Blue thermally activated delayed fluorescence emitter using modulated triazines as electron acceptors

Article abstract of DOI:10.1016/j.dyepig.2019.107864

Three types of thermally activated delayed fluorescence (TADF) emitters, namely, moTrSAc, tmTrSAc, and motmTrSAc, are reported that emit blue-shifted emission with high external quantum efficiencies (EQEs). These emitters have electron donating spiroacridine in common and various triazine-based electron acceptors. The electronic and structural control on the electron acceptor moiety adjusts the reduction potential of the molecule to shift the emission wavelength to the blue region. Moreover, as these emitters become widened, the light out-coupling efficiency increases due to the enhanced horizontal emitting dipole orientation. As a result, OLEDs based on moTrSAc, tmTrSAc, and motmTrSAc emit blue light in a range of 460–480 nm with high EQEs of 21.3, 15.5, and 19.5%, respectively.

Full text of DOI:10.1016/j.dyepig.2019.107864

DyesandPigments172(2020)107864
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Blue thermally activated delayed fluorescence emitter using modulated
triazines as electron acceptors
Youngnam Leea, Seung-Je Woob, Jang-Joo Kimb, Jong-In Honga,∗
a Department of Chemistry, Seoul National University, Seoul, 08826, Republic of Korea
b Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Keywords:
Three types of thermally activated delayed fluorescence (TADF) emitters, namely, moTrSAc, tmTrSAc, and
motmTrSAc, are reported that emit blue-shifted emission with high external quantum efficiencies (EQEs). These
emitters have electron donating spiroacridine in common and various triazine-based electron acceptors. The
electronic and structural control on the electron acceptor moiety adjusts the reduction potential of the molecule
to shift the emission wavelength to the blue region. Moreover, as these emitters become widened, the light out-
coupling efficiency increases due to the enhanced horizontal emitting dipole orientation. As a result, OLEDs
based on moTrSAc, tmTrSAc, and motmTrSAc emit blue light in a range of 460–480 nm with high EQEs of 21.3,
15.5, and 19.5%, respectively.
Organic light emitting diode (OLED)
Thermally activated delayed fluorescence
(TADF)
Blue emission
Light out-coupling efficiency
Emitting dipole orientation
1. Introduction
the emitter itself but also fully extract the light generated in the EML.
The light emission from the emitter is mostly perpendicular to its
Thermally activated delayed fluorescence (TADF) has drawn con-
siderable attention, particularly in the field of organic light emitting
diodes (OLEDs) because it can enhance the internal quantum efficiency
(IQE) to 100% using pure organic materials only [1]. TADF enables
overcoming the limitations of fluorescent and phosphorescent mole-
cules developed for the emitting layer (EML) of OLEDs [2–4]. In gen-
eral, TADF materials consist of distorted electron donor and acceptor
groups to reduce the overlap of the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) [5].
Therefore, conversion of the triplet to the singlet state through the re-
verse intersystem crossing (RISC) is plausible due to the reduced energy
gap between the singlet and triplet states (ΔEST). Red, green, and blue
TADF emitters have been developed by introducing various electron
donors and acceptors. However, the intrinsic issues of blue emission
have retarded the development of blue TADF emitters as compared to
red and green emitters [6–10].
The interactions between light and substrates allow for only a re-
stricted number of photons to come out because the light should pass
the glass substrate after being emitted from the EML [11,12]. Therefore,
the light out-coupling efficiency, which is generally 0.2 in the case of
isotropic emitters, should be considered [13,14]. To produce OLEDs
with high external quantum efficiencies (EQEs), it is important to not
only increase the intrinsic photoluminescence quantum yield (PLQY) of
transition dipole moment [15]. When the emitter has a vertical emitting
dipole orientation (EDO) to the substrate plane, a large percentage of
the light will be trapped in the glass. Thus, to increase the light out-
coupling efficiency, emitters should be horizontally oriented. It has
been known that the emitter having an anisotropic molecular shape
(e.g. linear or planar shape) is arranged horizontally to the substrate to
reduce the surface energy of the substrate [16]. Therefore, high effi-
ciency OLEDs can be achieved with anisotropic molecular shapes.
Triazine is a strong electron acceptor having a planar six-membered
benzene-like ring but with three carbons replaced by nitrogens.
Therefore, triazine has been linked to various electron donors to de-
velop blue-green emitters [17–24]. Recently, spiroacridine has been
introduced to TADF emitters as an electron donor due to restricted
molecular motions and moderate electron-donating ability [24–28].
The TADF emitter TrSAc consists of spiroacridine as an electron donor
and 2,4,6-triphenyl-1,3,5-triazine as an electron acceptor [25]. The
distorted structure of TrSAc between spiroacridine and a phenylene
spacer separates the HOMO and LUMO, resulting in efficient TADF
emission as well as enhanced PLQY. TrSAc also exhibits high EQE due
to efficient light extraction resulting from the horizontal orientation of
its linear shape. We expect that the structural modification of the
triazine acceptor unit of sky-blue emitting TrSAc would push the
emission wavelength to the blue region.
∗ Corresponding author.
E-mail addresses: jjkim@snu.ac.kr (J.-J. Kim), jihong@snu.ac.kr (J.-I. Hong).
https://doi.org/10.1016/j.dyepig.2019.107864
Received 2 August 2019; Received in revised form 5 September 2019; Accepted 5 September 2019
Availableonline05September2019
0143-7208/©2019ElsevierLtd.Allrightsreserved.

Y. Lee, et al.
DyesandPigments172(2020)107864
and LUMO were distributed on the spiroacridine and triaryltriazine
units, respectively. Because of the poor HOMO LUMO overlap,
moTrSAc, tmTrSAc, and motmTrSAc exhibited a small ΔEST value of
0.01 eV, which is identical to that of TrSAc. The result indicates that
modulations on the triphenyltriazine unit have little effect on the TADF.
TADF emitter moTrSAc with p-methoxy substitution on the terminal
diphenyltriazine moiety showed higher LUMO (1.80 eV) than that of
TrSAc (2.01 eV) because of the electron-donating ability of the methoxy
group. The triazine of tmTrSAc was distorted by 27° with respect to the
central methylphenylene linker due to the methyl substitution, which
caused destabilization of the conjugation. Consequently, tmTrSAc with
deconjugated tri(o-tolyl)triazine elevated the LUMO (1.87 eV) as com-
pared to the methyl-free TrSAc (2.01 eV). In other words, methoxy and
methyl substitutions raised the LUMO energy by 0.21 and 0.14 eV in
moTrSAc and tmTrSAc, respectively. The methyl substitution in the
linker and acceptor elevated the LUMO by 0.06 and 0.08 eV, respec-
tively (see Fig. S1 and Table S1). In the case of motmTrSAc, the si-
multaneous introduction of methoxy and methyl groups raised the
LUMO (0.21 eV + 0.14 eV), resulting in the highest LUMO (1.66 eV)
and Egap among the triazine series. Therefore, the electronic and
structural modulation allowed the emission wavelength to be shifted
into the blue region through an increase in the Egap
.
Fig. 1. Design concept of the TADF emitters with modulated triazines.
2.2. Synthesis
Herein, we report three blue TADF emitters, moTrSAc, tmTrSAc
and motmTrSAc, which were designed through the electronic and
structural modulation of the triphenyltriazine unit (Fig. 1). These
modulations did not affect the TADF, but led to a blue-shifted emission
and enhanced horizontal EDO as compared to TrSAc. Results show that
the OLED devices based on the modulated triazines shifted the CIE color
coordinates to the blue region with fairly good EQEs by enhanced light
out-coupling efficiency. moTrSAc, tmTrSAc, and motmTrSAc-based
devices showed CIE color coordinates of (0.17, 0.27), (0.17, 0.27), and
(0.16, 0.22) and EQEs of 21.3, 15.5, and 19.5%, respectively. These
results suggest that electronic and structural modulation of triazine-
based electron acceptors can be a strategy to shift the emission wave-
length and increase light out-coupling efficiency.
The synthetic strategy employed to obtain the three emitters is il-
lustrated in Scheme 1, where 1, 2, and 3 were synthesized according to
the previous report [29]. The bromine-lithium exchange reaction of 2
and 3 with n-butyllithium (n-BuLi) followed by transmetalation with
trimethyl borate furnished 4 and 5, respectively. The reaction of cya-
nuric chloride with Grignard reagents prepared from monoaryl bro-
mides afforded the diaryltriazine compounds (6, 7, and 8). The Suzuki-
Miyaura cross-coupling reaction between appropriate boronic acid (4,
5) and diaryltriazine compounds (6, 7, 8) provided moTrSAc,
tmTrSAc, and motmTrSAc. The three emitters were purified by column
chromatography, followed by recrystallization and temperature-gra-
dient sublimation. Their chemical structures were fully characterized
by 1H NMR, 13C NMR, elemental analysis, and high-resolution mass
spectrometry.
2. Results and discussion
2.1. Theoretical calculations
2.3. Electrochemical properties
We calculated the optimized molecular structures and energies of
the frontier molecular orbitals through density functional theory (DFT)
calculations at the B3LYP/6-31G(d) level using Gaussian 09. Calculated
data are presented in Fig. 2 and summarized in Table 1. The optimized
molecular structures showed the distorted shape due to the steric hin-
drance between spiroacridine and the phenylene spacer. The HOMO
The electrochemical properties of these compounds were analyzed
using cyclic voltammetry (CV), and their corresponding voltammo-
grams are presented in Fig. 3a and b and summarized in Table 2. The
oxidation potentials of moTrSAc, tmTrSAc, and motmTrSAc were
nearly identical to that of TrSAc because they have the same electron
donors. The HOMO energy levels were calculated from the onset of the
Fig. 2. Optimized molecular structures.
2

Y. Lee, et al.
DyesandPigments172(2020)107864
Table 1
Calculated data.
HOMO[eV]
LUMO [eV]
Egap [eV]
ESinglet [eV]
ETriplet [eV]
ΔEST [eV]
θa [o]
θb [o]
θc [o]
TrSAc
4.96 eV
4.90 eV
4.93 eV
4.87 eV
2.01 eV
1.80 eV
1.87 eV
1.66 eV
2.95 eV
3.10 eV
3.06 eV
3.21 eV
2.43 eV
2.57 eV
2.55 eV
2.68 eV
2.42 eV
2.56 eV
2.54 eV
2.67 eV
0.01 eV
0.01 eV
0.01 eV
0.01 eV
90
90
90
90
0
0
27
26
0
0
27
30
moTrSAc
tmTrSAc
motmTrSAc
spectra and found to be 5.35 eV for all these molecules. However, the
reduction potentials were different depending on the electronic and
structural modulations. The LUMO energy levels of moTrSAc and
tmTrSAc (2.75 eV) were 0.1 eV higher than that of TrSAc (2.85 eV).
Therefore, substitution of two methoxy groups and three methyl groups
in motmTrSAc further elevated its LUMO energy level (2.65 eV) by the
summation of electrical and structural variations. Therefore, we ex-
pected that the adjustment of the LUMO energy by electrical and
structural modulations could shift the emission wavelength to the blue
region.
further proves CT character (Fig. S2). The PL spectra of moTrSAc,
tmTrSAc, and motmTrSAc in toluene solution showed emission wa-
velengths of 476, 470, and 467 nm, respectively (Fig. 3c). As predicted
from the DFT calculations and CV data, the emission wavelengths
moved to the blue region as compared to TrSAc (λ = 484 nm) because
of the widened Egap
.
PL measurements performed at 300 and 77 K in toluene revealed the
singlet and triplet characteristics, respectively (Fig. S3). The singlet and
triplet energies were calculated from the onset of the spectra and are
summarized in Table 2. The fluorescence and phosphorescence spectra
of TrSAc, moTrSAc, tmTrSAc, and motmTrSAc overlapped sig-
nificantly, indicating a small ΔEST. Therefore, TADF emission was ex-
pected in moTrSAc, tmTrSAc, and motmTrSAc as was observed in
TrSAc because the ΔEST values of moTrSAc, tmTrSAc, and
motmTrSAc were also significantly low (~0.01 eV).
Photophysical properties of thin films were also investigated. All
films were fabricated by doping 10 wt% emitter using bis[2- (diphe-
nylphosphino)phenyl] ether oxide (DPEPO) as a host with high triplet
energy [30]. The emission wavelength of films was shifted to a blue
region in a similar manner as was observed in solution (Fig. 3d).
2.4. Photophysical properties
Photophysical properties of TrSAc, moTrSAc, tmTrSAc, and
motmTrSAc were evaluated using ultraviolet–visible (UV–Vis) ab-
sorption, photoluminescence (PL), time-resolved PL, and angle-depen-
dent PL measurements. As shown in the UV–Vis spectra, the absorption
peaks at 350–450 nm indicate the intramolecular charge transfer (CT)
transition between the electron donor and acceptor in each emitter
(Fig. 3c). The emission spectral shift depending on the solvent polarity
Scheme 1. Synthetic routes for moTrSAc, tmTrSAc, and motmTrSAc. (i) CuI, 1,2-diaminocyclohexane, K2CO3, 1,4-dioxane, 100 °C; (ii) n-BuLi, THF, −78 °C; (iii) Pd
(PPh3)4, K2CO3, toluene/H2O, 100 °C; (iv) I2, Mg, THF, 70 °C, 3 h; (v) THF, 50 °C, 12 h (R1 = 6, R2 = 7, R3 = 8).
3

Y. Lee, et al.
DyesandPigments172(2020)107864
Fig. 3. (a) Oxidation potential curves, (b) reduction potential curves, (c) absorption and emission spectra in toluene (10−5 M), (d) emission spectra of 10 wt% doped
film in DPEPO of TrSAc, tmTrSAc, tmTrSAc, and motmTrSAc.
However, because of the polarity of DPEPO, the emission wavelengths
of films were red-shifted compared to those of the toluene solution state
[17,26]. moTrSAc, tmTrSAc, and motmTrSAc showed lower PLQYs of
70, 62, and 51% in the film state, respectively, as compared to TrSAc
(80.1%) [27], presumably because of decreased CT character and ad-
justed vibrational modes [22,31,32].
Fig. 4 shows the transient PL curves in film states, and lifetimes are
summarized in Table 2. Transient PL measurements of the thin films of
four emitters exhibited bi-exponential decays with the prompt and
delayed fluorescence components, which indicates that all emitters ef-
ficiently underwent ISC to the triplet state and RISC from the triplet
state. These results confirmed that electronic and structural modula-
tions of the triaryltriazine moiety maintained the TADF characteristics.
Angle-dependent PL of 10 wt% doped films in DPEPO was measured
to determine the EDO of TrSAc, moTrSAc, tmTrSAc, and motmTrSAc
(Fig. 5). Linear-shaped TrSAc itself showed the horizontal EDO of 78%,
which is different from the horizontal EDO values in mCPCN and mCP/
TSPO1 hosts due to different host-guest interactions [24,25,33].
Methoxy-substituted moTrSAc and methyl-substituted tmTrSAc
showed enhanced horizontal EDOs of 85% and 80%, respectively, be-
cause of widened molecular shapes compared to TrSAc [16]. Of the
three emitters, motmTrSAc having both methoxy and methyl groups
exhibited the highest horizontal EDO of 88%. As a result, despite re-
latively low PLQYs of moTrSAc, tmTrSAc, and motmTrSAc with blue-
shifted emission, their OLED devices could maintain high efficiencies
because of the enhanced horizontal dipole orientation.
2.5. Thermal properties
Thermogravimetric analysis (TGA) of moTrSAc, tmTrSAc, and
Table 2
Electrochemical and photophysical data.
b
b
b
c
c
HOMOa [eV]
LUMOa [eV]
λMaxb/c, [nm]
PLQYc [%]
S1 [eV]
T1 [eV]
ΔEST [eV]
τ1 [ns]
τ2 [μs]
θ//d [%]
TrSAc
5.35
5.35
5.35
5.35
2.85
2.75
2.75
2.65
484/492
470/482
476/479
467/469
80.1
70
62
2.87
2.94
2.96
2.97
2.86
2.93
2.95
2.96
0.01
0.01
0.01
0.01
33
29
24
31
1.6
3.4
2.5
3.0
78
85
80
88
moTrSAc
tmTrSAc
motmTrSAc
51
a
red
Estimated from the onset potentials (oxEonset and
Measured in toluene solution (10−5 M).
Measured using 10 wt% doped films in DPEPO.
Horizontal emitting dipole ratio.
E
onset
[eV] against Fc/Fc+ redox couple) in CV experiments.
b
c
d
4

Y. Lee, et al.
DyesandPigments172(2020)107864
Fig. 4. Transient-PL decay curves of 10 wt% in DPEPO film of (a) TrSAc, (b) moTrSAc, (c) tmTrSAc, and (d) motmTrSAc.
motmTrSAc was conducted to measure the thermal decomposition
temperature (Td). Td of moTrSAc, tmTrSAc, and motmTrSAc were
423, 384, and 409 °C, respectively. All these emitters showed higher
thermal stability than that of TrSAc (381 °C). The TGA thermograms of
the emitters are presented in Fig. S4.
with decreased PLQY by increasing the light out-coupling efficiency.
3. Conclusion
We synthesized triazine-based TADF emitters moTrSAc, tmTrSAc,
and motmTrSAc with spiroacridine as the electron donor and modu-
lated triazines as the acceptor. Modulations of the triazine moiety
shifted the emission wavelength to the blue region while maintaining
the TADF characteristics. Moreover, as the shape of the emitters became
more planar, the horizontal dipole orientation increased, resulting in
enhanced light out-coupling efficiency. Results show that the OLEDs
based on moTrSAc, tmTrSAc, and motmTrSAc had EQEs of 21.3, 15.5,
and 19.5%, respectively. These results indicated that modulation of the
triazine electron acceptor moiety can be a strategy to shift the emission
wavelength to the blue region and enhance the light out-coupling ef-
ficiencies.
2.6. Device properties
Multilayer devices were fabricated based on TrSAc, moTrSAc,
tmTrSAc, and motmTrSAc to verify the OLED characteristics as follows
(Fig. 6a): ITO (150 nm)/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)
benzidine (NPB, 80 nm)/1,3-di(9H-carbazol-9-yl)benzene (mCP,
10 nm)/DPEPO: emitter (10 wt%, 20 nm)/DPEPO (10 nm)/2,2′,2”-
(1,3,5- benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi, 40 nm)/
LiF (1 nm)/Al (100 nm). The device data are summarized in Table 3.
The devices of TrSAc, moTrSAc, tmTrSAc and motmTrSAc showed
emission maxima at 484, 476, 472 nm, and 468 nm, respectively
(Fig. 6b). Emission wavelengths were shifted to the blue region as ex-
pected from the photophysical characteristics when the methoxy and
methyl groups were introduced on the triphenyltriazine. Although the
color coordinates of TrSAc were in the sky blue to green region, those of
moTrSAc, tmTrSAc, and motmTrSAc were in the blue region with y
coordinates under 0.3. The device efficiency of TrSAc, moTrSAc,
tmTrSAc, and motmTrSAc was 23.8, 21.3, 15.5, and 19.5%, respec-
tively (Fig. 6d). motmTrSAc was expected to have the lowest EQE
because of the lowest PLQY with the emission wavelength shifted to the
blue region. However, motmTrSAc showed better efficiency than that
of tmTrSAc because motmTrSAc had the highest degree of horizontal
dipole orientation. This suggests that high EQEs can be obtained even
4. Experimental
4.1. Quantum chemical calculations
All quantum chemical calculations were performed using Gaussian
09 program package. Geometry optimizations and energy calculations
for the lowest excited singlet and triplet states were carried out using
DFT and time-dependent DFT calculations at the B3LYP/6-31G(d) level.
4.2. Synthesis and characterization
Commercially available reagents and solvents were used without
5

Y. Lee, et al.
DyesandPigments172(2020)107864
Fig. 5. Angle-dependent PL intensities of (a) TrSAc, (b) moTrSAc, (c) tmTrSAc, and (d) motmTrSAc.
further purification unless otherwise noted. 1H and 13C NMR spectra
were recorded using Agilent 400-MR DD2 400 MHz or Varian/Oxford
As-500 500 MHz in CDCl3. 1H NMR chemical shifts in CDCl3 were re-
ferenced to CHCl3 (7.27 ppm). 13C NMR chemical shifts in CDCl3 were
reported relative to CHCl3 (77.23 ppm). High-resolution mass spectro-
metric data (JEOL, JMS-700) with electron impact (EI) and fast atom
bombardment (FAB) positive mode were received directly from the
National Centre for Inter-University Research Facilities. Elemental
analyses were carried out using a Thermo Scientific FlashEA 1112.
excitation. Photoluminescence decay traces were obtained through the
time-correlated single photon counting (TCSPC) techniques by using a
PicoQuant, FluoTime 250 instrument. 377 nm pulsed laser was used as
an excitation source. For angle-dependent PL (ADPL) measurements, p-
polarized lights emitted from PL samples were measured by attaching
the film substrate to half-cylinder lens with index-matching oil and
changing the angle between the sample and the detector from −90° to
90° using a motorized rotational stage.
4.5. Device fabrication and measurements
4.3. Electrochemical and thermal analysis
The patterned ITO (150 nm) substrates were washed with water and
isopropyl alcohol, followed by 10 min UV−ozone treatment. Organic
layers, LiF, and Al were thermally evaporated at a deposition rate of
1–2 Å s−1 for organic layers, 0.1 Å s−1 for LiF, and 3–5 Å s−1 for the Al
electrode. OLED properties were measured using Keithley source meter
2400 and PR-650 spectrascan colorimeter.
Cyclic voltammetry (CV) experiments were conducted using CH
instruments 650B electrochemical analyzer in DMF solution (1.00 mM)
with 0.1 M tetrabutylammonium perchlorate (TBAP) as the supporting
electrolyte. A glassy carbon electrode was employed as the working
electrode and referenced to the Ag reference electrode. All potential
values were calibrated against the ferrocene/ferrocenium (Fc/Fc+
)
redox couple. The onset potential was determined from the intersection
of two tangents drawn at the rising and background current of the
cyclic voltammogram. Thermal analyses were performed with TA in-
strument Q50 thermogravimetric analyzer in nitrogen atmosphere at
4.6. Materials
heating rate of 10 °C min−1
.
4.6.1. Synthesis of 10H-spiro[acridine-9,9′-fluorene] (1, SAc)
1 was prepared according to the literature procedure [20]. Com-
pound 1 (11.60 g, 40%) was obtained as a white powder.
4.4. Photophysical property analysis
UV–visible spectra were recorded with Jasco V-730 spectrometer.
Fluorescence and phosphorescence spectra were recorded with Jasco
FP-8300 spectrophotometer. PLQYs were measured using mono-
chromator-attached photomultiplier tube (PMT) with a PL sample in an
integrating sphere using continuous wave 325 nm He/Cd laser for
4.6.2. Synthesis of 10-(4-bromophenyl)-10H-spiro[acridine-9,9′-fluorene]
(2)
2 was prepared according to the literature procedure [20]. Com-
pound 2 (2.4 g, 54.5%) was obtained as a white solid.
6

Y. Lee, et al.
DyesandPigments172(2020)107864
Fig. 6. (a) Device structure, (b) EL spectra (inset: color coordinates), (c) current density-voltage-luminance (J-V-L) spectra, (d) external quantum efficiency-current
density (ηEQE-J) spectra. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
was purified by column chromatography (SiO2, CHCl3:hexane = 1:4) to
afford compound 3 (2.4 g, 54.5%) as a white solid.
Table 3
Summarized device data.
1H NMR (400 MHz, CDCl3) δ (ppm): 7.87 (d, J = 8.3 Hz, 1H), 7.80
(d, J = 7.6 Hz, 2H), 7.43–7.32 (m, 5H), 7.28–7.18 (m, 3H), 6.97–6.89
(m, 2H), 6.60–6.52 (m, 2H), 6.46–6.30 (m, 4H), 2.54 (s, 3H). 13C NMR
(100 MHz, CDCl3) δ (ppm): 156.55, 141.22, 140.97, 140.20, 139.18,
134.94, 133.41, 130.11, 128.35, 127.86, 127.58, 127.20, 125.73,
124.77, 120.71, 119.89, 114.50, 56.72, 23.16.
a
e
Turn on
Voltage
(V)
EQEMax (%) CEb
PEc
CIEd
Coordinates
(x, y)
λmax
(cd
(lm
(nm)
A−1
)
W−1
)
TrSAc
moTrSAc
tmTrSAc
3.9
4.2
4.0
23.8
21.3
15.5
19.5
50.1
40.9
28.7
21.3
21.8
0.19,0.36
0.17,0.27
0.17,0.27
0.16,0.22
484
472
476
468
36.6
28.5
29.2
motmTrSAc 4.2
a
4.6.4. Synthesis of (4-(10H-spiro[acridine-9,9′-fluoren]-10-yl)phenyl)
boronic acid (4)
External quantum efficiency.
Current efficiency.
Power efficiency.
CIE 1931 color coordinates.
Emission wavelength at 5 V.
b
c
10-(4-bromophenyl)-10H-spiro[acridine-9,9′-fluorene]
(1.08 g,
d
e
2.05 mmol) (2) was dissolved in dry THF (82 mL) under a nitrogen
atmosphere. This solution was cooled to −78 °C followed by dropwise
addition of 1.6 M n-butyl lithium solution in hexane (1.9 mL,
3.08 mmol). This mixture was stirred for 2 h after which trimethylbo-
rate (0.46 mL, 4.1 mmol) was added. After stirring at room temperature
overnight, the reaction mixture was added to an aqueous HCl solution
(1 N) and extracted with chloroform. The combined organic extracts
were dried over sodium sulfate, concentrated in vacuo to afford com-
pound 4. 4 was used for the next reaction without further purification.
4.6.3. Synthesis of 10-(4-bromo-3-methylphenyl)-10H-spiro[acridine-9,9′-
fluorene] (3)
A
mixture of 10H-spiro[acridine-9,9′-fluorene] (1) (4.50 g,
13.60 mmol), 1-bromo-4-iodo-2-methylbenzene (4.45 g, 15 mmol),
copper iodide (260 mg, 0.1.36 mmol), ( )-trans-1,2-diaminocyclo-
hexane (0.34 mL, 2.8 mmol) and sodium tert-butoxide (2.60 g,
2.80 mmol) in 1,4-dioxane (15 mL) was refluxed overnight under a ni-
trogen atmosphere. The reaction mixture was then filtered through a
pad of silica and extracted with chlorofrom. The organic layer was
washed with water and brine, and dried over anhydrous sodium sulfate.
The filtrate was concentrated in vacuo to give a crude mixture, which
4.6.5. Synthesis of (2-methyl-4-(10H-spiro[acridine-9,9′-fluoren]-10-yl)
phenyl)boronic acid (5)
10-(4-bromo-3-methylphenyl)-10H-spiro[acridine-9,9′-fluorene]
(4.2 g, 8.40 mmol) (3) was dissolved in dry THF (168 mL) under a
7

Y. Lee, et al.
DyesandPigments172(2020)107864
nitrogen atmosphere. This solution was cooled to −78 °C followed by
dropwise addition of 1.6 M n-butyl lithium solution in hexane (7.9 mL,
12.6 mmol). The mixture was stirred for 2 h after which trimethylborate
(1.9 mL, 16.8 mmol) was added. After stirring at room temperature
overnight, the reaction mixture was added to an aqueous HCl solution
(1 N) and extracted with chloroform. The combined organic extracts
were dried over sodium sulfate, concentrated in vacuo to afford com-
pound 5, which was used in the next reaction without further pur-
ification.
triazine (8) (514 mg, 1.44 mmol), (2-methyl-4-(10H-spiro[acridine-
9,9′-fluoren]-10-yl)phenyl)boronic acid (5) (805 mg, 1.73 mmol), tet-
rakis(triphenylphosphine)palladium(0) (81 mg, 0.07 mmol) and po-
tassium carbonate (400 mg, 2.88 mmol) in toluene (14 mL) and water
(3 mL) was refluxed overnight under a nitrogen atmosphere. The re-
action mixture was then filtered through a pad of silica and extracted
with chlorofrom. The organic layer was washed with water and brine,
and dried using anhydrous sodium sulfate. The filtrate was con-
centrated in vacuo to give a crude mixture, which was purified by
column chromatography (SiO2, CHCl3: hexane = 1 : 1) to afford com-
pound motmTrSAc (1 g, 94%) as a yellow solid.
4.6.6. Synthesis of 10-(4-(4,6-bis(4-methoxyphenyl)-1,3,5-triazin-2-yl)
phenyl)-10H-spiro[acridine-9,9′-fluorene] (moTrSAc)
1H NMR (400 MHz, CDCl3) δ (ppm): 8.51 (d, J = 8.0 Hz, 1H), 8.38
(d, J = 8.7 Hz, 2H), 7.80 (d, J = 7.5 Hz, 2H), 7.50 (d, J = 9.7 Hz, 2H),
7.44 (d, J = 7.5 Hz, 2H), 7.37 (t, J = 7.4 Hz, 2H), 7.29–7.24 (m, 2H),
6.94 (td, J = 8.6, 1.7 Hz, 4H), 6.88 (d, J = 2.4 Hz, 2H), 6.57 (t,
J = 7.5 Hz, 2H), 6.48 (d, J = 8.3 Hz, 2H), 6.41 (dd, J = 7.8, 1.2 Hz,
2H), 3.89 (s, 6H), 2.91 (s, 3H), 2.88 (s, 6H). 13C NMR (101 MHz, CDCl3)
δ (ppm): 173.11, 172.85, 161.73, 156.58, 142.99, 141.99, 141.60,
141.00, 139.18, 136.80, 134.08, 133.93, 133.42, 128.65, 128.57,
128.35, 127.79, 127.54, 127.20, 125.78, 124.74, 120.63, 119.85,
117.24, 114.74, 111.51, 56.78, 55.34, 23.21, 22.28. Elem. Anal. calcd
for C51H40N4O2 C 82.68, H 5.44, N 7.56; found C 82.91, H 5.44, N 7.50.
A mixture of 2-chloro-4,6-bis(4-methoxyphenyl)-1,3,5-triazine (6)
(583 mg,
1.78 mmol),
(4-(10H-spiro[acridine-9,9′-fluoren]-10-yl)
phenyl)boronic acid (4) (960 mg, 2.13 mmol), tetrakis(triphenylpho-
sphine)palladium(0) (104 mg, 0.09 mmol) and potassium carbonate
(492 mg, 3.56 mmol) in toluene (18 mL) and water (4 mL) was refluxed
overnight under a nitrogen atmosphere. The reaction mixture was then
filtered through a pad of silica and extracted with chlorofrom. The
organic layer was washed with water and brine, and dried using an-
hydrous sodium sulfate. The filtrate was concentrated in vacuo to give a
crude mixture, which was purified by column chromatography (SiO2,
CHCl3: hexane = 2 : 1) to afford compound moTrSAc (970 mg, 78%) as
a yellow solid.
HRMS (FAB+): calcd for
740.3160.
C : 740.3151; found:
51H40N4O2 [M]+
1H NMR (400 MHz, CDCl3) δ (ppm): 9.06 (d, J = 8.4 Hz, 2H), 8.77
(d, J = 8.9 Hz, 4H), 7.80 (d, J = 7.5 Hz, 2H), 7.70 (d, J = 8.4 Hz, 2H),
7.46 (d, J = 7.5 Hz, 2H), 7.38 (t, J = 7.4 Hz, 2H), 7.27 (t, J = 8.0 Hz,
2H), 7.09 (d, J = 8.9 Hz, 4H), 6.99–6.85 (m, 2H), 6.58 (t, J = 7.4 Hz,
2H), 6.50–6.37 (m, 4H), 3.94 (s, 6H). 13C NMR (101 MHz, CDCl3) δ
(ppm): 171.16, 170.53, 163.37, 156.50, 144.76, 140.98, 139.20,
136.79, 131.63, 131.47, 130.86, 128.72, 128.37, 127.84, 127.58,
127.25, 125.77, 124.86, 120.74, 119.88, 114.62, 113.99, 56.78, 55.46.
Elem. Anal. calcd for C48H34N4O2 C 82.50, H 4.90, N 8.02; found C
4.6.9. Synthesis of 2-chloro-4,6-bis(4-methoxyphenyl)-1,3,5-triazine (6)
To a solution of magnesium (779 mg, 32.04 mmol), iodine (68 mg,
0.27 mmol) in anhydrous THF (26 mL), 1-bromo-4-methoxybenzene
(5 g, 26.7 mmol) was added dropwise under inert conditions. After
stirring at 70 °C for 3 h, the mixture was cooled to room temperature.
The resulting Grignard solution was added dropwise to a solution of
cyanuric chloride (1.48 g, 8.01 mmol) in anhydrous THF (40 mL). When
the addition was completed, the mixture was stirred at 50 °C overnight
and then cooled to room temperature. The mixture was poured into a
1 N HCl aqeous solution, and the organic layer was extracted with di-
chloromethane and then dried using anhydrous sodium sulfate. The
filtrate was concentrated in vacuo to give a crude mixture, which was
purified by column chromatography (SiO2, CH2Cl2: hexane = 2 : 1) to
afford compound 6 (1.5 g, 58%) as a white solid.
82.56, H 4.88, N 8.04, HRMS (FAB+): calcd for C48H34N4O2 [M]+
698.2682; found: 698.2678.
:
4.6.7. Synthesis
methylphenyl)-10H-spiro[acridine-9,9′-fluorene] (tmTrSAc)
mixture of 2-chloro-4,6-di-o-tolyl-1,3,5-triazine (7) (426 mg,
1.44 mmol), (2-methyl-4-(10H-spiro[acridine-9,9′-fluoren]-10-yl)
of
10-(4-(4,6-di-o-tolyl-1,3,5-triazin-2-yl)-3-
A
phenyl)boronic acid (5) (805 mg, 1.73 mmol), tetrakis(triphenylpho-
sphine)palladium(0) (81 g, 0.07 mmol) and potassium carbonate
(400 mg, 2.88 mmol) in toluene (14 mL) and water (3 mL) was refluxed
overnight under a nitrogen atmosphere. The reaction mixture was then
filtered through a pad of silica and extracted with chlorofrom. The
organic layer was washed with water and brine, and dried using an-
hydrous sodium sulfate. The filtrate was concentrated in vacuo to give a
crude mixture, which was purified by column chromatography (SiO2,
CHCl3: hexane = 1 : 2) to afford compound tmTrSAc (860 mg, 88%) as
a yellow solid.
1H NMR (400 MHz, CDCl3) δ (ppm): 8.54 (d, J = 8.9 Hz, 4H), 6.99
(d, J = 8.9 Hz, 4H), 3.89 (s, 6H). 13C NMR (101 MHz, CDCl3) δ (ppm):
172.50, 171.59, 163.98, 131.35, 126.97, 114.06, 55.48. HRMS (EI+):
calcd for C17H14ClN3O2 [M]+: 327.0775; found: 327.0772.
4.6.10. Synthesis of 2-chloro-4,6-di-o-tolyl-1,3,5-triazine (7)
To a solution of magnesium (1.7 g, 70.2 mmol) and iodine (150 mg,
0.6 mmol) in anhydrous THF (60 mL), 1-bromo-2-methylbenzene (10 g,
58.5 mmol) was added dropwise under inert conditions. After stirring at
70 °C for 3 h, the mixture was cooled to room temperature. The
Grignard solution was added dropwise to a solution of cyanuric
chloride (3.24 g, 17.6 mmol) in anhydrous THF (90 mL). When the
addition was completed, the mixture was stirred at 50 °C overnight and
then cooled to room temperature. The mixture was poured into a 1 N
HCl aqeous solution, and the organic layer was extracted with di-
chloromethane and then dried using anhydrous sodium sulfate. The
filtrate was concentrated in vacuo to give a crude mixture, which was
purified by column chromatography (SiO2, CH2Cl2: hexane = 1 : 1) to
afford compound 7 (2.74 g, 53%) as a white solid.
1H NMR (499 MHz, CDCl3) δ (ppm): 8.59 (d, J = 8.0 Hz, 1H), 8.31
(d, J = 7.6 Hz, 2H), 7.82 (d, J = 7.6 Hz, 2H), 7.56–7.38 (m, 12H), 7.28
(dd, J = 13.1, 5.7 Hz, 2H), 6.96 (t, J = 7.3 Hz, 2H), 6.60 (t, J = 7.4 Hz,
2H), 6.50 (d, J = 8.4 Hz, 2H), 6.43 (t, J = 9.2 Hz, 2H), 2.95 (s, 3H),
2.87 (s, 6H). 13C NMR (101 MHz, CDCl3) δ (ppm): 174.08, 173.27,
156.58, 143.33, 142.27, 140.97, 139.20, 138.93, 136.30, 136.00,
134.25, 134.10, 131.89, 131.32, 131.05, 128.79, 128.37, 127.84,
127.57, 127.22, 126.15, 125.79, 124.78, 120.69, 119.87, 114.71,
56.78, 22.41, 22.33. Elem. Anal. calcd for C49H36N4 C 86.44, H 5.33, N
8.23; found C 86.41, H 5.31, N 8.17. HRMS (FAB+): calcd for C49H36N4
[M]+: 680.2940; found: 680.2940.
1H NMR (499 MHz, CDCl3) δ (ppm): 8.20 (d, J = 7.9 Hz, 2H), 7.46
(t, J = 6.9 Hz, 2H), 7.35 (dd, J = 13.9, 7.5 Hz, 4H), 2.74 (s, 6H). 13C
NMR (101 MHz, CDCl3) δ (ppm): 175.50, 170.95, 139.62, 134.16,
132.06, 131.86, 131.56, 126.18, 22.25. HRMS (EI+): calcd for
4.6.8. Synthesis
of 10-(4-(4,6-bis(4-methoxy-2-methylphenyl)-1,3,5-
triazin-2-yl)-3-methylphenyl)-10H-spiro[acridine-9,9′-fluorene]
(motmTrSAc)
C
17H14ClN3 [M]+: 295.0876; found: 295.0876.
A
mixture of 2-chloro-4,6-bis(4-methoxy-2-methylphenyl)-1,3,5-
8

Y. Lee, et al.
DyesandPigments172(2020)107864
4.6.11. Synthesis of 2-chloro-4,6-bis(4-methoxy-2-methylphenyl)-1,3,5-
triazine (8)
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To a solution of magnesium (729 mg, 30 mmol) and iodine (63 mg,
0.25 mmol) in anhydrous THF (24 mL), 1-bromo-4-methoxy-2-methyl-
benzene (5 g, 25 mmol) was added dropwise under inert conditions.
After stirring at 70 °C for 3 h, the mixture was cooled to room tem-
perature. The Grignard solution was added dropwise to a solution of
cyanuric chloride (1.4 g, 7.5 mmol) in anhydrous THF (38 mL). When
the addition was completed, the mixture was stirred at 50 °C overnight
and then cooled to room temperature. The mixture was poured into a
1 N HCl aqeous solution, and the organic layer was extracted with di-
chloromethane and then dried using anhydrous sodium sulfate. The
filtrate was concentrated in vacuo to give a crude mixture, which was
purified by column chromatography (SiO2, CH2Cl2: hexane = 2 : 1) to
afford compound 8 (1.47 g, 55%) as a white solid.
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1H NMR (400 MHz, CDCl3) δ (ppm): 8.28 (d, J = 8.7 Hz, 2H),
6.90–6.76 (m, 4H), 3.86 (s, 6H), 2.75 (s, 6H). 13C NMR (101 MHz,
CDCl3) δ (ppm): 174.36, 170.40, 162.35, 142.44, 133.81, 126.72,
117.42, 111.52, 55.32, 23.19. HRMS (EI+): calcd for C19H18ClN3O2
[M]+: 355.1088; found: 355.1089.
Conflicts of interest
[21] Wada Y, Kubo S, Kaji H. Adamantyl substitution strategy for realizing solution-
processable thermally stable deep-blue thermally activated delayed fluorescence
materials. Adv Mater 2018;30(8):1705641.
[22] Chan C-Y, Cui L-S, Kim JU, Nakanotani H, Adachi C. Rational molecular design for
deep-blue thermally activated delayed fluorescence emitters. Adv Funct Mater
2018;28(11):1706023.
There are no conflicts of interest to declare.
Acknowledgement
[23] Jeong S, Lee Y, Kim JK, Jang D-J, Hong J-I. Non-doped thermally activated delayed
fluorescent organic light-emitting diodes using an intra- and intermolecular ex-
ciplex system with a meta-linked acridine–triazine conjugate. J Mater Chem C
2018;6(34):9049–54.
[24] Woo S-J, Kim Y, Kwon S-K, Kim Y-H, Kim J-J. Phenazasiline/spiroacridine donor
combined with methyl-substituted linkers for efficient deep blue thermally acti-
vated delayed fluorescence emitters. ACS Appl Mater Interfaces
2019;11(7):7199–207.
This work was supported by the NRF grant (No.
2018R1A2B2001293) funded by the MSIP. We thank the Samsung
Display Co., Ltd for partial financial support.
Appendix A. Supplementary data
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Supplementary data to this article can be found online at https://
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