Photophysics and Photodeprotection Reactions of p-Methoxyphenacyl Phototriggers: An Ultrafast and Nanosecond Time-Resolved Spectroscopic and Density Functional Theory Study

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• 作者：Hui-Ying An ; Wai Ming Kwok ; Chensheng Ma ; Xiangguo Guan ; Jovi Tze Wai Kan ; Patrick H. Toy ; David Lee Phillips
• 刊名：Journal of Organic Chemistry
• 出版年：2010
• 出版时间：September 3, 2010
• 年：2010
• 卷：75
• 期：17
• 页码：5837-5851
• 全文大小：1478K
• 年卷期：v.75,no.17(September 3, 2010)
• ISSN：1520-6904

文摘

Time-resolved spectroscopic experiments were performed to investigate the kinetics and mechanisms of the photodeprotection reactions for p-methoxyphenacyl (pMP) compounds, p-methoxyphenacyl diethyl phosphate (MPEP) and diphenyl phosphate (MPPP). The experimental results reveal that compared to the previous reports for the counterpart p-hydroxyphenacyl (pHP) phosphates, the ³nπ*/ππ* mixed character triplet of pMP acts as a reactive precursor that leads to the subsequent solvent and leaving group dependent chemical reactions and further affects the formation of photoproducts. The MPPP triplet in H₂O/CH₃CN and in fluorinated alcohols shows a rapid heterolytic cleavage (τ ≈ 5.4 ns) that results in deprotection and formation of a solvolytic rearrangement product, whereas the MPPP triplet in CH₃CN and the MPEP triplet in CH₃CN and H₂O/CH₃CN and fluorinated alcohols decay on a much longer time scale (τ ≈ 100 ns) with little observation of the rearrangement product. The density functional theory (DFT) calculations reveal a substantial solvation effect that is connected with the methoxy versus hydroxyl substitution in accounting for the different deprotection reactivity of pMP and pHP compounds. The results reported here provide new insight in elucidating the solvent and leaving group dependent dual reactivity of pMP compounds on the formation of the rearrangement versus reductive photoproduct.