Synthesis, characterization and nonlinear optical properties of symmetrically substituted dibenzylideneacetone derivatives

Article abstract of DOI:10.1016/j.cplett.2014.10.043

We report here the nonlinear optical (NLO) properties of eight bis-chalcones of D-π-A-π-D type. These dibenzylideneacetone (DBA) derivatives are synthesized by Claisen-Schmidt reaction. The compounds are characterized by UV-vis, FTIR, ¹H NMR, <

Full text of DOI:10.1016/j.cplett.2014.10.043

Chemical Physics Letters 616–617 (2014) 142–147
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Chemical Physics Letters
journal homepage: www.elsevier.com/locate/cplett
Synthesis, characterization and nonlinear optical properties of
symmetrically substituted dibenzylideneacetone derivatives
N. Sunil Kumar Reddya, Rajashekar Badama, Romala Sattibabub, Muralikrishna Mollib,
V. Sai Muthukumarb, S. Siva Sankara Saib, G. Nageswara Raoa,∗
a Department of Chemistry, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Andhra Pradesh 515134, India
b Department of Physics, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Andhra Pradesh 515134, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2014
In final form 19 October 2014
Available online 24 October 2014
We report here the nonlinear optical (NLO) properties of eight bis-chalcones of D-␲-A-␲-D type. These
dibenzylideneacetone (DBA) derivatives are synthesized by Claisen–Schmidt reaction. The compounds
are characterized by UV–vis, FTIR, 1H NMR, 13C NMR, mass spectroscopy and powder XRD. By substitut-
ing different groups (electron withdrawing and electron donating) at ‘para’ and ‘meta’ positions of the
aromatic ring, we observed an enhancement in second harmonic generation with substitution at ‘para’
position. These compounds have also showed higher two-photon absorption compared to other chal-
cones reported in literature. These compounds, exhibiting both second and third order NLO effects, are
plausible candidate materials in photonic devices.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
The enhanced NLO response of organic chromophores could
be mainly attributed to effective tuning and alteration of inter-
The curiosity of scientists in synthesizing organic molecules
for nonlinear optical (NLO) applications such as optical switches,
THz wave generation [1], electro-optic modulators [2–5], passive
optical limiters and frequency conversion [6,7] has exponentially
increased in recent years. The organic molecules have overpowered
inorganic materials due to their high optical nonlinearity, ultra-
fast response and versatile ability to tune the optical properties
through structural modifications [8]. All these characteristics make
them unique and attractive for applications in organic photonic
devices. Various types of organic compounds have been inves-
tigated for their second and third order NLO properties. These
include chalcones [1,7], stilbazolium compounds [9], fullerene
based compounds [10], inorganic–organic hybrids [11,12] and
many more. Optical limiters based on nonlinear optical absorption
(NLA) have been reported using phthalocyanines, organometal-
lic cluster compounds [13], complexes [14,15] and several other
inorganic compounds like metal nanoparticles, semiconductor
quantum dots [16]. Generally nonlinear absorption in these mate-
rials arise from effects like saturable absorption, two-photon
or multiphoton absorption, free-carrier absorption, excited state
absorption, etc. [14].
molecular and intramolecular interactions. The intramolecular
charge transfer between strong donor and acceptor groups aids
in enhancing hyperpolarizabilties at molecular level. For exam-
ple, conjugated TTF-Quinone molecules have exhibited higher
third order NLO response owing to increase in dipole moment
arising from intramolecular charge transfer [17]. Similarly, the
intermolecular interaction like hydrogen bonding favour head
to tail alignment of molecules that leads to formation of non-
centrosymmetric crystal structures which ultimately results in
efficient second harmonic generation. An optimized NLO chro-
mophore is expected to possess (i) an extended conjugated system,
(ii) a large dipole moment difference between excited state and
ground state electronic configuration (charge asymmetry). The
charge asymmetry is achieved by introducing different functional
groups substituted in the molecule. The presence of appropriate
strong electron donor and strong acceptor groups can improve
the polarizability in either or both ground and excited electronic
states leading to large molecular hyperpolarizabilities and good
crystallizability [18]. The extensive delocalization of ␲-electrons
which favours easier polarizability is achieved by the presence of
strong electron donor (D) and strong acceptor (A) groups with a
␲-electron bridge joining D and A. The presence of D and A no
doubt enhances the nonlinear absorption, but the co-planarity of
the molecule plays a key role in enhancing the extent of conjuga-
tion, which in turn improves the polarizability of the molecule [19].
∗
Corresponding author.
E-mail address: gnageswararao@sssihl.edu.in (G.N. Rao).
http://dx.doi.org/10.1016/j.cplett.2014.10.043
0009-2614/© 2014 Elsevier B.V. All rights reserved.

N. Sunil Kumar Reddy et al. / Chemical Physics Letters 616–617 (2014) 142–147
143
Table 1
Various design strategies have been established in the past to tailor
Yield and melting points of DBA derivatives.
the molecules with large hyperpolarizabilities. They are asymmet-
ric D-␲-A; symmetric D-␲-D; A-␲-A; D-␲-A-␲-D; A-␲-D-␲-A; and
branched (A)n-D and (D)n-A motifs where n is greater than 2 [19].
Most of the D-␲-A-␲-D type, extended ␲-conjugated molecules
may have the band gap occurring in either the visible region or in
the UV region. This feature enables them to have high two-photon
absorption (2PA) cross-section (non-resonant nonlinearity) in the
near infrared region or at visible region respectively, where they
are transparent.
Sample label
Melting point◦C
Recrystallizing solvent
Yield
%
3-DBDBA
4-DBDBA
4-DTDBA
4-DNMDBA
4-DIDBA
3-DCDBA
2-DCDBA
4-DCDBA
128–130
220–222
177–179
198–201
88–90
118–120
116–117
192–194
MeOH
MeOH-CHCl3
MeOH
Pet.ether-CH2Cl2
MeOH
MeOH
66
74
85
61
78
80
77
76
MeOH
MeOH-CHCl3
Of all the motifs aforementioned, D-␲-A-␲-D has very capti-
vating features as well as applications. Diarylideneacetones with
D-␲-A-␲-D molecular configuration are closely related to the class
of organic chromophores known as ‘chalcones’. In recent years,
this class of molecules have been extensively used in numerous
applications ranging from anti-cancer [20,21], radio-protective and
anti-viral activities [22], synthons for heterocycles [23], chemopro-
tective agents, phase 2 enzyme inducers, radical scavengers [24],
catalysis [25,26] and nonlinear optics [27]. Dibenzylideneacetone
derivatives are known for their anti-cancer activity [28–34]. Some
of these compounds showed considerable anti-bacterial [35] and
anti-malarial activity [36]. Photo-physical properties of some of
these compounds have also been investigated [37]. Though chal-
cone derivatives have been extensively investigated for their SHG
NLO activity [1,7,27], similar studies on bis-chalcones viz., diben-
zylideneacetone derivatives are sparse.
recrystallization. Melting points of all the samples were determined
by open capillary method and are uncorrected.
2.2. Instrumentation
Powder X-ray diffraction patterns of all the samples were
recorded with PANalytical X’Pert Pro MPD diffractometer using
˚
Cu K˛ radiation (ꢀ = 1.54 A) as the source with the following sett-
ings: voltage 45 kV, current 40 mA and scan step size 0.050. The
FTIR spectra were recorded between 400 and 4000 cm−1 using KBr
pellets employing Thermo-Nicolet Avatar 370 spectrophotometer.
The UV–vis spectra in chloroform were recorded in the wavelength
range 200–600 nm using a Shimadzu 2450 spectrophotometer. 1
H
NMR spectra were obtained on VARIAN 400 MHz, 13C NMR on VAR-
IAN 100 MHz using TMS as the internal standard and CDCl3 as
solvent. For mass spectra AGILENT 6430 Triple Quad LC/MS was
employed.
In this article, we report the synthesis, characterization and
nonlinear optical properties of these new class of bis-chalcones
derived from DBA, namely, (1E, 4E)-1,5-bis (3-bromophenyl)-1,4-
pentadiene-3-one (3-DBDBA), (1E, 4E)-1,5-bis(4-bromophenyl)-
1,4-pentadiene-3-one
phenyl)-1,4-pentadiene-3-one
N,N-dimethylaminophenyl)-1,4-pentadiene-3-one (4-DNMDBA),
(1E,4E)-1,5-Bis(4-isopropylphenyl)-1,4-pentadiene-3-one (4-
(1E,4E)-1,5-bis(3-chlorophenyl)-1,4-pentadiene-3-one
(1E,4E)-1,5-Bis(2-chlorophenyl)-1,4-pentadiene-3-
one (2-DCDBA), (1E,4E)-1,5-bis(4-chlorophenyl)-1,4-pentadiene-
3-one (4-DCDBA). The nonlinear optical properties, viz., Second
Harmonic Generation (SHG) and Multiphoton absorption of these
compounds have been investigated. Finally, we have attempted
to correlate the observed NLO enhancement to different elec-
tron pumping and withdrawing groups substituted at different
positions in the aromatic ring. Some of these compounds namely
4-DTDBA and 4-DBDBA showed very high SHG compared to
related compounds [1,38–41]. These two compounds also have
superior third order NLO properties exhibiting higher two photon
absorption than reported DBAs [42].
(4-DBDBA),
(1E,4E)-1,5-bis(4-methyl-
2.3. Nonlinear optical measurements
(4-DTDBA),
(1E,4E)-1,5-Bis(4-
2.3.1. Powder SHG measurement
The SHG efficiency measurement was carried out using the
conventional Powder (Kurtz and Perry) SHG technique [44] with
Nd:YAG laser excitation wavelength at 1064 nm. The pulse energy
of 6 mJ/pulse was used as an excitation source with a pulse width of
8 ns at a repetition rate of 10 Hz. It was optically steered to be inci-
dent on to the microcrystalline powder samples which were tightly
packed in a glass capillary. Second harmonic separator was used to
remove the fundamental harmonic from the output obtained. The
second harmonic wavelength (532 nm) generated from the sample
was detected by a sensitive photomultiplier tube and the SHG sig-
nal was converted into an electrical signal. The converted electrical
signals were displayed on an oscilloscope. Finely ground urea crys-
tals with uniform particle size were used as the reference in the
SHG experiment. The SHG efficiency of the samples with reference
to urea is listed in Table 2.
DIDBA),
(3-DCDBA),
2. Experimental
2.3.2. Third order NLO measurement
2.1. Synthesis of various substituted dibenzylideneacetones
Z-scan technique [45] was employed for the investigation of the
third order nonlinearity in all the DBA derivatives. A Q-switched
frequency-doubled (532 nm) Nd:YAG laser (Surelite III, Continuum)
with a 10 ns pulse width was used as the excitation source. The
input pulse was divided into two parts using a beam splitter. The
reflected part from the beam splitter was taken as the reference for
the incident light energy; and the transmitted part was focused on
to the sample using a converging lens (with focal length 20 cm) that
yields a gradual variation in the incident intensity as the sample was
translated across the focal plane. The reference beam and the trans-
mitted beam were monitored using calibrated silicon photodiode
(UDT sensors). The sample was mounted on a computer controlled
automated translation stage which varies the sample’s position
along the z-axis with respect to the focal point (z = 0). By keeping
constant incident laser energy, the light transmission through the
The substituted dibenzylideneacetones (DBAs) were synthe-
sized by Claisen–Schmidt reaction [43]. A solution of ethanol
(50 ml) and 10% sodium hydroxide (50 ml) were taken in a round
bottomed flask (rbf). One-half of previously prepared mixture of
substituted benzaldehyde (0.05 mol) and acetone (0.025 mol) was
added to the NaOH-EtOH solution with stirring at room tem-
perature. A yellow flocculent solid precipitated within 2–3 min
of addition. After 15 min, the remaining half of the substituted
benzaldehyde–acetone mixture was added into the rbf. The mix-
ture was stirred for further 45 min. The contents of the rbf were
filtered and washed repeatedly with ice-cold water to eliminate
the residual alkali. The solid thus obtained was dried overnight at
room temperature in a desiccator. The compounds were purified by

144
N. Sunil Kumar Reddy et al. / Chemical Physics Letters 616–617 (2014) 142–147
Figure 1. Molecular structure of various DBA derivatives synthesized.
sample was measured as a function of the sample position. In order
to preclude the influence of accumulative thermal effects, the laser
was operated in a single-shot mode. The data collections from both
photodetectors were done using the digital oscilloscope (YOKO-
GAWA DL1700) and retrieved to a PC for analysis using LabVIEW®.
Throughout our nonlinear optical measurements, the concentra-
tion of all the DBA derivatives was fixed at 3 mg/ml in chloroform.
The linear transmittance of all the samples was adjusted to be ∼82%
at 532 nm.
Figure 2. UV–visible absorption spectra of all DBA derivatives.
value. Bromo compounds also have similar values as their chloro
analogues. Because of the strong electron-pumping nature of N,N-
dimethylamino group, 4-DNMDBA has the largest ꢀmax of all the
DBAs. The isopropyl group in 4-DIDBA is more electron pumping
compared to the methyl group of 4-DTDBA and hence was found
to have a larger ꢀmax value.
3. Results and discussion
3.1. Compounds characterization
The DBA derivatives were characterized using UV–visible
absorption spectroscopy, FTIR, 1H NMR, 13C NMR, mass spectro-
scopic technique and powder XRD. In the supplementary material,
1H NMR, 13C NMR and mass spectroscopy data have been provided.
3.1.3. Energy band gap determination
The UV–visible absorption spectroscopy is frequently used to
determine the energy band gap. In the present case, optical trans-
mission spectra of DBA derivatives dispersed in chloroform were
recorded between 200 nm and 600 nm. The absorption coefficient
(˛) was calculated from the transmission values and a tauc plot was
generated [46]. The tauc equation used for the analysis is given by,
3.1.1. Physical data
All the compounds have been purified by recrystallization and
the solvents for recrystallization, melting points and significant
yields have been listed in Table 1. In general crystals with higher
melting point are preferred for making devices. Figure 1 shows the
molecular structure of each DBA derivative that has been synthe-
sized.
(˛hꢁ)2 = const · (hꢁ − Eg)
(1)
where Eg is the energy band gap. The linear portion of the graph
was extrapolated to the energy axis and the energy band gap values
were determined (Table 2).
3.1.2. UV–visible absorption spectroscopy
UV–visible absorption spectra of all the DBA derivatives have
been shown in Figure 2. Typically all these compounds showed
two absorption maxima. The absorption maximum (ꢀmax) in these
␣,␤-unsaturated carbonyl compounds in the UV–visible region
can be assigned to the n → ␲* transition of carbonyl. The UV–vis
spectra can be explained taking terminal substitution of various
electron donating groups into consideration. The lone pair on
chlorine of 2-DCDBA was found to be more in conjugation with
the carbonyl compared to 3-DCDBA and thus has a larger ꢀmax
3.1.4. FT-IR vibrational spectroscopy
The recorded FTIR spectra revealed the presence of characteris-
tic peaks (shown in Table 3) corresponding to different functional
groups present in different DBA derivatives.
3.1.5. Powder XRD studies
It was inferred from the diffraction patterns in Figure 3 that all
the samples are crystalline in nature. The d-spacing in Å of various
Table 2
UV–visible absorption maxima, SHG efficiency, energy band gap and two-photon absorption coefficient values of all DBA derivatives.
S. no.
Sample
UV–vis absorbance
maxima
nm
SHG signal comparison
with urea
× times
Energy band gap
eV
Two-photon
absorption coefficient
m/W
1
2
3
4
5
6
7
8
3-DBDBA
4-DBDBA
4-DTDBA
4-DIDBA
3-DCDBA
2-DCDBA
4-DCDBA
4-DNMDBA
324, 242
335, 236
343, 237
341, 311
325, 237
330, 239
335, 237
458, 254
0.01
0.35
6.84
0.01
0.01
0.25
5.03
0.45
3.49
3.38
3.26
3.28
3.51
3.44
3.36
2.46
1.8e−11
7e−11
7.4e−11
3.6e−11
3.5e−11
3.2e−11
0.98e−11a
5.98e−11a
a
Reference [42].

N. Sunil Kumar Reddy et al. / Chemical Physics Letters 616–617 (2014) 142–147
145
Table 3
Assignment of functional groups in DBA derivatives from FTIR spectra.
Sample label
ꢁc=o
cm−1
␯
␯
(Ar)
ArC-H (oop)
cm−1
ꢁmisc
cm−1
c=c
cm−1
c=c
cm−1
3-DBDBA
4-DBDBA
4-DTDBA
4-DNMDBA
1653
1649
1667
1634
1627
1592
1644
1602
1557, 1469
1560, 1486
1566, 1509
1560, 1510
658, 791, 874
ꢁC-Br: 993
ꢁC-Br: 1008
823
822
817
ꢁsp3 C-H: 2916
ꢁC-N
:
1344,sp3C-H:
2894, 2802
ꢁsp3 C-H:
4-DIDBA
1648
1623
1564, 1511
830
2958,2869
ꢁC-Cl: 1076
ꢁC-Cl: 1039
ꢁC-Cl: 1091
3-DCDBA
2-DCDBA
4-DCDBA
1655
1668
1667
1629
1615
1626
1561, 1479
1560, 1467
1564, 1489
684, 794, 875
763
822
DBA derivatives have been reported in the supplementary infor-
mation (Table S1).
highest SHG efficiency of 2.46 times that of urea because of strong
resonance effect of N,N-dimethyl amino group in the para position.
N,N-dimethyl amino is a stronger electron donating group than
methyl but has lesser SHG efficiency because 4-DNMDBA absorbs
in visible region. 4-DCDBA had higher SHG value than 4-DBDBA
due to greater resonance effect of Cl than Br. This is because the
energy difference involving 3p orbital of chlorine and 2p orbital of
benzene carbon is less compared to energy difference of bromine
4p orbital and 2p orbital of benzene carbon. Meta substituted
analogues showed lesser SHG efficiency than the p-substituted
derivatives because the substituents at meta position are not in
direct conjugation with carbonyl group (Figure 4).
3.2. SHG measurement
For compounds to show good SHG there should be an exten-
sive conjugation within the system. Both electron donating and
withdrawing groups play a major role in enhancing this type of
conjugation. In the present systems the benzene ␲ electrons are
in cross conjugation with the carbonyl group. All the compounds
under study were symmetrical about the central carbonyl group.
The chlorine and bromine atoms are amphiprotic, i.e., can act as
both electron donor and acceptor. Thus the molecules with Cl and
Br also fall into the category of D-␲-A-␲-D. According to Zhao
et al. [47], the ability of electron donation of the Cl depends on the
acceptors strength. The SHG efficiency of the samples with refer-
ence to urea has been listed in Table 2. Among all the compounds
that were studied, 4-DTDBA was found to have the highest SHG
efficiency and was found to be 6.84 times that of urea, because the
methyl group in para position is a strong electron donating group
by inductive effect and hyperconjugation. The SHG efficiency of
4-DTDBA was higher than the dibenzylidenecyclopentanones
reported [38] and also highest when compared to its many coun-
terparts of recent times [1,39–41]. However the SHG efficiency of
4-DTDBA was less than that of p-methoxydibenzylideneacetone
[48]. 4-DIDBA showed lesser SHG efficiency than that of 4-DTDBA,
although the isopropyl group is inductively better donor group
than methyl. This was attributed to the better hyperconjugation
effect of methyl group than isopropyl. 4-DNMDBA showed next
3.3. Third order NLO measurement
Z-scan method was used to investigate the third order NLO
property of these compounds. It is a highly sensitive measure-
ment with its entire simple experimental configuration. It has
been extensively used to determine the magnitude and sign of
the optical nonlinearity and a wide variety of samples have been
investigated. Conventionally, it is used in two major configurations
namely, ‘closed aperture’ and ‘open aperture’ that estimates non-
linear refraction and nonlinear absorption parameters respectively.
We have adopted the ‘open aperture’ configuration to measure the
intensity dependent nonlinear absorption. Typically, in an open
aperture z-scan, the nonlinear optical transmittance of the sample
is measured as a function of sample position, which is translated
across the focal plane of a converging lens focusing the intense laser
beam.
In general, organic molecules and chromophores express
various kinds of nonlinear optical absorption through various
mechanisms like free-carrier absorption, saturable absorption,
multiphoton absorption and excited state absorption. Open aper-
ture z-scan configuration is sensitive to the presence of NLA but will
not be able to infer the kind of NLA. In general, numerical modelling
is adopted to fit the experimental for determining the type of NLA.
We have fitted the data using the following nonlinear transmis-
sion equation which could incorporate different types of nonlinear
absorption based on Multiphoton absorption [49].
(1 − R)2 exp(−˛0L)
T(z) =
√
ꢂp0
ꢁ
ꢃ
ꢀ
ꢂ
+∞
×
ln
1 + p20 exp(−2x2) + p0 exp(−x2) dx
(2)
−∞
Here z is the sample position with respect to the focal point,
is the linear absorption coefficient, R is the Fresnel reflection at
˛
0
the interface of the sample material with air, L (= l) is the sample
length, and pn0 = nꢃ(n+1)((1 − exp(−n˛0l))/n˛0)(1 − R)nIn, I0 being
0
the intensity at the focal point, pn0 = q0 for a two-photon absorption
Figure 3. Powder XRD graphs of substituted DBA derivatives.

146
N. Sunil Kumar Reddy et al. / Chemical Physics Letters 616–617 (2014) 142–147
Figure 4. Open aperture z-scan curve for DBA derivatives fitted with 2PA equation in the ns excitation regime.
process with n = 1 and q0(z) = (ˇI0Leff /(1 + (Z2/Z02)) and ꢃ(n+1) is
the nonlinear absorption co-efficient.
the auxochrome is para substituted, then the extent of conjugation
is greater than when it is at the meta position. This can be eas-
ily understood by drawing the canonical forms of the molecules.
So, the nature of auxochrome and its position are important crite-
ria for increasing the extent of ␲-conjugation of the chromophore.
Among the various auxochromes we have employed, the molecule
with CH3 as a substituent at the 4th position was found to be
having the highest 2PA coefficient. This is because of the aforemen-
tioned reasons (hyperconjugation and inductive effect of CH3). This
molecule has shown better NLA than all the molecules of the DBA
family reported earlier [42].
In case of all the DBA derivatives, the mechanism of NLA has been
deduced to be an effective two-photon absorption (2PA) process.
Particularly, 4-DTDBA has shown highest nonlinear absorption
with two photon absorption coefficient (ˇ) of 7.4 × 10−11 m/W fol-
lowed by 4-DBDBA (7 × 10−11 m/W), 4-DIDBA (3.6 × 10−11 m/W)
and 3-DCDBA (3.5 × 10−11 m/W) (Table 2) that were found to be
higher than that of 4-DCDBA (0.98 × 10−11 m/W) reported earlier
[42].
The 2PA property of these molecules can be attributed to their
peculiar D-␲-A-␲-D type molecular structure. The coefficient of
2PA can be varied by the variation of ␲-electron donor and accep-
tor. The donor and the acceptor groups variation alter the extent
of ␲-electron delocalization. The introduction of strong ␲-electron
donor or acceptor increases the extent of ␲-electron delocalization
in the ground state. Consequently this leads to a large hyper-
polarizability that results in the improvement of NLO response
to the incident electric field [50]. Auxochrome is a strong ␲-
electron donating substituent that induces bathochromic shift to
the absorption maxima of the parent chromophore. The presence of
auxochrome increases the extent of ␲-electron conjugation which
is an outcome of the reduction of the electronic energy levels in
the chromophore. This can be easily understood by comparing the
absorption maxima of the chromophores. The larger the absorption
maxima, the greater the extent of conjugation. Another important
criteria is the position of the auxochrome on the benzene ring. If
4. Conclusion
Eight substituted dibenzylideneacetone derivatives have been
synthesized and were purified by recrystallization. These bis-
chalcones have also been well characterized by various spectro-
scopic techniques (UV–vis, FTIR, NMR and MS) and their crystalline
nature has been validated by powder XRD. Kurtz Powder method
and z-scan technique have been employed to investigate the sec-
ond and third order NLO properties respectively. By substituting
different groups – electron withdrawing and electron donating –
at the ‘para’ and ‘meta’ positions of the aromatic ring, we observed
an enhancement in the second harmonic generation with substitu-
tion only at the ‘para’ position for chromophores like 4-DTDBA and
4-DCDBA. Further, extensive conjugation in certain bis-chalcones
(4-DTDBA and 4-DBDBA) resulted in enhancement of third order

N. Sunil Kumar Reddy et al. / Chemical Physics Letters 616–617 (2014) 142–147
147
NLO effects. Open aperture z-scan measurement revealed stronger
two photon absorption in these organic chromophores. Thus, these
bis-chalcones with D-␲-A-␲-D type structure exhibiting both sec-
ond and third order NLO effects are plausible candidate materials
in photonic devices like wavelength convertors and optical limiting
devices.
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