M06-2X Functionals Research Articles

Prediction of Partition Coefficients in SDS Micelles by DFT Calculations

A computational methodology using Density-Functional Theory (DFT) calculations was developed to determine the partition coefficient of a compound in a solution of Sodium Dodecyl Sulfate (SDS) micelles. Different sets of DFT calculations were used to predict the free energy of a set of 63 molecules in 15 different solvents with the purpose of identifying the solvents with similar physicochemical characteristics to the studied micelles. Experimental partition coefficients were obtained from Micellar Electrokinetic Chromatography (MEKC) measurements. The experimental partition coefficient of these molecules was compared with the predicted partition coefficient in heptane/water, cyclohexane/water, N-dodecane/water, pyridine/water, acetic acid/water, decan-1-ol/water, octanol/water, propan-2-ol/water, acetone/water, propan-1-ol/water, methanol/water, 1,2-ethane diol/water, dimethyl sulfoxide/water, formic acid/water, and diethyl sulphide/water systems. It is observed that the combination of pronan-1-ol/water solvent was the most appropriated to estimate the partition coefficient for SDS micelles. This approach allowed us to estimate the partition coefficient orders of magnitude faster than the classical molecular dynamics simulations. The DFT calculations were carried out with the well-known exchange correlation functional B3LYP and with the global hybrid functional M06-2X from the Minnesota functionals with 6-31++G ** basis set. The effect of solvation was considered by the continuum model based on density (SMD). The proposed workflow for the prediction rate of the participation coefficient unveiled the symmetric balance between the experimental data and the computational methods.

Computational survey on the Pt-decorated ZnO nanosheet as a chemical sensor for chlorobenzene: Explaining the experimental observations

Following an experimental work, we investigated the sensing performance of a zinc oxide nanosheet (ZnON) in detection of the toxic chlorobenzene (CB) gas using dispersion-corrected TPSS, M06-2X, ωB97X-D, PBE, and B3LYP density functionals. We showed that the pristine ZnON cannot sense the CB gas, but the Pt atom decoration on the ZnON surface significantly increases the ZnON sensitivity in agreement with the experimental results. The calculated Pt@ZnON sensing response is in the range of 36–52 which is in good agreement with the experimental value of 30. Also, we investigated the selectivity, recovery time, and solvent effects. We introduced a theoretical methodology which can interpret the experimental observations at the molecular level. Based on our calculations, the Pt@ZnON paves the way for CB sensor development.

The Se-S Bond Formation in the Covalent Inhibition Mechanism of SARS-CoV-2 Main Protease by Ebselen-like Inhibitors: A Computational Study.

The inhibition mechanism of the main protease (Mpro) of SARS-CoV-2 by ebselen (EBS) and its analog with a hydroxyl group at position 2 of the benzisoselenazol-3(2H)-one ring (EBS-OH) was studied by using a density functional level of theory. Preliminary molecular dynamics simulations on the apo form of Mpro were performed taking into account both the hydrogen donor and acceptor natures of the Nδ and Nε of His41, a member of the catalytic dyad. The potential energy surfaces for the formation of the Se–S covalent bond mediated by EBS and EBS-OH on Mpro are discussed in detail. The EBS-OH shows a distinctive behavior with respect to EBS in the formation of the noncovalent complex. Due to the presence of canonical H-bonds and noncanonical ones involving less electronegative atoms, such as sulfur and selenium, the influence on the energy barriers and reaction energy of the Minnesota hybrid meta-GGA functionals M06, M06-2X and M08HX, and the more recent range-separated hybrid functional wB97X were also considered. The knowledge of the inhibition mechanism of Mpro by the small protease inhibitors EBS or EBS-OH can enlarge the possibilities for designing more potent and selective inhibitor-based drugs to be used in combination with other antiviral therapies.

A DFT study on the Ag-decorated ZnO graphene-like nanosheet as a chemical sensor for ethanol: Explaining the experimental observations

Following an experimental work, density functionals B3LYP, TPSS, PBE, M06-2X, and ωB97X-D were exploited to examine the impact of decorating an Ag atom on a ZnO nanosheet sensitivity to the ethanol gas. The interaction of the pristine ZnO sheet with the ethanol was found to be weak, and the sensing response is 6.2 at 300 K based on the B3LYP results, in agreement with experiment. Decorating an Ag atom on the ZnO sheet increases the adsorption energy of ethanol from −6.1 to −20.0 kcal/mol. Energy decomposing analysis indicates that the interaction converts from noncovalent to covalent by the Ag decoration. Also, the sensing response significantly rises to 72 (experimental value ~55). We showed that the Ag decorated ZnO sheet can selectively detect ethanol gas in the presence of benzene, formaldehyde, toluene, and acetone. A short recovery time of 35 s is found, being comparable with experimental value of 25 s. We introduced a theoretical methodology which can reproduce the experimental results. Both theory and experiment suggest that Ag-decorated ZnO nanosheet may be highly sensitive and selective ethanol sensor with a short recovery time.

Effect of the mixture composition of C4mimBF4/acetonitrile on the charge transfer in Coumarin 153: DFT and TD-DFT analysis

In this work, we studied by means of density functional theory (DFT) and time-dependent DFT(TD-DFT) using the effect of the mixture composition C4mimBF4/acetonitrile on the charge transfer in Coumarin 153(C153) after photoexcitation. The mixture composition was characterize by their corresponding static dielectric constant εm. The PBE0 and M06-2X functionals combined with linear response (LR) and state specific (SS) solvation schemes were used to obtain various electronic properties of C153 in both ground and excited states. Our results show that the calculated fluorescence Stoke shift, using the state specific solvation scheme correlates well with the corresponding experimental data obtained for C153 dissolved in other solvents have the same static dielectric constant as of the C4mimBF4/acetonitrile mixture. The charge transfer was quantified using descriptors such as charge qCT, distance dCT, and the dipole moment μCT between the ground and the excited state. These descriptors were calculated based on four different partial atomic charge models, namely Mulliken, Natural Populations Analysis, Hirshfeld, and Merz–Kollman. The charge transfer also was quantified using descriptors based on the electrostatic surface potential namely the polarity index. Both PBE0 and M06-2X functionals combined with the Linear Response solvation scheme result in a systematic increase of the qCT, dCT, and μCT with increasing εm, while they decrease for most of the partial atomic charge models when the State Specific solvation scheme is used. This later result points out that this solvation scheme is not suitable for the description of the excited state of C153 in this mixture. Our results show that the extent of change of these descriptors is small and indicates that the effect of the mixture composition on the charge transfer in C153 is weak.

Anharmonicity modeling in hydrogen bonded solvent dimers

Harmonic and anharmonic frequencies of dimers and mixed dimers of water, methanol and benzene were computed and the results were critically analysed to investigate the anharmonicity of the normal mode vibrations within density functional theory (DFT) with empirically included Grimme correction for dispersion (D3). From several options, the B3LYP-D3/6-31++G* level of theory was selected as a good compromise between accuracy and calculation speed, suitable for future modeling of larger solvent clusters. The obtained raw harmonic and anharmonic second-order perturbation theory of vibrational frequencies (VPT2) were additionally scaled using a two-range procedure (below and above 2000 cm−1) and compared with available experimental values for the studied dimers. Additionally, the Morse and 4th order polynomial fittings of small normal mode deflections from the equilibrium geometry were used to model anharmonicity of the studied dimers. Compared to B3LYP-D3, the VPT2 vibrations calculated with APFD and M06-2X functionals very poorly model the anharmonicity of the H-bonded dimers. The surprising observation was related to the performance of CCSD/6-31++G* and CCSD(T)/6-31++G* in predicting harmonic frequencies of H-bonded dimers of water, water-methanol and methanol-water of similar quality, as compared to B3LYP-D3/6-31++G*. The obtained results suggest using of B3LYP-D3/6-31++G* scaled harmonic frequencies for the larger solvent clusters as a good alternative to anharmonic frequencies.

Structural characteristics of Mile lignite and its molecular model construction

The understanding of the structural characteristics of lignite is of very importance to the lignite utilization. The structure parameters of Mile lignite in Yunnan were ascertained via Fourier transform infrared spectroscopy, 13C solid-state nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy and ultimate analysis. The results indicate that the aromaticity and number of aromatic ring substituents of Mile lignite are 38.79% and 3, respectively. The aromatic carbon structure typically contains benzene and naphthalene, while the aliphatic carbon structure mainly includes methyl and methylene. Oxygen dominantly exists in ether oxygen, carboxyl and carbonyl; nitrogen occurs in the form of pyrrole nitrogen and pyridine nitrogen; and sulfur is mainly present in thiophenol and mercaptan. According to the analysis results, a molecular structure model of Mile lignite is constructed, with a molecular formula of C147H148O36N2S. The semi-empirical PM3 basis set and the density functional theory M06-2X were adopted to optimize the molecular configuration. The optimized model has a significant three-dimensional configuration, in which the aromatic layers are arranged irregularly in space and the aromatic rings are connected by methyl, methylene, methoxy and alicyclic rings. The simulated FT-IR spectrum and simulated 13C NMR spectrum are in great agreement with the experimental spectrum, which proves the accuracy and rationality of the molecular model of Mile lignite.

Intermolecular interaction study of l-Threonine in polar aprotic Solvent: Experimental and theoretical study

The present paper accounts for the interacting nature of CO, CH and OH vibrational modes of l-Threonine in polar aprotic solvent Dimethyl Formamide(DMF) using Raman spectroscopic and infrared(IR) techniques. The intermolecular interaction between l-Threonine and DMF are analyzed using Density Functional Theory (DFT), IEFPCM and M062X methods, each with a basis set 6–311++G (d, p)to predict the favourable interacting sites of the two molecules and to validate the experimental data with the theoretical calculations. The variation in peak frequencies has been explained for neat l-Threonine and their interactions at different concentrations (0.1 M, 0.3 M, 0.5 M, 0.7 M and 0.9 M). The wavenumbers of all the stretching modes (CO, CH and OH) shows a redshift. The intensity and the topology parameters of the intermolecular hydrogen bond at the bond critical points have been analyzed using the AIM theory of DFT and M062X methods. The intermolecular hydrogen bonding for the mentioned complexes and the study of the surface charge that encompasses the molecular cavity has also been carried out using the IEF-PCM solvation model under the same basis set. Electronic properties such as MEP surface study, frontier orbital analysis, and their corresponding energy gap have also been analyzed using DFT calculation. The frequencies derived from the computational and experimental data are found in good correlation to each other.

Electronic and spectroscopic properties of A-series nerve agents

A-series nerve agents lack accurate experimental data on toxicity and other physicochemical properties. In this work, we computed molecular, spectroscopic, and electronic properties of the A-230, A-232, A-242, and A-262 agents employing Density Functional Theory (DFT) with the hybrid exchange-correlation B3LYP and M06-2X functionals, and the second-order Møller-Plesset Perturbation Theory. Computed infrared, Raman activity, ultraviolet–visible, electronic circular dichroism, and nuclear magnetic resonance spectra provide useful information for the accurate characterization of these agents. Electronic properties suggest that the four molecules have similar reactivities, though are less reactive than VX and VR nerve agents. Electrostatic potential surfaces and population analysis strongly indicate that A-series molecules have two electropositive centers. DFT lipophilicity values confirm these compounds' high lipophilic character, although their values are smaller than for VX and VR. These results are an important contribution for investigating new possibilities of identification, treatment, prevention and destruction/neutralization of these compounds.

TD-DFT assessment of UV-vis spectra palladium and platinum complexes with thiols and disulfides.

Time-dependent density functional theory (TD-DFT) and spectrophotometric methods were used for speciation analysis in systems disulfides (cystine, cystamine, homocystine, 3,3-dithiodipropionic acid) - [PdCl4]2- or [PtCl4]2-. We use the M06-2X and CAM-B3LYP density functionals with Def2-SVP basis set to reproduce the experimental UV-vis spectra; the polarized continuum solvation model (PCM) was fitted to take into account solvation effects of the medium (water). Used methods have shown the good agrees with the experiment - theoretical values of transition energies differ from real parameters within ±0.15eV for functional CAM-B3LYP. Binuclear disulfide complexes of Pd(II) with cystine and cystamine have form S,N-coordination sites, instead of S,S-conformation. It was shown that Pd(II)thiolate complexes formed by cleavage of the disulfide bond exist as [PdCl3L] and [Pd2S2L2]. Pt(II)-disulfide systems have confirmed the presence of [Pt2Cl6(R-SS-R)] and [PtCl4(S-R)] complex species. The DFT/CAM-B3LYP/Def2-SVP/SMD level can be recommended for theoretical estimations of absorption spectra of complexes of palladium or platinum and sulfur-containing ligands.

Quantum-chemical calculations of electronic spectra absorption: ab initio or semiempirical methods?

In order to develop approaches to predict the spectral properties of organic dyes for solar cells the test calculations of typical π-conjugated systems with various structural fragments, have been performed. Among the structural elements there are benzene, oxazole, oxsadiazole, thiophene and coumarin fragments. Nitro, methoxy, dimethylamino and diethylamino groups are substituents. According to the obtained experimental data, the diethylamino group at position 7 of the coumarin moiety gave the highest bato- and hyperchromic shifts of spectra. Experimental absorption spectra were measured in various solvents with different polarity. Among them are cyclohexane, dimethoxyethane, tetrahydrofuran, methanol, acetonitrile, and dimethylsulfoxide. It has been shown that there are no significant changes in the λ(max) absorption of coumarin-based compounds when the solvent is changed to a more polar one, but there is a noticeable tendency to increase the intensity of the absorption spectra. For the theoretical interpretations of electronic spectra absorption ab initio density functional theory (DFT) as well as semi-empirical methods (PPP/CIS, ZINDO/S, AM1/CIS) were used. In the DFT calculations the functionals B3LYP, CAM-B3LYP, M06-2x, PBE1PBE, wB97XD were used. A significant discrepancy in the estimations of electronic excitations is demonstrated by the DFT for the different functionals. It is concluded that DFT calculations should be performed by using both B3LYP and CAM-B3LYP (or M06-2x) functionals. Linear response theory has been used to evaluate the solvatochromic properties of π-conjugated compounds in the DFT frameworks. In general it was found that semi-empirical approaches especially π-electron method PPP/CIS and all valence method ZINDO/S can provide adequate estimations of excitation energies of π-conjugated dyes for moderate computer resources.

Diradical character of the bond breaking in the reaction of Br2 with benzene: Reliable barriers using the CR-CC(2,3) method

The transition state for the substitution reaction involving one Br2 species with benzene as a model system has a long Br–Br distance, leading to high multiconfigurational character of the wavefunction in apolar medium. Single reference methods can become erratic on this condition and even the CCSD(T) fails for this system. To describe accurately this reaction, the CR-CC(2,3) method was used because predicts a reliable dissociation curve for the Br2 when compared to MRCISD + Q calculations. The activation barriers for the reaction of one and two Br2 molecules with benzene were calculated with the CR-CC(2,3) method and used as benchmark to evaluate the performance of the functionals B3LYP, M06-2X, M08-HX, ωB97X-D and B2GP-PLYP. The M08-HX and the B2GP-PLYP are the best functionals, with mean absolute deviation close to 3 kcal mol−1.

Theoretical investigation of X12O12 (X = Be, Mg, and Ca) in sensing CH2N2: A DFT study

The feasibility of detecting diazomethane (CH2N2) in the gas phase by adsorption onto the exterior surface of inorganic-based X12O12 (where X can be Be, Mg, or Ca) nanocages is investigated here using DFT. All the structures, including those of the pristine CH2N2 and of the nanocages, as well as of the CH2N2/nanocage systems, have been optimized using the B3LYP-D3, M06-2X, ωB97XD, and CAM-B3LYP functionals, in conjunction with 6-311G(d) basis set. NBO, NCI, and QTAIM analyses results are in good agreement with each other. Furthermore, the Density Of States (DOSs), the natural charges, the Wiberg Bond Indices (WBI), and natural electron configurations were considered to investigate the nature of intermolecular interactions. The energy calculations indicate a strong size-dependent adsorption, with the nanocages comprised of large atoms being able to attract CH2N2 more strongly, and hence bind with it more effectively. The adsorption incurs also significant changes to HOMO and LUMO energies.

Effect of ortho- and para-chlorine substitution on hydroxychlorochalcone.

This work describes a comparative molecular structure of two hydroxychlorochalcones with an emphasis on their planarity. Hirshfeld surface analysis investigates the effect of ortho- and para-chlorine substitution on supramolecular arrangement and physical chemical properties. The molecular conformation of 2'-hydroxy-4',6'-dimethyl-2-chlorochalcone and 2'-hydroxy-4',6'-dimethyl-4-chlorochalcone chalcones was obtained through DFT with the exchange-correlation functional M06-2X and the 6-311++G(2d,2p) basis set, and the results were compared with the experimental X-ray data in order to get insights on the effect of ortho- and para-chlorine substitution. The charge transfer into entire main carbon chain was also investigated using frontier molecular orbitals (HOMO and LUMO), NBO, and MEP map in order to describe the comparative conformational stability due to the resonance effect produced by π electron displacements. Finally, the intermolecular observed interactions were analyzed by QTAIM, with the M06-2X/6-311G++(d,p) theory level.

Phosphates branching effect on the structure, linear and NLO properties of linear phosphazenes

In this paper, we studied the structure, dipole moment, polarizability, and static first hyperpolarizability of linear phosphazenes. The relationship between the nonlinear optical (NLO) properties and the energy gaps was also taken into account. The structure of these phosphazenes has been performed using the B3LYP, ωB97X–D and M06–2X functionals. The linear and NLO properties of these compounds have shown selective responses to the different DFT levels that are in good agreement with the experimental values of similar compounds. The ωB97X–D functional gives a high static first hyperpolarizability compared to the B3LYP and M06–2X levels. An inverse relationship has been obtained between the HOMO–LUMO gaps and βtot. This theoretical study confirms the suitability of these phosphazenes for optoelectronic and optical devices.

How the stability, reactivity and optical response of the protonated base pairs differ with other biologically important adenine–thymine pairs: a DFT and TD-DFT approach

The chemical behaviour of six biologically important Adenine (A)–Thymine (T) base pairs formed as a result of the interaction between Watson–Crick(WC) type Adenine, Thymine, rare Adenine (A*) and rare Thymine (T*) bases have been studied using density functional theory (DFT) and time-dependent DFT (TD-DFT). The geometrical optimization and other relevant properties have been calculated by employing the hybrid functional CAM-B3LYP and M06-2X with 6-311++G(d,p) basis set for the reliable treatment of dispersion interaction in the gas phase. The energetic parameters show that the A*T* base pair has the highest binding energy. The characteristic Raman modes due to stretching vibrations show significant change for conformational and structural alteration. The absorption spectra of all AT conformers belong to the UV region and the excitations are due to π → π* and π → ryd* transitions. A distinct absorption peak has been observed for the protonated base pairs at a relatively higher wavelength. Natural transition orbital and molecular orbital analysis define charge transfer states associated with the electronic transitions. The lowest ionization potential, positive electron affinity and least value of hardness of the A*T* compared to the other AT base pairs suggest more reactivity of A*T* base pair than the others in chemical and biological reactions. Naturally, these structural rearrangements affect various biological and chemical processes, therefore, this study may be helpful to find out the best fit between the structurally flexible ligand and receptor and how the interaction will affect the chemistry of these important molecules.

Mechanistic investigation on rhodium(III)-catalyzed cycloaddition of 2-vinylphenol derivatives with ethyne or carbon monoxide by DFT study

Rhodium-catalyzed cycloaddition reaction was calculated by density functional theory M06-2X method to directly synthesize benzoxepine and coumarin derivatives. In this work, we conducted a computational study of two competitive mechanisms in which the carbon atom of acetylene or carbon monoxide attacked and inserted from two different directions of the six-membered ring reactant to clarify the principle characteristics of this transformation. The calculation results reveal that: (i) the insertion process of alkyne or carbon monoxide is the key step of the reaction; (ii) for the (5+2) cycloaddition reaction of acetylene, higher energy is required to break the Rh−O bond of the reactant, and the reaction tends to complete the insertion from the side of the Rh−C bond; (iii) for the (5+1) cycloaddition of carbon monoxide, both reaction paths have lower activation free energy, and the two will generate a competition mechanism.

Adsorption of 1-chloro-1,2,2,2-tetrafluoroethane on pristine, Al, Ga-doped boron nitride nanotubes: a study involving PBC-DFT, NBO analysis, and QTAIM

In the present investigation, the feasibility of detecting the 1-chloro-1,2,2,2-tetrafluoroethane gas molecule on the outer surface of pristine single-walled boron nitride nanotube, as well as its aluminium- and gallium-doped structures, was carefully evaluated. For achieving this goal, a periodic boundary condition density functional theory level of study using both HSE06 and B3LYP-D3 functionals together with a 6-311G(d) basis set has been used. Subsequently, the CAM-B3LYP, ωB97XD, and M06-2X functionals with a 6-311G(d) basis set were also employed to consider the single point energies. Natural bond orbital and quantum theory of atoms in molecules were implemented by using the HSE06/6-311G(d) method and the results were compatible with the electronic properties. In this regard, the total density of state, the Wiberg bond index, natural charge, natural electron configuration, donor–acceptor natural bond orbital interactions, and the second-order perturbation energies are performed to explore the nature of the intermolecular interactions. All of the energy calculations and population analyses show that by adsorbing of the gas molecule onto the surface of the considered nanostructures, the intermolecular interactions are of the type of strong chemical adsorption. Between the doped nanotubes, aluminium-doped nanotube has very high adsorption energy compared with gallium. Generally, it was revealed that the sensitivity of the adsorption will be increased when the gas molecule interacts with decorated nanotubes and decrease the HOMO–LUMO band gap; therefore, the change of electronic properties can be used to design suitable nanosensors.

Computational Study on Metal-Ion-Decorated Prismane Molecules for Selective Adsorption of CO2 from Flue Gas Mixtures.

Selective adsorption of CO2 from flue gas is extremely significant because of its increasing concentration in air and its deleterious effect on the environment. In this work, we have explored metal-ion-bound prismane molecules for selective CO2 adsorption from the flue gas mixture. The Ca2+-bound prismane complex exhibits superior CO2 selectivity and adsorption capacity. The calculated binding energy and molecular electrostatic potential (MESP) analysis showed that the rectangular face of prismane binds strongly with metal ions as compared to its triangular face. The CBS-QB3 and density functional theory-based functional M06-2X/6-311+G(d) calculations show that the prismane molecule can bind to one Li+, K+, Mg2+, and Ca2+ ion with favorable binding energy. The metal-ion-bound prismane complexes have been examined for their CO2, N2, and CH4 adsorption capacity. Prismane–Ca2+ can bind with six CO2 molecules strongly with an average binding energy of −18.1 kcal/mole as compared to six N2 (−12.6) and five CH4 (−13.4) gas molecules. The gravimetric density calculated for the CO2-adsorbed prismane–Ca2+ complex has been found to be 69.1 wt %. The discrete hydrocarbon structure for selective separation of CO2 is rare in the literature and can have potential applications for cost-effective CO2 capture from the flue gas mixture.

Exploration of Chromone-Based Thiosemicarbazone Derivatives: SC-XRD/DFT, Spectral (IR, UV-Vis) Characterization, and Quantum Chemical Analysis.

By the condensation of thiosemicarbazide with coumarin aldehyde, two novel substituted thiosemicarbazones with chemical formulae C24H25N3O3S (3a) and C26H23N3O3S (3b) have been synthesized. The synthesized compounds were resolved using SC-XRD, and structure elucidation was carried out using 1H NMR, 13C NMR, UV–visible, and FT-IR spectroscopic analyses. Computational calculations at the B3LYP/6-311+G(d,p) level of theory were performed to countercheck the experimental (UV–vis, FT-IR) findings and explore the electronic (FMO, NBO, MEP) properties of 3a–b. The nonlinear optical (NLO) properties of 3a–b were estimated using B3LYP, HF, LC-BLYP, CAM-B3LYP, M062X, and M06 functionals in combination with the 6-311+G(d,p) basis set. The crystallographic data revealed that compounds were crystallized as an orthorhombic crystal lattice with the Pbcn space group and the triclinic crystal lattice with the P̅1 space group. A good concurrence among experimental SC-XRD-generated bond lengths, bond angles, FT-IR, UV–vis, and corresponding DFT results was found, which confirms the purity of both compounds. The NBO analysis confirmed the presence of intramolecular hydrogen bonding and hyperconjugative interactions, which not only were the pivotal cause of stability of the investigated compounds but also led to an overwhelming NLO response. The energy differences calculated for HOMO/LUMO are 3.053 and 3.118 eV in 3a and 3b, respectively. The crystal 3b showed a higher value of first-order polarizability at all levels of theory than 3a. Overall results show that the crystals under investigation are polarized in nature with a good dipole moment. A comparative analysis with urea molecules clearly indicates that the studied compounds are acceptable NLO candidates and they can be used for future technological applications.