Synthesis of pure blue emissive poly(2,7-carbazole)s anchored by electron donor pendant

Article abstract of DOI:10.1002/pola.29523

Three novel poly(2,7-carbazole)s having hole injection and transporting pendent moieties of carbazole and triphenylamine at the N-position were synthesized for achieving pure blue electroluminescence. The N-pendants in the polymers correspond to N-phenylcarbazol-2-yl (P1), N,N-diphenylamino-N-phenylcarabazol-2-yl (P2), and 4-phenyl having a hydrocarbon chain with a triphenylamine terminal (P3), respectively. Electronic, optical, and electroluminescence properties of these polymers were compared with those of a poly(2,7-carbazole) directly connected with triphenylamine at the N-position (P0) having an aggregation-induced emissive property. The photoluminescence (PL) spectra suggested that they could emit in the region of blue light in the film state. Especially, P2 that has the fixed and large diphenylaminocarbazolyl pendant showed a deep-blue fluorescence with CIE(x, y) = (0.15, 0.07). The P0, P2, and P3 based light emitting diode devices showed maximum electroluminescence wavelengths in the range of 430–450 nm. The P2 device showed pure blue emission (CIE[x, y] = [0.18, 0.16]), high luminance (1130 cd/m²) and current density (628 mA/cm²) at 8 V, whereas low-energy emissions around 500–600 nm were emerged at higher than 9 V. The P0 and P3 devices also showed a blue electroluminescence in the range of 8–11 V, but their luminance and efficiency were low.

Full text of DOI:10.1002/pola.29523

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Synthesis of pure blue emissive poly(2,7-carbazole)s anchored by electron
donor pendant
3
Takashi Inada,1 Toshinobu Shinnai,2 Masashi Kijima
1Institute of Materials Science, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba,
Ibaraki 305-8573, Japan
2Central Research Laboratory Technology and Development Division, Kanto Chemical Co., Inc., 1-7-1 Inari, Soka-City, Saitama
340-0003, Japan
3Department of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki
305-8573, Japan
Correspondence to: M. Kijima (E-mail: kijima@ims.tsukuba.ac.jp)
Received 26 July 2019; Revised 25 September 2019; accepted 26 September 2019
DOI: 10.1002/pola.29523
ABSTRACT: Three novel poly(2,7-carbazole)s having hole injection
and transporting pendent moieties of carbazole and triphenylamine
at the N-position were synthesized for achieving pure blue elec-
troluminescence. The N-pendants in the polymers correspond to
N-phenylcarbazol-2-yl (P1), N,N-diphenylamino-N-phenylcarabazol-
2-yl (P2), and 4-phenyl having a hydrocarbon chain with a
triphenylamine terminal (P3), respectively. Electronic, optical,
and electroluminescence properties of these polymers were
compared with those of a poly(2,7-carbazole) directly connected with
triphenylamine at the N-position (P0) having an aggregation-induced
emissive property. The photoluminescence (PL) spectra suggested
that they could emit in the region of blue light in the film state. Espe-
cially, P2 that has the fixed and large diphenylaminocarbazolyl
pendant showed a deep-blue fluorescence with CIE(x, y) = (0.15, 0.07).
The P0, P2, and P3 based light emitting diode devices showed maxi-
mum electroluminescence wavelengths in the range of 430–450 nm.
The P2 device showed pure blue emission (CIE[x, y] = [0.18, 0.16]),
high luminance (1130 cd/m2) and current density (628 mA/cm2) at 8 V,
whereas low-energy emissions around 500–600 nm were emerged at
higher than 9 V. The P0 and P3 devices also showed a blue electrolu-
minescence in the range of 8–11 V, but their luminance and efficiency
were low. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
Chem. 2019
KEYWORDS: conjugated polymers; light-emitting diodes (LED);
luminescence; polycarbazole; donor pendant
Conjugated poly(2,7-carbazole)s are a structural analog of
polyfluorenes whose carbon atom at 9-position is replaced with
nitrogen to form a strained planer unit of an imino-bridged
biphenylylene. This structural difference extinguishes the keto-
defect and realizes a pure blue color emission with high brightness
on the OLED application. Thus, the polycarbazole has been consid-
ered as a candidate for blue light emitting materials as an alternative
to polyfluorene for a long time.13,14 Poly(2,7-carbazole)s having a
phenyl group at the N-position showed a good solubility, high
number-average molecular weight, and luminescent proper-
ties superior to N-alkyl derivatives in terms of blue emission
and fluorescence quantum yields,15 which is due to their rigid
structures. It also has been reported that several types of poly
(N-phenyl-2,7-carbazole)s have some good properties for
application to PLEDs.15–21 The poly(N-phenyl-2,7-carbazole)
directly linked with a diphenylamino pendant (P0 shown in
Fig. 1) displayed a pure blue emission in Commission Interna-
tional de I’Éclairange (CIE) chromaticity diagram (x, y = 0.16,
INTRODUCTION Polymer light-emitting diode (PLED) has
much attracted attention because it has great potential to
fabricate flexible and large area illuminating devices and
replace the traditional liquid crystal display.1,2 Polymers can
simplify a process of fabricating large area organic light-
emitting diodes (OLEDs) by solution-based processing such
as gravure, inkjet, and screen. 3–7 To realize a full-color PLED
display, development of a polymer emitting a pure blue color,
the highest energy emission in RGB colors, is indispensable
in addition to a good stability and high quantum efficiency of
the PLED devices.
Polyfluorene-based conjugated polymer materials have been
investigated for blue-light emitting materials8–10 and could show
blue emissions and good brightness on the OLED application,
although they give rise to change of emitting color from blue to
green due to the presence of a residual keto-defect at 9-position
of fluorene.11,12
Additional supporting information may be found in the online version of this article.
© 2019 Wiley Periodicals, Inc.
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EXPERIMENTAL
General Method Instrumentation
N
n
All synthetic manipulations were performed by a standard
technique using a Schlenk tube under an argon atmosphere. Col-
umn chromatography was performed using silica gel (Kanto
Chem., 60 N, 63–120 μm). NMR spectra were recorded on JEOL
EX-270 spectrometer. H and C chemical shifts are given in units
of δ (ppm) relative to δ (TMS) = 0.00 and δ (CHCl3) = 77.0 ppm,
respectively. Elemental analyses were carried out with a Perkin-
Elmer type 2400. The number-average molecular weight (Mn)
and the weight-average molecular weight (Mw) of the polymers
were estimated by gel permeation chromatography (GPC)
equipped with a UV detector (Jasco) based on polystyrene stan-
dards using THF as the eluent. UV–vis and PL measurements of the
polymer samples in CHCl3 and in a form of a thin film coating on
quartz glass were performed using a U-3500 spectrophotometer
(Hitachi) and an F-4500 fluorescence spectrophotometer (Hitachi).
The measurement of the HOMO energy level of the polymer films
on a Pt disk was performed at a scan rate of 50 mVÁs−1 in acetoni-
trile (0.1 M Et4NBF4) at room temperature under Ar using a satu-
rated calomel electrode (SCE) as the reference and a platinum wire
as the counter electrode. The electrochemical data (vs. SCE)
obtained by cyclic voltammetry were corrected with the redox
potential (4.8 eV) of ferrocene/ferrocenium+.23
Ar
P0:
P1:
EHO
N
Ar =
C H
8
N
Ar =
17
OMe
EHO
P3:
P2:
EHO
Ar =
N
N
N
O(CH ) O
2 10
Ar =
OMe
EHO
O
EHO =
FIGURE 1 Chemical structures of poly(2,7-carbazaole)s having
hole injection and transporting moieties.
0.17) with the 1250 cd/m2 luminance in the device configura-
tion of ITO/PEDOT-PSS/polymer/Ba/Al.18 A poly(N-phenyl-
2,7-carbazole) with a long carbazolyl side chain at p-position
of the N-phenyl group also showed a high efficiency of
2.05 cd/A at 4 V.17
Device Fabrication
An ITO glass was cleaned by ultrasonication in a solution of
detergent for 5 min. It was rinsed with flowing water, dried with
a spin coater (3000 rpm for 60 s), and then treated with ultravi-
olet irradiation (Filgen Inc., UV253, Nagoya, Japan) for 20 min.
In the previous study, poly(2,7-carbazole)s having
triarylamine at N-position showed small conformational
change of the polymer backbone between solution and film
states considering from little change of their absorption and
fluorescence spectra. Their small Stokes shifts also suggest
that these polymers have little structural difference between
the ground and excited states.16 In addition, the triarylamino
group has good hole injection and transport properties, which
is expected to work as an interlayer buffering moiety
to protect the electron donor polycarbazole from peroxidation
and maintain carrier balance of the electroluminescence
(EL) device.10,17 However, fluorescence quantum yields of sev-
eral poly(N-triarylamino-2,7-carbazole)s in CHCl3 were quite
low (ϕf < 0.2) compared to usual poly(N-phenylcarbazsole)s
(ϕf ≳ 0.7),16 which might be disadvantageous for applicative
works in soft media such as light emitting electrochemical
cells.22 Introduction of a rigid carbazolyl group with electron-
donor function might be substitute for superior role of the
triarylamino pendent in the poly(N-triarylamino-2,7-carbazole)s
and suppress quenching in solution.
PEDOT-PSS aq (Baytoron PVP Al 4083) that had been filtered
through a 0.45-mm pore filter was spin coated onto the cleaned
ITO glass at 200 rpm for 5 s and 1000 rpm for 60 s. To remove
ꢀ
water, it was dried on a hot plate for 15 min at 200 C. A poly-
mer solution (such as in toluene, chloroform, o-xylene, anisole,
THF, and their mixture) that filtered out through a 0.5-mm pore
filter was spin coated over the PEDOT-PSS-coated ITO glass at
500 rpm for 5 s and 2000 rpm for 60 s. To remove solvent, it
was dried under a reduced pressure (ca. 40 Pa). Finally, CsF and
Al were vacuum deposited on the substrate, respectively, under
a high vacuum using an Ulvac VTR-350 M/ERH. The device con-
figuration was ITO (150 nm)/PEDOT-PSS (90 nm)/polymer (P0:
100 nm, P2: 54 nm, P3: 70 nm)/CsF (2 nm)/Al (150 nm). The
evaluation of the PLED devices that have an active surface area
of 2 mm × 2 mm was carried out with a Hamamatsu C9920-12
system with a sweep rate of 1.25 V s−1
.
In this article, we synthesized novel poly(N-aryl-2,7-carbazole)s
in order to develop high-performance blue light emitting poly-
mers for OLED application according to the synthetic strategy of
direct connection of a rigid carbazolyl group (P1) and a sterically
hindered N-triphenylaminated carbazolyl group (P2) with the
2,7-carbazolylene at the N-position as shown in Figure 1. To
investigate the effect of the triarylamine group in the polymer,
properties of P0 and P3 also constructed are compared with
those of P1 and P2.
Materials
DMF, CH2Cl2, and toluene were distilled after drying with CaH2
under an argon atmosphere. THF and 1,4-dioxane were distilled
after drying with sodium under an Ar atmosphere. The other sol-
vents and all commercially available reagents were used without
further purification. 2-Bromo-7-methoxy-9H-carbazole (2),24
2,7-dichloro-9H-carbazole (4),25and 1-(2-ethylhexylxy)-
4-iodobenzene (10)26 were prepared according to the litera-
ture procedures.
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Detailed preparation procedures and analysis data for other
compounds (1, 3, 6, 7, 8, 9, 13, 14, 15, 16), and polymers
(P1, P2, and P3) shown in Scheme 1 and Scheme 2 were
shown in the Supporting Information. Positions of compounds
5, 11, and 16 are illustrated in the Supporting Information
Figures S1–S3.
a
I
H N
2
34%
1
Br
OMe
I
OMe
b, c
N
H
N
2
+
3
1
C H
8
17
Cl
Cl
Cl
Cl
N
N
b
d
n
N
H
+
3
4
C H
8 17
N
C H
8
N
17
5
P1
84%
96%
OMe
OMe
Br
OMe
N
H
Br
OMe
f
I
OMe
2
e
N
N
+
F
NO
NO
2
2
88%
72%
NO
7
6
2
Cl
Cl
Cl
Cl
N
N
h
g
Cl
Cl
N
H
4
H N
N
O N
N
2
2
+
7
9
8
OMe
OMe
84%
96%
EHO =
O
Cl
Cl
N
N
n
EHO
EHO
EHO
9
g
d
+
N
N
N
N
EHO
I
11
P2
10
OMe
98%
OMe
49%
EHO
SCHEME 1 Syntheses of monomers (5 and 11), P1, and P2. (a) NaNO2, H2SO4, KI, acetone, H2O, 0 ꢀC to 65 ꢀC; (b) CuI, K3PO4, CHDA,
1,4-dioxane, 100 ꢀC; (c) CuI, NaI, CHDA, 1,4-dioxane, 100 ꢀC; (d) Ni(COD)2, COD, bpy, DMF-THF, 70 ꢀC; (e) K2CO3, DMF, 145 ꢀC; (f) KI,
I2, Ni, DMF, 150 ꢀC; (g) Pd(OAc)2, P(t-Bu)3, t-BuONa, toluene, 110 ꢀC; (h) SnCl2˙2H2O, EtOH, reflux.
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2,7-Dichloro-N-[2-Methoxy-N-(4-Octylphenyl) Carbazol-
7-yl]Carbazole (5)
C59H61N3Cl2O3: C, 76.11; H, 6.60; N, 4.51. Found: C, 75.59; H,
6.68; N, 4.34.
A mixture of 4 (135 mg, 0.57 mmol), CuI (4.6 mg, 0.024 mmol),
potassium phosphate (306 mg, 1.44 mmol), 1,4-dioxane
(2 mL), trans-1,2-cyclohexanediamine (11 mg, 0ꢀ.096 mmol)
and 3 (244 mg, 0.48 mmol) was stirred at 100 C for 24 h.
After the reaction was cooled to room temperature, the
reaction mixture was subjected to column chromatography on
silica gel eluted with CH2Cl2/hexane (1:4) to give 5 (251 mg,
84% yield) as a white solid.
2,7-Dichloro-N-[4-[[10-(4-(N,N-Bis(4-t-Butylphenyl)-
Aminophenoxy))Decyl]Oxy]Phenyl]Carbazole (17)
A mixture of 16 (200 mg, 0.35 mmol), Pd(OAc)2 (3.93 mg,
0.018 mmol), sodium t-butoxide (168 mg, 1.75 mmol), toluene
(5 mL), P(t-Bu)3 (10 wt % in hexane [102 μL, 0.035 mmol])
and 12 (452 mg, 1.74 mmol) was stirred at 110 ꢀC for 38 h.
After the reaction was cooled to the room temperature,
CH2Cl2 was added to the reaction mixture and subjected to
short-path column chromatography on silica gel. After evapo-
ration of the solvent, the residue was subjected to column
chromatography on silica gel eluted with hexane/CH2Cl2 (4:1)
to give 17 (162 mg, 55% yield) as a pale yellow solid. 1H
NMR (CDCl3, 270 MHz): δ 7.97 (d, J = 8.6 Hz, 2H; a), 7.68–7.60
(6H; 7, 10), 7.36 (d, J = 8.9 Hz, 2H; 2), 7.38–7.33 (4H; 3, b),
7.22–7.16 (8H; 6, 11, d), 4.06 (4H; ─OCH2─), 1.91–1.73 (4H;
─OCH2CH2─), 1.66 (4H; ─CH2─) 1.48–1.27 (26H; ─CH3,
─CH2─).; 13C NMR (CDCl3, 67.5 MHz): δ 158.9 (5), 155.3 (4),
146.1 (12), 144.5 (9), 142.3 (8), 141.1 (e), 132.2 (1), 129.0 (c),
128.7 (2), 127.2 (11), 125.8 (10), 122.3 (6), 121.0 (a), 120.9
(f), 120.5 (7), 116.3 (3), 115.8 (b), 110.2 (d), 68.4 (─OCH2─),
68.2 (─OCH2─), 34.2 (─C(CH3)3), 31.7 (─C(CH3)3), 29.6
(─CH2─), 29.4 (─CH2─), 26.1 (─CH2─). IR (KBr):2930, 1592,
1512, 1455, 1237, 1066, 829, 795 cm−1; Anal. Calcd for
1H NMR (CDCl3, 270 MHz): δ 8.12 (d, J = 8.1 Hz, 1H; 1), 7.98
(d, J = 8.6 Hz, 1H; 12), 7.87 (d, J = 8.4 Hz, 2H; a), 7.38–7.11
(10H; b, d, 2, 4, 14, 15), 6.88 (dd, J = 8.6, 2.3 Hz, 1H; 11), 6.81
(d, J = 2.2 Hz, 1H; 9), 3.78 (s, 3H; ─OCH3), 2.58 (t, 2H;
─Ar─CH2─), 1.61–1.53 (m, 2H; ─Ar─CH2CH2─), 1.24–1.17
(10H; ─CH2─), 0.80–0.75 (m, 3H; ─CH3).; 13C NMR (CDCl3,
67.5 MHz): δ 159.5 (10), 143.3 (3), 142.9 (5), 142.4 (e), 141.8
(8), 134.3 (13), 132.6 (16), 131.8 (c), 129.9 (15), 126.6 (14),
123.5 (7), 121.2 (1), 121.0 (12), 120.9 (a), 120.6 (b), 118.9
(f), 116.3 (6), 110.2 (d), 109.1 (2), 108.5 (4, 11), 94.1 (9),
55.7 (─OCH3), 48.1 (─Ar─CH2─), 38.6 (─CH2─), 35.8
(─CH2─), 31.9 (─CH2─), 31.4 (─CH2─), 29.5 (─CH2─), 29.3
(─CH2─), 23.2 (─CH2─), 22.7 (─CH2─), 14.2 (─CH3). IR (KBr):
3047, 1604, 1455, 1329, 1200, 1065, 961, 794 cm−1; Anal.
Calcd for C39H36N2Cl2O: C, 75.60; H, 5.86; N, 4.52. Found: C,
75.18; H, 6.09; N, 4.22.
C62H76N2Cl2O2: C, 77.21; H, 7.20; N, 3.34. Found: C, 77.23; H,
7.29; N, 3.34.
2,7-Dichrolo-N-[2-Methoxy-N-(4-(N,N-Bis
(4-(2-Ethylhexyloxy)Phenyl)Amino)Phenyl)Carbazol-7-yl]
Carbazole (11)
A mixture of 9 (170 mg, 0.325 mmol), Pd(OAc)2 (3.7 mg,
0.016 mmol), sodium t-butoxide (156 mg, 1.62 mmol), toluene
(7 mL), P(t-Bu)3 (10 wt % in hexane, 95 μL, 0.033 mmol), and
A General Procedure for Homopolymerization
Yamamoto polymerization27 was carried out under modified
conditions to obtain the polymer (P1–P3) in good yield with
high-molecular weight. The GPC results are shown in Table 1. A
mixture of bpy (91 mg, 0.58 mmol), Ni(COD)2 (160 mg,
0.58 mmol), DMF (1.5 mL), and COD (62.9 mg, 0.58 mmol) was
ꢀ
10 (541 mg, 1.63 mmol) was stirred at 110 C for 24 h. After
ꢀ
stirred at 55 C for 10 min. To the mixture was added a solu-
the reaction was cooled to the room temperature, CH2Cl2 was
added to the reaction mixture and subjected to short path col-
umn chromatography on silica gel. After evaporation of the
solvent, the residue was subjected to column chromatography
on silica gel eluted with hexane/CH2Cl2 (2:1) to give 11
(148 mg, 88% yield) as a white solid.
tion of corresponding monomer (5, 11, ꢀor 17) (0.24 mmol) in
THF (2 mL), and this was stirred at 65 C for 48 h. The crude
polymer was purified by reprecipitation from methanol. Poly-
mer was dried under vacuum at 100 ꢀC.
RESULTS AND DISCUSSION
1H NMR (CDCl3, 270 MHz): δ 8.12 (d, J = 8.2 Hz, 1H; 1), 7.98
(d, J = 8.6 Hz, 1H; 12), 7.90 (d, J = 8.2 Hz, 2H; a), 7.30 (d, J = 1.3 Hz,
1H; 4), 7.23–7.14 (7H; b, d, 9, 15), 7.04 (d, J = 9.0 Hz, 4H, 18),
6.94 (d, J = 8.9 Hz, 2H; 14), 6.88 (dd, J = 8.6, 2.3 Hz, 1H; 11), 6.81
(d, J = 8.7 Hz, 1H; 2), 6.76 (d, J = 9.0 Hz, 4H; 19), 3.81 (s, 3H;
─OCH3), 3.72 (4H; ─OCH2─), 1.67–1.58 (m, 2H; ─OCH2CH<),
1.49–1.17 (16H; ─CH2─), 0.87–0.81 (12H; ─CH2CH3).; 13C NMR
(CDCl3, 67.5 MHz): δ 159.5 (10), 156.1 (20), 148.6 (3), 143.6 (e),
142.5 (17), 142.1 (5), 139.8 (8), 132.5 (13, 16), 131.8 (c), 127.9
(14), 127.4 (15), 127.1 (19), 123.3 (7), 121.2 (1), 120.9 (a, b),
120.5 (f), 119.7 (12), 118.8 (6), 116.2 (18), 115.3 (d), 110.2 (2),
108.9 (4), 108.6 (11), 94.2 (9), 70.6 (─OCH2─), 55.7 (─OCH3),
39.5 (─OCH2CH<), 30.6 (─CH2─), 29.1 (─CH2─), 23.9 (─CH2─),
23.1 (─CH2─), 14.2 (─CH3), 11.2 (─CH3). IR (KBr): 2926, 1603,
1505, 1457, 1320, 1238, 1065, 963, 827 cm−1; Anal. Calcd for
Synthetic Procedure
Scheme 1 shows the synthetic route of a monomer with the car-
bazolyl group (5) and P1. To prepare the monomer 5 for P1, the
carbazolyl moiety 3 was introduced to 2,7-dichlorocarbazole 4 at
N-position by the CuI/trans-1,2-cyclohexanediamine (CHDA) cat-
alyzed reaction. First, 4-Iodooctylbenzene 1 was prepared from
4-aminooctylbenzene by Sandmeyer reaction. To synthesize N-
arylcarbazole 3, N-arylation of 2-bromo-7-methoxycarbazole 27
with iodobenzene 1 was carried out by the CuI/CHDA catalyzed
method.28 An exchange reaction of bromo to iodo group on the
carbazole moiety occurred during the N-arylation, forming a mix-
ture of bromocarbazole and iodocarbazole. Thus, complete iodin-
ation of the halogenocarbazoles was carried out under the
similar conditions but using NaI instead of K3PO4.29
4
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a
+
Br
I
12
Br(CH ) Br
92%
b
O N
2
OH
O N
2
O (CH ) Br
2 10
2 10
84%
13
b
13
+
HO
I
O N
2
O(CH )
O
I
2 10
100%
14
Cl
Cl
Cl
Cl
Cl
Cl
N
N
c
d
N
H
4
+
O(CH )
O
NO
O(CH )
O
NH
2
2 10
2 10
2
14
16
15
95%
100%
Cl
Cl
N
N
n
e
f
16 12
+
O(CH )
O
N
O(CH )
O
N
2 10
2 10
17
P3
96%
55%
SCHEME 2 Syntheses of monomer 17 and P3. (a) CuI, NaI, CHDA, 1,4-dioxane, 100 ꢀC; (b) K2CO3, acetone, 55 ꢀC; (c) CuI, K3PO4,
CHDA, 1,4-dioxane, 100 ꢀC; (d) SnCl2•2H2O, EtOH, reflux; (e) Pd(OAc)2, P(t-Bu)3, t-BuONa, toluene, 110 ꢀC; (f) Ni(COD)2, COD, bpy,
DMF-THF, 70 ꢀC.
Scheme 1 also illustrates the synthetic route of poly(N-
carbazolyl-2,7-carbazole) with triphenylamine moiety
dichloro-N-[2-methoxy-N-(4-aminophenyl)carbazol-7-yl]carbazole
with 1-(2-ethylhexyloxy)-4-iodobenzene was carried out by the
Pd-catalyzed reaction to give the monomer 9 for P2.
a
(P2). 2-Bromo-7-methoxycarbazole 2 was reacted with p-
fluoronitrobenzene according to the reported procedure.30
To improve reactivity of N-carbazolylation, iodination of
bromocarbazole 6 was carried out under the Ni-catalyzed
reaction (an alternate method for step c in Scheme 1)
reported by Chang et al.,31 giving 2-iodo-7-methoxy-N-(4-
nitrophenyl)carbazole 7. The N-carbazolylation of 2,7-
dichlorocarbazole was carried out under the Pd-catalyzed
reaction32 to give 2,7-dichloro-N-[2-methoxy-N-(4-nitro-phe-
nyl)carbazol-7-yl]carbazole 8 in a good yield (84%). Using SnCl2,
8 was reduced to an amino compound, 2,7-dichloro-N-[2-methoxy-
N-(4-aminophenyl)carbazol-7-yl]carbazole 9. N-Arylation of 2,7-
Scheme 2 illustrates the synthetic route of poly(N-aryl-2,-
7-carbazole) having a pendant side chain with a triphenylamine
terminal (P3). Reaction of p-nitrophenol with excessive
1,10-dibromodecane gave 13. Moreover, 14 was prepared from
4-iodophenol with 13. N-arylation of 2,7-dichlorocarbazole with
iodobenzene 14 was carried out by the CuI/CHDA catalyzed
reaction, giving 15 in a high yield. After the terminal nitroben-
zene moiety was reduced to amino, the monomer 17 for P3
was prepared from 16 by the same method for N-arylation of
11 using 12.
All the polymers were prepared by the Ni0-catalyzed dehaloge-
native polycondensation of the monomers 5, 11, and 17, using
the Yamamoto method, respectively.27 All the polymers were sol-
uble in the usual organic solvents such as THF and CHCl3, but P1
had low solubility in toluene.
TABLE 1 GPC Analysis Results of Polymers
Polymers
M
n (×10−3 a
)
M
w (×10−3 a
57.0
108
181
)
PDI
D.P.
P1
P2
P3
12.7
16.4
30.0
4.5
6.6
6.0
23.0
19.0
38.9
The results of number-average molecular weight (Mn) and the
weight average molecular weight (Mw) of the polymers deter-
mined by gel permeation chromatography (GPC) are summarized
a Determined by GPC versus polystyrene standards in THF.
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in Table 1. All the polymers showed a good degree of polymeri-
zation (DP) with large polydispersity indices (PDI). DP of P2 was
a little smaller than P1, which is due to the larger side pendant
of the carbazolyl portion with the triarylamino group, which hin-
dered the polymerization a little.
shape, and their difference of Em λmax was a little about
10 nm, which was the smallest of all the polymers. This result
suggests that the rigid and large steric hindered structure of
P2 is effective to suppress the concentration quenching of
emissions from the main chain. The smaller spectral change
for P1 compared to P0 suggests that the carbazolyl-carbazole
skeleton in P1 is more rigid than the triphenylamino-
carbazole skeleton in P0. Interestingly, the spectral change of
P3 was similar to P0. This indicates that the rigidness of the
emissive poly(2,7-carbazole) main chain of P3 having the N-
phenyl moiety with the enchained triarylamino group is simi-
lar to that of P0, which directly connected with the large
triarylamino group at the N-position. Nevertheless, all the
polymers preserved blue emission. Note that P2 showed a
deep blue emission (CIE: 0.15, 0.06) (Table 2).
Optical Properties
The UV–vis spectra of the polymers in CHCl3 and in the thin film
state are depicted in Figure 2 and the spectral results are summa-
rized in Table 2. All the polymers in chloroform had an absorption
peak around 390 nm due to π–π* transition of the conjugated
main chain. The bands around 330 nm of P1 and P2 are due to
the carbazolyl side pendant.33 Similarly, the absorption band
around 300 nm of P3 is attributed to the triphenylamino group.16
P2 also has the band due to the triphenylamino moiety, but it is
involved in the carbazolyl band around 330 nm. These polymer
films exhibit absorption spectra similar to those in solution except
a red shift about 5 nm. The HOMO-LUMO energy gaps (Eg) of the
polymers estimated from the absorption edge of each thin film
were around 2.85 eV in all cases.
The fluorescence quantum yield of P1 (ϕf = 0.78) in CHCl3
was satisfactorily high as well as those of general poly(N-phe-
nyl-2,7-carbazole)s (ϕf = 0.8), while the quantum yields of P2
(ϕf = 0.22) and P3 (ϕf = 0.26) were lower than them. These
results are similar to those of poly(N-phenyl-2,7-carbazole)s
with diphenylamino group (ϕf = 0.01–0.19) in our previous
reports.16 The result indicates that an exciton quenching
might occur between the triarylamino moiety and the main
chain in the polymers, but the pendent carbazolyl moiety has
no effect on the quenching. In order to investigate the
quenching effect of the triarylamine moiety in polycarbazoles,
the emission behavior of P0 was reinvestigated. As shown in
Figure 2, the fluorescence spectrum of the P0 film is rather
broad with a slight red shift in wavelength compared to that
PL spectra of the polymers in CHCl3 and films are also shown
in Figure 2, and the results are summarized in Table 2. Their
emission maximum wavelengths (λmax[em]) in CHCl3 are in
the range from 418 to 421 nm. The spectral changes of fluo-
rescence between the solution and film state are due to
vibronic effect and π-aggregations, which were observed as
shoulder emissions around 455 and 480 nm. The PL spectra
of P2 in CHCl3 and film state showed almost the same spectral
in CHCl3
in CHCl3
P0
P1
P2
P3
P0
P1
P2
P3
in film state
in film state
250
300
350
400
450
500
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
FIGURE 2 Absorption (left) and PL spectra (right) of the polymers in CHCl3 (upper) and in film state (lower).
6
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TABLE 2 Absorption and Fluorescence Spectral Data of the Polymers
In film stateb
Abs λmax (nm) Ege (eV) Em λmaxf (nm) HOMOg (eV) LUMOh (eV) CIE (x,y)i
a
In CHCl3
Polymers Abs λmax (nm) Em λmaxc (nm) ϕfd
P1
P2
P3
P0
390
389
387
391
419
421
415
418
0.78 396
0.22 404
0.26 391
0.19 397
2.84
2.85
2.86
2.90
433, 454
431, 455
427, 450
430, 457
−5.29
−5.22
−5.19
−5.27
−2.45
−2.37
−2.33
−2.37
(0.16, 0.11)
(0.15, 0.07)
(0.16, 0.12)
(0.15, 0.14)
a Absorption and fluorescence spectra at 1.0 × 10−5 M per unit, respec-
tively, at room temperature.
e Band gaps estimated from the onset of the absorption band edge.
f Polymers were dissolved in chloroform and spin coated onto a quartz
substrate and excited at 350 nm with a Xe lamp. Photon measurement
range of PL was 400–700 nm.
b Cast film on a quartz glass plate from CHCl3.
c The excitation wavelength is almost the same as λmax absorption in
each case because the excitation spectrum of each polymer almost mat-
ched at absorption spectrum.
g Determined by electrochemical analysis.
h Calculated based on the HOMO level and lowest energy absorption
edge of the UV-spectrum (Eg).
d Determined using 9,10-diphenylanthracene (ϕf = 0.97 in cyclohexane)
as the standard.
i Estimated from florescence spectrum.
in dilute CHCl3 solution. The fluorescence quantum yield of
P0 in CHCl3 was ϕf = 0.19, which is comparable to P2 and P3,
but ϕf of the thin film is reported being 0.32.18 This phenome-
non is considered being a kind of aggregation-induced emis-
sion 34 in the combination of triphenylamine and carbazole.
efficiency (ηc = 0.30 cd/A at 9 V), and an adequately high lumi-
nance (2902 cd/m2 at 9 V). The turnon voltage was 4 V, which
was the lowest of all. The EL spectra between 4 V and 9 V
were similar to the PL spectrum in the film state (Figs. 2 and 3),
and intensities of their similar figure were reversibly changed
between these voltages. The steric hindrance of the rigid pendant
with electron-donor ability might keep away from aggregation of
the polymer main chains during the EL processes. The maximum
luminance was 9870 cd/m2 (ηc = 0.60 cd/A) at an applied volt-
age of 11 V, although the emission color irreversibly changed
from blue to bluish green. The higher the operating voltage is
applied to the device, the more intense additional emission bands
longer than 490 nm appear (Fig. 3) and the luminance decreases
with time. These results suggest that the carrier injection/trans-
port balance of the P2 device is appropriately keeping during the
operation voltages in the range of 4–9 V, but disruption of balance
for the emission from an exciton originated from the polycarbazole
main chains occurs in the range of high operating voltages, leading
to low-energy emissions from oxidized species. The tendency of the
EL spectral change was similar to those of poly-2,7-carbazoles
having the N-aryl groups,19 but the change was suppressed to
some extent, probably due to presence of the triarylamine
moiety. The irreversible spectral change might be due to hyp-
eroxidation at 3,6-positions of the hole-injected 2,7-carbazol
moieties and concentrated hole species near the interface of a
reactive cathode under high applied voltages.17,37 Thus, the
triarylamine moiety should work as a buffer medium to pre-
vent the hyperoxidation of polycarbazole in addition to the
inherent hole injection and transporting functions under the
operating conditions.
Analogous polymers with this combination have shown similar
tendency; that is, ϕf of thin film was higher than that in CHCl3
while ϕf in toluene was higher than that in CHCl3.15,18,21
Electrochemical and EL Properties
The HOMO energy levels, the LUMO energy levels, and Eg for
all the polymers are summarized in Table 2. The HOMO
energy levels were estimated from an onset potential of the
oxidation waves.35,36 The LUMO energy levels were estimated
from the HOMO energy levels and Eg values. The pendants of
the N-phenylcarbazol-2-yl for P1 (N,N-diphenyl-amino)-N-phe-
nylcarabazol-2-yl for P2 and triphenylamino for P3 have simi-
lar donating ability to lower the ionization potential of the
polymers as well as the triphenylamino pendant in P0. How-
ever, the pendent carbazolyl moiety does not stabilize EL in
blue light region of poly(2,7-carbazole)s compared to the pen-
dent triarylamino moiety in the OLED device having an
ITO/PEDOT-PSS/polymer/CsF/Al structure in the previous
report.17 In addition, P1 having no triphenylamine structure
had low solubility in organic solvent to make uniform thin film
device. Thus, EL performance of P2 is investigated compared to
those of P3 and P0 in the same device structure, ITO/PEDOT-
PSS/polymer/CsF/Al, in this work to confirm the effect of the
triphenyl amine pendant, and the results are summarized in
Table 3 and Figure 3. Since usual polycarbazole LED devices in
this configuration showed a blue EL at lower than 8 V operat-
ing voltages,17,19,20 criterion performance (luminance, effi-
ciency, and CIE value) of each device at 8 V is listed in Table 3
for evaluation of blue light emitting polymer materials.
On the other hand, the P0 device showed stable bluish emis-
sions during the operation voltages thanks to the buffering
effect of the directly linked triarylamine moiety, but its lumi-
nance was very low. This result suggests that there is limitation
of hole injection to make exciton on the donor polycarbazole
emitter in competition with the directly linked triarylamine
moieties, although a P0 device having different configuration
(ITO/PEDOT-PSS/polymer/Ba/Al)18 gave better results than in
Table 3 in terms of luminance, efficiency, and purity of blue
emission color.
The device embedded with P2 which has the (N,N-
diphenylamino)-N-phenylcarabazol-2-yl pendant showed
purple-blue to blue emissions (Em λmax = 430 nm, CIE(x, y) =
(0.17, 0.13) at 6 V– (0.20, 0.22) at 9 V), a modest current
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Comparison of the EL results of each polymer device at 8 V in
Table 3 suggests that several factors determine the trade-off
performance. To summarize of this point, the triphenylamine
moiety is oxidized first at the anode to generate a hole. The
hole is trapped at the triphenylamine moiety, but it can trans-
fer to another triphenylamine moiety by a hopping mecha-
nism or a donor carbazolyl moiety with a little energy gap
toward the cathode under an applied voltage. As a result,
the donor poly(2,7-carbazole) chain can undergo p-doping to
generate a hole such as a polaron and a bipolaron. The more
p-doping proceeds, the more conductivity along the polymer
chain increases and the bandgap narrows. Thus, the directly
linked triphenylamine moiety in P0 traps a hole and stabilizes
the polycarbazole luminophore against the hyperoxidation. On
the other hand, the difficulty of the hole injection to the
luminophore due to the stabilization and the subsequent low
conductivity of the polymer chain at a low-level p-doping
result in the very low luminance, but the good current effi-
ciency probably due to keeping a balance of carriers’ recombi-
nation. The N-carbazolyltriphenylamine moiety in P2 might
work more flexible in the hole trapping and hole transferring
in association with a moderate p-doping, which brings about
the highest luminance with an enough current flow among
three polymers. The sterically hindered N-carabazolyl pendant
might inhibit converting P2 to a narrow band-gap quinoid
structure with controlling the p-doping level, which results
in high luminance with keeping blue emission at 8 V. The
pendent triphenylamine moiety in P3 mainly functions as
the hole trapping and hopping with a little participating in the
p-doping of the polycarbazole luminophore, which results in
the low luminance and low efficiency.
TABLE 3 EL Properties of the Polymers
Polymer Vona (V) Lb cd m−2 (V) ηc cd A−1 (V) CIEd (x, y)
P0
P2
P3
8
4
5
5 (8)
272 (17)
1130 (8)
9870 (11)
28 (8)
0.29 (8)
0.37 (10)
0.18 (8)
0.60 (11)
0.03 (8)
0.13 (13)
(0.20, 0.19)
(0.20, 0.24)
(0.18, 0.16)
(0.25, 0.41)
(0.20, 0.18)
(0.21, 0.30)
1506 (13)
a Turn-on voltage.
b Upper is luminance at 8 V and lower is maximum luminance and the
operating voltage.
c Upper is efficiency at 8 V and lower is maximum efficiency and the
operating voltage.
d Upper is CIE index at 8 V and lower is data at voltage showing maxi-
mum luminance.
The P3 device also showed stable bluish emissions during
operation voltages as well as the P0 device. The luminance
was higher while the efficiency was lower compared to the
results of the P0 device (Table 3), which suggests that hole
injection and transport in the P3 device mainly proceed
through the triarylamine moieties separated from the poly-
carbazole main chains by a hopping mechanism.
5.0
16 V
P0
PL (film)
4.0
14
(normalized)
3.0
12
2.0
1.0
0
20
10
CONCLUSIONS
8 V
In summary, three poly(2,7-carbazole)s, P1–P3, which have
hole injection and hole transfer functional moieties of carba-
zole and/or triphenylamine at N-position were synthesized
and characterized to be applied in blue light emitting PLED.
80
11 V
10
P2
PL (film)
60
40
20
0
(normalized)
10
9
The fluorescence quantum yield of P1 having N-(2-carbazolyl)
moiety in CHCl3 was much higher than those of P0, P2, and P3;
they all have a triphenylamino group bonded directly at the N-
position, linked via the N-(2-carbazolyl) moiety, and connected
as a flexible pendant, respectively. The low-emissive phenome-
non in CHCl3 for P0, P2, and P3 is interpreted as an aggregate-
induced emissive property, that is, combination of the poly-
carbazole and triarylamine give rise to self-quenching in dilute
solution of a good solvent.
8
7
6 V
12
13 V
P3
PL (film)
(normalized)
12
12
8
4
0
11
The shape of PL spectrum of P2 in CHCl3 was preserved that
in a film state, realizing a deep blue emission in the film state
(CIE: 0.15, 0.07), which is due to steric and electronic effects
of the rigid and donor carbazolyl-triphenylamine moiety.
Similar tendency was observed for P1 that has the bulky
and donor 2-carbazolyl moiety. On the other hand, the
triphenylamine moieties in P0 and P3 were not very effec-
tive to preserve shapes of PL spectra between in CHCl3
and film.
10
9
7
400 450 500 550 600 650
Wavelength /nm
FIGURE 3 EL spectral changes of the P0, P2, and P3 devices at
different applied voltages in the first sweep.
8
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11 K. Becker, J. M. Lupton, J. Feldmann, B. S. Nehls,
F. Galbrecht, D. Gao, U. Scherf, Adv. Funct. Mater. 2006, 16, 364.
Introduction of the carbazolyl moiety lowered the ionization
potential as well as the triarylamino groups. As the result, all
the obtained polymers had the shallow values of HOMO levels
between −5.29 and −5.13 eV.
12 M. R. Craig, M. M. de Kok, J. W. Hofstraat, A. P.
H. J. Schenning, E. W. Meijer, J. Mater. Chem. 2003, 13, 2861.
13 N. Blouin, M. Leclerc, Acc. Chem. Res. 2008, 41, 1110.
P2 and P3 which have good solubility in toluene and an
aggregate-induced emissive property were used as emitting
layer materials in PLEDs device with the configuration of
ITO/PEDOT-PSS/polymer/CsF/Al for blue light emission in
comparison with performance of P0. The P2 device kept deep
blue to pure blue EL, modest efficiency and luminance at
5–9 V with the aid of the rigid donor carbazolyltriarylamino
pendant and buffering effect of the triarylamine moiety, but
the color turned to greenish blue similar to usual poly-
carbazoles over 9 V. The EL performance of the P3 device
showed similar tendency with that of P0 except quite lower
efficiency, which might be interpreted that hole injection and
transport occur at the enchained triphenylamine pendants
with a hopping mechanism.
14 J. -F. Morin, M. Leclerc, D. Adès, A. Siove, Macromol. Rapid
Commun. 2005, 26, 761.
15 M. Kijima, R. Koguchi, S. Abe, Chem. Lett. 2005, 34, 900.
16 N. Kobayashi, R. Koguchi, M. Kijima, Macromolecules 2006,
39, 9102.
17 R. Koguchi, N. Kobayashi, T. Shinnnai, K. Oikawa,
K. Tsuchiya, M. Kijima, Macromol. Chem. Phys. 2008, 209, 439.
18 N. Kobayashi, M. Kijima, Appl. Phys. Lett. 2007, 91, 081113.
19 T. Mori, T. Shinnai, M. Kijima, Polym. Chem. 2011, 2, 2830.
20 T. Horii, T. Shinnai, K. Tsuchiya, T. Mori, M. Kijima, J. Polym.
Sci. Part A: Polym Chem. 2012, 50, 4557.
21 H. Yi, A. Iraqi, M. Stevenson, C. J. Elliott, D. G. Lidzey,
Macromol. Rapid Commun. 2007, 28, 1155.
22 E. Fresta, R. D. Costa, J. Mater. Chem. C 2017, 5, 5643.
23 T. Yamamoto, A. Morita, Y. Miyazaki, T. Maruyama,
H. Wakayama, Z. –H. Zhou, Y. Nakamura, T. Kanbara, Macro-
molecules 1992, 25, 1214.
ACKNOWLEDGMENTS
The authors thank Dr. Norifumi Kobayashi, University of
Tsukuba, for his valuable comments on the synthetic design. We
also thank Chemical Analysis Division, Research Facility Center
for Science and Technology, University of Tsukuba, for facilities
of the NMR, elemental analysis, and PL measurements.
24 D. A. Patrick, D. W. Boykin, W. D. Wilson, F. A. Tanious,
J. Spychalaz, B. C. Bender, J. E. Hall, C. C. Dykstra,
K. A. Ohemeng, R. R. Tidwell, Eur. J. Med. Chem. 1997, 32, 781.
25 J. -F. Morin, M. Leclerc, Macromolecules 2001, 34, 4680.
26 A. R. A. Palmans, M. Eglin, A. Montali, C. Weder, P. Smith,
Chem. Mater. 2000, 12, 472.
27 D. Neher, Macromol. Rapid Commun. 2001, 22, 1365.
REFERENCES AND NOTES
28 A. Klapars, J. C. Antilla, X. Huang, S. L. Buchwald, J. Am.
Chem. Soc. 2001, 123, 7727.
1 D. D. C. Bradley, J. H. Burroughes, A. R. Brown, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burn, A. B. Holmes, Nature 1990,
347, 539.
29 A. Klapars, S. L. Buchwald, J. Am. Chem. Soc. 2002, 124,
14844.
2 L. Akcelrud, Prog. Polym. Sci. 2003, 28, 875.
30 H. Jian, J. M. Tour, J. Org. Chem. 2003, 68, 5091.
3 R. T. Hebner, C. C. Wu, D. Marcy, H. M. Lu, C. J. Sturm, Appl.
Phys. Lett. 1998, 72, 519.
31 S. H. Yang, C. S. Li, C. H. Cheng, J. Org. Chem. 1987, 52, 691.
4 M. Suzuki, H. Fukagawa, Y. Nakajima, T. Tsuzuki, T. Takei,
T. Yamamoto, S. Tokito, J. Soc. Inf. Disp. 2009, 17, 1037.
32 Z. Suo, M. Drobizhev, C. W. Spangler, N. Christensson,
A. Rebane, Org. Lett. 2005, 7, 4807.
5 J. Birnstock, J. Blässing, A. Hunze, M. Scheffel, Appl. Phys.
Lett. 2001, 78, 3905.
33 Y. Fu, Y. Li, J. Li, S. Yan, Z. Bo, Macromolecules 2004, 37,
6395.
6 D.-Y. Chung, J. Huang, D. D. C. Bradley, A. J. Campbell, Org.
Electron. 2010, 11, 1088.
34 J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu,
H. S. Kwok, X. Zhan, Y. Liu, D. Zhu, B. Z. Tang, Chem. Commun.
2001, 1740. https://doi.org/10.1039/B105159H
7
A. Sandstrom, H. F. Dam, F. C. Krebs, L. Edman, Nat.
Commun. 2012, 3, 1002.
35 J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt,
H. Bässler, M. Porsch, J. Daub, Adv. Mater. 1995, 7, 551.
8 K.–H. Weinfurtner, H. Fujikawa, S. Tokito, Y. Taga, Appl. Phys.
Lett. 2000, 76, 2502.
36 S. Gauvin, F. Santerre, J. P. Dodelet, Y. Ding, A. R. Hlil,
H. –A. S. Hay, J. Anderson, N. R. Armstrong, T. C. Gorjanc, M. D’Iorio,
Thin Solid Films 1999, 353, 218.
9 M. Gross, D. C. MuÈller, H.-G. Nothofer, U. Scherf, D. Neher,
C. BraÈuchle, K. Meerholz, Nature 2000, 405, 661.
10 C.-W. Huang, C.-L. Tsai, C.-Y. Liu, T.-H. Jen, N.-J. Yang, S.-
A. Chen, Macromolecules 2012, 45, 1281.
37 G. Zotti, G. Schiavon, S. Zecchin, J. –F. Morin, M. Leclerc,
Macromolecules 2002, 35, 2122.
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