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and many derivatives of Schiff bases have found applications in di-
verse physiological and coordination chemistry area, due to prom-
ising antibacterial and antivirus activities as well as metal
chelating effect and other pharmacological effects [1–3]. In the
meantime, 4-aroyl pyrazolone derivatives have also received con-
siderable attention because of their advantages compared to com-
monly seen b-diketone; and many 4-aroyl pyrazolone derivatives
have been reported to be superior reagents in biological, pharma-
cological, clinical, and analytical applications and as efficient
extractants and chelators of metal ions [4–7]. Furthermore, the
excellent photoelectric properties of 4-aroyl pyrazolone deriva-
tives add to their wide use in photoelectric functional materials
[8–11] and display device like organic light-emitting diode (OLED)
[12,13]. Jia et al. [14,15] analyzed the crystal structure of a series of
4-acyl pyrazolone thiosemicabazone derivatives; and they re-
ported the photochromic properties of the derivatives in the solid
state and proposed a photochromic mechanism of intermolecular
proton transfer through hydrogen bonds. Jadeja and Shah [16]
studied the three tautomeric forms of pyrazolone based Schiff base
and confirmed intermolecular proton transfer through hydrogen
bonds of these Schiff base. In our previous work, we have synthe-
sized a series of porphyrins compounds and benzimidazoles com-
pounds which contain pyrazole group and found that the
introduction of pyrazole group leads to stronger fluorescence emit
[17–19], adding to their application as emitting materials in organ-
ic light-emitting diode (OLED) and time-resolved fluoroimmunoas-
say and DNA probe.
sources and used as-received; solvents used in this study were
purified following standard procedures.
General procedure for preparing the Schiff bases
1-aryl-3-methyl-4-benzoyl-5-pyrazolones
were
prepared
according to published procedures [21,22]. Known structures of
as-synthesized products were verified by comparing their data
with those reported in the literature.
A certain amount of 1-aryl-3-methyl-4-benzoyl-5-pyrazolones
(4 mmol) was dissolved in 50 mL ethanol. Into resultant solution
was dropwise added the ethanol solution containing a proper
amount (0.44 g, 4 mmol) of o-phenylenediamine (OPD) or p-phen-
ylenediamine (PPD). Resultant mixed solution was refluxed in a
water bath for 4 h, followed by rotary evaporating to remove sol-
vent and cooling to room temperature. As-separated yellow crys-
talline precipitates were collected by filtration and recrystallized
with ethanol-chloroform (1:3, V/V). The experimental details and
data are available in the Supporting information.
Single crystal X-ray crystallography
As-synthesized products 1a and 1b were used as typical exam-
ples for single crystal crystallographic analysis, where single crys-
tal specimens 1a (0.47 mm  0.33 mm  0.11 mm) and 1b
(0.39 mm  0.38 mm  0.07 mm) were acquired via slow evapora-
tion of their ethanol solutions at room temperature. The reflection
Unfortunately, little is currently available about the fluores-
cent properties of acylpyrazolone-based Schiff bases containing
different substituents in the phenyl group and the correlation be-
tween their molecular structure and emission properties, which
greatly hinders their applications in biological and environmental
sciences. Thus we report a simple procedure for synthesizing
Schiff base compounds containing pyrazole group as well as their
molecular and crystal structures and fluorescent properties. Here
the equilibrium geometries and vibrational frequencies of as-syn-
thesized Schiff bases in their ground state (S0) are determined
using the B3LYP method with 6-31G(d) basis set, and their
absorption spectra are theoretically calculated using the TD-
B3LYP method with cc-pVDZ basis set and compared to the
experimental ones.
data were collected at 291(2) K in an
x/2h scan mode with graphite
monochromated Mo-K radiation (k = 0.71073 Å) as the excitation
a
source. The reflections of single crystal 1a were measured in a 2h
range of 2.07–26.00°, and those of single crystal 1b were measured
in a 2h range of 1.88–26.00°; and 3866 and 3684 independent
reflections were measured for 1a and 1b, 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 = 0.0451 and wR2 =
0.1050; and that for 1b gave R = 0.0508 and wR2 = 0.1357.
Results and discussion
Synthesis and characterization of the products
Experiment
In our previous paper [19], a series of benzimidazoles were ob-
tained from 1-arylpyrazole-4-carbaldehyde and o-phenylenedi-
amine, where mono-Schiff base was obtained as an unstable
intermediate which was eventually transformed to benzimidaz-
oles. However, when we used 1-aryl-3-methyl-4-benzoyl-5-pyraz-
olones to replace 1-arylpyrazole-4-carbaldehyde and react with o-
phenylenediamine, we obtained mono-Schiff bases but not benz-
imidazoles as the final products, possibly because the benzene ring
connected with the carbonyl group possesses a stronger steric hin-
drance effect than the H atom connected with the carbonyl.
The molecular structures of the products are such that they can
exist in three tautomeric forms as imine-one, imine-ol and amine-
one, respectively [16]. Amine-one type products are obtained from
the condensation reaction of b-diketone and aromatic amine in the
present research, the same as what is reported elsewhere [23]. The
IR spectra of the products exhibit two characteristic bands in the
ranges 3340–3405 cmÀ1 and 1610–1630 cmÀ1, which can be as-
Instruments and materials
Various as-synthesized products were pressed into pellets with
KBr; and then their infrared (IR) spectra were recorded with a
Nicolet 170 SXFT-IR spectrometer in a wavenumber range of
400–4000 cmÀ1. An Agilent 1100LC-MS mass spectrometer (MS)
was performed to record the atmosphere pressure chemical ioniza-
tion mass spectra (APCI-MS) of as-synthesized products. The nucle-
ar magnetic resonance spectra of the products were recorded in
CDCl3 with an INOVA-400 NMR spectrometer in the presence of
tetramethylsilane as the internal standard. Room temperature
fluorescence spectra of the products were measured using a Hit-
achi F-7000 fluorescence spectrometer with a Xe arc lamp as the
light source. Room temperature ultraviolet-visible light (UV-Vis)
absorption spectra of the products in dimethylformamide (DMF)
were measured with a Hitachi U-4100 spectrometer.
The ground-state (S0) equilibrium geometries and vibrational
frequencies of the as-synthesized products were determined by
B3LYP method of 6–31G(d,p) basis set, and their absorption spectra
were estimated using TD-B3LYP method of cc-pVTZ basis set [20].
All the analytical grade reagents were purchased from commercial
signed to mHNAH and mC@O of the tautomeric amine-one form (liter-
ature [16]: 3220–3245 and 1610–1630 cmÀ1). The 1H NMR spectra
of all the products appear as a singlet corresponding to one proton
in the range of 12.41–12.86, which can be assigned to NH (litera-
ture [16]: 12.83–12.99). The molecular structures of the products
Guo, Jia
