Tunable crystal packing for enhanced electroluminescent properties based on novel thiazole derivatives with different connecting positions of carbazole

Article abstract of DOI:10.1016/j.dyepig.2016.03.031

Two novel deep-blue fluorescent compounds, namely, 2-(4-(9-phenyl-9H- carbazol-3-yl)phenyl)benzo [d]thiazole (BCzBTZ) and 2-(4'-(9H-carbazol-9-yl)-[1.1'- biphenyl]-4-yl)benzo [d]thiazole (CzBBTZ) were designed, synthesized and characterized. It is particu

Full text of DOI:10.1016/j.dyepig.2016.03.031

Accepted Manuscript
Tunable crystal packing for enhanced electroluminescent properties based on novel
thiazole derivatives with different connecting positions of carbazole
Yongqi Bai, Bingwu Wei, Xinhua Ouyang, Zhiyang Liu, Weigang Jiang, Wang Li, Lei
Zhang, Ling Hong, Gufeng He, Yali Chen, Ziyi Ge
PII:
S0143-7208(16)30091-2
10.1016/j.dyepig.2016.03.031
DYPI 5156
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 15 January 2016
Revised Date: 16 March 2016
Accepted Date: 17 March 2016
Please cite this article as: Bai Y, Wei B, Ouyang X, Liu Z, Jiang W, Li W, Zhang L, Hong L, He G, Chen
Y, Ge Z, Tunable crystal packing for enhanced electroluminescent properties based on novel thiazole
derivatives with different connecting positions of carbazole, Dyes and Pigments (2016), doi: 10.1016/
j.dyepig.2016.03.031.
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ACCEPTED MANUSCRIPT
Tunable crystal packing for enhanced electroluminescent properties based on
novel thiazole derivatives with different connecting positions of carbazole
1
,2
3
2
2
2
Yongqi Bai, Bingwu Wei, Xinhua Ouyang, Zhiyang Liu, Weigang Jiang, Wang
2
2
2
3
1
2
Li, Lei Zhang, Ling Hong, Gufeng He* ,Yali Chen, * Ziyi Ge *
1
Department of Chemistry, Innovative Drug Research Center, Shanghai University,
Shanghai 200444, China
2
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of
Sciences, Ningbo 315201, P. R. China
3
National Engineering Lab for TFT-LCD Materials and Technologies, and
Department of Electronic Engineering, Shanghai Jiao Tong University, Shanghai
2
00240, People’s Republic of China
Corresponding Authors: geziyi@nimte.ac.cn; ylchen@staff.shu.edu.cn;
gufenghe@sjtu.edu.cn
Abstract Two novel deep-blue fluorescent compounds, namely, 2-(4-(9-phenyl-9H-
carbazol-3-yl)phenyl)benzo[d]thiazole (BCzBTZ) and 2-(4'-(9H-carbazol-9-yl)-[1,1'-
biphenyl]-4-yl)benzo[d]thiazole (CzBBTZ)
were designed, synthesized and
characterized. It is particularly intriguing to compare their crystal packing of BCzBTZ
and CzBBTZ, both of them construct with the same heterocyclic units and linker.
Their crystal packing can be effectively regulated by changing the connecting position
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of carbazole. Their thermal stabilities, optical and electrochemical properties were
studied systematically and exhibited ideal performance for electroluminescent
emitters. The device based on BCzBTZ as emitter shows deep-blue emission with the
CIE(x, y) of (0.15, 0.08), which is close to the blue standard (0.14, 0.08) of National
Television System Committee (NTSC). The maximal external quantum efficiency is
1
.4 % and current efficiency is 1.39 cd/A with low efficiency roll-off.
Keywords Thiazole derivatives; Electroluminescence; Tunable crystal packing
Introduction
Heterocyclic compounds have been attracting extensive research interest for organic
light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic field-effect
transistors (OFETs) due to their semiconducting features [1-2]. For OLEDs, the
balance of carries play an important role to achieve high device performance [3]. To
solve this issue, some effective strategies have been demonstrated including the
fabrication of multilayer devices and development of novel bipolar molecules [4-6].
Regarding the promising potential of bipolar structures for low-cost OLEDs, it is
highly desirable to design and synthesize novel multifunctional materials with
different heterocyclic units.
In the past decades, numerous multifunctional materials have been developed and
some of them show excellent performance, including triarylamine-imidazole,
triarylboron-bis(diphenylamino)carbazole,
phenoxazine-quinoline,
carbazole-1,3,4-diaryloxadiazole, triarylamine-1,3,4-diaryloxadiazole, and so on,
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especially for the derivatives of triarylamine-imidazole with hybridized local and
charge-transfer characteristics [7-14]. By scanning these heterocyclic structures,
thiazole, a well-known molecule in the azole family by replacing a carbon with
nitrogen atom of thiophene, has been studied and exhibit modest electron-deficient
properties, indicating a good candidate for constructing functional emitters. However,
to the best of our knowledge, the research on thiazole and its derivatives for
electroluminescence is still limited [15]. On the other hand, molecular packing in film
or solid state greatly affects their charge transport properties and fluorescent quantum
yield. Generally, the transport of carries is mainly depended on their electronic
couplings and the reorganization energies [16]. The electronic coupling is strongly
based on their molecular packing modes [17]. Therefore, tunable molecular packing
or crystal packing are desired to obtain effective electroluminescent materials.
Herein, a couple of benzothiazole derivatives, 2-(4-(9-phenyl-9H-carbazol-3-yl)-
phenyl)benzo[d]thiazole (BCzBTZ) and 2-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-
yl)benzo[d]thiazole (CzBBTZ), was designed and synthesized with a strong electron-
donating carbzole ( Cz ) and electron-accepting thiazole units as shown in Scheme 1.
Both of them construct with the same heterocyclic units and linker and only the
connecting position of Cz is changed. It is particularly intriguing to compare their
crystal packing of BCzBTZ and CzBBTZ. Their crystal packing modes are effectively
regulated. The thermal stabilities, optical and electrochemical properties were studied
systematically and exhibited ideal performance for electroluminescence emitters. The
electroluminescent device based on BCzBTZ as emitter shows deep-blue emission
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with the CIE(x, y) of (0.15, 0.08), which is close to the blue standard (0.14, 0.08) of
NTSC. The maximal external quantum efficiency is 1.4 % and current efficiency is
1
.39 cd/A. Furthermore, at the high luminescence, the device still indicated good
performance with relatively low efficiency roll-off.
2
. Experimental
2
.1 Chemicals and instruments
The reagents and starting materials, including 2-(4-bromophenyl)benzo[d]thiazole,
bis(pinacolato)diboron, 3-bromo-9-phenyl-9H-carbazole and
-(4-bromophenyl)-9H-carbazole, were purchased from local suppliers or TCI and
9
1
used without further purification. H NMR spectra was measured on a Bruker
DRX-400 spectrometer. Thermogravimetric analysis (TGA) were performed on a TA
Q500 instrument. Their optical properties (UV-Vis and fluorescent emission) were
done on a Shimadzu UV-2550 and Shimadzu RF-5301PC spectrophotometers. Cyclic
voltammetry (CV) measurements were performed on a CHI 660D electrochemical
workstation using a Pt wire as the counter electrode, glass-carbon as the working
electrode, and a Hg/HgCl electrode as the reference electrode in a dichloromethane
solution containing 0.1 M of tetrabutylammonium hexafluorophosphate as the
supporting electrolyte. Single-crystal XRD data was collected on Bruker SMART
1
000 CCD diffractometer collection. The empirical absorption correction was applied
by using the SADABS program [18]. Single crystals of them were solved using direct
2
method, and refined by full-matrix least-squares on F [19].
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2
2
.2 Synthesis
.2.1 Synthesis of 2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)benzo[d]-
thiazole
A
mixture of 2-(4-bromophenyl)benzo[d]thiazole (5.80 g, 20 mmol),
bis(pinacolato)diboron (7.62 g, 30 mmol), PdCl (dppf) (150 mg, 0.2 mmol) and
2
KOAc (8.00 g, 81 mmol) suspended in 70 mL of 1,4-dioxane under the protection of
o
argon was stirred at 87 C for 4 h. After cooling, the mixture was forced through a
short pad of silica with dichloromethane (DCM). The solvent was removed under
reduced pressure and the crude product was absorbed onto silica. Chromatography on
1
silica gel with gradient elution and a white solid was got (6.40 g, yield: 95%). H
NMR (400 MHz, CDCl ) δ [ppm] 8.05-8.10 (m, 3H), 7.87-7.95 (m, 3H), 7.48 (t, 1H,
3
J=7.54Hz), 7.37 (t, 1H, J=7.40Hz), 1.24 (s, 12H).
2
.2.2 Synthesis of 2-(4-(9-phenyl-9H-carbazol-3-yl)phenyl)benzo[d]thiazole (BCzBTZ)
2
-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)benzo[d]thiazole (1.69 g, 5
mmol), 3-bromo-9-phenyl-9H-carbazole (1.61 g, 5 mmol) and PdCl (PPh ) (100 mg,
2
3 2
0
2
.14 mmol) were added to a 250 ml flask with 40 mL toluene, 20 mL 2M K CO and
2 3
o
0 mL ethanol. The mixture was heated to 100 C and stirred for 24 h. After cooling,
the mixture was extracted with DCM, organic layer was collected and dried with
MgSO . The solvent was removed and purified by chromatography on silica gel with
4
1
gradient elution. 1.63g white solid was obtained with yield of 72%. H NMR (400
MHz, CDCl ) δ[ppm] 8.43 (s, 1H), 8.20-8.24 (m, 3H), 8.11 (d, 1H, J=8.24 Hz), 7.93
3
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(d, 1H, J=7.95 Hz), 7.86 (d, 2H, J=8.30 Hz), 7.72 (d, 1H, J=8.67 Hz), 7.57-7.66 (m,
1
3
4
H), 7.44-7.54 (m, 3H), 7.37-7.45 (m, 3H), 7.30-7.35 (m, 1H). C NMR (400 MHz,
CDCl ) δ 168.1, 154.0, 144.7, 141.4, 140.8, 137.5, 134.9, 132.1, 131.5, 130.0, 128.1,
3
1
1
7
27.7, 127.6, 127.1, 126.4, 126.3, 125.3, 125.2, 124.0, 123.4, 123.1, 121.6, 120.4,
20.3, 118.9, 110.2, 110.0. Anal. Calcd for C H N S: C, 82.27; H, 4.45; N, 6.19; S,
3
1
20
2
+
.09; Found: C, 82.20; H, 4.49; N, 6.25; S, 7.06. ESI-MS (m/z): 452.99 (M ). FTIR
-1
(
KBr, cm ) 3039 (C-H), 1625 (C=N) ,1596, 1502, 1473, 1453 (C=C), 1233 (C-N),
9
65 (C-S).
2
.2.3 Synthesis of 2-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)benzo[d]thiazole
(CzBBTZ)
The synthesis of CzBBTZ is carried out in the same procedure as BCzBTZ.
1
Yied=75%. H NMR (400 MHz, CDCl ) δ [ppm] 8.24-8.28 (m, 2H), 8.20 (d, 2H,
3
J=7.79Hz), 8.15 (d, 1H, J=7.99Hz), 7.97 (d, 1H, J=7.84Hz), 7.89-7.73 (m, 2H),
1
3
7
.83-7.87 (m, 2H), 7.69-7.73 (m, 2H), 7.41-7.58(m, 6H), 7.32-7.37(m, 2H). C NMR
(
400 MHz, CDCl ) δ 167.6, 154.1, 142.8, 140.8, 139.0, 137.6, 135.0, 132.8, 128.5,
3
1
28.2, 127.6, 127.4, 126.5, 126.0, 125.3, 123.5, 123.2, 121.7, 120.4, 120.1, 109.8.
Anal. Calcd for C H N S: C, 82.27; H, 4.45; N, 6.19; S, 7.09; Found: C, 82.17; H,
3
1
20
2
+
-1
4
1
2
.40; N, 6.24; S, 7.19. ESI-MS (m/z): 453.01 (M ). FTIR (KBr, cm ) 3041 (C-H),
622 (C=N), 1595, 1508, 1479, 1450 (C=C), 965 (C-S).
.3. Device fabrication and characterization
Before the fabrication of devices, BCzBTZ and CzBBTZ were further purified by
sublimation. The ITO-coated glass substrates were thoroughly cleaned in an
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ultrasonic bath using detergent, deionized water, acetone and isopropyl alcohol in turn
and then treated with UV-ozone for 15 min. The device was constructed with the
structure of MoO (3 nm)/NPB (50 nm)/emission layer (30 nm)/TPBI (30 nm)/LiF/Al.
3
-1
The deposition rate of organic compounds was 0.9-1.1 Å s . The electroluminescence
spectra and the Commission Internationale de l'Eclairage coordination of the device
were tested on a PR655 spectra scan spectrometer. The luminance-current and
density-voltage characteristics were measured simultaneously from the measurement
of the EL spectra by combining the spectrometer with a Keithley 2400 programmable
voltage-current source.
3
3
. Results and discussion
.1 Synthesis and crystal structures
The synthetic routes of BCzBTZ and CzBBTZ were shown in Scheme 1. Both of
them were prepared through one step of Suzuki coupling with
2
9
-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)benzo[d]-thiazole
and
-(4-bromophenyl)-9H-carbazole/3-bromo-9-phenyl-9H-carbazole. The important
intermediate of 2-(4- (4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)benzo[d]-
thiazole was synthesized by Suzuki-Miyaura reaction with
-(4-bromophenyl)benzo[d]thiazole and 4,4,4',4',5,5,5',5'-octamethyl-2,2'-bi(1,3,2-
2
dioxaborolane). The target compounds were identified by NMR and Single crystal
XRD.
Single crystals of BCzBTZ and CzBBTZ were obtained by the slow solvent vapor
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diffusion method [20]. The detailed crystallographic data are summarized in Tables 1.
The single crystals with dimensions of 0.25 mm × 0.14 mm × 0.02 mm for BCzBTZ
and 0.30 mm × 0.17 mm × 0.03 mm for CzBBTZ were mounted on a Smart 1000
CCD diffractometer using a graphite-monochromatic Cu-Kα radiation at 296K and
2
93K, respectively. As shown in Figure 1, both of the crystals belonged to monoclinic
system and were asymmetric. Figure 1(b) shows the stacking structure with all atoms
along the Axis b for BCzBTZ and the Axis c for CzBBTZ. An intermolecular
hydrogen bond between the N atom and the H atom in the crystal package of
BCzBTZ is observed. The stacking structures omitting hydrogen atoms for clarity
were shown in Figure 1(d).
As well-known, the better planarity for a molecule means a better π-electronic
conjugation and it is very important for OLED materials. However, a large plane will
quench their fluorescence in the film. Therefore, it is very important to choose a
balance both of them. From the Figure 1(d), a small twisted angle is found between
the carbazole unit and the benzene ring in BCzBTZ, while the benzene ring and
benzothiazole block are almost on a plane, which is contributed to intramolecular
electron-transfer and hole-transfer [21]. In crystal package of BCzBTZ, the plane of
the two adjacent molecules exhibits a good parallelism and means a better conjugation
of π-electronic cloud between them, that is beneficial to the transfer of carries
between molecules in the film. For CzBBTZ, although the benzene ring and
benzothiazole units have a good planarity, while the carbazole is almost
perpendicular to the benzene ring, which means the carries can not transport fluently
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between carbazole and benzothiazole. In crystal package of CzBBTZ, the plane of the
two adjacent molecules is almost vertical and it will affect the carrier transfer in the
devices.
3
.2 Thermal and electrochemical properties
The thermal properties of BCzBTZ and CzBBTZ were measured by TGA under a
nitrogen atmosphere. Results are shown in Table 2 and Figure 2(a). Their
decomposition temperatures (T , corresponding to 5% weight loss) are found to be
d
3
40 and 347 °C for CzBBTZ and BCzBTZ, respectively. Such T values indicate that
d
both of them are stable and have the potential to be fabricated into devices by vacuum
thermal evaporation technology. The energy levels of them are calculated according to
the measurement of cyclic voltammetry (Figure 2(b)) and film absorption (Figure
3
(a)). As shown in Figure 2(b), the oxidation onset potentials of them are 0.91 eV for
BCzBTZ and 0.92 eV for CzBBTZ, the corresponding highest occupied molecular
orbital (HOMO) levels can be estimated to be -5.71 eV for BCzBTZ and -5.70 eV for
CzBBTZ, respectively, by comparing with ferrocene (Fc) (HOMO =−(E + 4.8) eV)
ox
[
22]. Apparently, the HOMO levels are elevated significantly compared to that of
TPBI (HOMO level of -6.2 eV), implying an enhanced hole injection ability [23]. By
combining the values of energy gaps from film absorption, their lowest unoccupied
molecular orbital (LUMO) energy levels are -2.73 eV for BCzBTZ and -2.65 eV for
CzBBTZ. Likewise, their LUMO levels are close to that of TPBI (LUMO level of
-2.7 eV), showing suitable electron injection ability.
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3
.3 Absorption and photoluminescent properties
The ultraviolet-visible (UV-vis) absorption and photoluminescent (PL) properties of
BCzBTZ and CzBBTZ in dilute DCM solution as well as film are studied as shown in
Figure 3 and Table 1. As illustrated in Figure 3(a), both of them show similar
absorption profiles with two peaks at ~340 nm and ~300 nm in the dilute solution,
which is assigned to the internal charge transfer (ICT) transition and the π−π*
transition, respectively [24]. For the absorption of neat films, their maximal
absorption is red-shifted in relation to the solution measurements due to the H-type
molecular aggregation [25]. According to the absorption edges of films, optical
opt
energy band gaps (Eg ) of BCzBTZ and CzBBTZ are 2.98 and 3.07 eV, respectively.
Their fluorescence properties were studied by measuring their PL spectra in both
DCM solution and solid-state thin films on quartz substrates. As seen in Figure 3(b),
they exhibit a deep-blue emission with the maximal wavelength of 448 nm for
BCzBTZ and 452 nm for CzBBTZ. It should be noted that BCzBTZ show negligibly
small peak shifts in their PL spectra from dichloromethane solutions to solid states.
This indicates that the highly twisted structure between the thiazole and Cz units as
well as the noncoplanar N-phenylcarbazole moiety can effectively suppress the
intermolecular π−π stacking in the solid state. In addition, the PL spectrum of
BCzBTZ and CzBBTZ shows obvious solvatochromic shift, in which their emission
color is red-shifted with increasing solvent polarity (Figure 3 (c) and (d)). This
indicates the occurrence of charge transfer upon photoexcitation.
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3
.4 Theoretical calculations
In order to understand the electronic structures, their molecular configurations and
orbital distributions were predicated by using Gaussian software with density
functional theory (DFT) method at the B3LYP/6-31G(d,p) level. As shown in Figure
4
, the HOMO level mainly locates on the Cz part for CzBBTZ, while BCzBTZ shows
on the whole molecule. In other words, the Cz moiety contributes less to the HOMO
energy in BCzBTZ compared with that of CzBBTZ. The calculated HOMO levels of
them are -5.31 eV and -5.37 eV, respectively. The LUMO levels mostly locate on the
benzothiazole ring and their linkers between donor and acceptor. It is noted that the
large overlap of LUMO and HOMO in BCzBTZ would be beneficial for the charge
transfer as the emitter in OLED. On the other hand, it could facilitate the charge
transfer process upon excitation, which was also confirmed by the solvatochromic
phenomenon observed in the solvents with a different polarity.
3
.5 Electroluminescent properties
To investigate their electroluminescent performance, non-dopant fluorescence OLEDs
with the following configuration: ITO/MoO (3 nm)/NPB (50 nm)/BCzBTZ or
3
CzBBTZ (30 nm)/TPBI (30 nm)/LiF (1 nm)/Al was fabricated, where MoO and LiF
3
were utilized as a hole-injection layer and an electron-injection layer, respectively;
NPB acted as a hole-transporting layer; TPBI was used as the electron-transporting
and the hole-blocking layer. The energy levels of the used materials were shown in
1
1

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Figure 5. Their current density–voltage (J–V) characteristics, voltage–luminescence
(V–L) profiles, current efficiencies-current density, and electroluminescent spectra for
the devices were plotted in the Figure 6 and some key paramaters were summarized in
Table 3.
Figure 6 (a) shows the current density-voltage (J-V) curves of BCzBTZ or CzBBTZ.
-2
The turn-on voltage of the device with BCzBTZ is 3.2 V at the luminance of 1 cd m ,
while the device with CzBBTZ is up to 5.5 V, which is about twice higher than that of
BCzBTZ-based device. It means that the charges injection is easy in the device with
BCzBTZ as emitter. The voltage-luminance results are shown in Figure 6 (b).
-2
Obviously, the maximum luminance brightness of BCzBTZ is 8295 cd m at 9 V,
-2
while the corresponding CzBBTZ exhibits only 812 cd m . The brightness of
BCzBTZ-based device is more than 10 times higher than those obtained from the
CzBBTZ-based device, which can be attributed to the low fluorescent quantum yield
and difficult charges injection. As shown in Figure 6 (c), the maximum current
-1
efficiency for BCzBTZ is 1.39 cd A , and external quantum efficiency (EQE) is 1.4%.
CzBBTZ exhibited a low performance with the maximum current efficiency of 0.52
-1
cd A , and external quantum efficiency (EQE) of 0.2%, respectively. It is notable that
the devices with BCzBTZ as emitter exhibits a low efficiency roll-off at high current
density.
The maximum EL emission λmax of BCzBTZ and CzBBTZ is located at 440 nm and
the FWHM value is 50 and 60 nm, respectively. Compared with PL, there is a 10 nm
blue-shift for the emission peak in EL spectrum. The blue-shift can be ascribed to the
1
2

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face-to-face π-π stacking in the vacuum-deposited film [26]. When the current density
2
is at the brightness of 100 cd/m , the CIE coordinates (x, y) of BCzBTZ device is
found to be (0.15, 0.08), which is close to the pure blue standard (0.14, 0.08) of
NTSC.
4
. Conclusions
In summary, we demonstrated two novel deep-blue fluorescent compounds with
thiazole as electron-transporting and carbazole as hole-transporting blocks for
electroluminescent emitters. Their thermal stabilities, optical and electrochemical
properties were studied systematically and exhibited ideal performance for OLED
emitters. Interestingly, their crystal packing can be effectively regulated by changing
the connecting position of carbazole. The device based on BCzBTZ as emitter shows
pure deep-blue emission with the CIE (x, y) of (0.15, 0.08) and good performance
with maximal external quantum efficiency of 1.4 % and current efficiency of 1.39
cd/A, implying that thiazole has potential application in the design of new fluorescent
molecules for OLEDs.
Acknowledgements This work was financially supported from National Natural
Science Foundation of China (21574144, 51273209, 51411140244),
CAS Interdisciplinary Innovation Team, Zhejiang Provincial Natural Science
Foundation of China (LR16B040002), and Ningbo Municipal Science and
Technology Innovative Research Team (2015B11002).
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Tables
Table 1 Crystallographic data and structure refinement parameters of BCzBTZ and
CzBBTZ
Table 2 The physical parameters of the compounds BCzBTZ and CzBBTZ
Table 3 Electroluminescent characteristics of the devices with the structure of
ITO/MoO (3 nm)/NPB (50 nm)/BCzBTZ or CzBBTZ (30 nm)/TPBI (30 nm)/LiF (1
3
nm)/Al.

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Table 1.
Compound
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
BCzBTZ
CzBBTZ
C H N S
C H N S
30 20 2
3
0
20
2
452.55
296(2)
452.55
293(2)
Monoclinic
Monoclinic
P2(1)/n
P2(1)/n
15.88(5)
8.1907(18)
b (Å)
7.82(2)
34.463(7)
c (Å)
17.46(5)
8.3321(18)
α (°)
90
90
β (°)
92.54(4)
103.940(3)
γ (°)
90
90
3
V (Å )
2165(11)
2282.7(8)
Z
4
4
3
D (Mg/m )
1.388
1.317
c
−
1
ꢀ
(mm )
0.174
0.165
F(000)
944
944
Reflns collected
Independent reflns
Completeness
R(int)
9931
11866
3758
7317
98.1 %
99.6%
0.0877
0.0245
2
2
Refinement method
Full-matrix least-squares on F
Full-matrix least-squares on F
7317/1/615
Data / restraints / parameters 3758 / 0 / 307
2
GOF on F
0.952
1.024
a
R1[I>2σ (I )], wR2
0.0645, 0.1130
0.0427,0.0928
0.0547,0.1010
R1[all data], wR2
0.1283, 0.1397
a
2
2 2
2 2 1/2
R =Σ||F | − |F ||/Σ|F |, wR =[Σ[w(F − F ) ]/Σw(F ) ]
1
o
c
o
2
o
c
o

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Table 2
cal
HOMO/LUMO
a
b,c
b,c
exp
Compound Td
λAbs
λmaxPL
HOMO/LUMO
opt e
f
Φ
(
Eg ) (eV)
o
opt d
s
( C)
(nm)
(nm)
(Eg ) (eV)
BCzBTZ 347
344/352
448/447 -5.71/-2.73(2.98)
-5.31/-1.60
-5.37/-1.85
0.52
0.33
CzBBTZ 340 294,342/296,352 452/448 -5.72/-2.65(3.07)
a)Loss of 5 wt%; b) UV-vis absorption and PL spectra in CH Cl ; c) UV-vis
2
2
absorption and PL spectra in neat film; d) Obtained from CV and the onset of UV-vis
absorption spectra in film; e) Obtained from DFT calculations using
B3LYP/6-31G(d,p); f) Measured by the integrating sphere system with neat film.

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Table 3
-
2
-2
Emitter
CIE
Lmax
CEmax
cd/A
EQEmax Devices @100 cd m
Devices @1000 cd m
2
(x,y)
cd/m
%
ηc(cd/A) ηe (%)
ηc(cd/A) ηe (%)
BCzBTZ
CzBBTZ
(0.15, 0.08)
(0.15, 0.10)
8295
812
1.39
0.52
1.40
0.20
1.37
0.31
1.39
0.11
1.39
--
1.39
--

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Figures and Scheme
Figure 1 (a) the molecule structure; (b) the stacking structure with all atoms along the
Axis b for BCzBTZ and the Axis c for CzBBTZ; (c) the stacking structure omitting
hydrogen atoms along the Axis b for BCzBTZ and the Axis a for CzBBTZ;(d) The
spatial distribution of the two adjacent molecules in crystal package.
Figure 2 (a) TGA profiles of BCzBTZ and CzBBTZ ; (b) Cyclic voltammetry curves
of BCzBTZ and CzBBTZ.
Figure 3 a) UV-vis absorption of BCzBTZ and CzBBTZ in DCM solution and thin
film; b) PL spectra of BCzBTZ and CzBBTZ in DCM solution and thin film; c) PL
spectra of BCzBTZ in different solvents; d) PL spectra of CzBBTZ in different
solvents.
Figure 4 Calculated spatial distributions of HOMOs and LUMOs of TPABTZ,
BCzBTZ and CzBBTZ.
Figure 5 HOMO–LUMO levels of the used materials.
Figure 6 (a) J–V characteristics; (b) V-L curves; (c) current efficiency; (d) EL
B
spectra of BCzBTZ and CzBBTZ based OLEDs.
Scheme 1 Synthesis and structures of target compounds.
1

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Figure 1
BCzBTZ
CzBBTZ
(
(
(
a)
b)
c)
(
d)
2

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Figure 2
1
00
(
a)
(b)
8
6
4
2
0
0
0
0
0
BCzBTZ
CzBBTZ
BCzBTZ
CzBBTZ
1
00
200
300
400
500
0.0
0.2
0.4
0.6
0.8
1.0
1.2
o
Temperature ( C)
Potential (V vs Ag/AgCl)
Figure 3
1.0
0.8
0.6
0.4
0.2
0.0
1.0
(b)
BCzBTZ (DCM)
CzBBTZ (DCM)
BCzBTZ(film)
CzBBTZ(film)
(a)
BCzBTZ(in DCM)
CzBBTZ(in DCM)
BCzBTZ(flilm)
0.8
0.6
0.4
0.2
0.0
CzBBTZ(flilm)
300
400
500
600
350
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
1
.0
.8
1.0
0.8
0.6
0.4
0.2
0.0
hexane
THF
DCM
DMF
Methnol
(d)
hexane
THF
DCM
DMF
Methnol
(
c)
0
BCzBTZ
0.6
0.4
0.2
0.0
CzBBTZ
350
400
450
500
550
600
650
350
400
450
500
550
600
650
700
Wavelength (nm)
Wavelength (nm)
3

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Figure 4
HOMO
LUMO
BCzBTZ:
CzBBTZ:
Figure 5
4

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Figure 6
800
600
400
200
0
(a)
BCzBTZ
CzBBTZ
(b)
BCzBTZ
CzBBTZ
8
6
4
2
000
000
000
000
0
0
2
4
6
8
0
2
4
6
8
Voltage (V)
Valtage (V)
1.4 (c)
1.0
(d)
BCzBTZ
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
CzBBTZ
BCzBTZ
CZBBTZ
0.8
0.6
0.4
0.2
0.0
20
40
60
80
100
120
4
00
500
600
700
2
Current Density (mA/cm )
Wavelength (nm)
5

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Scheme 1
6

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Highlights
ꢀ
ꢀ
Two novel benzothiazole derivatives were synthesized and characterized.
The differences of their performance were discussed according to the crystal
structure.
ꢀ
The device based on BCzBTZ as emitter shows deep-blue emission with the
CIE(x, y) of (0.15, 0.08).