Synthesis of quinoline derivatives containing pyrazole group and investigation of their crystal structure and spectroscopic properties in relation to acidity and alkalinity of mediums

Article abstract of DOI:10.1016/j.saa.2014.03.018

Two series of quinoline derivatives containing pyrazole group were synthesized and characterized by means of ¹H NMR, FT-IR, MS, elemental analysis and X-ray single crystal diffraction, and their UV-vis absorption behavior and fluorescence properties were also measured. Moreover, the effects of acetic acid and triethylamine on the spectroscopic properties of synthesized products were examined with compounds 3a and 5a as examples. It has been found that all synthesized quinoline derivatives show maximum absorption peak at 303 nm and emission peaks around 445 nm. Besides, both acetic acid and triethylamine can change the acidity of the medium, thereby influencing the UV-vis absorption spectra and fluorescence spectra of synthesized products. Moreover, theoretical investigations indicate that the integration of H ⁺ and N atom of quinoline ring favors the formation of a new product in the presence of acetic acid, and the product obtained in this case shows a new UV-vis absorption peak at 400 nm.

Full text of DOI:10.1016/j.saa.2014.03.018

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 7–13
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis of quinoline derivatives containing pyrazole group
and investigation of their crystal structure and spectroscopic properties
in relation to acidity and alkalinity of mediums
a
a
Tiegang Ren a, Jie Wang a, Guihui Li b, , Hongbin Cheng , Yongzhe Li
⇑
a Fine Chemistry and Engineering Research Institute, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, People’s Republic of China
b Key Laboratory of Ministry of Education for Special Functional Materials, Henan University, Kaifeng 475004, People’s Republic of China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
A series of quinoline derivatives
containing pyrazole group were
synthesized and characterized.
The UV–vis spectra and fluorescent
spectra of various as-synthesized
products were measured.
The effect of acetic acid and
triethylamine on the spectroscopic
properties of as-synthesized products
was examined.
a r t i c l e i n f o
a b s t r a c t
Article history:
Two series of quinoline derivatives containing pyrazole group were synthesized and characterized by
means of 1H NMR, FT-IR, MS, elemental analysis and X-ray single crystal diffraction, and their UV–vis
absorption behavior and fluorescence properties were also measured. Moreover, the effects of acetic acid
and triethylamine on the spectroscopic properties of synthesized products were examined with com-
pounds 3a and 5a as examples. It has been found that all synthesized quinoline derivatives show maxi-
mum absorption peak at 303 nm and emission peaks around 445 nm. Besides, both acetic acid and
triethylamine can change the acidity of the medium, thereby influencing the UV–vis absorption spectra
and fluorescence spectra of synthesized products. Moreover, theoretical investigations indicate that the
integration of H+ and N atom of quinoline ring favors the formation of a new product in the presence
of acetic acid, and the product obtained in this case shows a new UV–vis absorption peak at 400 nm.
Ó 2014 Elsevier B.V. All rights reserved.
Received 22 January 2014
Received in revised form 12 March 2014
Accepted 15 March 2014
Available online 22 March 2014
Keywords:
Quinoline derivative
Pyrazole group
Synthesis
Acidity and alkalinity of medium
Spectroscopic properties
Theoretical investigations
Introduction
derivatives are significant intermediates in pharmaceutical indus-
try [2], because as a kind of integrase inhibitors they can effectively
As a class of important heterocyclic compounds, quinoline com-
pounds display a wide range of applications and development
prospects in healthcare, ion recognition, fluorescent probe and
optical functionalization [1]. Particularly, 8-hydroxyquinoline
inhibit HIV-1s [3], impede retroviral integrase [4], prevent proto-
zoa and retroviral mixed infection [5], and eliminate free radicals
and inhibit lipid peroxidation [6]. Furthermore, 8-hydroxyquino-
line derivatives can also be applied as organic photoelectric func-
tional materials. For example, in 1987, Tang et al. reported a
green emitting device prepared from 8-hydroxyquinoline alumi-
num as the light emitting layer [7]. Since then, many quinoline
⇑
Corresponding author. Tel.: +86 378 2866141.
E-mail address: rtg@henu.edu.cn (G. Li).
http://dx.doi.org/10.1016/j.saa.2014.03.018
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

8
T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 7–13
compounds have been designed, synthesized and used as photo-
electric functional materials. In the meantime, as an important
family of organic fluorescent compounds, pyrazole derivatives
are useful reagents for the extraction and separation of various me-
tal ions [8,9], and they are also of significance in anti-virus, anti-
cancer, anti-fungus, anti-inflammatory, and anti-oxidation as well
as for treatment of hypoglycemia and physiological disorders
[10,11]. This reminds us that, by integrating quinoline with pyra-
zole group, it may be feasible to synthesize novel quinoline deriv-
atives as multifunctional pharmaceutical intermediates or even
drugs.
In our previous work, we synthesized a series of Schiff base com-
pounds and benzimidazole compounds containing pyrazole group,
and found that the introduction of pyrazole group to the molecular
chain of Schiff base or benzimidazole compounds led to enhanced
fluorescence emissions [12–14]. Unfortunately, little is currently
available about the fluorescent properties of quinoline derivatives
containing pyrazole group and about the correlation between their
molecular structure and emission properties, which greatly hinders
their applications in biological and environmental sciences. Thus in
this article we report a simple procedure for synthesizing quinoline
derivatives containing pyrazole group as well as their molecular
and crystal structures and fluorescent properties.
160 °C for 4 days and then cooled to room temperature. Resultant
mixed solution was poured into 100 mL H2O, followed by extrac-
tion with CH2Cl2 (3 Â 50 mL) and rotary evaporation to remove sol-
vent. As-separated crystalline precipitates were dissolved in 25 mL
DMF, followed by dropwise addition of 20 mL of aqueous HCl (vol-
ume fraction: 36%) at 80 °C in a reaction period of 5 h. Then the
reactants were allowed to react for additional 4 h after 25 mL of
triethylamine was added dropwise. Upon completion of the reac-
tion, the hot mixture was poured into ice water (250 mL) and stir-
red overnight, followed by extraction with CH2Cl2 (4 Â 100 mL).
The combined organic layers were washed with saturated NaCl
solution and dried with anhydrous Na2SO4. Crude mixed products
were obtained after residual solvent was evaporated under re-
duced pressure, and as-obtained crude products were purified by
column chromatography (silica gel, ethyl acetate/petroleum ether).
(E)-2-(2-(1-(3,4-dimethylphenyl)-3,5-dimethyl-1H-pyrazol-4-
yl)vinyl)quinolin-8-ol (1a), pale-yellow solid 0.94 g, yield 50.8%.
Electrospray ionization mass spectra (ESI-MS, m/z): 370.20(M+).
1H NMR ((CD3)2CO) d: 2.31 (s, 3H, CH3), 2.33 (s, 3H, CH3), 2.48 (s,
3H, CH3), 2.50 (s, 3H, CH3), 2.89 (s, 1H, OAH), 7.08–7.13 (m, 2H,
quinolin-H), 7.22–7.40 (m, 5H, quinolin-H, ArAH), 7.77–7.79 (d,
J = 8.0 Hz, 1H, quinolin-H), 7.99–8.01 (d, J = 8.0 Hz, 1H, C@CAH),
8.23–8.25 (d, J = 8.0 Hz, 1H, C@CAH). IR (KBr, cmÀ1
) m: 3370.87,
1642.72, 1456.31, 1145.63, 951.46. Anal. Calc.: C, 78.02; H, 6.27;
N, 11.37. Found: C, 77.85; H, 6.09; N, 11.27.
Experiments
(E)-2-(2-(3,5-dimethyl-1-(p-tolyl)-1H-pyrazol-4-yl)vinyl)quin-
olin-8-ol (2a), pale-yellow solid 0.88 g, yield 49.4%. ESI-MS (m/z):
356.20(M+). 1H NMR ((CD3)2CO) d: 2.39 (s, 3H, CH3), 2.48 (d,
J = 4.0 Hz, 6H, CH3), 3.37 (s, 1H, OAH), 7.07–7.13 (m, 2H, quino-
lin-H), 7.33–7.41 (m, 6H, quinolin-H, ArAH), 7.78–7.80 (d,
J = 8.0 Hz, 1H, quinolin-H), 7.97–7.99 (d, J = 8.0 Hz, 1H, C@CAH),
Physical measurement and materials
Mass spectra (MS) were determined with an Agilent 1100LC-MS
mass spectrometer. Infrared (IR) spectra of obtained products
within 400–4000 cmÀ1 were recorded with a Nicolet 170 SXFT-IR
spectrometer (mixed with KBr and pressed into pellets). Nuclear
magnetic resonance (1H NMR) spectra in (CD3)2CO solvent were
recorded with an INOVA-400 spectrometer in the presence of tet-
ramethylsilane as an internal standard. Elemental analysis was
conducted with a PE2400 elemental analysis apparatus. Ultravio-
let–visible light (UV–vis) absorption spectra of target compounds
in a wavelength range of 200–700 nm were measured with a Hit-
achi U-4100 spectrophotometer (to-be-tested compounds were
separately dissolved in spectral grade dimethylfomamide (DMF)
at a concentration of 1.0 Â 10À5 mol/L). The fluorescence spectra
of various target compounds separately dissolved in spectral grade
DMF at a concentration of 1.0 Â 10À5 mol/L were recorded with a
Hitachi F-7000 spectrofluorometer in right angle detection mode
(each solution was excited at kmax and the corrected fluorescence
emission spectrum was recorded also at a wavelength of 200–
700 nm). Specifically, target compounds 3a and 5a were separately
dissolved in spectral grade DMF at a concentration of 1.0 Â 10À5
mol/L while the concentration of acetic acid or triethylamine was
adjusted within 3.0 Â 10À5–1.75 Â 10À3 mol/L so as to explore
the influence of acidity and alkalinity of the medium on the spec-
troscopic properties of target products.
8.23–8.25 (d, J = 8.0 Hz, 1H, C@CAH). IR (KBr, cmÀ1
) m: 3340.12,
1638.83, 1456.31, 1145.63, 955.34. Anal. Calc.: C, 77.72; H, 5.96;
N, 11.82. Found: C, 77.69; H, 6.10; N, 11.68.
(E)-2-(2-(3,5-dimethyl-1-phenyl-1H-pyrazol-4-yl)vinyl)quino-
lin-8-ol (3a), pale-yellow solid 0.89 g, yield 52.0%. ESI-MS (m/z):
342.20(M+). 1H NMR ((CD3)2CO) d: 2.39 (s, 3H, CH3), 2.52 (s, 3H,
CH3), 3.37 (s, 1H, OAH), 7.07–7.14 (m, 2H, quinolin-H), 7.34–7.45
(m, 3H, ArAH), 7.52–7.57 (m, 4H, quinolin-H, ArAH), 7.79–7.81
(d, J = 8.0 Hz, 1H, quinolin-H), 7.98–8.00 (d, J = 8.0 Hz, 1H, C@CAH),
8.23–8.25 (d, J = 8.0 Hz, 1H, C@CAH). IR (KBr, cmÀ1
) m: 3389.03,
1634.95, 1429.13, 1130.10, 955.34. Anal. Calc.: C, 77.40; H, 5.61;
N, 12.31. Found: C, 77.24; H, 5.41; N, 12.19.
(E)-2-(2-(1-(4-fluorophenyl)-3,5-dimethyl-1H-pyrazol-4-yl)vin
yl)quinolin-8-ol (4a), pale-yellow solid 0.77 g, yield 42.7%. ESI-MS
(m/z): 360.2(M+). 1H NMR ((CD3)2CO) d: 2.48 (s, 3H, CH3), 2.49 (s,
3H, CH3), 3.36 (s, 1H, OAH), 7.07–7.13 (m, 2H, quinolin-H), 7.28–
7.40 (m, 4H, ArAH), 7.55–7.59 (m, 2H, quinolin-H), 7.78–7.80 (d,
J = 8.0 Hz, 1H, quinolin-H), 7.96–7.98 (d, J = 8.0 Hz, 1H, C@CAH),
8.22–8.24 (d, J = 8.0 Hz, 1H, C@CAH). IR (KBr, cmÀ1
) m: 3356.82,
1642.84, 1455.22, 1155.28, 960.14. Anal. Calc.: C, 73.52; H, 5.05;
N, 11.69. Found: C, 73.36; H, 4.84; N, 11.53.
(E)-2-(2-(1-(4-chlorophenyl)-3,5-dimethyl-1H-pyrazol-4-yl)vin
yl)quinolin-8-ol (5a), pale-yellow solid 0.87 g, yield 46.0%. ESI-MS
(m/z): 376.20(M+). 1H NMR ((CD3)2CO) d: 2.49 (s, 3H, CH3), 2.53 (s,
3H, CH3), 3.34 (s, 1H, O-H), 7.07–7.14 (m, 2H, quinolin-H), 7.34–
7.40 (m, 2H, quinolin-H), 7.55–7.58 (m, 4H, ArAH), 7.78–7.80 (d,
J = 8.0 Hz, 1H, quinolin-H), 7.96–7.98 (d, J = 8.0 Hz, 1H, C@CAH),
All chemicals and solvents are of commercial reagent grade and
used without further purification. 1-Arylpyrazole-4-carbaldehyde
was prepared according to procedures available elsewhere [15].
Known structures of 1-arylpyrazole-4-carbaldehyde were verified
by comparing their data with those reported in the literature
[13–15].
8.23–8.25 (d, J = 8.0 Hz, 1H, C@CAH). IR(KBr, cmÀ1
) m: 3345.31,
1642.95, 1145.38, 959.22. Anal. Calc.: C, 70.30; H, 4.83; N, 11.18.
General procedure for preparing (E)-2-(2-(1-aryl-1H-pyrazol-4-yl)
vinyl)quinolin-8-ol
Found: C, 70.08; H, 4.45; N, 10.95.
(E)-2-(2-(1-(4-bromophenyl)-3,5-dimethyl-1H-pyrazol-4-yl)vin
yl)quinolin-8-ol (6a), pale-yellow solid 0.96 g, yield 45.7%. ESI-MS
(m/z): 422.10(M+). 1H NMR ((CD3)2CO) d: 2.50 (s, 3H, CH3), 2.56 (s,
3H, CH3), 2.87 (s, 1H, OAH), 7.08–7.16 (m, 2H, quinolin-H),
7.34–7.42 (m, 2H, quinolin-H), 7.52–7.56 (m, 2H, ArAH), 7.71–7.74
5 mmol 1-Arylpyrazole-4-carbaldehyde, 5 mmol 2-methyl-8-
hydroxyl quinoline and 20 mL acetic anhydride were stirred and
sealed in a Teflon-lined stainless steel autoclave (25 mL), kept at

T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 7–13
9
(m, 2H, ArAH), 7.78–7.80 (d, J = 8.0 Hz, 1H, quinolin-H), 8.00–8.02 (d,
J = 8.0 Hz, 1H, C@CAH), 8.24–8.26 (d, J = 8.0 Hz, 1H, C@CAH). IR (KBr,
specimens 1a (0.45 mm  0.39 mm  0.11 mm) and 6b (0.43 mm
 0.35 mm  0.26 mm) were acquired via slow evaporation of
their ethanol solutions at room temperature. The reflection data
cmÀ1
) m: 3366.92, 1642.70, 1454.74, 1145.63, 955.34. Anal. Calc.: C,
62.87; H, 4.32; N, 10.00. Found: C, 63.05; H, 3.75; N, 9.86.
were collected at 296(2) K in an
x/2h scan mode with graphite
(E)-2-(2-(1-(3,4-dimethylphenyl)-1H-pyrazol-4-yl)vinyl)quino-
lin-8-ol (1b), pale-yellow solid 0.91 g, yield 53.2%. ESI-MS (m/z):
342.20(M+). 1H NMR ((CD3)2CO) d: 2.29 (s, 3H, CH3), 2.34 (s, 3H,
CH3), 2.87 (s, 1H, OAH), 7.10–7.12 (d, J = 8.0 Hz, 1H, quinolin-H),
7.25–7.42 (m, 4H, quinolin-H, ArAH), 7.57–7.59 (m, 1H, quinolin-
H), 7.67–7.71 (m, 2H, quinolin-H), 7.96–7.98 (d, J = 8.0 Hz, 1H,
C@CAH), 8.05 (s, 1H, pyrazol-H), 8.24–8.26 (d, J = 8.0 Hz, 1H,
monochromated Mo K radiation (k = 0.071073 nm) as the excita-
a
tion source. The reflections of single crystal 1a were measured in a
2h range of 1.96–25.00°, and those of single crystal 6b were mea-
sured in a 2h range of 2.26–17.97°; and 2421 and 3812 indepen-
dent reflections were measured for 1a and 6b, respectively.
SADABS multi-scan empirical absorption corrections were adopted
for data processing. The crystal structure was solved by direct
method and refined based on full-matrix least-squares on F2. The
final least square cycle of refinement for 1a gave R = 0.0465 and
wR2 = 0.1244; and that for 6b gave R = 0.0879 and wR2 = 0.1385.
C@CAH), 8.58 (s, 1H, pyrazol-H). IR (KBr, cmÀ1
) m: 3377, 1640,
1459, 1164, 966. Anal. Calc.: C, 77.40; H, 5.61; N, 12.31. Found:
C, 61.83; H, 3.73; N, 6.20.
(E)-2-(2-(1-(p-tolyl)-1H-pyrazol-4-yl)vinyl)quinolin-8-ol (2b),
pale-yellow solid 1.01 g, yield 61.6%. ESI-MS (m/z): 328.20(M+).
1H NMR ((CD3)2CO) d: 2.35 (s, 3H, CH3), 3.38 (s, 1H, OAH), 7.08–
7.11 (dd, J = 4.0 Hz, J = 8.0 Hz, 1H, quinolin-H), 7.29–7.41 (m, 5H,
quinolin-H, ArAH), 7.70–7.76 (m, 3H, ArAH), 7.94–7.96 (d,
J = 8.0 Hz, 1H, C@CAH), 8.08 (s, 1H, pyrazol-H), 8.24–8.26 (d,
Results and discussion
Synthesis
The synthetic route of 2-(2-(1-aryl-1H-pyrazol-4-yl)vinyl)quin-
olin-8-ol is outlined in Fig. 1.
J = 8.0 Hz, 1H, C@CAH), 8.61 (s, 1H, pyrazol-H). IR (KBr, cmÀ1
) m:
3370.33, 1636.97, 1458.10, 1153.40, 950.87. Anal. Calc.: C, 77.04;
2-(2-(1-Aryl-1H-pyrazol-4-yl)vinyl)quinolin-8-ol was synthe-
sized by Perkin reaction with 2-methyl-8-hydroxy quinoline and
1-arylpyrazol-4-carbaldehyde as the starting materials. In the
presence of acetic anhydride as the solvent, the 4 days reaction un-
der 160 °C initially yields an acetate derivative. The acetoxyl group
of the acetate derivative is hydrolyzed in the presence of hydro-
chloric acid to yield hydrochloric salt which is treated with trieth-
ylamine to afford desired target compound. Since the substrate of
aryl aldehydes and the solvent (acetic anhydride) react to form car-
bonyl acetal ester, it is imperative to protect the carbonyl while
aryl aldehyde is consumed to decrease the yield of the condensa-
tion reaction. Findings show that acidic medium favors the forma-
tion of carbonyl acetal ester but inhibits the formation of desired
condensation product. Specially, substituent -CH3 on the pyrazole
group leads to decrease in the yield of target products (a-series),
which might be due to larger steric hindrance of -CH3 than that
of H atom. Coupling constants of the hydrogen in the vinyl group
of various target compounds suggest that they are of trans-confor-
mation, which can be further confirmed by the IR spectrum and
single crystal structure of compounds 1a and 6b as typical
examples.
H, 5.23; N, 12.84. Found: C, 76.93; H, 5.02; N, 12.74.
(E)-2-(2-(1-phenyl-1H-pyrazol-4-yl)vinyl)quinolin-8-ol
(3b),
pale-yellow solid 0.94 g, yield 59.9%. ESI-MS (m/z): 314.10(M+).
1H NMR ((CD3)2CO) d: 3.34 (s, 1H, OAH), 7.55–7.57 (dd,
J = 4.0 Hz, 1H, quinolin-H), 7.76–7.86 (m, 4H, quinolin-H, ArAH),
7.97–8.01 (t, J = 8.0 Hz, 2H, ArAH), 8.15–8.17 (d, J = 4.0 Hz, 1H,
quinolin-H), 8.35–8.37 (d, J = 4.0 Hz, 2H, quinolin-H), 8.44–8.46
(d, J = 8.0 Hz, 1H, C@CAH), 8.56 (s, 1H, pyrazol-H), 8.71–8.73 (d,
J = 8.0 Hz, 1H, C@CAH), 9.11 (s, 1H, pyrazol-H). IR (KBr, cmÀ1
) m:
3392.31, 1641.23, 1459.74, 1194.47, 951.70. Anal. Calc.: C, 76.66;
H, 4.82; N, 13.41. Found: C, 70.00; H, 4.47; N, 13.20.
(E)-2-(2-(1-(4-fluorophenyl)-1H-pyrazol-4-yl)vinyl)quinolin-8-
ol (4b), pale-yellow solid 0.89 g, yield 53.6%. ESI-MS (m/z):
332.20(M+). 1H NMR ((CD3)2CO) d: 3.37 (s, 1H, OAH), 7.09–7.11
(m, 1H, quinolin-H), 7.28–7.41 (m, 5H, quinolin-H, ArAH), 7.70–
7.72 (d, J = 8.0 Hz, 1H, C@CAH), 7.89–7.98 (m, 3H, quinolin-H),
8.10 (s, 1H, pyrazol-H), 8.25–8.27 (d, J = 8.0 Hz, 1H, C@CAH), 8.64
(s, 1H, pyrazol-H). IR (KBr, cmÀ1
) m: 3404.48, 1641.78, 1459.78,
1154.20, 952.22. Anal. Calc.: C, 72.50; H, 4.26; N, 12.68. Found: C,
72.30; H, 3.90; N, 12.46.
(E)-2-(2-(1-(4-chlorophenyl)-1H-pyrazol-4-yl)vinyl)quinolin-8-ol
(5b), pale-yellow solid 0.97 g, yield 55.9%. ESI-MS (m/z):
348.10(M+). 1H NMR ((CD3)2CO) d: 7.10–7.12 (dd, J = 4.0 Hz, 1H,
quinolin-H), 7.30–7.43 (m, 3H, quinolin-H, ArAH), 7.53–7.57 (m,
2H, ArAH), 7.89–7.93 (d, J = 4.0 Hz, 1H, quinolin-H), 7.89–7.95
(m, 2H, quinolin-H), 7.95–7.99 (d, J = 8.0 Hz, 1H, C@CAH), 8.12 (s,
1H, pyrazol-H), 8.25–8.27 (d, J = 8.0 Hz, 1H, C@CAH), 8.65 (s, 1H,
Crystallography and characterization
The crystallographic data, selected bond lengths and bond an-
gles for target compounds 1a and 6b are listed in Tables s1–s3,
respectively. The molecular structures of 1a and 6b are shown in
Fig. 2. The NAC distances of compound 1a (1.330(2) Å of
N(1)AC(9), 1.368(2) Å of N(1)AC(1), and 1.426(2) Å of
N(3)AC(17)) lie between those of typical double bond C@N
(1.287 Å) and single bond CAN (1.471 Å); the O(1)AC(2) distance,
1.359(2) Å, is shorter than typical single bond CAO (1.43 Å) and
pyrazol-H). IR (KBr, cmÀ1
) m: 3341.49, 1640.91, 1459.45, 1192.34,
947.59. Anal. Calc.: C, 69.07; H, 4.06; N, 12.08. Found: C, 69.06;
H, 3.60; N, 11.88.
(E)-2-(2-(1-(4-bromophenyl)-1H-pyrazol-4-yl)vinyl)quinolin-
8-ol (6b), pale-yellow solid 1.04 g, yield 53.2%. ESI-MS (m/z):
393.1(M+). 1H NMR ((CD3)2CO) d: 2.89 (s, 1H, OAH), 7.09–7.11
(dd, J = 4.0 Hz, 1H, quinolin-H), 7.31–7.43 (m, 3H, quinolin-H,
ArAH), 7.69–7.71 (m, 3H, quinolin-H, ArAH), 7.85–7.89 (m, 2H,
quinolin-H), 7.98–8.00 (d, J = 8.0 Hz, 1H, C@CAH), 8.12 (s, 1H, pyra-
zol-H), 8.26–8.28 (d, J = 8.0 Hz, 1H, C@CAH), 8.67 (s, 1H, pyrazol-H).
indicates the formation of p–p conjugated systems; and the dis-
tances of C(9)AC(10) (1.461(2) Å) and C(11)AC(12) (1.448(2) Å)
are shorter than typical single bond CAC (1.54 Å), due to the for-
mation of conjugated systems. The bond lengths of compound 6b
are similar to those of compound 1a (see Table s3). Particularly,
the C(10)AC(11) (1.325(2) Å) of 1a and C(10)AC(11) (1.298(6) Å)
of 6b are shorter than typical double bond C@C (1.34 Å). In the
meantime, there are no intermolecular hydrogen bonds but only
intramolecular hydrogen bonds in the tautomers of 1a (see
Fig. s1, Table s2) and 6b (see Fig. s2, Table s3). The distances of
the hydrogen bonds (O(1)AH(1). . .N(1)) of compounds 1a and 6b
are 2.6614(19) Å and 2.690(4) Å, respectively.
IR (KBr, cmÀ1
) m: 3340.85, 1639.24, 1458.92, 1192.22, 947.04. Anal.
Calc.: C, 61.24; H, 3.60; N, 10.71. Found: C, 61.69; H, 2.92; N, 10.58.
Single crystal X-ray crystallography
Synthesized products 1a and 6b were used as typical examples
for single crystal crystallographic analysis, where single crystal

10
T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 7–13
Fig. 1. The synthetic route of 2-(2-(1-aryl-1H-pyrazol-4-yl)vinyl)quinolin-8-ol.
Fig. 2. Structure of compounds 1a and 6b.
Compound 6b has planar molecular structure, and all of the
3.0
2.5
2.0
1.5
1.0
.5
atoms in 6b molecule are located on the same plane, which is
favorable for decreasing the energy levels of the molecule
(Fig. s3). However, due to the existence of ACH3, the atoms (except
H in ACH3) in 1a molecule are located in two planes, and the dihe-
dral angle is 35.3° (Fig. s4).
1b
2b
3b
4b
5b
6b
UV–vis spectra
Figs. 3 and 4 show the UV–vis spectra of the two series of target
compounds. It can be seen that compounds 1a–6a show three
absorption peaks while compounds 1b–6b show two absorption
peaks. Namely, compounds 1a–6a and compounds 1b–6b show
the same maximum absorption peak at 302–304 nm and the sec-
ond absorption peak at 340–344 nm. Compounds 1a–6a show
0.0
250
300
350
400
450
500
Wavelength/nm
Fig. 4. UV–vis spectra of compounds 1b–6b.
3.0
1a
2a
3a
4a
2.5
the third absorption peak at 252 nm, but compounds 1b–6b do
not show this absorption peak. The reason may lie in that com-
pounds 1a–6a contain two methyl groups connected with pyrazole
ring, and the introduction of the alkyl group to the conjugated sys-
5a
6a
2.0
1.5
1.0
0.5
0.0
tems allows the electron of alkyl CAH bond to overlap with the
p
electron of the conjugated system (the so-called hyperconjuga-
tion). In the meantime, substituent R of the phenyl group con-
nected with pyrazole ring also influences the absorption
wavelength and absorbance. Namely, alkyl groups such as ACH3
and 3,4-di-CH3 lead to shift of the absorption peak towards longer
wavelength, and the introduction of auxochrome groups such as
AF, ACl and ABr to the phenyl group allows conjugation of non-
250
300
350
400
450
bonded electron with
p electron to form p–p conjugation thereby
Wavelength/nm
leading to enhanced electronic scope of operation and shift of
Fig. 3. UV–vis spectra of compounds 1a–6a.
absorption peak towards longer wavelength.

T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 7–13
11
Fluorescence spectra
8000
The fluorescence spectra of the two series of target compounds
are shown in Figs. 5 and 6. It can be seen that the two series of tar-
get compounds show an emission peak at 440–448 nm when their
DMF solutions are excited at 290 nm (a series of products) or
275 nm (b series of products). Obviously, the shape and position
of the emission peaks of the two series of target compounds are
similar. However, the fluorescence intensity of b series of products
is much higher than that of a series of products, which may be
attributed to the planar molecular structure of b series of products.
Moreover, the substituent R2 of the phenyl group has a minor influ-
ence on the emission peak position and fluorescence intensity of
target compounds, which may be a compromise between the elec-
tronic effect and space effect of the substituent.
1b
2b
3b
4b
5b
6b
6000
4000
2000
0
400
500
Wavelength/nm
600
700
Influence of acidity or alkalinity of mediums on spectral properties of
Fig. 6. Fluorescence spectra of compounds 1b–6b.
compounds 3a and 5a
Pyrazole as a twisted intramolecular charge transfer compound
possesses structural units of electron donor-electron acceptor.
Therefore, their intramolecular charge distribution as well as their
spectral properties is closely related to the acidity or alkalinity of
mediums. In the meantime, hydroxyquinoline compounds contain-
ing different active groups are able to form a variety of possible
new compounds in acid and alkaline medium conditions (Fig. 7)
thereby affecting the optical performance. For this reason, we
choose compounds 3a and 5a as examples to explore the influence
of the acidity or alkalinity of mediums on their spectral properties
and to investigate the possible reaction mechanisms based on cal-
culations of density functional theory (DFT) and time-dependent
density functional theory (TD–DFT).
acetic acid are also simulated with PCM model of TD–DFT. Theoret-
ical calculations indicate that the new species are formed via
hydrogenation path (path b in Fig. 7). The theoretical spectrum
of the hydrogenation product 3a, (E)-2-(2-(3,5-dimethyl-1-phe-
nyl-1H-pyrazol-4-yl)vinyl)-8-hydroxyquinolinium, covers three
absorption peaks located at 273.12 (f = 0.1423), 317.29
(f = 0.3472), and 411.70 nm (f = 1.2393). Considering the solvent
effect and experimental error, we can reasonably infer that the the-
oretically calculated UV spectral data of product 3a are well consis-
tent with their experimental ones (compound 3a shows
experimental absorption peaks at 271, 320 and 410 nm). Similarly,
the absorption peaks of compound 5a at 270, 320 and 411 nm are
consistent with their theoretically calculated absorption peaks at
278, 316 and 410 nm. When 3a reacts with acetic acid to form
hydrogenation product, the lengths of the bond connecting the
quinoline ring and pyrazole ring of the product are averaged. In
other words, C(10)AC(11) bond is elongated by 0.021 Å, and
C(9)AC(10) and C(11)AC(12) bonds are shortened by 0.036 Å and
0.031 Å, respectively. In the meantime, dihedral angle
C(11)AC(12)AC(13)AC(18) of the hydrogenation product is
174.75°, larger than that of 3a (163.25°). This implies that the
hydrogenation reaction of compound 3a in acetic acid expands
the delocalization of the conjugated systems thereby tending to
average the lengths of related bonds. Furthermore, according to
the energy levels in association with homologous frontier orbitals,
Influence of acidity or alkalinity of mediums on UV–vis spectra of
compounds 3a and 5a
The effect of acetic acid on the UV–vis spectra of compounds 3a
and 5a is shown in Figs. 8 and 9. It can be seen that acetic acid leads
to red-shifts of absorption peaks and form three new absorption
peaks. In the meantime, with increasing concentration of acetic
acid, the intensity of the absorption peak near 400 nm obviously
rises but that of the peaks near 263 nm and 320 nm varies slightly.
This suggests that new species are generated upon contact of com-
pounds 3a and 5a with acetic acid via possible pathways shown in
Fig. 7. To identify relevant products, we adopt DFT and TD–DFT to
optimize their full geometries with B3LYP and M06 methods [16–
18]. The UV–vis absorption spectra of compounds 3a and 5a in
the energy gap value, e, between the highest occupied molecular
orbital and the lowest unoccupied molecular orbital (HOMO–
LUMO) of the hydrogenation product is smaller than that of reac-
tant 3a (reactant 3a and its hydrogenation product have
e of
6000
4.218 eV and 3.673 eV, respectively). Similar calculation results
are also obtained for compound 5a. By comprehensively consider-
ing the geometric structures and electronic transitions, we can in-
fer that, compared with reactants 3a and 5a, the changes in the
spectroscopic properties of their hydrogenation products are
attributed to enlarged conjugated system with enhanced molecu-
lar planarity and decreased energy gap of HOMO–LUMO.
5000
1a
2a
3a
4a
5a
4000
3000
6a
The effect of triethylamine on UV–vis spectra of compounds 3a
and 5a is shown in Figs. 10 and 11. It can be seen that the absor-
bance obviously increases and the absorption peak position
slightly red-shifts with increasing concentration of triethylamine.
This suggests that the alkaline medium may influence the intramo-
lecular charge distribution of compounds 3a and 5a thereby affect-
ing their spectral properties. In other words, the alkaline medium
may facilitate the formation of new species containing AOÀ groups
that are combined with ANEt3 and AOH, thereby changing
molecular dipole moment.
2000
1000
0
400
500
600
700
800
Wavelength/nm
Fig. 5. Fluorescence spectra of compounds 1a–6a.

12
T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 7–13
Fig. 7. Possible reaction of hydroxyquinoline compounds with HOAc.
2.0
1.5
1.0
.5
2.0
1.5
1.0
.5
0.0
0.0
250
300
350
400
450
500
250
300
350
400
450
500
Wavelength/nm
Wavelength/nm
Fig. 8. Influence of acetic acid on UV–vis spectra of 3a.
Fig. 10. Influence of triethylamine on UV–vis spectra of 3a.
2.5
2.0
1.5
1.0
.5
2.0
1.5
1.0
.5
concentration increase
0.0
0.0
250
300
350
400
450
500
250
300
350
400
450
500
550
Wavelength/nm
Wavelength/nm
Fig. 11. Influence of triethylamine on UV–vis spectra of 5a.
Fig. 9. Influence of acetic acid on UV–vis spectra of 5a.
Influence of acidity or alkalinity of mediums on fluorescence spectra of
compounds 3a and 5a
HOMO–LUMO energy gap possesses strong UV–vis absorbance
but weak fluorescence emission, which is possibly because the
interaction between cationic -NH+ and anionic AAcÀ leads to fluo-
rescence quenching. The new emission peak at 582 nm further con-
firms that the hydrogenation product contains enlarged conjugated
system and decreased HOMO–LUMO energy gap as compared with
compounds 3a and 5a.
The effect of triethylamine on the fluorescence spectra of com-
pounds 3a and 5a is shown in Figs. s5 and s6. It can be seen that the
reaction of 3a and 5a with triethylamine leads to a new emission
peak at 545 nm, and the fluorescence intensity of the maximum
The influence of acetic acid on the fluorescence spectra of com-
pounds 3a and 5a is shown in Figs. 12 and 13. It can be seen that
synthetic products 3a and 5a show two new emission peaks at
344 nm and 582 nm after they react with acetic acid. Obviously,
the fluorescence intensity of the maximum emission peak at
440 nm obviously decreases and the emission peak position slightly
red-shifts with increasing concentration of acetic acid. This implies
that the hydrogenation product containing enlarged conjugated
system attributed to enhanced molecular planarity and decreased

T. Ren et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 7–13
13
7000
6000
5000
4000
3000
2000
1000
0
widely used in biomedical fields. For this reason, we choose
compounds 1b and 3b as examples to explore their in vitro antitu-
mor activity. Their antiproliferative activity against K562 (human
leukemia cell line) was evaluated by in vitro MTT assays. Amona-
fide was tested as a reference compound. The biological results
were shown in Table 1. It can be seen from Table 1 that the com-
pounds 1b and 3b have showed antiproliferative activity against
K562 and can inhibit the growth of K562 cells.
concentration increase
Conclusions
Two series of novel quinoline derivatives containing pyrazole
group have been successfully synthesized in high yields with a
simple condensation reaction route. The molecular structure of
1a and 6b as representative examples were determined by sin-
gle-crystal X-ray diffraction. The UV–vis absorption spectra and
fluorescent spectra of synthetic products have been systematically
investigated, and the influence of acetic acid and triethylamine on
their spectroscopic properties has been examined with compounds
3a and 5a as typical examples. It has been found that synthetic
quinoline derivatives containing pyrazole group have good fluores-
cent properties, and the introduction of acetic acid and triethyl-
amine changes the acidity or alkalinity of medium environment
thereby influencing the fluorescent characteristics of synthetic
products. Moreover, it is feasible to manipulate the molecular
structure and spectroscopic properties of pyrazole and quinoline
derivatives by properly adjusting the acidity of medium. This,
hopefully, is to help to promote and broaden the application of pyr-
azole and quinoline derivatives in material science, medicine and
ion recognition.
400
500
600
Wavelength/nm
Fig. 12. Effect of acetic acid on fluorescence spectra of 3a.
7000
concentration increase
6000
5000
4000
3000
2000
1000
0
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.03.018.
400
500
600
700
Wavelength/nm
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We predict that the synthetic products have biological activity
for the quinoline derivatives and pyrazole derivatives have been