Showing papers on "Hyperpolarizability published in 2010"

Optical second harmonic generation of single metallic nanoparticles embedded in a homogeneous medium.

Abstract: We report the optical second harmonic generation from individual 150 nm diameter gold nanoparticles dispersed in gelatin. The quadratic hyperpolarizability of the particles is determined and the input polarization dependence of the second harmonic intensity obtained. These results are found in excellent agreement with ensemble measurements and finite element simulations. These results open up new perspectives for the investigation of the nonlinear optical properties of noble metal nanoparticles.

All-Optical Molecular Orientation

Abstract: We report clear evidence of all-optical orientation of carbonyl sulfide molecules with an intense nonresonant two-color laser field in the adiabatic regime. The technique relies on the combined effects of anisotropic hyperpolarizability interaction and anisotropic polarizability interaction and does not rely on the permanent dipole interaction with an electrostatic field. It is demonstrated that the molecular orientation can be controlled simply by changing the relative phase between the two wavelength fields. The present technique brings researchers a new steering tool of gaseous molecules and will be quite useful in various fields such as electronic stereodynamics in molecules and ultrafast molecular imaging.

Modulated Nonlinear Optical Responses and Charge Transfer Transition in Endohedral Fullerene Dimers Na@C60C60@F with n-Fold Covalent Bond (n = 1, 2, 5, and 6) and Long Range Ion Bond

Abstract: Isomer structures of four endohedral fullerene dimers Na@C60C60@F with an n-fold bond (n = 1, 2, 5 and 6) are obtained for the first time by using density functional theory. The n-fold bond depends on the dimeric pattern between endohedral fullerenes Na@C60 and F@C60. The pattern includes point−point (n = 1), side−side (n = 2), and face−face (n = 5, 6) mode. The four structures [1 + 1], [2 + 2], [5 + 5] and [6 + 6] have larger n-fold bond energies, as compared to that of the neutral π-(C60)2 dimer. In addition, the electronic properties of the endohedral dimers are first investigated. The dimers exhibit a strong nonlinear optical (NLO) response: large static first hyperpolarizabilities. Moreover, the first hyperpolarizability depends on the dimeric pattern. The large first hyperpolarizabilitiy is up to 25 169 au for [5 + 5], which is almost 110 times larger than that of the NaF molecule (228 au). The great enhancement of the first hyperpolarizability relates to the geometric effect of expanding the Na···F...

Breakdown of the first hyperpolarizability/bond-length alternation parameter relationship

Abstract: We have investigated the dependence of the static first hyperpolarizability on the bond-length alternation (BLA) parameter. Our analysis indicates that the validity of the first hyperpolarizability/BLA parameter relationship is restricted to the no-field, vacuum, limit, while it successively breaks down along with increasing polarity of a surrounding medium, becoming invalid, for instance, in an aqueous solution. This contention is based on a series of TD-DFT, TD-DFT/PCM and hybrid TD-DFT/MM calculations of the first hyperpolarizability for a set of molecular configurations generated from Car–Parrinello hybrid QM/MM simulations of the stilbazolium merocyanine chromophore in chloroform and water solvents, and on a rationalization by means of the two-state model for the first hyperpolarizability. The BLA dependence of the three parameters entering the two-state model is shown to be qualitatively different in vacuum and in solvents. Particularly, in the vacuum case, the difference between ground and excited state dipole moments goes to zero for a vanishing BLA, which is not true in the presence of an aqueous medium. In the aqueous medium, an opposing behavior of the parameters involved in the two-state model results in an almost constant first hyperpolarizability with varying BLA parameter.

Method for Computing the Nonlinear Refractive Index via Keldysh Theory

Abstract: A procedure for computation of the nonlinear refractive index of a gaseous medium from the intensity dependence of the ionization rate is reported. The ionization rate is calculated from Keldysh theory via a Kramers-Kronig transform. Peremolov-Popov-Terent'ev (PPT) theory is analyzed in the perturbative limit of multiphoton ionization for a completely analytical expression for the nonlinear refractive index. The method requires knowledge of only the particle density and the ionization energy of the gas. Example calculations are performed for the inert gases and compared to experimental data and atomic model calculations for the hyperpolarizability of the respective media. Excellent agreement between reference data and the computed values derived from the Kramers-Kronig transform is found in the visible and infrared spectral range. Additionally, higher-order nonlinear refraction is discussed.

Molecular structure, vibrational spectroscopic, first-order hyperpolarizability and HOMO, LUMO studies of 3-hydroxy-2-naphthoic acid hydrazide

Abstract: The Fourier-transform infrared spectrum of 3-hydroxy-2-naphthoic acid hydrazide (3H2NAH) was recorded in the region 4000–400 cm−1. The Fourier-transform Raman spectrum of 3H2NAH was also recorded in the region 3500–10 cm−1. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 3H2NAH were carried out by density functional theory (DFT/B3LYP) method with 6-31G(d,p) as basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the electric dipole moment (µ) and the first-order hyperpolarizability (β) of the investigated molecule were computed using ab initio quantum mechanical calculations. The UV spectrum was measured in ethanol solution. The calculation results also show that the 3H2NAH molecule might have microscopic nonlinear optical (NLO) behavior with non-zero values. A detailed interpretation of the infrared and Raman spectra of 3H2NAH is also reported based on total energy distribution (TED). The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The theoretical FT-IR and FT-Raman spectra for the title molecule have also been constructed. Copyright © 2009 John Wiley & Sons, Ltd.

Calculation of the first static hyperpolarizability tensor of three-dimensional periodic compounds with a local basis set: A comparison of LDA, PBE, PBE0, B3LYP, and HF results.

Abstract: The computational scheme for the evaluation of the second-order electric susceptibility tensor in periodic systems, recently implemented in the CRYSTAL code within the coupled perturbed Hartree-Fock (HF) scheme, has been extended to local-density, gradient-corrected, and hybrid density functionals (coupled-perturbed Kohn-Sham) and applied to a set of cubic and hexagonal semiconductors. The method is based on the use of local basis sets and analytical calculation of derivatives. The high-frequency dielectric tensor (epsilon(infinity)) and second-harmonic generation susceptibility (d) have been calculated with hybrid functionals (PBE0 and B3LYP) and the HF approximation. Results are compared with the values of epsilon(infinity) and d obtained from previous plane-wave local density approximation or generalized gradient approximation calculations and from experiment. The agreement is in general good, although comparison with experiment is affected by a certain degree of uncertainty implicit in the experimental techniques.

How the Number and Location of Lithium Atoms Affect the First Hyperpolarizability of Graphene

Abstract: How do the number and location of lithium atoms affect the first hyperpolarizability (βtot) of graphene? In this paper, based on pentacene, a series of graphene (multi)lithium salts Lin@pentacene (n = 1, 2, 3, 4, 5, and 6) have been designed to answer this question. βtot obviously increases stepwise with an increase in the number of lithium atoms: 1369−1843 for Li@pentacence < 3510−4081 for Li2@pentacence < 6933−7934 for Li3@pentacence < 11 188−12 145 for Li4@pentacence < 14 904 au for Li5@pentacence, which are much larger than pentacence. This pattern suggests that the lithium salt effect on the first hyperpolarizability is very large. Unexpectedly, when an additional lithium atom is doped into the graphene multilithium salt Li5@pentacence, which leads to Li6@pentacence, the βtot value dramatically increases to a value of 4 501 764 au with a remarkable increase of 302-fold in contrast to Li5@pentacence. On the other hand, when the number of lithium atoms is equal, the location of lithium atoms also affec...

First hyperpolarizability dispersion of the octupolar molecule crystal violet: multiple resonances and vibrational and solvation effects.

Abstract: The first hyperpolarizability (β) dispersion curve is measured for the first time for an octupolar nonlinear optical (NLO) molecule (crystal violet, CV) and modeled theoretically, yielding an in-depth understanding of the electronic structure and vibronic and solvation effects on such octupolar conjugated systems. Tunable wavelength hyper-Rayleigh scattering (HRS) measurements were performed on this prototypical octupolar molecule in the broad fundamental wavelength range of 620−1580 nm, showing significant shortcomings of the commonly used β dispersion models. Three well-separated β resonances involving the lowest-energy state and several higher excited states are clearly observed, including a significant contribution from a nominally one-photon forbidden transition. The experimental results for second-harmonic wavelengths above 330 nm are successfully modeled by means of a vibronically coupled essential-state description for octupolar chromophores, developed by Terenziani et al. (J. Phys. Chem. B 2008, ...

Molecular structure, spectroscopic (FTIR, FTIR gas phase, FT-Raman) first-order hyperpolarizability and HOMO–LUMO analysis of 4-methoxy-2-methyl benzoic acid

Abstract: Vibrational spectral analysis was carried out for 4-methoxy-2-methyl benzoic acid (4M2MBA) by using Fourier transform infrared (FT-IR) (solid, gas phase) and FT-Raman spectroscopy in the range of 400–4000 and 10–3500 cm−1 respectively. The effects of molecular association through OH···O hydrogen bonding have been described by the single dimer structure. The theoretical computational density functional theory (DFT) and Hatree-Fock (HF) method were performed at 6–311++G(d,p) levels to derive the equilibrium geometry, vibrational wavenumbers, infrared intensities and Raman scattering activities. The scaled theoretical wavenumbers were also shown to be in good agreement with experimental data. The first-order hyperpolarizability (β0) of this novel molecular system and related properties (β, α0 and Δα) of 4M2MBA are calculated using the B3LYP/cc-pvdz basis set, based on the finite-field approach. A detailed interpretation of the infrared and Raman spectra of 4M2MBA is reported. The theoretical spectrograms for FT-IR and FT-Raman spectra of the title molecule were also constructed and compared with the experimental one. Copyright © 2010 John Wiley & Sons, Ltd.

Solvent Effects on the Second-Order Nonlinear Optical Responses in the Keto−Enol Equilibrium of a 2-Hydroxy-1-naphthaldehyde Derivative

Abstract: Hyper-Rayleigh scattering experiments and ab initio calculations are combined to investigate the solvent effects on the second-order nonlinear optical responses of a 2-hydroxy-1-naphthaldehyde derivative that commutes between an enol and a keto form. Different binary mixtures of cyclohexane and ethanol are used to displace the tautomeric equilibrium. We show that increasing the solvent polarity increases the population of the keto form, shifts the lowest energy band of the absorption spectra to lower energy, and gives rise to a large enhancement of the first hyperpolarizability. Using theoretical calculations, the global solvent effect on the latter is shown to originate from both the displacement of the tautomeric equilibrium and the modification of the second-order nonlinear optical response of the individual tautomeric forms.

Push–pull electron effects of the complexant in a Li atom doped molecule with electride character: a new strategy to enhance the first hyperpolarizability

Abstract: Differing from the reported strategy of push or pull electron effects of the complexant, a new strategy of the combination effects of both push and pull electrons of the complexant to enhance the first hyperpolarizability is performed with two Li atom doped complexants with a pair of difluorophenyl subunit rings. Large variance of the static first hyperpolarizabilities (β0) are exhibited at the MP2/6-311++G(d,p) level. The order of the β0 values is 2.9 ×102 (complexant UD) ≪ 5.9 × 103 (LL) < 1.9 × 104 (H-L) < 2.3 × 104 (HF-L) < 3.2 × 104 (L-L) < 7.8 × 105 a.u. (HF-LF). It is found that HF-LF with the edge-type push–pull electronic effect of the complexant has the largest β0. The edge-type push–pull electronic effect brings a 2700 times increase in the β0 from the UD to HF-LF structure. It shows that the push–pull electronic effect is a highly effective strategy to enhance the β0 value. The β0 (7.8 × 105 a.u.) of the HF-LF is considerable, due to the small ΔE and the very large Δμ (18.085 a.u.), which comes from the corresponding long-range charge transfer transition. It is interesting that a pair of subunit rings of the complexant may have different electronic effects. In H-L and HF-LF, the left ring with a longer distance between Li and the subunit ring exhibits a push electronic effect, while the right ring with the shorter distance exhibits a pull electronic effect. This work may contribute to the development of potential high-performance nonlinear optical materials.

Reduced dimensionality in organic electro-optic materials: theory and defined order.

Abstract: Identification of electronic intermolecular electrostatic interactions that can significantly enhance poling-induced order is important to the advancement of the field of organic electro-optics. Here, we demonstrate an example of such improvement achieved through exploitation of the interaction of coumarin pendant groups in chromophore-containing macromolecules. Acentric order enhancement is explained in terms of lattice-symmetry effects, where constraint of orientational degrees of freedom alters the relationship between centrosymmetric and acentric order. We demonstrate both experimentally and theoretically that lattice dimensionality can be defined using the relationship between centrosymmetric order and acentric order. Experimentally: Acentric order is determined by attenuated total reflection measurement of electro-optic activity coupled with hyper-Rayleigh scattering measurement of molecular first hyperpolarizability, and centrosymmetric order is determined by the variable angle polarization referenced absorption spectroscopy method. Theoretically: Order is determined from statistical mechanical models that predict the properties of soft condensed matter.

Basis set effects on the hyperpolarizability of CHCl3: Gaussian-type orbitals, numerical basis sets and real-space grids.

Abstract: Calculations of the hyperpolarizability are typically much more difficult to converge with basis set size than the linear polarizability. In order to understand these convergence issues and hence obtain accurate ab initio values, we compare calculations of the static hyperpolarizability of the gas-phase chloroform molecule (CHCl3) using three different kinds of basis sets: Gaussian-type orbitals, numerical basis sets, and real-space grids. Although all of these methods can yield similar results, surprisingly large, diffuse basis sets are needed to achieve convergence to comparable values. These results are interpreted in terms of local polarizability and hyperpolarizability densities. We find that the hyperpolarizability is very sensitive to the molecular structure, and we also assess the significance of vibrational contributions and frequency dispersion.

Synthesis, characterization and studies on the nonlinear optical parameters of hydrazones

Abstract: Three hydrazones, 2-(4-methylphenoxy)- N ′-[(1E)-(4-nitrophenyl)methylene]acetohydrazide (compound-1), 2-(4-methylphenoxy)- N ′-[(1E)-(4-methylphenyl)methylene]acetohydrazide ((compound-2) and N ′-{(1E)-[4-(dimethylamino)phenyl]methylene}-2-(4-ethylphenoxy) acetohydrazide(compound-3) were synthesized and their third order nonlinear optical properties were investigated using a single beam z-scan technique with nanosecond laser pulses at 532 nm. Open aperture data obtained from the three compounds indicates two photon absorption at this wavelength. The nonlinear refractive index n 2 , the nonlinear absorption coefficient β , the magnitude of the effective third order susceptibility χ (3) , the second order hyperpolarizability γ h and the coupling factor ρ have been estimated. The values obtained are comparable with the values obtained for 4-methoxy chalcone derivatives and dibenzylidene acetone derivatives. Among the compounds studied, compounds-1 and 3 exhibited the better optical power limiting behaviour at 532 nm. Our studies suggest that compounds-1, 2 and 3 are potential candidates for optical device applications such as optical limiters and optical switches.

Predicting the Frequency Dispersion of Electronic Hyperpolarizabilities on the Basis of Absorption Data and Thomas−Kuhn Sum Rules

Abstract: Successfully predicting the frequency dispersion of electronic hyperpolarizabilities is an unresolved challenge in materials science and electronic structure theory. We show that the generalized Thomas-Kuhn sum rules, combined with linear absorption data and measured hyperpolarizability at one or two frequencies, may be used to predict the entire frequency-dependent electronic hyperpolarizability spectrum. This treatment includes two- and three-level contributions that arise from the lowest two or three excited electronic state manifolds, enabling us to describe the unusual observed frequency dispersion of the dynamic hyperpolarizability in high oscillator strength M-PZn chromophores, where (porphinato)zinc(II) (PZn) and metal(II)polypyridyl (M) units are connected via an ethyne unit that aligns the high oscillator strength transition dipoles of these components in a head-to-tail arrangement. We show that some of these structures can possess very similar linear absorption spectra yet manifest dramatically different frequency-dependent hyperpolarizabilities, because of three-level contributions that result from excited state-to-excited state transition dipoles among charge polarized states. Importantly, this approach provides a quantitative scheme to use linear optical absorption spectra and very limited individual hyperpolarizability measurements to predict the entire frequency-dependent nonlinear optical response.

Fluorinated β-Diketonate Diglyme Lanthanide Complexes as New Second-Order Nonlinear Optical Chromophores: The Role of f Electrons in the Dipolar and Octupolar Contribution to Quadratic Hyperpolarizability

Abstract: The second-order nonlinear optical (NLO) properties of [Ln(hfac)(3)(diglyme)] (hfac = hexafluoroacetylacetonate; diglyme = bis(2-methoxyethyl)ether; Ln = La, Ce, Pr, Sm, Eu, Gd, Er, Lu) complexes have been investigated by a combination of electric-field second harmonic generation (EFISH) and harmonic light scattering (HLS) techniques, providing evidence for the relevant role of f electrons in tuning the second-order NLO response dominated by the octupolar contribution. These lanthanide NLO chromophores allow a clean valuation of the influence of f electrons on the quadratic hyperpolarizability and on its dipolar and octupolar contributions. Molecular quadratic hyperpolarizability values measured by the EFISH method, beta(EFISH), initially increase rapidly with the number of f electrons, the value for the Gd complex being 11 times that of the La complex, whereas this increase is much lower for the last seven f electrons, the beta(EFISH) value of the Lu complex being only 1.2 times that of the Gd complex. The increase of beta(HLS), which is dominated by an octupolar contribution, is much lower along the Ln series. Remarkably, the good beta(HLS) values of these simple systems, well known for their luminescence properties, are reached at no cost of transparency.

Electronic and vibrational contributions to first hyperpolarizability of donor-acceptor-substituted azobenzene.

Abstract: In this study we report on the electronic and vibrational (hyper)polarizabilities of donor–acceptor-substituted azobenzene. It is observed that both electronic and vibrational contributions to the electric dipole first hyperpolarizability of investigated photoactive molecule substantially depend on the conformation. The contributions to the nuclear relaxation first hyperpolarizability are found to be quite important in the case of two considered isomers (cis and trans). Although the double-harmonic term is found to be the largest in terms of magnitude, it is shown that the total value of the nuclear relaxation contribution to vibrational first hyperpolarizability is a result of subtle interplay of higher-order contributions. As a part of the study, we also assess the performance of long-range-corrected density functional theory in determining vibrational contributions to electric dipole (hyper)polarizabilities. In most cases, the applied long-range-corrected exchange-correlation potentials amend the drawbacks of their conventional counterparts.

Basis set effects on the hyperpolarizability of CHCl_3: Gaussian-type orbitals, numerical basis sets and real-space grids

Abstract: Calculations of the hyperpolarizability are typically much more difficult to converge with basis set size than the linear polarizability. In order to understand these convergence issues and hence obtain accurate ab initio values, we compare calculations of the static hyperpolarizability of the gas-phase chloroform molecule (CHCl_3) using three different kinds of basis sets: Gaussian-type orbitals, numerical basis sets, and real-space grids. Although all of these methods can yield similar results, surprisingly large, diffuse basis sets are needed to achieve convergence to comparable values. These results are interpreted in terms of local polarizability and hyperpolarizability densities. We find that the hyperpolarizability is very sensitive to the molecular structure, and we also assess the significance of vibrational contributions and frequency dispersion.

Theoretical studies of surface enhanced hyper-Raman spectroscopy: The chemical enhancement mechanism

Abstract: Hyper-Raman spectra for pyridine and pyridine on the surface of a tetrahedral 20 silver atom cluster are calculated using static hyperpolarizability derivatives obtained from time dependent density functional theory. The stability of the results with respect to choice of exchange-correlation functional and basis set is verified by comparison with experiment and with Raman spectra calculated for the same systems using the same methods. Calculated Raman spectra were found to match well with experiment and previous theoretical calculations. The calculated normal and surface enhanced hyper-Raman spectra closely match experimental results. The chemical enhancement factors for hyper-Raman are generally larger than for Raman (102−104 versus 101−102). Integrated hyper-Raman chemical enhancement factors are presented for a set of substituted pyridines. A two-state model is developed to predict these chemical enhancement factors and this was found to work well for the majority of the molecules considered, providing a rationalization for the difference between hyper-Raman and Raman enhancement factors.