Donor–acceptor (E)-2-[2-(2,2′-bithiophen-5-yl)vinyl]benzo[d]thiazole: synthesis, optical, electrochemical studies and charge transport characteristics

Article abstract of DOI:10.1016/j.mencom.2019.09.030

Condensation of 2-methylbenzothiazole with 2,2′-bithiophene-5-carbaldehyde affords the title compound, a new chromophore. This compound was used for the doping of poly[9,9-bis(6-diethoxylphosphorylhexyl)fluorene], and the obtained composites demonstrated high electron mobility (1.50 × 10^?4 cm² V^?1 s^?1) in contrast to dopant-free matrixes.

Full text of DOI:10.1016/j.mencom.2019.09.030

Mendeleev
Communications
Mendeleev Commun., 2019, 29, 567–569
Donor–acceptor (E)-2-[2-(2,2'-bithiophen-5-yl)vinyl]benzo[d]thiazole:
synthesis, optical, electrochemical studies and charge
transport characteristics
Sergey D. Tokarev,a Yulia A. Sotnikova,a Alexander V. Anisimov,a Yurii V. Fedorov,b
Gediminas Jonusauskas,c Dmitriy A. Lypenko,d Vladimir V. Malov,d Alexey R. Tameev,d
Eugene I. Mal’tsevd and Olga A. Fedorova*a,b
a Department of Chemistry, M. V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation.
Fax: +7 495 932 8568; e-mail: fedorova@ineos.ac.ru
b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow,
Russian Federation. Fax: +7 499 135 5085
c Laboratoire Ondes et Matière d’Aquitaine – UMR CNRS 5798, Bordeaux University, Talence 33405, France
d A. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
199071 Moscow, Russian Federation. Fax: +7 495 952 5308
DOI: 10.1016/j.mencom.2019.09.030
Condensation of 2-methylbenzothiazole with 2,2'-bithio-
phene-5-carbaldehyde affords the title compound, a new
chromophore. This compound was used for the doping of
poly[9,9-bis(6-diethoxylphosphorylhexyl)fluorene], and the
obtained composites demonstrated high electron mobility
(1.50×10–4 cm2 V–1 s–1) in contrast to dopant-free matrixes.
ꢄ
ꢅ
ꢅ
ꢄ
ꢅ
PꢂꢃEP
ꢅ
ꢄ
ꢅ
ꢅ
ꢄ
ꢅ
ꢅ
ꢅ
N
S
S
S
IꢁO
SiO2
Al
ꢅ
ꢄ
ꢅ
ꢄ
V
Small molecular chromophores have attracted much attention as
active components in organic photonic devices due to their
reproduciblepreparation, easyfunctionalization, facilepurification
and high monodispersity.1–6 Donor–acceptor (D–A) typed
p-conjugated organic compounds are widely explored as active
materials for organic solar cells7–10 with the aim to reduce the
band gap for broadening the range of absorption.1,2,11 Moreover,
they were shown to have a great potential to get high power
conversion efficiency (PCE) and demonstrated good ease of
device fabrication.12 Another important field of application is the
use of molecular organic semiconductors (MOSs) as active
charge transporting layers in various devices of flexible
electronics.13–15 The relationship between the structure and
properties of p-type, n-type and ambipolar semiconductors is
still intensively studied. The latter have been developed to a
much lesser extent although they are key components for
realizing complementary metal-oxide semiconductor (CMOS)
digital integrated circuits16–19 and organic light-emitting
transistor (OLET) devices.20–22
poly[9,9-bis(6-diethoxylphosphorylhexyl)fluorene]
(PF-EP).
Compound 1 contains a p-electron donor thiophene moieties
connected through a double bond as a linker with a p-electron
heterocyclic acceptor. The synthesis of compound 1 involved the
Vilsmeier–Haack formylation of 2,2'-bithiophene.23 Obtained
2,2'-bithiophene-5-carbaldehyde was subjected to condensation
with 2-methylbenzothiazole in the presence of KOH (see Online
Supplementary Materials).
n
(EtO)2(O)P(CH2)6 (CH2)6P(O)(OEt)2
PF-EP
The absorption and emission maxima of compound 1 in
different solvents are outlined in Table 1 and Figure 1. The
positions of absorption and fluorescence bands are not
dependent on the solvent nature, whereas the quantum yield
and life time of excited state increase remarkably in DMSO as
compared with acetonitrile and ethyl acetate. The effect could
be connected with the higher viscosity of DMSO. The low
value of the fluorescence quantum yield is known for
styrylthiophene derivatives and is due to the occurrence of
competitive fast ISC (intersystem crossing) process or non-
radiative relaxation.24 It is noteworthy that large Stokes shift
(>120 nm) was observed for compound 1. The redox potentials
of compound 1 are summarized in Table 1. The cyclic
voltammogram in MeCN is shown in Figure S6 (see Online
Supplementary Materials).†
We synthesized and studied bithiophene derivative 1 containing
vinylbenzo[d]thiazole moiety (Scheme 1) for the doping of
i
S
S
H
S
S
O
S
ii
N
S
S
1, 62%
In contrast to fluorescence, irradiation of compound 1 with
light at l = 436 nm brings about E,Z-photoisomerization with
Scheme 1 Reagents and conditions: i, Me2NCHO, POCl3, CH2Cl2; ii,
2-methylbenzothiazole, KOH, DMSO.
© 2019 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
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Mendeleev Commun., 2019, 29, 567–569
Table 1 Optical and electrochemical characteristics of dye 1.a
Solvent
l
abs/nm
lfl/nm
Ffl
F
E–Z/FZ–E
t/ps
tradiative/ns
E/eV HOMO
E/eV LUMO
EtOAc
MeCN
DMSO
474
472
474
596
597
605
0.005
0.0045
0.014
55
30
11
0.55/0.13
6.7
7.5
–5.87
–3.23
105
a labs – maximum absorption position, lfl – maximum fluorescence position, Ffl – quantum yield of fluorescence, FE–Z/FZ–E – quantum yields of forward and
backward E–Z-photoisomerization, t – excited state lifetime, tradiative – radiative excited state lifetime, E HOMO – energy level of the highest occupied
electronic level, E LUMO – energy level of the lowest unoccupied electronic level.
ꢄaꢅ
ꢄ
ꢅ
ꢅ
ꢄ
ꢅ
PꢂꢃEP
ꢅ
0.ꢀ
0.ꢁ
0.ꢂ
0.2
ꢄ
ꢅ
ꢅ
Absorꢆtion
ꢇluorescence
ꢄ
ꢄ
ꢅ
ꢅ
ꢅ
N
S
IꢁO
S
S
Al
ꢅ
SiO2
0.1
0.0
ꢅ
ꢄ
V
ꢂ00
ꢁ00
ꢀ00
ꢈ00
ꢉ00
ꢋavelengthꢃnm
Figure 2 Schematic diagram of MIS-CELIV measurement device.
ꢄbꢅ
1.ꢁ
Table 2 LUMO–HOMO levels (eV) and charge carrier mobility
(cm2 V–1 s-1) in polymer matrix doped with 5 wt% of compound 1.
1.2
1.0
0.ꢊ
0.ꢈ
0.ꢁ
Material
PF-EP
LUMO Electron mobility HOMO
Hole mobility
–2.2
2.50×10–5
1.50×10–4
–5.7
1.94×10–4
3.27×10–5
PF-EP + 1 –3.23
–5.87
0.2
0.0
ambipolar charge transport ability due to the presence of both
electron donor and acceptor groups in the molecules (Table 2).
HOMO and LUMO levels are responsible for the hopping
transport of hole and electrons, respectively. Molecules of 1 can
participate in the charge transport since the mean distance
between them in the polymer matrix is about 2 nm, provided
they are distributed uniformly.‡
ꢂ00 ꢁ00
ꢉ00
ꢊ00
ꢀ00 ꢈ00
ꢋavelengthꢃnm
Figure 1 (a) Absorption and fluorescence spectra of dye 1, lex = 400 nm;
(b) change of absorption spectra upon irradiation with light 436 nm,
C1 = 3×10–5 mol dm–3, MeCN, T = 294 K.
The electron mobility value in the PF-EP/1 composite turned
out to be six times larger than that in the neat PF-EP. This is a
considerable evidence for the electron transport over the dye
molecules. As the LUMO level of the dye is located 1 eV lower
than that of the polymer, electron trapping by the polymer is
impossible. Moreover, owing to this an additional manifold of the
electron transporting sites within bandgap of the polymer forms.
On the contrary, the hole mobility value in the composite is
found to be less than that in the neat PF-EP. In this case, we
suggest that the HOMO levels of the polymer positioned only
0.17 eV higher than that of dyes serve as traps for the holes
hopping over dye molecules. In turn, the dye molecules can
serve as steric hindrance for the holes hopping over the polymer
HOMO levels.
To conclude, novel D–p-A chromophore 1 in solution
demonstrates the effective photoisomerization to Z-isomer, low
quantum yield of fluorescence and quite large Stokes shift. The
combination of benzothiazole residue with thiophene fragments
provides the chemical compound that exhibits efficient ambipolar
charge transport ability in composition with PF-EP polymer. The
photoisomerization of compound 1 in polymeric matrix has not
been observed. The fact indicates that the irradiation does not affect
charge transport, which was found early for some photochromes.29
The future synthesis and analysis of benzothiazole–thiophene
structures may be promising in the search for new compounds with
better optoelectronic characteristics.
sufficiently high quantum yield (0.55), while the back
Z,E-isomerization is less effective (see Table 1).
For clarifying the charge transport mechanism, polymer and
dye composite films were prepared from the solutions. In this
study, PF-EP served as a wide band-gap host polymer with
HOMO and LUMO levels of 5.7 and 2.2 eV, respectively.26
A thin (100–130 nm) PF-EP/1 (5 wt%) composite layer was
deposited onto the SiO2(70 nm)/ITO/glass substrate by spin
coating of the 5 mg ml–1 solution in the ethanol/acetonitrile
(95:5 v/v) mixture at the rate of 1000 rpm and dried at 60 °C for
3 h. Then an 80 nm thick Al top electrode was deposited onto the
composite layer by thermal evaporation under 10–6 mbar vacuum
at the rate of 1 E s–1 (Figure 2). Charge carriers mobility in films
of neat PF-EP and dye 1 composite was measured using the
MIS-CELIV technique.27,28 The dye composite possesses
†
UV-VIS spectra were measured using a two-channel spectrophotometer
Varian-Cary 300 and an Avantes AvaSpec-2048 spectrophotometer.
To determine the quantum yields of the forward and backward reactions
®
of E Z-photoisomerization of 1, we preliminarily calculated the absorption
¬
spectra of the corresponding Z-isomer and the ratios of quantum yields
®
for the forward and backward reactions of E Z-photoisomerization using
¬
the Fisher method25 from the absorption spectra of the E-isomer and the
spectra of two photostationary states obtained by photoirradiation at two
different wavelengths. Fluorescence spectra were measured at 20 1 °C
with a FluroLog-3-221 spectrofluorometer (Horiba Scientific). Anthracene
(jfl = 0.27) in ethanol was used as a reference for the fluorescence
quantum yield measurements.
‡
See detail description in Online Supplementary Materials.
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Mendeleev Commun., 2019, 29, 567–569
13 A. S. Sizov, E. V. Agina and S. A. Ponomarenko, Russ. Chem. Rev.,
This work was supported by the Russian Science Foundation
2018, 87, 1226.
(grant no. 18-73-00047). The use of equipment from Center of
collective facilities of A. N. Nesmeyanov Institute of Organo-
element Compounds is gratefully acknowledged.
14 C. Wang, H. Dong, W. Hu, Y. Liu and D. Zhu, Chem. Rev., 2012, 112,
2208.
15 C. Di, F. Zhang and D. Zhu, Adv. Mater., 2013, 25, 313.
16 J. Zaumseil and H. Sirringhaus, Chem. Rev., 2007, 107, 1296.
17 H.Yan, Z. Chen,Y. Zheng, C. Newman, J. R. Quinn, F. Dötz, M. Kastler
and A. Facchetti, Nature, 2009, 457, 679.
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2019.09.030.
18 H. Klauk, U. Zschieschang, J. Pflaum and M. Halik, Nature, 2007, 445,
745.
19 F. S. Kim, X. Guo, M. D. Watson and S. A. Jenekhe, Adv. Mater., 2010,
22, 478.
20 M. Muccini, Nat. Mater., 2006, 5, 605.
References
1 B. Walker, C. Kim and T.-Q. Nguyen, Chem. Mater., 2011, 23, 470.
2 Y. Li, Q. Guo, Z. Li, J. Pei and W. Tian, Energy Environ. Sci., 2010, 3,
1427.
21 R. Capelli, S. Toffanin, G. Generali, H. Usta,A. Facchetti and M. Muccini,
Nat. Mater., 2010, 9, 496.
3 J. Roncali, Acc. Chem. Res., 2009, 42, 1719.
22 M. Muccini, W. Koopman and S. Toffanin, Laser Photonics Rev., 2012,
6, 258.
23 Y.-S. Kim and Y.-A. Son, Mol. Cryst. Liq. Cryst., 2011, 551, 163.
24 G. Ginocchietti, E. Cecchetto, L. De Cola, U. Mazzucato and A. Spalletti,
Chem. Phys., 2008, 352, 28.
4 M. Lloyd, J. Anthony and G. Malliaras, Mater. Today, 2007, 10, 34.
5 A. N. Solodukhin, Yu. N. Luponosov, M. I. Buzin, S. M. Peregudova,
E. A. Svidchenko and S. A. Ponomarenko, Mendeleev Commun., 2018,
28, 415.
6 E. V. Lukovskaya, N. V. Dyachenko, A. V. Khoroshutin, A. A. Bobyleva,
A. V. Anisimov, V. A. Karnoukhova, G. Jonusauskas, Yu. V. Fedorov
and O. A. Fedorova, Mendeleev Commun., 2018, 28, 543.
7 B. Walker, A. B. Tamayo, X.-D. Dang, P. Zalar, J. H. Seo, A. Garcia,
M. Tantiwiwat and T.-Q. Nguyen, Adv. Funct. Mater., 2009, 19, 3063.
8 H. Shang, H. Fan, Y. Liu, W. Hu, Y. Li and X. Zhan, Adv. Mater., 2011,
23, 1554.
9 S. Loser, C. J. Bruns, H. Miyauchi, R. P. Ortíz, A. Facchetti, S. I. Stupp
and T. J. Marks, J. Am. Chem. Soc., 2011, 133, 8142.
10 B. Yin, L. Yang, Y. Liu, Y. Chen, Q. Qi, F. Zhang and S. Yin, Appl. Phys.
Lett., 2010, 97, 023303.
25 E. Fischer, J. Phys. Chem., 1967, 71, 3704.
26 B. Zhang, C. Qin, J. Ding, L. Chen, Z. Xie, Y. Cheng and L. Wang,
Adv. Funct. Mater., 2010, 20, 2951.
27 A. Armin, G. Juska, M. Ullah, M. Velusamy, P. L. Burn, P. Meredith and
A. Pivrikas, Adv. Energy Mater., 2014, 4, 1300954.
28 V.V. Malov, T. Ghosh,V. C. Nair, M. M. Maslov, K. P. Katin, K. N. N. Unni
and A. R. Tameev, Mendeleev Commun., 2019, 29, 218.
29 Y. Kim, T. J. Hellmuth, D. Sysoiev, F. Pauly, T. Pietsch, J. Wolf, A. Erbe,
T. Huhn, U. Groth, U. E. Steiner and E. Scheer, Nano Lett., 2012, 12,
3736.
11 Y.-J. Cheng, S.-H. Yang and C.-S. Hsu, Chem. Rev., 2009, 109, 5868.
12 R. K. Kanaparthi, J. Kandhadi and L. Giribabu, Tetrahedron, 2012, 68,
8383.
Received: 10th April 2019; Com. 19/5878
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