Synthesis, X-ray crystal structure and optical properties of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(6-methoxy-3-methylbenzofuran-2-yl)-1,3, 4-oxadiazole

Article abstract of DOI:10.1016/j.saa.2011.10.021

A series of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(6-methoxy-3- methylbenzofuran-2-yl)-1,3,4-oxadiazole derivatives has been synthesized from 6-methoxy-3-methylbenzofuran-2-carboxylic acid and ethyl 3-aryl-1H-pyrazole-5- carboxylate. The structures of compou

Full text of DOI:10.1016/j.saa.2011.10.021

Spectrochimica Acta Part A 86 (2012) 181–186
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, X-ray crystal structure and optical properties of novel 5-(3-aryl-1H-
pyrazol-5-yl)-2-(6-methoxy-3-methylbenzofuran-2-yl)-1,3,4-oxadiazole
Zhen-Ju Jiang, Jin-Ting Liu∗, Hong-Shui Lv, Bao-Xiang Zhao∗
Institute of Organic Chemistry, School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 July 2011
Received in revised form 10 October 2011
Accepted 14 October 2011
A series of novel 5-(3-aryl-1H-pyrazol-5-yl)-2-(6-methoxy-3-methylbenzofuran-2-yl)-1,3,4-oxadiazole
derivatives has been synthesized from 6-methoxy-3-methylbenzofuran-2-carboxylic acid and ethyl 3-
aryl-1H-pyrazole-5-carboxylate. The structures of compounds obtained were determined by IR, 1H NMR
and HRMS spectra. Typically, the spatial structure of compound 7e was determined by using X-ray
diffraction analysis. UV–vis absorption and fluorescence spectral characteristics of the compounds in
dichloromethane and acetonitrile were investigated. The results showed that the absorption maxima
of the compounds vary from 321 to 339 nm depending on the substituents in N-1 position of pyrazole
moiety and para position of benzene moiety. The maximum emission spectra of compounds in two dif-
ferent solvents were mainly dependent on groups in N-1 position of pyrazole moiety. The intensity of
absorption and fluorescence was also correlated with substituents on the aryl ring bonded to pyrazole
moiety. In addition, the absorption and emission spectra of these compounds change with increasing
solvent polarity.
Keywords:
1,3,4-Oxadiazole
Pyrazole
Benzofuran
Synthesis
UV absorption
Fluorescence
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
The design and synthesis of fluorescent small molecules with
desirable bioactivities is of considerable current interest in biology
1,3,4-Oxadiazoles are five-membered aromatic heterocycles
with great utility in synthetic, medicinal, and material chemistry
[1–13]. 1,3,4-Oxadiazole derivatives are highly attractive com-
pounds in the research and development of materials for organic
electroluminescent (EL) devices since these compounds possess
high electron-accepting properties and exhibit strong fluores-
cence with high quantum yields [14]. Thus, compounds involving
1,3,4-oxadiazole rings have been used as electron-transporting
materials and emitters in organic EL devices [15–17]. Recently,
1,3,4-oxadiazole derivatives have aroused considerable interests
in the area of organic light-emitting diodes (OLEDs) [18–21].
Pyrazole and benzofuran unit are important core structures
in a number of natural products. Many pyrazole derivatives are
known to exhibit a wide range of biological properties such
as anti-hyperglycemic, analgesic, anti-inflammatory, anti-pyretic,
anti-bacterial, antifungal, anti-hypoglycemic, sedative-hypnotic
activity, antitumor and anticoagulant activity [22–24]. Benzofuran
derivatives have also been reported to show broad spectrum of
biological activities including antimicrobial, anticonvulsant, anti-
inflammatory, antitumor, anticancer, anti-HIV-1, etc. [25–28].
research [29,30]. Thus, in continuation of our efforts in syn-
thesizing various bioactive molecules [31–36] and fluorescent
small molecules [37–39], we would like to synthesize novel small
molecules with both potential bioactivity and fluorescent property.
Based on a fragmented approach, we proposed that 1,3,4-
oxadiazole linking benzofuran and pyrazole might have interesting
bioactivities such as anticancer activity. On the other hand, three
aromatic rings construct ␲-conjugation system that has cause for
expecting improvement in UV–vis absorption and fluorescence
spectral characteristics.
Herein, we would like to report the synthesis and UV–vis
absorption and fluorescence spectral characteristics of novel
2-(6-methoxy-3-methylbenzofuran-2-yl)-5-(3-phenyl-1H-
pyrazol-5-yl)-1,3,4-oxadiazole derivatives.
2. Experimental
2.1. General
Thin-layer chromatography (TLC) was conducted on silica gel
60 F254 plates (Merck KGaA). 1H NMR spectra were recorded on
a Bruker Avance 400 (400 MHz) spectrometer, using CDCl3 or
DMSO-d6 as solvent and tetramethylsilane (TMS) as internal stan-
dard. Melting points were determined on an XD-4 digital micro
melting point apparatus. IR spectra were recorded with an IR
∗
Corresponding authors. Tel.: +86 531 88366425; fax: +86 531 88564464.
E-mail addresses: jintliu@sdu.edu.cn (J.-T. Liu), bxzhao@sdu.edu.cn,
sduzhao@hotmail.com (B.-X. Zhao).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.10.021

182
Z.-J. Jiang et al. / Spectrochimica Acta Part A 86 (2012) 181–186
spectrophotometer VERTEX 70 FT-IR (Bruker Optics). HRMS spec-
tra were recorded on a Q-TOF6510 spectrograph (Agilent). UV–vis
spectra were recorded on a U-4100 (Hitachi). Fluorescent mea-
surements were recorded on a Perkin-Elmer LS-55 luminescence
spectrophotometer.
2.5.2. 2-(3-(4-Chlorophenyl)-1H-pyrazol-5-yl)-5-(6-methoxy-3-
methylbenzofuran-2-yl)-1,3,4-oxadiazole
(7b)
Orange red powder, yield 27%, mp 270–274 ◦C; IR (KBr, cm−1):
3190 (N–H), 1611 (C C), 1491 (C N), 1440 (N-N), 1313 (C–N–N),
1274 (C–O–C). 1H NMR (400 MHz, DMSO-d6) ı: 2.64 (3H, s, CH3),
3.87 (3H, s, OCH3), 7.03 (1H, d, J = 7.8 Hz, Ar-H), 7.33 (1H, s, Pyrazole-
H), 7.47 (1H, s, Ar-H), 7.58 (2H, d, J = 7.0 Hz, Ar-H), 7.70 (1H, d,
J = 8.4 Hz, Ar-H), 7.92 (2H, d, J = 6.6 Hz, Ar-H), 14.13 (1H, s, Pyrazole-
NH). HRMS (ESI) calcd for [M+H]+ C21H16N4O3Cl: 407.0911, found:
407.0909.
2.2. General procedure for the synthesis of 3-aryl-Nꢀ-(6-methoxy-
3-methylbenzofuran-2-carbonyl)-1H-pyrazole-5-carbohydrazide
(6a–c)
The acid chloride 3 (2 mmol) and suitable 3-aryl-1H-pyrazole-
5-carbohydrazide 5a–c (2 mmol) were taken in dried DMF (20 mL),
and then triethylamine (2 mmol) was added. The mixture was
stirred at room temperature for 3–4 h, after then the mixture was
poured into ice water (50 mL). The precipitate was filtered under
reduced pressure, washed with water and dried. The crude product
was recrystallized from ethanol to afford desired compound 6a–c
in 59–66% yields.
2.5.3. 2-(6-Methoxy-3-methylbenzofuran-2-yl)-5-(3-(4-
methoxyphenyl)-1H-pyrazol-5-yl)-1,3,4-oxadiazole
(7c)
Orange red powder, yield 30%, mp 284–289 ◦C; IR (KBr, cm−1):
3232 (N–H), 1618 (C C), 1509 (C N), 1456 (N-N), 1314 (C–N–N),
1276 (C–O–C). 1H NMR (400 MHz, DMSO-d6) ı: 2.64 (3H, s, CH3),
3.87 (3H, s, OCH3), 3.92 (3H, d, OCH3), 7.03 (1H, dd, J = 2.0, J = 8.6 Hz,
Ar-H), 7.07 (2H, d, J = 8.7 Hz, Ar-H), 7.35 (1H, d, J = 8.0 Hz, Ar-H),
7.58 (1H, s, Pyrazole-H), 7.71 (1H, d, J = 8.6 Hz, Ar-H), 7.83 (2H, d,
J = 8.0 Hz, Ar-H), 13.98 (1H, s, Pyrazole-NH). HRMS (ESI) calcd for
[M+H]+ C22H19N4O4: 403.1406, found: 403.1400.
2.3. General procedure for the synthesis of
3-aryl-1-benzyl-Nꢀ-(6-methoxy-3-methylbenzofuran-2-
carbonyl)-1H-pyrazole-5-carbohydrazide
(6d–f)
2.5.4. 2-(1-Benzyl-3-phenyl-1H-pyrazol-5-yl)-5-(6-methoxy-3-
methylbenzofuran-2-yl)-1,3,4-oxadiazole
(7d)
The acid chloride 3 (2 mmol) and suitable 3-aryl-1-benzyl-
1H-pyrazole-5-carbohydrazide 5d–f (2 mmol) were taken in dried
dichloromethane (20 mL), then triethylamine (2 mmol) was added.
The mixture was stirred at room temperature for 3–4 h, after then
the mixture was concentrated under reduce pressure. The residue
obtained was recrystallized from methanol to afford desired com-
pound 6d–f in 45–61% yields.
Pale yellow powder, yield 22%, mp 200–201 ◦C; IR (KBr, cm−1):
1615 (C C), 1493 (C N), 1469 (N-N), 1349 (C–N–N), 1278 (C–O–C).
1H NMR (400 MHz, CDCl3) ı: 2.66 (3H, s, CH3), 3.90 (3H, s, OCH3),
6.02 (2H, s, CH2), 6.98 (1H, dd, J = 2.1, J 8.7 Hz, Ar-H), 7.08 (1H, d,
J = 2.1 Hz, Ar-H), 7.24 (1H, s, Pyrazole-H), 7.28–7.31 (3H, t, J = 7.2 Hz,
Ar-H), 7.36 (1H, t, J = 7.3 Hz, Ar-H), 7.43–7.47 (4H, m, Ar-H), 7.51
(1H, d, J = 8.7 Hz, Ar-H), 7.91 (2H, d, J = 7.3 Hz, Ar-H). HRMS (ESI)
calcd for [M+H]+ C28H23N4O3: 463.1770, found: 463.1773.
2.4. General procedure for the synthesis of 5-(3-aryl-1H-pyrazol-
5-yl)-2-(6-methoxy-3-methylbenzofuran-2-yl)-1,3,4-oxadiazole
derivatives (7a–f)
2.5.5. 2-(1-Benzyl-3-(4-chlorophenyl)-1H-pyrazol-5-yl)-5-(6-
methoxy-3-methylbenzofuran-2-yl)-1,3,4-oxadiazole
(7e)
Pale yellow powder, yield 29%, mp 217–221 ◦C; IR (KBr, cm−1):
1616 (C C), 1494 (C N), 1470 (N-N), 1350 (C–N–N), 1278 (C–O–C).
1H NMR (400 MHz, CDCl3) ı: 2.66 (3H, s, CH3), 3.90 (3H, s, OCH3),
6.01 (2H, s, CH2), 6.98 (1H, d, J = 8.6 Hz, Ar-H), 7.08 (1H, s, Ar-H),
7.26–7.30 (4H, m, Pyrazole-H, Ar-H), 7.43 (4H, m, Ar-H), 7.52 (1H,
d, J = 8.6 Hz, Ar-H), 7.83 (2H, d, J = 8.0 Hz, Ar-H). HRMS (ESI) calcd for
[M+H]+ C28H22N4O3Cl: 497.1380, found: 497.1383.
To
a
round-bottomed
flask
Nꢀ-(6-methoxy-3-
methylbenzofuran-2-carbonyl)-3-phenyl-1H-pyrazole-5-
carbohydrazide 6a–f (1 mmol) and POCl3 (10 mL) were added, and
the mixture was stirred at 70–80 ◦C for 5–8 h. Excess POCl3 was
distilled off and the residue was poured into ice water, stirred
vigorously and then the mixture was neutralized with diluted
sodium hydroxide solution to pH 7. The precipitate was filtered
under reduced pressure, washed with water, petroleum ether and
dried. The crude solid was purified by column chromatography
on silica gel and recrystallized from ethanol to afford desired
compound 7a–f in 22–31% yields.
2.5.6. 2-(1-(4-(Tert-butyl)benzyl)-3-(4-chlorophenyl)-1H-
pyrazol-5-yl)-5-(6-methoxy-3-methyl
benzofuran-2-yl)-1,3,4-oxadiazole (7f)
Pale yellow powder, yield 31%, mp 205–206 ◦C; IR (KBr, cm−1):
1612 (C C), 1494 (C N), 1470 (N-N), 1324 (C–N–N), 1275 (C–O–C).
1H NMR (400 MHz, CDCl3) ı: 1.26 (9H, s, tert-butyl), 2.67 (3H, s,
CH3), 3.90 (3H, s, OCH3), 5.98 (2H, s, CH2), 6.98 (1H, dd, J = 2.1,
J = 8.7 Hz, Ar-H), 7.08 (1H, d, J = 2.1 Hz, Ar-H), 7.24 (1H, s, Pyrazole-
H), 7.32 (2H, d, J = 8.3 Hz, Ar-H), 7.40 (4H, m, J = 8.0 Hz, Ar-H), 7.52
(1H, d, J = 8.7 Hz, Ar-H), 7.8 (2H, d, J = 8.3 Hz, Ar-H). HRMS (ESI) calcd
for [M+H]+ C32H30N4O3Cl: 553.2006, found: 553.1996.
2.5. The spectroscopic data of compounds (7a–f)
2.5.1. 2-(6-Methoxy-3-methylbenzofuran-2-yl)-5-(3-phenyl-1H-
pyrazol-5-yl)-1,3,4-oxadiazole
(7a)
Orange powder, yield 26%, mp 237–240 ◦C; IR (KBr, cm−1): 3196
(N–H), 1617 (C C), 1546 (C N), 1466 (N-N), 1313 (C–N–N), 1274
(C–O–C). 1H NMR (400 MHz, DMSO-d6) ı: 2.64 (3H, s, CH3), 3.86
(3H, s, OCH3), 7.03 (1H, dd, J = 2.0, J = 8.6 Hz, Ar-H), 7.36 (1H, d,
J = 2.0 Hz, Ar-H), 7.41–7.47 (2H, m, Pyrazole-H, Ar-H), 7.52 (2H, t,
J = 7.6 Hz, Ar-H), 7.71 (1H, d, J = 8.6 Hz, Ar-H), 7.91 (2H, d, J = 7.4 Hz,
Ar-H), 14.16 (1H, s, Pyrazole-NH). HRMS (ESI) calcd for [M+H]+
C21H17N4O3: 373.1301, found: 373.1300.
2.6. X-ray crystallography
Suitable single crystals of 7e for X-ray structural analysis
were obtained by slow evaporation of a solution of the solid in
dichloromethane at room temperature for 10 days. The crystals
with approximate dimensions of 0.10 mm × 0.10 mm × 0.08 mm
for 7e were mounted on a Bruker Smart Apex II CCD equipped

Z.-J. Jiang et al. / Spectrochimica Acta Part A 86 (2012) 181–186
183
Fig. 1. Synthetic route for the new 1,3,4-oxadiazoles.
˚
synthesized by the reaction of acid chloride
1H-pyrazole-5-carbohydrazide derivatives
3
and 3-aryl-
in 45%-66%
with a graphite monochromated MoK␣ radiation (ꢀ = 0.71073 A) by
5
using ϕ and ω scan modes and the data were collected at 298(2) K.
The structure of the crystal was solved by direct methods and
refined by full-matrix least-squares techniques implemented in the
SHELXTL-97 crystallographic software. The non-hydrogen atoms
were refined anisotropically. The hydrogen atoms bound to carbon
were located by geometrical calculations, with their position and
thermal parameters being fixed during the structure refinement.
The final refinement converged at R1 = 0.0437, wR2 = 0.1178 for 7e.
yields. It is noted that the solvents used in the reaction for
3-aryl-1H-pyrazole-5-carbohydrazide 6a–c and 3-aryl-benzyl-
1H-pyrazole-5-carbohydrazide derivatives 6d–f were different.
That is, for 6a–c, DMF must be employed to ensure substrates
soluble, in the case of 6d–f, however, dichloromethane was used
for feasible reaction and workup. Finally, proposed compounds
7a–f were synthesized by the cyclization of diacylhydrazides 6 in
the presence of phosphorus oxychloride in 22–31% yields.
3. Results and discussion
3.2. Structure characterization
3.1. Synthesis
The proposed structures of compounds 7a–f were proved by IR,
1H NMR and HRMS spectra. For example compound 7a, obtained
as orange solid, gave a [M+H]-ion peak at m/z 373.1300 in the
HRESIMS, in accord with the molecular formula C21H16N4O3. The
IR spectra of compound 7a showed the characteristic absorp-
tion bands at 3196 (N–H), 1617 (C C), 1546 (C N), 1466 (N-N),
and 1274 (C–O–C) cm−1. The 1H NMR spectra (DMSO-d6) of com-
pound 7a revealed three singlet peaks at ı 2.64 (3H, CH3), 3.86
(3H, OCH3) and 14.16 (1H, Pyrazole-NH) ppm which were read-
ily assigned to the proton of methyl, methoxyl and NH of pyrazole
moiety, respectively. It is noted that another proton of pyrazole
moiety should reveal singlet peak inserts region of 7.41–7.47 ppm.
Moreover, the double doublet peaks in 7.03 ppm with coupling
constant 2.0 and 8.6 Hz assigned to the proton in 5-position of
benzofuran ring. The doublet peaks revealed in 7.36 ppm with cou-
pling constant 2.0 Hz were assigned to the proton in 7-position
of benzofuran ring. The proton in 4-position of benzofuran ring
revealed in 7.71 ppm as doublet peaks with coupling constant
8.6 Hz. The protons of benzene bonded to 3-position of pyra-
zole moiety showed doublet peaks in 7.91 ppm with coupling
constant 7.4 Hz and multiplet peaks in region of 7.41–7.47 and
7.50–7.54 ppm.
Most of protocols reported in the literature for the synthesis
of 1,3,4-oxadiazoles mainly involve the cyclization of diacylhy-
drazides with a variety of reagents such as thionyl chloride,
phosphorus oxychloride, or PPA, usually under harsh reaction con-
ditions [40–42], the oxidation of acylhydrozones [43–45], and the
condensation of carboxylic acids with acyl hydrazides [46,47]. In
the present study, we adopted the strategy in which diacylhy-
drazide cyclized in the presence of phosphorus oxychloride to
afford desired compounds as shown in Fig. 1.
Starting 7-methoxy-4-methyl-2H-chromen-2-one
1 can be
easily synthesized by the reaction of commercially available 3-
methoxyphenol and ethyl acetoacetate according to the literature
[48]. Then compound 2 was obtained by the bromination of
compound 1 with NBS in the presence of ammonium sulfate in
acetonitrile, a modified literature method [49], in 69% yield. Acid
chloride 3 was synthesized by the reaction of compound 2 with
10% ethanolic potassium hydroxide at reflux for 2 h and followed
the reaction with thionyl dichloride in 82–87% yields.
3-Aryl-1H-pyrazole-5-carbohydrazide derivatives
5
were
synthesized by the reaction of ethyl 3-aryl-1H-pyrazole-5-
carboxylate derivatives 4 and hydrate hydrazine according to
our previous report [50]. Subsequently, diacylhydrazides 6 were

184
Z.-J. Jiang et al. / Spectrochimica Acta Part A 86 (2012) 181–186
Table 1
Table 2
Summary of crystallographic data and structure refinement details for 7e.
Hydrogen-bond geometry for 7e.
a
7e
X–H· · ·A/␲
X–H H· · ·A/␲ X· · ·A/␲
X–H· · ·A/␲ Symmetry
codes
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
C28H21ClN4O3
496.94
298(2)
0.71073 A
Monoclinic
P2(1)/n
◦
˚
a = 11.4821(10) A, ˛ = 90.00
b = 15.7957(14) A, ˇ = 96.570(2)
C10–H10A· · ·N3
C6–H6· · ·Cg1
0.97 2.52
0.93 2.98
3.097(4)
3.394(4)
118
109
3/2 − x, 1/2 + y,
˚
1/2 − z
C21–H21B· · ·Cg2 0.96 2.91
3.783(4)
151
2 − x, −y, 1 − z
a
Cg1 and Cg2 are the centriods of 1,3,4-oxadiazole ring and the furan ring, respec-
Unit cell dimensions
tively.
◦
˚
˚
◦
c = 12.9560(11) A, ꢁ = 90.00
Volume
Z
Calculated density
Absorption coefficient
F(0 0 0)
2334.4(4) A3
4
1.414 Mg/m3
0.204 mm−1
1032
Crystal size
 range for data collection
Limiting indices
0.10 mm × 0.10 mm × 0.08 mm
2.04–23.26◦
−10 ≤ h ≤ 12, −17 ≤ k ≤ 16, −14 ≤ l ≤ 14
9787/3344 [R(int) = 0.0336]
99.6%
Reflections collected/unique
Completeness to Â
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2ꢂ(I)]
R indices (all data)
Largest diff. peak and hole
CCDC No.
None
0.9839 and 0.9799
Full-matrix least-squares on F2
3344/0/326
1.023
R1 = 0.0437, wR2 = 0.1178
R1 = 0.0670, wR2 = 0.1367
−3
˚
0.716 and −0.213 e A
830,628
Fig. 3. Molecular packing in 7e, showing details of the hydrogen bonds connectivity
and the ␲· · ·␲ interactions.
3.3. X-ray crystallography analysis
intermolecular hydrogen bonds generate centrosymmetric R22(8)
dimmers, which are linked to each other through C6–H9· · ·Cg1
intermolecular hydrogen bonds and the ␲· · ·␲ stacking interactions
The spatial structure of compound 7e was determined by using
X-ray diffraction analysis. A summary of crystallographic data col-
lection parameters and refinement parameters for 7e are compiled
in Table 1.
˚
between 4-chlorophenyl and furan rings (Cg2· · ·Cg4 3.8092(17) A
Fig. 2 shows that 7e contains a 1,3,4-oxadiazole bound to ben-
zofuran and pyrazole rings. The molecular structure is dominated
by the arrangement of the rings of the 1,3,4-oxadiazole, benzofu-
ran, pyrazole, benzyl and the phenyl. The molecular conformation
is stabilized by intramolecular C10–H10A· · ·N3 weak hydrogen
with symmetry operation: 3/2 − x, −1/2 + y, 1/2 − z; Cg2 and Cg4
are the centroids of furan and benzene ring, respectively), forming
a networks structure.
3.4. Absorption spectral
◦
˚
bond (C10· · ·N3 3.097(4) A and C10–H10A· · ·N3 118 ). The rings
of 1,3,4-oxadiazole, benzofuran and pyrazole are almost coplanar
with dihedral angle 3.32(13)◦ and 1.10(16)◦ respectively, indicating
that they are conjugated. However, the benzene ring C1–C6 is devi-
ated from th◦e conjugated plane (pyrazole ring) with dihedral angle
UV–vis absorption spectra of compounds 7a–f were observed in
dichloromethane and acetonitrile solution with the concentration
of 1 × 10−5 M, respectively, as shown in Figs. 4 and S1 and Table 3.
The results showed that the absorption maxima of the compounds
˚
of 14.21(15) . The distance of C9–C17 1.442(4) A is almost same as
˚
˚
that of C18–C19 1.443(4) A, and that of C4–C7 is 1.475(4) A.
The crystal packing of 7e is stabilized by the C–H· · ·␲
intermolecular hydrogen bonds and the ␲· · ·␲ stacking interac-
tions (Table 2 and Fig. 3). Interestingly, two C21–H21B· · ·Cg2
Fig. 4. UV–vis absorption spectra of compounds 7a–f taken in dichloromethane
(c = 1 × 10−5 M).
Fig. 2. The molecular structure of compound 7e.

Z.-J. Jiang et al. / Spectrochimica Acta Part A 86 (2012) 181–186
185
Table 3
The optical characteristics of compounds 7a–f.
Compound
ꢀmax (nm)
εmax (L mol−1 cm−1
)
(7a–f)
CH2Cl2
CH3CN
CH2Cl2
CH3CN
7a
7b
7c
7d
7e
7f
329
324
330
339
338
339
250
249
261
252
257
258
325
321
326
333
332
333
251
257
257
252
256
256
38,600
21,700
22,000
39,100
44,200
36,600
27,500
21,900
17,500
29,400
36,800
30,800
41,300
22,200
24,500
42,300
49,100
40,700
24,500
21,000
18,400
29,600
39,200
31,400
that without benzyl group 7a–c. In acetonitrile, for example, com-
pounds 7d–f red shifted about 17–22 nm. In addition, compound 7b
with chlorine group in para-position of phenyl moiety bonded to
pyrazole has less red shift compared with 7a without substituent
and 7c with methoxy, an electron-donating group. The intensity
of fluorescence was also correlated with substituents on two aryl
rings. Generally, intensity of fluorescence 7d–f was stronger then
7a–c in two different solvents, respectively.
4. Conclusion
A
series of novel benzofuran and pyrazole linked
1,3,4-oxadiazole derivatives has been synthesized from 6-
methoxy-3-methylbenzofuran-2-carboxylic acid and ethyl
3-aryl-1H-pyrazole-5-carboxylate. The structures of compounds
were determined by IR, 1H NMR and HRMS spectra, typically, the
spatial structure of compound 7e was determined by using X-ray
diffraction analysis. Absorption and fluorescence spectral charac-
teristics of the compounds in dichloromethane and acetonitrile
were investigated and results showed that the absorption spectra
and fluorescence characteristics were mainly dependent on the
groups in N-1 position of pyrazole moiety.
Fig. 5. Emission spectra of 7a–f in dichloromethane (c = 5 × 10−7 M).
vary from 321 to 339 nm that are attributed to ␲–␲* transition
depending on the substituents in N-1 position of pyrazole moiety
and para position of benzene moiety. It can be found that com-
pounds 7d–f with phenyl in N-1 position of pyrazole moiety have
red shift than that without benzyl group 7a–c. Moreover, the com-
pound 7b with chlorine group in para-position of phenyl group
bonded to pyrazole has a blue shift compared with 7a without sub-
stituent and 7c with methoxy, an electron-donating group. These
phenomena can be explained by the enhancement of electron delo-
calization in conjugation system. In addition, the effects of polarity
of solvent on the absorption maxima were also obvious. That is,
the maximum absorption wavelength of 7a–f in dichloromethane
is larger than that in acetonitrile resulting in red shift about 5 nm.
Acknowledgement
This study was supported by the National Natural Science Foun-
dation of China (20972088).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.10.021.
3.5. Fluorescence
References
Fluorescence spectral characteristics of the compounds 7a–f
in dichloromethane and acetonitrile solution with the concentra-
tion of 5 × 10−7 M were investigated. From Figs. 5 and S2 and
Table 4 it can be found that the maximum emission spectra of com-
pounds in two different solvents are also mainly dependent on the
groups in N-1 position of pyrazole moiety. Thus, compounds 7d–f
with phenyl group in N-1 position of pyrazole have red shift than
[1] J.A. Joule, K. Mills, Heterocyclic Chemistry, fifth ed., Wiley-Blackwell, Chich-
ester, 2010, pp. 569–573.
[2] G.D. Wilkie, G.I. Elliott, B.S.J. Blagg, S.E. Wolkenberg, D.R. Soenen, M.M. Miller,
S. Pollack, D.L. Boger, J. Am. Chem. Soc. 124 (2002) 11292–11294.
[3] S.E. Wolkenberg, D.L. Boger, J. Org. Chem. 67 (2002) 7361–7364.
[4] G.I. Elliott, J.R. Fuchs, B.S.J. Blagg, I. Hayato, J. Am. Chem. Soc. 128 (2006)
10589–10595.
[5] M. Akhter, A. Husain, B. Azad, M. Ajmal, Eur. J. Med. Chem. 44 (2009) 2372–2378.
[6] F. Liu, X.Q. Luo, B.A. Song, Bioorg. Med. Chem. 16 (2008) 3632–3640.
[7] A.A. El-Emam, O.A. Al-Deeb, M. Al-Omar, J. Lehmann, Bioorg. Med. Chem. 12
(2004) 5107–5113.
[8] Z.M. Liu, G.F. Yang, X.H. Qin, J. Chem. Technol. Biotechnol. 76 (2001) 1154–1158.
[9] N. Tamoto, C. Adachi, K. Nagai, Chem. Mater. 9 (1997) 1077–1085.
[10] Y. Qian, Z.F. Lu, C.G. Lu, Z.M. Chen, Y.P. Cui, Dyes Pigments 75 (2007) 641–646.
[11] L.H. Feng, Z.B. Chen, F.L. Bai, Spectrochim. Acta A 60 (2004) 3029–3032.
[12] E. Wolarz, E. Chrzumnicka, T. Fischer, J. Stumpe, Dyes Pigments 75 (2007)
753–760.
Table 4
Data of fluorescence spectra of compounds 7a–f at 5 × 10−7 M.
Compound
ꢀex (nm)
ꢀem (nm)
Stoke’s shift (nm)
(7a–f)
CH2Cl2
CH3CN
CH2Cl2
CH3CN
CH2Cl2
CH3CN
[13] H. Fujiwara, Y. Sugishima, K. Tsujimoto, Tetrahedron Lett. 49 (2008) 7200–7203.
[14] G. Hughes, M.R. Bryce, J. Mater. Chem. 15 (2008) 94–107.
[15] Y. Shirota, H. Kageyama, Chem. Rev. 107 (2007) 953–1010.
[16] A.P. Kulkarni, C.J. Tonzola, A. Babel, S.A. Jenekhe, Chem. Mater. 16 (2004)
4556–4573.
7a
7b
7c
7d
7e
7f
330
330
330
340
340
340
330
330
330
340
340
340
385
390
384
399
399
400
388
389
385
408
406
406
55
60
54
59
59
60
58
59
55
68
66
66
[17] K. Ono, H. Ito, A. Nakashima, M. Uemoto, M. Tomura, K. Saito, Tetrahedron Lett.
49 (2008) 5816–5819.

186
Z.-J. Jiang et al. / Spectrochimica Acta Part A 86 (2012) 181–186
[18] Y.T. Tao, Q. Wang, Y. Shang, C.L. Yang, L. Ao, J.G. Qin, D.G. Ma, Z.G. Shuai, Chem.
Commun. 45 (2009) 77–79.
[34] W.Y. Liu, H.Y. Li, B.X. Zhao, D.S. Shin, S. Lian, J.Y. Miao, Carbohydr. Res. 344
(2009) 1270–1275.
[19] Y.T. Tao, Q. Wang, C.L. Yang, Z.Q. Zhang, T.T. Zou, J.G. Qin, D.G. Ma, Angew. Chem.
Int. Ed. 47 (2008) 8104–8107.
[35] S. Lian, H. Su, B.X. Zhao, W.Y. Liu, L.W. Zheng, J.Y. Miao, Bioorg. Med. Chem. 17
(2009) 7085–7092.
[20] L.Q. Chen, C.L. Yang, J.G. Qin, J. Gao, H. You, D.G. Ma, J. Organomet. Chem. 691
(2006) 3350–3519.
[36] X.L. Ding, H.Y. Zhang, L. Qi, B.X. Zhao, S. Lian, H.S. Lv, J.Y. Miao, Bioorg. Med.
Chem. Lett. 19 (2009) 5325–5328.
[21] Z.W. Xu, Y. Li, X.M. Ma, X.D. Gao, H. Tian, Tetrahedron 64 (2008) 1860–1867.
[22] L.D. Via, A.M. Marini, S. Salerno, C.L. Motta, M. Condello, G. Arancia, E.
Agostinelli, A. Toninello, Bioorg. Med. Chem. 17 (2009) 326–336.
[23] M. Li, C.L. Liu, J.C. Yang, J.B. Zhang, Z.N. Li, H. Zhang, Z. Li, J. Agric. Food Chem.
58 (2010) 2664–2667.
[24] S. Fustero, R. Román, J.F. Sanz-Cervera, A. Simón-Fuentes, A.C. Cun˜at, S. Vil-
lanova, M. Murguía, J. Org. Chem. 73 (2008) 3523–3529.
[25] H.A. Abdel-Aziz, A.A.I. Mekawey, Eur. J. Med. Chem. 44 (2009) 4985–4997.
[26] K.M. Dawood, H. Abdel-Gawad, M. Ellithey, H.A. Mohamed, B. Hegazi, Arch
Pharm. Chem. Life Sci. 339 (2006) 133–140.
[37] Z.L. Gong, L.W. Zheng, B.X. Zhao, D.Z. Yang, H.S. Lv, W.Y. Liu, S. Lian, J. Photochem.
Photobiol. A 209 (2010) 49–55.
[38] W.Y. Liu, Y.S. Xie, B.X. Zhao, B.S. Wang, H.S. Lv, Z.L. Gong, S. Lian, L.W. Zheng, J.
Photochem. Photobiol. A 214 (2010) 135–144.
[39] H.S. Lv, B.X. Zhao, J.K. Li, Y. Xia, S. Lian, W.Y. Liu, Z.L. Gong, Dyes Pigments 86
(2010) 25–31.
[40] S. Berg, G. Estenne-Bouhtou, K. Luthman, I. Csöregh, W. Hemelink, U. Hacksell,
J. Org. Chem. 60 (1995) 311–320.
[41] H.L. Li, S.S. Kang, Z.T. Xing, H.S. Zeng, H.B. Wang, Dyes Pigments 80 (2007)
163–167.
[27] I. Hayakawa, R. Shioya, T. Agatsuma, H. Furukawa, Y. Sugano, Bioorg. Med.
Chem. Lett. 14 (2004) 3411–3414.
[28] S.M. Rida, S.A.M. El-Hawash, H.T.Y. Fahmy, A.A. Hazza, M.M.M. El-Meligy, Arch.
Pharmacal. Res. 29 (2006) 16–25.
[42] C.K. Kwak, C.H. Lee, T.S. Lee, Tetrahedron Lett. 48 (2007) 7788–7792.
[43] V.S. Rao, K.V.G. Chandra Sekhar, Synth. Commun. 34 (2007) 2153–2157.
[44] C. Dobrotã, C.C. Paraschivescu, I. Dumitru, M. Matache, I. Baciu, L.L. Rutã, Tetra-
hedron Lett. 50 (2009) 1886–1888.
[29] G. Wells, M. Suggitt, M. Coffils, M.A.H. Baig, P.W. Howard, P.M. Loadman,
J.A. Hartley, T.C. Jenkins, D.E. Thurston, Bioorg. Med. Chem. Lett. 18 (2008)
2147–2151.
[30] S. Chattopadhaya, R. Srinivasan, D.S.Y. Yeo, G.Y.J. Chen, S.Q. Yao, Bioorg. Med.
Chem. 17 (2009) 981–989.
[31] Y.S. Xie, H.L. Zhao, H. Su, B.X. Zhao, J.T. Liu, J.K. Li, H.S. Lv, B.S. Wang, D.S. Shin,
J.Y. Miao, Eur. J. Med. Chem. 45 (2010) 210–218.
[32] L.W. Zheng, Y. Li, D. Ge, B.X. Zhao, J.T. Liu, H.S. Lv, J. Ding, J.Y. Miao, Bioorg. Med.
Chem. Lett. 20 (2010) 4766–4770.
[45] M. Dabiri, P. Salehi, M. Baghbanzadeha, M. Bahramnejad, Tetrahedron Lett. 47
(2006) 6983–6986.
[46] B. Chandrakantha, P. Shetty, V. Nambiyar, N. Isloor, A.M. Isloor, Eur. J. Med.
Chem. 45 (2010) 1206–1210.
[47] H.A. Rajapakse, H. Zhu, M.B. Young, B.T. Mott, Tetrahedron Lett. 47 (2006)
4827–4830.
[48] A.N. Brubaker, J. DeRuiter, W.L. Whitmer, J. Med. Chem. 29 (1986) 1094–1099.
[49] B. Das, K. Venkateswarlu, A. Majhi, V. Siddaiah, K.R. Reddy, J. Mol. Catal. A:
Chem. 267 (2007) 30–33.
[33] L.W. Zheng, L.L. Wu, B.X. Zhao, W.L. Dong, J.Y. Miao, Bioorg. Med. Chem. 17
(2009) 1957–1962.
[50] Y. Xia, Z.W. Dong, B.X. Zhao, X. Ge, N. Meng, D.S. Shin, J.Y. Miao, Bioorg. Med.
Chem. 15 (2007) 6893–6899.