D-A-π-D Synthetic approach for thienyl chalcones - NLO - a structure activity study

Article abstract of DOI:10.1016/j.jphotochem.2016.03.009

With the growing interest for organic molecules in Nonlinear Optical (NLO) applications, we have synthesized nine novel thienyl chalcones based on the D-A-π-D design. In order to establish the identity, these have been characterized in detail. Having followed the design based synthetic route, we have focused on two prime criteria for comparison; namely second harmonic generation (SHG) and non-linear absorption. In this work the role of the electron withdrawing groups, electron donating groups and extended conjugation, have been extensively studied vis-à-vis the NLO properties. The change in these properties by virtue of the molecular structure has been elucidated in this work as the structure activity relationship. Optical nonlinearity is studied using ultrafast (100 fs) laser pulses at 800 nm, employing the open aperture Z-scan technique. The compounds exhibit large effective three-photon absorption (3PA) coefficients, in the order of 10^-28 m³/W². These observations show that these compounds possess potential for application in all-optical limiting and switching devices.

Full text of DOI:10.1016/j.jphotochem.2016.03.009

Accepted Manuscript
Title: D-A-␲-D synthetic approach for thienyl chalcones –
NLO – a structure activity study
Author: P.J. Tejkiran M.S. Brahma Teja P. Sai Siva Kumar
Pranitha Sankar Reji Philip S. Naveen N.K. Lokanath G.
Nageswara Rao
PII:
S1010-6030(15)30322-1
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.jphotochem.2016.03.009
JPC 10163
To appear in:
Journal of Photochemistry and Photobiology A: Chemistry
Received date:
Revised date:
Accepted date:
14-12-2015
6-3-2016
8-3-2016
Please cite this article as: P.J.Tejkiran, M.S.Brahma Teja, P.Sai Siva Kumar,
Pranitha Sankar, Reji Philip, S.Naveen, N.K.Lokanath, G.Nageswara Rao, D-A-
rmpi-D synthetic approach for thienyl chalcones ndash NLO ndash a structure
activity study, Journal of Photochemistry and Photobiology A: Chemistry
http://dx.doi.org/10.1016/j.jphotochem.2016.03.009
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Title: D-A-π-D SYNTHETIC APPROACH FOR THIENYL CHALCONES –NLO- A
STRUCTURE ACTIVITY STUDY (JPC 10163)
[
a]
[a]
[a]
[b]
[b]
[c]
Tejkiran P J , Brahma Teja M S , Sai Siva Kumar P , Pranitha Sankar , Reji Philip , Naveen S ,
[
d]
[a]*
Lokanath N K , Nageswara Rao G .
[
a]
Department of Chemistry, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, A.P. 515134,
India.
*Email: gnageswararao@sssihl.edu.in
[
b]
Ultrafast and Nonlinear Optics Lab, Light and Matter Physics Group, Raman Research Institute,
Bangalore 560080, India.
[c]Institution of Excellence, University of Mysore, Manasagangotri, Mysore 570023, India
[d]Department of Studies in Physics, Manasagangotri, University of Mysore, Mysore, Karnataka, 570
0
06, India
Corresponding author: Dr. Nageswara Rao G, Professor, Department of Chemistry,
Sri
Sathya Sai Institute of Higher learning, Prasanthi Nilayam-515134, India,
Ph:
+919492595462, email: gnageswararao@sssihl.edu.in

GRAPHICAL ABSTRACT
Highlights

Based on D-A-π-D SYNTHETIC APPROACH we could synthesize nine novel thienyl chalcones with
high effective 3 photon absorption coefficient (3 PA) of order 10-28 m /W .
3
2
Of these, T-CHL-NDM was found to have the highest 3PA coefficient of about 105.0 x 10-28 m /W .
Structure activity relationship based on the functional group vis-à-vis its NLO properties was
established, and making minor modifications in the structure of the chalcones, desired 3PA values
could be obtained.
3
2




Structures of all compounds have been characterized by adequately.
These compounds will be useful in various applications like optical devices, communications, etc.

Abstract: With the growing interest for organic molecules in Nonlinear Optical (NLO) applications, we
have synthesized nine novel thienyl chalcones based on the D-A-π-D design. In order to establish the
identity, these have been characterized in detail. Having followed the design based synthetic route, we
have focused on two prime criteria for comparison; namely second harmonic generation (SHG) and non-
linear absorption. In this work the role of the electron withdrawing groups, electron donating groups and
extended conjugation, have been extensively studied vis-à-vis the NLO properties. The change in these
properties by virtue of the molecular structure has been elucidated in this work as the structure activity
relationship. Optical nonlinearity is studied using ultrafast (100 fs) laser pulses at 800 nm, employing the
open aperture Z-scan technique. The compounds exhibit large effective three-photon absorption (3PA)
coefficients, in the order of 10-28 m /W . These observations show that these compounds possess potential
3
2
for application in all-optical limiting and switching devices.
Keywords: Thienyl chalcones; Z-Scan, nonlinear optical properties (NLO); three photon absorption;
second harmonic generation (SHG).

1
. Introduction
In the scenario of modern research, nonlinear optical (NLO) studies have assumed unquestionable
importance, due to their applications in optical data storage, optical processing, optical computing, sensor
protection, optical switching, and various other photonic technologies. Improved research has extended
their application in THz wave generators, passive optical limiters, electro-optic modulators, and frequency
converters. 1-4 The choice of the material in these applications is based on, response times in picoseconds
5
or less, large nonlinear refractive and/or absorptive coefficients, and broad spectral response. Therefore
1
determination of nonlinear properties and response times of the compounds is decisive. In the process of
realizing this goal, organic compounds are chosen primarily due to their large diversity, and the flexibility
they offer in the synthesis, strength of electron acceptor or donor groups 6, 6a-6c, planarity in the molecule
7,
the molecular symmetry, and extended conjugation stretches. 8, 9 The susceptibilities of these molecules
can be additionally enriched by increasing the length of conjugation. However, these changes result in the
7
consequent decrease of the HOMO-first excited state energy gap. In order to obtain the best from these
molecules, researchers have established various strategies to design organic molecules with enhanced
nonlinear optical responses. These include synthesis and development of Acceptor-Donor-Acceptor (A-
2
D-A), Donor-Acceptor- Donor (D-A-D), Donor-π- Donor (D-π-D) types of organic systems. Chalcones
exhibit intra-molecular charge transfer, and this allows for the use of design-based synthesis achieving the
desired results. Molecules with similar structure allow for comparison with focus on the effect of
substituents upon the properties under study. The Structure Activity Relation therewith allows to assign
the change in the observed phenomena to the specific functional groups on the molecule.
An additional benefit of chalcones is that they have blue-light transmittance, and high propensity to
crystallize in non-Centro symmetric structure. 11,11a,12 Chalcones being organic molecules cannot be used
right away in applied photonic device applications as they get degraded or bleached when exposed to
extreme optical signals. 13-15 In order to overcome this shortcoming, they can be either doped into a
polymer matrix or made into a solution. 16 However the polymer matrix is cumbersome to formulate and
hence solutions of the compounds were made and the nonlinear optical studies were conducted. The
solvent of choice must essentially be transparent towards the laser signal, must possess high thermal and
photochemical stability. 17-20

Thienyl-chalcones which have a D-A-π-D molecular configuration are related to the class of organic
chromophores, chalcones. 3 Apart from their optical properties, they have been used in numerous
applications ranging from anti-cancer, radio-protective, cytotoxic 21 and anti-viral activities; as synthons
for heterocycles, chemo- protective agents, phase two enzyme inducers, radical scavengers, and catalysts;
and in nonlinear optics. 22-25 Thiophene containing polymeric compounds have been investigated, and are
found to exhibit good nonlinear optical properties by the effective 3PA process. 26 Owing to the numerous
2
7
applications of thienyl-chalcones and high nonlinear optical activity , in the present work we studied
nine chalcones, and report their synthesis, characterization, and nonlinear optical properties. Optical
nonlinearity is investigated using the Z-scan technique, employing ultrafast (femtosecond) laser pulses for
excitation. The observed effective three-photon absorption and the consequent optical limiting behavior
are discussed in detail. Second Harmonic Generation (SHG) of these compounds also has been
investigated. Finally, we correlate the observed NLO enhancement to the presence of extended
conjugation and different electron pumping and withdrawing groups substituted at different positions in
the aromatic ring.
2
2
. RESULTS AND DISCUSSION.
.1. Characterization.
The compounds were synthesized by Claisen-Schmidt condensation 28 and were characterized by UV-vis,
1
13
IR, H-NMR, C-NMR, and MS. The data is reported in Table-S in the supplementary data.
2
.1.1. Linear Optical Properties.
UV-visible absorption spectra for all the compounds is shown in Fig.1 and the λmax values are reported in
Table-1. All the compounds were found to have two absorption maxima. The λmax values for these α, β-
unsaturated carbonyl compounds can be attributed to the π
π* transition of the carbonyl group. The
spectra can be interpreted by taking the substitutions into consideration comparing with a non-substituted
one i.e. T-CHL-B whose λmax value stands at 320 nm. The λmax value for the compound T-CHL-NDM at
4
28 nm is the highest among the others, due to the conjugation by the electron pumping nature of the N,
N- dimethyl amino group. This is followed by T-CHL-SM, T-CHL-OH, and T-CHL-OM with λmax values
of about 363 nm, 356 nm, and 349 nm respectively. In all these compounds the absorption increases with
increasing capacity of donating electrons. Due to the increase in the conjugation between both the rings,

the λmax value for T-CHL-2T stands at 352 nm. Due to the nature of the iso-propyl group, which is a good
electron donating group, T-CHL-ISO has a λmax value of 331 nm. Whereas the λmax value for T-CHL- Cl
is 323 nm.
2
.1.2. FT-IR, NMR, & Mass spectra.
-1
In the FT-IR spectrum of T-CHL-B the νC=O is observed at 1650 cm which is characteristic of chalcones.
2
5
The frequency of this band decreased as the electron donating nature of the substituent on the benzene
-1
ring increased and the lowest value of 1630 cm is seen in the case of T-CHL-NDM due to the powerful
electron donating ability of –N(Me)
. 30 The pmr spectra of these compounds were completely analyzed
2
and the data is given in Table-S. Proton H-1 which is highly deshielded is observed at ~ δ7.80 - 8.14 as a
double doublet with an ortho and meta coupling (J = 3.6 – 4.0 Hz and 0.8 – 1.2 Hz). H-2 is seen as a
double doublet at δ7.17 – 7.34 with two ortho couplings (J = 4.8 – 5.2 and 3.6 – 4.0 Hz). H-3 signal
appeared at ~ δ7.66 – 7.94 as a dd (J=4.8-5.2 and 0.8-1.2 Hz). The two olefinic protons H-6 (δ6.99 – 7.56)
and H-7 (δ7.62 – 7.97) signals appeared as doublets with a large coupling constant (J = 13 – 16 Hz)
indicating the trans double bond. 31 In case of chalcones with the substituent at para position on the
benzene ring the ortho and meta protons gave a pair of doublets with a J value of 7.2 – 8.4 Hz. In T- CHL-
B and TCHL-CNA the ortho-protons are seen as 2-H doublet, meta-protons 2-H triplet and para-proton
1
-H triplet. In the PMR spectrum of T-CHL-CAN four olefinic proton signals were observed. The CH
in T-CHL-MO and protons of S—CH in T-CHL-SM are seen as singlets at δ3.05 (3H) and δ2.52 (3H)
respectively. The OH proton in T-CHL-OH, which is D O exchangeable, is observed as a singlet at δ10.1.
In T-CHL-NDM, the two methyl groups of –NMe gave a singlet at δ3.04 (6H). The CNMR spectra of
3
O-
3
2
1
3
2
these chalcones indicated the presence of C=O by the signal at ~ δ182. Other signals as expected for the
2
thienyl group, olefinic carbons and the aryl ring are observed in sp C region of δ 111 to 162 as given in
Table-S.
2
.1.3 Single Crystal XRD of T-CHL-ISO.
The details of the crystal structure and data refinement are given in supplementary data (Table-S1). The
list of bond lengths and bond angles of the non-hydrogen atoms is given in (Table S2 and Table S3)

respectively. The space group was found to be P 21/c; with cell dimensions a = 9.3268(2) Å, b =
o
o
o
1
0.3323(2) Å, c = 27.8159(5) Å, α= 90.00 , β = 91.6770(10) , γ = 90.00 . Figure 2 represents the ORTEP
of the molecule with thermal ellipsoids drawn at 50% probability. There are two molecules in an
asymmetric unit and the molecule is non-planar. This non planarity is confirmed by the dihedral angle
o
o
values of 9.76(14) and 26.43(13) between the two aromatic rings. The thiophene ring is affected by the
π-conjugation. This can be explained by the longer C = S bonds values for S1A-C2A = 1.720(3) Å, S1B-
C2B = 1.724(3) Å, S1A-C5A = 1.696(3) Å, S1B-C5B = 1.702(3) Å. The olefinic double bond is in E-
configuration and is CSP2 hybridized. This is evident from the bond length values for C8A-C9A =
1
.335(4) Å and C8B-C9B = 1.338(4) Å.
1
5
Similar conformation was reported in earlier studies. The bond angle values for O7A-C6A-C2A =
o
o
o
o
1
19.8(2) , O7B-C6B- C2B = 120.6(2) , C2A-C6A-C8A=117.8(2) , C2B-C6B- C8B=116.9(2) and O7A-
o
o
C6A-C8A = 122.4(2) , O7B-C6B-C8B = 122.5(2) , about C6 indicates that the carbon atom is in a
distorted trigonal plane which is due to steric hindrance of the oxygen atom. Similar conformation was
3
2
observed in the molecule of 1-(2'-thiophen)-3-(2,3,5-trichlorophenyl)-2-propen-1-one.
Classic
hydrogen bonds are not observed in the crystal structure except for a weak C–H... π interaction that may
help to stabilize the structure. The packing of the molecule when viewed down along the b axis indicates
that the molecules are arranged in a zigzag manner to form a three- dimensional structure (Figure.3). The
CCDC number for the molecule is 1414507.
2
2
.2. Nonlinear optical properties.
.2.1. SHG measurement.
In SHG-active crystals, it is interesting to note that the arrangement of molecules inside the crystal is
critical to yield large effective nonlinearity, besides the non-centrosymmetric crystal structure. Hydrogen
bonds, parallel stacking and p–p interaction favour high second harmonic generation efficiency in
nonlinear materials. 33 In addition, an optimized alignment of the molecular dipoles with hb = 0 (where
hb is the angle between the charge transfer axis and the crystallographic b-axis) will establish a net
macroscopic second order polarization in the crystal by adding the dipole moments of each molecule,
maximizing the SHG efficiency.

Good SHG values are shown by compounds with an extensive conjugation within the system. Both
electron donating and withdrawing groups play a crucial role in enhancing the conjugation. In the current
scenario the π-electrons of both the benzene and thiophene rings are in cross conjugation with the carbonyl
group. Measured SHG efficiency of the samples with respect to urea are listed in Table-1. Among all the
compounds reported in this work, T- CHL-2T shows a value which is 52 times higher that of urea. 24 This
enhancement can be attributed not only to the conjugation, but also to the symmetry involved. This is
followed by T-CHL-OM, T-CHL- NDM, T-CHL-ISO and T-CHL-CNA with 0.94, 0.45, 0.29, and 0.27
times efficiency respectively, with respect to urea. However other T-CHL-B, T-CHL-OH, T-CHL-SM,
and T-CHL-Cl showed zero SHG activity. The behavior of the first three can be attributed to the electron
pumping nature of the substituents whereas that of the last one is due to the increased extended conjugation
between the carbonyl and the aromatic ring. Whereas the electron pumping ability of the groups are in the
order N, N-dimethyl amino > methoxy > isopropyl, the SHG activity is not in the same order. This is due
to the methyl groups present on the groups distorting the packing in the crystal structure.
A low SHG efficiency of 0.8 times urea has been reported for a chalcone derivative CMC and 0.15 times
that of urea for 4NP3AP due to an un-optimized alignment of molecular dipoles in their crystal structure.
3
4
2
.2.2 Nonlinear absorption measurement.
The synthesized molecules possess a D-A-π-D type of arrangement. The compounds have the thiophene
moiety as the donor followed by carbonyl group as an acceptor, and a π-bond and a phenyl group with a
substituent at the other end as donor. All compounds show strong optical limiting behavior as shown in
Fig. 4, where the sample transmittance decreases with increase in the pump fluence.
We found that the measured data numerically fits best to a three-photon absorption (3PA) type
nonlinearity, in which the sample transmission (T) can be described by the nonlinear transmission
2
6
equation-1 ,

ퟐ
(
ퟏ−푹) 퐞퐱퐩(−훂퐋)
ꢄ∞
푻 =
[∫−∞ 퐥퐧[ꢂퟏ + (풑 )²퐞퐱퐩(ꢃퟐ풕²) + 풑 exp(-t²)] 풅풕]
(1)
ퟎ
ퟎ
ꢀ
√ 흅ꢁ풑ퟎ
where α is the linear absorption coefficient, L is the sample length, and R is the Fresnel reflection
coefficient of the sample-air-interface. p is given by
0
ퟏ/ퟐ
ퟐ
ퟐ
[
ퟐ휸(ퟏ ꢃ 푹) 푰 푳풆풇풇]
(2)
ퟎ
where γ is 3PA coefficient, and I is the incident intensity. Leff is given by
0
ꢅퟏ ꢃ 풆풙풑(ꢃퟐ ∝ 푳)ꢆ
⁄
(3)
ퟐ ∝
The calculated values of the 3PA absorption coefficient (γ) are given in Table-1. Since the samples have
some weak absorption at 800 nm (linear transmission is 85%) the 3PA process will be resonantly
enhanced. In view of the absorption spectra which show enhanced absorption at the two-photon
wavelength of 400 nm and at the three-photon wavelength of 266.6 nm, the following three processes can
occur: (i) genuine 3PA which happens without the aid of real intermediate levels; (ii) genuine 2PA which
is followed by one-photon absorption; (iii) three sequential, individual one-photon absorption events.
Genuine 3PA will be the weakest of the above three processes. Therefore the nonlinear absorption in this
case is an effective 3PA process, so that we call γ the effective 3PA coefficient.
We observed that the 3PA coefficient of T-CHL-B can be enhanced by modifying the benzene ring. The
enhancement is reflected in the γ value of this compound (8.5 x 10-28 m /W ).Three types of structural
changes were effected; (1) introducing substituents at para position in the benzene ring, (2) extending the
π-system in between the carbonyl group and the benzene ring, and (3) replacing the benzene ring with a
3
2
5
-membered heterocyclic ring. In the first type of the structural change, a variety of substituents like
chloro, iso-propyl, methoxy, hydroxyl, methylthio and N,N-dimethyl amino are studied. The effect of
substituents on γ is represented graphically in Fig. 5.

When a chloro group is introduced at the para position on the benzene ring, the γ value of T-CHL-ClB
-28
3
2
(
10.0 x10 m /W ) is not much enhanced. The reason for this is that the –I effect dominates the +R-effect
shown by the chloride group.
When an iso-propyl group is introduced at the same position, the γ value (14.5 x10-28 m /W ) increases
due to the reason that this group donates electrons through +I-effect. Other groups introduced are methoxy,
methylthio, N, N-dimethyl amino, and hydroxyl. The γ values for these substituents are in the order N, N-
3
2
dimethyl amino (105.0 x10-28 m /W )> methylthio (68.0 x10 m /W )> methoxy (49.9 x10 m /W )>
3
2
-28
3
2
-28
3
2
hydroxyl (40.0 x10-28 m /W ). This is due to the fact that both methoxy and hydroxyl groups are electron
withdrawing by –I effect but donate electrons by +R effect. In the case of methylthio and N, N-dimethyl
amino groups –I effect is weak whereas +R effect is more dominating. Groups with a better electron
donating capability may increase the γ value.
3
2
In the second type of structural change made, the π-system is extended by using cinnamaldehyde instead
-28
3
2
of a substituted benzaldehyde and the γ value (25.0 x 10 m /W ) increased by two-fold. In the third type
of structural modification, thenaldehyde is used instead of benzaldehyde. As the latter is better electron
-28
3
2
donating than the benzene ring, the γ value (30.55 x10 m /W ) increases almost by three fold. Thus the
study reveals that the nonlinear absorption property of a compound is directly proportional to the electron
donating ability of the substituted groups. A.N.Prabhu et al. in their studies have also reported similar
findings. 35
To view the nonlinear absorption efficiency of the present materials in perspective, it is worthwhile to
refer to the nonlinear absorption coefficient values reported in literature for similar molecules. The
effective 3PA coefficient value reported in literature for poly {2, 2’-(3,4-didodecyloxythiophene-2,5-
-22
3
2 25
diyl)bis[5-(2-thienyl)-1,3,4-oxadiazole]}, a polymer, is quite high at 4.8 x 10 m /W . For the chalcone
‘VFC’, with 780 nm irradiation, the dominant absorption was 2PA at lower fluences (2PA coefficient =
.11 x 10-13 m/W) and 2PA induced excited state absorption at higher fluences (γ = 1.51 x 10-27 m /W ).
3
2
3
5
For the chalcones 3TF, 3TC, and 3TM, γ is in the range of 10-28 m /W . On the other hand the γ value
3
2 36
reported for thiazole based compounds is in the order of 10-31 m /W . Z-scan at 532 nm of stilbazolium
3
2 13
derivatives DASPI, ASPI, FeVPI, and FeSPI gave γ values in the order of 10-31 m /W . For conjugated
3
2 37
TTF-Quinone molecules, the γ values are reported to be much lower, in the order of 10-46 m /W . The
3
2 38
3
PA coefficient for a multi-branched chromophore in femto second regime was found to be 3.32 x 10-25

6
-2 39
cm GW . Also the co-crystals studied by E. D. D’silva shows less third order NLO properties compared
with that of the individual compounds. 40 It should be noted that since coefficients for effective nonlinear
absorption in a material are dependent on the excitation wavelength, excitation intensity and sample
concentration, reported values can vary in a wide range.
3
. CONCLUSIONS
In summary, we present the Thienyl chalcones, with their structure ascertained by the XRD of a
representative member. From the studies carried out it is evident that- (1) the substituents on the molecule
play a role in the optical properties, which is established via the Structure Activity Relation and (2) the
electronic distribution has a profound effect on the NLO properties; thus supporting the design based
synthetic route. The presence of electron donating groups or extended conjugation enhances the NLO
properties. The large magnitudes of the NLO coefficients obtained highlight their prospective advantage
in applications such as second order frequency conversion, optical switching, optical limiting, and
photonic devices.
4
4
.
EXPERIMENTATION
Synthesis
.1
All the compounds covered under this study were prepared by Claisen-Schmidt Reaction. 28 The starting
materials used, 2-acetylthiophene and the various aldehydes were purchased from Sigma-Aldrich
Chemical Company (India) with a stated purity of greater than 98%, and were used as such without any
further purification. A solution of ethanol (12.25 ml) - water (20 ml) was prepared under inert atmosphere
and 2.2g of sodium hydroxide were taken in a round bottomed flask. The corresponding aldehydes (0.043
o
mol) and (0.043 mol) of 2-acetythiophene were added to the solution at 5 C under nitrogen atmosphere.
The reaction mixture was stirred at room temperature and completion of the reaction was ascertained by
Thin Layer Chromatography. Upon completion of the reaction, the mixture was cooled for 12 hours. The
physical state of all the products was solid. The solid was filtered and washed free of alkali.

Recrystallization was carried out using distilled methanol. The reaction times, yields and the melting
points of the recrystallized products were determined and are reported in Table-2.
4
.2
Single Crystal growth and XRD analysis.
The single crystal growth of the compound T-CHL-ISO was done using the slow evaporation growth
technique at room temperature. The recrystallized compound was used to grow single crystals using a
variety of solvents ranging over methanol, ethanol, acetone, chloroform and some mixtures. Single
crystals from methanol were found to be best. A block shaped single crystal of dimensions 0.3×0.27×0.25
mm of the title compound was chosen for X-ray diffraction study. The X-ray intensity data were collected
at a temperature of 296 K on a Bruker Proteum2 CCD diffractometer equipped with an X-ray generator
operating at 45 kV and 10 mA, using CuK
α
radiation of wavelength 1.54178 Å. Data were collected for
2
4 frames per set with different settings of φ (0° and 90°), keeping the scan width of 0.5°, exposure time
of 2 s, the sample to detector distance of 45.10 mm and 2θ value at 46.6°. A complete data set was
processed using SAINT PLUS. 41 The structure was solved by direct methods and refined by full-matrix
least squares method on F2 using SHELXS and SHELXL programs. 42 All the non-hydrogen atoms were
revealed in the first difference Fourier map itself. All the hydrogen atoms were positioned geometrically
and refined using a riding model.
After ten cycles of refinement, the final difference Fourier map showed peaks of no chemical significance
and the residuals saturated to 0.0480. The geometrical calculations were carried out using the program
4
3
44
PLATON. The molecular and packing diagrams were generated using the software MERCURY.
4
.3
Instrumentation.
Single crystal X-ray diffraction pattern of the reported sample was recorded using Bruker Proteum2 CCD
1
13
diffractometer. HNMR spectra were obtained on VARIAN 400 MHz, CNMR on VARIAN 100 MHz
using TMS as the internal standard and CDCl as solvent. For mass spectra AGILENT 6430 Triple Quad
3
-1
LC/MS was employed. The FT-IR spectra were recorded in the range of 400-4000cm using KBr pellets
employing Thermo-Nicolet Avatar 370 spectrophotometer. UV-Vis spectra in methanol were recorded in
the wavering range 200-600 nm using Shimadzu 2450 spectrophotometer.

4
4
.4
Nonlinear Optical measurements.
.4.1 Nonlinear absorption measurement.
The absorptive optical nonlinearity of the samples was studied using the open aperture Z-scan technique.
Pulses of 100 fs duration (FWHM) at 800 nm obtained from a regeneratively amplified mode-locked Ti:
Sapphire laser, operating at a pulse repetition rate of 10 Hz, were used for excitation. A fast mechanical
shutter suitably synchronized to laser emission was used in the beam path to allow single pulses to pass
through, so that the experiment could be performed in the single-shot mode. In this way the effective
sample irradiation rate was reduced to about one pulse in five seconds, so that the possibility of sample
heating during measurement could be avoided. The laser pulses were divided by a beam splitter, and the
reflected part was used as a reference to monitor fluctuations in the incident pulse energy. The transmitted
part, which had an energy of about 5 micro joules, was focused using a converging lens (focal length =
1
0.75 cm) to achieve continuous variation in the incident intensity along the beam axis (z-axis), with
maximum intensity at the focal point (z=0). Each sample was appropriately diluted so that the linear
transmission was 85% at the excitation wavelength, when taken in a 1 mm cuvette. The sample cuvette
was mounted on an automated linear translation stage so that the sample could be moved to any desired
position along the z-axis with respect to the focal point. By keeping the incident laser energy constant,
light transmission through the sample was measured as a function of the sample position.
4
.4.2. Powder SHG measurement.
SHG efficiency measurement was carried out using the conventional Powder (Kurtz and Perry) SHG
technique with Nd:YAG laser (1064 nm, 8 ns) for excitation. The pulse energy was 6 mJ; and the pulse
repetition rate was 10 Hz. The beam was optically steered to be incident on the microcrystalline powder
samples which were tightly packed in a glass capillary. A dichroic mirror was used to remove the
fundamental from the generated second harmonic (532 nm), which was detected by a sensitive
photomultiplier tube (PMT). The PMT converts the SHG signal to an electrical signal, which was then
displayed on an oscilloscope. Finely ground urea crystals with uniform particle size were used as reference
for the SHG experiment.

Acknowledgements
The authors dedicate the work to the founder chancellor of Sri Sathya Sai Institute of Higher Learning,
Bhagawan Sri Sathya Sai Baba. We thank Prof. S. S. Rajan (Dept. of Biosciences, SSSIHL) and Prof. J
Sashidhara Prasad (Former Vice Chancellor, SSSIHL) for their valuable suggestions. We are grateful to
the Institution of Excellence, Vijnana Bhavana, University of Mysore, India, for providing the single-
crystal X-ray diffractometer facility. Pranitha Sankar is grateful to the Australia-India Strategic Research
Fund (AISRF) for a junior research fellowship. We also thank our fellow researchers R S Sai Siddhardha
and Swayamsiddha Kar.

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Fig. 1: UV-Vis absorption plot: a) T-CHL-B, b) T-CHL- SM, c) T-CHL-ClB, d) T-CHL-ISO, e) T-CHL-
OM, f) T-CHL-2T, g) T-CHL-OH, h) T-CHL-NDM, i) T-CHL-CAN

Fig. 2: ORTEP of the molecule with thermal ellipsoids drawn at 50% probability

Fig. 3: Packing of the molecules when viewed down along the b axis exhibiting zigzag
arrangement.

Fig. 4: Open aperture Z-scan curves measured for the samples, and the corresponding optical limiting
behaviour (calculated from the Z-scan data). Solid lines are numerical fits to the data points using Eq. (1).

Fig.5: Graphical representation of the effect of substituents on the effective three photon
absorption coefficient (γ).

Table-1: UV- Visible absorption maxima, SHG efficiency and effective 3PA absorption coefficients
of thienyl- chalcones.
Code
Linear Absorption
SHG values vs.
Urea
Effective 3PA coefficient
3
2
(
λ
max, nm)
(γ, m /W )
*
-28
T-CHL-B
T-CHL-Cl
T-CHL-ISO
T-CHL-CAN
T-CHL-2T
T-CHL-OH
T-CHL-OM
T-CHL-SM
T-CHL-NDM
320
323
331
0
0
8.5 x 10
*
-28
10.0 x 10
-
28
0.29
0.27
14.5 x 10
25.0 x 10-
30.6 x 10
40.0 x 10
28
352
350
356
349
363
428
*
-28
52
-28
0
49.9 x 10-
28
0.94
*
-28
0
68.0 x 10
105.0 x 10-
28
0.45
*24

Table 2: Reaction Time, Yield, and Melting Points of the Thienyl chalcones.
Reaction
Time(hrs) Yield (%)
Melting Point
o
Code
Φ- Group
IUPAC Name
( C)
2
,4-Pentadien-1-one, 5-phenyl-1-
T-CHL-CAN
(
2-thienyl)-, (2E,4E)-
16
95.0
89.2
101.8 - 102.8
2
-Propen-1-one, 1,3-di-2-thienyl-,
T-CHL-2T
(
2E)-
24
99.4 - 100.3
Reaction
Time(hrs) Yield (%)
Melting Point
o
Code
R-Group
IUPAC Name
( C)
2
-Propen-1-one, 3-phenyl-1-(2-
T-CHL-B
-H
thienyl)-, (2E)-
16
16
83.6
76.2
82.2 - 82.6
2
-Propen-1-one, 3-(4-chlorophenyl)-1-
T-CHL-Cl
-Cl
(
2-thienyl)-, (2E)
132.2 - 132.9
2
-Propen-1-one, 3-[4-(1-methylethyl)
T-CHL-ISO
-CH(CH
-OH
)
3 2
phenyl]-1-(2-thienyl)-,(2E)-
48
24
90.8
65.6
51.4 - 52.2
2
1
-Propen-1-one, 3-(4-hydroxyphenyl)-
-(2-thienyl)-, (2E)-
T-CHL-OH
166.7 - 167.3
2
-Propen-1-one, 3-(4-
T-CHL-OM
T-CHL-SM
T-CHL- NDM
-O (CH )
3
methoxyphenyl)-1-(2-thienyl)-, (2E)-
24
24
16
80.2
79.7
91.4
83.6 - 84.2
86.6 - 87.4
93.3 - 95.3
2
-Propen-1-one, 3-[4- (methylthio)
-S(CH3)
phenyl]-1-(2-thienyl)- ,(2E)-
2
-Propen-1-one, 3-[4-(dimethyl
-N (CH3)2
amino)phenyl]-1-(2-thienyl)-,(2E)