Papers by Keyword: Optical Activity

Abstract: Many natural materials have the ability to rotate the polarization level of linearly polarized laser beam and pass through it. This phenomenon is called optical activity. In the event that a light beam (linearly polarized) passes through an optically active material, such as a quartz crystal, and projected vertically on the optical axis, the output beam will be polarized equatorially, and the vibration level will rotate at a certain angle [1], [2], [3]. A number of crystals, liquids, solutions, and vapors rotate the electric field of linearly polarized light that passes through them [4], [5], [6], [7]. Many different physical effects are applied to optical isotropic and transparent materials that cause them to behave as optical active materials, where they are able to rotate the polarization level of the polarized light linearly and pass through it [8], [9], [10]. These effects include mechanical strength, electric field, and magnetic field. By placing one of these effects on an optically transparent medium, it changes the behavior of the light travelling through it [11].

Abstract: The polarizability theory of optical activity (OA) is used to investigate the correlation between structure peculiarities and optical properties of crystals of the langasite family. Optical rotation (OR) is calculated as the function of disordering structure parameters for La₃Ga₅SiO₁₄, La₃Ga_5.5Ta_0.5O₁₄ and Ca₃Ga₂Ge₄O₁₄ compounds. Using a single wavelength laser polarimeter the OR was measured on z-cut sample of langasite crystals La₃Ga₅SiO₁₄.

Abstract: The radical polymerization of a novel methacrylamide derivative, N-[o-(4-ethyl-4, 5-dihydro-1, 3-oxazol-2-yl) phenyl] methacrylamide ((S)-EtOPMAM), was carried out to obtained optically active polymers. The polymer yield and the chiroptical behavior of the resultant polymers have been examined in detail by using IR and ¹H NMR spectroscopies in comparison with our previous observation. The polymers showed relatively high molecular weights (Mn=8000-16000) and largest specific rotations ([α]₂₅^D =+120.6^o). Particularly, the largest specific optical rotation of the polymer is almost the six times of the monomer.

Abstract: An optical active Acrylate end-functionalized poly (lactic acid) (DPLA) was synthesized via melt polycondensation, with lactic acid, polyalcohol and acrylic acid as raw materials. The prepolymer products in each process were characterized by FT-IR, ¹H-NMR. The curing PLA coating (CPLA) was prepared using optical active DPLA, reactive diluent and photoinitiator. Gel fraction, thermal stability and degradation properties of the UV curing PLA coating properties were evaluated. The results show that branched structure of hydroxyl-terminated poly (lactic acid) (OHPLA) is beneficial to increase acrylic end capping rate (Da), Da ois as high as 88%. The structure of prepolymer and the performance of the coating are adjusted by changing content of polyalcohol. After crosslinking modification, degradation rate of CPLA is reduced and CPLA has better thermal stability than the pure PLA.

Abstract: In this paper, the ellipsometry based on polarization technique used to determination of sucrose concentrates. And then we used multi-wavelength radiation from a halogen lamp provided spectral, is described and applied to the determination of optically active of sucrose. The instrument has no moving parts, and optical rotation measurements are an apparent absorbance. Apparent absorbance measurements can be combined with over a wide spectral range. Results obtained by this two technique have showed good.

Abstract: A novel type of chiral N-substituted methacrylamide derivatives bearing an oxazoline pendant (OPMAM) had been synthesized. Radical polymerization were carried out to produced corresponding polymers with high specific rotation in moderate yields. The polymerization characteristics and the chiroptical behavior of the resultant polymers have been examined in detail by using HPLC and CD and UV-vis spectra. The polymers showed relatively high molecular weights(Mn=5000-15000). The abolutely value of the specific rotation of poly(OPMAM)s basically increased with increasing the molecular weights.

Abstract: A novel type of chiral methacrylamide derivative, N-[o-(4-phenyl-4,5-dihydro-1,3-oxazol-2-yl) phenyl]methacrylamide ((R)-PhOPMAM), was synthesized and radically polymerized to the corresponding polymers in moderate yields. The polymerization characteristics and the chiroptical behavior of the resultant polymers have been examined in detail by using IR and ¹H NMR spectroscopies in comparison with our previous observation. The polymers showed relatively high molecular weights(Mn=5000-10000) and large specific rotations([α] ₂₅^D = -326.0°～-357.4°).

Abstract: The photoluminescence from III-V wide band-gap semiconductors as InGaN is characterized by localized large intensity fluctuations, known as blinking, that, despite decades of research, is not yet completely understood. In structures where there is a three-dimensional confinement, as for example semiconductors nanocrystals, the phenomena is supposed to be related to temporary quenching due to highly efficient non-radiative recombination processes (for example, Auger). Nevertheless, in typical InGaN devices, the band structure is an infinitely wide quantum well, so the understanding of the blinking phenomenon remains elusive. We present experimental data and a model that suggests that the discussed optical fluctuations are a general phenomena caused by the slow beating between THz thermal vibrations of the Quantum Well. These minuscule displacements are occurring naturally all over the device, the displacements along the growth direction induce a modulation of the matrix elements that drives the optical emission process; this have measurable effect on the device photo-luminescence. In presence of impurities or gradient of concentration, the vibrations have locally slight frequency differences on adjacent domains, this give rise to a band of beats, and we observe the lower frequency tail of this band.

Abstract: The radical polymerization of optically active methacrylamide derivatives, N-[o-(4-phenyl-4,5-dihydro-1,3-oxazol-2-yl) phenymethacrylamide ((R)-PhOPMAM) and N-[o-(4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl) phenymethacrylamide ((S)-PrⁱOPMAM), were carried out under various conditions. The effect of the Lewis acid, that is, rare earth metal trifluoromethanesulfonates on the free-radical polymerization were examined under different solvents. The Lewis acids are effective in enhancing the isotacticity in the polymerization of (S)-PrⁱOPMAM. The same phenomenon were not happened in the polymerization of (R)-PhOPMAM. The polymerization characteristics and the chiroptical behavior of the resultant polymers have been examined by using circular dichroism (CD), UVVis, and NMR spectroscopies.

Abstract: The radical polymerization of optically active methacrylamide derivative, N-[o-(4-isopropyl-4,5-dihydro -1,3-oxazol-2-yl)phenyl] methacrylamide ((S)-MeOPMAM), was carried out under various conditions. The effect of Lewis acid, that is, rare earth metal trifluoromethanesulfonates on the free-radical polymerization were examined under different solvents. The polymerization in the presence of rare earth metal trifluoromethanesulfonates produced isotactic-rich polymers compared with those obtained without the Lewis acid. The polymerization characteristics and the chiroptical behavior of the resultant polymers have been examined by using circular dichroism (CD), UV–Vis, and NMR spectroscopies.