We explored the optoelectronic and vibrational properties of a new class of halogen-terminated carbon atomic wires in the form of polyynes using UV–vis, infrared absorption, Raman spectroscopy, X-ray single-crystal diffraction, and DFT calculations. These polyynes terminate on one side with a cyanophenyl group and on the other side, with a halogen atom X (X = Cl, Br, I). We focus on the effect of different halogen terminations and increasing lengths (i.e., 4, 6, and 8 sp-carbon atoms) on the π-electron conjugation and the electronic structure of these systems. The variation in the sp-carbon chain length is more effective in tuning these features than changing the halogen end group, which instead leads to a variety of solid-state architectures. Shifts between the vibrational frequencies of samples in crystalline powders and in solution reflect intermolecular interactions. In particular, the presence of head-to-tail dimers in the crystals is responsible for the modulation of the charge density associated with the π-electron system, and this phenomenon is particularly important when strong I··· N halogen bonds occur.

中文翻译：

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卤素封端和链长对卤素封端多炔的π电子共轭和振动性能的影响

我们利用紫外-可见光、红外吸收、拉曼光谱、X 射线单晶衍射和 DFT 计算，探索了一种新型多炔形式的卤素封端碳原子线的光电和振动特性。这些多炔一侧以氰基苯基封端，另一侧以卤素原子 X (X = Cl、Br、I) 封端。我们重点关注不同卤素末端和增加长度（即 4、6 和 8 个 sp-碳原子）对 π 电子共轭和这些系统的电子结构的影响。 sp-碳链长度的变化在调节这些特性方面比改变卤素端基更有效，后者反而导致了各种固态结构。晶体粉末和溶液中样品的振动频率之间的变化反映了分子间相互作用。特别是，晶体中头尾二聚体的存在负责调节与 π 电子系统相关的电荷密度，并且当出现强 I·N 卤素键时，这种现象尤其重要。