Asymmetric thermally activated delayed fluorescence (TADF) emitters with 5,9-dioxa-13: B -boranaphtho[3,2,1- de] anthracene (OBA) as the acceptor and highly efficient blue-emitting OLEDs

Article abstract of DOI:10.1039/c9tc04115j

A series of new organic emitters was prepared by introducing various donors (Ds) to the meta-position of the boron atom in the central phenyl ring in the acceptor (A) of 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (OBA). Moreover, their thermal, photophysical, electrochemical and electroluminescent (EL) properties were characterized in detail. The photophysical results revealed that these OBA-based molecules adopted a D-A configuration and exhibited efficient thermally activated delayed fluorescence (TADF) properties with a reverse inter-system crossing constant (k_RISC) in the order of 10⁵ s^-1. It has been shown that introducing the -Br group to the OBA acceptor could increase k_RISC by 2 to 3 times. Importantly, the deep-blue TADF emitter OBA-O showed a high photoluminescent quantum yield (PLQY) of 0.84, while its blue analog OBA-BrO with the -Br group exhibited an even higher PLQY of 0.92 in the doped film state. Benefitting from their high PLQYs as blue-emitting TADF emitters, the doped organic light-emitting diodes (OLEDs) based on these OBA-based TADF emitters exhibited attractive electroluminescent (EL) performances. The blue-emitting OLEDs with CIE (0.17, 0.17) showed the maximum external quantum efficiency (η_ext) of 17.8%, current efficiency (η_L) of 33.2 cd A^-1 and power efficiency (η_P) of 34.2 lm W^-1, while that for the bluish-green device were 22.5%, 49.2 cd A^-1 and 56.9 lm W^-1, respectively. Thus, the great potential of these TADF emitter-based OBA acceptors was clearly demonstrated by their EL data. In addition, these asymmetric OBA-based molecules will enrich the structural diversity of this type of TADF emitter.

Full text of DOI:10.1039/c9tc04115j

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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC04115J
Journal Name
ARTICLE
Asymmetric thermally activated delayed fluorescence (TADF)
emitters with 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene
(OBA) as acceptor and highly efficient blue-emitting OLEDs
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Dongdong Song,a Yue Yu,b Ling Yue,a Daokun Zhong,a Yindi Zhang,a Xiaolong Yang,a Yuanhui
Sun,a Guijiang Zhou,*a Zhaoxin Wu*b
www.rsc.org/
A series of new organic emitters have been prepared through introducing various donors (D) to the meta-position of the
boron atom in central phenyl ring in the acceptor (A) of 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (OBA). Their
thermal, photophysical, electrochemical and electroluminescent (EL) properties have been characterized in detail. The
photophysical results have revealed that these OBA-based molecules adopting D-A configuration can exhibit efficient
thermally activated delayed fluorescence (TADF) properties with reverse inter-system crossing constant (kRISC) in the order
of 105 s−1. It has been shown that introducing –Br group to the OBA acceptor can increase kRISC by 2 to 3 times. Importantly,
deep-blue TADF emitter OBA-O can show high photoluminescent quantum yield (PLQY) of 0.84, while the blue analog
OBA-BrO with –Br group can possess even high PLQY of 0.92 in the doped film. Benefitting from their high PLQYs as blue-
emitting TADF emitters, the doped organic light-emitting diodes (OLEDs) based on these OBA-based TADF emitters can
achieve attractive electroluminescent (EL) performances. The blue-emitting OLEDs with CIE (0.17. 0.17) can show the
maximum external quantum efficiency (ηext) of 17.8%, current efficiency (ηL) of 33.2 cd A−1 and power efficiency (ηP) of 34.2
lm W−1, while the data for the bluish-green device are 22.5%, 49.2 cd A−1 and ηP of 56.9 lm W−1. The great potential of
these TADF emitters based OBA acceptor has been clearly indicated by these EL data. In addition, these asymmetric OBA-
based molecules will enrich structural diversity of this kind of TADF emitters.
generally adopt D–A-type or D–A–D-type (D = electron donor,
Introduction
A = electron acceptor) configuration to promote the RISC
14
procedure by reducing ΔEST.13,
Therefore, on this basis,
After being demonstrated by Adachi,1-5 thermally activated
delayed fluorescence (TADF) emitter have received substantial
research endeavors, since they can harness both singlet and
triplet excitons in the electroluminescent (EL) process without
the aid of precious metal ions through reverse intersystem
various TADF emitters have been successfully developed by
employing donors, such as acridine,15-17 phenoxazine18-20 and
phenothiazine21, 22 etc. as well as acceptors including aromatic
nitrogen heterocyclic units,23-25 sulphonyl groups,26, 27 aromatic
ketones,28, 29 aryl phosphine oxide (APO) groups30-32 and so on.
With these novel TADF emitters, highly efficient OLEDs have
been constructed with diverse EL wavelengths required to
crossing (RISC).6, With these new-generation emitters, the
7
organic light-emitting diodes (OLEDs) can still fulfill high EL
efficiencies without costly Pt(II) and Ir(III) phosphorescent
complexes.8, 9 To maintain highly efficient RISC process, TADF
emitters possess typically small energy difference (ΔEST)
between the first singlet excited state (S1) and the first triplet
excited state (T1).10-12 To meet this purpose, TADF molecules
make Red(R)-Green(G)-Blue(B) full-color displays and white
33-36
OLEDs (WOLEDs).12,
All these encouraging results have
clearly indicated the great potential of these TADF molecules
in the field of OLEDs.
Recently, organic borons have been employed as acceptors
for the TADF molecules,37-39 especially for the blue emitters.
40
For example, B(Mes)2,37,
10H-phenazaborin41 and 10H-
a. MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed
Matter, Department of Chemistry, School of Science, State Key Laboratory for
Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, P. R.
China.
42
phenoxaborin37,
have exhibited great potential of furnish
high EL efficiencies to the concerned TADF emitters. More
importantly, some advanced rigid polycyclic boron-containing
aromatic skeletons were introduced into TADF molecules
which can bring highly efficient blue-emitting OLEDs showing
good color quality. For example, Lee and coworkers had
E-mail: zhougj@mail.xjtu.edu.cn. Fax: +86-29-8266-3914
b. Key Laboratory of Photonics Technology for Information, School of Electronic
and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R.
China.
E-mail: zhaoxinwu@mail.xjtu.edu.cn.
† Electronic supplementary information (ESI) available: Synthetic details for
intermediate compounds, CV curves and some EL data.
adopted
5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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ARTICLE
Journal Name
(OBA)-type acceptor to develop high-performance blue- voltammetry measurements were carried out on a Princeton
View Article Online
DOI: 10.1039/C9TC04115J
emitting TADF molecules through attaching carbazole-based Applied Research model 2273 A potentiostat through three-
donor to the central phenyl ring of OBA unit on the para- electrode configuration with
a
glassy carbon working
Pt-wire
position of the boron atom, showing extremely high external electrode, Pt-sheet counter electrode and
a
a
quantum efficiency (ηext) of 38.15% and color coordinates of reference electrode in electrolyte of 0.1 M [Bu4N]PF6 in
(0.15, 0.28). Deep-blue emission can also be achieved by one degassed CH3CN. All the potentials were quoted with
of this OBA-type emitters with ηext of 21.50% and attractive reference to the ferrocene/ferrocenium (Fc/Fc+) couple as an
color coordinates of (0.15, 0.06).43 Recently, Peng and Wang et internal calibrant.
al have introduced acridine moiety to different positions of
each of the two terminal phenyl rings in OBA unit.44 The OLEDs
Synthesis
The key intermediate compounds OBr, SBr, OBA, OB, and SB were
with these OBA-based TADF emitters can achieve very higher
synthesized according the literature method45-49 with the synthetic
ηext of 20.5%. 44 Clearly, the great potential of boron-containing
details presented in Electronic Supplementary Information (ESI).
units as acceptors of the TADF molecules can be seen.
Unfortunately, this kind of acceptors is still remained General procedure for synthesis of OBA-Br and OBA-2Br
unexplored compared other type acceptors aforementioned.
Hence, developing new TADF molecules with boron-containing
acceptors should be of great importance for bringing high EL
efficiencies.
N-Bromosuccinimide (NBS) (1.2 equiv, 0.395 g, 2.221 mmol)
for the synthesis of OBA-Br or (2.5 equiv, 0.823 g, 4.627 mmol )
for the synthesis of OBA-2Br was added to a solution of OBA
(1.0 equiv, 0.500 g, 1.851 mmol) in THF (10 mL) at room
temperature under nitrogen atmosphere. After the mixture
In this contribution, a series of new TADF molecules
was stirred at room temperature for 3 h, it was cooled to 0 °C
adopting asymmetric configuration have been reported with
and added to water, the reaction mixture was extracted with
OBA-type acceptor and phenoxazine or phenothiazine as
CH2Cl2. The organic layer was dried over anhydrous Na2SO4
donor. Different from all the reported symmetric TADF
and evaporated under reduced pressure, then purified by
molecules with the OBA-type acceptor, the donors in these
column chromatography over silica gel using petroleum ether
new OBA-based TADF molecules have been introduced to the
as the eluent. A white solid of the title compound was
central phenyl ring of OBA unit on meta-position of the boron
obtained.
atom. Clearly, this substitution mode and molecular structure
1
OBA-Br. Petroleum ether (PE); Yield: 67%. H NMR (400 MHz,
CDCl3): δ (ppm) 8.70 (d, J = 8.0 Hz, 2H), 7.99 (d, J = 8.0 Hz, 1H),
7.78–7.71 (m, 2H), 7.68 (d, J = 4.0 Hz, 1H), 7.55 (d, J = 8.0 Hz,
1H), 7.45–7.39 (m, 2H), 7.17 (d, J = 8.0 Hz, 1H); 13C NMR (100
MHz, CDCl3): δ (ppm) 176.8, 160.3, 153.1, 137.7, 134.6, 134.5,
134.0, 133.9, 123.4, 123.1, 118.8, 118.5, 110.1, 100.8; FAB-MS
(m/z): 348, 350 [M]+; Anal. Calcd for C18H10BBrO2: C, 61.95; H,
2.89; found: C, 61.85; H, 2.78.
will definitely enrich structure-activity relationship information
for the OBA-based TADF molecules. Critically, based on these
new OBA-based emitters, highly efficient blue-emitting OLEDs
have been constructed with CIE (0.17. 0.17), ηext of 17.8%, ηL of
33.2 cd A−1 and ηP of 34.2 lm W−1. In addition, even higher EL
performances have been furnished in bluish green devices
with EL efficiencies of 22.5%, 49.2 cd A−1 and ηP of 56.9 lm W−1.
Experimental
General information
OBA-2Br. Petroleum ether (PE); Yield: 56%. 1H NMR (400 MHz,
CDCl3): δ (ppm) 8.70 (dd, J = 7.6, 1.2 Hz, 2H), 8.24 (s, 1H), 7.80-
7.76 (m, 2H), 7.68 (d, J = 8.0 Hz, 2H), 7.45 (t, 2H); 13C NMR (100
MHz, CDCl3): δ (ppm) 158.4, 156.4, 133.1, 132.3, 128.4, 127.3,
121.8, 120.5, 117.5, 110.7; FAB-MS (m/z): 428 [M]+; Anal.
Calcd for C18H9BBr2O2: C, 50.53; H, 2.12; found: C, 50.39; H,
2.18.
Commercial chemicals were used without further purification.
All reactions were carried out under nitrogen atmosphere.
Prior to use, solvents were carefully dried and distilled from
appropriate drying agents. All reactions were monitored by
thin-layer chromatography (TLC) from Merck & Co., Inc.
Column chromatography and preparative TLC was conducted General synthetic procedure for the asymmetric OBA-based
1
by using silica gel from Shenghai Qingdao (300−400 mesh). H emitters
and 13C NMR spectra were recorded in CDCl3 or DMSO on a
Bruker Avance 400 or 600 MHz spectrometer. The chemical
Under a nitrogen atmosphere, OBA-Br (1.0 equiv, 0.10 g, 0.287
mmol)/OBA-2Br (1.0 equiv, 0.1 g, 0.235 mmol), OB/SB (1.3
equiv), and Pd(PPh3)4 (0.033 g, 0.029 mmol) were added to
degassed toluene (10 mL) and K2CO3 (3 mL, 2 M). The reaction
shifts were quoted on the solvent residual peak at δ 7.26 ppm
1
for H and 77.0 ppm for 13C NMR. Fast atom bombardment
mass spectrometry (FAB-MS) spectra were obtained on a
mixture was heated to 110 oC and stirred for 18 h. After
Finnigan MAT SSQ710 system. UV-vis spectra were recorded
cooling to room temperature, the mixture was extracted into
on
a
Shimadzu UV-2250 spectrophotometer. The
CH2Cl2 and dried with anhydrous Na2SO4. After evaporated to
dryness, the residue was purified by column chromatography
over silica gel using proper eluent.
photoluminescent spectra and lifetimes of these OBA-based
emitters were measured on Edinburgh Instruments FLS920
spectrophotometer. The photoluminescent quantum yields
(PLQYs) were determined in toluene solutions with an
integrating sphere. With a scan rate of 100 mV s−1, cyclic
1
OBA-O. CH2Cl2/petroleum ether (1:5, v:v); Yield: 62%. H NMR
(400 MHz, CDCl3): δ (ppm) 8.12 (d, J = 7.2 Hz, 2H), 7.86 (d, J =
7.2 Hz, 2H), 7.41 (dd, J = 8.0, 4.4 Hz, 3H), 7.35–7.16 (m, 6H),
2 | J. Name., 2012, 00, 1-3
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Journal of Materials Chemistry C
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6.97 (d, J = 8.4 Hz, 1H), 6.70-6.60 (m, 6H), 6.07 (d, J = 9.2 Hz, (Scheme 1). The brominated compounds OBr aVniedw ASrBticrlewOnelirnee
2H); 13C NMR (100 MHz, CDCl3): δ (ppm) 158.7, 158.5, 157.5, synthesized by Ullmann cross-coupling between 1-bromo-4-
DOI: 10.1039/C9TC04115J
154.3, 144.0, 138.8, 137.0, 134.6, 133.2, 133.0, 132.6, 132.0, iodobenzene and 10H-phenoxazine for OBr or 10H-
130.3, 130.2, 128.5, 128.4, 123.8, 123.3, 123.1, 122.9, 122.1, phenothiazine for SBr with Cu as catalyst and Cs2CO3 as base.
121.2, 117.1, 115.6, 115.4, 113.4, 110.0; FAB-MS (m/z): 527 Then, OBr and SBr had been converted into the corresponding
[M]+; Anal. Calcd for C36H22BNO3: C, 81.99; H, 4.20; N, 2.66 boronic acid pinacol esters OB and SB by Suzuki cross-coupling
found: C, 81.89; H, 4.11; N, 2.55.
in high yield of ca. 80%. Finally, the OBA-based emitters OBA-
O and OBA-S were obtained by Suzuki cross-coupling between
OBA-Br and OB/SB, while the analogs OBA-BrO and OBA-BrS
were prepared with similar strategy with OBA-2Br as staring
material.
1
OBA-S. CH2Cl2/petroleum ether (1:5, v:v); Yield: 54%. H NMR
(400 MHz, CDCl3): δ (ppm) 8.12 (d, J = 7.2 Hz , 2H), 7.87 (d, J =
8.4 Hz, 2H), 7.43 (dd, J = 11.2, 1.6 Hz, 3H), 7.31 (td, J = 8.8, 1.6
Hz, 2H), 7.2-7.1 (m, 4H), 7.02 (dd, J = 7.2, 1.6 Hz, 2H), 6.97 (d, J
= 8.4 Hz, 1H), 6.89 (t, J = 7.6 Hz, 2H). 6.81 (t, J = 7.6 Hz, 2H).
6.39 (dd, J = 8.0, 0.8 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ
(ppm) 160.5, 160.3, 157.6, 153.7, 139.2, 139.1, 138.1, 136.1,
134.8, 134.7, 134.1, 134.0, 132.8, 132.4, 132.1, 130.6, 130.4,
123.4, 122.6, 122.3, 120.4, 118.8, 118.7, 117.7, 109.5; FAB-MS
(m/z): 543 [M]+; Anal. Calcd for C36H22BNO2S: C, 79.57; H, 4.08;
N, 2.58 found: C, 79.49; H, 4.05; N, 2.47.
Chemical structures of these asymmetric OBA-based TADF
emitters have been characterized by NMR spectroscopies,
mass spectrometry and elemental analyses. A characteristic
doublet signal at δ ca. 8.1 ppm for all the OBA-based TADF
emitters can be assigned to the two protons attached to the
carbon atoms adjacent to the boron-bonded carbon atoms in
the OBA unit. The doublet resonance peak at δ ca. 7.9 ppm can
be ascribed to the two protons close to the OBA unit on phenyl
ring between OBA acceptor and corresponding donor. For
OBA-BrO and OBA-BrS, the singlet signal at δ ca. 7.6 ppm
should be induced by the proton in between –Br group and
donor on the OBA unit. The other several sets of resonance
peaks after ca. 7.1 ppm can be safely assigned to the protons
on phenoxazine or phenothiazine groups. These NMR spectral
data have clearly confirmed the chemical structures of these
OBA-based TADF emitters (Figure S1-4).
1
OBA-BrO. CH2Cl2 / petroleum ether (1:3, v:v); Yield: 58%. H
NMR (400 MHz, CDCl3): δ (ppm) 8.13 (d, J = 7.2 Hz, 2H), 7.85 (d,
J = 8.4 Hz, 2H), 7.63 (s, 1H), 7.40 (d, J =8.4 Hz, 2H), 7.32 (t, J =
6.8 Hz, 3H), 7.22–7.13 (m, 3H), 6.70–6.61 (m, 6H), 6.06 (d, J =
9.2 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ (ppm) 158.3, 158.2,
153.3, 153.2, 144.0, 137.6, 137.4, 134.4, 133.1, 133.0, 132.9,
132.0, 130.3, 128.5, 128.4, 123.4, 123.3, 123.2, 121.2, 117.4,
117.0, 115.4, 113.4, 102.5; FAB-MS (m/z): 605, 607 [M]+; Anal.
Calcd for C36H21BBrNO3: C, 71.32; H, 3.49; N, 2.31 found: C,
71.19; H, 3.37; N, 2.18.
OBA-BrS. CH2Cl2/petroleum ether (1:3, v:v); Yield: 46%. 1H
NMR (400 MHz, CDCl3): δ (ppm) 8.12 (d, J = 7.2 Hz, 2H), 7.85 (d,
J = 8.4 Hz, 2H), 7.66 (s, 1H), 7.45 (d, J = 8.4 Hz, 2H), 7.35-7.15
(m, 6H), 7.03 (dd, J = 7.6, 1.6 2H), 6.90(t, J = 7.6 Hz, 2H), 6.82 (t,
J = 7.6Hz, 2H), 6.38 (dd, J = 8.0, 0.8 Hz, 2H); 13C NMR (100 MHz,
CDCl3): δ (ppm) 160.2, 160.0, 152.8, 152.6, 139.0, 138.6, 136.0,
134.6, 134.3, 134.2, 134.1, 132.7, 132.3, 132.0, 131.8, 130.5,
130.2, 126.9, 123.6, 123.4, 122.6, 122.2, 118.8, 118.7, 117.5,
116.7, 101.5; FAB-MS (m/z): 621, 623 [M]+; Anal. Calcd for
C36H21BBrNO2S: C, 69.48; H, 3.40; N, 2.25 found: C, 69.36; H,
3.31; N, 2.19.
Different from the substitution pattern employed by
literature analogs,43,44 introducing donors to the meta-position
of the boron atom in the central phenyl ring of OBA unit can
facilitate the synthesis of these OBA-based TADF emitters with
diverse structures at the same time providing new information
about structure-property relationship of this type of TADF
emitters.
Thermal and photophysical properties
Under nitrogen flow, thermal properties of these asymmetric
OBA-based emitters had been characterized by both
thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC). Indicated by the TGA data (Figure S5), all
the OBA-based emitters can show good thermal stability with
decomposition temperature (Td) ranging from 362 to 393 °C
(Table 1). Introducing –Br group, OBA-BrO and OBA-BrS can
possess higher Td than OBA-O and OBA-S (Table 1), which
should be ascribed to the conjugation effect between –Br
group and OBA ring to stabilize C-B bond. The DSC traces
reveal no glass transition process for these asymmetric OBA-
based emitters to benefit their EL application, indicating their
high phase stability induced by their twist structures due to
introducing donor to the meta-position of the boron atom in
the central phenyl ring of OBA unit.
Results and discussion
Synthesis and structural characterization
The synthetic strategies for the asymmetric OBA-based TADF
emitters are outlined in Scheme 1 and the synthetic details for
the literature compounds are provided in ESI. From Scheme 1,
the preparation of the designed TADF emitters is fulfilled by
Suzuki cross-coupling between the compound of boronic acid
pinacol ester containing donor group OB or SB and the
corresponding brominated OBA derivative OBA-Br or OBA-2Br
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ARTICLE
O
O
Br
B
H
N
Bis(pinacolato)diboron
Pd(dppf)Cl2, KOAc
110 o
Cu
160 o
I
Br
+
C
N
X
X
N
X
C
X : O
X : S
OBr
SBr
X : O
X : S
X : O
OB
X : S
SB
OH
i) nBuLi, 0 to 70 o
C
O
O
O
O
Cs2CO3, CuBr
ii) BBr3, -40 to 40 o
C
+
160 o
C
B
Br
Br
ii) iPr2NEt, 0 to 120 o
C
OBA
1.2 equv NBS
2.5 equv NBS
25 o
C
25 o
C
X
X
N
N
Br
O
Br
Br
O
Br
OB SB
or
OB SB
or
O
O
O
O
O
O
Pd(PPh3)4
Pd(PPh3)4
B
B
B
B
2M Na2CO3
2M Na2CO3
110 o
C
110 o
C
OBA-Br
OBA-2Br
OBA-O
OBA-S
X : O
X : S
OBA-BrO
OBA-BrS
X : O
X : S
Scheme 1 Synthesis of the OBA-based TADF emitters.
Table 1. Photophysical and thermal data of these asymmetric OBA-based emitters
f
Absorption a
λabs (nm)
Emission
λem (nm)
Td
Compounds
OBA-O
PLQY
(oC)
283 (4.69), 299 (3.92), 309 (4.57), 338
(4.15), 386 (4.27)
444 b/450c
456 b/470c
470 b/476c
478 b/470c
0.76d/0.84e
0.63d/0.75e
0.84d/0.92e
0.53d/0.55e
362
385
393
391
283 (4.74), 300 (4.54), 310 (4.58), 342
(4.03), 387 (4.30)
OBA-S
282 (4.34), 301 (4.13), 312 (4.18), 385
(3.93), 391 (3.95)
OBA-BrO
OBA-BrS
282 (4.60), 301 (4.36), 312 (4.41), 385
(4.15), 392 (4.17)
a Measured at a concentration of ca. 10-5 M in toluene at room temperature and log  values in parentheses are presented. b Measured
in toluene at 293 K. c Measured in doped mCP film (doping ratio: 10 wt.%) at 293 K. d Absolute PL quantum yield (PLQY) in toluene
measured with an integrating sphere at room temperature. e Absolute PL quantum yield (PLQY) in doped mCP film (doping ratio: 10
wt.%) measured with an integrating sphere at 293 K. f Td is the decomposition temperature.
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literature results.38, 50-54 With –Br group, the low-energy absorption
bands for OBA-BrO and OBA-BrS can show slight bathochromic
effect compared with those from OBA-O and OBA-S without –Br
group (Figure 1a).
(a)
OBA-O
OBA-S
OBA-BrO
OBA-BrS
1.0
0.8
0.6
0.4
0.2
0.0
In order to get deep insight into the absorption feature of
these asymmetric OBA-based emitters, key front molecular
orbitals (MOs) have been obtained by theoretical calculation
based on their ground states (S0) (Figure 2). From the MO
pattern of these OBA-based emitters, obvious separation
between their highest occupied molecular orbital (HOMO) and
the lowest unoccupied molecular orbital (LUMO) can be seen
clearly (Figure 2). It indicates that the lowest energy transition
processed in these asymmetric OBA-based emitters originate
from π orbitals of the donor groups to the π* orbitals of the
acceptor group of OBA unit, exhibiting obvious intra-molecular
charge transfer (CT) feature. Thus, the low-energy
structureless broad absorption bands of OBA-O, OBA-S, OBA-
BrO and OBA-BrS should be induced by the intra-molecular
charge transfer transition process. In addition, the CT feature
of their low-energy absorption has been indicated by the
structureless broad spectral line-shape (Figure 1a). Obviously,
introducing electron-withdrawing –Br group to the acceptor
OBA unit will definitely facilitate the intra-molecular CT
process in these asymmetric OBA-based emitters to stabilize
their CT states. Hence, the low-energy CT absorption bands of
OBA-BrO and OBA-BrS can show bathochromic effect
compared with those of OBA-O and OBA-S free of –Br group
(Figure 1a). Clearly, the experimental results are consistent
well with the theoretical results, indicating the validity of the
theoretical calculations.
300
350
400
450
Wavelength (nm)
(b)
OBA-O
OBA-S
OBA-BrO
OBA-BrS
1.0
0.8
0.6
0.4
0.2
0.0
Photoluminescent (PL) spectra of these asymmetric OBA-
based emitters are shown in Figure 1b. Generally, these
asymmetric OBA-based emitters can show PL spectra in blue
light region with broad spectral line-shape (Figure 1b). The
broad spectral lines without fine structure also indicate the CT
features of their emission behavior. Owing to the stronger
donating ability associated with phenothiazyl group, OBA-S (ca.
456 nm) and OBA-BrS (ca. 478 nm) can show longer emission
wavelength than their corresponding analogs OBA-O (ca. 444
nm) and OBA-BrO (ca. 470 nm) with phenoxazyl donor (Figure
1b and Table 1). Based on the optimized structures of these
asymmetric OBA-based emitters, the phenoxazyl group can
adopt perfect planar configuration (Figure 2), showing higher
rigidity than the nonplanar phenothiazyl group. The highly rigid
phenoxazyl group should show advantage of restraining the
nonradiative processes in OBA-O and OBA-BrO.20 Hence, OBA-
O possesses higher PLQY than OBA-S and so does OBA-BrO
350
400
450
500
600
650
Wavelength5(5n0m)
Fig. 1 UV−vis absorption (a) and PL (b) spectra for these asymmetric
OBA-based emitters in toluene at 293 K.
Figure 1a shows UV−vis absorption spectra of these asymmetric
OBA-based emitters in toluene at 293 K and the corresponding data
have been summarized in Table 1. For all these asymmetric OBA-
based emitters, they typically exhibit two major absorption bands
(Figure 1a). The high-energy strong absorption bands before 350
nm should be assigned to the π → π* transitions in aromatic
systems in both OBA unit and donor groups. However, besides
these high-energy absorption bands, these asymmetric OBA-based
emitters can show a relatively weaker absorption band around 390
nm with broad structureless spectral line (Figure 1a). These broad
structureless low-energy absorption bands should be induced by
the charge-transfer (CT) process in these asymmetric OBA-based
emitters, regarding as a character to show TADF behavior based on than OBA-BrS (Table 1).
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DOI: 10.1039/C9TC04115J
Fig. 2 Molecular orbital patterns (isocontour value = 0.025) for the asymmetric OBA-based emitters based on their optimized S0
geometries. (a) OBA-O, (b) OBA-S, (c) OBA-BrO and (d) OBA-BrS.
Table 2. TADF data of these asymmetric OBA-based emitters
τPF
τDF
ФPF
ФDF
kPF
kDF
kISC
kRISC
S1
T1
∆EST
(ns)c
(µs)c
(%)d
(%)d
(107 s-1)e (105 s-1)e (106 s-1)f
(105 s-1)f
Compound
(eV)a
(eV)a
(eV)b
3.15
3.17
3.25
3.19
OBA-O
OBA-S
OBA-BrO
OBA-BrS
3.06
3.08
3.21
3.12
0.09
0.09
0.04
0.07
90.7
77.9
33.1
47.8
4.14
4.80
3.74
0.81
27.0
27.1
19.8
24.5
57.0
48.0
72.2
30.5
0.30
0.35
0.60
0.51
1.38
1.01
1.93
3.75
2.02
2.22
4.70
2.84
4.28
2.76
8.97
8.41
a Experimental data were determined from onsets of the fluorescence and phosphorescence (77 K) spectra in doped mCP film (doping ratio: 10 wt.%). b ∆EST = ES1 - ET1
.
c
The prompt fluorescence lifetime (τPF) and delayed fluorescence lifetime (τDF) were measured in doped mCP film at 300 K. d The prompt fluorescence quantum yields
(ФPF) and delayed fluorescence quantum yields (ФDF) were estimated according to the prompt and delayed proportions in transient decay curves. e The rate constants
of PF and DF (kPF and kDF) evaluated according to experimental data: kPF = ФPF / τPF and kDF = ФDF / τDF
kRISC) are further estimated according to kISC = ФDF kPF / (ФPF + ФDF) and kRISC = kDF kPF ФDF / (kISC ФPF).
.
f The rate constants of intersystem crossing and reverse (kISC and
TADF behaviors
S0 → T1 transitions based on the optimized S1 and T1
geometries of these asymmetric OBA-based TADF emitters
have been obtained through theoretical calculations (Figure 4).
Due to the fact that both HOMO and LUMO patterns are
obtained on the basis of the S0 state,41, 43-45 NTOs based on
excited states should be reasonably employed to interpret
their TADF behavior involving the excited states of these OBA-
based emitters. From the NTO patterns for both S0 → S1 and S0
→ T1 transitions, there is a distinct separation between hole
and particle orbitals of these asymmetric OBA-based emitters
(Figure 4). Furthermore, the large twisting angle > 90o
between donor and acceptor OBA group can also furnish
distinct separation of the NTOs as well (Figure 4). For sure,
these characters associated with the asymmetric OBA-based
emitters should definitely favor their TADF behaviors.
Adopting D-π-A configuration facilitating their TADF behavior,
all these asymmetric OBA-based emitters should possess TADF
ability. In order to characterize their TADF behavior, the
transient decay curves have been obtained in both doped film
in mCP and degassed toluene at different temperature (Figure
3). Clearly, in both mCP doped film and toluene, two decay
processes can be observed. The prompt decay processes show
short lifetimes in the order of dozens of nanoseconds, while
the delayed decay processes can show much longer lifetimes
in the order of microsecond which is shortened with increasing
of temperature (Figure 3 and Table 2). All these characteristic
phenomena have indicated the TADF feature for the emission
behavior of these asymmetric OBA-based emitters. Critically,
even at 77 K, they still can maintain the delayed decay process
(Figure 3), indicating their efficient reverse intersystem
crossing (RISC) process even at very low temperature.
With the aim to interpret their different TADF behavior,
natural transition orbital (NTO) patterns for both S0 → S1 and
6 | J. Name., 2012, 00, 1-3
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(a)
(b)
100
10-1
10-2
10-3
100
10-1
10-2
100
77 K
150 K
300 K
100
10-1
10-2
77 K
150 K
300 K
10-1
0
1
2
3
4
5
0
1
2
3
4
5
10-2
0
2
4
6
8
0
2
4
6
8
Time (s)
Time (s)
100
10-1
10-2
10-3
10-4
(c)
(d)
100
10-1
10-2
77 K
150 K
300 K
100
10-1
10-2
10-3
10-4
77 K
150 K
300 K
100
0
1
2
3
4
5
10-1
0.0
0.3
0.6
0.9
1.2
1.5
0
2
4
6
8
0
1
2
3
4
Time (s)
Time (s)
Fig. 3 Transient PL decays for these asymmetric OBA-based emitters doped in mCP film (doping ratio: 10 wt.%). The inset shows
the temperature dependence of transient PL decay in degassed toluene. (a) OBA-O, (b) OBA-S, (c) OBA-BrO and (d) OBA-BrS,
0.07 eV, respectively (Table 2). Owing to their smaller ∆EST
Based on the photophysical results, critical parameter ∆EST values, OBA-BrO and OBA-BrS can show higher kRISC values of
has been obtained for these asymmetric OBA-based emitters. 8.97 × 105 s-1 and 8.41 × 105 s-1 than OBA-O (ca. 4.28 × 105 s-1)
Clearly, all the experimental ∆EST values are less than 0.1 eV and OBA-S (ca. 2.76 × 105 s-1) (Table 2). Reasonably, electron-
(Table 2), which is also supported by the theoretical results withdrawing –Br group on OBA acceptor will promote
(Figure 4). The small ∆EST values associated with these separation of the MOs of these asymmetric OBA-based TADF
asymmetric OBA-based emitters will also furnish high TADF emitters, which will favor the TADF procedure of OBA-BrO and
ability. With –Br group, OBA-BrO and OBA-BrS can show OBA-BrS. Hence, they can possess higher kRISC value as
higher rate constants of intersystem crossing (kISC,
4.70 × 106 s-1 aforementioned. In addition, the OBA-based TADF emitters
and 2.84 × 106 s-1, respectively) compared with OBA-O (2.02 × 106 OBA-O and OBA-BrO with rigid phenoxazyl group can possess
s-1) and OBA-S (2.22 × 106 s-1) due to the heavy-atom effect higher kRISC values compared with their analogs OBA-S and
induced by –Br group (Table 2). Also, owing to the heavy-atom OBA-BrS with phenothiazyl group, respectively (Table 2). This
effect, OBA-BrO and OBA-BrS can possess shorter prompt result might be ascribed to the fact that the rigidity associated
fluorescence lifetime (τPF) than OBA-BO and OBA-BS (Table 2). with the phenoxazyl group in OBA-O and OBA-BrO can reduce
It should be noted that introducing –Br group can bring even the chance of competition with RISC process from the
small ∆EST values. The ∆EST values are 0.09 eV for OBA-O and nonradiative procedure due to the molecular flexibility. 20
OBA-S, while those for OBA-BrO and OBA-BrS are 0.04 and
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Fig. 4 Natural transition orbital patterns (isocontour value = 0.025) for both S0 → S1 and S0 → T1 excitations based on the optimized S1 and
T1 geometries, respectively, together with the S0 geometry showing twisting angle between donor and acceptor.
Electrochemical properties
This reduction process can be safely assigned to the reduction
of the acceptor OBA group. Owing to the electron-withdrawing
–Br group on the OBA unit, OBA-BrO and OBA-BrS can show
reduction potentials (Epc) of -2.37 V and -2.46 V, less negative
than those of OBA-O (ca. -2.49 V) and OBA-S (ca. -2.52 V),
respectively (Table 3). Due to the stronger electron-donating
ability of sulfur atom than oxygen atom, the phenothiazyl
group make the OBA acceptor in OBA-S and OBA-BrS more
difficult to be reduced. Hence Epc of -2.52 V for OBA-S is lower
than Epc of -2.49 V for OBA-O. Comparing with the Epcs of OBA-
BrO and OBA-BrS, the same trend can be observed.
Electrochemical data of these asymmetric OBA-based TADF
emitters had been measured through cyclic voltammetry (CV)
with ferrocene as the internal standard. In the anodic scan, all
the OBA-based TADF emitters can exhibit reversible oxidation
processes (Table 3 and Figure S6). The reversible oxidation
processes with oxidation potential (Epa) in the range from 0.32
to 0.35 V can be ascribed to the oxidation the donor groups in
these OBA-based TADF emitters (Table 3). There is an
irreversible reduction process observed for all these
asymmetric OBA-based TADF emitters (Table 3 and Figure S1).
Table 3. Redox properties of these asymmetric OBA-based emitters
Epa (V)
Epc (V)
EHOMO (eV) c
ELUMO (eV)d
EgCV (eV)e
Compound
OBA-O
OBA-S
0.35a,0.49 a
0.34a
-2.49 b
-2.52b
-5.15
-5.14
-2.31
-2.28
2.84
2.86
0.33a
0.32a
-2.37b
-2.46b
-5.13
-5.12
-2.43
-2.34
2.70
2.78
OBA-BrO
OBA-BrS
a Reversible. The value was set as E1/2 b Irreversible. The value was derived from the cathodic peak potential. c EHOMO = – (4.8 + Epa
. )
eV. d ELUMO = – (4.8 + E1pc) eV, E1pc : First reduction potential. e CV energy gap Egcv = LUMO – HOMO.
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9.2%, ηL of 20.3 cd A−1 and ηP of 20.9 lm W−1 thVainewdAretivcliecOenBlin2e
with OBA-S as emitter (Figure 8 and Table 4). Obviously,
Electroluminescent ability
DOI: 10.1039/C9TC04115J
Inspired by the blue emission and high PLQY of these
asymmetric OBA-based emitters, their doped OLEDs had been
constructed with device configuration of ITO/ HATCN (5 nm)/
TAPC (40 nm)/x-wt% Emitter : mCP (20 nm)/ TmPyPB (40 nm)/
LiF (1 nm)/ Al (100 nm) (Figure 5). Considering practical
application, well-known functional materials have been
employed to make the devices. Dipyrazino[2,3-f:2',3'-
h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HATCN) and di-
[4-(N,N-ditolylamino)phenyl]cyclohexan (TAPC) serve as hole
injector and hole transporter. 1,3-Bis(carbazol-9-yl)benzene is
the host material. 1,3,5-Tri[(3-pyridyl)-phen-3-yl]benzene
(TmPyPB) has been employed to serve the function of both
hole-blocking and electron-transporting, while LiF and Al are
used as the electron injection layer (EIL) and cathode,
respectively.
devices based on OBA-O and OBA-BrO can show much higher
EL efficiencies than the ones with OBA-S and OBA-BrS (Figure
8 and Table 4). This result might be ascribed to the higher
PLQY for OBA-O (ca. 0.84) and OBA-BrO (ca. 0.92) than that of
OBA-S (ca. 0.75) and OBA-BrS (ca. 0.55) (Table 1). All these
encouraging EL data should indicate the great potential of the
OBA moiety in developing highly efficient TADF emitters.
N
Al (100 nm)
LiF (1 nm)
TmPyPB (40 nm)
N
N
x wt% :mCP (20 nm)
TAPC (40 nm)
HATCN (5 nm)
ITO (100 nm)
Glass
When adding a proper driving voltage to the OLEDs, EL
emission can be recorded (Figure 6). The EL spectra (Figure 6)
of the optimized OLEDs exhibit great resemblance to the PL
spectra of the involved OBA-based TADF emitters with
bathochromic effect. From the energy diagram involved in
these OLEDs, these asymmetric OBA-based TADF emitters
should be mainly excited by energy-transfer from mCP host to
the TADF guests. The current density-voltage-luminance (J-V-L)
curves and efficiency-luminance relationship of the devices are
shown in Figures 7, 8 and ESI (Figure S7, S8 and S9)
respectively. The EL data are tabulated in Table 4.
TmPyPB
N
N
mCP
2.00 eV
2.28 eV
2.31 eV
2.34 eV
NC
N
CN
N
2.43 eV
2.40 eV
2.70 eV
N
N
NC
CN
Compared with the PL spectra (Table 1), the EL wavelength
(Table 4) exhibits red-shift effect compared with the
corresponding PL wavelength. Furthermore, magnitude of the
red-shift effect is in proportion to the PL wavelength (Table 1
and 4). This result can be ascribed to the exciton stabilization
effect from the polar host mCP molecules. For TADF emitter
with D-A structure, the emitter with longer emission
wavelength can generate excitons with higher polarity with
larger dipole-moment, which can interact strongly with polar
mCP molecules and hence induce much stronger exciton
stabilization effect to effectively lower energy-level of the
excitons. As a result, compared with analog with shorter
emission wavelength, the emitter with longer emission
wavelength should generate EL with much longer wavelength
compared with its PL wavelength obtained in low polar
toluene. Hence, larger red-shift effect from PL to the
corresponding EL spectrum can be observed for the emitter
with the longer emission wavelength.
With OBA-O as the emitter, the device A2 emitting the bluest
color of 446 nm with CIE (0.17, 0.17) can be turned on at a
very low voltage of 2.7 eV. Importantly, device A2 can achieve
maximum ηext of 17.8%, ηL of 33.2 cd A−1 and ηP of 34.2 lm W−1
with maximum luminance (Lmax) of 6785.2 cd m-2 at 13.2 V
(Figure 8a and Table 4). The device C2 based on OBA-BrO can
also show attractive EL ability with ηext of 22.5% and ηL of 49.2
cd A−1 respectively (Figure 8c and Table 4). With low turn-on
voltage (Vturn-on) of 2.7 V, the highest ηP of 56.9 lm W−1 can be
afforded by device C2. Despite of its inferior EL performances
with respect to those of devices A2 and C2, device D2 based
on OBA-BrS still show much higher EL efficiencies with ηext of
N
N
NC
CN
HATCN
5.12 eV
5.13 eV
5.14 eV
5.15 eV
5.60 eV
mCP
5.90 eV
6.70 eV
Dopant
Devices and doping level
OBA-O
OBA-S
A1 (3 wt%), A2 (5 wt%), A3 (7 wt%)
B1 (3 wt%), B2 (5 wt%), B3 (7 wt%)
OBA-BrO C1 (3 wt%), C2 (5 wt%), C3 (7 wt%)
OBA-BrS D1 (3 wt%), D2 (5 wt%), D3 (7 wt%)
Fig. 5 Device structure of the vacuum evaporated OLEDs together
with energy level diagram and molecular structures of the materials
employed in the fabricated OLEDs.
Device A2
Device B2
Device C2
Device D2
1.0
0.8
0.6
0.4
0.2
0.0
400
700
Wavelengt6h00(nm)
500
Fig. 6 EL spectra for the optimized OLEDs based on these
asymmetric OBA-based emitters at ca. 5 V.
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104
103
102
101
100
10-1
1000
800
600
400
200
0
Device A2
Device B2
Device C2
Device D2
4
6
8
10
12
14
Voltage (V)
Fig. 7 Current density-voltage-luminance (J-V-L) characteristics for the optimized OLEDs based on these asymmetric OBA-based
emitters.
10
10
1
10
1
10
1
1
0.1






L
P
L
P
0
0.1
0
0.1
0






ext
1E-3
1E-4
ext
(a)
(b)
1000
0.1
10
100
1000
-2
10
100
-2
Luminance (cd m
)
Luminance (cd m )
100
10
1
10
1
10
1
10
1


0.1
0


L
L
0.1
0


P
P
0.1
0






1E-3
1E-4
ext
ext
(c)
(d)
0.1
1E-3
1
10
100
1000
1
10
100
Luminance (cd m-2
)
-2
Luminance (cd m
)
Fig. 8 Relationship between EL efficiencies and luminance for the optimized devices. (a) Device A2, (b) Device B2, (c) Device C2 and (d)
Device D2
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Table 4. EL performance of these asymmetric OBA-based TADF emitters.
View Article Online
DOI: 10.1039/C9TC04115J
Vturn-on Luminance Lmax
(V)
ext
(%)
L
(cd A-1)
P
(lm W-1)
max
(nm) d
Device
Dopant
(cd m-2) a
14.1 (3.1) a
11.7 b
26.2 (3.1)
22.7
10.7
27.0 (3.1)
21.2
446
(0.17, 0.17)
A1
OBA-O (3.0 wt %)
3.1
4735.3 (13.2)
5.8 c
6.6
17.8 (3.1) a
33.2 (3.1)
28.3
16.3
34.2(3.1)
26.5
11.7
446
(0.17, 0.17)
A2
A3
B1
B2
B3
C1
C2
C3
OBA-O (5.0 wt %)
OBA-O (7.0wt %)
OBA-S (3.0 wt %)
OBA-S (5.0 wt %)
OBA-S (7.0wt %)
2.7
3.1
3.4
3.4
3.1
3.1
2.7
2.7
6785.2 (13.2)
4763.0 (13.6)
3051.9 (14.6)
3582.6 (14.2)
3525.6 (14.2)
1618.7 (11.5)
1694.8 (10.2)
1621.4 (9.2)
15.5 b
8.5 c
10.8 (3.1) a
20.0 (3.1)
11.3
5.4
2.4 (3.4)
0.8
0.7
6.3 (3.4)
1.7
1.0
4.9 (3.4)
1.4
0.8
26.4 (3.1)
9.1
1.6
49.2 (2.7)
26
7.1
38.7 (2.7)
22.5
20.6 (3.1)
9.5
3.1
2.2 (3.4)
0.5
0.2
5.8 (3.4)
1.2
0.3
4.5 (3.4)
0.9
0.3
27.5 (4.1)
27.1
4.3
56.9 (2.7)
22.5
4.3
44.8 (2.7)
18.6
446
(0.17, 0.17)
5.8 b
2.9 c
1.7 (3.7) a
0.6 b
488
(0.20, 0.31)
0.5 c
4.4 (3.4) a
1.3 b
488
(0.20, 0.31)
0.7 c
3.4 (3.4) a
0.95 b
488
(0.20, 0.31)
0.6 c
12.1 (3.1) a
4.1 b
500
(0.21, 0.38)
OBA-BrO (3.0 wt %)
OBA-BrO (5.0 wt %)
OBA-BrO (7.0 wt %)
0.8 c
22.5 (2.7) a
12.5 b
500
(0.21, 0.38)
3.1 c
17.7 (2.7) a
10.5 b
500
(0.21, 0.38)
2.2 c
4.8
2.7
7.6 (3.1) a
0.7 b
16.8 (3.1)
1.6
17.3 (3.1)
0.8
520
(0.29, 0.46)
D1
D2
D3
OBA-BrS (3.0 wt %)
OBA-BrS (5.0 wt %)
OBA-BrS (7.0 wt %)
3.1
2.7
2.7
891.6 (14.2)
959.4 (14.2)
908.6 (13.9)
9.2 (3.1) a
0.8 b
20.3 (3.1)
1.7
20.9 (3.1)
0.9
520
(0.29, 0.46)
8.2 (3.1) a
0.8 b
18.1 (3.1)
1.8
18.7 (3.1)
1.0
520
(0.29, 0.46)
a Maximum values of the devices. Values in the parentheses are the voltages at which they were obtained. b Values collected at 100 cd m-2. c
Values collected at 1000 cd m-2. d Values were collected at 7 V and CIE coordinates (x, y) are showed in parentheses.
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6
M. Saigo, K. Miyata, S. i. Tanaka, H. Nakanotani, C. Adachi
and K. Onda, J. Phys. Chem. Lett., 2019, 10, 2475-2480.
D. Li, Y. Hu and L.-S. Liao, J. Mater. Chem. C, 2019, 7, 977-985.
C. H. Yang, Y. M. Cheng, Y. Chi, C. J. Hsu, F. C. Fang, K. T.
Wong, P. T. Chou, C. H. Chang, M. H. Tsai and C. C. Wu,
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P. Ganesan, W. Y. Hung, J. Y. Tso, C. L. Ko, T. H. Wang, P. T.
Chen, H. F. Hsu, S. H. Liu, G. H. Lee and P. T. Chou, Adv. Funct.
Mater., 2019, 29, 1900923.
Conclusions
7
8
Through attaching donor groups to the meta-position of 5,9-
dioxa-13b-boranaphtho[3,2,1-de]anthracene (OBA) unit, four
novel organic TADF emitters with asymmetric configuration
have been developed with the highest kRISC of 8.97×105 s−1. It
has been found that introducing –Br group to the OBA unit can
enhance the TADF ability of these asymmetric OBA-based
TADF emitters. Importantly, deep-blue TADF emission at 440
nm can be achieved in these asymmetric OBA-based TADF
emitters with very high PLQY of ca. 0.84 in doped film. In
addition, with these novel OBA-based TADF emitters, the
doped OLEDs can exhibit attractive EL performances in blue-
emitting OLEDs with a maximum ηext of 17.8%, ηL of 33.2 cd A−1,
ηP of 34.2 lm W−1 and EL maximum 448 nm associating CIE
(0.17, 0.17). In addition, the bluish green OLEDs can achieve
even higher EL performances with a maximum ηext of 22.5%, ηL
of 49.2 cd A−1, ηP of 56.9 lm W−1. All these promising results
not only provide critical information of structure-activity
relationship for OBA-based emitters, but also indicate the
great potential of the OBA moiety as acceptor group to
develop TADF emitters with advanced EL capacity.
9
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Acknowledgements
We thank the National Natural Science Foundation of China
(Grants 21875179, 21572176, 21602170, and 51803163) for
financial support. The characterization assistance from the
Instrument Analysis Center of Xi’an Jiaotong University was
also acknowledged.
Conflicts of interest
There are no conflicts to declare.
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DOI: 10.1039/C9TC04115J
TOC
Asymmetric thermally activated delayed fluorescence (TADF) emitters with 5,9-dioxa-13b-
boranaphtho[3,2,1-de]anthracene (OBA) as acceptor and highly efficient blue-emitting OLEDs †
Dongdong Song, Yue Yu, Ling Yue, Daokun Zhong, Yindi Zhang, Xiaolong Yang, Yuanhui Sun,
Guijiang Zhou, Zhaoxin Wu
With 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (OBA) as acceptor, thermally activated delayed
fluorescence (TADF) emitters adopting asymmetric configuration can achieve highly efficient blue-
emitting OLEDs.
14 | J. Name., 2012, 00, 1-3
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