Versatile functionalization of trifluoromethyl based deep blue thermally activated delayed fluorescence materials for organic light emitting diodes

Article abstract of DOI:10.1039/c7nj04482h

Thermally activated delayed fluorescence (TADF) materials have been thoroughly developed and have proven to be the most promising means to generate an efficient deep blue emission. In this work, we prepared a series of deep blue TADF emitters based on trifluoromethyl featuring phenyl and N-heterocyclic rings as electron-withdrawing units and carbazole as electron-donating moieties. Efficient organic light-emitting diodes (OLEDs) utilizing these emitters have a deep blue emission and a high external quantum efficiency of up to 20.4%. These blue emitters are among the bluest in the TADF based OLED category. They can also be implemented in OLED as hosts for green phosphorescent iridium(iii) complexes, exhibiting high brightness and a decent external quantum yield.

Full text of DOI:10.1039/c7nj04482h

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January 2016 Pages 1–846
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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
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Paper
Versatile functionalization of trifluoromethyl based deep blue
thermally activated delayed fluorescence materials for organic
light emitting diodes
Received 00th January 20xx,
Accepted 00th January 20xx
a
b
b
b
b,*
a,*
a
DOI: 10.1039/x0xx00000x
Xiao Liang, Hua-Bo Han, Zhi-Ping Yan, Liang Liu , You-Xuan Zheng , Hong Meng ,Wei Huang
www.rsc.org/
Thermally activated delayed fluorescence (TADF) materials have been throroughly developed and proven to be the most
promising means to generate efficient deep blue emission. In this work, we prepared a series of deep blue TADF emitters
based on trifluoromethyl featuring phenyl and N-heterocyclic rings as electron-withdrawing units and carbazole as
electron-donating moieties. Efficient organic light-emitting diodes (OLEDs) utillizing these emitters have deep blue
emission and high external quantum efficiency up to 20.4%. These blue emitters are among the bluest in TADF based OLED
category. They can also be implemented in OLED as hosts for green phosphorescent iridium(III) complexes, exhibiting high
brightness and decent external quantum yield.
lot of efficient blue emitters with TADF characteristics were
5
, 11-22, 52-53
Introduction
developed
. Indeed, the diversity of TADF molecular
design has made it much easier to achieve blue emission than
tradition iridium or platinum complexes. In order to obtain
TADF molecules with high efficiency, two key requirements
The development of organic light-emitting diodes (OLEDs) has
1
been robustly grown since C.W. Tang reported the first
generation OLED based on fluorescent emitters. But the
traditional fluorescent materials can only harvest the singlet
excitons during the electroluminescence process, limiting the
2
3
have to be fulfilled simultaneously : 1. Spatially separated
HOMO (highest occupied molecular orbital) and LUMO (lowest
unoccupied molecular orbital) moieties to provide a small
overlap between HOMO and LUMO; 2. Strong resonance from
2
theoretical external quantum efficiency to merely 25% . The
introduction of heavy metals such as iridium and platinum
breaks the limitation due to strong spin-orbit coupling effect,
endowing the emitter with the ability to harvest both singlet
1 0
S to S to ensure efficient radiative decay. The first
requirement can be achieved simply by introducing the
electron withdrawing groups and electron donating groups
3
and triplet excitons , boosting theoretical quantum yield up to
4
00% . However, the introduction of heavy metals also
2
4
with a relatively large torsion angle in between . Numerous
TADF emitters bearing this concept with various electron
1
restricts the potential of developing efficient deep blue
5
emitters and increases the overall cost of OLED. It remains to
6
,
25-29
30-34
withdrawing groups such as triazine
, sulfones
, etc. have been reported.
) is an interesting electron-withdrawing
,
3
5-40
14, 41-46
cyanobezenes
, boron
be a bottleneck for traditional phosphorescent materials until
the recent breakthrough with thermally activated delayed
Trifluoromethyl (-CF
3
6
-9
group and has been mostly employed in phosphorescent
materials to increase the electron-transporting ability and
fluorescence (TADF) reported by Adachi. et.al . The TADF
molecules can overcome the demerit of traditional fluorescent
4
7
decrease molecule stacking . However, only few molecules
with -CF as electron-withdrawing groups have been reported
materials by recursive energy transfer from T
1 1
to S due to the
3
small energy gap between S and T , providing a significantly
1
1
4
8
1
efficient pathway to harvest the triplet energy . Since then, a
0
for TADF materials . In an aim to expand the diversity of TADF
species and produce more potential deep blue emitters, we
3
designed a series of TADF molecules with -CF substituted
phenyl or pyridine rings as electron-withdrawing units and
carbazole-phenyl as electron-donating unit. The different
3
substitution position of -CF groups can yield various emitters
with significantly diversified photophysical, electrochemical
and thermal properties, etc. Additionally, we exploited the
potential of these deep blue emitters as hosts for iridium
complex, which could further promote the application of TADF
emitters in OLED design and fabrication.
†
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CF
3
N
Br
N
CF
3
1
F
3
C
N
N
CF
3
F
3
C
CF
3
LDA,0 oC, 1 h
, 0 oC, RT.
CF
B(OH)
3
N
F
3
C
N
CF
3
2.0 M HCl
2
CF
3
B(i-PrO)
3
F
3
C
C
N
CF
3
2
Pd(PPh
3 4
)
N
N
B(OH)
2
K CO ,THF/H O
2
3
2
reflux, 24 h
F
3
CF
3
3
TN3T-PCZ
TN4T-PCZ
DTF-PCZ
B(OH)
2
CF
3
N
N
B(OH)
2
CF
3
3 4
Pd(PPh )
N
N
4
+
N
K
2
CO
3 2
, THF/H O,
reflux, 24 h
N
Br
NTN-PCZ
Scheme 1: Synthetic procedures of four trifluoromethyl based compounds.
Results and discussion
Synthesis of four compounds
spectrometer in degassed toluene solutions with an integer sphere.
All deep blue emitters show decent quantum yields (71.84-86.93%)
(
Table 1) and could be potentially solid blue emitter candidates for
All four trifluoromethyl based compounds were synthesized
OLED application.
through Suzuki coupling reaction using Pd(PPh
3 4
) as catalyst
(Scheme 1). TN3T-PCZ, TN4T-PCZ and DTF-PCZ were obtained by
direct coupling of corresponding boric acid derivatives and 9-(4-
bromophenyl)-9H-carbazole, while NTN-PCZ was synthesized from
coupling reaction of (4-(9H-carbazol-9-yl)phenyl)boronic acid and 5-
bromo-2-(trifluoromethyl)pyrimidine. Compounds 1 and 2 were
(a)
DTF-PCZ
NTN-PCZ
TN3T-PCZ
TN4T-PCZ
4
9
prepared according to our previous work . All compounds were
comprehensively characterized and detailed information can be
found in cf. Experimental Section.
Photophysical property
Photophysical properties of four compounds were investigated by
UV-vis absorption and photoluminescence spectra at room
temperature, as depicited in Fig. 1 and Table 1. The maximum
emission wavelengths in toluene solutions are 387, 406, 428, 411
nm for DTF-PCZ, NTN-PCZ, TN3T-PCZ, TN4T-PCZ, respectively. All
compounds exhibit strong emission in deep blue region or even
ultraviolet region. To our best knowledge, these emitters are
3
00
320
340
360
380
400
420
440
Wavelength (nm)
(b)
DTF-PCZ
NTN-PCZ
TN3T-PCZ
TN4T-PCZ
5
0
among the bluest in TADF based device criterion . The energy gaps
between HOMO and LUMO of these materials were determined by
calculating from the red-edge onset of UV absorption spectra,
which correlate well with the trend of corresponding
photoluminescence spectra. Compounds TN3T-PCZ and TN4T-PCZ
have quite different emission profiles despite the similarities in
terms of molecular structures due to the increased steric hindrance
4
00
450
500
550
600
Wavelength (nm)
Fig. 1 (a) Normalized absorption and (b) photoluminescence spectra
-5
in degassed toluene solution (5×10 M) at 300 K.
3
from –CF units in TN3T-PCZ and also the HOMO/LUMO distribution
patterns that are simultaneously affected by the position of –CF
3
groups and pyridine rings. The absolute photoluminescence
quantum yields of all compounds are determined on a Horiba FL-3
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Table 1. Photophysical and electrochemical properties of four compounds
[
a]
[b]
g
[c]
[d]
abs
[e]
[f]
[g]
[h]
o
[i]
[k]
UV/λmax
E
PL/λmax
(nm)
387
φ
FWHM
(nm)
49
HOMO /LUMO
T
g
/T
d
ΔEST
[
j]
Compounds
CIEx,y
(nm)
(eV)
3.37
3.25
3.13
3.20
(%)
(eV)
( C)
(eV)
0.07
0.12
0.09
0.10
DTF-PCZ
NTN-PCZ
TN3T-PCZ
TN4T-PCZ
327,339
328,339
75.98
74.16
71.84
86.93
-5.73/-2.36
-5.76/-2.51
-5.74/-2.61
-5.76/-2.56
185/221
-/241
(0.16,0.02)
(0.16,0.03)
(0.15,0.05)
(0.15,0.03)
406
56
327,340,348
326,338
428
57
282/265
207/246
411
59
-
5
[
a] Maximum absorption wavelength in toluene solution (5×10 M);[b] Band gap energies calculated from onset of UV spectrum using
-5
E
g
=hc/λ; [c] Maximum photoluminescence wavelength in toluene solution (5×10 M); [d] Absolute photoluminescence quantum yield in
degassed toluene solution; [e] Full width at half maxima of photoluminescence spectrum; [f] HOMO energy level calculated from oxidation
potentials from cyclic voltammetry using ferrocene as standard; [g] LUMO energy level determined by HOMO and E ; [h] Glass transition
temperature from DSC; [i] Decomposition temperature from TGA corresponds to 5% weight loss. [j] CIE coordinates of corresponding
g
photoluminescence spectrum in toluene; [k] Energy gap between S
toluene, Fig. S5-Fig. S8 (ESI†).
1 1
and T from onset of fluorescence and phosphorescence at 77 K in
Theoretical Calculation
Thermal stability
To gain insight into the transitional properties and understand Thermogravimetric analysis (TGA) and differential scanning
o
the detail of HOMO/LUMO distributions, theoretical calorimetry (DSC) curves at a heating rate of 10 C/min were
calculations based on density functional theory (DFT) with conducted on these compounds to investigate their thermal
B3LYP (6-31g) basis set were performed on these emitters. As stability. All compounds exhibit moderate stability with
o
illustrated in Fig. 2, HOMO and LUMO moieties are all decomposition temperatures higher than 220 C. TN4T-PCZ
d
sufficiently separated, which contribute to the small ΔEST. The has the highest T , and even though compounds TN3T-PCZ and
HOMO moieties are mostly localized on carbazole fragments TN4T-PCZ have the same molecule weight, their thermal
and phenyl-bridges, wherein LUMO moieties are mainly stability is quite different from each other. The above
3
localized on phenyl/pyridine-rings substituted by –CF groups. mentioned torsion angle α could be attributed to such
A small portion of overlap can be observed at phenyl-bridge difference in terms of thermal stability, and further affect the
between the electron donor and acceptor units, which not overall OLED performances. Nevertheless, it is still adequate
only creates a reasonable torsion angle (α), c.f. Table S5 (ESI
†)
for OLED fabrication utilizing these four compounds as guests
to decrease the energy gap between S and S , but also in emitting layer and also feasible for applications as hosts for
1
0
facilitate the subsequent radiative decay. TN3T-PCZ differs other emitters.
from other three molecules with a much larger torsion angle
Electroluminescence properties
between electron acceptor unit and phenyl-bridge, leading to
a weaker oscillating strength, as demonstrated in Table S5 Since all four compounds exhibit strong emission in deep blue
(
ESI†), and also a
relatively lower photoluminescence region with large energy gap between HOMO and LUMO
energy levels, they can not only be anticipated as strong
quantum yield.
candidates as emitters in OLED emission layer, but also
sufficiently as hosts for tradition phosphorescent emitters,
such as iridium complexes. To further evaluate their
electroluminescence properties, two types of devices with
configurations as follows were fabricated: Device type 1: MoO
TAPC (di-[4-(N,N-ditolyl-amino)-phenyl] cyclohexane) / 2,6-
3
/
DCzppy (2,6-bis(3-(9H-carbazol-9-yl)phenyl) pyridine) : x wt%
guest / TmPyPB (1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene) / LiF/
Al; Device type 2) MoO /TAPC/ Host : x wt% iridium complex
3
/TmPyPB/LiF/Al. The schematic energy diagram of each
configuration can be found in Fig. 3a and 3b. In all device
configurations, we employed MoO3 as hole injecting layer
(
HIL), TAPC as hole-transporting layer (HTL), TmPyPB as
electron-transporting layer (ETL), LiF as electron injecting layer
HIL). For the device type 1, 2, 6-DCzppy was employed as the
Fig. 2 HOMO and LUMO energy level diagram and distributions
of four molecules.
(
host, TN4T-PCZ or NTN-PCZ was the guest. The optimal device
configurations of two compounds are MoO (2 nm)/TAPC(7
3
nm)/ (2,6-DCzppy: 6 wt% NTN-PCZ) (10 nm)/ TmPyPB (15 nm)
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6
5
4
3
2
1
(a)
TN4T-PCZ
NTN-PCZ
NTN-PCZ
TN4T-PCZ
4
00
450
Wavelength (nm)
500
550
0
500
1000
1500
2000
-2
Luminance (cd m )
25
TN4T-PCZ
NTN-PCZ
(b)
Fig. 3 (a) Device structure energy diagram for type 1; (b)
Device structure energy diagram for type 2 and materials
employed in two types of devices.
20
15
10
and MoO
3
(2 nm)/ TAPC (15 nm) /(2,6-DCzppy: 6 wt% TN4T-
5
0
PCZ) (5 nm)/ TmPyPB (30 nm) for NTN-PCZ and TN4T-PCZ
,
respectively. In device type 2 configuration, four compounds
are employed as hosts for a green phosphorescent emitter
5
00
1000
1500
2000
-2
Luminance (cd m )
Ir(tfmppy)
2
tpip (tfmppy= 2-(4-(trifluoromethyl)phenyl)pyridine,
N-(diphenylphosphoryl)-P,P-diphenylphosphinic Fig. 4 (a) Luminance-voltage and (b) current efficiency-
amide) , which is an efficient green emitter previously luminance curves for type 1 devices.
tpip=
4
9
47
reported in our group . The general thickness of each layer is
almost identical for all four compounds except for the doping
concentrations of Ir(tfmppy)
device configurations are MoO
wt% iridium complex) (10 nm)/ TmPyPB (30 nm)/ LiF/ Al, with
2
tpip, c.f. Fig. 3. The optimized
for TN4T-PCZ, respectively.
3
(2 nm) /TAPC (30 nm)/ (Host: x
In device type 1, both devices based on NTN-PCZ and TN4T-PCZ
6
1
wt% iridium complex for TN3T-PCZ
,
NTN-PCZ
,
DTF-PCZ and exhibit efficient energy transfer from 2,6-DCzppy host to the
6 wt%
emitters. However, as shown in Fig. 4 Fig. S17 and Table 2,
Table 2. Electroluminescence performances of two types of devices.
[
f]
[a]
[b]
[c]
c,max
-1
-2 [d]
-2 [e]
CIE
(x,y)
[f]
V
turn-on
L
max
η
η
c
at 100 cd m
(cd A )
η
c
at 1000 cd m
EQEmax
(%)
Device Type
-2
-1
-1
(
V)
(cd m )
(cd A )
(cd A )
Type 1: NTN-PCZ
Type 1: TN4T-PCZ
Type 2: DTF-PCZ
Type 2: NTN-PCZ
Type 2: TN3T-PCZ
Type 2: TN4T-PCZ
4.1 V
4.2 V
4.5 V
3.9 V
4.9 V
6.4 V
2337
1.38
0.87
2.69
1.30
4.74
(0.17,0.06) 3.8
(0.16,0.03) 20.4
(0.30,0.64) 13.7
(0.30,0.64) 14.1
(0.30,0.64) 18.6
(0.29,0.62) 17.5
5377
23263
11265
14270
18171
5.01
53.01
54.61
57.00
66.56
36.33
30.33
53.79
24.61
32.14
21.52
34.62
19.93
-
2
[
a] turn-on voltage; [b] maximum brightness; [c] maximum current efficiency; [d] current efficiency at the brightness of 100 cd m ; [e]
-2
current efficiency at the brightness of 1000 cd m ; [f] CIE coordinates of electroluminescence spectrum; [g] maximum external efficiency.
4
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4
2
2
1
1
5
.5x10
(a)
and Fig.S16 (ESI
†). TN3T-PCZ serves as a suitable host for
DTF-PCZ
NTN-PCZ
TN3T-PCZ
TN4T-PCZ
2
Ir(tfmppy) tpip since the corresponding device has a relatively
4
.0x10
lower turn-on voltage and the highest external quantum
efficiency of 18.6%. It is also worth mentioning that the doping
concentration for device with TN4T-PCZ as host is surprisingly
high, it requires 16 wt% of guest emitter to ensure the energy
transfer from host to guest, but the energy conversion is still
insufficient in the case of TN4T-PCZ and a small portion of
emission from TN4T-PCZ can still be observed in the
4
.5x10
4
.0x10
3
.0x10
0
.0
electroluminescence spectrum, Fig. S16 (ESI
rationalized by the strong oscillating strength (f) between S
and S , which promote the subsequent radiative decay of
†). This can be
6
8
10
12
14
16
1
Voltage (V)
0
2
0
1
1
1
TN4T-PCZ instead rather than energy transfer to guest emitter.
This could also explain the higher turn-on voltage of 6 V, and
indicating TN4T-PCZ as a less proper candidate for application
as host in OLED structure.
(b)
DTF-PCZ
NTN-PCZ
TN3T-PCZ
TN4T-PCZ
1
0
Conclusions
0
0
Four trifluoromethyl based TADF emitters DTF-PCZ
, NTN-PCZ,
TN3T-PCZ, TN4T-PCZ exhibit strong deep blue emission and
are among the bluest emitters in TADF category. When used as
blue emitter in pragmatic OLED applications, device based on
TN4T-PCZ has significantly high external quantum efficiency up
to 20.4% with moderate efficiency roll-off. These TADF
materials can also serve as hosts for phosphorescent emitters.
High external quantum efficiency and small efficiency roll off
can be attained utilizing an efficient green iridium complex
doped in these trifluoromethyl based TADF compounds.
Especially, device with TN3T-PCZ as host yields a maximum
-
1
10
1
10
100
1000
10000
-2
Luminance (cd m )
Fig. 5 (a) Luminance-voltage and (b) current efficiency-
luminance curves for type 2 devices.
device based on TN4T-PCZ shows superior performance
compared to the device based on NTN-PCZ. The maximum
-2
brightness of 23267 cd m and a maximum external quantum
-2
brightness for device based on TN4T-PCZ is 5377 cd m .
efficiency of 18.6% with relatively small efficiency roll-off. Even
though the overall performances of these devices are still
inferior to the conventional bipolar hosts, the strategy of
introducing TADF molecules as host and guest can still be a
useful alternative for OLED application.
-1
Though the current efficiency is only 5.01 cd A , the external
quantum efficiency of this device can reach 20.4% because a
large portion of the emission spectrum covers the ultraviolet
region, which cannot be detected by the photomultiplier used
in our laboratory. These results are remarkable in deep blue
2
4
TADF category . The electroluminescence spectrum also
correlates well with the emission spectrum in toluene solution. Experimental section
Both devices show moderate turn-on voltages, and relatively
Synthetic procedures and characterization
small efficiency roll-off.
Synthesis of (2,6-bis(trifluoromethyl)pyridin-3-yl)boronic acid (1)
The employment of TADF materials as hosts for
phosphorescent emitters can help dilute the density of triplet
and (2,6-bis(trifluoromethyl)pyridin-4-yl) boronic acid (2). To a
5
1
solution of 2,6-bis(trifluoromethyl) pyridine (2.15 g, 10 mmol) in 50
excitons and increase the rate of exciton utilization . The
high-lying triplet state of TADF materials can also help reduce
o
ml anhydrous ether was added LDA (1.5 M, 10 mmol) at -78 C in N
2
5
0
atmosphere under stirring for 1 h before the addition of triisopropyl
borate (2.26 g, 12 mmol). The reaction mixture was then slowly
warmed to room temperature and the resulting solution was then
added 2 M NaOH until the pH value reached 10 and the organic
phase was discarded. The resulting water solution was then added
the reverse energy transfer from guest to host . On the basis
of these reasons, we further exploited the potential of using
these TADF materials as hosts for iridium complexes. All
devices show decent overall performance. For devices utilizing
DTF-PCZ and NTN-PCZ as hosts, the turn-on voltages are
relatively lower than the other two candidates (Table 2), which
could originate from the smaller energy barrier between
LUMOs of hosts and ETL, resulting in much easier electron
injection and transportation. Device with DTF-PCZ as host
2
2
M HCl until the pH of the solution reached 6 and extracted with
0 ml ether for three times. The organic phase was then combined
and solvent was removed under reduced pressure, giving a light-
brownish liquid (1.03 g, 40%) which was the mixture of 1 and 2. To
reduce the loss on column chromatography, the mixture was
directly put into next step without further purification.
-2
exhibits the highest brightness of 23263 cd m and smallest
efficiency roll off even though the external quantum efficiency
are the lowest in all four devices as revealed in Fig. 5,Table 2
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Synthesis of TN3T-PCZ, TN4T-PCZ. The mixture of 2.58 g (10 mmol)
2,6-bis(trifluoromethyl)pyridin-3-yl)boronic acid (1) with (2,6-
bis(trifluoromethyl)pyridin-4-yl)boronic acid (2) and 9-(4-
bromophenyl)-9H-carbazole (3.86 g, 12 mmol), K CO (1.38 g, 10
mmol), Pd(PPh (0.35 g, 0.3 mmol) in a bottle wad degassed and
filled with N , then 50 ml THF : H O = 1 : 1 was added. The reaction
Conflicts of interest
(
There are no conflicts to declare.
2
3
3 4
)
Acknowledgements
2
2
This work is supported by National Natural Science Foundation
of China (21402088, 51773088) and the Natural Science
Foundation of Jiangsu Province (BY2016075-02).
mixture was refluxed for 24 h. After cooling to room temperature,
the solvent was removed and purified through column
chromatography with petroleum ether: ethyl acetate = 10 : 1 as
eluent, yielding TN3T-PCZ (1.59 g, 35%) and TN4T-PCZ (1.92 g, 42%)
as white powders. Then they were purified again through
1
Notes and references
sublimation prior to device fabrication. TN3T-PCZ: H NMR(CDCl
3
,
4
00 MHz) δ 8.17 (d, J = 7.3 Hz, 4H), 8.00 – 7.91 (m, 2H), 7.86 – 7.77 1.
C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 1987, 51,
913-915.
1
3
(
m, 2H), 7.53 – 7.40 (m, 4H), 7.34 (ddd, J = 8.0, 6.8, 1.4 Hz, 2H);
C
2
3
4
5
.
.
.
.
Y. Tao, K. Yuan, T. Chen, P. Xu, H. Li, R. Chen, C. Zheng, L.
Zhang and W. Huang, Adv. Mater., 2014, 26, 7931-7958.
C. Adachi, M. A. Baldo, M. E. Thompson and S. R. Forrest, J.
Appl. Phys., 2001, 90, 5048-5051.
D. F. O. B. M. A. Baldo, Y. You, A. Shoustikov, S. Sibley, M. E.
Thompson, S. R. Forrest, Nature, 1998, 151-154.
H. Nakanotani, T. Higuchi, T. Furukawa, K. Masui, K.
Morimoto, M. Numata, H. Tanaka, Y. Sagara, T. Yasuda and
C. Adachi, Nat. Commun., 2014, 5, 4016.
H. Tanaka, K. Shizu, H. Miyazaki and C. Adachi, Chem.
Commun., 2012, 48, 11392-11394.
T. Nakagawa, S. Y. Ku, K. T. Wong and C. Adachi, Chem.
Commun., 2012, 48, 9580-9582.
3
NMR(CDCl , 101 MHz): δ 151.54, 149.77, 149.42, 140.34, 140.27,
1
1
3
34.26, 128.84, 127.86, 126.23, 123.80, 122.30, 120.81, 120.61,
20.54, 119.56, 109.60; Elemental Analysis: calculated: C: 65.79, H:
.09; N: 6.14; experimental: C: 65.70; H: 3.10; N: 6.21; ESI-MS:
1
calculated: 456.39, [M+1]: 457.18. TN4T-PCZ: H NMR(CDCl
3
, 400
MHz) δ 8.17 (dt, J = 7.6, 0.9 Hz, 2H), 8.07 (d, J = 8.0 Hz, 1H), 7.99 (d,
J = 8.0 Hz, 1H), 7.76 – 7.67 (m, 2H), 7.62 – 7.55 (m, 2H), 7.53 – 7.41
1
3
(
m, 4H), 7.33 (ddd, J = 8.1, 6.9, 1.3 Hz, 2H); C NMR(CDCl
MHz) δ 141.95, 140.55, 138.63, 134.60, 130.21, 126.85, 126.12, 6.
23.64, 122.74, 120.45, 120.36, 109.67, 95.98; Elemental Analysis:
calculated: C: 65.79, H: 3.09; N: 6.14; experimental: C: 65.89, H:
.17; N: 6.14; ESI-MS: calculated: 456.39, [M+1]: 457.30.
3
, 101
1
7
8
9
.
.
.
3
G. Mehes, H. Nomura, Q. Zhang, T. Nakagawa and C. Adachi,
Angew. Chem. Int. Ed., 2012, 51, 11311-11315.
K. Goushi, K. Yoshida, K. Sato and C. Adachi, Nat. Photonics,
2012, 6, 253-258.
Synthesis of DTF-PCZ. A mixture of (3,5-bis(trifluoromethyl)phenyl)-
boronic acid (2.58 g, 10 mmol) and 9-(4-bromophenyl)-9H-carbazole
(
3.86 g, 12 mmol), K
2
CO
3
(1.38 g, 10 mmol), Pd(PPh
3 4
) (0.35 g, 0.3
mmol) was dissolved in 50 ml THF : H
2
O = 1 : 1 and refluxed for 24 h 10.
H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi,
Nature, 2012, 492, 234-238.
L. S. Cui, H. Nomura, Y. Geng, J. U. Kim, H. Nakanotani and C.
Adachi, Angew. Chem. Int. Ed., 2017, 56, 1571-1575.
H. Shin, J. H. Lee, C. K. Moon, J. S. Huh, B. Sim and J. J. Kim,
Adv. Mater., 2016, 28, 4920-4925.
M. Kim, S. K. Jeon, S. H. Hwang, S. S. Lee, E. Yu and J. Y. Lee,
Chem. Commun., 2016, 52, 339-342.
T. Hatakeyama, K. Shiren, K. Nakajima, S. Nomura, S.
Nakatsuka, K. Kinoshita, J. Ni, Y. Ono and T. Ikuta, Adv.
Mater., 2016, 28, 2777-2781.
before cool down to room temperature. The resulting mixture was
dealt similar to the above mentioned process and purified through
1
1.
column chromatography to yield 3.87 g (85%) product as white
1
12.
powder. DTF-PCZ: H NMR(CDCl
3
, 400 MHz) δ 8.17 (dt, J = 7.6, 0.9
Hz, 2H), 8.07 (d, J = 8.0 Hz, 1H), 7.99 (d, J = 8.0 Hz, 1H), 7.76 – 7.67
1
1
3.
4.
(
m, 2H), 7.62 – 7.55 (m, 2H), 7.53 – 7.41 (m, 4H), 7.33 (ddd, J = 8.1,
13
6
1
1
3
4
3
.9, 1.3 Hz, 3H); C NMR(CDCl , 101 MHz) δ 141.95, 140.55, 138.63,
34.60, 130.21, 126.85, 126.12, 123.64, 122.74, 120.45, 120.36,
09.67, 95.98; Elemental Analysis: calculated: C: 68.57, H: 3.32; N:
.08; experimental: C: 68.65; H: 3.30; N: 3.05; ESI-MS: calculated: 15.
55.40, [M+1]: 456.52.
Q. Zhang, D. Tsang, H. Kuwabara, Y. Hatae, B. Li, T.
Takahashi, S. Y. Lee, T. Yasuda and C. Adachi, Adv. Mater.,
2
015, 27, 2096-2100.
Synthesis of NTN-PCZ. A mixture of (4-(9H-carbazol-9-yl)phenyl)-
1
1
6.
7.
D. R. Lee, M. Kim, S. K. Jeon, S. H. Hwang, C. W. Lee and J. Y.
Lee, Adv. Mater., 2015, 27, 5861-5867.
H. Kaji, H. Suzuki, T. Fukushima, K. Shizu, K. Suzuki, S. Kubo,
T. Komino, H. Oiwa, F. Suzuki, A. Wakamiya, Y. Murata and
C. Adachi, Nat. Commun., 2015, 6, 8476.
boronic acid (3.44 g, 12 mmol) and 5-bromo-2-(trifluoromethyl)
pyrimidine (2.27 g, 10 mmol), K
0.35 g, 0.3 mmol) was dissolved in 50 ml THF : H
refluxed for 24 h and processed similar to abovementioned
2
CO
3
(1.38 g, 10 mmol), Pd(PPh
3 4
)
(
2
O = 1 : 1 and
procedure. The final product was purified through column 18.
Y. J. Cho, B. D. Chin, S. K. Jeon and J. Y. Lee, Adv. Funct.
Mater., 2015, 25, 6786-6792.
Y. J. Cho, K. S. Yook and J. Y. Lee, Adv. Mater., 2014, 26,
chromatography to yield 3.54 g (91%) NTN-PCZ as white powder.
1
NTN-PCZ: H NMR (CDCl
3
, 400 MHz) δ 9.21 (s, 2H), 8.17 (dt, J = 7.7, 19.
4
050-4055.
0
8
1
1
.9 Hz, 2H), 7.91 – 7.78 (m, 4H), 7.53 – 7.40 (m, 4H), 7.33 (ddd, J =
1
3
20.
F. B. Dias, K. N. Bourdakos, V. Jankus, K. C. Moss, K. T.
Kamtekar, V. Bhalla, J. Santos, M. R. Bryce and A. P.
Monkman, Adv. Mater., 2013, 25, 3707-3714.
Q. Zhang, J. Li, K. Shizu, S. Huang, S. Hirata, H. Miyazaki and
C. Adachi, J. Am. Chem. Soc., 2012, 134, 14706-14709.
S. Youn Lee, T. Yasuda, H. Nomura and C. Adachi, Appl. Phys.
Lett., 2012, 101, 093306.
3
.0, 6.9, 1.3 Hz, 2H); C NMR (CDCl , 101 MHz) δ 155.73, 155.43,
40.41, 139.58, 135.36, 131.57, 128.81, 128.03, 126.20, 123.74,
21.06, 120.54, 120.51, 118.32, 109.60, 77.33, 77.22, 77.02, 76.70;
2
2
1.
2.
Elemental Analysis: calculated: C: 70.95, H: 3.62; N: 10.78;
experimental: C: 70.89; H: 3.67; N: 10.79; ESI-MS: calculated:
389.38, [M+1]: 390.54.
6
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New Journal of Chemistry
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DOI: 10.1039/C7NJ04482H
Graphical abstract
400
450
500
550
600
Wavelength (nm)
Four deep blue TADF compounds with trifluoromethyl-substituted phenyl/
N-heterocyclic rings were investigated both as hosts and guests in decent OLEDs.