Configurationally Stable Platinahelicene Enantiomers for Efficient Circularly Polarized Phosphorescent Organic Light-Emitting Diodes

Article abstract of DOI:10.1002/chem.201900955

Chiral materials with circularly polarized luminescence (CPL) are potentially applicable for 3D displays. In this study, by decorating the pyridinyl-helicene ligands with -CF₃ and -F groups, the platinahelicene enantiomers featured superior configurational stability, as well as high sublimation yield (>90 %) and clear CPPL properties, with dissymmetry factors (|g_PL|) of approximately 3.7×10^?3 in solution and about 4.1×10^?3 in doped film. The evaporated circularly polarized phosphorescent organic light-emitting diodes (CP-PhOLEDs) with two enantiomers as emitters exhibited symmetric CPEL signals with |g_EL| of (1.1–1.6)×10^?3 and decent device performances, achieving a maximum brightness of 11 590 cd m^?2, a maximum external quantum efficiency up to 18.81 %, which are the highest values among the reported devices based on chiral phosphorescent Pt^II complexes. To suppress the effect of reverse CPEL signal from the cathode reflection, the further implementation of semitransparent aluminum/silver cathode successfully boosts up the |g_EL| by over three times to 5.1×10^?3.

Full text of DOI:10.1002/chem.201900955

A Journal of
Accepted Article
Title: Configurationally stable platinahelicene enantiomers for efficient
circularly polarized phosphorescent organic light-emitting diodes
Authors: Zhi-Ping Yan, Xu-Feng Luo, Wei-Qiang Liu, Zheng-Guang
Wu, Xiao Liang, Kang Liao, Yi Wang, You-Xuan Zheng, Liang
Zhou, Jing-Lin Zuo, Yi Pan, and Hongjie Zhang
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
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the VoR from the journal website shown below when it is published
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201900955
Link to VoR: http://dx.doi.org/10.1002/chem.201900955
Supported by

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Chemistry - A European Journal
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Configurationally stable platinahelicene enantiomers for efficient
circularly polarized phosphorescent organic light-emitting diodes
Zhi-Ping Yan[a], Xu-Feng Luo[a], Wei-Qiang Liu [b], Zheng-Guang Wu[a], Xiao Liang[a], Kang Liao[a], Yi Wang[a],
You-Xuan Zheng[a]*, Liang Zhou[b]*, Jing-Lin Zuo[a]*, Yi Pan[a], Hongjie Zhang[b]
Abstract: The chiral materials with circularly polarized luminescence
(CPL) are potentially applicable for 3D display. In this study, by
decorating the pyridinyl-helicene ligands with -CF3 and -F groups, the
platinahelicene enantiomers feature superior configurational stability, as
well as high sublimation yield (>90%) and obvious CPPL property with
dissymmetry factors (|gPL|) of ∼3.7×10-3 in solution and ∼4.1×10-3 in doped
film. The evaporated circularly polarized phosphorescent organic light-
emitting diodes (CP-PhOLEDs) with two enantiomers as emitters exhibit
symmetric CPEL signals with |gEL| of 1.1~1.6×10-3 and decent device
inability to utilize triplet excitons, the internal quantum efficiency of these
fluorescent materials in organic light-emitting diodes (OLEDs) is limited to
25%.[11] On the contrary, phosphorescent materials could harvest both
singlet and triplet excitons leading to 100% internal quantum efficiency,
which plays an important role in OLEDs.[12] In 2015, our group reported
highly efficient circularly polarized phosphorescent OLEDs (CP-
PhOLEDs) with |gEL
complexes as the emitters.[13] Later, Zhao’s group also reported CP-
PhOLEDs based on chiral Ir(III) isocyanide complexes achieving the |gEL
|
of 2.6×10-3 by introducing chiral iridium(III)
|
performances, achieving
a
maximum brightness of 11590 cd/m2,
a
of 3×10-3, which is the highest value among the reported CP-PhOLEDs
based on Ir(III) complexes.[14]
maximum external quantum efficiency up to 18.81%, which are the highest
values among the reported devices based on chiral phosphorescent Pt(II)
complexes. To suppress the effect of reverse CPEL signal from the cathode
reflection, the further implementation of semitransparent aluminum/silver
cathode successfully boosts up the |gEL| by over three times to 5.1×10-3.
Among the chiral units, helicene derivatives are a type of polycyclic
compounds with non-planar skeleton forming a spiral structure which
endows them with the characteristic of chirality.[15] These unique features
make helicene an effective chiral source for constructing chiral materials
such as polymers and metallahelicenes.[16] Recently, [n]helicene derivatives
were also used in CP-POLED and CP-PhOLEDs.[17] But as we know,
conventional enantiopure [n]helicene derivatives with n≤6 are difficult to
maintain stable configuration at high temperatures,[18] meanwhile, the
reported metallahelicenes have the relatively poor thermal stability.[17b] In
light of this, these helicene derivatives are often used in solution-processed
devices, which makes them difficult to obtain high performances. For
example, Autschbach and Crassous et. al. developed a series of chiral
metallahelicenes featuring good CPPL signals, which provide efficient
access to achieve chiral transition metal complexes.[16b],16c),16d)] Later,
Fuchter group reported a solution-processed CP-PhOLED based on one of
their platinahelicenes (Scheme 1a, 1) with very high |gEL| of 0.38, but the
device performances (maximum luminance of 222 cd/m2 with current
efficiency of 0.25 cd/A) are inadequate for practical application.[16b] Hence,
it remains a significant challenge to develop configurationally stable
metallahelicenes for high performance CP-PhOLEDs with relative high
|gEL| factors.
Chirality is a common nature phenomenon,[1] and the circular dichroism
(CD) allows one to probe the chiral structure at ground state, whereas
circularly polarized luminescence (CPL) is a probe for chirality of the
excited state by default. The degree of circularly polarized
photoluminescence (CPPL) or circularly polarized electroluminescence
(CPEL) is prescribed as the dissymmetry factor (g factor) which is defined
as g = 2× ΔI /I =2 × (IL - IR)/ (IL + IR). In this way, there is no circular
polarization with the g of zero, while +2 and -2 refers to ideal left- or right-
handed CP light. To date, the CPL[2] is of great interest in optical data
storage,[3] quantum computing,[4] bioresponsive imaging,[5] optical
spintronics,[6] backlights in 3D and liquid crystal displays, etc.[7] Generally
for practical application, CP light is often obtained from nonpolarized light
by introducing filters, which could cause significant loss in term of
outcoupling efficiency with a relatively higher cost and bulky device
structures.[8] So, it is essential to develop a new generation of devices that
can emit CP light directly.
The pioneering work of CPEL could date back to 1997, Meijer and co-
worker used a chiral-substituted poly(p-phenylenevinylene) derivative for
fabricating polymer organic light-emitting diode (POLED) with evident
CPEL properties.[9] Recently, Nuzzo et. al. adopted enantiomerically pure
poly(fluorine-alt-benzothiadiazole) (c-PFBT) as a light-emitting material
achieving high levels of circular polarization of electroluminescence with
gEL reaching -0.8 by the molecular self-assembles.[10] However, due to the
a)
This work
Reported
CF3
CF3
N
tBu
tBu
tBu
tBu
O
O
N
N
N
O
O
O
O
Pt
Pt
Pt
OCH3
Platinahelicene 1
F
F
Helicene 2
P-Pt
M-Pt
B(OH)2
CF3
N
b)
O
CF3
Br
CF3
CF3
F
[a]
Mr. Z.-P. Yan, Mr. X.-F. Luo, Dr. Z.-G. Wu, Mr. X. Liang, Mr. K. Liao,
Dr. Y. Wang, Prof. Y.-X. Zheng, Prof. J.-L. Zuo, Prof. Y. Pan
State Key Laboratory of Coordination Chemistry, Collaborative
Innovation Center of Advanced Microstructures, Jiangsu Key
Laboratory of Advanced Organic Materials, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing, 210023, P. R.
China.
tBu
N
O
N
i
N
O
Pt
O
F
iii,iv
v,vi
tBu
PPh3
F
F
Br
PPh3Br
1a
-Pt
(P/M)
ii
E-mail: yxzheng@nju.edu.cn, zuojl@nju.edu.cn
Mr. W. Q. Liu, Prof. L. Zhou, Prof. H. J. Zhang
State Key Laboratory of Rare Earth Resource Utilization,
Changchun Institute of Applied Chemistry, Chinese Academy of
Sciences, Changchun 130022, P.R. China
Scheme 1. a) Chemical structures of reported helicene dopants,
platinahelicene and the (P/M)-Pt complex studied in this work; b) Synthetic
procedures of the (P/M)-Pt complex: i) Pd(PPh3)4, K2CO3, THF : H2O = 3 : 1,
75 oC, 10 h; ii) THF, reflux, 10 h; iii) n-BuLi, THF, -70 oC, 5 min, then rt, 30 min,
then 2 h; iv) Propylene oxide, I2, hv, toluene, 4 h; v) EtOCH2CH2OH : H2O = 3 :
1, 100 oC, 16 h; vi) EtOCH2CH2OH, 90 oC, 10 h.
[b]
E-mail: zhoul@ciac.ac.cn
Supporting information for this article is given via a link at the end of
the document.
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In most cases, the fluorine-containing moieties can increase the
volatility and emission intensity of the metal complexes. In this work, a
novel helical core decorated with -F and -CF3 groups was adopted as
cyclometallated ligand for chiral platinahelicene complex ((P/M)-Pt,
Scheme 1a) with good configurational stability which can be evaporated
without changing the CPL property. Generally, the evaporated OLEDs
always show better performances than the solution-processed OLEDs,
including higher efficiency and lower efficiency roll-off. Therefore, the
evaporated CP-PhOLEDs employing P-Pt and M-Pt enantiomers manifest
higher external quantum efficiency (EQE) up to 18.8% with |gEL| of 1.1-
1.6×10-3. In addition, by evaporating the semitransparent electrode in the
devices, the |gEL| value could be increased to 3.7-5.1×10-3.
1a (Figure S14c), there are two peaks at 229 and 280 nm which can be
ascribed to the spin-allowed π-π* transitions of the ligands. Moreover, due
to the strong spin-orbital coupling effect of the transition metal, it shows a
wide and low energy band ranging from 350 to 500 nm, which belongs to
the mixed singlet and triplet MLCT (metal-to-ligand charge-transfer)
transitions. On the other hand, the location of transition can also be
simulated by theoretical calculations (Table S5). For example, the excited
state 1 is dominant by HOMO-LUMO transition (2.7 eV, 450 nm) which is
generated by the large conjugate system with the Pt(Ⅱ) center (Figure S19).
Meanwhile, the photoluminescence spectrum of (P/M)-Pt complex at room
temperature demonstrates the main emission peak at 612 nm with the
Commission Internationale de L'Eclairage (CIE) coordinates of (0.63, 0.36).
When measured at 77 K, the emission peak is hypochromatic shift to 599
nm with a shoulder peak at 640 nm, which could be assigned to 1MLCT and
3MLCT,[20] respectively. Furthermore, the phosphorescence lifetime of
(P/M)-Pt is 15.7 μs (Figure S14b) and the absolute photoluminescence
quantum yield (PLQY) is 0.27 (Figure S14a), which is in the range of
reported Pt(II) complexes.[21]
As shown in Scheme 1b, the helicene derivative 2-(4-
fluorobenzo[c]phenanthren-1-yl)-5-(trifluoromethyl)pyridine
1a
was
chosen as the cyclometalated ligand which could be prepared by the
reported method (Supporting information).[16b] Though the helical curvature
(hc, the angle between two terminal helicene rings) of 1a is 39o, it is hard to
be separated into configurationally stable enantiomers due to the rapid
racemization at room temperature. However, for the presence of
coordination bond, platinahelicene complex (P/M)-Pt is configurationally
stable, which could be separated into two enantiomers P-Pt and M-Pt with
enantiomeric purity higher than 99% by using chiral HPLC (Figure S10 and
S11).
450
300
150
0
45
30
15
0
Abs
PL at 298 K
PL at 77 K
(b)
(a)
P-Pt
M-Pt
-150
-300
-450
-15
-30
-45
Thermal and configurational stability of the chiral emitter is a vital
parameter for fabricating evaporated CP-PhOLEDs. The thermogravimetric
analysis (TGA, Figure S20) curve of (P/M)-Pt gives the decomposition
temperature (Td, 5% loss of weight) up to 294oC. The introduction of large
sterically hindered groups weakens the accumulation between molecules, as
a consequence, the enantiomers hold relatively low sublimation temperature
at around 200 oC under vacuum of 1×10-4 Pa with over 90% sublimation
yield. Furthermore, the configuration of these enantiomers can be well
preserved with ee value of over 99% (Figure S12 and S13).
300 400 500 600 700 800
Wavelength (nm)
300 400 500 600 700 800
Wavelength (nm)
9
6
9
6
M-Pt
P-Pt
M-Pt
(d)
(c)
P-Pt
3
3
0
0
-3
-6
-9
-3
-6
-9
550 600 650 700 750 800
Wavelength (nm)
550 600 650 700 750 800
Wavelength (nm)
Figure 2. Photophysical properties in CH2Cl2 (5×10-5 mol/L): a) Normalized
absorption and PL spectra of (P/M)-Pt; b) CD and CPPL spectra of P-Pt and
M-Pt; c) gPL vs wavelength curves of P-Pt and M-Pt; d) gPL vs wavelength
curves of P-Pt and M-Pt in 26Dczppy film (4 wt%).
CD and CPL spectra further characterized the chiroptical properties of P-
Pt and M-Pt enantiomers. As illustrated in Figure 2b, P-Pt shows obvious
negative and positive Cotton effect at 249 and 313 nm, meanwhile, M-Pt
displays the opposite signals at the same positions. Consequently, the
spectrograms of P and M configurations form symmetric “S” type from 350
to 220 nm indicating of the right- and left-handed helix,[22] consistent with
their single crystal structures. Relatively weak Cotton effect observed in the
range of 400 - 500 nm is generated by the MLCT process, which further
confirms the metal participate in the large chiral conjugate system. As for
the CPPL spectra and gPL curves (Figure 2b and 2c), P-Pt and M-Pt show
perfectly symmetrical spectra at 500-800 nm with the gPL of ±3.7×10-3 in
CH2Cl2 solution. To simulate the state of the device, the CPPL properties of
the film with 4 wt% of P-Pt and M-Pt in the host material 26DCzppy (2,6-
bis(3-(9H-carbazol-9-yl)phenyl)pyridine) prepared through vacuum
evaporation were also investigated. As depicted in Figure 2d, the gPL values
of P-Pt and M-Pt doped films are slightly higher than that in the solution
state with the gPL value up to -4.1×10-3 and 4.9×10-3, respectively.
Figure 1. Oak Ridge thermal ellipsoidal plot (ORTEP) diagrams of P-Pt (left)
and M-Pt (right).
The single crystal diffraction analysis confirmed the preconceived
molecular structures. As shown in Figure 1, both enantiomers adopt twisted
planar structures with perfect mirror symmetry. The twist angle between
pyridine and the coordinate five-membered ring is 10.9o, and the
consecutive twist angles between the fused rings (18.4o, 12.5o, 12.4o and
11.3o) lead to hc value of 59o, which are similar to the reported values in
[6]helicene derivatives (hc ~50o).[19] Therefore, both enantiomers possess
non-planar skeleton forming spiral structures with inherent chirality.
The ultraviolet-visible (UV-vis) absorption and photoluminescence (PL)
spectra of (P/M)-Pt complex are depicted in Figure 2a and the relevant data
are demonstrated in Table S3. Compared with the absorption spectrum of
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Meanwhile, the CPPL spectra for the reported plantiahelicne 1 (Scheme 1a)
were also measured in the same test condition with the |gPL| around 6.5×10-3
in CH2Cl2 solution and 4.5×10-3 in doped film (Figure S31), which is similar
to our work.
HATCN (0.2 wt%) : TAPC (50 nm)/ P-Pt or M-Pt (4 wt%) : TcTa (4,4',4''-
tris(carbazol-9-yl)triphenylamine, 10 nm)/ P-Pt or M-Pt (4 wt%)
:
26DCzPPy (10 nm)/ Tm3PyP26PyB (60 nm)/ LiF (1 nm)/ Al (100 nm)
(Figure S21), which were named as P-DD and M-DD, respectively. As is
well known, the double-emissive-layer structures structure can theoretically
broaden the electron-hole recombination region which would enhance the
utilization of electron-hole pairs and suppress the efficiency roll-off.
Notably, due to the increase of device thickness, P-DD and M-DD show
slightly higher turn-on voltages of 3.2 and 3.4 V, respectively. However, the
device performances were further improved with the Lmax of 9732 cd/m2, the
ηc,max of 19.52 cd/A and the EQEmax of 16.29%, the ηp,max of 15.39 lm/W for
P-DD, and 11590 cd/m2, 22.52 cd/A, 18.81%, 18.62 lm/W for M-DD,
respectively. At the practical brightness of 100 cd/m2, the current
efficiencies of P-DD and M-DD are still as high as 19.11 and 21.34 cd/A,
respectively. The efficiency roll-off ratio for both devices are favorable in
terms of OLEDs display. Due to the long lifetime (τ298 K ≈ 20 μs) in the
doped film (Figure S15), the triplet-triplet annihilation (TTA) becomes
serious at high brightness leading to a relatively large efficiency roll-off. For
example, at the brightness of 1000 cd/m2, the current efficiencies of P-DD
and M-DD are maintained at 12.20 and 15.43 cd/A, respectively.
Considering the efficient phosphorescence and CPPL properties of two
enantiomers, the CP-PhOLEDs using 4 wt% P-Pt or M-Pt co-doped with
26DCzppy host as the emissive layers were then investigated. The devices
with the single emissive layer of ITO/ HATCN (hexa-azaztriphenylene-
hexacabonitrile, 6 nm)/ HATCN (0.2 wt%) : TAPC (di-[4-(N,N-ditolyl-
amino)-phenyl] cyclohexane, 50 nm)/ P-Pt or M-Pt (4 wt%) : 26DCzPPy
(10 nm)/ Tm3PyP26PyB (1,3,5-tris(6-(3-(pyridin-3-yl)phenyl)pyridin-2-
yl)benzene, 60 nm)/ LiF (1 nm)/ Al (100 nm) were named as P-SD and M-
SD, respectively. The schematic energy diagrams of devices and structures
of relevant materials were depicted in the Figure S21. Both P-SD and M-SD
devices were turned on at low voltages of 3.2 and 3.1 V, respectively, with
good performances that the maximum luminance (Lmax), maximum current
efficiency (ηc,max), external quantum efficiency (EQEmax
) and power
efficiency (ηp,max) are 8424 cd/m2, 18.8 cd/A 16.26% and 16.97 lm/W for P-
SD, 9425 cd/m2, 19.09 cd/A, 15.15% and 17.64 lm/W for M-SD,
respectively.
All devices emit red light which are almost identical to the PL spectra of
the (P/M)-Pt complex, suggesting that the EL spectra derive from the triplet
excited state of the phosphors. Owing to the configurational stability of the
platinahelicene enantiomers, the two enantiomer-based CP-PhOLEDs still
display obvious CPEL property (Figure 3c) with opposing dissymmetry
factor (gEL) signals of -1.6×10-3 for P-SD, 1.1×10-3 for M-SD, -1.6×10-3 for
P-DD and 1.4×10-3 for M-DD (Figure 3d), respectively. Although the
resulting |gEL| values are not as high as those CP-OLEDs based on the chiral
lanthanide complexes and chiral polymers,[10,23] the luminance and
efficiency of the phosphorescent emission CP-OLEDs were improved
greatly, especially for devices with chiral Pt(II) phosphors as emitters.
(a)
(b)
20
10
10
104
103
102
101
1.0
0.8
0.6
0.4
0.2
0.0
P-SD
M-SD
P-DD
M-DD
P-SD
M-SD
P-DD
M-DD
200
400
600
800 1000
2
3 4 5 6 7 8 9 10
Wavelength (nm)
Voltage (V)
10
100
1000
10
100
1000
2
2
Luminance (cd/m )
Luminance (cd/m )
M-SD
M-DD
M-SD
M-DD
(d)
(c)
3.0
1.5
10
5
M-TSD bw
P-TSD bw
M-TSD fw
P-TSD fw
45
30
15
(a)
30
15
0
(b)
0
0.0
0
-5
-10
-1.5
-3.0
-15
-30
-45
-15
-30
P-SD
P-DD
P-SD
P-DD
500 550 600 650 700 750 800 850
Wavelength (nm)
500 550 600 650 700 750 800 850
Wavelength (nm)
500 550600 650 700 750800 850
Wavelength (nm)
550 600 650 700 750 800
Wavelength (nm)
15
M-TSD bw
P-TSD bw
M-TSD fw
P-TSD fw
10
(d)
(c)
10
5
5
0
Figure 3. Characteristics of P/M-SD and P/M-DD devices: a) External quantum
efficiency- luminance (EQE) curves and normalized EL spectra at 100 mA; b)
Current efficiency-luminance (ηc-L) and current density-luminance-voltage (J-L-
V) curves; c) CPEL spectra; d) gEL vs wavelength curves.
0
-5
-5
-10
-15
550
-10
550
600
650
700
750
800
600
650
700
750
800
Wavelength (nm)
Wavelength (nm)
Figure 4. a) CPEL spectra of forward side of M-TSD and P-TSD devices; b)
CPEL spectra of backward side of M-TSD and P-TSD devices; c) gEL vs
wavelength curves of forward side of M-TSD and P-TSD devices; d) gEL vs
wavelength curves of backward side of M-TSD and P-TSD devices.
Table 1. EL performances of the devices based on P-Pt and M-Pt.
a
b
c
d
e
f
g
Von
Lmax
ηc,max
ηc,L1000
EQEmax
(%)
ηp,max
gEL
Device
(V)
(cd/m2)
8424
(cd/A)
(cd/A)
(lm/W)
(10-3)
-1.6
P-SD
M-SD
P-DD
M-DD
3.2
18.8
9.27
16.26
15.15
16.29
18.81
16.97
3.1
3.2
3.4
9425
9732
19.09
19.52
22.52
11.42
12.2
17.64
15.39
18.62
1.1
-1.6
1.4
It is found that the gEL values are distinctly smaller than the
corresponding gPL values both in solution and film. According to the
hypothesis of Bari and co-workers,[23b] the spiral direction of CP light would
reverse after the reflection from cathode, which would impair the degree of
circular polarization. In order to reduce this effect, devices with
aluminum/silver (Al/Ag) as semitransparent cathode were then fabricated
with configuration of ITO/ HATCN (6 nm)/ HATCN (0.2 wt%) : TAPC (50
nm)/ P-Pt or M-Pt (4 wt%) : 26DCzPPy (10 nm)/ Tm3PyP26PyB (60 nm)/
11590
15.43
a) Turn-on voltage recorded at
a
luminance of 1
cd/m2. b) Maximum
luminance. c) Maximum current efficiency. d) Current efficiency at 1000 cd/m2.
e) Maximum external quantum efficiency. f) Maximum power efficiency. g) gEL
around maximum emission peak.
In order to further improve the EL performances, double emissive layers
devices were also fabricated with configuration of ITO/ HATCN (6 nm)/
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K. Ho, A. Alsimaree, O. Woodford, P. Waddell, J. Bogaerts, W. Herrebout, J.
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Polzik, Nature 2006, 443, 557-560.
LiF (1 nm)/ Al (4 nm)/ Ag (50 nm), which were denoted as P-TSD and M-
TSD, respectively, and their performances are presented in Figure S26 and
Table S8. Because of the reduction of cathode thickness, the cathode could
maintain nearly 50% transmittance (Figure S23) and the CP light could be
emitted from both the forward direction (through the ITO glass, fw) and the
backward direction (through the semitransparent cathode, bw). The Lmax and
ηc,max are 4403 cd/m2 and 10.11 cd/A for the fw of P-TSD, 8716 cd/m2 and
15.95 cd/A for the fw of M-TSD, 145 cd/m2 and 0.77 cd/A for the bw of P-
TSD, 203 cd/m2 and 0.81 cd/A for the bw of M-TSD, respectively.
Although the performances of these semitransparent devices are poorer than
[3]
[4]
[5]
[6]
M. C. Heffern, L. M. Matosziuk, T. J. Meade, Chem. Rev. 2014, 114, 4496-
4539.
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Lett. 2011, 98, 162508.
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Adv. Mater. 2001, 13, 577-580.
the regular device due to the immature preparation technology, the |gEL
|
values did improve in both sides.
[9]
E. Peeters, M. Christiaans, R. Janssen, H. Schoo, H. Dekkers, E. W. Meijer, J.
Am. Chem. Soc. 1997, 119, 9909–9910.
Compared with the normal single emissive layer P-SD and M-SD
devices, the gEL values of P-TSD and M-TSD measured from the fw
increase slightly with the values of -2.5×10-3 and 2.2×10-3 (Figure 4c),
presumably due to the weakened reflection of light by the semitransparent
cathode. Owing to the elimination of reflection effects, the gEL values of P-
TSD and M-TSD detected from the bw are improved dramatically with the
gEL values of -3.7×10-3 and 5.1×10-3 (Figure 4d), which are comparable to
the gPL data in solution and film. Due to the poor device performance of bw,
it is hard to maintain the brightness of the bw, which leads to a rough CPEL
curve and a little offset of the peak position. But it shows obvious opposite
CPEL signals, more importantly, these increased gEL values clearly
demonstrate that the reflection effects could be suppressed by utilizing
semitranparent devices. As a result, the strategy would be beneficial for
showing CPEL properties of the material and the |gEL| values could show
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a
thermally and configurationally stable chiral
platinahelicene complex was synthesized and the enantiomers possess
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This work was supported by the National Natural Science Foundation of
China (51773088, 21771172).
Keywords: chiral platinahelicene • dissymmetry factor • CP-PhOLEDs •
high efficiency • semitransparent device
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10.1002/chem.201900955
Chemistry - A European Journal
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
Zhi-Ping Yan[a], Xu-Feng Luo[a], Wei-Qiang
Liu[b], Zheng-Guang Wu[a], Xiao Liang[a]
,
Kang Liao[a]
,
Yi Wang[a]
,
You-Xuan
Zheng[a]*, Liang Zhou[b]*, Jing-Lin Zuo[a]*
Yi Pan[a], Hongjie Zhang[b]
,
Page No. – Page No.
Configurationally stable platinahelicene
enantiomers for efficient circularly
polarized phosphorescent organic light-
emitting diodes
Two platinahelicene enantiomers with configurational stability and good CPPL property were used as emitters in efficient evaporated circularly
polarized phosphorescent organic light-emitting diodes (CP-PhOLEDs), achieving a maximum brightness of 11590 cd/m2, a maximum external
quantum efficiency up to 18.81% and symmetric CPEL signals with |gEL| of 1.1~1.6×10-3. The further implementation of semitransparent
silver/aluminum cathode successfully boosts up the |gEL| by over three times to 5.1×10-3.
This article is protected by copyright. All rights reserved.