Red-Emitting Thermally Activated Delayed Fluorescence Polymers with Poly(fluorene- co-3,3′-dimethyl diphenyl ether) as the Backbone

Article abstract of DOI:10.1021/acs.macromol.8b02050

A series of red-emitting thermally activated delayed fluorescence (TADF) polymers have been designed and synthesized based on poly(fluorene-co-3,3′-dimethyl diphenyl ether) (PFDMPE) as the backbone. Compared with polyfluorene (PF, 2.16 eV), the introduction of 3,3′-dimethyl diphenyl ether into the main chain of PFDMPE leads to the increased triplet energy of 2.58 eV, which is higher enough than the tethered red TADF guest (2.13 eV) to prevent the unwanted triplet energy back-transfer. Meanwhile, there is a good overlap between the absorption spectrum of the red guest and the photoluminescence (PL) spectrum of the polymeric host, ensuring the efficient energy transfer from host to guest. Consequently, the resultant polymers PFDMPE-R01 to PFDMPE-R10 in solid states show obvious red TADF properties with delayed fluorescence lifetimes of 126-191 μs and PL quantum yields of 0.18-0.55. Among them, PFDMPE-R05 obtains the best device performance, revealing a bright red electroluminescence peaked at 606 nm and a promising current efficiency of 10.3 cd/A (EQE = 5.6%). The results compete well with those of red phosphorescent polymers and indicate that PFDMPE other than PF is a suitable polymeric host for the construction of efficient red TADF polymers.

Full text of DOI:10.1021/acs.macromol.8b02050

Article
pubs.acs.org/Macromolecules
Cite This: Macromolecules XXXX, XXX, XXX−XXX
Red-Emitting Thermally Activated Delayed Fluorescence Polymers
with Poly(fluorene-co-3,3′-dimethyl diphenyl ether) as the
Backbone
Yun Yang,†,‡ Lei Zhao,† Shumeng Wang,*,† Junqiao Ding,*,†,‡ and Lixiang Wang†,‡
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, P. R. China
‡University of Science and Technology of China, Hefei 230026, P. R. China
S
* Supporting Information
ABSTRACT: A series of red-emitting thermally activated
delayed fluorescence (TADF) polymers have been designed
and synthesized based on poly(fluorene-co-3,3′-dimethyl
diphenyl ether) (PFDMPE) as the backbone. Compared
with polyfluorene (PF, 2.16 eV), the introduction of 3,3′-
dimethyl diphenyl ether into the main chain of PFDMPE
leads to the increased triplet energy of 2.58 eV, which is
higher enough than the tethered red TADF guest (2.13 eV) to
prevent the unwanted triplet energy back-transfer. Meanwhile,
there is a good overlap between the absorption spectrum of
the red guest and the photoluminescence (PL) spectrum of the polymeric host, ensuring the efficient energy transfer from host
to guest. Consequently, the resultant polymers PFDMPE-R01 to PFDMPE-R10 in solid states show obvious red TADF
properties with delayed fluorescence lifetimes of 126−191 μs and PL quantum yields of 0.18−0.55. Among them, PFDMPE-
R05 obtains the best device performance, revealing a bright red electroluminescence peaked at 606 nm and a promising current
efficiency of 10.3 cd/A (EQE = 5.6%). The results compete well with those of red phosphorescent polymers and indicate that
PFDMPE other than PF is a suitable polymeric host for the construction of efficient red TADF polymers.
example, Cheng et al. designed a series of conjugated polymers
with a backbone-donor/pendant-acceptor architecture, reveal-
ing bright orange TADF accompanied by an external quantum
efficiency (EQE) up to 19.4% and Commission Internationale
de L’Eclairage (CIE) coordinates of (0.51, 0.47).14 With an
insulating backbone and varying ratios of 2-(10H-phenothia-
zin-10-yl)dibenzothiophene-S,S-dioxide as a pendant TADF
unit, Bryce et al. reported green-emitting TADF polymers and
obtained a maximum EQE of 20.1% and CIE coordinates of
(0.36, 0.55).15 Until recently, a novel molecular design for
blue-emitting TADF polymers has been proposed based on a
nonconjugated polyethylene backbone with through-space
charge transfer effect between pendant electron donor (D)
and acceptor (A) units. A high EQE of 12.1% was achieved
together with CIE coordinates of (0.18, 0.27).17 It should be
noted that the EL wavelength of most reported TADF
polymers mainly covers 470−590 nm, and there are few
studies on red-emitting ones with an emission peak above 600
nm.20
1. INTRODUCTION
Since Friend et al. demonstrated the electroluminescence (EL)
from poly(p-phenylenevinylene) (PPV) in 1990,1 numerous
conjugated and nonconjugated polymers based on fluores-
cence, phosphorescence, and thermally activated delayed
fluorescence (TADF) have been explored for high-perform-
ance polymer light-emitting diodes (PLEDs).2−7 Among them,
fluorescent polymers suffer from the limited internal quantum
efficiency (IQE) below 25% because 75% of the electrically
generated triplet excitons are dissipated as heat.2,8,9 The
bottleneck is broken by phosphorescent polymers, which can
harvest both singlet and triplet excitons to realize a theoretical
100% IQE.3,10 However, these phosphorescent polymers seem
to be rather expensive and unsustainable given that they
contain Ir(III), Pt(II), and Os(II) complexes and so forth.
Therefore, an alternative approach for 100% IQE is developed
using TADF polymers without any rare metals.6,7,11 Thanks to
their small energy difference (ΔEST) between the lowest singlet
(S1) and triplet excited states (T1), triplet excitons can be
upconverted from T1 to S1 by absorbing environmental
thermal energy and then radiatively decay from S1 to yield
delayed fluorescence.12
Here we report the design and synthesis of red-emitting
TADF polymers for efficient PLEDs. As depicted in Figure 1, a
In view of the anticipated high efficiency and low cost,
nowadays much attention has been paid for the development
of TADF polymers showing different emissive colors.13−19 For
Received: September 24, 2018
Revised: November 14, 2018
© XXXX American Chemical Society
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Figure 1. Molecular structures of red-emitting TADF polymers (a) and the corresponding polymeric hosts and red dopant (b).
Figure 2. Photophysical and electrochemical properties of ROC8. (a) Chemical structure as well as HOMO and LUMO distributions simulated by
TD-DFT at the B3LYP/6-31G* level. For simplicity, octyloxy is replaced with methoxyl. (b) CV curves in DCM and THF for anodic and cathodic
sweeping, respectively. (c) UV−vis absorption, fluorescence, and phosphorescence spectra in toluene. (d) Transient decay spectra in an O2-free
cyclohexane.
red TADF emitter 2-(N-(4-octyloxyphenyl)diphenylamino)-
4′-anthraquinone (ROC8) acts as the side chain. At the same
time, poly(fluorene-co-3,3′-dimethyl diphenyl ether)
(PFDMPE) with a triplet energy higher than polyfluorene
(PF) is used as the backbone to avoid the unwanted loss of
triplet excitons. Consequently, the resultant polymers
PFDMPE-R01 to PFDMPE-R10 can well maintain the
TADF property of ROC8 benefiting from the effective energy
transfer from PFDMPE to ROC8 in solid states. Among them,
PFDMPE-R05 displays the best device performance and gives
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Figure 3. (a) Phosphorescence spectra of PF and PFDMPE in film compared with that of ROC8 in toluene under 77 K. (b) PL spectrum of
PFDMPE in film and UV−vis absorption spectrum of ROC8 in toluene. The shadow part shows their overlap.
a
Scheme 1. Synthetic Route of Red-Emitting TADF Polymers
a
Reagents and conditions: (i) 1,10-phenanthroline monohydrate, CuI, toluene, 110 °C; (ii) BBr3, DCM, 0 °C to rt; (iii) bis(pinacolato)diboron,
Pd(dppf)Cl2, KOAc; (iv) 2-bromoanthracene-9,10-dione, Pd(PPh3)4, K2CO3, Aliquat 336, H2O, toluene, 110 °C; (v) 1,8-dibromooctane,
tetrabutylammonium bromide, K2CO3, THF, 75 °C; (vi) 2,7-dibromo-9-octyl-9H-fluorene, KOH, DMF, 70 °C; (vii) 2,2,6,6-tetramethylheptane-
3,5-dione, CuI, Cs2CO3, DMF, 110 °C; (viii) Pd2(Dba)3, S-Phos, Aliquat 336, K2CO3, H2O, toluene, 96 °C.
a bright red EL peaked at 606 nm with a promising EQE of
5.6% and current efficiency of 10.3 cd/A.
reported to emit an efficient red light with a peak wavelength
of 624 nm and EQE of 12.5%. Promoted by this result, a
simple D−A type red TADF emitter ROC8 is then designed
based on anthraquinone as A and triphenylamine as D (Figure
1). Meanwhile, an alkyoxyl group is introduced into triphenyl-
amine to favor the next linkage between the TADF guest and
2. RESULTS AND DISCUSSION
2.1. Molecular Design. According to the literature,21
anthraquinone-based D−A−D type TADF materials have been
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polymeric host. The ground state geometry of ROC8 is
optimized using TD-DFT at the B3LYP/6-31G* level in the
gas phase (Figure 2a). The highest occupied molecular orbital
(HOMO) is mainly distributed on the alkyoxyl-functionalized
triphenylamine, whereas the lowest unoccupied molecular
orbital (LUMO) is localized on anthraquinone. The observed
good HOMO and LUMO separation leads to a relatively low
ΔEST (0.31 eV for calculated value; 0.18 eV for experimental
value), which is beneficial for the effective upconversion from
T1 to S1. Because of the small twisted dihedral angle between
anthraquinone and alkyoxyl-functionalized triphenylamine (33
°C), moreover, there exists a partial molecular orbital overlap
on the linked phenyl ring of anthraquinone to ensure a certain
oscillator strength and high photoluminescence quantum yield
(PLQY).22 Cyclic voltammetry (CV) was then used to
investigate the electrochemical property of ROC8 (Figure
2b). Both reversible oxidation and reduction processes appear
during the anodic and cathodic sweepings, and the HOMO
and LUMO energy levels of ROC8 are determined to be −5.21
and −3.51 eV, respectively. In addition, ROC8 exhibits a
distinct absorption band in the range 400−550 nm (Figure
2c), which can be ascribed to the charge transfer (CT) state
from alkyoxyl-functionalized triphenylamine to anthraquinone.
A maximum emission at about 593 nm is also observed for the
PL spectrum of ROC8 in cyclohexane together with a
moderate PLQY of 0.24. The corresponding prompt and
delayed fluorescent lifetimes are found to be 3.0 ns and 338 μs,
respectively (Figure 2d). The values match well with the D−
A−D type red TADF emitters21 and clearly indicate the TADF
nature of ROC8.
iodo-2-methylbenzene, 4,4′-oxybis(1-bromo-2-methylben-
zene) (7) was obtained and converted to its corresponding
borate 2,2′-(oxybis(2-methyl-4,1-phenylene))bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolane) (8). Finally, with 7-dibromo-9,9-
dioctyl-9H-fluorene, 6 and 8 in hand, a typical Suzuki
polymerization using Pd2(dba)3 as the catalyst and S-Phos as
the ligand was adopted to synthesize the red-emitting TADF
polymers PFDMPE-R01 to PFDMPE-R10. As determined by
gel permeation chromatography (GPC), the number-average
molecular weights (Mn) and polydispersity index (PDI) of
PFDMPE-R01 to PFDMPE-R10 are about 83−149 kDa and
1.6−1.8, respectively (Table 1), and they are found to be
Table 1. Physical Properties of Red-Emitting TADF
Polymers PFDMPE-R01 to PFDMPE-R010 Compared with
the PFDMPE Backbone
ROC8 in the
polymers (mol %)
b
c
d
feed
ratio
actual
a
Mn
(kDa) PDI
Tg
Td
b
polymers
ratio
(°C)
(°C)
PFDMPE
0
0
149
120
132
126
83
1.6
1.6
1.7
1.7
1.8
86
88
88
86
87
403
424
427
429
428
PFDMPE-R01
PFDMPE-R05
PFDMPE-R07
PFDMPE-R10
0.010
0.050
0.070
0.100
0.010
0.048
0.064
0.096
a
b
Calculated from the 1H NMR spectra. Determined by GPC in THF
c
using polystyrene as the standard. Glass transition temperatures
determined by TGA in N2. Decomposition temperatures corre-
d
sponding to a 5% weight loss.
On the other hand, as for side-chain type TADF polymers,
the triplet energy of the polymeric host is required to be larger
than that of the tethered TADF guest so as to prevent the
triplet energy back-transfer (TEBT) from guest to host.6,23−25
Unfortunately, PF has a triplet energy of about 2.16 eV (Figure
3a), very close to that of ROC8 (2.13 eV). So 3,3′-dimethyl
diphenyl ether is incorporated into PF to interrupt the
conjugation length of the backbone. And the resultant
polymeric host PFDMPE shows an enhanced triplet energy
of 2.58 eV, high enough to avoid the TEBT from ROC8 to
PFDMPE. Furthermore, there is a good overlap between the
absorption spectrum of ROC8 and the PL spectrum of
PFDMPE (Figure 3b). The observation implies the efficient
energy transfer from PFDMPE to ROC8, which will be
discussed below. With these considerations, it is expected that
PFDMPE other than PF can act as the good host of ROC8 for
the construction of red-emitting TADF polymers.
thermally stable with decomposition temperatures over 400 °C
and glass transition temperatures close to 90 °C (Figure S1).
Noticeably, the introduced content of ROC8 into the polymer
can be calculated quantitatively from their 1H NMR. There are
two characteristic proton signals at 8.34 and 8.51 ppm
originating from ROC8, which could be distinguished from
those of PFDMPE (Figure 4). Hence, by comparison of the
integrals of these two signals related to all the signals, the
actual ROC8 content is estimated to be well comparable to the
feed ratio. This suggests that the red TADF fragment ROC8
has been successfully incorporated into the backbone of
PFDMPE during polymerization.
2.2. Synthesis and Characterization. The synthetic
route of polymers PFDMPE-R01 to PFDMPE-R10 is shown in
Scheme 1. Starting from the commercially available 4-bromo-
N-phenylaniline and 1-iodo-4-methoxybenzene, 4-bromo-N-
(4-methoxyphenyl)diphenylamine (1) was prepared via a C−
N coupling, followed by demethylation and boric acid
esterification to give 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboro-
lan-2-yl)-N-(4-hydroxyphenyl)diphenylamine (3). Then a
Suzuki−Miyaura coupling was performed between 3 and 2-
bromoanthraquinone to produce 2-(N-(4-hydroxyphenyl)-
diphenylamino)-4′-anthraquinone (4), which was attached to
2,7-dibromo-9-octyl-9H-fluorene through a nonconjugated
linkage to form the key monomer 2-(N-(4-((8-(2,7-dibromo-
9-octylfluoren-9-yl)octyl)oxy)phenyl)diphenylamino)-4′-an-
thraquinone (6). At the same time, after a selective Ullmann
reaction between 4-bromo-3-methylphenol and 1-bromo-4-
Figure 4. 1H NMR spectra of red-emitting TADF polymers
PFDMPE-R01 to PFDMPE-R010 compared with PFDMPE and
ROC8.
D
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Figure 5. (a) UV−vis absorption spectra in films for red-emitting TADF polymers PFDMPE-R01 to PFDMPE-R010 (inset: CT absorption). (b)
Their corresponding PL spectra in films (inset: PL spectra in toluene).
Table 2. Photophysical Properties of Red-Emitting TADF Polymers PFDMPE-R01 to PFDMPE-R010 Compared with ROC8
a
a
b
c
c
d
compounds
λabs [nm]
λem [nm]
Φem
τp [ns]
τd [us]
S1/T1/ΔEST [eV]
ROC8
334/365/469
320/379/492
320/378/491
320/376/494
321/378/500
593
579
592
598
602
0.24
0.55
0.32
0.27
0.18
3.0
9.6
4.2
4.5
4.5
338
191
126
132
145
2.31/2.13/0.18
PFDMPE-R01
PFDMPE-R05
PFDMPE-R07
PFDMPE-R10
a
b
Measured in toluene for ROC8 and in film for red-emitting TADF polymers. Measured by integrating sphere in degassed toluene for ROC8 and
c
in film under N2 for red-emitting TADF polymers. Measured in degassed cyclohexane for ROC8 and in film under N2 for red-emitting TADF
d
polymers, and the prompt and delayed lifetimes (τp and τd) were calculated using τav = ∑Aiτi2/∑Aiτi. S1 and T1 were estimated from the onset of
the fluorescence and phosphorescence spectra, and ΔEST is the difference between S1 and T1.
2.3. Photophysical Properties. Figure 5 illustrates the
UV−vis and PL spectra for PFDMPE-R01 to PFDMPE-R10 in
films. As can be clearly seen, all the polymers exhibit one
intense absorption band peaked at 320 nm together with two
weak but discernible absorption bands in the ranges 350−400
and 400−550 nm (Figure 5a). According to the UV−vis
spectrum of ROC8, the former could be reasonably attributed
to the absorption of the polymeric backbone PFDMPE, and
the latter two are from the attached red TADF emitter ROC8.
Additionally, except for PFDMPF-R01 with an emission
residue of PFDMPE, an almost complete energy transfer
from PFDMPF to ROC8 is observed, leading to only ROC8
emission for PFDMPF-R05, PFDMPF-R07, and PFDMPF-
R10 (Figure 5b). By contrast, the emission from PFDMPF
dominates their whole PL spectra in solution associated with a
very weak emission from ROC8 (inset in Figure 5b). The
difference indicates that the intermolecular other than
intramolecular energy transfer plays an important role on the
photophysical properties of PFDMPE-R01 to PFDMPE-R10
in solid states.26 With the increasing feed ratio, moreover, the
emission maxima are obviously red-shifted from 579 nm of
PFDMPF-R01 to 602 nm of PFDMPF-R10 because of the
existing aggregation. Correspondingly, the measured PLQY is
reduced from 0.55 of PFDMPF-R01 to 0.18 of PFDMPF-R10
(Table 2).27
PFDMPF-R10 display delayed emissions with a similar lifetime
of 126−145 μs in addition to prompt emissions with a similar
lifetime of 4.2−4.5 ns. As mentioned above, the complete
energy transfer from the polymeric host to the attached TADF
fragment may contribute to the shorter lifetimes of PFDMPF-
R05, PFDMPF-R07, and PFDMPF-R10 compared with
PFDMPF-R01.28,29 Albeit this, they all emit delayed
fluorescence to some degree as a result of an initial intersystem
crossing (ISC) to the triplet state followed by repopulation of
the singlet state via reverse intersystem crossing (RISC).30
With PFDMPF-R05 as an example, the temperature depend-
ence of the transient PL is also investigated in the temperature
range 80−300 K (Figure S2). As one can see, the delayed
emission is gradually decreased when temperature is down
from 300 to 150 K. This means that the efficient T1 to S1
upconversion activated by the thermal energy is weakened,
which is a direct evidence of TADF, and the conversely
enhanced delayed emission from 150 to 80 K can be
tentatively ascribed to the predominant phosphorescence
under low temperature, consistent with the literature.31
2.4. EL Properties. To evaluate the EL properties of
PFDMPE-R01 to PFDMPE-R10, PLEDs were fabricated with
a structure of ITO/PEDOT:PSS (50 nm)/EML (40 nm)/
TmPyPB (50 nm)/LiF (1 nm)/Al. Here PEDOT:PSS stands
for poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate)
and serves as the hole-injection layer; TmPyPB stands for
1,3,5-tri(m-pyrid-3-ylphenyl)benzene and acts as the electron-
transporting layer;32 and the red-emitting TADF polymers
PFDMPE-R01 to PFDMPE-R10 are used as the emitting layer
(EML). Figure 7a−d plots the EL spectra, current density−
To probe the TADF properties of these polymers, their
transient PL spectra in neat films were also recorded under
nitrogen at 298 K. A prompt fluorescent lifetime of 9.6 ns as
well as a delayed fluorescent lifetime of 191 μs is observed for
PFDMPF-R01 (Figure 6); PFDMPF-R05, PFDMPF-R07, and
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Figure 6. Transient decay spectra in films for PFDMPE-R01 (a), PFDMPE-R05 (b), PFDMPE-R07 (c), and PFDMPE-R10 (d).
voltage, and luminance−voltage characteristics together with
the current density dependence of current efficiency and EQE.
The device performance is also summarized in Table 3. As one
can see, the EL is only from the red-emitting TADF polymers
although a small bathochromic shift is observed with respect to
their PL counterparts (Figure 7a). When the introduced
ROC8 content in the polymer increases from PFDMPE-R01 to
PFDMPE-R10, the EL spectra turn out to shift toward a long
wavelength, and an improved energy transfer efficiency is
obtained. Besides the major emission from the TADF guest,
PFDMPE-R01 still shows an obvious emission from the
polymeric host, whereas this residue is completely quenched
for PFDMPE-R05, PFDMPE-R07, and PFDMPE-R10. Their
EL maxima are 591, 606, 607, and 611 nm together with
corresponding CIE coordinates of (0.49, 0.42), (0.57, 0.42),
(0.58, 0.42), and (0.59, 0.41), respectively.
case, the favored charge injection and enhanced current
density are expected for PFDMPE-R10. Therefore, among
these polymers, PFDMPE-R05 achieves the best device
performance, revealing a maximum luminance of 1677 cd/
m2, a peak current efficiency of 10.3 cd/A, and a peak EQE of
5.6% (Figure 7c,d). The results can compete well with red-
emitting phosphorescent polymers,33−35 indicating the great
potential of red-emitting TADF polymers used for high-
performance PLEDs. Also, we note that the EQE decays
significantly to 1.05% at a high luminance of 500 cd/m2
(Figure S3 and Table 3). Similar to the literature,21 the long
delayed lifetime above 100 μs may be responsible for the
observed severe efficiency roll-off induced by triplet−triplet
annihilation.
3. CONCLUSIONS
It should be noted that the current density at the same
driving voltage first decreases from PFDMPE-R01 to
PFDMPE-R05 and PFDMPE-R07 and then goes up
considerably to PFDMPE-R10 (Figure 7b). Given that the
HOMO/LUMO levels of ROC8 (−5.20/−3.51 eV) locate
between those of PFDMPE (−6.03/−2.44 eV), ROC8 may act
as charge trap at a low doping concentration and lead to the
observed reduced current density for PFDMPE-R05 and
PFDMPE-R07. As the concentration of ROC8 elevates to
about 10%, carriers are not first injected into PFDMPE and
then trapped by ROC8 but directly injected into ROC8. In this
In summary, we demonstrate a series of red-emitting TADF
polymers with poly(fluorene-co-3,3′-dimethyl diphenyl ether)
as the backbone. Owing to its higher triplet energy than the red
guest and the good overlap between the guest absorption and
the host PL, an effective energy transfer is anticipated for the
resultant polymers PFDMPE-R01 to PFDMPE-R10 in solid
states. As a result, they can well maintain the TADF property
from the tethered guest, giving a peak current efficiency of 10.3
cd/A (EQE = 5.6%) and a bright red EL peaked at 606 nm.
This work, we believe, will shed light on the development of
red-emitting TADF polymers for high-performance PLEDs.
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Figure 7. Device performance for red-emitting TADF polymers PFDMPE-R01 to PFDMPE-R010: (a) EL spectra at 12 V; (b) current density−
voltage plots and energy level alignment inset; (c) luminance−voltage plots; and (d) current efficiency and EQE as a function of current density.
a
Table 3. Device Performance of Red-Emitting TADF Polymers PFDMPE-R01 to PFDMPE-R010
polymers
Von (V)
Lmax (cd/m2)
CEmax (cd/A)
PEmax (lm/W)
EQE (%)
λem (nm)
CIE (x, y)
PFDMPE-R01
PFDMPE-R05
PFDMPE-R07
PFDMPE-R10
10.2
9.8
8.6
1546
1677
1365
1275
9.3
10.3
8.3
2.5
3.2
2.7
2.1
4.07 (3.19)
5.62 (1.02)
4.64 (0.83)
2.90 (0.72)
591
606
607
611
(0.49, 0.42)
(0.57, 0.42)
(0.58, 0.42)
(0.59, 0.41)
6.4
4.8
a
Von: turn-on voltage at 1 cd/m2; Lmax: maximum luminance; CEmax: maximum current efficiency; PEmax: maximum power efficiency; EQE:
maximum external quantum efficiency, and data at 500 cd/m2 are given in parentheses.
ferrocene/ferrocenium (Fc/Fc+). Fluorescence lifetime were carried
out with Edinburgh fluorescence spectrometer (FLS980).
4. EXPERIMENTAL SECTION
4.1. Measurements and Characterization. H and 13C NMR
spectra were recorded with a Bruker Avance 400 NMR spectrometer.
MALDI/TOF (matrix-assisted laser desorption ionization/time-of-
flight) mass spectra were performed on an AXIMA CFR MS
apparatus (COMPACT). Molecular weights of the polymers were
determined by GPC in THF using polystyrene as the standard.
Thermal gravimetric analysis (TGA) and differential scanning
calorimetry (DSC) were performed under a flow of nitrogen with
PerkinElmer-TGA 7 and PerkinElmer-DSC7 systems, respectively.
UV−vis absorption and PL spectra were measured with a PerkinElmer
Lambda 35 UV−vis spectrometer and a PerkinElmer LS 50B
spectrofluorometer, respectively. The PLQYs of the TADF polymer
films on quartz plates were measured using a quantum yield
measurement system (C10027, Hamamatsu Photonics) excited at
375 nm. The CV was performed on a CHI660a electrochemical
analyzer with Bu4NClO4 (0.1 mol/L) as the electrolyte at a scan rate
of 100 mV/s. A glass carbon electrode, a saturated calomel electrode,
and a Pt wire were used as the working electrode, the reference
electrode, and the counter electrode, respectively. The model
compound ROC8 was tested in solutions (dichloromethane and
THF for anodic and cathodic sweeping, respectively), and the TADF
polymers were directly spin-coated on the working electrode for the
measurement in acetonitrile. All the potentials were calibrated by
1
4.2. Device Fabrication and Testing. The indium tin oxide
(ITO) (20 Ω/square) substrates were cleaned with acetone,
detergent, and distilled water and then in an ultrasonic solvent
bath. After baking in a heating chamber at 130 °C for 2 h, the ITO-
glass substrates were treated with UV-ozone for 25 min. First,
PEDOT:PSS (Batron-P4083, Bayer AG) was spin-coated on top of
the ITO at a speed of 5000 rpm for 60 s and baked at 120 °C for 45
min. After being transferred into a nitrogen-filled glovebox,
subsequently, solutions of the TADF polymers in toluene were
spin-coated on PEDOT:PSS as the emissive layer at a speed of 1500
rpm for 60 s and annealed at 80 °C for 0.5 h. Finally, the other layers
including TmPyPB (50 nm), LiF (1 nm), and Al (100 nm) were
deposited in a vacuum chamber at a base pressure of less than 4 ×
10−4 Pa. The EL spectra and CIE coordinates were measured using a
PR650 spectra colorimeter. The current−voltage and brightness−
voltage curves of devices were measured using a Keithley 2400/2000
source meter and a calibrated silicon photodiode. All the measure-
ments were performed at room temperature under ambient
conditions.
4.3. Synthesis. All chemicals and reagents were used as received
from commercial sources without further purification. Solvents for
G
DOI: 10.1021/acs.macromol.8b02050
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chemical synthesis were purified according to the standard
procedures.
ether/ethyl acetate (v/v = 20/1) as eluent to give 5 as a red powder
(8.63 g, 78%). H NMR (400 MHz, CDCl3): δ 8.51 (d, J = 1.5 Hz,
1H), 8.34 (dd, J = 8.5, 3.2 Hz, 3H), 7.98 (dd, J = 8.2, 1.7 Hz, 1H),
7.86−7.77 (m, 2H), 7.60 (d, J = 8.6 Hz, 2H), 7.29 (d, J = 7.9 Hz,
2H), 7.19−7.09 (m, 7H), 6.88 (d, J = 8.9 Hz, 2H), 3.96 (t, J = 6.4 Hz,
2H), 3.42 (t, J = 6.8 Hz, 2H), 1.96−1.72 (m, 4H), 1.61−1.25 (m,
8H).
1
4-Bromo-N-(4-methoxyphenyl)diphenylamine (1). 4-Bromodi-
phenylamine (40.00 g, 161.20 mmol), p-iodoanisole (49.05 g,
209.60 mmol), 1,10-phenanthroline monohydrate (2.90 g, 16.12
mmol), CuCl (1.61 g, 16.12 mmol), and KOH (90.16 g, 1610.00
mmol) were charged in a 1000 mL three-neck flask, and then 600 mL
of dry toluene was added. The mixture was heated to 110 °C under
argon and stirred for 36 h. After cooling to room temperature, the
mixture was extracted with dichloromethane, washed with deionized
water, dried by anhydrous sodium sulfate, and concentrated under
vacuum. The crude product was purified by column chromatography
on silica gel using petroleum ether/ethyl acetate (v/v = 25/1) as
eluent to give 1 as a colorless oil (27.00 g, 60%). 1H NMR (400 MHz,
C6D6): δ 7.12 (m, 2H), 7.08−6.97 (m, 4H), 6.93−6.87 (m, 2H),
6.86−6.80 (m, 1H), 6.78−6.71 (m, 2H), 6.69−6.62 (m, 2H), 3.27 (s,
3H).
4-Bromo-N-(4-hydroxyphenyl)diphenylamine (2). Compound 1
(26.70 g, 75.42 mmol) was charged into a 500 mL three-neck flask, to
which was added 300 mL of dry dichloromethane. Then BBr3 (21.42
mL, 2.65 g/mL) was dropwisely added to the flask under argon at 0
°C. After the mixture was stirred for 5 h, the reaction was quenched
by water. The mixture was washed with water, dried by anhydrous
sodium sulfate, and then concentrated. Purification of the crude
product by column chromatography on silica gel using petroleum
ether/dichloromethane (v/v = 10/1) as eluent give 2 as a colorless oil
(21.74 g, 85%). 1H NMR (400 MHz, d6-DMSO): δ 9.43 (s, 1H), 7.35
(d, J = 8.8 Hz, 2H), 7.26 (t, J = 7.8 Hz, 2H), 7.03−6.88 (m, 5H),
6.83−6.73 (m, 4H).
2-(N-(4-((8-(2,7-Dibromo-9-octyl-fluoren-9-yl)octyl)oxy)phenyl)-
diphenylamino)-4′-anthraquinone (6). A mixture of 5 (5.20 g, 7.90
mmol), 2,7-dibromo-9-octylfluorene (3.96 g, 9.08 mmol), and KOH
(4.42 g, 79.00 mmol) were dissolved in 150 mL of DMF under argon.
The mixture was heated to 70 °C and stirred for 12 h. After cooling to
room temperature, the mixture was extracted with dichloromethane
and washed with water. After the organic phase was dried by
anhydrous sodium sulfate and concentrated under vacuum, the crude
product was purified by column chromatography on silica gel with
petroleum ether/ethyl acetate (v/v = 30/1) as eluent. After
recrystallized from ethanol, the monomer 6 was obtained as a red
1
acicular crystal (5.30 g, 65%). H NMR (400 MHz, d6-DMSO): δ
8.37 (d, J = 1.6 Hz, 1H), 8.24 (m, 3H), 8.18 (m, 1H), 7.95 (m, 2H),
7.85−7.71 (m, 4H), 7.68 (d, J = 1.6 Hz, 2H), 7.58−7.49 (m, 2H),
7.37−7.30 (m, 2H), 7.08 (t, J = 8.0 Hz, 5H), 6.96 (m, 4H), 3.90 (t, J
= 6.2 Hz, 2H), 2.07−1.94 (m, 4H), 1.61 (m, 2H), 1.14 (m, 18H),
0.78 (t, J = 7.1 Hz, 3H), 0.44 (m, 4H). 13C NMR (126 MHz, CDCl3):
δ 183.43, 182.84, 156.34, 152.68, 152.07, 149.15, 147.39, 146.39,
139.77, 139.08, 138.43, 134.12, 133.92, 133.77, 133.67, 132.45,
131.40, 131.37, 130.90, 130.37, 130.17, 129.41, 129.30, 128.08,
127.90, 127.79, 127.36, 127.24, 127.18, 126.16, 124.58, 124.10,
123.00, 121.48, 121.32, 121.15, 115.48, 68.33, 57.15, 55.71, 40.17,
40.12, 37.98, 32.57, 31.81, 31.61, 29.94, 29.76, 29.24, 29.19, 29.17,
29.14, 29.10, 28.77, 25.95, 23.60, 22.50, 14.12. MALDI-TOF MS: m/
z 1013.3.
4,4′-Oxybis(1-bromo-2-methylbenzene) (7). 4-Bromo-3-methyl-
phenol (20.00 g, 107.00 mmol), 1-bromo-4-iodo-2-methylbenzene
(41.28 g, 139.00 mmol), CuI (0.20 g, 1.07 mmol), 2,2,6,6-
tetramethylheptane-3,5-dione (1.97 g, 10.70 mmol), and Cs2CO3
(69.76 g, 214 mmol) were added in 100 mL of DMF under argon.
The mixture was heated to 110 °C and stirred for 15 h. After the
reaction was finished, the mixture was extracted with dichloro-
methane. The combined organic phase was washed with water and
then dried by anhydrous sodium sulfate. After removal of the solvent
under vacuum, the crude product was purified by column
chromatography on silica gel with n-hexane as eluent to give 7 as a
white solid (26.00 g, 70%). 1H NMR (400 MHz, CDCl3): δ 7.45 (d, J
= 6.9 Hz, 2H), 6.87 (d, J = 2.8 Hz, 2H), 6.69 (dd, J = 8.6, 2.9 Hz,
2H), 2.36 (s, 6H).
2,2′-(Oxybis(2-methyl-4,1-phenylene))bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolane) (8). To a 250 mL three-neck flask was added 7
(15.00 g, 42.13 mmol), bis(pinacolato)diboron (27.82 g, 109.54
mmol), Pd(dppf)Cl2 (4.13 g, 5.06 mmol), KOAc (28.90 g, 294.91
mmol), and 120 mL of dry DMF under argon. The mixture was
heated to 110 °C and stirred for 24 h. After cooling to room
temperature, the mixture was extracted with dichloromethane three
times. The combined organic phase was washed with water, dried by
anhydrous sodium sulfate, and concentrated under vacuum. The
crude product was applied to column chromatography on silica gel
with petroleum ether/ethyl acetate (v/v = 30/1) as eluent. After
recrystallized from a mixture of methylene chloride and ethanol, the
monomer 8 was obtained as a white needle crystal (11.34 g, 60%). 1H
NMR (400 MHz, CDCl3): δ 7.73 (dd, J = 7.3, 1.5 Hz, 2H), 6.80 (s,
3H), 6.78 (s, 1H), 2.50 (s, 6H), 1.33 (s, 24H). 13C NMR (126 MHz,
CDCl3): δ 159.13, 147.47, 137.89, 120.17, 115 0.37, 83.35, 24.94,
21.89. MALDI-TOF MS: m/z 450.3.
General Synthesis of Red-Emitting TADF Polymers with
PFDMPE-R01 as an Example. 2,7-Dibromo-9,9-dioctylfluorene
(0.1357 g, 0.2475 mmol), monomer 6 (0.0025 g, 0.0025 mmol),
monomer 8 (0.1125 g, 0.25 mmol), Pd2(dba)3 (1.0 mg, 0.001 mmol),
2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (S-Phos) (3.1 mg,
0.0075 mmol), and Aliquat 336 (0.1 mL) were added to a mixture of
toluene (5 mL) and aqueous K2CO3 (2.5 mL, 2 M) under argon. The
4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)-N-(4-
hydroxyphenyl)diphenylamine (3). Compound 2 (17.37 g, 51.10
mmol), bis(pinacolato)diboron (19.46 g, 76.60 mmol), potassium
acetate (15.00 g, 153.3 mmol), and Pd(dppf)Cl2 (1.25 g, 1.53 mmol)
were dissolved in 150 mL of dry DMF under argon. The mixture was
stirred at 85 °C for 24 h. After cooling to room temperature, the
mixture was extracted with dichloromethane three times. The organic
phase was combined and washed with water, dried by anhydrous
sodium sulfate, and then concentrated under vacuum. The crude
product was applied to column chromatography on silica gel with
petroleum ether/ethyl acetate (v/v = 5/1) as eluent to give 3 as a
1
white powder (11.47 g, 58%). H NMR (400 MHz, d6-DMSO): δ
9.49 (s, 1H), 7.48 (d, J = 7.9 Hz, 2H), 7.29 (t, J = 7.6 Hz, 2H), 7.03
(d, J = 7.8 Hz, 3H), 6.94 (d, J = 8.4 Hz, 2H), 6.78 (dd, J = 7.8, 3.6 Hz,
4H), 1.26 (s, 12H).
2-(N-(4-Hydroxyphenyl)diphenylamino)-4′-anthraquinone (4).
Compound 3 (7.60 g, 19.64 mmol), 2-bromoanthracene-9,10-dione
(5.13 g, 17.85 mmol), tetrakis(triphenylphosphine)palladium (0.41 g,
0.36 mmol), and Aliquat 336 (0.1 mL) were added to a mixture of
toluene (200 mL) and aqueous K2CO3 (17.85 mL, 2 M) under argon.
The mixture was heated to 100 °C and stirred for 24 h. After cooling
to room temperature, the mixture was extracted with dichloromethane
and then washed with water. The organic phase was dried by
anhydrous sodium sulfate and then concentrated under vacuum. The
residue was purified by column chromatography on silica gel with
petroleum ether/ethyl acetate (v/v = 5/1) as eluent to give 4 as a red
1
powder (2.27 g, 75%). H NMR (400 MHz, d6-DMSO): δ 9.53 (s,
1H), 8.36 (s, 1H), 8.23 (d, J = 8.1 Hz, 3H), 8.17 (d, J = 8.0 Hz, 1H),
8.00−7.88 (m, 2H), 7.73 (d, J = 8.4 Hz, 2H), 7.33 (t, J = 7.7 Hz, 2H),
7.13−7.05 (m, 3H), 7.05−6.99 (m, 2H), 6.97 (d, J = 8.5 Hz, 2H),
6.81 (d, J = 8.5 Hz, 2H).
2-(N-(4-((8-Bromooctyl)oxy)phenyl)diphenylamino)-4′-anthra-
quinone (5). A mixture of 4 (7.85 g, 16.79 mmol), 1, 8-
dibromooctane (22.83 g, 83.95 mmol), K2CO3 (11.56 g, 83.95
mmol), and tetrabutylammonium bromide (0.27 g, 0.84 mmol) were
dissolved in 200 mL of THF under argon. The mixture was heated to
reflux and stirred for 12 h. After cooling to room temperature, the
mixture was extracted with dichloromethane three times. The
combined organic phase was dried by anhydrous sodium sulfate
and then concentrated under vacuum. Purification of the crude
product by column chromatography on silica gel with petroleum
H
DOI: 10.1021/acs.macromol.8b02050
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Article
mixture was heated to 95 °C and stirred for 5 h. Subsequently,
benzeneboronic acid (30 mg) in 5 mL of toluene was added, and the
mixture was refluxed for 5 h. Then 0.5 mL of bromobenzene was
added, and the mixture was kept refluxed for another 5 h. Finally,
sodium diethyldithiocarbamate trihydrate (1.0 g) dissolved in
deionized water (15 mL) was added into the mixture. The solution
was kept at 80 °C with vigorous stirring under argon for 24 h. After
cooling to room temperature, the mixture was extracted by
dichloromethane, which was washed five times with deionized water
and dried by anhydrous sodium sulfate. After removal of the solvent,
the resulting polymers were received by precipitation in methanol.
The final purification was performed by Soxhlet extraction with
acetone for about 24 h and then precipitated in methanol to give the
desired polymer PFDMPE-R01 (96.0 mg, 65%). 1H NMR (400 MHz,
CDCl3): δ 8.51 (s, 0.0109H), 8.34 (d, J = 6.4 Hz, 0.0329H), 7.98 (d, J
= 9.3 Hz, 0.0363H), 7.78 (d, J = 8.1 Hz, 2H), 7.59 (d, J = 8.6 Hz,
0.0661H), 7.52 (s, 0.0681H), 7.33 (d, J = 6.2 Hz, 6H), 7.17−7.10 (m,
0.1512H), 7.05 (s, 2H), 7.01 (d, J = 7.9 Hz, 2H), 6.85 (d, J = 8.5 Hz,
0.0745H), 3.90 (s, 0.0288H), 2.33 (s, 6H), 2.01 (s, 4H), 1.31−0.99
(m, 20H), 0.82 (t, J = 7.0 Hz, 6H), 0.76 (s, 4H). 13C NMR (101
MHz, CDCl3): δ 156.44, 150.85, 140.16, 139.65, 137.73, 137.40,
131.19, 128.14, 124.10, 120.64, 119.40, 116.26, 55.23, 40.51, 31.87,
30.11, 29.34, 29.28, 23.98, 22.70, 20.92, 14.16.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.8b02050.
■
S
Figures S1−S18 (DOCX)
AUTHOR INFORMATION
Corresponding Authors
*E-mail wangshumeng@ciac.ac.cn.
*E-mail junqiaod@ciac.ac.cn.
■
ORCID
Junqiao Ding: 0000-0001-7719-6599
Lixiang Wang: 0000-0002-4676-1927
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors acknowledge the financial support from the
National Key Research and Development Program
(2016YFB0401301), the 973 Project (2015CB655001), and
the National Natural Science Foundation of China (Nos.
51873205 and 51573183).
PFDMPE-R05 (106.8 mg, 70%). 2,7-Dibromo-9,9-dioctylfluorene
(0.1303 g, 0.2375 mmol), monomer 6 (0.0127 g, 0.0125 mmol), and
1
monomer 8 (0.1125 g, 0.25 mmol) were used. H NMR (400 MHz,
CDCl3): δ 8.51 (s, 0.0490H), 8.34 (m, 0.1448H), 7.97 (d, J = 7.5 Hz,
0.0810H), 7.78 (d, J = 8.0 Hz, 2H), 7.59 (d, J = 7.6 Hz, 0.1430H),
7.52 (s, 0.0784H), 7.33 (d, J = 7.0 Hz, 6H), 7.17−7.10 (m, 0.3770H),
7.05 (s, 2H), 7.01 (d, J = 8.1 Hz, 2H), 6.85 (d, J = 8.4 Hz, 0.2015H),
3.90 (s, 0.1039H), 2.33 (s, 6H), 2.01 (s, 4H), 1.31−0.99 (m, 20H),
0.82 (t, J = 7.0 Hz, 6H), 0.76 (s, 4H). 13C NMR (101 MHz, CDCl3):
δ 156.43, 150.85, 140.16, 139.65, 137.73, 137.40, 131.19, 128.14,
124.09, 120.64, 119.40, 116.26, 55.22, 40.51, 31.86, 30.10, 29.34,
29.28, 23.98, 22.70, 20.92, 14.17.
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1
monomer 8 (0.1125 g, 0.25 mmol) were used. H NMR (400 MHz,
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= 8.2 Hz, 0.1120H), 7.78 (d, J = 8.0 Hz, 2H), 7.59 (d, J = 8.5 Hz,
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1
monomer 8 (0.1125g, 0.25 mmol) were used. H NMR (400 MHz,
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CDCl3): δ 8.51 (s, 0.1030H), 8.33 (s, 0.2815H), 7.98 (d, J = 7.7 Hz,
0.1870H), 7.78 (d, J = 6.7 Hz, 2H), 7.59 (d, J = 7.7 Hz, 0.2692H),
7.52 (s, 0.1269H), 7.34 (s, 6H), 7.17−7.10 (m, 0.7105H), 7.05 (s,
2H), 7.01 (d, J = 6.9 Hz, 2H), 6.85 (d, J = 8.1 Hz, 0.2520H), 3.90 (s,
0.1800H), 2.33 (s, 6H), 2.01 (s, 4H), 1.31−0.99 (m, 20H), 0.82 (t, J
= 7.0 Hz, 6H), 0.76 (s, 4H). 13C NMR (101 MHz, CDCl3): δ 183.48,
182.96, 156.44, 150.86, 140.17, 139.66, 137.74, 137.40, 134.17,
134.00, 133.89, 133.74, 131.44, 131.19, 129.42, 128.14, 127.99,
127.86, 127.32, 127.26, 124.65, 124.10, 123.03, 121.67, 120.65,
119.40, 116.26, 115.56, 68.27, 55.23, 40.51, 31.86, 30.10, 29.34, 29.27,
26.06, 23.98, 22.69, 20.91, 14.16.
PFDMPE (102.6 mg, 70%). 2,7-Dibromo-9,9-dioctylfluorene
(0.1371 g, 0.25 mmol) and monomer 8 (0.1125 g, 0.2 5 mmol)
were used. 1H NMR (400 MHz, CDCl3): δ 7.78 (d, J = 8.0 Hz, 2H),
7.33 (d, J = 6.1 Hz, 6H), 7.05 (s, 2H), 7.00 (d, J = 8.2 Hz, 2H), 2.33
(s, 6H), 2.01 (s, 4H), 1.31−0.99 (m, 20H), 0.82 (t, J = 7.0 Hz, 6H),
0.76 (s, 4H). 13C NMR (101 MHz, CDCl3): δ 156.44, 150.85, 140.16,
139.65, 137.73, 137.40, 131.19, 128.14, 124.10, 120.64, 119.40,
116.26, 55.23, 40.51, 31.86, 30.11, 29.34, 29.28, 23.98, 22.70, 20.91,
14.16.
I
DOI: 10.1021/acs.macromol.8b02050
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DOI: 10.1021/acs.macromol.8b02050
Macromolecules XXXX, XXX, XXX−XXX