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Comparison of the Photochemistry of Acyclic and Cyclic 4-(4-Methoxy-phenyl)-4-oxo-but-2-enoate Ester Derivatives.
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2020-08-05 , DOI: 10.1021/acs.jpca.0c04319 Sujan K Sarkar 1 , Ranaweera A A Upul Ranaweera 1 , Rajkumar Merugu 1 , Nayera M Abdelaziz 1 , Jendai Robinson 1 , Heidi A Day 1 , Jeanette A Krause 1 , Anna D Gudmundsdottir 1
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2020-08-05 , DOI: 10.1021/acs.jpca.0c04319 Sujan K Sarkar 1 , Ranaweera A A Upul Ranaweera 1 , Rajkumar Merugu 1 , Nayera M Abdelaziz 1 , Jendai Robinson 1 , Heidi A Day 1 , Jeanette A Krause 1 , Anna D Gudmundsdottir 1
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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 λmax ∼ 400 nm (τ ∼ 125 ns). This transient is assigned to the first triplet excited state (T1) 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 (τ ∼ 20 and 440 ns), which are assigned to T1 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.
中文翻译：
无环和环状4-（4-甲氧基-苯基）-4-氧代-丁-2-烯酸酯衍生物的光化学比较。
为了阐明三重态激发态表面上简单烯烃的顺式-反式异构化机理，比较了以对甲氧基苯乙酮部分为内置三重态敏化剂的无环和环状乙烯基酮的光化学反应（分别为1和2）。照射时，酮1产生其顺式异构体，而酮2不产生任何光产物。的酮激光闪光光解1产率瞬态谱λ最大〜400纳米（τ〜125毫微秒）。该瞬态被分配给第一三线态激发态（T 1）的1，这大概衰减以形成三重双基（1BR）的寿命短于三联体酮。相比较而言，的激光闪光光解2揭示了两个瞬时电压（τ〜20个440纳秒），其被分配至T 1的2和三重态双自由基2BR分别。密度泛函理论计算支持表征三重态激发态和辐照酮1和2时形成的双自由基中间体，并允许比较双自由基中间体的物理性质。由于2BR中的双自由基中心通过共轭稳定，因此2BR比1BR刚性更高。因此，2BR的使用寿命更长 可以归因于效率低的系统间交叉到基态。
更新日期：2020-09-18
中文翻译：
无环和环状4-（4-甲氧基-苯基）-4-氧代-丁-2-烯酸酯衍生物的光化学比较。
为了阐明三重态激发态表面上简单烯烃的顺式-反式异构化机理，比较了以对甲氧基苯乙酮部分为内置三重态敏化剂的无环和环状乙烯基酮的光化学反应（分别为1和2）。照射时，酮1产生其顺式异构体，而酮2不产生任何光产物。的酮激光闪光光解1产率瞬态谱λ最大〜400纳米（τ〜125毫微秒）。该瞬态被分配给第一三线态激发态（T 1）的1，这大概衰减以形成三重双基（1BR）的寿命短于三联体酮。相比较而言，的激光闪光光解2揭示了两个瞬时电压（τ〜20个440纳秒），其被分配至T 1的2和三重态双自由基2BR分别。密度泛函理论计算支持表征三重态激发态和辐照酮1和2时形成的双自由基中间体，并允许比较双自由基中间体的物理性质。由于2BR中的双自由基中心通过共轭稳定，因此2BR比1BR刚性更高。因此，2BR的使用寿命更长 可以归因于效率低的系统间交叉到基态。
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