Quadrupolar fluorophores with tetrafluorobenzene central electron acceptor

Article abstract of DOI:10.1016/j.jfluchem.2021.109735

Seven novel quadrupolar chromophores based on 1,2,4,5-tetrafluorobenzene (TFB) central electron acceptor unit and methoxythiophene peripheral donor were synthetized and described. Fundamental structure-property relationships were elucidated via thermal, e

Full text of DOI:10.1016/j.jfluchem.2021.109735

Journal of Fluorine Chemistry 243 (2021) 109735
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Quadrupolar fluorophores with tetrafluorobenzene central
electron acceptor
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Jirí Kulhanek, Milan Klikar, Oldrich Pytela, Numan Almonasy, Jirí Tydlitat*, Filip Bures
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Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentska 573, Pardubice, 53210, Czech Republic
A R T I C L E I N F O
A B S T R A C T
Keywords:
Seven novel quadrupolar chromophores based on 1,2,4,5-tetrafluorobenzene (TFB) central electron acceptor unit
and methoxythiophene peripheral donor were synthetized and described. Fundamental structure-property re-
lationships were elucidated via thermal, electrochemical and optical measurements. These revealed that the
Tetrafluorobenzene
Methoxythiophene
Push-pull chromophore
Fluorescence
properties are mostly affected by the used π-linker. Variation of the π-linker resulted in tuning of the HOMO-
LUMO gap. The LUMO clearly reflects planarity, polarizability and electronic transparency of the utilized
π
-linker. The absorption maxima of target chromophores were found within the range of 346–412 nm and the
emission maxima of emissive derivatives were found within the range of 411–499 nm. Novel TFBs were
compared with TFBs previously described in the literature. The experimental data are further corroborated by
theoretical calculations.
1. Introduction
electronegativity. Moreover, its small size avoids undesired steric hin-
drance. Property tuning using fluorine substitution has tremendous
Organic electronics (OE) gained considerable attention over the past
decades. As the 20th century has created the basis for portable elec-
tronics, 21st century further develops this trend by investigating new
and powerful organic compounds and materials that are advantageous
for several reasons: i) they possess easy structural modification and
allow tailoring of their specific properties, ii) processing of organic
materials can be carried out at low temperature, iii) organic materials
can be transparent, iv) flexible and v) the final device is generally light-
weight. Moreover, many electronic devices with organic active com-
ponents have already been commercialized. Thus, small organic mole-
cules and polymers with enhanced properties for OE are of tremendous
interest and attract considerable research interest.
potential in biologically active compounds [2–4] but it is also known in
OE materials [5,6]. Among other fluorine-based acceptors such as (per)
fluoroalkyl chains or (per)fluoro(hetero)aromates [6], 1,2,4,5-tetra-
fluorobenzene (TFB) occupies prominent position. TFB-derived mate-
rials found numerous applications in organic solar cells (OSCs) [7–12],
organic field effect transistors (OFETs) [13–15], organic light emitting
diodes (OLEDs) [16,17], charge transporting [18] and fluorescent [19]
materials, bioelectronics applications [20] and other high-performance
organic devices [21].
Based on our ample experience with push-pull compounds of various
shapes and arrangements [22] such as A-π-D-π-A [23–27] and D-π-A-π-D
[23,28,29] quadrupolar systems and our previous investigation on TFB
[30], we have designed new TFB chromophores 1–7 (Fig. 1) bearing two
methoxythiophene electron donors and systematically varied and
A typical architecture of OE materials involves interconnection of
various building blocks into a π-conjugated scaffold. Push-pull mole-
cules, consisting of an electron donor (D) and an electron acceptor (A)
attached to a -linker, belong to such group of -conjugated compounds.
In this respect, thiophene is often used -conjugated, electron-rich and
polarizable unit. [1] It can be utilized as a chromophore central unit, an
elongated π-linker. The fundamental properties of chromophores 1–7
π
π
were studied by UV/Vis absorption and emission spectra, electrochem-
istry and DSC measurements that are corroborated by DFT calculation.
Furthermore, these were critically compared to previously reported TFB
derivatives A and B (Fig. 1).
π
auxiliary electron donor, a part of the π-linker or may also be a part of
larger systems such as oligo- and polythiophenes. On the other hand,
attachment of fluorine atom into the chromophore backbone brings
rather opposite electron-withdrawing effect due to its strong
* Corresponding author.
´
E-mail address: jiri.tydlitat@upce.cz (J. Tydlitat).
https://doi.org/10.1016/j.jfluchem.2021.109735
Received 23 November 2020; Received in revised form 14 January 2021; Accepted 15 January 2021
Available online 27 January 2021
0022-1139/© 2021 Elsevier B.V. All rights reserved.

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J. Kulhanek et al.
Journal of Fluorine Chemistry 243 (2021) 109735
2. Results and discussion
2.2. Thermal properties
2.1. Synthesis
Thermal behavior of compounds 1–7 was studied by differential
scanning calorimetry (DSC). Table 1 lists measured melting points (Tm)
as well as temperatures of thermal decompositions (Td). All recorded
DSC curves are depicted in the Supporting Information. The measured
melting points of 1–7 range from 166 to 225 ◦C. The temperatures of
decomposition were estimated within the range of 130–300 ◦C. From the
obtained DSC data is obvious that thermal behavior of target molecules
is clearly driven by the nature of the interconnection between the pe-
ripheral methoxythiophene donors and the central TFB acceptor. If these
Similarly to our previous report [30], TFB-derivatives 1–7 were
gradually constructed in one to three reaction steps. The synthesis of
compounds 1–6 outlined in Scheme 1 utilizes commercially available 1,
4-diiodotetrafluorobenzene and its two-fold cross-coupling reaction.
Based on the last reaction step, different cross-coupling reactions were
performed. While Suzuki-Myiaura cross-coupling reaction using boronic
acid pinacol esters 9–11, 13 and 14 provided chromophores 1–3, 5 and
6, the chromophore 4 was synthesized from terminal acetylene 12 via
Sonogashira reaction. A different strategy was adopted to prepare
chromophore 7 (Scheme 2). The starting 1,4-dimethyl-TFB 15 was
gradually dibrominated and transformed into 17, which undergoes
two-fold Horner-Wadsworth-Emmons reaction to target olefinic chro-
mophore 7. All used precursors, except 13 (see the Supporting Infor-
mation for its synthesis) were synthesized according to the following
literature protocols: 9 [31], 11 [32], 12 [33], 14 [32], 8 [34], 16 [35]
and 17. [35] Compounds 10, 1,4-diiodo- and 1,4-dimethyl-TFBs are
commercially available. Due to sparing solubility of target chromo-
phores 1–7, they were purified by multiple washing with dichloro-
methane, which however reduced the attained yields to 25–83 %.
are connected by a single bond (1) or a simple π-linker such as 1,4-phe-
nylene moiety (3), double (7) or triple (4) bond, easy-to-interpret
thermograms were recorded (Fig. 2). These molecules clearly under-
went melting process and following thermal decomposition upon heat-
ing. On the other hand, target compounds with complex π-linker such as
2,5-thienylene (2), ethynylthiophene (5) or ethynylbenzene (6)
decomposed directly without previous melting and their DSC curves also
showed endothermic solid-solid transitions (≈150 ◦C). Whereas this
transition is well separated from the exothermic degradation in the case
of 2, both processes were overlapped for compounds 5 and 6 (see the
Supporting Information). From the measured DSC data we can clearly
deduce
a general trend that the presence of acetylene π-linker
Fig. 1. Structures of target compounds 1–7 and recently described TFB analogs A and B.
2

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J. Kulhanek et al.
Journal of Fluorine Chemistry 243 (2021) 109735
Scheme 1. i) PdCl2(PPh3)2, Na2CO3, THF/H2O, 80 ◦C (4:1) ii) NBS, CHCl3/AcOH (1:1), 25 ◦C, 18 h iii) PdCl2(PPh3)2, CuI, THF/iPr2EtN (15:1), 50 ◦C, 18 h.
Scheme 2. i) NBS, AIBN, CHCl3, reflux, 18 h ii) P(OEt)3, 160 ◦C, 4 h iii) 5-methoxythiophene-2-carbaldehyde, tBuOK, THF, 25 ◦C, 18 h.
dramatically reduces thermal robustness of target compounds. Tem-
peratures of thermal decomposition of 4–6, found between 130–200 ◦C,
are significantly lower as compared to other analogs in the series
(Table 1). Compounds 1–3 and 7 without embedded triple bonds
exhibited very close decomposition temperatures (Td = 270–300 ◦C). In
these cases, the π-linker structure influences thermal degradation only
3

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J. Kulhanek et al.
Journal of Fluorine Chemistry 243 (2021) 109735
the HOMO-LUMO gap is dictated mostly by the LUMO level, which is in
Table 1
Thermal and electrochemical properties of target chromophores 1–7.
accordance to expected trends. [38] In contrast to parent molecule 1
Comp.
Tm
Tdb
Ecp(ox1)
Ecp(red1)
ΔEc
EdHOMO
EdLUMO
a
with ΔE =3.29 eV, the planarized and extended π-systems of 4 and 7
(◦C)
(◦C)
(V)
(V)
(V)
(eV)
(eV)
reduce the HOMO-LUMO gap to 2.89 and 2.56 eV, respectively. An
opposite effect is observed when using nonplanar -linker hindering
sufficient D-A interaction. Although elongated -system, 1,4-phenylene
π
1
2
3
4
5
6
7
166
/
300
270
300
200
175
130
285
1.22
1.21
1.32
1.39
1.29
1.24
1.02
–2.07
–1.59
–2.06
–1.50e
–1.44e
–1.87
–1.54e
3.29
2.80
3.38
2.89
2.73
3.11
2.56
–5.53
–5.52
–5.63
–5.70
–5.60
–5.55
–5.33
–2.24
–2.72
–2.25
–2.81
–2.87
–2.44
–2.77
π
213
190
/
π
-linker in 3 limits the intramolecular charge-transfer (ICT) due to its
out-of-plane arrangement and the HOMO-LUMO gap is increased to 3.38
eV, see Fig. 5. As compared to 1,4-phenylene, polarizable and auxiliary
/
donor such as 2,5-thienylene π-linker(s) significantly reduce the energy
225
gap as can be seen on e.g. 3 vs. 2 with ΔE = 3.38 vs. 2.80 eV. Elongation
and/or partial planarization of the -linker via additional acetylene
-linker decreases energy gap similarly (compare e.g. 2/3 vs. 5/6 → ΔE
= 2.80/3.38 vs. 2.73/3.11 eV). Further planarization and extension of
aTm = melting point (the point of intersection of a baseline and a tangent of
π
thermal effect = onset). bTd = thermal decomposition (pyrolysis in N2 atmo-
π
c
sphere). Ep(ox1) and Ep(red1) are peak potentials of the first oxidation and
reduction, respectively, as measured by CV at scan rate 100 mVs–1; all potentials
are given vs. SSCE, ΔE = Ep(ox1) – Ep(red1)
.
d –EHOMO/LUMO = Ep(ox1/red1) + 4.35 (in
the whole D-π-A-π-D system via polarizable olefinic π-linker(s) as in 7
enables the most efficient ICT and narrows the energy gap to 2.56 eV.
DMF vs. SCE) [36] – 0.036 [difference between SCE (0.241 vs. SHE) and SSCE
(0.205 vs. SHE)] [37]. e(Quasi)reversible process.
2.4. Quantum-chemical calculations
negligibly and is rather reflected in the melting temperatures. Com-
pound 3 bearing simple 1,4-phenylene linker turned out to be the most
thermally robust with Tm/Td = 213/300 ◦C.
To get an insight into the molecular structures and electron distri-
butions in 1–7, density functional theory (DFT) calculations were
2.3. Electrochemistry
The electrochemical characterization of target chromophores 1–7
was carried out in DMF containing 0.1 M Bu4NPF6 in a three-electrode
cell by cyclic voltammetry (CV). The acquired data are summarized in
Table 1, CV diagrams and further electrochemical details are given in
the Supporting Information.
The first oxidations and reductions were mostly determined as irre-
versible consecutive processes that reflect quadrupolar character of
examined compounds (see the Supporting Information for more details).
It is assumed that the first reduction is most likely localized at the central
TFB acceptor while the first oxidation probably involves the peripheral
methoxythiophene donor(s). The Ep(ox1) and Ep(red1) values were found
within the range of 1.02 to 1.39 and –1.44 to –2.07 V, respectively, and
were further recalculated to the HOMO/LUMO levels (Table 1). The
deduced HOMO-LUMO levels and the corresponding gaps are visualized
in energy level diagrams (Fig. 3 and S25). As can be seen from Table 1
and Figure S25, the HOMO level is steady across the whole series of
target molecules 1–7. It indicates that the HOMO occupies methox-
Fig. 3. Electrochemical (yellow), calculated (orange) and optical energy gaps
ythiophene donors and
negligibly. On the other hand, the
on the LUMO level. The LUMO clearly reflects planarity, polarizability
and electronic transparency of the utilized -linker. As a consequence,
π
-linker tuning influences its energy only
(gray) as a dependency on the used π-linker in target chromophores 1–7. (For
π-linker variation has a direct impact
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article).
π
Fig. 2. Representative DSC thermographs of TFB derivatives 1, 3, 4 and 7.
4

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J. Kulhanek et al.
Journal of Fluorine Chemistry 243 (2021) 109735
performed. Their geometries were optimized using the DFT B3LYP/
6ꢀ 311 G(2d,p) and DFT B3LYP/6ꢀ 311+G(2df,p) methods imple-
mented in Gaussian W09 package [39]. The HOMO and LUMO energies,
their differences, and the ground state dipole moments were calculated
using the DFT B3LYP/6ꢀ 311++G(2df,p) as well as long-range
CAM-B3LYP/6ꢀ 311++G(2df,p) methods, both in DMF. In contrast to
CAM-B3LYP results, the B3LYP-calcualted data shown in Table 2
showed tighter correlation with the electrochemical and optical values
(Tables 1 and 3) and, therefore, is considered as reasonable tool for
description of electronic parameters of 1–7. This is in accordance to our
previous observations made for various charge-transfer molecules.
[23–29,31] See the Supporting Information for further comparison of
both DFT methods.
Table 3
UV/Vis and photoluminescence data in CH2Cl2 solution.
a
λAmax[nm
(eV)]
λEmax
Comp.
ε
qF
Stokes
shift
[103 mol–1 dm3
[nm
cm–1
]
(cm–1
)
(eV)]
1
2
3
4
5
6
7
A
B
352 (3.52)
412 (3.01)
346 (3.58)
398 (3.12)
404 (3.07)
358 (3.46)
376 (3.30)
331 (3.75)
282 (4.40)
39.6
46.8
59.3
53.2
63.9
70.7
31.9
36.1
32.2
411
499
433
–
489
426
–
426
377
0.17
0.54
0.68
–
0.21
0.04
–
0.93
0.13
4078
4231
5807
–
4303
4459
–
6738
8936
a
Localization of the frontier molecular orbitals in representative
chromophores 2, 4 and 5 is shown in Fig. 4; see Table S2 for complete
listing. The HOMOs of compounds 1–7 are mainly spread over the pe-
The fluorescence quantum yields (qF) were measured using quinine sulfate
(qF = 0.54 in 0.5 mol dm–3 H2SO4) [42].
ripheral methoxythiophene units and across the adjacent π-linker, while
the LUMOs occupy mostly 1,4-positions of the central TFB unit as well as
the closest part of the used π-linker. Both orbitals are separated and,
therefore, the investigated molecules can be considered as charge-
transfer chromophores.
The calculated HOMO and LUMO energies ranged from –5.27 to
–5.63 and from –2.02 to –2.65 eV, respectively. It is obvious that both
EHOMO/LUMO values are dependent on the structural features of 1–7.
Figs. 3 and S25 further demonstrate that the calculated values and their
differences obey the same trends as seen by electrochemistry. The
largest HOMO-LUMO gaps were identified for chromophores 3 and 6.
An inspection of their optimized structures (Fig. 5 and Table S3) reveals
their nonplanar arrangement with the torsion angles, between the TFB
central acceptor and the adjacent rings, of around 45◦. This is in high
contrast to other chromophores in the investigated series with both rings
close to be coplanar. Moreover, the torsion angle between thiophene and
benzene rings in 3 is 21◦, which further hinders efficient ICT. An addi-
tional acetylenic linker inserted between both rings as in 6 reduces the
E
LUMO by 0.2 eV.
2.5. UV/Vis spectroscopy
Fig. 4. Representative HOMO/LUMO localizations in 2, 4 and 5 visualized in
OPchem [40] (blue for LUMO, red for HOMO). (For interpretation of the ref-
erences to colour in this figure legend, the reader is referred to the web version
of this article).
Electronic absorption and photoluminescence properties of chro-
mophores 1–7 were investigated in dichloromethane at concentration of
2 × 10–5 mol dm–3. The spectroscopic data are presented in Table 3, the
absorption spectra of derivatives 1–7 are shown in Fig. 6. For a conve-
nient comparison, properties of two previously synthetized TFB analogs
A and B are also included in Table 3. The λmax values of the longest-
wavelength absorption bands were found within the range of 346–412
shifted the λmax by 24 and 46 nm as compared to 1. These trends are
in accordance to electrochemical conclusions. The highest red shift of 60
and 52 nm (2 and 5 vs. 1) was observed for compounds containing 2,5-
nm. The molar absorption coefficients
ε
range from 31.9–70.7 × 103
thienylene unit as a part of the π-linker. A comparison of chromophore 3
mol–1 dm3 cm–1 and, except for olefinic chromophore 7, increase with
with the former derivatives A and B revealed its bathochromically
shifted CT-band with λmax =346 nm (vs. 331 nm for A and 282 nm for B),
the extension of the whole π-system (Table 3). The absorption maxima
which is due to its larger and polarizable π-system. [30] In general,
strongly depend on structural features of the used
that -linker extension leads to a gradual bathochromic shift of the ab-
sorption maxima. On the other hand, twisted 1,4-phenylene -linker
decreases λmax. Hence, very close λmax values were recorded for com-
π-linker. It is obvious
methoxythiophene-terminated chromophores showed a similar range of
the absorption maxima (346–412 nm) to previous N,N-dimethylami-
no-terminated chromophores (331–409 nm). [30] Hence, both donors
imparts similar ICT into the chromophore.
π
π
pounds 3/6 vs. 1 (346/358 vs. 352 nm). Planarization and
π
-linker
Except olefinic and acetylenic chromophores 4 and 7, investigated
TFB-derivatives showed fluorescence with the emission maxima
appearing between 411 and 499 nm. Representative spectra of de-
rivatives 1–3 are shown in Fig. 7. Chromophores 1–3, 5 and 6 exhibited
significantly different quantum yields (qF) 0.04 to 0.68 (Table 3). As
extension by introducing olefinic (7) or acetylenic (4)
π-linkers red-
Table 2
DFT calculated properties of chromophores 1–7.
Comp.
Symmetry group
EHOMOa (eV)
ELUMOa (eV)
ΔE (eV)
μ (D)
compared to parent chromophore 1, elongation of the
thienylene (2) or 1,4-phenylene (3) units increased the qF from 0.17 to
0.54 and 0.68 respectively. On the contrary, extension of the -system by
π-system by 2,5-
1
2
3
4
5
6
7
C2h
C2
–5.54
–5.27
–5.63
–5.60
–5.37
–5.64
–5.28
–2.03
–2.46
–2.02
–2.51
–2.65
–2.22
–2.47
3.51
2.81
3.61
3.09
2.72
3.42
2.81
0.0
0.1
0.0
0.0
0.0
2.4
0.0
π
Ci
acetylenic unit caused either significant decrease (qF of 2 vs. 5, 0.54 vs.
0.21) or nearly quench (qF of 6 is 0.04) of the emissive properties. The
recorded fluorescence parameters are comparable to those obtained for
derivatives A and B. [30] In general, higher Stokes shifts were recorded
for nonplanar chromophores (e.g. 3 with 5807 cm–1), which is
C2h
C2h
C2
C2h
a
Calculated at the DFT B3LYP/6ꢀ 311++G(2df,p) level in DMF as a solvent.
5

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J. Kulhanek et al.
Journal of Fluorine Chemistry 243 (2021) 109735
Fig. 5. Torsion angles in degrees amongst TFB, 1,4-phenylene and thiophene for 3 and 6 (structures were optimized using the DFT B3LYP/6-311+G(2df,p) method
and visualized with Mercury [41]).
Fig. 6. UV/Vis absorption spectra of chromophores 1–7 measured in dichloromethane (c = 2 × 10–5 mol dm–3).
attributable to larger structural re-arrangement of their exited states.
3. Conclusion
In summary, series of D-π-A-π-D quadrupolar chromophores with
tetrafluorobenzene central electron acceptor and peripheral methox-
ythiophene electron donors was designed and synthetized. Length,
composition and spatial arrangement of the used
π-linker affected
thermal, electrochemical and optical properties most significantly. The
experimental structure-property relationships were further supported by
DFT calculations. Thermal properties were strongly affected by
composition of the π-linker; the acetylenic π-linker (in 4–6) brings sig-
nificant thermal instability. 1,4-Phenylene moiety (3 and 6) is another
important structural feature affecting thermal, electrochemical as well
as optical properties. Electrochemical, optical and DFT-calculated
HOMO–LUMO gap of 3 and 6 were the highest from the whole series
of chromophores. Due to nonplanar arrangement, Stokes shifts of these
two chromophores are also the largest. The torsion angle between 1,4-
phenylene and TFB units was calculated close to 46◦. In comparison
with previously synthetized methoxy- and dimethylamino-TFBs
exhibited methoxythiophene-TFBs optical properties closer to dime-
thylamino derivatives. It was found that UV/Vis absorption of methox-
ythiophene and dimethylamino series gain similar values in range about
Fig. 7. UV/Vis emission spectra of chromophores 1–3 measured in
dichloromethane.
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J. Kulhanek et al.
Journal of Fluorine Chemistry 243 (2021) 109735
330–410 nm while range of UV/Vis emission of methoxythiophene-TFBs
calcd. for C28H18F4O2S2+ 526.0684 [M]+; found 526.0707.
is blue shifted about 10 nm.
4.5. 1,4-Bis[(5′-methoxythiophene-2′-yl)ethynyl]-2,3,5,6-
4. Experimental
tetrafluorobenzene 4
See Supporting Information for further details and synthesis of 13.
In a Schlenk flask, 1,4-diiodotetrafluorobenzene (350 mg, 0.9 mmol)
and 2-ethynyl-5-methoxythiophene 12 (300 mg, 2.60 mmol) were dis-
solved in a mixture of 30 ml anhydrous THF and ethyldiisopropylamine
(2 mL, 11.50 mmol). Argon was bubbled through the solution for 10
min, whereupon PdCl2(PPh3)2 (80 mg, 0.11 mmol) and copper iodide
(40 mg, 0.07 mmol) were added and the resulting reaction mixture was
stirred at 50 ◦C overnight. The reaction mixture was diluted with water
(100 mL) and extracted with CH2Cl2 (3 × 50 mL). The combined organic
extracts were dried over anhydrous Na2SO4 and the solvents were
evaporated in vacuo. Twofold decantation of the crude product gave
4.1. General procedure for the Suzuki–Miyaura cross-coupling
(compounds 1–3, 5 and 6)
In a Schlenk flask, 1,4-diiodotetrafluorobenzene (402 mg, 1.00
mmol) and appropriate boronic acid pinacol ester (2.50 mmol) were
dissolved in the mixture of THF/H2O (50 mL, 4:1). Argon was bubbled
through the solution for 10 min, whereupon [PdCl2(PPh3)2] (98 mg,
0.14 mmol) and Na2CO3 (318 mg, 3.00 mmol) were added and the re-
action mixture was stirred at 80 ◦C for 12 h. The reaction mixture was
diluted with water (100 mL) and extracted with CH2Cl2 (3 × 50 mL). The
combined organic extracts were dried (Na2SO4), the solvents were
evaporated in vacuo and the crude product was purified by twofold
decantation from dichloromethane.
yellow-brownish solid 4 (115 mg, 31 %): mp 190 ◦C; IR (HATR):
ν 2200,
1712, 1458, 1415, 1206, 971, 773 cm–1; 1H NMR (400 MHz, CDCl3): δ =
3.93 (s, 6H, OCH3), 6.15 (d, 2H, J =4.2 Hz, CHTh), 7.09 (d, 2H, J =4.2
Hz, CHTh) ppm; 13C NMR (100 MHz, CDCl3): δ = 60.6, 97.5, 104.9,
107.6, 133.4, 145.0, 145.1, 147.4, 147.5, 147.6, 169.3 ppm; 19F NMR
(376 MHz, CDCl3): δ =141.01 ppm; EIMS (70 eV) m/z (rel. int.): 422
(M+, 100), 407 (73), 392 (59); HRMS (MALDI), m/z: calcd. for
C20H10F4O2S+2 422.0058 [M]+; found 422.0058.
4.2. 1,4-Bis(5′-methoxythiophene-2′-yl)-2,3,5,6-tetrafluorobenzene 1
The title compound was synthesized from 1,4-diiodotetrafluoroben-
zene (402 mg, 1.00 mmol) and 5-methoxythiophene-2-yl boronic acid
pinacol ester 9 (600 mg, 2.50 mmol) following the general procedure for
Suzuki-Miyaura cross-coupling. Twofold decantation gave grey-
4.6. 1,4-Bis{5′-[(5′′-methoxythiophene-2′′-yl)ethynyl]thiophene-2′-yl}-
2,3,5,6-tetrafluorobenzene 5
brownish solid 1 (234 mg, 25 %): mp 166 ◦C; IR (HATR):
ν
2359,
The title compound was synthesized from 1,4-diiodotetrafluoroben-
zene (175 mg, 0.44 mmol) and 5-[(5′-methoxythiophene-2′-yl)ethynyl]
thiophene-2-yl boronic acid pinacol ester 13 (380 mg, 1.10 mmol)
following the general procedure for Suzuki-Miyaura cross-coupling.
Twofold decantation gave brown solid 5 (130 mg, 51 %): mp 175 ◦C
1551, 1474, 1419, 1210, 963, 759 cm–1; 1H NMR (400 MHz, CDCl3): δ =
3.95 (s, 6H, OCH3), 6.27 (d, 2H, J =4.2 Hz, CHTh), 7.31 (d, 2H, J =4.2
Hz, CHTh) ppm; 13C NMR (100 MHz, CDCl3): δ = 60.5, 104.5, 114.5,
129.0, 142.8, 169.2 ppm; 19F NMR (376 MHz, CDCl3): δ =145.77 ppm;
EIMS (70 eV) m/z (rel. int.): 374 (M+, 82), 359 (100), 344 (30); HRMS
(MALDI), m/z: calcd. for C16H10F4O2S+2 374.0058 [M]+; found
374.0054.
(dec.); IR (HATR):
ν
2359, 1711, 1463, 1415, 1208, 961, 771 cm–1; 1H
NMR (400 MHz, CDCl3): δ = 3.91 (s, 3H, OCH3), 3.92 (s, 3H, OCH3),
6.10–6.13 (m, 2H, CHTh), 6.95 (d, 1H, J =4.0 Hz, CHTh), 6.99 (d, 1H, J
=4.0 Hz, CHTh), 7.04 (d, 1H, J =4.0 Hz, CHTh), 7.11 (d, 1H, J =4.0 Hz,
CHTh), 7.27 (d, 1H, J =4.0 Hz, CHTh), 7.58 (d, 1H, J =4.0 Hz, CHTh) ppm;
13C NMR (100 MHz, CDCl3): δ = 60.4, 60.5, 83.7, 84.2, 88.7, 90.1,
102.1, 104.5, 104.6, 108.8, 122.7, 124.1, 129.1, 131.5, 131.8, 131.9,
132.8, 138.2, 168.1 ppm; 19F NMR (376 MHz, CDCl3): δ =143.42 ppm;
HRMS (MALDI), m/z: calcd. for C28H14F4O2S+4 585.9813 [M]+; found
585.9815.
4.3. 1,4-Bis[(5′′-methoxy-2′′,2′-bithiophene)-5′-yl]-2,3,5,6-
tetrafluorobenzene 2
The title compound was synthesized from bis(5-bromothiophene-2-
yl)tetrafluorobenzene 8 (118 mg, 0.25 mmol) and 5-methoxythio-
phene-2-yl boronic acid pinacol ester
9 (180 mg, 0.75 mmol)
following the general procedure for Suzuki-Miyaura cross-coupling.
Twofold decantation gave dark brown solid 2 (80 mg, 60 %): mp 270 ◦C
4.7. 1,4-Bis{4′-[(5′′-methoxythiophene-2′′-yl)ethynyl]phenyl}-2,3,5,6-
(dec.); IR (HATR):
ν
2359, 1712, 1464, 1361, 1221, 965, 776 cm–1; 1H
tetrafluorobenzene 6
NMR (400 MHz, CDCl3): δ = 3.92 (s, 6H, OCH3), 6.16 (d, 2H, J =4.0 Hz,
CHTh), 6.91 (d, 2H, J =4.0 Hz, CHTh), 7.05 (d, 2H, J =4.0 Hz, CHTh), 7.55
(d, 2H, J =4.0 Hz, CHTh) ppm; 13C NMR (100 MHz, CDCl3): δ = 52.1,
103.2, 117.2, 131.5, 132.2, 136.0, 136.7, 166.9, 179.9 ppm; 19F NMR
(376 MHz, CDCl3): δ = 141.31 ppm; HRMS (MALDI), m/z: calcd. for
The title compound was synthesized from 1,4-diiodotetrafluoroben-
zene (233 mg, 0.58 mmol) and 4-[(5′-methoxythiophene-2′-yl)ethynyl]
phenyl boronic acid pinacol ester 14 (490 mg, 1.44 mmol) following the
general procedure for Suzuki-Miyaura cross-coupling. Twofold decan-
tation gave brown solid 6 (128 mg, 45 %): mp 120 ◦C (dec.); IR (HATR):
C
24H14F4O2S+4 537.9813 [M]+; found 537.9841.
ν
2360, 1710, 1420, 1361, 1220, 820, 777 cm–1
;
1H NMR (400 MHz,
4.4. 1,4-Bis[4′-(5′′-methoxythiophene-2′′-yl)phenyl]-2,3,5,6-
CDCl3): δ = 3.91 (s, 6H, OCH3), 6.11 (d, 2H, J =4.0 Hz, CHTh), 6.96 (d,
2H, J =4.0 Hz, CHTh), 7.52–7.57 (m, 8H, CHPh) ppm; 13C NMR (100
MHz, CDCl3): δ = 60.4, 84.6, 91.1, 104.4, 109.7, 122.7, 127.0, 131.0,
131.9, 140.0, 167.4 ppm; 19F NMR (376 MHz, CDCl3): δ =147.20 ppm;
HRMS (MALDI), m/z: calcd. for C32H18F4O2S+2 574.0684 [M]+; found
574.0677.
tetrafluorobenzene 3
The title compound was synthesized from 1,4-diiodotetrafluoroben-
zene (167 mg, 0.42 mmol) and 4-(5′-methoxythiophene-2′-yl)phenyl
boronic acid pinacol ester 11 (332 mg, 1.05 mmol) following the general
procedure for Suzuki-Miyaura cross-coupling. Twofold decantation gave
ocher solid 3 (131 mg, 59 %): mp 213 ◦C; IR (HATR):
ν
2359, 1712,
4.8. 1,4-bis[(5′-methoxythiophene-2′-yl)ethenyl]-2,3,5,6-
1425, 1361, 1220, 818, 768 cm–1; 1H NMR (400 MHz, CDCl3): δ = 3.93
(s, 3H, OCH3), 3.94 (s, 3H, OCH3), 6.19–6.22 (m, 2H, CHTh), 6.99 (d, 1H,
J =4.0 Hz, CHTh), 7.05 (d, 1H, J =4.0 Hz, CHTh), 7.48–7.59 (m, 8H,
CHPh) ppm; 13C NMR (100 MHz, CDCl3): δ = 60.5, 105.1, 105.2, 120.9,
121.8, 125.0, 125.4, 125.6, 127.3, 130.8, 133.9, 135.8, 138.8, 166.3
ppm; 19F NMR (376 MHz, CDCl3): δ =147.57 ppm; HRMS (MALDI), m/z:
tetrafluorobenzene 7
Product 7 was synthesized via modified literature procedure. [43] A
25 mL Schlenk flask was charged with tetraethyl((perfluoro-1,
4-phenylene)bis(methylene))bis(phosphonate) 17 (450 mg, 1.00
mmol), 5-methoxythiophene-2-carbaldehyde (355 mg, 2.50 mmol) and
7

´
J. Kulhanek et al.
Journal of Fluorine Chemistry 243 (2021) 109735
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anhydrous THF (15 mL) and purged with argon. Potassium tert-butoxide
(280 mg, 2.50 mmol) in anhydrous THF (5 mL) was slowly added via
syringe at RT. The reaction mixture was stirred at 25 ◦C overnight. The
mixture was quenched with water (50 mL) and the precipitate was
filtered off. Twofold decantation of the crude product gave orange solid
7 (352 mg, 83 %): mp 225 ◦C; IR (HATR):
ν 2359, 1712, 1452, 1419,
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1194, 1047, 737 cm–1
;
1H NMR (400 MHz, CDCl3): δ = 3.92 (s, 6H,
OCH3), 6.12 (d, 2H, J =4.2 Hz, CHTh), 6.55 (d, 2H, J =16.4 Hz, CH), 6.79
(d, 2H, J =4.2 Hz, CHTh), 7.43 (d, 2H, J =16.4 Hz, CH) ppm; 13C NMR
(100 MHz, CDCl3): δ = 60.4, 104.7, 110.3, 127.6, 129.5, 130.8, 167.9
ppm; 19F NMR (376 MHz, CDCl3): δ =148.66 ppm; EIMS (70 eV) m/z
(rel. int.): 426 (M+, 93), 411 (100), 396 (46); HRMS (MALDI), m/z:
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Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
[17] L. Xie, D. Liu, New tetrafluorophenylene/carbazole hybrid host materials for
phosphorescence organic light-emitting diodes, New J. Chem. 42 (2018)
15397–15404, https://doi.org/10.1039/c8nj03453b.
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units by direct arylation for organic electronics, Chem. Asian J. 14 (2019)
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Acknowledgements
[19] S. Hayashi, A. Takigami, T. Koizumi, Solvent control over supramolecular gel
formation and fluorescence for a highly crystalline π-Conjugated polymer, Chem.
Authors appreciate financial support from the project “High-sensi-
tive and low-density materials based on polymeric nanocomposites” -
NANOMAT (No. CZ.02.1.01/0.0/0.0/17_048/0007376) and grant
LM2018103 from the Ministry of Education, Youth and Sports of the
Asian J. 13 (2018) 2014–2018, https://doi.org/10.1002/asia.201800941.
[20] Z.S. Parr, R. Halaksa, P.A. Finn, R.B. Rashid, A. Kovalenko, M. Weiter, J. Rivnay,
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J. Krajcovic, C.B. Nielsen, Glycolated thiophene-tetrafluorophenylene copolymers
for bioelectronic applications: synthesis by direct heteroarylation polymerisation,
ChemPlusChem. 84 (2019) 1384–1390, https://doi.org/10.1002/cplu.201900254.
´
Czech Republic. This article is dedicated to Prof. Grzegorz Mloston to his
[21] S. Hayashi, Elastic organic crystals of π-conjugated molecules: anisotropic densely
70th birthday anniversary.
packed supramolecular 3D polymers exhibit mechanical flexibility and shape
tunability, Polym. J. 51 (2019) 813–823, https://doi.org/10.1038/s41428-019-
0201-8.
Appendix A. Supplementary data
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Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.jfluchem.2021.10
9735.
´
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[23] M. Speratova, J. Jedyrka, O. Pytela, I.V. Kityk, A.H. Reshak, F. Bures, M. Klikar,
Novel dibenzothiophene chromophores with peripheral barbituric acceptors,
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[24] J. Tydlitat, S. Achelle, J. Rodríguez-Lopez, O. Pytela, T. Mikýsek, N. Cabon,
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F. Robin-le Guen, D. Miklík, Z. Růzickova, F. Bures, Photophysical properties of
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9