Magnetic Field Dependence of the 31P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T-−S Mechanism
Magnetic Field Dependence of the 31P CIDNP in the Photolysis of a Benzyl Phosphite. Evidence for a T-−S Mechanism
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亚磷酸苄酯光解中 31P CIDNP 的磁场依赖性 T-−S 机制的证据。
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发表时间：
1996
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通讯作者：
W. Bentrude
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作者：
I. Koptyug;Gregory W. Sluggett;N. Ghatlia;Margaret S. Landis;N. Turro;S. Ganapathy;W. Bentrude
对乙酰基苄基亚磷酸二甲酯光化学的 31P 化学诱导动态核极化 (CIDNP) 研究 (1) 为光化学生成的三线态自由基对的相对罕见的 T-−S 系间窜越机制的运行提供了证据。由 1 产生的三重态自由基对对乙酰基苄基 (2) 和二甲氧基膦酰基 (3) 的系间窜越机制受到 3 的大 31P hfcc 的影响，并从相对较低磁场 (18.8 kG) 中的 T-−S 机制切换到较高磁场 (58.8 kG) 下的传统 T0−S 途径。这种机制的变化可以通过在自由基清除剂（卤代烃、苯硫酚）存在下 1 的光解得到证明，该光解通过 3 的原子抽象产生相应的产物，其中 3 已经逃离了最初的自由基笼。这些逃逸产物在高场 (T0−S) 下呈吸收偏振，但在较低场 (T-−S) 下呈发射偏振，特别清晰地显示了磁效应。
31P chemically induced dynamic nuclear polarization (CIDNP) studies of the photochemistry of p-acetylbenzyl dimethyl phosphite (1) provide evidence for the operation of the relatively rare T-−S intersystem crossing mechanism for a photochemically generated triplet free radical pair. The mechanism of intersystem crossing of the triplet radical pair p-acetylbenzyl (2) and dimethoxyphosphonyl (3), generated from 1, is influenced by the large 31P hfcc of 3 and switches from the T-−S mechanism in a relatively low magnetic field (18.8 kG) to the conventional T0−S pathway at a higher field (58.8 kG). This change in mechanism is evidenced by the photolysis of 1 in the presence of radical scavengers (halocarbons, thiophenol) which yields the corresponding products from atom abstraction by 3 that has escaped the initial radical cage. These escape products are absorptively polarized at high field (T0−S) but are emissively polarized at lower field (T-−S) in a particularly well-defined display of the effect of magneti...