The study of the photochemical and photophysical properties of moiety “tropolone” in colchicine and thiocolchicine.
酮 ； 秋水仙素 ； 甲硫秋水仙素 ； 量子效應 ； HASH(0xbe9c9ac) ； tropolone ； colchicine ； thiocolchicine ； quantum effect ； Woodward－Hoffmann
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The photochemical and photophysical properties of moiety “tropolone” in colchicine〈1〉and thiocolchicine〈5〉were studied. Irradiation of colchicine〈1〉in methanol gives mainly two photoproducts：β－lumicolchicine〈2〉andγ－lumicolchicine〈3〉. Further irradiation of β－lumicolchicine〈2〉in methanol gives the photoproduct ofα－lumicolchicine〈4〉. Irradiation of thiocolchicine〈5〉in methanol gives mainly two photoproductsβ－lumithiocolchicine〈6〉andγ－lumithiocolchicine〈7〉. The low lying（π、π*） excited singlet state is responsible for the photochemistry of colchicine〈1〉and thiocolchicine 〈5〉 based on their UV-Vis absorption spectrum、fluorescence emission spectrum as well as fluorescence lifetime measurement. In comparison of the quantum effect (ψ) of compound〈1〉and compound〈5〉 in different polarity solvents, the results of the 3 aspects are obtained as follows : Ⅰ、the disappearance quantum yield of compound〈1〉：ψin methanol ≒ψin benzene. （ψ〈1〉methanol＝－1.25×10-6, ψ〈1〉benzene＝－1.15×10-6） Ⅱ、the disappearance quantum yield of compound〈5〉：ψin methanol ＜＜ψin benzene. （ψ〈5〉methanol＝－4.90×10-9, ψ〈5〉benzene＝－6.66×10-8） Ⅲ、the quantum yield of photoadducts β/γ ratio of compound〈1〉＞the quantum yield of photoadducts β/γ ratio of compound〈5〉. （in benzene：β/γ〈1〉＝6.5, β/γ〈5〉＝2.1） （in methanol：β/γ〈1〉＝13, β/γ〈5〉＝2.2） The results of Ⅰand Ⅲ show that the photochemical mechanism of colchicine〈1〉is not affected by solvent polarity but by the molecular steric selectivity. This infers that the mechanism of colchicine〈1〉 favor Woodward－Hoffmann electrocyclic reaction. The results of Ⅱand Ⅲ show that the photochemical inactivity of thiocolchicine〈5〉is dominated by solvent polarity as well as the mesomeric effect of thiomethoxy group which can stabilize the charge transfer singlet excited state. So it is inferred that the mechanism of thiocolchicine〈5〉favors the concomitant charge separation of the excited singlet state of tropolone chromophore。 In summarize, results show that the key point of the photochemical behavior of mechanism of colchicine〈1〉and thiocolchicine〈5〉favors Woodward－Hoffmann electrocyclic concerted reaction due to the N-H—O bonded of moiety, tropolone, which is ended up with the 2+2（π, π*）single excited state energy transfer. The mechanism of colchine 〈1〉 favors the (2+2) electrocyclic concerted addition, whereas that of thiocolchicine〈5〉favor the concomitant charge separation of tropolone step-wised slower cycloaddition.
理學院 > 化學系