Spectrum and polarizability of polyphenyls in the Pariser-Parr-Pople approximation

The Pariser-Parr-Pople approximation is used to calculate the electronic structure, electronic absorption spectrum, and polarizability for biphenyl, terphenyl, and quaterphenyl. The self-consistent MO are taken as basis functions for the multiconfiguration approximation. The minimum number of singly excited configurations is included. Bond orders, bond lengths, transition energies, oscillator strengths, and wave functions of the excited states are given in that approximation. The results are compared with published data and, where possible, with experiment. Calculation of the -electron polarizability with allowance for configuration interaction is discussed. The agreement with experiment is satisfactory for all the characteristics calculated.     

Polarization justified Fukui functions: the theory and applications for molecules

The Fukui functions based on the computable local polarizability vector have been presented for a group of simple molecules. The necessary approximation for the density functional theory softness kernel has been supported by a theoretical analysis unifying and generalizing early concepts produced by the several authors. The exact relation between local polarizability vector and the derivative of the nonlocal part of the electronic potential over the electric field has been demonstrated. The resulting Fukui functions are unique and represent a reasonable refinement when compared to the classical ones that are calculated as the finite difference of the density in molecular ions. The new Fukui functions are strongly validated by their direct link to electron dipole polarizabilities that are reported experimentally and by other computational methods.     

External electric field effects on absorption, fluorescence, and phosphorescence spectra of diphenylpolyynes in a polymer film

External electric field effects on absorption, fluorescence, and phosphorescence spectra of a series of unsubstituted diphenylpolyynes have been examined in a PMMA film. The analysis of the electroabsorption spectra indicates that the shorter diphenylpolyynes exhibit only the change in molecular polarizability, whereas the longer ones exhibit the change both in dipole moment and in molecular polarizability following absorption. The finding of the change in dipole moment following absorption of centrosymmetric diphenylpolyynes is interpreted in terms of the symmetry distortion upon doping a polymer film. When the external electric field is applied, the fluorescence yield is reduced and enhanced, respectively, in diphenylacetylene and diphenyloctatetrayne, indicating that the rate of the nonradiative process from the fluorescence state is accelerated in diphenylacetylene and decelerated in diphenyloctatetrayne by an external electric field. All of the diphenylpolyynes used in the present study exhibit the change in molecular polarizability following the phosphorescence process.     

Self-assembly of a tripodal pseudorotaxane on the surface of a titanium dioxide nanoparticle

This paper describes the self-assembly of a heterosupramolecular system consisting of a tripodal viologen, adsorbed at the surface of a titanium dioxide nanoparticle, that threads a crown ether to form a pseudorotaxane. The viologen, a 1,1'-disubstituted-4,4'-bipyridinium salt with a rigid tripodal anchor group, has been synthesized. This viologen is adsorbed at the surface of a titanium dioxide nanoparticle in solution. As intended, this tripodal viologen is both oriented normal to and displaced from the surface of the nanoparticle and threads a crown ether to form the heterosupramolecular complex. The threading of the crown ether by the tripodal viologen to form the above pseudorotaxane complex at the surface of a titanium dioxide nanoparticle has been studied by (1)H NMR, optical absorption spectroscopy, and cyclic voltammetry.     

Solvatochromic behavior of donor-acceptor-polyenes: dimethylamino-cyano-diphenylbutadiene

4-(Dimethylamino)-4'-cyano-1,4-diphenylbutadiene (DCB) and 4-(dimethylamino)-2,6-dimethyl-4'-cyano-1,4-diphenylbutadiene (DMDCB) have been characterized spectroscopically. Quantum chemical calculations were performed for comparison. Solvatochromic shifts of the fluorescence were strong and showed a linear dependence on the solvent polarity parameters, whereas shifts in the absorption spectra are very weak only correlate better with the polarizability of the solvents. Excited state dipole moments derived from fluorescence using the Onsager model are very large and similar for both compounds. It is concluded that a strongly allowed and highly dipolar pi, pi* state is the lowest excited state in polar solvents. The strong difference in absorption and fluorescence solvatochromic slopes suggests that the simple Onsager model with a point dipole approximation is not sufficient here.     

Depolarization ratio of Rayleigh scattered radiation by molecules

The depolarization ratios of Rayleigh scattered radiation by molecules has been used to measure the ratio of anisotropic polarizability to isotropic (average) polarizability in the laboratory. The authors have calculated the depolarization ratio for N2, CH3Cl, and H2O from the first principles. It is shown that the depolarization ratio derived from input polarizabilities differs by a factor of about 4 for 1Sigma diatom N2, by a factor of about 2.9 for symmetric top CH3Cl, and by a factor of about 5 for asymmetric top H2O. These large discrepancies arise because in deriving the ratio of anisotropic polarizability to isotropic (average) polarizability from the measured depolarization ratio, the constraints imposed by the conservation of angular momentum have been completely ignored.     

Wavelength-dependent Coulomb explosion in carbon disulphide (CS2) clusters: generation of energetic multiply charged carbon and sulphur ions

A gigawatt laser-induced Coulomb explosion has been observed in carbon disulphide (CS(2)) clusters generating energetic, multiply charged [C](m+) (m = 1-4) and [S](n+) (n = 1-6) atomic ions of carbon and sulphur. The Coulomb explosion shows wavelength dependence. Comparison of these results with our earlier work shows that the polarizability and dipole moment might help in energy absorption from the laser field but they are not mandatory conditions for this low-intensity Coulomb explosion. The results show that in a field of 10(9) W/cm(2), absorption of 266 and 355 nm laser radiation by CS(2) clusters leads to multiphoton dissociation/ionization whereas at 532 nm the whole cluster explodes generating multiply charged atomic ions.     

Dynamic polarizabilities and raman intensities of CO,N2, HCl and Cl2

We have performed first-order (identical to coupled Hartree-Fock) and second-order polarization propagator calculations of the dynamic dipole polarizability tensor for the CO, N₂, HCl and Cl₂ molecules. The derivatives of the polarizability tensor with respect to the internuclear distance at the equilibrium internuclear separation are compared with related data obtained from non-resonance Raman spectra. In most cases the correlation contributions beyond the coupled Hartree-Fock approximation have a more pronounced effect on the derivatives of the polarizability tensor than on the polarizability tensor itself. At both levels of approximation we found that derivatives of the dynamic polarizability tensor with respect to the internuclear separation increase with 10–15% for variation of the frequency from 0 (static polarizability) to about 28500 cm^?1. The depolarization ratio calculated from the polarizability derivatives shows no variation with frequency in the same frequency range.     

Chemical effects in SERS of pyrazine adsorbed on Au-Pd bimetallic nanoparticles: a theoretical investigation

Chemical enhancement in surface-enhanced Raman scattering (SERS) of pyrazine adsorbed on Au-Pd nanoclusters is investigated by using density functional theory. Changing Pd content in the bimetallic clusters enables modulation of the direct chemical interactions between the pyrazine and the clusters. The magnitude of chemical enhancement is correlated well with the induced polarizability for the complexes with low Pd content, which fails for the complexes with high Pd content. Furthermore, the dependence of chemical enhancement on cluster size and coupling is also described by the induced polarizability. Additionally, the chemical enhancement in the cluster-molecule-cluster junction is found to account for as much as 10(3), which suggests that a chemical mechanism might be more important than previously believed, in particular for Au-Pd bimetallic nanoparticle aggregates.     

Controlled interparticle spacing for surface-modified gold nanoparticle aggregates

Aggregation of gold nanoparticles of increasing size has been studied as a consequence of adsorption of 2-aminothiophenol (ATP) on gold nanoparticle surfaces. The capping property of ATP in the acidic pH range has been accounted from UV-vis absorption spectroscopy and surface-enhanced Raman scattering (SERS) studies. The effect of nanoparticle size (8-55 nm) on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects among the gold particles have been critically examined. Various techniques such as transmission electron microscopy, X-ray diffraction, zeta-potential, and average particle size measurement were undertaken to characterize the nanoparticle aggregates. The aggregate size, interparticle distances, and absorption band wavelengths were found to be highly dependent on the pH of the medium and the concentration of the capping agent, ATP. The acquired SERS spectra of ATP relate the interparticle spacing. It has been observed that the SERS signal intensities are different for different sized gold nanoparticles.     

Between geometry, stability, and polarizability: density functional theory studies of silicon clusters Sin (n = 3-10)

The relationship between the polarizability, stability, and the geometry of small-size silicon clusters has been investigated by the density functional theory methods. Results obtained at local density approximation/Vosko-Wilk-Nusair and general gradient approximation/BLYP levels with polarized even-tempered basis set of quadruple zeta quality are presented and compared with those obtained by the B3LYP method, as well as with the ab initio results in recent literature. We have found that the polarizability is directly related to the size of the energy gap between symmetry-compatible bonding and antibonding molecular orbitals, but not necessarily to the size of the HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap. Furthermore, we have defined two structural parameters, namely, the averaged Si-Si distances and the standard deviation of the Si-Si distances, which were found to correlate remarkably well with the binding energy of the clusters and the HOMO-LUMO gap, respectively. These straightforward correlations would, therefore, provide a means to predict the physical properties, in particular, the polarizability and the stability, simply based on the structural information of the cluster.     

Resonance scattering spectroscopy of gold nanoparticle

The gold nanoparticles in diameter of 10-95 nm have been prepared by Frens procedure, all of which exhibit a resonance scattering peak at 580 nm. The mechanism of resonance scattering for gold nanoparticle has been considered according to the wave motion theory of nanoparticle in liquid. The principle of superamolecular interface energy band(SIEB) has been set up and utilized to explain the relationship between the diameter and colors for gold nanoparticle in liquid. A novel spectrophotometric ruler for the determination of the diameter has been proposed according to the relationship of the maximum absorption wavelength and diameter.     

共轭烯烃的共轭极化势

Based on the conjugated polarization theory,it is expressed as the conjugated polarizability potential （CPP）that the discrepancy between the average electrostatic energy of dipolar state and the electrostatic energy of non-polar state in the conjugated polarizability procedure for the conjugated alkenes. The correlation between CPP and the energy of ultraviolet absorption maximum,and the correlation between the energy of frontier molecular orbital obtained by ab initio calculation of quantum chemistry and the energy of ultraviolet absorption maximum have been carried out for the conjugated alkenes. Both correlation equations show a similar estimated precision. Further, the contribution of alkyl polarizability effect to the stability of dipolar state for the alkyl substituted alkenes with the effective polarizability effect index（PEI（ef））was quantified. Relating the above two parameters CPP and PEI（ef）to the energy of ultraviolet absorption maximum of the substituted alkenes in a two-parameter expression with a good prediction ability was obtained:v=1.1746+5.0187CPP-0.43204PEI （ef）,R=0.9995,s=0.0403,F=10853.28,n=23. The investigated results also indicate that it is less effective to reduce the energy of ultraviolet absorption maximum by means of increasing the alkyl substituent groups than lengthening the conjugated backbone chain in the conjugated alkenes.     

Refractometric studies of mesogenic molecules in isotropic solutions

The Lorenz-Lorentz equation for binary isotropic mixtures, consisting of anisotropic molecules, has been derived using the point-dipole approximation taking into account only pair molecular correlations. This permits the calculation of the effect of molecular correlations on the refractive index. Special attention has been paid to the case of infinite dilution in the solvents consisting of isotropic molecules, where an experimental check of the equations is possible. The specific refraction of some solutes with different molecular polarizability anisotropy and polarity has been studied in various solvents. It has been shown, that the main theoretically predicted features are observed in these experiments, but for a quantitative comparison information on the two-particle distribution function is needed.     

Time-dependent quantum theory II. Absorption of light by dimers: Quantum theory and classical analogy

The quantum theory of light absorption by a pair of neighboring absorbers is developed in the point dipole approximation for the circumstance where excited states decay only by radiative damping. Comparison with classical local field theories, in which the monomers are represented by constant, frequency-dependent complex polarizabilities, shows that these local field theories are valid for non-harmonic absorbers only in the weak interaction limit, and only when there exist no states with both monomers simultaneously excited (e.g. one excited vibrationally, the other electronically) that are nearly degenerate with the single excitation states and also connected to them by appreciable transition moments. Failure of the local field theories is, thus, shown to be a consequence of the non-harmonic nature of real absorbers. Using a general relation between the level-shift function and complex polarizability, a recipe is formulated for calculating the complex polarizability and spectrum of a dimer.     

Electric polarizability of small metal spheres

The electric polarizability of small sodium spheres is calculated in a semiclassical approximation based on the spherical jellium model and on the Vlasov equation. Static and dynamic polarizabilities are compared for two kinds of mean field with a smooth and a sharp surface. It is deduced that the position of the centroid of the surface-plasmon resonance is not sensitive to the surface diffuseness of the mean field. Comparison with analogous quantum calculations suggests that an unrealistic feature of the zero-range exchange-correlation force employed in the local-density approximation might play an important role in increasing the static polarizability and decreasing the frequency of the surface-plasmon resonance.     

Cyanobacterial chlorophyll as a sensitizer for colloidal TiO2

Chlorophyll has been extracted from cyanobacteria. The adsorption of chlorophyll on the surface of colloidal TiO(2) through electrostatic interaction was observed. The apparent association constant (K(app)) of chlorophyll-TiO(2) obtained from absorption spectra is 3.78x10(4)M(-1). The K(app) value of chlorophyll-TiO(2) as determined from fluorescence spectra is 1.81x10(4)M(-1), which matches well with that determined from the absorption spectra changes. These data indicate that there is an interaction between chlorophyll and colloidal TiO(2) nanoparticle surface. The dynamics of photoinduced electron transfer from chlorophyll to the conduction band of colloidal TiO(2) nanoparticle has been observed and the mechanism of electron transfer has been confirmed by the calculation of free energy change (DeltaG(et)) by applying Rehm-Weller equation as well as energy level diagram. Lifetime measurements gave the rate constant (k(et)) for electron injection from the excited state chlorophyll into the conduction band of TiO(2) is 4.2x10(8)s(-1).     

The effects of hydrogen and ph on plasmon absorption of gold hydrosol. Electrochemical reactions on nanoelectrodes

A short-wavelength shift in the plasmon absorption band of 3-nm gold nanoparticles at their hydrosol saturation with hydrogen has been discovered and analyzed. It has been shown that dissociative adsorption of hydrogen occurs on a gold nanoparticle followed by the transfer of hydrogen in the form of a proton to a dispersion medium, with an electron remaining on the nanoparticle; i.e., a hydrogen nanoelectrode is realized. A linear increase in the magnitude of the experimentally observed shift in the plasmon resonance band with solution pH has been qualitatively explained.     

Controlling the Formation of Silver Nanoparticles on Silica by Photochemical Deposition and Other Means†

Silver nanoparticles (Ag-NP) on silica were produced in aqueous solution by deposition of silver on colloidal silica in a small cuvette using radiation from a xenon-mercury lamp. Ag-NP were also synthesized on a much larger scale with low-level, long-term visible light irradiation for several months. In both cases, the nanoparticle production was monitored by the appearance of the surface plasmon resonance (SPR) band at around 410 nm. The growth of the nanoparticles was directly related to the time exposed to radiation, which could be tracked spectrophotometrically over time. We also investigated the possibilities of rapid nanoparticle production without the assistance of radiation though silver oxide by adding alkali hydroxide, which is a relatively unexplored approach for syntheses of Ag-NP on silica. The SPR absorption of Ag-NP was used as a tool in evaluating the size and shape of the resulting nanoparticles along with dynamic light scattering and transmission electron microscopy data. In order to better utilize and understand Ag-NP, we present various ways to control their production through initial concentration adjustments, irradiation effects, gravitational fractionation, sonication and silver oxide formation.