diodes (OLEDs) have been attracting extensively attention
from scientific and industrial fields due to the importance in flat-panel displays (FPD)
[
1-3]
and solid-state lighting (SSL) resources.
Generally, a high color saturation or color
rendering index of white OLEDs requires at least a deep-blue emission with a
[
4]
Commission Internationale de l’Eclairage (CIE) y coordinate value of less 0.10. The
development of deep-blue, even violet-blue materials, is of special significance
because such emitters can not only effectively reduce the power consumptions of FPD
and SSL, but also be utilized to generate light of other colors by energy cascade to a
[
5]
lower-energy fluorescent or phosphorescent.
In the past decades, numerous compounds have been developed to be used as blue
[
6]
emitters, and some of them exhibited good performance. However, the present
compounds with violet-blue or violet emission are still very rare. In view of this, the
research about the violet-blue emitters with high performance is still the active field
[
7]
of OLEDs. Due to the larger HOMO-LUMO gap, the design and synthesis of this
are still the challenges for us. Recently, some researchers put forward the thought of
introduction donor-π-acceptor type molecules to obtain highly-efficient violet-blue
[
8]
emitters. The effective method is to choose some weak electron-donating (D) and
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[
9]
accepting (A) units to reduce the ability of intramolecular charge transfer. Thus, it
will lead to many functional groups with high fluorescent yields which cannot be
[
10]
[11]
introduced owing to their large π conjugation, such as anthracene,
fluorene,
[
12]
[13]
styrylarylene and pyrene derivatives and so forth. Furthermore, the weak D-π-A
type emitters will either decrease the fluorescent quantum yield and
[
14]
charge-transporting ability, or to some extent increase the synthetic difficulty when
large molecular weight and/or bulky structure are usually required for good thermal
[
15]
and morphological stability. Therefore, if the D-A type emitters containing strong
D and A units also can be used as highly efficiency violet-blue emission by effective
management of their intramolecular charge transfer (ICT), it will be the best choice to
develop the violet-blue OLEDs. Unfortunately, to our best knowledge, the violet-blue
OLEDs with strong D and A units have not been reported to date.
Herein, we demonstrate a couple of phenanthrene derivatives, which contain the
strong electron-donating triphenylamine (TPA) unit and electron-accepting imidazole
unit,
3'-(phenanthren-9-yl)-N,N-diphenyl-5'-(1-phenyl-1H-phenanthro
[9,10-d]
imidazol-2-yl)-[1,1'-biphenyl]-4-amine (m-PTPAPI) and 4'-(1-(4- (phenanthren-9-yl)
phenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-diphenyl-[1,1'-biphenyl]-4-amine
(p-PTPAPI) (Scheme 1). As shown in the Scheme 1, it is particularly intriguing to
compare the electroluminescent properties of m-PTPAPI and p-PTPAPI, both have the
same molecular constructing D, A and π-conjugating units. We only changed the
connecting mode of π-conjugating linkers between the D and A units from para- to
meta-position. Their electronic transitions of the charge-transfer (CT) excited states
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can effectively managed. The corresponding electroluminescence based on them as
non-doped OLEDs emitter shows from deep-blue to blue-violet emission. The OLEDs
based on m-PTPAPI as emitter achieved an external quantum efficiency of 2.39 % and
a deep-blue CIE(x,y) of (0.15, 0.05), which was the first time to obtain a blue-violet
emitter with strong D (TPA) and A (imidazole) units in a nondoped system to our
knowledge.
Results and discussion
Synthesis As shown in Scheme1, the synthetic processes of m-PTPAPI and
p-PTPAPI are similarly by three synthetic steps with good yields. The important
intermediate for the synthesis of m-PTPAPI was 4'-(diphenylamino)-5-(phenanthren-
9
-yl)-[1,1'-biphenyl]-3-carbaldehyde (3), which was synthesized by two steps of
Suzuki couplings from 3,5-dibromobenzaldehyde, (4-(diphenylamino)phenyl)boronic
acid and phenanthren-9-ylboronic acid using Pd(PPh ) Cl as catalysis. While the
3
2
2
compound p-PTPAPI was synthesized through a Suzuki coupling with 4'-(1-(4-
bromophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N- diphenyl-[1,1'- biphenyl]-
4
-amine (5) and phenanthren-9-ylboronic acid. 4'-(diphenylamino)-[1,1'-biphenyl]-4
[
16]
-carbaldehyde (4) was synthesized followed the method reported literature.
The
compound 5 was prepared from 4'-(diphenylamino)-[1,1'-biphenyl]-4-carbaldehyde,
phenanthrene-9,10-dione and 4-bromoaniline. All of new compounds were
1
13
characterized using mass spectrometry, H NMR, C NMR spectroscopy, and
elemental analysis.
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Thermal and electrochemical properties The thermal properties of m-PTPAPI and
p-PTPAPI were studied by thermogravimetric analysis (TGA) and differential
-1
scanning calorimetry (DSC) under a nitrogen atmosphere with a rate of 10 °C min .
As shown in Fig. 1, their decomposition temperatures (T , corresponding to 5%
d
weight loss) are 475 °C (m-PTPAPI) and 478 °C (p-PTPAPI), respectively. No
obvious glass transition temperatures (T ) are observed for them. Obviously, the T of
g
d
p-PTPAPI are higher than that of m-PTPAPI, which indicates the introduction of
para-configuration will improves the morphological stability. The high T values
d
indicate that these molecules are stable and have the potential to be fabricated into
devices by vacuum thermal evaporation technology. The electrochemical properties of
them were measured by cyclic voltammetry with three electrodes system. As shown in
Fig. 2, both of them exhibit similar oxidation and reduction processes. In the cathodic
scan, m-PTPAPI and p-PTPAPI appeared the oxidation processes originating from
their p-type TPA unit. Thus, they exhibited similar HOMO energy levels of about –
5
.30 eV. The LUMO levels of the two materials were calculated to be about –2.57 eV
for p-PTPAPI, –2.4 eV for m-PTPAPI, respectively. Although both of them have the
same reduction imidazole unit, the LUMO level of p-PTPAPI is 0.17 eV higher than
that of m-PTPAPI, the imidazole is designed as para-configuration, which makes
ec
reduction occur more easily. The values found for the energy band gap (E ) of
g
ec
PTPAPI using cyclic voltammetry according to the equation E = (HOMO-LUMO)
g
are 2.73 eV and 2.90 eV for p-PTPAPI and m-PTPAPI, respectively. The higher
electrochemical band gap is found to be the energy barrier of charge transfer at the
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[
17]
electrodes during electrochemical measurements.
Photophysical Properties Photophysical properties of PTPAPI were studied by using
ultraviolet−visible (UV−vis) and photoluminescence (PL) spectrometers. The results
are shown in Fig. 3 and summarized in Table 1. As shown in the absorption, the
different absorptive profiles are found, the compound m-PTPAPI appears only one
strong peak in chloroform and film at ~310 nm and a shoulder at ~350 nm. While the
corresponding p-PTPAPI appears two absorption peaks at ~305 and ~370 nm.
Obviously, the absorption at ~370 nm is ascribed to the ICT transition, and the peak at
[18]
~
305 nm is from the triphenylamine-centered n-π* transition. By comparison with
the absorption of them, the charge transfer absorption band from the electron donor to
the electron-withdrawing imidazole in m-PTPAPI is much lower than that of
p-PTPAPI, indicating the meta-configuration will be benefit to prevent or reduce the
charge transfer from D to A units. From the film onset absorptions, both of the band
gaps (E ) of PTPAPI are determined to be 3.15 eV for m-PTPAPI and 2.92 eV for
g
p-PTPAPI, respectively. As shown in photoluminescent (PL) spectra, m-PTPAPI
exhibits a narrow emission around 410 nm with a FWHM (full width at half
maximum) of 51 nm, while p-PTPAPI shows a relatively red-shifted emission at 446
nm with a FWHM of 65 nm. Therefore, the film fluorescent emissions of both
compounds are located in the short-wavelength spectral region of the whole visible
light spectrum. Their ICT characteristics are studied by increasing the polarity of
solvents, the gradually red-shifted and broadened fluorescent emissions are found as
shown in Fig. 4, which shows a large increase of the dipole moment from the ground
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[
19]
[20]
state to the excited state.
By calculating with the Lippert−Mataga
theory, the
value is 34.5 D for p-PTPAPI and 17.6 D for m-PTPAPI, The value of p-PTPAPI is
larger than that of m-PTPAPI, further reflecting the ICT process in p-PTPAPI is
stronger than that of m-PTPAPI.
Theoretical Calculation. To gain insight into the electronic structures of the
compounds, a DFT calculation was performed at the B3LYP/6-31G (d) level. As is
shown in Fig. 5, the HOMO level of m-PTPAPI mainly populate on the TPA moiety
and on the linkers, while the corresponding p-PTPAPI mainly locate on the TPA and
imidazole moieties. Obviously, by changing the mode of connection, a large
difference of electronic density is found. In comparison of the compound of
m-PTPAPI, the TPA moiety contributes less to the HOMO energy in p-PATPA.
According to DFT simulation results, m-PTPAPI seems ambipolar with the separated
HOMO and LUMO on donor and acceptor, respectively, while the HOMO of
p-PTPAPI partially extended to imidazole group. So, the bathochromic shift of
p-PTPAPI's emission should be attributed to conjugation extension of its para-linked
diphenylene. The calculated HOMO level is 4.88 eV for m-PTPAPI and 4.89 eV for
p-PTPAPI, suggesting that the change at the mode of connection does not have
significant effect on the HOMO energy of the compounds. The LUMO levels mostly
populate on the phenanthrene and the linkers between the donor and the acceptor. It is
noted that both of LUMO and HOMO show a little overlapping; on one hand it would
contribute for the balanced charge transfer as the emitter in OLED, but on the other
hand it could facilitate the charge transfer process upon excitation, which was also
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confirmed by the solvatochromic phenomenon observed in the solvent with a different
[
21]
polarity.
Electroluminescence (EL) properties. To investigate the EL performance of PTPAPI,
non-doped fluorescent OLEDs were fabricated with a configuration of ITO/HATCN
(5 nm)/NPB (x nm)/TCTA (5 nm)/PTPAPI (y nm)/TPBi (z nm)/LiF (1 nm)/Al (90
nm). In order to fully exhibit their EL performance as emitters, we regulated the
thickness of NPB, PTPAPI and TPBi. In these devices, indium tin oxide (ITO) is used
as the anode, hexaazatriphenylenehexacabonitrile (HATCN) used as the hole injection
layer, N,N’-di-1-naphthyl-N,N’-diphenylbenzidine (NPB) as hole- transporting layer,
4
1
,4’,4’’- tri(N-carbazolyl)-triphenylamine (TCTA) as electron- blocking layer,
,3,5-tri(phenyl-2-benzimidazolyl)benzene (TPBi) as electron- transporting and
hole-blocking layer, and LiF used as the electron injecting layer. Some of important
performance parameters of these OLEDs are summarized in Table 2.
By comparing to the performance of these devices, it can be seen that the device
with the structure of ITO/HATCN (5 nm)/NPB (40 nm)/TCTA (5 nm)/PATPA (20
nm)/TPBi (40 nm)/LiF (1 nm)/Al (100 nm) gives the best performance in terms of
luminescent (η ), power (η ), and external quantum (η ) efficiencies. In particular, the
c
p
e
efficiencies (η , η , η ) based on p-PATPA of respectively 3.73 cd/A, 3.47 lm/W, and
c
p
e
3
.71% were obtained. The device also has a low onset voltage (defined as the voltage
2
required to obtain a luminance of 1 cd/m ) of 3.2 V and low operating voltages (4.2
2
and 5.7 V, respectively, to give a luminance of 100 and 1000 cd/m ). All of
p-PTPAPI-based devices exhibit the steady deep blue emission of CIE coordinates
8

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(0.15, 0.15) (peaked at 450 nm). While the corresponding m-PTPAPI-based devices
show the similar trend except that the emission is violet-blue with the CIE coordinates
(0.15, 0.05) (peaked at 408 nm).
The EL spectra of the devices with the best performance at different driving
voltages were shown in Fig. 6, the present EL spectra are identical to the
corresponding PL spectra of their neat films and show little change under different
driving voltages, implying a good confinement of excitons in the emission layers. It
can be attributed to the wide band gaps of the adjacent TCTA (3.4 eV) and TPBi (3.5
eV). The current density− voltage−luminescence (J-V-L) and brightness-efficiencies
relationships by using them as emitters are shown in Fig. 7. From the current
density−voltage−luminescence (J-V-L) plots, it can be seen that the PTPAPI-devices
exhibit low turn-on voltages of 3.2 V, as well as much higher current densities under
the same voltage as compared to the m-PTPAPI devices. These might be owing to the
better charge-transporting ability of p-PTPAPI. However, the m-PTPAPI-based
device exhibits relatively lower efficiencies with maximum EQE of 2.39%, CE of
0
.78 cd/A, and PE of 0.72 lm/W, while the device based on p-PTPAPI presents
impressive EL performance with high maximum EQE, CE, and PE of 3.71%, 3.73
cd/A and 3.47 lm/W, respectively. Notably, the CE and PE in this work based on
m-PATPA show the CIE y < 0.05 (Table 2), which is violet-blue emission.
2
Meanwhile, even at the practical luminescence of 1000 cd/m , the EQE and CE of the
m-PTPAPI device still remain high as 2.1% and 0.69 cd/A, indicative of a relatively
low efficiency roll-off. It is noteworthy that internal quantum efficiency (IQE) of the
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device based on p-PTPAPI and m-PTPAPI reaches 29.7% and 25.9 % by the
[
22]
Monkman’s theory , which exceed the limit of traditional fluorescent OLEDs. It can
be attributed to mechanism of hybridized local and charge-transfer (HLCT), which
[
23]
has been demostrated by Ma and coworkers.
In order to effectively elaborate the ICT process, we developed a model as shown
in Fig. 8. As far as the compound of p-PTPAPI was concerned, the linear connection
would be benefit to the charge transfer between the strong D (TPA) and A (imidazole)
units. In the meantime, another ICT process with the same connection also may be
existed from phenanthrene to imidazole sectors. The good carries transfer and balance
would be achieved based the compound of p-PTPAPI and the device will show good
performance, which has been demonstrated. However, the strong the ICT will induce
the red-shift emission, which will not be good for design materials with violet-blue
[24]
emission. While the corresponding m-PTPAPI, the nonlinear connection between
D and A units, the strong ICT will be effectively reduced, especially from
phenanthrene to imidazole sectors. Therefore, the present emission will be shifted to
violet. Meanwhile, the same constructing groups with p-PTPAPI, it can guarantee the
good abilities of carries transfer and balance.
Conclusions
In conclusion, a couple of highly efficient deep-blue to violet-blue emitters,
p-PATPA and m-PATPA, have been demonstrated by introducing D-π-A structure
strategy to manage effectively their ICT processes. Their physical properties (PL, Td,
Φ, etc) were found to be good candidates for devices. Nondoped devices based on
1
0

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them exhibit deep-blue light emissions with CIE coordinates of (0.15, 0.11) for
2
p-PTPAPI and (0.16, 0.05) for m-PTPAPI at 100 cd/m , respectively. Interestingly, by
introducing strong D and A in the compound of m-PTPAPI, we also achieved
violet-blue emission by regulating the connecting mode to manage its ICT process. Its
electroluminescence device shows good performance with EQE, CE, and PE of 2.39%,
0
1
0
.78 cd/A, and 0.72 lm/W, respectively. Furthermore, at the high luminescence of
2
000 cd/m , the EQE and CE of the m-PATPA device still remain high as 2.1% and
.69 cd/A, indicative of a relatively low efficiency roll-off. Our results here
successfully provide an efficient design strategy with strong D and A for violet-blue
emitters.
Experimental section
1
13
General Procedures. H NMR and C NMR spectra were determined in CDCl with
3
a Bruker DRX 400 MHz spectrometer. Chemical shifts (δ) were given relative to
tetramethylsilane (TMS). The coupling constants (J) were reported in Hz. ESI-Ms
spectra were performed with a FINNIGAN Trace DSQ mass spectrometer at 70 eV.
Elemental analyses were recorded with a Perkin-Elmer 2400 analyzer. Fluorescence
emission spectra and decay curves of these samples were measured with a FLSP920
spectrophotometer. The film photoluminescence quantum yield was measured by the
integrating sphere method. The absorption was recorded on a Hitachi U-3010 UV−vis
spectrophotometer. The electrochemical properties of them were studied by cyclic
voltammetry with a CHI600A analyzer. All starting materials were purchased from
TCI and J&K Chemical companies. The reagents were obtained from sinopharm
11

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chemical reagent Co. Ltd. and used without further purification. Experiment course
was monitored by TLC. Column chromatography was carried out on silica gel
(200-300 mesh).
Synthesis of 5-bromo-4'-(diphenylamino)-[1,1'-biphenyl]-3-carbaldehyde (2) (4-(di-
phenylamino)phenyl)boronic acid (1.445 g, 5.0 mmol), 3,5-dibromobenzaldehyde
(
2.641 g, 10 mmol) and Pd(PPh ) (50 mg, 0.10 mmol) were suspended in toluene (25
3 4
o
mL) and 10 mL 2M K CO . The reaction was stirred at 105 C for 8 h and cooled to
2
3
room temperature. The mixture solution was added 20 mL brine and then extracted
with CH Cl (40 mL), washed with water (2 x 20 mL), dried (MgSO ) and evaporated
2
2
4
to dryness. After drying under vacuum, then, it was purified by dichloromethane/
petroleum ether (1:3) as an eluent to afford light yellow solid, Yield: 1.168 g, 54.6%.
-1
FTIR (KBr, cm ): 3095, 3068, 2942, 2918, 2894, 2866, 1698, 1499, 1506, 1409,
1
1
392, 744; H NMR(CDCl , 400 MHz, ppm) δ:10.02 (s, 1H), 7.97 (t, 3H, J = 14.8
3
Hz), 7.48 (d, 2H, J=8.66 Hz), 7.32 (t, 4H, J=7.42 Hz), 7.18 (d, 6H, J=8.67 Hz), 7.10 (t,
+
+
2
H, J=7.42 Hz); EI-MS (m/z): 430.3 (M +H), 428.1 (M +H); Anal. Calcd for
C H BrNO: C, 70.10; H, 4.24; N, 3.27; Found: C, 70.12; H, 4.18; N, 3.32.
25
18
Synthesis of 4'-(diphenylamino)-5-(phenanthren-9-yl)-[1,1'-biphenyl]-3-carbaldehyde
3) 5-bromo-4'-(diphenylamino)-[1,1'-biphenyl]-3-carbaldehyde (1.071 g, 2.5 mmol),
phenanthren-9-ylboronic acid (0.666 g, 3 mmol) and Pd(PPh ) (25 mg, 0.05 mmol)
(
3
4
were suspended in toluene (20 mL), 5 mL ethanol and 5 mL 2M K CO . The reaction
2
3
o
was stirred at 105 C for 12 h and cooled to room temperature. The mixture solution
was added 10 mL brine and then extracted with CH Cl (20 mL), washed with water
2
2
1
2

ACCEPTED MANUSCRIPT
(
2 x 10 mL), dried (MgSO ) and evaporated to dryness. After drying under vacuum,
4
then, it was purified by dichloromethane/ petroleum ether (1:1) as an eluent to afford
-1
light yellow solid, Yield: 1.084 g, 82.6%. FTIR (KBr, cm ): 3098, 3083, 3068, 2933,
1
2
908, 2877, 2833, 1689, 1501, 1403, 1392, 1322, 732; H NMR(CDCl , 400 MHz,
3
ppm) δ:10.19 (s, 1H), 8.84 (d, 1H, J=7.99 Hz), 8.78 (d, 1H, J=8.17 Hz), 8.22 (s, 1H),
.04 (d, 2H, J=15.25 Hz), 7.94 (d, 2H, J=8.29 Hz), 7.78 (s, 1H), 7.73 (t, 2H, J=8.30
8
Hz), 7.67 (t, 1H, J=7.32 Hz), 7.61 (t, 3H, J=8.43 Hz), 7.31 (t. 4H, J=7.92 Hz), 7.19 (t,
+
6
H, J=7.42 Hz), 7.09 (t, 2H, J=7.71 Hz); EI-MS (m/z): 525.3 (M ); Anal. Calcd for
C H rNO: C, 89.11; H, 5.18; N, 2.66; Found: C, 89.20; H, 5.19; N, 2.65.
39
27
Synthesis
of
4'-(1-(4-bromophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-N,N-
diphenyl-[1,1'- biphenyl]-4-amine (5) A mixture of 4-bromoaniline (4.310 g, 25
mmol), phenanthrene-9,10-dione (1.041 g, 5 mmol), 4'-(diphenylamino)-[1,1'-
biphenyl]-4-carbaldehyde (1.047 g, 4 mmol), ammonium acetate (1.694 g, 22 mmol),
o
and acetic acid (40 mL) was heated for 12 h under argon at 125 C. After cooled and
filtered, the residue was purified by column chromatography with dichloromethane/
petroleum ether (1:1) to obtain a white powder. Yield, 1.426 g, 51.5%; FTIR (KBr,
-1
1
cm ): 3023, 3015, 2912, 2898, 1608, 1501, 1459, 1421, 1387, 733; H NMR(CDCl ,
3
4
00 MHz, ppm) δ:8.91 (d, 1H, J=8.06 Hz), 8.80 (d, 1H, J=8.23 Hz), 8.72 (d, 1H,
J=8.75 Hz), 7.76 (d, 3H, J=7.89 Hz), 7.68 (t, 1H, J=7.53 Hz), 7.61 (d, 2H, J=7.59 Hz),
.55 (d, 3H, J=8.16 Hz), 7.50 (d, 2H, J=8.25 Hz), 7.43 (d, 2H, J=7.84 Hz), 7.36-7.24
7
(m, 6H), 7.15 (d, 6H, J=7.43 Hz), 7.07 (t, 2H, J=7.02 Hz); EI-MS (m/z): 691.3, 693.2
+
(
M ); Anal. Calcd for C H BrN: C, 78.03; H, 4.37; N, 6.07; Found: C, 78.11; H,
4
5
30
1
3

ACCEPTED MANUSCRIPT
4
.41; N, 6.09.
Synthesis of 3'-(phenanthren-9-yl)-N,N-diphenyl-5'-(1-phenyl-1H-phenanthro [9,10-d]
imidazol-2-yl)-[1,1'-biphenyl]-4-amine (m-PTPAPI) A mixture of aniline (2.165 g,
1
2.5 mmol), phenanthrene-9,10-dione (0.521 g, 2.5 mmol), 4'-(diphenylamino)-5-
(phenanthren-9-yl)-[1,1'-biphenyl]-3-carbaldehyde (1.051 g, 2 mmol), ammonium
acetate (0.847 g, 11 mmol), and acetic acid (20 mL) was heated for 12 h under argon
o
at 125 C. After cooled and filtered, the residue was purified by column
chromatography with dichloromethane/ petroleum ether (2:1) to obtain a white
-1
powder. Yield, 1.191 g, 75.5%; FTIR (KBr, cm ): 3043, 3032, 2893, 2881, 1601,
1
1
531, 1488, 1392, 742; H NMR (400MHz, CDCl ): δ 8.91 (d, 1H, J=7.91 Hz), 8.87
3
(d, 2H, J=7.92 Hz), 8.74-8.70 (m, 2H), 7.99 (s, 1H), 7.88 (d, 1H, J=7.90 Hz), 7.80 (d,
1
H, J=8.79 Hz), 7.77-7.61 (m, 12H), 7.54-7.50 (m, 3H), 7.43(d, 2H, J=8.79 Hz),
13
7
.30-7.24 (m, 6H), 7.16-7.12 (m, 6H), 7.05 (t, 2H, J=7.91 Hz); C NMR (100MHz,
CDCl ): δ 147.6, 141.2, 140.6, 138.1, 134.0, 131.5, 130.9, 130.6, 130.4, 130.1, 129.4,
3
1
1
4
29.3, 128.7, 127.9, 127.7, 126.8, 127.7, 126.5, 126.3, 124.5, 124.2, 123.7, 123.1,
+
22.9, 122.5, 120.9; EI-MS (m/z): 789.2 (M ); Anal. Calcd for C H N : C, 89.70; H,
5
9
39
3
.98; N, 5.32; Found: C, 89.74; H, 4.77; N, 5.49.
Synthesis of 4'-(1-(4- (phenanthren-9-yl)phenyl)-1H-phenanthro[9,10-d]imidazol-2-
yl)-N,N-diphenyl-[1,1'-biphenyl]-4-amine (p-PTPAPI) phenanthren-9-ylboronic acid
(0.555 g, 2.5 mmol), 4'-(1-(4-bromophenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)-
N,N-diphenyl-[1,1'- biphenyl]-4-amine (1.384 g, 2 mmol) and Pd(PPh ) (20 mg, 0.04
3
4
mmol) were suspended in toluene (20 mL), 4 mL ethanol and 8 mL 2M K CO . The
2
3
1
4

ACCEPTED MANUSCRIPT
o
reaction was stirred at 105 C for 12 h and cooled to room temperature. The mixture
solution was added 15 mL brine and then extracted with CH Cl (30 mL), washed
2
2
with water (2 x 15 mL), dried (MgSO ) and evaporated to dryness. After drying under
4
vacuum, then, it was purified by dichloromethane/ petroleum ether (3:1) as an eluent
-1
to afford white solid, Yield: 1.327 g, 82.4%. FTIR (KBr, cm ): 3053, 3041, 2956,
1
2
911, 1597, 1499, 1422, 1392, 725; H NMR (400MHz, CDCl ): δ 8.98 (br, 1H), 8.83
3
(t, 2H, J=7.27 Hz), 8.76 (t, 2H, J=9.29 Hz), 8.80-7.95 (m, 2H), 7.88 (s, 1H), 7.82-7.56
(m, 15H), 7.52 (d, 2H, J=8.57 Hz), 7.48 (d, 1H, J=8.00Hz), 7.41 (d, 1H, J=6.86 Hz),
1
3
7
.30-7.25 (m, 4H), 7.14 (d, 6H, J=6.29 Hz), 7.05 (t, 2H, J=6.86 Hz); C NMR
(100MHz, CDCl3): δ 147.8, 147.5, 123.0, 121.3, 130.6, 130.2, 129.4, 129.1, 128.8,
1
28.5, 128.1, 127.7, 127.2, 126.8, 126.5, 126.2, 124.6, 124.3, 123.6, 123.3, 122.7,
+
1
21.0; EI-MS (m/z): 789.1 (M ); Anal. Calcd for C H N : C, 89.70; H, 4.98; N, 5.32;
59
39
3
Found: C, 89.48; H, 5.01; N, 5.51.
Computational Details The geometric and electronic structure of them were optimized
by Density functional theory (DFT) level of theory with the three-parameter
Becke-style hybrid functional (B3LYP). The HOMO and LUMO energy levels are
predicated by 6-31G (d,p) basis set. All of calculations about the molecule have been
performed on the huge computer origin 2000 server centre using the Gaussian 03
program package. The compositions of molecular orbits were analysed using the
GaussView 3.0 program.
Devices fabrication Before fabrication of the OLED devices, both of PTPAPI are
purified by sublimation. The ITO-coated glass substrate was first immersed
1
5

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sequentially in ultrasonic baths of acetone, alcohol and deionized water for 10 min,
respectively, and then dried in an oven. The resistance of a sheet ITO is 10-15 ꢀ/□.
The devices were fabricated in a multi-source organic molecule gas deposition system.
Different organic materials were deposited on the ITO-coated glass substrate
according to the designed structure. LiF buffer layer and Al were deposited as a
-4
co-cathode under a pressure of 5×10 Pa. Electroluminescent spectra and commission
international De L’ Eclairage(CIE) coordination of these devices were measured by a
PR655 spectra scan spectrometer. The luminescent brightness (L)-current (I)-voltage
(V) characteristics were recorded simultaneously with the measurement of the EL
spectra by combining the spectrometer through a Keithly model 2400 programmable
voltage-current source. The layer thicknesses of the deposited materials were
monitored in situ using a model FTM-V oscillating quartz thickness monitor made in
Shanghai, China. All the measurements were carried out at room temperature under
ambient conditions.
Acknowledgements.
This work was financial supported from National Natural Science Foundation of
China (21102156, 51273209), the External Cooperation Program of the Chinese
Academy of Sciences (No. GJHZ1219), the Natural Science Foundation of Ningbo
(201401A6105063), Ningbo International Cooperation Foundation (2013D10013),
and the Open Research Fund of State Key Laboratory of Polymer Physics and
Chemistry (Changchun Institute of Applied Chemistry, Chinese Academy of Sciences)
and State Key Laboratory of Luminescence and Applications (Changchun Institute of
1
6

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Optics, Fine Mechanics and Physics, Chinese Academy of Sciences)
References and notes
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04-311.
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Table Captions
Table 1. Physical data of p-PTPAPI and m-PTPAPI.
Table 2. Electroluminescent characteristics of the devices with the structure of
ITO/HATCN (5 nm)/NPB (x nm)/TCTA (5 nm)/emitters (y nm)/TPBi (z nm)/LiF (1
nm)/Al (90 nm).
Table 1
Compounds
Td
Abs
PL
Φ
HOMO(eV)
LUMO(eV)
energy gap(eV)
o
(
C)
(nm)
(nm) (%) (electro/calculated)
(electro/calculated)
(electro/calculated)
p- PTPAPI
m- PTPAPI
478 305,370
475 310
446
410
50.3
36.9
-5.3/-4.88
-5.3/-4.97
-2.57/-2.42
-2.4/-2.11
2.73/2.46
2.9/2.86

ACCEPTED MANUSCRIPT
Table 2
-2
-2
emitter
thickness
CIE
Lmax
ηc
ηp
ηe
Devices @100 cd m
Devices @1000 cd m
2
x,y,z, (nm)
(x,y)
cd/m cd/A lm/W (%)
η (cd/A) η (lm/W) ηe (%) ηc (cd/A) ηp (lm/W) ηe (%)
c
p
3
6
4
3
0, 30, 40
0, 20, 50
0, 20, 40
0, 30, 40
(0.16, 0.15) 11936 3.14 2.29 3.12
(0.16, 0.15) 9076 2.87 1.49 2.89
(0.15, 0.15) 10574 3.73 3.47 3.71
(0.16, 0.05) 2425 0.65 0.34 1.99
(0.16, 0.05) 2471 0.64 0.24 1.96
(0.15, 0.05) 3126 0.78 0.72 2.39
3.07
2.66
3.46
0.61
0.59
0.78
2.14
1.40
2.59
0.30
0.24
0.51
3.06
2.65
3.45
1.93
1.91
2.37
3.12
2.87
3.25
0.64
0.64
0.69
2.13
1.19
1.80
0.24
0.20
0.28
2.99
2.62
3.23
1.68
1.72
2.10
p-PTPAPI
m-PTPAPI
60, 20, 50
0, 20, 40
4

ACCEPTED MANUSCRIPT
Figure Captions
Fig. 1. TGA curves of p- PTPAPI and m- PTPAPI
Fig. 2. Cyclic voltammograms curves of p- PTPAPI and m- PTPAPI.
Fig. 3. Normalized UV absorption and photoluminescent spectra of p- PTPAPI and
m- PTPAPI in film
Fig. 4. Fluorescence spectra of TPABBI and TPABBBI in various polarity solvents;
and solvent polarity (f) dependence of the fluorescence maxima of p- PTPAPI (insert
Fig. a) and m-PTPAPI (insert Fig. b)
Fig. 5. Spatial distributions of HOMO and LUMO of p-PTPAPI and m- PTPAPI
Fig. 6. The electroluminescent (EL) spectra of p-PTPAPI (a) and m-PTPAPI (b) with
different current densities
Fig. 7. The EL performance of p-PTPAPI and m-PTPAPI, (a) current density-
voltage-luminance (J–V–L); (b) brightness-luminescent efficiencies curves; (c)
brightness-power efficiencies curves; (d) brightness-external quantum efficiencies
curves.
Fig. 8. The diagram of ICT process in the molecules of p-PTPAPI and m-PTPAPI
Scheme Captions
Scheme 1. The synthetic routes of p-PTPAPI and m- PTPAPI

ACCEPTED MANUSCRIPT
1.0
0.8
0.6
0.4
0.2
0.0
m-PATPA
p-PATPA
Wavelength (nm)
3
00
350
400
450
500
550
600
650
Fig. 1
p-PTPAPI
m-PTPAPI
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0
0.5
1.0
1.5
Potential vs. Fc/Fc+ (V)
Fig. 2
100
90
80
70
60
50
40
30
20
m-PTPAPI
p-PTPAPI
100
200
300
400
500
600
700
o
Temperature ( C)
Fig. 3

ACCEPTED MANUSCRIPT
1
,4-dioxane
Aceton
Cyclohexane
DMF
MeOH
Petro ether
THF
(b) m-PTPAPI
1,4-dioxane
Chloroform
DCM
EtOH
n-Hexane
Toluene
Aceton
Cyclohexane
DMF
MeOH
Petro ether
THF
(
a) p-PTPAPI
Chloroform
DCM
EtOH
n-Hexane
Toluene
Acetonitrile
p-PTPAPI
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
1.0
0.8
0.6
0.4
0.2
Ethyl acetate
Acetonitrile
Ethyl acetate
7
6
000
000
6000
m-PTPAPI
5
4
000
000
CT
CT
5000
HLCT
HLCT
4
3
000
000
-
3000
-0.05
0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.00
0.05
0.10
0.15
0.20
0.25
0.30
f
f
0.0
400 450 500 550 600 650 700 750 800
350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Wavelength (nm)
Fig. 4
Compounds
HOMO
LUMO
m- PTPAPI
4
.97 eV
1.11eV
p-PTPAPI
4.88 eV
Fig. 5
1.42 eV

ACCEPTED MANUSCRIPT
1
0
0
0
0
0
.0 (a)
2
1.0 (b)
.8
1
00 mA/cm
2
2
00 mA/cm
2
50 mA/cm
2
.8
.6
.4
.2
100 mA/cm
2
0
2
2
1
1
1
0
0 mA/cm
50 mA/cm
0 mA/cm
2
10 mA/cm
2
0.6
0.4
0.2
0.0
2
mA/cm
1
mA/cm
2
.1 mA/cm
m-PTPAPI
p-PTPAPI
.0
400
450
500
550
600
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 6
4
3
2
1
0
1
1
1
1
0
(b)
700
600
500
400
300
200
100
0
(
a)
0
0
0
1
m-PATPA
p-PATPA
p-PATPA
m-PATPA
10
0.1
3
4
5
6
7
8
9
10
11
12
100
1000
2
10000
Voltage (V)
Brightness (cd/m )
(d)
(c)
m-PATPA
p-PATPA
1
1
m-PATPA
p-PATPA
0.1
0.1
1
00
1000
10000
100
1000
10000
2
2
Brightness (cd/m )
Brightness (cd/m )
Fig. 7

ACCEPTED MANUSCRIPT
Fig. 8
B(OH)
2
N
N
(
HO) B
N
2
Br
Br
OHC
OHC
OHC
3 2 2 2 3
Pd(PPh ) Cl , K CO
Pd(PPh ) Cl , K CO
3
2
2
2
3
Br
2
3
O
O
N
N
2
H N
N
N
N
4
NH OAc, HOAc
N
m-PTPAPI
p-PTPAPI
3
O
C
B(OH)2
2
K
,
2
l
C
2
CHO
)
3
h
P
P
O
O
Br
(
d
(
HO) B
N
P
2
Br
N
N
N
Pd(PPh
3
2
) Cl
2 2
, K CO
3
N
H
2
N
Br
CHO
NH
4
OAc, HOAc
4
5
Scheme 1

ACCEPTED MANUSCRIPT
Research highlights
►
Novel phenanthrene isomers were synthesized and characterized. ► Management
of their intramolecular charge transfer (ICT) processes for violet-blue emitters ► The
results were found to be good candidates as emitters for organic light emitting diodes
(OLEDs) ► The devices exhibit violet-blue light emissions with CIE coordinates of
2
0
.16, 0.05) for m-PATPA at 100 cd/m , respectively. ► The results provide an
efficient design strategy with strong donor (D) and acceptor (A) for violet-blue
emitters.