Electronic Structure and Electrooptical Properties of Radicals Formed upon Reduction of N-Alkyl 4,4′-Bipyridylium Salts

Article abstract of DOI:10.1134/S0036023618060189

N-Alkyl 4,4'-bipyridylium salts were synthesized and characterized. Cyclic voltammetry investigation showed that monosubstited 4,4'-bipyridylium salts are prone to reversible single-electron reduction. The formal redox potentials vs. a saturated silver chloride electrode were determined for different potential sweep rates. High-resolution ESR spectra of the radical cations formed upon the reduction of N-substituted 4,4'- bipyridylium salts in acid media were measured and interpreted. The substituent structure and the type of anion in the molecule have a considerable effect on the spin density distribution, current–voltage characteristics, and elctrooptical properties. The applicability of monosubstituted 4,4'-bipyridylium salts as photoelectrochromic compounds was studied.

Full text of DOI:10.1134/S0036023618060189

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2018, Vol. 63, No. 6, pp. 815–821. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © V.V. Minin, M.I. Zakirov, N.N. Efimov, P.V. Mel’nikov, E.L. Nodova, B.I. Shapiro, V.M. Novotortsev, 2018, published in Zhurnal Neorganicheskoi Khimii,
2018, Vol. 63, No. 6, pp. 770–776.
PHYSICAL METHODS
OF INVESTIGATION
Electronic Structure and Electrooptical Properties of Radicals
Formed upon Reduction of N-Alkyl 4,4'-Bipyridylium Salts
a,
b
a
c
d
V. V. Minin *, M. I. Zakirov , N. N. Efimov , P. V. Mel’nikov , E. L. Nodova ,
c
a
B. I. Shapiro , and V. M. Novotortsev
a
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia
b
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, 119991 Russia
c
Lomonosov Moscow State University of Fine Chemical Technology, Moscow, 119571 Russia
International University of Nature, Society, and Man “Dubna,” Moscow, 141980 Russia
d
*
e-mail: minin@igic.ras.ru
Received October 3, 2017
Abstract⎯ N-Alkyl 4,4'-bipyridylium salts were synthesized and characterized. Cyclic voltammetry investiga-
tion showed that monosubstited 4,4'-bipyridylium salts are prone to reversible single-electron reduction. The
formal redox potentials vs. a saturated silver chloride electrode were determined for different potential sweep
rates. High-resolution ESR spectra of the radical cations formed upon the reduction of N-substituted 4,4'-
bipyridylium salts in acid media were measured and interpreted. The substituent structure and the type of
anion in the molecule have a considerable effect on the spin density distribution, current–voltage character-
istics, and elctrooptical properties. The applicability of monosubstituted 4,4'-bipyridylium salts as photoelec-
trochromic compounds was studied.
DOI: 10.1134/S0036023618060189
Disubstituted 4,4'-bipyridylium salts (viologens)
In this communication, we report the synthesis of a
are widely used as herbicides [1], electro- [2] and pho- number of monosubstituted 4,4'-bipyridylium salts.
tochromic [3] compounds, and thin-film catalysts for The radical cations derived from monosubstituted
fuel cells [4]. Conversely, monosubstituted 4,4'-bipyr- 4,4'-bipyridylium salts were studied and characterized
idylium salts have not aroused much interest, but have by electron spin resonance (ESR). The radical cations
been used as intermediates for the preparation of were obtained by electro- and photochemical reduc-
unsymmetrical viologens.
tion.
It is known that reduction of viologens affords rad-
ical cations (RC) that exhibit chromism. This term
stands for the reversible color change under the action
of electric current or on exposure to light or electron
beam. If the color changes under the action of ultravi-
olet radiation and changes back on exposure to visible
light, this phenomenon is called photochromism. If
the color change is induced by electron beam, this is
cathodochromism, and the electric field-induced
color change is called electrochromism.
Study of monosubstituted bipyridylium salts shows
that the radicals resulting from reduction of the initial
salts tend to form chelates. The formation of these
chelates has been described in the literature [5]. The
electrochemical reduction of N-methyl-4,4'-bipyridy-
lium in acidic aqueous solutions (pH 2–5.3) is accom-
panied by protonation of the unsubstituted nitrogen to
give intensely colored RC [6]:
e−
−
+
R N
N
R N
N
−e
EXPERIMENTAL
The monoalkyl 4,4'-bipyridylium salts of the gen-
eral formula
2
3
3' 2'
−
R N1
N A
1'
6
5
6' 5'
(
1, 2, R = CH , A = I, PF ; 4, 5, R = CH –CH=CH ,
3 6 2 2
A = Br, PF ; 6, 7, R = CH C H , A = Cl, PF ) for this
6
2
6
5
6
study were prepared by procedures described below.
1
The products were characterized by H NMR spec-
troscopy, elemental analysis, and MALDI mass spec-
trometry.
In order to increase the solubility of monoalkyl
4
,4'-bipyridylium salts in less polar solvents, the halide
Me N
NH
anion was replaced by the hexafluorophosphate anion
815

8
16
MININ et al.
via addition of an aqueous solution of ammonium repeated several times until gas evolution was no lon-
hexafluorophosphate to a stirred aqueous solution of ger detected. Then the cell was filled with argon.
bipyridylium salt followed by collection of the precip-
itate on a glass filter.
The radicals were generated by irradiating the sam-
ples with a 100 W gas discharge mercury lamp. This
1
-Methyl-4,4'-bipyridylium iodide. 4,4'-Bipyridine induced a change in the solution color, with the ESR
(
6.24 g, 40 mmol) and iodomethane (2.73 g, 44 mmol) signal being increased with increasing color intensity.
were stirred at room temperature in acetone for 24 h.
The precipitate was collected on a glass filter and
recrystallized from an isopropyl alcohol–water mix-
ture to give a yellow powder. The yield was 75%.
1
The ESR spectra were run on a Bruker E-680X
ELEXSYS radiospectrometer at room temperature
within 5–10 min after the start of photolysis or mixing
of solutions. For increasing the spectrometer resolu-
H NMR (500 MHz, D O as the solvent, and TMS tion, a modulation frequency of 30 kHz was used.
2
as the reference) (δ): 8.95 (d, 2H); 8.84 (d, 2H); 8.75
d, 2H); 7.99 (d, 2H); 4.39 (s, 3H).
The theoretical simulation of the ESR spectra was
carried out using a dedicated Spectrum Analyzer soft-
(
For C H N I, anal. calc. (%): C, 44.31; H, 3.72; ware (P. V. Mel’nikov).
11
11
2
N, 9.40; I, 42.57.
Cyclic voltammograms were measured using an
Ekotest-VA voltammetric analyzer manufactured by
the LLC Ekonix-Expert. Prior to recording cyclic vol-
tammograms, oxygen was eliminated from the systems
by bubbling argon for 5 min. DMF was used as the sol-
vent; 0.15 M tetrabutylammonium bromide served as
the supporting electrolyte; and a saturated silver chlo-
ride reference electrode was used.
The electrooptical characteristics of DMF solu-
tions of the monosubstituted salts were measured in
glass cells (Fig. 1a). An experimental setup was
designed to study characteristics of electrochromic
devices (Fig. 1b). A direct voltage was applied to sam-
ple (3) from power source (4). In the experiment,
Found (%): C, 4.25; H, 3.76; N, 9.36; I, 42.61.
m/z: 171.
1
-Allyl-4,4'-bipyridylium bromide. 4,4'-Bipyridine
(
4.68 g, 30 mmol) and allyl bromide (3.63 g, 30 mmol)
were stirred at room temperature in acetone for 24 h.
The precipitate was collected on a glass filter and
recrystallized from isopropyl alcohol to give a pink
powder. The yield was 79%.
1
H NMR (500 MHz, D O as the solvent, and TMS
2
as the reference) (δ): 8.88 (d, 2H); 8.65 (d, 2H); 8.31
d, 2H); 7.81 (d, 2H); 6.10 (m, 1H); 5.48 (m, 2H); 5.20
d, 2H).
(
(
For C H BrN , anal. calcd. (%): C, 56.34; H, a light beam from light source (1) having passed
1
3
13
2
4
.73; N, 10.10; Br, 28.83.
through diaphragm (2) was measured with sensor
5) of spectrometer (8) connected to computer (6).
(
Found (%): C, 56.27; H, 4.79; N, 10.04; Br, 28.88.
m/z: 197.
The voltage drop in the resistor connected in series
with the sample was applied to oscilloscope (7). The
resistance of the resistor was adjusted in such a way
that it had no noticeable effect on the current through
the sample (not more than 10% of the sample resis-
tance). The data recorded by the oscilloscope were
used to calculate the dependence of the charge passed
through the sample on the coloring and/or bleaching
1
-Benzyl-4,4'-bipyridylium chloride. 4,4'-Bipyridine
(
4.68 g, 30 mmol) and benzyl chloride (3.81 g, 30 mmol)
were refluxed in toluene for 4 h. The mixture was
cooled and the precipitate was collected on a glass fil-
ter and recrystallized from a toluene–isopropyl alco-
hol mixture to give a white powder. The yield was 50%.
1
H NMR (500 MHz, D O as the solvent, and TMS time and electrochromic efficiency. The absorption
2
and transmission spectra were recorded on a USB HR
as the reference) (δ): 9.02 (d, 2H); 8.76 (d, 2H); 8.40
4000 spectrometer (OceanOptics) (8).
(d, 2H); 7.89 (d, 2H); 7.53 (s, 5H); 5.87 (s, 2H).
For C H N Cl anal. calcd. (%): C, 72.20; H, 5.35;
17
15
2
N, 9.91; Cl, 12.54.
RESULTS AND DISCUSSION
According to cyclic voltammetry data, monoalkyl
,4'-bipyridylium halide salts are prone to reversible
Found (%): C, 72.10; H, 5.40; N, 9.86; Cl, 12.62.
m/z: 247.
4
The concentration of monosubstituted 4,4'-bipyridy- single-electron reduction (Fig. 2). This type of curves
lium salts in solutions for photochemical reduction was is typical of all monosubstituted 4,4'-bipyridylium
–3
salts.
chosen most often to be around (1–2) × 10 mol/L; the
solvents were 96% ethanol, acetonitrile, and
According to the Nernst theory [7], the ΔE value
N,N-dimethylformamide (DMF). Solutions of the for a reversible single-electron electrochemical pro-
quaternary bipyridylium salts in the specified solvent cess should be 59 mV. However, the influence of
were degassed prior to experiments. For removal of uncompensated resistance of the solution and other
atmospheric oxygen, solutions of the samples were factors leads to increase in ΔE to 60–70 mV, which is
frozen by liquid nitrogen directly in the electrochemi- similar to the result that we obtained at low sweep
–3
cal cell, evacuated to a residual pressure of 10
mmHg, and then unfrozen; these operations were ΔE increases (Fig. 2).
rates. It is also known that with increasing sweep rate,
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ELECTRONIC STRUCTURE AND ELECTROOPTICAL PROPERTIES
817
(a)
20
50 mV/s
100 mV/s
15
1
10
2
3
2
5
0
–1300
–1100
–900
–700
–500
–
–
–
–
5
10
15
20
1
(b)
Voltage, mV
–25
4
3
Fig. 2. Cyclic voltammograms of 1-allyl-4,4'-bipyridylium
bromide (3) in DMF; 0.15 M tetrabutylammonium bro-
mide as the supporting electrolyte, a saturated silver chlo-
ride reference electrode; potential sweep rate, mV/s: (1) 5;
7
6
(2) 10; (3) 20; (4) 50; (5) 100, (6) 150.
8
1
5
deviation of the model data from the experiment
served as the target function. The optimization meth-
ods included the coordinate descent and conjugate
gradients. The calculation results are summarized in
Table 2.
The ESR spectra of the radical cations generated
from the monosubstituted 4,4'-bipyridylium salts
upon electrochemical or photochemical reduction are
identical.
2
Fig. 1. (a) Structure of the electrochromic cell: (1) glass,
(
2) transparent conducting indium tin oxide (ITO) layer,
3) EC composition; (b) diagram of the experimental setup
(
for testing EC devices: (1) light source, (2) diaphragm, (3)
sample, (4) direct voltage source, (5) spectrometer sensor,
(
6) computer, (7) oscilloscope, (8) spectrometer.
According to quantum chemical calculations, the
H
H
H
Table 1 presents the experimental redox potentials
of monosubstituted 4,4'-bipyridylium salts. As the
N
N'
splitting constants α , α , α 2,6), α
, α , and
(
(2',6')
(3,5)
H
anion bulk grows in the series 1 (A = I) < 2 (A = PF ),
α
(3',5')
are not equal and the corresponding nitrogen
6
and hydrogen nuclei are non-equivalent. It should be
3
(A = Br) < 4 (A = PF ), 5 (A = Cl) < 6 (A = PF ),
6 6
noted that high convergence of the spectra close to
00% was attained using the phenomenological
the potential increases. Apparently, this trend is
caused by the fact that counter-ion migration slows
down as its size increases.
1
model. The experimental and simulated ESR spectra
of the radicals are identical in the form and the num-
ber of HFS components; this allows more accurate
determination of the pattern of spectral splitting and
calculation of HFS constants.
The best resolution was obtained in the ESR spec-
tra of radicals generated by photochemical reduction.
Figure 3a shows the high-resolution ESR spectrum of
the radical of 1-methyl-4,4'-bipyridylium iodide (1)
generated by photochemical reduction in 96% etha-
nol. The pattern of spectral splitting was determined to
The theoretical simulation of the ESR spectra was
carried out using a phenomenological model of the
hyperfine structure (HFS). It is a linear combination
of Lorentzians corresponding to single spectral transi-
tions taking account of spectral density components
for dynamic perturbations.
For developing an adequate model for reliable HFS
simulation, one should know the limiting equilibrium
conformation of the radical.
For open shells, ab initio LCAO MO SCF calcula-
tions were carried out by the unrestricted Hartree–
Fock (UHF) method with the 6-31G basis set using
the FireFly quantum chemical program package [8],
which partially uses the GAMESS code (US) [9]. As a
result, groups of spectrally equivalent atomic nuclei
composing the HFS simulation scheme were distin-
guished. The dynamic perturbations were included by
adding equations relating spectral parameters (multi-
plet line widths and positions) to reduce the number of
variable parameters and to increase the speed and
robustness of optimization. The root-mean-square
Table 1. Cyclic voltammetry characteristics
Compound
E, V
ΔE, mV
1
2
3
4
5
6
–0.879 ± 0.008
–0.950 ± 0.011
–0.840 ± 0.010
–0.908 ± 0.008
–0.826 ± 0.011
–0.891 ± 0.006
78
72
79
71
77
79
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 63 No. 6 2018

8
18
MININ et al.
Table 2. HFS constants in the ESR spectra of neutral radicals generated from monosubstituted 4,4'-bipyridylium salts by
the photochemical process
Splitting constants, G
Com-
pound
HFS simulation scheme for the ESR spectrum
αN
αN' α(H
H
(2,6)
H
(2',6')
H
(3,5)
H
(3',5')
α
α
α
α
alpha)
1
2
3
4
5
6
6.089 3.940 4.120 1.177 1.650 1.388 1.590 3N × 3N' × 4H(CH ) × 3H(C ) × 3H(C ') × 3H(C ) × 3H(C ')
3 2 2 3 3
5.904 3.932 4.080 1.292 1.674 1.477 1.512 3N × 3N' × 4H(CH ) × 3H(C ) × 3H(C ') × 3H(C ) × 3H(C ')
3
2
2
3
3
5.336 4.405 2.593 1.276 1.680 1.453 1.529 3N × 3N' × 3H(Calpha) × 3H(C ) × 3H(C ') × 3H(C ) × 3H(C ')
2
2
3
3
5.501 4.293 2.720 1.339 1.549 1.392 1.429 3N × 3N' × 3H(Calpha) × 3H(C ) × 3H(C ') ×3H(C ) × 3H(C ')
2
2
3
3
5.323 4.415 2.647 1.245 1.590 1.454 1.574 3N × 3N' × 3H(Calpha) × 3H(C ) × 3H(C ') × 3H(C ) × 3H(C ')
2
2
3
3
5.551 4.257 2.685 1.370 1.542 1.427 1.442 3N × 3N' × 3H(Calpha) × H(C ) × 3H(C ') × 3H(C ) × 3H(C ')
2
2
3
3
be 3N × 3N' × 4H(CH ) × 3H(C ) × 3H(C2',6') × 3H(C ) × 3H(C ) × 3H(C ) × 3H(C ) and the
3
2,6
2,6
2',6'
3,5
3',5'
N
N'
3
H(C ) × 3H(C ) and the constants were calcu- constants were calculated to be: α = 5.904 G, α
lated to be α = 6.089 G, α = 3.940 G, α (CH ) =
.120 G, α (H = 1.177 G, α
=
=
3,5
3',5'
N
N'
H
H
(2,6)
H
H
3
3.932 G, α (CH ) = 4.080 G, α
= 1.292 G, α
(2',6')
3
H
(2',6')
H
H
3,5)
H
4
= 1.650 G, α
=
2,6)
(3,5)
1.674 G, α( = 1.477 G, α
= 1.512 G.
(3',5')
.388 G, α(H
3',5')
1
= 1.590 G.
Figure 4 shows the ESR spectrum of the 1-allyl-
,4'-bipyridylium bromide (3) radical generated by
photochemical reduction in 96% ethanol. The spec-
trum contains about 30 lines instead of 2187 lines. This
is attributable to the lack of equivalence of resonating
atoms and, hence, different HFS constants, giving rise
4
Figure 3b shows the high-resolution ESR spectrum
of the 1-methyl-4,4'-bipyridylium hexafluorophos-
phate (2) radical cation generated by photochemical
reduction in acetonitrile. The pattern of spectral split-
ting was determined to be 3N × 3N' × 4H(CH ) × to overlap and superimposition of spectral lines. The
3
(a)
10 G
(b)
Fig. 3. ESR spectrum of the radical generated from (a) methyl-substituted 4,4'-bipyridylium salt 1 (A = I) in 96% ethanol;
b) 2 (A = PF ) in acetonitrile.
(
6
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ELECTRONIC STRUCTURE AND ELECTROOPTICAL PROPERTIES
819
10 G
Fig. 4. ESR spectrum of the radical generated from 1-allyl-4,4'-bipyridylium bromide 3 (A = Br) in 96% ethanol.
ESR spectra of compounds 3 and 4 are identical in the
H
H
constants α . Therefore, the splitting constants α
,
(
x)
(2,6)
form and the number of observable HFS components;
H
H
H
the pattern of spectral splitting is also the same: 3N × α(2',6'), α , α
are not equal and the correspond-
(3,5)
(3',5')
3
N' × 3H(C ) × 3H(C ) × 3H(C ) × 3H(C ) × ing protons are non-equivalent.
alpha
2,6
2',6'
3,5
3
H(C ); however, the corresponding HFS constants
3',5'
A similar situation is encountered in the assign-
ment of the HFS constants in the ESR spectra of the
radicals generated from the allyl- (3 (A = Br), 4 (A =
PF )) and benzyl-substituted (5 (A = Cl), 6(A = PF ))
are not equal (Table 2). This may be caused by the
influence of the type of anion on the electronic struc-
ture and by the distribution of the unpaired electron
spin density in the molecule.
6
6
4
,4'-bipyridylium salts.
The ESR spectra of the radicals generated from
compounds 5 and 6 possess similar spectral character-
istics and similar splitting patterns, but have different
HFS constants, like in the case of compounds 3 and 4.
The difference between the HFS constants of
methyl-substituted radicals and those of allyl- or ben-
zyl-substituted radicals deserves mention. The rota-
tion of a methyl group is known to be free, resulting in
averaged splitting constants. Meanwhile, in the case of
allyl or benzyl substituent, one position of the trigonal
rotor is occupied by a more bulky group, which serves
as a sort of anchor preventing the rotation. The
observed splitting is related to the dihedral angle
between the π-system and the atomic nucleus in the
substituent and is described by the torsion angle func-
tion [10], whose special case is the Heller–McConnell
The influence of the nature of anions of monosub-
stituted 4,4'-bipyridylium salts on the unpaired elec-
tron spin density distribution in the molecule was
identified for the first time. The HFS constants we
found for compounds 1 (A = I), 3 (A = Br), 5 (A = Cl),
2
, 4, 6 (A = PF ) increase in the series 1 (A = I) < 2 (A =
6
PF ); 3 (A = Br) < 4 (A = PF ); 5 (A = Cl) < 6 (A =
6
6
−
6
−
−
−
PF ), or Cl < Br < I < PF . The observed trends are equation. The equilibrium orientation of the hydrogen
6
caused by the fact that the counter-ion migration nuclei in allyl and benzyl groups is such that the
slows down as its size increases, which is in good
agreement with the conclusion derived from current–
voltage characteristics. Also, this can be associated
with the electronegativity (on the Pauling scale) of the
H
observed splitting α(
is lower than the averaged
alpha)
value observed for the methyl-substituted derivative.
As an example, Fig. 5 shows the kinetic curves for
anion or anion complex and, as a consequence, with the current passed through the sample vs. time and the
the electrostatic interaction strength. One more possi- curves for transmittance and absorbance vs. time.
ble reason is that the aromatic protons are more sensi- These results were used to calculate the charge
tive to the change in the spin density at lower splitting through the sample per unit time
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 63 No. 6 2018

8
20
MININ et al.
(a)
where D and D are the absorbances of the colored and
0
2
Current, mA
bleached sample; S is the working layer area, cm ; q is
the passed charge, C; i is current, A; t is time, s.
12
10
The integration was done over the current passage
time up to coloring intensity of 90% of the maximum
value and the integration for absorbance was carried
out over the visible wavelength range.
Simultaneously, the transmittance vs. time curves
were used to calculate the contrast for coloring at the
absorption maximum
8
6
4
2
ΔTmax = 1 – (I/I ) × 100%,
0
where I and I are the light fluxes having passed
0
2
4
6
8
10
12
14
0
Time, s
through the colored and bleached sample, respec-
tively.
(b)
1
00
Also the integral transmittance ΔT was calculated
int
2
over the whole visible wavelength range
(
I I0
)
dλ .
(
)
0
.8
∫
7
5
The key characteristics of the visible spectra of solu-
tions of monosubstituted salts 1–6 in DMF and their
electrochromic characteristics are summarized in
Table 3.
5
0
0
.4
The differences between the electrochromic char-
acteristics of the initial bipyridines are related to their
chemical structure and predominant formation of
neutral radicals in the case of methyl-substituted salt 1
(A = I), resulting in a substantially higher absorbance,
high contrast, and short switch-on time of the effect.
As a consequence, the sample based on N-methyl-
4,4'-bipyridylium iodide shows a higher electrochro-
mic efficiency than the samples based on allyl- and
benzyl-substituted salts. Meanwhile, replacement of
the anion does not affect much the electrochromic
parameters in the series of compounds 1, 2, 3, 4, 5, and
6 and rather decreases the electrochromic efficiency. The
passed charge q and the related electrochromic efficiency
2
5
0
1
0
4
8
12
Time, s
Fig. 5. Kinetic curves of (a) current; (b) (1) transmittance
and (2) absorbance during current passage through the
sample.
q = idt,
∫
the electrochromic efficiency at the absorption maxi- η also change; the latter value approaches the corre-
mum (η ) for the wavelength λ corresponding to sponding value for a solution in DMF.
max
max
the absorption maximum
The results of measurements of the electrochromic
characteristics of monosubstituted 4,4'-bipyridylium
salts in solutions are in good agreement with the con-
clusion drawn from quantum chemical calculations
and phenomenological simulation of the HFS of the
ESR spectra of neutral radicals generated from mono-
substituted 4,4'-bipyridylium salts.
ηmax = ΔDS q =
(
D − D0
)
S
idt,
∫
and the integral electrochromic efficiency (ηint)
ηint D − D0 dλS idt,
=
(
)
∫
∫
Table 3. Electrochromic characteristics
2
2
Compound
Dmax
τ , s
λmax, nm
ΔTmax, %
ΔT , %
q, mC
ηmax, cm /C η , cm /C
int
90
int
1
2
3
4
5
6
0.48
0.48
0.46
0.46
0.39
0.39
13.4
14.3
15.6
16.2
18.9
19.8
601
605
568
572
564
564
92.4
92.1
89.0
89.4
88.7
89.2
46.6
46.0
45.8
45.1
39.9
39.3
78.2
80.9
89.1
92.1
98.4
102.3
132.7
131.2
110.4
108.7
99.3
50.5
50.3
46.2
45.8
41.0
40.2
97.5
τ
is the time required to reach 90% color intensity with respect to the maximum. The concentration of monosubstituted salts in solu-
0
9
tions is 0.1 mol/L.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 63
No. 6
2018

ELECTRONIC STRUCTURE AND ELECTROOPTICAL PROPERTIES
Thus, the following conclusions can be drawn.
821
Diagnostics of Materials with Paramagnetic Centers”
(
I.8P3) supervised by Academician Yu.A. Zolotov.
(
1) The distribution of the unpaired electron den-
sity in the radicals generated from monosubstituted
,4'-bipyridylium salts by two independent methods is
virtually identical.
4
REFERENCES
. W. R. Boon, Chem. Ind. (London), 782 (1965).
1
(
2) The nature of counter-ions in the radicals gen-
erated from monosubstituted 4,4'-bipyridylium salts
was found to affect the electrochemical reduction
potentials, HFS constants, and electrochromic prop-
erties.
2. H. T. Van Dam and J. J. Ponjee, J. Electrochem. Soc.
121, 1555 (1974).
3
4
5
. J. F. Willems, Photogr. Sci. Eng. 15, 213 (1971).
. I. Tabushi and A. Yazaki, Tetrahedron 37, 4185 (1981).
. T. Kamo and M. Kamura, Bull. Chem. Soc. Jpn. 45,
(3) A combination of quantum chemical calcula-
tions and phenomenological simulation of the HFS
for high-resolution ESR spectra was used to determine
the precise π-electron density distribution in the radi-
cals generated from monosubstituted 4,4'-bipyridy-
lium salts.
3
309 (1972).
6
. L. Roullier and E. Laviron, Electrochim. Acta 22, 669
1977).
. Organic Electrochemistry, Ed. by M. M. Baizer and H.
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. A. A. Granovsky, http://classic.chem.msu.su/gran/
firefly/index.html.
. M. W. Schmidt, K. K. Baldridge, J. A. Boatz, et al.,
J. Comput. Chem. 14, 1347 (1993).
(
7
(
4) The set of presented methods is suitable for
detailed investigation of systems of this type and for
their application as the base in photoelectrochromic
materials.
8
9
ACKNOWLEDGMENTS
1
0. E. A. Polenov, Izv. Akad. Nauk, Ser. Fiz. 68, 1066
(2004).
This work was supported by the Basic Research
Program of the Presidium of the RAS No. 10
Advancement of Magnetochemical Methods for
“
Translated by Z. Svitanko
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 63 No. 6 2018