A novel spiro-annulated host based on carbazole with good thermal stability and high triplet energy for efficient blue and green phosphorescent organic light-emitting diodes

Article abstract of DOI:10.1016/j.dyepig.2015.11.017

A novel spiro-annulated host based on carbazole was synthesized and fully characterized. The thermal, photophysical and electrochemical properties of this host material were investigated. The host exhibited good thermal stabilities with a decomposition temperature of 427 °C and also exhibited excellent morphological properties. A high triplet energy (2.90 eV) was obtained for the host due to its spiro-annulated structure. This host was proved to be effective for both blue and green phosphorescent organic light-emitting diodes. Four different blue devices were fabricated with the best performance that a maximum current efficiency of 12.2 cd A^-1 and a maximum power efficiency of 8.8 lm W^-1. The performance of the host was better than that of 4,4′-bis(9-carbazolyl)-biphenyl which is the benchmark host material in green PHOLED devices.

Full text of DOI:10.1016/j.dyepig.2015.11.017

Accepted Manuscript
A novel spiro-annulated host based on carbazole with good thermal stability and high
triplet energy for efficient blue and green phosphorescent organic light-emitting diodes
Guojian Tian, Wenqing Liang, Yi Chen, Ning Xiang, Qingchen Dong, Jinhai Huang,
Jian-Hua Su
PII:
S0143-7208(15)00453-2
10.1016/j.dyepig.2015.11.017
DYPI 5011
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 26 September 2015
Revised Date: 16 November 2015
Accepted Date: 20 November 2015
Please cite this article as: Tian G, Liang W, Chen Y, Xiang N, Dong Q, Huang J, Su J-H, A novel spiro-
annulated host based on carbazole with good thermal stability and high triplet energy for efficient blue
and green phosphorescent organic light-emitting diodes, Dyes and Pigments (2015), doi: 10.1016/
j.dyepig.2015.11.017.
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ACCEPTED MANUSCRIPT
A novel spiro-annulated host material (H2) based on carbazole for efficient blue and green
phosphorescent organic light-emitting diodes was synthesized and characterized. The devices
based on H2 exhibit excellent performance due to its high triplet energy (2.90 eV) and good
thermal stability. Four different blue devices were fabricated with the best performance of a
maximum current efficiency of 12.2 cd A-1 and a maximum power efficiency of 8.8 lm W-1. The
performance of H2 was better than that of 4,4’-bis(9-carbazolyl)-biphenyl (CBP) which is a star
host material in green devices.

ACCEPTED MANUSCRIPT
A novel spiro-annulated host based on carbazole with good thermal stability and
high triplet energy for efficient blue and green phosphorescent organic
light-emitting diodes
a
b
Guojian Tian† , Wenqing Liang† , Yi Chena, Ning Xianga, Qingchen Dongb*, Jinhai
Huanga* Jian-Hua Sua,
a Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China
University of Science & Technology, Shanghai 200237, P. R. China.
b MOE Key Laboratory for Interface Science and Engineering in Advanced Materials
and Research Center of Advanced Materials Science and Technology, Taiyuan
University of Technology, 79 Yingze West Street, Taiyuan 030024, P.R. China.
†These two authors contribute equally to this work.
Abstract: A novel spiro-annulated host based on carbazole was synthesized and fully
characterized. The thermal, photophysical and electrochemical properties of this host
material were investigated. The host exhibited good thermal stabilities with a
o
decomposition temperature of 427 C and also exhibited excellent morphological
properties. A high triplet energy (2.90 eV) was obtained for the host due to its
spiro-annulated structure. This host was proved to be effective for both blue and green
phosphorescent organic light-emitting diodes. Four different blue devices were
fabricated with the best performance that a maximum current efficiency of 12.2 cd A-1
Corresponding author. Tel./fax: +086-21-64252288; e-mail address: bbsjh@ecust.edu.cn (J.-H. Su).
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and a maximum power efficiency of 8.8 lm W-1. The performance of the host was
better than that of 4,4’-bis(9-carbazolyl)-biphenyl which is the benchmark host
material in green PHOLED devices.
Keywords: Phosphorescent organic light-emitting diodes; spiro-annulated carbazole
derivatives; amorphous materials; high triplet energy.
1. Introduction
Phosphorescent organic light-emitting diodes (PHOLEDs) have attracted
tremendous attention for boosting the theoretical internal quantum efficiency (IQE)
from 25% to 100% since the pioneering work by Forrest and Thompson in 1998 [1]. A
series of blue/green/red PHOLEDs with high efficiency have been reported [2-5].
Host materials play a crucial role in the PHOLEDs, and an ideal host material should
have the good thermal stability, a suitable HOMO-LUMO level, a high triplet energy
(ET) [6,7]. Therefore, developing novel promising host materials is important for the
development of useable efficient PHOLEDs.
Nowadays, considerable attention has been directed to the design of novel hosts
for effective PHOLEDs. In view of the above-mentioned key properties of host
materials, spiro-annulated structures have been proven to be beneficial for improving
the efficiency of PHOLEDs [8-10], because of the high thermal stability of the
sprio-annulated structures which could be attributed to their bulky and orthogonal
configuration [11,12]. Additionally, the perpendicular arrangements of the
spiro-conformation give rise to a highly steric rigid structure, the conjugation of the
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two units in each side of the spiro-carbon is disconnected by the central
sp3-hybridized spiro-carbon, thus, preserving a high triplet energy (ET) [13,14].
Therefore, these features make spiro-annulated structures highly attractive as potential
host materials for fabricating effective PHOLEDs. Various spiro-annulated structures
have been investigated as host materials for PHOLEDs [8-15].
It is well known that carbazole derivatives with excellent photophysical properties
have been widely used as host materials were in OLEDs [16-18]. In this work, by
combining the spiro-annulated structures and carbazole derivatives, we designed a
novel small molecule (H2) based on spiro-annulated carbazole structure. It can be
anticipated that H2 could keep the unique properties of carbazole with high triplet
energy and good hole transport ability by introducing a spiro-annulated structure. The
thermal, photophysical and electrochemical properties of H2 were fully investigated.
Atomic force microscopy (AFM) was also applied to explore the intrinsic morphology
of the thin film based on H2. Moreover, blue and green PHOLEDs with H2 as host
materials were fabricated, a maximum current efficiency of 12.2 cd A-1 and a
maximum power efficiency of 8.8 lm W-1 were obtained for blue PHOLEDs, the
H2-based device exhibited a greatly improved performance as compared to a
conventional 4,4’-bis(9-carbazolyl)-biphenyl (CBP)-based device for green
PHOLEDs.
2. Experimental
2.1 General Information
All reagents that we have used in the route were purchased from Shanghai Taoe
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chemical technology Co., Ltd. and received without further purification. Carbazole
and 1,2-dichlorobenzene were purchased from Adamas-beta.
The 1H and 13C NMR spectra were obtained using a Bruker AM 400 spectrometer,
the mass spectra were recorded on a Waters LCT Premier XE spectrometer. The cyclic
voltammograms were obtained using a Versastat II electrochemical workstation with
conventional three electrodes containing an SCE reference electrode (the
+
ferrocene/ferrocenium (Fc/FC ) redox couple as external standard), a glassy-carbon
working electrodes and a platinum-wire counter electrode. The UV/Vis spectra and PL
spectra were recorded on a Nicolet CARY 100 spectrophotometer and a Varian Cary
fluorescence spectrophotometer, respectively. The differential scanning calorimetry
(DSC) analysis and the thermogravimetric analysis (TGA) were performed under a
nitrogen atmosphere on a NETZSCH STA 409 PC/PG instrument and a TGA
instrument, respectively.
2.2. Synthesis
2.2.1. 9-(2-bromophenyl)-9H-carbazole (1)
In a one-neck flask, carbazole (3.3 g, 19.9 mmol), o-dibromobenzene (4.5 g, 19.9
mmol), CuI (0.8 g, 4.0 mmol), 1,10-phenanthroline monohydrate (0.8 g, 4.0 mmol)
and KOH (2.3 g, 40 mmol)were dissolved in o-x1ylene (50 mL). The mixture was
heated to reflux for 8 h under nitrogen. After the reaction had all reacted, the mixture
was allowed to cool to room temperature and then CH2Cl2 (50 mL) was poured into
the mixture. The organic layer was dried over anhydrous MgSO4 and concentrated
this by a rotary evaporator. The crude materials were purified by silica gel column
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chromatography (petroleum ether/CH2Cl2 = 4 : 1 v/v) to obtain a white solid 1.5 g,
39%. 1H NMR (400 MHz, DMSO-d6, TMS) δ: 8.25 (d, J = 7.6 Hz, 2 H), 8.00 (dd, J =
8.0, 1.2 Hz, 1 H), 7.68 (m, 2 H), 7.62 – 7.56 (m, 1 H), 7.45 – 7.38 (m, 2 H), 7.32 –
7.25 (m, 2 H), 7.00 (d, J = 8.0 H, 2 H). 13C NMR (126 MHz, CDCl3) δ: 140.84,
140.49, 134.25, 131.16, 130.64, 130.17, 129.78, 128.83, 125.94, 123.24, 120.36,
119.99, 110.14, 110.03. HRMS (m/z): [M+H]- calcd for C18H12BrN, 322.0231; found,
322.0250.
2.2.2 8H-indolo[3,2,1-de]acridin-8-one (3)
In a one-neck flask, carbazole (3.3 g, 19.9 mmol), methyl 2-iodobenzoate (5.7 g,
21.8 mmol), Cu (0.5 g, 7.1 mmol), CuI (0.34 g, 1.8 mmol) and K2CO3 (4.2 g, 30.4
mmol) were dissolved in 30 mL 1,2-dichlorobenzene, then heated the mixture to
reflux for 12 h under nitrogen. After the reaction was completed fully, the mixture was
allowed to cool to room temperature and then CH2Cl2 (50 mL) was poured into the
mixture. Filtered the mixture and washed the cake with CH2Cl2, concentrated the
filtrate by a rotary evaporator, then recrystallization the product from the concentrated
1
solution by ethanol to obtain a pale yellow solid 5.4 g, 89%. H NMR (400 MHz,
CDCl3, TMS) δ: 8.12 (t, J = 8.0 Hz, 3H), 7.75 (t, J = 7.6 Hz, 1H), 7.59 (t, J = 7.6 Hz,
2H), 7.37 (t, J = 7.6 Hz, 2H), 7.26 (t, J = 6.0 Hz, 2H), 7.12 (d, J = 8.2 Hz, 2H), 3.18 (s,
3H). Moreover, in a one-neck flask, put the previous product methyl
2-(9H-carbazol-9-yl)benzoate (2.0 g, 6.6 mmol) into polyphosphoric acid (10 mL),
o
o
heated the mixture to 180 C for 4 h. Cooled the mixture to about 80 C after the
reaction had full completed, poured H2O (15 mL) into the mixture and extracted with
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CH2Cl2 (20 mL × 3). The organic layer was dried over anhydrous MgSO4 and
concentrated this using a rotary evaporator. The crude materials were purified by
silica gel column chromatography (petroleum ether/CH2Cl2 = 3 : 1 v/v) to obtain a
pale yellow solid 1.2 g, 60%. 1H NMR (400 MHz, CDCl3, TMS) δ: 8.68 (dd, J = 8.0,
1.6 Hz, 1 H), 8.45 (dd, J = 7.6, 1.2 Hz, 2 H), 8.36 (dd, J = 7.6, 1.2 Hz, 1 H), 8.30 (d, J
= 8.4 Hz, 1 H), 8.20 – 8.17 (m, 1 H), 7.90 – 7.84 (m, 1 H), 7.67 – 7.60 (m, 2 H), 7.50
– 7.44 (m, 2 H). 13C NMR (126 MHz, CDCl3) δ: 134.10, 129.18, 127.92, 125.24,
124.52, 123.46, 123.21, 123.12, 121.64, 115.66, 114.11. HRMS (m/z): [M+H]- calcd
for C19H11NO, 270.0919; found, 270.0915.
2.2.3 8,8'-spirobi[indolo[3,2,1-de]acridine] (H2)
In a dry three-neck flask, 1.6 M n-BuLi in hexane (3.9 mL, 6.2 mmol,
15%solution) was added dropwise to a solution of 9-(2-bromophenyl)-9H-carbazole
(2.0 g, 6.2 mmol) in THF at -78 oC under nitrogen. After stirring the mixture for 1 h at
this temperature, 8H-indolo[3,2,1-de]acridin-8-one (1.7 g, 6.2 mmol) was added
dropwise into the mixture with stirring for 2 h and then stirred the mixture for 12 h at
the room temperature, which was poured into water and extracted with CH2Cl2 (20
mL × 3). The organic layer was dried over anhydrous MgSO4 and concentrated this to
obtain the crude materials by a rotary evaporator. Moreover, put the crude compound
into acetic acid (20 mL) with a little HCl and heated the mixture to reflux for 4 h.
Then, poured water (30 mL) into the mixture and extracted with CH2Cl2 (20 mL × 3).
Dried the organic layer over anhydrous MgSO4 and concentrated this using a rotary
evaporator. The crude materials were purified by silica gel column chromatography
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1
(petroleum ether/CH2Cl2 = 6 : 1 v/v) to obtain a white solid 1.2 g, 60%. H NMR
(400MHz, CDCl3, TMS) δ: 8.23 (d, J = 8.4 Hz, 2 H), 8.18 – 8.11 (m, 4 H), 7.79 (d, J
= 7.6 Hz, 2 H), 7.57 (t, J = 7.6 Hz, 2 H), 7.34 (t, J = 7.6 Hz, 2 H), 7.26 (t, J = 7.2 Hz,
2 H), 7.04 (t, J = 8.0 Hz, 4 H), 6.83 (t, J = 8.8 Hz, 4 H).13C NMR (126 MHz, CDCl3)
δ: 138.42, 135.11, 134.98, 134.00, 133.64, 130.00, 127.64, 126.75, 126.57, 126.26,
123.62, 122.99, 122.04, 121.26, 120.99, 117.78, 113.84, 113.45, 47.80. HRMS (m/z):
[M+H]- calcd for C37H22N2, 495.1861; found, 495.1886.
3. Results and discussion
3.1. Synthesis
The synthetic routes of target materials were illustrated in Scheme 1. It was easy
to obtain the key intermediates 9-(2-bromophenyl)-9H-carbazole and
8H-indolo[3,2,1-de]acridin-8-one. The final product H2 resulted from the addition of
the anion derived from the action of n-butyllithium on 1 to 3. All of the isolated
intermediates and the target materials in the synthesis were characterised by 1H NMR,
13C NMR and HRMS.
3.2. Thermal properties
The thermal properties of H2 were investigated by the differential scanning
calorimetry (DSC) analysis and the thermogravimetric analysis (TGA) in Fig. S1 (ESI
o
†). The endothermic glass transition (Tg) of H2 was determined to be 150 C in the
second scan by the DSC, whereas the melting point of H2 was determined to be 321
oC in the first scan by the DSC. From the TGA of H2, it was obvious that H2
exhibited high thermal stability with a decomposition temperature (Td, corresponding
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to 5% weight loss) of 427 oC. In view of the spirocycle induced steric hindrance of the
carbazole unit of H2, these thermal data were higher than those for other small
molecules based on the carbazole unit, which implied that H2 was favorable for high
efficient OLED device due to its good thermal stability.
3.3. Morphology property
Atomic force microscopy (AFM) was employed to investigate the possible effect
of morphology on the device performance. The AFM images of the thin films of CBP
and H2 were exhibited in Fig. 2. As shown in Fig. 2, the root-mean-square (RRMS
)
surface roughness of CBP and H2 thin films were determined to be 13.61 and 3.72 nm,
respectively. Moreover, it can be seen clearly from the AFM images that, both the
crystallinity and homogeneity of H2 are much better than CBP, which would facilitate
the carrier mobility and increase the recombination of electrons and holes, and thus
guarantee H2 to be an effective host material [19].
3.4. Photophysical properties
The UV-vis absorption, photoluminescence spectra (at room temperature in THF)
and phosphorescence spectrum (at 77 K in 2-methyl THF) of H2 are shown in Fig. 3.
There are two absorption peaks for H2, the stronger absorption peak at around 290 nm
could be assigned to carbazole π→π* transitions and the weaker absorption peak at
346 nm was ascribed to the n→π* transitions derived from the extended
phenylcarbazole conjugation. The optical energy bandgap (Eg) of H2 was determined
to be 3.22 eV from the threshold of the absorption spectra in THF. From the PL
spectrum of H2, the emission peak was located at 366 nm, which was similar to that
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of phenylcarbazole derivatives [20-23]. According to the phosphorescence spectrum
of H2 at 77 K in 2-methyl THF, the triplet energy level (ET) was determined to be
2.90 eV, which was higher than that of CBP [16]. The ET value of H2 was
considerable high due to its limited variation, which qualify it to be a potential host
material for blue and green PHOLEDs, because the high ET value could effectively
prevent the energy transfer from the dopant to host material.
3.5. Electrochemical properties
The cyclic voltammetry (CV) was performed to investigate the electrochemical
property of H2. Fig. 4 shows the irreversible oxidation process of H2, which is
accorded with the feature of carbazole derivatives. The HOMO and LUMO energy
level of H2 were obtained by calculation with the formula of EHOMO = - (4.7+Eonset-ox
)
eV and ELUMO = EHOMO + Eg, respectively. The onset oxidation potential of H2 was
calculated to be 0.88 eV from Fig. 4, so the corresponding HOMO and LUMO values
were determined to be -5.58 eV and -2.36 eV. These data were similar to the values of
CBP [12], the relatively high-lying HOMO level of H2 could facilitate the hole
injection to the emitting layer and the favorable LUMO level may facilitate the
electron injection, so the carrier recombination in the device could be more balanced
to some degree [24].
3.6. Eletrophosphorescent PHOLEDs
In view of the above favorable properties of H2, blue and green phosphorescent
devices based on H2 were fabricated. Four contrastive blue phosphorescent devices
based on H2 were investigated with the different hole injection layers (HIL) and the
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hole transport layers (HTL). The device structures were as follow: 1)
ITO/Pedot:PSS(50nm)/NPB(40nm)/H2:FIrpic(8wt%)(70nm)/TPBI(40nm)/LiF(1nm)/
Al;
ITO/Pedot:PSS(50nm)/DY(40nm)/H2:FIrpic(8wt%)(70nm)/TPBI(40nm)/LiF(1nm)/A
l; 3)
2)
ITO/MoO3(3nm)/NPB(40nm)/H2:FIrpic(8wt%)(70nm)/TPBI(40nm)/LiF(1nm)/Al; 4)
ITO/MoO3(3nm)/DY(40nm)/H2:FIrpic(8wt%)(70nm)/TPBI(40nm)/LiF(1nm)/Al. H2
was doped with 8 wt% FIrpic to form an emitting layer (EML). Pedot:PSS and MoO3
were used as the hole injection layers (HIL). NPB and DY were served as the hole
transport layers (HTL). TPBI and LiF were used as the electron transport layers (ETL)
and the electron injection layers (EIL), respectively. On the other hand, two green
phosphorescent devices were studied with CBP as a contrastive host material, the
corresponding
ITO/Pedot:PSS(50nm)/DY(40nm)/H2:Ir(ppy)3(8wt%)(50nm)/TPBI(40nm)/LiF(1nm)/
Al; 6)
structures
were
5)
ITO/Pedot:PSS(50nm)/DY(40nm)/CBP:Ir(ppy)3(8wt%)(50nm)/TPBI(40nm)/LiF(1nm
)/Al. H2 and CBP were doped with 8 wt% Ir(ppy)3 to form an emitting layer (EML),
the other materials served their corresponding roles in the green device as mentioned
above.
It was important for the hole injection and transport material in a phosphorescent
device due to its critical role in charge-carrier balance, so four different hole injection
and transport materials were introduced to study the performance of H2 as a blue
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phosphorescent host material. The pertinent performances and data of blue
phosphorescent devices were shown in Fig. 6 and Table 1, respectively. As shown in
Fig. 6, the maximum luminance for device 1-4 were 19283, 19058, 20856 and 17612
cd m-2, the corresponding maximum current density were 756, 818, 940 and 836 mA
cm-2. On the one hand, the maximum current efficiency for devices 1-4 were 10.8,
12.2, 10.5 and 8.9 cd A-1, the maximum power efficiency were 6.8, 8.8, 7.3 and 6.5 lm
W-1, respectively. On the other hand, allowing for the overall performances for device
1-4, device 2 was the best device with the maximum current efficiency (12.2 cd A-1)
and power efficiency (8.8 lm W-1), these values for blue small-molecule-PHOLEDs
were quite larger than that of some small molecules [25], and were attributed to the
excellent thermal stability, good film-forming ability and favorable triplet energy (ET)
of H2. The color coordinate of the blue PHOLEDs device for 1-4 were determined to
be (0.16, 0.28), (0.17, 0.27), (0.16, 0.26) and (0.17, 0.28), respectively, the relevant
electroluminescence spectra of 1-4 were shown in Fig. 6d, which were also analogous
due to the same emitting layers of these devices. In terms of the relationship between
eletrophosphorescent efficiency and structure for device 1-4, the group of
Pedot:PSS(50nm)/DY(40nm) as hole transport material was better than others, the
reason may be the charge-carrier was more balanced in this group. Due to the
limitation of device-optimization, just four different hole transport materials were
used in fabricating blue PHOLEDs, provided conducting optimization fully,
PHOLEDs with further optimization studies better performance could be confidently
obtained.
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To further study the properties of H2, green PHOLEDs based on H2 as host
material was fabricated and in comparison with conventional star host material CBP.
Fig. 7 exhibits the relevant performance of these two green PHOLEDs. The maximum
luminance of device 5 (3679 cd m-2) was bigger than that of device 6 (2542 cd m-2),
while the current density was 147 and 156 mA cm-2, respectively. It was obvious that
the performance of device 5 was better than that of device 6, which was further
confirmed from the current efficiency (device5 vs device 6 = 11.2 cd A-1 vs 6.0 cd A-1)
and power efficiency (device5 vs device 6 = 5.0 lm W-1 vs 2.0 lm W-1). These
properties could be derived from the thermal and morphology property of H2 and
CBP, as mentioned above, H2 was better than CBP in terms of thermal stability,
film-forming property and crystallinity. The triplet energy (ET) of H2 was 2.90 eV,
which was high enough for effective triplet exciton blocking [26,27]. The color
coordinate of the green PHOLED devices 5 and 6 were (0.27, 0.61) and (0.26, 0.60),
respectively, the corresponding electroluminescence spectra were shown in Fig. 7d.
By comparing with the performance of CBP, H2 could be a promising host material
for its excellent properties.
4. Conclusion
A novel small molecule (H2) based on spiro-annulated carbazole was synthesized
and characterized. It exhibits excellent properties such as good thermal stability (Td =
o
427 C), film-forming ability, suitable HOMO-LUMO level and high triplet energy
(ET = 2.90 eV), which eventually allow H2 to be competent for blue and green
phosphorescent devices. Four different hole transport materials were introduced to
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fabricate blue devices, the best-performing device with the group of
Pedot:PSS(50nm)/DY(40nm) as hole transport material exhibited a maximum current
efficiency of 12.2 cd A-1 and a maximum power efficiency of 8.8 lm W-1, these values
were high as compared to those values of other small molecule based blue emitting
devices. Moreover, the performance of the H2-based green device was better than that
of CBP-based green device. Given the favorable properties of H2 achieved, other
potential application such as use in white PHOLEDs is under further study.
Acknowledgments
Q. Dong thanks the financial support from the National Natural Science
Foundation of China (Grant No.: 61307030), Program for the Outstanding Innovative
Teams of Higher Learning Institutions of Shanxi (OIT), Fund Program for the
Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province,
the Natural Science Foundation for Young Scientists of Shanxi Province, China
(Grant No.: 2014021019-2), the Outstanding Young Scholars Cultivating Program,
Research Project Supported by Shanxi Scholarship Council of China (Grant No.:
2014-02) and the Qualified Personal Foundation of Taiyuan University of Technology
(Grant No.: 2013Y003, tyut-rc201275a).
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Table 1 Electroluminescence characteristics of the devices.
Device
Max
Current
efficiency(cd
A-1)a
Power
CIE(x,y)b
brightness(cd
m-2)
efficiency(lm
W-1)a
6.8
8.8
7.3
6.5
5.0
2.0
Blue-1
Blue-2
Blue-3
Blue-4
Green-5
Green-6
19283
19058
20856
17612
3679
10.8
(0.16,0.28)
(0.17,0.27)
(0.16,0.26)
(0.17,0.28)
(0.27,0.61)
(0.26,0.60)
12.2
10.5
8.9
11.2
2542
6.0
aEstimated at the luminance of 100 cdm-2. bMeasured from the EL spectra by inverting
into chromaticity coordinates on the CIE 1931 diagram.
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Fig. S1(ESI†). The differential scanning calorimetry (DSC) analysis and the
thermogravimetric analysis (TGA) spectra of H2.
Fig. 2. AFM images of the thermally evaporated thin films of CBP (a) and H2 (b).
Fig. 3. Absorption, photoluminescence spectra (at room temperature in THF) and
phosphorescence spectrum (at 77 K in 2-methyl THF) of H2.
Fig. 4. Cyclic voltammogram of H2 in dichloromethane with tetra(n-butyl)ammonium
hexafluorophosphate(0.1 M) as a supporting electrolyte for the oxidation scan.
Fig. 5. Energy-level diagram of blue and green PHOLEDs.
Fig. 6. a) Current density-voltage-luminance data of blue PHOLEDs; b) Current
efficiency-current density curves of blue PHOLEDs; c) Power efficiency-luminance
curves of blue PHOLEDs; d) Electroluminescence spectra of blue PHOLEDs.
Fig. 7. a) Current density-voltage-luminance data of green PHOLEDs; b) Current
efficiency-current density curves of green PHOLEDs; c) Power efficiency-luminance
curves of green PHOLEDs; d) Electroluminescence spectra of green PHOLEDs.
Scheme 1. The Synthetic routes of compound H2.
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Fig. 2. AFM images of the thermally evaporated thin films of CBP (a) and
H2 (b).
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1.0
0.8
0.6
0.4
0.2
0.0
UV-Vis
Solution PL
Low T PL
250 300 350 400 450 500 550 600
Wavelength/nm
Fig. 3. Absorption, photoluminescence spectra (at room temperature in THF) and
phosphorescence spectrum (at 77 K in 2-methyl THF) of H2.
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H2
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5
Potential/vs.V
Fig. 4. Cyclic voltammogram of H2 in dichloromethane with tetra(n-butyl)ammonium
hexafluorophosphate(0.1 M) as a supporting electrolyte for the oxidation scan.
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2.0
2.0
2.4
2.4
2.4
2.7
2.9
2.9
F
LiF/Al
Pedot:PSS MoO3
O
O
N
DY
5.4
NPB
FIrpic
8 wt%
H2
F
Ir
2
Blue
TPBI
4.7
4.7
N
ITO
ITO
5.1
5.1
5.5
2.4
5.6
5.8
2.7
FIrpic
6.7
2.7
2.0
2.4
H2
2.9
N
N
LiF/Al
Pedot:PSS
Ir(ppy)3
8 wt%
DY
5.4
NPB
Green
4.7
TPBI
ITO
5.1
5.5
5.6
N
N
N
Ir
6.7
N
N
N
N
N
N
TPBI
Ir(ppy)3
Fig. 5. Energy-level diagram of blue and green PHOLEDs.
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a)
1000
1
2
3
4
10000
1000
100
10
800
600
400
200
0
1
0
2
4
6
8
10
Voltage/ V
14 b)
1
2
3
4
12
10
8
6
4
2
0
0
50
100
150
200
Current Density/ mA cm-2
10
c)
1
2
3
4
8
6
4
2
0
0
5000
10000
15000
20000
Luminance/ cd A-1
1.0
0.8
0.6
0.4
0.2
0.0
d)
1
2
3
4
400
500
600
700
800
Wavelength/nm
Fig.6. a) Current density-voltage-luminance data of blue PHOLEDs; b) Current
efficiency-current density curves of blue PHOLEDs; c) Power efficiency-luminance
curves of blue PHOLEDs; d) Electroluminescence spectra of blue PHOLEDs.
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a)
5
1000
150
100
50
6
100
10
1
0
0.1
-2
0
2
4
6
8
10 12 14 16 18 20
Voltage/ V
12
10
8
b)
5
6
6
4
2
0
0
50
Current Density/ mA cm-2
100
c)
5
4
3
2
1
0
5
6
0
500
1000
1500
2000
Luminance/ cd m-2
1.0
0.8
0.6
0.4
0.2
0.0
5
6
d)
400
450
500
550
600
650
700
750
Wavelength/nm
Fig. 7. a) Current density-voltage-luminance data of green PHOLEDs; b) Current
efficiency-current density curves of green PHOLEDs; c) Power efficiency-luminance
curves of green PHOLEDs; d) Electroluminescence spectra of green PHOLEDs.
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Br
Br
CuI, KOH
H
Br
N
N
N
N
1
I
CuI
KOH
i) BuLi, THF
ii)
COOCH3
AcOH, HCl
O
COOCH3
PPA
N
N
H2
3
2
Scheme 1. The Synthetic routes of compound H2.
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Highlights
ꢀ
ꢀ
ꢀ
A novel spiro-annulated host based on carbazole has been synthesized and characterized.
The dye exhibits good thermal stability and high triplet energy.
Efficient blue and green phosphorescent organic light-emitting diodes based on the dye
have been fabricated.