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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Effect of Solvents on the Photoenolization of o-Methylanthrone at Low Temperatures. Evidence for H-Atom Tunneling from Nonequilibrating Triplets
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Effect of Solvents on the Photoenolization of o-Methylanthrone at Low Temperatures. Evidence for H-Atom Tunneling from Nonequilibrating Triplets

机译：溶剂对邻甲基蒽酮在低温下光致光化的影响。来自非平衡三重态的H原子隧穿证据

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摘要

The reactivity of 1, 4-dimethylanthrone (1, 4-MAT) and 1, 4-dimethylanthrone-d_8 (1, 4-DMAT) toward hydrogen transfer was investigated in methylcyclohexane (MCH), ethanol (EtOH), and 2, 2, 2-trifluoroethanol (TFE) by comparing their triplet-state emission spectra and lifetimes with those of compounds without the o-methyl substituent. A predominantly n, π~* lowest triplet state in nonpolar solvents such as MCH changes toward a less reactive π, π~* configuration in polar solvents such as EtOH and TFE. In EtOH, 1, 4-DMAT exhibits a temperature-dependent dual emission while the corresponding protio compound (1, 4-MAT) decays by reaction at all temperatures analyzed (ca. 15-90 K). Although compounds without the o-methyl group also presented dual emission, their relative intensities and lifetimes were shown to be temperature-independent, indicating the lack of thermal equilibration between the two triplets below 90 K. In the case of 1, 4-DMAT in EtOH, an Arrhenius plot based on the data from the short-lived component (mainly n, π~*) and detection of the enol between 19 and 80 K revealed that deuterium transfer occurs by quantum-mechanical tunneling (QMT). In agreement with results in MCH where a short-lived n, π~* state predominates, the D-tunneling rate constant was estimated to be ca. (1.5 - 7.5) * 10~3 s~(-1). The phosphorescence of anthrone derivatives in TFE was long-lived, with a strong π, π~* character, and highly heterogeneous, but not dual. A large isotope effect on phosphorescence is assigned to the isotope-dependent tunneling reaction from a predominant π, π~* state.
机译：在甲基环己烷（MCH），乙醇（EtOH）和2，2中研究了1，4-二甲基蒽酮（1，4-MAT）和1，4-二甲基蒽酮-d_8（1，4-DMAT）对氢转移的反应性，2-三氟乙醇（TFE），将它们的三重态发射光谱和寿命与没有邻甲基取代基的化合物进行比较。在非极性溶剂（例如MCH）中，最低的n，π**三元态主要朝着在极性溶剂（例如EtOH和TFE）中反应性较低的π，π**构型转变。在EtOH中，1，4-DMAT表现出与温度有关的双重发射，而相应的蛋白质化合物（1，4-MAT）在所有分析的温度下（约15-90 K）都会因反应而衰减。尽管没有邻甲基的化合物也表现出双重发射，但它们的相对强度和寿命显示出与温度无关，表明在90 K以下，两个三重态之间缺乏热平衡。对于1，4-DMAT， EtOH是一种基于短命组分（主要为n，π*）的数据的Arrhenius图，并且对烯醇的检测介于19到80 K之间，这表明氘的转移是通过量子机械隧穿（QMT）进行的。与短时的n，π〜*状态占主导地位的MCH中的结果一致，估计D隧道速率常数约为。 （1.5-7.5）* 10〜3 s〜（-1）。 TFE中的蒽酮衍生物的磷光寿命长，具有很强的π，π〜*特性，并且高度异质，但不是双重的。从磷的主要π，π〜*态起，对磷光的大同位素效应被赋予与同位素有关的隧穿反应。

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