Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones,Journal of the American Chemical Society

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Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2014-10-09 , DOI: 10.1021/ja508059p
Pramod Kumar Verma ₁ , Federico Koch ₁ , Andreas Steinbacher ₁ , Patrick Nuernberger ₁ , Tobias Brixner ₁

Affiliation

In photoinduced molecular reaction dynamics, the effects of electronic charge redistribution can lead to multiple pathways that are determined by the nature of the initial structures involved and the environment the molecule of interest is studied in. The β-diketones are a common example of this complexity. They show keto-enol tautomerism that is almost totally shifted toward the enolic form. However, compared to the gas phase, the photochemistry proceeds completely differently by virtue of the solvent environment for these compounds, which are used in commercial sunscreen agents due to a high absorption in the ultraviolet (UV) and fast deactivation processes. We disclose these dynamics by investigating three symmetrical β-diketones in various solvents. To observe these effects on an ultrafast time scale directly in the UV spectral region where the relevant electronic transitions take place, we have developed and employed femtosecond transient absorption with detection capability in the deep UV. Our studies confirm that electronic excitation of the chelated enol form does not lead to any ultrafast photochemistry other than proton transfer followed by rotamerization. The formation of the nonchelated conformers takes place on a picosecond time scale through a dark state, whereas the recovery to the stable chelated enol form is a comparably slow process.

中文翻译：

分子内氢键对称 β-二酮的超快紫外诱导光异构化

在光致分子反应动力学中，电荷重新分布的影响可导致多种途径，这些途径由所涉及的初始结构的性质和研究目标分子的环境决定。 β-二酮是这种复杂性的一个常见例子. 它们显示出几乎完全转向烯醇形式的酮-烯醇互变异构现象。然而，与气相相比，由于这些化合物的溶剂环境，光化学过程完全不同，由于对紫外线 (UV) 的高吸收和快速失活过程，这些化合物用于商业防晒剂。我们通过研究各种溶剂中的三种对称 β-二酮来揭示这些动力学。为了直接在发生相关电子跃迁的紫外光谱区以超快时间尺度观察这些影响，我们开发并采用了具有深紫外检测能力的飞秒瞬态吸收。我们的研究证实，螯合烯醇形式的电子激发不会导致除质子转移和旋转异构之外的任何超快光化学。非螯合构象异构体的形成发生在皮秒级的暗态，而恢复到稳定的螯合烯醇形式是一个相对缓慢的过程。我们的研究证实，螯合烯醇形式的电子激发不会导致除质子转移和旋转异构之外的任何超快光化学。非螯合构象异构体的形成发生在皮秒级的暗态，而恢复到稳定的螯合烯醇形式是一个相对缓慢的过程。我们的研究证实，螯合烯醇形式的电子激发不会导致除质子转移和旋转异构之外的任何超快光化学。非螯合构象异构体的形成发生在皮秒级的暗态，而恢复到稳定的螯合烯醇形式是一个相对缓慢的过程。

更新日期：2014-10-09

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