New push-pull systems based on indolo[3,2-b]carbazole and 1,2,4,5-tetrazine: synthesis, photophysical, and charge transport properties

Article abstract of DOI:10.1007/s11172-021-3191-6

5,11-Dihydroindolo[3,2-b]carbazoles were for the first time modified with acceptor 1,2,4,5-tetrazine fragments. The photophysical and charge-transport properties of the synthesized donor-acceptor heterocyclic systems were studied. It was shown that the in

Full text of DOI:10.1007/s11172-021-3191-6

Russian Chemical Bulletin, International Edition, Vol. 70, No. 6, pp. 1109—1117, June, 2021
110 9
New push-pull systems based on indolo[3,2-b]carbazole
and 1,2,4,5-tetrazine: synthesis, photophysical, and charge transport properties
A. S. Steparuk,а S. G. Tolshchina,а N. A. Kazin,а R. A. Irgashev,a,b E. F. Zhilina,а
A. E. Aleksandrov,c A. R. Tameev,c and G. L. Rusinova,b
aI. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences,
22/20 ul. S. Kovalevskoy, 620108 Ekaterinburg, Russian Federation.
Fax: +7 (343) 369 3058. E-mail: tolschina@ios.uran.ru
bUral Federal University named after the first President of Russia B. N. Yeltsin,
19 ul. Mira, 620002 Ekaterinburg, Russian Federation.
Fax: +7 (343) 374 3905
cA. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
31 Bldg. 4 Leninsky prosp., 119071 Moscow, Russian Federation.
Fax: +7 (495) 955 5308. E-mail: tameev@elchem.ac.ru
5,11-Dihydroindolo[3,2-b]carbazoles were for the first time modified with acceptor
1,2,4,5-tetrazine fragments. The photophysical and charge-transport properties of the synthe-
sized donor-acceptor heterocyclic systems were studied. It was shown that the introduction of
the 1,2,4,5-tetrazine moieties makes it possible to increase the hole and electron mobility by
one and two orders of magnitude, respectively, as compared to analogous 5,11-dihydroindolo-
[3,2-b]carbazole derivatives studied previously.
Key words: 1,2,4,5-tetrazines, nucleophilic substitution, indolo[3,2-b]carbazole, push-pull
systems.
Recently, the 5,11-dihydroindolo[3,2-b]carbazole
(ICZ) scaffold has been widely used as a constituent of
novel organic compounds used in the design of functional
materials for molecular electronics. Various ICZ deriva-
tives are of interest as semiconductor materials with hole
conductivity for solar cells1 or field-effect transistors,2,3
dyes for sensitized solar cells (Grätzel cells),4 light-
emitting diodes,5 as well as electrochromic6,7 or fluores-
cent materials with sensor properties.8,9 Previous studies
of photophysical and charge transport properties of
5,11-dialkyl-6,12-diaryl(hetaryl)-5,11-dihydroindolo-
[3,2-b]carbazoles10,11 revealed a considerable promise of
search for novel functional materials based on this class
of compounds.
1,2,4,5-Tetrazines are conjugated electrochemically
active molecules that possess strong electron-withdrawing
properties. They are characterized by absorption in the
visible region resulting from n—π* electronic transitions
and can undergo reversible reduction to radical anions.12
These features offer prospects for the search for novel
conductive organic compounds and materials for elec-
tronic devices and sensors in this class of chemical sub-
stances.
Compounds containing the donor ICZ fragment con-
jugated with acceptor tetrazine rings are unavailable at the
moment. However, such hybrid molecules are of interest
as potential building blocks for materials with unique
photophysical and electronic properties. To design the
systems in question, in this work we propose to modify
1,2,4,5-tetrazine using typical reactions of this compound,
viz., nucleophilic substitution of leaving azolyl groups13
under the action of ICZ bearing nucleophilic substi-
tuents. Reduction of three nitro derivatives of ICZ,
namely, compounds 1 and 2a,b,14 afforded new amino
derivatives 3 and 4a,b, respectively, in high yields of
74—82% (Scheme 1).
Further reactions of amines 3 and 4a,b with 3,6-bis-
(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine (DPTz),
which was synthesized following a known procedure,15 in
toluene at 60 °С respectively gave compounds 5 and 6a,b
(Scheme 2) representing the substitution products of one
3,5-dimethylpyrazolyl group in the tetrazine ring of DPTz.
Compounds 5 and 6a,b bear a mobile NH proton
capable of undergoing tautomeric transitions. To study
the effect of this proton on the properties of compounds
5 and 6a,b, we attempted to synthesize an N-alkylated
analogue to compound 5 containing no mobile proton.
To this end, compound 3 was acylated and then the acetyl
group was reduced to ethyl one under the action of alu-
* Dedicated to Academician of the Russian Academy of Sciences
V. N. Charushin on the occasion of his 70th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1109—1117, June, 2021.
1066-5285/21/7006-1109 © 2021 Springer Science+Business Media LLC

Steparuk et al.
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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 6, June, 2021
Scheme 1
R = F (a), OC6H13 (b)
Reactants and conditions. i. Zn + HCl (aq.)/THF, reflux 1 h.
Scheme 2
DPTz =
; 4,6: R = F (a), OC6H13 (b)

New indolocarbazole and tetrazine derivatives
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 6, June, 2021
1111
Scheme 3
minum hydride to give the N-ethylated derivative 7
(Scheme 3).
data, in both cases the major product was compound 5
containing no ethyl substituent at the amine nitrogen.
Based on the LC-HRMS data, the reaction mixture also
contained a very small amount of the target product 8;
however, we failed to isolate it in pure form. The reaction
afforded not only compounds 5 and 8, but also a colorless
product identified by 1Н NMR and LC-HRMS as pyrid-
azine 9 (Scheme 4).
We assumed that the reaction of compound 7 with
DPTz in toluene under reflux will result in a substitution
product similar to compounds 5 and 6; however, our
attempt failed. According to TLC data, the reaction mix-
ture contained only the starting compounds and a small
amount of side products. However, the reaction of 7 with
DPTz did proceed in mesitylene under reflux for 10 h or
when the starting compounds were fused under solvent-
Probably, the ethyl fragment in compound 7 is trans-
formed to vinyl one under the action of the starting tetr-
azine. Subsequent interaction of the vinyl group with DPTz
1
free conditions. According to Н NMR and LC-HRMS
Scheme 4

Steparuk et al.
1112
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 6, June, 2021
ε•10–3/L mol–1 cm–1
A
a
100
80
0.6
0.5
0.4
0.3
0.2
0.1
1
2
2
3
60
1
40
20
325
350 375
400
425 450 λ/nm
300
350
400
450
λ/nm
Fig. 1. Absorption spectra of solutions of compounds 5 (1), 6a (2),
and 6b (3) in CHCl3.
A
b
results in the formation of dihydropyridazine and its aro-
matization upon elimination of aminoindolocarbazole 3.
Then, the de-ethylated amine 3 reacted with DPTz in the
reaction mixture to give compound 5.
0.14
0.12
0.10
0.08
0.06
1
2
We studied the photophysical and electronic properties
of products 5 and 6a,b. The electronic absorption spectra
of these compounds in CHCl3 solution recorded at room
temperature are shown in Fig. 1. Electronic absorption,
which mainly occurs in the range of 310—400 nm, origi-
nates from intramolecular π—π* charge transfer from the
donor indolo[3,2-b]carbazole to the acceptor fragment.
The molar extinction coefficients ε at the absorption
maxima calculated from these spectra are listed in Table 1.
Compounds 5, 6a can form nanometer-thin solid lay-
ers (films) by solution coating on horizontally arranged
substrates. To study the possibility to use them in the
design of organic electronic devices, we studied the opti-
cal, electronic, charge transport properties, and the surface
morphology of the films.
425
450
λ/nm
Fig. 2. Absorption spectra of thin films of compounds 5 (1) and
6a (2) prepared by spin coating from solutions of these compounds
(С = 10 mg L–1) in CHCl3 (a) and magnified fragments of these
spectra (b); film thickness is ~100 nm.
a bathochromic shift of the absorption maximum by 1 and
10 nm, respectively. The optical band gap Eg was evaluated
from the long-wavelength absorption edge (see Table 1).
The electronic absorption spectra of thin films of
compounds 5 and 6a in the visible region (see Fig. 2) exhibit
Table 1. Optical and electronic properties of compounds 5 and 6a,b
Compound
λ1/nm
ε•10–3
λ2
λ3
Eg
EHOMO ELUMO
eV
/L mol–1 cm–1
nm
5
6а
6b
345
349
348
67.2
91.3
74.2
346
359
—
449
494
—
2.76
2.51
—
–5.32
–5.26
—
–2.56
–2.75
—
λ1 is the absorption maximum and the extinction coefficient (ε) measured in CHCl3 solution; λ2 is
the absorption maximum for the thin film, λ3 is the long-wavelength absorption edge; Eg is the
optical band gap calculated from the absorption edge using the expression Eg = 1240/λ3 (nm);
EHOMO is the energy of the highest occupied molecular orbital (HOMO) determined from the
UV photoelectron spectra; ELUMO is the energy of the lowest unoccupied molecular orbital
(LUMO) calculated from the equation ELUMO = Eg + EHOMO
.

New indolocarbazole and tetrazine derivatives
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 6, June, 2021
1113
I•104 (rel. units)
I•103 (rel. units)
a
b
30
150
125
100
75
25
20
15
10
5
50
25
18 16 14 12 10
I (rel. units)
8
6
4
2 Eb/eV
18 16 14 12 10
I (rel. units)
8
6
4
2
Eb/eV
c
d
1500
1250
1000
750
700
600
500
400
300
200
100
500
250
1.0
0.9
0.8
0.7
0.6
0.5 Eb/eV
1.0
0.9
0.8
0.7
0.6
0.5 Eb/eV
Fig. 3. UV photoelectron spectra of thin films prepared by spin coating from solutions of compounds 5 (a) and 6a (b) in CHCl3 and
magnified fragments of the spectra of these compounds (c) and (d), respectively; Eb is the binding energy; UV means excitation by
photons with an energy of 21.21 eV (HeI).
The UV photoelectron spectra of thin films of com-
pounds 5 (a) and 6a (b) are shown in Fig. 3. They were
used to determine positions of the energy levels of the
highest occupied molecular orbitals (HOMOs) of these
compounds.
The X-ray diffraction patterns (see Fig. 4) of untreated
thin films of compounds 5 and 6a (curves 1) exhibit no
diffraction reflections and correspond to amorphous state
of the films. Heat treatment (curves 2) was followed by
the appearance of broadened peaks indicating an increase
in the degree of crystallinity in these films.
To assess the charge transport properties of the new
compounds, the charge carrier mobility in thin layers of
compound 5 was measured using the metal—insulator—
semiconductor charge extraction at linear increasing
voltage (MIS-CELIV) method. The results obtained are
presented in Table 2. The MIS-CELIV method involves
the measurement of a transient current signal at linearly
increasing voltage applied to the sample of a MIS structure.
The conditions of our experiments were documented
elsewhere.16—18 The electron and hole mobility in the layer
of compound 5 is rather high, viz., of the order of
10–4 cm2 V–1 s–1 (see Table 2), being one or two orders of
magnitude higher than the mobility in thieno[3,2-b]indole,16
indolo[3,2-b]carbazoles,11,19 and in new boron-containing
indolocarbazole complexes.2 The charge carrier mobility
in indolocarbazoles depends on the character of molecu-
lar packing in the layer,20 which is in turn determined by
the molecular structure and by the film fabrication method
and conditions. We believe that the chain length in the
alkyl substituent in molecule 5 specifies the average inter-
molecular distance and mutual arrangement of molecules
in the mainly amorphous layers. For instance, a study of
oligomeric molecules with the same core showed18 that
a relatively high charge carrier mobility is achieved at the
optimum chain length in the alkyl substituent.

Steparuk et al.
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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 6, June, 2021
I (rel. units)
7000
a
I (rel. units)
7000
b
6000
5000
4000
3000
2000
1000
6000
5000
4000
2
1
2
1
4
6
8
10
12
2θ/deg
4
6
8
10
12
2θ/deg
Fig. 4. X-ray diffracrion patterns of thin films of compounds 5 (a) and 6a (b) on glassy substrate before (1) and after (2) heat treatment
for 10 min at 90 °С.
From the data of Table 2 it follows that the charge
carrier mobility in the film is strongly influenced by the
nature of the solvent used to prepare the film. The more
volatile solvent (chloroform) evaporates so rapidly that
molecules of compound 5 have no time to reach a ther-
modynamic equilibrium, which leads to scatter in the
electronic energy distribution of the HOMO and LUMO
levels and, as a consequence, certain molecules act as deep
charge carrier traps. If the solvent evaporates relatively
slowly (dimethylsulfoxide), a larger number of molecules
of compound 5 go to the thermodynamically equilibrium
state and, as a consequence, the scatter of the MO levels
decreases, while the charge carrier mobility increases.
One more feature of charge transport in the films of
compound 5, which is of importance for the design of
electronic devices, consists in that the electron and hole
mobilities are comparable in magnitude (see Table 2). For
instance, balanced electron and hole mobilities are neces-
sary for operation of functional layers in light-emitting
diodes and solar cells.
ring under the action of amino derivatives of ICZ. We also
studied the optical, electronic, and charge-transport
properties of the new compounds. It was found that com-
pound 5 exhibits ambipolar conductivity owing to the
presence of both donor (indolocarbazole) and acceptor
(tetrazine) fragments that act as transport centers for holes
and electrons, respectively. It was established that the
introduction of the 1,2,4,5-tetrazine moieties allows the
hole and electron mobility to increase by one and two
orders of magnitude, respectively, compared to those in
the previously studied related derivatives of 5,11-dihydro-
indolo[3,2-b]carbazole.
Experimental
The 1H and 13С NMR spectra were recorded on a Bruker
Avance DRX-400 spectrometer operating at 400 and 100 MHz,
respectively, in CDCl3 or DMSO-d6 with tetramethylsilane as
an internal reference. High-resolution mass spectra of solutions
in CH3CN were recorded on a Bruker maXis impact HD quad-
rupole time-of-flight mass spectrometer (positive ion mode,
electrospray ionization). Elemental analysis was performed on
a 2400 Series II CHNS elemental analyzer (Perkin—Elmer, USA).
Melting points were determined on a Boetius apparatus. The
course of the reactions and the purity of the compounds synthe-
sized was monitored by TLC using Silufol plates with PhH—
MeCN (1 : 1) mixture as eluent. Electronic absorption spectra
of solutions were recorded on a Shimadzu UV-2600 (Japan)
double-beam spectrophotometer. Electronic absorption spectra
of thin layers in the visible region were recorded on a Shimadzu
UV-3101PC (Japan) double-beam spectrophotometer. The
layer thickness was measured using an Alpha-Step D-100 stylus
profiler (KLA tencor, USA). The energy of the HOMO level was
determined by UV photoelectron spectroscopy on an Axis Ultra
DLD spectrometer (Kratos Analytical, United Kingdom). The
X-ray diffraction patterns of thin films were collected on an
EMPYREAN X-ray diffractometer (PANalytical B.V., The
Netherlands) in air at room temperature (Cu-Kα radiation,
Summing up, we demonstrated the possibility of en-
gineering new push-pull heterocyclic molecules contain-
ing the 5,11-dihydroindolo[3,2-b]carbazole scaffold and
the 1,2,4,5-tetrazine moiety using nucleophilic substitu-
tion of heterocyclic leaving groups in the 1,2,4,5-tetrazine
Table 2. Charge carrier mobility in layers prepared from
different solutions of compound 5
Solvent
T/°С
μ•10–4/cm2 V–1 s–1
electrons
holes
Chloroform
DMSO
61.2
189
0.6
6.8
1.1
6.6
T is the boiling point and μ is the charge carrier mobility.

New indolocarbazole and tetrazine derivatives
Russ. Chem. Bull., Int. Ed., Vol. 70, No. 6, June, 2021
1115
2θ scan range of 3—15 deg). Thin layers of compounds 5 and 6a
were prepared by spin coating from solutions in chloroform
(С = 10 mg L–1; centrifugation at 1000 rev min–1 for 1 min).
The carrier mobility was determined by the MIS—CELIV
method using sandwich-type samples prepared as follows. A glassy
substrate was coated with an ITO (mixture of In2O3 and SnO2)
conductive layer and then with a 70-nm SiO2 layer. Then, it was
successively coated with a layer of the compound under study
(layer thickness d = 100 nm) and with an Al layer (d = 80 nm)
as a counterelectrode. The SiO2 insulating layer played the role
of the blocking layer for both types of charge carriers, i.e., it
precluded injection of the charge carriers from ITO. When mea-
suring the transient hole current, a positive potential linearly
increasing at a rate of А = 5•104 V s–1 was applied to ITO; this
was accompanied by the extraction of holes at the Al electrode.
To measure the electron mobility, the polarity of the potential
applied to the electrode was reversed. The characteristic time
(tmax) corresponding to the maximum transient conduction
current was determined using the current signal detected at the
load resistor of a DL-Analog Discovery (Digilent Co.) oscillo-
scope. The carrier mobility was calculated using the expression
μ = 2d2/(At2max).18
С, 78.63; H, 7.12; N, 8.63. C42H44F2N4. Calculated (%):
С, 78.47; H, 6.90; N, 8.72. 1H NMR (C6D6, δ): 0.78—0.85
(m, 10 Н, 2 CH2CH3); 0.94—1.00 (m, 4 Н, 2 CH2); 1.08—1.15
(m, 4 H, 2 CH2); 1.35—1.41 (m, 4 H, 2 CH2); 2.74 (br.s, 4 Н,
2 NH2); 3.61—3.64 (m, 4 H, 2 NCH2); 6.16 (d, 2 H, C(1)H,
C(7)H, J = 2.2 Hz); 6.65 (dd, 2 H, C(3)H, C(9)H, J1 = 8.5 Hz,
J2 = 2.2 Hz); 6.94—6.98, 7.38—7.41 (both m, 4 Н each, 8 CHAr);
7.06 (d, 2 H, C(4)H, C(10)H, J = 8.5 Hz). 13С NMR (C6D6, δ):
14.17, 22.86, 26.73, 28.86, 31.75, 44.83, 108.91 (d, J = 98.4 Hz);
115.68 (d, 2 С, J = 23.9 Hz); 115.94, 117.36, 123.14, 124.51,
132.78 (d, 2 С, J = 7.7 Hz); 133.76, 135.80, 137.79, 139.34,
162.07, 164.03.
5,11-Dihexyl-6,12-bis(4-hexyloxyphenyl)-5,11-dihydroind-
olo[3,2-b]carbazole-2,8-diamine (4b). The yield was 597 mg
(74%). M.p. 174—175 °С. Rf = 0.75 (with THF as eluent).
Found (%): С, 80.11; H, 8.92; N, 6.76. C54H70N4O2. Calculat-
ed (%): С, 80.35; H, 8.74; N, 6.94. 1H NMR (C6D6, δ): 0.84
(t, 6 Н, 2 CH3, J = 7.3 Hz); 0.88—0.93 (m, 10 Н, 2 CH2, 2 CH3);
0.99—1.05 (m, 4 Н, 2 CH2); 1.12—1.19 (m, 4 H, 2 CH2);
1.22—1.31 (m, 8 H, 4 CH2); 1.36—1.42 (m, 4 H, 2 CH2);
1.46—1.54 (m, 4 H, 2 CH2); 1.67—1.72 (m, 4 H, 2 CH2); 2.76
(br.s, 4 Н, 2 NH2); 3.78—3.81 (m, 8 H, 2 NCH2, 2 OCH2); 6.49
(d, 2 H, C(1)H, C(7)H, J = 2.2 Hz); 6.66 (dd, 2 H, C(3)H, C(9)H,
Compounds 1, 2a,b14 and 3,6-bis(3,5-dimethylpyrazol-1-
yl)-1,2,4,5-tetrazine (DPTz)15 were synthesized following known
procedures. Commercially available reactants and solvents were
used without additional purification.
J1 = 8.4 Hz, J2 = 2.2 Hz); 7.03, 7.58 (both d, 4 Н each, 8 CHAr
J = 8.6 Hz); 7.10 (d, 2 H, C(4)H, C(10)H, J = 8.4 Hz).
,
Substitution of 3,5-dimethylpyrazolyl group in DPTz under
the action of amines 3 and 4a,b (general procedure). To a solution
of amine (0.5 mmol) in toluene (20 mL), DPTz (135 mg,
0.5 mmol in the case of amine 3 or 270 mg, 1 mmol in the case
of diamines 4a,b) was added. The reaction mixture was kept at
60 °С under stirring for 5 h and an additional 24 h at room tem-
perature. The precipitate was filtered off. Product 5 was washed
with CH3CN. Compounds 6a,b were recrystallized from DMF,
washed with acetonitrile, and dried at a pressure of 15 mbar and
at a temperature of 110 °С for 5 h.
Reduction of nitro derivatives 1 and 2a,b to amino derivatives
3 and 4a,b, respectively (general procedure). To a vigorously
stirred mixture of 2,8-dinitro derivative 2 (1 mmol) and zinc
powder (1.3 g, 20 mmol) in THF (40 mL), 12 М HCl (5.2 mL,
62.4 mmol) was added dropwise. The reaction mixture was re-
fluxed with stirring until complete dissolution of zinc. Then, 5%
NaOH (100 mL) was added and the product was extracted with
CH2Cl2 (3×20 mL). The solvent was evaporated at a reduced
pressure and a solid residue thus obtained was dissolved in THF
(3 mL), and ethanol (10 mL) was added. The precipitate (amino
derivative) was filtered off, washed with ethanol (2×2 mL), and
dried at 110 °C. Reduction of the mononitro derivative using this
procedure involved treatment of compound 1 (310 mg, 0.5 mmol)
with Zn powder (330 mg, 5 mmol) and 12 М HCl (1.3 mL,
15.6 mmol) in THF (10 mL).
5,11-Dihexyl-6,12-diphenyl-5,11-dihydroindolo[3,2-b]carb-
azol-2-amine (3). The yield was 243 mg (82%). M.p. 193—195 °С.
Rf = 0.71 (with THF as eluent). Found (%): С, 85.32; H, 7.58;
N, 6.98. C42H45N3. Calculated (%): С, 85.24; H, 7.66; N, 7.10.
1H NMR (C6D6, δ): 0.76—0.84 (m, 10 Н, 2 CH2CH3); 0.95—1.01
(m, 4 Н, 2 CH2); 1.09—1.17 (m, 4 H, 2 CH2); 1.40—1.47 (m, 4 H,
2 CH2); 2.75 (br.s, 2 Н, NH2); 3.69—3.72 (m, 4 H, 2 NCH2);
6.19 (d, 1 H, C(1)H, J = 2.2 Hz); 6.65 (dd, 1 H, C(3)H,
J1 = 8.5 Hz, J2 = 2.2 Hz); 6.98—7.00, 7.03—7.04 (both m,
1 Н each, С(8)Н, С(9)Н); 7.07 (d, 1 H, C(4)H, J = 8.5 Hz);
N-[6-(3,5-Dimethylpyrazol-1-yl)-1,2,4,5-tetrazine-3-yl]-
5,11-dihexyl-6,12-diphenyl-5,11-dihydroindolo[3,2-b]carbazol-
2-amine (5). The yield was 326 mg (85%). M.p. 211—213 °С.
Rf = 0.44 (with CH2Cl2 as eluent). Found (%): С, 76.85; H, 6.89;
N, 16.32. C49H51N9. Calculated (%): С, 76.83; H, 6.71; N, 16.46.
1H (DMSO-d6, δ): 0.80—0.90 (m, 10 Н, 2 CH2CH3); 1.04—1.12
(m, 4 Н, 2 CH2); 1.15—1.23 (m, 4 H, 2 CH2); 1.35—1.48 (m, 4 H,
2 CH2); 2.26, 2.48 (both s, 3 Н each, 2 CH3 in pyrazolyl);
3.74—3.82 (m, 4 H, 2 NCH2); 6.24 (s, 1 Н, С(4)Н in pyrazolyl);
6.36 (d, 1 H, C(10)H, J = 7.7 Hz); 6.76 (dd, 1 H, C(8)H,
J1 = 8.2 Hz, J2 = 7.0 Hz); 6.92 (d, 1 Н, C(1)H, J = 1.9 Hz); 7.30
(dd, 1 H, C(9)H, J1 = 7.7 Hz, J2 = 7.0 Hz); 7.41 (d, 1 H, C(7)H,
J = 8.2 Hz); 7.47 (d, 1 H, C(4)H, J = 8.8 Hz); 7.53 (dd, 1 H,
C(3)H, J1 = 8.8 Hz, J2 = 1.9 Hz); 7.59—7.72 (m, 10 Н, 2 Ph);
10.68 (br.s, 1 Н, NH). 13С NMR (DMSO-d6, δ): 12.33, 13.28,
13.73, 13.75, 21.91, 21.93, 25.60, 25.63, 28.14, 28.26, 30.71,
30.72, 43.65, 43.78, 108.63, 108.67, 108.72, 115.11, 117.71,
117.73, 117.90, 120.57, 121.60 (2 C), 122.02 (2 C), 122.13,
125.46, 128.21, 128.29, 128.33, 128.99 (2 C), 129.05 (2 C), 129.81
(2 C), 130.11 (2 C), 131.68, 132.11, 137.37, 137.97, 139.30,
141.40, 142.11, 150.16, 156.94, 160.41.
7.20 (d, 1 H, СНICZ, J = 8.2 Hz); 7.28—7.36 (m, 7 Н, 6 СНPh
,
1 CHICZ); 7.60—7.64 (m, 4 Н, 4 СНPh). 13С NMR (C6D6, δ):
14.20 (2 C), 22.88 (2 C), 26.65, 26.68, 28.86, 28.94, 31.72, 31.76,
44.66, 44.78, 108.72, 108.85, 109.20, 115.53, 118.47, 118.52,
123.05, 123.11, 123.34, 124.05, 124.63, 125.69, 127.89, 128.06,
128.31, 128.93 (2 C), 129.10 (2 C), 131.04 (2 C), 131.14 (2 C),
132.82, 133.91, 137.80, 139.20, 139.95, 139.97, 143.34.
N2,N8-Bis[6-(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine-
3-yl]-6,12-bis(4-fluorophenyl)-5,11-dihexyl-5,11-dihydroindolo-
[3,2-b]carbazole-2,8-diamine (6a). The yield was 307 mg (62%).
M.p. 334—335 °С. Rf = 0.74 (with EtOAc—C6H14 (1 : 1) as
6,12-Bis(4-fluorophenyl)-5,11-dihexyl-5,11-dihydroindolo-
[3,2-b]carbazole-2,8-diamine (4a). The yield was 508 mg (79%).
M.p. 274—275 °С. Rf = 0.73 (with THF as eluent). Found (%):
eluent). Found (%): С, 67.78; H, 5.78; N, 22.61. C56H56F2N16
.

Steparuk et al.
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Russ. Chem. Bull., Int. Ed., Vol. 70, No. 6, June, 2021
Calculated (%): С, 67.86; H, 5.69; N, 22.61. 1H NMR (DMSO-d6,
δ): 0.84 (t, 6 Н, 2 CH3, J = 7.3 Hz); 0.88—0.94 (m, 4 Н, 2 CH2);
1.07—1.13 (m, 4 Н, 2 CH2); 1.17—1.23 (m, 4 H, 2 CH2);
1.39—1.49 (m, 4 H, 2 CH2); 2.26, 2.50 (both s, 6 Н each, 4 CH3
in two pyrazolyls); 3.76—3.80 (m, 4 H, 2 NCH2); 6.24 (s, 2 Н,
2 С(4)Н in two pyrazolyls); 7.05 (s, 2 H, C(1)H, C(7)H);
7.46—7.50 (m, 6 Н, 4 CHAr, C(4)H, C(10)H); 7.62 (dd, 2 H,
C(3)H, C(9)H, J1 = 8.8 Hz, J2 = 1.7 Hz); 7.71—7.74 (m, 4 H,
4 CHAr); 10.81 (br.s, 2 Н, 2 NH). 13С (DMSO-d6, δ): 12.24,
13.28, 13.71, 21.97, 25.75, 28.24, 30.72, 43.89, 108.60, 108.90,
114.31, 116.13 (d, J = 21.2 Hz); 117.07, 120.22, 121.93 (d, 2 С,
J = 14.8 Hz); 128.75, 131.93 (d, 2 С, J = 7.8 Hz); 132.42,
133.40 (d, J = 3.2 Hz); 139.25, 141.47, 150.15, 156.90, 160.25,
161.33, 163.29.
Reaction of compound 7 with DPTz. А. To DPTz (135 mg,
0.5 mmol) in mesitylene (5 mL), ICZ 7 (310 mg, 0.5 mmol) was
added. The reaction mass was refluxed for 13 h, cooled to room
temperature, and transferred to a column with silica gel. The
mixture was separated by column chromatography with CH2Cl2
as eluent.
В. To DPTz (14 mg, 0.05 mmol), compound 7 (31 mg,
0.05 mmol) was added and the reaction mass was ground to
a homogeneous mixture, heated until melting (140 °С), and kept
at this temperature for 20 min. The mixture of products was
analyzed by LC-HRMS.
N-[6-(3,5-Dimethylpyrazol-1-yl)-1,2,4,5-tetrazine-3-yl]-
N-ethyl-5,11-dihexyl-6,12-diphenyl-5,11-dihydroindolo[3,2-b]-
carbazol-2-amine (8). Found: m/z 794.4630 [M + H]+. C51H56N9
.
+
N2,N8-Bis[6-(3,5-dimethylpyrazol-1-yl)-1,2,4,5-tetrazine-
3-yl]-5,11-dihexyl-6,12-bis(4-hexyloxyphenyl)-5,11-dihydro-
indolo[3,2-b]carbazole-2,8-diamine (6b). The yield was 352 mg
(61%). M.p. 285—286 °С. Rf = 0.86 (with EtOAc—C6H14 (1 : 1)
as eluent). Found (%): С, 70.63; H, 7.08; N, 19.23. C68H82N16O2.
Calculated (%): С, 70.68; H, 7.15; N, 19.40. 1H NMR (DMSO-d6,
δ): 0.83 (t, 6 Н, 2 CH3, J = 7.2 Hz); 0.88—0.93 (m, 10 Н, 2 CH3,
2 CH2); 1.06—1.12 (m, 4 Н, 2 CH2); 1.15—1.21 (m, 4 H, 2 CH2);
1.26—1.36 (m, 12 H, 6 CH2); 1.38—1.45 (m, 4 H, 2 CH2);
1.60—1.66 (m, 4 H, 2 CH2); 2.26, 2.48 (both s, 6 Н each, 4 CH3
in two pyrazolyls); 3.79—3.82 (m, 4 H, 2 NCH2); 4.00 (t, 4 H,
2 OCH2, J = 6.5 Hz); 6.23 (s, 2 Н, 2 С(4)Н in two pyrazolyls);
7.13 (d, 2 H, C(1)H, C(7)H, J = 1.9 Hz); 7.17 (d, 4 Н, 4 СН in
2 Ar, J = 8.5 Hz); 7.45 (d, 2 Н, C(4)H, C(10)H, J = 8.8 Hz);
7.50 (dd, 2 H, C(3)H, C(9)H, J1 = 8.8 Hz, J2 = 1.9 Hz); 7.53
(d, 4 Н, 4 СНAr, J = 8.5 Hz); 10.72 (br.s, 2 Н, 2 NH). 13С NMR
(DMSO-d6, δ): 12.30, 13.29, 13.71, 13.83, 21.99, 22.05, 25.08,
25.85, 28.33, 28.53, 28.92, 30.76, 30.99, 67.43, 108.55, 108.66,
115.04 (2 С), 115.23, 117.72, 120.38, 122.17, 122.20, 128.26,
128.93, 130.87 (2 С), 132.68, 139.38, 141.39, 150.07, 157.02,
158.64, 160.35.
N-Ethyl-5,11-dihexyl-6,12-diphenyl-5,11-dihydroindolo-
[3,2-b]carbazol-2-amine (7). To amine 3 (592 mg, 1 mmol),
pyridine (4 mL) and acetyl chloride (235 mg, 3 mmol) was
added and the mixture was stirred for 15 min at room temperature.
Then, H2O (50 mL) was added and the mixture was extracted
with CH2Cl2 (3×15 mL). The extract was concentrated, the
solid residue was added to a suspension prepared by adding small
portions of AlCl3 (445 mg, 3.33 mmol) to LiAlH4 (380 mg, 10 mmol))
in THF (10 mL) under ice cooling. The orange solution thus
prepared was refluxed for 1 h. The unreacted aluminum hydride
was decomposed by successively adding methanol (2 mL) and
1 mL 50% aqueous NaOH (all inorganic compounds formed
compact granules). The organic phase was decanted and the
solvents were removed at a reduced pressure. The bright yellow
product was recrystallized from isopropyl alcohol (5 mL), washed
with methanol (2×2 mL), and dried at 110 °C. The yield was
440 mg (71%). M.p. 144—145 °C. Rf = 0.72 (with THF as eluent).
Found (%): С, 85.17; H, 7.85; N, 6.65. C44H49N3. Calculat-
ed (%): С, 85.25; H, 7.97; N, 6.78. 1H NMR (C6D6, δ): 0.77—0.86
(m, 10 Н, 2 CH2CH3); 0.94 (t, 3 H, NCH2CH3, J = 7.1 Hz);
0.96—1.03 (m, 4 Н, 2 CH2); 1.09—1.17 (m, 4 H, 2 CH2);
1.42—1.50 (m, 4 H, 2 CH2); 2.79 (q, 2 Н, NCH2CH3, J = 7.1 Hz);
3.72—3.77 (m, 4 H, 2 NCH2); 6.15 (d, 1 H, C(1)H, J = 2.2 Hz);
6.72 (dd, 1 H, C(3)H, J1 = 8.5 Hz, J2 = 2.2 Hz); 6.97—7.00
(m, 1 Н, СНICZ); 7.05 (d, 1 Н, СНICZ, J = 7.6 Hz); 7.14—7.16
(m, 1 Н, СНICZ); 7.21 (d, 1 Н, СНICZ, J = 8.1 Hz); 7.27—7.36
(m, 7 Н, 6 СНPh, 1 CHICZ); 7.63—7.66 (m, 4 Н, 4 СНPh).
Calculated: [M + H]+ = 794.4653.
3,6-Bis(3,5-dimethylpyrazol-1-yl)pyridazine (9). 1H NMR
(CDCl3, δ): 2.31, 2.75 (both s, 6 Н each, 4 СН3 in two pyrazol-
yls); 6.07 (s, 2 Н, 2 С(4)Н in two pyrazolyls); 8.22 (s, 2 Н, С(4)Н,
С(5)Н in pyridazine). Found: m/z 269.1513 [M + H]+. C14H17N6
.
+
Calculated: [M + H]+ = 269.1509.
The authors express their gratitude to Cand. Sci.
(Chem.) A. I. Zvyagina for carrying out X-ray diffraction
experiments on facilities at the Center for Collective Use
of Physical Methods of Investigation at the A. N. Frumkin
Institute of Physical Chemistry and Electrochemistry,
Russian Academy of Sciences.
This work was financially supported by the Ministry
of Science and Education of the Russian Federation
within the framework of the State Assignment themes
(Nos AAAA-A19-119012490006-1, АААА-А19-
119012290116-9, and АААА-А19-119012290117-6) using
facilities at the Center for Collective Use "Spectroscopy
and Analysis of Organic Compounds" at I. Ya. Postovsky
Institute of Organic Synthesis, Ural Branch of the Russian
Academy of Sciences. Charge carrier mobility studies were
financially supported by the Russian Foundation for Basic
Research (Project No. 18-29-23045 mk). Experimental
UV photoelectron spectroscopy studies were carried out
on facilities at the "Nanochemistry and Nanomaterials"
Center for Collective Use, Department of Chemistry,
M. V. Lomonosov Moscow State University.
This paper does not contain descriptions of studies on
animals or humans.
The authors declare no competing interests.
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Received March 2, 2021;
in revised form April 5, 2021;
accepted April 7, 2021.