Second-order Nonlinear Optical Response Research Articles

Variable-Angle Surface Spectroscopy Reveals the Water Structure in the Stern Layer at Charged Aqueous Interfaces.

At charged aqueous interfaces, the second-order nonlinear optical response originates from water molecules within the diffuse part of the electrical double layer, which are ordered by the surface field and from water that additionally experiences chemical and physical interactions with the surface in the Stern layer. These two environments can either reinforce or diminish the overall signal and can be disentangled by varying the coherence length of their interaction with external laser fields. Here, we demonstrate a method in which the angle of incidence is varied to afford a significant change in the coherence length. When this technique was applied to the silica-water interface, it was observed that water molecules in the Stern and diffuse layers direct their hydrogen atoms toward the mineral surface at a low ionic strength and neutral pH. A decrease in the signal with increasing ionic strength is attributed to hydrated cation adsorption that competes with free water for deprotonated silanol sites.

A computational study on the second-order nonlinear optical response of a new unsymmetrical oxovanadium complex

A new unsymmetrical N2O2 Schiff base oxovanadium (IV) complex, VOLPy, was synthesized with excellent yield and characterized using conventional methods. The crystal structure of the VOLPy complex was determined through X-ray diffraction, revealing a distorted square pyramidal coordination configuration around the central vanadium ion. The solid-state structure is stabilized by various non-covalent short contacts, generating complex 3D supramolecular network. The electrochemical properties of the VOLPy complex were investigated in different media, demonstrating diffusion-controlled reversible or quasi-reversible processes within the potential range of 200–1000 mV, involving a single electron VV/VIV reduction. The diffusion coefficients were calculated using Levich plots Ilim = f(ω1/2). Using quantum calculations at the CAM-B3LYP level with a 6-311G**/LanL2DZ basis set, we systematically assessed various structural parameters, electronic properties, linear and nonlinear optical responses at static and dynamic regimes for oxovanadium complexes, V(V)OL and V(IV)OL, in both gaseous and solvent environments. The results reveal a robust alignment between quantum calculations and experimental data, with only minor deviations. This study anticipates that these specifically designated complexes hold substantial potential as excellent candidates for second-order nonlinear optical (NLO) materials.

Third Harmonic Generation in Thin NbOI2 and TaOI2.

The niobium oxide dihalides have recently been identified as a new class of van der Waals materials exhibiting exceptionally large second-order nonlinear optical responses and robust in-plane ferroelectricity. In contrast to second-order nonlinear processes, third-order optical nonlinearities can arise irrespective of whether a crystal lattice is centrosymmetric. Here, we report third harmonic generation (THG) in two-dimensional (2D) transition metal oxide iodides, namely NbOI2 and TaOI2. We observe a comparable THG intensity from both materials. By benchmarking against THG from monolayer WS2, we deduce that the third-order susceptibility is approximately on the same order. THG resonances are revealed at different excitation wavelengths, likely due to enhancement by excitonic states and band edge resonances. The THG intensity increases for material thicknesses up to 30 nm, owing to weak interlayer coupling. After this threshold, it shows saturation or a decrease, due to optical interference effects. Our results establish niobium and tantalum oxide iodides as promising 2D materials for third-order nonlinear optics, with intrinsic in-plane ferroelectricity and thickness-tunable nonlinear efficiency.

Control of Polar/Antipolar Layered Organic Semiconductors by the Odd-Even Effect of Alkyl Chain.

Some rodlike organic molecules exhibit exceptionally high layered crystallinity when composed of a link between π-conjugated backbone (head) and alkyl chain (tail). These molecules are aligned side-by-side unidirectionally to form self-organized polar monomolecular layers, providing promising 2D materials and devices. However, their interlayer stacking arrangements have never been tunable, preventing the unidirectional arrangements of molecules in whole crystals. Here, it is demonstrated that polar/antipolar interlayer stacking can be systematically controlled by the alkyl carbon number n, when the molecules are designed to involve effectively weakened head-to-head affinity. They exhibit remarkable odd-even effect in the interlayer stacking: alternating head-to-head and tail-to-tail (antipolar) arrangement in odd-n crystals, and uniform head-to-tail (polar) arrangement in even-n crystals. The films show excellent field-effect transistor characteristics presenting unique polar/antipolar dependence and considerably improved subthreshold swing in the polar films. Additionally, the polar films present enhanced second-order nonlinear optical response along normal to the film plane. These findings are key for creating polarity-controlled optoelectronic materials and devices.

Dynamic effects on the nonlinear optical properties of donor acceptor stenhouse adducts: insights from combined MD + QM simulations.

The second-order nonlinear optical (NLO) responses of a donor-acceptor stenhouse adduct (DASA) are investigated by using a computational approach combining molecular dynamics simulations and density functional theory (DFT) calculations. Specific force fields for the open and closed photoswitching forms are first parameterized and validated according to the Joyce protocol, in order to finely reproduce the geometrical features and potential energy surfaces of both isomers in chloroform solution. Then, DFT calculations are performed on structural snapshots extracted at regular time steps of the MD trajectories to address the influence of the thermalized conformational dynamics on the NLO responses related to hyper-Rayleigh scattering (HRS) experiments. We show that accounting for the structural dynamics largely enhances the HRS hyperpolarizability (βHRS) compared to DFT calculations considering solely equilibrium geometries, and greatly improves the agreement with experimental measurements. Furthermore, we show that the NLO responses of the NLO-active open form are correlated with the bond order alternation along the triene bridge connecting the donor and acceptor moieties, which is rationalized using simple essential state models.

Modulation of the NLO properties of p-coumaric acid by the solvent effects and proton dissociation

Solute-solvent interactions and deprotonation effects have been related to second-order nonlinear optical response modulators. This work takes advantage of sequential Monte Carlo/Quantum mechanics together with Time-Dependent Density Functional Theory, Coupled Cluster methods, and the hyper-Rayleigh scattering formalism to investigate how these effects influence the stability and optical response of p-coumaric acid (pCA) and its anionic and diionic forms. The solvent influences the chromophores in different ways, inducing bathochromic and hypsochromic solvatochromism so for the neutral pCA molecule as for its deprotonated derivatives. The results indicate a high sensitivity of the nonlinear optics (NLO) parameters with relation to proton dissociation. Ionization of the carboxyl group produces the lowest values of the first frequency-dependent hyperpolarizability (βHRS), while phenolic deprotonation leads to the highest values. The results show that proton removal can be used as a switch that modulates the NLO response within a wide range of values (159.15≤βHRS≤4393.97 au) greater than those reported for reference NLO chromophores like urea (37.3 au) and p-nitroaniline (74.3 au). Thermochemical analysis of enthalpies and Gibbs free energies indicate that both monoionic forms of the pCA molecule are the most stable in gas or water solvents. Furthermore, these structures represent the limits of NLO modulation in the gas and solvent phases. Analysis of the projected density of states and mapping of the molecular electrostatic potential indicate that increased contributions from conduction electrons found in the aromatic ring are the mechanism by which deprotonation enhances the NLO response. All the results show that ionic pCA forms are promising in the functionalization of optoelectronic devices.

Effect of charge transfer on the first hyper-polarizability of N,N-dimethylaniline and julolidine: a DFT based comparative study.

Quantum mechanical calculations involving electron correlation, frequency dispersion, and solvent effects were carried out to examine the second-order nonlinear optical response ofvarious acceptor, X (-CF3, -CN, -NO2) substituted in N,N-dimethylaniline (DMA) and julolidine(JLD). Here, both DMA and JLD acts as donor and the three substituted groups, X (-CF3, -CNand -NO2) at the para position of both the ring systems as acceptor. The NLO response (βHRS) of -CF3 and -CN substituted DMA and JLD is relatively lower compared to DMA-NO2 andJLD-NO2. The charge distribution is found higher in case of -NO2substituted DMA and JLD (±443 and ±449) compared to their -CF3 or -CN substitution. Electronic characteristics such asUV-Vis absorption spectra, crucial excited state parameters and charge transfer contribution to βHRS have been used to explain the NLO parameter of DMA-X and JLD-X. Variation of theincident optical frequency of light shows fluctuation of βHRS value and highest values of βHRS are obtain at the λmax frequency of each compound. Solvent polarity variation study on βHRSshows that βHRS varies linearly with the Kirkwood-Onsagar dielectric factor (D). All computational studies have been carried out using density functional theory (DFT) based method. Since CAM-B3LYP based hybrid functional improves the asymptotic behavior of theexchange interaction by dividing into short-range and long-range components, first hyperpolarizability values in the present study were computed using DFT/ CAM-B3LYP/ 6-31G+(d,p) level oftheory.

Design of High-Performance Organic Nonlinear Optical and Terahertz Crystals by Controlling the van der Waals Volume.

In the development of new organic crystals for nonlinear optical and terahertz (THz) applications, it is very challenging to achieve the essentially required non-centrosymmetric molecular arrangement. Moreover, the resulting crystal structure is mostly unpredictable due to highly dipolar molecular components with complex functional substituents. In this work, new organic salt crystals with top-level macroscopic optical nonlinearity by controlling the van der Waals volume (VvdW ), rather than by trial and error, are logically designed. When the VvdW of molecular ionic components varies, the corresponding crystal symmetry shows an observable trend: change from centrosymmetric to non-centrosymmetric and back to centrosymmetric. All non-centrosymmetric crystals exhibit an isomorphic P1 crystal structure with an excellent macroscopic second-order nonlinear optical response. Apart from the top-level macroscopic optical nonlinearity, new organic crystals introducing highly electronegative fluorinated substituents with strong secondary bonding ability show excellent performance in efficient and broadband THz wave generation, high crystal density, high thermal stability, and good bulk crystal growth ability.

Manipulation of nonlinear optical responses in layered ferroelectric niobium oxide dihalides

Realization of highly tunable second-order nonlinear optical responses, e.g., second-harmonic generation and bulk photovoltaic effect, is critical for developing modern optical and optoelectronic devices. Recently, the van der Waals niobium oxide dihalides are discovered to exhibit unusually large second-harmonic generation. However, the physical origin and possible tunability of nonlinear optical responses in these materials remain to be unclear. In this article, we reveal that the large second-harmonic generation in NbOX2 (X = Cl, Br, and I) may be partially contributed by the large band nesting effect in different Brillouin zone. Interestingly, the NbOCl2 can exhibit dramatically different strain-dependent bulk photovoltaic effect under different polarized light, originating from the light-polarization-dependent orbital transitions. Importantly, we achieve a reversible ferroelectric-to-antiferroelectric phase transition in NbOCl2 and a reversible ferroelectric-to-paraelectric phase transition in NbOI2 under a certain region of external pressure, accompanied by the greatly tunable nonlinear optical responses but with different microscopic mechanisms. Our study establishes the interesting external-field tunability of NbOX2 for nonlinear optical device applications.

Enriching the electronic populations of D-π-A type ON-OFF solar switches with sp2 hybridization: A TD-DFT possibility to create pull-push effect

The ability of specific molecular acceptors in photovoltaic devices is determined by their structure and chemical composition. Multiscale computations are important to protect investigation design; hence, efforts and money could be saved. Using Density Functional Theory (DFT), the effect of sp2 hybridized nitrogen substitutions (Ns) at the specific positions of a solar cell dye, 2,2′-((4-heptyl-4,9,9-trihexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis(methanylylidene)bis(3-oxo-2,3-dihydro-1H-indene-1-yl-2-ylidene)dimalononitrile (IDIC), is explored. The N-incorporated dyes (IDIC1-IDIC5) were optimized at their ground energy minima at the B3LYP level of DFT with 6-31G+(d,p) basis sets. From these optimized geometries, their UV–visible analysis was executed at the DFT functional of CAM-B3LYP/6-31G+(d,p) selected as a result of benchmarking their λmax values with experimental values of IDIC. The computed value was found to be 528 nm which was very near to its experimental value (540 nm). Interestingly, for all the new dyes, λmax had blue-shifted values of (502–513 nm) for IDIC1, IDIC2 and IDIC5 and red-shifted values (557–779 nm) for IDIC3 and IDIC4 as compared to IDIC. The highest second-order Non-Linear Optical (NLO) response of 1054 e.s.u was noted for IDIC4 and IDIC5 which had the lowest energy gaps. It was found that incorporating Ns has significantly decreased the energy gap of electron rearrangement.

Electronic, nonlinear optical, UV–vis and NBO analysis of methyl methacrylate for optoelectronic and optical applications: DFT study and impact of conformation

Using Density Functional Theory (DFT) and time-dependent DFT (TD-DFT), we studied a compound widely used in daily life, namely: Methyl Methacrylate (MMA) monomer in its two stable isomers, cis-MMA and trans-MMA. The impact of conformation on the optical and electronic properties of MMA was highlighted. Structural parameters and thermodynamic properties were also assessed, and allowed to discuss the stability and reactivity of this compound. In addition, analysis of optoelectronic and electronic properties, global reactivity descriptors, natural bond orbital (NBO), and hole and electron reorganization energies was performed. The absorption and fluorescence properties, as well as the linear and nonlinear optical (NLO) properties of MMA were also investigated. The findings show that MMA is an insulator due to its wide band gap of 6.20 eV. It also exhibits good optoelectronic properties with high average electric field values of about 5.90 × 109 Vm−1 for cis-MMA and 5.42 × 109 Vm−1 for trans-MMA and high electric displacement values of at least 14.65 × 10-2 cm−2 for cis-MMA and 14.33 × 10-2 cm−2 for trans-MMA, suggesting a potential use for the design of piezoelectric and pyroelectric materials. In addition, trans-MMA has a dielectric constant close to that of good insulators; while cis-MMA exhibits a dielectric behaviour close to that of polymeric substances. Further, these materials are thermodynamically stable in its two conformations, with a good reactivity which can lead to good ability of polymerization. The analysis of the UV–vis spectra revealed that both forms of MMA absorb and emit mainly in the UV and that the Stokes shift of MMA is low, reducing its potential use in devices such as solar cells. At NLO level, MMA isomers exhibit weak optical properties such as second- and third-order optical susceptibility and cannot suitable for second and third harmonic generation; however, the conformation enhances second-order NLO response by at least 2 times when moving from cis- to trans-MMA, whereas the third-order response is almost unaffected. In addition, the conformation also affects the electronic and optoelectronic properties of MMA.

Density Functional Theory Study of the Secondorder Nonlinear Optical Properties of Novel Fluorenone Derivatives

Based on the molecular structure of novel fluorenone derivative named FO52, a series of new molecules have been designed by extending its π-conjugated bridge and introducing electron donor or acceptor substituents. The electronic transition and second-order non-linear optical response properties of these fluorenone derivatives were theoretically studied in detail by using the density functional theory computational methods. The results showed that the non-linear optical response of the molecule FO52 can be improved by introducing five-membered heterocycles into its skeleton structure. In addition, the introduction of strong substituents results in significant enhancement of the first hyperpolarizability of molecular nonlinear optical properties. These fluorenone derivatives could be treated as excellent candidates for nonlinear optical materials due to the narrow energy gap of its frontier molecular orbitals, distinct intramolecular charge transfer character and large first hyperpolarizabilities

Theoretical Perspective on Two-State "ON-OFF" NLO Switch of Rh(III)-Azobenzene Complex with Considerable First Hyperpolarizability.

In this paper, a light-induced Rh(III)-azobenzene (azo) complex in its two conformations (cis- and trans-form) is analyzed via density functional theory methods, focusing on the geometrical and electronic structure, linear and second-order nonlinear optical (NLO) properties, as well as UV-vis absorption spectra. The results show that trans-Rh exhibits more obvious charge separation and more extensive π-conjugation than cis-Rh. The energy gaps (Egap) between the highest occupied molecular orbital and lowest unoccupied molecular orbital of cis-Rh and trans-Rh are as small as 0.28 and 0.36 eV, respectively. The unusual small Egap facilitates electronic transition and accompanies large NLO responses. In particular, cis-Rh and trans-Rh possess considerably large second-order NLO responses with the first hyperpolarizability (βtot) up to 7.0 × 104 a.u. ("OFF" state) and 8.5 × 104 a.u. ("ON" state), respectively. trans-Rh shows good π-conjugation and obvious electric delocalization relative to cis-Rh and thus a considerable βtot value. The switchable ratio of βtot (trans-Rh)/βtot (cis-Rh) is equal to 1.2, showing switch characteristics. UV-vis analyses indicate that the ON and OFF states can finely tune the absorption range due to the strongest absorption peaks of cis-Rh (301 nm) and trans-Rh (446 nm) lying in the UV and vis region, respectively. It is expected that the studied Rh(III)-azo complexes may be applied in the field of optoelectronics.

Host-Guest Symmetry Matching in Two Crystalline Magnesium Sulfate Oxalates Obtained Via a Solvent-Free Route.

The combination of π-conjugated oxalate anion with sulfate group has been explored in the solvent-free synthesis of two new magnesium sulfate oxalates. One of them has a layered structure crystallized in the noncentrosymmetric space group Ia, while the other has a chainlike structure crystallized in the centrosymmetric space group P21/c. The noncentrosymmetric solid has a wide optical bandgap and exhibits a moderate second-harmonic-generation response. Density functional theory calculations were carried out to disclose the origin of its second-order nonlinear-optical response.

BN-Doped Carbon Nanotubes and Nanoribbons as Nonlinear-Optical Functional Materials for Application in Second-Order Nonlinear Optics

Pure carbon-based nanomaterials with good π conjugation and thermal stability, e.g., nanotubes and nanoribbons, have long served as promising conjugated materials for application in second-order nonlinear-optical (NLO) devices but suffer from two inherent structural problems: weak polarity (or even nonpolarity) and high chemical reactivity ascribed to zigzag edge states. In the present work, boron nitride (BN) chains are used to divide carbon nanotubes and nanoribbons, forming a functional block to tune the electronic structure, and thus induce charge redistribution or modify the molecular energy gap for second-order NLO materials or integrated electronic materials. A balance between the electronic kinetic stability and second-order NLO properties is established by structural manipulation. The strong second-order NLO responses in the visible and near-infrared regions make these hybridized carbon-based molecules potential NLO materials for applications in biological nonlinear optics. The application of BN to tune the electronic structure of carbon nanomaterials paves a path for fabricating nanoelectronic and nano-NLO devices.

Influence of the Nature of the Lipid Building Blocks on the Second-Order Nonlinear Optical Responses of an Embedded Di-8-ANEPPS Probe.

The extensive collection of lipids found in cell membranes is justified by the fact that each lipid contributes to their overall structure, dynamics, and properties and so to the biological processes taking place within them. It also showcases that, in order to deepen our understanding of membranes, we need to have a tool to differentiate lipid bilayers of varying composition. In this work, we investigate a suite of single-component saturated glycerophospholipids varying only in their headgroup structure by analyzing the second harmonic generation (SHG) nonlinear optical (NLO) response of a probe, di-8-ANEPPS, embedded into the membranes. The seven hydrophilic heads chosen (phosphatidylcholine (PC), phosphatidylethanolamine (PE), diaglycerol (GL), phosphatidylserine (PS), phosphatidylglycerol (PG), phosphatidylinositol (PI), and phosphatidyc acid (PA)) represent all the major headgroups that are part of mammalian plasma membranes and provide an assortment of neutral, zwiterrionic, and charged species. First, molecular dynamics simulations revealed that the lipidic arrangement is strongly sensitive to the nature of the hydrophilic head and less to the variety in the hydrophobic region. Membranes exhibiting drastically opposite structural properties can be pointed out: 1,2-dihexadecanoyl-rac-glycerol (DPGL) is the thickest and most ordered and aligned system, whereas 1,2-diacyl-sn-glycero-3-phospho-(1'-sn-glycerol) (DPPG) is thinnest and least ordered and aligned system. The structural analyses are then confronted with the molecular NLO responses, β, computed at the time-dependent density functional theory (TDDFT) level. As the orientation of the chromophore is impacted by the various degrees of order within the lipid bilayers, the diagonal component of the β tensor parallel to the bilayer normal, βZZZ, is as well. In the end, this computational approach provides insights into the link between lipid building blocks and the NLO responses of the embedded dye.

Open honeycomb frameworks of sulphides AHg4Ga5S12 (A = Rb, Cs) exhibiting infrared nonlinear optical properties.

A crystal structure with a diamond-like anionic framework belongs to a non-centrosymmetric macrostructure due to the aligned arrangement of tetrahedral units, meeting the premise of second-order nonlinear optical (NLO) materials. Herein, two new Hg-based sulphides, namely RbHg4Ga5S12 (1) and CsHg4Ga5S12 (2), which are isostructural and crystallise in the trigonal space group R3, are successfully isolated in sealed silica tubes by a solid-state reaction. The features of their three-dimensional open honeycomb frameworks are attributed to the parallel alignment of tetrahedral MS4 (M is disordered by 0.444 Hg and 0.555 Ga) building motifs, accompanied by Rb+ (or Cs+) reseating in the cavities. Notably, although the band gap values of 1 and 2 are 2.30 and 2.36 eV, separately, their thermal expansion anisotropies (0.15 and 0.41, respectively) are favourable for achieving laser-induced damage thresholds (5.6 and 5.8 times that of AgGaS2 for 1 and 2, respectively). In addition, the strong polarisability of tetrahedral MS4 building motifs in the diamond-like anionic structures is responsible for the promising second-harmonic generation (SHG) intensities (1.1 and 1.8 times that of AgGaS2 for 1 and 2, respectively) in the particle size range of 50-75 μm with non-phase-matchable behaviour at 1910 nm. Furthermore, theoretical investigation elaborates that electron transitions in compounds 1 and 2 mainly occur from valence band S-3p to conduction band Hg-6s and Ga-4s states, demonstrating that the linear and nonlinear optical properties originate primarily from the synergy of tetrahedral MS4 units.

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.

Investigation of first hyper-polarisability molecular switches between enol–keto equilibrium of phenyl benzodifurantrione: a DFT-based computational study

The contrast of the second-order nonlinear optical response between the enol (anti and syn) and keto tautomeric equilibrium of 7-Phenyl-7H-benzo[1,2-b;4,5-b’]difuran-2,3,6-trione (PBDT) with donor/acceptor substitution at the para position of phenyl group have been computed involving electron correlation, frequency dispersion, and solvent polarity effects. The Hyper Rayleigh Scattering (HRS) first-hyperpolarisability contrast between the enol and keto forms for PBDT and Nitro-substituted PBDT is 3.5 and 2.8, respectively. However, in NMe2-substituted PBDT, a large contrast (12 times) of HRS first hyper-polarisability between enol (anti and syn) and keto form is observed. Present study reveals that electron donor group (–NMe2) in PBDT plays a pivotal role for obtaining very high contrast in the first hyper-polarisability (β HRS and β vec) values between the enol and keto forms compare to the electron acceptor (–NO2) group substitution at the same position. The solvent effect also plays a significant role in further improving the first hyper-polarisability value and its switching behaviour between the enol and keto forms of NMe2-PBDT. NLO switching contrast between the enol and keto forms of donor/acceptor substituted PBDT is also explained using the electronic features including UV-Vis absorption spectra, HOMO–LUMO electron densities, optical energy gaps, charge transfer contribution etc.

Toward the design of inorganic–organic hybrid Ir(III) complexes containing borazine and benzene ligands with excellent second-order NLO responses: An appropriate substitution and π-conjugated extension

The high nonlinear optical (NLO) efficiency and good chemical stability render inorganic–organic hybrid materials widely applied in NLO filed. In this paper, we theoretically design a sequence of new cationic Ir(III) complexes based on parent complex Ir[(C^N)2(N^N)]+ (C^N = 2-phenylpyridine, N^N = 2,2′-bipyridine) through substituting pyridine by borazine ligands or extending borazine/benzene ligands on C^N/N^N position. The geometric and electronic structures, second-order NLO properties and absorption spectrum are evaluated by employing density functional theory (DFT) and time-dependent DFT methods. All designed complexes have smaller HOMO-LUMO energy gaps (0.74–1.82 eV) than parent complex (2.78 eV). N-5 (with borazine-benzene-borazine π-conjugated long chain on N^N ligands) has an unusually small Egap of 0.74 eV which may facilitate an easier electronic transition than other complexes. Interestingly, introducing borazine ligands on parent complex can increase first hyperpolarizability (βtot), but further addition of borazine not lead to positive effect on increasing βtot values. Hybridizing borazine and benzene ligands significantly improve the second-order NLO properties. Thereinto, the maximum βtot of N-5 is found to be 27,648 a.u. which is about 22 times larger than parent complex. The origin of largest βtot values can be reasonably explained by the two-level model due to low transition energy and high transition dipole moment. Further, the UV–Vis spectrum analysis is performed for all complexes, indicating that substituting or hybridizing inorganic and organic ligands are feasible way to make the maximum absorption wavelength red-shifted toward longer wavelength. Our proposed complexes may be used as efficient infrared (IR) NLO materials because of there is no obvious absorption detected in the IR region. This work may offer valuable guidelines for designing high-performance second-order NLO materials.