Synthesis, growth, physicochemical properties and DFT calculations of 2-naphthol substituted Mannich base 1-(morpholino(phenyl) methyl) naphthalen-2-ol: A non linear optical single crystal

Article abstract of DOI:10.1016/j.molstruc.2017.06.133

2-Naphthol substituted Mannich base 1-morpholino(phenyl)methyl)naphthalen-2-ol (MPMN), a potential NLO active organic single crystal was developed using acetonitrile as a solvent by slow evaporation method. The experimental and theoretical analysis made t

Full text of DOI:10.1016/j.molstruc.2017.06.133

Accepted Manuscript
Synthesis, growth, physicochemical properties and DFT calculations of 2-naphthol
substituted Mannich base 1-(morpholino(phenyl) methyl) naphthalen-2-ol: A non
linear optical single crystal
A. Dennis Raj, M. Jeeva, M. Shankar, G. Venkatesa Prabhu, M. Vimalan, I. Vetha
Potheher
PII:
S0022-2860(17)30914-6
10.1016/j.molstruc.2017.06.133
MOLSTR 24019
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 6 January 2017
Revised Date: 29 June 2017
Accepted Date: 30 June 2017
Please cite this article as: A. Dennis Raj, M. Jeeva, M. Shankar, G. Venkatesa Prabhu, M. Vimalan,
I. Vetha Potheher, Synthesis, growth, physicochemical properties and DFT calculations of 2-naphthol
substituted Mannich base 1-(morpholino(phenyl) methyl) naphthalen-2-ol: A non linear optical single
crystal, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.06.133.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
1
Synthesis, Growth, Physicochemical properties and DFT calculations of 2-naphthol
substituted Mannich base 1-(morpholino(phenyl) methyl) naphthalen-2-ol:
A Non linear Optical Single crystal
A. Dennis Raja, M. Jeevab, M. Shankarc, G. Venkatesa Prabhub, M. Vimaland,
I. Vetha Potheherc*
aDepartment of Physics, Mookambigai College of Engineering, Pudukkottai - 622502, India.
bDepartment of Chemistry, National Institute of Technology, Tiruchirappalli-620015, India.
cDepartment of Physics, University College of Engineering, Bharathidasan Institute of
Technology Campus, Anna University, Tiruchirappalli-620 024, India.
dDepartment of Physics, Thirumalai Engineering College, Kilambi, Kancheepuram-631531,
India.
Abstract
2-Naphthol substituted Mannich base 1-morpholino(phenyl)methyl)naphthalen-2-ol
(MPMN), a potential NLO active organic single crystal was developed using acetonitrile as a
solvent by slow evaporation method. The experimental and theoretical analysis made towards
the exploitation in the field of electro-optic and NLO applications. The cubic structure with non-
centrosymmetric space group Cc was confirmed and cell dimensions of the grown crystal were
obtained from single crystal X-ray diffraction (XRD) study. The formation of the C-N-C
vibrational band at 1115 cm-1 in Fourier Transform Infra-Red (FTIR) analysis confirms the
formation of MPMN compound. The placement of protons and carbons of MPMN were
identified from Nuclear Magnetic Resonance Spectroscopy (NMR) analysis. The wide optical
absorption window and the lower cutoff wavelength of MPMN show the suitability of the
material for the various laser related applications. The presence of dislocations and growth
pattern of crystal were analyzed using chemical etching technique. The second harmonic
generation (SHG) of MPMN was found to be 1.57 times greater than the standard KDP crystal.
The laser damage threshold was measured by using Nd: YAG laser beam through the sample and

ACCEPTED MANUSCRIPT
2
it was found to be 1.006 GW/cm2. The electronic structure of the molecular system and the
optical properties were also studied from quantum chemical calculations using Density
Functional Theory (DFT) and reported for the first time.
Keywords: Mannich Base, Molecular structure, Single crystal XRD, Density Functional Theory,
Laser damage threshold.
*Corresponding Author: Dr. I. Vetha Potheher, Assistant Professor of Physics, University
College of Engineering, Bharathidasan Institute of Technology Campus, Anna University,
Tiruchirappalli- 620024, India. Mobile: +919942994274, Email: potheher11@gmail.com

ACCEPTED MANUSCRIPT
3
1. Introduction
In the recent years, Non-Linear Optical (NLO) crystals have attracted the researchers due
to their potential applications in high power laser for inertial confinement fusion research [1, 2],
electro-optic switches, frequency conversion [3], color display and photonics including optical
information processing [4-7]. To have strong second-order NLO properties, the compound must
possess a large first-order molecular hyper polarizability (β), and also must crystallize in a
noncentro symmetric structure to have nonzero second-order polarizability (χ2) [8]. It has been
generally understood that, for a material to have useful and high efficient NLO properties, the
constituting molecules must possess large molecular hyper polarizabilities, which are normally
characterized by a highly extended π-conjugated electron donor–acceptor pairs at the ends [9].
Apart from the high nonlinear optical response, the NLO materials must also satisfy few other
technological needs for practical applications such as wide optical transparency extending down
to UV region, thermal stability, chemical stability and mechanical stability [8]. Comparing to
inorganic materials, organic compounds are efficient materials to exhibit high NLO response
which may be due to the presence of conjugated π electrons along with weak van der Waals
interactions between the hydrogen bonds and available. These parameters are quite essential for
most of their NLO properties [10]. The analyzes towards the device fabrication, organic NLO
crystals are better than inorganic crystals due to their high conversion efficiency for second and
higher order harmonic generation, good transparency in the visible region and high resistance
offering for laser damage. Because of these properties, the organic materials can be applicable to
many devices particularly optical storage devices and optical telecommunications. In addition,
existing molecular flexibility is an added advantage to increase the nonlinearity of organic
crystal in a desired manner [11, 12].

ACCEPTED MANUSCRIPT
4
In recent trends, Mannich bases give much attention for the synthesis of various potential
agents of high medicinal values like anti-inflammatory, anticancer, antibacterial, antifungal,
anticonvulsant and various bio active molecular applications [13-16]. They also find a wide
verity of commercial applications such as detergent additives, resins, polymers, surface active
agents and corrosion inhibitors [17, 18]. Mannich reaction is a three component reaction in
which a nonenolizable aldehyde, i.e. formaldehyde, a primary or secondary amine and an
enolizable carbonyl compound react and give the end products known as Mannich bases. This
reaction was developed by the Italian chemist Mario Betti in which the enolizable carbonyl
compound is replaced by a molecule of β-naphthol or phenol. This is a useful method to
synthesize aminoalkyl phenols or naphthols based compounds [19, 20]. Mannich bases possess
short intramolecular hydrogen bond interaction between the hydroxyl group and the nitrogen of
amine group which increases the NLO activity of the product molecule.
In order to search the theoretical and experimental uniformity, quantum chemical
calculations were carried out with complete geometry optimizations of the molecule. It is an
excellent method in the designing of novel NLO molecules and support to predict some
molecular properties such as dipole moment, polarizabilities and hyperpolarizabilities. Among
several computational methods, Density Functional Theory (DFT) an efficient tool to provide
great accuracy to calculate electronic structure of molecular systems and to reproduce the
experimental values in dipole moments, chemical hardness, atomic charges, electron negativity,
etc., [21, 22]. In the present investigation, the authors were concentrated and succeeded in the
synthesis and single crystal growth of 2-naphthol substituted Mannich base from an active
nitrogen compound with suitable secondary amine and an aromatic aldehyde for NLO
application such as second harmonic generation. Slow evaporation technique was employed to

ACCEPTED MANUSCRIPT
5
achieve optically good quality single crystals of the synthesized compound. The crystalline
compound was confirmed by single crystal XRD, FTIR and NMR spectroscopic studies. The
grown crystals were also characterized by optical, laser damage and quantum chemical
calculations and reported for the first time.
2. Experimental procedure
2.1. Material Synthesis and Growth
All the starting materials and solvent used for the synthesis of MPMN ligand were
purchased from Merck chemical company and used without further purification. The ligand
MPMN was synthesized successfully using the reactants 2-naphthol, morpholine and
benzaldehyde by taking in the equal molar ratio (1:1:1). The active nitrogen compound 2-
naphthol (4.33 g, 0.03 M) was dissolved first in a small amount of ethanol and then it was mixed
with secondary amine morpholine (2.7 ml, 0.03 M) by a continuous stirrer at room temperature
until a clear solution was obtained. Thereafter benzaldehyde (3.0 ml, 0.03 M) was added slowly
to this mixture with constant stirring. After 12 hours a brown colored salt was precipitated and it
was washed with distilled water for several times and then dried in a hot air oven at 60 °C. The
scheme of reaction is as shown in Figure 1. The separated synthesized material was dissolved in
the various solvent to obtain the defect-free good quality single crystal. Among the various
solvents, acetonitrile was selected as a better solvent to grow the optically good quality single
crystal. The separated synthesized material was recrystallized from acetonitrile by the slow
evaporation method and a single crystal of dimension 10 x 5 x 2 mm3 was obtained in a period of
20 - 25 days. Figure 2 shows the photograph of an as-grown single crystal of MPMN.

ACCEPTED MANUSCRIPT
6
2.2. Characterization
The crystallographic data of MPMN were collected at 293 K by an ENRAF NONIUS
CAD4 –MV31 single crystal X-ray diffractometer [λ (Mo Kα) = 0.71073Å]. The powdered
specimen of MPMN single crystal was subjected to FTIR analysis by using PERKIN
ELMER/SPECTRUM 2- Fourier Infrared Spectrometer and various functional groups are
1
identified. The H NMR and 13C NMR data of MPMN were recorded in DMSO-d6 using
BRUKER AVANCE III 500 MHz (AV 500) multi nuclei solution NMR Spectrometer. The UV-
Visible spectrum of the compound was recorded by using UV/VISIBLE/
SPECTROPHOTOMETER - (LAMBDA35 PERKIN ELMER) in the wavelength range between
190 and 1100 nm. The chemical etched pattern of grown crystal of MPMN was examined by
EUROMAX optical microscope under transmission mode. The non-linear optical property such
as Second Harmonic Generation (SHG) was examined by the Kurtz and Perry powder technique
[23]. The intensity of Nd: YAG laser was measured in order to measure the laser damage
threshold of MPMN single crystal along (110) plane. The quantum chemical calculations of
MPMN were carried out using the Gaussian 09 program package [24] with familiar DFT using
Becke’s three-parameter hybrid method with the Lee, Yang and Parr correlation functional
methods (DFT-B3LYP) at the level of POPLE basis set 6-31G (d, p). For DFT calculations the
structure of MPMN molecule was optimized by feeding its experimental Crystallographic
Information File (CIF) and all other calculations were computed by the optimized structure of
MPMN.

ACCEPTED MANUSCRIPT
7
3. Results and discussion
3.1. Single crystal X-ray diffraction study
Single crystal X-ray diffraction is one of the most powerful techniques of unambiguously
determines the complete three-dimensional structures of crystals. It is employed for finding unit
cell parameters, space groups, and three-dimensional coordinates of atoms and molecules in the
unit cell [25]. X-ray crystallography has emerged as the main source of the information on the
solids and molecular structure of the compound. The single crystal of MPMN with dimensions
0.35 x 0.35 x 0.30 mm3 was chosen for X-ray diffraction study. The structure of MPMN was
solved by the direct method using SHELXS-97 [26] and refined by the full-matrix least squares
methods on F2 using SHELXL-97 [27]. The molecular structure with atom numbering scheme of
MPMN at 50 % thermal displacement ellipsoid and optimized geometrical structure is shown in
Figure 3. The calculated unit cell parameters are a = 10.6592Å, b = 18.9868Å, c = 16.7475Å, α =
90 °, β = 101.087 °, γ = 90 °. The unit cell volume is found to be 3326.2 Å3. The obtained lattice
parameters are in good agreement with the reported values [28]. From the single crystal XRD
studies, it has been found that the compound molecule crystallizes in a monoclinic crystal system
with non-centrosymmetric space group Cc. The other crystallographic information and structure
refinement for MPMN is provided in Table 1.
There are two independent molecules (A & B) in the asymmetric unit of the crystallized
compound MPMN. The molecular structures of the asymmetric parts of the MPMN are stabilized
through two classical intramolecular O—H...N interactions [43O-45H...42N from A, 43O-
45H...42N from B]. Whereas, due to the lack of suitable donor and acceptor atoms for classical
intermolecular hydrogen bonds, the crystal packing is stabilized through intermolecular C—H...O
interactions. These C—H...O interactions lead to primary chain motifs, which are further

ACCEPTED MANUSCRIPT
8
connected and form chain motifs around inversion centers of the unit cell [29]. Hydrogen bonding
geometries are given in Table 2. Two interactions of 4C-5H...44O (i) and 7C-8H...44O (i) from A
1
leads to two chain C(10) motifs extending along b-axis of the unit cell and a ring R2 (6) motif
(Figure 4). Further, 4C-5H...44O (i) and 9C-10H...43O (ii) interactions from B lead to two chain
C(8) and C(10) motifs extending along a- and b-axes of the unit cell, respectively. Further, these
6
two primary chain motifs are intersected leading to secondary ring R6 (46) motif (Figure 5).
Another chain C(10) motif extending along ab-plane of the crystal is observed through 24C-
25H...44O (iii) interaction from B. This chain C(10) motif and a chain along the a-axis C(8) motif
4
[4C-5H...44O (i)] from B are overlapped and form a ring R4 (32) motif (Figure 6). These
secondary ring motifs are stabilizing the crystal structure in a greater extent.
The six member ring of morpholine moiety in MPMN adopts a chair conformation with the
evident of ring puckering parameters [30] (Q = 0.576 (2) Å; θ = 180.00 (19) ° and ф = 2 (5) °) and
q2 = 0.0240 (19) Å; q3 = -0.577 (2) Å). It can also be described by the cyclic torsion angles 30C-
33C-44O-36C = 57.8 (2) °, 36C-39C-42N-30C = -57.8 (2) °, 33C-30C-42N-39C = 58.1(2) °, 39C-
36C-44O-33C = -57.9 (2) °, 42N-30C-33C-44O = -59.2 (5) ° and 44O-36C-39C-42N = 59.4 (2) °.
Each atom in six member ring of morpholine moiety are deviated from the mean plane of MPMN,
viz., 42N = 0.248 (16) Å, 30C = -0.242 (2) Å, 33C = 0.228 (2) Å, 44O = -0.221 (17) Å, 36C =
0.229 (2) Å, 39C = -0.243 (2) Å which ensures the chair confirmation [31].
The selected bond lengths, bond angles and torsion angles for MPMN are listed in Table 3.
As can be seen from the Table the bond lengths and bond angles are extremely closed and slightly
longer than the experimental values. The torsion angle for 16C-17C-42N-39C is experimentally
observed as 172.83 (15) ° and 67.03 (17) ° from A and B whereas, the theoretical computation
shows this value as 67.036 ° for lower energy conformation of the molecule. The conformation of

ACCEPTED MANUSCRIPT
9
the morpholine moiety shows large value for its conformation angle for lower energy confinement.
The dihedral angles between phenyl and naphthyl ring moieties obtained as 15C-16C-17C-19C =
85.42 (19) °, 1C-16C-17C-19C = -88.43 (19) ° from B and 15C-16C-17C-19C = -87.40 (19) °,
1C-16C-17C-19C = 89.5 (2) ° from A which are nearly equal to the reported values [28] such as
11C-17C-10C-9C = 85.6 (2) °, 11C-17C-10C-1C = -88.9 (2) ° and 19C-18C-34C-28C = -87.8 (2)
°, 23C-18C-34C-28C = 89.8 (3) °. The differences between the experimental and calculated
geometrical parameters can be attributed due to the fact that the theoretical calculations were
carried out with isolated molecules in the gaseous phase while the experimental values were based
on the molecules in the solid state are different in nature. The crystallographic data (CIF) for the
molecule compound structure reported in this paper have been deposited in the Cambridge
Crystallographic Data Centre as supplementary material number CCDC 1029398.
3.2. FT-IR analysis
FT-IR spectrum of MPMN recorded in KBr medium in the spectral range (4000-400
cm-1) which exhibited a number of bands as shown in Figure 7. The compound shows a number
of IR absorption bands and the absorption frequencies are in a slightly shifted position in
comparison with those of the reactants, 2-naphthol, and morpholine. A broadband observed at
3404 cm-1 is assigned to the νO-H stretching vibration. The aromatic stretching νCH occurs at 3058
cm-1.
The absorption band due to asymmetric and symmetric stretching vibration of alicyclic
νCH2 occurs at 2966 and 2842 cm-1. The νC=C stretching vibration occurs at 1598 and 1470 cm-1.
The δOH in-plane bending and νring + δCH vibrations appear at 1236, 1414 and 1454 cm-1
respectively. A small and sharp absorption band observed around 747 cm-1 may be due to phenyl
ring out of plane bending vibration. The νC-N-C and νC-O-C stretching vibrations occur at 1157,

ACCEPTED MANUSCRIPT
10
1143 and 1093 cm-1. The absorption band due to the newly formed C-N-C appears at 1115 cm-1
which favorably indicates the substitution on 2-naphthol and morpholine and the formation of a
new compound. The FT-IR data was also obtained theoretically by GAUSSIAN using frequency
command and it is shown all vibrational modes observed as real with positive frequencies. The
data is given as supplementary information.
3.3 1H NMR, 13C NMR – analysis
1
The H NMR data for the compound MPMN in DMSO-d6 is shown in Figure 8. The
multiplet observed at δ 7.204 – 7.303 ppm is attributed to the protons of the phenyl ring. The O-
CH2 and N-CH2 proton of morpholine observed as two triplets at δ 3.564 and 2.499 ppm
respectively. The CH protons of the naphthyl ring appear as a doublet and multiplet at 7.102 and
7.619-7.749 ppm respectively. The OH proton appears as a singlet 13.181 ppm, whereas the
methane CH proton appears at 5.360 ppm. The signal of the methine CH proton indicates the
formation of a new compound.
The 13C NMR spectrum of the compound MPMN was recorded in DMSO-d6 and is
13
shown in Figure 9. The C NMR data for the title compound in DMSO-d6 shows the chemical
shifts of phenyl ring carbons 1’, 2’ & 6’, 3’ & 5’and 4’ appears at δ 139.837, 128.727, 229.789
and 129.212 ppm respectively. The signals observed at δ 52.423 and δ 66.566 ppm is due to the
N-CH2 and O-CH2 carbons of morpholine. The signal for the naphthyl carbons 1’- 10’ appears at
δ 109.120, 154.903, 116.167, 128.341, 127.992, 122.003, 126.583, 123.001, 132.503 and
129.094 ppm respectively. The signal for the newly formed CH carbon occurs at δ 70.390 ppm,
13
which imitates the formation of a new compound. The C NMR signals of the compound and
1
the various assignments to the different carbon atoms are in good agreement with the H NMR
data.

ACCEPTED MANUSCRIPT
11
3.4. UV-Vis-NIR studies
A good optical transmittance is a very desirable property for an NLO crystal [32]. A well
polished and transparent single crystal of MPMN with 2 mm thickness was used for the UV-vis
absorption studies. The plot of absorbance versus wavelength with inset of Tauc’s plot is shown
in Figure 10. There is no absorption peak observed between 360 and 1100 nm, the lower cutoff
wavelength is observed at 228.09 nm and 354.02 nm for MPMN and the lower percentage of
absorption indicates that the crystal readily allows the transmission of the laser beam in the range
between 360 nm and 1100 nm. The optical absorption bands at 228.09 nm and 354.02 nm can be
assigned to π to π* and n to π* electronic transitions of aromatic groups of MPMN. From the
observations, it is understood that the grown crystal has a good transparency in UV, visible, and
near-IR region indicating that it can be used for various NLO applications [33]. The Tauc’s plot
[34] was drawn between the photon energy (hυ) and (αhν)2 and used to estimate the energy band
gap of the crystalline material. It was determined by extrapolating the straight line portion of the
curve to (αhν)2 = 0. From the plot, the optical energy band gap of MPMN is estimated as 3.3 eV.
3.5. Etching
The nonlinear optical efficiency of a crystal mainly depends on the quality of the grown
crystal. The presence of impurities and dislocations during growth may affect the quality of the
grown crystal. The chemical etching is a significant method for revealing the crystal defects that
are affected by such as chemical homogeneity, electron mobility, light absorption, refractive
index and stress [35]. It can able to develop some feature such flat-bottomed pits, etch hillocks,
and etch spirals on the surface of the crystal. The etch pits are developed due to chemical attack
of the etchants at the strain field surrounding the dislocation line. The shape, size, and orientation
of the pits can be related to the crystal symmetry [36]. In the present study grown MPMN single

ACCEPTED MANUSCRIPT
12
crystal was fully immersed in ethanol etchant for 20 and 40 seconds at room temperature. The
etched surfaces were dried gently by pressing them between filter papers and immediately
examined the microstructure surface using computerized optical microscope by transmission
mode. The microphotographs of the crystal plane (110) before and after etching is shown in
Figure 11. From the Figure, the rectangular etch pits were observed at the site of dislocations in
20 seconds. The etching time increases by 40 seconds, the size of the etch pits were also
increased which confirms that the size of the etch pattern increases with increase in etching time.
The etch pits density was calculated as 786 cm-2 from etch pattern formed at 40 seconds after
etching. There is no change was found in the size of etch pits over 40 seconds, which suggest
that the etch pits are due to dislocations.
3.6. NLO test
Kurtz and Perry powder technique represents the first real means of screening,
experimentally large number of unknown materials for second order nonlinear optical activity
[23]. In this technique, the grown crystalline compound was ground into a fine microcrystalline
powder and was filled into a fine microcapillary tube of diameter 1.4 mm. The filled
microcapillary tube was taken along the path of Nd: YAG laser operated at 1.9 mJ/pulse energy
with the fundamental wavelength 1064 nm with 8 ns pulse width at a repetition rate of 10 Hz.
The second harmonic radiation generated by the randomly oriented microcrystals was focused by
a lens and detected by a photomultiplier tube and digitalizing oscilloscope assembly. The final
output was displayed on a digital storage oscilloscope and the second harmonic signal generated
was confirmed from the emission of bright green light of wavelength 532 nm from the powdered
sample cell. The output second harmonic signal of 58 mV, 37 mV were obtained from MPMN,

ACCEPTED MANUSCRIPT
13
standard inorganic KDP crystal powder. The conversion efficiency of MPMN sample is found to
be 1.57 times greater than KDP from the observed result.
3.7. Laser damage threshold
For NLO device applications, laser damage threshold plays a significant role. The usage
of NLO crystal depends not only on the linear and nonlinear optical properties but also its ability
to withstand for high power lasers [37]. Usually, organic crystal shows a very high damage
threshold value compared to inorganic counterpart [38]. The laser damage threshold studies have
been carried out for MPMN single crystal using a Q-switched Nd: YAG laser (λ = 1064 ꢀm) of
multishot with the pulse duration of 10 ns at a frequency rate of 10 HZ. The lens with focal
length of 35 cm was used to position the different sites in the laser beam. The laser beam of 1
mm was focused on the polished face of the MPMN along (110) plane. The applied input energy
of laser was increased gradually and at 79 mJ the cracks were developed on the surface of
MPMN single crystal. The power density (Pd) was calculated using the formula,
ꢀ
Pd = τꢁ
--- (1)
Where E is the input energy measured in millijoules, τ is the pulse width and A is the area
of the circular spot. The measured multiple shots surface damage threshold value is 1.006
GW/cm2. The laser induced damage pattern of MPMN shows (Figure 12) cracks developed
around the core of damage with small blobs. These damages are mainly due to the thermal
effects such as heat induced by the absorption of the laser radiation, multiphoton ionization and
thermal diffusivity of MPMN which was resulting in melting, solidification, and decomposition
of the material [39].

ACCEPTED MANUSCRIPT
14
3.8. Quantum chemical calculation
3.8.1 Non-Linear Optical Properties
The Quantum chemistry based calculation of non-linear optical properties of a molecule
has a significant role for the design of materials in modern communication technology and
optical signal processing [40]. It gives an important contribution to the understanding of the
electronic polarization underlying the molecular NLO process and the structure-property
relationship [41]. The quantum chemical calculations of polarizabilities and hyperpolarizabilities
have become available through the strong theoretical basis for analyzing molecular interactions.
They made the possible determination of the elements of these tensors from derivatives of the
dipole moment with respect to finite field approach. DFT is an efficient method for providing a
suitable theoretical framework and structure sensitive method for calculating molecular
polarizabilities, dipole moment and electronic charge distribution extracted from the output of
any standard electronic structure program.
The total static dipole moment (ꢀ), the mean polarizability (α), the anisotropy
polarizability (∆α) and first hyper polarization (β) using the components x, y, z are given below,
2
2
2
Total static dipole moment
The mean polarizability
ꢀ = ꢀ + ꢀ +ꢀ
z
--- (2)
--- (3)
ꢂ
x
y
αxx+αyy+αzz
α =
ꢃ
ꢄ
2
2
2
2
ꢆ
The anisotropy of polarizability ∆α =
ꢇαxx – αyyꢈ +ꢇαyy – αzzꢈ +ꢇαzz – αxxꢈ +6 α
--- (4)
xx
ꢅ
√
The first order hyperpolarizability is a third-rank tensor that can be described by a 3x3x3
matrix. Accordance with Kleinman symmetry the 27 components of the 3D matrix can be
reduced to 10 components [42]. The complete equation for calculating the magnitude of the first
order hyperpolarizability as follows,

ACCEPTED MANUSCRIPT
15
β = (β +β +β )2 + (β +β +β )2 + (β +β +β )2 --- (5)
ꢂ
xxx
xyy
xzz
yyy
xxy
yzz
zzz
xxz
yyz
Since the values of the polarizability and hyperpolarizability of the GAUSSIAN 09
output are reported in atomic units (a.u), the calculated values have been converted into
electrostatic units (esu) (α: 1 a.u. = 0.1482 x 10-24 esu; β: 1 a.u. = 8.641 x 10-33 cm5 esu-1). The
calculated values of ꢀ, α, ∆α and β for MPMN calculated were 1.6863 D, 23.9211x10-24 esu,
73.0372 x 10-24 esu and 2.1191 x 10-30 cm5 esu-1 and compared with the prototypical molecule
like urea. Since urea is one of the prototypical molecules used in the study of NLO properties of
molecular systems, it was used frequently as the threshold value for comparative purpose. The
polarizability, anisotropy polarizability and first order hyperpolarizability of MPMN were
observed 8.3966, 5.8759 and 5.2452 times greater than the urea molecule in the gas phase.
3.8.2 Frontier molecular orbital (FMO) analysis
The HOMO and LUMO are often called as frontier molecular orbital. The frontier
molecular orbital is mainly composed of π-atomic orbital so that an electron transition from the
HOMO to the LUMO is mainly derived from π – π* electronic transition. The FMO analysis
indicates that the transition of the electron from ground to first excited state and is mainly
described by one electron excitation for the highest occupied molecular orbital (HOMO) to the
lowest unoccupied orbital (LUMO). The molecular energies of HOMO and LUMO have been
calculated as 5.3783 and – 0.9082 eV and the plots are given in Figure 13 respectively. The
energy gap between HOMO and LUMO was found to be 4.4701 eV which indicates that the title
compound having higher energy barrier for the transition of electrons from highly occupied
molecular orbital to lowest unoccupied molecular orbital. The partaking of each fragment of
MPMN and their HOMO and LUMO percentage is calculated using the QMForge software tool
[43]. In MPMN, 92 % of HOMO and 85 % of LUMO are significantly contributed by the

ACCEPTED MANUSCRIPT
16
naphthyl moiety (F-I), which implies the maximum electronic charge transfer takes place
through the fragment molecule which is essential requirement to obtain the large second order
NLO response. The difference between the theoretical and experimental values (UV-Vis-optical
absorbance) of energy barrier is due to the isolated molecule of MPMN in a gas phase and the
three-dimensional crystalline solid is different in nature.
Accordance with Koopman theorem [44], the chemical hardness (η), the electronic
chemical potential (ꢀ) and electrophilicity index (ω) of MPMN can be calculated as below. The
chemical hardness is associated with the stability and reactivity of a chemical system. The
smaller in energy gap implies soft molecules where large energy gap leads harder molecule. In a
molecule, it measures the resistance to change in the electron distribution or charge transfer.
Based on frontier molecular orbital, chemical hardness (η) corresponds to the gap between the
HOMO and LUMO.
(ELUMO - EHOMO
)
η =
--- (6)
ꢅ
Where ELUMO and EHOMO are the energies of LUMO and HOMO. The larger the HOMO-
LUMO energy gap, the harder and more stable/less reactive molecule.
The electronic chemical potential is defined as the negative of electronegativity of a molecule
which describes the escaping tendency of the electron from an equilibrium system. It is
determined as,
(EHOMO + ELUMO
)
ꢀ =
--- (7)
ꢅ
Electrophilicity index measures the capacity of a species to accept electrons [45]. It is the
measure of the stabilization in energy after a system accepts additional amount of electronic
charge from the environment which is given as,

ACCEPTED MANUSCRIPT
17
ꢀ2
ω= 2η
--- (8)
The chemical hardness, electrochemical potential, and electrophilicity index of MPMN were
obtained from FMO analysis are 2.2350, -3.1432 and 2.2102 eV. From the results, it could be
observed that the title compound molecules possess good chemical hardness in nature [46].
3.8.3 Molecular electrostatic potential
The total electrostatic effect or field produced at a point in space around a molecule due
to net charge distribution electron and nuclei is termed as molecular electrostatic potential V(r)
(MEP). It is expressed as below [47],
ꢎ )
ZA
ꢍ ꢊ ꢏꢊ´
∑
V(r) =
-
ꢌ
--- (9)
ꢋ
⃓
⃓RA ꢉꢊ⃓
ꢊ´ꢉꢊ
Where ZA is the charge on nucleus located at distance RA and ρ(r) is the electron density. The
MEP is correlated with dipole moments, electronegativity and chemical reactivity of the
molecule. It gives the visual inspection of the polarity of the molecule. The electrostatic potential
region was taken between -1.366 × e-2 and 1.366 × e-2 and the map is shown in Figure 14. The
electrostatic potential surface of the molecule can be represented by different color grading. The
red represents the most negative electrostatic potential region, whereas blue represents the most
positive electrostatic potential region and green represent the region of zero potential. The
negative electrostatic potential corresponds to an attraction of proton by the concentrated
electron in the molecules which give the electrophilic attack or reactive sites of the molecular
system. The positive electrostatic potential corresponding to the repulsion of the proton by
atomic nuclei in the regions of low electron density excites which gives nucleophilic attack or
reactive sites of the molecular system. These sites give the information about the region from
where the compound can have intermolecular interaction.

ACCEPTED MANUSCRIPT
18
3.8.4 Mulliken charge analysis
The total atomic charges of MPMN molecule obtained from Mulliken charge population
by DFT method. Atomic charges play a vital role in quantum chemistry and more research
continues to being done to refine the concept of an atomic charge. Mulliken atomic charge
populations give one of the simplest pictures of charge distribution and predict the net atomic
charges in the molecule [48]. The charge distribution of all atoms in the investigated molecule is
shown in Figure 15. Also from the Figure, it could be observed that the atomic charges of the
molecule are ranging between 0.3441 and -0.6015. The highest value is observed at C1 and H45
atom, where the lowest value is observed in N42, O43, and O44 atoms. Almost maximum
hydrogen atoms exhibited positive charge, whereas the maximum of carbon and nitrogen atoms
possess the negative charge.
4. Conclusion
2-naphthol substituted Mannich base MPMN was synthesized and crystallized
successfully using suitable acetonitrile solvent by slow evaporation method at room temperature.
The single crystal XRD confirms that the MPMN crystallizes in monoclinic crystal system with
the non-centrosymmetric space group Cc. The different vibrational modes of functional groups
are presented in MPMN were confirmed by FTIR analysis. The 1H NMR and 13C NMR confirms
the formation of a new compound by the observed signal of the methine CH proton at 5.360 ppm
and the signal occurs at δ 70.390 ppm due to CH carbon. The UV-Vis absorption spectrum
confirms, the lower cutoff wavelengths observed at 228.09 nm and 354.02 nm which ensures
wider optical transparency range in entire visible and near infrared region. The chemical etching
pattern formed by the suitable etchant revealed that MPMN single crystal has minimum
dislocation sites during growth. The SHG response of MPMN crystal revealed that the efficiency

ACCEPTED MANUSCRIPT
19
is 1.57 times greater than KDP which ensures the crystal can be suitable for NLO applications.
The laser damage threshold of MPMN was found to be 1.006 GW/cm2. The quantum chemical
studies revealed the favorable NLO response in the dipole moment, molecular polarizability,
hyperpolarizability and chemical hardness of MPMN in the gas phase.

ACCEPTED MANUSCRIPT
20
Reference
[1] N. Zaitseva, and L. Carman, Rapid growth of KDP-type crystals, Prog. Crystal Growth
and Charact. 43 (2001) 1-118.
[2] X.J. Liu, Z.Y. Wang, X.Q. Wang, G.H. Zhang, S.X. Xu, A.D. Duan, S.J. Zhang, Z.H. Sun,
D. Xu, Morphology and Physical Properties of L-Arginine Trifluoroacetate Crystals,
Cryst. Growth Des. 8 (2008) 2270–2274.
[3] J. Badan, R. Hierle, A. Perigaud, J. Zyss, NLO properties of Organic Molecules and
Polymeric Materials, ACS Symp. Ser. 233, Am. Chem. Soc. Washington, DC, 1993.
[4] P.N. Prasad, Polymeric Materials for Nonlinear Optics and Photonics, Polym. 32 (1991)
1746-1751.
[5] B.G. Penn, B.H. Cardelino, C.E. Moore, A.W. Shields, D.O. Frazier, Growth of bulk
single crystals of organic materials for nonlinear optical devices: An overview, Prog.
Cryst. Growth Charact. 22 (1991) 19-51.
[6] B.E.A. Saleh, M.C. Teich, Fundamental of Photonics, Wiley, New York, 1991.
[7] S.R. Marder, S.E. Sohn, G.D. Stucky, Material for Nonlinear Optics Chemical
Perspective, ACS Symp. Ser. 455, Am. Chem.Soc. Washington, DC, 1991.
[8] Venkataraya Shettigar, P.S. Patil, S. Naveen, S.M. Dharmaprakash, M.A. Sridhar, J.
Shashidhara Prasad, Crystal growth and characterization of new nonlinear optical
chalcone derivative: 1-(4-Methoxyphenyl)-3-(3, 4-dimethoxyphenyl)-2-propen-1-one, J.
Cryst. Growth 295 (2006) 44-49.
[9] D.R. Kanis, M. A. Ratner, T.J. Marks, Design and construction of molecular assemblies
with large second-order optical nonlinearities. Quantum chemical aspects, Chem. Rev. 94
(1994) 195-242.

ACCEPTED MANUSCRIPT
21
[10] T. Pal, T. Kar, Gabriele Bocelli, Lara Rigi, Synthesis, Growth, and Characterization of L-
Arginine Acetate Crystal: A Potential NLO Material, Cryst. Growth Des. 3 (2003) 13-16.
[11] V. Krishnakumar, R. Nagalakshmi, Vibrational spectroscopic studies of an organic non-
linear optical crystal 8-hydroxyquinolinium picrate, Spectrochim. Acta Part A, 66 (2007)
924-934.
[12] N. Vijayan, R. Ramesh Babu, M. Gunesekaran, R.Gopalakrishnan, R. Kumarasan,
P.Ramasamy, C.W. Lan, Studies on the growth and characterization of p-
hydroxyacetophenone single crystals, J. Cryst. Growth, 249 (2003) 309-315
[13] M. Kosal, N. Gokhan, E. Kupeli, E. Yesilada, H. Erdogan, Analgesic and anti-
inflammatory acivites of some new Mannich bases of 5-nitro-2-benzoxazolinones, Arch.
Pharm. Res. 30 (2007) 419-424.
[14] J.R. Dimmock, N.M. Kandepu, U. Das, G.A. Zello, K.H. Nienaber, Antimycobacterial
arylidenecyclohexanones and related Mannich bases, Pharmazie, 59 (2004) 502-505.
[15] S.C. Vashishtha, G.A. Zello, K.H. Nienaber, J. Balzarini, E. De Clercq, J.P. Stables, J.R.
Dimmock, Cytotoxic and anticonvulsant aryloxyaryl Mannich bases and realated
compounds, Eur. J. Med. Chem., 39 (2004) 27-35.
[16] E. Bennet-Jenkins, C. Bryant, Novel sources of anthelmintics, Int. J. Parasitol., 26 (1996)
937-947.
[17] M. Tramontini , L. Angiolini , Mannich Bases - Chemistry and Uses , CRC Press,1994.
[18] M. Jeeva, G. Venkatesa Prabhu, M.S. Boobalan, C.M. Rajesh, Interactions and Inhibition
Effect of Urea-Derived Mannich Bases on a Mild Steel Surface in HCl, J. Phys. Chem. C
119 (2015) 22025-22043.
[19] M. Betti, Synthesis of Betti base, Org. Synth. Collective 1 (1941) 381-383.

ACCEPTED MANUSCRIPT
22
[20] M. Betti, On the addition of benzyl amine to naphthol, Gazz. Chim. Ital. 30 (1900) 301-
309.
[21] M. Amalanathan, I. Hubert Joe, V.K. Rastogi, Density functional theory studies on
molecular structure and vibrational spectra of NLO crystal L-phenylalanine
phenylalanium nitrate for THz application, J. Mol. Struc. 1006 (2012) 513-526.
[22] Y. Koysal, H. Tanak, Crystal structure, spectroscopic investigations and density functional
studies of 4-(4-methoxyphenethyl)-5-benzyl-2H-1,2,4-triazol-3(4H)-one monohydrate,
Spectrochim. Acta Part A 93 (2012) 106– 115.
[23] S.K. Kurtz, T.T. Perry, A Powder Technique for the Evaluation of Nonlinear Optical
Materials, J. Appl. Physics, 39 (1968) 3798-3813.
[24] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P.
Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai,
T. Vreven, J.A. Montgomery, Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E.
Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M.
Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R.
Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W.
Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador, J.J.
Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J.
Cioslowski, and D.J. Fox, Gaussian, Inc., Wallingford CT, 2010.
[25] G.H. Stout, L. H. Jenssen, X-ray Structure determination, Macmillon, Newyork, 1968.

ACCEPTED MANUSCRIPT
23
[26] G.M. Sheldrick, SHELXS-97; Program for crystal structure solution, University of
Gottigen, Germany, 1997.
[27] G.M. Sheldrick, SHELXL-97; Program for refinement of crystal structures, University of
Gottigen, Germany, 1997.
[28] Min Min Zhao and Ping Ping Shi, 1-[Morpholino(phenyl)methyl]-2- Naphthol, Acta
Cryst. E66, o1406, (2010).
[29] J. Bernstein, R.E. Davis, L. Shimoni, and N.L. Chang, Patterns in hydrogen bonding:
functionality and graph set analysis in crystals, Angew. Chem. Int. Ed. Engl. 34 (1995)
1555–1573.
[30] D. Cremer, J.A. Pople, General definition of ring puckering coordinates, J. Amer. Chem.
Soc. 97 (1975) 1354-1358.
[31] J.C.A. Boeyens, The conformation of six-membered ring, J. Cryst. Mol. Struct. 8 (1978)
317-320.
[32] V.G. Dmitriev, G.G. Gurzadyan, D.N. Nikoyosyan, Hand Book of Nonlinear Optical
Crystals, Third Revised Edition, Springer Series in Optical Sciences, 64 (1999) 1-413.
[33] Z.Y. Wang, Near-Infrared Organic Materials and Emerging Applications, CRC press,
Taylor and Francis group, 2013.
[34] J. Tauc, R. Grigorovici, A. Vance, Optical properties and electronic structure of
amorphous germanium, Phys. Status Solidi B, 15 (1966) 627-637.
[35] X. He, D. Xue, Doping mechanism of optical-damage-resistant ions in lithium niobate
crystals, Opt. Commun. 265 (2006) 537-541.

ACCEPTED MANUSCRIPT
24
[36] S. Mukerji, T. Kar, Surface Micromorphology of Different Crystallographic Faces of L-
arginine Hydrochloride Monohydrate Etched in Organic Solvents, Jpn. J. Appl. Phys. 38
(1999) 832-837.
[37] P. Vijayakumar, G. Anandha Babu, P. Ramasamy, Synthesis, crystal growth and
characterization of nonlinear optical organic crystal: p-Toluidinium p-toluenesulphonate,
Mater. Res. Bull. 47 (2012) 957-962.
[38] P.S. Patil, M.S. Bannur, D.B. Badigannavar, S.M. Dharmaprakash, Study on nonlinear
optical properties of 2,4,5-trimethoxy-4′-bromochalconesinglecrystal, Opt. Laser Technol.
55 (2014) 37-41.
[39] G. Anandha Babu, P. Ramasamy, Growth and characterization of 2-amino-4-picolinium
toluene sulfonate single crystal, Spectrochim. Acta Part A 82 (2011) 521-526.
[40] D. Sajan, H. Joe, V.S. Jayakumar, J. Zaleski, Structural and electronic contributions to
hyperpolarizability in methyl p-hydroxy benzoate, J. Mol. Struct. 785 (2006) 43-53.
[41] J.Y. Lee, K.S. Kim, Relationship between spectral intensities and nonlinear optical
properties, J. Chem. Phys. 107 (1997) 6515–6520.
[42] D.A. Kleinman, Nonlinear Dielectric Polarization in Optical Media, Phys. Rev. 126
(1962) 1977-1979.
[43] A.L. Tenderholt, QMForge, Version 2.1; Stanford University: Stanford, CA, USA.
[44] T. Koopmans, Uber die Zuordnung von Wellenfunktionen und Eigenwerten zu
deneinzelnen Elektronen eines Atoms, Physica 1 (1934) 104-113.
[45] R.G. Parr, L. Szentpaly, S. Liu, Electrophilicity Index, J. Am. Chem. Soc. 121 (1999)
1922-1924.

ACCEPTED MANUSCRIPT
25
[46] C.A. Mebi, DFT study on structure, electronic properties, and reactivity of cis-isomers of
[(NC5H4-S)2Fe(CO)2], J. Chem. Sci. 123 (2011) 727-731.
[47] P. Politzer and J.S. Murray, The fundamental nature and role of the electrostatic potential
in atoms and molecules, Theor. Chem. Acc. 108 (2002) 134-142.
[48] R.S. Mulliken, Electronic population analysis on LCAO-MO molecular wave functions, J.
Chem. Phys. 23 (1955) 1833-1840.

ACCEPTED MANUSCRIPT
26
List of Figures
1. Reaction scheme for the synthesis of Mannich base MPMN
2. Photograph of as grown single crystal of MPMN
3. ORTEP diagram and optimised geometry of MPMN
1
4. Two chain C(10) motifs extending along b-axis of the unit cell and a ring R2 (6) motif of
MPMN
5. Chain C(8) and C(10) motifs extending along a- and b-axes leads to secondary ring
6
R6 (46) motif of MPMN
4
6. Primary chain C(8) and C(10) motifs overlapped leading to secondary ring R4 (32) motif
of MPMN
7. FT-IR spectrum of MPMN
8. 1H NMR spectrum of MPMN
9. 13C NMR spectrum of MPMN
10. UV-Vis absorption spectrum along with Tauc’s plot of MPMN single crystal
11. Etch patterns of MPMN before and after etching
12. Laser damage pattern of MPMN single crystal
13. HOMO and LUMO plot of MPMN
14. Electro Static Potential Map of MPMN
15. Mulliken’s charge distribution of MPMN
List of Tables
1. Crystallographic parameters for MPMN single crystal
2. Hydrogen bonding geometry of MPMN from single crystal XRD

ACCEPTED MANUSCRIPT
27
3. Comparison between selected optimized geometrical parameters and experimental
crystallographic parameters for MPMN
4. Molecular polarizabilities and dipole moment of MPMN

ACCEPTED MANUSCRIPT
28
Fig. 1. Reaction scheme for the synthesis of Mannich base MPMN
Fig. 2. Photograph of as grown single crystal of MPMN