Synthesis, Spectroscopic and Quantum Chemical Studies of N-Pentylhydrazinylthiazole Derivatives

Abstract Herein, a series of N-pentylhydrazinylthiazole based compounds (EP1–EP7) were synthesized via three step synthetic strategy. The intermediates (TH1–TH7) were prepared with Hantzsch’s approach followed by N-pentylation through substitution reaction to obtain targeted N-pentylhydrazinylthiazoles (EP1–EP7). The proposed structures were established with different spectroscopic methods like FTIR, 1H-, 13C-NMR, and HRMS. Further, the non-linear optical (NLO) effect of established structures was explored via quantum chemical investigations. NLO, ultraviolet–visible (UV–Vis), natural population analysis (NPA), global reactivity parameters (GRPs), and natural bond orbital (NBO) investigations were executed at M06/6-311G(d,p) level of density functional theory (DFT). UV–Vis analysis revealed that the yielded systems (EP1–EP7) exhibited absorption wavelength in UV–Vis spectrum in the range of 328.61–389.58 nm. EP1 exhibited the highest λmax value (389.58 nm) among all examined compounds due to its minimal Egap of 4.028 eV. The widening of the energy gap was observed from EP1 to EP7 (4.028–4.492 eV) as elucidated by Frontier molecular orbital (FMO) investigation. The GRPs were correlated with the results of energy gap. As EP1 depicted the minimum band gap (4.028 eV), so it exhibited the highest value of softness (0.248 eV−1) along with lower-most value of hardness (2.014 eV). NBO analysis revealed valuable insights into the charge delocalization and stability of the compounds (EP1–EP7). The dipole moment (μtot), average linear polarizability , first and second order hyperpolarizabilities (βtot and γtot) were also executed for EP1–EP7 at the above-mentioned level. Consequently, the maximum βtot (2.10 × 10−29 esu) and γtot (9.31 × 10−35 esu) values were depicted by EP1 and EP3, respectively. Thus, all these outcomes unveiled that EP1 depicted robust response and proved to be the best NLO candidate for various hi-tech applications such as signal processing, fiber optics and data storage.


Introduction
Now-a-days, researchers are trying to synthesize those scaffolds which have large number of applications in various fields by adopting simple synthetic strategies in which cheaper raw materials are employed. 13][4] In medicinal chemistry, thiazole class is unique in a sense, as it is a part of many commercially available drugs (Meloxicam, 5,6 Sulfathiazole, 7 Ritonavir, 8 etc.) and also possess many applications like antibacterial, 9 antiviral, 10 antiallergic, 11 anticancer, 12 etc.Besides these applications of thiazole based molecules in pharmaceutical industry, they have a large number of applications in material science as well.][15] The demand for efficient and innovative optoelectronic materials is steadily rising in today's high-tech society.Due to potential applications in a diverse advanced integrated photonic high-tech, such as two-photon and fluorescence imaging, 16 optical power limiting, 17,18 optical communication, [19][20][21] and data storage, 22,23 the growth of non-linear optical (NLO) materials is an progressive research area for the experimental and theoretical society. 249][40] Organic based NLO materials are demanding due to their low cost, easy synthetic method, and low dielectric constant values. 28,30,413][44] Taking into consideration the aforementioned benefits of organic based NLO materials, we herein reported the quantum chemical and synthesis research on thiazole based compounds (EP1-EP7).A detailed literature study determined that the synthesized compounds have not been previously reported and their NLO effect has not been considered using the density functional theory (DFT) approach.Hence, in this article, we have established comprehensive theoretical and experimental research to discuss the structural and quantum chemical investigations of thiazole-based EP1-EP7.We anticipated that these thiazole-based EP1-EP7 optoelectronic organic systems might be magnificent NLO compounds.

Material and methods
The syntheses of N-pentylated hydrazinylthiazoles were achieved with the help of commercially available pure reagents and solvents.The solvents and reagents were gotten from Sigma-Aldrich (St. Louis, MO), Merck (Darmstadt, Germany), and Riedel-de-Hean (Hanover, Germany).The purity of products and reaction progress was determined with thin layer chromatography (TLC) pre-coated silica gel 60 F 254 on aluminum sheets with thickness of 0.2 mm (Merck, Germany).The melting points (M.P.) of the synthesized systems were learned utilizing an A&E Lab (UK) M.P. device and are reported without correction.Shimadzu Nicolet iS10 FT-IR spectrophotometer apparatus was used to detect the functional groups like; carbonyl, C-H aliphatic, aryl C ¼ C, C-N, and C-O in the synthesized compounds.Total numbers of proton and carbon signals in the compounds were recorded with Bruker Avance 300 and 75 MHz spectrometer, correspondingly.The multiplicities of the signals are labeled as singlet, doublet, triplet, doublet of doublets and multiplets.Bruker Micro TOF-ESI positive targeted mode spectrometer was used to record the HRMS results.

Syntheses of EP1-EP7
Ethyl 2-(2-arylidenehydrazinyl)thiazole-4-carboxylates (TH1-TH7) (1.0 mmol) and potassium carbonate (3.0 equivalent) in acetone were heated to reflux for 30 min.Pentyl chloride (1.2 equivalent) was then added to the hot reaction mixture drop wise within 10-15 min. 45The reaction mixture was subjected to reflux further for 5-6 h.The consumption of the reactant was indicated by TLC, taken regularly, after every 30 min.The presence of a single spot on the TLC plate indicated the successful conversion of ethyl 2-(2-arylidenehydrazinyl)thiazole-4carboxylates to ethyl 2-(2-arylidene-1-pentylhydrazinyl)thiazole-4-carboxylates (EP1-EP7).After completion, the reaction mixture was carefully poured onto crushed ice, leading to the precipitation.The obtained precipitates were subjected to filtration, followed by thorough washing with cold water and subsequent drying at room temperature.The obtained solid was recrystallized in tetrahydrofuran (THF) to attain maximum purity.The NMR spectra of recrystallized compounds (EP1-EP7) were taken in DMSO-d 6 using 300 MHz ( 1 H) and 75 MHz ( 13 C) frequency.

Computational procedure
The quantum chemical computations for EP1-EP7 were executed using DFT by applying Gaussian 09 program. 46At first, the structures of the EP1-EP7 were drawn and input files were generated using Gauss View-6.0 software.These input files were then executed using the Gaussian 09 package to perform the optimization in the gas phase.Geometrical optimization of all the examined chromophores (EP1-EP7) was carried out via DFT approach by utilizing M06/6-311G(d,p) level 47 .NBO 3.1 48 package was employed to perform NBO analysis to determine intermolecular charge transfer (ICT) and non-covalent interactions between different fragments of investigated chromophores (EP1-EP7).Furthermore, NPA, FMO, ultraviolet-visible (UV-Vis), and NLO analyses were accomplished at the aforementioned level.The programs such as Avogadro, 49 Gauss view 5.0, 50 Gauss Sum, 51 and Chemcraft 52 were applied to interpret the output files.The following Equation (1) calculated the dipole moment. 53 <a> was calculated via employing Equation (2). 54 The Gaussian output files yielded ten hyperpolarizability tensors whose orientations were along x, y, and z axes.The outcomes of b tot was computed by Equation (3). 55 c tot is calculated via employing Equation (4). 56 Where, c i ¼
The structures of ethyl 2-(2-arylidene-1-pentylhydrazinyl)thiazole-4-carboxylates (EP1-EP7) were firstly confirmed with change in physical parameters like; color change from yellow to brown, decrease in M.P. and increase in retardation factor (R f ) values with respect to compounds TH1-TH7.Further different spectroscopic methods were utilized for the geometrical confirmation (see Figures S9-S34).
Characteristic absorptions of functional groups were observed in IR spectra to justify the respective functional groups presence in the proposed structures.The absorptions of CH-aliphatic stretching were observed at 2921-2969 cm À1 .The carbonyl group absorptions appeared at 1714-1726 cm À1 .Furthermore the disappearance of -NH absorption in the final product was another evidence for the N-pentylation at the desired final products.
Total numbers of 1 H-and 13 C-signals were indicated from NMR study.Three proton triplet (J ¼ 6.0-6.6 Hz) at 0.85-0.87ppm was assigned to methyl (-CH 3 ) of pentyl chain.Multiplet of seven protons was observed at 1.21-1.44ppm assigned to two methylene units (-CH 2 -) of pentyl chain and methyl (-CH 3 ) of ester functionalities.A singlet of one proton of thiazole ring was identified at 7.12-7.89ppm.Another one proton signal of azomethine (-CH ¼ N-) appeared as singlet at 8.01-8.29 ppm.Aromatic protons were observed within the characteristic aromatic region relative to the substituents attached at the arylidene ring.Most of the aromatic proton signals for all compounds were observed as multiplets except EP4.For EP4, two doublets (J ¼ 8.1 Hz) within the aromatic region were observed at 7.50 and 7.73 ppm, confirmed the formation of proposed structure.In 13 C-NMR data, characteristic carbons of pentyl chain were recorded within range of 13.9-28.8ppm.Signals of carbons, -CH 2 N-, and -OCH 2 -were appeared at 44.5-45.2 and 60.9-61.1 ppm, respectively.Thiazole carbons at position 2, 4, and 5 were observed at 169.6-170.6,143.2-143.6,and 120.3-122.4ppm, respectively.The carbon of azomethinic functionality was recorded at 132.7-148.3ppm.Six carbon signals were observed for all compounds except EP3 and EP4 due to attachment of substituent at the meta position of arylidene ring.Four carbons were appeared within the aromatic region for compounds EP3 and EP4 due to substituent attached at the para position of arylidene ring.NMR data successfully justify the total number of protons and carbons within the proposed structures.Finally, the authentication of formation of compounds was achieved with HRMS results.In HRMS, the calculated were in good agreement of their observed values.

Configuration of investigated chromophores
The currently investigated derivatives (EP1-EP7) have been synthesized experimentally and their theoretical study has been carried out which suggested that the entitled compounds (EP1-EP7) have significant NLO response.The properties of these derivatives have been studied by using some important parameters including; (i) <a>, (ii) b tot , (iii) c tot , (iv) NBO transitions (v) maximum absorption wavelength, and (vi) energy difference between HOMO and LUMO.In the recent study, we divided all chromophores in three portions such as; (i) fragment 1, (ii) fragment 2, and (iii) fragment 3 as depicted in Scheme 2. The fragment 3 is varied in all these compounds (EP1-EP7) having different electron withdrawing moieties by keeping fragment 1 as well as fragment 2 unchanged.The chemical structures of all these studied compounds (EP1-EP7) are represented in Figure 1, while their optimized structures are exhibited in Figure 2. Ethoxycarbonyl is utilized as fragment 1, whereas 2-(2-methylene-1-pentylhydrazinyl)thiazole is acting as fragment 2 in all these investigated chromophores (EP1-EP7).Moreover, 1-nitro-2-phenylmethylidene amino is considered fragment 3 in EP1 which is substituted with 1-methoxy-2-phenylmethylidene amino, 1-bromo-4-phenylmethylidene amino, 1-chloro-4-phenylmethylidene amino, 1-bromo-2-phenylmethylidene amino, 1-chloro-2-phenylmethylidene amino and 1-methyl-2phenylmethylidene amino in EP2 to EP7, respectively.Thus, considerable change in NLO properties has been observed via employing various different electron-withdrawing units as 3rd fragment in all these chromophores (EP1-EP7).We hope that this work will trigger the researchers further to put their efforts in obtaining efficient NLO materials owing to their excellent response.

Frontier molecular orbitals (FMOs) investigation
Frontier molecular orbitals (FMOs) study is an effective to investigate the electronic features of the compounds. 60,613][64] The energy difference between molecular orbitals (E gap ¼ E LUMO À E HOMO ) of compounds is closely related to their kinetic and chemical stability, reactivity, chemical softness, and hardness. 65The lower the results of DE, the  higher will be the polarizability resulting in excellent NLO results. 66,67Table 1 illustrates DE values of the investigated compounds (EP1-EP7).
It is revealed by the data presented in Table 1 that EP7 exhibited highest value of computationally determined HOMO/LUMO energy difference (DE) i.e. 4.492 eV among all the investigated chromophores (EP1-EP7).The E gap value for EP2 reduced to 4.427 eV because of the substitution of methyl group with methoxy at ortho position in fragment 3.This moiety caused the enhancement of electron density over the ring through resonance factor and conjugation in EP2 which resulted in abridged E gap value.Furthermore, in EP6 and EP5, E gap is further lowered (4.386, 4.373 eV), which may be due to the replacement of chloro and bromo groups in fragment 3 in both compounds at ortho position, respectively.The highly electronegative nature of halogens i.e. chloro and bromo groups enhance the acceptor's capacity to pull electrons, which may result in decrease in the band gap of EP6 (4.386 eV) and EP5 (4.373 eV).Interestingly, the HOMO-LUMO energy gap in EP4 and EP3 is further dropped to 4.341 and 4.332 eV due to their chemical structures that are further modified by incorporating chloro and bromo groups in fragment 3 of EP4 and EP3 at para position, respectively.It is anticipated that higher the electronegativity of the molecules, more will be the transition of electrons in the direction of acceptor unit owing to negative inductive effect. 68Moreover, energy gap in EP4 and EP3 is lesser as compared to EP6 and EP5 owing to the difference of position (ortho, para) of attached groups (chloro, bromo).Furthermore, EP1 indicated the smallest energy band gap as compared to the aforementioned compounds i.e. 4.028 eV due to incorporation of -NO 2 moiety in this molecule.As -NO 2 has both negative inductive effect (-I) and negative resonance effect (-R), so it showed higher electron-withdrawing effect than the groups that have only -I effect.
Briefly, the decreasing order of HOMO-LUMO band gap is in the following order: EP7 > EP2 > EP6 > EP5 > EP4 > EP3 > EP1.These finding confirmed that different electronegative units in the investigated compounds (EP1-EP7) played a substantial role to reduce the E gap values consequently, enhancing the NLO behavior.The FMO analysis also provided an explanation for the associated orbital energies and charge-transfer phenomenon for the examined chromophores as shown in Figure 3.Moreover, other findings are illustrated in Figures S1-S7 and Table S1. Figure 3 reveals that charge density in LUMOs of the considered chromophores (EP1-EP7) is majorly located over the fragment 3, while minorly over the fragment 2. The charge density of HOMOs is predominantly distributed over both the fragments i.e. fragment 1 and 2 except some atoms of fragment 2. The charge density in HOMOs is also present on some atoms of fragment 1 as well.The E gap of HOMO-1/LUMO þ 1 and HOMO-2/LUMO þ 2 along with their pictographic representation are depicted in Table S1 and Figures S1-S7, respectively.Magnificent CT explored that yielded chromophores could be expressed higher NLO nature.

UV-Vis analysis
UV-Vis investigation is employed to obtain the absorption properties of said molecules.The outcomes of the k max are frequently enhanced attributed to electron-withdrawing groups presence.The values of k max shift bathochromically as a result of the addition of extended conjugated electron-withdrawing moieties. 69,70The outcomes of absorption spectrum of the investigated compounds (EP1-EP7) are represented in Tables 2 and S14-S20.
The outcomes revealed that all the studied molecules (EP1-EP7) displayed wavelengths in the range of 328.609-389.581nm.It is noted that the change of substituents shifted the absorption wavelength toward the visible region.The calculated highest absorption peak for EP7 is noticed as 328.609 nm with 3.773 eV excitation energy and 0.544 value of f os along with 98% MO contribution from HOMO to LUMO.The induction of the methoxy group at ortho position in EP2 enhanced the wavelength to 335.083 nm with 3.700 eV transition energy.Furthermore, the wavelength of EP6 and EP5 is found to be 337.225and 339.460 nm which is larger than EP2 owing to the chloro and bromo groups at ortho position.A further increase in wavelength is observed in EP4 and EP3 (341.677 and 342.962 nm) as a result of incorporation of chloro and bromo moieties at para position.The maximum value of k max (389.581nm) is noted in EP1 with 3.183 eV transition energy as well as 93% HOMO toward LUMO and 4% HOMO to LUMO þ 1 MO contribution.The examined compound (EP1) exhibited the highest red-shifted absorption wavelength owing to its lowest HOMO/LUMO energy gap value (4.028 eV).Overall, the declining order of k max for all the entitled compounds is: A graph is plotted between the results of molar absorptivity coefficient and wavelengths for the studied chromophores as depicted in Figure 4. Conclusively, this investigation showed that the absorption spectrum of all the synthesized chromophores (EP1-EP7) is obtained in UV-Vis region and red-shifted behavior is observed in the investigated compounds by the use of various strong electronegative groups.Therefore, it is indicated that our entitled molecules (EP1-EP7) with low excitation energies and high absorption wavelengths are suitable candidates for use in non-linear optics.

Global reactivity parameters (GRPs)
Global reactivity parameters (GRPs) can be employed to assess the reactivity and stability of the examined systems (EP1-EP7) by considering their energy gap (GRPs). 19The E gap is a dynamic factor that affects GRPs. 71The ability of a molecule to donate electrons is denoted by its ionization potential, while its electrons attraction capability is referred to as its electronegativity.Molecules exhibiting the highest values of hardness (g) and chemical potential (l) are considered to be kinetically stable compounds, as they possess favorable characteristics for stability.Furthermore, these factors are directly correlated with orbitals E gap values and inversely associated with global softness (r). 72Additionally, the molecule with a greater E gap shows greater stability, lower reactivity, and a high value of hardness. 73The GRPs have been defined by Koopman's Equations. 74The IP, 75 X, 76 EA, 62 g, 77 r, 78 l 79 , and x 80 are calculated by using Equations (5-11), accordingly: x Table 3 indicates that the IP of EP1 is found to be greatest with value of 6.152 eV than all the other studied chromophores.The decreasing order of IP is: EP1 > EP4 >EP3 > EP6 > EP5 > EP7 > EP2 with values as: 6.152 > 6.084 > 6.079 > 6.048 > 6.047 > 5.965 > 5.775 eV, correspondingly.
The largest value of softness among all of the entitled compounds, i.e. 0.248 eV À1 is revealed by EP1, which exhibited maximum polarizability owing to its greater reactivity.This value of softness is lowered to 0.231 eV À1 in EP3.Significant drop in the values is viewed in the case of EP4, EP5, EP6, and EP2 of 0.230, 0.229, 0.228, and 0.226 eV À1 , correspondingly.The smallest value of softness is determined in EP7 (0.223 eV À1 ) which indicated its least reactivity with lowest polarizability.The order for the lowering of softness is evaluated as: EP1 > EP3 > EP4 > EP5 > EP6 > EP2 > EP7.Among the studied systems, the highest value of hardness (2.246 eV) is observed for EP7, whereas the lowest value is exhibited by EP1 (2.014 eV) as a consequence of its lowest HOMO/LUMO band gap (4.028 eV).The order of global hardness is found to be exactly opposite to that of global softness values.However, all the investigated compounds showed higher global softness with the lower global hardness values, but EP1 is found to be the softest and least hard chromophore among all these entitled compounds.This maximum value of global softness indicates the greatest chemical reactivity of this molecule.Thus, the titled chromophores (EP1-EP7) might prove to be highly efficient compounds and exhibit significant NLO characteristics accordingly.

Natural bonding orbitals (NBO) analysis
2][83] In this analysis, the variables, the variables j and i represent the acceptor and donor, correspondingly, while the stabilization energy is denoted by E (2)84 , which coordinates with the electronic delocalization among the donor and acceptor from the below equation; In the above equation, q i denotes donor orbital occupancy, e i , e j represent diagonal NBO Fock matrix elements, while F i,j shows off-diagonal NBO Fock matrix elements, correspondingly. 85The major outcomes are tabulated in Table 4, whereas the other outcomes are shown in Tables S2-S8 in supplementary data.
Similarly, the highest values of r !r Ã are found in following bonds:   Overall, the results showed the stability of compounds is considerably influenced by the delocalization of electrons.As a result, we may conclude that the extended hyperconjugation is present in the entitled molecules (EP1-EP7), which plays a significant part in their stability, and produce highly efficient NLO materials.increased comprehension of conjugated system. 86,87The Mullikan charges of the entitled compounds (EP1-EP7) are presented in Figure S8.
The charge density dispersal reveals that the sulfur atom carries a positive charge, whereas the oxygen atoms exhibit a negative charge.This charge distribution can be attributed to the influence of electronegativity, with sulfur being less electronegative than oxygen.Furthermore, bromine atom in EP3 and EP5 associated with hydrogen are positively charged, while chlorine in EP5 and EP6 are negatively charged.Some carbon atoms possess positive charge because of direct linkage with more electronegative atoms.The complete Mulliken charges investigation showed that the uneven dissemination of charge on the investigated molecules is owing to the presence of electronegative atoms i.e. nitrogen and oxygen atoms.

Non-linear optical (NLO) investigation
NLO chromophores are widely employed in optoelectronic, signal processing and communication networking devices. 88The electrical characteristics of a molecule are directly linked to its polarizability < a > and nonlinear responses, specifically the first hyperpolarizability (b tot) and second hyperpolarizability (c tot ).These properties play a crucial role in determining how the molecule behaves optically. 81,89ICT as well as hyperpolarizability characterize the correspondence among molecular structure and nonlinearity.High NLO effect is equivalent to enhanced hyperpolarizability, polarizability along with dipole moment.Linear polarizability (a) is the strength of electric field that distort electron dispersal all over the system.However, molecular as well as atomic nonlinearity dependent on wide-spread NLO effect is called hyperpolarizability (b, c, etc.).Utilizing substituents (electron donating and accepting) at suitable position within the conjugated system can increase the delocalization strength of the electrons in ompound. 90Furthermore, it is intriguing to explore how the NLO properties vary when modifying the fragments of molecules.In this study, the NLO responses of a series of dyes, referred to as EP1-EP7, were estimated and the results are presented in Table 5, whereas other findings are exhibited in Tables S9-S13.
Among all the designed chromophores, EP1 exhibits the highest l tot of 6.584 D. The l tot of the computed molecules follow the decreasing order: EP1 > EP6 > EP5 > EP2 > EP7 > EP4 > EP3.These results indicate that EP1 has the greatest value of l tot , suggesting enhanced intramolecular charge transfer (ICT) and electron transport rate.On the other hand, the results of linear polarizability are comparable for all the derivatives except EP4.Nevertheless, EP3 exhibited the highest value of hai i.e. 4.43 Â 10 À23 esu which may be due to the inductive effect as well as resonance effect of bromo group at para position while, EP4 has chloro at para position in third fragment, showed the lowest <a> value of 0.68 Â 10 À23 esu.Among these newly synthesized compounds (EP1-EP7), the order of <a> for all the investigated chromophores is as follows: The compounds EP1-EP7 exhibit strong ICT, which is associated with their first hyperpolarizability (b tot).EP1 shows the highest b tot value of 2.10Â 10 À29 esu, indicating the strongest NLO response, while EP3 has the minimum b tot value of 0.98 Â 10 À29 esu.The attachment of strong electron-withdrawing units in fragment 3 of the studied compounds (EP1-EP7) has a significant impact on their b tot values, indicating their high efficiency and strong NLO responses.The declining order of b tot values for the investigated compounds is EP1 > EP6 > EP5 > EP7 > EP2 > EP4 > EP3, indicating EP1 as the structure with the highest NLO response.To support the obtained results, the comparison of b tot values with the reference molecule urea was performed, highlighting the enhanced NLO responses of the investigated compounds.Observation revealed that the first-order hyperpolarizability values of EP1-EP7 are 57, 29, 26, 28, 45, 46, and 30 times more relative to urea, correspondingly.
Phenomenon of two-photon absorption (TPA) in NLO materials is thought to be the foundation for the third order NLO (c tot ) effect in a system.As demonstrated in Table S11, a significant c tot response is seen along the x-axis in all the examined chromophores, with EP3 having the largest value (9.31 Â 10 À35 esu) of c tot among the derivatives.The declining trend of c tot for the above-mentioned systems is: EP3 > EP4 > EP1 > EP6 > EP5 > EP2 > EP7.These findings highlight the substantial NLO potential of the designed compounds, indicating their suitability for applications in nonlinear optics. 91

Conclusion
Seven novel N-pentylated derivatives of hydrazinylthiazole were reported in this article.The structures of reported compounds (EP1-EP7) were assured with all possible available spectro-analytical techniques (FTIR, NMR, and HRMS).The impact of altered substituents on the terminal part in fragment 3 of all the studied compounds is carefully studied to observe their NLO response.FMO analysis depicted that an effective charge transfer is noticed in all the examined molecules with greater chemical reactivity by displaying reduction in band gap from EP7 to EP1.Furthermore, charge density is observed on the all systems except the pentyl chain.Maximum absorption spectrum value of 389.581 nm with 3.183 eV transition energy and 0.141 value of f os has been observed for EP1 as a consequence of its smallest band gap (4.028 eV) among its molecular orbitals.EP1 is noted to have least hardness (2.014 eV), greatest softness (0.248 eV À1 ), and highest chemical potential value as compared to the other chromophores.NBO investigation displayed that larger stabilization energy along with the most probable transition is demonstrated by all the chromophores (EP1-EP7).The highest dipole moment value of 6.5843 D is perceived in EP1 which demonstrated that greater polarizability is noted in EP1.Furthermore, the investigated compounds (EP1-EP7) display remarkable NLO characteristics, among the compounds, EP3 and EP1 stand out with the highest <a> , b tot and c tot (4.43 Â 10 À23 , 2.10 Â 10 À29 , and 9.31 Â 10 À35 esu) values, showcasing their significant NLO potential for applications in nonlinear optics.It is contemplated that our synthesized chromophores (EP1-EP7) especially EP1 might prove to be valuable for potential NLO applications in advanced optical devices.

Table 5 .
Computed <a> , l tot , b tot, and c tot of compounds EP1-EP7.tot in Debye (D); hai, b tot , and c tot. are in esu.