Studies on the Substituent Effects on the Photochemical Behavior of trans-4-(N-Phenylamino)stilbenes

• Main Authors: Kang-ling Liau, 廖康廩
• Other Authors: Jye-Shane Yang
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/53910101240426509743

碩士 === 國立中央大學 === 化學研究所 === 90 === This thesis is a follow-up study on the “amino conjugation effect” of trans-4-aminostilbenes. N-phenyl substitution of trans-4-aminostilbene leads to a more planar ground-state geometry about the amino nitrogen atom, a larger charge-transfer character, a slower rate constant for photoisomerization, and thus a higher fluorescence quantum yield. To investigate the substituent effect on the photochemical behavior of trans-4-N-phenylaminostilbene, we have synthesized compound series 2-6, which have substituents on the N-phenylamino group, and compound series 7 and 8, which contain strong electron-withdrawing groups at the 4’ position of the stilbene group. More detained photochemical studies were performed on compound series 2 and 7. Electron-donating groups result in red-shifted absorption and emission spectra for compounds 2, which is valid in a variety of solvents. In hexane, the fluorescence quantum yield of compound 2 is larger for substituents with a stronger electron-withdrawing ability. Such a behavior is however not observed in other solvents. When the substituent in 2 is an ester or a cyano group, the fluorescence quantum yield is particular low in medium or polar solvents, which can be attributed to the formation of twisted internal charge-transfer (TICT) states. In the case of compounds 7, a significant solvent-dependent fluorescence spectra were recorded as a result of the presence of both strong electron-donating and electron-withdrawing groups. In polar solvents, both fluorescence and photoisomerization quantum yields are low, which might be a consequence of TICT formation.