Molecular Design of Thermally Activated Delayed-Fluorescent Emitters Using 2,2′-Bipyrimidine as the Acceptor in Donor–Acceptor Structures

Article abstract of DOI:10.1002/asia.201700889

Donor–acceptor–donor (D–A–D)-type thermally activated delayed fluorescence (TADF) emitters 5,5′-bis{4-[9,9-dimethylacridin-10(9H)-yl]phenyl}-2,2′-bipyrimidine (Ac-bpm) and 5,5′-bis[4-(10H-phenoxazin-10-yl)phenyl]-2,2′-bipyrimidine (Px-bpm), based on the 2,2′-bipyrimidine accepting unit, were developed and their TADF devices were fabricated. The orthogonal geometry between the donor unit and the 2,2′-bipyrimidine accepting core facilitated a HOMO/LUMO spatial separation, thus realizing thermally activated delayed fluorescence. The exhibited electroluminescence ranged from green to yellow, depending on the donor unit, with maximum external quantum efficiencies of up to 17.1 %.

Full text of DOI:10.1002/asia.201700889

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Molecular design of thermally activated delayed fluorescent
emitters using 2,2'-bipyrimidine as an acceptor in donor-acceptor
structure
Authors: Hee-Jun Park, Si Hyun Han, and Jun Yeob Lee
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To be cited as: Chem. Asian J. 10.1002/asia.201700889
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10.1002/asia.201700889
Chemistry - An Asian Journal
Molecular design of thermally activated delayed fluorescent emitters using 2,2’-bipyrimidine as an
acceptor in donor-acceptor structure
Hee-Jun Park, Si Hyun Han, Jun Yeob Lee*
H.-J. Park, S. H. Han, Prof. J. Y. Lee
School of Chemical Engineering, Sungkyunkwan University
2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi, 440-746, Korea
E-mail: leej17@skku.edu
Keywords: thermally activated delayed fluorescencedopant quantum efficiencysingle hostmixed host
Abstract
D-A-D type thermally activated delayed fluorescence (TADF) emitters, 5,5’-bis(4-(9,9-
dimethylacridin-10(9H)-yl)phenyl)-2,2’-bipyrimidine (Ac-bpm) and 5,5’-bis(4-(10H-phenoxazin-
10-yl)phenyl)-2,2’-bipyrimidine (Px-bpm), based on 2,2’-bipyrimidine accepting unit were
developed and their TADF devices were fabricated. The orthogonal geometry between the donor
unit and the 2,2’-bipyrimidine accepting core facilitated a HOMO/LUMO spatial separation, thus
realizing thermally activated delayed fluorescence. They exhibited electroluminescence ranging
from green to yellow, depending on the donor unit, with a maximum external quantum
efficiencies of up to 17.1%.
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Introduction
Recently, thermally activated delayed fluorescent (TADF) materials have emerged as an emissive
dopant in organic light-emitting diodes (OLEDs) due primarily to their high external quantum
efficiencies comparable to that of conventional phosphorescent emitter.1-2 The high efficiencies
are practicable by harvesting both singlet (S1) and triplet (T1) excitons through efficient reverse
intersystem crossing (RISC) in which the T1 can be up-converted to the S1 by thermal activation.3-
9
The efficient RISC can be generated by a small energy splitting (ΔEST) between the S1 and T1
states of the TADF materials, so that twisted structures composed of electron donor (D) and
acceptor (A) units are required for the highest occupied molecular orbital (HOMO)/lowest
unoccupied molecular orbital (LUMO) separation which causes a small ΔEST. Therefore, TADF
materials are based on the design such as D-A or D-A-D molecular framework having a strong
electron-donating and -accepting ability. However, unlike D units, the range of choice for usable
A units is limited. Electron-deficient aromatic systems such as triazine,9-11 triazole4 and
oxadiazole12 are generally considered as A units. Furthermore, fragments such as sulfone,13,14
phenone15,16, phenylborane17 have been reported as alternative acceptors for TADF emitter. More
recently, pyrimidine-based acceptor units have been developed as a new building block for TADF
materials.18,19 These TADF materials are appropriate as sky-blue or blue emitters because of less
electron-deficient character compared with 1,3,5-triazine and the consequent increase of the band
gap energy, so that tuning the energy gap through the modification of pyrimidine unit is required.
Herein, we report twisted D-A-D type TADF molecules comprising a 2,2’-bipyrimidine
accepting core coupled with acridine or phenoxazine donor unit through a phenyl linker. Owing to
the coplanar structure between each pyrimidine unit, a 2,2’-bipyrimidine core has more electron-
deficient nature compared with a single pyrimidine unit, giving deeper LUMO levels and
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decreased energy band gaps. The new emitters reported in this work demonstrated the green
electroluminescence (EL) emission and the rather high efficiency.
Results and discussion
Synthesis and theoretical calculations
The two new materials, Ac-bpm and Px-bpm were prepared using the procedures shown in
Scheme 1. For access to two materials, firstly, the dibrominated bipyrimidine acceptor, 5,5’-
dibromo-2,2’-bipyrimidine (2Br-bpm), was prepared by bromination of 2,2’-bipyrimidine20 with
molecular bromine. Secondly, (4-(9,9-dimethylacridin-10(9H)-yl)phenyl)boronic acid (A2) and
(4-(10H-phenoxazin-10-yl)phenyl)boronic acid (B2) were prepared in two steps starting from 9,9-
dimethyl-9,10-dihydroacridine and phenoxazine, respectively. The two donor units, A2 and B2
were coupled with 2Br-bpm by Suzuki reaction, giving 5,5’-bis(4-(9,9-dimethylacridin-10(9H)-
yl)phenyl)-2,2’-bipyrimidine (Ac-bpm) and 5,5’-bis(4-(10H-phenoxazin-10-yl)phenyl)-2,2’-
bipyrimidine (Px-bpm) in moderate yields. As shown in Fig. 1, the geometry optimization and the
electron densities of Ac-bpm and Px-bpm were performed via TD-DFT using the B3LYP/6-31G*
basis set of Gaussian 09 program. For Ac-bpm and Px-bpm, the donor units were perpendicular to
the phenyl linker (dihedral angle ~ 90°), whereas the dihedral angles between the central 2,2’-
bipyrimidine and the phenyl linker are 36.6° and 37.4°, respectively, resulting in a
HOMO/LUMO spatial separation which is critical factor for a small singlet-triplet splitting energy.
For a central core of Ac-bpm, a twist angle between each pyrimidine unit was calculated to be
17.3°, while Px-bpm displayed a coplanar central core. As depicted in Fig. 2a, the structure of Px-
bpm was further confirmed by X-ray diffraction analysis. Single crystals of Px-bpm were grown
by a low pressure sublimation at 300 °C. The phenyl linker is nearly perpendicular to the
phenoxazine donor (dihedral angle ~ 79°), whereas the twist angle between the phenyl linker and
the 2,2’-bipyrimidine core was determined to be 40.8°. In addition, the central 2,2’-bipyrimidine
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core showed a coplanar geometry. As shown in Fig. 2b, Px-bpm displayed a zig-zag type
arrangement in an intermolecular stacking. The orthogonal arrangement between the donor and
the acceptor units is expected to reduce the intermolecular interactions, thus preventing the
excimer emission.
Physical and electrochemical properties
The UV-vis absorption of emitters in tetrahydrofuran solution, photoluminescence (PL) and
phosphorescence spectra in the doped solid film in the host material are shown in Fig. 3, and the
data are summarized in Table 1. For Ac-bpm, the intense band at around 300 nm is attributable to
the π-π* transitions, and weak band ranging from 350 to 450 nm is ascribed to the n-π* transitions.
Compared to Ac-bpm, the absorption bands of Px-bpm are slightly bathochromic-shifted
presumably due to the stronger donating ability of phenoxazine. Singlet and triplet energies of
Ac-bpm were calculated to be 2.98 and 2.70 eV, respectively, whereas those of Px-bpm were
estimated to be 2.79 and 2.63 eV in polystyrene film. The singlet-triplet splitting energy gaps
were 0.28 and 0.16 eV for Ac-bpm and Px-bpm, respectively. For Ac-bpm and Px-bpm doped
into host materials, photoluminescence quantum yields (PLQYs) were 54% and 28% under
atmosphere, and 75% and 38% in oxygen-free condition from integrating sphere measurement,
respectively. The quantum yields diminished with an increase in doping concentration possibly
because of the aggregation-induced quenching effect of the stick-like structure (Fig. S7).
The ionization potentials (IPs) and electron affinities (EAs) of Ac-bpm and Px-bpm were
calculated from the onset potentials of redox curves using cyclic voltammetry measurement (CV)
(Fig. S1). Due to the electron-rich effect of phenoxazine unit relative to acridine unit, Px-bpm has
a less negative IP (-5.70 eV) compared to that (-5.84 eV) of Ac-bpm. EAs of Ac-bpm and Px-bpm
are nearly the same (-3.13 and -3.15 eV, respectively) because EAs stem from the reduction of the
same acceptor unit, 2,2’-bipyrimidine.
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To prove the TADF character of Ac-bpm and Px-bpm, transient PL measurement was
conducted with films of bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO): Ac-bpm (20
wt%) and 1,3-bis(N-carbazolyl)benzene (mCP): 2,2’,2’’-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-
benzimidazole) (TPBi): Px-bpm (3 wt%) at room temperature (Fig. 4). The two emitters display
both prompt and delayed components, indicating the TADF behaviour. The excited state lifetimes
of the delayed components were reported to be 37.5 and 25.0 μs for Ac-bpm and Px-bpm,
respectively. Furthermore, the delayed component increased with rising of temperature from 100
K to 297 K, proving the characteristic of TADF behaviour (Fig. S2).
As shown in Fig. S3, thermal properties of Ac-bpm and Px-bpm were studied using thermal
gravimetric analysis (TGA). Ac-bpm and Px-bpm showed good thermal stability with
decomposition temperature (Td, corresponding to 5% weight loss) of 442 °C and 504 °C,
respectively. In contrast, glass transitions were not observed in both emitters.
Electroluminescence properties
The EL performances of Ac-bpm and Px-bpm were evaluated in TADF devices fabricated with
the following two configurations: [Single-host system, Device A] ITO/PEDOT:PSS (60
nm)/TAPC (20 nm)/mCP (10 nm)/DPEPO:Ac-bpm or Px-bpm (25 nm, x%)/TSPO1 (5 nm)/TPBi
(20 nm)/LiF (1.5 nm)/Al (200 nm), x = 10-30% and [Mixed-host system, Device B]
ITO/PEDOT:PSS (60 nm)/TAPC (20 nm)/mCP (10 nm)/mCP:TPBi:Ac-bpm or Px-bpm (25 nm,
x%)/TSPO1 (5 nm)/TPBi (40 nm)/LiF (1.5 nm)/Al (200 nm), x = 3-10% (Fig. 5). N,N-
Dicarbazolyl-3,5-benzene (mCP) and diphenyl-4-triphenylsilylphenyl phosphine oxide (TSPO1)
between the emission layer and charge transporting layer were employed as the hole- and
electron-transport type exciton blocking layer, respectively. The device characteristics are shown
in Fig. 6 and Fig. S5, S6, and device performances are summarized in Table 2. In the device A,
the direct charge trapping on an emitter could be the main EL mechanism, presumably due to the
deeper LUMO and shallower HOMO energy levels relative to those of DPEPO host material. In
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the device B, in contrast, the host-dopant energy transfer would be a predominant EL mechanism
because HOMO and LUMO energy levels of mixed host materials are comparable to those of
adjacent transport layers. As shown in Fig. 6, Ac-bpm based device A and Px-bpm based device
B displayed EL emissions with peaks of 517 and 547 nm, and CIE coordinates of (0.29, 0.53) and
(0.41, 0.54), respectively.
Ac-bpm exhibited an EQE of 17.1 % in 20% doping concentration, whereas Px-bpm showed a
reduced EQE (4.6%) in the same doping concentration. To study the origin of the low EQE of the
Px-bpm device, single carrier devices were prepared. As shown in Fig. S6, the hole-only and
electron-only devices were fabricated with the structures of PEDOT (60 nm)/TAPC (20 nm)/mCP
(10 nm)/DPEPO:Ac-bpm or Px-bpm (25 nm, 20%)/TAPC (5 nm)/Al (200 nm) and PEDOT (60
nm)/TSPO1 (10 nm)/DPEPO:Ac-bpm or Px-bpm (25 nm, 20%)/TSPO1 (5 nm)/TPBi (40 nm)/LiF
(1.5 nm)/Al (200 nm), respectively. There was little difference of the hole and electron density in
the two devices, suggesting that carrier imbalance is not the reason for the low EQE of the Px-
bpm devices. Therefore, the low EQE of the Px-bpm device is due to strong intermolecular
interaction induced quenching because of high doping concentration. At low doping concentration,
carrier imbalance reduced the EQE and intermolecular quenching decreased the EQE at high
doping concentration. To improve the EQE, emitters were tested in mCP:TPBi mixed-host device
B in which mCP and TPBi were used as a hole-transport-type and an electron-transport-type host
respectively, and the EQE of Px-bpm reached up to 14.4% in 3% doping concentration. Ac-bpm
based device showed the severe efficiency roll-off, primarily attributable to the longer T1 excited-
state lifetime,21 whereas Px-bpm based device displayed a suppressed efficiency roll-off relative
to Ac-bpm device. Furthermore, the efficiency roll-off of mixed host devices was generally
suppressed compared to single host one owing to the enhanced charge balance.22
Conclusions
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In conclusion, we developed two novel D-A-D type TADF emitters, Ac-bpm and Px-bpm, composed of
2,2’-bipyrimidine as a new acceptor unit and acridine or phenoxazine as a donor unit. The
perpendicularity of donor unit with respect to the 2,2’-bipyrimidine accepting core facilitates a
HOMO/LUMO spatial separation, thus realizing thermally activated delayed fluorescence. Ac-bpm
exhibited a green emission and a maximum EQE of 17.1% in single-host device. In contrast, Px-bpm
showed a yellow emission with a maximum EQE of 14.4% in mixed-host device. A novel 2,2’-
bipyrimidine accepting core allows the emission colour tuning through the combination with various
donor units.
Experimental
Materials. All reactions were carried out under nitrogen atmosphere unless otherwise noted. Standard
Schlenk techniques were employed to manipulate air sensitive solutions while workup procedures were
done in air. All solvents utilized in this work were obtained from Fisher Scientific (HPLC grade) unless
otherwise noted. Tetrahydrofuran (THF) and toluene were dried over Na/benzophenone and were
subsequently distilled under nitrogen prior to use. All deuterated solvents were purchased from Aldrich.
2,2’-bipyrimidine was prepared according to literature procedure.20 Chromatographic purification (Silica
Gel 60, 230-400 mesh, Merck) of all compounds was performed on the bench top.
X-ray crystallography. Single crystals of Px-bpm suitable for the X-ray crystallography were grown by
a low pressure sublimation at 300 °C. Diffraction data were collected on a Bruker SMART X-ray
diffractometer at room temperature using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å ).
The structure was solved by direct methods (SHELXS-97) and refined against all F2 data (SHELX-
97).23,24 All non-hydrogen atoms were refined anisotropic thermal parameters, and the hydrogen atoms
were treated as idealized contributions.
1
13
Instruments. H NMR spectra were recorded on an Avans 500 MHz spectrometer and C NMR spectra
1
were recorded on an Avans III HD 850 MHz spectrometer. Chemical shifts for H NMR spectra are
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10.1002/asia.201700889
Chemistry - An Asian Journal
relative to a residual proton in the deuterated solvents (CDCl3,  = 7.24 ppm). All coupling constants are
reported in hertz. HRMS data were obtained at Korea Basic Science Institute. Electronic absorption
spectra were recorded on a JASCO spectrophotometer. Cyclic voltammetry were performed by purging
the acetonitrile (spectroscopic grade) solution by dry nitrogen gas for 10 min. The supporting electrolyte
was 0.1 M tetrabultylammonium perchlorate (TBAClO4). Glassy carbon and Ag/AgCl (0.01 M NaCl)
were used as a working and a reference electrode, respectively. The scan rate was maintained at 100 mV/s.
5,5'-dibromo-2,2'-bipyrimidine (2Br-bpm)
2,2’-Bipyrimidine (1.87 g, 11.8 mmol), bromine (1.2 mL, 23.6 mmol) and nitrobenzene (25 mL) were
placed in a sealed tube, and the solution was stirred for 48 h at 135 °C. The product was extracted with
chloroform and washed with saturated aqueous Na2S2O3 three times. The crude product was purified by
column chromatography on silica gel. Elution with methanol/CH2Cl2 (1:100) gave 2Br-bpm as brown
solid. Yield: 1.68 g (5.31 mmol, 45%) 1H NMR (500 MHz, CDCl3):  9.03 (s, 4 H), MS (FAB) m/z 315
[(M+H)+].
10-(4-bromophenyl)-9,9-dimethyl-9,10-dihydroacridine (A1)
9,9-Dimethyl-9,10-dihydroacridine (5.0 g, 24.0 mmol), 1-bromo-4-iodobenzene (6.8 g, 24.0 mmol),
copper(I) iodide (46 mg, 0.24 mmol), sodium tert-butoxide (3.45 g, 36.0 mmol) and trans-1,2-
cyclohexanediamine (0.29 mL, 2.4 mmol) were added to 1,4-dioxane (100 mL). The mixture was stirred
at 100 °C for 12 h, then cooled to room temperature. The product was extracted with chloroform and
washed with brine three times. The crude product was purified by column chromatography on silica gel.
1
Elution with Hexane/CH2Cl2 (3:1) gave A1 as white solid. Yield: 4.35 g (12.0 mmol, 50%). H NMR
(500 MHz, CDCl3):  7.75 (d, J = 9.0 Hz, 2 H), 7.46 (dd, J1 = 1.5 Hz, J2 = 7.5 Hz, 2 H), 7.22 (d, J = 8.5
Hz, 2 H), 6.99-6.92 (m, 4 H), 6.25 (dd, J1 = 1.0 Hz, J2 = 8.0 Hz, 2 H), 1.68 (s, 6 H) ; MS (FAB) m/z 364
[(M+H)+].
(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)boronic acid (A2)
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Chemistry - An Asian Journal
n-BuLi (2.1 mL, 3.29 mmol) was added dropwise to a solution of A1 (1.0 g, 2.75 mmol) and THF (40
mL) at -78 °C. After the solution was stirred for 30 min, B(OMe)3 (0.46 mL, 4.13 mmol) was added. The
mixture was stirred at room temperature for 12 h. The product was extracted with chloroform and washed
with brine three times. The crude product was purified by column chromatography on silica gel. Elution
1
with methanol/CH2Cl2 (1:100) gave A2 as white solid. Yield: 0.60 g (1.82 mmol, 66%). H NMR (500
MHz, CDCl3):  8.56 (d, J = 8.0 Hz, 2 H), 7.54 (d, J = 8.0 Hz, 2 H), 7.49 (dd, J1 = 1.5 Hz, J2 = 7.5 Hz, 2
H), 7.01-6.92 (m, 4 H), 6.33 (dd, J1 = 1.0 Hz, J2 = 8.0 Hz, 2 H), 1.72 (s, 6 H) ; MS (FAB) m/z 330
[(M+H)+].
5,5'-bis(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)-2,2'-bipyrimidine (Ac-bpm)
A2 (0.63 g, 1.9 mmol), 2Br-bpm (0.25 g, 0.79 mmol), Pd(PPh3)4 (91 mg, 0.08 mmol) and potassium
carbonate (0.66 g, 4.74 mmol) were added to a THF/water (10 mL/2 mL) solution. After the solution was
heated at 70 °C for 12 h, the reaction mixture was cooled to room temperature. The product was extracted
with chloroform and washed with brine three times. The crude product was purified by column
chromatography on silica gel. Elution with methanol/CH2Cl2 (1:100) gave Ac-bpm as yellow solid.
Yield: 0.35 g (0.48 mmol, 61%). 1H NMR (500 MHz, CDCl3):  9.41 (s, 4 H), 7.99 (d, J = 6.5 Hz, 4 H),
7.58 (d, J = 8.0 Hz, 4 H), 7.50 (dd, J1 = 1.5 Hz, J2 = 7.5 Hz, 4 H), 7.05-6.96 (m, 8 H), 6.34 (dd, J1 = 1.0
13
Hz, J2 = 8.0 Hz, 4 H), 1.63 (s, 12 H); C NMR (214 MHz, CDCl3):  160.83, 156.12, 142.76, 140.63,
133.76, 132.67, 130.24, 129.73, 126.47, 125.44, 120.93, 114.99, 114.03, 36.04, 31.30; MS (FAB) m/z
725 [(M+H)+].
10-(4-bromophenyl)-10H-phenoxazine (B1)
A procedure similar to that used for A1 was followed but with phenoxazine (4.38 g, 24.0 mmol) instead
1
of 9,9-Dimethyl-9,10-dihydroacridine. Yield: 3.64 g (10.8 mmol, 45%). H NMR (500 MHz, CDCl3): 
7.72 (d, J = 8.5 Hz, 2 H), 7.23 (d, J = 8.5 Hz, 2 H), 6.70-6.65 (m, 4 H), 6.60 (t, J = 8.0 Hz, 2 H), 5.91 (d, J
= 7.5 Hz, 2 H); MS (FAB) m/z 338 [(M+H)+].
(4-(10H-phenoxazin-10-yl)phenyl)boronic acid (B2)
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10.1002/asia.201700889
Chemistry - An Asian Journal
A procedure similar to that used for A2 was followed but with B1 (1.0 g, 2.96 mmol) instead of A1.
Yield: 0.58 g (1.92 mmol, 65%). 1H NMR (500 MHz, CDCl3):  8.50 (d, J = 8.0 Hz, 2 H), 7.53 (d, J = 5.0
Hz, 2 H), 6.73-6.60 (m, 6 H), 5.98 (br, 2 H); MS (FAB) m/z 304 [(M+H)+].
5,5'-bis(4-(10H-phenoxazin-10-yl)phenyl)-2,2'-bipyrimidine (Px-bpm)
A procedure similar to that used for Ac-bpm was followed. B2 (0.46 g, 1.52 mmol), 2Br-bpm (0.20 g,
0.63 mmol), Pd(PPh3)4 (73 mg, 0.06 mmol), potassium carbonate (0.52 g, 3.78 mmol) and THF/water (10
mL/2 mL). Yield: 0.27 g (0.40 mmol, 63%). 1H NMR (500 MHz, CDCl3):  9.35 (s, 4 H), 7.95 (d, J = 8.5
Hz, 4 H), 7.59 (d, J = 8.5 Hz, 4 H), 6.74 (d, J = 7.5 Hz, 4 H), 6.69 (t, J = 7.5 Hz, 4 H), 6.64 (t, J = 8.0 Hz,
4 H), 6.02 (d, J = 8.0 Hz, 4 H); 13C NMR (214 MHz, CDCl3):  161.04, 156.09, 143.97, 133.99, 133.93,
133.39, 132.23, 129.90, 123.35, 123.32, 121.73, 115.68, 113.23; MS (FAB) m/z 673 [(M+H)+].
Device Fabrication
Device structure of the TADF OLEDs was indium tin oxide (50 nm)/PEDOT:PSS (poly(3,4-
ethylenedioxythiophene):poly(styrenesulfonate)) (60 nm)/TAPC (4,4′-cyclohexylidenebis[N,N-bis(4-
methylphenyl)benzenamine]) (20 nm)/mCP (1,3-Bis(N-carbazolyl)benzene) (10 nm)/DPEPO (bis[2-
(diphenylphosphino)phenyl]ether oxide):TADF dopant (25 nm)/TSPO1 (diphenyl-4-triphenylsilylphenyl-
phosphineoxide) (5 nm)/TPBi (2,2′,2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)) (20
nm)/LiF (1.5 nm)/Al (200 nm). Ac-bpm or Px-bpm were doped in the DPEPO at doping concentration
range from 10% to 30%.
Acknowledgements
This work was supported by Basic Science Research Program through the National Research Foundation
of Korea (NRF) funded by the Ministry of Education (NRF-2016R1A6A3A11933789,
2016R1A2B3008845).
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Chemistry - An Asian Journal
[14] S. Wu, M. Aonuma, Q. Zhang, S. Huang, T. Nakagawa, K. Kuwabara and C. Adachi, J. Mater.
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List of tables
Table 1. Physical properties and TD-DFT results.
Table 2. Summarized device performances of TADF devices.
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10.1002/asia.201700889
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Table 1. Physical properties and TD-DFT results.
Experimental
Calculated
a
b
c
d
g
Emitter
λabs
λem
Φair/ΦN2
[%]
S1/T1/ΔEST
HOMO/LUMOf
S1/T1/ΔEST
[eV]
τp[ns]/τd[μs]
IP/EA [eV]e
[nm]
287
293
[nm]
471
524
[eV]
[eV]
Ac-bpm
Px-bpm
54/75
28/38
63/37.5
77/25.0
2.98/2.70/0.28
2.79/2.63/0.16
-5.84/-3.13
-5.70/-3.15
-4.98/-2.17
-4.75/-2.28
2.44/2.44/0.00
2.11/2.10/0.01
a Measured in THF solution. b Measured in polystyrene film (1 wt%). c Obtained from integrating sphere. d Singlet (S1) and triplet (T1) energies
were estimated from onset wavelengths of the emission spectra at room temperature and 77 K in polystyrene films, respectively. ΔEST = ES – ET. e
Estimated from onset potentials of cyclic voltammetry. f Calculated by TD-DFT at B3LYP/6-31G*. g S1 and T1 were the energies of the first singlet
and triplet state.
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10.1002/asia.201700889
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Table 2. Summarized device performances of TADF devices.
Doping
QEa
[%]
CEb
PEc
Device
Emitter
Ac-bpm
Px-bpm
Ac-bpm
Px-bpm
conc.
[%]
10
20
30
10
20
30
3
5
10
3
5
10
[cd A-1]
[lm W-1]
16.2
17.1
12.9
6.0
4.6
3.5
10.9
13.6
12.7
14.4
12.7
11.6
47.6
52.8
40.5
17.7
12.7
9.2
29.4
38.3
36.3
42.4
36.8
33.1
42.7
48.1
42.4
14.1
10.5
7.6
26.4
34.4
32.6
33.3
29.6
29.4
A
B
a Maximum external quantum efficiency at 1,000 cd/m2. b Maximum current efficiency. c Maximum power efficiency.
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List of figures
Scheme 1. Synthetic procedure of Ac-bpm and Px-bpm
Figure 1. HOMO and LUMO distribution of Ac-bpm and Px-bpm
Figure 2. (a) Single crystal structure of Px-bpm. (b) Intermolecular stacking interactions of
Px-bpm. Hydrogen atoms were omitted for clarity.
Figure 3. UV-vis absorption and PL spectra of Ac-bpm and Px-bpm. Solid PL (polystyrene).
Low Temp. PL (polystyrene).
Figure 4. Transient decay curves of Ac-bpm and Px-bpm.
Figure 5. Energy level diagram ((a) single host, (b) mixed host) and chemical structure of
materials
Figure 6. (a) Current density-voltage-luminance (I-V-L) curve, (b) quantum efficiency-
luminance curve and (c) EL spectra of Ac-bpm in device A. (d) Current density-voltage-
luminance (I-V-L) curve, (e) quantum efficiency-luminance curve and (f) EL spectra of Px-
bpm in device B.
16
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10.1002/asia.201700889
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Scheme 1. Synthetic procedure of Ac-bpm and Px-bpm
17
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10.1002/asia.201700889
Chemistry - An Asian Journal
Figure 1. HOMO and LUMO distribution of Ac-bpm and Px-bpm
18
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10.1002/asia.201700889
Chemistry - An Asian Journal
Figure 2. (a) Single crystal structure of Px-bpm. (b) Intermolecular stacking interactions of
Px-bpm. Hydrogen atoms were omitted for clarity.
19
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Figure 3. UV-vis absorption and PL spectra of Ac-bpm and Px-bpm. Solid PL (polystyrene).
Low Temp. PL (polystyrene).
20
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10.1002/asia.201700889
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Figure 4. Transient decay curves of Ac-bpm and Px-bpm.
21
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10.1002/asia.201700889
Chemistry - An Asian Journal
Figure 5. Energy level diagram ((a) single host, (b) mixed host) and chemical structure of
materials
22
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10.1002/asia.201700889
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Figure 6. (a) Current density-voltage-luminance (I-V-L) curve, (b) quantum efficiency-
luminance curve and (c) EL spectra of Ac-bpm in device A. (d) Current density-voltage-
luminance (I-V-L) curve, (e) quantum efficiency-luminance curve and (f) EL spectra of Px-
bpm in device B.
23
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