Molecular Hyperpolarizability Research Articles

Dihydro‐1H‐Pyrazoles as Donor Blocks in Donor–Acceptor Chromophores for Electro‐Optics: A DFT Study of Hyperpolaizability and Electronic Excitations

ABSTRACTA diverse set of promising donors for donor–acceptor chromophores based on dihydro‐1H‐pyrazole (pyrazoline) for use in electro‐optics was investigated using DFT at M06‐2X/aug‐cc‐pVDZ level of theory. These calculations showed that it is possible to achieve a molecular hyperpolarizability of up to 1700*10−30 esu (up to three times higher compared to conventional diethylaniline donors) for a simple tricyanofuran‐based acceptor by carefully tuning the donor structure. It was shown that the molecular hyperpolarizability is mainly affected by the substituents in the aryl rings in positions 3 and 1 of the pyrazoline cycle, while the substituents of the aryl ring in position 5 and the pyrazoline ring itself can be varied without significant effects on the hyperpolarizability. For one of the compounds, a detailed study of the lowest energy electronic excitation was performed using the TD‐DFT, confirming the role of the pyrazoline ring as a secondary donor.

Harmonic Light Scattering to Study Supramolecular Assembly Processes

Characterization of complex dynamical processes such as supramolecular aggregation, (electro)chemical reactions or phase transitions, requires in-situ measurement techniques to provide insight into morphology changes, symmetry changes, concentration, or phase changes during the process. Currently available techniques are often not sensitive to all these aspects or too slow for in-situ studies. Instead, very fast and sensitive techniques are needed. Recently, we developed a method based on second-and third harmonic scattering that partially satisfies these requirements (1-3).Second-harmonic scattering is a nonlinear scattering process in which two incident photons of frequency ω are annihilated to create a new photon at the double frequency 2ω. It is a very sensitive tool to study dynamical processes since it is fast, sensitive to the symmetry of the scatterer and extremely sensitive to aggregation.For molecular scatterers, the intensity of the scattered second-harmonic light I2ω is given by:I2ω ∼ N<β2> Iω 2 With N the number scatterers, β the first hyperpolarizability, Iω the intensity of the incident light and < > refers to orientational averaging. Information about the point group symmetry of the scatterer can be inferred by analyzing the polarization components of the scattered light. For aggregated or correlated scatterers I2ω is given by: I2ω ∼ N'<(Mf(β))2> Iω 2 with N’ the number of scatterers, M the number of molecules in each aggregate, and f(β) a combination of molecular hyperpolarizability components. Also in this case, an analysis of the polarization components of the scattered light will yield information about the symmetry of the aggregated scatterers.Similar formula’s hold for third harmonic scattering where part of the incident light at frequency ω is scattered at the triple frequency 3ω . For molecular scatterers I3ω is given by I3 ω ∼ N<γ2> Iω 3 and for correlated scattersI3 ω ∼ N'<(Mf(γ))2> Iω 3 with γ the second hyperpolarizability.While both techniques may seem similar, there is an important difference: the symmetry selection rules are very different. Second-harmonic scattering is only allowed if the scatterer is non centrosymmetric, while third-harmonic scattering does not have any symmetry constraints. As such, both techniques are highly complementary. The combination of both, referred to as harmonic scattering, has been used as a very versatile method to study in-situ supramolecular aggregation of macrocycles and conjugated polymers with the ability to completely unravel the nucleation and aggregation dynamics.Now, we have extended this measurement platform to also include multi-photon fluorescence, linear light scattering, UV/Vis absorption and optical rotation. Hence, in total we can monitor 6 observables for any dynamical process in-situ. Several examples will be given on how this methodology can provide new insights in the mechanism and dynamics of supramolecular aggregation processes.References1) Moris, M. et al., Harmonic light scattering study reveals structured clusters upon the supramolecular aggregation of regioregular poly(3-alkylthiophene). COMMUNICATIONS CHEMISTRY, 2, Art.No. ARTN 130 (2019).2) Hattori, S., et al. Vortex-Induced Harmonic Light Scattering of Porphyrin J-Aggregates. JOURNAL OF PHYSICAL CHEMISTRY B, 125 (10), 2690-2695 (2021)3) Dok, A.R., et al. Nonlinear optical probes of nucleation and crystal growth: recent progress and future prospects. JOURNAL OF MATERIALS CHEMISTRY C, 9 (35), 11553-11568 (2021).

Enhanced molecular first hyperpolarizabilities with Reichardt’s type of zwitterions: a computational study on roles of various monocyclic aromatic bridges

ContextThis work reports structure–property correlations of 27 zwitterions Reichardt’s types of zwitterions. Focuses are twofold, to see the (1) impacts of metamerism with Reichardt’s vs Brooker’s types of zwitterions and (2) impacts of monocyclic aromatic rings as bridges. All the molecules considered here have pyridinium (common acceptor: A) and p-phenylene-dicyanomethanide (common donor: D). Fundamental molecular properties like dipole moments (μ), polarizabilities (α), hyperpolarizabilities (β), and adiabatic absorptions were computed only for the Reichardt types and compared with the literature reported respective Brooker’s types of zwitterions. As an impact of metamerism, in general 2–3 times enhanced hyperpolarizabilities (β) were observed for Reichardt’s compared to Brooker’s types. Exceptions were observed with some triazine bridges and furan bridge, where Brooker’s types were found to be more efficient. As impacts of aromatic bridges, in general, 6–sevenfold enhanced β compared to well-known traditional bridges and enhanced β were observed compared to D-A directly connected zwitterion (benzene bridge: sixfold enhanced β). Current findings show that the aromatic bridge control with Reichardt’s types of zwitterions is more efficient and thus may be employed as an effective strategy for the designing of functional molecular chromophores for various other fundamental areas.MethodsAll computations were performed with Gaussian 09. Geometry optimizations and computations of fundamental properties were carried out with HF, B3LYP, CAM-B3LYP, and ωB97xD methodologies, with 6-31G(d,p) and aug-cc-pVDZ basis sets. For adiabatic excitations, computations were carried out using TDDFT and TDHF approaches. For the computations of the response properties (like the nonlinear optical responses), CPHF approach was used.

Non-covalent interaction, topology, molecular properties, spectral and quantum chemical analysis of 2,5-dinitrophenol

Density functional theory (DFT) using the Becke-3-Parameter-Lee-Yang-Parr (B3LYP) functional and Ab-initio (HF) with the 6–311++G(d,p) basis set were employed to investigate the geometry, electronic structure, and absorption spectra of 2,5-Dinitrophenol(25DNP). The vibrational spectrum was utilized to identify functional groups. The ultraviolet–visible (UV–Vis) spectrum was simulated in the gas phase using TD-DFT to determine the range and percentage of transmission. The computed HOMO and LUMO energies indicate that charge transfer occurs within the molecule. The compound exhibits a molecular first hyperpolarizability (second-order optical nonlinearity) value of 1.690 × 10−30 esu, which is approximately five times greater than that of urea. For hyperpolarizability calculations, the hybrid Hartree-Fock exchange-correlation functional was used in conjunction with the 6–311++G(d,p) basis set. Fukui indices were employed to identify local reactive sites in the chemical system during electrophilic, nucleophilic, radical, and dual descriptor attacks. Docking simulations were performed using the Lamarckian Genetic Algorithm (LGA) and local search approach, ensuring proper establishment of the ligand molecules' starting position, orientation, and torsion. According to the molecular electrostatic potential (MEP) map, positive potential sites are found around hydrogen atoms, while negative potential sites are near electronegative atoms, providing insights into regions where the molecule may interact with other molecules, both internally and externally. Similarly, Mulliken charges and Fukui indices within the organic complex sustain the intermolecular hydrogen bonds.

Impact of substituents at the para position of C-Nitroso over N-Nitroso diphenylamine on static and frequency dependent nonlinear optical Properties: DFT and TD-DFT

The nonlinear optical property of N and C-nitroso diphenylamine is the focus of the current work but the D-π-A skeleton-based para substituted nitroso benzene served as the starting point for this investigation. For p-methoxy nitroso benzene, a maximum β0 of 10.47 x 10-30 esu was attained. Diphenylamine analogue was letter on chosen for further improvement. For these nitroso diphenylamines, substituent effects of electron donating groups (EDGs) at the para position have been studied for the nonlinear optical property (NLO). The NMe2 derivative of C-nitroso was found to have the highest value of hyperpolarizability (β0) of 57.46 × 10-30 esu, including 570 × 10-30 Debye.esu as molecular hyperpolarizability (µ×β0), out of these two nitroso forms with substituents Me, OMe, OEt, NH2, and NMe2 at para position. H < Me < OMe < OEt < NH2 < NMe2 is the ascending effect for the β0 in the N-nitroso whereas H < Me < OMe < NH2 < OEt < NMe2 in the C-nitroso. These β0 value shows 155.29, 73.69, 13.12 fold increment as compared to diphenylamine (DPA), urea and p-nitroaniline (PNA) respectively. Upon increasing the λmax, value of calculated βTDω also increases calculated in TD-DFT calculations (βTD1064 <βTD1340 <βTD1460 < βTD1907). These values have shown a deviation range of 7–38 % in case of N-nitroso and 11–52 % in case of C-nitroso as compared to static values. Whereas βHRSω increases with increase in the optical frequency (βHRS1064 >βHRS1340 >βHRS1460 > βHRS1907). These values have shown a deviation range of 4–91 % in case of N-nitroso and 1to > 100 in case of C-nitroso as compared to static values.

Effect of spirocyclization of xanthene dyes on linear and nonlinear optical properties by considering D-π-A and D-A-D Systems: DFT and TD-DFT approach

Spirocyclization, a unique feature of xanthene dyes, makes it a promising candidate for developing fluorescent ratiometric probes for sensing, imaging, tracking, and labeling. How will this feature of xanthene dyes influence the linear and nonlinear optical properties? To examine the effect of spirocyclization of xanthene dyes, we have selected both the open-close form of rhodamine B and π-extended xanthene dyes substituted with thienyl and thieno[3,2-b]thienyl group at position 3 and 6. Here, rhodamine B will serve as the (Donor)D-π-A(Acceptor) system and thiophene-substituted xanthene dyes will serve as the D-A-D system. The geometry optimization of the close-open form of xanthene dyes at B3LYP/6–311++G(d,p) and CAM-B3LYP/6–311++G(d,p) revealed that the open form is energetically more stable in the S0 state than the closed form. The vertical excitation energy (ΔE), from Time-Dependent-Density Functional Theory (TD-DFT) calculation at B3LYP/6–311++G(d,p), CAM-B3LYP/6–311++G(d,p), ωB97XD/6–311++G(d,p) revealed that (ΔE)open < (ΔE)close. Further, the open form of xanthene dyes displays red-shifted absorption compared to the closed form. The λVt of xanthene dyes (open-close forms) is mainly assigned to HOMO → LUMO transition (S0 → S1) with % orbital contribution for open form ∼ 90 % and close form ∼ 60 %. The oscillator strength of xanthene dyes is obtained in the range of 0.01 – 1.74. The λVt of xanthene dyes is in agreement with experimental absorption. The static polarizability (α0), first-order hyperpolarizability (β0), second-order hyperpolarizability (γ), molecular hyperpolarizability (µβ0), and frequency-dependent hyperpolarizability (β1064), of the open form of xanthene dyes, were found to be higher than the close form. Thus, the open form of xanthene dyes will show superior linear and nonlinear optical properties than the closed form. The thienyl[3, 2-b] thieno substituted xanthene dye with red-shifted absorption shows higher α0, β0, γ, µβ0, β1064, and γ values, show better linear and NLO properties than thienyl and diethylamine substituted xanthene dyes.

Pseudo-Stilbene- and Azobenzene-Type Systems for Optical Frequency Conversion: Estimating the First-Order Molecular Hyperpolarizability

This study investigates the potential of a set of pseudo-stilbene and azobenzene molecular structures to become optical frequency converters for optical communications based on a detailed exploration of the first-order molecular hyperpolarizability (βHRS), which is the microscopic counterpart of second harmonic generation (SHG). βHRS values were obtained via quantum chemical calculations using the Gaussian 16 software package in solvent and gas-phase media at different wavelengths, i.e., 1064 nm, 1310 nm, and 1510 nm. The latter two wavelengths are of particular interest for optical communications. Our study focused on discerning how the molecular structure influences the βHRS response, explicitly highlighting the influence of the azomethine group (CH=N). The results revealed that the molecular planarity, affected by this group, plays a crucial role in modulating the optical properties. The highest βHRS value in a solvent medium using the CAM-B3LYP/6-311+G(2d,p) level of theory achieved in this work was around 1400 ×10−30cm4startvolt−1, four orders of magnitude higher than KDP (0.2 ×10−30cm4startvolt−1), which is a reference in SHG experiments at 1064 nm. The highest calculated βHRS value at the same level of theory and solvent at 1310 nm and 1550 nm was 631 × 10−30cm4startvolt−1 and 456 × 10−30cm4startvolt−1, respectively. All these values belong to molecular structures with azo-coupling with donor (4-NMe2) and acceptor (4′-NO2) peripheral groups, designated as AB-3.

Exploring nonlinear and linear optical properties of N, N’-bis(salicylidene)-o-phenylenediamine (salophen) through Z-scan technique and TD-DFT computational analysis

This investigation delves into the comprehensive analysis of the linear and nonlinear optical characteristics exhibited by N, N’-bis(salicylidene)-o-phenylenediamine (salophen) using a combination of Z-scan methodology and quantum chemistry calculations. The Z-scan technique facilitated meticulous computations of the third-order susceptibility, nonlinear absorption coefficient, and nonlinear refractive index of the specimen. Specifically, in the solvent DMSO, the assessed values for the nonlinear refractive index, nonlinear absorption coefficient, and third-order susceptibility were determined to be 0.035 × 10–10 cm2 W −1 , −0.024 × 10–5 cm W −1 , and 0.596 × 10–5 esu, respectively. Furthermore, quantum mechanical analyses were employed to meticulously calculate the molecular hyperpolarizabilities (β and γ), dipole moment (μ), and dipole polarizability (α) of salophen. This thorough exploration highlighted a notable congruence between the outcomes derived from experimental observations and those obtained through quantum mechanical simulations. The collective findings from both theoretical computations and experimental assessments distinctly showcase the robust nonlinear potential inherent in salophen. These insights suggest its promising suitability and potential as a viable candidate for applications in optical devices. The alignment between theoretical predictions and experimental results underlines the reliability and potential practicality of salophen in the realm of optical technology, emphasizing its significance as a potential material for advancing optical device functionalities.

Disentangling the molecular polarizability and first hyperpolarizability of methanol-air interfaces.

Liquid-air interfaces have extensive implications in different areas of interest because the dynamical processes at the interface can be different from those in bulk. Thus, its characterization, understanding, and control may be pivotal in advancing discoveries. However, characterizing the interface requires special and selective tools to avoid signals from the bulk region. This surface specificity and versatility is achieved by using the second harmonic generation (SHG) responses. This study adopts multiscale simulation methods to evaluate the surface SHG responses of methanol-air interfaces with submonolayer resolution tackled by sequentially using classical molecular dynamics simulations under different temperatures and then employing quantum chemistry methods to compute the molecular first hyperpolarizabilities (β). This approach ensures the configurational diversity required to evaluate the average β values. The main achievements are (i) a quasi-absence of surface sensitivity of the mean polarizability 〈α〉 with values about 2% larger than those obtained in bulk, (ii) conversely, smooth variations on the polarizability anisotropy Δα are observed up to the fourth molecular layer at around 20 Å from the interface, and (iii) narrow interfacial effects on the SHG responses, β(-2ω;ω,ω), which are limited to the first molecular layer (∼3.0 Å) and characterized by a high contrast in the βZZZ(-2ω;ω,ω) tensor component between the first and the subsequent layers. Similar trends are obtained at different temperatures or when increasing the number of methanol molecules treated at the quantum chemistry level, indicating the robustness of the approach for describing the dipolar molecular responses of air-liquid interfaces.

Studying the first order hyperpolarizability spectra in chalcone-based derivatives and the relation with one- and two-photon absorption transitions.

The first-order molecular hyperpolarizability (β) dispersion was measured in seven chalcone-based molecules utilizing the tunable femtosecond hyper-Rayleigh scattering (tHRS) technique. Additionally, a theoretical model based on photophysical parameters was employed to better understand β dispersion. Due to the distinct substitution patterns of the aryl/heteroaryl rings within the chalcone structure, varying profiles of one- and two-photon absorption spectra and β dispersion were observed. The applied model highlighted two important factors contributing to achieving high β values: (i) the presence of red-shifted one-photon and two-photon absorption bands; and (ii) the number of discernible absorption bands. To contextualize these results with other molecular structures, we employed the HRS figure of merit (FOM). Remarkably, it was revealed that chemically engineered small chalcone molecules exhibit a FOM comparable to larger quadrupolar and octupolar ones. This underscores the significance of tHRS scattering measurements and their correlation with absorptive parameters in the design and characterization of nonlinear optical materials.

Deciphering ethynyl single crystal for NLO applications: Synergistic studies on the structural, Hirshfeld surface, photophysical and DFT assessment

In this contribution, we have integrated multiple approaches in investigating the profiles and behaviour of simple ethynyl derivative, 1-[4-(4-(dimethylaminophenyl)ethynyl)phenyl]ethanone (4DME) tolane which is known to be integrated widely in molecular electronics as conjugated building block in functional molecules. Prepared via simplified aerobic Sonogashira cross-couping reaction, symmetrical chromophore of 4DME crystallizes in monoclinic with complex framework containing the space group of P21/n and includes four molecules within a unit cell. The fingerprint plots and Hirshfeld surface analyses demonstrate the presence of synergism between molecules supporting nonlinear optical response of the compound. It was shown that C⋯H contact (44.5 %) is the major contribution of intermolecular interaction executed by Hirshfeld surface area. The investigation on their spectroscopic, thermal analysis and density functional theory (DFT) analysis operating under B3LYP/6-31G (d,p) were conducted to determine the energies of the LUMO and HOMO level, NLO behaviour, intermolecular charge transport facilitated by global chemical reactivity descriptors, molecular electrostatic potentials (MEP) and hyperpolarizability analyses. From the simulated DFT calculation, it shows that 4DME has good polarizability properties with HOMO-LUMO energy gap of 3.89 eV. Calculated total first hyperpolarizability βtot of 4DME were 1261.40 × 10−30 esu which can be potentially applied as good nonlinear optical materials. The preliminary outcomes prove that this simple ethynyl derivative is capable of being used in optoelectronic industry as NLO-based products. A CW diode laser operating at 532 nm wavelength was used to perform the Z-scan measurements and 4DME showed an effective value of χ(3) in order of 10−6, indicating good nonlinear properties.

Quantification of Stern Layer Water Molecules, Total Potentials, and Energy Densities at Fused Silica:Water Interfaces for Adsorbed Alkali Chlorides, CTAB, PFOA, and PFAS.

We have employed amplitude- and phase-resolved second-harmonic generation spectroscopy to investigate ion-specific effects of monovalent cations at the fused silica:water interface maintained under acidic, neutral, and alkaline conditions. We find a negligible dependence of the total potential (as negative as -400 mV at pH 14), the second-order nonlinear susceptibility (as large as 1.5 × 10-21 m2 V-1 at pH 14), the number of Stern layer water molecules (1 × 1015 cm-2 at pH 5.8), and the energy associated with water alignment upon going from neutral to high pH (ca. -24 kJ mol-1 to -48 kJ mol-1 at pH 13 and 14, close to the cohesive energy of liquid water but smaller than that of ice) on chlorides of the alkali series (M+ = Li+, Na+, K+, Rb+, and Cs+). Attempts are presented to provide estimates for the molecular hyperpolarizability of the cations and anions in the Stern layer at high pH, which arrive at ca. 20-fold larger values for αtotalions(2) = αM+(2) + αOH-(2) + αCl-(2) when compared to water's molecular hyperpolarizability estimate from theory and point to a sizable contribution of deprotonated silanol groups at high pH. In contrast to the alkali series, a pronounced dependence of the total potential and the second-order nonlinear susceptibility on monovalent cationic (cetrimonium bromide, CTAB) and anionic (perfluorooctanoic and perfluorooctanesulfonic acid, PFOA and PFOS) surfactants was quantifiable. Our findings are consistent with a low surface coverage of the alkali cations and a high surface coverage of the surfactants. Moreover, they underscore the important contribution of Stern layer water molecules to the total potential and second-order nonlinear susceptibility. Finally, they demonstrate the applicability of heterodyne-detected second-harmonic generation spectroscopy for identifying perfluorinated acids at mineral:water interfaces.

DFT-Based Calculation of Molecular Hyperpolarizability and SFG Intensity of Symmetric and Asymmetric Stretch Modes of Alkyl Groups.

Vibrational sum frequency generation (SFG) spectroscopy has been extensively used for obtaining structural information of molecular functional groups at two-dimensional (2D) interfaces buried in the gas or liquid medium. Although the SFG experiment can be done elegantly, interpreting the measured intensity in terms of molecular orientation with respect to the lab coordinate is quite complicated. One of the main reasons is the difficulty of determining the hyperpolarizability tensors of even simple molecules that govern their SFG responses. The single-bond polarizability derivative model has been proposed to estimate the relative magnitude of SFG-active hyperpolarizability by assuming that the perturbation associated to each vibration is negligible. In this study, density functional theory was used to calculate the polarizability and dipole derivative tensors of the CH3 stretch mode of CH3I, CH3CH2I, CH3OH, and CH3CH2OH. Then, the hyperpolarizability tensors of symmetric and asymmetric vibration modes were calculated considering the Boltzmann distribution of representative conformers, which allowed us to theoretically calculate their SFG intensities at all polarization combinations as a function of the tilt angle of the CH3 group with respect to the surface normal direction. Then, the ratios of the calculated SFG intensities for the CH3 symmetric and asymmetric stretch peaks used in experimental studies for the CH3 tilt angle determination were compared. This comparison clearly showed that the effect of vibrational coupling among neighboring functional groups is significant and cannot be assumed to be negligible. This study presents new parameters that can be used in determining the average tilt angle of the CH3 group at the 2D interface with SFG measurements as well as limitations of the method.

A quantum chemical investigation of the second hyperpolarizability of p-nitroaniline.

Recent measurements of the third harmonic scattering responses of molecules have given a new impetus for computing molecular second hyperpolarizabilities (γ) and for deducing structure-property relationships. This paper has employed a variety of wavefunction and density functional theory methods to evaluate the second hyperpolarizability of the p-nitroaniline prototypical push-pull π-conjugated molecule, addressing also numerical aspects, such as the selection of an integration grid and the impact of the order of differentiation vs the achievable accuracy by using the Romberg quadrature. The reliability of the different methods has been assessed by comparison to reference Coupled-Cluster Singles and Doubles with perturbative treatment of the Triples results. On the one hand, among wavefunction methods, the MP2 scheme offers the best accuracy/cost ratio for computing the static γ. On the other hand, using density functional theory, γ remains a challenging property to compute because all conventional, global hybrid or range-separated hybrid, exchange-correlation functionals underestimate static γ values by at least 15%. Even tuning the range-separating parameter to minimize the delocalization errors does not enable to improve the γ values. Nevertheless, the original double-hybrid B2-PLYP functional, which benefits from 27% of PT2 correlation and 53% Hartree-Fock exchange, provides accurate estimates of static γ values. Unfortunately, the best performing exchange-correlation functionals for γ are not necessarily reliable for the first hyperpolarizability, β, and vice versa. In fact, the β of p-nitroaniline (pNA) could be predicted, with a good accuracy, with several hybrid exchange-correlation functionals (including by tuning the range-separating parameter), but these systematically underestimate γ. As for γ, the MP2 wavefunction method remains the best compromise to evaluate the first hyperpolarizability of pNA at low computational cost.

Theoretical investigation of the performance of nonlinear optical properties in Push–pull chromophores derivatives of acrylo–azobenzene

Due to their strong molecular hyperpolarizability, organic push–pull materials are gaining interest for nonlinear optical applications. We were able to characterize the intramolecular charge transfer and the distribution of the electron cloud within the molecular unit by exciting these materials under the influence of an electric field. The series products of conjugated monomers derived from acrylo–azobenzene containing in the para position the attracting groups (–H, –NO2, –COOC2H5, –SO3H and –COOH) exhibit good nonlinear optical activity. We computed the nonlinear optical characteristics of these compounds as well as exploiting the theoretical calculations of DFT and AM1 to determine their hyperpolarizabilities. Besides, we investigated the increase in hyperpolarizability in the push–pull model of organic compounds under the effect of the strength of attracting groups, the existence of the conjugated [Formula: see text]-electron and the azo bridge.

Synthesis–dependent structural and optoelectronic properties of semicrystalline LiNbO3:SiO2 hybrid silicates

Polycrystalline ceramics of lithium niobate (LNO) were prepared via standard hydrothermal and solid–state chemistry reactions, and by the sol–gel method implementing acrylamide polymerization. Congruent LiNbO3 trigonal perovskite phases crystallized in the R3c (161) space group [3 m (C3v) polar point group] were obtained in all cases. Depending on the implemented synthetic route, the average grain and crystallite sizes were estimated to 127–895 nm and 35–40 nm, respectively. As prepared LNO powders were embedded in a–SiO2 mesoporous sonogel networks at different doping rates to conform LiNbO3:SiO2 semicrystalline hybrid silicates with differentiated structural and optoelectronic (OE) properties. Intensive morphological, structural, spectroscopic, and nonlinear optical (NLO) characterizations were performed to explore these novel composites’ structural and photophysical properties for lead–free ferroelectric and optical applications. Results show that the massive porosity of the sonogel glasses and related defective bonding environment promote generalized host–guest molecular interactions influencing the oxidation states and radiative transitions of the dopant compounds via surface–assisted mechanisms and chemical charge–transfers. Additionally, due to the ferroelectric nature of LNO and average macroscopic alignment attained along the polycondensation stage of the solid solutions, SHG activity was observed from the hybrid sonogel (HSG) phases. Bulk NLO susceptibilities and molecular hyperpolarizabilities were estimated within the 9.62 × 10−11 and 10−23 esu range, respectively. Finally, depending on the synthesis methodology and in–gap hybridized levels, energy gap (Eg) narrowing was also observed for all LNO/HSG glasses, showing Eg values as low as 3.05 eV.

Observation of the two-photon transition enhanced first hyperpolarizability spectra in cinnamaldehyde derivatives: A femtosecond regime study.

The application of nonlinear optical effects in optoelectronic devices is still scarce because the irradiance threshold necessary to induce a specific effect is very high. In this context, knowing the frequency-resolved first order molecular hyperpolarizability (β) is essential to identifying regions where this response is intense enough to allow for applications in commercial devices. Thus, herein, we have determined the β spectral dependence of five new push-pull cinnamylidene acetophenone derivatives using femtosecond laser-induced Hyper-Rayleigh Scattering (HRS). A considerable increase in β values was observed in molecules. We found remarkable β values in regions near the two-photon resonance, which are mediated by electron withdrawing and donating groups. This effect was mapped using wavelength-tunable femtosecond Z-scan technique. Furthermore, it was modeled in light of the sum-over-states approach for the second- and third-order nonlinearities. Finally, our outcomes suggest a strategy to obtain large β values mediated by the 2PA transition.

Molecular properties and In silico bioactivity evaluation of (4-fluorophenyl)[5)-3-phen-(4-nitrophenyl yl-4,5-dihydro-1H-pyrazol-1-yl]methanone derivatives: DFT and molecular docking approaches

ObjectivesMolecular structures, spectroscopic properties, charge distributions, frontier orbital energies, nonlinear optical (NLO) properties and molecular docking simulations were analyzed to examine the bio-usefulness of a series of (4-fluorophenyl)[5-(4-nitrophenyl)-3-phenyl-4,5-dihydro-1H-pyrazol-1-yl]methanone derivatives. MethodsThe compounds were studied through computational methods. Equilibrium optimization of the compounds was performed at the B3LYP/6-31G(d,p) level of theory, and geometric parameters, frequency vibration, UV–vis spectroscopy and reactivity properties were predicted on the basis of density functional theory (DFT) calculations. ResultsThe energy gap (ΔEg), electron donating/accepting power (ω−/ω+) and electron density response toward electrophiles/nucleophiles calculated for M1 and M2 revealed the importance of substituent positioning on compound chemical behavior. In addition, ω−/ω+ and ΔEn/ΔEe indicated that M6 is more electrophilic because of the presence of two NO2 groups, which enhanced its NLO properties. The hyperpolarizability (β0) of the compounds ranged from 5.21 × 10−30 to 7.26 × 10−30 esu and was greater than that of urea; thus, M1–M6 were considered possible candidates for NLO applications. Docking simulation was also performed on the studied compounds and targets (PDB ID: 5ADH and 1RO6), and the calculated binding affinity and non-bonding interactions are reported. ConclusionThe calculated ω− and ω+ indicated the electrophilic nature of the compounds; M6, a compound with two NO2 groups, showed enhanced effects. Molecular electrostatic potential (MEP) analysis indicated that amide and nitro groups on the compounds were centers of electrophilic attacks. The magnitude of the molecular hyperpolarizability suggested that the entire compound had good NLO properties and therefore could be explored as a candidate NLO material. The docking results indicated that these compounds have excellent antioxidant and anti-inflammatory properties.

Na3SiS3F: A Wide Bandgap Fluorothiosilicate with Unique [SiS3F] Unit and High Laser‐Induced Damage Threshold

AbstractThe exploration of antilaser damage wide bandgap infrared (IR) nonlinear optical (NLO) materials is urgent but challenging. Herein, by introducing the idea of fluorination into chalcogenides, a wide bandgap IR NLO material Na3SiS3F with unprecedented [SiS3F] tetrahedra is designed and synthesized. Na3SiS3F shows a wide bandgap of 4.75 eV (the largest one in the reported quaternary metal chalcogenides), resulting in a high laser damage induced threshold of ≈5 × AgGaS2(AGS). Meanwhile, the compound has a moderate NLO response (≈0.3 ×AGS) with phase‐matching behavior, large birefringence (0.15@1064 nm), and wide IR transparent region. The introduction of fluorine breaks the structural symmetry and broadens the highest occupied molecular orbital‐lowest unoccupied molecular orbital (HOMO‐LUMO) gap, polarizability anisotropy, and hyperpolarizability of the Si–S tetrahedral unit. The results indicate that Na3SiS3F is a promising IR NLO material for the high‐power laser application and open an avenue for the design of new wide bandgap IR NLO materials based on NLO‐active [SiSxF4−x] (x = 1, 2, 3) mixed anionic tetrahedral group.

Nonlinear Optical Materials: Predicting the First-Order Molecular Hyperpolarizability of Organic Molecular Structures

Experimental nonlinear optics (NLO) is usually expensive due to the high-end photonics and electronic devices needed to perform experiments such as incoherent second harmonic generation in liquid phase, multi-photon absorption, and excitation. Nevertheless, exploring NLO responses of organic and inorganic compounds has already opened a world of new possibilities. For example, NLO switches, NLO frequency converters, and a new way to obtain biological images through the incoherent second harmonic generation (SHG) originate from first-order molecular hyperpolarizability (β). The microscopic effect of the coherent or incoherent SHG is, in fact, the β. Therefore, estimating β without using expensive photonic facilities will optimize time- and cost-efficiency to predict if a specific molecular structure can generate light with double its incident frequency. In this work, we have simulated the β values of 27 organic compounds applying density functional theory (PBE0, TPSSh, wB97XD, B3LYP, CAM-B3LYP, and M06-2X) and Hartree–Fock methods using the Gaussian software package. The predicted β was compared with the experimental analogs obtained by the well-known Hyper–Rayleigh Scattering (HRS) technique. The most reliable functionals were CAM-B3LYP and M06-2X, with an unsigned average error of around 25%. Moreover, we have developed post-processing software—Hyper-QCC, providing an effortless, fast, and reliable way to analyze the Gaussian output files.