Showing papers on "Hyperpolarizability published in 2003"

Combining second-order Jahn-Teller distorted cations to create highly efficient SHG materials: synthesis, characterization, and NLO properties of BaTeM2O9 (M = Mo6+ or W6+).

Abstract: Two new oxides, BaTeMo2O9 and BaTeW2O9, have been synthesized, by standard solid-state techniques, that have strong SHG intensities of approximately 600 x SiO2, on the order of LiNbO3. Both materials contain cations susceptible to second-order Jahn-Teller (SOJT) distortions, resulting in asymmetric coordination environments. The SOJT distortion polarizes the M6+-O and Te4+-O bonds. Equally importantly, these polarizations constructively add, resulting in the large SHG responses. Powder SHG measurements on BaTeM2O9 (M = Mo6+ or W6+) indicated that both materials are phase-matchable and have a deffexp of 28 and 22 pm/V, respectively. Using bond hyperpolarizability values (beta's) of 130 x 10-40 and 305 x 10-40 m4/V for Te4+-O and Mo6+-O respectively, we calculate a deffcalc of 20pm/V for BaTeMo2O9. In addition, through the powder SHG measurements, we are able to give a more reasonable value for beta(W6+-O), 230 x 10-40 m4/V. This value is consistent with the smaller polarizability and magnitude of the intra-octahedral distortion of W6+ compared with Mo6+.

The Influence of σ and π Acceptors on Two‐Photon Absorption and Solvatochromism of Dipolar and Quadrupolar Unsaturated Organic Compounds

Abstract: Two-photon absorption cross sections delta and solvatochromic properties were determined for a series of quadrupolar and dipolar compounds by using femtosecond excitation in the spectral range between 710 and 960 nm. The compounds investigated were distyrylbenzenes and polyenes bearing appropriate pi or sigma acceptors. The delta values for the centrosymmetric compounds trans, trans- 1,4-bis[2-(2',5'-dihexyloxy)phenylethenyl]-2,3,5,6-tetrafluorobenzene (6), trans, trans-1,4-bis[2-(4'-dibutylamino)phenylethenyl]- 2,3,5,6-tetrafluorobenzene (2), trans, trans-1,4-bis[2-(4'dimethylamino)phenylbutadienyl]- 2,3,5,6-tetrafluorobenzene (7), trans,-trans-1,4-bis[2-(4'-dimethylamino)phenylethenyl]2,5- dicyanobenzene (4) and trans,trans-1,4-bis[2-(4'-dimethylamino)phenylethenyl]-2- propylsulfonyl-5-(2-ethylhexyl)sulfonylbenzene (3) are on the order of 600, 1400, 1700, 3000, and 4100 x 10(-50) cm4 s photon-1, respectively. The corresponding dipolar compounds trans-2-(4'- dimethylaminophenyl)ethenyl-2,3,4,5,6-pentafluorobene (8), trans-4-(4'-dimethylaminophenyl)butadienyl-2,3,4,5,6-pentafluorobenzene (9), trans-6-(4'-dimethylaminophenyl)hexatrienyl-2,3,4,5,6- pentafluorobenzene (10) were additionally investigated. All centrosymmtric compounds are good fluorescent materials, while the dipolar chromophores 8-10 exhibit low fluorescence quantum yields. Solvatochromism was also observed for the fluorophores 2-10 as a result of intramolecular charge transfer (ICT). Furthermore, a reasonable correlation was obtained between measured and calculated delta. Quantum chemical calculations were performed by using the INDO Hamiltonian with a MRDCI scheme. The results show that the sum over states (SOS) expression for the second hyperpolarizability gamma is appropriate to describe the mechanism of two-photon absorption. Mechanistic investigations of quadrupolar compounds showed that the energy of the two-photon excited state is higher than S1.

Rational design of organic electro-optic materials

Abstract: Quantum mechanical calculations are used to optimize the molecular first hyperpolarizability of organic chromophores and statistical mechanical calculations are used to optimize the translation of molecular hyperpolarizability to macroscopic electro-optic activity (to values of greater than 100 pm V−1 at telecommunications wavelengths). Macroscopic material architectures are implemented exploiting new concepts in nanoscale architectural engineering. Multi-chromophore-containing dendrimers and dendronized polymers not only permit optimization of electro-optic activity but also of auxiliary properties including optical loss (both absorption and scattering), thermal and photochemical stability and processability. New reactive ion etching and photolithographic techniques permit the fabrication of three-dimensional optical circuitry and the integration of that circuitry with semiconductor very-large-scale integration electronics and silica fibre optics. Electro-optic devices have been fabricated exploiting stripline, cascaded prism and microresonator device structures. Sub-1 V drive voltages and operational bandwidths of greater than 100 GHz have been demonstrated. Both single-and double-ring microresonators have been fabricated for applications such as active wavelength division multiplexing. Free spectral range values of 1 THz and per channel modulation bandwidths of 15 GHz have been realized permitting single-chip data rates of 500 Gb s−1. Other demonstrated devices include phased array radar, optical gyroscopes, acoustic spectrum analysers, ultrafast analog/digital converters and ultrahigh bandwidth signal generators.

A distinctive example of the cooperative interplay of structure and environment in tuning of intramolecular charge transfer in second-order nonlinear optical chromophores.

Abstract: The strongly enhanced coop- erative influence of medium polarity and organic structural design on the first hyperpolarizability of a novel family of highly polarizable azinium-(CHCH- thienyl)-dicyanomethanido chromo- phores 1 ± 3 is described. The dyes can be efficiently synthesized by regioselec- tive protonation/alkylation of the corre- sponding bidentate anion precursors. Consecutive annelation of the pyridyl ring of 1 (pyridine quinoline acri- dine) and medium polarity effects are responsible for an extraordinarily varia- ble range of intramolecular charge transfer (ICT), leading to a large set of -electron distribution patterns. Ac- cordingly, systems with remarkably dif- ferent zwitterionic/quinoid character in the ground and excited states present values in a broad range, eventually switching from negative to positive. Our investigation is based on a combi- nation of experimental (UV/Vis spec- troscopy, multinuclear NMR spectrosco- py, and electrooptical absorption meas- urements) and computational (ab initio) approaches. It is shown that: 1) and are dramatically influenced, even by orders of magnitude, by a complex, non-monotonic interplay of structure and medium action, which in turn affects molecular ICT and bond length alterna- tion (BLA), 2) the computations, vali- dated by different experimental data, are to be recommended as an extremely useful tool in the search for a greatly improved set of molecular nonlinear optical (NLO) responses (in the case of 1 ± 3 they show that such conditions may be attained only in a narrow and limited range of dielectric constants in which the annelation effect operates most effi- ciently), and 3) the search for the most favorable molecular NLO response of a highly polarizable chromophore both in solution and in solid matrices should simultaneously take into account not only the molecular design supplemented by annelation effects but also the polar- ity of the medium.

Accurate electric multipole moment, static polarizability and hyperpolarizability derivatives for N2

Abstract: We report accurate values of the electric moments, static polarizabilities, hyperpolarizabilities and their respective derivatives for N2. Our values have been extracted from finite-field Moller–Pleset perturbation theory and coupled cluster calculations performed with carefully designed basis sets. A large [15s12p9d7f] basis set consisting of 290 CGTF is expected to provide reference self-consistent-field values of near-Hartree–Fock quality for all properties. The Hartree–Fock limit for the mean hyperpolarizability is estimated at γ=715±4e4a04Eh−3 at the experimental bond length Re=2.074 32a0. Accurate estimates of the electron correlation effects were obtained with a [10s7p6d4f] basis set. Our best values are Θ=−1.1258ea02 for the quadrupole and Φ=−6.75ea04 for the hexadecapole moment, ᾱ=11.7709 and Δα=4.6074e2a02Eh−1 for the mean and the anisotropy of the dipole polarizability, C=41.63e2a04Eh−1 for the mean quadrupole polarizability and γ=927e4a04Eh−3 for the dipole hyperpolarizability. The latter v...

Nonlinear optical (NLO) properties of novel organometallic complexes: high accuracy density functional theory (DFT) calculations

Abstract: Density Functional Theory (DFT) calculations are performed to determine the accurate first static hyperpolarizability ( β ) of nitrogen bound low valent (M 0 ) group six metal carbonyls representing the class of chromophores displaying weak coupling between donor and acceptor. The nonlinear optical (NLO) response of this class of second-order NLO metal complexes is dominated by metal-to-ligand charge transfer excitations involving low lying, filled metal-carbonyl based orbitals and empty π ∗ orbitals of nitrogen bound ligand. We report novel organometallic systems with high β values. The full geometry optimizations of chromium and tungsten carbonyls were performed using DFT method at B3LYP/LanL2DZ level of theory using gaussian 98W. The calculations of the first hyperpolarizability ( β ) of these complexes were performed at the same level of theory. The calculated values of β were compared with available data in the literature. To understand the variation of β in these complexes, we examined the molecular HOMO and molecular LUMO generated via gaussian 98W. The present study concludes that these organometallic systems may contribute to the development of NLO materials.

Large Off-Diagonal Contribution to the Second-Order Optical Nonlinearities of Λ-Shaped Molecules

Abstract: The diagonal and off-diagonal tensor components of the first hyperpolarizability of a series of A-shaped molecules are compared by means of ab initio and semiempirical molecular orbital calculations. The calculated results are rationalized using expressions derived from a simple valence-bond charge-transfer model in which one ground and two excited state are described as a combination of one valence-bond (VB) and two charge-transfer (CT) states. In addition to the CT character, the angle (2θ) between the two donor (D)/acceptor (A) branches is a key parameter to determine the relative magnitudes between the β x x z and β z z z components. In the VB-2CT model, β x x z presents a maximum value for 2θ = 109.47°, whereas β x x z and μ z have the same sign. On the other hand, β z z z decreases monotonically with θ, and its variations with the CT character follow a curve with two extrema like for one-dimensional D/A chromophores. The ab initio and semiempirical calculations as well as the VB-2CT model show that A-shaped molecules with large first hyperpolarizability and specific η = β x x z /β z z z can be designed in order to build phase-matchable second-harmonic generation crystals.

First-principles calculations of structural, electronic, vibrational, and magnetic properties of C60 and C48N12: A comparative study

Abstract: The structural, electronic, vibrational, and magnetic properties of the C48N12 azafullerene and C60 are comparatively studied from the first-principles calculations. Full geometrical optimization and Mulliken charge analysis are performed. Electronic structure calculations of C48N12 show that the highest occupied molecular orbital (HOMO) is a doubly degenerate level of ag symmetry and the lowest unoccupied molecular orbital (LUMO) is a nondegenerate level of au symmetry. The calculated binding energy per atom and HOMO-LUMO energy gap of C48N12 are about 1 eV smaller than those of C60. Because of electron correlations, the HOMO-LUMO gap decreases about 5 eV and the binding energy per atom increases about 2 eV. The average second-order hyperpolarizability of C48N12 is about 55% larger than that of C60. Our vibrational frequency analysis predicts that C48N12 has 58 infrared-active and 58 Raman-active vibrational modes. Two different methods for calculating nuclear magnetic shielding tensors of C60 and C48N12...

Organometallic complexes for nonlinear optics. 33. Electrochemical switching of the third-order nonlinearity observed by simultaneous femtosecond degenerate four-wave mixing and pump-probe measurements

Abstract: The molecular inorganic compound 1,3,5-{trans-[RuCl(dppe)2]C≡C-4-C 6 H 4 C≡C} 3 C 6 H 3 (1) is reversibly oxidized in solution using an optically transparent thin-layer electrochemical (OTTLE) cell, the oxidation to 1 3 + resulting in the appearance of a strong absorption band at 11 200 cm - 1 in contrast to 1, which is optically transparent at frequencies below 20 000 cm - 1 . This linear electrochromic behavior is accompanied by third-order nonlinear optical electrochromic behavior, which has been probed by a combination of femtosecond degenerate four-wave mixing (DFWM) and pump-probe experiments at 12 500 cm - 1 . DFWM studies of 1 and 1 3 + reveal an order of magnitude increase in the hyperpolarizability, ‖γ‖, upon oxidation with ‖γ‖ values of 2000 × 10 - 3 6 esu and 20 000 x 10 - 3 6 esu, respectively; the DFWM signal of the latter is dominated by a delayed response (relaxation time ca. 1 ps). The transient absorption (TA) data for 1 reveal efficient two-photon absorption (σ 2 10 3 GM), whereas the TA data for 1 3 + reveal saturable absorption (decay time ca. 1 ps). The switching of third-order nonlinearity in the 1/1 3 + pair represents the first demonstration of femtosecond time-scale processes being responsible for nonlinear electrochromism.

Size and Electric Dipole (Hyper)polarizability in Small Cadmium Sulfide Clusters: An ab Initio Study on (CdS)n, n = 1, 2, and 4

Abstract: We report conventional ab initio and B3LYP/DFT calculations for the static electric (hyper)polarizability of small CdS clusters. Our results indicate a strong reduction of the (per atom) mean dipole polarizability with size, supporting the recent LDA findings by Troparevsky and Chelicowsky [J. Chem. Phys. 2001, 114, 943]. The same trend is observed for the second dipole hyperpolarizability. The computational complexity of the determination of the electric properties varies considerably with cluster size. B3LYP and conventional ab initio values are not in good agreement for the monomer but the gap is drastically reduced for the dimer and the tetramer.

Solvent dependence of solvatochromic shifts and the first hyperpolarizability of para-nitroaniline: A nonmonotonic behavior

Abstract: Solvent dependence of the electronic structure and nonlinear optical properties of the para-nitroaniline (pNA) molecule on the polarity of the solutions has been studied using the polarizable continuum model in combination with the hybrid density functional theory. With a supermolecular approach, specific hydrogen bonding effects have also been fully considered. Good agreement between theory and experiments are obtained for both solvatochromic shifts of the charge transfer state and the solvent-induced first hyperpolarizability of pNA.

Ultrafast nonresonant third-order optical nonlinearity of fullerene-containing polyurethane films at telecommunication wavelengths

Abstract: High-optical-quality polyurethane films containing a high load of (60)fullerene (C60) were prepared by reaction of the hydroxy-containing C60 and triisocyanate with the goal of obtaining enhanced nonresonant third-order optical nonlinearity. Optical nonlinearity was measured using the Z-scan technique in the wavelength range 1150–1600 nm. This revealed a positive Kerr coefficient with nonresonant n2 equal to 2.0(±0.6)×10−3 cm2/GW and excellent linear-absorption and nonlinear-absorption figures of merit at 1550 nm. The technique reported herein is a new approach to obtain fullerene films with the capacity to realize a high number density of C60 moieties. These resulted in more than 2 orders of enhancement in the third-order susceptibility over recently reported C60 sol and gel, and an enlarged second-order hyperpolarizability resulting from further enhanced charge transfer processes.

Nonlinear optical response properties of molecules in condensed phases using the coupled cluster/dielectric continuum or molecular mechanics methods

Abstract: In this work we present the first derivation and implementation of quadratic response theory as described within the combined coupled cluster/dielectric continuum (CC/DC) and the combined coupled cluster/molecular mechanics (CC/MM) methods. In the former approach, the solvent is represented as a homogeneous dielectric medium, whereas the latter approach accounts for the discrete nature of the solvent molecules. Furthermore, the CC/MM model includes polarization effects. The CC models implemented are CC2 and CCSD. Sample calculations are performed on liquid water and solvent effects on the first hyperpolarizability of water are found to be significant. In particular, the experimental observed sign change in the first hyperpolarizability of water is reproduced in both the CC/DC and CC/MM descriptions though larger basis sets are needed in the former approach.

Push–pull porphyrins as non-linear optical materials: ab initio quantum chemical calculations

Abstract: We report accurate ab initio quantum chemical calculations of the first static hyperpolarizability ( β ) of porphyrin systems containing porphyrin moiety as the electron donor and quinone and pyromellitimide as the electron acceptors separated by a spacer which influence the electronic communication between donor and acceptor. Geometries of all porphyrin molecules were optimised at the Hartree–Fock level with STO-3G minimal basis set and with the 3-21G split valence basis set using gaussian 98W. In addition to non-linear properties, polarizabilities ( α ) of these molecules are also reported. The calculated values of β were compared with β of tertraphenyl porphyrin derivatives reported in the literature. We examine the HOMO and LUMO generated via gaussian 98W in order to explain the variation of β in these highly conjugated molecular systems. The study suggested that these porphyrin molecules in general may have potential applications in the development of non-linear optical materials.

A discrete solvent reaction field model for calculating frequency-dependent hyperpolarizabilities of molecules in solution

Abstract: We present a discrete solvent reaction field (DRF) model for the calculation of frequency-dependent hyperpolarizabilities of molecules in solution. In this model the solute is described using density functional theory (DFT) and the discrete solvent molecules are described with a classical polarizable model. The first hyperpolarizability is obtained in an efficient way using time-dependent DFT and the (2n+1) rule. The method was tested for liquid water using a model in which a water molecule is embedded in a cluster of 127 classical water molecules. The frequency-dependent first and second hyperpolarizabilities related to the electric field induced second harmonic generation (EFISH) experiment, were calculated both in the gas phase and in the liquid phase. For water in the gas phase, results are obtained in good agreement with correlated wave function methods and experiments by using the so-called shape-corrected exchange correlation (xc)-potentials. In the liquid phase the effect of using asymptotically c...

Resonance hyper-Raman scattering from conjugated organic donor-acceptor "push-pull" chromophores with large first hyperpolarizabilities.

Abstract: Resonance hyper-Raman spectra have been obtained using 1064 nm excitation for several electron donor−acceptor-substituted, π-conjugated “push−pull” molecules that have large second harmonic hyperpolarizabilities. The hyper-Raman spectra are nearly identical to the resonance Raman spectra measured with 532 nm excitation. This indicates that both the second harmonic hyperpolarizability and the linear absorption are dominated by the same, single electronic transition that is both one- and two-photon allowed. Comparison of resonance Raman and resonance hyper-Raman spectra is proposed as an experimental test of the common two-electronic-state model for the first hyperpolarizability.

A Dipole Interaction Model for the Molecular Second Hyperpolarizability

Abstract: A dipole interaction model (IM) for calculating the molecular second hyperpolarizability, γ, of aliphatic and aromatic molecules has been investigated. The model has been parametrized from quantum chemical calculations of γ at the self-consistent field (SCF) level of theory for 72 molecules. The model consists of three parameters for each element p: an atomic polarizability, an atomic second hyperpolarizability, and an atomic parameter, Φp, describing the width of the atomic charge distribution. The Φp parameters are used for modeling the damping of the interatomic interactions. Parameters for elements H, C, N, O, F, and Cl were determined, and typical differences between the molecular γ derived from quantum chemical calculations and from the IM are below 30% and on average around 10%. As a preliminary test, the dipole interaction model was applied to the following molecular systems not included in the training set: the urea molecule, linear chains of urea molecules, and C60. For these molecules deviati...

Chiral and Achiral Contributions to Sum-Frequency Generation from Optically Active Solutions of Binaphthol†

Abstract: The nonlinear sum- and difference-frequency generation spectroscopies can be probes of molecular chirality in optically active systems. We present a tensorial analysis of the chirality-specific electric-dipolar sum-frequency-generation susceptibility and the achiral electric-quadrupolar and magnetic-dipolar nonlinearities at second order in isotropic media. The chiral and achiral contributions to the sum-frequency signal from the bulk of optically active solutions of 1,1‘-bi-2-naphthol (2,2‘-dehydroxy-1,1‘-binaphthyl) can be distinguished, and the former dominates. Ab initio computations reveal the dramatic resonance enhancement that the isotropic component of the electric-dipolar three-wave mixing hyperpolarizability experiences. Away from resonance its magnitude rapidly decreases, asunlike the vector componentit is zero in the static limit. The dispersion of the first hyperpolarizability is computed by a configuration interaction singles sum-over-states approach with explicit regard to the Franck−Condon...

Is the Hyperpolarizability of Cu2 Negative? A Study of Basis Set and Electron Correlation Effects

Abstract: The dipole (hyper)polarizability of the copper dimer has been obtained from conventional ab initio and density functional theory calculations. A very large (23s16p12d6f) basis set consisting of 346 Gaussian-type functions is thought to provide reference results of near-Hartree−Fock quality for all properties. We obtain ᾱ = 102.54 and Δα = 41.89 for the mean and the anisotropy of the dipole polarizability (ααβ/e2a02Eh-1). For the Cartesian components and the mean of the hyperpolarizability (10-3γαβγδ/e4a04Eh-3) we obtain γzzzz = 309, γxxxx = 209, γxxzz = 87, and γ = 244. Electron correlation lowers ᾱ but increases considerably Δα. The effect on the hyperpolarizability is enormous, as the longitudinal component γzzzz is drastically reduced, while γxxxx and γxxzz are nearly halved. At the CCSD(T) level of theory with a [7s6p6d2f] basis set we obtain ᾱ = 93.82, Δα = 67.09 and γzzzz = 18, γxxxx = 101, γxxzz = 35, and γ = 86. The dipole polarizability varies as [ᾱ(R) − ᾱ(Re)]/e2a02Eh-1 = 28.09(R − Re) + 4.69(...

Investigation of NLO properties of substituted (M)-tetrathia-[7]-helicenes by semiempirical and DFT methods

Abstract: In this article, we propose a theoretical study of static and dynamic polarizability α, first hyperpolarizability β, and second hyperpolarizability γ of substituted (M)-tetrathia-[7]-helicenes. Both a semiempirical approach, in the case of static and dynamic properties, and density functional theory, in the case of static electric properties, were used. The nonlinear optical (NLO) properties of a set of 10 molecules were investigated to predict the couple of donor–acceptor substituents that could best enhance the optical properties of (M)-tetrathia-[7]-helicene. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

Saturation of the Third-Order Polarizability of Carbon Nanotubes Characterized by a Dipole Interaction Model

Abstract: An atomic dipole interaction model has been used for calculating the second hyperpolarizability of carbon nanotubes on a length scale up to 75 nm. It is demonstrated that an atomistic representation of mesoscale systems such as nanotubes can be used to obtain a cubic response property up to a size of the system where the property scales linearly with increasing size. In particular, it demonstrates that atomistic models are useful also for designing nonlinear molecular materials, where local modifications may give large macroscopic contributions. The saturation length has been calculated for carbon nanotubes. It is found that carbon nanotubes are comparable to conjugated polymers with respect to the magnitude of the second hyperpolarizability and are therefore very promising candidates for future nonlinear optical materials.