Water-Assisted Self-Photoredox of 3-(Hydroxymethyl)benzophenone: An Unusual Photochemistry Reaction in Aqueous Solution

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• 作者：Xuebo Chen ; Qiangqiang Zhang ; Yanchang Xu ; Weihai Fang ; David Lee Phillips
• 刊名：The Journal of Organic Chemistry
• 出版年：2013
• 出版时间：June 7, 2013
• 年：2013
• 卷：78
• 期：11
• 页码：5677-5684
• 全文大小：448K
• 年卷期：v.78,no.11(June 7, 2013)
• ISSN：1520-6904

文摘

An unusual photochemistry of water-assisted self-photoredox of 3-(hydroxymethyl) benzophenone 1 has been investigated by CASPT2//CASSCF computations. The water-assisted self-photoredox is found to proceed via three sequential reactions: an excited-state intermolecular proton transfer (ESIPT), a photoinduced deprotonation, and a self-redox reaction. Upon photoexcitation at 243 nm, the system of 1 is taken to the Franck鈥揅ondon region of a short-distance charge transfer (SCT) state of S_SCT(¹蟺蟺*) and then undergoes ESIPT with a small barrier of 3.4 kcal/mol producing the intermediate 2. Subsequently, the singlet鈥搕riplet crossing (STC) of STC (¹蟺蟺*/³蟺蟺*) relays 2 by intersystem crossing to the T_SCT(³蟺蟺*) state followed by a deprotonation reaction overcoming a moderate barrier of 8.0 kcal/mol and finally produces the triplet biradical intermediate 3. Another moderate barrier (5.8 kcal/mol) in the T_SCT(³蟺蟺*) state has to be overcome so as to relax to a second singlet鈥搕riplet crossing STC(T/S₀) that allows an efficient spin-forbidden decay to the ground state. The self-redox reaction aided by water molecules occurs with tiny barriers in the S₀ state via two steps, protonation of the benzhydrol carbon to produce intermediate 4 and then deprotonation from the benzylic oxygen to yield the final product 3-formylbenzhydrol 5.