Theoretical and experimental comparative studies of nonlinear optical properties for selected melaminium compounds

The bis(melaminium) sulphate dihydrate, 2,4,6-triamine-1,3,5-triazin-1,3-ium tartrate monohydrate, 2,4,6-triamine-1,3,5-triazin-1-ium hydrogenphthalate, 2,4,6-triamine-1,3,5-triazin-1-ium acetate acetic acid solvate monohydrate, 2,4,6-triamine-1,3,5-triazin-1-ium bis(selenate) trihydrate, melaminium diperchlorate hydrate, melaminium bis(trichloroacetate) monohydrate and melaminium bis(4-hydroxybenzenesulphonate) dihydrate were discovered recently as perspective materials for nonlinear optical applications. On the basis of X-ray structures for eight melaminium compounds the time dependent Hartree Fock (TDHF) method was used for calculation of the polarizability, and first and second hyperpolarizability. Detailed directional studies of calculated hyperpolarizability for all investigated melaminium compounds are shown. The theoretical results are compared with experimental values of β.     

Bulk optical properties in binary mixtures of antiferroelectric liquid crystal compounds showing V-shaped switching

In order to clarify the origin of the V-shaped switching observed in thin cells ofantiferroelectric/ ferrielectric liquid crystals, bulk properties have been studied by means of helical pitch and conoscope measurements using thick free-standing films of binary mixtures with various mixing ratios. In the temperature range showing V-shaped switching in thin cells, helical structure clearly exists, indicating the existence of ordered phases. Some indistinct phase changes with temperature, coexistence of phases and quasi-continuous phase changes with an applied electric field were observed, suggesting a system with weak inter-layer correlation. By comparing the phase diagrams made using thin homogeneous cells and thick free-standing films, it was found that V-shaped switching occurs in the region where various subphases exist in the bulk. The appearance of many indistinct phases is consistent with the weak interlayer correlation. In this way, it was concluded that the V-shaped switching occurs in tilted smectic layers, in which the tilt direction is weakly correlated along the layer normal.     

Electronic and optical properties of quaternary selenides for optoelectronic applications: Insights from DFT+U-computations

The optical properties, electronic charge density, electronic structure of the new layered selenides materials, BaGdCuSe₃, CsUCuSe₃, CsZrCuSe₃, and CsGdZnSe₃ compounds have been calculated by using the full potential and linear augmented plane wave (FP-LAPW) methods as applied in the WIEN2k package, which is based on the density functional theory. The ALnMSe3 compound's structure of these was (A = Cs, Ba; Ln = Zr, Gd, U; M = Cu, Zn) is composed of (n = 1, 2) layers, which might be separated by A atoms. It is to be observed that there is strong hybridization between the s, p, and d states of Zr, Gd, and Cu atoms. Around the gadolinium atom, the charge density contours are completely circular, but the Gadolinium “Gd” atom shows an ionic nature. To calculate the refractive index, we used Kramer's Kronig correlations with the imaginary part dielectric function. The decrease in the refractive index is due to the lack of probability for direct excitation of the electrons, resulting in a loss of energy. The value of the static refractive index for all reference compounds is about 1.75–2.25, which is indication that the material used in optoelectronic devices.     

Theoretical studies on nonlinear optical properties of formaldehyde oligomers by ab initio and density functional theory methods

The first and second hyperpolarizability beta and gamma are obtained for formaldehyde oligomers (H2CO)n (n = 1-7) using computational methods. We have used the finite field (FF) approach and hyperpolarizability density analysis (HDA) to predict the microscopic first and second nonlinear hyperpolarizability of the formaldehyde oligomers. The spatial contributions of electrons to the hyperpolarizability by using plots of HDA are presented. It has been found from the numerical stability checking of the hyperpolarizability calculations that the calculated values by FF method are more stable than those by HDA approach. The values of beta are zero when n is even as the molecule possesses centrosymmetry, and when n is odd, the differences among beta values are not clear. The gamma values are increased with increase in n.     

Orbital functional theory of linear response and excitation

Orbital functional theory (OFT) is based on a rule that determines a single‐determinant reference state Φ for any exact N‐electron eigenstate Ψ. An OFT model postulates an explicit correlation energy functional E_c of occupied orbital functions {?_i} and occupation numbers {n_i}. The orbital Euler–Lagrange equations are analogous to Kohn–Sham equations, but do not in general contain local potential functions. Time‐dependent Hartree–Fock theory is generalized in OFT to a formally exact linear response theory that includes electronic correlation. In the exchange‐only limit, the theory reduces to the random‐phase approximation of many‐body theory. The formalism determines excitation energies. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Vibrational spectra and non linear optical proprieties of L-histidine oxalate: DFT studies

This paper presents the results of our calculations on the geometric parameters, vibrational spectra and hyperpolarizability of a nonlinear optical material L-histidine oxalate. Due to the lack of sufficiently precise information on geometric structure in literature, theoretical calculations were preceded by re-determination of the crystal X-ray structure. Single crystal of L-histidine oxalate has been growing by slow evaporation of an aqueous solution at room temperature. The compound crystallizes in the non-Centro symmetric space group P2(1)2(1)2(1) of orthorhombic system. The FT-IR and Raman spectra of L-histidine oxalate were recorded and analyzed. The vibrational wave numbers were examined theoretical with the aid of Gaussian98 package of programs using the DFT//B3LYP/6-31G(d) level of theory. The data obtained from vibrational wave number calculations are used to assign vibrational bands obtained in IR and Raman spectroscopy of the studied compound. The geometrical parameters of the title compound are in agreement with the values of similar structures. To investigate microscopic second order non-linear optical NLO behaviour of the examined complex, the electric dipole μ(tot), the polarizability α(tot) and the hyperpolarizability β(tot) were computed using DFT//B3LYP/6-31G(d) method. According to our calculation, the title compound exhibits non-zero β(tot) value revealing microscopic second order NLO behaviour.     

Conclusive evidence on the insensitivity of additive rules to the combinational details of exchange and correlation functional in hybrid DFT methods

This account is a quest to evaluate the sensitivity of additive rules among total electronic energies of some triple molecular sets to the employed computational level. To achieve the goal, seven randomly generated hybrid functionals have been constructed and employed for calculation on a test set of 29 molecules containing second and third row elements. The computational results based on these nonoptimized DFT methods in conjunction with those of standard B3LYP method clearly demonstrates that in contrast to atomization or isomerization energies, additive rules among total electronic energies are insensitive to reliability or precision of computational method. This insensitivity to details of exchange‐correlation functional indicates that additive rules can be generally well considered using simple computational methods. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Understanding the synergistic effects,optical and electronic properties of ternary Fe/C/S‐doped TiO2 anatase within the DFT + U approach

Although TiO₂ is an efficient photocatalyst, its large band gap limits its photocatalytic activity only to the ultraviolet region. An experimentally synthesized ternary Fe/C/S‐doped TiO₂ anatase showed improved visible light photocatalytic activity. However, a theoretical study of the underlying mechanism of the enhanced photocatalytic activity and the interaction of ternary Fe/C/S‐doped TiO₂ has not yet been investigated. In this study, the defect formation energy, electronic structure and optical property of TiO₂ doped with Fe, C, and S are investigated in detail using the density functional theory + U method. The calculated band gap (3.21 eV) of TiO₂ anatase agree well with the experimental band gap (3.20 eV). The defect formation energy shows that the co‐ and ternary‐doped systems are thermodynamically favorable under oxygen‐rich condition. Compared to the undoped TiO₂, the absorption edge of the mono‐, co‐, and ternary‐doped TiO₂ is significantly enhanced in the visible light region. We have shown that ternary doping with C, S, and Fe induces a clean band structure without any impurity states. Moreover, the ternary Fe/C/S‐doped TiO₂ exhibit an enhanced photocatalytic activity, a smaller band gap and negative formation energy compared to the mono‐ and co‐doped systems. Moreover, the band edges of Fe/C/S‐doped TiO₂ align well with the redox potentials of water, which shows that the ternary Fe/C/S‐doped TiO₂ is promising photocatalysts to split water into hydrogen and oxygen. These findings rationalize the available experimental results and can assist the design of TiO₂‐based photocatalyst materials.     

Thermodynamic, electronic and structural properties of Cu/CeO2 surfaces and interfaces from first-principles DFT+U calculations

The thermodynamic, structural and electronic properties of Cu-CeO(2) (ceria) surfaces and interfaces are investigated by means of density functional theory (DFT+U) calculations. We focus on model systems consisting of Cu atoms (i) supported by stoichiometric and reduced CeO(2) (111) surfaces, (ii) dispersed as substitutional solid solution at the same surface, as well as on (iii) the extended Cu(111)/CeO(2)(111) interface. Extensive charge reorganization at the metal-oxide contact is predicted for ceria-supported Cu adatoms and nanoparticles, leading to Cu oxidation, ceria reduction, and interfacial Ce(3+) ions. The calculated thermodynamics predict that Cu adatoms on stoichiometric surfaces are more stable than on O vacancies of reduced surfaces at all temperatures and pressures relevant for catalytic applications, even in extremely reducing chemical environments. This suggests that supported Cu nanoparticles do not nucleate at surface O vacancies of the oxide, at variance with many other metal/ceria systems. In oxidizing conditions, the solid solutions are shown to be more stable than the supported systems. Substitutional Cu ions form characteristic CuO(4) units. These promote an easy and reversible O release without the reduction of Ce ions. The study of the extended CeO(2)(111)/Cu(111) interface predicts the full reduction of the interfacial ceria trilayer. Cu nanoparticles supported by ceria are proposed to lie above a subsurface layer of Ce(3+) ions that extends up to the perimeter of the metal-oxide interface.     

Structure, bonding, and linear optical properties of a series of silver and gold nanorod clusters: DFT/TDDFT studies

DFT/TDDFT calculations have been carried out for a series of silver and gold nanorod clusters (Ag(n), Au(n), n = 12-120) whose structures are of cigar-type. Pentagonal Ag(n) clusters with n = 49-121 and hexagonal Au(n) clusters with n = 14-74 were also calculated for comparison. Metal-metal distances, binding energies per atom, ionization potentials, and electron affinities were determined, and their trends with cluster size were examined. The TDDFT calculated excitation energies and oscillator strengths were fit by a Lorentz line shape modification, which gives rise to the simulated absorption spectra. The significant features of the experimental spectra for actual silver and gold nanorod particles are well reproduced by the calculations on the clusters. The calculated spectral patterns are also in agreement with previous theoretical results on different-type Ag(n) clusters. Many differences in the calculated properties are found between the Ag(n) and Au(n) clusters, which can be explained by relativistic effects.     

Variational calculation of vibrational linear and nonlinear optical properties

A variational approach for reliably calculating vibrational linear and nonlinear optical properties of molecules with large electrical and/or mechanical anharmonicity is introduced. This approach utilizes a self-consistent solution of the vibrational Schrodinger equation for the complete field-dependent potential-energy surface and, then, adds higher-level vibrational correlation corrections as desired. An initial application is made to static properties for three molecules of widely varying anharmonicity using the lowest-level vibrational correlation treatment (i.e., vibrational M?ller-Plesset perturbation theory). Our results indicate when the conventional Bishop-Kirtman perturbation method can be expected to break down and when high-level vibrational correlation methods are likely to be required. Future improvements and extensions are discussed.     

Detection of palytoxin-like compounds by a flow cytometry-based immunoassay supported by functional and analytical methods

Palytoxin (PLTX) is a complex marine toxin produced by zoanthids (i.e. Palythoa), dinoflagellates (Ostreopsis) and cyanobacteria (Trichodesmium). PLTX outbreaks are usually associated with Indo-Pacific waters, however their recent repeated occurrence in Mediterranean–European Atlantic coasts demonstrate their current worldwide distribution. Human sickness and fatalities have been associated with toxic algal blooms and ingestion of seafood contaminated with PLTX-like molecules. These toxins represent a serious threat to human health. There is an immediate need to develop easy-to-use, rapid detection methods due to the lack of validated protocols for their detection and quantification. We have developed an immuno-detection method for PLTX-like molecules based on the use of microspheres coupled to flow-cytometry detection (Luminex 200™). The assay consisted of the competition between free PLTX-like compounds in solution and PLTX immobilized on the surface of microspheres for binding to a specific monoclonal anti-PLTX antibody. This method displays an IC₅₀ of 1.83 ± 0.21 nM and a dynamic range of 0.47–6.54 nM for PLTX. An easy-to-perform extraction protocol, based on a mixture of methanol and acetate buffer, was applied to spiked mussel samples providing a recovery rate of 104 ± 8% and a range of detection from 374 ± 81 to 4430 ± 150 μg kg⁻¹ when assayed with this method. Extracts of Ostreopsis cf. siamensis and Palythoa tuberculosa were tested and yielded positive results for PLTX-like molecules. However, the data obtained for the coral sample suggested that this antibody did not detect 42-OH-PLTX efficiently. The same samples were further analyzed using a neuroblastoma cytotoxicity assay and UPLC-IT-TOF spectrometry, which also pointed to the presence of PLTX-like compounds. Therefore, this single detection method for PLTX provides a semi-quantitative tool useful for the screening of PLTX-like molecules in different matrixes.     

Electronic and optical properties of edge modified peritetracene: a DFT study

Peritetracene (PTA) molecules have promising applications in organic electronics and organic light-emitting diodes, but the major constraints come from their poor stability with higher energy gap. We have investigated the stability, electronic, and optical properties of different electron-donating- and electron-withdrawing-substituted PTA molecule groups using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. On substituting suitable electron donor and acceptor groups, the energy gap of PTA molecules reduces up to 0.37 eV with an increase in their stability. The stabilities of considered PTA molecules have been investigated using the distribution pattern of frontier molecular orbital energies. The charge transfer properties with smaller ionization potential and larger electron affinity for PTA molecule have been evaluated using Koopmans’ theorem. Enhancement in dipole moment, polarizability, and hyperpolarizability of PTA substituted with electron-donating groups shows the presence of NLO properties. Also, we have investigated the spectroscopic properties of different electron-donating- and electron-withdrawing-substituted PTA molecule groups. Our spectroscopic properties show the bathochromic shift and small hypsochromic shifts in wavelengths of PTA with substituents groups. It is therefore concluded that the –NCH₃ and –NO₂ substituent groups on PTA are observed to have the strongest and highest stability than the other substituent groups considered.

     

Synthesis and optical properties of hyperbranched polyarylenes and linear polyacetylenes

New hyperbranched polyarylenes (HPAs) and linear polyacetylenes (LPAs) containing chromophoric moieties were synthesized in high yields (up to 97%) by coablt- and tantalum-catalyzed polycyclotrimerizations and tungsten-catalyzed metathesis polymerizations, respectively. The polymers possessed high molecular weights (M_w up to 113 000 Da) and were completely soluble in common organic solvents. The HPAs emitted strong UV light of 400 nm in high quantum yields (Φ_F up to 0.98) and limited intense laser pulses, whose limiting threshold and signal suppress power were better than those of C₆₀, a well-known optical limiter. The electroluminescence (EL) devices of the LPAs emitted blue light of ∼460 nm and exhibited maximun brightness, current efficiency, and external quantum efficiency of 1118 cd/m², 1.53 cd/A, and 0.85%, respectively.     

Structural and optical properties of a neutral Nickel bisdithiolene complex: density functional versus ab initio methods

Density functional theory (DFT) and ab initio computations are applied to examine different properties of diamagnetic, square planar neutral nickel complexes that contain two bidentate ligands derived from bis ((ethylene)-1,2-dithiolato) ligands. Geometry, vibrational spectra (IR and Raman) are well reproduced in the density functional framework whereas TD-DFT methods are clearly insufficient to reproduce absorption properties. Multiconfigurational perturbation theory based on a complete active space self-consistent field wave function, i.e. MRPT2 and MRPT4 methods, reveal the pronounced multiconfigurational character of the ground state wave function. The singlet–triplet energy gap, the energy gained from symmetry breaking and the singlet diradical character are discussed in the DFT and ab initio frameworks. The complex of interest does not display a strong singlet diradical character. This molecule having a peculiar electronic structure; strong delocalization as shown by a new electron pair localization function analysis (EPLF); exemplifies the fragility of the TD-DFT method and thus, caution should be taken in the determination of the energetic properties of such compounds.     

Construction and properties of drug molecules modifying octamolybdate hybrid compounds

By introducing antibacterial drug pipemidic acid into octamolybdates, two new compounds, (HPPA)₄[Mo₈O₂₆] 2H₂O (1) and [Ni₂(PPA)₂(H₂O)₄] [Mo₈O₂₆] 3H₂O (2) (PPA?=?8-ethyl-5,8-dihydro-5-oxo-2-(1-piperazinyl)pyrido(2,3-d)pyrimidine-6-carboxylic acid), have been synthesized and characterized by physical methods. Single-crystal X-ray analysis reveal that 1 and 2 crystallize in the triclinic system, space group P-1, in which supramolecular interactions play vital roles in stabilizing the structure of 1 and 2. The results of their antitumor activities in vitro show that the compounds exhibit good anti-SGC7901 and anti-SMMC7721 activities, which indicates that the antitumor activities of Polyoxometalates can be modulated by the surface modification with drugs.