Department of Chemistry, Columbia University, New York 10027, United States.
Department of Chemistry, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark.
J Am Chem Soc. 2021 Jan 20;143(2):983-991. doi: 10.1021/jacs.0c11260. Epub 2020 Dec 30.
Here we report the synthesis of two polyhelicene frameworks consisting, from end-to-end, of 18 and 24 fused benzene rings. The latter exhibits the largest electronic circular dichroism in the visible spectrum of any molecule. These shape-persistent helical nanoribbons incorporate multiple helicenes, a class of contorted polycyclic aromatic molecules consisting of -annulated rings. These conjugated, chiral molecules have interesting chemical, biological, and chiroptical properties; however, there are very few helicenes with extraordinary chiroptical response over a broad range of the visible spectrum-a key criterion for applications such as chiral optoelectronics. In this report, we show that coupling the polyhelicene framework with multiple perylene-diimide subunits elicits a significant chiroptic response. Notably, the molar circular dichroism increases faster than the absorptivity of these molecules as their helical axis lengthens. Computational analysis reveals that the greatly amplified circular dichroism arises from exciton-like interactions between the perylene-diimide and the helicene moieties. We predict that even greater chiroptic enhancement will result from further axial elongation of these nanoribbons, which can be readily enabled via the iterative synthetic method presented herein.
在这里，我们报告了两种由 18 和 24 个稠合苯环首尾相连组成的聚轮烯框架的合成。后者在可见光谱中表现出任何分子中最大的电子圆二色性。这些形状保持的螺旋纳米带包含多个螺旋烯，螺旋烯是一类由 -annulated 环组成的扭曲多环芳烃分子。这些共轭的手性分子具有有趣的化学、生物和圆二色性性质；然而，在可见光谱的广泛范围内具有非凡圆二色性响应的螺旋烯非常少——这是手性光电应用的关键标准。在本报告中，我们表明，将聚轮烯框架与多个苝二酰亚胺亚基耦合会引起显著的圆二色性响应。值得注意的是，随着这些分子的螺旋轴的延长，摩尔圆二色性的增加速度快于其吸光度的增加速度。计算分析表明，这种大大放大的圆二色性源于苝二酰亚胺和螺旋烯部分之间的激子样相互作用。我们预测，通过本文提出的迭代合成方法进一步延长这些纳米带的轴向长度，将导致更大的圆二色性增强，这是可以实现的。
