Showing papers on "Hyperpolarizability published in 2005"
TL;DR: The present investigation reveals a new idea and different means for designing and synthesizing high-performance NLO materials and finds that the excess electron from the Li atom plays an important role in the large first hyperpolarizability of Li@calix[4]pyrrole.
Abstract: A new compound with electride characteristics, Li@calix[4]pyrrole, is designed in theory. The Li atom in Li@calix[4]pyrrole is ionized to form a cation and an excess electron anion. Its structure with C(4v) symmetry resembles a cup-like shape. It may be a stable organic electride at room temperature. The first hyperpolarizability of the cup-like electride molecule is first investigated by the DFT (B3LYP) method. The result shows that this electride molecule has a considerably large first hyperpolarizability with beta(0) = 7326 au (63.3 x 10(-30) esu), while the beta(0) value of the related calix[4]pyrrole system is only 390 au. Obviously, the Li atom doped in calix[4]pyrrole brings a dramatic change to the electronic structure, so that the first hyperpolarizability of Li@calix[4]pyrrole is almost 20 times larger than that of calix[4]pyrrole. We find that the excess electron from the Li atom plays an important role in the large first hyperpolarizability of Li@calix[4]pyrrole. The present investigation reveals a new idea and different means for designing and synthesizing high-performance NLO materials.
307 citations
TL;DR: In this paper, the second hyperpolarizability of singlet diradical systems is investigated using a model compound, the p-quinodimethane (PQM) molecule with different both-end carbon−carbon (C−C) bond lengths, by several ab initio molecular orbital and density functional theory methods.
Abstract: The dependence of the second hyperpolarizability (γ) on the diradical character (y) for singlet diradical systems is investigated using a model compound, the p-quinodimethane (PQM) molecule with different both-end carbon−carbon (C−C) bond lengths, by several ab initio molecular orbital and density functional theory methods. The diradical character based on UHF calculations indicates that at equilibrium geometry PQM is in a singlet ground state and primarily exhibits a quinoid structure, whereas the diradical character increases when increasing both-end C−C bond lengths. At the highest level of approximation, that is, using the UCCSD(T) method with the 6-31G*+diffuse p (ζ = 0.0523) basis set, the longitudinal static γ of PQM presents a maximum value for intermediate diradical character (y ≈ 0.5) while the γ values are larger for intermediate and large diradical character (y ≈ 0.5−0.7) than for small diradical character (y < 0.2). This feature suggests that the γ values of singlet diradical systems in the i...
282 citations
TL;DR: Based on the Ehrenfest theorem, an equation of motion that takes relaxation into account has been presented in wave-function theory, and the resulting response functions are nondivergent in the off-resonant as well as the resonant regions of optical frequencies.
Abstract: Based on the Ehrenfest theorem, an equation of motion that takes relaxation into account has been presented in wave-function theory, and the resulting response functions are nondivergent in the off-resonant as well as the resonant regions of optical frequencies. The derivation includes single- and multideterminant reference states. When applied to electric dipole properties, the response functions correspond to the phenomenological sum-over-states expressions of Orr and Ward [Mol. Phys. 20, 513 (1971)] for polarizabilities and hyperpolarizabilities of an isolated system. A universal dispersion formula is derived for the complex second-order response function. Response theory calculations are performed on lithium hydride and para-nitroaniline for off-resonant and resonant frequencies in the electro-optical Kerr effect and second-harmonic generation.
181 citations
TL;DR: Basis set investigations evidence that the linear and nonlinear responses of the radical cation necessitate the use of a less extended basis set than its neutral analog, and basis sets resulting from removing not necessary diffuse functions from the augmented correlation consistent polarized valence double zeta basis set have been shown to provide (hyper)polarizability values of similar quality.
Abstract: The basis set and electron correlation effects on the static polarizability (alpha) and second hyperpolarizability (gamma) are investigated ab initio for two model open-shell pi-conjugated systems, the C(5)H(7) radical and the C(6)H(8) radical cation in their doublet state. Basis set investigations evidence that the linear and nonlinear responses of the radical cation necessitate the use of a less extended basis set than its neutral analog. Indeed, double-zeta-type basis sets supplemented by a set of d polarization functions but no diffuse functions already provide accurate (hyper)polarizabilities for C(6)H(8) whereas diffuse functions are compulsory for C(5)H(7), in particular, p diffuse functions. In addition to the 6-31G(*)+pd basis set, basis sets resulting from removing not necessary diffuse functions from the augmented correlation consistent polarized valence double zeta basis set have been shown to provide (hyper)polarizability values of similar quality as more extended basis sets such as augmented correlation consistent polarized valence triple zeta and doubly augmented correlation consistent polarized valence double zeta. Using the selected atomic basis sets, the (hyper)polarizabilities of these two model compounds are calculated at different levels of approximation in order to assess the impact of including electron correlation. As a function of the method of calculation antiparallel and parallel variations have been demonstrated for alpha and gamma of the two model compounds, respectively. For the polarizability, the unrestricted Hartree-Fock and unrestricted second-order Moller-Plesset methods bracket the reference value obtained at the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples level whereas the projected unrestricted second-order Moller-Plesset results are in much closer agreement with the unrestricted coupled cluster singles and doubles with a perturbative inclusion of the triples values than the projected unrestricted Hartree-Fock results. Moreover, the differences between the restricted open-shell Hartree-Fock and restricted open-shell second-order Moller-Plesset methods are small. In what concerns the second hyperpolarizability, the unrestricted Hartree-Fock and unrestricted second-order Moller-Plesset values remain of similar quality while using spin-projected schemes fails for the charged system but performs nicely for the neutral one. The restricted open-shell schemes, and especially the restricted open-shell second-order Moller-Plesset method, provide for both compounds gamma values close to the results obtained at the unrestricted coupled cluster level including singles and doubles with a perturbative inclusion of the triples. Thus, to obtain well-converged alpha and gamma values at low-order electron correlation levels, the removal of spin contamination is a necessary but not a sufficient condition. Density-functional theory calculations of alpha and gamma have also been carried out using several exchange-correlation functionals. Those employing hybrid exchange-correlation functionals have been shown to reproduce fairly well the reference coupled cluster polarizability and second hyperpolarizability values. In addition, inclusion of Hartree-Fock exchange is of major importance for determining accurate polarizability whereas for the second hyperpolarizability the gradient corrections are large.
137 citations
TL;DR: The "metal-induced" NLO activity enhancement is confirmed as a general property of f-block elements, and the direct participation of f electrons to the hyperpolarizability beta is strongly supported by experimental data.
Abstract: This study descibes for the first time the nonlinear optical (NLO) properties of multipolar lanthanide complexes, Na3[Ln(dipic)3]. The “metal-induced” NLO activity enhancement is confirmed as a general property of f-block elements, and the direct participation of f electrons to the hyperpolarizability β is strongly supported by experimental data.
128 citations
TL;DR: Qualitative ZINDO/SCI quantum chemical calculations indicate that, in [Ni(L)(MePhCHNH2)], the beta orientation strongly depends on the laser wavelength, raising the possibility for a new type of molecular switch.
Abstract: An H2L Schiff-base ligand that was obtained from the monocondensation of diaminomaleonitrile and 4-(diethylamino)salicylaldehyde is reported together with four related nickel(II) complexes formulated as [Ni(L)(L‘)] (L‘ = MePhCHNH2, iPrNH2, Py, and PPh3). Crystal structures have been solved for H2L, [Ni(L)(MePhCHNH2)], and [Ni(L)(iPrNH2)]. Surprisingly, the complexation process leads to the formation of a rather unusual nickel amido (−NH−NiII) bond by deprotonation of the primary amine of H2L. A reduction of the quadratic hyperpolarizability (β) from 38 × 10-30 to 17.5 × 10-30 cm5 esu-1 is evidenced on H2L upon metal complexation by the electric-field-induced second-harmonic (EFISH) technique. Qualitative ZINDO/SCI quantum chemical calculations indicate that, in [Ni(L)(MePhCHNH2)], the β orientation strongly depends on the laser wavelength. In particular, a β rotation strictly equal to 90° could be obtained with 1.022 μm incident light on passing from [Ni(L)(MePhCHNH2] to a hypothetical [Ni(HL)(MePhCHNH2]+...
113 citations
TL;DR: A series of alpha,omega-diarylpolyynes has been synthesized and a notably improved synthesis of 1,16-diphenylhexadecaoctayne is described, showing a substantial increase in molecular hyperpolarizability (gamma) as a function of increasing length.
103 citations
TL;DR: In this article, the structure, atomic charges, natural bond orbital, and thermodynamic functions of 4-phenyl-1-(propan-2-ylidene)thiosemicarbazide have been analyzed at HF/6-311G∗∗ and B3LYP/6 -311G ∗ levels of theory for the title compound of 4 -phenyl 1-propane 2-ylidsene, and the second-order optical nonlinearity has been calculated by time-dependent density functional theory.
Abstract: Ab initio calculations of the structure, atomic charges, natural bond orbital, and thermodynamic functions have been performed at HF/6-311G∗∗ and B3LYP/6-311G∗∗ levels of theory for the title compound of 4-phenyl-1-(propan-2-ylidene)thiosemicarbazide. The calculated results show that the sulfur atom and all of the nitrogen atoms have bigger negative charges and they are the potential sites to react with the metallic ions, which make the title compound become a multidentate ligand. The coordination ability of the sulfur atom and the nitrogen atom of C=N double bond will increase with the increase of the polarity of the solvent. Electronic absorption spectra have been calculated by time-dependent density functional theory (TD-DFT) method. The calculation of the second-order optical nonlinearity also has been carried out, and the molecular hyperpolarizability is 3.068×10−30 esu.
86 citations
TL;DR: The NLO properties of the alkalides complexes for the first time are investigated and it is found that inverse sodium hydride AdzH(+)Na- has a considerably large NLO response and the first hyperpolarizability of inverse salt increases with the charge value of the sodium anion.
Abstract: "Inverse sodium hydride" (AdzH(+)Na-) is an alkalide compound synthesized in recent experiments containing the unusual charge distribution H+ and Na- (inverse charge state). The new class of compounds interests scientists to investigate their especial structures and properties. In this paper, the structures of three alkalides compounds, (Me)3NH(+)Na-, AdzH(+)Na-, and AdzLi(+)Na-, have been obtained in theory. Especially, the structure of AdzLi(+)Na- is still researched by experimental scientists. We investigated the NLO properties of the alkalides complexes for the first time and found that inverse sodium hydride AdzH(+)Na- has a considerably large NLO response beta0 = 5.7675 x 10(4) au by density functional theory (DFT). To understand the essential features of the large NLO properties, four related systems have been also calculated. Their first hyperpolarizabilities are beta0 = 7.357 x 10(3) au for (Me)3NH(+)Na-, beta0 = 3.9 au for (Me)3NH+, beta0 = 1.10 x 10(2) au for (Me)3NH(+)Cl-, and beta0 = 6.20681 x 10(5) au for AdzLi(+)Na-, respectively. By comparing, we found that, first, the Na- anion plays a crucial role in the considerably large first hyperpolarizability of inverse sodium hydride and, second, the first hyperpolarizability of inverse sodium hydride increases with the charge value of the sodium anion. The above results are useful for designing potential NLO materials.
81 citations
TL;DR: In this article, a single crystal of methyl 3-(4-methoxyphenyl)prop-2-enoate was grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier Transform IR spectroscopy.
Abstract: Single crystals of methyl 3-(4-methoxyphenyl)prop-2-enoate were grown by the slow evaporation technique and vibrational spectral analysis was carried out using near-IR Fourier transform Raman and Fourier transform IR spectroscopy. Ab initio quantum computations were also performed at the HF/6–311G (d,p) level to derive the equilibrium geometry, vibrational wavenumbers and intensities and first hyperpolarizability. The large NLO efficiency predicted for the first time in this new class of compounds was confirmed by powder efficiency experiments. Hartree–Fock calculations reveal that the endocyclic angle at the junction of the propeonate group and the phenyl ring is decreased from 120° by 2.5°, whereas the two neighbouring angles around the ring are increased by 2.1° and 1.2°, associated with charge-transfer interaction. Vibrational analysis indicates the lowering of asymmetric stretching modes of Me1 and Me2 due to the electronic effects simultaneously caused by back-donation and induction due to the presence of the oxygen atom. The occurrence of Fermi resonance is also identified. The carbonyl stretching vibrations were lowered owing to conjugation and the hydrogen bonding network inside the crystal. The vibrational spectra confirm that the charge-transfer interaction between the COOCH3 group and phenyl ring through the ethylenic bridge must be responsible for simultaneous IR and Raman activation of C7C18 stretching and ring modes 8 and 19. The large intensity differences observed between the 8a and 8b modes in both the IR and Raman spectra are due to the algebraic difference of the electronic effects of the substitutents. The charge transfer interaction between the COOCH3 group and phenyl ring through the ethylenic bridge resulting in π-electron cloud movement from donor to acceptor can make the molecule highly polarized. Intramolecular charge transfer must be responsible for the NLO activity of MMP. Copyright © 2004 John Wiley & Sons, Ltd.
74 citations
TL;DR: This work investigated the first hyperpolarizability of pNA in 1,4-dioxane solution using a quantum mechanics/molecular mechanics (QM/MM) model and the inclusion of local-field effects was found to be crucial and neglecting them led to results which are significantly larger.
Abstract: In this work we have investigated the first hyperpolarizability of pNA in 1,4-dioxane solution using a quantum mechanics/molecular mechanics (QM/MM) model. The particular model adopted is the recently developed discrete solvent reaction field (DRF) model. The DRF model is a polarizable QM/MM model in which the QM part is treated using time-dependent density-functional theory and local-field effects are incorporated. This allows for direct computation of molecular effective properties which can be compared with experimental results. The solvation shift for the first hyperpolarizability is calculated to be 30% which is in good agreement with the experimental results. However, the calculated values, both in the gas phase and in solution, are by a factor of 2 larger than the experimental ones. This is in contrast to the calculation of the first hyperpolarizability for several small molecules in the gas phase where fair agreement is found with experimental. The inclusion of local-field effects in the calculations was found to be crucial and neglecting them led to results which are significantly larger. To test the DRF model the refractive index of liquid 1,4-dioxane was also calculated and found to be in good agreement with experiment.
TL;DR: A series of donor−π-acceptor ruthenium acetylide systems built around thiophene-based π-conjugating spacers of different lengths have been developed as mentioned in this paper.
TL;DR: A class of nonlinear optical chromophores that not only are well-suited for single-molecule imaging but also offer additional beneficial properties such as a significant ground-state dipole moment, moderate hyperpolarizability, and sensitivity to local environment are discussed.
Abstract: Fluorescence imaging of single molecules at room temperature is a powerful technique for studying complex condensed phase systems and revealing structure and dynamics hidden by ensemble measurements. Successful single-molecule spectroscopic experiments rely upon strong emitters that can be detected at the level of individual copies above the relevant background signals. This Account discusses a class of nonlinear optical chromophores that not only are well-suited for single-molecule imaging but also offer additional beneficial properties such as a significant ground-state dipole moment, moderate hyperpolarizability, and sensitivity to local environment. An overview of the photophysical properties of several members of this class of molecules as well as a mechanism to help understand the environmental sensitivity is presented. Some preliminary applications of the chromophores as single-molecule reporters in cellular and polymer systems are discussed, along with detection of the emitters by two-photon fluorescence.
TL;DR: The molecular orbital character analysis reveals that organoimido-to-polyanion charge transfer may be responsible for the NLO properties of this kind of molybdate derivatives.
Abstract: The first hyperpolarizabilities and origin of nonlinear optical (NLO) properties of arylimido molybdate derivatives have been investigated by density functional theory (DFT). The molecular orbital character analysis reveals that organoimido-to-polyanion charge transfer may be responsible for the NLO properties of this kind of molybdate derivatives. The NLO study shows intra-ion charge transfer is helpful to increase the first hyperpolarizability of arylimido molybdate derivatives. The lengthening of organoimido π-conjugation enhances the βvec value. System 4 has the largest βvec value at the static electronic field, 1.238 × 10-27esu. Orbital analysis shows that the degree of charge transfer between polyanion cluster and organic segment was increased when the second organoimido polyanion was introduced. The present investigation provides important insight into NLO origin and properties of polyanion arylimido molybdate derivatives.
TL;DR: In this article, the authors describe the synthesis and the microscopic nonlinear optical properties of two different types of the heterocyclic chromophores and synthesize them, which are electron donating groups which can facilitate the charge transport of the carrier.
Abstract: Factors such as high NLO susceptibility, fast response time, low dielectric constant, small dispersion in the refractive index, structural flexibility, and ease of material processing are advantageous in organic NLO materials systems. Taking advantage of these factors can lead to the application of the organic NLO materials systems to various photonic devices such as high speed EO modulators and switches. To achieve good device functionality, the NLO chromophore has to simultaneously possess the following criterion: high microscopic molecular nonlinearity (µβ), good thermal stability and photostability, low absorption, and weak molecular electrostatic interaction in the polymer matrix. Much effort was made to develop the highly functional chromophore with high molecular hyperpolarizability, β, and to improve the thermal/photo-stability. Recently, very large nonlinearities were achieved by employing heterocyclic rings such as thiophene and thiazole as a conjugative unit since they have lower resonance stabilization energy upon charge delocalization than benzene ring does. Phenothiazine and carbazole used in this study are electron donating groups which can facilitate the charge transport of the carrier. Those moieties were often employed to photorefractive materials due to the property of charge carrier generation under light irradiation. In order to improve the figure of merit for photorefractivity, we designed four chromophores and synthesized them. These two building blocks exhibited different geometry each other. Carbazole units place perfectly in a plane-like geometry to stack themselves much more easily than the phenothiazine units since the center six membered ring in phenothiazine showed bent form arising from the dihedral angle in C-N-C (140.0 o ) and C-S-C (141.9 o ). 7 Therefore, the electrostatic interaction can be reduced between the chromophores that are even in high concentration of the phenothiazine-based chromophore. Accordingly, the phenothiazine chromophores can be expected to improve the macroscopic nonlinearity and its stability. Some electron-deficient heterocyclic compounds have been known as strong acceptors for nonlinear optical materials. Particularly, 2-cyanomethylene-3-cyano-4,5,5trimethyl-2,5-dihydrofuran (TCF) was well adopted as a strong electron acceptor that induces significantly high dipole moment (µ), first-order molecular hyperpolarizability (β), and their product (µβ). 8-13 In this report, we describe the synthesis and the microscopic nonlinear optical properties of two different types of the heterocyclic chromophores. Additional donor of diethylaminostyryl group was tethered to phenothaizine or carbazole that plays as conjugative donor bridge in DEAPTZ-TCF and DEA-CBZ-TCF (see Figure 1). 2-Cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) was commonly employed as a strong electron acceptor to
TL;DR: In this paper, the vibrational frequencies and potential energy distribution (PED) of melaminium cations were calculated by B3LYP method and the assignment of the bands has been made on the basis of the calculated PED.
Abstract: The melaminium cation can occur in three form: singly, doubly or triply protonated. The geometry and nonlinear optical properties (NLO) for all forms were computed by ab initio method. The restricted open Hartree–Fock (ROHF) computational method with 6-311+G basis set was used. Comprehensive studies of electronic and molecular structures have been performed. The theoretical vibrational frequencies and potential energy distribution (PED) of melaminium cations were calculated by B3LYP method. The calculated frequencies were compared with measured one for newly obtained compounds where melaminium cations are common component. The assignment of the bands has been made on the basis of the calculated PED. The restricted Hartree–Fock (RHF) methods were used for calculation of the hyperpolarizability for each ion. For comparison, analogous calculations were carried out for the closed-shell neutral melamine. The theoretical results can be used in design of new molecular compounds with nonlinear optical properties.
TL;DR: Accurate static dipole polarizabilities and hyperpolarizabilities are calculated for the ground states of the Al, Si, P, S, Cl, and Ar atoms using various ab initio methods including Moller-Plesset perturbation theory and the coupled cluster approach.
Abstract: Accurate static dipole polarizabilities and hyperpolarizabilities are calculated for the ground states of the Al, Si, P, S, Cl, and Ar atoms. The finite-field computations use energies obtained with various ab initio methods including Moller-Plesset perturbation theory and the coupled cluster approach. Excellent agreement with experiment is found for argon. The experimental alpha for Al is likely to be in error. Only limited comparisons are possible for the other atoms because hyperpolarizabilities have not been reported previously for most of these atoms. Our recommended values of the mean dipole polarizability (in the order Al-Ar) are alpha/e(2)a(0) (2)E(h) (-1)=57.74, 37.17, 24.93, 19.37, 14.57, and 11.085 with an error estimate of +/-0.5%. The recommended values of the mean second dipole hyperpolarizability (in the order Al-Ar) are gamma/e(4)a(0) (4)E(h) (-3)=2.02 x 10(5), 4.31 x 10(4), 1.14 x 10(4), 6.51 x 10(3), 2.73 x 10(3), and 1.18 x 10(3) with an error estimate of +/-2%. Our recommended polarizability anisotropy values are Deltaalpha/e(2)a(0) (2)E(h) (-1)=-25.60, 8.41, -3.63, and 1.71 for Al, Si, S, and Cl respectively, with an error estimate of +/-1%. The recommended hyperpolarizability anisotropies are Deltagamma/e(4)a(0) (4)E(h) (-3)=-3.88 x 10(5), 4.16 x 10(4), -7.00 x 10(3), and 1.65 x 10(3) for Al, Si, S, and Cl, respectively, with an error estimate of +/-4%.
TL;DR: In this article, a range of novel bimetallic molecular systems, coupled with group eight metal carbonyls, were designed and the full geometry optimisations were performed using DFT method at B3LYP/LanL2DZ level of theory using the gaussian 98W.
Abstract: Organometallic and coordination complexes are interesting candidates for NLO purposes. Among these materials bimetallic complexes belong to a new class of second order NLO materials. The objective of this investigation was to design a range of novel bimetallic molecular systems, which show high nonlinear optical activity. In this investigation, main attention was drawn to the ferrocenyl systems coupled with group eight metal carbonyls, where charge transfer occurs from ferrocene to the metal carbonyl moiety. These novel ferrocene bimetallic systems show high first static hyperpolarizability values. We report novel organometallic systems with high β values. The high accuracy density functional theory (DFT) was used for the investigation of NLO properties of these complexes. The full geometry optimisations of designed bimetallic systems were performed using DFT method at B3LYP/LanL2DZ level of theory using the gaussian 98W. The calculations of the first static hyperpolarizabilities of these systems were performed at the same level of theory.
TL;DR: A time-dependent quantum-chemical analysis on merocyanine aggregates is presented to understand the insight of the intermolecular interactions and to find the relationship between structural and collective nonlinear optical properties.
Abstract: We present a time-dependent quantum-chemical analysis on merocyanine aggregates to understand the insight of the intermolecular interactions and to find the relationship between structural and collective nonlinear optical properties. The first hyperpolarizabilities are evaluated for monomer and aggregates of a series of zwitterionic merocyanine dyes, whose synthesis and formation of H and J type aggregates in solvents are reported recently in the literature (J. Am. Chem. Soc. 2002, 124, 9431). The molecular geometries are obtained via B3LYP/6-31G (hybrid density-functional theory) optimization including PCM approach, while the dynamic NLO properties are calculated with the TD-DFT/SOS and ZINDO/CV method including solvent effects. It has been observed that the first hyperpolarizability changes tremendously as monomers undergo aggregation, and the magnitude of first hyperpolarizabilities highly depends on the nature of the aggregates. It is found that solvents play a remarkable role on the structure and first hyperpolarizabilities of merocyanine monomers and aggregates. Changing the solvent from low to high dielectric causes not only an increase in magnitude of beta but also a change in sign, therefore passing through zero at intermediate dielectric. The importance of our results on the design of electrooptic materials have been discussed.
TL;DR: Experimental and theoretical studies of the third-order nonlinear optical coefficients of methyl orange solutions under different pH conditions suggest that even at low pH, when the probability of cis-trans isomerization is increased, the trans conformation of the methyl orange molecule should dominate the nonlinear spectra of this compound.
Abstract: We describe experimental and theoretical studies of the third-order nonlinear optical coefficients of methyl orange solutions under different pH conditions. A combination of semiempirical and ab initio methods was adopted to investigate the most stable geometrical structures possible for this molecule. The experimental data obtained using the Z-scan technique for the third-order nonlinear optical properties of this compound has allowed the determination of the nonlinear refractive index and nonlinear absorption coefficient under picosecond excitation in the visible (532 nm) spectral region. From those experimental results, the second hyperpolarizability of methyl orange was inferred both for acidic and alkaline solutions. Comparison of these values to the results predicted by semiempirical methods suggests that even at low pH, when the probability of cis-trans isomerization is increased, the trans conformation of the methyl orange molecule should dominate the nonlinear spectra of this compound. The theoretical results were used as an auxiliary tool to identify possible trends on the nonlinear properties changes as a function of the distinct molecular conformations adopted by the methyl orange molecule under different pH conditions.
TL;DR: This work provides a general scheme for calculating the vibrational hyperpolarizability of any infrared- and Raman-active mode, regardless of the molecular symmetry or complexity of the structure.
Abstract: Nonlinear vibrational spectroscopies such as visible-infrared sum-frequency spectroscopy may serve as powerful probes of interfacial structure. Obtaining quantitative orientation information, however, has been limited by the required knowledge of the corresponding molecular-level nonlinear optical properties. We provide a general scheme for calculating the vibrational hyperpolarizability of any infrared- and Raman-active mode, regardless of the molecular symmetry or complexity of the structure. Our method involves all atoms and therefore does not rely on making any local mode approximations. We show how this information is used together with experimental data to arrive at the tilt and twist angles of a surfactant headgroup at the air/water interface. Since our approach is completely general, it may be used for the analysis of any adsorbate at an isotropic interface.
TL;DR: This is the first demonstration of the feasibility of sum-frequency measurements of sulfate modes in the 1100 cm-1 region, opening possibilities for future investigations of surfactant behavior in this spectral region at aqueous and solid interfaces.
Abstract: We have used vibrational sum-frequency spectroscopy to provide the first measurement of the spectrum and orientation of the polar headgroup of a charged alkyl surfactant at the air/water interface. Sum-frequency spectra of sodium dodecyl sulfate (SDS) are used to arrive at all participating elements of the second-order susceptibility tensor. We use these χ(2) elements, together with calculated values of the hyperpolarizability, to determine the tilt of the S−O bond attached to the alkyl chain and the twist of the S−O−C plane. Thus, a full characterization of the orientation of the surfactant headgroup has been achieved. This is the first demonstration of the feasibility of sum-frequency measurements of sulfate modes in the 1100 cm-1 region, opening possibilities for future investigations of surfactant behavior in this spectral region at aqueous and solid interfaces.
TL;DR: In this article, the third-order nonlinear susceptibility χ(3) and second-order hyperpolarizability γ of poly{[3-octylthiophene-2,5-diyl]-[p-aminobenzylidenequinomethane]-bonded multiwalled carbon nanotubes (POTABQ-MWNTs) were measured in chloroform solution using degenerate four-wave mixing at 532nm under nanosecond pulse excitation.
Abstract: Third-order nonlinear susceptibility χ(3) and second-order hyperpolarizability γ of poly{[3-octylthiophene-2,5-diyl]-[p-aminobenzylidenequinomethane]-bonded multiwalled carbon nanotubes (POTABQ-MWNTs) were measured in chloroform solution using degenerate four-wave mixing at 532nm under nanosecond pulse excitation. Effective nonlinear absorption coefficient βeff and nonlinear refraction index n2 were obtained using open aperture and close aperture Z-scan technique at the same wavelength, respectively. Optical limiting property of the sample was also investigated. The resulting POTABQ-MWNTs exhibited large third-order nonlinear optical responses mainly due to the formation of intramolecular photoinduced charge-transfer system of polymers and carbon nanotubes.
TL;DR: In this paper, the second-order nonlinear optical responses of homo- and hetero-helicenes were investigated using the time-dependent Hartree-Fock approach and the Austin Model I semi-empirical Hamiltonian.
TL;DR: The results suggest that the investigated ligands might have microscopic nonlinear optical (NLO) behavior with nonzero values, implying nonzero microscopic first hyperpolarizability.
TL;DR: The static and dynamic first hyperpolarizabilities for a series of substituted metallabenzene-based nonlinear optical (NLO) chromophores were determined by time-dependent density functional theory (TDDFT).
Abstract: The static and dynamic first hyperpolarizabilities for a series of substituted metallabenzene-based nonlinear optical (NLO) chromophores were determined by time-dependent density functional theory (TDDFT). The electronic excitation contributions to the first hyperpolarizability are rationalized in terms of the two-level model. The effects on the hyperpolarizabilities of (a) the metal center (Os, Ir, Pt); (b) the ligand environment (PH3, CO, Cl); (c) various donor and acceptor substituents (NH2, OH, Me, H, Cl, Br, I, COOMe, COOH, CN, NO2); and (d) the length of pi-conjugation were studied. Our calculations predict that metallabenzenes have significant second-order NLO susceptibilities, ranging from = 1.0 x 10(-29) to 5.6 x 10(-28) esu and from mu = 3.0 x 10(-47) to 1.1 x 10(-44) esu, that can be tuned by changing the metal center and/or ligand environment.
TL;DR: In this paper, the first static hyperpolarizabilities of model complexes [CoCp(H 2 PCH 2 CH 2 PH 2 )( p -NCC 6 H 4 R)] 2+ were determined, which are due to weak electronic coupling between organometallic fragment and the nitrile ligands.
Abstract: Density functional theory calculations were performed to determine first static hyperpolarizabilities ( β ) of model complexes [CoCp(H 2 PCH 2 CH 2 PH 2 )( p -NCC 6 H 4 R)] 2+ . The results show that these complexes have low hyperpolarizabilities which are due to weak electronic coupling between the organometallic fragment and the nitrile ligands. It was shown that in these complexes the electronic excitation responsible for second-order non-linear optical response is a ligand to metal charge transfer. The results also show the inverse relationship between the first hyperpolarizability and the corresponding electronic transfer energy gaps.
TL;DR: The first implementation of the quadratic response function for multiconfigurational self-consistent-field wave functions of solvated molecules described by a polarizable continuum model employing a molecule-shaped cavity is presented.
Abstract: We present the first implementation of the quadratic response function for multiconfigurational self-consistent-field wave functions of solvated molecules described by a polarizable continuum model employing a molecule-shaped cavity. We apply the methodology to the first hyperpolarizability β and, in particular, the second-harmonic generation process for a series of conjugated push-pull oligomers, as well as for para-nitroaniline. The effect of solvation on the dispersion of the hyperpolarizability and the change in the hyperpolarizability for increasing chain length of the oligomers in vacuum and in solution is considered. The effect of a correlated description is analyzed by comparing the Hartree-Fock hyperpolarizabilities to the multiconfigurational self-consistent-field hyperpolarizabilities. The effect of geometry relaxation in the solvent on the properties of the solvated molecules are also investigated.
TL;DR: The simulation results are in good agreement with experimental frequency spectra obtained from Kerr effect and related spectroscopies, but fail to reproduce the experimental band near 60 cm(-1).
Abstract: A molecular dynamics simulation study is presented for the dynamics of the polarizability anisotropy of liquid water using the SPC/E model and a dipolar induction scheme that involves the intrinsic polarizability and first hyperpolarizability tensors obtained from ab initio quantum chemical calculations at the MP2/6-311++G(d,p) level. The time-correlation functions for the collective polarizability anisotropy, the optical Kerr effect response, and the frequency spectra are analyzed in terms of the intrinsic and induced polarizability contributions. At short times, the simulated Kerr nuclear response exhibits maxima near 15, 50 and 180 fs, followed by a diffusive tail which has been fitted by a bi-exponential with time constants ca. 0.4 and 2.5 ps. The short time features are in good agreement with available simulation and experimental results. The agreement with experiments is less satisfactory for the diffusive components. The main features of the frequency spectrum include a rotational-diffusion peak centered around 3 cm−1, a collision-induced (hindered translations) band near 200 cm−1, and a broad librational band at 450 cm−1. The simulation results are in good agreement with experimental frequency spectra obtained from Kerr effect and related spectroscopies, but fail to reproduce the experimental band near 60 cm−1.
TL;DR: In this article, the microscopic origin of the nonlinear response has been investigated by using semi-empirical ZINDO∕S calculations in conjunction with standard time-dependent perturbation theory to evaluate the molecular hyperpolarizability tensor of a model α-helix composed of glycine residues.
Abstract: Quantitative measurements of second-harmonic generation optical activity (SHG-OA) have been performed for α-helical polypeptides poly-(γ-benzyl-L-glutamate) and poly-(γ-ethyl-L-glutamate) adsorbed at the air∕water interface, with the fundamental frequency ℏω=2.96eV (λ=417nm). The chiral component of the nonlinear susceptibility χXYZ(2) is small for both polymers, being comparable in magnitude with the susceptibility χXXZ(2) of the clean air∕water interface. The microscopic origin of the nonlinear response has been investigated by using semiempirical ZINDO∕S calculations in conjunction with standard time-dependent perturbation theory to evaluate the molecular hyperpolarizability tensor of a model α-helix composed of glycine residues. Calculated nonlinear susceptibilities (per monomer unit) are in good agreement with experimental measurements for both the chiral and achiral response. The computational results indicate that charge transfer transitions of the α-helix have a large influence on the achiral comp...