Design, synthesis and nonlinear optical properties of (E)-1-(4-substituted)-3-(4-hydroxy-3-nitrophenyl) prop-2-en-1-one compounds

Article abstract of DOI:10.1016/j.cplett.2016.04.084

A new series of (E)-1-(4-substituted)-3-(4-hydroxy-3-nitrophenyl) prop-2-en-1-one compounds have been synthesized by Claisen-Schmidt condensation reaction. Nonlinear optical characterization were carried out using z-scan technique with nanosecond pulses. These samples are found to exhibit strong nonlinear absorption at 532 nm and the nonlinear absorption coefficient of these samples exponentially increases with the increase of phonon characteristic energy. This relation speaks the role of phonon in the origin of nonlinear absorption in these compounds. The reported dependence of optical nonlinearity of the chalcone derivatives on the phonon characteristic energy will help in designing similar class of new molecules with high nonlinear coefficients.

Full text of DOI:10.1016/j.cplett.2016.04.084

Accepted Manuscript
Design, Synthesis and nonlinear optical properties of (E)-1-(4-substituted)-3-
(4-hydroxy-3-nitrophenyl) prop-2-en-1-one compounds
Amrita Saha, Vijay Shukla, Sudip Choudhury, J. Jayabalan
PII:
S0009-2614(16)30268-8
DOI:
http://dx.doi.org/10.1016/j.cplett.2016.04.084
CPLETT 33828
Reference:
Chemical Physics Letters
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Received Date:
Accepted Date:
5 February 2016
26 April 2016
Please cite this article as: A. Saha, V. Shukla, S. Choudhury, J. Jayabalan, Design, Synthesis and nonlinear optical
properties of (E)-1-(4-substituted)-3-(4-hydroxy-3-nitrophenyl) prop-2-en-1-one compounds, Chemical Physics
Letters (2016), doi: http://dx.doi.org/10.1016/j.cplett.2016.04.084
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Design, Synthesis and nonlinear optical properties of
(E)-1-(4-substituted)-3-(4-hydroxy-3-nitrophenyl)
prop-2-en-1-one compounds
Amrita Sahaa, Vijay Shuklab, Sudip Choudhurya, J. Jayabalanb,∗
aDepartment of Chemistry, Assam University, Silchar, India-788011.
bUltrafast Spectroscopy Laboratory, Laser Physics Applications Section, Raja Ramanna
Centre for Advanced Technology, Indore, India-452013.
Abstract
A new series of (E)-1-(4-substituted)-3-(4-hydroxy-3-nitrophenyl)prop-2-en-
1-one compounds have been synthesized by Claisen-Schmidt condensation
reaction. Nonlinear optical characterization were carried out using z-scan
technique with nanosecond pulses. These samples are found to exhibit strong
nonlinear absorption at 532 nm and the nonlinear absorption coefficient of
these samples exponentially increases with the increase of phonon character-
istic energy. This relation speaks the role of phonon in the origin of nonlinear
absorption in these compounds. The reported dependence of optical nonlin-
earity of the chalcone derivatives on the phonon characteristic energy will
help in designing similar class of new molecules with high nonlinear coeffi-
cients.
Keywords: Chalcone, Nonlinear absorption, Phonon Contribution,
Two-Photon Absorption.
1. Introduction
Large nonlinear optical coefficient, good transparency, high thermal and
chemical stability are some of the most important requirements for a good
nonlinear optical (NLO) material [1, 2, 3]. In the field of photonics, the search
for advanced nonlinear optical materials possessing all these properties are
∗Corresponding author
Email address: jjaya@rrcat.gov.in (J. Jayabalan )
Preprint submitted to Chemical Physics Letters
April 26, 2016

important areas of research. Efforts are being made in recent years to de-
velop such materials for their applications in telecommunication, optical data
storage, nonlinear metamaterials and optical information processing [4, 5, 6].
Organic materials have most of the characteristics required for a good NLO
material like high optical nonlinearity, ultrafast response and high damage
resistance. In the quest for good nonlinear materials it is essential to identify
how the nonlinear behaviour of the material scales with its other physical
properties. Such scaling functions can be used for designing new materials
and the structure can be modified by functional substitution to get desired
optical nonlinear response. Conjugated compounds with electron donor and
acceptor substituents are extensively studied for such optimizations. These
materials generally show high second harmonic generation efficiency due to
the presence of delocalized electrons. Chalcone based materials portray prop-
erties of a good nonlinear material like higher power conversion efficiency,
chemical resistance with high damage threshold and these properties can be
further enhanced with a suitable electron donor and acceptor substitution.
Due to the conjugation the chalcone derivatives also display excellent blue
light transmittance, large non-linear optical coefficients, and relatively short
cutoff wavelength in transmission [7, 8, 9, 10, 11, 12, 13, 14, 15].
A series of new chalcones were synthesized with a minor modification in
the well known (D-π-A-π-D) or (D-π-A-π-D) motif [16]. Chalcones are cross
conjugated system as the carbonyl (C=O) group in the center operates as
an electron acceptor. So, charge transfer is assumed to initiate from the
ends of the molecule towards its center portion [17]. For each of the four
compounds reported in this work, the -OH group acts as a donor group
in conjugation with the α, β unsaturated carbonyl group. The motif was
further tuned with the introduction of electron withdrawing -NO2 group in
ortho position to the hydroxyl group. In another part of the system, different
kinds of substituents were incorporated. In the first sample, the substitution
is -H, which has no electron donating or electron withdrawing effect. In
the second sample, an electron withdrawing effect was introduced using -Br
substituent. An even higher electron withdrawing effect with -Cl substitution
was brought about in the third sample. The substituent Methoxy group, -
OCH3, (-OMe) was chosen to insert electron donating effect in the fourth
compound. The structure of these compounds were identified using NMR
spectrometer. Linear optical properties of the samples were studied using
emission and absorption spectra. A comparative study of their nonlinear
optical properties was done by z-scan measurements.
2

2. Experimental
2.1. Chemicals
Para Chloro Acetophenone, (GC 98%), para bromo acetophenone (GC
98%) and Para methoxy acetophenone (GC 99%) were obtained from Sisco
Research Laboratories Pvt. Ltd, Para hydroxy benzaldehyde (GC 98%)
and benzaldehyde (GC 98%) were obtained from Spectrochem. Chemical
reagents were used without any further purification.
2.2. Synthesis
Synthesis of 4-hydroxy-3 nitro benzaldehyde was accomplished via ni-
tration of para hydroxy benzaldehyde following the method similar to that
reported by P. Ionita [18]. These compounds were synthesized following
the conventional method of Claisen-Smith reaction. A solution of acetophe-
none derivative (3.6 mmol) and 4-hydroxy-3-nitrbenzaldehyde (3.6 mmol) in
ethanol (10 ml) was warmed to 30-40o C in water bath. This hot solution
was treated with a small portion of NaOH (10 mM). The reaction mixture
was stirred for 1-4 hr and then left overnight. Progress of the reaction was
monitored by thin layer chromatography using chloroform: methanol (9:1)
as developing solvent. The resulting red solution was poured into crushed ice
and carefully acidified using concentrated hydrochloric acid. The chalcones,
which separated as a yellow solid, were collected by filtration after washing
with water. The compounds were further purified by silica gel column (60-
120 mesh) chromatography using chloroform as eluent. The general scheme
of reaction and the structures of the compounds are given in Fig.1. In this
article, the compounds with the substitution -R as Cl, Br, H and OCH3 were
coded as OHNH, OHNBr, OHNCl and OHNMe respectively.
2.3. Instrumentation
1H (400 MHz spectrometer) and 13C (500 MHz spectrometer) Nuclear
magnetic resonance spectra were recorded on Bruker DPX and the chemical
shifts are expressed in ppm using tetramethylsilane as internal standard.
Steady-state absorption spectra were recorded on a Shimadzu UV-1601PC
absorption spectrophotometer. Fluorescence spectra of the samples were
measured with a PerkinElmer LS 45 spectrofluorometer and the spectra were
corrected for the instrument response function. Quartz cuvettes of 10 mm
optical path length received from PerkinElmer, USA (part no. B0831009)
3

Figure 1: Reaction scheme for the synthesis of 1-(4-substituted)-3-(4-hydroxy-3-
nitrophenyl) prop-2-en-1-one compounds. Here R represents any one of -Cl, -Br, -H,
or -OCH3.
and Hellma, Germany (type 111-QS) were used for measuring absorption and
fluorescence spectra, respectively.
Z-scan measurements were carried out with the second harmonic of a
Q-switched Nd-YAG laser pulses at 532 nm with a pulse duration of 28 ns
(FWHM) with 1 Hz repetition rate. The laser beam was focused with a 20
cm focal length lens and the spot size at the focus was ∼60 µm. During
Z-scan the sample was kept in 1 mm path-length cell . Concentration of the
samples used in the z-scan experiment was 1.3 × 10−8 M. The linear spectrum
was found to remain same before and after the Z-scan measurements which
ensured the stability of the compounds throughout the measurement.
3. Results and Discussion
3.1. NMR Spectrum
1. (E)-1-(4-bromophenyl) -3- (4-hydroxy-3-nitrophenyl) prop-2-en-1-one
(OHNBr): yellow solid, 1H NMR (400 MHz, CDCl3) 10.76 (s, 1H),
8.39(s, 1H), 7.47 (d, 1H, J 15.6 Hz), 7.78(d, 1H, J 15.6 Hz), 7.23(d,
1H, J 8 Hz) 7.87-7.91(m, 4H), 7.89-7.86(dd, 1H, J 2Hz and J 2Hz) 13C
(500 MHz, CDCl3) 188.6, 156.4, 142.1, 136.6, 136.5, 132.1, 130.0,
127.5, 121.1, 121.9, 120.9
2. (E)-1-(4-chlorophenyl) -3- (4-hydroxy-3-nitrophenyl) prop-2-en-1-one
1
(OHNCl) yellow solid, H NMR (400 MHz, CDCl3) 10.76(s, 1H),
8.39 (s, 1H), 7.47 (d, 1H, J 15.6 Hz), 7.78(d, 1H, J 15.6 Hz), 7.23 (d, 1H,
J 8Hz), 7.99-7.95 (m, 4 H), 7.87.89-7.89 (dd, 1H, J 2Hz and J 2Hz) 13C
(500 MHz, CDCl3) 188.4, 188.3, 156.3, 142.0, 136.6, 129.9, 129.8,
129.0, 125.1, 121.9, 120.9
4

Figure 2: UV-Vis absorption spectra of the four Chalcone derivatives.
3. (E) -3- (4-hydroxy-3-nitrophenyl) -1- (4-methoxyphenyl) prop-2-en-1-
1
one (OHNOMe): yellow shiny solid, H NMR (400 MHz, CDCl3)
10.74(s, 1H), 8.37(s, 1H), 7.47(d, 1H, J 15.6 Hz), 7.75(d, 1H, J 15.6
Hz), 7.22(d, 1H, J 8 Hz), 6.98-7.01(m, 2H), 7.89-7.86 (dd, 1H, J 2Hz
and J 2Hz) 3.09(s, 3H) 13C (500 MHz, CDCl3) 188.5, 187.9, 156.0,
140.7, 136.6, 130.9, 130.6, 127.9, 122.4, 120.8, 113.9, 55.5
4. (E) -3- (4-hydroxy -3- nitrophenyl) -1- phenylprop -2- en-1-one (OHNH),
1
pale yellow shiny solid, H NMR (400 MHz, CDCl3) 9.96(s, 1H),
8.39 (s, 1H), 7.28(d, 1H, J 16 Hz), 7.78 (d, 1H, J 16 Hz), 7.33(d,1H, J
8 Hz), 7.51-7.56(m, 1H), 7.61(d, 2H, J 8 Hz), 8.17-8.14 (dd, 1H, J 2Hz
and J 2Hz).
3.2. Linear Optical Properties
The linear absorption spectra of the chalcone derivatives are represented
in Fig.2. The spectra of all the compounds were recorded at room tempera-
ture in chloroform solution with of 0.5 × 10−8 M concentration. Clearly, all of
them show two strong peaks in the UV-region, which are due to π-π* and n-
π* transitions (Table. 1). The π-π* and n-π* transitions are attributable to
the presence of aromatic ring and C=O group respectively. The compounds
studied here belong to a group of α, β unsaturated aromatic compounds.
The aromatic benzene ring is the source of π electrons. In the present case,
the aromatic ring is in conjugation with the carbonyl carbon. Interaction be-
tween the benzene ring and the carbonyl carbon induces an opposite polarity
and the ring becomes electron deficient. The presence of carbonyl group gives
5

Figure 3: Normalized emission spectra of the four Chalcone derivatives when excited with
320 nm wavelength light.
Table 1: Peak attribution in the absorption and emission spectrum for all the samples.
Absorption Band
Peak (nm) Peak Attribution Peak (nm) Width (nm)
Emission Band
Compound
OHNH
257
315
318
394
321
400
316
395
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
π-π*
n-π*
454
318
452
446
90
82
OHNBr
OHNMe
OHNCl
105
94
6

the possibility of n-π* and also π-π* transitions. Unsaturated molecules that
contain oxygen undergo n-π* transitions due to the presence of non-bonding
electrons in the oxygen atom [19]. In the spectral region from 420 nm to 800
nm the compounds are nearly transparent. Note that the linear absorption
coefficient of the samples is negligible at the wavelength of Z-scan measure-
ments (532 nm). Figure 3 shows the emission spectra of the compounds when
excited at 320 nm. All the compounds have an emission maximum near 450
nm and the emission spectra has a full width at half maximum of nearly
100 nm. We attribute the shift between the absorption band edge and the
emission peak wavelength to the solvent induced stokes-shift [20, 21].
The optical energy gap was calculated from the absorption spectrum of
each sample (Fig.4) [22]using the Tauc’s plot. Where α is the linear absorp-
tion coefficient, h is the Planck’s constant and ν is the optical frequency.
In case of indirect bandgap materials, both the bandgap (Eg) and phonon
characteristic energy (Ep) defines the variation of linear absorption with inci-
dent photon energy. The dual slope behavior of the Tauc plot near the band
edge clearly indicates that the compounds have indirect bandgap [23]. By
fitting two straight lines to the near band edge data (as presented in Fig.4)
and identifying where it intersects the photon energy axis, we estimated the
values of (Eg − Ep) and (Eg + Ep) for each of the sample [23]. From these
two parameters the Eg and Ep were calculated. The values of the bandgap
obtained by this method are 2.9 eV, 2.88 eV, 2.96 eV, and 2.89 eV for OHNH,
OHNCl, OHNBr, and OHNMe respectively and their corresponding phonon
characteristic energies are 0.25 eV, 0.41 eV, 0.34 eV and 0.37 eV. (Table-2).
3.3. Nonlinear Optical Properties
Figure 5 shows the open aperture data of Z-scan measurements with 532
nm beam for the samples. Single laser pulse energy was ∼ 570 µJ. When
the samples are far off the focal point of the beam the transmission (larger z
values) is ∼ 1.0, as at 532 nm the samples have negligible absorption at low
intensities. On the other hand, near the focal point the transmission reduces
and reaches a minimum at z = 0. The lowering of transmission at higher
intensities refers to nonlinear absorption.
The rate of change in intensity (I) as the beam propagates through a
sample which has absorption originating only from third-order susceptibility
can be written as
dI
= −βI2,
(1)
dz
7

Figure 4: Tauc plot of the compounds for estimation of the bandgap. Solid curve is the
experimental data. Blue dashed lines and red dotted lines are the linear fit to a part of
the data to calculate the values of (Eg − Ep) and (Eg + Ep) respectively.
8

Figure 5: Open aperture z-scan data of the chalcone derivatives measured with pulse
energy ∼ 570 µJ. Solid lines are the best fit to the data using Eq.3.
9

where β is the nonlinear absorption coefficient related to the imaginary part of
third-order nonlinearity of the sample. For a Gaussian intensity distribution
(in space and time), when the sample is kept at z, the intensity distribution
at the entrance segment of the sample is given by,
[
]
(
)
( )
2
2
I0
r
t
I (r, t, z) =
exp −2
−
,
(2)
1 + (z/z0)2
ω0
t0
where ω0 is the beam radius, I0 is the peak intensity and t0 is the pulse width.
z0 is the Rayleigh range given by z0 = πω02/λ, where λ is the wavelength of
light used. Using Eq.1 and Eq.2 the energy of the pulse transmitted through
the sample kept at z (T) can be obtained by integration over space and time
and is given by [24],
∫
∞
[
(
)]
1
ln 1 + q (0, 0, z) exp −τ2 dτ
(3)
√
T (z) =
πq (0, 0, z)
−∞
where, q(r, t, z) = βI(r, t, z)L and L is the thickness of the sample. The
experimental z-scan data was fit to Eq.3 by solving it numerically with β
as the fitting parameter. The best fit values of β are given in the Table.2.
Among the four samples, OHNCl showed the maximum nonlinear absorption
which is nearly 3 times than that of the OHNH. Note that the samples show
some emission at 532 nm. This implies that there are some states which can
absorb the wavelength at which the z-scan experiment was performed. At
higher intensities these carriers which are excited by a single 532 nm photon
may farther get excited to higher energy states at 266 nm where the sample
has strong absorption (Fig. 2). Hence, we attribute the measured nonlinear
absorption to the two-step two-photon absorption involving vibrational states
[25].
As discussed earlier, the substituents in the compounds have different
electron donating or withdrawing effects. Methoxy group (-OMe) has elec-
tron donating capacity, -Br and -Cl has electron withdrawing effect while
H has no electron donating or electron withdrawing effect. However, the
nonlinear absorption did not show any correlation with electron donating or
withdrawing effects. On an average, the nonlinear absorption coefficient of
the samples reported here is much higher as compared to other compounds
of similar genre [26, 27, 28]. Thus, the (E)-1-(4-substituted)-3-(4-hydroxy-
3-nitrophenyl) prop-2-en-1-one derivatives are strong nonlinear absorption
materials for operation at 532 nm.
10

Figure 6: Variation of nonlinear absorption coefficient of the four samples (a) with the
phonon characteristic energies, Ep, and (b) with the (2hν − Eg + Ep). The red line is the
best fit to the data with an exponential growth and linear functions for the above two
cases respectively.
We found that the nonlinear absorption of (E)-1-(4-substituted)-3-(4-
hydroxy-3-nitrophenyl)prop-2-en-1-one derivatives do not reveal any consis-
tent variation with the bandgap of the material (See Table.2) but mani-
fested intriguing relation with the phonon characteristic energy. Figure 6(a)
shows the variation of nonlinear absorption of the four compounds with the
phonon characteristic energies. The nonlinear absorption increases exponen-
tially with the increase in photon characteristic energies. Studies depicted
that phonons can play a strong role in the nonlinear absorption properties of
different kinds of materials [25, 29, 30, 31, 32]. Hence, the phonons and the
vibrational states must be playing a strong role in the nonlinear absorption
observed in the present samples in nanosecond time scale [25].
A. R. Hassan has theoretically studied the dependence of two-photon
absorption on the indirect bandgap of bulk semiconductors and semiconduc-
tors confined in one or two dimensions [33]. They have affirmed that the
two-photon absorption coefficient scales with (2hν − Eg + Ep)σ where ν is
the frequency at which β was measured. The value of σ depends on the
dimensions of the semiconductor [33]. Although chalcones are very different
from semiconductors, it would be interesting to see how the measured non-
linear absorption scales with (2hν − Eg + Ep). In this present report, we
explored that the nonlinear absorption coefficients of the samples increase
nearly linearly with (2hν − Eg + Ep) (Fig.6(b)).
11

Table 2: The measured nonlinear absorption coefficient of the samples along with their
corresponding bandgap (Eg) and phonons characteristic energies (Ep)
Compound Eg (eV) Ep (eV) β (cm/GW)
OHNH
OHNBr
OHNMe
OHNCl
2.9
0.25
0.34
0.37
0.41
11.5
17
22
2.96
2.89
2.88
32
4. Conclusions
Four new chalcone derivatives, abbreviated as OHNH, OHNBr, OHNMe
and OHNCl were synthesized using a green and cheap synthetic method.
Among them, OHNCl showed the maximum and OHNH had the least non-
linear absorption coefficient . We have shown that the measured nonlinear
absorption coefficient of these samples increases exponentially with the in-
crease in phonon characteristic energy and the nonlinear absorption coeffi-
cient scales linearly with (2hν −Eg +Ep). The origin of nonlinear absorption
in nanosecond time scale must be strongly mediated by phonon contribu-
tions. The compounds presented here exhibits satisfactory nonlinear optical
responses and thus can be considered for designing suitable optical devices
for optoelectronic applications.
Acknowledgments
A. S. would like to thank DST, INSPIRE Fellowship New Delhi, Govern-
ment of India for award of research fellowship and NMR Research Centre,
IISc Banglore for providing the NMR data. J. J. thank Mr. Salahuddin
Khan, USL, LPAS, RRCAT and Mr. S. Ananthakumar, Crystal Growth
Centre, Anna University for their suggestions and fruitful discussions. Au-
thors are grateful to Dr. Rama Chari, USL, LPAS, RRCAT for her support
in this work. The authors also thank Dr. H.S. Rawat, Head, LPAS, RRCAT
for his encouragement and support in this work.
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16

Highlights
Synthetic method of a new series of (E)-1-(4-substituted)-3-(4-hydroxy-3-
nitrophenyl)prop-2-en-1-one nonlinear optical compounds is reported.
It has been shown that the measured nonlinear absorption coefficient of
these materials depend on the phonon characteristic energies, indicating
the role of phonon in the origin of nonlinear absorption.

Graphical Abstract
The
variation
of
nonlinear
absorption
coefficient
of
the
(E)-1-(4-substituted)-3-(4-hydroxy-3-nitrophenyl) prop-2-en-1-one compounds (a) with the
phonon characteristic energies, Ep and (b) with the (2h - Eg + Ep). The red line is the best fit
to the data with an exponential growth function and linear function for the above two cases
respectively.