• Bulletin of the Korean Chemical Society
• /
• v.20 no.11
• /
• pp.1281-1287
• /
• 1999

The low-lying electronic states of diazirine and 3,3'-dimethyldiazirine have been studied by high level ab initio quantum chemical methods. The equilibrium geometries of the ground state and the first excited singlet and triplet states have been optimized using the Hartree-Fock (HF) and complete active space SCF (CASSCF) methods, as well as using the Møller-Plesset second order perturbation (MP2) theory and the single configuration interaction (CIS) theory. It was found that the first excited singlet state is of 1 B1 symmetry resulting from the n- π* transition, while the first excited triplet state is of 3 B2 symmetry resulting from the π- π* transition. The harmonic vibrational frequencies have been calculated at the optimized geometry of each electronic state, and the scaled frequencies have been compared with the experimental frequencies available. The adiabatic and vertical transition energies from the ground electronic state to the low-lying electronic states have been estimated by means of multireference methods based on the CASSCF wavefunctions, i.e., the multiconfigurational quasidegenerate second order perturbation (MCQDPT2) theory and the CASSCF second-order configuration interaction (CASSCF-SOCI) theory. The vertical transition energies have also been calculated by the CIS method for comparison. The computed transition energies, particularly by MCQDPT2, agree well with the experimental observations, and the electronic structures of the molecules have been discussed, particularly in light of the controversy over the existence of the so-called second electronic state.

• Proceedings of the Korean Magnetic Resonance Society Conference
• /
• 2002.08a
• /
• pp.70-71
• /
• 2002

Exchange-coupled cluster of transition-metal ions are relevant to many different scientific areas, ranging from chemistry to solid-state physics, biology, material science and has been the subject of much research in recent years(1,2). Single crystal EPR spectroscopy works as a very effective tool for the measurement of J values for small exchange interactions. This makes EPR technique very suitable for detection of weak exchange coupling transmitted over long distances via extended atomic and melecular bridges. Large polyoxometallates (3) may provide ideal structural environments for the study of interactions between paramagnetic ions. The detailed nature of magnetic interaction (positive sign and magnitude of J~0.006 $cm^{-1}$ /) was clearly determined for di-copper(II) system by single crystal EPR spectroscopy (4). The single-triplet (S-T) transitions are forbidden by different symmetries of the wave functions. However, when the singlet ground state is mixed into triplet states, the S-T transitions can be allowed and observed as weak lines. These weak S-T lines are positioned symmetrically with respect to the main transitions in the distance equals to 2J from the center of the spectrum. This lines allow one to determine the J-value with very high accuracy when │J│ ＜ hv 0.32 $cm^{-1}$ /. Unfortunately, the S-T transitions in the single crystal were detected by EPR method only in a few complexes until now. We have measured single-triplet transition lines for several magnetically coupled cluster systems and determined their J values accurately. The temperature dependency of J was studied by monitoring the changes in S-T.

• Bulletin of the Korean Chemical Society
• /
• v.25 no.8
• /
• pp.1231-1237
• /
• 2004

Rate constants for photolytic reactions of p-substituted 2-diazopropiophenones were determined in acetonitrile. The reactions show a comparatively low value of activation energy and activation enthalpy to alkylcarbenes or other arylcarbenes. The transition state corresponds to the step of a new carbonyl bond formation. The high negative ρ -values are shown in Hammett plots. The kinetics results and EPR spectrum are in accord with a phenomenon that occurs in interconversion between singlet and triplet carbenes.

• Bulletin of the Korean Chemical Society
• /
• v.12 no.4
• /
• pp.441-444
• /
• 1991

The intramolecular proton transfers of 2-hydroxy-4,5-naphthotropone in room temperature solutions are studied using static and time-resolved absorption and emission spectroscopy. Dual normal and tautomer fluorescence is observed in ethanol solution, while only the tautomer fluorescence is observed in cyclohexane solution. The fluorescence lifetimes and quantum yields in ethanol and cyclohexane solutions indicate that in hydrocarbon solvents, rapid intersystem crossing competes with proton transfer in the first excited singlet state. Transient absorption spectra and kinetics indicate that proton transfer also undergoes in the first triplet state with a transfer time of ∼ 3 ns. No transient absorption from the tautomer ground state indicates a rapid back proton transfer in the ground state.

• Asian Pacific Journal of Cancer Prevention
• /
• v.13 no.5
• /
• pp.1863-1867
• /
• 2012

Background: Maintenance chemotherapy is one strategy pursued in recent years with intent to break through the chemotherapy plateau for advanced non-small cell lung cancer (NSCLC). However, given the toxicity, platinum-based combinations are rarely given for this purpose. We carried out the present prospective study of triplet platinum-based combination sequential chemotherapy in advanced NSCLC to investigate if patients could tolerate and benefit from such intensive treatment. Methods: From Dec 2003 to Dec 2007, 190 stage IIIB and IV NSCLC patients in Sun yat-sen University sequentially received the 3 platinum-based combination (TP-NP-GP) treatment (T: paclitaxol175$mg/m^2$ d1; N: vinorelbine25$mg/m^2$ d1 and 8; G: gemcitabine1$g/m^2$ d1 and 8; P: cisplatin20$mg/m^2$ d1-5; repeated every 3 weeks). Patients were followed up to at least 3 years to obtain survival data. Treatment toxicities and the quality of life (QOL) were assessed during the whole treatment. Results: There were 187 patients evaluable. The TP, NP and GP response rates with sequential use were 42.8% (80/187), 41.1% (65/158) and 28.8% (21/73) respectively. Median survival time was 18.2 months and the 1, 2 and 3 year overall survival (OS) rates were 78.7%, 38.5% and 21.3%. Patients receiving > 6 cycles of chemotherapy had significantly longer OS and TTP (MST 25.3 vs. 14.5 months, TTP 15.1 vs. 9.1 months). The QOL on the whole for the patients was improved after chemotherapy. Conclusions: The sequential chemotherapy strategy with triplet platinum-based combination regimens can improve the survival outcome and the quality of life of advanced non-small cell lung cancer patients.

• Bulletin of the Korean Chemical Society
• /
• v.17 no.8
• /
• pp.745-749
• /
• 1996

Fluorescence from the electronically excited thiophosgene (Cl2CS) in its first excited singlet state (S1) is efficiently quenched by collision. Rates of the collision-induced electronic relaxation were obtained for various vibrational levels in the S1 state by measuring the fluorescence lifetimes. We found that the relaxation process is strongly energy-dependent; the rate consistently increases by a factor of ~40 with the increase of vibrational energy from 0 to 1450 cm-1. Collision-induced intersystem crossing from the S1 to the first triplet state (T1) is attributed to the major process responsible for the electronic relaxation.

• Bulletin of the Korean Chemical Society
• /
• v.7 no.6
• /
• pp.416-421
• /
• 1986

The solvent coordination effect on the excited state processes of Mg(II)- and Zn(II)-phthalocyanines has been described. The triplet state of these compounds decays with mixed first and second order kinetics or mainly second order kinetics depending on the solvents used. The first order component of the rate constants decrease along with the series, dimethylsulfoxide (5-coordinated), 1-chloronaphthalene (4-coordinated) and piperidine (6-coordinated), while the second order rate constant is dependent on the diffusion rate constant of the solvents. The excited state quenching by methylviologen or p-benzoquinone is discussed. And ion recombination rate constant is given.

• Journal of Information Display
• /
• v.8 no.2
• /
• pp.15-19
• /
• 2007

We have studied the effect of host materials on the electrophosphorescence properties by comparing three different host materials such as tris(8-hydroxyquinoline)-aluminum (III) $(Alq_3)$, bis(8-hydroxyquinoline)-zinc (II) $(Znq_2)$, and 4,4'-N,N' dicarbazole-biphenyl (CBP) doped with a red-emissive phosphorescent dye, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum (II) (PtOEP). The EL spectra show a strong red emission (peak at 650 nm) from the triplet excited state of PtOEP and a very weak emission from an electron transport layer of $Alq_3$ and a hole transport layer of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine (TPD). We find that the triplet exciton lifetime and the quantum efficiency decrease in the order of CBP, $Alq_3$, and $Znq_2$ host materials. The results are interpreted as a poor exciton confinement in $Alq_3$, and $Znq_2$ host compared with in CBP. Therefore, it is very important for the triplet-exciton confinement in the emissive layer for obtaining a high efficiency.

• Bulletin of the Korean Chemical Society
• /
• v.15 no.2
• /
• pp.154-161
• /
• 1994

Studies have been conducted to explore single electron transfer (SET) induced photocyclization reactions of N-(trimethylsilylmethylthioalkyl)phthalimides (alkyl=ethyl, n-propyl, n-butyl, n-pentyl, and n-hexyl). Photocyclizations occur in methanol in modest to high yields to produce cyclized products in which phthalimide carbonyl carbon is bonded to the carbon of side chain in place of the trimethylsilyl group. Mechanism for these photocyclizations involving intramolecular SET from sulfur in the ${\alpha}$-silylmethylthioalkyl groups to the singlet excited state phthalimide moieties followed by desilylation of the intermediate ${\alpha}$ -silylmethylthio cation radicals and cyclization by radical coupling is proposed. In contrast, photoreactions of N-(trimethylsilylmethylthioalkyl)phthalimides in acetone follow different reaction routes to produce another cyclized products in which carbon-carbon bond formation takes place between the phthalimide carbonyl carbon and the carbon ${\alpha}$ to silicon and sulfur atoms via triplet carbonyl hydrogen abstraction pathway. The normal singlet SET pathway dominates this triplet process for photoreactions of these substances in methanol while the triplet process dominates the singlet SET pathway for those in acetone. The efficient and regioselective cyclization reactions observed for photolyses in methanol represent synthetically useful processes for construction of medium and large ring heterocyclic compounds.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.2
• /
• pp.166-172
• /
• 1992

Studies have been conducted to explore single electron transfer (SET) induced photocyclization reactions of N-(trimethylsilylmethoxyalkyl)phthalimides(alkyl=E thyl, n-propyl, n-butyl, n-pentyl, and n-octyl). Photocyclizations occur in methanol in high yields to produce cyclized products in which phthalimide carbonyl carbon is bonded to the carbon of side chain in place of the trimethylsilyl group. Mechanism for these photocyclizations involving intramolecular SET from oxygen in the $\alpha-silylmethoxy$ groups to the singlet excited state phthalimide moieties followed by desilylation of the intermediate $\alpha-silylmethoxy$ cation radicals and cyclization by radical coupling are proposed. In contrast, photoreaction of N-(trimethylsilylmethoxyethyl) phthalimide in acetone follows different reaction routes to produce two cyclized products in which carbon-carbon bond formation takes place between the phthalimide carbonyl carbon and the carbon $\alpha$ to silicon and oxygen atoms via triplet carbonyl hydrogen abstraction triplet carbonyl silyl group abstraction pathways. The normal singlet SET pathway dominates these triplet processes for photoreaction of this substance in methanol. The efficient and regioselective cyclization reactions observed for photolysis in methanol represent synthetically useful processes for construction of medium and large ring heterocyclic compounds.