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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Comparison of the Photochemistry of Acyclic and Cyclic 4-(4-Methoxy-phenyl)-4-oxo-but-2-enoate Ester Derivatives
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Comparison of the Photochemistry of Acyclic and Cyclic 4-(4-Methoxy-phenyl)-4-oxo-but-2-enoate Ester Derivatives

机译：无环和环状4-（4-甲氧基 - 苯基）-4-氧代除-2-烯酸酯衍生物的光化学的比较

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摘要

To clarify the cis-trans isomerization mechanism of simple alkenes on the triplet excited state surface, the photochemistry of acyclic and cyclic vinyl ketones with a p-methoxyacetophenone moiety as a built-in triplet sensitizer (1 and 2, respectively) was compared. When irradiated, ketone 1 produces its cis-isomer, whereas ketone 2 does not yield any photoproducts. Laser flash photolysis of ketone 1 yields a transient spectrum with lambda(max) similar to 400 nm (tau similar to 125 ns). This transient is assigned to the first triplet excited state (T-1) of 1, which presumably decays to form a triplet biradical (1BR) that is shorter lived than the triplet ketone. In comparison, laser flash photolysis of 2 reveals two transients (tau similar to 20 and 440 ns), which are assigned to T-1 of 2 and triplet biradical 2BR, respectively. Density functional theory calculations support the characterization of the triplet excited states and the biradical intermediates formed upon irradiation of ketones 1 and 2 and allow a comparison of the physical properties of the biradical intermediates. As the biradical centers in 2BR are stabilized by conjugation, 2BR is more rigid than 1BR. Therefore, the longer lifetime of 2BR can be attributed to less-efficient intersystem crossing to the ground state.
机译：为了阐明在三重态激发状态表面上简单烯烃的顺式反式异构化机制，比较了与p-甲氧基乙酮部分作为内置三重态敏化剂（分别的环乙烯基酮部分的无环和环状乙烯基酮的光化学。当照射时，酮1产生其顺式异构体，而酮2不产生任何光调节。激光闪光光解酮1产生瞬态光谱，其λ（最大）类似于400nm（Tau类似于125 ns）。该瞬变被分配给第一三重态激发态（T-1），其可能衰减以形成比三重酮酮更短的三重态肱骨（1BR）。相比之下，激光闪光光解2显示出两个瞬态（Tau，类似于20和440ns），分别分配给T-1和三重态均线2BR。密度函数理论计算支持三重态激发态的表征和在酮1和2的照射时形成的荚膜中间体，并允许比较荚膜中间体的物理性质。随着2BR中的荚膜中心通过缀合稳定，2BR比1BR更加刚性。因此，2BR的寿命较长，可以归因于跨越地面状态的较低的基础系统。

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