Chemical growth dynamics of 4-Methyl-4′-Hydroxy Benzylidene Aniline NLO single crystal structure and spectroscopic applications

Article abstract of DOI:10.1016/j.molstruc.2021.130054

An aromatic Schiff bases organic nonlinear optical single crystal of 4-methyl-4′-hydroxy benzylidene aniline (MHBA) was grown by slow evaporation solution growth technique and the solubility of MHBA in ethanol at increasing temperature was esteemed. The u

Full text of DOI:10.1016/j.molstruc.2021.130054

Journal of Molecular Structure 1233 (2021) 130054
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
ꢀ
Chemical growth dynamics of 4-Methyl-4 -Hydroxy Benzylidene
Aniline NLO single crystal structure and spectroscopic applications
R. Sakunthaladevia,b, L. Jothic,∗
a Department of Physics, Trinity College for Women, Namakkal, 637002, India
b Periyar University, Palkalai Nagar, Salem, 636011, Tamil Nadu, India
c Department of Physics, Namakkal Kavignar Ramalingam Government Arts College for Women, Namakkal, 637001, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
ꢀ
Article history:
An aromatic Schiff bases organic nonlinear optical single crystal of 4-methyl-4 -hydroxy benzylidene ani-
line (MHBA) was grown by slow evaporation solution growth technique and the solubility of MHBA in
ethanol at increasing temperature was esteemed. The unit cell proportions were gained by both single
crystal and powder X-ray diffraction analysis. The structural refinement of MHBA shows that it crys-
tallizes in the orthorhombic system with space group Pbcn. The molecule chiefly consists of two non –
planar benzene rings attached by carbon and nitrogen atoms. The various planes of reflection were iden-
tified from the powder X-ray diffraction study and the unit cell proportions were same for single crystal
XRD. Functional assemblies were entrenched by using Fourier transform infrared and FT Raman analysis
by the molecular vibrations in the MHBA crystal. The assignment of protons and carbons in the grown
MHBA crystals were recognized from 1H and 13 C Nuclear Magnetic Resonance Spectroscopy analyses. The
UV- visible and fluorescence spectral evaluate were carried out and to find the optical transmission and
emission range of MHBA. The second harmonic generation productivity of MHBA is about 1.04 times than
that of a standard sample of potassium dihydrogen orthophosphate. The thermal constancy of the grown
crystal was investigated by differential scanning calorimetric, thermo gravimetric and a differential ther-
mal analysis which confirms the decomposition of the sample occurs at 120 °C. Mechanical stuff, the
hardness number, yield strength and Young’s modulus of the grown material were studied using Vick-
ers micro hardness tester and the work hardening coefficient reveals that MHBA belongs to the family
of soft materials. The dielectric measurements with frequency and temperatures were used to find the
power dissipation of the grown MHBA crystals.
Received 24 December 2020
Revised 23 January 2021
Accepted 31 January 2021
Available online 9 February 2021
Keywords:
Crystal structure
X-Ray Diffraction
Single crystal growth
Organic compounds
Nonlinear optical materials
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
protection, optical image processing, under water communication,
biomedical, signal processing analysis, etc. [5]. The NLO proper-
Studies on the design and synthesis of molecular materials
with larger hyper-polarizabilities have become a hot research topic
in current years because of their high optical nonlinearity [1–
3]. Materials that display high optical nonlinearity find potential
applications in devices for optical communications, optical pro-
cessors, wavelength filters, modulators, data storage and optical
switches [4]. Nonlinear optical (NLO) materials usually used in op-
tical switching, optical data storage for the embryonic technolo-
gies in telecommunications, frequency mixing, optical parametric
oscillation, optical bi-stability, optical logic gates, laser radiation
ties of organic materials depend on their molecular level inside
the material. The reallocate of dipolar environment initiates the
electrochemical switching of the second-order NLO response at the
molecular level [6]. Aromatic organic NLO materials are charming a
great deal of attention for possible uses in optical devices because
of their large optical nonlinearity, low cutoff wavelength, short re-
sponse time and high laser damage thresholds [7]. Several organic
materials showing considerable NLO effects have been identified
and synthesized. However, only a rare of them could be crystal-
lized and explored for a second order or third order NLO appli-
cations. Significant work has been done to understand the micro-
scopic origin of the nonlinear behavior of organic aromatic materi-
als [8–10]. Any compounds of the type Ar-CH=N-Ar (‘Ar’ is the aro-
matic ring formation) called Schiff bases exhibit large second order
∗
Corresponding author.
E-mail address: jothilakshmanan@gmail.com (L. Jothi).
https://doi.org/10.1016/j.molstruc.2021.130054
0022-2860/© 2021 Elsevier B.V. All rights reserved.

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
NLO properties due to their thermochromism and photochromism
[11]. Condensation of primary amines with aldehydes or ketones
yields Schiff bases containing imine (C=N) functional group of the
above type [12]. The benzylidene aniline derivatives are such kinds
of materials and it is obvious material for the incredible transmit-
ter of green light and form a good stable crystal [13]. Its deriva-
tives exhibit conformational changes due to the rotation along the
longest molecular axis, and consequently the molecules result in
dynamic disorder in their crystal structures [14]. Also, benzylidene
aniline derivatives are referred to as imines, anils, azomethines,
Schiff bases, etc. due to the presence of C=N pond. The linkage
of H-C=N in the certain reactions prompted us to design noncen-
trosymmetric class for the application of quadratic nonlinear opti-
cal effects [15].
Some of the following benzylidene derivatives 4-methoxy-
ꢀ
ꢀ
4 -dimethylamino benzylidene aniline [16], 4-chloro-4 -bromo
Scheme 1. Reaction mechanism of MHBA.
ꢀ
benzylidene aniline [17], 4-nitro-4 -methyl benzylidene aniline
ꢀ
[18] and Metal doped 4-chloro-4 -bromo benzylidene aniline
[19] are already reported and exhibit NLO properties higher than
ꢀ
KDP. The titled compound 4-methyl-4 -hydroxy benzylidene ani-
line is a new aromatic imine compound with molecular formula
C14 H13NO. It crystallizes in the orthorhombic system in the chiral
space group Pbcn with two independent molecules in the asym-
metric unit. The type of crystalline space group to have a depen-
dence on the non-linear optical properties of the materials [20]. So
in this article, we account for the material synthesis, growth, struc-
ture, optical, thermal, mechanical, and dielectric and NLO proper-
2.2. Growth of MHBA crystal
Re-crystallized salt was dissolved in ethanol and the solution
was maintained at the desired temperature, and stirred continu-
ously to ensure homogenization of the solution. On attainment, the
saturation, the quantity of the salt in the solution was estimated
gravimetrically. The same practice was repetitive at the tempera-
tures of 30 oC to 55 oC with an increase of 5 oC and the results
are shown in Fig. 1. The solubility graph undoubtedly states that
the solubility directly increases with the increase in temperature.
ꢀ
ties of 4-methyl-4 -hydroxy benzylidene aniline single crystal.
2. Experimental details
ꢀ
2.1. Material synthesis
The 4-methyl-4 -hydroxy benzylidene aniline exhibits good solu-
bility and positive solubility with temperature incline in ethanol.
ꢀ
The title compound was synthesized by condensation reactions
between 4-hydroxy benzaldehyde (p-HB) and 4-methyl aniline (p-
MA) taken in the equimolar ratio. The basic compounds of high
purity are purchased from Sigma Aldrich and used without purifi-
cation.The reaction combination was relaxed in ethanol for about
8 hour, and the solution was filtered and the resulting prod-
Single crystals of 4-methyl-4 -hydroxy benzylidene aniline were
grown by slow evaporation at room temperature. About 250 ml of
saturated solutions was equipped at room temperature and it was
carefully filtered using Whatman filter paper of pore size 11 μm.
The filtered solution was reserved in a beaker, which was tightly
closed for controlling a solvent slow evaporation [21]. Transpar-
ent neutral single crystal of dimension 20 × 20 × 2.5 mm3 was
harvested in an evolutionary period of seven days and the grown
crystal is shown in Fig. 2.
ꢀ
uct of 4-methyl-4 -hydroxy benzylidene aniline (MHBA) was ob-
tained as a colorless crystalline powder. The reaction mechanism
is described in Scheme 1. The synthesized salt was purified from
ethanol by a successive recrystallization process.
Fig. 3
Fig. 1. Solubility curve of MHBA.
2

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Table 1
Crystal data and structure refinement for MHBA.
Empirical formula
Formula weight
C14 H13 N O
211.25 g/mol.
293(2) K
Temperature
˚
Wavelength
0.71073 A
Crystal system, space group
Unit cell dimensions
Orthorhombic, Pbcn
˚
a = 21.6180(10) A alpha = 90 deg.
˚
b = 11.0561(6) A beta = 90 deg.
˚
c = 9.3318(5) A gamma = 90 deg.
3
˚
Volume
2230.4(2) A
Z
8
Calculated density
Absorption coefficient
F(000)
1.258 Mg/m3
0.079 mm−1
896
Crystal size
0.30 × 0.20 × 0.20 mm
3.01 to 25.00 deg.
−25 ≤ h ≤ 22, −13 ≤ k ≤ 13, −9 ≤ l ≤ 11
11,344
Theta range for data collection
Limiting indices
Reflections collected
Unique Reflections
Completeness to theta = 25.00
Absorption correction
Max. and min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
1961 [R(int) = 0.0283]
99.9%
Semi-empirical from equivalents
0.971 and 0.923
Full-matrix least-squares on F2
1961 / 0 / 148
Fig. 2. As grown single crystal of MHBA.
1.075
R1 = 0.0356, wR2 = 0.0900
R1 = 0.0500, wR2 = 0.0999
0.0028(10)
3. Results and discussions
−3
˚
0.190 and −0.139 eA
3.1. Single crystal X-ray diffraction
Single crystal X-ray diffraction analysis was performed on the as
grown MHBA crystal using Enraf-Nonius CAD-4. The concentration
data of the title compound were collected at 293 K on an SAD-
The value of important hydrogen co-ordinates and torsion
angles in Tables and 6. From the ORTEP scheme of the
5
˚
ABS [22] system using MoKa (λ = 0.71073 A) graphite monochro-
MHBA molecule, it contains two phenyl rings bridged by a C=N
imino moiety, the planes of which are disposed at an angle of
49.40(5°), screening significant deviation of the molecule from pla-
narity as observed in similar assemblies [23–25]. The C9-C8-N1-
C5 = 171.11(13°) torsion angles indicates that the terminal phenyl
rings are twisted relative to the plane in which the C=N bi-
matic radiation. Crystal data and enhancement details are canned
in Table 1.
The atomic coordinates and the selected bond distances are
listed in Tables 2 and 3. The molecular assembly of MHBA was re-
fined by the least-squares method using anisotropic displacement
parameters specified in Table 4. The compound crystallizes in an
orthorhombic crystal system with a Pbcn space group. The param-
˚
˚
nary bond lies. The C9-C8 [1.451(2) A] and N1-C5 [1.4221(19) A]
distances confirm π-electron delocalization between the benzene
rings and the molecule can be observed as a partially delocalized
π electron system.
˚
˚
eter values intended are a = 21.6180(10) A, b = 11.0561(6) A, c =
˚
9.3318(5) A and Z = 8.
Fig. 3. ORTEP plot of MHBA.
3

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Table 4
Anisotropic displacement parameters (A x 103). The anisotropicdis-
2
˚
Table 2
2
placement factor exponent takes the form: −2 π [h2 a∗2 U11 + ...
Atomic coordinates (x 104) and equivalent isotropic dis-
+ 2 h k a∗ b∗
U12 ].
2
3
˚
placement parameters (A ×10 ) for MHBA. U (eq) is de-
fined as one third of the trace of the orthogonalized Uij
tensor.
Atom
U11
U22
U33
U23
U13
U12
C(1)
60(1)
39(1)
43(1)
45(1)
37(1)
50(1)
54(1)
43(1)
39(1)
37(1)
42(1)
39(1)
36(1)
42(1)
40(1)
48(1)
75(1)
50(1)
57(1)
39(1)
33(1)
38(1)
38(1)
28(1)
29(1)
32(1)
26(1)
30(1)
32(1)
28(1)
32(1)
37(1)
74(1)
49(1)
44(1)
43(1)
33(1)
40(1)
54(1)
38(1)
35(1)
36(1)
37(1)
35(1)
54(1)
50(1)
33(1)
52(1)
19(1)
12(1)
4(1)
−9(1)
3(1)
19(1)
6(1)
Atoms
x
y
z
U(eq)
C(2)
C(3)
−7(1)
1(1)
−4(1)
−1(1)
1(1)
C(1)
9840(1)
9443(1)
9387(1)
9021(1)
8686(1)
8751(1)
9123(1)
7806(1)
7417(1)
7612(1)
7251(1)
6684(1)
6481(1)
6843(1)
8305(1)
6316(1)
−3138(2)
−2257(2)
−1070(2)
−257(1)
−621(1)
−1801(1)
−2599(2)
−122(1)
613(1)
5166(2)
4351(2)
4797(2)
4060(2)
2876(2)
2398(2)
3135(2)
1573(2)
652(2)
70(1)
46(1)
48(1)
42(1)
34(1)
43(1)
48(1)
36(1)
34(1)
35(1)
35(1)
34(1)
41(1)
40(1)
35(1)
46(1)
C(4)
−2(1)
4(1)
C(2)
C(5)
4(1)
C(3)
C(6)
−2(1)
1(1)
−3(1)
2(1)
5(1)
C(4)
C(7)
11(1)
2(1)
C(5)
C(8)
2(1)
7(1)
C(6)
C(9)
−1(1)
−1(1)
2(1)
4(1)
4(1)
C(7)
C(10)
C(11)
C(12)
C(13)
C(14)
N(1)
O(1)
2(1)
−1(1)
−1(1)
7(1)
C(8)
3(1)
C(9)
−3(1)
0(1)
1(1)
C(10)
C(11)
C(12)
C(13)
C(14)
N(1)
O(1)
1717(1)
2347(1)
1891(1)
797(1)
84(2)
−2(1)
4(1)
−2(1)
−1(1)
4(1)
−872(2)
−1301(2)
−740(2)
215(2)
5(1)
1(1)
2(1)
8(1)
−12(1)
−1(1)
172(1)
241(1)
2168(1)
−2270(1)
2442(1)
Table 5
Hydrogen coordinates (× 104) and isotropic displacement
2
3
˚
parameters (A ×10 ).
Table 3
Atom
x
y
z
U(eq)
Bond distances and bond angles.
H(1A)
H(1B)
H(1C)
H(3)
10,178
9999
9597
9599
9001
8543
9160
7683
7993
7389
6099
6702
6475(4)
−2713
−3738
−3525
−814
544
5605
4519
5894
5610
4363
1578
2805
1744
359
104
104
104
58
˚
Moiety
Distance(A)
Moiety
Angle(°)
C(1)-C(2)
1.504(2)
0.9600
C(2)-C(1)-H(1A)
C(2)-C(1)-H(1B)
H(1A)-C(1)-H(1B)
C(2)-C(1)-H(1C)
H(1A)-C(1)-H(1C)
H(1B)-C(1)-H(1C)
C(7)-C(2)-C(3)
109.5
C(1)-H(1A)
C(1)-H(1B)
C(1)-H(1C)
C(2)-C(7)
109.5
H(4)
51
0.9600
109.5
H(6)
−2055
−3390
−915
2033
51
0.9600
109.5
H(7)
58
1.382(2)
1.383(2)
1.381(2)
0.9300
109.5
H(8)
44
C(2)-C(3)
109.5
H(10)
H(11)
H(13)
H(14)
H(1)
42
C(3)-C(4)
117.54(15)
121.59(17)
120.87(17)
121.28(16)
119.4
3083
−1234
−1011
578
42
C(3)-H(3)
C(4)-C(5)
C(7)-C(2)-C(1)
486
49
1.381(2)
0.9300
C(3)-C(2)-C(1)
−561
3149(17)
48
C(4)-H(4)
C(5)-C(6)
C(4)-C(3)-C(2)
−2500(6)
55
1.387(2)
1.4221(19)
1.378(2)
0.9300
C(4)-C(3)-H(3)
C(2)-C(3)-H(3)
C(3)-C(4)-C(5)
C(5)-N(1)
C(6)-C(7)
119.4
120.58(15)
119.7
C(6)-H(6)
C(7)-H(7)
C(8)-N(1)
C(8)-C(9)
C(3)-C(4)-H(4)
C(5)-C(4)-H(4)
C(4)-C(5)-C(6)
The flared of the exocyclic angle O1-C12-C11 = [123.45(14°)]
0.9300
119.7
may be caused by steric collaboration between atoms H11 and
1.279(2)
1.451(2)
0.9300
118.63(14)
118.68(13)
122.66(14)
120.04(16)
120.0
˚
H1 (H11….H1 = 2.3029(1) A) [Fig. 4]. The N1-C8-C9 [124.80(14°)]
C(4)-C(5)-N(1)
C(6)-C(5)-N(1)
C(7)-C(6)-C(5)
is more than the normal value of 120°; this might be a sign
C(8)-H(8)
C(9)-C(14)
C(9)-C(10)
C(10)-C(11)
C(10)-H(10)
C(11)-C(12)
C(11)-H(11)
C(12)-O(1)
C(12)-C(13)
C(13)-C(14)
C(13)-H(13)
C(14)-H(14)
O(1)-H(1)
1.394(2)
1.396(2)
1.375(2)
0.9300
of repulsion between the lone pair of electrons on N1 and H10
˚
C(7)-C(6)-H(6)
C(5)-C(6)-H(6)
C(6)-C(7)-C(2)
(N1…H10
=
2.6892(1) A) attached to C10. The crystal struc-
120.0
–
ture is steadied by intermolecular O H...N hydrogen bond linking
the neighboring molecules into an infinite chain along the a-axis
(Fig. 5).
121.84(16)
119.1
1.386(2)
0.9300
C(6)-C(7)-H(7)
C(2)-C(7)-H(7)
N(1)-C(8)-C(9)
N(1)-C(8)-H(8)
C(9)-C(8)-H(8)
C(14)-C(9)-C(10)
C(14)-C(9)-C(8)
C(10)-C(9)-C(8)
C(11)-C(10)-C(9)
C(11)-C(10)-H(10)
C(9)-C(10)-H(10)
C(10)-C(11)-C(12)
C(10)-C(11)-H(11)
C(12)-C(11)-H(11)
O(1)-C(12)-C(11)
O(1)-C(12)-C(13)
C(11)-C(12)-C(13)
C(14)-C(13)-C(12)
C(14)-C(13)-H(13)
C(12)-C(13)-H(13)
C(13)-C(14)-C(9)
C(13)-C(14)-H(14)
C(9)-C(14)-H(14)
C(8)-N(1)-C(5)
C(12)-O(1)-H(1)
119.1
1.3496(18)
1.390(2)
1.372(2)
0.9300
124.80(14)
117.6
3.2. Powder X-ray diffraction analysis
117.6
117.61(14)
119.57(13)
122.63(13)
121.17(13)
119.4
0.9300
The grown crystal was characterized by powder X-ray diffrac-
0.8811
tion using a Bruker D8 Advance, Germany instrument with Cu K
α
radiation (λ = 1.5406Ǻ). The sample was skimmed in the range
1° to 80° at a scan rate of 1°min−1 and the lattice parameters
were calculated by the unit cell software program. Shrill peaks in
the spectrum point to the good crystallinity of the grown crys-
tal [26] which confirmed by the powder X-ray diffraction study of
MHBA crystal. Peaks perceived from the X-ray diffraction spectrum
(Fig. 6) were indexed and these standards approve well with the
consistent values obtained from single crystal XRD.
119.4
120.39(14)
119.8
119.8
123.45(14)
117.38(13)
119.16(14)
120.19(14)
119.9
119.9
3.3. Fourier Transform Infrared Spectral analysis
121.47(14)
119.3
119.3
Fourier Transform Infrared spectrum of the grown MHBA crys-
tal was recorded in the range 400 cm−1 - 4000 cm−1 using Perkin
Elmer (Model RX1). The arranged sample was followed by the
pressed KBr pellet technique. The FT-IR spectrum gives the vibra-
118.71(13)
109.5
4

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Fig. 4. The molecular arrangement in the unit cell.
Fig. 5. A packaging diagram viewed along ‘a’ axis.
tional studies of the grown compound using infrared radiation and
can provide the strong confirmation for the inter and intra molec-
ular interaction occurrence in the compound as given in Fig. 7.
In the maximum of the benzylidene aniline results C=N stretch-
ing vibrations occurs nearly 1600 cm−1 caused by the formation of
imine group [27]. In the MHBA spectrum, it was detected at 1592
cm−1 which confirms the presence of the imine group in the ti-
3.4. Investigation of Raman spectrum
The FT Raman spectrum of the MHBA was recorded on a
BRUKER RFS 27 spectrometer equipped with an FRA 106 accessory
in the region of 4000 cm−1 - 500 cm−1. The spectrum in Fig. 8
gives the Raman scattering of molecules and the inelastic scatter-
ing of photons in a material. The Raman shift at 1575 cm−1 con-
firms the imine group (C=N) formation and also confirms the Ra-
man activeness of imine group. Aromatic ring stretching vibration
of C=C occurs for grown MHBA crystal is at 1444 cm−1. The ex-
ternal modes which are due to translator and rotatory motion of
molecules in the crystalline lattice have been appeared below 200
cm−1 [31].
–
tled compound. The O H stretching vibration was mostly observed
in a range from 3200 cm−1 to 3570 cm−1 [28] in the MBHA peak
obtained at 3410 cm−1. Para-di-substituted benzenes display C H
–
deformation vibration in the region from 800 cm−1 to 840 cm−1
in this work appears at 828 cm−1 [18]. The bands found between
828 cm−1 and 530 cm−1 are due to C H out of plane deformation
–
[29]. Aldehyde distinctive band customarily present at 2720 cm−1
but the absence of which indicates the final product is not an alde-
hyde [30].
The various peak values of characteristic FT Raman and FT IR
are presented in Table 7. The vibrational bands pragmatic in both
the spectra sustenance the structure of MHBA. Both FT IR and FT
5

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Fig. 6. Powder X-ray diffraction pattern of MHBA.
Fig. 7. FTIR spectrum of MHBA.
Raman spectroscopy are ideal methods for identification of molec-
ular vibrations.
=143 ppm, C(8) at δ =161 ppm, C(5) at δ =123 ppm, C(12) at
δ=117 ppm and C(1) at δ =77 ppm [33] all are shown in Fig. 10.
The molecular structure of MHBA was verified by the carbon hy-
drogen bonded (C=H) network.
3.5. 1H and 13 C NMR spectral analyses
ꢀ
The 300 MHz proton NMR spectrum of 4-methyl-4 -hydroxy
benzylidene aniline measured in DMSO using Bruker instrument
is integrated for a total of 10 protons. The recorded 1H- NMR spec-
trum for MHBA is shown in Fig. 9. A triplet at 2.457 ppm is due
to CH3 protons. The vest at 9.979 ppm is dispensed to the hy-
droxyl group attached to the carbon in the benzene ring. The vest
at 8.4 ppm is due to CH proton and a singlet at 8.404 due to the
construction of the C=N imine group. The doublets at 7.307 ppm,
6.627 ppm, 7.806 ppm and 7.165 ppm correspond to the protons
present in the benzene rings [32]. The compounds structure is fur-
ther confirmed from its 13C NMR spectrum. There are ten sets of
carbon existing in the compound. Two correspondent carbonyl car-
bons C(3) and C(7) resonate at δ=130 ppm, equivalent C(4) and
C(6) were reverberating at δ =129 ppm. Additional carbon reso-
nance signals can be dispensed as C(10) and C(14) at δ =134 ppm,
C(11) and C(13) at δ =134 ppm, C(9) at δ =151 ppm, C(12) at δ
3.6. UV-VIS spectral studies
The optical transmission spectrum of MHBA single crystal was
recorded in the region from 100 nm to 1100 nm using Perkin
Elmer Lamda 35 spectrophotometer. It gives appreciated informa-
tion about the structure of molecules because the absorption of UV
and visible light involves the promotion of electrons in σ and π
orbital from the ground state to a higher energy state [34]. The
extreme transmittance is about 98% for MHBA crystal of 2 mm
thickness and the lower cut-off wavelength is obtained at 219 nm.
Fig. 11 displays that the crystal has a wide transparent opening in
the UV, visible and infrared regions [35], in the range from 390 nm
to 1100 nm, which point to that this crystal can be used as a po-
tential material for SHG or other optical applications in the visible
and NIR regions [36].
6

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Fig. 8. FT-Raman spectrum of MHBA.
Fig. 9. 1H - NMR spectrum of MHBA.
7

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Fig. 10. 13 C NMR spectrum of MHBA.
Fig. 11. UV–VIS Transmission spectrum of MHBA.
8

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Table 6
3.8. SHG studies
Torsion angles [degrees].
C(7)-C(2)-C(3)-C(4)
C(1)-C(2)-C(3)-C(4)
C(2)-C(3)-C(4)-C(5)
C(3)-C(4)-C(5)-C(6)
C(3)-C(4)-C(5)-N(1)
C(4)-C(5)-C(6)-C(7)
N(1)-C(5)-C(6)-C(7)
C(5)-C(6)-C(7)-C(2)
C(3)-C(2)-C(7)-C(6)
C(1)-C(2)-C(7)-C(6)
N(1)-C(8)-C(9)-C(14)
N(1)-C(8)-C(9)-C(10)
C(14)-C(9)-C(10)-C(11)
C(8)-C(9)-C(10)-C(11)
C(9)-C(10)-C(11)-C(12)
C(10)-C(11)-C(12)-O(1)
C(10)-C(11)-C(12)-C(13)
O(1)-C(12)-C(13)-C(14)
C(11)-C(12)-C(13)-C(14)
C(12)-C(13)-C(14)-C(9)
C(10)-C(9)-C(14)-C(13)
C(8)-C(9)-C(14)-C(13)
C(9)-C(8)-N(1)-C(5)
C(4)-C(5)-N(1)-C(8)
C(6)-C(5)-N(1)-C(8)
0.3(3)
The second harmonic generation (SHG) intensity of the grown
crystals was recorded using Kurtz and Perry powder technique
[43]. A Nd: YAG laser beam of a wavelength 1064 nm with pulses
of 9 ns with the repetition rate of 10 Hz was used. The crystalline
sample of MHBA and the reference sample of KDP were powdered
to the particle size of ≈ 125 μm. The SHG intensity is subject to
the particle size of the sample [44]. The release of green light with
a power of 166.4 mV and 160 mV were measured for the MHBA
and KDP correspondingly. The SHG efficiency of MHBA was found
to be 1.04 times greater than that of KDP.
−179.72(16)
2.0(2)
−3.5(2)
178.62(14)
2.7(2)
−179.48(14)
−0.4(3)
−1.1(3)
178.95(17)
−171.69(15)
13.4(2)
−0.1(2)
174.95(14)
−0.3(2)
3.9. Thermal analyses
−177.82(13)
0.7(2)
The grown MHBA crystal was subjected to Thermo Gravimet-
ric Analysis (TGA) and Differential Thermal Analysis (DTA) and the
spectra are shown in Fig. 13. They were documented using a simul-
taneous thermal analyzer TGA Q500 V20 in a nitrogen atmosphere
for a temperature range from 30 oC to 600 oC 10 oC at a heating
rate of 10oC/min. The decomposition switches nearly from 120 oC
to 225 oC and a major weight loss of 99% obtained at 208°C. The
weight loss directed that the decomposition nature of the sample
and NLO applications MHBA was used below 120°C [45]. However,
there is no weight loss was detected below 100 °C which shows
there is no water molecule in MHBA [46].
177.90(14)
−0.7(2)
0.3(2)
0.1(2)
−175.12(14)
−171.11(13)
−147.79(14)
34.4(2)
The bandgap energy of a sample is premeditated by using the
formula [37],
A sharp exothermic peak at 121 °C was obtained in the DTA
spectrum of MHBA which indicates the melting point of the grown
sample. The weight loss was spotted at 121 °C from this the de-
composition starts before melting. The acuity of the peaks indi-
cates a good degree of crystallinity of the sample [47,48]. The dif-
ferential scanning calorimetry (DSC) measurement of MHBA was
carried by using a sample of 10 g with a thermal analyzer of Net-
zsch DSC 204. A DSC plot of MHBA crystal is exposed in Fig. 14.
Very sharp endothermic peak detected at 121 °C with an area of
99 J/g well coincided with the TG-DTA spectrum of MHBA.
1240
Eg =
nm
)
(
λ
where λ is lower cut off a wavelength in the UV – VIS transmis-
sion spectrum and the value obtained is 267 nm. Using the above
formula, the calculated bandgap energy value of MHBA crystal is
4.6 eV. The optical transmission range and the transparency cutoff
wavelength are essential for materials used in optoelectronic ap-
plications [38].
3.7. Fluorescence studies
3.10. Vickers microhardness studies
Fluorescence may be expected generally in molecules that are
aromatic or contain multiple conjugated double bonds with a high
degree of resonance stability [39]. The excitation and emission
spectra of the MHBA were recorded using JOBINVYON FLURO LOG
3 spectrofluorometer. The emission spectrum was restrained in the
range 300 nm – 600 nm as shown in Fig. 12.
Mechanical stuff on the grown MHBA crystal was tested by us-
ing the Vickers hardness indentor with varying load from 25 g to
100 g with constant indentation time of 10 s. The profile of the
impression depends on the material, its structure and which face
verified [49]. The hardness number HV for the grown crystals can
also be estimated by using the relation,
It is detected that the crystal was excited at 271 nm, the con-
sistent emission was observed at 396 nm. In MHBA fluorescences
are caused by carbonyl chromophore and the central C=N bond
[40,41]. The optical band gap of MHBA is determined as 4.6 eV,
which concurs well with the bandgap calculated from the UV-VIS
optical transmission spectrum. Fluorescence finds extensive appli-
cation in the branches of biochemistry, medicine and analytical
tools and detection methods in material science [42].
ꢀ
ꢁ
1854P
d2
Hv =
Kgm−2
where P is the applied load for testing in g and d is the diagonal
length of the indentor used in mm [50]. The hardness number for
various loads like 25 g, 50 g and 100 g are calculated by using the
above formula and shown in Fig. 15. On the additional increase of
Table 7
FTIR and FT Raman band assignments of MHBA crystal.
FTIR (cm−1
)
FT Raman (cm−1
)
Assignments
3031
2985
2867
1592
1449
1241
1160
828
3056
2915
2886
1590
1444
1287
1165
821
C-H symmetric stretching
C-H stretching in CH3
C-H asymmetric stretching
C=N stretching
C=C stretching in aromatic ring
Asymmetric and Symmetric deformation mode of methyl group
–
Aromatic C-H plane bending
C-H bending mode
645
656
Out of plane bending of hydroxy group
–
530
540
C
C deformation
9

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Fig. 12. Fluorescence spectrum of MHBA.
Fig. 13. TGA-DTA curve of MHBA.
the load beyond 100 g, cracks established on the surface of the
crystal caused by the release of internal stress generated locally by
indentation [51]. The C11 (elastic stiffness constant) was calculated
from Hv by using the formula [37],
pression in only one direction otherwise called elastic modulus.
Using the Vickers microhardness number, the Young’s modulus of
the crystal also calculated using the relation [53],
ꢂ
ꢃ
ꢀ
ꢁ
0.45Hv
E =
Nm−2
7/4
)
b
a
C11
=
H
GPa
( )
(
v
0.1406 −
there are two important aspects in determining the value of C11
.
where b and a are the shorter and longer indentation diagonal
lengths of the indentor impressed through the material. The elas-
tic modulus is an intrinsic property of a material, up to a primary
level E is a measure of the bond strength between the atoms in a
material.
The opening aspect is the tightness of bonding between the neigh-
boring atoms. The next aspect is the rate of variation with the
position of the atoms of the forces of attraction and repulsion
between them [52]. The elastic stiffness constant value of MHBA
crystals for a load of 25 g is 14.10 GPa. The Young’s Modulus de-
scribes the elastic properties of a solid undergoing tension or com-
The greater the modulus, the stiffer the material but the value
is 0.2540 × 1010 Nm−2 for a load of 25 g. The minimum value
10

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Fig. 14. DSC curve of MHBA.
Fig. 15. Hardness Vs. Load for MHBA.
of Youngs modulus indicate that MHBA crystal an example of soft
material. The Meyers index number or work hardening coefficient
(n) is calculated from Meyers law by,
3.11. Dielectric studies
The dielectric properties normally correlate with the electro-
optical property of crystals [63] and also provide information about
the superiority of the materials [64]. The grown MHBA single crys-
tal was subjected to dielectric studies using HIOKI 3532 - 50 LCR
HITESTER impedance meter. The cut and polished surface of the
sample was electrode with silver paste for electrical contact. The
experiment was carried out for the frequencies from 0 Hz to 1
MHz with the temperatures of 30°C, 40°C, 50°C and 60 °C. In gen-
eral, the dielectric response would be good in the lower region
for the organic crystals. From the Fig. 16 to find that the dielec-
tric constant decreases with increasing frequency at all measured
temperatures. In low frequency nearly 500 kHz the value of a di-
electric constant is very small of the order of 98 at temperature
30 °C but at temperature 60°C the dielectric constant is rise to 283.
Also the frequency above 500 kHz the value of dielectric constant
P = adn
the relation involving the applied load and diagonal length d of the
indenter used for testing. It is also used to measure the mechani-
cal strength of the materials, and that could be calculated from the
slope of a straight line between log P and log d2. Onitsch [54] and
Hanneman [55] indicate that n lies between 1.0 and 1.6 for hard
material and is more than 1.6 for soft materials. The work harden-
ing coefficient is inverse to the hardness of the material [56]. The
n value detected in the present studies is just around 2.583 sig-
nifying that MHBA crystals are moderately soft materials. Table 8
shows the comparison of microhardness number and work hard-
ening index of MHBA with some organic crystals.
11

R. Sakunthaladevi and L. Jothi
Journal of Molecular Structure 1233 (2021) 130054
Table 8
Comparison of microhardness number (Hv) and work hardening index (n).
Crystals
Crystal System
Hv
n
Reference
Benzamidazole
Orthorhombic
Orthorhombic
Orthorhombic
Monoclinic
29
2.06
2.04
1.65
1.50
2.40
1.65
2.58
[57]
P- hydroxy acetophenone
25
[58]
ꢀ
4, 4 -dimethyl benzophenone
17.2
23
[59]
2 amino–5 chloro benzophenone
L – Alanine triethanol amine
L – Alaninium maleate
[60]
Orthorhombic
Orthorhombic
Orthorhombic
24
[61]
64
[62]
ꢀ
4-methyl-4 -hydroxy benzylidene aniline
65
Present work
zylidene aniline derivatives which is also confirmed by FT Raman
spectral analyses. The consistent resonance frequency of the nuclei
in a molecule is detected by 1H and 13C NMR spectra. It showed
a peak at 193.8 in 1H and 10.0 ppm in 13C respectively of (HC=N)
bonding, which was assigned to the azomethine carbon atom in
the grown MHBA crystal. The optical transmission study exposed
that the MHBA crystal was optically transparent in the entire vis-
ible and NIR region. The bandgap energy intended from UV-VIS
and fluorescence spectrum is almost equivalent to 4.6 eV and it
is an important parameter in optoelectronic applications. The sec-
ond harmonic generation (SHG) efficiency was investigated to ex-
plore the nonlinear optical characteristics of the MHBA crystal, and
it was 1.04 times that of KDP in green light emission. The thermal
steadiness of the MHBA crystal nearly 120 °C which is confirmed
by both the TG/DTA and DSC analyses. There is no weight loss be-
low 100 °C which shows there is no water molecule in MHBA and
the MHBA crystal is used below 120 °C in NLO applications. The
mechanical strong point of the MHBA crystal was measured by
Vickers micro hardness test and it shows reverse indentation size
effect. The Young’s modulus value and work hardening coefficient
value of MHBA is 0.2540 × 1010 Nm−2 and 2.58 respectively and
it directed that MHBA crystal belongs to soft material type. The
dielectric behavior has been evaluated and testified as a function
of frequency with rise in temperature. High values of a dielectric
constant in low frequency for measured temperatures lead to more
power dissipation of MHBA crystals.
Fig. 16. Variation of a dielectric constant of MHBA as function of frequency at dif-
ferent temperatures.
changes gradually and above 1 MHz it attains nearly a saturation
value at all the measured temperatures. The high values of εr at
low frequencies might be caused by the presence of the four po-
larizations namely, space charge, orientational, ionic and electronic
and its low value at high frequencies might be caused by gradual
significance loss of these polarizations [65]. From the above results
it is clear that the dielectric constant inversely depends on both
the temperature and frequency. The dielectric constant was pre-
meditated using the relation [66],
Declaration of competing interest
The authors declare that they have no known competing finan-
cial interestsor personal relationships that could have appeared to
influence the work reported in this paper.
Cd
εr =
ε0A
Acknowledgements
which relates the capacitance (F), thickness of the crystal used (m),
vacuum dielectric constant (8.854 × 10-12 Fm-1) and area of the
crystal used (m2).
One of the authors (LJ) thanks Sophisticated Instrumentation
centre, Indian Institute of Technology, Chennai for the support in
single crystal XRD, Fluorescence, DSC and TG/DTA data collection.
LJ also, thanks to Prof. P.K. Das, Indian Institute of Science, Ban-
galore for having protracted laser facilities for SHG measurements
and Central Electro Chemical Research Institute (CECRI), Karaikudi
for NMR measures.
The inverse association between a dielectric constant and fre-
quencies is an important property for the fabrication of materials
towards ferroelectric, photonic and electro-optic devices [67].
4. Conclusions
A new aromatic Schiff base organic NLO material of MHBA
was synthesized by the condensation process and the solubility of
MHBA was determined with an increase in temperature. The ob-
tained MHBA single crystals were transparent and colorless with
a dimension of 20 × 20 × 2.5 mm3. The intensity data of the
MHBA crystal was recognized by the single-crystal X-ray analysis
and the refinement details are summarized. The molecular struc-
ture of MHBA was refined by the least squares method and it
crystallized into orthorhombic with Pbcn space group. This is com-
pared with powder X-ray diffraction studies and confirmed the re-
sults obtained from single crystal XRD. In FT-IR spectra the peak
near 1600 cm−1 confirmed the (C=N) stretching vibration in ben-
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