Supermolecule Approach Research Articles

Study of Nonlinear Optical Properties of a Self-Healing Organic Crystal.

Recently a noncentrosymmetric single crystal of a dibenzoate derivative, namely, dimethyl-4,4'-(methylenebis(azanediyl))dibenzoate, with second harmonic generation activities at 405 nm and ultrafast self-healing activity was reported by Mondal et al. in Nature Communications in 2023. Here, the linear and nonlinear optical properties of this notable molecular crystal were simulated using 1,611,464 atoms in the Supermolecule approach at the DFT/CAM-B3LYP/aug-cc-pVTZ level. Our results for the second order nonlinear optical properties of dimethyl-4,4'-(methylenebis(azanediyl))dibenzoate show that the second harmonic generation is more significant at 532 nm. In addition, the density functional theory calculations of the electro-optical parameters for the crystals in the pristine state and after the fracture mechanical self-healing process show small differences, confirming the efficiency of the self-healing process. Additionally, the crystal displays significant third-order nonlinear optical properties, particularly pronounced at a shorter wavelength of 330 nm. Thus, the self-healing dimethyl-4,4'-(methylenebis(azanediyl))dibenzoate crystal shows relevant second and third order nonlinear optical properties which make it a very interesting material for optical applications.

Understanding Nonlinear Optical Phenomena in N-Pyrimidinyl Stilbazolium Crystals via a Self-Consistent Electrostatic Embedding - DFT Approach.

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) have been used to investigate the nonlinear optical (NLO) properties of phenolic N-pyrimidinyl stilbazolium cationic chromophore in its corresponding noncentrosymmetric crystals. Such a cationic chromophore, the OPR (4-(4-hydroxystyryl)-1-(pyrimidin-2-yl)pyridinium), consists of a strong electron donor, the 4-hydroxyphenyl group, and a strong electron acceptor, the N-pyrimidinylpyridinium group based on two electron-withdrawing groups. The in-crystal NLO properties were determined by applying a supermolecule approach in combination with an iterative electrostatic scheme, in which the surrounding molecules of a unit cell are represented by point charges. With CAM-B3LYP, our absolute estimates for the largest diagonal component of the second-order nonlinear susceptibility tensor of OPR-based crystals range from 64.00 to 80.34 pm/V in the static regime and from 162.09 to 175.52 pm/V at 1907 nm. These values are significant when compared to those of benchmark stilbazolium-based crystals. Furthermore, the third-order susceptibility, which is related to the nonlinear optical process of the intensity-dependent refractive index, is also significant compared to the results for other organic crystals, such as chalcone derivatives. With TD-CAM-B3LYP, the two-state model effectively explains the similarity in the first hyperpolarizability values in the crystalline phase. This similarity arises from the combination of the oscillator strength and the charge transfer of the crucial transition. Therefore, phenolic organic salt crystals show great promise for various nonlinear optical applications.

A comparative study of structural and spectroscopic properties of three structurally similar mechanically bending organic single crystals – 2-Amino-3-nitro-5-halo (halo = Cl, Br, or I) pyridine

In recent years, scientists have been very interested in single crystals of monoaromatic compounds with mechanical softness, but they are hard to find. The present work reports a comparative study of structural, spectroscopic, and quantum chemical investigations of three structurally similar mechanically bending monoaromatic compounds, namely, 2-amino-3-nitro-5-chloro pyridine (I), 2-amino-3-nitro-5-bromo pyridine (II), and 2-amino-3-nitro-5-iodo pyridine (III). The mechanical responses of the three organic crystals studied here are very intriguing due to the similarity of their chemical structures, which only differ in the presence of halogen atoms (Cl, Br, and I) at the fifth position of the pyridine ring and are explained through examining intermolecular interaction energies from energy frameworks analysis, slip layer topology, and Hirshfeld surface analysis. The crystals of all the three feature one dimensional ribbons comprising alternating NaminoH⋯Onitro and NaminoH⋯Npyridine hydrogen bonds that form R22(12) and R22(8) dimeric rings, respectively. In (III), weak I⋯I interactions link the adjacent ribbons forming a two dimensional sheet. Layer-like structures are observed in all three crystals, with no significant interactions between the adjacent architectures (ribbons or sheets). Energy framework calculations are used for estimating the bending ability of the three compounds, with the three following the order Cl ≪ Br < I. The iterative electrostatic scheme coupled with the supermolecule approach (SM) at the DFT/CAM-B3LYP/aug-cc-pVTZ level is used to calculate the third-order nonlinear susceptibility (χ3) values in a simulated crystalline environment for the static case as well as two typical electric field frequency values, (λ = 1064 nm) and (λ = 532 nm). In addition, estimates of the topological studies (localized orbital locator and electron localization function) and reactivity characteristics (global reactivity parameters, molecular electrostatic potential, and Fukui function) are made for the compounds under investigation. Docking studies done using AutoDock software with a protein target (PDB ID: 6CM4) revealed that three compounds could be used to treat Alzheimer's disease.

A Minimum Quantum Chemistry CCSD(T)/CBS Data Set of Dimeric Interaction Energies for Small Organic Functional Groups: Heterodimers.

We extend our previous quantum chemistry calculations of interaction energies for 31 homodimers of small organic functional groups (the SOFG-31 data set) by including 239 heterodimers with monomers selected within the SOFG-31 data set, thus resulting in the SOFG-31+239 data set. The minimum-level theoretical scheme contains (1) the basis set superposition error corrected supermolecule (BSSE-SM) approach for intermolecular interactions; (2) the second-order Møller–Plesset perturbation theory (MP2) with the Dunning’s aug-cc-pVXZ (X = D, T, Q) basis sets for the geometry optimization and correlation energy calculations; and (3) the single-point energy calculations with the coupled cluster with single, double, and perturbative triple excitations method at the complete basis set limit [CCSD(T)/CBS] using the well-tested extrapolation methods for the MP2 energy calibrations. In addition, we have performed a parallel series of energy decomposition calculations based on the symmetry adapted perturbation theory (SAPT) in order to gain chemical insights. That the above procedure cannot be further reduced has been proven to be very crucial for constructing reliable data sets of interaction energies. The calculated CCSD(T)/CBS interaction energy data can serve as a benchmark for testing or training less accurate but more efficient calculation methods, such as the electronic density functional theory. As an application, we employ a segmental SAPT model previously developed for the SOFG-31 data set to predict binding energies of large heterodimer complexes. These model energy “quanta” can be used in coarse-grained molecular dynamics simulations by avoiding large-scale calculations.

Predicting the Thermodynamics of Ionic Liquids: What to Expect from PC-SAFT and COSMO-RS?

Two popular thermodynamic modeling frameworks, namely, the PC-SAFT equation of state and the COSMO-RS model, are benchmarked for their performance in predicting the thermodynamic properties of pure ionic liquids (ILs) and the solubility of CO2 in ILs. The ultimate goal is to provide an illustration of what to expect from these frameworks when applied to ILs in a purely predictive way with established parametrization approaches, since the literature generally lacks their mutual comparisons. Two different modeling approaches with respect to the description of the molecular structure of ILs are tested within both models: a cation-anion pair as (i) a single electroneutral supermolecule and (ii) a pair of separately modeled counterions (ion-based approach). In general, we illustrate that special attention should be paid when estimating unknown thermodynamic data of ILs even with these two progressive thermodynamic frameworks. For both PC-SAFT and COSMO-RS, the supermolecule approach generally yields better results for the vapor pressure and the vaporization enthalpy of pure ILs, while the ion-based approach is found to be more suitable for the solubility of CO2. In spite of some shortcomings, COSMO-RS with the supermolecule approach shows the best overall predictive capabilities for the studied properties. The ion-based strategy within both models has significant limitations in the case of the vaporization properties of ILs. In COSMO-RS, these limitations can, to a certain extent, be surpassed by additional quantum mechanical calculations of the ion pairing in the gas phase, while the ion-based PC-SAFT approach still needs a sophisticated improvement to be developed. As an initiating point, we explore one possible and simple route considering a high degree of cross associations between the counterions in the gas phase.

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.

Relating the crystal structure and third-order nonlinear susceptibility of a new Neolignan derivative

Theoretical results for electronic properties of a synthesized nitro chalcone with a neolignan moiety (NOPP) whose crystal structure was elucidated by using Single Crystal X-ray Diffraction (SCXRD) are presented. The NOPP crystal structure suggests that its potential for nonlinear applications is related to the chalcone moiety planarity and that the lamellar NOPP crystal packing along with dimer formation maximize the electronic properties. The in-crystal absorption spectrum and static and dynamic electric properties were determined by applying a supermolecule approach in combination with an iterative electrostatic scheme, in which the surrounding molecules are represented by point charges. It is found that the environment polarization effect is mild for absorption spectrum and linear polarizability, but it is marked for second hyperpolarizability of NOPP molecule. Estimates of macroscopic quantities from the results of an explicit unit cell of crystal, including environment polarization effect and partially the exchange and dispersion effects, are presented. The results illustrate the role played by these interactions on the third-order nonlinear susceptibility of the NOPP crystal, and a theoretical (λ=532nm) prediction of 2.81×10−20 (m/V)2 for χ(3)(−ω;ω,ω,ω) suggests that the NOPP crystal is a very promising NLO material.

Many-electron atom confinement by a penetrable prolate spheroidal cavity

Confinement effects on the ground-state energy of many-electron atoms located inside a penetrable prolate spheroidal cavity are studied within a variational treatment of the Thomas–Fermi–Dirac–Weizsacker density functional scheme. Given a confining cavity size and shape as well as barrier height, isotropic and anisotropic confinement effects on the energy evolution, ionization potentials and pressure are discussed as well as their different conditions for electron escape. Comparison of the spheroidal box results for the energy evolution with corresponding ab initio calculations for endohedral confinement of Ne within the supermolecule approach $$\hbox {Ne@}\hbox {Ne}_{\mathrm {10}}$$ ( $$\hbox {He}_{\mathrm {10}})$$ suggests that reasonable agreement between both types of calculation is achieved provided the atom-in-a-box model incorporates the mean size of surrounding atoms with nuclei positioned at the spheroidal baseline of the cavity and a realistic choice of the mean confining barrier height.

Many-Body Dispersion.

A broad range of approaches to many-body dispersion are discussed, including empirical approaches with multiple fitted parameters, augmented density functional-based approaches, symmetry adapted perturbation theory, and a supermolecule approach based on coupled cluster theory. Differing definitions of "body" are considered, specifically atom-based vs molecule-based approaches.

A minimum quantum chemistry CCSD(T)/CBS dataset of dimeric interaction energies for small organic functional groups.

We have performed a quantum chemistry study on the bonding patterns and interaction energies for 31 dimers of small organic functional groups (dubbed the SOFG-31 dataset), including the alkane-alkene-alkyne (6 + 4 + 4 = 14, AAA) groups, alcohol-aldehyde-ketone (4 + 4 + 3 = 11, AAK) groups, and carboxylic acid-amide (3 + 3 = 6, CAA) groups. The basis set superposition error corrected super-molecule approach using the second order Møller-Plesset perturbation theory (MP2) with the Dunning's aug-cc-pVXZ (X = D, T, Q) basis sets has been employed in the geometry optimization and energy calculations. To calibrate the MP2 calculated interaction energies for these dimeric complexes, we perform single-point calculations with the coupled cluster with single, double, and perturbative triple excitations method at the complete basis set limit [CCSD(T)/CBS] using the well-tested extrapolation methods. In order to gain more physical insights, we also perform a parallel series of energy decomposition calculations based on the symmetry adapted perturbation theory (SAPT). The collection of these CCSD(T)/CBS interaction energy values can serve as a minimum quantum chemistry dataset for testing or training less accurate but more efficient calculation methods. As an application, we further propose a segmental SAPT model based on chemically recognizable segments in a specific functional group. These model interactions can be used to construct coarse-grained force fields for larger molecular systems.

A Study of the Nonlinear Optical Properties of Stilbazolium Derivative Crystal

In this report we start from ab initio calculations to get the structural properties of an isolated molecule of an organic crystal. Since the knowledge of the effects of neighboring molecules their study became necessary for an appropriated description of nonlinear optical properties in the solid state and more efficient design of such materials requires theoretical models that describes in detail the structural and electronic properties of the crystalline environment. The derivative of an organic stilbazolium single crystal, (E)-1-ethyl-2-(4-nitrostyryl) pyridin-1-ium iodide (NSPI); the NSPI crystallizes in the centric triclinic system with the P1space group. Here the dipole moment, the linear polarizability, and second hyper polarizability of the asymmetric unit of the compound were investigated through a super molecule approach in combination with an iterative scheme. In this approach the electrostatic interactions of the atoms of molecules embedded are represented by point charges. In addition to these calculations, other interesting results are obtained when we compare the results for isolated molecule and the molecule under the influence of its crystalline environment (embedded molecule); under such an influence we find a very interesting result for the average 2nd hyperpolarizability: 290,000% higher in the isolated molecule when compared to the embedded one.

An analysis of spectroscopic, computational and biological activity studies of L-shaped sulfamoylbenzoic acid derivatives: A third order nonlinear optical material

The current article focuses mainly on investigation of structural, reactivity, topology studies, and third order nonlinear optical properties of the synthesized 2-(benzylamino)-4-chloro-5-sulfamoylbenzoic acid (BACSBA) with the aid of spectroscopic techniques and computational methods. The structure in the solid state was obtained unambiguously by SCXRD study that revealed that BACSBA has L-shaped structure stabilized by N–H⋯O intramolecular hydrogen bond. Further, the two dimensional sheet like architecture formation by linking of molecules via O–H⋯O and N–H⋯O hydrogen bonds, were visualized both qualitatively and quantitatively by Hirshfeld surface analysis. Also, a topological analysis made through Quantum Theory of Atoms In Molecules (QTAIM) highlights the observations N–H⋯O bonds on solid state. The quantum chemical calculation was performed at DFT/6–311++G (d,p) level of basis set. The analysis of each vibrational wave number was performed with the help of potential energy distribution (PED) using VEDA4 software and correlation with experimental data shows good concurrence. The reactive sites have been predicted and visualized by molecular electrostatic surface potential (MESP) and Fukui function calculation, together with hydrogen bond dissociation energy (H-BDE) for the BACSBA compound. Frontier molecular orbitals (FMO), global reactivity parameters, natural bond orbital analysis (NBO), localized orbital locator (LOL) and electron localization function (ELF) properties have also been studied for the titled compound. The super molecule (SM) approach with 372,680 atoms at the DFT/CAM-B3LYP/6–311++G (d,p) level was used for calculating the nonlinear optical properties of the crystal. The electrical parameters such as total dipole moment, average linear polarizability and average second IDRI hyperpolarizability were calculated. In addition, the linear refractive index and the nonlinear third order macroscopic susceptibility of the crystal was estimated as a function of the frequency of the applied electric field. The value of third order nonlinear susceptibility for the BACSBA crystal at 532 nm was found to be 45.57 times greatest than the experimentally measured result of organic crystal (2E)-1-(3-bromophenyl)-3-[4 (methylsulfanyl)phenyl]prop-2-en-1-one (3Br4MSP) demonstrating that BACSBA crystal could be a good potential candidate for nonlinear optical applications. In addition, the thermal stability was studied showing that the crystal as potential optical devices at temperature up to 234 °C. Furthermore, preliminary studies revealed that BACSBA compound displayed promising antifungal and antioxidant activities compared with the standard drugs.

Synthesis, crystal structure, spectroscopic and nonlinear optical properties of organic salt: A combined experimental and theoretical study

The 2-methoxy-pyrido[1,2-a]quinoxalin-11-ylium bromide (2MPQYB) crystal was characterized from single crystal X-ray diffraction (SCXRD) and spectroscopy analysis. The fluorescence spectrum of the compound showed one broad peak at 473 nm. The supramolecular arrangement in solid state was confirmed by 2D-fingerprint plots and Hirshfeld surface analysis. An additional topological analysis from quantum theory of atoms in molecules (QTAIM) highlights the observed halogen bonds on solid state for 2MPQYB. Also the supermolecule (SM) approach was used to simulate the crystalline environment with 246,064 atoms and an ab-initio calculation method, which includes the Density Functional Theory (DFT) at CAM-B3LYP/6–311++G(d,p) level, was used to estimate the crystal linear refractive index and the third-order nonlinear susceptibility at the frequency of ω=0.086a.u. (λ = 532 nm) and the obtained values were 1.85 and χ3=621.14×10−22m2/V2 respectively. This χ3-value is up to 312.13 times greater than obtained for others organic crystals of the literature, thus indicating that the 2MPQYB can be considered for various applications of NLO materials.

On the potential as nonlinear optical material of a new chalcone derivative and its crystal and topological analysis

We report a study of the structural and the linear and nonlinear optical and electrical properties of a new chalcone. Using the Møller-Plesset Perturbation and the Density Functional approaches, the dipole moment, linear polarizability and second hyperpolarizabilities were calculated in static and dynamic electric fields. The supermolecule approach was used to simulate the crystalline environment of our crystal and the linear refractive index. Lorentz local field correction factor and third order macroscopic susceptibility were calculated, and the effects of solvent media on the non-linear optical properties are also taken into account through the Polarizable Continuum Model. This chalcone is almost planar, except for slight rotations in its open-chain which allows electron delocalization. This is also confirmed by an intramolecular hydrogen bond formed between the carbonyl and amine groups. Interestingly, a good third order macroscopic susceptibility value of 13.31 × 10−22m2V−2 was calculated, which is even higher than those reported for related chalcone derivatives.

Growth and characterization of a new chlorine substituted chalcone: A third order nonlinear optical material

In this present study, the structural, molecular, electronic, thermal studies, and the nonlinear optical (NLO) properties of a newly synthesized chalcone derivative 3-(2-chloro-phenyl)-1-[3-(2-oxo-2-phenyl-ethoxy)-phenyl]-propan-1-one (CPPO) were performed. The molecular structure of titled compound was described by single crystal X-ray diffraction, nuclear magnetic resonance spectroscopy (1H and 13C NMR) and thermal analysis (TGA-DTG analysis). The supramolecular arrangement in solid state was confirmed by Hirshfeld surface analysis and 2D-fingerprint plots. The CPPO compound was crystallized on non-centrosymmetric monoclinic space group P21 and the supermolecule approach (SM) at DFT/CAM-B3LYP/6-311++G(d,p) level was used to analyze the nonlinear optical properties in crystalline environment. The total moment of dipole, the averages of linear polarizability α(−ω;ω) and first and second hyperpolarizabilities, linear refractive index and the third-order nonlinear susceptibility (χ(3)) were calculated as function of the electric field frequency. The χ(3)-value of the CPPO crystal at 532 nm is 266 times greater than the experimental result of organic crystal (2E)-1-(3-bromophenyl)-3-[4(methylsulfanyl)phenyl]prop-2-en-1-one [1], demonstrating that CPPO crystal has good potential for use as NLO material.

Modeling and spectral simulation of formic acid dimer in Ar matrix using ONIOM calculations

The supermolecule approach has been used to model molecules embedded in a solid argon matrix. The interaction between the guest and the host atoms in the first solvation shell (FSS) are evaluated using density functional calculations while that beyond the FSS is incorporated using ONIOM calculations to extend the results of our previous study [F. Ito, J. Chem. Phys. 133 (2010) 214502]. The vibrational spectra of a formic acid dimer (FAD) in an Ar matrix was simulated using (FAD)-Arn clusters (n = 94–1095). Structural relaxation in the first solvation shell is crucial to quantitatively reproduce the matrix shifts of fundamental bands, according to calculations at the B971/6-31++G(3df,3pd) level. Moreover, the influence of the outer Ar atoms is negligible.

The interplay and strength of the π⋯HF, C⋯HF, F⋯HF and F⋯HC hydrogen bonds upon the formation of multimolecular complexes based on C2H2⋯HF and C2H4⋯HF small dimers.

The conception of this theoretical research was idealized aiming to unveil the intermolecular structures of complexes formed by acetylene or ethylene and hydrofluoric acid. At light of computational calculations by using the B3LYP/6-311++G(d,p) method, the geometries of the C2H2⋯(HF), C2H2⋯2(HF), C2H2⋯4(HF), C2H4⋯(HF), C2H4⋯2(HF) and C2H4⋯4(HF) hydrogen-bonded complexes were fully optimized. Moreover, the Post-Hartree-Fock calculations MP2/6-311++G(d,p), MP2/aug-cc-pVTZ, MP4(SDQ)/6-311++G(d,p) and CCSD/6-311++G(d,p) also were also used. The infrared spectra were analyzed in order to identify the new vibrational modes and frequencies of the proton donors shifted to red region. Through the modeling of charge-fluxes on the basis of the Quantum Theory of Atoms In Molecules (QTAIM) and, by contradicting the expectation of the hydrofluorination mechanisms of acetylene or ethylene, C⋯HF was recognized as a new type of hydrogen bond instead of the already well known π⋯H. The calculations of the Natural Bonding Orbital (NBO) and Charges derived from the Electrostatic Potential Grid-based (ChElPG) were also applied to interpret the shifting frequencies as well as measuring of the punctual charge-transfer after the formation of the complexes. Finally, the determination of the stabilization energy was carried out through the arguments of the Fock matrix in NBO basis and through the supermolecule approach. Also it is worthwhile to notice that some algebraic formulations were used for determining the electronic cooperative effect (CE).

Using the Supermolecule Approach To Predict the Nonlinear Optics Potential of a Novel Asymmetric Azine.

Organic molecules with electron acceptors or withdrawal substituents terminal at π-conjugated system are promising candidates to be explored as materials with high linear and nonlinear optical properties. On the basis of these features, a novel asymmetric azine ( 7E, 8E)-2-(3-methoxy-4-hydroxy-benzylidene)-1-(4-nitrobenzylidene)hydrazineC15H13N3O4 (NMZ) was synthesized. The molecular structure of NMZ was elucidated by X-ray crystallography and the supramolecular arrangement was analyzed from Hirshfeld surface methodology. An iterative electrostatic scheme using a super molecule approach, where neighboring molecules are represented by charge points, was employed to investigate optical dipole moment (μ), the linear polarization (α) and the first (β) and second (γ) hyperpolarizabilities. The NMZ crystallized in the centrosymetric space group P21/n and packs via combined O-H···O, C-H···O, and N···π interactions. The macroscopic property of third order χ(3) found for the NMZ is 298.62 times greater than values reported for chalcone derivative (2 E)-1-(3-bromophenyl)-3-[4 (methylsulfanyl)phenyl]prop-2-en-1-one. The results for NMZ indicate a good nonlinear optical effect.

Third-Order Nonlinear Optical Properties of a Carboxylic Acid Derivative

We report a study of the structural and electrical properties of a carboxylic acid derivative (CAD) with structural formula C5H8O2 ((E)-pent-2-enoic acid). Using the M∆ller-Plesset Perturbation Theory (MP2) and the Density Functional Theory (DFT/CAM-B3LYP) with the 6-311++G(d,p) basis set the dipole moment, the linear polarizability and the first and second hyperpolarizabilities are calculated in presence of static and dynamic electric field. Through the supermolecule approach the crystalline phase of the carboxylic acid derivative is simulated and the environment polarization effects on the electrical parameters are studied. Static and dynamic estimation of the linear refractive index and the third-order nonlinear susceptibility of the crystal are obtained and compared with available experimental results. The characteristic vibrational modes and functional groups present in CAD were analyzed by Fourier Transform Infrared Spectrum (FTIR) in the region of 400-4000 cm-1. Through the Hirshfeld surface analysis the molecular structure and the vibrational modes properties of the CAD crystal are explored. The effects of solvent medium on the molecular properties are taken into account through the Polarizable Continuum Model (PCM). Also, the frontiers molecular orbitals, the band gap energy, and the global chemical reactivity descriptors are discussed. All the properties studied suggest that the present material may be considered for nonlinear optical material.

NLO properties of a triphenlyguanidine salt: The importance of pseudo-symmetry

Using a combined experimental and computational approach, we were able to trace the quasi-vanishing of the second-order nonlinear optical (NLO) properties of a newly synthesized organic salt, bis(triphenylguanidinium) l-malate, to the pseudo-centrosymmetry of its structure. The employed experimental techniques were single crystal X-ray diffraction to determine the structure, “open-aperture” Z-scan technique to measure the nonlinear absorption, Kurtz and Perry powder method and Maker fringes techniques for second- and third-harmonic generation. The molecular hyperpolarizability tensors (β and γ) were calculated within Density Functional Theory (DFT) and the macroscopic second- and third-order susceptibility tensors were estimated by combining the supermolecule approach with the oriented gas model. The calculations performed with global hybrid GGA and range-separated functionals reproduced the correct order of magnitude of the observed second- and third-order susceptibilities.