The third-order nonlinear optical susceptibility χ^〈3〉 of octupolar molecule with three double bonds was measured using degenerate four wave mixing technique at 532 nm in tetrahydrofuran solution. For comparison, we also measured its analogous dipolar subunit. We found that the χ^〈3〉 value for octupolar molecule is about twice larger than its dipolar subunit.
We investigate the dichroism characteristics of poly (methyl methacrylate) PMMA thin films doped with DO11, DO3, DSR13 and DSR1 dye molecules, which change under illumination with visible light. Our data show that photoisomerisation, phototautomerization reactions and light-induced polar orientation are dependent on the molecular structure of the polymer. Polar structure and molecular size, as well as the chemical structure of PMMA host, are the dominant parameters that determine both the extent and speed of dichroism buildup and relaxation processes. Two forms of DO11 molecules (keto and enol forms), and two other forms of azo-based dyes ( trans and cis forms) are responsible for the interaction with irradiating laser light and forming an anisotropic structure inside the PMMA/dye thin films.
The semi-isolating GaAs (100) samples irradiated with fluence 3 × 10^{15} ions/cm^{2} of In^{+} ions were characterized by using the methods: Rutherford backscattering spectroscopy, nuclear reaction analysis and ellipsometric spectroscopy. The values of the thicknesses layers enriched with oxygen and the implanted were determined by the methods of nuclear reaction analysis and Rutherford backscattering spectroscopy. Multilayer models were applied for determination of the optical constants (refraction and extinctions coefficients) of investigated samples. The thickness of native oxide covering the surface of implanted GaAs and refraction coefficients were increased after implantation with indium. The spectrum of extinction indexes as a function of light wavelength has two bands near the light wavelengths 400 nm and 480 nm. The observed effects can be interpreted as formation of local oxides of In and InAs precipitates or ternary alloys in enriched with oxygen layers at the surfaces of implanted GaAs.
The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizers 3,4-pyridinedicarbonitrile, 3-aminophthalonitrile, 4-aminophthalonitrile and 4-methylphthalonitrile were studied based on density functional theory using the hybrid functional B3LYP. Ultraviolet-visible spectra were investigated by time dependent density functional theory. The features of electronic absorption spectra in the visible and near-UV regions were assigned based on time dependent density functional theory calculations. The absorption bands are assigned to π → π* transitions. Calculated results suggest that the three lowest energy excited states of 3,4-pyridinedicarbonitrile, 3-aminophthalonitrile, 4-aminophthalonitrile and 4-methylphthalonitrile are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO_2 electrode and dye sensitizers 3,4-pyridinedicarbonitrile, 3-aminophthalonitrile, 4-aminophthalonitrile and 4-methylphthalonitrile is due to an electron injection process from excited dyes to the semiconductor's conduction band. The role of amide and methyl groups in phthalonitrile in geometries, electronic structures, and spectral properties were analyzed in a comparative study of 3,4-pyridinedicarbonitrile, 3-aminophthalonitrile, 4-aminophthalonitrile and 4-methylphthalonitrile for the improvement of dye sensitized solar cells.
Linear dichroism, dichroic ratio, contrast ratio and order parameters of Sudan III/PMMA guest-host thin films have been investigated with visible polarized laser light. Dichroism increased in an exponential fashion with increase of the pump intensity. Light-induced dichroism and polar order of the dye molecules within the polymer network were reversible. These parameters showed fast increase in their values in an exponential fashion as the pumping process takes place. Also, they decay rapidly in an exponential fashion when the pump light is cut off. Photoisomerisation and polar orientation are dependent on both the molecular structure of the dye and polymer. Two forms of Sudan III molecules (trans and cis) are responsible for the interaction with laser light and forming an anisotropic structure inside the PMMA/Sudan III films. However, there is another set of forms of the dye (keto and enol) has to be considered, which may contribute to dichroism.
Spectroscopic and photophysical properties of the poly(azomethine)s with triphenylamine moieties were investigated by UV-vis, X-ray diffraction and atomic force microscopy methods. Current-voltage measurements were performed on ITO/polymer/Alq_3/Al, ITO/PEDOT/polymer:MWCNT/Al and ITO/polymer:MWCNT/Al devices. Multiwall carbon nanotubes were blended with polymer in the ratio 1:1. The lowest optical band gap value at 2.33 eV was detected. Moreover, an absorption coefficient α was calculated from transmission and reflectivity measurements. In this paper, we presented photophysical and structural properties of the poly(azomethine)s in solid state of great interest for the emerging field of molecular electronics and for their uses as active layers in (opto)electronic devices such as solar cells.
We separate the electronic and nuclear contributions to the third-order nonlinear optical susceptibilities χ_{ijkl}^{〈3〉} using degenerate four wave mixing. This method allows to know the physical origin of the optical nonlinearities of new soluble tetrathiafulvalene derivatives and deduce the values of the second-order hyperpolarisabilities γ. The values of γ for the studied compounds are about 10^{5} greater than for CS_{2}.
The tight binding Hamiltonian of Su, Schrieffer, and Heeger has been used to describe the physical properties of the polyacetylene chain. The chain temperature is calculated from the potential energy which is directly related to the CH group displacement. Two different forms of the displacements have been considered: random and Gaussian. The third harmonic generation susceptibility spectra have been plotted in terms of the temperature using the four-wave mixing formula. The results show that a second peak at the mid gap energy has occurred for room temperature which is in good agreement with the experimental data.
We investigate the absorption spectra of poly (methyl methacrylate) (PMMA) thin films doped with Disperse Orange 11 (DO11) dye molecules which change under illumination with visible light. Dichroism measurements of the kinetics of the transmission changes at 472 nm at room and low temperatures (-60° C ± 2 °C) have been investigated. Our data show that the photoisomerisation reaction and the light-induced polar orientation depend on the molecular structure of the polymer. Simultaneous UV-visible spectroscopy at low temperature confirms the existence of two forms of DO11 molecules (keto and enol forms), which are responsible for the interaction with irradiating laser light and forming an anisotropic structure inside the PMMA/DO11 thin film.
In this work, we study the influence of the PEDOT to PSS ratio on the optical properties of PEDOT:PSS thin solid films using spectroscopic ellipsometry and UV-vis spectrometry. In the data analysis, we develop a consisted composition dependent optical model of PEDOT:PSS. This enabled us to account for contributions from PSS part within the Tauc-Lorentz optical model and from PEDOT part within the Drude-Lorentz optical model. Moreover, we relate the optical properties of PEDOT:PSS thin solid films to their electrical specific conductivities in the frame of the generalized effective medium theory. Determined in this manner electrical conductivities of five commercially available water dispersions of PEDOT:PSS are compared with their nominal values.
Positron annihilation lifetime spectroscopy was used to measure the free-volume size and distributions as a function of temperature in polystyrene with and without 400 psi CO_2 sorption. The transition temperatures in the polystyrene with CO_2 sorption obtained from ortho-positronium lifetimes were found to depend on the thermal cycles and a meta-stable state showing a negative thermal expansion coefficient was observed between 53°C and 82°C during the first heating up experiment. The observed T_g in polystyrene with, and without CO_2 sorption after annealing from ortho-positronium lifetimes were found to be 86°C and 91°C, which are 5°C higher, and 10°C lower than from the differential scanning calorimetry data, respectively. The observed free-volume variations are discussed in terms of hole expansion, creation, free-volume relaxation, plasticization, and hole filling in amorphous polymers.
Slow dynamics of the initially photoinduced state has been observed by the pump-probe type time-resolved reflection spectroscopy in the charge separated phase of the half-filled strong dimer system, Et_2Me_2Sb[Pd(dmit)_2]_2 (dmit = 1,3-dithiol-2-thione-4,5-dithiolate). We have succeeded to reproduce the probe photon energy dependence of the time profile qualitatively in the time delay range from 10 ps to 1 ns assuming the dynamical expansion of the domain of the photo-induced dimer-Mott insulating phase in the host charge-separated one.
Hematite (α-Fe_{2}O_{3}) nanoparticles and hematite nanoparticles coated with polyvinylpyrrolidone (PVP) are synthesized chemically by co-precipitation. Prolysis and microemulsion methods respectively. An average size of nanoparticles (both coated and uncoated) was found by the broadening of the X-ray diffraction peaks using Scherrer's formula. It was found that coating reduced particle sizes. The attachment of the polymer on the surface of particles was confirmed by the Fourier transform infrared spectroscopy and thermogravimetric analysis. Optical ultraviolet/visible reflectance test also indicated the presence of PVP in coated nanohematites. In magnetic studies, it was observed that coating does not change main magnetic character of the α-Fe_{2}O_{3} nanoparticles however it reduces DC magnetization (as a function of applied field and temperature) to a considerable amount. Moreover it was observed that after coating Morin transition temperature T_{M} and its width ΔT_{M} shifts to lower values, which is another indication of size reduction.
Seeding and growth processes of thin diamond films on fused silica optical fibres have been investigated. Glass pre-treatment by dip coating in two detonation nanodiamond (DND) seeding media has been studied. The DND suspension in ethyl alcohol and dispersion of DND in dimethyl sulfoxide (DMSO) with polyvinyl alcohol (PVA) were chosen for the seeding purpose. The grain size distribution of nanodiamond particles in both seeding media was kept at the same level (approximately 10-50 nm). After the seeding nanocrystalline diamond films were deposited on the fibres using microwave plasma assisted chemical vapour deposition system. The results of the process were investigated using numerical analysis of scanning electron microscopy images. The molecular structure of diamond has been examined with micro-Raman spectroscopy. Thickness, roughness and optical properties of the nanocrystalline diamond films in VIS-NIR wavelength range were investigated on reference samples using spectroscopic ellipsometry. Light reflection at the fibre end-face for different deposition parameters was also investigated. Proposed seeding method can be further effectively applied for manufacturing of optical fibre sensors. Due to extraordinary properties of diamond, which include high chemical and mechanical resistance, such films are highly desired for optical sensing purposes.
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