D–π–A polysulfones for blue electroluminescence

Article abstract of DOI:10.1002/pola.28233

Donor–π–acceptor type fluorene-based copolymers with a sulfone unit were designed and synthesized for application in efficient pure-blue light emitting. The electroluminescence behaviors of these copolymers were investigated by fabricating light-emitting diodes and electrochemical cell devices. The former device little functioned but the latter worked well. The electrochemical cell devices having a configuration of ITO/PEDOT:PSS/copolymer:ionic liquid/Al exhibited purplish blue electroluminescence with an emission maximum at 434 nm (CIE coordinates (x, y) = (0.17, 0.10)) measured at 7 V. The initial positive scan of the D–π–A polysulfone based light emitting electrochemical cell with a sweep rate of 0.1 V s^?1 afforded a maximum luminance of 1080 cd m^?2 with a current efficiency of 1.96 cd A^?1 at an operating voltage of 12.5 V.

Full text of DOI:10.1002/pola.28233

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
D–p–A Polysulfones for Blue Electroluminescence
1
,2
1,2
2,3
2,3,4,5
ZhongMin Geng, Go Sato, Kazuhiro Marumoto, Masashi Kijima
1
Institute of Materials Science, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba,
Ibaraki 305-8573, Japan
2
Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki
3
05-8573, Japan
3
Division of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki
3
05-8573, Japan
4
Algae Biomass and Energy System R&D Center (ABES), University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573,
Japan
5
National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Correspondence to: M. Kijima (E-mail: kijima@ims.tsukuba.ac.jp)
Received 3 June 2016; accepted 12 July 2016; published online 00 Month 2016
DOI: 10.1002/pola.28233
ABSTRACT: Donor–p–acceptor type fluorene-based copolymers
with a sulfone unit were designed and synthesized for applica-
tion in efficient pure-blue light emitting. The electrolumines-
cence behaviors of these copolymers were investigated by
fabricating light-emitting diodes and electrochemical cell devi-
ces. The former device little functioned but the latter worked
well. The electrochemical cell devices having a configuration of
ITO/PEDOT:PSS/copolymer:ionic liquid/Al exhibited purplish
blue electroluminescence with an emission maximum at
The initial positive scan of the D–p–A polysulfone based light
21
emitting electrochemical cell with a sweep rate of 0.1 V s
22
afforded a maximum luminance of 1080 cd m with a current
21
efficiency of 1.96 cd A at an operating voltage of 12.5 V. VC
2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
Chem. 2016, 00, 000–000
KEYWORDS: p-conjugation; donor-p-acceptor; polysulfones; fluo-
rene; light-emitting electrochemical cells
434 nm (CIE coordinates (x, y) 5 (0.17, 0.10)) measured at 7 V.
INTRODUCTION In the past decades, high performance
organic light-emitting diodes (OLED) with blue light emitting
polymers have attracted considerable scientific and commer-
cial interests for their potential utility in full-color dis-
larger than E of the polymer is applied between the electro-
g
des, the mobile ions redistribute to allow for making p–n
combination of the electrochemical dopants, which enable to
form excitons in the active layer. The presence of the mobile
ions facilitates reasonable conductivity of the doped layer
and makes electrical double layer interfaces, which contrib-
utes to lowering the barrier for charge injection and leads
independence of work functions of electrodes used in
1
,2
plays.
Development of novel high performance polymers
with pure blue light emission exceeding color coordinates in
the Commission Internationale de L’Eclairage (CIE) chroma-
ticity diagram within the standard blue region (NTSC (1987)
primary blue color (x 5 0.155, y 5 0.07); generally (x < 0.20
and y < 0.20 are preferable for deep blue) remains a great
challenge, since high efficiency and pure blue light emission
have been incompatible in the OLED devices bearing wide
1
2,13
LECs.
Although LECs have these advantages, a pure blue
LEC device with high efficiency has been difficult to be
achieved. So far, Chen et al. have developed a pale blue green
LEC [CIE(x, y) 5 (0.21, 0.33)] showing a maximum luminance
3
,4
22
bandgap (E ) polymer. While, another area-emitting poly-
g
(Lmax) of 5.3 cd m at 4 V with current efficiency (gmax) of
mer device having an architecture of light-emitting electro-
21 14
2
.6 cd A
.
He et al. have reported a pale greenish blue
5
–7
8
chemical cells (LECs)
has been proposed in 1995, and it
22
LEC [(CIE(x, y) 5 (0.20, 0.28)] with L
gmax of 0.65 cd A at 6.5 V.
of 39 cd m
and
max
has characteristics of less relying on kinds of charge-injective
21
15
9
10,11
electrodes compared to OLED. Polymer LECs
are basi-
cally a single layer device consisting of an emitting layer of
conjugated polymers blended with electrolytes or ionic
liquids between two electrodes. When an appropriate voltage
One strategy to obtain electroluminescence materials with
high efficiency might be to construct donor–p–acceptor (D–
p–A) type copolymers, because they generally possess high
Additional Supporting Information may be found in the online version of this article.
2016 Wiley Periodicals, Inc.
V
C
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000
1

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
0
(
2-ethylhexyl)fluorene (4), and 4,4 -bis(7-bromo-9,9-bis(2-
ethylhexyl)-9H-fluorene-2-yl)diphenylsulfone (5) shown in
Scheme 1 were prepared according to the reported methods
1
6,22,23
with modifications,
and the experimental details of these
compounds were described in the Supporting Information.
0
Poly[2,7-(9,9-bis(2-ethylhexyl)fluorene)-alt-4,4 -diphenylsulfone]
(
PFDSO). A mixture of 3 (0.42 g, 0.8 mmol), 2 (0.30 g, 0.8
2
3
mmol), aqueous K CO3 [2M (mol dm ), 1.88 mL] and
2
Pd(PPh ) (46.2 mg) in toluene (6.5 mL) was refluxed with
3
4
vigorous stirring for 3 days under an argon atmosphere.
After the reaction solution was cooled to room temperature,
the resultant polymer was precipitated from methanol/HCl
2
FIGURE 1 Chemical structures of PFDSO, and PF DSO.
aq, and reprecipitated from methanol/NH
3
aq and from
methanol, respectively. The precipitate was successively
washed and extracted with acetone, hexane, and CHCl3 by
fluorescence quantum yields and good charge carrier trans-
1
6
port properties. However, intramolecular charge–transfer
in the D–p–A structure of the copolymers enlarges p conju-
gation in the main chain and leads to undesirable red shifts
Soxhlet extraction. The CHCl extract was again precipitated
3
from methanol. The final product was dried under vacuum
1
overnight, affording a light yellow solid (0.396 g, 82%).
H
1
7
of fluorescence. Consequently, blue luminescence has basi-
NMR (400 MHz, CDCl ) d 5 8.07 (d, J 5 8.4 Hz 4H), 7.74–
3
cally limited to small-molecule D–p–A fluorophores such as
7
.80 (m, 6H), 7.56 (d, J 5 8.4 Hz 4H), 2.05 (d, J 5 5.2 Hz 4H),
1
8
arylamine-phosphine oxide linked materials. Thus, restric-
tion of p-conjugation is important for realization of blue
emission from these D–p–A copolymers.
13
0
.70–0.88 (m, 18H), 0.56–0.47 (m, 12H). C NMR (100 MHz,
CDCl ) d 5 151.6, 141.1, 137.8, 137.7, 128.2, 127.8, 126.5,
22.9, 120.5, 55.2, 44.3, 34.6, 33.7, 28.1, 27.0, 22.6, 14.0,
3
1
1
0.3. Anal Calc. for C41
H
50
O
2
S (606.91): C, 81.14; H, 8.30;
In this paper, new D–p–A type polymers with p-conjugation
are attempted to develop for efficient blue electrolumines-
cence. Sulfone was chosen as the electron-acceptor (A) unit for
Found: C, 80.14; H, 7.86.
0
Poly[2,7’-(9,9,9’9’-tetrakis(2-ethylhexyl)fluorene)-alt-4,4 -diphe-
1
9
its excellent electron injection properties and as the control-
ling unit for limitation of the p conjugation extent. On the other
hand, fluorene was selected as the emissive and electron-
donor (D) unit for hole injection and transport functions. Fur-
thermore, phenylene was linked between the D and A units as
p-junction for controlling the p-conjugation and conformation.
The tetrahedral structure of the phenylenesulfone linkage has
been not only key portion for manufacturing engineering plas-
2
nylsulfone] (PF DSO). Under an argon atmosphere, a solution
of bis(1,5-cyclooctadiene)nickel(0) (Ni(cod) ) (0.17 g, 0.62
2
mmol), 2,2’-bipyridine (bpy) (0.11 g, 0.71 mmol) and 1,5-
cyclooctadiene (cod) (0.15 g, 1.38 mmol) in DMF (2 mL) was
heated for 30 min at 80 8C. To the DMF solution was added
5
(0.31 g, 0.27 mmol) dissolved in THF (2 mL) under argon.
The reaction solution was heated for 3 days at 80 8C. After
the reaction solution was cooled to room temperature, the
resultant polymer was precipitated from methanol/HCl aq,
and reprecipitated from methanol/NH3 aq and from metha-
nol, respectively. The precipitate was successively extracted
2
0,21
tics of polysulfones
but also a sterically hindrance factor
for close packing of polymer chains in the solid state, which
could prevent excimer formation and fluorescence quenching.
Therefore, two D–p–A type copolymers, poly(2,7-dialkylfluor-
3
with acetone, hexane and CHCl by Soxhlet extraction. The
CHCl3 extract was again precipitated from methanol. The
0
0
ene-alt-4,4 -diphenylsulfone) (PFDSO) and poly(2,7 -bis(dial-
0
kylfluorene)-alt-4,4 -diphenylsulfone) (PF DSO), shown in
2
final product was dried under vacuum overnight, affording a
Figure 1 were designed, synthesized, and characterized.
1
light yellow solid (0.23 g, 84%). H NMR (400 MHz, CDCl )
3
EXPERIMENTAL
Materials and Methods
Reagents and solvents were purchased from Kanto Chemical,
Tokyo Chemical Industry, Aldrich and Nacalai Tesque. Tetrahy-
drofuran (THF) distilled after drying with sodium was stored
under an argon atmosphere. Dimethylformamide (DMF) and
CH Cl distilled after drying with CaH were stored under an
2
2
2
argon atmosphere. The other solvents and all commercially avail-
able reagents were used without further purification. Methyl-
trioctylammonium trifluoromethanesulfonate (MATS), an ionic
liquid, was purchased from Aldrich. Bis(4-bromophenyl)sulfide
(1), bis(4-bromophenyl)sulfone (2), 2,7- bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)–9,9-bis(2-ethylhexyl)fluorene (3), 7-
bromo(2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2yl)–9,9-bis
2
SCHEME 1 Synthetic routes of PFDSO and PF DSO.
2
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
TABLE 1 GPC and TGA Results of the Polymers
ultraviolet–ozone chamber. A thin layer (40 nm) of PEDOT:PSS
was spin-coated on the ITO at 3000 rpm in 3 min and air-dried
at 110 8C for 10 min on a hot plate. The substrate was trans-
M
n
M
w
T
d
21
21
a
b
Polymer
(kg mol
)
(kg mol
)
M
w
/M
n
DP
(8C)
ferred to a glove box under N atmosphere. The toluene solu-
2
tions of copolymers for OLED and copolymers and MATS at
various blending ratios for LEC were subsequently spin-coated
on the PEDOT:PSS layer. Al (100 nm) and LiF (0.5 nm) (in the
case of OLED) were deposited on the emitting layer with conven-
PFDSO
18.3
11.0
32.9
13.5
1.80
1.26
30.3
11.1
386
375
2
PF DSO
a
n
Degree of polymerization (DP) was estimated from M .
Temperature of 5% weight loss determined by TGA under an argon
b
tional thermal evaporation at the chamber pressure lower than
atmosphere.
24
5
2
3 10 Pa, which provided the devices with an active area of
2
3 2 mm . The thickness of emitting layers and PEDOT:PSS
d 5 8.08 (d, J 5 7.6 Hz 4H), 7.81–7.76 (m, 8H), 7.61–7.58 (m,
layers were measured using a stylus-type film thickness meter
(ULVAC E. S., Tokyo, Japan, Dektak). The luminance–current den-
sity–voltage (L–J–V) curves were measured using Keithley
2612A and TOPCON BM-9M with measurement angle at 0.2 Å.
1
3
8H), 2.08–2.07 (m, 8H), 0.90–0.51 (m, 60H). C NMR (100
MHz, CDCl ) d 5 153.9, 153.8, 145.0, 144.6, 141.8, 137.4,
3
1
3
37.2, 134.4, 133.9, 130.9, 128.2, 127.8, 120.2, 55.2, 44.3, 34.7,
3.6, 28.2, 27.1, 22.7, 14.0, 10.4. Anal Calc. for C H O S
6
8 86 2
(967.49): C, 84.42; H, 8.96; Found: C, 83.31; H, 9.43.
RESULTS AND DISCUSSION
Synthesis and General Characteristics
Measurements and Characterizations
The synthetic routes toward the monomers and polymers
are depicted in Scheme 1. 1-Bromo-4-iodobenzene was
reacted with sulfur in the presence of the copper catalyst to
give sulfide 1. Oxidation of 1 with KMnO4 gave sulfone 2.
Diboronic ester 3 was synthesized by coupling of 2,7-
dibromo-9,9- bis(2-ethylhexyl)fluorene and bis(pinacolato)-
All synthetic manipulations were performed by a standard
technique using a Schlenk tube under an argon atmosphere.
Column chromatography was performed using a silica gel
(Kanto Chem., 60N, 63–120 lm). The number-average molecu-
lar weight (M ) and the weight-average molecular weight (M )
n
w
of the polymers were estimated by a gel permeation chroma-
tography (GPC) system (Shimadzu, LC solution) using polysty-
rene standards with CHCl3 as an eluent. Nuclear magnetic
resonance (NMR) spectra were recorded on a JEOL JNM-ECS
diboron in the presence of PdCl (dppf). The reaction of
2
monolithiated 2,7-dibromo-9,9-bis(2-ethylhexyl)fluorene with
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
gave
1
13
monoboronic ester 4. The coupling reaction of 2 with two
equivalents of 4 gave 5. Suzuki coupling polymerization of 2
with 3 gave copolymer PFDSO. Homopolymerization of 5 by
4
00 spectrometer. The H and C chemical shifts are given in
units of (ppm) relative to (TMS) 5 0.00 and
CDCl ) 5 77.0 ppm, respectively. Photoabsorption in the
d
d
d
(
3
the Yamamoto reaction afforded PF DSO.
2
range of ultraviolet–visible (UV–vis) and photoluminescence
PL) measurements of the polymer samples in CHCl and in a
(
3
Both of the polymers had good solubility in the usual organ-
form of a drop-cast thin film coating on a quartz glass were
performed using a Shimadzu UV-1800 spectrophotometer and
an F-4500 fluorescence spectrophotometer (Hitachi) at room
ic solvents such as toluene, CHCl , and so forth. The polymer
3
structures were identified by NMR, IR, and elemental analy-
ses. The results of GPC are summarized in Table 1. The Mn
temperature. The fluorescence quantum yield (U ) in CHCl3
21
fl
of PFDSO and PF DSO were 18.3 and 11.0 kg mol , respec-
2
were relative to 9,10-diphenylanthracene in cyclohexane
(Ufl 5 0.90) as a standard. Elemental analyses were carried
tively, which were not so high but enough to investigate their
basic properties and to examine basic characteristics of
out with a Perkin-Elmer type 2400 apparatus. Thermal gravi-
metric analysis (TGA) and differential thermal analysis (DTA)
were carried out by an Extar 7000 TG/DTA (Seiko) analyzer at
21
a heating rate of 10 8C min in an argon atmosphere. Cyclic
voltammetry (CV) of polymers in thin film on a Pt disk was
2
1
performed at a scan rate of 50 mV s in acetonitrile contain-
ing 0.1M Et NBF at room temperature under Ar using a satu-
4
4
rated calomel electrode (SCE) as the reference and platinum
wire as the counter electrode. The electrochemical data (vs.
SCE) obtained by cyclic voltammetry was made a correction
2
4,25
with the redox potential (4.8 eV) of ferrocene/ferricinium.
Fabrications and Measurements of OLED and LEC Devices
The OLED devices were fabricated in the structure of ITO/
PEDOT:PSS/copolymer/LiF/Al, while the LEC devices were fab-
ricated in the configuration of ITO/PEDOT:PSS/copolymer:-
MATS/Al. The patterned ITO (conductivity: 10 X/square) glass
was precleaned by ultrasonication in 2-propanol and successive-
ly in acetone. The precleaned ITO glass was treated in an
FIGURE 2 TGA curves of the polymers.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000
3

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
2 3
FIGURE 3 UV–vis and PL spectra of PFDSO and PF DSO in CHCl (a) and film state (b).
polymer light emitting devices. TGA results are shown in Fig-
ure 2. Both of the copolymers showed temperatures of 5%
aggregations or interactions between the polymer chains in
the solid state. The optical band gap (Eg ) between highest
opt
weight loss (T ) higher than 370 8C.
occupied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) of the PFDSO estimated from the
onset of the absorption spectrum in the film state was 3.20
d
Optical and Electrochemical Properties and Their
Supports by DFT Calculation
eV, which was larger than that of PF DSO (3.05 eV). Similar-
2
The photophysical properties of dilute solution and thin
films of all the polymers were investigated by UV–vis and
PL, and the results are shown in Figure 3. The UV–vis and
PL spectra data for the polymers are summarized in Table 2.
ly, the PL spectra of PFDSO and PF DSO in the film state
were slightly red shifted compared with those in solution.
2
Electrochemical properties of the polymers were investigated
by CV. The cyclic voltammograms are shown in Figure 4 and
related data are summarized in Table 2. In the anodic scan,
both polymers showed irreversible oxidation waves. In the
Figure 3(a) shows the absorption and PL spectra of PFDSO
and PF
wavelength observed at 349 nm for PFDSO and 365 nm for
PF DSO are due to p–p* transition of the conjugated sys-
2 3
DSO in CHCl . The absorption maxima (kmax) in
case of PF DSO, the energy level of HOMO (EHOMO) estimated
2
2
from the onset oxidation potential was 25.79 eV, which was
higher about 0.26 eV than that of PFDSO (26.05 eV). This
tems. The absorption kmax of PF DSO is longer in wavelength
2
compared with that of PFDSO, which indicates that p-
2
could be attributed to the longer p-conjugation of PF DSO than
conjugation of PF DSO is longer than that of PFDSO. The
2
that of PFDSO. In the cathodic scan, PFDSO exhibited quasi-
photoluminescence kmax in solution were observed at
reversible reduction waves, whereas PF DSO showed weak
2
4
09 nm for PFDSO and 415 nm for PF DSO. The Stokes shift
irreversible ones. The energy levels of LUMO (ELUMO) of PFDSO
2
(Dk) of PFDSO in the solution was 60 nm, which was slight-
and PF DSO were 22.68 and 22.63 eV, respectively, according
2
ly larger than that of PF DSO (50 nm). The larger Dk is
to the onset potentials of reduction. From these results, degrees
2
attributed to the lager structural change between ground
and excited states, which might affect lowering Ufl.
of p-conjugation extents of these polymers mainly affect EHOMO.
ec
The bandgaps (E ) of PFDSO and PF DSO determined by cal-
g
2
culating from the electrochemical data of EHOMO and ELUMO
The absorption and PL spectra of PFDSO and PF DSO in the
thin film state are shown in Figure 3(b). The absorption
2
were 3.37 and 3.16 eV, respectively, which were comparable to
opt
g
E
values obtained from the absorption spectra.
bands of PFDSO and PF DSO in the film state are slightly
2
broadened and red-shifted compared with the absorption
spectra in solution, which indicates that there are some
In order to understand the difference of EHOMO values between
PFDSO and PF DSO, the electronic structures of arylsulfone-
2
TABLE 2 Optical Properties, HOMO–LUMO Energy Gaps, and the Energy Levels of the Polymers
kmax, Abs (nm)
kmax, PL (nm)
a
opt
g
ec
g
Polymer
in CHCl
3
Film
in CHCl
3
Film
U
fl
E
(eV)
EHOMO (eV)
E
LOMO (eV)
E
(eV)
PFDSO
349
365
350
368
409
415
414
420
0.60
0.68
3.20
3.05
26.05
25.79
22.68
22.63
3.37
3.16
2
PF DSO
a
3
Fluorescence quantum efficiencies in CHCl were determined by using 9,10-diphenylanthracene in cyclohexane (Ufl 5 0.90) as a standard.
4
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
copolymers based OLEDs did not emit or give only very weak
light, unfortunately. These results might be attributed to break-
ing of p-conjugation in the polymer chains by the sulfone unit,
which should significantly lower the conductivity of emitting
layer and interfere the carriers’ injection, transport, and
recombination.
The next attempt was to make LEC devices using these copoly-
mers. The LEC based on PFDSO and PF DSO were fabricated
2
with a device configuration of ITO/PEDOT:PSS (40 nm)/
copolymer:MATS/Al (100 nm). Incorporation of the
PEDOT:PSS layer in the LEC devices can significantly improve
the operation stability due to blockings of oxygen transfer
from ITO into the emissive layer and smoothing of anode sur-
face to inhibit electrical shorts as well as usual OLED devi-
2
6
ces.
The LEC devices as prepared were operated
continuously under nitrogen atmosphere, and significant deg-
radation in brightness was not observed after several times
scans. When the LEC devices were sealed with a cover glass
and an epoxy adhesive resin, they could be handled and oper-
ated continuously in air for many hours. MATS was used to
introduce mobile ions into the emitting copolymers to easily
2
FIGURE 4 Cyclic voltammograms of PFDSO and PF DSO.
2
sandwiched models for PFDSO and PF DSO were investigated
using density functional theory (DFT) in the Gaussian 09 pro-
gram at the B3LYP/6-31G (d) basis set. The optimized geome-
try and electron density distributions in the HOMO and LUMO
for the respective methyl substituted dimer models are shown
in Figure 5. It appears that the electrons well delocalized along
the whole fluorene and phenylene chains between the sulfone
units on both the HOMO and LUMO, and the scope of delocali-
2
7
process free-standing film in good quality. The active layer
consisted of the copolymers and MATS in the mass ratio of
5
1
0:1 was fabricated by spin coating at a speed of 1000 rpm for
min, giving a thin layer with approximate 65 nm thickness.
Firstly, time dependent luminance (L), current density (J),
zation of PF DSO is larger than that of PFDSO. The calculated
2
and current efficiency (g) curves of the PF DSO LEC devices
2
results of PF DSO showed the deeper EHOMO, similar ELUMO,
2
under applying a constant voltage higher than the turn on
voltage (Vturn on) were measured to examine the LEC pro-
cess, which are summarized in Figure 6. At the 10 V operat-
ing, L steeply increased and attained maximum luminance
and narrower E , in comparison with those of PFDSO, which is
g
consistent with the experimental results.
2
2
Electroluminescent Properties of D–p–A Polysulfones
In order to explore the application potential of PFDSO and
(L ) (602 cd m ) at about 190 s and decreased to 70 cd
max
2
2
m
after 1000 s. At a lower operating voltage of 9 V, after
PF DSO, electroluminescence performance was firstly investi-
an injection period about 100 s, L gradually increased to a
2
2
2
gated by using these polymers as an emitting layer material for
OLEDs with a device structure of ITO/poly(3,4-ethylenedioxy-
thiophene):poly(styrene sulfonate) (PEDOT: PSS) (40 nm)/
copolymer/LiF (0.5 nm)/Al (100 nm). In this case, these
L
m
(479 cd m ) by 760 s and slowly decreased to 70 cd
which was kept even after 3000 s. Considering the
max
2
2
change of g, electrochemical oxidation and reduction of
PF DSO surely proceeded at respective working electrodes
2
2
FIGURE 5 Geometry and orbitals of HOMO and LUMO of arylsulfone-sandwiched models for PFDSO and PF DSO, optimized by
DFT calculation with Gaussian 09 program at the B3LYP/6-31G(d) basis set.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000
5

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
2
FIGURE 8 L and J versus V curves of the PFDSO and PF DSO-
2
1
based LECs at a sweep rate of 0.01 V s
.
was negatively biased. As shown in Figure 7, the current
increased with increasing forward bias voltage, which indi-
2
FIGURE 6 Time-dependent curves of L, J, and g of PF DSO-
cated typical rectifying characteristics. The L
higher than
max
based LEC devices.
22
1
000 cd m was attained with the maximum current densi-
2
2
ty (Jmax) of 55 mV cm and the maximum current efficiency
during the injection period. These electrochemically doped
species are moved to each opposite electrode under the con-
stant applied voltage, and should recombine to form exciton
in the middle region of the electrolytic layer, being deacti-
vated by reactions with surrounding chemicals, or direct
electrolysis near the counter electrode. According to increase
of concentration of the redox species with time, an optimal
state for light emission with showing gmax could be attained
and gradually transferred to an equilibrium state in due
course.
21
(gmax) of 1.96 cd A at an operating voltage of 12.5 V. Over
this voltage, L suddenly decreased but J still increased, which
suggests that electrolyses of the electrolytes and polymers
occur beyond control of the reversible electrochemical dop-
ings. The V
of this device (at which luminance is larger
turn on
22
than 5 cd m ) was high about 10 V, which involves an ini-
tial time-consuming process to form p–n junction during the
21
0.1 V s
scan under limited mobility of ions in the solid-
state active layer.
Therefore, the PFDSO and PF DSO based LEC devices were
investigated under operation conditions with a slow sweep
2
Furthermore, the PF DSO based LEC device was operated
2
2
1
with a sweep rate of 0.1 V s same to the measuring condi-
tions of OLED. The forward bias current was obtained when
the ITO electrode was positively biased and the Al electrode
2
FIGURE 7 L and J versus V curves of PF DSO-based LEC at a
21
sweep rate of 0.1 V s
.
2
FIGURE 9 EL spectra of PFDSO and PF DSO-based LECs.
6
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
a
2
TABLE 3 Characteristics of PFDSO and PF DSO-Based LECs
22
22
21
Polymer
L
max (cd m [V])
J
max (mA cm [V])
g
max (cd A [V])
kmax, EL (nm)
CIE coordinates (x, y)
PFDSO
139 [8.5]
890 [6.8)
1080 [12.5]
50 [8.5]
56 [6.8]
55 [12.5]
0.28 [8.5]
1.60 [6.8]
1.96 [12.5]
449
434
–
0.18, 0.15
0.17, 0.10
–
PF
2
DSO
DSO
b
PF
2
a
b
21
The device structure was ITO/PEDOT:PSS (40 nm)/copolymer:MATS/Al
The LEC device was operated with a scan rate of 0.1 V s
.
21
(
100 nm), which was operated with a scan rate of 0.01 V s
.
21
rate of 0.01 V s , and the L–V and J–V curves were com-
pared (Fig. 8). The Vturn on of the PFDSO based LEC device
was about 7.4 V, which was higher compared with that of
respectively. Moreover, the PF DSO based device showed a
2
2
2
21
high Lmax of 1080 cd m
with gmax of 1.96 cd A
at an
2
1
operating voltage of 12.5 V with a sweep rate of 0.1 V s
.
the PF
2
DSO based one (5.6 V). L of the PFDSO based LEC
These results indicated that the D–p–A polysulfones are
effective emitting polymer materials with proper controlled
p-conjugation for blue LEC, but further modifications and
improvement of the LEC devices and their operating condi-
tions must be required for the practical application.
2
2
device increased rapidly up to 139 cd m and J of 50 mA
2
2
21
cm at 8.5 V with gmax of 0.28 cd A . On the other hand,
2
2
the PF DSO based LEC device showed L
of 890 cd m
with gmax of 1.60 cd A
2
max
2
2
21
and Jmax of 56 mV cm
were
observed at a rather small operating voltage of 6.8 V. It was
found that the PF DSO-based LEC showed higher perfor-
2
mance than the PFDSO-based one. The longer p-conjugation
ACKNOWLEDGMENTS
unit in PF DSO might enhance the emission performance.
2
We thanks Chemical Analysis Division, Research Facility Center
for Science and Technology, University of Tsukuba, for facilities
of the NMR, elemental analysis, and TGA.
The Vturn on are largely depend on the sweep rate, but obser-
21
vation of L–V curves with the slow sweep rate of 0.01 V s
suggested plausible values for Vturn on of these devices.
The electroluminescent (EL) spectra of both LEC devices
REFERENCES AND NOTES
based on PFDSO and PF DSO are shown in Figure 9, which
2
1
H. J. Liang, X. X. Wang, X. Y. Zhang, Z. Y. Ge, X. H. Ouyang,
exhibited EL peaks maxima at 449 and 434 nm and their
CIE coordinates were (0.18, 0.15) and (0.17, 0.10), respec-
tively. These results are also summarized in Table 3. Com-
pared to corresponding PL spectra in film state, each EL
spectrum is slightly red-shifted. The preserving blue light
emission of EL of this polymer LECs is due to the existence
of the tetrahedral diphenylsulfone unit in the electrolytic
medium, which has prevented intermolecular aggregation
between polymer chains.
S. D. Wang, Dyes Pigments 2014, 108, 57–63.
2
3
M. Kijima, IOP Conf. Ser. Mater. Sci. Eng. 2014, 54, 012017.
J. H. Seo, K. H. Lee, B. M. Seo, J. R. Koo, S. J. Moon, J. K.
Park, S. S. Yoon, Y. K. Kim, Org. Electron. 2010, 11, 1605–1612.
M. H. Ho, Y. S. Wu, S. W. Wen, T. M. Chen, C. H. Chen, Appl.
Phys. Lett. 2007, 91, 83515.
4
5
M. M. Richter, Chem. Rev. 2004, 104, 3003–3036.
6
S. M. Meier, D. Tordera, A. Perteg aꢀ s, C. Rold aꢀ n-Carmona, E.
Ort ꢀı , H. J. Bolink, Mater. Today 2014, 17, 217–223.
7
8
Z. Liu, W. Qi, G. Xu, Chem. Soc. Rev. 2015, 44, 3117–3142.
CONCLUSIONS
Q. Pei, G. Yu, C. Zhang, Y. Yang, A. J. Heeger, Science 1995,
A new series of D–p–A polysulfones for blue electrolumines-
cence were designed and synthesized by controlling p-
conjugation of fluorene based sequence with the sulfone
unit. These copolymers showed good solubility in common
organic solvents, enough high molecular weights to make
thin films, and good thermal stability showing about 380 8C
of temperature at 5 wt % loss in TGA. Both of them exhib-
ited blue-violet PL with high Ufl more than 0.60 in CHCl3,
while they showed purplish blue PL in the film state. They
had not so deep EHOMO (26.05, 25.79 eV) and proper
bandgaps for blue emission. The D–p–A structure enhanced
electrochemical redox activity of these polymers. Electrolu-
minescent properties of these polymers were investigated
for the applications in OLEDs and LECs. These copolymers
based LEC devices showed good performances, although the
OLED devices little worked. The LECs based on PFDSO and
269, 1086–1088.
9 A. Perteg aꢀ s, N. M. Shavaleev, D. Tordera, E. Ort ꢀı , M. K.
Nazeeruddin, H. J. Bolink, J. Mater. Chem. C 2014, 2, 1605–
1
611.
1
0 Y. Z. Bin, L. Ku, G. H. Er, P. Q. Bing, Sci. China Chem. 2013,
5
6, 1075–1086.
1
1 S. Tang, A. Sandstrom, J. Fang, L. Edman, J. Am. Chem.
Soc. 2012, 134, 14050–14055.
2 E. Zysman-Colman, J. D. Slinker, J. B. Parker, G. G.
Malliaras, S. Bernhard, Chem. Mater. 2008, 20, 388–396.
3 S. van Reenen, P. Matyba, A. Dzwilewski, R. A. J. Janssen,
L. Edman, M. Kemerink, J. Am. Chem. Soc. 2010, 132, 13776–
1
1
1
3781.
1
2
4 B. Chen, Y. H. Li, W. Yang, W. Luo, H. B. Wu, Org. Electron.
011, 12, 766–773.
1
5 L. He, L. Duan, J. Qiao, R. J. Wang, P. Wei, L. D. Wang, Y.
Qiu, Adv. Funct. Mater. 2008, 18, 2123–2131.
PF DSO exhibited EL peaked at 449 and 434 nm with deep
blue region of CIE coordinates, (0.18, 0.15) and (0.17, 0.10),
16 J. Ye, Z. Chen, M. K. Fung, C. Zheng, X. Ou, X. Zhang, Y.
Yuan, C. S. Lee, Chem. Mater. 2013, 25, 2630–2637.
2
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000
7

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
1
7 S. L. Lin, L. H. Chan, R. H. Lee, M. Y. Yen, W. J. Kuo, C. T.
Chen, R. J. Jeng, Adv. Mater. 2008, 20, 3947–3952.
8 C. Liu, Y. Gu, Q. Fu, N. Sun, C. Zhong, D. Ma, J. Qin, C.
Yang, Chem. Eur. J. 2012, 18, 13828–13835.
23 R. Abbel, C. Grenier, M. J. Pouderooijen, J. W. Stouwdam,
P. E. L. G. Lecl e` re, R. P. Sijbesma, E. W. Meijer, A. P. H. J.
Schenning, J. Am. Chem. Soc. 2009, 131, 833–843.
1
24 J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt,
H. B
554.
aꢀ ssler, M. Porsch, J. Daub, Adv. Mater. 1995, 7, 551–
1
2
9 H. Sasabe, Y. Seino, M. Kimura, J. Kido, Chem. Mater. 2012,
4, 1404–1406.
20 F. Lufrano, G. Squadrito, A. Patti, E. Passalacqua, J. Appl.
25 A. K. Agrawal, S. A. Jenekhe, Chem. Mater. 1996, 85, 579–
Polym. Sci. 2000, 77, 1250–1256.
1 A. Filimon, R. M. Albu, E. Avram, S. Ioan, J. Macromol. Sci.
B: Phys. 2013, 52, 545–560.
2 Y. Lin, Y. Chen, T. L. Ye, Z. K. Chen, Y. F. Dai, D. G. Ma, J.
589.
2
26 Q. J. Sun, C. H. Yang, G. F. He, Y. F. Li, H. Q. Wang, Synth.
Met. 2003, 138, 561–565.
2
27 M. C. Ho, C. H. Chao, C. H. Chen, R. J. Wu, W. T. Whang,
Macromolecules 2012, 45, 3010–3016.
Photochem. Photobiol. A Chem. 2012, 230, 55–64.
8
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 00, 000–000