The optical properties, synthesis and characterization of novel 5-aryl-3-benzimidazolyl-1-phenyl-pyrazoline derivatives

Article abstract of DOI:10.1016/j.saa.2012.08.036

A series of novel 5-aryl-3-benzimidazolyl-1-phenyl-pyrazoline derivatives were synthesized by the reaction of benzimidazolyl chalcone and phenylhydrazine in 41-72% yields. The compounds were characterized using IR, ¹H NMR and HRMS. Absorption and fluorescence spectra were measured in different organic solvent. An intense absorption maxima was noted at ca. 370 nm and emission maxima was noted at ca. 460 nm. The absorption spectra of the pyrazoline derivatives reveal that 5-aryl group attached to the pyrazoline ring hardly influenced the maximum absorption. The fluorescence spectra of these compounds indicated the emission wavelength was red shifted and the fluorescence intensity was decreased with the increase in solvent polarity.

Full text of DOI:10.1016/j.saa.2012.08.036

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 76–80
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
The optical properties, synthesis and characterization of novel
5-aryl-3-benzimidazolyl-1-phenyl-pyrazoline derivatives
b,
Xiao Qun Cao a, Xiao Hui Lin a, Yan Zhu a, Yan Qing Ge a, , Jian Wu Wang
⇑
⇑
a Taishan Medical University, Taian, Shandong 271016, PR China
b School of Chemistry and Chemical Engineering, Shandong University, Jinan, Shandong 250100, PR China
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
Novel pyrazoline derivatives were
prepared and fully characterized.
UV–vis absorption and fluorescence
spectroscopy of all compounds were
measured.
O
NaOH / ethanol
reflux 4-6 h
N
N
Ar
N
3
"
N
+
NH
HN
N
H
Ar
NH2
"
Influence of solvent on UV–vis
absorption and fluorescence
spectroscopy was examined.
1
2
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 March 2012
Received in revised form 9 August 2012
Accepted 14 August 2012
Available online 26 August 2012
A series of novel 5-aryl-3-benzimidazolyl-1-phenyl-pyrazoline derivatives were synthesized by the reac-
tion of benzimidazolyl chalcone and phenylhydrazine in 41–72% yields. The compounds were character-
ized using IR, 1H NMR and HRMS. Absorption and fluorescence spectra were measured in different
organic solvent. An intense absorption maxima was noted at ca. 370 nm and emission maxima was noted
at ca. 460 nm. The absorption spectra of the pyrazoline derivatives reveal that 5-aryl group attached to
the pyrazoline ring hardly influenced the maximum absorption. The fluorescence spectra of these com-
pounds indicated the emission wavelength was red shifted and the fluorescence intensity was decreased
with the increase in solvent polarity.
Keywords:
Synthesis
Pyrazoline
Benzoimidazole
UV absorption
Fluorescence
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
ogy research. The advent of sensitive fluorescence detectors
has enabled advances in biological imaging and the emergence
Pyrazoline derivatives have attracted increasing attention due
to their pharmaceutical applications such as antimicrobial [1–3],
antiamoebic [4,5], antinociceptive [6], anticancer [7], antidepres-
sant [8] and anti-inflammatory [9–13], They also have potential
applications in conjugated fluorescent dyes emitting blue fluores-
cence with high fluorescence quantum yield [14,15] and electrolu-
minescence fields [16–18]. Attempts have been made to synthesize
and elucidate the effects of substituent on the absorption and fluo-
rescence properties of this class of compounds [19–24].
of the field of single molecule spectroscopy [25,26]. To date
there have been relatively few studies of the cellular localization
of agents in which small molecule is linked to a fluorophore,
such as coumarin [27,28]. Thus, in continuation of our efforts
on the synthesis of various biologically and optically active het-
erocycles [29–34], we would like to synthesize novel small mol-
ecules with both potential bioactivity and fluorescent property.
Recently, Zhao reported the synthesis and optical properties of
1,3,5-triaryl pyrazoline derivatives and ferrocenyl pyrazoline
derivatives [35,36]. In light of few report concerning the fluores-
cent property of benzoimidazolyl pyrazoline, herein, we would
like to report the synthesis, characterization and optical proper-
ties of novel 5-aryl-3-benzimidazolyl-1-pyridazinyl-pyrazoline
derivatives.
The design and synthesis of fluorescent small molecules with
desirable properties are of considerable current interest in biol-
⇑
Corresponding authors. Tel.: +86 538 6292362; fax: +86 531 6236837.
E-mail addresses: yqge@yahoo.cn (Y.Q. Ge), jwwang@sdu.edu.cn (J.W. Wang).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.08.036

X.Q. Cao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 76–80
77
Scheme 1. Synthesis of 5-aryl-3-benzimidazolyl-1-phenyl-pyrazoline derivatives.
NaOH (2.0 mmol) and the reaction mixture was refluxed for 3–
6 h as shown in Scheme 1. The progress of the reaction was mon-
itored by TLC. After completion, the reaction mixture was cooled to
room temperature and the precipitate was filtered, washed with
water and ethanol, and then dried to give pure 3.
Results and discussion
Fig. 1. Structure of compound 3d.
Synthesis of compound 3
Materials and methods
General
Thin-layer chromatography (TLC) was conducted on silica gel
The synthetic procedures of compounds 3a–f are shown in
Scheme 1. Starting chalcone 1 can be easily prepared by Claisen–
Schmidt condensation between 2-acetyl-1H-benzo[d]imidazole
and aromatic aldehydes in the presence of ethanolic solution of so-
dium hydroxide according to the literatures [36]. The 3,5-diaryl
pyrazoline derivatives 3a–f were obtained by the reaction of chal-
cone 1 with phenylhydrazine 2 at reflux condition in 41–72%
yields. Comparing the yield of 3a and 3b (69% and 72%, respec-
tively), we found that the reaction of 2 and 1a or 1b with trifluoro-
methyl group had higher yield than that of 1c or 1d with dioxol or
methyl group, respectively, by reason of difference in electron
withdrawing.
60 F254 plates (Merck KGaA). 1H NMR spectra were recorded on a
Bruker Avance 300 (300 MHz) spectrometer, using CDCl3 as solvent
and tetramethylsilane (TMS) as internal standard. IR spectra were
recorded with an IR spectrophotometer VERTEX 70 FT-IR (Bruker
Optics). HRMS spectra were recorded on a Q-TOF6510 spectro-
graph (Agilent). UV–vis spectra were recorded on a U-4100 (Hit-
achi). Fluorescent measurements were recorded on
PerkineElmer LS-55 luminescence spectrophotometer.
a
General procedure for the synthesis of compound 3
Structure characterization
To a stirred solution of substituted chalcone (1) (1.0 mmol) in
ethanol (20 mL) was added phenylhydrazine (2) (1.2 mmol) and
The structures of products 3a–f were characterized by spectro-
scopic methods (1H NMR, IR, and HRMS). In the 1H NMR spectra
1000
900
800
700
600
500
400
300
200
100
0
3a
3b
3c
3d
3e
3f
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
-100
200
300
400
500
600
700
Wavelength / nm
Fig. 2. Absorption and emission spectra of compounds 3a–f in cyclohexane solution.

78
X.Q. Cao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 76–80
0.28
3a + DMF
3b + DMF
3c + DMF
3a + Cyclohexane
3b + Cyclohexane
3c + Cyclohexane
0.26
0.24
0.22
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
-0.02
240 260 280 300 320 340 360 380 400 420 440 460
Wavelength / nm
0.5
0.4
0.3
0.2
0.1
0.0
3d + DMF
3e + DMF
3f + DMF
3d + Cyclohexane
3e + Cyclohexane
3f + Cyclohexane
240 260 280 300 320 340 360 380 400 420 440 460
Wavelength/nm
Fig. 3. UV–vis spectra of 3a–f in different solvents.
(CDCl3) of pyrazoline, protons HA and HB that are geminal protons
at C4 carbon, appear in the region 3.43–3.68 and 3.93–4.12 ppm
respectively as doublet of doublets in all compounds. The data
indicate that the structure of 5-aryl ring has definite effects on
the chemical shift. The chemical shifts of compounds 3a–d with
substituted phenyl group are similar while 3e and 3f with furanyl
and thiophenyl group change more compared with 3a–d. The CH
proton at C5 also appeares as doublet of doublets in the region of
5.30–5.69 ppm. Similar to the chemical shifts of the CH proton at
C4, the group at position 5 also has very strong influence on the
chemical shift. Furthermore, different from the CH proton shift at
C4, the substituent on the phenyl group also has very strong influ-
ence on the chemical shift of the CH proton shift at C5. The IR spec-
600
500
400
300
200
100
0
Excition
Emmision
3a
3b
3c
3d
3e
3f
tra of all the compounds show C@N stretch at 1591–1595 cmÀ1
,
which indicates that the structure of 5-aryl ring has little effects
on the absorption. For example, compound 3d (Fig. 1), obtained
as yellow crystals, gave an [M+H]-ion peak at m/z 353.1765 in
the HRMS, in accordance with the molecular formula C23H21N4.
The IR spectra showed the characteristic absorption bands at
1593 (C@N). In the 1H NMR spectra (CDCl3) of pyrazoline, it re-
vealed a singlet at d 2.29 (3H, –CH3). Protons Ha and Hb that are
geminal protons at C4 carbon, appears at 3.46 and 4.09 ppm as
200
300
400
500
600
700
Wavelength / nm
Fig. 4. The flurescence excitation and emission spectra of compounds 3a–f in
dichloromethane.

X.Q. Cao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 76–80
79
800
700
3a + Cyclohexane
3a + DCM
600
3a + CH3CN
500
3a+ DMF
400
300
200
100
0
-100
350
400
450
500
550
600
650
Wavelength / nm
1000
800
600
400
200
0
3d + Cyclohexane
3d + DCM
3d + CH3CN
3d + DMF
400
450
500
550
600
650
Wavelength / nm
Fig. 5. Emission spectra of compounds 3a and 3d in different solution.
Table 1
The optical characteristics of the compounds 3a–f in cyclohexane and DMF.
kmax (nm)
kex (nm)
Fmax (nm)
Stokes shift (nm)
CHX
Eg (eV)
CHX
UF
CHX
DMF
CHX
DMF
DMF
DMF
CHX
3a
3b
3c
3d
3e
3f
372
369
372
372
374
372
373
372
374
374
371
374
380
380
380
380
380
380
441
441
444
447
442
442
456
454
459
459
454
456
69
72
72
75
68
70
83
82
85
85
83
82
2.97
2.97
2.97
2.96
2.98
2.98
2.97
2.97
2.97
2.95
2.98
2.95
0.11
0.10
0.13
0.12
0.15
0.18
doublet of doublets. The CH proton at C5 also appeared as doublet
of doublets at 5.36 ppm due to vicinal coupling with two non-
equivalent geminal protons of C4 carbon.
the wavelength range from 220 to 420 nm, while almost no
absorption was observed beyond 420 nm. The data indicated that,
electron-withdrawing groups (CF3) and electron-donating group
(CH3) attached to 5-aryl group hardly influenced the maximum
absorption. Actually, the chromophoric system is composed of
the two aryl substituents in the 1- and 3-position and three atoms
(N1–N2–C3) out of the five pyrazoline ring. The remaining two car-
bon atoms (C4 and C5) of the ring are sp3 hybridized and are not
part of the conjugated system. The attached aromatic (Ar) in C5
Absorption spectral characteristics of the compounds 3a–f
For UV–vis absorption measurements, the dye concentration
was 1 Â 10À6 mol LÀ1, and the UV–vis absorption spectra of com-
pounds 3a–f measured in cyclohexane solutions are given in
Fig. 2 and Table 1. Several absorption peaks could be observed in
cannot extend to the
p-conjugation system because they are al-

80
X.Q. Cao et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 76–80
most perpendicular to
donor [36].
p-system, although they are strong electron
Appendix A. Supplementary data
Furthermore, the absorption spectra of the compounds 3a–f in
different solvents with the concentration of 1 Â 10À6 mol LÀ1 are
presented in Fig. 3. It is observed that the absorption spectra of
these compounds change little with increasing solvent polarity,
indicating that there is no charge transfer in the ground state.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.08.036.
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In summary, a series of novel 5-aryl-3-benzimidazolyl-1-phe-
nyl-pyrazoline derivatives were synthesized by the reaction of
benzimidazolyl chalcone and phenylhydrazine in 41–72% yields.
The compounds were characterized using IR, 1H NMR, and HRMS.
Absorption and fluorescence spectra were measured in different
organic solvent; an intense absorption maxima was noted at ca.
370 nm and emission maxima was noted at ca. 460 nm. The
absorption and fluorescence spectra of the pyrazoline derivatives
reveal that 5-aryl group attached to the pyrazoline ring hardly
influenced the maximum absorption. The fluorescence spectra of
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shifted and the fluorescence intensity was decreased with the in-
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