Organic Nonlinear Optical Material Research Articles

Synthesis and characterization of crystalline perfection on l-Lysine co-doping glycine barium chloride/C6H14N2O2 (L-LGBCAC) single crystal for NLO materials

The aim on l-Lysine single crystal has been developed by the novel organic nonlinear optical (NLO) materials. The l-Lysine with and without Co-DopedGlycine Barium Chloride (GBC)/C6H14N2O2 (Amino acid – AC) was grown of the crystal by the controlled for the solution to slow evaporation techniques. The l-Lysine single crystal is used in XRD to control its cell parameters. The l-Lysine single crystal is analysed in the FTIR spectrum to conform with the crystal structure. The morphology studies were doped solutions to varying rates of reflected in form of XRD values. It is concluded that the l-Lysine single-crystal based on the diffraction data which that too fits of monoclinic crystallographic system. The form of the cell occupied in space group P-21/n and the parameters are a = 4.573(6), b = 24.567(6), c = 7.617(5)Å, β = 90.146(8)°, V = 1048.756 Å. They are studied in TG, DTA exposed in thermal properties and optical was included transmission spectrum. The second harmonic generation was studied in NLO properties. l-Lysine single-crystal response to NLO have been verified with the Nd: YAG laser. The damage threshold value of laser has greater than that of potassium dihydrogen phosphate.

Efficient Construction of Near-Infrared Absorption Donor–Acceptor Copolymers with and without Pt(II)-Incorporation toward Broadband Nonlinear Optical Materials

Organic nonlinear optical (NLO) materials have attracted immense scientific interest in various fields. Broadband NLO response extending to near-infrared (NIR) region is extremely important and remains challenging. Herein, two diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A)-type π-conjugated copolymers with and without Pt(II) incorporation are rationally designed and synthesized toward broadband NLO response materials. The broad intramolecular charge transfer (ICT) absorption reaching 1000 nm due to the strong D-A interaction is well demonstrated by photophysical characterizations. The NLO properties of copolymers are studied using Z-scan technology. Owing to their extended π-conjugated D-A systems and near-infrared ICT absorption properties, both copolymers exhibit laser-induced NLO response to nanosecond as well as picosecond laser pulses upon the wavelengths of 532 and 1064 nm. Interestingly, introducing Pt(II) into the copolymer backbone can evidently improve the NLO property or unexpectedly switch the NLO response from saturable absorption to reverse saturable absorption. Meanwhile, both copolymers are successfully employed as optical limiting materials and exhibit broadband optical limiting abilities. Therefore, we present an efficient strategy toward broadband NLO materials, which may significantly facilitate the understanding of organic molecular structure-property relationship and promote their practical application.

Crystal structure analysis and quantum chemical study of two macrocyclic compounds

The synthesis of new organic macrocyclic nonlinear optical materials with good performance has taken the prime focus of research due to the unlimited design possibilities. Two macrocyclic structures, confirmed by 1H, 13C NMR and FT-IR, namely spiro pyrrolidine grafted methyl macrocycle C28H26N2O3 and 1,2,3 triazole bridged pyrrolidine grafted chloro macrocycle C29H27Cl1N4O30.5(H2O) are analysed by single crystal X-ray diffraction method. The UV–Vis spectra of the two compounds show that these crystals are transparent in the entire visible region. The global reactivity descriptors such as ionization potential, electron affinity, electronegativity, chemical hardness, chemical potential, chemical softness, electrophilicity index and nonlinear optical parameters such as dipole moment (μ) and static second order hyperpolarizability (γ) are determined in gas phase at the molecular level by semiempirical quantum chemical method with the coordinates obtained from X-ray diffraction as the starting geometry. In addition, the bioactivity scores were calculated from the chemical skeleton.

Synthesis, structural, growth, optical, electrical, thermal and third order nonlinear optical properties of a novel organic single crystal: p -Toluidinium malonate

Abstract Novel organic nonlinear optical material; p-Toluidinium malonate (PTM) was grown from aqueous solution by slow evaporation technique. The lattice parameters were evaluated from single crystal X-ray diffraction analysis and found that crystal system belongs to monoclinic with centrosymmetric space group P21/c. The solid state parameters; valence electrons, Plasma energy, Penn gap and Fermi energy were evaluated theoretically. These estimated values are used to calculate the electronic polarizability of PTM crystal. The functional groups exist in the compound were identified using FT-IR and FT-RAMAN spectroscopy. PTM crystal showed transmittance in the entire visible region with lower cut off wavelength of 311 nm and band gap energy of 3.8 eV. The photoluminescence spectrum was recorded to explore the emission and thermal behaviour of PTM crystal by employing TG/DTA analysis. Dielectric measurement was carried out on the grown crystal at different temperatures to evaluate electrical properties. The third-order nonlinear optical parameters were estimated by Z-scan technique using 532 nm diode pumped CW Nd:YAG Laser.

Synthesis, growth and characterization of organic nonlinear optical 3-(4-fluorophenyl)-1-(4-methoxyphenyl) single crystal grown by vertical Bridgman technique

Abstract Single crystal of organic nonlinear optical material 3-(4-Fluorophenyl)-1-(4-methoxyphenyl) (FMP) was grown with the help of single walled glass ampoule in vertical Bridgman technique. The structural analysis confirmed the cell parameters and crystallinity of the single crystal with the space group of Pbca. The presences of desired components in the single crystal were confirmed by the NMR spectrum. The lower cut off wavelength of the single crystal was observed at 423 nm from the absorption spectra of the single crystal. The electrical property of grown single crystal was studied by measuring the dielectric constant and dielectric loss. The surface hardness test and amount of damage caused by incident laser beam on the surface of the single crystal determined the mechanical strength of the crystal. The FMP single crystal was found to exhibit negative photoconductive nature. The etch pit density and non-linear optical properties were determined by etching measurement and by observation of green light in Kurtz-Perry powder method. The grown crystal was studied thermal stability and melting point with TGA-DSC analysis.

Synthesis, structural, dielectric, laser damage threshold, third order nonlinear optical and quantum chemical investigations on a novel organic crystalline material: Pyrrolidin-1-ium 2-chloro-4-nitrobenzoate 2-chloro-4-nitrobenzoic acid for opto-electronic applications

It is reported that a novel third order organic nonlinear optical material namely, Pyrrolidin-1-ium 2-chloro-4-nitrobenzoate 2-chloro-4-nitrobenzoic acid (PCNCN) has been synthesized and grown by isothermal solvent evaporation solution growth technique. Single crystal X-ray diffraction analysis revealed that PCNCN belonged to monoclinic crystal system with a centrosymmetric space group of P21/c. The morphology of the as grown PCNCN crystal compared well with that obtained by theoretically generated morphology. The molecular vibrations of PCNCN were analyzed through Fourier transform infrared and NMR spectrum analyses. Optical properties such as transmittance, photoluminescence, and laser damage threshold were studied. The thermal stability of PCNCN was measured through TG-DTA measurement. The dielectric properties such as dielectric constant, dielectric loss, ac conductivity and activation energy of PCNCN single crystal were studied as a function of frequency at different temperatures. The PCNCN single crystals were further characterized for their third order nonlinear optical properties such as nonlinear absorption coefficient, nonlinear refractive index and optical limiting behavior using continuous wave Nd: YAG laser. The quantum chemical investigations were performed using B3LYP/6-311++G(d, p) basis set.

Crystal Growth of the Acentric Organic Nonlinear Optical Material Methyl-p-hydroxybenzoate: Morphological Variations in Crystals Grown by Physical Vapor Transport

Single crystals of the acentric compound methyl-p-hydroxybenzoate were grown by self-nucleation and seeded growth from the vapor phase by the physical vapor transport (PVT) process. In the temperature range of 80–95 °C (nucleation supersaturation 0.97 to 0.88), all crystals were of the polymorphic form as produced by room-temperature solution growth. Self-nucleated crystals varied in macromorphology from columnar to octahedral to skewed octahedral and finally to skewed columnar but retained the same crystal forms indicated by theoretical calculations. Micromorphological studies of growth faces indicated that these variations result from changes in growth mechanisms that influence both the defect structure and perfection of the growing crystal. X-ray topographic studies confirmed that growth under the most ideal conditions, when the dominant faces of the crystals were growing by a dislocation induced Burton, Cabrera, and Frank mechanism, yielded the structurally most perfect crystals. Preliminary studies of seeded growth were performed as a prelude to using PVT for the growth of larger crystals. The seeded growth followed a different pattern of supersaturation dependence. All crystals showed the same asymmetric growth along the polar axis that has come to be regarded as characteristic of these highly polar acentric materials when grown from solution.

Benchmark study of the linear and nonlinear optical polarizabilities in proto-type NLO molecule of para-nitroaniline

In the present investigation, for the first time, we have performed a thorough study about different functionals and basis sets for linear and nonlinear optical (NLO) properties of para-nitroaniline ([Formula: see text]-NA), which is considered as proto-type NLO molecule, among organic NLO materials. There is a dire need of such data base for [Formula: see text]-NA because many investigators are using such values of [Formula: see text]-NA for comparative analysis. A range of different functionals including HF, BLYP, PW91, PBE, B3LYP, M06, M06-2X, PBE0, BHandHLYP, CAM-B3LYP, LC-BLYP, and B3LYP-D3 are applied in conjugation with several commonly basis sets such as 6-31G*, 6-311G*, 6-311G**, 6-311+G**, cc-pVDZ, and cc-pVTZ. A variety of functional and basis sets combinations are calculated and graphically compared with each other. The calculated total dipole moment for the [Formula: see text]-NA is found to be 6.79[Formula: see text]D which is quite closer to experimentally determined value. The lowest calculated value for linear isotropic polarizability at HF/6-31G* level of theory is [Formula: see text] esu while higher values observed with remaining all methods especially 14% polarizability increases in presence of basis set with diffuse functions and similar trend of variation is also observed in linear anisotropic polarizability. Similarly, the calculated value of frequency dependent second-order polarizability is found to be [Formula: see text] esu at PBE0/6-311+G** level of theory which is quite closer to experimental value of [Formula: see text] esu. A comparison between the calculated and experimental results shows good agreement among geometries, dipole moments and NLO polarizabilities for [Formula: see text]-NA. Moreover, the frontier molecular orbital (FMO) and electron density difference map (EDDM) analysis along with density of state (DOS) plots are also presented to get more physical intuitions into the structure–property relationship and electronic communications between terminal accepter and donor groups through [Formula: see text]-conjugation. The present investigation provides benchmark data including various commonly used functionals and basis sets for the calculation of NLO properties of [Formula: see text]-NA. Thus, the present investigation will put straight several future studies when it comes to comparative NLO study of organic materials.

Synthesis, growth, structural, thermal, third order nonlinear and computational studies of organic single crystal: 2-Amino-4-picolinium 2-chloro-4-nitrobenzoate

Novel organic third-order nonlinear optical material, 2-Amino-4-picolinium-2-chloro-4-nitrobenzoate (2A4P2C4N) was synthesized and grown into single crystal by slow solvent evaporation method at room temperature. Single crystal X-ray diffraction analysis reveals that the title compound crystallizes in monoclinic crystal system with a centrosymmetric space group of P21/n. From UV–Visible spectrum, the optical transparency and band gap were determined. Thermal stability of the title material was established by thermogravimetry (TG) and differential thermal analysis (DTA) analyses. The third-order nonlinear susceptibility was determined experimentally and it was found to be 2.56 × 10−8 esu. The quantum chemical calculations were performed to analyze Hirshfeld surface, electrostatic potential, HOMO-LUMO and global quantum chemical reactivity descriptors of the titled molecule at B3LYP/6–311++G (d,p) level of theory. A comparative analysis computationally calculated showed that the <γ> amplitude for 2A4P2C4N molecule was found to be three 3 times greater than that of compared para-Nitroaniline (p-NA).

Synthesis, experimental and computational spectroscopic investigations of third-order nonlinear optical material (E)-N′-(benzo[d][1,3]dioxol-5-ylmethylene)benzohydrazide

An organic nonlinear optical material (E)-N′-(benzo[d][1,3]dioxol-5-ylmethylene)benzohydrazide (BDMB) has been successfully synthesized and characterized using spectroscopic techniques. Vibrational analysis has been carried out with the help of potential energy distributions to identify the functional groups. The 13C and 1H-NMR chemical shift values are in good agreement with the theoretical results. Intramolecular stabilization by donor–acceptor interactions could be witnessed through natural bond orbital analysis. The one-electron excitation from the conduction band to the valence band was expressed by π–π* transition at 324 nm. The energy gap (3.96 eV) is calculated from the optical spectrum which explains the charge transfer mechanism of BDMB. The hyperpolarizability of the BDMB molecule is 30.8538 × 10−30 esu, which is 82 times greater than that of urea (β0 = 0.3728 × 10−30 esu). The third-order nonlinear absorption coefficient (β) and nonlinear refractive index (n2) are calculated to be 6.24 × 10−5 cm W−1 and 1.19 × 10−9 cm2 W−1, respectively. Based on these points, BDMB can be projected with nonlinear properties for realizing new applications.

Fluorine-Mediated Benzothiadiazole Derivatives for Second-Order Nonlinear Optics

With increasing research interests in the field of light-matter interactions, various methods have been developed for regulating nonlinear optical (NLO) materials. However, the design and synthesis of organic molecular materials for second-order nonlinear optics remain a great challenge because of the strict requirement of the materials to possess a noncentrosymmetric structure. In this work, two benzothiadiazole (BTD) derivatives referred to as BTD-H and BTD-F were synthesized, and their NLO properties in the crystalline states were studied. It was found that introducing fluorine into the BTD backbone effectively tuned the crystal packing styles of BTD derivatives to a noncentrosymmetric system for effective second-order NLO responses. Such a strategy to induce the noncentrosymmetric structure by introducing the fluorine atoms and halogen interactions may provide guidance for future engineering of organic NLO molecular materials.

Studies on a novel organic NLO single crystal: L-asparaginium oxalate

A new organic nonlinear optical (NLO) material, L-asparaginium Oxalate (ASOX) was synthesized and single crystals of ASOX with dimension (10*5*5) mm3 was grown from aqueous solution by slow evaporation solution growth technique. Single crystal XRD data reveals that ASOX belongs to triclinic crystallographic system with non-centrosymmetric space group P1. The grown organic NLO crystal was subjected to various characterizations like PXRD, FT-IR analysis, thermal studies, micro hardness test and optical studies for identifying the transparency range and the emission spectrum. The laser damage threshold value was found to be 2.04 GW/cm2. The second harmonic efficiency of the grown crystal was examined using Kurtz Perry powder technique and it was found to be 68% that of KDP. Hence it can be effectively employed for various optoelectronic and photonic applications.

Experimental and theoretical investigations of an organic nonlinear optical material p-toluidinium picrate – A comparative study

The structure analysis of p-toluidinium picrate (PTP) crystal was performed by X-ray diffraction method and the spectral characterization was performed by FT-Raman spectroscopic technique. The optimization of PTP structure was carried out by using the four common functionals (B3LYP-D3BJ, B3LYP, CAM-B3LYP, and M05-2X). The obtained structural parameters were compared with the crystallographic data. The B3LYP-D3BJ functional was chosen for further analysis, since it allowed reliable reproduction of experimental bond lengths and angles (correlation coefficients > 0.98). The vibrational assignment of the fundamental modes was proposed on the basis of potential energy distribution (PED) calculations. The stability of the molecule due to hyper-conjugative interaction and charge delocalization was studied by natural bond orbital (NBO) analysis. The ultraviolet–visible (UV–Vis) spectrum of PTP was recorded in the region 200–600 nm and the electronic properties such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies were measured by time-dependent density functional theory (TD-DFT) approach. The small energy gap between the HOMO and LUMO is an indicator of intramolecular charge transfer which is responsible for nonlinear optical (NLO) properties. The first order hyperpolarizability result confirmed the nonlinear optical activity of the molecule. Molecular electrostatic potential (MEP) analysis was performed to predict the reactive sites of the molecule. The theoretical results showed good agreement with the experimental values. The Hirshfeld surface analysis was made to find out the various intermolecular non-covalent interactions in the PTP molecule.

A new organic nonlinear optical material: L-asparagine cetrimonium bromide single crystal for photonic applications

Abstract The new organic nonlinear optical material, L-Asparagine Cetrimonium Bromide (LACB) was synthesized by using slow evaporation method at ambient conduction. The crystallographic data was analyzed by single crystal X-ray diffraction (XRD) and crystalline perfection was studied under high resolution powder X-ray diffraction technique. The functional groups were found out by FT-IR spectroscopy and various optical parameters were performed by using UV–Vis NIR spectroscopy. In fluorescence spectrum the sharp emission peak was observed at 529 nm it reveals the green emission. The second harmonic generation efficiency was determined by the Kurtz powder method using Nd-YAG laser. The laser induced damage threshold value was found to be higher than most of the reported organic single crystals. The dielectric permittivity and dielectric loss were analyzed as a function of frequency. The photoconductivity study implies that the grown crystal has positive photoconductive nature. Different mechanical properties were analyzed by Vickers microhardness test.

A Twist on Nonlinear Optics: Understanding the Unique Response of π-Twisted Chromophores.

Materials with large nonlinear optical (NLO) response have the ability to manipulate the frequency and phase of incident light and exhibit phenomena that form the basis of modern telecommunication systems. In molecule-based materials, the second- and third-order NLO performance is related to the hyperpolarizability (β) and second hyperpolarizability (γ) of the constituent molecules. The search for higher β materials is driven by the desire to keep pace with expanding demand for high speed data transmission, while discovery of high γ chromophores is crucial for the development of emergent photonic technologies reliant on manipulation of "light-with-light". For decades, it was believed that for highest performance, organic NLO materials must be composed of planar π-system chromophores, and much exploratory research focused on subtle molecular modifications, which generally yielded incremental increases in μβ, where μ is the molecular dipole moment. The surprising recent discovery that twisted π-system chromophores can exhibit dramatically higher β values than their planar analogues has revealed a new design paradigm and stimulated the development of high performance twisted intramolecular charge transfer (TICT) chromophores, which are composed of electron-donating and electron-accepting π-substituents joined by a sterically constrained twisted biaryl fragment. In such chromophores, the twisting of the π-system enforces charge separation in the electronic ground state, leading to large dipole moments and low-lying charge-transfer excitations. This unique electronic structure forms the basis for enhanced NLO response, with an archetypal TICT chromophore, TMC-2, exhibiting very large second- ( μβ = 24 000 × 10-48 esu) and third-order (γ = 1.4 × 10-33 esu) metrics in dilute low-polarity solutions. This Account summarizes several approaches to enhance μβ in various environments, including (1) manipulating the biaryl torsional angle, (2) modifying the electron accepting fragment, (3) extending conjugation, (4) adding multiple twisted fragments, (5) modifying chromophore side chains, and (6) tuning the chromophore environment. Another set of modifications is explored to enhance γ, including (1) coupling to a cyanine dye to hybridize the cyanine and TICT orbitals, (2) manipulating the donor and acceptor group identity. The extensive modifications described above yield a detailed understanding of TICT chromophore molecular NLO response and unambiguous evidence that such chromophores have the potential to revolutionize organic electro-optics.

Pluripotent Features of Doubly Thiophene-Fused Benzodiphospholes as Organic Functional Materials.

Linear ladder-type π-conjugated molecules have attracted much interest because of their intriguing physicochemical properties. To modulate their electronic structures, an effective strategy is to incorporate main-group elements into ladder-type π-conjugated molecules. In line with this strategy, a variety of ladder-type π-conjugated molecules with main-group elements have been synthesized to explore their potential utility as organic functional materials. In this context, phosphole-based π-conjugated molecules are highly attractive, owing to their unique optical and electrochemical properties, which arise from the phosphorus atom. Herein, the synthesis and physicochemical properties of doubly thiophene-fused benzodiphospholes, as a new class of phosphole-based ladder-type π-conjugated molecule, are reported. Systematic investigations into the physicochemical properties of doubly thiophene-fused benzodiphospholes revealed their pluripotent features: intense near-infrared fluorescence, excellent two-photon absorption property, and remarkably high electron-transporting ability. This study demonstrates the potential utility of doubly thiophene-fused benzodiphospholes as organic functional materials for biological imaging, nonlinear optics, organic transistors, and organic photovoltaics.

Growth, Vibrational, Optical, Mechanical and DFT Investigations of an Organic Nonlinear Optical Material – Phenylurea

Abstract In this work, combined experimental and computational studies of an organic nonlinear optical material, phenylurea (PU), are reported. Optical quality single crystal of PU, was successfully grown by the slow evaporation method. The unit cell parameters of the grown PU crystal belong to the monoclinic system and these belong to the non-centrosymmetric (NCS), P21, space group. Morphology of the crystal was indexed and it reveals its 14 distinct faces. Vibrational modes of PU functional groups were assigned successfully using FTIR and Raman spectrum. The grown crystal exhibits low cutoff wavelength at UV region with good optical transparency and blue wavelength emission. The preliminary measurements confirmed that second harmonic generation (SHG) activity (∼7.6 KDP and ∼2.2 urea) with excellent laser induced threshold damage (LDT) having a value of 2.92 GW/cm2 (∼1.95 urea). TG/DTA analysis shows that endothermic nature of grown crystal with thermal stability up to 154 °C. The Vickers micro hardness test confirms soft material behavior of PU crystal and it was further explored by crystal void percentage calculation. Electrical properties such as dielectric and photoconductivity measurements were carried out for grown crystal. Furthermore, density functional theory (DFT) studies such as Mulliken charge distribution, frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) map and first order hyperpolarizability (β) were determined to probe the structure-property relationship. These results suggest that PU single crystal can be a better alternate for urea in NLO applications.

One-Drop Self-Assembly and Size Control of Organic Nonlinear Optical Crystal DSNS Nanowires

In this study, we demonstrate a one-drop self-assembly method for fabricating nanowires (NWs) of organic second-order nonlinear optical (NLO) material, 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium 2-naphthalenesulfonate (DSNS). By controlling the parameters of the self-assembly process, we successfully controlled the length of DSNS from a few micrometers to millimeters. The obtained NWs have very high surface quality with surface roughness < 150 pm, which is highly beneficial for fabricating integrated optical devices. DSNS NW has the same triclinic crystal structure as that of bulk crystal and exhibits excellent second-order NLO and fluorescent properties, which could provide wide opportunities for on-chip optoelectronic devices and integrated photonic systems. Furthermore, the one-drop self-assembly method only requires reagents in microgram quantities, and thus this method is extremely environmentally friendly.

Density Functional Theoretical and Experimental investigation on L - Asparaginium Picrate-a nonlinear optical material

An organic nonlinear optical material, L-Asperginium picrate has been successfully synthesized and by slow evaporation method, good quality single crystal was grown. The structure of LAsP was elucidated using single crystal X-ray diffraction data. For synthesized compound, the functional group was confirmed by FTIR spectral analysis. The thermal stability of the crystal was revealed by Thermogravimetric and differential thermal analyses. Density functional theory(DFT) calculations with B3LYP/6-31G(d, p) basis sets was used to determine ground state molecular geometries, vibrational frequencies The optical properties such as optical band gap and cut off wavelength of the title material were obtained from the UV–visible spectrum, the band gap (Eg) is found to be 4.5eV.

Generic Classification Scheme for Second-Order Dipolar Nonlinear Optical Organometallic Complexes That Exhibit Second Harmonic Generation.

The molecular design rules of organic nonlinear optical (NLO) materials are well established, especially those pertaining to the first-order molecular hyperpolarizability, β, which governs second-harmonic generation (SHG): a phenomenon that is responsible for the frequency doubling processes in many optical applications. The availability of these rational guidelines has propelled the development of new organic SHG chromophores. Conversely, the development of organometallic SHG-active complexes has not been steered so clearly. Many reports on individual series of complexes suggest a singular correlation between their structure and SHG properties. Several reviews have catalogued such results, but these have only distinguished compounds by chemical type, while their SHG properties are described one-by-one for each chemical. We herein propose a generic classification scheme that can systematically rationalize dipolar SHG properties for all organometallic complexes. This classification method stands to provide the holistic information that is needed to generate a rational set of guidelines for the systematic molecular design of dipolar SHG-active organometallic chromophores. Our scheme shows that only a simple set of molecular design rules is required to relate the chemical structure of an organometallic complex to its second-order dipolar SHG properties. This is despite the fact that these molecular design rules are rooted in a complicated panoply of ligand- and crystal-field theory, resonance structures, intramolecular charge transfer considerations, metal oxidation states, and metal coordination attributes. While the roots of these rules can be derived at the individual chemical level, their derivation via our workflow of simple decision-making processes which connect these rules within a simple classification scheme, stands to facilitate a rational molecular design approach toward the materials discovery of organometallic complexes for SHG applications.