Department of Process Research and Development, Merck and Co., Inc., Rahway, New Jersey 07065, United States.
J Am Chem Soc. 2020 Apr 15;142(15):7066-7074. doi: 10.1021/jacs.0c00646. Epub 2020 Apr 3.
We report the synthesis of a new perylene-diimide-based helical nanoribbon, which exhibits the largest molar electronic circular dichroism in the visible range of any molecule. This nanoribbon also displays a substantial increase in molar circular dichroism relative to a smaller helical analogue, even though they share a similar structure: both nanoribbons incorporate two conformationally dynamic double-[4]helicene termini and a rigid [6]helicene-based core within their helical superstructures. Using DFT and TDDFT calculations, we find that the double-[4]helicenes within both nanoribbons orient similarly in solution; as such, conformational differences do not account for the disparities in circular dichroism. Instead, our results implicate the configuration of the double-[6]helicene within the larger nanoribbon as the source of the observed chiroptical amplification.
我们报告了一种新型基于苝二酰亚胺的螺旋纳米带的合成，该纳米带在可见范围内表现出任何分子中最大的摩尔电子圆二色性。与较小的螺旋类似物相比，这种纳米带的摩尔圆二色性也有显著增加，尽管它们具有相似的结构：两个纳米带都在其螺旋超结构中包含两个构象动态的双-[4]螺旋末端和一个刚性的[6]螺旋基核心。通过 DFT 和 TDDFT 计算，我们发现两个纳米带中的双-[4]螺旋在溶液中取向相似；因此，构象差异不能解释圆二色性的差异。相反，我们的结果表明较大纳米带中双-[6]螺旋的构型是观察到的手性放大的来源。
