Sky-blue thermally activated delayed fluorescence material employing a diphenylethyne acceptor for organic light-emitting diodes

Article abstract of DOI:10.1039/c7tc02763j

The strong electronegativity of sp-hybridized carbons, contributed by their large s character (50%), inspired the development of diphenylethyne as an electron acceptor to construct a sky-blue thermally activated delayed fluorescence material, 1,2-bis(4-(10H-phenoxazin-10-yl)phenyl)ethyne (DPE-DPXZ), using 10H-phenoxazine (PXZ) as an electron donor fragment. A sky-blue organic light-emitting diode employing DPE-DPXZ as the emitter demonstrated an external quantum efficiency exceeding 10%. Furthermore, another alkyne derivative, 1,2-bis(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)ethyne (DPE-DDMAc), in combination with 9,9-dimethyl-9,10-dihydroacridine (DMAc) as the donor was also studied to explore the singlet-triplet splitting energy governed by donor-acceptor alternation.

Full text of DOI:10.1039/c7tc02763j

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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DOI: 10.1039/C7TC02763J
Journal Name
ARTICLE
Sky-blue Thermally Activated Delayed Fluorescence Material
Employing Diphenylethyne Acceptor for Organic Light-Emitting
Diode Application
Received 00th January 20xx,
Accepted 00th January 20xx
Zuozheng He,† Xinyi Cai,† Zhiheng Wang, Yunchuan Li, Zhida Xu, Kunkun Liu, Dongcheng Chen,
and Shi-Jian Su*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Considering the strong electronegative of sp hybridized carbons contributed by a large s character (50%), diphenylethyne
was firstly developed as an electron acceptor to construct a sky-blue thermally activated delayed fluorescence material, 1,2-
bis(4-(10H-phenoxazin-10-yl)phenyl)ethyne (DPE-DPXZ), using 10H-phenoxazine (PXZ) as an electron donor fragment. Sky-
blue organic light-emitting diode employing DPE-DPXZ as the emitter demonstrates an external quantum efficiency
exceeding 10%. In addition, another alkyne derivative of 1,2-bis(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)ethyne (DPE-
DDMAc) in combination with 9,9-dimethyl-9,10-dihydroacridine (DMAc) as the donor was also studied, for exploring singlet-
triplet splitting energy governing via donor and acceptor alternation.
respectively).10-12 Following such a guideline, molecular design
strategy like employing largely twisted intramolecular charge
transfer (TICT) framework for the break of π-conjugation and
Introduction
Recently, replacing light-emitting materials, i.e. traditional
fluorophores with limited capability of harvesting only 25% electro-
generated singlet excitons and noble-metal containing
phosphorescent emitters with unity exciton utilization ratio, with
pure aromatic compounds has proved to be one of the most
attractive fields by far for future highly efficient, low cost and large-
scale display and illumination applications.1-6 Thermally activated
delayed fluorescence (TADF, E-typed fluorescence) mechanism,
whose achievement requires the narrowing of singlet-triplet splitting
energy (ΔEST) for effective reverse intersystem crossing (RISC)
process under ambient thermal energy activation turns out to be one
of the most potential candidates for realizing 100% internal quantum
efficiency (IQE) organic light-emitting diodes (OLEDs).7-9 As this
technique is still in its infancy, the route to pursue pure aromatic
compounds with capacity to harvest triplet excitons is continuously
ongoing.
the combination of donors (D) and acceptors (A) with high
triplet energy (T1) become the most successful means to design
TADF molecules. To date, numerous D-A compounds have been
reported utilizing diverse chemical moieties. Emitters for OLEDs
based on acceptors such as sulfone, carbonyl, nitrogen
heterocyclic, benzonitrile, boron heterocyclic, phosphorus
oxide, cyclophosphazene, etc. have achieved not only
wonderful performances in match with those of
phosphorescent OLEDs but covered the full RGB and near infra-
red (NIR) spectrum.8, 10, 13-27
To achieve small ΔEST, the frontier molecular orbitals (FMOs)
tightly related to the lowest energy transition should exhibit
small electronic wave function overlap integral (<φi|φf>, φi
denotes initial state orbitals and φf denotes final state orbitals),
which is directly proportional to electron exchange energy (J).
The small FMOs overlap results in small J value and eventuates
in efficient RISC process revealed by Boltzmann equation (kRISC
∝
exp(-ΔEST/kBT), in which kRISC, kB and T denote the rate
constant of RISC process, Boltzmann constant and temperature,
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: mssjsu@scut.edu.cn
†The authors contribute equally to this work. Electronic Supplementary Information
(ESI) available: [synthesis routes, computation summary, photo-physical properties
and OLED device characterization data]. See DOI: 10.1039/x0xx00000x
Fig. 1 a, Relative electronegativities of carbon atoms. b,
Relative acid strengths and electrostatic potential maps of
ethane, ethylene and ethyne.
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For alkyne groups, on the one hand, they were usually used
as “p-type” units or π bridges,28-30 due to the two electron-rich
π bonds of carbon-carbon triple bond, which were thought as a
View Article Online
β=89.7o
=89.9o
DOI: 10.1039/C7TC02763J
cylinder of electrons in wrapping around the
σ bond. On the
other hand, according to hybrid orbital theory, the more s
character in a hybrid orbital, the more electronegative is the
hybridized carbon atom, owing to the fact that the electrons in
s orbitals are closer with the nucleus than those in p orbitals.
Thus, the sp hybridized carbons are more electronegative than sp2
hybridized carbons, which are more electronegative than sp3
hybridized carbons. Ethyne is, therefore, a stronger acid than
ethylene and ethane (Fig. 1). Electronegativity increases with
increasing percentage of s character in the orbital, indicating the
potential of alkyne groups as acceptor moieties. Moreover, the
electron-accepting ability of DPE moiety is also originated from the
moderate energy level as compared to that of DMAc and PXZ units.
In this work, considering the strong electronegativity of sp
hybridized carbons contributed by a large s character (50%), we
firstly used an alkyne unit, diphenylethyne (DPE) that has been
seldom considered as an electron-withdrawing group, as an
electron acceptor. And a sky-blue TADF emitter was accidentally
discovered by containing diphenylethyne (DPE) acceptor and
10H-phenoxazine (PXZ) donor moiety (Fig. 2). The lowest singlet
(S1) and triplet (T1) state energies of the molecule were
governed delicately by the combination of donors with
moderate electron-donating ability and weak electron-
withdrawing DPE moiety to guarantee a small ΔEST and a large
energy gap for blue emission. For the first time, sky-blue OLED
using DPE-DPXZ as an emitter exhibited an external quantum
efficiency (EQE) surpassing 10% with an emission peak at 475
nm. Insight of the material design is thoroughly analysed in this
article.
LUMO
ESP
HOMO
Fig. 2 Molecular structures, frontier molecular orbitals and
electrostatic potential distribution of two investigated
compounds DPE-DDMAc and DPE-DPXZ calculated in B3LYP/6-
31G* level in gas phase (α and β denote the dihedral angles
between the electron donors and acceptor).
Ultraviolet−visible absorption spectra were recorded using
Perkin-Elmer
Lambda
950-PKA
UV/VIS
while
photoluminescence (PL) and 77 K phosphorescence spectra
were recorded by FluoroMax-4 spectrofluorometer (Horiba
Jobin Yvon), respectively. PL quantum yields (PLQYs) were
measured utilizing an integrating sphere of Hamamatsu
absolute PL quantum yield spectrometer (C11347). Transient PL
decay at room temperature was measured using Quantaurus-
Tau fluorescence lifetime measurement system (C11367-03,
Hamamatsu Photonics Co., Japan). Transient PL decays of film
samples at various temperatures were investigated under N2
atmosphere using Quantaurus-Tau fluorescence lifetime
measurement system (C11367-03, Hamamatsu Photonics Co.,
Japan) equipped with Oxford Instruments nitrogen cryostat
(Optistat DN).
Experimental
1H and 13C NMR spectra were recorded on a Bruker NMR
spectrometer operating at 600 and 150 MHz, respectively. All
data were recorded in deuterated chloroform (CDCl3) solution
at room temperature. Mass spectra were recorded on a Waters
Synapt G2 Mass Spectrometer. Thermogravimetric analyses
(TGA) were performed on Netzsch TG 209 under nitrogen flow
at a heating rate of 10 °C/min. Differential scanning calorimetry
(DSC) measurements were performed on Netzsch DSC 209
under nitrogen flow at several heating and cooling cycles with a
heating rate of 10 °C/min and a cooling rate of 20 °C/min. Cyclic
voltammetry (CV) was carried out on the CHI-600D
electrochemical workstation using Platinum as working
electrode and a Pt wire as counter electrode and Ag/AgCl as
reference electrode at a scanning rate of 100 mV/s in nitrogen-
saturated 0.1 mol/L n-Bu4NPF6 anhydrous acetonitrile and
dichloromethane (DCM) solution. Single crystals of DPE-DDMAc
were grown from chloroform/methanol mixtures. Processing of
the intensity data was carried out using Rigaku R-AXIS, and the
structure solution and refinement were carried out by the
SHELXTL suite of X-ray programs. The crystal structure was
deposited at CCDC with deposition number 1555726.
Fig. 3 Orbital hybridization schematic diagram of acetylene
bond.
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Table 1. Simulated results (TD-DFT) of the investigated compounds DPE-DDMAc and DPE-DPXZ. Fragments for constructing the
DOI: 10.1039/C7TC02763J
compounds are also shown for comparison.
a)
OHF EVA (S1, OHF)
E0-0 (1CT)
(eV)
2.98
2.73
E0-0 (3CT)
(eV)
2.83
2.72
E0-0 (3LE) ΔEST
Eg
Compounds
q
HOMO (eV)
LUMO (eV)
(%)
(eV)
(eV)
2.54
2.55
2.65
2.98
2.61
(eV)
(eV)
3.23
2.88
4.45
4.82
4.44
DPE-DDMAc 0.85 35.5
3.22
2.97
-
-
-
0.44 -4.94a)/-5.19b) -1.71a)/-2.17b)
0.18 -4.72a)/-4.98b) -1.84a)/-2.15b)
DPE-DPXZ
PXZ
0.86 36.3
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-4.68a)
-4.88a)
-5.69a)
-0.23a)
-0.06a)
-1.25a)
DMAc
DPE
a) HOMO, LUMO levels and energy gap (Eg) calculated in B3LYP/6-31G* level. b) Ionization potential (IP) and electron affinity potential (EA)
calculated from CV results. EIP is estimated from (Eonsetox + 4.303) and EEA is roughly approximated from EIP – Eonsetabs (Eonsetabs is optical
absorption onset energy estimated in toluene solution).
Compound DPE-DPXZ was easily synthesized from Hartwig- the energy levels of two conformers, according to the DFT
Buchward C-N coupling reaction with high yield (>80%).31 For calculation.
comparison, reference compound DPE-DDMAc was also
The geometries, FMOs distribution and electrostatic surface
synthesized following the same procedure, using 9,9-dimethyl- potential (ESP) analysis of two molecules are presented in Fig.
9,10-dihydroacridine (DMAc) as the donor. Molecular 2. Due to the steric hindrance effect of the adjacent hydrogen
structures of two alkyne compounds DPE-DDMAc and DPE-DPXZ atoms on six-member rings and DPE backbone, the defined
are shown in Fig. 2, and the characterizations are included in the donors and acceptor are almost orthogonal to each other
ESI. Thermal properties of DPE-DDMAc and DPE-DPXZ were (α=89.9° and β=89.7°, respectively). Uncovered by the ESP
examined by using thermogravimetric analyses (TGA) and distribution (Fig. 3, S11 and S14), the negative site was induced
differential scanning calorimetry (DSC) under a nitrogen by the centre acetylene bond contributed by the large s
atmosphere. These two compounds showed good thermal character (50%) in sp hybridization pattern, among which the
stability with decomposition temperatures above 380°C, peripheral electron cloud was tightly confined within the triple
enabling the feasibility for film deposition process via vacuum bond. In that case, the acetylene bond provides moderate
thermal evaporation technique (Fig. S21). In addition, no glass electron-withdrawing ability. Further evidence can be found in
transition was found for DPE-DDMAc, and the glass transition the highest occupied molecular orbital (HOMO) and lowest
temperature (Tg) of DPE-DPXZ is above 120 °C, which could unoccupied molecular orbital (LUMO) distributions for HOMO
ensure their morphology stability.
was dominantly located on PXZ or DMAc moieties while LUMO
mainly on DPE unit, certifying that DPE plays the role of acceptor
(Fig. 3, S12 and S15).
Results and discussion
Based on the optimized ground state conformers, time-
dependent DFT (TD-DFT) simulation was carried out to gain
insight into the excited-state paradigm of these two compounds.
Initially, the charge transfer amount (q) was calculated and the
optimal Hartree-Fock percentage (OHF) was reckoned,
respectively (Fig. S9 and Table 1).32 Such an amendment can
minimize so-called self-interaction error or electron correlation
problem in TD-DFT simulation which could have under- or over-
estimate the ICT transition energies.33-35 Taking it into account,
the zero-zero lowest charge transfer singlet state energy (E0-0
(1CT)), lowest CT triplet state energy (E0-0 (3CT)) and lowest
locally triplet excited state energy (E0-0 (3LE)) were calculated
and compared (see SI)36. For both emitters, the E0-0 (3LE) were
almost the same (≈2.55 eV) and fallen below their
corresponding E0-0 (3CT), indicating their T1 presented LE
character (Table 1). Further computational evaluation of the
separated molecular fragments (DPE, DMAc and PXZ)
demonstrated that the T1 state could be dominated by centre
DPE unit for the simulated E0-0 (3LE) of PXZ and DMAc moieties
were much higher than that of DPE (2.61 eV). Given that slight
bathochromic shift of E0-0 (3LE) of compounds DPE-DDMAc and
DPE-DPXZ than that of DPE fragment, moderate electron
interaction between D and A could be anticipated to endow
moderate FMOs overlap for increased transition possibility
under optical excitation.37 Additionally, in view of the stronger
Computation simulation
To explore the molecular diagram of these compounds, density
functional theory (DFT) simulation was conducted and the
ground state geometries were initially optimized in B3LYP/6-
31G* level in gas phase. Interestingly, the centre DPE moiety
can adopt two conformers (horizontal and vertical type) for
both optimized geometries which were confirmed with no
imaginary frequency (Fig. S10 and S13). As we all known, triple
bond consists of one σ bond and two π bonds, of which σ bond
is formed by sp-sp orbital overlap and π bonds are formed by
side-to-side overlap of unhybridized p orbitals (Fig. 3). Because
the two unhybridized
p orbitals on each carbon are
perpendicular to each other, the conjugation of the DPE
backbone can be well maintained for both horizontal and
vertical conformers and ensured moderate edge to edge
overlap between the triple bond and adjacent phenyl rings.
Given horizontal conformers of two compounds were more
stable in energy than that of vertical conformers, we took the
former as initial guess for the subsequent simulation, which was
supported by single-crystal X-ray structure analysis of DPE-
DDMAc. As shown in Fig. S17, the molecular conformation of
DPE-DDMAc in single crystal structure was confirmed to be
horizontal conformer, consistent with the relationship between
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30
25
20
15
10
5
1.2
0.9
0.6
0.3
0.0
30
25
20
15
10
5
1.2
DOI: 10.1039/C7TC02763J
a)
b)
DPE-DDMAc
Toluene
THF
DPE-DPXZ
Toluene
THF
DCM
DMF
0.9
0.6
0.3
0.0
DCM
DMF
0
0
300
350
400
450
500
550
600
650
300
350
400
450
500
550
600
650
Wavelength (nm)
Wavelength (nm)
Fig. 4 Solvents-dependent UV-vis absorption and photoluminescence spectra of compounds (a) DPE-DDMAc and (b) DPE-DPXZ
measured in diluted solutions with a concentration of 0.01 mM L-1.
electron-donating ability of PXZ than DMAc unit, E0-0 (1CT) of (Table 1). From this perspective, DPE-DPXZ could possess TADF
DPE-DPXZ was 0.25 eV lower than that of DPE-DDMAc, character and potential for blue emission considering its large
eventuating a narrow calculated zero-zero band ΔEST (0.18 eV) CT gap (2.88 eV).
Photophysical properties
of DPE. The emission of DPE-DPXZ is red-shifted in comparison
Photo-physical investigation validates our computational with DPE-DDMAc due to the stronger electron-donating ability
prediction and analysis. UV-vis absorption and PL spectra of of PXZ than that of DMAc.
dilute solutions in a variety of solvents (from the nonpolar to
In
addition,
low-temperature
fluorescence
and
polar range) are shown in Fig. 4. Rather small molar extinction phosphorescence spectra of two alkyne compounds and their
coefficient (<5 mM cm-2) of two alkyne compounds was corresponding molecular fragments were acquired in toluene
observed due to the large dihedral angle between the donor solution. In good agreement with the TD-DFT analyses, the LE
and DPE units for suppressed transition possibility (Fig. 2). character phosphorescence of DPE-DDMAc and DPE-DPXZ was
Obviously, their PL spectra showed dependence on the polarity experimentally confirmed and dominated by the DPE unit. As
of solvent. The toluene solution of DPE-DDMAc and DPE-DPXZ shown in Fig. 5, the phosphorescence spectra of two emitters
emit deep-blue and pure-blue emissions centered at 428 and displayed dramatically departure from that of their
468 nm, respectively. The emission peak of DPE-DDMAC red- corresponding donor sections. On the contrast, there is little
shifted to 501 nm in acetonitrile solution. The emission deviation from the mutual DPE fragment in T1 emission.
wavelength undergoes a larger bathochromic shift from 468 to Moreover, the phosphorescence spectra of both compounds
551 nm for DPE-DPXZ as the polarity of the solvent increases. exhibited specific vibrational structures that were quite similar
Solvatochromism effects indicated the ICT character to that of DPE. Those results affirmed that the T1 of the
fluorescence of two compounds, confirming the acceptor role investigated compounds were localized in the DPE centre.
The slight red-shift of T1 emissions of DPE-DDMAc and DPE-
DPXZ could be explained by the incomplete D-A electronic
Fluo in 77 K
Phos in 77 K
decoupling.38 For greater understanding, potential surface
DMAc
scans were conducted along the dihedral angles between the
electron donors and acceptor for two alkyne compounds in gas
PXZ
phase from B3LYP/6-31G* level. The potential surface scan
revealed that these molecules can be less rigid given that rather
smooth energy distribution among small range of dihedral angle
DPE
alternation (±20°) between the optimized ones (Fig. S16). The
steeper trend of energy rise when reducing the α angle
DPE-DDMAc
indicated the electronic interaction of DPE-DDMAc could be
weaker than that of DPE-DPXZ, explaining the more red-shift 3LE
DPE-DPXZ
emission of DPE-DPXZ than DPE-DDMAc. Therefore, increased
300
400
500
600
electronic decoupling can be potential for maintaining high T1
state. Thus, for two alkyne compounds, displacement of the
donor moieties with different electron-donating ability affects
not only the S1 energy level but also slightly manages the T1
energy level, resulting in the distinction of exchange energy
(Scheme 1 and Table S1). As a result, ΔEST of DPE-DDMAc and
Wavelength (nm)
Molecular structure
Fig. 5 Normalized fluorescence and phosphorescence spectra of
DPE-DDMAc, DPE-DPXZ and their corresponding molecular
fragments measured in toluene solution with a concentration of
0.01 mM L-1 at 77 K.
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DPE-DPXZ were evaluated to be 0.55 and 0.40 eV, respectively,
via low-temperature fluorescence/phosphorescence spectra.
The HOMO energy levels of DPE-DDMAc and DPE-DPXZ were
examined by using cyclic voltammetry (Fig. S22), and LUMO
energy levels were further estimated from the optical
absorption onset energy in toluene solution. The HOMO and
LUMO energy levels are estimated to be −5.19 and −2.17 eV
for DPE-DDMAc, and −4.98 and −2.15 eV for DPE-DPXZ,
respectively (Table 1). Compared to DPE-DDMAc, the stronger
electron-donating capability of PXZ makes the HOMO energy
level of DPE-DPXZ 0.21 eV shallower. While, there was slight
difference in LUMO energy level between two alkyne
compounds, on account of the LUMO dispersing over the same
acceptor (DPE), according to DFT simulation.
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DOI: 10.1039/C7TC02763J
RISC
DMAc
PXZ
RIC
1CT
△EST
3CT
IC
ISC
IC
3LE (DPE)
F
P
ISC
P
P
P
S0
Scheme 1. Schematic diagram of singlet-triplet splitting energy
governing via donor and acceptor alternation.
the ratio of DF significant monotonically enhanced from 21.3%
at 100 K to 66.9% at 300 K, evidencing the occurrence of
thermally activated process. Conversely, the DF ratio dropped
down to 53.1% when further increasing the temperature to 350
K. This can be explained by significantly enhanced non-radiative
(internal conversion) channel for depletion of long lifetime
excitons.15, 41
For approximating the situation in OLED application, DPE-
DDMAc and DPE-DPXZ were evaluated in solid-state films. Given
the high S1 and T1 energy levels of the investigated materials,
bis(2-(diphenylphosphino)phenyl)etheroxide (DPEPO) with
ultrahigh T1 (3.30 eV) was selected as the host and 10 wt% low
doping concentration was adopted to avoid severe bimolecular
interaction.39 When DPE-DDMAc was doped into DPEPO, there
was only nano-second range lifetime of 6.70 ns observed (Fig.
S20), as a result of high ΔEST value making the up-conversion of
triplet excitons impossible. In good agreement with TD-DFT
simulation results, the relatively small ΔEST of DPE-DPXZ was
achieved by delicate tuning of S1 and T1 states, which enabled
RISC take place to harvest triplet excitons, yielding delayed
fluorescence (DF). As shown in Fig. 6, DPE-DPXZ initially decays
promptly with a lifetime of 5.58 ns then followed a delayed
OLED characterization
According to computation simulation and photophysical
property analysis, DPE-DPXZ was proved to possess TADF
character, while DPE-DDMAc with no TADF character. Therefore,
DPE-DPXZ was confirmed more appropriate to be employed in
OLED devices. Three device architectures are: I. ITO (95 nm)/
TAPC (35 nm)/ DPE-DPXZ (25 nm)/ TmPyPB (40 nm)/ LiF (0.8
nm)/ Al (100 nm); II. ITO (95 nm)/ TAPC (35 nm)/ 10 wt% DPE-
DPXZ in CBP (25 nm)/ TmPyPB (40 nm)/ LiF (0.8 nm)/ Al (100
nm); III. ITO (95 nm)/ TAPC (35 nm)/ DAcDB (10 nm)/ 10 wt%
DPE-DPXZ in DPEPO (25 nm)/ DPEPO (10 nm)/ TmPyPB (40 nm)/
LiF (0.8 nm)/ Al (100 nm). As severe concentration quenching
effect was noted for the DPE-DPXZ neat film, device I exhibited
very poor performance with maximum EQE of 2.89% (Fig. 8), in
consistent with photo-physical property analysis (Fig. S20).
decay with a lifetime of 542.70 s, verifying its TADF character.
Millisecond level τDF was noted in vacuum condition considering
the ΔEST > 0.2 eV, which means more chances for quenching
processes by oxygen in the air (Fig. 6). As mentioned, the small
kTADF (on the order of 2) should be responsible for the long τDF
because the reverse up-conversion process plays the “rate-
limiting” role in controlling the excited-state lifetime of DF
(τDF).40 To further verify the TADF nature of DPE-DPXZ,
temperature-dependent transient PL spectra were measured
from 77 to 350 K (Fig. 7). Following the increase of temperature,
105
10 wt% DPE-DPXZ in DPEPO_air
10 wt% DPE-DPXZ in DPEPO_vacuum
104
100
103
10-1
102
10-2
0
20
40
60
80
100
Time (ns)
101
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Time (ms)
Fig. 7 Temperature-dependent transient PL decays of 10 wt% DPE-
DPXZ in DPEPO doped film measured in vacuum condition. Owning
to the wide impulse response function (flash lamp with long decay
signals), the delayed fluorescence ratio was reckoned and showed
(inset) using the proportion of integration area cutting from the
fitting line (grey lines) and the axis and the overall integration area
calculated from the curves and the axis.
Fig. 6 Transient PL decays of 10 wt% DPE-DPXZ in DPEPO
measured in air and vacuum condition using a fluorescence
lifetime spectrometer (C11367-01, Hamamatsu Photonics) in
TCC900 mode, respectively. Inset shown was the prompt
component of the decay recorded in M9003-01 mode.
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Moreover, device
I
showed the highest onset voltage (Von) from severe singlet-triplet annihilation (STA) and VtireiwplAerttic-lterOipnllienet
DOI: 1a0n.1d03i9m/Cb7aTlCa0n2c7e63oJf
among three groups of devices, proving the worst charge carrier annihilation (TTA) effect owing to the large τDF
balance which could be ascribed to the imbalance of hole and charge carrier injection and transport.46,
47
From this
electron injecting and transporting ability of DPE-DPXZ. In perspective, further strategies to reduce the ΔEST and device
device II, better performance was achieved for the less optimization could be potential for better performing OLEDs
bimolecular interaction caused concentration quenching effect. based on DPE derivative compounds and further work is already
Much lower Von and higher maximum brightness of the device under investigation.
were noted considering more balanced charge carrier injection
and transport were realized when DPE-DPXZ was doped into
4,4’-bis(carbazol-9-yl)biphenyl (CBP) host. For device III, in
Conclusions
which electron-blocking and hole-blocking layers were
introduced, EQE exceeding 10% was achieved and blue emission
with a peak at 475 nm was observed, which is quite close to the
PL peaks of DPE-DPXZ in toluene solution and 10 wt% DPE-DPXZ
in DPEPO doped film. The triplet excitons of DPE-DPXZ was
better confined within the emissive layer, which can result in a
higher performance than those of the other two groups of
devices. Considering that the relatively low photoluminescence
quantum yield of the DPE-DPXZ doped film (30.0 3.0%), the
achievement of high EQE might be ascribed to the enhanced
light out-coupling efficiency. It is reported that rigid and bar-
shaped TADF emitters tend to flatly orientate within the EML,
which could result in enhanced light out-coupling efficiency and
thus high EQE (see SI).27, 42-45 However, owing to the poor charge
carrier mobility of DPEPO, the maximum brightness was low. At
exact the same operation voltage, the current density of device
II employing bipolar host CBP was much larger than that of
device III. In high operation current density, TADF-OLED suffers
Herein, we firstly put forward TADF emitter based on DPE
acceptor and apply it in OLED device. The DPE moiety was
confirmed to be a weak acceptor from the special sp-
hybridization of carbon-carbon triple bond with high s character
,
which is a potential fragment for blue TADF material design. The
3LE state of the emitters can be delicately governed by
electronic interaction between the D-A decoupling. Reduced
interaction can further elevate the 3LE state, which can prompt
reverse up-conversion for more effective TADF process. Though
DF phenomenon was observed for DPE-DPXZ, further
decreasing the ΔEST is critical for more enhanced RISC process,
which is beneficial towards highly efficient and low efficiency
roll-off OLED application operating at high current density and
brightness.
Acknowledgements
The authors greatly appreciate the financial support from the
National Key R&D Program of China (2016YFB0401004), the
National Natural Science Foundation of China (51625301,
51573059 and 91233116), 973 Project (2015CB655003), and
Guangdong Provincial Department of Science and Technology
(2016B090906003 and 2016TX03C175).
-1.4
a
-2.1
-2.0
-2.7
-2.4
-4.2
-5.1
-5.0
-5.3
-5.6
Notes and references
-6.1
1. C. W. Tang and S. A. VanSlyke, Appl. Phys. Lett., 1987, 51, 913.
2. M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M.
E. Thompson and S. R. Forrest, Nature, 1998, 395, 151-154.
3. Y. G. Ma, H. Y. Zhang, J. C. Shen and C. M. Che, Synth. Met.,
1998, 94, 245-248.
4. C. Adachi, M. A. Baldo, M. E. Thompson and S. R. Forrest, J.
Appl. Phys., 2001, 90, 5048-5051.
5. S. Reineke, Nat. Photonics, 2014, 8, 269-270.
6. S. Reineke, Nat. Mater., 2015, 14, 459-462.
7. A. Endo, M. Ogasawara, A. Takahashi, D. Yokoyama, Y. Kato
and C. Adachi, Adv. Mater., 2009, 21, 4802-4806.
8. H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi,
Nature, 2012, 492, 234-238.
9. Q. Zhang, D. Tsang, H. Kuwabara, Y. Hatae, B. Li, T. Takahashi,
S. Y. Lee, T. Yasuda and C. Adachi, Adv. Mater., 2015, 27, 2096-
2100.
III
-6.7
102
101
100
10-1
10-2
10-3
10-4
104
103
102
101
100
1.2
0.9
0.6
0.3
0.0
b
d
Device I
Device II
Device III
0
2
4
6
8
10
Voltage (V)
101
100
c
10-3
10-2
10-1
100
101
102
400 500 600 700 800
Current Density (mA cm-2)
Wavelength (nm)
10.
Q. Zhang, H. Kuwabara, W. J. Potscavage, Jr., S. Huang, Y.
Hatae, T. Shibata and C. Adachi, J. Am. Chem. Soc., 2014, 136
,
18070-18081.
Fig. 8 (a) Device architectures and materials used in OLEDs. (b)
Current density-voltage-luminance (J-V-L), (c) external quantum
efficiency-current density (EQE-J) characteristics of the devices I, II,
and III, and (d) electroluminescence (EL) spectra of the
corresponding devices at a current density of 0.1 mA/cm2.
11.
Q. Zhang, J. Li, K. Shizu, S. Huang, S. Hirata, H. Miyazaki and
C. Adachi, J. Am. Chem. Soc., 2012, 134, 14706-14709.
K. Goushi, K. Yoshida, K. Sato and C. Adachi, Nat.
12.
Photonics, 2012, 6, 253-258.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 8
Journal of Materials Chemistry C
Please do not adjust margins
Journal Name
ARTICLE
13. Q. S. Zhang, B. Li, S. P. Huang, H. Nomura, H. Tanaka and C.
Adachi, Nat. Photonics, 2014, , 326-332.
14. G. Xie, X. Li, D. Chen, Z. Wang, X. Cai, D. Chen, Y. Li, K. Liu, Y.
Cao and S.-J. Su, Adv. Mater., 2016, 28, 181-187.
15. X. Y. Cai, B. Gao, X. L. Li, Y. Cao and S. J. Su, Adv. Funct. Mater.,
2016, 26, 8042-8052.
16. Y. C. Li, X. L. Li, D. J. Chen, X. Y. Cai, G. Z. Xie, Z. Z. He, Y. C. Wu,
A. Lien, Y. Cao and S. J. Su, Adv. Funct. Mater., 2016, 26, 6904-
6912.
17. S. Y. Lee, T. Yasuda, Y. S. Yang, Q. Zhang and C. Adachi, Angew.
Chem., Int. Ed., 2014, 53, 6402-6406.
43. L. Zhao, T. Komino, M. Inoue, J. H. Kim, J. C. Ribierre and C.
View Article Online
8
Adachi, Appl. Phys. Lett., 2015, 106, 063301.
DOI: 10.1039/C7TC02763J
44. C. S. Oh, C.-K. Moon, J. M. Choi, J.-S. Huh, J.-J. Kim and J. Y. Lee,
Org. Electron., 2017, 42, 337-342.
45. M. Liu, R. Komatsu, X. Y. Cai, K. Hotta, S. Sato, K. K. Liu, D. C. Chen,
Y. Kato, H. Sasabe, S. Ohisa, Y. Suzuri, D. Yokoyama, S.-J. Su, and
J. Kido, Chem. Mater. 2017, 29, 8630.
46. K. Masui, H. Nakanotani and C. Adachi, Org. Electron., 2013, 14,
2721-2726.
47. T. Furukawa, H. Nakanotani, M. Inoue and C. Adachi, Sci. Rep.,
2015, 5, 8429.
18. S. Hirata, Y. Sakai, K. Masui, H. Tanaka, S. Y. Lee, H. Nomura,
N. Nakamura, M. Yasumatsu, H. Nakanotani, Q. Zhang, K.
Shizu, H. Miyazaki and C. Adachi, Nat. Mater., 2015, 14, 330-
336.
19. L. S. Cui, H. Nomura, Y. Geng, J. U. Kim, H. Nakanotani and C.
Adachi, Angew. Chem., Int. Ed., 2017, 56, 1571-1575.
20. 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.
21. J. Lee, N. Aizawa, M. Numata, C. Adachi and T. Yasuda, Adv.
Mater., 2017, 29, 1604856.
22. S. Y. Lee, C. Adachi and T. Yasuda, Adv Mater, 2016, 28, 4626-
4631.
23. T. Nishimoto, T. Yasuda, S. Y. Lee, R. Kondo and C. Adachi,
Mater. Horiz., 2014, 1, 264-269.
24. D. D. Zhang, M. H. Cai, Y. G. Zhang, D. Q. Zhang and L. Duan,
Mater. Horiz., 2016, , 145-151.
3
25. S. Wang, X. Yan, Z. Cheng, H. Zhang, Y. Liu and Y. Wang, Angew.
Chem., Int. Ed., 2015, 54, 13068-13072.
26. T. A. Lin, T. Chatterjee, W. L. Tsai, W. K. Lee, M. J. Wu, M. Jiao, K.
C. Pan, C. L. Yi, C. L. Chung, K. T. Wong and C. C. Wu, Adv. Mater.,
2016, 28, 6976-6983.
27. P. Rajamalli, N. Senthilkumar, P. Y. Huang, C. C. Ren-Wu, H. W.
Lin and C. H. Cheng, J. Am. Chem. Soc., 2017, 139, 10948-10951.
28. A. Abate, M. Planells, D. J. Hollman, V. Barthi, S. Chand, H. J.
Snaith and N. Robertson, Phys. Chem. Chem. Phys., 2015, 17
,
2335-2338.
29. S. Kazim, F. J. Ramos, P. Gao, M. K. Nazeeruddin, M. Grätzel
and S. Ahmad, Energy Environ. Sci., 2015, 8, 1816-1823.
30. W. Shi, L. Wang, M. Umar, T. Awut, H. Mi, C. Tan and I. Nurulla,
Polym. Int., 2009, 58, 800-806.
31. M. J. Mio, L. C. Kopel, J. B. Braun, T. L. Gadzikwa, K. L. Hull, R.
G. Brisbois, C. J. Markworth and P. A. Grieco, Org. Lett., 2002,
4
, 3199-3202.
32. T. Lu and F. Chen, J. Comput. Chem., 2012, 33, 580-592.
33. A. Dreuw and M. Head-Gordon, J. Am. Chem. Soc., 2004, 126
4007-4016.
,
,
34. R. J. Magyar and S. Tretiak, J. Chem. Theory. Comput., 2007,
3
976-987.
35. A. Dreuw and M. Head-Gordon, Chem. Rev., 2005, 105, 4009-
4037.
36. S. Huang, Q. Zhang, Y. Shiota, T. Nakagawa, K. Kuwabara, K.
Yoshizawa and C. Adachi, J. Chem. Theory. Comput., 2013,
3872-3877.
37. M. Fagnoni, Angew. Chem., Int. Ed., 2010, 49, 6709-6710.
9,
38. P. Data, P. Pander, M. Okazaki, Y. Takeda, S. Minakata and A. P.
Monkman, Angew. Chem., Int. Ed., 2016, 128, 5833-5838.
39. C. Han, Y. Zhao, H. Xu, J. Chen, Z. Deng, D. Ma, Q. Li and P. Yan,
Chem. Eur. J., 2011, 17, 5800-5803.
40. X. Y. Cai, X. L. Li, G. Z. Xie, Z. Z. He, K. Gao, K. K. Liu, D. C. Chen, Y.
Cao and S. J. Su, Chem. Sci., 2016, 7, 4264-4275.
41. J. Li, T. Nakagawa, J. MacDonald, Q. Zhang, H. Nomura, H.
Miyazaki and C. Adachi, Adv. Mater., 2013, 25, 3319-3323.
42. T. Komino, Y. Sagara, H. Tanaka, Y. Oki, N. Nakamura, H. Fujimoto
and C. Adachi, Appl. Phys. Lett., 2016, 108, 5.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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Journal of Materials Chemistry C
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View Article Online
DOI: 10.1039/C7TC02763J
TOC graphic:
Blue Thermally Activated Delayed Fluorescence Material Employing
Diphenylethyne Acceptor for Organic Light-Emitting Diode Application
Zuozheng He, Xinyi Cai, Zhiheng Wang, Yunchuan Li, Zhida Xu, Kunkun Liu, Dongcheng Chen,
and Shi-Jian Su*
DPE-DPXZ is the first reported blue thermally activated delayed fluorescence molecule
containing diphenylethyne as the acceptor.