Dimers with thermally activated delayed fluorescence (TADF) emission in non-doped device

Article abstract of DOI:10.1039/d1tc00428j

Two novel TADF molecules, with donor#1-σ-donor#2-π-acceptor (D1-σ-D2-π-A) conformation, were designed and synthesized through-bond charge transfer (TBCT) and through-space charge transfer (TSCT). These two materials differ only in the D1 groups with triphenylamine forSFCCNand 10-phenyl-10H-phenoxazine forSFCCNO. Due to the unconjugated linkage, both materials showed very similar emission to that from D2-π-A TBCT effect in dilute solution.SFCCNOcan form dimers at the aggregation state and exhibit intermolecular D1/A TSCT emission because of the planar D1 conformation. Therefore, a non-doped device based onSFCCNOexhibited efficiencies of 12.9% at 100 cd m^?2and 10.4% at 1000 cd m^?2, which are much higher than theSFCCNbased device.

Full text of DOI:10.1039/d1tc00428j

Journal of
Materials Chemistry C
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PAPER
Dimers with thermally activated delayed
fluorescence (TADF) emission in non-doped
device†
Cite this: J. Mater. Chem. C, 2021,
, 4792
9
a
a
a
a
a
b
Xing Chen, Aziz Khan, Sheng-Nan Zou, Yun Li, Qi-Sheng Tian, Cheng Zhong,*
ac
a
ac
Man-Keung Fung,
*
Zuo-Quan Jiang * and Liang-Sheng Liao
Two novel TADF molecules, with donor#1–s–donor#2–p–acceptor (D1–s–D2–p–A) conformation,
were designed and synthesized through-bond charge transfer (TBCT) and through-space charge transfer
(TSCT). These two materials differ only in the D1 groups with triphenylamine for SFCCN and 10-phenyl-
Received 29th January 2021,
Accepted 11th March 2021
10H-phenoxazine for SFCCNO. Due to the unconjugated linkage, both materials showed very similar
emission to that from D2–p–A TBCT effect in dilute solution. SFCCNO can form dimers at the aggregation
state and exhibit intermolecular D1/A TSCT emission because of the planar D1 conformation. Therefore,
DOI: 10.1039/d1tc00428j
ꢀ2
a non-doped device based on SFCCNO exhibited efficiencies of 12.9% at 100 cd m
and 10.4% at
ꢀ
2
rsc.li/materials-c
1000 cd m , which are much higher than the SFCCN based device.
In many reports, the D/A blocks were linked in one conjugated
Introduction
molecule with twisted configuration to minimize the DEST and
12,13
In recent years, through the constant efforts of research groups gave a covalent through-bond charge transfer (TBCT) emission.
across the world, thermally activated delayed fluorescence This is a typical paradigm for achieving TADF, but recently,
(
TADF) emitter-based organic light-emitting diodes (OLEDs) researchers have found that through-space charge transfer (TSCT)
1
–4
14–17
have gained tremendous achievements.
A basic description model can be an alternative.
A representative TSCT model is
of the TADF mechanism is as follows: in a TADF emitter, the D/A complex, or known as exciplex, which constitutes a small
1
8
single energy (S
1 1
) and triplet energy (T ) levels are strongly DEST corresponding to the intermolecular spatial CT process
coupled, which allows intersystem crossing (ISC) between the (Scheme 1a). Chemists have further been trying to merge D/A
5
,6
two levels. In this regard, the TADF emitter has much smaller blocks together in one molecule with an unconjugated linkage,
energy difference between the S and T (DE ) levels than typical and an intramolecular spatial CT would lead to TADF emission
1
1
ST
organic molecules, which enables reverse intersystem crossing if there is a short D/A distance in space (Scheme 1b and c). These
(
RISC) to occur. This strategy can provide a new up-conversion new approaches undoubtedly enrich the structural diversity of
19
avenue to harvest the additional 75% triplets and thus achieve TADF materials.
1
7
–9
00% internal quantum efficiency (IQE) in theory.
In this study, a new configuration called D1–s–D2–p–A for
According to TADF designed strategy, the alignment of TADF is constructed to exhibit intermolecular CT emission at
2
0,21
electron donor (D)/acceptor (A) and the charge transfer (CT) the aggregation state.
The two target molecules, SFCCN and
process between them are very important, and normally, the SFCCNO, have very similar structure except that the latter one
HOMO dispersed at the donor and LUMO located on the has one more electron-donating oxygen to strengthen the donor
1
0,11
acceptor should have a small overlap to obtain a small DEST
.
strength of D1 (SFCCN: D1 = triphenylamine; SFCCNO:
D1 = oxygen-bridged triphenylamine; D2 = carbazole, A =
4
,6-diphenyl-1,3,5-triazine). As shown in Scheme 1d, the intra-
a
Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices,
molecular electronic interaction between D1 and A are inter-
cepted because: (i) the TBCT path is blocked by the unconjugated
spiro-carbon, (ii) the intramolecular TSCT path is also impossible
due to the long D1/A distance and unfavorable D1/A con-
formation.
the conjugative D2–p–A linkage and the distance between them
is shorter than that of D1/A in this special molecular design.
However, the CT emission from D1 to A of SFCCNO can be
Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University
99 Ren’ai Road, Suzhou, Jiangsu 215123, China. E-mail: mkfung@suda.edu.cn,
1
zqjiang@suda.edu.cn
b
Hubei Key Lab on Organic and Polymeric Optoelectronic Materials,
Department of Chemistry, Wuhan University, 299 Bayi Road, Wuhan, 430072,
Hubei, P. R. China. E-mail: zhongcheng@whu.edu.cn
22–25
By contrast, D2/A coupling is conspicuous for
c
Macao Institute of Materials Science and Engineering, Macau University of Science
and Technology, Taipa, Macau SAR, 999078, P. R. China
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/d1tc00428j
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Scheme 1 (a) Charge transfer in two different molecules; (b) charge transfer in a single molecule; (c) charge transfer in two molecules with the same
structure; (d) CT emissions in different states between SFCCN and SFCCNO; route 1 = Intramolecular through-bond charge transfer (TBCT) emission;
route 2 = Blocked intra-TBCT path in solution for long distance in D1/A; route 3 = Inter-molecular through-space charge transfer (TSCT) emission in
aggregation state.
clearly observed as compared to the referential pristine SFCCN 7.73 (t, J = 7.8 Hz, 2H), 7.68–7.57 (m, 10H), 7.54–7.53 (m, 3H),
film. Non-doped TADF OLEDs were constructed and the SFCCNO 7.50–7.46 (m, 2H), 7.42–7.43 (m, 1H), 7.37 (d, J = 7.0 Hz, 1H), 7.31
based device exhibits external quantum efficiencies (EQEs) of (d, J = 7.8 Hz, 1H), 6.95 (t, J = 1.5 Hz, 2H), 6.62 (t, J = 1.0 Hz, 2H),
ꢀ
2
ꢀ2
13
1
2.9% at 100 cd m and 10.4% at 1000 cd m . Our novel non- 6.53 (d, J = 1.6 Hz, 2H), 6.39 (d, J = 1.2 Hz, 2H). C NMR
heterodimeric emissive system has a comparable device perfor- (101 MHz, Chloroform-d) d 171.83, 170.93, 156.92, 155.09, 141.58,
mance to those OLEDs using conventional D/A complexes with 141.47, 141.37, 141.13, 140.91, 139.90, 139.92, 139.88, 139.24,
2
6–29
dimeric inter-TSCT emission.
136.15, 135.02, 134.17, 132.68, 131.23, 131.09, 130.71, 129.03,
1
1
1
8
28.73, 128.50, 128.46, 127.88, 127.80, 127.64, 127.23, 126.66,
26.39, 125.97, 125.86, 124.87, 124.34, 123.94, 120.60, 120.54,
Experimental section
20.00, 119.08, 118.76, 114.66, 110.21, 110.11, 56.67. MS (EI) m/z:
+
79.271 [M ]. Calcd for C64
41 5
H N :880.067.
0
0
The molecule (3,3 ), (4,4 ) and 5 were synthesized according to
1
6,30
our previous work.
3
-(9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazol-3-
0
0
3
-(9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazol-3-
yl)spiro[fluorene-9,9 -quinolino[3,2,1-kl]phenoxazine]
(SFCCNO)
0
yl)-10-phenyl-10H-spiro[acridine-9,9 -fluorene] (SFCCN)
A mixture of 3-bromo-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)- A mixture of 3-bromo-9-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-
0
9
1
3
H-carbazole (1.30 g, 2.35 mmol), 10-phenyl-3 -(4,4,5,5-tetramethyl- 9H-carbazole (1.50 g, 2.71 mmol), 3-(4,4,5,5-tetramethyl-1,3,2-
0
0
,3,2-dioxaborolan-2-yl)-10H-spiro[acridine-9,9 -fluorene] (1.50 g, dioxaborolan-2-yl)spiro[fluorene-9,9 -quinolino[3,2,1-kl]phenoxazine]
.25 mmol), (molecule 4 and 5) Pd(PPh ) (136 mg) and Na CO
0
(1.78 g, 3.25 mmol),(molecule 4 and 5) Pd(PPh ) (157 mg) and
3
4
2
3
3 4
2 3
(1.24 g, 11.74 mmol, water 12.5 mL) in THF (50 mL) was heated to Na CO (1.44 g, 13.55 mmol, water 12.5 mL) in THF (50 mL) was
reflux under argon and stirred for 24 hours. The reaction mixture heated to reflux under argon and stirred for 24 h. Then the
was then dissolved in ethyl acetate and washed thrice with water reaction mixture was dissolved in ethyl acetate and washed
(
3 ꢁ 30 mL). The combined organic layer was dried with Na
2
SO
4
,
thrice with water (3 ꢁ 30 mL). The combined organic layer
filtered and evaporated under reduced pressure. The crude was dried with Na
2
SO , filtered and evaporated under reduced
4
product was purified by column chromatography using petro- pressure. The crude product was purified by column chromato-
leum ether (PE)/dichloromethane (DCM) (7 : 3 v/v) as an eluent graphy using PE/DCM (7 : 3 v/v) as an eluent to obtain a white
1
1
to obtain a white product and weighed (1.72 g, 83%). H NMR product and weighed (2.01 g, 85%). H NMR (600 MHz, Chloro-
600 MHz, Chloroform-d) d 9.06 (d, J = 8.6 Hz, 2H), 8.85 (d, J = form-d) d 9.04 (d, J = 18.9 Hz, 2H), 8.82 (d, J = 7.3 Hz, 4H), 8.54
.4 Hz, 4H), 8.47 (s, 1H), 8.25 (d, J = 7.6 Hz, 1H), 8.14 (s, 1H), 7.93 (s, 1H), 8.29 (d, J = 24.9 Hz, 1H), 8.19 (d, J = 20.9 Hz, 1H),
d, J = 7.5 Hz, 1H), 7.87 (d, J = 1.8 Hz, 2H), 7.79 (d, J = 1.8 Hz, 1H), 8.02 (s, 1H), 7.85 (d, J = 34.8 Hz, 4H), 7.75 (d, J = 8.3 Hz, 1H),
(
1
(
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7
(
(
.62 (m, 10H), 7.44 (d, J = 21.9 Hz, 2H), 7.39–7.29 (m, 2H), 7.19 Table 1 Physical properties of SFCCN and SFCCNO
m, 1H), 7.06 (m, 4H), 6.82 (t, J = 7.6 Hz, 1H), 6.77 (m, 1H), 6.67
a
b
c
T
d
/T
g
(1C)
l
max (nm) HOMO/LUMO (eV) DEST (eV)
1
3
t, J = 7.9 Hz, 2H), 6.25 (d, J = 42.8 Hz, 2H). C NMR (101 MHz,
Chloroform-d) d 171.82, 170.90, 148.54, 146.78, 141.53, 140.90,
SFCCN
SFCCNO 491/212
554/264
421
420
ꢀ5.15/ꢀ2.09
ꢀ5.11/ꢀ2.04
0.23
0.24
1
1
1
1
37.12, 136.13, 135.04, 133.94, 132.68, 131.15, 130.70, 130.52,
29.32, 129.29, 129.02, 128.72, 127.19, 126.65, 126.42, 123.97,
23.78, 123.44, 122.96, 120.63, 120.28, 118.98, 117.60, 116.94,
15.32, 114.22, 110.12, 56.90. MS (EI) m/z: 893.284 [M +]. Calcd
a
T
d
obtained from TGA measurements and T
g
obtained from DSC
b
c
measurements. PL spectra measured in a toluene solution. DEST
estimated from the experimental S and T energies.
1 1
39 5
for C64H N O: 894.050.
fluorescence spectra with an emission peak at 431 and 428 nm,
respectively (Fig. 1a). Apart from that, another TADF compound
called SFCC, synthesized in our previous work, with the same
Results and discussion
1
6
backbone also exhibited a very similar peak at 434 nm. This
was not a coincidence but indicated that the TBCT emission
mainly originated from the conjugated D2–A interaction while
the D1/A TSCT interaction can be ignored because of the
unconjugated linkage and long distance between them. How-
ever, in the aggregation state, the fluorescence spectra for
SFCCNO (512 nm) showed a significant red-shift as compared
to the SFCCN (458 nm) (Fig. 1b). The PL spectrum (493 nm) of
the SFCCN : SFCCNO (1 : 1) mixed film is also shown in Fig. S9
Synthesis and characterization
The detailed synthetic routes of the target molecules SFCCN
and SFCCNO are depicted in Scheme 2. Intermediates 3 and 3
were synthesized by a two-step continuous reaction under the
same conditions. Correspondingly, intermediates 4 and 4 were
synthesized via the Miyaura borylation reaction. Resultantly,
SFCCN and SFCCNO were successfully obtained in good quantity
through the Suzuki–Miyaura coupling reaction with 3-bromo-9-(4-
0
0
(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9H-carbazole and respective
(ESI†). Thus, we preliminarily hypothesize that SFCCNO has
intermediate reagents. The molecules SFCCN and SFCCNO were
an additional oxygen to strengthen the electron donating
capability in D1, which might contribute to an apparent red-
shift in the photoluminescence process (intermolecular TSCT
emission from D1 to A), and the details will be discussed below.
Besides, fluorescence spectra of bis[2-(diphenylphosphino)phe-
nyl] ether oxide (DPEPO) films doped with SFCCN and SFCCNO
1
13
fully characterized by H NMR, C NMR and MALDI-TOF with
their spectral detail mentioned in the ESI† (Fig. S1–S6).
Thermal property
Thermogravimetric analysis (TGA) was performed to study the
thermal stability of SFCCN and SFCCNO. As shown in Table 1,
(5 wt% to 30 wt%) are shown in Fig. S10 in ESI.† Photolumi-
the decomposition temperatures (T
54 and 491 1C for SFCCN and SFCCNO, respectively, which
indicate that both materials have good thermal stability. More-
d
, at 5% weight-loss) are
nescence quantum yields (PLQYs) of SFCCNO in the DPEPO
host matrix under nitrogen atmosphere were measured. As the
interaction between SFCCNO molecules is strictly suppressed
by the low doping ratio, 5 wt% SFCCNO-doped film exhibits a
low PLQY of 56% due to the low radiative local excited states.
With an increase in the doping ratio, more effective inter-
molecular TSCT transition becomes the critical radiative decay
5
over, they have relatively high glass transition temperature (T
of 264 and 212 1C, respectively (Fig. S7 and S8, ESI†).
g
)
Photophysical properties
The photophysical properties of SFCCN and SFCCNO were channel and a PLQY of 81% was observed for 30 wt% SFCCNO
ꢀ5
recorded at room temperature in toluene solution (10 M). doped film. More importantly, the SFCCNO neat film still
Phosphorescence spectra were measured at a low temperature exhibits a comparable PLQY of 71%, which indicates that
using the same solvent. SFCCN and SFCCNO show very similar intermolecular TSCT transition would significantly suppress
Scheme 2 Synthetic routes to target molecules SFCCN & SFCCNO.
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Fig. 1 The fluorescence spectra of SFCCN and SFCCNO (a) in toluene solution and (b) as a neat film; (c and d) UV-Vis absorptions (300 K) in CH
fluorescence spectra (77 and 300 K) and phosphorescence spectra (77 K) of SFCCN and SFCCNO in toluene.
2 2
Cl ,
the concentration quenching effect. We further measured can be seen that the delay times of 30 wt% doped SFCCN and
UV-Vis absorption (300 K) in CH Cl , fluorescence spectra 30 wt% doped SFCCNO were 0.3 ms and 5.8 ms, respectively.
2
2
(77 and 300 K) and phosphorescence spectra (77 K) in toluene SFCCNO showed nearly 20 times delay effect compared to the
for SFCCN and SFCCNO, respectively, as shown in Fig. 1c and d. SFCCN. Fig. S11 (ESI†) shows the transient PL decay spectra
DEST of SFCCN (0.23 eV) and SFCCNO (0.24 eV) were obtained of SFCCNO neat film and doped SFCCNO at a lower concentration.
accordingly and their physical properties are summarized in The SFCCNO neat film exhibits an obvious delay time of 2.1 ms,
Table 1. Besides, Fig. 2 shows the transient PL decay spectra of which is much longer than the 5% doped SFCCNO (0.02 ms). It is
SFCCN (30 wt%) and SFCCNO (30 wt%) in the film state with then confirmed that more obvious TADF properties can be obtained
two decay processes in nanosecond and microsecond scales. It under increased doping ratio.
Fig. 2 Transient photoluminescence spectra of DPEPO: SFCCN (30 wt%) and DPEPO: SFCCNO (30 wt%) in film state.
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Electrochemical properties
(5 nm)/TmPyPB (40 nm)/Liq (2 nm)/Al (120 nm) (Fig. 4a). The
molecular structures of other materials applied in this device
are shown in Fig. 4b. Here, indium tin oxide (ITO) and Al acted
From cyclic voltammetry (CV) tests along with the optical
bandgaps calculated from the UV-vis spectra, the HOMO/LUMO
energy levels were estimated to be ꢀ5.15/ꢀ2.09 eV and ꢀ5.11/
0
0
as the anode and cathode, respectively. Dipyrazino[2,3-f:2 ,3 -h]
quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) and 8-hydroxy-
quinolinolatolithium (Liq) were the hole- and electron-injecting
layers. Di[4-(N,N-ditolyl-amino)-phenyl] cyclohexane (TAPC) and
tris(4-(9H-carbazol-9-yl) phenyl) amine (TCTA) were employed as
the hole transport layer with favorable hole mobility. 1,3-Bis(N-
carbazolyl)benzene (mCP) was used as the electron-blocking layer
for efficient exciton utilization. DPEPO was applied as the host due
to its high triplet energy. 1,3,5-Tri[(3-pyridyl)-phen-3-yl]benzene
ꢀ
2.04 eV for SFCCN and SFCCNO, respectively (Table 1 and
Fig. S12, ESI†). These HOMO values indicate that the introduction
of oxygen can merely slightly enhance the donor strength. Thus,
the electron-donating ability of the two donors should be different.
Besides, the stronger electron-donating strength of 10-phenyl-
10H-phenoxazine in SFCCNO might not be the real cause for the
unexpected fluorescence red-shift in the film state.
(
TmPyPB) was the electron-transporting layer. 5 nm DPEPO acted
Theoretical calculations
as the exciton-blocking layer to confine the excitons, which helped
control the charge recombination. The device performances of two
TADF emitters at low concentration (5 wt%) to high concentration
We found the answer through DFT calculations (finished at
PBE0/def2-SVP and TD-PBE0/def2SVP level with Grimme’s D3BJ
empirical dispersion correction). Only SFCCNO can form a dimer
by the stacking of the donor moiety from one and the acceptor
moiety from the other molecule. It is mainly because oxygen
introduction can planarize the D1 group, which facilitates face-to-
face D/A spatial interaction and forms TSCT. The hole is distributed
on the donor group and the electron is distributed on the acceptor
(30 wt%) are all shown in Table S4 (ESI†). As expected, at the
concentration of 5 wt%, both devices exhibited the same emission
at 460 nm, wherein the dimer cannot be formed at such a low
concentration. However, in 30 wt% doped devices, the EL emission
peaks at 516 nm for SFCCNO (with 12.9% EQE) and 472 nm for
SFCCN (with 10.0% EQE) are obtained, which confirmed what we
speculated. Also, Fig. S14 (ESI†) exhibits progressive red-shifts of
EL spectra under concentrations varying from 3 to 30 wt%.
Then, we finally fabricated non-doped devices by only chan-
ging the emissive layer. The EQE of the non-doped device based
on SFCCN dramatically decreased to 3.8% because of serious
concentration quenching effect. Remarkably, the non-doped
device based on SFCCNO had an obviously higher efficiency,
which exhibited a maximum EQE of 13.0% and maximum
1 1
group for both the adiabatic S and T states, as shown in Fig. 3. The
small hole-electron centroid distance and the large hole-electron
spatial separation lead to large red shift of the emission wavelength
(Table S1, ESI†). Besides, more DFT calculations and the frontier
orbital levels of SFCCN and SFCCNO in their ground state are all
shown in Tables S2 and S3 and Fig. S13 (ESI†), respectively.
Electroluminescence properties
ꢀ1
To evaluate the TADF materials and further confirm the con- current efficiency of 41.0 cd A (Table 2). The device perfor-
jecture, we fabricated a doped OLED device with the following mance comparison between the doped and non-doped OLEDs
structure: ITO/HAT-CN (10 nm)/TAPC (40 nm)/TCTA (10 nm)/ is shown in Fig. 4c and d. In the aggregation state, SFCCNO
mCP (10 nm)/DPEPO: SFCCN/SFCCNO (X wt%, 20 nm)/DPEPO dimeric CT emission is formed with two functional moieties
Fig. 3 Calculated hole and electron distribution of the adiabatic S1 and T1 states of SFCCN, SFCCNO and SFCCNO dimer.
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Fig. 4 (a) Energy level diagrams of devices; (b) chemical structures of other materials applied in the OLED devices; (c) EQE–luminance characteristics of
the doped and non-doped devices; (d) PE–current density characteristics of the doped and non-doped devices.
Table 2 Electroluminescence performance of the doped and non-doped to exciplex emission. The difference is that the dimeric emission
devices
in our case is based on the same molecules, whereas exciplex
a
b
c
needs at least two kinds of materials. The comparison between
SFCCNO and representative traditional exciplexes are displayed
in Table 3. It can be seen that the PLQY of SFCCNO dimer (71%)
Doping
V on Peak CE
ꢀ1
d
b
ratio (%) (V) (nm) (cd A
)
EQE (%)
CIE (X, Y)
SFCCN
30
00
SFCCNO 30
00
3.8 472
3.8 472
3.7 516
3.6 520
15.1
8.0
36.5
41.0
10.0/7.3/3.1
3.8/3.4/2.0
12.9/12.5/8.8 (0.29,0.48)
13.0/12.9/10.4 (0.32, 0.55)
(0.16,0.23)
1
(0.20, 0.26) is the highest among all the D/A exciplexes, and the SFCCNO
based device also has one of the highest EQE.
1
a
ꢀ2
b
Driving voltage at 0.2 mA cm
.
Measured at a current density
d
ꢀ2
c
at 5 mA cm
1
.
Maximum current efficiency. Maximum EQE, at
ꢀ2
ꢀ2
00 cd m and at 1000 cd m
.
Conclusions
In summary, we designed and synthesized two novel TADF
approaching each other. Furthermore, the device had low molecules, SFCCN and SFCCNO, based on a new configuration
efficiency roll-off in which the EQE merely drops from 12.9% called D1–s–D2–p–A. Because two materials have identical
ꢀ
2
to 10.4% for device luminance increasing from 100 cd m to ‘‘D2–p–A’’ TBCT segments, they exhibited nearly the same
ꢀ
2
1
000 cd m . The emission is not from the TADF molecule itself photoluminescence in solution, but an abnormal red shift in
but from the intermolecular TSCT species, which is very similar the fluorescence of SFCCNO in the film state was observed. The
oxygen bridge could increase the electron-donating ability in D1
moiety of SFCCNO, but it is not the main reason for this phenom-
enon. The planar conformation of 10-phenyl-10H-phenoxazine
Table 3 Summary of related TADF OLEDs based on exciplex emitters
could form face-to-face interaction with the planar triazine acceptor
in different molecules of SFCCNO, which is the main reason for the
Emitters
lPL (nm) ffilm (%) VON (V) EQEmax (%) Ref.
SFCCNO
520
476
/
472
554
71
51
41
/
/
20
/
3.6
2.5
2.2
/
2.0
/
2.6
4.0
/
13.0
13.0
9.5
8
7.8
2
2.61
3.3
0.93
This work red shift. This dimeric inter-TSCT emission from D1 to A in the
CDBP:POT2T
CPF:POT2T
mCP:POT2T
TCTA/3P-T2T
m-MTDATA: PBD 540
TCTA: Bphen
DPNC: Bphen
31
aggregation state did not exist in SFCCN film. In the non-doped
32
33
devices, SFCCNO as an emitter exhibited an EQE of 12.9% at
ꢀ
2
ꢀ2
34
35
36
37
38
100 cd m and an EQE of 10.4% at 1000 cd m , which is much
higher than that of SFCCN. This kind of dimeric TADF emission,
which is much similar to the two-component exciplex emission,
proves a new emission behavior in aggregation state.
464
580
/
36
TCTA: B3PYMPM 490
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J. Mater. Chem. C, 2021, 9, 4792–4798 | 4797

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Conflicts of interest
17 W.-C. Chen, B. Huang, S.-F. Ni, Y. Xiong, A. L. Rogach,
Y. Wan, D. Shen, Y. Yuan, J.-X. Chen, M.-F. Lo, C. Cao,
Z.-L. Zhu, Y. Wang, P. Wang, L.-S. Liao and C.-S. Lee, Adv.
Funct. Mater., 2019, 29, 1903112.
There are no conflicts to declare.
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1
2
8 Q.-S. Tian, S. Yuan, W.-S. Shen, Y.-L. Zhang, X.-Q. Wang,
F.-C. Kong and L.-S. Liao, Adv. Opt. Mater., 2020, 8, 2000556.
9 C. Zhang, R.-H. Liu, D. Zhang and L. Duan, Adv. Funct.
Mater., 2020, 30, 1907156.
0 D.-D. Song, Y. Yu, L. Yue, D.-K. Zhong, Y.-D. Zhang,
X.-L. Yang, Y.-H. Sun, G.-J. Zhou and Z.-X. Wu, J. Mater.
Chem. C, 2019, 7, 11953–11963.
Acknowledgements
The authors thank the financial supports from the National Natural
Science Foundation of China (No. 61875144, No. 51873160), and
the Natural Science Foundation of Jiangsu Province of China
(BK20181442). This project was also funded by the Collaborative
Innovation Center of Suzhou Nano Science & Technology, the
Priority Academic Program Development of Jiangsu Higher
Education Institutions (PAPD), and the 111 Project of The State
Administration of Foreign Experts Affairs of China.
2
1 D.-K. Zhong, Y. Yu, D.-D. Song, X.-L. Yang, Y.-D. Zhang,
X. Chen, G.-J. Zhou and Z.-X. Wu, ACS Appl. Mater. Inter-
faces, 2019, 11, 27112–27124.
2
2 F. Chen, J. Hu, X. Wang, S. Shao, L. Wang, X. Jing and
F. Wang, Sci. China: Chem., 2020, 63, 1112–1120.
3 J.-T. Ye, L. Wang, H.-Q. Wang, X.-M. Pan, H.-M. Xie and
Y.-Q. Qiu, J. Phys. Chem. C, 2018, 122, 18850–18859.
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J. Mater. Chem. C, 2021, 9, 4792–4798
This journal is © The Royal Society of Chemistry 2021