#### Substituent effects on the photoisomerization of 5(E)-styryl-1,3-dimethyluracil = 5(E)-스티릴-1,3-디메틸우라실의 광이성질화 반응에대한 치환기 효과

Fluorescence quantum yields of 5(E)-styryl-1, 3-dimethyluracils (4-X-5(E)-SDUs) are more affected by the solvent viscosity than by its polarity except 5 (E)-(4-nitrostyryl)-1,3-Dimethyluracil (4-NO$_2$-5(E)-SDU). The fluorescence maxima shift slightly to the long wavelengh with increasing the solvent polarity indicating that the lowest excited fluorescent states are the 1($\pi,\;\pi^\ast$) states. However, the lowest singlet state of 4-NO$_2$-5(E)-SDU has (n,$\pi^\ast$) character in non-polar solvents, but with increasing the solvent polarity the lowest singlet state changes from ($\pi,\;\pi^\ast$) to ($\pi,\;\pi^\ast$) state. Relatively weak fluorescence of the substituted 5 (E)-SDUs implies the significant contribution of the ($\pi,\;\pi^\ast$) state introduced by the heteroatom to the lowest excited singlet state leading to the fast internal conversion or intersystem crossing. Photoisomerization quantum yields of 4-halogen substitution are similarly influenced by solvent viscosity as the unsubstituted 5(E)-SDU while little affected by solvent polarity. However, photoisomerization quantum yields of 4-OCH$_3$-and 4-CH$_3$-5(E)-SDUs depend on the nature of the solvents, while for 4-nitro derivative it is strongly affected by solvent polarity. The azulene quenching experiments on the direct and sensitized photoisomerization of the substituted 5(E)-SDUs indicate that singlet mechanism for the direct photoisomerization of 4-OCH$_3$-and 4-CH$_3$-5(E)-SDUs is operative, and both singlet and triplet mechanism for 4-halogen substituted 5(E)-SDUs are operative. However, direct photoisomerization of 4-NO$_2$-SDU occurs in the triplet manifold.
Shim, Sang-Chulresearcher심상철researcher
Publisher
한국과학기술원
Issue Date
1989
Identifier
66570/325007 / 000871337
Language
eng
Description

학위논문(석사) - 한국과학기술원 : 화학과, 1989.2, [ vii, 58 p. ]

URI
http://hdl.handle.net/10203/32542
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=66570&flag=t
Appears in Collection
CH-Theses_Master(석사논문)
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