Emitters with a pyridine-3,5-dicarbonitrile core and short delayed fluorescence lifetimes of about 1.5 μs: Orange-red TADF-based OLEDs with very slow efficiency roll-offs at high luminance

Article abstract of DOI:10.1039/c8tc01698d

The efficiency roll-off with increasing brightness in thermally activated delayed fluorescence (TADF)-based OLEDs greatly impedes their future applications. The combination of varying numbers of phenoxazine (PXZ) donors with pyridine-3,5-dicarbonitrile (PCN) acceptors has afforded three orange-red TADF emitters PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN. The singlet-triplet energy gap (ΔE_ST) of the molecules is in good agreement with that predicted by corrected time-dependent density functional theory. When bis-PXZ-PCN is doped into the host material CBP (10 wt%), the ΔE_ST value of 0.04 eV is achieved, and this facilitates effective reverse intersystem crossing (RISC, k_RISC = 9.8 × 10⁵ s^-1). Bis-PXZ-PCN endows its device with orange-red electroluminescence peak at 600 nm, accompanied by maximum external quantum efficiency of 9.8% and an impressive slow efficiency roll-off of 15% at a high luminance of 1000 cd m^-2, which is among the lowest roll-off value of the reported orange-red to red TADF-based OLEDs.

Full text of DOI:10.1039/c8tc01698d

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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JPolueransael odfoMnaotetraiadljsuCsht emmairsgtriynsC
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DOI: 10.1039/C8TC01698D
Journal Name
ARTICLE
Pyridine-3,5-dicarbonitrile cored emitters with short delayed
fluorescence lifetimes of about 1.5 μs: orange-red TADF based
OLEDs with very slow efficiency roll-offs at high luminance
Received 00th January 20xx,
Accepted 00th January 20xx
Zhanxiang Chen,a Zhongbin Wu,c Fan Ni,a Cheng Zhong,a Weixuan Zeng,a Danqing Wei,a Kebin An,a
Dongge Ma*c,d and Chuluo Yang*a,b
DOI: 10.1039/x0xx00000x
www.rsc.org/
The efficiency roll-off with increasing brightness in thermally activated delayed fluorescence (TADF)-based OLEDs greatly
impedes their future applications. The combination of varying number of phenoxazine (PXZ) donor with pyridine-3,5-
dicarbonitrile (PCN) acceptor has afforded three orange-red TADF emitters of PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN. The
singlet-triplet energy gap (∆EST) of the molecules is good agreement with that predicted by corrected time-dependent
density functional theory. When doped into the host material of CBP (10 wt%), the ∆EST value of 0.04 eV in bis-PXZ-PCN was
achieved to facilitate effective reverse intersystem crossing (RISC, kRISC = 9.8 × 105 s-1). Bis-PXZ-PCN endowed its device with
orange-red electroluminescence peak at 600 nm, accompanied by maximum external quantum efficiency of 9.8% and an
impressive slow efficiency roll-off of 15% at a high luminance of 1000 cd.m−2, which is among the lowest roll-off value of the
reported orange-red to red TADF-based OLEDs so far.
maintain high efficiency at high luminescence.22 The triplet
excitons are easily quenched at high current density through
multi-particle quenching channels of triplet-triplet annihilation
(TTA) and triplet-polaron quenching (TPQ).23,24 Thus, it is
essential to reduce the triplet exciton density for improving the
roll-off behavior by delicately tuning of the structure-property
relationships in orange-red TADF emitters.
A practical strategy has been employed to enhance the high-
brightness performance in blue and green TADF-based OLEDs
by decreasing ∆EST and the excited-state lifetime of the used
emitters.25-29 Recently, our group revealed an efficient channel
to fulfill high-performance solution-processed OLEDs with slight
efficiency roll-off.16 Increasing the donor number of substitution
groups in a series of triarylboron-based emitters effectively
reduce the ∆EST and shorten the exciton lifetime. At the same
time, through similar strategy in the emitters, Xu et al.30
reported a series of phosphine oxide-based emitters with
gradually decreased ∆EST and high-efficiency TADF-based OLEDs
featuring slow efficiency roll-off at high luminance. These
positive results inspired us to take the same strategy to tackle
efficiency roll-off in orange-red TADF-based OLEDs. In this work,
a series of branched D-π-A systems with pyridine-3,5-
dicarbonitrile (PCN) as the acceptor moiety, phenoxazine (PXZ)
as donor moiety and phenyl (Ph) as π-conjugated bridge,
Introduction
In recent years, thermally activated delayed fluorescence (TADF)
materials have aroused continuous interest due to the unity
internal electroluminescence quantum efficiency in theory.1-6
Efficient thermal activated conversion of triplet excitons into
singlet ones in TADF materials is achieved in donor-acceptor (D-
A) type pre-twisted molecules featuring with well separation of
the highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO), which can lead to a small
energy gap (∆EST) between the lowest singlet excited state and
the lowest triplet excited state.7-19 Given the prevalence of the
energy gap law, large non-radiative internal conversion rates
(kIC) from the lowest singlet states (S1) poses a substantial
barrier to the photoluminescence quantum yield (PLQY) of
orange-red TADF materials, even when the frontier molecular
orbital (FMO) overlaps in a certain degree.20,21 And the more
noteworthy issue for orange-red TADF-based OLEDs is how to
a.Hubei Key Lab on Organic and Polymeric Optoelectronic Materials, Department of
Chemistry, Wuhan University, Wuhan 430072, P. R. China. E-mail:
clyang@whu.edu.cn
b.Shenzhen Key Laboratory of Polymer Science and Technology, College of
Materials Science and Engineering, Shenzhen University, Shenzhen 518060, P. R.
China.
namely
4-(4-(10H-phenoxazin-10-yl)phenyl)-2,6-
c. State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China.
d.State Key Laboratory of Luminescent Materials and Devices, Institute of Polymer
Optoelectronic Materials and Devices, South China University of Technology,
Guangzhou 510640, P. R. China. E-mail: msdgma@scut.edu.cn
†Electronic Supplementary Information (ESI) available: Experimental details; DSC
and TGA, CV curves; PL and EL spectra; theoretical data; characteristics of these
devices. CCDC 1821566 and 1821567. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/x0xx00000x
diphenylpyridine-3,5-dicarbonitrile (PXZ-PCN), 2,6-bis(4-(10H-
phenoxazin-10-yl)phenyl)-4-phenylpyridine-3,5-dicarbonitrile
(bis-PXZ-PCN)
yl)phenyl)pyridine-3,5-dicarbonitrile
and
2,4,6-tris(4-(10H-phenoxazin-10-
(tri-PXZ-PCN), were
designed and synthesized. The selection of pyridine ring was
due to its high T1 energy level as well as its strong electron
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Fig. 2 Pictorial representation of natural transition orbitals (hole and particle) of the S1
and T1 states for PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN. The weight of the hole-particle
contribution to the excitation is also included.
Theoretical calculations
Fig. 1 (a)The optimized geometries and frontier molecular orbitals (FMOs) obtained from
density functional theory calculations [B3LYP; 6-31G(d)] for the ground states (S0) of PXZ-
PCN, bis-PXZ-PCN and tri-PXZ-PCN. (b) Single crystal structure of PXZ-PXN and bis-PXZ-
PCN without showing hydrogen atoms.
Ground state optimizations of these molecules were
investigated by density functional theory (DFT) calculations at
the B3LYP/6-31G(d) level of theory.31 In Fig. 1, the HOMO
positions of the three molecules are mainly located in PXZ
segment, whereas the LUMOs are mainly spread on the
pyridine-3,5-dicarbonitrile (PCN) core, indicating the adequate
HOMO-LUMO spatial separation. The optimized geometries of
the three molecules demonstrate large torsion angles between
the acceptor and the donor parts. The dihedral angles between
PXZ and the connected phenyl are evaluated to be
approximately 76o for PXZ-PCN, 72o for bis-PXZ-PCN and 71o for
tri-PXZ-PCN. Furthermore, single crystals of PXZ-PCN and bis-
PXZ-PCN were also obtained by slow evaporation of solvent
from n-hexane/trichloromethane mixed solutions and
examined by X-ray analysis. The geometrical parameters of the
optimized ground states of PXZ-PCN and bis-PXZ-PCN are in
good agreement with their crystallographic information (Fig. 1).
As to obtain the low-lying excitation energies, natural
transition orbitals (NTO) describing the S1 and T1 excitations of
the three molecules were calculated (Fig. 2). Linear-response
time-dependent density functional theory (TD-DFT) was applied
by using the functional (TD-LC-ωPBE) and basis set (6-31G(d)).
According to the calculation results, the increasing numbers of
PXZ donor moieties lead to the decreasing S1 and T1 energies
levels (Table 1). To better figure out the nature of the S1 and T1
excited states, it is valuable to involve the NTO analysis. It is
noted that the “hole” and “particle” of the S1 states in the three
emitters mainly distribute on the phenoxazine donor and
pyridine-3,5-dicarbonitrile acceptor moieties, respectively.
Thus, PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN show the charge-
withdrawing property. The incorporation of two cyano (CN)
units at the 3,5-position of pyridine core efficiently deepened
the LUMO level and contributed to the red emission of the three
molecules. As a proof of concept, one, two or three
phenoxazine donors attached to the π bridge were connected
with the PCN core to construct the intramolecular charge
transfer (ICT) emission, respectively. PXZ-PCN, bis-PXZ-PCN and
tri-PXZ-PCN realized red emission with high fluorescent
quantum yields. In the three emitters, tri-PXZ-PCN showed the
reddest emission at around 649 nm in toluene solution. Bis-PXZ-
PCN with the smallest ∆EST and the largest kRISC demonstrated
the shortest delayed fluorescence (DF) lifetime of 1.4 μs. After
the elaborative OLED device fabrication, the bis-PXZ-PCN-based
OLED device exhibited the orange-red emission of 600 nm with
a maximum external quantum efficiency (EQE) of 9.8% and an
impressive slow efficiency roll-off of 15% at a high luminance of
1000 cd.m−2.
Results and discussion
Synthesis and thermal properties
PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN were synthesized via a
palladium-catalyzed C-N cross-coupling of phenoxazine (PXZ)
with the corresponding chlorinated precursors in good yields.
1
The three compounds were identified by H NMR, 13C NMR
spectroscopy and high resolution mass spectrometry. The glass
transition temperature (Tg) through differential scanning
calorimetry (DSC) and decomposition temperature (Td) with 5%
weight loss in the thermal gravimetric analysis (TGA) were
measured to be 141 oC and 318 oC for PXZ-PCN, 166 oC and 418
oC for bis-PXZ-PCN, 181 oC and 517 oC for tri-PXZ-PCN (Figure S7
and Table S2, ESI†), respectively, which demonstrate their ideal
thermal stabilities for vacuum-deposited OLED devices.
transfer (CT) type transitions for S0→S1 excitaions. But for the
T1 states, due to the weak D-A electronic coupling originating
from its nearly perpendicular structure, the hole and electron
wavefunctions for PXZ-PCN are confined on the central phenyl-
pyridine-carbonitrile molecular fragment demonstrating the
characteristic of a locally excited state. Interestingly, the NTO
hole and electron wavefunctions of the S0→T1 excitaions for bis-
2 | J. Name., 2012, 00, 1-3
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PXZ-PCN and tri-PXZ-PCN primarily distribute on the
phenoxazine fragment and pyridine-3,5-dicarbonitrile acceptor
moieties, respectively. Thus, the T1 states have a charge-
transfer excitation. This difference in T1 state characters can be
explained well in terms of the molecular structures. The
dihedral angles between phenylene bridge at the 2,6-positoin
of pyridine and PCN acceptor are about 33o in all the three
molecules, while the dihedral angle between phenylene bridge
at the 4-positoin of pyridine and PCN acceptor is 65o, owing to
steric hindrance of two cyano groups. As a result, the energy of
the 3CT state is lower than the energy of the 3LE state in bis-PXZ-
PCN and tri-PXZ-PCN while the situation is the opposite in PXZ-
PCN (see Fig. S17, ESI†).
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DOI: 10.1039/C8TC01698D
Photophysical properties
The effects of attaching different numbers of PXZ donor are
particularly prominent on the UV-Vis absorption, fluorescence
and phosphorescence spectra. PXZ-PCN, bis-PXZ-PCN and tri-
PXZ-PCN in the toluene solution exhibit predominantly π-π*
absorption and weak charge-transfer (CT) absorption from the
HOMO of the PXZ donor to the LUMO of the pyridine-3,5-
dicarbonitrile (PCN) acceptor. As shown in Fig. 3, the
fluorescence spectra of the three molecules in toluene solution
exhibit broad emission bands. With increasing number of the
donor units, obvious red-shift in emission maxima for mono-,
bis- and tri-PXZ-PCN is observed from 616, 640 to 649 nm. The
phosphorescent emission spectra of PXZ-PCN, bis-PXZ-PCN and
tri-PXZ-PCN measured at 77 K in doped CBP (4,4'-di(9H-
carbazol-9-yl)-1,1'-biphenyl) films (10 wt%) are centered on 555,
596 and 600 nm, respectively. From the onset of their
fluorescence and phosphorescence spectra in the CBP host (10
wt%), the singlet/triplet energies are calculated to be 2.53/2.52
eV, 2.34/2.30 eV, 2.34/2.29 eV, respectively. Thus, the ∆ESTs for
PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN are estimated to be 0.01
eV, 0.04 eV and 0.05 eV, respectively. The rather small ∆ESTs of
the three molecules imply the TADF characters with efficient
RISC of exciton from the T1 to the S1 state.
Fig. 3 (a) UV-Vis absorption spectra and steady-state fluorescence spectra of the three
emitters in toluene solution (1.0 × 10-4 M). (b) UV-Vis absorption spectra, fluorescence
spectra (both measured at room temperature) and phosphorescence spectra (measured
at 77 K) of the three emitters doped into CBP films (10 wt%). (c) Transient decay spectra
of the three emitters doped into CBP films (10 wt%) measured at 300 K. (d) Emission
decay profiles of bis-PXZ-PCN doped into CBP films (10 wt%) measured at various
temperatures.
exhibit two components, of which one is the prompt portion
derived from the direct S1
17.7 ns for bis-PXZ-PCN, 16.2 ns for tri-PXZ-PCN) and the other
is the delayed portion resulted from the recursive S1 S0
→ S0 transition (12.9 ns for PXZ-PCN,
→
transition (1.6 μs for PXZ-PCN, 1.4 μs for bis-PXZ-PCN and 1.5 μs
for tri-PXZ-PCN). Moreover, as to validate the TADF mechanism,
the temperature dependence spectra of the three compounds
doped into CBP films (10 wt%) were measured from 77 K to 300
K (see Fig. 3 (d) and Fig. S9-S10, ESI†). The delayed component
exhibits an obvious temperature dependence, which
demonstrated the essential role of a thermally activated
mechanism in the promotion of the delayed emission. As the
transient PL decay curve at 300 K in argon atmosphere fitted
well in a double-exponential function, the prompt (τp) and
delayed fluorescence lifetimes (τd) as well as the prompt (Фp)
and delayed fluorescence PLQY (Фd) can be extracted for
successive calculation. kp, kd, kISC, kRISC are estimated using the
In order to validate our design of introducing donors to
monitor the transient photoluminescence (PL) lifetime, the
corresponding transient PL decay profiles in the doped films
were recorded at 300 K, respectively. As shown in Fig. 3, the PL
lifetimes of PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN obviously
formulas (see Equations (1)-(5), ESI†), with the assumption that
20,32
kRISC >> kr,T+knr,T
.
Table 1 Photophysical data for the investigated compounds
e
e
f
g
g
h
h
h
h
Compound
λabs,max
(nm)
sola
419
460
λem,max
(nm)
sola/filmb
616/565
640/601
649/606
S1c,d(eV)
T1c,d(eV)
∆ESTc,d(eV)
τp
(ns)
τd
ΦPL
Φp
Φd
kp
kd
kISC
kRISC
(μs)
(%)
(%)
(%)
(×107
s-1)
7.8
5.6
6.2
(×105
s-1)
6.3
7.1
6.8
(×107
s-1)
1.8
1.5
1.4
(×105
s-1)
8.3
9.8
8.8
PXZ-PCN
bis-PXZ-PCN
tri-PXZ-PCN
2.53 (2.58) 2.52 (2.40) 0.01 (0.18) 12.9
2.34 (2.15) 2.30 (2.14) 0.04 (0.01) 17.7
2.34 (2.25) 2.29 (2.05) 0.05 (0.20) 16.2
1.58
1.40
1.48
57
36
34
44
26
26
13
10
8
460
a Measured in toluene solution at room temperature (10-4 M). b Measured in doped CBP films at room temperature (10 wt%). c Experimental data were determined from
onsets of the fluorescence and phosphorescence spectra of the three emitters doped into CBP films (10 wt%). d Data were estimated from TD-DFT simulations. e The
prompt and delayed fluorescence lifetimes of the investigated molecules doped into CBP films (10 wt%) at 300 K under oxygen-free conditions. f Absolute PL quantum
yields for the investigated molecules doped into CBP (10 wt%) evaluated using an integrating sphere under oxygen-free conditions at room temperature. g The prompt
or delayed fluorescence PLQY under oxygen-free conditions. h The rate constants of the prompt fluorescence, the delayed fluorescence, ISC or RISC processes.
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Fig. 4 (a) Schematic diagrams of the basic structures of quadruple-layer device and the chemical structures of the materials used for OLED fabrication. (b) Energy level alignment of
all the materials used in the current study showing electron injection and hole extraction. (c) Current density-voltage (J-V) and luminance-voltage (L-V) characteristics of the devices.
Inset: normalized EL spectra of the divices on the operation voltages of 9 V. (d) EL characteristic plots of the devices: external quantum efficiency (EQE), current efficiency (CE) and
power efficiency (PE) versus luminance.
centered at 568, 600 and 608 nm, respectively. The EL spectra
Electroluminescent (EL) Properties
(Figure S18-20, ESI†) show little changes as the driving voltage
increased from 6 V to 9 V, suggesting efficient host-guest energy
transfer. Moreover, low turn-on voltages (Von) of 2.6 V for PXZ-
PCN, 2.9 V for both bis-PXZ-PCN and tri-PXZ-PCN are observed,
indicating a low charge-carrier injection barrier. For the EL
efficiency, PXZ- PCN endowed orange TADF devices with the
maximum external quantum efficiency (EQEmax), current
efficiency (CEmax) and power efficiency (PEmax) of 15.1%, 41.5
cd.A-1 and 48.3 lm.W-1. The EQEs of the devices using bis-PXZ-
PCN and tri-PXZ-PCN as the emitters can be up to 9.8% and 9.7%
with efficiency roll-offs of 15.0% and 17.5% at the luminance of
1000 cd.m-2, respectively. As shown in Table 3, the performance
To evaluate the electroluminescent properties of these new
TADF emitters, the OLED devices were fabricated. The device
configuration was indium tin oxide (ITO)/Molybdenum
trioxide(MoO3) (10 nm)/4,4’-(cyclohexane-1,1-diyl)bis(N,N-di-
p-tolylaniline) (TAPC) (50 nm)/1,3-carbazol-benzene (mCP)
(10nm)/N,N’-Dicarbazolyl-4,4’-biphenyl (CBP) : 10 wt% TADF
(20 nm)/4,7-diphenyl-1,10-phenanthroline (Bphen) (45
nm)/Lithium fluoride (LiF)/Aluminium (Al). In the devices, mCP
was elected as an electron blocking layer (EBL). MoO3 and LiF
acted as hole injection layer (HIL) and electron injection layer
(EIL), respectively. TAPC and Bphen served as hole transport
layer (HTL) and electron transport layer (ETL), respectively. The
energy-level diagram, current density-voltage-luminance (J-V-L),
power efficiency-luminance (PE-L), EQE-luminance (EQE-L)
characteristics and EL spectra of these devices are shown in
Fig.4. PXZ-PCN, bis-PXZ-PCN and tri-PXZ-PCN-based devices
display orange to orange-red emission with the main peaks
of orange-red to red TADF emitter-based OLED devices (ELmax
≥
600 nm) are summarized.11,20,33-40 The reported orange-red to
red devices showed dramatic efficiency roll-off at the luminance
of 1000 cd.m-2. Though the EQEs of ca. 10% in this work are not
the highest among the orange-red to red TADF based OLEDs,
Table 2 Electroluminescence characteristics of the devices
a
Emitter
Von
[V]
2.6
2.9
2.9
CEb
PEc
EQEd
[%]
15.1, 12.0, 11.2
9.8, 8.3, 5.9
9.7, 8.0, 5.2
ELpeak
[nm]
568
600
608
FWHM
[nm]
102
114
125
CIEe
(x, y)
(0.48, 0.51)
(0.55, 0.44)
(0.56, 0.44)
[cd A-1]
[lm W-1]
PXZ-PCN
bis-PXZ-PCN
tri-PXZ-PCN
66.9, 55.3, 42.7
19.5, 16.7, 11.9
18.3, 15.0, 9.7
48.3, 17.9, 11.9
18.2, 7.8, 3.9
17.9, 6.8, 3.1
a The turn-on voltage at 1 cd.m-2. Maximum value, values at 1000 cd.m-2 and 5000 cd.m-2. b Current efficiency; c Power efficiency; d External quantum efficiency. e The
Commission Internationale de L’Eclairage coordinates recorded at 9 V.
4 | J. Name., 2012, 00, 1-3
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Table 3. Summary of performances of orange-red to red TADF emitters-based OLED devices (ELmax≥600 nm)
DOI: 10.1039/C8TC01698D
a
Emitter
ELmax [nm]
τd
∆EST
[eV]
0.04
0.05
0.19
0.08
0.17
0.02
0.08
0.28
0.18
0.24
0.08
0.03
0.11
0.22
0.10
0.23
0.13
0.11
0.14
CIE
(x, y)
EQEmax
[%]
9.8
EQE [%] at 1000
EQE roll-off at
Ref.
[μs]
1.4
1.5
616
20.3
48.0
3.57
1.7
579
60
416
2.4
6.9
29
185
82.1
0.8
86.2
49
cd m-2
1000 cd m-2
bis-PXZ-PCN
tri-PXZ-PCN
MeODP-DBPHZ
6AcBIQ
HAP-3TPA
POZ-DBPHZ
1
DPA-DCPP
Da-CNBQx
b1
DMAC-DCPP
Ac-CNBPz
BTZ-DMAC
b2
600
608
≈600
≈600
610
≈600
613
616
617
624
624
630
636
637
644
644
668
670
693
(0.55, 0.44)
(0.56, 0.44)
-
(0.55, 0.44)
(0.60, 0.40)
-
8.3
8.0
6.3
4.4
-
-
-
-
15
18
39
61
-
-
-
-
-
82
-
-
-
81
-
-
85
-
This work
This work
[11]
[35]
[33]
[11]
[37]
[36]
[39]
[20]
[36]
[39]
[13]
[20]
[36]
[38]
[34]
9.7
10.3
11.2
17.5
≈16
16.8
10.4
20.0
12.5
10.1
16.2
8.8
-
(0.61, 0.38)
(0.59, 0.41)
(0.61, 0.39)
(0.60, 0.40)
(0.61, 0.39)
(0.61, 0.39)
(0.63, 0.37)
(0.64, 0.36)
(0.62, 0.38)
(0.68, 0.32)
(0.66, 0.34)
-
-
2.3
-
-
-
1.7
-
-
1.5
-
-
9.0
DPA-Ph-DCPP
TPA-QCN
TPA-DCPP
Da-CNBPz
APDC-DTPA
15.1
14.5
9.8
15.0
10.2
[39]
[40]
-
-
a Lifetime of delayed component.
the efficiency roll-off values of 15.0% and 17.5% at the This work was supported by the National Basic Research
luminance of 1000 cd.m-2 are the smallest among the orange- Program of China (973 Program 2015CB655002), the National
red to red TADF based OLEDs. The small roll-off values should Natural Science Foundation of China (No. 91433201 and
contribute to the short delay fluorescence lifetime of the two 51125013),
and
Shenzhen
Peacock
Plan
TADF emitters (ca. 1.5 μs). This work reveals that a short τd and (KQTD20170330110107046).
large kRISC can be beneficial to achieve effective RISC to reduce
triplet exciton involved quenching and realize low efficiency
roll-off.
Notes and references
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In summary, we have developed a series of new orange-red
TADF emitters with pyridine-3,5-dicarbonitrile (PCN) as the
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Journal of Materials Chemistry C
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DOI: 10.1039/C8TC01698D
The device with bis-PXZ-PCN reveals a maximum external quantum efficiency of 9.8% and a
slow efficiency roll-off of 15%.