• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.415.1-415.1
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• 2014

Carrying out first-principles calculations, we study N-doped capped carbon nanotube (CNT) electrodes applied to DNA sequencing. While we obtain for the face-on nucleobase junction configurations a conventional conductance ordering where the largest signal results from guanine according to its high highest occupied molecular orbital (HOMO) level, we extract for the edge-on counterparts a distinct conductance ordering where the low-HOMO thymine provides the largest signal. The edge-on mode is shown to operate based on a novel molecular sensing mechanism that reflects the chemical connectivity between N-doped CNT caps that can act both as electron donors and electron acceptors and DNA functional groups that include the hyperconjugated thymine methyl group[1].

• Journal of the Korean Applied Science and Technology
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• v.17 no.2
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• pp.120-125
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• 2000

The tfTZ(4,4',4''-trifluoro-triazine) was used as a hole blocking material for the electroluminescent devices(ELDs) in this study. In general, the holes are outnumbered the electrons in hole transport and emitting layers because the hole transport is more efficient in most organic ELDs. The hole blocking layer are expected to control the excess holes to increase the recombination of holes and electrons and to decrease current density. The former study using the 2,4,6-triphenyl-1,3,5-triazine(TTA) as hole blocking layer showed that the TTA did not form stable films with vapor deposition technique. The tfTZ can generate stable evaporated films, moreover the fluorine group can lower the highest occupied molecular orbital(HOMO) level, which produces the energy barrier for the holes. The tfTZ has high electron affinities according to the data by the Cyclic-Voltammety(CV) method, which is developed for the measurement of HOMO and lowest occupied molecular orbital(LUMO) level of organic thin films. The lowered HOMO level is made the tfTZ to be applied for a hole blocking layer in ELDs. We fabricated multilayer ELDs with a structure of ITO/hole blocking layer(HBL)/hole transporting layer(HTL)/emitting layer/electrode. The hole blocking properties of this devices is confirmed from the lowered current density values compared with that without hole blocking layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.142.2-142.2
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• 2016

The metal intercalation to an organic semiconductor is of importance since the charge transfer between a metal and an organic semiconductor can induce the highly enhanced conductivity for achieving efficient organic electronic devices. In this regard, the changes of the electronic structure of copper phthalocyanine (CuPc) caused by the intercalation of potassium are studied by ultraviolet photoemission spectroscopy (UPS) and density functional theory (DFT) calculations. Potassium intercalation leads to the appearance of an intercalation-induced peak between the highest molecular occupied orbital (HOMO) and the lowest molecular unoccupied orbital (LUMO) in the valence-band spectra obtained using UPS. The DFT calculations show that the new gap state is attributed to filling the LUMO+1, unlike a common belief of filling the LUMO. However, the LUMO+1 is not conductive because the ${\pi}$-conjugated macrocyclic isoindole rings on the molecule do not make a contribution to the LUMO+1. This is the origin of a metal-insulator transition through heavily potassium doped CuPc.

• Proceedings of the KIEE Conference
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• 2008.05a
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• pp.181-182
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• 2008

고 효율의 유기 발광 소자 개발을 위해 무엇보다 발광 소자의 각층의 에너지 대 구조를 고려한 구조 개선과 새로운 유기물질 합성을 통해 구동전압을 낮춤으로써 전력효율을 높이고, 소모 전력을 낮추며, 수명을 증가시킬 수 있어, 많은 연구자들이 유기 발광 소자의 효율을 향상시키기 위해 다양한 노력들을 시도하고 있다. 본 연구에서는 고 효율화를 위한 방법으로 유기 발광 소자에 있어서 전자주입에 필요한 전압을 낮추고 전자 주입을 촉진시키기 위하여 발광물질의 LUMO(LOWEST UNOCCUPIED MOLECULAR ORBITAL) 준위와 음극 금속의 페르미 준위를 고려하여 전자 주입시 전위 장벽을 낮출 수 있는 에너지 대 구조를 가진 전자 주입 층을 검토하였고, 정공 주입을 촉진시키기 위하여 양극 금속의 페르미 에너지 준위와 발광 층의 HOMO(HIGHEST OCCUPIED MOLECULAR ORBITAL) 준위를 고려하여 정공 주입시 전위장벽을 낮출 수 있는 적절한 에너지 대 구조를 가진 정공 주입 층에 대하여 고찰하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.190.1-190.1
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• 2014

The interfacial electronic structure of a bilayer of chloroaluminum phthalocyanine (ClAlPc) and pentacene grown on indium tin oxide (ITO) has been studied using synchrotron radiation-excited photoelectron spectroscopy. The energy difference between the highest occupied molecular orbital (HOMO) level of the pentacene layer and the lowest unoccupied molecular orbital (LUMO) level of the ClAlPc layer (EDHOMO - EALUMO) was determined and compared with that of C60/pentacene bilayers. The EDHOMO - EALUMO of a heterojunction with ClAlPc was found to be 1.4 eV, while that with C60 was 1.0 eV. This difference is discussed in terms of the difference of the ionization energy of each acceptor materials. We also obtained the complete energy level diagrams of ClAlPc/pentacene/ITO and C60/pentacene/ITO, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.473-473
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• 2012

유기발광소자는 낮은 구동전압, 빠른 응답속도, 넓은 시야각 등의 장점으로 소형 디스플레이에 사용되며 차세대 조명으로 관심을 받고 있다. 고효율의 유기발광소자를 제작하기 위해서 다양한 유기 인광물질 합성 및 연구가 진행되고 있으며, 다양한 호스트 물질을 사용하여 전자와 정공의 주입을 향상하여 고효율의 인광 유기발광소자를 제작하였다. 본 논문에서는 발광층에 N,N'-dicarbazolyl-3,5-benzene (mCP)와 1,3,5-tri(phenyl-2-benzimidazole)-benzene (TPBi)를 혼합 호스트로 사용하였으며 tris(2-phenylpyridine)iridium ($Ir(ppy)_3$)청색 인광물질을 도핑하여 고효율의 인광 유기발광소자를 제작하였다. 유기발광소자의 발광층에 단일 호스트와 혼합 호스트의 전기적 및 광학적 특성을 비교 분석하여 전자 및 정공 수송 메커니즘을 규명하였다. 혼합 호스트 TPBi의 lowest unoccupied molecular orbital (LUMO) 준위와 엑시톤 저지층 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)의 LUMO 준위와 비슷하여 전자의 주입을 향상시키는 역할을 하며, 다른 혼합 호스트 mCP는 highest occupied molecular orbital (HOMO)와 정공수송층 N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB)의 HOMO와 비슷하여 정공의 주입을 향상시키는 역할을 하여, $Ir(ppy)_3$에 전자와 정공의 주입이 향상되어 고 효율의 인광 유기발광소자를 제작할 수 있었다. 이와 같은 실험결과는 인광 유기발광소자의 호스트 물질에 따른 전하주입 메커니즘을 설명 하였으며 고효율의 인광 유기발광소자 제작에 도움을 줄 것이다.

• Bulletin of the Korean Chemical Society
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• v.30 no.1
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• pp.205-213
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• 2009

This study reports on the geometry optimizations and electronic structure calculations for methyl pyropheophorbide (MPPa), tropolonyl methyl pyropheophorbides (TMPPa, ITMPPa), and cationic tropolonyl methyl pyropheophorbides ($TMPPa^+{{\cdot}BF_4}^-,\;ITMPPa^+{{\cdot}BF_4}^-,\;TMPPa^+,\;and\;ITMPPa^+$) using Local Spin Density Approximation (LSDA/ 6-31G*) and the Restricted Hatree-Fock (RHF/6-31G*) level theory. From the calculated results, we found that substituted cationic tropolonyl groups have larger structural effects than those of substituted neutral tropolonyl groups. The order of structural change effects is $ITMPPa^+ > ITMPPa^+{{\cdot}BF_4}^-$ > ITMPPa, as a result of the isopropyl group. Because it is an electron-releasing group, the substituted isopropyl group electronic effect on a 3-position tropolone increases the Highest Occupied Molecular Orbital and Lowest Unoccupied Molecular Orbital (HOMO-LUMO) energy gap. It was constituted that the larger the cationic characters of these photosensitizers, the smaller the HOMOLUMO band gaps are. The orbital energies of the cationic systems and the ions are stronger than those of a neutral system because of a strong electrostatic interaction. However, this stabilization of orbital energies are counteracted by the distortion of chlorin macrocycle, which results in a large destabilization of chlorin-based compound HOMOs and smaller destabilization of LUMOs as shown in TMPPa (ITMPPa), $TMPPa^+{{\cdot}BF_4}^- (ITMPPa^+{{\cdot}BF_4}^-),\;and\;TMPPa^+\;(ITMPPa^+)$ of Figure 6 and Table 6-7. These results are in reasonable agreement with normal-coordinate structural decomposition (NSD) results. The HOMO-LUMO gap is an important factor to consider in the development of photodynamic therapy (PDT).

• Journal of Integrative Natural Science
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• v.15 no.4
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• pp.179-186
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• 2022

The c-Jun N-terminal kinase (JNK3) play major role in neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, cerebral ischemia and other Central Nervous System disorders. Since JNK3 is primarily stated in the brain and stimulated by stress-stimuli, this situation is conceivable that inhibiting JNK3 could be a possible treatment for the mechanisms underlying neurodegenerative diseases. In this study drugs from Zinc15 database were screened to identify the JNK3 inhibitors by Molecular docking and Density functional theory approach. Molecular docking was done by Autodock vina and the ligands were selected based on the binding affinity. Our results identified top ten novel ligands as potential inhibitors against JNK3. Molecular docking revealed that Venetoclax, Fosaprepitant and Avapritinib exhibited better binding affinity and interacting with proposed binding site residues of JNK3. Density functional theory was used to compute the values for energy gap, lowest unoccupied molecular orbital (LUMO), and highest occupied molecular orbital (HOMO). The results of Density functional theory study showed that Venetoclax, Fosaprepitant and Avapritinib serves as a lead compound for the development of JNK3 small molecule inhibitors.

• Journal of the Korean Chemical Society
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• v.53 no.6
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• pp.671-676
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• 2009

Described here for the first time is an investigation on geometrical and electronic molecular structure of metol (N-methyl-p-aminophenol sulphate) as corrosion inhibitor of steel using density functional theory (DFT) calculations. Quantum chemical parameters such as highest occupied molecular orbital energy (EHOMO), lowest unoccupied molecular orbital energy (ELUMO), energy gap ((${\Delta}E$), Mulliken charges (($q_M$) and natural atomic (($q_n$) charge have been calculated both for gas and aqueous phases by using B3LYP/6-31G+(d,p) basis set. The relation between the inhibition efficiency and quantum chemical parameters have been discussed in order to elucidate the inhibition mechanism of the title compound.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.182-183
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• 2008

We fabricated a pentacene thin film transistor with Poly-vinylalcohol (PVA) as a dielectric. And we used Poly(9-vinylcarbazole) (PVK) as a buffer layer to improve the electrical characteristics. PVK is a material used often host material for OLED device, as it has good film forming properties, large HOMO-LUMO(highest occupied molecular orbital-lowest unoccupied molecular orbital) bandgap. The performance of a OTFT device with PVA gate dielectric was improved by using the PVK. Field effect mobility, threshold voltage, and on-off current ratio of device with PVK layer were about 0.6 $cm^2$/Vs, -17V, and $5\times10^5$, respectively.