A high Tg small-molecule arylamine derivative as a doped hole-injection/transport material for stable organic light-emitting diodes

Article abstract of DOI:10.1016/j.orgel.2018.04.012

High performant hole-injection materials find important applications in organic electronics. In this contribution we report a simple small-molecule organic hole-injection/transport material N,N,N′,N′-tetra(4-methoxyphenyl)-[2,2′-binaphthalene]-6,6′-diamine for organic light-emitting diodes (OLEDs). It shows a high thermal and morphological stability with a T_g of 99 °C. The ultraviolet photoelectron spectroscopy measurements reveal a favorable HOMO level of ?5.05 eV p-Doping with tetrafluorotetracyanoquinodimethane (F4-TCNQ) increases the hole conductivity up to 2.64 × 10^?4 S m^?1 vs. 1.68 × 10^?4 S m^?1 of the neat film. The characterization of the red and green phosphorescent OLEDs suggests that introducing this thick p-doped hole-injection layer may yield high electroluminescent efficiency and operational stability. Moreover the new compound shows enhanced thermal and conducting properties and thus better performances in contrast with a conventional hole-injection material N,N,N′,N′-tetra(4-methoxyphenyl)-[1,10-biphenyl]-4,4′- diamine (MeO-TPD) in the OLEDs.

Full text of DOI:10.1016/j.orgel.2018.04.012

Accepted Manuscript
A high T small-molecule arylamine derivative as a doped hole-injection/transport
g
material for stable organic light-emitting diodes
Xiao-Lan Huang, Jian-Hua Zou, Jun-Zhe Liu, Guang Jin, Jian-Bin Li, Sheng-Lin Yao,
Jun-Biao Peng, Yong Cao, Xu-Hui Zhu
PII:
S1566-1199(18)30168-X
10.1016/j.orgel.2018.04.012
ORGELE 4620
DOI:
Reference:
To appear in: Organic Electronics
Received Date: 13 February 2018
Revised Date: 4 April 2018
Accepted Date: 5 April 2018
Please cite this article as: X.-L. Huang, J.-H. Zou, J.-Z. Liu, G. Jin, J.-B. Li, S.-L. Yao, J.-B. Peng,
Y. Cao, X.-H. Zhu, A high T small-molecule arylamine derivative as a doped hole-injection/
g
transport material for stable organic light-emitting diodes, Organic Electronics (2018), doi: 10.1016/
j.orgel.2018.04.012.
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ACCEPTED MANUSCRIPT
p-Doping the hole-injection/transport material XL1 may provide high-efficiency OLEDs with very
promising stability.

ACCEPTED MANUSCRIPT
A high Tg small-molecule arylamine derivative as a doped hole-injection/transport material for
stable organic light-emitting diodes
Xiao-Lan Huang, Jian-Hua Zou, Jun-Zhe Liu, Guang Jin, Jian-Bin Li, Sheng-Lin Yao, Jun-Biao
Peng, Yong Cao, Xu-Hui Zhu*
State Key Laboratory of Luminescent Materials and Devices, and Institute of Polymer
Optoelectronic Materials and Devices, South China University of Technology (SCUT), Guangzhou
510640, China.
* Corresponding author. E-mail address: xuhuizhu@scut.edu.cn (X.-H. Zhu)
Abstract
High performant hole-injection materials find important applications in organic electronics. In
this contribution we report a simple small-molecule organic hole-injection/transport material N,N,
N',N'-tetra(4-methoxyphenyl)-[2,2'-binaphthalene]-6,6'-diamine for organic light-emitting diodes
o
(OLEDs). It shows a high thermal and morphological stability with a Tg of 99 C. The ultraviolet
photoelectron spectroscopy measurements reveal a favorable HOMO level of −5.05 eV. p-Doping
with tetrafluorotetracyanoquinodimethane (F4-TCNQ) increases the hole conductivity up to 2.64 ×
10–4 S m–1 vs. 1.68 ×10–4 S m–1 of the neat film. The characterization of the red and green
phosphorescent OLEDs suggests that introducing this thick p-doped hole-injection layer may yield
high electroluminescent efficiency and operational stability. Moreover the new compound shows
enhanced thermal and conducting properties and thus better performances in contrast with a
conventional hole-injection material N,N,N',N'-tetra(4-methoxy-phenyl)-[1,10-biphenyl]-4,4'-
diamine (MeO-TPD) in the OLEDs.
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Keywords: hole-injection materials, organic light-emitting diodes, p-doping, operational stability,
synthesis
1. Introduction
Hole-injection materials (HIMs) have been widely used in organic electronics such as organic
light-emitting diodes (OLEDs) and organic/hybrid solar cells [1-7]. As an anode buffer layer, a
prerequisite is that the HIMs should facilitate hole injection into the emitting layer of the OLEDs or
extraction out of the active layer of the solar cells. Over the years, a diversity of hole-injection
materials have been reported, including organic molecular compounds copper(II) phthalocyanine
(CuPc) [8,9], high HOMO aryl amines [10-15], strong electron acceptor 1,4,5,8,9,11-
hexaazatriphenylene hexacarbonitrile (HAT-CN) [16,17], conducting polymer PEDOT:PSS [18] and
high work-function inorganic metal oxides [19-22]. Being hydrophobic and transparent in the
visible, N,N,N',N'-tetra(4-methoxyphenyl)-[1,10-biphenyl]-4,4'-diamine (MeO-TPD, Fig. 1)
represents an early prototype of organic hole-injection materials [11], which possesses several
attractive features, such as i) a high HOMO level of ca. −5.07 eV [23], ii) forming an amorphous
film through low-temperature vacuum sublimation and iii) ease of availability. Moreover, p-doping
of MeO-TPD is capable of increasing the conductivity by several orders of magnitude and
o
meanwhile reducing the hole-injection barrier [13,24]. However, the low Tg of ~70 C hampers its
application in practical organic light-emitting diodes.
In this contribution, we present a simple arylamine compound N,N,N',N'-tetra(4-
methoxyphenyl)-[2,2'-binaphthalene]-6,6'-diamine (XL1, Fig. 1) with facile synthesis and
purification. As a rigid and bulky moiety, the naphthyl has been conveniently used to increase the
glass transition temperature. For instance, 4,4'-bis((1-naphthyl)phenylamino)biphenyl (NPB)
o
o
exhibits a Tg of 95 C vs. 65 C of 4,4'-bis(3-methylphenylphenylamino)biphenyl (TPD) [8]. We
have shown that the 2,2'-binaphthyl may benefit the morphological stability and charge transport in
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the electron-transport compound BiNa-BiDPO [25,26]. Consequently XL1 shows a Tg of 99 C in
addition to a high HOMO level of −5.05 eV. Upon p-doping, the hole conductivity of XL1:
F4-TCNQ was increased to 2.64 × 10–4 S m–1 (F4-TCNQ = tetrafluorotetracyanoquinodimethane).
Introducing this thick p-doped hole-injection material could offer high-efficiency OLEDs with very
promising stability.
Fig. 1. Chemical structures of MeO-TPD and XL1
2. Results and Discussion
2.1. Synthesis and optical properties of XL1
Scheme 1. Synthetic route to XL1: i) 4-iodoanisole, 1,10-phenanthroline monohydrate, CuI,
o
sodium butanolate, anhydrous toluene, 120 C; ii) bis(pinacolato)diboron, Pd(PPh3)2Cl2, anhydrous
KOAc, THF, 90 °C; iii) 6-bromo-2-N,N-bis(4-methoxyphenyl)aminonaphthalene, Pd(PPh3)4, 2 M
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Na2CO3 aqueous solution, ethanol, toluene, 100 °C.
The synthesis of XL1 is straightforward and outlined in Scheme 1. The Ullmann reaction of
the starting compounds 4-iodoanisole and 2-amino-6-bromonaphthalene yielded 6-bromo-2-N,
N-bis(4-methoxyphenyl)aminonaphthalene (1) in ca. 88% yield [27]. Subsequently, the catalytic
boronation of compound 1 with bis(pinacolato)diboron produces the Suzuki reagent 6-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)-2-N,N-bis(4-methoxyphenyl)aminonaphthalene (2) in about
90% yield. Finally the target compound XL1 is obtained by Suzuki coupling of compounds 1 and 2
in 70% yield.
13
The identity and purity of XL1 are confirmed by 1H NMR, C NMR, mass spectroscopy and
elemental analysis (See Fig. S1). Analytically pure XL1 is facilely available mainly through column
chromatography without involving sublimation technique.
The new compound shows a high solubility in toluene, For instance, 100 mg of XL1 can be
easily solubilized in 1 ML of toluene. It shows a main absorption peak at 357 nm with a shoulder
located at 395 nm in dilute toluene solution (See Fig. S2). The shoulder was slightly red shifted to
404 nm while the main absorption maximum remained unchanged as film. According to the
absorption onset of the film, the optical bandgap of XL1 is calculated as 2.7 eV.
The fluorescent spectrum of the XL1 film exhibits an emission peak at 467 nm, red-shifted by
17 nm from that in toluene solution. The triplet energy (ET) of XL1 is estimated as ca. 2.3 eV from
its solid-state phosphorescent spectrum at 77 K (See Fig. S3).
2.2. Thermal properties of XL1
Thermal gravimetric analysis (TGA) shows that compound XL1 begins to decompose at ca.
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374 C with an initial weight loss of 1% (Fig. 2a). Differential scanning calorimetry (DSC)
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measurements reveal that XL1 melts at ca. 162 C in the first heating run (Fig. 2b). No
o
crystallization is observed upon cooling. When reheated up to 250 C, a distinct glass transition
occurs at ca. 99 oC without further crystallization or remelting.
By contrast, MeO-TPD has a substantially lower glass-transition and decomposition
o
o
temperature 70 and 328 C [11], respectively (See Fig. S4). While it melts at 194 C in the first
heating run, the m.p. is decreased to 170 oC with a reduced heat of fusion in the second heating run.
Apparently, MeO-TPD may be prone to crystallization at elevated temperature with a Tc of 155 oC,
following glass transition.
Consequently, replacing the biphenyl-4,4’-diyl group in MeO-TPD with 2,2’-binaphthyl-
6,6’-diyl increased markedly the thermal and morphological stabilities. Moreover, the low
molecular weight of XL1 (m/z: 708.8) as well as a high solubility makes it versatile for processing.
Fig. 2. (a) Thermogravimetric analysis and (b) DSC diagrams of XL1
2.3. Ultraviolet photoelectron spectroscopy measurements
The UPS spectrum at the low kinetic energy region for a thin layer of XL1 (10 nm) on ITO
was shown in Fig. 3a, which resulted in a work function of 4.41 eV. The UPS spectrum near the
Fermi level region indicated that the HOMO edge for XL1 film on ITO was located at the binding
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energy of 0.64 eV below the Fermi level (Fig. 3b). Therefore the HOMO level of XL1 is deduced as
−5.05 eV, which is comparable to that of −5.07 eV of MeO-TPD [23]. The LUMO level was
roughly calculated as −2.35 eV, based on the HOMO level and the optical bandgap of 2.7 eV.
Fig. 3. UPS spectrum at the low-kinetic energy region (a) and at the valence band near the Fermi
level (b) for XL1 on ITO surface.
2.4. Hole transport measurements
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Fig. 4. The J−V characteristics of the hole–only devices (ITO/HIM:F4-TCNQ(150 nm, 4%)/Al) and
(ITO/HIM:F4-TCNQ(10 nm, 4%)/HIM(150 nm)/HIM:F4-TCNQ(10 nm, 4%)/Al): (a) J
−V, (b) and
(c) lg(J) lg(V). The solid lines are the simulated curves according to the space-charge-limited-
−
current (SCLC) model (See Equation 1). HIM = MeO-TPD and XL1.
The hole transport properties of compound XL1 are studied in the hole-only devices
(ITO/XL1:F4-TCNQ(150 nm)/Al) and (ITO/XL1:F4-TCNQ(10 nm)/XL1(150 nm)/XL1:F4-TCNQ
(10 nm)/Al), respectively. The analogue devices using MeO-TPD are fabricated for comparison.
We show that p-doping the hole-injection material increases the conductivity, which is about
2.52 × 10–4 S m–1 for MeO-TPD:F4-TCNQ and 2.64 × 10–4 S m–1 for XL1:F4-TCNQ, in contrast
with 1.35 × 10–4 and 1.68 × 10–4 S m–1 for the corresponding neat films (Fig. 4a). Further we can
roughly deduce the hole-mobility values (µh). At certain voltages, the current of these devices
exhibits a clear quadratic dependence on the voltage, indicating SCLC characteristics (Fig. 4b &
4c). Therefore, fitting the J–V curves in accordance with Mott–Gurney’s square law (Equation 1)
yielded mobility values of 0.868 × 10–4 and 1.47 × 10–4 cm2 V–1 s–1 for the neat films of MeO-TPD
and XL1, respectively [28]. Upon doping, µh was increased to 3.5 × 10–4 cm2 V–1 s–1 for
MeO-TPD:F4-TCNQ and 4.42 ×10–4 cm2 V–1 s–1 for XL1:F4-TCNQ.
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9
V 2
d3
J = εµ
8
(Equation 1)
where ε is the permittivity, ε = ε0εr (ε0 is the permittivity of the free space, and εr the relative
permittivity and assumed as approximately 3.0), d the thickness of the active layer, and V the
effective applied voltage (corrected by subtracting from the applied voltage (Vappl) the built-in
voltage (Vbi) and the voltage drop (Vs) resulting from the series resistance.
2.5. XL1 as a p-doped hole-injection layer in phosphorescent OLEDs with reference to MeO-TPD
Consequently, XL1 was first characterized as a doped HIM in the red phosphorescent OLED
(PHOLED): ITO/XL1:F4-TCNQ (100 nm, 4%)/NPB(20nm)/Bebq2:Ir(MDQ)2(acac)(40 nm, 5%)/
Phen-NaDPO:Liq(30 nm, 1:1)/Al, where NPB = 4,4'-bis((1-naphthyl)phenylamino)biphenyl as a
hole-transport layer, and Phen-NaDPO:Liq as an n-doped electron-transport layer (Phen-NaDPO =
2-(1,10-phenanthrolin-3-yl)naphth-6-yl)diphenylphosphineoxide, Liq = 8-hydroxyquinolatolithium)
[29-31]. All the layers excluding ITO were deposited by thermal sublimation. The reference OLED
involving MeO-TPD was fabricated for comparison. The chemical structures as well as the
HOMO/LUMO levels of organic materials involved in the devices are shown in Fig. S5.
At high luminances, the luminous efficiencies (LE) of both the OLEDs are very close. For
instance, at a luminance of ca. 1000 cd m−2, LE = 9.9 cd A−1 for the XL1 OLED, vs. 9.5 cd A-1 for
the MeO-TPD OLED (Fig. 5 and Table 1). Nevertheless, the XL1 OLED provides a higher power
efficiency (PE) of 6.2 lm W−1 @ 1000 cd m−2 due to the increased hole conductivity, in contrast
with 5.2 lm W−1 for the MeO-TPD OLED. The two OLEDs shows typical EL spectra peaking at
~618 nm with CIE (0.63, 0.37).
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Fig. 5. (a) J−V−L, (b) LE−L, (c) PE−L (d) EL spectra of the red PHOLEDs. Device structure:
ITO/HIM:F4-TCNQ(100 nm, 4%)/NPB(20 nm)/Bebq2:Ir(MDQ)2(acac)(40 nm, 5%)/Phen-NaDPO:
Liq (30 nm, 1:1)/Al. HIM = MeO-TPD and XL1.
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Table 1. The summary of the OLED data (ITO/HIM:F4-TCNQ(100 nm, 4%)/NPB(20nm)/Bebq2:Ir(MDQ)2(acac) (40
nm, 5%)/Phen-NaTPO:Liq (30 nm, 1:1)/Al. HIM = MeO-TPD and XL1.
@100 cd m−2
@1000 cd m−2
a)
Von
HIM
LE
PE
V
J
LE
PE
EQE
[v]
[cd A−1] [lm W−1]
[mA cm−2]
[cd A−1]
[lm W−1]
[v]
[%]
MeO-TPD
2.6
2.4
10.4
11.3
7.8
9.9
5.8
5
10.4
10.8
9.5
9.9
5.2
6.2
7.3
7.4
XL1
a) Defined at a luminance of ca. 1 cd m−2
We evaluated the operational stabilities of the above OLEDs at an initial luminescence of ca.
1000 cd m−2, driven under a constant current. Before testing, the devices aged at a current density of
20 mA cm−2 for 24 h. The preliminary results appear very promising (Fig. 6). The red PHOLED of
XL1 exhibited a t95 of ca. 230 h at an initial luminance of 1000 cd m−2, vs. only 65 h for the
analogue MeO-TPD OLED. The improved durability of the XL1 OLED may benefit from its
enhanced Tg and hole transport upon p-doping.
Fig. 6. Luminance decay characteristics of the encapsulated OLEDs (ITO/HIM:F4-TCNQ(100 nm,
4%)/NPB(20 nm)/Bebq2:Ir(MDQ)2(acac)(40 nm, 5%)/Phen-NaDPO:Liq (30 nm, 1:1)/Al, HIM =
MeO-TPD and XL1, driven under a constant current. The initial luminance was set as ~1000 cd
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m−2. Prior to testing, the device aged at a current density of 20 mA cm−2 for 24 h.
Finally we have successfully incorporated the hole-injection/transport material XL1 into high-
efficiency green phosphorescent OLEDs (ITO/XL1:F4-TCNQ(100 nm, 4%)/NPB(15 nm)/EBL(5
nm)/Host1:Host2:GE(1:1:15%, 30 nm)/ETM:Liq(1:1, 30 nm)/Al) with very long durability (See
Fig. S6 and S7). EBL, GD, Host1/Host2 and ETM are commercially available and denote
respectively the exciton-blocking/hole-transport layer, green phosphorescent emitter and its host
materials and electron-transport material. The EL spectrum shows a maximum at 520 nm with CIE
(0.302, 0.64). At a luminance of 1000 cd m−2, LE = 57.1 cd A−1 and PE = 64.0 lm W−1. Notably, the
lifetime t90 = 83 h @10000 cd m−2. The corresponding EQE of ~15.4% is well comparable to that
obtained in the analogue p-i-n green PHOLEDs that consisted of the green phosphorescent emitter
tris(2-phenylpyridine)iridium and the undoped hole-blocking layer with a high triplet energy [29].
We suspect that the OLED stability may be further extended with inclusion of the newly-developed
electron-transport material [31]. The work is in progress and shall be reported in due course.
3. Conclusion
In summary, we have described an easily-accessible hole-injection/transport material with the
HOMO/LUMO levels of −5.05/−2.35 eV. Introducing the binaphthyl moiety increases the Tg and
hole transport, with respect to the conventional MeO-TPD. p-Doping with F4-TCNQ enhances the
hole conductivity to 2.64 × 10–4 S m–1 from 1.68 ×10–4 S m–1 of the neat film. Moreover we show
that through optimizing the device architecture, the p-i-n phosphorescent OLEDs utilizing this thick
p-doped hole-injection layer provides high efficiency and very promising stability. The results
reported here should stimulate further research on this class of organic hole injection/transport
materials for optoelectronics.
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Experimental Section
All manipulations involving air-sensitive reagents were performed under an inert of dry
nitrogen. Tetrahydrofuran (THF) was dried over Na/benzophenone and distilled prior to use. All the
other starting materials were purchased commercially and used as received, unless otherwise
specified.
1H NMR measurements were carried out on Bruker 500 MHz DRX spectrometers with
tetramethylsilane (TMS) as the internal reference and 13C NMR measurements on Bruker 101 MHz
DRX spectrometers. Mass spectroscopy of XL1 was obtained on a Waters ACQUITY TQD liquid
chromatograph-mass spectrometer using APCI ionization while the intermediates 1 and 2 on a
Bruker Daltonics BIFLEX III MALDI-TOF Analyzer using MALDI mode. Thermogravimetric
analysis measurements were carried out on Netzsch TG 209 under a nitrogen flow at a heating rate
of 20 oC min−1. Differential scanning calorimetry measurements were performed on a Netzsch DSC
o
204 under nitrogen at a heating and cooling rate of 10 and 20 C min−1 respectively. UV–Vis
absorption spectra were recorded on an HP 8453 UV–Vis spectrophotometer. PL spectra were
recorded on an HORIBA Fluorolog-3 fluorescence spectrophotometer. The ultraviolet photoelectron
spectroscopy (UPS) characterization was conducted on a thermo ESCALAB 250 X-ray
photoelectron spectrometer.
Synthesis of 6-bromo-2-N,N-bis(4-methoxyphenyl)aminonaphthalene (1): Sodium butanolate
(7.0 g, 75.0 mmol) was added to a mixture of 4-iodoanisole (15.0 g, 64.0 mmol),
2-amino-6-bromonaphthalene (3.3 g, 15.0 mmol), 1,10-Phenanthroline monohydrate (1.23 g, 6.83
mmol) and CuI (0.89 g, 4.67 mmol) in anhydrous toluene (120 mL) under N2. The reaction was
heated at 120 °C for 48 h. After being cooled to room temperature, distilled water was added. The
organic layer was extracted with CH2Cl2, separated, dried over anhydrous MgSO4, filtered and
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concentrated under reduced pressure. The crude product was subject to column chromatography
over silica gel using petroleum ether/CH2Cl2 (v/v = 4/1) as the eluent to afford a laurel-green solid.
1
Yield: 5.8 g (88%). H NMR (500 MHz, DMSO) δ 7.99 (d, J = 1.8 Hz, 1H), 7.70 (d, J = 9.0 Hz,
1H), 7.54 (d, J = 8.9 Hz, 1H), 7.43 (dd, J1 = 8.8, J2 = 2.0 Hz, 1H), 7.12 – 7.07 (m, 2H), 7.05 (m,
13
4H), 7.00 – 6.86 (m, 4H), 3.75 (s, 6H). C NMR (101 MHz, DMSO) δ 156.46, 147.27, 140.36,
133.23, 129.81, 129.65, 129.00, 128.40, 127.31, 122.62, 116.39, 115.53, 114.19, 55.71. MS
(MALDI-TOF): m/z 432.97 (100%); calcd. 433.07.
Synthesis of 6-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2-N,N-bis(4-methoxyphenyl)-
aminonaphthalene (2): Pd(PPh3)2Cl2(145 mg, 0.21mmol) was quickly added to a mixture of
compound 1 (3.0 g, 6.9 mmol), bis(pinacolato)diboron (2.28 g, 8.98 mmol) and anhydrous KOAc
(2.03 g, 20.72 mmol) in anhydrous THF (80 ml) under N2. The reaction was heated at 90 °C
overnight. After being cooled to room temperature, the crude product was concentrated and distilled
water was added. The organic layer was extracted with CH2Cl2, separated, dried over-anhydrous
MgSO4, filtered and concentrated under reduced pressure. The residue was subject to column
chromatography over silica gel using petroleum ether/CH2Cl2 as eluent to afford a laurel-green
1
solid. Yield: 2.99 g (90%). H NMR (500 MHz, DMSO) δ 8.12 (s, 1H), 7.79 (d, J = 9.1 Hz, 1H),
7.52 (m, 2H), 7.11 – 7.06 (m, 4H), 7.05 (dd, J1 = 8.9, J2 = 2.4 Hz, 1H), 7.00 (d, J = 2.3 Hz, 1H),
13
6.97 – 6.92 (m, 4H), 3.76 (s, 6H), 1.31 (s, 12H). C NMR (101 MHz, DMSO) δ 156.55, 147.92,
140.29, 136.35, 136.06, 131.11, 129.95, 127.95, 127.51, 125.95, 121.30, 115.52, 113.58, 84.00,
55.71, 25.20. MS (MALDI-TOF): m/z 481.13(100%); calcd. 481.24.
Synthesis of N,N,N',N'-tetra(4-methoxyphenyl)-[2,2'-binaphthalene]-6,6'-diamine (XL1):
Pd(PPh3 )4 (100 mg, 0.087 mmol) was added quickly to a mixture of compound 1 (2.3 g, 5.29
mmol), compound 2 (2.1 g, 4.36 mmol) and Na2CO3 aqueous solution (2 M, 7 mL) in toluene (120
mL) and ethanol (7 mL) under N2. The reaction was heated at 100 °C for 12 h. After being cooled to
room temperature, the volatile was removed under vacuum. The residue was extracted with water
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and CH2Cl2. The organic layer was separated, dried over anhydrous MgSO4, filtered and
concentrated under reduced pressure. The raw product was purified through column
chromatography using petroleum ether/CH2Cl2 as eluent and further washed with ethanol to afford a
primrose solid. Yield: 2.1 g (70 %).1H NMR (500 MHz, DMSO) δ 8.15 (s, 1H), 7.85 – 7.76 (m,
13
2H), 7.68 (d, J = 8.7 Hz, 1H), 7.11 (m, 2H), 7.07 (m, 4H), 6.94 (m, 4H), 3.76 (s, 6H). C NMR
(101 MHz, DMSO) δ 156.26, 146.77, 140.66, 135.33, 133.76, 129.54, 129.25, 127.53, 127.07,
125.81, 125.05, 122.34, 115.46, 114.73, 55.70. MS (APCI) m/z: [M+H+]: calcd. for C48H41N2O4,
709.3; Found, 709.4 (100%). Anal. calcd. For C48H40N2O4: C 81.33, H 5.69, N, 3.95. Found: C
81.02, H 5.685, N 3.72.
OLED fabrication and characterization: The potentiality of XL1 as a doped thick
hole-injection/transport layer (HIM) was studied in OLEDs [ITO/XL1:F4-TCNQ(100 nm,
4%)/NPB (20nm)/Bebq2:Ir(MDQ)2(acac) (40 nm, 5%)/Phen-NaDPO:Liq (30 nm, 1:1)/Al], while
the reference OLED utilizing MeO-TPD:F4-TCNQ was fabricated for comparison. Patterned
indium-tin oxide (ITO, 15 U/square)-coated glass substrates were cleaned with distilled water,
acetone, detergent, distilled water and 2-propanol successively in an ultrasonic bath. All organic and
metal layers were thermally deposited through a mask in vacuum (< 2 × 10−7 Torr) with the
deposition speed and thickness monitored by a thickness/rate meter. In the deposition of the doping
layers, deposition rates of both host and guest were controlled by their correspondingly independent
quartz crystal oscillators. The devices were encapsulated immediately after preparation under a
nitrogen atmosphere using epoxy glue and glass lids. The emission area of the devices is 9 mm2 as
defined by the overlapping area of the anode and cathode. The electroluminescent (EL) spectra,
Commission International de I'Eclairage (CIE) color coordinates of the packaged devices were
obtained by
a
Konica Minolta CS2000 spectra system. The current density
(J)-voltage-(V)-luminance (L) characteristics were recorded simultaneously, using a computer-
controlled source meter (Keithley 2400) and multimeter (Keithley2000) with a calibrated silicon
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photodiode. All the measurements were carried out at room temperature under ambient conditions.
Single carrier hole-only devices were fabricated to measure hole mobility of the new
hole-injection material XL1, in comparison with MeO-TPD. The device structures as follows: ITO/
HIM:F4-TCNQ(150 nm, 4% wt)/Al and ITO/HIM:F4-TCNQ(10nm, 4% wt)/HIM/HIM: F4-TCNQ
(10nm, 4% wt)/Al. HIM = MeO-TPD and XL1.
Acknowledgments
XLH and JHZ contributed equally to this work. Financial support from SCUT, NSFC, MOST
and Department Science and Technology of Guangdong province is gratefully acknowledged under
Grant Nos. 2016YFB0400701 (National Key R&D Program of China), U1301243, 2015CB655000
and 2017A050503002. XHZ greatly acknowledges the support of DongGuan Major Special Project
(No.2017215117010).
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Supporting information
A high Tg small-molecule arylamine derivative as a doped hole-injection/transport material
for stable organic light-emitting diodes
Xiao-Lan Huang, Jian-Hua Zou, Jun-Zhe Liu, Guang Jin, Jian-Bin Li, Sheng-Lin Yao, Jun-Biao
Peng, Yong Cao, Xu-Hui Zhu*
Description of the following figures.
Fig. S1
Fig. S1-1. 1H NMR of compound 1
Fig. S1-2. 13C NMR of compound 1
Fig. S1-3. 1H NMR of compound 2
Fig. S1-4. 13C NMR of compound 2
Fig. S1-5. 1H NMR of compound XL1
Fig. S1-6. 13C NMR of compound XL1
Fig. S1-7. Mass spectrum of compound XL1
Fig. S1-8. Microanalysis data of compound XL1
Fig. S2. Normalized UV-vis and PL spectra of XL1 in toluene and as films on quartz
Fig. S3. Normalized phosphorescence spectrum of XL1 as films at 77 K
Fig. S4. (a) Thermogravimetric analysis and (b) DSC diagrams of MeO-TPD
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Fig. S5. The chemical structures of organic materials involved in the red phosphorescent OLEDs
Fig. S6. (a) J−V−L, (b) LE−L, (c) PE−L, (d) EL spectrum of the green phosphorescent OLED
Fig. S7. Luminance decay characteristics of the encapsulated green phosphorescent OLED
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Fig. S1-1. 1H NMR of compound 1 (DMSO, 500 MHz)
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Fig. S1-2. 13C NMR of compound 1 (DMSO, 101 MHz)
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Fig. S1-3. 1H NMR of compound 2 (DMSO, 500 MHz)
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Fig. S1-4. 13C NMR of compound 2 (DMSO, 101 MHz)
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Fig. S1-5. 1H NMR of compound XL1 (DMSO, 500 MHz)
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Fig. S1-6. 13C NMR of compound XL1 (DMSO, 101 MHz)
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Fig. S1-7. Mass spectroscopy of compound XL1 (APCI).
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Fig. S1-8. Microanalysis data of compound XL1, provided by the Instrumental Analysis &
Research Center, Sun Yat-Sen University, Guangzhou, China.
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