FT-IR, FT-Raman, HOMO-LUMO and UV-Visible spectral analysis of E-[N′-(1H-INDOL-3YL) METHYLENE ISONICOTINOHYDRAZIDE]

A combined experimental and theoretical study on molecular and vibrational structure of E-[N¢-(1H -indol-3yl) methylene isonicotinohydrazide] (ICINH) had been carried out. The FTIR, FT-Raman and UV-Vis spectra of ICINH were recorded in the solid phase. The optimized geometry was calculated by B3LYP method with 6-311++G(d,p) level of basis set. The harmonic vibrational frequencies, IR intensities and Raman scattering activities of the title compound were calculated at same level of theory. The scaled theoretical wavenumber showed very good agreement with the experimental values. The mulliken charges and thermodynamic functions of the ICINH were also performed at same level of theory. NLO and a study on the electronic properties such as excitation energies and wavelength, were performed by TD-DFT approach. HOMO–LUMO energy gap was also calculated and interpreted.


Introduction
Indole is an aromatic heterocyclic organic compound with a bicyclic structure.It consist of a sixmember benzene ring fused with five-member nitrogen containing pyrrole ring.It is of interest as it can be compared with tryptophane residue [1].The derivative of indole is present in both-animal and plants.The most important compound of this group is tryptophan, an essential amino acid in the human diet, which a 3substituted indole [2].Another important indole derivative is the indole-3-acetic acid, a phytohormone, coordinating several growths processing of plants [3].
The biological activity of the indole derivatives is in connection with the nature of substitution in position 3, on the pyrrole ring [4].Indole derivatives have an important role through individual biological functions.It is present in the side chain of amino acid tryptophan.
The chemical and spectroscopic properties of indole derivatives have been subject of many experimental and theoretical investigations [5][6][7].The indole tryptamine if one of the biogenic monoamines would play anti-tumor effects by either inhibiting cancer cell proliferation or stimulating the anti-cancer immunity [8].DFT method has become an efficient tool in the prediction of molecular structure of organic molecules and in evaluating various molecular properties like conjugation, hydrogen bonding, vibrational frequencies and IR & Raman activities of the bioactive molecule [9][10][11][12][13].
The new Donor-π-Acceptor type dyes D 1-3 , [7].To identify the stable structure, the theoretical conformational analysis was performed.The optimized molecular bond parameters were calculated using B3LYP/6-31G(d,p) basis set.The hyperconjugative interaction energy (E (2) ) and EDs of donor (i) and acceptor (j) bonds were calculated using NBO analysis.The intra-molecular hydrogen bonding interaction was studied between nitrogen and hydroxyl hydrogen (N-H--

Molecular Geometry
The optimized structural parameters of E-[N¢-(1H-indol-3-ylmethylene) isonicotinohydrazide] are calculated using B3LYP/6-311++G(d,p) basis set and listed in Table 1.The optimized structure is shown in from the calculated value.The dihedral angles are also calculated and listed in Table 1.

Vibrational Assignments
The harmonic vibrational frequencies were Hence linear scaling procedure is adopted to scale down the frequency values.In this study, we have followed scaling factor of 0.968 for DFT [17].The observed FT-IR, FT-Raman and simulated spectra of ICINH are shown in Figs. 2 and 3, respectively.

Ring Vibrations
The ring stretching vibrations are very prominent in the spectrum of pyridine and its derivatives and are highly characteristics of aromatic ring itself [18].which is the characteristic region for ready identification of this structure.In this region, the bands are not affected appreciably by the nature of the substituents.
In the present study, the peak at 3107 cm −1 in FT-IR and at 3109 cm −1 in FT-Raman are assigned to C−H stretching vibrations of the pyridine ring.The percentage of PED results show that these modes are  In-plane bending

S.No Type Fragment type Definition
Table 2.1 continued from page 9

S.No Type
Fragment type Definition

C=O Vibrations
The characteristic IR absorption wavenumber of C=O is normally strong in intensity and found in the region 1600-1800 cm −1 [21,22].In the present study, the strong peak at 1677 cm

N−H Vibrations
In primary amines, usually the N-H stretching vibrations occur in the region 3600-3300 cm −1 [23].In the present study, the N-H bond in the five member ring produce a well defined peak at 3531 cm −1 in FT-IR.A peak for the N 19 −H 20 bond present at the out-of-the ring is not active in both IR and Raman.Hence, the theoretical scaled value of 3540 cm −1 is assigned to N 15 −H 13 stretching mode.All the vibrations in this group are in excellent agreement with experimental results as well as with literature [24].

C=N and N−N Vibrations
The  3 shows that the first order hyperpolarizability value play an important role in determining the NLO activity of the molecule.The first order hyper polarizability (β 0 ) of the present molecule is 8.6424x10 -30 esu while that of urea is 0.3728x10 -30 esu.
The (β o ) of ICINH is 23 times greater than that of urea, hence, the molecule can be said to be highly NLO activity; which is naturally due to the contribution of oxygen atom which makes one part of molecule highly negative and other part as equally positive.

NBO Analysis
The NBO analysis is performed on ICINH using B3LYP/6-311++G(d,p) basis set and are listed in Table 4.In the study, the π bonds have higher ED than the σ bonds.Due to this reason, the σ-σ* transitions have minimum delocalization energy than the π-π* transitions.It is evident from the

HOMO-LUMO Analysis
The gap.In addition, the frontier molecular orbital energies are also calculated using the same basis set and are listed in Table 6.

UV-Vis Spectra
The UV absorption spectrum for ICINH is

Molecular electrostatic potential
In the present study, MEP surface map of ICINH is calculated using B3LYP/6-311++G(d,p) basis set and illustrated in Fig. 6 The MEP which is a plot of electrostatic potential map onto the constant ED surface.
In the majority of the MEPs, the maximum negative region which is the preferred site for electrophilic attack and the maximum positive region is the preferred site for nucleophilic attack.The importance of MEPs lies in the fact that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of colour scheme (Fig. 6) and is very useful in research of molecular

Thermodynamic Properties
On the basis of vibrational analysis, the standard statistical thermodynamic functions: heat capacity (C), entropy (S) and enthalpy changes (H) for the title molecule are obtained from the theoretical harmonic frequencies and are listed in Table 9.From Table 10, it can be observed that these thermodynamic functions are increasing with temperature ranging from 100 to 1000 K.The obvious reason for this is almost linear increase, and this is due to the increase in internal energy of the molecule in accordance with kinetic theory of gases due to the fact that the molecular vibrational intensities increase with temperature [30].The correlation equations between heat capacities, entropies, enthalpy, changes and temperatures are fitted by quadratic formulas and the corresponding fitting factors (R 2 ) for these thermodynamic properties are 0.99905, 0.9994 and 0.99998, respectively and the correlation graphics are shown in Fig. 8.
They can be used to compute the other thermodynamic energies according to relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics in thermo chemical field [31].In this study all thermodynamic calculations are done in gas phase and they could not be used in solution.

carrying 3 -
photovoltaic efficiency among the three dyes.This can be attributed to the longer electron lifetime and lower recombination rates.Additionally, a single crystal XRD study confirms the structure of a key intermediate.

Fig. 1 .
Fig. 1.The title molecule consists of pyridine and indole ring fused by hydrazone linkage.In ICINH, the hydrazone linkage plays an important role.For the carbonyl (C 21 =O 29 ) bond length in hydrazone link is calculated about 1.223Å using DFT and corresponding Xray data value is 1.236Å.The bond length of N 18 -N 19 is acted as bridge between the phenyl and pyridine ring and its bond length is calculated using DFT calculation at 1.368Å, while the corresponding X-rays value is 1.392Å.Similarly, the C 21 -N 19 /C 16 =N 18 bond lengths are calculated as: 1.384 : DFT; 1.330Å : X-rays data/1.288: DFT; 1.278Å : X-rays data, respectively.In the present study, the average value of C-C bond lengths in indole ring is 1.403Å (DFT).Bikas et al., [16], observed the bond angle of O-C-C at 120.6˚, which was in consistent with calculated value 121.49˚ (O 29 -C 21 -C 22 ) and its corresponding DFT value is positively deviated (~ 1˚) The C−C stretching vibrations of pyridine derivatives usually appear in the region between 1650-1400 cm −1 and 1100−1000 cm −1[19].In the present study, the peaks identified at 1006 cm −1 in FT-IR and 1009 cm −1 in FT-Raman are assigned to C−C stretching vibrations.Due to the absence of peaks, the theoretically scaled values at 1553, 1318 and 1025 cm −1 are assigned as C−C stretching vibrations of the rest of other modes in pyridine ring .The presence of nitrogen in the ring of the pyridine structure gives rise to two C−N stretching vibrations.Identifying these vibrations is rather a difficult task as their vibrational frequency lies within the C−C stretching region.As expected, the peaks for C−N stretching vibrations are found at 1244 cm −1 in FT-IR and 1254 cm −1 in FT-Raman spectrum.The theoretically scaled values of this mode are found to be in good agreement with experimental values.According to PED results, the C−C stretching vibrations of six and five members are assigned.The C−C stretching vibrations are observed at 1608, 1501 and 1336 cm −1 in FT-IR and 1606, 1563, 1345 and 1284 cm −1 in FT-Raman spectrum.The theoretically predicted scaled values are in excellent correlation with that of the experimental values.C−H Vibrations Four C−H bonds in the pyridine ring of the title molecule give rise to four C−H stretching vibrations.The hetero-aromatic structure shows the presence of C−H stretching vibrations in the region 3000−3100 cm −1 [20],

Fig. 2 .Fig. 3 .
Fig. 2. The combined theoretical and experimental FT-IR spectra of ICINH identification of C=N stretching vibrations are difficult task since these are usually coupled with ring stretching and C-H in-plane bending vibrations.A bond C 21 =N 19 at out of the ring possesses three vibrational normal modes.Since all these vibrations are inactive in both the spectra, the theoretically predicted wavenumbers 1604, 849 and 535 cm −1 are ascribed to C=N stretching, in-plane bending and out-of-plane bending, respectively.Similarly, the N−N stretching and bending vibrations are not present in both IR and Raman.Hence, the theoretically scaled values of 1074, 647 and 166 cm −1 are attributed to N−N stretching, inplane bending and out-of-plane bending vibrations, respectively.NLO PropertyNon linear effect arise from the interactions of electromagnetic fields in various media to produce new fields altered in phase, frequency, amplitude or other propagation characteristics from incident fields[25].The first hyperpolarizability (β 0 ), dipole moment μ and polarizability α are calculated using DFT/6-311++G(d,p) basis set.The computed total static dipole moment (μ), the mean polarizability (α 0 ) the mean first hyperpolarizability (β 0 ), for the molecule under study are presented in Table

30 esu)
: esu-electrostatic unit www.openaccesspub.org| JNDC CC-license DOI : 10.14302/issn.2377-2549.jndc-17-1459Vol-1 Issue -3 Page No- HOMO-LUMO plot of ICINH molecule is shown in Fig. 4 In HOMO diagram, the colored portions indicate the prominent donor levels which contribute in the electronic transitions and similarly the LUMO diagram indicates the prominent acceptors level through colored shades which involve in the electronic transitions.Homo localized in the indole and carbonyl group.The LUMO is located over the pyridine and hydrazone linkage.The molecule ICINH has lower energy gap and hence the probability of π-π* proton transition is highly possible in between HOMO and LUMO orbitals.The HOMO/LUMO energies are calculated using B3LYP/6-311++G(d,p) level.By using HOMO and LUMO energy value ICINH, the global chemical reactivity descriptors such as hardness (η), chemical potential (μ), softness (S), electronegativity (χ) and electrophilicity index (ω) have been calculated and are listed in Table 5.It can be expressed through HOMO and LUMO orbital energies as I=-E HOMO and A=-E LOMO , the electron affinity I and Ionization potential A of title molecule ICINH are also calculated by using B3LYP/6-311++G(d,p) basis set.The calculated values of the softness, hardness, chemical potential electronegativity and electrophilicity index, Homo, Lumo and energy gap of the molecule are: 4.341 eV, 3.954 eV, 3.954 eV and 1.801 eV, -6.125 eV, -1.784 eV and 4.341 eV, respectively.The soft molecule has small energy gap and hard molecule has large energy Fig. 5.

Table 4
the acceptor orbitals: C 22 -C 24 and C 23 -C 25 , respectively.There occurs a strong intra-molecular hyperconjugative interaction of π electron from C 23 -C 25 bond to the π*C 22 -C 24 →C 30 -N 32 bonds, which increases the EDs: 0.3281 and 0.3727 kJ/mol, respectively.The lone pair electrons