View of Molecular Dynamic Simulations, Geometrical, and Vibrational Spectral studies of α,α,ά,ά Tetra bromo-m-Xylene

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Annals of R.S.C.B., ISSN:1583-6258, Vol. 25, Issue 6, 2021, Pages. 10294 - 10310 Received 25 April 2021; Accepted 08 May 2021. 10294

Molecular Dynamic Simulations, Geometrical, and Vibrational Spectral studies of α,α,ά,άTetrabromo-m-Xylene

C. Uma Devi ^a, B. Jayasutha^a*,M.Arivazhagan^b

aPG and Research Department of Physics, H.H The Rajah’s college, Affiliated to Bharathidasan University, Pudukkottai, Tamilnadu, India

bPG and Research Department of Physics, Government Arts college Affiliated to Bharathidasan University, Tiruchirappalli, India

E-mail address: [email protected] ABSTRACT

Density functional theory (DFT) approach has become one of the most cost- effective means to investigate the molecular structure and vibrational spectra are finding widespread use in the applications related to biological systems. Investigations (experimental and calculated) on the molecular structure, and charactistics of α,α,ά,ά tetra bromo-m-xylene are reported in this work. The structure of the molecule was optimized and structural characteristics were determined by DFT using the B3LYP method with 6-311+ G (d, p) and 6- 311++G (d, p) basis sets. The detailed vibrational assignments were made on the basis of potential energy distribution. A good coherence between the observed and calculated spectra was achieved. Besides, the HOMO- LUMO, Mulliken analysis and Non-linear optical effects were performed. In this review, the present xylene derivatives for spectral and quantum chemical calculations are also discussed.

KEY WORDS: FT-IR, FT-Raman, B3LYP, HOMO-LUMO, NLO

1. INTRODUCTION

Xylene can be found in three forms: Meta-xylene (m-xylene), Ortho -xylene (o-xylene)

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http://annalsofrscb.ro 10295

methyl groups substituted in benzene at various positions. The xylene is used as a cleaning agent and paint thinner. Small amounts of xylene are also present in airplane fuel and gasoline.

m-xylene, used as a thermally stable aramid fibers. It is used as thinners and solvents in paints, varnishes, adhesives and inks [1].It is a major petrochemical produced by the carbonization of coal in the manufacturing of coke fuel [2]. The p-xylene have intensive health impacts associated with cardiovascular or blood toxicity, developmental toxicity, gastro intestinal or liver toxicity, immune toxicity, Neurotoxicity, respiratory toxicity and skin sensitivity [3]. M- xylene also used as varnish solvent in varnish and wood stains industries dyes, organic synthesis, Insecticide and aviation fuel. The bromine compounds are the main key of manufacturing such pharmaceutical drug. It is also used in many areas such as agricultural chemicals, dyestuffs and chemical intermediates [4]. Though the present compound has rich pharmaceutical and industrial impact, same of the physical and chemical properties related to its pharmaceutical importance of α,α,ά, ά, Tetra bromo-m-Xylene(4αTBX)due to its bromination, extensive experimental and theoretical quantum chemicals studies were carried out to obtain a complete consistent and precise vibrational study and structural characteristics of the compound. The assignments of band in the vibrational spectra of molecule are an essential step in the application of vibrational spectroscopy for solving various structural chemical problems. In the present study, the detailed vibrational analysis of 4αTBX was performed by combining the experimental and theoretical information using density functional theory (DFT).

In the framework of DFT approach, different exchange and correlation functional are routinely used. Among these B3LYP combination is the most used since it proved its ability in reproducing various molecular properties, including vibrational spectra. The combined use of B3LYP functional and standard basis sets 6-311+G (d, p) and 6-311++G(d, p) provide an excellent agreement between accuracy and computational efficiency of vibrational spectra for large and medium size molecules. The aim of this work is to check the performance of B3LYP density functional force field of 4αTBX with the use of the standard 6-311+G (d, p)and 6- 311++G(d, p) basis sets. The HOMO-LUMO and Mulliken analysis have been computed with same level of calculations to get charge transfer information of the molecule.

2. EXPERIMENTAL DETAILS

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The compound under investigation namely 4αTBX is purchased from sigma-Aldrich chemicals, U.S.A., which is of spectroscopic grade and hence used for recording the spectra as such without any further purification. The FTIR spectrum of the compound were recorded in the range of 4000-400cm⁻¹using a BRUKER IFS-66V FTIR spectrometer equipped with a cooled MCT detector, a KBR beam splitter and a global arc source. The spectral resolution is

±1 cm⁻¹.

The FT-Raman spectrum of the title compound have been recorded in the stokes region (3500-50cm⁻¹) on a computer interfaced BRUKER IFS model interferometer equipped with FRA-106 FT-Raman accessory using Nd: YAG laser source operating at 1.064nm excitation wavelength line width with 200mW power. The reported wave numbers are expected to be accurate within ±1 cm⁻¹.

3. COMPUTATIONAL DETAILS

The molecular structure optimization of the title molecule and corresponding vibrational frequencies were performed using DFT with Becke-3-Lee-Yang-Parr (B3LYP) combined with 6-311+G(d, p) and 6-311++G(d, p) basis sets using GAUSSIAN09W program package. Initial geometry generated from the standard geometrical parameters was minimized without any constraint in the potential energy surface at B3LYP level, adopting the standard6- 311++G (d, p) basic set. This geometry was then re-optimized again at DFT level employing the Becke 3LYP keyword, which invokes Becke’s three-Parameter hybrid method using the correlation function of Lee et.al [5 ] .implemented with the same basic set. Vibrational bonds were assigned by visual inspection of the vibrations using both the frequency sequence and the intensity pattern and by comparison with other studies. The calculated vibrational frequencies were compared with experimental frequencies were also analyzed in detail. The calculated vibrations frequencies obtained by quantum chemical calculations are typically larger than their experimental details and they have to be scaled by empirical scaling factors B3LYP using MOLVIB 7.0 version written by Tomsundius [6].These scaling factors depend on both the method and basis sets and they are determined and experimental frequencies [7].

The optimized geometrical parameters, fundamental vibrational frequencies, Atomic

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calculated [8-16]. By combining the results of the GAUSSVIEW [17] program with symmetry consideration vibrational frequency assignment were made with a high degree of accuracy.

However, the defined coordinates forms complete set and matches quite well with motions were observed using the Gauss View program.

4. RESULT AND DISCUSSIONS 4.1Molecular geometry

The Optimized molecular structure has been obtained from Gaussian 09W Program.

The title molecule 4αTBX belongs to Cs point group symmetry. In the benzene base, four hydrogen atoms of two methyl groups were replaced by bromine atoms (tetra substitution) were connected in meta positions. The optimization of geometry was achieved by DFT model theories, the zero point vibrational energy of the compound at B3LYP/6-311++G(d, p)and 6- 311+G(d, p) were 73.30 and 73.44 kcal/mol respectively. The benzene of the title molecular structure was much fractured multiply by methyl groups and tetra addition of Br atoms. The most important feature that has greater influence upon determining molecular parameters found to be bond angle (BA) and dihedral angle (DA).The title molecule 4αTBX contained exactly 18 bond lengths, 30 bond angles and 36 dihedral angles. The complete geometry of the title molecule was shown in Fig.1. In most of the cases, the physical and chemical properties of substitutional groups and atoms were dominated on the substituent and the entire properties are driven through the ligand properties. So the altered chemical properties of the brominated xylene enable the pharmaceutical use. The optimized structure of 4αTBX indicates that the inclusion of methoxy groups and bromine atom known for their strong electron-donating and electron withdrawing nature, respectively. This is the cause for enlarge in bond length of C7- BR15 (1.968 and 2.012 Å by lower and higher basis sets, respectively). The carbon and hydrogen atoms are bonded with the σ-bond in benzene [18, 19]. The substitution of methoxy groups and bromine atom for hydrogen changes the electron density. From the bond lengths, bond angles and dihedrals angles are given in Table.1, the benzene rings seems to be indistinct due to the substituent’s and is differing from the angle of 120° . For bromine atom, at third position of the benzene ring, the angles C1-C2-C3 are found as

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Fig.1: Molecular structure of α,α,ά,ά tetra bromo-m-xylene along with numbering of atoms

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Table.1: Optimized geometrical structural parameters of α,α,ά,ά tetra bromo-m-xylene obtained by density functional calculations

Bond Length

Values(Å)

Bond Angle

Values(°)

Dihedral Angle

Values(°)

B3LYP B3LYP B3LYP B3LYP B3LYP B3LYP

6-311+G(d,p) 6-311++G(d,p) 6-311+G(d,p) 6-311++ G(d,p) 6-311+G (d,p) 6-311++G(d,p)

C1-C2 1.394 1.397 C2-C1-C6 119.4 119.6 C6-C1-C2-C3 -0.013 -0.005

C1-C6 1.401 1.404 C2-C1-C7 122.0 120.5 C6-C1-C2-H8 -180.0 179.9

C1-C7 1.492 1.490 C6-C1-C7 118.5 119.8 C7-C1-C2-C3 179.9 -179.9

C2-C3 1.394 1.397 C1-C2-C3 120.6 120.5 C 7-C1-C2-H8 0.007 0.008

C2-H8 1.085 1.080 C1-C2-H8 119.6 119.7 C2-C1-C6-C5 0.004 0.004

C3-C4 1.401 1.404 C3-C2-H8 119.6 119.7 C2-C1-C6-H12 -179.9 -179.9

C3-C9 1.492 1.490 C2-C3-C4 119.4 119.6 C7-C1-C6-C5 179.9 179.9

C4-C5 1.395 1.394 C2-C3-C9 122.0 120.5 C7-C1-C6-H12 -0.005 -0.009

C4-C10 1.086 1.082 C4-C3-C9 118.5 119.8 C2-C1-C7-H13 -179.9 -179.9

C5-C6 1.395 1.394 C3-C4-C5 120.2 120.1 C2-C1-C7-BR14 61.09 62.41

C5-H11 1.085 1.081 C3-C4-H10 119.8 119.9 C2-C1C7-BR15 -61.10 -62.37

C6-H12 1.086 1.082 C5-C4-H10 119.8 119.9 C6-C1-C7-H13 0.003 0.032

C7-H13 1.085 1.079 C4-C5-C6 120.0 120.0 C6-C1-C7-BR14 -118.8 -117.5

C7-BR14 1.968 2.012 C4-C5-H11 119.9 120.0 C6-C1-C7-BR15 118.8 117.6

C7-BR15 1.968 2.012 C6-C5-H11 119.9 120.1 C1-C2-C3-C4 0.021 0.003

C9-H16 1.968 2.012 C1-C6-C5 120.2 119.9 C1-C2-C3-C9 179.9 179.9

C9-H17 1.968 2.012 C1-C6-H12 119.8 119.9 H8-C2-C3-C4 -179.9 -179.9

C9-H18 1.085 1.079 C5-C6-H12 119.8 113.4 H8-C2-C3-C9 -0.019 -0.007

C1-C7-H13 112.2 111.7 C2-C3-C4-C5 -0.028 -0.009

C1-C7-BR14 112.5 111.7 C2-C3-C4-H10 179.9 179.9

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C1-C7-BR15 112.5 105.3 C9-C3-C4-C5 -179.9 -179.9

H13-C7-

BR14 104.5 105.3 C9-C3-C4-H10 0.016 0.008

H13-C7-B15 104.5 108.8 C2-C3-C9-BR16 -61.09 -62.43

BR14-C7-

BR15 109.8 111.7 C2-C3-C9-BR17 61.10 62.35

C3-C9-

BR116 112.5 112.5 C2-C3-C9-H18 -179.9 179.9

C3-C9-BR17 112.5 112.5 C4-C3-C9-BR16 118.8 117.5

C3-C9-H18 112.2 112.2 C4-C3-C9-BR17 -118.8 -117.6

BR16-C9-

B17 109.8 109.8 C4-C3-C9-H18 -0.022 -0.045

BR17-C9-

H18 104.5 104.5 C4-C3-C9-C6 0.012 0.000

C3-C4-C5-H11 -179.9 -179.9

H10-C4-C5-C6 -179.9 180.00

H10-C4-C5-H11 -0.004 -0.001

C4-C5-C6-C1 -0.004 -0.002

C4-C5-C6-H12 179.9 -180.0

H11-C5-C6-C1 -179.9 179.9

H11-C5-C6-H12 0.004 -0.001

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120.6 and the angles C3-C4-C5, and C2-C1-C7 are calculated as 120.2 and 122.0 respectively.

4.2 Vibrational Assignments

The observed and calculated vibrational frequencies along with assignments have been summarized in Table.2. The observed infrared and Raman spectra of title compound were presented in Fig.2 and Fig.3, which is convenient to discuss the vibrational spectra of the title molecule as described below. The molecule belongs to Cs point group symmetry which contains 18 atoms in different planes, so it has 48 normal vibrational modes out of that fundamental vibrations of the present molecule are distributed as 33 in plane vibrations denoted by A’ species and 15 out of plane vibrations denoted by A” species, i.e., vib=33A’+15A֞ The observed FT-TR and FT-Raman frequencies and calculated fundamentals at B3LYP with 6-311++G(d, p) and 6-31+G(d, p) have been presented in Table.2 and were displayed as Fig.2 and Fig.3 respectively. Comparison of calculated frequencies with the experimental values reveal the over estimation of the calculated vibrational modes due to the neglect of a harmonicity in real system.

C-H vibrations

Generally, in aromatic benzene and its related derivatives, the C-H stretching vibrations are observed in the appropriate region of 3000-3100cm^-1[20]. But due to the substitutional effect. The observed range is fluctuated [21].The title molecule consists of two methyl groups.

The compound of this study was the bromine and methyl substituted benzene derivative where the aromatic C-H vibrations, were observed with medium and strong intensity at 2900cm^-1 and 2972 cm^-1in IR and Raman spectra respectively.

The C-H in-plane bending vibrations are expected to occur as a number of strong to weak intensity bands in the region 1000-1300cm^-1 [22 ]. In the present work the C-H stretching vibrations are observed at 3090,3030,3010,2940,2920cm^-1 in FT-IR spectrum, where as in the FT Raman spectrum, it is found at 2900,2942cm^-1. All the six stretching vibrations are within the expected range. The C-H in-plane bending vibrations and out-of-bending vibrations are normally expected in the region 1000-1300cm^-1and 750-1000 cm^-1respectively in the aromatic compounds.

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Fig.2: FTIR spectrum of α,α,ά, ά tetra bromo-m-xylene

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Fig.3: FT-Raman spectrum of α,α,ά,ά tetra bromo-m-xylene

For the title molecule the frequencies found at 1180, 1175, 1015cm^-1 and 1160, 1135cm^-1are assigned to C-H in-plane bending vibrations and the bands observed at 850,848,845,660,575 cm^-1and 790,530 cm^-1 are designated to C-H out-of-plane bending vibrations. In this work all the assigned vibrations are not affected by the substitution in the ring and are good agreement with theoretically calculated values.

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C=C and C-C Vibrations

The C-C stretching vibrations in the aromatic ring are generally observed at 1600 – 1460 cm^-1[23] in which two types of vibrations C=C and C-C are found. In the present case the phenyl ring C=C stretching vibrations were observed at 1605,1560,1550 , 1410,1390,and 1330cm^-1in IR spectrum and Raman bands at 1450,1290cm^-1have been assigned to C-C stretching modes of 4αTBX. The observed three vibrations were found in the expected range and no more in libation taking place in the π bonds of the ring.

Similarly, the stretching vibrations of C-C are normally excepted in the range 1450- 1360 cm^-1.the in-plane and out of plane ring breathing CCC vibrations are occurred one below 800cm^-1[24 ]. The CCC in- plane and out- of-plane vibrations of the molecule are found at 960,850,430 in IR spectrum and Raman bands 1000,980,960,850,450,445,350,310 cm^-1 respectively. The observed vibrations are very much below the expected region. Thus, it was concluded that the CCC bending vibrations were affected much due to the loading of Br atoms C-Br vibrations

The present studies of four hydrogens of two methyl groups were strongly replaced by Br atoms. Normally, the strong characteristic absorption due to the C-Br stretching vibration for organic bromide was found in the region 650-485 cm^-1[26] .In accordance with the literature. Four very strong bands observed in the IR and Raman spectra at 540, 515 , 480cm^-

1 and 530 cm^-1 The C-Br in plane and out-of-plane bending modes of 4αTBX have been identified and listed in Table 2 .

5. FRONTIER MOLECULAR ANALYSIS

The electronic reconfiguration and electronic excitations in frontier molecular orbitals are very much useful for studying the electric and optical properties of the organic molecules.

The stabilization of the bonding and destabilization of the anti bonding of molecular orbital

Table.2: The observed (FT-IR and FT-Raman) and calculated (unscaled and scaled) frequencies, and assignments of α,α,ά,ά tetra bromo-m-xylene using B3LYP with 6-311+G(d,p) and 6-31++G(d,p)basis set

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SI.N o

Symmetr y Species

(Cs)

Vibrational Observed

Frequency (cm^-1)

B3LYP/6- 311++G(d,p)

B3LYP/6- 311+G(d,p)

Assignment s with TED(%) FTI

R

FT Rama

n

Unscale d

Scale d

Unscale

d Scaled

1. A 3090 - 3211 3098 3221 3095 νC-H(98)

2. A 3030 - 3206 3035 3209 3020 νC –H(99)

3. A 3010 - 3192 3015 3191 3007 νC-H(99)

4. A 2970 2972 3191 2975 3188 2968 νC-H(97)

5. A 2940 - 3189 2944 3186 2938 νC-H(98)

6. A - 2900 3184 2905 3183 2902 νC-H(97)

7. A 1605 - 1658 1608 1656 1603 νC=C(87)

8. A 1560 - 1632 1565 1632 1562 νC=C(87)

9. A 1550 - 1519 1555 1517 1552 νC=C(87)

10. A 1450 1450 1484 1455 1486 1452 νC-C(85)

11. A 1410 - 1398 1416 1369 1412 νC-C(87)

12. A 1390 - 1347 1395 1344 1392 νC-C(87)

13. A 1330 - 1303 1335 1302 1332 νC-C(85)

14. A - 1290 1231 1295 1242 1292 νC-C(87)

15. A - 1270 1218 1280 1230 1274 bC-H(71)

16. A 1180 - 1176 1185 1204 1182 bC-H(72)

17 A 1175 - 1197 1178 1199 1176 bC-H(71)

18. A - 1160 1195 1165 1198 1162 bC-H(72)

19. A - 1135 1171 1139 1167 1137 bC-H(71)

20. A 1015 - 1117 1019 1124 1017 bC-H(72)

21. A - 1000 1012 1005 1012 1002 Rsymd(70)

22. A - 980 983 990 975 982 Rasymd(70)

23. A 960 - 980 955 979 952 Rtrigd(78)

24. A - 930 923 928 925 932 bcc(77)

25. A 850 - 901 856 878 852 bcc(76)

26. A 848 - 782 852 814 846 ωC-H(65)

27 A 845 - 781 850 789 844 ωC-H(65)

28. A - 790 666 795 732 792 ωC-H(65)

29. A 750 - 646 756 688 753 ωC-H(65)

30. A 660 - 632 666 687 662 ωC-H(65)

31 A 575 - 619 576 631 573 ωC-H(65)

32 A 540 - 585 546 603 543 νC-BR(86)

33 A - 530 578 539 588 532 νC-BR(87)

34 A 515 - 570 520 573 517 νC-BR(87)

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35 A 480 - 515 487 516 482 νC-BR(87)

36 A - 450 425 453 447 448 tRtrigd(57)

37 A - 445 302 449 304 442 tRsymd(58)

38 A 430 - 267 437 269 432 tRsymd(56)

39 A - 420 259 428 245 423 bCBR(66)

40 A 390 390 251 396 235 393 bCBR(77)

41 A - 350 195 360 182 355 bCC(65)

42 A - 310 153 318 150 314 bCC(65)

43 A - 280 142 288 147 283 bC-BR(76)

44 A - 240 92 248 72 243 bC-BR(76)

45 A - 220 80 226 69 222 ωC-BR(56)

46 A - 200 54 210 59 205 ωC-BR(54)

47 A 180 - 31 188 17 183 ωC-BR(55)

48 A 150 - 27 158 13 152 ωC-BR(56)

.

can be made by the overlapping of molecular orbitals. The stabilization of the bonding molecular orbital and destabilization of the anti bonding can increases when overlap of two orbitals increases [27].

In molecular interaction, there are the two important orbitals that interact with each other. One is the highest energy occupied molecular orbital is called HOMO represents the ability to donate an electron. The other one is the lowest energy unoccupied molecular orbital is called LUMO as an electron acceptor. These orbitals are also called the frontier orbitals. The interaction between them is much stable and is called filled empty interaction. When the two

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region between two nuclei. The molecular orbital resulting from in phase interaction is defined as the bonding orbital which has lower energy than the original atomic orbital. The out of phase interaction forms the anti bonding molecular orbital.

The 3D plots of the frontier orbitals, HOMO and LUMO for present molecule are in gas, shown in figure. According to such figure, the HUMO is mainly localized by a charge distribution connects the carbon and hydrogen bond interaction taking place. From this observation, it is clear that, the in and out of phase interaction are present in HOMO and LUMO respectively. The HOMO-LUMO transition implies an electron density transferred within the molecule. The HOMO-LUMO energy gap of4αTBX was calculated at the DFT (B3LYP)/6- 311++G (d, p) levels and reveals that the energy gap reflects the chemical activity of the molecule. The HOMO and LUMO energy are -9.5424eV and 1.0117 eV in gas phase. Energy difference between HOMO and LUMO orbital is called as energy gap (Kubo gap) that is an important stability for structures. The calculated energy gap is 8.53eV, show the medium energy gap and reflect the high electrical activity of the molecule.

6. MULLIKEN ANAYLSIS

The reactive atomic charges [28] play an important role in the application of quantum chemical calculation to molecular system. Because of atomic charges affects dipole moment, polaraisability, electronic structure and more properties of molecular system.

LUMO ELUMO = 1.011742 eV

Energy gap E = 8.5307eV LUMO PLOT (First excited state)

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Fig.4: Frontier molecular orbitals and their energies of α,α,ά,ά tetra bromo-m-xylene

The corresponding Mulliken’s plot title compounds using B3LYP with 6-311++G (d, p) and 6-311+G(d,p) basis sets are shown in Fig 5.For 4αTBX molecule the atomic charge on C4, C5, C6, and BR atoms are negative where as the remaining atoms are positively charged.

Due to strong negative charges are accommodate higher positive charge and become more acidic .The negative values on atoms in the aromatic ring leads to a redistribution of electron density. For instance, atomic charge has been used to describe the processes of electro negativity equalization and charge transfer in chemical reactions [29].

7. NON-LINEAR OPTICAL (NLO) EFFECTS

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In the recent trends, a large number research of new materials exhibiting efficient NLO features has been of great interest because of potential applications as modern communication technology, telecommunication and optical signal Processing [30].Non-linear

optical (NLO) effects arise from the interactions of electromagnetic fields in various media to produce new fields altered in phase, frequency, amplitude or other propagation characteristics from the incident fields. The significance of the polarizability and the first hyper polarizability of molecular systems is dependent on the efficiency of electronic communication between acceptor and the donor groups as that will be the key of intra molecular charge transfer mechanism. The acceptor and donor groups have an important role in the polarizability and first hyperpolarizability measured of the NLO activity of the molecular system is associated with the resulting from the electron cloud movement through TT-Conjugated frame work from electron donor to electron acceptor groups [31]

The first hyper polarizability (0) of 4αTBX are calculated using the B2LYP/6-311++G (d,p) basis set, based on the finite field approach. In the presence of an applied electric field, the energy of a system is a function of the electric field. The first hyperpoarizability 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 due to the klein man symmetry. It can be given in the lower tetrahedral.

The first hyper polarizability (0) using the x, y, z components they are defined as follows

x =

(

^^xxx⁺^^xyy⁺^^xzz

)

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Fig. 5

:Mulliken plot by B3LYP with 6-311++G(d, p) and 6-311+G(d,p) basis set of α,α,ά,ά tetra bromo-m-xylene

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Table.3 Mulliken atomic charge of α,α,ά,άtetra bromo-m-xylene performed by density functional calculations

y =

(

yyy+xyy+yzz

)

Atoms

Mulliken Charges B3LYP/

6-311+G (d, p)

B3LYP/

6-311++G (d, p)

C1 0.093053 0.244496

C2 0.079397 0.505183

C3 0.093087 0.244650

C4 -0.100523 -0.591250

C5 -0.165029 -0.113025

C6 -0.100497 -0.591306

C7 -0.887379 -0.267672

H8 0.200138 0.166176

C9 -0.887368 -0.267764

H10 0.173343 0.131070

H11 0.162813 0.137850

H12 0.173344 0.131069

H13 0.299014 0.196529

BR14 0.141904 -.0.30634

BR15 0.141897 -0.030625

BR16 0.141844 -0.030688

BR17 0.141950 -0.030593

H18 0.299013 0.196534

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z =

(

zzz +xxz+yzz

)

0 = _x² + _y²+ _z²^{1/ 2}

The calculated first hyper polarizability (0) values of 4αTBX are 3.331810^-30esu. Urea is one of the prototypical molecules used in the study of the NLO properties of molecular systems.

Therefore it was used frequently as a threshold value for comparative purposes. The calculated value of 0 for the title compound is relatively higher than that of Urea. Hence, from the results of the present molecule 4αTBX refined that it supports in the development of new effective material for NLO applications.

CONCLUSION

The vibrational frequencies analysis by B3LYP method agrees satisfactorily with experimental results, assignments of all the fundamental vibrational modes of 4αTBX were examined and proposed. Therefore, the assigned made at higher level of the theory with basis set reasonable deviations from the experimental values, seems to be correct. HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule which are responsible for the bioactivity property of the molecule. FTIR and FT- Raman spectra of 4αTBX are recorded and the detailed vibrational assignments were obtained.

The Mulliken charge calculations have identified the negatively and positively charged atoms in the molecule, in order to stabilize the structure. The NLO activity of the present compound was also confirmed by the predicted large value of first order hyperpolarizability. The result of this study will help researchers to design and synthesis new materials.

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