Synthesis, physicochemical and quantum chemical studies on a new organic NLO crystal: Cinnamoylproline

Article abstract of DOI:10.1016/j.molstruc.2018.12.071

Cinnamoylproline was synthesized and the crystal was grown from solution by the slow evaporation method. The crystal belongs to the trigonal crystal system with non-centrosymmetric space group P3₁. The calculated geometry and experimental geome

Full text of DOI:10.1016/j.molstruc.2018.12.071

Accepted Manuscript
Synthesis, physicochemical and quantum chemical studies on a new organic NLO
crystal: Cinnamoylproline
M. Venkateshan, J. Suresh
PII:
S0022-2860(18)31504-7
DOI:
https://doi.org/10.1016/j.molstruc.2018.12.071
MOLSTR 26008
Reference:
To appear in: Journal of Molecular Structure
Received Date: 9 September 2018
Revised Date: 15 December 2018
Accepted Date: 18 December 2018
Please cite this article as: M. Venkateshan, J. Suresh, Synthesis, physicochemical and quantum
chemical studies on a new organic NLO crystal: Cinnamoylproline, Journal of Molecular Structure
(2019), doi: https://doi.org/10.1016/j.molstruc.2018.12.071.
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Synthesis, Physicochemical and Quantum chemical studies on a new organic
NLO crystal: Cinnamoylproline
M. Venkateshan*, J. Suresh
Department of Physics, The Madura College, Madurai – 625011, Tamilnadu, India.
Abstract:
Cinnamoylproline was synthesized and the crystal was grown from solution by the slow
evaporation method. The crystal belongs to the trigonal crystal system with non-centrosymmetric
space group P3 . The calculated geometry and experimental geometry from single crystal X-ray
1
data were compared. Intermolecular interactions were studied using Hirshfeld surface analysis
and its real space functions were calculated using Atoms In Molecules (AIM) and its isosurfaces
were visualized using Non-covalent interaction analysis. Optical transparency of the crystal was
analyzed by UV-Vis analysis and it was found that the crystal has good optical transparency in
the visible range and the lower cut-off wavelength was found to be 326 nm. In the
photoluminescence spectrum, a broad emission peak at 369 nm was observed. The functional
groups were analyzed using FTIR techniques and the vibrational frequencies from experimental
and theoretical values were compared. It was inferred from the TG-DTA studies that the crystal
was thermally stable up to 375°C. Kurtz-Perry powder SHG analysis was also carried out with
KDP as a reference. It showed that the crystal has 1.08 times greater efficiency than KDP. The
first hyperpolarizability tensor of the molecule was calculated theoretically and theoretical
second order susceptibility was obtained and compared with the experimental susceptibility.
Keywords: Crystal growth, First hyperpolarizability, QTAIM, Hirshfeld surface analysis, Non
Covalent Interaction (NCI), cinnamic acid.
*
Corresponding author: (M. Venkateshan)
Mobile: +91 9994344845
E-mail: m.venkateshan16@gmail.com

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1
. Introduction
Organic nonlinear optical (NLO) material are preferred over to the inorganic NLO
material due to their higher order optical conversion efficiency. NLO materials find application
in the fields of optical storage devices, terahertz wave generation, optical signal processing,
frequency conversion, LASER remote sensing and medical diagnostics [1-6]. In organic single
crystals, the organic molecules are packed or stabilized by intermolecular interactions like Van
der Waals interactions and hydrogen bonding [7] which contribute significantly to the physical
characteristics of the molecule. Hence a study of these interactions is important in our
understanding of the NLO properties of these crystals. Hirshfeld surface [8-10] and its related 2D
fingerprint plots [11] are simple tools that enable us to study and analyse these intermolecular
interactions. Density functional theory (DFT) is helpful in estimating various molecular
properties like equilibrium geometry, UV-Vis spectra, IR spectra, first order hyperpolarizability
of NLO materials and the SHG susceptibility theoretically.
Cinnamic acid derivatives showed some medicinal properties like anti-cancer [12], anti-
tuberculosis [13], anti-malarial [14], anti-fungal [15], anti-microbial [16], haemostatic agents
[17] and also possess non-linear optical behaviour [18]. Likewise, some compounds containing
proline showed NLO activity [19,20]. The amide derivatives of carboxylic acids can be prepared
by treating with amino acids in the basic medium by the activation of carboxylic acid using
2 3
carbodimides [21], SOCl [22] or POCl [23].
In the present work, single crystal of cinnamoylproline (CP) was grown by solvent
evaporation technique and characterized by single crystal X-ray diffraction, Powder X-ray
diffraction, UV-Visible spectra, FTIR spectra, Photoluminescence, TG-DTA and second

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harmonic generation NLO studies. Also, DFT calculation was used in the molecular orbital
analysis, UV-Vis absorption spectra, IR spectra, first order hyperpolarizability and second order
nonlinear susceptibility calculation. The intermolecular interactions like C-H…O and O-H…O
present in the crystal was studied using Hirshfeld surface analysis and 2D fingerprint plots. The
topological analysis using Quantum Theory of Atoms In Molecules (QTAIM) [24] at the Bond
Critical Point (BCP) was carried out to estimate its real space values to find hydrogen bond
strengths. Non Covalent Interactions (NCI) [25,26] method has been used for visualizing the
various types of interactions present in the crystal.
2
2
. Experimental and theoretical methods
.1 Synthesis
Cinnamoylproline was synthesized from the reaction of cinnamoyl chloride (98% purity)
and proline (99% purity). Starting materials were purchased from Sigma Aldrich and Himedia.
Cinnamoyl chloride (0.083 g) was dissolved in 5ml of THF (100mM) and 0.212 g of K PO
200mM) was added and stirred for 1 hour. L-proline (0.058 g) was taken in 5ml of THF
100mM) and added to the above stirred mixture (Fig. 1). This reaction mixture was refluxed for
2 hours and then solvent was removed. To the precipitate, 20ml of water was then added and
3
4
(
(
1
filtered. The insoluble material was filtered off. The filtrate was extracted with ethyl acetate. To
the aqueous layer 2N HCl was added to get the pH of 2. After washing with water the solid
product was the synthesized compound. (Yield : 78%).
2
.2 Crystal growth
The synthesized compound was dissolved in methanol and stirred for 5 minutes to obtain
a homogeneous solution. This solution was poured into a beaker and covered with perforated

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polyethylene cover and kept in an undisturbed, dust free environment and allowed to evaporate
slowly. After a few days colorless, hexagonal shaped crystals were formed.
2
.3 Single crystal X-ray diffraction (SXRD)
A good quality optically clear 0.21 x 0.20 x 0.18 mm sized crystal was mounted on the
3
goniometer head of Bruker kappa APEX II diffractometer using the MoKα radiation source for
X-ray data collection. The intensity data were collected at 20°C. Absorption correction for data
was carried out using the SADABS program with multi-scan method. The structure was solved
using SHELXS in direct method and refined least squares method using SHELXL embedded in
SHELXTL-2014 [27,28]. Hydrogen atoms were fixed on the basis of riding model and refined
isotropically and all other atoms were refined anisotropically. In final refinement cycles, the
structure was refined as an inversion twin using TWIN/BASF commands with the BASF value
of -0.13501. This yields the final, absolute structure parameter of (Flack [29] parameter x) -0.1
(15). Refined structure was validated using the software named PLATON [30] finally the CIF
was validated using CheckCIF from IuCr. Thermal ellipsoid image and molecular packing
diagrams were generated using ORTEP [31] and Mercury [32]. Intermolecular interactions were
revealed from the PARST [33] program. Crystallographic data and refinement parameters were
listed in Table 1.
2
.4 Powder X-ray diffraction
Powder X-ray diffraction data were collected on Bruker ECO D8 powder diffractometer
at room temperature using Cu Kα radiation with wavelength 1.5406Å. The 2θ scan range was
1
0-50°, with a step size of 0.02°.
2
.5 Computational details

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Theoretical DFT calculations for geometry optimization were done using the
computational package ORCA 3.0.3 [34]. The experimentally obtained structure and optimized
structure was overlaid and presented in Fig. S1. First hyperpolarizability tensor for the
calculation of second order nonlinear susceptibility calculations was done using the software
package Dalton [35,36]. The input file for ORCA to calculate geometry optimization was
generated from experimental crystal data as initial coordinates with the DFT B3LYP level of
theory with 6-311G(2d,2p) [37] basis set. This optimized geometry was used for finding UV-vis
absorption wavelength, corresponding oscillator strength and IR vibrational frequencies. Non-
linear properties like polarizability, hyper polarizabilities were calculated at the CAM-B3LYP
[
38] level of theory with NLO-V [39,40] as a basis set. NLO-V basis sets downloaded from the
basis set exchange portal.
For the analysis of QTAIM and NCI, the Single Point energy calculation was done using
the single crystal X-ray geometry as input. The molecules and its aggregates were selected in
order to cover all the interactions (Fig. S2). The output wavefunction file was used for the
analysis. For QTAIM analysis Multiwfn [41] software was used and for NCI study, NCIPLOT
[42] program was used. The combined outputs were visualized using VMD [43] software.
3
3
. Results and discussion
.1 Single crystal X-ray diffraction studies
CP was crystallized in the trigonal crystal system with non-centrosymmetric space group
P3 . Its unit cell values are a = 15.9976(10) Å, b = 15.9976(10) Å, c = 13.4251(7) Å and V =
1
3
2
975.5(4) Å . The asymmetric unit contains three crystallographically independent molecules of
CP (say A, B, and C) (Fig. 2). The molecules A, B and C were overlaid and shown in Fig. S3. In
all the three molecules the phenyl ring (C1-C6) is nearly a planar with the r.m.s deviation of 0.01

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1
Å/0.0105 Å/0.006 Å for molecules A/B/C with the fitted atoms. The conformation angles χ (N1-
2
3
4
C13-C12-C11), χ (C13-C12-C11-C10), χ (C12-C11-C10-N1), χ (C11-C10-N1-C13) and θ
(C10-N1-C13-C12) of a pyrrolidine ring of A, B and C molecules are reported in Table 2. In all
β
three molecules pyrrolidine ring (N1, C10-C13) adopts C -C12 -exo conformation [44,45]. This
s
is confirmed by Cremer-Pople puckering parameters (q φ ) [46] and the flap atom C12 from the
2
,
2
mean plane drawn for another four atoms (Table 2). The atom C12 flap from the mean plane of
N1, C10, C11, C13 for molecules A/B/C are 0.518(1) Å/0.558(1) Å/0.508(1) Å. The similar
characters are observed in many analogous structures [45,47].
The pyrrolidine ring makes a dihedral angle of 32.10(2)°/30.92(2)°/36.31(2)° with the
phenyl ring in A/B/C. The sum of the angle around N1 is 359.18 (2)°/359.71 (3)°/359.41 (2)° for
2
A/B/C reveals that N1 is in sp hybridization [48].
The crystal is stabilized through C – H … O and O – H … O interactions. In molecule A
an intermolecular interaction O2A - H2A1 … O1A links symmetry related molecules forming a
one dimensional chain motif C(7) (Fig. 3 (a)) with a base vector [001]. This similar pattern is
followed in molecules B and C. Molecule A interconnects B through C2A – H2A … O3B,
molecule B links C through the interaction C8B – H8B … O3C and C connects to A through the
intermolecular interaction C1C – H1C … O3A. These C – H … O interactions form a three
dimensional network (Fig. 3 (b)). The possible intermolecular interactions produced from
PARST were listed in Table 3. C – H … π interactions are also observed. Since they are so weak
so that they have omitted from the discussion.
3
.2 Powder X-ray diffraction (PXRD) analysis
Powdered sample of as grown crystal was subjected to PXRD analysis to identify the
crystallanity also to confirm that the crystal structures represent the bulk material in truth. PXRD

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pattern was simulated and the peaks were indexed using Mercury software from experimental
SXRD data. Fig. 4 represents the correlated spectrum of experimental and simulated PXRD
patterns. The two spectra were matched well, which proves the synthesized bulk material is same
as the single crystal and the well-defined peaks defines the crystallanity.
3
.3 Hirshfeld surface analysis
SXRD data reveal the presence of intermolecular interactions present in the crystal
structure. To study, the percentage of contribution of different intermolecular interactions present
in the structure, Hirshfeld surface (HS) analysis was carried out. HS [9,49] along with 2D
fingerprint plots [8,11] are interesting tools for visualizing and studying about intermolecular
interactions. In order to construct HS and its associated 2D fingerprint plots the software called
Crystal Explorer 3.1 [50] was used. 3D HS with the surface property of dnorm is an easy
visualization tool generated from d , d and van der Walls radii. The d is the ratio between the
norm
i
e
distance of the point from the surface to the interior atom (d ) and the exterior atom (d ) to the
i
e
vdw
van der Walls radii (r ). If the distance of an atom from the surface is lower than the van der
Walls radii, then the dnorm will be negative shows that closer proximity indicates an interaction.
This is specified as red spots. If the distance of an atom from the surface is higher than the van
der Walls radii, then the dnorm will be positive shows that there is no possible interaction. This is
specified as blue spots. The 2D fingerprint plot is another view of interaction, plotted from d vs
i
d .
e
In order to find out whether all the three molecules have equal proportions of
interactions, HS study was carried out for those molecules independently. The results were
shown in Fig 5. It was inferred from the analysis in all respects that, all the molecules have equal

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contributions to the crystal packing. Therefore molecule B was arbitrarily chosen for further
analysis.
2
Fig. S4 shows the 3D dnorm surface generated with a surface area of 292.86 Å and
3
volume of 324.41 Å . The globularity (G) [51] (defines how much the structure varies from
sphere (G = 1) of similar volume) value is 0.780 and the asphericity (ꢀ) [52] (defines the
anisotropy of the structure) value is 0.295 suggests that the structure is nearly an oblate (for
oblate ꢀ = 0.25) [52]. In this figure, there are two bright red spots corresponds to O - H…O
interaction and one light red spot appearing corresponds to C – H…O interaction. For the O – H
…
O interactions the sum of distances d
van der Waals radii of 2.61 Å [53,54] indicate a bright red spot, and for C – H …O interaction di
de is 2.41 Å which is smaller than the van der Waals radii of 2.61 Å indicate a light red spot on
i e
and d is 1.81 Å which is very much smaller than the
+
the surface. 3D HS was translated to 2D fingerprint plots and they are presented in Fig. 5. In the
FP plot O…H/H…C interaction shows two distinct sharp spikes [55]. The fingerprint analysis
does not show the equal contribution of O … H and H … O interactions. O … H interactions are
depicted as a sharp spike on the bottom left area and H … O interactions are presented as a sharp
spike on the bottom right of fingerprint plot. O … H interactions contribute slightly higher
(
13.9%) than the H … O interactions (12.5%) (See supplementary data Fig. S5). C … H
interactions were plotted as a pair of wings shaped [56], in this C … H interaction contributes
13.9%) higher than the H … C interaction (11.2%) (See supplementary data Fig. S6). These
(
contributions may be arrising from the presence of weak C – H … π interactions and van der
Walls interactions. Fig. S7 shows the individual contributions of interactions from HS analysis.
3
.4 QTAIM and NCI

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Bader’s QTAIM theory was used to quantify the interaction energies present in the
structure. The interaction energy is directly related to the electron density (ρ) at the BCP between
the two atoms. In order to be a non-covalent interaction like hydrogen bonds, van der Walls
interactions; the derivative of electron density called Laplacian of the electron density (
∇ꢀ
ꢁ) should be positive. This Laplacian is further divided into three Eigenvalues (ꢂ , ꢂ and ꢂ ).
ꢃ ꢀ ꢄ
The NCI index uses the sign of the ꢂ in order to differentiate attractive or repulsive interactions.
ꢀ
The positive sign of ꢂ represent the repulsive steric crowding, the negative sign of ꢂ represent
ꢀ
ꢀ
the attractive hydrogen bonds and the value near to zero corresponds to a van der Walls
interaction. The NCI index also uses another derivative of density called reduced density
gradient (S) which has a value nearer to zero at the BCPs. A graph plotting with sign(ꢂ )ρ versus
ꢀ
S is very helpful in understanding the type of interactions present in the structure. The NCI
isosurface is red-green-blue colour coded based on the sign(ꢂ )ρ value. Red represents repulsion,
ꢀ
green for van der Walls interaction and blue represents strong hydrogen bonds [25,35].
ꢀ
QTAIM descriptors like electron density (ρ), Laplacian of the electron density (∇ ꢁ),
potential energy density (V), Lagrangian kinetic energy (G) at the BCP’s were represented in the
Table 4. The hydrogen bond energies were calculated using the relation EHB = V(r)/2. According
ꢀ
to Popelier [57] for a hydrogen bond ρ must fall in the range 0.002 to 0.035 a.u and ∇ ꢁ value in
between the range 0.024 to 0.139 a.u.
Results obtained from the topological analysis of the selected bonds from PARST
program are tabulated in Table 4. From this table the estimated ρ value ranges from 0.00221 to
ꢀ
0
.02894 a.u. and ∇ ꢁ value ranges from 0.0118 to 0.11025 a.u. The Laplacian values of some C-
H…O bonds are well below from the required value and these bonds have very minimum
interaction energies. These can be ratified from the SXRD data of bond lengths and bond angles

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of these bonds (Table 3). So these interactions may be considered as van der Walls interactions.
Therefore, we have only considered the first seven hydrogen bond interactions in Table 4, which
obeys the value given by Popelier.
In the title compound O-H…O interactions plays the major role for molecular packing by
giving the moderately strong interactions as expected. This can be supported by the NCI plot
with a light blue isosurface surrounds a QTAIM BCP in between the O-H…O bond and well
separated broad blue spike in the 2D reduced density gradient graph (Fig. 6). The energy values
-1
are in the range -31.81 to -30.027 kJ.mol . These values are in good agreement with the
previously reported O – H … O energy values. Chahkandi [58] and co-workers analyzed the O –
H …O and C – H … O interactions of 4-[(4-chlorophenyl)amino]-4-oxobutanoic acid and
reported its interaction energies. For O – H … O interaction they have reported energies of -
-
1
5
0.08 and -44.61 kJ.mol in D…A distance of 2.625 Å and 2.946 Å. In the title compound we
have found energies corresponding to O – H … O interactions as -31.81, -30.608 and -30.027
-1
kJ.mol with D…A distance of 3.333, 3.355 and 3.403 Å respectively (Table 3 and 4).
Further C – H …O analysis was done and obtained energies were lying between -8.027 to
-1
-
7.581 kJ.mol . The existence of these interactions was also identified by the formation of
corresponding BCPs from QTAIM analysis and ratified from the NCI plot by an isosurface
enclosed that BCP. These values are also concurred with the already existing C – H … O bond
energies [59]. In comparison with the reported values, our values match adequately with the
support of experimental SXRD bond lengths and bond angles. The smaller interaction energies
were already assigned to van der Walls interactions are also present in the NCI plot isosurface
and 2D reduced gradient graph.
3
.5 HOMO - LUMO analysis

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The studies on frontier molecular orbital expose the chemical reactivity, chemical
hardness or softness of the molecule and kinetic stability [56]. The energy of HOMO (Highest
Occupied Molecular Orbital) level is -6.642 eV and for LUMO (Lowest Unoccupied Molecular
Orbital) level energy is -2.178 eV. The 3D plots of frontier molecular orbitals and energies of the
HOMO, HOMO-1, HOMO-2, HOMO-3, HOMO-4, HOMO-5, HOMO-6, LUMO and LUMO+1
of CP computed at the B3LYP/6-311G(2d,2p) level are shown in Fig. 7. The positive phase is
denoted as blue and negative phase is red. The HOMO level has the electron releasing capability
and LUMO has the electron withdrawing capability. The energy gap between these levels is
4
.464 eV. This energy gap is an important parameter to determine some of the molecular
properties like chemical hardness (η), electronegativity (χ), electronic chemical potential (µ) and
global electrophilicity index (ω).
HOMO level of energy is assigned as the ionization potential (I) and LUMO is assigned
as electron affinity (A), I = -EHOMO and A = -ELUMO. The electronegativity (χ) of a compound
which measures the ability of attracting electrons towards its side can be calculated using the
(
ꢆꢇꢈ)
ꢀ
relation, ꢅ =
. From this relation electronegativity of CP is χ = 4.41 eV. Chemical potential
(µ) can be described as the escaping capacity of electrons from its equilibrium state [60], it can
(
ꢆꢇꢈ)
ꢀ
be calculated using, ꢉ = −
. By using this chemical potential of CP is µ= -4.41 eV. The
chemical hardness or softness tells about the reactivity, stability of a molecule. It can be obtained
(
ꢆꢋꢈ)
ꢀ
ꢃ
-1
using the relations, ꢊ =
, ꢌ = . Using these relations, η = 2.232 eV, S = 0.224 eV . This
ꢀꢍ
indicates that CP possesses high chemical stability. The global electrophilicity index (ω) is
ꢐ
ꢏ
defined as ꢎ = ꢀꢍ. This defines the electron accepting ability or power of a molecule from the

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surrounding without changing its stability [56]. The global electrophilicity index (ω) of CP is
found to be ω = 4.356 eV.
3
.6 UV-Vis analysis
Optical transparency and cut-off wavelength are necessary properties of a material to be
acting as a NLO material [61]. The UV- Vis analysis was carried out in the wavelength range
between 200 - 800 nm. The correlated theoretical and observed electronic spectra were shown in
Fig. 8. Experimental and calculated electronic absorption wavelength, Excitation energy (E),
Oscillator strength (f), orbital contribution calculated at B3LYP/6-311G(2d,2p) level were shown
in Table S1.The calculated spectra obtained in gas phase consists of five absorption peaks
centered at 210 nm, 219 nm, 244 nm, 270 nm and 292 nm. In the observed spectra the absorption
peaks were found at 206 nm, 218 nm, 248 nm, 276 nm and 284 nm. The absorptions at 206 nm,
2
18 nm, 248 nm and 276 nm were corresponded to π→π* transition, 284 nm attributed due to the
transition n→π* [62]. The CP has a lower cut-off wavelength at 326 nm and shows transmission
in the entire visible region which makes it a potential material for NLO applications.
3
.7 Photoluminescence
Photoluminescence (PL) is a process of spontaneous emission of light radiation when
excited by an excitation light of a particular wavelength. The molecule with conjugated π bonds
may exhibit PL activity. The PL emission spectra of CP was recorded in the range 320 to 500 nm
at an excitation wavelength of 326 nm. The maximum emission was occurring at 369 nm which
is in the UV region (Fig. 9). The PL spectra shows a broad emission, which supports the
presence the strong intermolecular interactions.
3
.8 FTIR analysis

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The presence of functional groups of CP was analyzed from FTIR spectra and it was
compared with the theoretical values calculated from DFT methods and a comparison was
tabulated in Table 5 and pictured in Fig. 10. There are 91 normal modes of vibrations with no
imaginary frequency were identified from theoretical calculations. There is some mismatch in
frequencies arose due to the fact that the DFT calculation was carried out for geometry optimized
structure in gas phase whereas the experimental frequencies were observed in solid crystal.
-1
In the FTIR spectrum the peak at 3599 (3591) cm is assigned to the O-H stretching of
COOH group. The vibrations corresponding to C-H stretching of phenyl ring and pyrrolidine
-1
-1
ring are observed at 3194 (3197) cm and 3099 (3097) cm respectively. The observed peak at
-1
1
736 (1745) cm is assigned to C=O anti-symmetric stretching of carboxylic acid group. C=C
-1
-1
skeletal vibration is observed at 1647 (1683) cm . The vibration at 1571 (1587) cm is assigned
-1
to C=O stretching. Aromatic C-C stretching is observed at 1446 (1497) cm . The vibration peak
-1
-1
at 1323 (1336) cm is due to C-H in-plane deformation. The peaks at 1255 (1249) cm and 1193
-1
-1
(
1199) cm are due to C-N stretching. The band at 977 (983) cm is attributed to C-H out of
-1
plane deformation. The aromatic C-H wagging occurs at 902 (902) cm . The vibration at 767
-1
(
757) cm is due to C-H out of plane bending. C-H bending mode of vibration occurs at 653
-1
(
651) cm . The values in the parenthesis indicate the theoretical wavenumber.
.9 Thermal studies
Thermal stability is an important property for a potential NLO material. To analyze the
3
thermal stability and to confirm the melting point of the material, the Thermo Gravimetric
Analysis (TGA) and Differential Thermal Analysis (DTA) were carried out using a Perkin Elmer
thermal analyzer from room temperature to 730°C at a heating rate of 20°C/min in the air. The
results were depicted in Fig. 11. The crystal undergoes three steps degradation. Below 100°C

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there is no significant weight loss was observed, hence, there is no solvent molecule was
included into the crystal. In the DTA there is a sharp endothermic peak at 375.7°C; this is
assigned to the melting point of the material. This shows that CP is suitable for high energy laser
applications. The first weight loss of 4.5 % was observed at 303°C. The second stage
degradation occurred between 305°C to 420°C, third stage between 420°C to 504°C. The second
and third stage degradations are due to the evolution of some volatile compounds.
3
.10 NLO SHG analysis
The second harmonic generation efficiency of powdered CP was analyzed using Kurtz
and Perry powder technique [63]. A Q-switched Nd:YAG laser of wavelength 1064 nm was used
as a radiation source. CP was uniformly grounded with the same particle size as that of KDP,
which was used as a reference for SHG measurements. The SHG property of CP was confirmed
from the emission of green wavelength (532 nm). Comparison of SHG efficiency of CP with
KDP is depicted in Fig. 12. From the figure it can be concluded that SHG efficiency of CP is
1
.08 times to that of KDP.
The quantum chemical approach is an easy and effective way of predicting NLO
properties from the molecular electronic structure [64]. In order to calculate the SHG efficiency,
polarizability and first order hyperpolarizability must be calculated. The polarizability and first
order hyperpolarizability are the measure of an ability of an electric field to distort the electronic
distribution of a molecule.
The total static dipole moment (ꢁ), the mean polarizability (α), the anisotropy
polarizability (∆α) and first hyperpolarizability (β) using the components x, y, z can be
calculated using the relations given below.
ꢀ
ꢀ
ꢀ
Total static dipole moment, ꢉ = ꢑꢉ + ꢉ + ꢉ
ꢔ
ꢒ
ꢓ

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ꢖꢗꢗꢇꢖꢘꢘꢇꢖꢙꢙ
ꢄ
The mean polarizability, ꢕ =
The anisotropy of polarizability is,
1
ꢀ
ꢀ
ꢀ
ꢀ
Δꢕ =
ꢚ(ꢕꢒꢒ − ꢕ ) + (ꢕ − ꢕ ) + (ꢕ − ꢕ ) + 6ꢕ
ꢓꢓ ꢓꢓ ꢔꢔ ꢔꢔ ꢒꢒ ꢒꢒ
√
2
The First order hyperpolarizability equation is,
ꢛ = ꢚ(ꢛꢒꢒꢒ + ꢛꢒꢓꢓ + ꢛꢒꢔꢔ)ꢀ + (ꢛꢓꢓꢓ + ꢛꢒꢒꢓ + ꢛꢓꢔꢔ)ꢀ + (ꢛꢔꢔꢔ + ꢛꢒꢒꢔ + ꢛꢓꢓꢔ)ꢀ
The outputs from Dalton software are reported in atomic units (a.u). Therefore, the
-24
calculated values have been converted into electrostatic units (esu) (α: 1 a.u. = 0.1482 x10 esu;
-33
5
-1
β: 1 a.u. = 8.641 x 10 cm esu ). The calculated values of ꢁ, α, ∆α and β for the compound
-24
-24
-30
5
-1
were found to be 7.54759 D, 82.621 x10 esu, 71.9583 x 10 esu, and 3.307 x 10 cm esu
respectively. The non-zero value of dipole moment indicates that CP is a polar compound. The
values of the dipole moment, polarizability and first hyperpolarizability components were listed
in Table 6. From the calculated β value it is possible to calculate the second order susceptibility
(
2)
χ . The SHG susceptibility of a bulk material can be obtained using the relation [65],
(
ꢀ)
ꢅ
(−2ꢎ; ꢎ, ꢎ) = ꢟꢠꢛꢜꢝꢞ(−2ꢎ; ꢎ, ꢎ)
ꢜꢝꢞ
Where, ꢟ = 1⁄ꢡꢞꢢꢣꢣ (Vcell is the unit cell volume). L is the local field correction factor.
ꢐ
ꢦ ꢇꢀ
ꢄ
ꢠ = ꢤꢜꢀꢥꢤ ꢤ and ꢤ
ꢥ
ꢥ
ꢀꢥ
=
ꢧ
=
.Here n
is the refractive index and α
is the first
ꢝ
ꢞ
ꢜ
ω
ω
ꢄ
(ꢄꢋꢨꢩꢪꢖꢧ)
order polarizability. The value of L was calculated with the approximation of α = α [66].
2
ω
ω
(
2)
(2)
(ꢀ)
The experimental value of χ (exp)can be calculated with χ (exp) = ꢫ × ꢅ (KDP).
(
2)
Where, χ (KDP) = 2d , b is the NLO efficiency compared with KDP (for CP the value of b is
3
6
-9
1
.08). The selected valued36 of KDP is the average value 1.6 x 10 esu. The second order
(
2)
-9
(2)
-9
susceptibility of CP was obtained as, χ (cal) = 1.2506 x 10 esu and χ (exp) = 3.456 x 10 esu.

ACCEPTED MANUSCRIPT
4
Conclusions
The optically transparent NLO material CP was synthesized and grown from slow
evaporation technique. PXRD revealed the crystallanity. From the comparison of PXRD
diffractograms the phase purity was confirmed. FTIR and SXRD studies confirmed the structure
of CP. Also SXRD revealed the non-centrosymmetric nature of CP. SXRD exposed the presence
of O – H … O and C – H … O intermolecular interactions, which were further confirmed by
Hirshfeld surface analysis of 3D surface and 2D finger print plots. Also interaction energies were
quantified by QTAIM and its isosurfaces were visualized through colour coded NCIPLOT. UV-
Vis analysis revealed the lower cut-off wavelength as 326 nm and also the existence of π→π*
and n→π* transitions. Also, it revealed the transparency of the CP in the entire visible range.
The broad emission of CP around 369 nm proven by PL with an excitation wavelength of 326
nm suggested that the CP can be used to design a UV laser. Thermal stability of the material was
analyzed by TG-DTA which showed that the CP has a thermal stability up to 375°C. Also, it
exposed the nature of three step degradation of CP. Kurtz-Perry powder method revealed the
presence of SHG with an efficiency of 1.08 times greater than KDP. Theoretical calculations
were performed for UV-vis absorption analysis, FTIR vibrational frequencies, HOMO-LUMO
molecular orbital analysis and NLO SHG susceptibility. HOMO-LUMO analysis revealed the
band gap of CP as 4.464 eV. From the HOMO-LUMO values, varies molecular properties
related to its chemical stability were calculated. Theoretical first hyperpolarizability of CP was
-30
5
-1
found to be 3.307 x 10 cm esu and the experimental and theoretical second order
-9
-9
susceptibility values were obtained as 1.2506 x 10 esu and 3.456 x 10 esu respectively.
5
Supplementary crystallographic data

ACCEPTED MANUSCRIPT
CCDC 1832360 contains the supplementary crystallographic data for this paper. The data can be
obtained free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/structures.
Acknowledgements
The authors thank the management of The Madura College for their support, SAIF, IIT
madras, Chennai for SXRD data collection, also SAIF, Cochin for TG-DTA analysis. The
authors also thank Kalasalingam Academy of Research and Education for Powder XRD
measurement. They also thank Department of chemistry, The Madura College for UV and FTIR
support, Department of chemistry, V.H.N.S.N college, Virudhunagar for PL studies. MV thank
Dr. Gajanan G. Muley, Asst. Prof., Sant Gadge Baba University, Amravati, for NLO studies.
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Table caption
Table 1: SXRD crystallographic data of CP.
Table 2: Conformation angles of Pyrrolidine ring.
Table 3: Hydrogen bonds of CP from PARST [Å and °].
Table 4: QTAIM descriptors of the BCPs for the intermolecular interactions present in the
structure.
Table 5: FTIR vibrational frequencies assignment.
Table 6: Calculated dipole moment, polarizability, first-order hyperpolarizabilities (β) and
(
2)
second-order susceptibility χ .

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Table 1: SXRD crystallographic data of CP.
Empirical formula
Formula weight
Temperature
14 3
C H15 N O
245.27
293(2) K
0.71073 Å
Trigonal
P 31
Wavelength
Crystal system
Space group
Unit cell dimensions
a = 15.9976(10) Å;
b = 15.9976(10) Å;
c = 13.4251(7) Å;
3
Volume
Z
2975.5(4) Å
9
3
Density (calculated)
1.232 Mg/m
-1
Absorption coefficient
F(000)
0.087 mm
1170
3
Crystal size
0.21 x 0.20 x 0.18 mm
Theta range for data collection
Index ranges
1.470 to 25.350°.
-19<=h<=19, -19<=k<=19, -16<=l<=16
36504
Reflections collected
Independent reflections
Completeness to theta = 25.242°
Max. and min. transmission
Data / restraints / parameters
7262 [R(int) = 0.0745]
100.0 %
0.974 and 0.967
7262 / 1 / 489
2
Goodness-of-fit on F
1.001
Final R indices [I>2sigma(I)]
R indices (all data)
R1 = 0.0464, wR2 = 0.0880
R1 = 0.1309, wR2 = 0.1140
-0.1(15)
Absolute structure parameter
Extinction coefficient
0.0028(6)
-3
0.164 and -0.145 e.Å
Largest diff. peak and hole

ACCEPTED MANUSCRIPT
Table 2: Conformation angles of pyrrolidine ring.
1
2
3
4
Molecule
χ
χ
χ
χ
θ
q
2
φ
2
A
B
C
30.8(6) -35.2(8) 24.9(8) -4.6(7) -16.5(6)° 0.334(8) (Å) 100.0(11)°
33.9(6) -36.8(6) 25.1(6) -3.0(6) -19.4(6)° 0.360(7) (Å) 102.5(10)°
30.6(6) -35.1(7) 25.1(7) -5.6(7) -15.2(6)° 0.333(7) (Å) 97.9(10)°