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Theoretical studies of cyclometalated phenylpyrazol Ir(III) complex using density functional theory
No Gill Park,,Jung Eun Lee,Young Sik Kim,Gyu Cheol Choi 한국물리학회 2005 Current Applied Physics Vol.5 No.1
The ground state and low-lying excited electronic states in the Ir(III) complexfac-Ir(ppz)3 are studied using density functionaltheory where ppz¼ phenylprazol and fac¼ facial. We reported before that this complex was pure blue phosphorescent material withabout 450 nm of electroluminescent peak. Herein, the electronic properties of the molecule are studied using the B3LYP functionaland the structure analysis of the optimized geometries are processed in comparison with structures of ppz ligand andfac-Ir(ppy)3.Excited triplet and singlet states are examined using time-dependent density functional theory (TD-DFT). The calculated energies ofthe lowest triplet and singlet states are 3.14 and 3.56 eV. All of the low-lying transitions calculated in this study are categorized asmetal-to-ligand charge-transfer (MLCT) transitions because the metal orbitals involved in the transitions have signicant admixtureof ligand p orbitals with amount of metal 5d character of three highest occupied molecular orbitals which are 50.2%, 47.8% and47.8%, respectively. From the analysis of absorption spectrum of this complex, it was found that the singlets and triplets calculatedin this study are distributed in the range of 270350 and 340410 nm in absorption spectrum.
Theoretical studies of cyclometalated phenylpyrazol Ir(III) complex using density functional theory
Park, No Gill,Choi, Gyu Cheol,Lee, Jung Eun,Kim, Young Sik Elsevier 2005 CURRENT APPLIED PHYSICS Vol.5 No.1
<P><B>Abstract</B></P><P>The ground state and low-lying excited electronic states in the Ir(III) complex <I>fac</I>-Ir(ppz)<SUB>3</SUB> are studied using density functional theory where ppz=phenylprazol and <I>fac</I>=facial. We reported before that this complex was pure blue phosphorescent material with about 450 nm of electroluminescent peak. Herein, the electronic properties of the molecule are studied using the B3LYP functional and the structure analysis of the optimized geometries are processed in comparison with structures of ppz ligand and <I>fac</I>-Ir(ppy)<SUB>3</SUB>. Excited triplet and singlet states are examined using time-dependent density functional theory (TD-DFT). The calculated energies of the lowest triplet and singlet states are 3.14 and 3.56 eV. All of the low-lying transitions calculated in this study are categorized as metal-to-ligand charge-transfer (MLCT) transitions because the metal orbitals involved in the transitions have significant admixture of ligand π orbitals with amount of metal 5d character of three highest occupied molecular orbitals which are 50.2%, 47.8% and 47.8%, respectively. From the analysis of absorption spectrum of this complex, it was found that the singlets and triplets calculated in this study are distributed in the range of 270–350 and 340–410 nm in absorption spectrum.</P>
No Gill Park,Gyu Cheol Choi,Young Hee Lee,Young Sik Kim 한국물리학회 2006 Current Applied Physics Vol.6 No.4
The ground state and low-lying excited electronic states in the Ir(III) complexes,fac-Ir(dfpp)3, Ir(dfpp)2(acac) and FIrpic, arestudied using the density functional theory, where dfpp = 2-(2,4-diuorophenyl)pyridine, acac = acetylacetonate, pic = picolinic acidand fac= facial. Herein, the electronic properties of these molecules are studied using the B3LYP functional and the structural anal-ysis of the optimized geometries are done in comparison with the structures of the dfpp ligand and Ir complexes. Excited triplet andsinglet states are examined using the time-dependent density functional theory (TD-DFT). The calculated energies of triplets are2.8 eV, 2.69 eV and 2.73 eV, in the order described above, which are all higher than that offac-Ir(ppy)3with 2.60 eV, whereppy = 2-phenylpyridine. Nearly all of the low-lying excitations calculated in this study are categorized as metal-to-ligand charge-transfer (MLCT) transitions because HOMOs are strongly mixed between thep orbital of the dfpp ligand and the d orbital ofthe centric Ir atom.
An Inner-spherical Continuously Variable Transmission for Electric Bicycles
Park, Moon-Woo,Lee, Hyoung-Woo,Park, No-Gill Korean Society for Precision Engineering 2008 International Journal of Precision Engineering and Vol.9 No.1
A new continuously variable transmission (CVT) for electric bicycles was developed using a traction drive mechanism with inner and outer spherical rotors. This electric bicycle CVT permits three propulsion modes: human-power only, motor-power only, or a combination of motor power and human power. In addition, the electric bicycle CVT has high power efficiency, large torque capacity, improved drivability, and good packageability. A prototype was manufactured based on a conceptual design, a performance analysis, and a detailed design. This prototype has a rated power of 250 W and input motor speed of 20 rad/s for an overall speed ratio in the range 0.3-1.2. A bench test was conducted to measure the power transmission performance of the prototype.
An Inner-spherical Continuously Variable Transmission for Electric Bicycles
Moon-Woo Park,Hyoung-Woo Lee,No-Gill Park 한국정밀공학회 2008 International Journal of Precision Engineering and Vol.9 No.1
A new continuously variable transmission (CVT) for electric bicycles was developed using a traction drive mechanism with inner and outer spherical rotors. This electric bicycle CVT permits three propulsion modes: human-power only, motor-power only, or a combination of motor power and human power. In addition, the electric bicycle CVT has high power efficiency, large torque capacity, improved drivability, and good packageability. A prototype was manufactured based on a conceptual design, a performance analysis, and a detailed design. This prototype has a rated power of 250 W and input motor speed of 20 rad/s for an overall speed ratio in the range 0.3-1.2. A bench test was conducted to measure the power transmission performance of the prototype.
Theoretical investigation of tetra-substituted pyrenes for organic light emitting diodes
Yong Hwan Park,Hyeon Hee Rho,No Gill Park,Young Sik Kim 한국물리학회 2006 Current Applied Physics Vol.6 No.4
Pyrene derivatives have been developed to blue uorescent light emitting materials for organic light emitting diodes (OLEDs).Luminescence eciency of pyrene molecule is very low, however pyrenes substituted with large group can give a bright blue uo-rescence. Substituted pyrenes were investigated to increase luminescence eciency and color purity. In this paper, we studied 1,3,6,8-tetra-substituted pyrenes theoretically. The investigation was studied by ab initio method. Density functional theory (DFT) utilizingthe B3LYP functional with the 6-31G(d) basis set was used for energy calculation and geometry optimization of the ground elec-tronic state of those compounds. The geometry optimization of the rst excited electronic states was determined using congurationinteraction with single excitations (CIS) method. Energies of vertical and adiabatic transition were calculated using time-dependentdensity functional theory (TD-DFT) with B3LYP/6-31G(d) calculation. The investigation on 1,3,6,8-tetra-substituted pyrenes withthe eect of the aromatic substituents showed that the energy gap between the highest occupied molecular orbital (HOMO) and thelowest unoccupied molecular orbital (LUMO) was decreased as the conjugation length was increased. This trend was also appearedwhen the nitrogen atom was substituted with carbon atom in the aromatic substituents. Also the substituted pyrenes with large moi-more than that of the pyrene molecule. In this paper, t(dpe)py molecule was proposed as a new ecient blue emitter for OLED fromcalculated result.