Thermally activated delayed fluorescence enantiomers for solution-processed circularly polarized electroluminescence

Article abstract of DOI:10.1039/c9tc04941j

Circularly polarized organic light-emitting diodes (CP-OLEDs) with thermally activated delayed fluorescence (TADF) characteristics are receiving increasing interest, as they have shown improving efficiencies of circularly polarized electroluminescence (CPEL). Here, we developed a series of TADF enantiomers based on chiral binaphthalene, an acceptor (A) of cyanopyridine, and donors (D) of carbazoles in a chiral-A-D architecture. Good solubility, high luminescence yields, and excellent chiral stability with a photoluminescence dissymmetry factor (g_PL) up to 5.8 × 10^-4 were achieved. Efficient CP-OLEDs using these chiral TADF molecules as dopants were successfully fabricated, exhibiting high external quantum efficiencies (EQEs) up to 12.4% and opposite CPEL signals with g_EL of 6 × 10^-4/-8.6 × 10^-4 in vacuum-deposited devices. More impressively, the solution-processed TADF CP-OLEDs result in much larger g_EL values (3.5 × 10^-3/-3.9 × 10^-3) with EQEs up to 10.6%. This discovery is encouraging and instructive, which could stimulate the development of high-performance CP-OLEDs using chiral TADF molecules through solution-processing approaches.

Full text of DOI:10.1039/c9tc04941j

Volume 7 Number 46 14 December 2019 Pages 14399–14754
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
rsc.li/materials-c
ISSN 2050-7526
PAPER
Runfeng Chen, Guohua Xie, Wei Huang et al.
Thermally activated delayed fluorescence enantiomers
for solution-processed circularly polarized
electroluminescence

Journal of
Materials Chemistry C
View Article Online
View Journal | View Issue
PAPER
Thermally activated delayed fluorescence
enantiomers for solution-processed circularly
polarized electroluminescence†
Cite this: J. Mater. Chem. C, 2019,
7, 14511
Sibing Sun,a Jun Wang,a Lingfeng Chen,a Runfeng Chen, *a Jibiao Jin,a
a
a
Cailin Chen,a Shufen Chen,
Guohua Xie, *b Chao Zhenga and Wei Huang
*
Circularly polarized organic light-emitting diodes (CP-OLEDs) with thermally activated delayed fluorescence
(TADF) characteristics are receiving increasing interest, as they have shown improving efficiencies of
circularly polarized electroluminescence (CPEL). Here, we developed a series of TADF enantiomers
based on chiral binaphthalene, an acceptor (A) of cyanopyridine, and donors (D) of carbazoles in a
chiral–A–D architecture. Good solubility, high luminescence yields, and excellent chiral stability with a
photoluminescence dissymmetry factor (gPL) up to 5.8 ꢀ 10ꢁ4 were achieved. Efficient CP-OLEDs using
these chiral TADF molecules as dopants were successfully fabricated, exhibiting high external quantum
efficiencies (EQEs) up to 12.4% and opposite CPEL signals with gEL of 6 ꢀ 10ꢁ4/ꢁ8.6 ꢀ 10ꢁ4 in vacuum-
deposited devices. More impressively, the solution-processed TADF CP-OLEDs result in much larger gEL
values (3.5 ꢀ 10ꢁ3/ꢁ3.9 ꢀ 10ꢁ3) with EQEs up to 10.6%. This discovery is encouraging and instructive,
which could stimulate the development of high-performance CP-OLEDs using chiral TADF molecules
through solution-processing approaches.
Received 7th September 2019,
Accepted 2nd October 2019
DOI: 10.1039/c9tc04941j
rsc.li/materials-c
design strategies, typically including using light-emitting
polymers modified with chiral sidechains14 or dopants10 and
Introduction
Circularly polarized (CP) luminescence, traditionally obtained developing novel chiral emissive molecules or complexes.11–13
from unpolarized light through a filter, has attracted consider- Nevertheless, although CP-OLEDs with strong CPEL and high
able attention due to the wide potential applications in optical gEL up to 1.1314 have been fabricated, they are mainly based on
data storage, optical recognition sensors, quantum computing, chiral transition metal complexes or polymers, and the device
optical communication, and 3D displays.1–3 It becomes even efficiencies are generally low.15,16
more attractive when CP light can be directly generated in
To improve the efficiencies of OLEDs, thermally activated
organic light emitting diodes (OLEDs) using chiral materials.4,5 delayed fluorescence (TADF) has been introduced to harvest both
Pioneering work can be dated back to 1997, when Meijer and singlet and triplet excitons for electroluminance with theoretically
co-workers firstly observed circularly polarized electrolumines- 100% internal quantum efficiency by the up-conversion of excitons
cence (CPEL) from a chiral conjugated polymer.6 Since then, from the lowest triplet (T1) to singlet (S1) excited states through
significant efforts have been devoted to developing chiral efficient reverse intersystem crossing (RISC) under small singlet–
illuminants to prepare efficient CP-OLEDs with strong CPEL.7–9 triplet splitting energy (DEST).17–21 Pieters et al. constructed the
The CPEL signal, which is characterized by the electroluminescence first CP TADF molecule using a chiral binaphthol moiety, a
dissymmetry factor (gEL), can be enhanced by many molecular donor of carbazole and an acceptor of dicyanobenzene; an
external quantum efficiency (EQE) of 9.1% and a CP photo-
luminance dissymmetry factor (gPL) of 1.3 ꢀ 10ꢁ3 were observed
a Key Laboratory for Organic Electronics and Information Displays & Jiangsu Key
in solution, but no CPEL was obtained.22 With the same
Laboratory for Biosensors, Institute of Advanced Materials (IAM), Jiangsu National
building blocks of the chiral perturbation group, and donor
and acceptor units, Tang et al. improved the EQE to 9.3% and
gEL up to +0.026/ꢁ0.021 with the aid of asymmetric molecular
structure and aggregation-induced emission behaviour.23 Recently,
Chen et al. achieved both high EQE up to 19.8% and an intense
CPEL signal of 2.3 ꢀ 10ꢁ3 by introducing chiral 1,2-diamino-
cyclohexane into the achiral TADF unit.24 Zheng et al. further
Synergistic Innovation Center for Advanced Materials (SICAM), Nanjing University
of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210023, China.
E-mail: iamrfchen@njupt.edu.cn, iamwhuang@njtech.edu.cn
b Sauvage Center for Molecular Sciences, Hubei Key Lab on Organic and Polymeric
Optoelectronic Materials, Department of Chemistry, Wuhan University, Wuhan,
430072, China. E-mail: guohua.xie@whu.edu.cn
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9tc04941j
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C, 2019, 7, 14511--14516 | 14511

View Article Online
Paper
Journal of Materials Chemistry C
improved the EQE to 32.6% using chiral octahydro-binaphthol- mirror-image circular dichroism (CD) and circularly polarized
based TADF molecules.25 However, all the TADF CP-OLEDs luminescence (CPL) activities (gPL up to 5.8 ꢀ 10ꢁ4). The
reported so far were fabricated by vacuum deposition technology. CP-OLEDs based on these facilely prepared TADF enantiomers
This is due to the relatively high requirements in designing TADF demonstrate not only high EQEs up to 12.4% in vacuum-
materials with both high photoluminescence quantum yields deposited TADF OLEDs and 10.6% in solution-processed
(PLQYs) and efficient RISC,26 and the solubility and chirality devices, but also decent CPEL signals with gEL of 6 ꢀ 10ꢁ4
/
issues would make it even more challenging to develop chiral ꢁ8.6 ꢀ 10ꢁ4 in vacuum-deposited devices and higher gEL of
TADF molecules for solution processing.27 But it is worth noting 3.5 ꢀ 10ꢁ3/ꢁ3.9 ꢀ 10ꢁ3 in solution-processed TADF devices.
that solution-processed OLEDs have been widely considered to The amplified chirality and high EQEs of the solution-
be fundamentally important for low-cost and large-area displays processed TADF OLEDs illustrate large progress of CP-OLEDs,
and lighting.28–30
which should initiate the investigation of highly soluble CP
Here, we developed a series of solution-processible TADF TADF molecules in chiral–A–D architectures for solution-processed
enantiomers with strong CPEL based on chiral binaphthol, chiral devices.
cyanopyridine, and carbazoles for CP-OLEDs. The binaphthol unit
has good solubility, strong conjugation effects, high stability upon
electro/photo-excitation against racemization, and an excellent
Results and discussion
Synthesis and characterization
ability to induce CP emission through chiral perturbation.31,32
Cyanopyridine acts as an acceptor (A) unit of the TADF materials
to modulate the degree of intra-molecular charge transfer (ICT)
The enantiomerically pure TADF emitters S-CPDCz, R-CPDCz,
S-CPDCB and R-CPDCB were conveniently prepared on the gram
for TADF emission and, more importantly, to acquire high
solution processability of the resulting materials.33 Carbazole
scale by an optimized one-pot sequential procedure starting
from commercially available compounds (Scheme S1, ESI†).23
and 3,6-di-tert-butyl-9H-carbazole with high triplet energy (ET)23
Tetrafluoro cyanopyridine with enantiopure 1,10-bi-2-naphthol
(BINOL) and carbazoles and K2CO3 as a base were added into
N,N-dimethylformamide (DMF) to produce the target molecules
at room temperature with overall yields over 80% after purifica-
tion by silica gel column chromatography. These easily prepared
chiral compounds through the above straightforward and cost-
effective procedure were fully characterized (Fig. S1–S18, ESI†).
are donor (D) moieties of the chiral TADF molecules for sky-blue
emission (Fig. 1a). These newly designed TADF enantiomers in
a chiral–A–D architecture can be prepared facilely through
a scalable one-pot sequential synthetic procedure at room
temperature in high yields (480%). Excellent TADF character-
istics were observed along with excellent solubility and strong
sky-blue photo-luminance with high chiral stability and
Benefiting from the stable central chirality of enantiomerically
pure BINOL,34 no racemization of the chiral TADF emitters occurs
during the synthesis and post treatments of the target TADF
enantiomers with high enantiomeric excess (499%, according
to chiral HPLC, see Fig. S19 and S20, ESI†).
The newly obtained chiral TADF molecules possess good
solubility in commonly used organic solvents, which is important
for the solution-processing of the devices. Very high decomposi-
tion temperatures (Td) over 420 1C were observed for the carbazole-
based TADF molecules, while those of the tert-butylcarbazole-
based ones show even higher values up to 439 1C, according to
thermogravimetric analysis. Differential scanning calorimetry also
reveals high glass transition temperatures (Tg) of these chiral
compounds, which are 329 1C/326 1C and 248 1C/244 1C for
R- and S-CPDCz and R- and S-CPDCB, respectively (Fig. S21,
ESI†). These excellent thermal stability properties are due to the
highly rigid and twisted molecular structures, endowing these
enantiomers with high thermal and morphological stability of
films for high-performance device applications.35
Theoretical investigations
Time-dependent density-functional-theory (TD-DFT) calcula-
tions show that the highest occupied molecular orbital (HOMO)
is dominated by the donor of carbazoles, while the acceptor of
the central cyanopyridine determines the lowest unoccupied
molecular orbital (LUMO) and the chiral perturbation group
of BINOL has limited contribution to both the HOMO and
Fig. 1 (a) Molecular design, chemical structures and (b) frontier molecular
orbital distributions of the chiral TADF materials.
14512 | J. Mater. Chem. C, 2019, 7, 14511--14516
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Journal of Materials Chemistry C
Paper
LUMO (Fig. 1b). This clear spatial electronic separation of the molecules, and a broad emission band owing to the ICT effects
HOMO and LUMO is a key feature of TADF molecules in with typical emission peaks around 510–520 nm, which can be
realizing a small DEST for efficient RISC.21 It should be also red-shifted by increasing the solvent polarity from CHCl3 to
noted that a small spatial overlap of the HOMO and LUMO on cyclohexane (Fig. S23, ESI†). Similar photophysical behaviours
the cyanopyridine moiety with an overlap extent (IH/L) of about of these chiral TADF molecules were observed in films (Fig. 2b);
33% can be observed, which is important for high lumines- the small red-shifts (o11 nm) of the spectra in the solid state
cence efficiency of TADF emitters.21 Therefore, their absolute indicate weak intermolecular interactions due to the twisted
PLQYs measured using an integrating sphere are up to 37% in molecular structure caused by the chiral BINOL units. It should
dilute tetrahydrofuran (THF) solution and 55% in the doped be noted that the ICT absorption bands of the spin-coated
(10 wt%) film of 1,3-bis(carbazol-9-yl) benzene (mCP). More- films are relatively stronger than those of vacuum-deposited
over, good morphology of the spin-coated thin films on ITO was films (Fig. S24, ESI†). The higher ICT due to stronger D–A
also observed by atomic force microscopy (Fig. S22, ESI†) with a interactions of the solution-processed films may lead to a higher
surface roughness lower than 0.4 nm, demonstrating clearly dissymmetry factor of the luminescence. The introduction of
their great potential in solution-processed devices.39
the bulky tert-butyl groups further reduces the intermolecular
interactions, leading to a very small red-shift (o2 nm) in the
solid film state.35 In addition, due to the introduction of four
Photophysical properties
The UV-vis absorption and photoluminescence (PL) spectra of electron-donating tert-butyl groups, which results in stronger
the TADF enantiomers were studied in both dilute solutions ICT effects for smaller energy bandgaps, the absorption and PL
and thin films. As illustrated in Fig. 2a, almost identical spectra spectra of R- and S-CPDCB undergo a red-shift of 30 nm in both
of the enantiomers were observed in THF solutions, exhibiting solution and film states (Table S1, ESI†).36 The low-temperature
a strong absorption band around 320 nm assigned to the emission properties of the enantiomers were studied to explore
BINOL absorption,23 a weak absorption peak at about 410 nm their TADF properties (Fig. S25, ESI†). Taking S-CPDCz as an
associated with the intramolecular charge transfer (ICT) process example (Fig. 2c), the fluorescence band of S-CPDCz in THF
derived from the chiral–A–D electronic structures of these TADF solution at 77 K is centered at 467 nm, which indicates an
S1 energy of 2.65 eV. Meanwhile, the phosphorescence band
of S-CPDCz at 484 nm suggests a T1 energy of 2.57 eV. Thus,
DEST of S-CPDCz was measured to be 0.08 eV in THF solution.
From their small DEST values (o0.08 eV) (Table S2, ESI†), TADF
features should be successfully established in these chiral
molecules in the chiral–A–D architecture. Further, the transient
PL decay profiles exhibit two distinct lifetimes; the fast one in
several nanoseconds presents the prompt fluorescent emission,
while the slow one in several microseconds is related to the
delayed fluorescent emission through RISC, giving direct
evidence of the TADF characteristic (Fig. 2d).20 Also, signifi-
cantly reduced PL lifetimes were observed at low temperatures
(Fig. S26, ESI†), indicating again the TADF emission feature,
which is sensitive to temperature.24
Chiroptical properties
The chiroptical properties of these optically stable TADF
enantiomers were investigated using CD and CPL spectra in
both THF solution and neat films. From Fig. 2e and f, the CD
spectra of the chiral TADF molecules display an obvious mirror-
image relationship with the maximum band centred around
320 nm, which matches well the corresponding BINOL absorp-
tion band.23 These results indicate that the chiral unit in the
TADF enantiomers has successfully induced the TADF mole-
cules to produce chirality in the ground state. Consequently,
almost mirror-image CPL spectra of the TADF emission were
recorded with gPL of 3.4 ꢀ 10ꢁ4/ꢁ3.0 ꢀ 10ꢁ4 for R-/S-CPDCz and
3.2 ꢀ 10ꢁ4/ꢁ2.1 ꢀ 10ꢁ4 for R-/S-CPDCB in THF, respectively
(Fig. 3a and b), which further confirms the chiroptical proper-
ties of the enantiomers in the excited state. More interestingly,
when the neat films of these chiral molecules were fabricated by
spin-coating, larger average gPL values of 3.7 ꢀ 10ꢁ4/ꢁ3.3 ꢀ 10ꢁ4
Fig. 2 (a and b) UV-vis absorption and PL spectra of the chiral TADF
molecules in (a) dilute THF solutions (B10ꢁ5 mol Lꢁ1) and (b) thin films at
room temperature (RT). (c) Fluorescence and phosphorescence spectra of
S-CPDCz in THF at 77 K. (d) Transient decays of the emission peaks
(excited at 315 nm), photographs (inset left) and fluorescence decay curves
(inset right) of the chiral TADF molecules doped in mCP films (10 wt%).
(e and f) CD spectra of the chiral TADF molecules in (e) THF and (f) neat
films at RT.
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C, 2019, 7, 14511--14516 | 14513

View Article Online
Paper
Journal of Materials Chemistry C
Fig. 3 (a and c) CPL spectra and (b and d) gPL values of the chiral TADF
molecules in (a and b) dilute THF solutions (B10ꢁ5 mol Lꢁ1) and (c and d)
neat films at RT.
and 5.8 ꢀ 10ꢁ4/ꢁ4.0 ꢀ 10ꢁ4 were detected (Fig. 3c and d).
Possibly, this is because the chiral molecules exist in an isolated
state in solution, whereas in the neat film state formed by spin-
coating, chiral aggregates could be slight oriented, leading to
chiroptical amplification in spin-coated films.40 All in all, our
strategy of incorporating a chiral unit into TADF architectures
in a chiral–A–D structure is efficient in producing chiral TADF
molecules with CD and CPL properties, which should be instruc-
tive to develop high-performance CP-OLEDs with intense CPEL.
Fig. 4 (a and b) Energy level diagrams of the related materials, and (c and
d) current density–luminance–voltage, and (e and f) efficiency–luminance
curves in (a, c and e) vacuum-deposited and (b, d and f) solution-processed
CP-OLEDs based on TADF emitters of S-CPDCz and S-CPDCB. Inset: EL
spectra and device structures.
CP-OLEDs (Fig. S28, ESI†) under the following device configu-
ration: ITO/PEDOT:PSS (30 nm)/TAPC (20 nm)/mCP:TADF
dopants (10 wt%, 20 nm)/TmPyPB (30 nm)/LiF (1 nm)/Al
(100 nm).38 Almost identical spectra of the PL and electro-
luminescence (EL) of the TADF molecules were observed,
exhibiting excellent energy transfer from the host to the guest
material for the sky-blue EL peaks at 492 and 515 nm of the
R-/S-CPDCz and R-/S-CPDCB based devices, respectively
(Table 1). Due to the higher HOMO energy levels and larger
PLQYs of R-/S-CPDCB, superior device performance with a
maximum current efficiency (CE) of 39.5 cd Aꢁ1, power efficiency
(PE) of 30.3 lm Wꢁ1, and EQE of 12.4% resulted (Fig. 4c–e). More
impressively, when these TADF emitters were used in solution-
processed OLEDs with the simplified device configuration
(Fig. S29, ESI†): ITO/PEDOT:PSS (30 nm)/mCP:TADF dopants
(10 wt%, 40 nm)/DPEPO (10 nm)/TmPyPB (50 nm)/Liq (1 nm)/Al
(100 nm),39 high device performances were also observed
(Fig. 4d–f). The EQEs of both the S-CPDCz and S-CPDCB based
OLEDs are over 10% with identical EL spectra to those of
the solution-processed devices (Fig. S30 and S31, ESI†). It
should be noted that this is the first report of solution-processed
OLED performance
These TADF enantiomers were then used as the emissive dopants
(10 wt%) in multilayer OLEDs to investigate their electrolumines-
cence (EL) properties. The HOMO and LUMO energy levels of
R- and S-CPDCz were found to be at ꢁ5.8 and ꢁ2.9 eV, while
these of R- and S-CPDCB were identified to be ꢁ5.7 and ꢁ2.9 eV,
as measured by the oxidation onsets of cyclic voltammetry curves
(Fig. S27, ESI†) and optical bandgaps from the absorption edges
of thin films (Fig. 2b).37 The higher HOMO levels of R- and
S-CPDCB are due to the electron-donating effects of the tert-butyl
groups. With the frontier orbital energy levels, mCP was chosen
as the host material of these chiral TADF emitters, poly(3,4-
ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS)
and LiF as the hole- and electron-injecting materials, and 4,40-
cyclohexylidenebis[N,N-bis(4-methylphenyl)aniline] (TAPC) and
1,3,5-tri(m-pyrid-3-yl-phenyl)-benzene (TmPyPB) as hole- and electron-
transporting materials, respectively, in the vacuum-deposited
Table 1 Device performance of the sky-blue TADF CP-OLEDs based on S-CPDCz and S-CPDCB
b
c
Compound
Method
Va (V)
lmax (nm)
Lmax (cd mꢁ2
)
CEd (cd Aꢁ1
)
PEd (lm Wꢁ1
)
EQEd (%)
gEL
S-CPDCz
S-CPDCB
S-CPDCz
S-CPDCB
Vacuum
Vacuum
Solution
Solution
3.80
3.70
3.60
3.60
492
515
496
516
3700
7700
923
21.4
39.5
24.6
33.3
15.7
30.3
19.3
26.1
8.4
12.4
10.1
10.6
ꢁ5.5 ꢀ 10ꢁ4
ꢁ8.6 ꢀ 10ꢁ4
ꢁ3.7 ꢀ 10ꢁ3
ꢁ3.9 ꢀ 10ꢁ3
1785
a
b
c
d
Turn-on voltage at a brightness of 1 cd mꢁ2
.
EL peak wavelength at 1000 cd mꢁ2
.
Maximum luminance. Maximum efficiencies.
14514 | J. Mater. Chem. C, 2019, 7, 14511--14516
This journal is ©The Royal Society of Chemistry 2019

View Article Online
Journal of Materials Chemistry C
Paper
with amplified chirality. Owing to the effective separation but
slight overlap of their HOMO/LUMO distributions for small
DEST and high PLQY, excellent TADF properties of these enantio-
mers were achieved, along with good solubility, excellent optical
stability, mirror-image CD and CPL activities. Sky-blue CP-OLEDs
using these chiral TADF molecules as dopants exhibit not only high
EQEs of up to 12.4% in vacuum-deposited TADF OLEDs and
10.6% in solution-processed devices, but also intense opposite
CPEL signals with gEL values of 6 ꢀ 10ꢁ4/ꢁ8.6 ꢀ 10ꢁ4 (vacuum-
deposited devices) and 3.5 ꢀ 10ꢁ3/ꢁ3.9 ꢀ 10ꢁ3 (solution-processed
OLEDs). These promising device performances, which are among
the best results of CP-OLEDs and BINOL-based TADF OLEDs
reported so far, are encouraging. The amplified chirality of the
TADF CP-OLEDs through solution-processing using chiral–A–D
molecules is fundamentally important and conceptually instructive,
which should promote significantly the investigations of solution-
processible TADF enantiomers for CP-OLEDs.
Fig. 5 (a and b) gEL spectra of R-/S-CPDCz as a function of emission
wavelength in (a) vacuum-deposited and (b) solution-processed devices.
(c and d) gEL values at the maximum emission wavelength of (c) R- and (d)
S-enantiomers.
Conflicts of interest
There are no conflicts to declare.
TADF CP-OLEDs by overcoming the intrinsic difficulties to
simultaneously achieve good solubility, chiroptical properties,
TADF features, and matched frontier orbital energy levels of the
materials.
Acknowledgements
Owing to the high conformational stability of the BINOL-
based enantiomers, these high-performance TADF OLEDs show
intense CPEL, even after the thermal evaporation for the vacuum
deposition of the emitting layer during the device fabrication
(Fig. S32–S35, ESI†). As shown in Fig. 5, the two different chiral
TADF molecules of R/S-CPDCz and R/S-CPDCB result in typical
CPEL of their OLEDs with opposite gEL signals, and the gEL
values are slightly higher than the corresponding gPL, reaching
up to 4.0 ꢀ 10ꢁ4/ꢁ5.5 ꢀ 10ꢁ4 and 6.0 ꢀ 10ꢁ4/ꢁ8.6 ꢀ 10ꢁ4 in
the vacuum-deposited devices, respectively. More interestingly,
these gEL values further increase to 2.5 ꢀ 10ꢁ3/ꢁ3.7 ꢀ 10ꢁ3 and
3.5 ꢀ 10ꢁ3/ꢁ3.9 ꢀ 10ꢁ3 in the solution-processed devices.
It should be noted that the gEL values of the solution-processed
CP-OLEDs are almost an order of magnitude higher than those
of the vacuum-deposited devices. The higher gEL in the spin-
coated emitting layers are coincident with the higher gPL of the
spin-coated films (Fig. S32, S33 and Table S3, ESI†), which could
be ascribed to the oriented chiral molecules by the centrifugal
force during the spin-coating.40 To the best of our knowledge,
these gEL values and device efficiencies are comparable to the
best results of CP-OLEDs (Table S4 and Fig. S36, ESI†). This
discovery is encouraging, since the solution-processing of TADF
enantiomers can significantly increase the gEL of CP-OLEDs.
The authors acknowledge the financial support from the National
Natural Science Foundation of China (61875090, 91833306,
21674049, 21604039, 51873159, and 61575146), 1311 Talents
Program of Nanjing University of Posts and Telecommunications
(Dingshan), the Six Talent Plan (2016XCL050), and Postgraduate
Research & Practice Innovation Program of Jiangsu Province
(46030CX18043).
Notes and references
1 R. Carr, N. H. Evans and D. Parker, Chem. Soc. Rev., 2012,
41, 7673.
2 T. Zhao, J. Han, X. Jin, Y. Liu, M. Liu and P. Duan, Angew.
Chem., 2019, 58, 15.
3 Y. Yang, R. C. da Costa, M. J. Fuchter and A. J. Campbell,
Nat. Photonics, 2013, 7, 634–638.
4 M. Grell, M. Oda, K. S. Whitehead, A. Asimakis, D. Neher
and D. D. Bradley, Adv. Mater., 2001, 13, 577–580.
5 J. R. Brandt, F. Salerno and M. Fuchter, J. Nat. Rev. Chem.,
2017, 1, 0045.
6 E. Peeters, M. P. T. Christiaans, R. A. J. Janssen, H. F. M.
Schoo, H. P. J. M. Dekkers and E. W. Meijer, J. Am. Chem.
Soc., 1997, 119, 9909–9910.
7 F. Zinna, M. Pasini, F. Galeotti, C. Botta, L. Di Bari and
U. Giovanella, Adv. Funct. Mater., 2017, 27, 1603719.
8 D. Di Nuzzo, C. Kulkarni, B. Zhao, E. Smolinsky, F. Tassinari,
S. C. J. Meskers, R. Naaman, E. W. Meijer and R. H. Friend,
ACS Nano, 2017, 11, 12713.
Conclusions
In summary, we succeed in developing two couples of BINOL-
based TADF enantiomers using a typical donor of carbazoles,
acceptor of cyanopyridine, and chiral unit of BINOL in a chiral–
A–D architecture for the first solution-processible CP-OLEDs
9 Y. Yang, R. C. da Costa, D.-M. Smilgies, A. J. Campbell and
M. J. Fuchter, Adv. Mater., 2013, 25, 26242628.
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C, 2019, 7, 14511--14516 | 14515

View Article Online
Paper
Journal of Materials Chemistry C
10 M. Craig, P. Jonkheijm, S. Meskers, A. Schenning and 25 Z.-G. Wu, H.-B. Han, Z.-P. Yan, X.-F. Luo, Y. Wang, Y.-X. Zheng,
E. Meijer, Adv. Mater., 2003, 15, 1435–1438. J.-L. Zuo and Y. Pan, Adv. Mater., 2019, 31, 1900524.
11 J. Han, J. You, X. Li, P. Duan and M. Liu, Adv. Mater., 2017, 26 X. Ban, F. Chen, Y. Liu, J. Pan, A. Zhu, W. Jiang and Y. Sun,
29, 1606503. Chem. Sci., 2019, 10, 3054–3064.
12 J. Kumar, T. Nakashima, H. Tsumatori and T. Kawai, J. Phys. 27 D. Liu, W. Tian, Y. Feng, X. Zhang, X. Ban, W. Jiang and Y. Sun,
Chem. Lett., 2014, 5, 316–321. ACS. Appl. Mater. Interfaces, 2019, 11(29), 26165–26173.
13 T.-Y. Li, Y.-M. Jing, X. Liu, Y. Zhao, L. Shi, Z. Tang, Y.-X. Zheng 28 X. Zeng, T. Zhou, J. Liu, K. Wu, S. Li, X. Xiao, Y. Zhang, S. Gong,
and J.-L. Zuo, Sci. Rep., 2015, 5, 14912. G. Xie and C. Yang, Adv. Opt. Mater., 2018, 6, 1801071.
14 D.-M. Lee, J.-W. Song, Y.-J. Lee, C.-J. Yu and J.-H. Kim, Adv. 29 Y. Zou, S. Gong, G. Xie and C. Yang, Adv. Opt. Mater., 2018,
Mater., 2017, 29, 1700907. 6, 1800568.
15 H. Sakai, S. Shinto, J. Kumar, Y. Araki, T. Sakanoue, 30 Y. Liu, C. Li, Z. Ren, S. Yan and M. R. Bryce, Nat. Rev. Mater.,
T. Takenobu, T. Wada, T. Kawai and T. Hasobe, J. Phys.
Chem. C, 2015, 119, 13937–13947.
2018, 3, 18020.
´
31 E. M. Sanchez-Carnerero, F. Moreno, B. L. Maroto, A. R.
16 T.-Y. Li, Y.-M. Jing, X. Liu, Y. Zhao, L. Shi, Z. Tang, Y.-X. Zheng
and J. L. Zuo, Sci. Rep., 2015, 5, 14912.
Agarrabeitia, M. J. Ortiz, B. G. Vo, G. Muller and S. de la Moya,
J. Am. Chem. Soc., 2014, 13, 3346.
17 Q. Zhang, B. Li, S. Huang, H. Nomura, H. Tanaka and 32 Y. Wang, Y. Zhang, W. Hu, Y. Quan, Y. Li and Y. Cheng, ACS
C. Adachi, Nat. Photonics, 2014, 8, 326–332. Appl. Mater. Interfaces, 2019, 11, 26165–26173.
18 S. Hirata, Y. Sakai, K. Masui, H. Tanaka, S. Y. Lee, 33 K.-C. Pan, S.-W. Li, Y.-Y. Ho, Y.-J. Shiu, W.-L. Tsai, M. Jiao,
H. Nomura, N. Nakamura, M. Yasumatsu, H. Nakanotani,
Q. Zhang, K. Shizu, H. Miyazaki and C. Adachi, Nat. Mater.,
2014, 14, 330.
W.-K. Lee, C.-C. Wu, C.-L. Chung, T. Chatterjee, Y.-S. Li,
K.-T. Wong, H.-C. Hu, C.-C. Chen and M.-T. Lee, Adv. Funct.
Mater., 2016, 26, 7560.
19 H. Nakanotani, K. Masui, J. Nishide, T. Shibata and 34 Y. S. Kim, S. Matsunaga, J. Das, A. Sekine, T. Ohshima and
C. Adachi, Sci. Rep., 2014, 4, 3640. M. Shibasaki, J. Am. Chem. Soc., 2000, 122, 6506.
20 Y. Tao, K. Yuan, T. Chen, P. Xu, H. Li, R. Chen, C. Zheng, 35 S. Xu, H. Li, R. Chen, Z. Chen, L. Xu, Y. Tang and W. Huang,
L. Zhang and W. Huang, Adv. Mater., 2014, 26, 7931. Adv. Opt. Mater., 2018, 6, 1701105.
21 R. Chen, Y. Tang, Y. Wan, T. Chen, C. Zheng, Y. Qi, Y. Cheng 36 H. Li, L. Xu, Y. Tang, Y. Tao, S. Xu, C. Zheng, G. Xing,
and W. Huang, Sci. Rep., 2017, 7, 6225.
X. Zhou, W. Huang and R. Chen, J. Mater. Chem. C, 2016, 4,
22 S. Feuillastre, M. Pauton, L. Gao, A. Desmarchelier,
10047–10052.
A. J. Riives, D. Prim, D. Tondelier, B. Geffroy, G. Muller, 37 R.-F. Chen, G.-H. Xie, Y. Zhao, S.-L. Zhang, J. Yin, S.-Y. Liu
G. Clavier and G. Pieters, J. Am. Chem. Soc., 2016, 138, 3990. and W. Huang, Org. Electron., 2011, 12, 1619–1624.
23 F. Song, Z. Xu, Q. Zhang, Z. Zhao, H. Zhang, W. Zhao, Z. Qiu, 38 L. Chen, S. Zhang, H. Li, R. Chen, L. Jin, K. Yuan, H. Li, P. Lu,
C. Qi, H. Zhang, H. H. Y. Sung, I. D. Williams, J. W. Y. Lam, B. Yang and W. Huang, J. Phys. Chem. Lett., 2018, 9, 5240.
Z. Zhao, A. Qin, D. Ma and B. Z. Tang, Adv. Funct. Mater., 39 Y. Zou, S. Gong, G. Xie and C. Yang, Adv. Opt. Mater., 2018,
2018, 28, 1800051. 6, 1800568.
24 M. Li, S.-H. Li, D. Zhang, M. Cai, L. Duan, M.-K. Fung and 40 J. Li, C. Yang, C. Huang, Y. Wan and W.-Y. Lai, Tetrahedron
C.-F. Chen, Angew. Chem., 2018, 57, 2889–2893. Lett., 2016, 57, 1256.
14516 | J. Mater. Chem. C, 2019, 7, 14511--14516
This journal is ©The Royal Society of Chemistry 2019