Reaction Mechanisms of Photoinduced Quinone Methide Intermediates Formed via Excited-State Intramolecular Proton Transfer or Water-Assisted Excited-State Proton Transfer of 4-(2-Hydroxyphenyl)pyridine,The Journal of Physical Chemistry Letters

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Reaction Mechanisms of Photoinduced Quinone Methide Intermediates Formed via Excited-State Intramolecular Proton Transfer or Water-Assisted Excited-State Proton Transfer of 4-(2-Hydroxyphenyl)pyridine
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2021-11-26 , DOI: 10.1021/acs.jpclett.1c03600
Yan Guo ₁ , Xuyang Li ₁ , Jiani Ma ₁ , David Lee Phillips ₂

Affiliation

Femtosecond and nanosecond transient absorption spectroscopies combined with theoretical calculations were performed to investigate the formation mechanisms of quinone methides (QMs) from 4-(2-hydroxyphenyl)pyridine (1). In acetonitrile (ACN), the singlet excited state of 1 (1(S₁)) with the cis-form underwent a thermodynamically favorable and ultrafast ESIPT to produce the singlet excited state QM, which could either relax first into highly vibrational states of its ground state followed by hydrogen transfer to return to the starting compound or alternatively may undergo a dehydrogenation to produce a radical species (1-R). In ACN–H₂O, 1(S₁) interacted with water molecules to form a solvated species, which induced water-assisted ESPT to the pyridine nitrogen to generate the singlet excited state QM in a concerted asynchronous manner that was initiated by deprotonation of the phenolic OH. These results provide deeper insights into the formation mechanisms of QMs in different solvent environments, which is important in the application of QMs in biological and chemical systems as well as in the design of molecules for efficient QM formation.

中文翻译：

4-(2-羟基苯基)吡啶的激发态分子内质子转移或水辅助激发态质子转移形成的光致醌甲基化物中间体的反应机理

飞秒和纳秒瞬态吸收光谱与理论计算相结合，用于研究 4-(2-羟基苯基) 吡啶 ( 1 )中醌甲基化物 (QM) 的形成机制。在乙腈 (ACN) 中，具有顺式形式的1 ( 1 (S ₁ ))的单线激发态经历了热力学有利且超快的 ESIPT 以产生单线激发态 QM，它可以首先弛豫到其高度振动状态基态，然后是氢转移以返回起始化合物，或者可以进行脱氢以产生自由基物质 ( 1- R)。在乙腈-H ₂ O, 1(S ₁ )与水分子相互作用形成溶剂化物质，其将水辅助的ESPT诱导为吡啶氮，以协调的异步方式产生单线激发态QM，该方式由酚OH的去质子化引发。这些结果对不同溶剂环境中 QMs 的形成机制提供了更深入的了解，这对于 QMs 在生物和化学系统中的应用以及有效 QM 形成的分子设计具有重要意义。

更新日期：2021-12-09

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