Synthesis and physical properties of benzopyridazine-based conjugated molecules

Article abstract of DOI:10.1002/cjoc.201300509

A series of novel organic conjugated molecules (5a-5d) comprising 2,3-benzopyridiazine as electron-withdrawing core and thiophene derivatives as electron-donating arms have been synthesized successfully in good yields. The ultraviolet-visible (UV-Vis) absorption spectra and fluorescence spectra of 5a-5d revealed that the optical properties are strongly influenced by the interactions between nitrogen and sulfur atoms in the conjugated backbone, as well as the position of the alkyl chains in the thiophene rings. The experimental results and theoretical calculation data clearly indicated that the band gap and the energy levels of LUMO and HOMO could be fine-tuned by the position of alkyl chains in the thiophene rings. Thus, the structure-property correlation of this class of conjugated molecules can be well established. A series of organic conjugated molecules containing 2,3-benzopyridiazine as electron-withdrawing core and thiophene derivatives as electron-donating arms have been synthesized successfully. The optical properties and electrochemical behaviors of these molecules can be fine-tuned through changing the position of alkyl chains in the thiophene rings. Copyright

Full text of DOI:10.1002/cjoc.201300509

FULL PAPER
DOI: 10.1002/cjoc.201300509
Synthesis and Physical Properties of Benzopyridazine-Based
Conjugated Molecules
Yuezeng Su,a Wei Xu,a Feng Qiu,b Dongqing Wu,b Ping Liu,b Minzhao Xue,b and Fan Zhang*,b
a School of Aeronautics and Astronautics, Shanghai Jiao Tong University, Shanghai 200240, China
b School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
A series of novel organic conjugated molecules (5a－5d) comprising 2,3-benzopyridiazine as electron-with-
drawing core and thiophene derivatives as electron-donating arms have been synthesized successfully in good yields.
The ultraviolet-visible (UV-Vis) absorption spectra and fluorescence spectra of 5a－5d revealed that the optical
properties are strongly influenced by the interactions between nitrogen and sulfur atoms in the conjugated backbone,
as well as the position of the alkyl chains in the thiophene rings. The experimental results and theoretical calculation
data clearly indicated that the band gap and the energy levels of LUMO and HOMO could be fine-tuned by the po-
sition of alkyl chains in the thiophene rings. Thus, the structure-property correlation of this class of conjugated
molecules can be well established.
Keywords benzopyridiazine, heterocycles, conjugated molecules, optoelectronic properties
N N
S
Introduction
S
S
Organic conjugated molecules have been investi-
gated intensively due to their optoelectronic properties[1]
and potential applications in many fields,[2] such as or-
ganic field effect transistors[3,4] (OFETs), organic
photovoltaics[5] (OPVs), electrochromic devices, and
organic light emitting diodes[6] (OLEDs). One of the
most critical challenges in organic electronics is to de-
sign and synthesize novel conjugated molecules, of
which structures exert the key effect on photophysical
properties and electronic behaviors. Typically, incorpo-
ration of substituted group or heteroatom into the con-
jugated backbone has been taken into account as an effi-
cient strategy for achieving a functional system.[7-10]
Recently, nitrogen-based heterocycles, named N-hetero-
acenes, including pyridazine, pyrimidine and pyrazine,
have received great attentions.[11] As an example, pyri-
dazine containing two electron-withdrawing imine ni-
trogen atoms represents a very promising candidate for
n-type organic conjugated molecules because of its
electron-deficient character.[12] However, pyridazine-
based compounds are still rarely reported, which are
typically depicted in Figure 1.[13-15] In view of extended
conjugation, these compounds might suit to be explored
as promising materials for organic electronics. As far as
we know, fused pyridazine-cored oligothiophene deriva-
tives have not been reported.
S
N N
O
O
C12H25
S
S
N N
C12H25
O
O
N N
N N
S
S
R
S
S
n
N N
R
Figure 1 Chemical structures of representative diazine contain-
ing conjugated compounds.
abilities and self-assembly behaviors. Yamamoto and
co-workers[16] reported a series of conjugated polymers
with D-A-D repeat unit using thiophene and pyridazine
as electron-donating and electron-accepting moieties,
respectively, showing strong intermolecular interaction
(Figure 1). Recently, our group reported the synthesis
and physical properties of a new family of N-hetero-
acenes, comprising a tetraazaanthracene core and four
thiophene derivative arms.[17] The electrochemical
characterization revealed their classical electrochemical
characters. Additionally, the short S－N distances can
Donor-acceptor (D-A) conjugated molecules are
highly attractive due to their excellent light harvesting
*
E-mail: fan-zhang@sjtu.edu.cn; Tel.: 0086-021-54748964
Received June 30, 2013; accepted August 11, 2013; published online September 16, 2013.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201300509 or from the author.
Chin. J. Chem. 2013, 31, 1397—1403
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Su et al.
FULL PAPER
be observed supporting the existence of substantial in-
tramolecular S－N attraction in thiophene-azine deriva-
tives. Herein, we report the design and synthesis of a
series of novel organic conjugated molecules compris-
ing 2,3-benzopyridiazine as electron-withdrawing core
and thiophene derivatives as electron-donating arms,
with the following considerations: (1) enabling an ex-
tended conjugated plane over the pyridazine; (2)
achieving substantial intramolecular S-N interaction
leading to locked conformation between donor and ac-
ceptor parts; (3) constructing a D-A-D conjugated sys-
tems. Besides, the effect of the substituted alkyl chains
at different position of the thiophene ring on the proper-
ties of these molecules has been explored. Finally, opti-
cal and electrical properties of the molecules have been
systematically investigated for elucidation of structure-
property correlation.
Results and Discussion
Synthesis and characterization
The synthetic approach to 2,3-benzodiazine-based
molecules 5a－5c was shown in Scheme 1. The key
intermediate 2, containing S-pyridinyl moieties as good
leaving groups, was prepared by treatment of 2-mercap-
topyridine with phthaloyl dichloride at 0 ℃, using TEA
(triethylamine) as catalyst.[17] The pure compound 2 was
obtained as pale-yellow solid by recrystallization from
its dichloromethane/diethyl ether solution (yield 46%).
Afterward, compound 4 was effectively achieved
through the reaction of the thienyl Grignard reagents
with 2 in THF. Notably, the reaction quenched by HCl
Scheme 1 Synthetic routes for 5a－5c
N
N
S
(a)
S
Cl
Cl
O O
O O
2
1
(c)
(c)
(b)
S
S
S
S
S
S
S
N N
O O
Br
4a
5a
S
3a
S
(b)
O O
C6H13
N N
C6H13
C6H13
Br
C6H13
C6H13
5b
S
3b
(c)
(b)
C6H13
C6H13
C6H13
C6H13
S
S
S
S
N N
O O
C6H13
Br
5c
4c
S
4a: 66%
4b: 71%
4c: 67%
5a: 67%
5b: 98%
5c: 95%
3c
Reagents and conditions: (a) 2-mercaptopyridine, TEA,THF, 0 ℃; (b) (1) Mg, THF, 35 ℃; (2) THF, 0 ℃; (c) N2H4, C2H5OH, r.t. or 100 ℃
Scheme 2 Synthetic route for 5d
(e)
(d)
Br
Br
S
S
S
S
N
N
N
N
C6H13
SnBu3
5a
6
S
C6H13
C6H13
S
S
S
S
N
N
5d
Reagents and conditions: (d) NBS, 0 oC; (e) Pd(PPh3)4, DMF, 100 ℃
www.cjc.wiley-vch.de © 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
5d: 80%
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Synthesis and Physical Properties of Benzopyridazine-Based Conjugated Molecules
is necessary in order to avoid the rearrangement side
reaction. Purified by column chromatography (CH2Cl2/
petroleum ether), compounds 4a－4c were obtained
with the yields of 66%, 71% and 67%, respectively. Fi-
nally, these compounds were readily converted to target
molecules 5a－5c in the yields from 67% to 95%, re-
spectively, upon treated with hydrazine hydrate in etha-
nol at room temperature.
locking such a molecular conformation with S atoms of
the thiophene units and N atoms of the 2,3-benzopyri-
diazine unit in the same side; on the other hand, the
steric effect from the hexyl group at the β position in
each thiophene ring adjacent to the 2,3-benzopyridiazine
moiety might restrict the intramolecular rotation to form
the above conformation. On the contrary, an obvious red
shift of 21 nm was observed for the absorption maxi-
mum of 5c, whose two hexyl chains at the α-terminal
parts of the thiophene units offer electron-donating ef-
fect. Obviously, incorporating alkyl chain at the differ-
ent position of the thiophene ring can exert essential
effects on the optical properties of the 2,3-benzopyri-
diazine-based molecules. As expected, the absorption
spectrum of compound 5d exhibits a noticeable red shift
of 51 nm, as well as significantly enhanced absorption
intensity, by compared with that of 5a, which are typi-
cally attributed to the increase in conjugated chain
length.
Moreover, bromination of 5a was carried out by us-
ing N-bromosuccinimide (NBS) in DMF, resulting in
compound 6 (Scheme 2). The cross coupling reaction
between 6 and 5-hexylthiophen-2-yl-tripropylstannane
in the presence of Pd(PPh3)4 at 100 ℃, afforded com-
pound 5d in 80% yield after purified through column
chromatography.
1
All compounds have been fully characterized by H
NMR and 13C NMR and high-resolution mass spectra,
which are greatly in agreement with the chemical struc-
tures of these molecules. The benzopyridazine core was
successfully introduced in compounds, which was esti-
1
mated from H NMR analyses by integrating the two
aromatic signals at δ 8.5 and 7.9, which are distinctly
different from the proton peaks of naphthalene ring at δ
8.2 and 7.6 in analogous compound 1,4-bis(2-thienyl)-
naphthalene.[18]
Optical properties
The UV-vis absorption spectra of molecules 5a－5d
were measured in CH2Cl2 (Figure 2a). The spectra of 5a,
5b and 5c exhibit one main absorption peak in near UV
region (λ＝300－400 nm), which are ascribed to π-π*
transitions. While for 5d, besides a weaker absorption
band in above region (at 317 nm), a strong absorption
peak at 423 nm is observed, which is assigned to an in-
tramolecular charge transfer (ICT) transition. 1,4-Bis(2-
thienyl)-naphthalene shows an absorption maximum at
327 nm,[18] which is 18 nm blue shift by compared to its
structural analogue 5a, which arises from incorporation
of nitrogen atoms into the conjugated backbone of 5a to
form D-A structure.
The absorption maxima are shown in a sequence of
5d＞5c＞5a＞5b. Corresponding data are summarized
in Table 1. In comparison with 5a, the absorption
maximum of 5b shows a blue shift of 22 nm, presuma-
bly due to a declined conjugated planarity, because of
the two competition effects: on the one hand, in-
tramolecular S－N interaction would be favorable for
Figure 2 Ultraviolet-visible spectra of 5a－5d in dichloro-
vmethane.
The fluorescence spectra of compounds 5a－5d in
CH2Cl2 solutions were found between 350 nm and 700
nm (concentration 1.5×10−5 mol•L−1, Figure 3). Nor-
mally, conjugated molecules comprising diazine moie-
ties can essentially lead to weakening their fluores-
cence.[11,19,20] Such phenomenon also was observed in
the case of compounds 5a－5c. However, compound 5d
exhibits strong fluorescence emission, which is in ac-
cordance with its intensive absorption. Obviously,
enlongation of conjugated chain length via introduction
of thiophene units could remarkably change the optical
properties of molecules.
Table 1 Optoelectronic and electrochemical properties of 5a－5d
Compd
5a
λmax,abs/nm
345
λmax,em/nm Egopta/eV Ereda/V
LUMOb/eV
HOMOc/eV
LUMOd/eV
HOMOd/eV
−5.97
−5.65
−5.55
−5.33
386
359
413
585
3.10
3.33
2.95
2.52
−2.10
−1.94
−2.13
−1.95
−2.70
−2.86
−2.67
−2.84
−5.80
−6.19
−5.62
−5.36
−2.31
−2.28
−2.34
−2.38
5b
323
5c
366
5d
423
a The values of HOMO and LUMO energy levels were estimated from reduction potentials and UV-vis absorption edge (CV measured in
0.1 mol•L−1 CH2Cl2 solution of n-Bu4NPF6 at a scan rate of 100 mV•s−1); b LUMO＝−Ered−4.80 eV; c HOMO＝LUMO−Eg
opt
d
;
Calcu-
lated by density functional theory.
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Figure 3 Fluorescence spectra of 5a－5d in dichloromethane.
Electrochemical properties
The electrochemical behaviors of 5a－5d were stud-
ied by means of cyclic voltammetry (CV), as depicted in
Figure 4. The CV profiles of 5a, 5c and 5d show a re-
versible one-electron reduction, but compound 5b
showed irreversible reduction process. Ered1 values of
as-maded molecules are increased in an order of 5c＜5a
＜5d＜5b. Consequently, the energy levels of the low-
est unoccupied orbitals (LUMOs) are in a sequence of
5b＜5d＜5a＜5c. For compound 5c, the lowest conju-
gated effect might weaken the electron-donating effect
of thiophene units, and strengthen the electron-with-
drawing effect. Thus, compound 5c shows the highest
energy level of LUMO. While for compound 5d, the
positive conjugated effect can lead to lowering the
LUMO energy level. The values of optical band gap (Eg)
of these compounds were calculated from the absorption
edges. Compound 5b possesses the largest band gap,
likely due to the lowest coplanarity as aforementioned,
whereas compound 5d with the longest conjugated
backbone certainly owns the narrowest band gap. The
smaller band gap for compound 5c than that of 5a is
assigned to the electron-donating effect of the alkyl
chains at the α-terminal positions of the thiophene units.
Accordingly, as shown in Table 1, compound 5d exhib-
its the lowest energy level of HOMO with a significant
drop by 0.39 eV in comparison with that of compound
5a, probably due to the higher conjugated system in the
former case. Compound 5c processes a slightly higher
HOMO value (−5.62 eV) than 5a (−5.80 eV), likely at-
tributed to the weaker electron-donating effect of the
alkyl substituents. Reasonably, compound 5d with the
longest conjugated backbone, shows much higher
HOMO level than the other compounds. Therefore, both
substituted side chain and conjugated length have pro-
nounced influence on the electronic behaviors of the
benzopyridiazine-based conjugated molecules through
fine-tuning the frontier molecular orbitals (HOMO and
LUMO).
Figure 4 Cyclic voltammograms of 5a－5d in dichloromethane
(scanning rate at 100 mV•s−1).
molecular orbitals, the geometries as well as the elec-
tronic structures of 5a－5d were calculated by using
density functional theory (DFT) (B3LYP/6-31G(d) level)
(Figure 5 and Table 1). A calculated dihedral angle of
0.0o between benzopyridazine and thiophene moieties
for 5c is much smaller than that of 29.3o dihedral angle
for 5a, demonstrating a higher π-conjugated planarity in
the former case, also in agreement with its narrower
optical band gap. While, 5d possessing a larger calcu-
lated dihedral angle of 29.6o between benzopyridazine
and thiophene moieties, but the smallest optical band
gap of 2.52 eV, demonstrated the significant effect of
the prolonged conjugated chain length on the extended
π-conjugated system. It is noticed that the LUMOs for
5a, 5c and 5d primarily reside on the benzopyridazine
moieties with similar electron density distributions,
supporting the strong electron-withdrawing character of
the benzopyridazine moiety. While the HOMOs of 5a,
5c and 5d are localized over the full conjugated back-
bone with higher electron density distributions on the
thiophene rings.
However, for compound 5b, the LUMO and HOMO
are mostly localized over the benzopyridazine and thio-
phene moieties, respectively, indicating the lower con-
jugated effect between benzopyridazine and thiophene
moieties, which is geometrically supported by a larger
calculated dihedral angle of 57.2o between two moieties,
and in line with the declined coplanarity of the molecu-
lar backbone. Thus, the LUMO and HOMO of com-
pound 5b are separately decided by the electron-with-
drawing and electron-donating moieties. Since benzo-
pyridazine core plays a critical role on the LUMO level
for all these compound 5a－5d, their LUMO values
displayed less variation. The HOMO and LUMO energy
levels of 5a, 5c and 5d show similar trends to those
achieved in optoelectronic characterization. Additionally,
in the case of 5b, the larger deviations of the calculated
values from the experimental results are likely attributed
Density functional theory calculations
To make insight into the energy level of the frontier
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Chin. J. Chem. 2013, 31, 1397—1403

Synthesis and Physical Properties of Benzopyridazine-Based Conjugated Molecules
Synthesis of 1,2-di(S-(pyridine-2-yl)) benzenedithio-
ate (2)
to the opposite effects from the steric effect of alkyl
chain and intramolecular interaction induced by N and S
atoms as mentioned above, which make it difficult to
establish an optimum conformational modeling.
To a solution of 15 mL TEA in 150 mL dry THF was
added 2-mercaptopyridine (10.7 g, 0.10 mol) at 0 ℃
under nitrogen and a solution of phthaloyl dichloride
(9.1 g, 0.045 mol) in 50 mL of THF was added immedi-
ately. After the addition, the reaction was stirred for 10
min, then quenched by adding HCl (10%, 100 mL). The
organic layer was extracted with CH2Cl2, and the com-
bined organic layers were washed with NaOH (10%,
100 mL), NaHCO3 (1 mol•L−1, 100 mL), and water and
dried over MgSO4. After recrystallization from CH2Cl2/
diethyl ether, the pure product 2 (13.3 g, 84%) was ob-
1
tained as white crystals. H NMR (400 Hz, CDCl3) δ:
8.64 (d, J＝4.4 Hz, 2H, Ph), 7.89 (dd, J＝5.6, 3.2 Hz,
2H, Ph), 7.79 (d, J＝1.6 Hz, 2H, Py), 7.77 (d, J＝2.0 Hz,
2H, Py), 7.66 (dd, J＝5.6, 3.2 Hz, 2H, Py), 7.34－7.30
(m, 2H, Py).
Figure 5 Density-functional theory (DFT) molecular simulation
results: HOMO/LUMO energy levels and their topographical
representation.
Synthesis of 1,2-phenylenebis(thiophene-2-yl-metha-
none) (4a)
Experimental
Under a nitrogen atmosphere, a solution of 2-bromo-
thiophene (2.45 g, 14.89 mmol) in 50 mL dry THF was
added to Mg (0.38 g, 15.60 mmol). After the reaction
mixture was stirred for 3 h, it was drop wise added to 2
(2.5 g, 7.09 mmol) in 40 mL of THF at 0 ℃. Next the
resulting dark brown solution was stirred at room tem-
perature overnight and then quenched by adding HCl
(10%, 100 mL). The organic layer was extracted with
diethyl ether, and the combined organic layers were
washed with NaOH (10%, 100 mL), NaHCO3 (1
mol•L−1, 100 mL), and water and dried over MgSO4.
Yellow solid product 4a (1.37 g, 66%) was purified by
Materials
All chemical reagents and solvents were purchased
from Aladdin, J&K Chemical or Sinopharm Chemical
Reagent. Tetrahydrofuran (THF) was dried over sodium
and freshly distilled prior to use. Triethylamine (TEA)
was dried over calcium hydride. Dichloromethane
(CH2Cl2) for Cyclic Voltammetry (CV) and Ultravio-
let-visible (UV-vis) spectra studies was dried over cal-
cium hydride. The optimum separation and purification
of compounds were conducted by column chroma-
togram with 100－200 silica gel.
1
recrystallization from CH2Cl2/n-hexane. H NMR (400
Measurement
Hz, CDCl3) δ: 7.73 (dd, J＝5.6 3.2 Hz, 2H, Ph), 7.66
(dd, J＝5.2, 1.2 Hz, 2H, Ph), 7.63 (dd, J＝5.6, 3.2 Hz,
2H, Th), 7.47 (dd, J＝4.0, 1.2 Hz, 2H, Th), 7.06 (dd,
J＝4.8, 3.6 Hz, 2H, Th); 13C NMR (100 Hz, CDCl3) δ:
188.52, 144.29, 139.58, 135.36, 135.19, 130.85, 129.45,
128.25; m.p. 146 ℃.
All new compounds were characterized by H, 13C
1
Nuclear Magnetic Resonance (NMR), melting point
measurement and mass spectrometry. H NMR and 13C
1
NMR spectra were recorded on a Mercury Plus 400
(400 MHz for proton) spectrometer using chloroform
(CDCl3) as solvent in all cases at ambient temperature.
Melting points were measured with Jing Song X-4A
Melting Point Apparatus. Mass spectrometry was meas-
ured with a BrukermicroTof-Q-II System. UV-vis ab-
sorption spectra were recorded on a HITACHI U-4100
spectrophotometer. The PL emission spectra were ob-
tained with a FluoroMax-4 spectrophotometer. CV was
performed on a Chenhua 650D electrochemical analyzer
in 0.1 mol•L−1 n-Bu4NPF6 CH2Cl2 solution at 298 K. A
conventional three-electrode cell was used with a plati-
num working electrode (surface area of 0.3 mm2) and a
platinum wire as the counter electrode. The Pt working
electrode was routinely polished with a polishing alu-
mina suspension and rinsed with acetone before use.
The measured potentials were recorded with respect to
an Ag/AgNO3 (0.01 mol•L−1) reference electrode. All
electrochemical measurements were carried out under
an atmospheric pressure of argon.
Synthesis of 1,2-phenylene bis((3-hexylthiophene-2-
yl)methanone) (4b)
Under an nitrogen atmosphere, a solution of
3-bromo-2-hexylthiophene (5 g, 0.02 mol) in 25 mL dry
THF was added to Mg (0.59 g, 0.024 mol). After the
reaction mixture was stirred for 3 h, it was drop wise
added to 2 (2.38 g, 6.7 mol) in 30 mL of THF at 0 ℃.
Next the resulting dark brown solution was stirred at
room temperature overnight and then quenched by add-
ing HCl (10%, 150 mL). The organic layer was ex-
tracted with diethyl ether, and the combined organic
layers were washed with NaOH (10%), NaHCO3 (1
mol•L−1), and water and dried over MgSO4. Orange oil
substance 4b (2.22 g, 71%) was purified by column
chromatography (CH2Cl2/petroleum ether); 1H NMR
(400 Hz, CDCl3) δ: 7.64 (dd, J＝5.6, 3.2 Hz, 2H, Ph),
7.51 (dd, J＝5.6, 3.2 Hz, 2H, Ph), 7.38 (d, J＝4.8 Hz,
2H, Th-CH-3), 6.95 (d, J＝5.2 Hz, 2H, Th-CH-4), 2.80
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FULL PAPER
(t, J＝8.0 Hz, 4H, CH2), 1.58－1.50 (m, 4H, CH2), 1.30
－1.21 (m, 12H, CH2), 0.85 (t, J＝7.2 Hz, 6H, CH3);
13C NMR (100 Hz, CDCl3) δ: 189.14, 151.89, 141.40,
135.73, 131.82, 131.21, 130.33, 129.24, 31.87, 30.49,
30.27, 29.47, 22.84, 14.34.
(t, J＝8.0 Hz, 2H, CH2), 1.55 (td, J＝15.2, 7.6 Hz, 2H,
CH2), 1.18－1.09 (m, 6H, CH2), 0.76 (t, J＝7.2 Hz, 3H,
CH3); 13C NMR (100 Hz, CDCl3) δ: 154.63, 143.98,
132.54, 130.92, 129.25, 127.00, 126.77, 31.69, 30.74,
29.45, 29.15 22.68, 14.25; HRMS-ESI m/z: [M＋H]
calcd for C28H34N2S2 463.2242, found 463.2244.
Synthesis of 1,2-phenylenebis((5-hexylthiophene-2-
yl)methanone) (4c)
Synthesis of 1,4-bis(5-hexylthiophene) benzopyri-
dazine (5c)
Under an nitrogen atmosphere, a solution of 5-
bromo-2-hexylthiophene (1 g, 4.05 mmol) in 5 mL dry
THF was added to Mg (0.12 g, 4.85 mmol). After the
reaction mixture was stirred for 3 h, it was drop wise
added to 2 (0.47 g, 1.35 mmol) in 30 mL of THF at 0 ℃.
Next the resulting dark brown solution was stirred at
room temperature overnight and then quenched by add-
ing HCl (10%, 100 mL). The organic layer was ex-
tracted with diethyl ether, and the combined organic
layers were washed with NaOH (10%), NaHCO3 (1
mol•L−1), and water and dried over MgSO4. Orange oil
substance 4c (0.42 g, 67%) was purified by column
chromatography (CH2Cl2/petroleum ether) to provide
Under a nitrogen atmosphere, a solution of hydrazine
hydrate (0.057 g, 1.03 mmol) and 4c (0.4 g, 0.86 mmol)
in 20 mL ethanol was stirred overnight at room tem-
perature. After exposed to air, the reaction mixture was
heated up to 80 ℃ and stirred for more than 24 h. The
combined organic layers were dried over MgSO4 and
evaporated. Product 5c (0.38 g, 95%) was purified by
1
column chromatography (CH2Cl2/petroleum ether). H
NMR (400 Hz, CDCl3) δ: 8.57 (dd, J＝6.4, 3.6 Hz, 1H),
7.92 (dd, J＝6.4, 3.2 Hz, 1H), 7.54 (d, J＝3.6 Hz, 1H),
6.93 (d, J＝3.6 Hz, 1H), 2.92 (t, J＝8.0 Hz, 2H, CH2),
1.81－1.73 (m, 2H, CH2), 1.48－1.40 (m, 2H, CH2),
1.38－1.31 (m, 6H, CH2), 0.91 (t, J＝7.2 Hz, 3H, CH3);
13C NMR (100 Hz, CDCl3) δ: 152.2, 150.47, 136.70,
132.37, 130.06, 126.26, 125.19, 31.85, 30.57, 29.10,
22.86, 14.37; HRMS-ESI m/z: [M ＋H] calcd for
C28H34N2S2 463.2242, found 463.2239; m.p. 63 ℃.
1
the title compound. H NMR (400 Hz, CDCl3) δ: 7.69
(dd, J＝5.6, 3.2 Hz, 2H, Ph), 7.59 (dd, J＝5.6, 3.2 Hz,
2H, Ph), 7.25 (d, J＝4.0 Hz, 2H, Th-CH-3), 6.74 (d, J＝
4.0 Hz, 2H, Th-CH-4), 2.80 (t, J＝7.6 Hz, 4H, CH2),
1.70－1.62 (m, 4H, CH2), 1.39－1.27 (m, 12H, CH2),
0.89 (t, J＝6.8 Hz, 6H, CH3); 13C NMR (100 Hz, CDCl3)
δ: 188.24, 157.56, 141.84, 139.61, 136.02, 130.60,
129.31, 125.82, 31.72, 31.53, 30.95, 28.92, 22.77,
14.30.
Synthesis of 1,4-bis(5-bromothiophene-2-yl) benzo-
pyridazine (6)
To a solution of 5a (0.50 g, 1.70 mmol) in 100 mL
CHCl3 was added NBS (0.64 g, 3.57 mmol) in 30 mL
DMF over a period of 15 min at 0 ℃. Under a lucifugal
condition, the resulting solution was stirred for 1 d at
room temperature. The reaction mixture was poured into
ice and the organic layer was taken off while the water
phase was extracted with CH2Cl2. The combined or-
ganic phase was washed with 100 mL sodium chloride
solution. After the solvent was removed by rotary
evaporation product 9 (0.67 g, 88%) was obtained by
Synthesis of 1,4-bis(2-thienyl) benzopyridazine (5a)
A solution of hydrazine hydrate (0.47 g, 9.38 mmol)
and 4a (1.4 g, 4.7 mmol) in 125 mL ethanol was stirred
overnight at room temperature. The combined organic
layers were evaporated. Pale yellow solid 5a (0.92 g,
67%) was purified by recrystallization from ethyl ace-
1
tate/petroleum ether. H NMR (400 Hz, CDCl3) δ: 8.57
1
(dd, J＝3.2, 6.0 Hz, 1H, Ph), 7.95 (dd, J＝3.6, 6.4 Hz,
1H, Ph), 7.73 (d, J＝3.6 Hz, 1H, Th), 7.61 (d, J＝5.2 Hz,
1H, Th), 7.27－7.26 (m, 1H, Th); 13C NMR (100 Hz,
CDCl3) δ: 152.58, 139.25, 132.71, 129.98, 129.37,
127.90, 126.25, 125.40; HRMS-ESI m/z: [M＋H] calcd
for C16H10N2S2 295.0364, found 295.0367; m.p. 140 ℃.
column chromatography (CH2Cl2) as a clear liquid. H
NMR (400 Hz, CDCl3) δ: 8.52 (dd, J＝3.6, 6.4 Hz, 1H),
7.98 (dd, J＝4.0, 6.4 Hz, 1H), 7.49 (d, J＝4.0 Hz, 1H),
7.22 (d, J＝6.4 Hz, 1H); 13C NMR (100 Hz, CDCl3) δ:
151.69, 140.99, 133.04, 130.29, 125.60, 125.60, 125.02,
117.42; m.p. 187 ℃.
Synthesis of 1,4-bis(3-hexylthiophene-2-yl) benzo-
pyridazine (5b)
Synthesis of 1,4-bis(5'-hexy-[2,2'-bithiophene]-5-yl)
benzopyridazine (5d)
Under a nitrogen atmosphere, a solution of hydrazine
hydrate (0.24 g, 4.74 mmol) and 4b (2.07 g, 4.43 mmol)
in 20 mL ethanol was stirred overnight at room tem-
perature. After exposed to air, the reaction mixture was
heated up to 80 ℃ and stirred for more than 24 h. The
combined organic layers were dried over MgSO4 and
evaporated. Product 5b (2.05 g, 98%) was purified by
Under an nitrogen atmosphere, a mixture of 9 (0.05 g,
1.11 mmol), 5-hexylthiophen-2-yl-tributylstannane
(0.76 g, 1.67 mmol) and Pd(PPh3)4 (0.1 g) in 30 mL
DMF was heated together at 100 ℃ with a reflux con-
denser. Then, the reaction mixture was stirred for 24 h.
After cooling down to room temperature, the solvent
was removed by rotary evaporation, and product 5d
(0.83 g, 80%) was obtained by column chromatography
1
column chromatography (CH2Cl2/petroleum ether). H
1
NMR (400 Hz, CDCl3) δ: 8.05 (dd, J＝6.27, 3.32 Hz,
1H, Ph), 7.86 (dd, J＝6.35, 3.26 Hz, 1H, Ph), 7.51 (d,
J＝5.11 Hz, 1H, Th), 7.14 (d, J＝5.12 Hz, 1H, Th), 2.58
(CH2Cl2) as an orange solid. H NMR (400 Hz, CDCl3)
δ: 8.59 (td, J＝3.2, 6.4 Hz, 1H, Ph), 7.96－7.93 (m, 1H,
Ph), 7.64 (t, J＝3.8 Hz, 1H, Th), 7.23 (t, J＝3.7 Hz, 1H,
1402
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 1397—1403

Synthesis and Physical Properties of Benzopyridazine-Based Conjugated Molecules
Th), 7.15 (t, J＝3.1 Hz, 1H, Th), 6.74 (t, J＝2.7 Hz, 1H,
Th), 2.83 (t, J＝8.6 Hz, 2H, CH2), 1.71 (t, J＝0.1 Hz,
2H, CH2), 1.35－1.32 (m, 6H, CH2), 0.93－0.88 (m, 3H,
CH3); 13C NMR (100 Hz, CDCl3) δ: 151.83, 146.75,
141.97, 137.49, 134.44, 132.63, 130.66, 126.09, 125.30,
125.11, 124.68, 123.69, 31.80, 30.47, 29.93, 29.01,
22.82, 14.33; HRMS-ESI m/z: [M ＋H] calcd for
C36H38N2S4 627.1997, found 627.2001; m.p. 179 ℃.
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Conclusions
In summary, a series of new organic conjugated
molecules comprising 2,3-benzodiazine and thiophene
moieties have been synthesized successfully. Our ex-
perimental and theoretical investigations revealed that
both introduction of the heteroatoms in the conjugated
backbone and substituted side chains at the different
position of the conjugated building blocks have signifi-
cant influence on the optical properties and electro-
chemical behaviors of these compounds via varying the
geometric and electronic structures for tuning the energy
levels of LUMO and HOMO. The electron-withdrawing
benzopyridiazine and electron-donating thiophene moie-
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conjugated system, respectively, to form a new class of
D-A-D conjugated system. These fundamental results
will not only provide some new candidate molecules for
application in optoelectronic materials, but also help-
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Acknowledgement
We acknowledge funding support from Natural Sci-
ence Foundation of China (NSFC, No. 21174083), the
Shanghai Committee of Science and Technology (No.
11JC1405400), Shanghai Pujiang Program (No.
12PJ1405300) and Shanghai Jiao Tong University (211
Project).
(Lu, Y.)
Chin. J. Chem. 2013, 31, 1397—1403
© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
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