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  • FT-IR, FT-Raman, Homo-Lumo and UV-Visible Spectral Analysis of E-(N′-(1H-INDOL-3YL) Methylene Isonicotinohydrazide)

    D.Sumathi  a     H. Saleem a       A. Nathiya a     N.RameshBabu  b     D.Usha  c    

    aDepartment of Physics, Annamalai University, Annamalainagar-608 002, Tamil Nadu, India

    bDepartment of Physics, MIET Engineering College, Tiruchirappalli – 620 007, Tamil Nadu, India

    cDepartment of Physics, Women’s Christian college, Nagercoil – 629 001, Tamil Nadu, India

    Abstract

    A combined experimental and theoretical study on molecular and vibrational structure of E- (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.

    Received 14 Feb 2017; Accepted 25 Mar 2017; Published 22 May 2017;

    Academic Editor:Dr. Ashish Kumar, Associate Professor and HOD -Department of Chemistry, Lovely Professional University Phagwara

    Checked for plagiarism: Yes

    Review by: Single-blind

    Copyright©  2017 D Sumathi, et al

    License
    Creative Commons License    This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

    Competing interests

    The authors have declared that no competing interests exist.

    Citation:

    D.Sumathi , H. Saleem, A. Nathiya, N.RameshBabu , D.Usha (2017) FT-IR, FT-Raman, Homo-Lumo and UV-Visible Spectral Analysis of E-(N′-(1H-INDOL-3YL) Methylene Isonicotinohydrazide). Journal of new Developments in Chemistry - 1(3):1-37.
    Download as RIS, BibTeX, Text (Include abstract )
    DOI10.14302/issn.2377-2549.jndc-17-1459

    Introduction

    Indole is an aromatic heterocyclic organic compound with a bicyclic structure. It consist of a six-member 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 3-substituted 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 D1-3 carrying 3-(1-hexyl-1H-indol-3-yl)-2-(thiophen-2-yl) acrylonitrile as backbone with three different acceptor units were designed and synthesized by Babu, 14, using sensitizers for solar cell application. The new dyes were characterized by various spectral and elemental analyses. Their optical and electrochemical properties were investigated using spectrophotometry and cyclic voltammetry, respectively. The DFT study was carried out to investigate their Frontier MO energy states. The above study reveals that the dye carrying 4-aminobenzoic acid as an acceptor showed the highest 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.

    The stability of the syn and anti structures of the non-steroidal anti-inflammatory drug indomethacin were investigated by Hassan et al., 15, using the DFT/B3LYP and ab initio MP2 calculations with the 6-311G(d,p) basis set. The molecule indomethacin was predicted at the DFT and MP2 levels of calculation to have the syn (C1N7C10C18 ~ 40˚) form being about 1.7 and 1.5 kcal/mol, respectively, lower in energy than the anti (C1N7C10C18 ~ 140˚) structure. The calculated CNCC torsional angles for the chlorobenzene and indole rings syn-anti conformational interconversion was in a good qualitative agreement with the reported XRD angles (C1N7C10C18 ~ 29 and 155˚) for the syn and anti conformers, respectively. Indomethacin was estimated from the calculated Gibb’s free energies to have an equilibrium mixture of 95% syn and 5% anti structures at 298.15 K. The vibrational wavenumbers were calculated at the same level of theory. The complete vibrational assignments were provided on the basis of theoretical and NCA combined with experimental IR and Raman data of the molecule. The analysis of the observed spectra supported the presence of indomethacin in only one conformation at room temperature.

    The (E)-2-(2-hydroxybenzylidenamino)-3-(1H-indol-3yl) propionic acid was synthesized by Saleem et al., 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 dipole moment (µ) and first order hyperpolarizability (β0) were calculated. The band gap energy was analyzed by UV–Vis recorded spectra and compared with theoretical band gap (TD-DFT/B3LYP/6-31G(d,p)) value. The intra-molecular hydrogen bonding interaction was studied between nitrogen and hydroxyl hydrogen (N-H---O).

    The molecular structure, complete vibrational spectra and the quantum mechanical calculations of the title compound were not yet reported. Therefore, the vibrational spectrum and the quantum mechanical calculations for the title compound in the ground state by DFT method with the standard 6-311++G(d,p) level of basis set were reported. Electronic absorption spectra of the title compound were predicted by using TD-DFT method. The excitation energies, wavelength and oscillator strengths were obtained at the same level of theory. Besides the molecular parameters, dipole moments, NLO, thermodynamic properties, linear polarizability and first hyperpolarizability, were calculated. The results obtained from theoretical calculations and experimental were compared.

    Experimental Details

    Synthesis Procedure

    1H-indole-3-carbaldehyde (1.45 g, 0.01 mol) and isonicotinic acid hydrazide (1.37 g, 0.01 mol) were added to ethanol (10 ml) and stirred for an hour in the presence of hydrochloric acid to form a white precipitate. The precipitate was washed with sodium bicarbonate solution and filtered and again washed with petroleum ether (40–60%) and dried in air. The compound was recrystallized from absolute ethanol.

    Results and Discussion

    Molecular Geometry

    The optimized structural parameters of E- are calculated using B3LYP/6-311++G(d,p) basis set and listed in Table 1. The optimized structure is shown in Figure 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 (C21=O29) bond length in hydrazone link is calculated about 1.223Å using DFT and corresponding X-ray data value is 1.236Å. The bond length of N18-N19 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 C21-N19/C16=N18 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˚ (O29-C21-C22) and its corresponding DFT value is positively deviated (~ 1˚) from the calculated value. The dihedral angles are also calculated and listed in Table 1.

    Figure 1. The optimized molecular structure of ICINH
    Figure 1.

    Table 1. The optimized bond parameters of ICINH using B3LYP/6-311++G(d,p)basis set
    Bond Parameters B3LYP/6-311++G(d,p) XRDa
    Bond Lengths (Å)
    C1-C2 1.416
    C1-C6 1.396
    C1-N15 1.383 1.347
    C2-C3 1.404
    C2-C8 1.451 1.445
    C3-C4 1.387
    C3-H9 1.084
    C4-C5 1.408
    C4-H10 1.084
    C5-C6 1.388
    C5-H11 1.084
    C6-H12 1.084
    C7-C8 1.385
    C7-H14 1.078
    C7-N15 1.372
    C8-C16 1.455 1.437
    H13-N15 1.007
    C16-H17 1.087
    C16-N18 1.288 1.278
    N18-N19 1.368 1.392
    N19-H20 1.019
    N19-C21 1.384 1.33
    C21-C22 1.496 1.495
    C21-O29 1.223 1.236
    C22-C23 1.398
    C22-C24 1.401
    C23-C25 1.388
    C23-H26 1.083
    C24-H27 1.082  
    C24-N31 1.335
    C25-C28 1.394
    C25-H29 1.084
    C28-H30 1.0867
    C28-N31 1.336  
    Bond Angles (°)
    C2-C1-C6 122.55
    C2-C1-N15 107.12 109.56
    C6-C1-N15 130.34
    C1-C2-C3 118.87
    C1-C2-C8 107.31
    C3-C2-C8 133.81
    C2-C3-C4 118.9
    C2-C3-H9 120.86
    C4-C3-H9 120.24
    C3-C4-C5 121.19
    C3-C4-H10 119.6
    C5-C4-H10 119.2
    C4-C5-C6 121.18
    C4-C5-H11 119.4
    C6-C5-H11 119.42
    C1-C6-C5 117.31
    C1-C6-H12 121.52
    C5-C6-H12 121.17
    C8-C7-H14 130.27  
    C8-C7-N15 109.75
    H14-C7-N15 119.85 123.3
    C2-C8-C7 106.01
    C2-C8-C16 123.89 130.5
    C7-C8-C16 129.95
    C1-N15-C7 109.81
    C1-N15-H13 125.49
    C7-N15-H13 124.69
    C8-C16-H17 115.93
    C8-C16-N18 130.93
    H17-C16-N18 113.14
    C16-N18-N19 117.96 113.29
    N18-N19-H20 119.23
    N18-N19-C21 123.39 120.33
    H20-N19-C21 112.73
    N19-C21-C22 119.89 114.64
    N19-C21-O29 118.6 124.7
    C22-C21-O29 121.49 120.6
    C21-C22-C23 117.13
    C21-C22-C24 124.87
    C23-C22-C24 117.85
    C22-C23-C25 119.05
    C22-C23-H26 119.22
    C25-C23-H26 121.73
    C22-C24-H27 120.51
    C22-C24-N31 123.46
    H27-C24-N31 116.03
    C23-C25-C28 118.39
    C23-C25-H29 121.19
    C28-C25-H29 120.41
    C25-C28-H30 120.46
    C25-C28-N31 123.5
    H30-C28-N31 116.05
    C24-N31-C28 117.73
    C6-C1-C2-C3 -0.05
    C6-C1-C2-C8 -179.54
    N15-C1-C2-C3 179.79
    N15-C1-C2-C8 0.29
    C2-C1-C6-C5 -0.29
    C2-C1-C6-H12 179.72
    N15-C1-C6-C5 179.92
    N15-C1-C6-H12 -0.07
    C2-C1-N15-C7 -0.26
    C2-C1-N15-H13 179.33
    C6-C1-N15-C7 179.56
    C6-C1-N15-H13 -0.85
    C1-C2-C3-C4 0.41
    C1-C2-C3-H9 -179.24
    C8-C2-C3-C4 179.74
    C8-C2-C3-H9 0.09
    C1-C2-C8-C7 -0.22
    C1-C2-C8-C16 -176.16
    C3-C2-C8-C7 -179.61
    C3-C2-C8-C16 4.45
    C2-C3-C4-C5 -0.44
    C2-C3-C4-H10 179.88
    H9-C3-C4-C5 179.21
    H9-C3-C4-H10 -0.47
    C3-C4-C5-C6 0.11
    C3-C4-C5-H11 -179.77
    H10-C4-C5-C6 179.78
    H10-C4-C5-H11 -0.09
    C4-C5-C6-C1 0.26
    C4-C5-C6-H12 -179.75  
    H11-C5-C6-C1 -179.87
    H11-C5-C6-H12 0.12
    H14-C7-C8-C2 -175.75
    H14-C7-C8-C16 -0.14
    N15-C7-C8-C2 0.06
    N15-C7-C8-C16 175.67
    C8-C7-N15-C1 0.12
    C8-C7-N15-H13 -179.48
    H14-C7-N15-C1 176.44
    H14-C7-N15-H13 -3.16
    C2-C8-C16-H17 20.44
    C2-C8-C16-N18 -158.81
    C8-C16-N18-N19 -154.47
    H17-C16-N18-N19 26.29  
    C16-N18-N19-H20 2.17
    C16-N18-N19-C21 -177.1
    N18-N19-C21-C22 21.38
    N18-N19-C21-O32 175.42
    H20-N19-C21-C22 21.29
    H20-N19-C21-O32 -160.76
    N19-N21-C22-C23 176.81
    N19-N21-C22-C24 -5.23
    O32-C21-C22-C23 -156.35
    O32-C21-C22-C24 28.1
    C21-C22-C23-C25 25.76
    C21-C22-C23-H26 -149.79
    C24-C22-C23-C25 -177.41
    C24-C22-C23-H26 2.29
    C21-C22-C24-H27 -1.54
    C21-C22-C24-N31 178.16
    C23-C22-C24-H27 -3.35
    C23-C22-C24-N31 175.99
    C22-C23-C25-C28 -178.87
    C22-C23-C25-H29 0.47
    H26-C23-C25-C28 1.25
    H26-C23-C25-H29 -179.2
    C22-C24-N31-C28 -178.45
    H27-C24-N31-C28 1.1
    C23-C25-C28-H30 0.92
    C23-C25-C28-N31 -179.72
    H29-C25-C28-H30 179.8
    H29-C25-C28-N31 0.18
    C25-C28-N31-C24 0.25
    H30-C28-N31-C24 -179.37

    Vibrational Assignments

    The harmonic vibrational frequencies were calculated using B3LYP/6-311++G(d,p) basis set. The title molecule belongs to C1 point group symmetry and it had 90 vibrational normal modes of same symmetry species are listed in Table 2.1. The internal and symmetry coordinates of ICINH are listed in Table 2.1 and Table 2.2, respectively. The percentage of PED obtained from MOLVIB program package was used for assigning vibrational peaks. The exclusion of anharmonicity factor and the level of basis set used, certain theoretical frequencies are not matched with that of the experimental values. 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 Figure 2 and Figure 3, respectively.

    Table 2. 1. Possible internal co-ordinates of ICINH
    S.No Type Fragment type Definition
    8-Jan C-C Double ring C1-C2, C2-C3, C3-C4, C4-C5, C5-C6, C6-C1, C2-C8, C7-C8
    9,10 C-N C1-N15, C7-N15
    15-Nov C-H C3-H9, C4-H10, C5-H11, C6-H12, C7-H14
    16 N-H N15-H13
    17-20 C-C Pyridine ring C22-C23, C22-C24, C23-C25, C25-C28
    21,22 C-N C24-N31, C28-N31
    23-26 C-H C23-H26, C24-H27, C25-H29, C28-H30
    27,28 C-C Out-of the ring C8-C16, C21-C22
    29 C=O C21-O32
    30 N-H N19-H20
    31 C-H C16-H17
    32,33 C-N C16-N18, C21-N19
    34 N-N N18-N19
    In-plane bending
    35-45 C-C(N)-C(N) Double ring C1-C2 -C3, C2-C3-C4, C3-C4 -C5, C4-C5 -C6, C5-C6 -C1, C6-C1-C2, C1-C2-C8, C2-C8-C7, C8-C7-N15, C7-N15-C1
    N15-C1 -C2
    46-55 C(N)-C-H C2-C3 -H9, C4-C3 -H9, C3-C4 -H10, C5-C4 -H10, C4-C5 -H11, C6-C5 -H11, C1-C6 -H12, C5-C6 -H12, C8-C7 -H14, N15-C7 -H14
    56,57 C-N-H C1-N15-H13, C7-N15-H13
    58,59 C-C-C(N) C6-C1-N15, C3-C2-C8
    60,61 C-C-H Out-of the ring C8-C16-H17, N18-C16-H17
    62,63 C-C-N C8-C16-N18, C22-C21-N19
    64,65 C-N-N   C16-N18-N19, C21-N19-N18
    66,67 C(N)-N-H C21-N19-H20, N18-N19-H20
    68,69 C(N)-C=O C22-C21-O32, N19-C21-O32
    70-73 C-C-C C21-C22 -C23, C21-C22-C24, C2-C8 -C16, C7-C8-C16
    74-79 C-C(N)-C(N) Pyridine ring C22-C23 -C25, C23-C25-C28, C25-C28 -N31, C28-N31-C24, N31-C24-C22, C24-C22-C23
    80-87 C(N)-C-H C22-C23-H26, C25-C23-H26, C22-C24-H27, N31-C24-H27, C23-C25-H29, C28-C25-H29, C25-C28-H30, N31-C28-H30
    Out-of-plane bending
    88-98 C(N)-C(N)-C(N)-C(N) Double ring C1-C2-C3-C4, C2-C3-C4-C5, C3-C4-C5-C6, C4-C5 -C6-C1, C5-C6-C1-C2, C6-C1-C2-C3, C1-C2 -C8-C7, C2-C8-C7-N15, C8-C7-N15-C1, C7-N15-C1-C2, N15-C1 -C2-C8
    99-103 H-C(N)-C-C(N) H9-C3-C2-C4, H10-C4-C3-C5, H11-C5-C4-C6, H12-C6-C1-C5, H13-N15-C1-C7, H14-C7-C8-N15
    105,106 C-C-C-C Out-of the ring C16-C8-C2-C7, C21-C22-C23-C24
    107 O-C-C-N O32-C21-C22-N19
    108 H-N-N-C H20-N19-N18-C21
    109 H-C-C-N H17-C16-C8-N18
    110 C-N-N-C C16-N18-N19-C21
    111-114 N-C-C-C N19-C21-C22-C23, N19-C21-C22-C24,
    C2- C8- C16-N18, C7-C8-C16-N18
    115-120 C(N)-C(N)-C(N)-C(N) Pyridine C22-C23-C25-C28, C23-C25-C28-N31, C25-C28-N31-C24, C28-N31-C24-C22, N31-C24-C22-C23, C24-C22-C23-C25
    121-124 H-C-C-C H26-C23-C22-C25, H27-C24-C22-N31, H29-C25-C23-C28, H30-C28-C25-N31
    125,126 C(N)-C-C-C Torsion C3-C2-C8-C16, N15-C7-C8-C16
    127,128 C-C-C-C(N) Butterfly C8-C2-C1-C6, C3-C2-C1-N15

    Table 2. 2. Local Symmetry coordinates of ICINH
    S.No Type Fragment type Definition
    8-Jan C-C Double ring R1, R2, R3, R4, R5, R6, R7, R8
    9,10 C-N R9, R10
    15-Nov C-H R11, R12, R13, R14, R15
    16 N-H R16
    17-20 C-C Pyridine ring R17, R18, R19, R20
    21,22 C-N R21, R22
    23-26 C-H R23, R24, R25, R26
    27,28 C-C Out-of the ring R27, R28
    29 C=O R29
    30 N-H R30
    31 C-H R31
    32,33 C-N R32, R33
    34 N-N R34
    In-plane bending
    35 C(N)-C(N)-C(N) Double ring
    36
    37
    38
    39
    40-44 C(N)-C-H (β46-β47)/√2(β48-β49)/2(β50-β51)/2(β52-β53)/2(β54-β55)/2
    (β56-β57)/√2

    45 C-N-H
    46,47 C(N)-C(N)-C(N) b58, b59
    48 C-C-H Out-of the ring
    (β60-β61)/2

    49,50 C-C-N
    51 C-N-N
    (β64-β65)/2(β66-β67)/2(β68-β69)/2(β70-β71)/2(β72-β73)/2

    52 C(N)-N-H
    53 C(N)-C=O
    54,55 C-C-C
    56 C-C(N)-C(N) Pyridine ring
    57
    58
    59-62 C(N)-C-H (β80-β81)/√2(β82-β83)/2(β84-β85)/2
    , (β86-β87)/2

    ,
    Out-of-plane bending
    63 C(N)-C(N)-C(N)-C(N) Double ring
    64
    65
    66
    67
    68-73 H-C(N)-C-C(N) g99, g100, g101, g102, g103, g104
    74,75 C-C-C-C Out-of the ring g105, g106
    76 O-C-C-N g107
    77 H-N-N-C g108
    78 H-C-C-N g109
    79 C-N-N-C g110
    80,81 N-C-C-C (γ111-γ112)/2(γ113-γ114)/2

    82 C(N)-C(N)-C(N)-C(N) Pyridine
    83
    84 (γ127-γ128)/2
    85-88 H-C-C-C g121, g122, g123, g124
    89 C(N)-C-C-C Ring Torsion (γ125-γ126)/2
    (γ127-γ128)/2

    90 C-C-C-C(N) Butterfly

    Table 2. 3. The experimental and calculated frequencies of ICINH using B3LYP/6-311++G(d,p) level of basis set harmonic frequencies (cm−1) IR Raman intensities (Km/mol) reduced masses (amu) and force constants (mdynA°−1)
    Mode No Exp. IR Exp. Raman Frequencies Scaled Red. Masses Force IR Raman Intensity Vibrational Assignments
    frequencies constants Intensity
    1 - - 23 22 5.6685 0.0017 0.05 41.46 gring (90)
    2 - - 31 30 6.2039 0.0035 0.26 47.75 gring (93)
    3 - - 38 37 4.7887 0.0041 0.29 50.62 g(py)ring (97)
    4 - - 73 70 6.1906 0.0192 0.52 0.88 g(py)ring (98)
    5 - 89 93 90 6.2748 0.0318 0.06 10.04 gring (89)
    6 - - 132 128 6.7417 0.0692 0.31 3.54 gC=O (69), gring (23)
    7 - - 151 146 5.367 0.0716 0.35 3.71 gring (66), gN−N (26)
    8 - - 171 166 4.8316 0.0835 0.2 5 gN−N(54), gring (37)
    9 - - 196 190 5.1729 0.1176 0.19 3.45 g(py)ring (67), Butterfly (21)
    10 - - 223 216 4.1358 0.1213 2.07 1.51 Butterfly (89)
    11 - - 236 229 5.5815 0.1835 2.48 4.94 β(py)ring (78)
    12 - - 295 285 7.0353 0.3595 0.36 0.27 tring (94)
    13   - 376 363 5.8348 0.4847 0.8 0.48 gring (62), goutC−C(21)
    14 - - 402 389 3.5462 0.3379 0.58 1.55 goutC−N(43), gN−N(18), gring(14)
    15 - - 418 405 5.2085 0.5367 0.63 1.35 gring (69), g(py)ring (24)
    16 - - 426 412 2.5799 0.2753 6.89 0.44 goutC−C(50), bC−N(22), bN−H(10)
    17 426 - 440 426 1.5194 0.1731 7.82 0.87 gN−H(78)
    18 - - 449 434 3.4966 0.415 3.38 0.38 goutC−C(56), gC−H (22)
    19 - - 498 482 5.8526 0.8561 0.62 1.6 βring (49),goutC−C(19), gring (18)
    20 - - 552 535 5.1322 0.9221 1.85 2.76 gC=N(61), gring (26)
    21 - - 563 545 5.496 1.0281 0.54 2.03 βring (72)
    22 - - 582 564 2.8828 0.5762 1.76 4.01 βoutC-C (46), βN‒H (23)
    23 - - 589 570 3.2755 0.6698 7.32 2.24 goutN−H(63), βC−H (18)
    24 581 - 606 587 5.2868 1.1458 11.97 3.94 β(py)ring (68), goutN−H(22)
    25 615 - 637 616 6.325 1.5108 2.52 1.88 βoutC-C (58), βC‒H (20), βN‒H (14)
    26 - - 643 623 2.7471 0.6694 0.95 1.01 βring (52), gC−H (24)
    27 - - 668 647 2.6474 0.6964 2.08 15.49 βN-N (50), βC‒N (18), β(py)ring (14)
    28 682 - 702 679 4.4972 1.3055 1.36 2.28 βring (51), β(py)ring (27)
    29 - - 719 696 2.1818 0.6637 3.21 0.31 βoutC-C (47), βoutC−H (20), βring (17)
    30 - - 748 724 3.0533 1.0053 12.23 4.31 βoutC-N (57), βpyring (18), βC=O (13)
    31 - - 751 727 1.4353 0.477 18.39 0.67 gC-H (79)
    32 - - 754 730 4.3578 1.4603 3.85 4.77 gC-H (74), β(py)ring (13)
    33 752 - 774 749 3.9285 1.3867 0.53 1.49 βoutC-H (48), βring (21)
    34 - - 784 759 4.6888 1.6972 4.98 9.52 βring (56), β(py)ring (23)
    35 793 795 828 802 1.3744 0.5555 1.89 1.51 gC-H (88)
    36 - - 840 813 1.9452 0.808 2.26 1.91 g(py)C-H (92)
    37 830 - 855 828 1.4952 0.6446 0.98 0.25 βC=O (60), β(py)ring (19)
    38 - - 877 849 3.9613 1.796 23.55 3.59 βC=N (45), βring (24), β(py)ring (18)
    39 - - 893 864 4.4426 2.0861 3.75 0.23 βring (78)
    40 - - 919 890 1.4668 0.7301 1.25 6.07 gC-H (91)
    41 912 - 944 913 1.3666 0.717 0.23 0.11 gC-H (87)
    42 - - 949 919 1.3956 0.7404 0.86 0.11 g(py)C-H (90)
    43 - - 981 949 1.2808 0.7258 0.01 0.06 bN-H (59), bC−H(21)
    44 953 - 986 955 1.4487 0.8303 0.17 0.01 g(py)C-H (92)
    45 - - 1006 974 1.3774 0.8218 0.47 0.09 g(py)C-H (92)
    46 - - 1035 1002 2.1293 1.3435 1.87 6.9 υC-C (41), βC‒H (28)
    47 1006 1009 1040 1007 4.2574 2.715 2.2 2.57 υ(py)C-C (52), β(py)C‒H (29)
    48 - - 1059 1025 3.2592 2.1539 0.09 13.5 υ(py)C-C (68), β(py)C‒H (24)
    49 1047 1041 1066 1032 4.5472 3.0425 4.45 1.84 υoutC-C (45), βring (20), βC‒H (14)
    50 - - 1109 1074 3.4326 2.4881 18.31 16.64 υN-N(52), β(py)C‒H (18), βoutC‒H (13)
    51 - 1092 1129 1093 1.5981 1.2012 5.03 1.73 β C-H (47), βN‒H (22), υC‒N(17)
    52 - - 1139 1102 1.4616 1.1167 0.86 0.43 β(py)C-H (50), υ(py)C‒C (27)
    53 - - 1155 1118 1.4763 1.1596 8.68 0.69 βC-H (69)
    54 1126 1125 1160 1123 2.4869 1.9719 14.1 1.24 υoutC-C (42), υoutC‒N (28) β(py)C‒H (15),
    55 - - 1178 1140 1.1543 0.9431 0.36 0.39 υC-C (53), υC‒N (19), βC‒H (15)
    56 - - 1225 1186 1.4787 1.3081 2.73 1.51 β(py)C-H (72), υ(py)C‒N (20)
    57 - - 1251 1211 2.7583 2.5422 12.8 0.79 βC-H (52), υC‒N(18), βN‒H (14)
    58 - - 1263 1222 1.8362 1.7252 7.35 10.89 υC-N (54), βC‒H (31)
    59 1244 1254 1285 1244 7.2124 7.0219 2.07 1.25 υ(py)C-N (59), β(py)C‒H (22)
    60 - 1284 1325 1282 2.4286 2.5111 0.37 5.82 υC-C (62), βC‒H (20)
    61 1298 - 1339 1296 2.3836 2.5178 54.46 0.89 β C‒H (49), υC‒N(19), βoutC‒H (17)
    62 - - 1361 1318 3.0228 3.3 71.69 18.1 υ(py) C‒C (50), βC‒H (21), υoutC‒C (12)
    63 - - 1365 1322 1.2876 1.4144 0.5 0.8 υoutC‒N (58), βC‒H (23)
    64 1336 1345 1371 1327 5.9533 6.5908 6.32 4.61 υC‒C (72), βC‒H (21)
    65 1360 1368 1410 1364 1.5509 1.8154 16.15 8.86 boutC‒H (59), υC‒N (15), βN‒H (12)
    66 - - 1442 1396 2.1721 2.6626 6.54 4.66 υC‒C (49), βC‒H (27)
    67 1408 - 1447 1401 2.2447 2.7699 2.37 1.22 β(py)C‒H (65), υ(py) (24)
    68 - - 1473 1426 1.7655 2.2568 30.11 9.65 βoutN-H (60), υoutC-N (17), υoutC‒C (14)
    69 - - 1483 1436 2.3645 3.064 4.89 0.81 βC-H (54), υC-C (21), βoutN‒H (18)
    70 1447 1455 1508 1460 2.2353 2.9957 1.61 3.14 β(py) C-H (48), υ(py) (23), υoutC-C (10)
    71 - - 1524 1475 2.7967 3.8252 0.94 0.21 υC−N (43), υC−C (24), βC−H (18)
    72 1501 - 1554 1505 4.4312 6.307 20.77 41.94 υC=C (68), βC−H (19)
    73 - - 1604 1553 5.2119 7.9032 1.13 0.34 υ(py) C−C (69), βC−H (22)
    74 - 1563 1615 1563 5.7905 8.8973 0.09 6.24 υC−C (53), βN−H (25)
    75 - - 1628 1575 5.6711 8.851 11.33 13.99 υ(py) C−N (56),υ(py)C−C (23),β(py)C−H(14)
    76 - - 1657 1604 7.6432 12.3614 5.91 100 υout.C=N (56), υC−C (23), βC−H (14)
    77 1608 1606 1658 1605 6.6961 10.8407 2.95 28.6 υC−C (52), υC=N (28), βC−H (12)
    78 1677 - 1718 1663 7.9762 13.8766 100 14.72 υC=O (71), βN−H (23)
    79 - - 3147 3046 1.0879 6.3482 1.02 0.82 υout.C−H (98)
    80 - - 3150 3049 1.0892 6.366 4.06 2.6 υas(py) C−H (95)
    81 - - 3167 3066 1.0858 6.4172 0.15 0.55 υasC−H (96)
    82 3078 - 3174 3073 1.0887 6.463 0.72 2.26 υasC−H (96)
    83 - - 3184 3082 1.0936 6.532 4.39 1.24 υasC−H (95)
    84 - - 3185 3083 1.0909 6.5186 2.94 2.8 υas(py)C−H (92)
    85 - - 3194 3092 1.0971 6.5933 3.03 5.67 υsC−H (97)
    86 - - 3201 3099 1.092 6.593 2.66 0.24 υas(py)C−H (91)
    87 3107 3109 3202 3100 1.0948 6.6134 0.13 3.81 υas(py)C−H (94)
    88 3159 - 3253 3149 1.097 6.8395 0.27 0.6 υC−H (99)
    89 - - 3471 3360 1.0748 7.6289 7.5 3.16 υout.N−H (99)
    90 3531 - 3664 3540 1.0805 8.5473 21.55 1.77 υN−H (100)

    Figure 2. The combined theoretical and experimental FT-IR spectra of ICINH
    Figure 2.

    Figure 3. The combined theoretical and experimental FT-Raman spectra of ICINH
    Figure 3.

    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. 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, 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 very pure modes. Similarly, the peaks appeared at 3159 and 3078 cm−1 in FT-IR are ascribed to C−H stretching vibrations of the benzene ring of the title molecule.

    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−1 in FT-IR is assigned to C=O stretching. The calculated value of C=O stretching mode at B3LYP/6-311++G(d,p) shows good agreement with the experimental value. The C=O in-plane bending vibration is identified at 830 cm−1 in FT-IR. A peak for C=O out-of-plane bending vibration is not active in both IR and Raman spectra. Hence the theoretically predicted value (128 cm-1/mode no: 6) is assigned to this mode.

    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 N19−H20 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 N15−H13 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 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 C21=N19 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, in-plane bending and out-of-plane bending vibrations, respectively.

    NLO Property

    Non 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 (β0), 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 (α0) the mean first hyperpolarizability (β0), for the molecule under study are presented in Table 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 (β0) of the present molecule is 8.6424x10-30 esu while that of urea is 0.3728x10-30 esu. The (βo) 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.

    Table 3. The NLO measurements of ICINH
    Parameters B3LYP/6-311++G(d,p)
    Dipole moment ( μ ) Debye
    μx 1.6403
    μy 0.4934
    μz 0.1242
    Μ 1.7174Debye
    Polarizability ( α0 ) x10-30esu
    αxx 351.00
    αxy -4.96
    αyy 194.94
    αxz 1.53
    αyz 4.90
    αzz 132.91
    αo 0.5902x10-30esu
    Hyperpolarizability ( β0 ) x10-30esu
    βxxx -1163.89
    βxxy 31.69
    βxyy 148.04
    βyyy -106.30
    βxxz -196.67
    βxyz -19.08
    βyyz 12.83
    βxzz 46.85
    βyzz -42.47
    βzzz -35.40
    β0 8.6424x10-30esu

    Standard value for urea (μ=1.3732 Debye, β0=0.3728x10-30esu): esu-electrostatic unit

    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 Table 4. The ED of π(C30-N32) bond transfer energy 116.4, 52.38 kJ/mol to the acceptor orbitals: C22-C24 and C23-C25, respectively. There occurs a strong intra-molecular hyperconjugative interaction of π electron from C23-C25 bond to the π*C22-C24→C30-N32 bonds, which increases the EDs: 0.3281 and 0.3727 kJ/mol, respectively. The lone pair electrons are readily available for the interaction with excited electrons of antibonding orbital. During n-π* transition, more energy delocalization takes place: N19→C16-N18; C21→O29 and N15→C1-C2; C7-C8. The corresponding excitation energy values are, 102.42, 170.41 and 140.71, 160.41, respectively. In which, these (N19→C21-O29 & N15→C7-C8) two transitions give the strongest stabilization to the system.

    Table 4. The Second order perturbation theory analysis of Fock Matrix in NBO basis for ICINH
    Type Donor NBO (i) ED/e Acceptor NBO (j) ED/e aE(2) bE(j)-E(i) cF(i,j)
    KJ/mol a.u. a.u.
    σ -σ* BD ( 1) C 1 - C 2 1.959 BD*(1) C 1 - C 6 0.021 18.95 1.23 0.07
    BD*(1) C 2 - C 3 0.022 14.06 1.24 0.06
    BD*(1) C 2 - C 8 0.027 8.2 1.16 0.04
    BD*(1) C 3 - H 9 0.014 10.59 1.11 0.05
    BD*(1) C 6 - H 12 0.013 9.41 1.1 0.05
    BD*(1) C 8 - C 16 0.036 17.95 1.15 0.06
    BD*(1) H 13 - N 15 0.016 16.82 1.04 0.06
    π -π* BD ( 2) C 1 - C 2 1.596 BD*(2) C 3 - C 4 0.301 79.16 0.29 0.07
    BD*(2) C 5 - C 6 0.319 76.11 0.28 0.07
    BD*(2) C 7 - C 8 0.349 78.7 0.26 0.06
    σ -σ* BD ( 1) C 1 - C 6 1.976 BD*(1) C 1 - C 2 0.027 20.21 1.25 0.07
    BD*(1) C 1 - N 15 0.027 8.91 1.15 0.04
    BD*(1) C 2 - C 8 0.027 5.86 1.21 0.04
    BD*(1) C 5 - C 6 0.013 11.59 1.3 0.05
    BD*(1) C 5 - H 11 0.012 9.46 1.16 0.05
    BD*(1) C 6 - H 12 0.014 4.18 1.14 0.03
    BD*(1) C 7 - N 15 0.013 6.53 1.15 0.04
    σ -σ* BD ( 1) C 1 - N 15 1.986 BD*(1) C 1 - C 2 0.027 4.44 1.36 0.03
    BD*(1) C 1 - C 6 0.021 8.54 1.38 0.05
    BD*(1) C 2 - C 3 0.022 9.87 1.38 0.05
    BD*(1) C 7 - H 14 0.012 9.12 1.23 0.05
    BD*(1) C 7 - N 15 0.013 6.4 1.26 0.04
    σ -σ* BD ( 1) C 2 - C 3 1.974 BD*(1) C 1 - C 2 0.027 15.44 1.24 0.06
    BD*(1) C 1 - N 15 0.027 7.11 1.13 0.04
    BD*(1) C 2 - C 3 0.022 16.48 1.22 0.06
    BD*(1) C 3 - C 4 0.013 5.1 1.25 0.04
    BD*(1) C 7 - C 8 0.019 12.84 1.21 0.06
    BD*(1) C 7 - H 14 0.012 18.95 1.07 0.06
    BD*(1) C 7 - N 15 0.013 5.44 1.09 0.03
    BD*(1) C 8 - C 16 0.036 10.08 1.13 0.05
    BD*(1) C 16 - N 18 0.01 9.5 1.25 0.05
    σ -σ* BD ( 1) C 3 - C 4 1.978 BD*(1) C 2 - C 3 0.023 13.77 1.27 0.06
    BD*(1) C 2 - C 8 0.027 19.25 1.19 0.07
    BD*(1) C 3 - H 9 0.014 4.69 1.14 0.03
    BD*(1) C 4 - C 5 0.016 10.84 1.26 0.05
    BD*(1) C 5 - H 11 0.012 8.49 1.15 0.04
    π -π* BD ( 2) C 3 - C 4 1.721 BD*(2) C 1 - C 2 0.477 75.1 0.28 0.07
    BD*(2) C 5 - C 6 0.319 82.34 0.28 0.07
    σ -σ* BD ( 1) C 3 - H 9 1.979 BD*(1) C 1 - C 2 0.027 17.24 1.06 0.06
    BD*(1) C 4 - C 5 0.016 16.07 1.08 0.06
    σ -σ* BD ( 1) C 4 - C 5 1.979 BD*(1) C 3 - C 4 0.013 11.17 1.28 0.05
    BD*(1) C 3 - H 9 0.014 10.46 1.13 0.05
    BD*(1) C 5 - C 6 0.013 10.92 1.27 0.05
    BD*(1) C 6 - H 12 0.013 11.05 1.12 0.05
    σ -σ* BD ( 1) C 4 - H 10 1.98 BD*(1) C 2 - C 3 0.022 15.98 1.08 0.06
    BD*(1) C 5 - C 6 0.013 15.94 1.1 0.06
    σ -σ* BD ( 1) C 5 - C 6 1.976 BD*(1) C 1 - C 6 0.021 13.97 1.27 0.06
    BD*(1) C 1 - N 15 0.026 25.98 1.14 0.08
    BD*(1) C 4 - C 5 0.015 10.54 1.27 0.05
    BD*(1) C 4 - H 10 0.012 8.28 1.15 0.04
    BD*(1) C 6 - H 12 0.013 5.27 1.13 0.03
    π -π* BD ( 2) C 5 - C 6 1.729 BD*(2) C 1 - C 2 0.477 82.01 0.28 0.07
    BD*(2) C 3 - C 4 0.301 72.63 0.29 0.06
    σ -σ* BD ( 1) C 5 - H 11 1.98 BD*(1) C 1 - C 6 0.022 14.69 1.08 0.06
    BD*(1) C 3 - C 4 0.014 15.69 1.11 0.06
    σ -σ* BD ( 1) C 6 - H 12 1.98 BD*(1) C 1 - C 2 0.027 17.66 1.07 0.06
    BD*(1) C 4 - C 5 0.016 15.06 1.09 0.06
    σ -σ* BD ( 1) C 7 - C 8 1.972 BD*(1) C 2 - C 3 0.023 20.42 1.28 0.07
    BD*(1) C 2 - C 8 0.027 12.18 1.21 0.05
    BD*(1) C 7 - H 14 0.012 6.53 1.13 0.04
    BD*(1) C 8 - C 16 0.036 12.34 1.2 0.05
    BD*(1) H 13 - N 15 0.017 14.02 1.09 0.05
    BD*(1) C 16 - H 17 0.022 4.23 1.13 0.03
    π -π* BD ( 2) C 7 - C 8 1.801 BD*(2) C 1 - C 2 0.477 66.23 0.3 0.07
    BD*(2) C 7 - C 8 0.349 8.87 0.29 0.02
    BD*(2) C 16 - N 18 0.212 73.6 0.29 0.06
    σ -σ* BD ( 1) C 7 - H 14 1.984 BD*(1) C 1 - N 15 0.026 12.26 1.01 0.05
    BD*(1) C 2 - C 8 0.027 8.66 1.06 0.04
      BD*(1) C 7 - C 8 0.019 6.07 1.13 0.04
    σ -σ* BD ( 1) C 7 - N 15 1.985 BD*(1) C 1 - C 6 0.021 17.03 1.39 0.07
    BD*(1) C 1 - N 15 0.026 7.32 1.26 0.04
    BD*(1) C 7 - C 8 0.019 5.06 1.38 0.04
    BD*(1) C 8 - C 16 0.036 16.07 1.3 0.06
    σ -σ* BD ( 1) C 8 - C 16 1.979 BD*(1) C 1 - C 2 0.027 4.81 1.23 0.03
    BD*(1) C 2 - C 8 0.027 14.31 1.18 0.06
    BD*(1) C 7 - C 8 0.019 14.81 1.24 0.06
    BD*(1) C 7 - N 15 0.013 4.48 1.13 0.03
    BD*(1) C 16 - N 18 0.01 9.54 1.29 0.05
    σ -σ* BD ( 1) H 13 - N 15 1.99 BD*(1) C 1 - C 2 0.027 7.41 1.24 0.04
    BD*(1) C 7 - C 8 0.019 5.73 1.26 0.04
    σ -σ* BD ( 1) C 16 - H 17 1.969 BD*(1) C 7 - C 8 0.019 20.08 1.07 0.06
    BD*(1) N 18 - N 19 0.03 35.31 0.89 0.08
    σ -σ* BD ( 1) C 16 - N 18 1.988 BD*(1) C 2 - C 8 0.027 4.98 1.39 0.04
    BD*(1) C 8 - C 16 0.036 9.37 1.38 0.05
    BD*(1) N 19 - C 21 0.073 10.33 1.33 0.05
    π -π* BD ( 2) C 16 - N 18 1.942 BD*(2) C 7 - C 8 0.349 32.55 0.35 0.05
    σ -σ* BD ( 1) N 18 - N 19 1.986 BD*(1) C 16 - H 17 0.022 8.62 1.27 0.05
    BD*(1) C 21 - O 29 0.021 5.69 1.44 0.04
    σ -σ* BD ( 1) N 19 - H 20 1.983 BD*(1) C 21 - C 22 0.066 15.1 1.09 0.06
    σ -σ* BD ( 1) N 19 - C 21 1.99 BD*(1) C 16 - N 18 0.01 8.91 1.42 0.05
    BD*(1) C 22 - C 23 0.021 4.39 1.39 0.03
    BD*(1) C 25 - C 23 0.026 4.23 4.67 0.06
    σ -σ* BD ( 1) C 21 - C 22 1.974 BD*(1) N 19 - H 20 0.042 10.96 1.03 0.05
    BD*(1) C 21 - O 29 0.021 5.27 1.24 0.04
    BD*(1) C 22 - C 23 0.021 7.07 1.23 0.04
    BD*(1) C 22 - C 24 0.033 8.12 1.22 0.04
    BD*(1) C 23 - C 25 0.015 9.08 1.25 0.05
    BD*(1) C 25 - N 32 0.015 9.5 1.21 0.05
    σ -σ* BD ( 1) C 21 - O 29 1.992 BD*(1) N 18 - N 19 0.03 7.28 1.39 0.04
    BD*(1) C 21 - C 22 0.066 7.11 1.45 0.05
    BD*(1) C 22 - C 24 0.033 5.61 1.59 0.04
    π -π* BD ( 2) C 21 - O 29 1.979 BD*(2) C 22 - C 24 0.328 13.85 0.42 0.04
    σ -σ* BD ( 1) C 22 - C 23 1.973 BD*(1) N 19 - C 21 0.073 8.49 1.13 0.04
    BD*(1) C 21 - C 22 0.066 7.07 1.12 0.04
    BD*(1) C 22 - C 24 0.033 14.85 1.26 0.06
    BD*(1) C 23 - C 25 0.0148 10.84 1.29 0.05
    BD*(1) C 24 - H 27 0.023 9.5 1.15 0.05
    BD*(1) C 25 - H 28 0.013 10.59 1.14 0.05
    σ -σ* BD ( 1) C 22 - C 24 1.979 BD*(1) C 21 - C 22 0.066 6.23 1.13 0.04
    BD*(1) C 21 - O 29 0.021 6.65 1.29 0.04
    BD*(1) C 22 - C 23 0.021 16.07 1.27 0.06
    BD*(1) C 23 - H 26 0.014 10.42 1.16 0.05
    BD*(1) C 24 - H 27 0.023 4.35 1.15 0.03
    BD*(1) C 24 - C 30 0.015 5.9 1.26 0.04
    π -π* BD ( 2) C 22 - C 24 1.61 BD*(2) C 21 - O 29 0.274 74.39 0.29 0.07
    BD*(2) C 23 - C 25 0.287 97.53 0.28 0.07
    BD*(2) C 28 - N 31 0.372 68.03 0.27 0.06
    σ -σ* BD ( 1) C 23 - C 25 1.979 BD*(1) C 21 - C 22 0.066 12.01 1.13 0.05
    BD*(1) C 22 - C 23 0.021 12.22 1.27 0.05
          BD*(1) C 25 - H 28 0.014 4.35 1.15 0.03
          BD*(1) C 30 - H 31 0.024 9.25 1.14 0.05
    π -π* BD ( 2) C 23 - C 25 1.639 BD*(2) C 22 - C 24 0.329 69.33 0.29 0.06
    BD*(2) C 30 - N 32 0.373 123.22 0.27 0.08
    σ -σ* BD ( 1) C 23 - H 26 1.979 BD*(1) C 22 - C 24 0.033 16.99 1.08 0.06
    σ -σ* BD ( 1) C 24 - H 27 1.979 BD*(1) C 22 - C 23 0.021 17.45 1.08 0.06
    BD*(1) C 30 - N 32 0.016 20.33 1.06 0.06
    σ -σ* BD ( 1) C 24 - N 31 1.986 BD*(1) C 21 - C 22 0.066 9.41 1.25 0.05
    BD*(1) C 22 - C 24 0.033 8.12 1.38 0.05
    BD*(1) C 28 - H 30 0.024 8.74 1.25 0.05
    σ -σ* BD ( 1) C 25 - C 23 1.985 BD*(1) C 23 - C 25 0.015 10.59 1.3 0.05
    BD*(1) C 23 - H 26 0.014 11.63 1.16 0.05
    BD*(1) C 30 - N 32 0.016 5.86 1.26 0.04
    σ -σ* BD ( 1) C 25 - H 23 1.979 BD*(1) C 22 - C 23 0.021 14.52 1.09 0.06
    BD*(1) C 30 - N 32 0.016 17.87 1.07 0.06
    σ -σ* BD ( 1) C 30 - H 31 1.982 BD*(1) C 23 - C 25 0.015 14.73 1.11 0.06
    BD*(1) C 25 - N 32 0.015 20.17 1.07 0.06
    σ -σ* BD ( 1) C 30 - N 32 1.987 BD*(1) C 24 - H 27 0.023 8.79 1.27 0.05
    BD*(1) C 25 - H 29 0.013 6.11 1.26 0.04
    π -π* BD ( 2) C 30 - N 32 1.705 BD*(2) C 22 - C 24 0.328 116.4 0.32 0.09
    BD*(2) C 23 - C 25 0.287 52.38 0.32 0.06
    n -π* LP ( 1) N 15 1.613 BD*(2) C 1 - C 2 0.476 140.71 0.3 0.09
    BD*(2) C 7 - C 8 0.349 160.41 0.29 0.1
    n -σ* LP ( 1) N 18 1.921 BD*(1) C 8 - C 16 0.036 42.76 0.87 0.09
    BD*(1) C 16 - H 17 0.022 16.74 0.8 0.05
    BD*(1) N 19 - H 20 0.042 33.05 0.75 0.07
    n -π* LP ( 1) N 19 1.679 BD*(2) C 16 - N 18 0.212 102.42 0.3 0.08
    BD*(1) C 21 - O 29 0.021 5.4 0.87 0.03
    BD*(2) C 21 - O 29 0.274 170.41 0.33 0.1
    n -σ* LP ( 1) N 32 1.917 BD*(1) C 22 - C 24 0.033 39.46 0.89 0.08
    BD*(1) C 24 - H 27 0.023 16.57 0.78 0.05
    BD*(1) C 25 - C 23 0.026 8.16 4.18 0.08
    BD*(1) C 30 - H 31 0.023 17.11 0.77 0.05
    n -σ* LP ( 1) O 29 1.979 BD*(1) C 21 - C 22 0.066 8.24 1.12 0.04
    n -σ* LP ( 2) O 29 1.868 BD*(1) N 19 - C 21 0.073 99.66 0.68 0.12
    BD*(1) C 21 - C 22 0.066 73.35 0.68 0.1
    BD*(1) C 25 - C 23 0.026 6.9 4.1 0.08
    π*-π* BD*( 2) C 1 - C 2 0.477 BD*(2) C 3 - C 4 0.301 1195.8 0.01 0.08
    π*-π* BD*( 2) C 7 - C 8 0.349 BD*(2) C 1 - C 2 0.477 711.11 0.01 0.06
    π*-σ* BD*( 2) C 21 - O 29 0.274 BD*(1) C 21 - O 29 0.021 18.24 0.54 0.11
    π*-π* BD*( 2) C 30 - N 32 0.373 BD*(2) C 22 - C 24 0.328 604.96 0.02 0.08
    BD*(2) C 23 - C 25 0.287 714.04 0.02 0.08

    HOMO–LUMO Analysis

    The HOMO–LUMO plot of ICINH molecule is shown in Figure 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.

    Figure 4. The frontier molecular orbitals of ICINH
    Figure 4.

    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=-EHOMO and A=-ELOMO, 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 gap. In addition, the frontier molecular orbital energies are also calculated using the same basis set and are listed in Table 6.

    Table 5. The Physico-chemical properties of ICINH
    Parameters Values
    HOMO -6.125 eV
    LUMO -1.784 eV
    Energy gap 4.341 eV
    Ionization potential (IP) 6.125 eV
    Electron affinity (EA) 1.784 eV
    Electrophilicity Index (ω) 1.801
    Chemical Potential (µ) 3.954
    Electronegativity (χ) -3.954
    Hardness (η) -4.341
    Softness (S) 8.682

    Table 6. The frontier molecular orbitals of ICINH
    Occupancy Orbital energies(a.u) Orbital energies(eV) Kinetic energies(a.u)
    O52 -0.269 -7.319 1.267
    O53 -0.267 -7.265 1.605
    O54 -0.262 -7.129 1.871
    O55 -0.254 -6. 911 1.250
    O56 -0.228 -6.203 1.576
    V57 -0.071 -1.931 1.664
    V58 -0.055 -1.496 1.519
    V59 -0.034 0. 925 1.367
    V60 0.025 0.680 0.381
    V61 0.023 0.625 1.250

    UV-Vis Spectra

    The UV absorption spectrum for ICINH is recorded in the range 200-800 nm. All the structures allow strong π-π* and σ-σ* transition in the UV-Vis region with high extinction coefficients. The calculated results involving in the vertical excitation energies, oscillator strength (f) and wavelength are carried out and compare with measured experimental wavelength. Typically, according to Frank-Condon principle, the maximum absorption peaks (λmax) in a UV-Vis spectrum correspond to vertical excitation. The λmax of ICINH molecule are calculated using TD-DFT/6-311++G(d,p) basis set. It is evident from the Table 7, the possible π-π* transitions, with absorption maximum at 413.14, 389.2, 357.32 nm, belong to gas phase and the oscillator strength for respective transitions are 0.0009, 0.0136 and 0.0296, respectively. The calculated absorption maxima has been found to be 357.32 nm which is moderately coincides with the experimental value 342.42 nm. The combined theoretical and experimental UV-Vis absorption spectra are shown in Figure 5.

    Table 7. The electronic transition of ICINH
    Calculated at B3LYP/6-311++G(d,p) Oscillator strength CalculatedBand gap (ev/nm) ExperimentalBand gap (ev/nm) Type
    Excited State-1 Singlet-A (f=0.0009) 3.0010 eV/413.14 nm
    69 -> 70 0.6908
    Excited State-2 Singlet-A (f=0.0136) 3.1849 eV/389.29 nm
    66 -> 70 -0.1059
    68 -> 70 0.6587
    68 -> 71 0.1308
    Excited State-3 Singlet-A (f=0.0296) 3.4698 eV/357.32 nm 342.42 π-π*
    66 -> 70 0.1243
    66 -> 71 0.1564
    68 -> 70 -0.1275
    68 -> 71 0.4689
    69 -> 71 -0.4067

    Figure 5. The combined theoretical and experimental UV-Visible spectra of ICINH
    Figure 5.

    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 Figure 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 (Figure 6) and is very useful in research of molecular structure with its physiochemical property relationship 26, 27. The color scheme for the MEP surface is as follows: red for electron rich, partially negative charge: blue correspond to electron deficient, partially positive charge: green for neutral, respectively 28, 29. The electrostatic potential increases in the order of red<orange<yellow<green<blue. The color code of the map range between -9.185 e-2 (deepest red) to 9.185 e-2 (deepest blue). It is seen from the MEP map of the title molecule, the regions having the negative potential over the electronegative atom (oxygen atom), and the regions having the positive potential over all the hydrogen atoms in indole ring. The oxygen atom indicates the strong repulsion with other atom. These two ends of the molecule which are positively and negatively charged are prone to electrophilic and electrophobic reactions with other molecules.

    Figure 6. The molecular electrostatic potential map of ICINH
    Figure 6.

    Mulliken Atomic Charges

    It is well known that the atomic charges are very much dependent on how the atoms are defined. It also plays an important role in the application of quantum chemical calculation to molecular system because of atomic charges affect the dipole moment, molecular polarizability, electronic structure and a lot of properties of molecular systems. The mulliken charges calculated at B3LYP/6-311++G(d,p) basis set for the molecule under study are given in Table 8. The mulliken atomic charges plot for ICINH is shown in Figure 7

    The C2 atom has high positive charge which is due to the indole group. Similarly the C16 atom has high negative charge due to the attachment of C16=N18 group. All the hydrogen atoms have positive charge.

    Table 8. The Mulliken atomic charges of ICINH
    Atoms Charges Atoms Charges
    1C -0.2987 17H 0.1624
    2C 1.3144 18N 0.0896
    3C -0.6692 19N -0.0922
    4C -0.5107 20H 0.2843
    5C -0.0917 21C -0.5353
    6C -0.6358 22C 0.7243
    7C -0.2138 23C 0.0949
    8C 0.8639 24C -0.5605
    9H 0.1424 25C -0.1468
    10H 0.1605 26H 0.2244
    11H 0.1674 27H 0.2180
    12H 0.1439 28C -0.2971
    13H 0.3039 29H 0.1812
    14H 0.2100 30H 0.1860
    15N -0.0449 31N -0.0054
    16C -1.1123 32O -0.2591

    Figure 7. The Mulliken atomic charges of ICINH
    Figure 7.

    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 (R2) for these thermodynamic properties are 0.99905, 0.9994 and 0.99998, respectively and the correlation graphics are shown in Figure 8.

    Table 9. The calculated total energy (a.u), zero point vibrational energies (Kcal/mol), rotational constants (GHz) and entropy (cal/mol K-1) for ICINH
    Parameters B3LYP/6-311++G(d,p)
    Total Energies -873.259
    Zero-point Energy 154. 930 (Kcal/Mol)
    Rotational constants (GHZ) 1.119
    0.128
    0.120
    Entropy
    Total 131.409
    Translational 42.613
    Rotational 34.185
    Vibrational 54.610

    Table 10. Thermodynamic Properties of ICINH at different temperatures
    T (K) S (J/mol.K) Cp (J/mol.K) ddH (kJ/mol)
    100.00 362.62 109.42 7.39
    200.00 460.26 183.91 21.90
    298.15 549.35 268.44 44.07
    300.00 551.01 270.03 44.57
    400.00 640.10 351.39 75.73
    500.00 726.10 419.62 114.40
    600.00 807.63 474.29 159.20
    700.00 884.14 517.90 208.89
    800.00 955.68 553.15 262.50
    900.00 1022.55 582.09 319.31
    1000.00 1085.17 606.19 378.76

    Figure 8. The thermodynamic properties of ICINH at different temperatures
    Figure 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.

    C0p,m = 6.76926 + 0.02858T + 2.52495x10-5 T2 (R2 = 0.99905)

    S0m = 1.40875 + 0.00595T + 5.25468x10-5 T2 (R2 = 0.99998)

    ΔH0m = 4.06057 + 0.01714T + 1.51461x10-5 T2 (R2 = 0.9994)

    Conclusion

    The FT-IR, FT-Raman and UV-Vis spectra of the compound ICINH had been recorded and analyzed. The detailed interpretations of the vibrational spectra had been carried out. The optimized geometrical parameters were calculated and compared with the reported XRD data. The vibrational assignments were further justified with help of the PED analysis. The HOMO-LUMO energy gap indicated the stability and reactivity of the title compound. The good correlation between the UV-Vis, absorption maxima and calculated electronic absorption maxima were found. The donor-acceptor interaction, as obtained from NBO analysis could fairly explains the decrease of occupancies of σ bonding orbital and the increase of occupancy of π* anti-bonding orbitals. In addition, mulliken atomic charges, MEP, Thermodynamic parameters, first order hyperpolarizabilities and dipole moment of the title compound were also calculated.

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