Transient Absorption Studies of the Photochromic Behavior of 3H-Naphtho[2,1-b]pyrans Linked to Thiophene Oligomers via an Acetylenic Junction

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• 作者：Baptiste Moine ; Julien Ré ; hault ; Sté ; phane Aloï ; se ; Jean-Claude Micheau ; Corinne Moustrou ; André ; Samat ; Olivier Poizat ; Guy Buntinx
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：May 29, 2008
• 年：2008
• 卷：112
• 期：21
• 页码：4719 - 4726
• 全文大小：185K
• 年卷期：v.112,no.21(May 29, 2008)
• ISSN：1520-5215

文摘

The photophysical and photochemical properties of four 3,3-diphenyl-3H-naphtho[2,1-b]pyrans substituted, via an acetylenic junction, to (thiophene)_n oligomers (n = 0−3 units) were investigated by transient absorption in the femtosecond to microsecond time domain and by stationary absorption and fluorescence. The decay of the initially produced excited S₁(ππ*) state is found to occur via three competing processes: fluorescence, intersystem crossing, and a ring-opening reaction leading to a colored merocyanine product, with relative yields varying drastically with n. Whereas ultrafast (sub-picosecond) reaction dynamics and high product quantum yield are observed for n = 0 and 1, the reaction is considerably slowed down on going to the n = 2 (105 ps) compound and does not occur for n = 3. A reaction scheme that accounts for this behavior is proposed and the effect of the oligothiophenic chain length on the photoinduced properties is discussed. It is suggested that increasing the chain length from 1 to 3 thiophene units stabilizes the S₁(ππ*) state by π conjugation and induces an excited-state potential barrier along the reaction pathway.