Synthesis and spectroscopical study of rhodanine derivative using DFT approaches

Accepted Manuscript Synthesis and spectroscopical study of rhodanine derivative using DFT approaches R. Anbarasan, A. Dhandapani, S. Manivarman, S. Subashchandrabose, H. Saleem PII: DOI: Reference:

S1386-1425(15)00271-1 http://dx.doi.org/10.1016/j.saa.2015.02.097 SAA 13399

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

6 November 2014 28 January 2015 19 February 2015

Please cite this article as: R. Anbarasan, A. Dhandapani, S. Manivarman, S. Subashchandrabose, H. Saleem, Synthesis and spectroscopical study of rhodanine derivative using DFT approaches, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.02.097

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Synthesis and spectroscopical study of Rhodanine derivative using DFT approaches R. Anbarasana, A. Dhandapania, S. Manivarmana* S. Subashchandraboseb, H.Saleemc a

Post Graduate and Research department of chemistry, Government Arts College, C-Mutlur, Chidambaram-608102, Tamil Nadu, India. b Centre for Research & Development, PRIST University, Vallam, Thanjavur-613403, Tamil Nadu, India. c Department of Physics, Annamalai University, Annamalai nagar-608002, Chidambaram, Tamil Nadu, India.

Abstract The optimized molecular structure, vibrational frequencies, corresponding vibrational assignments of (E)-5-Benzylidine-2-thioxothiazolidine-4-one (E5BTTO) have been investigated experimentally and theoretically based on Density Functional Theory (DFT) approach. The FTRaman and FT-IR spectra of E5BTTO were recorded in solid phase. Theoretical calculations were performed at the DFT level using the gaussian03 program. The experimental bands were assigned and characterized on the basis of the scaled theoretical wavenumber by their Total Energy Distribution (TED). The results of the calculation were applied to simulate infrared and raman spectra of the title compound which showed good agreement with the observed spectra. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Stability arising from Hyperconjugative interactions leading to its NLO activity and charge delocalization were analyzed using Natural Bond Orbital (NBO) analysis.

Keywords: Rhodanine; TED; NLO; NBO; HOMO-LUMO; *Corresponding author

E-mail : [email protected] (Dr. S. Manivarman). : [email protected] (Dr. S. Subashchandrabose) Mobile : +91 9842483139.

1

1. INTRODUCTION Rhodanine is a five-membered heterocyclic ring with diverse applications particularly in biochemistry, medicinal chemistry, photochemistry, industry and coordination chemistry [1]. Rhodanine represents a privileged scaffold in drug discovery [2] and its derivatives, which are common reagents in analytical and coordination chemistry, attract special interest in medicine, biochemistry, and photochemistry. Rhodanine derivatives modified at the methylene group (ylidenerhodanines) possess antibacterial [3], antifungal [4-6], antidiabetic [7], and anticancer activity [8]. This accounts for the use of rhodanine in the pharmaceutical industry. Chemical properties of rhodanine and its derivatives are of interest due to coordination capacity and their use as metal extracting agents and as analytical reagents [9, 10]. Azo compounds based on rhodanine were synthesized as potential medical preparations [11–14]. The rhodanine moiety has been synthesized by various methods such as addition of isothiocyanate to mercaptoacetic acid followed by acid catalyzed cyclisation, or the reaction of ammonia or primary amines with carbon disulfide and chloroacetic acid in the presence of bases [15, 16]. Recently, substituted rhodanines were investigated for tau aggregation inhibitor properties [17]. Rhodanines are classified as non-mutagenic [18] and a long-term study on the clinical effects of the rhodanine-based Epalrestat as an anti-diabetic, demonstrated that it is well tolerated [19]. Additionally, rhodanines have been designed as inhibitors of various enzymes such as bacterial β-lactamase and Mur ligases. Rhodanine derivatives were found to have marked mildew-proofing activity [20]. Arylidenerhodanines are frequently identified as potent hits in high throughput screening against various prokaryotic and eukaryotic targets. Photo physical studies for complex molecules having both a donor and an acceptor moiety separated by a πbridge are very important in optical spectroscopy and the study of intramolecular charge transfer (ICT) processes [21–23]. Recent studies have shown that this type of molecular framework is interesting for its potential in the design and synthesis of non-linear optical (NLO) materials [24, 25], due to their asymmetric charge distribution and large molecular hyperpolarizabilities. The optical absorption properties of azo dye rhodanine derivatives thin films have been studied by ElGhamaz et al. [26]. Authors identified the values of the energy band gap, Eg for derivatives were in the range1.77–2.29 eV depending on the nature of the substituent. Therefore, the synthesis of these rhodanine derivatives shows considerable interest in optical studies. The literature survey reveals that no attempt has been made so far to investigate the vibrational spectra and theoretical calculations for (E)-5-benzylidene-2-thioxothiazolidin-4-one. Hence, we set out to explore the vibrational and Non-linear optical behaviors of (E)-5benzylidene-2-thioxothiazolidin-4-one theoretically based on Density Functional Theory calculations. The aim of this work is to carry out an experimental and theoretical study on this compound with quantum chemical methods in order to better understand its structural and vibrational properties. The obtained parameters may be used to gain chemical and vibrational 2

insights into related compounds. Moreover, density functional theory (DFT), natural bond orbital (NBO) and thermodynamic property calculations were performed to analyze the energies and geometrical parameters of (E)-5-benzylidene-2-thioxothiazolidin-4-one in the gas phase as well as the magnitude of intramolecular interactions. 2. Experimental 2.1 Synthesis of (E)-5-benzylidene-2-thioxothiazolidin-4-one: An efficient synthesis of (E)-5-Benzylidine-2-thioxothiazolidine-4-one by the condensation of benzaldehyde with 2-thioxo thiazolidine-4-one in sodium acetate/acetic acid under ethanol medium at 90°C for 3 hours. After the completion of the reaction was monitored by TLC, the obtained yellow crystals are separated and dried. The crude product was purified by recrystallized with absolute ethanol. The observed melting point of the compound is 202 °C (lit. melting point 198-202 °C) [27]. The yield of the product was about 80%. The schematic diagram of synthesis is shown in Figure.1. 2.2. FT-IR and FT-Raman spectra The FT-IR spectrum of the synthesized rhodanine was measured in the 4000–400 cm−1 region at the spectral resolution of 4 cm−1 using on SHIMADZU FT-IR affinity Spectrophotometer (KBr pellet technique) made in Japan. The FT-IR spectrum was recorded in Faculty of Marine Biology, Annamalai University and only noteworthy absorption levels are listed. The FT-Raman spectrum of the title compound was recorded on BRUKER: RFS27 spectrometer operating at laser 100mW in the spectral range of 4000–50 cm−1. FT-Raman spectral measurements were carried out from Sophisticated Analytical Instrument Facility (SAIF), Indian Institute of Technology (IIT), Chennai. 3. Computational details The quantum chemical calculations of E5BTTO have been performed using the B3LYP level of theory supplemented with the standard 6-311++G(d,p) basis set, using the Gaussian 03 program. The entire calculations were performed at DFT levels on a Pentium IV/3.02 GHz personal computer using Gaussian 03W [28] program package, invoking gradient geometry optimization [28, 29]. Initial geometry generated from standard geometrical parameters was minimized without any constraint in the potential energy surface at DFT level, adopting the standard 6-311++G(d,p) basis set. The optimized structural parameters were used in the vibrational frequency calculations at the DFT level to characterize all stationary points as minima. Then, vibrationaly averaged nuclear positions of E5BTTO were used for harmonic vibrational frequency calculations resulting in IR and Raman frequencies together with intensities and Raman depolarization ratios. In this study, the DFT method (B3LYP/6311++G(d,p)) was used for the computation of molecular structure, vibrational frequencies and energies of optimized structures. The vibrational modes were assigned on the basis of TED 3

analysis using VEDA4 program [30]. It should be noted that the Gaussian 03W package able to calculate the Raman activity. The Raman activities were transformed into Raman intensities using Raint program [31] by the expression:

I i = 1 0 − 1 2 × (ν 0 − ν i ) 4 ×

1

νi

× R Ai

(1)

Where Ii is the Raman intensity, Ai is the Raman scattering activities, νi is the wavenumber of the normal modes and ν0 denotes the wavenumber of the excitation laser [32]. For meeting the requirements of both accuracy and computing economy, theoretical methods and basis sets should be considered. Density functional theory (DFT) has been proved to be extremely useful in treating electronic structure of molecules. The basis set 6-311++G(d,p) was used as an effective and economical level to study. After the most stable conformer of the title compound determined, geometry optimizations of this conformer have been performed by B3LYP method. 4. RESULTS AND DISCUSSION 4.1 Molecular Geometry (E)-5-benzylidene-2-thioxothiazolidin-4-one (E5BTTO) is subjected to geometry optimization in the ground state. The optimized structure belongs to C1 point group symmetry. The optimized molecular structure of E5BTTO is shown in Figure 2, with numbering scheme adopted in this study. The calculated geometrical parameters of E5BTTO calculated by B3LYP with 6-311++G(d,p) basis set are listed in Table 1. To the best of our knowledge there is no exact crystal data is available for this compound. Therefore, we compare the bond length and angles with related molecule. Baryshnikov et al., [33] reported the bond lengths of C−C and C−S for simple rhodanine molecule is 1.525 and 1.836 Å, respectively. In our present study, the corresponding bond lengths of C1−C2 and C2−S6 are calculated as 1.4846 and 1.7923 Å, these values are lesser than the rhodanine molecule due to the attachment of benzaldehyde carbon atom. These bonds are contracted due to wander waals contraction. The bond distance of C=S, C=O and N−H of E5BTTO is 1.7923, 1.2144 and 1.0127 Å, respectively. These bond distances are in good agreement with the 1.771, 1.213 and 1.016 Å bond distances of rhodanine ring [33]. On the other hand, the C−C bond length (C10−C12, C12−C15, C15−C17, C17−C13, C13−C11 and C11−C10) of six membered rings are relatively equal to 1.39 Å/B3LYP with some exceptions. Because in benzene, all the C-C bond lengths are equal (equal distribution of π-electrons around the benzene ring). The bond angles of S6−C3−N4, C3−N4−C1, N4−C1−C2, C1−C2−S6, C2−S6−C3, S6−C3−S7, S7−C3−N4 and N4−C1−O8 are 108.2, 120.46, 109.0, 108.9, 93.2, 125.4, 126.2 and 121.8°, respectively. These bond angles are relatively equal to simple rhodanine molecule. The bond length, bond angles of E5BTTO were listed in Table S1.

4

4.2 Vibrational assignments The aim of the vibrational analysis is to find vibrational modes connected with specific molecular structures of calculated compound. The title molecule consists of 21 atoms, which undergo 57 normal modes of vibrations. It is in agreement with C1 point group symmetry, major vibrations are active in both Raman and infrared absorption. The detailed vibrational assignment of the experimental wavenumber based on normal mode analyses and a comparison with theoretically scaled wavenumber with TED using VEDA4 program [30]. The calculated frequencies are usually higher than the corresponding experimental quantities, due to the combination of electron correlation effects and basis set deficiencies. These discrepancies overcome by applying the appropriate scaling factors; the theoretical calculations reproduce the experimental data well in agreement. Calculated Raman activities and IR intensities help us to distinguish and more precisely assign those fundamentals, which are close in frequency. The simulated and spectra of FT-IR and FT-Raman spectra are shown in Figures 3 and 4, respectively. The experimental and scaled theoretical harmonic vibrational frequencies along with the calculated Total Energy distribution values were given in Table 1. We know that ab initio HF and DFT potentials systematically overestimate the vibrational wavenumber. These discrepancies are corrected either by computing anharmonic corrections explicitly or by introducing a scaled field or by directly scaling the calculated wavenumber with a proper factor [34]. 4.2.1 N−H vibration The vibrations belonging to N−H stretching always occur in the region 3450–3250 cm−1 which is the characteristic region for ready identification of this structure [35, 36]. In this region, the bands are not affected appreciably by the nature of the substituents. In the present work, the scaled N−H stretching vibration is calculated at B3LYP/6-311++G(d,p) at 3450 cm−1 and the corresponding stretching vibration is observed as a medium band in FT-IR at 3431 cm−1(mode no.1). The stretching vibration of N−H is identified as pure mode with 100% TED values. Sert et al., have observed these modes at 3465 and 3450 cm−1 for 6-(2-methylpropyl)-4-oxo-2sulfanylidene-1,2,3,4-tetrahydropyrimidine-5-carbonitrile [37]. For the meantime, Srivastava et al., have calculated the N−H stretching vibrations at 3458 and 3456 cm−1 at B3LYP for 2-(2,4dichlorophenyl)-N-(1,3-thiazol-2-yl)acetamide [38]. Conversely, no Raman band is observed for the N−H stretching modes in the experimental spectra. The N−H in-plane bending vibrations are observed at 1393 and 1137 cm−1 from B3LYP (mode nos. 14 and 22). All of these modes are strongly coupled with the other in plane, out of plane bending and torsional vibrations. Therefore, the bending vibrations of N−H were shifted to lower wavenumber. The torsional vibration of H−N−C−C were observed at 505 cm−1 at theoretical wavenumber and its corresponding TED value is 92%. Tamer et al., reported the out of plane H−N−C−C at 607 and 532 cm−1 for B3LYP level [39]. 5

4.2.2 C=O vibration Stretching vibration of C=O group is expected to appear at 1715–1680 cm−1 [40]. Carbonyl absorptions are very sensitive and both the carbon and the oxygen atoms move during the vibration having nearly equal amplitude. Carbonyl group vibrations give rise to characteristic bands in vibrational spectra and for this reason, such bands have been subject of extensive studies [41]. Any deviation of the calculated wavenumber for this mode can be attributed to πelectron delocalization due to the conjugation or formation of hydrogen bonds [42]. In the present case the C1=O8 stretching band is observed as very strong band at 1697 cm−1 in FT-IR spectrum and 1680 cm−1 as medium band in FT-Raman spectrum are observed for corresponding mode. The theoretical wavenumber at 1680 cm−1 shows very good agreement with experimental value and TED corresponding to this vibration suggests that it is a pure mode and exactly contributing to 82%. The in-plane bending and out-of-plane bending vibrations of CO is calculated at 714, 497, 416 and 358 cm−1 (mode no’s: 36, 44, 46 and 48) correlates well with band observed at 708 and 434 cm−1 in FT-Raman and 428 cm−1 in FT-IR spectrum. 4.2.3 C=S and C-S vibrations In general, the assignment of band due to the C–S stretching vibration in different compounds is difficult in the infrared, since the band is of variable intensity and may be found over the wide region 1035–245 cm−1, whereas, C–S stretching vibration results in strong bands in Raman spectra which are normally easy to identify [43]. Xavier et al., reported that the C–S group is less polar than carbonyl links and has a considerably weaker band. In consequence, the band is not intense, and it falls at lower frequencies, where it is much more susceptible to coupling effects and identification is therefore difficult and uncertain [44]. In this study, the C3=S7 stretching vibration is observed as medium band at 1029 cm−1 in FT-Raman spectrum and the theoretical wavenumber observed at 1030 cm−1 well matches with the experimental one(mode no: 24). Its TED contribution is about 42%. Besides the stretching vibrations, the sulfur atom gives rise to bending vibrations with neighboring atoms. The C2-S6 vibrations were observed with coupled vibrations of neighboring atoms. The strong C-S stretching vibrations are observed at 949 and 648 cm−1 in B3LYP and these vibration modes are coincide with FT-IR band at 634 cm−1 (mode no’s: 33 and 38). The phenyl ring deformation vibration is observed very strongly at 810 cm−1 in FT-IR spectrum and its corresponding theoretical wavenumber assigned at 808 cm−1 from B3LYP. The rhodanine breathing mode is strongly observed at 524 cm−1 in FT-IR and as medium band at 521 cm−1 in FT-Raman, the theoretical wavenumber well coincides at 524 cm−1 from B3LYP. The C−S vibrations accompanied with phenyl ring deformation and breathing mode vibrations of rhodanine. The in-plane bending and out-of-plane bending vibrations of C−S group were also found well within the characteristic region [45, 46]. 6

4.2.4 C−N vibration The identification of C–N and C=N vibrations are a very difficult task, since the mixing of several modes are possible in the region. The C−N stretching vibration coupled with scissoring of N−H, is moderately to strongly active in the region 1300 cm−1 [47]. Saima jabeen at al., [48] reported the C−N stretching vibrations of rhodanine molecule at 1234, 1187 and 820 cm−1 in FT-IR spectrum and bands at 1230, 1176 and 878 cm−1 in FT-Raman. Ramalingam et al., [49] reported the C−N stretching vibration at 1316cm−1 and 1213cm−1 for morpholine-4ylmethylthiourea. In accordance with the above conclusion, the C−N stretching vibrations are observed at 1393 and 1230 cm−1 from theoretical wavenumber, which shows good agreement with the strong vibrational band observed at 1236 cm−1 in FT-IR spectrum. The counterpart vibration in FT-Raman observed as medium band at 1222cm−1 (mode no: 18). Subashchandrabose at al., [50] assigned the C−N out-of-plane bending vibration at 664 cm (FT-IR)/666 cm−1(FT-Raman). The in-plane and out-of plane-bending vibrations of C−N bonds are observed at 988, 743, 674, 619, 529 and 373 cm−1 in B3LYP. The band observed at 634 cm−1 in FT-IR spectrum and band observed at 708 cm−1 in FT-Raman spectrum shows good agreement with the theoretical wavenumber. The TED of C−N bending vibrations lies in the range 10-92%. −1

4.2.5 C-H vibrations In aromatic molecules, the C−H stretching vibrations appear in the range of 3100–3000 −1 cm [51]. The phenyl C−H stretching modes are typically exhibited as multiplicity of weak to moderate bands compared with the aliphatic C−H stretching [52]. The aromatic C−H stretching vibration shows a signal at 3061 cm−1 in FT-IR and bands observed at 3065 and 3015 cm−1 in FT-Raman also corresponds to the same vibration mode. The harmonic wavenumber corresponds to aromatic C−H vibrations calculated at 3110, 3067, 3057, 3045, 3037 and 2997 cm−1 (mode no’s: 2-7). Moreover, its total energy distribution value shows greater than 90%. As it is evident from Table 1, these vibrations are almost pure modes. It is well known that the aliphatic C−H stretching vibrations are observed at lower wavenumber than the ring C−H stretching vibrations. The C9−H21 stretching vibration was observed at 2997 cm−1 and is lesser than the aromatic C−H stretching vibrations. The C−H in plane bending ring vibrations normally are shown as a number of strong to weak sharp bands in the region 1300–1000 cm−1 [53, 54]. The C−H in-plane bending vibrations of the title compound are identified at 1309, 1160, 1067 and 998 cm−1 in FT-Raman spectrum and 1068 cm−1 in FT-IR spectrum, respectively. The theoretically calculated frequencies for the C−H in-plane bending vibration are calculated at 1368, 1314, 1171, 1141, 1137 and 1072 cm−1 (mode no’s: 15, 16, 20, 21, 22 and 23). The theoretically calculated wavenumber shows good agreement with the experimental values. The C−H out-of-plane bending vibrations are strongly coupled vibrations and normally observed in the region 950-809 cm−1 [55, 56]. In the present study, the C−H out-of-plane bending bands are observed at 914 and 765 cm−1/FT-IR and 851 7

cm−1/FT-Raman. The theoretically calculated wavenumber are at 960, 921, 879, 827 and 747 cm−1 (mode no’s: 28, 30, 31, 32 and 34) shows well agreement with the experimental values. 4.2.6 Ring vibrations The ring stretching vibrations are very much important in the IR spectrum of benzene derivatives because they are highly characteristic modes of the aromatic rings. Many ring vibrations are affected by the substitution to the aromatic ring of benzene derivatives. The six ring carbon atoms undergo coupled vibrations, called skeletal vibration. The ring C=C and C−C stretching vibrations, known as semicircle stretching usually occurs in the region 1400–1625 cm−1. The actual positions of these modes are determined not so much by the nature of the substituents but by the form of substitution around the ring [57, 58]. Zhang et al., reported the aromatic C=C stretching vibrations at 1488, 1436 and 1409 cm−1 for HBAH [59]. Balachandran et al., reported the FT-IR bands identified at 1595, 1583, 1571, 1476, 1452, 1418 and 1368 cm−1 and the FT-Raman bands at 1569, 1472, 1438, 1411 and 1356 cm−1 are assigned to C=C stretching vibrations of NpMBA. Based on the above literature, the C=C stretching vibration for the title compound is observed at 1589, 1435, 1296, 1190 and 1014 cm−1 in FT-IR spectrum and bands at 1592, 1570, 1441 and 1182 cm−1 in FT-Raman spectrum. These experimental bands shows good correlation with the bands observed at 1579, 1557, 1535, 1424, 1282, 1189 and 1013 cm−1 from theoretically calculated wavenumber. In our present study, the band observed at 976 and 1013 cm−1 in B3LYP theoretical wavenumber is assigned to trigonal bending and breathing mode of the phenyl ring and it shows good agreement with experimental FT-IR medium band at 1014 cm−1 (mode no: 25). It is evident from Table 1, in our present study the C−C−C in-plane bending vibrations are observed at 976, 740, 609 and 577 cm−1. The out-of-plane bending vibrations are observed at 486 and 106 cm−1 in theoretically calculated wavenumber. The torsional modes of C−C−C−C in theoretical wavenumber is observed at 674, 486, 404 and 358 cm−1. The vibration observed very strongly at 675 cm−1/FT-IR and 673 cm−1/FT-Raman shows good agreement with calculated torsional modes. The rest of the observed, calculated wavenumber and the corresponding assignment of the title molecule are shown in Table 1. 4.3 Non-Linear Optics The first hyperpolarizabilities (β0, α0 and ∆α) of (E)-5-benzylidene-2-thioxothiazolidin-4one is calculated using B3LYP/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. First hyperpolarizability is a third rank tensor that can be described by a 3x3x3 matrix. The 27 components of the 3D matrix can be reduced to 10 components due to Kleinman symmetry [60]. It can be given in the lower tetrahedral format. It is obvious that the lower part of the 3x3x3 matrix is a tetrahedral. The components of β are defined as the coefficients in the Taylor series 8

expansion of the energy in the external electric field. When the external electric field is weak and homogeneous, this expansion becomes: (2)

E = E 0 − µα Fα − 1/ 2α αβ Fα Fβ − 1/ 6 βαβγ Fα Fβ Fγ 0

Where E is the energy of the unperturbed molecules, Fα is the field at the origin, and

µα , ααβ , βαβγ

are the components of the dipole moment, polarizability and the first

hyperpolarizabilities, respectively. The total static dipole moment µ, the mean polarizability α0, the anisotropy of polarizability ∆α and the mean first hyperpolarizability β0, using the x, y, z components are defined as [61]

µ = (µx2 + µy2 + µz2 )1/ 2 α0 =

(3)

α xx + α yy + α zz

∆ α = 2 − 1 / 2  (α 

(4)

3 xx

−α

yy

)

2

+ (α

yy

−α

zz

)

2

+ (α

zz

−α

xx

)

2

+ 6 (α

2 xy

+α

2 yz

+α

2 xz

) 

1/ 2

(5) (6)

β 0 = (β x2 + β y2 + β z2 )

1/ 2

Many organic molecules, containing conjugated π electrons are characterized by large values of molecular first hyperpolarizabilities, were analyzed by means of vibrational spectroscopy [62-65]. The intra molecular charge transfer from the donor to acceptor group through a single-double bond conjugated path can induce large variations of both the molecular dipole moment and the molecular polarizability, making IR and Raman activity strong at the same time [66]. Theoretical investigation plays an important role in understanding the structure–property relationship, which is able to assist in designing novel NLO materials. It is well known that the higher values of dipole moment, molecular polarizability, and hyperpolarizability are important for more active NLO properties. The present study reveals that the π-π interaction can make larger intramolecular interaction and hence the polarizability of the molecule increases. It is evident from Table S2, the molecular dipole moment (µ), molecular polarizability and hyperpolarizability are calculated about 1.6470 (D), 0.507 and 4.414 x10-30esu, respectively. The β0 value of the title compound is twelve times greater than that of urea. 4.4 Natural bond orbital analysis

NBO analysis provides an efficient method for studying intra and intermolecular bonding and interaction among bonds and also provides a convenient basis for investigation charge transfer or conjugative interactions in molecular system. Another useful aspect of NBO 9

method is that it gives information about interactions in both filled and virtual orbital spaces that could enhance the analysis of intra and intermolecular interactions. The hyperconjugation may be given as stabilizing effect that arises from an overlap between an occupied orbital with another neighboring electron deficient orbital when these orbitals are properly orientation. This non-covalent bonding–antibonding interaction can be quantitatively described in terms of the NBO analysis, which is expressed by means of the second-order perturbation interaction energy (E(2)) [67–70]. This energy represents the estimation of the off-diagonal NBO Fock matrix elements. It can be deduced from the second-order perturbation approach [71] E

(2)

= ∆ E ij = q i

F (i, j ) 2 ε j − εi

(6)

Where, qi is the donor orbital occupancy, εi and εj are diagonal elements (orbital energies) and F(i, j) is off diagonal NBO Fock matrix elements. NBO analysis was performed by the B3LYP level of theory with 6-311++G(d,p) basis set for the molecule E5BTTO and are listed in Table 2. NBO theory allows the assignment of hybridization of atomic lone pairs and of the atoms involved in bond orbitals. These are important data in spectral interpretation as the frequency ordering is related to the bond hybrid composition. Transitions between non-bonding atomic orbitals holding unshared pair of electrons from sulfur and nitrogen to anti-bonding π orbitals shows strong delocalization occurring within the rhodanine ring. The hyperconjugative interaction energies from non-bonding N4 and S6 to anti-bonding orbitals C1−O8, C3−S7 and C2−C9, C3−S7 shows the energies of 208.03, 280.83 and 66.90, 159.49 kJ/mole, respectively, shows the charge delocalization of the rhodanine ring. The electron densities of N4 and S6 are 1.6075 and 1.7118, respectively. The intramolecular hyperconjugative interactions energies are formed by the orbital overlap between π(C−C) and π*(C−C) bond orbitals, which results intra molecular charge transfer (ICT) causing stabilization of the system. The electron density (ED) of the three conjugated double bonds of the phenyl rings (~1.631e) clearly demonstrates strong delocalization. Ravikumar et al., reported the electron density (ED) of the six conjugated double bonds of the phenyl rings (∼1.661e) clearly demonstrates strong delocalization for bis(4-nitrophenyl)carbonate [72]. The NBO analysis of donor-acceptor interactions showed that the very small resonance for LP(S6)→σ*(C1−C2), σ*(C3−N4) and σ*(C3−S7) are 7.03, 7.24 and 5.52 kJ/mole, respectively. The orbital interaction energy between π(C1−O8)→π*(C2−C9), π(C2−C9)→π*(C10−C11) and π(C10−C11)→π*(C12−C15) are 451.29, 680.23 and 836.13 kJ/mole (Table. 2). The increasing interaction energies are due to strong ICT interactions from rhodanine ring to the phenyl ring leading to the stabilization of the molecule. 4.5 Molecular electrostatic potential

Electrostatic potential maps are very useful three dimensional diagrams of molecules. To accurately analyze the charge distribution of a molecule, a very large quantity of electrostatic 10

potential energy values must be calculated. The best way to convey this data is to visually represent it, as in an electrostatic potential map. Electrostatic potential correlates with dipole moment, electronegativity, and partial charges. The Electrostatic Potential map of E5BTTO is shown in Figure 5. It provides a visual method to understand the relative polarity of a molecule. The importance of MEPs lies in the fact that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of color grading and is very useful in research of molecular structure with its physicochemical property relationship [73, 74]. MEP and electrostatic potential are useful quantities to illustrate the charge distributions of molecules and used to visualize variably charged regions of a molecule. Therefore, the charge distributions can give information about how the molecules interact with another molecule. MEP is widely used as a reactivity map displaying most probable regions for the electrophilic attack of charged point-like reagents on organic molecules [75]. The Molecular Electrostatic Potential (MEP) is the most useful electrostatic property to study the relation between structure and activity. At any given point r(x,y,z) in the vicinity of a molecule, the electrostatic potential, V(r) is defined in terms of the interaction energy between the electrical charge generated from the molecule of electrons and nuclei and a positive test charge (a proton) located at r. The molecular electrostatic potential (MEP) is related to the electronic density and a very useful descriptor for determining sites for electrophilic attack and nucleophilic reactions as well as hydrogen-bonding interactions [76, 77]. The MEP maps of the title molecule are shown in Figure 5, whereas electrophilic attack is presented by negative (red) regions, nucleophilic reactivity is shown by the positive (blue) regions of MEP map of E5BTTO. As seen from the Figure 5, the electrophilic region (red) is around the phenyl ring and in ketone group of the rhodanine. Whereas the nucleophilic region (blue) is localized in N−H group of the rhodanine ring. The neutral sites of the molecule are indicated by the green region. This predicted the most reactive site for both electrophilic and nucleophilic attack.

4.6 Mulliken atomic charges

The Mulliken charge is directly related to the vibrational properties of the molecule, and quantifies how the electronic structure changes under atomic displacement; it is therefore related directly to the chemical bonds present in the molecule. It affects dipole moment, polarizability, electronic structure and more properties of molecular systems. Mulliken atomic charge calculation has an important role in the application of quantum chemical calculation to molecular system [78]. The Mulliken population analysis in E5BTTO molecule was calculated using B3LYP level with 6-311++G(d,p) basis set. The Mulliken charge distribution structure of E5BTTO is shown in Figure 6.

11

The Mulliken charges for the title compound are listed in Table 3. The charge distribution of E5BTTO shows that the carbon atoms attached with hydrogen atoms are negative whereas the other carbon atoms are positive. All hydrogen atoms are positively charged. The S, N and O atoms shows negative charge and these represents the hydrogen bond acceptors. The hydrogen atom attached to the nitrogen atom show higher positive charge than the other hydrogen atoms. The Mulliken charge distribution shows the most negative charge observed at C12. The most positive charge observed at C10 for the title molecule. 4.7 Frontier molecular orbital analysis

The highest occupied molecular orbitals (HOMOs) and the lowest–lying unoccupied molecular orbitals (LUMOs) are named as frontier molecular orbitals (FMOs). The FMOs play an important role in the optical and electric properties, as well as in quantum chemistry and UV– Vis. spectra [79]. The HOMO represents the ability to donate an electron, LUMO as an electron acceptor represents the ability to obtain an electron. The energy gap between HOMO and LUMO determines the kinetic stability, chemical reactivity and optical polarizability and chemical hardness– softness of a molecule [80]. Considering the chemical hardness, large HOMO–LUMO gap means a hard molecule and small HOMO–LUMO gap means a soft molecule. One can also relate the stability of the molecule to hardness, which means that the molecule with least HOMO–LUMO gap means it is more reactive. The frontier molecular orbital analysis for the title molecule was calculated at the B3LYP/6-311++G(d,p) level, which reveals that the energy gap reflects the chemical activity of the molecule. The atomic orbital compositions of the frontier molecular orbitals are sketched in Figure 7. The eigen values of LUMO and HOMO and their energy gap reflect the chemical activity of the molecule. The HOMO is located over mainly in sulphur atom in rhodanine ring and in carbon atoms in phenyl ring and the energy of HOMO level is 6.4712eV. The LUMO is located all over the molecule and the energy is 3.0273eV. The energy gap of the title molecule is 3.4439eV. HOMO LUMO ∆E

= = =

6.4712eV 3.0273eV 3.4439eV

The calculated self-consistent field (SCF) energy of E5BTTO is -1311.47773452 kJ mol . In addition, the energy gap of HOMO−1→LUMO+1 is 5.082 eV and the HOMO−2→LUMO+2 is 7.4625 eV, respectively. Moreover, the lower in the HOMO and LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule. The corresponding energy gap values are listed in Table 4. −1

12

4.8 Thermodynamic properties

The statistical thermo chemical analysis of E5BTTO is carried out considering the molecule to be at room temperature of 298.15 K and one atmospheric pressure. The thermodynamic quantities such as entropy Stotal, heat capacity at constant pressure (Cp) total, enthalpy (H–E)/T, Gibb’s free energy (G–E)/T and internal thermal energy (E) for various ranges (100–1000 K) of temperatures are determined and these results are presented in the Table 5. From Table 5, it can be observed that these thermodynamic functions are increasing with temperature ranging from 100 to 1000 K due to the fact that the molecular vibrational intensities increase with temperature [81]. The variation of the thermodynamic functions such as entropy, heat capacity, internal energy, enthalpy, and Gibb’s free energy with temperature are graphically represented in Figure 8. All the thermodynamic data supply helpful information for the further study on the E5TTO. They can be used to compute the other thermodynamic energies according to relationships of thermodynamic functions and estimate directions of chemical reactions according to the second law of thermodynamics in thermochemical field.

5. CONCLUSION

This work presents the experimental and theoretical vibrational IR and Raman spectra of the title compound. All the vibrational bands, which are observed in the FT-IR and FT-Raman spectra of the title compound, are completely assigned for the first time with the help of TED. The observed FT-IR and FT-Raman spectral values were agree well with the calculated wavenumber. The frontier molecular orbitals have been visualized and the HOMO–LUMO energy gap (3.4439 eV) has been calculated. First hyperpolarizablity analysis reveals that the title compound possesses considerable NLO properties. The NBO analysis have been made with which the stability and intra molecular interactions have been interpreted and the transactions give stabilization to the structure have been identified by second order perturbation energy calculations. The Mulliken atomic charges of the present molecule has been calculated and also plotted. Finally, the thermodynamic properties of the title compound have been calculated at different temperatures and are plotted.

13

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18

Figure 1. The schematic diagram of synthesis of (E)-5-benzylidene-2-thioxothiazolidin-4-one

Figure 2. Optimized structure of (E)-5-benzylidene-2-thioxothiazolidin-4-one (E5BTTO)

20

Figure 3. The combined experimental and theoretical spectra of E5BTTO.

21

Figure 4. The combined experimental and theoretical spectra of E5BTTO

22

Figure 5. 3D mapped MEP surface of E5BTTO.

-9.157e-2

9.157e-2

23

1.5

Mulliken/B3LYP 1.0

0.0

C1 C2 C3 N4 H5 S6 S7 O8 C9 C10 C11 C12 C13 H14 C15 H16 C17 H18 H19 H20 H21

Atomic Charge

0.5

-0.5

Atoms -1.0

Figure 6. The Mulliken atomic charges of E5BTTO

24

HOMO = 6.4712

∆E= 3.4439 eV

LUMO = 3.0273

HOMO-1 = 6.6589

LUMO+1 = 1.5769

HOMO-2

LUMO+2

= 7.5553

Figure 7. The frontier molecular orbitals of E5BTTO 25

= 0.0928

Entropy Vs Constant Pressure Vs Enthalpy

900

S Cp ddH

800 700 600 500 400 300 200 100 0 0

200

400

600

800

1000

Temperature

Figure 8. Thermodynamic parameters graph of E5BTTO.

26

Table 1. The experimental and calculated frequencies of E5BTTO using B3LYP/6-311++G(d,p) level of basis set [harmonic frequency (cm−1), IR, Raman intensities (Km/mol), reduced masses (amu) and force constants (mdynA°−1)]. Mode No

1

Calculated frequencies (cm-1) Un Scaled Scaled 3590 3450

Observed Frequencies (cm-1) FTFT-IR Raman 3431m

IR Intensity

Raman Intensity

Reduced Masses

Force Consts.

Vibrational Assignments ≥ 10% TED

Abs. 81.31

Rel. 15.90

Abs. 42.11

Rel. 0.63

1.08

8.19

νN4H5(100)

28.37

5.55

14.28

0.21

1.09

6.75

νC12H16(99)

21.13

4.13

185.43

2.78

1.10

6.59

νC13H18(96)

2

3237

3110

3

3192

3067

4

3181

3057

17.80

3.48

64.02

0.96

1.09

6.51

νC15H19(93)

5

3170

3045

0.31

0.06

51.42

0.77

1.09

6.44

νC17H20(93)

6

3161

3037

4.62

0.90

14.85

0.22

1.09

6.40

νC11H14(91)

7

3119

2997

5.17

1.01

15.11

0.23

1.09

6.23

νC9H21(99)

8

1757

1688

1697vs

1680w

266.28

52.06

57.98

0.87

9.81

17.85

νC1O8(82)

9

1643

1579

1589vs

1592vs

20.91

4.09

79.33

1.19

5.60

8.90

νC1C2(82)

10

1620

1557

1570vs

83.02

16.23

6667.56 100.00

5.08

7.86

νC9C2(60)+βH21C9C2(15)

11

1598

1535

91.61

17.91

5520.77

82.80

5.46

8.21

νC15C17(45)+βH20C17C15(12)

12

1523

1464

1492m

6.84

1.34

416.79

6.25

2.08

2.84

βH19C15C12(65)

13

1482

1424

1435vs

12.39

2.42

521.85

7.83

2.19

2.83

νC12C15(55)+βH18C13C17(18)

14

1449

1393

325.04

63.55

514.51

7.72

2.21

2.74

νC1N4(28)+βC1N4H5(50)

15

1424

1368

195.04

38.13

820.60

12.31

1.47

1.75

βH21C9C2(58)

16

1368

1314

4.79

0.94

54.69

0.82

1.56

1.72

βH14C11C10(55)

17

1335

1282

1296vs

10.84

2.12

416.30

6.24

4.88

5.12

νC11C13(45)

18

1280

1230

1236vs

1222m

70.74

13.83

445.64

6.68

4.40

4.25

νC3N4(27)+βC1N4C3(40)

19

1237

1189

1190vs

1182s

17.13

3.35

848.56

12.73

2.69

2.43

νC10C11(40)

3061vs

3065m

3015w

1441vs

1309m

1

20

1219

1171

21

1188

22

1160w

1.82

0.36

523.77

7.86

1.18

1.03

βH16C12C10(52)

1141

200.64

39.23

328.04

4.92

1.34

1.12

βH18C13C17(50)

1184

1137

511.44 100.00

776.49

11.65

2.01

1.66

νC3N4(14)+βC1N4H5(18)+βH20C17C15(20)

23

1115

1072

24

1072

1030

25

1054

1013

26

1024

984

27

1016

28

1068m

1067w

23.06

4.51

5.05

0.08

1.68

1.23

νC12C15(20)+βH20C17C15(26)

1029m

72.17

14.11

57.32

0.86

11.96

8.10

νC3S7(42)+νC3S6(22)

4.06

0.79

235.17

3.53

2.22

1.45

νC17C13(30)+βH18C13C17(12)

0.60

0.12

3.37

0.05

1.31

0.81

τH16C12C15H19(77)+ГC17C13C15H20(15)

976

1.06

0.21

982.51

14.74

6.18

3.76

βC12C15C17(50)

1000

960

0.12

0.02

3.20

0.05

1.35

0.79

29

988

949

7.78

1.52

141.61

2.12

5.34

3.07

30

958

921

8.87

1.73

5.14

0.08

1.44

0.78

τH14C11C13H18(57)+ГC17C13C15H20(25) νC2C1(14)+νC2S6(12)+βC9C2S6(18)+βC10C9C2(15)+ βC2C1N4(16) ГC11C10C13H14(15)+τH16C12C10C9(28)+τH14C11C13H18(12)

31

915

879

9.60

1.88

27.44

0.41

1.36

0.67

ГC9C2C10H21(71)

32

861

827

1.16

0.23

1.62

0.02

1.25

0.55

ГC11C10C13H14(45)+τH16C12C10C9(35)

33

841

808

810vs

6.55

1.28

312.47

4.69

6.18

2.58

νC10C9(16)+νC2S6(28)

34

777

747

765vs

18.65

3.65

17.28

0.26

1.88

0.67

ГC17C13C15H20(20)+τH16C12C10C9(14)+τC10C12C17C15(12)

35

771

740

5.32

1.04

21.88

0.33

5.17

1.81

νC2C1(22)+βC10C9C2(18)

36

743

714

708w

46.37

9.07

0.67

0.01

5.90

1.92

ГC2O8C1N4(70)+ГC9C1C2S6(12)

37

701

674

675vs

673w

30.85

6.03

0.73

0.01

1.93

0.56

τC12C15C13C17(42)

38

674

648

634w

49.44

9.67

120.99

1.81

8.67

2.32

νC2C1(12)+νC3S6(48)+βC2C1N4(10)

39

634

609

2.70

0.53

75.26

1.13

6.51

1.54

βC17C13C11(40)

40

619

595

67.66

13.23

16.82

0.25

1.11

0.25

τH5N4C1C2(92)

41

601

577

19.81

3.87

43.84

0.66

7.17

1.52

βC15C17C13(42)

42

546

524

2.73

0.53

191.90

2.88

16.51

2.90

νC3N4(12)+νC2S6(28)+βC2C1N4(30)

43

529

508

3.82

0.75

1.69

0.03

8.86

1.46

ГC3S6N4S7(82)

1014m 998s

914m 851vw

524vs

521m

2

44

517

497

43.09

8.42

164.30

2.46

7.41

1.17

βC1N4C3(12)+βC2C1O8(35)

45

506

486

6.33

1.24

17.67

0.27

3.14

0.47

τC13C11C17C15(15)+ГC9C10C12C11(45)

46

433

416

4.55

0.89

1355.64

20.33

22.33

2.46

νC2C1(10)+νC3S6(18)+βC2C1O8(16)+βC3S6C2(25)

47

420

404

0.16

0.03

7.42

0.11

3.04

0.32

τC12C15C13C17(42)

48

373

358

0.75

0.15

54.63

0.82

4.25

0.35

τC10C12C17C15(10)+ГC2O8C1N4(16)+ГC9C1C2S6(48)

49

276

265

5.43

1.06

249.15

3.74

13.26

0.59

βC9C2S6(12)+βS6C3S7(40)+βC3S6C2(15)

50

275

264

0.37

0.07

20.43

0.31

4.66

0.21

τC10C12C17C15(16)+τC10C9C2S6(30)

51

263

253

3.78

0.74

334.07

5.01

7.87

0.32

βC9C2S6(12)+βC12C10C9(15)+βS6C3S7(18)

52

201

193

0.01

0.00

26.83

0.40

7.44

0.18

βC9C2S6(14)+βC10C9C2(18)+βS6C3S7(15)

53

137

131

3.18

0.62

12.64

0.19

10.46

0.12

τC1N4C2S6(72)+τC2C1S6C3(16)

54

118

113

0.63

0.12

52.72

0.79

7.73

0.06

55

110

106

109m

0.27

0.05

188.05

2.82

6.48

0.05

56

45

43

62m

0.07

0.01

211.54

3.17

6.38

0.01

βC9C2S6(12)+βC10C9C2(16)+βS6C3S7(14) τC12C15C13C17(10)+τC10C9C2S6(12)+τC1C4C2C6(10)+ τC2C1C3S6(30)+ГC9C10C12C11(20) τC2C9C10C12(32)+τC10C9C2S6(41)+τC1C4S6C3(12)

57

32

31

0.00

0.00

49.14

0.74

6.91

0.00

τC2C9C10C12(40)+τC1C4S6C3(24)+ГC9C1S6C2(25)

428m

434m

264m

ν: Stretching, δ: in-plane-bending, Γ: out-of-plane bending, vw: very week, w:week, m:medium, s:strong, vs:very strong, a Scaling factor: 0.9608, b Relative IR absorption intensities normalized with highest peak absorption equal to 100, c Relative Raman intensities calculated by Equation (1) and normalized to 100. d Total energy distribution calculated at B3LYP/6-311++G(d,p) level.

3

Table 2. Second order perturbation theory analysis of Fock matrix in NBO basis for E5BTTO Type

Donor (i)

ED/e

σ −σ* C1−C2

1.97473

σ −σ* C1−N4

1.98614

σ −σ* C1−O8

1.99207

π −π* C1−O8 σ −σ* C2−S6

1.97614 1.96648

σ −σ* C2−C9

1.98069

π −π*

C2−C9

1.84032

σ −σ* C3−N4

1.99102

σ −σ* C3−S6

1.97513

σ −σ* C3−S7

1.98869

π −π* C3−S7 σ −σ* N4−H5

1.97252 1.98204

σ −σ* C9−C10

1.97107

σ −σ* C9−H21

1.96907

a (2)

Accepted (j) C1−O8 C2−C9 N4−H5 C9−H21 C2−C9 C3−N4 C3−S7 C1−C2 C3−N4 C2−C9 C1−O8 C2−C9 C3−N4 C3−S7 C9−C10 C1−C2 C9−C10 C9−H21 C10−C11 C1−O8 C10−C11 C1−N4 C1−O8 C2−C9 N4−H5 C1−N4 C3 − N4 C3−S7 C1−C2 C3−S6 C2−S6 C2−C9 C10−C11 C10−C12 C11−C13 C12−C15 C1−C2

ED/e

0.01294 0.01792 0.02290 0.01445 0.01792 0.07352 0.01209 0.07615 0.07352 0.21754 0.01294 0.01792 0.07352 0.01209 0.02813 0.07615 0.02813 0.01445 0.02193 0.29728 0.40182 0.08597 0.01294 0.01792 0.02290 0.08597 0.07352 0.42908 0.07615 0.08392 0.03166 0.01792 0.02193 0.02615 0.01456 0.01515 0.07615 1

E kJ/mol 9.46 13.64 11.97 8.03 8.24 7.15 14.1 11.55 5.61 16.53 17.87 4.35 4.98 18.49 21.21 12.84 21.17 4.77 5.1 81.8 37.74 5.19 8.49 9.16 19.08 10.96 4.98 13.14 8.7 14.52 13.81 25.77 8.7 11.51 8.08 6.86 32.93

b

E(j)−E(i) a.u 1.29 1.28 1.07 1.11 1.41 1.23 1.14 1.49 1.49 0.4 1.23 1.22 1.04 0.95 1.1 1.18 1.24 1.18 1.33 0.29 0.32 1.27 1.47 1.27 1.06 1.15 1.17 0.23 1.09 0.85 0.85 1.26 1.23 1.24 1.27 1.27 0.92

c

F(i, j) a.u 0.048 0.058 0.049 0.041 0.047 0.042 0.055 0.058 0.041 0.038 0.065 0.032 0.032 0.058 0.067 0.055 0.071 0.033 0.036 0.07 0.051 0.036 0.049 0.047 0.062 0.05 0.034 0.027 0.043 0.049 0.047 0.079 0.045 0.052 0.044 0.041 0.077

Type

Donor (i)

ED/e

σ −σ* C10−C11

1.97314

π −π*

C10−C11

1.60718

σ −σ* C10−C12

1.97271

σ −σ* C11−C13

1.97901

σ −σ* C11−H14

1.98067

σ −σ* C12−C15

1.97894

π −π*

C12−C15

1.64941

σ −σ* C12−H16

1.97788

σ −σ* C13−C17

1.9796

π −π*

C13−C17

1.63526

σ −σ* C13−H18

1.97989

a (2)

Accepted (j) C2−C9 C10−C12 C2−C9 C9−C10 C10−C12 C11−C13 C12−H16 C13−H18 C2−C9 C12−C15 C13−C17 C9−C10 C9−H21 C10−C11 C11−H14 C12−C15 C12−H16 C15−H19 C9−C10 C10−C11 C13−C17 C17−H20 C10−C12 C13−C17 C9−C10 C10−C12 C12−H16 C15−C17 C17−H20 C10−C11 C13−C17 C10−C11 C12−C15 C15−C17 C11−C13 C11−H14 C15−C17 C15−H19 C10−C11 C12−C15 C10−C11

ED/e

0.01792 0.02615 0.01792 0.02813 0.02615 0.01456 0.02075 0.01375 0.21754 0.27923 0.32968 0.02813 0.01445 0.02193 0.01386 0.01515 0.02075 0.01377 0.02813 0.02193 0.01641 0.01347 0.02615 0.01641 0.02813 0.02615 0.02075 0.01642 0.01347 0.40182 0.32968 0.02193 0.01515 0.01642 0.01456 0.01386 0.01642 0.01377 0.40182 0.27923 0.02193 2

E kJ/mol 5.48 22.38 12.84 9.75 13.97 11.55 9.04 9.16 99.33 78.28 79.71 12.05 4.56 15.1 9.67 10.92 4.35 8.87 12.51 12.22 11.72 9.67 17.11 15.56 15.86 11.88 4.85 11.38 9.58 80.42 91.92 18.62 4.27 16.19 11.92 10.71 10.54 9.92 95.02 73.89 16.74

b

E(j)−E(i) a.u 1.1 1.08 1.27 1.15 1.25 1.27 1.18 1.13 0.26 0.29 0.28 1.15 1.09 1.24 1.13 1.28 1.18 1.14 1.17 1.25 1.28 1.15 1.08 1.1 1.16 1.26 1.19 1.27 1.14 0.27 0.28 1.05 1.1 1.08 1.29 1.14 1.28 1.15 0.28 0.29 1.06

c

F(i, j) a.u 0.034 0.068 0.056 0.046 0.058 0.053 0.045 0.045 0.074 0.067 0.066 0.051 0.031 0.06 0.046 0.052 0.031 0.044 0.053 0.054 0.054 0.046 0.06 0.057 0.059 0.053 0.033 0.053 0.046 0.065 0.07 0.061 0.03 0.058 0.054 0.048 0.051 0.047 0.071 0.065 0.058

Type

Donor (i)

ED/e

σ −σ* C15−C17

1.98078

σ −σ* C15−H19

1.98001

σ −σ* C17−H20

1.98079

n −π*

N4

1.60753

n −σ*

S6

1.98137

n −π*

S6

1.71182

n −σ*

S7

1.98056

n −σ*

S7

1.85322

n −σ*

O8

1.97503

n −σ*

O8

1.85169

π −π* π −π* π −π*

C1−O8 C2−C9 C10−C11

0.29728 0.21754 0.40182

a (2)

a (2)

Accepted (j) C15−C17 C12−C15 C12−H16 C13−C17 C13−H18 C10−C12 C13−C17 C11−C13 C12−C15 C1−O8 C3−S7 C1−C2 C3−N4 C3−S7 C2−C9 C3−S7 C3−N4 C3−S6 C3−N4 C3−S6 C1−C2 C12−H16 C1−C2 C1−N4 C12−H16 C2−C9 C10−C11 C12−C15

ED/e

0.01642 0.01515 0.02075 0.01641 0.01375 0.02615 0.01641 0.01456 0.01515 0.29728 0.42908 0.07615 0.07352 0.01209 0.21754 0.42908 0.07352 0.08392 0.07352 0.08392 0.07615 0.02075 0.07615 0.08597 0.02075 0.21754 0.40182 0.27923

E kJ/mol 14.85 10.84 9.04 10.67 10.25 16.86 15.48 15.56 15.52 208.03 280.83 7.03 7.24 5.52 66.9 159.49 19.12 19.12 56.23 64.31 11.88 8.28 77.78 117.24 12.22 451.29 680.23 836.13

E means energy of hyper conjugative interaction (stabilization energy). Energy difference between donor(i) and acceptor(j) NBO orbitals. c F(i,j) is the fork matrix element between i and j NBO orbitals.

b

3

b

E(j)−E(i) a.u 1.1 1.29 1.19 1.27 1.14 1.07 1.09 1.11 1.11 0.28 0.21 1.08 1.08 0.98 0.27 0.18 1.13 0.89 0.61 0.37 1.11 1.2 0.68 0.66 0.77 0.02 0.01 0.01

c

F(i, j) a.u 0.056 0.052 0.045 0.051 0.047 0.059 0.057 0.057 0.057 0.108 0.106 0.039 0.039 0.032 0.06 0.076 0.065 0.058 0.083 0.069 0.051 0.043 0.102 0.124 0.044 0.076 0.07 0.081

Table 3. The Mulliken atomic charges of E5BTTO

Atoms 1C 2C 3C 4N 5H 6S 7S 8O 9C 10C 11C 12C 13C 14H 15C 16H 17C 18H 19H 20H 21H

Charges 0.699759 -0.065138 0.179771 -0.147768 0.363608 -0.436707 -0.520805 -0.274954 -0.244754 1.329145 0.276787 -1.164350 -0.350209 0.153318 -0.393235 0.173700 -0.278926 0.174247 0.197538 0.161075 0.167897

4

Table 4. The Frontier molecular orbital of E5BTTO

Occupancy

Orbital energies (a.u)

Orbital energies (eV)

O55

-0.27765

7.5553

O56

-0.24472

6.6589

O57

-0.23781

6.4712

V58

-0.11125

3.0273

V59

-0.05795

1.5769

V60

-0.03318

0.0928

O-Occupied orbital V-Virtual orbital

5

Table .5 Thermodynamic parameters of E5BTTO.

T(K) 100.00 200.00 298.15 300.00 400.00 500.00 600.00 700.00 800.00 900.00 1000.00

S(J/mol.K) 321.68 396.94 463.23 464.44 528.39 588.59 644.70 696.76 745.02 789.86 831.64

Cp(J/mol.k) 85.13 139.54 195.93 196.96 248.64 290.92 324.30 350.71 371.92 389.26 403.65

6

ddH(kJ/mol) 5.89 17.06 33.54 33.91 56.26 83.32 114.14 147.94 184.11 222.20 261.87

Highlights:
Synthesis of E5BTTO
Structural conformation
Vibrational characterization
Study of NLO property
NBO band gap analysis

7

Graphical abstract

-9.157e-2

9.157e-2

MEP of E5BTTO

8