L. Kamath, A.P. Menezes, R. Bairy et al.
Journal of Molecular Structure 1245 (2021) 131019
Fig. 1. Scheme for the synthesis of FMBC.
donor/acceptor groups. The azomethine group/ hydrazone core be-
ing an electron donor, the substitution of a more functional group
on the hydrazone moiety further enhances the number of donor
sites and thus the molecular nonlinearity [10]. The integration of
various substituents with appropriate donor/acceptor strength into
the aromatic rings also boosts the molecular binding affinities via
intermolecular interactions and π−electron delocalization and as
a consequence the optical nonlinear behavior increases. Keeping
these aspects in mind, we synthesized a Schiff base, N’-((E)- (4-
fluoro Phenyl)methylidene)biphenyl-4-carbohydrazide (FMBC) hav-
ing large conjugation length [11]. Since the material crystallizes in
centrosymmetric C2/c space group second-order nonlinearity hard
to observe. Therefore, the third-order nonlinear properties such as
nonlinear absorption (β), nonlinear refractive index (n2), and the
nonlinear optical susceptibility (χ(3)) were extracted by perform-
ing a single beam z-scan experiment. Herein, we report the syn-
thesis, thermal, photoluminescence, linear, and nonlinear optical
studies of FMBC. The structural details obtained from single-crystal
X-ray diffraction is also provided for ready reference. The contri-
bution of intermolecular interactions to crystal packing and non-
linear behavior is analyzed through the Hirshfeld surface analysis
(HS), interaction energy calculations, enrichment ratios, 3D energy
framework, and 2D fingerprint plots.
tial thermal (DT) analysis of FMBC. The sample was scanned in the
temperature range 30°C - 600 °C at the heating rate of 10 °C/min in
the nitrogen atmosphere using SDT Q600 V20.9 Build 20 thermal
analyzer. The linear optical absorption/transmission spectrum was
recorded in the wavelength region 200 nm to 900 nm using a UV-
1601PC UV-Visible spectrophotometer. The specimen is dissolved
in DMF (0.01M) and taken in a 1 mm thick quartz cuvette and
exposed to the radiation. The photoluminescence (PL) study was
carried out on FMBC using the FluoroMax-4CP spectrometer. The
sample was dissolved in DMF and the experiment was conducted
in the range 400 nm to 800 nm at room temperature by exciting
the sample with a radiation of wavelength 380 nm. The signal was
detected using the R928P photomultiplier tube with a resolution
of 0.2 nm. The interatomic contacts present in the solid structure
which contribute to the stabilization of bulk structure were an-
alyzed by Crystal Explorer 17.5. The Hirshfeld surfaces (HSs), 2D
fingerprint plots (FPs) interaction energies and energy 3D-frame
works of FMBC were obtained using the crystallographic informa-
tion file (.cif) as the input [12]. The third-order nonlinear optical
parameters were evaluated by performing the classical Z scan ex-
periment [13]. A continuous-wave laser beam of wavelength 532
nm with 200 mW output power from a diode-pumped solid-state
laser source was focused onto a 1 mm thick cuvette containing the
0.01M solution of FMBC prepared in DMF. The laser beam of peak
input intensity of I0 = 8.48 × 107W/m2 was focused using a lens
of focal length 28.6 cm. The thin sample approximation is appli-
cable in this case as the sample thickness is much smaller than
the equivalent Rayleigh length z0 (8.86 mm). The beam waist at
the focus was estimated to be equal to 38.75 microns. The sample
is moved using a computer-controlled translational stage and far-
field light intensity variation is noted with and without aperture in
front of the detector using Laser Probe Rj-7620 Energy Meter with
pyroelectric detectors.
2. Materials and methods
2.1. Synthesis
The title compound, N’-[(E)-(4-fluorophenyl) methylidene]
biphenyl-4-carbohydrazide (FMBC) was synthesized using 4-
fluorobenzaldehyde and biphenyl-4-carbohydrazide as the starting
materials. The chemicals with 99.99% purity were procured from
Sigma Aldrich Inc. and were used without further purification.
Equimolar quantities of the precursors were dissolved separately
in 30 ml of ethanol. Two drops of Conc. HCl acid was added, and
the mixture was refluxed for 3 h. The mixture is then allowed
to cool, the solid precipitate formed was washed with water
and dried. Shown in Fig. 1 is the synthesis process schematic.
The composition of the product - Found (calculated): C: 75.40 %
(75.46%); H: 4.78 % (4.75 %); N: 8.73% (8.80%). The single crystals
were grown by slow evaporation of the solvent method at ambient
temperature choosing DMF as the solvent.
3. Results and discussions
The recorded IR spectrum of the title compound is displayed in
Fig. 2. The spectrum shows a broad absorption band at 3403 cm−1
corresponding to the N-H vibration and the weak band at 2937
cm−1 represents the presence of aromatic C-H stretching vibration.
The strong band at 1645 cm−1 indicates the –C=O- group while
the C-F stretching is confirmed by the weak band observed at 1089
cm−1. The medium intensity peak at 1395 cm−1 confirms the C-
N stretching vibrations. Thus, the analysis of the FT-IR spectrum
confirms the formation of the title compound, FMBC.
2.2. Characterization and computational techniques
The formation of the compound was confirmed by identifying
the functional groups present in FMBC through FT-IR spectroscopy.
The spectrum is recorded using the pellet technique wherein the
sample is mixed with KBr powder and a disk is formed. The spec-
trum is recorded in the wavenumber range 4000-400 cm–1 using
a SHIMADZU-8400S FT-IR spectrometer with a spectral resolution
of 0.1 cm–1. To explore the temperature range over which the ma-
terial can be used, the melting point and the decomposition tem-
perature was determined by thermogravimetric (TG) and differen-
Fig. 3 depicts 1D 1H (Hydrogen) NMR spectra of the title
compound – FMBC. The 1H – Chemical shifts are referenced to
DimethylSulfoxide (DMSO-d6 peak 2.49 ppm, solvent reference)
and were analyzed in accordance with standard 1H Chemical shift
database. The occurrence of crowded aromatic hydrogen signals in
the 1H chemical shift range of 7 – 8 ppm indicates signal arising
from 13-methine protons (C-1H) from the aromatic ring of dibenzyl
moiety. The upfield shifted aliphatic methine (C-1H) is found at 3.3
ppm which arises from the carbon linking dibenzyl and flouroben-
2