Theoretically designed M@diaza[2.2.2]cryptand complexes: the role of non-covalent interactions in promoting NLO properties of organic electrides.

Organic excess electron compounds with significant nonlinear optical (NLO) properties are widely employed in optoelectronic applications. Herein, single-alkali metals with diaza[2.2.2] cryptand (M@crypt,M=Li, Na, and K) are investigated for optoelectronic and NLO properties by using the density functional theory. Thermodynamic and kinetic stabilities of present complexes are computed through interaction energy (Eint) and ab-initio molecular dynamic (AIMD) simulations. M@crypt complexes carry excess electrons and mimic molecular electrides. Quantum theory of atoms in molecules (QTAIM) analysis and reduced density gradient (RDG) spectra demonstrate the roles of the weak van der Waals (vdW) interactions between metal and complexant. The remarkable hyperpolarizability (ßo) value up to 1.41 × 106 au may be credited to the presence of loosely bound excess electrons. The hyper Rayleigh scattering hyperpolarizability (ßHRS) is recorded up to 1.31 × 106 au for the K@crypt. Furthermore, frequency-dependent first-order and second-order hyperpolarizability is more prominent at the applied frequency of ω = 0.042823 au. The electron localizing function (ELF) and localized orbital locator (LOL) analysis further disclose the nature of interaction between alkali metal and complexant. The TD-DFT method is adopted to get excited state parameters and absorbance properties. An electron density difference map (EDDM) is exploited to evaluate the orbital contributions in excited states. Hence, the studied electride may become a promising candidate for NLO materials. We anticipate that the present work will provide insight into further development of molecular electride for optoelectronic applications.

Organic electrides M@cryptand [2.2.2] (where M=Li, Na, and K) are examined as excess electrons, where vdW forces play important roles in promoting the NLO properties.

Superalkali nature of the Si9M5 (M = Li, Na, and K) Zintl clusters: a theoretical study on electronic structure and dynamic nonlinear optical properties.

Zintl clusters have attracted widespread attention because of their intriguing bonding and unusual physical properties. We explore the Si9 and Si9M5 (where M = Li, Na, and K) Zintl clusters using the density functional theory combined with other methods. The exothermic nature of the Si9M5 cluster formation is disclosed, and the interactions of alkali metals with pristine Si9 are shown to be noncovalent. The reduced density gradient analysis is performed, in which increased van der Waals interactions are observed with the enlargement of the size of alkali metals. The influence of the implicit solvent model is considered, where the hyperpolarizability (ßo) in the solvent is found to be about 83 times larger than that in the gas phase for Si9K5. The frequency-dependent nonlinear optical (NLO) response for the dc-Kerr effect is observed up to 1.3 × 1011 au, indicating an excellent change in refractive index by an externally applied electric field. In addition, natural bonding orbitals obtained from the second-order perturbation analysis show the charge transfer with the donor-acceptor orbitals. Electron localization function and localized orbital locator analyses are also performed to better understand the bonding electrons in designed clusters. The studied Zintl clusters demonstrate the superalkali character in addition to their remarkable optical and nonlinear optical properties.

Polaron Formation in Conducting Polymers: A Novel Approach to Designing Materials with a Larger NLO Response.

Substantial efforts have been made to design and investigate new approaches for high-performance nonlinear optical (NLO) materials. Herein, we report polaron formation in conducting polymers as a new approach to designing materials with a large NLO response. A comparative study of polypyrrole and polypyrrole-based polaron (nPy+ where n = 1, 3, 5, 7, and 9) is carried out for optoelectronic and NLO properties. The studied polarons (PPy+) show excellent electronic properties and have reduced ionization potential (IP) as compared to neutral PPy, and a monotonic decrease is observed with increased chain lengths (1Py to 9Py). Interesting trends of global reactivity descriptors can be seen; the softness (S) increases with an increase in the chain length of PPy, while the hardness (η) decreases in the same fashion. The EH-L gaps for the PPy+ polaronic state are significantly lower than their corresponding neutral PPy. In the polaronic model (PPy+), radicals decisively reduce the crucial excitation energy, reminiscent of excess electrons (alkali metals). The performed TDOS spectral analysis further justifies the better conductive and electronic properties of polarons (PPy+) with increased chain lengths (conjugation). The static hyperpolarizability response (ßo) is recorded up to 1.3 × 102 au for 9Py, while for polaron 9Py+, it has increased up to 3.2 × 104 au. The static hyperpolarizability of the 9Py+ polaronic state is 246 times higher than that of the corresponding neutral analogue, 9Py. It is observed that the values of ßo obtained at the CAM-B3LYP/6-311+G(d,p) level of theory are comparable to those obtained at the LC-BLYP and ωB97XD functionals. The ßvec values show a strong correlation with the total hyperpolarizability (ßo). Furthermore, the calculated second harmonic generation (SHG) values are up to 4.0 × 106 au at 532 nm, whereas electro-optic Pockel's effect (EOPE) is much more pronounced at the smaller dispersion frequency (1064 nm). The TD-DFT study reveal the red-shifted absorption maxima (λmax) with an increased length of PPy+. A significant reduction in excitation energy (ΔE) is observed with increased length of PPy and PPy+, which also favors the improved NLO response. Hence, the studied thermally conducting polypyrrole-based polarons (PPy+) are new entries into NLO materials with better electrical and optical features.

Insights into the crystal structure investigation and virtual screening approach of quinoxaline derivatives as potent against c-Jun N-terminal kinases 1.

Quinoxaline derivatives are an important class of heterocyclic compounds in which N replaces one or more carbon atoms of the naphthalene ring and exhibit a wide spectrum of biological activities and therapeutic applications. As a result, we were encouraged to explore a new synthetic approach to quinoxaline derivatives. In this work, we synthesized two new derivatives namely, ethyl 4-(2-ethoxy-2-oxoethyl)-3-oxo-3,4-dihydroquinoxaline-2-carboxylate (2) and 3-oxo-3,4-dihydroquinoxaline-2-carbohydrazide (3) respectively. Their structures were confirmed by single-crystal X-ray analysis. Hirshfeld surface (HS) analysis is performed to understand the nature and magnitude of intermolecular interactions in the crystal packing. Density functional theory using the wb97xd/def2-TZVP method was chosen to explore their reactivity, electronic stability and optical properties. Charge transfer (CT) and orbital energies were analyzed via natural population analysis (NPA), and frontier molecular orbital (FMO) theory. The calculated excellent static hyperpolarizability (ßo) indicates nonlinear optical (NLO) properties for 2 and 3. Both compounds show potent activity against c-Jun N-terminal kinases 1 (JNK 1) based on structural activity relationship studies, further subjected to molecular docking, molecular dynamics and ADMET analysis to understand their potential as drug candidates.Communicated by Ramaswamy H. Sarma.

XRD/DFT, Hirshfeld surface analysis and molecular modelling simulations for unfolding reactivity of newly synthesized vanillin derivatives: excellent optical, NLO and protein binding efficiency.

New vanillin derivatives, namely, ethyl (4-formyl-2-methoxyphenoxy)acetate (2a) and 2-(4-formyl-2-methoxyphenoxy)-N-phenylacetamide (2b), respectively, were synthesized and characterized by NMR (1H and 13C), IR, mass spectra and confirmed by single-crystal X-ray analysis. Hirshfeld surface (HS) analysis was performed to probe intra- and intermolecular interactions and surface reactivity. 2D fingerprint plots (FP) were used to study the nature and percentage contribution of intermolecular interactions leading to the formation of the crystal unit. Density functional theory (DFT) simulations were used to obtain the electronic structure and reactivity of the new molecules. Natural population analysis (NPA) and frontier molecular orbital (FMO) calculations reveal significant charge transfer and a reduced HOMO-LUMO gap up to 4.34 eV for 2b. Bader's quantum theory of atoms in molecules (QTAIM) study is utilized to understand the surface topological and bonding nature of 2a and 2b. The performed molecular electrostatic potential (MESP) and density of states (DOS) study further suggest sites likely to be attractive to incoming reagents. At the same time, hyperpolarizability (ßo) is used to characterize the nonlinear optical properties, and TD-DFT study shows the excitation energy and absorption behavior. In silico studies were performed, including docking, binding free energies (MMBGSA) and molecular dynamics simulations. Compounds 2a and 2b were docked with RdRp of SARS-Cov-2, and the MMBGSA for 2a and 2b were -30.70 and -28.47 kcal/mol, respectively, while MD simulation showed the stability of protein-ligand complexes.Communicated by Ramaswamy H. Sarma.

Color properties and non-covalent interactions in hydrated (Z)-4-(1-cyano-2-(2,4,5-trimethoxyphenyl)-vinyl)pyridin-1-ium chloride salt: Insights from experimental and theoretical studies.

The optical charge-transfer (CT) property and the crystal structure of (Z)-4-(1-cyano-2-(2,4,5-trimethoxyphenyl)vinyl)pyridin-1-ium chloride monohydrate salt (I), which belongs to an acrylonitrile family, was studied. The title salt, I, was characterized using different spectroscopy techniques and a single-crystal X-ray diffraction study combined with quantum chemical computations. The results showed that the color properties of I are determined by the CT, changes in bandgap, optical absorption, and various non-covalent interactions. The HOMO-LUMO energy gaps are 5.41 eV and 5.23 eV for the precursor and salt, respectively. It was demonstrated that π-π stacking interactions lead to the formation of intercalated dimers and donor-acceptor interactions assisted by hydrogen bonds; the dimers and interactions are different between the precursor and the salt. The cation moiety is mainly stabilized by N(1)+-H···Cl, and the anion is predominantly stabilized by strong O(1W)- H⋯ Cl- bonds as well as the hydrogen bonds with the MeO group O(2W)-H⋯O(1) and O(2W)-H⋯O(1W). The charge transfer between cation and anion moieties in the structure is established through NBO analysis.

Synthesis, structural and X-ray analysis evaluations and computational studies of newly tetrahydroisoquinoline derivatives as potent against microsomal prostaglandin E synthase 1.

Tetrahydroisoquinolines (THIQs) are a significant class within the broad range of natural compounds known as isoquinoline alkaloids. Natural and manmade drugs based on THIQ have a variety of biological effects that protect against different infectious pathogens and neurological diseases. In this study, two new THIQ derivatives were synthesized and characterized using by X-ray crystallographic analysis. The performed Hirshfeld analysis shows the intermolecular interactions and reactive sites of compounds. The 2D fingerprints reveal dominants H···C interactions up to 8.8% in 3a while 43% H···H elemental interactions are observed in compound 3b. In studied compound 3a, the repulsion energies (k-rep) dominate the other energies where the highest amount of 63.8 kJ/mol is obtained whereas 3b has a significant contribution from E-dis to the total energy of the molecule from the energy framework study. Moreover, the density functional theory study reveals better thermodynamic and electronic stabilities. These compounds have reduced HOMO-LUMO gaps (EH-L) ranging from 3.66 to 3.60 eV, indicating their remarkable conductive and electronic properties. The significant reduction in EH-L also guarantees our synthesized compounds' soft nature and reactivity. Our studied compound's NBO charges and MEPs analysis show electron-rich sites and donor-acceptor mechanism. Our synthesized compounds have remarkable polarizability (αo) and hyperpolarizability (ßo) values (446.23 - 1312.73 au), which indicates their optical and nonlinear optical properties. The density of states spectra further illustrates their notable structural-electronic properties and reduced band gaps. Based on structural activity relationship studies, we found that these tetrahydro-isoquinolines derivatives are potent against microsomal prostaglandin E synthase 1(MPGES1), the docking analysis shows that studied compounds have a good binding affinity with MPGES1, and further ADME/T analysis was carried out for both compounds. In addtion to this molecular dynamics, studies were performed to understand the binding stability of both compounds in protien complex system during 100 ns simulation.Communicated by Ramaswamy H. Sarma.

Geometric, Electronic, and Optoelectronic Properties of Carbon-Based Polynuclear C3O[C(CN)2]2M3 (where M = Li, Na, and K) Clusters: A DFT Study.

Carbon-based polynuclear clusters are designed and investigated for geometric, electronic, and nonlinear optical (NLO) properties at the CAM-B3LYP/6-311++G(d,p) level of theory. Significant binding energies per atom (ranging from -162.4 to -160.0 kcal mol-1) indicate excellent thermodynamic stabilities of these polynuclear clusters. The frontier molecular orbital (FMOs) analysis indicates excess electron nature of the clusters with low ionization potential, suggesting that they are alkali-like. The decreased energy gaps (EH-L) with increased alkali metals size revael the improved electrical conductivity (σ). The total density of state (TDOS) study reveals the alkali metals' size-dependent electronic and conductive properties. The significant first and second hyperpolarizabilities are observed up to 5.78 × 103 and 5.55 × 106 au, respectively. The ßo response shows dependence on the size of alkali metals. Furthermore, the absorption study shows transparency of these clusters in the deep-UV, and absorptions are observed at longer wavelengths (redshifted). The optical gaps from TD-DFT are considerably smaller than those of HOMO-LUMO gaps. The significant scattering hyperpolarizability (ßHRS) value (1.62 × 104) is calculated for the C3 cluster, where octupolar contribution to ßHRS is 92%. The dynamic first hyperpolarizability ß(ω) is more pronounced for the EOPE effect at 532 nm, whereas SHG has notable values for second hyperpolarizability γ(ω).

Extremely large static and dynamic nonlinear optical response of small superalkali clusters NM3M' (M, M'=Li, Na, K).

Exploring novel nonlinear optical (NLO) materials with excess electron properties is essential for advancing the use of excess electron compounds in optics. The studied superalkali clusters NM3M' (M, M' = Li, Na, K) are thermodynamically stable and their binding energies range from -27.10 to -53.84 kcal mol-1. The observed significant values for VIPs suggest their electronic stabilities. Being excess electron candidate these clusters show significant ßo value (3.9 × 107 au), which nicely correlates the hyperpolarizability reported by a two-level model (ßtl). Furthermore, these clusters exhibit a remarkable static second hyperpolarizability (γo) value of 1.1 × 1010 au for the NK4 superalkali cluster. The hyper Rayleigh scattering (ßHRS) is also computed where the highest value of 2.9 × 107 is recorded for NNa3K superalkali. The obtained values of ßvec values (projection of hyperpolarizability on dipole moment vector) also signify the excellent nonlinearity of clusters. Besides, the calculated electro-optica pockel's effect ß(-ω; ω,0) and second harmonic generation ß(-2ω; ω, ω) values are much pronounced at larger dispersion frequency ω = 1064 nm. Moreover, the frequency-dependent second hyperpolarizability γ(ω) with dc-Kerr effect γ(-ω; ω,0,0) and electric field induced second harmonic generation γ(-2ω; ω,ω,0) show larger values at ω = 1064 nm. Thus the highest value of the dc-Kerr constant increases up to 1.0 × 1011 au which also signifies the larger nonlinear refractive index of the studied cluster. We hope this work could open up new possibilities using superalkali clusters as NLO materials for optoelectronics, laser, second harmonic generation and as frequency doubler.

Oxacarbon superalkali C3X3Y3 (X = O, S and Y = Li, Na, K) clusters as excess electron compounds for remarkable static and dynamic NLO response.

An intriguing class of excess electron oxacarbon superalkali clusters is explored for nonlinear optical response through density functional theory (DFT) methods at CAM-B3LYP/6-311++G(d,p). These superalkali clusters shows noticeable binding energies per atom (Eb) which reveals their thermodynamic stabilities (-86.45 âˆ¼ -119.44 kcal mol-1). The obtained significant VIPs values also suggest the electronic stability of these clusters. The VIP values range from 2.06 eV to 3.42 eV. These clusters show remarkable electronic properties and their HOMO-LUMO gaps (EH-L) are significantly reduced. The lowest H-L gap of 0.96 eV is obtained for C3O3K3 while the highest H-L gap of 2.07 eV is calculated for C3S3Li3. The obtained PDOS spectra further provide evidence for the superior electronic properties of these clusters. The clusters show excellent nonlinear optical properties as revealed from remarkable values (1.6 × 106 au) of static first hyperpolarizability. The controlling factors for hyperpolarizability are also explored by using conventional two-level model. The calculated values of ßo are correlated nicely with ßtl. The crucial excitation energy is the key factor in controlling the first hyperpolarizability. In these excess electron clusters, the second hyperpolarizability (γo) response increases up to 4.3 × 109 au. Moreover, the calculated scattering hyperpolarizability (ßHRS) values are quite significant in these clusters and the highest value of 1.3 × 106 au is calculated for C3S3K3. Additionally, these clusters also possess larger dynamic nonlinearities. The dynamic second hyperpolarizability with dc-Kerr effect increases up to 1.0 × 1011 au. The remarkable values for refractive index (n2) also suggest the excellent nonlinearity of these superalkali clusters.

Germanium-based superatom clusters as excess electron compounds with significant static and dynamic NLO response; a DFT study.

Herein, the geometric, electronic, and nonlinear optical properties of excess electron zintl clusters Ge5AM3, Ge9AM5, and Ge10AM3 (AM = Li, Na, and K) are investigated. The clusters under consideration demonstrate considerable electronic stability as well as superalkali characteristics. The NBO charge is transferred from the alkali metal to the Ge-atoms. The FMO analysis shows fabulous conductive properties with a significant reduction in SOMO-LUMO gaps (0.79-4.04 eV) as compared with undoped systems. The designed clusters are completely transparent in the deep UV-region and show absorption in the visible and near-IR region. Being excess electron compounds these clusters exhibit remarkable hyperpolarizability response up to 8.99 × 10-26 esu, where a static second hyperpolarizability (γ o) value of up to 2.15 × 10-30 esu was recorded for Ge9Na5 superatom clusters. The excitation energy is the main controlling factor for hyperpolarizability as revealed from the two-level model study. The electro-optical Pockel's effect and the second harmonic generation phenomenon (SHG) are used to investigate dynamic nonlinear optical features. At a lower applied frequency (=532 nm), the dynamic hyperpolarizability and second hyperpolarizability values are significantly higher for the studied clusters. Furthermore, for the Ge9K5 cluster, the hyper Rayleigh scattering (HRS) increases to 5.03 × 10-26 esu.

Alkaline earth metals serving as source of excess electron for alkaline earth metals to impart large second and third order nonlinear optical response; a DFT study.

Continuous strides are made to explore new strategies for the design of materials with remarkable nonlinear optical response. Herein, we report the geometric, electronic, and nonlinear optical properties of novel bis-alkaline earth metal doped complexes of Janus all-cis-1,2,3,4,5,6-hexafluorocyclohexane F6C6H6 (1). These complexes contain unprecedented involvement of alkaline earth metals as sources of excess electron for the 2nd alkaline earth metal atom in the complex. Geometric electronic and thermodynamic properties of studied complexes AE-1-AE (where AE = Be, Mg, Ca) are obtained at M06-2X/6-31+G(d,p) level of theory. The NBO analysis is performed to predict the charge transfer. Moreover, the excess electron nature of these complexes is validated through frontier molecular orbital (FMOs) analysis. The PDOS and TDOS analysis are also performed to further rationalize the electronic properties. The remarkable static first hyperpolarizability (ß0) and second hyperpolarizability (γ0) response up to 2.91 × 104 au and 4.08 × 106 au, respectively, are recorded for these complexes. Furthermore, the two-level model is also employed to get a comprehensive picture of the controlling factors for hyperpolarizability. Moreover, to get nonlinearity response from the experimental point of view, hyper Rayleigh scattering (ßHRS) has been calculated and the highest value of 7.38 × 103 au is noticed for the complex I (Ca-1-Ca). These compounds besides providing a new entry into excess electron compounds will also pave the path for designing and synthesis of further novel NLO materials.