• Bulletin of the Korean Chemical Society
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• v.21 no.5
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• pp.465-470
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• 2000

The conformations and energies of p-tert-butylcalix[4] crown-6-ether (1) and its alkyl ammonium complexes have been simulated by AM1 semi-empirical quantum mechanics and molecular mechanics calculations using a variety of forcefields (MM2, MM+, CVFF). We performed molecular dynamics calculations to simulate the behavior of these coplexes primartily focusing on the three representative conformations (cone, partial cone, 1,3-alternate) of host molecule 1. When we performed AM1 semi-empirical and molecular mechanics calculations, the one conformation was generally found to be most stable for all the employed calculation methods. The primary binding site of host 1 for the recognition of alkyl ammonium guests was confirmed to be the central part of the crown moiety. The complexation enthalpy calculations revealed that the alkyl amonium cations having smaller and linear alkyl group showed the better complexation efficiencies when combined with p-tert-butylcalix[4]crown-6-ether, that is in satisfactory agreement with the experimental results.

• Bulletin of the Korean Chemical Society
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• v.22 no.11
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• pp.1248-1254
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• 2001

The conformations and energies of p-tert-butylcalix[4]crown-6-ether (1) and its alkyl ammonium complexes have been calculated by ab initio HF/6-31G quantum mechanics method. The cone conformation was found to be most stable for free host 1. We hav e determined the binding site of these host-guest complexes focusing on the crown-6-ether or p-tert-butylcalix[4]arene pocket of the cone conformation of host molecule 1. The primary binding site of host 1 for the recognition of alkyl ammonium guests was confirmed to be the central part of the crown moiety of cone conformation. The complexation energy calculations revealed that the ammonium cation without alkyl group showed the highest complexation efficiency when combined with host 1, that is in satisfactory agreement with the experimental results.

• Current Photovoltaic Research
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• v.10 no.1
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• pp.16-22
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• 2022

The long-term stability of PSCs against visual and UV light, moisture, electrical bias and high temperature is an important issue for commercialization. In particular, since the operation temperature of solar cell can rise above 85℃, a study on thermal stability is required. In this study, the cause of thermal-induced degradation of PSCs was investigated using the SCAPS-1D simulation tool. First, PSCs of TiO₂/CH₃NH₃PbI₃/Spiro-OMeTAD/Au structure were exposed to a constant temperature of 85℃ to observe changes in conversion efficiency and quantum efficiency. Because the EQE reduction above 500 nm was remarkable, we simulated PSCs performance as a function of lifetime, doping density of perovskite and spiro-OMeTAD. Consequently, the main cause of thermal-induced degradation is considered to be the change in the perovskite doping concentration and lifetime due to ion migration of perovskite.

• Korean Journal of Materials Research
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• v.9 no.6
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• pp.635-653
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• 1999

The present work considers work considers research strategies to address global warming. Specifically, this work considers the development of technologies of importance for the reduction of greenhouse gas emission and, especially, the materials that are critical to these technologies. It is argued that novel materials that are essential for the production of environmentally friendly energy may be developed through a special kind of engineering: interface engineering, rather than through classical bulk chemistry. Progress on the interface engineering requires to increase the present state of understanding on the local properties of materials interfaces and interfaces processes. This, consequently, requires coordinated international efforts in order to establish a strong background in the science of materials interfaces. This paper considers the impact of interfaces, such as surfaces and grain boundaries, on the functional properties of materials. This work provides evidence that interfaces exhibit outstanding properties that are not displayed by the bulk phase. It is shown that the local interface chemistry and structure and entirely different than those of the bulk phase. In consequence the transport of both charge and matter along and across interfaces, that is so important for energy conversion, is different than that in the bulk. Despite that the thickness of interfaces is of an order to a nanometer, their impact on materials properties is substantial and, in many cases, controlling. This leads to the conclusion that the development of novel materials with desired properties for specific industrial applications will be possible through controlled interface chemistry. Specifically, this will concern materials of importance for energy conversion and environmental monitoring. Therefore, there is a need to increase the present state of understanding of the local properties of materials interfaces and the relationship between interfaces and the functional properties of materials. In order to accomplish this task coordinated international efforts of specialized research centres are required. These efforts are specifically urgent regarding the development of materials of importance for the reduction of greenhouse gases. Success of research in this area depends critically on financial support that can be provided for projects on materials of importance for a sustainable environment, and these must be considered priorities for all of the global economies. The authors of the present work represent an international research group economies. The authors of the present work represent an international research group that has entered into a collaboration on the development of the materials that are critical for the reduction of greenhouse gas emissions.

• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1233-1242
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• 2008

The hydration effect on the intrinsic magnetism of natural salmon double-strand DNA was explored using electron magnetic resonance (EMR) spectroscopy and superconducting quantum interference device (SQUID) magnetic measurements. We learned from this study that the magnetic properties of DNA are roughly classified into two distinct groups depending on their water content: One group is of higher water content in the range of 2.6-24 water molecules per nucleotide (wpn), where all the EMR parameters and SQUID susceptibilities are dominated by spin species experiencing quasi one-dimensional diffusive motion and are independent of the water content. The other group is of lower water content in the range of 1.4-0.5 wpn. In this group, the magnetic properties are most probably dominated by cyclotron motion of spin species along the helical π -way, which is possible when the momentum scattering time (${\tau}_k$) is long enough not only to satisfy the cyclotron resonance condition (${\omega}_c{\tau}_k$ > 1) but also to induce a constructive interference between the neighboring double helices. The same effect is reflected in the S-shaped magnetization-magnetic field strength (M-H) curves superimposed with the linear background obtained by SQUID measurements, which leads to larger susceptibilities at 1000 G when compared with the values at 10,000 G. In particular, we propose that the spin-orbital coupling and Faraday's mutual inductive effect can be utilized to interpret the dimensional crossover of spin motions from quasi 1D in the hydrate state to 3D in the dry state of dsDNA.

• Journal of the Korean Applied Science and Technology
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• v.29 no.3
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• pp.459-465
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• 2012

We had synthesized a green dopant material based on the binaphthyl group, 7,7'-(2,2'dimethoxy-1,1'-binaphthyl-3,3'-diyl) bis(4-(thiophen -2-yl) benzo[e][1,2,5] thiadiazole (TBT). We also fabricated the white organic light emitting diode (OLED) with a phosphorescent blue emitter : iridium(III)bis[(4,6-di-fluoropheny)-pyridinato -N,C2]picolinate (FIrpic) doped in N,N'-dicarbazolyl-3,5-benzene (mCP) of hole transport type host material and both TBT and bis(2-phenylquinolinato)- acetylacetonate iridium(III) (Ir(pq)2acac) doped in 1,3,5-tris(N-phenylbenzimidazole -2-yl)benzene (TPBi) of electron transport type host material. As a result, the property of white OLED using TBT, which demonstrated a maximum luminous efficiency and external quantum efficiency of 5.94 cd/A and 3.23 %, respectively. It also showed the pure white emission with Commission Internationale de I'Eclairage (CIE) coordinates of (0.34, 0.36) at 1000 nit.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.503-505
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• 2008

A host material containing tetraphenylsilane, 9-(4-triphenylsilanyl-(1,1'4,1")-terphenyl-4"-yl)-9H-cabazole (TSTC), was synthesized for green phosphorescent organic emitting diodes. $Ir(ppy)_3$ based OLEDs using TSTC host and DTBT (2,4-diphenyl-6-(4'yl)-1,3,5-triazine) hole blocking layer (HBL) showed the maximum external quantum efficiency of 19.8 %, the power efficiency of 59.4 lm and high operational stability with a half lifetime of 160,000 h at an initial luminance of $100\;cd/m^2$.

• Korean Journal of Environmental Biology
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• v.20 no.3
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• pp.197-204
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• 2002

Gourd seeds were irradiated with the doses of 0-20 Gy to investigate the effect of the low dose $\gamma$-radiation on the early growth and physiological activity. The stimulating effects of the low dose y- radiation on the early growth were not noticeably high, but were increased generally at 4-16 Gy irradiation group. The catalase and peroxidase activity of cotyledon from seeds irradiated with $\gamma$- radiation were increased at 8 Gy irradiation group. The photochemical activity of leaf was noticeably high at 4 Gy irradiation group. The photochemical yield of PSII, estimated as Fv/Fm, decreased with increasing illumination time by 50% after 4 hrs in the control and 8 Gy irradiation group, while Fo slightly increased. However, Fv/Em in the 4 Gy irradiation group decreased by 40% of inhibition, indicating that photoinhibition decreased by the low dose $\gamma$- radiation. Changes in the effective quantum yield of PSII, $\varphi_{PSII}$ and 1/Fo- l/Fm, a measure of the rate constant of excitation trapping by the PSII reaction center, showed similar pattern to Fv/Em. NPQ decreased by 70% after photoinhibitory treatment with showing similar pattern between the control and the irradiation group. These results showed the positive effect of low dose $\gamma$- radiation on the seedling growth and the reduction of photoinhibition in the 4 Gy irradiation group.

• Journal of radiological science and technology
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• v.26 no.4
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• pp.39-46
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• 2003

Digital radiographic systems based on solid-state detectors, commonly referred to as flat-panel detectors, are gaining popularity in clinical practice. Large area, flat panel solid state detectors are being investigated for digital radiography. The purpose of this work was to evaluate the active matrix flat panel digital x-ray detectors in terms of their modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). In this paper, development and evaluation of a selenium-based flat-panel digital x-ray detector are described. The prototype detector has a pixel pitch of $139\;{\mu}m$ and a total active imaging area of $14{\times}8.5\;inch^2$, giving a total 3.9 million pixels. This detector include a x-ray imaging layer of amorphous selenium as a photoconductor which is evaporated in vacuum state on a TFT flat panel, to make signals in proportion to incident x-ray. The film thickness was about $500\;{\mu}m$. To evaluate the imaging performance of the digital radiography(DR) system developed in our group, sensitivity, linearity, the modulation transfer function(MTF), noise power spectrum (NPS) and detective quantum efficiency(DQE) of detector was measured. The measured sensitivity was $4.16{\times}10^6\;ehp/pixel{\cdot}mR$ at the bias field of $10\;V/{\mu}m$ : The beam condition was 41.9\;KeV. Measured MTF at 2.5\;lp/mm was 52%, and the DQE at 1.5\;lp/mm was 75%. And the excellent linearity was showed where the coefficient of determination ($r^2$) is 0.9693.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2093-2098
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• 2013

Density functional theory (DFT) was used to determine the ground state geometries of indigo and new design dyes (IM-Dye-1 IM-Dye-2 and IM-Dye-3). The time dependant density functional theory (TDDFT) was used to calculate the excitation energies. All the calculations were performed in both gas and solvent phase. The LUMO energies of all the dyes were above the conduction band of $TiO_2$, while the HOMOs were below the redox couple (except IM-Dye-3). The HOMO-LUMO energy gaps of new design dyes were smaller as compared to indigo. All new design dyes were strongly red shifted as compared to indigo. The improved light harvesting efficiency (LHE) and free energy change of electron injection ${\Delta}G^{inject}$ of new designed sensitizers revealed that these materials would be excellent sensitizers. The broken coplanarity between the benzene near anchoring group having LUMO and the last benzene attached to TPA unit in all new design dyes consequently would hamper the recombination reaction. This theoretical designing will the pave way for experimentalists to synthesize the efficient sensitizers for solar cells.