Photochemistry of new psoralen derivatives새로운 소랄렌 유도체의 광화학

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A new monofunctional psoralen, pyrazinopsoralen (PzPs), was efficiently synthesized by Suzuki coupling reaction as a key step starting from 5-bromo-6-methoxybenzofuran and methyl 3-iodopyrazine 2-carboxylate. Demethylative lactonization of coupling product with $BBr_3$ gave PzPs. PzPs has UV absorption spectra similar to other psoralens except that it absorbs more strongly in the long-UVA than 8-methoxypsoralen. The solvent effects on the UV absorption and fluorescence emission spectra indicate that the lowest excited singlet state is the $π,π^*$ state like other psoralens. It shows much lower fluorescence quantum yield (0.0008 in ethanol at room temperature) than other psoralens as expected by increased proximity effects (vibronic perturbation) due to close $^1(n,π^*)$ to $^1(π,π^*)$ states. The fluorescence lifetime was 1.05 ns in methylcyclohexane with single exponential decay, while more than two components were observed in other solvents with the short-lived component being the major (>95%). The triplet state of PzPs could not be detected by phosphorescence, laser flash excitation (T-T absorption) and singlet oxygen formation probably due to very low intersystem crossing quantum yield ($Φ_ISC, S_1$ to $T_1$), or short lifetime of the triplet state ($τ_T$) caused by the fast $T_1$ to $S_0$ intersystem crossing. Pyrazinocoumarin (PzC), 7-methoxypyrazinocoumarin (7-MOPzC) and 5,7-dimethoxypyrazinocoumarin (5,7-DMPzC) show the similar UV absorption spectra as the corresponding coumarins except for more distinct shoulders in the near UV absorption band (300 ~ 350 nm), probably due to $n → π^*$ transition. Fluorescence excitation spectra of PzC derivatives in nonpolar solvents have the lowest energy maxima in the region of shoulders of UV absorption, indicating the lowest fluorescent state to have the same energy as these shoulders. Fluorescence quantum yields of PzC derivatives are on the order of $10^{-2} ~ 10^{-4}$, much lower than the corresponding coumarins...
Advisors
Shim, Sang-Chul심상철
Description
한국과학기술원 : 화학과,
Publisher
한국과학기술원
Issue Date
1999
Identifier
151501/325007 / 000965414
Language
eng
Description

학위논문(박사) - 한국과학기술원 : 화학과, 1999.2, [ xiii, 125 p. ]

Keywords

Photocycloaddition; Proximity effect; Psoralen; Phototoxicity; 광독성; 광고리화첨가반응; 근접효과; 소랄렌

URI
http://hdl.handle.net/10203/31493
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=151501&flag=dissertation
Appears in Collection
CH-Theses_Ph.D.(박사논문)
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