Novel bipolar carbazole-containing polyphenylquinoxalines: Synthesis and photophysical properties

Full text of DOI:10.1134/S0012500811020054

ISSN 0012ꢀ5008, Doklady Chemistry, 2011, Vol. 436, Part 2, pp. 39–42. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © M.L. Keshtov, A.I. Stakhanov, S.I. Pozin, E.I. Mal’tsev, P.V. Petrovskii, A.R. Khokhlov, 2011, published in Doklady Akademii Nauk, 2011, Vol. 436,
No. 6, pp. 780–784.
CHEMISTRY
Novel Bipolar CarbazoleꢀContaining
Polyphenylquinoxalines:
Synthesis and Photophysical Properties
M. L. Keshtova, A. I. Stakhanova, S. I. Pozinb, E. I. Mal’tsevb,
P. V. Petrovskiia, and Academician A. R. Khokhlova
Received September 23, 2010
DOI: 10.1134/S0012500811020054
In recent time, conjugated electroluminescent noxalines (PPQs) will show higher electronꢀwithꢀ
drawing properties owing to the presence of four
electronꢀwithdrawing heteroatoms. A promising
approach to improve the quantum yield is provided
not only by the balance of the electron and hole
conduction but also by design of multilayer bipolar
(donor–acceptor) emission polymers.
polymers have attracted much attention from both
the scientific and practical viewpoint due to their
application as electroactive materials for lightꢀ
emitting diodes [1–3]. It has been found that
intense electroluminescence (EL) in polymer
requires high electron–hole conduction of a
medium related to the mobility of charge carriers
and a balance of injection of carriers of both signs
from opposite electrodes into the emission polyꢀ
meric layer. However, the majority of EL polymers
are holeꢀtransport materials, which leads to the
imbalance of charge injection and a poor quantum
yield. A search for new efficient electronꢀtransport
polymers is required to improve performance of
electrooptical devices, which is achieved in particuꢀ
lar by introducing into macromolecules electronꢀ
withdrawing fragments: triazole [4], oxadiazole [5],
quinoline [6], and quinoxaline [7]. The latter is the
least studied. One can suppose that polyphenylquiꢀ
In this work, to solve this problem, we have used a
combination of carbazoleꢀ and quinoxalineꢀcontainꢀ
ing fragments in PPQ macromolecules. Such moleꢀ
cules are known to show high thermal and oxidative
stability, good mechanical and filmꢀforming properꢀ
ties, and solubility in organic solvents [8]. In continuꢀ
ation of our studies [9–11], we have prepared and
studied novel bipolar carbazoleꢀcontaining PPQs as
efficient electron–hole and transport materials; for
this purpose, we obtained previously unknown bis(
diketone) III. A common method for the synthesis of
bis( ꢀdiketone)s is the oxidation of bis(phenylethyꢀ
αꢀ
α
nyl)arenes obtainable from aromatic dibromides and
arylacetylene.
We have proposed a new method for the synthesis
a Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28, Moscow,
119991 Russia
b Frumkin Institute of Physical Chemistry and
Electrochemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
of bis(
reaction of fluorodiketone II, already containing
bis( ꢀdicarbonyl) groups, with dicarbazole accordꢀ
ing to Scheme 1.
αꢀdiketone) III by the nucleophilic substitution
α
I
39

40
KESHTOV et al.
FeCl3
H
N
N
H
N
H
I
K2CO3
I + 2
F
N
O O
II
O O
N
O O
III
Scheme 1.
The reaction led to compound III in good yield (2H,
J = 7.2 Hz) ppm. Signal assignment in these
(88%) without affecting the carbonyl groups. The
composition and structure of target compound III
were confirmed by elemental analysis data, IR specꢀ
troscopy, and 1H and 13C NMR. In particular, the IR
spectra was made on the basis of integrated intensity
ratio and spin–spin coupling constants (Fig. 1a). The
13C NMR spectra of compound III in the range of
δ =
110–150 ppm show 20 intense signals, eight of which
are due to quaternary carbon atoms. A feature of these
spectra of compound III is the presence of downfield
spectra of the bis(
bands in the region of 1665 cm–1 typical for the C=O
group of ꢀdiketone fragment.
The 1H NMR spectra of compound III show three
multiplets at = 8.1–8.3 (4H), 7.7–7.8 (6H), and
7.4–7.58 (4H) ppm, one singlet at = 8.37 ppm, one
doublet at 7.99 ppm (4H, = 8.1 Hz), and three well
= 7.64 (2H), 7.4 (2H), and 7.32 of macromolecules according to Scheme 2.
αꢀdiketone) show strong absorption
α
signals of two different carbonyl groups of the
αꢀdikeꢀ
tone fragment at = 194 and 193 ppm (Fig. 1b).
δ
δ
Bis( ꢀdiketone) III was used for the synthesis of
α
δ
PPQs containing dicarbazole groups in the main chain
J
resolved triplets at
δ
N
N
N
N
O
O
O
O
R
n
H N
NH
NH
N
N
N
N
2
2
R
+
H N
2
2
III
IVa–IVc
Va–Vc
(R = – (a), –CH2– (b), –O– (c)).
Scheme 2.
Polymers Va
aromatic tetraamines IVa
III in an ꢀcresol solution at 190
tion proceeded homogeneously to give the polymers IR spectra of the prepared polymers lack absorption
–
Vc were obtained by the reaction of with high viscosity characteristics (
IVc with bis( ꢀdiketone) 0.94 dL/g). The structure of the polymers was conꢀ
C for 7 h. The reacꢀ firmed by the data of IR and NMR spectroscopy. The
η = 0.79–
–
α
m
°
DOKLADY CHEMISTRY Vol. 436
Part 2
2011

NOVEL BIPOLAR CARBAZOLEꢀCONTAINING POLYPHENYLQUINOXALINES
41
f
e
(a)
g
h
d
c
k
j
i
N
l
O
O
a
b
N
O
O
j, g
b, c, k
h, d
i
a
f
l
e
8.8
8.4
8.0
7.6
7.2
6.8 δH, ppm
11
(b)
2
5 20
19 18
4
14
17
3
9
6
13
12
10
15
8
23
N
O
O
16
21
11
10
12
7
22
13
15 16
21 22
2
3
1920
18
1
23
N
4
14
17
5
O
O
9
6
7
8
200
190
180
170
160
150
140
130
120
110 δС, ppm
1
13
Fig. 1. (a) H and (b) C NMR spectra of compound III
.
1000
1000
(а)
(b)
2
2
3
1
1
1000
1000
500
500
3
500
0
500
0
400
300
400
500
600
700
800
500
600
700
800
Wave length, nm
Wave length, nm
–4
Fig. 2. Fluorescence spectra of polymers (
1)
Va , (2)
Vb, and (
3)
Vc in (a) chloroform (
c
= 10 mol/L) and (b) films.
DOKLADY CHEMISTRY Vol. 436 Part 2
2011

42
KESHTOV et al.
Table 1. Certain characteristics of PPQs
ηred
С, DMF),
dL/g
T10%
,
°
C
Tensile properties of films
Polymer
R
(25°
Tg, °C
argon
air
σ, MPa
ε, %
Va
Vb
Vc
–
0.92
0.81
0.75
340
315
329
630
610
615
610
590
600
127
95
46
52
62
–CH2–
–O–
100
Table 2. Certain photophysical characteristics of polymers
λabs, max, nm*
V in solution and as films
λfl, max, nm****
Polymer
E
opt, eV**
λbeg, nm***
solution
film
solution
film
Va
Vb
Vc
430
410
420
426
408
416
2.51
2.64
2.61
493
469
476
564
544
554
554
510
520
* Absorption spectra maximum of polymers.
** Optical gap width of a polymer determined from the equation E = 1240/λ
*** λ of the beginning of absorption spectra in films.
.
beg
opt
**** Maximum of the fluorescence spectra of polymers.
bands in the ranges of 3200–3400 and 1660–1680 cm–1
related to the stretching vibrations of the C=O and
NH2 groups of the initial compounds, and show
chain extension. The optical gap widths (
E
opt) deterꢀ
mined from the absorption spectra of films are in the
range 2.51–2.64 eV. Typical fluorescence curves in
solution and solid films are shown in Fig. 2.
absorption bands at 1640 cm–1 typical of the C=N
bonds in quinoxaline rings. The 13C NMR spectra of
all the polymers also lack signals at
due to ꢀdiketone fragments. The thermal properties
of the polymers were studied by DSC and TGA within
250–700 C range. Some of PPQ characteristics are
given in Table 1. Glass transition temperatures found
from DSC curves are within 315–340 C. According to
TGA in air and argon, all PPQs begin to lose 10% of
weight at 590–610 and 610–630 C, respectively,
depending on chemical structure. Good solubility of
PPQs in organic solvents ( ꢀcresol, NMP, phenols)
allowed preparation from solution polymer films
showing tensile strength = 95–127 MPa and specific
elongation = 46–62% (Table 1).
δ = 190–195 ppm
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DOKLADY CHEMISTRY Vol. 436
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2011