• Bulletin of the Korean Chemical Society
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• 제3권3호
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• pp.115-119
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• 1982

The photoreaction of maleimide, one of the best model compounds of DNA molecules for psoralen-DNA photoreactions, is studied in order to investigate the photoreactivity and the mechanism of the maleimide-psoralen photoreaction. The (2+2) photocyclodimer of maleimide was obtained in solution state by direct or sensitized irradiation. The rate constant of dimerization is determined by quenching studies and found to be of the order of $10^9 M^{-1}sec^{-1}$. The direct dimerization of maleimide is found to undergo through the triplet excited state. The quantum yields of dimerization are dependent on the maleimide concentration.

• Bulletin of the Korean Chemical Society
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• 제14권5호
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• pp.614-618
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• 1993

The photoacid generation efficiency of four N-hydroxyphthalimide sulfonate derivatives was studied by photo-crosslinking reaction of poly(glycidyl methacrylate) in solid film state. The relative photoacid generation efficiency was increased in the order of N-hydroxyphthalimide methanesulfonate > -toluenesulfonate > -nitrobenzenesulfonate > -dinitrobenzensulfonate, and the reaction was efficiently sensitized by benzophenone suggesting that this photoreactions is likely to proceed through its triplet excited state.

• 대한화학회지
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• 제34권3호
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• pp.255-259
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• 1990

Benoxaprofen (BXP)의 들뜬상태를 직접 검출하기 위하여, 질소 레이저 플래쉬 광분해 분광기를 제작하였다. 이 분광기의 성능을 확인하기 위하여 표준시료로써 안트라센을 사용하여 실험하였다. 에탄올에 녹은 BXP의 레이저 광들뜸을 질소기체 존재하에서 수행하였으며 파장범위 400-600 nm에 걸쳐 순간흡수 스펙트럼을 측정하고 이에 대한 산소 및 베타 카로틴의 효과를 조사하였다. 그 결과 415nm에서의 최대순간흡수띠는 BXP의 삼중항 상태에 기인하며 삼중항 에너지는 22 Kcal/mole 이상임을 확인하였다. 또한, BXP의 라디칼로 추정되는 중간체에 기인하는 최대순간 흡수띠가 520nm에 관측되었다. 이들 결과에 의해 BXP의 광증감 메카니즘을 논의하였다.

• Bulletin of the Korean Chemical Society
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• 제15권10호
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• pp.857-860
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• 1994

We have calculated the ${\pi}$-electron density, atom self-polarizability, and free valence on each atom of N-(2-chlorobenzyl)-pyridinium, N-(benzyl)-2-chloropyridinium, and N-(2-chlorobenzyl)-2-chloropyridinium salts using a simple Huckel method in order to discuss their intramolecular photocyclization reaction in a qualitative method. Our calculation qualitatively predicts that photocyclization occurs through forming radicals as a reaction intermediate by breaking a C-Cl bond after photoexcitation into a triplet state via intersystem crossing from an initially excited singlet state. We noticed that this C-Cl bond breaking is aided by ${\pi}$-complex formation between a chlorine atom and the ${\pi}$ -electrons of the neighboring ring in the triplet state and a stronger ${\pi}$-complex bond makes C-Cl bond breaking, i.e., radical formation, much easier. A chlorine atom will form a stronger ${\pi}$ -complex bond to a benzyl ring of N-(benzyl)-2-chloropyridinium than a pyridinium ring of N-(2-chlorobenzyl)-pyridinium because the former can donate its ${\pi}$-electron more easily than the latter. The chlorine at position 15 of N-(2-chlorobenzyl)-2-chloropyridinium salt in the excited state also provides its ${\pi}$-electron to the benzyl ring. So this ${\pi}$-electron can increase the bond strength of the $\pi-complex.$ Therefore, the strength of ${\pi}$-complex follows the order of N-(2-chlorobenzyl)-2-chloropyridinium, N-(benzyl)-2-chloropyridinium, and N-(2-chlorobenzyl)-pyridinium salts and thus the radical formation rate. This provides us with an intramolecular photocyclization reaction rate of the same order as given above.

• 대한화학회지
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• 제10권4호
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• pp.166-174
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• 1966

cinnamoylated photosensitive polymer의 광증감 경화반응기구를 반응속도론적으로 연구했다. Cinnamic acid(C)와 증감제(S)의 first excited singlet and lowest triplet energy level diagram과 증감제의 농도증가에 따른 sensitivity의 포화 등의 사실로부터 이 반응의 주요과정은 C와 S의 광 energy흡수에 의한 $C^{*(1)}$ 및 $S^{*(1)}$로의 여기, $S^{*(1)}{\to}S^{*(3)}$ intersystem crossing, S의 excimer 형성, $S^{*(3)}{\to}C^{*(3)}$ energy transfer 그리고 $C^{*(3)}$와 C의 termination 등임을 가정하고 다음 반응속도를 구했다. $-\frac{d[C]}{dt} = \frac{K_1[C]}{K_2 + [C]}[\frac{I^c_{abs}}{K_3 + [S]} + \frac{K_4[C]}{(K_5 + [C])(K_6 + [S])}(I^s_{abs} + \frac{K_7I^c_{abs}[S]}{K_8 + [S]})]$ $I^c_{abs}$와 $I^s_{abs}$ ;C 및 S의 광흡수율 $K_n$;상수 적외선 흡수스펙트럼 분석의 결과, Cinnamoyl 에스테르화도와 sensitivity의 관계 및 증감제의 농도와 sensitivity의 관계에 대하여 발표된 실험 data는 윗식을 만족시키므로 가정한 반응기구에 대한 뒷받침을 얻었다.

• Bulletin of the Korean Chemical Society
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• 제11권3호
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• pp.241-244
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• 1990

The photochemistry of 1-Methyl-2-cyclohexenyl aryl ketones (phenyl ketone 7a, p-toluyl ketone 7b, biphenyl ketone 7c and -naphthyl ketone 7d) is reported. The aryl ketone 7a, 7b and 7c undergo photo-racemization with efficiencies of 0.75, 0.79 and 0.76 respectively on direct irradiation. Direct irradiation of the ketone 7d, however, undergoes 1,3-shift with an efficiency of 0.02. Triplet states are responsible for the racemizations and singlet state is responsible for 1,3-shift as in general. The ketone 7a, 7b and 7c are good example of a few ${\beta},{\gamma}$-unsaturated ketones which undergo efficient intersystem crossing on direct irradiation.

• Journal of Information Display
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• 제8권2호
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• pp.15-19
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• 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
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• 제15권2호
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• pp.154-161
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• 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
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• 제13권2호
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• pp.166-172
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• 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.

• Bulletin of the Korean Chemical Society
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• 제28권8호
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• pp.1249-1255
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• 2007

We have investigated the photophysical properties of dansyl-N-methylaminobenzoic acid (DABAH) as a ligand and its lanthanide (Ln3+)-cored complexes (Ln3+-(DABA)3(terpy)) in order to determine the main energy transfer pathway for sensitized near infrared emission of Ln3+ ions (Ln3+ = Nd3+ and Er3+) in Ln3+- (DABA)3(terpy). The fluorescence spectrum of DABAH shows a large Stokes shift with increasing solvent polarity. This large Stokes shift might be due to the formation of a twisted intramolecular charge transfer (TICT) state, as demonstrated by the large dipole moment in the excited state. It is in good agreement with the result that the phosphorescence even in the Gd3+-cored complex based on the DABAH ligand was not observed, maybe due to the highly forbidden character of the S1 → T1 transition in the DABAH ligand. A short decay component (ca. 1 ns) was observed in Er3+-(DABA)3(terpy) whereas the fluorescence lifetimes of DABAH and its Gd3+-(DABA)3(terpy) are observed about ~10 ns. The short component could be originated from the energy transfer process between the ligand and the Ln3+ ion. Based on the fluorescence of DABAH its Ln3+- (DABA)3(terpy), the sensitization of Ln3+ luminescence in the Ln3+-(DABA)3(terpy) takes place by the energy transfer via the TICT state of DABAH in the excited singlet state rather than via the excited triplet state.