Carbazole-functionalized cobalt(ii) porphyrin axially bonded with C60/C70derivatives: Synthesis and characterization

Article abstract of DOI:10.1039/d1nj00980j

Two supramolecular cobalt(ii) porphyrin-fullerene systems, (PyC60)2CoDTBCP/(Py2C70)CoDTBCP, self-assembled via axial coordination of 1-N-methyl-2-(pyridin-4-yl)-3,4-fullero[60]pyrrolidine and 2,5-di-(pyridin-2-yl)-3,4-fullero[70]pyrrolidine by (5,15-bis[3

Full text of DOI:10.1039/d1nj00980j

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Carbazole-functionalized cobalt(II) porphyrin
axially bonded with C60/C70 derivatives: synthesis
Cite this: DOI: 10.1039/d1nj00980j
and characterization†
a
a
E. N. Ovchenkova, *a N. G. Bichan,
M. S. Gruzdev,
A. A. Ksenofontov,a
F. E. Gostev,b I. V. Shelaev,b V. A. Nadtochenko
and T. N. Lomova
b
a
Two supramolecular cobalt(II) porphyrin–fullerene systems, (PyC60)2CoDTBCP/(Py2C70)CoDTBCP,
self-assembled via axial coordination of 1-N-methyl-2-(pyridin-4-yl)-3,4-fullero[60]pyrrolidine and 2,5-
di-(pyridin-2-yl)-3,4-fullero[70]pyrrolidine by (5,15-bis[3,5-bis(tert-butyl)phenyl]-10,20-bis[4,6-(4-(3,6-di-
tert-butyl-9H-carbazol-9-yl)phenyl)pyrimidin-5-yl]porphinato)cobalt(II), respectively, were prepared and
characterized for the first time. Target carbazole-functionalized cobalt(II) porphyrin was synthesized
by direct metallation of the corresponding porphyrin that was in its turn obtained by tetra-substitution
of 5,15-bis[4,6-dichloropyrimidin-5-yl]porphyrin with 4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenol. All
compounds synthesized were fully characterized by mass spectrometry and UV-vis, IR, and 1H NMR
spectroscopy. Chemical structure and spectral properties of the triad/dyad were additionally described
using chemical thermodynamics, kinetics, and DFT calculations. The analysis of the geometric and elec-
tronic structures of the (PyC60)2CoDTBCP and (Py2C70)CoDTBCP FMOs in the ground state and the
study of their femtosecond transient absorption spectra points to the existence of photoinduced elec-
tron transfer in the triad and dyad. The data obtained are required for further photoelectrochemical
study of the triad/dyad and determining their potential in the building of photovoltaic devices.
Received 26th February 2021,
Accepted 31st March 2021
DOI: 10.1039/d1nj00980j
rsc.li/njc
their electron-donor properties and the ability to form charge
transfer complexes they are used extensively in organic
1. Introduction
Supramolecular architectures based on carbon nanoforms photovoltaics9 and as a building block for optoelectronic
(C60, C70 derivatives) and porphyrins are of considerable inter- materials.10 Carbazole derivatives have been widely used in
est. The combination of the specific properties of porphyrins medicine too as active components in antitumor, antimicro-
and fullerenes in these systems often leads to a synergy effect, bial, antihistaminic, antioxidative, anti-inflammatory, and
which makes these compounds unique and promising for psychotropic drugs.11–14 For example, a variety of carbazole
use in various fields of science, technology, medicine, and substituted compounds are a potential drug candidate for the
biotechnology. Advances in the synthesis of fullerenes and treatment of chronic diseases,15,16 Alzheimer’s disease17 and
tetrapyrrole macroheterocycles make it possible to obtain a acute myeloid leukemia.18
number of supramolecular systems with a set of practically
important properties.
Kimura and co-workers have synthesized carbazole-fused
zinc phthalocyanine, studied the influence of the carbazole
There has been increasing interest in the synthesis of groups on the optical and electrochemical properties of phtha-
carbazole-functionalized porphyrins/phthalocyanines in recent locyanines, and reported their performance in dye-sensitized
decades.1–7 The carbazole derivatives are a well-known class of solar cells (DSSCs) which show wide light-harvesting properties
aromatic heterocyclic compounds with high UV-vis absorption, in the 400–800 nm range.19 In the paper,20 the series of zinc
efficient fluorescent emission and high photostability.8 Due to porphyrin based sensitizers containing carbazole groups in the
meso-substituted porphyrin core were synthesized to investigate
their performance in DSSCs. Theoretical calculations have
revealed that the carbazole unit does not significantly affect
the electronic properties of the dyes but crucially it helps in the
suppression of the aggregation of the dyes on the TiO2
a G. A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences
Akademicheskaya str., 1, Ivanovo, Russia. E-mail: enk@isc-ras.ru
b N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of
Sciences, Kosygina St., 4, Moscow, Russia
surface, which leads to the higher conversion efficiency of the
device.20 Xu and co-workers have synthesized three dendritic
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
d1nj00980j
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carbazole-based porphyrins with intramolecular energy transfer
properties and showed that these macromolecules could emit
intense red light with high fluorescence quantum yields and so
might be good candidates for photonic devices.21 Carbazole-
functionalized iron porphyrin has been explored for its suit-
ability as a catalyst for CO2 electroreduction by immobilizing it
inside the microporous CO2-absorbing material.22
There has only been one report on the synthesis of supramo-
lecular fullerene systems based on carbazole-containing phtha-
locyanine complexes, where D’Souza and co-workers reported
tetracarbazole-substituted zinc phthalocyanine axially coordi-
nated to a phenylimidazole-functionalized fulleropyrrolidine.23
It was established that the stability constant of this donor–
acceptor complex was an order of magnitude higher than that
observed earlier for similar complexes due to the electronic
effect induced by the carbazole entities. Also, this system
exhibited photoinduced energy transfer from the carbazole
to zinc phthalocyanine with a reasonable light-to-energy con-
version efficiency in devices.23 Cobalt(II) porphyrins (CoPs) can
be considered as a good donor platform primarily because they
are thermally/chemically/electro/photo stable and soluble in
organic solvents. They show a strong absorbance in the visible
region, rich redox chemistry, and the ability to form thermo-
dynamically stable donor–acceptor complexes with organic N-
bases due to the large coordination capacity of the central
ion.24–28 Self-assembly in the cobalt(II) porphyrin/phthalocya-
nine–pyridyl-substituted fulleropyrrolidine systems, leading to
the formation of systems with photoinduced electron transfer
(PET), has been established in earlier publications.27–30
Fig. 1 Chemical structure of the compounds studied.
Despite the fact that the results of femtosecond studies show
shorter lifetimes (12 ꢀ 4 ps) for excited states of cobalt(II)
porphyrins31,32 compared with zinc porphyrins, CoPs are used
as donor building blocks for charge transfer systems. Charge-
transfer C70/C60–cobalt porphyrin cocrystals prepared by a
solution-processable co-assembly strategy have been character-
causing the reduction of the electron-accepting SWNT and,
simultaneously, the oxidation of the electron-donating por-
phyrin. Transient absorption measurements confirm the for-
mation of radical ion pairs displaying lifetimes in the
microsecond range.37
ized by
a
collection of experimental and theoretical
Taking into account the interesting photophysical properties
of both carbazole entities and porphyrins, we have synthesized for
the first time a cobalt(II) porphyrin containing 3,5-di-tert-
butylphenyl and 4,6-di-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)
phenoxy)pyrimidyl meso-substituents, CoDTBCP, and its coor-
dination complexes with pyridyl-substituted fullero[60]/[70]
pyrrolidines, (PyC60)2CoDTBCP/(Py2C70)CoDTBCP, for which
we expect an improvement of the applied properties (Fig. 1).
We also report here the peculiarities of the self-assembly of the
donor–acceptor systems above and their geometric/electronic
structures obtained by the methods of thermodynamics/
kinetics, UV-vis, NMR, IR, mass spectrometry and DFT calcula-
tions, respectively.
methods.33,34 These supramolecular architectures, character-
ized by strong intermolecular interactions between the C60/C70
and cobalt porphyrin, display a significantly high electrical
conductivity and high hole mobility as well as an extraordina-
rily high thermal stability. As shown in ref. 35 and 36 using
time-resolved spectroscopic measurements and theoretical cal-
culations, the origin of the enhanced electrocatalytic activity of
the graphene oxide (GO)–cobalt porphyrin hybrid complexes
(CoIIAPFP) is provided by the formation of an generated charge-
separated state, GOꢁ–(CoIIAPFP)+, undergoing fast charge
recombination (o10 ps) between the GOꢁ and (CoAPFP)+
moieties, which is directly related to the quick neutralization
+
II
of (Co APFP) and the reduction in the dead time of inactive
III
Co APFP after the electrocatalytic reduction reaction. Guldi
et al.37 have integrated single-wall carbon nanotubes (SWNTs),
several water soluble pyrenes, and a number of water-soluble
porphyrins including CoP into functional nanohybrids through
the combination of associative van der Waals and electrostatic
2. Experimental section
Synthesis
3,6-Di-tert-butyl-9H-carbazole (1). Carbazole (5.0 g, 0.03 mol)
interactions. The photoexcitation of these nanohybrid systems and anhydrous AlCl3 (4.0 g, 0.03 mol) were dissolved in CH2Cl2
with visible light leads to rapid intrahybrid charge separation (100 mL). When the mixture was cooled to 0 1C, the solution of
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tert-BuCl (6.6 mL, 0.06 mol) in CH2Cl2 (20 mL) was added Ar-H), 8.59 (2 H, d, J = 4.8 Hz, Ar-H), 7.29 (4 H, s, Ar-H),
slowly. After that, the ice-bath was removed and the resulting 1.51 (36 H, s, –CH3), ꢁ2.50 (2 H, s, NH). MALDI-TOF-MS,
mixture was stirred for 24 h at room temperature. Then, the m/z: calc. 982.94, found: 983.05 [M + H]+. This compound
mixture was poured into water, extracted with CH2Cl2, and was prepared under the same conditions as the literature
dried with anhydrous Na2SO4. The solvent was evaporated to procedure.38
afford the crude products, which were twice recrystallized from
5,15-Bis[3,5-bis(tert-butyl)phenyl]-10,20-bis[4,6-(4-(3,6-di-tert-
butyl-9H-carbazol-9-yl)phenyl)pyrimidin-5-yl]porphyrin (5).
hexane giving 4.5 g (54%) of a white solid, mp: 233.0–235.0 1C.
1H NMR (CDCl3, 300 MHz, ppm): d = 8.07 (2 H, s, Ar-H), 7.84
(1 H, s, NH), 7.46 (2 H, d, Ar-H), 7.32 (2 H, d, Ar-H), 1.45 (18 H, s,
–CH3). MALDI-TOF-MS, m/z: calc. 279.2, found: 280.0 [M + H]+.
A
solution of 4 (17.15 mg, 0.0175 mmol) and 3 (39.05 mg,
0.24 mmol) in 10 mL dry DMF was prepared, and K2CO3
(117 mg, 0.83 mmol) was added. The mixture was stirred for
48 hours at 60 1C. Then it was cooled and poured into 50 mL
dichloromethane. The organic layer was washed with distilled
water and dried over MgSO4. The drying agent was filtered off,
and the filtrate was evaporated. Column chromatography
(silica/DCM : EtAO 10 : 1), (silica/DCM : heptane 4 : 1), (Al2O3/
DCM : EtAO 10 : 1) was performed. The yield was 71.3%,
42 mg. UV-vis (toluene) lmax nm (log e): 423 (5.78), 517 (4.77),
551 (4.41), 594 (4.23), 650 (4.04). 1H NMR (CDCl3,
400 MHz, ppm): d = 8.90 (4 H, s, Hb), 8.89 (4 H, s, Hb), 8.10
(2 H, s, Ar-H), 7.80–7.98 (24 H, m, Carb-H), 7.07–7.35
(22 H, m, Ar-H), 1.99 (36 H, s, –CH3), 1.46 (36 H, s, –CH3),
1.28 (36 H, s, –CH3), ꢁ2.54 (2 H, s, NH). MALDI-TOF-MS, m/z: calc.
2323.20, found: 2324.05 [M + H]+.
3,6-Di-tert-butyl-9-(4-methoxyphenyl)-9H-carbazole (2). 3,6-
Di-tert-butyl-9H-carbazole (2.8 g, 0.01 mol), 1-iodo-4-
methoxybenzene (2.5 g, 0.011 mol), Cu2O (3.0 g, 0.021 mol),
and dimethylacetamide (15 mL) were mixed in a flask under an
argon atmosphere and heated to 160 1C in an oil bath for 24 h.
Then, the mixture was cooled to the room temperature and
filtered. The filtrate was poured into 200 mL CH2Cl2 and
washed 5 times with water. The organic layer was separated
and dried with anhydrous Na2SO4. The product was purified by
chromatography (silica gel, hexane) giving 3.2 g (83%) of a
white solid, mp: 162.0–164.0 1C. 1H NMR (CDCl3, 500 MHz, ppm):
d = 8.14 (2 H, s, Ar-H), 7.45–7.42 (4 H, m, Ar-H), 7.24 (2 H, d, Ar-H),
7.08 (2 H, d, Ar-H), 3.91 (3 H, s, –OMe), 1.46 (18 H, s, –CH3).
MALDI-TOF-MS, m/z: calc. 385.5, found: 386.3 [M + H]+.
(5,15-Bis[3,5-bis(tert-butyl)phenyl]-10,20-bis[4,6-(4-(3,6-di-tert-
butyl-9H-carbazol-9-yl)phenyl)pyrimidin-5-yl]porphinato)cobalt(II)
CoDTBCP. The reaction of Co(OAc)2ꢂ4H2O (42 mg, 0.1686 mmol)
with 5 (40.0 mg, 0.0172 mmol) was carried out in dimethylfor-
mamide (10 mL) with heating for 10 min. Reaction completion
was monitored by TLC until no traces of the starting material
were detected. The reaction mixture was cooled and diluted
with water. Products were extracted into chloroform and pur-
ified by flash chromatography (Al2O3/CHCl3). The yield was
30.8 mg (77%). UV-vis (toluene) lmax nm (log e): 419 (5.32), 532
(4.11). IR [(KBr), nmax/cmꢁ1]: 3049 n(C–H); 2963, 2854 n(C–H) of
tert-butyl groups; 1732; 1593 n(CQN); 1556, 1506, 1479, 1459,
1419, 1364, 1330 n(CQC); 1295 nas(QC–O–C–); 1260, 1201
n(C–N); 1091; 1020 ns(QC–O–C–); 930, 862, 798, 746, 728, 704,
661, 635, 611, 567, 513; 472 n(Co–N); 400. 1H-NMR (CDCl3,
400 MHz, ppm): d = 16.29 (4 H, br s, Hb), 15.05 (4 H, br s, Hb),
12.11 (4 H, br s, Ar-H), 10.86 (2 H, s, Ar-H), 9.41 (2 H, s, Ar-H),
7.76 (12 H, m, Carb-H), 7.55–7.17 (8 H, m, Ar-H), 6.88 (12 H, m,
Carb-H), 6.39 (5 H, m, Ar-H), 5.97 (3 H, m, Ar-H), 2.47 (36 H, s,
–CH3), 1.59–1.42 (36 H, m, –CH3), 1.16 (36 H, s, –CH3). MALDI-TOF-
MS, m/z: calc. 2378.1, found: 2378.57 [M]+.
4-(3,6-Di-tert-butyl-9H-carbazol-9-yl)phenol (3). A solution of
boron tribromide (BBr3) (0.86 mL, 8.9 mmol) in 5 mL of dry
CH2Cl2 was added dropwise into a solution of 3,6-di-tert-butyl-
9-(4-methoxyphenyl)-9H-carbazole (2.3 g, 6.0 mmol) in 40 mL of
dry CH2Cl2 at room temperature. After being stirred at room
temperature for 24 h, the mixture was slowly poured into H2O
(200 mL) and stirred for 1 h. The organic phase was separated
and the compound from the water phase was extracted in
CH2Cl2 until the phase became colorless. Both CH2Cl2 solu-
tions were combined and dried over anhydrous Na2SO4. The
crude product was chromatographed on silica gel with hexane/
CH2Cl2 (1 : 3) as the eluent affording 2.0 g (90%) of a white
solid, mp: 198.0–200.0 1C. 1H NMR (CDCl3, 300 MHz, ppm):
d = 8.13 (2 H, s, Ar-H), 7.45 (2 H, d, Ar-H), 7.43 (2 H, d, Ar-H),
7.24 (2 H, d, Ar-H), 7.03 (2 H, d, Ar-H), 1.46 (18 H, s, –CH3).
MALDI-TOF-MS, m/z: calc. 371.5, found: 372.1 [M + H]+.
5,15-Bis[3,5-bis(tert-butyl)phenyl]-10,20-bis[4,6-dichloropyrimidin-5-yl]
porphyrin (4). A solution of 3,5-bis(tert-butyl)phenyldipyrromethane
(0.5 g, 1.89 mmol) and 4,6-dichloropyrimidine-5-carbaldehyde
(0.34 g, 1.89 mmol) in dichloromethane (500 mL) was deox-
ygenated by purging with argon for 15 min. Boron trifluoride
etherate (0.02 g, 0.19 mmol) was added via syringe, and the
Materials
solution was stirred under argon and protected from light for All chemicals, solvents and chromatographic materials were
1 h at room temperature. p-Chloranil (0.454 g, 1.89 mmol) was obtained from Sigma-Aldrich and Acros Organics and were
added, and the mixture was refluxed for 1 h. The solvent was used as received. The purity of C60 and C70 was quoted as
removed and the residue was purified by chromatography 99.9% and 98.6% by weight, respectively. Details of the PyC60
(silica gel, dichloromethane) yielding porphyrin as a purple and Py2C70 synthesis together with the MALDI-TOF mass
solid (0.445 g, 53%). UV-vis (CH2Cl2): lmax (log e) 420 (5.82), spectra (Fig. S1 and S2, ESI†) are given in the ESI.† They were
1
516 (4.47), 549 (3.79), 592 (3.83), 649 (3.60). H NMR (CDCl3, prepared according to a general procedure of fulleropyrrolidine
400 MHz, ppm): d = 9.05 (8 H, s, Hb), 8.76 (2 H, d, J = 4.8 Hz, synthesis developed by Prato39 and Troshin (with coworkers).40
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We changed the procedure (the ratio of reagents, the reaction same theory level in order to characterize the stationary points
time, and the purification method) somewhat, which led to an as true minima, representing equilibrium structures on
increase in the yield of the product.
potential energy surfaces. The spin multiplicity for the Co atom
in (PyC60)2CoDTBCP and (Py2C70)CoDTBCP is a doublet and
singlet, respectively. The Unrestricted Hartree–Fock (UHF) cal-
culation was used in the case of (PyC60)2CoDTBCP. The UCSF
Chimera44 and ChemCraft 1.845 were used to analyze results
and molecular graphics.
Methods
Kinetics. The kinetics of the slow CoDTBCP reaction with
PyC60/Py2C70 in toluene at 298 K were studied spectrophotome-
trically using the method of superfluous concentrations. The
UV-vis spectra were recorded with an Agilent 8454 UV-visible
spectrophotometer. The upper concentration limit of fullerene
was determined by its solubility in toluene. Absorbance mea-
surements were carried out for the solution series at a constant
concentration of CoDTBCP (3.86 ꢃ 10ꢁ6 M) appropriate for
observing the porphyrin Soret band with different additions of
PyC60/Py2C70. The PyC60/Py2C70 spectra with concentrations the
same as in the stock solution were used as a zero line. The first
order rate constant values, kobs, were calculated using the
equation kobs = 1/tꢂln((A0 ꢁ AN)/(At ꢁ AN)), where A0, At, and
AN are the absorbance values at a working wavelength for
CoDTBCP, a reaction mixture at t time and a reaction product.
The relative error in kobs determination did not exceed 10%.
Thermodynamics. The equilibrium constant values for the
reaction between CoDTBCP and PyC60/Py2C70 in toluene were
calculated using the equation for a three-component equili-
brium system with two colored components:
Femtosecond laser photolysis setup. The output of a Ti:Sap-
phire oscillator (800 nm, 80 MHz, 30 fs, ‘‘Tsunami’’, Spectra-
Physics, USA) was amplified using a regenerative amplifier
(‘‘Spitfire Pro’’, Spectra-Physics, USA). The repetition rate of
the amplified laser pulses was set at 100 Hz. This frequency is
small enough to eliminate permanent bleaching of the sample
and at the same time corresponds to the maximum perfor-
mance of the registration system.
The amplified pulses (800 nm, 100 Hz, 1.5 mJ, 40 fs) were
split into two beams. One of the beams was attenuated to 1–2 mJ
and focused into a nonlinear optical crystal (a-BBO) to produce
the second harmonic radiation which was used as a pump
pulse. The pump pulse had a Gaussian pulse shape centered at
a wavelength of 400 nm, 50 fs duration, and 100 nJ pulse
energy. This energy is optimal for obtaining a signal of suffi-
cient amplitude, and at the same time is small enough to
exclude nonlinear processes in the sample.
The second beam was attenuated to 0.8 mJ and directed to a
non-collinear optical parametric amplifier (‘‘Topas-white’’,
Light Conversion, Lithuania) whose radiation (900 nm, 3 5 fs,
10 mJ) was attenuated to 1 mJ and focused into a thin quartz cell
with pure H2O to produce a supercontinuum probe pulse. The
supercontinuum probe pulse was attenuated and spectrally
filtered from excess radiation at a wavelength of 900 nm and
had a smooth spectrum in the wavelength range of 380–850 nm
and negligible energy (B1 nJ) to exclude its influence on the
observed signal.
ðAi ꢁ A0Þ=ðA1 ꢁ A0Þ
K ¼
1 ꢁ ðAi ꢁ A0Þ=ðA1 ꢁ A0Þ
1
ꢂ
ðCF0ullerene ꢁ CC0 oDTBCP ꢂ ðAi ꢁ A0Þ=ðA1 ꢁ A0ÞÞ
here, C0Fullerene and C0CoDTBCP are initial concentrations of PyC60
/
Py2C70 and CoDTBCP in toluene, respectively; and A0, Ai, and
AN are absorbance values at a working wavelength of an initial
complex, an equilibrium mixture at a definite fullerene concen-
tration, and a reaction product. The relative error in K determi-
nation did not exceed 30%.
NMR, IR and mass spectroscopy. 1H NMR spectra were
recorded with a Bruker Avance III-500 NMR spectrometer using
deuterochloroform (CDCl3) as a solvent. IR spectra were
recorded with a VERTEX 80v spectrometer in KBr. In order to
record the IR spectra of donor–acceptor complexes, we pre-
pared the solid residue of dyad/triad by removing the solvent
in vacuum. Mass spectra were obtained using a Shimadzu
Confidence spectrometer. Samples were put on the target in
2,5-dihydroxybenzoic acid (DHB) matrices.
The pump and probe pulses were delayed relative to each
other by a computer-controlled delay line in the range of 0–500 ps,
with a resolution from 3.3 fs to 1 ps. The pulses were then
attenuated, recombined, and focused onto the flow sample cell.
The pump and probe light spots had diameters of 300 and
120 mm, respectively. The relative polarizations of the pump and
probe beams were adjusted to 54.71 (the magic angle).
The experiments were carried out at 278 K. The circulation
rate in the flow cell was fast enough to avoid multiple excita-
tions in the sample volume and was 8 mL minꢁ1. Pure dry
argon was fed into the flow system to avoid contact of the
DFT calculations. DFT calculations for CoDTBCP and PyC60
/
Py2C70 were performed using the PC GAMESS v.12 program sample solution with air.
package.41 The electronic structures of CoDTBCP and PyC60
The supercontinuum probe signal out of the sample was
/
Py2C70 were studied using Density Functional Theory with the dispersed using a polychromator (‘‘Acton SP-300’’, Roper Scien-
B3LYP functional and the def2-SVP basis set.42 The influence of tific, USA) and detected using a CCD camera (‘‘Newton’’, Andor,
intramolecular dispersion interactions on the molecular struc- USA). Transient absorption spectral changes DA(t, l) were
ture was explored using the dispersion corrections introduced recorded within the range of 380–850 nm. The measured
by Grimme et al. (D3).43 Geometric optimization of the por- spectra were corrected for group delay dispersion of the super-
phyrin–fullerenes was carried out without limitation in sym- continuum using the procedure described previously.46,47
metry. Harmonic vibration frequencies were calculated at the The zero time delay between pump and probe pulses was
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determined in control experiments by recording the signal of a material for CoDTBCP was prepared by tetra-substitution of
non-resonant coherent burst from pure de-aerated toluene. 4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenol (3) with 5,15-bis[4,6-
Particular attention was paid to the ‘‘coherence spike’’ or dichloropyrimidin-5-yl]porphyrin (4). Compound 3 was in turn
‘‘coherent artifact’’, which is observed at initial delays during synthesized by the treatment of 3,6-di-tert-butyl-9H-carbazole
the overlap of pump and probe pulses and complicates the (1) with 1-iodo-4-methoxybenzene, and Cu2O in dimethylaceta-
analysis of the measurement results at delays of o70 fs. The mide to obtain 3,6-di-tert-butyl-9-(4-methoxyphenyl)-9H-
problem of the resonance signal of a chromophore molecule in carbazole (2), the further treatment of which by boron tribro-
solution for the ‘‘coherent spike’’ time window was analyzed in mide in CH2Cl2 at room temperature leads to the formation of
accordance with ref. 48.
3. Compound 4 was obtained by reaction of 3,5-bis(tert-
butyl)phenyldipyrromethane with 4,6-dichloropyrimidine-5-
carbaldehyde in CH2Cl2 under an argon atmosphere for
15 min with the further addition of boron trifluoride etherate
and p-chloranil. Identification of the chemical structure of the
3. Results and discussion
Synthesis and characterization of CoDTBCP
compounds synthesized was achieved using standard spectral
1
Fig. 2 shows the synthetic route for the target cobalt(II) por- techniques: UV-vis, IR, H NMR spectroscopy and MALDI-TOF
phyrin bearing peripherally 3,5-di-tert-butylphenyl and bulky mass spectrometry (Experimental section). Spectral analysis is
4,6-di-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenoxy)pyrimidyl consistent with their proposed structures.
substituents (CoDTBCP). The presence of the tert-butyl groups
The UV-vis absorption spectra of the free base, 5 and
in CoDTBCP facilitates its high solubility in most organic CoDTBCP were recorded in toluene at the room temperature.
solvents. The free base porphyrin 5 (Fig. 2) used as the starting The corresponding lmax values reported in Table S1 (ESI†) were
Fig. 2 Scheme of the CoDTBCP synthesis.
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compared with other meso-substituted porphyrins and their of the b-protons as two broad singlets at 16.29 and 15.05 ppm
complexes with cobalt. The free-base porphyrin, 5 exhibits a (Experimental section). The signals of the phenyl ortho-protons
well-defined strong Soret band at 423 nm and four weaker in the 3,5-di-tert-butylphenyl substituents appear as a broad
Q-bands between 517 and 649 nm, which is consistent with the singlet at 12.11 ppm. Phenyl and carbazole fragment protons in
literature data.24,49,50 The CoDTBCP spectrum, with the Soret the 4,6-di-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenoxy)pyrimidyl
and Q bands at 419 nm and 532 nm, respectively, is slightly groups resonate in the 8.18–5.94 ppm range. The signals in the
hypsochromically shifted compared with the free base. The four 2.47–1.16 ppm range correspond to the tert-butyl group protons.
Q bands of free porphyrin turn into a single band in agreement Thus, the 1H NMR spectrum clearly demonstrates the paramag-
with the insertion of cobalt in the porphyrin core. The UV-vis netic nature of the sample indicating the Co(II) complex.
CoDTBCP spectrum, being similar to those for porphyrin com-
Self-assembly of the porphyrin–fullerene systems
plexes of cobalt(II) (Table S1, ESI†), describes the substance
under consideration as tetra-coordinated cobalt(II) porphyrin. The self-assembly of the donor–acceptor complexes based on
The CoDTBCP solid and toluene solution is stable at room CoDTBCP and PyC60/Py2C70 was studied by means of spectral
temperature for a long time.
methods and chemical thermodynamics/kinetics. The spectral
The CoDTBCP chemical structure was confirmed by IR and analysis of the CoDTBCP reaction with fullero[60]/[70]pyrroli-
1H NMR spectroscopy data. The disappearance of N–H proton dine has allowed the determination of different stoichiometric
signals (ꢁ2.54 ppm) of 5 in the 1H NMR spectrum of CoDTBCP mechanisms of PyC60 and Py2C70 coordination. In the case of
shows that the metalloporphyrin was successfully synthesized PyC60, the two-stage process leading to the triad, (PyC60 2-
)
(Experimental section). The CoDTBCP IR spectrum obtained CoDTBCP, and the one-stage formation of (Py2C70)CoDTBCP
from KBr pellets contains the characteristic vibrations signals were respectively observed.
of the porphyrin macrocycle and the carbazole moieties. The
Spectral analysis of the CoDTBCP reaction with PyC60 has
absorption bands in the range of 2854–2963 and 1364 cmꢁ1 allowed the detection and description of the fast equilibrium
correspond to the stretching and deformation C–H vibrations and slow two-way reaction of PyC60 coordination simulta-
in the tert-butyl groups. The n(C–H) frequency at 3049 cmꢁ1 neously due to using the original method for information
suggests the presence of the aromatic benzene rings in collection during spectrophotometric titration at t = 0 and over
CoDTBCP. The intense bands at 1593 and 1260, and 1201 time (time-dependent titration52). The spectral changes during
cmꢁ1 are assigned to the n(CQN) and n(C–N) vibrations, the transformation of CoDTBCP with PyC60 in toluene solution
respectively. The characteristic vibrations of nas(QC–O–C–) at zero time, namely in the first stage, are shown in Fig. 3a. The
and ns(QC–O–C–) were observed at 1295 cmꢁ1 and 1020 cmꢁ1
,
bonding of PyC60 to CoDTBCP in the first stage is characterized
respectively. The frequencies of the aromatic n(CQC) are in the by both a gradual decrease of the intensity at 419 nm in
range from 1459 to 1556 cmꢁ1. The peaks of the cobalt(II) the CoDTBCP spectrum and the appearance of the new band
porphyrin in the region of 513–930 cmꢁ1 are caused by vibrations at 436 nm in the form of a shoulder. One PyC60 molecule
of the macrocycle skeleton. The weak signal at 472 cmꢁ1 is is bonded by CoDTBCP, as followed from the slope of the
observed in the range of stretching vibrations of Co–N bonds.51 log I–log CPyC60 dependence (Fig. 3a).
This signal is absent in the IR spectrum of free base, 5.
The following slow interaction leading to equilibrium in the
The paramagnetic character of CoDTBCP was determined by CoDTBCP–PyC60 systems of all compositions taken is accom-
1H NMR spectroscopy. The chemical shifts in the 1H NMR panied by the gradual decrease in the absorption at 419 nm
spectra of the cobalt(II) complexes with different substituted together with the appearance of the new Soret band 436 nm.
porphyrins are summarized in Table S2 (ESI†). CoDTBCP hav- The intensity ratio of the Q-bands is also varied so that the form
ing the CoII ground state configuration 3d7 exhibits the signals of the spectrum becomes typical of six-coordination cobalt
Fig. 3 UV-vis spectrum transformations during the titration of CoDTBCP with PyC60 (CPyC60 = 0 C 1.47 ꢃ 10ꢁ4 M) in toluene at t = 0 (a) and t = N (b).
Inset: Plots of log I vs. log CPyC60 at t = 0 (a) and t = N (b).
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Table 1 Chemical structure, formation reaction equations and corresponding equilibrium/rate constants for (PyC60)2CoDTBCP and (Py2C70)CoDTBCPa
Reaction equation
CoDTBCP + PyC60
Equilibrium constant, K, L molꢁ1 rate constant, k
(6.06 ꢀ 1.73) ꢃ 104
k1
Ð
(PyC60)CoDTBCP, fast
K2;k2
(1.52 ꢀ 0.42) ꢃ 105 k2 = 5.06 ꢀ 0.17 molꢁ1 L sꢁ1
k
= 3.33 ꢃ
ꢁ2
10ꢁ5 sꢁ1
(PyC60)CoDTBCP + PyC60
Ð
(PyC60)2CoDTBCP,
k2:
over time
K;k
Ð
(8.25 ꢀ 1.59) ꢃ 104 k = 67.23 ꢀ 3.44 molꢁ1 L sꢁ1
k
= 8.15 ꢃ
CoDTBCP + Py2C70
over time
(Py2C70)CoDTBCP,
ꢁ
10ꢁ4 sꢁ1
k:
The stability constant of the triad, b = K1 ꢃ K2 is (9.21 ꢀ 2.89) ꢃ 109 L2 molꢁ2
.
a
complexes.53 One PyC60 molecule participates in the reaction
The coordination of one Py2C70 molecule with CoDTBCP
second stage, which follows from the tan a numerical value of giving the donor–acceptor dyad, (Py2C70)CoDTBCP, which is
the slope log I ꢁ log CPyC60 (Fig. 3b). The reaction reversibility is accompanied by the UV-vis spectrum change (Fig. 4) proceeds
confirmed experimentally by diluting mixtures with respect to as a one-stage reversible process (see the reaction equation in
the PyC60 concentration. The isosbestic points are observed Table 1). The formation of the five-coordination cobalt(II)
during the transformation of the UV-vis spectra (Fig. S3, ESI†). porphyrin complex over time is characterized by both the
The equilibrium in the mixtures studied is established within gradual intensity decrease of the band at 419 nm and the
700–1200 seconds depending on the PyC60 concentration. Fig. appearance of the shoulder near 437 nm with the preservation
S3 (ESI†) shows the UV-vis spectrum transformations typical of of the isosbestic points at 401, 427 nm. The reaction rate
the reaction mixtures at CPyC60 between 2.75 ꢃ 10ꢁ5 and 1.47 ꢃ constants (kobs) are shown in Table 3.
10ꢁ4 M. Thus, the formation of the donor–acceptor triad can be
The first order with respect to CoDTBCP was determined
represented as two successive two-way reactions with corres- during the kinetic measurements (Fig. S6, ESI†). The straight-
ponding equilibrium constants (Table 1). As indicated above, line dependence of log kobs vs. log CPy2C70 indicates that the
the second equilibrium is established over time, which allows reaction order with respect to Py2C70 is close to unity (Fig. S7,
measurement of the reaction rate constants (k2obs) (Table 2). ESI†). The rate constants of the direct (k) and inverse reactions,
The first orders with respect to CoDTBCP (Fig. S4, ESI†) and
PyC60 (Fig. S5, ESI†) are determined and the k2 and k rate
ꢁ2
constants of the direct and inverse reaction are calculated
(Table 1).
Table 2 Rate constants of the CoDTBCP reaction with the second
molecule PyC60 in toluene at 298 K
CPyC60 ꢃ 105, M
2.75
(k2obs ꢀ dk2obs) ꢃ 103, sꢁ1
2.67 ꢀ 0.09
3.66
4.58
5.49
6.41
7.33
9.16
11.0
12.8
14.7
3.15 ꢀ 0.20
4.06 ꢀ 0.13
4.60 ꢀ 0.12
5.20 ꢀ 0.19
5.71 ꢀ 0.24
6.54 ꢀ 0.26
7.33 ꢀ 0.44
7.98 ꢀ 0.36
8.81 ꢀ 0.47
Fig. 4 Transformation in the UV-vis spectrum of the mixture of CoDTBCP
and 2.82 ꢃ 10ꢁ5 M Py2C70 in toluene at 298 K over 600 seconds.
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Table 3 Rate constants for the reaction of CoDTBCP with Py2C70 in
toluene at 298 K
CPy2C70 ꢃ 105, M
(kobs ꢀ dkobs) ꢃ 102, sꢁ1
2.26
2.82
3.38
3.95
4.51
5.08
5.64
6.77
1.36 ꢀ 0.11
1.50 ꢀ 0.03
1.78 ꢀ 0.09
2.24 ꢀ 0.13
2.42 ꢀ 0.04
2.75 ꢀ 0.12
2.82 ꢀ 0.13
2.93 ꢀ 0.24
(k ) were found by optimization of the dependence in Fig. S7
ꢁ
(ESI†) and as ratio k/K (Table 1), respectively. To construct the
titration curve (Fig. 5) and calculate K (Table 1) for the reaction
between CoDTBCP and Py2C70, solutions were maintained
until the end of the slow reactions. The one Py2C70 molecule
participates in the equilibrium that follows from the numerical
value of the slope of the straight line in the coordinates
log I–log CPy2C70, tan a 0.85 (Fig. 5b).
Fig. 6 IR spectra of CoDTBCP (black) and its triad with PyC60 (red) in KBr.
In this way, the CoDTBCP–fullero[60]/[70]pyrrolidine mix-
tures in organic solvent are self-organizing systems suitable for
obtaining the fullerene-containing coordination complexes
with various stoichiometries. The donor–acceptor complexes,
(PyC60)2CoDTBCP and (Py2C70)CoDTBCP, exhibit moderately
high stability, which follows from the K values being much
higher than one. Comparison of the numerical values K1 and K
(Table 1) shows that their stability is commensurate within the
margin of error but (Py2C70)CoDTBCP stays coordinationally
saturated in comparison with intermediate (PyC60)CoDTBCP.
Bands corresponding to vibrations of PyC60 are denoted with asterisks.
of coordinated PyC60 appear in the IR spectrum of the triad
(Fig. 6, red line). The signals at 1179, 574, and 527 cmꢁ1
54
correspond to the vibrations of the C60 moiety in PyC60 and
their positions are unchanged in the spectrum of the triad. The
PyC60 frequencies in the (PyC60)2CoDTBCP spectrum assigned
to vibrations of the pyridine and pyrrolidinyl rings are shifted
by 1–5 cmꢁ1 compared with those of free PyC60. The appearance
of the new low-intensity signal at 427 cmꢁ1 presumably corre-
Chemical structure of porphyrin–fullerene systems
sponded to the Co–NPyC bond 51 and the shift of the n(Co–N)
60
signal to 479 cmꢁ1 also confirms the formation of the supra-
molecular systems. The mentioned shift is probably related to
the Co axial displacement due to the appearances of PyC60 in
the triad structure. Really, the quantum chemical calculations
below show that the Co atom is displaced from the macrocycle
plane respectively by 0.20 Å and 0.55 Å in (PyC60)2CoDTBCP and
(Py2C70)CoDTBCP, respectively.
The formation of (PyC60)2CoDTBCP and (Py2C70)CoDTBCP was
1
also monitored by the change in IR and H NMR spectra. The
formation of (PyC60)2CoDTBCP was accompanied by a change
in the signal intensity ratios of the macrocycle n(CQN), n(CQC)
and n(C–N) vibrations in the triad IR spectrum compared with
CoDTBCP (Fig. 6). A high-frequency shift of these signals was
also observed. The signals of n(CQN), n(CQC) and n(C–N)
appear at 1596, 1560 cmꢁ1 and 1261, and 1208 cmꢁ1 respec-
tively. The frequencies of the C–H stretching vibrations of the
tert-butyl groups remain unchanged due to their distant loca-
tion from the macrocycle plane. The new signals at 2921, 2784,
1463, 1334, 1314, 1179, 1162, 909, 767, 707, 663, 598, 574, 553,
541, 527, 504, 448, 427, and 402 cmꢁ1 assigned to the vibrations
Some relatively strong bands at 1590, 794, 672, 642, 578 and
534 cmꢁ1, which are unique for C70,55 are present unchanged in
the (Py2C70)CoDTBCP IR spectrum (Fig. S8, ESI†). The bands
assigned to vibrations of pyridine and pyrrolidinyl rings of the
Py2C70 are shifted by 1–4 cmꢁ1 in the dyad IR spectrum
compared with free Py2C70. With respect to vibrations of the
macrocyclic ligand, the n(CQN), nas(QC–O–C–), and n(C–N)
signals undergo the largest shift (Fig. S8, ESI†) when the
transition from the CoDTBCP spectrum to the (Py2C70)-
CoDTBCP spectrum takes place and the new low-intensity
signal at 427 cmꢁ1 corresponding to the Co–NPy2C70 bond
appears.
The addition of PyC60 and Py2C70 to the CoDTBCP solution
in CDCl3 (Fig. 5a) is accompanied with a shift of the signals of
CoDTBCP protons located in the macrocycle or in close proxi-
mity to it in the strong field (Fig. 7). The signals of the
(PyC60)2CoDTBCP b-protons are displayed as a broad multiplet
Fig. 5 Spectrophotometric titration curve (a) and plot of log I vs. log
CPy C (b) for the reaction of CoDTBCP with Py2C70 at t = N.
2
70
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both coordination complexes orients one carbazole fragment.
The deviation from coplanarity between the carbazole moiety
aromatic plane and the plane of the nearest hexagonal ring of
the fullerene in (PyC60)2CoDTBCP is from 20.31 to 44.11. This
deviation in (Py2C70)CoDTBCP is 15.41. The distance between
the carbazole moieties and the hexagonal rings of two C60
moieties is 3.280 Å and 5.001 Å, of one C70 moiety is 3.574 Å.
DFT calculations show that the HOMO and LUMO are
localized on the electron donor porphyrin and the electron
acceptor fullerene, respectively, which may shed light on the
nature of the charge transfer states.56–58 Calculation of the
(PyC60)2CoDTBCP/(Py2C70)CoDTBCP electronic structure has
given a very interesting result, namely the presence of intra-
molecular photoinduced electron transfer (PET) clearly arising
from the data in Fig. 8. The HOMOꢁ3 and HOMOꢁ2 of both
coordination complexes are localized on the carbazole moi-
eties, while HOMO and HOMOꢁ1 are localized on the macro-
cycle. However, the LUMO and LUMO + n are completely
localized in the C60 and C70 moieties. Using frontier molecular
orbital (FMO) analysis of (PyC60)2CoDTBCP and (Py2C70)-
Fig. 7 The informative fragment of the 1H NMR spectra of CoDTBCP (a),
and its triad (PyC60)2CoDTBCP (b), and dyad (Py2C70)CoDTBCP (c) in
CDCl3.
and shifted to 14.15 ppm. These signals remain as two broad
singlets shifted upfield to 16.01 and 14.89 ppm in the (Py2C70)-
CoDTBCP spectrum (Fig. 7c). The signals of the phenyl ring
ortho-protons in the 3,5-di-tert-butylphenyl substituents are
also shifted upfield when the donor–acceptor complexes are
formed. Their most noticeable shift occurs in the case of
(PyC60)2CoDTBCP (Table S2, ESI†). The upfield shift of the
PyC60/Py2C70 protons in the spectra of the coordination com-
plexes (Fig. S9, ESI†) indicates the reduced de-shielding by the
macrocycle ring current arising in the macroring in a magnetic
field, which clearly points to axial ligation of the substituted
fullerenes to the central atom. The magnitude of the shift
depends on the distance of the protons from the porphyrin
ring, therefore the pyridyl protons in (PyC60)2CoDTBCP and the
pyrrolidinyl protons in (Py2C70)CoDTBCP display a shift indi-
cating that coordination occurs via these groups. These con-
clusions agree well with the IR spectroscopy data above
concerning the deformation of the coordination centers in
(PyC60)2CoDTBCP and (Py2C70)CoDTBCP leading to a decrease
in the macrocycle aromaticity. The observed p-stacking between
the carbazole fragments and the fullerene moieties (see below)
also supports this idea.
CoDTBCP, the strong electronic interaction of the PyC60
/
Py2C70 moiety with CoDTBCP (Fig. 8) is revealed. Besides, the
electronic interaction due to PET between CoDTBCP as the
electron donor and PyC60/Py2C70 as the acceptor (Fig. 9) is
established. Similar behavior was observed by us for the other
coordination dyads/triads.24,25,27–29 The high values both stabi-
lity constant and HOMO–LUMO gap of (PyC60)2CoDTBCP com-
pared with (Py2C70)CoDTBCP (Fig. 9) may indicate a greater
efficiency of PET in the triad (see section ‘‘Transient absorption
spectroscopy’’).
Transient absorption spectroscopy
Femtosecond transient absorption measurements were per-
formed at the excitation wavelength of 400 nm corresponding
to CoDTBCP excitation. De-aerated toluene was used as a
medium because it is stable under strong laser irradiation
and demonstrates good solubility of the compound being
studied. The transient absorption spectrum of CoDTBCP con-
tains the negative peak at 521 nm, corresponding to the ground
DFT calculations
To examine the geometric and electronic structures of (PyC60)2- state bleaching, and the positive peaks at 430, 552 and 578 nm,
CoDTBCP and (Py2C70)CoDTBCP (Fig. S10, ESI†), theoretical corresponding to the excited state (Fig. S11, ESI†). The time
calculations were carried out. The CoDTBCP is energetically profile of CoDTBCP absorbance at 430 nm can be well fit using
favorable for the axial bonding of two substituted C60 molecules three exponential decay components with different lifetimes.
but only one Py2C70 molecule. This stoichiometric difference Two short lifetimes distinguishable in Fig. S11 (ESI†), at 0.99
may be because one of the CoDTBCP carbazole moieties and 3.18 ps, are the main contributors, while a small but
obstructs the coordination center, which hinders coordination discernible long lifetime component 16.76 ps is in the tail of
of a second Py2C70. The cobalt(II) ion has an octahedral and the whole decay profile.
pyramidal environment in (PyC60)2CoDTBCP and (Py2C70)-
The femtosecond transient absorption spectra of (PyC60)2-
CoDTBCP, respectively. The average value of the Co–NPyC60 CoDTBCP and (Py2C70)CoDTBCP at different delay times in
and Co–NPy2C70 bond length is 2.283 Å and 2.315 Å, respectively, toluene are shown in Fig. 10 and 11, respectively. These were
which is in agreement with the bonding energy (Table S3, ESI†). using to determine the charge separation/charge recombina-
The formation of (PyC60)2CoDTBCP and (Py2C70)CoDTBCP tion constants. The femtosecond transient spectrum of triad/
is accompanied by the macrocycle deviation from planarity dyad largely resembles that of CoDTBCP, where only small
by 2.861 and 2.771, respectively. An interesting feature is that shifts of the bands are observed. The negative peaks at 407, and
the carbazole fragments in the dyad and triad take part in 522 nm and the positive peaks at 432, and 572 nm are revealed
p-stacking with the fullerene moieties. The fullerene residue in upon excitation of (PyC60)2CoDTBCP. The negative peak at
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Fig. 8 Frontier molecular orbitals of (PyC60)2CoDTBCP (a) and (Py2C70)CoDTBCP (b).
521 nm and the positive peaks at 426, 550, and 575 nm are
The time constants for charge separation and charge recom-
observed for (Py2C70)CoDTBCP. Unfortunately, the conditions bination were obtained by fitting of the time profile of the
of the experiment (the spectral range of our instrument setup 432 nm and 426 nm peaks for (PyC60)2CoDTBCP and (Py2C70)-
from 400 to 900 nm) do not allow detection of the transient CoDTBCP, respectively. The rise time of 0.82 ps for (PyC60 2-
)
ꢁ
ꢄ
band of PyC60 in the triad/dyad, which is apparent in the CoDTBCP results in the rate of charge separation kCS = 1.29 ꢃ
range from 950 to 1020 nm.37
1012 sꢁ1 suggesting the occurrence of ultrafast charge
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1.29 ps for (Py2C70)CoDTBCP results in kCS = 7.75 ꢃ 1011 sꢁ1
while the biexponential decay with the time constants of
4.49 and 20.65 ps results in kCR values of 2.2 ꢃ 1011 sꢁ1 and
4.84 ꢃ 1010
s
ꢁ1, respectively. These results indicate the exis-
tence of electron transfer from CoDTBCP to coordinated PyC60
/
Py2C70 in the triad/dyad. The analysis of the kCR values shows
not too large a lifetime for the radical ion-pairs of the triad/
dyad in toluene. The lifetime for excited states of cobalt(II)
porphyrins can be changed by variation of the solvent
properties.32
4. Conclusions
Fig. 9 Mechanism of PET in (PyC60)2CoDTBCP and (Py2C70)CoDTBCP
(the HOMO–LUMO gap for (PyC60)2CoDTBCP and (Py2C70)CoDTBCP is
5.63, and 5.48 eV, respectively).
Carbazole-functionalized cobalt(II) porphyrin was synthesized
for the first time to obtain its architectures with substituted
fullerenes. Self-assembly in the mixtures of (5,15-bis[3,5-bis(tert-
butyl)phenyl]-10,20-bis[4,6-(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)
separation in the triad. However, the decay was found to be pyrimidin-5-yl]porphinato)cobalt(II) and 1-N-methyl-2-(pyridin-4-
biexponential (Fig. 10b) with the time constants of 2.13 and yl)-3,4-fullero[60]pyrrolidine or 2,5-di-(pyridin-2-yl)-3,4-fullero[70]
19.43 ps resulting in the rate of charge recombination kCR
=
pyrrolidine in toluene results in the porphyrin–fullerene coordi-
4.7 ꢃ 1011
s
ꢁ1 and 5.15 ꢃ 1010
s
ꢁ1, respectively. The rise time of nation system of moderately high stability. The formation of the
Fig. 10 Femtosecond transient absorption spectrum of (PyC60)2CoDTBCP in toluene at the excitation wavelength of 400 nm (a) and the time profile of
the transient peaks of (PyC60)2CoDTBCP (b).
Fig. 11 Femtosecond transient absorption spectrum of (Py2C70)CoDTBCP in toluene at the excitation wavelength of 400 nm (a) and the time profile of
the transient peaks of (Py2C70)CoDTBCP (b).
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triad, (PyC60)2CoDTBCP, and the dyad, (Py2C70)CoDTBCP,
respectively, in the case of CoDTBCP–PyC60 and CoDTBCP–
Py2C70 were established by thermodynamic/kinetic description
of the self-assembly. This result was confirmed by IR and
1H NMR spectroscopy methods and DFT calculation. The pecu-
liarity of the chemical structure of the coordination complexes
studied is the displacement of Co from the macrocycle plane not
only in the dyad (0.55 Å) but also in the triad (0.20 Å), which is
reflected in the corresponding IR and 1H NMR spectra. DFT
calculations and femtosecond investigations have confirmed the
existence of photoinduced electron transfer in the triad and
dyad. The data obtained are required for further study of both
the (PyC60)2CoDTBCP/(Py2C70)CoDTBCP photoelectrochemical
properties and their potential in the building of photovoltaic
devices.
Author contributions
E. N. Ovchenkova: conceptualization, formal analysis, writing –
original draft, writing – review and editing; N. G. Bichan:
methodology, investigation, writing – original draft, funding
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A. Ksenofontov: formal analysis, writing – original draft, visua-
lization; F. E. Gostev: methodology, investigation, writing –
original draft; I. V. Shelaev: methodology, investigation, visua-
lization; V. A. Nadtochenko: writing – review and editing,
resources; T. N. Lomova: writing – review and editing, project
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Acknowledgements
We are grateful to the center of the scientific equipment
collective use ‘‘The upper Volga region center of physic-
chemical research’’, N. N. Semenov federal research center for
chemical physics Russian academy of sciences and the Inter-
disciplinary Supercomputer Center of the Russian Academy of
Sciences (Moscow) for providing MVS-100K cluster resources.
This work was supported by the Russian Foundation for Basic
Research and the government of the region of the Russian
Federation, Grant No. 18-43-370023 (self-assembly of the por-
phyrin–fullerene systems), grant of Council on grants of the
President of the Russian Federation: MK-1741.2020.3 (the synth-
esis of carbazole-functionalized porphyrin and its complex with
cobalt(II)) and MK-197.2021.1.3 (DFT calculations).
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