Second-order nonlinear optical properties of two chalcone derivatives: insights from sum-over-states

Article abstract of DOI:10.1039/d0cp06469f

In this study, a combined experimental and theoretical study of the nonlinear optical properties (NLO) of two chalcone derivatives, (E)-3-(2-methoxyphenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-2-en-1-one (MPSP) and (E)-3-(3-nitrophenyl)-1-(2-(phenylsulfo

Full text of DOI:10.1039/d0cp06469f

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Second-order nonlinear optical properties of
two chalcone derivatives: insights from
Cite this: Phys. Chem. Chem. Phys.,
sum-over-states†
2
021, 23, 6128
a
a
b
Jean M. F. Custodio, b Giulio D. C. D’Oliveira, Fernando Gotardo,
b
a
Leandro H. Z. Cocca, Leonardo de Boni, Caridad N. Perez,
Hamilton B. Napolitano,
c
de
cf
Francisco A. P. Osorio and Clodoaldo Valverde
*
In this study, a combined experimental and theoretical study of the nonlinear optical properties (NLO) of
two chalcone derivatives, (E)-3-(2-methoxyphenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-2-en-1-one
(MPSP) and (E)-3-(3-nitrophenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-2-en-1-one (NPSP), in DMSO is
reported. The single crystal structures of the compounds, which differ only by the type and position of
one substituent, were grown using the slow evaporation technique, and the main structural differences
are discussed. The two-photon absorption and first-order hyperpolarizability measurements were
performed via the Z-scan technique and hyper-Rayleigh scattering experiment in DMSO. The theoretical
calculations were performed using the Density Functional Theory (DFT) at the CAM-B3LYP/6-
3
11++G(d,p) level, and the sum-over-states (SOS) approach in both static and dynamic cases. Besides
the electron conjugation achieved by the aromatic rings, olefins, and carbonyl groups, both compounds
have a nearly flat chalcone backbone, which is believed to contribute to the nonlinear optical properties.
MPSP and NPSP have different positions, even though they have roughly the same conformation and
form C–Hꢀ ꢀ ꢀO interactions. For several studied frequencies, the HRS first hyperpolarizability values for
MPSP are greater than those for NPSP, indicating that in most cases the NLO properties of MPSP are
better. The comparison among the theoretical and experimental HRS first hyperpolarizability results
showed a good agreement. In addition, the two-dimensional second order nonlinear optical spectra
obtained from the sum-over-states model indicate good second-order NLO responses of the two
chalcone derivatives under external fields. Our findings are important not only to show the potential
nonlinear optical application of the two new compounds but also to gain an insight into how different
chemical compositions might affect the crystal structures and physico-chemical properties.
Received 14th December 2020,
Accepted 10th February 2021
DOI: 10.1039/d0cp06469f
rsc.li/pccp
1
,2
telecommunications, photonic devices,
absorption of two
1
. Introduction
3
,4
photons, fluorescence microscopy excited by the absorption
5
,6
7,8
In recent decades, nonlinear optics (NLO) has been one of the of two photons,
photodynamic therapy,
and optical
9
main areas in technological and research development with an limiters. In this context, organic materials are widely studied
increasing number of applications in various fields including and represent a promising group with NLO properties due to
their ease of synthesis and p conjugation, thus allowing the
control of these properties.
a
Instituto de Qu ´ı mica, Universidade Federal de Goi a´ s, Goi aˆ nia, GO, 74690-970,
Brazil
Organic molecules with p-conjugated structures as well as
donor and acceptor groups are compounds of great interest in
b
c
Instituto de F ´ı sica de S a˜ o Carlos, Universidade de S a˜ o Paulo, S a˜ o Paulo, SP,
1
3566-590, Brazil
1
0
the area of nonlinear optics. The change of the substituent
groups bound to the aromatic rings make the chalcone molecules
acquire specific properties due to the change of the electronic
distribution of the compound; hence, new properties can be
explored, with each new substituent being added or substituted
Campus de Ci ˆe ncias Exatas e Tecnol ´o gicas, Universidade Estadual de Goi a´ s,
An a´ polis, GO, 75132-903, Brazil. E-mail: valverde@ueg.br
Pontif ´ı cia Universidade Cat o´ lica de Goi a´ s, Goi aˆ nia, GO, 13566-590, Brazil
Instituto de F ´ı sica, Universidade Federal de Goi a´ s, 74.690-900, Goi aˆ nia, GO,
Brazil
d
e
f
Universidade Paulista, Goi aˆ nia, Goi a´ s, 74845-090, Brazil
11
to the compound.
†
Electronic supplementary information (ESI) available. CCDC 1904244 and
904245. For ESI and crystallographic data in CIF or other electronic format
The purpose of the present study is to examine the
nonlinear optical properties of two chalcone derivatives,
1
see DOI: 10.1039/d0cp06469f
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(
E)-3-(2-methoxyphenyl)-1-(2-(phenylsulfonylamine)phenyl)prop- 1 mM formic acid. All analyses were done in the positive mode.
-en-1-one (MPSP) and (E)-3-(3-nitrophenyl)-1-(2-(phenylsulfony- The configuration of the ESI† (+) was: nitrogen gas nebulizer at
lamine)phenyl)prop-2-en-1-one (NPSP). The crystalline structural a temperature of 200 1C, a pressure of 0.4 bar and a flow rate of
2
ꢁ1
properties were studied using single-crystal X-ray diffraction, and 4 L min of drying gas; voltage in the capillary of ꢁ4 kV; 200 1C
the main differences were discussed. The absorption spectra of temperature in the transfer capillary; endplate offset of ꢁ500 V;
the two compounds, which differ only by the type and position of 35 V skimmer and ꢁ1.5 V collision voltage. Each spectrum was
one substituent, were measured and compared. The two-photon acquired using 2 micro scans and processed using Data Analysis
absorption and first-order polarizability measurements are Software (Bruker Daltonics, Bremen, Germany).
performed using the Z-scan technique and hyper-Rayleigh
The infrared spectroscopy analyses were performed using a
scattering experiments in DMSO, respectively. Also, an ab initio PerkinElmer, Frontier Dual Range FT-IR/MIR Spectrometer,
calculation method, which includes Functional Density Theory and read using an ATR (attenuated total reflectance) apparatus.
(DFT) at the CAM-B3LYP/6-311++G(d,p) level, and the sum-over- The melting points were determined with the solid-supported
states (SOS) were used to calculate the hyper-Rayleigh scattering on glass coverslips and subjected to heating in a melting point
first hyperpolarizability (bHRS) of the molecules of the MPSP apparatus (Karl Kolb, Frankfurt, M. Germany). The purity of the
1
and NPSP compounds dissolved in the DMSO, and the results compounds was determined by the H spectrum, the proportion
were compared with the experimental data, showing a good of the areas between the peaks assigned to the structure, and the
agreement between them.
total area of all peaks attributed to the material under analysis.
.1.2. Synthesis of compounds MPSP and NPSP. For each
2
compound, 3.19 g (56.8 mmol) of potassium hydroxide was
solubilized in a minimum amount of water and 400 mL of
ethanol. Then, 5.51 g (20 mmol) of (a) and either 2.72 g
2
. Experimental: materials
and methods
(20 mmol) of 2-methoxybenzaldehyde (for MPSP) or 3.02
2
.1. Synthesis
(20 mmol) of 3-nitrobenzaldehyde (for NPSP) were added and
solubilized. The progress of the reaction was monitored by
thin-layer chromatography (TLC) in the normal phase with a
solution of hexane and ethyl acetate (85 : 15) used as the mobile
phase. After reacting for 2 h 30 min at room temperature, the
reactions were quenched by the slow addition of 37% (w/w)
hydrochloric acid in an equimolar amount to potassium
hydroxide.
The MPSP and NPSP compounds were purified by filtering
the solution, suspending in 100 mL of ethanol, and pouring
them into 400 mL of water. The solutions were then extracted
with 200 mL of dichloromethane. The organic phases were
filtered with anhydrous sodium sulfate and allowed to evaporate
slowly. Before completely dried, the crystals were collected and
rinsed with ethanol.
0
2.1.1. General procedures. The compound 2 N-phenylsulfonyl-
acetophenone (a) was used as the intermediate for the synthesis
of MPSP and NPSP. The compound (a) was synthesized by the
reaction between benzenesulfonyl chloride and 2-amino-
acetophenone in dichloromethane (Scheme 1), based on the
1
2,13
condition previously described.
Compounds MPSP and
NPSP were synthesized using Claisen–Schmidt condensation
of the intermediate (a) and a benzaldehyde via basic catalysis in
ethanolic medium (Scheme 2).
NMR spectra were obtained using a Bruker Avance III
11.75 T apparatus, operating at the frequency of 500.13 MHz
for the hydrogen nucleus or 125.76 MHz for the carbon nucleus
at room temperature. The experiments were performed in
5
mm diameter tubes and collected using Topspin 3.1 software
developed by Bruker BioSpin. Samples (10 mg) were solubilized
in 600 mL of deuterated chloroform, with trimethylsil as an
internal reference.
(E)-3-(2-Methoxyphenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-
2-en-1-one (MPSP). Yellow crystalline solid, yield 93.5%, purity of
1
Mass spectrometry analyses were performed using
a
99.1%, m.p. 118–120 1C. H NMR (CDCl
3
) d 3.94 (s, 3H), d 6.96
s
MicroTOF-Q III spectrometer (Bruker Daltonics, Bremen, (d, J 8.35 Hz, 1H), d 7.00 (t, J 7.53, 1H), d 7.13 (ddd, J 1.13 Hz,
Germany) equipped with a commercial ESI† ion source (Bruker 7.35 Hz, 7.88 Hz, 1H), d 7.36–7.44 (m, 4H), d 7.46 (d, J 15.65 Hz,
Daltonics, Bremen, Germany). Analyses were done by direct 1H), d 7.46–7.49 (m, 1H), d 7.57 (dd, J 1.58 Hz, 7.68 Hz, 1H),
ꢁ
1
infusion (3 mL min ) after extraction under acetonitrile and d 7.75 (dd, J 0.85 Hz, 8.30 Hz, 1H), d 7.82–7.84 (m, 2H), d 7.85
0
Scheme 1 General conditions for the synthesis of 2 N-phenylsulfonylacetophenone (a).
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Scheme 2 General conditions for the synthesis of compounds MPSP (I) and NPSP (II).
1
6,17
(
(
dd, J 1.40 Hz, 8.10 Hz, 1H), d 8.00 (d, J 15.65 Hz, 1H), d 11.30 solved with the ShelXT
structure solution program using
1
3
16,18
s, 1H); C NMR (CDCl ) d 55.6, 111.4, 120.6, 120.8, 122.7, 123.1, Intrinsic Phasing and refined with the ShelXL
refinement
3
1
1
23.5, 125.0, 127.3, 129.0, 129.4, 130.7, 132.3, 132.8, 134.1, package using Least Squares minimization. MPSP was refined
39.5, 139.9, 141.7, 159.0, 193.3; IR 1632 (m), 1489 (m), 1328 with no restraints or constraints. Atoms C16 E C21 E C20 E
(
m), 934 (m), 749 (s); HRMS calculated for C22
H
20NO
4
S 394.1113, C19 E C18 E C17 of NPSP (see Fig. 1) were refined with
restrained Uaniso within 2A with a Sigma of 0.04 and s for
terminal atoms of 0.08. All hydrogens of C(H) and N(H) groups
found 394.1002.
(
E)-3-(3-Nitrophenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-2-
were refined following the riding model with fixed Uiso at
.2 times (for MPSP and NPSP), and hydrogens of the
C(H,H,H) groups were refined as rotating groups with fixed
en-1-one (NPSP). Yellow crystalline solid (3.24 g, 39.7%), purity
1
1
of 98%, m.p. 190–195 1C. H NMR (CDCl
H), d 7.40–7.43 (m, 2H), d 7.46–7.47 (m, 1H), d 7.50
d, J 15.55 Hz, 1H), d 7.53 (t, J 8.03 Hz, 1H), d 7.64 (t, J
3
) d 7.17 (t, J 7.70 Hz,
1
(
7
1
(
(
1
1
U
iso at 1.5 times (for MPSP). The programs used for (a) the
19,20
21
validation of chemical parameters are Platon
and Parst,
.95 Hz, 1H), d 7.72 (d, J 15.60 Hz, 1H), d 7.76 (d, J 8.35 Hz,
H), d 7.85 (d, J 7.50 Hz, 2H), d 7.89 (d, J 7.80 Hz, 2H), d 8.28
and (b) the generation of tables, pictures, and images are
22
14
23
Mercury, Olex2, and UCSF Chimera. Crystallographic data
for MPSP and NPSP were deposited at the Cambridge Crystal-
lographic database under codes 1904244 and 1904245.†
dd, 1.18 Hz, 8.08 Hz, 1H), d 8.47 (t, J 1.80 Hz, 1H), d 11.18
1
3
s, 1H); C NMR (CDCl
3
) d 120.45, 122.34, 123.19, 123.97,
24.72, 125.02, 127.27, 129.05, 130.19, 130.81, 132.96, 134.48,
34.96, 136.20, 139.45, 140.22, 142.68, 148.79, 192.01; IR 1646
2.3. Linear and nonlinear optical properties
(
m), 1450 (m), 1333 (m), 930 (m), 747 (m); HRMS calculated for
C H N O S 409.0858, found 409.0562.
2.3.1. Absorption spectrum measurement. To obtain the
2
1
17 2 5
absorption spectrum, the MPSP and NPSP compounds were
dissolved in dimethyl-sulfoxide (DMSO) with at a concentration
Single crystals of C22 19NO S (MPSP) and C21H N O S (NPSP) of about 10 mol L . A 1 mm width silica fused cuvette was
2
.2. Single-crystal analysis
ꢁ
4
ꢁ1
H
4 16 2 5
were grown via the slow evaporation of dichloromethane solution. filled with each of the solutions of the compound and placed
Suitable crystals were selected and mounted on a Bruker APEX-II inside a commercial spectrophotometer SHIMADZU 1800 – UV
CCD diffractometer equipped with monochromated MoKa Vis, which gives the absorption spectrum of the samples. Also,
(
l = 0.71073 Å) radiation. The crystals were kept at 296.15 K fluorescence was measured using a commercial fluorimeter
1
4,15
during data collection. Using Olex2,
the structures were HITACHI F7000 with a 1 cm width silica fused cuvette in which
Fig. 1 ORTEP diagrams at 50% probability representing the thermal displacement of MPSP (a) and NPSP (b) and the numbering scheme adopted.
Hydrogen atoms are presented as spheres with arbitrary radii.
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the solutions to be analyzed were prepared at a concentration of beam that collects the second harmonic (532 nm) scattered by
ꢁ
5
ꢁ1
25
about 10 mol L . None of the chalcone derivatives showed the solution. The intensity of the second harmonic generated
fluorescence.
is related to the intensity of the incident beam by:
2
.3.2. Two-photon absorption measurements. Two-photon
M
X
2
i
2
absorption (2PA) spectrum was obtained using a Z-scan technique
that monitors a focused laser beam transmittance that passes
through a sample and is detected using a photodetector. The
transmittance depends on the position of the samples (Z). As the
laser beam is focused on a lens, for each position Z in the z-axis,
the sample molecules are subjected to a different intensity of
light. The transmittance in the far-field (far from the focal region)
does not present any nonlinear effects. Meanwhile, the trans-
mittance can be significantly decreased around the focus region
due to nonlinear effects, as the induced 2PA is proportional to the
decrease in transmittance, allowing the quantification of its 2PA
cross-section. The normalized ratio between the transmittance in
the far-field and samples position Z gives the 2PA cross-section,
which can be evaluated using eqn (1). The experiment was set up
using the laser CPA-2001 Clark-MXR Ti:sapphire that delivers a
Ið2oÞ ¼
GNib I ðoÞ;
(3)
i¼1
3
i
in which N is the concentration (molecules per cm ), G is an
experimental constant, and b is the first hyperpolarizability.
i
Index i corresponds to all components in the solution (in this
case, M = 2, chalcone derivative, and solvent DMSO). G depends
on the HRS setup in each experiment and involves experimental
parameters such as laser waist, geometry, several optical
devices, temporal width of pulse train, and frequency of the
laser beam. A reference method is used to calibrate the experiment
so that G no long is an issue. For this experiment, the well-known
pNa molecule dissolved in DMSO was used as a calibration sample
ꢁ
30
5
ꢁ1
and presented a b(1064 nm) = 26.2 ꢂ 10
cm esu . HRS
experiments for several concentrations of chalcone derivatives
yield an angular coefficient achalcone that comes from the linear
dependency of I(2o) and N . Repeating the same procedure with
i
several concentrations of pNA samples yields an angular coeffi-
cient apNA, which is a consequence from eqn (3) given by Gb . First
1
kHz frequency pulsed laser beam with 775 nm wavelength and a
pulse width of about 150 fs. This laser beam is used in an optical
parametric amplifier (TOPAS), which changes the pulse width to
2
1
20 fs and permits the chance to select the wavelength in the
hyperpolarizability bchalcone can be determined by:
range between 460 and 2000 nm to perform the Z-scan and
measure the transmittance of the focused laser beam into a
chalcone solution along the z-axis. The measurements in this
study were taken with wavelengths between 460 and 800 nm and
the beam was focused using a 15 cm lens. The transmitted light
was detected using a Silicon photodetector that converts it into a
signal that is amplified and averaged using a locking amplifier.
rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
achalcone
2
bchalcone
¼
b
:
(4)
pNA
a
pNA
2
.4. Theoretical calculations: linear and nonlinear optical
properties
Eqn (1) relates the transmittance with the nonlinear absorption The total dipole moment was calculated from the components
coefficient.
x, y, and z, using the expression:
ð
1
h
i
1
t2
À
Á1
ln 1 þ q0ðz; 0Þeꢁ dt;
(1)
2
x
2
2
2
TðzÞ ¼ pffiffiffi
in which q0 ¼ a2PAI0 1 þ
m ¼ m þ my þ mz
:
(5)
pq0ðz; 0Þ
ꢁ1
ꢀ
ꢁꢁ1
The first hyperpolarizability considered here is the hyper-
is Rayleigh scattering first hyperpolarizability (bHRS) defined by
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
z2
, L is the optical path length, z
0
z02
the Rayleigh length, a2PA is the nonlinear absorption coefficient
2
2
bHRS
¼
hb
i þ hb
i
(6)
ZZZ
XZZ
0
and I is the laser intensity. 2PA cross-sections (s2PA) unit is GM
(
G o¨ ppert–Mayer) (16) and is related to a2PA by:
in which the laboratory system of reference is adopted as X,
Y, and Z coordinates. The X-direction is assumed as the funda-
mental light beam propagation, polarized in the Z-direction.
ꢀh o
N
s2PA ¼
a2PA:
(2)
2
2
3
The hb
i and hb
i are macroscopic averages calculated
ZZZ
XZZ
in which N is the density (molecules per cm ), hꢀ is the Planck
constant divided by 2p, and o is the angular frequency of the
from the first hyperpolarizability components (bijk) through the
ꢁ
50
4
ꢁ1
expressions:
light. 1 GM = 1 ꢂ 10
.3.3. First-order
Hyperpolarizability, b, can be acquired by implementing the
cm s photon
.
ꢀ
ꢁ
2
hyperpolarizability
measurements.
ꢂ
ꢃ
1
30d þ 12ðd þ d þ d Þ þ 6ðd þ d Þ
2
1
2
3
5
4
6
bZZZ ¼ 2
;
10
þ2ðd þ d þ d Þ þ 4d þ d
7
8
11
9
10
2
4
hyper-Rayleigh scattering (HRS) experiment. In order to do
this, a 1064 nm Nd:YAG pulsed laser delivers a train of pulses in
which each pulse is separated from the next one by 13 ns;
knowing that laser has a 100 ps pulse width. The 1064 nm laser
ꢀ
ꢁ
ꢂ
ꢃ
1
6
ðd1 ꢁ d3 ꢁ d5 þ d7Þ þ 8d2 þ 18d4
2
bXZZ ¼ 2
;
10
þ4d6 ꢁ d8 ꢁ 2d9 þ 3d10 ꢁ d11
beam enters a dark box through a filter that allows only the and the coefficients d are defined in Table 1.
n
1064 nm to pass. A lens then focuses it into a cuvette containing
The research focuses on the response of second-harmonic
the solution composed of the samples to be analyzed. A photo- generation, b(ꢁo;o,o), more precisely, on the HRS first hyper-
2
6
multiplier is positioned at 901 in relation to the incident laser polarizability bHRS(ꢁ2o;o,o).
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n
Table 1 HRS first hyperpolarizability coefficients (d )
X
X
X
2
d1 ¼
d4 ¼
biii
;
;
d2 ¼
biiibijj;
d3 ¼
d6 ¼
biiiðbjij þ bjjiÞ;
i
i;j
i;j
X
X
X
2
2
bijj
d5 ¼
b ðb þ b Þ;
ðbjij þ b Þ ;
ijj jij
jji
jji
i;j
i;j
i;j
X
X
X
d7 ¼
bijjbikk;
d8 ¼
ðbjij þ b Þðb þ bkkiÞ;
d9 ¼
b ðb þ bkkiÞ;
ijj kik
jji
kik
i;j;k
i;j;k
i;j;k
X
X
2
d10 ¼
ðbijk þ bikjÞ ;
d11 ¼
ðbijk þ bikjÞðbjjk þ bjkiÞ:
i;j;k
i;j;k
2
7–30
2
.4.1. Sum-over-states approach. The SOS (sum-over-states
)
3. Results and discussion
method is one of the most commonly used methods for
theoretical estimation of hyperpolarizability. The expression
for first hyperpolarizability using the sum-over-states approach
is defined as
3.1. Solid-state characterization
3.1.1. Structural properties. MPSP and NPSP are hybrid
compounds that have both sulfonamide and chalcone back-
bones in their structures. Having almost the same chemical
composition, they differ by the aromatic ring A – MPSP has an
ortho-bonded methoxy group, whereas a nitro group is bonded
at a meta-position in NPSP. Both compounds have one molecule
per asymmetric unit and four molecules in the unit cell.
Although MPSP and NPSP share the same crystal system (mono-
clinic), MPSP crystallized under the centrosymmetric space
^
bxyzðꢁos; o1; o2Þ ¼ P½xðꢁosÞ; yðo1Þ; zðo2Þꢃ
"
#
x
y
z
(7)
X X
m m m
0i
ij j0
ꢂ
;
ðei ꢁ osÞðej ꢁ o2Þ
ia0 ja0
P
x
ij
x
x
ij
x
ij
x
00
where m ¼ hij m^ jji; m ¼ m ꢁ m dij; os ¼
oi, and o is the
i
1 1
group P2 /n, and NPSP crystallized under P2 /c. Fig. 1 presents
energy of external fields, o = 0 corresponds to the static electric the ORTEP diagrams showing the thermal displacement at 50%
i
field, and e stands for excitation energy of state i concerning probability and the numbering scheme used. Further information
ˆ
ground state 0. Here P is permutation operator that acts on the about the crystals, refinement, and equipment used can be found
x
xyz indices of the b-components; mij is the x component of in Table 2.
transition dipole moment between state i and j.
Fig. 2 shows an overlapping of MPSP and NPSP, highlighting
2.4.2. Solvent medium. For the calculation of the nonlinear the main differences between their molecular structures.
optical (NLO) parameters of the compounds MPSP and NPSP Although MPSP and NPSP have a sulfonamide portion, both
two distinct models to describe the solvent responses to the the planarity and conjugation of the chalcone backbone play an
3
3,34
perturbation of a solute embedded in a dielectric continuum important role in their nonlinear optical properties.
In this
medium were considered.
sense, a slight deviation from planarity is observed in MPSP
First at PCM/DFT/CAM-B3LYP/6-311++G(d,p) level of theory when compared to NPSP – a result of the twists around C8–C9
the first hyperpolarizability components (b ) were calculated and C9–C10 bonds. This is supported by the dihedral angles
ijk
3
1
via Gaussian-09, using the analytic derivatives method with C7–C8–C9–C10 (+MPSP = ꢁ171.211 and +NPSP = ꢁ175.031)
the solvent in the equilibrium conditions. i.e., considering that and C8–C9–C10–C15 (+MPSP = 171.071 and +NPSP = 178.911)
the solvent had time to fully respond to the solute present. and the angle formed between the aromatic rings A and B
Then using eqn (6) bHRS(ꢁ2o;o,o) was calculated.
In order to calculate the first hyperpolarizability components, O1–C9–C5–C4 (for MPSP, +MPSP = ꢁ170.961) and O1–C9–
;o ,o
), given by eqn (7) within the sum-over-states C2–N2 (for NPSP, +NPSP = 2.281) indicate that the substituent
(+MPSP = 7.061 and +NPSP = 2.151). The torsion angles
b
xyz(ꢁo
s
1
2
(
SOS) scheme the dielectric was considered in the non- methoxy adopts an ꢁantiperiplanar conformation regarding
equilibrium conditions. In this case, the dielectric polarization the carbonyl group in MPSP. The substituent nitro has a
response, which accompanies instantaneous perturbation of the +synperiplanar conformation also regarding the carbonyl group
solute embedded in the dielectric continuum medium is con- in NPSP.
sidered. With the solvent in the non-equilibrium configuration
The crystal packing of MPSP is presented in its side [100]
the transition dipole moments between the states i and j were and top [010] views in Fig. 3a and b, respectively. The side view
calculated at TDDFT/PCM/CAM-B3LYP/6-311++G(d,p) level using reveals chains (cyan color, Fig. 3a) running along [010], which
3
1
the Gaussian-09. Then the bxyz-component was calculated are stabilized by the C17–H17ꢀ ꢀ ꢀO3, C21–H21ꢀ ꢀ ꢀO1, and
3
2
SOS
using the Multiwfn software package and bHRS(ꢁ2o;o,o) was C1–H1Aꢀ ꢀ ꢀO2 interactions. These interactions involve the
then calculated using eqn (6). A significant difference was aromatic rings A, B, and sulfonyl and carbonyl groups with the
observed, particularly in the SOS scheme, in the calculation C(5), C(9), and C(11) motifs, respectively (Fig. 3c). On the other
results of the first hyperpolarizability with the solvent under hand, it is possible to note chains that are parallel to [100] from
equilibrium and non-equilibrium conditions. The last one the top view. These chains are stabilized by the C22–H22Bꢀ ꢀ ꢀO2
proves to be more suitable to the SOS first hyperpolarizability interaction, which involves both sulfonyl and methoxy groups with
calculation.
a C(13) motif. Also, this conformation enables a pseudo-ring in
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Table 2 Crystallographic parameters for both MPSP and NPSP
MPSP
NPSP
Chemical formula
C
22
H
19NO
4
S
21 16 2 5
C H N O S
408.42
M
r
393.44
Crystal system, space group
Temperature (K)
a, b, c (Å)
Monoclinic, P2
296
11.6707 (12), 12.5558 (13), 13.3311 (14)
101.004 (3)
1
/n
1
Monoclinic, P2 /c
296
14.0149 (16), 7.6562 (9), 18.380 (2)
101.242 (4)
b (1)
3
V (Å )
1917.6 (3)
1934.4 (4)
Z
4
4
Radiation type
m (mm
Mo Ka
0.20
Mo Ka
0.20
ꢁ
1
)
Crystal size (mm)
Diffractometer
0.31 ꢂ 0.30 ꢂ 0.25
Bruker APEX-II CCD
0.040
0.629
0.050, 0.139, 1.12
3952
0.46 ꢂ 0.22 ꢂ 0.10
Bruker APEX-II CCD
0.047
0.635
0.053, 0.119, 1.05
3950
R
int
ꢁ1
(
sin y/l)max (Å
R[F 4 2s(F )], wR(F ), S
)
2
2
2
No. of reflections
No. of parameters
Drmax, Drmin (e Å
254
0.51, ꢁ0.43
271
0.25, ꢁ0.32
ꢁ3
)
structure of the chalcone derivatives changed the lineshape of
the 1PA spectra. The chalcone derivative with the methoxy
group in the ortho position presents two 1PA bands with
maxima centered at ca. 315 and 360 nm and molar absorptivity
3
3
ꢁ1
ꢁ1
of approximately 12 ꢂ 10 and 18 ꢂ 10 L mol
cm ,
respectively. The nitro group also presents two 1PA bands with
maxima centered at ca. 300 and 350 nm and molar absorptivity
3
3
ꢁ1
ꢁ1
of approximately 23 ꢂ 10 and 7 ꢂ 10 L mol cm
.
2
PA cross-section spectra for both chalcone derivatives are
also depicted in Fig. 5 as open red circles. 2PA cross-sections
were calculated by adjusting eqn (1) and (2) according to the
Fig. 2 Overlapping of MPSP (blue I) and NPSP (cyan II) showing their main transmitted light acquired by the Z-scan experiment. Both
differences. Hydrogen atoms were omitted for better visualization.
compounds present similar behaviour for this parameter.
MPSP presents three 2PA bands, in which two of them are also
observed in the linear absorption spectrum related to the states
located at 310 and 355 nm, as these bands are centered at
MPSP involving amine and carbonyl groups with a S(6) motif
(Fig. 3d). The geometric parameters of these intermolecular
620 and 710 nm. Cross-section values for these two bands
interactions are presented in Table 3.
resulted in 8 and 6 GM, following the values observed in
the literature. The third 2PA band observed is centered at
approximately 560 nm but is not observed in the 1PA spectra,
indicating an excited state with the same parity as the ground
state. This is the most energetic 2PA band observed with a
cross-section of 24 GM. An increase in the 2PA cross-section for
wavelengths shorter than 500 nm occurs due to the resonance
enhancement effect. This compound has a more symmetrical
charge distribution than NPSP as it can be seen by comparing
the two least energetic 2PA bands with the two 1PA bands, in
which the one with a higher e presents the lowest s2PA and
vice-versa for the electronic transition. This ‘‘inversion’’ in
intensity shows that if there is a high probability of accessing
an excited state via 1PA, access to the same state via 2PA is less
probable and vice-versa.
The crystal packing of NPSP is stabilized only by weak
C–Hꢀ ꢀ ꢀO intermolecular interactions. It is also presented in
its side [100] and top [010] views in Fig. 4a and b, respectively.
Connecting the sulfonyl group and aromatic ring C, the C20–
H20ꢀ ꢀ ꢀO4 interaction assembles molecules of NPSP along [010]
with a ladder-like motif [S(6)] (Fig. 4c). Also, there is a chain
running along [001] stabilized by one trifurcated intermolecular
interaction in which atom O5 receives protons from carbons
C11, C8, and C5 in the C(7), C(8) and C(11) motifs, respectively
(Fig. 4d). Finally, there is also one more intermolecular inter-
action involving the sulfonyl group and aromatic ring C running
along both [100] and [001] directions.
3.2. Linear absorption, first-order hyperpolarizability, and
two-photon absorption spectrum
NPSP also presents three 2PA bands in which the two least
The molar absorptivity of both chalcone derivatives, see dashed energetic bands are observed in the 1PA spectrum, and the
blue lines in Fig. 5, presents absorption in the range from most energetic one is not. This one is centered at approximately
2
1
50 to 400 nm with the maximum values of approximately 570 nm, around the same wavelength as NPSP, with s2PA D
3
ꢁ1
ꢁ1
3
-1
-1
8 ꢂ 10 L mol cm for MPSP and 23 ꢂ 10 L mol cm for 17 GM. The other two bands are centered at 610 and 705 nm
NPSP. The groups methoxy or nitro added to the typical with s2PA values of 8 and 3 GM, respectively.
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Fig. 3 Side [100] (a) and top [010] (b) views of the crystal packing of MPSP, highlighting the observed chains using cyan color; intermolecular interactions
observed along [010] (c) and [100] (d).
3
7,38
Table 3 Hydrogen-bond geometry (Å, 1) for both MPSP and NPSP
used to adjust the curve is:
D–Hꢀ ꢀ ꢀA
MPSP
D–H
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
5
1
28 ðpÞ
SOS
4
s2PAðnÞ ¼
L
5
ðchnÞ
N1–H1ꢀ ꢀ ꢀO1
C21–H21ꢀ ꢀ ꢀO1
C17–H17ꢀ ꢀ ꢀO3
0.95
0.93
0.93
0.93
0.96
1.98
2.54
2.70
2.67
2.60
2.590 (2)
3.380 (3)
3.401 (3)
3.526 (3)
3.298 (4)
119.7
150.6
132.7
153.5
129.5
i
ꢅ
ii
2
01
2
01
2
02
2
02
ðDm ꢀ m Þ ꢀ G01
ðDm ꢀ m Þ ꢀ G02
ii
þ
C1–H1Aꢀ ꢀ ꢀO2
ðo ꢁ 2oÞ þ G01
2
2
ðo ꢁ 2oÞ þ G03
2 2
iii
01
02
C22–H22Bꢀ ꢀ ꢀO2
ꢀ
ꢁꢆ
NPSP
2
2
2
01
2
14
2
01
o
ðm13 ꢀ m Þ ꢀ G04
ðm ꢀ m Þ ꢀ G04
N1–H1ꢀ ꢀ ꢀO1
0.86
0.93
0.96
0.95
0.93
0.93
1.86
2.63
2.65
2.42
2.36
2.62
2.566 (2)
3.515 (2)
3.585 (2)
3.329 (2)
3.246 (4)
3.486 (4)
138.0
160.3
164.6
160.9
158.5
156.0
þ
þ
;
2
2
2
2
2 2
iv
ðo01 ꢁ oÞ þ G01 ðo ꢁ 2oÞ þ G04
ðo ꢁ 2oÞ þ G04
C8–H8ꢀ ꢀ ꢀO5
03
04
v
C11–H11ꢀ ꢀ ꢀO5
(9)
iv
C5–H5ꢀ ꢀ ꢀO5
v
C20–H20ꢀ ꢀ ꢀO4
vi
C19–H19ꢀ ꢀ ꢀO3
in which G0i is the damping constant of the transition 0 - i
which, in most cases, has a value of approximately 0.3 eV
for organic molecules at the UV-VIS region. Dipole moment
values for the chalcone derivatives are shown in Table 4.
Values obtained for the dipole moments and s2PA are in good
agreement with other chalcone-based structures reported in the
Symmetry codes: (i) ꢁx + 1/2, y ꢁ 1/2, ꢁz + 1/2; (ii) ꢁx + 1/2, y + 1/2, ꢁz +
1
2
/2; (iii) x + 1, y, z, (iv) x, ꢁy + 1/2, z + 1/2; (v) x, y + 1, z; (vi) x ꢁ 1, ꢁy + 3/
, z ꢁ 1/2.
Electronic properties can be obtained with 1PA and 2PA
spectra. Transition dipole momentum from the ground state to
an excited state i can be calculated using:
13
literature.
3
5
Comparing the s2PA spectra of both samples to similar
molecules reported in the literature, it is possible to see a good
agreement between the s2PA values. For example, unsubstituted
and mono-substituted chalcones with similar conjugation
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ð
ꢄ
ꢄ
3
ꢄ* ꢄ
3 ꢂ 10 lnð10Þ ꢀh c n
ꢄ m ꢄ ¼
eðoÞdo;
(8)
0i
3
2
ð2pÞ NAo0i
L
3
5
39
lengths have presented s2PA of about 15 GM. Abeg ˜a o et al.
in which N
A
is Avogadro’s number, o0i is the transition fre- studied five chalcone-based molecules dissolved in dichloro-
2
2
quency to the excited state i and L = 3n /(2n + 1) is the Onsager methane, in which all five have shown s2PA values ranging from
local field factor, in which n = 1.42 is the DMSO refractive 10 GM to 45 GM. Bromine chalcone with a similar structure
index. Transition dipole momentum from an excited state i to compared to the ones reported here has shown the maxima
3
6
13
another excited state j (m ; i a j), as well as the difference of s2PA values of about 11 GM and 16 GM for the two two-photon
ij
4
0
permanent dipole moment between an excited state and the allowed bands. Also, in an earlier report, in which three
ground state (Dm0i = m ꢁ m ) can be obtained by applying the benzenesulfonyl chalcones were studied, similar s2PA spectral
ii
00
sum-over-states (SOS) method. This is a theoretical–experi- values have been reported. Chalcones derivatives, known as
4
1,42
mental method that fits a curve (the continuous black line in dibenzylideneacetone
with symmetrical charge distribution,
Fig. 1) to the s2PA spectrum. For both samples, the equation have shown s2PA maxima values from 15 GM to 40 GM.
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Fig. 4 Side [100] (a) and top [010] (b) views of the crystal packing of NPSP, highlighting the observed chains using cyan color; intermolecular interactions
observed along [010] (c) and [001] (d).
The first-order hyperpolarizability results of both samples with pNA dissolved in DMSO. A quadratic dependency of the
are depicted in Fig. 6. The experimental setup was calibrated intensity of the second harmonic scattered (532 nm)
Fig. 5 Two-photon absorption (open red circles) spectra and linear absorption (e) (dashed blue lines) of the two chalcone derivatives dissolved in the
DMSO solvent. The SOS model (black line) adjusts the theoretical–experimental data.
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Table 4 Transition dipole moments and differences of permanent dipole resonance peaks are observed. The static bHRS(0;0,0)-value for
moment between an excited state and the ground state obtained with
eqn (8) and (9). All are in Debye units
ꢁ30
ꢁ30
MPSP is 21.1 ꢂ 10
esu and that for NPSP is 12.7 ꢂ 10
esu.
The ratio between the HRS hyperpolarizabilities of MPSP
and NPSP compounds as a function of frequency is shown in
Fig. 8. The bHRS values of NPSP are higher than those of MPSP,
only for three frequencies: 0.08, 0.085, and 0.100 a.u.
~
m
D ~m 01
~m 13
~m 01
D ~m 02
~m 14
Chalcone derivatives
01
MPSP
NPSP
2.8
1.0
5.8
1.0
10.2
22.5
2.9
6.0
8.2
3.6
10.0
25.0
3
.3.2 Comparison with the experimental results. Table 5
shows the theoretical and experimental results for the HRS first
concerning the pump intensity (1064 nm) can be observed in hyperpolarizabilities for the compounds MPSP and NPSP at l =
SOS
HRS
the top-left inset in Fig. 6 for MPSP. Each curve corresponds to 1064 nm in DMSO. b (ꢁ2o;o,o) was obtained considering
the data acquired for different molecular concentrations, while 300 states. As can be seen the theoretical results for b -values
HRS
the continuous line is a second-order polynomial best fit. The for NPSP, obtained using the derivatives method via Gaussian-
2
31
main graph of Fig. 6 displays a linear behavior of I(2o)/I (o) as 09 (bHRS(ꢁ2o;o,o) and those obtained in the SOS scheme
SOS
ꢁ30
ꢁ30
a function of the molecular concentration (open symbols are (b (ꢁ2o;o,o)) are very close, 12.9 ꢂ 10
and 13.3 ꢂ 10
esu,
HRS
data acquired, and the continuous lines are a linear fit for respectively. However, the theoretical results for MPSP present
ꢁ
30
SOS
compounds MPSP, NPSP and pNA). Linear fitting gives angular a greater difference, b
= 26.2 ꢂ 10
and b
= 31.6 ꢂ
HRS
HRS
ꢁ30
coefficient a, used in eqn (4) to obtain b values displayed in the 10
esu – the SOS results with 300 states is 1.21 times the
inset as a column graph in Fig. 6 (top-right inset).
value obtained using the derivative method. The SOS results
of the HRS first hyperpolarizability show the importance of
considering transitions between higher excited states, mainly
for NPSP, since the bHRS-value obtained with simplest two-state
3
.3. Theoretical results
.3.1. Nonlinear optical properties. The dipole moment
value (m) obtained for both compounds in DMSO were
5.31 D (MPSP) and 4.89 D (NPSP). As can be seen, the m-value
3
2SA
ꢁ30
approximation (2SA) is bHRS= 64.6 ꢂ 10
esu and the
incorporation of more states in the summation (300) decreases
1
this value to one fifth. For MPSP the behavior of the bHRS value
for the MPSP is more than three times greater than for NPSP.
This can be explained due to the greater electronegativity of the
ꢁ30
is different, the results obtained in 2SA (28.5 ꢂ 10
esu) is
ꢁ30
much closer than the full SOS result (31.6 ꢂ 10
esu).
NO group (NPSP) than the OMe group (MPSP). Fig. 7 shows the
2
Table 5 also provides the experimental results of b
value
HRS
DFT/CAM-B3LYP/6-311++G(d,p) results for bHRS(ꢁ2o;o,o)
plotted as a function of the electric field frequency for both
compounds MPSP and NPSP in DMSO. As can be seen the
in DMSO. For MPSP the experimental value of b
is 24 ꢂ
HRS
ꢁ30
10
esu and present a better agreement with the theoretical
result obtained using the derivative method, bHRS = 26.2 ꢂ
b
HRS(ꢁ2o;o,o)-values, for both compounds, present
a
ꢁ30
10
esu mainly if the experimental error is taken into con-
smooth increase with the increase in the frequency at the range,
SOS
sideration (see Fig. 6). The bHRS value is 1.32 times the MPSP
experimental value.
0
o o r 0.07 a.u. For frequency values above 0.07 a.u.,
However, for NPSP, both the theoretical results are more
than 1.6 times greater than the value obtained experimentally
ꢁ30
(8.0 ꢂ 10
esu), and in this case, the discrepancy between the
results goes beyond the limits of the experimental error.
It is important here also to use a phenomenological
approach to estimate HRS first hyperpolarizability values and
compare to the experimental ones by using parameters
obtained with one- and two-photon experiments, such as
transition dipole moments and difference between the permanent
dipole moments of the electronic states. These parameters are
reported in Table 4 and can be used in a dynamic first order
hyperpolarizability approach considering a simplified three-level
2
model (3LM) described by eqn (10):
"
#
2
2
3
2
jDm jjm j
3jDm jjm j
0
1
01
2
02
02
2
b3LMðꢁ2o; o; oÞ ¼
þ
Dðo; o0Þ;
10)
ð ꢀh o01Þ
2
ð ꢀh o02Þ
(
2
Fig. 6 The main graph shows the linear dependence of I(2o)/I (o) as a
function of molecular concentration for chalcone derivatives: pNA (circles),
MPSP (triangles) and NPSP (squares), lines represent linear fits. Top-left
inset shows the intensity quadratic dependence of the second harmonic
scattered (532 nm) light as a function of the pump intensity (1064 nm)
and MPSP concentration. Top-right inset shows b values obtained with
eqn (4).
in which o01 and o02 are the frequencies of the electronic
transitions from the ground state to the first and second excited
4
2
2
2
2
states, respectively. D(o,o
0
) = o01/[(o01 ꢁ 4o )(o01 ꢁ o )] repre-
sents the frequency dispersion factor, in which o is the laser
angular frequency. By substituting the respective values of Table 4
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Fig. 7 Dynamic HRS first hyperpolarizability as a function of the electric field frequency for MPSP and NPSP in DMSO.
starts to absorb light, interfering on the total absorption increasing
errors in the amplitude, as well, in the determination of the
frequency of the electronic states.
The experimental results of the HRS hyperpolarizability for
the MPSP dissolved in DMSO obtained here are 1.5 times
greater than the results for (E)-1-(4-methoxyphenyl)-3-
3
9
phenylprop-2-en-1-one dissolved in DCM and 1.14 times the
values obtained for three other chalcone derivatives reported in
4
0
the literature.
The difference in the NLO responses of the two compounds
is directly related to the transition energies toward the most
absorbing excited state. Moreover, the methoxy group (MPSP)
has a pi-donor character, while the nitro group (NPSP) has a
pi-acceptor character. Owing to the presence of the pi-acceptor
carbonyl group in the chalcone derivatives, including a nitro
group on the terminal phenyl ring, makes the NPSP compound
more symmetrical and therefore reduces its second-order
NLO response. Reversely, using a methoxy group enhances
the push–pull character of MPSP and in turn its first hyper-
polarizability. Also the energy difference between the HOMO
and LUMO orbitals for MPSP is smaller than that for NPSP,
see Fig. S1, ESI.† Another important fact is that the highest
oscillator strength was found in the second excited
state ( f = 0.6421 a.u., energy 3.8049 eV and wavelength
325.85 nm) for the MPSP and in the first excited state ( f =
Fig. 8
bHRS-ratio of compounds MPSP and NPSP as function of the
electric field frequency.
Table 5 Theoretical and experimental values of the HRS first hyperpolar-
izabilities (10
ꢁ30
esu) for MPSP and NPSP in DMSO solvent at l = 1064 nm
NPSP
MPSP
b
HRS(ꢁ2o;o,o)
12.9
13.3
8.0
26.2
31.6
24.0
10
SOS
bHRS(ꢁ2o;o,o)
1
.0053 a.u., energy 3.5077 eV and wavelength 353.47 nm) for
the NPSP.
Fig. 9 shows the strong second order NLO responses of the
NPSP and MPSP structures in the presence of an external
Experimental-HRS
b
3LM
5.2
in eqn (10), the calculated b3LM values are shown in Table 5. One electric field. The one-photon resonances are observed at
can see that the 3LM approach underestimates the first order 6.20 and 9.45 eV; and, 6.53 and 9.3 eV; for NPSP and
hyperpolarizability when compared to the theoretical approach. MPSP respectively. The optical rectification for NPSP occur at
For NPSP, the 3LM value is about 1.5 times smaller than the (ꢁ6.2, 6.2 eV) and (ꢁ9.45, 9.45 eV) and for MPSP at (ꢁ6.53,
experimental value. In the case of MPSP, 3LM value is 2.4 times 6.53 eV) and (ꢁ9.3, 9.3 eV). The Pockels electro-optical effect
smaller than the experimental value. This is understandable are observed at energies: (0.0, 6.2 eV), (0.0, ꢁ6.2 eV), (0.0,
because higher excited states are not considered in this model, 9.45 eV) and (0.0, ꢁ9.45 eV), for NPSP, and at energies (0.0,
which should contribute as extra terms inside of the brackets in 6.53 eV), (0.0, ꢁ6.53 eV), (0.0, 9.3 eV) and (0.0, ꢁ9.3 eV)
eqn (10). However, for wavelength shorter than 250 nm, the solvent for MPSP.
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Fig. 9 Two-dimensional second-order nonlinear optical spectra.
4
. Conclusions
states at the TDDFT/PCM/CAM-B3LYP/6-311++G(d,p) level
3
1
with the Gaussian-09, then we used the Multiwfn software
In this study, the synthesis and characterization using single-
crystal X-ray diffraction and spectroscopic analysis of two
chalcone derivatives, (E)-3-(2-methoxyphenyl)-1-(2-(phenylsulfo-
nylamine) phenyl)prop-2-en-1-one (MPSP) and (E)-3-(3-
nitrophenyl)-1-(2-(phenylsulfonylamine)phenyl)prop-2-en-1-one
32
package to calculate the bxyz-component and finally we used
eqn (6) to calculate bHRS(ꢁ2o;o,o).
The hyper Rayleigh hyperpolarizabilities were calculated for
the compounds in DMSO as a function of the electric field
frequencies. The solvent effects on the electrical parameters
were considered via the Polarizable Continuum Model (PCM).
We have shown that, for several studied frequencies, the MPSP
presents HRS hyperpolarizability values greater than those of
NPSP, indicating that in most cases, the NLO properties of
MPSP are better than those of NPSP. Therefore, the substituent
(NPSP), which differ only by the type and position of one
substituent, were reported. Measurements of the two-photon
absorption (2PA) spectrum and the HRS first hyperpolarizabil-
ity were made using the Z-scan technique and the hyper-
Rayleigh scattering (HRS) experiment, respectively. Besides
the electron conjugation achieved by the aromatic rings, olefins
and carbonyl groups, both compounds have a nearly flat
chalcone backbone, which is believed to contribute to the
nonlinear optical properties. Despite bearing different groups
in different positions, MPSP and NPSP have roughly the same
conformation and form C–Hꢀ ꢀ ꢀO interactions.
2 3
change of NO (NPSP) to OCH (MPSP) benefits the nonlinear
optical properties of the compounds. Significantly the DFT/
CAM-B3LYP/6-311++G(d,p) result for HRS hyperpolarizability
(bHRS(ꢁ2o;o,o) at l = 1064 nm was compared with the experi-
mental result and an excellent agreement was observed for
MPSP, with a percentage error of 8.4%. However, for NPSP
the theoretical method presents a greater difference when
compared with the experimental result. The SOS method was
used to describe the NLO properties of the MPSP and NPSP
structures and a good agreement with the experimental results
was observed.
The Z-scan technique results showed that the measured
2PA cross-section spectra of MPSP and NPSP are nearly
identical. This result indicates that a change from an ortho-
bonded methoxy to a para-bonded nitro group is not enough
to substantially affect this parameter. However, MPSP and
NPSP have slightly different linear absorption. Cross-section
values for these two bands resulted in 8 and 6 GM, respectively,
which are in agreement with the values reported in the
literature.
Our findings are relevant not only for showing the NLO
potential of the two new compounds, but also for gaining
insights into how different chemical compositions might affect
the crystal structure and, consequently, the physico-chemical
properties of the NLO materials.
Both MPSP and NPSP NLO properties were also calculated
3
1
using the derivative method from Gaussian-09 at the PCM/
DFT/CAM-B3LYP/6-311++G(d,p) level of theory, and the theoretical
estimation of hyperpolarizability using the sum-over-states (SOS)
approach with 300 states was conducted as follows: first we
Conflicts of interest
calculated the transition dipole moments between the i and j There are no conflicts to declare.
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