• Bulletin of the Korean Chemical Society
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• v.21 no.5
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• pp.497-502
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• 2000

Quantum mechanical analysis is presented for the photodissociation dynamics of the v'=4 levels of the $A^2Σ^+$ state of the OH molecule. We focus on the effects of the multichannel interactions between the asymptotically degenerate states in the recoupling region to see how they affect the dynamics near the predissociating resonances. Both the scalar (total cross section and branching ratios) and the vector properties (angular distributions and alignment parameters) of O($^3P_j, j=0, 1, 2) are treated. The resonances are predicted to be highly Lorentzian, and the branching ratios do not change much across them. Vector properties, however, show very delicate effects of the multichannel interactions and overlapping near the isolated and overlapping resonances. Computed resonance lifetimes agree reasonably well with experimental results.

• Bulletin of the Korean Chemical Society
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• v.19 no.3
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• pp.308-313
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• 1998

A thermally irreversible photochromic system, 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride (MTMA), has been studied by semi-empirical molecular orbital methods. There are one pair of stable conformations for the closed-ring form and three pairs for the open-ring form, each pair consisting of two mirror-image conformations. Interconversion between the parallel and anti-parallel conformations of the open-ring form is restricted due to high energy barriers. Only the anti-parallel conformation appears to be responsible for photochromic cyclization. Thermostability of the compound is attributed to an avoided crossing at high energy in the ground states of the isomers, whereas the photoreactivity can be explained by the mutually connected excited singlet (S1) states of the isomers, forming a double well potential with a low energy barrier. The large solvent effects can be partly explained with the low dipole moment of the anti-parallel conformation of MTMA in the S1 state. The large variation of quantum efficiency suggests that excess vibronic energy can be utilized to provide the activation energy for the photochromic reaction.

• Bulletin of the Korean Chemical Society
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• v.24 no.6
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• pp.763-770
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• 2003

The $BH_5$ molecule, which is suggested as an intermediate of the acidolysis of $BH_4^-$, contains a weak two-electron-three-center bond and it requires extremely high-level of theories to calculate the energy and structure correctly. The structures and energies of $BH_5$ and the transition state for the hydrogen scrambling have been studied using recently developed multi-coefficient correlated quantum mechanical methods (MCCMs). The dissociation energies and the barrier heights agree very well with the previous results at the CCSD(T)/ TZ(3d1f1g, 2p1d) level. We have also calculated the potential energy curves for the dissociation of $BH_5$ to $BH_3$ and $H_2$. The lower levels of theory were unable to plot correct potential curves, whereas the MCCM methods give very good potential energy curves and requires much less computing resources than the CCSD(T)/ TZ(3d1f1g,2p1d) level. The potential energy of the $BH_5$ scrambling has been obtained by the multiconfiguration molecular mechanics algorithm (MCMM), and the rates are calculated using the variational transition state theory including multidimensional tunneling approximation. The rate constant at 300 K is 2.1 × $10^9s^{-1}$, and tunneling is very important.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1583-1586
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• 2006

All non-dopant white organic light-emitting diodes (WOLEDs) have been realized by using solid state highly fluorescent red bis(4-(N-(1- naphthyl)phenylamino)phenyl)fumaronitrile (NPAFN) and amorphous bipolar blue light-emitting 2-(4- diphenylamino)phenyl-5-(4-triphenylsilyl)phenyl- 1,3,4-oxadiazole (TPAOXD), together with well known green fluorophore tris(8- hydroxyquinolinato)aluminum $(Alq_3)$. The fabrication of multilayer WOLEDs did not involve the hard-tocontrol doping process. Two WOLEDs, Device I and II, different in layer thickness of $Alq_3$, 30 and 15 nm, respectively, emitted strong electroluminescence (EL) as intense as $25,000\;cd/m^2$. For practical solid state lighting application, EL intensity exceeding $1,000\;cd/m^2$ was achieved at current density of $18-19\;mA/cm^2$ or driving voltage of 6.5-8 V and the devices exhibited external quantum efficiency $({\eta}_{ext})$ of $2.6{\sim}2.9%$ corresponding to power efficiency $({\eta}_P)$ of $2.1{\sim}2.3\;lm/W$ at the required brightness.

• Journal of the Korean Chemical Society
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• v.55 no.3
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• pp.354-363
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• 2011

Quantum-chemistry study was explored to investigate the electronic structures, absorption and phosphorescence mechanism, as well as electroluminescence (EL) properties of three red-emitting Ir(III) complexes, $(fpmqx)_2Ir$(L) {fpmqx=2-(4-fluorophenyl)-3-methyl-quinoxaline; L=triazolylpyridine (trz) (1); L=picolinate (pic) (2) and L=acetylacetonate (acac) (3)}. The calculated results show that the HOMO distribution for 1 is mainly localized on trz moiety due to its stronger ${\pi}$-electron acceptor ability, and HOMO for 2 and 3 is the combination of Ir d- and phenyl ring ${\pi}$-orbital. The higher phosphorescence yields and differences among 1-3 are investigated in this paper. In addition, the reasons of higher EL efficiency of 2 than 1 and 3 have been rationalized.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.775-782
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• 2014

The importance of including spin-orbit interactions for the correct description of structures and vibrational frequencies of haloiodomethanes is demonstrated by density functional theory calculations with spin-orbit relativistic effective core potentials (SO-DFT). The vibrational frequencies and the molecular geometries obtained by SO-DFT calculations do not match with the experimental results as well as for other cations without significant relativistic effects. In this sense, the present data can be considered as a guideline in the development of the relativistic quantum chemical methods. The influence of spin-orbit effects on the bending frequency of the cation could well be recognized by comparing the experimental and calculated results for $CH_2BrI$ and $CH_2ClI$ cations. Spin-orbit effects on the geometries and vibrational frequencies of $CH_2XI$ (X=F, Cl, Br, and I) neutral are negligible except that C-I bond lengths of haloiodomethane neutral is slightly increased by the inclusion of spin-orbit effects. The $^2A^{\prime}$ and $^2A^{{\prime}{\prime}}$ states were found in the cations of haloiodomethanes and mix due to the spin-orbit interactions and generate two $^2E_{1/2}$ fine-structure states. The geometries of $CH_2XI^+$ (X=F and Cl) from SO-DFT calculations are roughly in the middle of two cation geometries from DFT calculations since two cation states of $CH_2XI$ (X=F and Cl) from DFT calculations are energetically close enough to mix two cation states. The geometries of $CH_2XI^+$ (X=Br and I) from SO-DFT calculations are close to that of the most stable cation from DFT calculations since two cation states of $CH_2XI$(X=Br and I) from DFT calculations are energetically well separated near the fine-structure state minimum.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2737-2740
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• 2013

The layered $KTiNbO_5$ was successfully synthesized with titanium(IV) isopropoxide and niobium oxalate by a novel polymerized complex (PC) method. The morphology and structure of the as-prepared sample was characterized by means of High-Resolution Transmission Electron Microscope, powder X-ray diffraction, and Laser Raman Spectroscopy. The spectral response characteristic was recorded by using UV-vis Diffuse Reflectance Spectroscopy. Results show that $KTiNbO_5$ as-prepared by PC method presents an uniform morphology of nano-particles, the mean particle sizes is ca. 28 nm corresponding to the (002), and the crystal structure can be well indexed to the orthorhombic phase. The sample as-prepared by PC method has higher band gap energy than that of the sample prepared by a solid-state reaction method due to the quantum size effect.

• Bulletin of the Korean Chemical Society
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• v.32 no.12
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• pp.4210-4214
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• 2011

Quasiclassical trajectory (QCT) calculations of Ne + ${H_2}^+$ reaction have been carried out on the adiabatic potential energy surface of the ground state $1^2$ A'. The reaction probability of the title reaction for J = 0 has been calculated, and the QCT result is consistent with the previous quantum mechanical wave packet result. Quasiclassical trajectory calculations of the four polarization-dependent differential cross sections have been carried out in the center of mass (CM) frame. The P(${\theta}_r$), P(${\phi}_r$) and P(${\theta}_r$, ${\phi}_r$) distributions, the k-k'-j' correlation and the angular distribution of product rotational vectors are presented in the form of polar plots. Due to the well in $1^2$ A' PES, the reagent vibrational excitation has greater influence on the polarization of the product rotational angular momentum vectors j' than the collision energy.

• Journal of Photoscience
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• v.6 no.4
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• pp.165-170
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• 1999

Asymmetric recognition of chiral alcohol by fluorenone derivatives with chiral substituents through intermolecular hydrogen bonding interaction in the singlet excited state was attempted. 1-((1S, 2R, 5S)-(+)-Menthyloxycarbonyl)aminofluoren-9-one (1-MAF) and 1-((1S, 2R, 5S)-(+)-menthyloxycarbonyl)oxyfluoren-9-one (1-MOF) were synthesized and their photophysical behaviors were characterized by the measurement of absorption and fluorescence spectra, as well as the quantum yield and the lifetime of fluorescence. The excited singlet states of 1-MAF and 1-MOF were revealed to have characteristics similar to those of fluorenone, though the intramolecular CT nature was fairly suppressed as compared with 3- and 4-substituted aminofluorenones. Fluorescences of 1-MAF and 1-MOF in acetonitrile were quenched by the addition of alcohols. Differences in fluorescence quenching efficiency were hardly observe for rather small chiral alcohols such as (R)-(-)- or (S)-(+)-2-butanol, while bulky alcohols such as menthol and isopinocampheol showed chiral recognition effects in their fluorescence quenching of 1-MAF in either acetonitrile or butyronitrile.

• Applied Microscopy
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• v.41 no.2
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• pp.89-98
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• 2011

Atom Probe Tomography (APT) can provide 3-dimensional information such as position and chemical composition with atomic resolution. Despite the ability of this technique, APT could not be applied for poor conductive materials such as semiconductor. Recently APT has dramatically developed by applying the laser pulsing and combining with Focused Ion Beam (FIB). The invention and combination of these techniques make possible site-specific sample preparation and permit the investigation of various materials including insulators. In this paper, we introduced the recently achieved state of the art applications of APT focusing on Si based FET devices, LED devices, low dimensional materials.