Vibrational spectra, molecular structure, NBO, UV, NMR, first order hyperpolarizability, analysis of 4-Methoxy-4′-Nitrobiphenyl by density functional theory

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141

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Vibrational spectra, molecular structure, NBO, UV, NMR, first order hyperpolarizability, analysis of 4-Methoxy-40 -Nitrobiphenyl by density functional theory K. Govindarasu, E. Kavitha ⇑ Department of Physics (Engg.), Annamalai University, Annamalainagar 608 002, India

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 The FTIR and FT-Raman spectra of

4M40 NBPL were reported.  The first order hyperpolarizability

was calculated.  UV–Vis spectra were recorded and

compared with calculated values.  NMR and MEP studies were analyzed.

a r t i c l e

i n f o

Article history: Received 24 September 2013 Received in revised form 16 October 2013 Accepted 31 October 2013 Available online 9 November 2013 Keywords: 4-Methoxy-40 -Nitrobiphenyl TD-DFT NBO UV–Vis NMR Hyperpolarizability

a b s t r a c t In this study, geometrical optimization, spectroscopic analysis, electronic structure and nuclear magnetic resonance studies of 4-Methoxy-40 -Nitrobiphenyl (abbreviated as 4M40 NBPL) were investigated by utilizing HF and DFT/B3LYP with 6-31G(d,p) as basis set. The equilibrium geometry, vibrational wavenumbers and the first order hyperpolarizability of the 4M40 NBPL have been calculated with the help of density functional theory computations. The FT-IR and FT-Raman spectra were recorded in the region 4000– 400 cm1 and 3500–50 cm1 respectively. Natural Bond Orbital (NBO) analysis is also used to explain the molecular stability. The UV–Vis absorption spectra of the title compound dissolved in chloroform were recorded in the range of 200–800 cm1. The HOMO–LUMO energy gap explains the charge interaction taking place within the molecule. Good correlation between the experimental 1H and 13C NMR chemical shifts in chloroform solution and calculated GIAO shielding tensors were found. The dipole moment, linear polarizability and first order hyperpolarizability values were also computed. The linear polarizability and first order hyperpolarizability of the studied molecule indicate that the compound is a good candidate of nonlinear optical materials. The chemical reactivity and thermodynamic properties of 4M40 NBPL at different temperature are calculated. In addition, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations. Ó 2013 Published by Elsevier B.V.

Introduction The nonlinear optical responses induced in various materials are of great interest in recent years because of the applications in ⇑ Corresponding author. Tel.: +91 9442477462. E-mail address: [email protected] (E. Kavitha). 1386-1425/$ - see front matter Ó 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.saa.2013.10.122

photonic technologies such as optical communications, data storage and image processing [1]. In recent years, the synthetic approaches to various biphenyl derivatives and their biological activity were studied. Analysis of the scientific and patent literature indicates that the biphenyl group is used to create a wide range of the drugs and products for agriculture [2,3]. Some biphenyl derivatives are patented and widely used in medicine as the

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141

anti androgenic and hypotensive drugs [4,5]. Antimicrobial preparations based on biphenyl derivatives are of great interest and are used in medicine and in agriculture [6–8]. 4-Methoxy-3-Nitrobiphenyl is a biphenyl derivative which displays a twisted conformation with the two benzene rings making a dihedral angle of 36.69° [9]. Our molecule 4M40 NBPL has the following properties: Pale yellow solid: m.p.: 107–108 °C [10] Stille et al. [11] reported organic synthesis of 4M40 NBPL. Anne Colonna et al. [12] investigate the chirped molecular vibration in a stilbene derivative (4-Methoxy-40 -nitrostilbene) in solution. Hulliger et al. [13] reported on intrinsic and extrinsic defectforming mechanisms determining the disordered structure of 4-iodo-40 -Nitrobiphenyl crystals. To best of our knowledge, there is not any review summarizing the literature on the TD-DFT frequency calculations of 4M40 NBPL have been reported so far. The FTIR and FT Raman spectroscopy combined with Quantum chemical computations have been recently used as an effectively tool in vibrational assignments of nonlinear optical molecule. The present work mainly deals with detailed structural conformation, experimental FT-IR and FT-Raman spectra, vibrational assignments using total energy distribution (TED) and NLO activity as well as HF and DFT/B3LYP calculations for 4M40 NBPL. The electron density (ED) in various bonding and anti bonding orbital and E2 energies have been calculated by Natural Bond Orbital (NBO) analysis using DFT method. The UV spectroscopic studies along with HOMO–LUMO analysis have been used to explain the charge transfer within the molecule. Experimental details

a stated purity greater than 98% and it was used as such without further purification. The FT-IR spectrum of this compound was recorded in the range of 4000–400 cm1 on a Perkin Elmer FT-IR spectrometer using KBr pellet technique. The spectrum was recorded in the room temperature, with scanning speed of 10 cm1. FT-Raman spectrum of the title compound was recorded using 1064 nm line of Nd:YAG laser as excitation wavelength in the region 3500–50 cm1 on a BRUKER RFS 27 FT-Raman Spectrometer equipped with FT-Raman molecule accessory. The spectral resolution was set to 2 cm1 in back scattering mode. The laser output was kept at 100 mW for the solid sample. The ultraviolet absorption spectra of 4M40 NBPL were examined in the range 200–800 nm using Cary 5EUV–VIS–NIR spectrometer. The UV pattern is taken from a 10–5 M solution of 4M40 NBPL, dissolved in chloroform. The theoretically predicted IR and Raman spectra at B3LYP/6-31G(d,p) level calculation along with experimental FT-IR and FT-Raman spectra are shown in Figs. 1 and 2. The spectral measurements were carried out at Indian Institute of Technology (IIT), Chennai. Computational details In the present study, the HF and density functional theory (DFT/B3LYP) at the 6-31G(d,p) basis set level was adopted to calculate the optimized parameters and vibrational wavenumbers of the normal modes of the 4M40 NBPL molecule. All the theoretical calculations were performed using the Gaussian 03 W program package [14] with the default convergence criteria, without any constraint on the geometry [15]. The equilibrium geometry corresponding with the true minimum on the potential energy surface (PES) was effectively obtained by solving self-consistent field equation. The vibrational spectra of the 4M40 NBPL were obtained by taking the second derivative the energy, computed

1338

The compound 4-Methoxy-40 -Nitrobiphenyl in the solid form was purchased from TCI INDIA chemical company at Chennai with

814

1164 1090

1459

2899

3067

1587

1251

IR intensity (arb.units)

B3LYP/6-31 G(d,P)

1378

1406

1123 1224

1520

563 1500

1000

839

Wavenumber

(cm-1)

696

2000

1016

2500

1342

3000

1186

1482 1509

3500

900

1197

2659

3003

2445

2836 2930

3062

1935

Transmittance (%)

1636

Experimental

4000

131

500

Fig. 1. Comparison of experimental and theoretical B3LYP/6-31G(d,p) FT-IR spectra for 4-Methoxy-40 Nitrobiphenyl.

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141

1338

132

222

619 518

794

410

74

1090 989

1170

3500

3000

2500

2000

1500

76

1000

298

421

897 801

1013

1158

1474

3081

1108

Experimental

1337

1596

2899

3067

Raman intensity (arb.units)

1264

1587

B3LYP/6-31G(d,p)

500

Wavenumber (cm-1) Fig. 2. Comparison of experimental and theoretical B3LYP/6-31G(d,p) FT-Raman spectra for 4-Methoxy-40 Nitrobiphenyl.

analytically. The optimized structural parameters were used in the vibrational frequency calculations at DFT levels to characterize all stationary points as minima using the GAUSSVIEW animation program [16]. By the use of total energy distribution (TED) using VEDA 4 program [17] along with available related molecules, the vibrational frequency assignments were made with a high degree of accuracy. The Natural Bond Orbital (NBO) calculations were performed using NBO 3.1 program [18] as implemented in the Gaussian 03W [16] package at the DFT/B3LYP level. 1H and 13C NMR chemical shifts were calculated with GIAO approach [19,20] by applying B3LYP method. The theoretical 1H and 13C NMR chemical shift values were obtained by subtracting the GIAO calculation [21,22]. We have utilized HF and DFT/B3LYP approach with 6-31G(d,p) as basis set for computation of molecular structure, vibrational frequencies and energies of optimized structures, in the present work. Prediction of Raman intensities The Raman activities (SRa) calculated with Gaussian 03 program [14] converted to relative Raman intensities (IRa) using the following relationship derived from the intensity theory of Raman scattering [23,24]

Ii ¼

f ðmo  mi Þ4 Si mi ½1  expðhcmi =ktÞ

where mo is the laser exciting wavenumber in cm1 (in this work, we have used the excitation wavenumber mo = 9398.5 cm1, which

corresponds to the wavelength of 1064 nm of a Nd-YAG laser), mi the vibrational wavenumber of the ith normal mode (cm1) while Si is the Raman scattering activity of the normal mode mi. f (is a constant equal to 1012) is a suitably chosen common normalization factor for all peak intensities. h, k, c and T are Planck and Boltzmann constants, speed of light and temperature in Kelvin, respectively. For the simulation of calculated FT-Raman spectra have been plotted using pure Lorentizian band shape with a bandwidth of Full Width at Half Maximum (FWHM) of 10 cm1. Results and discussion Conformational stability In order to describe conformational flexibility of the title molecule, the energy profile as a function of C17AO16AC4AC3 torsion angle was achieved with B3LYP/6-31G(d,p) method (supplementary material S1). The conformational energy profile shows two maxima near 150° and 210° for (C17AO16AC4AC3) torsion angle. The maximum energies are obtained 782.5191 and 782.5194 Hartree for 150° and 210° respectively. It is clear from supplementary material S1, there are two local minima (stable conformers) observed at 0° or 360° having the energy of 782.5289 Hartree and 180° having the energy of 782.5207 Hartree for T (C17AO16AC4AC3). Therefore, the most stable conformer is for 0° torsion angle for C17AO16AC4AC3 rotation. Further results are based on the most stable conformer of 4M40 NBPL molecule to clarify molecular structure and assignments of vibrational spectra.

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Molecular geometry The optimized geometric parameters such as bond lengths, bond angles and dihedral angles of the title molecule were given in Table 1 using HF and Density functional theoretical calculation with 6-31G(d,p) as a basis set. The atom numbering scheme adopted in this study is given in Fig. 3. Owing the absence of experimental data of the molecule 4M40 NBPL is compared with XRD data of closely related molecule 4-Methoxy-3-Nitrobiphenyl [9]. Our

title molecule contains two phenyl rings and Methoxy group is substituted to 4th position (atom C4) of the phenyl ring A and Nitro group is substituted to 40 th position (atom C10) of the phenyl ring B. In the benzene ring, CAC bond length is about 1.396 Å [25]. From the Table 1 the optimized bond lengths of CAC in phenyl ring fall in the range from 1.386 to 1.480 Å at B3LYP method and 1.375 to 1.487 Å at HF method. From the theoretical values, it is found that most of the optimized bond lengths are slightly larger than the experimental values due to fact that the theoretical

Table 1 Calculated optimized parameter values of the 4-Methoxy-40 -Nitrobiphenyl [Bond length in (Å), angles in (°)].

a

Bond length

B3LYP

HF

a

Bond angle

B3LYP

HF

C1AC2 C1AC6 C1AC7 C2AC3 C2AH18 C3AC4 C3AH19 C4AC5 C4AO16 C5AC6 C5AH20 C6AH21 C7AC8 C7AC12 C8AC9 C8AH22 C9AC10 C9AH23 C10AC11 C10AN13 C11AC12 C11AH24 C12AH25 N13AO14 N13AO15 O16AC17 C17AH26 C17AH27 C17AH28

1.402 1.409 1.480 1.395 1.086 1.400 1.083 1.404 1.361 1.386 1.085 1.086 1.409 1.409 1.389 1.085 1.394 1.083 1.394 1.467 1.389 1.083 1.085 1.232 1.232 1.421 1.091 1.097 1.097

1.386 1.398 1.487 1.388 1.076 1.386 1.073 1.394 1.345 1.375 1.074 1.076 1.395 1.395 1.381 1.074 1.383 1.072 1.383 1.455 1.381 1.072 1.074 1.195 1.194 1.401 1.080 1.086 1.086

1.384 1.387 1.473 1.370 0.930 1.385 0.930 1.398 1.336 1.370 – 0.930 1.383 1.381 1.377 0.930 1.363

C2AC1AC6 C2AC1AC7 C6AC1AC7 C1AC2AC3 C1AC2AH18 C3AC2AH18 C2AC3AC4 C2AC3AH19 C4AC3AH19 C3AC4AC5 C3AC4AO16 C5AC4AO16 C4AC5AC6 C4AC5AH20 C6AC5AH20 C1AC6AC5 C1AC6AH21 C5AC6AH21 C1AC7AC8 C1AC7AC12 C8AC7AC12 C7AC8AC9 C7AC8AH22 C9AC8AH22 C8AC9AC10 C8AC9AH23 C10AC9A H23 C9AC10AC11 C9AC10AN13 C11AC10AN13 C10AC11AC12 C10AC11AH24 C12AC11AH24 C 7AC12AC11 C7AC12AH25 C11AC12AH25 C10AN13AO14 C10AN13AO15 O14AN13AO15 C4AO16AC17 O16AC17AH26 O16AC17AH27 O16AC17AH28 H26AC17AH27 H26AC17AH28 H27AC17AH28

117.5 121.3 121.2 121.8 119.6 118.6 119.6 119.3 121.1 119.4 124.8 115.8 120.2 118.5 121.3 121.4 119.6 119.0 121.0 121.0 118.1 121.3 119.5 119.1 118.9 121.7 119.4 121.6 119.2 119.2 118.8 119.4 121.8 121.3 119.5 119.1 117.8 117.8 124.5 118.4 106.0 111.6 111.6 109.2 109.2 109.2

117.7 121.2 121.1 121.8 119.7 118.5 119.6 119.1 121.3 119.4 124.7 115.9 120.3 118.6 121.2 121.3 119.7 119.0 120.7 120.8 118.5 121.1 119.7 119.1 118.8 121.2 120.0 121.7 119.2 119.2 118.8 120.0 121.2 121.1 119.7 119.2 117.7 117.7 124.5 119.9 106.2 111.4 111.4 109.2 109.1 109.4

Taken from Ref. [9].

Exp

1.358 1.376 0.930 0.930 – A 1.420 0.960 0.960 0.960

a

Exp

116.2

109.5 109.5 109.5

Dihedral angle

B3LYP

HF

C6AC1AC2AC3 C6AC1AC2AH18 C7AC1AC2AC3 C7AC1AC2AH18 C2AC1AC6AC5 C2AC1AC6AH21 C7AC1AC6AC5 C7AC1AC6AH21 C2AC1AC7AC8 C2AC1AC7AC12 C6AC1AC7AC8 C6AC1AC7AC12 C1AC2AC3AC4 C1AC2AC3AH19 H18AC2AC3AC4 H18AC2AC3AH19 C2AC3AC4AC5 C2AC3AC4AO16 H19AC3AC4AC5 H19AC3AC4AO16 C3AC4AC5AC6 C3AC4AC5AH20 O16AC4AC5AC6 O16AC4AC5AH20 C3AC4AO16AC17 C5AC4AO16AC17 C4AC5AC6AC1 C4AC5AC6AH21 H20AC5AC6AC1 H20AC5AC6AH21 C1AC7AC8AC9 C1AC7AC8AH22 C12AC7AC8AC9 C12AC7AC8AH22 C1AC7AC12AC11 C1AC7AC12AH25 C8AC7AC12AC11 C8AC7AC12AH25 C7AC8AC9AC10 C7AC8AC9AH23 H22AC8AC9AC10 H22AC8AC9AH23 C8AC9AC10AC11 C8AC9AC10AN13 H23AC9AC10AC11 H23AC9AC10AN13 C9AC10AC11AC12 C9AC10AC11AH24 N13AC10AC11AC12 N13AC10AC11AH24 C9AC10AN13AO14 C9AC10AN13AO15 C11AC10AN13AO14 C11AC10AN13AO15 C10AC11AC12AC7 C10AC11AC12AH25 H24AC11AC12AC7 H24AC11AC12AH25 C4AO16AC17AH26 C4AO16AC17AH27 C4AO16AC17AH28

0.12 178.21 179.76 1.68 0.14 178.26 179.98 1.86 144.30 35.66 35.58 144.47 0.24 179.11 178.35 1.01 0.11 179.90 179.23 0.75 0.14 179.29 179.85 0.73 0.28 179.73 0.27 178.40 179.15 1.01 179.98 1.69 0.02 178.27 179.74 1.97 0.22 178.07 0.21 179.45 178.09 1.15 0.15 179.88 179.41 0.62 0.09 179.31 179.88 0.67 180.00 0.03 0.03 180.00 0.28 178.03 179.48 1.18 179.67 60.88 61.57

0.10 178.69 179.80 1.21 0.13 178.74 179.97 1.36 137.00 42.97 42.90 137.13 0.21 179.34 178.82 0.73 0.09 179.92 179.45 0.54 0.14 179.43 179.86 0.57 0.47 179.54 0.25 178.87 179.31 0.69 179.98 1.41 0.04 178.57 179.77 1.64 0.21 178.38 0.22 179.58 178.40 0.96 0.15 179.88 179.52 0.50 0.10 179.44 179.88 0.54 179.65 0.34 0.38 179.64 0.28 178.32 179.61 1.01 179.61 60.84 61.63

a

Exp

36.6 36.2

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K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141

in studies on molecular conformations and reaction kinetics [31]. The title molecule consists of 28 atoms, which undergo 78 normal modes of vibrations. It agrees with C1 point group symmetry, all vibrations are active both in Raman and infrared absorption. The detailed vibrational assignment of fundamental modes of 4M40 NBPL along with the calculated IR and Raman frequencies and normal mode descriptions using TED are reported in Table 2. The calculated frequencies are usually higher than the corresponding experimental quantities, due to the combination of electron correlation effects and basis set deficiencies. After applying the scaling factors, the theoretical calculations reproduce the experimental data well in agreement. In our study we have followed scaling factor of 0.9026 for HF/6-31G(d,p) and 0.9608 for B3LYP/6-31G(d,p) respectively. Fig. 3. Optimized Molecular structure and atomic numbering of 4-Methoxy-40 Nitrobiphenyl.

calculations belong to isolated molecules in gaseous phase and the experimental results belong to molecules in solid state [26]. Many authors [27–29] have been explained the changes in frequency or bond length of the CAH bond on substitution due to change in the charge distribution on the carbon atom of the benzene ring. The optimized molecular structure of title molecule reveals that the substituted nitro group is in planar with the benzene ring (C11AC10AN13AO14 = 0.03°). Inclusion of the NO2 group known for its strong electron-withdrawing nature, in the 4’th (atom C10) position is expected to increase a contribution of the resonance structure, in which the electronic charge is concentrated at this site. This is the reason for the shortening of bond lengths N13AO14 = 1.195 Å and N13AO15 = 1.194 Å obtained by HF method. The same bond lengths calculated by DFT method is found to be 1.232 and 1.232 Å. The benzene ring appears to be a little distorted because of the NO2 group substitution as seen from the bond angles C9AC10AC11, which are calculated as (121.7°) and (121.6°) respectively, by HF and B3LYP methods and are larger than typical hexagonal angle of (120°). With the electron donating (methoxy) substituents on the benzene ring, the symmetry of the ring is distorted, yielding ring angles smaller than (120°) at the point of substitution [30]. Due to the electron donating effect of methoxy group, it is observed that the bond angle at the point of substitution C3AC4AC5 (119.4°) for both DFT and HF method. All the CAH bond lengths are presented as nearly equal values at 1.086 Å and 1.076 Å for the C6AH21 and C2AH18 bonds, for both DFT and HF methods respectively, in benzene ring. On the otherhand, a small increment occurs in the methyl group C17AH27 and C17AH28 bonds which are almost 1.097 Å at DFT and 1.085 Å at HF method. In the methoxy group of H27 and H28 atoms are alone lying out-of-plane of the molecule. Owing to this reason, the bond angles and dihedral angles are varied in the above case. The bond angle O16AC17AH26 and O16AC17AH27 and O16AC17AH28 are calculated at (106.0°) and (111.6°) and (111.6°) at DFT method and (106.2°) and (111.4°) and (111.4°) at HF method. The dihedral angles are calculated according to following atoms C4AO16AC17AH27 is (60.88°) at DFT method and (60.84°) at HF method and C4AO16AC17AH28 is (61.57°) at DFT method and (61.63°) at HF method. The dihedral angle C6AC1AC7AC8 between two phenyl rings is (35.58°) at DFT method which is good agreement with experimental value (36.2°). Vibrational assignments Vibrational spectroscopy has been shown to be effective in the identification of functional groups of organic compounds as well as

CAH vibrations The aromatic structure shows the presence of CAH stretching vibration in the region 3100–3000 cm1, which is the characteristic region for the prepared recognition of CAH stretching vibration [32,33]. In this region, the bands are not affected appreciably by the nature of the substituent. In our present work the CAH stretching band observed at 3101, 3061, 3017, 2968, and 2930 cm1 in FTIR spectrum and 3080 cm1 in FT-Raman spectrum. The calculated wavenumbers at 3062, 3044, 3028, 2985, 2933 and 2873 cm1 in HF method and 3101, 3081, 3068, 3031, 2963, and 2901 cm1 in B3LYP method are assigned to CAH stretching vibration. As evident from the TED column, they are pure vibrations almost contributing to 93%. The CACAH in-plane bending vibrations are normally occurred as a number of strong to weak intensity bands in the region 1300–1000 cm1 [34]. In our case CACAH in-plane bending vibrations observed at 1600, 1574, 1508, 1486, 1400, 1301, 1273, 1185 and 1118 cm1 in FT-IR spectrum and 1508, 1395, 1291, and 1108 cm1 in FT-Raman spectrum. The computed wavenumbers at 1680, 1626 1535, 1460, 1430, 1305, 1200, 1179,1120 and 1083 cm1 in HF method and 1604, 1584,1504, 1412, 1386, 1299, 1262, 1168, 1100 and 1088 cm1 in B3LYP method are assigned to CACAH in-plane bending vibrations. The CAH out-of-plane bending vibrations are well identified in the recorded spectra within their characteristic region 1000–750 cm1 [35]. In our case the CAH out-of-plane bending vibrations are observed at 1483, 1476, 1171 and 1145 cm1 in HF method and 1457, 1446, 1164 and 1131 cm1 in B3LYP method. No bands observed for CAH out-ofplane bending vibrations both FT-IR and FT-Raman spectra. CAC and CACAC vibrations The ring carbon–carbon stretching vibrations occur in the region 1625–1430 cm1 [33]. Varsanyi [36] observed these bands are of variable intensity at 1625–1280 cm1. In the present study CAC stretching vibration observed at 1400, 1301, 1273, 1250, 1185 and 1015 cm1 in FT-IR spectrum and 1595, 1395, 1291, 1192, 1012 and 420 cm1 in FT-Raman spectrum. The computed wavenumbers at 1640, 1430, 1305, 1183, 1179, 1016, and 428 cm1 in HF method and 1597, 1386, 1299, 1250, 1168, 1006, and 422 cm1 in B3LYP method are assigned to CAC stretching vibration. The theoretically calculated CAC stretching vibrations show good agreement with recorded spectral data. The in-plane deformation vibration is at higher frequencies than the out-ofplane vibrations. Shimanouchi et al. [37] gave the frequency data for these vibrations for different benzene derivatives as a result of normal coordinate analysis. In our case the CACAC in-plane bending vibrations observed at 1574, 1486, 999, 722 and 625 cm1 in FT-IR spectrum and 627, 420 and 115 cm1 in FT-Raman spectrum. The computed wavenumbers at 1626, 1505, 1011, 731,633, 428, 276 and 142 cm1 in HF method and 1584, 1471, 991, 710, 629, 422, 271 and 139 cm1 in B3LYP method are assigned to CACAC in plane bending vibration. The CACAC out of

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K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 Table 2 Comparison of the experimental and calculated vibrational spectra and proposed assignments of 4-Methoxy-40 -Nitrobiphenyl. Mode Nos.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71

Experimental wavenumbers/cm1

Theoretical wavenumbers/cm1

FT-IR

Unscaled

Scaled

a

3419 3419 3393 3382 3373 3373 3356 3355 3308 3249 3183 1862 1817 1802 1774 1754 1700 1667 1643 1636 1633 1618 1584 1546 1452 1446 1433 1408 1329 1311 1306 1298 1286 1269 1241 1208 1200 1182 1125 1120 1113 1110 1101 1094 1079 982 965 952 945 928 884 862 810 799 784 702 690 660 615 586 563 538 474 468 461 452 393 306 284 261 232

3086 3086 3062 3053 3045 3044 3029 3028 2985 2933 2873 1680 1640 1626 1601 1583 1535 1505 1483 1476 1474 1460 1430 1395 1311 1305 1293 1271 1200 1183 1179 1171 1161 1145 1120 1090 1083 1067 1016 1011 1005 1002 994 987 974 887 871 859 853 838 798 778 731 721 708 633 623 596 555 529 508 485 428 423 416 408 355 276 257 235 209

0.65 0.68 13.36 8.49 4.10 6.93 10.66 12.29 43.36 52.54 55.62 427.94 134.31 76.97 30.54 54.11 125.28 17.52 4.47 611.16 6.07 64.49 0.50 4.22 4.94 30.56 449.42 5.76 31.58 21.56 29.35 35.65 3.02 2.56 53.13 10.73 2.52 62.89 2.58 0.18 0.36 1.37 0.37 3.85 0.51 12.46 62.53 0.24 77.79 9.16 1.18 55.22 7.28 20.93 6.27 1.06 0.76 5.64 3.28 4.82 7.99 14.71 4.41 5.53 1.07 1.12 0.75 3.80 2.40 1.32 1.20

FT-Raman

3101

3080 3061 3017 2968 2930 1600 1595 1574

1508 1486

1508

1400 1342

1395 1338

1301

1291

1273 1250 1185

1192

1118

1033 1015 999

863 839

1108

1012

858

800 756 722

625

627

603 550 529 492 420

358

HF/6-31G(d,p)

Vibrational assignments with TED (P10%) B3LYP/6-31G(d,p)

IIR

b

IRa

0.02 0.02 0.43 0.28 0.13 0.23 0.36 0.41 1.51 1.92 2.15 55.42 18.19 10.59 4.32 7.82 19.13 2.77 0.73 100 1.00 10.75 0.09 0.76 0.99 6.16 91.97 1.21 7.29 5.09 6.97 8.55 0.73 0.64 13.66 2.88 0.68 17.41 0.77 0.05 0.11 0.42 0.11 1.2 0.16 4.52 23.27 0.09 29.81 3.6 0.5 24.03 3.45 10.09 3.1 0.61 0.44 3.48 2.22 3.46 6.02 11.74 4.09 5.2 1.03 1.1 0.87 5.85 4 2.43 2.51

Unscaled

Scaled

a

3245 3244 3227 3216 3207 3206 3194 3193 3155 3084 3020 1670 1663 1649 1622 1603 1566 1531 1517 1505 1489 1470 1442 1393 1368 1352 1335 1318 1313 1301 1216 1212 1205 1178 1145 1135 1132 1076 1047 1031 1017 993 989 970 956 882 868 854 847 828 823 766 739 731 709 654 642 615 561 542 518 500 439 430 423 418 364 282 263 234 217

3118 3117 3101 3090 3082 3081 3069 3068 3031 2963 2901 1604 1597 1584 1559 1540 1504 1471 1457 1446 1431 1412 1386 1338 1314 1299 1283 1266 1262 1250 1168 1164 1158 1131 1100 1091 1088 1034 1006 991 977 954 950 932 918 847 834 820 814 796 791 736 710 703 681 629 617 590 539 521 498 480 422 413 406 402 349 271 253 225 208

1.30 0.35 11.60 7.01 3.36 6.08 7.25 8.53 25.35 38.48 64.99 84.13 105.55 196.12 32.90 82.42 69.01 55.10 58.91 6.06 21.48 0.87 6.45 557.85 28.57 82.20 3.30 140.71 8.80 276.62 59.17 13.73 37.33 0.72 8.23 7.36 93.24 59.30 6.15 0.72 2.69 0.54 0.13 0.98 0.78 11.01 53.66 0.19 57.17 8.51 0.95 19.01 13.06 7.27 9.44 0.96 0.63 9.27 2.42 2.03 6.40 10.80 6.01 3.19 0.54 0.29 0.51 2.38 2.71 1.04 0.70

IIR

b

IRa

0.04 0.01 0.33 0.2 0.1 0.18 0.22 0.25 0.78 1.27 2.27 11 13.91 26.23 4.53 11.6 10.13 8.41 9.14 0.95 3.44 0.14 1.09 100 5.28 15.47 0.63 27.62 1.74 55.43 13.21 3.08 8.45 0.17 2.02 1.83 23.22 15.95 1.72 0.21 0.79 0.16 0.04 0.31 0.25 3.95 19.67 0.07 21.67 3.33 0.37 8.26 5.96 3.36 4.55 0.51 0.34 5.37 1.57 1.37 4.58 8.09 5.25 2.86 0.49 0.27 0.56 3.46 4.26 1.86 1.36

tCH(83) tCH(84) tCH(93) tCH(82) tCH(90) tCH(89) tCH(81) tCH(89) tCH(91) tCH(99) tCH(91) tCC(20) + dHCC(11) tCC(75) + dCNO(11) tCC(55) + dHCC(14) + dCCC(13) tCC(44) + dCCC(10) tCC(72) dHCC(66) + dCCC(11) dHCC(51) + dCCC(11) dHCH(80) + cCHOH(14) dHCH(82) + cCHOH(14) dHCH(82) tCC(24) + dHCC(20) tCC(39) + dHCC(18) tON(75) + dONO(12)

tCC(51) tCC(12) + dHCC(29) tCC(12) + dHCC(72) tCC(18) + dHCC(20) tCC(21) + dHCC(14) tCC(45) tCC(11) + dHCC(58) dHCH(11) + cCHOH(62) dHCC(56) dHCH(14) + cCHOH(84) dHCC(54)

tCC(14) tCC(62) + dHCC(11) tOC(66) tCC(10) + dCCC(13) dCCC(56) dCCC(21)

sHCCC(78) sHCCC(78) sHCCC(83) sHCCH(89) sHCCC(11) + sHCCC(66) tON(22) + dONO(42) sHCCC(97) sHCCC(69) + sHCCC(12) sHCCC(82) tCC(26) cCCCC(12) + cNCCC(49) dONO(20) + dCCC(29) cNCCC(13) + sCCCC(56)

sCCCC(60) dCCC(25) dCCC(58) dCCC(25)

cCCCC(61) dCNO(54) dCNO(12) + dCOC(10) + cCCCC(17) dCOC(19) + cCCCC(27) tCC(12) + dCCC(21)

sCCCC(64) sHCCC(14) + sCCCC(63) dCCC(17) + dCOC(10) cNCCC(10) + cCCCC(47) dCCC(10) + dCNO(30) + dCOC(10) + sHCOC(11) + sCCCC(13) dCCO(17) + dCOC(17) + sHCOC(21) + sCCCC(14) + cCCCC(11) dCNO(24) + sHCOC(38) tCC(13) + dCCC(12) + sHCOC(13) + sCCCC(11) (continued on next page)

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Table 2 (continued) Mode Nos.

72 73 74 75 76 77 78

Experimental wavenumbers/cm1

Theoretical wavenumbers/cm1

FT-IR

Unscaled

FT-Raman 173 115 76

HF/6-31G(d,p)

213 157 96 77 65 49 42

Scaled 192 142 87 69 58 44 38

Vibrational assignments with TED (P10%) B3LYP/6-31G(d,p)

a

IIR 2.24 0.75 5.70 1.02 1.87 0.67 0.15

b

IRa 5.14 2.38 30.2 6.87 15.05 7.15 1.86

Unscaled 200 144 102 81 66 51 39

Scaled

a

b

IIR

192 139 98 77 64 49 38

IRa

1.72 0.38 4.18 1.18 1.09 0.81 0.18

3.66 1.14 18.13 6.57 7.35 7.18 2.07

dCNO(15) + sCCCC(24) dCCC(13) + cCCCC(22) + sCCOC(16) dCCC(15) + sCCCC(12) + sCCOC(51)

sCCCC(78) dCCC(34) + cCCCC(10) + sCCOC(11) + sCCCC(10)

cCCCC(49) cCCCC(50)

m – stretching; d – in-plane-bending; c – out-of-plane bending; s – torsion; w – weak; s – strong; vs – very strong; vw – very weak; m – medium. a b

IIR-IR Intensity (K mmol1). IRa-Raman intensity (Arb units) (intensity normalized to 100%).

plane bending vibration observed at 550 and 492 cm1 in FT-IR spectrum and 358 and 115 cm1 in FT-Raman spectrum. The theoretically predicted wavenumbers at 555, 508, 355 and 142 cm1 in HF method and 539, 498, 349 and 139 cm1 in B3LYP method are assigned to CACAC out of plane bending vibration. The computed wavenumbers at 721, 708, 416, 192, 69, and 58 cm1 in HF method and 703, 681, 406, 192, 77 and 64 cm1 in B3LYP method are assigned to CACACAC inplane bending vibration. This vibration experimentally observed at 173 and 76 cm1 in FT-Raman spectrum. The theoretically computed wavenumbers at B3LYP method gives good agreement with experimental data, when compare to HF method. CAO vibrations The CAO stretching band of the aromatic ether in IR spectrum is characterized by the frequencies around 1270–1230 cm1, while the band in Raman spectrum usually presents a weak activity in the region of 1310–1210 cm1. In our case CAO stretching vibration observed at 1033 cm1 in FT-Raman spectrum. The computed wavenumbers at 1067 cm1 in HF method and 1034 cm1 in B3LYP method are assigned to CAO stretching vibration. The TED corresponding to this vibration suggests that it is a strong mode and exactly contributing to 66%. The theoretically predicted wavenumber at 257 cm1 in HF method and 253 cm1 in B3LYP method are assigned to CACAO in-plane mode. OACH3 vibrations Electronic effects such as back-donation and induction, mainly caused by the presence of atom adjacent to CH3 group, can shift the position of CH stretching and bending modes [38–41]. The asymmetric stretching vibrations of CH3 are expected in the region 3000–2925 cm1 and the symmetric CH3 stretching vibrations in the range 2940–2905 cm1 [42,43]. In the present study the asymmetric stretching vibrations of CH3 are observed at 3017 and 2968 cm1 in FT-IR spectrum. The theoretically predicted wavenumbers at 2933 and 2085 cm1 in HF method and 3031 and 2963 cm1 in B3LYP method assigned to CAH asymmetric stretching vibration of the CH3 group. As evident from the TED column, they are pure stretching vibrations almost contributing to 99%. The symmetric stretching vibrations of CH3 are observed at 2930 cm1 in FT-IR spectrum. The theoretically predicted wavenumbers at 2873 cm1 in HF method and 2901 cm1 in B3LYP method assigned to CAH symmetric stretching vibration of the CH3 group. The TED corresponding to this vibration suggests that it is a pure mode and exactly contributing to 91%. The computed wavenumbers at 1483 and 1476 cm1 in HF method and 1457 and 1446 cm1 in B3LYP method are assigned to scissoring of the CH3 unit. The calculated TED corresponding to this mode is also as a mixed mode with 82% of scissoring mode. The computed wavenumbers at 1171 and 1145 cm1 in HF method and 1164

and 1131 cm1 in B3LYP method are assigned to rocking mode of the CH3 unit. The calculated TED corresponding to this mode is also as a mixed mode with 14% of rocking mode. NO2 vibrations Aromatic nitro compounds have strong absorptions due to asymmetric and symmetric stretching vibrations of the NO2 group at 1570–1485 and 1370–1320 cm1, respectively, Hydrogen bonding has a little effect on the NO2 asymmetric stretching vibrations [44,45]. In our present work OAN stretching vibrations observed at 1342 and 839 cm1 in FT-IR spectrum and 1338 cm1 in FT-Raman spectrum. The computed wavenumbers at 1395 and 871 cm1 in HF method 1338 and 834 cm1 in B3LYP method are assigned to NAO stretching vibration of NO2 group. The deformation vibrations of NO2 group are in the low frequency region [46]. In our molecule the in-plane bending vibrations of the NO2 group are observed at 1342, 839 and 722 cm1 in FT-IR spectrum and 1338 cm1 in FTRaman spectrum. The theoretically predicted wavenumbers at 1395, 871 and 731 cm1 in HF method and 1338, 834 and 710 cm1 in B3LYP method are assigned to in-plane bending vibrations of the NO2 group. The calculated wavenumbers are good agreement with experimental findings. NBO analysis The natural bond orbitals (NBO) calculations were performed using NBO 3.1 program [47] as implemented in the Gaussian 03 package at the DFT/B3LYP level in order to understand various second-order interactions between the filled orbitals of one subsystem and vacant orbitals of another subsystem, which is a measure of the intermolecular delocalization or hyper conjugation.NBO analysis provides the most accurate possible ‘natural Lewis structure’ picture of ‘j’ because all orbital details are mathematically chosen to include the highest possible percentage of the electron density. A useful aspect of the NBO method is that it gives information about interactions of both filled and virtual orbital spaces that could enhance the analysis of intra and inter molecular interactions. The second-order Fock-matrix was carried out to evaluate the donor–acceptor interactions in the NBO basis. The output obtained by the 2nd-order perturbation theory analysis is normally the first to be examined by the experienced NBO user in searching for significant delocalization effects. However, the strengths of these delocalization interactions, E(2), are estimated by second order perturbation theory as estimated by the following equation. 2

E2 ¼ DEij ¼ qi

Fði; jÞ ej  ei

qi is the donor orbital occupancy; Ei, Ej is the diagonal elements and Fij is the off diagonal NBO Fock matrix element.

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The larger E(2), value the more intensive is the interaction between electron donors and acceptor, i.e. the more donation tendency from electron donors to electron acceptors and the greater the extent of conjugation of the whole system [48]. In this present work the p electron delocalization is maximum around C1AC2, C3AC4, C5AC6 distributed to p* antibonding of C5AC6, C1AC2 and C3AC4 with a stabilization energy of about 20.68, 16.93 and 21.34 kJ/mol as shown in Table 3. The other interaction energy in this molecule is p electron donating from p(C7AC12)?p* (C10AO11), p(C8AC9)?p*(C7AC12), p(C10AC11)?p*(N13AO14) resulting a stabilization energy of about 25.39, 21.26 and 26.02 kJ/mol. The most important interaction is LP(1)O16 ? r* (C3AC4), r*(C7AH26), r*(C7AH27), r*(C7AH28) and with a stabilization energy of about 7.60, 1.83, 1.26 and 1.22 kJ/mol. The another most important interaction energy is LP(2)O14 ? r* (C10AN13), r*(N13AO15) and LP(2)O15 ? p*(N13AO14) and LP(2)O16 ? p*(C3AC4) of about 12.32, 19.24 and 162.56 and 31.87 kJ/mol shows higher values than those of the other delocalization around the ring. The p*(C3AC4) of the NBO conjugated with p*(C1AC2), p*(C5AC6) resulting to stabilization of 308.53 and 263.61 kJ/mol respectively shown in Table 3. 13

C and 1H NMR spectral analysis

The molecular structure of 4M40 NBPL compound was optimized by using B3LYP method in conjunction with 6-31G(d,p) as basis set. Then, gauge-including atomic orbital (GIAO) 13C and 1H chemical shift calculations of the compound were made. The GIAO [49,50] method is one of the most common approaches for calculating nuclear magnetic shielding tensors. For the same basis set size GIAO method is often more accurate than those calculated with other approaches [51]. NMR spectra are recorded on MERCURY (400 MHz for 1H NMR, 100 MHz for 13C NMR) spectrometers; chemical shifts are expressed in ppm (dunits) relative to TMS signal as internal reference in CHCl3 [52]. The NMR spectra calculations were performed for CHCl3 solvent. The chemical shifts with

respect to tetramethylsilane (TMS). The recorded 1H, 13C and NMR spectra of 4M40 NBPL in chloroform solution are shown in supplementary material S2 and S3. Theoretical and experimental chemical shifts of title molecule in 13C and 1H NMR spectra are gathered in supplementary material S4 [52]. Taking into account that the range of 13C NMR chemical shifts for a typical organic molecule usually is >100 ppm [53,54], the accuracy ensures reliable interpretation of spectroscopic parameters. In the present work, 13C NMR chemical shifts in the ring for the title compound are >100 ppm, as they would be expected. The oxygen and nitrogen atoms polarize the electron distribution in its bond to carbon and decrease the electron density at the ring carbon. Therefore, the calculated 13C chemical shifts values of (C4) and (C10) bonded to the oxygen and nitrogen atoms that are too high in the rings. The chemical shift values of C4 and C10 which are in the ring has been observed at 158.6 and 133.4 ppm (CAO and CAN) and calculated 149.3 and 137.2 ppm respectively. Similarly, other three carbon peaks in the rings are observed at 55.3, 114.1 and 127.7 ppm and are calculated at 47.2, 115.1 and 122.8 ppm in chloroform. In the 1 H NMR spectrum just one type of protons appears at 3.85 ppm as a singlet (OACH3), where as the chemical shift value of 3.82 ppm in chloroform have been determined, the values are listed in supplementary material S3. In that, we calculated chemical shifts for H20 and H21 and H22 are 6.97 and 7.49 and 7.54 ppm also give a good correlation with the experimental observations of 6.97 and 7.48 and 7.93 ppm, respectively. This shows that the correlations between theory and experiment chemical shifts for the title compound are good. Nonlinear optical (NLO) effects The polarizability (a) and the hyper polarizability (b) and the electric dipole moment (l) of the 4-Methoxy-40 -Nitrobiphenyl are calculated by finite field method using HF/6-31G(d,p) basis set. To calculate all the electric dipole moments and the first hyper polarizabilities for the isolated molecule, the origin of the Cartesian

Table 3 Second order Perturbation theory analysis of Fock Matrix in NBO basis for 4-Methoxy-40 -Nitrobiphenyl. Donor (i)

ED (i)(e)

p(C1AC2)

1.656

p(C3AC4)

1.646

p(C5AC6)

1.711

p(C7AC12)

1.605

p(C8AC9)

1.666

p(C10AC11)

1.640

LP(2)O14

1.899

LP(2)O15 LP(2)O16 p*(C3AC4)

1.450 1.833 0.393

p*(C5AC6)

0.305

LP(1)O16

1.964

Acceptor (j) *

p (C3AC4) p*(C5AC6) p*(C1AC2) p*(C5AC6) p*(C1AC2) p*(C3AC4) p*(C8AC9) p*(C10AO11) p*(C7AC12) p*(C10AC11) p*(C7AC12) p*(C8AC9) p*(N13AO14) r*(C10AN13) r*(N13AO15) p*(N13AO14) p*(C3AC4) p*(C1AC2) p*(C5AC6) RY*(3)C5 RY*(4)C6 r*(C3AC4) r*(C7AH26) r*(C7AH27) r*(C7AH28)

ED Means electron density. a E(2) Means energy of hyper conjugative interactions. b Energy difference between donor and acceptor i and j NBO orbitals. c F(i,j) is the Fock matrix element between i and j NBO orbitals.

ED (j)(e)

E(2)a (kJ mol1)

E(j)E(i)b a.u

F(i,j)c a.u

0.393 0.305 0.374 0.305 0.374 0.393 0.290 0.392 0.355 0.392 0.356 0.290 0.633 0.102 0.057 0.633 0.393 0.374 0.305 0.001 0.000 0.029 0.007 0.019 0.019

17.74 20.68 22.66 16.25 16.93 21.34 17.10 25.39 21.26 18.89 17.19 20.91 26.02 12.32 19.24 162.56 31.87 308.53 263.61 2.11 2.02 7.60 1.83 1.26 1.22

0.27 0.28 0.29 0.29 0.29 0.28 0.28 0.27 0.29 0.28 0.29 0.29 0.15 0.58 0.70 0.14 0.34 0.01 0.01 0.62 0.78 1.10 1.00 0.98 0.98

0.063 0.069 0.073 0.062 0.064 0.071 0.063 0.074 0.070 0.066 0.063 0.071 0.059 0.075 0.105 0.138 0.098 0.080 0.082 0.082 0.091 0.082 0.039 0.031 0.031

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coordinate system (x, y, z) = (0, 0, 0) was chosen at own center of mass of 4M40 NBPL. The NLO activity provide the key functions for frequency shifting, optical modulation, optical switching and optical logic for the developing technologies in areas such as communication, signal processing and optical interconnections [55,56]. The first static hyperpolarizability (bo) and its related properties (b, ao and Da) have been calculated using HF/6-31G(d,p) level based on finite field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field and the first hyperpolarizability is a third rank tensor that can be described by a 3  3  3 matrix. The 27 components of the 3D matrix can be reduced to 10 components because of the Kleinman symmetry [57]. The matrix can be given in the lower tetrahedral format. It is obvious that the lower part of the 3  3  3 matrices is a tetrahedral. The components of b are defined as the coefficients in the Taylor series expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion is given below:

E ¼ Eo  la F a  1=2aab F a F b  1=6babc F a F b F cþ...... where Eo is the energy of the unperturbed molecules, Fa is the field at the origin, la,aab and babc are the components of dipole moment, polarizability and first hyperpolarizability, respectively. The total static dipole moment l, the mean polarizability ao, the anisotropy of the polarizability Da and the mean first hyperpolarizability bo, using the x, y and z components are defined as: Dipole moment is

l ¼ ðl2x þ l2y þ l2z Þ

1=2

Static polarizability is

a0 ¼ ðaxx þ ayy þ azz Þ=3 Total polarizability is

Da ¼ 21=2 ½ðaxx  ayy Þ2 þ ðayy  azz Þ2 þ ðazz  axx Þ2 þ 6a2xz 

1=2

First order hyperpolarizability is

b ¼ ðb2x þ b2y þ b2z Þ

1=2

where

bx ¼ ðbxxx þ bxyy þ bxzz Þ by ¼ ðbyyy þ byzz þ byxx Þ bz ¼ ðbzzz þ bzxx þ bzyy Þ b ¼ ½ðbxxx þ bxyy þ bxzz Þ2 þ ðbyyy þ byzz þ byxx Þ2 þ ðbzzz þ bzxx þ bzyy Þ2 

1=2

Since the values of the polarizabilities (a) and hyperpolarizability (b) of the Gaussian 03 output are reported in atomic units (a.u.), the calculated values have been converted into electrostatic units (esu) (For a: 1a.u. = 0.1482  1024 esu; For b: 1a.u. = 8.639  1033 esu). The mean polarizability ao and total polarizability Da of our title molecule are 22.735  1024 esu and 22.932  1024 esu respectively. The total molecular dipole moment and first order hyperpolarizability are 2.775 Debye and 15.589  1030 esu, respectively and are depicted in Table 4. Total dipole moment of 4M40 NBPL molecule is approximately two times greater than that of urea and first order hyperpolarizability is 41 times greater than that of urea (l and b of urea are 1.3732 Debye and 0.3728  1030 esu obtained by HF/6-311G(d,p) method). This result indicates the good nonlinearity of the title molecule. Electronic properties UV–Vis spectral analysis The time dependent density functional method (TD-DFT) is able to detect accurate absorption wavelengths at a relatively small computing time which correspond to vertical electronic transitions computed on the ground state geometry, especially in the study of solvent effect [58–60]; thus TD-DFT method is used with B3LYP function and 6-31G(d,p) basis set for vertical excitation energy of electronic spectra. Calculations are performed for gas phase, and CHCl3 environment. The calculated visible absorption maxima of k which are a function of the electron availability have been reported in Table 5. The excitation energies, absorbance and oscillator strengths for the title molecule at the optimized geometry in the ground state were obtained in the frame work of TD-DFT calculations with the B3LYP/6-31G(d,p) method. TD-DFT methods are computationally more expensive than semi-empirical methods but allow easily studies of medium size molecules [61,62]. Experimentally, electronic absorption spectra of title molecule in chloroform solvent showed two bands at 240 and 340 nm (Fig. 4) .The computed UV spectra predicts one intense electronic transition at 303.15 nm with an oscillator strength f = 0.0049 a.u in chloroform solvent and electronic transition at 291.16 nm with an oscillator strength f = 0.0003 a.u in gas phase that shows good agreement with measured experimental data k (exp) = 340 nm. Calculations of molecular orbital geometry show that the visible absorption maxima of title molecule correspond to the electron transition between frontier orbitals such as transition from HOMO to LUMO. As can be seen from the UV–Vis spectra absorption maxima values have been found to be 240 and 340 nm. The kmax is a function of substitution, the stronger the donor character of the substitution, the more electrons pushed into the molecule, the larger kmax. These values may be slightly shifted by solvent effects. The role of substituents and of the solvent influence on the UV-spectrum. This band may be due to electronic transition of the ring B to ring A

Table 4 The electric dipole moment, polarizability and first order hyperpolarizability of 4-Methoxy-40 -Nitrobiphenyl by HF/6-31G(d,p) method. Dipole moment, l (Debye)

Polarizability a

Parameter

Value (DB)

Parameter

a.u.

esu (1024)

Parameter

a.u.

esu (1033)

lx ly lz l

2.039 0.011 1.887 2.775

axx axy ayy axz ayz azz ao Da

214.091 12.356 76.061 54.860 21.533 170.077 153.409 154.735

31.728 1.831 11.272 8.130 3.191 25.205 22.735 22.932

bxxx bxxy bxyy byyy bxxz bxyz byyz bxzz byzz bzzz btot

1103.338 50.933 32.745 0.267 870.261 19.476 50.306 472.376 44.441 115.892 1804.606

9531.734 440.010 282.883 2.3100 7518.188 168.256 434.591 4080.859 383.926 1001.192 15589.992 b = (15.589  1030 esu)

First order hyperpolarizability b

K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 Table 5 The experimental and computed absorption wavelength k (nm), excitation energies E (eV), absorbance and oscillator strengths (f) of 4-Methoxy-40 -Nitrobiphenyl in Chloroform solution and gas phase.

Atomic charges

2.0

The mulliken atomic charges are calculated at B3LYP/631G(d,p) level by determining the electron population of each atom as defined by the basis function. It may be the reason of the substitution of methoxy group, the carbon atoms C4 (0.357e) have the highest positive charge when compared with all other carbon atoms as shown in the histogram supplementary material S6. Mulliken atomic charges show that the H23 and H24 atoms have maximum and equal positive atomic charges [(0.136e for both H23, H24)] than the other hydrogen atoms. The methoxy group oxygen atoms have the maximum negative charge value O16 (0.514e) compare to other oxygen atom of the nitro group, O14 (0.402e) and O15 (0.402e) atoms respectively at B3LYP method. Nitrogen atom has large positive charge value N13 (0.382e). This is due to the presence of electronegative atom in the nitro group.

1.5

Molecular electrostatic potential (MEP)

Experimental

TD-DFT/B3LYP/6-31G(d,p)

Chloroform

Chloroform

Gas

Abs.

k(nm)

E(eV)

F(a.u)

k(nm)

E(eV)

f(a.u)

– 240 340

– 2.0479 2.5209

396.81 320.35 303.15

3.1245 3.8703 4.0898

0.4435 0.0018 0.0049

361.06 330.37 291.16

3.4339 3.7529 4.2582

0.3787 0.0050 0.0003

340

k(nm)

240

2.5

Abs

139

1.0

The molecular electrostatic potential, V(r) is related to the electronic density and is a very useful descriptor for determining sites for electrophilic attack and nucleophilic reactions as well as hydrogen bonding interaction [71,72]. MEP values were calculated using the equation [73]:

0.5 0.0 200

300

400

500

600

700

800

Wavelength (nm) Fig. 4. The UV–Vis spectrum (CHCl3) of 4-Methoxy-40 -Nitrobiphenyl.

through bridge (transition of p–p*). Both the (HOMO) and (LUMO) are the main orbitals that take part in chemical stability [63]. Frontier molecular orbitals The HOMO represents the ability to donate an electron, LUMO as an electron acceptor represents the ability to obtain an electron [64]. The frontier molecular orbitals play an important role in the electric and optical properties, as well as in UV–Vis spectra and chemical reactions [65,66]. The atomic orbital compositions and energy levels of the HOMO and LUMO orbitals computed at the B3LYP/6-31G(d,p) level for the title compound is shown in supplementary material S5. Molecular orbital and their properties like energy are very useful to the physicists and chemists and their frontier electron density used for predicting the most reactive position in p-electron system and also explained several types of reaction in conjugated systems [67]. Owing to the interaction between HOMO and LUMO orbital of a structure, transition state transition of p–p* type is observed with regard to the molecular orbital theory [68]. Therefore, while the energy of the HOMO is directly related to the ionization potential, LUMO energy is directly related to the electron affinity. Energy difference between HOMO and LUMO orbital is called as energy gap that is an important stability for structures [69]. The energy gap between HOMO and LUMO is a critical parameter in determining molecular electrical transport properties [70]. In addition, according to B3LYP/631G(d,p) calculation, the energy band gap of the 4M40 NBPL molecule is 3.760 eV. The HOMO are localized mainly on the both the ring. On the other hand, the LUMO are localized mainly on biphenyl ring and exception of methyl group.

HOMO energy ¼ 6:093eV LUMO energy ¼ 2:333eV HOMO  LUMO energy gap ¼ 3:760eV

VðrÞ ¼

X

ZA=jRA  rj 

Z

qðr0 Þ=jr0  rjd3r0

where ZA is the charge of nucleus A located at RA, q(r0 ) is the electronic density function of the molecule, and r’ is the dummy integration variable. To predict reactive sites for electrophilic and nucleophilic attack for the title molecule, MEP was calculated at the B3LYP/6-31G(d,p) optimized geometry. In the majority of the MEPs, while the maximum negative region which preferred site for electrophilic attack indications as red color, the maximum positive region which preferred site for nucleophilic attack symptoms as white color and blue represents the region of zero potential. The importance of MEP lies in the fact that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of color grading and is very useful in research of molecular structure with its physicochemical property relationship [74,75]. In the present study, a 3D plot of MEP of title molecule is illustrated in supplementary material S7. The color code of these maps is in the range between 0.0409 a.u. (deepest red) and +0.0500 a.u. (white) in our molecule. As can be seen from the MEP map of the 4M40 NBPL molecule, while regions having the negative potential are over the electronegative atom (oxygen atom), the regions having the positive potential are over the hydrogen atoms. The negative potential value is 0.0409 a.u. for oxygen atom. A maximum positive region localized on the H atoms bond has value of +0.0500 a.u. The negative (red color) regions of MEP were related to electrophilic reactivity and the positive (white color) ones to nucleophilic reactivity. Global reactivity descriptors By using HOMO and LUMO energy values for a molecule, the global chemical reactivity descriptors of molecules such as hardness (g), chemical potential (l), softness (S), electronegativity (v) and electrophilicity index (x) have been defined [76,77]. On the basis of EHOMO and ELUMO, these are calculated using the below equations. Using Koopman’s theorem for closed-shell molecules, The hardness of the molecule is

g ¼ ð1  AÞ=2

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The chemical potential of the molecule is

l ¼ ð1 þ AÞ=2 The softness of the molecule is

S ¼ 1=2g The electronegativity of the molecule is

v ¼ ð1 þ AÞ=2 The electrophilicity index of the molecule is

x ¼ l2 =2g where A is the ionization potetional and I is the electron affinity of the molecule. I and A can be expressed through HOMO and LUMO orbital energies as I = EHOMO and A = ELUMO. The Ionization potetional A and an electron affinity I of our molecule 4M40 NBPL calculated by B3LYP/6-31G (d,p) method is 2.333 eV and 6.093 eV respectively. The calculated values of the Hardness, Softness, Chemical potential, electronegativity and electrophilicity index of our molecule is 1.880, 0.266, 4.213, 4.213 and 4.721 respectively as shown in supplementary material S8. Considering the chemical hardness, large HOMO–LUMO gap represent a hard molecule and small HOMO–LUMO gap represent a soft molecule. Thermodynamic properties Based on the vibrational analysis of our title molecule at B3LYP 6-31G(d,p) basis set, the thermodynamic parameters such as Heat capacity C 0p;m , entropy (S0m ) and enthalpy (H0m ) were calculated using perl script THERMO.PL [78] and are listed in Supplementary material S9. From the Supplementary material S8 it can be seen that, when the temperature increases from 100 to 1000 K the thermodynamic functions (C 0p;m , S0m , H0m ) are also increases, because molecular vibrational intensities increase with temperature [79]. Fitting factor (R2) of the thermodynamic functions such as heat capacity, entropy and enthalpy changes are 0.995, 0.965 and 0.974 respectively. The correlation graphics of temperature dependence of thermodynamic functions for 4M40 NBPL molecule are shown in Supplementary material S10. Vibrational zero-point energy of the 4M40 NBPL is 569.60 kJ/mol. Conclusion The optimized geometry and FT-IR and FT-Raman vibrational analysis of the molecule 4-Methoxy-40 -Nitrobiphenyl have been carried out with the help of HF and DFT method using 6-31G(d,p) as basis set. The calculated vibrational modes are compared with experimental values. It has been observed that all scaled frequencies are in good agreement with experimental values. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The UV spectrum was measured in chloroform solution and results are compared with theoretical results. The NBO analysis revealed that the p*(C3AC4) ? p*(C1AC2) interaction gives the strongest stabilization to the system around at 308.53 kJ/mol. The 1H and 13C NMR magnetic isotropic chemical shifts were calculated by B3LYP/631G(d,p) basis set and compared with experimental findings. Total dipole moment of 4M40 NBPL molecule is approximately two times greater than that of urea and first order hyperpolarizability is 41 times greater than that of urea. The calculated first order hyperpolarizability for 4M40 NBPL (15.589  1030 esu) gives information about it’s for NLO applications. The difference in HOMO and LUMO energy supports the interaction of charge transfer within the molecule. The MEP map shows that the negative potential sites are around oxygen atoms as well as the positive potential sites are

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