Photoconversion of 尾-Lapachone to 伪-Lapachone via a Protonation-Assisted Singlet Excited State Pathway in Aqueous Solution: A Time-Resolved Spectroscopic Study

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• 作者：Lili Du ; Ming-De Li ; Yanfeng Zhang ; Jiadan Xue ; Xiting Zhang ; Ruixue Zhu ; Shun Cheung Cheng ; Xuechen Li ; David Lee Phillips
• 刊名：Journal of Organic Chemistry
• 出版年：2015
• 出版时间：August 7, 2015
• 年：2015
• 卷：80
• 期：15
• 页码：7340-7350
• 全文大小：668K
• ISSN：1520-6904

文摘

The photophysical and photochemical reactions of 尾-lapachone were studied using femtosecond transient absorption, nanosecond transient absorption, and nanosecond time-resolved resonance Raman spectroscopy techniques and density functional theory calculations. In acetonitrile, 尾-lapachone underwent an efficient intersystem crossing to form the triplet state of 尾-lapachone. However, in water-rich solutions, the singlet state of 尾-lapachone was predominantly quenched by the photoinduced protonation of the carbonyl group at the 尾 position (O₉). After protonation, a series of fast reaction steps occurred to eventually generate the triplet state 伪-lapachone intermediate. This triplet state of 伪-lapachone then underwent intersystem crossing to produce the ground singlet state of 伪-lapachone as the final product. 1,2-Naphthoquinone is examined in acetonitrile and water solutions in order to elucidate the important roles that water and the pyran ring play during the photoconversion from 尾-lapachone to 伪-lapachone. 尾-Lapachone can also be converted to 伪-lapachone in the ground state when a strong acid is added to an aqueous solution. Our investigation indicates that 尾-lapachone can be converted to 伪-lapachone by photoconversion in aqueous solutions by a protonation-assisted singlet excited state reaction or by an acid-assisted ground state reaction.