Exploration of structural, electronic and third order nonlinear optical properties of crystalline chalcone systems: Monoarylidene and unsymmetrical diarylidene cycloalkanones

Article abstract of DOI:10.1016/j.molstruc.2021.130685

In the current study monoarylidene and unsymmetrical diarylidene cycloalkanes, MBMHP, MABP, MBHP, and MBCP have been prepared. Their molecular structures were confirmed by SC-XRD. Accompanying the experimental studies, quantum chemical investigation is performed at the M06/6-311+G(d,p) level, with the natural bond orbital analysis (NBO) performed at the ωB97XD/6-311+G(d,p) level. NBO study showed that the hyper-conjugation and intermolecular charge transfer play a remarkable role in stabilizing the crystals and also endorsed the SC-XRD investigations. Furthermore, the band gap of orbitals explained the chemical reactivity and charge transfer phenomena in the above-mentioned crystals. The smallest HOMO/LUMO band gap (4.127 eV) is exhibited by MABP molecule while the highest gap value is found for MBHP to be 4.768 eV. Global reactivity parameters (GRP) are also explored from the energies of HOMO/LUMO. Among all crystals MBHP has higher value of hardness (η = 2.384 eV) while MABP showed higher global softness (σ = 0.242307 eV). So, from GRP it is revealed that all the studied crystals are less reactive but more stable as suggested by NBO and SC-XRD investigations. NLO study showed that the crystal MBMHP has the higher value of linear polarizability<α> and second hyperpolarizability <γ> 216.36 and 1.06 × 10⁴ a.u respectively, among all the synthesized crystals. NLO properties of these synthesized crystals may play a significant contribution for the NLO technological applications.

Full text of DOI:10.1016/j.molstruc.2021.130685

Journal of Molecular Structure 1241 (2021) 130685
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Exploration of structural, electronic and third order nonlinear optical
properties of crystalline chalcone systems: Monoarylidene and
unsymmetrical diarylidene cycloalkanones
Akbar Alia,1, Muhammad Khalidb,1,∗, Zia Ud Dinc,∗, Hafiz Muhammad Asifd,∗
,
Muhammad Imrane, Muhammad Nawaz Tahirf, Muhammad Ashfaqf,
Edson Rodrigues-Filhoc
a Department of Chemistry, Government College University Faisalabad, Pakistan
b Department of Chemistry, Khwaja Fareed University of Engineering and Information Technology, Rahim Yar Khan 64200, Pakistan
c LaBioMMi, Departamento de Química, Universidade Federal de São Carlos, CP 676, São Carlos, SP 13.565-905, Brazil
d Institute of Chemical Sciences, Bahauddin Zakariya University, Multan 60800, Pakistan
e Department of Chemistry, Faculty of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia
f Department of Physics, University of Sargodha, Sargodha, Pakistan
a r t i c l e i n f o
a b s t r a c t
Article history:
In the current study monoarylidene and unsymmetrical diarylidene cycloalkanes, MBMHP, MABP, MBHP,
and MBCP have been prepared. Their molecular structures were confirmed by SC-XRD. Accompanying
the experimental studies, quantum chemical investigation is performed at the M06/6-311+G(d,p) level,
with the natural bond orbital analysis (NBO) performed at the ωB97XD/6-311+G(d,p) level. NBO study
showed that the hyper-conjugation and intermolecular charge transfer play a remarkable role in stabi-
lizing the crystals and also endorsed the SC-XRD investigations. Furthermore, the band gap of orbitals
explained the chemical reactivity and charge transfer phenomena in the above-mentioned crystals. The
smallest HOMO/LUMO band gap (4.127 eV) is exhibited by MABP molecule while the highest gap value
is found for MBHP to be 4.768 eV.. Global reactivity parameters (GRP) are also explored from the ener-
gies of HOMO/LUMO. Among all crystals MBHP has higher value of hardness (η = 2.384 eV) while MABP
showed higher global softness (σ = 0.242307 eV). So, from GRP it is revealed that all the studied crys-
tals are less reactive but more stable as suggested by NBO and SC-XRD investigations. NLO study showed
that the crystal MBMHP has the higher value of linear polarizability<α> and second hyperpolarizability
<γ > 216.36 and 1.06 × 104 a.u respectively, among all the synthesized crystals. NLO properties of these
synthesized crystals may play a significant contribution for the NLO technological applications.
Received 14 February 2021
Revised 23 April 2021
Accepted 10 May 2021
Available online 18 May 2021
Keywords:
Arylidene Cycloalkanones
SC-XRD
DFT Study
NLO
© 2021 Elsevier B.V. All rights reserved.
Introduction
anti-viral [10], antimitotic [11], anti-tubulin [12], antitumor [13],
anti-fertility [14], anti-parasitic [15], anticancer [16], and neuro-
Monoarylidene and unsymmetrical diarylidene alkanones are
pharmaceutically active compounds [1]. Synthetic bis(arylidene)s
are well known for their cytotoxic capability against human ovar-
ian tumor cell line A2780-CP70 that is found resistant towards
the famous cisplatin [2]. Moreover, monoarylidene and unsym-
metrical diarylidene alkanones derivatives have also been found
to have anti-inflammatory [3] antibacterial [4], antimicrobial [5],
anti-tubercular [6],antimalarial [7], antifungal [8], antioxidant [9],
protective [17] capabilities. Both symmetrical and unsymmetri-
cal curcuminoids have shown their medicinal importance [18].
Together with their medicinal importance, these diarylidene cy-
cloalkanone derivatives have been studied for their photophysi-
cal properties along with their electron donor-acceptor ability and
found to have potential applications in the two-photon absorption
(TPA) processes [19]. In recent time, the nonlinear optical (NLO)
properties exploration has attracted significant attention of the sci-
entific community (both theoretical and experimental researchers)
as materials with strong NLO properties have found momentous
applications in various fields of science and technology [20], es-
pecially the areas of nuclear science, medicine, biophysics, solid
physics, chemical dynamics, surface-interface and materials science
∗
Corresponding authors.
E-mail addresses: khalid@iq.usp.br (M. Khalid), zia.ufscar@gmail.com (Z.U. Din),
hmasifc@gmail.com (H.M. Asif).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.molstruc.2021.130685
0022-2860/© 2021 Elsevier B.V. All rights reserved.

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
Scheme 1. Synthesis and structural features of monoarylidene and unsymmetrical diarylidene alkanones compounds
are worth mentioning[21]. It is important to mention that organic
materials are capable of strong NLO behavior and have significant
advantages over the inorganic counterparts due to their ease of so-
lution process ability, low cost, flexibility for device fabrications
and low toxic nature [22]. There are various classes of organic
compounds that show significant NLO responses. Among these or-
ganic compounds conjugated molecules, perylenes, phosphonate
compounds, fullerenes, polymers, thiophenes and organic dyes are
important to mention [23]. Arylidene alkanones (both monoaryli-
dene and unsymmetrical diarylidene alkanones) are also a signif-
icant class of organic compounds that have been investigated for
the NLO properties [24]. Density functional theory (a computa-
tional modelling approach) is extensively used for the exploration
of nonlinear optical ability of organic materials. Here, we present
our investigation related to the synthesis of monoarylidene and
unsymmetrical diarylidene cycloalkanones (Scheme 1), their com-
plete structural verification by single-crystal analysis along with
their nonlinear optical exploration via detailed DFT calculations.
was washed with a solution of NaHSO3. After the workup, the sep-
arated organic layer was dried over anhydrous Na2SO4. Finally, the
purified product was obtained using vacuum distillation yielding
compound 3 that was recrystallized using ethanol (See Scheme 2).
Preparation of compound 4
To a stirred solution of compound 3 and p-methoxy benzalde-
hyde in ethanol (5 mL) at room temperature, the NaOH solution
in ethanol (4 mL, 50 mol) was added and stirring was continued.
After completion (observed by TLC), the solvent of the reaction
mixture was evaporated by rotary evaporator. The reaction mix-
ture was diluted in ethyl acetate and then the extraction was per-
formed with NaHSO3 solution. The organic layer was dried over
anhydrous Na2SO4. Upon concentrating using rotary evaporator,
the crude product was recovered as yellow precipitate that was
purified using column chromatography. Upon recrystallization us-
ing ethanol, pure crystals of compound 4 were recovered and used
for the SC-XRD analysis (See Scheme 2).
Experimental Section
Characterization of compounds
Chemistry
(1). (E)-2-(2-methylbenzylidene)cyclopentanone (MBMHP)
Chemicals utilized in this research work were bought from
renowned standard companies like Acros Chemicals and Sigma-
Aldrich and were used as received. In order to observe the reaction
speed TLC plates (pre-coated silica gel G-25-UV254) were used.
The NMR studies (1H and13C) were performed using the Brüker
AVANCE 400 at 400 MHz and 100 MHz, respectively, where the
tetramethyl silane (TMS) was used as internal reference.
The spectroscopic data of the title compound was found to be
in total correspondence to the reports in literature [25]. 1H NMR
(400 MHz, CDCl3) δ 7.59 (t, J = 2.7 Hz, 1H), 7.42 (dd, J = 7.4, 1.9
Hz, 1H), 7.29 – 7.17 (m, 3H), 2.90 (td, J = 7.2, 2.7 Hz, 2H), 2.51 –
2.34 (m, 5H), 2.01 (p, J = 7.5 Hz, 2H); 13C NMR (100 MHz, CDCl3)
δ 207.9, 138.9, 136.8, 134.3, 130.5, 129.8, 129.2, 128.6, 125.8, 38.0,
29.4, 20.5, 20.0.
General Procedure
(2). ((E)-2-(4-(dimethylamino)benzylidene)cyclopentanone
(MABP)
Preparation of compounds 1 and 2
The spectroscopic data of the title compound was found in total
correspondence to the reported literature26 1H NMR (400 MHz,
.
Cyclopentanone and aldehyde (o-methyl benzaldehyde in case
of compound 1 and p-nitro benzaldehyde in case of compound
2) were taken in a ratio of 1:1, in a two necked (50 mL) round
bottom flask. Through this reaction mixture, HCl gas was passed
till it turns red colored. Stirring was continued for 8 h. The reac-
tion mixture was washed with NaHSO3 solution after diluting with
toluene. After separating the organic layer it was dried over anhy-
drous Na2SO4 and the solvent was removed by rotary evaporation.
The purified product was obtained via vacuum distillation to yield
the compounds 1 and 2 and recrystallization was performed using
ethanol (See Scheme 2).
CDCl3) δ 7.46 (d, J = 8.9 Hz, 2H), 7.34 (t, J = 2.6 Hz, 1H), 6.75 (d,
J = 8.1 Hz, 2H), 3.02 (s, 6H), 2.94 (td, J = 7.2, 2.5 Hz, 2H), 2.36 (t,
J = 8.0 Hz, 2H), 2.00 (p, J = 7.6 Hz, 2H); 13C NMR (100 MHz, CDCl3)
δ 208.1, 150.6, 133.2, 132.5, 131.4,112.2, 111.0, 40.4, 37.8, 29.4, 20.2.
(3). (E)-3-(2,3-dimethoxybenzylidene)dihydro-2H-pyran-4(3H)-
one (MBHP)
The spectroscopic data of the title compound was found in total
.
correspondence to the reported literature26 1H NMR (400 MHz,
CDCl3) δ 7.73 (s, 1H), 6.98 (t, J = 8.0 Hz, 1H), 6.89 (dd, J = 8.2,
1.4 Hz, 1H), 6.60 (dd, J = 7.8, 1.1 Hz, 1H), 4.64 (d, J = 2.1 Hz, 2H),
3.99 (t, J = 6.1 Hz, 2H), 3.80 (s, 3H), 3.74 (s, 3H), 2.61 (t, J = 6.1 Hz,
2H); 13C NMR (100 MHz, CDCl3) δ 196.2, 152.8, 148.5, 134.2, 131.2,
128.5, 123.7, 122.0, 113.8, 68.7, 65.6, 61.1, 55.8, 39.9.
Preparation of compound 3
The compound 3 was synthesized following the above pro-
cedure for the synthesis of compounds 1 and 2. Accordingly,
tetrahydro-4H-pyran-4-one and o,m-dimethoxy benzaldehyde were
taken in a two-necked round-bottom flask (50 mL) in 1:1 ratio fol-
lowed by passing of the HCl gas through the reaction mixture and
waited for the reaction mixture to turns red colored. The reaction
mixture was stirred for 8 h before diluting it with toluene and then
(4). 3-((E)-2,3-dimethoxybenzylidene)-5-((E)-4-
methoxybenzylidene)tetrahydro-4H-pyran-4-one (MBCP)
1H NMR (400 MHz, CDCl3) δ 8.03 (d, J = 1.8 Hz, 1H), 7.82 (d,
J = 5.6 Hz, 1H), 7.32 (dd, J = 8.6, 3.8 Hz, 2H), 7.10 (dd, J = 10.6, 5.3
2

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
Scheme 2. Synthetic route for the accomplishment of the organic crystalline compounds:1(MBMHP), 2 (MABP), 3 (MBHP), and 4 (MBCP).
Fig. 1. ORTEP illustration of MBMHP, MABP, MBHP and MBCP drawn at 50% probability level. H-atoms are shown by tiny rings of arbitrary radii.
Hz, 1H), 7.00 – 6.95 (m, 3H), 6.73 (dt, J = 11.2, 5.6 Hz, 1H), 4.96
(d, J = 1.8 Hz, 2H), 4.79 (t, J = 5.3 Hz, 2H), 3.93 – 3.90 (m, 3H),
3.88 (s, 3H), 3.83 (s, 3H).13C NMR (100 MHz, CDCl3) δ 185.5, 160.6,
153.0, 148.4, 136.5, 134.1, 132.6, 131.6, 131.2, 129.2, 127.6, 123.8,
122.2, 114.3, 113.5, 69.0, 68.7, 61.4, 55.9, 55.4.
group D is unevenly planar with root mean square (r.m.s) devia-
˚
tion of 0.0675 A. The dihedral angle of basal plane B with group
C and D is 39.25 (4)° and 11.5 (7)°, respectively, whereas the di-
hedral angle between C/D is 31.12 (4)°. The C-H…O bonding is re-
sponsible for the intermolecular linkage. The molecules are inter-
linked in the form of dimers to form R12(7) loop by two types of
C-H…O bonding, where O-atom is from carbonyl oxygen attached
to tetrahydro-2H-pyran ring A. In first type of C-H…O bonding,
CH is from the ring part of anisole moiety (C16-C22/O5) while in
second type of C-H…O bonding, CH is from the terminal methyl
moiety of the anisole part. These dimers are interlinked by C18-
H18…O3 and C18-H18-O4 bonding as revealed in Fig. 2 and spec-
ified in Table 2. The O-atom of anisole moiety and O-atom di-
rectly attached with carbon atom (C7) are not engaged in hydrogen
bonding. Moreover, the presence of C-H…π interaction gives fur-
ther stability in the crystal packing. One of the ring CH of group C
of a molecule located at asymmetric position is interacted with the
In the MBMHP (Fig. 1, Table 1), the tetrahydro-2H-pyran ring
A (C10-C14/O4) is not planar but the basal plane B (C10-C14/O3)
˚
is planar with r.m.s (root mean square) deviation of 0.0387 A. The
ring O-atom is out of basal plane B and deviated at the distance
˚
of -0.6833 (2) A from the basal plane B. Ring Puckering inspec-
tion manifests that the tetrahydro-2H-pyran ring A has puckering
˚
amplitude Q=0.5235(12) A with θ=124.20(14)° and ϕ=167.58(18)°.
The part of aldehyde group named as 3-methylbenzene-1,2-diol
group C (C1-C6/C9/O1/O2) is found to be planar with r.m.s devi-
˚
ation of 0.0235 A. The terminal carbon atoms (C7/C8) of methoxy
˚
groups are at the distance of 1.1686 (2) and 0.2678 (2) A, respec-
tively, from the plane of group C. The 1-methoxy-4-methylbenzene
3

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
Table 1
Experimental data of the title compounds.
MBMHP
MABP
MBHP
MBCP
CCDC
2017959
22H22O5
2017960
2017961
2017962
Chemical formula
Mr
C
C14H17NO
215.28
C14H16O4
C13H14
186.24
O
366.39
248.27
Crystal system, space group
Temperature (K)
Monoclinic, P21/c
Monoclinic, P21/c
150(2)
Monoclinic, P21/n
150(2)
Orthorhombic, Aba2
150(2)
150(2)
˚
a, b, c (A)
11.309 (3), 8.779 (2), 18.800
13.372 (2), 7.4908 (11),
12.2915 (18)
90, 111.436 (3), 90
1146.0 (3)
4
4.0235 (1), 13.9297 (5),
21.7483 (7)
90, 93.573 (1), 90
1216.54 (7)
4
14.7638 (7), 19.9779 (10),
(4)
6.9582 (3)
90, 90, 90
2052.32 (17)
8
α, β, γ (°)
90, 101.987 (5), 90
3
˚
V (A )
1825.8 (8)
4
Z
Density (Mg/m3)
F(000)
1.333
776
1.248
1.356
1.206
464
528
800
Radiation type
Mo Kα
Mo Kα
Cu Kα
Cu Kα
˚
˚
˚
˚
Wavelength (λ)
0.71073 A
0.71073 A
1.54178 A
1.54178 A
μ (mm−1
)
0.094
00.078
0.817
0.578
Crystal size (mm)
0.45 × 0.23 × 0.12
0.55 × 0.35 × 0.14
0.18 × 0.17 × 0.15
0.34 × 0.21 × 0.17
Data collection
Diffractometer
Bruker APEXII CCD
diffractometer
Bruker APEXII CCD
diffractometer
Bruker APEXII CCD
diffractometer
Bruker APEXII CCD
diffractometer
Absorption correction
multi-scan (SADABS; Bruker,
2007)
multi-scan (SADABS;
Bruker, 2007)
multi-scan (SADABS;
Bruker, 2007)
multi-scan (SADABS;
Bruker, 2007)
No. of measured, independent
and observed [I > 2σ(I)]
reflections
11440, 3872, 3225
12361, 2441, 2212
15676, 2144, 2000
6661, 1762, 1748
Rint
0.018
0.019
0.030
0.020
Theta range for data collection
Index ranges
1.841-26.730
1.636-26.743
-16≤ h ≤16, -9≤ k ≤9,
-15≤ l ≤ 11
0.633
3.770- 66.580
-4≤ h ≤4, -16≤ k ≤16,
-25≤ l ≤ 25
0.595
4.426-66.574
-17≤ h ≤16, -23≤ k ≤23,
-8≤ l ≤ 8
-14≤ h ≤14, -11≤ k ≤8, -23≤ l
≤ 22
−1
˚
(sin θ/λ)max (A
)
0.633
0.595
Refinement
R[F2 > 2σ(F2)], wR(F2), S
0.035, 0.092, 1.03
0.037, 0.098, 1.03
0.032, 0.086, 1.07
0.028, 0.070, 1.08
No. of reflections
3872
2441
2144
1762
No. of parameters
No. of restraints
247
147
165
129
-
-
-
1
H-atom treatment
H-atom parameters
constrained
0.22, −0.20
H-atom parameters
constrained
0.22, −0.21
H-atom parameters
constrained
0.20, −0.19
H-atom parameters
constrained
0.14, −0.21
−3
˚
ꢀρmax, ꢀρmin (e A
)
Table 2
Hydrogen-bond geometry (A, ) for the title compounds.
˚
º
D—H···
A
D—H
H···
A
D···
A
D—H···A
C8—H8A···O3i
0.98
0.95
0.95
0.95
0.98
C—H
0.95
0.99
D—H
0.98
0.95
0.99
0.99
C—H
0.98
0.98
D—H
0.98
0.99
0.95
0.98
D—H
0.99
0.95
C—H
0.99
0.95
2.31
2.53
2.54
2.41
2.59
3.2231 (18)
3.2309 (17)
3.2939 (16)
3.2945 (16)
3.4171 (19)
155
131
137
156
142
C—H···
47
C18—H18 O3ii
···
C18—H18 O4iii
···
MBMHP
C20—H20 O2iv
···
C22—H22A O3ii
···
C—H···
π
H···
π
2.91
C···
π
π
C5—H5 Cg(3)iv
3.5703(17)
···
C13—H13A Cg(3)v
2.83
3.7043(17)
57
···
D—H···
A
H···
A
D···
A
D—H···
162
160
170
170
C—H···
67
A
C14—H14B O1vi
2.56
2.59
2.57
2.47
3.5025(15)
3.4943 (14)
3.5547 (15)
3.4509 (14)
···
C8—H8 O1vii
C4—H4B O1viii
C3—H3A O1ix
···
···
···
MABP
C—H···
π
H···
π
3.00
C···
π
π
C13—H13A Cg(2)x
3.8240(15)
···
C14—H14A Cg(2)xi
2.77
3.6254(14)
58
···
D—H···
A
H···
A
D···
A
D—H···
133
132
161
177
D—H···
131
166
C—H···
66
A
C8—H8A O4xii
2.56
2.60
2.59
2.37
3.3009 (16)
3.3429 (16)
3.4994 (16)
3.3520 (16)
···
C12—H12A O3xiii
C5—H5 O3xiv
C7—H7C O1xiii
···
MBHP
MBCP
···
···
D—H···
A
H···
A
D···A
3.303 (2)
A
C2—H2B O1xv
2.56
···
···
C10—H10 O1xvi
2.56
3.484 (2)
C—H···
π
H···
π
2.80
C···
π
π
C3—H3A Cg(2)xvii
3.696(2)
···
C9—H9 Cg(2)xv
2.99
3.7246(19)
45
···
4

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
˚
atom (C3) is at the distance of 0.4287 (2) A from basal plane B.
Ring Puckering inspection manifests that the cyclopentane ring A
has an envelope conformation on atom number C3. The N,N,4-
trimethylaniline group C (C6-C14/N1) is planar with r.m.s deviation
˚
of 0.0281 A and is oriented at the dihedral angle of 21.7 (4)° with
respect to basal plane B. The molecules are interlinked in the form
of dimers through C-H…O interaction to form R22(14) loop, where
CH is from the aromatic six-membered ring as shown in Fig. 2 and
given in Table 2. The two C-atoms (C3/C4) of cyclopentane ring A
(for numbering see Fig. 1) are act as donor for O-atom of neighbor-
ing molecule also C14-H14B…O1 bonding is responsible for crys-
tal packing. The presence of C-H…π interaction gives further assis-
tances in strengthening of the crystal packing. CH of the dimethy-
lamine moiety D of a molecule located at the asymmetric position
is interacted with the phenyl ring of a molecule positioned at −x,
…
˚
2−y, −z with H π distance of 2.77 A as shown in Fig. S1 and given
in Table 2. Similarly, the other CH of the dimethylamine moiety D
of a molecule located at asymmetric position is interacted with the
phenyl ring situated at −x, y+1/2, −z+1/2 with H…π distance of
˚
3.00 A.
In the MBHP (Fig. 1, Table 1), the tetrahydro-2H-pyran ring
A (C10-C14/O4) is not planar but the basal plane B (C10-C14) is
˚
found to be planar having r.m.s deviation of 0.0828 A. The car-
bonyl O-atom is not in the plane B this time. The ring O-atom and
carbonyl O-atom are deviated at the distance of 0.6451 (2) and -
˚
0.2642 A, respectively from basal plane B. Ring Puckering inspec-
tion manifests that the tetrahydro-2H-pyran ring A has puckering
˚
amplitude Q = 0.5148(12) A with θ = 42.22(14)° and ϕ=338.0(2)°.
The part of aldehyde group named as 3-methylbenzene-1,2-diol
group C (C1-C6/C9/O1/O2) is found to be planar with r.m.s devi-
˚
ation of 0.0188 A. The terminal carbon atoms (C7/C8) of methoxy
˚
groups are at the distance of -1.2280 (2) and 0.1724 A, respectively
from plane of group C. The molecules are associated with each
other in such a way to form dimers via C-H…O interaction to form
R22(16) loop. Moreover, in this case CH is from the phenyl ring of
1,2-dimethoxybenzene while O-atom is from tetrahydro-2H-pyran
ring E as shown in Fig. 2 and given in Table 2. The CH of or-
tho and meta-positioned methoxy group of 1,2-dimethoxybenzene
moiety act as donor for O-atom of ortho-positioned methoxy group
and carbonyl O-atom, respectively to connect molecules with each
other. Similarly, CH of the tetrahydro-2H-pyran ring acts as donor
for O-atom of same ring of another molecule to connect them.
In this compound, the packing of molecules is further stabilized
by the presence of cycle stacking interaction. The phenyl ring of
molecule located at asymmetric positon interact with phenyl ring
of a neighboring molecule located at –x+1, y, z with distance of
˚
4.024 A between the centroids as shown in Fig. S1.
In the MBCP (Fig. 1, Table 1), the cyclopentane ring A (C1–C5)
is found to be not planar but the basal plane B (C1/C2/C4/C5/O1) is
˚
found to be planar having r.m.s deviation of 0.0072 A. The apical
˚
carbon atom (C3) is at the distance of -0.4741 (3) A from basal
plane B. Ring Puckering inspection manifests that the cyclopen-
tane ring A has an envelope conformation on atom number (C3).
The toluene group C (C6–C13) is in plan having r.m.s deviation
Fig. 2. Packing diagram of MBMHP, MABP, MBHP and MBCP showing dimerization
of molecules through C–H...O bonding. H-atoms not engaged in hydrogen bonding
are removed for clarity.
˚
of 0.0199 A oriented at the dihedral angle of 34.13 (6)° with re-
spect to basal plane B. The molecules are interlinked through two
types of C–H…O bonding. In first type of C–H…O bonding, CH is
from phenyl ring whereas in second type of C–H…O bonding, CH
is from cyclopentane ring as shown in Fig. 2 and given in Table 2.
Molecules form infinite C14 chains through these C–H…O bonding
along [100] crystallographic direction. Moreover, packing is further
stabilized by the presence of C-H…π interaction. One of the CH
of the cyclopentane ring A of a molecule located at asymmetric
position is interacted with the phenyl ring of toluene group of a
phenyl ring of anisole moiety of a molecule located at −x, y−1/2,
…
˚
−z+1/2 with H π distance of 2.91 A as shown Fig. S1 and given in
Table 2. Similarly, One of the CH of the tetrahydro-2H-pyran ring
A of a molecule located at asymmetric position is interacted with
the phenyl ring of anisole moiety of a molecule located at −x, −y,
…
˚
−z+1 with H π distance of 2.83 A.
In the MABP (Fig. 1, Table 1), the cyclopentane ring A (C1-C5)
is found to be not planar but the basal plane B (C1/C2/C4/C5/O1)
˚
˚
molecule located at −x, −y+1/2, z with H…π distance of 2.80 A as
is planar with r.m.s deviation of 0.0017 A. The apical carbon
5

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
shown in Fig. S1 and given in Table 2. Similarly, One of the CH of
the methyl group attached to phenyl ring of a molecule situated at
asymmetric position is interacted with the phenyl ring of toluene
group of a molecule positioned at −x+3/2, y, z−1/2 with H…π dis-
the DFT investigated data of aforementioned bond lengths are ob-
˚
served as 1.342, 1.5, 1.491, and 1.502 A, respectively as shown in
Table S1. Similarly, for MABP the bond lengths in C3-C7, C5-C6, C7-
˚
C8, and C8-C9 are seen as 1.481, 1.544, 1.348, and 1.456 A (XRD).
˚
tance of 2.99 A.
On the other hand, the computationally explored data of aforesaid
˚
Symmetrycodes:(i) x, −y+1/2, z−1/2 (ii) −x, −y+1, −z+1 (iii) x,
−y+1/2, z+1/2 (iv) −x, y−1/2, −z+1/2 (v) −x, −y, −z+1 (vi) x−1,
−y+3/2, z−1/2 (vii) −x+1, −y+2, −z+1 (viii) −x+1, y−1/2, −z+1/2
(ix) x, −y+3/2, z−1/2 (x) −x, y+1/2, −z+1/2 (xi) −x, 2−y, −z (xii)
−x+3/2, y−1/2, −z+1/2 (xiii) x−1, y, z; (xiv) −x+1, −y, −z; (xv)
−x+3/2, y, z−1/2 (xvi) x, y+1/2, z−1/2 (xvii) −x, −y+1/2, z.
bond lengths are determined as 1.482, 1.537, 1.345 and 1.445 A,
respectively as shown in Table S2.
In MBHP, bond lengths O1-C6, O2-C7, O3-C15 and O4-C18 have
˚
been observed as 1.379, 1.367, 1.425 and 1.216 A (SC-XRD), whereas
the simulated values of aforementioned bond lengths are calcu-
˚
lated as 1.359, 1.352, 1.406 and 1.211 A, respectively (Table S3).
˚
Similarly, the bond length in MBCP is 1.218 A for O1-C2 as noted
by XRD, while the explored values of aforesaid bond length is ob-
Computational details
˚
tained as 1.207A, as shown in Table S4. Moreover, for MBHP the
bond lengths in C13-C14, C14-C15, C14-C18, and C16-C17 are ob-
With the assistance of Gaussian 09 program package [26], quan-
tum chemical investigation of the title crystals has been per-
formed. The primary structures of MBMHP, MABP, MBHP and
MBCP have been obtained by the SC-XRD. The Density Func-
tional Theory (DFT) [27–29] is study was performed at the M06/6-
311+G(d,p) level [30]to obtain the optimized geometries. The M06
is more recently developed functional from Minnesota group of
functionals as designed by Zhao and Truhlar [31,32]. It is the most
advance functional of DFT and more considerably used now a days
as an excellent agreement is found between experimental and DFT
study at this level However, an infinitesimal difference is always
foreseen for the reason that the experimental data correlate to the
structures in solid phase, whereas DFT calculations are coupled to
the gaseous phase. The absence of imaginary frequencies showed
that the structures are successfully optimized. Furthermore, fron-
tier molecular orbital analysis (FMOs) and nonlinear optical anal-
ysis (NLO) investigations were performed at the aforesaid level
by using the optimized geometries of the title compounds. More-
over, the NBO study was performed with the help of NBO3.1 pack-
age [33] at ωB97XD/6-311+G(d,p) level [34] as non-covalent in-
teraction in a crystal can magnificently be analyzed at this level
[35].The results were interpreted by utilizing GaussView 5.0 [36],
GaussSum [37], Avogadro [38] and ChemCraft [39] software.
˚
served as 1.34, 1.514, 1.498 and 1.515 A, whereas simulated bond
˚
lengths yielded 1.344, 1.507, 1.493 and 1.515 A, respectively. Fur-
thermore, for MBCP the bond lengths in C2-C3, C3-C4 and C7-C8
˚
are seen as 1.506, 1.532 and 1.469 A (XRD), whereas the DFT exam-
ined data of aforesaid bond lengths are found as 1.515, 1.524 and
˚
1.456 A, respectively. From above discussion it may be concluded
that simulated and experimental bond lengths are found in well
correlation.
In MBMHP, the bond angles such as C7-C6-C11=118.4°, C6-C7-
C8=121°, C6-C11-C10=120.3° and C9-C10-C11= 121° are explored
by XRD, whereas the simulated explored values of aforesaid bond
angles are found as 118.7, 120.5, 120.5 and 120.7° respectively. Sim-
ilarly, the bond angles: C7-O1-C12= 114.5°, O1-C7-C8= 119.7°, O2-
C8-C7= 115.8° and O3-C16-C17= 121.4° are observed by SC-XRD,
whereas the investigated values of aforesaid bond angles are seen
as 115.2, 120.2, 116 and 121.8°, respectively. Furthermore, for MABP
the bond angles like C4-C3-C7= 108.6°, C3-C7-C8= 120.2°, C6-C7-
C8=131.1°, C8-C9-C14= 124.2°and C11-C12-C13= 117.1° are found
by XRD, nevertheless the theoretical values of bond angles are de-
termined as 107.4, 119.7, 131.5, 124.6 and 117.2°, respectively. The
bond angles: O1-C3-C4= 125°, O1-C3-C7= 126.3°, C12-N2-C15=
120.9°, N2-C12-C11= 121.6° and C15-N2-C16= 118.4° are found
(XRD) whereas the computed values of aforesaid bond angles are
found as 125.7, 126.9, 119.9, 121.4 and 119.3°, respectively. (Tables
S1–S2)
Molecular geometric parameters
In MBHP, the bond angle values in C6-C5-C10=118.5°, C5-
C6-C7=120.8°, C5-C10-C9=120.6°, C7-C8-C9=119.9° and C15-C14-
C18=117.8° are found by (XRD), whereas the aforementioned
bond angles are observed as 118.7, 120.6, 120.5, 119.9 and 118.1°
(DFT) respectively. Similarly, the values of bond angles in C6-O1-
C11=113.3°, O1-C6-C5=118.5°, C7-O2-C12=117.5°, O2-C7-C8=124.6°
and C15-O3-C16=109.9° were observed by SC-XRD, while the com-
puted values are determined as 115.1, 119.2, 118.2, 124.6 and
111.3°, respectively. Similarly, for MBCP values of bond angles in
C2-C6-C7=120.3°, C4-C5-C6=104°, C9-C8-C13=118.9°and C10-C11-
C12=119.3° are observed by (XRD), whereas theoretical values of
bond angles are found to be 119.9, 103.8, 119 and 119.7°, respec-
tively. Furthermore, the bond angles in O1-C2-C3=126.2° and O1-
C2-C6=125.3° as observed by (XRD). On the other hand the cal-
culated values of aforesaid bond angles are found as 126.2 and
126.5°, respectively. (Tables S3– S4) The above discussion describes
that a tremendous understanding is found in experimental and DFT
findings.
Systematic computational optimization of MBMHP, MABP,
MBHP and MBCP is done to measure structural parameters. The re-
sults of DFT and SC-XRD are found to be in a good agreement (Ta-
bles S1–S4), except some variations which might be due to the DFT
computations being performed in gaseous phase and XRD done in
solid phase. Overall, the variation in bond lengths are found within
the range of 0.029 0.008, 0.013 0.007, 0.026 0.002, and 0.013
˚
0.009 A while in bond angles are in 1.4 ° 1.2°, 1.2 ° 0.9°, 1.4
°
1.8° and 1.2 °
spectively.
In MBMHP and MABP bond lengths for C-C in benzene rings
1.2° in MBMHP, MABP, MBHP and MBCP re-
˚
˚
are obtained within the range of 1.381-1.46 A, 1.379-1.413 A (XRD),
˚
while simulated values are examined to be 1.389-1.45 A, 1.379-
˚
1.408 A respectively. Similarly, the C-C bond lengths in benzene
˚
rings for MBHP and MBCP are obtained as 1.377-1.404 A, 1.387-
˚
˚
˚
1.411 A through XRD and 1.379-1.403 A, 1.39-1.411 A through DFT,
respectively as shown in Tables S1–S4. In MBMHP bond lengths
for O1-C7, O2-C8, O3-C16 and O4-C19 are obtained as 1.38, 1.364,
˚
1.224 and 1.427 A (XRD), while simulated values are explored to be
˚
1.359, 1.353, 1.217 and 1.407 A, respectively. (Table S1). For MABP,
Natural bond orbital (NBO) analysis
bond lengths for O1-C3, N2-C12, N2-C15 and N2-C16 are detected
˚
to be 1.223, 1.367, 1.448 and 1.447 A (SC-XRD), whereas the calcu-
NBO exploration has been viewed as one of the most relevant
method that plays a crucial role in the study of intra and inter-
molecular H-bonding [40,41]. Besides, it exhibited an impressive
understanding of the interaction and charge transfer processes of
molecules. The second order stabilization energy (E(2)) determin-
lated values of aforesaid bond lengths are measured as 1.21, 1.374,
˚
1.444 and 1.443 A, respectively as shown in Table S2. Furthermore,
for MBMHP the bond lengths in C14-C15, C15-C19, C16-C17 and
˚
C17-C18 are seen as 1.342, 1.5, 1.495 and 1.503 A (XRD), whereas
6

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
ing the strength of interaction within donor and acceptor, filled or-
bitals and the empty orbitals can be clarified by the NBO investi-
gations [42,43]. E(2) can be described by the Eq. (1),
LP(2)-O1→σ∗(C2-C3), LP(2)-O1→σ∗(C2-C12), LP(1)-O1→σ∗(C2-
C12) and LP(1)-O1→σ∗(C2-C3) yielding stabilization energies
as 27.07, 25.13, 2.55 and 1.88 kcal/mol, respectively. The tran-
sition from σ→π∗ is observed as σ(C46-H49)→π∗(C23-C25),
σ(C4-H5)→π∗(O1-C3), σ(C31-H33)→π∗(O4-C34) and σ(C9-
H10)→π∗(C12-C13) with stabilization energies; 5822.67, 9.36, 2.35
and 6.58 kcal/mol for MBMHP, MABP, MBHP and MBCP, respec-
tively, as shown in Tables S5–S8. From above analysis it could be
concluded that the stronger intra-molecular hyper-conjugation are
responsible for the stability of the title compounds.
ꢀ ꢁ
2
F
ij
2
( )
E
= q
(1)
i εj − εi
Where qi is donor orbital occupancy, εj and εi are diagonal el-
ements and F is off-diagonal NBO fock matrix element [44].
(i, j)
Some prominent π→π∗ transitions are seen like:
π(C39-C41)→π∗(C36-C37),
π(C19-C21)→π∗(C16-C17),
π(C7-
C8)→π∗(C10-C12), π(C22-C24)→π∗(C18-C20) having higher
stabilization energies as 40.90, 47.13, 34.91 and 37.82 kcal/mol
in MBMHP, MABP, MBHP and MBCP respectively. Furthermore,
σ→σ∗ transitions are found as σ(C9-H10)→σ∗(O2-C19), σ(C19-
H20) →σ∗(N2-C26), σ(C28-H29)→σ∗(C25-H26), and σ(C12-
C13)→σ∗(C6-C9), showing lower stabilization energies: 0.5, 0.5,
0.51, 0.5 kcal/mol, respectively, for MBMHP, MABP, MBHP and
MBCP as shown in Tables S5–S8.
Natural population analysis (NPA)
Electrical potentials, NMR chemical shifts, dipole moments
and electromagnetic spectra were favorable parameters to reveal
molecular properties which correlate reasonably to atomic charges
in the organic compounds [45]. The scientific reports related to
structural characteristics of chemical compounds abundantly rely
on atomic charges concept [46]. The characterization of atomic
charges could be helpful to understand the non-covalent interac-
tion pattern in any chemical structure [47].
Furthermore, for MBMHP, the π→π∗ hyper-conjugative interac-
tions are found like π(C42-C44)→π∗(C39-C41), π(C8-C9)→π∗(C6-
C7) and π(C42-C44)→π∗(C36-C37) with stabilization energies:
36.95, 29.86 and 26.83 kcal/mol, respectively. The conjugative in-
teractions (σ→σ∗) are determined as σ(C46-H49)→σ∗(O2-C19),
σ(O5-C41)→σ∗(C15-H16), and σ(C46-H49)→σ∗(C25-C26), with
stabilization energies as 147.14, 103.38, and 77.72, kcal/mol, re-
spectively. Similarly, for MABP, the π→π∗ hyper-conjugative
interactions are found like π(C16-C17)→π∗(C22-C24), π(C22-
C24)→π∗(C19-C21) and π(C13-C14)→π∗(O1-C3) with stabilization
energies: 38.44, 33.68 and 30.76 kcal/mol, respectively. The con-
jugative interactions (σ→σ∗) are noticed as σ(C30-H31)→σ∗(C30-
H33), σ(N2-C30)→σ∗(C30-H33) and σ(C14-H15)→σ∗(C10-C13),
with stabilization energies as 33.86, 19.79, and 8.69, kcal/mol, re-
spectively. For MBMHP, the LP→σ∗ interactions are recognized
as LP(1)-O3→σ∗(C15-H16), LP(1)-O3→σ∗(C46-H47) and LP(1)-O2
→σ∗(C25-C26) with stabilization energies: 1214.38, 146.7 and
28.04 kcal/mol, respectively as shown in Tables S5-S8. Similarly,
the LP→π∗ transitions have been seen as LP(1)-O3→π∗(C23-C25),
LP(2)-O5→π∗(C39-C41) with stabilization energies: 330.33 and
42.04 kcal/mol, respectively. Similarly, for MABP, the LP→σ∗ inter-
actions are recognized as LP(2)-O1→σ∗(C3-C4), LP(2)-O1→σ∗(C3-
C13) and LP(1)(N2)→σ∗(C26-H28), with stabilization energies:
27.21, 24.49 and 7.88 kcal/mol, respectively as shown in Ta-
bles S5–S8. Moreover, the LP→π∗ transitions are seen as
LP(1)(N2)→π∗(C19-C21) with stabilization energy; 60.6 kcal/mol.
In MBHP the π→π∗ transitions are observed as π(C5-
Frontier molecular orbital analysis
Frontier molecular orbital energies and their band gaps are
contemplated as very viable parameters in quantum chemistry
[48,49].HOMO and LUMO energies specify nucleophilic and elec-
trophilic characters, respectively [50].Moreover, FMOs play a vital
role in discovering optical and electrical properties, chemical reac-
tivity, and intermolecular interactions for various compounds. Lit-
erature shows that a greater HOMO-LUMO gap is associated with
higher stability and lower reactivity of compounds [51].HOMO-
LUMO low energy gap accounts for a lower stability and higher re-
activity of compounds with remarkable NLO properties. The study
of FMOs was carried out and results are shown in Table S9.
The energy gap for the title molecules namely MBMHP, MABP,
MBHP and MBCP are 4.144, 4.127, 4.768, and 4.762 eV, respec-
tively. The overall diminishing order of the band gap is obtained
to be MBHP>MBCP>MBMHP>MABP, showing that the energy
gap of the MABP is less than all the other crystals showing
greater reactivity and more efficient intra-molecular charge trans-
fer (ICT), whereas the MBHP shows less reactivity and hence
is more stable. The FMO contour surfaces are showing the pat-
tern of the density circulation of electrons and the transmis-
sion of charge in HOMO and LUMO. For MBMHP, the HOMO
is populated on the (E)-3-(4-methoxybenzylidene) tetrahydro-4H-
pyran-4-one moiety and small effect exist on some other carbon
atoms while, the LUMO is occupied on the ((E)-2-benzylidene)-5-
((E)-4-hydroxybenzylidene)tetrahydro-4H-pyran-4-one moiety but
small effect on both benzene carbon atoms (Fig. 4). While for
MABP, the HOMO has been populated on the entire molecule
except some carbon atoms of cyclopentane group whereas; the
LUMO is also populated on the entire molecule except both
methyl groups and some carbon atoms of benzene ring (Fig. 4).
Nevertheless, for MBHP the HOMO is populated on the (Z)-3-
(2,3-methoxybenzylidene) moiety and small effect exist on some
carbons and oxygen atom of tetrahydro-4H-pyran-4-one moiety
whereas, the LUMO is located on the (Z)-3-benzylidenetetrahydro-
4H-pyran-4one moiety except on some carbons and oxygen atom
of tetrahydro-4H-pyran-4-one moiety (Fig. 4).
C6)→π∗(C10-C12),
π(C10-C12)→π∗(C7-C8)
and
π(C22-
C24)→π∗(O4-C34) with stabilization energies: 30.56, 29.83 and
28.12 kcal/mol, respectively as shown in Tables S5–S8. Similarly,
for MBCP, the π→π∗ hyper-conjugative interactions are found like
π(C18-C20)→π∗(C15-C16), π(C15-C16)→π∗(C18-C20) and π(C15-
C16)→π∗(C22-C24) with stabilization energies: 37.45, 33.62 and
33.36 kcal/mol, respectively. The σ→σ∗ transitions for MBHP are
determined as σ(O4-C34)→σ∗(C31-H33), σ(C24-C34)→σ∗(C28-
H30) and σ(C31-H32)→σ∗(O4-C34) with stabilization energies
as 127.59, 18.48 and 10.41 kcal/mol, respectively. Furthermore for
MBCP some important σ→σ∗ transitions like σ(C13-H14)→σ∗(C9-
C12), σ(C25-H26)→σ∗(C15-C24) and σ(C13-C15)→σ∗(C12-C13)
are seen with stabilization energies as 9.86, 5.33 and 4.97kcal/mol
respectively as shown in Tables S5–S8. For MBHP, the LP→σ∗
hyper-conjugative interactions like LP(1)-O4→σ∗(C31-H33), LP(2)-
O4→σ∗(C28-H30) and LP(2)-O4→σ∗(C31-C34) with stabilization
energies: 44.52, 30.69 and 19.21 kcal/mol. While the LP→π∗ tran-
sitions has been seen as LP(1)-O1→π∗(C5-C6) with stabilization
energy 9.16 kcal/mol as shown in Tables S5–S8. For MBCP some
significant LP-σ∗ conjugative interactions are also observed as
For MBCP, the HOMO is located on the (E)-2-(2-
methylbenzylidene)cyclopentan-1-one except some carbon atoms
of cyclopentane ring and small contribution is made by the methyl
group whereas the LUMO is also located on the entire molecule
except some carbon atoms of cyclopentane ring and methyl group
(Fig. 4).
7

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
Fig. 4. Frontier molecular orbitals of title compounds.
The energy gaps between HOMO and LUMO help to derive
parameters used to describe stability and reactivity by evaluat-
ing global reactivity parameters [52]. The values of these param-
eters, including Ionization potential (IP) [53], electron affinity (EA),
global electrophilicity (ω) [54, 55] global hardness (η)[56,57], elec-
tronegativity (X)[58],chemical potential (μ)[59], and global softness
[60] (σ) are determined by the EqS. (2)–(3), and their results are
evaluated in Table S10.
For global softness (σ) following equation was used.
1
σ =
(7)
2η
By Parr et al. the calculation of electrophilicity index (ω) is per-
formed using Eq. (8) [62].
μ2
2η
ω =
(8)
The ability to lose or gain electrons of the title compounds is
categorized by their ionization potential and the electron affinity
values, respectively. The compound MBCP has the maximum IP
value of 6.742 eV, while MABP has the minimum value of 5.746 eV
(Table S10) The MBMHP crystal possessed highest EA value; 2.181
eV while MABP contained least EA value; 1.619 eV. Moreover, the
IP values of all the four compounds are analyzed lower in extent
than EA values which showed that the studied molecules contained
excellent electron-donating ability. In addition, chemical potential
values (μ) have been taken into account for the understanding of
the stability and reactivity of any molecule, which indicates that
compound with lesser chemical potential is favored as less steady
and reactive compound or vice versa. In investigated compounds,
the chemical potential values decreasing order given as, -4.361 >
-4.336 > -4.253 > -3.6825 which indicates that MBCP is highly re-
active compound (Table S10)
IP = −EHOMO
(2)
EA = −ELUMO
(3)
Where IP = ionization potential (eV), EA = electron affinity (eV).
Koopmans’s theorem [61] has been used to calculated the the
electronegativity (X), the chemical potential (μ) and the chemical
hardness by using Eqs. (4)–(7).
IP + EA
E
LUMO + EHOMO
[
]
[
]
X =
η =
μ =
= −
= −
(4)
(5)
(6)
2
2
IP − EA
E
[
LUMO − EHOMO
[
]
]
2
2
EHOMO + ELUMO
2
8

A. Ali, M. Khalid, Z.U. Din et al.
Journal of Molecular Structure 1241 (2021) 130685
Table 3
all the studied crystals are less reactive and more stable as sug-
gested by NBO and SC-XRD investigations. NLO study described
that the crystal MBMHP have the higher value of linear polarizabil-
ity <α> and third order polarizability<γ > 216.36 and 1.06 × 104
a.u respectively, among all the synthesized crystals. The simulated
structural parameters of aforesaid crystals and experimental X-ray
crystallographic determinations are established in a close harmony.
All the four compounds disclosed remarkable NLO responses which
can be notable for their utilization in advanced applications.
Computated polarizabilities and hyper-
polarizability of title compounds.
Compounds
< α >
<γ>
MBMHP
MABP
MBHP
MBCP
379.41
281.60
216.36
218.37
8.96×105
5.70×105
1.06×104
1.64×105
Nonlinear optical (NLO) properties
Declaration of Competing Interest
The investigation of compounds with extraordinary NLO proper-
ties is a vast area of exploration because of their flexible use in op-
toelectronics and telecommunications [63,64]. The concepts of po-
larizability <α> and second hyper polarizability <γ > in NLO stud-
ies are used to clarify the structure-property relationships with the
assistance of quantum chemical calculations. Herein, the <α> and
<γ > of MBMHP, MABP, MBHP and MBCP are calculated at M06
level and results are tabulated in Tables S11,S12 while some im-
portant results are shown in Table 3.
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgment
M. Imran express appreciation to the Deanship of Scientific Re-
search at King Khalid University Saudi Arabia for funding through
research groups program under grant number R.G.P. 2/28/42.
Table 3 illustrated that the least value for linear polarizabil-
ity <α> and second order hyperpolarizability<γ > is analyzed
in MBHP to be 216.36 and 1.06×104 a.u respectively, among all
the investigated molecules. This might be due that the methoxy
group that along with the positive resonate effect (+R) also have
negative inductive (-I) effect as by σ-bonds, it can withdraw the
electron and lower the charge transfer, moreover the presence of
tetrahydro-2H-pyran ring which is not planar ring also decreased
the conjugation hence, a powerful push pull architecture does cre-
ated so exhibit lower NLO responses. These values increase to
218.37 and 1.64×105 a.u, in MBCP than enlarge to 281.60 and
5.70×105 a.u in MABP for <α> and <γ > respectively, as the con-
jugation extended. However, the highest value of linear polarizabil-
ity and second order hyperpolarizability is examined in MBMHP
which is 379.41 and 8.960×105 a.u respectively, among all entitled
compounds. This might be due to that in MBMHP the no of atom
increased as the polarizability naturally grows with the number of
atoms in the molecules. Additionally, the extended conjugation and
D-π-A-π-D type structure created a strong push pull mechanism
in this molecule, hence shows excellent NLO results. The overall
decreasing order of <α> and <γ > is: MBMHP > MABP > MBCP
> MBHP. This urea comparative study suggested that all molecules
under investigation are suitable NLO candidates.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.130685.
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