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首页> 外文期刊>Chemistry: A European journal >Sequence-controlled oligomers fold into nanosolenoids and impart unusual optical properties
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Sequence-controlled oligomers fold into nanosolenoids and impart unusual optical properties

机译：序列控制的寡聚体折叠成纳米电磁体，并赋予其异常的光学性能

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摘要

Controlled syntheses give unique block oligomers with alternating flexible ethylene glycol and rigid perylenetetracarboxylic diimide (PDI) units. The number of rigid units vary from n=1 to 10. PDI units were stitched together by using efficient phosphoramidite chemistry. The resulting oligomers undergo folding in most solvents, including chloroform. In their ground state, these folded oligomers were characterized by using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS), NMR spectroscopy, and electronic absorption spectroscopy. FTICR-MS revealed the exact masses of these sequence-controlled oligomers, which confirmed the chemical composition and validated the synthetic strategy. The NMR neighboring ring-current effect (NRE) indicates the formation of cofacial π stacks; the stacked aromatic rings have nearly coaxial alignment akin to a nanosoleniod. Nanosolenoidal shielding in π stacks causes all aromatic protons to shift upfield, whereas NOE in a cyclic hetero-chromophoric dimer supports a rotated, cofacial π-stacking orientation separated by about 3.5?. Electron-phonon coupling is much stronger than excitonic coupling in these self-folded PDI oligomers; thus, Franck-Condon factors dictate the observed spectral features in visible spectra. The absorbance spectrum exhibits weak hypochromism due to π stacking with increasing stacking units n. Finally, ab initio calculations support the experimental observations, indicating 3.5? cofacial spacing in which one molecule is rotated 30° from the eclipsed orientation and higher oligomers can adopt, without a compensating energy penalty, either the right/left-handed helices or the 1,3-eclipsed structures. Both theory and experiments validate the nano-π-solenoids and their novel photophysical properties.
机译：受控的合成可生成独特的嵌段低聚物，并带有交替的柔性乙二醇和刚性per四羧酸二酰亚胺（PDI）单元。刚性单元的数量在n = 1到10之间变化。通过使用有效的亚磷酰胺化学方法将PDI单元缝合在一起。所得的低聚物在大多数溶剂（包括氯仿）中经历折叠。这些折叠的低聚物在其基态下通过傅里叶变换离子回旋共振质谱（FTICR-MS），NMR光谱和电子吸收光谱进行表征。 FTICR-MS揭示了这些序列控制的低聚物的确切质量，证实了化学组成并验证了合成策略。 NMR邻环电流效应（NRE）表示界面π堆栈的形成;堆叠的芳环几乎类似于纳米螺线管的同轴排列。 π堆中的纳米电磁螺线屏蔽使所有芳香族质子向高场移动，而环状异发色二聚体中的NOE支持旋转的，界面π堆积方向，相距约3.5?。在这些自折叠的PDI低聚物中，电子-声子耦合比激子耦合强得多。因此，弗兰克-康登因子决定了可见光谱中观察到的光谱特征。由于π堆积随着堆积单位n的增加，吸收光谱表现出弱的减色性。最后，从头算计算支持实验观察，表明3.5？可以将一个分子从偏光方向旋转30°并使用更高的低聚物的表面间距，而无需补偿能量损失，可以选择右旋/左旋螺旋或1,3偏光结构。理论和实验均验证了纳米-π-电磁体及其新颖的光物理性质。

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