• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2175-2179
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• 2010

Quantum mechanical properties of unsymmetrical and unfunctionalized trans-stilbene derivatives 1-3, which had been prepared by solid-phase parallel syntheses, were characterized using mPW1PW91/6-311G(d,p) (hybrid HF-DF) calculations. The total electronic energies, normal vibrational modes, Gibbs free energies, and HOMOs and LUMOs of sixteen different structures from three different groups were analyzed. The energy differences between the HOMOs and LUMOs of the various unsymmetrical trans-stilbenes are in accord with the maximum absorption peaks of the experimental UV spectra of 1-3. The calculated normal vibrational modes of 21 were comparable with its experimental IR spectrum. The $\pi$-conjugation in the para-connected biphenyl group of 2 is better than the one in the metaconnected biphenyl group on the shorter side of 3.

• Journal of the Mineralogical Society of Korea
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• v.22 no.2
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• pp.81-86
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• 2009

The luminescence and fluorescence were investigated by photoluminescence spectroscopy for six gemstones which exhibit color change effect. The shape of luminescence peaks appears different when observed by a photoluminescence spectroscopewith a 514 nm Ar laser source. However, it was not possible to observe the difference in the spectra between the natural and synthetic origins for the same type of gemstones. It was found that the photoluminescence spectrum was related to the crystal structure of the stones. Photoluminescence spectra using a 325 nm He-Cd source reveal that fluorescence is relatively strong for synthetic alexandrite, synthetic color change sapphire and natural alexandrite comparing to the rest of gemstones examined.

• Journal of the Korean Chemical Society
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• v.34 no.6
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• pp.616-621
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• 1990

The spectrophotometric methods for the determination of Nd, Pr, Sm, Eu, Ho, Er were developed, using the multicomponent method of absorption spectra cointerference. The absorption spectra of individual Nd, Pr, Sm, Eu, Ho, Er, mixture of Sm, Eu, Ho, Er in hydrochloric acid solutions were investigated, and also a band register which includes the molar absorptions for all trivalent Nd, Pr, Sm, Eu, Ho and Er absorption band maxima were measured. The spectrophotometric determination of Nd, Pr, Sm, Eu, Ho and Er were investigated using the analytically significant absorption bands at 444.2, 575.1, 401.7, 394.2, 416.6, and 379.7 nm, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.19
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• pp.6.2-7
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• 1994

• Bulletin of the Korean Chemical Society
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• v.31 no.7
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• pp.1875-1880
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• 2010

A dicycle pyrazoline derivative, 1-phenyl-5-(p-fluorophenyl)-3,4-($\alpha$-p-fluoro-tolylenecyclohexano) pyrazoline, was synthesized and characterized by elemental analysis, IR, UV-vis, fluorescence spectra and X-ray single crystal diffraction. Density function theory (DFT) calculations were performed by using B3LYP method with 6-$311G^{**}$ basis set. The optimized geometry can well simulate the molecular structure. Vibrational frequencies were predicted, assigned and compared with the experimental values, which suggest that B3LYP/6-$311G^{**}$ method can well predict the IR spectra. Both the experimental electronic absorption spectra and the predicted ones by B3LYP/6-$311G^{**}$ method reveal three electron-transition bands, with the theoretical ones having some red shifts compared with the experimental data. Natural bond orbital analyses indicate that the absorption bands are mainly derived from the contribution of n $\rightarrow\pi^*$ and $\pi\rightarrow\pi^*$ transitions. Fluorescence spectra determination shows that the title compound can emit blue-light at about 478 nm. On the basis of vibrational analysis, the thermodynamic properties of title compound at different temperature have been calculated, revealing the correlations between $C^0_{p,m}$, $S^0_m$, $H^0_m$ and temperature.

• Korean Journal of Materials Research
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• v.22 no.2
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• pp.91-96
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• 2012

AC and ZnS modified $TiO_2$ composites (AC/ZnS/$TiO_2$) were prepared using a sol-gel method. The composite obtained was characterized by Brunauer-Emmett-Teller (BET) surface area measurements, X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, scanning electron microscope (SEM) analysis, and according to the UV-vis absorption spectra (UV-vis). XRD patterns of the composites showed that the AC/ZnS/$TiO_2$ composites contain a typical single and clear anatase phase. The surface properties as observed by SEM present the characterization of the texture of the AC/ZnS/$TiO_2$ composites, showing a homogenous composition in the particles showing the micro-surface structures and morphology of the composites. The EDX spectra of the elemental identification showed the presence of C and Ti with Zn and S peaks for the AC/ZnS/$TiO_2$ composite. UV-vis patterns of the composites showed that these composites had greater photocatalytic activity under visible light irradiation. A rhodamine B (Rh.B) solution under visible light irradiation was used to determine the photocatalytic activity. The degradation of Rh.B was determined using UV/Vis spectrophotometry. An increase in the photocatalytic activity was observed. From the photocatalytic results, the excellent activity of the Y-fullerene/$TiO_2$ composites for the degradation of methylene blue under visible irradiation could be attributed to an increase in the photo-absorption effect caused by the ZnS and to the cooperative effect of the AC.

• Korean Journal of Agricultural Science
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• v.35 no.1
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• pp.11-17
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• 2008

This study was conducted to isolate polyacetylenes from the Acanthopanax senticosus and to identify the chemical structure of the polyacetylenes by UV, IR, $^1H$-NMR and $^{13}C$-NMR. One of the liposoluble materials was extracted with petroleum ether. Polyacetylene compounds were collected through solvent fractionation at silica gel column chromatograph. The HPLC was used for the semi-preparative separation IR spectra of fraction 5 showed triple bonds at $2256cm^{-1}$ and double bond at $1654cm^{-1}$, respectively, $^1H$-NMR spectra of Fraction 5 showed the double bond at 5.35-5.48 ppm. Triple bond at 64.0. 71.2, 74.2, 80.2 ppm and double bond at 121.89, 133.0 ppm were observed in the $^{13}C$-NMR spectra.

• Journal of Astronomy and Space Sciences
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• v.29 no.2
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• pp.181-189
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• 2012

To broaden the understanding of classical Cepheid structure, evolution and atmospheres, we have extended our continuing secret lives of Cepheids program by obtaining XMM/Chandra X-ray observations, and Hubble space telescope (HST) / cosmic origins spectrograph (COS) FUV-UV spectra of the bright, nearby Cepheids Polaris, ${\delta}$ Cep and ${\beta}$ Dor. Previous studies made with the international ultraviolet explorer (IUE) showed a limited number of UV emission lines in Cepheids. The well-known problem presented by scattered light contamination in IUE spectra for bright stars, along with the excellent sensitivity & resolution combination offered by HST/COS, motivated this study, and the spectra obtained were much more rich and complex than we had ever anticipated. Numerous emission lines, indicating $10^4$ K up to ${\sim}3{\times}10^5$ K plasmas, have been observed, showing Cepheids to have complex, dynamic outer atmospheres that also vary with the photospheric pulsation period. The FUV line emissions peak in the phase range ${\varphi}{\approx}0.8-1.0$ and vary by factors as large as $10{\times}$. A more complete picture of Cepheid outer atmospheres is accomplished when the HST/COS results are combined with X-ray observations that we have obtained of the same stars with XMM-Newton & Chandra. The Cepheids detected to date have X-ray luminosities of log $L_X{\approx}28.5-29.1$ ergs/sec, and plasma temperatures in the $2-8{\times}106$ K range. Given the phase-timing of the enhanced emissions, the most plausible explanation is the formation of a pulsation-induced shocks that excite (and heat) the atmospheric plasmas surrounding the photosphere. A pulsation-driven ${\alpha}^2$ equivalent dynamo mechanism is also a viable and interesting alternative. However, the tight phase-space of enhanced emission (peaking near 0.8-1.0 ${\varphi}$) favor the shock heating mechanism hypothesis.

• Journal of the Korean Chemical Society
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• v.20 no.5
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• pp.398-405
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• 1976

A new compound, 1,2-bispyrazyl ethylene,is synthesized starting from pyrazine carboxylic acid and methyl pyrazine. The compound is characterized utilizing UV-VIS, IR, NMR and mass spectra along with elemental analysis. Spectroscopic properties are studied from UV-VIS and fluorescence spectra. From unusual salt effects on fluorescence spectra, it is believed that $(n,\;{\pi}^*)$ state has about the same energy as $({\pi},\;{\pi}^*)$ state. The compound fluoresces from $({\pi},\;{\pi}^*)$ state with the quantum yield of 0.025 at $77^{\circ}K$ compared to near unity for stilbene at the same temperature indicating the efficient intersystem crossing to triplet state, because of strong $(n,\;{\pi}^*)$ and $({\pi},\;{\pi}^*)$ mixing in the lowest excited state.

• Bulletin of the Korean Chemical Society
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• v.20 no.6
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• pp.677-682
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• 1999

Conjugated polycarbosilanes with diacetylene and aromatic groups of thiophene or phenylene simultaneously present in the polymer backbone such as poly[[1,4-bis(thiophenyl)buta-1,3-diyne]-alt-(dimethylsilane)], poly[[1,4-bis(thiophenyl)buta-1,3-diyne]-alt-(diphenylsilane)], poly[[1,4-bis(phenyl)buta-1,3-diyne]-alt-(dimethylsilane)],and poly[[1,4-bis(phenyl)buta-1,3-diyne]-alt-(diphenylsilane)] have been prepared. The characteristic C=C stretching frequencies appear at 2177-2179㎝-1 in the IR spectra of the polymers. The molecular weights of these polymers were detemined by GPC. All of these materials are soluble in organic solvents such as THF and chloroform, and thermally stable up to 200℃ in general without any weight loss under nitrogen. The prepared materials in THF solvent show a maximum absorption peak in the range of 334-356 nm with a molar absorptivity of 10³∼10ⁿ(n=5)L/(cm·mol) in the UV-visible absorption spectra. A maximum emission peak in the range of 403-550 nm is also observed in the fluorescence emission spectra. Both absorption and emission spectra strongly indicate that the obtained polycarbosilanes contain the new conjugated systems along the polymer main chain.