New Quinoxaline-Containing Monomers for Narrow-Bandgap Polymers

Article abstract of DOI:10.1134/S001250081809001X

Two new fused quinoxaline-containing monomers—2,3-bis(9-(2-decyltetradecyl)-9H-carbazol-3-yl)dithieno[3,2-f:2'3'-h]quinoxaline (М1) and 2,5-di(nonadecan-3-yl)bis[1,3]thiazolo[4,5-a:5',4'-c]bisthieno[3,2-h:2',3'-j]phenazine (М2)—have been synthesized in high yields of 88 and 83% as promising building blocks of D-A polymers for photovoltaic applications. The optical bandgaps, found from the absorption edge, are 2.79 and 2.88 eV, respectively. The HOMO/LUMO energies of М1 and М2 are–5.83/–2.96 and–5.83/–2.98 eV, respectively. Both monomers have low-lying HOMO levels, which is favorable for a high open-circuit voltage and a high stability in air in the development of PSCs. The E_g^ec values of monomers М1 and М2 are 2.87 and 2.85 eV and are consistent well with the optical bandgap (2.79 and 2.88 eV, respectively).

Full text of DOI:10.1134/S001250081809001X

ISSN 0012-5008, Doklady Chemistry, 2018, Vol. 482, Part 1, pp. 195–200. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © M.L. Keshtov, S.A. Kuklin, I.O. Konstantinov, D.Yu. Godovskii, Y. Zou, I.E. Ostapov, E.E. Makhaeva, A.R. Khokhlov, 2018, published in Doklady Akademii
Nauk, 2018, Vol. 482, No. 1.
CHEMICAL TECHNOLOGY
New Quinoxaline-Containing Monomers
for Narrow-Bandgap Polymers
a
a,
a
a
c
b
M. L. Keshtov , S. A. Kuklin *, I. O. Konstantinov , D. Yu. Godovskii , Y. Zou , I. E. Ostapov ,
b
a
E. E. Makhaeva , and Academician A. R. Khokhlov
Received May 21, 2018
Abstract—Two new fused quinoxaline-containing monomers—2,3-bis(9-(2-decyltetradecyl)-9H-carbazol-
3
-yl)dithieno[3,2-f:2'3'-h]quinoxaline (М1) and 2,5-di(nonadecan-3-yl)bis[1,3]thiazolo[4,5-a:5',4'-c]bis-
thieno[3,2-h:2',3'-j]phenazine (М2)—have been synthesized in high yields of 88 and 83% as promising build-
ing blocks of D-A polymers for photovoltaic applications. The optical bandgaps, found from the absorption
edge, are 2.79 and 2.88 eV, respectively. The HOMO/LUMO energies of М1 and М2 are –5.83/–2.96 and
–
5.83/–2.98 eV, respectively. Both monomers have low-lying HOMO levels, which is favorable for a high
ec
open-circuit voltage and a high stability in air in the development of PSCs. The Eg values of monomers M1
and M2 are 2.87 and 2.85 eV and are consistent well with the optical bandgap (2.79 and 2.88 eV, respectively).
DOI: 10.1134/S001250081809001X
In the last decade, bulk heterojunction polymer
(d) a high molecular weight and good solubility in
solar cells (PSCs) have attracted considerable atten- common organic solvents.
tion of researchers owing to their advantages (over
inorganic photovoltaics), such as low cost, small mass,
processability, good mechanical flexibility, and the
possibility of fabricating large-area devices [1].In
recent few years, PSCs have significantly advanced in
efficiency, overcoming 13% [2, 3]. This success has
been mainly achieved through the synthesis of new
conjugated polymers. However, it is believed that the
efficiency exceeding 15% is necessary for commercial-
ization. To further enhance the efficiency, new
approaches and new ideal high-performance conju-
gated polymers are required.
With taking into account these requirements, it has
been demonstrated that an efficient way for creating
ideal high-performance copolymers is to use the
donor–acceptor (D–A) approach. Various classes of
conjugated polymers have been suggested for PSCs.
Narrow-bandgap conjugated D–A polymers based on
benzodithiophene and/or thieno[3,4-b]thiophene
and 5,6-difluoro-2,1,3-benzothiadiazole structures
are frequently used and recommend themselves as
high-performance semiconductor materials for PSCs
[
4, 5]. To further improve the characteristics of
devices, some efficient approaches have been used,
such as introducing fused heterocycles and conjugated
side chains into the polymer chain and addition of
functional groups. However, most of the highly effi-
cient donor polymers are synthesized through compli-
cated multistep routes, which increases the production
To design an ideal conjugated polymeric donor
material, the following conditions should be met:
(
a) broad and strong absorption in the visible and
near-IR ranges;
(
b) the HOMO and LUMO energies appropriate cost [6]. In this respect, quinoxaline (Qx) derivatives
for providing the highest open-circuit voltages and the are unique building blocks for the development of var-
difference between the LUMO energies of the donor ious optoelectronic polymers because of their straight-
and acceptor sufficient for exciton dissociation;
forward synthesis, planar and rigid conjugated struc-
ture, and the ease of modification by introducing flex-
ible alkyl chains (to improve solubility and
crystallinity) and conjugated side groups (to addition-
ally affect the energy levels, absorption, charge mobil-
ity, morphology, and microstructure of active layers)
and by creating multi-fused structures (to reduce the
bandgap by increasing the effective conjugation
length), which results in a considerable increase in the
short-circuit current density and fill factor in PSCs.
Qx derivatives are also of significant interest and are
(
c) high and balanced charge mobility for increas-
ing the fill factor (FF) and short-circuit current (J );
sc
a
Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, Moscow, 119991 Russia
b
Moscow State University, Moscow, 119991 Russia
c
Central South University, Changsha, China
*
e-mail: ineos-50@mail.ru
195

1
96
KESHTOV et al.
O
S
O
S
O
S
O
S
O N N O
H N NH2
2
TBAF
NH2OH · HCl
SnCl 2
C H
C12H25
1
2
25
Py/EtOH
Si
Si
S
S
S
S
C H
C H
10 21
1
0
21
1
2
3
4
N
N
N
N
S
Br
S
C12H25
C10H21
C H
10 21
O
5
N
ClOCCOCl
Py
C H
N
M1
12
25
NaH
O
N
N
C H
H
6
8
12 25 C H
C H
1 25
7
10 21
2
C H
21
1
0
OH
O
NH2
O
OH
1. CDI
2. NH3 · aq
C H
C H
2 5
2
5
LDA, TMEDA, EtI
THF
C H
33
1
6
O
THF
C H
C H
16 33
1
6
33
9
11
10
Br
S
C2H5
NH2
S
S
1. t-BuLi
N
C H
O
C H
2 5
N
2
5
Br
2. CBr4
LR
THF
O
cat. HCl
THF
C H
1
6
33
C H
C2H5
C H
16 33
C2H5
1
6
33
12
14
13
Br Br
C H
C H
16 33
1
6
33
C H
C H
16 33
N
N
S
S
16 33
1
. t-BuLi
1
. LDA
C H
C H
2 5
2
5
2. (CO2Et)2
S
N
S
S
N
S
2. CuCl2 C H5
C H
N
N
C H
2 5
2
2
5
C2H5
S
S
N
N
THF
THF
1
6
C H
6
C H
16 33
1
33
O
O
15
AcOH
THF
+
H N NH2
2
S
S
4
M2
Scheme 1.
widely used in many fields, such as light-emitting PSCs. Thus, it can be stated that Qx-based polymers
diodes [7], nonlinear optical devices [8], electrolumi- have a large potential for high-performance PSCs [11].
nescent materials [9], and pharmacology [10]. Although the efficiency of Qx-based PSCs has
Recently, the efficiency of PSCs based on Qx poly- achieved high values in a last few years, they are still
mers exceeded 11%, which is one of the best among below the desired level [12]. It is believed that further
Table 1. Optical and electrochemical properties of monomers M1 and M2
λmax, nm
ox
red
EHOMO(eV) ELUMO(eV)
ec
E go pt (eV)
Monomer
E
(V)
E
(V)
Eg (eV)
onset
onset
solution
294; 408
263; 305; 405 264; 305; 405
film
М1
М2
294; 412
1.44
1.42
–1.43
–1.43
–5.83
–5.83
–2.96
–2.98
2.87
–2.85
2.79
2.88
DOKLADY CHEMISTRY
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NEW QUINOXALINE-CONTAINING MONOMERS
197
C12H25
C10H21
N
N
C12H25
C10H21
N
S
N
S
8.8
8.6
8.4
8.2
8.0
7.8
7.6
7.4
7.2
8
7
6
5
4
3
2
1
1
Fig. 1. H NMR spectrum of monomer М1 in CDCl .
3
development of Qx-based monomers will lead soon to chloride in the presence of pyridine to give an α-dike-
PSC efficiencies not inferior to the world standards. In tone,
1,2-bis(9'-(2''-decyltetradecyl)carbazol-3'-
this paper we report new fused quinoxaline-contain- yl)ethan-1,2-dione (8). The condensation of diamine
ing monomers—2,3-bis(9-(2-decyltetradecyl)-9H- 4 [13] with α-diketone 8 led to the target monomer
carbazol-3-yl)dithieno[3,2-f:2'3'-h]quinoxaline (М1) (М1) in a high yield of 88%. Monomer М2 was syn-
and
2,5-di(nonadecan-3-yl)bis[1,3]thiazolo[4,5- thesized according to Scheme 1: in this case, α-dike-
a:5',4'-c]bisthieno[3,2-h:2',3'-j]phenazine (М2)—as tone 16 was synthesized in seven stages through suc-
promising building blocks of D–A polymers for appli- cessive transformations involving (i) the synthesis of
cations and consider the effect of the molecular struc- α-ethylstearic acid 10 by treating compound 9 with
ture on optoelectronic and electrochemical properties. LDA in the presence of tetramethylethylenediamine
Compound М1 was synthesized in seven stages and, then, with ethyl iodide; (ii) the reaction of α-eth-
according to Scheme 1 through successive transforma- ylstearic acid with carbonyldiimidazole (CDI) and
tions beginning from 2,7-ditrimethylsilylthieno[3,2-g] aqueous ammonia to give α-ethylstearamide 11;
[
1]benzothiophene-4,5-dione (1) introduced into the (iii) the treatment of 11 with Lawesson’s reagent (LR)
reaction with tetrabutylammonium fluoride to give to produce ethylstearic acid thioamide 12. 2-(1-Ethyl-
thieno[3,2-g][1]benzothiophene-4,5-dione
(2), heptadecyl)-1,3-thiazole 13 was synthesized by
which was treated with hydroxylamine hydrochloride cyclization of compound 12 in the presence of bromo-
in the presence of pyridine to give N,N'-dihydroxy- acetaldehyde diethylacetal and a catalytic amount of
thieno[3,2-g] [1]benzothiophene-4,5-diimine (3) in hydrochloric acid. The lithiation of compound 13 with
8
5% yield. The latter was reduced with anhydrous the subsequent treatment with CBr gave bromide 14.
4
SnCl
to
thieno[3,2-g][1]benzothiophene-4,5- The latter was treated with LDA and СuCl to give aro-
2
2
diamine (4) in 59% yield. Then, carbazole was reacted matic dibromide 15 in 91% yield. The lithiation of
with 1-bromo-2-octyldodecane in the presence of 4,4'-dibromo-2,2'-bis(1-ethylheptadecyl)-5,5'-bi-
sodium hydride to yield 9-(2-decyltetradecyl)-9H- 1,3-thiazole (15) followed by the treatment with
carbazole (7), which was then acylated with oxalyl diethyl oxalate gave α-diketone 16 in 37% yield. The
DOKLADY CHEMISTRY Vol. 482 Part 1 2018

1
98
KESHTOV et al.
C16H33
N
C16H33
C2H5
S
N
S
S
C2H5
N
N
S
9
8
7
6
5
4
3
2
1
1
Fig. 2. H NMR spectrum of monomer М2 in CDCl .
3
condensation of diamine 4 [13] with α-diketone 16 (Fig. 2) shows two signals at δ 8.86 and 7.66 ppm from
resulted in the target monomer, 2,5-di(nonadecan-3- two aromatic protons of the thiophene moiety. The
yl)bis[1,3]thiazolo[4,5-a:5',4'-c]bisthieno[3,2-h:2',3'- high-field range at δ 3.60, 2.15–1.75, 1.10, and
j]phenazine (М2) in 83% yield.
0.89 ppm shows the signals characteristic of the pro-
tons of the СН groups adjacent to the thiazole rings
2
The composition and structure of intermediate
compounds 2–16 as well as of the target products—
and terminal СН groups. The signals of the other
3
2
,3-bis(9-(2-decyltetradecyl)-9H-carbazol-3-
30 aliphatic protons of the alkyl chain are observed in
yl)dithieno[3,2-f:2'3'-h]quinoxaline (М1) and 2,5- the range of δ 1.20–1.50 ppm. In the spectrum of М2,
di(nonadecan-3-yl)bis [1, 3]thiazolo[4,5-a:5',4'- the integrated intensity ratio of all the signals corre-
c]bisthieno[3,2-h:2',3'-j]phenazine (М2)—were con- sponds to the suggested structure.
1
13
firmed by elemental analysis data and Н and
NMR. The Н NMR spectrum of М1 (Fig. 1) shows
multiplets at δ (ppm) 8.73–8.68 (m, 2H), 8.52–8.42
С
The optical properties of М1 and М2 were studied
by UV spectroscopy: the results are summarized in
Table 1, and the absorption spectra of М1 and М2
films are shown in Fig. 3. The absorption maxima for
М1 and М2 in solution and films are observed at 233,
1
(
m, 2H), 8.10 (d, J = 7.6 Hz, 2H), 7.74–7.56 (m, 4H),
7
.52–7.40 (m, 4H), and 7.32–7.13 (m, 4H) from 18
aromatic protons; the signal at δ 4.15 (d, J = 7.3 Hz,
2
93, and 407 and 264, 305, and 407; 233, 294, and 412;
4
H) corresponds to the four protons of the methylene
and 266, 311, and 413 nm, respectively. The absorption
spectra of the monomers in films are slightly red-
shifted as compared to the spectrum of solutions; most
groups adjacent to the nitrogen atom of the carbazole
groups. The singlet at 2.12 ppm (br s, 2H) is assigned
to two ternary aliphatic protons of alkyl groups. The
multiplets in the range of δ 1.31–0.85 ppm (80H) arise likely, this is related to a more ordered structure in the
1
opt
from the other alkyl protons. Although the H NMR
solid state (Table 1). The optical bandgaps (Eg ) of
spectrum of М1 is complicated, the aromatic-to-ali-
М1 and М2, found from the absorption edges (λedge)
phatic integrated intensity ratio corresponds to the
opt
g
1
suggested structure. The Н NMR spectrum of М2 by the equation E
= 1240/λedge, are 2.79 and 2.88 eV.
DOKLADY CHEMISTRY
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NEW QUINOXALINE-CONTAINING MONOMERS
199
Normalized absorption
.0
1
0.8
0.6
0.4
0.2
0
М2
М1
300
400
500
600
700
Wavelength, nm
Fig. 3. Normalized absorption spectra of monomers М1 and М2 in films.
М1
M2
ꢀ
2.0 ꢀ1.5 ꢀ1.0 ꢀ0.5 0 0.5 1.0 1.5 2.0 ꢀ2.0 ꢀ1.5 ꢀ1.0 ꢀ0.5
0
0.5 1.0 1.5 2.0
+
+
Potential, V (vs. Ag/Ag )
Potential, V (vs. Ag/Ag )
Fig. 4. CVA curves of monomers М1 and М2 in thin films at a sweep rate of 50 mV/s.
The electrochemical properties of М1 and М2
were studied by cyclic voltammetry (CVA); the results
are presented in Table 1, and the corresponding CVA
curves are shown in Fig. 4. CVA of the films was car-
ried out in a 0.1 M Bu NPF solution in acetonitrile at
ec
the bandgap width (E ) of the monomers were calcu-
g
lated by the following equations:
ox
onset
HOMO = –(E
+ 4.4) (eV),
4
6
a sweep rate of 50 mV/s. A platinum electrode was used
as a counter electrode, and the external reference was
red
onset
LUMO = –(E
+ 4.4) (eV),
+
ec
ox
onset
red
onset
Fс/Fс . The CVA curve (Fig. 4) shows one reduction
Еg = (E
– E
) (eV).
peak at negative voltages and one oxidation peak at
positive voltages. The cathodic peak of reduction is
presumably related to the formation of radical anions
of the thiophene derivative and the anodic peak of oxi-
dation, to the radical cations of the thiophene moiety.
The HOMO/LUMO energies of monomers М1
and М2 are –5.83/–2.96 and –5.83/–2.98 eV, respec-
tively. Both monomers have low HOMO energies,
which is favorable for a high open-circuit voltage (V )
oc
From the oxidation and reduction onset potentials and a high stability in air of polymers based on them
ox
onset
red
onset
ec
(
E
and E
, respectively) of the CVA curves of and PSCs. The electrochemical band gaps (E ) of
g
the monomers, the HOMO and LUMO energies and monomers M1 and M2, found from the CVA curves,
DOKLADY CHEMISTRY Vol. 482 Part 1 2018

2
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KESHTOV et al.
5. Zhang, S., Ye, L., and Hou, J., Adv. Energy Mater.,
are 2.87 and 2.85 eV and are consistent well with the
optical band gap (2.79 and 2.88 eV, respectively)
within the experimental error.
2016, vol. 6, p. 1502529.
6. Powell, D.M., Fu, R., Horowitz, K., Basore, P.A.,
Woodhouse, M., and Buonassisi, Energy Environ. Sci.,
2015, vl.. 8, pp. 3395–3408.
ACKNOWLEDGMENTS
7. Cui, Y., Zhang, X., and Jenekhe, S.A., Macromolecules,
1
999, vol. 32, pp. 3824–3826.
This work was supported by the Russian Founda-
tion for Basic Research (project no. 18–53—
8
. Gubbelmans, E., Van den Broeck, K., Verbiest, T., Van
Beylen, M., Persoons, A., and Samyn, C., Eur. Polym.
J., 2003, vol. 39, pp. 969–976.
5
3031NNS_a) and the Division of chemistry and
materials science of the Presidium of the RAS (pro-
gram no. 0085–2018–0009).
9
. JungS.H., Suh, D.H., and Cho, H.N., Polym. Bull.,
2
003, vol. 50, pp. 251–258.
1
0. Lainne, E.S., William, J.S., and, Robert, C.R., J. Med.
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DOKLADY CHEMISTRY
Vol. 482
Part 1
2018