Asymmetrical/symmetrical D-π-A/D-π-D thiazole-containing aromatic heterocyclic fluorescent compounds having the same triphenylamino chromophores

Article abstract of DOI:10.1021/jo401384g

A family of linear asymmetrical D-π-A and symmetrical D-π-D types of thiazole-based aromatic heterocyclic fluorescent compounds bearing various electron-donating and electron-withdrawing tails (bromo, triphenylamino, pyridyl, thienyl and benzoic acid) have been designed and prepared successfully. Synthetic, structural, thermal, spectral and computational comparisons have been carried out for related compounds because of their adjustable electronic properties. It is interesting to mention that compound 2 can be prepared from 5-bromothiazole by one-pot Suzuki-Miyaura coupling and subsequent C-H activation reactions via a 5-TPA-substituted thiazole intermediate 1. X-ray single-crystal structures of six compounds indicate that they all crystallize in the triclinic P1I... space group and the thiazole core exhibits different dihedral angles with its adjacent benzene ring of the triphenylamino group (3.6(3)-40.8(3)). The photophysical and electrochemical results demonstrate that compound 7 exhibits high electrochemical activity with a green fluorescence emission. Meanwhile, compounds 1, 2, and 6 show high luminescence quantum yields, and compound 8 exhibits excellent thermal stability (Td₁₀ = 503 C).

Full text of DOI:10.1021/jo401384g

Article
pubs.acs.org/joc
Asymmetrical/Symmetrical D−π−A/D−π−D Thiazole-Containing
Aromatic Heterocyclic Fluorescent Compounds Having the Same
Triphenylamino Chromophores
Tao Tao, Bin-Bin Ma, Yu-Xin Peng, Xiao-Xu Wang, Wei Huang,* and Xiao-Zeng You
State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing 210093, People’s Republic of China
S
* Supporting Information
ABSTRACT: A family of linear asymmetrical D−π−A and symmetrical
D−π−D types of thiazole-based aromatic heterocyclic fluorescent
compounds bearing various electron-donating and electron-withdrawing
tails (bromo, triphenylamino, pyridyl, thienyl and benzoic acid) have been
designed and prepared successfully. Synthetic, structural, thermal, spectral
and computational comparisons have been carried out for related
compounds because of their adjustable electronic properties. It is
interesting to mention that compound 2 can be prepared from 5-
bromothiazole by one-pot Suzuki−Miyaura coupling and subsequent C−
H activation reactions via a 5-TPA-substituted thiazole intermediate 1. X-
ray single-crystal structures of six compounds indicate that they all
crystallize in the triclinic P1 space group and the thiazole core exhibits
̅
different dihedral angles with its adjacent benzene ring of the
triphenylamino group (3.6(3)−40.8(3)°). The photophysical and
electrochemical results demonstrate that compound 7 exhibits high electrochemical activity with a green fluorescence emission.
Meanwhile, compounds 1, 2, and 6 show high luminescence quantum yields, and compound 8 exhibits excellent thermal stability
(Td = 503 °C).
10
structures of thiazolyl-capped conjugated skeletons.10 Further-
INTRODUCTION
■
more, different from macromolecules, organic small molecules
are excellent model compounds and they show the better
crystalline characteristics. X-ray single-crystal diffraction, which
is widely regarded as a bridge between the theory and the
experiment, has been proved to be one of the most powerful
tools to characterize the molecular geometry and packing
information.11
In our previous work, a series of symmetrical 1,10-
phenanthroline, oligothiophene, and bithiazole-centered heter-
ocyclic aromatic compounds and their photoresponsive self-
assembled nanocomposite films and nanodevices have been
investigated.12 As an extensive study in this area, we aim to
reduce the symmetry of our target molecules by using one
asymmetrical thiazole core with different electron-donating and
electron-withdrawing terminal groups. Generally, compounds
with lower symmetry show fascinating properties, such as
ferroelectric, near-infrared absorption, nonlinear optic, electro-
generated chemiluminescence, single-molecular magnet, and
asymmetrical catalysis.13 The motivation of incorporating
various donor and acceptor units into one molecule is to finely
tune their electronic structures and compare their spectro-
Recently, π-functional materials1 are of increasing interest on
the studies of organic electronics, such as organic photovoltaics
(OPVs), organic field-effect transistors (OFETs), and organic
light-emitting diodes (OLEDs). For instance, many scientific
efforts have been made on the extended aromatic heterocyclic
systems, such as benzothiadiazole,2 thiophene,3 carbazole,4
diazine,5 naphthalene diimide,6 perylene diimide,7 and 1,10-
phenanthroline,8 which could act as effective components for
the molecule-based photovoltaic and optoelectronic nano-
devices. Furthermore, all these investigations present both
opportunities and challenges to the rational design and
synthesis of conjugated heterocyclic aromatic units for the
applications of high-performance optoelectronic materials.
In view of the molecular design, one important problem is
the fine-tuning of the electronic structures in a wide range and
the precise control of the solid-state structures to achieve
appropriate intermolecular interactions for bulk materials.9 On
the basis of the above-mentioned two considerations, it is
believed that the linear thiophene/thiazole-containing con-
jugated compounds with different D−A hybrids are good
candidates, and they represent an intriguing and promising class
of π-conjugated oligomers. For example, Wakamiya and co-
workers have demonstrated that the B(C6F5)3 coordination/
cyclization protocol can be effective for tuning the electronic
Received: June 28, 2013
Published: August 13, 2013
© 2013 American Chemical Society
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Article
a
Scheme 1. Synthetic Route of Thiazole-Containing Triphenylamino Compounds
a
(i) 4-(diphenylamino)phenylboronic acid, [Pd(PPh3)4], Cs2CO3, dioxane, H2O; (ii) 4-pyridinylboronic acid, [Pd(PPh3)4], Cs2CO3, toluene, H2O;
(iii) 4-boronobenzoic acid, [Pd(PPh3)4], Cs2CO3, toulene, H2O; (iv) 2-thiophenylboronic acid, [Pd(PPh3)4], Cs2CO3, dioxane, H2O; (v)
bis(pinacolato)diboron, [Pd(PPh3)4], KOH, dioxane, H2O; (vi) 2,5-bis(trimethylstannyl)thiophene, [Pd(PPh3)2Cl2], THF; (vii) 5,5′-bis(trimethyl-
stannyl)-2,2′-bithiophene, [Pd(PPh3)2Cl2], THF.
scopic, electrochemical, and thermal properties. As a result, a
family of symmetrical/asymmetrical thiazole-based heterocyclic
aromatic fluorescent compounds with high thermal stability and
good solubility has been described, where various electron-
donating and electron-withdrawing terminal groups (bromo,
triphenylamino, pyridyl, thienyl, and benzoic acid) are
introduced, as illustrated in Scheme 1. Besides the conventional
C−C coupling reactions, such as Suzuki−Miyaura, Stille, and
homocoupling, the C−H activation reaction is achieved to
prepare the unexpected TPA-functionalized thiazole compound
2 by the one-pot Suzuki−Miyaura coupling and the following
C−H activation reactions via a 5-TPA-substituted thiazole
intermediate 1, and the possible reaction mechanism is
proposed.
ring shows better reaction activity than its 5-position in the
aspects of facilitating the C−C bond cross-coupling reactions
and improving the final yields.15 This difference in the reaction
activity is successfully utilized to synthesize further asym-
metrical thiazole-based compounds 5−7 and 10 with ease.
Moreover, different from our previously reported bithiazole
derivatives where the two TPA chromophores are introduced
to 5-and 5′-positions of the central bithiazole unit,12g the C−C
bond homocoupling reaction is first used to prepare 2 and 2′
TPA-substituted bithiazole compound 8 with a high yield
(78%) in the presence of bis(pinacolato)diboron. All the
heterocyclic aromatic compounds have been characterized by
1H, 13C NMR, and EI-TOF-MS spectra, and the results clearly
demonstrate the formation of expected molecules. Further-
more, compounds 7, 8, 11, and 12 have been confirmed by the
1H−1H correlation spectroscopy (COSY) NMR, as illustrated
in Figures SI6b, SI7b, SI10b, and SI11b (Supporting
Information).
It is interesting to mention that the reaction between 1 equiv
of 5-bromothiazole with 2 equiv of 4-(diphenylamino)phenyl-
boronic acid under the conventional Suzuki−Miyaura coupling
condition yields the expected compound 1 in a yield of 61%, as
shown in Scheme 1. However, an unexpected byproduct 2 is
also obtained simultaneously in a yield of 12%. This reaction
can be monitored directly by a UV-light detector excited at 365
nm, in which the color of fluorescence emission alters from
blue for the starting materials to yellow (1) and green (2). As a
RESULTS AND DISCUSSION
■
Syntheses. Thiazole is an asymmetrical molecule compared
with thiophene, and the two α positions of the sulfur atom have
distinguishable reaction activities. However, the synthesis of
asymmetrical thiazole-containing compounds remains more
challenging than the symmetrical thiazole molecules.14 Our
synthetic strategy was based on the routes shown in Scheme 1,
in which most of the thiazole-containing compounds were
prepared by the Pd-catalyzed Suzuki−Miyaura and Stille cross-
coupling reactions. The asymmetrical precursors 3 and 9 were
synthesized from 2,5-dibromothiazole and respective boron
reagents with high yields, where the 2-position of each thiazole
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Scheme 2. Possible Mechanism for the Formation of Unexpected Compound 2 Based on the One-Pot Suzuki−Miyaura Cross-
Coupling and C−H Activation Reactions via a 5-TPA-Substituted Thiazole Intermediate 1
control experiment, thiazole was used to repeat the synthetic
procedure instead of 5-bromothiazole, but no reaction took
place and compound 4 was not found. The result indicates the
low reactivity of C−H activation in this case, which is
consistent with the previously reported literature.16
to obtain as many as single-crystal structures of our
compounds. As a result, six asymmetrical D−π−A and
symmetrical D−π−D types of thiazole-containing triphenyla-
mino compounds, that is, 2, 3, 5, and 7−9 (Table 2 and Table
SI1, Supporting Information), have been structurally charac-
terized. All six compounds crystallize in the same triclinic P1
space group, indicative of the low symmetry of molecules. The
molecular lengths of compounds 2, 3, 5, 7, and 8 are longer
than 1.30 nm. The two sulfur atoms from the thiazole ring and
its neighboring thiophene ring in 7 and 8 are found to point to
the opposite directions, exhibiting the common trans
configuration with very small dihedral angles of 1.2(3)° or
3.0(3)° in 7 and 0° in 8. The thiazole core exhibits
distinguishable dihedral angles with its adjacent benzene ring
of the triphenylamino group in the range of 3.6(3)−40.8(3)°,
as shown in Figure 2. The C−C bond length between the
triphenylamino and thiazolyl units in six compounds is ca. 1.46
Å, exhibiting a somewhat double-bond character.
The crystal packing view of this family of linear heterocyclic
aromatic compounds 2, 3, 5, and 7−9 is shown in Figure SI12
(Supporting Information). It is worth mentioning that the
packing structure of 9 has the π−π stacking interactions
between neighboring thiazole and pyridine rings with the
centroid-to-centroid separation of 3.846(1) Å. However, strong
π−π stacking interactions are not observed in the other five
TPA-functionalized molecules mainly because of the steric
hindrance effects of large triphenylamino groups.
Taking all the above-mentioned results into consideration, it
is concluded that at least two steps are required in this one-pot
reaction. Namely, compound 1 was synthesized first by the
classical Suzuki−Miyaura cross-coupling reaction, where the 5-
TPA-substituted thiazole would activate the 2-position of the
thiazole ring for the next reaction, and then compound 2 was
generated from compound 1 by the normal Pd-catalyzed C−H
activation reaction. A possible two-step reaction mechanism for
producing compounds 1 and 2 is given in Scheme 2 to explain
our experimental phenomena, where the details of each
reaction can be easily formulated, including the processes of
well-known oxidation−addition and reduction−elimination.17
Spectral Characterizations. As shown in Figure 1, all new
heterocyclic aromatic compounds show characteristic absorp-
tions at 346−425 nm in their electronic spectra corresponding
to the π−π* transitions between adjacent aromatic heterocycles
in the asymmetrical D−π−A and symmetrical D−π−D system.
It is noted that the conjugated thiazole molecules have a high
molar absorption coefficient (>10 000 L·mol−1·cm−1) because
of their unique D−A structures. Furthermore, this family of
linear asymmetrical/symmetrical heterocyclic aromatic com-
pounds is fluorescent-active from blue to yellow to green
(446−566 nm). In particular, compound 2 shows an
extraordinarily strong fluorescence peak at 488 nm with the
luminescence quantum yield (Φ) of 41% (Table 1) (see the
Supporting Information for details). At the same time, it
exhibits a strong UV−vis absorption peak at 398 nm (ε = 35
700 L·mol−1·cm−1). In comparison with compound 1, similar
bathochromic shifts have been found in the fluorescence
emission spectra of compounds 2, 3, 5−8, and 10−12 when the
delocalized π-system of molecules is increased. Compared with
compound 5, it is noted that its structural isomer compound 10
shows bathochromic shifts of 6 and 32 nm in the electronic
absorption and luminescence spectra, respectively, which are in
good agreement with the following theoretical studies. The
luminescence quantum yield studies indicate that compounds
3, 5, 9, and 10 show low values of Φs (<10%) because of the
fluorescence quenching effects of the bromo and/or pyridyl
groups.18
̅
Thermal Stability. In this work, eleven thiazole-based
aromatic heterocyclic compounds have been checked by the
TGA measurements and a parameter of Td (10% weight-loss
10
temperature) is used to describe the thermal durability of these
compounds (Table 1). In general, the thermal stability of
heterocyclic aromatic compounds has an important impact on
the device performance based on the thermal annealing
method, which is one of the most essential parameters for
the fine-tuned optoelectronic applicability.19 However, π-
conjugated organic compounds with the Td value higher
10
than 400 °C are not very common. Therefore, according to the
lessons learned from those successful or unsuccessful
examples,12f−h we have reconsidered the molecular design
and try to come up with a solution to increase the thermal
stability of our compounds. The introduction of triphenylamino
chromophores with a strong donor property is found to be an
efficient approach in this work.
Single-Crystal and Molecular Packing Structures of 2,
3, 5, and 7−9. To have deeper insight into the molecular
geometry and interesting supramolecular interactions, we tried
The TGA curves of 1−3, 5−8, and 10−12 indicate that they
can remain unchangeable when the temperature is below 250
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compounds was examined by the cyclic voltammetry (CV)
and the differential pulse voltammetry (DPV) measurements in
their 1.0 × 10−3 mol·L−1 CH2Cl2 solutions containing 0.10 mol·
L−1 TBAClO4 as the supporting electrolyte at different scan
rates (20, 50, 80, and 100 mV/s). All potentials reported herein
were calibrated with the ferrocene/ferrocenium couple (Fc/
Fc+) as an internal standard. The oxidation onset potentials
(Eoxonset) as well as the HOMO/LUMO energy levels were
determined by the DPV and electronic spectral data, which are
summarized in Table 1. The onset oxidation was measured
relative to the Fc/Fc+ couple where an energy level of −5.10 eV
versus vacuum was assumed.20
As depicted in Figures 4a and SI15d (Supporting
Information), compound 7 shows a reversible and well-defined
redox response in the CV measurements. Besides, the DPV
method is used to further explore the electrochemical
properties for related compounds. As can be seen in Figure
4c, two or three oxidation waves have been observed for all
compounds, and the oxidation potentials and the measured
currents are found to be dependent on their molecular
structures. For example, compound 7 displays three oxidation
waves in the range of 0.5−1.1 V, indicative of the existence of
three stable cation-radical species, which are suggested to be the
first oxidation states of triphenylamine (0.51 V), thiophene
(0.79 V), and thiazole (1.05 V).21
1
The first oxidation potentials Eox of these π-functionalized
thiazole compounds were determined to be 0.51 V for 7, 0.52 V
for 1, 0.53 V for 6, and 0.54 V for 10, respectively. It is
generally believed that the HOMO of the D−A oligomer is
determined by the HOMO of the donor unit, whereas the
LUMO of the D−A oligomer is controlled by the LUMO of the
acceptor unit. TPA is known to be an efficient chromophore
with a strong donor property.22 Therefore, these molecules
show similar HOMO energy levels in this case, which can guide
us to rationally design the donor materials and finely tune the
LUMO energy levels by means of introducing different
electron-withdrawing groups for these TPA-based dyes.
Density Function Theory (DFT) Computations. DFT
calculations are carried out with the Gaussian 09, revision C.01
program, using the B3LYP method and 6-31G* basis set.23 The
fixed atom coordinates of 12 thiazole-containing compounds,
which are based upon the structural parameters determined by
the X-ray single-crystal diffraction method and the full
optimization, are used for the HOMO and LUMO gap
calculations (Table 1).
The resultant HOMO−LUMO gaps for thiazole-incorpo-
rated heterocyclic aromatic compounds 5 and 10 are 3.23 and
3.19 eV, respectively, which are analogous to their UV−vis
absorption peaks. In addition, the DFT and DPV results show
that compounds 5 and 10 have similar HOMO, but different
LUMO, energy levels. It is believed that the introduction of
electron-donating groups raises the HOMO energy levels,
whereas the introduction of electron-withdrawing groups
lowers the LUMO energy levels, which will greatly decrease
the HOMO−LUMO gaps of resultant compounds. That is to
say, the introduction of a pyridyl group at the 2-position of the
thiazole unit is more effective than the 5-position in increasing
the strength of D−A charge transfer for identical molecular
formulas.
Figure 1. UV−vis absorption spectra (a), fluorescence emission
excited at 350 nm (b), and their visual photographs (c) for the
thiazole-containing triphenylamino compounds in their methanol
solutions at room temperature with the same concentration of 5.0 ×
10−5 mol·L−1.
°C and the Td values for them are found to range from 271 to
10
503 °C in Figure 3. Moreover, the thiazole derivatives 2 and 5−
8 show higher thermal stability compared with other thiazole-
containing compounds. It is noted that the T value for the
d10
TPA-extended bithiazole compound 8 reaches as high as 503
°C, indicative of the excellent thermal stability. Compared with
our previously reported compounds,12g this family of molecules
shows enhanced thermal stability due, in large part, to the
removal of two n-butyl alkyl chains in the central bithiazole
units and the increase of crystallization characteristics on the
premise of keeping solubility in organic solvents.
Electrochemical Properties. To further reveal the electro-
chemical activity and energy level information, the electro-
chemical behavior of thiazole-based heterocyclic aromatic
As shown in Figure 5, according to the DPV measurements,
further analyses of the frontier orbitals reveal that there is a
nearly linear relationship between the experimentally deter-
mined energy levels (DPV and UV−vis absorption spectra) and
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Table 1. UV−vis Absorption and Fluorescence Emission Data, Optical, Electrochemistry, Calculated HOMO−LUMO Energy
Gaps (Eg), and Internal Reorganization Energy (λ) for Related Heterocyclic Aromatic Compounds
fluorescence
d
10
a
b
e
f
g
h
i
onset
Egopt
Egcalcd
λmax
(nm)
Eox
(V)
EHOMO
(eV)
ELUMO
(eV)
λTZ
λT
Td
UV−vis λmax
c
compd
[nm (eV)]
ε (L·mol−1·cm−1
)
(eV)
(eV)
Φs
(°C)
(eV)
(eV)
1
2
346 (3.58)
398 (3.12)
369 (3.36)
397 (3.12)
387 (3.20)
387 (3.20)
422 (2.94)
306 (4.05)
403 (3.08)
421 (2.94)
425 (2.92)
49 100
35 700
41 800
33 600
18 400
45 100
15 500
4910
3.21
2.77
3.01
2.76
2.84
2.85
2.53
3.56
2.64
2.50
2.47
3.83
3.57
3.27
3.23
3.11
3.26
2.93
4.44
3.19
2.75
2.64
446
488
493
534
496
490
510
396
566
503
509
0.53
0.41
0.04
0.07
0.40
0.32
0.20
0.02
0.03
0.16
0.16
315
399
271
354
442
349
503
190
329
323
318
0.40
0.26
0.47
0.38
0.36
0.39
0.33
1.07
0.40
0.25
0.34
−5.50
−5.36
−5.57
−5.48
−5.46
−5.49
−5.43
−6.17
−5.50
−5.35
−5.44
−2.29
−2.59
−2.56
−2.72
−2.62
−2.64
−2.90
−2.61
−2.86
−2.85
−2.97
0.17
0.27
0.12
0.13
0.16
0.21
0.23
0.37
0.18
0.23
0.23
0.23
0.35
0.22
0.21
0.23
0.29
0.34
0.38
0.21
0.32
0.29
3
5
6
7
8
9
10
11
12
17 800
25 800
46 500
a
b
Optical energy gaps determined from the UV−vis absorptions in their methanol solutions. The geometries are calculated by the B3LYP method
and 6-31G* basis set. Photoluminescence quantum yields. 10% weight-loss temperature. Oxidation onset potentials determined from DPV.
Calculated from EHOMO = −(Eox
containing compounds. Calculated internal reorganization energy for thiophene-based compounds.
c
d
e
f
g
h
onset
+ 5.10). Calculated from ELUMO = EHOMO + Egopt
. Calculated internal reorganization energy for thiazole-
i
Table 2. Crystal Data and Structure Refinement Details for Six Compounds 2, 3, 5, and 7−9
compd
2·EtOH·CHCl3
3
(5)2·CH3CN
C54H41N7S2
7
8·2H2O
9
formula
C42H36N3SOCl3
737.16
C21H15BrN2S
407.32
C25H18N2S2
410.55
C42H34N4S2O2
690.85
C8H5BrN2S
241.11
formula wt
T (K)
852.06
291(2)
291(2)
291(2)
291(2)
291(2)
291(2)
wavelength (Å)
cryst size (mm)
cryst syst
space group
a (Å)
0.71073
0.71073
0.71073
0.71073
0.71073
0.71073
0.10 × 0.10 × 0.10
triclinic
0.16 × 0.18 × 0.20
triclinic
0.08 × 0.10 × 0.10
triclinic
0.10 × 0.12 × 0.12
triclinic
0.10 × 0.10 × 0.10
triclinic
0.10 × 0.12 × 0.12
triclinic
P1
P1
P1
P1
P1
P1
̅
̅
̅
̅
̅
̅
10.020(7)
10.250(7)
18.583(13)
78.568(11)
87.828(11)
75.839(12)
1814(2)
10.0378(9)
10.1977(9)
10.4509(9)
71.289(2)
72.671(2)
65.066(1)
902.18(14)
2/1.499
10.2017(14)
12.9072(17)
17.458(2)
85.786(2)
85.243(2)
73.689(2)
2195.6(5)
2/1.289
10.3933(10)
12.6851(12)
16.6669(16)
97.372(2)
105.335(1)
98.675(2)
2062.0(3)
4/1.322
10.237(4)
11.233(4)
15.634(5)
78.122(4)
85.747(5)
79.296(5)
1727.5(11)
2/1.328
5.8778(18)
7.415(2)
9.975(3)
84.049(5)
87.505(5)
77.632(4)
422.3(2)
2/1.896
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z/Dcalcd (g/cm3)
2/1.350
F(000)
μ (mm−1
768
412
892
856
724
236
)
0.349
2.399
0.168
0.272
0.198
5.052
max/min transmission
hmin/hmax
0.9660/0.9660
−11/11
0.7001/0.6455
−11/11
0.9867/0.9834
−7/12
0.9733/0.9681
−9/12
0.9805/0.9805
−7/12
0.6320/0.5824
−6/6
kmin/kmax
−12/10
−10/12
−15/15
−15/14
−13/13
−8/8
lmin/lmax
−22/22
−12/12
−20/20
−19/19
−18/18
−11/7
data/parameter
final R indices [I > 2θ(I)]
6296/479
R1 = 0.0894
wR2 = 0.2226
R1 = 0.1228
wR2 = 0.2537
0.95
3153/226
R1 = 0.0411
wR2 = 0.0982
R1 = 0.0529
wR2 = 0.1013
0.93
7596/569
R1 = 0.0654
wR2 = 0.1805
R1 = 0.0994
wR2 = 0.2037
0.97
7162/542
R1 = 0.0495
wR2 = 0.1338
R1 = 0.0887
wR2 = 0.1520
1.03
5977/445
R1 = 0.0719
wR2 = 0.1948
R1 = 0.0849
wR2 = 0.2038
1.02
1460/109
R1 = 0.0526
wR2 = 0.1373
R1 = 0.0574
wR2 = 0.1404
1.01
a
a
R indices (all data)
S
max./min. Δρ [e·Å−3
R1 = ∑||Fo| − |Fc||/∑|Fo|, wR2 = [∑[w(Fo − Fc2)2]/∑w(Fo )2]1/2
]
1.36/−0.51
0.32/−0.49
0.29/−0.59
0.18/−0.25
1.63/−1.25
0.76/−1.15
a
2
2
.
the theoretically calculated ones for the HOMOs and LUMOs
of these thiazole-containing heterocyclic aromatic hybrids,
which is consistent with our previous work.12g On the one
hand, these molecules show similar HOMO energy levels
because of the presence of a strong electron-donating group of
the TPA chromophore. On the other hand, increasing the
conjugated molecular length and enhancing the strength of
electron-withdrawing groups greatly lower the LUMO energy
levels and partly decrease the HOMO−LUMO gaps of
resultant compounds simultaneously. More importantly, this
relationship demonstrates that, despite the uncertainty in the
calculated absolute values, theoretical calculations can act as a
very useful tool to predict and guide the synthesis of future
thiazole-based oligomer materials.
To make further comparisons from a theoretical and
experimental perspective, investigations of the internal
reorganization energy (λ) have been done at the B3LYP/6-
31G* level for a series of π-conjugated thiazole-based
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Figure 2. ORTEP diagrams (30% thermal probability ellipsoids) of the molecular structures of 2, 3, 5, and 7−9 showing the dihedral angles and
relative configurations between adjacent aromatic heterocycles. The solvent molecules are omitted for clarity.
zole-containing triphenylamino chromophore compounds have
smaller λ values, which can be explained commendably by the
presence of intermolecular hydrogen bonds and/or small
dihedral angles between the thiazole and the thiophene/
benzene/pyridine rings in their crystal structures.
Solid-State Conductance Properties. To further reveal
the solid-state conductance of linear aromatic heterocyclic
compounds 11 and 12, two ends of their solid samples are
covered by a pair of electrodes made of conductive silver paste,
and the corresponding I−V curves are recorded between the
pair of electrodes by means of a four-probe system under the
same experimental condition for comparison. As shown in
Figure 6, linear fitting of the two obtained I−V curves gave the
average resistivity of 1.3 × 106 Ω·m for compound 11 and 1.1 ×
106 Ω·m for compound 12, exhibiting typical semiconducting
characteristics. The better conjugacy for the central thiophene/
thiazole extended aromatic rings as well as the abundant
supramolecular interactions, such as S···S contact, hydrogen
bonding, and π−π stacking, plays important roles in increasing
the conductivity of compounds 11 and 12, because the solid-
state conductance of semiconducting compounds strongly
relies on the delocalized π-system of the whole molecules
and their packing fashions. Compared with compound 11, the
enhancement of solid-state conductance for compound 12 is
mainly ascribed to its lower band gap (2.75 and 2.64 eV for
compounds 11 and 12, as depicted in Table 1).
Figure 3. Thermograms of thiazole-containing triphenylamino
compounds 1−3, 5−8, and 10−12.
derivatives and the corresponding thiophene-based counter-
parts. According to Marcus theory,24 the self-exchange rate and
the charge mobility are determined by the electronic coupling
between adjacent molecules (t), which needs to be maximized,
and the reorganization energy (λ), which needs to be small for
efficient charge transport.9f The reorganization energy (λ)
depicts the changes in the geometry of two molecules during
the electron-transfer reaction. It has two contributions, that is,
an internal one and an external one. The contribution of the
environmental factor (intermolecular) to the reorganization
energy is expected to be small in an organic solid, and hence,
only the intramolecular reorganization energy is calculated.25 In
this paper, the thiazole derivatives exhibit a slightly smaller
internal reorganization energy than the thiophene counterparts,
which means that the former may be good candidates for
investigations of the design and synthesis of π-conjugated
oligomers for OFET materials from a theoretical and
experimental perspective. Comparatively speaking, the thia-
CONCLUSION
■
In summary, a family of thermally stable and soluble thiazole-
based heterocyclic aromatic fluorescent compounds having the
same triphenylamino chromophores are described herein. All of
these multiple N-donor-containing compounds have effective
π-conjugated systems and different triphenylamino, pyridine,
thiophene, and benzoic acid tails showing symmetrical D−π−D
and asymmetrical D−π−A structures. Investigations of the
differences between the coupling approaches and experimental
conditions on C−C bond formation and C−H bond activation;
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Figure 4. CV (a, b) and DPV (c, d) for related heterocyclic aromatic compounds in CH2Cl2 (1.0 × 10−3 mol·L−1) containing 0.10 mol·L−1 of
TBAClO4 under argon. In CV, different scanning rates of 20, 50, 80, and 100 mV/s are used for compounds 7 (a) and 11 (b) vs Fc/Fc+.
the molecular conformation and dihedral angles between
neighboring heterocycles; the energy gaps and energy levels;
the thermal stability; the electronic, fluorescence, and electro-
chemistry spectra; and the DFT computations have been
systematically carried out.
It is interesting to mention that compound 2 can be prepared
by the Suzuki−Miyaura coupling and subsequent C−H
activation from a 5-TPA-substituted thiazole intermediate 1
via a one-pot reaction, where a possible two-step reaction
mechanism is given based on the distinguishable reaction
activity for 2- and 5-positions of one thiazole ring. X-ray single-
crystal structures of six compounds indicate that they all
TGA studies indicate that compound 8 has excellent thermal
stability with a Td value as high as 503 °C.
10
The acquirement of these linear symmetrical/asymmetrical
heterocyclic aromatic compounds, especially the single-crystal
structures, promotes us to further explore the possible rules
between their structures and properties. Therefore, the
theoretical and experimental studies have been made to reveal
the differences from related compounds with adjustable
electronic properties. Comparatively speaking, the thiazole
derivatives exhibit a slightly smaller internal reorganization
energy than the corresponding thiophene units, which suggests
that the former may be good candidates for investigations of
the design and synthesis of new π-conjugated oligomers for
OFET materials from a theoretical and experimental
perspective. Further studies are being undertaken on the
field-effect, light-emitting, photoresponsive, and photovoltaic
properties of these linear multiple N-donor-containing aromatic
heterocycle-based nanowires, nanocomposite films, and nano-
devices in our laboratory.
crystallize in the same triclinic P1 space group and the thiazole
̅
cores exhibit different dihedral angles with their adjacent
benzene ring of the triphenylamino group (3.6(3)−40.8(3)°).
Fluorescence spectral studies reveal that compounds 1, 2, and 6
show high luminescence quantum yields (Φs = 40−53%).
Moreover, the electrochemical results demonstrate that
compound 7 exhibits high electrochemical activity, and the
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Figure 5. (a) HOMOs and LUMOs of 2, 5−8, and 10−12 calculated with B3LYP/6-31G*. (b) Energy level correlation between the DPV, UV−vis
absorption spectra, and the computational data.
76.80; H, 4.91; N, 8.53%. Found: C, 76.68; H, 5.03; N, 8.41%. The
yellow single crystals of compound 2 suitable for X-ray diffraction
determination were grown from a mixed solution of chloroform and
ethanol (v/v = 1:1) by slow evaporation in air at room temperature for
1 week. 2: mp > 250 °C. Main FT-IR absorptions (KBr pellets, cm−1):
3437 (b), 1585 (s), 1480 (s), 1410 (m), 1325 (m), 1273 (m), 1183
1
(m), 1112 (w), 965 (w), 869 (m), 753 (m), 697 (s), 623 (w). H
NMR (500 MHz, CDCl3): δ 7.88 (s, 1H, thiazolyl), 7.80 (d, 2H, J =
8.8 Hz, triphenylamino), 7.44 (d, 2H, J = 8.6 Hz, triphenylamino),
7.31−7.27 (m, 8H, triphenylamino), 7.15−7.12 (t, 8H, triphenylami-
no), 7.09−7.04 (m, 8H, triphenylamino). 13C NMR (125 MHz,
CDCl3): δ 166.2, 149.5, 147.9, 147.3, 147.1, 138.2, 138.1, 129.4, 127.4,
127.2, 125.1, 124.7, 123.7, 123.4, 122.4. EI-TOF-MS (m/z): calcd for
[C39H29N3S]+ 571.2(100.0), 572.2(44.4), found 571.1(100.0),
572.1(51.0). Anal. calcd for C39H29N3S: C, 81.93; H, 5.11; N,
7.35%. Found: C, 81.67; H, 5.19; N, 7.21%.
Compounds 2 and 3. These compounds were synthesized
according to the above procedure by minor modifications. The
Figure 6. I−V curves for two narrow band gap semiconducting
compounds 11 and 12 in the solid state at room temperature.
contents of a degassed three-neck flask containing 2,5-dibromothiazole
(0.97 g, 4.00 mmol), 4-(diphenylamino)phenylboronic acid (1.73 g,
6.00 mmol), [Pd(PPh3)4] (0.12 g, 0.10 mmol), and cesium carbonate
(1.95 g, 6.00 mmol) were dissolved in a degassed mixture of toluene
(50 mL) and water (5 mL). The mixture was stirred and heated to
reflux for 48 h under an argon atmosphere. The mixture was then
allowed to cool to the room temperature and extracted with
chloroform. The resulting organic layer was dried over anhydrous
sodium sulfate and filtered. Compounds 2 and 3 were purified by silica
gel column chromatography using hexane and dichloromethane (v/v =
1:1) as an eluent to give the yellow solid in yields of 0.41 g (18%) for 2
and 1.09 g (67%) for 3, respectively. 2: see the above. The yellow
single crystals of compound 3 suitable for X-ray diffraction
determination were grown from a solution of chloroform by slow
evaporation in air at room temperature for 4 days. 3: mp > 250 °C.
Main FT-IR absorptions (KBr pellets, cm−1): 3437 (b), 1583 (s), 1481
EXPERIMENTAL SECTION
■
Syntheses and Characterizations of Heterocyclic Aromatic
Compounds 1−3 and 5−12. Compounds 1 and 2. A mixture of 5-
bromothiazole (0.16 g, 1.00 mmol), 4-(diphenylamino)phenylboronic
acid (0.58 g, 2.00 mmol), [Pd(PPh3)4] (0.06 g, 0.05 mmol), cesium
carbonate (0.65 g, 2.00 mmol), toluene (20 mL), and water (4 mL)
was degassed for 10 min and heated to reflux for 48 h under an argon
atmosphere. The mixture was then allowed to cool to the room
temperature and extracted with chloroform. The resulting organic
layer was dried with anhydrous sodium sulfate and filtered.
Compounds 1 and 2 were purified by silica gel column
chromatography using hexane and dichloromethane (2:1) as an eluent
to give the yellow solid in yields of 0.20 g (61%) for 1 and 0.07 g
(12%) for 2, respectively. 1: mp 133−134 °C. Main FT-IR absorptions
(KBr pellets, cm−1): 3442 (b), 1589 (s), 1527 (m), 1487 (s), 1322
(m), 1275 (s), 1110 (w), 874 (w), 835 (m), 757 (s), 694 (s), 513 (m).
1H NMR (500 MHz, CDCl3): δ 8.69 (s, 1H, thiazolyl), 7.99 (s, 1H,
1
(s), 1331 (m), 1269 (m), 758 (m), 695 (s). H NMR (500 MHz,
CDCl3): δ 7.70 (s, 1H, thiazolyl), 7.67 (d, 2H, J = 7.4 Hz,
triphenylamino), 7.31−7.28 (t, 4H, triphenylamino), 7.14 (d, 4H, J =
7.6 Hz, triphenylamino), 7.11−7.08 (t, 2H, triphenylamino), 7.05 (d,
2H, J = 8.8 Hz, triphenylamino). 13C NMR (125 MHz, CDCl3): δ
169.5, 150.0, 147.0, 144.6, 129.5, 127.2, 126.3, 125.3, 124.0, 122.0,
107.2. EI-TOF-MS (m/z): calcd for [C21H15BrN2S]+ 408.0 (100.0),
406.0 (98.1), found 408.0 (75.3), 406.0 (100.0). Anal. calcd for
C21H15BrN2S: C, 61.92; H, 3.71; N, 6.88%. Found: C, 61.68; H, 3.83;
N, 6.72%.
thiazolyl), 7.42 (d, 2H, J = 8.4 Hz, triphenylamino), 7.28−7.26 (t, 4H,
triphenylamino), 7.12 (d, 4H, J = 8.2 Hz, triphenylamino), 7.08−7.04
(m, 4H, triphenylamino). 13C NMR (125 MHz, CDCl3): δ 151.3,
148.2, 147.3, 139.4, 138.1, 129.4, 127.8, 124.8, 124.6, 123.5, 123.3. EI-
TOF-MS (m/z): calcd for [C21H16N2S]+ 328.1 (100.0), 329.1 (22.9),
found 328.0 (100.0), 329.0 (11.6). Anal. calcd for C21H16N2S: C,
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Compound 5. A mixture of compound 3 (0.41 g, 1.00 mmol), 4-
pyridinylboronic acid (0.15 g, 1.20 mmol), cesium carbonate (0.39 g,
1.20 mmol), [Pd(PPh3)4] (0.06 g, 0.05 mmol), dioxane (30 mL), and
water (5 mL) was degassed for 0.5 h and heated to reflux for 40 h
under an argon atmosphere. After the mixture was cooled to room
temperature, chloroform (50 mL) was added, and the organic phase
was washed with brine, separated, and dried over anhydrous sodium
sulfate. The organic solvent was evaporated under reduced pressure,
and the solid residue was purified by silica gel column chromatography
using a mixture of hexane and dichloromethane (v/v = 1:2) as an
eluent to provide the desired product 5 as a dark yellow solid in a yield
of 0.36 g (89%). The yellow single crystals of compound 5 suitable for
X-ray diffraction determination were grown from a mixed solution of
chloroform and acetonitrile (v/v = 1:1) by slow evaporation in air at
room temperature for 3 weeks. 5: mp 208−210 °C. Main FT-IR
absorptions (KBr pellets, cm−1): 3442 (b), 1589 (s), 1486 (s), 1433
(m), 1415 (s), 1331 (m), 1291 (s), 1265 (m), 1184 (m), 817 (m), 755
(m), 702 (s), 614 (m), 543 (m). 1H NMR (500 MHz, CDCl3): δ 8.63
(d, 2H, J = 4.4 Hz, pyridyl), 8.16 (s, 1H, thiazolyl), 7.81 (d, 2H, J = 8.5
Hz, triphenylamino), 7.48 (d, 2H, J = 5.0 Hz, pyridyl), 7.33−7.29 (t,
4H, triphenylamino), 7.16 (d, 4H, J = 8.0 Hz, triphenylamino), 7.13−
7.10 (t, 2H, triphenylamino), 7.08 (d, 2H, J = 8.6 Hz, triphenylamino).
13C NMR (125 MHz, CDCl3): δ 169.6, 150.3, 149.8, 146.8, 141.7,
139.7, 134.6, 129.6, 127.9, 126.1, 125.4, 124.1, 121.7, 120.6. EI-TOF-
MS (m/z): calcd for [C26H19N3S]+ 405.1 (100.0), 406.1 (30.0), found
405.1 (100.0), 406.1 (19.6). Anal. calcd for C26H19N3S: C, 77.01; H,
4.72; N, 10.36%. Found: C, 76.79; H, 4.86; N, 10.20%.
TOF-MS (m/z): calcd for [C25H18N2S2]+ 410.1 (100.0), 411.1 (29.4),
found 410.1 (100.0), 411.1 (12.2). Anal. calcd for C25H18N2S2: C,
73.14; H, 4.42; N, 6.82%. Found: C, 72.98; H, 4.58; N, 6.69%.
Compound 8. Compound 3 (0.45 g, 1.10 mmol), bis(pinacolato)-
diboron (0.14 g, 0.55 mmol), and KOH (0.62 g, 11.00 mmol) were
dissolved in a degassed dioxane/water mixture (24 mL, 5:1), argon
was bubbled through the solution for 5 min, then the [Pd(PPh3)4]
(0.06 g, 0.05 mmol) was added, and the reaction mixture was kept
under stirring and refluxing for 10 h. After the mixture was cooled to
room temperature, CHCl3 (50 mL) was added, and the organic phase
was washed with brine, separated, and dried over anhydrous Na2SO4.
The organic solvent was evaporated under reduced pressure and the
solid residue was purified by silica gel column chromatography using
CHCl3 as an eluent to provide the desired product 8 as a yellow solid
in a yield of 0.28 g (78%). The red single crystals suitable for X-ray
diffraction determination were grown from a solution of ethanol by
slow evaporation in air at room temperature for 1 week. mp > 250 °C.
Main FT-IR absorptions (KBr pellets, cm−1): 3437 (b), 1583 (s), 1481
1
(s), 1410 (m), 1323 (m), 1285 (s), 1143 (w), 758 (m), 696 (s). H
NMR (500 MHz, CDCl3): δ 7.85 (s, 2H, thiazolyl), 7.78 (d, 4H, J =
8.6 Hz, triphenylamino), 7.32−7.29 (t, 8H, triphenylamino), 7.15 (d,
8H, J = 8.2 Hz, triphenylamino), 7.12−7.09 (t, 4H, triphenylamino),
7.07 (d, 4H, J = 8.8 Hz, triphenylamino). 13C NMR (125 MHz,
CDCl3): δ 167.3, 149.9, 147.0, 140.7, 129.5, 127.5, 126.4, 125.3, 124.0,
122.0. EI-TOF-MS (m/z): calcd for [C42H30N4S2]+ 654.2 (100.0),
655.2 (48.5), 656.2 (10.5), found 654.1 (100.0), 655.2 (66.0), 656.2
(4.0). Anal. calcd for C42H30N4S2: C, 77.03; H, 4.62; N, 8.56%. Found:
C, 76.79; H, 4.76; N, 8.38%.
Compound 6. The contents of a degassed three-neck flask
containing compound 3 (1.63 g, 4.00 mmol), 4-boronobenzoic acid
(0.73 g, 4.40 mmol), cesium carbonate (1.95 g, 6.00 mmol), and
[Pd(PPh3)4] (0.12 g, 0.10 mmol) were dissolved in a degassed
dioxane/water mixture (55 mL, 10:1). The mixture was stirred and
refluxed under argon for 28 h. After being cooled to room
temperature, the light yellow solid was obtained in the reaction
mixture. The precipitate was filtered, washed with CHCl3 and
methanol, and then dried in vacuo to produce compound 6 in a
yield of 1.52 g (85%). mp 241−245 °C. Main FT-IR absorptions (KBr
pellets, cm−1): 3429 (b), 1591 (s), 1544 (m), 1481 (m), 1395 (s),
1329 (m), 1277 (m), 699 (m). 1H NMR (500 MHz, CD3OD): δ 8.18
(s, 1H, thiazolyl), 8.08 (d, 2H, J = 8.2 Hz, phenyl), 7.83 (d, 2H, J = 8.5
Hz, triphenylamino), 7.77 (d, 2H, J = 7.4 Hz, phenyl), 7.36−7.33 (t,
4H, triphenylamino), 7.14 (d, 4H + 2H, J = 7.8 Hz, triphenylamino),
7.14 (d, 2H, J = 8.4 Hz, triphenylamino). 13C NMR (125 MHz,
CD3OD): δ 169.3, 151.4, 148.2, 140.3, 131.2, 130.6, 130.5, 130.2,
128.8, 128.3, 126.7, 126.4, 125.2, 122.5. EI-TOF-MS (m/z): calcd for
[C28H20N2O2S]+ 448.5, found 448.1. Anal. calcd for C28H20N2O2S: C,
74.98; H, 4.49; N, 6.25%. Found: C, 74.75; H, 4.53; N, 6.13%.
Compound 7. A mixture of compound 3 (0.81 g, 2.00 mmol), 2-
thiophenylboronic acid (0.28 g, 2.20 mmol), cesium carbonate (0.72 g,
2.20 mmol), [Pd(PPh3)4] (0.12 g, 0.10 mmol), dioxane (50 mL), and
water (5 mL) was degassed for 0.5 h and heated to reflux for 18 h
under an argon atmosphere. After the mixture was cooled to room
temperature, chloroform (50 mL) was added, and the organic phase
was washed with brine, separated, and dried over anhydrous sodium
sulfate. The organic solvent was evaporated under reduced pressure
and the solid residue was purified by silica gel column chromatography
using dichloromethane as an eluent to provide the desired product 7 as
a dark yellow solid in a yield of 0.69 g (84%). The yellow single
crystals of compound 7 suitable for X-ray diffraction determination
were grown from a solution of chloroform by slow evaporation in air at
room temperature for 5 days. mp 192−194 °C. Main FT-IR
absorptions (KBr pellets, cm−1): 3435 (b), 1589 (s), 1487 (s), 1322
(m), 1275 (s), 1141 (w), 969 (w), 843 (m), 748 (m), 702 (s), 631
(w), 513 (w). 1H NMR (500 MHz, CDCl3): δ 7.86 (s, 1H, thiazolyl),
7.80 (d, 2H, J = 8.6 Hz, triphenylamino), 7.31 (t, 4H, triphenylamino),
7.29 (d, 1H, J = 7.8 Hz, thienyl), 7.21 (d, 1H, J = 3.4 Hz, thienyl), 7.15
(d, 4H, J = 7.6 Hz, triphenylamino), 7.12−7.09 (t, 2H,
triphenylamino), 7.07 (d, 2H, J = 8.8 Hz, triphenylamino), 7.05 (t,
1H, thienyl). 13C NMR (125 MHz, CDCl3): δ 166.6, 149.8, 147.0,
139.0, 133.4, 131.3, 129.5, 127.9, 127.4, 125.4, 125.3, 123.9, 122.1. EI-
Compound 9. The contents of a degassed three-neck flask
containing 2,5-dibromothiazole (2.43 g, 10.00 mmol), 4-pyridinebor-
onic acid (1.35 g, 11.00 mmol), [Pd(PPh3)4] (0.24 g, 0.20 mmol), and
Cs2CO3 (3.91 g, 12.00 mmol) were dissolved in a degassed mixture of
dioxane (50 mL) and H2O (5 mL). The mixture was stirred and
refluxed under an argon atmosphere for 48 h. After the mixture was
cooled to room temperature, CHCl3 (100 mL) was added, and the
organic phase was washed with brine, separated, and dried with
anhydrous Na2SO4. The organic solvent was evaporated under
reduced pressure and the solid residue was purified by silica gel
column chromatography using CHCl3 as an eluent to provide the
desired product 9 as a light yellow solid in a yield of 1.81 g (75%). The
yellow single crystals of 9 suitable for X-ray diffraction determination
were grown from a solution of CHCl3 by slow evaporation in air at
room temperature for 4 days. mp 174−175 °C. Main FT-IR
absorptions (KBr pellets, cm−1): 3421 (b), 1599 (s), 1544 (m),
1410 (s), 1308 (m), 1230 (m), 1112 (m), 994 (w), 868 (s), 814 (s),
1
703 (m), 562 (m). H NMR (500 MHz, CDCl3): δ 8.73 (d, 2H, J =
5.1 Hz, pyridyl), 7.85 (s, 1H, thiazolyl), 7.76 (d, 2H, J = 5.6 Hz,
pyridyl). 13C NMR (125 MHz, CDCl3): δ 150.7, 145.7, 133.0, 132.1,
131.9, 128.5, 120.0. EI-TOF-MS (m/z): calcd for [C8H5BrN2S]+ 241.9
(100.0), 239.9 (98.2), found 241.9 (88.2), 239.9 (100.0). Anal. calcd
for C8H5BrN2S: C, 39.85; H, 2.09; N, 11.62%. Found: C, 39.67; H,
2.11; N, 11.54%.
Compound 10. Compound 9 (0.24 g, 1.00 mmol), 4-(diphenyl-
amino)phenylboronic acid (0.29 g, 1.00 mmol), and cesium carbonate
(0.32 g, 1.00 mmol) were dissolved in a degassed toluene/water
mixture (24 mL, 5:1), argon was bubbled through the solution for 10
min, then the [Pd(PPh3)4] catalyst (0.06 g, 0.05 mmol) was added,
and the reaction mixture was kept under stirring and refluxing for 36 h.
The mixture was then allowed to cool to the room temperature and
extracted with chloroform. The resulting organic layer was dried over
anhydrous Na2SO4 and filtered. The organic solvent was evaporated
under reduced pressure and the solid residue was purified by silica gel
column chromatography using CHCl3 as an eluent to provide the
desired product 10 as a green solid in a yield of 0.37 g (91%). mp >
250 °C. Main FT-IR absorptions (KBr pellets, cm−1): 3438 (b), 1583
(s), 1488 (s), 1436 (s), 1414 (s), 1289 (s), 1179 (s), 818 (m), 700 (s),
612 (m), 538 (s). 1H NMR (500 MHz, CDCl3): δ 8.70 (d, 2H, J = 5.0
Hz, pyridyl), 8.01 (s, 1H, thiazolyl), 7.80 (d, 2H, J = 5.8 Hz, pyridyl),
7.53 (d, 2H, J = 7.5 Hz, triphenylamino), 7.30−7.27 (t, 4H,
triphenylamino), 7.14 (d, 4H, J = 7.6 Hz, triphenylamino), 7.09 (m,
8677
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4H, triphenylamino). 13C NMR (125 MHz, CDCl3): δ 175.8, 159.5,
149.2, 146.9, 144.3, 139.9, 132.2, 129.5, 127.9, 125.2, 124.0, 123.0,
122.4, 121.4. EI-TOF-MS (m/z): calcd for [C26H19N3S]+ 405.1
(100.0), 406.1 (30.0), found 405.1 (100.0), 406.1 (19.5). Anal. calcd
for C26H19N3S: C, 77.01; H, 4.72; N, 10.36%. Found: C, 76.81; H,
4.80; N, 10.24%.
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Compound 11. A mixture of compound 3 (0.41 g, 1.00 mmol), 2,5-
bis(trimethylstannyl)thiophene (0.20 g, 0.49 mmol), and the catalyst
[Pd(PPh3)2Cl2] (0.014 g, 0.02 mmol) was refluxed for 6 h in dry THF
(20 mL) under an argon atmosphere. After the mixture was cooled to
room temperature and evaporated under reduced pressure, the residue
was dissolved in CHCl3. The organic phase was washed twice with a
saturated solution of NaHCO3 and then with water. After drying on
MgSO4 and evaporation of solvent, the crude was purified by silica gel
column chromatography using CHCl3 as an eluent to give compound
11 as the red solid (0.19 g, 54% yield). 11: mp > 250 °C. Main FT-IR
absorptions (KBr pellets, cm−1): 3427 (b), 2971 (m), 1589 (m), 1487
1
(m), 1409 (m), 1047 (s), 882 (w), 748 (w), 694 (m). H NMR (500
MHz, CDCl3): δ 7.85 (s, 2H, thiazolyl), 7.78 (d, 4H, J = 8.4 Hz,
triphenylamino), 7.32−7.29 (t, 8H, triphenylamino), 7.15 (d, 8H, J =
8.0 Hz, triphenylamino), 7.12 (s, 2H, thienyl), 7.10−7.07 (t, 8H,
triphenylamino). 13C NMR (125 MHz, CDCl3): δ 166.8, 149.9, 149.8,
147.0, 140.7, 139.4, 129.5, 127.5, 127.4, 125.9, 125.3, 124.0, 122.0. EI-
TOF-MS (m/z): calcd for [C46H32N4S3]+ 736.2 (100.0), 737.2 (53.6),
738.2 (13.6), found 736.2 (100.0), 737.2 (30.7), 738.2 (3.86). Anal.
calcd for C46H32N4S3: C, 74.97; H, 4.38; N, 7.60%. Found: C, 74.77;
H, 4.42; N, 7.52%.
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Handbook of Thiophene-Based Materials: Applications in Organic
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1854.
Compound 12. The procedure for the synthesis of compound 11
was repeated except that 5,5′-bis(trimethylstannyl)-2,2′-bithiophene
(0.24 g, 0.49 mmol) was used instead of 2,5-bis(trimethylstannyl)-
thiophene (0.20 g, 0.49 mmol). Yield: 0.27 g (68%). mp > 250 °C.
Main FT-IR absorptions (KBr pellets, cm−1): 3442 (b), 1589 (s), 1487
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1
(s), 1408 (m), 1322 (m), 1275 (s), 1110 (m), 756 (m), 694 (s). H
NMR (500 MHz, CDCl3): δ 7.86 (s, 2H, thiazolyl), 7.78 (d, 4H, J =
7.6 Hz, triphenylamino), 7.32−7.29 (t, 8H, triphenylamino), 7.15 (d,
8H, J = 8.2 Hz, triphenylamino), 7.12 (d, 4H, J = 4.2 Hz, thienyl),
7.10−7.07 (t, 8H, triphenylamino). 13C NMR (125 MHz, CDCl3): δ
167.3, 149.9, 147.0, 140.7, 132.1, 132.0, 128.5, 127.5, 125.7, 125.3,
124.0, 122.0. EI-TOF-MS (m/z): calcd for [C50H34N4S4]+ 818.2
(100.0), 819.2 (57.7), 820.2 (18.1), found 818.1 (100.0), 819.1 (63.5),
820.1 (8.9). Anal. calcd for C50H34N4S4: C, 73.32; H, 4.18; N, 6.84%.
Found: C, 73.08; H, 4.24; N, 6.78%.
ASSOCIATED CONTENT
■
S
* Supporting Information
Tables of selected bond lengths and angles and intermolecular
1
hydrogen bonds; figures of π−π stacking interactions; H, 13C,
1H−1H COSY NMR and EI-TOF-MS spectra; DFT computa-
tional details; and electrochemistry diagrams for related
compounds. CCDC numbers 946825−946830 for compounds
2, 3, 5, and 7−9. This material is available free of charge via the
Internet at http://pubs.acs.org.
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Wiesler, U. M.; Vosch, T.; Hofkens, J.; De Schryver, F. C.; Mullen, K.
Chem.Eur. J. 2001, 7, 4844−4853. (b) Addicott, C.; Oesterling, I.;
Yamamota, T.; Mullen, K.; Stang, P. J. J. Org. Chem. 2005, 70, 797−
801. (c) Shin, W. S.; Jeong, H. H.; Kim, M. K.; Jin, S. H.; Kim, M. R.;
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C 2013, 117, 10743−10749.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: whuang@nju.edu.cn.
Notes
The authors declare no competing financial interest.
(8) Selected examples: (a) Chan, S.-C.; Chan, M. C. W.; Wang, Y.;
Che, C.-M.; Cheung, K.-K.; Zhu, N.-Y. Chem.Eur. J. 2001, 7, 4180−
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C.-H. Terahedron 2006, 62, 10072−10078. (c) Engel, Y.; Dahan, A.;
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ACKNOWLEDGMENTS
■
This work was financially supported by the Major State Basic
Research Development Programs (Nos. 2013CB922101 and
2011CB933300), the National Natural Science Foundation of
China (Nos. 21171088 and 21021062), and the Qing Lan
Project.
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The Journal of Organic Chemistry
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