Second-order Hyperpolarizability Research Articles

First and second order hyperpolarizabilities of flavonol derivatives: A density functional theory study

In this study, seventeen flavonol derivatives (1–17) were evaluated with regard to their first- and second-order hyperpolarizability parameters. For this purpose, the molecular geometries of 1–17 were optimized by using B3LYP/6–311++G(d,p) level. Spectroscopic characterizations for 1–17 were executed through the calculations of IR, UV–vis, 1H NMR and 13C NMR spectra. The quantum chemical parameters such as electronegativity, chemical hardness, chemical potential and electrophilicity indexes were obtained by using the frontier molecular orbital (FMO) energies. The potential energy distribution (PED) analysis was used to provide a detailed assignment of vibrational bands. Important contributions to electronic absorption bands from FMOs were also evaluated. The distribution of FMOs to the whole molecule was investigated to determine the nature of electronic charge transfers in 1–17. The static and dynamic first- and second-order hyperpolarizability parameters for 1–17 were calculated by using B3LYP/6–311++G(d,p) level. The static β and γ were calculated at the ranges of 9.8279–0.0303 × 10-29 esu and 80.200–268.40 × 10-36 esu. The dynamic β and γ (ω = 532 nm) were also obtained in the field of 1.0440–71.786 × 10-29 esu and 306.20–3607.00 × 10-36 esu. This wide range of β and γ values indicate that flavonol derivatives with rational substitution may be promising candidates for first- and second-order NLO applications.

Polarity effects on the optical responses of some biologically active molecules with different substituents

Environment polarity characteristics of biomolecules as an important factor can enhance their optical behaviors. Hence, knowledge of environment polarity effects can give valuable information about the function of molecules in different phenomena. In this work, linear, first, and second-order hyperpolarizability of (E)-2-benzylidene-2,3-dihydro-5,6-dimethoxyinden-1-one as pharmacologically important compounds were studied in different environments. The analysis was done by using environment multi-parameter polarity parameters. According to the results, environment polarity has different effects on the linear and nonlinear optical properties of samples. A quantitative study indicated that general solvent effects play important roles in molecular linear behaviors. Furthermore, environments with strong hydrogen bond acceptor ability increase molecular nonlinearity. On the other hand, environment polarity indicated the same effects on the molecular first and second-order nonlinearity. In this case, the studies on the molecular first-order nonlinearity in different solvents can give valuable information about environment effects on the molecular higher-order nonlinearity.

Linear, nonlinear optical properties and structure-property relationships in ESIPT-rhodols

Linear and nonlinear optical (NLO) properties of three ESIPT-rhodol derivatives, spirocyclic and open-forms of 10, 11, and 12 estimated by spectroscopic based mathematical calculations and compared with computed values by using density functional theory (DFT) calculations. The group of global and range-separated hybrid functionals were used for theoretical estimation of NLO properties. Spectroscopic based mathematical calculations were used for estimation of polarizabilty (α), and second-order hyperpolarizability (γ) in series of solvents. Benchmarking strategies were applied to used functionals for investigation of NLO characteristics. BHHLYP and ωB97 functionals performed well in the company of GHs and RSHs functionals to evaluate the NLO characteristics. The resulting NLO characteristics for open 10, 11, and 12 are higher than the consequences observed for close 10, 11, and 12. The computed polarizabilty (α), and second-order hyperpolarizability (γ) follow the trend 10 > 11 > 12, while the first-order hyperpolarizability (β) and molecular hyperpolarizability (µβ) follow the trend 12 > 10 > 11 for both forms. The observed trends in NLO parameters for compounds 10, 11, and 12 are supported by electron correlation analysis.

Structure-Property Relationship of Three 2-Chloro-4-fluoro Chalcone Derivatives: A Comprehensive Study on Linear and Non-linear Optical Properties, Structural Characterizations and Density Functional Theory

This work focused on the relationship between molecular structure and non-linear optical (NLO) property of the chalcone derivatives. The NLO property is well known increased by push-pull effect, therefore we have explored donor-acceptor substitutions on both rings to develop excellent NLO materials. Three new crystals of 2-chloro-4-fluorochalcone derivatives bearing various donor end groups were synthesized in order to evaluate the donor dependence of their second-order hyperpolarizability γ. The grown crystals were spectroscopically confirmed and crystallographically analysed. Their intermolecular interactions were visualized by Hirshfeld surface analysis. The electronic absorption spectrums were investigated by experimental and theoretical methods, to discuss the intramolecular charge transfer and energy gap of solution sample, which defined significantly affected NLO properties. Theoretical electronic properties have been simulated with density functional theory (DFT) at B3LYP/6-311++G (d,p) level and compared with experimental results. Thermally-induced NLO parameters such as non-linear absorption (NLA) coefficient (α2∼10−5 cmW−1), non-linear refractive (NLR) index (n2 ∼10−9cm2W−1), third-order susceptibility [χ(3)(-ω;ω,ω,-ω) ∼10−8 esu] and γ(-ω;ω,ω,-ω)∼ 10−27 esu] were measured by Z-scan technique under continuous-wave laser excitation (532 nm). The solution samples exhibit two-photon assisted reverse saturable absorption and self-defocusing non-linear refraction, optical limiting and all-optical switching behaviours. We have determined that γ depends on the strength of donor/acceptor substituents, which is the result of the two contributions: the energy gap and the transition dipole moment between the ground and first excited states. A large value of γ was found for compound I which bearing strong donor hydroxy substituent, thus the hydroxychalcone derivatives as a potential material with excellent NLO performance.

Influence of End-Capped Modifications in the Nonlinear Optical Amplitude of Nonfullerene-Based Chromophores with a D-π-A Architecture: A DFT/TDDFT Study.

Nonlinear optical (NLO) materials have several uses in many fields such as solid physics, biology, medicine, nuclear physics, and material research. Therefore, a series of nonfullerene-based derivatives (CC10D1–CC10D8) with a D−π–A configuration was planned for the NLO investigation using CC10R as the reference molecule with structural alternations at acceptor moieties. Natural bonding orbital (NBO), UV–vis spectra, frontier molecular orbitals (FMOs), global reactivity parameters (GRPs), transition density matrix (TDM), and density of states (DOS) were analyzed using the M06/6-311G(d,p) functional in chloroform solvent to understand the NLO responses of CC10R and CC10D1–CC10D8. The highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) band gaps of CC10D1–CC10D6 were illustrated to be lower than that of CC10R, with the larger bathochromic shift (726.408–782.674 nm) resulting in a significant NLO response. Along with the band gap, the FMO method also identified an efficient interfacial charge transfer from D to A moieties via a π-bridge, which was further supported by the DOS and TDM map. Moreover, NBO calculations demonstrated that extended hyperconjugation and strong internal molecular interactions were important in their stabilization. The dipole moment (μ), linear polarizability ⟨α⟩, hyperpolarizability (βtotal), and second-order hyperpolarizability (γtotal.) were studied for CC10R and CC10D1–CC10D8. Among all of the derivatives, CC10D2 was proven to be the most appropriate candidate because of its suitable NLO behavior such as being well-supported by a reduced band gap (2.093 eV) and having a suitable maximum absorption wavelength (782.674 nm). Therefore, CC10D2 was reported to have a greater value of first hyperpolarizability (208 659.330 a.u.) compared with other derivatives and CC10R. For the second hyperpolarizability, a greater value was obtained for CC10R (5.855 × 107 a.u.), and its derivatives showed results comparable to that of the parent chromophore for γtotal. This theoretical framework reveals that structural customization with different acceptor units plays a significant role in obtaining attractive NLO materials for optoelectronic applications.

Investigation of dielectric, linear, and nonlinear optical properties of synthesized 2D Ruddlesden-Popper-type halide perovskite

Ruddlesden-Popper-type halide perovskites (RPPs) have been widely investigated because of their tunable optical properties. The BA2MAPb2I7 (BA = CH3(CH2)3NH3 and MA = CH3NH3) powder is synthesized by a chemical solution-based method at low temperature and deposited on a glass substrate by spin coating technique. The optical transmission, reflection, and absorption investigations are conducted to determine the optical constants of the nano-powder and thin film of BA2MAPb2I7. The obtained results reveal that the optical band gap energy of BA2MAPb2I7 thin film and BA2MAPb2I7 nanoparticles are ∼ 1.95 and ∼ 2.02 eV, which is close to the photoluminescence (PL) peak at around 2.15 eV (576 nm). The optical indexes such as n, k, ε1, and ε2 are assessed based on reflectance spectra data and the Kramers-Kronig (KK) method. Moreover, the third-order nonlinear optical (NLO) characteristics, including nonlinear absorption coefficient (β), nonlinear refractive index (n2), third-order susceptibility (χ(3)) and second-order hyperpolarizability (γ) are investigated at different laser power. The positive signs of the n2 and β reveal that the BA2MAPb2I7 thin film exhibits self-focusing and saturable absorption (SA) properties due to thermal nonlinearity under the continuous wave (CW) laser regime. The magnitude of χ3 is from 20.275 ×10-2 to 29.908 ×10-2esu and the value of γ is from 19.633 ×10-27 to 28.961 ×10-27esu. The superior NLO responses of BA2MAPb2I7 thin-film open the path for the future design and synthesis of desirable and distinct materials for optoelectronic devices.

Phenothiazine metal-organic framework materials with excellent third-order nonlinear properties

The third-order nonlinear optical material with excellent performance is a molecule with a large π-conjugated structure for absorption structure and a high degree of delocalization. Nitrogen-sulfur derivatives have lone pairs of electrons in their N and S atoms, which makes them have a strong intramolecular charge transfer ability, which is conducive to the formation of donor-acceptor molecules. In this paper, phenothiazine is used as the matrix structure of the third-order nonlinear optical material, modified, and then metal coordination is performed to obtain [Zn(Py)2Cl2]n and [Cd(Py)2Cl2]n. Its structure is characterized by infrared spectroscopy, single crystal X-ray diffraction and powder X-ray diffraction. The morphology of the material was characterized by scanning electron microscopy. The photophysical properties, thermal properties and third-order nonlinear properties were tested, and the theoretical verification was carried out with the DFT calculation method, and the relationship between the structure and the third-order nonlinear properties was summarized. The experimental results show that phenothiazine has good electron donating ability, the two-photon absorption coefficient β is between 1.334–38.400 × 10−10 m/W, and the third-order nonlinear polarizability χ(3) is between 2.752–79.247 × 10−11 esu, The second-order hyperpolarizability γ of the ligand molecule is 5.213 × 10−34 esu. The χ(3) values of [Zn(Py)2Cl2]n and [Cd(Py)2Cl2]n are 4 orders of magnitude higher than ordinary α-quartz (χ(3) = 2.6 × 10−14 esu).

Exploration of Nonlinear Optical Properties for the First Theoretical Framework of Non-Fullerene DTS(FBTTh2)2-Based Derivatives.

Organic compounds having significant nonlinear optical (NLO) applications are being employed in the optoelectronics field. In the current work, a series of non-fullerene acceptor (NFA) based compounds are designed by modifying the acceptors with different substituents using DTS(FBTTh2)2R1 as a reference compound. To study the NLO responses to the tuning of various acceptors, DFT and TD-DFT based parameters were calculated at the M06 level along with the 6-31G(d,p) basis set. The designed compounds (MSTD2–MSTD7) showed smaller values of the energy gap in comparison to the reference compound. The energy gaps of the title compounds were linked to global reactivity insights; MSTD7 provided a lower band gap, with smaller and larger quantities for hardness and softness characteristics, respectively. Further, UV–vis analyses were performed for all of the designed compounds, displaying wavelengths red-shifted from that of DTS(FBTTh2)2R1. The intraelectron transfer (ICT) process and stability of the title compounds were explored via frontier molecular orbital (FMO) and natural bond orbital (NBO) studies, respectively. Out of all the designed compounds, the highest value of linear polarizability ⟨α⟩ of 3.485 × 10–22 esu, first hyperpolarizability (βtotal) of 13.44 × 10–27 esu and second-order hyperpolarizability ⟨γ⟩ of 3.66 × 10–31 esu were exhibited by MSTD7. In short, all of the designed compounds exhibited promising NLO properties because of their low charge transport resistance. These NLO properties may be useful for experimental researchers to uncover NLO materials for modern applications.

Spectroscopic Recognition of Metal Ions and Non-Linear Optical (NLO) Properties of Some Fluorinated Poly(1,3,4-Oxadiazole-Ether)s

In this paper, we examined the sensing ability of some fluorinated 1,3,4-oxadiazole-containing assemblies toward various metal ions and their nonlinear optical (NLO) properties. The changes in the spectral characteristics of these compounds in the existence of Mg2+, Mn2+, Ni2+, Cd2+, Zn2+, Co2+, Cu2+, Hg2+, Sn2+, and Ag+ metal ions were performed, and they were found to be selective and more sensitive toward the addition of Ag+, Co2+, and Cu2+ ions (new bands appeared). Instead, spectral changes in the presence of Mg2+, Mn2+, Ni2+, Cd2+, Zn2+, Hg2+, and Sn2+ were not significant, so we did not evaluate the corresponding binding parameters. Therefore, all of these compounds were found to be selective and sensitive to Ag+, Co2+, and Cu2+ ions. Furthermore, the first-order polarizability (αCT), the first-order hyperpolarizability (βCT), and the second-order hyperpolarizability (γCT) were evaluated using the solvatochromic approach, and the intramolecular charge transfer (ICT) characteristics were investigated using a generalized Mulliken–Hush (GMH) analysis.

Effect of new DFT methods on spectroscopy and NLO analysis of 2-Bromo-5-nitrothiozole and nitrosodimethylamine.

The present study reports the effect of new DFT methods introduced in Gaussian 16 viz B2PLYP, B2PLYPD, DSDPBEP86, and MPW2LPLYP on spectroscopy and nonlinear optical (NLO) properties. The 2-Bromo-5-nitrothiozole and nitrosodimethylamine are considered for the study. In addition to new methods, old DFT, MP2, and HF methods are also considered. The spectroscopic study of geometrical parameters, vibrational, electronic absorption spectra, and HOMO-LUMO gap with their molecular orbitals have been reported. The geometrical parameters such as optimized energy, dipole moment, bond length, and angles have been reported. The diffuse and polarized basis set 6-311 + + G(d,p) has been used for the study. The first- and second-order hyperpolarizabilities have also been reported for both molecules at all methods. This study shows that these two molecules are responsive to nonlinear optical (NLO), which reflects its enhanced applicability in the development of photonic devices. The finite field approach has been applied for calculating first (β) and second hyperpolarizabilities (ϒ) respectively. The HOMO-LUMO energy gap of nitrosodimethylamine is found to be greater than that of 2-Bromo-5-nitrothiozole. Gaussian16 program package has been used for all these calculations.

Electrically Tunable Second Harmonic Generation in Atomically Thin ReS2.

Electrical tuning of second-order nonlinearity in optical materials is attractive to strengthen and expand the functionalities of nonlinear optical technologies, though its implementation remains elusive. Here, we report the electrically tunable second-order nonlinearity in atomically thin ReS2 flakes benefiting from their distorted 1T crystal structure and interlayer charge transfer. Enabled by the efficient electrostatic control of the few-atomic-layer ReS2, we show that second harmonic generation (SHG) can be induced in odd-number-layered ReS2 flakes which are centrosymmetric and thus without intrinsic SHG. Moreover, the SHG can be precisely modulated by the electric field, reversibly switching from almost zero to an amplitude more than 1 order of magnitude stronger than that of the monolayer MoS2. For the even-number-layered ReS2 flakes with the intrinsic SHG, the external electric field could be leveraged to enhance the SHG. We further perform the first-principles calculations which suggest that the modification of in-plane second-order hyperpolarizability by the redistributed interlayer-transferring charges in the distorted 1T crystal structure underlies the electrically tunable SHG in ReS2. With its active SHG tunability while using the facile electrostatic control, our work may further expand the nonlinear optoelectronic functions of two-dimensional materials for developing electrically controllable nonlinear optoelectronic devices.

Remarkable Nonlinear Properties of a Novel Quinolidone Derivative: Joint Synthesis and Molecular Modeling.

A novel 4(1H) quinolinone derivative (QBCP) was synthesized and characterized with single crystal X-ray diffraction. Hirshfeld surfaces (HS) analyses were employed as a complementary tool to evaluate the crystal intermolecular interactions. The molecular global reactivity parameters of QBCP were studied using HOMO and LUMO energies. In addition, the molecular electrostatic potential (MEP) and the UV-Vis absorption and emission spectra were obtained and analyzed. The supermolecule (SM) approach was employed to build a bulk with 474,552 atoms to simulate the crystalline environment polarization effect on the asymmetric unit of the compound. The nonlinear optical properties were investigated using the density functional method (DFT/CAM-B3LYP) with the Pople’s 6-311++G(d,p) basis set. The quantum DFT results of the linear polarizability, the average second-order hyperpolarizability and the third-order nonlinear susceptibility values were computed and analyzed. The results showed that the organic compound (QBCP) has great potential for application as a third-order nonlinear optical material.

Synthesis of Crystalline Fluoro-Functionalized Imines, Single Crystal Investigation, Hirshfeld Surface Analysis, and Theoretical Exploration.

This investigation is focused on the synthesis of two halo-functionalized crystalline Schiff base (imine) compounds: (E)-2-methoxy-6-(((3-(trifluoromethyl)phenyl)imino)methyl)phenol (MFIP) and (E)-1-(((2-fluorophenyl)imino)methyl)naphthalen-2-ol (FPIN) by the condensation reaction of substituted benzaldehydes and substituted aniline. The crystal structures of MFIP and FPIN were determined unambiguously by single-crystal X-ray diffraction (SC-XRD) studies. Intermolecular interactions and the role of fluorine atoms in the stabilization of the crystal packing are explored for both compounds using Hirshfeld surface analysis. Accompanied with experimental studies, quantum chemical calculations were also performed for comprehensive structure elucidation at the M06/6-311G(d,p) level of theory. A comparison of experimental and density functional theory results for geometrical parameters exhibited excellent agreement. Interestingly, Frontier molecular orbitals and natural bond orbital (NBO) findings revealed that intramolecular charge transfer and hyper-conjugation interactions had played a significant role to stabilize the molecules. Both compounds exhibited a relatively larger value of hardness with a smaller global softness, which, as proposed by the SC-XRD and NBO study, shows a higher stability. Nonlinear optical (NLO) findings showed that FPIN manifested a larger value of linear polarizability (<a> = 293.06 a.u.) and second-order hyperpolarizability (<γ> = 3.31 × 105 a.u.) than MFIP (<a> = 252.42 and <γ> = 2.08 × 105 a.u.) due to an extended conjugation. The above-mentioned findings of the entitled compounds may play a crucial role in NLO applications.

Synthesis, crystal structure, characterization, Hirshfeld analysis, molecular docking and DFT calculations of 5-Phenylamino-isophthalic acid: A good NLO material

5-Phenylamino-isophthalic acid (H2L) (C15H13NO4) has been synthesized, characterized via single-crystal X-ray diffraction, spectroscopic techniques and also studied theoretically using DFT approach. The compound crystallizes in a monoclinic crystal system with a P21/c space group with Z = 2 and the following unit cell dimensions: a = 10.4415(14) Å, b = 16.472(2) Å, c = 7.5305(10) Å. DFT calculations were carried out by B3LYP/6–311++G(d,p) level and geometry optimization, vibrational analysis, MEP, ELF, NBO, NHO, and FMO analysis were also carried out. The calculated values showed excellent agreement with the experimental data. The vibrational frequencies were evaluated using density functional theory (DFT) with the complete PED analysis. The Molecular Frontiers Orbitals (FMO) or HOMO/LUMO energy values showed that there wasa satisfying interchange of charge occurring within the molecule. Hirshfeld surface analysis was carried out to study 3-D and 2-D interactions in crystal. Molecular docking was done with 4 protein receptors to find the best ligand-protein interactions. The nonlinear optical characteristics of the title compound have been evaluated using the Z-scan method with CW diode laser working at 520 nm. The third-order nonlinear refraction coefficient (n2), nonlinear absorption (β), nonlinear susceptibility χ(3), and second-order hyperpolarizability (γ) are of the order of 10−8 cm2/ W, 10−3 cm/ W, 10−7 esu, and 10−27 esu, respectively.

Experimental and theoretical investigation on the nonlinear optical properties of LDS 821 dye in different solvents and DNA

Linear and nonlinear optical properties of near-infrared laser grade dye LDS 821 in different solvents and Salmon Deoxyribonucleic acid (DNA) were studied using spectroscopic and Z-scan techniques. UV–Vis absorption spectrum of the dye shows a bathochromic shift with a decrease in the solvent polarity parameter, and in DNA, the dye exhibits a hypochromic shift. The fluorescence spectrum of the dye does not show any notable correlation with the solvent polarity parameter, but in DNA, the fluorescence intensity of the dye decreases with the incremental addition of DNA. Molecular docking studies reveal that the dye intercalates on the major grooves of DNA. Nonlinear optical properties of the dye in different solvents and phosphate buffer solution with varying DNA concentrations were studied using the Z-scan technique using a Q-switched Nd: YAG laser operating at fundamental and second harmonics. A closed and open aperture Z-scan of dye in different solvents was carried out to estimate the nonlinear refractive index, excited-state absorption cross-section, and two-photon absorption coefficient (TPA). The variation in nonlinear optical properties of the dye in different solvents was due to solvent-induced structural modifications. Theoretical investigation on nonlinear optical properties of the dye in different solvents was carried out using density function theory. The theoretical first and second-order hyperpolarizability was calculated using B3LYP functional. The predicated nonlinear optical parameters of the dye in different solvents does not show any direct correlation with solvent polarity. Nonlinear absorption of the dye in phosphate buffer solution (PBS) and DNA were estimated. The nonlinear absorption of the dye in PBS decreases with the addition of DNA. Molecular docking studies were carried out to determine the structural changes induced in dye due to the intercalation with DNA.

Diagrammatic theory of linear and nonlinear optics for composite systems

We present a general formalism to model and calculate linear and nonlinear optical processes in composite systems, based on a graphical representation of light-matter interactions by loop diagrams associated with Feynman rules. Through this formalism, we recover the usual second-order response of a simple system by drawing four times fewer loop diagrams than doubled-sided ones. For composite systems, we introduce coupling Hamiltonians between subsystems (for example, a molecule and a substrate), graphically represented by virtual bosons. In this way, we enumerate all the diagrams describing the second-order response of the system and show how to select those relevant for the calculation of the molecular second-order hyperpolarizabilities under the influence of the substrate, including effective second-order contributions from the molecular third-order response. As it applies to all nonlinear processes and an arbitrary number of interacting partners, this representation provides a general frame for the calculation of the nonlinear response of arbitrarily complex systems.

Experimental and theoretical approach on third-order optical nonlinearity of a highly efficient anthracene-based chalcone derivative for optical power limiting

Herein the study reports a dual approach on theoretical and experimental studies of nonlinear optical properties of a novel chalcone derivative, (2E)-1-(Anthracen-9-yl)-3-(biphenyl-4-yl)prop-2-en-1-one [biphenyl-ANC]. The obtained experimental results have been supported by the theoretical calculations performed by density functional theory. The FT-IR, FT-Raman, and UV-visible absorption spectra were recorded and analyzed. The structural, electronic and charge transfer analyses were computed by B3LYP level of theory with 6–311++G(d,p) basis set. The second-order hyperpolarizability has been theoretically predicted using B3LYP and CAM-B3LYP hybrid functional. The third-order nonlinear optical properties, along with the optical limiting studies of biphenyl-ANC in polar and nonpolar solvents, were carried out by z-scan technique using Q-switched Nd:YAG laser with 5 ns pulses at 532 nm. The z-scan results reveal that the compound can act as a promising candidate for photonic and optoelectronic applications.

Crystal structure elucidation, experimental and computational optical properties of novel acceptor-donor-acceptor organic material: A suitable candidate for nonlinear applications

A new organic nonlinear optical (NLO) material, 2-(4-chlorophenoxy)-N'-[(1E)-1-(4-fluorophenyl) ethylidene] acetohydrazide (4CP4FPEA), has been synthesized and single crystals were grown using DMF as solvent. The compound was characterized by 1H NMR and single X-ray diffraction analyses. Analysis of intermolecular interactions was carried out by mapping Hirshfeld surfaces over 2D fingerprint plots, dnorm and curvedness using Crystal Explorer. Open aperture Z-Scan experimental curve showed that the 4CP4FPEA molecule exhibits lower transmittance at the focus at 532 nm wavelength. 4CP4FPEA exhibits good optical limiting behavior at the wavelength 532 nm. Estimated excited state absorption cross-section (σex) and ground state absorption cross-section (σg) are found to be 3.59 × 10−17cm2 and 1.9 × 10−21 cm2 respectively (σg <<< σex) indicating that nonlinear absorption is due to Reverse Saturable Absorption. Semi-empirical calculations were implemented to calculate static and frequency dependent mean polarizability, first-order hyperpolarizability and second-order hyperpolarizability using time-dependent Hartree–Fock (TDHF) method. We have observed enhancement in nonlinear optical property compared to our previous reported molecule 2-(4-chlorophenoxy)-N'-[(1E)-1-(4-methylphenyl) ethylidene] acetohydrazide (4CP4MPEA).

Anionic dependency of electronic and nonlinear optical properties of ionic liquids

Nonlinear optical phenomena play significant roles in the bulk properties and responsive characteristics of ionic liquids, especially when used under strong electric fields. The variability of the anion-cation pair in ionic liquids makes them designer solvents; thus, the anion or cation dependency of the physicochemical properties should be understood in depth. Accordingly, the electric field-induced characteristics of eight ionic liquids with [Br]−, [BF4]−, [PF6]−, [Ac]−, [TFAc]−, [MS]−, [NTf2]−, and [Tos]− anions paired with the 1-butyl-3-methyl imidazolium cation were investigated using density functional theory modeling at four theoretical levels: B3LYP-6-31G(d), M06-2X 6-31G(d), M06-2X 6-311++G(d,p), and M06-2X aug-cc-PVTZ. The frontier molecular orbitals, electrostatic potential surface, and electron density difference maps were obtained to visualize the electrostatic characteristics. The permanent electric dipole moment, linear electric polarizability, and first-order and second-order hyperpolarizabilities were also determined. While the static dipole moment and dipole polarizabilities could be obtained using low-level quantum chemistry at a satisfactory level, the functionalization of more intensive methods was required to accurately obtain the nonlinear optical properties.

Third-order NLO studies of 2, 4-Bis (4-fluorophenyl)-2, 3-dihydro-1H-1, 5-benzodiazepine using Z-scan technique and DFT method

The present work discusses the nonlinear optical properties of 2, 4-Bis (4-fluorophenyl)-2, 3-dihydro-1H-1, 5-benzodiazepine. The structural characterizations have been performed using FT-IR, FT-Raman, and UV-Visible absorption spectroscopic techniques. The optimized geometry, vibrational wavenumbers, natural bond orbital analysis, HOMO-LUMO analysis, natural population analysis were calculated using the B3LYP/6-311++G (d, p) level of theory. Unambiguous vibrational assignments have been performed using potential energy distribution values obtained from normal coordinate analysis using MOLVIB program. The theoretical second-order hyperpolarizability was calculated using B3LYP and CAM-B3LYP hybrid functional at the DFT level. The second-order hyperpolarizability (γ),third-order susceptibility (χ(3)), nonlinear refractive index (n2), nonlinear absorption coefficient (β)) have been investigated using the Z-scan technique. The Z-scan results confirm that the compound exhibits positive nonlinear absorption and negative nonlinear refractive index. The second harmonic generation efficiency was investigated using the Kurtz and Perry method and was found to be 1.44 times higher than urea. The obtained results reveal that the title compound is a promising material for laser assisted applications.