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DFT study
Accepted Manuscript 5-METHYL-2-THIOPHENECARBOXALDEHYDE: Experimental and TD/DFT Study
Davut Avcı, Ömer Tamer, Adil Başoğlu, Yusuf Atalay PII:
S0022-2860(18)30861-5
DOI:
10.1016/j.molstruc.2018.07.042
Reference:
MOLSTR 25447
To appear in:
Journal of Molecular Structure
Received Date:
08 December 2017
Accepted Date:
11 July 2018
Please cite this article as: Davut Avcı, Ömer Tamer, Adil Başoğlu, Yusuf Atalay, 5-METHYL-2THIOPHENECARBOXALDEHYDE: Experimental and TD/DFT Study, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.07.042
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ACCEPTED MANUSCRIPT 5-METHYL-2-THIOPHENECARBOXALDEHYDE: AND TD/DFT STUDY
EXPERIMENTAL
Davut Avcı*, Ömer Tamer, Adil Başoğlu and Yusuf Atalay Sakarya University, Faculty of Art and Science, Department of Physics, 54187, Serdivan, Türkiye Abstract: The 5-Methyl-2-thiophenecarboxaldehyde (MTC) and its derivatives present a wide range of biological activities. In this regard a combined experimental and theoretical analysis for MTC and its derivatives can help to understand the electronic factors involved in the mode of action in biological systems. In the present work we used FT-IR and UV-vis techniques to investigate the spectroscopic properties of MTC. The conformational and vibrational analyses were theoretically explored using DFT calculation at DFT//B3LYP/6311++G(d,p) level. A full electronic analysis of compound was performed using TDDFT/B3LYP/6-311++G(d,p) calculations in gas phase and in ethanol solvent with the CPCM model. The NLO parameters (β, γ and χ(3)) and FMO energies for MTC were calculated at the same level of theory. The relation between linear polarizability (α) and refractive index (n) were used to describe the polarization behavior of MTC in ethanol solvent. Our results indicate that MTC can be considered as a candidate to microscopic thirdorder NLO material. Keywords: 5-Methyl-2-thiophenecarboxaldehyde; FT–IR and UV–vis spectra; NLO; Refractive index; FMO; TD/DFT-B3LYP.
*Corresponding author, E-mail address: [email protected] (D. Avcı).
ACCEPTED MANUSCRIPT 1. Introduction Thiophene and its derivatives are occasionally found in coal, petroleum, and other natural fossil fuels at a low percent concentration [1-3]. Their structural features have been growing interest due to in the presence of these units in natural and synthetic products, as well as their several important applications [4,5]. The thiophene system and its derivatives have gathered great attention in the material sciences due to applications as good inhibitors of abrasion of metals in acidic media [6] and building blocks for the oligo- and polythiophenes [7]. Polythiophenes are a significant class of conducting conjugated polymers which found application in the area of new materials owing to chemical, electrical and thermal stabilities, as well as simplicity of preparation. They are also used in electronic devices [812], in the detection of biological [13] and genetic material [14]. Besides, the thiophene carboxaldehydes have applications both in agriculture owing to their herbicidal, fungicidal and insecticidal activity [15,16], and in medicinal chemistry because of anti-inflammatory, antineoplasic or antiviral agents [17−28]. In the literature, there are many experimental and theoretical studies that focus on thermochemical properties [1,4,5,7,29]. However, in spite of their wide importance, the knowledge of the electronic properties of these compounds is still limited. Considering the progress in design and synthesis of these compounds, the survey of experimental and theoretical studies is inevitable. To understand behavior of the versatility of a material/compound, its spectral, electronic and optical properties are required presentation experimentally and theoretically. To the best of our knowledge, there is no study concerning a detailed characterizations of MTC. In this regard, we characterized a detailed experimental and theoretical spectral analysis study in gas phase and ethanol solvent for MTC. The refractive index, non-linear optical (NLO) parameters, experimental and theoretical band gap parameters were also investigated. Furthermore, the comparison of the experimental and theoretical results obtained for MTC provided a powerful insight into molecular structure analysis for the derivatives of MTC. 2. Experimental and computational procedure 5-Methyl-2-thiophenecarboxaldehyde (MTC) (98%) was purchased from Sigma Aldrich. All chemicals for measurement were used as received without further purification. FT–IR spectrum for MTC was recorded on a PerkinElmer FT–IR spectrophotometer (with ATR equipment) at the region of 4000−400 cm-1. The UV−Vis absorption spectrum of MTC was
ACCEPTED MANUSCRIPT examined in the range 800−200 nm using a HITACHI U-2900 UV/VIS spectrophotometer in ethanol. All calculations for MTC were carried out by using GAUSSIAN 09 Rev: D.01 program [30], and the obtained results were visualized with the aid of GaussView 5 program [31]. The conformational parameters and vibrational frequencies of MTC in gas phase were obtained by applying of DFT/B3LYP [32,33] method with 6-311++G(d,p) basis set. Furthermore, the assignments of vibrational modes were fulfilled based on the potential energy distribution (PED) by using VEDA program [34]. By consideration of the optimized MTC structures, the electronic absorption wavelengths and oscillator strengths of MTC were obtained using the time dependent DFT (TD−B3LYP level) [35] method and 6-311++G(d,p) basis set using CPCM model [36] in ethanol solvent and gas phase. The NLO parameters (β, γ and χ(3)) and frontier molecular orbital (FMO) energies of MTC were calculated by using the same level of theory. Furthermore, according to the Lorentz−Lorenz equation [37], the relation between linear polarizability (α) and refractive index (n) were investigated to observe polarization behavior of MTC in ethanol solvent. 3. Results and discussion 3.1. Conformational analysis Fig. 1 shows the most stable optimized structure of MTC obtained through a conformational analysis at B3LYP/6-311++G(d,p) level. The potential energy curves of MTC varying the dihedral angles S5–C1–C8–O10 and S5–C4–C11–H14 by the interval of 10o are shown in Fig. 2. At the same time, the minimum and maximum energy conformers on the potential energy surface (PES) for S5–C1–C8–O10 and S5–C4–C11–H14 dihedral angles are depicted in Fig. 2. The lowest energy value was considered as 0.0 kcal/mol the corresponding -705.764 and -705.7635 Hartree energy values, and so other energy values are determined as relative energy. The lowest energy conformer is calculated at 0.02o with 0.0 kcal/mol relative energy value (at point A for Fig. 2a). The saddle point known as local minimum is obtained at 179.98o with 1.88 kcal/mol relative energy value (at point C for Fig. 2a). Two maximum points called as global and local maxima have been found to be 11.92 kcal/mol relative energy value at 89.98o and 269.98o, as can be seen in points B and D for Fig. 2a. On the other hand, Fig. 2b for S5– C4–C11–H14
dihedral angle shows three maximum and four minimum points called as
ACCEPTED MANUSCRIPT global/local maxima and minima. The lowest energy conformers in A, C, E and G points are calculated at -179.99o, -59.99o, 60.00o and 180.00o with 0.0 kcal/mol relative energy value (Fig. 2b). The highest energy conformers in B, D and F points are obtained at -119.99o, 0o and 120.00o with 0.50 kcal/mol relative energy value (Fig. 2b). 3.2. Vibrational frequency analysis We have examined vibrational modes connected with molecular structure of MTC by the percentage PED contributions (see Table 1). The FTIR and simulated IR spectra in gas phase are shown in Fig. 3. The symmetric and asymmetric stretching modes υ (CH) in disubstituted thiophene ring are observed at the range of 3089−2691 cm−1 in FT−IR, as would be expected. Calculated these modes in the gas phase are appeared at 3077 and 3063 cm−1 with the PED contribution of 99 and 100% (see Fig. 3). The stretching modes υ (CH) of CH3 and –CHO substiuents are also obtained at 2986−2908 cm−1 range (100% with PED) and 2780 cm−1 (99% with PED). In MTC, the stretching modes υ (CO) originated from carbonyl group are observed at 1691 and calculated at 1670 cm−1 (88% with PED) in the gas phase. The stretching mode ν (SC) resulted from thiophene ring is emerged at 1161 cm−1 in FT−IR spectrum, this mode is found to be 678 cm−1 with 68% with PED contribution, as can be seen in Fig. 3. 3.3. UV-Vis, FMOs and band gap analyses Fig. 4 shows two different absorption peaks for MTC at 348.3 and 237.2 nm (ethanol solvent) that are attributed to the n→π*, π→π* transitions, respectively. The corresponding bands in TD−B3LYP calculations are found at range of 336.8−259.0 nm in gas phase and 324.0−268.9 nm in ethanol, as can be seen in Table 2. The remarkable contributions of electronic transitions between FMOs and the corresponding λabs values were determined with the aid of SWizard//Chemissian programs [38,39], as can be seen in Table 2. The TD−DFT computations display that the electronic absorption at the λabs mainly constituted by two electronic transition modes H−1→L(+96%) [T(100%)→T
ACCEPTED MANUSCRIPT (47%)+A(53%)] and H−2→L(+97%) [T(100%)→T(46%)+A(54%)] are obtained at 336.8 nm (in gas phase) and 324.0 nm (in ethanol solvent) with minor difference in percentage. The other peaks calculated in high energy region (λmax = 268.9 nm and λmax = 259.0 nm in ethanol solvent and gas phase) stem from H−1→L(+83%) and H→L(+14%) in ethanol, H−2→L(+78%) and H→L(+18%) in gas phase. Besides, the peaks calculated at 287.1 and 273.9 nm in ethanol solvent and gas phase are formed by H→L(+84%) and H−1→L(+14%) in ethanol, H→L(+79%) and H−2→L(+18%) in gas phase. It is clear from Table 2 and Fig. 5 that presumably transitions confirm intramolecular interactions due to the electron-accepting strength of the aldehyde group substituent and the electron-donating strength of the thiophene ring. In this paper, the used absorption coefficient (α) was calculated from the absorbance data using the Lambert Law formula [40–43]. The optical band gap energy was obtained by using the Tauc and Menth's relation [40–43]. Considering Fig. 6, the optical band gap energy is found to be 3.34 eV. FMO energies of MTC are calculated by using the B3LYP/6-311++G(d,p). The occupied and unoccupied MOs for MTC in ethanol solvent are given in Fig. 5. It is well known that the relationship between energy gap and FMOs explains the molecular chemical stability, chemical reactivity and spectroscopic properties of the molecules. While the theoretical energy gap values for MTC in gas phase and ethanol solvent are obtained as 4.631 and 4.758 eV, the experimental one is found to be 3.34 eV. It is clear that the results are comparable. This difference is consistent with previous band gap of the Cu(ii) complex [57]. In addition, the HOMO and LUMO energy values for thiophene by HF/6-31+G(d,p) level were obtained to be -9.09 eV, 2.13 eV [44]. It is stated that the differences between our FMO results and values reported by Mandal et. al [44] originate from the electron-accepting aldehyde group and electron-donating methyl group in disubstituted thiophene ring. It is noted that the molecular electrostatic potential (MEP) surface plots have been used as method of mapping electrostatic potential (ESP) onto the iso–electron density surface [45]. In addition, the MEP shows molecular shape, size and ESP regions depending color classification. Besides, in the research of relation between the molecular structure and physicochemical property of molecules containing bio molecules and drugs have been used
ACCEPTED MANUSCRIPT [46–51]. In this regard, the MEP and ESP surfaces are given in Fig. 7a. The color code of MEP for MTC is in the range of 7.688e-2 a.u. (deepest blue) and -7.688e-2 a.u. (deepest red). Herein the negative potential are over the electronegative O atom of carbonyl group. Likewise, the negative regions of ESP are usually associated with the lone pair of electronegative atoms (see Fig. 7b). Owing to Fig. 7, the carbonyl group displays the most negative potential regions while the hydrogen atoms exhibit the most positive regions. Zero potential regions depict the carbon atoms. 3.4. Refractive index and NLO analyses Nonlinear optics (NLO) have been widely investigated due to providing key functions of frequency shifting, optical modulation, fiber optical materials for the arising technologies in areas such as signal processing, telecommunications [5257]. Investigation of NLO parameters for molecular systems is important with regard to the efficiency of electronic communication between electron accepting and donating groups playing a key role in identifying the intramolecular charge. Moreover, it could be determined that the relation between α and refractive index which shows the polarization of the compounds through the electromagnetic field of the light. It means that the value of χ(n) susceptibility is inversely proportional the value of the strength(s) of the applied electric field(s) and the path length needed to achieve the given nonlinear optical effect [5658]. The refractive index of MTC was obtained by using equations given references therein [44,59–61]. The plot of the refractive index in the IR region is shown in Fig. 8. It is worthy that the refractive index values change between 4000 and 400 cm−1, and there are the peaks because of vibrational absorption. In this region, the value of the average refractive index is 1.51. Total static dipol moment (μ, in Debye), the mean linear polarizability (‹α›, in 10-24 esu), refractive index (n), anisotropy of linear polarizability (Δα, in 10-24 esu), mean first and second−order hyperpolarizabilities (‹β› and ‹γ› in 10-30 and 10-36 esu), and third−order susceptibility (χ(3), in 10-13 esu) for MTC are calculated by using equations given therein [62−66]. The calculated parameters are given in Table 3. It is can be seen in Table 3, the β and γ values are calculated as 4.54×10-30 and 12.26×10-36 esu and 8.64×10-30 and 30.11×10-36 esu by using B3LYP/6−311++G(d,p) level in gas phase and ethanol solvent, respectively. In
ACCEPTED MANUSCRIPT order to evaluate these parameters without doing any experimental study, the results of p−Nitroaniline (pNA) [67−69] and urea [70] have been used as the prototypical compounds. In comparison of β results, the β values are 1.76 times lower than pNA (8×10-30 esu) in gas phase while the β values are 34.92 and 66.46 times higher than urea (0.130×10-30 esu) in gas phase and ethanol solvent. It is clear that the substantial β values were obtained with respect to the urea. It is clearly seen in Table 3, the difference between obtained the β and γ results in gas phase and ethanol solvent is 1.90 times and 2.456 times. This differences is not observed for energy gap values in same solvent. However, the β and γ results in gas phase and ethanol solvent is inversely proportional to energy gap. This statement is compatible with our previous studies [57,6266]. When it comes to γ, the γ values are about 2.01 times higher than pNA (15×10-36 esu) in ethanol solvent, obtained γ value in ethanol solvent could be remarkably indicator microscopic third−NLO material. Obtained 4.68 and 6.41 D values for μ in different solvents are 1.92 and 2.63 times higher than pNA (2.44 D). The α values are found to be 13.96×10-24 and 19.26×10-24 esu in gas phase and ethanol solvent, these values are ~1.58, and ~1.14 times lower than pNA (22×10-24 esu). Hinchliffe and Soscún [71] reported the dipole polarizability values for five-membered heterocyclics calculated using different levels. The electrondonating effect of thiophene ring was uncovered at these parameters. Another study containng this group displays the same tendency [66]. According to these results, it is commented that there are both partial molecular charge distribution and charge movement in MTC irrespective of gas phase and ethanol solvent. In this work, the real part of χ(3) irrespective of doing experimental study related to the γ parameter is calculated at B3LYP level. The calculated refractive index and χ(3) values in gas phase and ethanol solvent are presented in Table 3. The n and χ(3) parameters are obtained at 1.92/25.13 and 1.81/33.30 in mentioned solvents, respectively. In comparison of n and χ(3) results, obtained results are consistent with that results of different molecular systems [72−74]. 4. Conclusion Vibrational and electronic spectral properties of MTC were investigated by using FT−IR and UV−Vis techniques. The conformational structures based on different dihedral angles, the assignments of vibrational frequency and electronic transitions, second− and third−NLO
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Figure Captions Fig. 1. The optimized molecular structure of MTC obtained at B3LYP/6-311++G(d,p) in gas phase. Fig. 2. One-dimensional potential energy surface (PES) scan of the calculated energies versus dihedral angles (a) S5-C1-C8-O10 and (b) S5-C4-C11-H14 for MTC obtained at B3LYP/6311++G(d,p) in gas phase. Fig. 3. The comparison of experimental and theoretical IR spectra of MTC. Fig. 4. The comparison of experimental and theoretical UVVis spectra in ethanol solvent and gas phase for MTC. Fig. 5. The occupied and unoccupied molecular orbitals being the most active in electronic transition for MTC in ethanol solvent. Fig. 6. The optical band gap energy graph for MTC in ethanol solvent. Fig. 7. (a) The MEP and (b) ESP surfaces for MTC in ethanol solvent. Fig. 8. The plot of the refractive index dependence on the wavenumber in the IR region.
ACCEPTED MANUSCRIPT Highlights
The conformer structures for 5-Methyl-2-thiophenecarboxaldehyde was obtained. Optical band gap was obtained by UV−vis spectrum. The NLO parameters (β, γ and (3)) were investigated. TD/DFT calculations were performed to support experimental results.
ACCEPTED MANUSCRIPT
Mode
Assignments via PED% at B3LYP level
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
ν(CH) 99% ν(CH) 100% ν(CH) 100% ν(CH) 100% ν(CH) 100% ν(CH) 99% ν(OC) 88% ν(CC) 63%+β(HCC) 10% ν(CC) 36%+β(HCH) 15% ν(CC) 11%+β(HCH) 51% β(HCH) 78%+ τ(HCCC) %12 β(HCH) 92% β(HCC) 10%+β(HCO) 66% ν(CC) 39% +β(HCC) 18%+β(HCO) 16% β(HCC) 63% ν(CC) 45% +β(CCC) 23% ν(CC) 39% + ν(SC) 10% ν(CC) 21% +β(HCC) 55% β(HCH) 28%+τ(HCCC) 50% τ(HCCC) 81% ν(CC) 12%+τ(HCCC) %42 τ(HCCC) %76+τ(CCCC) %12 τ(HCCC) %87 β(CCC) 56%+β(OCC) 16% ν(SC) 68% ν(CC) 11%+ β(CCC) 16%+β(OCC) 12%+β(SCC) 42% ν(CC) 22%+ β(CCC) 10%+β(OCC) 22%+β(SCC) 13% τ(CCCC) 61%+γ(CCSC) 15% τ(SCCC) 42%+γ(CCSC) 33% ν(CC) 21%+ β(CCC) 16%+β(SCC) 21% γ(CCSC) 74% β(CCS) 74% τ(OCCC) 29%+ τ(SCCC) 33%+ τ(CCSC) 17% β(OCC) 18%+β(CCS) 68% τ(OCCC) 48%+ τ(SCCC) 14%+γ(CCSC) 25% γ(HCCC) 91%
FT−IR [cm-1] 3086 2973 2920 2803 2742 2695 1650 1530 1456 1382 1340 1231 1216 1165 1049 972 894 801 755 685 670 600 569 546 480 430
Scaled freq. [cm-1]a B3LYP 3080 3067 2989 2960 2911 2783 1672 1515 1448 1426 1421 1363 1355 1295 1191 1184 1130 1031 1015 966 951 868 781 768 686 659 616 582 488 436 329 312 197 157 108 83
Table 1. Compar ison of FT-IR and calculat ed vibratio n frequen cies for the 5Methyl2thiophe necarbo xaldehy de
ACCEPTED MANUSCRIPT υ: Stretching; β: in plane bending; γ: out–of plane bending; τ: twisting. aThe calculated vibrational frequencies of 5Methyl-2-thiophenecarboxaldehyde were scaled as 0.961 for frequencies higher than 800 cm−1and as 1.001 for frequencies lower than 800 cm−1 at the B3LYP/6-311++G(d,p) level.
ACCEPTED MANUSCRIPT Table 2. Electronic transitions, wavelengths and oscillator strengths for MTC in gas phase and ethanol solvent Solvent
Exp.
TD/B3LYP/6-311++G(d,p)
λabs (nm)
λabs (nm) 336.8 273.9 259.0 4 324.0 287.1 268.9 8
Gas phase
Ethanol
348.3 237.2
f(osc. str.) 0.0002 0.2586 0.1127 0.0002 0.3496 0.1437
Major contributions (%) obtained via SWizard//Chemissian programs [H: HOMO; L: LUMO; T: Thiophene; A: Aldehyde] H-1→L(96%)//T(100%)→ T(47%)+A(53%) H→L(79%), H-2→L(18%)//T(100%)→T(47%)+A(53%) H-2→L(78%), H→L(18%)//T(100%)→T(47%)+A(53%) H-2→L(97%)//T(100%)→T(46%)+A(54%) H→L(84%), H-1→L(14%)//T(100%)→T(46%)+A(54%) H-1→L(83%), H→L(14%)//T(100%)→T(46%)+A(54%)
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Table 3. Total static dipol moment (μ, in Debye), the mean linear polarizability (‹α›, in 10-24 esu), refractive index (n), anisotropy of linear polarizability (Δα, in 10-24 esu), mean first and second−order hyperpolarizabilities (‹β› and ‹γ› in 10-30 and 10-36 esu), and third−order susceptibility (χ(3), in 10-13 esu) for MTC. B3LYP/6–311++G(d,p) Property Gas phase Ethanol solvent μ 4.68 6.41 μ 2.44 [67−69] <α>
13.96
<α>
19.26 22 [67−69]
n Δα
1.92 9.74
1.81 13.72
<β>
4.54
8.64
<β>
8 [67−69], 0.13 [70]
<γ>
12.26
30.11
(3)
25.13
33.30
<γ>
15 [67−69]
Davut Avcı, Ömer Tamer, Adil Başoğlu, Yusuf Atalay PII:
S0022-2860(18)30861-5
DOI:
10.1016/j.molstruc.2018.07.042
Reference:
MOLSTR 25447
To appear in:
Journal of Molecular Structure
Received Date:
08 December 2017
Accepted Date:
11 July 2018
Please cite this article as: Davut Avcı, Ömer Tamer, Adil Başoğlu, Yusuf Atalay, 5-METHYL-2THIOPHENECARBOXALDEHYDE: Experimental and TD/DFT Study, Journal of Molecular Structure (2018), doi: 10.1016/j.molstruc.2018.07.042
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ACCEPTED MANUSCRIPT 5-METHYL-2-THIOPHENECARBOXALDEHYDE: AND TD/DFT STUDY
EXPERIMENTAL
Davut Avcı*, Ömer Tamer, Adil Başoğlu and Yusuf Atalay Sakarya University, Faculty of Art and Science, Department of Physics, 54187, Serdivan, Türkiye Abstract: The 5-Methyl-2-thiophenecarboxaldehyde (MTC) and its derivatives present a wide range of biological activities. In this regard a combined experimental and theoretical analysis for MTC and its derivatives can help to understand the electronic factors involved in the mode of action in biological systems. In the present work we used FT-IR and UV-vis techniques to investigate the spectroscopic properties of MTC. The conformational and vibrational analyses were theoretically explored using DFT calculation at DFT//B3LYP/6311++G(d,p) level. A full electronic analysis of compound was performed using TDDFT/B3LYP/6-311++G(d,p) calculations in gas phase and in ethanol solvent with the CPCM model. The NLO parameters (β, γ and χ(3)) and FMO energies for MTC were calculated at the same level of theory. The relation between linear polarizability (α) and refractive index (n) were used to describe the polarization behavior of MTC in ethanol solvent. Our results indicate that MTC can be considered as a candidate to microscopic thirdorder NLO material. Keywords: 5-Methyl-2-thiophenecarboxaldehyde; FT–IR and UV–vis spectra; NLO; Refractive index; FMO; TD/DFT-B3LYP.
*Corresponding author, E-mail address: [email protected] (D. Avcı).
ACCEPTED MANUSCRIPT 1. Introduction Thiophene and its derivatives are occasionally found in coal, petroleum, and other natural fossil fuels at a low percent concentration [1-3]. Their structural features have been growing interest due to in the presence of these units in natural and synthetic products, as well as their several important applications [4,5]. The thiophene system and its derivatives have gathered great attention in the material sciences due to applications as good inhibitors of abrasion of metals in acidic media [6] and building blocks for the oligo- and polythiophenes [7]. Polythiophenes are a significant class of conducting conjugated polymers which found application in the area of new materials owing to chemical, electrical and thermal stabilities, as well as simplicity of preparation. They are also used in electronic devices [812], in the detection of biological [13] and genetic material [14]. Besides, the thiophene carboxaldehydes have applications both in agriculture owing to their herbicidal, fungicidal and insecticidal activity [15,16], and in medicinal chemistry because of anti-inflammatory, antineoplasic or antiviral agents [17−28]. In the literature, there are many experimental and theoretical studies that focus on thermochemical properties [1,4,5,7,29]. However, in spite of their wide importance, the knowledge of the electronic properties of these compounds is still limited. Considering the progress in design and synthesis of these compounds, the survey of experimental and theoretical studies is inevitable. To understand behavior of the versatility of a material/compound, its spectral, electronic and optical properties are required presentation experimentally and theoretically. To the best of our knowledge, there is no study concerning a detailed characterizations of MTC. In this regard, we characterized a detailed experimental and theoretical spectral analysis study in gas phase and ethanol solvent for MTC. The refractive index, non-linear optical (NLO) parameters, experimental and theoretical band gap parameters were also investigated. Furthermore, the comparison of the experimental and theoretical results obtained for MTC provided a powerful insight into molecular structure analysis for the derivatives of MTC. 2. Experimental and computational procedure 5-Methyl-2-thiophenecarboxaldehyde (MTC) (98%) was purchased from Sigma Aldrich. All chemicals for measurement were used as received without further purification. FT–IR spectrum for MTC was recorded on a PerkinElmer FT–IR spectrophotometer (with ATR equipment) at the region of 4000−400 cm-1. The UV−Vis absorption spectrum of MTC was
ACCEPTED MANUSCRIPT examined in the range 800−200 nm using a HITACHI U-2900 UV/VIS spectrophotometer in ethanol. All calculations for MTC were carried out by using GAUSSIAN 09 Rev: D.01 program [30], and the obtained results were visualized with the aid of GaussView 5 program [31]. The conformational parameters and vibrational frequencies of MTC in gas phase were obtained by applying of DFT/B3LYP [32,33] method with 6-311++G(d,p) basis set. Furthermore, the assignments of vibrational modes were fulfilled based on the potential energy distribution (PED) by using VEDA program [34]. By consideration of the optimized MTC structures, the electronic absorption wavelengths and oscillator strengths of MTC were obtained using the time dependent DFT (TD−B3LYP level) [35] method and 6-311++G(d,p) basis set using CPCM model [36] in ethanol solvent and gas phase. The NLO parameters (β, γ and χ(3)) and frontier molecular orbital (FMO) energies of MTC were calculated by using the same level of theory. Furthermore, according to the Lorentz−Lorenz equation [37], the relation between linear polarizability (α) and refractive index (n) were investigated to observe polarization behavior of MTC in ethanol solvent. 3. Results and discussion 3.1. Conformational analysis Fig. 1 shows the most stable optimized structure of MTC obtained through a conformational analysis at B3LYP/6-311++G(d,p) level. The potential energy curves of MTC varying the dihedral angles S5–C1–C8–O10 and S5–C4–C11–H14 by the interval of 10o are shown in Fig. 2. At the same time, the minimum and maximum energy conformers on the potential energy surface (PES) for S5–C1–C8–O10 and S5–C4–C11–H14 dihedral angles are depicted in Fig. 2. The lowest energy value was considered as 0.0 kcal/mol the corresponding -705.764 and -705.7635 Hartree energy values, and so other energy values are determined as relative energy. The lowest energy conformer is calculated at 0.02o with 0.0 kcal/mol relative energy value (at point A for Fig. 2a). The saddle point known as local minimum is obtained at 179.98o with 1.88 kcal/mol relative energy value (at point C for Fig. 2a). Two maximum points called as global and local maxima have been found to be 11.92 kcal/mol relative energy value at 89.98o and 269.98o, as can be seen in points B and D for Fig. 2a. On the other hand, Fig. 2b for S5– C4–C11–H14
dihedral angle shows three maximum and four minimum points called as
ACCEPTED MANUSCRIPT global/local maxima and minima. The lowest energy conformers in A, C, E and G points are calculated at -179.99o, -59.99o, 60.00o and 180.00o with 0.0 kcal/mol relative energy value (Fig. 2b). The highest energy conformers in B, D and F points are obtained at -119.99o, 0o and 120.00o with 0.50 kcal/mol relative energy value (Fig. 2b). 3.2. Vibrational frequency analysis We have examined vibrational modes connected with molecular structure of MTC by the percentage PED contributions (see Table 1). The FTIR and simulated IR spectra in gas phase are shown in Fig. 3. The symmetric and asymmetric stretching modes υ (CH) in disubstituted thiophene ring are observed at the range of 3089−2691 cm−1 in FT−IR, as would be expected. Calculated these modes in the gas phase are appeared at 3077 and 3063 cm−1 with the PED contribution of 99 and 100% (see Fig. 3). The stretching modes υ (CH) of CH3 and –CHO substiuents are also obtained at 2986−2908 cm−1 range (100% with PED) and 2780 cm−1 (99% with PED). In MTC, the stretching modes υ (CO) originated from carbonyl group are observed at 1691 and calculated at 1670 cm−1 (88% with PED) in the gas phase. The stretching mode ν (SC) resulted from thiophene ring is emerged at 1161 cm−1 in FT−IR spectrum, this mode is found to be 678 cm−1 with 68% with PED contribution, as can be seen in Fig. 3. 3.3. UV-Vis, FMOs and band gap analyses Fig. 4 shows two different absorption peaks for MTC at 348.3 and 237.2 nm (ethanol solvent) that are attributed to the n→π*, π→π* transitions, respectively. The corresponding bands in TD−B3LYP calculations are found at range of 336.8−259.0 nm in gas phase and 324.0−268.9 nm in ethanol, as can be seen in Table 2. The remarkable contributions of electronic transitions between FMOs and the corresponding λabs values were determined with the aid of SWizard//Chemissian programs [38,39], as can be seen in Table 2. The TD−DFT computations display that the electronic absorption at the λabs mainly constituted by two electronic transition modes H−1→L(+96%) [T(100%)→T
ACCEPTED MANUSCRIPT (47%)+A(53%)] and H−2→L(+97%) [T(100%)→T(46%)+A(54%)] are obtained at 336.8 nm (in gas phase) and 324.0 nm (in ethanol solvent) with minor difference in percentage. The other peaks calculated in high energy region (λmax = 268.9 nm and λmax = 259.0 nm in ethanol solvent and gas phase) stem from H−1→L(+83%) and H→L(+14%) in ethanol, H−2→L(+78%) and H→L(+18%) in gas phase. Besides, the peaks calculated at 287.1 and 273.9 nm in ethanol solvent and gas phase are formed by H→L(+84%) and H−1→L(+14%) in ethanol, H→L(+79%) and H−2→L(+18%) in gas phase. It is clear from Table 2 and Fig. 5 that presumably transitions confirm intramolecular interactions due to the electron-accepting strength of the aldehyde group substituent and the electron-donating strength of the thiophene ring. In this paper, the used absorption coefficient (α) was calculated from the absorbance data using the Lambert Law formula [40–43]. The optical band gap energy was obtained by using the Tauc and Menth's relation [40–43]. Considering Fig. 6, the optical band gap energy is found to be 3.34 eV. FMO energies of MTC are calculated by using the B3LYP/6-311++G(d,p). The occupied and unoccupied MOs for MTC in ethanol solvent are given in Fig. 5. It is well known that the relationship between energy gap and FMOs explains the molecular chemical stability, chemical reactivity and spectroscopic properties of the molecules. While the theoretical energy gap values for MTC in gas phase and ethanol solvent are obtained as 4.631 and 4.758 eV, the experimental one is found to be 3.34 eV. It is clear that the results are comparable. This difference is consistent with previous band gap of the Cu(ii) complex [57]. In addition, the HOMO and LUMO energy values for thiophene by HF/6-31+G(d,p) level were obtained to be -9.09 eV, 2.13 eV [44]. It is stated that the differences between our FMO results and values reported by Mandal et. al [44] originate from the electron-accepting aldehyde group and electron-donating methyl group in disubstituted thiophene ring. It is noted that the molecular electrostatic potential (MEP) surface plots have been used as method of mapping electrostatic potential (ESP) onto the iso–electron density surface [45]. In addition, the MEP shows molecular shape, size and ESP regions depending color classification. Besides, in the research of relation between the molecular structure and physicochemical property of molecules containing bio molecules and drugs have been used
ACCEPTED MANUSCRIPT [46–51]. In this regard, the MEP and ESP surfaces are given in Fig. 7a. The color code of MEP for MTC is in the range of 7.688e-2 a.u. (deepest blue) and -7.688e-2 a.u. (deepest red). Herein the negative potential are over the electronegative O atom of carbonyl group. Likewise, the negative regions of ESP are usually associated with the lone pair of electronegative atoms (see Fig. 7b). Owing to Fig. 7, the carbonyl group displays the most negative potential regions while the hydrogen atoms exhibit the most positive regions. Zero potential regions depict the carbon atoms. 3.4. Refractive index and NLO analyses Nonlinear optics (NLO) have been widely investigated due to providing key functions of frequency shifting, optical modulation, fiber optical materials for the arising technologies in areas such as signal processing, telecommunications [5257]. Investigation of NLO parameters for molecular systems is important with regard to the efficiency of electronic communication between electron accepting and donating groups playing a key role in identifying the intramolecular charge. Moreover, it could be determined that the relation between α and refractive index which shows the polarization of the compounds through the electromagnetic field of the light. It means that the value of χ(n) susceptibility is inversely proportional the value of the strength(s) of the applied electric field(s) and the path length needed to achieve the given nonlinear optical effect [5658]. The refractive index of MTC was obtained by using equations given references therein [44,59–61]. The plot of the refractive index in the IR region is shown in Fig. 8. It is worthy that the refractive index values change between 4000 and 400 cm−1, and there are the peaks because of vibrational absorption. In this region, the value of the average refractive index is 1.51. Total static dipol moment (μ, in Debye), the mean linear polarizability (‹α›, in 10-24 esu), refractive index (n), anisotropy of linear polarizability (Δα, in 10-24 esu), mean first and second−order hyperpolarizabilities (‹β› and ‹γ› in 10-30 and 10-36 esu), and third−order susceptibility (χ(3), in 10-13 esu) for MTC are calculated by using equations given therein [62−66]. The calculated parameters are given in Table 3. It is can be seen in Table 3, the β and γ values are calculated as 4.54×10-30 and 12.26×10-36 esu and 8.64×10-30 and 30.11×10-36 esu by using B3LYP/6−311++G(d,p) level in gas phase and ethanol solvent, respectively. In
ACCEPTED MANUSCRIPT order to evaluate these parameters without doing any experimental study, the results of p−Nitroaniline (pNA) [67−69] and urea [70] have been used as the prototypical compounds. In comparison of β results, the β values are 1.76 times lower than pNA (8×10-30 esu) in gas phase while the β values are 34.92 and 66.46 times higher than urea (0.130×10-30 esu) in gas phase and ethanol solvent. It is clear that the substantial β values were obtained with respect to the urea. It is clearly seen in Table 3, the difference between obtained the β and γ results in gas phase and ethanol solvent is 1.90 times and 2.456 times. This differences is not observed for energy gap values in same solvent. However, the β and γ results in gas phase and ethanol solvent is inversely proportional to energy gap. This statement is compatible with our previous studies [57,6266]. When it comes to γ, the γ values are about 2.01 times higher than pNA (15×10-36 esu) in ethanol solvent, obtained γ value in ethanol solvent could be remarkably indicator microscopic third−NLO material. Obtained 4.68 and 6.41 D values for μ in different solvents are 1.92 and 2.63 times higher than pNA (2.44 D). The α values are found to be 13.96×10-24 and 19.26×10-24 esu in gas phase and ethanol solvent, these values are ~1.58, and ~1.14 times lower than pNA (22×10-24 esu). Hinchliffe and Soscún [71] reported the dipole polarizability values for five-membered heterocyclics calculated using different levels. The electrondonating effect of thiophene ring was uncovered at these parameters. Another study containng this group displays the same tendency [66]. According to these results, it is commented that there are both partial molecular charge distribution and charge movement in MTC irrespective of gas phase and ethanol solvent. In this work, the real part of χ(3) irrespective of doing experimental study related to the γ parameter is calculated at B3LYP level. The calculated refractive index and χ(3) values in gas phase and ethanol solvent are presented in Table 3. The n and χ(3) parameters are obtained at 1.92/25.13 and 1.81/33.30 in mentioned solvents, respectively. In comparison of n and χ(3) results, obtained results are consistent with that results of different molecular systems [72−74]. 4. Conclusion Vibrational and electronic spectral properties of MTC were investigated by using FT−IR and UV−Vis techniques. The conformational structures based on different dihedral angles, the assignments of vibrational frequency and electronic transitions, second− and third−NLO
ACCEPTED MANUSCRIPT parameters in gas phase and ethanol solvent have been also examined by using TDDFT/B3LYP/6-311++G(d,p) level. It can be noted remarkable that there is a good agreement between the experimental and corresponding theoretical results for MTC. Although among the β and γ parameters are minor difference in above solvents, these parameters are found with 1.9 and 2.5 times differences. The γ demonstrates that MTC could be a material which has substantial microscopic third−order NLO parameters. In brief, it could be clearly seen that microscopic third−NLO parameters that of MTC are notable and exhibit a positive solvatochromic behavior within in gas phase and ethanol solvent. And so obtained results could be used to thiophene and its derivatives in future work. References [1] M.A.V.R. da Silva, A.F.L.O.M. Santos, Experimental thermochemical study of the three methyl substituted 2-acetylthiophene isomers, J. Chem. Thermodynamics, 40 (2008) 1309– 1313. [2] L. Zechmeister, J.W. Sease, A Blue-fluorescing Compound, Terthienyl, Isolated from Marigolds, J. Am. Chem. Soc. 69 (1947) 273–275. [3] R.M. Buitelaar, A.A.M. Langenhoff, R. Heidstra, J. Tramper, Growth and thiophene production by hairy root cultures of Tagetes patula in various two-liquid-phase bioreactors, Enzyme Microbiol. Technol. 13 (1991) 487–494. [4] M.A.V.R. da Silva, A.F.L.O.M. Santos, Experimental thermochemical study of 3-acetyl-2methyl-5-phenylthiophene, J. Chem. Thermodynamics 42 (2010) 128–133. [5] M.A.V.R. da Silva, A.F.L.O.M. Santos, Calorimetric study of methyl and ethyl 2thiophenecarboxylates and ethyl 2- and 3-thiopheneacetates, J. Chem. Thermodynamics 41 (2009) 926–931. [6] M. Benabdellah, A. Aouniti, A. Dafali, B. Hammouti, M. Benkaddour, A. Yahyi and A. Ettouhami, Investigation of the inhibitive effect of triphenyltin 2-thiophene carboxylate on corrosion of steel in 2 M H3PO4 solutions, Appl. Surf. Sci. 252 (2006) 83418347. [7] M.A.V.R. da Silva, A.F.L.O.M. Santos, Energetics of some sulphur heterocycles thiophene derivatives, J. Therm. Anal. Cal. 95 (2009) 333–344. [8] R. D. McCullough, The chemistry of conducting polythiophenes, Adv. Mater. 10 (1998) 93116. [9] F. Garnier, G. Horowitz, X. Peng and D. Fichou, An all‐organic "soft" thin film transistor with very high carrier mobility, Adv. Mater. 2 (1990) 592–594.
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Figure Captions Fig. 1. The optimized molecular structure of MTC obtained at B3LYP/6-311++G(d,p) in gas phase. Fig. 2. One-dimensional potential energy surface (PES) scan of the calculated energies versus dihedral angles (a) S5-C1-C8-O10 and (b) S5-C4-C11-H14 for MTC obtained at B3LYP/6311++G(d,p) in gas phase. Fig. 3. The comparison of experimental and theoretical IR spectra of MTC. Fig. 4. The comparison of experimental and theoretical UVVis spectra in ethanol solvent and gas phase for MTC. Fig. 5. The occupied and unoccupied molecular orbitals being the most active in electronic transition for MTC in ethanol solvent. Fig. 6. The optical band gap energy graph for MTC in ethanol solvent. Fig. 7. (a) The MEP and (b) ESP surfaces for MTC in ethanol solvent. Fig. 8. The plot of the refractive index dependence on the wavenumber in the IR region.
ACCEPTED MANUSCRIPT Highlights
The conformer structures for 5-Methyl-2-thiophenecarboxaldehyde was obtained. Optical band gap was obtained by UV−vis spectrum. The NLO parameters (β, γ and (3)) were investigated. TD/DFT calculations were performed to support experimental results.
ACCEPTED MANUSCRIPT
Mode
Assignments via PED% at B3LYP level
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
ν(CH) 99% ν(CH) 100% ν(CH) 100% ν(CH) 100% ν(CH) 100% ν(CH) 99% ν(OC) 88% ν(CC) 63%+β(HCC) 10% ν(CC) 36%+β(HCH) 15% ν(CC) 11%+β(HCH) 51% β(HCH) 78%+ τ(HCCC) %12 β(HCH) 92% β(HCC) 10%+β(HCO) 66% ν(CC) 39% +β(HCC) 18%+β(HCO) 16% β(HCC) 63% ν(CC) 45% +β(CCC) 23% ν(CC) 39% + ν(SC) 10% ν(CC) 21% +β(HCC) 55% β(HCH) 28%+τ(HCCC) 50% τ(HCCC) 81% ν(CC) 12%+τ(HCCC) %42 τ(HCCC) %76+τ(CCCC) %12 τ(HCCC) %87 β(CCC) 56%+β(OCC) 16% ν(SC) 68% ν(CC) 11%+ β(CCC) 16%+β(OCC) 12%+β(SCC) 42% ν(CC) 22%+ β(CCC) 10%+β(OCC) 22%+β(SCC) 13% τ(CCCC) 61%+γ(CCSC) 15% τ(SCCC) 42%+γ(CCSC) 33% ν(CC) 21%+ β(CCC) 16%+β(SCC) 21% γ(CCSC) 74% β(CCS) 74% τ(OCCC) 29%+ τ(SCCC) 33%+ τ(CCSC) 17% β(OCC) 18%+β(CCS) 68% τ(OCCC) 48%+ τ(SCCC) 14%+γ(CCSC) 25% γ(HCCC) 91%
FT−IR [cm-1] 3086 2973 2920 2803 2742 2695 1650 1530 1456 1382 1340 1231 1216 1165 1049 972 894 801 755 685 670 600 569 546 480 430
Scaled freq. [cm-1]a B3LYP 3080 3067 2989 2960 2911 2783 1672 1515 1448 1426 1421 1363 1355 1295 1191 1184 1130 1031 1015 966 951 868 781 768 686 659 616 582 488 436 329 312 197 157 108 83
Table 1. Compar ison of FT-IR and calculat ed vibratio n frequen cies for the 5Methyl2thiophe necarbo xaldehy de
ACCEPTED MANUSCRIPT υ: Stretching; β: in plane bending; γ: out–of plane bending; τ: twisting. aThe calculated vibrational frequencies of 5Methyl-2-thiophenecarboxaldehyde were scaled as 0.961 for frequencies higher than 800 cm−1and as 1.001 for frequencies lower than 800 cm−1 at the B3LYP/6-311++G(d,p) level.
ACCEPTED MANUSCRIPT Table 2. Electronic transitions, wavelengths and oscillator strengths for MTC in gas phase and ethanol solvent Solvent
Exp.
TD/B3LYP/6-311++G(d,p)
λabs (nm)
λabs (nm) 336.8 273.9 259.0 4 324.0 287.1 268.9 8
Gas phase
Ethanol
348.3 237.2
f(osc. str.) 0.0002 0.2586 0.1127 0.0002 0.3496 0.1437
Major contributions (%) obtained via SWizard//Chemissian programs [H: HOMO; L: LUMO; T: Thiophene; A: Aldehyde] H-1→L(96%)//T(100%)→ T(47%)+A(53%) H→L(79%), H-2→L(18%)//T(100%)→T(47%)+A(53%) H-2→L(78%), H→L(18%)//T(100%)→T(47%)+A(53%) H-2→L(97%)//T(100%)→T(46%)+A(54%) H→L(84%), H-1→L(14%)//T(100%)→T(46%)+A(54%) H-1→L(83%), H→L(14%)//T(100%)→T(46%)+A(54%)
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Table 3. Total static dipol moment (μ, in Debye), the mean linear polarizability (‹α›, in 10-24 esu), refractive index (n), anisotropy of linear polarizability (Δα, in 10-24 esu), mean first and second−order hyperpolarizabilities (‹β› and ‹γ› in 10-30 and 10-36 esu), and third−order susceptibility (χ(3), in 10-13 esu) for MTC. B3LYP/6–311++G(d,p) Property Gas phase Ethanol solvent μ 4.68 6.41 μ 2.44 [67−69] <α>
13.96
<α>
19.26 22 [67−69]
n Δα
1.92 9.74
1.81 13.72
<β>
4.54
8.64
<β>
8 [67−69], 0.13 [70]
<γ>
12.26
30.11
(3)
25.13
33.30
<γ>
15 [67−69]