Molecular Engineering of Isomeric Benzofurocarbazole Donors for Photophysical Management of Thermally Activated Delayed Fluorescence Emitters

Article abstract of DOI:10.1002/chem.201905473

Benzofurocarbazole moieties are commonly used donor structures in the design of thermally activated delayed fluorescence (TADF) emitters. However, only 5 H-benzofuro[3,2-c]carbazole (34BFCz) has been reported and, to the best of our knowledge, no other be

Full text of DOI:10.1002/chem.201905473

A Journal of
Accepted Article
Title: Molecular engineering of isomeric benzofurocarbazole donor
for photophysical management of thermally activated delayed
fluorescent emitters
Authors: Mina Jung, Kyung Hyung Lee, and Jun Yeob Lee
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201905473
Link to VoR: http://dx.doi.org/10.1002/chem.201905473
Supported by

10.1002/chem.201905473
Chemistry - A European Journal
Molecular engineering of isomeric benzofurocarbazole donor for photophysical
management of thermally activated delayed fluorescent emitters
Mina Jung, Kyung Hyung Lee, Jun Yeob Lee*
School of Chemical Engineering, Sungkyunkwan University
2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi, 16419, Republic of Korea
E-mail: leej17@skku.edu
Abstract
The benzofurocarbazole moieties are well-known donor moiety for the design of the
thermally activated delayed fluorescence (TADF) emitters. However, only 5H-benzofuro[3,2-
c]carbazole (34BFCz) was reported and no other benzofurocarbazole derivatives were
covered in the literature. Herein, two benzofurocarbazole moieties, 12H-benzofuro[3,2-
a]carbazole (12BFCz) and 7H-benzofuro[2,3-b]carbazole (23BFCz) were synthesized to
investigate the effect of donor structure on photophysics and device parameters of TADF
emitters. Two benzofurocarbazole derived TADF emitters, 12-(2-(4,6-diphenyl-1,3,5-triazin-
2-yl)phenyl)-12H-benzofuro[3,2-a]carbazole (o12BFCzTrz) and 7-(2-(4,6-diphenyl-1,3,5-
triazin-2-yl)phenyl)-7H-benzofuro[2,3-b]carbazole (o23BFCzTrz), were compared with 5-(2-
(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (oBFCzTrz). The
benzofurocarbazole donor structure governed the TADF characteristics such as charge
transfer property and emission color. The 12BFCz donor was effective to blue-shift the
emission color and 34BFCz was useful to improve the EQE. The 12BFCz derived
o12BFCzTrz showed blue-shifted color coordinate of (0.159, 0.288) compared to (0.178,
0388) of o23BFCzTrz and (0.169, 0.341) of oBFCzTrz. The 34BFCz derived oBFCzTrz
exhibited EQE of 22.9% compared to 19.2% of o12BFCzTrz and 21.1% of o23BFCzTrz.
Keywords: organic light emitting diodes, thermally activated delayed fluorescence,
benzofurocarbazole, donor
1
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
Introduction
Organic light-emitting diodes (OLEDs) have been widely researched since the first practical
organic electroluminescence device developed by Tang and Van Slyke in 1987.1 One of the
major researches is the development of emitters represented by fluorescent2-4 and
phosphorescent emitters.5-7 Recently, the thermally activated delayed fluorescence (TADF)
emitters were developed as the third-generation emitting materials overcoming the drawbacks
of fluorescent and phosphorescent emitting materials.8-12 The TADF emitters can harvest
triplet excitons through efficient up-conversion process by reverse intersystem crossing
(RISC) from triplet excited state (T1) to the singlet excited state (S1).13-14 The TADF material
should have a sufficiently small energy gap between S1 and T1 (ΔES-T) for the RISC process
by introducing the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular
orbital (LUMO) separation.15-17
In the TADF emitters, electron donor and acceptor moieties are introduced and one of the
most common donor moieties is carbazole.18-22 Many carbazole derivatives have been studied
because of good electron donor character, easy chemical modification, and thermal
stability.23-26 TADF device performances using carbazole derived electron donor moiety are
shown in Table S1. Among the many carbazole derived donors, the benzofurocarbazole
moiety has been effective as the donors of the TADF materials by tempered the donor
character of the carbazole donor.27-30 The benzofurocarbazole donor was known as a stable
donor moiety enabling high efficiency and stable driving of the TADF emitters. However,
only one benzofurocarbazole donor, 5H-benzofuro[3,2-c]carbazole (34BFCz), was reported in
the literature31-33 although several benzofurocarbazole isomers are available for TADF
emitters. Therefore, the synthesis of benzofurocarbazole isomers and further study about the
application of them as the donors of the TADF emitters is needed for enhanced TADF devices
performances.
2
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
In this work, three isomeric benzofurocarbazole donors were synthesized to study the effect
of the donor design on the photophysical and device parameters of the TADF emitters. Three
benzofurocarbazole type donors, 12H-benzofuro[3,2-a]carbazole (12BFCz), 7H-
benzofuro[2,3-b]carbazole (23BFCz), 5H-benzofuro[3,2-c]carbazole (34BFCz), were used to
study the effect of donor structure on the TADF properties of the donor-acceptor type TADF
emitters. Two TADF emitters, 12-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-12H-
benzofuro[3,2a]carbazole (o12BFCzTrz), 7-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-7H-
benzofuro[2,3-b]carbazole (o23BFCzTrz) were newly synthesized and they were compared
with 5-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (oBFCzTrz)
reported in our previous work.29 It was described that the donor structure control in the
benzofurocarbazole donor governs the emission color and TADF characteristics of the TADF
emitters. Blue shift of the emission color was observed in the o12BFCzTrz and high external
quantum efficiency (EQE) was noticed in the oBFCzTrz.
Results and Discussion
Figure 1 shows the chemical structure of the benzofurocarbazole donors synthesized in this
work. To investigate the photophysical and device performances of the bezonfurocarbazole
donor design of TADF, 12BFCz, 23BFCz, and 34BFCz were synthesized as the donors. The
34BFCz was reported in our previous work,27 the 23BFCz has the carbon-carbon linkage at
the same position of 34BFCz but oxygen at 2 position of carbazole, and 12BFCz has the
oxygen at the same position of 23BFCz but carbon-carbon linkage at 1 position of carbazole.
The comparison of the three donors would reveal the effect of oxygen and carbon-carbon
linkage position on the donor character of the three donors.
3
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
Figure 1. Chemical structure of benzofurocarbazole donor molecules.
The o12BFCzTrz, o23BFCzTrz and oBFCzTrz consisted of a benzofurocarbazole electron
donor moiety and a 2,4-diphenyl-1,3,5-triazine electron acceptor moiety interconnected
through the ortho- position of a phenyl linker. The ortho- connection concept is well-known in
the design of the TADF emitters to strengthen the charge transfer (CT) character and to
decrease ΔES-T by the spatial separation of the HOMO and LUMO orbital distribution.
The synthetic scheme of 12BFCz, 23BFCz, o12BFCzTrz and o23BFCzTrz is shown in
Scheme 1. The starting materials, 1-bromo-2-nitrobenzene and dibenzo[b,d]furan-2-ylboronic
acid were coupled by the Suzuki coupling reaction, and then 12BFCz and 23BFCz were
synthesized by ring closing reactions. Then the synthesis of o12BFCzTrz and o23BFCzTrz
was carried out using a F functionalized 2,4,6-triphenyl-1,3,5-triazine intermediates and
benzofurocarbazole intermediates. The F unit of (2-fluorophenyl)-4,6-diphenyl-1,3,5-triazine
was substituted with a synthesized benzofurocarbazole moiety by the Cs2CO3 mediated
reaction. Synthetic procedures of 34BFCz and oBFCzTrz were described in our previous
work.
4
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
Scheme 1. Syntheses scheme of o12BFCzTrz and o23BFCzTrz (DW is distilled water).
To estimate the frontier molecular orbitals of 12BFCz, 23BFCz, and 34BFCz, electronic
calculation of optimized molecular structure was performed through Gaussian 16 software
based on the B3LYP 6-31G* basis set. Figure 2 shows the molecular orbital distribution of
benzofurocarbazole donors. The calculated HOMO/LUMO energy levels of 12BFCz, 23BFCz
and 34BFCz were -5.43/-0.92, -5.32/-0.92 and -5.30/-0.80 eV, respectively, indicating that the
23BFCz and 34BFCz are stronger donor than 12BFCz. The benzofurocarbazole donors with a
linkage through 3 position of carbazole showed shallow HOMO level because the 3 position
of carbazole is the HOMO rich position. The benzofuran unit of the benzofurocarbazole
affected the HOMO level by the electron sharing through the HOMO dominating 3 position
of carbazole.
5
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
Figure 2. The HOMO-LUMO orbital distribution of the benzofurocarbazole moieties. The
DFT calculation results using Gaussian 16 software based on the B3LYP 6-31G* basis set.
Overall material characteristics of o12BFCzTrz, o23BFCzTrz and oBFCzTrz were also
estimated by electronic calculation of the optimized molecular structure and orbital
distribution. Figure 3 shows the calculated optimized structure and the molecular orbital
distribution of o12BFCzTrz, o23BFCzTrz and oBFCzTrz. Gaussian 16 software based on the
B3LYP 6-31G* basis set was used for the calculation of the TADF molecules. The donor
moiety had little effect on the HOMO and LUMO distribution. In all materials, the HOMO
was dispersed over the benzofurocarbazole electron-donating group, and the LUMO was
dominantly dispersed in the diphenyltriazine electron acceptor moiety. The n-π* electron
interaction between triazine moiety and non-bonding electron of nitrogen in
benzofurocarbazole was also similar in all three TADF phenyl linker.34 The dihedral angles
between phenyl linker and diphenyltriazine moiety of three compounds were similarly in the
range of 35-38º. The calculated LUMO energy level was also similar in the three compounds.
On the other hand, the dihedral angles between benzofurocarbazole and phenyl linker of
o12BFCzTrz, o23BFCzTrz and oBFCzTrz were 77.7, 66.7, and 68.8º, respectively. In the
6
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
case of o12BFCzTrz, the donor was largely distorted due to the steric hindrance between the
phenyl molecules. The torsion angle between linker and benzofuran unit of
benzofurocarbazole oriented to the phenyl linker direction.
Figure 3. The calculated optimized structures of o12BFCzTrz, o23BFCzTrz and oBFCzTrz.
The calculated HOMO energy levels of o12BFCzTrz, o23BFCzTrz, and oBFCzTrz were -
5.27, -5.20, and -5.18 eV, respectively. The HOMO level of the TADF emitters was
dominated by the donor moiety because the HOMO was localized on the donor moiety
(Figure S1). The shallow HOMO level of the 23BFCz and 34BFCz donors with nitrogen at 3
position of dibenzofuran resulted in the shallow HOMO in the o23BFCzTrz and oBFCzTrz
emitters. All calculated data of the TADF emitters are presented in Table 1.
Table 1. The calculated data of the o12BFCzTrz, o23BFCzTrz and oBFCzTrz.
o12BFCzTrz
o23BFCzTrz
oBFCzTrz
7
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
LUMO[a]
- 1.84 eV
- 5.27 eV
- 3.38 eV
- 6.15 eV
- 1.84 eV
- 5.20 eV
- 3.41 eV
- 6.07 eV
- 1.86 eV
- 5.18 eV
- 3.40 eV
- 6.10 eV
HOMO[a]
LUMO[b]
HOMO[b]
[a] The calculation based on the B3LYP 6-31G* basis set.
[b] The measured values by cyclic voltammetry (CV).
The calculated HOMO and LUMO values were confirmed experimentally by cyclic
voltammetry (CV). The HOMO/LUMO levels of o12BFCzTrz, o23BFCzTrz and oBFCzTrz
were estimated to be -6.15/-3.38, -6.07/-3.41 and -6.10/-3.40 eV, respectively (Figure S2).
The trend of the HOMO/LUMO levels coincided with the calculation results.
The photophysical analysis of the TADF emitters was performed to correlate the donor
structure with the light absorption and emission behaviors. Figure S3 shows the ultraviolet-
visible (UV-Vis) absorption spectra of the TADF emitters. The UV/Vis absorption data
provided strong absorption bands below λ = 355 nm assigned to n-π* transition and π-π*
transition of the donor-acceptor skeletons, and broad absorption bands between 360 and 440
nm assigned to intramolecular CT absorption. The CT absorption of the o23BFCzTrz and
oBFCzTrz emitters was rather strong because of the strong donor strength of the 23BFCz and
34BFCz donors embedded in the two TADF materials, respectively. The UV-Vis absorption
edges of the o12BFCzTrz, o23BFCzTrz and oBFCzTrz emitters were 431, 443, and 448 nm,
respectively. The absorption edge of o12BFCzTrz was relatively positioned at short
wavelength by the weak CT character attributed to the weak 12BFCz donor.
Differences in the CT characteristics can also be seen in the PL spectra measured in solvents
with different polarities. (Figure S4). In the PL measurement of the emitters in toluene and
methylene chloride, the PL peak position was red-shifted by 40 nm in the o23BFCzTrz (476
to 516 nm) and oBFCzTRZ (477 to 518 nm), while it was bathochromically shifted only by
8
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
22.5 nm in the o12BFCzTrz (495.5 to 473 nm). This supports the weak CT character of the
o12BFCzTrz emitter.
(a)
(b)
(c)
1.0
0.8
0.6
0.4
0.2
0.0
300
400
400
400
500
600
600
600
700
700
700
Wavelength (nm)
1.0
0.8
0.6
0.4
0.2
0.0
300
500
Wavelength (nm)
1.0
0.8
0.6
0.4
0.2
0.0
300
500
Wavelength (nm)
Figure 4. The fluorescence and phosphorescence spectra of o12BFCzTrz (a), o23BFCzTrz
(b) and oBFCzTrz (c) at 77 K.
Table 2. Photophysical data of the o12BFCzTrz, o23BFCzTrz and oBFCzTrz.
9
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
o12BFCzTrz
2.77 eV
o23BFCzTrz
2.66 eV
oBFCzTrz
2.70 eV
Band gap[a]
Singlet energy[b]
Triplet energy[c]
ΔES-T
3.092 eV
3.077 eV
0.015 eV
3.000 eV
2.958 eV
0.042 eV
2.994 eV
2.992 eV
0.002 eV
[a]Measured by the cyclic voltammetry. [b]Singlet energy was calculated from the onset
wavelength of fluorescence emission. [c]Triplet energy was calculated from the onset
wavelength of phosphorescence emission.
The photoluminescence (PL) emission spectra of the o12BFCzTrz, o23BFCzTrz and
oBFCzTrz emitters collected from THF solution (1.0 x 10-5 M) at low temperature (77 K) are
in Figure 4. ΔES-T of TADF molecules were estimated from the low-temperature fluorescence
and phosphorescence data.35 The measured singlet/triplet energy of o12BFCzTrz,
o23BFCzTrz and oBFCzTrz were 3.09/3.08, 3.00/2.96, and 2.99/2.99 eV, respectively (Table
2). In the case of singlet energy, o12BFCzTrz exhibited high singlet energy due to weak CT
character relative to o23BFCzTrz and oBFCzTrz as can be estimated from the weak donor
character of 12BFCz. The triplet energy was also high in the o12BFCzTrz by the large
distortion of the donor from the phenyl linker which hinders the extension of the degree of
conjugation. All three TADF molecules showed CT emission characters in the fluorescence
spectra. In the case of phosphorescence, the o12BFCzTrz showed combined emission from
local and CT triplet excited states by the weak CT character, but the o23BFCzTrz and
oBFCzTrz exhibited CT dominant triplet emission by the strong CT character.
Table 3. Photophysical properties of o12BFCzTrz, o23BFCzTrz and oBFCzTrz
krS
(107
s-
kRICS
(105
s-
S
kp
(107 (105
s-1) s-1)
kd
knr
kISC
(107
s-1)[a]
PLQY ꞇprompt ꞇdelayed
(%) (ns) (us)
ΦF
ΦTADF
(107
s-1)[a]
1 [a]
1 [a]
)
)
10
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
o12BFCzTrz
o23BFCzTrz
oBFCzTrz
82.7
85.7
88.7
35.2
24.8
32.9
4.09
4.22
3.06
2.84 2.44 0.27 0.56
4.03 2.37 0.47 0.38
3.04 3.27 0.50 0.39
2.08 0.435 0.318 2.76
3.12 0.542 0.364 2.61
2.62 0.548 0.082 3.37
100
10-1
10-2
10-3
(a)
50
100
150
200
250
300
Time (ns)
100
10-1
10-2
10-3
10-4
10-5
(b)
10
20
30
40
50
Time (s)
Figure 5. Transient PL results showing prompt component (a) and delayed fluorescence
component (b) of o12BFCzTrz, o23BFCzTrz and oBFCzTrz.
Figure 5 represents transient PL decays of o12BFCzTrz, o23BFCzTrz and oBFCzTrz. The
lifetime of prompt/delayed component of o12BFCzTrz, o23BFCzTrz and oBFCzTrz was
35.21 ns/4.09μs 24.8 ns/4.22 μs, and 32.9 ns/ 3.06 μs, respectively. The RISC rate constants
(kRISC) of o12BFCzTrz, o23BFCzTrz and oBFCzTrz by calculation from the transient PL
decay were 2.61, 2.76, and 3.37  105, respectively.36 The oBFCzTrz showed a fast RISC
process due to the small ΔES-T. The PL quantum yields (PLQYs) of o12BFCzTrz,
o23BFCzTrz and oBFCzTrz measured under a nitrogen condition were 82.7, 85.2 and 88.7%,
respectively. All material analysis data are summarized in Table 3.
11
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
The photophysical study of the o12BFCzTrz, o23BFCzTrz and oBFCzTrz emitters
proposed that they would function as TADF emitters. Therefore, OLED devices doped with
o12BFCzTrz, o23BFCzTrz and oBFCzTrz in the emitting layer were fabricated using bis[2-
(diphenylphosphino)phenyl] ether oxide (DPEPO) host. Device structure is explained in the
Experimental section and Figure S5. The concentration of the TADF dopant was optimized to
20 wt%, and data at other concentrations can be found in supporting information (Figure S6,
Table S2). The device behavior of the oBFCzTrz, o23BFCzTrz and oBFCzTrz is presented in
Figure 6. The current density and luminance to driving voltage curves of the devices are
shown in Figure 6 (a). The EQE values of TADF devices are plotted in Figure 6 (b). In the
case of maximum EQE, o12BFCzTrz, o23BFCzTrz, and oBFCzTrz showed EQEs of 19.2,
21.1 and 22.9%, respectively. The relative order of the EQE was in agreement with that of the
PLQY, suggesting that the PLQY is the critical factor for the EQE. The electroluminescence
(EL) spectra in Figure 6 (c) showed that the EL emission is blue-shifted in the o12BFCzTrz as
can be projected from the PL spectra. The o23BFCzTrz and oBFCzTrz devices with strong
CT properties, showed CIE color coordinates of (0.18, 0.39) and (0.17, 0.34), respectively,
whereas that of the o12BFCzTrz was (0.16, 0.29). All device performances are summarized in
Table 4.
12
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
100
80
60
40
20
0
10000
1000
100
10
(a)
(b)
(c)
1
0.1
1
2
3
4
5
6
7
8
9
10
Voltage (V)
25
20
15
10
5
o12BFCzTrz
o23BFCzTrz
oBFCzTrz
1
10
100
1000
10000
Luminance (cd/m2)
1.0
0.8
0.6
0.4
0.2
0.0
400
500
600
700
Wavelength (nm)
Figure 6. The current density-voltage-luminance (a), EQE-luminance (b) and EL spectra (c)
of o12BFCzTrz, o23BFCzTrz, and oBFCzTrz devices.
Table 4. The device performances of o12BFCzTrz, o23BFCzTrz and oBFCzTrz.
o12BFCzTrz
19.2
o23BFCzTrz
21.1
oBFCzTrz
22.9
EQEmax (%)
Power efficiencymax
(lm W-1)
30.3
41.2
42.4
Current efficiencymax
(cd A-1)
37.2
(0.159, 0.288)
478
49.6
(0.178, 0.388)
484
49.5
(0.169, 0.341)
488
CIE (x, y)
ELmax (nm)
13
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
Conclusion
In conclusion, the synthesis of benzofurocarbazole electron donor moieties, 12BFCz,
23BFCz, and 34BFCz, and application of them as the donors of the TADF emitters revealed
that the 12BFCz donor was effective to blue-shift the emission color and 34BFCz was useful
to improve the EQE. The 12BFCz derived 12BFCzTrz showed blue-shifted color coordinate
of (0.159, 0.288) compared to (0.178, 0388) of o23BFCzTrz and (0.169, 0.341) of oBFCzTrz.
The 34BFCz derived oBFCzTrz exhibited EQE of 22.9% compared to 19.2% of o12BFCzTrz
and 21.1% of o23BFCzTrz. Therefore, the molecular management of the benzofurocarbazole
donor could selectively control the device performances of the TADF OLEDs.
Corresponding author
Correspondence to Prof. Jun Yeob Lee (leej17@skku.edu)
References
[1] C. W. Tang, S. A. VanSlyke, Appl. Phys. Lett. 1987, 51, 913.
[2] J. Shia, C. W. Tang, Appl. Phys. Lett. 2002, 80, 3201.
[3] Y. Sun, L. Duan, D. Zhang, J. Qiao, G. Dong, L. Wang, Y. Qiu, Adv. Funct. Mater. 2011,
21, 1881–1886.
[4] M. Jung, J. Lee, H. Jung, S. Kang, A. Wakamiya, J. Park, Dyes. Pigm. 2018, 158, 42-49.
[5] M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M. E. Thompson, S. R.
Forrest, Nature 1998, 395, 151–154.
[6] C. Adachi, M. A. Baldo, M. E. Thompson, S. R. Forrest, J. Appl. Phys. 2001, 90, 10.
[7] Y. Seino, H. Sasabe, Y. –J. Pu, J. Kido, Adv.Mater. 2014, 26, 1612–1616.
14
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
[8] K. Sato, K. Yoshimura, T. Kai, A. Kawada, H. Miyazaki, C. Adachi, Appl. Phys. Lett.
2011, 98, 083302.
[9] J. Lee, K. Shizu, H. Tanaka, H. Nomura, T. Yasuda, C. Adachi, J. Mater. Chem. C 2013, 1,
4599–4604.
[10] Y. J. Cho, S. K. Jeon, B. D. Chin, E. Yu, J. Y. Lee, Angew. Chem. Int. Ed. 2015, 54,
5201 –5204.
[11] Y. Liu, G. Xie, K. Wu, Z. Luo, T. Zhou, X. Zeng, J. Yu, S. Gong, C. Yang, J. Mater.
Chem. C 2016, 4, 4402-4407.
[12] M. Jung, K. H. Lee, W. P. Hong, J. Y. Lee, J. Mater. Chem. C 2019, 7, 7760-7767.
[13] A. Jablonski, Nature 1933, 131, 839–840.
[14] G. N. Lewis, D. Lipkin, T. T. Magel, J. Am. Chem. Soc. 1941, 63, 3005–3018.
[15] H. Kaji, H. Suzuki, T. Fukushima, K. Shizu, K. Suzuki, S. Kubo, T. Komino, H. Oiwa, F.
Suzuki, A. Wakamiya, Y. Murata, C. Adachi, Nature Commun. 2015, 6, 8476.
[16] J. Lee, K. Shizu, H. Tanaka, H. Nakanotani, T. Yasuda, H. Kaji, C. Adachi, J. Mater.
Chem. C 2015, 3, 2175-2181.
[17] L. ‐S. Cui, H. Nomura, Y. Geng, J. U. Kim, H. Nakanotani, C. Adachi, Angew. Chem.
Int. Ed. 2017, 56, 1571-1575.
[18] T. Serevicius, T. Nakagawa, M. –C. Kuo, S. –H. Cheng, K. –T. Wong, C. –H. Chang, R.
C. Kwong, S. Xiae, C. Adachi, Phys. Chem. Chem. Phys. 2013, 15, 15850-15855.
[19] D. Zhang, X. Cao, Q. Wu, M. Zhang, N. Sun, X. Zhang, Y. Tao, J. Mater. Chem. C 2018,
6, 3675-3682.
[20] M. Kim, S. K. Jeon, S. –H. Hwang, S. Lee, E. Yu, J. Y. Lee, Chem. Commun. 2016, 52,
339—342.
[21] Y. Im, S. H. Han, J. Y. Lee, J. Mater. Chem. C 2018, 6, 5012-5017.
[22] H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature 2012, 492, 234-238.
[23] J. –R. Cha, C. W. Lee, J. Y. Lee, M. –S. Gong, Dyes. Pigm. 2016, 134, 562-568
15
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
[24] D. Karthik, S. Y. Lee, D. H. Ahn, H. Lee, J. Y. Lee, J. H. Kwon, J. H. Park, Org.
Electron. 2019, 74, 282–289.
[25] P. Rajamalli, N. Senthilkumar, P. Gandeepan, C. –C. R. -Wu, H. –W. Lin, C –H. Cheng,
ACS Appl. Mater. Interfaces 2016, 8, 27026−27034.
[26] Q. Zhang, S. Sun, W. J. Chung, S. J. Yoon, Y. Wang, R. Guo, S. Ye, J. Y. Lee, L. Wang,
J. Mater. Chem. C 2019, 7, 12248-12255.
[27] D. R. Lee, S. –H, Hwang, S. K. Jeon, C. W. Lee, J. Y. Lee, Chem. Commun. 2015, 51,
8105-8107.
[28] C. Bian, Q. Wang, Q. Ran, X. –Y. Liu, J. Fan, L. -S. Liao, Org. Electron. 2018, 52, 138–
145.
[29] D. R. Lee, J. M. Choi, C. W. Lee, J. Y. Lee, ACS Appl. Mater. Interfaces 2016, 8,
23190−23196.
[30] Q. Zhang, S. Xiang, Z. Huang, S. Sun, S. Ye, X. Lv, W. Liu, R. Guo, L. Wang, Dyes.
Pigm. 2018, 155, 51–58.
[31] M. –S. Gong, J. –R. Cha, C. W. Lee, Org. Electron. 2017, 42, 66-74.
[32] C. Bian, Q. Wang, X. –Y. Liu, J. Fan, L. –S. Liao, Org. Electron. 2017, 46, 105-114.
[33] H. L. Lee, K. H. Lee, J. Y. Lee, W. P. Hong, J. Mater. Chem. C 2019, 7, 6465—6474.
[34] X.-K. Chen, B. W. Bakr, M. Auffray, Y. Tsuchiya, C. D. Sherrill, C. Adachi, J. –L.
Bredas, J. Phys. Chem. Lett. 2019, 10, 3260−3268.
[35] R. S. Nobuyasu, Z. Ren, G. C. Griffiths, A. S. Batsanov, P. Data, S. Yan, A. P.
Monkman, M. R. Bryce, F. B. Dias, Adv. Optical Mater. 2016, 4, 597–607.
[36] H. Noda, H. Nakanotani, C. Adachi, Sci. Adv. 2018, 4, eaao6910.
16
This article is protected by copyright. All rights reserved.

10.1002/chem.201905473
Chemistry - A European Journal
17
This article is protected by copyright. All rights reserved.