High Nonlinear Optical Response Research Articles

Quantum chemical framework for designing high-performance ladder-shape NLO molecules and study of implicit vs explicit solvent effects on their NLO properties

Researchers in materials science are greatly fascinated by helicene chemistry due to its excellent optical and structural properties. In this work, we introduced symmetrical substitution of donor and acceptor groups on the [7]helicene ([7]HC-1 to [7]HC-5). DFT analysis is used to explore nonlinear optical (NLO) response for designed compounds. For [7]HC-5, the linear isotropic (αiso) and anisotropic polarizability (αaniso) are 31.59 × 10−24 esu and 59.86 × 10−24 esu, respectively. [7]HC-5 has the highest average third-order NLO polarizability (<γ>) of 47.24 × 10−36 esu which is approximately six times greater than that of para-nitroaniline, a well-known prototype NLO molecule. The effect of implicit and explicit solvents on <γ> and αiso of three selected compounds ([7]HC-1, [7]HC-3, and [7]HC-5) is also evaluated. As compared to explicit and gas phase methods, PCM model predicts an overestimation by an increment of ∼ 4-5 times for selected compounds. TD-DFT calculations show a higher transition dipole moment (4.24) and a lower transition energy (3.414 eV) for [7]HC-5. The higher NLO response is explained based on frontier molecular orbitals (FMOs), electron density difference (EDD), and molecular electrostatic potentials (MEPs). There is a red shift for studied compounds based on UV-visible results. The C-N stretching at 1372 cm-1 for [7]HC-5 indicates the presence of -N(CH3)2. Additionally, we studied photovoltaic parameters and found that [7]HC-5 has the maximum open circuit voltage and the lowest dye regeneration of 2.71 eV and 0.06 eV, respectively.

Decoding the commutable first hyperpolarisability of keto–enol tautomer using DFT and AI-based soft computing method

ABSTRACT Non-linear optical (NLO) parameter of a series of donor–acceptor substituted N-salicylidene-4-benzenesulfonylaniline (SBSA) derivatives with a contrast of first hyperpolarisability has been investigated using density functional-based theory. The derivative of SBSA with both the donor and acceptor substitution (NMe2-SBSA-NO2) exhibits the highest first hyperpolarisability ( ∼ 3 × 103 a.u in gas phase) value. Frequency and solvent polarity responsive behaviours of first hyperpolarisability are utilised to demonstrate the variation of NLO as switchable electrical parameter. Each of the studied compounds displays very high NLO response at frequency corresponding to the absorption maxima of their electronic state. Likewise, the increase of solvent polarity induces a substantial increase of first hyperpolarisability. The computation of NLO responsive first hyperpolarisability by varying the frequency and solvent dielectric constant within a wide domain is very tedious and time-consuming. To overcome the lacuna, we implemented machine learning tools such as artificial neural networks (ANNs), fuzzy logic (FL) and adaptive neuro-fuzzy inference system (ANFIS) to predict the computation data of the NMe2-SBSA-NO2 and moderately good results were obtained using ANFIS as soft computing tool.

Superalkalides based on stacked janus molecule with improved optical nonlinearity

Research is actively being carried out to design new materials with exceptional nonlinear optical (NLO) responses. In this context, a systematic investigation of designing novel hypothetical materials e.g., superalkalides based on stacked Janus dimer, all-cis-1,2,3,4,5,6-hexafluorocyclohexane (C6H6F6)2 has been reported using high-level density functional simulations. The superalkalides are designed here by doping alkali metals on the fluorine face and superalkalis on the hydrogen face of Janus dimer. The thermodynamic stability of newly designed complexes is demonstrated by the interaction energies (Eint), ranging between −13.64 and −33.12 kcal/mol. Moreover, the superalkalide nature of these complexes is proved by negative charge and HOMO on superalkalis in natural bond orbitals (NBO) and frontier molecular orbitals (FMO) analyses, respectively. Energy gaps (Eg) between HOMO and LUMO orbitals of the designed complexes lie in the range of 0.63–0.83 eV. UV–Vis analysis is performed to gain idea about the transparent region of electromagnetic spectrum for nonlinear activity. The nonlinear activity of the designed superalkalide(s) is studied by static first hyperpolarizability β0, dynamic first hyperpolarizability β(ω) and dynamic second hyperpolarizability γ(2- ω; ω, ω). The highest β0, β(ω), and γ(2- ω; ω, ω) ranges up to 1.1 × 107, 2.9 × 106 and 2.9 × 1012 au, respectively for designed complexes. A comprehensive examination of these superalkalides based on stacked Janus dimers with exceptionally high NLO response highlights their potential for use in nonlinear optical materials.

Superalkalis with Hydrogen as Central Electronegative Atom and their Possible Applications: Ab Initio and DFT Study.

Superalkalis are unusual species having ionization energies lower than that of the alkali metals. These species with various applications are of great importance in chemistry due to their low ionization energies and strong reducing property. A typical superalkali contains a central electronegative core decorated with excess metal ligands. In the quest for novel superalkalis, we have designed the superalkalis HLi2, HLiNa and HNa2 using hydrogen as central electronegative atom for the first time employing high level ab initio (CCSD(T), MP2) and density functional theory (ωB97X-D) methods. The superalkalis exhibit very low ionization energies, even lower than that of cesium. Stability of these species is verified from binding energy and dissociation energy values. The superalkalis are capable of reducing SO2, NO, CO2, CO and N2 molecules by forming stable ionic complexes and therefore can be used as catalysts for the reduction or activation of systems possessing very low electron affinities. The superalkalis form stable supersalts with tailored properties when interact with a superhalogen. They also show remarkably high non-linear optical responses, hence could have industrial applications. It is hoped that this work will enrich the superalkali family and spur further theoretical and experimental research in this direction.

Benzo‐bisimidazole based nanosheets having porphyrin like internal core with high second order nonlinear optical response: A theoretical perspective

AbstractThe 2D network having porphyrin like internal core are well established in literature due to their remarkable molecular tunability, photophysical and optoelectronics properties. Therefore, in the quest to attain the high performance nonlinear optical (NLO) response we have designed single Benzo‐bisimidazole (BIZ) unit which has porphyrin like motif and expanded it strategically in such a way that it forms cage and further it convert into 2D nanosheet. Density functional theory (DFT), sum‐over‐state models and time dependent‐DFT (TD‐DFT) simulation were performed for geometric and electronic properties calculation. Expanding the BIZ plays a pivotal role in enhancement of the first static hyperpolarizability (βtot) from 205.65 to 13754.59 au. Further, alkali metals substitution leads to gigantic enhancement of βtot value from 2200.17 to 636673.60 au which is enormously higher than that of recently reported porphyrin derivative (47950 au). Calculated results revealed that the gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) become narrow down from 6.28 eV (1) to 1.70 eV (6). It is to note that the designed molecules exhibit red shift of absorption. Further, density of states (DOS), and transition density matrix (TDM) analysis have also performed to explore the charge transfer and structure property relationship.

A Rational Design of Alkali Metal-Doped Germanium Carbide Nanoclusters for High Nonlinear Optical Response and Ultraviolet Transparency

A Rational Design of Alkali Metal-Doped Germanium Carbide Nanoclusters for High Nonlinear Optical Response and Ultraviolet Transparency

Boron sub-phthalocyanine chloride deposited on PA substrate towards flexible optoelectronic devices: Structural, optical, and electrical characterization

Flexible thin film photovoltaic devices have been a way of interest for researchers through the last decade. Creating suitable ultrathin films of any material is necessary for the realization of flexible systems. Therefore, the current study aims to study the impact of the thickness of the Boron sub-phthalocyanine chloride B(SubPc)Cl deposited on flexible Polyacetate (PA) as a polymer substrate. The structural properties of B(SubPc)Cl/PA with different thicknesses have been investigated using XRD and AFM. The investigated samples show an amorphous characterization with grain size slightly changed from 107 to 131 nm for thicknesses of 76 and 300 nm respectively, which is affected by the effect of the thickness. The optical transmission and absorption were studied in the spectral range of 300–2500 nm where the characteristic bands of a metallic phthalocyanine known as B and Q bands were observed in this range of the spectrum. The dispersion parameters, optical dielectric, SELF, and VELF for B(SubPc)Cl/PA were calculated and interpreted. Also, by using Tauc's extrapolation, the optical energy gap (Eg) was calculated. The Eg has values of 1.76 and 3.19 for a thickness of 76 nm which increased by increasing the film thickness. The nonlinear optical properties of B(SubPc)Cl/PA have been investigated, and the values obtained showed a high nonlinear optical response. The research outcomes candidate B(SubPc)Cl/PA for optoelectronics applications such as solar cells, sensors, and nonlinear optical devices.

Enhanced nonlinear optical response of alkalides based on stacked Janus all-cis-1,2,3,4,5,6-hexafluorocyclohexane

Significant efforts are continuously exerted by the scientific community to explore new strategies to design materials with high nonlinear optical responses. An effective approach is to design alkalides based on Janus molecules. Herein, we present a new approach to remarkably boost the NLO response of alkalides by stacking the Janus molecules. Alkalides based on stacked Janus molecule, M-n-M' (where n = 2 & 3 while M and M′ are Li/Na/K) are studied for structural, energetic, electrical, and nonlinear optical properties. The thermodynamic stability of the designed complexes is confirmed by the energetic stabilities, which range between -14.07 and -28.77 kcal/mol. The alkalide character of alkali metals-doped complexes is confirmed by the NBO charge transfer and HOMO(s) densities. The HOMO densities are located on the doped alkali metal atoms, indicating their alkalide character. The absorptions in UV–Vis and near IR region confirm the deep ultraviolet transparency of the designed complexes. The maximum first static and dynamic hyperpolarizabilities of 5.13 × 107 and 6.6 × 106 au (at 1339 nm) confirm their high NLO response, especially for K-2-M′ complexes. The NLO response of alkalides based on stacked Janus molecules is 1–2 orders of magnitude higher than the alkalide based on Janus monomer. The high values of dc-Kerr and electric field-induced response e.g., max ∼107 and 108 au, respectively have been obtained. These findings suggest that our designed complexes envision a new insight into the rational design of stable high NLO performance materials.

Beyond Universal Volume Scaling: Tailoring Two-Photon Absorption in Nanomaterials by Heterostructure Design.

Colloidal semiconductor nanomaterials present broadband, with large cross-section, two-photon absorption (2PA) spectra, which turn them into an important platform for applications that benefit from a high nonlinear optical response. Despite that, to date, the only means to control the magnitude of the 2PA cross-section is by changing the nanoparticle volume, as it follows a universal volume scale, independent of the material composition. As the emission spectrum is connected utterly to the nanomaterial dimensions, for a given material, the magnitude of the nonlinear optical response is also coupled to the emission spectra. Here, we demonstrate a means to decouple both effects by exploring the 2PA response of different types of heterostructures, tailoring the volume dependence of the 2PA cross-section due to the different dependence of the density of final states on the nanoparticle volume. By heterostructure engineering, one can obtain 1 order of magnitude enhancement of the 2PA cross-section with minimum emission spectra shift.

Tuning nonlinear optical properties of tetracyclopentatetraphenylnene by superhalogens doping: Quantum chemical perspective of novel NLO materials for modern optoelectronic applications

Fabrication of stable NLO materials is highly demanding because of their numerous applications in optoelectronic and optical devices. This research attempts to theoretically design superhalogens (LiF2, BeF3, MgF3, LiCl2, BeCl3, MgCl3) doped tetracyclopentatetraphenylnene (TCPTP) as potential NLO materials for cutting-edge NLO applications. Density functional theory (DFT) computations explore their geometric, thermodynamic, electrical, and nonlinear optical (NLO) properties. NCI analysis, DOS, FMO, MEP, TDM, and NBO analysis are performed to confirm the type of interaction, participation of various fragments, and charge transfer, respectively. The computational findings demonstratedthat the superhalogen-doped isomers of TCPTP have remarkablethermodynamic stabilities, with the highestbinding energy of −81.344 kcalmol−1. The HOMO–LUMO energy gap was significantly decreased from 1.5319 eV (TCPTP) to 1.2807––1.2269 eV by superhalogens doping. The TD-DFT analysis demonstrates that these proposed complexes have sufficient transparency in the UV region, which is necessary to add a high nonlinear optical response for valuable applications in optoelectronics. Magnification in the dipole moment (µ0), polarizability (α0), and hyperpolarizability (β0) values from 0.0 D, 325.00 a.u. and 0.0 a.u to 18.23 D, 463.92 a.u and 4.11 × 104 a.u respectively, is achieved upon superhalogens doping on TCPTP surface. These complexes also had considerably large initial hyperpolarizability (βo) from 1.57 × 103 to 4.11 × 104 au, which was particularly noteworthy. This research with promising initial hyperpolarizability (βo) value will provide new opportunities for experimental and theoretical researchers to develop innovative NLO materials.

Rational Design, Stabilities and Nonlinear Optical Properties of Non-Conventional Transition Metalides; New Entry into Nonlinear Optical Materials.

Electronic and nonlinear optical properties of endohedral metallofullerenes are presented. The endohedral metallofullerenes contain transition metal encapsulated in inorganic fullerenes X12Y12 (X = B, Al & Y = N, P). The endohedral metallofullerenes (endo-TM@X12Y12) possess quite interesting geometric and electronic properties, which are the function of the nature of the atom and the size of fullerene. NBO charge and frontier molecular orbital analyses reveal that the transition metal encapsulated Al12N12 fullerenes (endo-TM@Al12N12) are true metalides when the transition metals are Ni, Cu and Zn. Endo-Cr@Al12N12 and endo-Co@Al12N12 are at the borderline between metalides and electrides with predominantly electride characteristics. The other members of the series are excess electron systems, which offer interesting electronic and nonlinear optical properties. The diversity of nature possessed by endo-TM@Al12N12 is not prevalent for other fullerenes. Endo-TM@Al12P12 are true metalides when the transition metals are (Cr-Zn). HOMO-LUMO gaps (EH-L) are reduced significantly for these endohedral metallofullerenes, with a maximum percent decrease in EH-L of up to 70%. Many complexes show odd-even oscillating behavior for EH-L and dipole moments. Odd electron species contain large dipole moments and small EH-L, whereas even electron systems have the opposite behavior. Despite the decrease in EH-L, these systems show high kinetic and thermodynamic stabilities. The encapsulation of transition metals is a highly exergonic process. These endo-TM@X12Y12 possess remarkable nonlinear optical response in which the first hyperpolarizability reaches up to 2.79 × 105 au for endo-V@Al12N12. This study helps in the comparative analysis of the potential nonlinear optical responses of electrides, metalides and other excess electron systems. In general, the potential nonlinear optical response of electrides is higher than metalides but lower than those of simple excess electron compounds. The higher non-linear optical response and interesting electronic characteristics of endo-TM@Al12N12 complexes may be promising contenders for potential NLO applications.

Non‐Centrosymmetric 2D Nb3SeI7 with High In‐Plane Anisotropy and Optical Nonlinearity

AbstractIntegrating anisotropy and nonlinearity of physical properties in 2D materials is of great importance to the progress of nanoelectronic, nanophotonic, and nano‐optoelectronic applications. In this work, Nb3SeI7, a newly discovered ternary layered material with non‐centrosymmetric lattices, is introduced, which exhibits strong second harmonic generation (SHG), in‐plane anisotropic electricity, and light absorption. Symmetry breaking of 2D Nb3SeI7 induced by the polar off‐center displacement of niobium leads to a high nonlinear optical response with a second‐order susceptibility of 6.71 pm V−1 and a high anisotropic factor of photoresponsivity up to 4.6, which are higher than most of the 2D materials. These properties of 2D Nb3SeI7 create new possibilities for chip‐integrated nonlinear optics devices and future‐proof polarization‐sensitive optoelectronic systems.

Designing Excess Electron Compounds by Substituting Alkali Metals to a Small and Versatile Tetracyclic Framework: A Theoretical Perspective.

Organic compound-based nonlinear optical (NLO) materials have sparked a lot of attention due to their multitude of applications and shorter optical response times than those of inorganic NLO materials. In the present investigation, we designed exo-exo-tetracyclo[6.2.1.13,6.02,7]dodecane (TCD) derivatives, which were obtained by replacing H atoms of methylene bridge carbon with alkali metals (Li, Na, and K). It was observed that upon the substitution of alkali metals at bridging CH2 carbon, absorption within the visible region occurred. Moving from 1 to 7 derivatives, the maximum absorption wavelength of the complexes exhibited a red shift. The designed molecules showed a high degree of intramolecular charge transfer (ICT) and excess electrons in nature, which were responsible for rapid optical response time and significant large molecular (hyper)polarizability. Calculated trends also inferred that the crucial transition energy decreased in order that also played a key role in the higher nonlinear optical response. Furthermore, to examine the effect of the structure/property relationship on the nonlinear optical properties of these investigated compounds (1-7), we calculated the density of state (DOS), transition density matrix (TDM), and frontier molecular orbitals (FMOs). The largest first static hyperpolarizability (βtot) of TCD derivative 7 was 72059 au, which was 43 times greater than that of the prototype p-nitroaniline (βtot = 1675 au).

Circularly polarized luminescence and nonlinear optical harmonic generation based on chiral zinc halides.

Chiral hybrid metal halides have grabbed extensive attention in linear and nonlinear chiroptics. Herein, 0D chiral zinc halides, (R-/S-2-MP)ZnCl4, have been fabricated, which demonstrate high efficiency second-order nonlinear optical responses. Incorporating Sb3+ into the chiral zinc halide matrix triggers the circularly polarized luminescence effectively with a balance between quantum yield and luminescence dissymmetry factor.

A remarkable third-order nonlinear optical behavior of single-crystal bromide organic-inorganic lead halide perovskite

The optical and structural aspects of methylamine lead bromide (MAPbBr3) single crystal (SC) are investigated. Based on Kramers–Kronig (KK) equations, the optical and dielectric parameters are investigated. The optical phonons Longitudinal optical (LO = 678 cm−1) and Transversal optical (TO = 578 cm−1) phonon modes are associated with the optical interaction with lattices in the visible region for MAPbBr3 SC. The Z-scan method is used to investigate the third-order nonlinear coefficients of SC hybrid organic–inorganic lead halide perovskites, MAPbBr3 with the 2.19 eV optical band gap energy. According to the nonlinear optical (NLO) properties, MAPbBr3 has a high third-order NLO response. The two-photon absorption (2PA) coefficient is found to be 3 × 10-4 cm W−1 using the transmission open aperture Z-scan technique. The nonlinear refraction (NLR) is obtained in the order of 10-9 cm2 W−1 utilizing a close aperture Z-scan, which revealed self-defocusing phenomena. This research shows that MAPbBr3 is a practical and low-priced nonlinear material for ultrafast photonics applications.

Alkali-Metal-Free Coinage Metalides: Specific Pairing and Location of Doping Atoms Bring Forth High Stability and Considerable Nonlinear Optical Response

The possibility to design alkali-metal-free coinage metalides as alternative species to the unstable alkalides has been explored by constructing a series of M-1-M’ (M; M’ = Cu, Ag, and Au) based on the facially polarized all-cis 1,2,3,4,5,6-hexafluorocyclohexane (1) in this work. Under the joint action of inherent polarization of 1 and the electronegativity difference between M’ and M, the s electron of Cu/Ag atom can be ejected to the Au atom, forming the diffuse excess electron around the Au– anions in the Cu+-1-Au– and Ag+-1-Au– complexes. Hence, they can be regarded as the first examples of alkali-metal-free coinage metalides. These two compounds not only have higher stability (larger VIE and Ec values) than previously reported alkalides but also exhibit remarkably larger β0 values than the reported coinage metalides M+-1-Au– (M = Li, Na, and K), demonstrating their great potential to serve as new molecular materials with considerable NLO responses. Taking Cu+-1-Cu– and Cu+-1-Ag– as examples, it is proved that the rest of the M-1-M’ compounds can also be converted into coinage metalides under oriented external electric fields (OEEFs), which provides an approach to obtain novel NLO molecular switches. This work will pave the way to design stable NLO materials by using coinage metal atoms instead of alkali metals, which are more likely to be synthesized in the laboratory.

Non-centrosymmetric features in nanostructured MoS2 and WS2 exfoliated in liquid phase

Exfoliation in liquid phase of Transition Metal Dichalcogenides promotes the industrialization of low dimensional structures in photonic and material science applications, due to its high nonlinear optical and piezoelectric responses on monolayers and few odd layers. Here, we report piezoelectricity and prospects of non-linear optics through Switching Spectroscopy Piezoresponse Force Microscopy (SS-PFM) and Fluorescence spectroscopy on MoS2 - and WS2 - flakes exfoliated in liquid phase. These features are intrinsically related to non-centrosymmetric structures and depend on the number of layers. SS-PFM signal in a small region reveals that the strength of AFM tip deflection was considerable just for an odd number of layers and negligible for even layers. Thin films were evaluated with ellipsometric measurements by constructing models mixing mono and few layers, resulting in a detailed description of the optical and surface properties of the nanostructures studied.

Surface functionalization of Si6Li6 cluster with superalkalis to achieve high nonlinear optical response: A DFT study

In this study, the nonlinear optical (NLO) response of pure and superalkali (Li3O, Na3O, and K3O) doped Si6Li6 clusters has been explored. The doping of superalkalis on the Si6Li6 cluster significantly narrowed the wide HOMO-LUMO energy gap (5.27 eV) of the pure Si6Li6 cluster up to 3.83 eV. All superalkali doped clusters reveal electride nature based on the HOMOs’ electron density. The thermodynamic stability of these electrides is anticipated through their interaction energies with the highest value (3.90 eV) for Si6Li6-Li3O. The NLO properties of superalkali doped Si6Li6 electrides are investigated through first and second-order hyperpolarizabilities. These complexes exhibit large first hyperpolarizabilities as compared to pristine Si6Li6. Among superalkali doped clusters, Si6Li6-K3O showed the highest first hyperpolarizability of 1.42 × 104 au. The small crucial excitation energies are responsible for such a high NLO response. For dynamic NLO response, electro-optic Pockel’s effect and second harmonic generation are calculated. A very large quadratic NLO response (3.61 ×10−9 au) is observed for the Si6Li6-Li3O complex. The quantum theory of atoms in molecules (QTAIM) analysis shows the electrostatic interaction between interacting species. All the electrides exhibit ultrahigh transparency in the UV–VISIBLE region. These intriguing results are self-serving to promote promising applications of Si6Li6-based clusters in high-performance nonlinear optical materials.

All-Organic Composite Films for High Flexibility and Giant Nonlinear Optical Limiting Responses.

Given the substantial π-electron delocalization observed in 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST), a high third-order nonlinear optical response can be expected that might manifest itself in various ways for potential applications. To probe the possibility and assess its potential, all-organic DAST-polymethyl methacrylate (PMMA) composite films were prepared by a simple solution casting method, and their nonlinear absorption performances were measured by an open-aperture Z-scan system. The results reveal that under irradiation by a 380 fs laser pulse at 520 nm or a 6 ns laser pulse at 532 nm, the DAST-PMMA composite films with a DAST concentration of 0.125 wt % exhibit similar giant optical limiting (OL) responses with OL threshold of 7.84 or 0.37 GW cm-2, both superior to those of most organic and inorganic OL materials measured under similar conditions. These all-organic composite films show high flexibility, and interestingly, their OL responses can remain stable even after exposure to air for 3 months. The superior OL behaviors of such materials in the femtosecond and nanosecond regimes are attributed to the two-photon absorption and the combination of two-photon absorption and excited-state absorption, respectively. The simple preparation, high flexibility, giant OL responses, and excellent environmental stability suggest that such novel all-organic composite films hold great potential for applications in flexible OL devices.

Influence of the surface modification of BaTiO3 nanoparticles by hydrolyzed chitosan obtained from shrimp exoskeletons on the optical response intensity of the second harmonic

Ferroelectric nanoparticles, due to their high non-linear optical response, are of considerable practical interest for their use as nanoprobes for the study of biological materials by multiphoton microscopy methods. To prevent toxic effects, it is necessary to modify the surface using biocompatible polymers. Here we report the results of the study on the effect of surface modification of BaTiO3 nanoparticles with hydrolyzed chitosan obtained from shrimp exoskeletons (Penaeus vannamei). It was found that increasing of the hydrolyzed chitosan concentration in the solution during surface modification from 1 to 3% leads to a significant reduction in nanoparticle agglomeration, while the intensity of the second harmonic generation changes insignificantly.Graphical abstract