Comparative study of 4-((4-aminophenyl)diazenyl)-2-((2-phenylhydrazono)methyl)phenol and N-(4-((4-hydroxy-3-((2-phenylhydrazono)methyl)phenyl)diazenyl)phenyl)acetamide - DFT method European Journal of Chemistry 15 (1) (2024) 50-70 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2024 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.15.1.50-70.2498 European Journal of Chemistry View Journal Online View Article Online Comparative study of 4-((4-aminophenyl)diazenyl)-2-((2-phenylhydrazono) methyl)phenol and N-(4-((4-hydroxy-3-((2-phenylhydrazono)methyl)phenyl) diazenyl)phenyl)acetamide - DFT method Richard Rajkumar Siluvairaj 1, Vallal Perumal Govindasamy 2, Rajarajan Govindasamy 2, Periyanayagasamy Vanathu Chinnappan 1 and Thanikachalam Venugopal 2,* 1 Department of Chemistry, St. Joseph’s College of Arts and Science, Cuddalore-607001, Tamilnadu, India 2 Department of Chemistry, Annamalai University, Annamalainagar-608002, Tamilnadu, India * Corresponding author at: Department of Chemistry, Annamalai University, Annamalainagar-608002, Tamilnadu, India. e-mail: pvta1998@yahoo.co.in (T. Venugopal). 10.5155/eurjchem.15.1.50-70.2498 Received: 31 October 2023 Received in revised form: 09 January 2024 Accepted: 06 February 2024 Published online: 31 March 2024 Printed: 31 March 2024 Theoretical calculation of 4-((4-aminophenyl)diazenyl)-2-((2-phenylhydrazono)methyl) phenol (1) and N-(4-((4-hydroxy-3-((2-phenylhydrazono)methyl)phenyl)diazenyl)phenyl) acetamide (2) was studied by DFT/B3LYP/6-311+G(d,p) basis set. The calculated values of geometric structural parameters, Fourier transform infrared spectral data, highest occupied molecular orbital and lowest unoccupied molecular orbital, natural bond orbital, nucleus- independent chemical shifts, Fukui function, polarizability, hyperpolarizability, and UV data of compounds 1 and 2 clearly indicate that substitution of the amino group alters the physical properties of compound 2. The nucleus-independent chemical shift values of the amino-substituted phenyl ring reduces the aromatic character due to the lone pair electron on nitrogen involved in inductive and conjunction effects, as well as due to OH, NH2 and OH, NHCOCH3 in compounds 1 and 2, respectively. The effect of the solvent on different parameters was studied, and it was found that increasing the dielectric constant increased the parameter studied. The stability and planarity of the molecule’s effects on dipole moment, energy, polarizability, and hyperpolarizability were studied extensively. NBO HOMO-LUMO Solvent effect UV-Vis studies Dihedral angle Dipole moment Cite this: Eur. J. Chem. 2024, 15(1), 50-70 Journal website: www.eurjchem.com 1. Introduction Zubrys and Siebenmann have synthesized condensation products of iso-nicotinylhydrazones, monohydroxyl benzalde- hydes, and the corresponding aldehyde phenoxyacetic acid. Of 6-methoxy-2-formylphenoxyacetic acid, these are considered to have the most pronounced antituberculous exertion combined with low toxin [1]. Thermal recyclization of 3- methyl-4-acetyl(benzoyl)furoxans(3-methyl-4-acetyl(benzoyl) -2-oxides)phenylhydrazonesto oximes of 5-acetyl-4-phenyl (methyl)-1-oxide and base-convinced mononuclear hetero- cyclic rearrangement of below phenylhydrazones to 4-phenyl (methyl)-5-(1-nitroethyl) were prepared by Baryshnikova and Makhova [2]. Dimmock et al. were synthesized colorful acetyl- hydrazones, oxamoylhydrazones, and semicarbazones as seeker anticonvulsants with a view to examining the viability of an apparent list thesis [3]. The natural results revealed that, in general, the acetylhydrazones and semicarbazones showed good protection against storms, whereas the oxamoyl-hydra- zones were significantly less active. Sevim Rollas et al. prepared a series of hydrazidehydrazones and 1,3,4-oxadiazolines of 4- fluorobenzoic acid hydrazide [4]. These compounds were tested for their antibacterial and antifungal conditioning against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans. Rosanna Maccari et al. [5] studied an in vitro antimycobacterial of isoniazid-related isonicotinoylhydrazones (ISNE), 2'-monosubstituted isonico- tino-hydrazides and cyanoboranes. The most intriguing result is that some hydrazides and ISNEs were shown to be more effective antimycobacterial agents than maternal isoniazid in a model of tuberculosis-infected macrophages. A new series of imidazo-(1,2-a)-pyrazine-2-carboxylic acid arylidenehydra- zides was prepared and characterized by infrared spectroscopy (IR), proton nuclear magnetic resonance (1H NMR), and fast atom bombardment mass spectrometry (FAB-MS) spectral data. Three compounds were also estimated for anti-tuber- culosis exertion against Mycobacterium tuberculosis H37Rv using the BACTEC460 radiometric system and BACTEC12B medium. The compound showed moderately good assets against mortal pathogenic microorganisms and is inactive against Mycobacterium tuberculosis H37Rv [6]. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.15.1.50-70.2498 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.15.1.50-70.2498 mailto:pvta1998@yahoo.co.in http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.15.1.50-70.2498&domain=pdf&date_stamp=2024-03-31 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 51 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Scheme 1. Synthesis scheme for N-(4-((4-hydroxy-3-((2-phenylhydrazono)methyl)phenyl)diazenyl)phenyl)acetamide (2). A series of 2-quinoxalinone-3-hydrazzone derivatives was prepared using a microwave oven system, structurally verified by logical and spectral data, and estimated for their antimicrobial conditioning. The mortal frame displayed pronounced energy as antimicrobial agents. The most active antibacterial agent was 3-{2-(1-(6-chloro-2-oxo-2H-chromen- 3-yl)ethylidene) hydra-zinyl} quinoxalin-2(1H)-one, while (propanylidene)hydrazinyl) quinoxalin-2(1H)-one, appeared to be the most active antifungal agent [7]. The colorimetric and turn-off fluorescent selective detec- tion of Cu2+ was attributed to the 2:1 complex of diarylethene and Cu2+ ions. In addition, the metal-responsive photochromic behavior of diarylethene was successfully applied to the construction of a molecular logic circuit [8]. A novel aryl hydra- zone was synthesized via the Japp-Klingemann reaction between diazotized 4-aminoantipyrine and barbituric acid. Various spectroscopic methods and X-ray single-crystal analysis have characterized it. The effect of pH on the azo- hydra-zone tautomerism of the ligand has been studied with UV-vis spectroscopy. Two types of complexes were obtained by reaction of the ligand with copper sulphatepentahydrate in methanol under different experimental conditions [9]. In the case of polymorphism, different structures melt into the same liquid. The same structure melts in different liquids [10]. Sumita and Enoch reported the Mg2+ ion sensing behavior of the phenylhydrazone derivative of difluorenylpiperidin-4-one [11]. The composition and binding strength of the Mg2+ complex of phenylhydrazone are determined. The compound shows an association constant of 3375.36 M-1 for binding to Mg2+ ions. The detection range and competitive binding behavior of Mg2+ ions are reported. The phenylhydrazone of difluorenylpiperi- din-4-one shows appreciable selectivity and detection sensitivity for Mg2+ ions. The molecular properties of 4- hydroxy-6-methyl-3-[(1E)-1-(2-phenylhydrazinylidene)ethyl]- 2H-pyran-2-one (DHAA-PH) [12], have been carried out using the hybrid Density Functional Theory (DFT) and Time- Dependent Density Functional Theory (TDFT) methods at B3LYP/6-31+G(d,p) levels of theory. To substantiate the sensitivity of functionally applied M06-2X/6-311++G(2d,2p) and mPWB1W/6-311++G(2d,2p) were used to calculate geometric, IR, 1H NMR, and energy gap calculations. DFT calculations with M06-2X and mPWB1W were predicted to agree with the experiment compared to B3LYP functional. Benzaldehydesemicarbazone (BSC) was grown by the slow evaporation technique for single crystals. The grown crystals were identified by the XRD method. The functional groups were identified from the FT-IR spectrum. UV-vis and thermal gravimetric analyses were performed [13]. The data of the literature show that no theoretical studies of the compounds 4- ((4-aminophenyl)diazenyl)-2-((2-phenyl hydrazono)methyl) phenol (1) and N-(4-((4-hydroxy-3-((2-phenylhydrazono)- methyl)phenyl)-diazenyl)phenyl)acetamide (2) was studied using the DFT/B3LYP/6-311+G(d,p). Compound 1 is not synthesized and is used only for theoretical comparisons. 2. Experimental 2.1. Synthesis of N-(4-((4- hydroxy-3-((2-phenylhydrazono) methyl)phenyl)diazenyl)phenyl)acetamide (2) A substituted imine derivative was synthesized as a two- step synthetic protocol. To the azo dye N-(4-((3-formyl-4- hydroxyphenyl)diazenyl)phenyl)acetamide (parent compound) (0.4 g) obtained, 0.5 g of phenylhydrazine hydrochloride and 0.8 g of sodium acetate were added and refluxed for 15 minutes in ethanol to obtain compound (N-(4-((4-hydroxy-3-((2- phenylhydrazono)methyl)phenyl)diazenyl)phenyl)acetamide) , from now referred to as compound 2, which was recrystallized from ethanol [14]. Microanalysis, IR, 1H, 13C NMR, and UV spectra characterized the compound obtained. The synthesized compound 2 and its amine counterpart 4-((4-amino phenyl) diazenyl)-2-((2-phenylhydrazono)methyl)phenol from now on referred to as compound 1 were studied using the DFT method (Scheme 1). N-(4-((4-Hydroxy-3-((2-phenyl hydrazono)methyl)phenyl) diazenyl)phenyl)acetamide (2): Color: Yellow. Yield: 78%. M.p.: 120-122 °C. FT-IR (KBr, ν, cm-1): 3300 (OH), 1650 (C=O). 1H NMR (400 MHz, DMSO-d6, ppm): 11.12 (s, 1H, NH), 10.56 (s, 1H, NH), 10.29 (s, 1H, OH), 8.223-6.772 (m, 12H, ArH + 1H, CH=N), 2.098 (s, 3H, CH3). 13C NMR (100 MHz, DMSO-d6, ppm): 169.17 (C-O), 158.53 (C=N), 148.00 (C-N), 145.90 (C-N), 145.18 (C-N), 142.20, 139.00, 137.00, 129.77, 129.77, 123.7, 119.60, 112.18 (Ar-C), 24.00 (C-H). Anal. calcd. for C21H19N5O2: C, 67.55; H, 5.13; N, 18.76. Found: C, 67.05; H, 5.08; N, 18.70%. UV/Vis (CHCl3, λmax, nm, (ε)): 355 (3.62). 2.2. Computational details Geometry optimization and vibrational frequency calcu- lations have been performed at DFT hybrid B3LYP/6- 311+G(d,p) level theory. The general tendency of the quantum chemical method is to overestimate the force constant at the exact equilibrium geometry of the molecule [15]. Hence, the hybrid DFT hybrid B3LYP functional method was used for obtaining considerably better agreement with experimental data [16]. The molecular orbital (MO) figures were prepared using the GaussView 3.09 package [17] with a contour value of 0.020, and the molecular orbital contributions (MOCs) of different molecular parts were calculated at the B3LYP/6- 311+G(d,p) level. A great variety of quantum chemical indices were taken from the calculation results, such as the energy of the highest occupied molecular orbital (HOMO), the energy of the lowest unoccupied molecular orbital (LUMO), electro- negativity, global hardness and softness, electron affinity, ionization potential, etc. These quantities are often defined following the Koopmans’ theorem [18]. Electronegativity (χ) is the measure of the power of an electron or a group of atoms to attract electrons toward itself [19], and according to the Koopmans’ theorem, it was estimated using Equation 1, so the other global parameters were calculated using Equations 2-4. 52 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Figure 1. Optimized structure of compound 1. Figure 2. Optimized structure of compound 2. The Fukui function (FF) [20] is one of the most widely used local density functional descriptors to model chemical reactivity and site selectivity. It is defined as the derivative of the electron density ρ(r) with respect to the total number of electrons N in the system at a constant external potential V(r) acting on an electron due to all nuclei in the system, and therefore Mulliken population analyzes were performed on the optimized geometries of neutral, cationic and anionic states of the investigated molecules. Mulliken charges of each atom in neutral and charged states were substituted in the equations proposed by Yang and Mortier [21], based on a finite-difference method. χ = 𝐸𝐸𝐻𝐻𝐻𝐻𝐻𝐻𝐻𝐻+𝐸𝐸𝐿𝐿𝐿𝐿𝐻𝐻𝐻𝐻 2 (1) 𝑓𝑓𝑘𝑘+ = 𝑞𝑞𝑘𝑘(N + 1) − 𝑞𝑞𝑘𝑘 (N) for nucleophilic attack (2) 𝑓𝑓𝑘𝑘−=𝑞𝑞𝑘𝑘(N) - 𝑞𝑞𝑘𝑘 (N-1) for electrophilic attack (3) 𝑓𝑓𝑘𝑘𝑜𝑜=𝑞𝑞𝑘𝑘(N+1) - 𝑞𝑞𝑘𝑘 (N) (4) For a radical attack to evaluate the Fukui indices. Again, Fukui indices and global indices were substituted in Equations 5-9 to determine the local reactivity indices such as local philicity, local softness, relative nucleophilicity (𝑆𝑆𝑘𝑘−/𝑆𝑆𝑘𝑘+), relative electrophilicity (𝑆𝑆𝑘𝑘+/𝑆𝑆𝑘𝑘−), dual descriptor (Δf(r)), dual local softness Δ𝑆𝑆𝑘𝑘, and multiphilic descriptor Δωk. ω𝑘𝑘 α = ω𝑓𝑓𝑘𝑘α (5) 𝑆𝑆𝑘𝑘α = S𝑓𝑓𝑘𝑘α (6) Δf(r) =[(𝑓𝑓+(r) - (𝑓𝑓− (r)] (7) Δ𝑠𝑠𝑘𝑘 = S (𝑓𝑓𝑘𝑘+ − 𝑓𝑓𝑘𝑘−) = 𝑠𝑠𝑘𝑘+ − 𝑠𝑠𝑘𝑘− (8) Δω𝑘𝑘 = [ω𝑘𝑘 + −ω𝑘𝑘 −] = ω [Δ𝑓𝑓𝑘𝑘] (9) where (α = +, -, and 0) represent local philic quantities that describe nucleophilic, electrophilic, and radical attacks, respectively. The condensed Fukui function, local softness, and multiphilic descriptor for each reactive atom of the candidate molecule was calculated using Mulliken population analysis [22]. Nuclear magnetic resonance (NMR)/nucleus-independent chemical shift (NICS) calculations [23,24] for all test molecules were performed using the gauge-including-atomic-orbital (GIAO) method with the basis set B3LYP/6-311+G(2d,p). NICS(1)zz was calculated using the component of the magnetic shift tensor in the z-direction, perpendicular to the plane of the ring, for a dummy atom 2 Å above [25], the plane of the ring. The NICS [23,24,26] probes (Bq) were placed up and down from the geometric center of the ring, perpendicular to the average ring plane, from -2 to +2 Å, in increments of 0.2 Å. The NICS values [23,24] were calculated for all ghost atoms using the Gaussian 09 software package [17]. The appropriate structural parameters of the optimized structure of the given molecule obtained using the B3LYP method with a 6-311+G(d,p) basis set have been used for the calculation of the Harmonic Oscillator Model of Aromaticity (HOMA) [24,27], values. The non-linear optical (NLO) properties were evaluated at the DFT level based. Based on the geometries of the ground state, where µ and αij have been calculated analytically [28]. βijk has been computed by using the afinite field procedure based on the numerical differentiation of the analytic polarizabilities evaluated under several electric field amplitudes. The first hyperpolarizability (β0) and related properties (β, 0, and ∆) for the respective molecules (from the components of β) were calculated. 3. Results and discussion 3.1. Optimized parameters The optimized parameters of compounds 1 and 2 are presented in Tables 1 and 2, and Figures 1 and 2, the C-C bond lengths of the phenyl ring vary between 1.3817-1.4159 Å for compound 1, 1.3848-1.4246 Å for compound 2. In the present study, the computed C-N bonds for compound 1 is from 1.3859 to 1.4365 Å and for compound 2 from 1.3862-1.4139 Å, and their XRD values are 1.3680-1.3776 Å [29,30]. Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 53 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 1. Geometric bond lengths (Å), bond angles, and dihedral angles (°) of compound 1 calculated with DFT-B3LYP/6-311+G(d,p) basis set. Bond length, Å B3LYP/6-311+G(d,p) Bond angle, ° B3LYP/6-311+G(d,p) Dihedral angle, ° B3LYP/6-311+G(d,p) C1-C2 1.3866 N15-C16-C18 120.1 C1-C6-N11-H13 161.4 C1-C6 1.4043 C17-C16-C18 119.5 C5-C6-N11-H12 -162.0 C1-H7 1.0850 C16-C17-C19 120.2 C5-C6-N11-H13 -21.1 C2-C3 1.3985 C16-C17-H20 119.6 C3-C14-N15-C16 179.9 C2-H8 1.0839 C19-C17-H20 120.3 N14-N15-C16-C17 -91.6 C3-C4 1.4043 C16-C18-C21 121.3 N14-N15-C16-C18 93.0 C3-N14 1.4166 C16-C18-H22 119.4 N15-C16-C17-C19 -176.4 C4-C5 1.3817 C21-C18-H22 119.3 N15-C16-C17-H20 3.7 C4-H9 1.0827 C17-C19-C23 120.8 C18-C16-C17-C19 -0.9 C5-C6 1.4107 C17-C19-H24 121.0 C18-C16-C17-H20 179.2 C5-H10 1.0856 C23-C19-H24 118.3 N15-C16-C18-C21 176.5 C6-N11 1.3856 C18-C21-C23 118.7 N15-C16-C18-H22 -3.7 N11-H12 1.0082 C18-C21-C27 118.7 C17-C16-C18-C21 1.0 N11-H13 1.0082 C23-C21-C27 122.6 C17-C16-C18-H22 -179.2 N14-N15 1.2487 C19-C23-C21 119.5 C16-C17-C19-C23 0.3 N15-C16 1.4365 C19-C23-O25 118.2 C16-C17-C19-H24 -179.5 C16-C17 1.3978 C21-C23-O25 122.2 H20-C17-C19-C23 -179.8 C16-C18 1.3861 C23-O25-H26 107.8 H20-C17-C19-H24 0.3 C17-C19 1.3886 C21-C27-H28 116.7 C16-C18-C21-C23 -0.5 C17-H20 1.0838 C21-C27-N29 121.3 C16-C18-C21-C27 179.6 C18-C21 1.4060 H28-C27-N29 122.0 H22-C18-C21-C23 179.7 C18-H22 1.0850 C27-N29-N30 122.4 H22-C18-C21-C27 -0.2 C19-C23 1.3968 N29-N30-H31 108.9 C17-C19-C23-C21 0.2 C19-H24 1.0835 N29-N30-C32 124.7 C17-C19-C23-O25 -180.0 C21-C23 1.4159 H31-N30-C32 114.4 H24-C19-C23-C21 -180.0 C21-C27 1.4579 N30-C32-C33 120.5 H24-C19-C23-O25 -0.2 C23-O25 1.3523 N30-C32-C34 120.0 C18-C21-C23-C19 -0.1 O25-H26 0.9828 C33-C32-C34 119.4 C18-C21-C23-O25 -179.9 C27-H28 1.0898 C32-C33-C35 120.0 C27-C21-C23-C19 179.8 C27-N29 1.2878 C32-C33-H36 119.6 C27-C21-C23-O25 0.0 N29-N30 1.3789 C35-C33-H36 120.4 C18-C21-C27-H28 0.9 N30-H31 1.0094 C32-C34-C37 120.3 C18-C21-C27-N29 -178.8 N30-C32 1.4222 C32-C34-H38 119.5 C23-C21-C27-H28 -179.0 C32-C33 1.4005 C37-C34-H38 120.2 C23-C21-C27-N29 1.3 C32-C34 1.3988 C33-C35-C39 120.5 C19-C23-O25-H26 -179.7 C33-C35 1.3916 C33-C35-H40 119.5 C21-C23-O25-H26 0.1 C33-H36 1.0834 C39-C35-H40 120.0 C21-C27-N29-N30 -177.9 C34-C37 1.3934 C34-C37-C39 120.2 H28-C27-N29-N30 2.5 C34-C38 1.0851 C34-C37-H41 119.6 C27-N29-N30-H31 -155.3 C35-C39 1.3953 C39-C37-H41 120.2 C27-N29-N30-C32 -15.2 C35-H40 1.0842 C35-C39-C37 119.6 N29-N30-C32-C33 69.7 C37-C39 1.3931 C35-C39-H42 120.2 N29-N30-C32-C34 -113.8 C37-H41 1.0842 C37-C39-H42 120.2 H31-N30-C32-C33 -152.0 C39-H42 1.0837 H31-N30-C32-C34 24.4 Bond angle, ° B3LYP/6-311+G(d,p) Dihedral angle, ° B3LYP/6-311+G(d,p) Dihedral angle, ° B3LYP/6-311+G(d,p) C2-C1-C6 120.2 H7-C1-C2-C8 -0.3 N30-C32-C33-C35 177.5 C2-C1-H7 120.1 C2-C1-C6-C5 0.1 N30-C32-C33-H36 -0.8 C6-C1-H7 119.7 C2-C1-C6-N11 177.7 C34-C32-C33-C35 1.0 C1-C2-C3 120.9 H7-C1-C6-C5 -179.7 C34-C32-C33-H36 -177.2 C1-C2-H8 120.8 H7-C1-C6-N11 -2.2 N30-C32-C34-C37 -176.2 C3-C2-H8 118.4 C1-C2-C3-C4 0.1 N30-C32-C34-H38 3.9 C2-C3-C4 119.1 C1-C2-C3-N14 -179.9 C33-C32-C34-C37 0.3 C2-C3-N14 115.9 H8-C2-C3-C4 -179.9 C33-C32-C34-H38 -179.6 C4-C3-N14 125.0 H8-C2-C3-N14 0.1 C32-C33-C35-C39 -1.3 C3-C4-C5 120.2 C2-C3-C4-C5 -0.1 C32-C33-C35-H40 180.0 C3-C4-H9 119.0 C2-C3-C4-H9 179.9 H36-C33-C35-39 176.9 C5-C4-H9 120.7 N14-C3-C4-C5 -180.0 H36-C33-C35-H40 -1.8 C4-C5-C6 120.8 N14-C3-C4-H9 -0.1 C32-C34-C37-C39 -1.3 C4-C5-H10 119.9 C2-C3-N14-N15 179.0 C32-C34-C37-H41 179.5 C6-C5-H10 119.3 C4-C3-N14-N15 -1.1 H38-C34-C37-39 178.6 C1-C6-C5 118.7 C3-C4-C5-C6 0.0 H38-C34-C37-H41 -0.6 C1-C6-N11 120.9 C3-C4-C5-H10 -179.8 C33-C35-C39-C37 0.3 C5-C6-N11 120.4 H9-C4-C5-C6 -179.9 C33-C35-C39-H42 -179.4 C6-C11-H12 117.3 H9-C4-C5-H10 0.3 H40-C35-C39-C37 179.0 C6-N11-H13 117.3 C4-C5-C6-C1 -0.1 H40-C35-C39-H42 -0.7 C12-N11-H13 113.8 C4-C5-C6-N11 -177.6 C34-C37-C39-C35 1.0 C3-N14-N15 115.9 H10-C5-C6-C1 179.7 C34-C37-C39-H42 -179.4 N14-N15-C16 113.8 H10-C5-C6-N11 2.2 H41-C37-C39-C35 -179.8 N15-C16-C17 120.2 C1-C6-N11-H12 20.5 H41-C37-C39-H42 -0.1 The optimized N-H bond distance ranges from 1.0082 to 1.0094 Å in compound 1, 1.0125-1.0144 Å in compound 2 are comparable to the literature value of 0.85 Å [31]. The optimized C-H bond lengths vary from 1.0809-1.0858 Å for compounds 1 and 2. The theoretical bond angles of C-C-C, C-C-H and C-N-N, C- N-H, C-N-N, N-N-C and N-N-H range from 115.9-120.4° [32]. The theoretical dihedral angles of the title molecules are given in Tables 1 and 2. Compound 1 is not synthesized and is used only for theoretical comparisons. 3.2. Vibrational assignments Vibrational spectroscopy is widely employed in organic chemistry for the identification of functional groups, to study molecular conformations, reactions, etc. The resulting vibra- tional wave numbers for the optimized geometry of compounds 1 and 2 and the proposed assignments are given in Tables 3 and 4. 54 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 2. Geometric bond lengths (Å), bond angles, and dihedral angles (°) of compound 2 calculated with DFT-B3LYP/6-311+G(d,p) basis set. Bond length, Å B3LYP/6-311+G(d,p) Bond angle, ° B3LYP/6-311+G(d,p) Dihedral angle, ° B3LYP/6-311+G(d,p) C1-C2 1.3876 H16-C15-H17 108.4 C1-C6-N11-C13 140.4 C1-C6 1.4012 H16-C15-H18 110.2 C5-C6-N11-H12 145.1 C1-H7 1.0846 H17-C15-H18 107.8 C5-C6-N11-C13 -42.6 C2-C3 1.3994 C3-N19-N20 115.3 C6-N11-C13-O14 -179.8 C2-H8 1.0836 N19-N20-C21 115.8 C6-N11-C13-C15 -1.0 C3-C4 1.4033 N20-C21-C22 1160 H12-N11-C13-O14 -7.2 C3-N19 1.4139 N20-C21-C23 124.8 H12-N11-C13-C15 171.6 C4-C5 1.3857 C22-C21-C23 119.1 N11-C13-C15-H16 -31.1 C4-H9 1.0821 C21-C22-C24 120.7 N11-C13-C15-H17 90.2 C5-C6 1.4046 C21-C22-H25 118.4 N11-C13-C15-H18 -152.8 C5-H10 1.0819 C24-C22-H25 120.8 O14-C13-C15-H16 147.7 C6-N11 1.4109 C21-C23-C26 121.3 O14-C13-C15-H17 -91.0 N11-H12 1.0125 C21-C23-H27 118.7 O14-C13-C15-H18 26.0 N11-C13 1.3862 C26-C23-H27 120.0 C3-N19-N20-C21 -179.9 C13-O14 1.2188 C22-C24-C28 120.3 N19-N20-C21-C22 179.7 C13-C15 1.5137 C22-C24-H29 121.4 N19-N20-C21-C23 -0.3 C15-H16 1.0903 C28-C24-H29 118.3 N20-C21-C22-C24 -180.0 C15-H17 1.0935 C23-C26-C28 118.7 N20-C21-C22-H25 0.0 C15-H18 1.0890 C23-C26-C32 119.1 C23-C21-C22-C24 0.0 N19-N20 1.2561 C28-C26-C32 122.2 C23-C21-C22-H25 -180.0 N20-C21 1.4100 C24-C28-C26 119.9 N20-C21-C23-C26 -179.9 C21-C22 1.4035 C24-C28-O30 118.2 N20-C21-C23-H27 0.0 C21-C23 1.3979 C26-C28-O30 121.9 C22-C21-C23-C26 0.0 C22-C24 1.3848 C28-O30-H31 108.2 C22-C21-C23-H27 180.0 C22-H25 1.0835 C26-C32-H33 116.9 C21-C22-C24-C28 -0.1 C23-C26 1.3970 C26-H32-N34 122.5 C21-C22-C24-H29 179.9 C23-H27 1.0834 H33-C32-N34 120.6 H25-C22-C24-C28 179.9 C24-C28 1.3975 C32-N34-N35 119.1 H25-C22-C24-H29 0.0 C24-H29 1.0830 N34-N35-H36 118.5 C21-C23-C26-C28 -0.1 C26-C28 1.4246 N34-N35-C37 123.2 C21-C23-C26-C32 179.9 C26-C32 1.4540 H36-N35-C37 118.2 H27-C23-C26-C28 180.0 C28-O30 1.3446 N35-C37-C38 122.5 H27-C23-C26-C32 0.0 O30-H31 0.9819 N35-C37-C39 118.1 C22-C24-C28-C26 0.1 C32-H33 1.0951 C38-C37-C39 119.4 C22-C24-C28-O30 -180.0 C32-N34 1.2913 C37-C38-C40 119.6 H29-C24-C28-C26 -180.0 N34-N35 1.3437 C37-C38-H41 120.3 H29-C24-C28-O30 0.0 N35-H36 1.0144 C40-C38-H41 120.1 C23-C26-C28-C24 0.0 N35-C37 1.3954 C37-C39-C42 120.2 C23-C26-C28-O30 -180.0 C37-C38 1.4005 C37-C39-H43 119.8 C32-C26-C28-C24 -180.0 C37-C39 1.4033 C42-C39-H43 120.0 C32-C26-C28-O30 0.0 C38-C40 1.3921 C38-C40-C44 121.2 C23-C26-C32-H33 0.5 C38-H41 1.0809 C38-C40-H45 118.9 C23-C26-C32-N34 -179.5 C39-C42 1.3894 C44-C40-H45 120.0 C28-C26-C32-H33 -179.5 C39-H43 1.0858 C39-C42-C44 120.6 C28-C26-C32-N34 0.5 C40-C44 1.3937 C39-C42-H46 119.3 C24-C28-O30-H31 180.0 C40-H45 1.0843 C44-C42-H46 120.2 C26-C28-O30-H31 0.0 C42-C44 1.3949 C40-C44-C42 119.0 C26-C32-N34-N35 -179.6 C42-H46 1.0842 C40-C44-H47 120.5 H33-C32-N34-N35 0.4 C44-H47 1.0832 C42-C44-H47 120.5 C32-N34-N35-H36 -0.7 Bond angle, ° B3LYP/6-311+G(d,p) Dihedral angles, ° B3LYP/6-311+G(d,p) Dihedral angles, ° B3LYP/6-311+G(d,p) C2-C1-C6 120.4 C6-C1-C2-C3 0.7 C32-N34-N35-C37 -178.1 C2-C1-H7 120.1 C6-C1-C2-H8 179.9 N34-N35-C37-C38 -0.4 C6-C1-H7 119.5 H7-C1-C2-C3 -178.7 N34-N35-C37-C39 179.7 C1-C2-C3 120.6 H7-C1-C2-H8 0.5 H36-N35-C37-C38 -177.8 C1-C2-H8 120.8 C2-C1-C6-C5 0.8 H36-N35-C37-C39 2.3 C3-C2-H8 118.6 C2-C1-C6-N11 177.9 N35-C37-C38-C40 -179.8 C2-C3-C4 119.0 H7-C1-C6-C5 -179.8 N35-C37-C38-H41 0.3 C2-C3-N19 116.0 H7-C1-C6-N11 -2.7 C39-C37-C38-C40 0.1 C4-C3-N19 125.0 C1-C2-C3-C4 -1.2 C39-C37-C38-H41 -179.8 C3-C4-C5 120.4 C1-C2-C3-N19 179.5 N35-C37-C39-C42 179.9 C3-C4-H9 119.0 H8-C2-C3-C4 179.6 N35-C37-C39-H43 -0.1 C5-C4-H9 120.6 H8-C2-C3-N19 0.3 C38-C37-C39-C42 0.0 C4-C5-C6 120.6 C2-C3-C4-C5 0.2 C38-C37-C39-H43 -180.0 C4-C5-H10 119.5 C2-C3-C4-H9 -178.3 C37-C38-C40-C44 0.0 C6-C5-H10 119.9 N19-C3-C4-C5 179.4 C37-C38-C40-H45 -180.0 C1-C6-C5 118.9 N19-C3-C4-H9 0.9 H41-C38-C40-C44 179.8 C1-C6-N11 118.5 C2-C3-N19-N20 -179.1 H41-C38-C40-H45 -0.1 C5-C6-N11 122.5 C4-C3-N19-N20 1.6 C37-C39-C42-C44 0.0 C6-N11-H12 116.3 C3-C4-C5-C6 1.3 C37-C39-C42-H46 180.0 C6-N11-C13 131.8 C3-C4-C5-H10 -176.9 H43-C39-C42-C44 179.9 H12-N11-C13 111.5 H9-C4-C5-C6 179.8 H43-C39-C42-H46 -0.1 N11-C13-O14 119.1 H9-C4-C5-H10 1.6 C38-C40-C44-C42 0.0 N11-C13-C15 119.0 C4-C5-C6-C1 -1.8 C38-C40-C44-H47 -180.0 O14-C13-C15 121.8 C4-C5-C6-N11 -178.8 H45-C40-C44-C42 179.9 C13-C15-H16 113.2 H10-C5-C6-C1 176.4 H45-C40-C44-H47 -0.1 C13-C15-H17 109.9 H10-C5-C6-N11 -0.5 C39-C42-C44-C40 0.0 C13-C15-H18 107.3 C1-C6-N11-C12 -31.9 C39-C42-C44-H47 -180.0 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 55 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 3. Vibrational wavenumbers obtained for compound 1 with DFT-B3LYP/6-311+G(d,p) (Harmonic frequency (cm-1), IR intensity, Raman activity (Km/mol), reduced masses (a.m.u.) and force constants (N/m)) *. Mode no Calculated freq. (cm-1) IR intensity Raman activity Reduced mass Force constant Vibrational assignments with >10% PED 1 3543 23.40 86.76 1.10 8.82 νN11-H12+N11-H13(50) 2 3462 34.20 298.58 1.08 8.23 νN30-H31(100) 3 3444 72.92 537.60 1.05 7.92 νN11-H12+N11-H13(50) 4 3279 383.25 95.10 1.07 7.32 νO25-H26(99) 5 3078 2.13 58.00 1.09 6.60 νC4-H9(97) 6 3066 9.68 209.34 1.09 6.58 νC17-H20(32)+C10-H24(67)+C35-H40(26)+C37-H41(11)+C39-42(32) 7 3064 4.96 101.33 1.09 6.56 νC2-H8(91) 8 3055 17.01 53.49 1.09 6.55 νC33-H36(50)+C37-H41(21)+C39-H42(23) 9 3046 13.45 110.29 1.09 6.50 νC17-H20(68)+C19-H24(32)+C33-H36(11)+C34-H38(17)+C35-40(18)+C437-H41(38)+ C39-H42(14) 10 3045 0.35 89.00 1.09 6.44 νC33-H36(10)+C34-H38(18)+C35-H40(18)+C39-H42(23) 11 3040 3.91 23.91 1.09 6.45 νC18-H22(98) 12 3039 18.57 123.82 1.09 6.42 νC1-H7(91) 13 3033 5.48 35.99 1.09 6.40 νC34-H38(60)+C37-H41(28) 14 3156 21.66 142.02 1.09 6.39 νC5-H10(97) 15 1602 27.99 774.98 4.74 7.75 νN29-C27(51) 16 1601 266.42 90.85 1.54 2.52 βH13-C39-C37(61) 17 1590 6.15 1163.86 5.49 8.86 νC16-C18(10)+C23-C19(22)+C18-C21(17) 18 1585 29.07 55.61 2.74 4.38 νΝC5-C4(19)+C2-C3(10)+βH13-N11-H12(23) 19 1582 27.07 45.61 4.75 4.38 νC39-C37(19)+C35-C39(22)+βC33-C35-C39(12)+H40-C35-C39(10) 20 1573 44.65 128.07 5.40 8.53 νC33-C35(28)+C39-C37(18)+βC32-C34-C35(10) 21 1564 19.30 14.88 5.00 7.80 νC32-C34(27)+C39-C39(15)+C32-C34(27) 22 1552 12.89 342.54 4.52 6.96 νC17-C16(17) 23 1549 13.03 205.62 5.68 8.70 νC2-C3(19)+C6-C1(20) 24 1505 379.59 2157.63 6.99 10.09 νN14-N15(19) 25 1471 25.50 27.69 1.58 2.18 βH31-N30-N29(45) 26 1467 5.22 932.58 2.75 3.78 νN14-N15(10)+βH9-C4-C5(18)+νN14-N15(100029 27 1453 210.40 235.06 2.83 3.81 βH20-C4-C19(10)+H22-C18-C21(16)+H24-C19-C23(25) 28 1423 6.71 91.74 2.28 2.97 νC16-C18(10)+βH26-O25-C23(22) 29 1409 41.24 215.10 3.25 4.14 νΝC5-C4(17)+νC1-C2(24)+βH7-C1-C2(13)+H10-H10-C5-C6(13)+νΝC1-C2(24) 30 1403 11.59 209.93 1.81 2.29 βH26-O25-C23(19)+H31-N30-N29(11)+H42-C39-C37(11) 31 1359 89.15 11.14 2.21 2.62 νC19-C17(15)+C18-C21(18)+βH26-O25-C23(18) 32 1312 16.89 7.29 1.65 1.84 βH28-C27-N29(39) 33 1307 0.23 11.22 5.19 5.69 νC4-C3(16)+C6-C1(24)C++C5-C4(17)+βH22-N11-C6(11) 34 1292 0.18 15.99 1.97 2.12 νC33-C35(14)+C34-C37(14)+βH36-C33-C25(19)+H38-C34-C37(21)+H42-C39-C37(11) 35 1281 3.99 427.97 3.81 4.02 νC16-C18(27)+C19-C17(12) 36 1274 4.69 13.25 1.60 1.67 βH7-C1-C2(12)+H8-C2-C1(18)+H9-C4-C5(18)+H10-C5-C6(17) 37 1259 145.63 68.30 3.18 3.23 νΝC1-C2(11)+N11-C6(44) 38 1257 48.23 6.76 2.70 2.73 νC32-C34(25)+C35-C39(11) 39 1242 221.10 8.36 2.78 2.75 νO25-C23(16)βH20-C17-C19(21) 40 1215 14.85 203.37 2.56 2.42 νC18-C21(23)+N15-C16(10)+βH22-C18-C21(15) 41 1196 97.47 176.07 3.15 2.89 νN30-C32(36) 42 1192 74.82 121.23 2.27 2.07 νC23-C19(12)+N14-C3(12)+N15-C16(10)+βH22-C18-C21(13) 43 1175 71.70 458.02 2.41 2.13 νC23-C19(15)+C21-C27(10)+N30-C32(14) 44 1146 6.95 29.18 1.14 0.96 βH36-C33-C35(22)+H38-C34-C37(22)+H40-C35-C38(16)+H41-C37-C39(17) 45 1132 0.39 6.35 1.11 0.92 βH40-C35-C39(19)+H41-C37-C39(19)+H42-C39-C37(38) 46 1126 67.72 40.62 1.52 1.24 νN15-C16(12)+βH9-C4-C5(12)+H22-C18-C32(14) 47 1108 222.63 655.51 1.76 1.39 βH8-C2-C1(21)+νN14-C3(12) 48 1096 20.91 32.26 1.21 0.93 νC5-C4(10)+C1-C2(12)+βH7-C1-C2(15)+H9-C4-C5(17) 49 1093 7.77 2.95 1.42 1.09 νC16-C18(10)+C19-C17(12)+βH20-C17-C19(10) 50 1063 29.67 2.08 1.93 1.40 νC33-C35(11)+N29-N30(22)+βH38-C34-C37(14) 51 1041 33.81 2.02 2.77 1.93 νC34-C37(13)+N29-N30(35) 52 1025 3.46 2.12 1.42 0.96 νC6-C1(16)+βH12-N11-C6(50) 53 976 1.05 0.36 2.57 1.57 βC5-C4-C3(40)+C1-C2-C3(24) 54 972 0.11 84.26 6.06 3.68 νC35-C39(11)+βC33-C35-C39(29)+C34-C37-C39(15)+C35-C39-C37(19) 55 961 0.32 0.68 1.29 0.77 τH40-C35-C39-C37(26)+C41-C37-C39-C35(14)+C42-C39-C37-C34(31)+ C35-C39-C37-C34(10) 56 947 23.77 16.74 3.00 1.73 βC19-C17-C16(10) 57 945 0.22 0.61 1.34 0.77 τH9-C4-C1-C6(44)+H16-C5-C6-N11(19)+C5-C4-C3-C2(13) 58 943 3.30 0.15 1.46 0.83 τH36-C33-C35-C39(18)+H38-C34-C37-C39(11)+C40-C35-C39-C37(10)+ C41-C37-C39-C35(31) 59 927 1.29 0.24 1.34 0.74 τH7-C1-C2-C3(14)+H8-C2-C1-C6(50)+C6-C1-C2-C3(18) 60 920 7.38 1.93 1.46 0.79 τH20-C17-C19-C23(17)+H24-C19-C23-C21(16)+H28-C27-N29-30(45)+ τH28-C27-N29-N30(45)+H23-C17-C19-C23(17)+H24-C19-C23-C21(16) 61 914 4.59 3.94 1.49 0.80 τH20-C17-C19-C23(20)+H24-C19-C23-C21(16)+H28-C27-N29-N30(29)+ C23-C19-C17-C16(12) 62 896 6.58 9.26 2.68 1.38 βN14-N15-C16(10) 63 886 4.91 5.98 1.91 0.96 τH36-C33-C35-C39(17)+C38-C34-C37-C39(17)+C42-C39-C37-C34(17) 64 839 3.79 10.69 1.83 0.83 τH22-C18-C21-C23(36) 65 833 12.05 13.07 2.66 1.19 τH22-C18-C21-C23(15) 66 813 16.01 8.48 1.72 0.73 τH10-C5-C6-N11(10)+H36-C33-C35-C39(10)+H38-C34-C37-C39(13) 67 812 29.42 3.36 1.54 0.65 τH7-C1-C2-C3(16)+H10-C5-C6-N11(23)+H38-C34-C37-C39(14) 68 797 28.75 28.18 2.09 0.85 τH20-C17-C19-C23(26)+H24-C19-C23-C21(16) 69 774 0.58 0.11 1.26 0.50 τH7-C1-C2-C3(36)+H8-C2-C1-C6(17)+H9-C4-C5-C6(15)+H10-C5-C6-N11(29) 70 756 26.12 34.34 4.81 1.85 βC35-C39-C37(16) 71 739 17.27 19.79 4.82 1.77 βN15-C16-C18(13)+νO25-C23(16) 72 719 22.63 2.74 2.26 0.79 τC40-C35-C39-C37(10)+C41-C37-C39-C35(12)+C42-C39-C37-C34(13)+ C32-C34-C37-C39(12)+γN30-C33-C34-C32(13) 73 707 97.05 0.96 1.13 0.38 τH26-O25-C23-C19(82) 56 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 3. (continued). Mode no Calculated freq. (cm-1) IR intensity Raman activity Reduced mass Force constant Vibrational assignments with >10% PED 74 705 0.38 2.80 3.38 1.09 τH22-C18-C21-C23(13)+H24-C19-C25-C21(14)+O25-C19-C21-C23(18) 75 705 1.31 0.96 3.91 1.25 τC5-C4-C3-C2(17)+C6-C1-C2-C3(12)+γ N11-C5-C1-C6(22) 76 692 73.54 2.28 2.32 0.71 βC19-C17-C16(13)+τH42-C39-C37-C34(10) 77 627 2.33 13.42 6.30 1.59 βC6-C1-C2(17)+C5-C4-C3(15)+C1-C2-C3(24) 78 605 0.70 4.41 6.19 1.46 βC33-C35-C39(21)+C34-C37-C39(36)+C32-C34-C37(20) 79 578 6.42 4.13 4.68 1.00 βC3-N14-N15(19) 80 534 122.62 36.08 2.15 0.39 τH31-N30-N29-C27(23)+γ N11-C5-C1-C6 81 526 43.06 54.00 2.04 0.36 τH31-N30-N29-C27(28)+γ N11-C5-C1-C6(11) 82 488 8.82 3.01 3.66 0.56 βC32-C34-C37(10)+γN30-C33-C34-C32 83 486 16.81 7.74 4.35 0.66 βO25-C23-C19(19)+γN11-C5-C1-C6(12) 84 463 47.75 3.61 3.48 0.48 βC6-C1-C2(11)τH12-N11-C6-C5(12)+H13-N11-C6-C5(11) 85 459 25.92 4.47 3.51 0.47 βN14-N15-C16(11)+τC23-C19-C17-C16(10) 86 450 141.34 17.98 2.76 0.36 γ O25-C19-C21-C23(10) 87 449 59.46 12.10 3.76 0.49 τN15-C16-C18-C21(13)+γ O25-C19-C21-C23(18) 88 433 238.12 47.57 2.40 0.29 τH12-N11-C6-C5(42)+H13-N11-C6-C5(16) 89 415 3.82 1.00 3.42 0.38 βO25-C23-C19(13)+τC1-C2-C3-N14(13)+C6-C1-C2-C3(18) 90 399 2.20 2.55 4.24 0.43 βO25-C23-C19(25)+τC5-C4-C3-C2(14) 91 378 10.53 18.02 4.38 0.40 βC18-C21-C27(14)+N30+C32-C34(12) 92 374 11.25 5.22 3.54 0.32 βC6-C1-C2(11)+N11-C6-C1(39) 93 354 3.76 12.87 4.75 0.38 βN30-C32-C34(14) 94 334 12.80 0.73 1.12 0.08 τH12-N11-C6-C5(42)+H13-N11-C6-C5(42) 95 320 1.99 0.36 3.70 0.24 βN11-C6-C1(13)+τC16-C18-C21-C27(12)+C33-C19-C17-C16(12) 96 291 0.96 2.64 5.86 0.32 τC1-C2-C3-N14(10)+γ C4-C2-N14-C3(23) 97 269 2.21 2.45 5.01 0.23 τC16-C18-C21-C27(12)+C21-C27-N29-N30(19)+N15-C16-C18-C21(12) 98 241 2.52 1.97 3.91 0.15 βN30-C35-C34(15)+τC27-N29-N30-C32(17)+C18-C21-C27-N29(21) 99 178 0.79 6.03 6.03 0.12 βN14-N15-C16(11)+τC19-C17-C16-C18(10) 100 166 2.13 1.26 5.67 0.10 τC5-C4-C3-C2(11)+C1-C2-C3-N14(14)+C6-C1-C2-C3(13) 101 135 2.13 3.26 6.11 0.07 βC3-N14-N15(22)+τC19-C17-C16-C18(23)+N15-C16-C18-C21(15) 102 129 0.55 1.08 5.54 0.06 βC18-C21-C27(15) 103 119 0.06 6.15 7.55 0.07 τN14-N15-C16-C18(62)+C2-C3-N14-N15(16) 104 87 1.16 8.75 5.52 0.03 τC16-C18-C21-C27(26)+C18-C21-C27-N29(19)+C21-C27-N29-N30(15) 105 59 2.29 4.71 5.05 0.01 βC27-N29-N30(16)+C21-C27-N29(11)+τN29-N30-C32-C33(23) 106 51 0.15 2.96 5.74 0.01 βN14-N15-N16(14)+τC2-C3-N14-N15(19)+γC17-C18-N15-C16(18) * ν: Stretching, β: In-plane bending, γ: Out-of-plane bending, ω: Wagging, t: Twisting, δ: Scissoring, ρ: Rocking. The vibrational spectral data obtained from the solid-phase FT-IR spectra are assigned on the basis of the results of the normal coordinate calculations using the VEDA program to the computed vibrational frequencies in the Gaussian suite. On the basis of the comparison between the calculated and experimental results, assignments of fundamental modes were carried out. The assignment of the experimental frequencies is based on the observed band frequencies in the infrared spectra of this species, confirmed by establishing a one-to-one correlation between the observed and theoretically calculated frequencies. The calculated frequencies are slightly higher than the observed values for the majority of normal modes. Two factors may be responsible for the discrepancies between the experimental and computed spectra of azodye 2. The first is caused by environmental conditions, and the second is due to the fact that the experimental value is an anharmonic frequency while the calculated value is a harmonic frequency [33]. The phenyl ring modes mostly involve C-C, and the vibrational frequency is associated with C-C stretching modes of the carbon skeleton. The C-C stretching modes predicted in the range 1600-1550 cm-1 are in agreement with the experimental observation of the IR value and the amine counterpart 1. The aromatic C-H stretching frequencies are found at 3090-3029 cm-1 (theoretical) for compound 2 (containing anilide moiety) coinciding with the experimental value of 3054 cm-1, and the same trend is also observed in compound 1 (3156-3033 cm-1) molecule as well. The stretching of CH between 3024-2992 cm-1 is due to the aliphatic group in compound 2, and a similar stretching is missing in compound 1 molecule. The C13=O14 stretching at 1677 cm-1 matches the experimental value at 1650 cm-1. N35-H36 is observed at 3387 cm-1, its experimental observation is around 3307 cm-1, and it is supported by a total energy distribution (TED) value of 99%, which is found at around 3462 cm-1 for N30-H31. The N-H stretching at 3543 cm-1 with a TED value of 50% is predicted in compound 1. The stretching of the OH of the molecule under study is observed at 3296 cm-1 (theoretical) and 3300 cm-1 (experimental) for compound 2, and it is around 3279 cm-1 (theoretical) in compound 1. The difference may be due to the absence of intermolecular hydrogen bonding in the gas phase. The C-N mode azo compounds are expected to appear in the region 1200 to 1300 cm-1. The wave number and intensity depend on the neighboring group effect because of neighboring substituents. Strong bands appear at 1450 cm-1 (FT-IR) originating from the stretching vibration bands assigned to νN19-N20, which is comparable with 1453 cm-1 (theoretical) and with 1505 cm-1 in compound 1. In compound 2, N35-N34 stretching is predicted at 1135 cm-1 with TED (30%), and for compound 1, N29-N30 is around 1063 cm-1, TED (22%). C32=N34 stretching at 1600 cm- 1 with a theoretical value of 1588 cm-1 for compound 2, and for compound 1 its 1602 cm-1 for C27=N29 with 51% TED [34]. 3.3. UV-vis data and FMO analysis Theoretical UV-vis spectral data for compounds 1 and 2 are given in Tables 5 and 6 and Figure 3. In UV-visible data, compound 2 exhibits two transitions in water, and the one with higher oscillator strength occurs at 378.7 nm. It is due to HOMO- 3 to LUMO (3%), HOMO-2 to LUMO (37%), and HOMO to LUMO (43%). In all solvents, there are two bands, one at 360-378 and 382-390 nm. The lowest wavelength 341.8 nm is obtained in water solvent [35]. Two transitions are identified in all the solvents. The highest wavelength is 360.9 nm, obtained for acetone, and the smallest is 342.6 nm for benzene solvent. It is H→L (53%) and H-1→L (41%), respectively. The experimental values coincide with the calculated λmax [36]. The calculated and experimental UV visible spectral values, such as energy, oscillator strength, and λmax for compound 2 are compared in Table 6. Two transitions are identified in all the solvents. The highest wavelength is 476.5 nm, obtained for DMSO, and the smallest is 396.3 nm for the benzene solvent. They are H- 1→L(98) and H-1→L(88), respectively. The experimental values coincide with the calculated λmax [30]. Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 57 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 4. Vibrational wavenumbers obtained for compound 2 with DFT-B3LYP/6-311+G(d,p) (Harmonic frequency (cm-1), IR intensity, Raman activity (Km/mol), reduced masses (a.m.u.) and force constants (N/m)) *. Mode No Exp. FTIR freq. (cm-1) Calc. freq. (cm-1) IR intensity Raman activity Reduced mass Force constant Vibrational Assignments with >10% PED 1 3437 41.64 411.9 1.08 8.11 νN11-H12(100) 2 3307 3387 11.80 1031.4 1.08 7.87 νN35-H36(99) 3 3300 3296 509.10 313.9 1.07 7.40 νO30-H31(99) 4 3090 3.96 59.9 1.09 6.65 νC38-H41(94) 5 3087 8.46 94.3 1.09 6.65 νC4-H9(66)+νC5-H10(33) 6 3076 6.12 199.5 1.10 6.61 νC24-H29(61)+νC22-H25(38)+νC22-H25(38) 7 3073 6.01 97.7 1.09 6.56 νC4-H9(32)+νC5-H10(63)+νC5-H10(63) 8 3070 24.87 348.3 1.10 6.59 νC40-H45(11)+νC42-H46(19)+νC44-H47(67)+νC42-H46(11) 9 3068 5.13 68.1 1.09 6.57 νC1-H7(11)+νC2-H8(85) 10 3066 3.87 36.6 1.09 6.53 νC23-H27(91) 11 3063 0.20 48.4 1.09 6.51 νC24-H29(35)+νC22-H25(56) 12 3054 3054 17.35 157.6 1.09 6.50 νC40-H45(32)+νC42-H46(57) 13 3046 1.60 92.8 1.09 6.44 νC1-H7(88)+νC2-H8(11)+νC44-H47(28)+νC40-H45(53)+νC42-H46(12) 14 3029 12.81 44.9 1.09 6.37 νC39-H43(87) 15 3024 12.94 102.0 1.10 6.44 νC15-H16(32)+νC15-H18(67) 16 2992 6.23 84.2 1.10 6.26 νC15-H17(42)+νC15-H16(42)+νC15-H18(16) 17 2930 46.13 35.2 1.09 5.96 νC32-H33(100) 18 2928 2.31 223.0 1.04 5.68 νC15-H17(57)+νC15-H16(26)+νC15-H18(17) 19 1650 1677 821.14 280.2 7.32 13.14 νO14-C13(79) 20 1600 1588 89.29 951.3 5.09 8.18 νN34-C32(19)+νC28-C24(19) 21 1584 2.99 2021.5 6.26 10.02 νN34-C32(24) 22 1578 608.20 3852.0 5.40 8.58 νC5-C4(11)+νC39-C42(13)+νC39-C42(14) 23 1565 43.28 1188.2 4.85 7.59 νC44-C40(16)+νC37-C38(20) 24 1553 76.21 2584.4 4.73 7.28 νC22-C21(17)+νν34-C32(11) 25 1535 1550 111.25 195.3 5.93 9.08 νC2-C3(18)+νC6-C1(23) 26 1494 1504 183.25 154.5 2.13 3.07 βH36-N35-N34(44)+νN35-C37(10) 27 1483 96.08 4604.3 3.43 4.81 νN19-νN20(23)+νN19-N20(10)+βH10-C5-C6(14) 28 1465 114.84 452.2 2.17 2.97 βH45-C40-C44(19)+βH43-C39-C42(19) 29 1457 281.19 4862.8 3.13 4.23 νN19-N20(12) 30 1450 1453 47.09 9503.1 3.12 4.20 βH9-C4-C5(11)+νN19-N20(20) 31 1431 69.84 836.7 1.84 2.41 βH12-N11-C13(27) 32 1426 7.95 66.5 1.19 1.55 βH16-C15-H18(34)+βH18-C15-H17(24)+τH18-C15-C13-11(13) 33 1421 12.82 3163.1 2.46 3.19 βH46-C42-C44(10)+βH47-C44-C42(13) 34 1414 26.88 14.5 1.06 1.35 βH17-C15-H16(49)+βH16-C15-H18(22) 35 1406 1412 12.56 666.5 2.11 2.70 βH31-O30-C28(26) 36 1372 25.03 19.7 2.60 3.14 νC24-C22(12)+νC23-C26(15) 37 1371 1369 13.41 3514.6 2.62 3.16 βH12-N11-C13(11)+νC5-C4(10) 38 1343 122.18 57.6 1.35 1.56 βH17-C15-H16(32)+βH18-C15-H17(35)+βH16-C15-H18(14) 39 1322 25.90 6.3 1.67 1.88 βH33-C32-N34(34) 40 1300 1299 11.50 51.8 2.05 2.22 νC38-C40(12)+νC39-C42(12)+βH41-C38-C40(18)+ βH47-C44-C42(13)+βH43-C39-C42(19) 41 1291 1.07 4119.4 3.45 3.70 νC21-C23(17) 42 1280 2.97 279.1 3.76 3.95 νC4-C3(15)+νC6-C1(11) 43 1273 1270 269.15 75.7 1.87 1.94 βH8-C2-C3(11)+βH9-C4-C5(11)+βH10-C5-C6(12) 44 1268 704.33 234.1 2.36 2.44 νN11-C13(30)+νN11-C6(12) 45 1257 1252 388.93 107.0 2.99 3.01 νO30-C28(32)+βH25-C22-C24(15) 46 1237 22.81 869.5 2.94 2.88 νN19-C3(10)+νN20-C21(14)+βH33-C32-N34(11) 47 1227 334.69 2.2 2.68 2.59 νN35-C37(20)+βH36-N35-N34(11) 48 1198 25.55 556.7 2.52 2.31 νN11-C6(20)+νC6-C1(16) 49 1191 33.22 98.3 1.81 1.65 νC28-C24(13)+βH27-C23-C26(18)+βH29-C24-C22(10) 50 1171 1173 21.40 3800.3 2.26 2.00 νC26-C32(11)+νN19-C3(13)+νC28-C24(14)+βH7-C1-C2(10) 51 1153 1149 24.39 111.6 1.14 0.96 βH41-C38-C40(20)+βH45-C40-C44(18)+βH46-C42-C44(19)+ βH43-C39-C42(21) 52 1135 202.71 342.1 2.28 1.89 νN34-N35(30) 53 1131 53.55 36.9 1.23 1.01 βH45-C40-C44(15)+βH46-C42-C44(17)+βH47-C44-C42(31) 54 1124 9.64 3046.0 1.65 1.33 νN34-N35(13)+βH9-C4-C5(13) 55 1110 1108 3.52 5219.9 2.06 1.63 νN20-C21(14)+βH27-C23-C26(11) 56 1083 27.60 82.0 1.30 0.98 νC1-C2(11)+βH8-C2-C3(10)+βH25-C22-C24(13)+βH9-C4-C5(14) 57 1072 1081 68.40 1296.2 1.43 1.08 βH25-C22-C24(25) 58 1057 19.13 5.7 1.64 1.18 νC38-C40(11)+βH41-C38-C40(16)+βH47-C44-C42(16) 59 1013 1011 14.77 4.6 1.74 1.14 βH16-C15-H18(17)+τH16-C15-C13-N11(38)+τH18-C15-C13- N11(14)+ϒO14-C15-N11-C13(20) 60 1002 2.35 70.5 2.17 1.40 νC42-C44(28)+νC44-C40(22) 61 986 72.25 1.1 1.58 0.99 βH17-C15-H16(10)+βH18-C15-H17(12)+τH17-C15-C13-N11(30)+ τH18-C15-C13-N11(12) 62 981 1.42 46.6 2.50 1.55 βC1-C2-C3(22)+βC5-C4-C3(36)+βH8-C2-C3(10) 63 965 966 6.44 260.7 5.74 3.44 βC38-C40-C44(19)+βC42-C44-C40(20)+βC39-C42-C44(34) 64 956 7.53 32.1 3.20 1.88 νC21-C23(21) 65 951 0.30 3.6 1.33 0.77 τH9-C4-C3-C2(46)+τH10-C5-C6-N11(28) 66 950 0.13 1.5 1.28 0.74 τH45-C40-C44-C42(30)+τH46-C42-C44-C40(13)+τH47-C44-C42-C39(29) 67 933 0.11 0.1 1.33 0.74 τH29-C24-C28-C26(29)+τH25-C22-C24-C28(42)+τC28-C24-C22-C21(16) 68 931 0.74 1.2 1.35 0.75 τH7-C1-C2-C3(25)+τH8-C2-C3-C4(45) 69 922 930 0.01 0.0 1.35 0.75 τH45-C40-C44-C42(26)+τH46-C42-C44-C40(44)+ τH43-C39-C42-C44(11)+τH41-C38-C40-C44(10) 70 903 26.85 8.7 1.50 0.79 τH27-C23-C26-C28(27)+τH33-C32-N34-N35(53) 71 889 3.58 17.6 5.28 2.68 νC4-C3(18) 72 885 4.37 30.6 4.13 2.08 νC15-C13(10)+βC6-C1-C2(11) 58 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 4. (Continued). Mode No Exp. FTIR freq. (cm-1) Calc. freq. (cm-1) IR intensity Raman activity Reduced mass Force constant Vibrational Assignments with >10% PED 73 873 2.78 3.9 1.43 0.70 τH27-C23-C26-C28(42)+τH33-C32-N34-N35(35)+ ϒC22-C23-N20-C21(11) 74 851 5.14 0.4 1.43 0.67 τH47-C44-C42-C39(33)+τH43-C39-C42-C44(24)+τH41-C38-C40-C44(30) 75 835 842 0.36 15.8 5.10 2.32 νC37-C38(10)+βC42-C44-C40(11) 76 829 52.89 4.7 1.71 0.76 τH7-C1-C2-C3(18)+τH9-C4-C3-C2(10)+τH10-C5-C6-N11(34)+ ϒC4-C2-N19-C3(13) 77 813 13.30 0.7 1.47 0.62 τH29-C24-C28-C26(38)+τH25-C22-C24-C28(32)+ϒO30-C24-C26-C28(11 78 801 3.13 13.9 1.28 0.53 τH7-C1-C2-C3(32)+τH10-C5-C6-N11(21)+τH9-C4-C3-C2(17)+τH8-C2- C3-C4(21) 79 788 0.47 0.5 1.26 0.50 τH41-C38-C40-C44(31)+τH45-C40-C44-C42(16)+ τH46-C42-C44-C40(12)+τH43-C39-C42-C44(37) 80 747 759 2.24 17.8 4.31 1.59 νC15-C13(28) 81 725 77.45 4.9 1.65 0.56 τC37-C38-C40-C44(18)+τH47-C44-C42-C39(22)+ϒN35-C38-C39-C37(15) 82 712 3.54 6.8 4.36 1.42 τC5-C4-C3-C2(13)+τC6-C1-C2-C3(16) 83 700 701 6.69 5.6 4.45 1.41 ϒO30-C24-C26-C28(19)+ϒC22-C23-N20-C21(10)+ τC28-C24-C22-C21(10) 84 688 682 83.04 0.4 1.23 0.37 τH31-O30-C28-C24(72)+τC37-C38-C40-C44(10) 85 669 27.30 5.4 6.48 1.86 βC24-C22-C21(13)+βC26-C32-N34(15) 86 663 3.61 0.2 1.74 0.49 τC39-C42-C44-C40(11)+τC42-C44-C40-C38(10)+ τH31-O30-C28-C24(16)+τC37-C38-C40-C44(28) 87 644 7.79 14.2 5.26 1.40 βC1-C2-C3(11) 88 625 105.12 33.4 2.06 0.52 τH12-N11-C13-C15(31)+ϒ O14-C15-N11-C13(32) 89 623 13.94 74.6 4.73 1.18 βC1-C2-C3(14) 90 618 9.97 27.0 6.36 1.56 βN34-N35-C37(15)+βC42-C44-C40(18) 91 605 3.72 5.5 6.38 1.50 βC37-C38-C40(11)+βC39-C42-C44(24)+βC38-C40-C44(37) 92 589 10.09 1.2 3.29 0.73 τC24-C22-C21-C23(12)+τC21-C23-C26-C32(18)+ τC3-N19-N20-C21(10)+τH25-C22-C24-C28(11) 93 546 2.67 19.1 4.74 0.91 βC3-N19-N20(10) 94 526 9.93 7.7 2.92 0.52 βO14-C13-C15(23)+ϒN11-C5-C1-C6(14) 95 517 62.38 48.4 4.55 0.78 βN19-N20-C21(10)+βO30-C28-C24(11) 96 502 45.44 77.0 1.88 0.30 τH18-C15-C13-N11(12)+ϒO14-C15-N11-C13(22)+ τH12-N11-C13-C15(35) 97 493 4.19 26.1 3.18 0.50 βO14-C13-C15(28) 98 487 21.43 0.9 2.63 0.40 τH45-C40-C44-C42(12)+τH46-C42-C44-C40(11)+ ϒN35-C38-C39-C37(44)+τC39-C42-C44-C40(13) 99 477 15.07 9.8 7.10 1.04 βN35-C37-C39(12)+βC37-C38-C40(16) 100 454 1.75 1.4 3.25 0.43 τH27-C23-C26-C28(13)+ϒO30-C24-C26-C28(17)+ ϒC22-C23-N20-C21(17)+τN20-C21-C23-C26(14) 101 440 4.87 41.0 5.04 0.62 βO30-C28-C24(33) 102 406 3.83 15.0 3.69 0.41 τC1-C2-C3-N19(13)+τC6-C1-C2-C3(31)+ϒN11-C5-C1-C6(11) 103 396 4.77 7.0 4.54 0.48 τC5-C4-C3-C2(23)+τN20-C21-C23-C26(10) 104 381 0.15 0.1 2.93 0.29 τC42-C44-C40-C38(34)+τC39-C42-C44-C40(35)+τH41-C38-C40-C44(10) 105 377 8.50 39.2 5.64 0.53 βC23-C26-C32(11) 106 376 45.42 11.9 1.43 0.13 τH36-N35-N34-C32(68) 107 376 19.29 13.9 4.09 0.37 βO30-C28-C24(11)+τH36-N35-N34-C32(13) 108 372 23.37 16.6 6.63 0.59 ϒC4-C2-N19-C3(10) 109 340 18.57 3.1 3.99 0.30 βN11-C6-C1(19)+βC15-C13-N11(34) 110 288 1.60 0.6 5.80 0.31 τC26-C32-N34-N35(28)+τC21-C23-C26-C32(19)+τN20-C21-C23-C26(14) 111 262 2.30 7.3 5.91 0.26 βC32-N34-N35(10) 112 233 1.78 9.8 7.13 0.25 βC22-C21-N20(10) 113 223 2.43 5.6 4.58 0.15 βC13-N11-C6(10) 114 217 8.93 4.2 3.15 0.10 τC23-C26-C32-N34(24) 115 204 1.57 4.4 5.04 0.13 τC42-C44-C40-C38(30)+ϒN35-C38-C39-C37(16) 116 190 5.86 1.4 5.49 0.13 τN19-N20-C21-C23(21)+τC24-C22-C21-C23(13)+τC28-C24-C22-C21(16) 117 188 8.17 28.3 5.30 0.12 βC23-C26-C32(12)+βN35-C37-C39(21) 118 177 0.68 1.3 1.12 0.02 τH16-C15-C13-N11(23)+τH17-C15-C13-N11(36)+ τH18-C15-C13-N11(12) 119 152 5.31 9.2 5.72 0.09 βC13-N11-C6(10) 120 107 2.44 2.8 6.23 0.05 τC2-C3-N19-N20(14)+τC15-C13-N11-C6(14) 121 96 0.48 0.9 5.71 0.03 τC23-C26-C32-N34(20)+τC26-C32-N34-N35(22)+τC21-C23-C26-C32(33) 122 81 3.87 1.5 6.50 0.03 τC13-N11-C6-C5(22) 123 65 0.78 0.7 6.64 0.02 τC15-C13-N11-C6(16) 124 57 0.92 7.5 6.51 0.01 βC32-N34-N35(13)+βC26-C32-N34(10)+βN34-N35-C37(12)+ τC13-N11-C6-C5(16) 125 49 4.62 12.7 3.90 0.01 βC13-N11-C6(13)+τC13-N11-C6- C5(23)+τC15-C13-N11-C6(21) 126 34 1.53 0.8 5.54 0.00 τC1-C2-C3-N19(22)+τC2-C3-N19-N20(27) 127 25 1.10 2.4 6.57 0.00 βN19-N20-C21(19)+βC3-N19-N20(16)+βC32-N34-N35(12)+ βC23-C26-C32(10)+βC26-C32-N34(10) 128 21 0.34 1.3 5.01 0.00 τN34-N35-C37-C38(61) 129 16 0.09 0.9 4.02 0.00 τN19-N20-C21-C23(23)+τC3-N19-N20-C21(10)+τC2-C3-N19-N20(19) 130 11 0.11 3.5 4.85 0.00 τC32-N34-N35-C37(60)+τC23-C26-C32-N34(19) * ν: Stretching, β: In-plane bending, γ: Out-of-plane bending, ω: Wagging, t: Twisting, δ: Scissoring, ρ: Rocking. 3.4. Solvent effect The molecular geometrics are obtained via DFT/6- 311+G(d,p) level optimization in the gas phase and then in 9 solvents (keyword, scrf=dipole) The calculated parameters like moment, energy, hyperpolarizability, polarizability of compounds 1 and 2 in different solvents. Regular variations in energy versus dielectric constant were observed. With increasing dielectric constant of solvent, the stability of compounds 1 and 2 increases. As the dielectric constant increases, the dipole moment, hyperpolarizability, and polarizability show a regular increase, which is evident in the increased reactivity of the molecules. Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 59 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 5. Calculated maximum absorption wavelength for compound 1. Solvent ΔE (eV) f (a.u.) λmax (nm) MO contributions Gas phase 3.2936 3.6275 0.0223 0.3020 376.4 341.8 H-3→L(25) H-2→L(41) H→L(30) H-1→L(2.9) H→L+1(92) Benzene 3.291 0.044 376.8 H-3→L(20) H-2→L(40) H→L(36) 3.620 0.795 342.6 H-1→L(53) H→L+1(41) DCM 3.281 0.050 377.9 H-3→L(17) H-2→L(38) H→L(41) 3.574 0.814 346.9 H-1→L(88) H→L+1(7) Acetone 3.265 0.097 379.8 H-3→L(3) H-1→L(87) H→L(4) H→L+1(2) 3.435 0.864 360.9 H-1→L(3) H→L+1(95) Ethanol 3.276 0.050 378.5 H-3→L(16) H-2→L(38) H→L(43) 3.563 0.792 348.0 H-1→L(89) H→L+1(5) Methanol 3.276 0.049 378.5 H-3→L(16) H-2→L(37) H→L(43) 3.565 0.785 347.8 H-1→L(89)H→L+1(5) Acetonitrile 3.275 0.050 378.6 H-3→L(16) H-2→L(37) H→L(43) 3.562 0.787 348.1 H-1→L(89)H→L+1(5) DMSO 3.274 0.050 378.7 H-3→L(16) H-2→L(37) H→L(43) 3.548 0.795 349.4 H-1→L(90) H→L+1(5) Water 3.274 0.045 378.7 H-3→L(16) H-2→L(37) H→ (43) 3.559 0.782 348.4 H-1→L(90) Table 6. Calculated maximum absorption wavelength for compound 2. Solvent ΔE (eV) f (a.u) λmax (nm) MO contributions λmax (nm) Exp. Gas phase 2.811 3.241 0.352 1.186 440.9 382.5 H→L(95) H→L+1(14) H-1→L(83) Benzene 2.691 0.437 460.7 H-2→L(97) 353.68 3.129 1.274 396.3 H-1→L(88), H→L+1(10) Dichloromethane 2.626 0.331 472.2 H→L(98) 3.115 1.376 398.0 H-1→L(88), H→L+1(10) 355.00, 239.00 Chloroform 2.649 0.361 468.1 H→L(97) 355.51 3.120 1.346 397.4 H-1→L(88), H→L+1(10) Acetone 2.612 0.299 474.6 H→L(98) 3.120 1.396 397.5 H-1→L(97) H→L+1(88) 368.00 Ethanol 2.610 0.298 475.0 H→L(98) 3.118 1.398 397.7 H-1→L(88) H→L+1(11) 362.53, 243.00 Methanol 2.609 0.288 475.2 H→L(98) 3.122 1.401 397.1 H-1→L(88) H→L+1(11) 264.62, 232.00 Acetonitrile 2.607 0.291 475.5 H→L(98) 3.120 1.402 397.5 H-1→L(88), H→L+1(11) 259.02 DMSO 2.602 0.306 476.5 H→L(98) 454.80 3.108 1.401 398.9 H-1→L(88), H→L+1(10) 375.33 Water 2.604 0.285 476.2 H→L(98) 3.120 1.406 397.4 H-1→L(88), H→L+1(11) 359.18 Comparing compounds 1 and 2 with increasing dielectric constant, compound 1 exhibits a higher variation in dipole moment ranging from 5.0 to 6.8 Debye than its counterpart. Two regions of dipole moment values are identified by plotting the dipole moment µ value against the solvent’s dielectric constant D, which offers light on strongly solvent-dependent molecular properties. D value ranges from 0 to 80 Debye, where the increase is seen; below the D value of zero, hardly any changes are noticed. As the dielectric constant increases, an increase in charge is expected for most of the atoms, but few atoms show a decrease in charge. In compound 1, C1, C2, C5, N11, N14, N15, C19, C21, O25, and N30, in compound 2, C2, C4, C6, C15, N19, N20, O30, N34, and N39, atoms found to have decreased charge although the dielectric constant increased. 60 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 7. Mulliken atomic charges and natural population analysis by B3LYP/6-311+G(d,p) method for compounds 1 and 2. Atom Compound 1 Atom Compound 2 Mulliken atomic charge NPA Mulliken atomic charge NPA C1 0.0776 -0.263 C1 -0.2734 -0.226 C2 -0.1758 -0.145 C2 -0.1438 -0.163 C3 -0.4218 0.044 C3 -0.2890 0.088 C4 0.1519 -0.165 C4 0.0136 -0.178 C5 -0.1577 -0.247 C5 -0.0007 -0.224 C6 -0.1485 0.189 C6 0.0923 0.164 H7 0.1084 0.205 H7 0.1232 0.211 H8 0.1329 0.222 H8 0.1326 0.220 H9 0.1441 0.229 H9 0.1531 0.232 H10 0.1084 0.204 H10 0.1253 0.213 N11 -0.3598 -0.779 N11 -0.2004 -0.631 H12 0.2335 0.379 H12 0.2808 0.403 H13 0.2337 0.379 C13 0.0800 0.687 N14 0.1823 -0.168 O14 -0.3184 -0.613 N15 0.0852 -0.220 C15 -0.3834 -0.673 C16 -0.5492 0.097 H16 0.1656 0.220 C17 0.2179 -0.189 H17 0.1713 0.226 C18 -1.0616 -0.180 H18 0.1798 0.236 C19 -0.0160 -0.240 N19 0.0768 -0.231 H20 0.1179 0.213 N20 0.0539 -0.228 C21 0.7960 -0.157 C21 -0.6864 0.162 H22 0.1077 0.209 C22 0.2931 -0.180 C23 -0.1559 0.347 C23 -0.4731 -0.186 H24 0.1291 0.219 C24 -0.2102 -0.258 O25 -0.3579 -0.691 H25 0.1354 0.220 H26 0.3923 0.502 C26 0.8095 -0.164 C27 -0.0706 0.052 H27 0.1409 0.226 H28 0.1307 0.182 C28 -0.3002 0.375 N29 -0.1498 -0.317 H29 0.1338 0.224 N30 -0.0070 -0.404 O30 -0.3404 -0.675 H31 0.2480 0.377 H31 0.3928 0.503 C32 -0.0130 0.126 C32 -0.0619 0.059 C33 0.2478 -0.220 H33 0.0822 0.167 C34 -0.2510 -0.222 N34 0.0489 -0.395 C35 -0.1483 -0.192 N35 -0.1113 -0.381 H36 0.1418 0.219 H36 0.2670 0.364 C37 -0.2671 -0.191 C37 -0.6068 0.159 H38 0.1192 0.208 C38 0.9359 -0.245 C39 -0.1863 -0.210 C39 -0.4175 -0.244 H40 0.1306 0.210 C40 -0.4329 -0.176 H41 0.1309 0.210 H41 0.1249 0.217 H42 0.1294 0.209 C42 -0.2233 -0.183 H43 0.1027 0.202 C44 -0.0238 -0.237 H45 0.1295 0.208 H46 0.1274 0.208 H47 0.1248 0.209 Figure 3. Absorption spectra of compound 2 in different solvents. The stability of compounds 1 and 2 increases with increasing dielectric constants; comparatively, compound 2 enjoys more stability than compound 1 [37]. Compound 1 exhibits maximum polarizability in water 11.2314, followed by DMSO 11.1825, which follows an order with respect to dielectric constant. As the dielectric constant increases, the polarizability also increases. In compound 2 also, the same trend is identified, that maximum is shown in water followed by DMSO. These molecules exhibit polarizability comparable to diethylamine and are candidates for a good electro-optic response [38]. Hyperpolarizability: On studying the hyperpolarizability values of compound 1, it is observed that the compound under study shows a maximum first-order hyperpolarizability of 5.00783×10-30 e.s.u. in water. An increasing trend of hyperpolarizability is observed as an increase in the dielectric constant. Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 61 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 8. Second-order perturbation theory analysis of Fock-Matrix in NBO basis for compound 1. Donor Occupancy Acceptor E(2), kcal/mol Ej-Ei, a.u. F(i,j), a.u. πC1-C2 1.9724 LP(1)C3 37.77 0.15 0.085 πC1-C2 1.9724 LP*(1)C6 56.45 0.14 0.096 πC4-C5 1.9725 LP(1)C3 37.02 0.15 0.085 πC4-C5 1.9725 LP*(1)C6 52.13 0.14 0.093 πN14-N15 1.9875 LP(1)C3 14.92 0.26 0.079 πC16-C18 1.9682 π*C17-C19 20.37 0.29 0.069 πC16-C18 1.9682 π*C21-C23 17.06 0.28 0.064 πC17-C19 1.9708 π*C16-C18 18.53 0.29 0.066 πC17-C19 1.9708 π*C21-C23 21.69 0.28 0.072 πC21-C23 1.9722 π*C27-N29 21.19 0.29 0.071 πC21-C23 1.9722 π*C17-C19 16.76 0.29 0.063 πC21-C23 1.9722 π*C27-N29 20.02 0.25 0.066 πC32-C34 1.9757 π*C33-C35 18.88 0.29 0.066 πC32-C34 1.9757 π*C37-C39 20.46 0.29 0.069 πC33-C35 1.9770 π*C32-C34 20.97 0.28 0.069 πC33-C35 1.9770 π*C37-C39 19.13 0.28 0.066 πC37-C39 1.6643 π*C32-C34 20.00 0.28 0.067 πC37-C39 1.6643 π*C33-C35 20.97 0.28 0.069 LP(1)C3 1.9992 π*C1-C2 75.30 0.14 0.110 LP(1)C3 1.9992 π*C4-C5 70.45 0.14 0.108 LP(1)C3 1.9992 π*N14-N15 66.54 0.10 0.091 LP*(1)C6 1.9991 π*C1-C2 53.19 0.15 0.100 LP*(1)C6 1.9991 π*C4-C5 50.19 0.15 0.099 LP(1)N11 1.9660 LP*(1)C6 58.89 0.18 0.117 LP(2)O25 1.9612 π*C21-C23 32.36 0.33 0.100 LP(1)N30 0.0030 π*C21-C23 25.30 0.30 0.078 LP(1)N30 0.0030 π*C27-C29 13.39 0.31 0.060 π*C21-C23 0.0294 π*C16-C18 263.14 0.01 0.078 π*C27-C29 0.0419 π*C21-C23 80.67 0.03 0.072 Maximum hyperpolarizability is observed in a water solvent for compound 2. Compound 2 also shows an increase in hyperpolarizability as the value of the dielectric constant increases. Compounds 1 and 2 in various solvents exhibit hyperpolarizability values higher than urea 0.65×10-30 e.s.u. When comparing compounds 1 and 2, the maximum value is identified in compound 1 (7.17672 Debye). Both compounds in water show maximum hyperpolarizability, dielectric constant, dipole, and deficient energy, indicating better NLO properties [39]. 3.5. Mulliken charges Mulliken charge calculation is important in quantum chemistry because it affects the electronic structure, molecular polarization, dipole moment, and many molecular properties. The distribution of charge in an atomic molecule is determined by the donor and acceptor pairs of electrons. Atomic charge is used in electronegativity processes, equalization, and charge transmission in chemical reactions [40-42]. The calculated Mulliken atomic charge by the DFT method on the basis set B3LYP/6-311+G(d,p) is shown in Table 7. It is notable that in compound 1, the atoms C1, C4, N14, N15, C17, C21 and C4, C6, C13, N19, N20, C22, C26 in compound 2 exhibit a positive charge. Negative charge is found on the atoms C2, C3, C5, C6, N11, C16, C18, C19, C23, O25, C27, N29, N30, C32 andC1, C2, C3, C5, N11, O14, C15, C21, C23, C24, C28, O30, C32 with respect to compounds 1 and 2 [35]. The maximum positive charge is exhibited by C21 on compound 1 and C26 on compound 2 and is attributed to the presence of a hydroxyl group adjacent to carbon and attachment of imine carbon directly on C21and C26. The maximum positive charge is due to the electron- withdrawing effect of oxygen and nitrogen, as well as the orientation of the atoms. An excess of electrons is seen on C18, C16 in compound 1, C21 and C23 in their counterparts. This negative charge accumulation may be due to the π channel and the push-pull mechanism of the electrons. An excess of negative charge is identified on C18, C6, C2, C3, C16, C17, C19, and C23, which is due to the π-conjugation of electrons from nitrogen in compound 1. This charge is reversed in compound 2, and hence, the reverse of the nucleophilic and electrophilic centers in compound 2. The reverse of charge accounted for is due to the anilide functional in place of the aniline group. On comparing Mulliken and NPA analyses, the results obtained are comparable with a few exceptions. H26 in compound 1, H31 in compound 2 show higher positive charge (0.3923) Mulliken, (0.502) NPA, and (0.3928) Mulliken, (0.503) NPA, respectively [43]. This is due to the electronegativity of O26 and O30 in the respective compounds and also to the hydrogen bonding interaction between O25-H26···N29 in compound 1 and O30- H31···N34 in compound 2. The intramolecular interaction is supported by an increase in C=N bond length and a decrease in the C=N stretching frequency. C27-N29 (1.294 Å, 1602 cm-1), C32-N34 (1.2936 Å, 1588 cm-1), and also decreased in O-H stretching frequency (O25-H26 3279 cm-1), (O30-H31 3296 cm- 1) in compounds 1 and 2, respectively. 3.6. NBO analysis The second-order Fock matrix evaluated donor-acceptor interactions on the basis of NBO [44]. The interactions result in a loss of occupancy from the localized NBO of the idealized Lewis structure into an empty non-Lewis orbital. For each donor (i) and acceptor (j), the stabilization energy E(2) associated with the delocalization i-j is estimated [45]. In the NBO analysis, a large value of E(2) shows the intensive interaction between electron donors and electron acceptors and the greater degree of conjugation in the whole system (Tables 8 and 9). π*C21-C23 to π*C16-C18 and π*C27-C29 to π*C21-C23 are intensive interactions in compound 1 and in compound 2 it is found to be π*C1-C6 to π*C4-C5 and π*C37- C38 to π*C40-C44. Between the two molecules under study, compound 1 shows the strongest interaction. Intramolecular hyperconjugative interactions are formed by orbital overlap between the π(C-C) bonding molecular orbital and the π*(C-C) anti-bonding molecular orbital of the phenyl ring of the title molecule [46,47]. For compound 1 donors, C16-C18, C16-C18, C17-C19, C17-C19, C21-C23, C21- C23, C32-C34, C32-C34, C33-C35, C33-C35, C37-C39, C37-C39, the corresponding acceptors are C17-C19, C21-C23, C16-C18, C21-C23, C27-N29, C17-C19, C27-N29, C33-C35, C37-C39, C32- C34, C37-C39, C32-C34, C33-C35, and their second order perturbation energy values are 20.37, 17.06, 18.53, 21.69, 21.19, 62 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 9. Second-order perturbation theory analysis of Fock-Matrix in NBO basis for compound 2. Donor Occupancy Acceptor E(2), kcal/mol Ej-Ei, a.u. F(i,j), a.u. πC1-C6 1.6439 π*C2-C3 21.93 0.29 0.072 πC1-C6 1.6439 π*C4-C5 16.76 0.29 0.064 πC2-C3 1.6087 π*C1-C6 20.19 0.27 0.066 πC2-C3 1.6087 π*C4-C5 20.40 0.28 0.070 πC2-C3 1.6087 π*N19-N20 20.03 0.24 0.064 πC4-C5 1.6949 π*C1-C6 21.41 0.28 0.070 πC4-C5 1.6949 π*C2-C3 17.42 0.29 0.064 πN19-N20 1.9148 π*C2-C3 10.54 0.39 0.062 πC21-C23 1.6119 π*N19-N20 16.67 0.23 0.058 πC21-C23 1.6119 π*C22-C24 21.27 0.28 0.070 πC37-C38 1.6404 π*C39-C42 16.89 0.29 0.063 πC37-C38 1.6404 π*C40-C44 22.24 0.30 0.073 πC39-C42 1.7080 π*C37-C38 21.31 0.28 0.071 πC39-C42 1.7080 π*C40-C44 16.18 0.30 0.063 πC40-C44 1.6673 π*C37-C38 19.21 0.27 0.066 πC40-C44 1.6673 π*C39-C42 22.69 0.28 0.071 LP(1)N11 1.6872 π*C1-C6 23.16 0.28 0.073 π*C1-C6 0.38987 π*C4-C5 235.93 0.01 0.081 π*C37-C38 0.40980 π*C40-C44 215.16 0.01 0.081 Figure 4. Energy, dipole moment versus dihedral angle of compound 1. Figure 5. Energy, dipole moment versus dihedral angle of compound 2. 16.76, 20.02, 18.88, 20.46,20.97, 19.13, 20.0, and 20.97 kcal/mol. Similarly for compound 2 the donors are C1-C6, C1- C6, C2-C3, C2-C3, C4-C5, C4-C5, N19-N20, C21-C23, C21-C23, C37-C38, C37-C38, C39-C42, C39-C42, C40-C44, C40-C44 the corresponding acceptors are C2-C3, C4-C5, C1-C6, C4-C5, N19- N20, C1-C6, C2-C3, C2-C3, N19-N20, C22-C24, C39-C42, C40- C44, C37-C38, C39-C42 and their second-order perturbation values are 21.93, 16.76, 20.19, 20.4, 20.03, 21.41, 17.42, 10.54, 16.67, 21.27,16.89, 22.24, 21.31, 16.18, 19.21, and 22.69 kcal/mol. 3.7. Dihedral angle studies 3.7.1. Potential energy The variation in energy and dipole moment of compounds 1 and 2 as a function of dihedral angle are shown in Figures 4 and 5. It is evident from Figure 4 that the conformers having a dihedral angle of -170, -5, 5, or 180° are stable ones with minimum energy in the case of compound 1 and it is due to the relaxed dihedral angle that places all the phenyl rings in a plane parallel to one another. In compound 2, the conformers with dihedral angles 0, 180, 9, -10, and -170° exhibit minimum energy and enjoy better stability because all three rings are in the plane. In compounds 1 and 2, the conformers with the phenyl ring perpendicular to their counterparts experience more strain, and they are explicitly less stable with high energy. The conformers with less stability are dihedral angles -97, 97, -87, 87, -108° and 99, -99, 89, 100, -80° in compounds 1 and 2, respectively [25,48]. Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 63 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Dihedral angle, ° HOMO LUMO 5 97 170 -170 -97 Figure 6. HOMO-LUMO diagrams of compound 1 at various dihedral angles. 3.7.2. Dipole moment The variation in energy and dipole moment of compounds 1 and 2 as a function of dihedral angle are shown in Figures 4 and 5. It is evident from the figure that as the dihedral angle increases, energy and dipole moment also increase and reach a maximum of 6.237 Debye at -87°, at which the aniline moiety is perpendicular to the phenoxy moiety. The dipole moment decreases as the dihedral angle increases further and reaches a second maximum of 5.390 Debye at 87°. The dipole moment is at its minimum whenever the molecule reaches a planar structure with minimal energy and stable configuration in compound 1. In contrast, the dipole moment reaches a maximum of 4.662 Debye at a dihedral angle of 0° and an energy minimum. Energy and dipole moment are inversely related in compound 2; the dihedral angle at which the maximum energy is obtained becomes the minimum for the dipole moment and vice versa [25]. This behavior is notably different from compound 1. 3.7.3. HOMO-LUMO, hardness, electrophilicity In compound 1, ∆E, the hardness and electrophilicity index of the compound are compared with dihedral angles at -170, 0, and 180°. The energy gap is found to be a minimum of 2.0812929 eV at -170°, which is found to be the most stable conformer with minimum energy. The molecule exhibits a maximum hardness of 1.7189918 at a dihedral angle of -97° and a conformer with maximum energy and minimum stability [48- 50]. At 97 °, the energy is at its peak and the electrophilicity index is found to be at its maximum point for compound 1. In compound 2, ∆E, the hardness and electrophilicity index of the compound are compared with dihedral angles at -170, -100, 1, 100, and 170°. The energy gap is found to be minimum 1.997214 eV at 170°, which is found to be a stable conformer with minimum energy and maximum dipole moment and also maximum hardness 1.5723, is recorded at the same point. At -100°, the energy is found to be maximum, the dipole is minimum, and the electrophilicity index is found at the maximum point for compound 2. When comparing the HOMO- LUMO diagrams (Figures 6 and 7) of compounds 1 and 2 at various dihedral angles, there is some similarity with the distribution of HOMO-LUMO orbitals at similar dihedral angles. The distribution of HOMO orbitals in compound 1 at 5° is mainly on ring 3 (phenylhydrazone moiety) and ring 2 (phenoxymoiety). When the angle changes to 97° the HOMO orbitals retain the position with respect to ring 2 and 3, but no lobe is identified on ring 1 (aniline moiety). The HOMOs at dihedral angles 5, 170, and -170° are similar with a difference in positive and negative charges. The HOMO of compounds 1 at 97° and -97° exhibits similar orbital orientations [51,52]. Planar geometry gives an extended conjugation throughout the chain and leads to a strong delocalization of holes in the HOMO [53]. LUMO of compound 1 at a dihedral angle of 5°, the lobes are located on ring 1 and ring 2 only; as the angle increases to 97° and to 170°, the lobe is red, which is a tribute to the azo group, and a little on ring 1. At dihedral angles of 170° and -170°, the lobes are similar with opposite charge distribution. At dihedral angles 0, 100, 170, -170, and -100°, the HOMO of compound 2 is densely distributed on ring 2 (phenoxymoiety) and ring 3 (phenylhydrazone moiety); on the contrary, LUMO at the dihedral angles mentioned above is solidly identified on ring 1(acetanilidemoiety). The energy gap (∆E) of compound 1 is found to be minimum at angle -170° and 0° in compound 2 and is found to be -1083.474796 and -1236.172885, respectively. 3.8. FMO properties The global reactivity descriptors such as chemical potential, electronegativity, hardness, softness, electrophilicity index, and local reactivity descriptors such as Fukui functions can be calculated using DFT. 64 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 10. HOMO and LUMO energy, chemical potential, hardness and electrophilicity index calculated by B3LYP/6-311+G(d,p) method for compounds 1 and 2. Parameters Compound 1 Compound 2 EHOMO (eV) -5.51 -5.74 ELUMO (eV) -1.93 -2.58 ELUMO-EHOMO (eV) 3.58 3.16 Electronegativity (eV) -3.72 -4.16 Hardness (eV) 1.79 1.58 Electrophilicity index (eV) 3.865 5.476 Softness (1/eV) 0.279 0.316 Dihedral angle, ° HOMO LUMO 0 100 170 -170 -100 Figure 7. HOMO-LUMO diagrams of compound 2 at various dihedral angles. The calculation procedure was illustrated and the values are listed in Table 10 [53]. The inverse of hardness is expressed as the global softness S=(1/2η). The global electrophilic index (ω = -µ2/2η) assesses the lowering of energy due to the maximal electron flow between donor and acceptor. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are vital parameters for quantum chemistry. We can determine how the molecule interacts with other species; hence, these are called the frontier orbitals. HOMO, which can be thought of as the outermost orbital containing electrons, tends to give these electrons as an electron donor. In contrast, LUMO is the innermost orbital, containing free orbitals to accommodate electrons [54]. The values of electro- negativity, chemical hardness, softness, and electrophilicity index for compounds 1 and 2 are given in Table 10. When the chemical hardness is considered, if one molecule has a large HOMO-LUMO gap, then it is a hard molecule and vice versa. If a molecule exhibits the least HOMO-LUMO gap, it is more reactive and softer [55,56]. In compound 1, Figure 8, HOMO is concentrated on the two azo nitrogen atoms, and LUMO is spread over the phenoxy ring and the amine ring. On the contrary, the HOMO in compound 1 is spread over the phenyl hydrazone moiety, the phenoxy moiety, and the LUMO exactly on the other side of the molecule. The energy difference between HOMO and LUMO is found to be 3.58 and 3.16 eV in 1 and 2, respectively, from which we argue for the enhanced reactivity of the molecules. The molecule with the lowest band gap (G) happens to be the one with the highest polarizability and dipole moment. It also has the highest molecular size and the highest planarity. This means that the molecule is the most reactive and polarizable, has the highest electro-optic response, and is the softest [56]. Compound 2, with a minimum band gap, is more reactive; it is a soft molecule with several transitions. Electronic communication between the donor and acceptor increases when the band gap decreases and is expected to increase more in compound 2. This minimum band gap in compound 2 can be attributed to increased conjugation throughout the molecule. Compound 1 exhibits a dipole moment of 4.99 and a polarizability of 8.2, which is comparable to its counterpart, and exhibits a planar structure, which enhances the reactivity of the molecule [54,56]. 3.9. Aromaticity indices The neutral and cation of compound 2 show a significant negative NICS value (Table 11), a more quantitative measure of the aromatic character than the anion. The maximum negative value is observed for 1.5 Bq -1 Bq (Distance of NICS probe from molecular plane–Bq) below and above the ring (zz) for the neutral moiety. Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 65 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 11. DFT-B3LYP/6-311+G (d,p) method calculated NICS (ppm) values (neutral, cation and anion) for compound 2. Bq NICS RING 1 (Anilide ring) Neutral Cation Anion Isotropic Anisotropic (zz) Isotropic Anisotropic (zz) Isotropic Anisotropic (zz) -0.2 -0.3839 -11.8430 -3.3091 -11.4238 -3.2921 -10.9051 -1.5 -5.3173 -17.0004 -4.9950 -14.7632 -6.1115 -13.5677 -1.0 -7.6962 -21.4586 -6.3111 -14.3814 -7.9417 -11.2753 -0.5 -8.6099 -18.5047 -5.2637 -4.9876 -5.5897 -3.0289 0.0. -7.3079 -8.2208 -3.6440 -2.8604 -4.0690 -0.3804 0.5 -0.0707 -11.0826 -5.2623 -5.5617 -7.1566 -5.6186 1.0 -9.3235 -21.5428 -6.1317 -14.3799 -8.8005 -13.2548 1.5 -7.6032 -21.8350 -4.8235 -14.4762 -6.1009 -13.7072 2.0 -5.0239 -16.4992 -3.2216 -11.1855 -3.2095 -10.2785 Bq NICS RING 2 (Hydroxy ring) Neutral Cation Anion Isotropic Anisotropic (zz) Isotropic Anisotropic (zz) Isotropic Anisotropic (zz) -0.2 -3.5505 -12.1407 -2.6422 -8.9955 -2.7917 -9.8515 -1.5 -5.6016 -16.8520 -3.8435 -10.6828 -4.3876 -12.6808 -1.0 -7.9255 -19.8116 -4.5803 -8.3668 -5.7799 -11.8673 -0.5 -8.4751 -14.2765 -3.3375 -1.6205 -5.2343 -2.3546 0.0 -7.1238 -4.4661 -1.8551 -9.1358 -4.2096 -4.8613 0.5 -7.9439 -9.9574 -3.3500 -1.5552 -5.4768 -4.1639 1.0 -8.4479 -19.1311 -4.5773 -8.3950 -5.7081 -12.4506 1.5 -6.5302 -18.5908 -3.8336 -10.676 -4.1676 -12.3699 2.0 -4.2568 -13.9636 -2.6344 -8.9805 -2.6092 -9.4348 Bq NICS RING 3 (Phenylhydrazine ring) Neutral Cation Anion Isotropic Anisotropic (zz) Isotropic Anisotropic (zz) Isotropic Anisotropic (zz) -0.2 -4.7384 -16.6854 -3.8708 -13.9433 -3.3201 -12.7870 -1.5 -7.3909 -22.5985 -6.0855 -19.0217 -5.6439 -18.2701 -1.0 -9.4836 -23.9394 -8.1244 -20.9990 -8.4273 -22.3315 -0.5 -8.7217 -14.5558 -7.6335 -13.1713 -9.1009 -17.9314 0.0 -7.9596 -9.8057 -6.0488 -4.7996 -7.1777 -7.1552 0.5 -9.5357 -20.3063 -7.6089 -13.0472 -8.0861 -11.4971 1.0 -8.6674 -24.2909 -8.1301 -20.9675 -9.3656 -21.1402 1.5 -5.9230 -19.5300 -6.1079 -19.0613 -7.4661 -21.2954 2.0 -3.6275 -13.6450 -3.8897 -13.0223 -4.6972 -16.1272 Compound 1 Compound 2 ELUMO = -1.93 eV ΔE = 3.58 eV EHOMO = -5.51 eV ELUMO = -2.58 eV ΔE = 3.16 eV EHOMO = -5.74 eV Figure 8. HOMO-LUMO of compounds 1 and 2. The decreasing order of NICS is neutral > cation > anion. However, in ring 2 (phenoxy ring), neutral and anions have a more considerable NICS negative value than the cation. The maximum negative value is obtained for -1Bq and 1Bq in neutral species below and above the ring (zz). The NICS order is cation ring 1 > ring 2 in compounds 1 and 2. Compound 1 shows a higher HOMA value than compound 2 in the anionic state when comparing rings 1 and 3. The hydroxyl ring (ring 2) in compound 2 produces 0.9201, compared to 0.8742 in ring 2 in compound 1. In the cationic state, compound 1 exhibits the same HOMA value for ring 1 and ring 2, and is higher compared to the value of ring 3. On the contrary, in compound 2, ring 3 shows a higher HOMA value, followed by ring 1 and ring 2. When the neutral state is excluded from all other states stated in compound 2, ring 2 shows a lower HOMA value than its counterpart. This is evident in the less aromatic character of ring 2, which is also supported by the orientation of LUMO to the hydroxyl ring and the lower NICS value [59]. 3.11. Fukui function A molecule is susceptible to nucleophilic attack at sites where fk+ is large. Similarly, a molecule is susceptible to electrophilic attack at sites where fk- is large, because these are the regions where electron removal destabilizes the molecule the least [60]. The calculated values of the Fukui function are presented in Tables 12 and 13. In compound 1, the increasing order of nucleophilic attack is C37 < C5 < C21 < C17 < C35 < C39 < O25 < C1 < N11 < N29 < C27 < C23 < C32 < C16 < C6 < N14 < N15 < C4. C4 carbon is more prone to nucleophilic attack. C23 in compound 1 is found to be the most reactive site to electrophiles [61]. The decreasing order of electrophilic attack is C23 > C2 > C6 > C32 > N29 > C3 > C17 > C33 > C27 > O25 > C37 > C18. In compound 2 the increasing order of nucleophilic attack is C40 < C42 < C44 < C5 < C3 < C24 < C38 < C4 < C21 < C6. C6 and C21, which are directly attached to the anilide and azo groups, are deficient in electron density and prone to nucleophilic attack [61]. The order of electrophilic attack is found to be C22 > C2 > C28 > C3 > C44 > C39 > C40 > C38 > C26 [62]. 3.12. MEP The MEP surface throws light on the reactivity of a molecule in that the negative region is prone to electrophilic sites, while the positive region is a nucleophilic site [63,64]. In Figure 9, the electrophilic region is shown as the negative region (red color) region, and the nucleophilic center is shown as the positive region (blue color) region of MEP. The potential increases as the color changes from red, orange, yellow, green, and blue. The negative potential for compound 1 starts at -9.48×10-2 and is distributed over the phenyl rings 1 and 2. It may be due to delocalization of π-electrons and is prone to electrophilic attack. The regions near nitrogen are blue, which is not a preferable site for an electrophilic attack. In compound 2, the negative potential starts at -6.33×10-2 and is found in the aromatic system. This may be due to the π-electron density. These are sites for electrophilic attack. Furthermore, the blue regions near nitrogen are less favourable for electrophilic attack [56,65]. Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 67 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 13. Calculated local reactivity properties of compound 2 using B3LYP/6-311+G(d,p)method for Mulliken derived charges. Atoms fk+ fk- ∆fk(r) Sk+ Sk- Sk+/Sk- ∆Sk(r) ωk+ ωk- ∆ωk(r) C1 -0.2167 -0.0748 -0.1418 -0.0685 -0.0237 2.8960 -0.0449 -1.1834 -0.4086 -0.7748 C2 -0.2989 0.1343 -0.4333 -0.0946 0.0425 -2.2255 -0.1370 -1.6328 0.7337 -2.3665 C3 0.1227 0.0671 0.0556 0.0388 0.0212 1.8288 0.0176 0.6701 0.3664 0.3037 C4 0.1812 -0.0556 0.2368 0.0573 -0.0176 -3.2572 0.0749 0.9896 -0.3038 1.2934 C5 0.0607 -0.0323 0.0931 0.0192 -0.0102 -1.8779 0.0294 0.3317 -0.1767 0.5084 C6 0.3410 -0.1554 0.4964 0.1078 -0.0492 -2.1937 0.1570 1.8624 -0.8489 2.7113 C21 0.2757 -0.1444 0.4201 0.0872 -0.0457 -1.9092 0.1329 1.5060 -0.7888 2.2949 C22 -0.1461 0.1391 -0.2852 -0.0462 0.0440 -1.0502 -0.0902 -0.7980 0.7599 -1.5580 C23 -0.0014 -0.0415 0.0400 -0.0005 -0.0131 0.0348 0.0127 -0.0079 -0.2265 0.2186 C24 0.1249 -0.0338 0.1587 0.0395 -0.0107 -3.6997 0.0502 0.6824 -0.1845 0.8669 C26 -0.0535 0.0029 -0.0564 -0.0169 0.0009 -18.560 -0.0178 -0.2924 0.0158 -0.3081 C28 -0.0561 0.1121 -0.1682 -0.0178 0.0355 -0.5007 -0.0532 -0.3066 0.6124 -0.9190 C37 -0.1309 -0.0253 -0.1056 -0.0414 -0.0080 5.1798 -0.0334 -0.7150 -0.1380 -0.5770 C38 0.1622 0.0118 0.1505 0.0513 0.0037 13.783 0.0476 0.8861 0.0643 0.8218 C39 -0.0505 0.0367 -0.0872 -0.0160 0.0116 -1.3758 -0.0276 -0.2757 0.2004 -0.4760 C40 0.0121 0.0228 -0.0107 0.0038 0.0072 0.5323 -0.0034 0.0663 0.1245 -0.0582 C42 0.0185 -0.0010 0.0195 0.0058 -0.0003 -17.974 0.0062 0.1008 -0.0056 0.1064 C44 0.0389 0.0438 -0.0050 0.0123 0.0139 0.8870 -0.0016 0.2122 0.2393 -0.0270 Table 14. The ab initio and DFT calculated the electric dipole moment (Debye), average polarizability (αtot×1024 e.s.u.), and hyperpolarizability (βtot×10-30/esu) for compounds 1 and 2. Parameters Compound 1 Compound 2 Dipole moment µx 2.4590 -3.9437 µy -4.3376 -2.0043 µz -0.3065 -0.3716 µ 4.9955 4.4340 Polarizability αxx 38.4646 -28.6233 αyy -23.1291 25.3421 αzz -15.3356 3.2812 αxy 0.5775 23.5234 αxz 6.7912 -2.9448 αyz -0.2194 -1.7860 α0 -2.7×10-28 -1.6×10-28 αtot 8.2038 8.0586 Hyperpolarizability βxxx 373.2941 -764.7209 βyyy -27.8990 -25.6061 βzzz -3.0043 -3.0245 βxyy -1.1266 -0.1180 βxxy -122.5290 94.7664 βxxz -54.6925 -42.7077 βxzz 18.6941 50.7200 βyzz -20.7543 0.5335 βyyz -1.6932 5.9881 βxyz 5.9700 -10.0915 βtot 430.8171 718.1616 β0 3.7219 6.2100 3.13. NMR Analysis In compound 1, the aromatic proton signals are found in the range of δ 6.54 to 7.92 ppm, which is the aromatic region. The H26 signal is obtained at δ 10.8 ppm due to the nucleus's deshielding by O25, and hydrogen bonding with N29 shifts the signal downfield. 13C NMR shows 19 different signals, representing the presence of different types of protons. C1 and C5 signals are shifted up-field due to the π-conjugation from N11 [57,58]. In compound 2, the aromatic protons fall in the aromatic region. H31 shows δ 11.0 ppm, which is accounted for by the presence of hydrogen bonding with N34. C13 represents the presence of different types of carbon. C1 and C5 carbon signals are seen in the range δ 126.54-127.38 ppm, which is contrary to comparing the position with compound 1. This is evident in the nonexistence of conjugation in compound 2 [63,64]. 3.14. NLO properties Polarizability and hyperpolarizability characterize the response of a molecule to an applied electric field. They affect the molecular interactions. The polarizability and hyper- polarizability values of the dyes are shown in Table 14. When comparing the two compounds, the polarizability of compound 1 is more significant than that of its counterpart, and it can act as a better dye than compound 2 [66]. Urea has good non-linear optical properties and is used as a critical parameter for comparative studies (µ = 1.3732 Debye and β = 3.7289×10-31 e.s.u.). For compounds 1 and 2, the first-order hyper- polarizability by the B3LYP/6-311+G(d,p) method is 3.7219 and 6.2100×10-30 e.s.u. Among the compounds studied, compound 1 exhibits value similar to that of urea and compound 2 shows twice the value of urea. Therefore, the compounds under study promote good nonlinear properties [67,68]. 3.15. Thermodynamic properties Thermodynamic parameters, such as zero-point vibrational energy (ZPVE) and entropy, are presented in Table 15. The variation in ZPVE is significant. The total energies of compounds 1 and 2 are presented. Of the two compounds, compound 1 shows the minimum total energy of -1083.4568 a.u. [69,70] parameter for comparative studies (µ = 1.3732 Debye and β = 3.7289×10-31 e.s.u.). 68 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 Table 15. Theoretically computed energies (a.u.), zero-point vibrational energy (kcal/mol), rotational constants (GHz), entropy (calmol-1 K-1) and dipole moment (Debye) for compounds 1 and 2. Parameters Compound 1 Compound 2 Total energies (Hartree) -1083.4568 -1236.1728 Zero-point energy (kcal/mol) 206.7092 230.2788 Rotational constants (GHz) A 0.3244 0.5996 B 0.0783 0.0406 C 0.0659 0.0383 Entropy (cal/mol. K) Total 155.1820 178.5390 Translational 43.2870 43.6430 Rotational 36.5040 37.0860 Vibrational 75.3910 97.8090 Dipole moment (Debye) 4.9955 4.4393 4. Conclusion The compound studied, C21H19N5O2 (2), was synthesized according to the procedures described in the literature and characterized by microanalysis, FT-IR, 1H, 13C and UV-visible spectroscopy techniques. It is theoretically compared with its amine derivative C19H17N5O (1). Compounds 1 and 2 were optimized to local minima using the Gaussian 09 package with the DFT/B3LYP method and the 6-311+G(d,p) basis set. Spectroscopic investigations were conducted for compound 2 according to the proposed structure. DFT-based FT-IR spectra and UV-vis absorption agreed with the experimental spectroscopic data of compound 2. In vertical excitation studies, two transitions were predicted for the test molecules in all solvents, and there was an increase in the solute-solvent interaction as a result of the increase in dielectric constants. In the FMO analysis, the minor energy gap is predicted in compound 2, at 3.16 eV; for compound 1, it is 3.58 eV, paving the way for the transition in compound 2. The stabilization of the optical gap is observed in the solvent effect. The NBO study sheds light on intermolecular charge transfer and intermolecular hydrogen bonding. Among the test molecules, there are more interactions seen in compound 1 than in its counterpart, making it a prominent candidate for NLO studies. The HOMO-LUMO diagram supports the aromatic nature predicted by NICS and HOMA. For the title compounds 1 and 2, the first-order hyperpolarizability is 3.72×10-30 and 6.21×10-30 e.s.u. Of the compounds under investigation, compound 2 shows greater hyperpolarizability than urea. Therefore, the compounds under study promote good non-linear properties and have the potential to be explored as candidates for NLO properties. Compound 1 is not synthesized and is used only for theoretical comparisons. Acknowledgements We thank the Department of Chemistry, Annamalai University, Chidambaram, for providing the lab and instrumentation facilities. Disclosure statement Conflict of interests: The authors declare that they have no conflict of interest. Ethical approval: All ethical guidelines have been adhered to. Sample availability: Samples of the compounds are available from the author. CRediT authorship contribution statement Conceptualization: Richard Rajkumar Siluvairaj, Thanikachalam Venugopal; Methodology: Richard Rajkumar Siluvairaj, Thanikachalam Venugopal; Software: Richard Rajkumar Siluvairaj, Vallal Perumal Govindasamy; Validation: Richard Rajkumar Siluvairaj, Thanikachalam Venugopal; Formal Analysis: Periyanayagasamy Vanathu Chinnappan; Investigation: Richard Rajkumar Siluvairaj, Thanikachalam Venugopal; Resources: Rajarajan Govindasamy, Vallal Perumal Govindasamy; Data Curation: Richard Rajkumar Siluvairaj, Vallal Perumal Govindasamy; Writing - Original Draft: Thanikachalam Venugopal, Richard Rajkumar Siluvairaj; Writing - Review and Editing: Thanikachalam Venugopal, Rajarajan Govindasamy; Visualization: Vallal Perumal Govindasamy; Supervision: Thanikachalam Venugopal; Project Administration: Thanikachalam Venugopal, Richard Rajkumar Siluvairaj. ORCID and Email Richard Rajkumar Siluvairaj richardrajkumar@gmail.com https://orcid.org/0000-0002-0064-8603 Vallal Perumal Govindasamy vallalg99@gmail.com https://orcid.org/0009-0003-4479-6928 Rajarajan Govindasamy rajarajang70@gmail.com https://orcid.org/0000-0002-4186-189X Periyanayagasamy Vanathu Chinnappan vpsamychem@gmail.com https://orcid.org/0009-0000-5370-1263 Thanikachalam Venugopal profvt.chemau@gmail.com pvta1998@yahoo.co.in https://orcid.org/0000-0003-1076-6272 References [1]. Zubrys, A.; Siebenmann, C. O. Antituberculous isonicotinylhydrazones of low toxicity. Can. J. Chem. 1955, 33, 11–14. [2]. Yoshino, J.; Kano, N.; Kawashima, T. Fluorescent azobenzenes and aromatic aldimines featuring an N–B interaction. Dalton Trans. 2013, 42, 15826–15834. [3]. Baryshnikova, E. L.; Makhova, N. N. Thermal and base-induced rearrangements of furoxanylketones phenylhydrazones. Mendeleev Commun. 2000, 10, 190–191. [4]. Dimmock, J. R.; Vashishtha, S. C.; Stables, J. P. Anticonvulsant properties of various acetylhydrazones, oxamoylhydrazones and semicarbazones derived from aromatic and unsaturated carbonyl compounds. Eur. J. Med. Chem. 2000, 35, 241–248. [5]. Rollas, S.; Gulerman, N.; Erdeniz, H. Synthesis and antimicrobial activity of some new hydrazones of 4-fluorobenzoic acid hydrazide and 3-acetyl-2,5-disubstituted-1,3,4-oxadiazolines. Farmaco 2002, 57, 171–174. [6]. Maccari, R.; Ottanà, R.; Vigorita, M. G. In vitro advanced antimycobacterial screening of isoniazid-related hydrazones, hydrazides and cyanoboranes: Part 14. Bioorg. Med. Chem. Lett. 2005, 15, 2509–2513. [7]. Özdemir, A.; Turan-Zitouni, G.; Kaplancikli, Z. A.; Tunali, Y. Synthesis and biological activities of new hydrazide derivatives. J. Enzyme Inhib. Med. Chem. 2009, 24, 825–831. [8]. Ajani, O. O.; Obafemi, C. A.; Nwinyi, O. C.; Akinpelu, D. A. Microwave assisted synthesis and antimicrobial activity of 2-quinoxalinone-3- hydrazone derivatives. Bioorg. Med. Chem. 2010, 18, 214–221. [9]. Li, L.; Li, H.; Liu, G.; Pu, S. A colorimetric and fluorescent chemosensor for selective detection of Cu2+ based on a new diarylethene with a benzophenone hydrazone unit. Luminescence 2017, 32, 1473–1481. [10]. Biju, S.; Kumar, S. S.; Sadasivan, V. Synthesis, spectral and single crystal X-ray characterization of 5-(2-(2,3-dimethyl-5-oxo-1-phenyl-2,5- dihydro-1H-pyrazol-4-yl)hydrazono)pyrimidine-2,4,6(1H,3H,5H)- trione and its copper(II) complexes. Polyhedron 2018, 144, 210–218. [11]. Bernades, C.; Carravetta, M.; Coles, S. J.; van Eck, E. R. H.; Meekes, H.; da Piedade, M. E. M.; Pitak, M. B.; Podmore, M.; de Ruiter, T. A. H.; Söğütoğlu, L.-C.; Steendam, R. R. E.; Threlfall, T. The curious case of acetaldehyde phenylhydrazone: Resolution of a 120 year old puzzle where forms with vastly different melting points have the same structure. Cryst. Growth Des. 2019, 19, 907–917. mailto:richardrajkumar@gmail.com https://orcid.org/0000-0002-0064-8603 mailto:vallalg99@gmail.com https://orcid.org/0009-0003-4479-6928 mailto:rajarajang70@gmail.com https://orcid.org/0000-0002-4186-189X mailto:vpsamychem@gmail.com https://orcid.org/0009-0000-5370-1263 mailto:profvt.chemau@gmail.com mailto:pvta1998@yahoo.co.in https://orcid.org/0000-0003-1076-6272 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 69 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 [12]. Sumathi, P.; Enoch, I. V. M. V. Fluorescence Chemosensing of Mg2+ by Phenylhydrazone of a Difluorenylpiperidin-4-one. Anal. Bioanal. Chem. Res. 2019, 6(2), 311–317. [13]. Ramesh Babu, R.; Vijayan, N.; Gopalakrishnan, R.; Ramasamy, P. Growth and characterisation of benzaldehyde semicarbazone (BSC) single crystals. J. Cryst. Growth 2002, 240, 545–548. [14]. Vogel, A. I.; Furniss, B. S. Vogel’s textbook of practical organic chemistry; Longman Scientific and Technical, 1989. [15]. Rauhut, G.; Pulay, P. Transferable scaling factors for density functional derived vibrational force fields. J. Phys. Chem. 1995, 99, 14572–14572. [16]. Scott, A. P.; Radom, L. Harmonic vibrational frequencies: An evaluation of Hartree−Fock, Møller−Plesset, quadratic configuration interaction, density functional theory, and semiempirical scale factors. J. Phys. Chem. 1996, 100, 16502–16513. [17]. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision A.1, Gaussian, Inc., Wallingford CT, 2003. [18]. Koopmans, T. Über die Zuordnung von Wellenfunktionen und Eigenwerten zu den Einzelnen Elektronen Eines Atoms. Physica 1934, 1, 104–113. [19]. Geerlings, P.; De Proft, F.; Langenaeker, W. Conceptual density functional theory. Chem. Rev. 2003, 103, 1793–1874. [20]. Pearson, R. G. Recent advances in the concept of hard and soft acids and bases. J. Chem. Educ. 1987, 64, 561–562. [21]. Yang, W.; Mortier, W. J. The use of global and local molecular parameters for the analysis of the gas-phase basicity of amines. J. Am. Chem. Soc. 1986, 108, 5708–5711. [22]. Mulliken, R. S. Electronic population analysis on LCAO-MO molecular wave functions. III. Effects of hybridization on overlap and gross AO populations. J. Chem. Phys. 1955, 23, 2338–2342. [23]. Portella, G.; Poater, J.; Solà, M. Assessment of Clar’s aromatic π‐sextet rule by means of PDI, NICS and HOMA indicators of local aromaticity. J. Phys. Org. Chem. 2005, 18, 785–791. [24]. Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. von R. Nucleus-independent chemical shifts (NICS) as an aromaticity criterion. Chem. Rev. 2005, 105, 3842–3888. [25]. Piekarski, A. M.; Mills, N. S.; Yousef, A. Dianion and dication of tetrabenzo[5.7]fulvalene. Greater antiaromaticity than aromaticity in comparable systems. J. Am. Chem. Soc. 2008, 130, 14883–14890. [26]. Zborowski, K.; Proniewicz, L. M. Theoretical studies on aromaticity of selected hydroxypyrones and their cations and anions. Part 2. Electron delocalisation in the OCCO group. J. Phys. Org. Chem. 2008, 21, 207–214. [27]. Iqbal, P.; Patel, D. S.; Bharatam, P. V. Ab initio study on N,N′,N″- triaminoguanidine. J. Phys. Org. Chem. 2007, 20, 1072–1080. [28]. Jacquemin, D.; André, J.-M.; Perpète, E. A. Geometry, dipole moment, polarizability and first hyperpolarizability of polymethineimine: An assessment of electron correlation contributions. J. Chem. Phys. 2004, 121, 4389–4396. [29]. Zeitouny, J.; Aurisicchio, C.; Bonifazi, D.; De Zorzi, R.; Geremia, S.; Bonini, M.; Palma, C.-A.; Samorì, P.; Listorti, A.; Belbakra, A.; Armaroli, N. Photoinduced structural modifications in multicomponent architectures containing azobenzene moieties as photoswitchable cores. J. Mater. Chem. 2009, 19, 4715–4724. [30]. Langhals, H. Color Chemistry. Synthesis, Properties and Applications of Organic Dyes and Pigments. 3rd revised edition. By Heinrich Zollinger. Angew. Chem. Int. Ed Engl. 2004, 43, 5291–5292. [31]. Datta, A.; Sheu, S.-C.; Liu, P.-H.; Huang, J.-H. DichloridoN′-[(pyridin-2- yl)methylidene-κN]acetohydrazide-κ2N′,Ocopper(II). Acta Crystallogr. Sect. E Struct. Rep. Online 2011, 67, m1852–m1852. [32]. Qian, H.-F.; Tao, T.; Feng, Y.-N.; Wang, Y.-G.; Huang, W. Crystal structures, solvatochromisms and DFT computations of three disperse azo dyes having the same azobenzene skeleton. J. Mol. Struct. 2016, 1123, 305–310. [33]. Kupka, T.; Buczek, A.; Broda, M. A.; Stachów, M.; Tarnowski, P. DFT studies on the structural and vibrational properties of polyenes. J. Mol. Model. 2016, 22, 101. [34]. Teimouri, A.; Chermahini, A. N.; Emami, M. Synthesis, characterization, and DFT studies of a novel azo dye derived from racemic or optically active binaphthol. Tetrahedron 2008, 64, 11776–11782. [35]. Thomas, K. R. J.; Kapoor, N.; Lee, C.-P.; Ho, K.-C. Organic dyes containing pyrenylamine-based cascade donor systems with different aromatic π linkers for dye-sensitized solar cells: Optical, electrochemical, and device characteristics. Chem. Asian J. 2012, 7, 738–750. [36]. Yıldırım, A. Ö.; Yıldırım, M. H.; Kaştaş, Ç. A. Studies on the synthesis, spectroscopic analysis and DFT calculations on (E)-4,6-dichloro-2- [(2-chlorophenylimino)methyl]-3methoxyphenol as a novel Schiff’s base. J. Mol. Struct. 2016, 1113, 1–8. [37]. Monajjemi, M.; Nouri, A.; Monajemi, H. Qm and ab initio investigation on the hydrogen bonding, nmr chemical shifts and solvent effects on the dppe. Indones. J. Chem. 2010, 7, 260–272. [38]. Targema, M.; Obi-Egbedi, N. O.; Adeoye, M. D. Molecular structure and solvent effects on the dipole moments and polarizabilities of some aniline derivatives. Comput. Theor. Chem. 2013, 1012, 47–53. [39]. Oyeneyin, O. E.; Adejoro, I. A.; Ogunyemi, B. T.; Esan, O. T. Structural and solvent dependence on the molecular and nonlinear optical properties of 10-octyl thiophene-based phenothiazine and substituted derivatives – a theoretical approach. J. Taibah Univ. SCI 2018, 12, 483–493. [40]. Omer, R.; Koparir, P.; Ahmed, L.; Koparir, M. Computational determination the reactivity of salbutamol and propranolol drugs. Turkish Computational and Theoretical Chemistry 2020, 4, 67–75. [41]. Sıdır, İ.; Sıdır, Y. G.; Kumalar, M.; Taşal, E. Ab initio Hartree–Fock and density functional theory investigations on the conformational stability, molecular structure and vibrational spectra of 7-acetoxy-6- (2,3-dibromopropyl)-4,8-dimethylcoumarin molecule. J. Mol. Struct. 2010, 964, 134–151. [42]. Arivazhagan, M.; Manivel, S.; Jeyavijayan, S.; Meenakshi, R. Vibrational spectroscopic (FTIR and FT-Raman), first-order hyperpolarizablity, HOMO, LUMO, NBO, Mulliken charge analyses of 2-ethylimidazole based on Hartree–Fock and DFT calculations. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2015, 134, 493–501. [43]. Demircioğlu, Z.; Kaştaş, Ç. A.; Büyükgüngör, O. Theoretical analysis (NBO, NPA, Mulliken Population Method) and molecular orbital studies (hardness, chemical potential, electrophilicity and Fukui function analysis) of (E)-2-((4-hydroxy-2-methylphenylimino) methyl)-3-methoxyphenol. J. Mol. Struct. 2015, 1091, 183–195. [44]. Chocholoušová, J.; Špirko, V.; Hobza, P. First local minimum of the formic acid dimer exhibits simultaneously red-shifted O–H⋯O and improper blue-shifted C–H⋯O hydrogen bonds. Phys. Chem. Chem. Phys. 2004, 6, 37–41. [45]. Alabugin, I. V.; Manoharan, M.; Weinhold, F. A. Blue-shifted and red- shifted hydrogen bonds in hypervalent rare-gas FRg−H···Y sandwiches. J. Phys. Chem. A 2004, 108, 4720–4730. [46]. Alabugin, I. V.; Gilmore, K. M.; Peterson, P. W. Hyperconjugation. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2011, 1, 109–141. [47]. Reed, A. E.; Weinstock, R. B.; Weinhold, F. Natural population analysis. J. Chem. Phys. 1985, 83, 735–746. [48]. Parr, R. G.; Chattaraj, P. K. Principle of maximum hardness. J. Am. Chem. Soc. 1991, 113, 1854–1855. [49]. Sebastian, K. L. On the proof of the principle of maximum hardness. Chem. Phys. Lett. 1994, 231, 40–42. [50]. Wang, S.; Cao, J.; Jia, W.; Guo, W.; Yan, S.; Wang, Y.; Zhang, P.; Chen, H.- Y.; Huang, S. Single molecule observation of hard–soft-acid–base (HSAB) interaction in engineered Mycobacterium smegmatisporin A (MspA) nanopores. Chem. Sci. 2020, 11, 879–887. [51]. Ashraf, R. S.; Kronemeijer, A. J.; James, D. I.; Sirringhaus, H.; McCulloch, I. A new thiophene substituted isoindigo based copolymer for high performance ambipolar transistors. Chem. Commun. (Camb.) 2012, 48, 3939–3941. [52]. Kanimozhi, C.; Yaacobi-Gross, N.; Chou, K. W.; Amassian, A.; Anthopoulos, T. D.; Patil, S. Diketopyrrolopyrrole–diketopyrrolo pyrrole-based conjugated copolymer for high-mobility organic field- effect transistors. J. Am. Chem. Soc. 2012, 134, 16532–16535. [53]. Parr, R. G.; Pearson, R. G. Absolute hardness: companion parameter to absolute electronegativity. J. Am. Chem. Soc. 1983, 105, 7512–7516. [54]. Gece, G. The use of quantum chemical methods in corrosion inhibitor studies. Corros. Sci. 2008, 50, 2981–2992. [55]. Sheela, N. R.; Muthu, S.; Sampathkrishnan, S. Molecular orbital studies (hardness, chemical potential and electrophilicity), vibrational investigation and theoretical NBO analysis of 4-4′-(1H-1,2,4-triazol-1- yl methylene) dibenzonitrile based on abinitio and DFT methods. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2014, 120, 237–251. [56]. Ajibade Adejoro, I.; Emmanuel Oyeneyin, O.; Temitope Ogunyemi, B. Computational investigation on substituent and solvent effects on the electronic, geometric and spectroscopic properties of azobenzene and some substituted derivatives. Int. J. Comput. Theor. Chem. 2015, 3, 50– 57. [57]. Feixas, F.; Matito, E.; Poater, J.; Solà, M. Quantifying aromaticity with electron delocalisation measures. Chem. Soc. Rev. 2015, 44, 6434– 6451. [58]. Stanger, A. Nucleus-independent chemical shifts (NICS): Distance dependence and revised criteria for aromaticity and antiaromaticity. J. Org. Chem. 2006, 71, 883–893. 70 Siluvairaj et al. / European Journal of Chemistry 15 (1) (2024) 50-70 2024 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.15.1.50-70.2498 [59]. Ostrowski, S.; Dobrowolski, J. C. What does the HOMA index really measure? RSC Adv. 2014, 4, 44158–44161. [60]. Parr, R. G.; Yang, W. Density functional approach to the frontier- electron theory of chemical reactivity. J. Am. Chem. Soc. 1984, 106, 4049–4050. [61]. Parr, R. G.; Szentpály, L. v.; Liu, S. Electrophilicity index. J. Am. Chem. Soc. 1999, 121, 1922–1924. [62]. Jamróz, M. H. Vibrational Energy Distribution Analysis VEDA 4, Warsaw, 2004-2010. [63]. Kolandaivel, P.; Praveena, G.; Selvarengan, P. Study of atomic and condensed atomic indices for reactive sites of molecules. J. Chem. Sci. (Bangalore) 2005, 117, 591–598. [64]. Okulik, N.; Jubert, A. H. Theoretical analysis of the reactive sites of non-steroidal anti-inflammatory drugs. Int. Elect, J. Mol. Des. 2005, 4, 17–30. https://biochempress.com/Files/IECMD_2003/ IECMD_2003_016.pdf (accessed May 4, 2023). [65]. Politzer, P.; Concha, M. C.; Murray, J. S. Density functional study of dimers of dimethylnitramine. Int. J. Quantum Chem. 2000, 80, 184– 192. [66]. Rashid, M. A. M.; Hayati, D.; Kwak, K.; Hong, J. Theoretical investigation of azobenzene-based photochromic dyes for dye-sensitized solar cells. Nanomaterials (Basel) 2020, 10, 914–937. [67]. Joshi, B. D. Chemical reactivity, dipole moment and first hyperpolarizability of aristolochic acid I. J. Inst. Sci. Technol. 2016, 21, 1–9. [68]. Pathak, S. K.; Srivastava, R.; Sachan, A. K.; Prasad, O.; Sinha, L.; Asiri, A. M.; Karabacak, M. Experimental (FT-IR, FT-Raman, UV and NMR) and quantum chemical studies on molecular structure, spectroscopic analysis, NLO, NBO and reactivity descriptors of 3,5-Difluoroaniline. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2015, 135, 283–295. [69]. Obot, I. B.; Johnson, A. S. Ab initio, DFT and TD-DFT electronic absorption spectra investigations on. Elixir Comp. Chem. 2012, 43, 6658–6661. https://www.elixirpublishers.com/articles/ 1687775307_201202028.pdf (accessed May 4, 2023). [70]. Issaoui, N.; Ghalla, H.; Muthu, S.; Flakus, H. T.; Oujia, B. Molecular structure, vibrational spectra, AIM, HOMO–LUMO, NBO, UV, first order hyperpolarizability, analysis of 3-thiophenecarboxylic acid monomer and dimer by Hartree–Fock and density functional theory. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2015, 136, 1227–1242. Copyright © 2024 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at https://www.eurjchem.com/index.php/eurjchem/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution, or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (https://www.eurjchem.com/index.php/eurjchem/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). https://biochempress.com/Files/IECMD_2003/%20IECMD_2003_016.pdf https://biochempress.com/Files/IECMD_2003/%20IECMD_2003_016.pdf https://www.elixirpublishers.com/articles/%201687775307_201202028.pdf https://www.elixirpublishers.com/articles/%201687775307_201202028.pdf https://www.eurjchem.com/index.php/eurjchem/terms http://creativecommons.org/licenses/by-nc/4.0 https://www.eurjchem.com/index.php/eurjchem/terms 1. Introduction 2. Experimental 2.1. Synthesis of N-(4-((4- hydroxy-3-((2-phenylhydrazono) methyl)phenyl)diazenyl)phenyl)acetamide (2) 2.2. Computational details 3. Results and discussion 3.1. Optimized parameters 3.2. Vibrational assignments 3.3. UV-vis data and FMO analysis 3.4. Solvent effect 3.5. Mulliken charges 3.6. NBO analysis 3.7. Dihedral angle studies 3.7.1. Potential energy 3.7.2. Dipole moment 3.7.3. HOMO-LUMO, hardness, electrophilicity 3.8. FMO properties 3.9. Aromaticity indices 3.10. HOMA 3.11. Fukui function 3.12. MEP 3.13. NMR Analysis 3.14. NLO properties 3.15. Thermodynamic properties 4. Conclusion Acknowledgements Disclosure statement CRediT authorship contribution statement ORCID and Email References PrintField10: PrintField11: PrintField12: PrintField13: PrintField14: PrintField15: PrintField16: PrintField17: PrintField18: PrintField19: PrintField110: PrintField111: PrintField112: PrintField113: PrintField114: PrintField115: PrintField116: PrintField117: PrintField118: PrintField119: PrintField120: PrintField20: PrintField21: PrintField22: PrintField23: PrintField24: PrintField25: PrintField26: PrintField27: PrintField28: PrintField29: PrintField210: PrintField211: PrintField212: PrintField213: PrintField214: PrintField215: PrintField216: PrintField217: PrintField218: PrintField219: PrintField220: