Now electrochromic polyphenylquinoxalines

Full text of DOI:10.1134/S0012500810110078

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 435, Part 1, pp. 297–301. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © M.L. Keshtov, V.S. Kochurov, A.R. Khokhlov, 2010, published in Doklady Akademii Nauk, 2010, Vol. 435, No. 3, pp. 347–351.
CHEMISTRY
Now Electrochromic Polyphenylquinoxalines
M. L. Keshtova, V. S. Kochurovb, and Academician A. R. Khokhlova
Received May 28, 2010
DOI: 10.1134/S0012500810110078
π
ꢀConjugated triarylꢀcontaining polymers have with high electron affinity and thermostability [10, 11]
received considerable recent attention not only as effiꢀ but also exhibit excellent electrochromic properties.
cient holeꢀtransport materials but also as promising However, TAAꢀcontaining PPQs have not been studꢀ
electrochromic materials [1–3]. The electrochemical ied as candidates for electrochromic materials. The
oxidation of triarylamine (TAA) readily yields a stable introduction of bulky TAA units into PPQs not only
radical cation with high charge mobility and long lifeꢀ enhances the solubility without detriment to useful
time, which is accompanied by a noticeable change in properties, but also imparts to polymers holeꢀtransꢀ
color [4, 5]. This renders TAA an attractive anodic port and electrochromic properties and improves
electrochromic “building block.” Various poliimides, chargeꢀcarrier transport. With the aim of obtaining
polyamides, polyphenylenes, and polyazomethines TAAꢀcontaining PPQs, we synthesized a series of new
with TAA units in the backbone, combining high therꢀ bisꢀ
mal stability and favorable photochemical and elecꢀ to give bis(4ꢀbromophenyl)arylamine
trochromic properties, have been synthesized [6–9]. then crossꢀcoupled with phenylacetylene. Compound
Polyphenylquinoxalines (PPQs) with TAA fragments II thus obtained was oxidized to target bisꢀ
ꢀdiketone
α
ꢀdiketones III. To this end, TAA was brominated
I, which was
α
are not only efficient electronꢀtransport
nꢀtype blocks III (Scheme 1).
N
R
Br
N
Br
R
I(a, b)
2
N
R
[Pd], CuI, Et3N
II(a, b)
a Nesmeyanov Institute of Organoelement Chemistry, Russian Academy of Sciences, ul. Vavilova 289, Moscow 119991 Russia
b Moscow State University, Moscow, 119991 Russia
297

298
KESHTOV et al.
N
KMnO4
[R = H(a), NO2(b)]
II(a), II(b)
O O
O O
III(a), III(b)
R
Scheme 1.
The composition and structure of compounds
I
,
lets at 7.67 and 7.77 ppm caused by overlap of the
signals of the meta and para protons of free phenyl
groups. The 13C NMR spectrum shows two signals
II, and target product III were confirmed by eleꢀ
1
mental analysis, IR spectroscopy, and H and 13C
NMR. In particular, the IR spectra of bisꢀ
α
ꢀdikeꢀ
of the carbonyl groups of the
at 195.12 and 194.66 ppm.
αꢀdiketone fragment
tone IIIb shows characteristic bands
αꢀdiketone
1
1
group stretches (1674 cm⎯ ). The H NMR specꢀ
Bisꢀαꢀdiketones IIIa and IIIb were used for synꢀ
trum shows four doublets at 8.21, 8.00, 7.81, and
7.21 ppm due to five types of protons and two tripꢀ thesizing PPQs IV according to Scheme 2.
N
N
N
H2N
H2N
NH2
NH2
O
O
O
O
+
N
R
N
R
N
n
III(a), III(b)
IV(a)–IV(c)
=
(a, b);
(c); R = H (a), NO2 (b)
.
H
C
8
C8H17
C H
17
17
8
Scheme 2.
PPQs were synthesized in
mꢀcresol for 5 h at 160°C. allowed us to obtain films with the breaking strength
The process occurred under homogeneous conditions
and afforded polymers with relatively high reduced
viscosity (ηred = 0.79–0.92 dL/g).
σ
= 85–95 MPa and the percent elongation
ε =
8
⎯10%. The absorption spectra of the polymers in
solutions and thin films show strong absorption with
maxima in the ranges 410–450 and 405–445 nm,
respectively. Under the same conditions, the fluoresꢀ
cence maxima are observed in the ranges 535–600 and
530–560 nm, respectively.
The structure of polymers IV was confirmed by IR
spectroscopy.
The spectra of all polymers show absorption bands
at 1640–1545 cm–1 typical of C=N stretches in quiꢀ
The electrochemical properties of the polymers
noxaline rings and lack the bands in the regions 1660– were studied by cyclic voltammetry (Table 2). All polyꢀ
1680 and 3200–3400 cm–1 due to the C=O and NH2
stretching vibrations of the initial compounds. The
glass transition temperatures of PPQs found from
DSC curves are in the range 224–315°C (Table 1).
The temperatures of 10% weight loss in argon and air
mers exhibit reversible redox properties and show a
redox couple in the range E1/2 = 0.92–1.25 eV. Typical
cyclic voltammograms for polymer IVa are shown in
Fig. 1. PPQ IVa shows a reversible redox couple at
E1/2 = 1.04 V which is assigned to the radical cation
are in the range 420–577 and 414–550°C, respecꢀ that emerges on removal of an electron from the nitroꢀ
tively. The solubility of PPQs in aprotic solvents gen atom of the TAA fragment [12]. The band gap
DOKLADY CHEMISTRY Vol. 435
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2010

NOW ELECTROCHROMIC POLYPHENYLQUINOXALINES
Table 1. Some characteristics of PPQs of general formula
299
N
N
N
N
N
R
n
IV(a)–IV(c)
Tensile properties of films
ηred, dL/g
ꢀcresol,
25 C)
T10%, °C*
(TGA,
= 20 K/min)
Tst, °C
Polymer
R
(m
σ
, MPa
95
ε
, %
°
ΔT
550
ꢀꢀꢀꢀꢀꢀ
IVa
IVb
H
0.81
0.92
308
315
8
577
507
ꢀꢀꢀꢀꢀꢀ
NO2
H
90
8
529
414
ꢀꢀꢀꢀꢀꢀ
IVc
0.79
224
85
10
420
H C
C81H7
C8H17
8
17
* The numerator pertains to heating in air and the denominator, to heating in argon.
Table 2. Some optical and electrochemical properties of polymers IVa–IVc
abs
max
fl
max
abs
λ
onset
4
HOMO *2
LUMO *3
eV
Eopt
*
E1/2
1
1
λ
*
λ
*
Polymer
nm
V
435
ꢀꢀꢀꢀꢀꢀ
535
ꢀꢀꢀꢀꢀꢀ
IVa
IVb
IVc
495
482
510
5.40
5.61
5.28
2.89
3.04
2.85
2.51
1.04
1.25
0.92
432
530
410
ꢀꢀꢀꢀꢀꢀ
600
ꢀꢀꢀꢀꢀꢀ
2.57
2.43
405
560
450
ꢀꢀꢀꢀꢀꢀ
535
ꢀꢀꢀꢀꢀꢀ
445
533
1
2
–4
*
In the numerator are absorption and luminescence maxima in chloroform (c = 10 mol/L) and in the denominator, the same in thin films.
+
* HOMO
= 4.8 eV (HOMOFc/Fc+ ) +
E
(polym) – 0.44 эВ (
E
= Fc/Fc ), where HOMOFc/Fc+ is the standard in vacuum, and
polym
1/2
1/2
E
(polym) is the external redox standard.
1/2
3
opt
* HLUMO = HOMO –
E
.
abs
4
opt
*
E
= 1240/
λ
.
onset
chemical data in Table 2 shows that polymer IVc
E1/2 = 0.92 eV) is more readily oxidized than polyꢀ
mers IVa E1/2 = 1.04 V) and IVb E1/2 = 1.25 V). It is
spectra of films (Table 2). Comparison of the electroꢀ likely that the introduction of electronꢀdonor groups
width (
were determined from the halfꢀwave potential (E1/2)
E
opt), HOMO, and LUMO of the polymers
(
abs
(
(
and the absorption onset wavelength
λ
in the
onset
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300
KESHTOV et al.
0.6
0.4
0.2
0
−
0.2
0
0.4
0.8
1.2
U, V
Fig. 1. Cyclic voltammograms of PPQ IVa in a 0.1 M tetrabutylammonium perchlorate–acetonitrile solution at a sweep rate of
50 mV/s.
D
410 nm
1.0
860 nm
0.5
g
f
e
d
c
b
a
0
400
500
600
700
800
λ, nm
Fig. 2. Electronic absorption spectra of PPQ IVb in a 0.1 M tetrabutylammonium perchlorate–acetonitrile solution
(vs. Ag/AgCl). Potentials, V: ( ) 0, ( ) 1.0, ( ) 1.2, ( ) 1.3, ( ) 1.5, ( ) 1.7, and ( ) 1.9.
a
b
c
d
e
f
g
decreases the oxidative potential of electroactive polyꢀ 1.9 V in the course of oxidation, the characteristic
mers.
peak at 410 nm corresponding to the neutral form of
PPQ IVb becomes gradually weaker and shifts to
391 nm; at the same time, a broad signal appears at
860 nm, which gradually builds up with increasing
applied potential due to the formation of the stable
radical cation assigned to the TAA fragment. This is
The electrochromic properties of PPQs were studꢀ
ied by means of an optically transparent thinꢀlayer
electrode interfaced with a UVꢀVIS spectrophotomeꢀ
ter. Typical electrochromic absorption spectra of polyꢀ
mer IVb recorded at different potentials are shown in
Fig. 2. With increasing the applied potential from 0 to accompanied by a change in the film color from yellow
DOKLADY CHEMISTRY Vol. 435
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NOW ELECTROCHROMIC POLYPHENYLQUINOXALINES
301
(neutral form) to claret (oxidized form). The time of
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DOKLADY CHEMISTRY Vol. 435
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2010