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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Influence of cage confinement on the photochemistry of matrix-isolated e -β-ionone: FT-IR and DFT study
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Influence of cage confinement on the photochemistry of matrix-isolated e -β-ionone: FT-IR and DFT study

机译：笼限制对基质分离的e-β-紫罗兰酮光化学的影响：FT-IR和DFT研究

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摘要

β-ionone, a model compound of carotenoids ring structure, was investigated by FT-IR spectroscopy in a low-temperature argon matrix as well as using B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) quantum-chemical calculations. The spectrum of matrix-isolated E-β-ionone was analyzed and attributed to six conformers of the compound. Then, matrix-isolated E-β-ionone was submitted to UV irradiation using either a broadband source (with different cutoff filters) or a narrowband laser/MOPO system (at various wavelengths). Upon 240 nm narrowband irradiation, the formation of both Z-retro-γ-ionone and Z-β-ionone was observed, the reactant and the photoproducts being in a photostationary equilibrium. Under these conditions, the matrix environment was found to hamper subsequent reactions of Z-retro-γ-ionone and Z-β-ionone, so that this last species could be observed directly for the first time. Furthermore, the formation of Z-retro-γ-ionone was shown to occur directly via an intramolecular [1,5] H-atom shift and thereby, under the constraints imposed by the matrix confinement, the conformations assumed by this photoproduct were found to be strictly determined by those initially assumed by the reactant molecules. Broadband irradiation resulted in the completion of the reaction (disappearance of the reactant) and the sole observation of Z-retro-γ-ionone. These results imply that under these conditions the Z-β-ionone is unstable, very likely decaying to additional conformers of Z-retro-γ-ionone, as reflected in the broader bands due to this photoproduct observed in the infrared spectra of the broadband irradiated matrix.
机译：β-紫罗兰酮是类胡萝卜素环结构的模型化合物，通过FT-IR光谱在低温氩气基质中以及使用B3LYP / 6-311 ++ G（d，p）和MP2 / 6-311 +进行了研究+ G（d，p）量子化学计算。分析了基质分离的E-β-紫罗兰酮的光谱，并将其归因于该化合物的六个构象异构体。然后，使用宽带光源（具有不同的截止滤光片）或窄带激光/ MOPO系统（各种波长）将基质分离的E-β-紫罗兰酮进行UV辐射。在240 nm窄带照射下，观察到Z-retro-γ-紫罗兰酮和Z-β-紫罗兰酮的形成，反应物和光产物处于光平稳平衡。在这些条件下，发现基质环境阻碍了Z-retro-γ-紫罗兰酮和Z-β-紫罗兰酮的后续反应，因此可以直接直接观察到该最后一个物种。此外，显示Z-retro-γ-紫罗兰酮的形成是直接通过分子内[1,5] H原子移位发生的，因此，在基质限制的约束下，发现该光产物假定的构象为由反应物分子最初假定的那些严格地确定。宽带辐射导致反应完成（反应物消失），并且仅观察到Z-retro-γ-紫罗兰酮。这些结果表明，在这些条件下，Z-β-紫罗兰酮是不稳定的，很可能会衰减为Z-retro-γ-紫罗兰酮的其他构象异构体，这是由于在宽带照射的红外光谱中观察到的这种光产物而在更宽的波段中反映出来的。矩阵。

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