Synthesis, spectroscopic, structural elucidation, NLO characteristic and Hirshfeld surface analysis of (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy)phenyl)prop-2-en-1-one: A dual approach of experimental and DFT calculations

Article abstract of DOI:10.1016/j.molstruc.2019.05.046

Single crystal of (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy)phenyl)prop-2-en-1-one (4EPC)was grown in acetonitrile via slow evaporation solution technique. The molecular structure of 4EPC was then confirmed by single crystal X-ray diffraction analysis and the

Full text of DOI:10.1016/j.molstruc.2019.05.046

Accepted Manuscript
Synthesis, spectroscopic, structural elucidation, NLO characteristic and Hirshfeld
surface analysis of (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy) phenyl)prop-2-en-1-one: A
dual approach of experimental and DFT calculations
Adibah Izzati Daud, Wan M. Khairul, Elccey Augustine, Suhana Arshad, Ibrahim
Abdul Razak
PII:
S0022-2860(19)30610-6
DOI:
https://doi.org/10.1016/j.molstruc.2019.05.046
MOLSTR 26553
Reference:
To appear in: Journal of Molecular Structure
Received Date: 22 January 2019
Revised Date: 12 May 2019
Accepted Date: 13 May 2019
Please cite this article as: A.I. Daud, W.M. Khairul, E. Augustine, S. Arshad, I.A. Razak, Synthesis,
spectroscopic, structural elucidation, NLO characteristic and Hirshfeld surface analysis of (E)-1-(4-
ethylphenyl)-3-(4-(heptyloxy) phenyl)prop-2-en-1-one: A dual approach of experimental and DFT
calculations, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/j.molstruc.2019.05.046.
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Graphical Abstract:
(a) The molecular structure of 4EPC with 50% ellipsoids probability (b) The twisted ethyl group from the planarity of the compound (c) The crystal
packing of 4EPC. Dashed lines represent the intermolecular C—H···O hydrogen bonds.

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Synthesis, spectroscopic, structural elucidation, NLO characteristic and Hirshfeld surface
analysis of (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy) phenyl)prop-2-en-1-one : A dual approach of
experimental and DFT calculations
Adibah Izzati Daud1,2, Wan M. Khairul1,*, Elccey Augustine1, Suhana Arshad3, Ibrahim Abdul Razak3
1School of Fundamental Science, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu,
Malaysia
2Faculty of Engineering Technology, Universiti Malaysia Perlis (UniMAP), Level 1, Blok S2, Kampus
UniCITI Alam, Sungai Chuchuh, 02100 Padang Besar, Perlis, Malaysia
3School of Physics, Universiti Sains Malaysia, 11800 USM Penang, Malaysia
*Corresponding author: wmkhairul@umt.edu.my
ABSTRACT
Single crystal of (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy)phenyl)prop-2-en-1-one (4EPC) was grown in
acetonitrile via slow evaporation solution technique. The molecular structure of 4EPC was then
confirmed by single crystal X-ray diffraction analysis and the crystal exhibited monoclinic with
centrosymmetric space group of C2/c. The synthesised molecule of 4EPC was fully characterized
using spectroscopic techniques by Fourier-Transform infrared (FT-IR) spectroscopy, Nuclear
Magnetic Resonance (1H and 13C NMR), thermal stability analysis via Thermogravimetric analysis
(TGA) and electronic transitions through UV-visible analysis. In addition, the theoretical
investigations on its electronic properties via UV-vis analysis of 4EPC was calculated using time-
dependent TD-DFT B3LYP/6-31G (d, p) level of theory. As predicted, the experimental results were
complimentary to the theoretical findings. The Hirshfeld surface analysis contributes to the study in
the aspect of the nature of intermolecular interactions as well as fingerprint plots which gave the
information on the percentage contribution from each individual contact. Molecular electrostatic
potential (MEP) analysis provides an initial information on the charge concentration throughout the
molecule 4EPC which designated the possible interaction site to occur. Moreover, the nonlinear
optical (NLO) properties of 4EPC was calculated to gain further understanding on the possibility of
developing this compound as NLO material. Calculated NLO results found that the polarizability and
1st order hyperpolarizability of 4EPC is -2.13 x 10-23 esu and 1.27 x 10-30 esu respectively which is
greater than the value of 1st order hyperpolarizability of urea (β = 0.372 x 10-30 esu). The high values
obtained from the calculated NLO were due to the dipole, molecular alignment and also from the non-
covalent interaction within crystal of 4EPC which can be developed further as potential organic light
emitting diode application.
Keywords: alkoxy-chalcone; DFT; NLO; spectroscopic; crystal structure
1. Introduction
Chalcones are from flavonoid family that consist of two aromatic rings with different array of
substitutions linked by α, β-unsaturated carbonyl moiety. These class of derivatives exhibit donor-π-
donor molecular system (D-π-D) which can enhance their functionality in various fields of interest. It

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possesses conjugated double bonds and a delocalized π-electron system on both aromatic rings [1-5].
Various different methods have been applied in order to synthesis chalcone derivatives, however, most
reported chalcones have been synthesized by simple and inexpensive method via condensation as a
product between aromatic aldehydes and aromatic ketones in the presence of strong base catalyst
known as Claisen-Schmidt reaction [6-8]. Chalcones are bichromophoric molecules separated by
ketovinylenic group (CO-CH=CH-) and π-conjugated bridges and they exhibit numerous chemical and
physical properties, such as optical and fluorescence properties [9-11], electrical properties [12] and
provide broad spectrum in biological activities [13-15]. Due to their excellent performances, chalcones
have attracted much attention for past decades due to their potential technological application in the
fields of photochemical sensors [16, 17], fluorescent probes [18], optical nonlinearities [19, 20] and as
conductive organic solar cells [21, 22]. The main characteristics of functionalized chalcone derivatives
are they adopt molecular flexibility, having strong donor-acceptor intermolecular interaction, rich in
the delocalized π-electrons system and attaining low dielectric constant. All these unique
characteristics show that chalcone derivatives hold high potential in photovoltaic devices applications.
In fact, the distinctive characteristics of low-lying π-π* transition occurs from the aromatic ring
to the alkene chain can permit the variation of the intense transition by adding suitable substituents to
the aromatic ring. Electronic profile of chalcone derivatives was carried out mostly at their singlet
states of π-π* transition to determine their absorption spectra of substituted chalcones. Conjugation
between substituted phenyl ring with alkene group gave a significant effect in the absorption
maximum with a greater extent compared to the thiourea moiety which involves conjugation between
carbonyl and aromatic ring [23]. Both systems, D-π-A and D-π-D can lower the energy level of Sπ-π*
state which is great significant in the development of molecular electronics. These promising
characteristics of chalcones derivatives have attracted researchers’ attention to design new classes of
chalcones featuring D-π-D which should provide further understanding on structural property
relationship related to non-linear optical properties. In development of new active materials in the
interest of molecular electronic application such as organic light emitting diode (OLED), optical
switching, photovoltaic organic solar cells and optical rectification, nonlinear optical (NLO) materials

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with large and fast NLO response and their hyperpolarizabilities are crucial factors for extensive
research in molecular electronic application. A large number of advanced materials have been
investigated for NLO properties, in which organic materials are attractive due to their variety, high
nonlinearity, ultra-fast response and the flexibility they offer to change the optical properties through
structural modification. Nowadays, great attention has been given to organic NLO materials because
of their first (β) and second (γ) hyperpolarizabilities and high laser damage resistance compared to
inorganic materials [24, 25]. A versatile synthetic organic chemistry can be applied to prepare, modify
and optimize targeted molecular structure to suit the need and requirement of molecular electronics
with a desired structure to maximize their utility in advanced industrial needs. Hence, organic
materials can simply be known as the “materials for future”.
In the view of fundamental aspect, the structure of organic materials exhibiting NLO
characteristics is based on π-bond system in which the overlapping of π-orbital increases the
delocalization of electronic charge distribution that gave high mobility of the electron density which in
turn exhibit enhanced optical nonlinearity related to the level of second-harmonic-generation (SHG)
[26, 27] that inherently depends upon its structural attributes. Chalcone derivatives have received
much consideration because of their good crystallizability and high optical nonlinearity due to its
extended conjugation length. The hydrogen bonding interaction and π-π interaction are the most
important factors of all intermolecular interactions due to their strength and directionality [28, 29],
where the strong hydrogen bonds are widely used to build multidimensional molecular structures. The
presence of strong intermolecular interactions such as hydrogen bonds can enhance level of charge
transfer between molecules, owing to their electrostatic and directed nature, thereby enhancing the
SHG response.
The theoretical calculations via quantum mechanical fluctuations techniques based on density
functional theory (DFT) can support and compare with our experimental values. In recent years, our
group have been involved in synthesis, characterization and computational chemistry studies of
various organic molecules in vast applications [30-32]. The outcomes have proven to be highly
successful in describing the structural properties and the simplest as well as the easiest methods to

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understand the electronic characteristics of any molecular system of interest that having specific
functionality. In fact, to identify the presence of functional groups substitution, structural behaviour,
molecular interaction and absorption maxima properties, spectroscopic studies have emerged as
excellent tools among materials characterisation techniques. The obtained experimental data were
counterchecked by DFT calculations and in addition to this, the X-ray single crystal data sets were
also compared. From DFT calculation, NLO properties of the synthesized molecule (4EPC) were
described along with a crystal engineering of molecule to attain a centrosymmetric network.
With respect to molecular electronic development, chalcones have achieved much
consideration because of their excellent NLO properties, exhibit higher power conversion energy,
chemical inertness, high damage threshold and phase matching properties. Moreover, this molecular
framework is also known for their excellent blue light transmittance, large NLO coefficients and short
cut-off wavelength of transmission contributed mainly due to the presence of conjugated double
bonds. Due to the effect from conjugation, electrons remain delocalized within the molecule and
influence the performance on electron polarizability. In organic molecules, the NLO properties like
molecular hyperpolarizability can be further enhanced by substituting different functional groups of
both sides of chalcone which promote highly polarizable conjugated bridge. Considering both aspects
of experimental and theoretical factors, the synthesis of new organic materials with enhanced NLO
property (second and third order NLO) is a continuing field of research. In this direction we are
reporting the synthesis and characterization of new chalcone derivatives, (E)-1-(4-ethylphenyl)-3-(4-
(heptyloxy)phenyl)prop-2-en-1-one (4EPC) along with its mechanical and thermal properties.
2. Materials and methods
All chemicals, solvents and reagents used in this study namely 4-hydroxyacetophenone, 1-
bromoheptane, 4-ethylbenzaldehyde, potassium carbonate, sodium hydroxide, hydrochloric acid,
dimethylformamide, ethanol, hexane and ethyl acetate were purchased from well-known local and
international suppliers as analytical reagents such as Merck, Across Organic, HmbG®, Sigma Aldrich
and R&M Chemicals and used as received without further purifications. Reactions involved were

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carried out under an ambient atmosphere without any precaution steps to omit humidity interferences
during synthetic work-up.
2.1 Characterisation and instrumentation
1H and 13C Nuclear Magnetic Resonance (NMR) spectra were recorded in CDCl3 using Bruker
Avance III 400 Spectrometer in the range δH 0-15 ppm and δC 0-200 ppm accordingly with reference
to the trimethylsilane (TMS) as internal standard. Fourier-Transform Infrared (FT-IR) spectra were
recorded via Perkin Elmer 100 FT-IR spectroscopy using potassium bromide (KBr) pellets within
spectral range 4000 – 450 cm-1. For electronic transition analysis, UV-Visible study was performed by
using Shimadzu UV-Vis in 1 cm3 cuvette. Afterwards, thermogravimetric analysis was carried out
using Perkin-Elmer TGA analyzer from 30 to 900°C at a heating rate 10° C/min under nitrogen flow
consistently.
2.2 Single Crystal X-Ray Diffraction Analysis
Single crystal suitable for X-ray analysis was performed on APEXII Duo CCD area-detector
using MoKα radiation (λ = 0.71073 Å). Data collection was performed using the APEX2 software
[33], whereas the cell refinement and data reduction were performed using the SAINT software [33].
The crystal structure was solved by direct method using the program SHELXTL [34] and refined by
full-matrix least squares technique on F2 using anisotropic displacement parameters by
SHELXTL2014 [35]. Absorption correction was applied to the final crystal data using the SADABS
software [33]. All geometrical calculations were carried out using the program PLATON [36]. The
molecular graphics were drawn using SHELXTL [35] and Mercury [37] programs. The non-hydrogen
atoms were refined anisotropically. All the hydrogen atoms were positioned geometrically (C—H =
0.93, 0.96 or 0.97 Å) and refined using riding model Uiso(H) = 1.2 Ueq(C). The ethyl substituent group
attached to one of the terminal benzene rings is disordered over two sites with refined occupancies of
0.731 (14): 0.269 (14). In the final refinement, one outlier (2 0 0) was omitted. A summary of crystal
data and relevant refinement parameters of the title compound is given in Table 1.

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Table 1 Crystallographic refinement data.
Refinement Parameters
CCDC deposition numbers
Molecular formula
Molecular weight
Crystal system
Space group
a (Å)
B (Å)
C (Å)
α (°)
CCDC 1867813
C24H30O2
350.48
Monoclinic
C2/c
46.746 (7)
8.3426 (12)
10.8945 (15)
90.00
92.993 (5)
β
γ
(°)
(°)
90.00
4242.9 (10)
8
V (Å3)
Z
Dcalc (Mg m−3)
Crystal Dimensions (mm)
ꢀ (mm−1)
1.097
0.46 x 0.45 x 0.25
0.07
Radiation λ (Å)
F(000)
0.71073
1520
Tmin/Tmax
Reflections measured
Ranges/indices (h, k, l)
0.8561/ 0.9534
55021
h = −60→60
k = −10→10
l = −14→14
1.8 - 27.7
4917
θ limit (°)
Unique reflections
Observed reflections
(I > 2σ(I))
1846
Parameters/Restraint
R1 [a], wR2 [b] [I ≥ 2σ(I)]
Goodness of fit [c] on F2
Rint
258/1
0.060/0.226
0.99
0.075
0.15 and − 0.10
Largest diff. peak and hole, e/Å-3
w = 1/[σ2(Fo ) + (0.0943P)2 + 0.8318P], where P = (Fo2 + 2Fc2)/3; [a] R = Σ||Fo| – |Fc||/Σ|Fo|, [b] wR= {wΣ(|Fo| –
|Fc|)2/Σw|Fo|2}}1/2, [c] GOF = {Σw(|Fo| – |Fc|)2/(n–p)}1/2, where n is the number of reflections and p the total
number of parameters refined.
2
2.3 Theoretical calculations: Density functional theory (DFT)
All the involved theoretical calculations were executed by Gaussian 09 program package [38]
featuring density functional theory (DFT). The initials geometry for 4EPC was retrieved from the
crystal structure. Optimization of 4EPC was carried out without using symmetry restrictions at the
theoretical level of DFT B3LYP/6-31G (d, p) basic set known to be as a practical strategy to compute

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the structure of 4EPC. FMOs and MEP properties were also executed at B3LYP/6-31G (d, p) level of
theory. Theoretical electronic transition for 4EPC was computed employing time-dependent density
functional theory (TD-DFT) with B3LYP level and 6-31G (d, p) basis set, while the input file and data
interpretation were organized and utilized via GaussView 5.0 [39].
3. Experimental work
3.1 Synthesis of 4-heptyloxyacetophenone
Reaction work-up details with respect to the synthesis of precursor 4-heptyloxyacetophenone
followed as stated in the previous literature [40]. 4-hydroxyacetophenone (0.14 g, 1 mmol), 1-
bromoheptane (0.18 g, 1 mmol) and potassium carbonate (0.40 g, 3 mmol) were charged into 2-neck
round bottom flask with 65 mL of dimethylformamide (DMF). The reaction mixture was put at reflux
with continuous stirring for 24 hours. Once the reaction was adjudged completion using Thin Layer
Chromatography (TLC) hexane: ethylacetate: 3:2, the reaction mixture was cooled to room
temperature, then poured over to 50 mL water and extracted with hexane (50 mL x 2). The organic
fractions collected was separated and washed with 1M aqueous NaOH (25 mL) and then with aqueous
1M HCl (25 mL). Organic layer obtained was dried over Na2SO4 and continually dried under reduced
pressure to yield 4-heptyloxyacetophenone. Scheme 1 illustrates the synthetic pathway to synthesis 4-
hydroxyacetophenone.
Scheme 1. Synthesis of 4-hydroxyacetophenone.
3.2 Synthesis of (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy) phenyl) prop-2-en-1-one (4EPC)
4EPC was synthesised via Claisen-Schmidt condensation reaction between substituted ketone
and aldehyde derivatives. The analytical grade starting material of p-ethylbenzaldehyde (0.13 g, 1
mmol) and the synthesised 4-hydroxyacetophenone (1) (0.23 g, 1 mmol) were dissolved in ethanol (40
mL) in the presence of catalytic amount of 15% NaOH solution (approximately 15 mL) was added

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drop-wise to the solution with vigorous stirring and put at reflux for ca. 3-4 hours. Once the reaction
was adjudged completion via Thin Layer Chromatography (TLC) hexane: ethylacetate: 3:2, the
reaction mixture was cooled to room temperature and then poured into beaker containing some ice
cubes. The resulting precipitate were then filtered, washed with distilled water and dried over silica
gel. The obtained crude product was subjected to recrystallisation from methanol to obtain the
corresponding alkoxy-chalcone derivative (4EPC) as in Scheme 2.
4EPC
Scheme 2. Synthesis of 4EPC.
4. Results and discussion
4.1 Spectroscopic studies
4.1.1 NMR analysis
The synthesised molecule (4EPC) was obtained via simple Claisen-Schmidt method in good
yield. To elucidate the synthesis of our targeted molecule, 4EPC was characterized via following
1
13
spectroscopic techniques. H and C NMR spectra were recorded operating at 400 MHz and 100.6
1
MHz for H and 13C respectively using standard parameters in CDCl3 solvent and trimethylsilane
1
(TMS) was used as an internal standard. Both H and 13C NMR spectra of 4EPC are shown in
1
Supplementary material 1. H NMR spectrum of 4EPC revealed triplet resonances at shielding
position of δH 0.828 ppm corresponded to the methyl (aliphatic) proton. Whilst, for methyl substitution
at aromatic position, the triplet resonances can be observed at δH 1.187 ppm. Multiplet overlapping
resonances at region δH 1.220 – 1.762 ppm were attributed to the CH2 (aliphatic) group. However,
CH2O was positioned at the deshielded region at δH 3.965 ppm due to the electronegative effect from
oxygen atom nearby. Additionally, there were aromatic phenyls protons appeared at δH 6.884 – 7.996
ppm corresponding to total of eight protons. The two doublets at δH 7.464 ppm and δH 7.702 ppm with

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characteristic coupling constants (J) of 15.6 Hz for both doublets are corresponded to α, β-unsaturated
protons (CH=CH) of aliphatic groups [41, 42]. The higher value of coupling constant proved the
existence of E-geometry of double bond in chalcones and also confirmed the purity of the synthesized
4EPC. For the 13C NMR, nine signals within shielded range δC 13.1 – 67.3 ppm represents alkyl
carbons. The aromatic phenyls carbons appeared at δC 127.5 – 161.9 ppm. Two consecutive moderate
signals at δC 113.2 ppm and δC 119.9 ppm are due to the presence of α, β-unsaturated carbons. The
peak resonated at δC 187.8 ppm was attributed to the presence of carbonyl (C=O) carbon atom.
4.1.2 Vibrational analysis
The FT-IR spectrum of 4EPC was recorded using Perkin Elmer 100 FTIR spectrophotometer
within the spectral range 4000-450 cm-1. The experimental and simulated FTIR spectrum using
DFT(B3LYP) method using 6–31G (d, p) functional are shown in Supplementary material 2. All the
experimental and theoretical vibrational frequencies for the synthesized compound, along with
corresponding vibrational assignments are given in Table 2. From experimental data, it showed five
absorption bands of interest represents the bending of CH3, CH (alkane), C=C, C=O and CH aromatic.
The sharp absorption band at 1650 cm-1 is due to the carbonyl (C=O) stretching of α, β-unsaturated
carbonyl group while the DFT calculation gives this mode at 1642 cm−1. Absorption of C=O was
observed at lower wavenumber due to the effect from delocalization of π-electrons between α and β
carbons which decreases the C=O order and thus, increasing the bond order between the carbonyl
carbon and α carbon atom. Additionally, another characteristic band shown by chalcone was C=C
stretching vibration between 1602 cm-1 and 1464 cm-1 in the IR spectrum and at 1588 and 1623 cm-1
theoretically, at which the wavenumbers were varies depending on the substituents group attached to
the chalcones molecular framework. Moreover, the medium intensity bands at around 2869 cm-1 –
2938 cm-1 are attributed to aliphatic C-H stretching vibrations while the DFT calculated vibration for
C-H were observed in the range 3119 – 3174 cm-1.Whilst two distinctive peaks at 1464 cm-1 and 1396
cm-1 in the IR spectrum and 1324 – 1394 cm-1 theoretically due to the presence of CH3 (bending).
Weak intensity bands at 3082 cm-1 (experimentally) and theoretically at 3058 – 3069 cm-1 was
assigned to C-H (aromatic).

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Table 2 Experimental and theoretical vibrational frequencies of the compound and their respective
assignments.
Theoretical IR (B3LYP/6-31G (d, p))
Experimental
IR (cm-1)
Freq (Scaled),
cm-1
Intensity Unscaled freq, cm-1 Vibrational assingments
3174
3168
3160
3156
3146
3142
3137
3119
3118
3113
3069
3065
3058
3053
3041
3027
3019
3004
2994
2993
2992
2990
2990
2986
2983
2975
2968
2962
2959
2953
1707
1642
1632
1623
1588
1584
1530
15.75
22.88
1.01
3.07
14.78
1.43
20.99
15.46
17.19
1.70
30.58
51.65
42.38
66.93
73.60
8.83
3229
3222
3214
3211
3200
3196
3191
3173
3172
3167
3122
3118
3111
3105
3094
3080
3071
3056
3045
3045
3044
3042
3041
3037
3035
3027
3020
3013
3010
3004
1737
1671
1660
1651
1616
1612
1557
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υCH
υC=O
υC=O
υC=O
υC=O
υCC
υCC
υCC
3082
58.19
0.03
41.68
23.57
38.24
38.38
0.11
43.89
0.17
80.21
12.50
3.74
2938
2869
1650
0.62
23.09
126.29
146.99
573.23
139.94
0.34
1602
34.21
9.76

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1528
1508
1502
1496
1495
1487
1487
1485
1480
1475
1475
1474
1438
1434
1416
1403
1398
1394
1384
1355
1345
1342
1338
1334
1330
1324
1319
1305
1305
1302
1297
1289
1280
1255
1255
1231
1225
1219
1210
1209
1189
1176
1174
1130
1128
1123
52.54
49.24
6.12
1.72
5.78
5.56
0.46
7.36
0.36
2.27
0.04
0.36
21.57
15.92
37.31
0.86
2.71
1.49
1554
1534
1527
1522
1521
1513
1512
1511
1506
1501
1501
1500
1463
1459
1440
1427
1422
1418
1408
1378
1368
1365
1361
1358
1353
1346
1342
1328
1327
1325
1320
1311
1303
1277
1277
1253
1246
1240
1231
1230
1210
1197
1194
1150
1148
1143
υCC
υCC
υCC
υCC
υCC
υOC
υCC
υCC
υCC
υCC
υCC
υOC
υCC
υCC
υCC
υCC
υCC
1464
1396
υCC
1.08
310.23
5.29
bCCC
bCCC
bHCC
bHCC
bHCC
bHCH
bHCH
bHCH
bHCC
bHCC
bHCC
bHCH
bHCC
bHCC
bHCC
bHCC
bHCC
bHCO
bHCH
bHCC
bHCH
bHCC
bHCH
bHCC
bHCC
bHCC
bHCH
bHCC
1.26
16.30
76.02
13.72
0.18
0.30
0.03
60.96
7.15
0.06
102.65
406.12
0.23
1.19
0.92
297.69
1.60
21.71
0.64
2.72
1.06
450.87
11.54
15.49
4.61

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1068
1065
1054
1053
1047
1041
1033
1018
1017
1014
1013
1004
985
976
957
952
948
936
926
893
887
869
846
837
836
831
823
812
802
781
774
755
737
730
725
718
674
645
637
633
554
537
518
509
492
465
2.69
21.13
9.40
7.32
60.02
1.58
164.17
19.29
1.35
48.10
0.46
25.06
2.55
0.27
5.04
0.24
0.27
1.01
0.01
2.52
0.60
0.36
6.04
0.91
13.63
0.40
73.10
0.37
5.70
0.77
1.68
8.29
0.21
4.15
4.64
3.65
3.26
2.31
31.65
43.92
22.31
2.56
7.22
1.54
13.34
0.81
1087
1084
1072
1071
1065
1059
1051
1036
1035
1031
1031
1021
1002
992
974
968
965
952
942
908
902
884
861
852
850
845
837
826
815
794
788
768
749
742
737
731
686
656
648
644
563
546
527
518
500
473
bHCH
bHCH
bHCH
bHCH
bOCC
bCCC
bCCC
bCCC
bCCC
bCCC
bCCC
bCCC
bCCC
bOCC
bCCC
bCCC
bCCC
bCCC
bCCO
bCOC
bCCC
bCCC
bCCC
bCCC
bCCC
bCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCOC
τHCOC
τHCCC
τHCCC
τHCCC

ACCEPTED MANUSCRIPT
446
416
410
394
376
364
340
302
289
263
242
238
216
213
171
162
158
146
136
130
116
106
96
4.86
0.02
0.34
1.01
1.43
0.96
0.10
0.19
5.62
0.74
0.01
0.02
0.07
1.37
2.16
0.82
0.05
1.67
0.39
0.62
0.36
0.01
0.44
1.49
0.22
0.19
0.02
0.11
0.03
0.47
0.09
0.04
0.05
453
423
417
401
383
370
346
308
294
267
246
242
220
217
174
165
161
149
139
132
118
108
98
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τHCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
τCCOC
τCOCC
τCCCO
τCCCC
τCCCC
τCCCC
τCCCC
τCCCC
wOCCC
wOCCC
wCCCC
wCCCC
84
61
51
47
43
32
26
20
85
62
52
48
44
33
26
20
14
11
14
11
ν:stretching; b:in plane bending; w:out-of-plane bending; τ: torsion.
4.2 Molecular and Crystal Structures Analysis
The molecular structure of 4EPC (Fig. 1. (a)) crystallizes in monoclinic crystal system with
C2/c space group where the unit cell parameters are a = 46.746 (7) Å, b = 8.3426 (12) Å, c = 10.8945
(15) Å,
β = 92.993 (5)°, α =γ = 90° and Z=8. The-para substituted ethyl group (C1 and C2) on the
terminal phenyl ring is disordered over two positions with refined site occupancies ratio of 0.731 (14):
0.269 (14). The bond lengths and angles are within the normal ranges and comparable with the

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previously reported structures of chalcone [43-45]. Table 3 lists the bond lengths and angles of the
optimized structure in comparison to the experimental values. The molecular structure of 4EPC adopts
s-cis configuration with respect to the C11=O1 and C9=C10 double bond distances of 1.227 (2) Å and
1.319 (3) Å, respectively. The ethyl substituent group is found to be twisted (Fig. 1. (b)) from the
essentially planar molecular structure [maximum deviation of 0.143 (4) Å at atom C24] with the C1—
C2—C3—C4 torsion angles being −106.5 (16)°. The corresponding torsion angle value for minor part
(C1X—C2X—C3—C4) is −30 (3)°. These torsion angle values showing that the major and minor
disordered ethyl groups are oriented in –anti-clinal and –syn-clinal conformations, respectively.
Furthermore, the planarity of the 4EPC is shown by the dihedral angles formed between the enone
moiety (O1/C9-C11; maximum deviation of 0.001(3) Å) with the terminal benzene ring (C3-C8) and
(heptyloxy)benzene moiety (O2/C12-C24) which are 3.77 (18)° and 0.73 (15)°, respectively.
Fig. 1. (a) The molecular structure of 4EPC with 50% ellipsoids probability with atomic numbering
scheme. All disordered components are shown (b) The twisted ethyl group from the planarity of the
compound where the minor disordered part has been omitted for clarity.
Table 3 Selected bond lengths and angles of the title compound.
Atoms
Geometric parameters (Å)
Experimental
DFT (B3LYP/6-31G (d,p)
Bond Lengths (Å)
O1—C11
O2—C15
O2—C18
C6—C9
1.227 (2)
1.356 (3)
1.423 (3)
1.443 (3)
1.232
1.359
1.430
1.461

ACCEPTED MANUSCRIPT
C9—C10
C10—C11
C11—C12
1.319 (3)
1.458 (3)
1.476 (3)
1.348
1.485
1.496
Bond Angles (°)
C1—C2—C3
C10—C9—C6
C9—C10—C11
C10—C11—C12
O1—C11—C10
116.0 (18)
128.6 (2)
121.1 (2)
120.7 (2)
119.7 (2)
118.44 (19)
112.8
128.2
119.7
119.3
120.7
119.1
C15—O2—C18
Torsion Angles (°)
C1—C2—C3—C4
C5—C6—C9—C10
C6—C9—C10—C11
C9—C10—C11—O1
C9—C10—C11—C12
O1—C11—C12—C13
C18—O2—C15—C16
O2—C18—C19—C20
C18—C19—C20—C21
−106.5 (16)
−178.6 (2)
−178.3 (2)
−0.2 (4)
178.9 (2)
−0.6 (4)
179.4 (2)
178.03 (19)
−178.9 (2)
-91.4
179.9
179.6
-2.5
177.9
-5.4
-179.7
-179.9
179.9
C19—C20—C21—C22
C20—C21—C22—C23
C21—C22—C23—C24
175.2 (2)
179.9 (2)
178.4 (3)
-179.9
179.9
-179.9
The crystal packing of 4EPC is shown in Fig. 2. The intermolecular C7—H7A···O1, C10—
H10A···O1 and C17—H17A···O1 hydrogen bonds (Table 4; symmetry code: x, −y+1, z−1/2) link the
1
molecules into a heart-shape character by the formation of two R2 (7) graph-set motifs [46]. These
heart-shape motifs are further connected into one-dimensional chain along the c-axis. The strong
intermolecular C—H···O hydrogen bonds (D—H···A angle: 170-176°) shows that the oxygen atom
(O1) of the carbonyl group has become the most reactive sites for a nucleophilic attack of the
hydrogen atoms from the chalcone ethylenic bridge and phenyl rings. Furthermore, the infinite one-
dimensional chains are also observed to cross-link with each other and stack along the b-axis.

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Fig. 2. The crystal packing of 4EPC. Dashed lines represent the intermolecular C—H···O hydrogen
bonds. Only major disordered components are shown.
Table 4 Hydrogen bond geometry of the compound.
Bond
D—H···A
Bond length, (Å)
Angle
D—H···A, (°)
176
D—H
0.93
0.93
H···A
2.50
2.47
D···A
C7—H7A···O1 (i)
3.427 (3)
3.394 (3)
3.407 (3)
C10—H10A···O1(i)
C17—H17A···O1(i)
Symmetry codes: (i) x, −y+1, z−1/2.
171
170
0.93
2.49
4.3 Thermal analysis
The thermal stability of the prepared 4EPC was evaluated using thermogravimetric analysis
(TGA) under nitrogen atmosphere and the obtained data are presented in Table 5, whereas Fig. 3
depicts TGA and DTG thermogram of 4EPC.

ACCEPTED MANUSCRIPT
100
80
60
40
20
0
0.00
-0.05
-0.10
-0.15
-0.20
200
400
600
800
Temperature (°C)
Fig. 3. TGA with DTG thermogram of 4EPC.
The thermal behavior of 4EPC was recorded from ambient temperature up to 900 °C in
nitrogen flow and did not show any weight loss up to 276 °C, indicated that crystal water molecules
and coordinated water molecules are not present in compound 4EPC. The results obtained from
TGA/DTG curves reveals that compound 4EPC started to degrade in single step at onset temperature
(Td) 276 °C, with maximum degradation occurred at 346 °C. The single decomposition stage occurred
in the temperature range of 276 – 355 °C with a mass loss of 95.2% consistent with the evaluation of
(E)-1-(4-ethylphenyl)-3-(4-(heptyloxy) phenyl) prop-2-en-1-one (loss of weight calculated 95.7%).
The final residue mass loss was about 4.8% which correspond to the char residue of CH3. Compound
4EPC decomposes at high temperature due to the introduction of long alkoxy chain in the molecular
framework. This high thermal stability of 4EPC probably arises because in its crystal packing, the
long chain is further stabilized by π-stacking between adjacent aromatic, carbonyl and C=C alkene. In
fact, the high thermal stability of 4EPC agrees with the nearly planar structure of 4EPC, favours in
this way the donor→donor interactions, through the intermolecular interactions of C—H···O hydrogen
bonds. Generally, the thermal behaviour obtained are supported with the previously reported related
compounds [47, 48] in term of their stability and stage of degradation.

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Table 5 Thermal stability analysis of 4EPC.
Onset
Compound temperature,
Td (°C)
Final
residue
(%)
Weight loss (%)
Expected moieties decomposition
276 – 355 °C
(95.2%); [calc: 95.7%]
(E)-1-(4-ethylphenyl)-3-(4-
(heptyloxy) phenyl) prop-2-en-1-one
276
4.8
4EPC
4.4 UV-visible analysis
Electronic absorption spectrum of 4EPC was recorded in the 200 – 600 nm range in
dichloromethane (DCM) solvent (c = 1 x 10-5 M). The value of maximum wavelength (λmax) of
absorption of molecule 4EPC was observed at 327 nm while the cut-off wavelength (λedge) is at 368
nm represent the intraligand charge transfer transitions of an electron from bonding to anti-bonding
(π→π*) which were attributed by aromatics nuclei and alkene C=C chromophores. Whilst, the
absorption minimum arised from electronic transition of non-bonding to anti-bonding (n→π*) which
was contributed from moieties C=O and C-O chromophores. The experimental and TD-DFT UV-vis
of 4EPC are shown in Fig. 4. Thus, the optical energy band gap for molecule 4EPC is 3.37 eV
according to the formula of ∆Egap = hc/λedge. TD-DFT is currently developed to determine the dynamic
and static features of the compounds in their excited states, allowing for the correlation between
computational output and experimental data based on the TD-DFT B3LYP/6-31G (d, p) level of
theory. The predictions were carried out in solvation model, in which IEF-PCM formalism was
considered. The calculated wavelength (λ), oscillator strength (fo), excitation energies (eV) and
spectral assignments with major contributors are shown in Table 6. Calculated UV-vis spectrum of
4EPC exhibited two intense allowed transition at λmax = 347 nm, fo = 1.1197 and λ = 313 nm, fo =
0.1213 which are corresponded to the experimental λmax value of 327 nm. In fact, the theoretical
transition peaks for 4EPC in DCM are red-shifted compared with the experimental data in which, the
assigned bands were attributed with HOMO→LUMO (n→π*) and HOMO-1→LUMO (π→π*)
transitions. For a better description of the electronic properties, the character of the orbitals involved in
the main electronic transitions of compound 4EPC are illustrated in Figure 5. The HOMO is attributed
to a π bonding system localized over phenyl and C=C moieties and a p-type orbital strongly located on
the oxygen atom. The HOMO-1 corresponds to a π bonding system spread over phenyl, C=C and

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carbonyl (C=O) moieties and a p-type orbital strongly located at the oxygen atom similar as described
for HOMO. In LUMO, electrons were spread to the entire molecules except for alkoxy chain.
Experimental 4EPC
TD-DFT 4EPC
50000
40000
30000
20000
10000
0
300
400
Wavelength (nm)
Fig. 4. The experimental and TD-DFT UV-vis for synthesized molecule 4EPC.
Table 6 The excitation energy, oscillator strength, calculated and experimental wavelength (nm) and
major contributions of electronic transitions from ground state (S0) to excited state (Sn).
Excitation
Wavelength (nm)
Oscillator
strength (fo) transition
Electronic
Assignments,
contributors (%)
major
energies
(∆E, eV)
3.56
Molecule
Experimental Calculated
347
1.1197
0.1213
S0→S1
S0→S2
HOMO→LUMO
(97%)
327
4EPC
313
3.95
HOMO-1→LUMO
(96%)
4.5 Frontier molecular orbitals (FMOs) analysis
The analysis of frontier molecular orbitals (FMOs) plays an important role to understand the
chemical stability of a molecule. The FMOs of the synthesised 4EPC was computed via TD-DFT
approach with B3LYP/6-31G (d, p) and are illustrated in Fig. 5. The HOMO-LUMO energy gaps
determine the chemical reactivity, chemical hardness and softness as well as the polarizability of the
synthesised molecule. In the case of 4EPC, the HOMO-LUMO energy gap is relatively small, i.e. 4.02
eV, indicating molecule 4EPC is soft which can exhibit good polarizability and nonlinear optical

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(NLO) properties. FMOs results revealed that the electron distribution in HOMO were spread mostly
on ethylenic bridge and aromatic rings with donor-donor substitution. However, in LUMO level, the
charge density is confined over the entire molecules (including ethylenic bridge, aromatic rings and
carbonyl functional group) except for alkoxy chain substitution. Moreover, for HOMO-1 and LUMO
both also lie almost over the whole molecule except at alkoxy chain. For 4EPC, there are two
electronic excitation energies were involved, i.e. the transition of electrons from the ground state (S0)
to the excited state (Sn), and the percentage of major contributions which the findings are tabulated in
Table 5. The first excitation energy involved (S0→S1) is 3.56 eV which are in close argument with the
experimental energy band gap 3.37 eV with 97% of the involved electronic transition is from ground
state to the first excited state are HOMO→LUMO transition and 96% of the transitions are HOMO-
1→LUMO involved in the second excitations (S0→S2) with the energy separation of 3.95 eV. The
energy separation between the HOMO and LUMO as well as their atomic orbitals compositions
known to have synergetic effect within the molecule, which subsequently affects the NLO properties
of each compound. From the obtained FMOs and electronic analysis suggest that the grown crystal of
4ECP can be the promising and potential candidate for optoelectronic devices.
Furthermore, the global chemical reactivity descriptors (GCRD) are another vital technique to
understand the chemical properties of a molecule such as chemical hardness (η), chemical potential
(ꢀ), chemical softness (S), electronegativity (χ) and electrophilic index (u). The formula (Eq. 1 to Eq.
5) to obtain GCRD is derived from HOMO-LUMO energies, taking the HOMO energy as ionization
potential (I) and LUMO as electron affinity (A) and the data are tabulated in Table 7.
Chemical hardness (η) = [(ELUMO - EHOMO)/2]
Chemical softness (S) = [1/2η]
Eq. 1
Eq. 2
Eq. 3
Eq. 4
Eq. 5
Chemical potential (ꢀ) = [(EHOMO + ELUMO)/2]
Electronegativity (χ) = [(I + A)/2]
Electrophilic index (u) = [ꢀ2/2η]

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From the calculation, it was found that 4EPC is kinetically stable with the hardness value of
2.01 eV, chemical potential of -4.09 eV, chemical softness of 0.25 e-1V-1 electronegativity of 4.09 eV
and the electrophilic index of 4.16 eV suggest that 4EPC possess excellent chemical strength and
stability.
Table 7 Molecular orbitals energies of HOMO and LUMO (eV) and the global chemical reactivity
descriptors (GCRD).
Molecule EHOMO
ELUMO
ꢁE (eV)
η (eV)
ꢀ (eV)
S (e-1V-1)
χ (eV) u (eV)
4.09 4.16
-6.1019 -2.0762
-4.02
2.01
-4.09
0.25
4EPC
Fig. 5. Molecular orbitals of title molecule 4EPC.

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4.6 Hirshfeld surface analysis
The intermolecular interaction, packing mode and molecular shape of the crystal
structure of 4EPC was studied using Hirshfeld surface analysis (HSA). The HSA is mapped
with dnorm (Fig. 6) and 2D fingerprint analysis plot for the crystal 4EPC was generated by
Crystal Explorer 3.1 program using crystallographic output file (.cif) obtained from single
crystal X-ray diffraction. The 2D fingerprint plot analysis of 4EPC was illustrated in Fig. 7,
consists of distribution graph of de vs di where de and di are the distance from a point on the
Hirshfeld surface to the nearest nucleus inside the surface and outside the surface,
respectively. The H-H and C-H interactions are the major intermolecular interactions in the
crystal structure of 4EPC (65.3% and 13.5%). Single sharp spike at the bottom area was
observed at the bottom left of 2D fingerprint plot, depicts the O-H interaction (5.2%) in the
4EPC crystal structure which corresponded to the weak intermolecular C-H/O hydrogen bond
represent at the circular depressions (deep red) visible on the Hirshfeld surface. Moderate
spike at the top right region indicates H-C interaction (11%), whilst, the single sharp spike at
top region indicates H-O interaction (4.4%). Strong interaction is determined by the more
space occupied compared to the weak interaction with less space occupied in the fingerprint
plot. The combination of de and di in the form of a 2D fingerprint plot give an information of
intermolecular contact in the crystal.
Fig. 6. The Hirshfeld surface of 4EPC mapped with dnorm
.

ACCEPTED MANUSCRIPT
Fig. 7. The 2D fingerprint plot of crystal 4EPC and the percentage of contribution to the total
Hirshfeld area.
4.7 Molecular electrostatic potential (MEP) analysis
The molecular electrostatic potential (MEP) analysis is one of the important tools to
determine the possible interaction site within 4EPC where the reactivity of 4EPC can be
determined by predicting the nucleophilic and electrophilic sites of the molecule. The
computed MEP using DFT B3LYP/6-31 G (d, p) is as shown in Fig. 8 in which the mapped
MEP surface gives us information on the charge distribution region of a molecule. The
distribution of charges governs the molecule interaction and the nature of the chemical bond.
The nucleophilic region of the molecule is described by the positive area of MEP surface
while the electrophilic site of the molecule is associated with the negative region of MEP
surface. For 4EPC, the negative charges are more concentrated on the oxygen atom of
carbonyl (C=O) with the colour code of the map is in the range between -5.825 x 10-2 a.u.

ACCEPTED MANUSCRIPT
(deepest red) towards 5.825 x 10-5 a.u. (deepest blue) in the map. This revealed that the
oxygen atom from C=O is the most reactive site to interact favourably with nucleophile.
Fig. 8. MEP surface of molecule 4EPC.
4.8 Nonlinear optical (NLO) properties: DFT calculation
Density functional theory (DFT) calculation was used to examine nonlinear optical (NLO)
properties for 4EPC in term of dipole moment (ꢀ), polarizability (α) and 1st hyperpolarizability (β)
indexes. The polarizability and hyperpolarizability components are the derivatives of molecular energy
with respect to the strength of applied electric field. The static dipole moment, polarizability and 1st
hyperpolarizability were calculated via DFT B3LYP/6-31G (d, p) and were calculated using the
following equations and the related parameters are tabulated in Table 8.
2
2
ꢀtot = (ꢀx + ꢀy + ꢀz2)1/2
Eq. 6
Eq. 7
<α> = ꢀꢁ (αxx + αyy + αzz)
ꢀ
2
∆α = √ꢂ [(αxx – αyy)2 + (αyy – αzz)2 + (αzz – αxx)2 + 6(αxy2 + αxz2 + αyz )]1/2
Eq. 8
Eq. 9
β-v = [(βxxx + βxyy + βxzz)2 + (βyyy + βyzz + βyxx)2 + (βzzz + βzxx + βzyy)2]1/2

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These present components indicate the non-uniform charge distribution along three magnitude.
The total dipole moment (ꢀtot) of 1A with D-π-D is found to be 2.68 which is the least compared to the
chalcone derivatives with D-π-A characteristic [49, 50]. Moreover, the mean polarizability (<α>) of
4EPC revealed to be 2.13 x 10-23 (esu) while the anisotropy of polarizability (∆α) for 4EPC is 7.51 x
10-24 (esu). In addition, the 1st order hyperpolarizability (β-v) of 4EPC is 1.27 x 10-30 (esu) about 2
times higher than standard reference of urea. However, the 1st order hyperpolarizability value of 1A
featuring D-π-D is of the weakest compared to other reported chalcone derivatives due to the
attachments of long alkoxy substituted chain which contributed to the long-range charge transfer and
might be due to the less conjugation involved throughout molecule. The polarizabilities and first-order
hyperpolarizabilities are recorded in atomic units (a.u.), the calculated values have been converted into
electrostatic units (esu) using conversion factor of 0.1482 × 10−24 esu for α and 8.6393 × 10−33 esu for
β. Thus, the title compound 4EPC has an ideal characteristic in potentially to be further taken as
candidate in NLO application.
Table 8 Static dipole moments, polarizability and 1st order hyperpolarizability components of title
compound 4EPC with B3LYP/6-31G (d, p) level of theory.
Dipole moment (Debye)
4EPC
0.8675
-2.5257
-0.2361
2.68
ꢀx
ꢀy
ꢀz
ꢀtot
Polarizability
αxx
αyy
αzz
αxy
αxz
αyz
-112.2849
-158.2421
-160.1713
10.9656
0.6285
0.3233
-2.13
<α> (x 10-24) in esu
∆α (x 10-24) in esu
7.51
1st Hyperpolarizability
βxxx
βxyy
βxzz
βyyy
βxxy
βyzz
-165.3517
-5.5160
31.8725
-24.2823
-23.0872
0.6083
βzzz
2.5437
βxxz
βyyz
βxyz
-2.9405
-2.7954
-5.7185
1.27
β-v (x 10-30) in esu

ACCEPTED MANUSCRIPT
Conclusions
New alkoxy substituted chalcone derivative (4EPC) of D-π-D was successfully synthesized
1
13
and characterized using FT-IR, H and C NMR, both UV-vis and TD-DFT for electronic transition
characteristics and the crystal structure of 4EPC was confirmed by single crystal X-ray diffraction
method. The crystallographic data indicate that 4EPC crystallized in monoclinic crystal system with
space group C2/c. The experimental UV-vis spectrum of 4EPC was performed in a dichloromethane
(DCM) and compared with calculated one via IEF-PCM model using TD-DFT B3LYP 6-31G (d, p)
level of theory. The results obtained were compliment to the experimental findings. The absorption
band at λmax = 327 nm was assigned to the electronic transition of HOMO → LUMO orbitals
corresponding to the predicted bands 313 nm and 343 nm, excitation energies of 3.56 eV and 3.95 eV
and oscillator strength of 1.1197 and 0.1213, where the HOMO-LUMO plot indicates the electron
charge mobility from phenyl ring, C=C to carbonyl (C=O) functional group. In addition, the global
chemical reactivity descriptors (GCRD) were calculated using frontier molecular orbital energies.
°
From TGA/DTG graph, 4EPC crystal is thermally stable up to 276 C with mass loss of 95.2% in
single step of degradation process. The Hirshfeld surface analysis and finger print plots were
examined to understand the occurrence of molecular interaction within the molecule. Results obtained
from Hirshfeld indicated that H…H (65.3%) and C…H (13.5%) interactions are the major contributor in
the crystal packing. The MEP analysis revealed the possible interaction can occur at C=O site of the
molecule for nucleophilic analyte addition. Since the synthesised chalcone derivative of 4EPC
exhibits larger NLO values in term of polarizability and 1st order hyperpolarizability compared to the
standard reference of reported urea, therefore 4EPC fits all the requirements to be an ideal candidate
to be developed as advanced NLO materials. By having excellent NLO properties, 4EPC also can be
an active layer in organic light emitting diode (OLED). Interestingly, from theoretical calculation of
4EPC, the findings showed that this chalcone derivative is found to be a soft material which having
high potential as active materials to be used in pharmaceutical, biological and medicinal interests.
Acknowledgements

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The authors would like to acknowledge the financial support from Ministry of Education, Malaysia for
Fundamental Research Grant Scheme FRGS 59515 (FRGS/1/2018/STG07/UMT/02/6), SLAB/SLAI
and Universiti Malaysia Perlis (UniMAP) for postgraduate scholarship, Institute of Marine
Biotechnology for NMR analysis and Universiti Malaysia Terengganu for research facilities and
supports.
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