Formation Reaction and Chemical Structure of a Novel Supramolecular Triad Based on Cobalt(II) 5,10,15,20-(Tetra-4-Tert-Butylphenyl)-21Н,23Н-Porphyrin and 1-Methyl-2-(Pyridin-4′-Yl)- 3,4-Fullero[60]Pyrrolidine

Article abstract of DOI:10.1134/S0022476618030320

Results of chemical kinetic/thermodynamic and spectroscopic studies of the reaction of cobalt(II) 5,10,15,20-(tetra-4-tert-butylphenyl)-21Н,23Н-porphyrin (Co^IITBPP) with 1-methyl-2-(pyridin-4′-yl)-3,4- fullero[60]pyrrolidine (PyF) in toluene at

Full text of DOI:10.1134/S0022476618030320

Journal of Structural Chemistry. Vol. 59, No. 3, pp. 711-719, 2018.
Original Russian Text © 2018 N. G. Bichan, E. N. Ovchenkova, M. S. Gruzdev, T. N. Lomova.
FORMATION REACTION AND CHEMICAL STRUCTURE
OF A NOVEL SUPRAMOLECULAR TRIAD BASED
ON COBALT(II) 5,10,15,20-(TETRA-4-TERT-BUTYLPHENYL)-
21Н,23Н-PORPHYRIN AND 1-METHYL-2-(PYRIDIN-4′-YL)-
3,4-FULLERO[60]PYRROLIDINE
N. G. Bichan, E. N. Ovchenkova, M. S. Gruzdev,
and T. N. Lomova*
Results of chemical kinetic/thermodynamic and spectroscopic studies of the reaction of cobalt(II)
II
5,10,15,20-(tetra-4-tert-butylphenyl)-21Н,23Н-porphyrin (Co TBPP) with 1-methyl-2-(pyridin-4′-yl)-3,4-
fullero[60]pyrrolidine (PyF) in toluene at 298 K, ending by the formation of donor-acceptor triad
II
(PyF)2Co TBPP, are presented. Kinetic and thermodynamic parameters of the two-way formation reaction
of the triad are obtained. The chemical structure of the obtained porphyrin-fullerene triad is identified by
1
UV, visible, fluorescent, IR, and H NMR spectroscopic techniques. The results are relevant for the
problems of searching for supramolecular systems capable of photoinduced charge separation.
DOI: 10.1134/S0022476618030320
Keywords: substituted cobalt(II) porphyrin, pyrrolidinofullerene, donor-acceptor triad, kinetics of
formation, thermodynamics of formation, spectroscopy.
INTRODUCTION
In recent decades, the design and research of donor-acceptor ensembles capable of photoinduced charge separation
and promising for practical application in photovoltaics have been of great interest. Metal porphyrins being very good
electron donors upon photoexcitation have well proven to be one of the components of these systems [1, 2]. Fullerenes are
electron acceptors and their ability to stimulate fast charge separation [3-5] make them promising components of photoactive
donor-acceptor ensembles.
Complexation by the axial binding of base molecules is widely used in the formation of porphyrin/phthalocyanine-
containing architectures [6-12]. Therefore, the basic properties of various pyridyl/imidazole derivatives of fullerene make
them building blocks to prepare promising supramolecular systems.
II
In [13] we have previously shown the possibility of forming donor-acceptor triad (Py3F)2PCo based on
(2,3,7,8,12,18-hexamethyl-13,17-diethyl,5-(pyridin-2-yl)(porphyrinato)cobalt(II) and [2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-
(pyridin-2-ylmethyl)pyrrolidino[3′,4′:1,2][60]fullerene. Kinetic and thermodynamic parameters and the formation mechanism
of the triad were determined and photoelectrochemical examinations were performed. The latter reveal that the photocurrent
Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia; *tnl@isc-ras.ru. Translated
from Zhurnal Strukturnoi Khimii, Vol. 59, No. 3, pp. 734-741, March-April, 2018. Original article submitted October 10, 2017.
0022-4766/18/5903-0711 © 2018 by Pleiades Publishing, Ltd.
711

Fig. 1. Chemical structures of the objects under study: cobalt(II)
5,10,15,20-(tetra-4-tert-butylphenyl)-21Н,23Н-porphyrin
1-methyl-2-(pyridin-4′-yl)-3,4-fullero[60]pyrrolidine (b).
(а),
II
densities are 4 and 31 times higher for the triad than those for separately taken Co P and Py3F respectively. Within the search
for the formation conditions of stable supramolecular systems with promising electron-optical properties, in this work we
explored the formation reaction of the porphyrin-fullerene triad based on the symmetrically substituted complex of cobalt(II)
with 5,10,15,20-(tetra-4-tert-butylphenyl)-21Н,23Н-porphyrin (Fig. 1).
EXPERIMENTAL
5,10,15,20-(Tetra-4-tert-butylphenyl)-21Н,23Н-porphin, H TBPP was synthesized by the procedure from [14].
2
To 100 ml of boiling propionic acid, pyrrol (3.39 g, 32 mmol) and 4-tert-butylbenzaldehyde (5.19 g, 32 mmol) were
successively added in drops with constant stirring. After the addition of aldehyde the reaction mass was refluxed with stirring
for 30 min. The solution was cooled to room temperature and placed in a freezer for 12 h. The precipitate formed was filtered
off, washed with methanol (3 times with 10 ml) and hot water (3 times with 30 ml). The obtained purple crystals were dried
in the air and then in vacuo. Yield 0.865 g. (12.89%) porphyrin. UV-vis in CHCl3 (λmax, nm): 421, 518, 554, 590, 649. IR
–1
1
spectrum (KBr) ν, cm : 3313, 2953, 2920, 2851, 1736, 1461, 1262, 1105, 964, 803, 789, 734, 713. H NMR (400 MHz,
CDCl3): δ, ppm, (J, Hz) 8.87(s, 8H), 8.17-8.14 (d, J = 8.2 Hz, 8H), 7.77-7.76 (d, J = 8.2 Hz, 8H), 1.62 (s, 36H), –1.38 (s, br,
1H), –2.72 (s, br, 1H).
II
(5,10,15,20-(Tetra-4-tert-butylphenyl)-21Н,23Н-porphinato)cobalt(II), Co TBPP was obtained by the reaction
of respective porphyrin (57 mg, 0.068 mmol) with Co(AcO)2⋅4H2O (119 mg, 0.48 mmol) in boiling dimethylformamide
(DMFA) for 40 min. After the completion of the reaction, which was detected by the disappearance of H2TBPP bands and the
end of changes in the electronic absorption spectrum of a sample of the reaction mixture in chloroform, the content of the
reaction retort was cooled and the products were extracted to chloroform after the dilution with water. The solution in CHCl3
was repeatedly washed with distilled water to remove DMFA. The solvent was partially removed, the product was
chromatographed on a column with Al2O3 (Brockmann activity grade II) using chloroform. The main orange zone of
II
respective Co TBPP was obtained. Yield was 78%. UV-vis in toluene (λmax, nm (lgε)): 415 (5.39), 530 (4.15), 613 (2.55). IR
–1
spectrum (KBr) ν, cm : 453, 484, 567, 588, 716, 743, 798, 814, 1003, 1073, 1109, 1193, 1207, 1245, 1268, 1311, 1351,
1
1362, 1394, 1461, 1474, 1505, 1546, 1608, 1687, 1807, 1912, 2867, 2903, 2961. H NMR (400 MHz, CDCl3): δ, ppm,
(J, Hz) 2.86 (s, 36Htert-butyl-), 9.98 (s, 8Hм), 13.24 (br.s, 8Hо), 16.05 (br.s, 8Hβ). Mass spectrum (MALDI-TOF): m/z 895.05
+
[M] (Calculated for С60H60CoN4 895).
1-Methyl-2-(pyridin-4′-yl)-3,4-fullero[60]pyrrolidine, PyF was synthesized by the procedure presented in [15],
which was changed in the reagent ratio, reaction time, and purification process to optimize the synthesis. С60 (100 mg,
0.14 mmol), pyridin-4-carboxyaldehyde (80 mg, 0.75 mmol) and N-methylglycine (43 mg, 0.48 mmol) were mixed in 90 ml
of toluene at a boiling temperature for 2 h, then the solvent was removed by vacuum distillation. The formation of 1-methyl-
2-(pyridin-4′-yl)-3,4-fullero[60]pyrrolidine was monitored by TLC and UV-vis of the reaction mixture by the appearance of
712

absorption with λmax = 433 nm, characteristic of pyrrolidine fullerenes [15, 16]. Yield 52% (64 mg). The reaction mixture was
chromatographed on a column with Al2O3 (Brockmann activity grade II) using toluene for the first zone from unreacted С60
and a toluene-ethylacetate mixture (20:1) for the second zone containing PyF. UV-vis in toluene (λmax, nm): 312, 328, 433. IR
–1
spectrum (KBr) ν, cm : 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, 1561, 1595, 1736, 2783, 2845, 2920,
1
2948. H NMR (400 MHz, CDCl3): δ, ppm (J, Hz) 2.83 (s, 3H), 4.31 (d, J = 9.77, 1H), 4.96 (s, 1H), 5.02 (d, J = 9.77, 1H),
+
7.82 (m, 2H), 8.71 (d, J = 5.49, 2H). Mass spectrum MALDI-TOF: m/z, (relative intensity, %) 853 (99) [M–H] , 854 (76)
+
[M] .
(5,10,15,20-(Tetra-4-tert-butylphenyl)21Н,23Н-porphinato)bis-(1-methyl-2-(pyridin-4′-yl)-3,4-fullero[60]
II
pyrrolidine)cobalt(II), (PyF) Co TBPP was synthesized by the original procedure involving the reaction between
2
II
Co TBPP and PyF (mole ratio 1:14) in toluene at 298 K for 7 min. The synthesis was completed when changes in UV-vis of
II
the reaction mixture ceased. Solid (PyF)2Co TBPP in a mixture with excess PyF was obtained by toluene distillation.
II
Spectral characteristics of individual triad (PyF)2Co TBPP were obtained by the quantitative subtraction of the spectra of
PyF. UV-vis in toluene (λmax, nm): 443 (I), 559 (II), 600 (III) with a relative band intensity order I > II > III. IR spectrum
–1
(KBr) ν, cm : 413, 430, 453, 479, 486, 505, 527, 541, 553, 567, 574, 584, 598, 636, 642, 663, 715, 744, 767, 797, 813, 832,
839, 866, 910, 939, 1001, 1033, 1075, 1109, 1163, 1179, 1188, 1206, 1245, 1267, 1314, 1351, 1362, 1393, 1409, 1422, 1430,
1
1462, 1505, 1543, 1561, 1596, 1686, 1803, 1907, 2784, 2866, 2902, 2959, 3026. H NMR (400 MHz, CDCl3): δ, ppm,
(J, Hz) 2.25 (s, HPyF), 2.45 (s, H-tert-butyl-), 3.24 (m, HPyF), 4.09 (m, HPyF), 5.16 (s, HPyF), 7.61 (m, HPyF), 9.01-8.92 (br.m, HPyF),
9.33 (s, Hм), 11.40 (br.s, Hо), 14.62 (br.s, Hβ).
Toluene (EKOS) was dried by potassium hydroxide and distilled before using (tboil = 110.6 °C). The water content
was determined by Fischer titration; it did not exceed 0.01%.
II
Kinetics of the Co TBPP reaction with PyF in toluene was analyzed spectrophotometrically at 298 K in the PyF
–5 –4
concentration range 2.53⋅10 -1.45⋅10 mol/l by the procedure of excessive concentrations. The upper PyF concentration
II
limit is governed by its solubility in toluene. The Co TBPP and PyF solutions in freshly distilled toluene was prepared
directly before their use to avoid the formation of peroxides in the solvent medium. Absorbance measurements for a series of
II
–6
solutions with the constant Co TBPP concentration of 3.5⋅10 mol/l and the variable concentration of substituted fullerene
were conducted at a working wavelength of 434 nm immediately after the mixing of reagents and with time. Since PyF has its
own electron absorption spectrum in the visible range, the spectra of the reacting system were measured in subtraction mode,
i.e., with the use of the spectrum of PyF with the same concentration as in the working solution as a zero line. The solutions
were thermostated at 298 K in closed quartz cuvettes in a special cell of the spectrophotometer. The error of thermostating
was 0.1 K. At different PyF concentrations the reaction rate constants were calculated by equation (1), formally first-order,
II
provided that there is an excess of PyF relative to Co TBPP
k
=1/ τ ⋅ ln((A − A ) /(A − A )).
0
(1)
eff
∞
τ
∞
Here Ао, Аτ, А∞ are the absorbances of the reaction mixture at a working wavelength at times 0, τ and after the reaction
completion.
II
The equilibrium of the Co TBPP reaction with PyF in toluene, the establishment of which completes the kinetically
controlled reactions in all reagent ratio ranges (see the above), was analyzed by spectrophotometric titration at 298 K in the
–4
extended PyF concentration range (0-1.45⋅10 mol/l). The titration was carried out by the mole ratio method. A series of
II
–6
solutions in toluene with a constant Co TBPP concentration (3.5⋅10 mol/l) and different PyF concentrations was prepared.
Equilibrium constants (K) were found by equation (2) for a three-component equilibrium system with two colored
compounds
(A − A )/(A∞ − A )
1
i
0
0
K =
⋅
,
(2)
0
(C − C
0
1− (A − A )/(A∞ − A )
⋅ (A − A )/(A∞ − A ))
II
i
0
0
PyF
i
0
0
Co TBPP
713

0
0
II
are the initial PyF and Co TBPP concentrations in toluene respectively; А0, Аi, А∞ are the absorbances
C
C
where
,
II
PyF
Co TBPP
II
at a working wavelength for Co TBPP, the equilibrium mixture at a certain concentration of PyF and the reaction product.
Numerical values of constants K were found from equation (2) by the least squares technique using the Microsoft Excel
program. The relative error in the determination of K did not exceed 30%. The reaction stoichiometry was determined as the
tangent of the line slope lg(Ai – A0)/(A∞ – Ai) – f(lgСPyF)(lgI – f(lgСPyF)).
1
Uv-vis, fluorescent, IR, H NMR, and mass spectra were measured on an Agilent 8453 spectrophotometer, a CM
2203 SOLAR spectrofluorimeter, VERTEX 80v and Bruker Avance III-500 spectrometers, and a Shimadzu Confidence mass
spectrometer respectively.
RESULTS AND DISCUSSION
II
The performed spectral analysis of the synthesized Co TBPP complex characterizes it as a porphyrin complex of
II
divalent cobalt. A change in the composition of the coordination sphere of Co porphyrin complexes causes great changes in
their UV-vis [17, 18], which makes convenient the study of their properties and reactions by electronic absorption
spectroscopy. A high affinity of nitrogen-containing ligands [19, 20] and the sensitivity to light irradiation [21] makes these
complexes promising components for photoactive systems.
II
To exclude the effect of PyF association and aggregation in the study of the Co TBPP reaction with PyF in toluene,
the satisfaction of the Burger-Lambert-Beer law was verified for the freshly prepared and stored PyF solutions in toluene in
the concentration ranges corresponding to the performance of the spectrophotometric experiment. The data obtained indicate
that fullerene exists in the solution in the unassociated form.
II
UV-vis of Co TBPP in toluene contains the Soret band (1a1g → 2eu) at 415 nm and Q-bands (1a1g → 1eu) at 530 nm
II
and 613 nm [22, 23]. The analysis of the spectral manifestation of the Co TBPP reaction with pyridyl-substituted
pyrrolidino[60]fullerene PyF for the first time enabled the determination of the two-step axial coordination reaction of the
base with metalloporphyrin, in which the first equilibrium is instantly established as soon as the reagent solutions are mixed,
and the second is established with time with a measurable rate. The original method of collecting information on the course
II
of an intricate reaction between Co TBPP and PyF (see EXPERIMENTAL), and the processing of spectrophotometric
titration data at τ = 0 and τ = ∞ (after the completion of a slow reaction at all mixture compositions) provided the quantitative
description of both equilibria and the rate of the second reaction step. The spectral transformation on passing from pure
II
Co TBPP in the solution to a product of the interaction with PyF at zero time, i.e. at the first step, is shown in Fig. 2.
After the establishment of equilibria at the first step at all compositions of reaction mixtures, a further slow
II
interaction in the Co TBPP–PyF system is accompanied by a gradual decrease in absorption at 415 nm and the appearance of
a new Soret band at 443 nm. The intensity ratio of Q-bands changes, too; the form of the spectrum becomes characteristic of
hexacoordinated cobalt complexes [20]. In the course of the UV-vis transformation isobestic points are observed along with
reversibility confirmed experimentally by diluting the mixture with respect to the fullerene concentration. The equilibrium is
established in 60-400 s depending on the fullerene concentration. Fig. 3 depicts the UV-vis changes typical of all studied
–5 –4
reaction mixtures at PyF concentrations of 2.53⋅10 -1.45⋅10 mol/l.
The formation of the hexacoordinated cobalt complex indicates the implementation of successive two-way reactions
that can be presented as equations (3) and (4)
K
1
⎯⎯→
←⎯⎯
II
Co TBPP + PyF
II
(PyF)Co TBPP, instantaneously;
(3)
(4)
K
1
⎯⎯→
←⎯⎯
II
(PyF)Co TBPP + PyF
II
(PyF)2Co TBPP, with time.
The calculation of equilibrium constant (3) from the data given in Fig. 3 yields a satisfactory magnitude of the
4 –1
equilibrium constant of (1.08 0.11)⋅10 l/mol .
714

Fig. 2. Change in the electron absorption spectrum of
II
Co TBPP in toluene at 298 K with the addition of PyF
–4
from 0 mol/l to 1.45⋅10 mol/l in toluene. The inset
depicts the corresponding spectrophotometric titration
curve obtained at a working wavelength of 415 nm.
Fig. 3. Change in the electron absorption spectrum of
II
Co TBPP in toluene at 298 K with an addition
–5
of 3.79⋅10 mol/l PyF during 350 s. Inset: dependence of
2 II
lgI on lgCPyF (R = 0.99) for the reaction of Co TBPP
with PyF at 298 K and τ = 0.
II
To plot the titration curve of the second step reaction between Co TBPP and PyF (Fig. 4a) the solutions were held
until the completion of slow reactions. As in the first step, the reaction involves one PyF molecule, which follows from the
magnitude of the tangent of the slope of the graphical dependence lgI = f(lgCPyF) (tgα = 0.8) (Fig. 4b). The numerical value of
6 –1
the equilibrium constant was found to be (1.21 0.32)⋅10 l/mol .
II
10
2
–2
The stability (formation) constant of (PyF)2Co TBPP written as K = K1K2 is (1.34 0.12)⋅10 l /mol .
As noted above, the equilibrium of (4) is established with time, which provides the possibility to measure the rate of
direct reaction (5) and calculate the rate constant k2 of the inverse reaction of equilibrium (4) with regard to constant K2
k
II
II
2
(PyF)Co TBPP + PyF ⎯⎯→ (PyF)2Co TBPP.
(5)
When studying the kinetics of this process, the first order with respect to metalloporphyrin was determined.
Effective rate constants (k2 eff) for this reaction are listed in Table 1. Linear dependences lgk2 eff – f(lgСPyF) with the tangent of
715

Fig. 4. Spectrophotometric titration curve (а) and the dependence lgI vs. lgCPyF for
II 2
the reaction of Co TBPP with PyF at 298 K (R = 0.98) at τ = ∞ (b).
II
TABLE 1. Effective Rate Constants (k2 eff) of the Reaction of (PyF)Co TBPP with PyF in Toluene at 298 K
4
СPyF⋅10 , mol/l
2
(k2 eff δk2 eff)⋅10 , s
–1
0.253
0.316
0.379
0.442
0.569
0.695
0.822
0.948
1.07
1.23 0.12
1.42 0.11
1.72 0.14
1.92 0.18
2.85 0.14
3.28 0.26
3.54 0.14
3.80 0.31
4.16 0.23
4.84 0.23
6.50 0.48
1.26
1.45
the slope close to 1 (tgα = 0.91) (Fig. 5) give evidence of the first order of the reaction with respect to PyF. The numerical
–1 –1
value of the rate constant k2 (71.5 7.5 mol ⋅l/s ) was found by the optimization of the dependence depicted in Fig. 5. The
–5 –1
–1
–1
6
–1
rate constant k2 is 5.9⋅10
As seen, the rate of forward reaction (4) is larger than that of the backward one by more than six orders of
magnitude. It is this fact that made it possible to apply the kinetic method of excessive concentrations to find the rate of
s (71.5 mol ⋅l/s / 1.21⋅10 l/mol ).
II 1
reaction (5). The formation of the donor-acceptor (PyF)2Co TBPP complex was additionally confirmed by IR, H NMR, and
fluorescent spectroscopy.
II
In the IR spectrum of the studied porphyrin-fullerene triad (PyF)2Co TBPP in KBr new signals were detected with
–1
–1
–1
–1
–1
–1
–1
–1
–1
frequencies of 1736 cm , 1561 cm , 1430 cm , 1422 cm , 1409 cm , 1188 cm , 1179 cm , 1033 cm , 910 cm ,
Fig. 5. Dependence lgk2 eff vs. lgСPyF for the reaction
II
of (PyF)Co TBPP with PyF in toluene at 298 K
2
(R = 0.98).
716

–1
866 cm , 832 cm , 767 cm , 642 cm , 636 cm , 598 cm , 574 cm , 553 cm , 541 cm , 527 cm , 505 cm , 479 cm ,
–1
–1
–1
–1
–1
–1
–1
–1
–1
–1
–1
–1
430 cm , and 413 cm , which correspond to vibrations of N-bonded PyF and are basent in the spectrum of Co TBPP. The
–1
II
–1
signals at 1430 cm , 1179 cm , 574 cm , and 527 cm correspond to vibrations of the С60 fullerene framework [24], which
–1
–1
–1
do not alter their positions during the formation of the triad. Vibrational frequencies of the pyridine and pyrrolidine rings in
–1
fullerene increase by approximately 2-27 cm as compared to bond vibrations of initial PyF (see EXPERIMENTAL). Based
–1
on the data of [25, 26], a new low-intensity signal at 413 cm seems to correspond to the Co–NPy bond.
Despite the absence of meso-protons in the H2TBPP porphyrin ring, which are most sensitive to the diamagnetic and
1 II
paramagnetic properties of the central cation of the complexing agent [17, 18], from the H NMR spectrum of the Co TBPP
7
complex in which the central atom is in the 3d configuration, the paramagnetic character of the complex is seen. This is
evidenced by a 6-8 ppm low-field shift of the signals of β-protons and protons of phenyl substituents relative to the
diamagnetic porphyrin complexes [17, 18]. The broadened signals of β-, ortho-protons at 16.05 ppm and 13.24 ppm also
1
II
confirm the paramagnetic nature of the complex. In the H NMR spectrum of the (PyF)2Co TBPP triad the above signals
undergo a strong-field shift to 14.62 ppm and 11.40 ppm respectively (Fig. 6). The signals of meta-protons and protons of
tert-butyl substituents undergo a strong-field shift by 0.65 ppm and 0.41 ppm respectively. These shifts of macrocycle
protons in the composition of the (PyF)2CoTBPP triad can be explained by a decrease in the effect of the ring current of the
porphyrin ring due to the formation of donor-acceptor Co–NPyF bonds. These changes may also indicate the electron transfer
from the macrocycle to the fullerene moiety within the triad supramolecule already in the unexcited state.
As it was mentioned in the beginning of this paper, the triad similar to the one described above based on
(2,3,7,8,12,18-hexamethyl-13,17-diethyl,5-(pyridin-2-yl)(porphyrinato)cobalt(II) and [2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-
(pyridin-2-ylmethyl)pyrrolidino[3′,4′:1,2][60]fullerene demonstrates photosensitivity due to the effect of photoinduction of
the state with charges separated between the macrocycle and the fullerene residue within the supramolecule [13]. In this
II
work, in order to detect a similar state in obtained triad (PyF)2Co TBPP its fluorescence was compared with the similar
II
property of its precursors (Fig. 7). Co TBPP does not have the fluorescent properties whereas its weak fluorescence is
II
manifested in the composition of supramolecular triad (PyF)2Co TBPP. At the same time, PyF fluorescence quenching is
observed on passing from pure PyF to the triad based on it. This fact can be explained by the electron density redistribution
from the macrocycle chromophore to fullerene. When initial metalloporphyrin has fluorescent properties, the fluorescence
band of the porphyrin macrocycle is quenched during the formation of porphyrin-fullerene diads [27, 28].
1 II
Fig. 6. H NMR spectra of Co TBPP (a), PyF (b), donor-acceptor triad
II
(PyF)2Co TBPP (c) in CDCl3.
717

Fig. 7. Fluorescence spectra (λexc = 450 nm) in
II –6
toluene: Co TBPP, СCo TBPP = 3.18⋅10 mol/l (1);
II
–5 II
PyF, СPyF = 4.77⋅10 mol/l (2); (PyF)2Co TBPP (3)
II
and (PyF)2Co TBPP with a PyF reference solution,
–5
PyF = 4.77⋅10 mol/l (4).
С
CONCLUSIONS
In the work, by chemical kinetic and thermodynamic methods the donor-acceptor complexation reaction of
II
(5,10,15,20-(tetra-4-tert-butylphenyl)21Н,23Н-porphinato)cobalt(II) (Co TBPP) with 1-methyl-2-(pyridin-4′-yl)-3,4-
II
fullero[60]pyrrolidine (PyF) is studied and porphyrin-fullerene triad (PyF)2Co TBPP is obtained with the stability constant K
9
2
–2
of (13.4 1.2)⋅10 l /mol . The triad stability is two orders of magnitude greater than that of the donor-acceptor complex with
a more intricate structure based on asymmetric (2,3,7,8,12,18-hexamethyl-13,17-diethyl,5-(2-pyridyl)(porphinato)cobalt(II)
and 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-2-ylmethyl)-2′,4′-dihydro-1′H-pyrrolo[3′,4′:1,2](C60–Ih)[5,6]fullerene
1
(Py3F) [13]. For the new triad the main spectral characteristics of UV, visible, IR, and H NMR spectra are obtained and
based on them, the chemical structure and the donor-acceptor nature of the triad are determined. By means of the
fluorescence spectra the triad capability of photoinduced charge separation is shown, which allows us to hope that this system
is promising in searching for components for photovoltaic devices.
The work was performed using the facilities of the Center for Collective Use “Upper Volga Region Center of
Physicochemical Research” and supported by RFBR grant No. 15-03-00646.
Fluorescence was explored within Program of the Presidium of the Russian Academy of Sciences No. 14 with the
technical assistance of A. A. Ksenofontov, which is gratefully acknowledged by the authors.
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