Helicenes have attracted considerable attention due to their inherent helical chirality and extended π-conjugation. Recently, rapid progress has been witnessed in the preparation of double, triple, quadruple, quintuple, and sextuple helicenes, where plural helicene moieties are symmetrically arranged in a single molecule. While synthetic efforts and X-ray crystallographic analyses devoted to these multiple helicenes and theoretical investigations on their isomerization and racemization behaviors have been relatively well documented and reviewed in the literature, the chiroptical properties of the multiple helicities have been somewhat overlooked. This review discourses the cumulative and systematic investigations on the chiroptical properties such as the circular dichroism (CD) and circularly polarized luminescence (CPL) of multiple helicenes. Although the number and structural variations of multiple helicenes reported to date have been fairly limited, this review overviews the current status of the chemistry of multiple helicenes from the viewpoint of chiroptical properties and provides insights into the design principle for advanced chiroptical materials through the proper arrangement of multiple helices, highlighting the impact of the molecular symmetry on the chiroptical responses.

中文翻译：

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对称双螺旋，三螺旋和多重螺旋的手性

螺旋藻由于其固有的螺旋手性和扩展的π共轭作用而引起了相当大的关注。近来，在制备双螺旋，三螺旋，四螺旋，五螺旋和六螺旋螺旋体中已经见证了快速的进展，其中多个螺旋烯部分对称地排列在单个分子中。尽管专门针对这些多重螺旋的合成努力和X射线晶体学分析以及有关其异构化和外消旋行为的理论研究已在文献中得到了相对充分的记录和审查，但多重螺旋的手性却被忽略了。这篇综述论述了对诸如多个螺旋的圆二色性（CD）和圆极化发光（CPL）的手性的累积和系统的研究。