Novel electron-withdrawing π-conjugated pyrene-containing poly(phenylquinoxaline)s

Full text of DOI:10.1134/S0012500814050036

ISSN 0012ꢀ5008, Doklady Chemistry, 2014, Vol. 456, Part 1, pp. 65–71. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © M.L. Keshtov, G.D. Sharma, D.Yu. Godovskii, N.M. Belomoina, Yanhou Geng, Yingping Zou, V.S. Kochurov, A.I. Stakhanov, A.R. Khokhlov, 2014,
published in Doklady Akademii Nauk, 2014, Vol. 456, No. 1, pp. 49–55.
CHEMISTRY
Novel ElectronꢀWithdrawing πꢀConjugated
PyreneꢀContaining Poly(phenylquinoxaline)s
M. L. Keshtova, G. D. Sharmab, D. Yu. Godovskiia,
N. M. Belomoinaa, Yanhou Gengc, Yingping Zoud, V. S. Kochurove,
A. I. Stakhanova, and Academician A. R. Khokhlova
Received December 30, 2013
DOI: 10.1134/S0012500814050036
The search for new efficient electronꢀtransport
polymers is necessary to improve the characteristics of
electrooptical devices, which is provided, in particuꢀ
lar, by the introduction of electronꢀwithdrawing fragꢀ
ments—triazole [6], oxodiazole [7], quinoline [8],
and quinoxaline [9]—into macromolecules. The latꢀ
ter are the least studied and show higher electronꢀ
withdrawing properties due to the presence of four
In recent time, conjugated polymers have attracted
considerable attention of researchers not only from
scientific but also from a practical viewpoint due to
their fundamental optoelectronic properties and
application as electroactive materials for organic light
emitting diodes [1], fieldꢀeffect transistors [2], and
photovoltaic devices [3]. Conjugated polymers are
prepared by Stille, Suzuki, and Yamamoto reactions
using nickel (Yamamoto) and palladium (Suzuki and
Stille) catalysts [4, 5]. However, the high cost of the
processes and difficulties of purification from metal
catalyst residues, which are undesirable impurities for
optoelectronic devices, are considerable drawbacks of
these reactions. New noncatalytic methods for the
synthesis of highꢀpurity conjugated polymers should
be developed to solve these problems. It has also been
found that intense electroluminescence and high
charge mobility in a polymer require a high electron–
hole conduction of a medium due to charge carriers
mobility and a balance of injection of carriers of both
signs from opposite electrodes into the emission polyꢀ
mer layer. However, the majority of conjugated polyꢀ
mers provide hole transport that causes imbalance of
charge injection and a poor quantum yield.
electronꢀwithdrawing heteroatoms.
π
ꢀConjugated
thiopheneꢀcontaining poly(phenylquinoxaline)s
(PPQs) have been obtained recently. These PPQs
behave as excellent electronꢀtransport materials for
organic lightꢀemitting diodes [10]. We prepared new
conjugated pyreneꢀcontaining PPQs as highꢀpurity
polymers by noncatalytic polycondensation reaction
to provide the balance of the hole and electron conꢀ
duction. The introduction of flat structures, such as
pyrene, into a conjugated polymer is supposed to
enhance intermolecular electronic interaction in the
solid state and result in formation of
π
– stacking
π
structures. In continuation of our studies [11, 12], we
prepared and studied new bipolar pyreneꢀcontaining
PPQs as efficient electronꢀhole and transport materiꢀ
als and thereby synthesized, previously unknown
bis(αꢀdiketone)s IV and VIII.
RESULTS
AND DISCUSSION
a Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28, Moscow,
119991 Russia
Novel pyreneꢀcontaining bis(αꢀdiketone)s IV and
eꢀmail: keshtov@ineos.ac.ru
VIII were obtained to prepare conjugated PPQs.
Compound IV was obtained by sequential transformaꢀ
tions including pyrene bromination, interaction of
b Jaipur Engineering College, SP 43, RIICO Industrial Area,
Delhi Road, Kukas, Jaipur 303101, India
c Changchun Institute of Applied Chemistry, Chinese Academy
of Sciences, No. 5625 Renmin Rd., Changchun, Jilin 130022,
China
compound I with a twofold molar amount of trimethꢀ
ylsilylacetylene followed by elimination of trimethylsꢀ
ilyl group, palladiumꢀcatalyzed cross coupling of 1,6ꢀ
diethynylpyrene (II) with a twofold molar amount of
d Central South University, Changsha, Hunan, China 410083
e Moscow State University, Moscow, 119991 Russia
65

66
KESHTOV et al.
t
a, b, c, d, e, f,
h, i, l
(a)
а
a
б
b
и
i
n, o, p,
q, r, s
h
в
з
c
г
ж
л
k
d
g
к
j
д
e
е
м
f
O O
l
O O
н
m
о
n
g
п
o
j
k
р
p
с
q
r
т
у
s
m
ф
t
CDCl3
9.5
(b)
8.5
7.5
6.5
5.5
4.5
3.5
2.5
1.5
0.5
Н, ppm
δ
1
15
16
30
14
13
2
3
12
11
4
5
21
20
10
9
6
22
18 17
19
7
8
23
24
O O
25
28
O O
26
29
27
28
32
29
9, 13
30
22
6
15, 16
3
31
23
32
33
19
10
27
31
18
17
26
25
33
2
8
21
20
4, 7, 11
1, 5, 12, 14, 24
190
170
150
130
110
90
70
50
30
10
С, ppm
δ
1
13
Fig. 1. H (a) and C (b) NMR spectra of bis(
α
ꢀdiketone) VIII
.
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NOVEL ELECTRONꢀWITHDRAWING
67
bromobenzene. Thus prepared 1,6ꢀbis(phenylethyꢀ alyl)pyrene (IV) in a rather high yield (78%). Comꢀ
nyl)pyrene (III) was oxidized with potassium permanꢀ pound VIII was obtained in 73% yield in a similar
ganate to give the target monomer 1,6ꢀ(phenylglyoxꢀ manner according to Scheme 1.
O
O
Br
Br
(1)
, [Pd]
Si
Br2
[Pd]
KMnO4
+ 2
(2) NaOH, CH3OH
CuI, Et3N,
Ph3P
Br
O
O
I
II
Br2
III
IV
Br
, [Pd]
Si
[Pd]
+
Br
Br
K2CO3, CH3OH
CuI, Et3N
C H
C H
C H
C H
8 17
8
17
8
17
8
17
V
VI
VII
KMnO4
O O
O O
C H
C H
8 17
8
17
VIII
Scheme 1.
The composition and structure of target comꢀ from the ratio of the integrated intensities of signals
and the values of spin–spin coupling constants.
The C NMR spectra of compound VIII display
pounds IV and VIII were confirmed by elemental
13
1
13
analysis, IR spectroscopy, and H and C NMR. In
particular, the IR spectra of bis( ꢀdiketone)s IV and
20 intense signals in the region
δ
= 110–150 ppm,
α
eight of which pertain to quaternary carbon atoms.
A specific feature of the spectra of compound VIII is
the presence of downfield signals of two different carꢀ
VIII show strong absorption bands at 1665 and
1702 cm–1, respectively, typical of the CO group of an
1
α
ꢀdiketone fragment. The H NMR spectra of comꢀ
bonyl groups of the
αꢀdiketone fragment at
δ
= 194
pounds IV and VIII show three multiplets at
8.3 (4H), 7.7–7.8 (6H), and 7.4–7.58 ppm (4H); one
singlet at = 8.37 ppm; one doublet at 7.99 ppm (4H,
= 8.1 Hz); and three wellꢀresolved triplets at = 7.64
(2H), 7.4 (2H), and 7.32 ppm (2H, = 7.2 Hz) (Fig. 1a).
δ
= 8.1–
and 193 ppm (Fig. 1b).
δ
The prepared bis(αꢀdiketone)s IV and VIII were
J
δ
used in the synthesis of PPQs containing pyrene
groups in the main and side chains of macromolecules
Signal assignment in the H NMR spectra was made in accordance with Scheme 2.
J
1
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68
KESHTOV et al.
O O
O O
C H
C H
8
8
17
17
VIII
+
O O
O O
IV
N
N
]
*
n
N
N
[
*
PPQꢀ1
H N
2
NH
2
+
NH
H2
H N
2
2
IX
N
N
N
N
[
]
*
n
*
C H
C H
8 17
8
17
PPQꢀ2
Scheme 2.
1640 cm–1 typical of the C=N bond in quinoxaline
rings. This is also confirmed by the 13C NMR spectra
of all polymers, which contain no signals in the region
PPQs were obtained by reacting aromatic tetꢀ
raamine IX with bis( ꢀdiketone)s IV and VIII in an
cresol solution at 190 for 7 h. The reaction proꢀ
ceeded under homogeneous conditions to lead to
polymers with high viscosity characteristics (
0.79 0.94 dL/g). The structure of PPQ was confirmed
by IR and NMR spectroscopy. The IR spectra of the
prepared polymers exhibit the lack of absorption
bands at 3200–3400 and 1660–1680 cm–1 related to
the C=O and NH2 stretching vibrations of the initial
α
mꢀ
°С
δ
= 190–195 ppm related to
The molecular weights of the polymers determined by
GPC vary within (188.3–222.5) and (61.8–
103 (Mw
68.7) with dispersity 2.7–3.6, respectively.
103 (Mn
α
ꢀdiketone fragments.
η
=
–
×
)
×
)
According to Xꢀray diffraction analysis, all the polyꢀ
mers are amorphous, which seems to be due to their
isomeric heterounit structure, and this feature is
compounds and the presence of absorption bands at responsible for the good solubility of PPQ in a wide
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NOVEL ELECTRONꢀWITHDRAWING
69
Table 1. Molecularꢀweight, thermal, and mechanical properties of poly(phenylquinoxaline)s
Stretching properties of films
Mn
103
Mw
×
103
Tg
,
°
C
T10%, °C *
ꢀꢀꢀꢀꢀꢀ
Polymer
η
, dL/g
Mn
×
Mw
σ
, MPa
ε, %
PPQꢀ1
PPQꢀ2
0.62
0.71
61.8
68.7
222.5
188.3
3.6
2.7
344
247
492 (515)
375 (463)
86
76
5.2
6.3
* Temperature of 10% weight loss in air and argon.
Table 2. Optical properties of poly(phenylquinoxaline)s in solutions and films
a
fl
λmax , nm *1
λmax , nm *2
Polymer
E
opt, eV *3
λ
onset, nm *4
solution
solution
film
PPQꢀ1
PPQꢀ2
347 (422)
359 (397)
491
478
525
500
2.68
2.81
463
441
1
2
3
4
*
*
*
*
Absorption spectra maximum for polymers.
Fluorescence spectra maximum for polymers.
Optical energy gap width for polymer found from equation E = 1240/λ
.
onset
opt
λ
is the absorption spectrum onset in polymers.
onset
range of organic aprotic and chlorinated solvents, such elongation of polymers PPQꢀ1 and PPQꢀ2 are 86,
as DMF, DMA, DMSO, chloroform, and dichloroꢀ 76 MPa and 5.2, 6.3%, respectively.
ethane.
Optical properties of the polymers were studied by
Thermal properties of PPQ were studied by therꢀ UV and photoluminescence spectroscopy in solution
mogravimetric analysis (TGA) and differential scanꢀ and as thin films; selected characteristics are presented
ning calorimetry (DSC), and the results are given in in Table 2. Figure 2 shows typical fluorescence curves
Table 1. Polymers PPQꢀ1 and PPQꢀ2 exhibit good for solution and solid films. The absorption spectra for
thermal stability in air and argon with T10% 492, polymers PPQꢀ1 and PPQꢀ2 in chloroform display
maxima at 347 (422) and 359 (397) nm, respectively.
The PPQs strongly fluoresce in chloroform. They
exhibit green emission with fluorescence maxima in
solution at 491 and 478 nm, respectively. The polymers
in solid films also fluoresce with maxima at 525 and
510 nm, respectively. The optical energy gap width
375 and 515, 463 С, respectively. Polymer PPQꢀ2 has
°
a lower stability as compared with PPQꢀ1 probably
because of the presence of an aliphatic fragment. The
glass transition temperature of polymers PPQꢀ1 and
PPQꢀ2 is rather high, 344 and 247 С, respectively
°
(Table 1). Both polymers show high viscosity characꢀ
teristics, which enables the preparation of films with
(
Eopt) found from the absorption spectra of films is
high strength characteristics. The tensile strength and 2.68 and 2.81 eV, respectively.
1.0
0.5
1.0
0.5
2
2
''
2
'
1
'
1
1
''
0
0
350 400 450 500 550 600 650
Wavelength, nm
Fig. 2. Absorption spectra of PPQꢀ1
(
1
) and PPQꢀ2
(
2
) and fluorescence spectra of PPQꢀ1
(1') and PPQꢀ2 (2') in chloroform
solution, fluorescence spectra of PPQꢀ1
(
1
'') and PPQꢀ2 (2
'') as films. Excitation wavelength is 350 nm.
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70
KESHTOV et al.
EXPERIMENTAL
(76.6 mmol) of bromobenzene, 0.8 g of a palladium
catalyst, 0.48 g of Cu I, 0.5 g of Ph3P, and 550 mL of
triethylamine. The reaction mixture was stirred under
reflux for 10 h. The precipitate was separated by filtraꢀ
tion, and the solvent was evaporated to dryness. The
residue was recrystallized from butyl acetate. Yield,
1
13
The H and C NMR spectra of the initial comꢀ
pounds and polymers were recorded on a Bruker
Avanceꢀ400 spectrometer operating at 400.13 and
100.62 MHz, respectively. The IR spectra were
obtained on a PerkinꢀElmer 1720ꢀX IR FT spectroꢀ
meter. TGA was performed on a PerkinꢀElmer TGAꢀ7
instrument at a heating rate of 20 K/min. The molecꢀ
ular weight distribution was analyzed by GPC using a
Bruker LC21 liquid chromatograph with refractometꢀ
ric and UV detectors. Chromatography conditions:
85%;
Tmp = 193–194°C.
1H NMR (DMSO,
δ, ppm): 8.6 (s, 2H), 8.2–8.5
(m, 6H), 7.8 (s, 4H), 7.5 (s, 6H).
1,6ꢀBis(phenylglyoxalyl)pyrene (IV). IR (KBr, ν,
cm–1): 1668.
methylene chloride, 1 mL/min,
= 390 nm. Calibraꢀ
λ
1H NMR (DMSO,
, ppm): 9.49 (d, 2H), 8.60–8.57
δ
tion was performed using PS standards. The absorpꢀ
tion spectra of thinꢀlayer structures were recorded on
a PC2000 fiberꢀoptical spectrophotometer. The fluoꢀ
rescence spectra of the polymers were recorded on a
Hitachi 850 spectrofluorimeter.
(m, 4H), 8.47 (d, 2H), 8.10 (d, 4H), 7.83 (t, 2H),
7.70–7.60 (m, 4H).
1ꢀBromopyrene (V). A 2ꢀL twoꢀnecked flask was
charged with 20.225 g (100 mmol) of pyrene and
500 mL of DMF. A solution of 17.779 g (100 mmol) of
bromosuccinimide in 500 mL of DMF was added
dropwise with vigorous stirring at ambient temperaꢀ
ture for 2 h and allowed to stand overnight. The preꢀ
cipitate was separated by filtration and recrystallized
1,6ꢀDibromopyrene (I). Twenty grams of pyrene
and 500 mL of carbon tetrachloride were placed into a
2ꢀL twoꢀnecked flask. A solution of 10 mL of bromine
in 500 mL of carbon tetrachloride was added dropwise
with vigorous stirring at ambient temperature for 5 h.
The mixture was stirred under the same conditions for
12 h. The precipitate was separated by filtration and
recrystallized from toluene. Yield, 61%; Tmp = 220–
222°C (lit.: 221–222°C).
from hexane. Yield, 78%;
T
mp = 100–103
°C.
1ꢀEthynylpyrene (VI). The compound was syntheꢀ
sized similarly to compound II. Yield, 95%; Tmp
=
110–111°C.
1,6ꢀDiethynylpyrene (II). 1,6ꢀDibromopyrene
(13.8 g, 38.8 mmol), 7.52 g (76.6 mmol) of trimethylꢀ
silylacetylene, 0.8 g of a palladium catalyst, 0.48 g of
Cu I, 0.5 g of Ph3P, and 550 mL of triethylamine were
placed in a 700ꢀmL threeꢀnecked flask equipped with
a reflux condenser, a stirrer, and an argon inlet. The
reaction mixture was heated at reflux with stirring for
10 h. The precipitate was separated by filtration, the
solvent was removed to dryness. The residue was
recrystallized from hexane. Yield, 75%; Tmp = 200–
202°C (lit.: 199–200°C).
IR (KBr,
, cm–1): 2097.
ν
1H NMR (CDCl3,
, ppm): 3.63 (s, 1H), 8.58 (d, 1H),
δ
8.24–8.02 (m, 8H).
2,7ꢀBis(1ꢀethynylpyrene)ꢀ9,9'ꢀdioctylfluorene (VII).
The compound was synthesized similarly to comꢀ
pound III. Yield, 65%.
1H NMR (CDCl3,
, ppm): 0.73 (4H), 0.8 (m,
δ
6H), 1.12 (12H), 1.18–1.21 (m, 4H), 2.10–2.13 (m,
4H), 7.72 (s, 2H), 7.75–7.80 (m, 4H), 8.03–8.13 (m,
6H), 8.16 (d, 2H), 8.21–8.27 (m, 8H), 8.75 (d, 2H).
1H NMR (CDCl3,
8.13, 8.55–8.58 (m, 8H).
δ, ppm): 0.39 (s, 18H), 8.10–
13C NMR (CDCl3,
29.21, 29.98, 31.72, 40.38, 55.35, 89.07 (C
(C C), 117.90, 120.06, 122.21, 124.29, 124.49,
δ, ppm): 13.97, 22.51, 23.74,
≡
C), 96.19
A mixture of 2.1 g (5.3 mmol) of the prepared
1,6ꢀbis(trimethylsilylethynyl)pyrene, 300 mL of
diethyl ether, 200 mL of methanol, and 100 mL of
1 N aqueous NaOH was stirred at ambient temperaꢀ
ture for 6 h. The organic layer was separated and dried
with magnesium sulfate. After removal of the solvent,
the residue was crystallized from a hexane–benzene
mixture. Yield, 48%.
≡
125.53, 125.90, 126.15, 127.17, 128.05, 128.24,
128.85, 129.55, 129.90, 130.89, 131.03, 131.15,
131.20, 131.79, 140.80, 151.25.
2,7ꢀBis(1ꢀglyoxalylpyrene)ꢀ9,9'ꢀdioctylfluorene
(VIII) was obtained similarly to compound IV
IR (KBr,
, cm–1): 1668.
1H NMR (CDCl3,
, ppm): 9.64–9.62 (d, 2H),
8.41–8.00 (m, 20H), 7.86 (d, 2H), 2.20–0.50 (m, 34H).
13C NMR (CDCl3,
, ppm): 13.99, 22.49, 23.83,
.
ν
1H NMR (CDCl3,
, ppm): 3.64 (s, 2H), 8.52 (d, 2H),
δ
δ
8.35–8.32 (m, 4H, Ar), 8.24 (d, 2H).
δ
1,6ꢀBis(phenylethynyl)pyrene (III). A threeꢀ
necked 700ꢀmL flask equipped with a reflux conꢀ 29.06, 29.70, 31.61, 39.66, 55.82, 121.29, 123.96,
denser, a stirrer, and an argon inlet was charged with 123.99, 124.58, 126.70, 126.98, 127.09, 127.34,
9.7 g (38.8 mmol) of 1,6ꢀdiethynylpyrene, 7.8 g 130.39, 131.14, 131.18, 131.33, 123.82, 124.81,
DOKLADY CHEMISTRY Vol. 456
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NOVEL ELECTRONꢀWITHDRAWING
71
2. Wu, Q., Wang, M., Qiao, X., Xiong, Y., Huang, Y.,
Gao, X., and Li, H., Macromolecules, 2013, vol. 46,
pp. 3887–3894.
124.99, 130.32, 130.80, 131.58, 133.45, 135.79,
145.53, 152.99, 194.78 (C O), 197.37 (C O).
Poly(phenylquinoxaline) PPQꢀ1. A 25ꢀmL threeꢀ
necked flask equipped with a mechanical stirrer, a
reflux condenser, and an argon inlet was charged with
0.2143 g (1 mmol) of 3,3',4,4'ꢀtetraminodiphenyl,
=
=
3. Wright, W. and Uddin, A., Sol. Energ. Mat. Sol. Cells
2012, vol. 107, pp. 87–111.
,
4. Carsten, B., He, F., Son, H., Xu, T., and Yu, L., Chem.
Rev., 2011, vol. 111, pp. 1493–1528.
0.9032 g (1 mmol) of bis(
2.5 mL of ꢀcresol. The reaction mixture was stirred
at ambient temperature for 2 h, next temperature was
increased to 170 C and heated under these conditions
αꢀdiketone) VIII, and
5. Duan, Ch., Zhang, K., Zhong, Ch., Huang, F., and
m
Cao, Y., Chem. Soc. Rev., 2013, vol. 42, pp. 9071–9104.
6. Strukelj, M.J., J. Am. Chem. Soc., 1995, vol. 117,
°
pp. 11976–11983.
for 5 h. Then the solution of polymer was cooled and
poured into 10ꢀfold excess of acetone. The precipitate
of polymer was separated by filtration, washed with
7. Zhang, X. and Jenekhe, S., Mater. Res. Symp. Proc.,
1998, vol. 488, pp. 539–544.
8. Jenekhe, S., Zhang, X., Chen, X., Choong, V.E.,
Cao, Y., and Hsieh, B., Chem. Mat, 1997, vol. 9,
pp. 409–412.
alcohol, and dried in a vacuum at 100
viscosity of PPQꢀ1 was 0.81 dL/g in
centration 0.5 g/dL and 25 C. PPQꢀ2 was obtained in
similar manner, its characteristics are presented in
Table 2.
°
C. The reduced
ꢀcresol at conꢀ
m
°
9. Karastatiris, P., Mikroyannidis, J., and Spiliopoulus, K.,
Macromolecules, 2004, vol. 37, pp. 7867–7878.
10. Cui, Y., Zhang, X., and Jenekhe, S., Macromolecules
1999, vol. 32, pp. 3824–3826.
,
ACKNOWLEDGMENTS
11. Keshtov, M.L., Mal’tsev, E.I., Lypenko, D.A., Brusꢀ
netsova, M.A., Sosnovyi, M.A., Vasnev, V.A., Pereguꢀ
dov, A.S., Vannikov, A.V., and Khokhlov, A.R., Vysokoꢀ
mol. Soedin. Ser. A 2007, vol. 49, no. 3, pp. 565–570.
This work was supported by the Russian Foundaꢀ
tion for Basic Research (project GFEN_a no. 12–03–
91175, GFEN_a no. 13–03–91166, and IND_a
no. 13–03–92709).
12. Keshtov, M.L, Mal’tsev, E.I, Lypenko, D.A., Brusentꢀ
seva, M.A., Sosnovyi, M.A., Il’ina, M.N., Vasnev, V.A.,
Peregudov, A.S., Petrovskii, P.V., Vannikov, A.V., and
Khokhlov, A.R., Vysokomol. Soedin. Ser. A, 2008,
vol. 50, no. 1, pp. 25–32.
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Translated by I. Kudryavtsev
pp. 875–962.
DOKLADY CHEMISTRY Vol. 456
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2014