Macromolecular ligands carrying side bipyridyl-containing groups and their metal-polymer complexes with iridium

Article abstract of DOI:10.1134/S1070427212110134

A series of copolyamides carrying side bipyridyl-containing groups and their metal-polymer complexes with iridium were synthesized. The stress-strain, thermal, molecular-weight, and luminescent characteristics of these compounds were examined. All the pol

Full text of DOI:10.1134/S1070427212110134

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 11, pp. 1703−1710. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © M.Ya. Goikhman, A.A. Polevoi, I.V. Podeshvo, N.L. Loretsyan, I.V. Gofman, R.Yu. Smyslov, E.N. Popova, Yu.V. Pokhvoshchev,
V.D. Krasikov, A.V. Yakimanskii, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 11, pp. 1793−1800.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Macromolecular Ligands Carrying Side Bipyridyl-Containing
Groups and Their Metal–Polymer Complexes with Iridium
M. Ya. Goikhmana,b, A. A. Polevoib, I. V. Podeshvoa, N. L. Loretsyana, I. V. Gofmana,
R. Yu. Smyslova, E. N. Popovaa, Yu. V. Pokhvoshcheva, V. D. Krasikova,
and A. V. Yakimanskiia
aInstitute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
bSt. Petersburg State University, St. Petersburg, Russia
e-mail: goikhman@hq.macro.ru
Received October 5, 2012
Abstract—Aseries of copolyamides carrying side bipyridyl-containing groups and their metal-polymer complexes
with iridium were synthesized. The stress-strain, thermal, molecular-weight, and luminescent characteristics of
these compounds were examined. All the polymers synthesized exhibit high performance in the stress-strain
characteristics and high thermal stability.
DOI: 10.1134/S1070427212110134
Metal-containing polymers, or metal-polymer
complexes (MPCs), have become an area of increased
interest in recent years due to their potential for diversified
technical applications. The presence of transition metals
in the polymer chain of metal complexes offers a broad
range of possibilities for combining their chemical,
electrical, magnetic, optical, and redox properties with
those of organic substances. This gave an impetus to rapid
progress in studying the functional properties of MPCs
and provided motivation for searching new application
fields for them. By now, a large number of soluble,
semiconducting [1], photovoltaic [2], and luminescent [3,
4] metal-polymer complexes have been synthesized and
examined. They have found several high-technological
applications, e.g., as active layers of LEDs, polymer solar
cells, and chemical sensors. Since recently, polymers
containing Ir(III) complexes have attracted considerable
attention owing to the great potentialities of these
materials for optoelectronic applications [5].
N-methylpyrrolidone (NMP), and propylene oxide were
commercial products and used without further purification.
Other reagents and solvents were purified before use:
4,4'-diaminodiphenylmethane (DADPM) by vacuum
distillation, mp 89–91°C; m-phenylenediamine (MPDA),
by vacuum distillation, mp 64–66°C; p-phenylenediamine
(PPDA), byvacuumdistillation, mp 143–145°C; 1,4-bis(4-
aminophenoxybenzene) (BAPB), by recrystallization
from ethanol, mp 173°C; thionyl chloride, by distillation,
mp 78°C; N,N-dimethylformamide (DMF), by drying
over calcium hydride, followed by vacuum distillation,
mp 153°C; acetic anhydride, by simple distillation,
mp 140°C; pyridine, by drying over granulated caustic
potash, followed by simple distillation, mp 115°C;
ethanol, by simple distillation, mp 78°C; and toluene, by
simple distillation, mp 110–111°C.*
For synthesis of 5-[5-(2-pyridyl)-4-azaphthalimido]
isophthaloyl dichloride (5) we used the procedure
described in [6], and for synthesis of terephthaloylbis(3-
methoxy-4-oxybenzoyl) dichloride, the procedure from
[7]. A binuclear iridium complex with 2-phenylpyridine
[Ir(ppy)2Cl]2 was synthesized by the technique described
in [8].
EXPERMENTAL
Isatin, 2-acetylpyridine, 2-phenylpyridine, IrCl3·3H2O,
vanillic acid, tеrephthalic acid, 5-aminoisophthalic acid,
1703

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GOIKHMAN et al.
All the polymers were synthesized by the following
of 10 deg min–1.The basic dimensions of the samples were
1.5×10 mm. The glass transition temperature Tg was taken
to be the maximum of the loss tangent–temperature curve.
general method. Diamine (0.001 mol) and NMP (6 ml)
were introduced into a 25-ml round-bottomed flask
equipped with a stirrer. The resulting mixture was stirred
until complete dissolution of diamine and cooled to
–15°C in an ice-salt bath, after which 0.00103 mol of
dichloroanhydride was added into the cooled solution.
The resulting suspension was stirred at the indicated
temperature for 30 min, after which 3 drops of propylene
oxide were added, and stirring was continued for 5 h at
room temperature.
The phase transition temperatures were also determined
with the use of a DSC 204 F1 Phoenix (NETZSCH)
differential scanning calorimeter. The target curve was
recorded during the second heating run at the heating
rate 10 deg min–1.
The thermal stability was determined thermo-
gravimetrically on a TG 209 F1 Iris (NETZSCH)
instrument, also at the heating rate of 10 deg min–1.
In the case when more than one diamine or
dichloranhydride were added, these compounds were
introduced at 15-min intervals into the cooled solution.
Elemental analysis was carried out using
a CHNOS elemental analyzer (Vario El III, Elementar
Analysensysteme GmbH, Hanau, FRG).
The polymer solution was filtered, cast onto a glass
The polymers were synthesized by low-temperature
polycondensation which technique gives polymer
solutions with good viscosity characteristics, capable of
forming mechanically strong self-supporting films. In
this technique, the first phase consists in synthesizing
a bifunctional monomer containing a ligand moiety to be
incorporated into the main or side chain of the polymer.
As objects of our study served polymers carrying side
bipyridyl-containing moieties, which are known [9, 10]
to offer a number of advantages, in particular, enhanced
flexibility of the polymer chain and its associated
improved solubility. Considering the above-said, we
synthesized a reactive bipyridyl-containing bifunctional
monomer for low-temperature polycondensation
reactions, 5-[5-(2-pyridyl)-4-azaphthalimido]isophthaloyl
dichloride (5), whose preparation procedure is based on
isatin chemistry. The synthesis route of this compound is
presented schematically below (Scheme 1).
substrate, and dried.
Metal-Polymer Complexes. The [Ir2(ppy)4Cl2]
complex was added to a polymer solution in NMP at the
molar ratio of 1.3:1.0. The resulting mixture was heated
to 110°C with stirring for 10 h, after which the polymer
was precipitated into ethanol and extracted in a Soxhlet
apparatus for 10 h. The resulting polymer was dried,
dissolved in NMP, and cast into films.
The 1H NMR spectra of 1% solutions were recorded
on anAvance-400 (Bruker, FRG) spectrometer operating
1
at H resonance frequency of 400 MHz, with Me4Si as
internal standard.*
The luminescence spectra were measured on an LS-
100 (PTI®, Canada) spectrofluorimeter. The choice of
the excitation wavelength of 380 nm was based on the
luminescence excitation spectra of the MPC. The spectral
width of the slit of the excitation and emission mono-
chromators was 4 nm; FEU 800 multiplication was used.
In the first stage, the Pfitzinger reaction between
isatin and 2-acetylpyridine gave 2-(2-pyridyl)-quinoline-
4-carboxylic acid (1) [4], which was oxidized with
potassium permanganate in an alkaline medium into
6-pyridyl-pyridine-2,3,4-tricarboxylic acid (2) in the
second stage. Under these conditions, the benzene
ring in the quinoline cycle is oxidized giving two
vicinal carboxy groups. The third stage consisted in
decarboxylation of 6-pyridyl-pyridine-2,3,4-tricarboxylic
acid in position 6 into 6-pyridyl-3,4-pyridinedicarboxylic
anhydride (3). A 9 : 1 acetic acid-acetic anhydride
mixture served as decarboxylating agent, which afforded
fairly mild reaction conditions and, thereby, selective
decarboxylation. Another benefit of this approach is
formation of an anhydride cycle simultaneously with
decarboxylation. In the fourth stage, the reaction of
The films were mechanically tested in the uniaxial
stretching mode using a UTS 10 universal testing machine
(UTS Testsysteme, FRG). We determined the modulus of
elasticity E, yield strength σy (the point of intersection of
the tangents to the initial linear portion of the stress–strain
curve and to the portion corresponding to development
of forced elastic deformation), tensile strength σb, and
elongation at break εb These characteristics were obtained
by averaging the testing results for seven samples.
The glass transition temperatures of the films
were determined by the dynamic mechanical analysis
technique on a DMA242 C (NETZSCH) instrument. The
measurements were conducted at the frequency of 1 Hz
with the deformation amplitude of 10 at the heating rate
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 11 2012

MACROMOLECULAR LIGANDS CARRYING SIDE BIPYRIDYL-CONTAINING GROUPS
1705
Scheme 1.
COOH
N
COOH
N
O
HOOC
HOOC
KMnO4
KOH
O +
N
N
N
N
H
O
1
2
HOOC
O
COOH
ClOC
O
COCl
O
HOOC
COOH
NH2
O
N
N
O
O
O
SOCl2
Ac2O, AcOH
_CO2
N
N
N
N
N
N
3
4
5
6-pyridyl-3,4-pyridinedicarboxylic anhydride with
5-aminoisophthalic acid gave 5-[5-(2-pyridyl)-4-aza-
phthalimido]isophthalic acid (4). This reaction proceeded
in two steps. In the first step, the anhydride cycle reacted
with amino group to give amido acid which was converted
to imide in the second step by chemical cyclization under
the action of an imidizing mixture (acetic anhydride-
pyridine). In the final, fifth stage, 5-[5-(2-pyridyl)-
4-azaphthalimido]isophthaloyl dichloride (5), was
synthesized by the reaction of 5-[5-(2-pyridyl)-4-aza-
phthalimido]isophthalic acid with an excess of thionyl
chloride. The structure of all the compounds synthesized
was confirmed by 1H NMR- and IR-spectroscopic, as well
as by elemental analysis data.
polycondensation, terephthaloylbis(3-methoxy-4-
oxybenzoyl) dichloride, was synthesized from vanillic
acid and terephthaloyl chloride in accordance with
Scheme 2.
To achieve the goal of this study, consisting in
examination of how the photoluminescent characteristics
of the metal-polymer complexes vary with the polymer
chain flexibility, we synthesized several series of
polyamides and MPCs on their basis. The chain
flexibility in these compounds was controlled by using
the following chemically different aromatic diamines
as polycondensation monomers: p-phenylenediamine,
m-phenylenediamine, 4,4'-diaminodiphenylmethane, and
1,4-bis(4-aminophenoxybenzene). Scheme 3 presents the
general synthetic route for the polymers and their metal-
In the second phase, the second comonomer for
Scheme 2.
O
O
Cl
O
O
HO
2
Cl
OH
Cl
O
O O
O
O
(1) NaOH
(2) SOCl2
O
O O
Cl
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 85 No. 11 2012

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GOIKHMAN et al.
Scheme 3.
ClOC
O
COCl
OMe
MeO
N
O
H2N
NH2
n
+ n + m
+ mClOC
O
CO
CO
O
COCl
R
N
N
OMe
O
MeO
H
H
N
H
H
N
N
N
R
OC
CO
O
R
CO
CO
CO
O
CO
m
n
N
O
N
N
OMe
O
MeO
H
H
N
H
H
N
H
H
N
N
N
N
R
CO
O
CO
R
CO
CO
O
R
CO
CO
CO
O
CO
m
p
n
N
N
O
O
[Ir(ppy)2Cl]2
n + p = 0.15
m = 0.85
N
N
N
N
Cl _
Ir+
N
N
O
O
R = (1)
1 : 1 (mol)
(2)
(3)
+
polymer complexes with iridium.
and its associated insolubility of such structures under the
actual reaction conditions. Therefore, we used a mixture
of PPDA and DADPM, taken in the molar ratio of 1 : 1.
The choice of the concentration for the ligand-
containing moiety (5) was dictated by the results of
our previous studies [6] in which the comonomer
concentration was optimized to be 15 mol%. Lower
values are disadvantageous because of reduction in the
luminescence intensity, and higher values, because of
concentration quenching of luminescence.
Thus, three series of polymers were synthesized,
specifically, series I based on MPDA, series II based
on (PPDA + DADPM), and series III based on BABP,
each comprising three different types of polymers: (1)
homopolymers based on terephthaloylbis(3-methoxy-4-
oxybenzoyl) dichloride and a specific diamine (samples
I-1, I-2, and I-3); (2) copolyamides containing 85 mol%
It should be noted that we failed to synthesize
polymers based on neat PPDA due to excessive rigidity
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MACROMOLECULAR LIGANDS CARRYING SIDE BIPYRIDYL-CONTAINING GROUPS
1707
Table 1. Molecular-weight characteristics of the polymers
terephthaloylbis(3-methoxy-4-oxybenzoyl) dichloride,
15 mol% ligand-containing moiety (5), and a specific
diamine (samples II-1, II-2, and II-3); and (3) metal-
polymer complexes of iridium based on a specific
copolyamide (samples III-1, III-2, and III-3).
Molecular weight
Polydispersity
index
Sample
Mw
I-1
64000
57000
42000
49000
47000
37000
114000
43000
36000
2.06
2.16
2.14
2.16
2.63
2.09
2.17
2.19
2.09
I-2
The composition and structure of all the polymers and
metal-polymer complexes synthesized were confirmed
by 1H NMR-spectroscopic and elemental analysis data.
I-3
II-1
II-2
II-3
III-1
III-2
III-3
The molecular weight of the polymers was determined
by size exclusion chromatography using polystyrene
standards.Afairly high molecular weight was revealed for
all the polymers, which suggests their high performance
in the stress-strain characteristics. The results of the
examinations are presented in Table 1.
Based on the NMR-spectroscopic data for the aliphatic/
aromatic ratio we estimated the degree of modification
(n)/(n + p) (Scheme 3) for the MPCs comprising Ir+-
containing moieties at 34, 36, and 37 mol% for I-3, II-3,
and III-3, respectively.
when passing the vicinity of the yield point.
By contrast, in the case of the series II and series III
films the rigidity of the material (modulus of elasticity
and yield strength) decreases in going from homo- to
copolymer, with a major decreasing trend preserved
for the elongation at break. As a result, the copolymer
films have considerably poorer strength characteristics
compared to the homopolymer films. In going from
copolymers to complexes the film rigidity further
decreases, which is also true of elongation at break.
The spectral, thermal, stress-strain, molecular-weight,
and luminescent properties of the polymers synthesized
were examined.
It should be emphasized that mechanically strong,
optically transparent films exhibiting high performance
in the stress-strain characteristics were prepared from all
the polymers (Table 2).
Examination of the stress-strain properties showed that
all the polymers and their corresponding polymer-metal
complexes exhibit predominantly plastic deformation:
The stress-strain curves display a more or less prominent
peak, a yield point, and this is followed by a tendency
for necking. However, already at fairly low strain levels
(15–25%) the stress begins to grow during stretching of
the sample, i.e., the phenomenon of strain hardening of
the material is observed, especially pronounced in the
case of series II samples.
Comparison of the properties of the films formed by
homopolymers from different series shows that II-1 and
Table 2. Stress-strain properties and transition temperatures of
the polymers synthesized
Mechanical characteristics
Transition
Sample
temperature, °С
E, GPa σy, MPa σb, MPa εb, %
I-1
3.66
4.36
4.35
6.04
4.96
4.34
3.91
3.75
3.37
126
152
–
128 28
145 20
110, 235
150, 240
For series I, in going from sample I-1 to sample
I-2 (introduction of the second dianhydride, leading
from homo- to copolymer), the rigidity significantly
increases (higher modulus of elasticity and yield strength)
simultaneously with a decrease (nearly twofold) in the
elongation at break. These two opposite trends resulted
eventually in an increase in strength in going to the
copolymer. In going from copolymer to MPC, the modulus
of elasticity of the film remains virtually unchanged, but
the elongation at break sharply decreases, which results in
breakage of the MPC films based on this series polymers
I-2
I-3
125
4.0 217
II-1
II-2
II-3
III-1
III-2
III-3
206
162
–
242 30
133, 206, 290
162
8.4 140, 217
5.3 118, 258
144
143
126
120
152 32
180, 230
117
118
14
10
137, 253, 295
152, 186
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GOIKHMAN et al.
III-1 films surpass I-1 film in the modulus of elasticity
and yield strength. The elongations at break of I-1, II-1,
and III-1 films are fairly close, 30–35%. The polymer
rigidity for the copolymer films from different series
tends to decrease as II-2, I-2, III-2 (PPDA + DADPM >
MPDA > BAPB), and this trend is preserved in the case
of the corresponding MPC films.
3 the glass transition temperature exhibits an increasing
trend (171, 180, and 191°C) owing to the contribution
from the polar side groups.
In the final stage of the study we examined the lumi-
nescent properties of the polymers synthesized in solu-
tions and films. For all the metal-polymer complexes we
revealed prominent luminescence characterized by broad
bands with maxima in the red region of the spectrum. For
series I (Fig. 1) and series 2 (Fig. 2), luminescence was
observed not only for the metal-polymer complexes but
also for all the three polymers.
To summarize, in all the three cases the MPC films are
exceeded in all the characteristics by the films formed by
the corresponding copolymers.
Unfortunately, we failed to establish any trends in
variation of the transition temperatures in going from
homo- to copolymer and, further, to complex. This may
be due to the contribution coming from additional factors
associated with the specific features of the loss of solvent
during drying of chemically different polymers. Also,
the compounds examined can comprise supramolecular
structures whose degradation during heating would be
responsible for the appearance of additional transitions
in the thermograms.
The films prepared from the homopolymers and co-
polymers that do not bear iridium complexes (Figs. 1 and
2, curves 1 and 2, respectively) gave a double-peaked
spectrum in the shortwave region with maxima at 490
and 540 nm for series I and at 500 and 550 nm for series
II. Obviously, after polymerization the monomers that do
not contain chromophore groups emitting in the visible
region exhibit excimeric luminescence, forming excimers
at fairly high energies. Comparison of the band intensi-
ties in Fig. 1 suggests that a shorter-wave component at
490 nm can be attributed to excimers formed by diamine
moieties, because upon introduction of a bulky ligand-
containing unit the amount of diamine moieties able of
efficient complexing decreases due to steric hindrance.
The longer-wave component can be associated with the
contribution from the terephthaloylbis(3-methoxy-4-
oxybenzoic) acid units.
For all the polymers synthesized we determined
the indices of thermal stability in an inert atmosphere
(TGA), as well as phase transition temperatures (DSC).
It was shown that, on the whole, all the polymers belong
to thermally stable materials characterized by the
decomposition onset temperatures τ0=342–378°C. Based
on the DSC data for the series III polymers, it can be safely
said that III-2 and III-3 are statistical copolymers because
their thermograms contain a single signal associated with
a transition from glassy to high-elasticity state at 180 and
190°C, respectively. Importantly, in going from the initial
polymer III-1 to copolymer III-2 and further to MPC III-
Figure 3 shows the luminescence spectra of polymer
I-3 in DMF solutions at three different concentrations and
in chloroform at one concentration. The spectra contain
two luminescence bands, at 380–500 and 600–650 nm.
Fig. 1. Luminescence spectra of the (1) I-1, (2) I-2, and (3) I-3
polymer films. (I) Intensity, arb. units, and (λ) wavelength, nm;
the same for Figs. 2–4.
Fig. 2. Luminescence spectra of the (1) II-1, (2) II-2, and (3)
II-3 polymer films.
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MACROMOLECULAR LIGANDS CARRYING SIDE BIPYRIDYL-CONTAINING GROUPS
1709
Fig. 3. Luminescence spectra of the I-3 polymer solutions
in (1–3) DMF and (4) chloroform. Solution concentration,
mg ml–1: (1, 4) 0.05, (2) 0.1, and (3) 0.2 mg ml–1.
Fig. 4. Luminescence spectra of the (1) I-3, (2) II-3, and (3)
III-3 MPC films.
The shift of the maximum of the excimeric luminescence
band to shorter waves (420 nm) suggests higher energies
for excimers in solution compared to the condensed phase.
The longer-wave band is evidently due to luminescence
from the MPC. In going to bad solvent (chloroform) the
shortwave band disappeared, and the integrated intensity
of the long-wave band increased. The latter finding can
be explained by strengthening of intermacromolecular
interactions, resulting in efficient transfer of the electronic
excitation energy to the iridium complex.
chain affects the luminescence spectrum of the metal-
polymer complexes. With a more flexible polymer
chain, more abundant low-energy excimer states will
be formed, thereby affecting the band broadening and
intensity reduction for nonexcimeric emission from the
iridium complex.
CONCLUSIONS
(1)Anew bipyridyl-containing reactive monomer for
polycondensation reactions was synthesized.
In going from solutions to polymer films prepared
from the MPCs based on MPDA (Fig. 4, curve 1), 50%
PPDA + 50% DADPM (curve 2), and BAPB (curve 3),
the luminescence band at 380–500 nm disappears, and
the spectra exhibit a prominent maximum of intensity at
620–630 nm.
(2) Copolyamides with side bipyridyl-containing
groups and their metal-polymer complexes with iridium
were synthesized. The stress-strain, thermal, molecular-
weight, and luminescent characteristics of the compounds
prepared were examined.
This finding is consistent with the data obtained
for solutions, specifically, on compactization of the
macromolecules in going from good (DMF) to bad
(chloroform) solvent. The phenomena observed both
in going from solution to film and from good (DMF) to
bad (chloroform) solvent, can be explained by efficient
transfer of the excitation energy to MPC as a result of
compactization of the polymer coils.
(3) Prominent luminescence at 600–650 nm was
revealed for all the metal-polymer complexes synthesized,
with the band intensity and position governed by the
flexibility of the polymer chain. With increasing chain
flexibility the luminescence band tends to decrease
somewhat in intensity and shifts by ca. 30 nm to longer
waves, which suggests the excimeric mechanism of
energy transfer.
In going from the most rigid (50% PPDA + 50%
DADPM) through less rigid (MPDA) to the most flexible
(BAPB) spacer, the luminescence band maximum shifts
to longer waves (632, 623, and 655 nm, respectively), and
this is accompanied by significant broadening of the band.
In the case of the MPC based on BAPB, excimeric emission
prevails over that by nonexcimeric mechanism because of
a larger emission bandwidth and a maximum red-shifted
by >30 nm relative to the MPC based on MPDA.
ACKNOWLEDGMENTS
This study was financially supported by the
Russian Foundation for Basic Research (project no.
11-03-12044-ofi-m-2011).
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