Mechanism of the Self-Assembly of Donor–Acceptor Triads Based on Cobalt(II) Porphyrin Complex and Fullero[60]pyrrolidine, According to Data Obtained by Spectroscopic and Electrochemical Means

Article abstract of DOI:10.1134/S0036024420060060

Abstract: Kinetics and equilibriums for reactions between cobalt(II) 5,10,15,20-(tetra-4-isopropylphen-yl)21H,23H-porphyrin (CoTIPP) and 1-methyl-2-(4-(1H-imidazole-1'-yl)phenyl)- and 1-methyl-2-(pyridine-4'-yl)-3,4-fullero[60]pyrrolidines (ImC₆₀ and PyC₆₀, respectively) resulting in the formation of donor–acceptor (ImC₆₀)₂CoTIPP/(PyC₆₀)₂CoTIPP supramolecular triads are studied. The chemical structure of the triads is identified by means of UV, visible, IR, ¹H NMR spectroscopy; their redox behavior is studied via cyclic voltammetry. It is shown that the formation of triads is accompanied by a shift in the redox potentials of the precursors, testifying to interactions between the π-systems of the donor and acceptor. It is concluded that the obtained results should be considered in further studies of donor–acceptor systems with predictable stability for photovoltaic cells.

Full text of DOI:10.1134/S0036024420060060

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2020, Vol. 94, No. 6, pp. 1159–1166. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Fizicheskoi Khimii, 2020, Vol. 94, No. 6, pp. 873–880.
STRUCTURE OF MATTER
AND QUANTUM CHEMISTRY
Mechanism of the Self-Assembly of Donor–Acceptor Triads Based
on Cobalt(II) Porphyrin Complex and Fullero[60]pyrrolidine,
According to Data Obtained by Spectroscopic
and Electrochemical Means
N. G. Bichana,*, E. N. Ovchenkovaa, V. A. Mozgovaa,b, N. O. Kudryakovaa,
M. S. Gruzdeva, and T. N. Lomovaa
a Krestov Institute of Chemistry of Solutions, Russian Academy of Sciences, Ivanovo, 153045 Russia
b Ivanovo State Chemical Technology University, Ivanovo, 153000 Russia
*e-mail: bng@isc-ras.ru
Received June 28, 2019; revised June 28, 2019; accepted September 17, 2019
Abstract—Kinetics and equilibriums for reactions between cobalt(II) 5,10,15,20-(tetra-4-isopropylphen-
yl)21H,23H-porphyrin (CoTIPP) and 1-methyl-2-(4-(1H-imidazole-1'-yl)phenyl)- and 1-methyl-2-(pyri-
dine-4'-yl)-3,4-fullero[60]pyrrolidines (ImC60 and PyC60, respectively) resulting in the formation of donor–
acceptor (ImC60)2CoTIPP/(PyC60)2CoTIPP supramolecular triads are studied. The chemical structure of
the triads is identified by means of UV, visible, IR, 1H NMR spectroscopy; their redox behavior is studied via
cyclic voltammetry. It is shown that the formation of triads is accompanied by a shift in the redox potentials
of the precursors, testifying to interactions between the π-systems of the donor and acceptor. It is concluded
that the obtained results should be considered in further studies of donor–acceptor systems with predictable
stability for photovoltaic cells.
Keywords: cobalt(II) porphyrin, fullero[60]pyrrolidines, supramolecular system, spectral properties, kinetics
and thermodynamics of formation
DOI: 10.1134/S0036024420060060
INTRODUCTION
allows us to suppress energy loss and undesirable
charge recombination. Employing aluminum porphy-
rin allows us to obtain supramolecules, where addi-
tional electron donors and acceptors can be covalently
bonded to the central aluminum atom. In a triad
obtained in [12], tetraphenylethylamine (TPE), an
additional electron donor, was bonded covalently, and
the ImC60 acceptor was bonded via coordination
bonds. It was shown that this triad is capable of stage-
wise light–induced charge separation, first between
TPE and aluminum(III) porphyrin (AlP) up to the
Metal–pyridine/imidazole complexation is often
used to obtain supramolecular systems with specific
properties [1]. This approach is employed in creating
photoactive porphyrin–containing systems [2]. The
axial coordination of ligands containing fullerene frag-
ments by metal porphyrins allows us to obtain supra-
molecules capable of the photoinduced separation of
opposite charges, a fundamental process needed for
both natural photosynthesis and the conversion of
solar energy [3]. Metal porphyrins act as donor plat-
forms in such supramolecular systems [4]. Most stud-
ies are performed for porphyrin/phthalocyanine–
fullerene systems, where the electron donors are zinc
porphyrins/phthalocyanines [5–10].
A promising approach for expanding the options in
designing photoactive supramolecular systems is to
use porphyrin/phthalocyanine complexes of other
metals [11–16], including cobalt [17–20]. The authors
of [11] have used ruthenium phthalocyanine as a
donor platform for obtaining supramolecules with
fullerenes. Using ruthenium(II) phthalocyanines
instead of the corresponding zinc(II) complexes
•+
•−
formation of
-
← ImC60, and then to
(TPE) (AlP)
the final state with charge separation,
•+-AlP ←
(TPE)
•−, with a lifetime of 25 ns. Interestingly, both
Im(C60)
states with charge separation are characterized by high
energies: 2.14 and 1.78 eV, respectively. The authors
therefore believed this triad was promising for the field
of artificial photosynthesis and photovoltaics.
The authors of [13] have performed a spectroscopic
study of the self-assembly of magnesium(II)
5,10,15,20-(tetraphenyl)-21H,23H-porphyrin (MgTPP)
with ImC60. The formation of the (ImC60)MgTPP
1159

1160
BICHAN et al.
615 (2.93). IR spectrum (KBr) ν, cm−1: 377, 447, 503,
diad with a fairly high stability constant of (1.5 0.3)
× 104 L mol−1 was detected, but the expected 572, 717, 753, 799, 813, 837, 853, 1002, 1032, 1055,
(ImC60)2MgTPP triad was not observed. The 1074, 1097, 1140, 1165, 1185, 1206, 1245, 1272, 1298,
1351, 1382, 1406, 1459, 1505, 1547, 1608, 1687, 1726,
(ImC60)MgTPP diad was capable of photoinduced
charge separation; the rate of direct electron transfer was
characterized by a constant of kCS = 1.1 × 1010 s−1 and
charge recombination constant of kCS = 8.3 × 107 s−1.
1
1804, 1910, 2869, 2927, 2959, 3022. H NMR spec-
trum (CDCl3), δ, ppm: 2.79 s (24H, CH3), 4.73 s (4H,
CH), 9.82 s (8Hm), 13.21 br. s. (8Ho), 16.06 br. s.
(8Hβ). Mass spectrum (MALDI TOF), m/z (Irel, %):
840.05 (100) [M]+).
To continue our studies of the formation and prop-
erties of supramolecular systems based on cobalt com-
plexes, this work presents data on the formation of
donor–acceptor complexes based on cobalt(II)
5,10,15,20-(tetra-4-isopropylphenyl)21H,23H-por-
phyrin (CoTIPP) and 1-methyl-4-(1H-imidazole-1'-
yl)phenylfullero[60]pyrrolidine (ImC60)/1-methyl-2-
(pyridine-4'-yl)-3,4-fullero[60]pyrrolidine (PyC60).
The data on the stability of these systems and their
electrooptical/electrochemical properties can allow us
to obtain of structure–property dependences that are
required for continuing research in developing systems
with predictable stability for photoelectrochemical
cells.
1-Methyl-2-(pyridine-4'-yl)-3,4-fullero[60]pyrro-
lidine (PyC60) was synthesized according to [22].
(Absorption spectra in toluene (λmax, nm): 312, 328,
433. IR spectrum (KBr) ν, cm−1: 404, 431, 448, 479,
504, 527, 553, 574, 598, 635, 664, 707, 737, 767, 785,
824, 840, 910, 940, 989, 1034, 1067, 1083, 1109,1123,
1179, 1215, 1246, 1268, 1314, 1334, 1409, 1430, 1463,
1
1561, 1595, 1736, 2783, 2845, 2920, 2948. H NMR
(CDCl3), δ, ppm: 2.83 s (3H), 4.96 s (1H), 4.31 d (1H,
J = 9.77 Hz), 5.02 d (1H, J = 9.77 Hz), 7.82 m (2H),
8.71 d (2H, J = 5.49 Hz). Mass spectrum (MALDI
TOF), m/z (Irel, %): 853 (99) [M–H]+, 854 (76)
[M]+).
1-Methyl-2-(4-(1H-imidazole-1'-yl)phenyl)ful-
lero[60]-pyrrolidine (ImC60) was synthesized accord-
ing to [22]. C60 (100 mg, 0.14 mmol), 4-(1H-imidaz-
ole-1-yl)benzaldehyde (120 mg, 0.70 mmol), and
N-methylglycine (40 mg, 0.45 mmol) were mixed in
90 mL of toluene at the boiling point for 2 h; the sol-
vent was then removed by vacuum distillation. The
reaction mixture was chromatographed on Al2O3 col-
umn (Brockmann activity II) using toluene as an eluent
for the first zone of unreacted C60, methanol for unre-
acted aldehyde, and a toluene–ethyl acetate (4 : 1) mix-
ture for the third zone containing ImC60. The yield was
51%. (Absorption spectra in toluene (λmax, nm): 312,
EXPERIMENTAL
5,10,15,20-(Tetra-4-isopropylphenyl)21H,23H-por-
phin (H2TIPP) was synthesized according to [21]. Pyr-
role (3.39 g, 32 mmol) and 4-isopropylbenzaldehyde
(4.74 g, 32 mmol) were consistently added dropwise to
100 mL of refluxing propionic acid with constant stir-
ring. After aldehyde was added, the reaction mixture
was refluxed for 30 min with stirring. The solution was
cooled to room temperature and placed into a freezer
for 12 h. The precipitate was filtered and washed using
methanol (3 times, 10 mL each) and hot water
(3 times, 30 mL each). The resulting purple crystals
were dried in air and then in vacuum. The yield was
20.25%. (Absorption spectra in CHCl3 (λmax, nm):
329, 434. IR spectrum (KBr) ν, cm−1: 376, 399, 430,
464, 476, 527, 544, 553, 562, 566, 575, 583, 599, 606,
617, 656, 694, 706, 727, 737, 746, 759, 767, 771, 789,
802, 833, 842, 863, 901, 908, 962, 1018, 1033, 1053,
1091, 1099, 1107, 1143, 1151, 1163, 1179, 1215, 1233,
1243, 1259, 1282, 1301, 1320, 1333, 1357, 1367, 1429,
1447, 1463,1483, 1521, 1540, 1610, 2328, 2346, 2779,
420, 450, 515, 555, 670. 1H NMR spectrum (CDCl3),
δ, ppm: –2.75 s.br. (2H, NH), 1.55 m (24H, CH3),
3.29–3.24 m (4H, CH), 7.61 d (8Hm, J = 7.6 Hz),
8.14 d (8Ho, J = 7.84 Hz), 8.87 s (8He). Mass spectrum
(MALDI TOF), m/z (Irel, %): 782 (95) [M]+).
(5,10,15,20-(Tetra-4-isopropylphenyl)21H,23H-
porphinato)cobalt(II), (CoTIPP), was obtained in the
reaction between the corresponding porphyrin
(64 mg, 0.082 mmol) and Co(AcO)2 · 4H2O (105 mg,
0.42 mmol) in refluxing dimethylformamide (DMFA)
for 40 min. At the end of the reaction, the reaction
mixture was cooled, and the products were extracted
with chloroform. The solution in CHCl3 was repeat-
edly washed with distilled water to remove DMFA.
The solvent was partially distilled, and the product was
chromatographed on a column filled with Al2O3
(Brockmann activity II) using chloroform as an elu-
ent. The main orange zone corresponding to CoTIPP
1
2839, 2919, 2946, 3114. H NMR (CDCl3), δ, ppm:
2.82 s (3H), 4.29 d (1H, J = 4.28 Hz), 5.00 m (2H),
7.17 m (1H), 7.32 t (1H, J = 1.35 Hz), 7.48 d (1H, J =
8.41 Hz), 7.90 m (2H).) Mass spectrum (MALDI
TOF), m/z (Irel, %): 920.75 (100) [M]+).
Toluene (EKOS) was dried over potassium hydrox-
ide and distilled before use (tboil = 110.6°C). The con-
tent of water determined via Karl Fischer titration did
not exceed 0.01%.
Kinetics of the reversible reaction of CoTIPP with
ImC60/PyC60 in toluene were studied spectrophoto-
metrically at 298 K in the 5.88 × 10−5 to 1.57 × 10−4
M
was obtained. The yield was 82%. (Absorbance spectra (ImC60) and 4.38 × 10−5 to 1.17 × 10–4 M (PyC60)
in toluene (λmax, nm (log ε)): 415 (5.21), 531 (3.97),
ranges of concentration using the excess concentration
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MECHANISM OF THE SELF-ASSEMBLY
1161
technique. The CoTIPP and ImC60/PyC60 solutions in with addition of the background electrolyte (0.1 M (n-
Bu)4NClO4) under an argon flow.
RESULTS AND DISCUSSION
Spectral analysis of the synthesized CoTIPP and
fullero[60]pyrrolidines (ImC60, PyC60) reliably char-
acterizes their chemical structures. The UV–Vis spec-
tra of fullero[60]pyrrolidines manifest characteristic
absorption in the range of 430 nm [22, 23]. The spec-
trum of CoTIPP, a complex of cobalt(II), contains a
Soret band (1a1g → 2eu) at 415 nm and a Q-band
(1a1g → 1eu) at 531 nm [24].
freshly distilled toluene were prepared immediately
before use to avoid the formation of peroxides in the
solvent medium. Absorbance was measured for a series
of solutions with a constant CoTIPP concentration
(6.28 × 10−6 M) and a variable concentration of substi-
tuted fullerene at a working wavelength of 415 nm
immediately after mixing the reagents. The UV–Vis
spectrum of the reacting system was obtained using
the spectrum of ImC60/PyC60 at the same concentra-
tion as in the working solution as the zero line. The
solutions were thermostatted at 298 0.1 K in closed
quartz cuvettes inside a special spectrophotometer
accessory. The reaction rate constants were calculated
according to the equation
The reaction of CoTIPP with ImC60 was studied via
spectrophotometry. Two equilibria can be detected for
processes that occur as a result of interaction between
CoTIPP and ImC60. The first is established instanta-
neously after the reagent solutions are poured
together, and the second is observed over time at a
measurable rate. Using an approach based on spectro-
photometric time–dependent titration (the data on
spectrophotometric titration are processed at τ = 0
and ∞ after the slow reaction is over for all mixture
compositions) allows us to describe quantitatively
both equilibria and the rate of the second stage of the
reaction. The scheme of the formation of supramolec-
ular porphyrin–fullerene complexes of CoTIPP and
ImC60 is shown in Fig. 1.
The evolution of spectra as a result of interaction
between CoTIPP and ImC60 at the first stage (at the
zero timepoint) are shown in Fig. 2. At the first stage
after equilibrium is established at all compositions of
the reaction mixture, the subsequent slow interaction
in the CoTIPP–ImC60 system is accompanied by a
gradual drop in the intensity of Soret band absorption
at 415 nm and the appearance of a new band at
436 nm. The dynamics of the spectrum clearly con-
firms the formation of a hexacoordinated cobalt com-
plex [25]. The second equilibrium in the cobalt(II)
porphyrin–substituted fullerene system is established
depending on the fullerene concentration on average
for 10–15 minutes (Fig. 3). The stoichiometry of the
forming donor–acceptor systems of CoTIPP with
ImC60 at the first and second stages was determined
keff = (1/τ)ln((A0 − A∞)/(Aτ − A∞)),
where A0, Aτ, A∞ are the values of the reaction mix-
ture’s absorbance at time points 0, τ, and the end of
the reaction.
The equilibrium of the reaction between CoTIPP
and ImC60/PyC60 in toluene was studied at 298 K in
the 1.46 × 10−6 to 1.31 × 10−4 M (PyC60) and 1.37 ×
10−6 to 1.57 × 10−4 M (ImC60) ranges of concentration
via time–dependent spectrophotometric titration
using the molar ratio technique. Equilibrium con-
stants K were determined according to the equation
(A − A0)/(A∞ − A0)
i
K =
1 − (A − A0)/(A∞ − A0)
i
1
×
,
(CL0 − CC0oTIPP)(A − A0)/(A∞ − A0))
i
0
0
where
and
are the initial concentrations of
CL
CCoTIPP
L (PyC60/ImC60) and CoTIPP in toluene, respec-
tively; A0, Ai, A∞ are the absorbance values of CoTIPP,
the equilibrium mixture at the given concentration of
L, and the reaction product. The relative error in esti-
mating K did not exceed 25%. The reaction stoichiom-
etry was determined as the slope of line
log I−f(log CL), where I = (Ai − A0)/(A∞ − Ai).
UV–Vis, IR, NMR, and mass spectra were
recorded using an Agilent 8453 spectrophotometer;
VERTEX 80v and Bruker Avance III-500 spectrome-
ters; and a Shimadzu Confidence mass spectrometer,
respectively.
Electrochemical measurements were made at
298 K under anaerobic conditions in a three–elec-
trode cell using a PI-50-Pro-3 pulse potentiostat with
the PS Pack 2 software. Voltammetric curves were
measured at the potential sweep rate of 100 mV/s. The
working and auxiliary electrodes were a platinum elec-
trode and platinum wire, respectively. The reference
electrode was a saturated calomel electrode. The elec-
trochemical properties of CoTIPP, PyC60/ImC60, and
donor–acceptor triads based on them were studied
with freshly prepared solutions in methylene chloride
from the linear logI–
dependences. The
logCImC
60
slope (tanα) of these lines at the first and second
stages is 1.02 and 1.27, respectively. The reaction equa-
tions, numerical values of equilibrium constants, and
overall constant of stability (of formation) (β) of the
(ImC60)2CoTIPP triad are presented in Table 1.
The first order with respect to (ImC60)CoTIPP,
and therefore to CoTIPP (quasiequilibrium), is deter-
mined by studying the slow direct reaction of the sec-
ond equilibrium stage (Eq. (2) in Table 1). The effec-
tive rate constants are given in Table 2. The log k2eff
–
dependence has a slope (order of the reac-
logCImC
60
tion with respect to the ImC60 concentration) close
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 94 No. 6 2020

1162
BICHAN et al.
N
CH3
N
N
N
Co
N
N
N
N
CH3
N
N
N
N
CoTIPP
Co
N
N
K2, k2
K1
N
instantly
N
N
N
N
CH3
+
+
k−2,
N
gradually
N
N
N
Co
N
N
CH3
N
N
CH3
(ImC60)CoTIPP
(ImC60)2CoTIPP
ImC60
Fig. 1. Formation of supramolecular porphyrin–fullerene complexes of CoTIPP with ImC
.
60
A
1.2
A
1.2
0.8
0.4
A
A
1.0
1.1
0.6
0.2
0.8
0.4
0.9
4
8
12 16
CImC60 × 10−5, mol/L
1
5
9
13
CImC60 × 10−5, mol/L
400
450
500 λ, nm
400
450
500 λ, nm
Fig. 3. Evolution of UV–Vis spectra of CoTIPP in toluene
−6
Fig. 2. Evolution of UV–Vis spectra of CoTIPP in toluene
at 298 K with a growing ImC additive (from 1.37 × 10
60
at 298 K with a growing ImC additive (from 0 to 1.57 ×
60
−4
to 1.76 × 10 M) in toluene at τ = ∞ (when the reactions
−4
10 M) in toluene at τ = 0. Inset: corresponding spectro-
were completed). Inset: corresponding spectrophotomet-
ric titration curve, obtained at a working wavelength of
415 nm.
photometric titration curve, obtained at a working wave-
length of 415 nm.
to 1 (tanα= 0.90, R2 = 0.99). The numerical value of rate
constant k2 for reaction (2), found by optimizing the
studied in a manner similar to the one used above, in
toluene (CCoTIPP = 5.31 × 10−6 M with
being var-
С
PyC60
logk2eff–
dependence, is 40.55 mol−1 L s−1.
logCImC
ied from 0 to 1.31 × 10−4 M). This reaction is also a
successive two–stage coordination of PyC60 mole-
cules with the cobalt atom within the porphyrin com-
60
The reaction between CoTlPP and 1-methyl-2-
(pyridine-4'-yl)-3,4-fullero[60]pyrrolidine (PyC60)
was studied to determine the effect the chemical struc-
ture of fullero[60]pyrrolidines on the stability of
donor–acceptor complexes based on cobalt(II) por-
plex (tanα for the logI–
linear dependences
at the first and second stages is 1.17 and 1.06, respec-
tively) resulting in the formation of a supramolecular
logСPyC
60
phyrin. The reaction between CoTIPP and PyC60 was 1 : 2 complex of (PyC60)2CoTIPP. The reaction equa-
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MECHANISM OF THE SELF-ASSEMBLY
1163
Table 1. Equations of reactions between cobalt(II) porphyrin and fullero[60]pyrrolidines and the corresponding stability
constants (β)
β = K1K2, L2 mol–2 (logβ)
Kn, L/mol (logKn)
Reaction equation
K1
⎯⎯→
CoTIPP + ImC
(ImC60)CoTIPP (1)
(3.29 0.49) × 104 (4.52)
(6.23 0.61) × 104 (4.79)
(1.59 0.45) × 104 (4.20)
(2.05 0.35) × 109 (9.31)
60 ←⎯⎯
(ImC60)CoTIPP + ImC
K2
⎯⎯→
(ImC ) CoTIPP (2)
60 2
60 ←⎯⎯
K1
(3.21 0.95) × 109 (9.51)
(4.69 1.23) × 109 (9.67)
(1.34 0.12) × 1010 (10.13)
(1.04 0.12) × 1010 (10.02)
(5.58 0.16) × 108 (8.75)
⎯⎯→
CoTIPP + PyC
(PyC60)CoTIPP (3)
60 ←⎯⎯
K2
(2.02 0.38) × 105 (5.31)
(5.43 1.21) × 104 (4.73)
⎯⎯→
(PyC60)CoTIPP + PyC
(PyC ) CoTIPP (4)
60 2
60 ←⎯⎯
K1
⎯⎯→
CoTPP + PyC
(PyC60)CoTPP
60 ←⎯⎯
K2
(8.69 1.39) × 104 (4.94)
(1.04 0.11) × 104 (4.02)
⎯⎯→
(PyC60)CoTPP + PyC
(PyC ) CoTPP [27]
60 2
60 ←⎯⎯
K1
⎯⎯→
CoTBPP + PyC
(PyC60)CoTBPP
60 ←⎯⎯
K2
60 ←⎯⎯
(1.21 0.32) × 106 (5.91)
(1.79 0.33) × 104 (4.25)
⎯⎯→
(PyC60)CoTBPP + PyC
(PyC ) CoTBPP [28]
60 2
K1
⎯⎯→
CoP + PyC
(PyC60)CoP
60 ←⎯⎯
K2
(5.76 0.60) × 105 (5.76)
(9.30 0.80) × 103 (3.97)
⎯⎯→
(PyC60)CoP + PyC
(PyC ) CoP [18]
60 ←⎯⎯
60 2
K1
⎯⎯→
CoP + Py3C
(Py3C60)CoP
60 ←⎯⎯
(Py3C60)CoP + Py3C
K2
⎯⎯→
(Py C ) CoP [19]
(6.0 1.2) × 104 (4.78)
60 ←⎯⎯
3
60 2
CoP = (2,3,7,8,12,18-hexamethyl-13,17-diethyl-5-(2-pyridyl)porphinato)cobalt(II); CoTBPP = 5,10,15,20-(tetra-4-tert-butylphenyl)-
21H,23H-porphinato)cobalt(II); K is a stepwise equilibrium constant.
n
tions, numerical values of equilibrium constants, and the macrocyclic ligand in the range of 2950–
2850 cm−1 during the formation of donor–acceptor
complexes fall by 1–3 cm−1, compared to the initial
CoTIPP. In the 440 to 460 cm−1 range of the vibrations
of cobalt–nitrogen bonds in the IR spectra of supra-
molecules, three signals are observed at frequencies of
443, 447, and 451 cm−1 for the (PyC60)2CoTIPP triad.
overall constant of (PyC60)2CoTIPP stability are given
in Table 1. The effective constants of the slow direct
reaction of the second equilibrium stage (Eq. (4) in
Table 1) are given in Table 2. The log k2eff
–
logСPyC
60
linear dependence is characterized by a tanα of 0.93
(R2 = 0.99). The numerical value of rate constant k2
for reaction (4) found using optimization of the
The broadening of the band at 447 cm−1 is observed
for (ImC60)2CoTIPP. All of these changes confirm the
formation of donor–acceptor complexes.
logk2eff
–
dependence is 81.32 mol−1 L s−1.
logСPyC
60
The formation of supramolecular (ImC60)2CoTIPP/
(PyC60)2CoTIPP triads is additionally confirmed by
1
The H NMR spectrum of CoTIPP is typical of
1
the data from IR and H NMR spectroscopy and
paramagnetic complexes [26]. The signals of β-pro-
tons and ortho-protons of phenyl substituents are
broadened singlets at 16.02 and 13.21 ppm, respec-
tively. The signal of meta-protons of the phenyl ring
cyclic voltammetry. The IR spectrum of CoTIPP con-
tains signals of the characteristic vibrations of macro-
cycle bonds, propyl substituents (in the range of 2950–
2850, 1381 cm−1), and a signal with the frequency of
446 cm−1 characteristic of Co–N coordination bonds
(Fig. 4a). When (ImC60)2CoTIPP/(PyC60)2CoTIPP
donor–acceptor triads form, new signals related to
coordinated fullero[60]pyrrolidines appear, compared
to the CoTIPP spectrum. To be specific, new signals
appear in the IR spectrum of (ImC60)2CoTIPP at
2851, 2782, 1522, 1485, 1431, 1333, 1261, 1244, 1109,
1032, 963, 842, 771, 767, 747, 726, 657, 620, 599, 583,
553, 527, 487, 476 cm−1 (Fig. 4c). The following sig-
nals correspond to vibrations of N-bonded PyC60 in
the IR spectrum of (PyC60)2CoTIPP: 2786, 2329,
1429, 1335, 1282, 1268, 1232, 1163, 1060, 963, 909,
832, 767, 747, 737, 541, 486, 479, 451, 447 cm−1. The
frequencies of the vibration of propyl substituents of
Table 2. Effective rate constants (k2eff) of the reaction
between (ImC60)CoTIPP and ImC60/(PyC60)CoTIPP with
PyC60 in toluene at 298 K
× 105,
M
× 105,
M
(k2eff δk2eff
×103, s−1
)
(k2eff δk2eff)
× 103, s−1
C
ImC60
С
PyC60
5.88
7.83
9.80
11.80
13.70
15.70
6.41 0.45
8.09 0.43
9.75 0.23
11.90 1.04
13.70 0.87
15.30 1.04
4.38
5.83
7.29
8.75
10.02
11.70
6.46 0.60
8.17 0.23
10.90 0.82
12.80 0.79
14.0 0.94
15.90 1.05
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BICHAN et al.
presence of electron–donating alkyl substituents in
(а)
the porphyrin ligand apparently stabilizes the donor–
acceptor supramolecules. The constants of the stabil-
ity of supramolecules based on CoTPP and CoTIPP
can be assumed to be comparable, allowing for the
experimental error.
(b)
(c)
The rate constants of the formation of CoTIPP-
based supramolecular complexes are approximately
comparable with those of the formation of donor–
acceptor porphyrin–based systems of (PyC60)2CoTBPP
[28], (PyC60)2CoP [18], (Py3C60)2CoP [19] containing
donor substituents at the macrocycle periphery and
exceed by four and eight times the constant for the
(PyC60)2CoTPP triad.
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
We can see that the reaction rate is most affected by
the macrocycle substituents, and not by the chemical
structure of fullero[60]pyrrolidines. Rate constants
k‒2 for processes (2) and (4) are 6.51 × 10−4 s−1
3000 2500 2000 1500 1000 500
сm−1
Fig. 4. IR spectra of (a) CoTIPP, (b) ImC , and (c)
60
(40.55 mol−1 L s−1/6.23 × 104 L mol−1) and 4.03 ×
10‒4 s−1 (81.32 mol−1 L s−1/2.02 × 105 L mol−1). The
ratio of rate constants of direct and reverse reactions
(k2 and k−2) testifies to the acceptability of ignoring the
reverse reaction in studying the kinetics of reversible
processes at the second stage of reactions between
CoTIPP and fullero[60]pyrrolidines (PyC60, ImC60).
(ImC ) CoTIPP in KBr.
60 2
appears as a singlet at 9.82 ppm. The great distance
between these protons and the central paramagnetic
cobalt atom (3d7) does not result in its broadening.
The signals corresponding to the protons of propyl
substituents H–CH and
also are observed as sin-
H
−CH3
(PyC60)2CoTIPP/(ImC60)2CoTIPP supramolecu-
lar systems and their components were studied via
cyclic voltammetry. Fig. 5 shows cyclic voltammo-
grams for PyC60 and ImC60 that have a similar shape
and contain the three pairs of peaks characteristic of
fullero[60]pyrrolidines [29, 30]. In the range of nega-
tive potentials, three fullerene reduction peaks (−0.66,
−1.01, −1.60 V) and the corresponding oxidation
peaks (−1.53, −1.02, −0.60 V) are observed for ImC60,
which agrees with the data in [12]. The CV of PyC60
was described in [27]. The CVs of donor–acceptor
(PyC60)2CoTIPP/(ImC60)2CoTIPP complexes are
measured under the conditions of constant molar ratio
corresponding to the equivalent point in the spectro-
photometric titration experiment. The CVs of diads
(Figs. 5c, 5d) in fact correspond to the sum of the
peaks of CoTIPP and fullero[60]pyrrolidine. In the
range of positive potentials, both diads have two peaks
associated with the oxidation of their porphyrin part
(0.85, 1.17 and 1.09, 1.32 V, respectively), while free
CoTIPP is characterized by three oxidation peaks with
potentials of 0.82, 0.95, 1.14 V. In the range of negative
potentials, peaks are observed which correspond to
processes occurring over the fullerene part of the diad.
Analysis of the peak positions shows the formation of
donor–acceptor complexes is accompanied by a shift
in the redox potentials of both fullero[60]pyrrolidine
and cobalt porphyrin, yet another confirmation of the
formation of supramolecules and presence of interac-
tions between the π-system of the donor and acceptor.
glets at 4.73 and 2.79 ppm, respectively. The formation
of the donor–acceptor (ImC60)2CoTIPP triad is
accompanied by an upfield shift in the signals of β-
and o-protons (Table 3), just as when the donor plat-
form in a supramolecule with PyC60 is CoTPP [27].
1
Such changes in the H NMR spectrum of the triad
can be explained by the change in the effect of the ring
current of the porphyrin ring due to the formation of
supramolecules with fullero[60]pyrrolidines.
As seen in Table 1, the stability of the obtained
supramolecules depends on the substituents in both
the macrocycle and the fullero[60]pyrrolidine. The
most
stable
donor–acceptor
triads
are
(PyC60)2CoTBPP [28] and (PyC60)2CoP [18]. The
Table 3. Chemical shifts of Hβ and Ho of cobalt porphyrin
complexes and supramolecular systems with fullero[60]pyr-
rolidines
8Hβ, ppm
8Ho, ppm
Complex
CoTIPP
16.06
13.55
14.31
15.94
13.50
16.05
14.62
13.21
11.36
10.97
13.16
9.88
(ImС60)2CoTIPP
(PyС60)2CoTIPP
CoTPP [27]
(PyС60)2CoTPP [27]
CoTBPP [28]
13.24
11.40
(PyС60)2CoTBPP [28]
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MECHANISM OF THE SELF-ASSEMBLY
(b)
1165
(a)
−2.0
−1.0
0
1.0
−2.0
−1.0
0
1.0
E, V (vs. SCE)
E, V (vs. SCE)
(c)
(d)
−2.0
−1.0
0
1.0
−2.0
−1.0
0
1.0
2.0
E, V (vs. SCE)
E, V (vs. SCE)
−4
−4
Fig. 5. Cyclic voltammograms of (a) PyC
(
= 4.03 × 10 M); (b) ImC
(
= 5.2 × 10 M); (c) (PyC ) CoTIPP;
С
C
60 PyC60
60 ImC60 60 2
(d) (ImC ) CoTIPP in methylene chloride with 0.1 M (n-Bu) NClO . The potential sweep rate is 100 mV/s.
60 2
4
4
CoTIPP paramagnetic complex” and “Synthesis and spec-
tral and electrochemical characterization of triads.”)
CONCLUSIONS
Supramolecular (ImC60)2CoTIPP/(PyC60)2Co-
TIPP triads were obtained. The reactions of their for-
mation were studied via chemical kinetics and ther-
modynamics. Spectral and electrochemical character-
istics of these donor–acceptor complexes were
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Translated by M. Ehrenburg
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 94
No. 6
2020