• Korean Journal of Optics and Photonics
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• v.9 no.2
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• pp.104-110
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• 1998

The energy transfer between two incident beams in a photorefractive Cu-doped(0.04 wt. %) ${(K_{0.5}Na_{0.5})}_{0.2}{(Sr_{0.61}Ba_{0.39})}_{0.9}Nb_2O_6$ crystal is investigated at 632.8 nm laser wavelength. In addition, the coherent two-wave coupling properties of a photoinduced refractive-index grating in the presence of amplitude modulation on the signal beam or reference beam are also experimentally investigated. Some preliminary exprimental results are presented for use as a dynamic photorefracitive combiners and pulse shaping elements in coherent optical communication systems and in optical signal processing.

• Korean Journal of Optics and Photonics
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• v.4 no.4
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• pp.464-473
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• 1993

The dynamics of phase grating formation with visible light in an optical fiber is investigated. Adopting a simple two-photon local bleaching model, it is shown that the grating self-organize into an ideal grating, where the writing frequency is always in the center of the local band gap, as it evolves. The evolution at each point in the fiber is described in terms of a universal parameter that reduces the coupled partial differential equations describing the system to ordinary differential equatior~s. These equations are used to prove that there exists a fixed point of the grating growth process that corresponds to a perfectly phase-mached grating.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1108-1114
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• 2013

Photochemical reactions of fluoro- vs. nonfluoro-substituted polymethylenoxy chain linked phthalimide were carried out to explore how electronegative fluorine atoms inside the donor chain influence photocyclization reaction efficiencies and to briefly determine the alkali metal binding properties of the photoproducts. The results of this study show that the fluorine-substituted donor chain linked phthalimide undergoes inefficient photocyclization via single electron transfer (SET)-induced excited state pathways to generate 14-membered cyclic amidol compared to nonfluoro-analog due to low electron donor ability of the terminal oxygen donor site. These results show that photoinduced intramolecular SET processes arising from ${\alpha}$-silyl ether electron donors to phthalimides are largely dependent on the kinds of substituents inside donor chain. Finally, a preliminary study with the cyclic amidols generated in this effort showed that they have weak alkali metal cation binding properties regardless of absence/presence of fluoro-substituents.

• Bulletin of the Korean Chemical Society
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• v.28 no.2
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• pp.271-275
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• 2007

γ -Glutamyl transpeptidase (EC 2.3.2.2) plays a key role in glutathione metabolism by catalyzing the transfer of the γ -glutamyl residue and hydrolysis of glutathione. The functional residues at the active site of the rat kidney γ -glutamyl transpeptidase were investigated by kinetic studies at various pH, the treatment of diethylpyrocarbonate (DEPC), and photooxidation in presence of methylene blue. An ionizable group affecting the enzymatic activity with an apparent pKa value of 7.1, which is in the range of pKa values for a histidine residue in protein, was obtained by examining the pH-dependence of kinetic parameters. The pH effect on the photoinduced inactivation rate of the enzyme corresponds to that expected for the photooxidation of the free histidine. The involvement of a histidine in the catalytic site of the enzyme was further supported by DEPC modification accompanied by an increase in absorbance at 240 nm, indicating the formation of Ncarbethoxyhistidine. The histidine located at the position of 382 in the precursor of the enzyme is primarily suspected based on the amino acid sequence alignment of the transpeptidases from various organisms.

• Bulletin of the Korean Chemical Society
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• v.28 no.1
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• pp.49-52
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• 2007

Prodigiosin (1) is the parent member of a class of polypyrrole natural products that exhibit promising anticancer activities. They can facilitate copper-promoted oxidative DNA damage by binding to copper ions, and this activity is thought to represent their mechanism of cytotoxicity in the dark. They also possess photoinduced cytotoxicity, although 1 is too toxic in the dark to be used effectively for the treatment of cancer by photodynamic therapies. To circumvent dark toxicity by prodigiosins, the semi-synthetic analogue 2, in which the N-pyrrolic atoms of 1 are methylated to block copper coordination, and the synthetic phenyl analogues 3 and 4, which lack the copper-coordinating A-pyrrole ring of 1, were tested for their ability to inhibit colony formation of HL-60 cancer cells in the absence and presence of visible light (λ > 495 nm). Our results show that 2-4 lack cytotoxicity in the dark, but are able to inhibit colony formation of HL-60 cells following irradiation for 30 min. The synthetic derivative 4 exhibits photo-induced cytotoxicity similar to that of the natural product 1, demonstrating the potential use of prodigiosin-based compounds for treatment of cancers following irradiation with visible light.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.667-670
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• 2009

The understanding of behaviors of hydroperoxyl/superoxide anion radicals (${H_2O_2}^./{O_2}^{-.}$) generated from a photoirradiated $TiO_2$ surface is essential to improve the efficiency of $TiO_2$ photocatalytic reactions by decreasing the recombination of photoinduced electron-hole ($e^--h^+$) pairs. In contrast with previous studies, we found that ${H_2O_2}^./{O_2}^{-.}$ generated on the surface of illuminated $TiO_2$ particles are mobile. ${H_2O_2}^./{O_2}^{-.}$ formed by the photocatalysis of $TiO_2$ particles immobilized onto the inner surface of a coil-quartz tube were forced under a continuous flow through a knotted tubing reactor (KTR) and into the aqueous phase completely separated from the $TiO_2$ particles, and were measured by a chemiluminescence (CL) technique using 2-methyl-6-(p-methoxyphenyl)-3,7-dihydroimidazo[ 1,2-a]pyrazin-3-one (MCLA) as the reagent. The initial concentration of the ${H_2O_2}^./{O_2}^{-.}$ stream entering the KTR was determined by its half-life (98 s) at pH 5.8. We suggests that the efficiency of $TiO_2$ photocatalytic reactions may be further improved by utilizing the mobility of ${H_2O_2}^./{O_2}^{-.}$.

• Bulletin of the Korean Chemical Society
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• v.28 no.11
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• pp.1967-1972
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• 2007

Photophysical properties of a newly-synthesized porphyrin derivative, trans-bis(ferrocene carboxylato)- (5,10,15,20-tetraphenylporphyrinato)tin(IV) [Sn(TPP)(FcCOO)2] were investigated by means of steady-state and fs-time resolved laser spectroscopic techniques, and compared with those of a standard molecule, trans-dichloro( 5,10,15,20-tetraphenyl-porphrinato)tin(IV) [Sn(TPP)Cl2]. The fluorescence spectrum of Sn(TPP)- (FcCOO)2 was observed to exhibit dual emission bands originating from the S2-state and the S1-state, which was greatly quenched as compared to those of Sn(TPP)Cl2. The fs-time resolved fluorescence and transient absorption spectroscopic measurements revealed that the fluorescence quenching is due to formation of the long-lived charge transfer state by intramolecular electron transfer from ferrocene to the S2-excited SnTPP in addition to the enhanced non-radiative deactivation processes.

• Bulletin of the Korean Chemical Society
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• v.22 no.7
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• pp.709-715
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• 2001

We have been studied photosensitization mechanism's additive effect, of perylene 3,4,9,10-tetracarboxyl-diimide and X-phthalocyanine (charge generation materials), using the photochemical and photoelectrochemical approach. It was found that the photoreceptor on the excited state reacts with metal oxide, which creates the charge transfer on the interface of SnO2/electrolyte. In the electrode (X5P1) made of five X-phthalocyanine and single perylene 3,4,9,10-tetracarboxyldiimide layers, the cathodic photocurrent of X-phthalocyanine in the 400-600 nm region was increased by the addition of perylene 3,4,9,10-tetracarboxyldiimide. The maximum wavelength of fluorescence of perylene 3,4,9,10-tetracarboxyldiimide showed no dependence on the temperature. The addition of 4-dibenzylamino-2-methylbenzaldehyde diphenylhydrazone known as charge transport material was represented as decreasing photocurrent for X-phthalocyanine and perylene 3,4,9,10-tetracarboxyldiimide, respectively. In the electrode (X1P1) made of single X-phthalocyanine and single perylene 3,4,9,10-tetracarboxyldiimide layers, an anodic photocurrent of about 10.5 nA was generated by addition of hydroquinone at 550 nm. And the characteristic of photoinduced discharge was shown to decrease by a factor of 5 and the speed of dark decay was increased by a factor of 1.2.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.343-344
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• 2012

It has been known since the mid 1960s that Ag can be photodissolved in chalcogenide glasses to form materials with interesting technological properties. In the 40 years since, this effect has been used in diverse applications such as the fabrication of relief images in optical elements, micro photolithographic schemes, and for direct imaging by photoinduced Ag surface deposition. ReRAM, also known as conductive bridging RAM (CBRAM), is a resistive switching memory based on non-volatile formation and dissolution of a conductive filament in a solid electrolyte. Especially, Ag-doped chalcogenide glasses and thin films have become attractive materials for fundamental research of their structure, properties, and preparation. Ag-doped chalcogenide glasses have been used in the formation of solid electrolyte which is the active medium in ReRAM devices. In this paper, we investigated the nature of thin films formed by the photo-dissolution of Ag into Ge-Se glasses for use in ReRAM devices. These devices rely on ion transport in the film so produced to create electrically programmable resistance states. [1-3] We have demonstrated functionalities of Ag doped chalcogenide glasses based on their capabilities as solid electrolytes. Formation of such amorphous systems by the introduction of Ag+ ions photo-induced diffusion in thin chalcogenide films is considered. The influence of Ag+ ions is regarded in terms of diffusion kinetics and Ag saturation is related to the composition of the hosting material. Saturated Ag+ ions have been used in the formation of conductive filaments at the solid electrolyte which is the active medium in ReRAM devices. Following fabrication, the cell displays a metal-insulator-metal structure. We measured the I-V characteristics of a cell, similar results were obtained with different via sizes, due to the filamentary nature of resistance switching in ReRAM cell. As the voltage is swept from 0 V to a positive top electrode voltage, the device switches from a high resistive to a low resistive, or set. The low conducting, or reset, state can be restored by means of a negative voltage sweep where the switch-off of the device usually occurs.

• Korean Journal of Materials Research
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• v.28 no.4
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• pp.214-220
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• 2018

We report on the fabrication and photoelectrochemical(PEC) properties of a $Cu_2O$ thin film/ZnO nanorod array oxide p-n heterojunction structure with ZnO nanorods embedded in $Cu_2O$ thin film as an efficient photoelectrode for solar-driven water splitting. A vertically oriented n-type ZnO nanorod array was first prepared on an indium-tin-oxide-coated glass substrate via a seed-mediated hydrothermal synthesis method and then a p-type $Cu_2O$ thin film was directly electrodeposited onto the vertically oriented ZnO nanorods array to form an oxide semiconductor heterostructure. The crystalline phases and morphologies of the heterojunction materials were characterized using X-ray diffraction and scanning electron microscopy as well as Raman scattering. The PEC properties of the fabricated $Cu_2O/ZnO$ p-n heterojunction photoelectrode were evaluated by photocurrent conversion efficiency measurements under white light illumination. From the observed PEC current density versus voltage (J-V) behavior, the $Cu_2O/ZnO$ photoelectrode was found to exhibit a negligible dark current and high photocurrent density, e.g., $0.77mA/cm^2$ at 0.5 V vs $Hg/HgCl_2$ in a $1mM\;Na_2SO_4$ electrolyte, revealing an effective operation of the oxide heterostructure. In particular, a significant PEC performance was observed even at an applied bias of 0 V vs $Hg/HgCl_2$, which made the device self-powered. The observed PEC performance was attributed to some synergistic effect of the p-n bilayer heterostructure on the formation of a built-in potential, including the light absorption and separation processes of photoinduced charge carriers.