Synthesis and properties of T-shaped organic conjugates based on 3,6-diarylpyridazine-fused tetrathiafulvalene

Article abstract of DOI:10.1039/c3ob40704g

A facile synthetic approach to the π-expanded tetrathiafulvalene derivatives is described. The Suzuki reaction of 3,6-dichloropyridazine-fused tetrathiafulvalenes with phenyl boronic acid or biphenyl boronic acid gave a series of novel T-shaped organic π-conjugates. The electronic properties of the conjugates were studied experimentally by the combination of cyclic voltammetry and UV-vis spectroscopy. Their HOMO and LUMO energy levels are estimated to be about -5 eV and -3.2 eV, which are the air operating stability ranges in the p-channel and n-channel field effect transistors, respectively. Only one conjugate bearing the longer alkyl chain (n = 1, R = n-C ₁₈H₃₇) was verified to self-assemble into lamellar structures in the mesogenic phase and the best measured charge carrier mobility of its thin-film devices was 4.5 × 10^-5 cm² V ^-1 s^-1.

Full text of DOI:10.1039/c3ob40704g

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Synthesis and properties of T-shaped organic
conjugates based on 3,6-diarylpyridazine-fused
Cite this: Org. Biomol. Chem., 2013, 11,
5100
tetrathiafulvalene†
Ningjuan Zheng,a Hongda Li,a Guangyan Sun,a Keli Zhongb and Bingzhu Yin*a
A facile synthetic approach to the π-expanded tetrathiafulvalene derivatives is described. The Suzuki reac-
tion of 3,6-dichloropyridazine-fused tetrathiafulvalenes with phenyl boronic acid or biphenyl boronic
acid gave a series of novel T-shaped organic π-conjugates. The electronic properties of the conjugates
were studied experimentally by the combination of cyclic voltammetry and UV-vis spectroscopy. Their
HOMO and LUMO energy levels are estimated to be about −5 eV and −3.2 eV, which are the air operat-
ing stability ranges in the p-channel and n-channel field effect transistors, respectively. Only one conju-
gate bearing the longer alkyl chain (n = 1, R = n-C18H37) was verified to self-assemble into lamellar
structures in the mesogenic phase and the best measured charge carrier mobility of its thin-film devices
Received 9th April 2013,
Accepted 31st May 2013
DOI: 10.1039/c3ob40704g
www.rsc.org/obc
was 4.5 × 10−5 cm2 V−1 s−1
.
for the preparation of organic field-effect transistors (OFETs),
due to the possibility of synthesising tailored derivatives. In
Introduction
Since the discovery of the first organic metal tetrathiaful- recent years, the study of the TTF-based OFETs, stimulated by
valene-7,7,8,8-tetracyanoquinodimethane (TTF-TCNQ) about Bourgoin’s report in 1993,6 has gained increasing popular-
forty years ago,1 tetrathiafulvalene (TTF) and its derivatives ity.4,7,8 The largest mobilities in TTF-based OFETs have been
have been successfully used as building blocks for charge found for single crystals prepared from a solution of dithio-
transfer salts, giving rise to a multitude of organic conductors phenetetrathiafulvalene (DT-TTF, μmax = 3.6 cm2 V−1 s−1),9
and superconductors, as well as for the preparation of a wide hexamethylene tetrathiafulvalene (HM-TTF, μmax = 10 cm2 V−1
range of molecular materials.2,3 TTF derivatives are mostly
s )
−1 10 and dibenzotetrathiafulvalene (DB-TTF, μmax = 1 cm2 V−1
achieved by simple synthetic paths and are easily chemically s−1).11 Because of the strong electron-donating property of
modified; they are generally soluble in common solvents and TTF, however, its derivatives are usually degraded during oper-
benefit the solution-processable devices; they show planar ation owing to moisture and oxygen. The high energy of the
molecular conformation and strong intermolecular inter- orbitals implicated in the transport process is the cause of the
actions in the solid state induced by π⋯π stacking and S⋯S degradation, making the material more sensitive to air and
interactions; and they show good electron donor ability with humidity,12 one of the main drawbacks of TTF for practical
the highest occupied molecular orbital (HOMO) levels close to applications. In this respect, one effective approach is the aro-
the work function of usual metallic electrodes, affording a low matic heterocycle connected to the TTF core to decrease the
energy barrier for charge injection from metal electrodes into energy of the HOMO orbitals, which could enhance the stabi-
their active layers.4,5 Considering thus all the above, TTF lity of p-type and/or n-type organic semiconductors. A few
derivatives also show promise to be good candidate molecules organic semiconductors have been synthesized in which the
TTF core is annulated to thiophene,9,13,14 pyrrole,15,16 or pyra-
zine17,18 units and all these compounds have oxidation poten-
aKey Laboratory of Natural Resources of Changbai Mountain and Functional
tials appreciably higher than that of TTF itself. Among the
Molecules (Ministry of Education), Department of Chemistry, Yanbian University,
heterocyclic-fused TTF donors, the dipyrazine-annulated TTF
Yanji 133002, P. R. China. E-mail: zqcong@ybu.edu.cn; Fax: +86-433-2732456;
derivatives showed excellent n-type FET performances in thin
films (μFET = 0.64 cm2 V−1 s−1, Ion/Ioff = ∼106) and the dithio-
phene-annulated TTF derivative exhibited good p-type FET per-
Tel: +86-433-2732298
bCollege of Chemistry, Chemical Engineering and Food Safety, Bohai University,
Jinzhou 121013, P. R. China. E-mail: zhongkeli2000@yahoo.com.cn;
Fax: +86-416-3719190; Tel: +86-13904060848
formances in single crystals (μFET = 1.4 cm2 V−1 s−1, Ion/Ioff
=
†Electronic supplementary information (ESI) available. CCDC 932895 and
932896. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3ob40704g
7 × 105). Annulation of pyrazine rings to the TTF skeleton was
effective in further reducing the electron-donating property,
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dichloropyridazino-TTFs 5a–d were easily synthesized starting
from 4a–d with refluxing POCl3 in ∼60% yields. Compounds
T3 and T5 were prepared through Suzuki coupling reaction in
the presence of tetrakis(triphenyl-phosphine) palladium (Pd-
(PPh3)4) and potassium carbonate in a mixed solvent (ethanol–
water–benzene = 1 : 1 : 2) in 59–77% yields. The structures of
the intermediates and target compounds were fully character-
ized using NMR spectra, MS spectra and elemental analysis
data and were shown to be in full agreement with the struc-
tures presented in Scheme 1.
Crystal structure analysis and optimized structures of T3a
and T5a
The structures of T3a and T5a were further confirmed by
single-crystal X-ray diffraction data. In this approach, two
single crystals were successfully obtained by slowly evaporating
the acetonitrile solution of T3a and the mixed solution of
benzene–methylene chloride of T5a at room temperature.
Single-crystal X-ray diffraction structure analysis indicated that
T3a crystallizes in a monoclinic system, P21/c space group
Scheme 1 Synthetic routes to the target compounds T3 and T5.
which was also useful in enhancing the stability of the FET
device to oxygen.13,14,17,18 Very recently, it was reported that
the tetrathiafulvalene fused-naphthalene diimides exhibit rela-
tively high hole and electron mobilities in air, and the best
performing device exhibited a hole mobility of up to 0.31 cm2
ˉ
(Table S1†), and T5a crystallizes in a triclinic system, P1 space
group (Table S2†). In the crystal structure of compound T3a,
C18 and [1,3]dithiolo[4,5-d] pyridazine, which consist of N1,
N2, C7 to C10, C17, S1 and S2 (M1), are almost coplanar with
the average deviation of 0.0504 Å. The two benzene rings (C1
to C6 (M2) and C11 to C16 (M3)) possess the dihedral angles
of 42.67 (9)° and 44.75 (9)° with the M1, respectively. In
addition, the dihedral angle of the two benzene rings is
8.35 (2)°. It is interesting that the TTF moiety does not lie in
the same plane in which the 1,3-dithiole unit in the M2 pos-
sesses a dihedral angle of 15.67 (7)° with the M4 formed by
C19, C20, S3 and S4, which is different from the previously
reported pyridazine-fused tetrathiafulvalenes.20 A butyl on one
side is almost coplanar with TTF and another one lies on the
other side extending along the long molecular axis with
the average deviation of 30°. In the crystal of compound T5a,
the atoms N1, N2, C13, C14, C15, C16, S1 and S2 nearly lie in
the same plane with the average deviation from a least-squares
plane (M1) of 0.0504 Å. The dihedral angles of M1 with the
neighboring benzene rings M2 (C7 to C12) and M3 (C17 to
C22) are 44.02 (44)° and 38.93 (47)°, respectively, while the di-
hedral angles of M1 with the two terminal benzene rings are
smaller with a value of 12.05 (79)° for M4 (C1 to C6) and
5.89 (80)° for M5 (C23 to C28), respectively. It should be noted
that the two butyls are nearly perpendicular to the TTF moiety
with cis style (Fig. 1a). As seen in Fig. S1,† in the crystal struc-
V−1 s−1 19
Taking a broad view of the previous reports,
.
however, most of the TTF-based organic semiconductors are
linear rod molecules. Recently, we introduced successfully a
pyridazine ring to the TTF skeleton to synthesize a series of
monopyridazine–TTF conjugates. Their HOMO energy levels
suggest that the conjugates can be considered as candidates
for hole (p-type) or electron (n-type) transporting organic semi-
conductor materials.20
Taking these factors into consideration, in order to esta-
blish structure–property relationships for this family of com-
pounds, we decided to synthesize a series of T-shaped organic
π-conjugates. In this paper, we describe the successful syn-
thesis and photophysical and electrochemical properties of the
novel T-shaped organic π-conjugates T3a–b with three aryl
rings and T5a–d with five aryl rings (Scheme 1). The self-
assembly in the mesophase state and hole transfer properties
in spin-coated thin films of some selected compounds were
also investigated.
Results and discussion
Synthesis
The synthetic routes to target compounds T3 and T5 are sum- ture of T3a, the intermolecular C1–H1⋯S1 interactions link
marized in Scheme 1. The new intermediates 1c and 1d were two molecules into a dimer with a C1–S1 distance of 3.68 (1) Å.
synthesized in 88% and 95% yields, respectively, by the reac- The dimers are further linked by intermolecular C27–
tion of bis(tetraethylammonium)-bis(1,3-dithiole-2-thione-4,5- H27A⋯N1 and C26–H26B⋯N2 hydrogen bonds with C⋯N dis-
dithiol) zincate with the corresponding alkyl bromides. The tances of 3.70 (2) Å and 3.52 (1) Å respectively, forming one-
cross-coupling reaction of 1a–d with ketone 2 in neat triethyl dimensional chains along a direction (see ESI, Fig. S1†). The
phosphite at reflux under nitrogen gave the intermediates 3a–d van der Waals forces stabilize the crystal structure. For T5a,
in 40–63% yields. Compounds 3a–d reacted with hydrazine the double intermolecular C37–H37a⋯S4 hydrogen bonds,
monohydrate in refluxing ethanol to give the pyridazinedione with a C37–S4 distance of 3.70 (3) Å, link the molecules into
derivatives 4a–d in good yields (>70%). The key intermediates dimers. The dimers are further linked by intermolecular
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Fig. 1 (a) Crystal structures and (b) the optimized structures of T3a and T5a.
C21–H21⋯S2 interactions, with a C21–S2 distance of 3.78 (2) Å,
forming one-dimensional chains along the [100] direction. In
addition, the weak intermolecular C–H⋯N hydrogen bonding,
with a C25–N2 distance of 3.88 (2) Å, links the chains into a
2-D network along (01−1) (see ESI, Fig. S1†).
Fig. 2 (a) UV-vis spectra of compounds T3a–b and T5a–d in CHCl3 (5 × 10−5 M).
(b) Variation of the UV-vis spectra of T5d in CHCl3 (5 × 10−5 M) upon successive
addition of varying amounts of HCl in ethanol (0→1000 equivalents).
The chemical structures of T3a and T5a were investigated
with theoretical calculations based on density functional
theory (DFT) for a comparison with crystal structures. The opti-
mized structures of T3a and T5a are very similar to their
single-crystal structures in which the TTF moiety is also not
lying in the same plane. The two benzene rings (C1 to C6 (M2)
and C11 to C16 (M3)) of compound T3a possess the same
dihedral angle of 42.42° with the M1. There is a difference
from the crystal structure in that the two butyls are nearly per-
pendicular to the TTF moiety with cis style. Much the same as
T3a, all benzene rings in T5a are not in the same plane as 1,3-
dithiolo[4,5-d]pyridazine (M1) in which the dihedral angle of
M1 with the neighboring benzene rings M2 (C7 to C12) and
M3 (C17 to C22) is 39.56 °, while that of M2 and M3 with the
two terminal benzene rings is smaller with a value of 35.63°
for M4 (C1 to C6) and M5 (C23 to C28), respectively. Two
butyls are nearly perpendicular to the TTF moiety with cis style
as in the crystal structure of T5a (Fig. 1b).
around 425 nm and a very intense absorption band around
310 nm, respectively. Only the absorption bands of T5a–T5d in
the UV region were red-shifted compared to those of T3a–T3b
(from 270 nm to 320 nm). The bands around 425 nm are
assigned to the intramolecular charge transfer (ICT) inter-
action between the donor (TTF) and the acceptor (pyridazine).
The strong bands in the UV region are characteristic of π–π*
transitions located on both the TTF and the diaryl-substituted
pyridazine subunits.21 The bands at the lower energy region
can be assigned to the HOMO–LUMO transition, and thus, the
onset of these bands allows us to estimate the HOMO–LUMO
gap (Eg )
opt 22,23 that, in all cases, is around 2.52 eV (see Table 1).
To rationalize the absorption spectra of target compounds,
DFT calculations were carried out for T3a and T5a by B3LYP/
6-31G* with the Gaussian 09 program package.24 The HOMOs
and LUMOs of T3a and T5a are shown in Fig. S2.† The calcu-
Photophysical properties and rationalization
The absorption spectra of target compounds T3 and T5 in lated absorption wavelengths of T3a and T5a are 421 nm/
CHCl3 solution (5 × 10−5 M) are shown in Fig. 2a. Compounds
2.91 eV, 297 nm/3.62 eV and 441 nm/2.82 eV, 342 nm/3.86 eV,
T3a–T3b show a very weak and broad absorption band around respectively, which are slightly lower/higher but in good agree-
425 nm and an intense absorption band around 270 nm with ment with the experimental results (Fig. 3). The lowest-energy
singlet transitions at 2.91 eV and 2.82 eV involve one-electron
a shoulder band around 320 nm, respectively. Similarly, com-
pounds T5a–T5d also show a weak and broad absorption band excitations from π-orbitals HOMO to LUMO (0.57% for T3a
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Table 1 UV-vis absorption spectroscopy data, and Eogpt, HOMO and LUMO energies obtained from cyclic voltammetry for T3 and T5
Compd.
λmax, UV/nm
λ10%, max/nm
Eogpt a/eV
E
red/onset/V
E
ox/onset/V
E
HOMO b/eV
E
LUMO b/eV
T3a
T3b
T5a
T5b
T5c
T5d
422
418
414
418
422
421
507
505
501
509
506
509
2.52
2.53
2.55
2.51
2.52
2.51
−1.13
−1.18
−1.13
−1.15
−1.15
−1.17
0.74
0.74
0.74
0.72
0.75
0.74
−5.09
−5.09
−5.09
−5.07
−5.10
−5.09
−3.22
−3.17
−3.22
−3.20
−3.20
−3.18
a Optical band gap according UV-vis absorption (onset method). Egopt = hc/λ10%max (ref. 22 and 23). b Energy level of the highest occupied
molecular orbital according to cyclic voltammetry. EHOMO/ELUMO = [−(Eonset − 0.45)−4.8] eV, where the value 0.45 V is for ferrocene versus Ag/Ag+
and 4.8 eV is the energy level of ferrocene below the vacuum (ref. 22 and 23).
1000 equivalents added, indicating the presence of only two
species in the chemical equilibria, namely compound T5d and
a mono-protonated species [T5d·H+]. The result is different
from the previously reported 2-pyridinylimidazole-fused tetra-
thiafulvalene where two protonation sites lie on two different
cycles separately,26 which could be explained with the lower
pK2 of pyridazine.
Electrochemical properties
In general, p-type organic semiconductors typically have
HOMO levels between −4.9 and −5.5 eV, whereas n-type
materials typically have LUMO levels between −3 and
−4 eV.27,28 To fit the energetic scheme of the organic semicon-
ductor materials, it is necessary to determine the energy levels
of the highest occupied molecular orbital (HOMO) and lowest
Fig. 3 Comparison of the experimental and calculated electronic absorption
spectra of T3a and T5a in chloroform with the B3LYP/6-31G* method.
unoccupied molecular orbital (LUMO) and the width of
the gap between the bands of each component through
electrochemistry.29
and 0.69% for T5a) and LUMO + 2 (0.41% for T3a and 0.13%
for T5a), suggesting that this absorption corresponds to the
charge-transfer absorption from the TTF part to the diarylpyri-
dazine part. The most intense absorptions at 282 and 342 nm
are predicted to be a combination of the one-electron exci-
tations from the localized TTF or arylpyridazine, which can be
attributed to one-electron excitations from π-orbitals HOMO −
1 to LUMO + 2 (0.67% for T3a and 0.57% for T5a). Two absorp-
tion bands in the UV-vis spectrum therefore bear ICT as well
as localized TTF or arylpyridazine π–π* characteristics, which
is very similar to a tetrathiafulvalene-diphenyl-1,3,4-oxadiazole
dyad (Fig. S2 and Table S3†).25
In order to explore further the ICT characteristics of the
T-shaped D-A molecules, taking T5d as an example, the proto-
nation characteristic was experimentally investigated in CHCl3
solution. Compound T5d has two protonation sites, namely,
the two nitrogen atoms on the pyridazine. The UV-vis spectra
of T5d dissolved in CHCl3 with successive addition of a 9 M
ethanolic solution of hydrochloride (HCl) are depicted in
Fig. 2b. Upon addition of HCl, for an initial concentration of
5 × 10−5 M of T5d, the strong absorption band at 308 nm and
the broad CT absorption band at 419 nm gradually decrease in
intensity and a new absorption band around 600 nm emerges.
These changes continued from 0 to 1000 equivalents. A
remarkable feature is the occurrence of three quite well
defined isosbestic points, at 322, 408 and 445 nm for up to
The electrochemical properties of T-shaped organic conju-
gates T3 and T5 were studied by cyclic voltammetry (CV) in
benzonitrile. All compounds exhibited two reversible single-
electron oxidation waves at about 0.80 and 1.11 V. The first oxi-
dation should be attributed to the bis(thioether)-substituted
half-unit, while the second arises from the pyridazine-substi-
tuted half-unit. Moreover, the compounds showed a quasi-
reversible reduction process at about −0.89 V, which can be
assigned to one-electron reduction of the pyridazine unit
(Fig. 4 and Fig. S3†).30 The redox properties of the target com-
pounds are similar to those of other similar TTF-fused D–A
ensembles.31 In comparison to TTF (E11/2 = 0.34 V, E21/2
=
0.73 V),32 the oxidation potentials of TTF units are positively
shifted by 360–480 mV owing to the annulation of the elec-
tron-withdrawing pyridazine ring. Moreover, all compounds
displayed very similar oxidation and reduction potentials,
suggesting that the length of alkyl chains does not appreciably
influence the redox processes. Interestingly, a unique cyclic
voltammogram was observed in the case of compound T5b
whose redox wave is broadened and the peak current is
lowered because of an aggregation phenomenon in concen-
trated solutions (Fig. 4a).33 The partial intramolecular charge
transfer from the TTF unit to the pyridazine moiety decreases
the electron density of the TTF ring; as a consequence, these
systems are expected to be more stable to oxygen exposure.
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Fig. 5 Absorption spectra of T5d (5 × 10−5 M) in CHCl3 after addition of
different equiv. of F4TCNQ (0→20 equivalents).
absorption bands at 585, 763 and 867 nm emerged. Two new
bands at 763 and 867 nm would be unambiguously assigned
to the intramolecular transition of the F4TCNQ˙− anion
radical,34 in which the band at 862 nm is likely mixed with the
CT component of the complex of T5d with F4TCNQ. The broad
band around 585 nm could be assigned to intramolecular tran-
sitions of the radical cation, TTF˙+; because of that, the tran-
sitions of the charge transfer (CT) complex between TTF˙+ and
F4TCNQ˙− generally appear in the NIR region. In the present
case, this band appeared in lower energy regions (587 nm)
than those of other TTF derivatives (470–480 nm) probably due
to the expansion of the conjugated system.34,35 Clearly, the
donating ability is in agreement with the results obtained
from the CV experiments.
Fig. 4 Cyclic voltammograms for oxidation (a) and reduction (b) of compounds
T5a and T5b in benzonitrile (1 mM, scanning rate 100 mV s−1) with platinum
wires as working and counter electrodes, respectively, Ag/AgCl as a reference
electrode, and n-Bu4NPF6 (0.1 M) as a supporting electrolyte.
Self-assembly
Controlled self-assembly by molecular design is a challenging
topic for interdisciplinary research in the fields of chemistry,
biology, and materials science because it provides spon-
taneous nanostructures with well-defined morphology, which
plays an influential role in determining the properties of
organic nanostructures.36 First, we investigated the thermal
phase behavior of compounds T3 and T5 by means of differen-
tial scanning calorimetry (DSC) and polarized-light optical
microscopy (POM). Only one conjugate T5b bearing the longer
alkyl chain (n = 1, R = n-C18H37) exhibited a mesogenic phase,
Their HOMO levels were estimated from the onset of oxidation
potentials to be between −5.07 and −5.10 eV and the LUMO
levels were estimated from the onset of reduction potentials to
be between −3.17 and −3.22 eV (Table 1). Clearly, all com-
pounds provide low HOMO and LUMO levels, which suggest
that the target organic π-conjugates are promising hole or elec-
tron transporting organic materials.
Electron donating properties
Taking advantage of the electron donating abilities of TTF, we which showed two endothermic peaks in the heating as well as
carried out preliminary complexation experiments with in the cooling cycle (Fig. 6a). T5b exhibits a liquid crystalline
different acceptors. However, the typical acceptors 7,7,8,8-tetra- phase at a melting state (123.9 °C), which was transformed to
cyanoethylene-p-quinodimethane (TCNQ) and 2,3-dichloro-5,6- an isotropic phase at 148.2 °C. On slow cooling of T5b from
dicyano-p-benzoquinone (DDQ) were found to show no signifi- the isotropic liquid to liquid crystalline phase, a natural schlie-
cant complexation ability with T5d, according to UV-vis experi- ren-like texture was observed at 130 °C by POM experiments,
ments in CHCl3. In contrast, addition of 2,3,5,6-tetrafluoro-7,7, which was transformed to a crystalline phase during cooling
8,8-tetracyanoquinodimethane (F4TCNQ), a strong electron (Fig. 6b). The DSC curves together with optical texture prelimi-
acceptor, to a CHCl3 solution of T5d (5 × 10−5 M) resulted in narily confirmed the presence of a lamellar mesophase.
dramatic changes in UV-vis spectra. The UV-vis spectra of T5d To investigate the molecular packing structure of T5b, we per-
dissolved in CHCl3 with successive addition of F4TCNQ are formed a small-angle X-ray scattering (SAXS) experiment after
depicted in Fig. 5. Upon addition of F4TCNQ, three new cooling to 130 °C (Fig. 6c). As seen in Fig. 6c, compound T5b has
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a layered structure with d-spacings of 4.61, 1.52, 1.15, 0.92,
0.76 and 0.65 nm, which agreed well with (100), (300), (400),
(500), (600) and (700) reflections of a lamellar packing struc-
ture. The d-spacing of 4.61 corresponds roughly to the mole-
cular length extended along its long molecular axis, suggesting
that the rod segments within the layers are parallel to the layer
planes and are face to face stacked to each other by π–π inter-
actions and the coil segments interdigitate with each other
through hydrophobic interaction to fill the spaces between two
TTF segments. Notably, compound T5b exhibits an additional
sharp reflection at a d-spacing of 1.57 nm and another reflec-
tion hid likely in a broad peak at about 8.23 nm, which might
be associated with the distance between two TTF segments.
Two additional sharp reflections suggest that the TTF seg-
ments in T5b organize into sublayers with a thickness of
1.57 nm within a layer (Fig. 6d). The existence of in-plane sub-
layers in the self-assembly of T-shaped rod-coil molecules has
been reported in the literature.37
To verify the applicability of our new semiconductors to
organic electronics, we have fabricated bottom-gate/bottom-
contact OFETs with thin films of T3a and T5b, which were pre-
pared by spin-coating of their solutions onto the substrates
(n-octadecyltrimethoxysilane (OTS) modified SiO2 surface). The
field-effect transistors were fabricated in air with conventional
techniques by using doped n-type Si as the gate electrode, Au
as both the source and drain electrodes and OTS-modified
SiO2 as the dielectric layer. The OFET devices were examined
in air, and the corresponding output characteristics and trans-
fer characteristics were measured (see ESI†). Both thin films
show typical p-type semiconducting behavior in the air. And
the mobilities of T3a and T5b were 3.4 × 10−6 cm2 V−1 s−1 and
4.5 × 10−5 cm2 V−1 −1, respectively. Fig. 7 shows the XRD pat-
s
terns of thin films of T5b annealed at different temperatures.
Weak diffraction peaks at 5.8°, 6.1°, 6.8°, 9.0°, 11.3°, 13.5°,
16.4°, 18.0°, 20.1°, 20.7°, 23.4°, 24.1°, and 24.7° were detected
for thin films of T5b after annealing at 80 °C. After annealing
at 100 °C, the peaks at 5.8°, 6.1°, 16.4°, 18.5°, 20.7°, 23.4°, and
24.1° disappear. After further annealing at 120 °C, the
Fig. 6 (a) DSC traces recorded during the second heating and the second
cooling scan, (b) optical polarized micrographs (40×) of the texture exhibited by
a lamellar phase at 130 °C, (c) X-ray diffraction patterns plotted against q =
4π sin θ/λ measured after cooling to 130 °C, and (d) the proposed molecular
arrangement in the liquid crystal of T5b.
Fig. 7 XRD patterns of thin films of T5b after annealing at 80 °C, 100 °C,
120 °C and 140 °C, respectively.
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remaining peaks at 6.8°, 9.0°, 11.3°, 13.5°, 18.0°, 20.1°, and (300 MHz, CDCl3, 25 °C, TMS): δ = 7.92–7.89 (m, 4H, Ar),
24.7° were largely enhanced. After annealing at 140 °C, the 7.56–7.47 (m, 6H, Ar), 2.81 (t, 3J (H,H) = 7.2 Hz, 4H, SCH2),
peak intensity at 6.8° weakens, whereas other diffraction peaks 1.57–1.46 (m, 4H, CH2), 1.39–1.25 (m, 4H, CH2), 0.91 ppm (t, 3J
still remain; but two new diffraction peaks appear at 3.6° and (H,H) = 7.3 Hz, 6H, CH3); 13C NMR (75 MHz, CDCl3): δ = 152.1,
4.5° with high intensity. These XRD data clearly show that 140.2, 136.6, 130.2, 128.9, 127.9, 115.4, 105.2, 36.0, 31.7, 21.6,
molecules of T5b are more orderly arranged for the thin film 13.5 ppm; MS (MALDI-TOF): m/z (%): 585.1 ([M+ + H], 100);
of T5b after annealing until 140 °C. Taking into account that elemental analysis calcd for C28H28N2S6: C 57.49, H 4.82, N
neither the substrate–semiconductor nor the semiconductor– 4.79; found: C 57.31, H 4.78, N 4.66.
dielectric interface was optimized, we expect a large amount of
potential improvement in the electron mobility.
Compound T3b. Recrystallization from acetone gave an
orange powder, yield 64.9%. m.p. 99–100 °C; 1H NMR
(300 MHz, CDCl3, 25 °C, TMS): δ = 7.92–7.88 (m, 4H, Ar),
7.59–7.54 (m, 6H, Ar), 2.80 (t, 3J (H,H) = 7.2 Hz, 4H, SCH2),
1.43–1.36 (m, 4H, CH2), 1.32–1.25 (m, 4H, CH2), 1.25–1.24 (m,
Experimental section
General methods
3
56H, CH2), 0.91 ppm (t, J (H,H) = 7.3 Hz, 6H, CH3); 13C NMR
(75 MHz, CDCl3): δ = 152.2, 140.2, 136.6, 130.2, 128.9, 128.0,
127.8, 115.6, 105.2, 36.4, 31.9, 29.7, 29.6, 29.5, 29.4, 29.1, 28.5,
22.7, 14.1 ppm; MS (MALDI-TOF): m/z (%): 977.8 ([M+ + H],
100); elemental analysis calcd for C56H84N2S6: C 68.80, H 8.66,
N 2.87; found: C 69.00, H 8.69, N 2.76.
NMR spectra were recorded in CDCl3 with a Bruker AV-300
spectrometer (300 MHz for 1H and 75 MHz for 13C) and chemi-
cal shifts were referenced relative to tetramethylsilane (δH/δC
=
0). MALDI-TOF-MS was performed on a Shimadzu Axima
CFR™ Plus using a 1,8,9-anthracenetriol (DITH) matrix. UV-vis
spectra were recorded on a Hitachi U-3010 spectrophotometer
in CHCl3 (5 × 10−5 M). Cyclic voltammetric studies were
carried out on a Potentiostat/Galvanostat 273A instrument in
benzonitrile (10−3 M) and 0.1 M Bu4PF6 was used as the sup-
porting electrolyte. The counter and working electrodes were
made of Pt and glassy carbon, respectively, and Ag/AgCl was
used as the reference electrode. A Perkin-Elmer Pyris Diamond
differential scanning calorimeter was used to determine the
thermal transitions, which were reported as the maxima and
minima of their endothermic or exothermic peaks; the heating
and cooling rates were controlled at 10 °C min−1. An Olympus
BX51-P optical polarized microscope (magnification: 40×),
equipped with a Mettler FP82 hot-stage and a Mettler FP90
central processor, was used to observe the thermal transitions
and to analyze the anisotropic texture. X-ray scattering
measurements were performed in the transmission mode with
synchrotron radiation from the 3C2 X-ray beam line at the
Pohang Accelerator Laboratory, Korea. X-ray diffraction (XRD)
measurements of the thin films were carried out in the reflec-
tion mode at room temperature using a 2 kW Rigaku X-ray
diffraction system. Compounds 1a,38 1b,39 3b,40 3a, 4a and
5a,20 and 241 were synthesized according to a literature
method. For the synthesis of 1c, 1d, 3c, 3d, 4b, 4c, 4d, 5b, 5c
and 5d, see ESI.†
Compound T5a. Recrystallization from CH2Cl2–CH3CN gave
a yellow powder, yield 73.7%. m.p. 216–217 °C; 1H NMR
3
(300 MHz, CDCl3, 25 °C, TMS): δ = 8.02 (d, J (H,H) = 8.13 Hz,
3
3
4H, Ar), 7.81 (d, J (H,H) = 8.28 Hz, 4H, Ar), 7.69 (d, J (H,H) =
8.13 Hz, 4H, Ar), 7.53–7.48 (m, 4H, Ar), 7.44–7.39 (m, 2H, Ar),
3
2.82 (t, J (H,H) = 7.3 Hz, 4H, SCH2), 1.65–1.56 (m, 4H, CH2),
1.49–1.37 (m, 4H, CH2), 0.92 ppm (t, 3J (H,H) = 7.23 Hz, 6H,
CH3); 13C NMR (75 MHz, CDCl3): δ = 51.8, 143.1, 140.3, 140.2,
128.9, 128.4, 127.9, 127.6, 127.2, 111.9, 105.2, 36.1, 31.7, 21.6,
13.6 ppm; MS (MALDI-TOF): m/z (%): 736.2 ([M+], 100);
elemental analysis calcd for C40H36N2S6: C 65.18, H 4.92,
N 3.80; found: C 65.22, H 4.98, N 4.02.
Compound T5b. Recrystallization from CH2Cl2–hexane gave
a yellow powder, yield 59.3%. m.p. 158–159 °C; 1H NMR
3
(300 MHz, CDCl3, 25 °C, TMS): δ = 8.0 2 (d, J (H,H) = 8.13 Hz,
3
3
4H, Ar), 7.81 (d, J (H,H) = 8.22 Hz, 4H, Ar), 7.69 (d, J (H,H) =
7.74 Hz, 4H, Ar), 7.53–7.48 (m, 4H, Ar), 7.42–7.39 (m, 2H, Ar),
3
2.81 (t, J (H,H) = 7.23 Hz, 4H, SCH2), 1.66–1.56 (m, 4H, CH2),
1.40–1.23 (m, 60H, CH2), 0.87 ppm (t, J (H,H) = 6.36 Hz, 6H,
3
CH3); 13C NMR (75 MHz, CDCl3): δ = 151.7, 143.1, 140.2, 135.3,
128.9, 128.4, 127.9, 127.6, 127.2, 115.7, 105.2, 36.4, 31.9, 29.7,
29.6, 29.5, 29.3, 29.1, 28.5, 22.7, 14.1 ppm; MS (MALDI-TOF):
m/z (%): 1130.0 ([M+ + H], 100); elemental analysis calcd
for C68H92N2S6: C 72.29, H 8.21, N 2.48; found: C 72.45,
H 8.50, N 2.55.
Compound T5c. Recrystallization from acetone gave an
Typical procedure for compounds T3 and T5
orange powder, yield 61.9%. m.p. 112–113 °C; 1H NMR
3
A mixture of 5 (0.21 mmol), arylboronic acid (0.82 mmol), (300 MHz, CDCl3, 25 °C, TMS): δ = 8.02 (d, J (H,H) = 8.25 Hz,
3
3
Pd(PPh3)4 (0.10 mmol) and K2CO3 (1.48 mmol) in a mixture of 4H, Ar), 7.80 (d, J (H,H) = 8.19 Hz, 4H, Ar), 7.69 (d, J (H,H) =
EtOH–H2O–C6H6 = 1 : 1 : 2 (10 mL) was stirred under N2 at 7.11 Hz, 4H, Ar), 7.52–7.47 (m, 4H, Ar), 7.43–7.36 (m, 2H, Ar),
90 °C for 12 h. After cooling, the resulting mixture was dis- 2.82 (d, 3J (H,H) = 6.06 Hz, 4H, SCH2), 1.73 (m, 4H, CH2),
solved in CH2Cl2, washed with water and dried over MgSO4. 1.61–1.55 (m, 4H, CH2), 1.36–1.34 (m, 6H, CH2), 1.25–1.23 (m,
After evaporation of the solvent, the crude product was puri- 52H, CH2), 0.89 ppm (t, 3J (H,H) = 6.51 Hz, 12H, CH3); 13C
fied by column chromatography on silica gel using CH2Cl2 to NMR (75 MHz, CDCl3): δ = 151.7, 143.0, 140.2, 140.1, 135.3,
give a solid.
128.9, 128.4, 128.0, 127.8, 127.6, 127.1, 41.1, 38.2, 32.8, 31.9,
Compound T3a. Recrystallization from CH3CN gave an 29.9, 29.8, 29.7, 29.6, 29.4, 26.5, 22.7, 14.1 ppm; MS (MALDI-
orange needle, yield 77.5%. m.p. 151–152 °C; 1H NMR TOF): m/z (%): 1185.5 ([M+ + H]); elemental analysis calcd for
5106 | Org. Biomol. Chem., 2013, 11, 5100–5108
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C72H100N2S6: C 72.92, H 8.50, N 2.36; found: C 72.65, H 8.33,
N 2.60.
Structure, Properties, and Theory, Prentice Hall, Englewood
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Compound T5d. Recrystallization from acetone gave an
orange powder, yield 59.0%. m.p. 114–115 °C; 1H NMR
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5 J. Casado, M. Z. Zgierski, M. C. R. Delgado, J. T. L.
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7 K. Gao, W. Qiu, Y. Liu, G. Yu and D. Zhu, Pure Appl. Chem.,
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N. Crivillers, J. Veciana and C. Rovira, Org. Electron., 2008,
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3
(300 MHz, CDCl3, 25 °C, TMS): δ = 8.02 (d, J (H,H) = 8.13 Hz,
3
3
4H, Ar), 7.80 (d, J (H,H) = 8.01 Hz, 4H, Ar), 7.69 (d, J (H,H) =
7.17 Hz, 4H, Ar), 7.52–7.47 (m, 4H, Ar), 7.43–7.36 (m, 2H, Ar),
3
2.82 (d, J (H,H) = 5.91 Hz, 4H, SCH2), 1.63–1.57 (m, 8H, CH2),
1.35–1.34 (m, 6H, CH2), 1.23 (m, 68H, CH2), 0.89 ppm (t, 3J (H,
H) = 6.68 Hz, 12H, CH3); 13C NMR (75 MHz, CDCl3): δ = 151.7,
143.0, 140.2, 140.1, 135.3, 18.9, 128.4, 128.0, 127.8, 127.5,
127.2, 41.1, 38.2, 32.8, 31.9, 29.9, 29.7, 29.4, 26.5, 22.7,
14.1 ppm; MS (MALDI-TOF): m/z (%): 1298.0 ([M+ + H], 100);
elemental analysis calcd for C80H116N2S6: C 74.02, H 9.01,
N 2.16; found: C 73.75, H 9.12, N 1.98.
10 Y. Takahashi, T. Hasegawa, S. Horiuchi, R. Kumai,
Y. Tokura and G. Saito, Chem. Mater., 2007, 19, 6382–6384.
Conclusions
In summary, we have synthesized a series of T-shaped π-conju- 11 M. Mas-Torrent, P. Hadley, S. T. Bromley, N. Crivillers,
gates from a new building block, dichloropyridazine-fused
J. Veciana and C. Rovira, Appl. Phys. Lett., 2005, 86, 012110/
TTFs, through the Suzuki reaction and they were fully charac-
1–012110/3.
terized. Spectroscopic and electrochemical studies revealed 12 S. Hoshino, M. Toshida, S. Uemura, T. Kodzasa,
that the pyridazine unit greatly facilitates electronic communi-
cation between the TTF moiety and the acceptor unit, thus
N. Takada, T. Kamata and K. Yase, J. Appl. Phys., 2004,
95, 5088–5093.
leading to intramolecular charge transfer, and the protonation 13 M. Mas-Torrent, M. Durkut, P. Hadley, X. Ribas and
of the pyridazine moiety showed an ICT band of the proto- C. Rovira, J. Am. Chem. Soc., 2004, 126, 984–985.
nated species. The HOMO and LUMO energy levels of target 14 M. Mas-Torrent, S. Masirek, P. Hadley, N. Crivillers,
compounds are estimated to be close to −5 eV and −3.2 eV,
N. S. Oxtobu, P. Reuter, J. Veciana, C. Rovira and A. Tract,
which are the air operating stability ranges in the p-channel
Org. Electron., 2008, 9, 143–148.
and n-channel field effect transistors, respectively, and the 15 I. Doi, E. Miyazaki, K. Takimiya and Y. Kunugi, Chem.
best measured charge carrier mobility of the spin-coated film Mater., 2007, 19, 5230–5237.
device of T5b bearing the longer alkyl chain (n = 1, R = 16 I. Doi, E. Miyazaki and K. Takimiya, Chem. Lett., 2008,
n-C18H37), which shows a lamellar mesophase, was 4.5 × 1088–1089.
10−5 cm2 V−1 s−1. Further structural modification and improve- 17 Naraso, J.-I. Nishida, S. Ando, J. Yamaguchi, K. Itaka,
ment of the mobility of the T-shaped conjugates are underway
in our laboratories.
H. Koinuma, H. Tada, S. Tokito and Y. Yamashita, J. Am.
Chem. Soc., 2005, 127, 10142–10143.
18 Naraso, J.-I. Nishida, D. Kumaki, S. Tokito and
Y. Yamashita, J. Am. Chem. Soc., 2006, 128, 9598–9599.
19 T. Luxi, G. Yunlong, Y. Yang, Z. Guanxin, Z. Deqing, Y. Gui,
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Acknowledgements
The authors acknowledge financial support from the National 20 Z. Ningjuan, L. Bao, M. Changwei, C. Tie, K. Yuhe and
Natural Science Foundation of China (grant no. 21062022) and Y. Bingzhu, Tetrahedron, 2012, 68, 1782–1789.
the Specialized Research Fund for the Doctoral Program of 21 C. J. Chang, C. H. Yang, K. Chen, Y. Chi, C. F. Shu,
Higher Education (grant no. 20102201110001).
M. L. Ho, Y. S. Yeh and P. T. Chou, Dalton Trans., 2007,
1881–1890.
22 Y. Bando, T. Shirahata, K. Shibata, H. Wada, T. Mori and
T. Imakubo, Chem. Mater., 2008, 20, 5119–5121.
23 D. A. M. Egbe, B. Cornelia, J. Nowotny, W. Gunther and
E. Klemm, Macromolecules, 2003, 36, 5459–5469.
24 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone,
B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng,
J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
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