The synthesis, X-ray crystal structure and optical properties of novel 1,3,5-triaryl pyrazoline derivatives

Article abstract of DOI:10.1016/j.jphotochem.2009.10.007

A series of novel 1,3,5-triaryl pyrazoline derivatives has been synthesized by the reaction of chalcone and 3-chloro-6-hydrazinylpyridazine in 47-82% yields. The structures of compounds obtained were determined by IR, ¹H NMR and HRMS spectra. Representatively, the spatial structure of compound 3d was determined by using X-ray diffraction analysis. Absorption and fluorescence spectral characteristics of the compounds were investigated in CHCl₃ by UV-vis absorption and emission spectra. The results showed that the absorption maxima of the compounds vary from 332 to 342 nm depending on the group bonded to benzene rings. The maximum emission spectra of compounds in CHCl₃ are dependent on groups in benzene ring in which a strong electron-donating group in benzene ring such as methoxyl group on C3 position of pyrazoline made the emission wavelength of 3e, 3f and 3g red shifted than that of compounds 3b, 3c and 3d with chlorine group. The intensity of absorption and fluorescence was also correlated with substituent on two aryl rings. In addition, the absorption spectra of these compounds change very little with increasing solvent polarity.

Full text of DOI:10.1016/j.jphotochem.2009.10.007

Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 49–55
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
The synthesis, X-ray crystal structure and optical properties of novel 1,3,
5-triaryl pyrazoline derivatives
Zhong-Liang Gong, Liang-Wen Zheng, Bao-Xiang Zhao∗, De-Zhong Yang,
Hong-Shui Lv, Wei-Yong Liu, Song Lian
Institute of Organic Chemistry, School of Chemistry and Chemical Engineering, Shandong University, 27 Shanda Nanlu, Jinan, Shandong 250100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 1,3,5-triaryl pyrazoline derivatives has been synthesized by the reaction of chalcone and
3-chloro-6-hydrazinylpyridazine in 47–82% yields. The structures of compounds obtained were deter-
mined by IR, 1H NMR and HRMS spectra. Representatively, the spatial structure of compound 3d was
determined by using X-ray diffraction analysis. Absorption and fluorescence spectral characteristics of the
compounds were investigated in CHCl3 by UV–vis absorption and emission spectra. The results showed
that the absorption maxima of the compounds vary from 332 to 342 nm depending on the group bonded
to benzene rings. The maximum emission spectra of compounds in CHCl3 are dependent on groups in
benzene ring in which a strong electron-donating group in benzene ring such as methoxyl group on C3
position of pyrazoline made the emission wavelength of 3e, 3f and 3g red shifted than that of compounds
3b, 3c and 3d with chlorine group. The intensity of absorption and fluorescence was also correlated with
substituent on two aryl rings. In addition, the absorption spectra of these compounds change very little
with increasing solvent polarity.
Received 16 July 2009
Received in revised form
18 September 2009
Accepted 17 October 2009
Available online 25 October 2009
Keywords:
Pyrazoline
Synthesis
Characterization
X-ray
UV absorption
Fluorescence
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
small molecules with both potential bioactivity and fluorescent
property.
Pyrazoline derivatives are attracting increasing interest of
many researchers, not only in medicinal chemistry because of
their bioactivity such as antimicrobial [1,2], antiamoebic [3,4],
antinociceptive [5], anticancer [6], antidepressant [7] and anti-
inflammatory [8–12], but also in conjugated fluorescent dyes
emitting blue fluorescence with high fluorescence quantum yield
[13,14] and electroluminescence fields [15–17]. Attempts have
been made to synthesize and elucidate the effects of substituent
on the absorption and fluorescence properties of this class of com-
pounds [18–23].
The design and synthesis of fluorescent small molecules with
desirable properties are of considerable current interest in biol-
ogy research. The advent of sensitive fluorescence detectors has
enabled advances in biological imaging and the emergence of the
field of single molecule spectroscopy [24,25]. 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
[26,27]. Thus, in continuation of our efforts in synthesizing vari-
ous bioactive molecules [28–33], we would like to synthesize novel
2. Materials and methods
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 as solvent
and tetramethylsilane (TMS) as internal standard. Melting points
were determined on an XD-4 digital micro melting point apparatus.
IR spectra were recorded with an IR spectrophotometer VERTEX 70
FT-IR (Bruker Optics). HRMS spectra were recorded on a Q-TOF6510
spectrograph (Agilent). UV–vis spectra were recorded on a U-4100
(Hitachi). Fluorescent measurements were recorded on a Perkin-
Elmer LS-55 luminescence spectrophotometer.
2.2. General procedure for the synthesis of compound 3
To a stirred solution of substituted chalcone (1) (1.0 mmol)
in ethanol (15 mL) was added 3-chloro-6-hydrazinylpyridazine
(2) (1.2 mmol) and 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 monitored by TLC. After completion, the reac-
∗
Corresponding author. Tel.: +86 531 88366425; fax: +86 531 88564464.
E-mail addresses: bxzhao@sdu.edu.cn, sduzhao@hotmail.com (B.-X. Zhao).
1010-6030/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2009.10.007

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Scheme 1. Synthesis of 1,3,5-triaryl pyrazoline derivatives.
68%; mp 183–184 ◦C; IR (KBr, cm−1) 1579.2 (C N); 1H NMR
(400 MHz, CDCl3): ı 3.24 (dd, 1H, J = 5.1, 17.5 Hz, 4Htrans), 3.83
(dd, 1H, J = 12.1, 17.5 Hz, 4Hcis), 5.79 (dd, 1H, J = 5.1, 12.1 Hz, 5H of
pyrazoline), 5.89 (s, 2H, OCH2O), 6.71 (d, 2H, J = 7.9 Hz, Ar-H), 6.81
(d, 1H, J = 7.9 Hz, Ar-H), 7.26 (d, 1H, J = 9.3 Hz, pyridazine-H), 7.39
(d, 2H, J = 8.5 Hz, Ar-H), 7.67 (d, 2H, J = 8.7 Hz, Ar-H), 7.69 (d, 1H,
J = 9.3 Hz, pyridazine-H); HRMS: calcd. for [M+H]+ C20H15Cl2N4O2:
413.0572; found: 413.0569.
3-Chloro-6-(3-(4-chlorophenyl)-5-(furan-2-yl)-4,5-dihydro-1H-
pyrazol-1-yl) Pyridazine (3d). Pale yellow solid, yield 82%; mp
243–244 ◦C; IR (KBr, cm−1) 1582.2 (C N); 1H NMR (400 MHz,
CDCl3): ı 3.56 (dd, 1H, J = 5.4, 17.3 Hz, 4Htrans), 3.69 (dd, 1H, J = 11.9,
17.3 Hz, 4Hcis), 6.00 (dd, 1H, J = 5.4, 11.9 Hz, 5H of pyrazoline), 6.28
(dd, 1H, J = 1.7, 3.2 Hz, furan-H), 6.43 (d, 1H, J = 3.2 Hz, furan-H), 7.27
(d, 1H, J = 1.7 Hz, furan-H), 7.27 (d, 1H, J = 9.3 Hz, pyridazine-H), 7.40
(d, 2H, J = 8.6 Hz, Ar-H), 7.66 (d, 1H, J = 9.3 Hz, pyridazine-H), 7.70
(d, 2H, J = 8.6 Hz, Ar-H); HRMS: calcd. for [M+H]+ C17H13Cl2N4O:
359.0466; found: 359.0467.
3-(3,5-Bis(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl)-6-
chloropyridazine (3e). Pale yellow solid, yield 47%; mp 121–123 ◦C;
IR (KBr, cm−1) 1582.6 (C N); 1H NMR (400 MHz, CDCl3): ı 3.29
(dd, 1H, J = 5.0, 17.5 Hz, 4Htrans), 3.75 (s, 3H, OCH3 of 5-benzene),
3.81 (dd, 1H, J = 12.0, 17.5 Hz, 4Hcis), 3.86 (s, 3H, OCH3 of 3-
benzene), 5.79 (dd, 1H, J = 5.0, 12.0 Hz, 5H of pyrazoline), 6.80
(d, 2H, J = 8.5 Hz, Ar-H), 6.94 (d, 2H, J = 8.6 Hz, Ar-H), 7.22 (d, 1H,
J = 9.0 Hz, pyridazine-H), 7.24 (d, 2H, J = 8.6 Hz, Ar-H), 7.67 (d, 1H,
J = 9.0 Hz, pyridazine-H), 7.69 (d, 2H, J = 8.5 Hz, Ar-H); HRMS: calcd.
for [M+H]+ C21H20ClN4O2: 395.1275; found: 395.1287.
tion mixture was cooled to room temperature and the precipitate
was filtered, washed with ethanol and water, and dried to give
pure 3.
2.3. The spectroscopic data of compound 3
3-Chloro-6-(5-(4-methoxyphenyl)-3-phenyl-4,5-dihydro-1H-
pyrazol-1-yl) pyridazine (3a). Pale yellow solid, yield 64%; mp
186–187 ◦C; IR (KBr, cm−1) 1580.6 (C N); 1H NMR (400 MHz,
CDCl3): ı 3.31 (dd, 1H, J = 5.3, 17.6 Hz, 4Htrans), 3.75 (s, 3H, OCH3),
3.87 (dd, 1H, J = 12.1, 17.6 Hz, 4Hcis), 5.82 (dd, 1H, J = 5.3, 12.1 Hz, 5H
of pyrazoline), 6.80 (d, 2H, J = 8.6 Hz, Ar-H), 7.23 (d, 1H, J = 9.4 Hz,
pyridazine-H), 7.24 (d, 2H, J = 8.3 Hz, Ar-H), 7.39–7.46 (m, 3H,
Ar-H), 7.70 (d, 1H, J = 9.4 Hz, pyridazine-H), 7.76 (d, 2H, J = 8.6 Hz,
Ar-H); HRMS: calcd. for [M+H]+ C20H18ClN4O: 365.1169; found:
365.1169.
3-Chloro-6-(3-(4-chlorophenyl)-5-(4-methoxyphenyl)-4,5-
dihydro-1H-pyrazol-1-yl) pyridazine (3b). Pale yellow solid,
yield 70%; mp 180–181 ◦C; IR (KBr, cm−1) 1578.5 (C N); 1H NMR
(400 MHz, CDCl3): ı 3.27 (dd, 1H, J = 5.4, 17.6 Hz, 4Htrans), 3.75
(s, 3H, OCH3), 3.84 (dd, 1H, J = 12.2, 17.6 Hz, 4Hcis), 5.83 (dd, 1H,
J = 5.4, 12.2 Hz, 5H of pyrazoline), 6.8 (d, 2H, J = 8.6 Hz, Ar-H), 7.23
(d, 1H, J = 8.6 Hz, pyridazine-H), 7.24 (d, 2H, J = 8.5 Hz, Ar-H), 7.40
(d, 2H, J = 8.4 Hz, Ar-H), 7.68 (d, 3H, J = 8.6 Hz, pyridazine-H and
Ar-H); HRMS: calcd. for [M+H]+ C20H17Cl2N4O: 399.0779; found:
399.0781.
3-(5-(Benzo[d][1,3]dioxol-5-yl)-3-(4-chlorophenyl)-4,5-dihydro-
1H-pyrazol-1-yl)-6-chloropyridazine (3c). Pale yellow solid, yield
Scheme 2. A proposed mechanism for the reaction of chalcone and 3-chloro-6-hydrazinylpyridazine.

Z.-L. Gong et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 49–55
51
3-(5-(Benzo[d][1,3]dioxol-5-yl)-3-(4-methoxyphenyl)-4,5-
dihydro-1H-pyrazol-1-yl)-6-chloropyridazine (3f). Pale yellow
solid, yield 73%; mp 150–151 ◦C; IR (KBr, cm−1) 1572.9 (C N); 1
H
NMR (400 MHz, CDCl3): ı 3.24 (dd, 1H, J = 5.3, 17.5 Hz, 4Htrans),
3.83 (dd, 1H, J = 12.0, 17.5 Hz, 4Hcis), 3.86 (s, 3H, OCH3), 5.75 (dd,
1H, J = 5.3, 12.0 Hz, 5H of pyrazoline), 5.89 (s, 2H, OCH2O), 6.71
(d, 1H, J = 8.0 Hz, Ar-H), 6.74 (d, 1H, J = 1.3 Hz, Ar-H), 6.82 (dd,
1H, J = 1.3, 8.0 Hz, Ar-H), 6.94 (d, 2H, J = 8.8 Hz, Ar-H), 7.23 (d, 1H,
J = 9.4 Hz, pyridazine-H), 7.68 (d, 1H, J = 9.6 Hz, pyridazine-H), 7.69
(d, 2H, J = 9.0 Hz, Ar-H); HRMS: calcd. for [M+H]+ C21H18ClN4O3:
409.1067; found: 409.1067.
Fig. 1. Structure of compound 3.
3-Chloro-6-(5-(furan-2-yl)-3-(4-methoxyphenyl)-4,5-dihydro-
1H-pyrazol-1-yl) Pyridazine (3g). Yellow solid, yield 78%; mp
193–195 ◦C; IR (KBr, cm−1) 1580.8 (C N); 1H NMR (400 MHz,
CDCl3): ı 3.56 (dd, 1H, J = 5.6, 17.2 Hz, 4Htrans), 3.69 (dd, 1H, J = 11.8,
17.2 Hz, 4Hcis), 3.86 (s, 3H, OCH3), 5.96 (dd, 1H, J = 5.6, 11.8 Hz,
5H of pyrazoline), 6.27 (dd, 1H, J = 1.8, 3.2 Hz, furan-H), 6.41 (d,
1H, J = 3.2 Hz, furan-H), 6.95 (d, 2H, J = 8.8 Hz, Ar-H), 7.24 (d, 1H,
J = 9.4 Hz, pyridazine-H), 7.26 (d, 1H, J = 1.8 Hz, furan-H), 7.65 (d,
1H, J = 9.4 Hz, pyridazine-H), 7.71 (d, 2H, J = 8.8 Hz, Ar-H); HRMS:
calcd. for [M+H]+ C18H16ClN4O2: 355.0962; found: 355.0962.
interesting how to distinguish the isomers. Generally, it is difficult
to determine the exact structures of isomers only by spectroscopic
date. Fortunately, in present study, the spatial structure of com-
pound 3d was determined by using X-ray diffraction analysis. Thus,
the structures of the products 3 were assigned by the analyses of
their spectral data including 1H NMR, IR and HRMS comparing with
X-ray diffraction analysis.
3.2. Structure characterization
2.4. X-ray crystallography
The IR spectra of all the compounds showed ꢁ(C N) stretch at
1573–1582 cm−1 consisting with pyrazoline and pyridazine moi-
ety. In the 1H NMR spectra of pyrazoline that is shown in Fig. 1,
protons HA and HB that are geminal protons at C4 carbon, appears
in the region 3.24–3.56 and 3.69–3.87 ppm as doublet of doublets
in all compounds. The CH proton at C5 also appeared as doublet
of doublets in the region of 5.75–6.00 ppm due to vicinal coupling
with two non-equivalent geminal protons of C4 carbon. Two ortho-
aromatic protons signals in chloropyridazine moiety appeared at
the range of ı = 7.23–7.27 and 7.65–7.70 ppm as doublet peaks
(J = 8.7–9.4 Hz), respectively. HRMS showed that found [M+H]-ion
peak accorded with calculated value. Moreover, typically, the struc-
ture of compound 3d was confirmed by X-ray diffraction analysis.
Suitable single crystals of 3d for X-ray structural analysis
were obtained by slow evaporation of a solution of the solid in
dichloromethane at room temperature for 7 days. The diffrac-
tion data was collected with a Bruker SMART CCD diffractometer
using a graphite monochromated Mo K␣ radiation (ꢀ = 0.71073 Å)
at 298(2) K. The structures were solved by direct methods with
SHELXS-97 program and refinements on F2 were performed with
SHELXL-97 program by full-matrix least-squares techniques with
anisotropic thermal parameters for the non-hydrogen atoms. All
H atoms were initially located in a difference Fourier map. The
methyl H atoms were then constrained to an ideal geometry,
with C–H = 0.96 Å and Uiso(H) = 1.5 Ueq(C). All other H atoms were
placed in geometrically idealized positions and constrained to ride
on their parent atoms, with C–H = 0.93 Å and Uiso(H) = 1.2 Ueq(C).
3.3. X-ray crystallography
The molecular view of 3d is shown in Fig. 2. A summary of crys-
tallographic data collection parameters and refinement parameters
for 3d are compiled in Table 1.
The structure of compound 3d is crystallized in monoclinic
space group P21/n. One benzene moiety, one furan ring and a pyri-
dazine moiety are bonded to the pyrazoline ring at the atoms of C7,
C9 and N2, respectively. Consistent with a pronounced electronic
interaction, the bond lengths of C4–C7, N2–C14 are significantly
3. Results and discussion
3.1. Synthesis of compound 3
The synthetic routes of the proposed compound 3 are out-
lined in Scheme 1. Starting chalcone 1 can be easily prepared by
Claisen–Schmidt condensation between acetophenone and aro-
matic aldehydes in the presence of ethanolic solution of sodium
hydroxide according to the literatures [4]. The 3,5-diaryl pyrazo-
line derivatives 3a–g were obtained by the reaction of chalcone
1 with 3-chloro-6-hydrazinylpyridazine 2 at reflux condition in
47–82% yields. It is noticed that the regioselectivity of the reaction
of chalcone 1 with 3-chloro-6-hydrazinylpyridazine 2 was satisfied
in which we obtained the purpose products rather than isomers.
It can be explained by a proposed mechanism of the reaction as
shown in Scheme 2. Nitrogen in 3-chloro-6-hydrazinylpyridazine
attacked firstly carbonyl carbon with more positive charge and then
dehydration took place to form an intermediate 4 that proceeds to
afford product 3 (1,2-addition route). In the present condition other
isomers 6 or 7 that should be formed by 1,4-addition route are not
found. The influences of the substituent in phenyl moiety of chal-
cone 1 on the yield are consistent with the mechanism. Comparing
the yield of 3a, 3b and 3e (64%, 70% and 47%, respectively), we found
that the reaction of 2 and 1b with chloro group had higher yield than
that of 1a or 1e with hydrogen or methoxyl group, respectively,
by reason of difference in electron withdrawing. In addition, it is
Fig. 2. The molecular structure of compound 3d, with displacement ellipsoids
drawn at the 30% probability level.

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Z.-L. Gong et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 49–55
Table 1
Summary of crystallographic data and structure refinement details for 3d.
3d
Empirical formula
Formula weight
Temperature
C17H12C12N4O1
359.21
298(2) K
Wavelength
Crystal system
Space group
0.71073 Å
Monoclinic
P21/n
a = 8.1600(9) Å, ˛ = 90◦
b = 11.2296(12) Å, ˇ = 101.499(2)◦
c = 17.7512(18) Å, ꢂ = 90◦
Unit cell dimensions
Volume
1594.0(3) Å3
Z
4
Calculated density
Absorption coefficient
F(0 0 0)
1.497 Mg/m3
0.419 mm−1
736
Crystal size
ꢃ range for data collection
Limiting indices
0.10 mm × 0.10 mm × 0.10 mm
2.16–27.54◦
−10 ≤ h ≤ 8, −14 ≤ k ≤ 14, −23 ≤ l ≤ 21
9225/3608 [R(int) = 0.0300]
98.1%
Semi-empirical from equivalents
0.9593 and 0.9593
Full-matrix least-squares on F2
3608/0/265
Reflections collected/unique
Completeness to ꢃ = 25.05◦
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I >2ꢄ(I)]
R indices (all data)
Largest diff. peak and hole
1.021
R1 = 0.0428, wR2 = 0.1173
R1 = 0.0673, wR2 = 0.1334
0.295 and −0.233 e Å−3
shorter as would be expected for a single bond. Moreover, the bond
lengths of N1–N2, N1–C7, C7–C8 agree well with the equivalent
ones in similar structures [34]. In the crystal of 3d, torsion angle
C14–N2–C9–C10 of −68.83◦ shows C10 in the pyridazine moiety
adopts an antiperiplanar conformation with respect to the C14 atom
of the benzene ring. In the asymmetry unit, the pyrazoline ring, ben-
zene ring and pyridazine are almost coplanar. And the pyrazoline
ring makes dihedral angles with benzene and pyridazine ring of
4.9(1)◦ and 4.3(1)◦, respectively, while the dihedral angle between
pyrazoline and furan moiety is 82.6(1)◦.
Regarding the crystal structure of 3d, there is one intramolecular
C15–H15· · ·N1 hydrogen bond forming a pseudo five-membered
ring. The molecules are connected by weak ␲· · ·␲ interactions
and further assigned into layers via intramolecular hydrogen
bond of C16–H16· · ·Cl1, H16· · ·Cl1 2.73(3) Å, C16· · ·Cl1 3.659(2) Å,
C16–H16· · ·Cl1 157(2)◦ with the symmetry code of 1/2 + x, 3/2 − y,
−1/2 + z, along the b-axis (Fig. 3). Besides the aforementioned
hydrogen bonds, there is also a weak C–H· · ·␲ interaction, which is,
however, important for the packing modes. Cl1· · ·Cg3 3.6126(12) Å
C1· · ·Cg3 4.042(3) Å C1–Cl1· · ·Cg3 91.16(8)◦.
Fig. 3. Crystal packing diagram of 3d along the c-axis (A) and b-axis (B). Dashed
lines show arrays of hydrogen bonds.
almost perpendicular to ␲-system, although they are strong elec-
tron donor. Thus the ꢀmax depends mainly on the substituent in
phenyl.
Furthermore, the absorption intensity was correlated with sub-
stituent on two aryl rings. The absorption spectra of representative
compounds 3a, 3b, 3e and 3d in different solvents with the con-
centration of 5 × 10−5 M are presented in Fig. 5. It was observed
that the absorption spectra of these compounds change very little
with increasing solvent polarity although there is a tendency of a
3.4. Absorption spectra
The absorption spectra of compounds 3a–g shown in Fig. 4 and
Table 2 have been recorded in chloroform solution with the con-
centration of 5 × 10−5 M. A small but definite substituent effect was
observed such that electron-withdrawing groups (Cl) result in a red
shift with respect to an electron-donating group (MeO). The data
indicated that, when a chlorine group is located on the phenyl ring
at position 3, the absorption peaks of 3b, 3c and 3d are at longer
wavelengths than those of 3e, 3f and 3g in which the methoxyl
group is bonded. The actual chromophoric ␲-system is composed
of the two aryl substituents in the 1- and 3-position and three out
of the five pyrazoline ring atoms (N1–N2–C3). The remaining two
carbon atoms (C4 and C5) of the ring are sp3 hybridized and are
not part of the conjugated ␲-system. The attached aromatic (Ar)
in C5 cannot extend to the pi-conjugation system because they are
Fig. 4. The UV–vis spectra of pyrazoline derivatives 3a–g in chloroform solution
with the concentration of 5 × 10−5 M.

Z.-L. Gong et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 49–55
53
Table 2
Maximum absorption wavelength (ꢀmax) and molar absorptivity (εmax) of pyrazoline derivatives 3a–g in chloroform.
Compounds
3a
3b
3c
3d
3e
3f
3g
ꢀmax (nm)
336
2.69
342
2.95
341
2.94
336
2.84
336
3.36
337
3.22
332
3.38
εmax (×104 M−1 cm−1
)
Fig. 5. The UV–vis spectra of 3a, 3b, 3e and 3d in different solvents with the concentration of 5 × 10−5 M.
shorter ꢀmax in CH3CN, indicating that there is no charge transfer
in the ground state [20] (Table 3).
3.5. Fluorescence
The maximum emission spectra of compounds 3a–g in CHCl3
are shown in Fig. 6 and Table 4. Their excitation wavelengths were
fixed at 329, 339, 332, 327, 335, 335 and 332 nm, respectively. It
can be found that their intensity of fluorescence differed from each
other. Similar to the absorption spectrum, the group at position 3
Table 3
Maximum absorption wavelength (ꢀmax) of pyrazoline derivatives 3a, 3b, 3d and 3e
in different solvents.
Compounds
CHCl3 (nm)a
THF (nm)a
CH3CN (nm)a
3a
3b
3d
3e
336
342
336
335
334
342
337
334
329
337
332
332
a
Static dielectric constant of CHCl3, THF and CH3CN are 4.81, 7.52 and 36.64,
respectively [J.A. Dean, Lange’s Handbook of Chemistry, 15th ed., 1999].
Fig. 6. Emission spectra of pyrazoline derivatives 3a–g in chloroform solution with
the concentration of 10−5 M.

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Table 4
was determined by using X-ray diffraction analysis. The absorption
maxima of the compounds vary from 332 to 342 nm depending on
the group bonded to benzene rings. The maximum emission spec-
tra of compounds in CHCl3 are dependent on group in benzene ring
in which a strong electron-donating group in benzene ring such as
methoxyl group on C3 position of pyrazoline made the emission
wavelength of 3e, 3f and 3g red shifted than that of compounds 3b,
3c and 3d with chlorine group. The intensity of absorption and fluo-
rescence was also correlated with substituents on two aryl rings. In
addition, the absorption spectra of these compounds change very
little with increasing solvent polarity.
Maximum wavelength (nm) of excitement and emission of fluorescence of com-
pounds 3a–g.
Name
3a
3b
3c
3d
3e
3f
3g
ꢀex
ꢀem
Stokes shift
329
470
141
339
459
120
332
466
134
327
466
139
335
512
177
335
513
178
332
481
149
5. Supplementary materials
CCDC 746323 contains the supplementary crystallographic
data for this paper. These data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/data request/cif, by email-
ing data request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB21EZ,
UK; fax: +44 1223 336033.
Acknowledgements
This study was supported by the Science and Technology Devel-
opmental Project of Shandong Province (2008GG10002034) and
973 Program (2009CB526507).
References
Fig. 7. Emission spectra of compounds 3b and 3d in different solution with the
concentration of 10−5 M.
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