Showing papers on "Hyperpolarizability published in 2004"
TL;DR: It is demonstrated that the optical and nonlinear optical (NLO) properties are strongly influenced by the symmetry of the complexes, the nature of the ligands (donor endgroups and pi linkers), and the natureof the metallic centers.
Abstract: A series of D 3 (Fe I I , Ru I I , Zn I I , Hg I I ) and D 2 d (Cu I , Ag I , Zn I I ) octupolar metal complexes featuring different functionalized bipyridyl ligands has been synthesized, and their thermal, linear (absorption and emission), and nonlinear optical (NLO) properties were determined. Their quadratic NLO susceptibilities were determined by harmonic light scattering at 1.91 μm, and the molecular hyperpolarizability (β 0 ) values are in the range of 200-657×10 - 3 0 esu for octahedral complexes and 70-157 x 10 - 3 0 esu for tetrahedral complexes. The octahedral zinc(n) complex 1e, which contains a 4,4'-oligophenylenevinylene-functionalized 2,2'-bipyridine, exhibits the highest quadratic hyperpolarizability ever reported for an octupolar derivative (λ m a x = 482 nm, β 1 . 9 1 (1e)=870 × 10 - 3 0 esu, β 0 (1e) =657 ×10 - 3 0 esu). Herein, we demonstrate that the optical and nonlinear optical (NLO) properties are strongly influenced by the symmetry of the complexes, the nature of the ligands (donor endgroups and π linkers), and the nature of the metallic centers. For example, the length of the n-conjugated backbone, the Lewis acidity of the metal ion, and the increase of ligand-to-metal ratio result in a substantial enhancement of β. The contribution of the metal-to-ligand (MLCT) transition to the molecular hyperpolarizability is also discussed with respect to octahedral d 6 complexes (M=Fe, Ru).
153 citations
TL;DR: This work has synthesized conjugated polyynes that contain up to 20 consecutive sp-hybridized carbons, and they have determined their nonresonant gamma-values as a function of the number of acetylene repeat units, with an exponent that is both larger than theoretically predicted for polyynes and substantially higher than that observed for polyenes or polyenynes.
Abstract: Polyynes represent a unique class of conjugated organic compounds. The third-order nonlinear optical response of polyynes has been extensively modeled theoretically, and it is generally believed that the increase in molecular second hyperpolarizability (gamma) as a function of length for polyynes should be lower than that for polyenes. Experimental evidence to test this prediction, however, has been absent. We have synthesized conjugated polyynes that contain up to 20 consecutive sp-hybridized carbons, and we have determined their nonresonant gamma-values as a function of the number of acetylene repeat units (n). These gamma-values demonstrate a power-law behavior versus n(gamma approximately n(4.28+/-0.13)), with an exponent that is both larger than theoretically predicted for polyynes and substantially higher than that observed for polyenes or polyenynes. Furthermore, no saturation of the linear or nonlinear optical properties is observed.
149 citations
TL;DR: In this article, the mean static first hyperpolarizability (β0) was obtained for (FH)2{e}(HF) and its neutral core (HF) 2{e](HF), at the CISD level of theory.
Abstract: A theoretical prediction of the nonlinear optical (NLO) properties of the hydrogen fluoride trimer anion (FH)2{e}(HF) reveals that this electron-solvated cluster possesses exceptionally large static first hyperpolarizability. Using the d-aug-cc-pVDZ basis set supplemented with diffusive bond functions (BF), we obtained the mean static first hyperpolarizability (β0) for (FH)2{e}(HF) and its neutral core (HF)2{}(HF) at the CISD level of theory. The β0 is 8.1 × 106 au for (FH)2{e}(HF) and 5.1 au for (HF)2{}(HF). Obviously, the excess electron is the key factor in bringing to (FH)2{e}(HF) the significantly large NLO response. The other properties of (FH)2{e}(HF) are also much larger than those of its neutral core. The values of the static dipole moment, mean polarizability, and anisotropy of the polarizability are, respectively, μ = 1.5764 au, α0 = 654.67 au, and Δα = 224.71 au for the anion, and μ = 0.9351 au, α0 = 17.34 au, Δα = 5.40 au for the neutral core. In addition, the field dependences of the polariz...
130 citations
TL;DR: The dispersion of cubic nonlinearity in the organometallic dendrimer 1,3, 5-(3,5-{trans-[(dppe)2(4-O2NC6H4CC)RuCC]}2C6H3CCC6H 4-4-CC)3C 6H3 can be understood in terms of an interplay of two-photon absorption and absorption saturation.
Abstract: The dispersion of cubic nonlinearity in the organometallic dendrimer 1,3,5-(3,5-{trans-[(dppe)2(4-O2NC6H4CC)RuCC]}2C6H3CCC6H4-4-CC)3C6H3 can be understood in terms of an interplay of two-photon absorption and absorption saturation. Simple dispersion relations reproduce the behavior of both the real and imaginary components of the hyperpolarizability.
107 citations
TL;DR: It is found that the dipole-bound excess electron is the key factor in the extraordinary first hyperpolarizability of (H2O-)(3) species, which will provide a future in the development of some materials with the excess electron that exhibit large nonlinear optical response.
Abstract: This work predicts the extraordinary hyperpolarizability of inorganic clusters: two water trimer anions. The first hyperpolarizabilities of (H2O-)(3) are considerable, beta(0)=1.715 x 10(7) a.u. for configuration A and beta(0)=1.129 x 10(7) a.u. for configuration B at MP2/d-aug-cc-pVDZ+x level. The first hyperpolarizabilities of (H2O-)(3) (configuration A) and related systems [(H2O)(3) and (H2O)(3)F-] are compared at the MP2/d-aug-cc-pVDZ+x level. These results are beta(0)=1.715 x 10(7) a.u. for (H2O-)(3), beta(0)=35 a.u. for (H2O)(3) [the neutral core of (H2O-)(3)], and beta(0)=46 a.u. for (H2O)(3)F-). Comparing the beta(0) values of related systems, we find that the dipole-bound excess electron is the key factor in the extraordinary first hyperpolarizability of (H2O-)(3) species. It will provide a future in the development of some materials with the excess electron (e.g., electrides) that exhibit large nonlinear optical response.
106 citations
TL;DR: The electronic and vibrational contributions to the dipole moment, polarizabilities, and first hyperpolarizabilities of HArF are reported and complementary data is provided for the understanding of the electronic structure of this interesting argon derivative.
Abstract: The electronic and vibrational contributions to the dipole moment, polarizabilities, and first hyperpolarizabilities of HArF are reported. These have been computed by using a series of systematically built basis sets and a hierarchy of computational methods. HArF has a very large first hyperpolarizability along the z axis. This has been rationalized by invoking the difference in the electronic structure between the ground and the first excited state. The argon fluorohydride has been recently derived and characterized. The present study provides complementary data for the understanding of the electronic structure of this interesting argon derivative.
100 citations
TL;DR: A survey of the largest second-order molecular susceptibilities finds what appears to be a universal gap between the experimental results and the fundamental limits of quantum sum rules, beta, which is due to an unfavorable arrangement of excited state energies.
Abstract: Quantum sum rules impose limits on the hyperpolarizability, β. A survey of the largest second-order molecular susceptibilities finds what appears to be a universal gap between the experimental results and the fundamental limits. In this work, we use theory, linear spectroscopy, Raman spectroscopy, and measured values of β (using hyper-Rayleigh scattering and Stark Spectroscopy) to show that this gap is due to an unfavorable arrangement of excited state energies. The question of whether this result is a universal property of a quantum system or a matter of present paradigms for making molecules is discussed.
95 citations
TL;DR: In this paper, the spin multiplicity effects on the second hyperpolarizability (γ) were investigated for a small-size open-shell neutral conjugated model, the C5H7 radical, in the doublet, quartet, and sextet stat
Abstract: The spin multiplicity effects on the second hyperpolarizability (γ) are investigated for a small-size open-shell neutral conjugated model, the C5H7 radical, in the doublet, quartet, and sextet stat...
76 citations
TL;DR: Second-order nonlinear optical properties of helicenes and phenylenes have been theoretically investigated at the time-dependent Hartree-Fock level using the Austin model 1 semiempirical Hamiltonian and it is found that beta increases monotonically with the size of the system and slightly depends on the nature of the helix.
Abstract: The second-order nonlinear optical properties of helicenes and phenylenes have been theoretically investigated at the time-dependent Hartree–Fock level using the Austin model 1 semiempirical Hamiltonian. Both the antisymmetric isotropic component of the first hyperpolarizability (β) and its projection on the dipole moment (β∥) have been determined for increasingly large helical systems as well as for their analogs substituted by donor/acceptor pairs. It is found that (i) in nonsubstituted helicenes and phenylenes, β increases monotonically with the size of the system and slightly depends on the nature of the helix; (ii) the corresponding β∥ is mostly determined by the radial component of the first hyperpolarizability vector; (iii) in helicenes, β∥ is positive and presents quasiperiodic oscillations with the helix; (iv) in phenylenes, β∥ depends upon the size of the helix and it can be either positive or negative as a result of the differences in evolution with N of the radial components of the dipole mo...
73 citations
TL;DR: The CC/MM results for the second harmonic generation second hyperpolarizability compare excellently with experimental data while a significant overestimation is found when using the CC/DC model, which has an enormous effects on this fourth-order property.
Abstract: In this article we report the first calculations of second harmonic generation second hyperpolarizability of liquid water using coupled cluster/molecular mechanics (CC/MM) methods or coupled cluster/dielectric continuum (CC/DC) methods. The latter approach treats the solvent as an isotropic homogeneous fluid while the former accounts for the discrete nature of the solvent molecules. The CC/MM approach may include or exclude polarization effects explicitly. Alternatively, polarization effects may be included using perturbation theory. The CC descriptions implemented are the coupled cluster second-order approximate singles and doubles (CC2) and coupled cluster singles and doubles models. The second harmonic generation second hyperpolarizabilities are, depending on the model, obtained using either an analytical implementation of the cubic response function or using an analytical implementation of the quadratic response function combined with the finite field technique. The CC/MM results for the second harmonic generation second hyperpolarizability compare excellently with experimental data while a significant overestimation is found when using the CC/DC model. Particular, the cavity radius in the CC/DC calculations have an enormous effects on this fourth-order property.
66 citations
TL;DR: In this paper, the dipole polarizability, first hyperpolarizability and UV-Vis spectrum of the recently identified nano-sized tetrahedral cluster of Au 20 have been investigated by using time-dependent density functional response theory.
TL;DR: It turns out that Hartree-Fock, second-order Møller-Plesset, and hybrid density functional theory (DFT) methods provide the incorrect sign for beta of short and medium size oligomers.
Abstract: We have investigated the geometries as well as the longitudinal dipole moment (μ), polarizability (α), and first hyperpolarizability (β) of polymethineimine oligomers using different approaches [Hartree–Fock (HF), second-order Moller–Plesset (MP2), and hybrid density functional theory (DFT) methods (B3LYP and PBE0)] for evaluating the geometries and the nonlinear optical properties. It turns out that (i) HF and the selected DFT methods provide the incorrect sign for β of short and medium size oligomers. (ii) The B3LYP and PBE0 electron correlation correction are too small for μ, too large for α, and for some oligomer lengths, they are in the wrong direction for β. (iii) On the contrary to polyacetylene, the hybrid-DFT geometries are in poor agreement with MP2 geometries; the former showing much smaller bond length alternations.
TL;DR: In this article, a comprehensive investigation of the class of compounds shown in Fig. 1 has been carried out at the semi-empirical level of the theory to determine their linear and non-linear optical properties.
Abstract: A comprehensive investigation of the class of compounds shown in Fig. 1 has been carried out at the semi-empirical level of the theory to determine their linear and non-linear optical properties. These molecular systems show very large non-linear optical activity. Geometries of all molecules were optimized at the semi-empirical level of the theory using AM1 Hamiltonian by MOPAC 6.0 computational package. The heats of formation, dipole moments (D), polarizabilities (α), static hyperpolarizabilities (β) and frontier molecular orbital energies are calculated as a function of the twist angle (1234), between the diaminomethylene unit and the six membered fused rings as shown in Fig. 1 using AM1 Hamiltonian using MOPAC 6.0 computational chemistry package. All β values that we report here are the magnitude of static hyperpolarizability. The frontier molecular orbital calculations clearly show the inverse relationship of HOMO–LUMO gap with the total static hyperpolarizability. The enormous enhancement of the hyperpolarizability for a particular dihedral angle of these designed novel molecular systems is also reported. The study reveals that these classes of organic compounds show very large non-linear optical properties and hence in general may influence in finding and developing potential non-linear optical materials.
TL;DR: In this paper, the authors used femtosecond degenerate four-wave mixing (DFWM) to study third-order nonlinear optical properties of electropolymerized Fe(III) tetrakis(p-hydroxyphenyl)porphyrin films.
Abstract: Femtosecond degenerate four-wave mixing (DFWM) was used to study third-order nonlinear optical properties of electropolymerized Fe(III) tetrakis(p-hydroxyphenyl)porphyrin films. Third-order nonlinear susceptibility χ1111(3)(−ω;ω,ω,−ω) was determined at 760−1350 nm. Susceptibility χ(3) values for a 500 nm thick porphyrin film ranged between (2−15)×10-20 m2V-2 ((1.4−10.7)×10-12 esu). The time response of electronic nonlinearities was faster than 120 fs. The sum-over-states model was applied to determine real and imaginary components for χ(3) and molecular second hyperpolarizability, γ. At wavelengths <800 nm, porphyrin film χ(3) is enhanced due to the 700 nm one-photon charge-transfer (CT) band. Nonlinear properties at longer wavelengths are determined by a two-photon resonance with a 17 400 cm-1 state. This state was not observed for other porphyrins and is attributed to a two-photon CT transition. Due to the resonance with the two-photon state, porphyrin Im χ(3) and two-photon absorption cross-section δ i...
TL;DR: In this article, the second-order nonlinear optical (NLO) materials have attracted a lot of interest because of foreseeable applications in optoelectronic technology, and organic compounds are attractive for this purpose because of their large and fast responses combined with the flexibility of organic synthesis which hastens the design of new chromophores.
Abstract: Second-order nonlinear optical (NLO) materials have attracted a lot of interest because of foreseeable applications in optoelectronic technology. In particular, organic compounds are attractive for this purpose because of their large and fast responses combined with the flexibility of organic synthesis which hastens the design of new chromophores. The first generation of NLO organic chromophores consists of one-dimensional (1D) p-conjugated systems end-capped with donor (D) and acceptor (A) moieties. Experimental and theoretical work has shown during the last decades how to choose the D/A strengths and p segments for optimizing the second-order NLO responses. Later, two-dimensional (2D) octupolar molecules such as 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) were shown to exhibit second-order NLO responses that can be as large as those of their dipolar analogues. In addition, with these 2D structures, some of the limitations of the 1D dipolar structures were displaced, if not overcome. Indeed, 1D compounds suffer from the transparency–efficiency tradeoff, which is difficult to achieve because the desirable increase in b(the first hyperpolarizability) is accompanied by a bathochromatic shift of the electronic transitions. Moreover, their dipolar nature and the predominance of dipole–dipole intermolecular interactions favor the formation of centrosymmetric crystal arrangements which exhibit no second harmonic generation (SHG) responses. In addition, phase-matching conditions cause only a fraction of the microscopic response to be preserved at the macroscopic scale. On the other hand, octupolar compounds present an improved nonlinearity/transparency tradeoff, enable non-centrosymmetric crystal structures owing to their lack of permanent dipole moment, and present large offdiagonal b tensor components that can give rise to large macroscopic SHG responses.
TL;DR: In this paper, the second-order hyperpolarizability of carbon nanotubes has been investigated in the light of a simple model of the optical nonlinearities near the optical band-gap.
Abstract: Femtosecond pump–probe experiments have been carried out on an ensemble of single-wall carbon nanotubes deposited on a glass substrate. Measurements of transient changes of transmission and reflection provide an estimate of the real and imaginary parts of the second-order hyperpolarizability of carbon nanotubes. These values are compared with previous measurements and are discussed in the light of a simple model of the optical nonlinearities near the optical band-gap.
TL;DR: To reexamine the established "auxiliary donor" effect of thiophene in nonlinear optical (NLO) chromophores, two isomeric donor-acceptor azo dyes are prepared, differing only in the position of theThiophene.
Abstract: To reexamine the established "auxiliary donor" effect of thiophene in nonlinear optical (NLO) chromophores, we have prepared two isomeric donor-acceptor azo dyes, differing only in the position of the thiophene. Experimental analysis of these chromophores, including electric field-induced second harmonic generation (EFISH) and X-ray crystallography, contradicts previous experimental findings on similar chromophores but is consistent with the majority of computational precedents. We have found that the thiophene on the donor side produces a compound with a larger dipole moment; however, the isomer with the thiophene on the acceptor side is more nonlinear and has a higher figure of merit for NLO device applications.
TL;DR: In this paper, the synthesis of a series of high temperature triaryl amino chromophores with unprecedented hyperpolarizability values for potential EO applications is described, which are bridged to powerful acceptors such as tricyanovinyldihydrofuran via vinyl thiophene linkages.
TL;DR: In this paper, the authors used equilibrium statistical mechanics and Monte Carlo (MC) methods in a lattice-based model, to investigate how the molecular properties translate into the electro-optic (EO) response of the material.
Abstract: The optical properties of organic chromophores, in the class of nonlinear optical molecules, have improved dramatically. These chromophores have large hyperpolarizability and large permanent dipole moments, in excess of 10 D. When these molecules are mixed with a host polymer at high chromophore density and processed using an aligning electric poling field, the resulting material does not have the electro-optic (EO) response promised by the individual molecules. We have used equilibrium statistical mechanics, and Monte Carlo (MC) methods in a lattice-based model, to investigate how the molecular properties translate into the EO response of the material. We compare our MC results with a previously developed analytic theory and find good agreement when certain assumptions about the analytic theory are made. By use of the MC methods to compute order parameters for chromophores at high density on a lattice in the presence of an external uniform poling field, we find that greater order and hence greater EO per...
TL;DR: The linear and nonlinear optical properties of the 3-methyl-4-nitropyridine-1-oxyde (POM) crystal have been evaluated using semiempirical quantum chemistry techniques and the validity of the multiplicative scheme is assessed.
Abstract: The linear and nonlinear optical properties of the 3-methyl-4-nitropyridine-1-oxyde (POM) crystal have been evaluated using semiempirical quantum chemistry techniques. The scheme includes (i) the evaluation of the polarizability and first hyperpolarizability of increasingly large one-dimensional, two-dimensional, and three-dimensional clusters of POM, (ii) the use of the time-dependent Hartree-Fock approach to determine the static and dynamic responses in combination with semiempirical Austin model 1 Hamiltonian, (iii) the assessment, for the POM monomer and dimer, of the electron correlation effects using second-order Moller-Plesset perturbation theory with several basis sets containing polarization and diffuse functions, (iv) the assessment of the validity of the multiplicative scheme and its application to get effective polarizability and first hyperpolarizability of the POM unit cell in the crystal, (v) the use of a sum-over-states approach to attribute the first hyperpolarizability to a dominant charge-transfer excited state, and (vi) comparison with experimental data as well as with calculated values obtained using the oriented gas approximation.
TL;DR: In this article, the static polarizability and second hyperpolarizability of fullerenes and carbon nanotubes were investigated by varying their structure. And the results showed that the carbon Nanotubes exhibit significantly larger second hyper polarizabilities compared to a fullerene containing the same number of carbon atoms.
Abstract: Utilizing a point-dipole interaction model, we present an investigation of the static polarizability and second hyperpolarizability of fullerenes and carbon nanotubes by varying their structure. The following effects are investigated: (1) the length dependence of the components of the static polarizability, (2) the static second hyperpolarizabilities of C60 and C70, (3) the symmetry effects on the static second hyperpolarizability, (4) the length dependence of the components of the static second hyperpolarizability, and (5) the diameter dependence of the static second hyperpolarizability. It is demonstrated that the carbon nanotubes exhibit significantly larger second hyperpolarizabilities compared to a fullerene containing the same number of carbon atoms. Furthermore, the calculations show that the carbon nanotubes have a much larger directionality of the static second hyperpolarizability than the fullerenes.
TL;DR: The wavelength dependence of the quadratic hyperpolarizability of 11 nm diam gold nanoparticles, is reported as measured by hyper Rayleigh scattering, and a strong enhancement is observed for harmonic frequencies in resonance with the dipolar surface plasmon excitation.
Abstract: The wavelength dependence of the quadratic hyperpolarizability of 11 nm diam gold nanoparticles, is reported as measured by hyper Rayleigh scattering An important photoluminescence background underlying the hyper Rayleigh signal is observed, a contribution attributed to radiative electron–hole recombinations following multiphoton excitation favored by adsorbed organic compound like citrate on the surface of the nanoparticles The absolute value of the quadratic hyperpolarizability of gold spherical nanoparticles is determined and a strong enhancement is observed for harmonic frequencies in resonance with the dipolar surface plasmon excitation No contribution of the interband transition is observed The absolute values reported, βC=51×10−26 esu at the second harmonic energy 239 eV, have been measured with femtosecond long laser pulse, and are 1 order of magnitude weaker that the one previously reported with nanosecond long pulses This difference can be related to similar measurements performed on the second order hyperpolarizability of gold nanoparticles and may be attributed to different electronic relaxation regimes Finally, the spectrum of the quadratic hyperpolarizability is compared to the theoretically expected one
TL;DR: In this paper, the authors reported the first measured second hyperpolarizability to breach the quantum gap, which is known as the Quantum Quantum gap, by cross-linking a C60-polymer film using delocalized electrons from neighboring three-dimensional C60 molecules.
Abstract: Sum rules predict the largest off-resonance electronic nonlinear susceptibility allowed by quantum mechanics. The range between (10-3/2 to 1) times the physical limit level has until now not been penetrated experimentally and has become known as the quantum gap. We report the first measured second hyperpolarizability to breach the quantum gap. Through cross-linking, the C60-polymer film reported used delocalized electrons from neighboring three-dimensional C60 molecules and realized significant red shift of its energy levels. An ultrafast second hyperpolarizability of 9.6 × 10-32 esu (55% of the physical limit) has been achieved.
TL;DR: A series of 1,3,5-tricyano-2,4,6-tris(styryl)benzene derivatives (1,2) and dendrimers (3) have been synthesized and their first hyperpolarizabilities (β) were determined.
Abstract: A series of 1,3,5-tricyano-2,4,6-tris(styryl)benzene derivatives (1,2) and dendrimers (3) have been synthesized and their first hyperpolarizabilities (β) were determined. Whereas the λmax values of 1–3 are similar, the oscillator strength increases with the molecular size. For all compounds, the Stokes shifts are significantly larger when NAr2 is used as the donor. The β(0) values of 1–3 range from 252 to 507 × 10–30 esu and increases with the number of octupolar units in the molecule. When the octupolar molecules are linked to the 1,3,5-position of the benzene ring by flexible ether linkages, the β(0) value increases by 1.7 fold. On the other hand, octupolar monodendron based on the nitrogen atom core and 1,3,5-tricyano-2,4,6-tris(p-diarylaminostyryl)benzene moieties at the periphery exhibits β(0) = 507 × 10–30 esu, which is one of the largest β(0) values reported for the octupolar molecules.
TL;DR: New push-pull NLO-phores based on lanthanide complexes featuring an annelated dibutylaminophenyl functionalised terpyridyl ligand have been synthesised and shown to exhibit large first-order hyperpolarizability.
TL;DR: In this article, a tricyanopyrroline acceptor is shown to yield a factor of approximately three improvement over the commonly used triciyanofuran acceptor, leading to routine realization of electro-optic coefficients greater than 100 pm/V at telecommunication wavelengths.
TL;DR: In this article, an ab initio molecular orbital theoretical approach to the origin of nonlinear optical properties in the NLO-based materials from the viewpoint of ''electron pairs'' assigned to the individual chemical bond was presented.
Abstract: We present an ab initio molecular orbital theoretical approach to the origin of nonlinear optical (NLO) properties in the $\mathrm{Te}{\mathrm{O}}_{2}$-based materials from the viewpoint of ``electron pairs'' assigned to the individual chemical bond. Localized static dipole moments, linear polarizabilities, and hyperpolarizabilities of the individual chemical bonds in the $\mathrm{Te}{\mathrm{O}}_{4}$ and $\mathrm{Te}{\mathrm{O}}_{3}$ structural units are calculated in terms of the localized molecular orbitals. While no significant difference is found between these structural units in both the static bond dipole moment and the linear polarizability, the hyperpolarizabilities exhibit large differences. The $\mathrm{Te}{\mathrm{O}}_{4}$ structural unit shows much higher second hyperpolarizability than the $\mathrm{Te}{\mathrm{O}}_{3}$ structural unit. It is shown that the lone pair of the electrons on Te atom has the very large nonlinear response property, which should cause the high third-order NLO efficiency of the $\mathrm{Te}{\mathrm{O}}_{2}$-based materials. Geometric dependency of the second hyperpolarizability is also discussed on the basis of the calculations on the several deformed structural units.
25 Oct 2004
TL;DR: In this article, a new benzimidazole, 2-(4′-amino-2′-hydroxyphenyl)-6-nitrobenzimidrazole (LEN), with promising applications in nonlinear optics were synthesized, purified and characterized by classical techniques.
Abstract: A new benzimidazole, 2-(4′-amino-2′-hydroxyphenyl)-6-nitrobenzimidazole (LEN), with promising applications in nonlinear optics were synthesized, purified and characterized by classical techniques. The UV–Vis and steady-state fluorescence of LEN in solution were applied in order to characterize the photophysical behaviour of this new fluorescent dye. The Hyper-Rayleigh Scattering study indicates a remarkable increase in the β absolute value (1197.3 ± 1.2 × 10 −30 esu) of the LEN in acetone at 1064 nm, when comparing with a previously described benzoxazole (BO6). The ratio between the experimental β and the maximum theoretical value using a two-level model was also improved by a factor 6. Ab initio and semi-empirical calculations of the dipole moments and the first hyperpolarizability are also presented. The enhancement in the experimental hyperpolarizability value in relation to BO6 is explained in terms of the benzimidazolic ring basicity and a prototropic effect (annular tautomerism) present in the LEN, identified as a resonance-assisted hydrogen bond, which leads to a stronger electronic delocalization.
TL;DR: A novel D-pi-A system in which tetrathiafulvalene and pi-extended TTFs as strong electron donors are covalently connected to a tricarbonyl (eta(6)-arene)chromium complex as the acceptor moiety through a systematically increased conjugated bridge of vinylene units has been synthesized by Wittig-Horner olefination reaction.
Abstract: A novel D-pi-A system in which tetrathiafulvalene (TTF) and pi-extended TTFs as strong electron donors are covalently connected to a tricarbonyl (eta(6)-arene)chromium complex as the acceptor moiety through a systematically increased conjugated bridge of vinylene units (12a-c, 16a-c) have been synthesized by Wittig-Horner olefination reaction The electronic spectra as well as the electrochemical data reveal a different behavior of TTF derivatives (12a-c) and of exTTF derivatives (16a-c) Cyclic voltammetry shows the influence of the tricarbonylchromium arene on the oxidation potentials in compounds 12a-c, and no remarkable effect is observed for exTTFs (16a-c) The nonlinear optical properties of 12a-c and 16a-c have been calculated by using the ab initio CPHF/6-31G//B3P86/6-31G model, and the time-dependent density functional theory (TD-DFT) method has been used for the calculation of the electronic transitions The calculations reveal that an intraligand charge-transfer transition (ILCT) and the metal to ligand charge-transfer transition (MLCT) are responsible for the nonlinear response In addition, the large angles formed by the ground-state dipole moment and the vectorial hyperpolarizability are responsible for the mubeta values determined experimentally by the EFISH technique
08 Mar 2004
TL;DR: In this paper, an ab initio HF and MP2 study of the static (hyper)polarizabilities of 2,4-substituted imidazoles and thiazoles is presented.
Abstract: An ab initio HF and MP2 study of the static (hyper)polarizabilities of 2,4-substituted imidazoles and thiazoles is presented. The comparison of the two types of five-membered heterocycles suggests, that the exocyclic heteroatoms have much more influence upon the calculated hyperpolarizabilities, than the ring heteroatoms. It has been found, that adding diffuse functions to the 6-31G** basis set and inclusion of the electron correlation result in drastic changes in the second hyperpolarizability. The changes are more pronounced for the structures with larger number of sulfur atoms. A HF/6-31G** investigation of a push–pull system, in which thiorhodanine has been chosen as acceptor fragment shows an enhancement of the molecular polarizabilities with respect to the corresponding typical donor-acceptor NH2/NO2 polyene. 2003 Elsevier B.V. All rights reserved.