Showing papers on "Hyperpolarizability published in 1997"

Large Molecular Third-Order Optical Nonlinearities in Polarized Carotenoids

Abstract: Garito and co-workers have suggested a mechanism to dramatically increase the second hyperpolarizability, γ, in linear π-electron–conjugated molecules. Polarization is introduced that leads to a difference between the dipole moments of the molecule’s ground state and excited state. Here a series of carotenoids was examined that had increasing intramolecular charge transfer (ICT) from the polyenic chain to the acceptor moiety in the ground state, and γ was measured for these compounds as a function of wavelength by third-harmonic generation. The compound with the greatest ICT exhibited a 35-fold enhancement of γ_(max)(the γ measured at the peak of the three-photon resonance) relative to the symmetric molecule β-carotene, which itself has one of the largest third-order nonlinearities known. Stark spectroscopic measurements revealed the existence of a large difference dipole moment, Δμ, between the ground and excited state. Quantum-chemical calculations underline the importance of interactions involving states with large Δμ.

Large Quadratic Hyperpolarizabilities with Donor–Acceptor Polyenes Exhibiting Optimum Bond Length Alternation: Correlation Between Structure and Hyperpolarizability

Abstract: Donor-acceptor polyenes of various lengths, and that combine aro- matic electron-donating moieties with powerful heterocyclic electron-withdraw- ing terminal groups, have been synthe- sized and characterized as efficient non- linear optical (NLO) chromophores. Their linear and nonlinear optical proper- ties have been investigated, and variations in these properties have been related to ground-state polarization (dipole p) and structure. In particular, unprecedented quadratic hyperpolarizabilities (p) have been achieved (up to p(0) =I500 x 10-30esu) by reduction of the bond- length alternation (BLA) in the polyenic chain. In each series of homologous com-

Synthesis, Characterization, Optical Spectroscopic, Electronic Structure, and Second-Order Nonlinear Optical (NLO) Properties of a Novel Class of Donor−Acceptor Bis(salicylaldiminato)nickel(II) Schiff Base NLO Chromophores

Abstract: The synthesis, characterization, thermal stability, optical spectroscopic, electronic structure, and second-order nonlinear optical (NLO) response of a series of donor−acceptor bis(salicylaldiminato)nickel(II) Schiff base complexes and the free ligand precursors are reported The effect of the metal center in such complexes is manifold: it templates the formation of acentric molecular structures, imparts high thermal stability to the chelate ring, and both “switches on” and enhances NLO response Metal complexation imparts new linear optical spectroscopic features, having metal-to-ligand charge transfer character, which are responsible for the second-order nonlinearity Moreover, the present synthetic strategy represents a novel route to inorganic NLO chromophores Solution-phase hyperpolarizability values, deduced by electric field-induced second-harmonic-generation experiments are as high as −79 × 10-30 cm5 esu-1 (hω = 092 eV) Experimental linear and nonlinear optical features are fully consistent wi

The free surface of water: molecular orientation, surface potential and nonlinear susceptibility

Abstract: The SPC/E model of water has been used to simulate the vapour–liquid interface along the orthobaric curve between 277 K and 548 K. Molecular dynamics simulations of 500 and 1000 water molecules are performed using a slab geometry with the long-range interactions calculated using the Ewald sum. The coexisting densities and the surface tension are predicted accurately over this temperature range. The model predicts different preferential orientation of the molecular dipoles on either side of the Gibbs dividing surface. The components of the second-order nonlinear susceptibility in the interface are calculated using the five independent elements of the molecular hyperpolarizability (the Kleinman relationships are not assumed). The susceptibility profiles are presented and the integrated susceptibility is positive in agreement with experiment. The temperature dependence of the components of susceptibility tensor is in reasonable agreement with experiment and in good agreement with density functional theory. T...

The role of London forces in defining noncentrosymmetric order of high dipole moment–high hyperpolarizability chromophores in electrically poled polymeric thin films

Abstract: Graphs of second harmonic generation coefficients and electro-optic coefficients (measured by ellipsometry, attenuated total reflection, and two-slit interference modulation) as a function of chromophore number density (chromophore loading) are experimentally observed to exhibit maxima for polymers containing chromophores characterized by large dipole moments and polarizabilities. Modified London theory is used to demonstrated that this behavior can be attributed to the competition of chromophore-applied electric field and chromophore–chromophore electrostatic interactions. The comparison of theoretical and experimental data explains why the promise of exceptional macroscopic second-order optical nonlinearity predicted for organic materials has not been realized and suggests routes for circumventing current limitations to large optical nonlinearity. The results also suggest extensions of measurement and theoretical methods to achieve an improved understanding of intermolecular interactions in condensed phase materials including materials prepared by sequential synthesis and block copolymer methods.

Time-dependent Density Functional Results for the Dynamic Hyperpolarizability of C 60

Abstract: The experimental, as well as theoretical, values for the frequency-dependent hyperpolarizability of ${\mathrm{C}}_{60}$ differ by orders of magnitude. We present the first density functional calculation of a molecular frequency-dependent hyperpolarizability. Our implementation is very economical, enabling the treatment of molecules of this size, in a potentially much more accurate way than can be obtained with alternative methods. Our results strongly support the recent results by Geng and Wright, who report much lower experimental values than previous authors.

Second-order polarization propagator approximation with coupled-cluster singles and doubles amplitudes - SOPPA(CCSD): the polarizability and hyperpolarizability of

Abstract: A new modification of the second-order polarization propagator approximation (SOPPA) is presented. In the new method, called SOPPA(CCSD), all first-order Moller - Plesset doubles and second-order Moller - Plesset singles correlation coefficients are replaced with the corresponding coupled-cluster singles and doubles (CCSD) and amplitudes. This is in contrast to the earlier coupled-cluster polarization propagator approximation (CCSDPPA) in which only one of the doubles correlation coefficients was replaced in the unrelaxed second-order density matrix. The importance of this modification is investigated for the dipole polarizability, dipole oscillator strength sum rules and second hyperpolarizability of , which is known to be a difficult case for perturbative methods. The SOPPA(CCSD) values are compared with previous and new full CI results for the same basis sets.

Highly Dipolar, Optically Nonlinear Adducts of Tetracyano-p-quinodimethane: Synthesis, Physical Characterization, and Theoretical Aspects

Abstract: A new series of nonlinear optical molecules are described where the ground state polarization is predominantly zwitterionic when the molecules are dissolved in solution. The molecules, which are derived in general from facile reactions between tertiary amines and tetracyano-p-quinodimethane (TCNQ), are of a type where the stabilization of the charge-separated ground state is favored by an increase in aromaticity over the neutral, quinoidal forms of the molecules. The measured second-order optical nonlinearity of one in the series has been measured by hyper-Rayleigh scattering and a figure of merit value, μβ(0), being the product of the dipole moment and static first hyperpolarizability, is found to be 9500 × 10^(-48) esu. This value, which is higher than most other reported values, is taken from studies in chlorinated solvents of relatively low polarity, but the discussion emphasizes the evolution of μβ(0) with solvent polarity, showing that even higher values could be expected with only modest increases in the polarity of the surrounding medium. The analysis of experimental data taken during dipole moment studies is thoroughly examined, and it is concluded that full account must be taken of the molecular shape to correlate the results with theoretical calculations. An ellipsoidal reaction field model is preferred for these highly one-dimensional molecules having strongly anisotropic polarizabilities.

Sum-frequency spectroscopy in total internal reflection geometry: signal enhancement and access to molecular properties

Abstract: The angular dependence of the sum-frequency signal radiated in a total internal reflection geometry is studied both theoretically and experimentally for a monolayer of octadecyl trichlorosilane chemisorbed upon CaF2. A predicted signal enhancement of 2 orders of magnitude is verified experimentally. The line amplitudes of the CH-stretching modes of the terminal methyl group depend strongly on the polarization geometry, the molecular hyperpolarizability, and the angles of incidence of the fundamental waves. By exploiting both the angular and the polarization dependence of the line amplitudes, one can obtain the molecular properties unambiguously. The hyperpolarizability tensor elements of the terminal methyl group are determined directly from the sum-frequency spectra.

Solvent dependence of the first molecular hyperpolarizability of p-nitroaniline revisited

Abstract: The solvent effect on the molecular first hyperpolarizability, β, of p-nitroaniline (pNA) has been investigated. Using the hyper-Rayleigh scattering technique, we have also determined β of pNA in D...

Ab Initio Coupled Hartree−Fock Investigation of the Static First Hyperpolarizability of Model all-trans-Polymethineimine Oligomers of Increasing Size

Abstract: The static first hyperpolarizability tensor of model all-trans-polymethineimine oligomers has been computed ab initio as a function of chain length using the coupled Hartree−Fock method with the 6-31G basis. Careful extrapolations were carried out to obtain reliable infinite polymer values per unit cell. For the most realistic structure the longitudinal component is about 4 times larger than any other and is of the same order of magnitude as in push−pull polyenes. A plot of this component vs chain length exhibits a characteristic “dromedary back” shape. The role of bond alternation and heteroatomicity in determining this shape through their effect on the electronic delocalization and two different types of asymmetry (backbone, chain end) is examined qualitatively as well as quantitatively. It is shown that the correct chain length dependence is not reproduced by the uncoupled Hartree−Fock approximation.

Push-Pull Phthalocyanines: A Hammett Correlation between the Cubic Hyperpolarizability and the Donor-Acceptor Character of the Substituents

Abstract: The nonlinear optical (NLO) properties at the molecular level of a family of unsymmetrically substituted metal-free phthalocyanines (3−9) have been studied for the first time. NLO characterization ...

Second-Harmonic Generation from Single Crystals of N-Substituted 4-Nitroanilines

Abstract: Six N-substituted derivatives of 2-methyl-4-nitroaniline (MNA) and two N-substituted derivatives of 4-nitroaniline were synthesized and their physical and optical properties were examined in the search for nonlinear optical materials with a sufficiently large second harmonic (SH) activity and applicability to practical use. Some derivatives produced single crystals and their structures were determined by X-ray crystallography. The trends of the SH intensity of these materials could be qualitatively explained based on the b tensor (the effective molecular hyperpolarizability in the crystal). Amongst the derivatives examined in this investigation, N-benzyl-MNA showed the highest SH activity (up to twice that of MNA), thermostability and phase-matching ability.

Ab initio calculations of the polarizability and the hyperpolarizability of C60

Abstract: The linear polarizability, α, and the second hyperpolarizability, γ, of C60 in gas phase have been computed by ab initio cubic response theory in the random phase approximation and with an efficien ...

Nonlinear optical and vibrational properties of conjugated polyaromatic molecules

Abstract: Raman spectra of oligo-p-phenylenes, oligorylenes, and oligoacenes of different chain lengths have been obtained in the solid state and in solution. Among the properties studied, particular attention is devoted to frequency and intensity dispersion of the Raman bands with increasing conjugation length and to the vibrational second order hyperpolarizability γ r. The results obtained are compared with those relative to polyenic systems. The behavior of the various classes of molecules studied is in some cases different both in absolute values and trends. This fact is discussed in order to clarify the influence of the topology of the π-electron system on the properties of conjugated materials and to determine whether the presence of aromatic rings in the main chain can confine π electrons and so reduce delocalization. Oligorylenes turn out to be the compounds with the largest vibrational γ r. The results also indicate that absolute Raman intensity shows strong intensity dispersion with conjugation length and...

Hyper-rayleigh scattering studies of an ionic species : solvent effect on hyperpolarizability of 1-anilinonaphthalene-8-sulfonic acid ammonium salt

Abstract: The hyperpolarizability β of an ionic species, 1-anilinonaphthalene-8-sulfonic acid ammonium salt (ANS), was determined in various solvents by the Hyper-Rayleigh scattering (HRS) technique. Increase in the solvent polarity led to a decrease in the hyperpolarizability; i.e. β=37.4±2.5×10 -30 esu in p-dioxane and β=10.3±1.3×10 -30 esu in water. The solvent effect was explained by considering the dissociation ratio of the sulfonic acid ammonium group in solution, which influences the intramolecular donor–acceptor interaction between phenylamino and sulfonic acid ammonium groups.

Linear and nonlinear polarizabilities of polydiacetylene and polybutatriene chains: An ab initio coupled Hartree–Fock investigation

Abstract: Ab initio Hartree–Fock 6-31G longitudinal polarizabilities and second hyperpolarizabilities of polydiacetylene and polybutatriene oligomers are computed and, then, extrapolated to the infinite polymer limit. Both the electronic and vibrational components are obtained with the latter evaluated in the double harmonic approximation. For static fields the electronic hyperpolarizability of the butatrienic form is almost 50 times larger than the acetylenic form; the ratio of the vibrational to the electronic component is 0.86 for the latter and 3.3 for the former. Thus, the two components are sensitive to the difference in bond length alternation (BLA) in different ways. Depending upon the particular nonlinear process it is shown that the vibrational hyperpolarizability may remain large even at optical frequencies. Three intense Raman-active k=0 modes dominate the vibrational component. At the level of theory used here these modes occur in the frequency range 1000–2500 cm−1 and they consist of changes in the BL...

Ab initio static polarizability and first hyperpolarizability of model polymethineimine chains. II. Effects of conformation and of substitution by donor/acceptor end groups

Abstract: An ab initio coupled Hartree–Fock study has been carried out on polymethineimine (PMI) oligomers with an increasing number of unit cells (up to N=20) to determine the effect of conformational differences, and of end-capping by a strong donor-acceptor pair, on the static electronic longitudinal polarizability (αL) and first hyperpolarizability (βL). For the unsubstituted polymer the differences in βL per unit cell among the four conformations examined—trans-transoid (TT), cis-transoid (CT), trans-cisoid (TC) and helical (HEL)—are large. βL/N is positive for the CT polymer, in contrast with the other conformers and with μL/N, which is negative in all cases. The TC polymer has the largest |βL|/N despite having a relatively small αL/N. Substitution of a strong acceptor (NO2) at the carbon end of an oligomer and a strong donor (NH2) at the nitrogen end results in a large increase of βL/N for small/medium N. In the case of the TT and, particularly, the CT conformer this leads to a maximum in |βL|/N vs N at N...

Control of the polarization dependence of optically poled nonlinear polymer films.

Abstract: We demonstrate the possibility of controlling the symmetry properties of photoinduced χ2 macroscopic susceptibility in polymer films. Ellipsometric adjustment of the write beams allows one to monitor the macroscopic χ2 symmetry from a dipolar to an octupolar configuration. Experimental results are in agreement with an irreducible spherical tensor-based model jointly applied to the molecular β hyperpolarizability and field tensors. We found a purely octupolar polarization-independent photoinduced second-harmonic-generation response in a Dispersed Red 1–methyl methacrylate thin film. Such a configuration, as generated by an octupolar tensor write field tensor made up of counterclockwise circularly polarized ω and 2ω beams, is not within the reach of the classical electric-field poling technique.

Effects of Two-Photon Fluorescence and Polymerization on the First Hyperpolarizability of an Azobenzene Dye

Abstract: The technique of hyper-Rayleigh scattering (HRS) has been employed to investigate the first hyperpolarizability (β) of the azo dye Disperse Red 19 and a polymer in which Disperse Red 19 appears as a side-chain moiety. In addition to HRS, these two molecules were found to exhibit substantial two-photon-induced fluorescence (TPF). The TPF spectra for these molecules were measured, and corrected HRS intensities were obtained. Using an external reference method, β values of (1480 ± 100) × 10-30 and (1470 ± 90) × 10-30 esu were determined for the dye and polymer systems, respectively, in dimethyl sulfoxide at 1064 nm. The difference between these two values is very small and shows that the effect of polymerization on the HRS intensity, in the dilute concentration limit, is negligible.

Calculation, with the inclusion of vibrational corrections, of the dc-electric-field-induced second-harmonic-generation hyperpolarizability of methane

Abstract: Calculations of γ(−2ω;ω,ω,0) for CH4 are reported for a number of frequencies (ω) This mean frequency-dependent second hyperpolarizability governs the nonlinear optical process: dc-electric-field-induced second-harmonic generation Two levels of calculation have been carried out: one is based on the random phase approximation and the other on the multiconfigurational random phase approximation using a complete active space self-consistent-field wavefunction This is the first calculation of γ(−2ω;ω,ω,0) that has been made for CH4 using electron-correlated wavefunctions Included in the calculations are corrections for vibrational effects of which the zero-point vibrational-averaging correction is both dominant and significant (13–18% of the electronic values) Comparison with experiment shows that not all the electron correlation is captured by our treatment The dispersion properties are also discussed

Heterocyclic Pyridinium Betaines, A New Class of Second-Order Nonlinear Optical Materials: Combined Theoretical and Experimental Investigation of First-Order Hyperpolarizability through ab Initio, INDO/S, and Hyper-Rayleigh Scattering

Abstract: The first hyperpolarizability, β, of one of the simplest heterocyclic pyridinium betaines, (1-pyridinio)benzimidazolate, was measured experimentally with the hyper-Rayleigh scattering technique and compared to the calculated values obtained by the semiempirical INDO/S and ab initio molecular orbital methods. Heterocyclic pyridinium betaines are characterized by their zwitterionic character where a negatively charged aromatic electron-donating group and a positively charged aromatic electron-withdrawing group are linked directly. The experimentally obtained |β| value, (115 ± 25) × 10-30 cm5 esu-1, was in good agreement with those derived from the INDO/S calculations. The first excited state was found to be characterized by a strong intramolecular charge-transfer state, where the electron transition occurs from a negatively charged aromatic electron-donating group (benzimidazole ring) to a directly linked, positively charged aromatic electron-withdrawing group (pyridinium ring). This nature of the excited s...

Second-order nonlinear optical properties of stilbene,benzylideneaniline and azobenzene derivatives. The effect of π-bridgenitrogen insertion on the first hyperpolarizability

Abstract: The second-order nonlinear optical (NLO) and electronic properties of stilbenes (CC bridge), benzylideneanilines (CN and NC bridges) and azobenzenes (NN bridge) containing either an N,N-dimethylamino donor and/or a nitro acceptor were investigated using EFISH, UV spectroscopy, cyclic voltammetry and PPP/SCF calculations. It appeared that although first hyperpolarizabilities of the ethylene and azo bridged donor–acceptor compounds are of comparable magnitude, substitution of one carbon by a nitrogen atom reduces the NLO activity. Differences in hyperpolarizabilities were rationalized with the aid of a two-level model, which revealed that they find their origin in the redox activity of the nitrogen-containing bridges.

Charge distribution and second-order nonlinear optical response of charged centrosymmetric chromophore aggregates. An ab initio electronic structure study of p-nitroaniline dimers

Abstract: This contribution presents a quantum chemical investigation of the nonlinear optical response of charged centrosymmetric aggregates of the archetypical chromophore p-nitroaniline using an ab initio supermolecular approach. Localized hole states, responsible for aggregate nonlinearity, are predicted to be more stable than delocalized states. The calculated aggregate hyperpolarizabilities are consistently larger than in the isolated chromophore, and the mechanism giving rise to the nonlinearity is essentially “intramolecular” in nature. The aggregate formation is predicted to stabilize the positive charge and to enhance the nonlinearity. Moreover, the calculations reveal that a (formally) centrosymmetric charged aggregate can possess a substantial dipole moment the principal axis of which is oriented perpendicular to the principal hyperpolarizability tensor; the dipole moment arises because electron localization breaks the charge distribution symmetry. These results explain a number curious features of chro...

Comment on “Molecular first hyperpolarizability of push-pull polyenes: Relationship between electronic and vibrational contribution by a two-state model”

Abstract: Castiglioni, Del Zoppo, and Zerbi [Phys. Rev. B 53, 13 319 (1996)] have developed a theory that attempts to demonstrate the equality (or near equality) of electronic and vibrational first hyperpolarizabilities in push-pull polyenes. In this Comment we draw attention to a serious flaw in their argument.

Does scaling or addition provide the correct frequency dependence of beta (omega ; omega, omega) at the correlated level? An investigation for six e sigma molecules

Abstract: The frequency dependent polarizability α(– ω σ; ω1) and the frequency dependent first hyperpolarizability β(– ω σ; ω1, ω2) have been calculated using both self consistent field (SCF) and multiconfigurational SCF (MCSCF) linear and quadratic response functions for six small molecules: BH, CO, HF, H2O, NH3, and H S. Two approximate ways of using the calculated dispersion at the SCF level to describe the frequency dependence at the correlated level, referred to as scaling and addition, have been tested. Calculated frequency dependent MCSCF results are used to investigate the validity of these approximations. Our results indicate that, if the correlation correction to the static average hyperpolarizability is large, then the approximations do not hold. The same conclusion holds if correlation changes the sign of the average first hyperpolarizability at zero frequency. There is also a tendency towards an underestimation of the frequency dependence if scaling or addition is applied. There does not seem to be a ...

Frequency dependent equation-of-motion coupled cluster hyperpolarizabilities: Resolution of the discrepancy between theory and experiment for HF?

Abstract: We formulate and apply the EOM-CC method to determine, recursively, any order and any process frequency dependent hyperpolarizability. Combining the theory with systematically chosen n-aug-cc-pVXZ bases, we attempt to converge to the basis set limit. Our best “relaxed” result is −9.8±0.5 a.u. for βSHG compared to an experimental value of −11.0±1 a.u. and 720±40 a.u. for γdc-SHG compared to 840±120 a.u. If orbital relaxation could be neglected, the results are −10.2±0.5 a.u. and 730±40 a.u., falling within the error bars.

A molecular design view on the first hyperpolarizability of salicylideneaniline derivatives

Abstract: Electron correlation effect was incorporated into the two-level framework through configuration interaction (CI) calculation including both occupied and unoccupied frontier orbitals, to evaluate the first hyperpolarizabilities of title compounds. Theoretical results are in excellent agreement with experimental data obtained by the solvatochromic method. Some detailed chemical and electronic information of the electron excitation process related to the nonlinear optical (NLO) properties were produced as well. Based on these data, effects of the character, number and position of donor and acceptor groups on the NLO properties are discussed from the viewpoint of molecular design. Not only the experimental data but also the theoretical analysis have suggested that a large number of intensive and properly located donor and acceptor groups may yield the optimal hyperpolarizabilities.