Accessing the Long-Lived Triplet Excited States in Bodipy-Conjugated 2-(2-Hydroxyphenyl) Benzothiazole/Benzoxazoles and Applications as Organic Triplet Photosensitizers for Photooxidations

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• 作者：Pei Yang ; Jianzhang Zhao ; Wanhua Wu ; Xuerong Yu ; Yifan Liu
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：July 20, 2012
• 年：2012
• 卷：77
• 期：14
• 页码：6166-6178
• 全文大小：735K
• 年卷期：v.77,no.14(July 20, 2012)
• ISSN：1520-6904

文摘

Bodipy derivatives containing excited state intramolecular proton transfer (ESIPT) chromophores 2-(2-hydroxyphenyl) benzothiazole and benzoxazole (HBT and HBO) subunits were prepared (7鈥?b>10). The compounds show red-shifted UV鈥搗is absorption (530鈥?80 nm; 蔚 up to 50000 M^鈥? cm^鈥?) and emission compared to both HBT/HBO and Bodipy. The new chromophores show small Stokes shift (45 nm) and high fluorescence quantum yields (桅_F up to 36%), which are in stark contrast to HBT and HBO (Stokes shift up to 180 nm and 桅_F as low as 0.6%). On the basis of steady state and time-resolved absorption spectroscopy, as well as DFT/TDDFT calculations, we propose that 7鈥?b>9 do not undergo ESIPT upon photoexcitation. Interestingly, nanosecond time-resolved transient absorption spectroscopy demonstrated that Bodipy-localized triplet excited states were populated for 7鈥?b>10 upon photoexcitation; the lifetimes of the triplet excited states (蟿_T) are up to 195 渭s. DFT calculations confirm the transient absorptions are due to the triplet state. Different from the previous report, we demonstrated that population of the triplet excited states is not the result of ESIPT. The compounds were used as organic triplet photosensitizers for photooxidation of 1,5-dihydroxylnaphthalene. One of the compounds is more efficient than the conventional [Ir(ppy)₂(phen)][PF₆] triplet photosensitizer. Our result will be useful for design of new Bodipy derivatives, ESIPT compounds, and organic triplet photosensitizers, as well as for applications of these compounds in photovoltaics, photocatalysis and luminescent materials, etc.