Studies on crystal growth, vibrational, dielectric, electronic, mechanical and thermal properties of new organic nonlinear optical crystal: 3-nitrocinnamic acid

Article abstract of DOI:10.1039/c3ce41408f

3-Nitrocinnamic acid (3NCA) was synthesized and its crystals were grown in aqueous solution by slow evaporation solution growth technique. The grown crystal was confirmed by powder XRD studies. The geometry, intermolecular hydrogen bonding, and harmonic vibrational wavenumbers of 3NCA were investigated with the help of B3LYP density functional theory (DFT) methods. The calculated molecular geometry has been compared with the experimental data obtained from XRD data. The assignments of the vibrational spectra have been carried out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). Vibrational spectral investigation confirms the formation of cyclic dimers in the crystal, with the carboxyl groups of each acid molecule bonded to those of adjacent molecules. The red shift of the O-H stretching wavenumber is due to the formation of strong O-H...O hydrogen bonds by hyperconjugation between the carbonyl oxygen lone electron pairs and the O-H σ* antibonding orbitals. Thermal stability of the grown crystal was examined by recording TGA/DTA. Mechanical strength of the grown material was tested by hardness studies. Second harmonic frequency generation was examined by Kurtz and Perry powder test and it reveals that the relative conversion efficiency is 0.8 times greater than that of urea. The theoretical first order hyperpolarizability value was calculated for the optimized structure.

Full text of DOI:10.1039/c3ce41408f

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Studies on crystal growth, vibrational, dielectric,
electronic, mechanical and thermal properties
of new organic nonlinear optical crystal:
3-nitrocinnamic acid†
Cite this: CrystEngComm, 2013, 15,
9176
S. Alen,ab D. Sajan, b K. Job Sabu,b K. Udaya Lakshmi,c V. Veeraiah,d K. Chaitanyae
*
and V. Bena Jothya
3-Nitrocinnamic acid (3NCA) was synthesized and its crystals were grown in aqueous solution by slow evaporation
solution growth technique. The grown crystal was confirmed by powder XRD studies. The geometry,
intermolecular hydrogen bonding, and harmonic vibrational wavenumbers of 3NCA were investigated with the
help of B3LYP density functional theory (DFT) methods. The calculated molecular geometry has been compared
with the experimental data obtained from XRD data. The assignments of the vibrational spectra have been carried
out with the aid of normal coordinate analysis (NCA) following the scaled quantum mechanical force field
methodology (SQMFF). Vibrational spectral investigation confirms the formation of cyclic dimers in the crystal, with
the carboxyl groups of each acid molecule bonded to those of adjacent molecules. The red shift of the O–H
stretching wavenumber is due to the formation of strong O–H⋯O hydrogen bonds by hyperconjugation between
the carbonyl oxygen lone electron pairs and the O–H σ* antibonding orbitals. Thermal stability of the grown
crystal was examined by recording TGA/DTA. Mechanical strength of the grown material was tested by hardness
studies. Second harmonic frequency generation was examined by Kurtz and Perry powder test and it reveals that
the relative conversion efficiency is 0.8 times greater than that of urea. The theoretical first order
hyperpolarizability value was calculated for the optimized structure.
Received 17th July 2013,
Accepted 6th September 2013
DOI: 10.1039/c3ce41408f
www.rsc.org/crystengcomm
1. Introduction
Nonlinear optical materials have been extensively studied
for many years.5–9 To design and fabricate NLO materials
Cinnamic acid derivatives are an important class of biologically
active compounds, playing an important role in the plants'
development, but may also present a wide range of actions:
antimicrobial, antioxidant, anti-inflammatory, antitumor1,2 and
nonlinear. The present study investigates the non-linear optical
properties of a cinnamic acid derivative, 3-nitrocinnamic acid
(NCA) using vibrational spectroscopic techniques. The spectro-
scopic studies of cinnamic acid and its certain derivatives have
been reported earlier.3,4
much effort is being devoted to understand the origin of
non-linearity in large systems and to relate NLO responses to
electronic structure and molecular geometry. Significant
interest still exists in the design and development of mate-
rials exhibiting large second-order NLO response because of
the potential application in telecommunications, optical
computing, optical signal processing, laser technology, data
storage and image processing.10–15 The design and synthesis
of optimized molecules is the key step in this area of
research. Recent efforts have been focused on developing
organic molecules with large molecular NLO response (β, first
hyperpolarizability), improved optical transparency and good
thermal stability. It has been found that the β value of mole-
cule can be greatly enhanced by the presence of charge trans-
fer interactions and this principle has been used to identify
many highly non-linear molecules.16 NLO techniques are con-
sidered to be among the most structure-sensitive methods to
study molecular structures and assemblies. Since the poten-
tial of organic materials for NLO devices have been proven,
NLO properties of the compounds have been investigated
both by experimental and theoretical methods.17 Vibrational
a Department of Physics, Women's Christian College, Nagercoil-629001, India.
E-mail: alenstvm@gmail.com (S. Alen), benaezhil@yahoo.com (V. Bena Jothy)
b Department of Physics, Bishop Moore College, Mavelikara, Alappuzha-690110,
Kerala, India. E-mail: dsajand@gmail.com, dsajanbmc@gmail.com
c Department of Physics, Saveetha School of Engineering, Saveetha University,
Thandalam, Chennai 602105D, India. E-mail: udayalakshmi@gmail.com
d Department of Physics, D.N.R. College (A), Bhimavaram, W.G.DT.A. P., India-
534202. E-mail: avruavru@gmail.com
e Department of Chemistry, Nanjing University of Science and Technology,
Xialingwei 200, Nanjing, People's Republic of China. E-mail: cskcmail@gmail.com
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c3ce41408f
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spectroscopy has been recently employed to investigate the
structural features responsible for the NLO properties. The
efforts toward deeper knowledge about the relationships
between molecular architecture, nonlinear response, and
hyperpolarizability, using vibrational spectra of the molecules,
can lead to discovery of new efficient materials for technologi-
cal applications. The present work deals with growth and
detailed vibrational spectral investigation of the crystal
3-nitrocinnamic acid (3NCA) to elucidate the correlation
between the molecular structure and NLO property, charge
transfer interactions, and first hyperpolarizability, aided by the
scaled quantum mechanical force field (SQMFF) technique
based on density functional theory (DFT) computation. The
UV-visible spectroscopic behavior of 3NCA was investigated in
order to predict the electronic properties of the molecule.
The present work describes the growth and vibrational
spectral studies on the relationship between the molecular
structural features and NLO properties, nonlinear optical
response and hyperpolarizability of the push–pull prospective
NLO chromophore, 3NCA, with special emphasis on the role
of intramolecular charge transfer (ICT) mechanism in such
organic materials.
2.3. Second harmonic generation efficiency measurements
The NLO SHG efficiency of 3NCA was measured by the
Kurtz–Perry powder SHG method18 using Q-switched Nd:YAG
laser of 1064 nm wavelength. The input laser beam was
passed through the sample after reflection from an IR detec-
tor. The output from the sample was filtered by an IR filter to
eliminate the fundamental and the second harmonic was
detected using monochromator and PMT. The second har-
monic efficiency of 3NCA was calculated to be 0.8 times that
of urea.
3. Crystal structure
Crystals of 3-nitrocinnamic acid (3NCA) belong to the mono-
clinic system with a = 3.7756 (2) Å, b = 9.4584 (13) Å, c =
19
24.295 (4) Å, the space group is P21/n
.
In the crystal, the
independent 3-nitrocinnamic acid molecules are linked by
complimentary intermolecular O–H⋯O hydrogen bonds.
Atom O20 acts as a hydrogen bond donor to carbonyl atom
O19 of another 3-nitrocinnamic acid molecule (−x + 1, −y − 1,
−z), the D⋯A distance being 2.636(3) Å and the D–H⋯A
angle being 169°. This hydrogen bonding interaction leads to
the formation of centrosymmetric dimers with a graph set
2
2. Experimental details
notation of R2 (8). The packing diagram exhibits stacking of
such dimers along the crystallographic a axis. The molecular
packing with intermolecular hydrogen bonding is shown in
Fig. S2 (ESI).†
2.1. Preparation
The title compound, (3-nitrocinnamic acid), was prepared by
dissolving m-nitrobenzaldehyde (6 g, 0.04 mol) and malonic
acid (8.3 g, 0.08 mol) in a mixture of 5 ml of pyridine and
0.25 ml of piperidine. The solution was allowed to reflux for
1 h, with rapid evolution of CO2. The resulting title com-
pound was recrystallized from ethanol. The grown crystal is
shown in Fig. S1 (ESI).†
4. Computational details
DFT calculations were carried out using the GAUSSIAN 09
program package.20 All calculations, which include geometry
optimizations and vibrational spectra, were performed on
isolated systems using the Becke's three parameter B3LYP
exchange correlation method21 in combination with cc/pvdz
basis set22 to derive the complete geometry optimizations
and normal mode analysis. The optimized geometry corre-
sponding to the minimum on the potential energy surface
have been obtained by solving the self-consistent field (SCF)
equations iteratively. Harmonic vibrational wavenumbers
have been calculated using analytic second derivatives to
confirm the convergence to minima on the potential surface
and to evaluate the zero-point vibrational energies without
imposing any molecular symmetry constraints. It is a well
known fact that ab initio calculations tend to overestimate
the vibrational wavenumber with respect to the experimental
ones. This is due to several reasons, for instance, the use
of a finite basis set, the incomplete implementation of the
electronic correlation and the neglect of anharmonicity effects
in the theoretical treatment. To improve the agreement
between the predicted and observed wavenumber, the com-
puted harmonic wavenumbers are usually scaled for compari-
son. In this work the force field was scaled according to
the SQM procedure,23 the Cartesian representation of the
force constants were transferred to a nonredundant set of
local symmetry coordinates, chosen in accordance to the
2.2. IR, Raman and UV measurements
The FT-IR spectrum of the synthesized material was recorded
in the wavenumber range 400–4000 cm−1 by KBr pellet tech-
nique (Thermo Nicolet AVATAR 370 DTGS FT-IR spectropho-
tometer). The NIR-FT-Raman spectra were recorded using a
Bruker RFS 100/S spectrometer. The measurements were car-
ried out in the range of 100–3700 cm−1 (Happ–Genzel
apodization, 2 cm−1 resolution, 1064 nm Nd:YAG laser excita-
tion, 450 mW power at the sample). The UV-Vis absorption
spectrum of the sample was recorded in ethanol solution
using a Shimadzu UV-Vis spectrophotometer in the spectral
region of 200–500 nm. Thermal analysis of 3NCA was carried
out using a Perkin Elmer simultaneous thermogravimetric/
differential thermal (TGA/DTA) analyzer. The sample was
scanned in the temperature range 20–400 °C at a rate of
10 °C min−1 in an inert nitrogen atmosphere. The differential
scanning calorimetry measurements were performed on a
METTLER-TOLEDO DSC 1 apparatus equipped with a low
temperature attachment. Heating and cooling scans were car-
ried out at 5 °C min−1 in the −80 °C–180 °C temperature
range. The powdered 3NCA sample weighed 2.92 mg. Alumi-
num pans were used.
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recommendations of Pulay et al.24 Normal coordinate analysis
was performed to obtain full description of the molecular
motion pertaining to the normal modes using MOLVIB pro-
gram version 7.0 written by Sundius.25,26 The Raman activities
calculated with Gaussian 09 program are converted to relative
Raman intensities using the following relationship.
which ranges from 0.33 × 10−30 to 0.57 × 10−30 esu (38–66 au).29
This indicates that the first hyperpolarizability value calculated
with B3LYP/cc-pvdz level agrees well with the experimental.
Therefore our calculated results show that the static and
dynamic first hyperpolarizability values of 3NCA are nearly 18
and 24 times larger than those of urea.
Geometrical parameters obtained from DFT calculation
were used to perform NBO analysis by the NBO 3.1 program30
implemented in Gaussian 09 at DFT/B3LYP level in order to
understand various second order interactions between the
filled orbital of another subsystem, which is a measure of the
delocalization or hyperconjugation. The hyperconjugation
interaction energy was deduced from the second-order per-
turbation approach:
f (0 i )4 Si
Ii 
ð1Þ

hc
kT






i 
i 1 exp




where, υ0 is the exciting wavenumber (in cm−1), υi is the vibra-
tional wavenumber of the ith normal mode, h, c and k are uni-
versal constants, and f is the suitably chosen common scaling
factor for all the peak intensities.27 The second order polariz-
ability or first hyperpolarizability was calculated using B3LYP
with cc-pvdz basis set on the basis of the finite-field approach.
The components of the first hyperpolarizability can be calcu-
lated using the following equation:
2
2
 F 
F
ij
ð5Þ
E 2  n
 
 n

* 
E
where 〈σ|F|σ〉2 or Fij is the Fock matrix element between i
and j NBO orbitals, εσ and εσ* are the energies of σ and σ*
NBO's and nσ is the population of the donor σ orbital.
The TD-DFT method was used to calculate energies, oscil-
lator strengths of electronic singlet–singlet transitions and
the absorption wavelengths. Solvent effects were considered
using the polarizable continuum model (PCM) developed by
Tomasi and co-workers.31–33
2
X
βi ¼ βiii þ 1=3
ðβijj þ βjij þ βjjiÞ; i≠j
ð2Þ
Using the x, y and z components, and the magnitude of
the first hyperpolarizability tensor can be calculated by
1=2
β ¼ ðβ2x þ β2y þ β2z Þ
ð3Þ
The complete equation for calculating the magnitude of
first hyper-polarizability from Gaussian '09W output is given
as follows:28
5. Optimized geometry
The optimized structural parameters of 3NCA for are given
in Table S1 (ESI).† The corresponding values from X-ray dif-
fraction are also given in the table for comparison. The opti-
mized molecular structure of the compound with atom
numbering scheme adopted in the computations is shown
in Fig. 1 (a) and (b) (monomer & dimer, respectively) with
Cartesian axes. From the table it can be seen that there are
some deviations in the computed geometrical parameters
from those reported in the XRD data19 and these differences
are probably due to the intermolecular interactions in the
crystalline state. The experimental values of the C–H bond
lengths are around 0.94 Å. The interesting structural features
of 3NCA are the shortening of endocyclic angle C9–C1–C2
at the junction of the phenyl ring and propenoate group
and increase of the two neighbouring angle around the ring
C1–C9–C7 and C1–C2–C4 resulting from the charge transfer
2
2
β ¼ ½ðβxxx þ βxyy þ βxzzÞ þ ðβyyy þ βyzz þ βyxxÞ þ ðβzzz
2 1=2
þ βzxx þ βzyyÞ ꢀ
ð4Þ
The
components
of
the
static
and
dynamic
hyperpolarizability tensor components of 3NCA and urea mole-
cule are shown in Table 1. The calculated first
hyperpolarizability value of urea (βtotal = 32 au) at λ = 1064 nm
is in good agreement with the experimental data obtained from
the EFISH (electric-field-induced second harmonic generation)
measurement in water solution is (0.45 0.12) × 10−30 esu,
Table 1 First order hyperpolarizability (β) components of 3NCA and urea (a.u.)
Static (λ = ∞)
Dynamic (λ = 1064 nm)
β
components
3NCA
Urea
3NCA
Urea
βxxx
βxxy
βxyy
βyyy
βxxz
βxyz
βyyz
663
245
−192
−43
0
0
0
6
944
369
6
−1
16
1
0
0
−1
18
1
0
0
−263
8
0
0
0
0
0
βxzz
βyzz
βzzz
β(total)
−1
−5
0
7
0
0
−1
9
0
0
32
−7
0
755
510
29
Fig. 1 Optimized structure of 3NCA (a) monomer (b) dimer.
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(CT) interaction of the phenyl ring and ester group through
C12–C14 double bond. The evidence of such interaction can
be inferred from XRD data.19 DFT calculation indicates an
increase of the angles C1–C9–C7 and C1–C2–C4 by 1.41°
and 0.5°, respectively, and a reduction in endocyclic angle
C9–C1–C2 by 1.76°, associated with the CT interaction. The
repulsion between H3 and H15 leads to the enlargement of
angles C2–C1–C12 and C1–C12–C14 by 2.75° and 7.51°, respec-
tively, from 120°. The C1–C12–C14–C16 torsion angle of
−179.9° indicates that the benzene ring and the carboxylic
acid group are in an E configuration about the C12–C14 bond
and the propenoic acid moiety exists in an extended conforma-
tion. The dihedral angle between the 3-nitro group and the
benzene ring is 8.9°. In a related structure, viz. p-nitrocinnamic
acid,34 the nitro group is coplanar (2.2°) with the benzene ring.
With respect to the plane of the benzene ring, the 3-nitro group
is oriented at an angle of 45.3° in 4-dimethylamino-3-
nitrocinnamic acid,35 3.6° in 3,5-dinitrocinnamic acid and
2.3° in the 3,5 dinitrocinnamic acid 2,5-dimethoxycinnamic
acid complex,36 3.0° in the 3,5-dinitrocinnamic acid 4-(N,
N-dimethylamino)benzoic acid complex and 6.1° in the 3,5
dinitrocinnamic acid 4-(N,N-dimethylamino)cinnamic acid
complex.37
the molecule with the same geometry but in the absence of
electronic delocalization. The most important interaction
between “filled” (donor) Lewis type NBOs and “empty”
(acceptor) non-Lewis NBOs is reported in Table 2. The
hyperconjugative interactions are formed by the orbital over-
lap between π(C–C) bond orbital and π*(C–C) antibonding
orbital, which results in intramolecular charge transfer (ICT)
causing stabilization of the system. This strong ICT is one
of the causes of the NLO activity. These interactions are
observed as an increase in electron density (ED) in the C–C
antibonding orbital, which weakens the respective bonds. In
the benzene ring the ED at the two conjugated π bond (~1.63 e)
and π* bond (~0.3 e) clearly demonstrates the strong delo-
calization. The strong delocalization of π electron in the ben-
zene ring leads to a stabilization of ~22.5 kcal mol−1. The
NBO analysis can be employed to identify and substantiate
the possible intra and intermolecular interactions that would
form the hydrogen bonded network.38 The existence of
intermolecular O–H⋯O hydrogen bonds, due to the interac-
tion between the lone pair (LP) of oxygen with the antibond-
ing orbital σ*, has been confirmed by the results of NBO
analysis. The energy contribution of LP1O40 → σ*(O38–H39),
LP2O40 → σ*(O38–H39), LP1O37 → σ*(O41–H42), LP2O37
→
σ*(O41–H42) values are 11.10 kcal mol−1, 28.42 kcal mol−1,
11.10 kcal mol−1 and 28.41 kcal mol−1, respectively. These
energy E(2) values are chemically significant and can be used
as a measure of the intermolecular O–H–O hydrogen bonding
interaction between the oxygen lone pair and the antibond-
ing orbitals. The strengthening and contraction of the C–H
bonds is due to rehybridization,39 which is revealed by the
6. Natural bond orbital analysis
Natural bond orbital (NBO) analysis provides an efficient
method for studying intra- and intermolecular bonding and
charge transfer or conjugative interaction in molecular sys-
tems. The NBO analysis allows us to estimate the energy of
Table 2 Second-order perturbation theory analysis of Fock matrix in NBO basis
Donor (i)
ED(i) (e)
Acceptor (j)
ED(j)(e)
E(2)a (kcal/mol)
E(j) − E(i)b (a.u.)
F(i·j)c (a.u.)
π(C1–C9)
π(C1–C9)
π(C2–C4)
π(C2–C4)
π(C5–C7)
π(C5–C7)
π(C1–C9)
π(C2–C4)
π(C12–C14
π(C12–C14
1.60343
1.60343
1.66169
1.66169
1.63859
1.63859
1.60343
1.66169
1.85166
1.85166
0.35964
1.97389
1.99640
1.97389
1.99640
1.89512
1.89429
1.83920
1.83920
1.75184
1.94747
1.83920
1.94748
1.83922
π*(C2–C4)
π*(C5–C7)
π*(C1–C9)
π*(C5–C7)
π*(C1–C9)
π*(C2–C4)
π*(C12–C14
π*(N11–O17
π*(C1–C9)
π*(C16–O40
π*(C12–C14
σ*(C12–H13
σ*(C14–H15
σ*(C30–H31
σ*(C32–H33
σ*(N11–O18
σ*(N11–O17
σ*(C14–C16
σ*(C16–O41
π*(C16–O40
0.34146
0.29661
0.35964
0.29661
0.35964
0.34146
0.09197
0.61854
0.35964
0.33110
0.09197
0.01869
0.01702
0.01869
0.01702
0.05643
0.05616
0.05355
0.07064
0.33110
0.08824
0.08824
0.08821
0.08821
22.33
18.61
17.01
20.71
22.51
20.13
16.00
25.11
11.96
21.48
61.30
0.52
0.28
0.28
0.30
0.30
0.29
0.28
0.30
0.15
0.30
0.28
0.02
1.12
1.50
1.12
1.50
0.72
0.72
0.78
0.73
0.31
1.04
0.71
1.04
0.71
0.071
0.066
0.064
0.071
0.072
0.068
0.067
0.060
0.057
0.072
0.065
0.022
0.034
0.022
0.034
0.106
0.107
0.103
0.100
0.126
0.097
0.129
0.097
0.129
)
)
)
)
)
)
π*(C1–C9)
σ(C1–C12
σ(C16–O40
σ(C19–C30
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
)
0.96
0.52
0.96
σ (C34–O37
LP (2) O17
LP(2)O18
LP(2)O40
LP(2)O40
LP(2)O41
LP(1)O40
LP(2)O40
LP(1)O37
LP(2)O37
)
19.16
19.16
16.25
16.47
61.93
11.10
28.42
11.10
28.41
σ*(O38–H39
σ*(O38–H39
σ*(O41–H42
σ*(O41–H42
a
b
c
E(2) means energy of hyperconjugative interactions; cf. eqn (5). Energy difference between donor and acceptor i and j NBO orbitals. F(i, j)
is the Fock matrix element between i and j NBO orbitals.
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