Synthesis and optical and electrochemical properties of 5,6-bis[9-(2-decyltetradecyl)-9H-carbazol-3-yl]naphtho[2,1-b:3,4-b’]dithiophene as a promising building block for photovoltaic applications

Article abstract of DOI:10.1134/S0012500816030022

A new carbazole-containing naphthodithiophene heteroaromatic compound, 5,6-bis[9-(2-decyltetradecyl)-9H-carbazol-3-yl]naphtho[2,1-b:3,4-b’]dithiophene (M1), was synthesized to be subsequently used as the weak donor structure for the construction of narrow bandgap D–A conjugated polymers in terms of the “weak donor–strong acceptor” concept. The composition and structure of M1 were confirmed by the data of elemental analysis and IR and ¹H and ¹³C NMR spectroscopy. The optical and electrochemical characteristics of the product were measured. The compound M1 was shown to have low-lying HOMO (–5.57 eV), which is favorable for high open-circuit voltage and to be suitable as a promising weak donor moiety in the D–A conjugated polymer for photovoltaic applications.

Full text of DOI:10.1134/S0012500816030022

ISSN 0012ꢀ5008, Doklady Chemistry, 2016, Vol. 467, Part 1, pp. 94–99. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © M.L. Keshtov, S.A. Kuklin, D.Yu. Godovskii, I.O. Konstantinov, M.M. Krayushkin, A.S. Peregudov, A.R. Khokhlov, 2016, published in Doklady Akademii
Nauk, 2016, Vol. 467, No. 1, pp. 48–53.
CHEMICAL
TECHNOLOGY
Synthesis and Optical and Electrochemical Properties
of 5,6ꢀBis[9ꢀ(2ꢀdecyltetradecyl)ꢀ9Hꢀcarbazolꢀ3ꢀyl]naphtho[2,1ꢀ
b:3,4ꢀb']dithiophene as a Promising Building Block
for Photovoltaic Applications
M. L. Keshtova, S. A. Kuklina, D. Yu. Godovskiia, I. O. Konstantinova,
M. M. Krayushkinb, A. S. Peregudova, and Academician A. R. Khokhlova
Received November 6, 2015
Abstract—A new carbazoleꢀcontaining naphthodithiophene heteroaromatic compound, 5,6ꢀbis[9ꢀ(2ꢀ
decyltetradecyl)ꢀ9 ꢀcarbazolꢀ3ꢀyl]naphtho[2,1ꢀ :3,4ꢀ ']dithiophene (M1), was synthesized to be subseꢀ
H
b
b
quently used as the weak donor structure for the construction of narrow bandgap D–A conjugated polymers
in terms of the “weak donor–strong acceptor” concept. The composition and structure of M1 were conꢀ
firmed by the data of elemental analysis and IR and 1H and 13C NMR spectroscopy. The optical and electroꢀ
chemical characteristics of the product were measured. The compound M1 was shown to have lowꢀlying
HOMO (–5.57 eV), which is favorable for high openꢀcircuit voltage and to be suitable as a promising weak
donor moiety in the D–A conjugated polymer for photovoltaic applications.
DOI: 10.1134/S0012500816030022
In recent years, considerable attention has been naphthalene moiety and representing planar strucꢀ
devoted to organic semiconductors as promising
materials for optoelectronic applications. Most of the
studied organic semiconductors are based on the synꢀ
tures with a
intramolecular
π
ꢀconjugated system favorable for strong
π
ꢀconjugation and intermolecular
π
ꢀ
stacking [8]. Naphthodithiophene derivatives with
clearꢀcut weak donor properties incorporated in conꢀ
jugated D–Aꢀcopolymers lower the highest occupied
molecular orbital (HOMO) level, which increases the
openꢀcircuit voltage, and, as a consequence, they
increase the efficiency of polymeric solar cell [9].
Recently, Wong and coꢀworkers [10] synthesized the
D–A copolymer with a narrow bandgap (1.6 eV) and
lowꢀlying HOMO (–5.22 eV) based on 5,6ꢀdialkoxꢀ
ynaphthodithiophene derivatives and employed this
copolymer to design solar cells with a bulk heterojuncꢀ
tion of 5.3% efficiency not inferior to world analogs.
The low position of the HOMO led to high openꢀcirꢀ
cuit voltage (Vхх = 0.68 V) and, hence, to higher effiꢀ
ciency [10]. You and coꢀworkers [11] proposed one
more novel naphthodithiopheneꢀcontaining narrow
bandgap polymer, approaching the “ideal polymer,”
with a band gap of 1.59 eV and lowꢀlying HOMO
(–5.35 eV) [11].
thesis of
π
ꢀconjugated structures such as oligothꢀ
iophenes [1], oligofluorenes [2], polycyclic aromatic
compounds [3], and fused heterocyclic aromatic
structures [4]. A special place in the series of these
compounds is occupied by fused thiophene derivaꢀ
tives, which are of interest from both scientific and
practical standpoints. In view of the unusual elecꢀ
tronic and optical features and high chemical and
thermal stabilities, these compounds are tested as
active layers for field effect transistors [5], light emitꢀ
ting diodes [6], and organic solar cells [7]. In particuꢀ
lar, fused thiophene derivatives are studied owing to
their planar geometry providing good ꢀstacking and
π
highly ordered molecular structure promoting effiꢀ
cient charge transfer.
Among these promising classes of heteroaromatic
compounds are naphthodithiophene (NDT) derivaꢀ
tives containing two thiophene rings fused with a
Here we developed and synthesized a new monoꢀ
mer, 5,6ꢀbis[9ꢀ(2ꢀdecyltetradecyl)ꢀ9 ꢀcarbazolꢀ3ꢀ
H
a Nesmeyanov Institute of Organoelement Compounds,
Russian Academy of Sciences, ul. Vavilova 28, Moscow,
119991 Russia
b Zelinskii Institute of Organic Chemistry, Russian Academy
of Sciences, Leninskii pr. 47, Moscow, 119991 Russia
eꢀmail: keshtov@ineos.ac.ru; ineosꢀ50@mail.ru
yl]naphtho[2,1ꢀ :3,4ꢀ ']dithiophene (M1), based
b
b
on NDT containing carbazole moieties in the 5ꢀ and
6ꢀpositions (Scheme 1). As noted above, compounds
of this type form highly ordered
π
ꢀstacked structures,
which enhances the hole conductivity.
94

SYNTHESIS AND OPTICAL AND ELECTROCHEMICAL PROPERTIES
95
The naphthodithiophene monomer is a weak give 1,2ꢀdibromoꢀ4,5ꢀdimethoxybenzene (
7) as large
donor, which, being incorporated in D–A polymers,
would promote a decrease in the HOMO level and an
increase in the openꢀcircuit voltage, and, as a conseꢀ
quence, would enhance the efficiency of a solar cell. It
is noteworthy that in all known compounds, the 5ꢀ and
6ꢀpositions of NDT had alkyl or alkoxyl groups.
Meanwhile, the use of carbazole moieties was not
reported previously. Presumably, the introduction of
carbazole moieties would induce additional conjugaꢀ
tion with the NDT moiety, and this would reduce the
bandgap width and enhance the light absorption. The
presence of the N–Hꢀgroup in carbazole would allow
the introduction of alkyl substituents promoting good
solubility in organic solvents.
white crystals (92% yield), which then reacts with
thiopheneꢀ3ꢀboronic acid affording 1,2ꢀbis(thiophenꢀ
3ꢀyl)ꢀ4,5ꢀdimethoxybenzene (8) in 85% yield. Succesꢀ
sive treatment of compound
8
with anhydrous ferric
chloride and BBr3 induces oxidative cyclization giving
first 5,6ꢀdimethoxynaphtho[2,1ꢀ :3,4ꢀ ']dithiophene
) (49% yield) and then compound 10 in high yield
b
b
(
9
(99%). Then, 10 is converted into bis(triflate) interꢀ
mediate 11 in 72% yield. The last step is treatment of
11 with pinacolꢀboron carbazole derivative
in the formation of the target product M1 in a good
yield (60%). Compound , 3ꢀ(1,3,2ꢀdioxoborolanꢀ2ꢀ
yl)ꢀ9 ꢀcarbazole, was synthesized in three steps comꢀ
prising the alkylation of carbazole ( ) with 2ꢀdecyltetꢀ
radecyl bromide ( ) to give compound in 92% yield,
bromination of the alkylated product with ꢀbromoꢀ
succinimide (formed in 64% yield), and reaction of
3ꢀbromoꢀ9ꢀ(2ꢀdecyltetradecyl)ꢀ9 ꢀcarbazole with
in 41% yield.
5, resulting
5
H
1
We presented two synthetic routes to 5,6ꢀbis[9ꢀ(2ꢀ
2
3
decyltetradecyl)ꢀ9
:3,4ꢀ ']dithiophene (M1).
The first route (Scheme 1) consists of nine steps
Hꢀcarbazolꢀ3ꢀyl]naphtho[2,1ꢀ
3
N
b
b
H
4
including bromination of 1,2ꢀdimethoxybenzene (6) to bis(pinacol)diborane to give 5
OMe OMe
OMe OMe
OMe
S
OMe
OMe
OMe
FeCl3
B(OH)2
Br2
PdCl2 ∗ dppf
Br
Br
S
S
S
S
6
7
8
9
Br
O
B
O
C8H17
Br
2
B
O
C10H21
O
NBS
NaH, DMSO
PdCl2 ∗ dppf
N
N
N
C12H25
C12H25
C10H21
1
C10H21
3
4
O
B
OMe OMe
HO
OH
OTf OTf
O
N
C12H25
5
BBr3
Tf2O
C10H21
PdCl2 ∗ dppf
M1
Py
S
S
S
S
S
S
9
10
11
Scheme 1.
The first route is lengthy, consists of nine steps, and posed an alternative route (Scheme 2). This route is
the overall yield of M1 is low, being only ~4%; thereꢀ shorter and consists of only six steps, in particular, the
fore, this method is not efficient. Therefore, we proꢀ reaction of 1,2ꢀdibromoꢀ4,5ꢀdiiodobenzene (12) with
DOKLADY CHEMISTRY Vol. 467
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96
KESHTOV et al.
9ꢀ(2ꢀdecyltetradecyl)ꢀ3ꢀ(4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdiꢀ cyltetradecyl)ꢀ9
oxoborolanꢀ2ꢀyl)ꢀ9 ꢀcarbazole ( ) to give 1,2ꢀbis(9ꢀ 3ꢀyl)benzene (14) in 77% yield. The oxidative cyꢀ
(2ꢀdecyltetradecyl)ꢀ9 ꢀcarbazolꢀ3ꢀyl)ꢀ4,5ꢀdibroꢀ clization of 14 induced by UV light gives rise to the
Hꢀcarbazolꢀ3ꢀyl)ꢀ4,5ꢀbis(thiophenꢀ
H
5
H
mobenzene (13) in a good yield (68%). The subsequent target compound M1. After column chromatograꢀ
Suzuki reaction of compound 13 with an excess of phy, the yield of M1 is 90%, and the overall yield
thiopheneꢀ3ꢀboronic acid furnishes 1,2ꢀbis(9ꢀ(2ꢀdeꢀ is 11.4%.
Br
C12H25
Br
C10H21
2
NBS
N
NaH, DMSO
N
C12H25
C10H21
N
C12H25
C10H21
1
3
4
C10H21
C10H21
C12H25
C12H25
N
N
Br
O
B
O
B
Br
O
B
O
O
O
I
12
I
PdCl2 ∗ dppf
PdCl2 ∗ dppf
N
C12H25
C10H21
Br
Br
5
13
C10H21
C10H21
C10H21
C10H21
C12H25
C12H25
C10H21
C12H25
C12H25
C10H21
C12H25
N
N
N
N
C12H25
N
N
S
hν, I2
B(OH)2
PdCl2 ∗ dppf
Br
13
Br
S
S
S
M1
S
14
Scheme 2.
refers to the Hg proton. The latter is vicinal to the Нf
which is responsible for the doublet at 7.14 ppm (
8.49 Hz). The Hb, Hc, Hd, and He proton signals are
observed at 8.09 (d, = 7.62 Hz), 7.23 (t, = 7.56 Hz),
7.46 (t, = 7.99 Hz), and 7.40 (d, = 8.10 Hz) ppm.
The two doublets at 7.56 and 8.11 ppm have spin–spin
,
=
The composition and structure of the intermediate
compounds and the target compound M1 were conꢀ
J
1
firmed by the data of elemental analysis and H and
13C NMR spectroscopy. In particular, the aromatic
region of the 1H NMR spectrum of the M1 monomer
(Fig. 1a) exhibits one singlet, two triplets, and seven
J
J
J
J
coupling constants of ~5.25 Hz and can be assigned to
the Hi and Hj protons of the thiophene moieties. The
singlet at 8.59 ppm corresponds to the Hh protons of
doublets. The doublet at 8.29 ppm (d,
J = 1.20 Hz)
corresponds to the Ha protons of the carbazole rings.
The signal at 7.27 ppm (dd, J1 = 8.45 Hz, J2 = 1.36 Hz)
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SYNTHESIS AND OPTICAL AND ELECTROCHEMICAL PROPERTIES
97
C10H21
C12H25
C12H25
C10H21
e
h
(a)
N
N
f
d
g
c
b
a
j
a
i
h
e
f
g
b
i
c
d
j
S
S
Alkyl
8.8 8.7 8.6 8.5 8.4 8.3 8.2 8.1 8.0 7.9 7.8 7.7 7.6 7.5 7.4 7.3 7.2 7.1 7.0 6.9 6.8 ppm
h
a
j
i, b
k
d, e
f
g, c
8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 ppm
(b)
14
15, 18
12
6
19
13
2
C10H21
7.17
140.0 139.8
9
C12H25
C12H25
1
140.2
C10H21
18 17
15
16
N
N
14
13
11
10
19
12
9
8
7
6
5
4
2
1
8
5
16
3
3
S
S
7, 17
11, 10
4
142 140 138 136 134 132 130 128 126 124 122 120 118 116 114 112 110 108 ppm
14
12
6
15, 18
19
13
2
9
1
16
7, 17
8, 3
5
4
11, 10
140 130 120 110 100
90
80
70
60
50
40
30
20
10 ppm
1
13
Fig. 1. (a) H and (b) C NMR spectra of the M1 monomer.
1
correspond to aliphatic carbon atoms of the alkyl
chains (Fig. 1b).
the naphthodithiophene moiety. The H NMR specꢀ
trum of M1 is fairly complex; however, the aliphatic to
aromatic integrated intensity ratio is in line with the
proposed structure. The aromatic region of the carbon
spectrum of M1 exhibits 19 signals, nine of which refer
The UV absorption spectra of M1 in solution and
in the film are shown in Fig. 2. The absorption peaks
to quaternary carbon atoms. The signals at 50–10 ppm of M1 occur at 310 and 360 nm with absorption edge
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98
KESHTOV et al.
Absorbance
1.0
0.8
0.6
0.4
1
2
1
2
0.2
0
300
400
500
600
700
800
900
1000
Wavelength, nm
–5
Fig. 2. Absorption spectra of M1 in (
1
) film and (
2
) chloroform (
с
= 10 M).
at 380 nm (Fig. 2). The optical bandgap width correꢀ
The electrochemical properties of M1 were studied
sponding to the absorption edge is 3.26 eV. The by cyclic voltammetry. The cyclic voltammogram (Fig. 3)
absorption spectrum of M1 in the film is somewhat has one reduction peak in the negative potential region
redꢀshifted with respect to that in solution. This is and one oxidation peak in the positive region. The
apparently due to more ordered structure existing in cathodic reduction peak refers apparently to the forꢀ
the solid state.
mation of radical anions of the thiophene derivative,
while the anodic oxidation peak corresponds to the
radical cations of the thiophene moiety. The oxidation
and reduction onset potentials in the cyclic voltamꢀ
mogram were used to calculate the HOMO and
LUMO levels of M1 by the following equations (e is
the electron charge)
ox
ons
HOMO = –
е
(
E
E
+ 4.48) eV
,
(1)
(2)
red
ons
LUMO = –
е
(
+ 4.48) eV.
The HOMO and LUMO levels found from the oxiꢀ
dation and reduction onset potentials using Eqs. (1)
and (2) are –5.57 and –3.88 eV, respectively. Comꢀ
pound M1 has a lowꢀlying HOMO level, which proꢀ
vides a high openꢀcircuit voltage in polymeric solar
cells and endows M1 with good air stability.
–1
0
1
ACKNOWLEDGMENTS
Potential, V
M.L. Keshtov, S.A. Kuklin, and D.Yu. Godovskii
are grateful to the Russian Science Foundation for
the financial support of experimental studies and
Fig. 3. Cyclic voltammogram of M1 in a 0.1 M solution of
lithium perchlorate in acetonitrile at a sweep rate of
50 mV/s.
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99
6. Grimsdale, A.C., Chan, K.L., Martin, R.E., Jokisz, P.G.,
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examination of spectral characteristics (project
no. 14–13–01444).
7. Keshtov, M.L., Mal’tsev, E.I., Lypenko, D.A., and
Pozin, S.I., Khokhlov, A.R, Vysokomol. Soedin., 2010,
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