Structural, spectroscopic, electronic, nonlinear optical and thermodynamic properties of a synthesized Schiff base compound: A combined experimental and theoretical approach

Article abstract of DOI:10.1016/j.molstruc.2017.01.089

A Schiff base compound, 2-[(1H-benzimidazol-2-ylimino)methyl]-4-bromophenol (BISB), was synthesized and its spectroscopic characterization was performed using experimental methods such as FT-IR, Raman, proton and carbon-13 NMR chemical shifts and UV–Vis. spectroscopies. Density functional theory (DFT/B3LYP/6-311G(d,p)) computations were used to investigate the optimized molecular geometry, conformational forms, harmonic vibrational wavenumbers, NMR chemical shifts, UV–Vis. spectroscopic parameters, natural bond orbital (NBO) analysis, HOMO-LUMO energies, nonlinear optical (NLO) properties, molecular electrostatic potential (MEP) map, atomic charges and thermodynamic properties of the BISB molecule. The assignments of vibrational modes were performed by means of potential energy distribution (PED) using VEDA4 program. The NBO analysis was used to investigate intramolecular hyrogen bonding (O[sbnd]H?N), bond species, hyperconjugation interactions and intramolecular charge transfers (ICTs). Considering the computed HOMO and LUMO energies, the quantum molecular descriptors such as ionization potential (I), electron affinity (A), chemical hardness (η), chemical softness (ζ), electronegativity (χ), chemical potential (μ) and electrophilicity index (ω) parameters were investigated for the BISB molecule. DFT computations were also performed to determine the dipole moment (μ), the mean polarizability (α), the anisotropy of the polarizability (Δα) and the first hyperpolarizability (β₀) values. The recorded experimental spectroscopic results are in a good harmony with the computed data.

Full text of DOI:10.1016/j.molstruc.2017.01.089

Accepted Manuscript
Structural, spectroscopic, electronic, nonlinear optical and thermodynamic properties
of a synthesized Schiff base compound: A combined experimental and theoretical
approach
Halil Gökce, Nuri Öztürk, Mehmet Kazıcı, Çiğdem Yörür Göreci, Serap Güneş
PII:
S0022-2860(17)30132-1
10.1016/j.molstruc.2017.01.089
MOLSTR 23394
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 26 December 2016
Revised Date: 31 January 2017
Accepted Date: 31 January 2017
Please cite this article as: H. Gökce, N. Öztürk, M. Kazıcı, E. Yörür Göreci, S. Güneş, Structural,
spectroscopic, electronic, nonlinear optical and thermodynamic properties of a synthesized Schiff base
compound: A combined experimental and theoretical approach, Journal of Molecular Structure (2017),
doi: 10.1016/j.molstruc.2017.01.089.
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Graphical Abstract

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Structural, Spectroscopic, Electronic, Nonlinear Optical and Thermodynamic Properties of a
Synthesized Schiff Base Compound: A Combined Experimental and Theoretical Approach
Halil Gökce1*, Nuri Öztürk2, Mehmet Kazıcı3,4, Çiğdem Yörür Göreci5, Serap Güneş3
1 Vocational School of Health Services, Giresun University, 28100, Giresun, Turkey
2 Dereli Vocational School, Giresun University, 28950, Giresun, Turkey
3 Yıldız Technical University, Faculty of Arts and Science, Department of Physics, Davutpasa Campus, 34210, Esenler,
Istanbul, Turkey
4 Siirt University, Faculty of Arts and Science, Department of Physics, 56100, Siirt, Turkey
5
Yıldız Technical University, Faculty of Arts and Science, Department of Chemistry, Davutpasa Campus, 34210,
Esenler, Istanbul, Turkey
ASchiff base compound, 2-[(1H-benzimidazol-2-ylimino)methyl]-4-bromophenol (BISB), was
synthesized and its spectroscopic characterizationwas performed using experimental methodssuch
as FT-IR, Raman, proton and carbon-13 NMR chemical shifts and UV-Vis. spectroscopies.Density
functional theory (DFT/B3LYP/6-311G(d,p)) computations were used to investigatethe optimized
molecular geometry, conformational forms, harmonic vibrational wavenumbers, NMR chemical
shifts, UV-Vis. spectroscopic parameters, natural bond orbital (NBO) analysis, HOMO-LUMO
energies, nonlinear optical (NLO) properties, molecular electrostatic potential (MEP) map, atomic
charges and thermodynamic properties of the BISB molecule. The assignments of vibrational
modes wereperformed by means of potential energy distribution (PED) using VEDA4 program. The
NBO analysis was used to investigate intramolecular hyrogen bonding (O-H...N), bond species,
hyperconjugation interactions and intramolecular charge transfers (ICTs). Considering the
computed HOMO and LUMO energies, the quantum molecular descriptors such as ionization
potential (I), electron affinity (A), chemical hardness (η), chemical softness (ζ), electronegativity
(χ), chemical potential (ꢀ) and electrophilicity index ( ) parameterswere investigated for the BISB
ω
molecule. DFT computations were also performed to determine the dipole moment (µ), the mean
polarizability (α), the anisotropy of the polarizability (∆α) and the first hyperpolarizability (β0)
values. The recorded experimental spectroscopic results are in a good harmony with the computed
data.
Keywords: Vibrational spectroscopy, NMR chemical shifts, Electronic properties, DFT
computations, NLO analysis, Thermodynamic properties
* Corresponding Author E-mail: halil.gokce@giresun.edu.tr, halilgokce.hg@gmail.com
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1. Introduction
Benzimidazoles which are members of heterocyclic compoundsconsist of the combination of
benzene ring and the imidazole ring having nitrogen heteroatom.The benzimidazoles also have
special significance due to their molecular arrangement with heteroaromatic and homoaromatic
parts. The different substitutions on rings and their derivatives provide additional features such as
functionality andenable easy modification of the electronic characteristics [1].Benzimidazole and its
derivatives have important functions with many pharmacological and biological activities such as
antiviral, antidiabetic and antitubercular, anticancer, antimicrobial, antioxidant, anti-hepatitis-C-
virus, antihistaminic, antiallergic etc. [2-6].
Also, Schiff bases known as azomethines or imines are also a crucialclass of organic
compounds because of their applications in many fields including biological, inorganic and physical
applications [7]. Properties of the benzimidazole molecule with Schiff baseswhen assembled in a
molecule skeleton, the structure characteristics are carried to a higher level [8,9].
In this study, we present molecular properties such as vibrational spectra (FT-IR and Raman),
proton and carbon-13 NMR chemical shifts, UV-Vis. spectral parameters, molecular geometric
parameters, HOMO and LUMO peroperties, quantum molecular descriptors, atomic charges, NBO
analysis, NLO roperties, MEP surface and thermodynamic properties of 2-[(1H-benzimidazol-2-
yl)iminomethyl]-4-bromophenol (BISB) molecule. Detailed analyses of structural, spectroscopic,
magnetic, electronic, optical and thetmodynamic propertiesof the BISB molecule are not available
in the literature. The quantum chemical investigations were performed by means of DFT/B3LYP
method with the 6-311G(d,p) basis set, for the first time. The quantum chemical computations have
been widely used to determine the structural, spectroscopic, magnetic, electronic, optical and
thermodynamic properties of molecular systems, without experimental data. Additionally, the
quantum chemical computations provides a powerful support for experimental studies.
2. Experimental
The condensation reaction was performed under the inert atmosphere of nitrogen. Ethanol was
purified and dried according to standard procedure. 5-Bromo-2-hydroxybenzaldehyde and 2-
Aminobenzimidazole (Merck) were used as purchased.
2.1.Physical Measurements
Melting points were obtained with a Gallenkamp Melting point apparatus in open capillaries.
The absorption spectra were recorded on an Agilent 8453 UV-Vis spectrometer that is the spectral
bandwidth of 1 nm. The UV-Vis. spectrum of 2-[(1H-benzimidazol-2-ylimino)methyl]-4-
bromophenol was recorded in chloroformusing quartzcell 1 cm.
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The IR (ATR) spectrum was recorded at the room temperature on a Perkin Elmer Spectrum
13
One Bv 5.0 spectrophotometer at the interval of 4000-400 cm-1a resolution of 4 cm-1.1H and C
NMR chemical shifts were recorded on a Bruker 500 MHz (CDCl3) spectrometer. Chemical shifts
(ppm) were referenced to the internal standard tetramethylsilane (TMS). Mass spectra (LC-MS)
were determined on a Agilent 1200 Infinity HPLC and Agilent 6460 Jet-Stream TripleQuad
spectrometer (350oC and 11L/min). Raman spectrum was measured with the Bruker Optics FT-
Raman Scope III System (an air-cooled 1064 nm Nd:YAG laserexcitation source) in the region of
4000-100 cm-1. Resolution and accumulation (scan number) for Raman spectrum are 4 cm-1 and 100
scans, respectively. The reactions were monitored by thin layer chromatography (TLC).
2.2. Synthesis of Schiff Base Ligand (BISB)
2-[(1H-benzimidazol-2-ylimino)methyl]-4-bromophenol
[10],
5-bromo-2-
hydroxybenzaldehyde (0.201 g, 1 mmol) was added to the 2-aminobenzimidazole (0.133 g, 1
mmol) in 10 mL absolute ethanol. Reaction mixture was stirred at reflux temperature for 6 h, under
nitrogen atmosphere. The resulting solution was reduced to approximately 1/2 of its volume by
rotary evaporation. The product precipitate was in pale orange solid form. The solid was filtered off,
washed with ethanol and recrystallized from chloroform/ hexane (1:1) mixture and dried under
vacuum. Yield: 86%. Orange crystals. m.p. 248°C; UV-vis: λmax (nm)= 386. IR (ATR-IR): ν(cm-1):
1
3317, 3068, 1620. H NMR (DMSO-d6, 500 MHz): δ (ppm)= 12.81 (s, 1H), 12.03 (s, 1H), 9.63 (s,
1H), 8.09-7.01 (m, 7H). LC-MS: m/z = 316 [M]+ (C14H10BrN3O).
HO
HO
N
O
H
N
dry Ethanol
reflux
NH2
N
+
N
H
N
H
Br
Br
BISB
Scheme 1. Preparation of Schiff base BISB.
3. Computational Details
DFT computations of molecular geometry, IR wavenumbers, proton and carbon-13 NMR
chemical shifts (in vacuum and DMSO), UV-Vis. spectroscopic parameters (in vacuum and
chloroform), NBO analysis, NLO properties, atomic charges, MEP surface, FMOs analyses and
thermodynamic parameters of the BISB molecule were doneusingGaussian 09W program package
[11]. The calculated results were visualized by via GauusView5 program [12].
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All computations were performed using DFT (Density Functional Theory)/B3LYP (Becke’s
three parameter exact exchange-functional (B3) combined with gradient-corrected correlational
functional of Lee, Yang, Parr (LYP)) method with the 6-311G(d,p) basis set [13,14]. The
computedharmonicvibrational wavenumbers were scaled with 0.967 for B3LYP/6-311G(d,p) level
[15]. The detailed vibrational assignments were performed on basis of potential energy distribution
1
(PED) analysis using VEDA 4 program[16].For H and 13C NMR isotropic chemical shift
calculations, the optimized molecular geometries of the BISBmolecule were first obtained at
B3LYP/6-311G(d,p) level in vacuum and DMSO using integral equation formalism polarizable
1
13
continuum model (IEFPCM). Then, H and C NMR chemical shifts of the BISB molecule were
performed usingaforementioned computational level and solventswith gauge invariant atomic
orbital (GIAO) approach [17-19].The UV-Vis. calculations of the BISB molecule were doneusing
TD-DFT method in vacuum and chloroform. The HOMO and LUMO energy values and their
shapes were simulated using B3LYP/6-311G(d,p) level. According to the computed HOMO and
LUMO energy values of the BISB molecule, the some molecular properties such as ionization
potential (I), electron affinity (A), chemical hardness (η), chemical softness (ζ), electronegativity
(χ), chemical potential (ꢀ) and electrophilicity index ( )werecomputed.The nonlinear optical (NLO)
ω
properties such as the dipole moment (µ), the mean polarizability (αtotal), the anisotropy of the
polarizability (∆α) andthe first hyperpolarizability (β0) were performedwith thementioned
computational level. The NBO analysis was done to understandthe interactions among bonds and
intramolecular charge transfers (ICTs) or hyperconjugative interactions in the BISB molecule. The
molecular electrostatic potential (MEP) and its contours surfaces was simulatedusing the optimized
molecular geometryof the BISB molecule.Finally, the atomic charges (Mulliken, APT and
NBO)and thermodynamic properties (termal energy (E), heat capacity (Cv), entropy (S), etc.) were
computed using B3LYP/6-311G(d,p) level.
4. Results and Discussion
4.1. Conformational Analysis and Molecular Structure
The optimized molecular structure with B3LYP/6-311G(d,p) level of the 2-[(1H-
benzimidazol-2-ylimino)methyl]-4-bromophenolis given in Fig. 1. The computed molecular
geometric parameters (bond lengths and bond angles) are summarized in Table 1. In the literature,
the experimental structural parameters, obtained with single crystal X-Ray analysis, are not
available for the BISB molecule. However,Liu et al. [20] recorded the molecular geometry and
structural parameters of 2-[(1H-benzimidazol-2-yl)iminomethyl]-4,6-dibromophenol ethanol
hemisolvate compound, which belongs to a similar structure with the BISB molecule, using
experimental single crystal X-Ray method. The computed root mean square deviation (RMSD) and
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linear correlation coefficients(R2) values for the conformer 1 were obtained as 0.088Å and 0.96979
(for the experimental and computed bond lengths) and 0.965° and 0.97989 (for the experimental
and computed bond angles), respectively.
The conformational analysis of the BISB molecule was performed for the C8-N18-C7-N16
torsion angle increasing by 2° steps from 0° to 180°. As a result of conformational analysis, the
potential energy surface (PES) map obtained as a function of the C8-N18-C7-N16 dihedral angle is
given in Fig. 2. According to Fig. 2, there are three conformational forms of the BISB molecule.
These conformational forms are computed at 0.0° (Conformer 1), 166.0° (Conformer 2) and 104.0°
(Conformer 3) values of the C8-N18-C7-N16 dihedral angle. The computed energy values for the
conformer 1, conformer 2 and conformer 3 are -3353.34936242 a.u. (or 0.000 kcal/mol), -
3353.34045992 a.u. (or 5.586 kcal/mol) and -3353.33645098 a.u. (or 8.102 kcal/mol), respectively.
Considering the computed energy values for all conformational forms, we can say that the
conformer 1 is the most stable state of the BISBmolecule.The computed vibrationalwavenumbers
with B3LYP/6-311G(d,p) level forthe conformer 1, conformer 2 and conformer 3 states of the BISB
molecule are listed in Table 2. As seen from the calculated vibrational wavenumbers given in Table
2, the conformer 3 has one imaginary frequency. This situation shows that the conformer 3is the
most unstable molecular geometryand itis a transition state.
The 2-[(1H-benzimidazol-2-ylimino)methyl]-4-bromophenol molecule wasformed by linking
azomethine (R1-CH=N-R2) group of 4-bromophenol and 1H-benzimidazole groups. The C8-C9
bond length betweenthe azomethine and 4-bromophenol groups is computed as 1.443 Å. The
C8=N18 bond length in the azomethine group of the BISB molecule is found as 1.298 Å. The C10-
O15, C13-Br19, C14-C13-Br19, C9-C10-O15 and C10-O15-H23 bond parameters in the 4-
bromophenol group of the BISB molecule are computed as 1.338 Å, 1.917 Å, 120.0°, 122.1° and
107.3°,respectively.The O15-H23, H23…N18,O15…N18 lengths and O15-H23…N18 angle as the
intra-molecular hydrogen bonding parameters of the BISB molecule are calculated as 0.989 Å,
1.755 Å, 2.642 Å and 147.3°, respectively.In the literature, the C8-C9, C8=N18, C10-O15, C13-
Br19, O15-H23, H23…N18, O15…N18 lengths and O15-H23…N18 anglewere experimentally
recorded as 1.470 (6) Å, 1.268 (6) Å, 1.352 (6) Å, 1.891 (5) Å, 0.820 Å, 1.897 Å, 2.618 (5) Å,
146.0° for2-[(1H-benzimidazol-2-yl)iminomethyl]-4,6-dibromophenol ethanol hemisolvate
molecule [20],1.452 (4) Å, 1.279 (4) Å, 1.350 (4) Å, 1.900 (4) Å, 0.825 Å, 1.830 Å, 2.586 (4) Å,
151.0°
for2-[(E)-(5-amino-2,3-diphenylquinoxalin-6-yl)iminomethyl]-4-bromophenol
one
[21],1.440 (11) Å, 1.264 (10) Å, 1.371 (12) Å, 1.878 (9) Å, 0.820 Å, 1.890 Å, 2.609 (10) Å, 146.0°
for (E)-4-bromo-2-[(4-ethylphenyl)iminomethyl] phenol [22] and 1.430 (7) Å, 1.290 (6) Å, 1.335
(5) Å, 1.887 (5) Å, 0.820 Å, 1.870 Å, 2.600 (6) Å 148.0°for2-[(1,3-benzothiazol-2-
yl)iminomethyl]-4-bromophenol one [23], respectively.For 4-bromophenol, Jan et al. [24]obtained
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the C-Br bond length as 1.919 Å, C-O length as 1.367 Å, O-H length as 0.963 Å, C-O-H bond angle
as 110°, C-C-Br bond angleas 120.3° andC-C-O bond length as122.8° with B3LYP/6-311++G(d,p)
level.The C7-N18 bond length between the azomethine and 1H-benzimidazole groups is computed
as 1.383 Å. This bond length was computed as 1.401 (5) Å [20] and 1.396 (6) Å values in the
literature. The C7=N16, C7-N17, C1-N17, C2-N16, N17-H29, N16-C7-N17, C2-N16-C7 and C1-
N17-C7 bond parameters in the 1H-benzimidazole group werecomputed at 1.313 Å, 1.378 Å, 1.380
Å, 1.381 Å, 1.007 Å, 113.3°, 105.1° and 107.1° values, while they were recorded at 1.309 (5) Å,
1.342 (6) Å, 1.374 (5) Å, 1.381 (6) Å, 0.860 Å, 114.4 (4)°, 104.0 (4)° and 107.0 (4)° values for the
2-[(1H-benzimidazol-2-yl)iminomethyl]-4,6-dibromophenol ethanol hemisolvate molecule [20],
respectively.Similarly, these bond parameters were experimentally obtained as 1.328 (2) Å, 1.364
(19) Å, 1.385 (2) Å, 1.391 (2) Å, 0.860, 112.7 (14)°, 104.9 (13)° and 107.3 (13)° for the 1,4-bis(1H-
benzimidazol-2-yl)benzene methanol monosolvate molecule, respectively [25]. The C-C bond
lengths in phenyl rings of the BISB molecule were computed at the interval 1.380 Å-1.421 Å, while
the C-C-C bond angles are calculated between 116.8° and 122.5°. The C7-N18-C8, C9-C8-N18,
C8-C9-C10 and N16-C7-N18 bond angles are found at 118.6°/120.3 (4)°, 122.1°/121.0 (4)°,
121.8°/121.4 (4)° and 128.5°/129.7 (4)°, respectively (calculated/experimental) [20].
4.2. Vibrational Frequency Analysis
There are 29 atoms and 81 vibrational modes of the 2-[(1H-benzimidazol-2-ylimino)methyl]-
4-bromophenol molecule. The BISB moleculebelongs to Cs point group. The 81 vibrational modes
are distributed as 55 Aʹ (in-plane vibrations) + 26 Aʺ (out-of-plane vibrations), under Cs symmetry.
The measured and computed (unscaled and scaled) vibrational frequencies, IR intensities, Raman
scattering activities, vibrational assignments and symmetry species of vibrational assignments are
given in Table 2. The recorded (in solid phase) and simulated IR and Raman spectra of the BISB
molecule are given in Fig. 3. The computed RMSD and R2 values were obtained as 36.251cm-1and
0.99767 (for the experimental and computed IR wavenumbers) and 9.904cm-1and 0.99950 (for the
experimental and computed Raman wavenumbers), respectively.
4.2.1. NH Vibrations
The absorption bands in the region of 3100-3700 cm-1result fromthe presence of OH and NH
stretching modes [26]. The observed band at 3317 cm-1 inexperimental IR spectra can be assigned
to NH stretching vibrationof theBISB molecule. The computed wavenumber value for this band is
3536 cm-1.The NH in-plane bending modes are observed at 1515 (IR)-1512 (R), 1367 (IR)-1378
(R), 1188 (IR)-1180 (R) and 1169 (IR)-1148 (R) cm-1 as associated with other vibrational bands,
while the NH out-of-plane bending bands is found at 493 cm-1(the computed at 482 cm-1 with 60%
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contribution of PED) and 457 cm-1 (the calculated at 452 cm-1 with PED contribution of 25%) in
Raman spectrum of the BISB molecule.
4.2.2. OH Vibrations
The OH vibration modes are very sensitive to hyrogen bonding interaction. Free OH
stretching gives rise toa sharp band inthe regionof 3700-3500 cm-1 [41]. But, this band shifts to
lower wavenumber under the presence of inter- and intra-molecular hydrogen bonding interactions
and it is observed at the interval of 3200-3250 cm-1 [26,27]. Due to O-H…N intar-molecular
hyrogen bonding interactions in the BISB molecule, the OH stretching band is observed at 3238
cm-1 in IR spectrum, while this band is computed at 3178 cm-1 with PED contribution of 99%. The
in-plane and out-of-plane bending vibrations for the free OH group in phenol compounds lead to
formation ofabsorption bands in the regions of 1330-1420 cm-1 and 650-770 cm-1, respectively [28].
The OH in-plane and out-of-plane bending modesare shifted to high frequency region for the BISB
molecule due to intramolecular O-H…N hydrogen bonding interaction. The OH in-plane bending
vibrationsare found at 1599 (IR)-1605 (R), 1437 (IR)-1439 (IR) and 1401 (IR) cm-1as mixed with
other bands. The computed bands for OH in-plane mode are found at 1605 (19%), 1545 (17%),
1458 (20%), 1434 (14%) and 1404 (11%) cm-1. Similarly, the OH out-of-plane bending vibration
isfound at 783 (IR)-793 (R) cm-1and it calculated at 787 cm-1with 85% contribution of PED.
4.2.3. CH Vibrations
The CH stretching vibrations in aromatic compounds appear in the region 3000-3100 cm-1.
[26-29]. The observed band at 3068 cm-1 can be attributed to the CH stretching modes in aromatic
rings of theBISB molecule. The CH stretching modes for aromatic groups are computed in the
region of 3063-3100 cm-1. The C8-H24 stretching mode is observed at 3030 cm-1, while this band is
calculated at 2996 cm-1 with 100% contribution of PED.Additionally, the CH in-plane bending
modes occur as mixed with other bands in the region of 1000-1600 cm-1, while the CH out-of-plane
bending (τHCCC or torsion CH) ones observe at the interval of 650-1000 cm-1 [26-29].The
observed bands as coupled with other vibrations at 995 (IR)-1000 (R), 1074 (IR)-1080 (R), 1102
(IR), 1119 (R), 1137 (IR), 1204 (R), 1216 (IR), 1266 (IR)-1277 (R), 1301 (IR)-1308 (R), 1401 (IR),
1437 (IR)-1439 (R) and 1473 (IR) cm-1 can be attributed to the CH in-plane bending vibrations,
while the CH out-of-plane bending bands are observed at 950 (R), 934 (IR), 872 (IR)-869 (R), 832
(R), 817 (IR)-817 (R) and 702 (IR)-692 (R) cm-1.Likewise, the CH in-plane mode in azomethine
gruop (-CH=N-) are found at1318 (IR)-1316 (R) cm-1 and it is computed at 1322 cm-1 with 29%
contribution of PED. But, the CH out-of-plane bending band in this group is not observed in
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experimental FT-IR and Raman spectra, whereas this band is calculated at 990 cm-1 with PED
contribution of 91%.
4.2.4. CC, NC and OC Vibrations
The CC stretching vibrations of aromatic rings (skeletal vibration) usually occur in the
interval of 1400-1650 cm-1 [30]. But, these bands can also be observed as combined with other
vibrations below 1400 cm-1. The CC stretching vibration modes in aromatic rings of the BISB
molecule are listed in Table 2. The vibrational bands observed at 507 (IR)-511 (R), 603 (IR)-607
(R), 624 (IR), 643 (IR)-632 (R), 739 (IR)-737 (R), 848 (IR), 899 (IR) and 995 (IR)-1000 (R) cm-
1are assigned to the CCC in-plane bending vibration modes in aromatic rings of the BISBmolecule.
Similarly, the CCCC torsional modesin aromatic rings are given rise to absorption bands at 215 (R),
240 (R), 349 (R), 368 (R), 457 (R), 547 (IR)-527 (R), 570 (IR)-587 (R) and 752 (R) cm-1.
The description of position in FT-IR and Raman spectra of NC stretching bands is very
difficult due to the combining with several bands in fingerprint region [26]. The characteristic N=C
stretching band for Schiff bases is observed in the region of 1600-1700 cm-1 [30-33]. But, this band
can be shifted below 1600 cm-1 due to intra-molecular hydrogen bonding interaction. The
azomethineN18=C8stretching band was observed at 1588 cm-1in FT-IR spectrum as associated with
other vibrational bands and it is computed at 1587 cm-1 with PED contibution of 38%. The obtained
values are in good agreement with the literature [33]. Similarly, the stretching vibration mode for
the other double bondN16=C7 is found at 1511 (IR)-1512 (R)/1495/14% and 1318 (IR)-1316
(R)/1322/14% cm-1 as combined with other bands (exp./cal./PED%) [34]. The stretching vibration
modes of the single bond NC are observed at 1367 (IR)-1378 (R), 1340 (IR)-1337 (R), 1240 (R)
and 1030 (IR)-1038 (R) cm-1. The NC stretching vibration modes of the BISB molecule are listed in
Table 2.
Silverstein and Webster [28] suggested that the OC stretching bands in phenol compounds it
could be observed in the regions of 1390-1330 and 1260-1180 cm-1.In this connection, the recorded
strong band at 1266 (IR)-1277 (R) cm-1 can be assigned to OC stretching modes in phenol group of
the BISB molecule [34]. The computed wavenumber value and PED contribution for this band are
1272 cm-1 and 35%, respectively. The in-plane bending vibrations between phenyl ring and OH
group is found at 464 (IR)-467 (R) cm-1/453 cm-1/56%, whereas the out-of plane bending vibrations
are obtained at 817 (IR)-817 (R) cm-1/813 cm-1/18%, 702 (IR)-692 (R) cm-1/693 cm-1/19% and 349
(R) cm-1/332 cm-1/18% as combined with other vibrational bands (exp./cal./PED).
4.2.5. CBr Vibrations
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The CBr stretching mode appears in the region of 200-480 cm-1 [34,35]. Mooney [36-38]
determined the position of vibrational modes for the C-X group (X=Cl, F, Br, I)in the frequency
range of 1129-480 cm-1. In this study, the CBr stretching mode is observed at 624 cm-1 in FT-IR
spectrum and it is calculated at 617 cm-1 with PED contiribution of 13%. Additionally, the observed
band at 302 cm-1 in Raman spectrum of the BISB molecule is assigned to CBr stretching mode and
it is computed at 292 cm-1 with 29% contribution of PED. Likewise, the calculated band at 260 cm-1
with PED contiribution of 23% is identified as the CBr stretching mode. The CBr stretching, in-
plane and out-plane bendings given in Table 2are ina good agreement with the obtained resultsfor
the similar structures in literature [35-40].
4.3. Proton and Carbon-13 NMRChemical Shift Analyses
The NMR isotropic chemical shift analysis allows us to identify relative ionic species, to
determined numbers of proton and carbon atoms and funtional groups in the molecular structure and
to calculate reliable magnetic properties which provide accurate predictions of molecular
1
geometries [41-44]. The experimental H and 13C NMR chemical shift spectra of the BISB
1
13
molecule were recorded in DMSO-d6 and they are given in Fig.4.The H and C NMR chemical
shifts of the BISB moleculewere calculated at B3LYP/6-311G(d,p) level in vacuum and DMSO
solvent using IEFPCM solvent model. The experimentaland calculated NMR chemical shift values
are listed in Table 3.The computed RMSD and R2 values were obtained as 6.156 ppm and 0.97361
13
(in vacuum) and 6.312 ppm and 0.98031 (in chloroform) for the experimental and computed C
NMR chemical shifts, respectively.
The 13C NMR chemical shifts were observed in the region of 110.57-163.12 ppm, while they
are calculated at the interval of 121.82-168.40 ppm in vacuum and 122.23-168.37 ppm in DMSO
for the BISB molecule.The C7, C8 and C10 atoms which are connected to the electronegative
atoms are given carbon-13 NMR chemical shift signals at 153.86, 159.41 and 163.12 ppm,
respectively. The chemical shift values of these atoms are higher than those of the other carbons in
the BISB molecule.The calculated values for these carbon atoms are at 154.93, 167.69 and 168.40
ppm in vacuum and 156.18, 168.25 and 168.37 ppm in DMSO, respectively.Aromatic carbon atoms
give resonance signals in the range of 100-150 ppm [41-44]. As expected, the NMR chemical shifts
for aromatic carbon atoms are observed at the interval of 110.57-142.29 ppm, while they are
computed at 111.51-147.65 ppm in vacuum and 114.04-147.22 ppm in DMSO.
Because of the intramolecular hyrogen bonding, the proton NMR chemical shift value of the
H23 atom in phenolic groupisgiven rise toresonance signals at 12.81 and 12.03 ppm [28]. The
computed value for H23 atom is 12.289 ppm in vacuum and 12.675 ppm in DMSO.The aromatic
rings produce large deshielding effects and their π-bonding electrons act as a conductor and
9

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chemical shift values for protons the bonded to carbon atoms in aromatic rings are observed in the
region of 6-8 ppm [41-44]. The chemical shift values for NH proton in amide, pyrrole and indole
groups give rise to resonance signals in the region of 5.00-8.50 ppm [28]. The H29 atom and proton
atoms of aromatic rings in the BISB molecule were given signals at the interval of 7.01-8.09 ppm.
The chemical shifts ofthe H29 atom and aromatic protonsarecalculated at 7.604/8.438 ppm and at
the interval of 6.911-7.829/7.056-7.830 ppm (in vacuum/in DMSO), respectively. Likewise, the
proton chemical shift signal for H24 atom is obtained at 9.63/9.761/9.708 ppm (exp./cal. in
vacuum/cal. in DMSO).
4.4. Frontier Molecular Orbital Analyses
The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) are called as the frontier molecule orbitals (FMOs) and they are the main orbitals taking
part in chemical reactions [45]. The HOMO represents the outermost orbital filled by electrons. It is
directly related to the ionization potential of the compound. Behaving as an electron donor, it can be
considered as valance band of the system. The LUMO implies the first empty innermost orbital
unfilled by electrons. It is directly related to the electron affinity. Behaving as an electron acceptor,
it can be thought as conductance band of the system. The HOMO-LUMO energy band gap is an
indication of molecular chemical stability. It is a very important parameter for determination of
molecular electrical properties. Furthermore, the quantum molecular descriptors such as ionization
potential,electron affinity, chemical reactivity, kinetic stability, polarizability, chemical hardness
and softness, aromaticity and electronegativity can be found using HOMO-LUMO energy band gap
[46]. The simulated HOMO-4, HOMO-3, HOMO-2, HOMO-1, HOMO, LUMO, LUMO+1,
LUMO+2, LUMO+3 and LUMO+4 shapes and their energy values with B3LYP/6-311G(d,p) level
are given in Fig. 5. The computed HOMO and LUMO energy values for the BISB molecule are
found as -2.551 and -2.526 eV in vacuum and -6.069 and -6.086 eV in chloroform, respectively.
The band gap between the HOMO and LUMO is obtained as 3.518 in vacuum and 3.559 eV in
chloroform. The HOMO is mainly localized on whole molecule, while the LUMO ise mainly
localized on other whole groups excluding Br atom. Both the HOMO and LUMO are mostly
formed from the p-bonding and p-antibonding type molecule orbitals.
Considering the computed HOMO and LUMO energy values, the quantum molecular
descriptors such as ionization potential, electron affinity, chemical hardness, softness,
electronegativity and electrophilicity index parameters are summarized in Supplementary Table
S1[46].
4.4. UV-Vis. Spectroscopic Analysis
10

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The experimental UV-Vis. electronic absorption spectrumof the BISB molecule was recorded
in the region of 200-600 nm in chloroform solvent. The simulated (in vacuum and chloroform) and
experimental UV-Vis. electronic absorption spectra are given in Fig. 6. The experimental and
computed UV-Vis. spectroscopic parameters and corresponding electronic transitionsare listed in
Table 4.The strong absorption bands below 400 nm (in the region 350-390 nm) in experimental
UV-Vis. spectrum of Schiff base compounds indicateenol-imine form of the structure under
investigation. These strong absorption bands in this region can be attributed to π→π* transition that
is resulted from azomethine and aromatic groups. In this connection, the strong absorption
wavelengths observed at 386 and 353 nm in the experimental UV-Vis. spectrum can be assigned to
π→π* electronic transition in the BISB molecule. The calculated values corresponding to these
experimental bands are at 387.09/394.45 nm and 341.80/341.98, respectively (in vacumm/in
chloroform). As known, the most possible electronic transition in a molecule is from HOMO to
LUMO. Therefore, the highest oscillator strength and major transitioncorresponding to strong
wavelength at 387/387.09/394.45 nm (exp. in chloroform/cal. in vacuum/cal. in chloroform) in UV-
Vis. spectra of the BISB molecule are computed as 0.68732/0.69817 and H→L, respectively.The
recorded absorption wavelength at 278 nm is assigned as π→π* electronic transition which is
resulted from aromatic groups (4-romophenol and 1H-benzimidazole) in the BISB molecule.The
electronic absorption wavelength observed at 245 nm can be assigned to n→σ* and this band
confirms intramolecular hydrogen bonding interaction (O-H…N) in the BISB molecule.The other
higher oscillator strength value and its major contribution in simulated UV-Vis. spectra are obtained
as 0.3288/0.3478 and H-1→L+2 for wavelengths of 216.47/217.49 nm, respectively
4.5. NBO Analysis
The NBO analysis is a powerful method to determine intra- and inter-molecular bonding
interactions, bond species, bond structures and natural atomic charges in the molecular
systems.Besides, it is used to investigate hyperconjugation interactions or charge transfers (ICT)
and the stability between Lewis type (bonding or lone pair) filled orbitals and non-Lewis type
(antibonding or Rydgberg) vacancy orbitals. The hyperconjugative interaction energy (or the
stabilization energy, E(2)) shows the interaction between donor and acceptor groups. Delocalization
of electron density between occupied Lewis type orbitals and formally unoccupied non-Lewis
orbitals correspond to a stabilizing donor-acceptor interaction[47].
The NBO data computed at B3LYP/6-311G(d,p) level are given in Table 5.The strong
hyperconjugation interactions or intramolecular charge transfers (ICTs) were computed between σ
and π bonding electrons of the C-N, C-C and C-H bonds and σ* and π* antibonding ones of C-C, C-
N, C-H, N-H, O-H andC-Br ones. In addition, other strong hyperconjugation interactions are also
11

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foundbetween the lone pair n electrons of O, N and Br atoms and σ* and π* antibonding ones of C-
C, C-N, C-H and O-H bonds. The stabilization energy values greater than 4 kcal mol-1 are
summarized in Table 5. The π bond electrons are weaker than σ bond electrons. Therefore, the
electron densityof the π bonded groups is less than the electron density of the σ bonded ones. For
the BISB molecule, the electron densitiesof the πbonds in donor (i) groups are calculated at the
interval of 1.69569 e-1.88342 e, whereas the electron densities of the σ bonds in donor (i) groups
are found between 1.96154 e and 1.98624 e. The electron densities of lone pair n electrons of O, N
and Br atoms in donor (i) groups are found between 1.61807 e and 1.97324 e. The electron densities
of σ* and π* antibonding bonds in acceptor (j) groups are computed at the intervals0.01427 e-
0.05955 e and 0.22630 e-0.39825 e, respectively.The strongest hyperconjugation interaction is from
the lone pair n electrons of N17 atom to antibonding π* electrons of C7-N16 bond. This interaction
is obtained as n(N17)→π*(C7-N16)[E(2)=50.06 kcal mol-1, ED(i)=1.61807 e, ED(j)=0.39825
e].The n(N18)→σ*(O15-H24) charge transferfor the intramolecular hydrogen bonding in the BISB
moleculeexhibited a strong hyperconjugation interaction with E(2)=22.38 kcal mol-1,
ED(i)=1.87519 e and ED(j)=0.05955 e values.The stabilization energy values for π(C3-
C4)→π*(C5-C6), π(C5-C6)→π*(C3-C4), π(C8-N18)→π*(C7-N16), π(C11-12)→π*(C13-C14) and
π(C13-C14)→π*(C11-C12) are computedas 32.97 kcal mol-1[ED(i)=1.71814 e, ED(j)=0.33446 e],
17.51 kcal mol-1[ED(i)=1.72682 e, ED(j)=0.30484 e], 20.47 kcal mol-1[ED(i)=1.88342 e,
ED(j)=0.39825 e], 16.67 kcal mol-1[ED(i)=1.69569 e, ED(j)=0.35550 e] and21.34 kcal mol-
1[ED(i)=1.72424 e, ED(j)=0.30112 e], respectively.Likewise, the σ(C2-N16)→σ*(C7-N18)
andσ(C5-C6)→σ*(C1-N17) hyperconjugation interactions are obtainedat 8.54 kcal mol-1
[ED(i)=1.97458 e, ED(j)=0.03986 e] and 6.73 kcal mol-1 [ED(i)=1.97461 e, ED(j)=0.02405 e]
values of stabilization energy, respectively.
4.6. NLO Analysis
The organic, inorganic and organometallic nonlinear optical (NLO) materials have been very
attractive in the fields of physics, chemistry and engineering, due to their future potential
applications in the optoelectronic and microelectronics such as optical telecommunications, signal
processing, optical interconnections, optical computing, optical information processing,sensor
protection, optical switching, dynamic image processing and various other photonic technologies
[48]. The mean polarizability (αtotal), the anisotropy of the polarizability (∆α) and the first
hyperpolarizability (β0) valuesareimportant key parametersto determine NLO properties of the
molecules. Therefore, recently, the synthesis and investigations of the novel nonlinear optic
materialswith high performance havecreated an interesting study area.
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Thepolarizabilities,first hyperpolarizabilities and dipole moments of the BISBmolecule are
calculatedwithB3LYP/6-311G(d,p) level using the finite field approach and they are summarizedin
Supplementary Table S2.Thepolarizabilityvalues werecomputed in atomic units (a.u) and theywere
transformed using 1 a.u = 0.1482×10-24 electrostatic unit (esu) for αvalues and1 a.u = 8.6393×10-33
esu for β values. Theµtotal,αtotal,∆α and β0 valueswere calculatedusing the following equations[49].
1
α total = (α xx
+ α yy + α zz )
3
1
2
1
2
2
2
∆
α
=
[(α xx
−
α
yy )2 + (α yy
−
α
zz )2 + (α zz
−
α
xx )2 + 6α xz + 6α xy + 6α yz
]
2
1
2
2
2
2
β0
=
[
(
β xxx
+
β xyy
µy2
+
β xzz
)
+
(
β yyy
+
β yzz
+
β yxx
)
+
(
β zzz
+
β zxx
+
β zyy
)
]
1
µtotal = (µx2
+
+ )
µz2
2
The dipole moment valuescalculated forthe BISB moleculeare-1.5701 Debye for
ꢀx, 2.5335
Debye for y, 0.1947 Debye for ꢀz and 2.9869 Debye for total Theαtotal and ∆αvalues are found as
ꢀ
ꢀ
.
355.1613×10-25 and 478.4220×10-25 esu, respectively. The calculatedvalue for theβ0 is found as
92.1329117×10-31 esu. In NLO studies, urea is one of the prototypical molecules. Hence, the NLO
properties of the molecules can beusually compared with those urea. The calculated values for urea
atB3LYP/6-311G(d,p) level are41.4969×10-25 esu for
α
total, 24,5049×10-25 esu for ∆αand
3.3014×10-31 esu for
β0. The mean polarizability, the anisotropy ofthe polarizability and first
hyperpolarizability values of the BISB molecule are approximately8.559, 19.524 and 126.192 times
greater than those of urea, respectively.
4.7. MEPSurface Analysis
The molecular electrostatic potential (MEP) is widely used as a method for mapping
electrostatic potential onto the iso-electron density surface. MEP was established extensively as a
helpful quantity to explain the hydrogen bonding, chemical reactivity, presence of intra- and inter-
molecular interactions, electronegativity and structure activity of molecule [50]. Three-dimensional
charge distribution of MEP is very useful that the negative electrostatic potential regions can be
regarded as nucleophilic centers, whereas the positive ones are potential electrophilic sites.
Moreover, the electrostatic potential makes the polarization of the electron density visible [64]. An
electron density isosurface mapped with electrostatic potential surface depicts the size, shape and
charge density of a molecule.
The MEP surface and its contours were simulated with B3LYP/6-311G(d,p) level in order to
determine the chemically reactive electrophilic and nucleophilic sites of the BISB molecule. They
13

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are given in Fig. 7. As seen from Fig. 7, the possible electrophilic sites or the negative electrostatic
potential regions are mainly placed around the O15 and N16 atoms, whereas the nucleophilic sites
or the positive ones are localized around the H29 atom and other hydrogen atoms. The calculated
values of electron densities on the O15, N16 and H29 atoms are obtained as -2.747, -3.704 (the
deepest negative) on MEP surface of the BISB molecule and 6.324 a.u. (the highest positive),
respectively.
4.8. Atomic Charges
Mulliken atomic charges arise from Mulliken population analysis [51]. Mulliken analysis is
the most common, oldest and simplest population analysis method that can be used to characterize
the electronic partial charge distribution of atoms in a molecular system. Atomic charges can relate
to the electronic structural properties and molecular behavior and reactivity of a molecules. Thus,
atomic charges play an important role in quantum chemistry computation. The Mulliken, APT
(atomic polar tensor) and NBO atomic charges of the BISB molecule were calculated using
B3LYP/6-311G(d,p) level and they are given in Supplementary Table S3. As seen from
Supplementary Table S3, all hydrogens have positive charges. It is clear that the H23 and H24
atoms have more positive atomic charge than other hydrogens due the electronegativity property of
the oxygen and nitrogen atoms. The computed Mulliken, APT and NBO atomic charge values for
these hydrogens are 0.2598, 0.3796 and 0.4979 a.u. for H23 atom and 0.2351, 0.2418 and 0.4126
a.u. for H29 one, respectively. The charges of the carbon atoms were computed as either positive or
negative at the interval -0.2197 - 0.5068 for Mulliken atomic charges, -0.4980 - 0.7018 a.u. for APT
ones and -0.2430 - 0.5823 a.u. for NBO ones. The C7, C8 and C10 carbon atoms which are
connected to electronegative O and N atoms belong to more positive atomic charge values.
Especially, C7 atom has more positive charge than others due to bonded three negative N atoms.
The computed Mulliken, APT and NBO atomic charge values for these carbon atoms were found as
0.5068, 0.7018 and 0.5823 a.u. (for C7 atom), 0.2442, 0.7126 and 0.1826 a.u. (for C8 atom) and
0.2313, 0.4386 and 0.3937 a.u. (for C10 atom), respectively. The Mulliken, APT and NBO atomic
charges for the electronegative O15, N16, N17 and N18 atoms were computed as -0.3502, -0.6640
and -0.6672 a.u., -0.3642, -0.4364 and -0.5328 a.u., -0.4595, -0.3455 and -0.5490 a.u. and -0.5048, -
0.6865 and -0.5851 a.u., respectively. The Br19 atom was computed at -0.0250 a.u. value for
Mulliken atomic charges, -0.2549 a.u. value for APT ones and 0.0525 a.u. value for NBO ones.
4.9. Thermodynamic Properties
Some of the thermodynamic parameters such as thermal energy, heat capacity, entropy,
rotational constants and temperature and zero-point vibrational energy (ZPVE), etc.were computed
14

ACCEPTED MANUSCRIPT
with B3LYP/6-311G(d,p) level at room temperature of 298.15 K, under 1 atm pressure and in
vacuum for the BISB and they werelisted in Supplementary Table S4. The partition function which
is called as the statical characteristics of a system in thermodynamic equilibrium is very important
for thermodynamic parameters. The partition function has four species as to be the translational
partition function, electronic one, vibrational one and rotational one. Thepartition functions can be
used to compute thermodynamicvariables (such as heat capacity, entropy, equilibrium constants,
total energy, free energy, pressure, thermal energy and rate constants, etc.) of a system.
Accordingly, it is well known that the total energy of any a molecular system is the sum of
electronic,vibrational, rotational and translation energies(or E = Ee + Ev + Er + Et). The computed
minimum total energy (E(RB3LYP)) valuesforthe BISB moleculewas found as -3353.34936242
Hartrees. The ZPVE value was computed as 134.90579 kcal/mol. As seen from Supplementary
Table S4, the computed value of total thermalenergy was found as144.309 cal/mol×K. The major
contribution to thermal energy is came from vibrational energywith 142.531 cal/mol×K value,
whereas the minor portions are belonged to electronic enegry with 0.000 cal/mol×K value,
transitional and rotational energies with 0.889 cal/mol×K one.Likewise, the calculated heatcapacity
(Cv) and entropy (S) valuesare obtained as 58.977and127.264 cal/mol×K, respectively. The
electronic, translational, rotational and vibrational energy cantributions to heat capacity and entropy
are found as 0.000, 2.981, 2.981 and 53.015 cal/mol×K for heat capacity and 0.000, 43,138, 35.109
and 49.017 cal/mol×K for entropy, respectively. The computed rotational temperatures (Kelvin) and
rotational constants (GHz) for the BISB molecule werefound as 0.04137, 0.00450 and 0.00405 K
and 0.86199, 0.09366 and 0.08448 GHz, respectively.
5. Conclusions
The structural, spectral, electronic, nonlinear optical and thermodynamic characterizations of
the synthesized 2-[(1H-benzimidazol-2-ylimino)methyl]-4-bromophenol (BISB) compound were
1
performed using both experimental and computationalprocedures. The vibrational frequencies, H
13
and C NMR chemical shifts and UV-Vis. electronic absorption wavelengths were computed and
the obtained calculation results were compared with experimental data.The HOMO-LUMO
analyses and some chemical properties depending on them, NLO properties, atomic charges, MEP
surface analysis and thermodynamic properties weretheoretically investigated for the BISB
molecule. The potential energy surface (PES)was obtaineddepending on the C8-N18-C7-
N16torsional angle. There are three points, namelyone global minimum (conformer 1; 0.0°), one
local minimum (conformer 2; 166.0°) and one global maximum (conformer 3;104.0°) on the PES
surface. The one imaginary frequency valuecalculated for conformer 3 shows that it is atransition
state for the BISB molecule. The imaginary frequency for the other two conformers was not
15

ACCEPTED MANUSCRIPT
computed. Due to intramolecular hydrogen bonding interaction in the BISB molecule, the positions
of the OH stretching band at 3238 cm-1and proton NMR chemical shifts at 12.81 ppm and 12.03
ppm of the OH hydrogen were investigated using experimental and calculation methods. The
n(N18)→σ*(O15-H24) intramolecular charge transfer with the stabilization energy value
ofE(2)=22.38 kcal mol-1in the BISB molecule was determined by via NBO analysis.The
strongabsorption wavelengts observed below 400 nm in experimental UV-Vis. spectrum indicate
the enol-imine form of the BISB molecule. Likewise, the observed absorption wavelength at 245
nm supports intramolecular hydrogen bonding interaction with the n→σ* transition. According to
NLO analysis,the BISB moleculesignificantlyexhibited polarizability and first hperpolarizability
properties when compared with those of urea and itcan be used as an effective NLO material.
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[34] A. Güder, H. Korkmaz, H. Gökce, Y.B. Alpaslan, G. Alpaslan, Isolation, characterization,
spectroscopic properties and quantum chemical computations of an important phytoalexin
resveratrol as antioxidant component from Vitis labrusca L. and their chemical compositions,
Spectrochim. Acta Part A 133 (2014) 378-395.
[35] M. Karabacak, M. Kurt, The spectroscopic (FT-IR and FT-Raman) and theoretical studies of
5-Bromo-salicylic acid, J. Mol. Struct. 919 (2009) 215-222.
[36] E.F. Mooney, The infrared spectra of chloro- and bromobenzene derivatives-I: Anisoles and
phenetoles, Spectrochim. Acta Part A19 (1963) 877-887.
[37] E.F. Mooney, The infra-red spectra of chloro- and bromobenzene derivatives-II.
Nitrobenzenes, Spectrochim. Acta Part A 20 (1964) 1021-1032.
[38] A. Gupta, S. Bee, N. Choudhary, S. Mishra, P. Tandon, Molecular structure, vibrational
spectroscopic, NBO and HOMO-LUMO studies of 2-amino 6-bromo 3-formylchromone,
Mol. Simul. 38 (2012) 567-581.
18

ACCEPTED MANUSCRIPT
[39] Y. Sert, A.A. Balakit, N. Öztürk, F. Ucun, G.A. El-Hiti, Experimental (FT-IR, NMR and UV)
and theoretical (M06-2X and DFT) investigation, and frequency estimation analyses on (E)-3-
(4-bromo-5-methylthiophen-2-yl)acrylonitrile, Spectrochim. Acta Part A 131 (2014) 502-511.
[40] V. Krishnakumar, N. Jayamani, R. Mathammal, K. Parasuraman, Density functional theory
calculations and vibrational spectra of 2-bromo-4-chloro phenol and 2-chloro-4-nitro phenol,
J. Raman Spectrosc. 40 (2009) 1551-1556.
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[42] R.J. Anderson, D.J. Bendell, and P.W. Groundwater, Organic Spectroscopic Analysis, The
Royal Society of Chemistry, Sanderland UK, 2004.
[43] H.O. Kalinowski, S. Berger, S. Braun, Carbon-13 NMR Spectroscopy, John Wiley&Sons,
Chichester, 1988.
[44] K. Pihlaja, E. Kleinpeter (Eds.), Carbon-13 Chemical Shifts in Structural and Sterochemical
Analysis,VCH Publishers, Deerfield Beach, 1994.
[45] K. Fukui, Role of frontier orbitals in chemical reactions, Science 218 (1982) 747-754.
[46] Y.B. Alpaslan, H. Gökce, G. Alpaslan, M. Macit, Spectroscopic characterization and density
functional
studies
of
(Z)-1-[(2-methoxy-5-
(trifluoromethyl)phenylamino)methylene]naphthalene-2(1H)-one, J. Mol. Struct. 1097 (2015)
171-180.
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Perspective, Cambridge University Press, New York, 2005.
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Boca Raton, Florida,1997.
[49] Ö. Tamer, D. Avcı, Y. Atalay, Synthesis, X-Ray crystal structure, photophysical
characterization and nonlinear optical properties of the unique manganese complex with
picolinate and 1,10 phenantroline: toward the designing of new high NLO response crystal, J.
Phys. Chem. Solids 99 (2016) 124-133.
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Science B.V, Amsterdam, The Netherlands, 1996.
[51] R.S. Mulliken, Electronic Population Analysis on LCAO-MO Molecular Wave Functions. I,
J. Chem. Phys. 23 (1955) 1833-1840.
19

ACCEPTED MANUSCRIPT
Table 1. The experimental and optimized molecular geometric parameters for all conformers of the BISB molecule.
Bond lengths (Å)
C1-C2
X-Raya
1.410(7)
1.393(7)
1.374(5)
1.396(6)
1.381(6)
1.369(8)
0.930
Conf. 1 Conf. 2 Conf. 3 Bond angles (°)
X-Raya
122.9(5)
104.5(4)
132.6(5)
118.9(5)
110.1(4)
131.0(5)
118.1(6)
120.9
Conf. 1 Conf. 2 Conf. 3
1.419
1.394
1.380
1.400
1.381
1.387
1.083
1.408
1.084
1.390
1.084
1.084
1.313
1.378
1.383
1.443
1.296
1.092
1.421
1.409
1.400
1.338
1.385
1.083
1.400
1.083
1.380
1.917
1.083
0.989
1.007
1.755
2.642
0.088
1.416
1.393
1.383
1.400
1.380
1.387
1.083
1.408
1.084
1.391
1.084
1.084
1.312
1.390
1.376
1.445
1.292
1.097
1.423
1.409
1.402
1.334
1.384
1.083
1.400
1.083
1.379
1.918
1.084
0.991
1.006
1.756
2.633
0.088
1.414
1.392
1.387
1.397
1.390
1.390
1.083
1.405
1.084
1.392
1.084
1.084
1.303
1.382
1.399
1.449
1.287
1.096
1.420
1.408
1.402
1.336
1.384
1.083
1.400
1.083
1.380
1.917
1.083
0.989
1.007
1.765
2.642
0.087
C2-C1-C6
122.5
104.4
133.1
119.6
110.4
130.0
118.1
120.1
121.8
121.5
119.5
119.0
121.5
119.2
119.3
116.8
122.0
121.3
113.0
128.4
118.7
122.1
118.0
119.9
121.8
119.0
119.2
119.3
122.1
118.6
120.7
118.4
121.0
120.0
120.0
120.0
120.5
119.6
120.0
120.4
119.1
120.6
107.3
105.1
107.1
127.9
125.1
118.6
147.3
0.965
122.5
104.6
132.9
119.7
110.5
129.7
118.1
120.0
121.9
121.4
119.6
119.0
121.6
119.2
119.2
116.7
122.1
121.2
112.6
122.6
124.8
121.8
115.9
122.3
121.4
119.3
119.3
118.9
122.7
118.4
120.9
118.1
121.0
120.0
120.0
120.0
120.4
119.6
119.9
120.5
119.2
120.3
108.2
105.4
106.8
125.8
126.8
123.1
145.1
1.969
122.6
104.4
133.0
119.7
110.6
129.8
118.1
120.1
121.8
121.4
119.5
119.1
121.4
119.3
119.2
116.7
122.0
121.2
113.7
125.8
120.5
122.2
116.7
121.0
121.3
119.2
119.5
119.0
122.6
118.5
120.7
118.3
121.0
120.1
119.9
119.9
120.4
119.6
120.0
120.3
119.2
120.4
108.1
104.7
106.6
127.3
125.7
119.7
145.8
1.196
C1-C6
C1-N17
C2-C3
C2-N16
C3-C4
C2-C1-N17
C6-C1-N17
C1-C2-C3
C1-C2-N16
C3-C2-N16
C2-C3-C4
C2-C3-H25
C4-C3-H25
C3-C4-C5
C3-C4-H26
C5-C4-H26
C4-C5-C6
C3-H25
C4-C5
C4-H26
C5-C6
C5-H27
C6-H28
C7-N16
C7-N17
C7-N18
C8-C9
1.380(8)
0.930
1.405(7)
0.930
120.9
123.2(5)
118.4
118.4
120.5(5)
119.8
119.8
116.3(5)
121.9
0.930
1.309(5)
1.342(6)
1.401(5)
1.470(6)
1.268(6)
0.930
1.401(6)
1.370(7)
1.392(6)
1.352(6)
1.373(7)
-
1.391(7)
0.930
1.386(6)
1.891(5)
0.930
C4-C5-H27
C6-C5-H27
C1-C6-C5
C8-N18
C8-H24
C9-C10
C9-C14
C10-C11
C10-O15
C11-C12
C11-H20
C12-C13
C12-H21
C13-C14
C13-Br19
C14-H22
O15-H23
N17-H29
H23…N18
O15…N18
RMSD
C1-C6-H28
C5-C6-H28
N16-C7-N17
N16-C7-N18
N17-C7-N18
C9-C8-N18
C9-C8-H24
N18-C8-H24
C8-C9-C10
C8-C9-C14
C10-C9-C14
C9-C10-C11
C9-C10-O15
C11-C10-O15
C10-C11-C12
C10-C11-H20
C12-C11-H20
C11-C12-C13
C11-C12-H21
C13-C12-H21
C12-C13-C14
C12-C13-Br19
C14-C13-Br19
C9-C14-C13
C9-C14-H22
C13-C14-H22
C10-O15-H23
C2-N16-C7
C1-N17-C7
C1-N17-H29
C7-N17-H29
C7-N18-C8
O15-H23…N18
RMSD
121.9
114.4(4)
129.7(4)
115.9(4)
121.0(4)
119.5
119.5
121.4(4)
119.1(4)
119.5(4)
119.1(5)
122.4(4)
118.5(4)
121.3(4)
-
0.820
0.860
1.900
2.618(6)
-
-
119.2(4)
120.4
120.4
119.9(5)
119.9(4)
120.2(4)
121.0(4)
119.5
119.5
109.5
104.0(4)
107.0(4)
126.5
R2
-
0.96979 0.96992 0.97070
126.5
120.3(3)
146.0
-
R2
-
0.97989 0.91445 0.96845
a Taken from Ref [20] and Conf.; Conformer.

ACCEPTED MANUSCRIPT
Table 2. The computed and experimental vibrational frequencies, their assignments and their symmetry species of the BISB molecule.
Exp. (cm-1)
The calculated vibrational parameters with B3LYP/6-311(d,p) level
Conformer 1 Conformer 2 Conformer 3
Unscaled Scaled
Sym. Assignments (PED%)
IR
Raman
Unscaled Scaled
Unscaled
Scaled
freq.
14
IIR
SRaman
freq.
3657
3287
3206
3198
3192
3191
3189
3178
3168
3098
1666
1660
1641
1621
1598
1546
1520
1508
1483
1466
1451
1425
1401
1367
1347
1331
1315
1302
1258
1253
1230
1190
freq.
3536
3178
3100
3092
3087
3086
3084
3073
3063
2996
1611
1605
1587
1567
1545
1495
1470
1458
1434
1418
1404
1378
1355
1322
1303
1287
1272
1259
1217
1212
1189
1151
freq.
15
40
45
99
freq.
-52
36
43
83
freq.
-50
35
41
80
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
νNH(100)
νOH(99)
νCH(98) in ring 1
νCH(93) in ring 3
νCH(95) in ring 1
νCH(99) in ring 1
νCH(92) in ring 3
νCH(99) in ring 3
3317
3238
-
-
-
-
61.416
387.906
2.687
20.653
0.321
0.892
24.614
8.996
0.398
8.107
11.988
36.689
203.176 4294.597
6.933 152.802
74.088
64.650
244.620
246.672
105.153
2.279
241.901
198.610
45.951
64.597
191.067
225.598
39
43
96
-
-
-
-
120
151
183
212
256
268
272
305
338
373
400
416
448
468
480
531
554
586
589
629
638
650
715
741
755
767
781
804
116
146
177
205
247
259
263
295
327
361
387
402
433
452
465
514
536
567
569
608
617
629
692
717
730
742
755
778
119
130
177
217
239
262
282
321
335
353
412
430
455
461
493
536
541
578
591
631
636
647
723
732
754
769
781
809
115
125
171
210
231
253
273
310
324
342
399
415
440
446
476
518
524
558
572
610
615
626
699
708
729
743
755
782
-
-
-
-
-
-
νCH(87) in ring 3
νC8H24(100)
νCC(51) in ring 3
3068
3030
1620
1599
1588
1561
-
-
-
-
νCC(39) in ring 1+δHOC(19)
νN18C8(38)+νCC(12) in ring 1+δHCN(10)
[νCC(23)+δring(13)] in ring 3+δring(10) in ring 2
νCC(22) in ring 1+δHOC(17)+νN18C8(12)+νC9C8(10)
νN18C7(20)+νN16C7(14)+δHNC(12)
[νCC(28)+δHCC(24)] in ring 1
[δHCC(28)+νCC(11)] in ring 1+δHOC(20)
[δring(20)+δHCC(11)] in ring 1+δHOC(14)
δHCC(30) in ring 3+δring(10) in ring 2
δHCC(12) in ring 3+δHOC(11)
νCC(13) in ring 1+δHNC(11)+νN17C7(10)
νCC(16) in ring 1+νN17C1(10)
δHCN(29)+νCC(14) in ring 3+νN16C7(14)
[νCC(52)+δHCC(10)] in ring 1+δHCN(11)
[δHCC(39)+νCC(13)] in ring 3
νOC(35)+[νCC(12)+δHCC(11)] in ring 1
νN16C2(39)+νCC(11) in ring 3
[δHCC(51)+νCC(12)] in ring 1
[δHCC(33)+νCC(12)] in ring 3
δHNC(19)+νCC(14) in ring 1+νC9C8(13)
δHNC(23)+δHCC(12) in ring 1+νC9C8(10)
1605
-
1567
-
155.917 1597.676
118.921 5473.505
26.091
1511
1473
-
1512
-
-
734.876
141.199 286.325
81.245 2206.390
40.777 2803.281
15.741 1501.712
52.350
65.227
12.272
7.106
17.303
74.311
57.800 2320.908
34.196
8.055
113.787
1437
-
1439
-
1401
1367
1340
1318
1301
-
-
1378
1337
1316
1308
-
801.986
105.420
245.306
713.343
259.000
24.261
1266
-
1216
-
1188
1169
1277
1240
-
1204
1180
1148
335.987
145.208
15.330
78.655 1323.029

ACCEPTED MANUSCRIPT
Aʹ
Aʹ
Aʹ
Aʹ
Aʹ
Aʺ
Aʹ
Aʺ
Aʺ
Aʺ
Aʹ
Aʹ
Aʺ
Aʹ
Aʺ
Aʺ
Aʺ
Aʹ
Aʺ
Aʹ
Aʺ
Aʺ
Aʺ
Aʹ
Aʹ
Aʹ
Aʺ
Aʹ
Aʺ
Aʹ
Aʺ
Aʹ
Aʺ
Aʺ
Aʹ
Aʺ
Aʺ
δHCC(51) in ring 3
1137
-
1102
1074
1030
-
995
-
934
915
899
-
872
848
-
817
783
-
-
1119
-
1080
1038
-
1000
950
-
922
-
1170
1153
1137
1092
1055
1024
1024
984
965
943
927
913
891
883
862
841
814
803
782
768
757
742
716
652
638
629
589
581
555
529
498
469
468
444
411
375
343
1131
1115
1100
1056
1020
990
990
952
934
912
897
883
861
854
834
813
787
776
756
743
732
717
693
631
617
608
570
562
537
512
482
453
452
429
397
363
332
2.662
6.798
3.924
16.551
1.017
5.704
8.330
0.066
0.150
1.958
12.443
0.329
9.128
2.994
0.579
12.261
110.909
9.624
5.764
24.499
62.850
5.396
1.981
22.912
17.617
4.700
1.625
21.769
14.319
4.603
54.924
12.450
32.238
0.177
1.690
0.736
0.324
917.585
50.007
24.056
24.822
7.902
9.338
65.775
0.149
834
851
861
875
882
912
924
944
966
806
823
833
846
853
882
893
913
934
947
952
976
997
1056
1098
1115
1132
1169
1181
1211
1215
1254
1277
1287
1306
1335
1343
1372
1380
1416
1427
1452
1471
1502
1546
1568
1597
811
844
863
871
890
908
925
941
970
785
816
834
842
861
878
895
910
938
[δHCC(55)+νCC(26)] in ring 1
[δHCC(51)+νCC(29)] in ring 3
[νCC(37)+δHCC(30)] in ring 1
νN17C1(17)+νN18C7(14)+δC3C2N16(11)+δring(10) in ring 2
τHCNC(91)
[δring(26)+δHCC(14)+νCC(10)] in ring 3
[τHCCC(69)+τring(15)] in ring 3
τHCCC(78) in ring 1
τHCCC(79) in ring 3
δring(38) in ring 1
δring(37) in ring 3+δring(17) in ring 1
τHCCC(71) in ring 1
δring(41) in ring 2+νCC(11) in ring 3
τHCCC(78) in ring 3
τHCCC(71) in ring 1+γOCCC(18)
τHOCC(85)
[νCC(23)+δring(15)] in ring 1+δOCC(11)
τC2N16C7N17(34)+[τring(20)+τHCCC(11)] in ring 3+γC3C1N16C2(18)
δring(10) in ring 1+δring(10) in ring 2
τHCCC(70) in ring 3
τHCCC(23) in ring 3+γNNNC(21)+γOCCC(10)
τHCCC(25) in ring 1+γOCCC(19)+γNNNC(13)
δring(28) in ring 1
0.285
0.098
980
985
983
950
977
987
292.680
17.956
0.202
134.331
0.748
0.561
0.719
33.002
0.614
16.071
0.032
1011
1021
1039
1093
1133
1153
1172
1195
1221
1247
1259
1286
1320
1324
1349
1377
1388
1422
1434
1473
1479
1504
1520
1573
1603
1626
1657
-
1009
1031
1092
1136
1153
1170
1209
1221
1252
1257
1297
1321
1330
1350
1381
1389
1419
1427
1465
1476
1502
1521
1554
1599
1622
1651
869
-
832
817
793
-
752
737
-
1005
1057
1096
1115
1133
1155
1180
1206
1217
1244
1276
1281
1305
1331
1342
1375
1387
1425
1430
1454
1469
1521
1550
1572
1603
-
739
-
-
-
1.007
2.181
5.436
702
643
624
603
570
-
547
507
-
464
-
435
-
692
632
-
607
587
-
527
511
493
467
457
427
414
368
349
δring(47) in ring 1+νBrC(13)
10.861
14.896
0.030
32.130
0.110
23.323
0.530
0.758
0.164
0.359
2.932
0.364
δring(54) in ring 3+δring(27) in ring 2
[τring(33)+τHCCC(14)] in ring 3+γC3C1N16C2(29)
δN17C7N16(25)+δring(20) in ring 3
[τring(42)+τHCCC(15)] in ring 3+γBrCCC(13)
δring(23) in ring 3+δC3C2N16(18)+δring(13) in ring 1
τHNCC(60)+γNNNC(11)
δOCC(56)+δCCC(10) in ring 1
τring(26) in ring 1+τHNCC(25)+γOCCC(11)
γC6N17C2C1(51)
δC14C9N18(23)+δC3C2N16(14)
τring(38) in ring 3+τring(14) in ring 2+γNNNC(11)
τring(47) in ring 1+γOCCC(18)+γBrCCC(15)
-
-
2.536

ACCEPTED MANUSCRIPT
Aʹ
Aʺ
Aʹ
Aʺ
Aʺ
Aʹ
Aʹ
Aʺ
Aʺ
Aʹ
Aʺ
Aʺ
νBrC(29)+δring(12) in ring 1
γC14C9C8N18(36)+γBrCCC(25)
νBrC(23)+δBrCC(23)
γC6N17C2C1(33)+τring(29) in ring 2+τC5C6C1N17(15)
-
-
-
-
-
-
-
-
-
-
-
-
302
272
-
240
215
191
-
-
-
-
-
-
302
277
269
257
221
185
150
120
99
292
268
260
249
213
179
145
116
96
0.830
7.963
4.011
0.651
1.518
1.241
1.071
0.155
1.868
0.008
0.002
2.636
3.596
1.474
7.416
0.660
0.953
0.491
2.229
5.523
2.193
5.309
0.997
3.917
1658
1668
3030
3167
3177
3185
3188
3193
3199
3207
3264
3663
1603
1613
2930
3063
3072
3080
3083
3087
3094
3101
3156
3542
1668
1680
3051
3166
3176
3188
3188
3193
3197
3207
3290
3657
1613
1624
2950
3062
3071
3083
3083
3088
3092
3101
3182
3537
τring(25) in ring 3+τC16C8N18C7(20)+τring(12) in ring 1+γC3C1N16C2(11)
δC9C8N18(16)+νC9C8(13)+νN18C7(12)
δBrCC(43)+δN18C7N16(14)+δC14C9C8(13)
τring(71) in ring 1
Lattice mode
Lattice mode
Lattice mode
46
42
27
44
41
26
Lattice mode
RMSD
36.251
9.904
R2 0.99767 0.99950
ν, stretching; δ, in-plane bending; τ, torsion; γ, out-of-plane bending; IIR, IR intensity (km/mol); SRaman, Raman scattering activity (Å4/amu); TED, total energy distribution.

ACCEPTED MANUSCRIPT
1
Table 3. The experimental and computed H and 13C NMR isotropic
chemical shifts (with recpect to TMS, all values in ppm) of the BISB
molecule.
Atoms δexp. (in DMSO-d6) δcal. (in vacuum) δcal. (in DMSO)
C1
C2
C3
C4
C5
C6
C7
C8
132.86
142.29
118.75
121.66
122.05
110.57
153.86
159.41
119.28
163.12
111.33
136.73
122.45
137.00
147.65
124.39
126.69
127.16
111.51
154.93
167.69
123.24
168.40
121.82
141.96
132.78
140.63
6.156
0.97361
6.91
7.34
7.44
12.29
9.76
7.83
7.35
7.30
7.31
7.60
137.76
147.22
122.70
126.80
127.32
114.04
156.18
168.25
123.81
168.37
122.23
142.59
131.90
141.38
6.312
0.98031
7.06
7.52
7.64
12.68
9.71
7.83
7.47
7.46
7.64
8.44
C9
C10
C11
C12
C13
C14
RMSD
R2
H20
H21
H22
H23
H24
H25
H26
H27
H28
H29
134.06
-
-
7.01-8.09
7.01-8.09
7.01-8.09
12.81 and 12.03
9.63
7.01-8.09
7.01-8.09
7.01-8.09
7.01-8.09
7.01-8.09

ACCEPTED MANUSCRIPT
Table 4. The computed and experimental UV-Vis. parameters of the BISB molecule (in vacuum/chloroform).
The calculated with B3LYP/6-311G(d,p) level
Exp. λ (nm) Transitions
Major
transition
H→L
H-2→L
H-3→L
H→L+2
Major
contribution
0.68732/0.69817
0.68275/0.68608
0.55614/0.58515
0.51207/0.56098
Excitation
energy (eV)
f (oscillator
strength)
λmax. (nm)
386
353
π→π*
π→π*
387.09/394.45
341.80/341.98
263.92/264.50
244.77/244.54
3.2030/3.1432
3.6274/3.6255
4.6978/4.6875
5.0653/5.0701
5.6058/5.6134
5.7276/5.7008
6.0959/6.0645
0.6336/0.8274
0.2331/0.2166
0.1517/0.1793
0.1768/0.1441
0.0630/0.1083
0.3288/0.3478
0.0885/0.1282
278
π→π*
221.17/220.87 H-2→L+1 0.48338/0.44281
216.47/217.49 H-1→L+2 0.47389/0.42760
245
n→σ*
203.39/204.44
H→L+4
0.48833/0.53020

ACCEPTED MANUSCRIPT
Table 5. The computed results with second order perturbation theory of Fock matrix in NBO of the BISB molecule.
ED(i)(e)
1.96568
1.96568
1.97481
1.97458
1.97695
1.71814
1.97809
1.97856
1.97856
1.97461
1.72682
1.97842
1.97911
1.98334
1.84140
1.98571
1.97094
1.88342
1.98624
1.97369
Donor (i)
σ(C1-C2)
σ(C1-C2)
σ(C1-C6)
σ(C2-N16)
σ(C3-C4)
π(C3-C4)
σ(C3-H25)
σ(C4-H26)
σ(C4-H26)
σ(C5-C6)
π(C5-C6)
σ(C5-H27)
σ(C6-H28)
σ(C7-N16)
π(C7-N16)
σ(C7-N17)
σ(C8-C9)
π(C8-N18)
σ(C8-H24)
σ(C9-C10)
ED(j)(e) Acceptor (j)
0.02272 σ*(C1-C6)
0.01724 σ*(N17-H29)
0.04143 σ*(C1-C2)
0.03986 σ*(C7-N18)
0.01986 σ*(C2-N16)
0.33446 π*(C5-C6)
0.04143 σ*(C1-C2)
0.02463 σ*(C2-C3)
0.01427 σ*(C5-C6)
0.02405 σ*(C1-N17)
0.30484 π*(C3-C4)
0.02272 σ*(C1-C6)
0.04143 σ*(C1-C2)
0.02463 σ*(C2-C3)
0.22630 π*(C8-N18)
0.02272 σ*(C1-C6)
0.03986 σ*(C7-N18)
0.39825 π*(C7-N16)
0.04002 σ*(C9-C10)
0.02281 σ*(C9-C14)
0.02511 σ*(C13-C14)
0.03468 σ*(C13-Br19)
0.02791 σ*(C12-C13)
0.03468 σ*(C13-Br19)
0.35550 π*(C13-C14)
0.04002 σ*(C9-C10)
0.02791 σ*(C12-C13)
0.02511 σ*(C13-C14)
0.30112 π*(C11-C12)
0.04002 σ*(C9-C10)
0.02791 σ*(C12-C13)
0.02487 σ*(C10-C11)
0.04002 σ*(C9-C10)
0.04143 σ*(C1-C2)
0.04948 σ*(C7-N17)
0.03986 σ*(C7-N18)
0.39825 π*(C7-N16)
0.02373 σ*(C7-N16)
0.02932 σ*(C8-H24)
0.05955 σ*(O15-H23)
0.35550 π*(C13-C14)
E(2)a (kcal/mol)
5.04
E(j)-E(i)b (a.u.)
1.24
1.06
1.24
1.22
1.17
0.28
1.04
1.08
1.09
1.14
0.29
1.08
1.05
1.42
0.30
1.39
1.14
0.35
1.06
1.24
1.28
0.79
1.26
0.80
0.28
1.04
1.07
1.11
0.30
1.04
1.08
1.29
1.09
0.89
0.79
0.81
0.28
0.94
0.79
0.78
0.31
F(i,j)c (a.u.)
0.071
0.063
0.070
0.091
0.070
0.068
0.060
0.059
0.059
0.078
0.065
0.059
0.061
0.079
0.041
0.074
0.064
0.082
0.061
0.063
0.067
0.059
0.064
0.058
0.062
0.061
0.060
0.062
0.072
0.062
0.062
0.073
0.082
0.070
0.080
0.038
0.106
0.087
0.078
0.120
0.052
4.69
4.97
8.54
5.17
20.15
4.39
4.01
4.03
6.73
17.51
4.00
4.34
5.48
6.67
4.93
4.49
20.47
4.34
4.05
4.35
5.60
4.01
5.26
16.67
4.40
4.16
4.42
21.34
4.51
4.53
5.22
7.68
6.72
9.94
2.14
50.06
9.54
9.31
1.96154. σ(C9-C14)
1.96154
1.96871
1.96871
1.69569
1.97521
1.97521
1.97713
σ(C9-C14)
σ(C11-C12)
σ(C11-C12)
π(C11-C12)
σ(C11-H20)
σ(C11-H20)
σ(C12-H21)
1.72424. π(C13-C14)
1.97648
1.97648
1.98596
1.97324
σ(C14-H22)
σ(C14-H22)
σ(O15-H23)
n(O15)
1.91492. n(N16)
1.91492
1.91492
1.61807
1.87519
1.87519
1.87519
1.94462
n(N16)
n(N16)
n(N17)
n(N18)
n(N18)
n(N18)
n(Br19)
22.38
9.42
ED is the electron density.
a E(2) is the energy of hyperconjugative interaction.
b Energy difference between donor (i) and acceptor (j) NBO.
c F(i,j) is the Fock matrix element between i and j NBO.

ACCEPTED MANUSCRIPT
Figure 1. The optimized molecular structure of the BISB molecule.
Figure 2. The potential energy surface around C8-N18-C7-N1 dihedral angle of the BISB molecule.

ACCEPTED MANUSCRIPT
Figure 3. Experimental ((b) and (c)) and simulated ((a) and (d)) IR and Raman spectra of the BISB molecule.