Thioether- and sulfone-functionalized dibenzopentalenes as n-channel semiconductors for organic field-effect transistors

Article abstract of DOI:10.1039/c8tc00970h

Dibenzo[a,e]pentalenes (DBPs) are promising candidates to be used as ambipolar or n-type semiconductors in organic field-effect transistors (OFETs). For n-channel conduction, low LUMO energy levels are required. Furthermore, a close molecular packing in t

Full text of DOI:10.1039/c8tc00970h

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PAPER
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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Thioether- and sulfone-functionalized dibenzopentalenes as
n-channel semiconductors for organic field-effect transistors
Mathias Hermann,a Ruihan Wu,b David C. Grenz,a Daniel Kratzert,c Hanying Li*b and Birgit Esser*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Dibenzo[a,e]pentalenes (DBPs) are promising candidates to be used as ambipolar or n-type semiconductors in organic
field-effect transistors (OFETs). For n-channel conduction, low LUMO energy levels are required. Furthermore, a close
molecular packing in the solid state is advantageous. Here we present thioether-functionalized DBPs with LUMO energies
down to −3.47 eV as well as a DBP sulfone with a LUMO energy of −3.94 eV. X-ray crystallography revealed 1-D π-stacking
or herringbone packing in the solid state with close intramolecular distances between the DBP cores. Two thio-DBPs and
the DBP sulfone showed n-channel conduction in FET measurements on well-aligned crystals with electron mobilities of up
to 0.18 cm2 V−1 s−1, up to date the highest reported values for n-channel conduction in DBP derivatives. The short synthetic
route will in the future allow for facile access to a variety of thio- and sulfone-DBPs for n-channel or ambipolar
semiconduction.
www.rsc.org/
achieved through substitution.23–25
Introduction
Dibenzo[a,e]pentalene (DBP,
1, Fig. 1) is a low bandgap,
organic semiconductor. Its low bandgap is caused by the non-
alternant nature of its π-system due to the presence of five-
membered rings, which causes a shift in orbital energies.1
Compared to acenes, solely consisting of six-membered rings,
a lowered LUMO energy results, which has also been observed
for many other non-alternant π-systems such as fullerenes,2
pentalene derivatives,3–6 indenofluorenes,7,8 azulenes,9,10 and
others.11 This makes DBPs of particular interest for an
application as n-type or ambipolar semiconductors in organic
field-effect transistors (OFETs). Compared to p-type materials,
fewer n-type or ambipolar OFET-materials exist.12–16 Several
diacenopentalenes or other DBP derivatives have been
investigated in p-channel OFETs.17–20 To achieve a sufficiently
low LUMO level for n-channel conduction between −3 eV and
−4 eV, structural modification of the DBP core is necessary.
Here, diacenopentalene dicarboximides21 as well as the
Fig.
1 Dibenzo[a,e]pentalene (DBP, 1) and thio-DBPs 2a–d as well as sulfone 3
investigated in this study.
We have recently shown that substituents at the 5,10-
positions in DBP (Fig. 1) are particularly effective in lowering
the LUMO energy.23,25 Herein, we present DBP derivatives 2a
–
d
with thioether substituents in the 5,10-positions with low
LUMO energies and their properties in n-channel OFETs. The
LUMO energies of 2a lay between −3.16 and −3.47 eV.
Through oxidation to sulfone , the LUMO could be further
–
d
3
structurally
related
dicyanomethylene-substituted
thienoquinoidals22 have been investigated in n-channel OFETs.
lowered to −3.94 eV. FET measurements on well-aligned
crystals, obtained using the droplet-pinned crystallization
method, gave n-channel (electron) mobilities of up to
0.18 cm2 V−1 s−1.26–28 Up to date, these are the highest
reported values for n-channel conduction in DBP
derivatives.21,22
Instead of ring fusion, a lowering of the LUMO level can also be
The advantages of incorporating sulphur atoms into organic
semiconductors have long been recognized in that
thienoacenes are excellent p-type, hole-conducting
molecules.29 Compared to acenes, the incorporation of sulphur
atoms typically leads to a lowering of the HOMO energy and
thus a higher stability towards oxidation. Strong van-der-Waals
interactions between sulphur atoms favour close molecular
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packing in the solid state,30 advantageous for charge transport between two DBP units amounts to 3.254 Å (Fig. 2e), and the
in OFETs.
molecules are displaced from each other by 4.47 Å.
Scheme 1 Synthesis of thio-DBPs 2a–d and sulfone 3.
A thio-substituted DBP has been reported only once before,31
however, no optoelectronic data was acquired, and the
synthesis was rather lengthy. The synthesis of thio-DBPs 2a–d
on the other hand, is facile and can be achieved in one step
from diphenyl succindandione ( , Scheme 1) or in three steps
,
4
from commercially available phenylacetic acid.
Results and discussion
Synthesis
Reacting diphenyl succindandione (
with the corresponding thiol in the presence of phosphorus
pentoxide afforded thio-DBPs 2a in yields of 45–50% as red-
coloured solids (Scheme 1). Oxidation of phenyl-substituted 2b
with meta-chloroperoxybenzoic acid led to sulfone in high
yield of 89%. Thio-DBPs 2a showed high thermal stability of
4, for synthesis see ESI)
Fig. 2 Molecular structure and packing of 2c (a, b) and 2b (c–e) in the solid state
(hydrogen atoms are omitted for clarity; in a and c, displacement ellipsoids are shown
at 50% probability).
–
d
3
Electrochemical and optical properties
–
d
up to 312 °C (Td,10%), as measured by thermal gravimetric
analysis. In differential scanning calorimetry (DSC)
measurements, a melting and recrystallization point was
Cyclic voltammetry measurements showed amphoteric redox
behaviour for thio-DBPs 2a
reversible reduction and oxidation (Fig. 3 and Table 1), only 2d
showed an irreversible oxidation. Sulfone displayed two
–c, where each featured a
observed for 2b
–
d
, but not for 2a, which exhibited no
, decomposition started at
3
recrystallization. For sulfone
3
reversible reduction waves, but no oxidation was visible in the
electrochemical window of the solvent (CH2Cl2 or THF). HOMO
and LUMO energies (Table 1) were obtained from the onsets
of the first oxidation/reduction peaks vs. Fc/Fc+, assuming an
289 °C (Td,10%) and no phase transition was visible in the DSC
curve (see ESI for more information).
ionization energy of 4.8 eV for ferrocene.32 Thio-DBPs 2a
showed LUMO energies between −3.16 eV for 2a and −3.47 eV
for 2d. The presence of the sulfone moieties in significantly
lowered its LUMO energy to −3.94 eV. The HOMO energies of
thio-DBPs 2a lay between −5.38 and −5.81 eV. DFT
–d
Solid-state structures
Layering of a CH2Cl2 solution with n-pentane or acetonitrile
provided single crystals suitable for X-ray diffraction analysis of
thio-DBPs 2b and 2c (Fig. 2). While the sulfur atoms lie in the
plane of the DBP units, the S-aryl groups are rotated by 61.5°
for 2b and 61.9°/63.9° for 2c relative to the plane of the DBP
core. The molecules of 2c pack in a one-dimensional π-stacked
structure with distances between the DBP units of 3.504 Å,
which lie in the range of π-π-interactions (Fig. 2b). In the π-
3
–
d
calculations provided orbital energies for comparison. The
B3LYP33-functional was used in combination with D334 and the
def2-TZVP35,36 basis set (Fig. 4). The calculated HOMO energies
lie reasonably close but below the experimental ones, while
the LUMO energies were overestimated in the calculations.
stacking directions, the molecules are displaced by 3.16 Å. 2b
,
on the other hand, shows a herringbone packing in the solid
state (Fig. 2d). In the π-stacking direction, the distance
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Table 1 Electrochemical and optical data for thio-DBPs 2a–d and sulfone 3.
Ered 1/2
Eox 1/2
EHOMO
(eV)a
ELUMO
(eV)a
Eg
Eg (opt)
(eV)b
(V)
(V)
(eV)
2a
2b
2c
2d
3
−1.71
−1.55
−1.46
−1.40
0.65
0.81
0.98
1.17c
-
−5.38
−5.54
−5.69
−5.81
-
−3.16
−3.32
−3.42
−3.47
−3.94
2.22
2.22
2.27
2.34
-
1.92
1.90
1.85
1.85
1.86
−1.42
−0.94
aFrom the onset of the reduction/oxidation peak vs. Fc/Fc+, assuming an
ionization energy of 4.8 eV for ferrocene;32 bfrom the onset of the longest
wavelength absorption band, canodic peak potential.
Fig. 3 Cyclic voltammograms of thio-DBPs 2a–d and sulfone 3 (1 m
n-Bu4NPF6, scan rate 0.1 V s−1, glassy carbon electrode).
M in CH2Cl2, 0.1 M
Fig. 5 Absorption spectra of thio-DBPs 2a–d and sulfone 3 in CH2Cl2 solution (Inset:
longest wavelength absorption plotted on a logarithmic scale).
The second lowest energy transitions appear with maxima
between 433 and 450 nm, while the global absorption maxima
are found between 286 and 290 nm with extinction
coefficients of log ε = 4.70–4.79.
Fig. 4 Energy diagram of experimental (from CV measurements in solution, determined
from the onset of the first reduction/oxidation peak vs. Fc/Fc+, assuming an ionization
energy of 4.8 eV for ferrocene32) and calculated (B3LYP-D3/def2-TZVP) HOMO/LUMO
energies of thio-DBPs 2a–d and sulfone 3. For calculations the n-butyl groups of 2a
were replaced with methyl groups denoted with an asterisk (2*).
OFET measurements
The relatively low LUMO levels of the thio-DBPs are a good
requisite for n-channel conduction, especially in the cases of 2c
The HOMOs in 2a–d (exemplarily shown for 2b in Fig. 4) are
(−3.42 eV), 2d (−3.47 eV) and sulfone
proceeded to examine the electron transport properties of
these DBP derivatives. For 2c 2d and , we obtained well-
3 (−3.94 eV). Next, we
localized on the DBP core with some contributions from the
sulphur atoms. In comparison, the LUMOs show a much higher
contribution of the thioether substituents. This explains the
significant influence of the thioether and sulfone groups on
,
3
aligned crystals that were suitable for OFET fabrication using
the droplet-pinned crystallization (DPC) method (see ESI for
details, Fig. S31).26–28 OFETs were fabricated with Ag as the
source and drain electrodes (Fig. 6c, inset) and tested in the
saturation regime under N2 atmosphere. Compared to
commonly employed Au electrodes, Ag has a lower work
the LUMO energies of 2a–d and 3.
The absorption spectra of thio-DBPs 2a
–d and sulfone 3 show
the transitions expected for DBP derivatives. In
centrosymmetric DBP derivatives of C2h symmetry, the HOMO-
LUMO transition is forbidden, since both transitions are of au
symmetry (Laporte’s rule).37 Here, in contrast to other DBP
derivatives,23,24 this transition is not even visible at the onset
of the longest wavelength absorption band. The lowest visible
function that better matches the LUMO energies of 2c
, d and
3. OFETs based on the three compounds all exhibited n-
channel behaviour. The corresponding gate modulation is
clearly shown by the transfer (Fig. 6a–c) and output
characteristics (Fig. 6d–f). The electron mobility, on-to-off
absorption bands range from 454 nm (2a) to 477 nm (
3) with
extinction coefficients of log ε = 3.94–4.29.
current ratios (Ion/Ioff
)
and threshold voltages (VT) were
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extracted (Table 2), and histograms of electron mobilities are plotted in Fig. 6g–i.
Journal of Materials Chemistry C
Fig. 6 FET characteristics of the 2c (a, d and g), 2d (b, e and h) and 3 crystals (c, f and i). (a–c) Typical transfer characteristics (VDS = 100 V). Inset in c): schematic representation of
the FET configuration, where S is the source, D the drain and G the gate. (d–f) Typical output characteristics. (g–i) Histograms of the electron mobility from 51, 35 and 60 devices,
respectively.
Table 2 FET characteristics of 2c, d and 3 crystals.
electron injection that is associated with its lower LUMO
energy level.38 Although the mobility achieved is relatively low
as compared to that of state-of-the-art n-channel materials,39–
41
higher performance is expected for the new n-channel
Compound
Mobility (cm2V−1s−1
)
Vt (V)
Ion/Ioff
μaverage = 8.4×10−2 ± 3.1×10−2
(range: 3.2×10−2 to 1.4×10−1
2c
27–73
>103
)
skeleton of the DBP unit through expanding the side chain
structures as well as by crystal engineering. For example, AFM
images show that the obtained crystals are not expressed by
smooth and flat terraces (Fig. S31c, f, i), indicative of the non-
intimate contact between the crystals and the device
substrates that is detrimental to the electron-conductive
channel. Further work is needed towards achieving smooth
crystalline surfaces by chemically modifying the DBP cores to
promote dense molecular packing.
μaverage = 8.2×10−2 ± 3.6×10−2
2d
3
16–41
12–72
>103
>102
(range: 3.8×10−2 to 1.8×10−1
)
μaverage = 2.9×10−2 ± 1.7×10−2
(range: 4.5×10−3 to 8.7×10−2
)
The electron mobilities for the three crystals are similar, with
the highest value of 0.18 cm2 V−1 s−1 measured for 2d
(0.10 cm2 V−1 s−1 for 2c and 0.08 cm2 V−1 s−1 for
3
). In
comparison, the output characteristics (Fig. 6f) for
3 exhibited
a better linearity at low VDS region, indicating of better
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1-butanethiol (0.18 mL, 1.7 mmol, 4 eq.), P4O10 (1.2 g,
4.2 mmol, 10 eq.) and CH2Cl2 (11 mL) were stirred at 40 °C for
24 h. Thio-DBP 2a was obtained after flash chromatography
(cyclohexane/CH2Cl2: 1/0 to 20/1) as a red solid (73.1 mg,
193 µmol, 45%). Rf 0.22 (cyclohexane); 1H NMR (400 MHz,
CDCl3): δ 7.40–7.35 (m, 2H), 7.13–7.08 (m, 2H), 7.00–6.94 (m,
4H), 3.06–3.01 (m, 4H), 1.73–1.61 (m, 4H), 1.50–1.40 (m, 4H),
0.90 (t, J = 7.4 Hz, 6H); 13C NMR (101 MHz, CDCl3): δ 149.4,
146.6, 135.1, 134.2, 127.9, 127.7, 122.9, 121.9, 34.0, 32.7,
21.9, 13.8; HRMS (pos. APCI): m/z calcd for C24H27S2 379.1549
[M+H]+, found 379.1548.
Conclusions
In conclusion, we have demonstrated thioether- and sulfone-
substituted DBPs 2a–d and 3 with low-lying LUMO energy
levels for n-channel conduction in field-effect transistors
(FETs). The molecular structures in the solid state showed a
one-dimensional π-stacking or herringbone packing mode with
close intermolecular distances between the DBP cores. The
three derivatives with the lowest LUMO energies, 2c, d and 3,
were used in FETs as well-aligned crystals and displayed n-
channel (electron) mobilities of up to 0.18 cm2 V−1 s−1. Our
synthetic strategy provides facile access to a variety of
thioether- and sulfone-functionalized DBPs.
5,10-bis(phenylthio)indeno[2,1-a]indene (2b). Following
general procedure, ketone
4 (35.1 mg, 150 µmol), thiophenol
(60 µL, 0.58 mmol, 4 eq.), P4O10 (0.56 g, 2.0 mmol, 13 eq.) and
CH2Cl2 (7.5 mL) were stirred at rt for 24 h. Thio-DBP 2b was
obtained after flash chromatography (hot cyclohexane) as a
red crystalline solid (31.3 mg, 74.8 µmol, 50%). Rf 0.20
(cyclohexane); 1H NMR (400 MHz, CDCl3): δ 7.52–7.47 (m, 4H),
7.33–7.23 (m, 6H), 6.83–6.75 (m, 6H), 6.68–6.64 (m, 2H);
13C NMR (101 MHz, CDCl3): δ 148.2, 146.3, 133.8, 133.2, 132.5,
130.5, 129.3, 127.8, 127.6, 127.2, 123.2, 122.2; HRMS (neg.
APCI): m/z calcd for C28H18S2 418.0855 [M]●−, found 418.0854.
Experimental
Materials and methods
Details on materials and methods can be found in the ESI.
Synthetic procedures
Synthesis of ketone 4. Diphenylsuccinic acid (6, 5.00 g,
5,10-bis((4-(trifluoromethyl)phenyl)thio)indeno[2,1-a]indene
18.5 mmol) was placed in a dried Schlenk tube. CF3SO3H
(30 mL, 50 g, 340 mol, 18 eq.) was transferred into the tube
using a PTFE cannula. The tube was sealed, and the mixture
was heated to 75 °C and stirred at that temperature for 18 h.
The reaction mixture was cooled to rt, poured onto ice
(150 mL) and extracted with CH2Cl2 (3 × 100 mL). The organic
layer was washed with sat. aq. Na2CO3 solution (100 mL) and
brine (100 mL) and dried over Na2SO4. The crude mixture was
(2c). Following the general procedure, ketone
4 (48.5 mg,
207 µmol), 4-(trifluoromethyl)thiophenol (115 µL, 0.839 mmol,
4 eq.), P4O10 (0.50 g, 1.8 mmol, 8 eq.) and CH2Cl2 (5 mL) were
stirred at rt for 24 h and at 40 °C for 2 h. Thio-DBP 2c was
obtained after flash chromatography (cyclohexane) as a red
crystalline solid (52 mg, 94 µmol, 45%). Rf 0.29 (cyclohexane);
1H NMR (500 MHz, CDCl3): δ 7.55 (s, 8H), 6.96–6.92 (m, 2H),
6.87–6.82 (m, 4H), 6.69–6.65 (m, 2H); 13C NMR (126 MHz,
CDCl3): δ 148.4, 148.0, 138.7, 133.5, 131.2, 129.5, 129.0 (q,
recrystallized from 2-propanol (400 mL) to yield diketone
4 as
a
light-yellow solid (2.83 g, 12.1 mmol, 65%). Rf 0.27
3
2JCF = 32.9 Hz), 128.8, 128.2, 126.2 (q, JCF = 3.5 Hz), 124.0 (q,
(cyclohexane/EtOAc: 6/1); 1H NMR (400 MHz, CDCl3): δ 7.92
(ddd, J = 7.8, 1.0, 0.8 Hz, 1H), 7.71 (ddd, J = 7.7, 1.3, 0.8 Hz,
1H), 7.67 (ddd, J = 7.8, 7.3, 1.3 Hz, 1H), 7.44 (ddd, J = 7.7, 7.3,
1.0 Hz, 1H); 13C NMR (101 MHz, CDCl3): δ 201.6, 149.9, 135.9,
135.1, 129.2, 126.7, 124.9, 52.7; HRMS (pos. APCI): m/z calcd
for C16H11O2 235.07536 [M+H]+, found 235.07533.
1JCF = 271.6 Hz), 123.6, 122.5; 19F NMR (471 MHz, CDCl3): δ
−62.59; HRMS (pos. APCI): m/z calcd for C30H17F6S2 555.0670
[M+H]+, found 555.0673.
5,10-bis((3,5-bis(trifluoromethyl)phenyl)thio)indeno[2,1-
a]indene (2d). Following the general procedure, ketone
4
(50.9 mg, 217 µmol), 3,5-bis(trifluoromethyl)thiophenol
General procedure for the synthesis of thio-DBPs 2. P4O10 (10
(0.15 mL, 0.89 mmol, 4 eq.), P4O10 (0.60 g, 2.1 mmol, 10 eq.)
and CH2Cl2 (6 mL) were stirred at 40 °C for 24 h. Thio-DBP 2d
was obtained after flash chromatography (cyclohexane/CH2Cl2:
1/0 to 20/1) as a red solid (66.8 mg, 96.7 µmol, 45%). Rf 0.33
(cyclohexane); 1H NMR (500 MHz, CDCl3): δ 7.84 (s, 4H), 7.73
(s, 2H), 7.01–6.98 (m, 2H), 6.91–6.84 (m, 4H), 6.62–6.59 (m,
2H); 13C NMR (126 MHz, CDCl3): δ 149.0, 147.4, 137.2, 133.1,
eq.) and diketone
4 were placed in a dried Schlenk tube. The
tube was evacuated and backfilled with argon. Anh. CH2Cl2 was
added, and next the respective thiol (4 eq.) was added to the
stirred green suspension. The mixture was stirred at the
indicated temperature for 24 h. The mixture was quenched
with H2O, diluted with CH2Cl2, and the aq. layer was extracted
with CH2Cl2 (3 ×). The combined organic layers were washed
with 20% aq. NaOH solution (2 ×), dried over Na2SO4, and the
volatiles were removed under reduced pressure. The crude
product was purified by column chromatography on silica gel
2
3
132.8 (q, JCF = 33.5 Hz), 130.0, 129.2, 128.9 (q, JCF = 3.3 Hz),
1
128.6, 123.9, 122.9 (q, JCF = 273.2 Hz), 122.5, 120.7 (sept,
3JCF = 3.8 Hz); 19F NMR (471 MHz, CDCl3): δ −63.14; HRMS (pos.
APCI): m/z calcd for C32H15F12S2 691.0418 [M+H]+, found
691.0420.
to yield thio-DBPs 2.
5,10-bis(butylthio)indeno[2,1-a]indene (2a). Following the
general procedure, ketone (100 mg, 427 µmol),
Synthesis of 5,10-bis(phenylsulfonyl)indeno[2,1-a]indene (3).
Thio-DBP 2b (46.6 mg, 111 µmol) was dissolved in CH2Cl2
4
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(11 mL). m-CPBA (70 wt% in H2O, 220 mg, 0.892 mmol, 8 eq.)
(2a*). TDDFT calculations were performed with the
was added, and the mixture was stirred at rt for 19 h. The TURBOMOLE v7.2.1 program package.43 The resolution-of-
mixture was quenched with sat. aq. NaHCO3 solution (4 mL), identity (RI, RIJDX for SP)44,45 approximation for the Coulomb
and 10% aq. NaOH solution (10 mL) was added. The aq. layer integrals was used in all DFT calculations employing matching
was extracted with CH2Cl2 (2 × 15 mL), dried over Na2SO4, and auxiliary basis sets def2-XVP/J.46 Further, the D3 dispersion
the volatiles were removed under reduced pressure. Sulfone
3
correction scheme34,47 with the Becke-Johnson damping
was obtained after flash chromatography (siliga gel, function was applied.48–50 The geometries of 2a*, 2b–d and
3
CH2Cl2/cyclohexane: 3/1) as a red solid (48.2 mg, 98.9 µmol, were optimized without symmetry restrictions at the PBEh-
89%). Rf 0.28 (CH2Cl2/cyclohexane 2/1); 1H NMR (400 MHz, 3c51-D3/def2-mSVP level followed by harmonic vibrational
CD2Cl2): δ 8.09–8.00 (m, 2H), 8.04–7.95 (m, 4H), 7.70–7.65 (m, frequency analyses to confirm minima as stationary points.
2H), 7.61–7.51 (m, 4H), 7.39–7.33 (m, 2H), 7.09–6.97 (m, 4H); Vertical excitation energies were calculated with TDDFT using
13C NMR (101 MHz, CD2Cl2): δ 151.1, 145.6, 140.6, 140.5, the B3LYP33,52 functionals with the def2-TZVP basis set.36
134.9, 132.0, 131.1, 130.2, 130.1, 129.2, 127.7, 124.7; HRMS
(pos. ESI): m/z calcd for C28H18O4S2Na 505.0539 [M+Na]+,
Conflicts of interest
found 505.0542.
There are no conflicts to declare.
FET device fabrication
Crystals
for
FETs
were
grown
on
a
divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB)42-
coated highly doped silicon wafer (1 cm2) with 300 nm
thermally oxidized SiO2, using the DPC method.26–28 BCB (Dow
Chemicals) thin layers were spin-coated from a mesitylene
(Fluka) solution (VBCB/Vmesitylene = 1:30) and then thermally
annealed in a N2 glovebox.
Acknowledgements
Generous support by the German Research Foundation (Emmy
Noether grant ES 361/2-1 and grant No. INST 40/467-1 FUGG),
the state of Baden-Württemberg through bwHPC and the
National Natural Science Foundation of China (51625304,
51461165301) is gratefully acknowledged.
Crystals were grown in situ on substrates for FETs. A solution
(20 mL) was dropped onto the substrate and a piece of silicon
wafer (0.4 × 0.4 cm2, pinner) on the substrate was used to pin Notes and references
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Journal of Materials Chemistry C
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DOI: 10.1039/C8TC00970H
Dibenzo[a,e]pentalenes, functionalized with thioether or sulfone groups, show high electron
mobilities in n-channel OFETs using well-aligned crystals.