Spirotriphenylamine based star-shaped D-A molecules meeting AIE chromophore for both efficient solution-processed doped and nondoped blue organic light-emitting diodes

Article abstract of DOI:10.1016/j.dyepig.2017.04.030

To explore the structure-property of donor-acceptor (D-A) type blue emitter, in this contribution, four star-shaped compounds of p-TPA, m-TPA, p-TPA-TPE and m-TPA-TPE using spirotriphenylamine as the donor unit and triazine as the acceptor core were designed and prepared. The tetraphenylethene (TPE) unit was introduced into the D-A molecules to enhance the emission efficiency in solid state. The photophysical properties of all compounds were comparatively studied through experimental and theoretical methods. All these D-A compounds displayed blue emission (443–487?nm) both in solution and neat film. Compared to p-TPA and m-TPA, p-TPA-TPE and m-TPA-TPE possessed clear aggregated-induced emission (AIE) property and higher emission efficiency in the solid state. Both the doped and non-doped organic light-emitting diodes (OLEDs) based on m-TPA and m-TPA-TPE were fabricated by solution-processable approach. The m-TPA-TPE based non-doped device showed a satisfying performance with a high current efficiency of 4.2?cd/A and an external quantum efficiency of 1.8% in the bluish-green region. This research demonstrates that integrating AIE unit into D-A molecule is an effective strategy for design high efficient blue emitter in non-doped OLEDs.

Full text of DOI:10.1016/j.dyepig.2017.04.030

Accepted Manuscript
Spirotriphenylamine based star-shaped D-A molecules meeting AIE chromophore
for both efficient solution-processed doped and nondoped blue organic light-emitting
diodes
Yafei Wang, Wanhui Liu, Zuoming Qu, Hua Tan, Yu Liu, Guohua Xie, Weiguo Zhu
PII:
S0143-7208(16)31462-0
10.1016/j.dyepig.2017.04.030
DYPI 5927
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 22 December 2016
Revised Date: 10 February 2017
Accepted Date: 18 April 2017
Please cite this article as: Wang Y, Liu W, Qu Z, Tan H, Liu Y, Xie G, Zhu W, Spirotriphenylamine
based star-shaped D-A molecules meeting AIE chromophore for both efficient solution-processed
doped and nondoped blue organic light-emitting diodes, Dyes and Pigments (2017), doi: 10.1016/
j.dyepig.2017.04.030.
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Graphic Abstract

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Spirotriphenylamine Based Star-Shaped D-A
Molecules Meeting AIE Chromophore for Both
Efficient Solution-Processed Doped and Nondoped
Blue Organic Light-Emitting Diodes
Yafei Wang†‡*, Wanhui Liu‡, Zuoming Qu‡, Hua Tan‡, Yu Liu‡, Guohua Xie∆*, Weiguo
Zhu†*
†
Jiangsu Key Laboratory of Environmentally Friendly Polymeric Materials, School of Materials
Science and Engineering, Jiangsu Collaboration Innovation Center of Photovoltaic Science and
Engineering, Changzhou University, Changzhou 213164, P. R. China
‡College of Chemistry, Key Lab of Environment-Friendly Chemistry and Application of the
Ministry of Education, Xiangtan University, Xiangtan 411105, PR China
∆Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials, Hubei Key
Lab on Organic and Polymeric Optoelectronic Materials, Department of Chemistry, Wuhan
University, Wuhan 430072, PR China
*To whom correspondence should be addressed
Y. Wang: qiji830404@hotmail.com
G. Xie: guohua.xie@whu.edu.cn
W. Zhu: zhuwg18@126.com

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Abstract
To explore the structure-property of donor-acceptor (D-A) type blue emitter, in this
contribution, four star-shaped compounds of p-TPA, m-TPA, p-TPA-TPE and
m-TPA-TPE using spirotriphenylamine as the donor unit and triazine as the acceptor
core were designed and prepared. The tetraphenylethene (TPE) unit was introduced
into the D-A molecules to enhance the emission efficiency in solid state. The
photophysical properties of all compounds were comparatively studied through
experimental and theoretical methods. All these D-A compounds displayed blue
emission (443~487 nm) both in solution and neat film. Compared to p-TPA and
m-TPA, p-TPA-TPE and m-TPA-TPE possessed clear aggregated-induced emission
(AIE) property and higher emission efficiency in the solid state. Both the doped and
non-doped organic light-emitting diodes (OLEDs) based on m-TPA and m-TPA-TPE
were fabricated by solution-processable approach. The m-TPA-TPE based non-doped
device showed a satisfying performance with a high current efficiency of 4.2 cd/A and
an external quantum efficiency of 1.8 % in the bluish-green region. This research
demonstrates that integrating AIE unit into D-A molecule is an effective strategy for
design high efficient blue emitter in non-doped OLEDs.
Keywords
Spirotriphenylamine;
Star-shaped
molecule;
Donor-acceptor
framework;
Aggregation-induced emission; Non-doped OLEDs

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1. Introduction
π-Conjugated chromophores consisting of electron donor (D) and electron acceptor
(A) groups are always actively pursued by both the academia and industry as organic
dyes for semiconductor devices due to their outstanding thermal stability, bipolar
charge transporting property, enhanced polarizability and tuned energy band gap [1-6].
Especially, these D-A molecules have recently made great progress in organic
light-emitting diodes (OLEDs), which covers the whole visable and near-infrared
spectrum [7-11]. On the other side of the coin, the intrinsic intramolecular charge
transfer (ICT) and largely separated HOMO (highest occupied molecular orbital) and
LUMO (lowest unoccupied molecular orbital) in D-A molecules usually leads to a
severe bathochromic shift and low emission efficiency [12].
To this end, many groups put forth their efforts to achieve the efficient blue emitter
based on D-A molecules [13-18]. One of the most effective strategies is to construct a
twisting D-A compound via introducing additional conjugated linked bridge (π unit)
to break the π-conjugation degree [19,20]. For instance,
a
series of
phenanthroimidazole-based D-π-A/D-π-A-π-D molecules were prepared, which
showed the deep blue electroluminescence with high external quantum efficiency
(EQE) in doped device [21-26]. Futhermore, engineering the interconnection position
between the donor/bridge/or acceptor moiety also effectively tuned the energy gap
leading to the blue emission, substantiated by our recent research [27]. Another
method to obtain the D-A type blue emitter is to employ the steric donor/or acceptor
group. Su and his co-workers successfully grafted the bulky spiro[fluorene-9,9′-

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thioxanthene-S,S-dioxide] unit into the blue emission material [28]. However, few of
these D-A compounds were regarded as the non-doped blue emitters. Considering the
potential phase separation and stability in the dopant−host system, therefore, it is
necessary to develop the D-A compound as the blue emitter in the non-doped OLEDs
[23,29,30].
Based on our previous work [27], the star-shaped D-π-A molecules containing
triazine core have a good thermal bility and satisfied blue emission. Encouraged by
our previous work and with an intention to further investigate the structure-property
of the star-shaped blue emitter, in this contribution, we would like to focus on the
triazine based D-A type blue emitter in non-doped OLEDs. Owing to the twist
conformation [31], spiro-annulated triphenylamine was initially chosen as the donor
unit, which is very scarce in the D-A blue emitter. To further enhance the efficiency of
the non-doped devices, the aggregated-induced emission (AIE) concept, reported by
Tang in 2001 [32], would be integrated into the D-A compound because they are
non-emissive in dilution solutions but have very intense luminescence in the solid
state [33,34]. As aforementioned, we designed two star-shaped D-A isomers with
different interconnection position, p-TPA-TPE and m-TPA-TPE, in which TPA is the
triazine core and spiro-annulated triphenylamine units and TPE is the
tetraphenylethene moiety (Figure 1 and Scheme 1). For comparison, the parent
compound without TPE unit, p-TPA and m-TPA, were also synthesized. Herein, the
photophysical property were systematically explored by experimental and theoretical
methods. As expected, all these D-A compounds showed the blue emission both in

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solution and neat film. The compounds with TPE unit definitely have an enhanced
emission efficiency in the solid state. To expolre the electroluminescent property of
these D-A compounds, both doped and non-doped devices employing m-TPA and
m-TPA-TPE as emitter were fabricated by solution-processable approach. The
m-TPA-TPE based non-doped device achieved a high current efficiency of 4.2 cd/A
and an EQE of 1.8 % in the bluish-green region.
2. Experimental Section
2.1 Materials and Measurement
2-bromoiodobenzene, 2-bromofluorenone and 2,7-dibromofluorenone are
commercial from Energy Chemical Company Ltd. Other reagents were purchased
from J&K Chemical and Aladdin companies. All reactions were carried out under N2
atmosphere. Compounds 1, 2, 5 and 6 were synthesized according to the reported
1
procedure [27,31]. H NMR and 13C NMR spectra were acquired using a Bruker
Dex-400 NMR instrument using CDCl3 as a solvent. Mass spectra (MS) were
recorded on a Bruker Autoflex MALDI-TOF instrument using dithranol as a matrix.
Elemental analysis was measured by Flash EA 1112. The UV-vis absorption and
photoluminescence (PL) spectra were measured with a Varian Cray 50 and
Perkin-Elmer LS50B luminescence spectrometer, respectively. Lifetimes and
emission efficiency in solid state were measured with Edinburgh analytical instrument
(FLS980 fluorescence spectrometer) in degassed toluene at room temperature.
Thermogravimetric analysis (TGA) was carried out with a NETZSCH STA449 from

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50°C to 600°C at a 20°C/min heating rate under N2 atmosphere. Electrochemical
property was evaluated by cyclic voltammetry (CV) with three typical electrodes in
degassed CH3CN solution with a rate of 100 mV/s. The CV system employed
Bu4NPF6 as electrolyte. Platinum disk was used as the working electrode, platinum
wire was regarded as the counter electrode and silver wire was used as the reference
electrode. Ferrocenium/ferrocen (Fc/Fc+) was used as the reference compound.
2.2 Devices fabrication and characterization
The devices employing m-TPA and m-TPA-TPE as the dopant were fabricated by
solution-processed
approach.
In
these
OLEDs,
poly(3,4-ethylenedioxythiophene:poly(styrenesulfonic acid) (PEDOT:PSS) was
spin-coated onto ITO substrate, which is utilized as the hole injection layer. The
9-[3-(9H-carbazol-9-yl)phenyl]-9H-carbazole (mCP) is used as the host matrix.
1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB) is the electron transporting layer
with 40 nm thick. Liq and Al are used as the composite cathode. Electroluminescent
spectra were recorded using an optical analyzer, Photo Research PR735. The features
of current density and brightness versus applied voltage were simultaneously obtained
by a source meter unit Keithley 2420 and PR735. EQE was calculated from the
luminance, current density, and EL spectrum, assuming a Lambertian distribution. The
device configurations are as follows:
Device I: ITO/PEDOT:PSS (30 nm)/mCP: m-TPA (90:10, 30 nm)/TmPyPB (40
nm)/Liq (1 nm)/Al
Device II: ITO/PEDOT:PSS (30 nm)/mCP: m-TPA-TPE (90:10, 30 nm)/TmPyPB (40

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nm)/Liq (1 nm)/Al
Device III: ITO/PEDOT:PSS (30 nm)/m-TPA (30 nm)/TmPyPB (40 nm)/Liq (1
nm)/Al
Device IV: ITO/PEDOT:PSS (30 nm)/m-TPA-TPE (30 nm)/TmPyPB (40 nm)/Liq (1
nm)/Al
2.3 Synthesis of compound 3
A mixture of 1-(4-bromophenyl)-1,2,2-triphenylethylene (4.0 g, 9.8 mmol),
bis(pinacolato)diboron (3.7 g, 14.6 mmol), CH3COOK (4.8 g, 48.8 mmol) and
1,1'-bis(diphenylphosphino)ferrocene palladium dichloride (214 mg, 0.3 mmol) in
1,4-dioxane (100 mL) was refluxed for 24 h under nitrogen. After cooling to room
temperature, the mixture was poured into water and extracted with CH2Cl2 (3×20 mL).
The organic phase was collected and washed with water (3×20 mL) and dried with
anhydrous Na2SO4. The solvent was removed under vacuum, and then the residue was
purified by column chromatography with petrolum ether (PE)/CH2Cl2 (4:1) as an
1
eluent to give compound 3 (3.6 g, yield: 79%) as a green solid. H NMR (400 MHz,
CDCl3), δ: 7.54 (d, J=8.0 Hz, 2H), 7.09-7.01 (m, 17H), 1.32 (s, 12H).
2.4 Synthesis of compound 4
To a dry round bottom flask was added compound 2 (2.2 g, 3.8 mmol), compound 3
(1.6 g, 3.5 mmol), tetrakis(triphenylphosphine)palladium (120 mg, 0.1 mmol),
potassium carbonate solution (2 M, 25 mL) and THF (80 mL). The mixture was
refluxed for 24 h under nitrogen. After cooling to room temperature, the mixture was
then poured into water and extracted with CH2Cl2 (3×20 mL). The organic phase was

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washed with water (3×20 mL) and dried with anhydrous Na2SO4. After Removing the
solvent under vacuum, the residue was purified by column chromatography with
PE/CH2Cl2 (4:1) as an eluent to get the compound 4 as a green solid (1.2 g, yeild:
42%). 1H NMR (400 MHz, CDCl3), δ: 7.82 (d, J=8.4 Hz, 1H), 7.74 (t, J=7.6 Hz, 2H),
7.68-7.55 (m, 5H), 7.49 (d, J=8.0 Hz, 3H), 7.33 (d, J=8.4 Hz, 2H), 7.21-7.05 (m,
16H), 6.97 (t, J=8.4 Hz, 3H), 6.62 (t, J=7.6 Hz, 2H), 6.45 (d, J=7.6 Hz 2H), 6.39 (d,
J=7.6 Hz, 2H).
2.5 Synthesis of p-TPA and m-TPA
A mixture of compound 1 or 2 (4 mol eq) , compound 5 or 6 (1 mol eq),
tetrakis(triphenylphosphine)palladium (0.03 mol eq), potassium carbonate solution (2
M, 15 mL) and THF (45 mL) was refluxed for 24 h under nitrogen. After cooling to
room temperature, the mixture was poured into water and extracted with CH2Cl2
(3×20 mL). The organic phase was washed with water (3×20 mL) and dried with
anhydrous Na2SO4. The solvent was removed under vacuum, and then the residue was
purified by column chromatography using PE/CH2Cl2 (2:1) as an eluent to get the
target compounds.
1
p-TPA: Light yellow solid. Yield: 45%. H NMR (400 MHz, CDCl3), δ: 8.83 (d,
J=8.0 Hz, 6H), 7.95 (d, J=8.0 Hz, 6H), 7.87 (t, J=9.2 Hz, 6H), 7.77-7.62 (m, 12H),
7.58-7.50 (m, 12H), 7.44 (t, J=7.2 Hz, 3H), 7.33 (t, J=8 Hz, 3H), 6.96 (t, J=8.0 Hz,
6H), 6.64 (t, J=8.0 Hz, 6H), 6.54 (d, J=7.6 Hz, 6H), 6.43 (d, J=8.2 Hz, 6H); 13C NMR
(101 MHz, CDCl3), δ: 171.29, 157.18, 156.79, 145.17, 141.43, 141.07, 140.48,
139.42, 138.61, 135.11, 131.19, 129.42, 128.59, 127.72, 127.36, 127.15, 125.86,

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124.78, 124.57, 120.70, 120.38, 120.17, 114.76, 77.36, 77.05, 76.73, 57.10 ppm;
TOF-MS (EI): m/z: calcd for C114H72N6: 1524.582 [M+]; found: 1525.000. CHN:
calcd for C114H72N6, C, 89.74; H, 4.76; N, 5.51%; found: C 89.40, H 4.81, N 5.70%.
1
m-TPA: Light yellow solid. Yield: 39%. H NMR (400 MHz, CDCl3), δ: 9.01 (s, 3H), 8.61 (d,
J=8.0 Hz, 3H), 7.97 (d, J=8 Hz, 3H), 7.91 (d, J=8.8Hz, 6H), 7.80 (dd, J=8.0 Hz, 13.2 Hz, 6H),
7.49-7.35 (m, 21H), 7.35 (t, J=8.4 Hz, 4H), 6.98 (t, J=8.8 Hz, 6H), 6.64 (t, J=8.0 Hz, 6H), 6.57 (d,
J=8 Hz, 6H), 6.42 (d, J=7.8 Hz, 6H); 13C NMR (101 MHz, CDCl3), δ: 171.72, 157.28, 156.18,
141.39, 140.67, 139.97, 138.90, 138.00, 137.52, 136.60, 131.30, 131.07, 129.05, 128.48, 127.90,
127.46, 126.89, 125.53, 124.56, 123.64, 120.58, 120.16, 114.72, 77.23, 76.75, 76.01, 57.15 ppm.
TOF-MS (EI): m/z: calcd for C114H72N6: 1524.582 [M+]; found: 1525.027. CHN: calcd for
C114H72N6, C, 89.74; H, 4.76; N, 5.51%; found: C 89.92, H 4.63, N 5.44%.
2.6 Synthesis of p-TPA-TPE and m-TPA-TPE
A mixture of compound 4 (4 mol eq), compound 5 or 6 (1 mol eq),
tetrakis(triphenylphosphine)palladium (0.03 mol eq), potassium carbonate solution (2
M, 15 mL) and THF (45 mL) was refluxed for 24 h under nitrogen. After cooling to
room temperature, the mixture was poured into water and extracted with CH2Cl2
(3×10 mL). The organic phase was washed with water for three times and dried with
anhydrous Na2SO4. The solvent was removed under vacuum, and then the residue was
purified by column chromatography with PE/CH2Cl2 (2:1) as an eluent to get the
target compounds.
p-TPA-TPE: Light green solid. Yield: 41%. 1H NMR (400 MHz, CDCl3), δ: 8.83 (d,
J=8.4 Hz, 6H), 7.92 (dd, J=7.6 Hz, 14.8 Hz, 6H), 7.84-7.62 (m, 24H), 7.54 (d, J=7.6

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Hz, 6H), 7.37 (d, J=8.4 Hz, 6H), 7.14-7.07 (m, 60H), 6.65 (t, J=7.6 Hz, 6H), 6.58 (d,
J=8.0 Hz, 6H), 6.43 (d, J=7.6 Hz, 6H); 13C NMR (101 MHz, CDCl3), δ: 171.31,
157.50, 157.18, 143.79, 141.28, 131.83, 131.37, 130.08, 129.44, 128.02, 127.61,
126.46, 120.76, 120.60, 114.79, 77.23, 77.03, 76.71, 57.20 ppm. TOF-MS (EI): m/z:
calcd for C192H126N6: 2515.004 [M+]; found: 2515.823. CHN: calcd for C192H126N6, C,
91.62; H, 5.05; N, 3.34%; found: C 91.39, H 5.14, N 3.17%.
m-TPA-TPE: Light green solid. Yield: 31%. 1H NMR (400 MHz, CDCl3), δ: 9.00 (s,
3H), 8.61 (d, J=8.4 Hz, 6H), 7.86 (m, 21H), 7.69 (d, J=7.6 Hz, 6H), 7.41 (m, 24H),
7.11 (m, 42H), 6.98 (t, J=8.8 Hz, 6H), 6.63 (dd, J=8.0 Hz, 8.0 Hz, 12H), 6.42 (d,
J=8.0 Hz, 6H); 13C NMR (101 MHz, CDCl3), δ: 171.71, 157.58, 156.54, 143.80,
142.85, 141.62, 141.10, 140.84, 140.51, 138.72, 137.93, 136.59, 131.83, 131.42,
131.05, 128.36, 127.19, 126.54 , 126.16, 125.06, 124.34, 120.77, 120.36, 114.74,
77.35, 77.04, 76.72, 57.21 ppm. TOF-MS (EI): m/z: calcd for C192H126N6: 2515.004
[M+]; found: 2514.673. CHN: calcd for C192H126N6, C, 91.62; H, 5.05; N, 3.34%;
found: C 91.45, H 5.40, N 3.05%.
3. Results and Discussion
3.1 Synthesis
The synthetic route of p-TPA, m-TPA, p-TPA-TPE and m-TPA-TPE are depicted in
Scheme 1. According to the previous report [27,31], The Ullmann reaction between
2-bromoiodobenzene
and
diphenylamine
yielded
N-(2-bromophenyl)-N-
phenylbenzenamine, which was followed by cyclization reaction with the commerical
2,7-dibromo-9H-fluoren-9-one (or 2-dibromo-9H-fluoren-9-one) to afford the key

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precursors
1
and 2. 1-Bromo-4-(1,2,2-triphenylvinyl)benzene reacted with
bis(pinacolato)diboron to yield compound 3 in the present of CH3COOK and
PdCl2(dppf) [dppf=1,1'-bis(diphenylphosphino)ferrocene]. Compound 4 and the target
compounds were achieved through the typcial Suzuki coupling reaction in good yields.
1
Definitely, p-TPA, m-TPA, p-TPA-TPE and m-TPA-TPE were characterized by H
13
NMR, C NMR, TOF-MS and elemental analysis. Evidenced by thermogravimetric
analysis (TGA), all compounds displayed good thermal stability with the
decomposition temperature (at 5 % weight loss) above 320oC (ESI†, Table 1).
3.2 Optical Properties
The UV-vis absorption property was investigated in toluene solution (10-5 M) at
room temperature (Figure 1), and the relevant photophysical data are summarized in
Table 1. Compounds p-TPA and m-TPA have the clear dual-absorption bands
between 250 nm and 400 nm. The absorption bands at short wavelength (ca. 285±5
nm) are attributed to the the π-π electron transition of aromatic rings [27,35]. Another
absorption band at 357 nm (p-TPA) and 325 (m-TPA), respectively, are assigned to
the intramolecular charge transfer (ICT) transition, as also evidenced by therotical
calculation (vide infra). On the other hand, compounds p-TPA-TPE and m-TPA-TPE
mainly present the ICT absorption band. Compared to the para- substituent isomers,
the mata- counterparts display narrow optical energy gap due to the changed
π-conjugation degree. Owing to the the intermolecular interaction, all compounds
show a distinctly red-shifted absorption spectra in the neat film compared to that in
solution (Figure 1 and ESI†).

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The photoluminescent (PL) property of all compounds measured in toluene (10-5 M)
at room tempearture are shown in Figure 2a. All compounds exhibit the structureless
emission profiles in the range of 440-486 nm, implying a nonnegligible ICT feature. It
is noted that compounds p-TPA and m-TPA have the nearly identical emission in the
solution, while p-TPA-TPE displays an apparent hypochromatic shift compared to
m-TPA-TPE. It is assumed that the distorted donor moity has a responsibility for this
result. In addition, the PL emissions in different solvents, such as CH2Cl2, THF and
toluene, present strong solvatochromism effect (ESI†), further proving the ICT in
these D-A molecules. In toluene solution, the emission lifetime (τ) of compounds
p-TPA and m-TPA were evaluated to be 11.5 ns and 12.1 ns, respectively, indicating
the emission originates from singlet-excited state. Unfortunately, the lifetime of
compounds with TPE unit could not be detected owing to the poor emission in the
solution. Compared to the emission in solution, all compounds showed a slight red
shift in the neat film (Figure 2b), suggesting the reduced intermolecular interaction
caused by the steric structure (Table 1). Definitely, p-TPA-TPE and m-TPA-TPE
possess very strong emission in the solid state due to the TPE-based AIEgens.
Therefore, the PL spectra of both p-TPA-TPE and m-TPA-TPE were further studied
in the THF/water mixture with different water fractions (fw) to verify the AIE property
(Figure 3 and ESI†). Taking m-TPA-TPE for example, the negligible emission are
observed in the pure THF solution even when the fw increases to 30 %, implying that
the compound still have a good solubility in this mixture [36]. Then, the PL intensity
has a sharply increase at fw > 50%, suggesting the aggregation suspension is formed.

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When fw was increased to 90 %, the emission intensity reaches its maximum in the
blue region (482 nm). Additioanly, the emission has a minor shift in the THF/water
mixture with different fw. As shown in Figure 3b, the emission intensity of
m-TPA-TPE at fw of 90% is 71 times higher than that in pure THF, which clearly
elucidates the AIE character. Similar AIE behaviors with a hypochromatic shift were
also observed for p-TPA-TPE, whose emission intensity increased by 41-fold (ESI†).
To further validate the AIE activity of both compounds, their emission quantum
efficiencies in solid state were determined to be 60% and 24% for p-TPA-TPE and
m-TPA-TPE, respectively, which is much higher than that in solution.
3.3 Electronic Properties
To further elucidate the relationship of structure and electronic distribution, density
functional theory (DFT) calculation was carried out using Gaussian 09 program with
B3LYP/6-31G(d) basis sets. From the optimized geometry (Figure 4), the
spiro-triphenylamine has an orthogonal structure, which to some extent suppresses the
intermolecular interaction. Furthermore, the torsion angles between the
spiro-triphenylamine moiety and the triazine core/or TPE unit are both ～36o.
Therefore, these molecules could be an effective emitter in solid state. In all D-A
compounds, the HOMO are localized on the spiro-triphenylamine moiety. In contrast,
the LUMO has a different spatial distributions for these molecules. For the p-TPA and
p-TPA-TPE, the LUMO is delocalized on both triazine and fluorene unit, while the
LUMO of m-TPA and m-TPA-TPE are mainly localized on the triazine moiety.
Actually, the TPE unit has little contribution for the electron distribution. The

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observed separated orbitals demonstrate the intrinsic ICT property in these molecular
systems.
3.4 Eletrochemical Properties
Cyclic voltammetry (CV) was carried out to evaluate the electrochemical property
of all compounds calibrated with ferrocene/ferrocenium (Fc/Fc+) as an reference, and
the data are listed in Table 1. All compounds show several irreversible oxidation
potential in the region of 0.5-1.8 V (ESI†), while their reduction potential did not be
detected between 2.0 and –2.0 V. Compared to para substituents, the mata
counterparts have a large oxidation potential caused by the effect of π-conjugated
degree. After introducing the TPE unit into the D-A molecules, an increased oxidation
potential were observed. Apparently, the connection position between donor and
acceptor and additional TPE unit have a clear effect on the electrochemcial property.
According to the empirical fomular of EHOMO = –(4.8 + Eox – EFC/FC+) eV, the HOMO
energy levels of all compounds are calculated to be –5.37～–5.45 eV (Table 1). Based
on the HOMO values and the optical energy gap, the LUMO energy levels were
estimated in the region of –2.0～–2.4 eV.
3.5 Eletroluminescent Properties
Owing to the poor solubility of p-TPA and p-TPA-TPE in chlorobenzene, the
devices prior employing compounds m-TPA (device I) and m-TPA-TPE (device II) as
the emitter were fabricated with the configuration of ITO/PEDOT:PSS (30
nm)/mCP:compound (90:10, 30 nm)/TmPyPB (40 nm)/Liq (1 nm)/Al (100 nm). In
this device, mCP (9-[3-(9H-carbazol-9-yl)phenyl]-9H-carbazole) is used as the host

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matrix due to its high triplet energy, which doped with the m-TPA/or m-TPA-TPE
serves as the emitter. TmPyPB (1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene) is the
electron-transporting and hole-blocking layer. Liq and Al are served as the composite
cathode
At 12 V, the devices I and II present the maximum electroluminescence (EL) at 420
nm and 472 nm, respectively (insert Figure 5). Their corresponding commission
international de L'Eclairage (CIE) coordinates are (0.19, 0.16) and (0.19, 0.26)
(Figure 5b), implying blue emission. The current density-voltage-luminance (J-V-L)
curves and external quantum efficiency (EQE) curves are illustrated in Figure 5 and
Figure 6. Obviously, m-TPA based device (device I) possesses an inferior performance
with a maximum luminance of 430 cd/m2, a current efficiency of 0.12 cd/A and EQE
of 0.15 %. Conversely, the device based on m-TPA-TPE (device II) exhibits a
maximum luminance of 4431 cd/m2, a current efficiency of 2.0 cd/A and EQE of
1.1 %. It is noted that the performances of device II is roughly 10- to 20-fold higher
than that of the device I. It is apparent that introducing the TPE unit into this D-A
molecule plays a key role on enhancing the device performance. Unfortunately, the
turn-on voltages of both devcies I and II are not dissatisfied (Table 2).
To further optimize the device performance, two non-doped devices (devices III
and IV) with the structure of ITO/PEDOT:PSS (30 nm)/compound (30 nm)/TmPyPB
(40 nm)/Liq (1 nm)/Al (100 nm) were fabricated. In this device, the pure compound
m-TPA/or m-TPA-TPE serves as the emitter. As shown in insert Figure 7, both devices
show the bluish-green emission with the maximum peak at about 486 nm and 500 nm

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for m-TPA and m-TPA-TPE, respectively. The EL spectra of these devices are similar
with their corresponding PL profiles, indicating the EL emission originated from the
intrinsic emission of the molecules. Correspondingly, the CIE coordinates of devices
III and device IV are located in (0.21, 0.32) and (0.22, 0.38). Interestingly, devices III
and IV have the relatively low turn-on voltage (ca. 4V) compared to devices I and II,
implying a better bipolar carriers transport in the non-doped devices.
As shown in Figure 7 and 8, the non-doped devices (III and IV) possess an
apparently enhanced performance compared to the corresponding dopant-host system,
probably due to the twisted D-A molecular structure. m-TPA based non-doped device
(device III) display a maximum luminance of 985 cd/m2, a current efficiency of 0.5
cd/A and EQE of 0.3 %. The device IV (m-TPA-TPE based device) exhibits a
satisfying EL efficiency with the maximum luminance of 3629 cd/m2, current
efficiency of 4.2 cd/A and EQE of 1.8 %. The performance of non-doped devcies
increases by ～1 time than their counterpart doped devices.
4. Conclusions
In summary, four novel star-shaped blue emitter bearing D-A framework were
synthesized and characterized. In these molecules, the different interconnection
position between donor and acceptor unit has a distinct effect on the solubility and
photophysical property. After grafted the TPE moiety into D-A compound,
p-TPA-TPE and m-TPA-TPE showed strong AIE emission and improved emission
efficiency in the solid state. The devices based on m-TPA-TPE showed 6~10 folds

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higher performance than that of m-TPA based devices. Furthermore, the non-doped
devices had a better performance than the doped counterpart. This result implys that
the additional TPE moiety plays a position role on improving the emission efficiency,
which provides an effective strategy for design D-A blue emitter with high efficient
emission in non-doped OLEDs
Acknowledgement
We thank the financial support from the Natural Science Foundation of China
(51473140, 61575146 and 51273168), the Petrochemical Joint Fund Between
National Natural Science Foundation & China Petroleum and Chemical Corporation

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(U1663229), the Program for Innovative Research Cultivation Team in University of
Ministry of Education of China (1337304)..
Supporting Information
The Supporting Information is available free of charge on the Publications website.
Detailed information on TGA, lifetime, PL spectrum and CV curves..

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Tables Captions
Table 1. Thermal properties of platinum complexes
Table 2. Photophysical parameter of platinum complexes

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Table 1. Photophysical data of all compounds
dФ
/%
7
eEox
/V
fEHOMO gELUMO hEg
opt
aUV-Vis
/nm
Emission/nm
aSolution Film
cTd
/oC
491
b
Compound
τ
/ns
/eV
/eV
/eV
p-TPA
280, 357
276,
454
443
479
485
11.5
<5
0.57
0.60
–5.37
–5.4
–2.32
–2.46
3.05
2.94
p-TPA-TPE
533 60
301, 370
295, 325
m-TPA
458
466
12.1
320 0.8
0.60
–5.4
–2.0
3.40

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m-TPA-TPE
270,
485
487
<5
335 24
0.65
–5.45
–2.41
3.04
292, 353
Measure conditions: a,b) in toluene solution (10-5 M) at room temperature; c) 5% weight loss in N2; d) in solid
state at room temperature; e) mesured in CH3CN solution at room temperature, and the data collected from the
Fc/Fc+
turn-on potential verse Fc/Fc+, Eox
= 0.076 V; f) EHOMO = – (Eox + 4.8) eV; g) evaluated from the UV-vis
absorption spectra, ELUMO = (Eoptg - EHOMO) eV; h) Eoptg = 1240/λabsorption
.
Table 2. The EL performance of devices I-IV
Device
Vturn-on
L
(cd/m2)
430
CE
(cd/A)
0.12
2.0
PE
(lm/W)
0.03
0.5
EQE
(%)
0.15
1.1
(V)
8
Device I
Device II
Device III
Device IV
8
4431
985
4
0.5
0.3
0.3
4
3629
4.2
1.66
1.8
Figures Captions
Chart 1 Structural evolutions of p-TPA, m-TPA, p-TPA-TPE and m-TPA-TPE
Scheme 1 Synthetic route of p-TPA, m-TPA, p-TPA-TPE and m-TPA-TPE
Figure 1 Normalized UV-vis spectra of compounds in toluene at room temperature
Figure 2 PL spectra of compounds both in toluene (a) and neat film (b) at room temperature
Figure 3 PL spectra (a) of m-TPA-TPE in THF/water mixture with different water fractions (fw) at

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room temperature; Plot of (I/I0, b) values versus the compositions of the aqueous mixtures. I0 =
emission intensity in pure THF solution. The inset graph is fluorescence images of m-TPA-TPE in
THF/water mixtures with different fw (0 % and 90%) taken under UV illumination.
Figure 4 Optimized geometries and spatial distributions of HOMO (green color) and LUMO
(red/blue color) in S0 state calculated using the B3LYP/6-31G(d) basis set
Figure 5 The EQE-current density curves, EL spectra and CIE coordinate for device I and II
Figure 6 The current density-voltage-luminance (J-V-L) curves for device I and II
Figure 7 The EQE-current density curves, EL spectra at 12 V and CIE coordinate for device III
and IV
Figure 8 The current density-voltage-luminance (J-V-L) curves for device III and IV

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Chart 1 Structural evolutions of p-TPA, m-TPA, p-TPA-TPE and m-TPA-TPE

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Reaction conditions: a) n-BuLi, THF, -78oC, 4 h; b) HCl, CH3COOH, reflux, 1 h; yield: 1: 63%,
2: 62%; c) bis(pinacolato)diboron, CH3COOK, PdCl2(dppf), 1,4-dioxane, 80oC, 24 h; yield: 79%;
d) 2 M K2CO3, Pd(PPh3)4, THF, 85oC, 24 h; yield: 42%; e) 2 M K2CO3, Pd(PPh3)4, THF, 85oC, 24
h; yield: p-TPA: 45%, m-TPA: 39%, p-TPA-TPE: 41%, m-TPA-TPE: 31%.
Scheme 1 synthetic route of p-TPA, m-TPA, p-TPA-TPE and m-TPA-TPE