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首页> 外文期刊>Chemistry: A European journal >Phenylene Ethynylene-Tethered Perylene Bisimide Folda-Dimer and Folda-Trimer: Investigations on Folding Features in Ground and Excited States
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Phenylene Ethynylene-Tethered Perylene Bisimide Folda-Dimer and Folda-Trimer: Investigations on Folding Features in Ground and Excited States

机译：苯乙撑乙炔系联撑双酰亚胺Folda-Dimer和Folda-Trimer：基态和激发态的折叠特征研究

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摘要

In this work, we have elucidated in detail the folding properties of two perylene bisimide (PBI) foldamers composed of two and three PBI units, respectively, attached to a phenylene ethynylene backbone. The folding behaviors of these new PBI folda-dimer and trimer have been studied by solvent-dependent UV/Vis absorption and 1D and 2D NMR spectroscopy, revealing facile folding of both systems in tetrahydrofuran (THF). In CHCl3 the dimer exists in extended (unfolded) conformation, whereas partially folded conformations are observed in the trimer. Temperature-dependent 1H NMR spectroscopic studies in [D-8] THF revealed intramolecular dynamic processes for both PBI foldamers due to, on the one hand, hindered rotation around C-N imide bonds and, on the other hand, backbone flapping; the latter process being energetically more demanding as it was observed only at elevated temperature. The structural features of folded conformations of the dimer and trimer have been elucidated by different 2D-NMR spectroscopy (e.g., ROESY and DOSY) in [D-8] THF. The energetics of folding processes for the PBI dimer and trimer have been assessed by calculations applying various methods, particularly the semiempirical PM6-DH2 and the more sophisticated B97D approach, in which relevant dispersion corrections are included. These calculations corroborate the results of NMR spectroscopic studies. Folding features in the excited states of these PBI foldamers have been characterized by using time-resolved fluorescence and transient absorption spectroscopy in THF and CHCl3, exhibiting similar solvent-dependent behavior as observed for the ground state. Interestingly, photoinduced electron transfer (PET) process from electron-donating backbone to electron-deficient PBI core for extended, but not for folded, conformations was observed, which can be explained by a fast relaxation of excited PBI stacks in the folded conformation into fluorescent excimer states.
机译：在这项工作中，我们已经详细阐明了两个分别由两个和三个PBI单元组成的二per双酰亚胺（PBI）折叠剂的折叠特性，它们分别连接至亚苯基亚乙炔主链。这些新的PBI折叠二聚体和三聚体的折叠行为已通过溶剂依赖性UV / Vis吸收以及1D和2D NMR光谱进行了研究，揭示了这两个系统在四氢呋喃（THF）中的简便折叠。在CHCl3中，二聚体以延伸（未折叠）构象存在，而在三聚体中观察到部分折叠的构象。 [D-8] THF中与温度有关的1H NMR光谱研究表明，两个PBI折叠子的分子内动力学过程，一方面是由于绕C-N酰亚胺键的旋转受阻，另一方面是主链拍打;由于仅在升高的温度下才观察到，后一种方法的能量要求更高。通过在[D-8] THF中的不同的2D-NMR光谱（例如，ROESY和DOSY）已经阐明了二聚体和三聚体的折叠构象的结构特征。 PBI二聚体和三聚体的折叠过程的能量已经通过应用各种方法的计算进行了评估，特别是半经验PM6-DH2和更复杂的B97D方法，其中包括相关的色散校正。这些计算证实了NMR光谱研究的结果。通过在THF和CHCl3中使用时间分辨荧光和瞬态吸收光谱法，已表征了这些PBI折叠剂激发态的折叠特征，表现出与基态相似的溶剂依赖性行为。有趣的是，观察到了从给电子主链到缺电子的PBI核的光致电子转移（PET）过程，用于扩展但不用于折叠的构象，这可以用折叠构象中激发的PBI叠层快速弛豫成荧光来解释。准分子状态。

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