Spectroscopic (FT-IR, FT-Raman, UV, 1H and 13C NMR) profiling and computational studies on methyl 5-methoxy-1H-indole-2-carboxylate: A potential precursor to biologically active molecules

Article abstract of DOI:10.1016/j.molstruc.2016.12.004

Methyl 5-methoxy-1H-indole-2-carboxylate (MMIC) was prepared via esterification of commercially available 5-methoxyindole-2-carboxylic acid. The title molecule MMIC was characterised using FT-IR and FT-Raman in the ranges of 4000–500 and 4000–50?cm^?1, respectively. The fundamental modes of the vibrations were assigned and the UV–visible spectrum of the MMIC molecule was recorded in the range of 200–400?nm to explore its electronic nature. The HOMO-LUMO energy distribution was calculated and the bonding and anti-bonding structures of the title molecule were studied and analysed using the natural bond orbital (NBO) approach. The reactivity of the MMIC molecule was also investigated and both the positive and negative centres of the molecule were identified using chemical descriptors and molecular electrostatic potential (MEP) analysis. The chemical shifts of the ¹H and ¹³C NMR spectra were noted and the magnetic field environment of the MMIC molecule are discussed. The non-linear optical (NLO) properties of the title molecule were studied based on its calculated values of polarisability and hyperpolarisability. All computations were obtained by DFT methods using the 6-311++G (d,p) basis set.

Full text of DOI:10.1016/j.molstruc.2016.12.004

Accepted Manuscript
1
13
Spectroscopic (FT-IR, FT-Raman, UV, H and C NMR) profiling and computational
studies on methyl 5-methoxy-1H-indole-2-carboxylate: A potential precursor to
biologically active molecules
Maha S. Almutairi, S. Xavier, M. Sathish, Hazem A. Ghabbour, S. Sebastian, S.
Periandy, Reem I. Al-Wabli, Mohamed I. Attia
PII:
S0022-2860(16)31294-7
10.1016/j.molstruc.2016.12.004
MOLSTR 23202
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 25 September 2016
Revised Date: 2 December 2016
Accepted Date: 2 December 2016
Please cite this article as: M.S. Almutairi, S. Xavier, M. Sathish, H.A. Ghabbour, S. Sebastian,
1
13
S. Periandy, R.I. Al-Wabli, M.I. Attia, Spectroscopic (FT-IR, FT-Raman, UV, H and C NMR)
profiling and computational studies on methyl 5-methoxy-1H-indole-2-carboxylate: A potential
precursor to biologically active molecules, Journal of Molecular Structure (2017), doi: 10.1016/
j.molstruc.2016.12.004.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Spectroscopic (FT-IR, FT-Raman, UV, 1H and 13C NMR) profiling and computational
studies on methyl 5-methoxy-1H-indole-2-carboxylate: A potential precursor to
biologically active molecules
f
a
b,c
b,d
a,e
b
,
Maha S. Almutairi , S. Xavier , M. Sathish , Hazem A. Ghabbour , S. Sebastian S. Periandy ,
Reem I. Al-Wablia, Mohamed I. Attiaa,g*
aDepartment of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, P.O. Box
2457, Riyadh 11451, Saudi Arabia
bDepartment of Physics, St. Joseph College of Arts and Science, Cuddalore, Tamilnadu 607001, India
cResearch scholar, Bharathiar University, Coimbatore, India
dResearch Scholar, Manonmaniam Sundaranar University, Thirunelveli 627012, India
eDepartment of Medicinal Chemistry, Faculty of Pharmacy, Mansoura University, Mansoura 35516,
Egypt
fDepartment of Physics, KMCPGS, Puducherry, India
gMedicinal and Pharmaceutical Chemistry Department, Pharmaceutical and Drug Industries Research
Division, National Research Centre (ID: 60014618), El Bohooth Street, Dokki, Giza 12622, Egypt
Abstract
Methyl 5-methoxy-1H-indole-2-carboxylate (MMIC) was prepared via esterification of
commercially available 5-methoxyindole-2-carboxylic acid. The title molecule MMIC was
characterised using FT-IR and FT-Raman in the ranges of 4000–500 and 4000–50 cm-1, respectively.
The fundamental modes of the vibrations were assigned and the UV-visible spectrum of the MMIC
molecule was recorded in the range of 200–400 nm to explore its electronic nature. The HOMO-
LUMO energy distribution was calculated and the bonding and anti-bonding structures of the title
molecule were studied and analysed using the natural bond orbital (NBO) approach. The reactivity of
the MMIC molecule was also investigated and both the positive and negative centres of the molecule
were identified using chemical descriptors and molecular electrostatic potential (MEP) analysis. The
1
chemical shifts of the H and 13C NMR spectra were noted and the magnetic field environment of the
MMIC molecule are discussed. The non-linear optical (NLO) properties of the title molecule were
studied based on its calculated values of polarisability and hyperpolarisability. All computations were
obtained by DFT methods using the 6-311++G (d,p) basis set.
Keywords: 5-Methoxyindole; FT-IR; FT-Raman; HOMO-LUMO; NLO

ACCEPTED MANUSCRIPT
1. Introduction
The pineal gland synthesises and releases the pineal hormone N-acetyl-5-methoxytryptamine
(melatonin, MLT) in a circadian rhythm, with high peripheral blood levels at night. It has been
reported that MLT has sleep-inducing properties, as well as pain modulatory, antitumour, anti-
inflammatory, and antioxidant effects [1-4]. Melatonin affects MT1 and MT2 receptors, which are G-
protein-coupled receptors, as well as a low-affinity putative MLT binding site called MT3 [5,6].
Nonlinear optical (NLO) materials are attracting a great deal of attention due to their great
impact on information technology and industrial applications [7,8]. NLO materials are characterised by
their nonlinear response to the electric field associated with the light of a laser beam. Organic
nonlinear optical materials have attracted growing interest due to their large optical susceptibilities,
inherent ultrafast response times, and high optical thresholds for laser power compared with inorganic
NLO materials [9]. Nevertheless, the burgeoning field of NLO research and applications is still in need
of new NLO materials for a wide variety of processes.
The indole nucleus constitutes the core structure of a large number of melatoninergic ligands
that can modulate melatonin receptors [10-12]. According to the literature, the molecular structure of
methyl 5-methoxy-1H-indole-2-carboxylate (MMIC) has not been previously investigated using
computational methods and hence its molecular characterisation will support the development of new
bioactive compounds. Therefore, the present work involves vibrational profiling, as well as
1
13
spectroscopic (FT-IR, FT-Raman, H and C NMR) characterisation and investigation of the NLO
properties, of the MMIC molecule using DFT computational approaches. Molecular electrostatic
potential (MEP) and HOMO-LUMO analyses were also performed. It is believed that the results of the
current investigation will give insight into the possible intermolecular interactions of the MMIC
molecule, which could help with the rationalisation of intermolecular drug-receptor interactions with
the purpose of designing new biologically active indole-bearing molecules.
2. Experimental details
2.1. General
The melting point was measured using a Gallenkamp melting point device and is
uncorrected. The FT-IR spectrum of the MMIC molecule was recorded using KBr pellets on a
Perkin Elmer RXL spectrometer (Waltham, Massachusetts, USA) with a spectral resolution of 2
cm−1. The FT-Raman spectrum was obtained using a Bruker RFS 100/s spectrophotometer
(Ettlingen, Germany) with an excitation wavelength of 1064 nm and using the emission of an
Nd:YAG laser source (Goettingen, Germany). The NMR sample was dissolved in DMSO-d6 and the
NMR spectra were recorded using Bruker NMR spectrometer at 500 MHz for 1H and 125.76 MHz for
13C at the Research Center, College of Pharmacy, King Saud University, Saudi Arabia.

ACCEPTED MANUSCRIPT
2.2. Synthesis
A few drops of concentrated sulphuric acid were added to a suspension containing 5-
methoxyindole-2-carboxylic acid (1, 2.00 g, 0.01 mol) in absolute methanol (30 mL). The reaction
mixture was heated to reflux for four hours, cooled to room temperature, and the precipitated solid
filtered off to give 2.1 g (96%) of MMIC (2) as yellow crystals, m.p. 450–451 K [13].
2.3. Crystal structure determination
The methanolic solution of the MMIC molecule was subjected to slow evaporation to give
single crystals suitable for X-ray analysis. Bruker SMART APEXII CCD diffractometer equipped with
graphite monochromatic Mo Kα radiation at 100 (2) K was used to collect the data. Cell refinement
and data reduction were carried out by Bruker SAINT [14]. The title structure was solved using
SHELXS-97 [15,16]. Full-matrix least-squares techniques with anisotropic thermal data for non-
hydrogen atoms on F2 were used to finalize the refinement. All the hydrogen atoms were placed in
calculated positions (Tables T1-T3). Crystallographic data of the MMIC molecule have been deposited
with the Cambridge Crystallographic Data Center (supplementary publication number CCDC-
1052719). Copies of the data may be obtained free of charge from the Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (deposit@ccdc.cam.ac.uk).
2.4. Quantum chemical calculations
Density functional theory (DFT) is an effective tool for calculating the electronic structures of
molecules. The basis set, 6-311++G (d,p), was augmented by a ‘d’ polarisation function for heavy
atoms and a ‘p’ polarisation for hydrogen atoms, in order to achieve a better representation of the polar
bonds in the molecule [17,18]. All calculations in the present work were performed using the Gaussian
09W [19] program package on a personal computer. Geometrical parameters and vibrational
wavenumbers were computed by optimising the geometry of the molecule using the B3LYP, M06-2X
and B3PW91 methods with 6-311++G (d,p) as the basis set. The vibrational frequency assignments
were calculated by the total energy distribution (TED) method using the vibrational energy distribution
analysis (VEDA) program [20]. The optimised geometry of the MMIC compound was further used to
complete a natural bond orbital (NBO) analysis using NBO version 3.1 [21], which is implemented in
the Gaussian 09W package. The NMR chemical shifts of the title compound were also calculated using
the gauge independent atomic orbitals (GIAO) method [22,23] with the B3LYP/6-311++G (d,p)
functional method. 1H and 13C isotropic magnetic shielding (IMS) of any X atom (carbon or hydrogen)
was applied according to the value of TMS, CSX = IMSTMS - IMSx. The energy distribution from
HOMO to LUMO was calculated using the Gausssum 2.2.1 software program.

ACCEPTED MANUSCRIPT
3. Results and discussion
3.1. Synthesis
The target molecule, MMIC (2), was prepared via esterification of the commercially available
5-methoxyindole-2-carboxylic acid (1) in methanol and a catalytic amount of sulphuric acid, as
illustrated in Scheme 1 according to the published procedure [13].
H3CO
H3CO
OH
O
OCH3
O
i
N
N
H
H
1
2
Reagents and conditions: i) methanol, H2SO4, reflux, 4h, 96%.
Scheme 1: Synthesis of the MMIC (2) molecule.
3.2. Structural geometry analysis
MMIC crystallizes in the monoclinic crystal system with space group P21/n with four
molecules per unit cell (Z = 4) and cell dimensions of a = 7.8956(6), b =5.8304(4) and c= 22.0407(16)
Å. The crystal packing of the molecule with Z = 4 units is shown in Figure 1. The molecule consists of
one methyl ester group and one methoxy group attached to the indole ring, as illustrated in Figure 2.
The geometrical parameters of the title compound were computed by B3LYP, M06-2X and B3PW91
functionals with the basis set 6-311++G (d, p) and the results, along with the XRD values, are
presented in Table 1. The geometrically optimized title molecule exhibited energy value of -
442924.7202 Kcal.mol-1. The calculated structural geometry parameters are well correlated with the
experimental values as indicated, with their correlation coefficient (R2) values calculated as 0.9878,
0.9867 and 0.9876 (for bond lengths) and 0.9004, 0.9018 and 0.8990 (for bond angles) using B3LYP,
M06-2X and B3PW91 functionals, respectively.

ACCEPTED MANUSCRIPT
Figure 1. Crystal packing of the MMIC molecule.
Figure 2. Optimized structure of the MMIC molecule.

ACCEPTED MANUSCRIPT
Table 1. Geometrical parameters [bond length (Å), bond angle (◦) and dihedral angle (◦)] of the MMIC
molecule.
B3LYP/6-311G++
(d,p)
Parameters
M06-2X/6-
B3PW91/6-
XRD
311G++ (d,p)
311G++ (d,p)
Gas
Ethanol
Phase
Phase
Bond length (Ǻ)
C1-C2
1.426
1.4229
1.4177
1.4228
1.414
C1-C6
1.403
1.429
1.395
1.375
1.389
1.084
1.415
1.081
1.388
1.373
1.083
1.378
1.078
1.381
1.464
1.008
1.215
1.347
1.439
1.091
1.088
1.091
1.419
1.089
1.096
1.096
1.4029
1.4251
1.3946
1.3694
1.3858
1.0844
1.4142
1.0826
1.3862
1.3664
1.0845
1.3791
1.0791
1.3751
1.4619
1.0083
1.2166
1.3365
1.4357
1.091
1.4007
1.4308
1.3943
1.3723
1.3835
1.0833
1.4129
1.0813
1.3826
1.3659
1.083
1.4007
1.4256
1.3929
1.37
1.413
1.421
1.396
1.371
1.372
0.949
1.416
0.950
1.369
1.374
0.950
1.369
0.950
1.377
1.455
0.891
1.211
1.239
1.448
0.980
0.980
0.980
1.416
0.979
0.980
0.980
C1-C7
C2-C3
C2-N14
C3-C4
1.386
C3-H9
1.0848
1.4123
1.0827
1.3855
1.3659
1.084
C4-C5
C4-H10
C5-C6
C5-O22
C6-H11
C7-C8
1.3703
1.0779
1.3737
1.4681
1.0081
1.2069
1.3354
1.4292
1.0903
1.0864
1.0903
1.4097
1.088
1.3767
1.0788
1.3755
1.4613
1.0074
1.2133
1.3412
1.4308
1.0917
1.0884
1.0917
1.4111
1.0899
1.0969
1.0969
C7-H12
C8-N14
C8-C15
H13-N14
C15-O16
C15-O17
C18-O17
C18-H19
C18-H20
C18-H21
C23-O22
C23-H24
C23-H25
C23-H26
Bond angle (°)
C2-C1-C6
C2-C1-C7
C6-C1-C7
C1-C2-C3
C1-C2-N14
1.0876
1.091
1.4191
1.0893
1.0952
1.0952
1.0951
1.0951
119.55
106.84
133.61
121.37
107.54
119.6074
106.8039
133.5887
121.4031
107.6847
119.5603
106.8566
133.5832
121.4677
107.6798
119.5737
106.829
120.03
106.59
133.39
121.46
108.06
133.5973
121.3741
107.5716

ACCEPTED MANUSCRIPT
C3-C2-N14
C2-C3-C4
131.09
118.17
121.54
120.29
121.10
118.68
120.22
120.85
123.31
115.84
118.96
121.74
119.29
106.97
127.66
125.37
109.58
132.08
118.33
109.07
127.87
123.06
123.50
112.56
123.94
115.84
110.49
105.35
110.48
110.63
109.22
110.64
118.94
105.81
111.65
111.65
109.12
109.12
109.38
130.9122
118.0923
121.4706
120.4371
121.1861
118.6405
120.1734
120.8611
123.0891
116.0498
118.85
130.8524
118.1029
121.4342
120.463
131.0543
118.1228
121.5811
120.2962
121.1636
118.665
130.48
117.48
121.39
121.29
121.78
119.08
119.15
121.33
113.67
125.08
117.92
121.08
121.00
107.19
126.41
126.41
109.70
130.54
119.70
108.44
126.39
123.99
124.91
112.04
123.05
116.78
109.54
109.45
109.40
109.46
109.46
109.52
117.19
109.50
109.46
109.48
109.47
109.44
109.48
C2-C3-H9
C4-C3-H9
C3-C4-C5
121.0232
118.6365
120.3403
120.9388
123.1238
115.9374
118.9071
121.9535
119.1394
106.5256
128.0832
125.3912
110.182
C3-C4-H10
C5-C4-H10
C4-C5-C6
120.1713
120.824
C4-C5-O22
C6-C5-O22
C1-C6-C5
123.2498
115.9262
118.9418
121.7665
119.2918
106.8286
127.7802
125.3911
109.668
C1-C6-H11
C5-C6-H11
C1-C7-C8
121.4815
119.6685
106.784
C1-C7-H12
C8-C7-H12
C7-C8-N14
C7-C8-C15
N14-C8-C15
C2-N14-C8
C2-N14-H13
C8-N14-H13
C8-C15-O16
C8-C15-O17
O16-C15-O17
C15-O17-C18
O17-C18-H19
O17-C18-C20
O17-C18-O21
H19-C18-H20
H19-C18-H21
H20-C18-H21
C5-O22-C23
O22-C23-H24
O22-C23-H25
O22-C23-H26
O24-C23-H25
O24-C23-H26
H25-C23-H26
127.5635
125.6526
109.6743
131.3485
118.9772
109.0531
127.04
131.6959
118.1221
108.756
132.1618
118.1702
109.1028
127.9496
122.9476
123.4144
112.5613
124.0244
115.4832
110.5861
105.5124
110.5858
110.525
127.9913
123.2528
123.3043
112.5556
124.1402
115.2102
110.2575
105.6595
110.2576
110.7369
109.1585
110.7368
118.1587
106.0639
111.3917
111.3912
109.2342
109.2347
109.4387
123.9069
123.5079
112.3885
124.1036
116.1871
110.4329
105.4598
110.4327
110.3967
109.6599
110.3966
118.6221
105.8793
111.5247
111.5246
109.1371
109.1372
109.5328
109.0773
110.5249
118.6156
105.9413
111.7444
111.7442
108.9868
108.987
109.3243
The geometrical parameters for the title compound are presented in Table 1. Morzyk-Ociepa
and Rozycka-Sokolowska [24] reported that the carboxylic acid bond lengths (C=O and C–O) are

ACCEPTED MANUSCRIPT
1.265 Ǻ and 1.270 Ǻ, respectively. The computed values among different methods for the 15C–16O
bond of the title compound are 1.215, 1.206 and 1.213 Ǻ using B3LYP, M06-2X and B3PW9,
respectively. The theoretical values are in good agreement with the XRD value (1.211 Ǻ). In the case
of the methoxy group connected to the left side of the indole ring, the bond lengths of 23C–22O
computed with B3LYP, M06-2X and B3PW9 are 1.419, 1.410 and 1.411Å, respectively, and they are
in good agreement with that of experimental value (1.416 Ǻ). Whereas the C–O bond (15C–17O) on
the right side of the ring is not as same as that of the computed values which has difference nearly ~1.1
Ǻ. In the case of the N–H bond (H13-N14), the computed values are found to be higher than the
experimental one (0.891 Ǻ). It is also found that all of the C–C, C–N, and C–H bond lengths of the
indole group are close to the experimental X-ray diffraction (XRD) values. In addition, the calculated
geometrical parameters for the title molecule in the liquid state (ethanol) using the B3LYP method
showed good agreement with the experimental XRD values, with correlation coefficients (R2) = 0.9892
and 0.9083 for bond lengths and angles, respectively.
The C–C bond lengths of the indole ring were found to be different from those of the benzene
ring, where the difference between the lengths of the double and single bonds is not clearly observed in
the benzene ring. Thus, the indole C–C single bond lengths (Ǻ) were found to be 1.421 (C1-C7), 1.413
(C1-C6), and 1.416 (C4-C5) and the C=C double bond lengths (Ǻ) were 1.369 (C5-C6), 1.372 (C3-
C4), and 1.396 (C2-C3). In contrast to the benzene ring, the differentiation of double and single bond
lengths is clearly observed. In the case of the C–N bond length (Ǻ), the values were found to be 1.371
(C2-N14) and 1.377(C8-N14). The calculated values were found to be in good agreement with the
XRD experimental values. There is a slight distortion of the indole bond lengths due to the attachment
of the carboxylic acid methyl ester on the right side of the indole ring and the methoxy group on the
left side of the indole ring. Upon comparing the optimised geometrical parameters with the
experimental XRD data [25] in Table 1, the computed parameters appear to deviate slightly from the
XRD values. This might be because the theoretical calculations were performed in the gas phase, while
the solid state was used in the experimental XRD measurements.
The angle for C8-C15-O16 is around 123o for the three computed methods, which is close to
the experimental value (124.91o). The angle between the methoxy and carbonyl groups is around 115o
and similarly the angle between indole and methoxy groups is around 118o, both are close to the
experimental values (116.78 and 117.19, respectively). The C7-C8-N14 angle was observed at around
110o, which is very close to the XRD value at 109.70o. The angle of the 16O–15C–17O functional
group was found to be around 124o and it is close to the experimental value (123.05o). The angle where
the carboxylic methyl ester group is connected with the indole ring (C8-C15-O17) was observed to be
around 112o, which is also close to the XRD value (112.04o).

ACCEPTED MANUSCRIPT
It can be concluded that the computed geometrical parameters produced a good approximation
of the structure and that they could be used as the foundation to calculate the other parameters in the
current work.
3.3. Crystal structure of the MMIC molecule
The asymmetric unit of the MMIC molecule, C11H11NO3, has one independent molecule with a
nearly planar indole residue. The crystal structure packing of the target molecule is stabilized by one
intermolecular hydrogen bond with N1 works as hydrogen bond donor while O1 works as hydrogen
bond acceptor. The distance of the interactions between N1—H1···O1 is 2.03 (1) Å and the angle is
160°. Symmetry code: −x, −y+1, −z. The atomic displacement parameters, fractional atomic
coordinates and selected data collection for the crystal are displayed in Tables T1, T2 and T3,
respectively.
3.4. Vibrational analysis
The vibrational spectral assignments were completed by recording the FT-IR and FT-Raman
spectra and the theoretically predicted wavenumbers using the density functional B3LYP/6-311++G
(d,p) method, as illustrated in Table 2. A scale factor was adopted for the computed infrared and
Raman wavenumbers of the title molecule according to Scott and Radon [26]. The RMS value between
the experimental and the predicted vibrational wavnumbers of the title molecule was calculated to be
26.4098. Figure S1 illustrates the correlation between the computed and experimental wavenumbers
with a coefficient (R2) value = 0.997. None of the predicted vibrational wavenumbers have any
imaginary frequencies, which proves that the optimised structure is located at the local lowest point on
the potential energy surface (PES). The title molecule possesses C1 point group symmetry and it is
distributed as:
Г3N-6 = 49A` (in-plane) + 23 A`` (out-of-plane)
(1)
Here "A`" represents the symmetric planar and "A``" represents the asymmetric non-planar
vibrations. Figures S2 and S3 illustrate the IR and Raman active vibrations of the title molecule,
respectively.

ACCEPTED MANUSCRIPT
Table 2. Vibrational wavenumbers obtained for the MMIC molecule at B3LYP/6-311++G(d,p) method [harmonic frequency (cm-1), IRint(Km/mol),
Raman Activity (Ǻ4/amu units)].
Experimental
Theoretical Wavenumber
Mode Nos.
TED≥10%
FT-IR
3482b
3126w
Raman
Scaled
IRInt
109.21
0.18
RamanAct
1
2
3532
3149
3102
3087
3072
3053
3026
3020
2953
2949
2899
1687
1614
1558
1520
1468
1453
1449
1442
1434
1434
1422
1415
1398
77.55
72.81
125.85
105.44
78.07
82.45
160.66
68.40
73.32
243.52
192.40
447.43
28.10
11.95
430.43
62.25
6.27
υNH (100)
υCH (99)
3
6.09
υCH (93)
4
3086vw
3048vw
3.76
υCH (99)
5
6.72
υCH (93)
6
13.69
26.59
18.82
42.75
44.86
72.39
470.40
39.67
12.56
224.35
0.07
asyυCH (81)
7
3031vw
2997w
2944w
asyυCH (92)
8
2992vw
2934w
asyυCH (98)
9
asyυCH (100)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
symυCH (100)
symυCH (92)
1784s
1746s
1713vs
1611s
1587s
1782m
1760ms
1745vs
1615w
1597ms
υOC (83)
υCC (62)
υCC (32) + βCCC (10)
υCCC (47)
υCC (42)
1456vs
44.84
11.25
8.68
βHCH (70)
16.75
16.63
17.79
15.55
2.96
βHCH (89)
βHCH (81) + γCHOH (11)
βHCH (82) + γCHOH (16)
γCHHH (48)
1434w
15.07
9.23
38.61
48.94
43.64
βHCO (41) + νCHOH (40)
βHCC (14) + νCHHH (34)
γCCCC(12) + υNC(25) + βCCC(12)
85.54
218.04
1381vs
1380vw

ACCEPTED MANUSCRIPT
+ βHNC(11)
25
26
27
28
29
1332vs
1307m
1264m
1220m
1352
1295
1275
1217
1206
44.55
130.73
12.76
17.25
48.07
υCC (11)
1309vw
1268vw
1220m
υCC (48) + υNC (17)
υOC (10) + βHCC (22) + βCCC (14)
υOC (31) + βHNC (11)
βCCC (12) + βHCC (35)
υNC(1O) + υOC (12) + βHNC (19)
+ βHCC (24)
126.93
179.23
15.44
1047.21
12.16
30
1200
50.24
8.18
υOC (10)
γCHOH(36)
+
βHCO (27)
+
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
1174m
1153s
1174
1162
1143
1131
1128
1121
1084
1024
988
66.61
70.64
38.95
0.71
38.80
23.67
7.84
3.33
3.04
8.93
11.22
3.74
6.31
110.32
0.79
0.61
0.24
4.05
2.16
0.30
1161m
βHCO (15) + γCHOH (16)
υOC (10) + γCHOH (12)
βHCH (17) + γCHOH (82)
βHCO (5O) + γCHOH (44)
υCC (13) + βHCC (64)
βHCC (40)
0.71
1096m
1039m
1010m
978m
24.49
33.31
36.38
48.09
6.42
1044w
1021s
980vw
υOC (53) + βHCC (14)
υNC(18) + υOC (47)
υOC (20) + βCNC (19)
βCCC (57)
924
905m
878w
914
0.33
884vw
808w
765w
891
1.75
τHCCH (89)
849
33.25
6.76
γCCCH (80)
812
υNC (11) + βCCC (21)
γCCCH (79) + γOCOC (13)
τHCCN (75)
815m
770vs
804
2.83
770
16.71
υOC (10) + βOCO (28) + βCOC
(11)
47
48
764
753
0.23
25.26
0.17
48.83
γCCCH (11) + γOCOC (54)

ACCEPTED MANUSCRIPT
49
50
723m
709s
729
718
14.70
10.83
18.06
0.05
υCC(23) + υOC (19) + βCNC (14)
τCCCC (57)
707m
682m
βCCC (10) + βCCN (11) + βCCO
(20)
51
52
621
607
3.89
0.07
6.12
1.21
604w
τCCCN (51) + τCCCC (10)
τHNCC (11) + τCCCN (31) +
τCCCC (37)
53
54
594s
587
557
13.09
16.44
0.01
3.21
552m
552m
βCCC (36) + βCOC (10)
βCCO (26) + βCCC (19) + βCOC
(13)
55
56
495ms
511
448
1.86
1.46
0.34
βHCC (14) + τHNCC(77) + γCHHH
(34)
464vs
71.37
υCC(13) + βOCO (10) + βCCC (11)
+ βCOC (14)
57
58
59
436
422
360
0.32
0.21
0.11
3.56
0.80
0.35
τCCCC (75)
351w
τCCCO (29) + τCCCN (38)
βCCN (18) + βCCO (15) + βCOC
(37)
60
61
62
357
289
280
15.29
14.06
2.11
0.76
2.23
7.13
298w
βOCO (10) + βCOC (55)
υ CC(24) + βCCC (12) + βOCO (11)
τCCCC (10) + τCCNC (35) +
τCNCC (11)
277vw
63
64
65
261vw
261
235
209
3.01
0.24
0.31
0.18
0.09
0.42
τHCOC (75)
βCCO (51) + βCOC (23)
υOC(10)
+
τHCOC (12)
+ τCCOC(20)
+
+
τCCNC(12)
66
67
165s
176
145
0.13
1.53
1.74
0.81
τCCCO(21) + τCNCC(13)
τHCOC (39) + τCCOC (22) +
140m

ACCEPTED MANUSCRIPT
τCCCO (13)
68
69
103vs
119
91
1.54
2.27
0.83
0.35
τHCOC (54) + τCCOC (27)
βCCO (22) + βCCC(47)
τNCCO (23) + τCCOC (20) +
τCNCC (30)
70
71
72
72
69
43
2.27
0.88
3.82
0.04
1.23
0.23
τNCCO (55) + τCCOC (26)
τCCOC (50) +τCNCC(21)
IR int-IR intensity;RamAct - Raman Activity; w-weak; vw- very weak; s-strong; vs-very strong; m-medium; br, sh- broad, shoulder, υ - stretching; υsym
symmetric stretching ; υasy- asymmetric stretching ; δ- in plane bending ; γ- out-of –plane bending ; τ- torsion.
–

ACCEPTED MANUSCRIPT
3.4.1. C–H vibrations
The heteroaromatic structure shows the presence of C–H stretching vibrations in the region of
3100–3000 cm-1, which is characteristic of such vibrations [27]. In this region, the bands are not
affected appreciably by the nature of the substituents. The C–H stretching modes usually appear with
strong Raman intensity and are highly polarised. This high polarisation might be the reason for the
absence of Raman bands in the experimental spectra. In the indole ring of the MMIC molecule, there
are four C–H bonds (C3-H9, C4-H10, C6-H11, and C7-H12), so we expected to observe four C–H
stretching, C–H in-plane and C–H out-of-plane bending vibrations. In the FT-IR spectrum of the
MMIC molecule, the weak bands at 3126 and 3086 cm-1were assigned to C–H stretching vibrations.
The theoretically computed wavenumbers for the title compound fall at 3149, 3102, 3087, and 3072
cm-1 (mode nos.2-5, respectively) with a TED contribution of about 95%, as shown in Table 2.
The C–H in-plane bending vibration is usually expected to occur in the region of 1300–1000
cm-1 and these vibrations are very useful for characterisation [27]. In the title MMIC molecule, the
medium bands at 1264 and 1220 cm-1 in the FT-IR spectrum and medium to weak bands at 1268 and
1220 cm-1 in the FT-Raman spectrum were assigned to the C–H in-plane bending modes of the C3-H9,
C4-H10, C6-H11, and C7-H12 units with a TED contribution of about 20%. The wavenumbers for
this mode at 1275, 1217, 1206, and 1200 cm-1 were assigned to C–H in-plane bending vibrations.
The C–H out-of-plane bending vibrations are normally observed as strongly coupled vibrations
and occur in the region of 1000–750 cm-1 [28]. The aromatic C–H out-of-plane bending vibrations fall
at 849, 804, 764, and 753 cm-1 (mode nos. 43, 45, 47, and 48, respectively) by the B3LYP/6-311++G
(d,p) method and they showed good agreement with the recorded FT-IR band at 815 cm-1 and the FT-
Raman bands at 808 and 765 cm-1. The computed, as well as the recorded spectral data, were found to
be very consistent with reported values [29,30]. The TED contribution is about 70% as a mixed mode
with other vibrations, as shown in Table 2.
3.4.2. O–CH3 vibrations
The vibrational wavenumbers of the methoxy groups in the MMIC molecule include a large number of
interesting interactions, such as electronic effects, intermolecular hydrogen bonding and Fermi
resonance [31]. The electronic effects, such as back donation and induction, are mainly caused by the
oxygen atom attached to the CH3 group, which alters the position of the C–H stretching and bending
modes [32,33]. The methoxy group vibrations were observed in both the IR and Raman spectra as
intense bands, with a large variation from the normal values of the methyl groups. This is due to the
electronic effect, which led to deviations from the expected values [34]. In the MMIC molecule, the
two methoxy carbon atoms lie in the same plane, which is evident from the optimised structure, as
shown in Figure 2. In the present study, the very weak bands observed in the FT-IR spectrum at 3048,

ACCEPTED MANUSCRIPT
2944 cm-1 were assigned to C18-H19, H20, and H21 (asymmetric stretching vibrations) and C23-H24,
H25, and H26 (symmetric stretching vibrations), respectively. The theoretically computed
wavenumbers for the asymmetric and symmetric stretching vibrations were at 3035, 3053, 2620, 3020,
2953 and 2949 cm-1 (mode nos.6-11) with a TED contribution of about 90%. The O–CH3 stretching
vibrational mode has been assigned at around 1040 cm-1 for anisole [35] and at 1000–100 cm-1 for
anisole and its derivatives [36]. In the MMIC molecule, the O–CH3 stretching mode appeared as a
medium strength band in the FT-IR spectrum at 1010 and 978 cm-1 and as a strong band to a very weak
band at 1021 and 980 cm-1 in the FT-Raman spectrum, showing good agreement with the computed
wavenumbers at 1028 and 988 cm-1 (mode nos. 38 and 39) and coinciding with the experimental
results, with a TED contribution of about 45%. Arslan and Algül [37] assigned the C–O–CH3 angle
bending mode to be around at 300 cm-1 for anisole, anda bending mode at 421 cm-1 for 4-methoxy
benzaldehyde was found by Campaqnaro and Wood [38]. Others [39] have assigned the C–O–CH3
bending mode in the region of 670–300 cm-1 for anisole and its derivatives, mixed with C–C–C angle
bending modes. We have assigned the predicted wavenumber at 360 cm-1 (mode no. 59) to be the C–
O–CH3 angle bending mode, which showed good agreement with the recorded FT-Raman band at 351
cm-1 with a TED contribution of 29%. The torsional mode of the O–CH3 group vibrations for anisole
has been predicted at around 100 cm-1 by some researchers [37-39]. Balafour [36] assigned this mode
at 82 cm-1, and Lakshmaiah and Rao [40] calculated these vibrations as 58 cm-1 for anisole and its
derivatives. In the MMIC molecule, these modes were calculated at 145 and 119 cm-1 and were
assigned to the O–CH3 torsional mode, showing good agreement with the observed FT-Raman spectral
data, as presented in Table 2.
3.4.3. C=O vibrations
The C=O stretching vibration typically appears to be free from other vibrations. In many
carbonyl-containing compounds, the C=O double bond has a force constant which is different from the
structural units, such as C=C, C–C, and C–H. Only the structural C=C units have force constants of
similar magnitudes to the C=O group. Carbonyl compounds show a very intense and narrow band in
the region of 1800–1600 cm-1 [41,42]. In the present study, the C15=O16 stretching vibrations were
recorded in the FT-IR and FT-Raman spectra at 1746 and 1760 cm-1, respectively, as strong bands.
The computed wavenumber for this mode of vibration was at 1687 cm-1 (mode no. 12) with a TED
contribution of 83%, showing moderate agreement with experimental and literature data [41,42].
3.4.4. Ring vibrations
The identification of C=N and C–N vibrations is a difficult task, since the mixing of several
bands is possible in the region. Silverstein et al. [41] assigned C=N stretching absorption in the region
of 1382–1266 cm-1 for aromatic amines. In benzamide, a band was observed at 1368 cm-1 and it was
assigned as C–N stretching [41]. In the present work, the FT-IR and FT-Raman bands observed at

ACCEPTED MANUSCRIPT
1307 and 978 cm-1, and 1309 and 980 cm-1, respectively, have been assigned as the C–N stretching
vibrations of the MMIC molecule. The predicted values of the C–N stretching vibrations were at 1295,
1200, and 988 cm-1 (mode nos. 26, 30, and 39). The benzene ring carbon–carbon stretching vibrations
occur in the region of 1430–1625 cm-1. In general, the bands are of variable intensities and are
observed at 1625–1590, 1575–1590, 1470–1540, 1430–1465, and 1280–1380 cm-1 from the frequency
ranges given by Varsanyi [43]. In this work, the wavenumbers computed by the B3LYP/6-311++G
(d,p) method for the MMIC molecule at 1614, 1558, 1468, 1352, 1295, 1275, 1217, 1174, 1143, 1121,
988, and 812 cm-1 (mode nos. 13, 14, 16, 25-28, 31, 33, 36, 39 and 44, respectively) were designated as
the C–C stretching vibrations. The TED corresponding to all C–C vibrations lies between 30 and 70%,
as shown in Table 2, in combination with C–H in-plane bending in this region. The in-plane
deformation vibrationsare found at higher wavenumbers than the out-of-plane vibrations. Shimanouchi
et al. [39] gave the frequency data for these vibrations for different benzene derivatives as a result of
normal coordinate analysis. The other vibrations computed by the B3LYP/6-311++G (d,p) method
showed good agreement with the recorded spectral data.
3.5. 1H and 13C NMR spectral analysis
Application of the gauge independent atomic orbitals (GIAO) [44] approach to molecular
systems is considerably more efficient when compared with ab initio self-consistent field (SCF)
calculations. The GIAO calculation procedure is superior since it exhibits faster convergence of the
calculated properties upon extension of the chosen basis set. Taking into consideration the
computational cost and the effectiveness of the calculations, the GIAO method seems to be preferable
in many aspects. Figure S4 illustrates the correlation between the computed and experimental chemical
1
shift values of the title molecule having correlation coefficients (R2) values = 0.865 and 0.990 for H
and 13C, respectively.
GIAO 1H and 13C chemical shift calculations for the MMIC molecule were computed using the
B3LYP/6-311++G (d,p) method for the gas and solution phases and the results are presented in Table
3. The signals of the aromatic protons were observed at 7.37–11.79 ppm. The hydrogen atom is the
smallest atom and it is typically localised at the periphery of the molecules. Therefore, its chemical
shift is more susceptible to intermolecular interactions in aqueous solution, compared with other
heavier atoms. Attached hydrogen atoms or nearby electron-withdrawing atoms or groups will be
subjected to reductions in shielding and their resonance will move towards a higher frequency. In
contrast, electron donating atoms or groups increase the shielding and move the resonance towards a
lower frequency. In the MMIC molecule, the observed and calculated chemical shifts for the hydrogen
atoms of methyl groups are quite low due to their attachment to electron-withdrawing oxygen atoms.
Thus, the methyl protons at C18 and C23 appeared as singlets, with three proton integrals at 3.87 and

ACCEPTED MANUSCRIPT
3.77 ppm, respectively. The observed chemical shift values for the other protons are in good agreement
with the computed ones (Table 3).
13
The range of C NMR chemical shifts for a typical organic molecule are usually expected to
be above 10-200 ppm [45,46]. This accuracy ensures reliable interpretation of spectroscopic
parameters. In the present study, the signals observed at 52.14 and 55.67 ppm in the 13C NMR
spectrum of the MMIC molecule were assigned to methoxy carbons (C18 and C23). The signals for the
aromatic carbons were observed at 102.43, 113.94, 116.77, 127.70, 133.23, and 154.44 ppm in the 13C
NMR spectrum for the title molecule, since those carbon atoms belong to the benzene ring. The indole
carbons (C7 and C8) were observed at 107.82 and 127.51 ppm, respectively. In general, the observed
chemical shift values of the carbons in the MMIC molecule are in good agreement with the calculated
values (Table 3).
1
Table 3. The experimental and theoretical 13C and H NMR chemical shift values of the MMIC
molecule.
13C
1H
δexp.
δcalc.
δexp.
δcalc.
Atom
Atom
DMSO
Solution
phase
DMSO
Solution
phase
7.64
7.34
7.44
7.25
8.57
3.98
3.78
3.98
4.08
3.81
3.81
Gas phase
Gas phase
C1
C2
127.70
133.23
116.77
113.94
154.44
102.43
107.82
127.51
162.17
52.14
135.71
137.84
114.16
111.85
161.84
113.35
111.58
133.82
168.98
53.50
135.16
138.03
115.49
112.35
161.97
113.00
111.23
133.82
169.82
53.93
H9
7.37
6.94
7.11
7.07
11.79
3.87
3.87
3.87
3.77
3.77
3.77
7.43
7.15
7.42
7.17
8.31
3.95
3.62
3.95
4.01
3.71
3.71
H10
H11
H12
H13
H19
H20
H21
H24
H25
H26
C3
C4
C5
C6
C7
C8
C15
C18
C23
55.67
55.15
55.49
3.6. UV-visible frontier molecular orbital analysis
The most common types of electronic transitions that occur in organic molecules are π → π*,
n→ π* and π*(acceptor) → π (donor) [47]. The Gausssum 3.0 program [48] was used to calculate
group contributions to the molecular orbitals (HOMO and LUMO) and prepare the density of the state
(DOS) spectrum, as shown in Figures 3 and S5, respectively. The DOS spectrum was calculated by
convoluting the molecular orbital information with a GAUSSIAN curve of the unit cell. The recorded
UV-vis absorption spectrum of the MMIC molecule was recorded in acetonitrile, along with the
theoretical simulated spectrum as shown in Figure S6. In order to understand the nature of the
electronic transitions, the positions of the experimental absorption peaks, the calculated absorption

ACCEPTED MANUSCRIPT
peak (λmax), the vertical excitation energies, and the oscillator strength (f) were calculated and are
presented in Table 4.
LUMO
4.08 eV
HOMO
Figure 3. HOMO-LUMO representation of the MMIC molecule.
Table 4. Calculated and experimental absorption wavelengths, energies and oscillator strengths of the
MMIC using TD-DFT method at the B3LYP/6-311++G (d,p).
Excitation
Gas Phase
Acetonitrile Phase
Wavelength
(nm)
Experimental Assignments
In solvent
major
contribution
(≥10%)
CI
Wavelength Oscillator
CI
Oscillator
Strength
expansion
coefficient
(nm)
Strength
expansion
coefficient
Excited state 1
Excited state 2
H→L (97%)
0.69760
344.68
288.05
0.0445
0.4696
0.69961
349.77
295.24
0.0594
0.5926
296
247
n→π*
n→π*
H-1→L
(93%)
0.68266
0.15527
0.69072
0.12666
Excited state 3
H→L+2
(96%)
-0.10932
0.67908
0.69274
248.79
0.0002
246.33
0.0253
228
n→π*
The first transition was from the O(22)CH3 to the carboxylate group C(O)OCH3 and the other
two transitions took place in the indole ring N14 to 8C–7C and 2C–1C. Table 4 shows the oscillator
strengths, which indicate the intensity of these transitions. The transitions in the gas phase are 0.0445,
0.4696, and 0.0002for O(22)CH3–C(O)OCH3, 8C–7C and 2C–1C, respectively. In the acetonitrile
phase, the same transitions are 0.0594, 0.592, and 0.025, respectively. These oscillator strength values
showed that only the first two transitions will be present in the experimental and theoretical UV-vis

ACCEPTED MANUSCRIPT
spectra. This is exactly what was observed in both the experimental and theoretical spectra in
acetonitrile, at wavelengths 295 and 246 nm in the experimental spectrum and at 349 and 295 nm in
the theoretical spectrum of the MMIC molecule. The corresponding values in the gas phase are at 344
and 288 nm, respectively. The surface of the frontier molecular orbital was described in order to
understand the bonding scheme of the MMIC molecule. Four important molecular orbitals were
examined i.e. the highest (HOMO) and the second highest occupied (HOMO-1) MOs, as well as the
lowest (LUMO) and the second lowest unoccupied (LUMO +1) MOs. The predicted HOMO-LUMO
molecular orbitals for the MMIC molecule are shown in Figure 3. The HOMO is located over the ether
group, the HOMO→LUMO transitions denote that the electron density will transfer from the ether
group to the ring system. The energy gap between the HOMO and LUMO of the title molecule in the
gas phase is 4.083 eV. The HOMO–LUMO contribution for the first transition is 93%, which is the
reason for the very high stabilisation energy and oscillator value for this transition. The absorption
wavelength values are almost equal in the gas phase and in acetonitrile, which indicates that the
influence of the solvent in the optical activity of the molecule is negligible.
Chemical hardness is a good indicator of the chemical stability. The chemical hardness of the
title molecule was found to be around 2.0 eV and this value is slightly decreased going from the gas
phase to the solvent phase using either the B3LYPor theB3PW9 method. The chemical softness was
around 0.5 eV, indicating that the chemical hardness is very high and hence, the compound is
chemically stable. Similarly, the calculated electronegativity using the B3LYP method was observed to
be 3.7 eV in the gas phase and 3.8 eV in ethanol phase. Electronegativity is a measure of the attraction
of an atom for electrons in a covalent bond. When two different atoms are covalently bonded, the
shared electrons will be more strongly attracted to the atom with greater electronegativity.
The electrophilicity index is a measure of the energy lowering due to the maximal electron flow
between the donor (HOMO) and the acceptor (LUMO). Table 5 shows that the electrophilicity index
of the MMIC molecule using the B3LYP method was 3.32 eV in the gas phase and 3.62 eV in ethanol.
These are moderate values, and ensure strong energy transformation between the HOMO and LUMO
[49]. The dipole moment in a molecule is another important electronic property. When a molecule has
a large dipole moment, intermolecular interactions are very strong. The calculated dipole moment
value for the title compound is 0.93 D in the gas phase and 1.39 D (using B3LYP) in the solvent phase.
These are comparatively high, indicating that the MMIC molecule has strong intermolecular
interactions.

ACCEPTED MANUSCRIPT
Table 5. HOMO, LUMO, Kubo gap, global electronegativity, global hardness and softness, global
electrophilicity index, and dipole moment of the MMIC molecule.
Parameters
EHOMO (eV)
Gas
Ethanol
B3LYP/ 6-
B3LYP/ 6-
B3PW91/ 6- M06-2X/ 6-
311G++ (d,p) 311G++ (d,p) 311G++(d,p) 311G++(d,p)
5.722
5.858
1.804
4.054
5.7692
1.8285
3.9406
6.9956
0.6576
6.3379
ELUMO (eV)
ꢀEHOMO - ELUMO gap (eV)
1.639
4.083
Chemical hardness (η)
Global softness(σ)
2.041
0.489
3.680
2.0271
0.493
3.831
1.9703
0.5075
3.7989
3.1689
0.6311
3.8266
Electronegativity(χ)
Electrophilicity index(ω)
Dipole moment (ꢁ)
3.318
3.621
3.6622
0.9277
2.3105
0.7434
0.9333
1.3852
3.7. Molecular electrostatic potential (MEP) analysis
The MEP is used to analyse the reactivity of molecules. In most MEP diagrams, electrophilic
attack is indicated as red and nucleophilic attack is represented in blue. The MEP diagram also
displays the molecular shape, size, and negative, positive and neutral electrostatic potential via colour
grading and helps researchers to analyse the physicochemical properties of molecules [50]. The
different colours in Figure S7 represent different values of electrostatic potential at the surface of the
MMIC compound. The electrostatic potential increases in the order red<orange<yellow<green<blue.
The colour code of the maps was found to be in the range of -0.454 a.u (deepest red) to 0.454 a.u
(deepest blue), where the red colour indicates the strongest repulsion and the blue colour indicates the
strongest attraction. Regions of negative V(r) are usually associated with the lone pair of an
electronegative atom. As seen in Figure S7, negative electrostatic potential is present over the oxygen
atoms of the C=O and OCH3 groups and a region with positive electrostatic potential is present over
the hydrogen atoms and ring system. The high proportion of the light green colour probably represents
the halfway point between the two extremes, red and blue. This analysis provides information about
regions where the compound can be subject to intermolecular interactions.
3.8. Hyperpolarisabilities
Properties such as polarisability and hyperpolarisability were calculated for the title molecule
in the gas phase. An isolated molecule of MMIC was taken and the NLO properties were studied using
the DFT technique in order to show any indication of NLO character according to its calculated
polarisability, hyperpolarisability and dipole moment. The hyperpolarisability and dipole moment
values of urea as studied by Cassidy et al. [51] were considered as a reference.

ACCEPTED MANUSCRIPT
Hyperpolarisabilities are very sensitive to the employed basis sets and levels of theoretical
approach [52-54]. Thus, the electron correlation can change the value of hyperpolarisability. It is
already established that the molecular hyperpolarisability and mechanical stabilities are enhanced in
organic molecules containing O–H and N–H groups, which are involved in the hydrogen bond
interactions [55]. Urea is one of the prototypical molecules used in the study of the nonlinear optical
(NLO) properties of molecular systems. Therefore, it has frequently been used as a threshold value for
comparative purposes. The highest values of the dipole moment were found to be 0.8352 and 0.8064 D
along µx computed from B3LYP and B3PW91 methods, respectively, at 6-311++G (d,p) basis set. For
the Y and Z directions, the values are equal to 0.4382 and 0.4586 D, and 0.0017 and 0.0005 D using
the B3LYP and B3PW91 methods, respectively. However, the dipole moment calculated by the M06-
2X/6-311++G (d,p) method is much lower than that obtained from the other two methods, as shown in
Table 6. The first order hyperpolarisability total value for the MMIC molecule calculated using the
B3LYP and B3PW91 methods with the 6-311++G (d,p) basis set are 11.146×10-30 and 11.124×10-30
esu, respectively, whereas the value obtained with M06-2X/6-311++G (d,p) is 9.443×10-30 esu, as
illustrated in Table 7. The first order hyperpolarisability of the MMIC molecule is about 30 (using
B3LYP and B3PW91) and 25 (using M06-2X) times greater than that of urea (0.3728 ×10-30 esu). This
large hyperpolarisability value of the title molecule indicates that it has considerable NLO optical
properties. Therefore, the title molecule can be subjected to future studies to investigate its NLO
properties.
Table 6. The calculated electric dipole moment (Debye components for the MMIC molecule) by
B3LYP, B3PW91 and M06-2X methods at 6-311++G (d,p) basis set.
B3LYP/6-311++G (d,p) B3PW91/6-311++G (d,p) M06-2X/6-311++G (d,p)
Parameter
µx
µy
µz
µ
0.8352
0.4382
0.0017
0.9432
0.8064
0.4586
0.0005
0.9277
0.4942
0.5553
0.0006
0.7434

ACCEPTED MANUSCRIPT
Table 7. Calculated β components and βtot (×10-30 esu) value of the MMIC molecule using B3LYP,
B3PW91 and M06-2X methods at 6-311++G (d,p) basis set.
β components
B3LYP/6-311++G (d,p)
a.u
B3PW91/6-311++G (d,p) M06-2X/6-311++G (d,p)
a.u a.u
βxxx
βxxy
βxyy
βyyy
βxxz
βxyz
βyyz
βxzz
βyzz
βzzz
βtot
-1356.6407
97.7461932
20.7961061
25.8027336
0.0367924
-1345.1045
-1133.9397
90.4670
10.1928
25.1735
0.03341
0.01567
-0.0129
40.1164
27.4046
0.07404
92.7165419
17.6896171
27.0419735
0.0341322
0.0162696
0.0155299
-0.015457
-0.0148109
49.625379
56.2656156
41.5670401
0.0917631
39.0049653
0.082628 5
11.124×10-30 esu
11.146×10-30 esu
9.443×10-30 esu
3.9. Natural bond orbital (NBO) analysis
NBO analysis is an effective tool for the chemical interpretation of hyperconjugative
interactions and electron density transfer from the filled lone pair orbital of one subsystem to the
vacant orbital of another subsystem. DFT calculations are used to analyse the various second order
interactions between the filled orbitals and vacant orbitals of a system, giving a measure of the
delocalisation and hyperconjugation [56,57]. The hyperconjugative interaction energy can be obtained
from the second order perturbation method as:
(2)
where <σ|F|σ>2 or Fij2 is the Fock matrix element between the i and j NBO orbitals,
energies of and σ* NBOs, and σ is the population of the donor orbital [58].The NBO analysis
εσ and εσ* are the
σ
n
σ
shows the various possible donors and acceptors in the molecule with their occupancy value in each
position. Similarly, the various possible transitions among these donors and acceptors are provided.
The intramolecular interaction is formed by orbital overlap between bonding C–C, C–O and C–H to
anti-bonding C–C, C–O and C–H, which leads to intramolecular charge transfer (ICT) to stabilise the
molecule. The E(2) value in Table 8 shows that the larger the E(2) values, the more intense the
interactions between the electron donors and acceptor groups i.e. the greater the electron donating
tendency from electron donors to electron acceptors, the greater the extent of conjugation in the whole
system.

ACCEPTED MANUSCRIPT
The electron density of the conjugated systems and of the double bond of the MMIC molecule
is (~1.6 to 1.9 e), which denotes the strong delocalisation in the molecule. For example, the
intramolecular hyperconjugation interaction of π (C3-C4) distributed to π*(C1-C2), (C1-C6) has
stabilisation energies of 17.11 and 18.30 KJ/mol; and the C5-C6 distributed to the π* (C1-C2 and C3-
C4) has stabilisation energies of 18.77 and 18.54 KJ/mol. In the same way, for the π→π* transition
observed in the indole ring C7-C8, energy is distributed to C1-C2 and C15-O16 with stabilisation
energies of 22.24 and 19.08 KJ/mol. The other transitions are shown in Table 8.
The magnitudes of the charge transfer from the lone pair of the nitrogen atom LPN14 to
various C–C bonds are as follows: C7-C18 and C1-C2 (n→π*, 37.03 and 35.94 KJ/mol, respectively),
LPO16 to C15-O17 and C8-C15 (n→π*, 31.49 and 16.33 KJ/mol, respectively), LPO17 to C13-O14
(n→π*46.17 kJ/mol) and O22 to C5-C6 (n→π* 25.65 KJ/mol). Transitions with higher stabilisation
energies are correlated with the UV-visible transitions.

ACCEPTED MANUSCRIPT
Table 8. Second order perturbation theory of the Fock matrix NBO analysis of the MMIC molecule.
E(2)
E(j)-E(i)
(a.u)
1.24
1.23
1.11
1.05
0.27
0.28
0.27
1.23
1.23
1.05
1.24
1.23
1.24
1.17
1.30
1.39
1.38
1.25
1.16
0.29
0.29
1.06
1.07
1.29
Donor (i)
Type
ED/e
Acceptor (j)
Type
ED/e
F(i,j) (a.u)
(Kj/Mol)
3.01
C1-C2
C1-C2
C1-C2
C1-C2
C1-C2
C1-C2
C1-C2
C1-C6
C1-C6
C1-C6
C1-C7
C1-C7
C2-C3
C2-C3
C2-C3
C2-N14
C2-N14
C2-N14
C3-C4
C3-C4
C3-C4
C3-H9
C3-H9
C4-C5
σ
σ
σ
σ
π
π
π
σ
σ
σ
σ
σ
σ
σ
σ
σ
σ
σ
σ
π
π
σ
σ
σ
1.95891
1.95891
1.95891
1.95891
1.56457
1.56457
1.56457
1.97339
1.97339
1.97339
1.97033
1.97339
1.97613
1.97613
1.97613
1.98535
1.98535
1.98535
1.97245
1.75388
1.75388
1.97908
1.97908
1.97779
C1-C6
C2-C3
C7-H12
H13-N14
C3-C4
C5-C6
C7-C8
C1-C2
C1-C7
C5-O22
C1-C6
C2-C3
C1-C2
C2-N14
C3-C4
C1-C6
C2-C3
C8-C15
C2-N14
C1-C2
C5-C6
C1-C2
C4-C5
C3-C4
σ*
σ*
σ*
σ*
π*
π*
π*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
π*
π*
σ*
σ*
σ*
0.01948
0.02138
0.01123
0.01806
0.35245
0.34778
0.33971
0.02864
0.01815
0.02944
0.01948
0.02138
0.02864
0.02381
0.01164
0.01948
0.02138
0.05994
0.02381
0.51136
0.34778
0.02864
0.02927
0.01164
0.055
0.065
0.055
0.059
0.067
0.065
0.066
0.058
0.061
0.054
0.063
0.060
0.066
0.047
0.054
0.050
0.050
0.051
0.074
0.067
0.067
0.059
0.057
0.054
4.26
3.44
4.15
20.40
18.34
19.24
3.38
3.81
3.43
3.93
3.70
4.35
2.33
2.81
2.26
2.23
2.52
5.96
17.11
18.30
4.13
3.77
2.85

ACCEPTED MANUSCRIPT
C4-C5
C4-H10
C4-H10
C5-C6
σ
σ
σ
σ
σ
π
π
σ
σ
σ
σ
σ
π
π
σ
σ
σ
σ
σ
σ
σ
π
σ
σ
σ
σ
σ
1.97779
1.97650
1.97650
1.97197
1.97197
1.69983
1.69983
1.99133
1.99133
1.97661
1.97355
1.97355
1.79173
1.79173
1.98149
1.98149
1.98248
1.97570
1.97570
1.98902
1.99522
1.98245
1.99277
1.99162
1.99462
1.99218
1.99462
C5-C6
C2-C3
σ*
σ*
σ*
σ*
σ*
π*
π*
σ*
σ*
σ*
σ*
σ*
π*
π*
σ*
σ*
σ*
σ*
σ*
σ*
σ*
π*
σ*
σ*
σ*
σ*
σ*
0.01949
0.02138
0.01949
0.02927
0.02927
0.02864
0.35245
0.01164
0.01948
0.02927
0.01948
0.01806
0.29065
0.51136
0.02103
0.02864
0.02138
0.01535
0.01494
0.01494
0.05994
0.33971
0.02103
0.05994
0.01535
0.09692
0.01535
4.07
3.47
3.85
3.84
4.41
18.77
18.54
1.02
1.42
4.65
5.39
3.32
22.24
16.08
3.17
2.07
4.40
3.77
3.47
1.79
2.09
4.76
1.92
2.32
0.54
2.80
0.54
1.28
1.10
1.11
1.24
1.24
0.28
0.28
1.47
1.47
1.05
1.29
1.10
0.27
0.29
0.98
1.07
1.37
0.96
1.29
1.27
1.52
0.42
1.37
1.27
0.79
0.89
0.79
0.065
0.055
0.058
0.062
0.066
0.069
0.065
0.035
0.041
0.065
0.075
0.054
0.070
0.066
0.050
0.042
0.069
0.054
0.060
0.043
0.051
0.043
0.046
0.049
0.019
0.046
0.019
C5-C6
C4-C5
C5-C6
C4-C5
C5-C6
C1-C2
C5-C6
C3-C4
C5-O22
C5-O22
C6-H11
C7-C8
C3-C4
C1-C6
C4-C5
C1-C6
C7-C8
H13-N14
C15-O16
C1-C2
C7-C8
C7-C8
C7-H12
C7-H12
C8-N14
C8-C15
C8-C15
H13-N14
C15-O16
C15-O16
C15-O17
O17-C18
C18-H19
C18-H20
C18-H21
C8-N14
C1-C2
C2-C3
C17-C18
C7-C8
C7-C8
C8-C15
C7-C8
C8-N14
C8-C15
O17-C18
C15-O17
O17-C18

ACCEPTED MANUSCRIPT
O22-C23
C23-H24
N14
σ
1.99335
1.99083
1.62108
1.62108
1.98023
1.85113
1.85113
1.96296
1.79555
1.96303
1.85531
C5-C6
C5-O22
C7-C8
σ*
σ*
σ*
σ*
σ*
π*
π*
σ*
π*
σ*
π*
0.01949
0.02944
0.01494
0.02864
0.05994
0.09692
0.05994
0.01911
0.29065
0.02927
0.34778
2.40
3.53
1.41
0.89
0.29
0.29
1.15
0.63
0.72
1.17
0.33
1.08
0.34
0.052
0.050
0.093
0.094
0.044
0.128
0.099
0.085
0.113
1.08
σ
LP(1)
LP(1)
LP(1)
LP(2)
LP(2)
LP(1)
LP(2)
LP(1)
LP(2)
37.03
35.94
2.09
N14
C1-C2
O16
C8-C15
C15-O17
C8-C15
C15-O16
C15-O16
C4-C5
O16
31.49
16.33
7.62
O16
O17
O17
46.17
6.75
O22
O22
C5-C6
25.65
0.089

ACCEPTED MANUSCRIPT
4. Conclusions
A complete vibrational analysis of methyl 5-methoxy-1H-indole-2-carboxylate (MMIC) was
carried out using various DFT methods with the 6-311G++(d,p) basis set. The computed geometrical
parameters produced a good approximation and they were used as a foundation to calculate the other
parameters in the current investigation. The FT-IR and FT-Raman spectra of the MMIC molecule were
recorded and the observed wavenumbers were found to be well consistent with the computed ones.
The TED contribution was about 70% as a mixed mode with other vibrations.
The absorption wavelength values in the UV study of the title molecule are almost equal in the
gas and liquid phases, indicating that the influence of the solvent in the optical activity of the molecule
is negligible. The calculated hyperpolarisability values of the MMIC molecule are higher than those of
the reference NLO compound (urea) and hence MMIC can be considered as a new NLO organic
material. The results of the current investigation might support the development of new bioactive
indole-bearing molecules.
Supplementary Information
Figures S1-S7 as well as the X-ray data Tables (T1-T3) are given in the supporting
information.
Acknowledgements
The authors acknowledge gratefully for the Quantum Computational Research Lab facilities
provided by the Administration of St. Joseph's college of Arts and Science (Autonomous), Cuddalore,
Tamilnadu, India, for all the computational works.The authors would like to extend their sincere
appreciation to the Deanship of Scientific Research at King Saud University for its funding of this
research through the Research Group Project no. RGP-196.
References
[1] M. Ambriz-Tututi, H.I. Rocha-González, S.L. Cruz, V. Granados-Soto, Melatonin: a hormone
that modulates pain, Life Sci. 84 (15) (2009) 489–498.
[2] J.J. Lu, L. Fu, Z. Tang, C. Zhang, L. Qin, J. Wang, Z. Yu, D. Shi, X. Xiao, F. Xie, W.
Huang, W. Deng, Melatonin inhibits AP-2β/hTERT, NF-κB/COX-2 and Akt/ERK and
activates caspase/Cyto C signaling to enhance the antitumor activity of berberine in lung cancer
cells, Oncotarget 7 (3) (2016) 2985–3001.
[3] G. Tahan, R. Gramignoli, F. Marongiu, S. Aktolga, A. Cetinkaya, V. Tahan, K. Dorko,
Melatonin expresses powerful anti-inflammatory and antioxidant activities resulting in
complete improvement of acetic acid-induced colitis in rats, Dig. Dis. Sci
720.
. 56 (3) (2011): 715–
[4] R.J. Reiter, D.X. Tan, J.C. Mayo, R.M. Sainz, J. Leon, Z. Czarnocki, Melatonin as an
antioxidant: biochemical mechanisms and pathophysiological implications in humans, Acta
Biochim. Pol. 50 (4) (2003) 1129–1146.
[5] V. Csernus, B. Mess, Biorhythms and pineal gland, Neuroendocrinol. Lett. 24 (6) (2003)
404–411.

ACCEPTED MANUSCRIPT
[6] O. Nosjean, M. Ferro, F. Coge, P. Beauverger, J.-M. Henlin, F. Lefoulon, J.-L. Fauchere, P.
Delagrange, E. Canet, J.A. Boutin, Identification of the melatonin binding site MT3 as the
quinine reductase 2, J. Biol. Chem. 275.(40) (2000) 31311–31317.
[7] D.S. Chemla, J. Zyss, Nonlinear optical properties of organic molecules and crystals,
Academic Press, New York, NY, USA, 1987.
[8] B.B. Ivanova, M. Spiteller, Possible application of the organic barbiturates as NLO materials,
Crys. Growth Des. 10 (6) (2010) 2470–2474.
[9] T. Pal, T. Kar, G.L. Bocelli, G. Rigi, Synthesis, growth, and characterization of L-arginine
acetate crystal: a potential NLO material, Crys. Growth Des. 3 (1) (2003) 13–16.
[10]
M.I. Attia, P.A. Witt-Enderby, J. Julius, Synthesis and pharmacological evaluation of
pentacyclic 6a,7-dihydrodiindole and 2,3-dihydrodiindole derivatives as novel melatoninergic
ligands, Bioorg. Med. Chem. 16 (16) (2008) 7654–7661.
[11]
C. Markl, M.I. Attia, J. Julius, S. Sethi, P.A. Witt-Enderby, D.P. Zlotos, Synthesis and
pharmacological evaluation of 1,2,3,4-tetrahydropyrazino [1,2-a]indole and 2-
[(phenylmethylamino)methyl]-1H-indole analogues as novel melatoninergic ligands, Bioorg.
Med. Chem. 17 (13) (2009) 4583–4594.
[12]
C. Markl, W.P. Clafshenkel, M.I. Attia, S. Sethi, P.A. Witt-Enderby, D.P. Zlotos, N-
Acetyl-5-arylalkoxytryptamine analogs: Probing the melatonin receptors for MT1-selectivity,
Arch. Pharm. Chem. Life Sci. 344 (10) (2011) 666–674.
[13]
D. Coowar, J. Bouissac, M. Hanbali, M. Paschaki, E. Mohier, B. Luu, Effects of indole
fatty alcohols on the differentiation of neural stem cell derived neurospheres, J. Med. Chem. 47
(25) (2004) 6270–6282.
[14]
[15]
[16]
Bruker. APEX2, SAINT and SADABS. Bruker AXS Inc., Madison, WI, USA, 2009.
G.M. Sheldrick, A short history of SHELX, Acta Cryst. A 64 (1) (2008) 112–122.
A.L. Spek, Structure validation in chemical crystallography, Acta Cryst. D: Biol. Cryst.
65 (2) (2009) 148–155.
[17]
G.A. Petersson, M.A. Al-Laham, A complete basis set model chemistry. II. Open‐shell
systems and the total energies of the first‐row atoms, J. Chem. Phys. 94 (9) (1991) 6081–6090.
[18]
G.A. Petersson, A. Bennet, T.G. Tensfeld, M.A. Al-Laham, W.A. Shirley, J. Mantzaris,
A complete basis set model chemistry. I. The total energies of closed‐shell atoms and hydrides
of the first‐row elements, J. Chem. Phys. 89 (4) (1988) 2193–2218.
[19]
M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P.
Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T.
Vreven, J.A. Montgomery, Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C.
Burant, S.S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B.
Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J.
Austin, R. Cammi, C. Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski,
G.A. Voth, P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian-09, Revision A.02, Gaussian, Inc., Wallingford
CT, 2009.
[20]
M.H. Jamroz, Vibrational energy distribution analysis VEDA 4, Warsaw, 2004.