New fused thiophene derivatives as promising building blocks for optoelectronic devices

Full text of DOI:10.1134/S0012500815020068

ISSN 0012ꢀ5008, Doklady Chemistry, 2015, Vol. 460, Part 2, pp. 50–56. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © M.L. Keshtov, S.A. Kuklin, S.N. Osipov, M.A. Topchii, I.O. Konstantinov, A.L. Gamov, A.R. Khokhlov, 2015, published in Doklady Akademii Nauk, 2015,
Vol. 460, No. 6, pp. 666–672.
CHEMISTRY
New Fused Thiophene Derivatives as Promising Building Blocks
for Optoelectronic Devices
M. L. Keshtov, S. A. Kuklin, S. N. Osipov, M. A. Topchii,
I. O. Konstantinov, A. L. Gamov, and Academician A. R. Khokhlov
Received October 23, 2014
DOI: 10.1134/S0012500815020068
In recent two decades, much attention has been dibromoꢀ4,6ꢀbis(
paid to organic semiconductors (OS), which are
':5,6ꢀ '']trithiophene (М1) and 2,5ꢀdibromoꢀ8ꢀ
extremely attractive materials for application in optoꢀ pentadecylꢀ10Hꢀbisthieno[2',3':6,7,3'',2'':4,5]indeno
electronic devices due to their unique properties, such [1,2ꢀ
][1,3]thiazole (M2), which are promising donor
as low density, low cost, flexibility, and possibility to monomers for preparing various photoꢀ and electroꢀ
nꢀoctylthienꢀ2ꢀyl)benzo[2,1ꢀb:3,4ꢀ
b
c
d
choose necessary physicochemical parameters. To
date, the bestꢀstudied organic optoelectronic devices
are the following: fieldꢀeffect transistor [1], lightꢀ
active polymers.
Monomer M1 was initially prepared from 3,3'ꢀ
emitting diodes [2], and solar cells [3–6]. Their design dibromodithiophene (
is associated mainly with the synthesis of conjugated Preparation sequence included: (1) double crossꢀcouꢀ
semiconducting polymers based on fused aromatic pling of compound with 2ꢀethynylthiophene [10]
derivatives of thiophene, carbazole, furan, fluorene, under Sonogashira reaction conditions to give the corꢀ
etc. The coplanar structure of these compounds favors responding diacetylene , (2) rhodiumꢀcatalyzed
their selfꢀorganization to build ordered condensed intramolecular condensation of compound
in the
molecular structures due to strong
interaction presence of elemental sulfur, and (3) subsequent selecꢀ
stacking) [7], which facilitates efficient charge transꢀ tive bromination of intermediate
with ꢀbromosucꢀ
fer [8].
cinimide (NBS) at the two free C positions of the
4) as a starting compound [9].
4
3
5
5
π π
–
(
6
N
2
This work deals with the search for efficient methꢀ benzothiophene fragment to form the target comꢀ
ods of synthesis of new fused benzothiophenes: 2,8ꢀ pound M1 (Scheme 1).
R
R
R
S S
S
Br
Br
3
S
S
3 2
Pd(PPh ) Cl2
NEt , 80°C
4
3
S
S
5
5
a 40%
b 45%
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28,
Moscow, 119991 Russia
eꢀmail: keshtov@ineos.ac.ru
50

NEW FUSED THIOPHENE DERIVATIVES
51
S
S
R
S
S
R
R
S
S
R
1. Rh(PPh ) Cl
3 3
NBS
2. S8
S
S
Br
S
S
Br
6
6
a 60%
b 62%
a: R = 2ꢀethylhexyl
b: R = nꢀoctyl
M1a 55%
M1b 50%
Scheme 1.
Low yields of compound
crossꢀcoupling are caused by the incomplete transforꢀ diiodoꢀ2,2'ꢀbisthiophene
mation of initial dibromide and the formation of a synthesis was carried out in two stages by sequential
large number of unidentified byproducts. Unfortuꢀ halogenation of bisthiophene , which considerably
5
(40–45%) at the stage of preparing monomer M1b from 5,5'ꢀdibromoꢀ3.3'ꢀ
9
as a key intermediate. It
4
7
nately, all our attempts to optimize this process failed. simplifies the known method recently reported by
Therefore, we developed an alternative strategy for Müllen and coꢀworkers [11] (Scheme 2).
I
I
NBS
NIS
Br
Br
Br
Br
S
S
S
S
S
S
8
80–85%
9
85–90%
7
Scheme 2.
Both the intermediate and final compounds monomer М1b in enhanced total yield (Scheme 3,
and
) were obtained in a pure state in high yields Method B).
(8
9
without using column chromatography. Both stages
are easily adapted to the hundredꢀgram scale.
The composition and structure of intermediate
compounds 10, as well as of target compound М1
3–
,
1
13
were confirmed by elemental analysis data, H and C
NMR spectroscopy. In particular, the proton specꢀ
trum of target product М1 (Fig. 1a) shows one singlet
and two doublets at 7.22, 7.09, and 6.89 ppm correꢀ
sponding to aromatic protons of the thiophene fragꢀ
ment. The aliphatic region includes one triplet at
We found that compound
9 readily reacts with 2
equivalents of acetylene at ambient temperature in
3
the presence of catalytic amounts (5 mol %) of
Pd(PPh ) Cl to give bisꢀethynyl derivative 10 in yield
3
2
2
up to 90% (Scheme 3), which is a brominated analog
of compound 5b
.
2.93 ppm typical for CH2 group directly bound to
thiophene ring. Signals related to other СН2 groups of
However, the subsequent intramolecular cyclizaꢀ
tion of compound 10 under the action of the Wilkinꢀ alkyl fragment are within 1.25–2.00 ppm. A triplet
typical for СН3 group of alkyl fragment is observed at
.91 ppm. Integral intensity ratio for aromatic and aliꢀ
son complex (Rh(PPh ) Cl) followed by addition of
3
3
0
sulfur led to formation of the target compound М1b in
only 12% yield (Scheme 3, Method A). At the same
time, we revealed that compounds 5a and 5b containꢀ
ing no bromine atoms underwent cyclization under
similar conditions to give the corresponding benꢀ
zothiophenes 6a and 6b in good yields (Scheme 1).
Therefore to increase the yield of desired monomer
М1b, we carried out the dehalogenation of dibromiꢀ
phatic portions of target product molecule agrees well
with the proposed structure. The downfield region of
carbon spectrum of М1 contains in the range 110–
50 ppm ten signals that belong to 10 nonequivalent
aromatic carbon atoms of thiophene fragment, while
aliphatic portion shows eight resonances in the range
1
3
2–14 ppm that belong to eight different aliphatic carꢀ
bon atoms (Fig. 1b).
de 10 under the action of
nꢀbutyllithium followed by
hydrolysis and then performed cyclization and bromiꢀ
Monomer М2 was synthesized according to
nation of compound 6b resulting in the target Scheme 4 via reaction of equimolar amounts of readily
DOKLADY CHEMISTRY Vol. 460
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2015

52
KESHTOV et al.
Method
A
C8H17
S
H C
C H
8
1
7
8
17
S S
S
C H
S
S
C H
8
17
8
17
3
1. Rh(PPh ) Cl
3 2
2
. S8
Pd(PPh ) Cl
2
Br
3 2
Br
S
S
NEt , 80°C
3
9
Br
S
S
Br
Br
Br
M1b 12% (Method A)
S
1
S
5
0% (Method B)
0
90%
1
2
. nꢀBuLi
. H O
NBS
2
Method
B
H C
C H
8 17
1
7
8
S
1
. Rh(PPh ) Cl
C H
C H
3
2
S
S
8
17
8
17
S S
2
. S8
S
S
6b
60%
S
S
5b
91%
Scheme 3.
1
COOEt
O
2
O
O
1'
Br
3
4
COOEt
2'
12
3'''
KOH
EtOH
S
3''
O
O
Na
S
11
S
S
S
S
1
4
60%
13
87%
C H
1
5
31
Br
S
O
N
O
FeCl3
C15H31C(S)NH2
NBS
S
S
Br
S
S
Br
S
S
Br
Br
1
5
16
M2 71%
Scheme 4.
available thiophenes 11 [12] and 12 [13] in the presꢀ The cyclization of compound 13 into dithiopheneꢀ
ence of sodium metal in anhydrous benzene resulting containing cyclopentenone 14 was conducted in 7%
in ethyl 3ꢀoxoꢀ2ꢀ(2'ꢀoxoꢀ2'ꢀthienꢀ3''ꢀylethyl)ꢀ4ꢀ KOH solution in EtOH–H O mixture (1 : 1) in 60%
2
thienꢀ3'''ꢀylbutanoate (13) in 87% yield.
yield. The treatment of compound 14 with iron chloꢀ
DOKLADY CHEMISTRY Vol. 460
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NEW FUSED THIOPHENE DERIVATIVES
53
k
i
a
b
c
g
e
j
h
S
(a)
f
d
S
S
c
c
k
Br
S
S
Br
a
b
0.92
0.97
1.00
f–j
7.35
7.25
7.15
7.05
6.95
6.85
a
d
b
e
0
.92 0.97 1.00
2.10
2.11
10.33
3.01
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
δ
H
1
8
1
6
(b)
8
7
9
14
7
12
1
7
4
10
15
S
6
5
1
3
S
S
11
3
14
1
2
11
13
5
1
12
4
16
Br
S
S
Br
130.6
130.4
130.2
130.0
2
9
8
4, 7
5
3
6
32.5
31.5
30.5
29.5
28.5
18
11−16
17
132 131 130 129 128 127 126 125 124
4
, 7, 9
2
8, 6
10
5
3
1
145
135
125
115
105
95
85
75
65
55
45
35
25
15
C, ppm
δ
Fig. 1. 1H (a) and 13C (b) NMR spectra of monomer M1b
.
1
13
ride resulted in benzodithiophene 15 whose brominaꢀ copy, and H and C NMR. In particular, the proton
tion followed by condensation with aliphatic thioamꢀ
ide led to desired compound M2 in 71% yield.
spectrum of monomer M2 shows two singlets at 8.16
and 7.39 ppm typical of the protons of thiophene ring,
singlet (3.90 ppm) and triplet (3.17 ppm) correspondꢀ
The structure of target monomer M2 was conꢀ
firmed by the data of elemental analysis, IR spectrosꢀ ing to the CH protons in the fiveꢀmembered carbon
2
DOKLADY CHEMISTRY Vol. 460
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54
KESHTOV et al.
r
(a)
p
q
n
o
l
m
j
k
h
i
f
g
d
e
S
N
c
r
H(alkyl
)
a
b
Br
S
S
Br
c
b
а
d
e
1
.00
1.01
2.11
2.14
2.23
27.48
3.33
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 0.5
δ
H, ppm
33
3
1
20, 21, 24−30
3
2
( бb )
29
3
0
27
2
8
2
5
4
26
2
3
31
2
21
23
22
19
6
1
9
2
20
1
S
5
3
N
6
4
35 34 33 32 31 30 29
8
7
9
18
1
0
17
16 Br
1
1
1
3 14
Br
S
1
S
15
2
1
0
1
8
13
14
8
4
7
9
1
1
2
0, 21, 24
−30
33
3
1, 6
32
136
134
132
130
128
126
124
23
4
8
, 18
10
, 1314
1
9
9
16
17
2
7
11
5
1
80 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10
δ
C, ppm
Fig. 2. 1H (a) and 13C (b) NMR spectra of monomer M2
.
ring and in the alkyl group directly bound to the thiaꢀ (Fig. 2a). The aromaticꢀtoꢀaliphatic integrated intenꢀ
zole ring. The spectrum displays a multiplet at 2.01– sity ratio corresponds to the suggested structure. The
1
.40 ppm related to the aliphatic protons of the alkyl aromatic portion of carbon spectrum of compound
groups and a triplet of the СН3 group at 0.90 ppm М2 exhibits 13 signals corresponding to 13 nonꢀequivꢀ
DOKLADY CHEMISTRY Vol. 460
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NEW FUSED THIOPHENE DERIVATIVES
55
2.0
1.6
1.2
0.8
0.4
I
2
1
1
2
0
3
−
1
0
V
1
(rel. Ag/Ag ), V
00
350
400
450
500
550
600
+
Wavelength, nm
Fig. 4. Cyclic voltammograms of monomers M1
M2 ) in 0.1 M lithium perchlorate solution in acetoniꢀ
trile at scan rate 50 mV/s.
(1) and
Fig. 3. Absorption spectra of compounds M1
(1) and
(2
–5
M2 (2) in chloroform (с = 1 × 10 ).
alent aromatic carbon atoms of thiophene fragment. for the monomers determined by cyclic voltammetry,
The aliphatic portion of the spectrum includes signals according to Eq. (3) is within 1.57–1.66 eV and insufꢀ
of carbon atoms of CH2 groups within 36–18 ppm and
a signal at 14.15 ppm typical for СН3 group.
opt
ficiently agrees with the band gap width (Eg ) deterꢀ
mined by optical method. It was found that the
Compounds M1 and M2 display absorption specꢀ obtained compounds have lowꢀenergy HOMO close
tra with several maxima inherent in flat conjugated to ideal value (5.4 eV), which provides a possibility to
systems. Absorption spectra of these compounds show reach high openꢀcircuit voltage in polymeric solar
maxima at 350, 362, and 400 nm with absorption cells.
edges at 385 and 455 nm, respectively (Fig. 3). Band
gap width corresponding to the position of absorption
edges of these derivatives is within 2.83–3.44 eV.
ACKNOWLEDGMENTS
The electrochemical properties of the monomers
were studied by cyclic voltammetry. Cyclic voltammoꢀ
gram (Fig. 4) shows one reduction peak in negative
region and one oxidation peak in the positive voltage
region. Cathode reduction peak is likely to be due to
formation of anion radicals of thiophene unit, while
anode oxidation peak corresponds to cation radicals of
thiophene fragment. HOMO and LUMO and band
gap width of compounds M1 and M2 were calculated
M.L. Keshtov, S.A. Kuklin, S.N. Osipov, and
M.A. Topchii thank the Russian Foundation for Basic
Research for financial support in the experimental
study of spectral characteristics (project no. 14–13–
01444).
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onset
1. Yu, Y., Adv. Mater., 2010, vol. 22, pp. 4427–4447.
from the onset oxidation potential (Eox ) and onset
onset
reduction potential (Ered ) of the monomers accordꢀ
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Ma, D., J. Mater. Chem., 2006, vol. 16, pp. 3332–3341.
ing to equations
onset
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Jia, S., and Williams, S.P., Adv. Mater., 2010, vol. 22,
pp. 3839–3856.
HOMO = –
е
(
Eox + 4.48) (eV)
,
(1)
(2)
(3)
onset
LUMO = –е(Ered + 4.48) (eV),
ec
onset
Eox
onset
4
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=
е(
– Ered ) (eV).
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DOKLADY CHEMISTRY Vol. 460
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56
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Translated by I. Kudryavtsev
DOKLADY CHEMISTRY Vol. 460
Part 2
2015