An efficient material via meta-position connection as thermally activated delayed fluorescence emitter for organic light-emitting diodes

Article abstract of DOI:10.1016/j.tetlet.2017.03.018

A novel compound was designed and synthesized by connecting a dicyanobenzene acceptor and two 9,9-dimethyl-9,10-dihydroacridine donors to the 1,3,5-position of a phenyl ring by meta-position connection. This compound, which is a novel emitter for OLED dev

Full text of DOI:10.1016/j.tetlet.2017.03.018

Accepted Manuscript
An efficient material via meta-position connection as thermally activated de-
layed fluorescence emitter for Organic Light-Emitting Diodes
Yuting Cui, Jianhui Liu
PII:
S0040-4039(17)30304-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.03.018
TETL 48719
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
12 January 2017
2 March 2017
7 March 2017
Please cite this article as: Cui, Y., Liu, J., An efficient material via meta-position connection as thermally activated
delayed fluorescence emitter for Organic Light-Emitting Diodes, Tetrahedron Letters (2017), doi: http://dx.doi.org/
10.1016/j.tetlet.2017.03.018
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An efficient material via meta-position connection as
thermally activated delayed fluorescence emitter for
Organic Light-Emitting Diodes
Yuting Cuia, Jianhui Liua, b *
aSchool of Petroleum and Chemical Engineering, Dalian University of Technology,
Panjin Campus, Panjin, Liaoning Province 124221, PR China
bState Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian
116024, PR China
* Corresponding author.
E-mail address: liujh@dlut.edu.cn (J. Liu).
Tel: +86-138-98426106
Abstract
A novel compound was designed and synthesized by connecting a
dicyanobenzene acceptor and two 9,9-dimethyl-9,10-dihydroacridine donors to the
1,3,5-position of a phenyl ring by meta-position connection. This compound, which is
a novel emitter for OLED devices, exhibits preferable heat stability. Moreover, the
energy gap between its singlet and triplet states is as small as 0.04 eV, resulting in this
molecule possesses thermally activated delayed fluorescence. Therefore, the
corresponding device showed efficient electroluminescent performances. The
maximum external quantum efficiency, maximum current efficiency, maximum power
efficiency and maximum luminance were 16.5%, 40.8 cd A-1, 45.8 lm W-1 and 5120
cd m-2, respectively. In addition, the CIEx,y only changed from (0.22, 0.38) to (0.22,
0.39) over the entire operating voltage range, which confirms that the device
possesses highly stable chromaticity with respect to the current density. Based on
these experimental results, meta-connected type structures may provide a new
approach for developing high-performance TADF emitters for OLED applications.
Keywords: TADF, donor-acceptor structure, meta-position connection, OLED
Introduction
In the past two decades, organic light-emitting diodes (OLEDs) have attracted
considerable attention due to their enormous potential for applications in both new
generation full-color flat-panel displays and solid-state lighting sources.1-3 As this new

technology rapidly evolves, the growth of organic emissive materials has also
increased rapidly.4-6 In particular, considerable successes have been reported for heavy
metal complex phosphorescent emitters, which can comprehensively utilize both
singlet (25%) and triplet (75%) excitons via spin orbit coupling between heavy metals
and their ligands to achieve an internal quantum efficiency (IQE) of nearly 100%.7, 8
However, rare metal elements, such as Ir, Pt, Ru, Os and Au, are indispensably
included in most phosphorescent emitters.9-11 Their high cost makes phosphorescent
emitters unpopular for large-scale commercial production. Therefore, an increasing
number of scientists have focused on pure organic thermally activated delayed
fluorescence (TADF) emitters, which are the newest type of emitters.6, 12 Due to
non-radiative triplet excitons that can be thermally driven into a radiative singlet state,
TADF emitters can theoretically approach an IQE of 100% without the use of noble
metals.13, 14 A small singlet-triplet energy gap (∆EST) is essential to realizing TADF
emission since the reverse intersystem crossing (RISC) process only occurs if the
energy barrier between the singlet and triplet states can be overcome.15, 16 To achieve a
small ∆EST, TADF emitters should be designed with separated highest occupied
molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). This
separation could allow for the triplet energy of the molecules to be maintained in a
high level to the largest extent.17, 18 Therefore, charge-transfer type molecules with
donor-acceptor structures might enable highly efficient TADF emitters.19, 20
Most of the previously reported TADF emitters include π-bridge units, such as a
benzene ring, to connect their donor and acceptor moieties. In addition, substantial
steric hindrance between the donor/acceptor and the π-bridge will result in large
dihedral angles and separated HOMO and LUMO distributions. In general, donor and
acceptor moieties are connected via the para-position of the phenyl linker to
empirically achieve high photoluminescence quantum yields (PLQYs). For example,
DMAC-DPS, which are constructed from diphenylsulfone and acridine, is a typical
representative of this type of emitter.21 However, the feasibility of achieving efficient
TADF emitters by connecting donor and acceptor components through the
meta-position has been neglected.6, 22 Herein, a novel compound that was designed by
connecting a dicyanobenzene acceptor and two 9,9-dimethyl-9,10-dihydroacridine
donors at the 1, 3, 5-position of a benzene ring was prepared as an efficient TADF
emitting molecule. The investigated emitter (DAB-DCNB) exhibited a small ∆EST of
0.04 eV and a short excited state lifetime of 7.1 µs. An emission peak at 497 nm and a
satisfactorily PLQY were obtained. Therefore, a sky-blue TADF device with an EQE
of 16.5% was demonstrated in this study. Furthermore, the reported EQE is one of the
highest among devices using meta-connected type emitters.23, 24
Results and discussion
DAB-DCNB was expected to exhibit a small ∆EST by controlling the charge
transfer (CT) and conjugation in an appropriate degree via connection at the
meta-position. The adoption of a meta-type connection will weaken the inductive
effect that originates from the electron withdrawing abilities of the acceptor unit,
prevents reduction of the singlet energies and causes a blue-shifted emission.

Moreover, because the meta-linkage can decrease the conjugation length of the entire
compound to a shorter extent than that in para-position compounds, it is beneficial to
maintain the triplet states at a high energy level. Therefore, meta-connected type
compounds can exhibit a small ∆EST and serve as TADF emitters. The suitable energy
levels, good thermal stability and distinct photophysical properties make DAB-DCNB
a good candidate for TADF OLEDs, and the pivotal electrochemical, photophysical
and thermal properties are summarized in Table 1.
Table 1. Physical properties of DAB-DCNB
PLQY
(neat
film)
[%]
PLQY
(doped
film)
[%]
Eogpt
a
a
b
λmax,Abs
λmax,PL
λmax,PL
HOMO
[eV]
LUMOc
[eV]
Calculated
Experimental
Td
[nm]
[nm]
[nm]
[eV]
∆EST [eV]
∆EST [eV]
[℃]
209
508
487
-5.07
-2.21
2.86
52
61
0.03 eV
0.04
383
a UV-vis absorption and PL peaks for neat thin film.
b PL peaks for doped thin film (10% emitter doped in mCP).
c Conclude from HOMO and ∆Egopt (∆Eogpt =1240/λonset, λonset is the onset wavelength of absorption spectra).
Figure 1 show the molecular model (Fig. 1a) as well as the HOMO and
LUMO distributions from density functional theory (DFT) calculations using the
B3LYP 6-31G (d) basis set as implemented in the Gaussian 09 program. The HOMO
was evenly located on the two acridine moieties and slightly permeated into the
central benzene ring of the relevant molecule, and the LUMO was primarily dispersed
over the dicyanobenzene unit (Fig. 1b). These results can be attributed to large torsion
angles between the donors/acceptor and the phenyl π-bridge due to the substantial
steric hindrance that effectively separate the HOMO and LUMO of DAB-DCNB.
Consistent with the original design intention of this emitter, a time-dependent density
functional theory (TD-DFT) simulation predicted that the ∆EST of DAB-DCNB will
be small as 0.03 eV, which is favorable to achieve TADF characteristics (Table 1). The
synthetic route and structure of DAB-DCNB is shown in Scheme 1. First, compound
1 was synthesized according to previously reported procedures.25 Then, precursor 2
was prepared via Suzuki cross-coupling reactions. Finally, the target product was
obtained via a palladium-catalyzed reaction and purified by column chromatography
followed by vacuum sublimation to afford the pure product in a 61% yield. 1H and 13C
NMR (Figs. S1-S6, Supplementary Material), mass spectrometer and elemental
analyses were employed to confirm the chemical structures of compound 1, precursor
2 and the target compound.

Figure 1. (a) Optimized molecular structure of DAB-DCNB and (b) HOMO and LUMO distributions
from the DFT calculations with the B3LYP/6-31G(d) basis set by using the Gaussian 09 program
Scheme 1. Synthetic route for DAB-DCNB
The thermal properties of the resulting TADF dopant material were measured
by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), as
shown in Figures 2a and 2b, respectively. However, no obvious phase transition
process or glass-transition temperature (Tg) was detected for this emitter during the
DSC characterization in the 50 to 300 °C range (Table 1). While its decomposition
temperature (Td), which indicates 5% weight loss, is 383 °C (Table 1). These results
suggest that this TADF emitter possesses good thermal and morphological stability
due to a rigid molecular backbone, and these features are prerequisites for device
processing and application.
Figure 2. (a) DSC and (b) TGA curves of DAB-DCNB
To determine the singlet and triplet energies, the low temperature (77 K) PL
spectra of DAB-DCNB in toluene were collected, as shown in Figure 3a. According
to the fluorescence and phosphorescence emissions, the singlet and triplet energies of

DAB-DCNB were determined to be 3.08 and 3.04 eV, respectively, and therefore, the
experimental ∆EST was determined to be 0.04 eV (Table 1). Such a small ∆EST and the
blue fluorescence emission were due to the meta-linkage which not only controls a
weak CT state, but also maintains a relatively high triplet energy. The PL and the
ultraviolet-visible (UV-Vis) absorption spectra of the studied TADF material in a neat
film under ambient condition are shown in Figure 3b. Because of the weak CT
interaction between the two 9,9-dimethyl-acridine donors and the dicyanobenzene
acceptor, which results from their connections at the meta-position, an apparent
intramolecular charge transfer band at approximately 350 nm along with a strong n-π*
absorption for the donor moieties at 286 nm were observed in the UV-Vis absorption
spectrum (Fig. 3b). The optical band gap of this material was estimated to be 2.86 eV
based on the crossing point of the absorption and PL spectra.26 Due to the rather
strong electron-donating capacity of 9, 9-dimethyl-acridine, the neat film of this
compound emitted green light with a peak at 508 nm, and the PLQY was 52% (Table
1). However, after blending DAB-DCNB into the 1,3-bis (N-carbazolyl)benzene
(mCP) matrix with a concentration of 10 w%, the emission peak shifted to 487 nm
with an increased PLQY of 61% (Table 1).
Figure 3. (a) Fluorescence and phosphorescence spectra of DAB-DCNB in toluene solution at low
temperature (77 K); (b) UV-vis and PL spectra of DAB-DCNB’s neat film
The delayed fluorescence behaviors of this compound in the doped film at
different temperatures were recorded, and the results are shown in Figure 4. At 300
and 200 K, due to the small ∆EST, DAB-DCNB exhibited a substantial delayed
fluorescence component with a lifetime on the microsecond scale. As the temperature
decreased to 100 and 10 K, the long lifetime component decreased. This phenomenon
indicates that the long lifetime component originated from TADF. The lifetime of the
delayed fluorescence at 300 K was 7.1 µs.

Figure 4. Photoluminescence decays for a thin film of 10 w% DAB-DCNB doped in mCP, measured at
temperatures of 10K, 100K, 200K and 300 K
The electrochemical analysis of DAB-DCNB was performed. Cyclic
voltammetry (CV) was employed to measure the HOMO energy level of this TADF
emitter by utilizing ferrocene/ferrocenium (Fc/Fc+) (with an energy level of 4.8 eV)
for calibration. Figure 5 shows the cyclic voltammetry curve, and the onset oxidation
potential was 0.27 V. The HOMO energy level of DAB-DCNB was calculated to be
-5.07 eV (Table 1) according to the following equation (1):
HOMO (eV) = -( Eooxnset + 4.8)
(1)
Therefore, the LUMO energy was estimated to be -2.21 eV (Table 1) by combining
the HOMO and optical band gap.
Figure 5. Cyclic voltammograms of DAB-DCNB
To assess the electroluminescence properties of DAB-DCNB, an OLED device
was fabricated by doping the emitter into a mCP host at a concentration of 10% on the
basic of photophysical and electrochemical measurement data. The device structure
was ITO (120 nm)/ TAPC (25 nm)/ TCTA (5 nm)/ DAB-DCNB 10%: mCP (10 nm)/
TmPyPB (50 nm)/ LiF (0.5 nm)/ Al (100 nm) (Fig. 6a), and the molecular structures
of the materials used in the OLED device are shown in Figure 6b. In this device, ITO
was used as the anode, TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane) was
utilized
as
the
hole-transporting
layer
(HTL),
TCTA
(4,4’4’’-tri(9-carbazoyl)triphenylamine) was employed as the exciton-blocking layer,

TmPyPB
(1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene)
was
applied
as
the
electron-transporting layer, and LiF/Al was used as the cathode.
(a)
(b)
Figure 6. Energy level diagram (a) and molecular structures of the materials used in the OLED
device (b)
Figures 7a and b shows the current density (J)-voltage (V)-luminance (L)
characteristic of the device as well as the EQE and power efficiency (PE) as a
function of the current density (J) curves. In addition, figure 7c shows the current
efficiency (CE)-current density (J) characteristic of the device. The OLED device,
which employed DAB-DCNB as an emitter, turned on at 3.0 V and reached a
maximum EQE of 16.5% (Table 2). Considering the limitation of conventional
fluorescence devices is only 5-6%, the high EQE is surely due to the contribution of
TADF. The maximum current efficiency, power efficiency and maximum luminance
were 40.8 cd A-1, 45.8 lm W-1 and 5120 cd m-2, respectively (Table 2). As the current
increases, the EQE decreased to 10.2%, when the brightness reached 500 cd m-2. This
roll-off of efficiency can be ascribed to annihilation of the triplet excitons, and the
unipolar characteristic of the mCP host leads to unbalanced charges at a high current
density.27 The key EL performance data for DAB-DCNB are summarized in Table 2.
The electroluminescence spectrum of the device is shown in Figure 7d. Only the
emission that originated from the emitters appeared in the electroluminescence
spectrum, which suggested that the charge recombination region was completely
confined in the emitting layer. The emission peak of the device was 493 nm (Table 2),
which is close to that of the PL spectrum of the emitting layer. The Commission
International de l’Eclairage (CIEx, y) coordinate was (0.22, 0.38) at 500 cd m-2. In
addition, the CIEx, y only varied from (0.22, 0.38) to (0.22, 0.39) over the full
operational voltage range (Fig. S7, Supplementary Material). The spectra of the
device demonstrated highly stable chromaticity with respect to voltage.

Table 2. EL performance of device based on DAB-DCNB
λmaxa [nm]
Lmax [cd/m2]
Vonb [eV]
CEmax [cd/A]
40.8
PEmax [lm/w]
45.8
EQEmax [%]
16.5
CIEa [x,y]
493
5120
3.0
[0.22,0.38]
a At current density of 10 mA cm-2.
b At luminance of 1 cd m-2.
Figure 7. (a) Current density–voltage–luminance curves; (b) EQE and power efficiency versus current
density characteristics; (c) Curren efficiency versus current density characteristics and (d) Emission
spectrum of the electroluminescence device.
Conclusion
In summary, we have designed and synthesized a novel TADF emitter by
connecting a dicyanobenzene acceptor and two 9,9-dimethyl-9,10-dihydroacridine
donors at the 1, 3, 5-position of a phenyl ring. This molecule displayed sky-blue
emission in a mCP doped film. The meta-connected type resulted in a relatively high
triplet energy and a small energy difference of 0.04 eV between T1 and S1. The novel
studied compound was used to manufacture a multilayer electroluminescence device,
achieving one of the best performances among devices based on emitters with
meta-connected types. Due to the TADF features of the emitter, a satisfactory external
quantum efficiency up to 16.5% was achieved. We believe that these results may
provide a new approach for developing high-performance TADF emitters with
meta-connected type structures for OLED applications.

Experimental section
Synthesis
2-iodoisophthalonitrile (1): isophthalonitrile (4.48 g, 35 mmol) was dissolved in 200
mL of anhydrous tetrahydrofuran. The solution was cooled to -90 ºC and retained for
0.5 h. Then 28 mL of lithium diisopropylamide (LDA, 1.5 M in tetrahydrofuran, 42
mmol) was added slowly. After the mixture was stirred for 2 h, iodine (12.35 g, 49
mmol) was added. The reaction was retained stirring at -90 ºC for another 2 h and
warmed slowly to room temperature. The reaction mixture was poured into water and
extracted with dichloromethane. The organic phase was combined and dried over
magnesium sulfate. After the solvent was removed, the product was purified by
column chromatography on silica gel and then recrystallized in hexane to afford a
1
white solid (4.89 g, 55%). H NMR (400 MHz, CDCl3, δ): 7.79 (d, J = 7.6 Hz, 2H),
7.62 (t, J = 8 Hz, 1H). 13C NMR (100 MHz, CDCl3, δ): 137.34, 129.25, 123.44,
118.28, 103.83. MS (APCI, m/z): [M]+ calcd for C8H3IN2: 254.9; found: 254.8.
2-(3,5-dibromophenyl)isophthalonitrile (2): A mixture of 3,5-dibromophenyl
boronic acid (2.51 g, 9 mmol), 1 (2.55 g, 10 mmol), Pd(PPh3)4 (100 mg) , sodium
carbonate (2.12 g, 20 mmol), THF (15 mL), toluene (30 mL), and distilled water (20
mL) was refluxed for 24 h under nitrogen protection. The mixture was extracted with
dichloromethane. The organic phases were combined and dried over magnesium
sulfate. The crude product was purified by column chromatography on silica gel to
afford a white solid (2.57 g, 79%).1H NMR (400 MHz, CDCl3, δ): 7.99 (d, J = 8 Hz,
13
2H), 7.86 (t, J = 2 Hz, 1H),7.66 (t, J=7.6 Hz, 1H),7.57 (d, J=1.6 Hz, 2H). C NMR
(100 MHz, CDCl3, δ): 145.67, 137.38, 137.16, 136.06, 130.92, 129.60, 123.66, 115.90,
114.55. MS (APCI, m/z): [M]+ calcd for C14H6Br2N2: 362.9; found: 362.7.
DAB-DCNB: 9,9-dimethyl-9,10-dihydroacridine (0.92 g, 4.4 mmol) and 2 (0.72 g, 2
mmol) were added into 50 ml toluene. After degassing for 10 min, palladium acetate
(22.4mg, 0.1mmol), 1,1'-bis(diphenylphosphino) ferrocene (0.17 g, 0.3 mmol) and
sodium tert-butoxide (0.58 g, 6 mmol) were added sucessively. Under protection with
nitrogen, the mixture was heated to reflux for 24 h with stirring. Then 200 mL of
water was added into the reaction mixture and extracted with dichloromethane. The
organic phase was combined and dried over magnesium sulfate. After the solvent was
removed, the product was purified by column chromatography on silica gel to afford
the target compound. The final product was further sublimed at 280 ºC and 4 × 10-3 Pa
1
to give a slight yellow solid (0.75 g, 61%). H NMR(400 MHz, CDCl3, δ): 8.00 (d, J
= 7.6 Hz, 2H), 7.67-7.63 (m, 3H), 7.57 (t, J =2.0 Hz, 1H), 7.45 (dd, J =1.6, 7.6 Hz,
4H), 7.12-7.08(m, 4H), 6.97(td, J = 1.2, 8.0Hz, 4H), 6.57(dd, J =1.2, 8.0Hz, 4H),
1.66(s, 12H). 13C NMR (100MHz, CDCl3, δ): 147.23, 145.09, 140.49, 139.39, 136.84,
136.02, 132.56, 130.51, 129.43, 126.94, 125.40, 121.34, 116.32, 114.70, 114.38,
36.12, 31.17. MS (APCI, m/z): [M]+ calcd for C44H34N4: 619.3; found: 619.2. Anal.
calcd for C44H34N4: C 85.41; H 5.54; N 9.05; found: C 85.38, H 5.42, N 9.01.

Acknowledgments
This work has been supported financially by the State Key Laboratory of Fine
Chemicals (Panjin) (Grant No. JH2014009) project and the Fundamental Research
Funds for the Central Universities.
References and notes
1. Zhang, J.; Li, J.; Chen, W. H.; Zheng, D.; Yu, J. S.; Wang, H.; Xu, B. S. Tetrahedron Letters.
2016, 57, 2044-2048.
2. Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987 , 51, 913-915.
3. Reineke, S.; Lindner, F.; Schwartz, G.; Seidler, N.; Walzer, K.; Lussem, B.; Leo, K. Nature.
2009, 459, 234-238.
4. Liao, Y.L.; Lin, C.Y.; Wong, K.T.; Hou, T.H.; Hung, W.Y. Org. Lett. 2007, 9, 4511-4514.
5. Liu, S.J.; He, F.; Wang, H.; Xu, H.; Wang, C.Y.; Li, F.; Ma, Y.G. J. Mater. Chem. 2008, 18,
4802-4807.
6. Park, Y.; Kim, S.; Lee, J.H.; Jung, D.H.; Wu, C.C.; Park, J. Org. Electron. 2010, 11, 864-871.
7. Kohler, A.; Wilson, J.S.; Friend, R.H. Adv. Mater. 2002, 14, 701-707.
8. Yersin, H.; Strasser, J. Coordin Chem. Rev. 2000, 208, 331-364.
9. Sasabe, H.; Takamatsu, J.; Motoyama, T.; Watanabe, S.; Wagenblast, G.; Langer, N.; Molt, O.;
Fuchs, E.; Lennartz, C.; Kido, J. Adv. Mater. 2010, 22, 5003-5007.
10. Fleetham, T.; Li, G.J.; Wen, L.L.; Li, J. Adv. Mater. 2014, 26, 7116-7121.
11. Gong, S.L.; Chen, Y.H.; Yang, C.L.; Zhong, C.; Qin, J.G.; Ma, D.G.; Adv. Mater. 2010, 22,
5370-5373.
12. Goushi, K.; Yoshida, K.; Sato, K.; Adachi, C. Nat. Photonics. 2012, 6, 253-258.
13. Zhang, Q.S.; Li, J.; Shizu, K.; Huang, S.P.; Hirata, S.; Miyazaki, H.; Adachi, C. J. Am. Chem.
Soc. 2012, 134, 14706-14709.
14. Nakanotani, H.; Higuchi, T.; Furukawa, T.; Masui, K.; Morimoto, K.; Numata, M.; Tanaka, H.;
Sagara, Y.; Yasuda, T.; Adachi, C. Nat. Commun. 2014, 5, 4016.
15. Serevicius, T.; Nakagawa, T.; Kuo, M.C.; Cheng, S.H.; Wong, K.T.; Chang, C.H.; Kwong,
R.C.; Xia, S.; Adachi, C. Phys. Chem. Chem. Phys. 2013, 15, 15850-15855.
16. Endo, A.; Sato, K.; Yoshimura, K.; Kai, T.; Kawada, A.; Miyazaki, H.; Adachi, C. Appl. Phys.
Lett. 2011, 98, 083302.
17. Lee, D.R.; Hwang, S.H.; Jeon, S.K.; Lee, C.W.; Lee, J.Y. Chem. Commun. 2015, 51,
8105-8107.
18. Hirai, H.; Nakajima, K.; Nakatsuka, S.; Shiren, K.; Ni, J.; Nomura, S.; Ikuta, T.; Hatakeyama,
T. Angew. Chem. Int. Edit. 2015, 54, 13581-13585.
19. Sun, J.W.; Baek, J.Y.; Kim, K.H.; Moon, C.K.; Lee, J.H.; Kwon, S.K.; Kim, Y.H.; Kim, J.J.
Chem. Mater. 2015, 27, 6675-6681.
20. Zhang, D.D.; Cai, M.H.; Zhang, Y.G.; Zhang, D.Q.; Duan, L. Mater. Horiz. 2016, 3, 145-151.
21. Zhang, Q.S.; Li, B.; Huang, S.P.; Nomura, H.; Tanaka, H.; Adachi, C. Nat. Photonics. 2014, 8,
326-332.
22. Huang, B.; Yin, Z.H.; Ban, X.X.; Jiang, W.; Dai, Y.; Zhang, J.Y.; Liu, Y.Y.; Yang, Y.P.; Sun,
Y.M. Dyes Pigments. 2015, 117, 141-148.

23. Lee, S.Y.; Yasuda, T.; Park, I.S.; Adachi, C. Dalton T. 2015, 44, 8356-8359.
24. Huang, B.; Qi, Q.; Jiang, W.; Tang, J.A.; Liu, Y.Y.; Fan, W.J.; Yin, Z.H.; Shi, F.C.; Ban, X.X.;
Xu, H.E.; Sun, Y.M. Dyes Pigments. 2014, 111, 135-144.
25. Usui, S.; Hashimoto, Y.; Morey, J.V.; Wheatley, A.E.H.; Uchiyama, M. J. Am. Chem. Soc.
2007, 129, 15102-15103.
26. Huang, S.P.; Zhang, Q.S.; Shiota, Y.; Nakagawa, T.; Kuwabara, K.; Yoshizawa, K.; Adachi, C.
J Chem Theory. Comput. 2013, 9, 3872-3877.
27. Masui, K.; Nakanotani, H.; Adachi, C. Org. Electron. 2013, 14, 2721-2726.

Graphical abstract

1. A dimethylacridines and dicyanobenzene based molecule has been designed and
synthesized as a novel TADF emitter.
2. The optical, electrochemical and thermal properties were investigated.
3. The molecule shows a singlet-triplet energy gap as small as 0.04 eV.
4. The doped OLEDs exhibited a high EQE of 16.5%.