Shedding Light on the Photoisomerization Pathway of Donor-Acceptor Stenhouse Adducts.
Shedding Light on the Photoisomerization Pathway of Donor-Acceptor Stenhouse Adducts.
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DOI：
10.1021/jacs.7b09081
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发表时间：
2017-11-08
影响因子：
15
通讯作者：
Feringa BL
中科院分区：
文献类型：
--
作者：
Di Donato M;Lerch MM;Lapini A;Laurent AD;Iagatti A;Bussotti L;Ihrig SP;Medved' M;Jacquemin D;Szymański W;Buma WJ;Foggi P;Feringa BL
供体-受体Stenhouse加合物（DASA）是一种具有广泛应用前景的负性光致变色化合物。优化其开关特性的关键是对光开关机制的详细理解，而这一点目前还不存在。在这里，我们表征DASA光开关的光化步骤和它的关键中间体，这是使用超快可见光和红外泵浦-探测光谱和TD-DFT计算相结合的研究。时间分辨的红外光谱与DFT计算的比较允许明确地识别中间体的结构，证实光吸收诱导连续反应路径，其中C2-C3的Z-E光异构化之后是围绕C3-C4的旋转和随后的热环化步骤。第一代和第二代DASA在氯化溶剂中具有共同的光异构化机制，激发态的动力学和寿命存在显着差异。第二代DASA的光生中间体在低温下光累积，并用时间分辨光谱探测，证明了异构化过程的光可逆性。总之，这些结果提供了分子水平上的DASA异构化途径的详细图片。
Donor–acceptor Stenhouse adducts (DASAs) are negative photochromes that hold great promise for a variety of applications. Key to optimizing their switching properties is a detailed understanding of the photoswitching mechanism, which, as yet, is absent. Here we characterize the actinic step of DASA-photoswitching and its key intermediate, which was studied using a combination of ultrafast visible and IR pump–probe spectroscopies and TD-DFT calculations. Comparison of the time-resolved IR spectra with DFT computations allowed to unambiguously identify the structure of the intermediate, confirming that light absorption induces a sequential reaction path in which a Z–E photoisomerization of C2–C3 is followed by a rotation around C3–C4 and a subsequent thermal cyclization step. First and second-generation DASAs share a common photoisomerization mechanism in chlorinated solvents with notable differences in kinetics and lifetimes of the excited states. The photogenerated intermediate of the second-generation DASA was photo-accumulated at low temperature and probed with time-resolved spectroscopy, demonstrating the photoreversibility of the isomerization process. Taken together, these results provide a detailed picture of the DASA isomerization pathway on a molecular level.
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