Meta Junction Promoting Efficient Thermally Activated Delayed Fluorescence in Donor-Acceptor Conjugated Polymers

Article abstract of DOI:10.1002/anie.202006034

The meta junction is proposed to realize efficient thermally activated delayed fluorescence (TADF) in donor–acceptor (D-A) conjugated polymers. Based on triphenylamine as D and dicyanobenzene as A, as a proof of concept, a series of D-A conjugated polymers has been developed by changing their connection sites. When the junction between D and A is tuned from para to meta, the singlet–triplet energy splitting (ΔE_ST) is found to be significantly decreased from 0.44 to 0.10 eV because of the increasing hole–electron separation. Unlike the para-linked analogue with no TADF, consequently, the meta-linked polymer shows a strong delayed fluorescence. Its corresponding solution-processed organic light-emitting diodes (OLEDs) achieve a promising external quantum efficiency (EQE) of 15.4 % (51.9 cd A^?1, 50.9 lm W^?1) and CIE coordinates of (0.34, 0.57). The results highlight the bright future of D-A conjugated polymers used for TADF OLEDs.

Full text of DOI:10.1002/anie.202006034

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Accepted Article
Title: Meta Junction Promoting Efficient Thermally Activated Delayed
Fluorescence in Donor-Acceptor Conjugated Polymers
Authors: Junqiao Ding
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10.1002/anie.202006034
Angewandte Chemie International Edition
RESEARCH ARTICLE
Meta Junction Promoting Efficient Thermally Activated Delayed
Fluorescence in Donor-Acceptor Conjugated Polymers
Jiancheng Rao, Liuqing Yang, Xuefei Li, Lei Zhao, Shumeng Wang,* Junqiao Ding,* Lixiang Wang
Abstract: The meta junction is proposed to realize efficient
thermally activated delayed fluorescence (TADF) in donor-acceptor
(D-A) conjugated polymers. Based on triphenylamine as D and
dicyanobenzene as A, as a proof of concept, a series of D-A
conjugated polymers has been developed by changing their
connection sites. When the junction between D and A is tuned from
para to meta, the singlet-triplet energy splitting (∆EST) is found to be
significantly decreased from 0.44 to 0.10 eV because of the
increasing hole-electron separation. Unlike the para-linked analogue
with no TADF, consequently, the meta-linked polymer shows a
strong delayed fluorescence. Its corresponding solution-processed
organic light-emitting diodes (OLEDs) achieve a promising external
quantum efficiency (EQE) of 15.4% (51.9 cd A-1, 50.9 lm W-1) and
Commission Internationale de l’Eclairage (CIE) coordinates of (0.34,
0.57). The results first highlight the bright future of D-A conjugated
polymers used for TADF OLEDs.
dynamic rocking of the D–A units about the orthogonal geometry
plays a crucial role on the achievement of efficient TADF.[10] On
the basis of these criteria, a great number of TADF small
molecules[11-17] have been successfully reported to give various
emission colors in the whole visible region as well as
comparable
electroluminescent
device
efficiencies
to
phosphors.[18,19]
Starting from D and A, however, it remains a big challenge
to design TADF polymers that are suitable for low-cost and
easily-scalable wet methods (Figure 1). For example, the
manipulation of ∆EST is assumed impossible in conjugated
polymers because they often display the lowest triplet state (T1)
to be 0.7 ± 0.1 eV below the lowest singlet state (S1).[20]
Accordingly, few reports have focused on D-A conjugated
polymers to realize TADF, where both D and A are incorporated
into the main chain.[21,22] To avoid this bottleneck, one approach
is to fix D in the main chain and graft A in the side chain directly
or via a spiro-linkage,[23-27] the other is to tether D and A in the
side chain simultaneously.[28-31] Benefitting from the intentional
separation between D and A in location, the developed
Backbone-D/Pendant-A and through-space charge transfer
(TSCT) polymers show a reduced molecular orbital overlap and
thus a small ∆EST. As a consequence, high-performance delayed
1. Introduction
Nowadays thermally activated delayed fluorescence (TADF)
has been widely adopted in organic light-emitting diodes
(OLEDs) to achieve a theoretical 100% internal quantum
efficiency without using rare metals.[1-4] Unlike the traditional
fluorescence,[5] the singlet-triplet energy splitting (∆EST) is
required to be negligible (< 0.3 eV) for TADF, so that triplets
generated upon electrical excitation could be up-converted into
singlets via a thermally-aided reverse intersystem crossing
(RISC).[6] From the molecular viewpoint, a donor-acceptor (D-A)
geometry is proposed to meet such a demand,[7] where the initial
and final molecular orbitals of the lowest excitation tend to
localize on the D and A units, respectively. Hence a small ∆EST
is within our expectation due to the limited molecular orbital
overlap.[8,9] Also, the electronic coupling between the local triplet
and the charge transfer states together with the effect of
fluorescence is obtained, revealing
a state-of-art external
quantum efficiency (EQE) over 15%.[26,29] Despite the
effectiveness, there still leaves a doubt whether D-A conjugated
polymers have a real potential in the TADF generation.
Additionally, D-A conjugated polymers possess some unique
features beneficial for OLEDs, such as the favored charge
transporting and ease tuning of the bandgap, because the
existed quinoidal structure can increase the planarity of the
polymeric backbone and enable π-delocalization along the
polymeric chain.[32,33] Therefore, much effort should be paid back
to the development of TADF polymers based on the D-A
conjugated backbone.
Herein, we demonstrate that meta junction can promote
efficient TADF in D-A conjugated polymers. As a proof of
concept (Figure 2), triphenylamine (TPA) and dicyanobenzene
(DCB) are selected as the D and A, respectively. By changing
their connection sites, four D-A conjugated polymers named
poly(TPAp-DCBp), poly(TPAp-DCBm), poly(TPAm-DCBp) and
poly(TPAm-DCBm) are constructed, where p and m denote para
and meta junctions, respectively. Following this sequence, the
energy of T1 is found to ascend faster with the para-to-meta
alteration than the energy of S1, in agreement with the
decreased hole-electron overlap. Compared with the non-TADF
poly(TPAp-DCBp) (0.44 eV), as a result, the ∆EST drops
significantly to 0.10 eV of poly(TPAm-DCBm), endowing it with a
strong delayed fluorescence. The corresponding solution-
processed OLEDs achieve a promising EQE as high as 15.4%
(51.9 cd A-1, 50.9 lm W-1) and Commission Internationalede
l’Eclairage (CIE) coordinates of (0.34, 0.57). To the best of our
knowledge, this is the first report on D-A type conjugated TADF
[*]
J. Rao, L. Yang, X. Li, Dr. L. Zhao, Dr. S. Wang, Prof. J. Ding, Prof.
L. Wang
State Key Laboratory of Polymer Physics and Chemistry
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences, Changchun 130022, P. R. China
E-mail: wangshumeng@ciac.ac.cn; junqiaod@ciac.ac.cn
J. Rao
University of Chinese Academy of Sciences
Beijing 100049, P. R. China
L. Yang, X. Li, Prof. J. Ding, Prof. L. Wang
University of Science and Technology of China
Hefei 230026, P. R. China
Prof. J. Ding
School of Chemical Science and Technology, Yunnan University
Kunming 650091, P. R. China
Supporting information for this article is given via a link at the end of
the document.
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10.1002/anie.202006034
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RESEARCH ARTICLE
Figure 1. Molecular design rules of TADF polymers starting from D and A units.
Figure 2. Molecular structures, hole and electron analysis of the S1 states for the D-A conjugated polymers. Sm is the overlap
function between hole and electron distributions, quantified by a Sm index ranging from 0 (no overlap) to 1 (complete overlap).
polymers, whose performance can well compete with the
Backbone-D/Pendant-A and TSCT polymers.
conjugated polymers poly(TPAp-DCBp), poly(TPAp-DCBm),
poly(TPAm-DCBp) and poly(TPAm-DCBm). Firstly, their
ground-state geometries are optimized at B3LYP/6-31G(d) level
by Gaussian09 software package. Since they contain the same
D and A units in the backbone, the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) levels are taken to almost match with each other
(Table S1). Subsequently, considering that ∆EST is sensitive to
2. Results and Discussion
2.1 Theoretical computation
Initially, theoretical computation was carried out to study the
effect of the junction between D and A in the designed four D-A
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Table 1. Summary of the molecular weight, photophysical, electrochemical and thermal properties.
a
c
d
e
g
i
j
Mn
λabs
λPL
τp / τd
S1 / T1 / ∆EST
HOMO / LUMO h
[eV]
Td
Tg
b
Compound
PDI
Φ f
[kDa]
[nm]
[nm]
[ns / μs]
[eV]
[oC]
[oC]
2.55 / 2.11 /
0.44
poly(TPAp-DCBp)
poly(TPAp-DCBm)
poly(TPAm-DCBp)
poly(TPAm-DCBm)
13.1
1.42
1.33
1.29
1.92
301, 354, 438 (514)
533 (71)
1.20 / n. d. 0.82 (0.90)
1.85 / 1.35 0.61 (0.85)
8.10 / 1.90 0.25 (0.64)
10.9 / 6.37 0.39 (0.80)
-5.14 / -2.42
-5.17 / -2.49
-5.18 / -2.48
-5.15 / -2.51
459
453
452
449
149
2.59 / 2.34 /
0.25
6.1
4.1
7.5
303, 344, 420 (496)
301 (455)
531 (77)
524 (79)
529 (88)
152
114
123
2.63 / 2.42 /
0.21
2.63 / 2.53 /
0.10
305 (448)
aNumber-averaged molecular weight; bPolydispersity index; cAbsorption peaks and onset values (in brackets) measured in neat films; dFluorescence peaks and
FWHM values (in brackets) measured in neat films; ePrompt and delayed fluorescence lifetimes obtained in neat films under nitrogen atmosphere with an
f
excitation wavelength of 375 nm; Absolute PLQYs measured in neat films and in 5 wt.% doped mCP films (in brackets) under nitrogen atmosphere with an
excitation wavelength of 400 nm; gS1 and T1 are estimated from the onsets of the film fluorescence and phosphorescence spectra, respectively, and ∆EST = S1 - T1;
i
j
hHOMO and LUMO levels are determined by cyclic voltammetry; Decomposition temperature corresponding to 5% weight loss; Glass transition temperature
determined by the middle value between break points.
the exchange interactions on the overlap between hole and
electron wave functions,[20] the vertical excitation calculation is
conducted by TD-DFT at the same level using the optimized
molecular structures, followed by the hole and electron
analysis[34,35] on S1 and T1 states. As one can see in Figure 2,
both the hole and electron of S1 are distributed along the
polymeric chain, and a large electron-hole overlap (Sm index =
0.1609) is determined for poly(TPAp-DCBp). When the D-A
junction is varied from para to meta, we note that the hole and
electron distributions are becoming more and more discrete.
With poly(TPAm-DCBm) as an example, the S1 hole and S1
electron are independently centered on TPA and DCB,
respectively, leading to a decreased Sm index of 0.0321. Also, a
similar trend is observed for the T1 state (Figure S1). These
observations imply that the meta junction plays an important
role on the reduction of the hole-electron overlap in D-A
conjugated polymers, which may further decrease the
iodobenzene via a Buchwald-Hartwig C-N coupling[37] to get 4-
bromo-N-(4-bromophenyl)-N-(4-octylphenyl)aniline (1) and 3-
bromo-N-(3-bromophenyl)-N-(4-octylphenyl)aniline (2), which
were then converted to their corresponding borate monomers
M1 and M2 by esterification, respectively. With the bromide
monomers
dibromoterephthalonitrile
2,5-dibromoterephthalonitrile
in hand,
and
typical
2,6-
Suzuki
a
polymerization[38,39] was then performed to afford four polymers
with different D-A junctions, namely poly(TPAp-DCBp),
poly(TPAp-DCBm), poly(TPAm-DCBp) and poly(TPAm-DCBm).
The molecular structures of these polymers were characterized
by gel permeation chromatography (GPC), 1H and 13C NMR,
and elementary analysis. The number-averaged weight (Mn)
ranges from 4.1 kDa to 13.1 kDa with polydispersity index (PDI)
from 1.29 to 1.92 (Table 1). Noticeably, the meta-involved
polymers
poly(TPAp-DCBm),
poly(TPAm-DCBp)
and
poly(TPAm-DCBm) seem to have a smaller Mn than that of
poly(TPAp-DCBp). The similar trend was also observed by A. D.
Schlüter early in 2005, but without a definite explanation.[40] At
present, we could tentatively deduce that, compared with the
para polymerization, the steric hinderance caused by the meta-
involved polymerization may slow down the transmetalation,[41]
leading to deborylation and thus small Mn. Furthermore, they
are readily soluble in common organic solvents, such as
toluene, chlorobenzene and chloroform etc., ensuring their
capability to form high quality films via solution processing. Also,
all of them possess a decomposition temperature (Td) around
450 oC and a glass transition temperature (Tg) ranging from 114
to 152 oC, indicative of the excellent thermal stability (Figure
S2). And their HOMO (-5.14 ~ -5.18 eV) and LUMO levels (-
2.42 ~ -2.51 eV), determined by cyclic voltammetry (CV), are
found to be nearly independent on the D-A conjunction (Figure
S3).
correlated ∆EST
.
To verify this point, finally, the energies of S1 and T1 are
calculated according to a semi-empirical descriptor-based
optimal Hartree-Fock (OHF) method, the so-called K-OHF
method.[36] Because of the reduced hole-electron overlap, as
mentioned above, the estimated ∆EST is found to be down from
0.3416 eV of poly(TPAp-DCBp) to 0.1638 eV of poly(TPAm-
DCBm) (Table S2). Furthermore, a much lower oscillator
strength
f
is predicted for poly(TPAm-DCBm) (0.0110)
compared to poly(TPAp-DCBp) (1.3988). The prediction is
consistent with the largely separated hole and electron
distributions observed in poly(TPAm-DCBm), which is also an
indicator of the charge transfer (CT) nature for S1.
2.2 Synthesis and characterization
The synthetic route of the designed D-A conjugated
polymers is depicted in Scheme S1. At first, 4-octylaniline was
reacted with 1-bromo-4-iodobenzene and 1-bromo-3-
2.3 Photophysical properties
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Figure 3. UV-Vis absorption, fluorescence and
phosphorescence spectra in neat films for the D-A
conjugated polymers (a), and their corresponding energy
level alignment of the lowest S1 and T1 excited states (b).
Figure 4. PL decay comparison between the neat films of
the D-A conjugated polymers (a), and the temperature-
dependent transient PL spectra of poly(TPAm-DCBm) (b).
Figure 3a plots the UV-Vis absorption, fluorescence and
phosphorescence spectra for neat films of poly(TPAp-DCBp),
poly(TPAp-DCBm), poly(TPAm-DCBp) and poly(TPAm-DCBm).
Compared with those of the components TPA and DCB (Figure
S4), the absorption in the range of 350-500 nm can be
reasonably ascribed to the π-π* transition of the conjugated
polymeric backbone mixed with CT from TPA to DCB. As
discussed above, the hole-electron separation is monotonically
enhanced due to the meta junction, leading to a strengthened
CT character. So the relative intensity of the longest-
wavelength absorption band declines following the sequence of
poly(TPAp-DCBp) > poly(TPAp-DCBm) > poly(TPAm-DCBp) >
In addition, the phosphorescence spectra are also measured
at 77 K, and the energy of T1 is estimated to be up from 2.11
eV of poly(TPAp-DCBp) to 2.53 eV of poly(TPAm-DCBm).
According to the literatures,[42,43] the shortened longest poly(p-
phenyl) chain in the molecular structure is responsible for the
elevated T1 energy when the meta junction is adopted.
Although the energies of S1 and T1 are both increased with the
para-to-meta modification, it should be noted that the increment
of T1 (0.42 eV) is much larger than that of S1 (0.08 eV) from
poly(TPAp-DCBp) to poly(TPAm-DCBm) (Figure 3b).
Consequently, a smaller ∆EST of 0.10 eV is measured for
poly(TPAm-DCBm) with regard to poly(TPAp-DCBp) (0.44 eV).
This is in well agreement with the theoretical predictions,
proving that the meta junction can effectively reduce the ∆EST of
D-A conjugated polymers induced by the enhanced hole-
electron separation.
poly(TPAm-DCBm) (Figure S5). And
a
concomitant
hypsochromic shift is observed because the continuity of the
backbone conjugation is broken by the meta junction. Ongoing
from poly(TPAp-DCBp) to poly(TPAm-DCBm), the fluorescence
spectra are blue-shifted correspondingly, accompanied by an
increased S1 energy from 2.55 to 2.63 eV (Table 1). Moreover,
the structureless spectral profile and broadened full width at
half maximum (FWHM) from 71 to 88 nm further confirm the
existence of CT in poly(TPAm-DCBm).
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Table 2. Summary of device performance.
LE e [cd A-1]
PE f [lm W-1]
EQE g [%]
d
c
h
Von
Lmax
λem
CIE i
(x, y)
Device
Maximum value / at 100 cd m-2 / at 500 cd m-2 / at 1000 cd m-2
[V]
[cd m-2]
[nm]
poly(TPAp-DCBp) a
poly(TPAm-DCBm) a
poly(TPAm-DCBm) b
4.0
4.2
3.2
11200
7200
6800
14.4 / 14.2 / 14.0 / 13.5
9.6 / 9.5 / 8.9 / 8.1
19.4 / 17.4 / 11.9 / 9.3
50.9 / 27.4 / 14.6 / 10.2
4.2 / 4.1 / 4.0 / 3.9
517
533
532
0.28, 0.61
0.34, 0.57
0.34, 0.57
29.6 / 28.2 / 20.9 / 17.1
8.8 / 8.6 / 6.3 / 5.2
51.9 / 36.7 / 22.3 / 16.8
15.4 / 10.9 / 6.6 / 5.0
aDevice using PEDOT:PSS as the hole-injection layer; bDevice using PFI modified PEDOT:PSS as the hole-injection layer; cTurn-on voltage at 1 cd m-2;
f
i
dMaximum luminance; eLuminous efficiency; Power efficiency; gExternal quantum efficiency; hPeak wavelength at 1000 cd m-2; CIE coordinates at 1000 cd m-2.
Figure 5. Device performance comparison between poly(TPAp-DCBp) and poly(TPAm-DCBm): (a) EL spectra at 1000 cd m-2;
(b) Current density-voltage-luminance characteristics; (c) EQE and luminous efficiency as a function of luminance; (d) Power
efficiency as a function of luminance.
fluorescence are observed for poly(TPAp-DCBm), poly(TPAm-
Given the obtained low ∆EST
, poly(TPAm-DCBm) is
DCBp) and poly(TPAm-DCBm) showing a delayed lifetime (τd)
of 1.35 μs, 1.90 μs and 6.37 μs, respectively. In accordance
with the decreased ∆EST, the RISC rate constant (kRISC) goes
up from 2.83104 of poly(TPAp-DCBm) to 5.94104 of
poly(TPAm-DCBp) and 1.01105 of poly(TPAm-DCBm) (Table
S3). As a result of the more and more rapid RISC process, the
expected to be able to generate efficient TADF. Therefore, the
transient photoluminescent (PL) spectra are recorded in solid
states under nitrogen atmosphere. As shown in Figure 4a,
poly(TPAp-DCBp) exhibits only a prompt fluorescence without
any delayed fluorescence, while both prompt and delayed
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5b). The observed tendency may be from the torsional
backbone and shortened conjugation length in the meta-linked
poly(TPAm-DCBm), which is believed to be detrimental to
intermolecular stacking and thus charge transporting. In spite of
this, the maximum luminous efficiency, power efficiency and
EQE are increased from 14.4 cd A-1, 9.6 lm W-1 and 4.2% of
poly(TPAp-DCBp) to 29.6 cd A-1, 19.4 lm W-1 and 8.8% of
poly(TPAm-DCBm) (Figure 5c and 5d). As discussed above,
poly(TPAp-DCBp) is a non-TADF emitter, whereas poly(TPAm-
DCBm) possesses a strong TADF due to a reduced ∆EST.
Therefore, both singlet and triplet excitons can be harvested in
poly(TPAm-DCBm) rather than poly(TPAp-DCBp), resulting in a
nearly doubled device efficiency.
Frankly speaking, the superior device performance of
poly(TPAm-DCBm) is achieved by partly sacrificing the charge
transporting capability. To solve this problem, a preliminary try
is performed by modifying the PEDOT:PSS layer with PFI
(perfluorinated ionomer).[45-47] After such an optimization, both
the current density-voltage and luminance-voltage plots move
backwards along the voltage axis (Figure S7). For example, the
turn-on voltage is distinctively lowered from 4.2 to 3.2 V, and
the luminance at a driving voltage of 5 V is elevated from 65 to
780 cd m-2. Meanwhile, the peak EQE is optimized to 15.4%
(51.9 cd A-1, 50.9 lm W-1) but with almost unchanged EL
spectrum (Figure 6). To our knowledge, the obtained
performance is comparable to those of Backbone-D/Pendant-A
and TSCT polymers,[26,29] and even among the highest ever
reported for TADF polymers.[48-50] Even though the PFI modified
PEDOT:PSS is used as the hole injection layer, we note that,
the current density of poly(TPAm-DCBm) is not recovered
completely yet in comparison to poly(TPAp-DCBp) (Figure S8).
Additionally, an obvious efficiency roll-off does exist, and the
EQE drops to 10.9% at 100 cd m-2 and 5.0% at 1000 cd m-2
(Table 2). This could be attributed to the charge imbalance
originating from the enhanced hole injection and transporting as
a result of the PFI modification and the unipolar feature of the
mCP host. On the other hand, when assuming the ratio of the
recombined carriers to the injected carriers (γ), the fraction of
Figure 6. EQE as a function of luminance and EL spectrum
(inset) for the optimized device of poly(TPAm-DCBm).
delayed fluorescence is found to be obviously enhanced.
Among them, poly(TPAm-DCBm) displays the strongest
delayed fluorescence, illustrating the superiority of the meta
junction in D-A conjugated polymers. The TADF nature of
poly(TPAm-DCBm) is further confirmed by the temperature-
dependent transient PL decay.[44] With the increasing
temperature from 50 to 300 K, the delayed component is
gradually increased in a scan time range of 0-25 μs (Figure 4b).
2.4 Electroluminescent properties
To evaluate the validity of poly(TPAm-DCBm) as the TADF
polymer, solution-processed OLEDs are fabricated with the
configuration of ITO/PEDOT:PSS (40 nm)/EML (50 nm)/TSPO1
(8 nm)/TmPyPB (42 nm)/LiF (1 nm)/Al (100 nm) (Figure S6).
Here,
poly(styrene
PEDOT:PSS
(poly(3,4-ethylenedioxythiophene):
TSPO1 (diphenyl-4-
sulfonate)),
triphenylsilylphenyl-phosphine oxide) and TmPyPB (1,3,5-tri[(3-
pyridyl)-phen-3-yl]benzene) serve as the hole-injection layer,
radiative excitons (ηr) and the light out-coupling constant (ηout
)
to be 1, 1 and 25%, respectively,[44] a high PLQY (ηPL) of 0.80
would correspond to an EQE limit of 20% according to the
equation:
exciton-blocking
layer
and
electron-transporting
layer,respectively. In order to suppress the aggregation caused
quenching, poly(TPAm-DCBm) is doped into mCP (1,3-
bis(9Hcarbazol-9-yl)benzene) at a 5 wt.% concentration to
constitute the emitting layer (EML), which has a higher PL
quantum yield (PLQY) than that of the nondoped film (0.80
versus 0.39, Table 1). Also, the control device of poly(TPAp-
DCBp) is prepared under the same conditions for comparison.
.
Therefore, a systematic investigation on device engineering
(such as using a higher conductive hole injection layer
combined with high-mobility electron-transporting layer, and
replacing mCP with a bipolar or an exciplex-type host etc.) is
further required to improve device efficiency and its roll-off,
which is under way.
Similar to their PL counterparts, poly(TPAm-DCBm)
displays a broader electroluminescence (EL) spectrum than
poly(TPAp-DCBp) because of the strengthened CT character
(Figure 5a). Although a hypsochromic EL onset is observed
3. Conclusion
from
poly(TPAp-DCBp)
to
poly(TPAm-DCBm),
their
In summary, four D-A conjugated polymers named
poly(TPAp-DCBp), poly(TPAp-DCBm), poly(TPAm-DCBp) and
poly(TPAm-DCBm) have been designed and synthesized with
TPA as D and DCB as A. Thanks to the para-to-meta tuning,
the hole-electron overlap is found to be obviously reduced from
corresponding CIE coordinates are red-shifted from (0.28, 0.61)
to (0.34, 0.57) (Table 2). In addition, the current density and
luminance of poly(TPAm-DCBm) are decreased compared with
those of poly(TPAp-DCBp) at the same driving voltage (Figure
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poly(TPAp-DCBp)
to
poly(TPAm-DCBm),
and
the
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ORCID
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Junqiao Ding: 0000-0001-7719-6599
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Notes
The authors declare no competing financial interest.
Acknowledgements
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The authors acknowledge the National Key Research and
Development Program (2016YFB0401301) and the National
Natural Science Foundation of China (51873205) for the
financial support.
22. Y. Hu, W. Cai, L. Ying, D. Chen, X. Yang, X.-F. Jiang, S. Su,
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Keywords: OLEDs; D-A conjugated polymer; TADF; meta
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J. Rao, L. Yang, X. Li, L. Zhao, S.
Wang*, J. Ding* and L. Wang
Page No. – Page No.
Meta Junction Promoting Efficient
Thermally
Activated
Delayed
Fluorescence
Conjugated Polymers
in Donor-Acceptor
DF + Linke
Meta junction has been introduced to promote efficient TADF in D-A conjugated polymers for the first time. As a result of the
enhanced hole-electron separation, the singlet-triplet energy splitting (∆EST) is found to be significantly decreased from 0.44
eV to 0.10 eV with the para-to-meta modification. And a strong delayed fluorescence is achieved for the meta-linked polymer,
revealing a peak EQE of 15.4% in solution-processed devices.
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