Synthesis, structure, photo-responsive properties of 4-(2- fluorobenzylideneamino)antipyrine: A combined experimental and theoretical study

Article abstract of DOI:10.1016/j.saa.2012.07.117

In this work, 4-(2-fluorobenzylideneamino)antipyrine (FBIAAP) was synthesized and characterized by elemental analysis, XRD, FT-IR, FT-Raman and UV-Vis techniques as well as density functional calculations. The studied molecule adopts a trans configuration about the imine CN bond, and adjacent molecules are linked through two kinds of weak hydrogen bonds to form supramolecular layered structures along the ab plane. Vibrational spectral analyses show that the benzene moiety directly attached to the central pyrazoline shows good vibrational isolation from the other moiety of pyrazole-imino-benzene presenting good vibrational resonances. UV-vis absorption bands mainly belong to n → π and π → π according to the electron transfer orbital assignments for the electron absorption spectrum of FBIAAP. The first-order hyperpolarizability of FBIAAP is 44.9 times that of urea theoretically. In addition, the thermodynamic properties were also obtained theoretically from the harmonic frequencies of the optimized structure.

Full text of DOI:10.1016/j.saa.2012.07.117

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, structure, photo-responsive properties of 4-(2-fluorobenzylideneamino)
antipyrine: A combined experimental and theoretical study
b
b
b
c
b,
Yuxi Sun a,b,c, , Cheng Yu , Zengwei Liu , Changliang Huang , Qingli Hao , Laixiang Xu
⇑
⇑
a Center of New Energy & Materials, Mianyang Normal University, Mianyang 621000, PR China
b Key Laboratory of Life-Organic Analysis, Qufu Normal University, Qufu 273165, PR China
c Key Laboratory of Education Ministry for Soft Chemistry and Functional Materials, Nanjing University of Science and Technology, Nanjing 210094, 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
"
"
"
"
"
The title compound was synthesized
in one step by an amine-anhydride
reaction.
The structural characteristic is
revealed by an X-ray diffraction
technique.
The vibrational spectra have been
precisely ascribed to the molecular
structure.
The theoretical first-order
hyperpolarizabilitie is nearly forty-
five times magnitude of urea.
The UV–vis spectrum is revealed by
the TD-DFT calculation and FMO
analysis.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 May 2012
Received in revised form 5 July 2012
Accepted 11 July 2012
Available online 4 August 2012
In this work, 4-(2-fluorobenzylideneamino)antipyrine (FBIAAP) was synthesized and characterized by
elemental analysis, XRD, FT-IR, FT-Raman and UV–Vis techniques as well as density functional calcula-
tions. The studied molecule adopts a trans configuration about the imine C@N bond, and adjacent mole-
cules are linked through two kinds of weak hydrogen bonds to form supramolecular layered structures
along the ab plane. Vibrational spectral analyses show that the benzene moiety directly attached to
the central pyrazoline shows good vibrational isolation from the other moiety of pyrazole-imino-benzene
Keywords:
presenting good vibrational resonances. UV–vis absorption bands mainly belong to n ? p⁄ and
p ?
p⁄
4-(2-fluorobenzylideneamino)antipyrine
Synthesis
Structure
Photo-responsive properties
Density functional calculations
according to the electron transfer orbital assignments for the electron absorption spectrum of FBIAAP.
The first-order hyperpolarizability of FBIAAP is 44.9 times that of urea theoretically. In addition, the ther-
modynamic properties were also obtained theoretically from the harmonic frequencies of the optimized
structure.
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
important kind of biomodel compounds in the biological and med-
ical fields for many years [10]. Recently, ADPs have exhibited many
Antipyrine and its derivatives have been widely used as
pharmaceuticals due to broad bioactivities, such as antitumor
[1–3], antimicrobial [4–6], antiviral [7,8], and analgesic [9] etc.,
and the antipyrine derivatives (APDs) have been accepted as a
attractive functional properties, such as coordinate [11], antioxi-
dant [12] antiputrefactive [13] and optical [14,15] characteristics,
in chemical and material fields. As a result, APDs have been used
widely as model compounds in biological, medial, material and
chemical fields.
With the social needs of photo-responsive materials, such as
bioelectrics [16,17], photovoltaics [18–20], photoluminescence
⇑
Corresponding authors. Tel.: +86 537 4456301; fax: +86 537 4456305.
E-mail addresses: yuxisun@163.com (Y. Sun), xulx@qfnu.edu.cn (L. Xu).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.07.117

1014
Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
Table 1
[21,22], nonlinear optics [23–25], etc., the photo-responsive char-
acteristics of substances have gradually become the focus of
researchers.
Crystal data and refinement parameters for the studied compound.
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C18H16FN3O
309.34
Orthorhombic
P212121
6.917 (2)
13.577 (3)
17.148 (4)
1610.4 (6)
4
1.276
0.09
0.980/0.983
Prism, yellow
0.23 ꢁ 0.20 ꢁ 0.19
17596
1933
1715
0.026
Considering the above-mentioned and as an extension of our
work [25–33], our group is interested in the continuous investi-
gation on APDs. In this work, we report the synthesis, molecular
and crystal structure of 4-(2-fluorobenzylideneamino)antipyrine
(FBIAAP), together with photo-responsive properties revealed by
vibrational spectra, UV–vis electron absorption and nonlinear op-
tics. The results are helpful to promote the further application for
the studied compound by presenting the relatively systematical
characteristics in this work.
b (Å)
c (Å)
V (Å3)
Z
Dc (Mg/m3)
l
mmꢀ1
)
Absorpt. Corr. Tmin/Tmax
Crystal shape/color
Crystal size (mm3)
Measured reflections
Independent reflections
Observed reflections (I > 2
Rint
Experimental and theoretical methods
r
(I))
Experimental
Ranges of h, k, l
R, wR [(I > 2r(I))]
ꢀ8/8, ꢀ17/17, ꢀ21/21
0.039, 0.098
0.044, 0.101
1.12
1933/210
0.12, ꢀ0.17
721322
General
Elemental analysis for carbon, hydrogen and nitrogen were per-
formed by a Perkin-Elmer 240C elemental instrument. The melting
point was determined on a Yanaco MP-500 melting point appara-
tus. Electronic absorption spectra in MeOH solution were
measured on a Shimadzu UV3100 spectrophotometer. The FT-IR
spectrum of the solid compound was recorded in the region
4000–400 cmꢀ1 in evacuation mode with a scanning speed of
30 cmꢀ1 minꢀ1 and the spectral width of 2.0 cmꢀ1 on Bruker IFS
66V spectrophotometer using KBr pellet. The FT-Raman spectrum
of the solid samples was measured in the region 3500–100 cmꢀ1
with a spectral resolution of 1.0 cmꢀ1 in the backscattering config-
uration on a RENISHAW inVia Raman microscope with a counter
current detector and a 785 nm diode laser excitation.
R, wR (all data)
Goodness-of-fit on F2
Reflections/parameters
D
qmax, Dqmin (e/Å)
CCDC
h
i
1=2
P
P
P
P
2
2
Note. R = ||F0| ꢀ |Fc||/ |F0|, wR ¼
wðF20 ꢀ Fc2Þ = wðF02Þ
.
2
w ¼ 1=½r2ðF2o Þ þ ð0:01897ðFo2 þ 2Fc2ÞÞ þ 0:02630ðFo2 þ 2F2c Þꢂ.
were placed in calculated positions [aromatic C–H = 0.93 Å
and with Uiso(H) = 1.2 Ueq(C), methyl C–H = 0.96 Å and with
Uiso(H) = 1.5 Ueq(C)]. All calculations to solve the structure, refine
the model proposed, and obtain derived result were carried out
with the computer programs SHELXS-97 and SHELX-L97 [38] and
SHELXTL [39]. Full use of the CCDC package was also made for
searching in the CSD database. The crystallographic data and
experimental details for the structural analysis are listed in Table 1.
Synthetic
All chemicals (reagent grade) were purchased from commercial
sources and used without further purification. The title compound
was synthesized according to the classical condensation of alde-
hydes with ammonia [34]. 4-Aminoantipyrine and 2-fluorobenzal-
dehyde with 1:1 stoichiometric ratio were dissolved in MeOH
solvent with stirring for about 1 h at room temperature to give a
clear yellow solution. After the solution had been kept in air at
room temperature for several days, yellow prism-shaped crystals
were formed. M.p. 189–190 °C. Yield: 94%. Calculated for
Theoretical
For meeting the requirements of both accuracy and computing
economy, theoretical methods and basis sets should be considered.
Density functional theory (DFT) has been proved to be extremely
useful in treating electronic structures of molecules. The basis set
6-31G(d) was used as a very effective and economical level to
study fairly large organic molecules [40]. Basing on the points,
the density functional three-parameter hybrid model (DFT/
B3LYP) at the 6-31G(d) basis set level was adopted to calculate
the properties of the studied molecule in this work. All the calcula-
tions were performed using Gaussian 09W program package [41]
with the default convergence criteria.
As the first step of our DFT calculations for the studied com-
pound, the initial geometrical configuration directly taken from
their X-ray crystallographic data was optimized without any con-
straints. Secondly, the harmonic vibrational frequencies were per-
formed to convince the optimized structure in a stable ground
state. Thirdly, the calculated IR and Raman spectra were assigned
C18H16FN3O: C 69.87, H 5.22, N 13.59%. Analysis found: C 69.77,
H 5.15, N 13.54%.
The synthetic route is shown in Scheme 1.
Crystallographic
A suitable single crystal was attached to a glass fiber. Data were
collected at 295(2) K on a Bruker AXS SMART APEX area-detector
diffractometer (MoKa radiation, k = 0.71073 Å) with SMART [35]
as the driving software; data integration was performed with
SAINTPlus [36]and multiscan absorption correction applied using
SADABS [37]. The structure was solved by direct method and dif-
ference Fourier and refined by least squares on F2 with anisotropic
displacement parameters for non-H atoms. H atoms attached to C
Scheme 1. The schematic diagram of the studied compound.

Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
1015
to its molecular structure basing on the fundamental normal vibra-
tional mode analysis with the aid of the GaussView program [42].
Fourthly, the statistical thermodynamic properties were theoreti-
cally predicted by the harmonic frequencies of the optimized struc-
ture. Fifthly, the molecular dipole moment, linear polarizability, and
first hyperpolarizability properties of the molecular system were
obtained from the molecular polarizabilities basing on the theoret-
ical calculation. Finally, the UV–Vis spectra and electronic absorp-
tion properties were explained effectively and illustrated visually
from the orientation of frontier molecular orbitals of FBIAAP.
with experimental results, the theoretically optimized parameters
were also listed in Table 2.
As seen from Table 2, the calculated geometric parameters rep-
resent good approximations to the XRD data on the whole. Most of
the optimized bond lengths are slightly longer than the experimen-
tal values agreeing within 0.032 (2) Å and the bond angles are
slightly different from the experimental ones agreeing within 6.6
(2)°, because the molecular states are different in the experimental
and theoretical processes. One isolated molecule is considered in
gas phase in the theoretical calculation, while many packing mol-
ecules are treated in condensed phase in the experimental
measurement.
Results and discussion
The same structural characteristics in the theoretical results can
be found as experimental ones, such as, the distances of C8–N3 and
N3–C12 show single–double and double bonds characteristics,
respectively, and the fairly large pi-electronic conjugated system
has been formed between the pyrazoline and No. 3 benzene rings
due to the imine bridging. As important geometrical characteristics
for FBIAAP, the theoretical bond distances of C@O, C@N show abso-
lute errors of ꢀ0.008 Å, +0.011 Å, respectively.
Crystal structure
The asymmetric unit of the compound consists of one indepen-
dent molecule, which is shown in Fig. 1 by the displacement ellip-
soid plot with atomic numbering. The atomic coordinates and
thermal parameters of the molecule can be obtained from the sup-
plementary material. All the bond lengths and angles in the com-
pound were comparable to the corresponding values observed in
other similar antipyrine Schiff bases cited above. The selected bond
lengths and angles were listed in Table 2. In the compound, the
C12@N3 bond length 1.280(2) Å is as expected for a normal imine
double bond. The bond length between N3 and C8 [1.388(2) Å] is
intermediate between classical C–N (1.43 Å) and C@N (1.28 Å)
bond lengths because of the molecular conjugated effect. Basing
on the reason, the dihedral angle of 14.5 (2)° formed by the substi-
tuted 2-fluorophenyl ring and the pyrazoline ring is less than the
one of 55.8 (2)° formed by the No. 1 benzene ring and the pyrazo-
line ring. As expected, the molecule adopts a trans configuration
about the imine C12@N3 bond.
An intramolecular weak hydrogen bonding of C12–H12ꢃ ꢃ ꢃO1
(Table 3) can be found in the compound, which is helpful to
strengthen the molecule stability (Fig. 2(a)). In the crystal structure
of FBIAAP, adjacent molecules are linked through weak hydrogen
bonding of C10–H10A An intramolecular weak hydrogen bonding
of O1i (i: ꢀ1 + x, y, z) and C15–H15ꢃ ꢃ ꢃO1ii (ii: 1 ꢀ x, ꢀ1/2 + y, 1/
2 ꢀ z) (Table 3), forming supramolecular layered structures along
the ab plane (Fig. 2(b)).
Although theoretical results are not exactly close to the exper-
imental values of the compound, they are generally accepted that
bond lengths and bond angles depend upon the method and the
basis set used in the calculation, and they can be used as founda-
tion to compute the molecular properties for the compound.
Vibrational spectra
It is well known that the harmonic frequencies obtained by DFT
calculation are usually higher than the corresponding experimen-
tal quantities due to the facts of the electron correlation approxi-
mate treatment, anharmonicity effect and basis set deficiency
etc.[43,44]. The theoretical frequencies corrected by empirical fac-
tors will match well with experimental ones. Basing on the point,
the theoretical harmonic frequencies were scaled by the empirical
factor of 0.9614 in this work referring to previous literatures
[44,45].
The experimental FT-IR and FT-Raman spectra along with the
corresponding theoretically simulated IR and Raman spectra are
shown in Figs. 3 and 4, respectively, where the experimental and
theoretical intensities are plotted against the vibrational wave-
numbers. In Raman spectra, the Raman scattering activities calcu-
lated by Gaussian 09W program have been suitably converted to
relative Raman intensities using the following relationship derived
Optimized structure
The first task for the computational work is to determine the
optimized geometry of the studied compound. In order to compare
Fig. 1. Molecular structure with atomic numbering for FBIAAP.

1016
Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
Table 2
Selected geometric parameters for the studied compound.
Experimental
Theoretical
Experimental
Theoretical
Bond lengths/Å
C1–C2
C2–C3
C3–C4
C4–C5
C5–C6
C1–C6
N1–C1
N1–N2
N1–C7
C7–C8
C8–C9
N2–C9
O1–C7
1.379 (3)
1.368 (3)
1.378 (4)
1.380 (3)
1.386 (3)
1.388 (3)
1.421 (2)
1.405 (2)
1.396 (2)
1.437 (2)
1.371 (2)
1.355 (2)
1.234 (2)
1.401
1.394
1.397
1.395
1.395
1.401
1.421
1.414
1.417
1.469
1.372
1.387
1.226
C9–C10
N2–C11
N3–C8
1.478 (3)
1.457 (2)
1.388 (2)
1.280 (2)
1.468 (3)
1.381 (3)
1.365 (3)
1.368 (4)
1.380 (4)
1.383 (3)
1.390 (3)
1.367 (3)
1.491
1.469
1.383
1.291
1.466
1.402
1.389
1.394
1.400
1.390
1.407
1.351
N3–C12
C12–C13
C13–C14
C14–C15
C15–C16
C16–C17
C17–C18
C13–C18
F1–C14
Bond angles/°
C2–C1–C6
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–C6
C1–C6–C5
N2–N1–C1
N2–N1–C7
C1–N1–C7
N1–N2–C9
N1–N2–C11
C9–N2–C11
N1–C1–C2
N1–C1–C6
O1–C7–N1
O1–C7–C8
N1–C7–C8
N3–C8–C7
120.8 (2)
119.5 (2)
120.7 (2)
119.8 (2)
120.3 (2)
118.8 (2)
120.0 (1)
109.0 (1)
121.5 (1)
107.2 (1)
117.7 (1)
125.7 (1)
118.1 (2)
121.1 (2)
123.3 (2)
131.3 (2)
105.3 (1)
128.8 (1)
120.1
119.4
120.8
119.5
120.5
119.7
119.0
109.8
123.9
106.6
114.1
119.1
118.8
121.1
124.4
130.9
104.6
129.1
N3–C8–C9
C7–C8–C9
N2–C9–C8
N2–C9–C10
C8–C9–C10
C8–N3–C12
N3–C12–C13
C12–C13–C14
C12–C13–C18
C14–C13–C18
C13–C14–C15
C14–C15–C16
C15–C16–C17
C16–C17–C18
C13–C18–C17
F1–C14–C13
F1–C14–C15
123.1 (1)
107.7 (1)
110.3 (1)
121.6 (1)
128.1 (2)
119.3 (1)
120.4 (2)
120.6 (2)
122.8 (2)
116.6 (2)
123.9 (2)
118.3 (2)
120.4 (2)
120.1 (2)
120.7 (2)
118.2 (2)
117.9 (2)
123.1
107.7
110.9
121.6
127.5
120.6
120.6
120.3
122.7
117.0
122.9
118.8
120.1
120.1
121.2
118.9
118.2
quencies and the normal coordinate analysis with the aid of the
GaussView program [42].
Table 3
Distances (Å) and angles (°) involving hydrogen bonding of the studied compound.a
As a whole, the theoretically scaled wavenumbers of the DFT
calculation are close to the experimental data, and the DFT/6-
31G(d) level can effectively predict the vibrational frequencies
for the compound. Owing to the fact that the detailed spectral
assignments have been given in the Table 4 and Figs. 3 and 4, we
decided to discuss the characteristics or strong peaks for these
spectral bands below.
Hydrogen bonding
D–H
Hꢃ ꢃ ꢃA
2.300
2.520
2.300
Dꢃ ꢃ ꢃA
2.974 (2)
3.457 (3)
3.200 (3)
D–Hꢃ ꢃ ꢃA
129.0
167.0
162.0
C12–H12ꢃ ꢃ ꢃO1
C10–H10Aꢃ ꢃ ꢃO1i
C15–H15ꢃ ꢃ ꢃO1ii
0.930
0.960
0.930
a
Symmetry codes: (i) ꢀ1 + x, y, z; (ii) 1 ꢀ x, ꢀ1/2 + y, 1/2 ꢀ z.
As seen from the Table 4 and Fig. 3, the C@O stretching vibra-
tion is characterized by very strong peak appearing at 1653 cmꢀ1
in the FT-IR spectra, while the same vibrational mode is shown
at the theoretical wavenumber of 1702 cmꢀ1 giving a positive devi-
ation. The error is caused by the fact that the theoretically calcu-
lated C@O bond distance is shorter than experimental one, which
indicate that the electrons of C@O bond have a great contribution
to the pyrazole moiety leading to show shorter bond lengths than
theoretical ones (Table 2), and the C@O stretching vibration is in-
fected with intermolecular hydrogen bonding interactions in the
crystal packing structure (Table 3).
The identification of pyrazoline ring vibrations is a difficult task
since the mixing of vibrations in this region. However, with the
help of theoretical calculations, the heterocyclic vibrations were
identified and assigned in this work. The pyrazole puckering modes
partly mixing adjacent phenyl ring are characterized by weak
peaks observed at 415, 450, 750 cmꢀ1 and found at 407, 437,
722 cmꢀ1 in IR of FBIAAP. The wavenumber at 569(observed)/
560(found) cmꢀ1 is assigned to the mixing angle bending of
C7C8C9 and No. 3 phenyl ring. The wavenumber at 623 cmꢀ1 is as-
cribed to the mixing angle bending of C7N1N2 and No. 1 phenyl
ring. The medium infrared peak appearing at 1305(observed)/
1276(found) cmꢀ1 is designated to the mixing mode of C1–N1
and N8–N3 stretching vibrations. All the theoretically computed
from the intensity theory of Raman scattering stated in previous
references [46,47]:
4
fðv0
vi 1 ꢀ exp
ꢀ
viÞ Si
ꢀ
h
ꢁi
Ii ¼
ð1Þ
ꢀhcvi
kT
where v0 is the exciting frequency (in cmꢀ1 units), vi is the vibra-
tional wavenumber of the ith normal mode, h, c and k are universal
constants, and f is the suitably chosen common scaling factor for all
the peak intensities. The simulated IR and Raman spectra have been
plotted using pure Lorentzian band shapes with a bandwidth of
10 cmꢀ1
.
The present molecule has C1 point group symmetry, 39 atoms
and 111 normal vibrational modes. For comparative purpose, the
observed experimental wavenumbers together with the corre-
sponding theoretical frequencies were tabulated in Table 4, where
the theoretical frequencies were given along with corresponding
theoretical IR and Raman intensities as well as the proposed vibra-
tional assignments for the optimized structure. Mode numbers are
extracted from the output results of the B3LYP calculation. The se-
lected vibrational modes were numbered from small to big fre-
quency in Table 4. The proposed vibrational assignments were
made on the basis of the relative intensities, magnitude of the fre-

Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
1017
1613 cmꢀ1 in FT-Raman spectrum and in the band of 1560–
1595 cmꢀ1 in FT-IR spectrum, which the corresponding theoretical
results show excellent agreements with the experimental ones.
The imine C–H in-plane bending can be observed experimen-
tally at 1361, 1381 cmꢀ1 and found theoretically at 1361,
1375 cmꢀ1 in IR spectra. The peak observed at 966 cmꢀ1 is ascribed
to the C–H out-of-plane wagging of imine, and the corresponding
theoretical wavenumber is at 985 cmꢀ1. The observed peaks at
878 cmꢀ1 in FT-IR and 876 cmꢀ1 in FT-Raman are assigned to the
imine in-plane wagging. The C@N stretching modes are coupled
with the adjacent C@C vibrations in the conjugated system linked
through the Schiff base imine, which are displayed at the theoret-
ical wavenumbers of 1578, 1596 and 1610 cmꢀ1
.
The observed medium peaks at 1041 and 1131 cmꢀ1 in FT-IR
spectrum are designated to the CH3 rocking vibrations. The theo-
retical values of 1031 and 1122 cmꢀ1 are in accordance with the
ones. The methyl C–H in-plane wagging vibrations are found in
the band of 1362–1421 cmꢀ1 and observed at 1361, 1412 and
1431 cmꢀ1
. The wavenumbers found in the band of 1448–
1485 cmꢀ1 and observed at 1453 and 1485 cmꢀ1 in the IR spectra
are ascribed to the scissoring vibrations of CH3. The peak observed
at 2933 cmꢀ1 and the bands found in 2926–3055 cmꢀ1 are as-
signed to the methyl C–H stretching vibrations.
In low frequency region, these bands are mainly ascribed to the
molecular skeleton wagging, rocking and torsion vibrations. In
high frequency region, the band of 2926–3127 cmꢀ1 is assigned
to the C–H stretching vibration of different moieties including
the methyl, phenyl and imine groups. The stretching vibrations
for the methyl and imine groups have been stated above. The band
of 3063–3127 cmꢀ1 is corresponding to the phenyl C–H stretching
vibrations theoretically.
In addition, the C@N bond exhibits hardly its own characteristic
peak in IR spectra, but it is tightly relative to the strongest Raman
scattering activities of the molecule. As seen in Table 4 and Fig. 4,
the stronger Raman intensities of the compound are closely related
to the molecular conjugative moiety linked through the Schiff base
imine.
By the vibrational analyses, we can find that the pyrazole-imi-
no-benzene moiety presents good vibrational resonances, while
the No. 1 benzene ring shows good vibrational isolation from the
imino-bridged moiety.
Fig. 2. Neighboring molecular structural diagrams of FBIAAP (the dashed lines
indicate hydrogen bonds).
Thermodynamic properties
wavenumbers for pyrazole ring show very good agreements with
the experimental results.
On the basis of vibrational analysis at B3LYP/6-31G(d) level for
the compound, the standard statistical thermodynamic functions,
viz., heat capacity at constant pressure (CHp;m), entropy (SmH), and en-
The phenyl puckering vibrations are found theoretically as weak
peaks at 480 cmꢀ1 for No. 3 ring and at 497 cmꢀ1 for No. 1 ring, and
observed at 483 and 503 cmꢀ1 respectively. The angle bending
vibration appears in the band of 530–839 cmꢀ1, and the same the-
oretical mode band of 519–827 cmꢀ1 shows good agreements with
the experimental results. The breathing vibrations of No. 1 phenyl
ring can be exhibited by weak peaks at the 997(observed)/
978(found) cmꢀ1 in Raman spectrum and 1017(observed)/
1006(found) cmꢀ1 in IR spectrum. However, the 2-fluoro substi-
tuted No. 3 phenyl ring is sensitive to the substituent group, and
exhibits hardly the breathing vibrations in IR and Raman spectra,
which is different from the similar compounds cited above. The
medium peak at 761(observed)/745(found) is assigned to the C–H
out-of-plane wagging vibrations of phenyl rings in the IR spectra.
The C–H out-of-plane and in-plane wagging for benzene rings are
in the bands of 483–952 cmꢀ1 and 1019–1338 cmꢀ1, respectively.
Apparently, the phenyl puckering and angle bending vibrations
are described as mixed modes as there are partial contributions
mainly from the C–H out-of-plane and in-plane wagging vibrations,
respectively. The C@C stretching vibrations are displayed by med-
ium peak at 1451 cmꢀ1, and by strong peaks at 1568, 1596,
thalpy change (
D
HHmð0 ! TÞ) were obtained from the theoretically
scaled frequencies of the optimized structure (the scaling factor
is also 0.9614), and the corresponding values were listed in Table 5.
As seen from Table 5, we can find that all the values of CHp;m, SmH
and
D
HHm are increasing with temperature ranging from 200 to
600 K due to the fact that the vibrational intensities of molecule in-
crease with the enhancement of temperature. The correlation
equations between these thermodynamic properties and tempera-
tures were fitted by quadratic, linear and quadratic formulas,
respectively, and the corresponding correlation coefficients are
all beyond 0.999. The corresponding fitting equations are as
follows:
CHp;m ¼ ꢀ13:2038 þ 1:3897T ꢀ 6:5218 ꢁ 10ꢀ4T2
SHm ¼ 307:65 þ 1:0930T
ð2Þ
ð3Þ
ð4Þ
D
HHm ¼ ꢀ6:4620 þ 0:0822T þ 4:3717 ꢁ 10ꢀ4T2

1018
Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
Fig. 3. IR spectra of FBIAAP: (a) observed, (b) simulated.
Fig. 4. Raman spectra of FBIAAP: (a) observed, (b) simulated.
All the thermodynamic data and equations may be used to fur-
Nonlinear optical effects
ther study on the compound, especially, they can be used to com-
pute the other thermodynamic energies basing on relationships of
thermodynamic functions and to estimate directions of chemical
reactions basing on the second law of thermodynamics in thermo-
chemical research field.
It is an important and inexpensive way to evaluate the nonlinear
optical (NLO) properties of materials by theoretical calculations.
Nowadays, density functional theory has been extensively used as
an effective method to investigate the organic NLO materials [48],

Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
1019
Table 4
Comparison of the observed and calculated vibrational spectra of FBIAAP.a
Mode
Experimental
IR
Theoretical
Freq.
Approximate assignments
Raman
IIR
10.5
28.0
14.5
7.9
IRaman
23
24
26
27
28
30
32
34
35
36
37
39
40
42
44
46
48
53
54
55
58
60
61
63
64
70
71
72
76
77
78
79
80
81
84
88
90
93
94
95
97
107
415
450
483
503
530
569
595
623
665
679
696
750
761
800
839
878
909
407
437
480
497
519
560
601
623
664
673
686
722
745
790
827
856
912
2.7
1.2
2.0
m
m
m
m
R2,3
R2
R3
0.6
R1
8.4
1.2
2.7
2.1
1.5
0.9
0.1
0.2
0.3
0.3
5.9
3.1
10.7
0.3
a
a
a
a
a
R1
C7C8C9+
R1,3
R1
R1
35.6
12.7
35.0
9.3
aR3
+
+
+
+
a
s
a
c
C7N1N2
R2
N3C12C13
CH of R1
R2
5.6
m
m
c
c
R1
R1
24.9
12.1
78.5
11.5
10.0
6.5
11.7
0.1
7.7
CH of R1
CH of R1,3
C8N3C12 +
R3
+
m
800
876
997
a
a
aR3
bimine
C7C8 +
hR1
CH of imine
hR1 N1N2
CH3
bCH of R1
bCH of R1,3
t
tC9N2 + qCH3
978
985
5.0
966
1017
1041
1068
1093
1131
1.1
1.7
5.1
6.2
4.2
1.8
17.2
45.7
35.3
2.4
5.4
7.7
0.3
12.4
4.0
21.9
1.5
0.9
98.9
41.9
15.5
2.3
3.2
1.6
c
1006
1031
1063
1079
1122
1134
1227
1261
1276
1316
1362
1375
1398
1421
1444
1454
1485
1578
1600
1610
1702
2929
3086
11.2
16.6
23.6
18.6
127.7
41.8
67.8
67.6
179.0
35.2
24.3
119.6
75.8
15.3
16.5
22.0
75.9
41.9
96.7
10.9
228.9
42.1
37.4
+ t
1034
1091
q
+
t
C7N1
tC7N1
+
q
q
CH3
CH3 + bCH of R3 + tC7N1 + tC8N3
1151
1231
1278
1229
1277
1305
1338
1361
1381
1412
1431
bCH of R3
bCH of R3
+ tC14F1
t
t
C1N1 +
C7N1 +
t
t
C8N3
1313
C9N2 + tC8N3 + bCH of R1
bCH of CH3 + bCH of imine
bCH of imine
1411
1451
t
C9C10 + bCH of CH3
bCH of CH3
C@C of R3 + bCH of R3
t
1453
1485
1560
1574
1595
1653
2933
3060
dCH3
dCH3 + bCH of R1
1568
1596
1613
t
t
t
t
t
t
C8C9 +
C8C9 +
N3C12 + tC@C of R3
C@O
CH of CH3
CH of R1
t
t
N3C12 +
N3C12 +
t
t
C@C of R1,3
C@C of R3
Mode numbers are extracted from the output result of the B3LYP calculation. Observed wavenumbers (IR and Raman) and vibrational frequencies are in cmꢀ1; theoretical
vibrational frequencies (Freq.) are in cmꢀ1; the calculated IR intensities are in km.molꢀ1; the calculated Raman scattering intensities (IRaman) are in arbitrary units by Eq. (1). R,
a
ring; subscripting numbers followed by R represent ring numbering modes shown in Scheme 1.
a
, angle bending; b, in-plane bending; c, out-of-plane bending; x, wagging; m,
puckering; h, breathing; d, scissoring; s, torsion; q, rocking; t, stretching.
Table 5
Table 6
Thermodynamic properties of FBIAAP at different temperatures.
The calculated electric dipole moments (Debye), static polariz-
ability components (a.u.) and first hyperpolarizability compo-
nents (a.u.) of FBIAAP.
CHp;m
SmH
D
HmH
T (K)
200.00
250.00
298.15
350.00
400.00
450.00
500.00
550.00
600.00
240.77
291.90
341.27
392.66
439.00
481.38
519.65
553.98
584.73
520.17
579.37
635.01
693.77
749.27
803.46
856.20
907.36
956.91
27.91
41.22
56.47
75.51
96.32
119.34
144.39
171.24
199.72
lx
ly
lz
axx
ayy
azz
bxxx
bxxy
bxyy
byyy
bxxz
byyz
bxzz
byzz
bzzz
ꢀ0.6152
1.7033
ꢀ0.0979
386.37
228.61
106.74
2221.68
ꢀ263.30
ꢀ223.66
159.28
254.35
ꢀ22.03
ꢀ67.56
60.09
Temperatures (T) are in K; standard heat capacities (CHp;m) are in J ꢃ molꢀ1 ꢃ Kꢀ1
;
standard entropies (SHm) are in J ꢃ molꢀ1 ꢃ Kꢀ1; standard enthalpy changes (
D
HHm) are
in kJ ꢃ molꢀ1
.
ꢀ51.64
and the calculations of the molecular dipole moment (
polarizability ( ) and first hyperpolarizability (b) from the Gaussian
output have been explained in detail previously [49,50].
In this work, the NLO related properties of the studied molecule
were calculated at the B3LYP/6-31G(d) level using Gaussian 09W
l), linear
a
program package. The calculated electric dipole moments, linear
polarizabilities and first hyperpolarizabilitis were listed in Table
6. And the values of the l0, a0 and b0 of the investigated molecule

1020
Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
are 1.8136 Debye, 35.6134 Å3 and 1,6755 ꢁ 10ꢀ29 cm5/esu, respec-
As we know that a common absorption band in UV–vis spectra
is associated to electronic transitions between the corresponding
frontier molecular orbitals involved in the photoabsorption re-
sponse of a molecule. When a molecule absorb or emit light from
one energy state to another, the wavelength of the light is related
to the energies of the two states by the Eq. (7).
tively, which are greater than those of urea (the l0, a0 and b0 of
urea are 1.3732 Debye, 3.8312 Å3 and 3.7289 ꢁ 10ꢀ31 cm5/esu cal-
culated with the same method), especially, the b0 of FBIAAP is 44.9
times that of urea theoretically, which is greater than those of re-
ported compounds [29,48–51], therefore, the compound is a prom-
ising organic NLO material.
In quest of the NLO structural characteristics, the molecular
orbital surfaces of the compound basing on the B3LYP/6-31G(d)
calculation have been shown in Fig. 5. Natural population analysis
is to invest on the frontier molecular orbitals (FMOs), which indi-
cate that the FMOs are mainly composed of atomic p-electron orbi-
tals, as shown by the surfaces of FMOs in Fig. 5. Obviously, the NLO
properties of the compound are caused easily by the transferring
effect of the p-electrons and inapparent FMO level gaps of the
molecule.
Efinal ꢀ Einitial ¼ hc=k
ð5Þ
Where h is Planck’s constant, c is the velocity of light and k is the
light wavelength.
A molecule can move from one electronic energy state to an-
other by absorbing or emitting a photon of energy. If it absorbs a
photon of energy, hc/k, it moves from a lower to a higher energy
state, and its energy increases by hc/k.
Therefore, the photoabsorption equation is as follows:
D
E ¼ Efinal ꢀ Einitial ¼ Ehigh ꢀ Elow ¼ hc=k
ð6Þ
UV–vis spectra
Actually, the time-dependent density functional theory (TD-DFT)
has been successfully used to present the most promising scheme
for evaluating the low-lying excited spectrum of conjugated mole-
cules, and has been the subject of countless applications even
allowing for bulk solvent effects [52,53]. So, in this work, the verti-
cal electronic transition energies of the studied molecule are deter-
mined by means of a TD-B3LYP/6-31G(d) calculation, and the
theoretical excitation wavelengths with oscillator strengths calcu-
The UV–vis absorption spectrum of the studied compound was
measured in MeOH solvent on a Shimadzu UV3100 spectropho-
tometer. Fig. 6 shows the experimental bands with fitted bands.
There are four broad absorption bands exhibited at 331.9, 251.8,
233.7 and 204.8 nm seemingly. In facts, there are six fitted peaks
as a minimum corresponding to the experimental spectral bands.
Fig. 5. Surfaces of FMOs of FBIAAP.

Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
1021
Fig. 6. Experimental UV–vis spectrum with fitted bands as well as the theoretical excitation wavelengths with oscillator strengths of FBIAAP.
lated are also shown in Fig. 6. The higher oscillator strength bands
including the mainly involved orbitals are listed in Table 7. Thus,
the experimental bands of the investigated compound are further
ascribed to the molecular electron transfer orbitals.
among the atoms of the biggest
p
-electron conjugated moiety
linked by the imine bond. HOMO-5 and HOMO-6 are almost pop-
ulated among the whole molecule. However, the LUMO+2 and
HOMO-4 orbitals are only delocalized among the terminal No. 1
As seen from Table 7 and Fig. 6, an experimental band is gener-
phenyl ring, and LUMO+3 is occupied by the the
p-electrons of
ally consisted of several electron transitions for the bigger p-conju-
the terminal No. 3 benzene ring, and HOMO-2 gives vital distribu-
tion in the lone electron pairs of O1 and N3 atoms of the molecule.
The electron transfers among the FMOs mentioned above lead to
the photoabsorption characteristics of the compound. The first
band of 331.9(observed)/343.48 (calculated) nm is related to the
lowest unoccupied molecular orbital (LUMO) and the highest occu-
pied molecular orbital (HOMO), and the frontier molecular orbitals
(FMOs) ranged from HOMO-6 to LUMO+5 are responsible for the
other bands as seen in Table 7 in details.
gated molecule, and the fitted bands except the band of 226.9 nm
show excellent agreements with theoretical results. The oscillator
strengths are higher if the moieties involved in the relatively adja-
cent orbitals are closer each other due to matching rule of orbitals
symmetry.
Natural population analysis indicates that these FMOs are
mainly composed of atomic p orbitals, so above electronic transi-
tions are mainly derived from the contributions of bands
p ?
p⁄
and n ? p⁄. As seen from Fig. 5, the HOMO-1 and LUMO+1 orbitals
are principally delocalized among the atoms of antipyrine moiety,
while HOMO, LUMO and LUMO+5 are principally delocalized
Concluding remarks
The title compound has been synthesized by the condensation
of 2-fluorobenzaldehyde and 4-aminoantipyrine in MeOH solution
in one step. The compound was characterized by elemental analy-
sis, FT-IR, FT-Raman, UV–vis absorption and X-ray single crystal
diffraction techniques. Density functional theory calculations at
B3LYP/6-31G(d) were performed to further study on the molecular
structure, vibrational spectra, thermodynamic properties, NLO ef-
fects, and photoabsorption properties. The results show that the
optimized geometries closely resemble the crystal structure and
the theoretical vibrational frequencies agree with experimental
Table 7
UV–vis absorption spectral wavenumbers of FBIAAP.a
Experimental
Theoretical
kAE =nm
kFE=nm
kT =nm
kT =eV
IT
Main involved orbitals (%)
331.9
341.5
302.6
343.48
322.86
300.38
275.85
262.07
251.17
244.01
238.13
219.98
214.40
212.32
211.71
204.07
201.58
3.610
3.840
4.128
4.495
4.731
4.936
5.081
5.207
5.636
5.783
5.839
5.856
6.076
6.151
0.6741
0.0951
0.2354
0.0643
0.1035
0.2167
0.1299
0.0270
0.0237
0.0634
0.0337
0.0582
0.0222
0.0375
81?82(92%)
79?82(64%) 80?82(31%)
80?82(61%)
81?83(92%)
79?83(53%) 80?83(37%)
80?83(58%) 79?83(36%)
76?82(38%) 81?85(38%)
81?85(49%) 76?82(36%)
80?85(77%)
79?84(47%) 75?82(29%)
77?83(65%)
75?82(30%)
76?83(70%)
81?87(64%)
79?82(32%)
data. The thermodynamic properties of CHp;m; SmH; HmH and these cor-
D
260.2
249.2
251.8
233.7
204.8
relations with temperatures were obtained on the basis of theoret-
ical vibrations of the optimized structure. Furthermore, the Raman
spectrum analysis indicates the strongest Raman activities of the
molecule are tightly relative to the molecular conjugative moiety
linked through the Schiff base imine bond. The predicted electronic
absorption spectra show good agreements with experimental val-
ues and molecular orbital coefficients analysis suggests that the
226.9
79?84(26%)
79?86(15%)
204.8
electronic spectra are assigned to
p ?
p⁄ and n ? p⁄ electronic
a
kAE are the apparent maximum absorption wavelengths experimentally mea-
transitions. NLO calculation indicates that the compound may be
a promising optical material. We hope the results are of assistance
in the quest of experimental and theoretical evidences for the title
compound.
sured in methanol solvent; kFE are the fitted absorption wavelengths for experi-
mental bands. kT are the theoretical excitation energies considering solvent effects,
IT are the theoretical oscillator strengths considering solvent. Orbital numbers are
extracted from the output result of the B3LYP calculation.

1022
Y. Sun et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 1013–1022
[23] C. Ravikumar, I.H. Joe, Phys. Chem. Chem. Phys. 12 (2010) 9452–9460.
Acknowledgements
[24] Y. Wang, Z. Yu, Y. Sun, Y. Wang, L. Lu, Spectrochimica Acta A 79 (2011) 1475–
1482.
This work was supported by Natural Science Foundations of
China (Nos. 31070332, 21073092 & 21103092), Jiangsu Postdoc-
toral Research Funds (No. 1001011C) and Sichuan Education
Department Funds (No. 12ZA080).
[25] Y. Sun, Q. Hao, W. Tang, Y. Wang, X. Yang, L. Lu, X. Wang, Mater. Chem. Phys.
129 (2011) 217–222.
[26] Y. Sun, R. Zhang, D. Ding, S. Liu, B. Wang, Y. Wang, Y. Lin, Struct. Chem. 17
(2006) 655–665.
[27] Y. Sun, R. Zhang, Q. Jin, X. Zhi, X. Lü, Acta Cryst. C62 (2006) o467–o469.
[28] Y. Sun, Chinese J. Struct. Chem. 26 (2007) 55–58.
[29] Y. Sun, Q. Hao, W. Wei, Z. Yu, L. Lu, X. Wang, Y. Wang, J. Mol. Struct.:
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Appendix A. Supplementary data
[30] Y. Sun, Q. Hao, Z. Yu, W. Wei, L. Lu, X. Wang, Mol. Phys. 107 (2009) 223–
235.
[31] Y. Sun, W. Wei, Q. Hao, L. Lu, X. Wang, Spectrochimica Acta A 73 (2009) 772–
781.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.07.117.
[32] R. Zhang, B. Du, G. Sun, Y. Sun, Spectrochimica Acta A 75 (2010) 1115–1124.
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