7-甲氧基香豆素和5,6,7,8-四甲氧基香豆素结构和紫外光谱的理论研究
Theoretical Study on Structure and UV Spectra of 7-Methoxycoumarin and 5,6,7,8-Tetramethoxycoumarin

采用密度泛函理论方法系统地研究了7-甲氧基香豆素和5,6,7,8-四甲氧基香豆素。相对于7-甲氧基香豆素，5,6,7,8-四甲氧基香豆素的C5、C6、C8上增加了吸电子基团甲氧基，导致5,6,7,8-四甲氧基香豆素的甲氧基中O与取代基位置C5、C6、C7、C8的键长C5-O11、C6-O12、C7-O13和C8-O14的键长都变长，且C5、C6、C8的电荷变为了正电荷。7-甲氧基香豆素在310 nm处峰和5,6,7,8-二甲氧基香豆素在312 nm处峰都是因为π→π*电荷转移激发；7-甲氧基香豆素在241 nm处峰和5,6,7,8-二甲氧基香豆素在244 nm处峰都是由于π→π*局域激发；7-甲氧基香豆素在197 nm处峰是由于π→π*局域激发而5,6,7,8-二甲氧基香豆素在211 nm处峰不仅由于π→π*局域激发还有n→π*局域激发。
7-methoxycoumarin and 5,6,7,8-tetramethoxycoumarin were studied systematically by density functional theory. Compared with 7-methoxycoumarin, C5, C6, and C8 of 5,6,7,8-tetramethoxycoumarin increased the electron-absorbing group methoxy, the C5-O11, C6-O12, C7-O13, and C8-O14 bond lengths of O in the methoxy group of 5,6,7,8-tetramethoxycoumarin and substituent’s C5, C6, C7, C8, become longer, and the charges of C5, C6, and C8 become positive. The peak at 310 nm of 7-methoxycoumarin and the peak at 312 nm of 5,6,7,8-dimethoxycoumarin are both due to π→π* charge transfer excitation. The peaks of 7-methoxycoumarin at 241 nm and 5,6,7,8-dimethoxycoumarin at 244 nm are both due to π→π* local excitation. The peak at 197 nm of 7-methoxycoumarin is due to π→π* local excita-tion while the peak at 211 nm of 5,6,7,8-dimethoxycoumarin is due not only to π→π* local exci-tation but also to n→π* local excitation.