Accessing π-expanded heterocyclics beyond dibenzothiophene: Syntheses and properties of phenanthrothiophenes

Article abstract of DOI:10.1002/jccs.201900509

A series of phenanthrothiophenes are designed and synthesized from polyarylthiophenes through regioselective Scholl reactions in one step using iron chloride as catalyst. The molecular structures of these heteroarenes displayed multiple twisted fjords, which perturb the shapes of the polycyclic frameworks to pack in slipped to near-perfect face-to-face styles in parallel or antiparallel packings. Field-effect transistor devices using single crystals of 6,12-difluorodiphenanthro[9, 10-b:9′, 10′]thiophene gave a hole mobility of 0.22 cm² V^?1 s^?1.

Full text of DOI:10.1002/jccs.201900509

Received: 25 December 2019
DOI: 10.1002/jccs.201900509
Accepted: 23 January 2020
S P E C I A L I S S U E P A P E R
Accessing π-expanded heterocyclics beyond
dibenzothiophene: Syntheses and properties
of phenanthrothiophenes
Samala Venkateswarlu1,2,3 | Suhendro Purbo Prakoso2,3
Yu-Tai Tao1
| Sushil Kumar1
|
1Institute of Chemistry, Academia Sinica,
Abstract
Taipei, Taiwan
2Taiwan International Graduate Program,
Sustainable Chemical Science and
Technology, Academia Sinica, Taipei,
Taiwan
3Department of Applied Chemistry,
National Chiao Tung University, Hsinchu,
Taiwan
A series of phenanthrothiophenes are designed and synthesized from pol-
yarylthiophenes through regioselective Scholl reactions in one step using iron
chloride as catalyst. The molecular structures of these heteroarenes displayed mul-
tiple twisted fjords, which perturb the shapes of the polycyclic frameworks to pack
in slipped to near-perfect face-to-face styles in parallel or antiparallel packings.
Field-effect transistor devices using single crystals of 6,12-difluorodiphenanthro[9,
10-b:90, 100]thiophene gave a hole mobility of 0.22 cm2 V−1 s−1.
Correspondence
Yu-Tai Tao, Institute of Chemistry,
Academia Sinica, Taipei, 115, Taiwan.
Email: ytt@gate.sinica.edu.tw
K E Y W O R D S
crystal packing, phenanthrothiophenes, scholl reactions, semiconducting molecules
Funding information
Ministry of Science and Technology,
Taiwan, Grant/Award Number: 108-2113-
M-001-022
1 | INTRODUCTION
organic electronics.[4] In the presence of one or more het-
eroatoms, such as sulfur, selenium, nitrogen, phospho-
In the past several decades, organic semiconducting
materials have evolved into prominent materials due to
their potential applications in flexible organic electronics,
such as organic light-emitting diodes, organic field-effect
transistors, photovoltaics, etc.[1] Yet, the availability of
new organic semiconducting molecules, normally with
an extended π-conjugation, are essential to the sustained
progress of organic electronics.[2] The π-conjugated poly-
cyclic aromatic hydrocarbons (PAHs) and polycyclic
heteroarenes (PHs) have been excellent candidates due to
their narrow bandgap, tunable absorption/emission prop-
erties, and possibly high charge mobility, which are the
required properties in many electronic applications.[3]
Mullen, Nuckolls, and others have studied PAHs exten-
sively and demonstrated their potential applications in
rus, and others in PHs, a great variety of new possibilities
in molecular shape, packing, redox property, optical
property, or charge mobility appears.[5] Among them, the
sulfur-containing PHs, such as thiophene-incorporated
polyaromatics, are of particular interest.[6] Fusion of ben-
zene and thiophene units in linear and angular ways
results in derivatives like dibenzothiophenes, ben-
zonaphthothiophenes, and dinaphthothiophenes, which
offer useful optical and semiconducting properties in
these materials.[7] The framework expansion beyond pla-
nar dibenzothiophene into nonplanar frameworks is also
interesting considering the possible co-facial packing
motifs and thus greater electronic couplings expected
between neighboring molecules for charge transfer.[8]
Diphenanthro[9,10-b:90,100-d]thiophene (DPT), which
© 2020 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2020;1–9.
http://www.jccs.wiley-vch.de
1

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VENKATESWARLU ET AL.
has a twisted framework due to several fjords in the mol-
ecule, was reported previously through a zinc-catalyzed
reaction.[9] Nevertheless, there had been no report on the
substituted derivatives, nor the properties such as crystal
packing, photophysical, and redox properties. Recently,
we reported a new series of benzo[3,4]phenanthro[1,2-b]
benzo[3,4]phenanthro[2,1-b]thiophene derivatives, from
which we observed that the substituents have much
impact on the crystal packing and thus the charge mobil-
ity achievable with these materials.[10] Here, we wish to
report the syntheses, characterization, and structural
properties of substituted DPTs. In our previous reports on
nitrogen-incorporated PHs, the phenanthrene- and
tetracene-fused carbazoles were obtained from respective
polyaryl-substituted carbazoles via simple Scholl reac-
tions.[11] Similarly, phenanthrotriphenylenes were suc-
cessfully prepared by performing Scholl reactions on
tetraphenylbenzenes (Scheme 1).[12]
In this work, we report the designs and syntheses of a
series of DPTs from respective polyarylthiophenes with
the Scholl reactions as the key step, using iron chloride
as the catalyst. Regioselective annulation reactions
occurred, yielding twisted PHs. The crystal packing,
photophysical, HOMO–LUMO energy levels, and other
properties were measured and compared. Among
them, the single-crystals of 6,12-difluorodiphenanthro
[9,10-b:90,100-d]thiophene were used to fabricate single-
crystal field-effect transistor devices, from which a hole
mobility up to 0.22 cm2 V−1 s−1 was obtained.
For the present conversions of polyarylthiophenes
4–7 and 9–13 to DPTs, we found that iron chloride was
suitable catalyst, except in the case of parent DPT, where
chlorination occurred at 6,12-positions. Nevertheless, the
aluminum chloride served the purpose well to give the
desired product, only after long reaction time (Scheme 4).
The polyarylthiophenes 5–7, with two R groups such as
methyl, fluoro, and chloro groups, gave Me-DPT, Flu-
DPT, and Cl-DPT, respectively, with iron chloride was
the annulation agent (Scheme 4). With different R sub-
stituents, the time required for Scholl reaction varied
from 0.5 h to 36 h, while reaction yields of annulated
products were no lower than 90% (Table 1, entries 1–9).
A shorter reaction time was needed for the methyl-
substituted polyarylthiophenes compared to the ones
with chlorine, fluorine substituents, presumably due to
the activating effect of methyl group versus others on the
cationic intermediate involved (as shown in proposed
mechanism in Scheme S1).
The Scholl reactions of polyarylthiophenes with four
R groups are shown in Scheme 5. Polyarylthiophenes
9–11 gave Me-DPT1, Flu-DPT1, and Cl-DPT1 success-
fully, whereas 12–13, in which eight fluorine atoms or
four trifluoromethyl groups are involved, could not be
annulated to give TFM-DPT and PFlu-DPT (Scheme 5,
Table 1, entries 8–9), again due to the deactivating effect
of multiple electron-withdrawing groups.[14]
Although cyclization at the fjord at the top will give a
six-membered ring of DBPT, this was not observed, possi-
bly because of the strain involved at the fjord. Other
annulated products such as Ph-BTT were not observed
either, agreeing with the proposed reaction mechanism
S1 (SI).
2 | RESULTS AND DISCUSSIONS
Schemes 2 and 3 show the preparations of pol-
yarylthiophenes 4–7 and 9–13 precursors, while
Schemes 4 and 5 present the syntheses of DPTs. Many
catalysts have been reported to effect the Scholl reactions.
These include iron chloride, copper salts, aluminum
chloride, DDQ with acid, and a few others, although
some complications may arise depending on the specific
cases.[13]
SCHEME 2 Preparation of polyarylthiophenes (4–7)
SCHEME 1 Representation of
Scholl reactions successfully aimed
by our group

VENKATESWARLU ET AL.
3
TABLE 1 Conversions of polyarylthiophenes (4–13) to the
annulated derivatives (DPTs) through iron/aluminum
chloride-mediated annulation reactions
Entry Reactant Product
Yield (%)a Time (hr)a
1
2
3
4
5
6
7
8
9
4
DPTb
90
98
91
95
98
92
94
—
—
18
0.5
4
5
Me-DPT
Flu-DPT
Cl-DPT
6
7
3
SCHEME 3 Preparation of polyaryl thiophenes (9–13)
9
Me-DPT1
Flu-DPT1
Cl-DPT1
TFM-DPTc
PFluc
0.5
14
12
36
36
10
11
12
13
aYields and time are given for iron chloride-mediated Scholl reactions.
bAluminum chloride-mediated annulation reaction.
cUnsuccessful Scholl reactions.
(a)
(c)
(b)
(d)
Representation of the twist angles
DPT
SCHEME 4 Preparation of disubstituted DPTs
Flu-DPT
Cl-DPT
FIGURE 1 Molecular structures of DPT, Flu-DPT, and Cl-
DPT, showing twist angles
successfully solved. Crystal structure analyses revealed
that these DPTs contain three twisted fjords (bridges a, b
and c) in their frameworks (Figure 1). The twist angle of
the fjord varies from 19ꢀ to 23ꢀ. Smaller twist angles (~4ꢀ
to ~10ꢀ) are observed for other two fjords.
The different twists in the fjords may contribute or
perturb their cofacial packing (Figure 2). The introduc-
tion of heteroatom into the framework results in a molec-
ular dipole (Table S1), which may also impact the
packing motifs. In the case of DPT series, near cofacial
packing and thus good π-π overlap of the frameworks for
nearest neighbors was obtained for DPT and Cl-DPT, pre-
sumably due to geometric complementarity, and possibly
the Cl…Cl interaction.[16]
SCHEME 5 Preparation of polysubstituted DPTs
2.1 | Single-crystal X-ray analyses
Single crystals of these thiophene derivatives were grown
by the physical vapor transport (PVT) method.[15] Among
them, crystal structures of three derivatives were
Whereas the Flu-DPT adopts antiparallel packing for
nearest neighbors, presumably because the molecular

4
VENKATESWARLU ET AL.
1.2
1.0
0.8
0.6
0.4
0.2
0.0
(a)
(c)
(b)
(d)
DPT
Me-DPT
Flu-DPT
Cl-DPT
(e)
(f)
300
350
400
450
Wavelength (nm)
FIGURE 4 Normalized UV–Vis (in DCM) spectra of
diphenanthrothiophenes (DPTs)
FIGURE 2 Packing motifs of (a,b) DPT, (c,d) Flu-DPT, and
(e,f) Cl-DPT
F-C (2.57 Å), C-H…Cl-C (3.06 Å) contacts (Figure 3), pos-
sibly because of the electronic effects two fluorines and
chlorines on the respective polycyclic frameworks. The
twisted geometries with cofacial packing of DPTs were
expected to contribute to their photophysical properties
as well.
(a)
(b)
2.2 | Photophysical, electrochemical, and
thermal properties
The UV–Vis spectra of the DPTs are shown in Figure 4
and S39a, with pertinent values given in Table 2. As seen
in Figure 4, the parent DPT gives three absorption bands
centered at the wavelengths of 286, 344, and 359 nm
respectively.
The absorption profile of this heteroarene was charac-
teristic of that observed for the benzothiophene deriva-
tives.[18] Bathochromic shift was noticed in its absorption
profile compared to the dibenzothiophene. The absorp-
tion spectra of the substituted DPTs gave further shifts,
depending on the electronic effects that methyl, fluorine,
and chlorine substituents could exert on the parent DPT.
These compounds showed deep blue emission in their
dilute solutions (Figure S39b–c). Like the absorption, the
substituted DPTs showed shifts in their emission profiles
depending on the substituent. In addition to photo-
physical properties, other properties such as HOMO and
LUMO of DPTs were determined both theoretically and
experimentally (using AC–2). HOMO plots of DPTs indi-
cate electron distribution over the thiophene portion and
the linearly fused benzenes (Figure S40). The HOMO
energy level is slightly altered by the substituents it
FIGURE 3 Packing motifs of (a) Flu-DPT and (b) Cl-DPT
showing C-F…H-C and C-Cl…H-C interactions
dipole is dominating the packing so as to minimize the
static repulsion. The twists in the molecule force the
framework to shift in their packing, reducing their π-π
overlaps. In their cofacial packing motifs, the π-π stacking
distance, as measured between the two planes containing
neighboring molecules, were found to be 3.62 Å to
3.72 Å. The packing motifs of DPTs were further exam-
ined to reveal interesting short contacts.[17] The fluoro-
and chloro-substituted derivatives such as Flu-DPT and
Cl-DPT, unlike the parent hydrocarbons, displayed C-H…

VENKATESWARLU ET AL.
5
TABLE 2 Photophysical data and HOMO−LUMO energies and thermal decomposition temperatures of DPTs
Compd.
DPT
λabs (nm)
λem. (nm)
402
EHOMO (eV)a
ELUMO (eV)b
Eg (eV)c
3.29
Td (ꢀC)d
316
359, 344, 286 (max)
364, 346, 287 (max)
356, 340, 286 (max)
368, 348, 288 (max)
366, 348, 288 (max)
354, 340, 282 (max)
367, 349, 289 (max)
5.66
5.50
5.90
5.89
5.45
—
2.37
2.25
2.64
2.64
2.22
—
Me-DPT
Flu-DPT
Cl-DPT
Me-DPT1
Flu-DPT1
Cl-DPT1
406
3.25
319
405
3.26
313
410
3.25
366
409
3.23
341
412
3.25
311
413
—
—
3.20
363
aEHOMO was recorded by using photoelectron spectrometer.
bELUMO = EHOMO − Eg.
cOptical bandgap, Eg, was determined from the intersections of normalized UV–Vis and emission spectra.
dThermal decomposition temperatures measured at 5% weight loss.
(a)
(b)
0.00
-0.05
-0.10
-0.15
-0.20
-0.25
-0.30
-0.35
1.0
0.8
0.6
0.4
0.2
0.0
10-6
10-7
10-8
10-9
10-10
VD: -60V
VG: -20 to -100V; Step: -16V
-100
-80
-60
-40
-20
0
-100
-80
-60
-40
-20
0
VD (V)
VG (V)
FIGURE 5 (a) Output characteristics of SCFET based on compound Flu-DPT. (b) transfer characteristics
carries, as shown in Table 2. These derivatives have good
thermal stability, with their Td values well above 300ꢀC (-
Figure S41, Table 2).
single-crystals. The maximum mobility was calculated to
be 0.22 cm2 V−1 s−1, while the on/off ratio was recorded
as high as 2.86 × 104 (Figure 5, Table S2).
2.3 | SCFET performance
3 | CONCLUSIONS
Single-crystal-based field-effect transistors (SCFETs) were
attempted for these derivatives.[19] Nevertheless, except
Flu-DPT, all other derivatives did not yield large enough
crystals for device fabrication. Thus, Flu-DPT single crys-
tal was used as the channel material in the fabrication of
a top-contact, top-gate device on glass substrate, with
painted colloidal graphite as the source, drain, and gate
electrodes, respectively. A thin layer of parylene grown
on the single crystal served as the dielectric material. The
channel length, width, and parylene thickness were mea-
sured to be 1.0–0.5 mm, 0.25–0.20 mm, and 1.8–2.5 μm,
respectively.
In conclusion, we synthesized a series of substituted
diphenanthrothiophenes from polyarylthiophenes. The
Scholl reactions of these polyarylthiophenes were
regioselective in the annulation step. The newly prepared
DPTs were characterized by spectroscopic techniques
including nuclear magnetic resonance (NMR), mass spec-
trometry, UV absorption, and further by single-crystal
X-ray analyses for selected ones. The X-ray analyses show
cofacial π-π stackings either in parallel or antiparallel
fashion. The potential of these derivatives as
semiconducting materials was demonstrated by the sin-
gle-crystal field-effect transistors based on 6,12-difluoro
diphenanthro[9,10:b]thiophene, which produced a maxi-
mum p–channel mobility of 0.22 cm2 V−1 s−1 and an
An average field-effect mobility of 0.14 cm2 V−1 s−1
was obtained from the 17 devices made using Flu-DPT

6
VENKATESWARLU ET AL.
average mobility of 0.16 cm2 V−1 s−1, with an on/off ratio
more than 104.
reaction. A 250 ml round-bottom flask was charged with
3,4-diphenyl-2,5-dibromothiophene (3) (1.0 mmol), aryl
boronic acid (2.1 mmol), PdCl2(PPh3)2 (36 mg),
triphenylphosphine (PPh3) (26 mg) aq. potassium carbon-
ate (1.39 g, 10.0 mmol, in 15 ml water), and toluene
(50 ml) was added to it. This reaction, under an inert
atmosphere, was conducted for 18 hr at 110ꢀC. While the
Suzuki coupling reaction progressed, the conversion of
product was monitored by using thin layer chromatogra-
phy. Cooling to room temperature led to two layers,
from which the toluene layer was separated. Column
chromatographic separation, using a mixture of dic-
hloromethane and hexane, followed by solvent evapora-
tion gave pure polyarylthiophenes.
General Suzuki C-C cross-coupling (protocol II): The
preparation of polyarylthiophenes (4 and 9–13) was car-
ried out in the following way using general Suzuki C-C
cross-coupling reaction. A 250 ml round-bottom flask
was charged with tetrabromothiophene (8) (1.0 mmol),
aryl boronic acid (4.1 mmol), PdCl2(PPh3)2 (72 mg),
triphenylphosphine (PPh3) (52 mg) aq. potassium carbon-
ate (2.77 g, 20.0 mmol, in 30 ml water), and toluene
(100 ml) was added to it. This reaction, under an inert
atmosphere, was conducted for 24 hr at a temperature of
110ꢀC. While the Suzuki coupling reaction progressed,
the conversion of product was monitored by using thin
layer chromatography. Cooling to room temperature gave
two layers, from which toluene layer was separated. Col-
umn chromatographic separation, using a mixture of dic-
hloromethane and hexane, followed by solvent removal
gave pure polyarylthiophenes.
4 | EXPERIMENTAL SECTION
The needed starting materials were directly purchased
from the commercial sources. The starting materials
such as 2,5-dibromo-3,4-diphenylthiophene (3),[20]
2,3,4,5-tetraphenylthiophene (4),[21] and 2,3,4,5-tetrakis
(4-trifluoromethylphenyl) thiophene (12)[22] were synthe-
sized according to literature reports. The coupling reac-
tions such as Suzuki and Scholl reactions were carried out
under inert atmosphere condition. The compounds were
purified by column chromatography over silica gel
(60–230 mesh). Solvents were distilled and dried before
performing spectrophotometric and spectrofluorimetric
analyses. Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker Avance III-400 MHz spectrometer in
CDCl3. UV–Vis spectra were recorded by using U-3310
UV/VIS spectrophotometer and fluorescence spectra were
measured on a HITACHI F-4500 fluorescence spectropho-
tometer. The HOMO energies were recorded using photo-
electron spectrometer AC-2 (Riken Keiki). HOMO-LUMO
plots were obtained from Spartan Pro program by the
semiempirical method at the AM1 level.
4.1 | 2,5-dibromo-
3,4-diphenylthiophene (3)[20]
In the absence of light, a DMF solution of N-
bromosuccinamide (10.4 g, 58.4 mmol) was added
dropwise to a solution of 3,4-diphenylthiophene (2)
(6.70 g, 28.3 mmol) in DMF (45 mL) at 0ꢀC. The reaction
mixture was stirred at 0ꢀC for 1 hr, followed by stirring
for 15 hr at room temperature. The reaction was moni-
tored using thin layer chromatography and after the
starting material was consumed completely, water was
added to the reaction mixture. The product was extracted
with dichloromethane. Removal of dichloromethane by
using a rotary evaporator gave the crude product, which
was then recrystallized from ethanol to give the pure and
colorless crystals. Yield: 10.2 g, 90%.
Preparation of 2,3,4,5-tetraphenylthiophene (4):[21]
General Suzuki C-C cross-coupling (protocol II) was used
to get compound 4, by reacting tetrabromothiophene (8)
with 4-phenylboronic acid (0.50 g, 4.1 mmol). Yield:
0.35 g, 89%. Spectroscopic characterization data of this
compound are available in the ref. [21].
Preparation
of
2,5-bis(4-methylphenyl)-3,4-dip-
henylthiophene (5): General Suzuki C-C cross-coupling
(protocol I) was used to get compound 5, by
reacting 3,4-diphenyl-2,5-dibromothiophene (3) with
4-methylphenylboronic acid (0.29 g, 2.1 mmol). Yield:
1
0.38 g, 91%. H NMR (CDCl3, 400 MHz) δ: 7.14–7.12 (m,
10H), 7.03–6.97 (m, 8H), 2.31 (s, 6H). 13C NMR (CDCl3,
100 MHz) δ: 139.1, 138.3, 136.9, 136.7, 131.4, 130.9, 129.0,
127.8, 126.5, 21.1. HRMS [MALDI-TOF] m/z {M+} calcd
for C30H24S 416.1599; found 416.1595.
4.2 | General synthetic protocols for the
preparation of polyaryl thiophenes (4–7
and 9–13)
Preparation of 2,5-bis(4-fluorophenyl)-3,4-diphenyl-
thiophene (6): General Suzuki C-C cross-coupling (proto-
col I) was used to get compound 6, by reacting
3,4-diphenyl-2,5-dibromothiophene (3) with 4-fluoro-
phenylboronic acid (0.30 g, 2.1 mmol). Yield: 0.40 g, 94%.
1H NMR (CDCl3, 400 MHz) δ: 7.21–7.17 (m, 4H),
General Suzuki C-C cross-coupling (protocol I): The prepa-
ration of polyarylthiophenes (5–7) was carried out in the
following way using general Suzuki C-C cross-coupling

VENKATESWARLU ET AL.
7
7.14–7.10 (m, 6H), 6.94–6.89 (m, 8H). 13C NMR (CDCl3,
100 MHz) δ: 163.3, 160.9, 139.6, 137.3, 136.2, 130.9, 130.8,
130.8, 130.3, 127.9, 126.8, 115.4, 115.2. HRMS [MALDI-
TOF] m/z {M+} calcd for C28H18F2S 424.1097; found
424.1092.
Preparation of 2,3,4,5-tetrakis(3,5-difluorophenyl)thio-
phene (13): General Suzuki C-C cross-coupling (protocol
II) was used to get compound 13, by reacting
tetrabromothiophene (8) with 3,5-difluorophenylboronic
acid (0.65 g, 4.1 mmol). Yield: 0.32 g, 61%. 1H NMR
(400 MHz, CDCl3) δ: 6.49–6.50 (m, 4H), 6.69–6.77 (m,
8H). 13C NMR (CDCl3, 100 MHz) δ: 164.2, 164.1, 164.1,
164.0, 161.7, 161.7, 161.6, 161.5, 138.2, 138.0, 137.9, 137.8,
137.7, 135.7, 135.6, 135.5, 113.5, 113.4, 113.3, 113.2, 112.2,
112.1, 112.0, 111.9, 104.1, 103.9, 103.8, 103.6, 103.6, 103.4.
HRMS [MALDI-TOF] m/z {M+} calcd for C28H12F8S
532.0532; found 532.0544.
Preparation
of
2,5-bis(4-chlorophenyl)-3,4-dip-
henylthiophene (7): General Suzuki C-C cross-coupling
(protocol I) was used to get compound 7, by reacting
3,4-diphenyl-2,5-dibromothiophene (3) with 4-chloro-
phenylboronic acid (0.33 g, 2.1 mmol). Yield: 0.42 g, 92%.
1H NMR (CDCl3, 400 MHz) δ: 7.20–7.10 (m, 14H), 6.94
(d J = 7.6 Hz, 4H). 13C NMR (CDCl3, 100 MHz) δ: 140.1,
137.4, 136.0, 133.4, 132.6, 130.7, 130.4, 128.6, 128.1, 126.9.
HRMS [MALDI-TOF] m/z {M+} calcd for C28H18Cl2S
456.0506; found 456.0504.
Preparation of diphenanthro[9,10-b:90,100-d]thiophene
(DPT): This compound was prepared by
a
cyclodehydrogenation protocol using compound 4 with a
mixture of Cu(II)trifluoromethanesulfonate and alumi-
num(III)chloride. In a standard procedure, a 500 mL
round-bottom flask was charged with 2,3,4,5-
tetraphenylthiophene (4) (0.39 g, 1.0 mmol), Cu(II)
trifluoromethanesulfonate (4.35 g, 12.0 mmol), and
aluminum(III) chloride (1.6 g, 12.0 mmol), followed by
the addition of CS2 (200 mL). Stirring under nitrogen for
18 h and standing as such for 2 h afforded product as pre-
cipitates from the solution. The crude product was fil-
tered and washed with aq. HCl, 10% ammonium
hydroxide solution, and methanol to remove the copper
and aluminum salts remained in the products. The dried
solid was characterized to be the desired product. Yield:
0.35 g, 90%. Further sublimation at 320ꢀC/270ꢀC/220ꢀC
under vacuum (7.8 × 10−5 Torr) give 0.19 g pure product
(Yield: 54%). Mp: 268–269ꢀC. 1H NMR (CDCl3, 400 MHz)
δ: 8.78–8.73 (m, 6H), 8.28–8.25 (m, 2H), 8.71–7.66 (m,
6H), 7.55 (t, J = 8.0 Hz, 2H). 13C NMR (CDCl3, 100 MHz)
δ: 137.4, 131.7, 130.1, 129.8, 129.2, 128.2, 127.5, 127.0,
126.9, 126.1, 125.3, 124.6, 123.8, 123.4. HRMS [MALDI-
TOF] m/z {M+} calcd for C28H16S 384.0973; found
384.0974.
Synthesis of 2,3,4,5-tetrakis(4-methylphenyl)thiophene (9):
General Suzuki C-C cross-coupling (protocol II) was used
to get compound 9, by reacting tetrabromothiophene (8)
with 4-methylphenylboronic acid (0.56 g, 4.1 mmol). Yield:
0.40 g, 91%. 1H NMR (CDCl3, 400 MHz) δ: 7.12 (d,
J = 8.0 Hz, 4H), 7.02 (d, J = 8.0 Hz, 4H), 6.92 (d,
J = 8.0 Hz, 4H), 6.84 (d, J = 8.0 Hz, 4H), 2.30 (m, 6H), 2.26
(m, 6H). 13C NMR (CDCl3, 100 MHz) δ: 139.2, 138.0, 136.8,
135.9, 133.8, 131.7, 130.8, 129.1, 129.0, 128.6, 21.3, 21.2.
HRMS [MALDI-TOF] m/z {M+} for C32H28S 444.1912;
found 444.1912.
Preparation of 2,3,4,5-tetrakis(4-fluorophenyl)thio-
phene (10): General Suzuki C-C cross-coupling (protocol
II) was used to get compound 10, by reacting
tetrabromothiophene (8) with 4-fluorophenylboronic acid
1
(0.57 g, 4.1 mmol). Yield: 0.43 g, 93%. H NMR (CDCl3,
400 MHz) δ: 7.20–7.16 (m, 4H), 6.96–6.82 (m, 12H). 13C
NMR (CDCl3, 100 MHz) δ: 163.4, 163.0, 161.0, 160.6,
138.3, 137.7, 132.4, 132.3, 132.0, 130.9, 130.8, 129.9, 115.6,
115.4, 115.3, 115.1. HRMS [MALDI-TOF] m/z {M+} calcd
for C28H16F4S 460.0909; found 460.0911.
Preparation of 2,3,4,5-tetrakis(4-chlorophenyl)thio-
phene (11): General Suzuki C-C cross-coupling (protocol
II) was used to get compound 11, by reacting
tetrabromothiophene (8) with 4-chlorophenylboronic
acid (0.64 g, 4.1 mmol). Yield: 0.48 g, 92%. 1H NMR
(CDCl3, 400 MHz) δ: 7.22 (d, J = 8.4 Hz, 4H), 7.15–7.11
(m, 8H), 6.85 (d, J = 8.4 Hz, 4H). 13C NMR (CDCl3,
100 MHz) δ: 138.3, 138.1, 134.1, 133.75, 133.2, 132.1,
132.0, 130.4, 128.8, 128.5. HRMS [MALDI-TOF] m/z
{M+} calcd for C28H16Cl4S 523.9727; found 523.9721.
Preparation of 2,3,4,5-tetrakis(4-trifluoromethylphenyl)
thiophene (12): General Suzuki C-C cross-coupling (pro-
tocol II) was used to get compound 12, by reacting
tetrabromothiophene (8) with 4-trifluoromethylphenyl
boronic acid (0.78 g, 4.1 mmol). Yield: 0.54 g, 81%. Spec-
troscopic characterization data of this compound was
available in the ref. [22].
4.3 | General method of Scholl reaction
for the preparation of DPTs
The Scholl reaction between polyarylthiophenes and iron
chloride afforded substituted DPTs. A general reaction
procedure involves the reaction between poly-
arylthiophene (1.0 mmol) with iron chloride (FeCl3)
(2.92 g, 18.0 mmol) in DCM and nitromethane (12 mL).
Thus, a solution of iron chloride in nitromethane was
added to polythiophenene in dichloromethane under
inert atmosphere. The dark reaction mixture obtained
was stirred for different length of time of 0.5-36 h,
depending on the substituent it carried. After the reaction
was complete, as judged from TLC, the product was

8
VENKATESWARLU ET AL.
precipitated by adding methanol to the reaction mixture.
The product was isolated by filtration and the filtered
solid product was washed with methanol and acetone.
124.4, 123.5, 123.2, 22.1, 21.9. HRMS [MALDI-TOF] m/z
{M+} calcd for C32H24S 440.1599; found 440.1583.
Preparation of 3,6,12,15-tetrafluorodiphenanthro[9,10-
b:90,100-d]thiophene (Flu-DPT1) A general Scholl reaction
protocol was used to get pure title compound, Flu-DPT1,
by reacting 2,3,4,5-tetrakis(4-fluoro phenyl)thiophene
(10) (0.46 g, 1.0 mmol) with iron chloride (Yield: 0.40 g,
92%). Further purification by temperature-gradient subli-
mation at 370ꢀC/320ꢀC/270ꢀC (9.5 × 10−5 Torr) gave
0.37 g (Yield: 90%). Mp: >350ꢀC. 1H NMR (CDCl3,
400 MHz) δ: 8.70–8.66 (m, 2H), 8.25–8.22 (m, 6H), 7.49
(d, J = 10.0 Hz, 2H), 7.36–7.32 (m, 2H). Due to poor solu-
bility, 13C NMR of this compound was not recorded.
HRMS [MALDI-TOF] m/z {M+} calcd for C28H12F4S
456.0596; found 456.0594.
Preparation of 3,6,12,15-tetrachlorodiphenanthro[9,10-
b:90,100-d]thiophene (Cl-DPT1): A general Scholl reaction
protocol was used to get pure title compound, Cl-DPT1,
reacting 2,3,4,5-tetrakis(4-chlorophenyl)thiophene (11)
(0.46 g, 1.0 mmol) with iron chloride (Yield: 0.49 g, 94%).
Further purification by temperature-gradient sublimation at
410ꢀC/360ꢀC/310ꢀC (9.2 × 10−5 Torr) gave 0.43 g (Yield:
87%). Mp: >350ꢀC. 1H NMR (CDCl3, 400 MHz) δ: 8.60–8.57
(m, 6H), 8.16 (d, J = 8.4 Hz, 2H), 7.69 (d, J = 8.4 Hz, 2H), 7.54
(d, J = 8.8 Hz, 2H). 13C NMR of this compound could not be
recorded due to poor solubility. HRMS [MALDI-TOF] m/z
{M+} calcd for C28H12Cl4S 519.9414; found 519.9408.
Preparation
of
6,12-dimethyldiphenanthro[9,10-
b:90,100-d]thiophene (Me-DPT): A general Scholl reaction
protocol was used to get the title compound, Me-DPT, by
reacting 3,4-diphenyl-2,5-di-p-tolylthiophene (5) with
iron chloride (Yield: 0.40 g, 98%). Further purification by
temperature-gradient sublimation at 350ꢀC/300ꢀC/250ꢀC
1
(9.8 × 10−5 Torr) gave 0.38 g (Yield: 95%). Mp: 299ꢀC. H
NMR (CDCl3, 400 MHz) δ: 8.75–8.72 (m, 4H), 8.51 (s,
2H), 8.12 (d, J = 8.0 Hz, 2H), 7.66–7.63 (m, 2H),
7.55–7.50 (m, 4H), 2.66 (s, 6H). 13C NMR (CDCl3,
100 MHz) δ: 137.1, 136.7, 131.1, 129.9, 129.8, 129.4, 129.0,
126.9, 126.1, 125.8, 125.1, 124.4, 123.8, 123.3, 22.1. HRMS
[MALDI-TOF] m/z {M+} calcd for C30H20S 412.1286;
found 412.1292.
Preparation of 6,12-difluorodiphenanthro[9,10-b:90,100-
d]thiophene (Flu-DPT): A general Scholl reaction protocol
was used to get pure title compound, Flu-DPT, by
reacting 2,5-bis(4-fluorophenyl)-3,4-diphenyl thiophene
(6) (0.43 g, 1.0 mmol) with iron chloride (Yield: 0.38 g,
91%). Further purification by temperature-gradient subli-
mation at 370ꢀC/220ꢀC/270ꢀC (9.2 × 10–5 Torr) gave
0.34 g (Yield: 90%). Mp: 340ꢀC. 1H NMR (CDCl3,
400 MHz) δ: 8.72 (d, J = 8.0 Hz, 2H), 8.61 (d, J = 8.4 Hz,
2H), 8.34 (dd, J = 13.2 Hz 3.2 Hz, 2H), 8.21–8.18 (m, 2H),
7.68 (t, J = 8.0 Hz, 2H), 7.57 (t, J = 7.6 Hz, 2H), 7.46–7.41
(m, 2H). Due to poor solubility, 13C NMR of this com-
pound was not recorded. HRMS [MALDI-TOF] m/z {M+}
calcd for C28H14F2S 420.0784; found 420.0782.
Preparation of 6,12-dichlorodiphenanthro[9,10-b:90,100-d]
thiophene (Cl-DPT) A general Scholl reaction protocol was
used to get pure title compound, Cl-DPT, by reacting 2,5-bis
(4-chlorophenyl)-3,4-diphenyl thiophene (7) (0.46 g,
1.0 mmol) with iron chloride (Yield: 0.43 g, 95%). Further
purification by temperature-gradient sublimation at
380ꢀC/3300ꢀC/280ꢀC (8.9 × 10–5 Torr) gave 0.38 g (Yield:
89%). Mp: >350ꢀC. 1H NMR (CDCl3, 400 MHz) δ: 8.75–8.66
(m, 6H), 8.18 (d, J = 8.4 Hz, 2H), 7.72–7.65 (m, 4H),
7.61–7.57 (m, 2H). Due to poor solubility, 13C NMR of this
compound was not recorded. HRMS [MALDI-TOF] m/z
{M+} calcd for C28H14Cl2S 452.0193; found 452.0200.
Preparation of 3,6,12,15-tetrakis(trifuoromethyl)diphe-
nanthro[9,10-b:90,100-d]thiophene (TFM-DPT): According
to the general Scholl reaction protocol, 2,3,4,5-tetrakis
(4-trifluoromethylphenyl)thiophene (12) (0.66 g, 1.0
mmol) reacted with iron chloride but the reaction was
not successful.
Preparation
of
2,4,5,7,11,13,14,16-octafluorodiphenanthro[9,10-b:90,100-d]
thiophene (PFlu-DPT): According to the general Scholl
reaction protocol, 2,3,4,5-tetrakis(3,5-difluorophenyl)thio-
phene (13) (0.53 g, 1.0 mmol) reacted with iron chloride
but the reaction was not successful.
ACKNOWLEDGMENT
We acknowledge the Ministry of Science and Technology,
Taiwan (Grant Number: 108-2113-M-001-022) for the
financial.
Preparation of 3,6,12,15-tetramethyldiphenanthro
[9,10-b:90,100-d]thiophene (Me-DPT1) A general Scholl
reaction protocol was used to get pure title compound,
Me-DPT1, reacting 2,3,4,5-tetrakis(4-methyl phenyl)thio-
phene (9) (0.44 g, 1.0 mmol) with iron chloride (Yield:
ORCID
Suhendro Purbo Prakoso https://orcid.org/0000-0003-
0783-7586
Yu-Tai Tao https://orcid.org/0000-0003-4507-0419
1
0.43 g, 98%). Mp: 310ꢀC. H NMR (CDCl3, 400 MHz) δ:
8.63 (d, J = 8.4 Hz, 2H), 8.50–8.49 (m, 4H), 8.10 (d,
J = 8.0 Hz, 2H), 7.49–7.47 (m, 2H), 7.36–7.34 (m, 2H),
2.63 (s, 12H). 13C NMR (CDCl3, 100 MHz) δ: 136.4, 136.2,
135.3, 131.1, 130.0, 129.5, 128.8, 127.3, 126.8, 126.5, 126.3,
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SUPPORTING INFORMATION
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How to cite this article: Venkateswarlu S,
Prakoso SP, Kumar S, Tao Y-T. Accessing
π-expanded heterocyclics beyond
dibenzothiophene: Syntheses and properties of
phenanthrothiophenes. J Chin Chem Soc. 2020;1–9.
https://doi.org/10.1002/jccs.201900509